6,381 research outputs found
Comments on "Limits on possible new nucleon monopole-dipole interactions from the spin relaxation rate of polarized He gas"
In the article "Limits on possible new nucleon monopole-dipole interactions
from the spin relaxation rate of polarized He gas", new limits on
short-range, Axion-like interactions are presented. In this comment it is shown
that the theoretical treatement of the data overestimates the sensitivity of
the proposed method. We provide the corrected limits
Noise-induced vortex reversal of self-propelled particles
We report an interesting phenomenon of noise-induced vortex reversal in a
two-dimensional system of self-propelled particles (SPP) with soft-core
interactions. With the aid of forward flux sampling, we analyze the
configurations along the reversal pathway and thus identify the mechanism of
vortex reversal. We find that statistically the reversal exhibits a
hierarchical process: those particles at the periphery first change their
motion directions, and then more inner layers of particles reverse later on.
Furthermore, we calculate the dependence of the average reversal rate on noise
intensity and the number of SPP. We find that the rate decreases
exponentially with the reciprocal of . Interestingly, the rate varies
nonmonotonically with and a minimal rate exists for an intermediate value
of .Comment: 4 pages, 5 figure
Green-Function-Based Monte Carlo Method for Classical Fields Coupled to Fermions
Microscopic models of classical degrees of freedom coupled to non-interacting
fermions occur in many different contexts. Prominent examples from solid state
physics are descriptions of colossal magnetoresistance manganites and diluted
magnetic semiconductors, or auxiliary field methods for correlated electron
systems. Monte Carlo simulations are vital for an understanding of such
systems, but notorious for requiring the solution of the fermion problem with
each change in the classical field configuration. We present an efficient,
truncation-free O(N) method on the basis of Chebyshev expanded local Green
functions, which allows us to simulate systems of unprecedented size N.Comment: 4 pages, 3 figure
Geometric phases in electric dipole searches with trapped spin-1/2 particles in general fields and measurement cells of arbitrary shape with smooth or rough walls
The important role of geometric phases in searches for a permanent electric
dipole moment of the neutron, using Ramsey separated oscillatory field nuclear
magnetic resonance, was first noted by Commins and investigated in detail by
Pendlebury et al. Their analysis was based on the Bloch equations. In
subsequent work using the spin density matrix Lamoreaux and Golub showed the
relation between the frequency shifts and the correlation functions of the
fields seen by trapped particles in general fields (Redfield theory). More
recently we presented a solution of the Schr\"odinger equation for spin-
particles in circular cylindrical traps with smooth walls and exposed to
arbitrary fields [Steyerl et al.] Here we extend this work to show how the
Redfield theory follows directly from the Schr\"odinger equation solution. This
serves to highlight the conditions of validity of the Redfield theory, a
subject of considerable discussion in the literature [e.g., Nicholas et al.]
Our results can be applied where the Redfield result no longer holds, such as
observation times on the order of or shorter than the correlation time and
non-stochastic systems and thus we can illustrate the transient spin dynamics,
i.e. the gradual development of the shift with increasing time subsequent to
the start of the free precession. We consider systems with rough, diffuse
reflecting walls, cylindrical trap geometry with arbitrary cross section, and
field perturbations that do not, in the frame of the moving particles, average
to zero in time. We show by direct, detailed, calculation the agreement of the
results from the Schr\"odinger equation with the Redfield theory for the cases
of a rectangular cell with specular walls and of a circular cell with diffuse
reflecting walls.Comment: 20 pages, 8 figure
Frequency shifts and relaxation rates for spin 1/2 particles moving in electromagnetic fields
We discuss the behaviour of the Larmor frequency shift and the longitudinal
relaxation rate due to non-uniform electromagnetic fields on an assembly of
spin 1/2 particles, in adiabatic and nonadiabatic regimes. We also show some
general relations between the various frequency shifts and between the
frequency shifts and relaxation rates. The remarkable feature of all our
results is that they were obtained without any specific assumptions on the
explicit form of the correlation functions of the fields. Hence, we expect that
our results are valid both for diffusive and ballistic regime of motion and
arbitrary cell shapes and surface scattering. These results can then be applied
to a wide variety of realistic systems
Pairwise entanglement and readout of atomic-ensemble and optical wave-packet modes in traveling-wave Raman interactions
We analyze quantum entanglement of Stokes light and atomic electronic
polarization excited during single-pass, linear-regime, stimulated Raman
scattering in terms of optical wave-packet modes and atomic-ensemble spatial
modes. The output of this process is confirmed to be decomposable into multiple
discrete, bosonic mode pairs, each pair undergoing independent evolution into a
two-mode squeezed state. For this we extend the Bloch-Messiah reduction
theorem, previously known for discrete linear systems (S. L. Braunstein, Phys.
Rev. A, vol. 71, 055801 (2005)). We present typical mode functions in the case
of one-dimensional scattering in an atomic vapor. We find that in the absence
of dispersion, one mode pair dominates the process, leading to a simple
interpretation of entanglement in this continuous-variable system. However,
many mode pairs are excited in the presence of dispersion-induced temporal
walkoff of the Stokes, as witnessed by the photon-count statistics. We also
consider the readout of the stored atomic polarization using the anti-Stokes
scattering process. We prove that the readout process can also be decomposed
into multiple mode pairs, each pair undergoing independent evolution analogous
to a beam-splitter transformation. We show that this process can have unit
efficiency under realistic experimental conditions. The shape of the output
light wave packet can be predicted. In case of unit readout efficiency it
contains only excitations originating from a specified atomic excitation mode
The Child is Father of the Man: Foresee the Success at the Early Stage
Understanding the dynamic mechanisms that drive the high-impact scientific
work (e.g., research papers, patents) is a long-debated research topic and has
many important implications, ranging from personal career development and
recruitment search, to the jurisdiction of research resources. Recent advances
in characterizing and modeling scientific success have made it possible to
forecast the long-term impact of scientific work, where data mining techniques,
supervised learning in particular, play an essential role. Despite much
progress, several key algorithmic challenges in relation to predicting
long-term scientific impact have largely remained open. In this paper, we
propose a joint predictive model to forecast the long-term scientific impact at
the early stage, which simultaneously addresses a number of these open
challenges, including the scholarly feature design, the non-linearity, the
domain-heterogeneity and dynamics. In particular, we formulate it as a
regularized optimization problem and propose effective and scalable algorithms
to solve it. We perform extensive empirical evaluations on large, real
scholarly data sets to validate the effectiveness and the efficiency of our
method.Comment: Correct some typos in our KDD pape
Rosetak Document 4: Rank Degeneracies and Least Square Problems
In this paper we shall be concerned with the following problem. Let A be an m x n matrix with m being greater than or equal to n, and suppose that A is near (in a sense to be made precise later) a matrix B whose rank is less than n. Can one find a set of linearly independent columns of A that span a good approximation to the column space of B? The solution of this problem is important in a number of applications. In this paper we shall be chiefly interested in the case where the columns of A represent factors or carriers in a linear model which is to be fit to a vector of observations b. In some such applications, where the elements of A can be specified exactly (e.g. the analysis of variance), the presence of rank degeneracy in A can be dealt with by explicit mathematical formulas and causes no essential difficulties. In other applications, however, the presence of degeneracy is not at all obvious, and the failure to detect it can result in meaningless results or even the catastrophic failure of the numerical algorithms being used to solve the problem. The organization of this paper is the following. In the next section we shall give a precise definition of approximate degeneracy in terms of the singular value decomposition of A. In Section 3 we shall show that under certain conditions there is associated with A a subspace that is insensitive to how it is approximated by various choices of the columns of A, and in Section 4 we shall apply this result to the solution of the least squares problem. Sections 5, 6, and 7 will be concerned with algorithms for selecting a basis for the stable subspace from among the columns of A.
Geometry of effective Hamiltonians
We give a complete geometrical description of the effective Hamiltonians
common in nuclear shell model calculations. By recasting the theory in a
manifestly geometric form, we reinterpret and clarify several points. Some of
these results are hitherto unknown or unpublished. In particular, commuting
observables and symmetries are discussed in detail. Simple and explicit proofs
are given, and numerical algorithms are proposed, that improve and stabilize
common methods used today.Comment: 1 figur
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