Is There a Negative Thermal Expansion in Supported Metal Nanoparticles? An In-Situ X-ray Absorption Study Coupled with Neural Network Analysis

Interactions with their support, adsorbates and unique structural motifs are responsible for the many intriguing properties and potential applications of supported metal nanoparticles (NPs). At the same time, they complicate the interpretation of experimental data. In fact, the methods and approaches that work well for the ex situ analysis of bulk materials may be inaccurate or introduce artifacts in the in situ analysis of nanomaterials. Here we revisit the controversial topic of negative thermal expansion and anomalies in the Debye temperature reported for oxide-supported metal NPs. In situ X-ray absorption experimental data collected for Pt NPs in ultrahigh vacuum and an advanced data analysis approach based on an artificial neural network demonstrate that Pt NPs do not exhibit intrinsic negative thermal expansion. Similarly as for bulk materials, in the absence of adsorbates the bond lengths in metal NPs increase with temperature. The previously reported anomalies in particle size-dependent Debye temperatures can also be linked to the artifacts in the interpretation of conventional X-ray absorption data of disordered materials such as NPs

Nematic and Polar order in Active Filament Solutions

Using a microscopic model of interacting polar biofilaments and motor proteins, we characterize the phase diagram of both homogeneous and inhomogeneous states in terms of experimental parameters. The polarity of motor clusters is key in determining the organization of the filaments in homogeneous isotropic, polarized and nematic states, while motor-induced bundling yields spatially inhomogeneous structures.Comment: 4 pages. 3 figure

Shear flow induced isotropic to nematic transition in a suspension of active filaments

We study the effects of externally applied shear flow on a model of suspensions of motors and filaments, via the equations of active hydrodynamics [PRL {\bf 89} (2002) 058101; {\bf 92} (2004) 118101]. In the absence of shear, the orientationally ordered phase of {\it both} polar and apolar active particles is always unstable at zero-wavenumber. An imposed steady shear large enough to overcome the active stresses stabilises both apolar and moving polar phases. Our work is relevant to {\it in vitro} studies of active filaments, the reorientation of endothelial cells subject to shear flow and shear-induced motility of attached cells.Comment: 8 pages, 4 figures submitted to Europhysics Letter

Effect of relativistic acceleration on localized two-mode Gaussian quantum states

We study how an arbitrary Gaussian state of two localized wave packets, prepared in an inertial frame of reference, is described by a pair of uniformly accelerated observers. We explicitly compute the resulting state for arbitrarily chosen proper accelerations of the observers and independently tuned distance between them. To do so, we introduce a generalized Rindler frame of reference and analytically derive the corresponding state transformation as a Gaussian channel. Our approach provides several new insights into the phenomenon of vacuum entanglement such as the highly non-trivial effect of spatial separation between the observers including sudden death of entanglement. We also calculate the fidelity of the two-mode channel for non-vacuum Gaussian states and obtain bounds on classical and quantum capacities of a single-mode channel. Our framework can be directly applied to any continuous variable quantum information protocol in which the effects of acceleration or gravity cannot be neglected.Comment: 21 pages, 13 figures. A few typos correcte

Comparison of the papers published in journal of shahrekord university of medical sciences with those published in other medical journals of Iran in view of methodology

Background and aim: Scientific and research journals are considered as one of the most important tools for scientific and research information and science advancement in any discipline. Publishing articles in these journals is known to be an important indicator for knowledge generation. Comparing and assessing medical journals which present research outcomes, quantitatively and qualitatively, is particularly important to improve and promote them. The present study was conducted to compare the papers published in scientific and research Journal of Shahrekord University of Medical Sciences (JSKUMS) with those published in other medical journals of Iran in view of methodology. Methods: This cross-sectional study examined and compared the observance of scientific writing of "Materials and Method" and "Results" of 113 articles published in JSKUMS with that of 269 articles published in other medical journals of Iran within 2010-2012 through random sampling using a validated questionnaire. The data were analyzed by SPSS software using Chi square, ANOVA, and t test. Results: The percentage of original, cross-sectional, clinical trial, and experimental studies published in JSKUMS in 2011-2012 was respectively 93, 48, 20, and 17. The mean number of authors of the articles was 4.9 ± 3 and the most common errors in JSKUMS and other medical journals of Iran were failure to mention method of sampling (29 and 42 respectively), sample size (7 and 9 respectively), the software used (39 and 10 respectively), methods of randomization and blinding (72 and 27 respectively), letter of consent and ethics committee's approval (11 and 4 respectively), failure to provide confidence intervals for descriptive indicators (9 and 14 respectively) and required analytical indicators (7 and 16 respectively), and failure to observe the instructions of drawing tables (30 and 17 respectively) and graphs (35 and 25 respectively). The number of case-control studies and cohorts was significantly higher in other medical journals of Iran compared to JSKUMS. Conclusion: Identifying the common errors in the examined journals provided the context for improving and promoting them quantitatively and qualitatively. Therefore, it seems helpful to inform the authors and consider the most common errors, to empower the reviewers and address the quality and quantity of workshops on research methodology and scientific writing, and to provide opportunities for publishing guidelines for research and writing research papers

Quantum gravitational optics: the induced phase

The geometrical approximation of the extended Maxwell equation in curved spacetime incorporating interactions induced by the vacuum polarization effects is considered. Taking into account these QED interactions and employing the analogy between eikonal equation in geometrical optics and Hamilton-Jacobi equation for the particle motion, we study the phase structure of the modified theory. There is a complicated, local induced phase which is believed to be responsible for the modification of the classical picture of light ray. The main features of QGO could be obtained through the study of this induced phase. We discuss initial principles in conventional and modified geometrical optics and compare the results.Comment: 10 pages, REVTex forma

Dimension Reduction via Colour Refinement

Colour refinement is a basic algorithmic routine for graph isomorphism testing, appearing as a subroutine in almost all practical isomorphism solvers. It partitions the vertices of a graph into "colour classes" in such a way that all vertices in the same colour class have the same number of neighbours in every colour class. Tinhofer (Disc. App. Math., 1991), Ramana, Scheinerman, and Ullman (Disc. Math., 1994) and Godsil (Lin. Alg. and its App., 1997) established a tight correspondence between colour refinement and fractional isomorphisms of graphs, which are solutions to the LP relaxation of a natural ILP formulation of graph isomorphism. We introduce a version of colour refinement for matrices and extend existing quasilinear algorithms for computing the colour classes. Then we generalise the correspondence between colour refinement and fractional automorphisms and develop a theory of fractional automorphisms and isomorphisms of matrices. We apply our results to reduce the dimensions of systems of linear equations and linear programs. Specifically, we show that any given LP L can efficiently be transformed into a (potentially) smaller LP L' whose number of variables and constraints is the number of colour classes of the colour refinement algorithm, applied to a matrix associated with the LP. The transformation is such that we can easily (by a linear mapping) map both feasible and optimal solutions back and forth between the two LPs. We demonstrate empirically that colour refinement can indeed greatly reduce the cost of solving linear programs