8,104 research outputs found
Estimation of squeeze-film damping and inertial coefficients from experimental free-decay data
The results are given for an experimental program concerned with a parametric identification of the damping and inertial coefficients of a cylindrical squeeze-film bearing, through an analysis of transient response data. The results enable the operating range for which a linear model of the squeeze-film is appropriate to be determined. Comparisons are made between the estimated coefficients and theoretical predictions. Presentation is by courtesy of the Council of the Institution of Mechanical Engineers, London
Systematic distortions in musicians' reproduction of cyclic three-interval rhythms
In a classic study, Fraisse (1956) demonstrated that sequences of four sounds defining three different interval durations exhibit characteristic distortions in reproduction: The two more similar intervals tend to be assimilated to each other, resulting in a rhythm containing just two interval durations. The present study examined whether highly trained musicians (including percussionists) are able to perform such rhythms accurately in a synchronization-continuation tapping paradigm. Eleven rhythms, a subset of those used by Fraisse, were presented cyclically at his original tempo and also at a slower tempo. The musicians produced significant rhythm distortions, though they were smaller than those observed by Fraisse and not always assimilative. They were relatively larger at the fast than at the slow tempo and occurred in both synchronization and continuation. In contrast to Fraisse’s data, the most variably reproduced target rhythm was the one in which the two longer intervals were identical. The pattern of distortions suggested attraction towards ideal rhythms in which all three interval durations are different, representing metrical categories with nominally simple interval ratios (some permutation of 1:2:3) that were probably activated by the cyclic presentation of the rhythms. However, these attractors themselves seemed to be somewhat distorted, perhaps reflecting the simultaneous presence of a nonmetrical attractor that differentiated two interval categories regardless of ratio, as observed by Fraisse
Bose-Einstein condensation of the magnetized ideal Bose gas
We study the charged non-relativistic Bose gas interacting with a constant
magnetic field but which is otherwise free. The notion of Bose-Einstein
condensation for the three dimensional case is clarified, and we show that
although there is no condensation in the sense of a phase transition, there is
still a maximum in the specific heat which can be used to define a critical
temperature. Although the absence of a phase transition persists for all values
of the magnetic field, we show how as the magnetic field is reduced the curves
for the specific heat approach the free field curve. For large values of the
magnetic field we show that the gas undergoes a "dimensional reduction" and
behaves effectively as a one-dimensional gas except at very high temperatures.
These general features persist for other spatial dimensions D and we show
results for D=5. Finally we examine the magnetization and the
Meissner-Ochsenfeld effect.Comment: 4 pages RevTex 2 column format with 4 eps figures, uses epsf.
Replaced version has missing acknowledgements and a discussion of two
references is corrected thanks to discussions with J. Daicic and N. Franke
Primary crustal melt compositions: Insights into the controls, mechanisms and timing of generation from kinetics experiments and melt inclusions
We explore the controls, mechanisms and timing of generation of primary melts and their compositions, and show that the novel studies of melt inclusions in migmatites can provide important insights into the processes of crustal anatexis of a particular rock. Partial melting in the source region of granites is dependent on five main processes: (i) supply of heat; (ii) mineral–melt interface reactions associated with the detachment and supply of mineral components to the melt, (iii) diffusion in the melt, (iv) diffusion in minerals, and (v) recrystallization of minerals. As the kinetics of these several processes vary over several orders of magnitude, it is essential to evaluate in Nature which of these processes control the rate of melting, the composition of melts, and the extent to which residue–melt chemical equilibrium is attained under different circumstances. To shed light on these issues, we combine data from experimental and melt inclusion studies. First, data from an extensive experimental program on the kinetics of melting of crustal protoliths and diffusion in granite melt are used to set up the necessary framework that describes how primary melt compositions are established during crustal anatexis. Then, we use this reference frame and compare compositional trends from experiments with the composition of melt inclusions analyzed in particular migmatites. We show that, for the case of El Hoyazo anatectic enclaves in lavas, the composition of glassy melt inclusions provides important information on the nature and mechanisms of anatexis during the prograde suprasolidus history of these rocks, including melting temperatures and reactions, and extent of melt interconnection, melt homogenization and melt–residue equilibrium. Compositional trends in several of the rehomogenized melt inclusions in garnet from migmatites/granulites in anatectic terranes are consistent with diffusion in melt-controlled melting, though trace element compositions of melt inclusions and coexisting minerals are necessary to provide further clues on the nature of anatexis in these particular rocks.This work was supported by the National Science Foundation [grants
EAR-9603199, EAR-9618867, EAR-9625517 and EAR-9404658], the Italian Consiglio Nazionale delle Ricerche, the European Commission
(grant 01-LECEMA22F through contract No. ERAS-CT-2003-980409;
and a H2020 Marie Skłodowska-Curie Actions under grant agreement
No. 654606), the Italian Ministry of Education, University and Research
(grants PRIN 2007278A22, 2010TT22SC and SIR RBSI14Y7PF), the
Università degli Studi di Padova [Progetto di Ateneo CPDA107188/10
and a Piscopia—Marie Curie Fellowship under grant agreement No.
600376], the Australian Research Council (Australian Professorial Fellowship
and Discovery Grants Nos. DP0342473 and DP0556700), and
the National Research Foundation (South Africa; Incentives For Rated
Researchers Program)
Exploring CP Violation with B_d -> D K_s Decays
We (re)examine CP violation in the decays B_d -> D K_s, where D represents
D^0, D(bar), or one of their excited states. The quantity can be extracted from the time-dependent rates for and , where the decays to
. If one considers a non-CP-eigenstate hadronic final state to
which both D(bar) and D^0 can decay (e.g. ), then one can obtain two
of the angles of the unitarity triangle from measurements of the time-dependent
rates for and .
There are no penguin contributions to these decays, so all measurements are
theoretically clean.Comment: 15 pages, LaTeX, no figure
The two-fluid model with superfluid entropy
The two-fluid model of liquid helium is generalized to the case that the
superfluid fraction has a small entropy content. We present theoretical
arguments in favour of such a small superfluid entropy. In the generalized
two-fluid model various sound modes of HeII are investigated. In a
superleak carrying a persistent current the superfluid entropy leads to a new
sound mode which we call sixth sound. The relation between the sixth sound and
the superfluid entropy is discussed in detail.Comment: 22 pages, latex, published in Nuovo Cimento 16 D (1994) 37
Determining the Quark Mixing Matrix From CP-Violating Asymmetries
If the Standard Model explanation of CP violation is correct, then
measurements of CP-violating asymmetries in meson decays can in principle
determine the entire quark mixing matrix.Comment: 8 pages (plain TeX), 1 figure (postscript file appended), DAPNIA/SPP
94-06, NSF-PT-94-2, UdeM-LPN-TH-94-18
Can One Measure the Weak Phase of a Penguin Diagram?
The b -> d penguin amplitude receives contributions from internal u, c and
t-quarks. We show that it is impossible to measure the weak phase of any of
these penguin contributions without theoretical input. However, it is possible
to obtain the weak phase if one makes a single assumption involving the
hadronic parameters. With such an assumption, one can test for the presence of
new physics in the b -> d flavour-changing neutral current by comparing the
weak phase of B_d^0-{\bar B}_d^0 mixing with that of the t-quark contribution
to the b -> d penguin.Comment: 20 pages, no figure
Retardation turns the van der Waals attraction into Casimir repulsion already at 3 nm
Casimir forces between surfaces immersed in bromobenzene have recently been
measured by Munday et al. Attractive Casimir forces were found between gold
surfaces. The forces were repulsive between gold and silica surfaces. We show
the repulsion is due to retardation effects. The van der Waals interaction is
attractive at all separations. The retardation driven repulsion sets in already
at around 3 nm. To our knowledge retardation effects have never been found at
such a small distance before. Retardation effects are usually associated with
large distances
Ultrathin Metallic Coatings Can Induce Quantum Levitation between Nanosurfaces
There is an attractive Casimir-Lifshitz force between two silica surfaces in
a liquid (bromobenze or toluene). We demonstrate that adding an ultrathin
(5-50{\AA}) metallic nanocoating to one of the surfaces results in repulsive
Casimir-Lifshitz forces above a critical separation. The onset of such quantum
levitation comes at decreasing separations as the film thickness decreases.
Remarkably the effect of retardation can turn attraction into repulsion. From
that we explain how an ultrathin metallic coating may prevent
nanoelectromechanical systems from crashing together.Comment: 4 pages, 5 figure
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