141 research outputs found
Interface charged impurity scattering in semiconductor MOSFETs and MODFETs: temperature dependent resistivity and 2D "metallic" behavior
We present the results on the anomalous 2D transport behavior by employing
Drude-Boltzmann transport theory and taking into account the realistic charge
impurity scattering effects. Our results show quantitative agreement with the
existing experimental data in several different systems and address the origin
of the strong and non-monotonic temperature dependent resistivity.Comment: Presented at SIMD, Dec. 1999 in Hawaii. To be published in
Superlattices and Microstructures, May 2000 issu
Latsidipiin arteriaalse hüpertensiooni ravis: kirjanduse ülevaade ja kasutamiskogemused Eesti raviasutustes
Arteriaalse hüpertensiooni (AH) all kannatavate haigete pikaajaliseks raviks kasutatakse tänapäeval mitut gruppi ravimpreparaate. AH ravi esimese valiku preparaatideks, mis sobivad nii mono- kui ka kombineeritud teraapiaks, peetakse diureetikume, α α α α α- ja β β β β β-blokaatoreid, AKE inhibiitoreid, AT1-retseptorite ja kaltsiumiantagoniste. Artiklis on käsitletud kaltsiumiantagonistide kolme põlvkonna preparaatide antihüpertensiivse toime iseärasusi ning lähemalt kolmanda põlvkonna preparaadi latsidipiini omadusi ja kasutamise kogemusi
Minimizing the Ground Effect for Photophoretically Levitating Disks
Photophoretic levitation is a propulsion mechanism in which lightweight
objects can be lifted and controlled through their interactions with light.
Since photophoretic forces on macroscopic objects are usually maximized at low
pressures, they may be tested in vacuum chambers in close proximity to the
chamber floor and walls. We report here experimental evidence that the terrain
under levitating microflyers, including the chamber floor or the launchpad from
which microflyers lift off, can greatly increase the photophoretic lift forces
relative to their free-space (mid-air) values. To characterize this so-called
"ground effect" during vacuum chamber tests, we introduced a new miniature
launchpad composed of three J-shaped (candy-cane-like) wires that minimized a
microflyer's extraneous interactions with underlying surfaces. We compared our
new launchpads to previously used wire-mesh launchpads for simple levitating
mylar-based disks with diameters of 2, 4, and 8 cm. Importantly, wire-mesh
launchpads increased the photophoretic lift force by up to sixfold. A
significant ground effect was also associated with the bottom of the vacuum
chamber, particularly when the distance to the bottom surface was less than the
diameter of the levitating disk. We provide guidelines to minimize the ground
effect in vacuum chamber experiments, which are necessary to test photophoretic
microflyers intended for high-altitude exploration and surveillance on Earth or
on Mars.Comment: 7 pages, 7 figures, including the Supplemental Materia
Possible Applications of Dissolution Dynamic Nuclear Polarization in Conjunction with Zero- to Ultralow-Field Nuclear Magnetic Resonance
The combination of a powerful and broadly applicable nuclear
hyperpolarization technique with emerging (near-)zero-field modalities offer
novel opportunities in a broad range of nuclear magnetic resonance spectroscopy
and imaging applications, including biomedical diagnostics, monitoring
catalytic reactions within metal reactors and many others. These are discussed
along with a roadmap for future developments.Comment: 12 pages, 5 figure
The HST/ACS Grism Parallel Survey: II. First Results and a Catalog of Faint Emission-Line Galaxies at z < 1.6
We present the first results from the HST/ACS Grism Parallel Survey, a large
program obtaining deep, slitless ACS grism spectroscopy of high-latitude HST
parallel fields. We report on 11 high Galactic latitude fields here, each with
grism integration times >12 ks. We identify 601 compact emission line galaxies
at z 5 E-18 ergs/cm^2/s (3
sigma). We determine redshifts by cross correlation of the target spectra with
template spectra, followed by visual inspection. We measure star formation
rates from the observed [OII] 3727, [OIII] 5007 and Halpha line fluxes.
Follow-up observations with the Keck telescope of one of the survey fields
confirms our classification and redshifts with sigma(z)~0.02. This is one of
the deepest emission line surveys to date, covering a total area of 121
arcmin^2. The rough estimate of the co-moving number density of emission-line
galaxies in our survey at 0.3 < z < 1.3 is ~4.5 E-3 h^{-3}_70 Mpc^{-3}. We
reach deeper into the emission-line luminosity function than either the STIS or
NICMOS grism parallel surveys, finding an apparent space density of emission
line galaxies several times higher than those surveys. Because of the ACS high
spatial resolution, our survey is very sensitive to faint, compact galaxies
with strong emission lines and weak continua. The ACS grism survey provides the
co-moving star formation density at z < 1.6 at a high level of completeness.Comment: 20 pages, 12 figures, Accepted to the Astronomical Journal, Also
available at: http://www.astro.spbu.ru/staff/dio/ACS_G800L/ACS_G800L.htm
Room-temperature optically detected magnetic resonance of single defects in hexagonal boron nitride
Optically addressable spins in materials are important platforms for quantum
technologies, such as repeaters and sensors. Identification of such systems in
two-dimensional (2d) layered materials offers advantages over their bulk
counterparts, as their reduced dimensionality enables more feasible on-chip
integration into devices. Here, we report optically detected magnetic resonance
(ODMR) from previously identified carbon-related defects in 2d hexagonal boron
nitride (hBN). We show that single-defect ODMR contrast can be as strong as 6%
and displays a magnetic-field dependence with both positive or negative sign
per defect. This bipolarity can shed light into low contrast reported recently
for ensemble ODMR measurements for these defects. Further, the ODMR lineshape
comprises a doublet resonance, suggesting either low zero-field splitting or
hyperfine coupling. Our results offer a promising route towards realising a
room-temperature spin-photon quantum interface in hexagonal boron nitride
A luminous X-ray transient in SDSS J143359.16+400636.0: a likely tidal disruption event
We present the discovery of a luminous X-ray transient, serendipitously
detected by Swift's X-ray Telescope (XRT) on 2020 February 5, located in the
nucleus of the galaxy SDSS J143359.16+400636.0 at z=0.099 (luminosity distance
Mpc). The transient was observed to reach a peak luminosity of
erg s in the 0.3--10 keV X-ray band, which was
times more than the peak optical/UV luminosity. Optical, UV, and X-ray
lightcurves from the Zwicky Transient Facility (ZTF) and Swift show a decline
in flux from the source consistent with , and observations with
NuSTAR and Chandra show a soft X-ray spectrum with photon index
. The X-ray/UV properties are inconsistent with well known
AGN properties and have more in common with known X-ray tidal disruption events
(TDE), leading us to conclude that it was likely a TDE. The broadband spectral
energy distribution (SED) can be described well by a disk blackbody model with
an inner disk temperature of K, with a large
fraction (%) of the disk emission up-scattered into the X-ray band. An
optical spectrum taken with Keck/LRIS after the X-ray detection reveals LINER
line ratios in the host galaxy, suggesting low-level accretion on to the
supermassive black hole prior to the event, but no broad lines or other
indications of a TDE were seen. The stellar velocity dispersion implies the
mass of the supermassive black hole powering the event is log(/), and we estimate that at peak the Eddington
fraction of this event was 50%. This likely TDE was not identified by
wide-field optical surveys, nor optical spectroscopy, indicating that more
events like this would be missed without wide-field UV or X-ray surveys.Comment: Accepted for publication by ApJ. Accepted version now replaces
initial submissio
A quantum coherent spin in a two-dimensional material at room temperature
Quantum networks and sensing require solid-state spin-photon interfaces that
combine single-photon generation and long-lived spin coherence with scalable
device integration, ideally at ambient conditions. Despite rapid progress
reported across several candidate systems, those possessing quantum coherent
single spins at room temperature remain extremely rare. Here, we report quantum
coherent control under ambient conditions of a single-photon emitting defect
spin in a a two-dimensional material, hexagonal boron nitride. We identify that
the carbon-related defect has a spin-triplet electronic ground-state manifold.
We demonstrate that the spin coherence is governed predominantly by coupling to
only a few proximal nuclei and is prolonged by decoupling protocols. Our
results allow for a room-temperature spin qubit coupled to a multi-qubit
quantum register or quantum sensor with nanoscale sample proximity
Increased DAPK1 but decreased CCL2 plasma levels of nucleic acids in patients with stable angina
Introduction: We hypothesized that patients with stable angina have increased plasma levels of mRNA from genes responsible for atherosclerotic plaque development and destabilisation, i.e. from death-associated protein kinase (DAPK1) and monocyte chemotactic protein-1 (CCL2).
Materials and methods: Nucleic acids were isolated from plasma of patients with stabile angina and healthy subjects as controls. mRNAs were transcribed to cDNAs, quantified by real-time PCR and standardized to the amount of a reference gene. Reagents for PCR quantification are declared to be mRNA specific, but in our test conditions DNA was found to interfere in both assays.
Results: Patients had 5.1-times higher plasma level of DAPK1 nucleic acids (mRNA and DNA) than controls (P < 0.001) and the highest levels were associated with the presence of diabetes. However, plasma levels of CCL2 tended to be lower than in controls, and in statin-treated patients the decre-ment reached significance (-66.3%; P = 0.041).
Conclusion: The estimated levels are explicable in terms of current knowledge. Further studies with specific assays for mRNA PCR quantification are reasonable to access whether this approach offers non-invasive in vivo assessment and monitoring of gene expression profile in atherosclerotic vascular beds
Mercury in the marine environment of the Canadian Arctic: Review of recent findings
AbstractThis review summarizes data and information which have been generated on mercury (Hg) in the marine environment of the Canadian Arctic since the previous Canadian Arctic Contaminants Assessment Report (CACAR) was released in 2003. Much new information has been collected on Hg concentrations in marine water, snow and ice in the Canadian Arctic. The first measurements of methylation rates in Arctic seawater indicate that the water column is an important site for Hg methylation. Arctic marine waters were also found to be a substantial source of gaseous Hg to the atmosphere during the ice-free season. High Hg concentrations have been found in marine snow as a result of deposition following atmospheric mercury depletion events, although much of this Hg is photoreduced and re-emitted back to the atmosphere. The most extensive sampling of marine sediments in the Canadian Arctic was carried out in Hudson Bay where sediment total Hg (THg) concentrations were low compared with other marine regions in the circumpolar Arctic. Mass balance models have been developed to provide quantitative estimates of THg fluxes into and out of the Arctic Ocean and Hudson Bay.Several recent studies on Hg biomagnification have improved our understanding of trophic transfer of Hg through marine food webs. Over the past several decades, Hg concentrations have increased in some marine biota, while other populations showed no temporal change. Marine biota also exhibited considerable geographic variation in Hg concentrations with ringed seals, beluga and polar bears from the Beaufort Sea region having higher Hg concentrations compared with other parts of the Canadian Arctic. The drivers of these variable patterns of Hg bioaccumulation, both regionally and temporally, within the Canadian Arctic remain unclear. Further research is needed to identify the underlying processes including the interplay between biogeochemical and food web processes and climate change
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