780 research outputs found
Towards Continuous Nano-Plastic Monitoring in Water by High Frequency Impedance Measurement with Nano-Electrode Arrays
We explore the potentiality of high frequency impedance measurements with CMOS nano-electrode arrays for nano-plastic pollutant particles monitoring in water. This technology offers benefits as nano-scale resolution, high parallelization, scalability, label-free single particle detection, and automatic measurements without operator intervention. Simple models are proposed for size and concentration estimation. The former integrates measurements of adjacent electrodes and shows uncertainty comparable to the nominal one with mean prediction error lower than 45 % down to 50 nm radius. The latter accounts for noise in the definition of the sensing volume. We report a worst-case concentration error lower than a factor 1.7 under stationary and continuous flow, which demonstrates the potential of this technology for automated measurements
XMM-Newton Observation of the Black Hole Microquasar GRS 1758-258
The XMM-Newton X-ray observatory pointed the galactic black hole candidate
and microquasar GRS 1758-258 in September 2000 for about 10 ks during a program
devoted to the scan of the Galactic Center regions. Preliminary results from
EPIC MOS camera data are presented here. The data indicate that the source
underwent a state transition from its standard low-hard state to an
intermediate state. For the first time in this source the ultra-soft component
of the accretion disk, which black hole binaries display in intermediate or
high-soft states, was clearly detected and measured thanks to the high spectral
capabilities of XMM-Newton.Comment: To appear in the Proc. of the Gamma-Ray Astrophysics 2001 Symposium,
4-6 April 2001, Baltimore, Maryland, U.S.A.. American Institute of Physics
(AIP) series: 5 pages, 6 PS figures, latex, uses aipproc.cls aipproc.st
The X-ray spectrum of the bursting atoll source 4U~1728-34 observed with INTEGRAL
We present for the first time a study of the 3-200 keV broad band spectra of
the bursting atoll source 4U 1728-34 (GX 354-0) along its hardness intensity
diagram. The analysis was done using the INTEGRAL public and Galactic Center
deep exposure data ranging from February 2003 to October 2004. The spectra are
well described by a thermal Comptonization model with an electron temperature
from 35 keV to 3 keV and Thomson optical depth, tau_T, from 0.5 to 5 in a slab
geometry. The source undergoes a transition from an intermediate/hard to a soft
state where the source luminosity increases from 2 to 12% of Eddington. We have
also detected 36 type I X-ray bursts two of which show photospheric radius
expansion. The energetic bursts with photospheric radius expansion occurred at
an inferred low mass accretion rate per unit area of \dot m ~ 1.7x10E3 g/cm2/s,
while the others at a higher one between 2.4x10E3 - 9.4x10E3 g/cm2/s. For
4U1728-34 the bursts' total fluence, and the bursts' peak flux are
anti-correlated with the mass accretion rate. The type I X-ray bursts involve
pure helium burning either during the hard state, or during the soft state of
the source.Comment: 11 pages, 7 figures, and 2 tables. Accepted for publication in A&
Neutral and charged electron-hole complexes in artificial molecules: quantum transitions induced by the in-plane magnetic field
We theoretically investigate the properties of neutral and charged excitons and of the biexciton in vertically coupled quantum dots, as a function of the in-plane magnetic field B-parallel to. The main effect of the field consists in the suppression of the bonding-antibonding splitting, and in the resulting enhancement of the interdot correlations. As a consequence, the excitons form with the additional carrier a bound or an unbound complex depending on the sign of the charging, whereas the biexciton undergoes a transition between different quantum states with increasing B-parallel to. The discussed behaviors and transitions show up in the field dependence of experimentally accessible quantities, such as the charged-exciton and biexciton binding energies
Effect of electron-electron interaction on the phonon-mediated spin relaxation in quantum dots
We estimate the spin relaxation rate due to spin-orbit coupling and acoustic
phonon scattering in weakly-confined quantum dots with up to five interacting
electrons. The Full Configuration Interaction approach is used to account for
the inter-electron repulsion, and Rashba and Dresselhaus spin-orbit couplings
are exactly diagonalized. We show that electron-electron interaction strongly
affects spin-orbit admixture in the sample. Consequently, relaxation rates
strongly depend on the number of carriers confined in the dot. We identify the
mechanisms which may lead to improved spin stability in few electron (>2)
quantum dots as compared to the usual one and two electron devices. Finally, we
discuss recent experiments on triplet-singlet transitions in GaAs dots subject
to external magnetic fields. Our simulations are in good agreement with the
experimental findings, and support the interpretation of the observed spin
relaxation as being due to spin-orbit coupling assisted by acoustic phonon
emission.Comment: 12 pages, 10 figures. Revised version. Changes in section V
(simulation of PRL 98, 126601 experiment
Local Optical Spectroscopy in Quantum Confined Systems: A Theoretical Description
A theoretical description of local absorption is proposed in order to
investigate spectral variations on a length scale comparable with the extension
of the relevant quantum states. A general formulation is derived within the
density-matrix formalism including Coulomb correlation, and applied to the
prototypical case of coupled quantum wires. The results show that excitonic
effects may have a crucial impact on the local absorption with implications for
the spatial resolution and the interpretation of near-field optical spectra.Comment: To appear in Phys. Rev. Lett. - 11 pages, 3 PostScript figures (1
figure in colors) embedded. Uses RevTex, and psfig style
Full configuration interaction approach to the few-electron problem in artificial atoms
We present a new high-performance configuration interaction code optimally
designed for the calculation of the lowest energy eigenstates of a few
electrons in semiconductor quantum dots (also called artificial atoms) in the
strong interaction regime. The implementation relies on a single-particle
representation, but it is independent of the choice of the single-particle
basis and, therefore, of the details of the device and configuration of
external fields. Assuming no truncation of the Fock space of Slater
determinants generated from the chosen single-particle basis, the code may
tackle regimes where Coulomb interaction very effectively mixes many
determinants. Typical strongly correlated systems lead to very large
diagonalization problems; in our implementation, the secular equation is
reduced to its minimal rank by exploiting the symmetry of the effective-mass
interacting Hamiltonian, including square total spin. The resulting Hamiltonian
is diagonalized via parallel implementation of the Lanczos algorithm. The code
gives access to both wave functions and energies of first excited states.
Excellent code scalability in a parallel environment is demonstrated; accuracy
is tested for the case of up to eight electrons confined in a two-dimensional
harmonic trap as the density is progressively diluted and correlation becomes
dominant. Comparison with previous Quantum Monte Carlo simulations in the
Wigner regime demonstrates power and flexibility of the method.Comment: RevTeX 4.0, 18 pages, 6 tables, 9 postscript b/w figures. Final
version with new material. Section 6 on the excitation spectrum has been
added. Some material has been moved to two appendices, which appear in the
EPAPS web depository in the published versio
Simultaneous X-ray and Radio Monitoring of the Unusual Binary LSI+61 303: Measurements of the Lightcurve and High-Energy Spectrum
The binary system, LSI+61 303, is unusual both because of the dramatic,
periodic, radio outbursts, and because of its possible association with the 100
MeV gamma-ray source, 2CG135+01. We have performed simultaneous radio and Rossi
X-ray Timing Explorer X-ray observations at eleven intervals over the 26.5 day
orbit, and in addition searched for variability on timescales ranging from
milliseconds to hours. We confirm the modulation of the X-ray emission on
orbital timescales originally reported by Taylor et al. (1996), and in addition
we find a significant offset between the peak of the X-ray and radio flux. We
argue that based on these results, the most likely X-ray emission mechanism is
inverse Compton scattering of stellar photons off of electrons accelerated at
the shock boundary between the relativistic wind of a young pulsar and the Be
star wind. In these observations we also detected 2 -- 150 keV flux from the
nearby low-redshift quasar QSO~0241+622. Comparing these measurements to
previous hard X-ray and gamma-ray observations of the region containing both
LSI+61 303 and QSO~0241+622, it is clear that emission from the QSO dominates.Comment: 23 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
A simple method for the preliminary analysis and benchmarking of automotive LiDARs in fog
The vast multitude of LiDAR systems currently available on the market makes the need for methods to compare their performances increasingly high. In this study, we focus our attention on the development of a method for the analysis of the effects induced by the fog, one of the main challenges for Advanced Driver Assist Systems (ADASs) and autonomous driving. Large experimental setups capable of reconstructing adverse weather conditions on a large scale in a controlled and repeatable way are certainly the best test conditions to analyze and compare LiDARs performances in the fog. Nonetheless, such large plants are extremely expensive and complex, therefore only available in a few sites in the world. In this study, we thus propose a measurement method, a data analysis procedure and, an experimental setup that are extremely simple and inexpensive to implement. The achievable results are reasonably less accurate than those obtainable with large plants. Nevertheless, the proposed method can allow to easily and quickly obtain a preliminary estimate of the performance in the presence of fog and a rapid benchmarking of different LiDAR systems
A comparison between the effects of over-expression of miRNA-16 and miRNA-34a on cell cycle progression of mesothelioma cell lines and on their cisplatin sensitivity
The prognosis of patients affected by malignant pleural mesothelioma (MPM) is presently poor and no therapeutic strategies have improved their survival yet. Introduction of miRNA mimics to restore their reduced or absent functionality in cancer cells is considered an important opportunity and a combination of miR's might be even more effective. In the present study, miR-16 and miR-34a were transfected, singularly and in combination, in MPM cell lines H2052 and H28, and their effects on cell proliferation and sensitivity to cisplatin are reported. Interestingly, the overexpression of both miRs, alone or combined, slows down the cell cycle progression, modulates the p53 and HMGB1 expression and increases the sensitivity of cells to cisplatin, producing a marked impairment of cell proliferation and strengthening the apoptotic effect of the drug. However, the co-overexpression of the two miRs results more effective only in the regulation of the cell cycle, but does not enhance the sensitivity of MPM cells to cisplatin. Consequently, although the potential of miR-16 and miR-34a is confirmed, we must conclude that their combination does not improve the response of MPM to chemotherapy
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