8,017 research outputs found
Charmonium Suppression by Comover Scattering in Pb+Pb Collisions
The first reports of and production from experiment NA50 at
the CERN SPS are compared to predictions based on a hadronic model of
charmonium suppression. Data on centrality dependence and total cross sections
are in good accord with these predictions.Comment: 9 pages, latex, 6 figures, epsf, figure added and text modified to
clarify result
Discovering baryon-number violating neutralino decays at the LHC.
Recently there has been much interest in the use of single-jet mass and jet substructure to identify boosted particles decaying hadronically at the LHC. We develop these ideas to address the challenging case of a neutralino decaying to three quarks in models with baryonic violation of R parity. These decays have previously been found to be swamped by QCD backgrounds. We demonstrate for the first time that such a decay might be observed directly at the LHC with high significance, by exploiting characteristics of the scales at which its composite jet breaks up into subjets
Negative Grid Valves and Their Circuits for Decimetre Waves
Abstract Not Provided
Near-optimal protocols in complex nonequilibrium transformations
The development of sophisticated experimental means to control nanoscale
systems has motivated efforts to design driving protocols which minimize the
energy dissipated to the environment. Computational models are a crucial tool
in this practical challenge. We describe a general method for sampling an
ensemble of finite-time, nonequilibrium protocols biased towards a low average
dissipation. We show that this scheme can be carried out very efficiently in
several limiting cases. As an application, we sample the ensemble of
low-dissipation protocols that invert the magnetization of a 2D Ising model and
explore how the diversity of the protocols varies in response to constraints on
the average dissipation. In this example, we find that there is a large set of
protocols with average dissipation close to the optimal value, which we argue
is a general phenomenon.Comment: 6 pages and 3 figures plus 4 pages and 5 figures of supplemental
materia
Measuring thermodynamic length
Thermodynamic length is a metric distance between equilibrium thermodynamic
states. Among other interesting properties, this metric asymptotically bounds
the dissipation induced by a finite time transformation of a thermodynamic
system. It is also connected to the Jensen-Shannon divergence, Fisher
information and Rao's entropy differential metric. Therefore, thermodynamic
length is of central interest in understanding matter out-of-equilibrium. In
this paper, we will consider how to define thermodynamic length for a small
system described by equilibrium statistical mechanics and how to measure
thermodynamic length within a computer simulation. Surprisingly, Bennett's
classic acceptance ratio method for measuring free energy differences also
measures thermodynamic length.Comment: 4 pages; Typos correcte
The Renormalized Stress Tensor in Kerr Space-Time: Numerical Results for the Hartle-Hawking Vacuum
We show that the pathology which afflicts the Hartle-Hawking vacuum on the
Kerr black hole space-time can be regarded as due to rigid rotation of the
state with the horizon in the sense that when the region outside the
speed-of-light surface is removed by introducing a mirror, there is a state
with the defining features of the Hartle-Hawking vacuum. In addition, we show
that when the field is in this state, the expectation value of the
energy-momentum stress tensor measured by an observer close to the horizon and
rigidly rotating with it corresponds to that of a thermal distribution at the
Hawking temperature rigidly rotating with the horizon.Comment: 17 pages, 7 figure
Globally controlled universal quantum computation with arbitrary subsystem dimension
We introduce a scheme to perform universal quantum computation in quantum
cellular automata (QCA) fashion in arbitrary subsystem dimension (not
necessarily finite). The scheme is developed over a one spatial dimension
-element array, requiring only mirror symmetric logical encoding and global
pulses. A mechanism using ancillary degrees of freedom for subsystem specific
measurement is also presented.Comment: 7 pages, 1 figur
Quantum Operation Time Reversal
The dynamics of an open quantum system can be described by a quantum
operation, a linear, complete positive map of operators. Here, I exhibit a
compact expression for the time reversal of a quantum operation, which is
closely analogous to the time reversal of a classical Markov transition matrix.
Since open quantum dynamics are stochastic, and not, in general, deterministic,
the time reversal is not, in general, an inversion of the dynamics. Rather, the
system relaxes towards equilibrium in both the forward and reverse time
directions. The probability of a quantum trajectory and the conjugate, time
reversed trajectory are related by the heat exchanged with the environment.Comment: 4 page
Molecular Structure of XeF6. II. Internal Motion and Mean Geometry Deduced by Electron Diffraction
The distribution of internuclear distances in gaseous XeF6 exhibits unusually diffuse XeF6 bonded and FâF geminal nonbonded peaks, the latter of which is severely skewed. The distribution proves the molecule cannot be a regular octahedron vibrating in independent normal modes. The instantaneous molecular configurations encountered by the incident electrons are predominantly in the broad vicinity of C3Ï
C3Ï
structures conveniently described as distorted octahedra in which the xenon lone pair avoids the bonding pairs. In these distorted structures the XeF bond lengths are distributed over a range of approximately 0.08 Ă
with the longer bonds tending to be those adjacent to the avoided region of the coordination sphere. Fluorines suffer angular displacements from octahedral sites which range up to 5° or 10° in the vicinity of the avoided region.Alternative interpretations of the diffraction data are developed in detail, ranging from models of statically deformed molecules to those of dynamically inverting molecules. In all cases it is necessary to assume that t1ut1u bending amplitudes are enormous and correlated in a certain way with substantial t2gt2g deformations. Notwithâstanding the small fraction of time that XeF. spends near OhOh symmetry, it is possible to construct a molecular potentialâenergy function more or less compatiable with the diffraction data in which the minimum energy occurs at OhOh symmerty. The most notable feature of this model is the almost vanishing restoring force for small t1ut1u bending distortions. Indeed, the mean curvature of the potential surface for this model corresponds to a Ï
4Ï
4 force constant F44F44 of 10â2 mdyn/Ă
or less. Various rapidly inverting nonâOhOh structures embodying particular combinations of t2gt2g and t1ut1u deformations from OhOh symmetry give slightly better radial distribution functions, however. In the region of molecular configuration where the gas molecules spend most of their time, the form of the potentialâenergy function required to represent the data does not distinguish between a JahnâTeller firstâorder term or a cubic V445V445 term as the agent responsible for introducing the t2gt2g deformation. The JahnâTeller term is consistent with Goodman's interpretation of the molecule. On the other hand, the cubic term is found to be exactly analogous to that for other molecules with stereochemically active lone pairs (e.g., SF4, ClF3). Therefore, the question as to why the XeF6 molecule is distorted remains open. The reported absence of any observable gasâphase paramagnetism weighs against the JahnâTeller interpretation.The qualitative success but quantitative failure of the valenceâshellâelectronâpairârepulsion theory is discussed and the relevance of the âpseudoâJahnâTellerâ formalism of LonguetâHiggins et al. is pointed out. Brief comparisons are made with isoelectronic ions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70641/2/JCPSA6-48-6-2466-1.pd
Effects of Electron Correlation in XâRay and Electron Diffraction. IV. Approximate Treatment for ManyâElectron Atoms
A simple scheme is proposed for predicting effects of electron correlation on intraâatomic electronâelectron radial distribution functions and on intensities of x rays scattered by gas atoms. It makes use of a relationship connecting the Coulomb hole function for an electron pair with the corresponding correlation energy. The method is applied to the beryllium atom in its ground state. Results compare favorably with results calculated directly from correlated and HartreeâFock wavefunctions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71228/2/JCPSA6-45-12-4700-1.pd
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