Comparison of Dissipative Particle Dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems

In this work we compare and characterize the behavior of Langevin and Dissipative Particle Dynamics (DPD) thermostats in a broad range of non-equilibrium simulations of polymeric systems. Polymer brushes in relative sliding motion, polymeric liquids in Poiseuille and Couette flows, and brush-melt interfaces are used as model systems to analyze the efficiency and limitations of different Langevin and DPD thermostat implementations. Widely used coarse-grained bead-spring models under good and poor solvent conditions are employed to assess the effects of the thermostats. We considered equilibrium, transient, and steady state examples for testing the ability of the thermostats to maintain constant temperature and to reproduce the underlying physical phenomena in non-equilibrium situations. The common practice of switching-off the Langevin thermostat in the flow direction is also critically revisited. The efficiency of different weight functions for the DPD thermostat is quantitatively analyzed as a function of the solvent quality and the non-equilibrium situation.Comment: 12 pages, introduction improved, references added, to appear in Phys. Rev.

Topological Hall effect and Berry phase in magnetic nanostructures

We discuss the anomalous Hall effect in a two-dimensional electron gas subject to a spatially varying magnetization. This topological Hall effect (THE) does not require any spin-orbit coupling, and arises solely from Berry phase acquired by an electron moving in a smoothly varying magnetization. We propose an experiment with a structure containing 2D electrons or holes of diluted magnetic semiconductor subject to the stray field of a lattice of magnetic nanocylinders. The striking behavior predicted for such a system (of which all relevant parameters are well known) allows to observe unambiguously the THE and to distinguish it from other mechanisms.Comment: 5 pages with 4 figure

Static and dynamic properties of the interface between a polymer brush and a melt of identical chains

Molecular dynamics simulations of a short-chain polymer melt between two brush-covered surfaces under shear have been performed. The end-grafted polymers which constitute the brush have the same chemical properties as the free chains in the melt and provide a soft deformable substrate. Polymer chains are described by a coarse-grained bead-spring model with Lennard-Jones interactions between the beads and a FENE potential between nearest neighbors along the backbone of the chains. The grafting density of the brush layer offers a way of controlling the behavior of the surface without altering the molecular interactions. We perform equilibrium and non-equilibrium Molecular Dynamics simulations at constant temperature and volume using the Dissipative Particle Dynamics thermostat. The equilibrium density profiles and the behavior under shear are studied as well as the interdigitation of the melt into the brush, the orientation on different length scales (bond vectors, radius of gyration, and end-to-end vector) of free and grafted chains, and velocity profiles. The viscosity and slippage at the interface are calculated as functions of grafting density and shear velocity.Comment: 12 pages, submitted to J Chem Phy

Anomalous Hall Effect due to the spin chirality in the Kagom\'{e} lattice

We consider a model for a two dimensional electron gas moving on a kagom\'{e} lattice and locally coupled to a chiral magnetic texture. We show that the transverse conductivity $\sigma\_{xy}$ does not vanish even if spin-orbit coupling is not present and it may exhibit unusual behavior. Model parameters are the chirality, the number of conduction electrons and the amplitude of the local coupling. Upon varying these parameters, a topological transition characterized by change of the band Chern numbers occur. As a consequence, $\sigma\_{xy}$ can be quantized, proportional to the chirality or have a non monotonic behavior upon varying these parameters.Comment: 8 pages, 7 figure

Direct calorimetric measurements of isothermal entropy change on single crystal W-type hexaferrites at the spin reorientation transition

We report on the magnetic field induced isothermal entropy change, \Delta s(Ha, T), of W-type ferrite with CoZn substitution. Entropy measurements are performed by direct calorimetry. Single crystals of the composition BaCo$_0.62$Zn$_1.38$Fe$_16$O$_27$, prepared by the flux method, are measured at different fixed temperatures under an applied field perpendicular and parallel to the c axis. At 296 K one deduces a value of K$_1$ = 8.7 \times 10^{4} J m$^-3$ for the first anisotropy constant, which is in good agreement with the literature. The spin reorientation transition temperature is estimated to take place between 200 and 220 K

Electrical transport properties of bulk Nic_{c}Fe1−c_{1-c} alloys and related spin-valve systems

Within the Kubo-Greenwood formalism we use the fully relativistic, spin-polarized, screened Korringa-Kohn-Rostoker method together with the coherent-potential approximation for layered systems to calculate the resistivity for the permalloy series Ni$_{c}$Fe$_{1-c}$. We are able to reproduce the variation of the resistivity across the entire series; notably the discontinuous behavior in the vicinity of the structural phase transition from bcc to fcc. The absolute values for the resistivity are within a factor of two of the experimental data. Also the giant magnetoresistance of a series of permalloy-based spin-valve structures is estimated; we are able to reproduce the trends and values observed on prototypical spin-valve structures.Comment: 6 pages, ReVTeX + 4 figures (Encapsulated Postscript), submitted to PR

Metallic properties of magnesium point contacts

We present an experimental and theoretical study of the conductance and stability of Mg atomic-sized contacts. Using Mechanically Controllable Break Junctions (MCBJ), we have observed that the room temperature conductance histograms exhibit a series of peaks, which suggests the existence of a shell effect. Its periodicity, however, cannot be simply explained in terms of either an atomic or electronic shell effect. We have also found that at room temperature, contacts of the diameter of a single atom are absent. A possible interpretation could be the occurrence of a metal-to-insulator transition as the contact radius is reduced, in analogy with what it is known in the context of Mg clusters. However, our first principle calculations show that while an infinite linear chain can be insulating, Mg wires with larger atomic coordinations, as in realistic atomic contacts, are alwaysmetallic. Finally, at liquid helium temperature our measurements show that the conductance histogram is dominated by a pronounced peak at the quantum of conductance. This is in good agreement with our calculations based on a tight-binding model that indicate that the conductance of a Mg one-atom contact is dominated by a single fully open conduction channel.Comment: 14 pages, 5 figure

eHealth in the support of people with mild intellectual disability in daily life:A systematic review

Background:  eHealth has recently made rapid progress in care, support and treatment. However, studies on the use of eHealth to support people with a mild intellectual disability in daily life are limited. A systematic review was conducted to provide an overview of this use of eHealth.  Methods:  Seven databases were searched for relevant studies and assessed according to the PRISMA guidelines. Descriptive analyses were deployed using the Matching Person to Technology model to evaluate the key areas contributing to successful eHealth use.  Results:  Most of the 46 studies included were small-scale case studies and focused on using eHealth to acquire daily living skills and vocational skills. In addition, several studies focused on eHealth use for self-support in daily living, and three studies focused on remote professional support.  Conclusions:  eHealth offers opportunities to support people with mild intellectual disability in various different contexts of daily life. Scientific research on this topic is in its early stage, and further high-quality research is needed

Staggered Fermions and Gauge Field Topology

Based on a large number of smearing steps, we classify SU(3) gauge field configurations in different topological sectors. For each sector we compare the exact analytical predictions for the microscopic Dirac operator spectrum of quenched staggered fermions. In all sectors we find perfect agreement with the predictions for the sector of topological charge zero, showing explicitly that the smallest Dirac operator eigenvalues of staggered fermions at presently realistic lattice couplings are insensitive to gauge field topology. On the smeared configurations, $4\nu$ eigenvalues clearly separate out from the rest on configurations of topological charge $\nu$, and move towards zero in agreement with the index theorem.Comment: LaTeX, 10 page

Photometric Constraints on the Redshift of z~10 candidate UDFj-39546284 from deeper WFC3/IR+ACS+IRAC observations over the HUDF

Ultra-deep WFC3/IR observations on the HUDF from the HUDF09 program revealed just one plausible z~10 candidate UDFj-39546284. UDFj-39546284 had all the properties expected of a galaxy at z~10 showing (1) no detection in the deep ACS+WFC3 imaging data blueward of the F160W band, exhibiting (2) a blue spectral slope redward of the break, and showing (3) no prominent detection in deep IRAC observations. The new, similarly deep WFC3/IR HUDF12 F160W observations over the HUDF09/XDF allow us to further assess this candidate. These observations show that this candidate, previously only detected at ~5.9 sigma in a single band, clearly corresponds to a real source. It is detected at ~5.3 sigma in the new H-band data and at ~7.8 sigma in the full 85-orbit H-band stack. Interestingly, the non-detection of the source (<1 sigma) in the new F140W observations suggests a higher redshift. Formally, the best-fit redshift of the source utilizing all the WFC3+ACS (and IRAC+K-band) observations is 11.8+/-0.3. However, we consider the z~12 interpretation somewhat unlikely, since the source would either need to be ~20x more luminous than expected or show very high-EW Ly-alpha emission (which seems improbable given the extensive neutral gas prevalent early in the reionization epoch). Lower-redshift solutions fail if only continuum models are allowed. Plausible lower-redshift solutions require that the H-band flux be dominated by line emission such as Halpha or [OIII] with extreme EWs. The tentative detection of line emission at 1.6 microns in UDFj-39546284 in a companion paper suggests that such emission may have already been found.Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letters, updated to match the version in pres