2,920 research outputs found
Coulomb blockade and transport in a chain of one-dimensional quantum dots
A long one-dimensional wire with a finite density of strong random impurities
is modelled as a chain of weakly coupled quantum dots. At low temperature T and
applied voltage V its resistance is limited by "breaks": randomly occuring
clusters of quantum dots with a special length distribution pattern that
inhibits the transport. Due to the interplay of interaction and disorder
effects the resistance can exhibit T and V dependences that can be approximated
by power laws. The corresponding two exponents differ greatly from each other
and depend not only on the intrinsic electronic parameters but also on the
impurity distribution statistics.Comment: 4 pages, 1 figure. Changes from v2: Dropped discussion of the
high-field regime. Added discussion of mesoscopic fluctuations and multiple
channels in the quasi-1D case. Improved presentation styl
Quantum creep and variable range hopping of one-dimensional interacting electrons
The variable range hopping results for noninteracting electrons of Mott and
Shklovskii are generalized to 1D disordered charge density waves and Luttinger
liquids using an instanton approach. Following a recent paper by Nattermann,
Giamarchi and Le Doussal [Phys. Rev. Lett. {\bf 91}, 56603 (2003)] we calculate
the quantum creep of charges at zero temperature and the linear conductivity at
finite temperatures for these systems. The hopping conductivity for the short
range interacting electrons acquires the same form as for noninteracting
particles if the one-particle density of states is replaced by the
compressibility. In the present paper we extend the calculation to dissipative
systems and give a discussion of the physics after the particles materialize
behind the tunneling barrier. It turns out that dissipation is crucial for
tunneling to happen. Contrary to pure systems the new metastable state does not
propagate through the system but is restricted to a region of the size of the
tunneling region. This corresponds to the hopping of an integer number of
charges over a finite distance. A global current results only if tunneling
events fill the whole sample. We argue that rare events of extra low tunneling
probability are not relevant for realistic systems of finite length. Finally we
show that an additional Coulomb interaction only leads to small logarithmic
corrections.Comment: 15 pages, 3 figures; references adde
Validation and reproducibility of computerised cell-viability analysis of tissue slices
BACKGROUND: The identification of live cells using membrane integrity dyes has become a frequently used technique, especially with articular cartilage and chondrocytes in situ where tissue slices are used to assess cell recovery as a function of location. The development of a reproducible computerised method of cell evaluation would eliminate many variables associated with manual counting and significantly reduce the amount of time required to evaluate experimental results. METHODS: To validate a custom computerised counting program, intra-person and inter-person cell counts of nine human evaluators (three groups – unskilled, novice, and experienced) were compared with repeated pixel counts of the custom program on 15 digitised images (in triplicate) of chondrocytes in situ stained with fluorescent dyes. RESULTS: Results indicated increased reproducibility with increased experience within evaluators [Intraclass Correlation Coefficient (ICC) range = 0.67 (unskilled) to 0.99 (experienced)] and between evaluators [ICC = 0.47 (unskilled), 0.85 (novice), 0.93 (experienced)]. The computer program had perfect reproducibility (ICC = 1.0). There was a significant relationship between the average of the experienced evaluators results and the custom program results (ICC = 0.77). CONCLUSIONS: This study demonstrated that increased experience in cell counting resulted in increased reproducibility both within and between human evaluators but confirmed that the computer program was the most reproducible. There was a good correlation between the intact cell recovery determined by the computer program and the experienced human evaluators. The results of this study showed that the computer counting program was a reproducible tool to evaluate intact cell recovery after use of membrane integrity dyes on chondrocytes in situ. This and the significant decrease in the time used to count the cells by the computer program advocate its use in future studies because it has significant advantages
Characteristic properties of the microstructure and microtexture of medium-carbon steel subjected to sulfide stress cracking
Increasing the resistance of steel products to sulfide stress cracking (SSC) is one of the topical issues of the oil and gas industry. Among various factors determining the SSC resistance of a material is the structure-phase state of the material itself and the crystallographic texture associated with it. This paper analyzes these features using the scanning electron microscopy (SEM), transmission electron microscopy (TEM), and microroentgen electron backscattered diffraction (EBSD) techniques. As the research material, a production string (PS) coupling made of medium-carbon steel was selected, which collapsed by the mechanism of hydrogen embrittlement and subsequent SSC. For the first time, by the SEM method, using the location and mutual orientation of cementite (Fe3C) particles, at high magnifications, the authors demonstrated the possibilities of identifying the components of upper bainite, lower bainite, and tempered martensite in steels. The presence of the detected structural components of steel was confirmed by transmission electron microscopy (TEM). Using the EBSD method, the detailed studies of microtexture were conducted to identify the type and nature of the microcrack propagation. It is established that the processes of hydrogen embrittlement and subsequent SSC lead to the formation of {101} , {100} , {122} , {013} , {111} , {133} , {3 } grain orientations. It is shown that the strengthening of orientations of {001} , {100} , {112} , and {133} types worsens the SSC resistance of the material. Using the EBSD analysis method, the influence of coincident site lattice (CSL) grain boundaries on the nature of microcrack propagation is estimated. It is found that the Σ 3 CSL grain boundaries between the {122} and {111} , {012} , {100} plates of the upper bainite inhibit the microcrack development, and the Σ 13b, Σ 29a, and Σ 39a CSL grain boundaries, contribute to the accelerated propagation of microcracks. For comparative analysis, similar studies were carried out in an unbroken (original) coupling before operation
Dynamic Fluctuation Phenomena in Double Membrane Films
Dynamics of double membrane films is investigated in the long-wavelength
limit including the overdamped squeezing mode. We demonstrate that thermal
fluctuations essentially modify the character of the mode due to its nonlinear
coupling to the transversal shear hydrodynamic mode. The corresponding Green
function acquires as a function of the frequency a cut along the imaginary
semi-axis. Fluctuations lead to increasing the attenuation of the squeezing
mode it becomes larger than the `bare' value.Comment: 7 pages, Revte
A facility to Search for Hidden Particles (SHiP) at the CERN SPS
A new general purpose fixed target facility is proposed at the CERN SPS
accelerator which is aimed at exploring the domain of hidden particles and make
measurements with tau neutrinos. Hidden particles are predicted by a large
number of models beyond the Standard Model. The high intensity of the SPS
400~GeV beam allows probing a wide variety of models containing light
long-lived exotic particles with masses below (10)~GeV/c,
including very weakly interacting low-energy SUSY states. The experimental
programme of the proposed facility is capable of being extended in the future,
e.g. to include direct searches for Dark Matter and Lepton Flavour Violation.Comment: Technical Proposa
Capabilities of the GAMMA-400 gamma-ray telescope to detect gamma-ray bursts from lateral directions
The currently developing space-based gamma-ray telescope GAMMA-400 will
measure the gamma-ray and electrons + positrons fluxes using the main top-down
aperture in the energy range from ~20 MeV to several TeV in the highly elliptic
orbit (without shadowing the telescope by the Earth and outside the radiation
belts) continuously for a long time. The instrument will provide fundamentally
new data on discrete gamma-ray sources, gamma-ray bursts (GRBs), sources and
propagation of Galactic cosmic rays and signatures of dark matter due to its
unique angular and energy resolutions in the wide energy range. The gamma-ray
telescope consists of the anticoincidence system (AC), the converter-tracker
(C), the time-of-flight system (S1 and S2), the position-sensitive and
electromagnetic calorimeters (CC1 and CC2), the top and bottom scintillation
detectors of the calorimeter (S3 and S4) and lateral detectors of the
calorimeter (LD). In this paper, the capabilities of the GAMMA-400 gamma-ray
telescope to measure fluxes of GRBs from lateral directions of CC2 are analyzed
using Monte-Carlo simulations. The analysis is based on second-level trigger
construction using signals from S3, CC2, S4 and LD detectors. For checking the
numerical algorithm the data from space-based GBM and LAT instruments of the
Fermi experiment are used, namely, three long bursts: GRB 080916C, GRB 090902B,
GRB 090926A and one short burst GRB 090510A. The obtained results allow us to
conclude that from lateral directions the GAMMA-400 space-based gamma-ray
telescope will reliably measure the spectra of bright GRBs in the energy range
from ~10 to ~100 MeV with the effective area of about 0.13 m2 (for each of the
four sides of CC2) and total field of view of about 6 sr.Comment: 19 pages, 18 figures, the paper will be submitted to Advances in
Space Researc
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Precision measurement of violation in decays
The time-dependent asymmetry in decays is
measured using collision data, corresponding to an integrated luminosity
of fb, collected with the LHCb detector at centre-of-mass energies
of and TeV. In a sample of 96 000 decays, the
-violating phase is measured, as well as the decay widths
and of the light and heavy mass eigenstates of the
system. The values obtained are rad, ps, andps, where the first uncertainty is
statistical and the second systematic. These are the most precise single
measurements of those quantities to date. A combined analysis with decays gives rad. All
measurements are in agreement with the Standard Model predictions. For the
first time the phase is measured independently for each polarisation
state of the system and shows no evidence for polarisation
dependence.Comment: 6 figure
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