78,256 research outputs found
Shot noise in diffusive ferromagnetic metals
We show that shot noise in a diffusive ferromagnetic wire connected by tunnel
contacts to two ferromagnetic electrodes can probe the intrinsic density of
states and the extrinsic impurity scattering spin-polarization contributions in
the polarization of the wire conductivity. The effect is more pronounced when
the electrodes are perfectly polarized in opposite directions. While in this
case the shot noise has a weak dependence on the impurity scattering
polarization, it is strongly affected by the polarization of the density of
states. For a finite spin-flip scattering rate the shot noise increases well
above the normal state value and can reach the full Poissonian value when the
density of states tends to be perfectly polarized. For the parallel
configuration we find that the shot noise depends on the relative sign of the
intrinsic and the extrinsic polarizations.Comment: 4 pages, 3 figure
Critical loads for nutrient nitrogen for soil-vegetation systems
Members of the UK Critical Loads Advisory Group (CLAG) have calculated critical loads for nutrient nitrogen to produce maps for Great Britain. The results of three methods, based upon the conclusions from the Lokeberg workshop are described below. Two of these methods use the empirical approachand the other the steady state equation ("mass balance") for nitrogen saturation
Semirelativistic stability of N-boson systems bound by 1/r pair potentials
We analyze a system of self-gravitating identical bosons by means of a
semirelativistic Hamiltonian comprising the relativistic kinetic energies of
the involved particles and added (instantaneous) Newtonian gravitational pair
potentials. With the help of an improved lower bound to the bottom of the
spectrum of this Hamiltonian, we are able to enlarge the known region for
relativistic stability for such boson systems against gravitational collapse
and to sharpen the predictions for their maximum stable mass.Comment: 11 pages, considerably enlarged introduction and motivation,
remainder of the paper unchange
Semiclassical energy formulas for power-law and log potentials in quantum mechanics
We study a single particle which obeys non-relativistic quantum mechanics in
R^N and has Hamiltonian H = -Delta + V(r), where V(r) = sgn(q)r^q. If N \geq 2,
then q > -2, and if N = 1, then q > -1. The discrete eigenvalues E_{n\ell} may
be represented exactly by the semiclassical expression E_{n\ell}(q) =
min_{r>0}\{P_{n\ell}(q)^2/r^2+ V(r)}. The case q = 0 corresponds to V(r) =
ln(r). By writing one power as a smooth transformation of another, and using
envelope theory, it has earlier been proved that the P_{n\ell}(q) functions are
monotone increasing. Recent refinements to the comparison theorem of QM in
which comparison potentials can cross over, allow us to prove for n = 1 that
Q(q)=Z(q)P(q) is monotone increasing, even though the factor Z(q)=(1+q/N)^{1/q}
is monotone decreasing. Thus P(q) cannot increase too slowly. This result
yields some sharper estimates for power-potential eigenvlaues at the bottom of
each angular-momentum subspace.Comment: 20 pages, 5 figure
Quark mass effects in high energy neutrino nucleon scattering
We evaluate the neutrino nucleon charged current cross section at
next-to-leading order in quantum chromodynamic corrections in the variable
flavor number scheme and the fixed flavor number scheme, taking into account
quark masses. The number scheme dependence is largest at the highest energies
considered here, GeV, where the cross sections differ by
approximately 15 percent. We illustrate the numerical implications of the
inconsistent application of the fixed flavor number scheme.Comment: 8 pages, 8 figures, v2: updated pdfs, version accepted for
publicatio
Reply to Comment by Galapon on 'Almost-periodic time observables for bound quantum systems'
In a recent paper [1] (also at http://lanl.arxiv.org/abs/0803.3721), I made
several critical remarks on a 'Hermitian time operator' proposed by Galapon [2]
(also at http://lanl.arxiv.org/abs/quant-ph/0111061).
Galapon has correctly pointed out that remarks pertaining to 'denseness' of
the commutator domain are wrong [3]. However, the other remarks still apply,
and it is further noted that a given quantum system can be a member of this
domain only at a set of times of total measure zero.Comment: 3 page
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