Viscoelastic Phase Separation in Shear Flow

We numerically investigate viscoelastic phase separation in polymer solutions under shear using a time-dependent Ginzburg-Landau model. The gross variables in our model are the polymer volume fraction and a conformation tensor. The latter represents chain deformations and relaxes slowly on the rheological time giving rise to a large viscoelastic stress. The polymer and the solvent obey two-fluid dynamics in which the viscoelastic stress acts asymmetrically on the polymer and, as a result, the stress and the diffusion are dynamically coupled. Below the coexistence curve, interfaces appear with increasing the quench depth and the solvent regions act as a lubricant. In these cases the composition heterogeneity causes more enhanced viscoelastic heterogeneity and the macroscopic stress is decreased at fixed applied shear rate. We find steady two-phase states composed of the polymer-rich and solvent-rich regions, where the characteristic domain size is inversely proportional to the average shear stress for various shear rates. The deviatoric stress components exhibit large temporal fluctuations. The normal stress difference can take negative values transiently at weak shear.Comment: 16pages, 16figures, to be published in Phys.Rev.

Phenomenological constraints on Lemaitre-Tolman-Bondi cosmological inhomogeneities from solar system dynamics

We, first, analytically work out the long-term, i.e. averaged over one orbital revolution, perturbations on the orbit of a test particle moving in a local Fermi frame induced therein by the cosmological tidal effects of the inhomogeneous Lemaitre-Tolman-Bondi (LTB) model. The LTB solution has recently attracted attention, among other things, as a possible explanation of the observed cosmic acceleration without resorting to dark energy. Then, we phenomenologically constrain both the parameters K_1 = -\ddot R/R and K_2 = -\ddot R^'/R^' of the LTB metric in the Fermi frame by using different kinds of solar system data. The corrections $\Delta\dot\varpi$ to the standard Newtonian/Einsteinian precessions of the perihelia of the inner planets recently estimated with the EPM ephemerides, compared to our predictions for them, yield K_1 = (4+8) 10^-26 s^-2, K_2 = (3+7) 10^-23 s^-2. The residuals of the Cassini-based Earth-Saturn range, compared with the numerically integrated LTB range signature, allow to obtain K_1/2 = 10^-27 s^-2. The LTB-induced distortions of the orbit of a typical object of the Oort cloud with respect to the commonly accepted Newtonian picture, based on the observations of the comet showers from that remote region of the solar system, point towards K_1/2 <= 10^-30-10^-32 s^-2. Such figures have to be compared with those inferred from cosmological data which are of the order of K1 \approx K2 = -4 10^-36 s^-2.Comment: LaTex2e, 18 pages, 3 tables, 3 figures. Minor changes. Reference added. Accepted by Journal of Cosmology and Astroparticle Physics (JCAP

A solution for galactic disks with Yukawian gravitational potential

We present a new solution for the rotation curves of galactic disks with gravitational potential of the Yukawa type. We follow the technique employed by Toomre in 1963 in the study of galactic disks in the Newtonian theory. This new solution allows an easy comparison between the Newtonian solution and the Yukawian one. Therefore, constraints on the parameters of theories of gravitation can be imposed, which in the weak field limit reduce to Yukawian potentials. We then apply our formulae to the study of rotation curves for a zero-thickness exponential disk and compare it with the Newtonian case studied by Freeman in 1970. As an application of the mathematical tool developed here, we show that in any theory of gravity with a massive graviton (this means a gravitational potential of the Yukawa type), a strong limit can be imposed on the mass (m_g) of this particle. For example, in order to obtain a galactic disk with a scale length of b ~ 10 kpc, we should have a massive graviton of m_g << 10^{-59} g. This result is much more restrictive than those inferred from solar system observations.Comment: 7 pages; 1 eps figure; to appear in General Relativity and Gravitatio

Analysis of Ductile Bursting in Pressure Vessels of Texture-Hardening and Filament-Wrapped Materials

Analyses are presented for predicting the strength governed by the plastic tensile instability (PTI) phenomenon in thin-walled cylindrical and spherical pressure vessels constructed of texture- hardening alloys and with or without over-wrapped filaments. These analyses are important in predicting ductile bursting of pressure vessels used in such high-performance applications as high-pressure storage bottles, liquid-propellant tankage, and solid rocket casings. The analyses cover cylindrical pressure vessels subject to any ratio of biaxial stresses. Also means of estimating the effect of finite length is presented. Spherical vessels of texture- hardening material and cylindrical vessels with filaments over wrapped on a texture-hardening metallic substrate are treated as special cases. The analytical results are compared with available experimental results with good success.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Asymmetric Dark Matter and Dark Radiation

Asymmetric Dark Matter (ADM) models invoke a particle-antiparticle asymmetry, similar to the one observed in the Baryon sector, to account for the Dark Matter (DM) abundance. Both asymmetries are usually generated by the same mechanism and generally related, thus predicting DM masses around 5 GeV in order to obtain the correct density. The main challenge for successful models is to ensure efficient annihilation of the thermally produced symmetric component of such a light DM candidate without violating constraints from collider or direct searches. A common way to overcome this involves a light mediator, into which DM can efficiently annihilate and which subsequently decays into Standard Model particles. Here we explore the scenario where the light mediator decays instead into lighter degrees of freedom in the dark sector that act as radiation in the early Universe. While this assumption makes indirect DM searches challenging, it leads to signals of extra radiation at BBN and CMB. Under certain conditions, precise measurements of the number of relativistic species, such as those expected from the Planck satellite, can provide information on the structure of the dark sector. We also discuss the constraints of the interactions between DM and Dark Radiation from their imprint in the matter power spectrum.Comment: 22 pages, 5 figures, to be published in JCAP, minor changes to match version to be publishe

A circular polarimeter for the Cosmic Microwave Background

A primordial degree of circular polarization of the Cosmic Microwave Background is not observationally excluded. The hypothesis of primordial dichroism can be quantitatively falsified if the plasma is magnetized prior to photon decoupling since the initial V-mode polarization affects the evolution of the temperature fluctuations as well as the equations for the linear polarization. The observed values of the temperature and polarization angular power spectra are used to infer constraints on the amplitude and on the spectral slope of the primordial V-mode. Prior to photon decoupling magnetic fields play the role of polarimeters insofar as they unveil the circular dichroism by coupling the V-mode power spectrum to the remaining brightness perturbations. Conversely, for angular scales ranging between 4 deg and 10 deg the joined bounds on the magnitude of circular polarization and on the magnetic field intensity suggest that direct limits on the V-mode power spectrum in the range of 0.01 mK could directly rule out pre-decoupling magnetic fields in the range of 10-100 nG. The frequency dependence of the signal is located, for the present purposes, in the GHz range.Comment: 28 pages, 12 included figures

Spin Glass Ordering in Diluted Magnetic Semiconductors: a Monte Carlo Study

We study the temperature-dilution phase diagram of a site-diluted Heisenberg antiferromagnet on a fcc lattice, with and without the Dzyaloshinskii-Moriya anisotropic term, fixed to realistic microscopic parameters for $IIB_{1-x} Mn_x Te$ (IIB=Cd, Hg, Zn). We show that the dipolar Dzyaloshinskii-Moriya anisotropy induces a finite-temperature phase transition to a spin glass phase, at dilutions larger than 80%. The resulting probability distribution of the order parameter P(q) is similar to the one found in the cubic lattice Edwards-Anderson Ising model. The critical exponents undergo large finite size corrections, but tend to values similar to the ones of the Edwards-Anderson-Ising model.Comment: 4 pages plus 3 postscript figure

Electroweak Supersymmetry around the Electroweak Scale

Inspired by the phenomenological constraints, LHC supersymmetry and Higgs searches, dark matter search as well as string model building, we propose the electroweak supersymmetry around the electroweak scale: the squarks and/or gluinos are around a few TeV while the sleptons, sneutrinos, bino and winos are within one TeV. The Higgsinos can be either heavy or light. We consider bino as the dominant component of dark matter candidate, and the observed dark matter relic density is achieved via the neutralino-stau coannihilations. Considering the Generalized Minimal Supergravity (GmSUGRA), we show explicitly that the electroweak supersymmetry can be realized, and the gauge coupling unification can be preserved. With two Scenarios, we study the viable parameter spaces that satisfy all the current phenomenological constraints, and we present the concrete benchmark points. Furthermore, we comment on the fine-tuning problem and LHC searches.Comment: RevTex4, 28 pages, 8 figures, 8 tables, version to appear in EPJ

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP)Observations: Beam Maps and Window Functions

Cosmology and other scientific results from the WMAP mission require an accurate knowledge of the beam patterns in flight. While the degree of beam knowledge for the WMAP one-year and three-year results was unprecedented for a CMB experiment, we have significantly improved the beam determination as part of the five-year data release. Physical optics fits are done on both the A and the B sides for the first time. The cutoff scale of the fitted distortions on the primary mirror is reduced by a factor of approximately 2 from previous analyses. These changes enable an improvement in the hybridization of Jupiter data with beam models, which is optimized with respect to error in the main beam solid angle. An increase in main-beam solid angle of approximately 1% is found for the V2 and W1-W4 differencing assemblies. Although the five-year results are statistically consistent with previous ones, the errors in the five-year beam transfer functions are reduced by a factor of approximately 2 as compared to the three-year analysis. We present radiometry of the planet Jupiter as a test of the beam consistency and as a calibration standard; for an individual differencing assembly. errors in the measured disk temperature are approximately 0.5%

Testing the Void against Cosmological data: fitting CMB, BAO, SN and H0

In this paper, instead of invoking Dark Energy, we try and fit various cosmological observations with a large Gpc scale under-dense region (Void) which is modeled by a Lemaitre-Tolman-Bondi metric that at large distances becomes a homogeneous FLRW metric. We improve on previous analyses by allowing for nonzero overall curvature, accurately computing the distance to the last-scattering surface and the observed scale of the Baryon Acoustic peaks, and investigating important effects that could arise from having nontrivial Void density profiles. We mainly focus on the WMAP 7-yr data (TT and TE), Supernova data (SDSS SN), Hubble constant measurements (HST) and Baryon Acoustic Oscillation data (SDSS and LRG). We find that the inclusion of a nonzero overall curvature drastically improves the goodness of fit of the Void model, bringing it very close to that of a homogeneous universe containing Dark Energy, while by varying the profile one can increase the value of the local Hubble parameter which has been a challenge for these models. We also try to gauge how well our model can fit the large-scale-structure data, but a comprehensive analysis will require the knowledge of perturbations on LTB metrics. The model is consistent with the CMB dipole if the observer is about 15 Mpc off the centre of the Void. Remarkably, such an off-center position may be able to account for the recent anomalous measurements of a large bulk flow from kSZ data. Finally we provide several analytical approximations in different regimes for the LTB metric, and a numerical module for CosmoMC, thus allowing for a MCMC exploration of the full parameter space.Comment: 70 pages, 12 figures, matches version accepted for publication in JCAP. References added, numerical values in tables changed due to minor bug, conclusions unaltered. Numerical module available at http://web.physik.rwth-aachen.de/download/valkenburg