226 research outputs found
A refined technique for the automated determination of friction losses in the toothing of multithreaded transmissions with differential mechanisms and planetary gears
Multithreaded transmissions, which using differential mechanisms for separating and summing up power flows, have been widely used in the transmissions of transport vehicles and special drives. The quality of such transmissions and the magnitude of frictional losses in the toothing significantly depend on the adopted kinematic scheme and the ratio of powers passing through the corresponding links of the differential mechanisms. With the existing automated analysis and synthesis of such transmissions, a matrix approach has recently been widely used. The proposed work provides a refined technique for the automated determination of friction losses in the toothing of multithreaded transmissions which containing differential mechanisms and planetary gears. It makes it possible to more accurately determine friction losses in the toothing and at the same time preserves the linear structure of the system of equations, which permit to continue using the matrix approach to analyze and synthesize such transmissions. Examples are given for the formation of equations systems describing the force interaction between the elements of the scheme for all variants of the links commutation of planetary rows operating as three-link differential mechanisms and planetary gears with one stopped link. The work is based on the analysis of existing methods for determining friction losses in the toothing and personal practical experience in the design and study of multithreaded stepped and stepless transmissions. The received results allow to apply the offered technique in the modern program complexes focused on the automated analysis and synthesis of multithread transmissions with use of the matrix approach. This makes it possible to significantly reduce the time to develop new multithreaded transmissions and increase their technical characteristics
Transitions between "" and "0" states in superconductor -- ferromagnet -- superconductor junctions
Experimental and theoretical study of superconductor (S) -- ferromagnet (F)
-- superconductor junctions showed that in certain range of parameters (e.g.,
the length of the ferromagnet , the exchange field, ) the
ground state of a SFS junction corresponds to superconducting phase difference
or 0. The phase diagram of a SFS junction with the respect to and 0
states is investigated in this letter in space. It is
shown that the phase diagram is very sensitive to the geometry of the system,
in particular, to the amount of disorder.Comment: Minor changes. References adde
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
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
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
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
Air entrainment through free-surface cusps
In many industrial processes, such as pouring a liquid or coating a rotating
cylinder, air bubbles are entrapped inside the liquid. We propose a novel
mechanism for this phenomenon, based on the instability of cusp singularities
that generically form on free surfaces. The air being drawn into the narrow
space inside the cusp destroys its stationary shape when the walls of the cusp
come too close. Instead, a sheet emanates from the cusp's tip, through which
air is entrained. Our analytical theory of this instability is confirmed by
experimental observation and quantitative comparison with numerical simulations
of the flow equations
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
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
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
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