Energy landscape, two-level systems and entropy barriers in Lennard-Jones clusters

We develop an efficient numerical algorithm for the identification of a large number of saddle points of the potential energy function of Lennard- Jones clusters. Knowledge of the saddle points allows us to find many thousand adjacent minima of clusters containing up to 80 argon atoms and to locate many pairs of minima with the right characteristics to form two-level systems (TLS). The true TLS are singled out by calculating the ground-state tunneling splitting. The entropic contribution to all barriers is evaluated and discussed.Comment: 4 pages, RevTex, 2 PostScript figure

Potential Energy Landscape and Long Time Dynamics in a Simple Model Glass

We analyze the properties of a Lennard-Jones system at the level of the potential energy landscape. After an exhaustive investigation of the topological features of the landscape of the systems, obtained studying small size sample, we describe the dynamics of the systems in the multi-dimensional configurational space by a simple model. This consider the configurational space as a connected network of minima where the dynamics proceeds by jumps described by an appropriate master equation. Using this model we are able to reproduce the long time dynamics and the low temperature regime. We investigate both the equilibrium regime and the off-equilibrium one, finding those typical glassy behavior usually observed in the experiments such as: {\it i)} stretched exponential relaxation, {\it ii)} temperature-dependent stretching parameter, {\it iii)} breakdown of the Stokes-Einstein relation, and {\it iv)} appearance of a critical temperature below which one observes deviation from the fluctuation-dissipation relation as consequence of the lack of equilibrium in the system.Comment: 11 pages (Latex), 9 ps figure

Free Energy Landscape Of Simple Liquids Near The Glass Transition

Properties of the free energy landscape in phase space of a dense hard sphere system characterized by a discretized free energy functional of the Ramakrishnan-Yussouff form are investigated numerically. A considerable number of glassy local minima of the free energy are located and the distribution of an appropriately defined ``overlap'' between minima is calculated. The process of transition from the basin of attraction of a minimum to that of another one is studied using a new ``microcanonical'' Monte Carlo procedure, leading to a determination of the effective height of free energy barriers that separate different glassy minima. The general appearance of the free energy landscape resembles that of a putting green: deep minima separated by a fairly flat structure. The growth of the effective free-energy barriers with increasing density is consistent with the Vogel-Fulcher law, and this growth is primarily driven by an entropic mechanism.Comment: 10 pages, 6 postscript figures, uses iopart.cls and iopart10.clo (included). Invited talk at the ICTP Trieste Conference on "Unifying Concepts in Glass Physics", September 1999. To be published in J. Phys. Cond. Ma

State encoding for low power embedded controllers

Power dissipation has become one of the main issues during embedded systems design in the recent years, due to the continuous increase of the integration level and the operating frequency. The present paper affords the problem of reducing the power dissipation in embedded controllers represented as Finite State Machines (FSMs). The aim of the work is to propose an approach to optimize state encoding for low power embedded FSMs, starting from a probabilistic description of the FSMs. Experimental results have been obtained by applying the proposed state encoding techniques to benchmark circuits. The results have also been compared to previous state encoding methods

Mammella: è possibile la chemioprevenzione?

La prevenzione delle malattie oncologiche riveste un grande interesse e rappresenta uno dei principali obiettivi di politica sanitaria. La prevenzione primaria, ovvero I' abolizione delle cause cancerogene, rimane I'obiettivo principale. Questo obiettivo e oggi pili vicino gra- =ie alla maggiore consapevolezza della popola- none dei rischi causati dai diversi cancerogeni :!IDbientali, dalle errate abitudini alimentari e :oluttuarie. :..a farmaco-prevenzione e una disciplina relati- ente nuova che si propone di agire sulle ::!ppe intermedie che portano alla manifestazio- ;;,~c1inica della neoplasia. ::"'erecenti conoscenze dei meccanisrni della can- _"fogenesi e l' acquisizione di nuove sostanze _~n attivita preventive ne hanno ampliato Ie -=-,plicazioni. - termini di prevenzione oncologic a e utile pun- ::!3lizzare la differenza tra "prevenzione prima- ~"e "prevenzione secondaria". Infatti, se si :sdude il tentativo di ridurre l' esposizione della -<Jpolazione a fattori di rischio noti, l'approc- pili frequente in oncologia e quello della Copyright 2002, ere Edizioni lnternazionali, Roma prevenzione secondaria, cioe una diagnosi pm precoce possibile per condizionare favorevol- mente la prognosi dei soggetti affetti. La farmaco-prevenzione si prop one di interve- nire a livello della sequenza di eventi che costi- tuiscono il processo di cancerogenesi al fine di prevenire la progressione neoplastica prima del- l'evento clinico terminale, cioe la formazione del tumore. Negli ultirni anni l'interesse per la farmaco-pre- venzione e progressivamente aumentato, poiche la prospettiva di una riduzione del rischio di tumore trarnite l'uso di farmaci e diventata plau- sibile grazie ai risultati di numerosi studi pre- clinici, epidemiologici e clinici

Endometrial Changes and Doppler Flow Evaluation in Postmenopausal Breast Cancer Patients on Tamoxifen (TAM): A Transvaginal Ultrasound (TVU)/Hysterescopy Study

The aim of the study was to assess the effect of TAM therapy on the endometrium and the usefulness of Doppler How assessment by TVU. 79 asymptomatic postmenopausal women (pmw) treated with TAM (20 mg/day) for at least 1 year were recruited. 20 healthy pmw served as controls. All patients (pts) underwent TVU to evaluate endometrial thickness (ET) and echotexture, and Doppler color flow was added to the assessments. FT value was increased during the 1st year of therap

Endometrial changes in postmenopausal breast cancer patients receiving tamoxifen: a transvaginal ultrasound study

Abstract: The purpose of the study was to evaluate the effects of tamoxifen therapy on the endometrium by transvaginal sonography. Seventy-nine asymptomatic postmenopausal women treated with tamoxifen (20 mg/day) for at least one year were recruited. Twenty healthy postmenopausal women served as controls. All patients underwent transvaginal ultrasound to evaluate endometrial thickness and echotexture