Showing papers by "University of Trento published in 1997"

Bose-Einstein condensation

Abstract: In 1924 the Indian physicist Satyendra Nath Bose sent Einstein a paper in which he derived the Planck law for black-body radiation by treating the photons as a gas of identical particles. Einstein generalized Bose's theory to an ideal gas of identical atoms or molecules for which the number of particles is conserved and, in the same year, predicted that at sufficiently low temperatures the particles would become locked together in the lowest quantum state of the system. We now know that this phenomenon, called Bose-Einstein condensation (BEC), only happens for "bosons" – particles with a total spin that is an integer multiple of h, the Planck constant divided by 2π.

The intrinsic normal cone

Abstract: Let $X$ be an algebraic stack in the sense of Deligne-Mumford. We construct a purely $0$ -dimensional algebraic stack over $X$ (in the sense of Artin), the intrinsic normal cone ${\frak C}_X$ . The notion of (perfect) obstruction theory for $X$ is introduced, and it is shown how to construct, given a perfect obstruction theory for $X$ , a pure-dimensional virtual fundamental class in the Chow group of $X$ . We then prove some properties of such classes, both in the absolute and in the relative context. Via a deformation theory interpretation of obstruction theories we prove that several kinds of moduli spaces carry a natural obstruction theory, and sometimes a perfect one.

A linguistic modeling of consensus in group decision making based on OWA operators

Abstract: In this paper, a model for group decision-making is proposed and defined in a linguistic context. A multiperson multicriteria decision problem is considered, in which a group of experts is involved in the evaluation of the performances of a set of alternatives with respect to a predefined set of criteria. The objective is to evaluate a consensual judgement and a consensus degree on each alternative. Both the experts' evaluations of the alternatives and the degree of consensus are expressed linguistically. A "soft" consensus degree referred to a fuzzy majority of the experts is proposed based on the concept of linguistic quantifier. The entire process is defined in a linguistic domain and modeled within fuzzy set theory by ordered weighted average (OWA) operators.

Hybrid or Unique?: the Japanese Welfare State Between Europe and America:

Abstract: In the contemporary welfare state literature, both Japan and Southern Europe are often held to be distinct regimes. A comparative examination of the evidence for Japan suggests that this is not tru...

Tax Evasion and Moral Constraints: some Experimental Evidence

Abstract: SUMMARY Tax evasion has been mainly studied as a problem of choice under uncertainty; like any portfolio manager, the taxpayer has to allocate her/his fixed gross income between two assets a risky asset, tax evasion, and a safe asset (with a zero return), tax payment. As suggested by the portfolio theory, the taxpayer's choice will be affected by her/his preferences — mainly by her/his attitude towards risk-taking — and by the return on the risky asset determined by the tax structure, which includes both the tax rate and the penalties in the case of evasion However, the pure gamble model appears unsatisfactory on various grounds. Among these and most importantly for our purpose, it neglects the psychological aspects of the decision to evade tax because it rules out any feeling of shame about evading or being detected and punished, and it ignores any intrinsic pleasure from successful evasion In other words, the pure gamble model does not take full account of the moral constraints involved in the tax evasion decision. The main objective of the experiment presented here was therefore to investigate the role played by moral constraints in determining the decision to evade taxes. The experimental evidence supports the thesis that the taxpayer's decisional process involves not only monetary elements but also psychological and moral factors. ZUSAMMENFASSUNG Die Steuerhinterziehung wurde bisher uberwiegend als Problem von Entscheidungen unter Unsicherheit untersucht Wie jeder Portfoliomanager muss auch der Steuerzahler sein Bruttoeinkommen zwischen zwei Anlageformen verteilen eine risikoreiche Anlageform. Steuerhinterziehung, und eine sichere Anlageform (ohne Gewinn), Steuerzahlung. Nach der Portfoliotheorie wird die Entscheidung des Steuerzahlers von seinen Praferenzen beeinflusst — vor allem von seiner Risiko-bereitschaft — und von der Gewinnaussicht der risikoreichen Anlageform, die vom Steuersystem abhangt, d.h. vom Steuersatz und den Strafen bei Steuerhinterziehung. Dieses Lotteriemodell ist jedoch aus mehreren Grunden unbefriedigend: es vernachlassigt die psycholgischen Aspekte der Steuerhinterziehung, weil es jegliches Schamgefuhl bei der Steuerhinterziehung bzw. der Entdeckung und Bestrafung ausschliesst und ein intrinsisches Vergnugen bei erfolgreicher Steuerhinterziehung ignoriert. Das Lotteriemodell zieht also nicht in Betracht, dass moralische Restriktionen die Entscheidung zur Steuerhinterziehung beeinflussen konnten Das hier vorgestellte Experiment wollte daher in erster Linie untersuchen, welche Rolle moralische Restriktionen bei der Entscheidung zur Steuerhinterziehung spielen. Die Ergebnisse des Experiments bestatigen die Hypothese, dass der Entscheidungsprozess des Steuerzahlers nicht nur durch monetare Elemente beeinflusst wird, sondern auch durch psychologische und moralische Faktoren. RESUME L'evasion fiscale a ete principalement etudiee en tant qu'un probleme de choix dans des conditions d'incertitude, comme n'importe quel gestionnaire de portfolio, le contribuable doit repartir son revenu brut fixe entre deux actifs un actif risque, l'evasion fiscale, et un actif sur (avec un taux d'interet zero), le payement des taxes. Comme suggere par la theorie du portfolio, le choix du contribuable sera affecte par ses preferences — principalement par son attitude vis-a-vis du risque — et par le benefice determine par la structure fiscale qui inclut a la fois le taux de taxation et les penalites prevues en cas d'evasion Cependant, le modele pur de jeu apparait insatisfaisant pour plusieurs rasisons Parmi celles-ci, le modele neglige les aspects psychologiques de la decision, limitation specialement importante pour notre objectif, puisqu'il ecarte tout sentiment de honte associe a la decouverte de l'evasion et a la punition ou encore il ignore le plaisir decoulant d'une evasion fiscale reussie. En resume, le modele pur de jeu ne prend pas pleinement en compte les contraintes morales qui influencent la decision. L'objectif principal de l'experimentation presentee ici etait d'analyser le role joue par les contraintes morales dans la prise de decision d'evasion fiscale. Les resultats confirment l'hypothese que le processus decisionel du contribuable depend non seulement des aspects financiers mais egalement des facteurs psychologiques et moraux.

Planning via Model Checking: A Decision Procedure for AR

Abstract: In this paper we propose a new approach to planning based on a “high level action language”, called AR, and “model checking”. AR is an expressive formalism which is able to handle, among other things, ramifications and non-deterministic effects. We define a decision procedure for planning in AR which is based on “symbolic model checking”, a technique which has been successfully applied in hardware and software verification. The decision procedure always terminates with an optimal solution or with failure if no solution exists. We have constructed a planner, called MBP, which implements the decision procedure.

Thermodynamics of a trapped Bose-condensed gas

Abstract: We investigate the thermodynamic behaviour of a Bose gas interacting with repulsive forces and confined in a harmonic anisotropic trap. We develop the formalism of mean field theory for non uniform systems at finite temperature, based on the generalization of Bogoliubov theory for uniform gases. By employing the WKB semiclassical approximation for the excited states we derive systematic results for the temperature dependence of various thermodynamic quantities: condensate fraction, density profiles, thermal energy, specific heat and moment of inertia. Our analysis points out important differences with respect to the thermodynamic behaviour of uniform Bose gases. This is mainly the consequence of a major role played by single particle states at the boundary of the condensate. We find that the thermal depletion of the condensate is strongly enhanced by the presence of repulsive interactions and that the critical temperature is decreased with respect to the predictions of the non-interacting model. Our work points out an important scaling behaviour exhibited by the system in large N limit. Scaling permits to express all the relevant thermodynamic quantities in terms of only two parameters: the reduced temperature t = T/T c 0 and the ratio between the T = 0 value of the chemical potential and the critical temperature T c 0 for Bose-Einstein condensation. Comparisons with first experimental results and ab-initio calculations are presented.

Ki-67 immunostaining in 322 primary breast cancers: Associations with clinical and pathological variables and prognosis

Abstract: Cell-proliferation markers are very important in the clinical management of cancer patients, and the identification of Ki-67 (a monoclonal antibody that recognizes proliferating cells) can make it easier to define the level of proliferative activity. This study investigated the associations between the Ki-67 levels measured by means of immunohistochemistry, and other clinical and pathological variables and prognosis in 322 breast-cancer patients. A significant association was found (p < 0.001) between Ki-67 values and tumor size, nodal status, estrogen and progesterone receptor status; multivariate analysis showed that Ki-67 levels were associated with disease-free and overall survival, thus confirming that it is an independent prognostic variable. Various statistical approaches were used in an attempt to establish the best cut-off point for dividing patients into groups at high or low risk of relapse but, in this series, we could find no evidence leading to a single "best" cut-off point. We conclude that the quantitative level of Ki-67 could be used as a prognostic factor in breast-cancer patients.

Reactive search, a history-sensitive heuristic for MAX-SAT

Abstract: The Reactive Search (RS) method proposes the integration of a simple history-sensitive (machine learning) scheme into local search for the on-line determination of free parameters. In this paper a new RS algorithm is proposed for the approximated solution of the Maximum Satisfiability problem: a component based on local search with temporary prohibitions (Tabu Search) is complemented with a reactive scheme that determines the appropriate value of the prohibition parameter by monitoring the Hamming distance along the search trajectory. The proposed algorithm (H-RTS) can therefore be characterized as a dynamic version of Tabu Search.In addition, the non-oblivious functions recently introduced in the framework of approximation algorithms are used to discover a better local optimum in the initial part of the searchThe algorithm is developed in two phases. First the bias-diversification properties of individual candidate components are analyzed by extensive empirical evaluation, then a reactive scheme is added to the winning component, based on Tabu Search.The final tests on a benchmark of random MAX-3-SAT and MAX-4-SAT problems demonstrate the superiority of H-RTS with respect to alternative heuristics.

Positive-operator-valued time observable in quantum mechanics

Abstract: We examine the longstanding problem of introducing a time observable in quantum mechanics; using the formalism of positive-operator-valued measures, we show how to define such an observable in a natural way and we discuss some consequences.

Spin-flip transitions in a magnetic trap

Abstract: There is currently a great deal of experimental interest in the trapping of alkali-metal atoms in magnetic traps. In this Brief Report we present a method for calculating nonadiabatic spin-flip transitions in such traps. We show that for realistic traps currently being used the loss rate due to this mechanism is exponentially small.

Continuity of care for patients with schizophrenia and related disorders: a comparative South-Verona and Groningen case register study.

Abstract: Background It is widely believed that for the severely mentally ill continuity of care is essential to ensure a better outcome and prevent long-term hospitalization However, not much progress has been made in the operationalization and measurement of this concept We used two indicators to compare continuity of care of schizophrenic patients in two kinds of mental health systems One is a community mental health system without the back-up of a mental hospital (South-Verona, Italy) The other is an institution-based system in which mental hospitals are still predominant (Groningen, The Netherlands) Methods The first indicator of continuity of care, readiness of aftercare, is the time from discharge from hospital to the first day-or out-patient contact Survival analysis was applied to correct for censored observations The second indicator, flexibility of care, is the use of combinations of in-, day-and out-patient care during 2-year follow-up Results More patients in South-Verona received community care within 2 weeks after discharge (715%), than in the Groningen register area (546%) The survival functions differed significantly Cox regression analysis revealed that in both systems a contact before admission, the time between this contact and admission and the duration of the admission are predictors for aftercare A higher percentage of patients made multiple service use (combinations of in-, day-and out-patient care) in South-Verona than in Groningen (62 v 45%) Conclusions Both indicators showed a higher continuity of care in the South-Verona system

On the mechanisms of target modification by ion beams and laser pulses

Abstract: A comparison is made between the importance of the following categories of processes in ion-surface and laser-surface interactions: ballistic, thermal-spike, residual-defect-induced, and electronic. It is shown that ballistic processes are important for ion sputtering, ion mixing, and ion composition change. Also, they exist with laser-pulse sputtering but are not important. The picture with thermal-spike processes is the inverse, such processes being unimportant in most ion-surface interactions, but very important indeed with laser-pulse sputtering. In the latter case one must distinguish between normal vaporization and phase explosion, both of which are fundamental. On the other hand, normal boiling may possibly be unimportant owing to the negligible density of heterogeneous nuclei formed in the bulk, ∼ 106 kg−1. However, it is essential to note that, if nuclei can be formed at the surface, the density will be much higher. Sputtering due to subsurface heating probably does not exist. Residual defects are basic to all ion-surface interactions, but most especially to ion mixing. Here most (∼90%) of the observed mixing is due to residual defects and only a lesser amount is due to ballistic events. But the role of thermal spikes in ion mixing appears to have been exaggerated. Finally, electronic processes are somewhat important to ion sputtering but have not yet been quantified for ion mixing and composition change. On the other hand, although they are very important indeed with laser-surface interactions, a basic qualification must be made: the primary laser-surface interactions are dominantly electronic, but most of the deposited energy is rapidly converted from excitation to heat, and it is for this reason that thermal-spike sputtering is so prominent. Finally, we consider the fact that laser sputtering has two aspects. These are the primary processes, which lead to particle expulsion, and the secondary processes. The latter arise due to collisions amongst the emitted particles, with the result that the particles, effectively, “lose memory” of the primary process.

Collective and single-particle excitations of a trapped Bose gas

Abstract: The density of states of a Bose-condensed gas confined in a harmonic trap is investigated. The predictions of Bogoliubov theory are compared with those of Hartree-Fock theory and of the hydrodynamic model. We show that the Hartree-Fock scheme provides an excellent description of the excitation spectrum in a wide range of energy, revealing a major role played by single-particle excitations in these confined systems. The crossover from the hydrodynamic regime, holding at low energies, to the independent-particle regime is explicitly explored by studying the frequency of the surface mode as a function of their angular momentum. The applicability of the semiclassical approximation for the excited states is also discussed. We show that the semiclassical approach provides simple and accurate formulas for the density of states and the quantum depletion of the condensate.

Growth and productivity: a model of cumulative growth and catching up

Abstract: Individually, neither the cumulative growth approach of the post-Keynesian tradition nor the catching-up theory of neoclassical derivation are able to account for the chief stylized facts of comparative economic growth. A pooled, cross-section, econometric model that integrates these two approaches is developed and tested by the authors over the period 1950-88 for a group of nine OECD countries, for a group of nine Latin American countries and for a group of seven East Asian countries. Purchasing power parities for 1985 are employed to measure productivity levels. The growth record of the OECD countries is satisfactorily assessed by the model. The catching-up effect is found to be relevant in explaining productivity growth in the OECD area and in East Asia, but not in Latin America. This differential outcome finds explanation in terms of the relative strength of dynamic increasing returns. Copyright 1997 by Oxford University Press.

Bone marrow micrometastases in 109 breast cancer patients: Correlations with clinical and pathological features and prognosis

Abstract: Background: The presence in bone marrow of cells which react with monoclonal antibodies against tumor-associated antigens has been proposed over the last few years as a new prognostic factor in breast cancer patients. Patients and methods: Bone marrow aspirates were obtained from 109 stage I and II breast cancer patients during or 2–4 weeks after primary surgery. The samples were processed for leukocyte separation on a Ficoll-Hypaque gradient and then used to prepare cytospin slides for immunocytochemical analysis. The slides were stained with a pool of monoclonal antibodies (MoAbs) which recognize tumor associated antigens, using the alkaline phosphatase anti-alkaline phosphatase method. The median follow-up was 36 months (range 15–62); 22 patients relapsed and 7 died. Results: Thirty-four of the 109 patients (31.1%) had MoAb positive bone marrow cells. The bone marrow was positive in 28/74 (37.9%) patients who had the aspirate taken during surgery and in 6/35 (17.1%) who had it taken after surgery (p = 0.055). No association was found between bone marrow positivity and tumour size, nodal status, menopausal status, estrogen receptor positivity or the proliferative index. No association was found between bone marrow and prognosis: the log-rank test was 0.291 (p > 0.5) for OS and 0.023 for DFS; the hazard ratio (positive vs negative) was 1.51 for OS (95% CI: 0.33–6.86) and 0.93 for DFS (95% CI: 0.35–2.45). Conclusions: In our series, bone marrow positivity did not correlate with prognostic parameters or prognosis. Of interest is the relative excess of positivity when the bone marrow was obtained during surgery.

Graded Lie Algebras of Maximal Class

Abstract: We study graded Lie algebras of maximal class over a field $ \mathbf {F}$ of positive characteristic $p$. A. Shalev has constructed infinitely many pairwise non-isomorphic insoluble algebras of this kind, thus showing that these algebras are more complicated than might be suggested by considering only associated Lie algebras of p-groups of maximal class. Here we construct $| \mathbf {F}|^{\aleph _{0}}$ pairwise non-isomorphic such algebras, and $\max \{| \mathbf {F}|, \aleph _{0} \}$ soluble ones. Both numbers are shown to be best possible. We also exhibit classes of examples with a non-periodic structure. As in the case of groups, two-step centralizers play an important role