On AdS2AdS_2 holography from redux, renormalization group flows and cc-functions

Extremal black branes upon compactification in the near horizon throat region are known to give rise to $AdS_2$ dilaton-gravity-matter theories. Away from the throat region, the background has nontrivial profile. We interpret this as holographic renormalization group flow in the 2-dim dilaton-gravity-matter theories arising from dimensional reduction of the higher dimensional theories here. The null energy conditions allow us to formulate a holographic c-function in terms of the 2-dim dilaton for which we argue a c-theorem subject to appropriate boundary conditions which amount to restrictions on the ultraviolet theories containing these extremal branes. At the infrared $AdS_2$ fixed point, the c-function becomes the extremal black brane entropy. We discuss the behaviour of this inherited c-function in various explicit examples, in particular compactified nonconformal branes, and compare it with other discussions of holographic c-functions. We also adapt the holographic renormalization group formulated in terms of radial Hamiltonian flow to 2-dim dilaton-gravity-scalar theories, which while not Wilsonian, gives qualitative insight into the flow equations and $\beta$-functions.Comment: Latex, 40pgs incl appendices; v2: minor tweaks, figure added; v3: minor clarifications added, matches version to be publishe

Hyperscaling violation and the shear diffusion constant

We consider holographic theories in bulk $(d+1)$-dimensions with Lifshitz and hyperscaling violating exponents $z,\theta$ at finite temperature. By studying shear gravitational modes in the near-horizon region given certain self-consistent approximations, we obtain the corresponding shear diffusion constant on an appropriately defined stretched horizon, adapting the analysis of Kovtun, Son and Starinets. For generic exponents with $d-z-\theta>-1$, we find that the diffusion constant has power law scaling with the temperature, motivating us to guess a universal relation for the viscosity bound. When the exponents satisfy $d-z-\theta=-1$, we find logarithmic behaviour. This relation is equivalent to $z=2+d_{eff}$ where $d_{eff}=d_i-\theta$ is the effective boundary spatial dimension (and $d_i=d-1$ the actual spatial dimension). It is satisfied by the exponents in hyperscaling violating theories arising from null reductions of highly boosted black branes, and we comment on the corresponding analysis in that context.Comment: Latex, 17pgs, v3: clarifications added on z<2+d_{eff} and standard quantization, to be publishe

Comprehensive review of key parameters for improving the performance of Solar Air Heaters

Due to declining supplies of once-affordable fossil fuels, research into renewable energy sources is being prioritized. Using solar energy for passive cooling and heating can significantly reduce the demand for primary energy sources. In this survey, we look at how changing a few variables might affect how well a solar air heater functions. It helps researchers learn more about these systems’ development, properties, and potential uses. This research analyses the current literature to emphasize the value of thermal properties. Focusing on laminar sublayer creation and increasing the heat transfer coefficient, it explores ways to increase the efficiency of solar air heaters. After reviewing several articles, it has been determined that rib roughness elements and their geometric characteristics play a significant role in enhancing the thermal performance of solar air heaters. The relative roughness height, pitch, angle of attack, and width are all important factors to consider

Role of trans-cerebellar diameter in estimating gestational age in second and third trimester of pregnancy

Background: Uncertain gestational age is associated with higher perinatal mortality rates and an increased incidence of low birth weight and spontaneous preterm delivery. Errors in gestational age estimation can lead to iatrogenic neonatal morbidity from prematurity. Precise determination of gestational age antenatally is a boon to modern obstetrics in context with improved neonatal survival. The most effective way to date pregnancy is by sonography. Several parameters can be considered for estimation of gestational age trans-cerebellar diameter is one such parameter. The objective of this study was to study the role of fetal trans-cerebellar diameter in estimating the gestational age in second and third trimester of pregnancy and its correlation with gestational age, BPD, HC, AC and FL. The design of this study was to hospital based prospective cohort study conducted at department of obstetrics of Government medical College Nagpur, over a period of 1 year.Methods: 500 women with sure dates between 7 and 11 weeks of gestation were booked. First trimester USG using crown rump length for confirmation of gestational age was done. These patients were advised to come for follow up till 40 weeks of gestation and repeat USG was done in second and third trimester. Trans-cerebellar diameter was correlated with expected gestational age with CRL, BPD, HC, AC and FL in weeks.Results: 98.56% of variability in gestational age could be explained by variation in trans-cerebellar diameter (TCD) only. Addition of other variables did not make any significant difference indicating that TCD alone is the strong predictor of gestational age.Conclusions: Normative cerebellar measurements throughout pregnancy permit estimation of gestational age independent of the shape of fetal head and also offer potential for evaluating abnormal fetal growth and anomalous development of central nervous system

Staphylococcal Enterotoxin A Induces Small Clusters of HLA-DR1 on B Cells

The superantigen SEA causes non-specific hyperactivation of T and B cells at low concentrations. Studies of mutants or soluble proteins suggest SEA is bivalent for its ligand, MHC class II. However, the interaction between these molecules on intact cells is unknown. On primary mouse B cells expressing the MHC class II allele HLA-DR1, measurements of Förster Resonance Energy Transfer between HLA-DR1 molecules on SEA-treated cells indicated specific clustering, not observed in untreated or monovalent superantigen treated cells. Tomographic visualization and electron microscopy of immunogold-labeled SEA-treated B cells revealed small clusters of surface HLA-DR1 (≤4 gold labels). These results present direct visual evidence of SEA-mediated clustering of MHC class II molecules on treated antigen presenting cells, and provide a new structural approach to addressing problems of this nature

Intracellular connections between basal bodies promote the coordinated behavior of motile cilia

Hydrodynamic flow produced by multiciliated cells is critical for fluid circulation and cell motility. Hundreds of cilia beat with metachronal synchrony for fluid flow. Cilia-driven fluid flow produces extracellular hydrodynamic forces that cause neighboring cilia to beat in a synchronized manner. However, hydrodynamic coupling between neighboring cilia is not the sole mechanism that drives cilia synchrony. Cilia are nucleated by basal bodies (BBs) that link to each other and to the cell\u27s cortex via BB-associated appendages. The intracellular BB and cortical network is hypothesized to synchronize ciliary beating by transmitting cilia coordination cues. The extent of intracellular ciliary connections and the nature of these stimuli remain unclear. Moreover, how BB connections influence the dynamics of individual cilia has not been established. We show by focused ion beam scanning electron microscopy imaging that cilia are coupled both longitudinally and laterally in the ciliat