Sur l'algébre enveloppante d'une algébre de Lie nilpotente

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Vecteurs totalisateurs d'une algèbre de von Neumann

We prove that the set of cyclic vectors for a von Neumann algebra in a Hilbert spaceH is aG set, which is empty or dense. We obtain some corollaries, for instance: if (A ₁,A ₂ ...) is a sequence of von Neumann algebras inH, and if eachA _n has a cyclic vector and a separating vector, then there exists a vector inH which is cyclic and separating for eachA _n. For algebras of local observables, we improve the known results connecting the infinite type of the algebras and the existence of cyclic and separating vectors.     

New answer to the solar neutrino problem

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New answer to the solar neutrino problem

We suggest a new answer to the problem of the solar neutrinos: a neutrino-photon interaction that would cause the neutrinos to disappear before they leave the sun or make them lose energy towards detection thresholds. We calculate the available energy in the system of the centre of mass, and show that the photons may be endowed with a pseudo-cross-section in the system of the sun. Under the assumption of an absorption, made to simplify the neutrino transport calculation, the chlorine experiment yields:σ _a =1.8( _−1.0 ^+0.7 )*10⁻⁹ barn, which is close tog _β/(ℏc)=4·49^*10⁻⁹ barn. The escape probability is substantially larger for the gallium neutrinos than for the chlorine neutrinos. Thermal radiation in the core of a supernova is suppressed by electrical conductivity, therefore the neutrinos from SN1987A could escape; they interacted with the photon piston in the outer layers of the supernova and the interaction has to be a scattering. The cosmological implications of a neutrino-photon interaction are discussed; Hubble’s constant may have to be modified. The case of an elastic scattering between neutrino and photon is discussed in more detail. An erratum to this article is available at .     

Etudes theoriques et pratiques sur la realisation et le fonctionnement de colonnes preparatives de diametre moyen. Modification de la structure interne de ces colonnes

The dependence of the efficiency and productivity of preparative-scale gas-chromatographic columns on various parameters is discussed. The minimum HETP is experimentally shown to increase almost proportionally to the column diameter in the range 1–5 cm. The HETP also increases with a power of the sample amount which depends on the quality of the column packing and can be as low as 1.2. High-diffusivity carrier gases (H₂ and He) arc shown to allow a three-fold increase of columns productivity.The productivity (amount of sample separated/unit time) increases with the column diameter. Given a fixed volume of stationary phase and a known mixture, the column diameter which will accept the largest sample can be calculated. The performance of a preparative unit is limited more by the loadability of columns than by loss of efficiency witli increasing diameters. The performances of preparative columns can be improved by putting rods parallel to the column axis regularly spaced in the packing. The column can be heated internally cither for programmed temperature separations or to allow thermal equilibrium to be reached rapidly.     

Compressibility, the measurement of surface tension, and particle size in molecular or nuclear matter

It is shown that the interface shrinkage resulting from the capillary pressure difference between both sides of a curved interface is the product of a "standard shrinkage"kappagamma (kappa is the isothermal compressibility, gamma the interfacial tension) by a dimensionless factor that depends only on the shape of the sample of matter under study. The behaviour of the standard shrinkage in the critical domain shows that it cannot be a measure of the thickness of the liquid-vapour interface in that domain. The standard shrinkage of classical liquids somewhat above triple point is usually near to 0.048 v(c)(1/3) (v(c) is the critical molecular volume); exceptions to this rule are discussed. The variation of the standard shrinkage along the liquid-vapour coexistence curves of water and argon is presented; the effect of the interface shrinkage on the measured surface tension of liquids can become important within about 15% of the critical temperature. The standard shrinkage of solids is less than that of the corresponding liquids, and is of no consequence when measuring the surface tension of solids. The standard shrinkage of the nuclear fluid is 0.23 fm=0.09 v(c)(1/3). The saturation density of infinite nuclear matter is about 9% less than its value in atomic nuclei, and a term proportional to A(1/3) (A is the mass number) must be added to the nuclear binding energy formula.     

Deux nouveaux facteurs de type II1

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Sur les homomorphismes d'Harish-Chandra

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