216 research outputs found
Extension of the operational lifetime of the proportional chambers in the HERMES spectrometer
Abstract The experience of the extension of the proportional chambers lifetime at the HERMES (DESY) experiment is presented. A non-invasive technique against the aging process while continuously operating the detectors in the gap of the HERMES spectrometer magnet was performed. It was found that adding 0.14% water to the 65%Ar+30%CO2+5%CF4 gas mixture perfectly cancelled the appearance of self-sustained current (Malter effect). The studies of the remedy for the lifetime extension were performed with the test prototypes of the original proportional chambers. For the complete recovery of the aged test proportional chambers a special training method was developed as well. Training of the aged proportional chamber at 80%CF4+20%CO2 mixture glow discharge with reversed high voltage demonstrated a complete recovery of the detector
On partial derivatives of multivariate Bernstein polynomials
It is shown that Bernstein polynomials for a multivariate function converge to this function along with partial derivatives provided that the latter derivatives exist and are continuous. This result may be useful in some issues of stochastic calculus
Microwave-induced pi-junction transition in a superconductor / quantum-dot / superconductor structure
Using the nonequilibrium Green function, we show that microwave irradiation
can reverse the supercurrent flowing through a superconductor / quantum-dot /
superconductor structure. In contrast with the conventional sideband effect in
normal-metal / quantum-dot / normal-metal junctions, the photon-assisted
structures appear near ,
where is the resonant energy level of the quantum dot and is
the frequency of microwave field. Each photon-assisted structure is composed of
a negative and a positive peak, with an abrupt jump from the negative peak to
the positive peak around . The
microwave-induced -junction transition is interpreted in the picture of
photon-assisted Andreev bound states, which are formed due to multiple
photon-assisted Andreev reflection between the two superconductors. Moreover,
the main resonance located at can also be reversed with proper
microwave strength and frequency.Comment: 10 pagres, 3 figure
Domain wall effects in ferromagnet-superconductor structures
We investigate how domain structure of the ferromagnet in
superconductor-ferromagnet heterostructures may change their transport
properties. We calculate the distribution of current in the superconductor
induced by magnetic field of Bloch domain walls, find the ``lower critical''
magnetization of the ferromagnet that provides vortices in the superconductor
DETERMINATION OF THE ELECTRIC DRIVE POWER FOR LIGHTLY ARMORED CATERPILLAR AND WHEELED VEHICLES USING SINGLE- OR TWO-STAGE MECHANICAL GEARBOXES
When designing electromechanical transmissions (EMT) for lightly armored caterpillar and wheeled vehicles (LACWV), there is often a problem that the coefficient of adaptability of the traction motor (TM) at the minimum design power is not sufficient to meet the requirements for the power range of the transmission. In the literature, several ways have been worked out to solve this problem, however, there was not found a single algorithm allowing to formalize and step by step pass the process of choosing the most rational structure of the EMT. The purposeof the proposed work is the formation of scientifically based methodology for evaluating the possibility of using single-stage gearboxes in EMT for LACWV and calculation of the required TM power of the selected type for single- or two-stage mechanical gearboxes. Methodology. To carry out the research, the theory of motion of caterpillar and wheeled vehicles was used. Result. A formalized methodology for determining the required mechanical power of the electric drive for the LACWV is proposed, depending on the power capabilities of the motor-generator set, the torque characteristics of the selected TM and the number of stages in the mechanical gearboxes. Scientific novelty. For the first time, a formalized connection has been established between the tactical and technical requirements for LACWV, the characteristics of the selected TM, the structure and parameters of the mechanical gearboxes. Practical value. The toolkit for the engineering and design personnel developing the EMT for the LACWV was obtained. Work with the algorithm is illustrated by the example of power selection and gear ratios of mechanical gearboxes for the multi-purpose lightly armored caterpillar tractor MT-LB
Josephson currents through spin-active interfaces
The Josephson coupling of two isotropic s-wave superconductors through a
small, magnetically active junction is studied. This is done as a function of
junction transparency and of the degree of spin-mixing occurring in the
barrier. In the tunneling limit, the critical current shows an anomalous 1/T
temperature dependence at low temperatures and for certain magnetic
realizations of the junction. The behavior of the Josephson current is governed
by Andreev bound states appearing within the superconducting gap and the
position of these states in energy is tunable with the magnetic properties of
the barrier. This study is done using the equilibrium part of the
quasiclassical Zaitsev-Millis-Rainer-Sauls boundary condition for spin-active
interfaces and a general solution of the boundary condition is found. This
solution is a generalization of the one recently presented by Eschrig [M.
Eschrig, Phys. Rev B 61, 9061 (2000)] for spin-conserving interfaces and allows
an effective treatment of the problem of a superconductor in proximity to a
magnetically active material.Comment: 8 pages + 3 eps figure
Spontaneous Spin Polarized Currents in Superconductor-Ferromagnetic Metal Heterostructures
We study a simple microscopic model for thin, ferromagnetic, metallic layers
on semi-infinite bulk superconductor. We find that for certain values of the
exchange spliting, on the ferromagnetic side, the ground states of such
structures feature spontaneously induced spin polarized currents. Using a
mean-field theory, which is selfconsistent with respect to the pairing
amplitude , spin polarization and the spontaneous current
, we show that not only there are Andreev bound states in the
ferromagnet but when their energies are near zero they support
spontaneous currents parallel to the ferromagnetic-superconducting interface.
Moreover, we demonstrate that the spin-polarization of these currents depends
sensitively on the band filling.Comment: 4 pages, 5 Postscript figures (included
Beam-helicity asymmetries for single-hadron production in semi-inclusive deep-inelastic scattering from unpolarized hydrogen and deuterium targets
A measurement of beam-helicity asymmetries for single-hadron production in
deep-inelastic scattering is presented. Data from the scattering of 27.6 GeV
electrons and positrons off gaseous hydrogen and deuterium targets were
collected by the HERMES experiment. The asymmetries are presented separately as
a function of the Bjorken scaling variable, the hadron transverse momentum, and
the fractional energy for charged pions and kaons as well as for protons and
anti-protons. These asymmetries are also presented as a function of the three
aforementioned kinematic variables simultaneously
Dynamics of gravity driven three-dimensional thin films on hydrophilic-hydrophobic patterned substrates
We investigate numerically the dynamics of unstable gravity driven
three-dimensional thin liquid films on hydrophilic-hydrophobic patterned
substrates of longitudinal stripes and checkerboard arrangements. The thin film
can be guided preferentially on hydrophilic longitudinal stripes, while fingers
develop on adjacent hydrophobic stripes if their width is large enough. On
checkerboard patterns, the film fingering occurs on hydrophobic domains, while
lateral spreading is favoured on hydrophilic domains, providing a mechanism to
tune the growth rate of the film. By means of kinematical arguments, we
quantitatively predict the growth rate of the contact line on checkerboard
arrangements, providing a first step towards potential techniques that control
thin film growth in experimental setups.Comment: 30 pages, 12 figure
Longitudinal double-spin asymmetries in semi-inclusive deep-inelastic scattering of electrons and positrons by protons and deuterons
A comprehensive collection of results on longitudinal double-spin asymmetries is presented for charged pions and kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons on the proton and deuteron, based on the full HERMES data set. The dependence of the asymmetries on hadron transverse momentum and azimuthal angle extends the sensitivity to the flavor structure of the nucleon beyond the distribution functions accessible in the collinear framework. No strong dependence on those variables is observed. In addition, the hadron charge-difference asymmetry is presented, which under certain model assumptions provides access to the helicity distributions of valence quarks
- …