528 research outputs found
Search for Oscillation of the Electron-Capture Decay Probability of Pm
We have searched for time modulation of the electron capture decay
probability of Pm in an attempt to confirm a recent claim from a group
at the Gesellschaft f\"{u}r Schwerionenforschung (GSI). We produced Pm
via the Sn(Na, 5n)Pm reaction at the Berkeley 88-Inch
Cyclotron with a bombardment time short compared to the reported modulation
period. Isotope selection by the Berkeley Gas-filled Separator is followed by
implantation and a long period of monitoring the Nd K x-rays
from the daughter. The decay time spectrum of the x-rays is well-described by a
simple exponential and the measured half-life of 40.68(53) seconds is
consistent with the accepted value. We observed no oscillatory modulation at
the proposed frequency at a level 31 times smaller than that reported by
Litvinov {\it et al.} (Phys. Lett. B 664 (2008) 162; arXiv:0801.2079
[nucl-ex]). A literature search for previous experiments that might have been
sensitive to the reported modulation uncovered another example in Eu
electron-capture decay. A reanalysis of the published data shows no oscillatory
behavior.Comment: 12 pages (double-spaced), 6 figure
Random Exchange Disorder in the Spin-1/2 XXZ Chain
The one-dimensional XXZ model is studied in the presence of disorder in the
Heisenberg Exchange Integral. Recent predictions obtained from renormalization
group calculations are investigated numerically using a Lanczos algorithm on
chains of up to 18 sites. It is found that in the presence of strong
X-Y-symmetric random exchange couplings, a ``random singlet'' phase with
quasi-long-range order in the spin-spin correlations persists. As the planar
anisotropy is varied, the full zero-temperature phase diagram is obtained and
compared with predictions of Doty and Fisher [Phys. Rev. B {\bf 45 }, 2167
(1992)].Comment: 9 pages + 8 plots appended, RevTex, FSU-SCRI-93-98 and
ORNL/CCIP/93/1
Transport Properties of the Quark-Gluon Plasma -- A Lattice QCD Perspective
Transport properties of a thermal medium determine how its conserved charge
densities (for instance the electric charge, energy or momentum) evolve as a
function of time and eventually relax back to their equilibrium values. Here
the transport properties of the quark-gluon plasma are reviewed from a
theoretical perspective. The latter play a key role in the description of
heavy-ion collisions, and are an important ingredient in constraining particle
production processes in the early universe. We place particular emphasis on
lattice QCD calculations of conserved current correlators. These Euclidean
correlators are related by an integral transform to spectral functions, whose
small-frequency form determines the transport properties via Kubo formulae. The
universal hydrodynamic predictions for the small-frequency pole structure of
spectral functions are summarized. The viability of a quasiparticle description
implies the presence of additional characteristic features in the spectral
functions. These features are in stark contrast with the functional form that
is found in strongly coupled plasmas via the gauge/gravity duality. A central
goal is therefore to determine which of these dynamical regimes the quark-gluon
plasma is qualitatively closer to as a function of temperature. We review the
analysis of lattice correlators in relation to transport properties, and
tentatively estimate what computational effort is required to make decisive
progress in this field.Comment: 54 pages, 37 figures, review written for EPJA and APPN; one parag.
added end of section 3.4, and one at the end of section 3.2.2; some Refs.
added, and some other minor change
Optimal inference with suboptimal models:Addiction and active Bayesian inference
When casting behaviour as active (Bayesian) inference, optimal inference is defined with respect to an agent's beliefs - based on its generative model of the world. This contrasts with normative accounts of choice behaviour, in which optimal actions are considered in relation to the true structure of the environment - as opposed to the agent's beliefs about worldly states (or the task). This distinction shifts an understanding of suboptimal or pathological behaviour away from aberrant inference as such, to understanding the prior beliefs of a subject that cause them to behave less 'optimally' than our prior beliefs suggest they should behave. Put simply, suboptimal or pathological behaviour does not speak against understanding behaviour in terms of (Bayes optimal) inference, but rather calls for a more refined understanding of the subject's generative model upon which their (optimal) Bayesian inference is based. Here, we discuss this fundamental distinction and its implications for understanding optimality, bounded rationality and pathological (choice) behaviour. We illustrate our argument using addictive choice behaviour in a recently described 'limited offer' task. Our simulations of pathological choices and addictive behaviour also generate some clear hypotheses, which we hope to pursue in ongoing empirical work
Single Spin Measurement using Single Electron Transistors to Probe Two Electron Systems
We present a method for measuring single spins embedded in a solid by probing
two electron systems with a single electron transistor (SET). Restrictions
imposed by the Pauli Principle on allowed two electron states mean that the
spin state of such systems has a profound impact on the orbital states
(positions) of the electrons, a parameter which SET's are extremely well suited
to measure. We focus on a particular system capable of being fabricated with
current technology: a Te double donor in Si adjacent to a Si/SiO2 interface and
lying directly beneath the SET island electrode, and we outline a measurement
strategy capable of resolving single electron and nuclear spins in this system.
We discuss the limitations of the measurement imposed by spin scattering
arising from fluctuations emanating from the SET and from lattice phonons. We
conclude that measurement of single spins, a necessary requirement for several
proposed quantum computer architectures, is feasible in Si using this strategy.Comment: 22 Pages, 8 Figures; revised version contains updated references and
small textual changes. Submitted to Phys. Rev.
Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV
We report the results of a study of color coherence effects in ppbar
collisions based on data collected by the D0 detector during the 1994-1995 run
of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8
TeV. Initial-to-final state color interference effects are studied by examining
particle distribution patterns in events with a W boson and at least one jet.
The data are compared to Monte Carlo simulations with different color coherence
implementations and to an analytic modified-leading-logarithm perturbative
calculation based on the local parton-hadron duality hypothesis.Comment: 13 pages, 6 figures. Submitted to Physics Letters
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
A shooting algorithm for problems with singular arcs
In this article we propose a shooting algorithm for a class of optimal
control problems for which all control variables appear linearly. The shooting
system has, in the general case, more equations than unknowns and the
Gauss-Newton method is used to compute a zero of the shooting function. This
shooting algorithm is locally quadratically convergent if the derivative of the
shooting function is one-to-one at the solution. The main result of this paper
is to show that the latter holds whenever a sufficient condition for weak
optimality is satisfied. We note that this condition is very close to a second
order necessary condition. For the case when the shooting system can be reduced
to one having the same number of unknowns and equations (square system) we
prove that the mentioned sufficient condition guarantees the stability of the
optimal solution under small perturbations and the invertibility of the
Jacobian matrix of the shooting function associated to the perturbed problem.
We present numerical tests that validate our method.Comment: No. RR-7763 (2011); Journal of Optimization, Theory and Applications,
published as 'Online first', January 201
The Influence of Dormitory Architecture On Resident Behavior
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66943/2/10.1177_001391657300500402.pd
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