762 research outputs found
Linear magnetoresistance in a quasi-free two dimensional electron gas in an ultra-high mobility GaAs quantum well
We report a magnetotransport study of an ultra-high mobility
(\,cm\,V\,s) -type GaAs
quantum well up to 33 T. A strong linear magnetoresistance (LMR) of the order
of 10 % is observed in a wide temperature range between 0.3 K and 60 K. The
simplicity of our material system with a single sub-band occupation and free
electron dispersion rules out most complicated mechanisms that could give rise
to the observed LMR. At low temperature, quantum oscillations are superimposed
onto the LMR. Both, the featureless LMR at high and the quantum
oscillations at low follow the empirical resistance rule which states that
the longitudinal conductance is directly related to the derivative of the
transversal (Hall) conductance multiplied by the magnetic field and a constant
factor that remains unchanged over the entire temperature range. Only
at low temperatures, small deviations from this resistance rule are observed
beyond that likely originate from a different transport mechanism for
the composite fermions
Anisotropic and strong negative magneto-resistance in the three-dimensional topological insulator Bi2Se3
We report on high-field angle-dependent magneto-transport measurements on
epitaxial thin films of Bi2Se3, a three-dimensional topological insulator. At
low temperature, we observe quantum oscillations that demonstrate the
simultaneous presence of bulk and surface carriers. The magneto- resistance of
Bi2Se3 is found to be highly anisotropic. In the presence of a parallel
electric and magnetic field, we observe a strong negative longitudinal
magneto-resistance that has been consid- ered as a smoking-gun for the presence
of chiral fermions in a certain class of semi-metals due to the so-called axial
anomaly. Its observation in a three-dimensional topological insulator implies
that the axial anomaly may be in fact a far more generic phenomenon than
originally thought.Comment: 6 pages, 4 figure
Rotational inhomogeneities from pre-big bang?
The evolution of the rotational inhomogeneities is investigated in the
specific framework of four-dimensional pre-big bang models. While minimal
(dilaton-driven) scenarios do not lead to rotational fluctuations, in the case
of non-minimal (string-driven) models, fluid sources are present in the pre-big
bang phase. The rotational modes of the geometry, coupled to the divergenceless
part of the velocity field, can then be amplified depending upon the value of
the barotropic index of the perfect fluids. In the light of a possible
production of rotational inhomogeneities, solutions describing the coupled
evolution of the dilaton field and of the fluid sources are scrutinized in both
the string and Einstein frames. In semi-realistic scenarios, where the
curvature divergences are regularized by means of a non-local dilaton
potential, the rotational inhomogeneities are amplified during the pre-big bang
phase but they decay later on. Similar analyses can also be performed when a
contraction occurs directly in the string frame metric.Comment: 21 pages, corrected typos, references added; to appear in Class.
Quantum Gra
Living with COVID-19: A Perspective from New York Area Ophthalmology Residency Program Directors at the Epicenter of the Pandemic
A high resolution line survey of IRC+10216 with Herschel. First results: Detection of warm silicon dicarbide SiC2
We present the first results of a high-spectral-resolution survey of the
carbon-rich evolved star IRC+10216 that was carried out with the HIFI
spectrometer onboard Herschel. This survey covers all HIFI bands, with a
spectral range from 488 to 1901GHz. In this letter we focus on the band-1b
spectrum, in a spectral range 554.5-636.5GHz, where we identified 130 spectral
features with intensities above 0.03 K and a signal-to-noise ratio >5. Detected
lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and,
surprisingly, silicon dicarbide (SiC2). We identified 55 SiC2 transitions
involving energy levels between 300 and 900 K. By analysing these rotational
lines, we conclude that SiC2 is produced in the inner dust formation zone, with
an abundance of ~2x10^-7 relative to molecular hydrogen. These SiC2 lines have
been observed for the first time in space and have been used to derive an SiC2
rotational temperature of ~204 K and a source-averaged column density of
~6.4x10^15 cm^-2. Furthermore, the high quality of the HIFI data set was used
to improve the spectroscopic rotational constants of SiC2.Comment: A&A HIFI Special Issue, 201
CO line observations of OH/IR stars in the inner Galactic Bulge: Characteristics of stars at the tip of the AGB
12CO and 13CO lines, as well as a mm-wave continuum, have been observed for a
sample of 22 OH/IR stars in directions within 2 degrees of the Galactic Centre.
Photometry data have been gathered from the literature to construct SEDs and to
determine pulsational variability. Radiative transfer models have been used to
interpret the data. All stars in the sample were detected in at least one CO
line, and 8 objects were detected in 324 GHz continuum. Based on luminosity
criteria, the sample is divided into 17 objects that most likely lie within the
inner Galactic Bulge, and 5 objects that are most likely foreground objects.
The median luminosity of the inner-Galactic-Bulge objects, 5600 Lsun,
corresponds to an initial mass in the range 1.2-1.6 Msun, indicating that these
OH/IR stars descend from solar-type stars. The objects in this sub-sample are
further divided into two classes based on their SED characteristics: 11 objects
have SEDs that are well matched by models invoking dust envelopes extending
from a few stellar radii and outwards, while 6 objects are better modelled as
having detached dust envelopes with inner radii in the range 200-600 au and
warmer central stars. The former objects have periodic variability, while the
latter objects are predominantly non-periodic. The median gas-mass-loss rate,
gas terminal expansion velocity, gas-to-dust mass ratio, and circumstellar
12CO/13CO abundance ratio have been estimated to be 2x10{-5} Msun/yr, 18 km/s,
200 (excluding the sources with detached dust envelopes, which show markedly
lower gas-to-dust ratios), and 5, respectively, for the inner-Galactic-Bulge
objects. The inner-Galactic-Bulge OH/IR stars studied here constitute an
excellent sample of equidistant objects for the purpose of understanding the
evolution of the mass-loss-rate characteristics at the tip of the AGB.Comment: 32 pages, 17 figure
VLTI/PIONIER reveals the close environment of the evolved system HD101584
Context: The observed orbital characteristics of post-asymptotic giant branch
(post-AGB) and post-red giant branch (post-RGB) binaries are not understood. We
suspect that the missing ingredients to explain them probably lie in the
continuous interaction of the central binary with its circumstellar
environment. Aims: We aim at studying the circumbinary material in these
complex systems by investigating the connection between the innermost and
large-scale structures. Methods: We perform high-angular resolution
observations in the near-infrared continuum of HD101584, which has a complex
structure as seen at millimeter wavelengths with a disk-like morphology and a
bipolar outflow due to an episode of strong binary interaction. To account for
the complexity of the target we first perform an image reconstruction and use
this result to fit a geometrical model to extract the morphological and thermal
features of the environment. Results: The image reveals an unexpected
double-ring structure. We interpret the inner ring to be produced by emission
from dust located in the plane of the disk and the outer ring to be produced by
emission from dust that is located 1.6[D/1kpc] au above the disk plane. The
inner ring diameter (3.94[D/1kpc] au), and temperature (T=154010K) are
compatible with the dust sublimation front of the disk. The origin of the
out-of-plane ring (with a diameter of 7.39[D/1kpc] au and a temperature of
1014K) could be due to episodic ejection or a dust condensation front in
the outflow. Conclusion: The observed outer ring is possibly linked with the
blue-shifted side of the large scale outflow seen by ALMA and is tracing its
launching location to the central star. Such observations give morphological
constraints on the ejection mechanism. Additional observations are needed to
constrain the origin of the out-of-plane structure.Comment: Accepted to A&A. 14 pages, 13 figure
Non-cytotoxic 1,2,3-triazole tethered fused heterocyclic ring derivatives display Tax protein inhibition and impair HTLV-1 infected cells
Human T cell lymphotropic virus type 1 (HTLV-1) is a human retrovirus that infects approximately 10–20 million people worldwide and causes an aggressive neoplasia (adult T-cell leukemia/lymphoma - ATL). Therapeutic approaches for the treatment of ATL have variable effectiveness and poor prognosis, thus requiring strategies to identify novel compounds with activity on infected cells. In this sense, we initially screened a small series of 25 1,2,3-triazole derivatives to discover cell proliferation inhibitors and apoptosis inducers in HTLV-1-infected T-cell line (MT-2) for further assessment of their effect on viral tax activity through inducible-tax reporter cell line (Jurkat LTR-GFP). Eight promising compounds (02, 05, 06, 13, 15, 21, 22 and 25) with activity ≥70% were initially selected, based on a suitable cell-based assay using resazurin reduction method, and evaluated towards cell cycle, apoptosis and Tax/GFP expression analyses through flow cytometry. Compound 02 induced S phase cell cycle arrest and compounds 05, 06, 22 and 25 promoted apoptosis. Remarkably, compounds 22 and 25 also reduced GFP expression in an inducible-tax reporter cell, which suggests an effect on Tax viral protein. More importantly, compounds 02, 22 and 25 were not cytotoxic in human hepatoma cell line (Huh-7). Therefore, the discovery of 3 active and non-cytotoxic compounds against HTLV-1-infected cells can potentially contribute, as an initial promising strategy, to the development process of new drugs against ATL
Generation of Functional CLL-Specific Cord Blood CTL Using CD40-Ligated CLL APC
PMCID: PMC3526610This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
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