Pressure gradients in molecular dynamics simulations of nano-confined fluid flow

Ein detailliertes Verständnis des Verhaltens von Schmierstoffen in engen Spalten ist für eine Reihe von medizinischen und industriellen Anwendungen entscheidend. Die hydrodynamischen Grundgleichungen bieten genaue Lösungen, sofern die kontaktierenden Körper ausreichend weit voneinander entfernt sind. Unter extremen Belastungsbedingungen werden jedoch Abweichungen von den Navier-Stokes-Fourier-Gleichungen beobachtet. Dies liegt hauptsächlich an der Bedeutung atomare Effekte, die eine homogenisierte Betrachtung im Rahmen von Kontinuumstheorien nicht mehr erlauben, sodass die Flüssigkeit als Ansammlung diskreter Partikel behandelt werden muss. Der multiskalige Charakter des Problems wird im Bereich der Grenzreibung umso deutlicher. In diesem Regime wird das Schmiermittel durch Druckgradienten angetrieben, die sich aus der Variation der Spalthöhe zwischen den kontaktierenden Körpern ergeben. In der atomistischen Modellierung werden üblicherweise Nichtgleichgewichts-Molekulardynamik (NEMD) Simulationen periodischer, repräsentativer Volumenelemente (RVE) verwendet, bei denen der Schmierfilm von flachen Wänden eingeschlossen wird. Aufgrund der Periodizität stellt das Einstellen von Druckgradienten in solchen Modellen eine Hürde dar. In dieser Arbeit wurde die ``Pump\u27\u27-Methode entwickelt, um Druckgradienten in periodischen Systemen einzuführen, indem eine lokale Störung aufgebracht wird, die unter Einhaltung der Impulserhaltung einen druckgetriebenen Fluss des Schmiermittels induziert. Dabei kann sowohl der Massenfluss als auch der Druckgradient, durch Festlegen atomarer Kräfte, als unabhängige Variable gewählt werden. Die Methode wurde für kompressible Fluide mit unterschiedlichen Benetzungseigenschaften und in Verbindung mit verschiedenen Thermostat-Strategien getestet. Dabei werden die thermodynamischen Feldgrößen Druck, Temperatur und Geschwindigkeit des Schmierstoffs in Spalthöhen bis zu drei Moleküldurchmessern gemessen. Die Pump-Methode kann auf Kanäle beliebiger Geometrie angewendet werden, was die Anwendung zur Untersuchung hydrodynamischer Kavitation ermöglicht -- ein Phänomen, welches in der Natur allgegenwärtig ist, jedoch auf molekularer Ebene bisher kaum untersucht wurde. Dazu wurde die Kanalgeometrie anhand einer Sensitivitätsanalyse optimiert. Anschließend wurde die Lebensdauer der Kavitationsblasen, sowie deren Wachstum und Zusammenbruch mit den theoretischen, hydrodynamischen Vorhersagen verglichen. Im Rahmen eines Multiskalenansatzes für Schmierungsprobleme kann die Pump-Methode zur Einstellung der Randbedingungen eines molekularen Systems im Einklang mit Kontinuumssimulationen verwendet werden

VOLUNTARY DISCLOSURE PRACTICES IN EMERGING CAPITAL MARKETS: THE CASE OF EGYPT

Corporate governance is a crucial issue that is being addressed widely by regulators, and capital market participants around the world. Disclosure is identified as one of the challenges facing the implementation of corporate governance especially in developing countries. The current study aims to contribute to corporate governance and disclosure literature by oroviding empirical evidence of the relationship between corporate governance, ownership structure and the voluntary disclosure in an emerging capital market, namely Egypt. The study assesses the extent of total voluntary disclosure and its categories in the annual reports of the most active non financial companies m the Cairo and Alexandria Stock Exchange over four years that witnessed a remarkable initiatives to enhance transparency and corporate governance. It employs a wider theoretical framework based mainly on the political ach and benefits from institutional theory. Using a sample of 182 annual reports of the most active Egyptian listed companies, the findings indicate that while the extent of voluntary disclosure is low, there was a gradual increase in the extent of total voluntary disclosure and its categories over the examined period. However, there is no significant difference between the voluntary disclosure over the four years. This suggests that companies manage their voluntary disclosure policy which is not a random practice but subject to certain influences. The reRression results indicate the board characteristics; board size and board composition; do affect the extent of voluntary disclosure. Interestingly, the findings indicate that the existence of family members on the board has a positive association with the extent of total voluntary disclosure. This suggests that family led companies may have a litigation and reputation cost concern.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Perceptions of clinical dental students toward online education during the COVID-19 crisis: An Egyptian multicenter cross-sectional survey

Objectives: To evaluate the perceptions of clinical dental students on the role of online education in providing dental education during the COVID-19 crisis. Materials and Methods: A cross-sectional online survey was sent to four Egyptian dental schools from the 20th of January 2021 to the 3rd of February 2021. Survey questions included the demographics, uses, experiences, perceived benefits, and barriers of distance learning in dentistry during the COVID-19 pandemic. Responses were collected from the clinical dental school students. Categorical data were presented as frequencies (n) and percentages (%) and were analyzed using Fisher’s exact test. Results: Three hundred thirty-seven clinical dental students across four Egyptian dental schools responded. Most students used either Google Classroom or Microsoft Teams to access the online content. The data showed that the COVID-19 pandemic affected the academic performance of most participants (97.4%) with varying degrees. On average, students were neutral when asked to rate the online lectures, but did not find online practical education as effective (81.3%) as online theoretical teaching. The commonly described barriers to online teaching included loss of interaction with educators, inappropriateness in gaining clinical skills, and the instability of the internet connection. Conclusion: Despite the reported benefits, clinical dental students in Egypt preferred the hybrid approach in dental education as distance learning represented a prime challenge to gain adequate clinical dental skills

Diffusion weighted MRI in evaluation of transplanted kidney: Preliminary clinical experience

Purpose: To evaluate the diagnostic performance ofDiffusion Weighted (DW) magnetic resonance(MR) imaging in evaluation of transplantedkidneys.Patients and methods: One hundred twelve patientswith transplanted kidney from live kidney donorswere evaluated with coronal T2w and DW MRI ofthe kidney. There was 86 males and 26 females andthe mean age was 26.911.5ys (range 10-55).Apparent diffusion coefficient (ADC) wascalculated and the kidneys studied for any areasdiffusion restriction. Our patients classified into 2groups: Group 1 included 81 patients with stablekidney function and normal serum creatinine andthe second group included 31 patients with alteredkidney function, it includes 18 patients with chronicnephropathies and 13 patients with acute cellularrejection.Results: The mean ADC values for group 1 was2.70.26 x 10-3 mm2 /sec (range 1.93-3.6). In casesof chronic nephropathies, the mean ADC valueswas 2.30.22mm2/sec (range 2.05-2.77) while incases of acute cellular rejection it was1.80.2mm2/sec (range 1.7-2.2). When we use the2.4mm2/sec as a low cutoff ADC value fordiagnosis of normal kidney function, the sensitivity,specificity and overall accuracy for DWI MRI was80%, 96% and 93.5% respectively.When we used the ADC value of 2mm2/sec as acutoff value between acute cellular rejection andchronic nephropathies, the sensitivity, specificityand overall accuracy of DWI MRI was 90%, 98%and 90% respectively.Conclusion: In this relatively large study includingstable and abnormal function in transplantedkidneys, we can conclude that DW MRI isrelatively a new technique that allows diagnosis oftransplanted kidney with normal and alteredfunction

Investigating Built Environment Indicators to Develop a Local Walkability Index

Many studies have been conducted over the last 20 years to determine and measure factors that affect the walkability of city streets. Walkability is an essential factor in deciding whether a city is green or sustainable. This paper creates a comprehensive walkability index by analysing built environmental indicators that affect walkability. This research was conducted on mixed land use streets in Cairo, Egypt, combining the results from an online survey and a walkability assessment model developed by multi-criteria decision analysis techniques. The results were based on a three-pillar approach starting with the theoretical background to frame the walkability indicator, numerical assessment over the Egyptian cases using a multi-criteria decision-making (MCDM) technique and a qualitative user perception survey. Our results confirm that determining to what extent Cairo’s streets are walkable is crucial to enhancing pedestrians’ perceptions of the walking environment. Furthermore, the results illustrated the essential factors within the built environment indicators that influence pedestrian walking behaviour

The Penile Perception Score after distal hypospadias repair with tubularized incised plate and Mathieu

Objective: The aim of this study was to evaluate the Penile Perception Score (PPS) after repair of distal penile hypospadias using tabularized incised plate (TIP) and Mathieu procedures.Methods: A randomized controlled study was conducted at urology department from October 2013 to May 2014. It included 60 children who were divided into three groups: group A included 20 patients with distal hypospadias corrected using TIP; group B included 20 patients with distal hypospadias corrected using Mathieu; and group C included 20 children with normal male genitalia who were circumcised and considered as a control group.Results: There were no statistically significant differences between group A and group B in urologists’ and parents’ average sum of PPS evaluation, but urologists’ satisfaction was more than parents’ satisfaction. The PPS for TIP was 8.43 and 7.80 for urologists and parents, respectively. The difference was significant. The PPS for Mathieu were 8.04 and 7.89 for urologists and parents, respectively, with no significance. There were no statistically significant differences between group A and group B in the postoperative evaluation by urologists and by parents in meatus, glans, shaft skin, and general appearance. There were complications in 10% of cases from group A in the form of fistula, in 30% of cases from group B in the form of fistula in 25% and meatal stenosis in 5%, and no complication in group C.Conclusion: TIP showed better PPS score compared with Mathieu in hypospadias repair. However, the results of this study were not statistically significant. PPS was a good scale to evaluate hypospadias repair after surgery.Keywords: hypospadias, parents and urology, Penile Perception Scor