Aeroelastic stability analysis of high aspect ratio aircraft wings

Free vibration and flutter analyses of two types of high aspect ratio aircraft wings are presented. The wing is idealised as an assembly of bending-torsion coupled beams using the dynamic stiffness method leading to a nonlinear eigenvalue problem. This problem is solved using the Wattrick-Williams algorithm yielding natural frequencies and mode shapes. The flutter analysis is carried out using the normal mode method in conjunction with generalised coordinates and two-dimensional unsteady aerodynamic theory of Theodorsen. This is essentially a complex eigenvalue problem in terms of both air-speed and frequency. The flutter determinant is solved by an iterative procedure covering a wide range of air-speeds and frequencies. The computed natural frequencies, mode shapes, flutter speeds and flutter frequencies are compared and contrasted for the two type of aircraft wings and some conclusions are drawn

An exact spectral dynamic stiffness theory for composite plate-like structures with arbitrary non-uniform elastic supports, mass attachments and coupling constraints

This paper presents an exact spectral dynamic stiffness (SDS) theory for composite plates and plate assemblies with arbitrary non-uniform elastic supports, mass attachments and elastic coupling constraints. The theory treats the above supports, attachments and constraints in a sufficiently general, but accurate manner, which can be applied to various SDS formulations as well as classical dynamic stiffness formulations for both modal and dynamic response analysis. The methodology is concise but can be easily applied to complex plate-like structures with any arbitrary boundary conditions. It retains all the advantages of a recently developed SDS method which gives exact results with excellent computation efficiency. The results computed by the present theory are validated against published results. In order to demonstrate the practical applicability of the theory, three wide ranging engineering composite structures are investigated. For benchmarking purposes, results computed from the current theory are accurate up to the last figure quoted

DETERMINANTS OF PARENTAL CHILD’S SCHOOL PREFERENCES IN QATAR

Purpose: The objective of this study is to investigate the impact of “Quality Education”, “Developing Better Social Skills”, “Homework Assignment”, “Using Private Tutors”, “Charging School Fees” and “Nationality” on “Parental School Preference” using primary data collected from preparatory and secondary school teachers in Qatar. Methodology: The population for this study consists of all parents in Qatar. The current study used a very large stratified sample size n = 1462 that was determined by the Social and Economic Survey Research Institute (SESRI) using a 95% confidence interval estimate. The nine items used in this study are part of a huge questionnaire measuring attitude and parental child’s school preferences. Kaisers-Meyer-Olkin (KMO) test and the Bartless test of sphericity were used to determine the appropriateness of using factor analysis. What are more; principal axis factoring and oblique rotation extracted three factors? Main findings: The representative sample Factor analysis extracted three dimensions (quality education, developing better social skills, homework assignment). The dependent variable (parental school choice) was regressed on the factor scores of these three extracted dimensions in addition to four independent variables (school fees, nationality, repeating a school grade, and parents’ disappointment if their child doesn’t go far in school). The results revealed that parental school choice is significantly determined by three explanatory variables: the quality of education, school fees, and nationality. Implications: Raising standards for teachers should be a key element in educational quality. What’s more, in the spirit of findings the policymakers in Qatar should make funding part of school fees for expatriates a priority. Novelty: This article empirically correlates two main fields of educational research: Parental School Choice is given Quality of Education, Charging School Fees, and Nationality.This work was supported by the Social and Economic Survey Research Institute, Qatar University. The authors would like to thank all the parents who took part in the 2015 Qatar Education Study. The authors would also like to thank Dr. Darwish Al-Emadi, Dr. Abdoulaye Diop, Dr. Elmogeira Elawad, and Mr. Anis Miladi, Mr. Isam Mohamed Abdelhameed in giving so generously of their time at various stages of the data collection and entry.Scopu

Interactive Multimedia Learning On Health Care Among Lebanese Women: An Exploratory Study

Multimedia learning greatly enhanced the learning outcome and experience of learners exposed to it. The proposed study will explore the usefulness of multimedia learning software devised to educate Lebanese pregnant women who have a low level of formal education about pregnancy and early infant care. The study will be based on the media richness theory. It is expected that through media rich programs, communication of information is facilitated, promoting the resolving of indecisiveness and ambiguity that stems out of the lack of knowledge or information about a given a subject and the inability to convey a meaning of what is being said respectively

Small Bowel Tumors: Clinical Presentation, Prognosis, and Outcome in 33 Patients in a Tertiary Care Center

Introduction. Small bowel cancers are rare. Accumulation of data regarding their clinical presentation, pathologic features, prognostic factors, treatment modalities, and outcome is difficult. Methods. This is a retrospective study of the medical records of 33 patients with small bowel cancers treated at the American University of Beirut-Medical Center over a 20-year period. Results. The study included 25 males (76%) and 8 females (24%). Median age at presentation was 56 years. Most common symptoms were abdominal pain (66.7%) and weight loss (57.6%). Thirteen patients presented with abdominal emergencies (39.3%). Lymphoma was the most common malignant tumor (36.4%), followed by adenocarcinoma (33.3%), leiomyosarcoma (15.2%), gastrointestinal stromal tumors (12.1%), and neuroendocrine tumors (3.0%). Tumors were located in the duodenum in 30% of patients, jejunum in 33%, and ileum in 36%. Resectability rate was 72.7% and curative R0 resection was achieved in 54.1% (13/24) of patients. 5-year survival of the 33 patients was 24.2%. Conclusion. Small bowel cancers are difficult to diagnose because of the nonspecific symptoms. Most patients present with advanced disease and have poor prognosis. Adenocarcinoma and duodenal location have the worst 5-year survival in contrast to stromal tumors and those with ileal location which have the best survival

Key Agreement Against Quantum Adversaries

Key agreement is a cryptographic scenario between two legitimate parties, who need to establish a common secret key over a public authenticated channel, and an eavesdropper who intercepts all their messages in order to learn the secret. We consider query complexity in which we count only the number of evaluations (queries) of a given black-box function, and classical communication channels. Ralph Merkle provided the first unclassified scheme for secure communications over insecure channels. When legitimate parties are willing to ask O(N) queries for some parameter N, any classical eavesdropper needs Omega(N^2) queries before being able to learn their secret, which is is optimal. However, a quantum eavesdropper can break this scheme in O(N) queries. Furthermore, it was conjectured that any scheme, in which legitimate parties are classical, could be broken in O(N) quantum queries. In this thesis, we introduce protocols à la Merkle that fall into two categories. When legitimate parties are restricted to use classical computers, we offer the first secure classical scheme. It requires Omega(N^{13/12}) queries of a quantum eavesdropper to learn the secret. We give another protocol having security of Omega(N^{7/6}) queries. Furthermore, for any k>= 2, we introduce a classical protocol in which legitimate parties establish a secret in O(N) queries while the optimal quantum eavesdropping strategy requires Theta(N^{1/2+k/{k+1}}) queries, approaching Theta(N^{3/2}) when k increases. When legitimate parties are provided with quantum computers, we present two quantum protocols improving on the best known scheme before this work. Furthermore, for any k>= 2, we give a quantum protocol in which legitimate parties establish a secret in O(N) queries while the optimal quantum eavesdropping strategy requires Theta(N^{1+{k}/{k+1}})} queries, approaching Theta(N^{2}) when k increases.Un protocole d'échange de clés est un scénario cryptographique entre deux partis légitimes ayant besoin de se mettre d'accord sur une clé commune secrète via un canal public authentifié où tous les messages sont interceptés par un espion voulant connaître leur secret. Nous considérons un canal classique et mesurons la complexité de calcul en termes du nombre d'évaluations (requêtes) d'une fonction donnée par une boîte noire. Ralph Merkle fut le premier à proposer un schéma non classifié permettant de réaliser des échanges securisés avec des canaux non securisés. Lorsque les partis légitimes sont capables de faire O(N) requêtes pour un certain paramètre N, tout espion classique doit faire Omega(N^2) requêtes avant de pouvoir apprendre leur secret, ce qui est optimal. Cependant, un espion quantique peut briser ce schéma avec O(N) requêtes. D'ailleurs, il a été conjecturé que tout protocole, dont les partis légitimes sont classiques, pourrait être brisé avec O(N) requêtes quantiques. Dans cette thèse, nous introduisons deux catégories des protocoles à la Merkle. Lorsque les partis légitimes sont restreints à l'utilisation des ordinateurs classiques, nous offrons le premier schéma classique sûr. Il oblige tout adversaire quantique à faire Omega(N^{13/12}) requêtes avant d'apprendre le secret. Nous offrons aussi un protocole ayant une sécurité de Omega(N^{7/6}) requêtes. En outre, pour tout k >= 2, nous donnons un protocole classique pour lequel les partis légitimes établissent un secret avec O(N) requêtes alors que la stratégie optimale d'espionnage quantique nécessite Theta(N^{1/2 + k/{k +1}}) requêtes, se rapprochant de Theta(N^{3/2}) lorsque k croît. Lors les partis légitimes sont équipés d'ordinateurs quantiques, nous présentons deux protocoles supérieurs au meilleur schéma connu avant ce travail. En outre, pour tout k >= 2, nous offrons un protocole quantique pour lequel les partis légitimes établissent un secret avec O(N) requêtes alors que l'espionnage quantique optimale nécessite Theta(N^{1+{k}/{k+1}}) requêtes, se rapprochant de Theta(N^{2}) lorsque k croît

A new double-layered kagome antiferromagnet ScFe6_6Ge4_4

ScFe$_6$Ge$_4$ with the LiFe$_6$Ge$_4$-type structure (space group $R{\bar{3}}m$), which has a double-layered kagome lattice (18$h$ site) of Fe crystallographically equivalent to that of a well-known topological ferromagnet Fe$_3$Sn$_2$, is newly found to be antiferromagnetic (AFM) with a high N\'eel temperature of $T_{\rm{N}} \approx 650$ K, in contrast to the ferromagnetic (FM) ground state previously proposed in a literature. $^{45}$Sc nuclear magnetic resonance experiment revealed the absence of a hyperfine field at the Sc site, providing microscopic evidence for the AFM state and indicating AFM coupling between the bilayer kagome blocks. The stability of the AFM structure under the assumption of FM intra-bilayer coupling is verified by DFT calculations.Comment: 13 pages, 1 tables, 4 figure

Flutter prediction of metallic and composite wings using coupled DSM-CFD models in transonic flow

Although flutter analysis is a relatively old problem in aviation, it is still challenging, particularly with the advent of composite materials and requirements for high-speed light airframes. The main challenge for this problem is at the transonic flow region. The transonic flow, being non-linear, poses a great challenge over traditional linear theories which fail to predict the aerodynamic properties accurately. Aerospace has been one of the primary areas of applications to take advantage of composite materials with the aim to reduce the total mass and improve control effectiveness. This work takes advantage of CFD methods advancement as the main flow solver for non-linear governing equations. In order to investigate the dynamic behaviour of composite aircraft wings, the dynamic stiffness method (DSM) for bending-torsion composite beam is used to compute the free vibration natural modes. The main objective of this work is coupling the dynamic stiffness method (DSM) with high fidelity computational fluid dynamics models in order to predict the transonic flutter of composite aircraft wings accurately and efficiently. In addressing the main aim of this study, Euler fluid flow solvers of an open source CFD code called OpenFOAM has been coupled with elastic composite wing, represented by the free vibration modes computed by DSM. The first part of this study is devoted to investigating the free vibration characteristics of two types of aircraft, namely sailplane type and transport airliner type. Two models of each type have been analysed and contrasted, which revealed the significance of the natural modes of aircraft wings and how these modes inherently capture the essential characteristics of the system. Then to validate the CFD code, two pitching and self-sustained two degrees of freedom airfoils under different flow condition have been modelled. The results have been compared against experimental measurements and numerical data from the literature which showed good agreement for the predicted force coefficients. Finally, the model has been extended to study a complete aircraft wing. Both metallic and composite Goland wings have been investigated under a wide range of flow conditions. The composite wing has been investigated using different material coupling values to show their effect on its aeroelastic behaviour. The results showed the significant influence of the material coupling on the aeroelastic characteristics of composite wings