Miscible displacement fronts of shear thinning fluids inside rough fractures

The miscible displacement of a shear-thinning fluid by another of same rheological properties is studied experimentally in a transparent fracture by an optical technique imaging relative concentration distributions. The fracture walls have complementary self-affine geometries and are shifted laterally in the direction perpendicular to the mean flow velocity {\bf U} : the flow field is strongly channelized and macro dispersion controls the front structure for P\'{e}clet numbers above a few units. The global front width increases then linearly with time and reflects the velocity distribution between the different channels. In contrast, at the local scale, front spreading is similar to Taylor dispersion between plane parallel surfaces. Both dispersion mechanisms depend strongly on the fluid rheology which shifts from Newtonian to shear-thinning when the flow rate increases. In the latter domain, increasing the concentration enhances the global front width but reduces both Taylor dispersion (due to the flattening of the velocity profile in the gap of the fracture) and the size of medium scale front structures

Two-photon transitions in primordial hydrogen recombination

The subject of cosmological hydrogen recombination has received much attention recently because of its importance to predictions for and cosmological constraints from CMB observations. While the central role of the two-photon decay 2s->1s has been recognized for many decades, high-precision calculations require us to consider two-photon decays from the higher states ns,nd->1s (n>=3). Simple attempts to include these processes in recombination calculations have suffered from physical problems associated with sequences of one-photon decays, e.g. 3d->2p->1s, that technically also produce two photons. These correspond to resonances in the two-photon spectrum that are optically thick, necessitating a radiative transfer calculation. We derive the appropriate equations, develop a numerical code to solve them, and verify the results by finding agreement with analytic approximations to the radiative transfer equation. The related processes of Raman scattering and two-photon recombination are included using similar machinery. Our results show that early in recombination the two-photon decays act to speed up recombination, reducing the free electron abundance by 1.3% relative to the standard calculation at z=1300. However we find that some photons between Ly-alpha and Ly-beta are produced, mainly by 3d->1s two-photon decay and 2s->1s Raman scattering. At later times these photons redshift down to Ly-alpha, excite hydrogen atoms, and act to slow recombination. Thus the free electron abundance is increased by 1.3% relative to the standard calculation at z=900. The implied correction to the CMB power spectrum is neligible for the recently released WMAP and ACBAR data, but at Fisher matrix level will be 7 sigma for Planck. [ABRIDGED]Comment: Matches PRD accepted version. 28 pages, 12 figure

CMB constraints on the fine structure constant

We study constraints on time variation of the fine structure constant alpha from cosmic microwave background (CMB) taking into account simultaneous change in alpha and the electron mass m_e which might be implied in unification theories. We obtain the constraints -0.097 < Delta alpha/alpha < 0.034 at 95% C.L. using WMAP data only, and -0.042 < Delta alpha/alpha < 0.026 combining with the constraint on the Hubble parameter by the HST Hubble Key Project. These are improved by 15% compared with constraints assuming only alpha varies. We discuss other relations between variations in alpha and m_e but we do not find evidence for varying alpha.Comment: 19 pages, 8 figure

How exactly did the Universe become neutral?

We present a refined treatment of H, He I, and He II recombination in the early Universe. The difference from previous calculations is that we use multi-level atoms and evolve the population of each level with redshift by including all bound-bound and bound-free transitions. In this framework we follow several hundred atomic energy levels for H, He I, and He II combined. The main improvements of this method over previous recombination calculations are: (1) allowing excited atomic level populations to depart from an equilibrium distribution; (2) replacing the total recombination coefficient with recombination to and photoionization from each level directly at each redshift step; and (3) correct treatment of the He I atom, including the triplet and singlet states. We find that the ionization fraction x_e = n_e/n_H is approximately 10% smaller at redshifts <~800 than in previous calculations, due to the non-equilibrium of the excited states of H, which is caused by the strong but cool radiation field at those redshifts. In addition we find that He I recombination is delayed compared with previous calculations, and occurs only just before H recombination. These changes in turn can affect the predicted power spectrum of microwave anisotropies at the few percent level. Other improvements such as including molecular and ionic species of H, including complete heating and cooling terms for the evolution of the matter temperature, including collisional rates, and including feedback of the secondary spectral distortions on the radiation field, produce negligible change to x_e. The lower x_e at low z found in this work affects the abundances of H molecular and ionic species by 10-25%. However this difference is probably not larger than other uncertainties in the reaction rates.Comment: 24 pages, including 18 figures, using emulateapj.sty, to appear in ApJ, the code recfast can be obtained at http://www.astro.ubc.ca/people/scott/recfast.html (in FORTRAN) and http://cfa-www.harvard.edu/~sasselov/rec/ (in C

Cryopyrin-Associated Periodic Syndrome: An Update on Diagnosis and Treatment Response

Cryopyrin-associated periodic syndrome (CAPS) is a rare hereditary inflammatory disorder encompassing a continuum of three phenotypes: familial cold autoinflammatory syndrome, Muckle-Wells syndrome, and neonatal-onset multisystem inflammatory disease. Distinguishing features include cutaneous, neurological, ophthalmologic, and rheumatologic manifestations. CAPS results from a gain-of-function mutation of the NLRP3 gene coding for cryopyrin, which forms intracellular protein complexes known as inflammasomes. Defects of the inflammasomes lead to overproduction of interleukin-1, resulting in inflammatory symptoms seen in CAPS. Diagnosis is often delayed and requires a thorough review of clinical symptoms. Remarkable advances in our understanding of the genetics and the molecular pathway that is responsible for the clinical phenotype of CAPS has led to the development of effective treatments. It also has become clear that the NLRP3 inflammasome plays a critical role in innate immune defense and therefore has wider implications for other inflammatory disease states