Single polymer gating of channels under a solvent gradient

We study the effect of a gradient of solvent quality on the coil-globule transition for a polymer in a narrow pore. A simple self-attracting self-avoiding walk model of a polymer in solution shows that the variation in the strength of interaction across the pore leads the system to go from one regime (good solvent) to the other (poor solvent) across the channel. This may be thought analogous to thermophoresis, where the polymer goes from the hot region to the cold region under the temperature gradient. The behavior of short chains is studied using exact enumeration whilst the behavior of long chains is studied using transfer matrix techniques. The distribution of the monomer density across the layer suggests that a gate-like effect can be created, with potential applications as a sensor.Comment: 5 Pages, 7 Figures, Accepted in Phys. Rev. E (2013

Low Mass Gluino within the Sparticle Landscape, Implications for Dark Matter, and Early Discovery Prospects at LHC-7

We analyze supergravity models that predict a low mass gluino within the landscape of sparticle mass hierarchies. The analysis includes a broad class of models that arise in minimal and in non-minimal supergravity unified frameworks and in extended models with additional $U(1)^n_X$ hidden sector gauge symmetries. Gluino masses in the range $(350-700)$ GeV are investigated. Masses in this range are promising for early discovery at the LHC at $\sqrt s =7$ TeV (LHC-7). The models exhibit a wide dispersion in the gaugino-Higgsino eigencontent of their LSPs and in their associated sparticle mass spectra. A signature analysis is carried out and the prominent discovery channels for the models are identified with most models needing only $\sim 1 \rm fb^{-1}$ for discovery at LHC-7. In addition, significant variations in the discovery capability of the low mass gluino models are observed for models in which the gluino masses are of comparable size due to the mass splittings in different models and the relative position of the light gluino within the various sparticle mass hierarchies. The models are consistent with the current stringent bounds from the Fermi-LAT, CDMS-II, XENON100, and EDELWEISS-2 experiments. A subclass of these models, which include a mixed-wino LSP and a Higgsino LSP, are also shown to accommodate the positron excess seen in the PAMELA satellite experiment.Comment: 37 pages, 8 figures, Published in PR

Suppression of Higgsino mediated proton decay by cancellations in GUTs and strings

A mechanism for the enhancement for proton lifetime in supersymmetric/supergravity (SUSY/SUGRA) grand unified theories (GUTs) and in string theory models is discussed where Higgsino mediated proton decay arising from color triplets (anti-triplets) with charges $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ is suppressed by an internal cancellation due to contributions from different sources. We exhibit the mechanism for an SU(5) model with $45_H+\bar{45}_H$ Higgs multiplets in addition to the usual Higgs structure of the minimal model. This model contains both $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ Higgs color triplets (anti-triplets) and simple constraints allow for a complete suppression of Higgsino mediated proton decay. Suppression of proton decay in an SU(5) model with Planck scale contributions is also considered. The suppression mechanism is then exhibited for an SO(10) model with a unified Higgs structure involving $144_H+\bar{144}_H$ representations.The SU(5) decomposition of $144_H+\bar{144}_H$ contains $5_H+\bar 5_H$ and $45_H+\bar{45}_H$ and the cancellation mechanism arises among these contributions which mirrror the SU(5) case. The cancellation mechanism appears to be more generally valid for a larger class of unification models. Specifically the cancellation mechanism may play a role in string model constructions to suppress proton decay from dimension five operators. The mechanism allows for the suppression of proton decay consistent with current data allowing for the possibility that proton decay may be visible in the next round of nucleon stability experiment.Comment: 26 pages, no figures. Revtex 4. To appear in Physical Review

Extra-weakly Interacting Dark Matter

We investigate a new type of dark matter with couplings to ordinary matter naturally suppressed by at least one order of magnitude compared to weak interactions. Despite the extra-weak interactions massive particles of this type (XWIMPs) can satisfy the WMAP relic density constraints due to coannihilation if their masses are close to that of the lightest state of the MSSM. The region in the parameter space of a suitably extended mSUGRA model consistent with the WMAP3 constraints on XWIMPs is determined. Plots for sparticles masses are given which can be subject to test at the LHC. We also discuss the sensitivity of the analysis to the top mass. As an example for an explicit model we show that such a form of dark matter can arise in certain $Z'$ extensions of the MSSM. Specifically we consider an abelian extension with spontaneous gauge symmetry breaking via Fayet-Iliopoulos D-terms in the hidden sector. The LSP of the full model arises from the extra $U(1)_X$ sector with extra-weak couplings to Standard Model particles due to experimental constraints. With R-parity conservation the new XWIMP is a candidate for cold dark matter. In a certain limit the model reduces to the \st extension of the MSSM without a Higgs mechanism, and wider ranges of models with similar characteristics are easy to construct

AFLOW-QHA3P: Robust and automated method to compute thermodynamic properties of solids

Accelerating the calculations of finite-temperature thermodynamic properties is a major challenge for rational materials design. Reliable methods can be quite expensive, limiting their applicability in autonomous high-throughput workflows. Here, the three-phonon quasiharmonic approximation (QHA) method is introduced, requiring only three phonon calculations to obtain a thorough characterization of the material. Leveraging a Taylor expansion of the phonon frequencies around the equilibrium volume, the method efficiently resolves the volumetric thermal expansion coefficient, specific heat at constant pressure, the enthalpy, and bulk modulus. Results from the standard QHA and experiments corroborate the procedure, and additional comparisons are made with the recently developed self-consistent QHA. The three approaches—three-phonon, standard, and self-consistent QHAs—are all included within the open-source ab initio framework aflow, allowing the automated determination of properties with various implementations within the same framework

The mediating role of perceived fairness in consumers’ response to post-purchase ‘out of stock’ in an online grocery context

This study investigates consumer response to a retailer’s substitution policy when facing post-purchase ‘out of stock’ (OOS) in an online grocery shopping context. Substitution policies (timeliness of OOS notification; and substituted product) can have detrimental effects on consumers’ satisfaction with the retailer and behaviour response (whether to accept or reject the substitution). As post-purchased OOS indicates a failure of service, the study focuses its investigation on the mediating effects of perceived fairness (PF) of retailers’ substitution policies on consumers’ response. It is predicted that procedural fairness will have a stronger effect on mitigating consumers’ negative OOS experience than distributive (outcome) fairness. The research will be conducted using three online scenario based experiments