Showing papers by "University of Trento published in 1985"
TL;DR: In this paper, conditions for the existence, stability and global attractivity of steady-state and periodic solutions are derived for a class of population models in which the parameters such as fecundity, mortality and interaction coefficients are assumed to be age-dependent.
Abstract: A class of population models is considered in which the parameters such as fecundity, mortality and interaction coefficients are assumed to be age-dependent. Conditions for the existence, stability and global attractivity of steady-state and periodic solutions are derived. The dependence of these solutions on the maturation periods is analyzed. These results are applied to specific single and multiple population models. It is shown that periodic solutions cannot occur in a general class of single population age-dependent models. Conditions are derived that determine whether increasing the maturation period has a stabilizing effect. In specific cases, it is shown that any number of switches in stability can occur as the maturation period is increased. An example is given of predator-prey model where each one of these stability switches corresponds to a stable steady state losing its stability via a Hopf bifurcation to a periodic solution and regaining its stability upon further increase of the maturation period.
90 citations
73 citations
TL;DR: In this paper, the authors use the inversion of the formal Laplace transform of R to analyze the regularity of the solution of U.S. Problem (1.1).
57 citations
TL;DR: In this paper, the authors consider a class of functionals of the strain (or of the gradient), whose main feature is that they are not coercive when the forces are zero, while they are coercive under suitable assumptions for the load.
Abstract: We consider a class of functionals of the strain (or of the gradient), whose main feature is that they are not coercive when the forces are zero, while they are coercive under suitable assumptions for the load. The main application is to the problem of static equilibrium for a class of elastic materials in which the stress is constrained to be negative semi-definite. Functions of bounded deformation and measure theory are a basic technical tool in the paper.
48 citations
TL;DR: A mixture of sponges of the East Pyrenean Mediterranean is shown to contain the known sponge products longifolin (1), avarol ((+)-3), and avarone (4) and the terrestrial plant product sesquirosefuran (2), besides to the new furano-sesquiterpenoids tavacfuran.
Abstract: A mixture of sponges of the East Pyrenean Mediterranean is shown to contain the known sponge products longifolin (1), avarol ((+)-3), and avarone (4) and the terrestrial-plant product sesquirosefuran (2), besides to the new furano-sesquiterpenoids tavacfuran (= 3-methyl-2-[(3′Z)-3′-methyl-4″-methyl-2″-furyl-3′-butenyl]furan; (5) and tavacpallescensin (= 5,10-dihydro-6,9-dimethyl-4H-benzo[5,6]cyclohepta[1,2-b]furan; 6) and the new furano-butenolide sesquiterpenoids tavacbutenolide-1 (= (±-4-ethoxy-2-methyl-4-)[(2′E)-2′-methyl-4′-(3″-methyl-2″-furyl)-2′-butenyl]-2-buten-4-olide; (±)-7) and tavacbutenolide-2 (= (±)-4-ethoxy-3-methyl-4-[2′E)-3′-methyl-4′-(4″-methyl-2″-furyl)-2′-butenyl]-2-buten-4-olide; (±)-8). Structural assignments are based on NMR data and on the synthesis of the (E)-isomer of 5. The sponge Dysidea tupha of the same area is also shown to contain the two sesquiterpenoids ent-furodysinin ((−)-14), which is enantiomeric to a product of a Dysidea sp. of Australian waters, and tuphabutenolide ((+)-15).
47 citations
01 Sep 1985
TL;DR: In this article, the momentum distributions in light nuclei like 4He, 16O and 40Ca are explicitly calculated within a phenomenological model which includes dynamical short range and tensor correlation effects.
Abstract: The momentum distributions in nuclei like4He,16O and40Ca are explicitly calculated within a phenomenological model which includes dynamical short range and tensor correlation effects. The common behaviour of such distributions in the high momentum region, already established in light nuclei, is extended to the medium weight region. Comparison with existing calculations is discussed and, for completeness, also form factors are evaluated within the same framework.
45 citations
TL;DR: In this article, the authors give sufficient conditions for the nonlinear stability of possibly nonsmooth stationary solutions of the two-dimensional Euler equation in symmetric bounded domains and investigate the stability of smooth solutions under perturbations of the boundary.
Abstract: We give sufficient conditions for the nonlinear stability of possibly nonsmooth stationary solutions of the two-dimensional Euler equation in symmetric bounded domains. We use, as Lyapunov functions, first integrals due to the symmetry of the problem. Moreover, we investigate the stability of smooth solutions under perturbations of the boundary. The last result is based on a generalization of the well known Arnold approach.
42 citations
TL;DR: In this paper, ground state properties of 3He clusters are investigated in the framework of the Hartree-Fock theory using an effective interaction of phenomenological type, and binding energies and density distributions are evaluated for clusters up to N = 168 atoms.
31 citations
TL;DR: Tuning measurements on the same ion-implanted niobium films show a fall of the measured value of 2\ensuremath{\Delta}(0)/${\mathrm{kT}}_{c}$ below the BCS value for very disordered films.
Abstract: New data on the depression of ${T}_{c}$ related to disorder effects for ${\mathrm{N}}^{+}$ ion-implanted niobium films are presented, extending up to a resistivity ${\ensuremath{\rho}}_{0}$\ensuremath{\simeq}150 \ensuremath{\mu}\ensuremath{\Omega} cm. The results are discussed in the framework of the existing theories. Tunneling measurements on the same ion-implanted films show a fall of the measured value of 2\ensuremath{\Delta}(0)/${\mathrm{kT}}_{c}$ below the BCS value for very disordered films.
31 citations
TL;DR: The title sponge is shown to contain eight new sesquiterpenoids for which a common, unusual biogenetic origin is postulated as mentioned in this paper, and two diols separated as the monoacetates are shown to be: (−)-(1R*,4R*)-3-(3′-furyl)methyl-2-p-menthen-7-yl acetate ((−)-8b) and (
Abstract: The title sponge is shown to contain eight new sesquiterpenoids for which a common, unusual biogenetic origin is postulated. The compounds are shown to be: (–)-(1R*,4R*)-3-(3′-furyl)methyl-2-p-menthen-7-yl acetate ((–)-8b); two diols separated as the monoacetates (–)-(1S*,4R*)-3-(3′-furyl)methyl-l-hydroxy-2-p-menthen-7-yl acetate ((–)-13a) and the (–)-(1R*,4R*)-epimer (–)-13b, the two C(4)-epimeric 4-ethoxy-3-(1′(7′),2′-p-menthadien-3′-yl)methyl-2-buten-4-olides ((+)-14a and (–)-14b), (–)-3-(3′-furyl)methyl-7-nor-2-p-menthen-l-one ((–)-11), (–)-(3Z)-1-(3′-furyl)-4,8-dimethylnona-3, 7-dien-2-yl acetate ((–)-17), and (+)-3-(5′,7′-seco-2′(10′)-pinen-7′-yl)methylfuran ((+)-15).
28 citations
TL;DR: In this paper, an ab initio ion-ion pair potential derived from the theory of metals for bulk Na is employed to investigate point defect jump dynamics on bcc (211), (110) and (100) surfaces using molecular dynamics.
TL;DR: In this paper, a sum rule approach is proposed for investigating the effects of triaxiality on the splitting of the M1 isovector rotational state, and the explicit dependence of the energy and M1 strength of these states on the deformation parameters ϵB and γ is derived.
TL;DR: The complete one-loop expression for the divergent parts of the three-gluon vertex in the light-cone gauge is calculated for pure Yang-Mills theories in this paper.
TL;DR: In this article, the authors studied the groups G in which each element commutes with all of its images under endomorphisms of G. They can be defined equivalently as groups G such that the near-ring generated by the endomorphism of G in the near ring of maps on G is actually a ring (see [7, Sect. 3; 3, Theorem 4.4.31; see also the remark following Lemma 3.6.4).
TL;DR: In this article, an effective interaction for Hartree-Fock calculations in 3He4He mixtures is proposed by generalizing an approach recently employed for pure 3He and 4He systems.
TL;DR: Ajugasterone-C, an ecdysteroid so far thought to be an exclusive and rare, terrestrial, plant product, and ecdysone, have been isolated from both wild and captive Mediterranean zoanthid Gerardia savaglia.
Abstract: Ajugasterone-C, an ecdysteroid so far thought to be an exclusive and rare, terrestrial, plant product, and ecdysone, have been isolated, in relatively large amounts (milligrams per gram dry animal), from both wild and captive Mediterranean zoanthid Gerardia savaglia.
TL;DR: An unprecedented phenol oxidative biogenetic pathway is suggested leading to 7-bromo-1,5-dihydroxy-2-azabicyclo, based on X-ray and NMR analysis and on the observation that acetylation of 3 affords two monoacetates.
Abstract: A novel, mildly antibacterial, α-bromoenone (7-bromocavernicolenone) has been isolated from the Mediterranean sponge Aplysina (= Verongia) cavernicola. Its structure, 7-bromo-1,5-dihydroxy-2-azabicyclo[3.3.1]non-6-en-3,8-dione (3), is based on X-ray and NMR analysis and on the observation that acetylation of 3 affords two monoacetates. An unprecedented phenol oxidative biogenetic pathway is suggested leading to 7-bromocavernicolenone via 3-bromotyrosine and 5-bromodopa.
TL;DR: In this article, the authors discuss some difficulties arising already at the two loop level in renormalization of the pure Yang-Mills theory in the light-cone gauge, and discuss the difficulties arising at the three loop level.
01 Jan 1985
TL;DR: In fact, age dependent fertility and mortality rates are among the most basic parameters in the theory of population dynamics and demography; and the mathematical problems arising, are interesting and challenging in their own rights.
Abstract: Mathematical models describing the evolution of age-structured populations have received increasing attention in recent years, both for the biological interest and for the mathematical one. In fact age dependent fertility and mortality rates are among the most basic parameters in the theory of population dynamics and demography; and the mathematical problems arising, are interesting and challenging in their own rights.
TL;DR: In this paper, the authors consider a Lagrangian density with nine terms linear or quadratic in the curvature and the torsion tensors and derive the conditions which the parameters have to satisfy in order to avoid zero-mass ghosts.
Abstract: In the framework of a Poincare gange theory, we consider a Lagrangian density containing nine terms linear or quadratic in the curvature and the torsion tensors. We consider the zero-mass normal modes of the linearized theory and we derive the conditions which the parameters have to satisfy in order to avoid zero-mass ghosts. We consider in detail the additional gauge transformations and the corresponding constraints on the sources which appear for some special values of the parameters. We conclude that a long-range propagation of the totally antisymmetric part of the torsion is not compatible with the absence of ghosts and of unphysical constraints on the sources.
Abstract: Light scattering measurements are made on superionic glasses (AgI)x(Ag2OnB2O3) 1−x from 2 to 400 cm−1 and in the temperature range 80 to 400 K. The data show the existence of a strong low frequency scattering which has a Lorentzian shape centered at zero frequency. A model is adopted from disordered crystals which treats such scattering as being due to the jumping of Ag ions. The fitting parameters are related to the probability of jump of the diffusing particles in various sites. An order of magnitude calculation relates the quantities obtained by the model with the completely independent measurements of conductivity and tracer diffusion; satisfactory agreement is found.
En cet article on presente des mesures de diffusion de la lumiere sur des verres superioniques de la famille (AgI)x (Ag2OnB2O3)1−x dans l'interval de frequences 2 a 400 cm−1 a plusieres temperatures entre 80 et 400 K. Les donnees montrent l'existence aux basses frequences d'une considerable diffusion, qui a la forme d'une lorentziane centree a la frequence nulle. A l'aide d'un model valable pour les cristaux desordonnes on traite cette diffusion par rapport a la migration par sauts des ions Ag parmi le differents endroits a l'interieur de la matrice vitreuse. Un calcul approxime a l'ordre de grandeur permit de mettre en correlation les quantites obtenues par le model avec les resultats des mesures de conductivite ionique de diffusion des tracants radioactifs. L'accord est satisfaisant.
TL;DR: In this article, the authors investigated spontaneous excitonic luminescence in GaSe from 80 to 300 K and at weak laser excitation intensity, and found that the exciton binding centres are deep neutral acceptors.
Abstract: Spontaneous excitonic luminescence in GaSe is investigated from 80 to 300 K and at weak laser excitation intensity. Radiative recombinations of direct and indirect free excitons are clearly observed. The analysis of the emission lines as a function of the temperature, of the excitation intensity, and of laser energy permits to attribute two lines of the intrinsic luminecsence to the recombination of direct and indirect excitons bound to defect centres localized in the energy gap. On the basis of recent theories on exciton-impurity complexes, it is found that in the crystals the excitonic binding centres are deep neutral acceptors. From the dissociation energy of the bound excitons the ionization energy of the acceptor levels is estimated. Moreover, the measurements seem to indicate that thermal equilibrium between direct and indirect excitonic states is lacking below about 100 K.
Die Spontane Exzitonenlumineszenz in GaSe wird zwischen 80 und 300 K und mit schwacher Laseranregungsintensitat untersucht. Strahlende Rekombination von direkten und indirekten freien Exzitonen wird deutlich beobachtet. Die Analyse der Emissionslinien in Abhangigkeit von der Temperatur, der Anregungsintensitat und der Laserenergie erlaubt, zwei Linien der intrinsischen Lumineszenz der Rekombination von direkten und indirekten Exzitonen zuzuordnen, die an in der Energielucke lokalisierten Defektzentren gebunden sind. Auf der Grundlage neuerer Theorien zu Exziton-Storstellenkomplexen wird gefunden, das in den untersuchten Kristallen die Exzitonenbindungszentren tiefe neutrale Akzeptoren sind. Aus der Dissoziationsenergie gebundener Exzitonen last sich die Ionisierungsenergie der Akzeptorniveaus berechnen. Daruberhinaus scheinen die Mesergebnisse zu zeigen, das unterhalb etwa 100 K kein thermisches Gleichgewicht mehr besteht zwischen direkten und indirekten Exzitonenzustatnden.
Journal Article•
TL;DR: In this paper, a modele utilise rend bien compte des positions spectrales and des formes de raie observees to reduce the effets des densites de porteurs inhomogenes.
Abstract: Mesures des spectres de luminescence a 4,2 K. Afin de reduire les effets des densites de porteurs inhomogenes, on utilise des trous stenopeiques et des echantillons fins. Observation de deux raies attribuees aux transitions directes et indirectes. Le modele utilise rend bien compte des positions spectrales et des formes de raie observees
TL;DR: Differences between term behavioral states exist both in continuously fed infants and in controls, and long term continuous nutrition does not allow for the establishment of the circadian modulation of HR.
TL;DR: Proteolysis of the fluid phase complement complex SC5b-9 transforms it into an arnphiphilic molecule which resembles the membrane attack complex of complement and reconstitutes into lipid vesicles, resulting in massive conductance increases.
Abstract: Proteolysis of the fluid phase complement complex SC5b-9 transforms it into an arnphiphilic molecule which resembles the membrane attack complex of complement and reconstitutes into lipid vesicles. Complement-containing vesicles prepared in this way can be made to fuse with planar lipid bilayers transferring their protein content to the host membrane. Massive conductance increases can thus be observed, which are due to the insertion of a large number of ionic channels into the membrane. Using low concentrations of vesicles, single channels can be studied.
TL;DR: In this article, the surface modifications were studied using scanning electron microscopy, X-ray diffractometry and Auger electron spectroscopy, and the high temperature oxidation of the specimens was studied by two series of experiments.
TL;DR: In this article, the temperature evolution of a copper bar during 100 keV Xe ions implantation has been experimentally recorded and quantitatively described by a simple model calculation, based on radiative energy dissipation from hightemperature surface regions intersected by ion impact.
Abstract: The temperature evolution of a copper bar during 100 keV Xe ions implantation has been experimentally recorded. The thermal behaviour of the implanted bar is quantitatively described by a simple model calculation. It is shown that the experimental results may be reproduced by considering a radiative energy dissipation from hightemperature surface regions intersected by ion impact. The quantities characterizing these “thermal-spike” regions like average temperature and lifetime are consistent with earlier thermodynamical estimations reported in the current literature.
TL;DR: In this article, a computer simulation of the partially ionic liquid alloy Li4Pb at 1085K is presented, based on the pairwise potentials used by Copestake et al. to describe the structure of this system: screened Coulomb interact ions plus a soft core repulsion.
Abstract: We present a computer simulation of the partially ionic liquid alloy Li4Pb at 1085K. The calculation is based on the pairwise potentials used by Copestake et al, to describe the structure of this system: screened Coulomb interact ions plus a soft core repulsion. Diffusion coefficients and static and dynamical structure functions are evaluated and compared with experimental results. Pair correlation functions are also presented. The dynamical structure factors show in addition to the interdiffusion mode a propagating mode which is most strongly visible in the Li-Li partial van Hove function. We interpret this mode as an optical-like mode in the liquid.
TL;DR: Various Acidiacea of the Eastern Pyrenean coast around Banyuls-sur-Mer have been screened for in vitro antifungal and antibacterial activity and, preliminarily, for natural products, finding 2′-deoxyribonucleosides.
Abstract: 1. 1. Various Acidiacea of the Eastern Pyrenean coast around Banyuls-sur-Mer have been screened for in vitro antifungal and antibacterial activity and, preliminarily, for natural products. 2. 2. Antifungal and antibacterial activities were found with Polyclinidae. 3. 3. One didemnid (Trididemnum cereum) has also been carefully screened for natural products, finding 2′-deoxyribonucleosides. 4. 4. In the marine environment such nucleosides have been previously isolated from only starfish.