Valley-Selective Landau-Zener Oscillations in Semi-Dirac p-n Junctions

We study transport across p-n junctions of gapped two-dimensional semi-Dirac materials: nodal semimetals whose energy bands disperse quadratically and linearly along distinct crystal axes. The resulting electronic properties --- relevant to materials such as TiO$_2$/VO$_2$ multilayers and $\alpha$-(BEDT-TTF)$_2$I$_3$ salts --- continuously interpolate between those of mono- and bi-layer graphene as a function of propagation angle. We demonstrate that tunneling across the junction depends on the orientation of the tunnel barrier relative to the crystalline axes, leading to strongly non-monotonic current-voltage characteristics, including negative differential conductance in some regimes. In multi-valley systems these features provide a natural route to engineering valley-selective transport.Comment: 7 pages, 7 figures, appendice

Seven year satellite observations of the mean structures and variabilities in the regional aerosol distribution over the oceanic areas around the Indian subcontinent

International audienceAerosol distribution over the oceanic regions around the Indian subcontinent and its seasonal and interannual variabilities are studied using the aerosol optical depth (AOD) derived from NOAA-14 and NOAA-16 AVHRR data for the period of November 1995?December 2003. The air-mass types over this region during the Asian summer monsoon season (June?September) are significantly different from those during the Asian dry season (November?April). Hence, the aerosol loading and its properties over these oceanic regions are also distinctly different in these two periods. During the Asian dry season, the Arabian Sea and Bay of Bengal are dominated by the transport of aerosols from Northern Hemispheric landmasses, mainly the Indian subcontinent, Southeast Asia and Arabia. This aerosol transport is rather weak in the early part of the dry season (November?January) compared to that in the later period (February?April). Large-scale transport of mineral dust from Arabia and the production of sea-salt aerosols, due to high surface wind speeds, contribute to the high aerosol loading over the Arabian Sea region during the summer monsoon season. As a result, the monthly mean AOD over the Arabian Sea shows a clear annual cycle with the highest values occurring in July. The AOD over the Bay of Bengal and the Southern Hemisphere Indian Ocean also displays an annual cycle with maxima during March and October, respectively. The amplitude of the annual variation is the largest in coastal Arabia and the least in the Southern Hemisphere Indian Ocean. The interannual variability in AOD is the largest over the Southeast Arabian Sea (seasonal mean AOD varies from 0.19 to 0.42) and the northern Bay of Bengal (seasonal mean AOD varies from 0.24 to 0.39) during the February?April period and is the least over the Southern Hemisphere Indian Ocean. This study also investigates the altitude regions and pathways of dominant aerosol transport by combining the AOD distribution with the atmospheric circulation. Keywords. Atmospheric composition and structure (Aerosols and particles) ? Meteorology and atmospheric dynamics (Climatology) ? Oceanography: physical (Ocean fog and aerosols

Empirical model for mean temperature for Indian zone and estimation of precipitable water vapor from ground based GPS measurements

Estimation of precipitable water (PW) in the atmosphere from ground-based Global Positioning System (GPS) essentially involves modeling the zenith hydrostatic delay (ZHD) in terms of surface Pressure (<I>P<sub>s</sub></I>) and subtracting it from the corresponding values of zenith tropospheric delay (ZTD) to estimate the zenith wet (non-hydrostatic) delay (ZWD). This further involves establishing an appropriate model connecting PW and ZWD, which in its simplest case assumed to be similar to that of ZHD. But when the temperature variations are large, for the accurate estimate of PW the variation of the proportionality constant connecting PW and ZWD is to be accounted. For this a water vapor weighted mean temperature (<I>T<sub>m</sub></I>) has been defined by many investigations, which has to be modeled on a regional basis. For estimating PW over the Indian region from GPS data, a region specific model for <I>T<sub>m</sub></I> in terms of surface temperature (<I>T<sub>s</sub></I>) is developed using the radiosonde measurements from eight India Meteorological Department (IMD) stations spread over the sub-continent within a latitude range of 8.5°–32.6° N. Following a similar procedure <I>T<sub>m</sub></I>-based models are also evolved for each of these stations and the features of these site-specific models are compared with those of the region-specific model. Applicability of the region-specific and site-specific <I>T<sub>m</sub></I>-based models in retrieving PW from GPS data recorded at the IGS sites Bangalore and Hyderabad, is tested by comparing the retrieved values of PW with those estimated from the altitude profile of water vapor measured using radiosonde. The values of ZWD estimated at 00:00 UTC and 12:00 UTC are used to test the validity of the models by estimating the PW using the models and comparing it with those obtained from radiosonde data. The region specific <I>T<sub>m</sub></I>-based model is found to be in par with if not better than a similar site-specific <I>T<sub>m</sub></I>-based model for the near equatorial station, Bangalore. A simple site-specific linear relation without accounting for the temperature effect through <I>T<sub>m</sub></I> is also found to be quite adequate for Bangalore. But for Hyderabad, a station located at slightly higher latitude, the deviation for the linear model is found to be larger than that of the <I>T<sub>m</sub></I>-based model. This indicates that even though a simple linear regression model is quite adequate for the near equatorial stations, where the temperature variations are relatively small, for estimating PW from GPS data at higher latitudes this model is inferior to the <I>T<sub>m</sub></I>-based model

Regulation of FcεRI Signaling in Mast Cells by G Protein-Coupled Receptor Kinase 2 and its RH Domain

Agonist-induced phosphorylation of G protein-coupled receptors (GPCRs) by GPCR kinases (GRKs) promotes their desensitization and internalization. Here, we sought to determine the role of GRK2 on FcεRI signaling and mediator release in mast cells. The strategies utilized included lentiviral shRNA-mediated GRK2 knockdown, GRK2 gene deletion (GRK2flox/flox/cre recombinase) and overexpression of GRK2 and its regulator of G protein signaling homology (RH) domain (GRK2-RH). We found that silencing GRK2 expression caused ∼50% decrease in antigen-induced Ca2+ mobilization and degranulation but resulted in ablation of cytokine (IL-6 and IL-13) generation. The effect of GRK2 on cytokine generation does not require its catalytic activity but is mediated via the phosphorylation of p38 and Akt. Overexpression of GRK2 or its RH domain (GRK2-RH) enhanced antigen-induced mast cell degranulation and cytokine generation without affecting the expression levels of any of the FcεRI subunits (α, β, and γ). GRK2 or GRK2-RH had no effect on antigen-induced phosphorylation of FcεRIγ or Src but enhanced tyrosine phosphorylation of Syk. These data demonstrate that GRK2 modulates FcεRI signaling in mast cells via at leasttwomechanisms. OneinvolvesGRK2-RHand modulates tyrosine phosphorylation of Syk, and the other is mediated via the phosphorylation of p38 and Akt. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc