364 research outputs found

    Non-uniqueness and energy dissipation for 2D Euler equations with vorticity in Hardy spaces

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    We construct by convex integration examples of energy dissipating solutions to the 2D Euler equations on R2\mathbb{R}^2 with vorticity in the real Hardy space Hp(R2)H^p(\mathbb{R}^2), for any 2/3<p<12/3<p<1

    Estudios computacionales de mecanismos moleculares de la inmunidad innata

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    Tesis in茅dita de la Universidad Complutense de Madrid, Facultad de Farmacia, le铆da el 20-12-2022Antimicrobial Resistance (AMR) is a worldwide health emergency. ESKAPE pathogens include the most relevant AMR bacterial families. In particular, Gram-negative bacteria stand out due to their cell envelope complexity, which exhibits strong resistance to antimicrobials. A key element for AMR is the chemical structure of bacterial lipopolysaccharide (LPS), and the phospholipid composition of the membrane, inflecting the membrane permeability to antibiotics. We have applied coarse-grained molecular dynamics simulations to capture the role of the phospholipid composition and lipid A structure in the membrane properties and morphology of ESKAPE Gram-negative bacterial vesicles. Moreover, the reported antimicrobial peptides Cecropin B1, JB95, and PTCDA1-kf were used to unveil their implications for membrane disruption. This study opens a promising starting point for understanding the molecular keys of bacterial membranes and promoting the discovery of new antimicrobials to overcome AMR...La resistencia a los antimicrobianos (AMR) es una emergencia sanitaria mundial. Los pat贸genos ESKAPE incluyen las familias bacterianas m谩s resistentes a antibi贸ticos y son altamente virulentas. En particular, las bacterias Gram negativas destacan por la complejidad de su pared celular, que presenta una fuerte resistencia frente a los antibi贸ticos. Un elemento clave para la AMR es la estructura qu铆mica del lipopolisac谩rido bacteriano (LPS) y la composici贸n de los fosfol铆pidos de la membrana bacteriana, que influyen en su permeabilidad a los antibi贸ticos. Se han empleado simulaciones de din谩mica molecular de grano grueso para captar el papel de la composici贸n de los fosfol铆pidos y la estructura del LPS en las propiedades y morfolog铆a de modelos de ves铆culas bacterianas Gram negativas ESKAPE. Adem谩s, se han empleado los p茅ptidos antimicrobianos Cecropin B1, JB95 y PTCDA1-kf para desvelar su mecanismo disrupci贸n de la membrana bacteriana. Este estudio abre un prometedor punto de partida para comprender las claves moleculares de la resistencia en membranas bacterianas y acelerar el descubrimiento de nuevos antibi贸ticos para hacer frente a la AMR...Fac. de FarmaciaTRUEunpu

    Computational and experimental investigation of elemental sulfur and polysulfide

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    Petroleum processing results in the generation of significant quantities of elemental sulfur (S8), leading to a surplus of sulfur worldwide. Despite its abundance and low cost, the use of sulfur in value-added organic compound synthesis is limited due to its unpredictable and misunderstood reactivity. This dissertation aims to address this issue by tackling it from two angles. Firstly, by utilizing Density Functional Theory (DFT) calculations, the reactivity of sulfur in the presence of nucleophiles is studied. This facilitates the identification of organic polysulfide intermediates that can be generated under different conditions, as well as the corresponding reactivity for each type of nucleophile. This computational study begins with a benchmarking of numerous DFT functionals against experimental data and high-accuracy ab initio computations to determine the best functional(s) for studying elemental sulfur and polysulfides in organic reactions. Using the best DFT method, the mechanism of monosulfide formation from cyanide and phosphines is explained. At the end of this computational study, the mechanism of 2-aminothiophene formation via the Gewald reaction is elucidated. Secondly, attempts are made to synthesize sulfur-based organic compounds using elemental sulfur or compounds with a sulfur source through the utilization of boron, imine, and aryne chemistry. In summary, this dissertation aims to expand the use of sulfur in organic chemistry by providing an understanding to predict its reactivity with nucleophiles, as well as demonstrating its potential for the low-cost synthesis of valuable sulfur-based organic compounds

    LIPIcs, Volume 258, SoCG 2023, Complete Volume

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    LIPIcs, Volume 258, SoCG 2023, Complete Volum

    Diffuse Optical Imaging with Ultrasound Priors and Deep Learning

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    Diffuse Optical Imaging (DOI) techniques are an ever growing field of research as they are noninvasive, compact, cost-effective and can furnish functional information about human tissues. Among others, they include techniques such as Tomography, which solves an inverse reconstruction problem in a tissue volume, and Mapping which only seeks to find values on a tissue surface. Limitations in reliability and resolution, due to the ill-posedness of the underlying inverse problems, have hindered the clinical uptake of this medical imaging modality. Multimodal imaging and Deep Learning present themselves as two promising solutions to further research in DOI. In relation to the first idea, we implement and assess here a set of methods for SOLUS, a combined Ultrasound (US) and Diffuse Optical Tomography (DOT) probe for breast cancer diagnosis. An ad hoc morphological prior is extracted from US B-mode images and utilised for the regularisation of the inverse problem in DOT. Combination of the latter in reconstruction with a linearised forward model for DOT is assessed on specifically designed dual phantoms. The same reconstruction approach with the incorporation of a spectral model has been assessed on meat phantoms for reconstruction of functional properties. A simulation study with realistic digital phantoms is presented for an assessment of a non-linear model in reconstruction for the quantification of optical properties of breast lesions. A set of machine learning tools is presented for diagnosis breast lesions based on the reconstructed optical properties. A preliminary clinical study with the SOLUS probe is presented. Finally, a specifically designed deep learning architecture for diffusion is applied to mapping on the brain cortex or Diffuse Optical Cortical Mapping (DOCM). An assessment of its performances is presented on simulated and experimental data

    Transformational leadership style and talent management practices in improving employee engagement in the Malaysian public sector: the mediating role of public service motivation

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    This thesis aims to examine the factors that influence employee engagement in the context of Malaysian public service. It focuses on three main concepts: transformational leadership, talent management practices, and public service motivation. The concept of employee engagement has become of great interest among researchers and practitioners due to its significant impact on organisational performance. The role of leadership, talent management practices and public service motivation are becoming crucial, especially in this volatile, uncertain, complex, and ambiguous world. Leaders must express understanding, concern, and empathy toward employees and their needs. This study is timely as it was conducted during the global pandemic crisis when the job demands of public servants have increased rapidly. Based on Job Demands-Resources Theory, high job demands will undermine employee engagement due to mental, emotional, and physical exhaustion. Therefore, examining public servants' behavioural and motivational factors during this time is crucial since they serve as frontline workers to benefit people and the nation. This study has shed light on how to engage public servants in the Malaysian public service to bring out their greatest potential at work. This is a cross-sectional study that employed the quantitative method approach. A questionnaire was designed to examine the associations between the proposed variables. The sample of this study comprised 318 Administrative and Diplomatic Officers currently serving the Malaysian public service. Both pre-test and pilot studies were conducted to assess the validity, language, and relevancy of the questions included in the questionnaire. In this study, Statistical Package for Social Sciences Statistics version 27 and structural equation modelling: Smart PLS 3 were used as analysing tools to assess the measurement and structural model in this study to test the relationship between the variables and the impact of the proposed model on employee engagement. The result showed that talent management practices, self-perceived transformational leadership style and public service motivation have a positive relationship with employee engagement and that public service motivation mediates talent management practices 鈥 employee engagement relationship and self-perceived transformational leadership style 鈥 employee engagement relationship. Overall, the data suggested that the public sector needs to develop talent management practices and employee resources to improve employee engagement

    Essays on Two-Sided Matching Theory:

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    Thesis advisor: M. Utku 脺nverThesis advisor: Tayfun S枚nmezThis thesis is a collection of three essays in market design concerning designs of matching markets with aggregate constraints, affirmative action schemes, and investigating boundaries of simultaneous efficiency-stability relaxation for one-to-one matching mechanisms.In Chapter 1, I establish and propose a possible solution for a college housing crisis, a severe ongoing problem taking place in many countries. Every year many colleges provide housing for admitted students. However, there is no college admissions process that considers applicants鈥 housing needs, which often results in college housing shortages. In this chapter, I formally introduce housing quotas to the college admissions problem and solve it for centralized admissions with common dormitories. The proposed setting is inspired by college admissions where applicants apply directly to college departments, and colleges are endowed with common residence halls. Such setting has many real-life applications: hospital/residents matching in Japan (Kamada and Kojima, 2011, 2012, 2015), college admissions with scholarships in Hungary (Bir贸, 2012), etc. A simple example shows that there may not be a stable allocation for the proposed setting. Therefore, I construct two mechanisms that always produce some weakened versions of a stable matching: a Take-House-from-Applicant-stable and incentive compatible cumulative offer mechanism that respects improvements, and a Not-Compromised-Request-from-One-Agent-stable (stronger version of stability) cutoff minimising mechanism. Finally, I propose an integer programming solution for detecting a blocking-undominated Not-Compromised-Request-from-One-Agent-stable matching. Building on these results, I argue that presented procedures could serve as a helpful tool for solving the college housing crisis. In Chapter 2, I propose a number of solutions to resource allocation problems in an affirmative action agenda. Quotas are introduced as a way to promote members of minority groups. In addition, reserves may overlap: any candidate can belong to many minority groups, or, in other words, have more than one trait. Moreover, once selected, each candidate fills one reserve position for each of her traits, rather than just one position for one of her traits. This makes the entire decision process more transparent for applicants and allows them to potentially utilize all their traits. I extend the approach of S枚nmez and Yenmez (2019) who proposed a paired-admissions choice correspondence that works under no more than two traits. In turn, I allow for any number of traits focusing on extracting the best possible agents, such that the chosen set is non-wasteful, the most diverse, and eliminates collective justified envy. Two new, lower- and upper-dominant choice rules and a class of sum-minimizing choice correspondences are introduced and characterized. In Chapter 3, I implement optimization techniques for detecting the efficient trade off between ex-post Pareto efficiency (for one side of a two-sided matching market) and ex-ante stability for small one-to-one matching markets. Neat example (Roth, 1982) proves that there is no matching mechanism that achieves both efficiency (for one side of the one-to-one matching market) and stability. As representative mechanisms I choose deferred-acceptance for stability, and top trading cycles for Pareto efficiency (both of them are strategy-proof for one side of the market). I compare performances of a randomized matching mechanism that simultaneously relaxes efficiency and stability, and a convex combination of two representative mechanisms. Results show that the constructed mechanism significantly improves efficiency and stability in comparison to mentioned convex combination of the benchmark mechanisms.Thesis (PhD) 鈥 Boston College, 2023.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Economics

    Equilibrium isotope fractionation factors of H exchange between steam and soil clay fractions

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    Rationale Steam equilibration overcomes the problem of the traditional measurements of H isotope compositions, which leave an arbitrary amount of adsorbed water in the sample, by controlling for the entire exchangeable H pool, including adsorbed water and hydroxyl-H. However, the use of steam equilibration to determine nonexchangeable stable H isotope compositions in environmental media (expressed as 未2Hn values) by mathematically eliminating the influence of exchangeable H after sample equilibration with waters of known H-isotopic composition requires the knowledge of the equilibrium isotope fractionation factor between steam-H and exchangeable H of the sample (伪ex-w), which is frequently unknown. Methods We developed a new method to determine the 伪ex-w values for clay minerals, topsoil clay fractions, and mica by manipulating the contributions of exchangeable H to the total H pool via different degrees of post-equilibration sample drying. We measured the 未2H values of steam-equilibrated mineral and soil samples using elemental analyzer-pyrolysis-isotope ratio mass spectrometry. Results The 伪ex-w values of seven clay minerals ranged from 1.071 to 1.140, and those of 19 topsoil clay fractions ranged from 0.885 to 1.216. The 伪ex-w value of USGS57 biotite, USGS58 muscovite, and of cellulose was 0.965, 0.871, and 1.175, respectively. The method did not work for kaolinite, because its small exchangeable H pool did not respond to the selected drying conditions. Structurally different mineral groups such as two- and three-layer clay minerals or mica showed systematically different 伪ex-w values. The 伪ex-w value of the topsoil clay fractions correlated with the soil clay content (r = 0.63, P =鈥0.004), the local mean annual temperature (r鈥=鈥0.68, P =鈥0.001), and the 未2H values of local precipitation (r鈥=鈥0.72, P <鈥0.001), likely to reflect the different clay mineralogy under different weathering regimes. Conclusions Our new 伪ex-w determination method yielded realistic results in line with the few previously published values for cellulose. The determined 伪ex-w values were similar to the widely assumed values of 1.00鈥1.08 in the literature, suggesting that the adoption of one of these values in steam equilibration approaches is appropriate

    Stable hydrogen isotope ratios in the clay fraction of soil

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    Die Untersuchung der nat眉rlichen H盲ufigkeit von stabilen Isotopen des Wasserstoffs (H) in organischen Substanzen hat neue Erkenntnisse f眉r die 枚kologische Forschung, die forensischen Wissenschaften und die Pal盲oklimatologie hervorgebracht. Fr眉here Studien haben gezeigt, dass das 虏H/鹿H-Isotopenverh盲ltnis (未虏H) von nicht-austauschbarem H (未虏Hn_{n}) des Bodens und der demineralisierten organischen Bodensubstanz mit dem 未虏H-Wert des lokalen Niederschlags in Zusammenhang steht. Bisher haben methodische Schwierigkeiten bei der Entfernung von austauschbarem H in der Tonfraktion des Bodens die Untersuchung einer 盲hnlichen Beziehung zwischen den 未虏Hn_{n}-Werten der Tonfraktionen des Bodens und dem 未虏H-Wert des lokalen Niederschlags erschwert. Das 眉bergeordnete Ziel meiner Arbeit besteht darin, die 未虏Hn_{n}-Werte von Tonfraktionen im Boden durch die Trennung von austauschbarem und nicht-austauschbarem H mittels Dampf盲quilibrierung zu bestimmen und deren Einflussfaktoren zu untersuchen. Zu diesem Zweck habe ich (1) die Dampf盲quilibrierungsmethode angepasst. Dies war erforderlich, um den Einfluss der klassischen Behandlung zur Separation von Tonfraktionen, einschlie脽lich der Entfernung von dithionitl枚slichem Eisen, organischer Substanz, Karbonaten und Salzen, auf die 未虏Hn_{n}-Werte von Tonmineralen zu testen. Anschlie脽end habe ich (2) untersucht, ob es eine globale Korrelation zwischen den 未虏H-Werten des lokalen Niederschlags und den 未虏Hn_{n}-Werten von Oberbodentonfraktionen gibt. Der Ansatz der Dampf盲quilibrierung erfordert den Gleichgewichtsfraktionsfaktor zwischen dem H des Dampfes und dem austauschbaren H der Probe (伪exw_{ex鈥憌}), der nicht bekannt ist. Daher habe ich (3) eine experimentelle Methode zur Bestimmung der probenspezifischen 伪exw_{ex鈥憌}-Werte entwickelt. Ich verwendete die Tonminerale Kaolinit, Illit, Montmorillonit und Vermiculit sowie Oberbodenproben von 24 Standorten auf f眉nf Kontinenten. Bei allen Proben wurden die Tonfraktionen separiert. Die 未虏Hn_{n}-Werte wurden mittels Dampf盲quilibrierung und Pyrolyse-Elementaranalysator-Isotopenverh盲ltnis-Massenspektrometrie bestimmt. Dar眉ber hinaus wurden die Oberbodenproben chemisch charakterisiert, einschlie脽lich der Konzentrationen von H, Corg_{org}, N, Na, Mg, Al, K, Ca, Fe und Fed_{d} sowie der potenziellen Kationenaustauschkapazit盲t. Die klassische Tonseparierung ver盲nderte die 未虏Hn_{n}-Werte von f眉nf verschiedenen Tonmineralien nicht wesentlich. Die 未虏Hn_{n}-Werte der Tonfraktionen aus verschiedenen Regionen der Welt reichten von 鈥167鈥娐扁1鈥娾 f眉r eine nordsibirische Probe bis 鈥44鈥娐扁4鈥娾 in Westkenia f眉r 伪exw_{ex鈥憌}鈥=鈥1 und von -191鈥娐扁5 bis -81鈥娐扁5鈥娾 f眉r 伪exw_{ex鈥憌}鈥=鈥1,08. Die 未虏H-Werte des lokalen Jahresniederschlags korrelierten signifikant mit den 未虏Hn_{n}-Werten der Tonfraktionen (r鈥=鈥0,88 f眉r 伪exw_{ex鈥憌}鈥=鈥1 und 0,65 f眉r 伪exw_{ex鈥憌}鈥=鈥1,08, p鈥<鈥0,001). Ein multiples Regressionsmodell, das zus盲tzlich zu den 未虏H-Werten des saisonalen Niederschlags auch die Hangneigung als m枚gliches Ma脽 f眉r die allochthone Tonakkumulation einbezog, erkl盲rte 86鈥% und 89鈥% der beobachteten Variation der 未虏H-Werte der Tonfraktionen f眉r 伪exw_{ex鈥憌}鈥=鈥1 bzw. 1,08. Die 伪exw_{ex鈥憌}-Werte von sieben Tonmineralen reichten von 1,071 bis 1,140 und von 19 Oberbodentonfraktionen von 0,885 bis 1,216. Die 伪exw_{ex鈥憌}-Bestimmungsmethode funktionierte nicht f眉r Kaolinit, wahrscheinlich wegen seines geringen austauschbarem H-Gehalts. Der 伪exw_{ex鈥憌}-Wert der Oberbodentonfraktionen korrelierte mit dem Tongehalt des Bodens (r鈥=鈥0,63, p鈥=鈥0,004), der lokalen Jahresmitteltemperatur (r鈥=鈥0,68, p鈥=鈥0,001) und den 未虏H-Werten des lokalen Niederschlags (r鈥=鈥0,72, p鈥<鈥0,001), was die unterschiedliche Tonmineralogie unter verschiedenen klimatischen Verwitterungsregimen widerspiegelt. Meine Ergebnisse zeigen, dass die 未虏Hn_{n}-Werte des Oberbodens als eine Mischung aus isotopisch schwereren H der organischen Bodensubstanz und isotopisch leichteren H der Tonfraktionen beschrieben werden k枚nnen. Die 未虏Hn_{n}-Werte der Tonfraktionen im Boden werden von den 未虏H-Werten der lokalen Niederschl盲ge beeinflusst. Wenn die klimatisch beeinflusste Mineralogie ber眉cksichtigt wird, k枚nnen unbekannte Bodenproben dem global variierenden 未虏H Niederschlagswerten zugeordnet werden. Die vorgeschlagene 伪exw_{ex鈥憌}-Bestimmungsmethode kann verwendet werden, um die Unsicherheit der Dampf盲quilibrierung zur Bestimmung der 未虏Hn_{n}-Werte von hygroskopischen Proben zu verringern

    Challenges and New Trends in Power Electronic Devices Reliability

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    The rapid increase in new power electronic devices and converters for electric transportation and smart grid technologies requires a deepanalysis of their component performances, considering all of the different environmental scenarios, overload conditions, and high stressoperations. Therefore, evaluation of the reliability and availability of these devices becomes fundamental both from technical and economicalpoints of view. The rapid evolution of technologies and the high reliability level offered by these components have shown that estimating reliability through the traditional approaches is difficult, as historical failure data and/or past observed scenarios demonstrate. With the aim topropose new approaches for the evaluation of reliability, in this book, eleven innovative contributions are collected, all focusedon the reliability assessment of power electronic devices and related components