On the consistency of the Horava Theory

With the goal of giving evidence for the theoretical consistency of the Horava Theory, we perform a Hamiltonian analysis on a classical model suitable for analyzing its effective dynamics at large distances. The model is the lowest-order truncation of the Horava Theory with the detailed-balance condition. We consider the pure gravitational theory without matter sources. The model has the same potential term of general relativity, but the kinetic term is modified by the inclusion of an arbitrary coupling constant lambda. Since this constant breaks the general covariance under space-time diffeomorphisms, it is believed that arbitrary values of lambda deviate the model from general relativity. We show that this model is not a deviation at all, instead it is completely equivalent to general relativity in a particular partial gauge fixing for it. In doing this, we clarify the role of a second-class constraint of the model.Comment: The wording has been revised in general, specially in abstract, introduction and conclusions. No changes in results. Version published in IJMP

Effect of debris size on the tribological performance of thermally sprayed coatings

This research aims to assess the effect of the debris particle size on the tribological performance and lubrication regime parameters of a Ni-based alloy coating. This is a key industrial problem, and its resolution can contribute to better machine endurance and proper maintenance. The debris particles are simulated by hard Al2O3 particles of size ranging from nanometers to 45 μm and dispersed in an oil lubricant. The coating studied is NiCrBSi deposited by flame spraying technique followed by the Surface Flame Melting (SFM) process. The counterpart disk sample was fabricated from quenched and tempered F-5220 steel (in line with A681(O1) ASTM). This pair was tested under linear sliding contact. Our results show that the addition of alumina particles contributes to a significant increase in wear, particularly for the largest particles (micrometric size). In the case of micrometric particles, it is possible to observe the formation of higher surface roughness, numerous microgrooves, and plastic flow of NiCrBSi coating perpendicular to the sliding direction, resulting in higher loss of volume. It was found that the actual surface roughness (obtained as a function of the debris particle size) allows better identification and prediction of the lubrication regime for wear processes instead of the traditional approach that uses the initial surface roughness as a parameter

Antimagnets: Controlling magnetic fields with superconductor-metamaterial hybrids

Magnetism is very important in science and technology, from magnetic recording to energy generation to trapping cold atoms. Physicists have managed to master magnetism - to create and manipulate magnetic fields- almost at will. Surprisingly, there is at least one property which until now has been elusive: how to 'switch off' the magnetic interaction of a magnetic material with existing magnetic fields without modifying them. Here we introduce the antimagnet, a design to conceal the magnetic response of a given volume from its exterior, without altering the external magnetic fields, somehow analogous to the recent theoretical proposals for cloaking electromagnetic waves with metamaterials. However, different from these devices requiring extreme material properties, our device is feasible and needs only two kinds of available materials: superconductors and isotropic magnetic materials. Antimagnets may have applications in magnetic-based medical techniques such as MRI or in reducing the magnetic signature of vessels or planes.Comment: 14 pages, 4 figure

Molecular Brightness Determined from a Generalized Form of Mandel’s Q-Parameter

AbstractMandel’s Q-parameter, which is determined from the first two photon count moments, provides an alternative to PCH analysis for determining the brightness of fluorophores. Here, the definition of the Q-parameter is generalized to include correlations between photon counts that are separated by a time τ. We develop and experimentally verify a theory that takes the effects of dead time, afterpulsing, and the finite sampling time on the generalized parameter Q(τ) into account. Q(0), which corresponds to the original Q-parameter, is severely affected by dead time and afterpulsing. Q(τ) for τ>0, on the other hand, is quite robust with respect to nonideal detector effects. Thus, analysis of Q(τ) provides a robust method for determining the brightness of fluorophores. We extend the theory to a mixture of species, which is characterized by an apparent brightness. The brightness of EGFP in CV-1 cells is measured as a function of protein concentration to demonstrate the feasibility of Q(τ) analysis in cells. In addition, we monitor protein association of the ligand-binding domain of retinoid X receptor in the presence and absence of 9-cis-retinoic acid by Q(τ) analysis

A dynamic density functional theory for particles in a flowing solvent

We present a dynamic density functional theory (dDFT) which takes into accou nt the advection of the particles by a flowing solvent. For potential flows we can use the same closure as in the absence of solvent flow. The structure of the resulting advected dDFT suggests that it could be used for non-potential flows as well. We apply this dDFT to Brownian particles (e.g., polymer coils) in a solvent flowing around a spherical obstacle (e.g., a colloid) and compare the results with direct simulations of the underlying Brownian dynamics. Although numerical limitations do not allow for an accurate quantitative check of the advected dDFT both show the same qualitative features. In contrast to previous works which neglected the deformation of the flow by the obstacle, we find that the bow-wave in the density distribution of particles in front of the obstacle as well as the wake behind it are reduced dramatically. As a consequence the friction force exerted by the (polymer) particles on the colloid can be reduced drastically.Comment: 7 pages, 5 figures, 2 tables, submitte

Cerebellum Transcriptome of Mice Bred for High Voluntary Activity Offers Insights into Locomotor Control and Reward-Dependent Behaviors.

The role of the cerebellum in motivation and addictive behaviors is less understood than that in control and coordination of movements. High running can be a self-rewarding behavior exhibiting addictive properties. Changes in the cerebellum transcriptional networks of mice from a line selectively bred for High voluntary running (H) were profiled relative to an unselected Control (C) line. The environmental modulation of these changes was assessed both in activity environments corresponding to 7 days of Free (F) access to running wheel and to Blocked (B) access on day 7. Overall, 457 genes exhibited a significant (FDR-adjusted P-value < 0.05) genotype-by-environment interaction effect, indicating that activity genotype differences in gene expression depend on environmental access to running. Among these genes, network analysis highlighted 6 genes (Nrgn, Drd2, Rxrg, Gda, Adora2a, and Rab40b) connected by their products that displayed opposite expression patterns in the activity genotype contrast within the B and F environments. The comparison of network expression topologies suggests that selection for high voluntary running is linked to a predominant dysregulation of hub genes in the F environment that enables running whereas a dysregulation of ancillary genes is favored in the B environment that blocks running. Genes associated with locomotor regulation, signaling pathways, reward-processing, goal-focused, and reward-dependent behaviors exhibited significant genotype-by-environment interaction (e.g. Pak6, Adora2a, Drd2, and Arhgap8). Neuropeptide genes including Adcyap1, Cck, Sst, Vgf, Npy, Nts, Penk, and Tac2 and related receptor genes also exhibited significant genotype-by-environment interaction. The majority of the 183 differentially expressed genes between activity genotypes (e.g. Drd1) were under-expressed in C relative to H genotypes and were also under-expressed in B relative to F environments. Our findings indicate that the high voluntary running mouse line studied is a helpful model for understanding the molecular mechanisms in the cerebellum that influence locomotor control and reward-dependent behaviors