3,662 research outputs found
On the order of a non-abelian representation group of a slim dense near hexagon
We show that, if the representation group of a slim dense near hexagon
is non-abelian, then is of exponent 4 and ,
, where is the near polygon
embedding dimension of and is the dimension of the universal
representation module of . Further, if , then
is an extraspecial 2-group (Theorem 1.6)
Constantly Proving The Opposite? A test of CPTO using a broad time horizon and correcting for discounting
Purpose: An important assumption underlying the quality-adjusted life year (QALY) model is that people trade off life years against health in the same proportion irrespective of the number of remaining life years. This is known as the constant proportional trade-offs (CPTO) condition. Previous studies have produced mixed empirical evidence about the validity of CPTO. This paper is the first to test CPTO using the time trade-off (TTO) method for a broad time horizon. Methods: In a sample of 83 students, we use a choice based TTO protocol to elicit TTO scores for back pain, using ten different gauge durations ranging between 1 and 46 years. The TTO scores are corrected for discounting, which is elicited by means of the direct method. Results: We find average TTO scores varying between 0.72 and 0.81. Although the scores do not differ much for different durations in absolute terms, some differences are significant, rejecting CPTO, with and without correcting for discounting. No clear relationship between TTO scores and gauge duration is found. An anchoring and rounding heuristic to some extent explains our results. Conclusions: Our findings highlight the importance of elicitation methods and context dependencies in QALY measurement and warrant detailed investigation of their influence
Spin and Charge Structure of the Surface States in Topological Insulators
We investigate the spin and charge densities of surface states of the
three-dimensional topological insulator , starting from the continuum
description of the material [Zhang {\em et al.}, Nat. Phys. 5, 438 (2009)]. The
spin structure on surfaces other than the 111 surface has additional complexity
because of a misalignment of the contributions coming from the two sublattices
of the crystal. For these surfaces we expect new features to be seen in the
spin-resolved ARPES experiments, caused by a non-helical spin-polarization of
electrons at the individual sublattices as well as by the interference of the
electron waves emitted coherently from two sublattices. We also show that the
position of the Dirac crossing in spectrum of surface states depends on the
orientation of the interface. This leads to contact potentials and surface
charge redistribution at edges between different facets of the crystal.Comment: Use the correct spin operator. Changes affect the surface states spin
structure, but not the spectru
Effects of interaction on an adiabatic quantum electron pump
We study the effects of inter-electron interactions on the charge pumped
through an adiabatic quantum electron pump. The pumping is through a system of
barriers, whose heights are deformed adiabatically. (Weak) interaction effects
are introduced through a renormalisation group flow of the scattering matrices
and the pumped charge is shown to {\it always} approach a quantised value at
low temperatures or long length scales. The maximum value of the pumped charge
is set by the number of barriers and is given by . The
correlation between the transmission and the charge pumped is studied by seeing
how much of the transmission is enclosed by the pumping contour. The (integer)
value of the pumped charge at low temperatures is determined by the number of
transmission maxima enclosed by the pumping contour. The dissipation at finite
temperatures leading to the non-quantised values of the pumped charge scales as
a power law with the temperature (), or with
the system size (), where is a
measure of the interactions and vanishes at . For a double
barrier system, our result agrees with the quantisation of pumped charge seen
in Luttinger liquids.Comment: 9 pages, 9 figures, better quality figures available on request from
author
Mechanical design and control of a new myoelectric hand prosthesis
The development of modern, myoelectrically controlled hand prostheses can be difficult, due to the many requirements its mechanical design and control system need to fulfill [1]. The hand should be controllable with few input signals, while being able to perform a wide range of motions. It should be lightweight and slim, but be able to actuate all fingers separately. To accomplish this, new control and mechanical design techniques are implemented in a modern hand prosthesis prototype
Signatures of tilted and anisotropic Dirac and Weyl cones
We calculate conductance and noise for quantum transport at the nodal point
for arbitrarily tilted and anisotropic Dirac or Weyl cones. Tilted and
anisotropic dispersions are generic in the absence of certain discrete
symmetries, such as particle-hole and lattice point group symmetries. Whereas
anisotropy affects the conductance g, but leaves the Fano factor F (the ratio
of shot noise power and current) unchanged, a tilt affects both g and F. Since
F is a universal number in many other situations, this finding is remarkable.
We apply our general considerations to specific lattice models of strained
graphene and a pyrochlore Weyl semimetal
Near polygons and Fischer spaces
In this paper we exploit the relations between near polygons with lines of size 3 and Fischer spaces to classify near hexagons with quads and with lines of size three. We also construct some infinite families of near polygons
Fluctuations of g-factors in metal nanoparticles: Effects of electron-electron interaction and spin-orbit scattering
We investigate the combined effect of spin-orbit scattering and
electron-electron interactions on the probability distribution of -factors
of metal nanoparticles. Using random matrix theory, we find that even a
relatively small interaction strength %(ratio of exchange constant and mean
level %spacing \spacing ) significantly increases -factor
fluctuations for not-too-strong spin-orbit scattering (ratio of spin-orbit rate
and single-electron level spacing 1/\tau_{\rm so} \spacing \lesssim 1), and
leads to the possibility to observe -factors larger than two.Comment: RevTex, 2 figures inserte
The Finite Field Kakeya Problem
A Besicovitch set in AG(n,q) is a set of points containing a line in every
direction. The Kakeya problem is to determine the minimal size of such a set.
We solve the Kakeya problem in the plane, and substantially improve the known
bounds for n greater than 4.Comment: 13 page
Quantum mechanical time-delay matrix in chaotic scattering
We calculate the probability distribution of the matrix Q = -i \hbar S^{-1}
dS/dE for a chaotic system with scattering matrix S at energy E. The
eigenvalues \tau_j of Q are the so-called proper delay times, introduced by E.
P. Wigner and F. T. Smith to describe the time-dependence of a scattering
process. The distribution of the inverse delay times turns out to be given by
the Laguerre ensemble from random-matrix theory.Comment: 4 pages, RevTeX; to appear in Phys. Rev. Let
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