Showing papers by "University of Trento published in 1984"
TL;DR: In this paper, a phenomenological "correlation length" is obtained from the study of the low-frequency peak of the various glasses, by introducing the values of the transverse and longitudinal sound velocities, obtained by ultrasonic measurements.
Abstract: Raman spectra in superionic glasses ${(\mathrm{AgI})}_{x}{({\mathrm{Ag}}_{2}\mathrm{O}\ifmmode\cdot\else\textperiodcentered\fi{}n{\mathrm{B}}_{2}{\mathrm{O}}_{3})}_{1\ensuremath{-}x}$ for various values of $x$ ($01\ensuremath{\le}x\ensuremath{\le}055$) and for various $n (2\ensuremath{\le}n\ensuremath{\le}4)$ are reported For comparison we also studied spectra of binary glasses (${\mathrm{Ag}}_{2}\mathrm{O}\ifmmode\cdot\else\textperiodcentered\fi{}n{\mathrm{B}}_{2}{\mathrm{O}}_{3}$) They provide light scattering experimental evidence of the network-modifier nature of the ${\mathrm{Ag}}_{2}$O in borate matrix The model of Martin and Brenig for the interpretation of the low-frequency Raman band in the glasses is applied to the series of our samples with increasing content of AgI: A phenomenological "correlation length" is obtained from the study of the low-frequency peak of the various glasses, by introducing the values of the transverse and longitudinal sound velocities, obtained by ultrasonic measurements That kind of calculation confirms our hypothesis of the increase on the correlation length from 8 \AA{} at $x=0 \mathrm{to} 12$ \AA{} at $x=055$
87 citations
TL;DR: In this article, a Harnack inequality for degenerate parabolic equations is proposed for partial differential equations, which is a generalization of the one we consider in this paper. pp. 719-749.
Abstract: (1984). A Harnack inequality for degenerate parabolic equations. Communications in Partial Differential Equations: Vol. 9, No. 8, pp. 719-749.
72 citations
TL;DR: In this paper, the authors developed a method to prove an estimate of Burkholder type for a class of processes defined by a stochastic convolution with a semigroup for p ≥ 2.
Abstract: We develop a method to prove an estimate of Burkholder type for a class of processes defined by a stochastic convolution with a semigroup for p ≥ 2; this result, for p = 2, has been obtained also by Kotelenez [6] using a martingale inequality due to him[5]
67 citations
TL;DR: In this paper, the authors compared the performance of canonical ensemble sampling with the usual microcanonical molecular dynamic (MDM) and a modification of molecular dynamics for canonical ensembles, focusing on three aspects: the mean square displacement of a representative point in configuration space, the persistence of correlation in the potential energyV and also in a function of interest in free energy-difference calculations.
Abstract: Computer methods for sampling statistical ensembles generate chains of configurations in which subsequent members differ only slightly. Statistical errors are determined by the number of independent configurations contained in the sample. A quantitative treatment of the persistence of correlation shows how the first two moments of the autocorrelation function of a variablef along the chain are connected with the expected variance of its mean. The variance of the potential energy in the canonical ensemble is shown be to larger than that in the microcanonical one by a factor which is the ratio of the system heat capacity to that of an ideal gas. A comparison has been made of the efficiency of Metropolis Monte Carlo (MC), the usual microcanonical molecular dynamic (MDM) and a modification of molecular dynamics for canonical ensemble sampling (MDC). The analysis is focused on three aspects: the mean square displacement of a representative point in configuration space, the persistence of correlation in the potential energyV and also in a function of interest in free-energy-difference calculations. In MDM simulations of crystalline solids, it was found thatV behaves as an «oscillatory» variable and that the variance of its mean is reduced by antithetic variations of its values.
53 citations
TL;DR: In this article, explicit saddle surfaces and return jump rates for model crystals are calculated for atomic jumps in solids, and a nonphysical effect, in which isotopic substitution causes a return jump catastrophe, is resolved by use of an exact momentum-dependent criterion to distinguish successful jumps.
Abstract: Explicit saddle surfaces and return jump rates are calculated for model crystals; the results establish the validity of rate calculations for atomic jumps in solids. A nonphysical effect, in which isotopic substitution causes a "return jump catastrophe," is resolved by use of an exact momentum-dependent criterion to distinguish successful jumps.
34 citations
TL;DR: In this paper, a thin torus, interrupted by weak links in series, is found to give an angular momentum contribution which depends parametrically on the steady absolute rotation of the torus.
Abstract: Superfluid $^{4}\mathrm{He}$ filling a thin torus, interrupted by $N$ weak links in series, is found to give an angular momentum contribution which depends parametrically on the steady absolute rotation of the torus. This in principle enables one to determine off-diagonal components of the local metric. Recent claims for a surprisingly high sensitivity of a similar system to gravitational waves and Lense-Thirring fields are unfortunately ill founded.
33 citations
TL;DR: The first chiral quinols from the Mediterranean sponge Aplysina and of 6 suggest phenol oxidative routes from tyrosine precursors for their formation as discussed by the authors.
Abstract: Butanolic extracts of the Mediterranean sponge Aplysina (= Verongia) cavernicola have given, by reverse-phase HPLC, the antibacterial quinols (±)-3-bromoverongiaquinol (= (±)-3-bromo-1-hydroxy-4-oxo-2,5-cyclohexadine-1-acetamide; 1d) and (±)-3-bromo-5-chloroverongiaquinol (= (±)-3-bromo-5-chloro-1-hydroxy-4-oxo-2,5-cyclohexadine-1-acetamide; 1c) besides the products of their formal cyclization 5-chlorohexadiene-1-acetamide; 1c) besides the products of their formal cyclization 5-chlorocavernicolin (= 5-cloro-3,3a,7,7aβ-tetrahydro-3aβ-hydroxy-2,6(1H)-indoledione; 6), the C(7)-epimerizing 7β-bromo-5-chlorocavernicolin (=7 β-bromo-5-chloro-3,3a,7,7aβ-tetrahydro-3aβ-hydroxy-2,6(1H)-indoledione; 4a and 7α-bromo-5-chlorocavernicolin (4b), and the C(7)-epimerizing 5-bromo-7β-chlorocavernicolin ( = 5-bromo-7β-chloro-3,3a,7,7aβ-tetrahydro-3aβ-hydroxy-2,6(1H)-indoledione; 5a) and 5-bromo-7α-chlorocavernicolin (5b). The latter four were isolated as mixtures of C(7)-epimerizing monoacetates 4a′/4b′ and 5a′/5b′. Both 1 and 1c proved to be racemic from NMR examination of their esterification products with (–)-methyl-oxyacetic acid, whilst 6 had a ca. 6% enantiomeric purity as shown by a 1H-NMR study of its monoacetate 6′ in the presence of a chiral shift reagent. These chiroptical data of the first chiral quinols from the Verongida and of 6 suggest phenol oxidative routes from tyrosine precursors for their formation. In view of their bioactivities, 1d and 1c have been synthesized from (p-hydroxyphenyl)acetic acid byt phenol oxidative routes.
32 citations
TL;DR: In this paper, the Jastrow wave function is used to model the nuclear momentum distribution in terms of dynamical interparticle correlations and two simple low-cluster-order approximations are proposed, one of which may be readily adapted to finite nuclei.
31 citations
TL;DR: In this article, an effective interaction for Hartree-Fock calculations in liquid 3 He was proposed to reproduce the density dependence of the effective mass and the binding energy, density and incompressibility at saturation.
29 citations
TL;DR: In this article, the La Salle invariance principle has been used to obtain the stability results of the null solution of a semilinear PDE, assuming only the precompactness of the orbits and the local existence.
25 citations
TL;DR: In this article, a methode generale is presented, which semble bonne pour etudier les proprietes de stabilite d'une grande classe d'equations non lineaires and qui n'a pas besoin de propriete de compacite.
Abstract: On presente une methode generale qui semble bonne pour etudier les proprietes de stabilite d'une grande classe d'equations non lineaires et qui n'a pas besoin de propriete de compacite
TL;DR: In this paper, it was shown that the perturbative S -matrix cannot be expressed in terms of well-defined distributions in a Hilbert space involving only physical states without conflicting with unitarity.
TL;DR: In this paper, hot aqueous 20 % sulphuric acid rapidly equilibrates the two isomers in a 1:4 ratio, which is the state of the art.
TL;DR: In particular, the stability under countable intersection enables us to give a precise meaning to the concept of ''minimal hull'' of a bounded set as mentioned in this paper, which is a property of Caccioppoli sets.
Abstract: We discuss some properties of Caccioppoli sets, whose boundaries minimize the area with respect to all compact perturbations which increase the sets. In particular, the stability under countable intersection enables us to give a precise meaning to the concept of «minimal hull» of a bounded set.
TL;DR: The first case of a marine natural product (monobromocavernicolin) with low enantiomeric purity is reported, after a number of unsuccessful attempts to clarify the origin of small optical rotations from polarimetric measurements coming from the sponge Aplysina cavernicola.
Abstract: Resulting from enzymatic reactions, natural products are the standard of reference for high optical purity. In fact, natural products commonly reveal specific rotations from polarimetric measurements. The few cases of racemic natural products and, particularly, the rare cases of quasi-racemic natural products [1] are of special biological interest. Therefore, we are pleased to be able to report on the first case of a marine natural product (monobromocavernicolin, 1) with low enantiomeric purity. These results were obtained after a number of unsuccessful attempts to clarify the origin of small optical rotations with 3 and its C-2-epimer [2], all these products coming from the sponge Aplysina cavernicola.
TL;DR: In this paper, free energy, entropy and volume differences between face-centered and body-centered cubic structures have been evaluated for model rare gas and alkali metal crystals by using the method of overlapping distributions.
Abstract: Free-energy, entropy and volume differences between face-centered and body-centered cubic structures have been evaluated for model rare gas and alkali metal crystals by using the method of overlapping distributions. Stable phases are predicted in agreement with the behaviour of real materials in the regions of validity of classical mechanics and in agreement with the results of previous dynamical-simulation studies of crystal nucleation from the melt and of polymorphic transformations. The existence of a stable b.c.c. phase at high pressure and temperatures is predicted in this way for Lennard-Jones solids, while no high-pressure f.c.c. phase is expected for model Rb and Cs systems. We also show the possibility of making calculations of free-energy barriers to displacive crystalline transformations along a prescribed trajectory in configuration space.
TL;DR: In this article, De Giorgi's Γ-limits are obtained via a decomposition of their carriers (carrier=sostegno) in the setting of completely distributive complete lattices.
Abstract: Sequential forms of De Giorgi's Γ-limits are obtained via a decomposition of their carriers (carrier=sostegno) in the setting of completely distributive complete lattices. Moreover, the notion of carrier enables us to calculate easily the K-limits of epi- or hipo-graphs of arbitrary Γ-limits.
TL;DR: In this article, the authors compare policies in Italy and the United States on the care and education of children from birth to 10 years of age, and find that the two countries differ both in the extent of government intervention and the criteria they use to single out groups with particular needs.
Abstract: Welfare states and their policies have come to define and shape childhood experiences. This paper compares policies in Italy and the United States on the care and education of children from birth to 10 years of age. The two countries differ both in the extent of government intervention and the criteria they use to single out groups with particular needs. There are two main consequences of these different approaches: first, differences in the perception of a normal child's experiences; and second, differences in the definition by which social rights are granted. Families in the two countries employ different resources and encounter unique limitations in defining and satisfying their children's needs.
01 Jan 1984
TL;DR: In this article, the construction of a fast silicon p doped low temperature bolometer is described, which is a 5 × 5 × 03 mm Si n-type chip whose surface has been implanted with p doses of the order of 1018cm−3.
TL;DR: In this paper, a 30% overall yield from α-santolinenone via the diastereoisomeric allylic alcohols (+)-4a/(+)-4b, which are oxidized to (+)-1 with Ag2CO3/Celite.
Abstract: Authentic α-santolinenone ( = (+)-(4R)-1(7)-p-menthen-2-one; (+)-1) is made available for the the first time in 30% overall yield from (+)-(4R)-p-menthene ((+)-2) via the diastereoisomeric allylic alcohols (+)-4a/(+)-4b, which are oxidized to (+)-1 with Ag2CO3/Celite. Yields are good, except for the last stage; indeed, only alcohol (+)-4a, with equatorial OH-group, undergoes oxidation, and (+)-1 is partly substracted via a hetero Diels-Alder dimerization giving a mixture of the diastereoisomeric dihydropyrans (+)-5a/(+)-5b. When Cr(VI) reagents ae used, (+)-4a/(+)-4b mainly give phellandral (6) and carvotanacetone (7), NnO2 reacts too sluggishly with (+)-4a/(+)-4b. A camphor pyrolyzate, previously thought to be 1 must be a different compound, probably 7.
TL;DR: In this article, the effect of temperature on the dispersion of surface phonons in a registered xenon monolayer physisorbed on the graphite basal plane was investigated.
TL;DR: The gorgonian Paragorgia arborea, collected in the Crozet Is. waters at a depth of 280 m during the cruise MD.30/BIOMASS, is shown to possess three C20H28O2 xeniolide diterpenoids, two of which are identical with those from a Corallium sp.
TL;DR: In this article, the sum rules for longitudinal and transverse excitations in normal Fermi liquids are calculated in the low-temperature limit using the Landau theory, and different mean excitation energies are defined in terms of sum rules and compared with the frequency of the collective motion.
Abstract: Sum rules for longitudinal and transverse excitations in normal Fermi liquids are calculated in the low-temperature limit using the Landau theory. The analysis provides a physical interpretation of sum rules in terms of the collective parameters of macroscopic models such as the hydrodynamic and the elastic models. Different mean excitation energies are defined in terms of sum rules and compared with the frequency of the collective motion of the system (zero sound).
TL;DR: In this article, a sum rule approach is presented to study the role of dynamical correlations in electron scattering reactions, where both the induced nucleon-nucleon repulsive short range and tensor correlations are taken into account in the explicit calculations of energy-weighted and non-energyweighted sum rules in /sup 16/O and /sup 12/C.
Abstract: A sum rule approach is presented to study in detail the role of dynamical correlations in electron scattering reactions. Both the induced nucleon-nucleon repulsive short range and tensor correlations are taken into account in the explicit calculations of energy-weighted and non-energy-weighted sum rules in /sup 16/O and /sup 12/C. The former are largely affected by tensor correlations in a wide region of momentum transfer, while the latter are mostly model independent. The theoretical results for the longitudinal and transverse integrated response functions of /sup 12/C are compared with available experimental data.
TL;DR: There are differences in both tertiary and quaternary structures between carp and human normal adult hemoglobins which could contribute to the great differences in the functional properties between these two proteins.
Abstract: The high-resolution proton nuclear magnetic resonance spectra of carp hemoglobin have been compared to those of human normal adult hemoglobin. Carp deoxy and carbonmonoxy hemoglobins in the deoxy-type quaternary state exhibit two downfield exchangeable proton resonances as compared to four seen in human normal adult deoxyhemoglobin. This suggests that two of the hydrogen bonds present in human normal adult deoxyhemoglobin are absent or occur in very different environments in carp hemoglobin. One of the exchangeable proton resonances of carp hemoglobin, while present in the deoxy-type quaternary state of the carbonmonoxy and deoxy derivatives, is absent in the oxy-type quaternary state of both, in agreement with the assignments of these quaternary structures by other methods. The ring-current-shifted proton resonances (sensitive tertiary structural markers) of carp carbonmonoxyhemoglobin are substantially different from those of human normal adult hemoglobin. The aromatic proton resonance region of carp hemoglobin has fewer resonances than that of human normal adult hemoglobin, consistent with its much reduced histidine content. The hyperfine-shifted proximal histidyl NH-exchangeable proton resonances of carp hemoglobin suggest that during the transition from the oxy to the deoxy quaternary structure, there is a greater alteration in the heme pocket of one type of subunits (presumably the β chain) than that in the other subunit. The present results suggest that there are differences in both tertiary and quaternary structures between carp and human normal adult hemoglobins which could contribute to the great differences in the functional properties between these two proteins.
01 Jan 1984
TL;DR: Path Integral Monte Carlo (PIMC) as discussed by the authors is one way of exploiting the connection between the diffusion equation and the Schrodinger equation for numerical computation based on sampling for quantum statistical mechanics.
Abstract: Path Integral Monte Carlo (PIMC) is one way of exploiting the connection between the diffusion equation and the Schrodinger equation for numerical computation based on sampling for quantum statistical mechanics. Starting from the introduction of the Wiener integral, that is the mathematical foundation supporting the numerical work, a number of methodological aspects of the implementation of PIMC are discussed, including suitable approximations to treat hard core particles, schemes for the calculation of free energy differences and of time dependent properties, and the problem of correlation and variance in the mean of estimators in Monte Carlo chains.
TL;DR: In this article, the authors measured selective luminescence and excitation spectra at 80 K over the energy range of the direct absorption features in the layer semiconductor GaSe.
TL;DR: It is shown that the protein is always inserted into a bilayer during this process, i.e. fusion of proteoliposomes with the artificial membrane occurs and the strong non linearity of the current-voltage curve of the hemocyanin pore could be used as a probe of the extent to which fusion preserves the orientation of the channel through the bilayer.
Abstract: Large unilamellar vesicles were prepared by detergent removal from micelles containing phosphatidylcholine, phosphatidylethanolam ine and phosphatidylserine. Liposomes were then interacted with Megathura crenulata hemocyanin, a well studied channel former. Incubation of the resulting proteoliposomes on one side of a phosphatidylserine-containing planar bilayer under fusion conditions yielded strong current increases. Such increase is due to insertion of ionic channels from the liposomes into the planar bilayer. Studying the effects of Ba²⁺ on the electrical properties of the channel we could show that the protein is always inserted into a bilayer during this process, i.e. fusion of proteoliposomes with the artificial membrane occurs. The strong non linearity of the current-voltage curve of the hemocyanin pore could be used as a probe of the extent to which fusion preserves the orientation of the channel through the bilayer.
TL;DR: For a wide class of linear connected semisimple Lie groups, one obtains formulas limiting the Langlands parameters of irreducible unitary representations obtained from maximal parabolic subgroups that confirm aspects of conjectures that relate unitary parameters to cohomological induction.
Abstract: For a wide class of linear connected semisimple Lie groups, one obtains formulas limiting the Langlands parameters of irreducible unitary representations obtained from maximal parabolic subgroups. The formulas relate unitarity to the number of roots satisfying certain conditions. Some evidence is presented that the formulas are sharp. The results confirm aspects of conjectures that relate unitary parameters to cohomological induction.