Analysis and optimisation of the tuning of the twelfths for a clarinet resonator

Even if the tuning between the first and second register of a clarinet has been optimized by instrument makers, the lowest twelfths remain slightly too large (inharmonicity). In this article, we study the problem from two different points of view. First, we systematically review various physical reasons why this inharmonicity may take place, and the effect of different bore perturbations inserted in cylindrical instruments. Applications to a real clarinet resonator and comparisons with impedance measurements are then presented. A commonly accepted idea is that the register hole is the dominant cause for this inharmonicity: it is natural to expect that opening this hole will raise the resonance frequencies of the instrument, except for the note for which the hole is at the pressure node. We show that the real situation is actually more complicated because other effects, such as open holes or bore taper and bell, introduce resonance shifts that are comparable but with opposite sign, so that a relatively good overall compensation takes place. The origin of the observed inharmonicity in playing frequencies is therefore different. In a second part, we use an elementary model of the clarinet in order to isolate the effect of the register hole: a perfect cylindrical tube without closed holes. Optimization techniques are then used to calculate an optimum location for the register hole; the result turns out to be close to the location chosen by clarinet makers. Finally, attempts are made numerically to improve the situation by introducing small perturbations in the higher part of the cylindrical resonator, but no satisfactory improvement is obtained.Comment: 28 June 2004 (submitted to Applied Acoustics

Bose-Einstein transition temperature in a dilute repulsive gas

We discuss certain specific features of the calculation of the critical temperature of a dilute repulsive Bose gas. Interactions modify the critical temperature in two different ways. First, for gases in traps, temperature shifts are introduced by a change of the density profile, arising itself from a modification of the equation of state of the gas (reduced compressibility); these shifts can be calculated simply within mean field theory. Second, even in the absence of a trapping potential (homogeneous gas in a box), temperature shifts are introduced by the interactions; they arise from the correlations introduced in the gas, and thus lie inherently beyond mean field theory - in fact, their evaluation requires more elaborate, non-perturbative, calculations. One illustration of this non-perturbative character is provided by the solution of self-consistent equations, which relate together non-linearly the various energy shifts of the single particle levels k. These equations predict that repulsive interactions shift the critical temperature (at constant density) by an amount which is positive, and simply proportional to the scattering length a; nevertheless, the numerical coefficient is difficult to compute. Physically, the increase of the temperature can be interpreted in terms of the reduced density fluctuations introduced by the repulsive interactions, which facilitate the propagation of large exchange cycles across the sample.Comment: two minor corrections, two refs adde

CERN workshop on Innovations in Scholarly Communication (OAI5)

Open archives (OA) started in physics more than 15 years ago with ArXiv, and have since played a more and more important role in the activity of the disciplin; actually, in many fields of physics, ArXiv has now become the major vector or scientific communication. We now have two communication channels in parallel, traditional scientific journals with peer review, and open archives, both with different functionalities and both indispensable. It it therefore interesting to try and transpose to other disciplins the scheme that has worked so well for physicists, which means that the reasons for the success of ArXiv should be analyzed. Scientists do not care about the technicalities, and whether or not the OA is centralized, or distributed with a high level of interoperability. What they wish is to have one single interface where all the scientific information in their domain is available, with the same scientific classifications, etc.. In case of collaborations beween different institutions, they do not wish to have to deposit their texts several times in several repositories. Moreover, they wish to use OA that are relatively homogeneous concernig the content, and for instance do not want to use systems where the free access to the full text is not garanteed, or articles are mixed up with reports or raw data (as is seometimes the case in OAI repositories). Finally, long term stability is absolutely essential, if only to offer the possibility to quote the content of the OA in subsequent work. In this respect, we know that much of the material made available on personal sites and laboratory sites does not have the necessary longetivity to be really useable scientifically. This analysis led the French CNRS to start the Hal project, a pluridisciplinary open archive strongly inspired by ArXiv, and directly connected to it. Hal actually automatically transfers data and documents to ArXiv for the relevant disciplins; similarly, it is connected to Pum Med and Pub Med Central for life sciences. Hal is customizable so that institutions can build their own portal within Hal, which then plays the role of an institutional archive (examples are INRIA, INSERM, ENS Lyon, and others). It includes a form of certification called "stamps". The rate of increase of the number of full text documents increases steadily, and now reaches around 1 500 per month, mostly due to self archiving from different communities (including humanities: archeololy, history, literature, etc.). A national agreement has been signed among most research French institutions to use Hal as a common archive. View Franck Laloe's biography </p

EPR argument and Bell inequalities for Bose-Einstein spin condensates

We discuss the properties of two Bose-Einstein condensates in different spin states, represented quantum mechanically by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions (perpendicular to the spin quantization axis), giving access to the relative phase of the two macroscopically occupied states. Before the first spin measurement, the phase is completely undetermined; after a few measurements, a more and more precise knowledge of its value emerges under the effect of the quantum measurement process. This naturally leads to the usual notion of a quasiclassical phase (Anderson phase) and to an interesting transposition of the Einstein-Podolsky-Rosen argument to macroscopic physical quantities. The purpose of this paper is to discuss this transposition, as well as situations where the notion of a quasiclassical phase is no longer sufficient to account for the quantum results, and where significant violations of Bell-type inequalities are predicted. Quantum mechanically, the problem can be treated exactly: the probability for all sequences of results can be expressed in the form of a double integral, depending on all parameters that define the experiment (number of particles, number and angles of measurements). We discuss the differences between this case and the usual two-spin case. We discuss the effect of the many parameters that the experimenters can adjust for their measurements, starting with a discussion of the effect of the angles of measurement (the “settings”), and then envisaging various choices of the functions that are used to obtain violation of Bell-Clauser-Horne-Shimony-Holt inequalities. We then discuss how the “sample bias loophole” (often also called “efficiency loophole”) can be closed in this case, by introducing a preliminary sequence of measurements to localize the particles into “measurement boxes.” We finally show that the same nonlocal effects can be observed with distinguishable spins

Quantum Mechanics

Volume 1.xv, 898 p. : il.; 22 cm

Quantum mechanics

Volume IIxv, 901-1524 p. : il.; 26 cm

Rapport sur le deroulement du symposium Alfred Kastler

SIGLECNRS AR 11602 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Axon morphogenesis and maintenance require an evolutionary conserved safeguard function of Wnk kinases antagonizing Sarm and Axed

International audienc