Social encounter networks : characterizing Great Britain

A major goal of infectious disease epidemiology is to understand and predict the spread of infections within human populations, with the intention of better informing decisions regarding control and intervention. However, the development of fully mechanistic models of transmission requires a quantitative understanding of social interactions and collective properties of social networks. We performed a cross-sectional study of the social contacts on given days for more than 5000 respondents in England, Scotland and Wales, through postal and online survey methods. The survey was designed to elicit detailed and previously unreported measures of the immediate social network of participants relevant to infection spread. Here, we describe individual-level contact patterns, focusing on the range of heterogeneity observed and discuss the correlations between contact patterns and other socio-demographic factors. We find that the distribution of the number of contacts approximates a power-law distribution, but postulate that total contact time (which has a shorter-tailed distribution) is more epidemiologically relevant. We observe that children, public-sector and healthcare workers have the highest number of total contact hours and are therefore most likely to catch and transmit infectious disease. Our study also quantifies the transitive connections made between an individual's contacts (or clustering); this is a key structural characteristic of social networks with important implications for disease transmission and control efficacy. Respondents' networks exhibit high levels of clustering, which varies across social settings and increases with duration, frequency of contact and distance from home. Finally, we discuss the implications of these findings for the transmission and control of pathogens spread through close contact

Elliptic Reciprocity

The paper introduces the notions of an elliptic pair, an elliptic cycle and an elliptic list over a square free positive integer d. These concepts are related to the notions of amicable pairs of primes and aliquot cycles that were introduced by Silverman and Stange. Settling a matter left open by Silverman and Stange it is shown that for d=3 there are elliptic cycles of length 6. For d not equal to 3 the question of the existence of proper elliptic lists of length n over d is reduced to the the theory of prime producing quadratic polynomials. For d=163 a proper elliptic list of length 40 is exhibited. It is shown that for each d there is an upper bound on the length of a proper elliptic list over d. The final section of the paper contains heuristic arguments supporting conjectured asymptotics for the number of elliptic pairs below integer X. Finally, for d congruent to 3 modulo 8 the existence of infinitely many anomalous prime numbers is derived from Bunyakowski's Conjecture for quadratic polynomials.Comment: 17 pages, including one figure and two table

Algebraic properties of generalized Rijndael-like ciphers

We provide conditions under which the set of Rijndael functions considered as permutations of the state space and based on operations of the finite field \GF (p^k) ($p\geq 2$ a prime number) is not closed under functional composition. These conditions justify using a sequential multiple encryption to strengthen the AES (Rijndael block cipher with specific block sizes) in case AES became practically insecure. In Sparr and Wernsdorf (2008), R. Sparr and R. Wernsdorf provided conditions under which the group generated by the Rijndael-like round functions based on operations of the finite field \GF (2^k) is equal to the alternating group on the state space. In this paper we provide conditions under which the group generated by the Rijndael-like round functions based on operations of the finite field \GF (p^k) ($p\geq 2$) is equal to the symmetric group or the alternating group on the state space.Comment: 22 pages; Prelim0

Rotas alternativas e caminhos para a identidade profissional dos professores: Explorando as diversas identidades dos membros Teach For America

Research on the development of professional identity for teachers who enter the profession through alternative routes is still in its infancy. In contrast to their peers who complete traditional initial teacher education programs, these teachers are exposed to different conditions and constraints that produce a range of sub-identities previously unidentified in the literature. This paper draws on interviews with 27 teachers who entered teaching through Teach For America and wrestled with these sub-identities as they considered their emerging professional identity. We argue that these sub-identities point to structural challenges embedded within Teach for America, and we highlight the need for additional research on the growing cadre of teachers entering the teaching profession through alternative routes, and subsequently influencing policymaking processes.La investigación sobre el desarrollo de la identidad profesional de los maestros que ingresan a la profesión a través de vías alternativas todavía está en su infancia. A diferencia de sus colegas que completan los programas tradicionales de formación docente inicial, estos maestros están expuestos a diferentes condiciones y limitaciones que producen una multitud de identidades no identificadas previamente en la literatura. Esta investigación se basa en entrevistas con 27 maestros que ingresaron a la enseñanza a través de Teach For America y lucharon con estas subidentidades cuando consideraban su identidad profesional emergente. Presentamos argumentos que estas subidentidades apuntan a desafíos estructurales integrados en Teach for America, y destacamos la necesidad de investigación adicional sobre el creciente grupo de profesores que ingresan a la profesión docente a través de rutas alternativas, y que posteriormente influyen en los procesos de formulación de pólitica.A pesquisa sobre o desenvolvimento da identidade profissional dos professores que entram na profissão através de meios alternativos ainda está em sua infância. Ao contrário de seus colegas que completam os tradicionais programas iniciais de treinamento de professores, esses professores estão expostos a diferentes condições e limitações que produzem uma multiplicidade de identidades não identificadas anteriormente na literatura. Esta pesquisa é baseada em entrevistas com 27 professores que entraram no ensino por Teach For America e lutaram com essas subidências quando consideraram sua identidade profissional emergente. Apresentamos argumentos de que essas subentendências apontam para desafios estruturais integrados no Teach for America e destacamos a necessidade de pesquisas adicionais sobre o crescente grupo de professores que entram na profissão docente através de rotas alternativas e que posteriormente influenciam os processos de formulação de pólitica

Compensation Benchmarking, Leapfrogs, and the Surge in Executive Pay

Scholars frequently argue whether the sharp rise in chief executive officer (CEO) pay in recent years is "efficient" or is a consequence of "rent extraction" because of the failure of corporate governance in individual firms. This article argues that governance failure must be conceptualized at the market rather than the firm level because excessive pay increases for even relatively few CEOs a year spread to other firms through the cognitively and rhetorically constructed compensation networks of "peer groups," which are used in the benchmarking process to negotiate the compensation of CEOs. Counterfactual simulation based on Standard and Poor's ExecuComp data demonstrates that the effects of CEO "leapfrogging" potentially explain a considerable fraction of the overall upward movement of executive compensation since the early 1990s

An Experimental Test of Tradeoffs between Discount Rates and Number of Firms in Supporting Collusion

One prediction of oligopoly theory is that there should be a tradeoff between discount rates (rates of time preference) and the number of competitors in a market, in supporting the possibility of collusive equilibria. Here we conduct a series of laboratory experiments with markets of 2, 3, and 4 firms, and discount rates explicitly accounted for, and examine whether the tradeoffs predicted in theory occur in the behavior of our subjects. We find that an increased number of firms in a market is associated with larger market output (and lower prices), reflecting the generalized Cournot result throughout. We fail to observe an impact of higher discount rates in further limiting collusive behavior

Oxidized low-density lipoprotein inhibits hepatitis C virus cell entry in human hepatoma cells.

Cell entry of hepatitis C virus, pseudoparticles (HCVpp) and cell culture grown virus (HCVcc), requires the interaction of viral glycoproteins with CD81 and other as yet unknown cellular factors. One of these is likely to be the scavenger receptor class B type I (SR-BI). To further understand the role of SR-BI, we examined the effect of SR-BI ligands on HCVpp and HCVcc infectivity. Oxidized low-density lipoprotein (oxLDL), but not native LDL, potently inhibited HCVpp and HCVcc cell entry. Pseudoparticles bearing unrelated viral glycoproteins or bovine viral diarrhea virus were not affected. A dose-dependent inhibition was observed for HCVpp bearing diverse viral glycoproteins with an approximate IC50 of 1.5 microg/mL apolipoprotein content, which is within the range of oxLDL reported to be present in human plasma. The ability of lipoprotein components to bind to target cells associated with their antiviral activity, suggesting a mechanism of action which targets a cell surface receptor critical for HCV infection of the host cell. However, binding of soluble E2 to SR-BI or CD81 was not affected by oxLDL, suggesting that oxLDL does not act as a simple receptor blocker. At the same time, oxLDL incubation altered the biophysical properties of HCVpp, suggesting a ternary interaction of oxLDL with both virus and target cells. In conclusion, the SR-BI ligand oxLDL is a potent cell entry inhibitor for a broad range of HCV strains in vitro. These findings suggest that SR-BI is an essential component of the cellular HCV receptor complex

Education Needs Assessment for Kaduna City, Nigeria

This educational needs assessment is part of series of working documents aiming to support the creation and implementation of urban development strategies in nine Millennium Cities in sub-Saharan Africa. This study explores the educational situation in Kaduna, Nigeria, and examines recent successes and the ensuing challenges in the education sector. The main objective of this assessment is to evaluate Kaduna's path to achieving Millennium Development Goals (MDGs) #2 and #3 – achieving universal primary education and achieving gender parity at all levels of education by 2015