Elastic response of filamentous networks with compliant crosslinks

Experiments have shown that elasticity of disordered filamentous networks with compliant crosslinks is very different from networks with rigid crosslinks. Here, we model and analyze filamentous networks as a collection of randomly oriented rigid filaments connected to each other by flexible crosslinks that are modeled as worm-like chains. For relatively large extensions we allow for enthalpic stretching of crosslinks' backbones. We show that for sufficiently high crosslink density, the network linear elastic response is affine on the scale of the filaments' length. The nonlinear regime can become highly nonaffine and is characterized by a divergence of the elastic modulus at finite strain. In contrast to the prior predictions, we do not find an asymptotic regime in which the differential elastic modulus scales linearly with the stress, although an approximate linear dependence can be seen in a transition from entropic to enthalpic regimes. We discuss our results in light of the recent experiments.Comment: 10 pages, 11 figure

Topology counts: force distributions in circular spring networks

Filamentous polymer networks govern the mechanical properties of many biological materials. Force distributions within these networks are typically highly inhomogeneous and, although the importance of force distributions for structural properties is well recognized, they are far from being understood quantitatively. Using a combination of probabilistic and graph-theoretical techniques we derive force distributions in a model system consisting of ensembles of random linear spring networks on a circle. We show that characteristic quantities, such as mean and variance of the force supported by individual springs, can be derived explicitly in terms of only two parameters: (i) average connectivity and (ii) number of nodes. Our analysis shows that a classical mean-field approach fails to capture these characteristic quantities correctly. In contrast, we demonstrate that network topology is a crucial determinant of force distributions in an elastic spring network.Comment: 5 pages, 4 figures. Missing labels in Fig. 4 added. Reference fixe

Evidence for coherent collective Rydberg excitation in the strong blockade regime

Blockade effects on the single quantum level are at the heart of quantum devices like single-electron transistors. The blockade mechanisms are based on strong interactions like the Coulomb interaction in case of single electrons. Neutral atoms excited into a Rydberg state experience abnormally strong interactions that lead to the corresponding blockade effect for Rydberg atoms. In this paper we report on our measurements of a strong van der Waals blockade, showing that only one out of several thousand atoms within a blockade volume can be excited. In addition, our experimental results demonstrate the coherent nature of the excitation of magnetically trapped ultracold atoms into a Rydberg state, confirming the predicted dependence of the collective Rabi frequency on the square root of the mesoscopic system size. This collective coherent behaviour is generic for all mesoscopic systems which are able to carry only one single excitation quantum.Comment: 5 pages, 4 figure

Direct evidence for the magnetic ordering of Nd ions in NdFeAsO by high resolution inelastic neutron scattering

We investigated the low energy excitations in the parent compound NdFeAsO of the Fe-pnictide superconductor in the $\mu$eV range by a back scattering neutron spectrometer. The energy scans on a powder NdFeAsO sample revealed inelastic peaks at E = 1.600 $\pm 0.003 \mu$eV at T = 0.055 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and finally merge with the elastic peak at about 6 K. We interpret the inelastic peaks to be due to the transition between hyperfine-split nuclear level of the $^{143}$Nd and $^{145}$Nd isotopes with spin $I = 7/2$. The hyperfine field is produced by the ordering of the electronic magnetic moment of Nd at low temperature and thus the present investigation gives direct evidence of the ordering of the Nd magnetic sublattice of NdFeAsO at low temperature

Comparative Interpretation Standards in Uniform International Law

In this chapter, the author offers a horizontal comparison of interpretation standards contained in international legal instruments of different origin. These legal instruments range from international treaties to model laws. They also originate from different law makers such as the United Nations or individual states as well as trade or academic organisations, mainly regulating civil and commercial matters. The author argues that this comparison can provide the basis for the development of a uniform standard in the application of such law, which is often referred to as uniform law because it provides a single source of law to regulate a multitude of situations spanning across national boundaries. The main point of reference is the 1969 Vienna Convention on the Law of Treaties, also known as the VCLT. This UN treaty specifically provides a general interpretation standard. From there newer standards occurring in subsequent uniform laws can be integrated using the lex specialis doctrine. This, in turn, provides opportunities for comprehensive usable methods to be developed for uniform law both in a public and private law settings. These then facilitate transparency, fairness and reasonableness. The correct identification of object and purposes of any given instrument is crucial for the successful interpretation of its content. It is this point that needs further research, and this chapter offers a starting point by providing some detailed examples from a range of uniform laws of varying nature including international sales laws, arbitration laws and Double Taxation Conventions

Efficient HTTP based I/O on very large datasets for high performance computing with the libdavix library

Remote data access for data analysis in high performance computing is commonly done with specialized data access protocols and storage systems. These protocols are highly optimized for high throughput on very large datasets, multi-streams, high availability, low latency and efficient parallel I/O. The purpose of this paper is to describe how we have adapted a generic protocol, the Hyper Text Transport Protocol (HTTP) to make it a competitive alternative for high performance I/O and data analysis applications in a global computing grid: the Worldwide LHC Computing Grid. In this work, we first analyze the design differences between the HTTP protocol and the most common high performance I/O protocols, pointing out the main performance weaknesses of HTTP. Then, we describe in detail how we solved these issues. Our solutions have been implemented in a toolkit called davix, available through several recent Linux distributions. Finally, we describe the results of our benchmarks where we compare the performance of davix against a HPC specific protocol for a data analysis use case.Comment: Presented at: Very large Data Bases (VLDB) 2014, Hangzho

Slave to the rhythm: seasonal signals in otolith microchemistry reveal age of eastern Baltic cod (Gadus morhua)

Annual growth zones in cod otoliths from the eastern Baltic stock are less discrete than in other cod stocks leading to biased age reading, which recently led to a failure of age-based assessment in the eastern Baltic cod stock. In this study, we explored the applicability of minor and trace element patterns in cod otoliths for age determination. By first identifying elements of interest in a stock without ageing problems, western Baltic cod, we then tested their applicability on another stock without ageing problems, North Sea cod, and finally applied this knowledge to estimate age of eastern Baltic cod. In western Baltic cod, matching patterns with respect to occurrence of minima and maxima in both otolith opacity and element concentrations were found for Cu, Zn, and Rb, and inverse patterns with Mg and Mn. No match was found for Pb, Ba, and Sr. In the test stock, the North Sea cod, the same patterns in Cu, Zn, Rb, Mg, and Mn signals occurred. All eastern Baltic cod with low visual contrast between growth zones exhibited clearly defined synchronous cycles in Cu, Zn, Rb and Pb. Using a combined finite differencing method and structural break models approach, the statistical significance of the local profile minima were identified, based on which their age could be estimated. Despite extensive environmental differences between the three areas examined, the element concentrations of Cu, Zn, and Rb were strongly correlated in all individuals with similar correlations in all three areas, suggesting that the incorporation mechanisms are the same for these elements and independent of environmental concentrations

Utilización de los diagramas de Minkowski para la enseñanza de la Teoría Especial de la Relatividad en la escuela secundaria

En este trabajo se presentan los resultados de la implementación de una etapa de una Secuencia de Enseñanza y Aprendizaje diseñada para abordar la Teoría Especial de la Relatividad en la escuela secundaria superior, en Argentina. Se adopta el modelo de Enseñanza para la Comprensión dentro de un marco teórico más amplio que promueve un aprendizaje significativo de la Teoría Especial de la Relatividad.El objetivo de esta investigación es analizar si la utilización de los diagramas de Minkowski, para establecer la simultaneidad de eventos en la Teoría Especial de la Relatividad, es una herramienta apropiada para la escuela secundaria.La metodología empleada en la investigación es cualitativa de tipo descriptiva. La implementación se realizó en dos cursos de secundaria superior de una escuela pública dependiente de la Universidad Nacional del Centro, conformados por 65 alumnos. Los resultados obtenidos evidencian rasgos de aprendizaje significativo de la Teoría Especial de la Relatividad, por parte de los alumnos.In this paper the results of the implementation of a step in a Teaching - Learning sequence designed to approach the Special Relativity Theory in high school in Argentina are presented. The purpose of this research is to analyze whether the use of Minkowski diagrams to establish the simultaneity of events in the Special Relativity Theory is an appropriate tool for high school. The methodology used in this research is qualitative and descriptive. The implementation was done in two courses of a public high school that is dependent of the Universidad Nacional del Centro (Argentina), with 65 students. The results show that students achieved meaningful learning in some topics of Special Relativity Theory.Fil: Cayul, Esther. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Grupo Educación en Ciencias con Tecnologías; ArgentinaFil: Arriassecq, Irene. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Grupo Educación en Ciencias con Tecnologías; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Production of a Fermi gas of atoms in an optical lattice

We prepare a degenerate Fermi gas of potassium atoms by sympathetic cooling with rubidium atoms in a one-dimensional optical lattice. In a tight lattice we observe a change of the density of states of the system, which is a signature of quasi two dimensional confinement. We also find that the dipolar oscillations of the Fermi gas along the tight lattice are almost completely suppressed.Comment: 4 pages, 4 figures, revised versio