7,401 research outputs found

    Development and assessment of learning-based vessel biomarkers from CTA in ischemic stroke

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    Modellbasierte Simulation und Kalibrierung eines multimodalen Systems aus OCT und Optoakustik zur nichtinvasiven, präoperativen Dickenbestimmung von melanomverdächtigen Hautläsionen

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    In this dissertation, methods for the calibration of optical coherence tomography (OCT) systems and for the simulation of optoacoustic signals are presented. The key question here is whether a multimodal system consisting of OCT and optoacoustics is suitable for noninvasive, preoperative thickness determination of skin lesions suspected of melanoma and what conditions, if any, must be met for this purpose. Given the current state of the art, such a modality for melanoma diagnosis would be very enriching for dermatology. In addition to the definition of malignant melanoma, the most common diagnostic procedures in dermatology will be explained. The current approach to melanoma diagnostics shows that there is a lot of potential for improvement in order to be able to make diagnoses preoperatively in the future and to prevent unnecessary surgical interventions. The project in which this work was developed is briefly presented. It also discusses the physical principles needed to simulate and calibrate the multimodal system. The methods presented in chapters 6 and 7 for calibrating the OCT and for simulating the optoacoustic signals then build on these fundamentals. The general setup of OCT systems as well as of two specific OCT devices is explained. The methods then presented for geometric calibration and refractive index correction are essential for the thickness determination of structures in OCT images. In chapter 7 different methods are presented which are suitable for the simulation of optoacoustic signals. On the one hand, the solution of the direct problem, i.e. the creation of optoacoustic signals, is shown as well as the solution of the indirect problem, in which conclusions can be drawn about the initial pressure profile if optoacoustic signals are available. Furthermore, optoacoustic signals of simulated melanomas are generated and evaluated, which is also important for answering the key question. The results of this dissertation are discussed in detail at the end and an outlook is given on how the work on the multimodal system will continue.In der vorliegenden Dissertation werden Methoden zur Kalibrierung von Optischen Kohärenztomographie (OCT)-Systemen und zur Simulation von Optoakustiksignalen präsentiert. Die Kernfrage hierbei ist, ob ein multimodales System aus OCT und Optoakustik für eine nichtinvasive, präoperative Dickenbestimmung von melanomverdächtigen Hautläsionen geeignet ist und welche Bedingungen hierfür gegebenenfalls erfüllt werden müssen. Beim derzeitigen Stand der Technik wäre solch eine Modalität für die Melanomdiagnostik sehr bereichernd f ¨ ur die Dermatologie. Neben der Definition eines malignen Melanoms werden die geläufigsten diagnostischen Verfahren in der Dermatologie erläutert. Das momentane Vorgehen bei der Melanomdiagnostik zeigt, dass hier sehr viel Potenzial für Verbesserungen ist, um zukünftig Diagnosen präoperativ vornehmen und unnötige operative Eingriffe verhindern zu können. Es wird kurz das Projekt vorgestellt, in dem diese Arbeit entstanden ist. Außerdem werden die physikalischen Grundlagen erörtert, die für die Simulation und Kalibrierung des multimodalen Systems benötigt werden. Auf diesen Grundlagen bauen dann die in Kapitel 6 und 7 vorgestellten Methoden zur Kalibrierung des OCT sowie zur Simulation der optoakustischen Signale auf. Es wird der allgemeine Aufbau von OCT-Systemen sowie von zwei speziellen OCT-Geräten erklärt. Die dann vorgestellten Methoden zur geometrischen Kalibrierung und zur Brechungsindexkorrektur sind unerlässlich für eine Dickenbestimmung von Strukturen in OCT-Bildern. In Kapitel 7 werden verschiedene Verfahren vorgestellt, die sich zur Simulation von optoakustischen Signalen eignen. Hier wird zum einen die Lösung des direkten Problems, also das Erzeugen von Optoakustiksignalen gezeigt sowie die Lösung des indirekten Problems, bei der Rückschluss auf das initiale Druckprofil geschlossen werden kann, wenn Optoakustiksignale vorliegen. Weiterhin werden Optoakustiksignale von simulierten Melanomen erzeugt und ausgewertet, was ebenfalls wichtig für die Beantwortung der Kernfrage ist. Die Ergebnisse dieser Dissertation werden zum Schluss ausführlich erörtert und es wird ein Ausblick darauf gegeben, wie die Arbeit am multimodalen System weitergeht

    Forschungsbericht / Hochschule Mittweida

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    Classical and quantum algorithms for scaling problems

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    This thesis is concerned with scaling problems, which have a plethora of connections to different areas of mathematics, physics and computer science. Although many structural aspects of these problems are understood by now, we only know how to solve them efficiently in special cases.We give new algorithms for non-commutative scaling problems with complexity guarantees that match the prior state of the art. To this end, we extend the well-known (self-concordance based) interior-point method (IPM) framework to Riemannian manifolds, motivated by its success in the commutative setting. Moreover, the IPM framework does not obviously suffer from the same obstructions to efficiency as previous methods. It also yields the first high-precision algorithms for other natural geometric problems in non-positive curvature.For the (commutative) problems of matrix scaling and balancing, we show that quantum algorithms can outperform the (already very efficient) state-of-the-art classical algorithms. Their time complexity can be sublinear in the input size; in certain parameter regimes they are also optimal, whereas in others we show no quantum speedup over the classical methods is possible. Along the way, we provide improvements over the long-standing state of the art for searching for all marked elements in a list, and computing the sum of a list of numbers.We identify a new application in the context of tensor networks for quantum many-body physics. We define a computable canonical form for uniform projected entangled pair states (as the solution to a scaling problem), circumventing previously known undecidability results. We also show, by characterizing the invariant polynomials, that the canonical form is determined by evaluating the tensor network contractions on networks of bounded size

    Development and assessment of learning-based vessel biomarkers from CTA in ischemic stroke

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    Algebraic solutions of linear differential equations: an arithmetic approach

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    Given a linear differential equation with coefficients in Q(x)\mathbb{Q}(x), an important question is to know whether its full space of solutions consists of algebraic functions, or at least if one of its specific solutions is algebraic. After presenting motivating examples coming from various branches of mathematics, we advertise in an elementary way a beautiful local-global arithmetic approach to these questions, initiated by Grothendieck in the late sixties. This approach has deep ramifications and leads to the still unsolved Grothendieck-Katz pp-curvature conjecture.Comment: 47 page

    Hyperbolic Image-Text Representations

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    Visual and linguistic concepts naturally organize themselves in a hierarchy, where a textual concept ``dog'' entails all images that contain dogs. Despite being intuitive, current large-scale vision and language models such as CLIP do not explicitly capture such hierarchy. We propose MERU, a contrastive model that yields hyperbolic representations of images and text. Hyperbolic spaces have suitable geometric properties to embed tree-like data, so MERU can better capture the underlying hierarchy in image-text data. Our results show that MERU learns a highly interpretable representation space while being competitive with CLIP's performance on multi-modal tasks like image classification and image-text retrieval.Comment: Technical repor

    Multistage DPG time-marching scheme for nonlinear problems

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    In this article, we employ the construction of the time-marching Discontinuous Petrov-Galerkin (DPG) scheme we developed for linear problems to derive high-order multistage DPG methods for non-linear systems of ordinary differential equations. The methodology extends to abstract evolution equations in Banach spaces, including a class of nonlinear partial differential equations. We present three nested multistage methods: the hybrid Euler method and the two- and three-stage DPG methods. We employ a linearization of the problem as in exponential Rosenbrock methods, so we need to compute exponential actions of the Jacobian that change from time steps. The key point of our construction is that one of the stages can be post-processed from another without an extra exponential step. Therefore, the class of methods we introduce is computationally cheaper than the classical exponential Rosenbrock methods. We provide a full convergence proof to show that the methods are second, third, and fourth-order accurate, respectively. We test the convergence in time of our methods on a 2D + time semi-linear partial differential equation after a semidiscretization in space

    Constructing a profile for proactive career self-management in public higher education institutions in Ghana

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    Text in English with abstracts and keywords in English, isiXhosa, and isiZuluThe principal focus of this research study was to investigate the relationship among psychosocial career pre-occupation, social connectedness, and organisational commitment, and to determine whether an overall proactive career management profile can be constructed to inform career self-management practices in public higher education institutions (HEIs) in Ghana. Again, the research study intended to provide a background for testing hypotheses and theories as well as moderating the effect of socio-demographic characteristics (age, gender, marital status and job level) on the relationship between psychosocial career pre-occupations, social connectedness and organisational commitment. A cross-sectional quantitative approach was conducted on a purposively selected sample of senior staff comprising academic and administrative staff (n = 288), from a single public higher educational institution in Ghana. The measuring instruments include a career pre-occupations inventory workplace friendship scale and an organisational commitment scale. Descriptive statistics (mean, standard deviation, skewness and kurtosis), bi-variate correlation analysis (Pearson product moment correlation coefficient), and inferential and multivariate statistics (SEM analysis, moderated regression analysis, ANOVAs and independent sample t-test) were used for the study. Descriptive, bi-variate correlation and inferential statistics revealed that individual psychosocial career pre-occupations, social connectedness and organisational commitment can be used as elements within a proactive career self-management framework within the Ghanaian higher education institutions. The results of the moderated analysis showed that respondents’ gender and job level moderated employees’ level of psychosocial career pre-occupations in predicting organisational commitment. Furthermore, the test for significant mean differences revealed that gender, marital status and job level differed marginally in their psychosocial career pre-occupations, social connectedness and commitment to the organisation. Theoretically and empirically, the results advanced the career construction theory by empirically validating the core elements of career self-management. Practically, a recommendation was made to inform human resource (HR) managers and HR practitioners in public higher education institutions in Ghana and the consequences indicated in the study offer the opportunity to monitor and provide strategies and interventions for employees in their quest for career choices.Ugqaliselo oluphambili kolu phononongo lophando yayikukuphanda ubudlelwane phakathi komsebenzi wangaphambi kwekhondo ngokwesimo sengqondo nangokwezentlalo (psychosocial career pre-occupation), ukuziphatha, nokunxulumana kwezinto zokuziphatha nezentlalo (social connectedness), kunye nokuzibophelela kulungelelaniso /kucwangciso lombutho (organisational commitment), nokuqonda ukuba ingaba iprofayili yeendlela zokulawula ikhondo elisebenzayo elipheleleyo inokwakhelwa ukwazisa izenzo zekhondo lomsebenzi lokuzilawula kumaziko emfundo ephakamileyo karhulumente/oluntu (HEIs) eGhana. Kwakhona , uphononongo lophando lwaluzimisele ukunikezela ngomhlaba osisiseko wokuvavanya ingcinga ethathwa njengeyinyaniso engekaqinisekiswa (hypothesis) neethiyori kwakunye nokumodereyitha impembelelo yeempawu zedemografi yoluntu, i-socio-demographic characteristics (iminyaka, isini, imeko yomtshato,kunye nenqanaba lomsebenzi) kubudlelwane phakathi kwemisebenzi yangaphambi kwekhondo nemeko yezengqondo nabantu (psychosocial career pre-occupations), unxulumano lwabantu kunye nokuzibophelela kumbutho (organizational commitment). Inkqubo yophando ngokobungakanani enqamlezileyo ngokwamacandelo ahlukeneyo (cross sectional quantitative approach) yenziwe kwisampulu ekhethwe ngenjongo kujoliswe kubasebenzi abaphezulu/abadala ababandakanya izifundiswa nabasebenzi bezolawulo (n = 288), besuka kwiziko elinye loluntu lemfundo ephakamileyo eGhana. Izixhobo zokulinganisa zibandakanya uluhlu lwezinto kwisikali semisebenzi yangaphambi kwekhondo ubudlelwane kunye nokuzibophelela kumbutho kwindawo yokusebenzela. Iinkcukacha-manani ezichazayo (i-avareji, ukutenxa kumgangatho (standard deviation), ubugoso (skewness) kunye nomlinganiselo weenkcukacha-manani osetyenziselwa ukuchaza ukuhanjiswa kwedatha ephawulweyo malunga nentsingiselo (kurtosis), uhlalutyo lolungelelwaniso oluphindwe kabini kunye neenkcukacha-manani ezinokuthelelelekwa (i- Pearson product moment correlation coefficient), kunye neenkcukacha manani ezizintlobo-ntlobo ezininzi ezinokuthelekelelwa (uhlalutyo lwe-SEM, uhlalutyo oluhlehlayo olonganyelweyo/ olumodareyithiweyo, i-ANOVA kunye novavanyo oluzimeleyo lwe-t-test) zasetyenziswa kolu phando/phononongo. Inkcukacha-manani ezichazayo, ulungelelwaniso/unxulumaniso oluphindwe kabini kunye nezinokuthelekelelwa ezinentsingiselo zibonise ukuba imisebenzi yangaphambi kwekhondo,ngokwemeko yengqondo neyentlalo, unxulumano lwentlalo yoluntu kunye nokuzibophelela kumbutho kunokusetyenziswa njengezinto ezingaphakathi kwesakhelo solawulo esisebenzayo ngaphakathi kumaziko emfundo ephakamileyo yaseGhana.Iziphumo zohlalutyo olumodareyithiweyo zibonise ukuba isini sabaphenduli nenqanaba lomsebenzi samodareyitha inqanaba labasebenzi kwimisebenzi yangaphambi kwekhondo kwimeko yengqondo nezentlolontle ekuqikeleleni ukuzibophelela kumbutho. Ngaphaya koko, uvavanyo olubalulekileyo lweeyantlukwano lubonise ukuba isini, meko yomtshato kunye nenqanaba lomsebenzi lahlukile kancinci ngokwe-avareji kwimisebenzi yaphambi kwekhondo labo yengqondo nentlalontle, unxibelelwano lwentlalo kunye nokuzinikela embuthweni. Ngokwethiyori nangobungqina, iziphumo ziqhubele phambili ithiyori yolwakhiwo lwekhondo lomsebenzi ngokuqinisekisa ngobuchule izinto ezingundoqo zokuzilawula kwekhondo lomsebenzi.Ngokwenene, kwenziwa isindululo sokwazisa abaphathi bezabasebenzi neengcali ze-HR kumaziko emfundo ephakamileyo yoluntu eGhana kwaye iziphumo ezibonakaliswe kuphononongo zinika ithuba lokubeka esweni nokubonelela ngezicwangciso-qhinga nongenelelo ngoncedo kubaqeshwa kwiphulo labo lokukhetha amakhondo omsebenzi.Lesi sifundo socwaningo sasigxile kakhulu ekuphenyeni ngobudlelwano phakathi kokucabanga ngomkhakha womsebenzi komuntu, ukuxhumana nabantu, ukuzibophezela komuntu emsebenzini, kanye nokunquma ukuthi iphrofayili yokukwazi ukuzilawula ngokuzenzela ekukhetheni umkhakha womsebenzi kungahlelwa yini ngendlela yokuthi kudlale indima ekuzilawuleleni maqondana nomkhakha womsebenzi ezikhungweni zezemfundo ephakeme zomphakathi (ama-HEI) eGhana. Kanti futhi, isifundo socwaningo sihlose ukunikeza umlando maqondana nokuhlola imicabango kanye nemibono yezinjulalwazi kanjalo nokulinganisa umphumela wezici zokuhleleka kwabantu emphakathini (iminyaka yobudala, ubulili, isimo somshado kanye nezinga lomsebenzi) ebudlelwaneni phakathi kokucabanga ngomkhakha womsebenzi komuntu, ukuxhumana nabantu, kanye nokuzibophezela emsebenzini. Kwalandelwa indlela yokubheka isibalo samaqoqo abantu emphakathini ngokukhetha ngokuqaphela isampula labasebenzi abasezikhundleni eziphezulu elibandakanya abasebenza ngezemfundo kanye nezokuphatha (n = 288), esikhungweni sezemfundo ephakeme somphakathi esisodwa eGhana. Amathuluzi okukala afaka kuwo isilinganiso sobungane basemsebenzini ekukhetheni ezinhlobeni zemikhakha ecatshangwayo kanye nesilinganiso maqondana nokuzibophezela kwabantu emsebenzini. Kulolu cwaningo kwasetshenziswa izibalo ezichazayo (okujwayelekile, ukuphambuka okuvamile, ukungalingani kanye nobukhali), ukuhlaziywa kokuhlobana okukhona phakathi kwezinombolo ezimbili (isilinganiso sokuxhumana kwezinombolo ezimbili ngokukaPearson), kanye nezibalo eziveza izimbangela nezibalo ezahlukahlukene (ukuhlaziywa kwe-SEM, ukuhlaziywa kokubuyelamuva okulingene, ama-ANOVA kanye nesampula elizimele lokuhlola). Izibalo ezichazayo, eziveza ukuhlobana phakathi kwezinombolo ezimbili kanye nezibalo eziveza izimbangela ziveze ukuthi ukucabanga ngomkhakha womsebenzi komuntu ngamunye, ukuxhumana nabantu nokuzibophezela emsebenzini kungasetshenziswa njengezinto ezikhona ohlakeni lokukwazi ukuzilawula ngokuzenzela ekukhetheni umkhakha ezikhungweni zezemfundo ephakeme zaseGhana. Imiphumela yokuhlaziywa okulingene yakhombisa ukuthi ubulili bababambiqhaza kanye nezinga labo ngokwezikhundla zomsebenzi kuhambisana nezinga abasebenzi abacabanga ngalo nomkhakha womsebenzi ekuqageleni indlela abazozibophezela ngayo emsebenzini. Ngaphezu kwalokho, ukuhlolwa komehluko omkhulu ojwayelekile kwaveza ukuthi ubulili, isimo somshado kanye nezinga ngokwesikhundla somsebenzi kwahluka kakhulu nendlela abacabanga ngayo ngomkhakha womsebenzi, ukuxhumana nabantu nokuzibophezela emsebenzini. Ngokombono wenjulalwazi nocwaningo olufakazelwe, imiphumela ithuthukise umbono wenjulalwazi wokuhlela umkhakha womsebenzi okuqinisekiswe ngokocwaningo olufakazelwe izinto ezinqala zokuzilawulela umkhakha womsebenzi. Ekusebenzeni, kwenziwa izincomo zokufundisa abaphathi babasebenzi (ba-HR) kanye nabasebenza ngezabasebenzi (ngezakwa-HR) ezikhungweni zezemfundo ephakeme zomphakathi eGhana, kanti nemiphumela evezwe ocwaningweni inikeza ithuba lokuqapha nokuhlinzeka amasu kanye nokungenelela kwabasebenzi ekwenzeni kwabo izinqumo zomsebenzi.Business ManagementPh. D. (Business Management

    Review of Path Selection Algorithms with Link Quality and Critical Switch Aware for Heterogeneous Traffic in SDN

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    Software Defined Networking (SDN) introduced network management flexibility that eludes traditional network architecture. Nevertheless, the pervasive demand for various cloud computing services with different levels of Quality of Service requirements in our contemporary world made network service provisioning challenging. One of these challenges is path selection (PS) for routing heterogeneous traffic with end-to-end quality of service support specific to each traffic class. The challenge had gotten the research community\u27s attention to the extent that many PSAs were proposed. However, a gap still exists that calls for further study. This paper reviews the existing PSA and the Baseline Shortest Path Algorithms (BSPA) upon which many relevant PSA(s) are built to help identify these gaps. The paper categorizes the PSAs into four, based on their path selection criteria, (1) PSAs that use static or dynamic link quality to guide PSD, (2) PSAs that consider the criticality of switch in terms of an update operation, FlowTable limitation or port capacity to guide PSD, (3) PSAs that consider flow variabilities to guide PSD and (4) The PSAs that use ML optimization in their PSD. We then reviewed and compared the techniques\u27 design in each category against the identified SDN PSA design objectives, solution approach, BSPA, and validation approaches. Finally, the paper recommends directions for further research
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