Mapping Monte Carlo to Langevin dynamics: A Fokker-Planck approach

We propose a general method of using the Fokker-Planck equation (FPE) to link the Monte-Carlo (MC) and the Langevin micromagnetic schemes. We derive the drift and disusion FPE terms corresponding to the MC method and show that it is analytically equivalent to the stochastic Landau-Lifshitz-Gilbert (LLG) equation of Langevin-based micromagnetics. Subsequent results such as the time quantification factor for the Metropolis MC method can be rigorously derived from this mapping equivalence. The validity of the mapping is shown by the close numerical convergence between the MC method and the LLG equation for the case of a single magnetic particle as well as interacting arrays of particles. We also found that our Metropolis MC is accurate for a large range of damping factors $\alpha$, unlike previous time-quantified MC methods which break down at low $\alpha$, where precessional motion dominates.Comment: 4 pages, 4 figures. Accepted for publication in Phys. Rev. Let

Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments

We study two continuous variable systems (or two harmonic oscillators) and investigate their entanglement evolution under the influence of non-Markovian thermal environments. The continuous variable systems could be two modes of electromagnetic fields or two nanomechanical oscillators in the quantum domain. We use quantum open system method to derive the non-Markovian master equations of the reduced density matrix for two different but related models of the continuous variable systems. The two models both consist of two interacting harmonic oscillators. In model A, each of the two oscillators is coupled to its own independent thermal reservoir, while in model B the two oscillators are coupled to a common reservoir. To quantify the degrees of entanglement for the bipartite continuous variable systems in Gaussian states, logarithmic negativity is used. We find that the dynamics of the quantum entanglement is sensitive to the initial states, the oscillator-oscillator interaction, the oscillator-environment interaction and the coupling to a common bath or to different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.

Patchy Amphiphilic Dendrimers Bind Adenovirus and Control Its Host Interactions and in Vivo Distribution

The surface of proteins is heterogeneous with sophisticated but precise hydrophobic and hydrophilic patches, which is essential for their diverse biological functions. To emulate such distinct surface patterns on macromolecules, we used rigid spherical synthetic dendrimers (polyphenylene dendrimers) to provide controlled amphiphilic surface patches with molecular precision. We identified an,. I optimal spatial arrangement of these patches on certain dendrimers that enabled their interaction with human adenovirus 5 (Ads). Patchy dendrimers bound to the surface of Ads formed a synthetic polymer corona that greatly altered various host interactions of Ads as well as in vivo distribution. The dendrimer corona (1) improved the ability of Ad5-derived gene transfer vectors to transduce cells deficient for the primary Ad5 cell membrane receptor and (2) modulated the binding of Ads to blood coagulation factor X, one of the most critical virus host interactions in the bloodstream. It significantly enhanced the transduction efficiency of Ad5 while also protecting it from neutralization by natural antibodies and the complement system in human whole blood. Ads with a synthetic dendrimer corona revealed profoundly altered in vivo distribution, improved transduction of heart, and dampened vector sequestration by liver and spleen. We propose the design of bioactive polymers that bind protein surfaces solely based on their amphiphilic surface patches and protect against a naturally occurring protein corona, which is highly attractive to improve Ad5-based in vivo gene therapy applications

Angular position of nodes in the superconducting gap of YBCO

The thermal conductivity of a YBCO single crystal has been studied as a function of the relative orientation of the crystal axes and a magnetic field rotating in the Cu-O planes. Measurements were carried out at several temperatures below T_c and at a fixed field of 30 kOe. A four-fold symmetry characteristic of a superconducting gap with nodes at odd multiples of 45 degrees in k-space was resolved. Experiments were performed to exclude a possible macroscopic origin for such a four-fold symmetry such as sample shape or anisotropic pinning. Our results impose an upper limit of 10% on the weight of the s-wave component of the essentially d-wave superconducting order parameter of YBCO.Comment: 10 pages, 4 figure

Submillimeter emission from the hot molecular jet HH 211

We observed the HH 211 jet in the submillimeter continuum and the CO(3-2) and SiO(8-7) transitions with the Submillimeter Array. The continuum source detected at the center of the outflow shows an elongated morphology, perpendicular to the direction of the outflow axis. The high-velocity emission of both molecules shows a knotty and highly collimated structure. The SiO(8-7) emission at the base of the outflow, close to the driving source, spans a wide range of velocities, from -20 up to 40 km s^{-1}. This suggests that a wide-angle wind may be the driving mechanism of the HH 211 outflow. For distances greater than 5" (1500 AU) from the driving source, emission from both transitions follows a Hubble-law behavior, with SiO(8-7) reaching higher velocities than CO(3-2), and being located upstream of the CO(3-2) knots. This indicates that the SiO(8-7) emission is likely tracing entrained gas very close to the primary jet, while the CO(3-2) is tracing less dense entrained gas. From the SiO(5-4) data of Hirano et al. we find that the SiO(8-7)/SiO(5-4) brightness temperature ratio along the jet decreases for knots far from the driving source. This is consistent with the density decreasing along the jet, from (3-10)x10^6 cm^{-3} at 500 AU to (0.8-4)x10^6 cm^{-3} at 5000 AU from the driving source.Comment: 3 pages, 3 figures. Accepted by Astrophysical Journal Letter

Fenton-Like Oxidation of 4−Chlorophenol: Homogeneous or Heterogeneous?

Heterogeneous Fenton-like catalysts have received considerable research attention because they could potentially be attractive for oxidative removal of organic contaminants from tertiary wastewater. However, process design is still hampered by insufficient understanding of the chemical pathways involved, and especially whether oxidation activity stems from heterogeneous surface chemistry or minute concentrations of dissolved metal ions in the homogeneous phase. Using inductively coupled plasma-optical emission spectroscopy (ICP-OES) in combination with pH monitoring and ultraviolet–visible spectroscopy (UV–vis) we have monitored the degradation of 4-chlorophenol (4-CP) over two Fenton-like heterogeneous systems, namely FeOx supported on TiO2 and CuFe2O4. We show conclusively that these systems proceed predominantly through a homogeneous route via dissolved metal ions from the solid phase catalysts. Control experiments with homogeneous Fe3+ or Cu2+ systems reveal that even minute concentrations (μM/subppm) of dissolved metal ions leached from the solid phases account for the observed 4-CP degradation rates in the heterogeneous systems. ICP-OES revealed that metal leaching was time-dependent and variable because of pH variations associated with changing acid release rates. Buffering solutions at pH 7.4 suppressed metal leaching (and hence 4-CP degradation) in the FeOx/TiO2 system, but not in others. For example, pH buffering did not entirely suppress metal leaching from CuFe2O4, for which 4-CP degradation was retained through small concentrations of Fe and Cu ions in solution. Our results highlight the importance of careful monitoring of metal content in the aqueous phase, certainly with analytical sensitivity below ppm concentrations of the dissolved metals, and also the crucial influence of time-dependent pH variations on the reaction process. Recyclability of catalysts, pH buffering of solutions or monitoring of metal content in the solid phase by less sensitive analytical methods, for example, chemical analysis, gravimetry, X-ray fluorescence, or energy dispersive X-ray analysis in electron microscopes, cannot exclude the homogeneous Fenton route in the presence of solid catalysts

Aspects of Scalar Field Dynamics in Gauss-Bonnet Brane Worlds

The Einstein-Gauss-Bonnet equations projected from the bulk to brane lead to a complicated Friedmann equation which simplifies to $H^2 \sim \rho^q$ in the asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to $q=2$ whereas $q=2/3$ & $q=1$ give rise to high energy Gauss-Bonnet (GB) regime and the standard GR respectively. Amazingly, while evolving from RS regime to high energy GB limit, one passes through a GR like region which has important implications for brane world inflation. For tachyon GB inflation with potentials $V(\phi) \sim \phi^p$ investigated in this paper, the scalar to tensor ratio of perturbations $R$ is maximum around the RS region and is generally suppressed in the high energy regime for the positive values of $p$. The ratio is very low for $p>0$ at all energy scales relative to GB inflation with ordinary scalar field. The models based upon tachyon inflation with polynomial type of potentials with generic positive values of $p$ turn out to be in the $1 \sigma$ observational contour bound at all energy scales varying from GR to high energy GB limit. The spectral index $n_S$ improves for the lower values of $p$ and approaches its scale invariant limit for $p=-2$ in the high energy GB regime. The ratio $R$ also remains small for large negative values of $p$, however, difference arises for models close to scale invariance limit. In this case, the tensor to scale ratio is large in the GB regime whereas it is suppressed in the intermediate region between RS and GB. Within the frame work of patch cosmologies governed by $H^2 \sim \rho^q$, the behavior of ordinary scalar field near cosmological singularity and the nature of scaling solutions are distinguished for the values of $q 1$.Comment: 15 pages, 10 eps figures; appendix on various scales in GB brane world included and references updated; final version to appear in PR

Origin of Life

The evolution of life has been a big enigma despite rapid advancements in the fields of biochemistry, astrobiology, and astrophysics in recent years. The answer to this puzzle has been as mind-boggling as the riddle relating to evolution of Universe itself. Despite the fact that panspermia has gained considerable support as a viable explanation for origin of life on the Earth and elsewhere in the Universe, the issue remains far from a tangible solution. This paper examines the various prevailing hypotheses regarding origin of life like abiogenesis, RNA World, Iron-sulphur World, and panspermia; and concludes that delivery of life-bearing organic molecules by the comets in the early epoch of the Earth alone possibly was not responsible for kick-starting the process of evolution of life on our planet.Comment: 32 pages, 8 figures,invited review article, minor additio

Theory of Transmission through disordered superlattices

We derive a theory for transmission through disordered finite superlattices in which the interface roughness scattering is treated by disorder averaging. This procedure permits efficient calculation of the transmission thr ough samples with large cross-sections. These calculations can be performed utilizing either the Keldysh or the Landauer-B\"uttiker transmission formalisms, both of which yield identical equations. For energies close to the lowest miniband, we demonstrate the accuracy of the computationally efficient Wannier-function approximation. Our calculations indicate that the transmission is strongly affected by interface roughness and that information about scale and size of the imperfections can be obtained from transmission data.Comment: 12 pages, 6 Figures included into the text. Final version with minor changes. Accepted by Physical Review

Epigenetic meta-analysis across three civilian cohorts identifies NRG1 and HGS as blood-based biomarkers for post-traumatic stress disorder

Aim: Trauma exposure is a necessary, but not deterministic, contributor to post-traumatic stress disorder (PTSD). Epigenetic factors may distinguish between trauma-exposed individuals with versus without PTSD. Materials & methods: We conducted a meta-analysis of PTSD epigenome-wide association studies in trauma-exposed cohorts drawn from civilian contexts. Whole blood-derived DNA methylation levels were analyzed in 545 study participants, drawn from the three civilian cohorts participating in the PTSD working group of the Psychiatric Genomics Consortium. Results: Two CpG sites significantly associated with current PTSD in NRG1 (cg23637605) and in HGS (cg19577098). Conclusion: PTSD is associated with differential methylation, measured in blood, within HGS and NRG1 across three civilian cohorts