542,187 research outputs found

    Scalar-Tensor Models of Normal and Phantom Dark Energy

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    We consider the viability of dark energy (DE) models in the framework of the scalar-tensor theory of gravity, including the possibility to have a phantom DE at small redshifts zz as admitted by supernova luminosity-distance data. For small zz, the generic solution for these models is constructed in the form of a power series in zz without any approximation. Necessary constraints for DE to be phantom today and to cross the phantom divide line p=ρp=-\rho at small zz are presented. Considering the Solar System constraints, we find for the post-Newtonian parameters that γPN<1\gamma_{PN}<1 and γPN,01\gamma_{PN,0}\approx 1 for the model to be viable, and βPN,0>1\beta_{PN,0}>1 (but very close to 1) if the model has a significantly phantom DE today. However, prospects to establish the phantom behaviour of DE are much better with cosmological data than with Solar System experiments. Earlier obtained results for a Λ\Lambda-dominated universe with the vanishing scalar field potential are extended to a more general DE equation of state confirming that the cosmological evolution of these models rule them out. Models of currently fantom DE which are viable for small zz can be easily constructed with a constant potential; however, they generically become singular at some higher zz. With a growing potential, viable models exist up to an arbitrary high redshift.Comment: 30 pages, 4 figures; Matches the published version containing an expanded discussion of various point

    A molecular-dynamics approach for studying the non-equilibrium behavior of x-ray-heated solid-density matter

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    When matter is exposed to a high-intensity x-ray free-electron-laser pulse, the x rays excite inner-shell electrons leading to the ionization of the electrons through various atomic processes and creating high-energy-density plasma, i.e., warm or hot dense matter. The resulting system consists of atoms in various electronic configurations, thermalizing on sub-picosecond to picosecond timescales after photoexcitation. We present a simulation study of x-ray-heated solid-density matter. For this we use XMDYN, a Monte-Carlo molecular-dynamics-based code with periodic boundary conditions, which allows one to investigate non-equilibrium dynamics. XMDYN is capable of treating systems containing light and heavy atomic species with full electronic configuration space and 3D spatial inhomogeneity. For the validation of our approach we compare for a model system the electron temperatures and the ion charge-state distribution from XMDYN to results for the thermalized system based on the average-atom model implemented in XATOM, an ab-initio x-ray atomic physics toolkit extended to include a plasma environment. Further, we also compare the average charge evolution of diamond with the predictions of a Boltzmann continuum approach. We demonstrate that XMDYN results are in good quantitative agreement with the above mentioned approaches, suggesting that the current implementation of XMDYN is a viable approach to simulate the dynamics of x-ray-driven non-equilibrium dynamics in solids. In order to illustrate the potential of XMDYN for treating complex systems we present calculations on the triiodo benzene derivative 5-amino-2,4,6-triiodoisophthalic acid (I3C), a compound of relevance of biomolecular imaging, consisting of heavy and light atomic species

    Evolution of matter density perturbations in viable f (R) theories of gravity

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    In the ΛCDM model, the late-time accelerated expansion of the Universe is explained via a dark energy fluid in the form of a cosmological constant. Such a cosmological constant dominates the energy budget of the Universe today, and yet, it is still a poorly understood species because it is not observed yet. A competitive theoretical approach to understand this is via the so-called f (R) extended theories of gravity, which explain the late acceleration epoch of the Universe resorting to a geometrical modification of the field equations. We illustrate how f (R) theories are constructed and how both the analysis of the cosmological expansion and the growth of matter density perturbations in these theories may differ from the standard Einsteinian results. We study the evolution of matter density perturbations in a viable f (R) model (Hu-Sawicki model) and explain why the Hu-Sawicki model is indeed a viable alternative to ΛCDM by discussing the Dynamical System approach as a method used to obtain the cosmological background solutions. A complete comparison of density perturbations in both the ΛCDM model and Hu-Sawicki model is presented

    Identifying tyre models directly from vehicle test data using an extended Kalman filter

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    Individual tyre models are traditionally derived from component tests, with their parameters matched to force and slip measurements. They are imported into vehicle models which should, but do not always properly provide suspension geometry interaction. Recent advances in Global Positioning System (GPS)/inertia vehicle instrumentation now make full state measurement viable in test vehicles, so tyre slip behaviour is directly measurable. This paper uses an extended Kalman filter for system identification, to derive individual load-dependent tyre models directly from these test vehicle state measurements. The resulting model therefore implicitly compensates for suspension geometry and compliance. The paper looks at two variants of the tyre model, and also considers real-time adaptation of the model to road surface friction variations. Test vehicle results are used exclusively, and the results show successful tyre model identification, improved vehicle model state prediction – particularly in lateral velocity reproduction – and an effective real-time solution for road friction estimation

    Preparation and characterization of a coacervate extended-release microparticulate delivery system for Lactobacillus rhamnosus

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    Sk Md Athar Alli Department of Pharmaceutical Technology, Jadavpur University, Kolkata, West Bengal, IndiaBackground: The purpose of this study was to develop a mucoadhesive coacervate microparticulate system to deliver viable Lactobacillus rhamnosus cells into the gut for an extended period of time while maintaining high numbers of viable cells within the formulation throughout its shelf-life and during gastrointestinal transit.Methods: Core coacervate mucoadhesive microparticles of L. rhamnosus were developed using several grades of hypromellose and were subsequently enteric-coated with hypromellose phthalate. Microparticles were evaluated for percent yield, entrapment efficiency, surface morphology, particle size, size distribution, zeta potential, flow properties, in vitro swelling, mucoadhesion properties, in vitro release profile and release kinetics, in vivo probiotic activity, and stability. The values for the kinetic constant and release exponent of model-dependent approaches, the difference factor, similarity factor, and Rescigno indices of model-independent approaches were determined for analyzing in vitro dissolution profiles.Results: Experimental microparticles of formulation batches were of spherical shape with percent yields of 41.24%&amp;ndash;58.18%, entrapment efficiency 45.18%&amp;ndash;64.16%, mean particle size 33.10&amp;ndash;49.62 &amp;micro;m, and zeta potential around -11.5 mV, confirming adequate stability of L. rhamnosus at room temperature. The in vitro L. rhamnosus release profile follows zero-order kinetics and depends on the grade of hypromellose and the L. rhamnosus to hypromellose ratio.Conclusion: Microparticles delivered L. rhamnosus in simulated intestinal conditions for an extended period, following zero-order kinetics, and exhibited appreciable mucoadhesion in simulated intestinal conditions.Keywords: Lactobacillus rhamnosus, mucoadhesive, microparticles, extended-release, intestin
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