152,961 research outputs found
Geometry and the anomalous Hall effet in ferromagnets
The geometric ideas underlying the Berry phase and the modern viewpoint of
Karplus and Luttinger's theory of the anomalous Hall effect are discussed in an
elementary way. We briefly review recent Hall and Nernst experiments which
support the dominant role of the KL velocity term in ferromagnets.Comment: 6 pages, 4 figures, conference proceedings, tutorial revie
Single Chain Force Spectroscopy: Sequence Dependence
We study the elastic properties of a single A/B copolymer chain with a
specific sequence. We predict a rich structure in the force extension relations
which can be addressed to the sequence. The variational method is introduced to
probe local minima on the path of stretching and releasing. At given force, we
find multiple configurations which are separated by energy barriers. A
collapsed globular configuration consists of several domains which unravel
cooperatively. Upon stretching, unfolding path shows stepwise pattern
corresponding to the unfolding of each domain. While releasing, several cores
can be created simultaneously in the middle of the chain resulting in a
different path of collapse.Comment: 6 pages 3 figure
Relativistic Coulomb Green's function in -dimensions
Using the operator method, the Green's functions of the Dirac and
Klein-Gordon equations in the Coulomb potential are derived for
the arbitrary space dimensionality . Nonrelativistic and quasiclassical
asymptotics of these Green's functions are considered in detail.Comment: 9 page
State space collapse and diffusion approximation for a network operating under a fair bandwidth sharing policy
We consider a connection-level model of Internet congestion control,
introduced by Massouli\'{e} and Roberts [Telecommunication Systems 15 (2000)
185--201], that represents the randomly varying number of flows present in a
network. Here, bandwidth is shared fairly among elastic document transfers
according to a weighted -fair bandwidth sharing policy introduced by Mo
and Walrand [IEEE/ACM Transactions on Networking 8 (2000) 556--567] []. Assuming Poisson arrivals and exponentially distributed document
sizes, we focus on the heavy traffic regime in which the average load placed on
each resource is approximately equal to its capacity. A fluid model (or
functional law of large numbers approximation) for this stochastic model was
derived and analyzed in a prior work [Ann. Appl. Probab. 14 (2004) 1055--1083]
by two of the authors. Here, we use the long-time behavior of the solutions of
the fluid model established in that paper to derive a property called
multiplicative state space collapse, which, loosely speaking, shows that in
diffusion scale, the flow count process for the stochastic model can be
approximately recovered as a continuous lifting of the workload process.Comment: Published in at http://dx.doi.org/10.1214/08-AAP591 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Small-angle scattering and quasiclassical approximation beyond leading order
In the present paper we examine the accuracy of the quasiclassical approach
on the example of small-angle electron elastic scattering. Using the
quasiclassical approach, we derive the differential cross section and the
Sherman function for arbitrary localized potential at high energy. These
results are exact in the atomic charge number and correspond to the leading and
the next-to-leading high-energy small-angle asymptotics for the scattering
amplitude. Using the small-angle expansion of the exact amplitude of electron
elastic scattering in the Coulomb field, we derive the cross section and the
Sherman function with a relative accuracy and ,
respectively ( is the scattering angle). We show that the correction of
relative order to the cross section, as well as that of relative
order to the Sherman function, originates not only from the
contribution of large angular momenta , but also from that of . This means that, in general, it is not possible to go beyond the accuracy
of the next-to-leading quasiclassical approximation without taking into account
the non-quasiclassical terms.Comment: 12 pages, 3 figure
Strength Modeling Report
Strength modeling is a complex and multi-dimensional issue. There are numerous parameters to the problem of characterizing human strength, most notably: (1) position and orientation of body joints; (2) isometric versus dynamic strength; (3) effector force versus joint torque; (4) instantaneous versus steady force; (5) active force versus reactive force; (6) presence or absence of gravity; (7) body somatotype and composition; (8) body (segment) masses; (9) muscle group envolvement; (10) muscle size; (11) fatigue; and (12) practice (training) or familiarity. In surveying the available literature on strength measurement and modeling an attempt was made to examine as many of these parameters as possible. The conclusions reached at this point toward the feasibility of implementing computationally reasonable human strength models. The assessment of accuracy of any model against a specific individual, however, will probably not be possible on any realistic scale. Taken statistically, strength modeling may be an effective tool for general questions of task feasibility and strength requirements
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