Negative Electron-electron Drag Between Narrow Quantum Hall Channels

Momentum transfer due to Coulomb interaction between two parallel, two-dimensional, narrow, and spatially separated layers, when a current I_{drive} is driven through one layer, is studied in the presence of a perpendicular magnetic field B. The current induced in the drag layer, I_{drag}, is evaluated self-consistently with I_{drive} as a parameter. I_{drag} can be positive or negative depending on the value of the filling factor \nu of the highest occupied bulk Landau level (LL). For a fully occupied LL, I_{drag} is negative, i.e., it flows opposite to I_{drive}, whereas it is positive for a half-filled LL. When the circuit is opened in the drag layer, a voltage \Delta V_{drag} develops in it; it is negative for a half-filled LL and positive for a fully occupied LL. This positive \Delta V_{drag}, expressing a negative Coulomb drag, results from energetically favored near-edge inter-LL transitions that occur when the highest occupied bulk LL and the LL just above it become degenerate.Comment: Text file in Latex/Revtex/preprint format, 7 separate PS figures, Physical Review B, in pres

Scalable Traffic-Aware Virtual Machine Management for Cloud Data Centers

Virtual Machine (VM) management is a powerful mechanism for providing elastic services over Cloud Data Centers (DC)s. At the same time, the resulting network congestion has been repeatedly reported as the main bottleneck in DCs, even when the overall resource utilization of the infrastructure remains low. However, most current VM management strategies are traffic-agnostic, while the few that are traffic-aware only concern a static initial allocation, ignore bandwidth oversubscription, or do not scale. In this paper we present S-CORE, a scalable VM migration algorithm to dynamically reallocate VMs to servers while minimizing the overall communication footprint of active traffic flows. We formulate the aggregate VM communication as an optimization problem and we then define a novel distributed migration scheme that iteratively adapts to dynamic traffic changes. Through extensive simulation and implementation results, we show that S-CORE achieves significant (up to 87%) communication cost reduction while incurring minimal overhead and downtime. Index Terms—Virtual Machine, Migration, Consolidation, Communication Cost, Scalable, Traffic-Aware, Data Center Networ

Charged Many-Electron -- Single Hole Complexes in a Double Quantum Well near a Metal Plate

It has been shown that the presence of a metal plate near a double quantum well with spatially separated electron and hole layers may lead to a drastic reconstruction of the system state with the formation of stable charged complexes of several electrons bound to a spatially separated hole. Complexes of both the Fermi and the Bose statistics may coexist in the ground state and their relative densities may be changed with the change of the electron and hole densities. The stability of the charged complexes may be increased by an external magnetic field perpendicular to the layers plane.Comment: to appear in Phys.Rev.Lett. 77, No.7 (1996). 4 pages, RevTeX, 1 figur

Effects of CO2 on H2O band profiles and band strengths in mixed H2O:CO2 ices

H2O is the most abundant component of astrophysical ices. In most lines of sight it is not possible to fit both the H2O 3 um stretching, the 6 um bending and the 13 um libration band intensities with a single pure H2O spectrum. Recent Spitzer observations have revealed CO2 ice in high abundances and it has been suggested that CO2 mixed into H2O ice can affect relative strengths of the 3 um and 6 um bands. We used laboratory infrared transmission spectroscopy of H2O:CO2 ice mixtures to investigate the effects of CO2 on H2O ice spectral features at 15-135 K. We find that the H2O peak profiles and band strengths are significantly different in H2O:CO2 ice mixtures compared to pure H2O ice. In all H2O:CO2 mixtures, a strong free-OH stretching band appears around 2.73 um, which can be used to put an upper limit on the CO2 concentration in the H2O ice. The H2O bending mode profile also changes drastically with CO2 concentration; the broad pure H2O band gives way to two narrow bands as the CO2 concentration is increased. This makes it crucial to constrain the environment of H2O ice to enable correct assignments of other species contributing to the interstellar 6 um absorption band. The amount of CO2 present in the H2O ice of B5:IRS1 is estimated by simultaneously comparing the H2O stretching and bending regions and the CO2 bending mode to laboratory spectra of H2O, CO2, H2O:CO2 and HCOOH.Comment: 12 pages, 11 figures, accepted by A&

Oral Delivery of the P2Y12 Receptor Antagonist Ticagrelor Prevents Loss of Photoreceptors in an ABCA4−/− Mouse Model of Retinal Degeneration

PURPOSE. Accumulation of lysosomal waste is linked to neurodegeneration in multiple diseases, and pharmacologic enhancement of lysosomal activity is hypothesized to reduce pathology. An excessive accumulation of lysosomal-associated lipofuscin waste and an elevated lysosomal pH occur in retinal pigment epithelial cells of the ABCA4 mouse model of Stargardt\u27s retinal degeneration. As treatment with the P2Y12 receptor antagonist ticagrelor was previously shown to lower lysosomal pH and lipofuscin-like autofluorescence in these cells, we asked whether oral delivery of ticagrelor also prevented photoreceptor loss. METHODS. Moderate light exposure was used to accelerate photoreceptor loss in albino ABCA4 mice as compared to BALB/c controls. Ticagrelor (0.1%–0.15%) was added to mouse chow for between 1 and 10 months. Photoreceptor function was determined with electroretinograms, while cell survival was determined using optical coherence tomography and histology. RESULTS. Protection by ticagrelor was demonstrated functionally by using the electroretinogram, as ticagrelor-treated ABCA4 mice had increased a-and b-waves compared to untreated mice. Mice receiving ticagrelor treatment had a thicker outer nuclear layer, as measured with both optical coherence tomography and histologic sections. Ticagrelor decreased expression of LAMP1, implicating enhanced lysosomal function. No signs of retinal bleeding were observed after prolonged treatment with ticagrelor. CONCLUSIONS. Oral treatment with ticagrelor protected photoreceptors in the ABCA4 mouse, which is consistent with enhanced lysosomal function. As mouse ticagrelor exposure levels were clinically relevant, the drug may be of benefit in preventing the loss of photoreceptors in Stargardt’s disease and other neurodegenerations associated with lysosomal dysfunction. © 2019 The Authors. All rights reserved

Frictional Coulomb drag in strong magnetic fields

A treatment of frictional Coulomb drag between two 2-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity $\rho_{21}$ is evaluated using diagrammatic techniques. The transresistivity is given by an integral over energy and momentum transfer weighted by the product of the screened interlayer interaction and the phase-space for scattering events. We demonstrate, by a numerical analysis of the transresistivity, that for well-resolved Landau levels the interplay between these two factors leads to characteristic features in both the magnetic field- and the temperature dependence of $\rho_{21}$. Numerical results are compared with recent experiments.Comment: RevTeX, 34 pages, 8 figures included in tex

Magneto-Coulomb drag: interplay of electron--electron interactions and Landau quantization

We use the Kubo formalism to calculate the transresistivity $\rho_{21}$ for carriers in coupled quantum wells in a large perpendicular magnetic field $B$. We find that $\rho_{21}$ is enhanced by approximately 50--100 times over that of the B=0 case in the interplateau regions of the integer quantum Hall effect. The presence of both electron--electron interactions and Landau quantization results in (i) a twin-peaked structure of $\rho_{21}(B)$ in the inter-plateau regions at low temperatures, and, (ii) for the chemical potential at the center of a Landau level band, a peaked temperature dependence of $\rho_{21}(T)/T^2$.Comment: 4 pages, RevTeX, 4 PS figures in text using eps

The Quantum Hall Effect in Drag: Inter-layer Friction in Strong Magnetic Fields

We study the Coulomb drag between two spatially separated electron systems in a strong magnetic field, one of which exhibits the quantum Hall effect. At a fixed temperature, the drag mimics the behavior of $\sigma_{xx}$ in the quantum Hall system, in that it is sharply peaked near the transitions between neighboring plateaux. We assess the impact of critical fluctuations near the transitions, and find that the low temperature behavior of the drag measures an exponent $\eta$ that characterizes anomalous low frequency dissipation; the latter is believed to be present following the work of Chalker.Comment: 13 pages, Revtex 2.0, 1 figure upon request, P-93-11-09

Performance analysis of single board computer clusters

The past few years have seen significant developments in Single Board Computer (SBC) hardware capabilities. These advances in SBCs translate directly into improvements in SBC clusters. In 2018 an individual SBC has more than four times the performance of a 64-node SBC cluster from 2013. This increase in performance has been accompanied by increases in energy efficiency (GFLOPS/W) and value for money (GFLOPS/$). We present systematic analysis of these metrics for three different SBC clusters composed of Raspberry Pi 3 Model B, Raspberry Pi 3 Model B+ and Odroid C2 nodes respectively. A 16-node SBC cluster can achieve up to 60GFLOPS, running at 80W. We believe that these improvements open new computational opportunities, whether this derives from a decrease in the physical volume required to provide a fixed amount of computation power for a portable cluster; or the amount of compute power that can be installed given a fixed budget in expendable compute scenarios. We also present a new SBC cluster construction form factor named Pi Stack; this has been designed to support edge compute applications rather than the educational use-cases favoured by previous methods. The improvements in SBC cluster performance and construction techniques mean that these SBC clusters are realising their potential as valuable developmental edge compute devices rather than just educational curiosities

The missense mutation in Abcg5 gene in spontaneously hypertensive rats (SHR) segregates with phytosterolemia but not hypertension

BACKGROUND: Sitosterolemia is a recessively inherited disorder in humans that is associated with premature atherosclerotic disease. Mutations in ABCG5 or ABCG8, comprising the sitosterolemia locus, STSL, are now known to cause this disease. Three in-bred strains of rats, WKY, SHR and SHRSP, are known to be sitosterolemic, hypertensive and they carry a missense 'mutation' in a conserved residue of Abcg5, Gly583Cys. Since these rat strains are also know to carry mutations at other genetic loci and the extent of phytosterolemia is only moderate, it is important to verify that the mutations in Abcg5 are causative for phytosterolemia and whether they contribute to hypertension. METHODS: To investigate whether the missense change in Abcg5 is responsible for the sitosterolemia we performed a segregation analysis in 103 F2 rats from a SHR × SD cross. Additionally, we measured tail-cuff blood pressure and measured intestinal lipid transport to identify possible mechanisms whereby this mutation causes sitosterolemia. RESULTS: Segregation analysis showed that the inheritance of the Gly583Cys mutation Abcg5 segregated with elevated plant sterols and this pattern was recessive, proving that this genetic change is responsible for the sitosterolemia in these rat strains. Tail-cuff monitoring of blood pressure in conscious animals showed no significant differences between wild-type, heterozygous and homozygous mutant F2 rats, suggesting that this alteration may not be a significant determinant of hypertension in these rats on a chow diet. CONCLUSION: This study shows that the previously identified Gly583Cys change in Abcg5 in three hypertension-susceptible rats is responsible for the sitosterolemia, but may not be a major determinant of blood pressure in these rats