2,963 research outputs found
Muon Pair Production by Electron-Photon Scatterings
The cross section for muon pair productions by electrons scattering over
photons, , is calculated analytically in the leading order. It is
pointed out that for the center-of-mass energy range, ,
the cross section for is less than b. The differential
energy spectrum for either of the resulting muons is given for the purpose of
high-energy neutrino astronomy. An implication of our result for a recent
suggestion concerning the high-energy cosmic neutrino generation through this
muon pair is discussed.Comment: a comment added, to appear in Phys. Rev. D, Rapid Communicatio
Effect of soil type on seismic demand
This paper investigates the validity of the soil considerations used in the determination of seismic demand as part of NZS1170.5, which currently specifies seismic design spectra corresponding to 5 different soil types. According to the current provisions stipulated in NZS1170.5, for all natural periods, the building demand for soft soil is either equal to or greater than that for hard soil. It is noted that this is opposite to the basic structural dynamics theory which suggests that an increase in stiffness of a system results in an increase in the acceleration response. In this pretext, a numerical parametric study is undertaken using a 1-D nonlinear site response analysis in order to capture the effect of soil characteristics on structural seismic demand and to scrutinize the validity of the current site specific seismic design spectra. It is identified that the level of input ground motion intensity and shear stiffness of the column (represented by its shear wave velocity, Vs) are the main parameters affecting the surface response. The study found some shortfalls in the way the current code defines seismic design demand, in particular the hierarchy of soil stiffness at low structural periods. It was found that stiff soils generally tend to have a higher spectral acceleration response in comparison to soft soils although this trend is less prominent for high intensity bed rock motions. It was also found that for medium to hard soil types the spectral acceleration response at short period is grossly underestimated by the current NZS1170.5 provisions. Based on the outcomes of the parametric numerical analyses, a revised strategy to determine seismic structural demand is proposed and demonstrated
Blow up criterion for compressible nematic liquid crystal flows in dimension three
In this paper, we consider the short time strong solution to a simplified
hydrodynamic flow modeling the compressible, nematic liquid crystal materials
in dimension three. We establish a criterion for possible breakdown of such
solutions at finite time in terms of the temporal integral of both the maximum
norm of the deformation tensor of velocity gradient and the square of maximum
norm of gradient of liquid crystal director field.Comment: 22 page
Gauged (2,2) Sigma Models and Generalized Kahler Geometry
We gauge the (2,2) supersymmetric non-linear sigma model whose target space
has bihermitian structure (g, B, J_{\pm}) with noncommuting complex structures.
The bihermitian geometry is realized by a sigma model which is written in terms
of (2,2) semi-chiral superfields. We discuss the moment map, from the
perspective of the gauged sigma model action and from the integrability
condition for a Hamiltonian vector field. We show that for a concrete example,
the SU(2) x U(1) WZNW model, as well as for the sigma models with almost
product structure, the moment map can be used together with the corresponding
Killing vector to form an element of T+T* which lies in the eigenbundle of the
generalized almost complex structure. Lastly, we discuss T-duality at the level
of a (2,2) sigma model involving semi-chiral superfields and present an
explicit example.Comment: 33 page
Fuzzy modeling and control for conical magnetic bearings using linear matrix inequality
A general nonlinear model with six degree-of-freedom rotor dynamics and electromagnetic force equations for conical magnetic bearings is developed. For simplicity, a T-S (Takagi Sugeno) fuzzy model for the nonlinear magnetic bearings assumed no rotor eccentricity is first derived, and a fuzzy control design based on the T-S fuzzy model is then proposed for the high speed and high accuracy control of the complex magnetic bearing systems. The suggested fuzzy control design approach for nonlinear magnetic bearings can be cast into a linear matrix inequality (LMI) problem via robust performance analysis, and the LMI problem can be solved efficiently using the convex optimization techniques. Computer simulations are presented for illustrating the performance of the control strategy considering simultaneous rotor rotation tracking and gap deviations regulation
Neural network force control for industrial robots
In this paper, we present a hierarchical force control framework consisting of a high level control system based on neural network and the existing motion control system of a manipulator in the low level. Inputs of the neural network are the contact force error and estimated stiffness of the contacted environment. The output of the neural network is the position command for the position controller of industrial robots. A MITSUBISHI MELFA RV-MI industrial robot equipped with a BL Force/Torque sensor is utilized for implementing the hierarchical neural network force control system. Successful experiments for various contact motions are carried out. Additionally, the proposed neural network force controller together with the master/slave control method are used in dual-industrial robot systems. Successful experiments an carried out for the dual-robot system handling an object
What Do We Know About the Strange Magnetic Radius?
We analyze the q^2-dependence of the strange magnetic form factor, \GMS(q^2),
using heavy baryon chiral perturbation theory (HBChPT) and dispersion
relations. We find that in HBChPT a significant cancellation occurs between the
O(p^2) and O(p^3) loop contributions. Consequently, the slope of \GMS at the
origin displays an enhanced sensitivity to an unknown O(p^3) low-energy
constant. Using dispersion theory, we estimate the magnitude of this constant,
show that it may have a natural size, and conclude that the low-q^2 behavior of
\GMS could be dominated by nonperturbative physics. We also discuss the
implications for the interpretation of parity-violating electron scattering
measurements used to measure \GMS(q^2).Comment: 9 pages, Revtex, 2 ps figure
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