Change search
Refine search result
1234567 151 - 200 of 350
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 151.
    Ludwig Barbosa, Vinícius
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    On the Ionospheric Influence on GNSS Radio Occultation Signals: Modelling and Assessment2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Radio Occultation (RO) is a well-established remote sensing technique that uses Global Navigation Satellite System (GNSS) signals to sound the Earth’s atmosphere. GNSS-RO measurements provide high-resolution, vertical profiles of physical parameters from the lower atmosphere (troposphere and stratosphere), e.g., refractivity, dry temperature, pressure, and water vapour, with primary application in weather forecasting and climatology models. The upper atmosphere (ionosphere) is also sounded during measurements, in which information about total electron content, electron density profiles, and scintillation indices compose the RO ionospheric data product.

    The ionosphere is a dispersive medium composed of ionized particles. It is extensively conditioned by Solar activity and shows seasonal, geographical, and day- and night-time variation. Despite the benefit of the upper atmospheric data, the ionosphere influences the retrievals in the lower atmosphere by (i) adding an inherent systematic bias in bending angles, i.e., residual ionospheric error (RIE), and (ii) disturbing the signal amplitude and phase, i.e., scintillation, in the presence of irregularities regions on the electron density along the ray path, e.g., equatorial plasma bubbles. In this dissertation, both aspects are investigated by modelling the equatorial ionosphere, and its small-scale irregularities in simulations of occultation events to (i) reproduce the effects observed in measurements and (ii) assess methods that can extract information about the ionosphere and support its monitoring and modelling.

    The multiple phase screen method was applied to model the GNSS signal propagation through quiet and disturbed ionospheric conditions. The small-scale irregularities in the F-region were modelled by a single slope power law to yield moderate to strong scintillation in the signals. Results were assessed according to the amplitude and phase scintillation indices, RIE, the standard deviation of the retrieved bending angles, and power spectral density (PSD). A subset of these parameters was taken as features to train a classifier based on the support vector machine algorithm. The purpose of this model was to detect RO measurements affected by ionospheric scintillation. Specifically, those in which PSD could provide further information about the irregularities according to the scintillation theory. Additionally, the back propagation (BP) method and its capability to estimate the mean distance between the receiver and irregularities were evaluated.

    Applying spectral analysis techniques to RO measurements may contribute to the characterization of small-scale irregularities in equatorial plasma bubbles. The results from simulations applying the single-slope power law to model the irregularities showed a good agreement with the selected cases. The automatic detection of occultations affected by ionospheric irregularities has achieved similar performance to models trained with ground-based measurements. Furthermore, the BP method can add the estimation of the mean location to the spectral analysis information. Such tools can enlarge the amount of ionospheric data retrieved -- especially for occultations with extended vertical range and when combined with other sounding techniques.

    Download full text (pdf)
    fulltext
  • 152.
    Ludwig Barbosa, Vinícius
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, J.
    Molflow, Gothenburg, SWE.
    Carlstrom, A.
    RUAG Space AB, SWE.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    A Simulation Study of the Effect of Ionospheric Vertical Gradients on the Neutral Bending Angle Error for GNSS Radio Occultation2017In: Progress in Electromagnetics Research Symposium, IEEE , 2017, p. 1540-1545Conference paper (Refereed)
    Abstract [en]

    Radio Occultation based on Global Navigation Satellite System signals (GNSS RO) is an increasingly important remote sensing technique. Its measurements are used to derive parameter of the Earth's atmosphere, e.g., pressure, temperature and humidity, with good accuracy. The systematic residual error present on the data processing is related to ionospheric conditions, such as the distribution of electrons and the resultant vertical gradient. This study investigates the relationship between these parameters and the residual ionospheric error (RIE) on the retrieved bending angle in the stratosphere. Chapman function combined to sinusoidal perturbations are used to model electron density profiles and compared to RO retrievals of the ionosphere to perform the investigation. The results confirmed that the major ionospheric influence on the retrieval error is related to the F-layer electron density peak, whereas small-scale vertical structures play a minor role.

    Download full text (pdf)
    fulltext
  • 153.
    Ludwig Barbosa, Vinícius
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Beyond Gravity Ab, Sweden.
    Carlstrom, Anders
    Beyond Gravity Ab, Sweden.
    Christensen, Jacob
    Beyond Gravity Ab, Sweden.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Location of Ionospheric Irregularities in Extended GNSS-RO Measurements Using Back Propagation Method2023In: 2023 35th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2023, Institute of Electrical and Electronics Engineers (IEEE), 2023Conference paper (Refereed)
    Abstract [en]

    Besides providing electron density profiles (EDP), GNSS Radio Occultation (GNSS-RO) measurements allow monitoring the frequency and the areas where ionospheric scintillations occur. In this work, RO measurements composing an experimental data set are processed with the back propagation (BP) method to estimate the location of sporadic E-clouds and equatorial plasma bubbles (EPB). The data set includes non-conventional measurements tracked up to 600 km (generally around 80 km), covering F-region heights, shortly before MetOp-A was decommissioned. Results indicate the combination of extended occultations and the BP method is promising for monitoring the occurrence and characterizing ionospheric irregularities in the F-region and the E-region. © 2023 International Union of Radio Science.

    Download full text (pdf)
    fulltext
  • 154.
    Ludwig Barbosa, Vinícius
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Molflow, SWE.
    Carlström, Anders
    RUAG Space AB, SWE.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    GNSS Radio Occultation Simulation Using Multiple Phase Screen Orbit Sampling2020In: IEEE Geoscience and Remote Sensing Letters, ISSN 1545-598X, E-ISSN 1558-0571, Vol. 17, no 8, p. 1323-1327, article id 8869926Article in journal (Refereed)
    Abstract [en]

    Wave optics propagators (WOPs) are commonlyused to describe the propagation of radio signals through earth’satmosphere. In radio occultation (RO) context, multiple phasescreen (MPS) method has been used to model the effects of theatmosphere in Global Navigation Satellite System (GNSS) signalsduring an occultation event. WOP implementation includes,in addition to MPS, a diffraction integral as the final step tocalculate the radio signal measured in the low-earth orbit (LEO)satellite. This approach considers vacuum as the propagationmedium at high altitudes, which is not always the case when theionosphere is taken into account in simulations. An alternativeapproach is using MPS all the way to LEO in order to samplethe GNSS signal in orbit. This approach, named MPS orbitsampling (MPS-OS), is evaluated in this letter. Different scenariosof setting occultation assuming a short segment of the LEO orbithave been simulated using MPS and MPS-OS. Results have beencompared to Abel transform references. Furthermore, a longsegment scenario has been evaluated as well. A comparison ofbending angle (BA) and residual ionospheric error (RIE) showsthe equivalence between MPS and MPS-OS results. The mainapplication of MPS-OS should be in occultation events with longsegments of orbit and including ionosphere, in which a standardWOP may not be appropriate.

    Download full text (pdf)
    GNSS Radio Occultation Simulation Using Multiple Phase Screen Orbit Sampling
  • 155.
    Ludwig Barbosa, Vinícius
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Beyond Gravity Sweden Ab.
    Sievert, Thomas
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Carlström, Anders
    Beyond Gravity Sweden Ab.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Christensen, Jacob
    Beyond Gravity Sweden Ab.
    Detection and localization of F-layer ionospheric irregularities with the back-propagation method along the radio occultation ray path2023In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 16, no 7, p. 1849-1864Article in journal (Refereed)
    Abstract [en]

    The back propagation (BP) method consists of diffractive integrals computed over a trajectory path, projecting a signal to different planes. It unwinds the diffraction and multipath, resulting in minimum disturbance on the BP amplitude when the auxiliary plane coincides with the region causing the diffraction. The method has been previously applied in GNSS Radio Occultation (RO) measurements showing promising results in the location estimate of ionospheric irregularities but without complementary data to validate the estimation. In this study, we investigate with wave optics propagator (WOP) simulations of an equatorial C/NOFS occultation with scintillation signatures caused by an equatorial plasma bubble (EPB), which was parametrized with aid of collocated data. In addition, a few more test cases were designed to assess the BP method regarding size, intensity and placement of single and multiple irregularity regions. The results show a location estimate accuracy of 10 km (single bubble, reference case), where in multiple bubble scenarios only the strongest disturbance would be resolved properly. The minimum detectable disturbance level and the estimation accuracy depend on the receiver noise level, and in the case of several bubbles on the distance between them. The remarks of the evaluation supported the interpretation of results for two COSMIC occultations.

    Download full text (pdf)
    fulltext
  • 156.
    Ludwig Barbosa, Vinícius
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Schlosser, Edson
    Machado, Renato
    Heckler, Marcos Vinício Thomas
    Beamforming of a Linear Array Applying PSO Algorithm with Restrictive Approach2016In: Journal of Communication and Information Systems, ISSN 1980-6604, Vol. 31, no 1, p. 118-126Article in journal (Refereed)
    Abstract [en]

    This paper presents a four-element linear arraycomposed of E-shaped microstrip antennas designed to switched-beam application in ISM band. Particle Swarm Optimization(PSO) algorithm is applied to optimize four different sets ofamplitude and progressive phase shift to achieve four distinctradiation patterns controlling the major lobe direction andsidelobe level. For this application, two restrictive approachesare presented for the implementation of PSO algorithm in orderto improve the algorithm convergence to feasible solutions.

    Download full text (pdf)
    fulltext
  • 157.
    Ludwig Barbosa, Vinícius
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Sievert, Thomas
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Carlström, Anders
    RUAG Space AB, SWE.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Molflow, SWE.
    Supervised Detection of Ionospheric Scintillation in Low-Latitude Radio Occultation Measurements2021In: Remote Sensing, E-ISSN 2072-4292, Vol. 13, no 9, article id 1690Article in journal (Refereed)
    Abstract [en]

    Global Navigation Satellite System (GNSS) Radio Occultation (RO) has provided high- quality atmospheric data assimilated in Numerical Weather Prediction (NWP) models and climatol- ogy studies for more than 20 years. In the satellite–satellite GNSS-RO geometry, the measurements are susceptible to ionospheric scintillation depending on the solar and geomagnetic activity, seasons, geographical location and local time. This study investigates the application of the Support Vector Machine (SVM) algorithm in developing an automatic detection model of F-layer scintillation in GNSS-RO measurements using power spectral density (PSD). The model is intended for future analyses on the influence of space weather and solar activity on RO data products over long time periods. A novel data set of occultations is used to train the SVM algorithm. The data set is composed of events at low latitudes on 15–20 March 2015 (St. Patrick’s Day geomagnetic storm, high solar flux) and 14–19 May 2018 (quiet period, low solar flux). A few conditional criteria were first applied to a total of 5340 occultations to define a set of 858 scintillation candidates. Models were trained with scintillation indices and PSDs as training features and were either linear or Gaussian kernel. The investigations also show that besides the intensity PSD, the (excess) phase PSD has a positive contribution in increasing the detection of true positives. 

    Download full text (pdf)
    fulltext
  • 158.
    Ludwig Barbosa, Vinícius
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Sievert, Thomas
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Molflow, SWE.
    Carlström, Anders
    RUAG Space AB, SWE.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Evaluation of Ionospheric Scintillation in GNSS Radio Occultation Measurements and Simulations2020In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 55, no 8, article id e2019RS006996Article in journal (Refereed)
    Abstract [en]

    Like any other system relying on trans-ionospheric propagation, GNSS Radio Occultation (GNSS-RO) is affected by ionospheric conditions during measurements. Regions of plasma irregularities in F-region create abrupt gradients in the distribution of ionized particles. Radio signals propagated through such regions suffer from constructive and destructive contributions in phase and amplitude, known as scintillations. Different approaches have been proposed in order to model and reproduce the wave propagation through ionospheric irregularities. We present simulations considering an one-component inverse power-law model of irregularities integrated with Multiple Phase Screen (MPS) propagation. In this work, the capability of the scintillation model to reproduce features in the signal amplitude of low latitude MetOp measurements in the early hours of DOY 76, 2015 (St. Patrick’s Day geomagnetic storm) is evaluated. Power spectral density (PSD) analysis, scintillation index, decorrelation time and standard deviation of neutral bending angle are considered in the comparison between the simulations and RO measurements. The results validate the capability of the simulator to replicate an equivalent total integrated phase variance in cases of moderate to strong scintillation.

    Download full text (pdf)
    fulltext
  • 159.
    Lundberg, Lars
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Boeva, Veselka
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    García Martín, Eva
    Handling non-linear relations in support vector machines through hyperplane folding2019In: ACM International Conference Proceeding Series, Association for Computing Machinery , 2019, p. 137-141Conference paper (Refereed)
    Abstract [en]

    We present a new method, called hyperplane folding, that increases the margin in Support Vector Machines (SVMs). Based on the location of the support vectors, the method splits the dataset into two parts, rotates one part of the dataset and then merges the two parts again. This procedure increases the margin as long as the margin is smaller than half of the shortest distance between any pair of data points from the two different classes. We provide an algorithm for the general case with n-dimensional data points. A small experiment with three folding iterations on 3-dimensional data points with non-linear relations shows that the margin does indeed increase and that the accuracy improves with a larger margin. The method can use any standard SVM implementation plus some basic manipulation of the data points, i.e., splitting, rotating and merging. Hyperplane folding also increases the interpretability of the data. © 2019 Association for Computing Machinery.

  • 160.
    Lundstrom, Patrik
    et al.
    University West.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    SIMPLICITY OF LEAVITT PATH ALGEBRAS VIA GRADED RING THEORY2023In: Bulletin of the Australian Mathematical Society, ISSN 0004-9727, E-ISSN 1755-1633, Vol. 108, no 3, p. 428-437Article in journal (Refereed)
    Abstract [en]

    Suppose that R is an associative unital ring and that E= (E-0, E-1, r, s) is a directed graph. Using results from graded ring theory, we show that the associated Leavitt path algebra L-R(E) is simple if and only if R is simple, E-0 has no nontrivial hereditary and saturated subset, and every cycle in E has an exit. We also give a complete description of the centre of a simple Leavitt path algebra.

    Download full text (pdf)
    fulltext
  • 161.
    Lundstrom, Patrik
    et al.
    University West.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Richter, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    NON-UNITAL ORE EXTENSIONS2023In: Colloquium Mathematicum, ISSN 0010-1354, E-ISSN 1730-6302, Vol. 172, no 2, p. 217-229Article in journal (Refereed)
    Abstract [en]

    We study Ore extensions of non-unital associative rings. We provide a characterization of simple non-unital differential polynomial rings R[x; delta], under the hy-pothesis that R is s-unital and ker(delta) contains a non-zero idempotent. This result gener-alizes a result by oinert, Richter and Silvestrov from the unital setting. We also present a family of examples of simple non-unital differential polynomial rings.

  • 162.
    Lundström, Patrik
    et al.
    University West, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Strongly graded leavitt path algebras2022In: Journal of Algebra and its Applications, ISSN 0219-4988, E-ISSN 1793-6829, Vol. 21, no 07, article id 2250141Article in journal (Refereed)
    Abstract [en]

    Let R be a unital ring, let E be a directed graph and recall that the Leavitt path algebra LR(E) carries a natural-gradation. We show that LR(E) is strongly-graded if and only if E is row-finite, has no sink, and satisfies Condition (Y). Our result generalizes a recent result by Clark, Hazrat and Rigby, and the proof is short and self-contained. © 2022 World Scientific Publishing Company

  • 163.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    A characterization of graded von Neumann regular rings with applications to Leavitt path algebras2021In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 567, p. 91-113Article in journal (Refereed)
    Abstract [en]

    We prove a new characterization of graded von Neumann regular rings involving the recently introduced class of nearly epsilon-strongly graded rings. As our main application, we generalize Hazrat's result that Leavitt path algebras over fields are graded von Neumann regular. More precisely, we show that a Leavitt path algebra LR(E) with coefficients in a unital ring R is graded von Neumann regular if and only if R is von Neumann regular. We also prove that both Leavitt path algebras and corner skew Laurent polynomial rings over von Neumann regular rings are semiprimitive and semiprime. Thereby, we generalize a result by Abrams and Aranda Pino on the semiprimitivity of Leavitt path algebras over fields. © 2020 The Author(s)

    Download full text (pdf)
    fulltext
  • 164.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Chain conditions for epsilon-strongly graded rings with applications to Leavitt path algebras2020In: Algebras and Representation Theory, ISSN 1386-923X, E-ISSN 1572-9079, Vol. 23, no 4, p. 1707-1726Article in journal (Refereed)
    Abstract [en]

    Let G be a group with neutral element e and let S=⊕g∈GSg be a G-graded ring. A necessary condition for S to be noetherian is that the principal component Se is noetherian. The following partial converse is well-known: If S is strongly-graded and G is a polycyclic-by-finite group, then Se being noetherian implies that S is noetherian. We will generalize the noetherianity result to the recently introduced class of epsilon-strongly graded rings. We will also provide results on the artinianity of epsilon-strongly graded rings. As our main application we obtain characterizations of noetherian and artinian Leavitt path algebras with coefficients in a general unital ring. This extends a recent characterization by Steinberg for Leavitt path algebras with coefficients in a commutative unital ring and previous characterizations by Abrams, Aranda Pino and Siles Molina for Leavitt path algebras with coefficients in a field. Secondly, we obtain characterizations of noetherian and artinian unital partial crossed products. © 2019, The Author(s).

    Download full text (pdf)
    fulltext
  • 165.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Induced quotient group gradings of epsilon-strongly graded rings2020In: Journal of Algebra and its Applications, ISSN 0219-4988, E-ISSN 1793-6829, Vol. 9, no 9, article id 2050162Article in journal (Refereed)
    Abstract [en]

    Let $G$ be a group and let $S=\bigoplus_{g \in G} S_g$ be a $G$-graded ring. Given a normal subgroup $N$ of $G$, there is a naturally induced $G/N$-grading of $S$. It is well-known that if $S$ is strongly $G$-graded, then the induced $G/N$-grading is strong for any $N$. The class of epsilon-strongly graded rings was recently introduced by Nystedt, Öinert and Pinedo as a generalization of unital strongly graded rings. We give an example of an epsilon-strongly graded partial skew group ring such that the induced quotient group grading is not epsilon-strong. Moreover, we give necessary and sufficient conditions for the induced $G/N$-grading of an epsilon-strongly $G$-graded ring to be epsilon-strong. Our method involves relating different types of rings equipped with local units (s-unital rings, rings with sets of local units, rings with enough idempotents) with generalized epsilon-strongly graded rings. 

  • 166.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    The graded structure of algebraic Cuntz-Pimsner rings2020In: Journal of Pure and Applied Algebra, ISSN 0022-4049, E-ISSN 1873-1376, Vol. 224, no 9, article id UNSP 106369Article in journal (Refereed)
    Abstract [en]

    The algebraic Cuntz-Pimsner rings are naturally $\mathbb{Z}$-graded rings that generalize both Leavitt path algebras and unperforated $\mathbb{Z}$-graded Steinberg algebras. We  classify strongly, epsilon-strongly and nearly epsilon-strongly graded algebraic Cuntz-Pimsner rings up to graded isomorphism. As an application, we characterize noetherian and artinian fractional skew monoid rings by a single corner automorphism.

    Download full text (pdf)
    The graded structure of algebraic Cuntz-Pimsner rings
  • 167.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    The structure of epsilon-strongly graded rings with applications to Leavitt path algebras and Cuntz-Pimsner rings2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The research field of graded ring theory is a rich area of mathematics with many connections to e.g. the field of operator algebras. In the last 15 years, algebraists and operator algebraists have defined algebraic analogues of important operator algebras. Some of those analogues are rings that come equipped with a group grading. We want to reach a better understanding of the graded structure of those analogue rings. Among group graded rings, the strongly graded rings stand out as being especially well-behaved. The development of the general theory of strongly graded rings was initiated by Dade in the 1980s and since then numerous structural results have been established for strongly graded rings.

     In this thesis, we study the class of epsilon-strongly graded rings which was recently introduced by Nystedt, Öinert and Pinedo. This class is a natural generalization of the well-studied class of unital strongly graded rings. Our aim is to lay the foundation for a general theory of epsilon-strongly graded rings generalizing the theory of strongly graded rings. This thesis is based on three articles. The first two articles mainly concern structural properties of epsilon-strongly graded rings. In the first article, we investigate a functorial construction called the induced quotient group grading. In the second article, using results from the first article, we generalize the Hilbert Basis Theorem for strongly graded rings to epsilon-strongly graded rings and apply it to Leavitt path algebras.  In the third article, we study the graded structure of algebraic Cuntz-Pimsner rings. In particular, we obtain a partial classification of unital strongly, epsilon-strongly and nearly epsilon-strongly graded Cuntz-Pimsner rings up to graded isomorphism.

    Download full text (pdf)
    fulltext
  • 168.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    The structure of epsilon-strongly group graded rings2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The development of a general theory of strongly group graded rings was initiated by Dade, Năstăsescu and Van Oystaeyen in the 1980s, and since then numerous structural results have been established.  In this thesis we develop a general theory of so-called (nearly) epsilon-strongly group graded rings which were recently introduced by Nystedt, Öinert and Pinedo and which generalize strongly group graded rings. Moreover, we obtain applications to  Leavitt path algebras, unital partial crossed products and algebraic Cuntz-Pimsner rings. 

    This thesis is based on five scientific papers (A, B, C, D, E). 

    Papers A and B are concerned with structural properties of epsilon-strongly graded rings. In Paper A, we consider an important construction called the induced quotient group grading. In Paper B, using results from Paper A, we obtain a Hilbert Basis Theorem for epsilon-strongly graded rings.  In Paper C, we study the graded structure of algebraic  Cuntz-Pimsner rings. In particular, we obtain a partial characterization of unital strongly graded, epsilon-strongly graded and nearly epsilon-strongly graded algebraic Cuntz-Pimsner rings up to graded isomorphism. 

    In Paper D, we give a complete characterization of group graded rings that are graded von Neumann regular.

    Finally, in Paper E, written in collaboration with Lundström, Öinert and Wagner, we consider prime nearly epsilon-strongly graded rings. Generalizing Passman's work from the 1980s, we give  necessary and sufficient conditions for a nearly epsilon-strongly graded ring to be prime. 

    Download full text (pdf)
    fulltext
    Download (pdf)
    Spikblad_official
  • 169.
    Lännström, Daniel
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Graded von Neumann regularity of rings graded by semigroups2022In: Beitraege zur Algebra und Geometrie, ISSN 0138-4821, E-ISSN 2191-0383Article in journal (Refereed)
    Abstract [en]

    In this article, we give a complete characterization of semigroup graded rings which are graded von Neumann regular. We also demonstrate our results by applying them to several classes of examples, including matrix rings and groupoid graded rings. © 2022, The Author(s).

    Download full text (pdf)
    fulltext
  • 170.
    Lännström, Daniel
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Wagner, Stefan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Lundström, Patrik
    University West, SWE.
    Prime group graded rings with applications to partial crossed products and Leavitt path algebrasManuscript (preprint) (Other academic)
    Abstract [en]

    In this article we generalize a classical result by Passman on primeness of unital strongly group graded rings to the class of nearly epsilon-strongly group graded rings which are not necessarily unital. Using this result, we obtain (i) a characterization of prime s-unital strongly group graded rings, and, in particular, of infinite matrix rings and of group rings over s-unital rings; (ii) characterizations of prime s-unital partial skew group rings and of prime unital partial crossed products; (iii) a generalization of the well-known characterization of prime Leavitt path algebras, by Abrams, Bell and Rangaswamy.

  • 171.
    Machado, Renato
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats I.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Dammert, Patrik
    Hellsten, Hans
    EMPIRICAL-STATISTICAL ANALYSIS OF AMPLITUDE SAR IMAGES FOR CHANGE DETECTION ALGORITHMS2015In: 2015 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM (IGARSS), 2015, p. 365-368Conference paper (Refereed)
    Abstract [en]

    This paper presents an analysis of pre-filtered clutter VHF SAR images. The image data are reorganized into sub-vectors based on the observation of the image-pair magnitude samples. Based on this approach, we present a statistical description of the SAR clutter obtained by the subtraction between two real SAR images. The statistical analysis based on bivariate distribution data organized into different intervals of magnitude can be an important tool to further understand the properties of the backscattered signal, which can be a valuable premise for change detection processing.

  • 172.
    Maddala, Sasanka
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Velugubantla, Veerababu
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Development of a Multi Sensor Android Application2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There has been an enormous growth in the usage of smartphones in recent times. Smartphones are not limited to communication purposes. It has various applications designed as per the daily requirements of humans such as web-searching, online shopping, bank transactions, games, etc. With the increase in the usage of the smartphone, the more useful information is captured and stored by it, which raises the question of security. The goal of this research is to develop two android applications. One is a sensor detector application and the second is a screen lock application.

    The first application will help the user to identify all the hidden sensors and working sensors on the mobile phone. This application even describes the features and usage of every sensor in detail. Using a graphical description of each sensor which depicts the behaviour of each sensor as per environment/movement. The second application is designed using a combination of two sensors. Screen lock applications contain two main factors. One is to work properly in all cases and efficiently do the functions that are required to do. The second is to maintain a smooth inner system interaction because in addition to locking the screen this application should make sure to hide the display of all the other applications without closing the process of these applications. With the increase in the usage of the smartphone, it becomes difficult for older generations to memorize the security pattern techniques and use them. This thesis develops a simple technique in the mobile authentication android application.

    The thesis is developed on the Android studio platform. The background functionality of the app is coded in java using android SDK tool and frontend of the application is designed using XML files. The GENYMOTION emulator and a mobile phone are used to test the output.

    Download full text (pdf)
    Development of a Multi Sensor Android Application
  • 173.
    Mai Hoang, Bien
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Quasi-duo differential polynomial rings2018In: Journal of Algebra and its Applications, ISSN 0219-4988, E-ISSN 1793-6829, Vol. 17, no 4, article id 1850072Article in journal (Refereed)
    Abstract [en]

    In this article we give a characterization of left (right) quasi-duo differential polynomial rings. We provide non-trivial examples of such rings and give a complete description of the maximal ideals of an arbitrary quasi-duo differential polynomial ring. Moreover, we show that there is no left (right) quasi-duo differential polynomial ring in several indeterminates.

  • 174.
    Mattsson, Linda
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Nyqvist, Robert
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    En helhetssyn på lärande via matematisk problemlösning2019Report (Other (popular science, discussion, etc.))
    Abstract [sv]

    Syftet med kursen Matematisk problemlösning

    är att genom utmanande problemlösning

    få studenter att träna på generella

    arbets- och förhållningssätt som är hållbara och

    värdefulla för fortsatta (matematik)studier.

    Genom övnings- och examinationsuppgifter

    som kräver kreativa matematiska resonemang

    tvingas studenter att fokusera på de

    matematiska komponenternas grunder vilket

    möjliggör utveckling av högre matematiska

    kompetenser.* Vidare skapar kursupplägget

    förutsättningar för utveckling av personliga

    och professionella förmågor* väsentliga för

    lärande i tillämpningsämnen och utövande av

    framtida yrkesroll.

    Download full text (pdf)
    fulltext
  • 175.
    Mattsson, Linda
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Nyqvist, Robert
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Filmade interaktioner mellan novis och expert: En alternativ metod för att undervisa ämnesinnehåll och studieteknik2021Report (Other (popular science, discussion, etc.))
    Abstract [sv]

    Som en del i undervisningen i såväl programmering som matematik använder vi oss av filmade interaktioner mellan novis och expert inom respektive område. I programmering ersätter filmerna konventionella föreläsningar och ligger till grund för ett upplägg med blended learning.

    Download full text (pdf)
    fulltext
  • 176. Mbiydzenyuy, Gideon
    et al.
    Widell, J
    Sandbreck, C-H
    Dahl, Mattias
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Effektutvärdering avkilometerskatt för tunga fordon: en omvärldsstudie2016Report (Other academic)
    Abstract [en]

    Over the last 15 years, distance-based road user charging schemes have been designed and deployed across the European Union. At least 10 EU countries today calculate, charge and collect fares for the use of road infrastructure following a differential model supported by positioning, communication, and other related technologies such as ANPR. As future road charging schemes are being developed, existing systems, although aimed at varying goals, will play a critical role in passing along their experiences to positively influence the development of future road charging schemes. This report set a high ambition to study the evaluation landscape in the domain of distance-based road user charging. Given the current efforts within the ARENA knowledge platform targeted toward the development of an evaluation methodology for a possible distance-based road user charging scheme in Sweden, the report was aimed at laying a solid foundation to ensure that the development of the methodology should as much as possible build on real world experiences. To that effect, 15 systems are identified and analysed, including two congestion-charging schemes (Gothenburg and Stockholm) and 13 distance-based charging schemes in Europe andother parts of the world. The predominantly literature review-based analysis aim to isolate the goals behind these different schemes, if and how the scheme was evaluated, including the questions that were raised in the evaluation, evaluation phases that were covered, the methods that were employed in collecting evaluation data, and analysing the data for possible effects. More important, the analysis aimed at understanding what proven effects were uncovered, as well as the lessons learned from the evaluation process. In order to perform an analysis, the above goals were disaggregated into concrete questions, e.g., for each specific system, what was the evaluation method employed. Secondary data was then collected mainly through Internet search within transport relevant databases. A number of criteria were consistently applied in filtering the secondary data sources, e.g., source quality. The analysis focused on determining if each evaluation report had a clear evaluation goal, motivation for choices of methods, based on real or synthetic data, and if there were clearly demonstrated effects that can be considered to be significant.The work in this study turned out to expose an unfortunate serious deficiency in evaluation material from existing distance-basedroad user charging schemes both from an ex-ante, and even more-so, from an ex-post perspective. Of the 15 systems identified (with the exception of the Gothenburg and Stockholm cases), only six had any material on evaluation, with half addressing an overall system perspective and the rest addressing some aspects of the system. Moreover, only one report actually conducted and related both ex-ante and ex-post perspectives (Switzerland) while most studies were limited to ex-ante.Overall, the analysis suggests that fiscal and environmental measures predominates the goal behind several distance-based road user charging schemes while traffic management and modal shift are on the opposite end. Results from evaluation of congestion schemes in Stockholm and Gothenburg, suggests significant reductions were observed in the overall traffic volume, although disproportionately between passenger cars and heavy vehicles. Results from distance-based road user charging schemes discussed in this report suggests the increasein transport costs to be consistent across different schemes, e.g., 5% to 7% in Germany. 4While this may be a fact, it is difficult to separate how much of it may be a result of speculation that in turn drives up prices and cost compared to real costs as aresult of the scheme. This is because distance-based charging schemes also benefits for transport organizations where they are implemented, e.g., when schemes provide subsidies for environmentally clean fleet such as in Germany and the Czech Republic, or when competition with foreign vehicles is normalized or when traffic adjustments results in reduced travel times as in Stockholm. Therefore, without hard facts it can be difficult to fully explain the net increase in transport costs as a consequence of distance-based road user charging.Expectations based on existing work are that as transport cost increases, so too will the shares in rail traffic and the income for infrastructure financing. Also, traffic volumes, empty runs, vehicle-km, and emissions, all turn to decrease due to the implementation of a distance-based road charging scheme. Schemes that account for the Euro class differentiations are seen to significantly alter that fleet demographics but no clear trends were reported. Most of the evaluation reports analysed lacked documentation on evaluation data which made it difficult to ascertain the quality of established impacts. This is not just a cost issue but also exposes a limitation in the entire evaluation methodology framework employed.A centralchallenge in conducting impact evaluation is to isolate specific effects within a system that can be associated specifically to distance-based road user charging. This is because such effects are often the results of several interdependent elements with versatile and far-reaching consequences all changing during the evaluation period. Based on the information analysed in this study, it can be recommended to consider as many indicators as possible when addressing impact evaluation for distance-based road user charging in Sweden. Such indicators should then provide a basis for collecting statistically representative data that span across several domains. We believe that it is better to have data about several indicators, even though such indicators may overlap, compared to having data about few indicators. A true representative sample should identify geographic areas of interest, vehicle categories of interest, as well as specific industries such as the forest industry. The sample should also cover a longer time period to emphasize the time variability of the data. The impacts and benefits of distance-based road user charging in Sweden can be amplified if; the control system design, ex-ante evaluation, and ex-post evaluation are all addressed simultaneously as these elements can significantly affect each other.

  • 177.
    Mittmann Voigt, Gustavo Henrique
    et al.
    Federal University of Pampa (UNIPAMPA), Brazil.
    Irion Alves, Dimas
    Aeronautics Institute of Technology (ITA), Brazil.
    Müller, Crístian
    Federal University of Pampa (UNIPAMPA), Brazil.
    Machado, Renato
    Aeronautics Institute of Technology (ITA), Brazil.
    Ramos, Lucas Pedroso
    Aeronautics Institute of Technology (ITA), Brazil.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    A Statistical Analysis for Intensity Wavelength-Resolution SAR Difference Images2023In: Remote Sensing, E-ISSN 2072-4292, Vol. 15, no 9, article id 2401Article in journal (Refereed)
    Abstract [en]

    This paper presents a statistical analysis of intensity wavelength-resolution synthetic aperture radar (SAR) difference images. In this analysis, Anderson Darling goodness-of-fit tests are performed, considering two different statistical distributions as candidates for modeling the clutter-plus-noise, i.e., the background statistics. The results show that the Gamma distribution is a good fit for the background of the tested SAR images, especially when compared with the Exponential distribution. Based on the results of this statistical analysis, a change detection application for the detection of concealed targets is presented. The adequate selection of the background distribution allows for the evaluated change detection method to achieve a better performance in terms of probability of detection and false alarm rate, even when compared with competitive performance change detection methods in the literature. For instance, in an experimental evaluation considering a data set obtained by the Coherent All Radio Band Sensing (CARABAS) II UWB SAR system, the evaluated change detection method reached a detection probability of 0.981 for a false alarm rate of 1/km2. © 2023 by the authors.

    Download full text (pdf)
    fulltext
  • 178.
    Molin, R.D.
    et al.
    Federal University of Santa Maria, Brazil.
    Fabrin, A.C.F.
    Federal University of Santa Maria, Brazil.
    Sperotto, P.
    Federal University of Santa Maria, Brazil.
    Alves, D.I.
    Federal University of Santa Maria, Brazil.
    Bayer, F.M.
    Federal University of Santa Maria, Brazil.
    Machado, Renato
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Dammert, P.
    Saab AB, SWE.
    Hellsten, H.
    Saab AB, SWE.
    Ulander, L
    Totalförsvarets Forskningsinstitut, SWE.
    Iterative Change Detection Algorithm for Low-Frequency UWB SAR2016Conference paper (Refereed)
  • 179.
    Molin, Ricardo D., Jr.
    et al.
    ITA, BRA.
    Rosa, Rafael A. S.
    Visiona Tecnol Espacial SA, BRA.
    Bayer, Fabio M.
    Univ Fed Santa Maria, BRA.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Machado, Renato
    ITA, BRA.
    A CHANGE DETECTION ALGORITHM FOR SAR IMAGES BASED ON LOGISTIC REGRESSION2019In: 2019 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM (IGARSS 2019), IEEE , 2019, p. 1514-1517Conference paper (Refereed)
    Abstract [en]

    This paper presents an incoherent change detection algorithm (CDA) for synthetic aperture radar (SAR) images based on logistic regression. The input data consists of a set of 24 SAR images acquired in a test site in northern Sweden [1]. Subsets of these images are trained based on pixel amplitude, flight heading and neighboring features such as local mean, standard deviation and skewness. The proposed method intends to explore the advantadges from both pixel- and object-based approaches, while evaluating multiple features in amplitude only SAR images. Preliminary results based on K-fold cross validation have shown that the proposed CDA achieves good performance when compared to the results presented in [1].

  • 180.
    Moreira, Paula S. E.
    et al.
    Universidade Federal de Santa Catarina, Florianópolis, Brazil.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Prime groupoid graded rings with applications to partial skew groupoid rings2024In: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate primeness of groupoid graded rings. We provide a set of necessary and sufficient conditions for primeness of a nearly-epsilon strongly groupoid graded ring. Furthermore, we apply our main result to get a characterization of prime partial skew groupoid rings, and in particular of prime groupoid rings, thereby generalizing a classical result by Connell and partially generalizing recent results by Steinberg. © 2024 The Author(s). Published with license by Taylor & Francis Group, LLC.

    Download full text (pdf)
    fulltext
  • 181.
    Musonda, John
    et al.
    The University of Zambia, ZMB.
    Richter, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Silvestrov, Sergei
    Mälardalens Högskola, SWE.
    Reordering in noncommutative algebras associated with iterated function systems2020In: Springer Proceedings in Mathematics and Statistics / [ed] Silvestrov S.,Malyarenko A.,Rancic M., Springer , 2020, Vol. 317, p. 509-552Conference paper (Refereed)
    Abstract [en]

    A general class of multi-parametric families of unital associative complex algebras, defined by commutation relations associated with group or semigroup actions of dynamical systems and iterated function systems, is considered. A generalization of these commutation relations in three generators is also considered, modifying Lie algebra type commutation relations, typical for usual differential or difference operators, to relations satisfied by more general twisted difference operators associated with general twisting maps. General reordering and nested commutator formulas for arbitrary elements in these algebras are presented, and some special cases are considered, generalizing some well-known results in mathematics and physics. © Springer Nature Switzerland AG 2020.

  • 182.
    Musonda, John
    et al.
    The University of Zambia, ZMB.
    Richter, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Silvestrov, Sergei
    Mälardalens Högskola, SWE.
    Twisted difference operator representations of deformed lie type commutation relations2020In: Springer Proceedings in Mathematics and Statistics / [ed] Silvestrov S.,Malyarenko A.,Rancic M., Springer , 2020, Vol. 317, p. 553-573Conference paper (Refereed)
    Abstract [en]

    Operator representations of deformed Lie type commutation relations, associated with group or semigroup actions of dynamical systems and iterated function systems are considered. In particular, it is shown that some multi-parameter deformed symmetric difference and multiplication operators satisfy these commutation relations. The operator representations are considered also in the context of twisted derivations. © Springer Nature Switzerland AG 2020.

  • 183.
    Narri, Vandana
    et al.
    Scania Cv Ab, SWE.
    Kulesza, Wlodek
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Performance Optimisation of Accelerated Tests: Simulation and Experimental Approach in Automotive Industry2020In: Proceedings of the 2020 24th International Conference Electronics, ELECTRONICS 2020 / [ed] Andriukaitis D.,Valinevicius A.,Sledevic T., Institute of Electrical and Electronics Engineers Inc. , 2020, article id 9141623Conference paper (Refereed)
    Abstract [en]

    This paper is focused on the performance evaluation of Accelerated Tests (AT), which are carried out in a rapid manner to estimate life-length of a Device Under Test (DUT). Manufacturers need to preform ATs on the prototype of the product to anticipate its reliability and lifetime. The requirements for higher reliability impose tests of DUT's materials and components in advance. ATs expose products to different stressing environments, which include Electrical Stress, Mechanical Vibration, Temperature Shock, Temperature Cycling, Humidity, and others. An AT profile consists of different parameters, which depend on the DUT, and the most common are: a type of stress, rate of change, stress extreme points. Although these tests are accelerated, they are still time consuming. Furthermore, for large and complex DUTs, the test reliability itself can be doubted due to the involved diversity and uncertainty. In this paper, different experimental methods are applied to optimize the virtual test parameters to obtain reliable results. © 2020 IEEE.

  • 184.
    Natanael, Rodrigues Gomes
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Viet Thuy, Vu
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Mats, Pettersson
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Patrik, Dammert
    SAAB EDS, SWE.
    Hans, Hellsten
    SAAB EDS, SWE.
    Likelihood ratio test for incoherent wavelength-resolution SAR change detection2016Conference paper (Refereed)
  • 185.
    Nedic, Mitja
    et al.
    University of Helsinki, FIN.
    Ehrenborg, Casimir
    Katholieke Universiteit Leuven, BEL.
    Ivanenko, Yevhen
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Ludvig-Osipov, Andrei
    Chalmers University of Technology, SWE.
    Nordebo, Sven
    Linnaeus University, SWE.
    Luger, Annemarie
    Stockholm University, SWE.
    Jonsson, Lars
    KTH, SWE.
    Sjöberg, Daniel
    Lund University, SWE.
    Gustafsson, Mats
    Lund University, SWE.
    Herglotz functions and applications in electromagnetics2021In: Advances in Mathematical Methods for Electromagnetics / [ed] Kazuya Kobayashi, Paul Denis Smith, Institution of Engineering and Technology , 2021, p. 491-514Chapter in book (Refereed)
    Abstract [en]

    Herglotz functions inevitably appear in pure mathematics, mathematical physics, and engineering with a wide range of applications. In particular, they are the pertinent functions to model passive systems, and thus appear in modeling of electromagnetic phenomena in circuits, antennas, materials, and scattering. In this chapter, we review the basic theory of Herglotz functions and its applications to determine sum rules and physical bounds for passive systems.

  • 186.
    Nelaturi, Ganesh Sreekhyath
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Poliki, Venkata Sai
    Automated Attendance System: Recognition System Based on Facial Features2022Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Consider a situation where you need to identify each and every person in a room and categorize each of the persons as present or absent. To mark the presence of hundreds of people in a room takes a lot of time, which means you can eventually be left out with less time to explain the main aim of that meeting, class, or some other things. In such cases, either we may need a lot of time for a meeting or we may need more people to accomplish the tasks. In the present world, time is considered equivalent to money. If you lose your time you will lose your money. Many education institutions and offices see this as a very important consideration to maintain their busy schedule.

     In this study, we came to know that many institutions and offices are facing the same issue, so as engineers we decided to take this as a challenge and try to find a solution to it. Our main objective of this project is to make a working model, which helps in marking the attendances of the person automatically and saves precious time. We can say that human effort is simply replaced by our end product which helps the person to spend more time efficiently.

     To replace the human effort with an easy and cost-efficient system that has accurate results, we are using a Raspberry Pi 4 Model B as a microcontroller and along with it, we are using a Raspberry Pi camera module to capture the image of the person. To control and give the commands to the microcontroller, we are using MATLAB as a programming language that interprets the commands given by the user. 

     Using this Raspberry Pi system with a camera module attached to the Raspberry Pi, We can capture the image of the person who comes in front of the camera. Once the person images are captured, the microcontroller starts running the program which can predict the face of a person from the pre-trained database that we have previously stored in the system. Once the prediction is done, the face of the person is automatically marked as present in an excel sheet under the predicted name.

     We are concluding that by using the automated attendance system one can avoid the manual marking of persons and save time. For further future works, one can use a good resolution camera module to capture the images clearly and can use the python coding method to access face recognition. We can also develop a mobile application, that can access the camera present in the smartphone which can be used to capture the images and mark the attendances automatically.

    Download full text (pdf)
    Automated Attendance System - Recognition System Based on Facial Features
  • 187.
    Nilsson, Fritjof
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Peng, Yanjun
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    An Evaluation Study of Leak Testing Technologies for Watertight Plate Heat Exchangers: Fast and sustainable leak testing technology for high energy efficiency products2023Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Background: One part of manufacturing a Plate Heat Exchanger (PHE) is to leak test them before delivery. Today, helium is used extensively in leak testing. How-ever, it is unsustainable to use helium in leak testing, because of its non-renewability and therefore becoming more and more expensive. Also, this technology is relatively complex. At the same, PHEs are rising in demand due to lack of energy resources in Europe. Therefore, possibilities emerged for using air based leak testing technologies in upcoming test lines and that is why an evaluation needs to be done to find the most suitable technology.

    Objectives: The objective of this master’s thesis is to evaluate and identify the most suitable leak testing technology for validating the watertightness requirement of 10−3 mbar·l/s at 1 bar pressure difference. There is a scientific gap in comparing how different air based leak testing technologies perform with different volumes of the test vessels. This thesis will identify the most suitable air based leak testing technology by evaluating three technologies: Pressure Decay, Differential Pressure Decay and Vacuum Decay. With the main focus on how different volumes impacts the performance of each technology. Lastly, this study aims to determine an optimal test pressure that achieves the shortest cycle time for the selected test technology. Choosing the most suitable test technologies will result in fewer production break-downs and interruptions. Additional, being able to phase out helium in leak testing.

    Methods: The workflow for evaluating the different leak testing technologies began with the implementation and installation of each test setup and ensuring the reliability of the gathered data. After verifying the absence of leakage in the system, a simulated leak was calibrated to match the requirement’s leak rate. Four test vessels with original volumes of 0.10, 0.45, 1.66 and 2.50 l were utilized. Various tests were then performed to answer the research questions, including measurements of leak rate at different pressures, analysis of outgassing characteristics, and determination of cycle time. Finally, by utilizing concept scoring, the most suitable leak testing technology was identified with respect to the volume.

    Results: The exhibited results in this thesis manifest how the different leak testing technologies perform depending on the volume. The relationship between leak rates and overpressures was obtained, which was then utilized to derive the theoretical detection time. The cycle time and accuracy were determined across various volumes. According to concept scoring, Pressure Decay was deemed the most suitable leak testing technology in terms of six different criteria.  

    Conclusions: All three technologies were able to determine a leak rate corresponding to the watertightness requirement. From the evaluation, Pressure Decay was the most suitable technology to use across the majority of the volumes, with an accuracy below 15%. The test cycle times were optimizable by selecting an optimum testing pressure.  Therefore, being able to replace the helium leak testing in future test lines.

    Download full text (pdf)
    fulltext
  • 188. Niyizamwiyitira, C.
    et al.
    Lundberg, Lars
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Utilization-Based Schedulability Test of Real-Time Systems on Virtual Multiprocessors2015In: 2015 44TH INTERNATIONAL CONFERENCE ON PARALLEL PROCESSING WORKSHOPS, IEEE Computer Society, 2015, Vol. 2015-January, p. 267-276Conference paper (Refereed)
    Abstract [en]

    The number of applications that use virtual systems is growing, and one would like to use this kind of systems also for real-time applications with hard deadlines. Virtual machines with many cores are interesting since the underlying physical infrastructure usually contains many cores. We consider hard real-time tasks that execute on a virtual machine with m cores. Tasks are scheduled globally on the cores using fixed-priority preemptive scheduling. This means that a task can execute on different virtual cores at different instances in time. In order to avoid Dhall’s effect, which may cause task sets with even very low utilization to miss deadlines, we classify tasks into two priority classes, namely heavy and light tasks. Heavy tasks have higher priority than light tasks. For light tasks we use rate monotonic priority assignment. In this paper we propose a utilization-based test that shows if a task set is schedulable or not. If the task set is schedulable the test provides the priority for each task. The input to the test is the task set, the number of cores in the virtual machine (m), a period for the virtual machine with m cores, and the blocking time when a virtual machine does not have access to the underlying hardware in each period. © 2015 IEEE.

  • 189.
    Nyqvist, Robert
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Automatiserad rättning av beräknings och programmeringsuppgifter2020Report (Other (popular science, discussion, etc.))
    Abstract [sv]

    Molntjänsten CoCalc erbjuder en smidig administration av inlämnings-

    och laborationsuppgifter direkt i den miljö där studenterna ska

    använda vid problemlösning. CoCalc kombinerar ett stort antal fria

    matematikprogram och programmeringsspråk tillsammans med en Linuxterminal.

    Download full text (pdf)
    Robert Nykvist_Automatiserad rättning av beräknings och programmeringsuppgifter
    Download (pdf)
    Presentation_Automatiserad rättning av beräknings och programmeringsuppgifter
  • 190.
    Nyqvist, Robert
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Examination med stor valfrihet  och tydliga bedömningskriterier: Hur kan man konstruera på enkelt sätt en projektuppgift som både engagerar kursdeltagarna och har tydliga kriterier för varje betyg?2022Report (Other (popular science, discussion, etc.))
    Abstract [sv]

    Önskelista för kursutvecklare När jag utvecklar en inlämnings- eller projektuppgift försöker jag uppnå följande: 

    • Uppgifterna ska få studenterna engagerade så till den grad att de gärna avsätter tid utanför schema-lagd. 
    • Helst ska studenten redan vid inlämning ha en god uppfattning vilket betyget hen kommer att få. 
    • Det ska vara enkelt att rätta och betygsätta. 
    Download full text (pdf)
    fulltext
  • 191.
    Nystedt, Patrik
    et al.
    Högskolan Väst, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Group gradations on Leavitt path algebras2020In: Journal of Algebra and its Applications, ISSN 0219-4988, E-ISSN 1793-6829, Vol. 19, no 9, article id 2050165Article in journal (Refereed)
    Abstract [en]

    Given a directed graph E and an associative unital ring R one may define the Leavitt path algebra with coefficients in R, denoted by LR(E). For an arbitrary group G, LR(E) can be viewed as a G-graded ring. In this paper, we show that LR(E) is always nearly epsilon-strongly G-graded. We also show that if E is finite, then LR(E) is epsilon-strongly G-graded. We present a new proof of Hazrat's characterization of strongly g-graded Leavitt path algebras, when E is finite. Moreover, if E is row-finite and has no source, then we show that LR(E) is strongly-graded if and only if E has no sink. We also use a result concerning Frobenius epsilon-strongly G-graded rings, where G is finite, to obtain criteria which ensure that LR(E) is Frobenius over its identity component. © 2020 World Scientific Publishing Company.

  • 192.
    Nystedt, Patrik
    et al.
    University West, Sweden.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Simple graded rings, non-associative crossed products and Cayley-Dickson doublings2020In: Journal of Algebra and its Applications, ISSN 0219-4988, E-ISSN 1793-6829, Vol. 19, no 12, article id 2050231Article in journal (Refereed)
    Abstract [en]

    We show that if a non-associative unital ring is graded by a hypercentral group, then the ring is simple if and only if it is graded simple and the center of the ring is a field. Thereby, we extend a result by Jespers from the associative case to the non-associative situation. By applying this result to non-associative crossed products, we obtain non-associative analogues of results by Bell, Jordan and Voskoglou. We also apply this result to Cayley-Dickson doublings, thereby obtaining a new proof of a classical result by McCrimmon.

  • 193.
    Nystedt, Patrik
    et al.
    Univ West, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pinedo, Hector
    Univ Ind Santander, COL.
    EPSILON-STRONGLY GROUPOID-GRADED RINGS, THE PICARD INVERSE CATEGORY AND COHOMOLOGY2020In: Glasgow Mathematical Journal, ISSN 0017-0895, E-ISSN 1469-509X, Vol. 62, no 1, p. 233-259, article id PII S0017089519000065Article in journal (Refereed)
    Abstract [en]

    We introduce the class of partially invertible modules and show that it is an inverse category which we call the Picard inverse category. We use this category to generalize the classical construction of crossed products to, what we call, generalized epsilon-crossed products and show that these coincide with the class of epsilon-strongly groupoid-graded rings. We then use generalized epsilon-crossed groupoid products to obtain a generalization, from the group-graded situation to the groupoid-graded case, of the bijection from a certain second cohomology group, defined by the grading and the functor from the groupoid in question to the Picard inverse category, to the collection of equivalence classes of rings epsilon-strongly graded by the groupoid.

  • 194.
    Nystedt, Patrik
    et al.
    University West, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pinedo, Héctor
    Industrial University of Santander, COL.
    Artinian and noetherian partial skew groupoid rings2018In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 503, p. 433-452Article in journal (Refereed)
    Abstract [en]

    Let α={α_g : R_{g^{−1}}→R_g}_{g∈mor(G)} be a partial action of a groupoid G on a (not necessarily associative) ring R and let S=R⋆G be the associated partial skew groupoid ring. We show that if α is global and unital, then S is left (right) artinian if and only if R is left (right) artinian and R_g={0}, for all but finitely many g∈mor(G). We use this result to prove that if α is unital and R is alternative, then S is left (right) artinian if and only if R is left (right) artinian and R_g={0}, for all but finitely many g∈mor(G). This result applies to partial skew group rings, in particular. Both of the above results generalize a theorem by J. K. Park for classical skew group rings, i.e. the case when R is unital and associative, and G is a group which acts globally on R. We provide two additional applications of our main results. Firstly, we generalize I. G. Connell's classical result for group rings by giving a characterization of artinian (not necessarily associative) groupoid rings. This result is in turn applied to partial group algebras. Secondly, we give a characterization of artinian Leavitt path algebras. At the end of the article, we relate noetherian and artinian properties of partial skew groupoid rings to those of global skew groupoid rings, as well as establish two Maschke-type results, thereby generalizing results by M. Ferrero and J. Lazzarin for partial skew group rings to the case of partial skew groupoid rings.

  • 195.
    Nystedt, Patrik
    et al.
    University West, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pinedo, Héctor
    Industrial University of Santander, COL.
    Epsilon-strongly graded rings, separability and semisimplicity2018In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 514, no Nov., p. 1-24Article in journal (Refereed)
    Abstract [en]

    We introduce the class of epsilon-strongly graded rings and show that it properly contains both the collection of strongly graded rings and the family of unital partial crossed products. We determine when epsilon-strongly graded rings are separable over their principal components. Thereby, we simultaneously generalize a result for strongly group-graded rings by Nastasescu, Van den Bergh and Van Oystaeyen, and a result for unital partial crossed products by Bagio, Lazzarin and Paques. We also show that the family of unital partial crossed products appear in the class of epsilon-strongly graded rings in a fashion similar to how the classical crossed products present themselves in the family of strongly graded rings. Thereby, we obtain, in the special case of unital partial crossed products, a short proof of a general result by Dokuchaev, Exel and Simon concerning when graded rings can be presented as partial crossed products.

  • 196.
    Nystedt, Patrik
    et al.
    Högskolan Väst, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences. Blekinge Inst Technol, Dept Math & Nat Sci, SE-37179 Karlskrona, Sweden..
    Richter, Johan
    Mälardalens högskola, SWE.
    NON-ASSOCIATIVE ORE EXTENSIONS2018In: Israel Journal of Mathematics, ISSN 0021-2172, E-ISSN 1565-8511, Vol. 224, no 1, p. 263-292Article in journal (Refereed)
    Abstract [en]

    We introduce non-associative Ore extensions, S = R[X; sigma, delta], for any non-ssociative unital ring R and any additive maps sigma, delta : R -> R satisfying sigma(1) = 1 and delta(1) = 0. In the special case when delta is either left or right R-delta-linear, where R-delta = ker(delta), and R is delta-simple, i.e. {0} and R are the only delta-invariant ideals of R, we determine the ideal structure of the non-associative differential polynomial ring D = R[X; id(R),delta]. Namely, in that case, we show that all non-zero ideals of D are generated by monic polynomials in the center Z(D) of D. We also show that Z(D) = R-delta[p] for a monic p is an element of R-delta [X], unique up to addition of elements from Z(R)(delta) . Thereby, we generalize classical results by Amitsur on differential polynomial rings defined by derivations on associative and simple rings. Furthermore, we use the ideal structure of D to show that D is simple if and only if R is delta-simple and Z(D) equals the field R-delta boolean AND Z(R). This provides us with a non-associative generalization of a result by Oinert, Richter and Silve-strov. This result is in turn used to show a non-associative version of a classical result by Jordan concerning simplicity of D in the cases when the characteristic of the field R-delta boolean AND Z(R) is either zero or a prime. We use our findings to show simplicity results for both non-associative versions of Weyl algebras and non-associative differential polynomial rings defined by monoid/group actions on compact Hausdorff spaces.

    Download full text (pdf)
    fulltext
  • 197.
    Nystedt, Patrik
    et al.
    Högskolan Väst, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Richter, Johan
    Mälardalens högskola, SWE.
    Simplicity of Ore monoid rings2019In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 530, p. 69-85Article in journal (Refereed)
    Abstract [en]

    Given a non-associative unital ring R, a monoid G and a set π of additive maps R→R, we introduce the Ore monoid ring R[π;G], and, in a special case, the differential monoid ring. We show that these structures generalize, in a natural way, not only the classical Ore extensions and differential polynomial rings, but also the constructions, introduced by Cojuhari, defined by so-called D-structures π. Moreover, for commutative monoids, we give necessary and sufficient conditions for differential monoid rings to be simple. We use this in a special case to obtain new and shorter proofs of classical simplicity results for differential polynomial rings in several variables previously obtained by Voskoglou and Malm by other means. We also give examples of new Ore-like structures defined by finite commutative monoids. © 2019 Elsevier Inc.

  • 198. Oloumi, Daniel
    et al.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Mousavi, P.
    Rambabu, K.
    Imaging of oil-well perforations using UWB synthetic aperture radar2015In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 53, no 8, p. 4510-4520Article in journal (Refereed)
    Abstract [en]

    Ultrawideband (UWB) synthetic aperture radar (SAR) as a tool for oil well perforation monitoring is experimentally investigated in this paper. Experiments are conducted on a lab prototype that emulates the small section of an oil well. Oil well perforations are scanned using the designed UWB radar system for different experimental conditions. High-resolution images in both down-range and cross-range are obtained by using UWB pulses and signal processing. High-quality images are constructed using SAR processing algorithm with the proposed modifications. Experiments are carried out for different perforation conditions such as open, partially clogged and fully clogged cases. It is shown by the experiments that the proposed radar technique and the data processing methods are capable of providing more revealing high-quality images. This approach can be applied effectively to monitor the oil well medium and detect well impairment locations.

  • 199.
    Olsson, Andreas
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Analysis and improvement of risk assessment methodology for offshore energy installations: Aspects of environmental impact assessment and as-built subsea cable verification2023Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the expansion of offshore sustainable energy systems, there is growing pressure on the environment and permit processes and the accumulation results in much higher total risk for accidents of future assets. Anticipating the problems at the design stage and improving verification is likely to increase energy development and reduce costs. This thesis explores offshore DST (Decision Support Tools) and risk verification of subsea cable assets.For subsea cables, a statistical method is proposed utilizing measurement data together with shipping traffic data (AIS) to estimate the environmental risk and risk of accidents of installed cable assets. This should partially solve issues of improving design using more data and surveys and utilizing mechanical and sensor-specific characteristics to improve the confidence and burial estimation, contrary to today’s methodology. The implication of the two studies of cable burial risk assessment techniques and verification shows how a developed methodology can solve issues for verifying the integrity of an installed asset. Putting our methodology into practice involves many challenges. 

    For the marine Decision Support Tool (DST) and sustainable energy development, to estimate potential savings if permit processes would be shorter and less burdensome without degrading the quality of the EIA (Environmental Impact Assessment). A method is proposed to model various scenarios of effective savings from the development of a DST to reduce costs spent on EIA permitting by the offshore energy developers. The study of the implication of the marine EIA DST shows a quantifiable estimate of the savings potential for permit processes for sustainable offshore development, and results indicate a need for optimization of DST development, which can be an essential factor in its implementation and success.

     

    Download full text (pdf)
    fulltext
  • 200.
    Olsson, Andreas
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Frånberg, Oskar
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Kulesza, Wlodek
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    A New Method for As-built Burial Risk Assessment for Subsea Cables2022In: SyNERGY MED 2022 - 2nd International Conference on Energy Transition in the Mediterranean Area, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2022Conference paper (Refereed)
    Abstract [en]

    A new method using burial measurements for risk assessment of subsea cable installations is proposed. Only methods comparing the design boundaries have previously been used to verify subsea cable installments. The disadvantage of utilizing design boundaries is the possibility of not fulfilling the risk requirements since the assumed burial depth of the cable and its measurement data can differ, leading to the challenge of assessing how the difference and its uncertainty affect burial risk. We proposed and tested the method for a scenario using seagoing vessel traffic data and sensor characteristics. The analysis is limited to white measurement noise but shows a deviation in risk estimation between the design-and measurement-based assessments. The presented result enables the approximation of the risk assessment for projects of varying specifications. The proposed statistical method is a less conservative way to assess the correct installment of a cable and possibly to evaluate verification specifications. © 2022 IEEE.

1234567 151 - 200 of 350
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf