Weak Field Collapse in AdS: Introducing a Charge Density

We study the effect of a non-vanishing chemical potential on the thermalization time of a strongly coupled large $N_c$ gauge theory in $(2+1)$-dimensions, using a specific bottom-up gravity model in asymptotically AdS space. We first construct a perturbative solution to the gravity-equations, which dynamically interpolates between two AdS black hole backgrounds with different temperatures and chemical potentials, in a perturbative expansion of a bulk neutral scalar field. In the dual field theory, this corresponds to a quench dynamics by a marginal operator, where the corresponding coupling serves as the small parameter in which the perturbation is carried out. The evolution of non-local observables, such as the entanglement entropy, suggests that thermalization time decreases with increasing chemical potential. We also comment on the validity of our perturbative analysis.Comment: 1+48 pages, multiple figures, published in JHE

Bose-Einstein Condensates with Large Number of Vortices

We show that as the number of vortices in a three dimensional Bose-Einstein Condensate increases, the system reaches a "quantum Hall" regime where the density profile is a Gaussian in the xy-plane and an inverted parabolic profile along z. The angular momentum of the system increases as the vortex lattice shrinks. However, Coriolis force prevents the unit cell of the vortex lattice from shrinking beyond a minimum size. Although the recent MIT experiment is not exactly in the quantum Hall regime, it is close enough for the present results to be used as a guide. The quantum Hall regime can be easily reached by moderate changes of the current experimental parameters.Comment: 4 pages, no figure

Vacuolar ATPase depletion contributes to dysregulation of endocytosis in bloodstream forms of Trypanosoma brucei

BACKGROUND Vacuolar H-ATPase (V-ATPase) is a highly conserved protein complex which hydrolyzes ATP and pumps protons to acidify vacuolar vesicles. Beyond its role in pH maintenance, the involvement of V-ATPase in endocytosis is well documented in mammals and plants but is less clear in Trypanosoma brucei. METHODS In this study, the subcellular localization of V-ATPase subunit B (TbVAB) of T. brucei was assessed via in situ N-terminal YFP-tagging and immunofluorescence assays. Transgenic bloodstream forms (BSF) of T. brucei were generated which comprised either a V-ATPase subunit B (TbVAB) conditional knockout or a V-ATPase subunit A (TbVAA) knockdown. Acridine orange and BCECF-AM were employed to assess the roles of V-ATPase in the pH regulation of BSF T. brucei. The endocytic activities of three markers were also characterized by flow cytometry analyses. Furthermore, trypanosomes were counted from trypanolysis treatment groups (either containing 1% or 5% NHS) and endocytosed trypanosome lytic factor (TLF) was also analyzed by an immunoblotting assay. RESULTS TbVAB was found to localize to acidocalcisomes, lysosomes and probably also to endosomes of BSF of T. brucei and was demonstrated to be essential for cell growth. TbVAB depletion neutralized acidic organelles at 24 hours post-tetracycline depletion (hpd), meanwhile the steady state intracellular pH increased from 7.016 ± 0.013 to 7.422 ± 0.058. Trypanosomes with TbVAB depletion at 24 hpd were found to take up more transferrin (2.068 ± 0.277 fold) but less tomato lectin (49.31 ± 22.57%) by endocytosis, while no significant change was detected in dextran uptake. Similar endocytic dysregulated phenotypes were also observed in TbVAA knockdown cells. In addition, TbVAB depleted trypanosomes showed a low uptake of TLF and exhibited less sensitive to lysis in both 1% and 5% NHS treatments. CONCLUSIONS TbVAB is a key component of V-ATPase and was found to play a key function in endocytosis as well as exhibiting different effects in a receptor/cargo dependent manner in BSF of T. brucei. Besides vacuolar alkalinization, the dysregulation of endocytosis in TbVAB depleted T. brucei is considered to contribute to the reduced sensitivity to lysis by normal human serum

Energy non-equipartition in systems of inelastic, rough spheres

We calculate and verify with simulations the ratio between the average translational and rotational energies of systems with rough, inelastic particles, either forced or freely cooling. The ratio shows non-equipartition of energy. In stationary flows, this ratio depends mainly on the particle roughness, but in nonstationary flows, such as freely cooling granular media, it also depends strongly on the normal dissipation. The approach presented here unifies and simplifies different results obtained by more elaborate kinetic theories. We observe that the boundary induced energy flux plays an important role.Comment: 4 pages latex, 4 embedded eps figures, accepted by Phys Rev

Dynamic bandwidth allocation using infinitesimal perturbation analysis

Advances in network management and switching technologies make dynamic bandwidth allocation of logical networks built on top of a physical network possible. Previous proposed dynamic bandwidth allocation algorithms are based on simplified network model. The analytical model is valid only under restrictive assumptions. Infinitesimal Perturbation Analysis, a technique which estimates the gradients of the functions in discrete event dynamic systems by passively observing the system, is used to estimate delay sensitivities under general traffic patterns. A new dynamic bandwidth allocation algorithm using on-line sensitivity estimation is proposed. Simulation results show that the approach further improves network performance. Implementation of the proposed algorithm in operational networks is also discussed.published_or_final_versio

Long-Term Variations of the Electron Slot Region and Global Radiation Belt Structure

We report the observations of changes of the nominal position of the quiet-time radiation belt slot over the solar cycles. It has been found that the slot region, believed to be a result of enhanced precipitation losses of energetic electrons due to their interactions with VLF waves in the magnetosphere, tends to shift to higher L (approximately 3) during a solar maximum compared to its canonical L value of approximately 2.5, which is more typical of a solar minimum. The solar-cycle migration of the slot can be understood in terms of the solar-cycle changes in ionospheric densities, which may cause the optimal wave-particle interaction region during higher solar activity periods to move to higher altitudes and higher latitudes, thus higher L. Our analysis also suggests that the primary wave-particle interaction processes that result in the slot formation are located off of the magnetic equator

Ultrafast all-optical switching via coherent modulation of metamaterial absorption

We report on the demonstration of a femtosecond all-optical modulator providing, without nonlinearity and therefore at arbitrarily low intensity, ultrafast light-by-light control. The device engages the coherent interaction of optical waves on a metamaterial nanostructure only 30 nm thick to efficiently control absorption of near-infrared (750-1040 nm) femtosecond pulses, providing switching contrast ratios approaching 3:1 with a modulation bandwidth in excess of 2 THz. The functional paradigm illustrated here opens the path to a family of novel meta-devices for ultra-fast optical data processing in coherent networks.Comment: 5 pages, 4 figure

Quantum Criticality of 1D Attractive Fermi Gas

We obtain an analytical equation of state for one-dimensional strongly attractive Fermi gas for all parameter regime in current experiments. From the equation of state we derive universal scaling functions that control whole thermodynamical properties in quantum critical regimes and illustrate physical origin of quantum criticality. It turns out that the critical properties of the system are described by these of free fermions and those of mixtures of fermions with mass $m$ and $2m$. We also show how these critical properties of bulk systems can be revealed from the density profile of trapped Fermi gas at finite temperatures and can be used to determine the T=0 phase boundaries without any arbitrariness.Comment: extended version, 9 pages, 7 eps figures, corrections of few typo