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Showing papers by "University of Trento published in 1981"


Journal ArticleDOI
TL;DR: In this paper, the authors give some rules to define measures which describe heat flow in homogeneous crystals and then study a particular model which is explicitly solvable: the one dimensional nearest neighborhood Ising model.
Abstract: We give some rules to define measures which could describe heat flow in homogeneous crystals. We then study a particular model which is explicitly solvable: the one dimensional nearest neighborhood Ising model. We analyze two cases. In the first one the spins at the two boundaries interact with reservoirs at different temperatures; in the thermodynamical limit the measure we introduce converges locally to Gibbs measures and a temperature profile is so derived. We obtain an explicit expression for the thermal conductivity coefficient which depends on the temperature. In the second case we study the asymptotic behavior starting from an initial state in which each half of the space is at a different temperature. We find again a temperature profile which asymptotically obeys the heat equation with the thermal conductivity coefficient previously derived. From a mathematical point of view, the analysis of the invariant measure is made possible by studying a “time-reversed” process related to a graphical representation of an associated process. This provides us with an explicit formula for then-fold correlation function and we study the limiting behavior using both this representation (for proving an exchangeability result) and a Donsker-type, spacetime renormalization procedure.

51 citations


Journal ArticleDOI
TL;DR: In this article, a detailed analysis of the luminescence intensity has been made as a function of exciting power and temperature, allowing one to ascribe some lines of the intrinsic part of emission spectrum to direct and indirect excitons bound to localized impurity levels in the energy gap of GaSe.
Abstract: Photoluminescence spectra of undoped crystals of the layer semiconductor GaSe have been measured from 80 K up to room temperature. The direct and indirect excitonic emissions are clearly observed in the intrinsic part of the spectrum. Moreover, a detailed analysis of the luminescence intensity has been made as a function of exciting power and temperature, allowing one to ascribe some lines of the intrinsic part of emission spectrum to direct and indirect excitons bound to localized impurity levels in the energy gap of GaSe.

49 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the mean curvature of such a surface is constant, if possibly a discontinuous function of the enclosed volume, and the boundary behaviour of the solutions is also discussed.
Abstract: We prove some facts concerning surfaces of minimal area bounding regions of prescribed volume in ℝn. The main result we prove is that the mean curvature of such a surface is constant, if possibly a discontinuous function of the enclosed volume. The boundary behaviour of the solutions is also discussed.

29 citations


Journal ArticleDOI
TL;DR: The P(3 and P(4) manifolds of the ν3 band of SF6 have been observed in a supersonic beam with a bolometric detection as mentioned in this paper.

28 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported the first observation of optical Ramsey fringes in the 10 ym spectral region using a supersonic seeded beam of 7% SF, in He, illuminated by a CO laser in spatially-separated field zones.
Abstract: We report a first observation of optical Ramsey fringes in the 10 ym spectral region using a supersonic seeded beam of 7% SF, in He, illuminated by a CO laser in spatially-separated field zones. We have used either three standing waves or four travelling waves and obtained highly contrasted fringes with a 23 kHz half-width corresponding to a 5 mm distance between zones. Laser excitation of the vibrational energy of molecules in a beam can be conveniently detected with a cryogenic bolometer [1] and a demonstration of this technique in the case of the V_ mode of SF, excited by CO or N„0 lasers has been recently given [2] . With this equipment the spatial analog of coherent transient effects such as the Rabi oscillations of the transition probability and the adiabatic rapid passage were shown to occur respectively with plane and curved wavefronts. In an attempt to investigate the potential use of this method for very high resolution spectroscopy and optical frequency standards we have made a preliminary experiment to detect the Ramsey fringes associated with saturation spectroscopy in an interaction geometry comprising three or four field zones [3-14]. For this experiment we used the P(4) F.. and E components of the . band of SF, which can be reached with a waveguide CO laser oscillating on the P(16) CO line at 10.55 Van. To control the frequency of this laser we locked it, with a tunable frequency offset, to a conventional reference laser locked to the 0(45) vj. SF, line. 1 b The beam from the waweguide laser was spatially filtered and magnified to have a waist of w = 6 mm. In the case of illumination by this single beam the resulting width (FWHM) of the observed line was a combination of transit broadening and residual first-order Doppler effect along the optical axis and amounted to 300 kHz.We used the Rabi oscillation to set the laser beam waist precisely on the molecular beam [2]. Four oscillations of the signal could be observed with a 40% contrast with successive minima obtained for a total power of M,4,9 and 16 mW. To obtain fringes ,part of the laser beam was intercepted before the interaction region by a screen which transmitted the light only through 1 mm wide slits. Two different geometries were used in these experiments. In the first one, three equidistant standing waves were generated by three equidistant slits of 5 mm separation together with a corner cube placed on the other side of the molecular beam to (*)Work supported in part by D.R.E.T. (+)Permanent address : Physics and Chemistry Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981802 C8-16 JOURNAL DE PHYSIQUE r e t r o r e f l e c t t h e l i g h t back through t h e slits. I n t h e second geometry, only two of t h e previous s l i t s were illuminated. An o f f s e t between t h e center of t h e s l i t s and t h e cen te r of t h e corner cube generated two counter-propagating s e t s of t r a v e l l i n g waves with a 5 mm d i s tance between adjacent co-propagating waves of each s e t . The spacing between t h e two s e t s can be a r b i t r a r y and was a c t u a l l y l O m m i n t h i s experiment. Highly contrasted f r inges have been obtained i n both cases and a s an example t h e f i g u r e d i sp lays t h e s igna l corresponding t o t h e four t r a v e l l i n g waves case. Use of purely t r a v e l l i n g waves t o ob ta in o p t i c a l Ramsey f r i n g e s has been suggested by t h e ana lys i s of references [4-5,101 and we have here a f i r s t demonstration of t h i s p o s s i b i l i t y together with t h e Ca beam experiment of Helmcke e t a1.[14] . The broad pedestal has a width QJ1.4 MHz corresponding t o t h e t r a n s i t broadening width across a s i n g l e zone. The f r inges themselves have a 23 kHz width (HTm) cons i s ten t with a QJ930 m/sec peak ve loc i ty of t h e SF6 molecules 1151 .

21 citations



Journal ArticleDOI
TL;DR: In this article, a comparison is made between time resolved laser-bolometric technique and alternative molecular beam diagnostic methods, and experimental results are presented and analyzed for pure SF6 and helium seeded with 5% SF6 beams.
Abstract: The laser-bolometric infrared spectroscopy is an efficient method for measuring the internal energy distributions of molecular beams. Additional informations about the kinetic energy distribution of molecules in a selected internal state can be obtained from time resolved experiments. A fast superconducting bolometer and a pulsed infrared CO2 laser have been used for testing the use of this technique as a universal tool for molecular beam diagnostics. Experimental results are presented and analyzed for pure SF6 and helium seeded with 5% SF6 beams. The efficiency of fast superconducting bolometers, used for molecular beam time-of-flight measurements, is discussed. A comparison is made between time resolved laser-bolometric technique and alternative molecular beam diagnostic methods.

17 citations


Journal ArticleDOI
TL;DR: In this paper, the usual dispersion relation of the vibrating potential model is generalized to include current effects and the model is explicitly solved for the isoscalar quadrupole and rotational modes and the role of the effective mass is pointed out.

16 citations


Journal ArticleDOI
M. Toller1
TL;DR: The convex closed cones which are stable under the restricted Lorentz group form a family parametrized by a new physical constant, in the simplest case a fundamental lenght as discussed by the authors.
Abstract: We consider the ten-dimensional vector space Open image in new window whose elements are generators of infinitesimal transformations of the tendimensional manifold Open image in new window of all the local reference frames. We indicate by Open image in new window the convex closed cone which contains the generators of the physically feasible transformations and we assume that Open image in new window is stable under a group Open image in new window of linear mappings of Open image in new window onto itself. The convex closed cones which are stable under the restricted Lorentz group form a family parametrized by a quantityl which we interpret as a new physical constant, in the simplest case a fundamental lenght. We discuss all the linear mappings which leave the cone Open image in new window stable and we show that, under reasonable assumptions, the symmetry group Open image in new window contains a group isomorphic to the restricted de Sitter groupSO2,3+ and possibly also a parity operator and the dilatations of the space Open image in new window .

14 citations


Journal ArticleDOI
L. Bonomi1, S. Perfetti1, R. Bellucci1, F. Massa1, Ettore Noya1 
TL;DR: The ocular hypotensive action of labetalol, a drug endowed with alpha- and beta-adrenergic receptor-blocking properties, was studied in both rabbit and human eyes and was found to be at least as effective as timolol and more active than pilocarpine or propranolol.
Abstract: The ocular hypotensive action of labetalol, a drug endowed with alpha- and beta-adrenergic receptor-blocking properties, was studied in both rabbit and human eyes. In the rabbit, using two different models of experimentally induced ocular hypertension, an impressive decrease of IOP was seen after topical administration of the drug. In this species labetalol was found to be at least as effective as timolol and more active than pilocarpine or propranolol. In human eyes suffering from glaucoma, however, its effectiveness was much less evident and clearly inferior to that of timolol.

14 citations


Journal ArticleDOI
TL;DR: In this article, the role of the symmetry energy in the giant dipole resonance was discussed with particular emphasis on surface effects, and a microscopics approach based on the evaluation of two sum rules was developed to derive the expression ω D = [( 1 3 mA) × (∫∇ 2 V 0 ϱ d ν + ∫ V sym |∇ϱ| 2 d Ͻ )] 1 2 for the energy of the dipole mode.

Journal ArticleDOI
TL;DR: The role of spin-orbit interaction, Jahn-Teller effect, and nonradiative transitions in determining the shape of the zero-phonon lines are discussed in this paper.
Abstract: Excitation spectra of divalent vanadium in MgO are reported. An accurate analysis of previously unobserved transitions is presented; the magnetic and vibration-induced electric dipole contributions are discussed; and experimental energies and intensities are compared to computed ones. The role of spin-orbit interaction, Jahn-Teller effect, and nonradiative transitions in determining the shape of the zero-phonon lines are discussed.

Journal ArticleDOI
M. Anderle1, Davide Bassi1, S. Iannotta1, S. Marchetti1, Giacinto Scoles1 
TL;DR: In this article, the spin-exchange cross section sigma for the collision of hydrogen atoms with O/sub 2/ and NO have been measured by means of stored atomic-beam spectroscopy.
Abstract: The spin-exchange cross section sigma for the collision of hydrogen atoms with O/sub 2/ and NO have been measured by means of stored atomic-beam spectroscopy. Average values at room temperature are sigma (H-O/sub 2/)10=(plus-or-minus1) x 10/sup -16/ cm/sup 2/ and sigma (H-NO)13=(plus-or-minus1) x 10/sup -16/ cm/sup 2/. A comparison between our data and pulsed-maser measurements is presented. The development of a passive hydrogen maser based on our bolometric detection technique is proposed.

Journal ArticleDOI
TL;DR: In this article, it was shown that the so-called spurious singularities, characteristic of the axial gauges, are related to the boundary conditions one can impose on the potentials.

Journal ArticleDOI
TL;DR: The electron longitudinal spin relaxation time of a nitroxide radical dissolved in toluene, has been measured in the concentration range 2.5 × 10-4┌5 M.
Abstract: The electron longitudinal spin relaxation time of a nitroxide radical dissolved in toluene, has been measured in the concentration range 2.5 × 10-4┌5 M The use of a new electron spin resonance technique with double transverse irradiation and longitudinal detection, allowed these extended measurements. The experimental values, which vary by orders of magnitude in the samples studied, are in good general accord with theory. The respective weights of different relaxation mechanisms have been evaluated at concentrations which it had not proved possible to study with other techniques.

Journal ArticleDOI
TL;DR: The electrochemical behavior and pitting corrosion resistance of ARMCO iron specimens implanted with nitrogen or boron ions have been studied in this article, where the implantation affects the anodic dissolution of iron, lowering the intergranular attack and enhancing the protective capacity of the oxide layers.

Journal ArticleDOI
TL;DR: In this article, a qualitative explanation of such behaviour is made in terms of phonon assisted activation of Frenkel defects, which increases more rapidly as the superionic transition temperature is approached.

Journal ArticleDOI
TL;DR: In this paper, the authors present condizioni necessari e sufficienti affinche for una fissata coppia di funzioni dinsieme ν, μ crescenti.
Abstract: In questo articolo si danno delle condizioni necessarie e sufficienti affinche per una fissata coppia di funzioni d’insieme ν, μ crescenti esista una funzionef tale che ν=∫fdμ. Si ottiene cosi una proposizione comprendente il teorema di R-N. classico e dei teoremi di R-N., presentati da altri autori, riguardanti le funzioni d’insieme finitamente additive e le funzioni d’insieme subadditive e continue per successioni crescenti.

Journal ArticleDOI
TL;DR: The scaling law in quasi-free electron scattering is broken due to the existence of exchange forces, leading to a finite mean value of the scaling variable y. This effect is considerably increased by wave function correlations, in particular by tensor correlations as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the assumption about the full diamagnetism of oxy-and carbonmonoxy-derivatives of hemoglobins is not warranted and that these derivatives display a variety of magnetic states of the iron ligand complex.
Abstract: Reconsidering early and recently published magnetic susceptibility data, we find that the assumption about the full diamagnetism of oxy- and carbonmonoxy-derivatives of hemoglobins is not warranted. It appears that these derivatives display a variety of magnetic states of the iron ligand complex, depending on conditions which must still be elucidated in full. The bearing of these results on debates of the past, the recent evidence from other spectroscopic techniques and the perspectives for future work are briefly discussed.

Journal ArticleDOI
TL;DR: In this paper, the shape of the zero-phonon line of MgO has been shown to reproduce Fano's formalism in terms of widths and splittings.
Abstract: The spin-orbit interaction in transition-metal ions induces fast nonradiative transitions among states of different spin; the transition rates can be directly measured by the homogeneous broadening of zero-phonon optical lines. The configuration-interaction formalism developed by Fano is well suited for the evaluation of the widths and shifts caused by these nonradiative processes. By taking the Jahn-Teller effect into account, we have shown that within the framework of Fano's formalism it is possible to reproduce the shape of the zero-phonon line of MgO: ${\mathrm{V}}^{2+}$ as regards both widths and splittings without making use of any fitting parameter. The model has also been applied to ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$: ${\mathrm{Cr}}^{3+}$, ${\mathrm{Cs}}_{2}$Si${\mathrm{F}}_{6}$: ${\mathrm{Mn}}^{4+}$, and MgO: ${\mathrm{Cr}}^{3+}$; its limits of validity have been discussed.

Journal ArticleDOI
TL;DR: In this article, a vibrating potential model (VPM) with non-locality effects is studied and the connection with sum rules is explicitly shown and the problem of the full self-consistency of the model is investigated.

Journal ArticleDOI
TL;DR: In this paper, the depolarization ratio of superionic AgI was measured as a function of temperature and the authors proposed a model to explain experimental results of ϱ(T) and I R (T) in which the situation of Ag + ions can be described by an antiferromagnetic-like model.


Journal ArticleDOI
TL;DR: In this paper, the defect level structure of GaSe(Cu) and the recombination kinetic model were investigated for the excitation intensity and temperature dependence of indirect excitonic lines.

Book ChapterDOI
01 Jan 1981
TL;DR: In this article, the analysis of the periodic orbits arising in the generalized Hopf bifurcation problem is discussed, and the existence of these periodic orbits has often been obtained by using techniques such as the Liapunov-Schmidt method or topological degree arguments.
Abstract: Publisher Summary This chapter discusses the analysis of the bifurcating periodic orbits arising in the generalized Hopf bifurcation problem. The existence of these periodic orbits has often been obtained by using techniques such as the Liapunov–Schmidt method or topological degree arguments. The approach, on the other hand, is based upon stability properties of the equilibrium point of the unperturbed system. The fruitfulness of this approach in studying bifurcation problems in R is shown. In the case of R, in contrast to that of Rn, n > 2, the stability arguments can be effectively applied because of the Poincare–Bendixson theory. Bifurcation problems in Rn can be reduced to that of R2 when two-dimensional invariant manifolds are known to exist. The existence of such manifolds occurs, when the unperturbed contains only two purely imaginary eigenvalues. The problem in Rn was first considered by Chafee. Using the Liapunov–Schmidt method, he obtained a determining equation.


Journal ArticleDOI
TL;DR: In this article, a large class of geometric Lagrangian forms defined in the manifold δ of the reference frames are considered. And they are classified according to their symmetry properties with respect to transformation groups acting on the linear space of the infinitesimal transformations of the frames.
Abstract: We consider a large class of geometric Lagrangian forms defined in the manifold δ of the reference frames. The theories described by those Lagrangians are such that, in an empty region, the manifold δ can be identified with one of the de Sitter groups. The Lagrangian forms are classified according to their symmetry properties with respect to transformation groups acting on the linear space of the infinitesimal transformations of the frames. Requiring invariance with respect to aSO(3) group and a reasonable physical behavior under space reflections, we obtain only three different theories. Then we show that every Lagrangian form of the kind we are considering, is equivalent to anSO(3)-invariant one.

Journal ArticleDOI
TL;DR: The gem-dimethoxy σ-adduct of methoxide addition to 2-methoxy-3-nitro-4,5-benzotropone reacts with either (C 2 H 5 ) 3 OBF 4, to change the nitronate into an oxime function, or (CH 3 ) 3 SiCl, to give 2-carbomethoxy-1-nitronaphthalene and the nitronic acid corresponding to the starting adduct as discussed by the authors.