542,187 research outputs found
Scalar-Tensor Models of Normal and Phantom Dark Energy
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 as admitted by supernova luminosity-distance data. For
small , the generic solution for these models is constructed in the form of
a power series in without any approximation. Necessary constraints for DE
to be phantom today and to cross the phantom divide line at small
are presented. Considering the Solar System constraints, we find for the
post-Newtonian parameters that and for
the model to be viable, and (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 -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 can
be easily constructed with a constant potential; however, they generically
become singular at some higher . 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
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
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
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
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%–58.18%, entrapment efficiency 45.18%–64.16%, mean particle size 33.10–49.62 µm, 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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