Dynamique des électrons dans les matériaux 2D

During this thesis, we have proposed theoretical and numerical methods to study the behavior of electrons in periodic materials, with a particular interest for 2D materials, like graphene, and topological insulators. The thesis consists in three parts, organized as follows.The first part provides a mathematically proven and simple algorithm to build localized Wannier functions, with the only requirement that the system has vanishing Chern numbers. Based on an explicit and constructive proof of homotopies for the unitary group, the algorithm is able to build localized Wannier for topological insulators such as the Kane-Mele model. The method is validated by numerical tests for several systems.In the second part, we propose an approximation method for Wannier functions that is adapted to the computation of tight-binding Hamiltonians in non-periodic van der Waals heterostructures, that is, layers of 2D materials stacked on top of each other, bound together by the comparatively weak van der Waals forces. This setting is challenging for the usual computational tools of solid-state physics, which rely on the periodicity of crystals. In this context, a first-order approximation is to consider the Wannier functions computed on each layer independently. We therefore propose an approximation scheme for Wannier functions that allows for an efficient computation of tight-binding matrix coefficients, even in the non-periodic case.The third part is theoretical and devoted to the study of independent electrons in a periodic crystal in their ground state, set in motion by a uniform electric field at some prescribed time. We rigorously define the current per unit volume and study its properties using both linear response and adiabatic theory. Our results provide a unified framework for various phenomena such as the quantification of Hall conductivity of insulators with broken time-reversibility, the ballistic regime of electrons in metals, Bloch oscillations in the long-time response of metals, and the static conductivity of graphene.Au cours de cette thèse, nous avons proposé des méthodes théoriques et numériques pour étudier le comportement des électrons dans les matériaux périodiques, avec un intérêt particulier pour les matériaux 2D, comme le graphène, et les isolants topologiques. La thèse se compose de trois parties, organisées comme suit. La première partie fournit un algorithme simple et doté d’une preuve mathématique pour construire des fonctions Wannier localisées, avec pour seule condition que le système ait des nombres de Chern triviaux. Sur la base d'une preuve explicite et constructive des homotopies pour le groupe unitaire, l'algorithme permet de construire des Wannier localisés pour des isolateurs topologiques tels que le modèle Kane-Mele. La méthode est validée par des tests numériques pour plusieurs systèmes.Dans la deuxième partie, nous proposons une méthode d'approximation des fonctions de Wannier adaptée au calcul des Hamiltoniens de tight-binding dans les hétérostructures de van der Waals non périodiques, c'est-à-dire des couches de matériaux 2D empilées les unes sur les autres, liées entre elles par des forces de van der Waals relativement faibles. Ce cadre n’est pas adapté pour les outils de calcul habituels de la physique des solides, qui reposent sur la périodicité des cristaux. Dans ce contexte, une approximation du premier ordre consiste à considérer les fonctions de Wannier calculées sur chaque couche indépendamment. Nous proposons donc un schéma d'approximation pour les fonctions de Wannier qui permet un calcul efficace des coefficients de matrice tight-binding, même dans le cas non périodique.La troisième partie est théorique et consacrée à l'étude des électrons indépendants à l’état fondamental dans un cristal périodique, mis en mouvement par un champ électrique uniforme à l’instant initial. Nous définissons rigoureusement le courant par unité de volume et étudions ses propriétés en utilisant à la fois la réponse linéaire et la théorie adiabatique. Nos résultats fournissent un cadre unifié pour divers phénomènes tels que la quantification de la conductivité de Hall des isolants topologiques, le régime balistique des électrons dans les métaux, les oscillations de Bloch dans la réponse en temps long des métaux et la conductivité statique du graphène

Stringent Internal Quality Control Procedures in Chemical Pathology Lead to Better Performance in External Proficiency Testing

Objective: To assess impact of stringent Internal Quality Control (IQC) checks on performance of proficiency testing Material and methods: This was a Prospective study conducted between September 2020 and April 2021 at Chemical pathology lab of Fauji Foundation Hospital Rawalpindi. External quality control data (EQC) from the month of September was evaluated. As part of corrective action plan IQC checks were enforced, internal quality control (IQC) data of the month of September 2020 and April 2022 were assessed. Performance characteristics of routine chemistry analytes coefficient of variance (CV), standard deviations (SD)and Bias were calculated and compared using paired –T- test. Results:  Proficiency testing report (NEQAPP) of cycle 10 round 1 showed 11% External Quality Control (EQC) failure among 18 biochemical parameters. Serum Creatinine and Total Protein failed acceptability criteria with Z-score of greater than 2. As part of corrective action IQC checks were done, which led to improvement in CV (SD) of these parameters. The next EQC lab report for routine chemistry analytes met the acceptability criteria with z-scores of all anaytes being less than 2. Conclusion: Precise & accurate IQC results lead to better performance in EQC result

Association of Beta-2 Adrenoreceptor Single Nucleotide Polymorphism with Risk of Type II Diabetes Mellitus

Objective: To determine the genotype of Arg16Gly & Gln27Glu polymorphism in type-2 diabetes mellitus and to find possible association of ADRβ2with type-2 diabetes mellitus. Methodology: A case control study was designed and a total of 192 subjects (98 in each group) were included. After formal approval, subjects were recruited from North West General Hospital (NWGH) Peshawar. After taking consent blood samples were collected from the participants and DNA analysis was done using commercially available kits by salting out protocols, while other biochemical parameters were analyzed using normal laboratory protocols for respective tests. Results: The comparative analysis of SNP rs1042713 indicates that allele G/A was 42(49.4%) in diabetic and 43(50.6%) in non-diabetic subjects. While GG was more frequent 22(59.5%) in diabetic as compare to non-diabetic 15(40.5%). Among AA allele, 19 (65.5%) were non-diabetic while 10(34.5%) were diabetic. However the difference was not statistically significant (p=0.22). In case of “rs1042714” gene the commonest allele was C/C 80 (41.7%) out of which, 47(58.8%) was found in diabetic and 33(41.2%) were non-diabetic. Similarly CG was second common allele out of which diabetics were 27(44.3%) while non-diabetics were 34(55.7%). Allele G/G was found only among 11 subjects (p=0.085). Conclusion: Based on the result of the present study, it is concluded that polymorphism in ADRB2 genes rs1042713 (Arg16Gly) and rs1042714 (Gln27Glu) is associated with susceptibility of T2DM through alteration in BMI & HbA1c

Prevalence of HBV and HBV vaccination coverage in health care workers of tertiary hospitals of Peshawar, Pakistan

<p>Abstract</p> <p>Background</p> <p>Hepatitis B Virus (HBV) may progress to serious consequences and increase dramatically beyond endemic dimensions that transmits to or from health care workers (HCWs) during routine investigation in their work places. Basic aim of this study was to canvass the safety of HCWs and determine the prevalence of HBV and its possible association with occupational and non-occupational risk factors. Hepatitis B vaccination coverage level and main barriers to vaccination were also taken in account.</p> <p>Results</p> <p>A total of 824 health care workers were randomly selected from three major hospitals of Peshawar, Khyber Pakhtunkhwa. Blood samples were analyzed in Department of Zoology, Kohat University of Science and Technology Kohat, and relevant information was obtained by means of preset questionnaire. HCWs in the studied hospitals showed 2.18% prevalence of positive HBV. Nurses and technicians were more prone to occupational exposure and to HBV infection. There was significant difference between vaccinated and non-vaccinated HCWs as well as between the doctors and all other categories. Barriers to complete vaccination, in spite of good knowledge of subjects in this regard were work pressure (39.8%), negligence (38.8%) un-affordability (20.9%), and unavailability (0.5%).</p> <p>Conclusions</p> <p>Special preventive measures (universal precaution and vaccination), which are fundamental way to protect HCW against HBV infection should be adopted.</p

Association of vitamin D deficiency and vitamin D receptor (VDR) gene single-nucleotide polymorphism (rs7975232) with risk of preeclampsia

Preeclampsia has a multifactorial-yet-elusive etiology. Recent reports suggest a link between preeclampsia and vitamin D (VD) metabolic axis. Genetic variations like single-nucleotide polymorphisms (SNPs) of vitamin D receptor (VDR) gene can alter the metabolic role of VD, which have been shown by several genetic association studies. However, there is discordance among these studies

Integrative Molecular Analysis of DNA Methylation Dynamics Unveils Molecules with Prognostic Potential in Breast Cancer

DNA methylation acts as a major epigenetic modification in mammals, characterized by the transfer of a methyl group to a cytosine. DNA methylation plays a pivotal role in regulating normal development, and misregulation in cells leads to an abnormal phenotype as is seen in several cancers. Any mutations or expression anomalies of genes encoding regulators of DNA methylation may lead to abnormal expression of critical molecules. A comprehensive genomic study encompassing all the genes related to DNA methylation regulation in relation to breast cancer is lacking. We used genomic and transcriptomic datasets from the Cancer Genome Atlas (TGCA) Pan-Cancer Atlas, Genotype-Tissue Expression (GTEx) and microarray platforms and conducted in silico analysis of all the genes related to DNA methylation with respect to writing, reading and erasing this epigenetic mark. Analysis of mutations was conducted using cBioportal, while Xena and KMPlot were utilized for expression changes and patient survival, respectively. Our study identified multiple mutations in the genes encoding regulators of DNA methylation. The expression profiling of these showed significant differences between normal and disease tissues. Moreover, deregulated expression of some of the genes, namely DNMT3B, MBD1, MBD6, BAZ2B, ZBTB38, KLF4, TET2 and TDG, was correlated with patient prognosis. The current study, to our best knowledge, is the first to provide a comprehensive molecular and genetic profile of DNA methylation machinery genes in breast cancer and identifies DNA methylation machinery as an important determinant of the disease progression. The findings of this study will advance our understanding of the etiology of the disease and may serve to identify alternative targets for novel therapeutic strategies in cancer

Melatonin rescues the mice brain against cisplatin-induced neurodegeneration, an insight into antioxidant and anti-inflammatory effects

Herein, we evaluated the neuroprotective effect of melatonin against cisplatin-induced oxidative damage, neuroinflammation, and synaptic dysfunction in mice. Cisplatin was administered at a dose of 2 mg/kg for eleven consecutive days to induce symptoms of cognitive impairment and neurodegeneration, while melatonin was administered at a 20 mg/kg dose for thirty consecutive days. We used various experimental techniques such as western blotting, immunofluorescence analysis, and oxidative stress marker assays to support our notion. Moreover, for cognitive impairment, we conducted behavioral analyses such as Morris Water Maze (MWM) and Y-Maze tests. The results indicated that melatonin attenuated oxidative stress by upregulating the expression of NF-E2-related factor-2 (Nrf2) dependent anti-oxidative protein levels. Similarly, melatonin positively modulated the expression of Sirt1 (a member of the sirtuin family), Phospho-AMPKα (Thr172), peroxisome proliferator-activated receptor (PPARγ), PPAR gamma coactivator 1 alpha (PGC-1α) coupled to downregulation of neuroinflammatory mediators and markers such as nuclear factor kappa-B (NF-κB), tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β). Moreover, melatonin significantly upregulated the expression of synaptic markers such as postsynaptic density protein -95 (PSD-95), synaptosomal-associated protein 23 (SNAP-23), and synaptophysin compared to the cisplatin alone group. Furthermore, the results of behavior tests suggested that melatonin significantly improved the cognitive functions of the cisplatin injected mice

Molecular epidemiology of hcv among health care workers of khyber pakhtunkhwa

<p>Abstract</p> <p>Background</p> <p>Studies of the molecular epidemiology and risk factors for hepatitis C virus (HCV) in health care workers (HCWs) of Peshawar, Khyber Pakhtunkhwa region are scarce. Lack of awareness about the transmission of HCV and regular blood screening is contributing a great deal towards the spread of hepatitis C. This study is an attempt to investigate the prevalence of HCV and its possible association with both occupational and non-occupational risk factors among the HCWs of Peshawar.</p> <p>Results</p> <p>Blood samples of 824 HCWs, aged between 20-59 years were analysed for anti-HCV antibodies, HCV RNA and HCV genotypes by Immunochromatographic tests and PCR. All relevant information was obtained from the HCWs with the help of a questionnaire. The study revealed that 4.13% of the HCWs were positive for HCV antibodies, while HCV RNA was detected in 2.79% of the individuals. The most predominant HCV genotype was 3a and 2a.</p> <p>Conclusion</p> <p>A program for education about occupational risk factors and regular blood screening must be implemented in all healthcare setups of Khyber Pakhtunkhwa province in order to help reduce the burden of HCV infection.</p

Rising burden of Hepatitis C Virus in hemodialysis patients

<p>Abstract</p> <p>Aim</p> <p>High prevalence of Hepatitis C virus (HCV) has been reported among the dialysis patients throughout the world. No serious efforts were taken to investigate HCV in patients undergoing hemodialysis (HD) treatment who are at great increased risk to HCV. HCV genotypes are important in the study of epidemiology, pathogenesis and reaction to antiviral therapy. This study was performed to investigate the prevalence of active HCV infection, HCV genotypes and to assess risk factors associated with HCV genotype infection in HD patients of Khyber Pakhtunkhwa as well as comparing this prevalence data with past studies in Pakistan.</p> <p>Methods</p> <p>Polymerase chain reaction was performed for HCV RNA detection and genotyping in 384 HD patients. The data obtained was compared with available past studies from Pakistan.</p> <p>Results</p> <p>Anti HCV antibodies were observed in 112 (29.2%), of whom 90 (80.4%) were HCV RNA positive. In rest of the anti HCV negative patients, HCV RNA was detected in 16 (5.9%) patients. The dominant HCV genotypes in HCV infected HD patients were found to be 3a (n = 36), 3b (n = 20), 1a (n = 16), 2a (n = 10), 2b (n = 2), 1b (n = 4), 4a (n = 2), untypeable (n = 10) and mixed (n = 12) genotype.</p> <p>Conclusion</p> <p>This study suggesting that i) the prevalence of HCV does not differentiate between past and present infection and continued to be elevated ii) HD patients may be a risk for HCV due to the involvement of multiple routes of infections especially poor blood screening of transfused blood and low standard of dialysis procedures in Pakistan and iii) need to apply infection control practice.</p