Showing papers by "University of Paris published in 1992"

Biorthogonal bases of compactly supported wavelets

Abstract: Orthonormal bases of compactly supported wavelet bases correspond to subband coding schemes with exact reconstruction in which the analysis and synthesis filters coincide. We show here that under fairly general conditions, exact reconstruction schemes with synthesis filters different from the analysis filters give rise: to two dual Riesz bases of compactly supported wavelets. We give necessary and sufficient conditions for biorthogonality of the corresponding scaling functions, and we present a sufficient condition for the decay of their Fourier transforms. We study the regularity of these biorthogonal bases. We provide several families of examples, all symmetric (corresponding to “linear phase” filters). In particular we can construct symmetric biorthogonal wavelet bases with arbitrarily high preassigned regularity; we also show how to construct symmetric biorthogonal wavelet bases “close” to a (nonsymmetric) orthonormal basis.

Time reversal of ultrasonic fields. I. Basic principles

Abstract: Time reversal of ultrasonic fields represents a way to focus through an inhomogeneous medium. This may be accomplished by a time-reversal mirror (TRM) made from an array of transmit-receive transducers that respond linearly and allow the incident acoustic pressure to be sampled. The pressure field is then time-reversed and re-emitted. This process can be used to focus through inhomogeneous media on a reflective target that behaves as an acoustic source after being insonified. The time-reversal approach is introduced in a discussion of the classical techniques used for focusing pulsed waves through inhomogeneous media (adaptive time-delay techniques). Pulsed wave time-reversal focusing is shown using reciprocity valid in inhomogeneous medium to be optimal in the sense that it realizes the spatial-temporal matched filter to the inhomogeneous propagation transfer function between the array and the target. The research on time-reversed wave fields has also led to the development of new concepts that are described: time-reversal cavity that extends the concept of the TRM, and iterative time-reversal processing for automatic sorting of targets according to their reflectivity and resonating of extended targets. >

A meta-analysis of thoracic radiotherapy for small-cell lung cancer.

Abstract: Background. In spite of 16 randomized trials conducted during the past 15 years, the effect of thoracic radiotherapy on the survival of patients with limited small-cell lung cancer remains controversial. The majority of these trials did not have enough statistical power to detect a difference in survival of 5 to 10 percent at five years. This meta-analysis was designed to evaluate the hypothesis that thoracic radiotherapy contributes to a moderate increase in overall survival in limited small-cell lung cancer. Methods. We collected individual data on all patients enrolled before December 1988 in randomized trials comparing chemotherapy alone with chemotherapy combined with thoracic radiotherapy. Trials that included only patients with extensive disease were excluded. Results. The meta-analysis included 13 trials and 2140 patients with limited disease. A total of 433 patients with extensive disease were excluded. Overall, 1862 of 2103 patients who could be evaluated died; the median follow-up peri...

The complete DNA sequence of yeast chromosome III.

Abstract: The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.

Management strategies in resection for hilar cholangiocarcinoma.

Abstract: Between 1960 and 1990, resection was performed in 23 of 122 patients who underwent surgical treatment for hilar cholangiocarcinoma. Local excision of the lesion alone was performed in 10 cases (43%). Hepatic resection for tumor extending to the secondary bile ducts or hepatic parenchyma was performed in 13 cases (57%): extended right hepatectomy (3), right hepatectomy (1), extended left hepatectomy (6), left hepatectomy (2), and left lobectectomy (1). In three other cases, resection by total hepatectomy and liver transplantation was performed, but these were not included in the analysis of results for resection. Significant operative complications occurred in only two cases (8.7%), and the operative mortality rate was zero. In four cases, complete excision of the tumor could not be achieved macroscopically (macroscopic curative resection rate 19/122; 15.6%). In nine cases, the margins of the resected specimens were free from tumor on histologic examination (microscopic curative resection rate, 9/122; 7.4%). In 10 cases, the resection margins were found to contain tumor on histologic examination. The overall survival rate was 87% at 1 year, 63% at 2 years, and 25% at 3 years (median survival, 24 months). The survival and freedom from recurrence rates for patients with free resection margins was superior to that for patients with involved resection margins or residual macroscopic disease. A potentially curative resection, with histologically negative margins and no recurrence to date, was achieved in seven patients using the following procedures: local excision for two type I lesions; left hepatectomy plus excision of segment 1 for two type IIIb lesions and one type IV lesion; right hepatectomy and right hepatectomy plus excision of segment 1 for two type IIIa lesions. These results indicate that improved survival in hilar cholangiocarcinoma can be achieved by resection, with minimal morbidity and zero mortality rates, if histologically free resection margins are obtained. To achieve this, we recommend the following procedures for each type of lesion, based on our experience and on anatomic considerations: local excision for type I; local excision plus resection of segment 1 for type II; local excision, resection of segment 1, and right or left hepatectomy for types IIIa and b; hepatectomy plus liver transplantation for type IV.

Occurrence of brown adipocytes in rat white adipose tissue: molecular and morphological characterization.

Abstract: Brown adipocytes are thermogenic cells which play an important role in energy balance. Their thermogenic activity is due to the presence of a mitochondrial uncoupling protein (UCP). Until recently, it was admitted that in rodents brown adipocytes were mainly located in classical brown adipose tissue (BAT). In the present study, we have investigated the presence of UCP protein or mRNA in white adipose tissue (WAT) of rats. Using polymerase chain reaction or Northern blot hybridization, UCP mRNA was detected in mesenteric, epidydimal, retroperitoneal, inguinal and particularly in periovarian adipose depots. The uncoupling protein was detected by Western blotting in mitochondria from periovarian adipose tissue. When rats were submitted to cold or to treatment with a beta-adrenoceptor agonist, UCP expression was increased in this tissue as in typical brown fat. Moreover, the expression was decreased in obese fa/fa rats compared to lean controls. Morphological studies showed that periovarian adipose tissue of rats kept at 24 degrees C contained cells with numerous typical BAT mitochondria with or without multilocular lipid droplets. Immunocytochemistry confirmed that multilocular cells expressed mitochondrial UCP. Furthermore, the number of brown adipocytes and the density of mitochondrial cristae increased in parallel with exposure to cold. These results demonstrate that adipocytes expressing UCP are present in adipose deposits considered as white fat. They suggest the existence of a continuum in rodents between BAT and WAT, and a great plasticity between adipose tissue phenotypes. The physiological importance of brown adipocytes in WAT and the regulation of UCP expression remain open questions.

Lambda-My-Calculus: An Algorithmic Interpretation of Classical Natural Deduction

Abstract: 1 INTRODUCTION This paper presents a way of extending the paradigm "proofs as programs" to classical proofs. The system we use is derived from the general Free Deduction system presented in [31. Usually when considering proofs as programs, one has only in mind some kind of intuitionistic proofs. There is an obvious reason for that restriction: only intuitionistic proofs are contructive, in the sense that from the proof of an existential statement, one can get a witness of this existential statement. But from the programming point of view, constructivity is only needed for E~-statements, for which classical and intuitionistic provability coincide. This means that, classical proofs are also candidates for being programs. In order to use them as programs, one has two tasks to achieve: (i) to find a system in which one can extract directly a program from a classical proof (and not by means of a translation to intuitionistic logic), and (ii) to understand the algorithmic meaning of classical constructions. The system we will consider is a natural deduction system with multiple conclusions, we will call it Classical Natural Deduction (the one with the absurdity rule being called Usual Natural Deduction). It is a particular subsystem of Free Deduction (FD) with inputs fixed to the left, chosen for its simplicity: it can be seen as a simple extension of intuitionistic natural deduction, whose algorithmic interpretation is very well known. In this context, the contribution of classical constructs to programming appears clearly: they correspond to control operators added to functional languages, like call/ce in Scheme. In both contexts, the role of the classical constructs is the same: they allow to take shorter routes in the construction of a proof~program. The link between control operators and classical constructs has first been made by T. Griffin in [1], where he proposes to type the C operator of Felleisen, with the type-~'-,A-* A. The system he obtains is not satisfactory from the logical point of view: the reduction is in fact a reduction strategy and the type assigned to C doesn't fit in general the reduction rule for C. C. Murthy further analysed the connections t91 between control operators, classical constructs and translations from classical logic to intuitionistic logic (see [4]). The difficulties met in trying to use-~-A ~ A (or the classical absurdity rule) as a type for control operators is not really due to classical logic, but much nore to …

The Thermomechanics of Plasticity and Fracture

Abstract: This book concentrates upon the mathematical theory of plasticity and fracture as opposed to the physical theory of these fields, and is presented in the thermomechanical framework. It follows the macroscopic, phenomenological approach which proposes equations abstracted from generally accepted experimental facts, studies the adequacy of the consequences drawn from these equations to those facts and then provides useful tools for designers and engineers. The material is drawn from the author's graduate course in Europe and the United States and may be used to form the basis for similar graduate courses on plasticity and fracture. Many worked examples are presented and each chapter concludes with problems for students. The book will thus undoubtedly establish itself as a core text for both students and researchers.

Consistent interpretations of quantum mechanics

Abstract: Within the last decade, significant progress has been made towards a consistent and complete reformulation of the Copenhagen interpretation (an interpretation consisting in a formulation of the experimental aspects of physics in terms of the basic formalism; it is consistent if free from internal contradiction and complete if it provides precise predictions for all experiments). The main steps involved decoherence (the transition from linear superpositions of macroscopic states to a mixing), Griffiths histories describing the evolution of quantum properties, a convenient logical structure for dealing with histories, and also some progress in semiclassical physics, which was made possible by new methods. The main outcome is a theory of phenomena, viz., the classically meaningful properties of a macroscopic system. It shows in particular how and when determinism is valid. This theory can be used to give a deductive form to measurement theory, which now covers some cases that were initially devised as counterexamples against the Copenhagen interpretation. These theories are described, together with their applications to some key experiments and some of their consequences concerning epistemology.

Stochastic Control of Partially Observable Systems

Abstract: Preface 1. Linear filtering theory 2. Optimal stochastic control for linear dynamic systems with quadratic payoff 3. Optimal control of linear stochastic systems with an exponential-of-integral performance index 4. Non linear filtering theory 5. Perturbation methods in non linear filtering 6. Some explicit solutions of the Zakai equation 7. Some explicit controls for systems with partial observation 8. Stochastic maximum principle and dynamic programming for systems with partial observation 9. Existence results for stochastic control problems with partial information References Index.

Some problems related to the assessment of sperm motility in freshwater fish

Abstract: The motility of the spermatozoa of freshwater fish is usually of short duration, but a precise description has rarely been provided. Motility requires a high dilution (more than 1,000-fold) for initiation of synchronous motility in 100% of spermatozoa; a two-step procedure is necessary, with an initial dilution of 1 to 100 in a medium that keeps the spermatozoa immotile and allows good mixing of the viscous semen. The second dilution (1 to 20) in the activating solution can be made directly under the microscope. Studies of carp sperm indicate that movement of live sperm is influenced by the ionic environment. The inhibition of motility in semen is mainly due to K+ ions in trout and osmotic pressure in carp, but other ions such as Na+, H+, and Mg2+ also interfere. Initiation of motility in trout requires external divalent cations. Immediately after dilution at 20°C, spermatozoa exhibit large circular trajectories (>400 μm in diameter), high beat frequencies (60 Hz), and velocities of 250 μm/sec. These values decrease rapidly. Within 20 sec after dilution, most spermatozoa stop moving, although some of them show some agitation with low beat frequency (< 10 Hz) and with very limited displacement during the next few minutes. A similar pattern is observed in carp, with active motility lasting 40 sec. Under certain ionic conditions, intratesticular spermatozoa are motile and have some fertilizing capacity.

Time-reversal of ultrasonic fields. III. Theory of the closed time-reversal cavity

Abstract: For pt.II see ibid., vol.39, no.5, p.567-78 (1992). A theoretical model for time-reversal cavities to optimize focusing in homogeneous and inhomogeneous media is described. The concept of the cavity can be understood as the most realistic approximation to an exact three-dimensional (3-D) time-reversal of ultrasonic fields; it is also a generalization of the time-reversal mirrors realized experimentally in the laboratory. The proposed method is based on an approach in the transient regime that is more general than the monochromatic formalism used in optics to analyze the phase conjugation mirrors efficiency. This method uses impulse diffraction theory to obtain the impulse response of the cavity in any inhomogeneous medium. An original interpretation of the limitations due to diffraction observed in wave field propagation in terms of the different waves generated inside the cavity is also proposed. The time-reversal focusing process using a closed cavity in a weakly inhomogeneous medium is compared with more classical techniques to compensate wavefront distortions, thus illustrating the focusing improvement due to the time-reversal method. >

On Some Exponential Functionals of Brownian Motion

Abstract: In this paper, distributional questions which arise in certain mathematical finance models are studied: the distribution of the integral over a fixed time interval [0, T]of the exponential of Brownian motion with drift is computed explicitly, with the help of computations previously made by the author for Bessel processes. The moments of this integral are obtained independently and take a particularly simple form. A subordination result involving this integral and previously obtained by Bougerol is recovered and related to an important identity for Bessel functions. When the fixed time T is replaced by an independent exponential time, the distribution of the integral is shown to be related to last-exit time distributions and the fixed time case is recovered by inverting Laplace transforms.

Travelling fronts in cylinders

Abstract: This work is concerned with travelling front solutions of semilinear parabolic equations in an infinite cylindrical domain Σ = R × ω where ω ⊂ Rn−1 is a bounded domain. We write for x in Σ, x = (x1, y), with y ∊ ω. The problems we consider are of the following type { Δ u − ( c + α ( y ) ) ∂ 1 u + f ( u ) = 0 in Σ ∂ u ∂ ν = 0 on ∂ ∑ u ( − ∞ , . ) = 0 , u ( + ∞ , . ) = 1 where the unknowns are the parameter c ∊ R and the function u. The function α ∈ C 0 ( ω ¯ ) and the nonlinear term f: [0, 1] → R are given. (More general coefficients than c + α (y), β (y, c) are also treated.) We obtain a fairly general resolution of this problem. The results depend on the type of nonlinearity considered. When f is of the bistable type, or of the “ignition temperature” type in combustion, we show the existence and uniqueness of c and of the profile u. In the case that f > 0 in (0, 1), we show the existence of c* ∊ R such that a solution exists if and only if c ≧ c*. These results extend to higher dimensions various classical results. In particular they extend the result of Kolmogorov, Petrovsky and Piskounov.

Sol-gel chemistry

Abstract: Sol-gel chemistry involves nucleophilic reactions The chemical reactivity of metal alkoxides toward hydrolysis, condensation and complexation mainly depends on the electronegativity of the metal atom, its coordination number and the steric hindrance of alkoxide groups Silicon alkoxides are poorly reactive Hydrolysis and condensation rates have to be enhanced by acid and base catalysis or nucleophilic activation Transition metal alkoxides are usually too reactive They have to be stabilized by complexation in order to avoid fast condensation The molecular design of alkoxide precursors opens the way to tailor-made materials

What's new in chitinase research?

Abstract: This review article deals with recent developments in molecular and physiological aspects of chitinases from plants, fungi, bacteria, insects and fishes

Sublinear elliptic equations in ℝn

Abstract: (1) - Au = p(x)u a in A n , n > 3 with 0 0, p not identically zero. We shall assume throughout the paper that p E L m We look for a solution u > 0, u not identically zero, so that, by the loc" strong maximum principle, if such a solution exists then u > 0 in in

Nosocomial bronchopneumonia in the critically ill. Histologic and bacteriologic aspects.

Abstract: To provide a comprehensive description of the histologic and bacteriologic characteristics of human nosocomial bronchopneumonia (BPN), the lungs of 83 critically ill patients decreased after a period of mechanical ventilation were examined in the immediate postmortem period. In addition, the accuracy of the protected minibronchoalveolar lavage (BAL) technique in the diagnosis of nosocomial BPN was evaluated. In each patient, a surgical pneumonectomy was performed at the bedside within 30 min following death. Each pulmonary lobe was sampled and bacteriologically analyzed using semiquantitative cultures in 50 patients and quantitative cultures in 33 patients. The entire lung was histologically analyzed using 5 to 10 slices per lung segment. In 69 patients, the bacteriologic result of a protected mini-BAL performed within 48 h preceding death was compared with histologic and bacteriologic results of study of the lung tissue itself. Histologic lesions of BPN were found in 43 of the 83 lungs examined. These lesions were (1) severe in the majority of patients (confluent BPN, n = 23; lung abscess, n = 6), (2) preferentially found in dependent lung segments, (3) often associated with nonspecific alveolar damage, (4) associated with positive lung cultures in 65% of patients (53% with gram-negative bacteria), (5) polymicrobial in 28% of patients, (6) characterized by a lobar bacterial burden greater than 10(3) cfu/g in 32% of cases. Using semiquantitative bacteriologic analysis, the sensitivity and the specificity of the protected mini-BAL in the diagnosis of nosocomial BPN were found to be 70 and 69%, respectively. Protected mini-BAL identified 77% of causative microorganisms of BPN.(ABSTRACT TRUNCATED AT 250 WORDS)

Genesis and evolution of mafic microgranular enclaves through various types of interaction between coexisting felsic and mafic magmas

Abstract: Thermal, mechanical and chemical exchange occurs between felsic and mafic magmas in dynamic magma systems. The occurrence and efficiency of such exchanges are constrained mainly by the intensive parameters, the compositions, and the mass fractions of the coexisting magmas. As these interacting parameters do not change simultaneously during the evolution of the granite systems, the exchanges appear sequentially, and affect magmatic systems at different structural levels, i.e. in magma chambers at depth, in the conduits, or after emplacement

Smoothing properties and retarded estimates for some dispersive evolution equations

Abstract: Smoothing properties, in the form of space-time integrability properties, play an important role in the study of dispersive evolution equations. A number of them follow from a combination of general arguments and specific estimates. We present a general formulation which makes the separation between the two types of ingredients as clear as possible, and we illustrate it with the examples of the Schrodinger equation, of the wave equation, and of a class of 1+1 dimensional equations related to the Benjamin-Ono equation. Of special interest for the Cauchy problem are retarded estimates expressed in terms of those properties. We derive a number of such estimates associated with the last example, and we mention briefly an application of those estimates to the Cauchy problem for the generalized Benjamin-Ono equation.

Infrared spectroscopy of DNA.

Abstract: Publisher Summary This chapter presents a general survey of the Fourier-transform infrared (FTIR) spectrum of a nucleic acid, describes the characterization of the different classic families of DNA conformations, and then discusses the way FTIR spectroscopy can be used in the study of DNA recognition, particularly in the case of triple-stranded structures and DNA–drug interactions. Compared to other techniques some of the advantages of infrared spectroscopy in the study of nucleic acids are (1) the possibility of obtaining data from samples under an extremely wide variety of physical states, (2) no limitation introduced by the size of the investigated molecule—that is, it can work well with short oligonucleotides as well as long polynucleotides, DNA fragments obtained by enzymatic or chemical cleavage, or high molecular weight native DNAs, (3) infrared spectroscopy is a nondestructive technique, which requires only small amounts of samples, and (4) it gives vibrational information characteristic of the helical conformations of the nucleic acids.

On the multifractal analysis of measures

Abstract: The multifractal formalism is shown to hold for a large class of measures.

New thermodynamic Bethe ansatz equations without strings.

Abstract: We present a computational framework not based on the string hypothesis for the thermodynamics of statistical and quantum field theory models solvable by the Bethe ansatz. In the cases of the XXZ Heisenberg chain and the sine-Gordon quantum field theory we derive a single nonlinear integral equation which determines the free energy (or ground-state scaling function). Our approach is very effective at high temperature, and correctly reproduces the low-temperature central charge and the analytic structure of the corrections

Role of gamma interferon and tumor necrosis factor alpha in resistance to Salmonella typhimurium infection.

Abstract: In mice infected with a sublethal dose of Salmonella typhimurium, the injection of an anti-gamma interferon (IFN-gamma) monoclonal antibody increased bacterial proliferation in the spleen and led to death on day 7 or 8. Depletion of both CD4+ and CD8+ T cells with monoclonal antibodies in vivo had a much less marked effect during the first week of infection than the administration of anti-IFN-gamma antibodies, suggesting that cells other than T lymphocytes participate in the production of IFN-gamma at this time. Administration of anti-tumor necrosis factor alpha (TNF-alpha) antibodies to mice infected with a sublethal dose of S. typhimurium induced the same effect as anti-IFN-gamma antibodies, while the administration of both antibodies resulted in a synergistic interaction. When mice were infected with an avirulent strain of S. typhimurium and challenged on day 7 either with a virulent strain of S. typhimurium or with Listeria monocytogenes, their resistance to reinfection was slightly depressed by anti-IFN-gamma or anti-TNF-alpha antibodies given 1 day before challenge and much more strongly depressed by the simultaneous administration of both antibodies. Taken together, these results indicate that IFN-gamma and TNF-alpha play an essential role in acquired resistance during the early phase of S. typhimurium infection.