Instabilités de calibration de phase

In very long baseline interferometry, the image reconstruction procedures are very sensitive to the potential instabilities of the phase calibration operation. The analysis presented in this Note reveals that these instabilities are due to the existence of secondary minima (more or less critical) of the phase calibration objective functional. By resolving the corresponding integer ambiguity problems in an appropriate manner, these minima can be explicitly identified and compared. The stability of the self-calibration procedures can thus be easily controlled. To cite this article: A. Lannes, C. R. Physique 4 (2003).     

Derivation of primary parameters and procedures for use in speech intelligibility predictions

The literature on various parameters that appear in the articulation index-type calculations of speech intelligibility is reexamined. Based on the reported data, the best estimates of these parameters and the most appropriate procedures for their use are suggested. These included: (1) the analysis and specification of the importance of various frequency bands to speech intelligibility; (2) the procedures used for measuring threshold and the calculation of threshold-based parameters used for predicting intelligibility of low-level speech; and (3) the calculation and measurement of relevant speech parameters. All results are given so that the calculations can be performed either in critical bands, 1/3 octaves, or octaves.     

Response of multiple coupled dynamic systems

Analytical procedures are developed to investigate the nature of the response of multiple coupled dynamic systems. The dynamic systems are one-dimensional and are coupled at junctions. The spatial extents of the dynamic systems are determined by these junctions; a dynamic system terminates at these junctions. The junctions are characterized by assigning reflection and transmission coefficients at the terminal positions of the dynamic systems. In addition, a dynamic system is characterized by a single propagation wavenumber. The wavenumber may be complex, accounting for possible spatial attenuation and for distributed damping in the dynamic system. Further damping—edge damping—may be accounted for by assigning non-conservative coefficients at the junction. Quadratic forms describing the dynamics of multiple coupled dynamic systems are also presented and discussed. Relationship of such forms to the statistical energy analysis (SEA) of complex dynamic systems is touched upon. This paper is concerned chiefly with the development of analytical procedures. Examples of application of these procedures will be dealt with in subsequent publications.     

直接法中的尝试法(Ⅱ)

应用直接法测定晶体结构,在归一化结构因子的计算,结构因子相位测定与分子模型建立中均需使用尝试法。本文就后两个问题提出了|E|值选取、起始套选择、原子种类判别、原子占有率确定等尝试法则,并用于测定未知晶体结构多例,获得了成功。 关键词：     

Phase transitions in Edwards-Anderson model by means of information theory

A numeric method to characterize phase transitions is presented, explained and applied to a two-dimensional disordered system that can be thought of as a diluted ferromagnet or an Edwards-Anderson model near the ferromagnetic limit. A computer simulation is implemented to define a time series for order parameters; a file stores the time evolution of each parameter for different dilution concentrations and for a series of temperatures. These files are compressed and they reach a maximum size for temperatures in agreement with critical temperatures for the ferromagnetic/paramagnetic transition obtained by other methods. Site order parameter gives optimum results for this method based on data compression. Data compression procedures are invoked to give a qualitative explanation of this phenomenon. The advantages of this method are discussed by comparing results and procedures with two established methods: the crossing of Binder cumulants and the crossing of time autocorrelation functions. Other possible applications and extensions of this method are also mentioned.     

Quantification of cross-irradiation and cross-illumination using a Risø TL/OSL DA-15 reader

The automated Risø TL/OSL DA-15 reader is widely used for luminescence dating applications. The nature of the device is such that the irradiation and illumination of a sample during the OSL procedures may affect discs in adjacent positions. It is critical to confirm that these factors do not introduce significant systematic errors. The effects of such cross-talk (cross-irradiation and cross-bleaching) are examined and quantified, both for specific and general cases. Depending upon the protocol used, cross-irradiation and cross-bleaching could accumulate to have an effect on the D_e estimate, and for the latter this could be significant (i.e. 10%).     

Heating and compression of laser-irradiated spherical targets

Heating and dynamics of compression of shell targets irradiated by a nanosecond laser pulse in the “Kal'mar” facility are investigated. Comprehensive procedures are developed and used to investigate the energy balance and the compression dynamics of the target scattered by the radiation plasma at the harmonic frequencies 2ω₀ and 3/2ω₀, and of the spectral distribution of the continuous x radiation. The use of the developed procedures has made it possible to clarify the dependence of the components of the energy balance on the target parameters, to establish new regularities governing the shell motion, to identify the phenomena that take place in the region of the critical and quarter-critical density, and to demonstrate experimentally the possibility of reaching in the “exploding pusher” regime densities much higher than the density of a solid body.     

Simple buckling and vibration analyses of beam or spring connected structures

The problem considered is the buckling or vibration of a system of n columns, or n general structures, which are suitably related to each other and are connected together by sets of springs, or inextensible beams, which are also suitably related to each other. It is shown that all the critical loads, natural frequencies and modes which are required in buckling and vibration problems can be found from n substitute systems which each consist of one column or structure and a single set of springs. The derivation of these substitute systems involves the solution of a very simple linear eigenvalue problem of order n, which has closed form solutions for several of the special cases considered. The reduction of the original system to n substitute systems has been adapted to permit the use of design procedures which avoid a complete analysis of each trial design.     

Evaluation of critical points in technology transfer of cryopreservation protocols to international plant conservation laboratories

Cryopreservation of plant tissues in liquid nitrogen is now used for long-term conservation of vegetatively-propagated crops. Development of standard techniques for cryopreservation is important to the international plant-conservation community for successful implementation of storage protocols in diverse and internationally dispersed laboratories. Evaluation of the critical points of each preservation technique will greatly assist in developing and validating internationally-used cryopreservation protocols. The goals of this project were to assess critical points of two major cryopreservation techniques (PVS2 vitrification and encapsulation dehydration) during their transfer to international laboratories; analyze post-storage viability for each technique and location; and develop recommendations based on the assessments and data from the participating laboratories. Investigators from Germany, Kazakhstan, Poland and UK participated in a 2-week training workshop in cryopreservation methods after which the techniques were tested in the home laboratories of the participants. After one-year site visits by the technology trainers identified critical points in the protocols. Critical points were identified as 1) Cryogenic (cryoprotection, LN exposure, rewarming); 2) Non-cryogenic (plant health status, pre- and post-storage culture); 3) Operational (skills transfer, training, interpretation of procedures); 4) Facility (growth room, ambient conditions, media preparation, equipment). The most critical factors in all laboratories were culture health, operator skills and experience, and clarification of the technical details of the procedures. Final results showed that correction of critical factors improved the post-storage recovery in all the laboratories.     

The influence of ambient illumination on colour adaptation in three fringe photoelasticity

In three fringe photoelasticity, a single colour isochromatic image is used to estimate the total fringe order by comparing the colour at each point with that of a calibration table. The generation of the calibration table is critical, and certain nuances involved therein are brought out in this paper. Ideally, the same specimen material and lighting conditions must be used for both the calibration and application experiments, which are often not possible in an industrial scenario, and colour adaptation is a simple way of suitably modifying the calibration table. Till date, only experimental analyses of the colour adaptation procedures are available in the literature; in this paper, the colour adaptation procedures are investigated from an analytical viewpoint. This study has brought out that a two-point colour adaptation scheme accounts not only for tint variation between the calibration and application specimens, but also for ambient illumination. This finding has also been experimentally verified for a benchmark problem, and thereafter extended for reflection photoelastic analyses.     

Light storage protocols in Tm:YAG

We present two quantum memory protocols for solids: a stopped light approach based on spectral hole burning and a storage in an atomic frequency comb. These procedures are well adapted to the rare-earth ion doped crystals. We carefully clarify the critical steps of both. In one case, we show that the slowing-down due to hole-burning is sufficient to produce a complete mapping of field into the atomic system. On the other side, we explain the storage and retrieval mechanism of the Atomic Frequency Comb protocol. These two critical stages of the protocols are implemented experimentally in Tm³⁺-doped yttrium-aluminum-garnet crystal.     

Multicritical behavior at the kosterlitz-thouless critical point

A multicritical critical point for the two dimensional planar model is analyzed by studying an exactly soluable limit of a related model—the generalized Villain model. The statistical mechanics of this model is written in terms of vortex and symmetry breaking excitations. In these terms, the problem reduces to a kind of two dimensional problem with interacting electric charges and magnetic monopoles. In this form, the problem is manifestly self-dual. The multicritical behavior is exhibited in a three-dimensional phase space in which the axes are the coupling strength of a “square” symmetry breaking which favors four possible directions for the planar model vectors. The analysis of this multicritical point shows that it is the intersection of at least six critical lines—each with continuously varying critical indices. Two of these lines are described by the exactly soluable gaussian model. The other four are isomorphic to one another, and each one has—as a point on the line—a critical point of the Ashkin-Teller model. We argue that each of these lines might be in an equivalent universality class to the line of critical points which occurs in the Baxter and Ashkin-Teller models. We make a suggestion about which point on these critical lines might be in the same universality class as our multicritical point. Correlation functions at the intersection point are calculated and used to develop an expansion of critical indices about this point. This expansion gives a potential method for calculating the critical behavior along the critical lines of the model.     

Numerical investigation of relativistic self-focusing of intense laser beam with LG01 mode in plasmas

In this paper, we numerically investigate the relativistic self-focusing of laser beam with LG₀₁ mode in plasmas. An effective potential is introduced to identify the critical power. Numerical methods are employed to solve the governing equations. To verify the numerical procedures, we compare the known analytical solution of the relativistic critical power for TEM₀₀ mode with our numerical method. It is shown that there is a good agreement between our numerical results and the analytical solution. The critical power for relativistic self-focusing of a LG₀₁ laser beam is about 6 times of that for a TEM₀₀ laser beam.     

Paradoxical vocal fold motion: Presentation and treatment options

Paradoxical vocal fold motion is a rare disorder in which adduction of the folds occurs on inspiration. The disorder presents with signs of airway obstruction and often airway distress, so proper diagnosis by the otorhinolaryngologist is critical to subsequent management. We present a retrospective review of 10 patients with the diagnosis of paradoxical vocal fold motion seen over a 6-year period. Eight patients were females, and 6 required an acute airway intervention at presentation; 3 patients eventually underwent tracheotomy for respiratory decompensation. Six patients had a prior diagnosis of asthma, and this was determined to contribute to their respiratory status. Five patients were treated with botulinum toxin and 2 with flexible nasolaryngoscopic biofeedback, which improved the outcome. A review of the literature confirms a female predominance of patients presenting with paradoxical adduction and airway distress, often with a history of asthma and psychopathology. Our experience with botulinum toxin and biofeedback suggests that these procedures are viable treatment options in the management of patients with this disorder.     

Critical Evaluation of Analytical Procedures for the Determination of Lead in Seawater

Abstract: This article presents a critical evaluation of the analytical procedures used for the determination of lead in seawater, which is important because lead is a good indicator of marine pollution caused by human activities. Sampling, storage, and pretreatment techniques are briefly overviewed, including the significance of systematic errors that cannot be corrected later on. The main techniques in this article are electrothermal–atomic absorption spectrometry (ET-AAS), inductively coupled plasma–mass spectrometry (ICP-MS), and voltammetry. Flame atomic absorption spectrometry (FAAS) and inductively coupled plasma–optical emission spectrometry (ICP-OES) are treated as well, although their limits of quantification are not sufficient for a determination of lead in unpolluted seawater. Even when separation and preconcentration techniques are applied, these techniques are only capable of detecting lead in polluted coastal seawater. Separation and preconcentration are actually also required for ET-AAS and ICP-MS in order to determine the lowest concentrations of lead found in unpolluted open-ocean seawater, which is still a challenge for the analytical chemist.     

Radiation damage to protein specimens from electron beam imaging and diffraction: a mini‐review of anti‐damage approaches,with special reference to synchrotron X‐ray crystallography

Recent research progress using X‐ray cryo‐crystallography with the photon beams from third‐generation synchrotron sources has resulted in recognition that this intense radiation commonly damages protein samples even when they are held at 100 K. Other structural biologists examining thin protein crystals or single particle specimens encounter similar radiation damage problems during electron diffraction and imaging, but have developed some effective countermeasures. The aim of this concise review is to examine whether analogous approaches can be utilized to alleviate the X‐ray radiation damage problem in synchrotron macromolecular crystallography. The critical discussion of this question is preceded by presentation of background material on modern technical procedures with electron beam instruments using 300–400 kV accelerating voltage, low‐dose exposures for data recording, and protection of protein specimens by cryogenic cooling; these practical approaches to dealing with electron radiation damage currently permit best resolution levels of 6 Å (0.6 nm) for single particle specimens, and of 1.9 Å for two‐dimensional membrane protein crystals. Final determination of the potential effectiveness and practical value of using such new or unconventional ideas will necessitate showing, by experimental testing, that these produce significantly improved protection of three‐dimensional protein crystals during synchrotron X‐ray diffraction.     

Experimentally based correction procedures for planar laser-induced fluorescence measurements of mean species concentration

Experimentally-based correction procedures are demonstrated which enhance the quantitative nature of planar laser-induced fluorescence (PLIF) images for mean species concentration by correcting for the influence of the electronic quenching rate coefficient. Implementation of these methods requires only the ability to make PLIF and laser-saturated fluorescence (LSF) measurements. Though applied herein to NO, these procedures are broadly applicable both in terms of species and users. Moreover, they are generally effective regardless of the error gradients associated with spatial variations in the electronic quenching rate coefficient. In such general environments, these methods produce quenching-corrected, spatially resolved PLIF images of mean species concentration with a total uncertainty equivalent to that of a single LSF measurement. Received: 22 November 1999 / Revised version: 3 March 2000 / Published online: 16 June 2000     

Statistical physics and practical training of soft-committee machines

Equilibrium states of large layered neural networks with differentiable activation function and a single, linear output unit are investigated using the replica formalism. The quenched free energy of a student network with a very large number of hidden units learning a rule of perfectly matching complexity is calculated analytically. The system undergoes a first order phase transition from unspecialized to specialized student configurations at a critical size of the training set. Computer simulations of learning by stochastic gradient descent from a fixed training set demonstrate that the equilibrium results describe quantitatively the plateau states which occur in practical training procedures at sufficiently small but finite learning rates. Received 16 December 1998