2,175 research outputs found
Density Matrix Perturbation Theory
An expansion method for perturbation of the zero temperature grand canonical
density matrix is introduced. The method achieves quadratically convergent
recursions that yield the response of the zero temperature density matrix upon
variation of the Hamiltonian. The technique allows treatment of embedded
quantum subsystems with a computational cost scaling linearly with the size of
the perturbed region, O(N_pert.), and as O(1) with the total system size. It
also allows direct computation of the density matrix response functions to any
order with linear scaling effort. Energy expressions to 4th order based on only
first and second order density matrix response are given.Comment: 4 pages, 2 figure
Test beam Characterizations of 3D Silicon Pixel detectors
3D silicon detectors are characterized by cylindrical electrodes
perpendicular to the surface and penetrating into the bulk material in contrast
to standard Si detectors with planar electrodes on its top and bottom. This
geometry renders them particularly interesting to be used in environments where
standard silicon detectors have limitations, such as for example the radiation
environment expected in an LHC upgrade. For the first time, several 3D sensors
were assembled as hybrid pixel detectors using the ATLAS-pixel front-end chip
and readout electronics. Devices with different electrode configurations have
been characterized in a 100 GeV pion beam at the CERN SPS. Here we report
results on unirradiated devices with three 3D electrodes per 50 x 400 um2 pixel
area. Full charge collection is obtained already with comparatively low bias
voltages around 10 V. Spatial resolution with binary readout is obtained as
expected from the cell dimensions. Efficiencies of 95.9% +- 0.1 % for tracks
parallel to the electrodes and of 99.9% +- 0.1 % at 15 degrees are measured.
The homogeneity of the efficiency over the pixel area and charge sharing are
characterized.Comment: 5 pages, 7 figure
Parallel suppression of superconductivity and Fe moment in the collapsed tetragonal phase of Ca0.67Sr0.33Fe2As2 under pressure
Using non-resonant Fe K-beta x-ray emission spectroscopy, we reveal that
Sr-doping of CaFe2As2 decouples the Fe moment from the volume collapse
transition, yielding a collapsed-tetragonal, paramagnetic normal state out of
which superconductivity develops. X-ray diffraction measurements implicate the
c-axis lattice parameter as the controlling criterion for the Fe moment,
promoting a generic description for the appearance of pressure-induced
superconductivity in the alkaline-earth-based 122 ferropnictides (AFe2As2). The
evolution of the superconducting critical temperature with pressure lends
support to theories for superconductivity involving unconventional pairing
mediated by magnetic fluctuations
Testing the Gaussianity of the COBE-DMR data with spherical wavelets
We investigate the Gaussianity of the 4-year COBE-DMR data (in HEALPix
pixelisation) using an analysis based on spherical Haar wavelets. We use all
the pixels lying outside the Galactic cut and compute the skewness, kurtosis
and scale-scale correlation spectra for the wavelet coefficients at each scale.
We also take into account the sensitivity of the method to the orientation of
the input signal. We find a detection of non-Gaussianity at per cent
level in just one of our statistics. Taking into account the total number of
statistics computed, we estimate that the probability of obtaining such a
detection by chance for an underlying Gaussian field is 0.69. Therefore, we
conclude that the spherical wavelet technique shows no strong evidence of
non-Gaussianity in the COBE-DMR data.Comment: latex file 7 pages, 6 figures, submitted to MNRA
Effects of fluoroquinolones and tetracyclines on mitochondria of human retinal MIO-M1 cells
Our goal was to explore the detrimental impacts of ciprofloxacin (CPFX) and tetracycline (TETRA) on human retinal Müller (MIO-M1) cells in vitro. Cells were exposed to 30, 60 and 120 μg/ml of CPFX and TETRA. The cellular metabolism was measured with the MTT assay. The JC-1 and CM-H2DCFDA assays were used to evaluate the levels of mitochondrial membrane potential (MMP) and ROS (reactive oxygen species), respectively. Mitochondrial DNA (mtDNA) copy number, along with gene expression levels associated with apoptotic (BAX, BCL2-L13, BCL2, CASP-3 and CASP-9), inflammatory (IL-6, IL-1β, TGF-α, TGF-β1 and TGF-β2) and antioxidant pathways (SOD2, SOD3, GPX3 and NOX4) were analyzed via Quantitative Real-Time PCR (qRT-PCR). Bioenergetic profiles were measured using the Seahorse® XF Flux Analyzer. Cells exposed 24 h to 120 μg/ml TETRA demonstrated higher cellular metabolism compared to vehicle-treated cells. At each time points, (i) all TETRA concentrations reduced MMP levels and (ii) ROS levels were reduced by TETRA 120 μg/ml treatment. TETRA caused (i) higher expression of CASP-3, CASP-9, TGF-α, IL-1B, GPX3 and SOD3 but (ii) decreased levels of TGF-B2 and SOD2. ATP production and spare respiratory capacity declined with TETRA treatment. Cellular metabolism was reduced with CPFX 120 μg/ml in all cultures and 60 μg/ml after 72 h. The CPFX 120 μg/ml reduced MMP in all cultures and ROS levels (72 h). CPFX treatment (i) increased expression of CASP-3, CASP-9, and BCL2-L13, (ii) elevated the basal oxygen consumption rate, and (iii) lowered the mtDNA copy numbers and expression levels of TGF-B2, IL-6 and IL-1B compared to vehicle-control cells. We conclude that clinically relevant dosages of bactericidal and bacteriostatic antibiotics can have negative effects on the cellular metabolism and mitochondrial membrane potential of the retinal MIO-M1 cells in vitro. It is noteworthy to mention that apoptotic and inflammatory pathways in exposed cells were affected significantly This is the first study showing the negative impact of fluoroquinolones and tetracyclines on mitochondrial behavior of human retinal MIO-M1 cells
Characterization of proton irradiated 3D-DDTC pixel sensor prototypes fabricated at FBK
In this paper we discuss results relevant to 3D Double-Side Double Type
Column (3D-DDTC) pixel sensors fabricated at FBK (Trento, Italy) and oriented
to the ATLAS upgrade. Some assemblies of these sensors featuring different
columnar electrode configurations (2, 3, or 4 columns per pixel) and coupled to
the ATLAS FEI3 read-out chip were irradiated up to large proton fluences and
tested in laboratory with radioactive sources. In spite of the non optimized
columnar electrode overlap, sensors exhibit reasonably good charge collection
properties up to an irradiation fluence of 2 x 10**15 neq/cm2, while requiring
bias voltages in the order of 100 V. Sensor operation is further investigated
by means of TCAD simulations which can effectively explain the basic mechanisms
responsible for charge loss after irradiation.Comment: Preprint submitted to Nuclear Instruments and Methods A, 11 pages, 13
fig
The Molecule-Rich Tail of the Peculiar Galaxy NGC 2782 (Arp 215)
We present the first detection of a large quantity of molecular gas in the
extended tail of an interacting galaxy. Using the NRAO 12m telescope, we have
detected CO (1 - 0) at five locations in the eastern tail of the peculiar
starburst galaxy NGC 2782. The CO velocities and narrow (FWHM = 50 km/s) line
widths in these positions agree with those seen in HI, confirming that the
molecular gas is indeed associated with the tail rather than the main disk. As
noted previously, the gas in this tail has an apparent `counter-rotation'
compared to gas in the core of the galaxy, probably because the tails do not
lie in the same plane as the disk. Assuming the standard Galactic conversion
N(H2)/I(CO) factor, these observations indicate a total molecular gas mass of 6
X 10**8 M(sun) in this tail. This may be an underestimate of the total H2 mass
if the gas is metal-poor. This molecular gas mass, and the implied H2/HI mass
ratio of 0.6, are higher than that found in many dwarf irregular galaxies.
Comparison with an available H-alpha map of this galaxy, however, shows that
the rate of star formation in this feature is extremely low relative to the
available molecular gas, compared to L(H-alpha)/M(H2) values for both spiral
and irregular galaxies. Thus the timescale for depletion of the gas in this
feature is very long.Comment: 19 pages, 6 figures, Latex. To appear in the Astronomical Journa
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