7,057 research outputs found
Composition-tuned smeared phase transitions
Phase transitions in random systems are smeared if individual spatial regions
can order independently of the bulk system. In this paper, we study such
smeared phase transitions (both classical and quantum) in substitutional alloys
AB that can be tuned from an ordered phase at composition to
a disordered phase at . We show that the ordered phase develops a
pronounced tail that extends over all compositions . Using optimal
fluctuation theory, we derive the composition dependence of the order parameter
and other quantities in the tail of the smeared phase transition. We also
compare our results to computer simulations of a toy model, and we discuss
experiments.Comment: 6 pages, 4 eps figures included, final version as publishe
Strength of Higher-Order Spin-Orbit Resonances
When polarized particles are accelerated in a synchrotron, the spin
precession can be periodically driven by Fourier components of the
electromagnetic fields through which the particles travel. This leads to
resonant perturbations when the spin-precession frequency is close to a linear
combination of the orbital frequencies. When such resonance conditions are
crossed, partial depolarization or spin flip can occur. The amount of
polarization that survives after resonance crossing is a function of the
resonance strength and the crossing speed. This function is commonly called the
Froissart-Stora formula. It is very useful for predicting the amount of
polarization after an acceleration cycle of a synchrotron or for computing the
required speed of the acceleration cycle to maintain a required amount of
polarization. However, the resonance strength could in general only be computed
for first-order resonances and for synchrotron sidebands. When Siberian Snakes
adjust the spin tune to be 1/2, as is required for high energy accelerators,
first-order resonances do not appear and higher-order resonances become
dominant. Here we will introduce the strength of a higher-order spin-orbit
resonance, and also present an efficient method of computing it. Several
tracking examples will show that the so computed resonance strength can indeed
be used in the Froissart-Stora formula. HERA-p is used for these examples which
demonstrate that our results are very relevant for existing accelerators.Comment: 10 pages, 6 figure
Bubble Shape Oscillations and the Onset of Sonoluminescence
An air bubble trapped in water by an oscillating acoustic field undergoes
either radial or nonspherical pulsations depending on the strength of the
forcing pressure. Two different instability mechanisms (the Rayleigh--Taylor
instability and parametric instability) cause deviations from sphericity.
Distinguishing these mechanisms allows explanation of many features of recent
experiments on sonoluminescence, and suggests methods for finding
sonoluminescence in different parameter regimes.Comment: Phys. Rev. Lett., in pres
Low temperature expansion for the 3-d Ising Model
We compute the weak coupling expansion for the energy of the three
dimensional Ising model through 48 excited bonds. We also compute the
magnetization through 40 excited bonds. This was achieved via a recursive
enumeration of states of fixed energy on a set of finite lattices. We use a
linear combination of lattices with a generalization of helical boundary
conditions to eliminate finite volume effects.Comment: 10 pages, IASSNS-HEP-92/42, BNL-4767
The synergistic integration of computational fluid dynamics and experimental fluid dynamics for ground effect aerodynamics studies
This article highlights the ‘synergistic’ use of experimental fluid dynamics (EFD) and computational fluid dynamics (CFD), where the two sets of simulations are performed concurrently and by the same researcher. In particular, examples from the area of ground effect aerodynamics are discussed, where the major facility used was also designed through a combination of CFD and EFD. Three examples are than outlined, to demonstrate the insight that can be obtained from the integration of CFD and EFD studies. The case studies are the study of dimple flow (to enhance aerodynamic performance), the analysis of a Formula-style front wing and wheel, and the study of compressible flow ground effect aerodynamics. In many instances, CFD has been used to not only provide complementary information to an experimental study, but to design the experiments. Laser-based, non-intrusive experimental techniques were used to provide an excellent complement to CFD. The large datasets found from both experimental and numerical simulations have required a new methodology to correlate the information; a new post-processing method has been developed, making use of the kriging and co-kriging estimators, to develop correlations between the often disparate data types
On the finite-size behavior of systems with asymptotically large critical shift
Exact results of the finite-size behavior of the susceptibility in
three-dimensional mean spherical model films under Dirichlet-Dirichlet,
Dirichlet-Neumann and Neumann-Neumann boundary conditions are presented. The
corresponding scaling functions are explicitly derived and their asymptotics
close to, above and below the bulk critical temperature are obtained. The
results can be incorporated in the framework of the finite-size scaling theory
where the exponent characterizing the shift of the finite-size
critical temperature with respect to is smaller than , with
being the critical exponent of the bulk correlation length.Comment: 24 pages, late
Overeducation across British regions
This paper analyses levels of over-education and wage returns to education for males across
eleven regions of the UK using Labour Force Survey data. Significant differences are found
in the probability of being over-educated across regions; also, differences are found in the
return to the ‘correct’ level of education in each region, in each case associated with
flexibility of movement between and into particular regions, which determines the ease of job
matching. Furthermore, evidence is found that, after controlling for the level of education
acquired, there exists a premium to the ‘correct’ level of education, which varies across UK
regions
Observability of the Bulk Casimir Effect: Can the Dynamical Casimir Effect be Relevant to Sonoluminescence?
The experimental observation of intense light emission by acoustically
driven, periodically collapsing bubbles of air in water (sonoluminescence) has
yet to receive an adequate explanation. One of the most intriguing ideas is
that the conversion of acoustic energy into photons occurs quantum
mechanically, through a dynamical version of the Casimir effect. We have argued
elsewhere that in the adiabatic approximation, which should be reliable here,
Casimir or zero-point energies cannot possibly be large enough to be relevant.
(About 10 MeV of energy is released per collapse.) However, there are
sufficient subtleties involved that others have come to opposite conclusions.
In particular, it has been suggested that bulk energy, that is, simply the
naive sum of , which is proportional to the volume, could
be relevant. We show that this cannot be the case, based on general principles
as well as specific calculations. In the process we further illuminate some of
the divergence difficulties that plague Casimir calculations, with an example
relevant to the bag model of hadrons.Comment: 13 pages, REVTe
Lattice Green Function (at 0) for the 4d Hypercubic Lattice
The generating function for recurrent Polya walks on the four dimensional
hypercubic lattice is expressed as a Kampe-de-Feriet function. Various
properties of the associated walks are enumerated.Comment: latex, 5 pages, Res. Report 1
Hyper-Ramsey Spectroscopy of Optical Clock Transitions
We present non-standard optical Ramsey schemes that use pulses individually
tailored in duration, phase, and frequency to cancel spurious frequency shifts
related to the excitation itself. In particular, the field shifts and their
uncertainties of Ramsey fringes can be radically suppressed (by 2-4 orders of
magnitude) in comparison with the usual Ramsey method (using two equal pulses)
as well as with single-pulse Rabi spectroscopy. Atom interferometers and
optical clocks based on two-photon transitions, heavily forbidden transitions,
or magnetically induced spectroscopy could significantly benefit from this
method. In the latter case these frequency shifts can be suppressed
considerably below a fractional level of 10^{-17}. Moreover, our approach opens
the door for the high-precision optical clocks based on direct frequency comb
spectroscopy.Comment: 5 pages, 4 figure
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