Semiflexible Filamentous Composites

Inspired by the ubiquity of composite filamentous networks in nature we investigate models of biopolymer networks that consist of interconnected floppy and stiff filaments. Numerical simulations carried out in three dimensions allow us to explore the microscopic partitioning of stresses and strains between the stiff and floppy fractions c_s and c_f, and reveal a non-trivial relationship between the mechanical behavior and the relative fraction of stiff polymer: when there are few stiff polymers, non-percolated stiff ``inclusions`` are protected from large deformations by an encompassing floppy matrix, while at higher fractions of stiff material the stiff network is independently percolated and dominates the mechanical response.Comment: Phys. Rev. Lett, to appear (4 pages, 2 figures

Electron Beam Nano-Etching in Oxides, Fluorides, Metals and Semiconductors

Etching, lithography, hole formation, surface restructuring and external machining can all be performed on a nanometre scale using an intense electron beam. Results are presented for a range of different materials which demonstrate the variety of mechanisms by which electron beam nano-etching can occur. For example, in crystalline 13-alumina hole formation occurs by surface indentations growing inwards to join up and form a nanometre diameter hole. In amorphous alumina, on the other hand, hole formation is from the inside-out: oxygen gas bubbles form under the electron beam, coalesce, and burst to leave a well defined nanometre diameter hole. In MgO and Si, holes develop from the electron exit surface: whereas in Al voids form along the irradiated volume, leading eventually to the development of a hole at the electron entrance surface. The potential of electron beam nano-etching to lithography and information storage is demonstrated by showing that the entire contents of the Encyclopaedia Britannica can be written on a pinhead

Give us a game : evaluating the opportunities that exist for English footballers to play in the English Premier League

The purpose of this study was to provide a detailed, large-scale retrospective analysis of the number of English footballers that have been developed to play in the English Premier League (EPL) over twenty seasons. Unlike previous research, we examined appearance data as opposed to percentage of squad data enabling a more accurate representation of English players appearing in the EPL. The findings revealed a steady decline in the number and proportion of appearances made by English players in the EPL throughout the twenty season period. However, the results also indicated that the rate of decline had abated since the inception of UEFA's home-grown rule. The results support the view that opportunities for indigenous players have diminished since the EPL's inception. Given the short-term, results-focused culture that prevails in the EPL, this would appear to present a major challenge for governing bodies, particularly those working in elite player development. Discussion surrounding how these challenges might be met is presented

New Integrable Sectors in Skyrme and 4-dimensional CP^n Model

The application of a weak integrability concept to the Skyrme and $CP^n$ models in 4 dimensions is investigated. A new integrable subsystem of the Skyrme model, allowing also for non-holomorphic solutions, is derived. This procedure can be applied to the massive Skyrme model, as well. Moreover, an example of a family of chiral Lagrangians providing exact, finite energy Skyrme-like solitons with arbitrary value of the topological charge, is given. In the case of $CP^n$ models a tower of integrable subsystems is obtained. In particular, in (2+1) dimensions a one-to-one correspondence between the standard integrable submodel and the BPS sector is proved. Additionally, it is shown that weak integrable submodels allow also for non-BPS solutions. Geometric as well as algebraic interpretations of the integrability conditions are also given.Comment: 23 page

Finite-temperature correlations in the one-dimensional trapped and untrapped Bose gases

We calculate the dynamic single-particle and many-particle correlation functions at non-zero temperature in one-dimensional trapped repulsive Bose gases. The decay for increasing distance between the points of these correlation functions is governed by a scaling exponent that has a universal expression in terms of observed quantities. This expression is valid in the weak-interaction Gross-Pitaevskii as well as in the strong-interaction Girardeau-Tonks limit, but the observed quantities involved depend on the interaction strength. The confining trap introduces a weak center-of-mass dependence in the scaling exponent. We also conjecture results for the density-density correlation function.Comment: 18 pages, Latex, Revtex

The native architecture of a photosynthetic membrane

In photosynthesis, the harvesting of solar energy and its subsequent conversion into a stable charge separation are dependent upon an interconnected macromolecular network of membrane-associated chlorophyll–protein complexes. Although the detailed structure of each complex has been determined, the size and organization of this network are unknown. Here we show the use of atomic force microscopy to directly reveal a native bacterial photosynthetic membrane. This first view of any multi-component membrane shows the relative positions and associations of the photosynthetic complexes and reveals crucial new features of the organization of the network: we found that the membrane is divided into specialized domains each with a different network organization and in which one type of complex predominates. Two types of organization were found for the peripheral light-harvesting LH2 complex. In the first, groups of 10–20 molecules of LH2 form light-capture domains that interconnect linear arrays of dimers of core reaction centre (RC)–light-harvesting 1 (RC–LH1–PufX) complexes; in the second they were found outside these arrays in larger clusters. The LH1 complex is ideally positioned to function as an energy collection hub, temporarily storing it before transfer to the RC where photochemistry occurs: the elegant economy of the photosynthetic membrane is demonstrated by the close packing of these linear arrays, which are often only separated by narrow 'energy conduits' of LH2 just two or three complexes wide

Doing more with less: Teacher professional learning communities in resource-constrained primary schools in rural China.

Teacher professional learning communities provide environments in which teachers engage in regular research and collaboration. They have been found effective as a means for connecting professional learning to the day-to-day realities faced by teachers in the classroom. In this article, the authors draw on survey data collected in primary schools serving 71 villages in rural Gansu Province as well as transcripts from in-depth interviews with 30 teachers. Findings indicate that professional learning communities penetrate to some of China’s most resource-constrained schools but that their nature and development are shaped by institutional supports, principal leadership, and teachers’ own initiative

Cavity-induced coherence effects in spontaneous emission from pre-Selection of polarization

Spontaneous emission can create coherences in a multilevel atom having close lying levels, subject to the condition that the atomic dipole matrix elements are non-orthogonal. This condition is rarely met in atomic systems. We report the possibility of bypassing this condition and thereby creating coherences by letting the atom with orthogonal dipoles to interact with the vacuum of a pre-selected polarized cavity mode rather than the free space vacuum. We derive a master equation for the reduced density operator of a model four level atomic system, and obtain its analytical solution to describe the interference effects. We report the quantum beat structure in the populations.Comment: 6 pages in REVTEX multicolumn format, 5 figures, new references added, journal reference adde

Career orientations and career cultures : individual and organisational approaches to beginning teachers’ careers

Despite the very large literature on teacher careers from an individual perspective, there is relatively little that links the perspectives of teachers themselves to how schools as organisations approach careers. The aim of this paper is, first, to outline how teachers’ orientations towards careers change across three dimensions, and, second, to examine how schools as organisations deal with career, developing a model of organisational responses, including developing a concept of ‘career culture’, derived from an analysis of interviews regarding the first three years of teaching conducted with senior leaders and second year teachers themselves. By considering the fit between individuals’ career orientations and school career cultures, the paper surfaces both the fluid nature of these orientations and the subsequent potential instability of the fit

A Study Of A New Class Of Discrete Nonlinear Schroedinger Equations

A new class of 1D discrete nonlinear Schr${\ddot{\rm{o}}}$dinger Hamiltonians with tunable nonlinerities is introduced, which includes the integrable Ablowitz-Ladik system as a limit. A new subset of equations, which are derived from these Hamiltonians using a generalized definition of Poisson brackets, and collectively refered to as the N-AL equation, is studied. The symmetry properties of the equation are discussed. These equations are shown to possess propagating localized solutions, having the continuous translational symmetry of the one-soliton solution of the Ablowitz-Ladik nonlinear Schr${\ddot{\rm{o}}}$dinger equation. The N-AL systems are shown to be suitable to study the combined effect of the dynamical imbalance of nonlinearity and dispersion and the Peierls-Nabarro potential, arising from the lattice discreteness, on the propagating solitary wave like profiles. A perturbative analysis shows that the N-AL systems can have discrete breather solutions, due to the presence of saddle center bifurcations in phase portraits. The unstaggered localized states are shown to have positive effective mass. On the other hand, large width but small amplitude staggered localized states have negative effective mass. The collison dynamics of two colliding solitary wave profiles are studied numerically. Notwithstanding colliding solitary wave profiles are seen to exhibit nontrivial nonsolitonic interactions, certain universal features are observed in the collison dynamics. Future scopes of this work and possible applications of the N-AL systems are discussed.Comment: 17 pages, 15 figures, revtex4, xmgr, gn