Variation of the speed of light with temperature of the expanding universe

From an extended relativistic dynamics for a particle moving in a cosmic background field with temperature T, we aim to obtain the speed of light with an explicit dependence on the background temperature of the universe. Although finding the speed of light in the early universe much larger than its current value, our approach does not violate the postulate of special relativity. Moreover, it is shown that the high value of the speed of light in the early universe was drastically decreased before the beginning of the inflationary period. So we are led to conclude that the theory of varying speed of light should be questioned as a possible solution of the horizon problem.Comment: 3 pages and 1 figure; Phys. Rev. D86, 027703 (2012

The critical dimension for a 4th order problem with singular nonlinearity

We study the regularity of the extremal solution of the semilinear biharmonic equation \bi u=\f{\lambda}{(1-u)^2}, which models a simple Micro-Electromechanical System (MEMS) device on a ball B\subset\IR^N, under Dirichlet boundary conditions $u=\partial_\nu u=0$ on $\partial B$. We complete here the results of F.H. Lin and Y.S. Yang \cite{LY} regarding the identification of a "pull-in voltage" \la^*>0 such that a stable classical solution u_\la with 0 exists for \la\in (0,\la^*), while there is none of any kind when \la>\la^*. Our main result asserts that the extremal solution $u_{\lambda^*}$ is regular $(\sup_B u_{\lambda^*} <1)$ provided $N \le 8$ while $u_{\lambda^*}$ is singular ($\sup_B u_{\lambda^*} =1$) for $N \ge 9$, in which case $1-C_0|x|^{4/3}\leq u_{\lambda^*} (x) \leq 1-|x|^{4/3}$ on the unit ball, where $C_0:= (\frac{\lambda^*}{\overline{\lambda}})^{1/3}$ and $\bar{\lambda}:= {8/9} (N-{2/3}) (N- {8/3})$.Comment: 19 pages. This paper completes and replaces a paper (with a similar title) which appeared in arXiv:0810.5380. Updated versions --if any-- of this author's papers can be downloaded at this http://www.birs.ca/~nassif

Doubly Special Relativity with a minimum speed and the Uncertainty Principle

The present work aims to search for an implementation of a new symmetry in the space-time by introducing the idea of an invariant minimum speed scale ($V$). Such a lowest limit $V$, being unattainable by the particles, represents a fundamental and preferred reference frame connected to a universal background field (a vacuum energy) that breaks Lorentz symmetry. So there emerges a new principle of symmetry in the space-time at the subatomic level for very low energies close to the background frame ($v\approx V$), providing a fundamental understanding for the uncertainty principle, i.e., the uncertainty relations should emerge from the space-time with an invariant minimum speed.Comment: 10 pages, 8 figures, Correlated paper in: http://www.worldscientific.com/worldscinet/ijmpd?journalTabs=read. arXiv admin note: substantial text overlap with arXiv:physics/0702095, arXiv:0705.4315, arXiv:0709.1727, arXiv:0805.120

Kinetics in one-dimensional lattice gas and Ising models from time-dependent density functional theory

Time-dependent density functional theory, proposed recently in the context of atomic diffusion and non-equilibrium processes in solids, is tested against Monte Carlo simulation. In order to assess the basic approximation of that theory, the representation of non-equilibrium states by a local equilibrium distribution function, we focus on one-dimensional lattice models, where all equilibrium properties can be worked exactly from the known free energy as a functional of the density. This functional determines the thermodynamic driving forces away from equilibrium. In our studies of the interfacial kinetics of atomic hopping and spin relaxation, we find excellent agreement with simulations, suggesting that the method is useful also for treating more complex problems.Comment: 8 pages, 5 figures, submitted to Phys. Rev.

EXAFS study of lead-free relaxor ferroelectric BaTi(1-x)Zr(x)O3 at the Zr K-edge

Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on perovskite relaxor ferroelectrics BaTi(1-x)Zr(x)O3 (BTZ) (x = 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to 4.5 A around the Zr atoms is obtained, revealing that the local structure differs notably from the average Pm-3m cubic structure deduced from X-ray diffraction. In particular, our results show that the distance between Zr atoms and their first oxygen neighbors is independent of the Zr substitution rate x and equal to that measured in BaZrO3, while the X-ray cubic cell parameter increases linearly with x. Furthermore, we show that the Zr atoms tend to segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is linked to random elastic fields generated by this particular chemical arrangement, rather than to random electric fields as is the case in most relaxors.Comment: 13 pages, 12 figures, 4 tables. Submitted to Phys. Rev.

Can we rely on smartphone applications?

Smartphones are becoming necessary tools in the daily lives of millions of users who rely on these devices and their applications. There are thousands of applications for smartphone devices such as the iPhone, Blackberry, and Android, thus their reliability has become paramount for their users. This work aims to answer two related questions: (1) Can we assess the reliability of mobile applications by using the traditional reliability models? (2) Can we model adequately the failure data collected from many users? Firstly, it has been proved that the three most used software reliability models have fallen short of the mark when applied to smartphone applications; their failures were traced back to specific features of mobile applications. Secondly, it has been demonstrated that the Weibull and Gamma distribution models can adequately fit the observed failure data, thus providing better means to predict the reliability of smartphone applications

Preliminary characterization of a Moroccan honey with a predominance of Bupleurum spinosum pollen

Honey with Bupleurum spinosum (zandaz) as a main pollen source has not been the subject of previous detailed study. Therefore, twelve Moroccan samples of this honey were subjected to melissopalynological, physicochemical and microbiological quality characterization, as well as antioxidant activity assessment. From a quality point of view, almost all samples were within the limits established by Codex Alimentarius, and/or the European legislation. All samples presented predominance of B. spinosum pollen (more than 48%). Relatively high levels of trehalose (1.3-4.0 g/100 g) and melezitose (1.5-2.8 g/100 g) were detected. Those sugars, not common in monofloral honeys, could be used as an important factor to discriminate zandaz honey. Flavonoid content correlated positively with the honey color, melanoidin and polyphenol content, and negatively with the IC50 values of scavenging ABTS (2,2' - azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) free radicals, while proline amount correlated negatively with IC50 values of nitric oxide scavenging activity and chelating power. This correlation supports the use of anti-oxidant activities as important variables for PCA (principal component analysis). Both components explained 70% from the given data, and showed certain homogeneity upon analyzed samples independent of the region, suggesting the importance of B. spinosum nectar in the resulting honey characteristics.Fundacao para a Ciencia e Tecnologia for Research Center [UID/BIM/04773/2013 CBMR 1334, UID/AGR/00239/2013, UID/BIA/04050/2013 (POCI-01-0145-FEDER-007569)]; ERDF through the COMPETE - Programa Operacional Competitividade e Internacionalizacao (POCI