Convective-Dynamical Instability in Radiation-Supported Accretion Disks

We study radiation-hydrodynamical normal modes of radiation-supported accretion disks in the WKB limit. It has long been known that in the large optical depth limit the standard equilibrium is unstable to convection. We study how the growth rate depends on location within the disk, optical depth, disk rotation, and the way in which the local dissipation rate depends on density and pressure. The greatest growth rates are found near the disk surface. Rotation stabilizes vertical wavevectors, so that growing modes tend to have nearly-horizontal wavevectors. Over the likely range of optical depths, the linear growth rate for convective instability has only a weak dependence on disk opacity. Perturbations to the dissipation have little effect on convective mode growth rates, but can cause growth of radiation sound waves.Comment: 20 pages, AAS LaTe

The Inverse Compton Thermostat in Hot Plasmas Near Accreting Black Holes

The hard X-ray spectra of accreting black holes systems are generally well-fit by thermal Comptonization models with temperatures $\sim 100$ keV. We demonstrate why, over many orders of magnitude in heating rate and seed photon supply, hot plasmas radiate primarily by inverse Compton scattering, and find equilibrium temperatures within a factor of a few of 100 keV. We also determine quantitatively the (wide) bounds on heating rate and seed photon supply for which this statement is true. Plasmas in thermal balance in this regime obey two simple scaling laws, one relating the product of temperature and optical depth to the ratio of seed photon luminosity to plasma heating rate $l_s/l_h$, the other relating the spectral index of the output power-law to $l_s/l_h$. Because $\alpha$ is almost independent of everything but $l_s/l_h$, the observed power law index may be used to estimate $l_s/l_h$. In both AGN and stellar black holes, the mean value estimated this way is $l_s/l_h \sim 0.1$. As a corollary, $\Theta \tau_T$ must be $\simeq 0.1$ -- 0.2, depending on plasma geometry.Comment: 26 pages, AASLaTeX, to appear in July 10 Ap.J. Figures available in uuencoded form at ftp://jhufos.pha.jhu.edu/pub/put/jhk/comptfigs.u

Parametri radiologici normali del piede dell' asino di razza amiatina.

RIASSUNTO Introduzione: lo scopo di questo studio è stato quello di determinare parametri di anatomia radiografica normale del piede dell’ asino di razza amiatina perchè in letteratura non sono presenti dati consistenti a riguardo. Materiali e metodi: è stato eseguito l’esame radiografico sul piede di entrambi gli arti anteriori di 20 soggetti di asino di razza amiatina utilizzando un protocollo che prevedeva tre proiezioni radiografiche: latero-mediale, dorso-palmare e dorsoprossimale-60°palmarodistale obliqua. Sui radiogrammi sono stati calcolati venti parametri angolari e lineari. Sono stati calcolati parametri statistici sul complesso dei valori calcolati. Risultati: sono stati stabiliti parametri di base per caratterizzare dal punto di vista radiografico il piede normale dell’asino e per creare un modello da applicare esclusivamente alla specie asinina. Conclusioni: la determinazione dei parametri radiografici del piede normale dell’asino risulta di vitale importanza per una diagnosi precoce di laminite e altre patologie podali. Parole chiave: asino, piede, radiografia, razza amiatina ABSTRACT Introduction: the aim of the present study was to determine normal radiographic anatomy parameters of the foot of the amiatina donkey breed; no consistent data have been published to our knowledge. Materials and methods: x-ray examination was performed on the foot of both forelimbs of 20 amiatina donkeys. Three radiographic views were taken of each front foot: lateromedial, dorsoproximal and dorsoproximal 60° palmarodistal oblique. Twenty angular and linear parameters were calculated on the radiograms. Statistical parameters were calculated on the total of the estimated values. Results: normal baseline parameters of donkey foot were established and a model to be used in this species was created. Conclusion: determining normal radiographic parameters of clinically normal donkeys’s feet is of utmost importance in the early diagnosis of laminitis and other foot conditions Key-words: donkey, foot, x-ray, amiatina bree

Biodegradable Polymeric Composites Based on Polyester Matrices and Organic and Inorganic Fillers

Con l’obiettivo di ottenere materiali ecocompatibili ad alte prestazioni, nuove formulazioni a base del poliestere microbico biodegradabile poli(3-idrossibutirrato) (PHB) sono state preparate, caratterizzate e anallizate riguardo al potenziale impatto ambientale del loro ciclo di vita. Il PHB è stato processato in fuso in presenza di additivi commerciali quali un composto antiidrolisi a base carbodiimidica e una miscela di antiossidanti fenolici e organofosfitici, i quali hanno mostrato una certa capacità di limitare la degradazione termica del PHB. Inoltre, sono stati preparati compositi a base di PHB rinforzati con cariche di natura organica (fibre naturali di bagassa di canna da zucchero e pura cellulosa) ed inorganica (argilla organofila), che però hanno mostrato una scarsa efficacia nel migliorare le proprietà meccaniche tensili del PHB. Infine, su alcuni materiali compositi rappresentativi (caricati sia con fibre di bagassa che con argilla organofila), è stata effettuata un’analisi comparativa del ciclo di vita (life cycle assessment). Tale analisi ha dimostrato che i compositi a base di PHB mostrano un alto potenziale ecologico, che però deriva quasi esclusivamente dal processo produttivo del PHB e non dalla formulazione dei compositi

Studio di fattibilita di sospensione automobilistica con controllo della cinematica

Il presente lavoro di tesi consiste nello studio di fattibilità di una sospensione automobilistica con controllo della cinematica. Utilizzando i dati costruttivi ricavati dal simulatore di guida presente nel DIMNP, tramite il software Adams®, sono stati calcolati gli sforzi nelle diverse condizioni di marcia delle sospensioni di due delle più diffuse architetture: il Mc Pherson e il Quadrilatero. Delle due soluzioni costruttive la seconda è risultata la più promettente mostrando carichi minori sugli snodi. Scelto quindi il Quadrilatero il passo successivo è stato lo studio approfondito del comportamento cinematico e dell’effetto sugli angoli caratteristici di deriva e camber dello spostamento degli snodi. Ottenuti tali dati, è stata creata una serie di simulazioni di prova in ambiente Matlab® per determinare il controllo ottimale degli angoli, valutandone gli effetti positivi sulla dinamica del veicolo, per individuare le specifiche dell’attuatore necessario a tale movimentazione e per verificare la caratteristica fail-safe del meccanismo. È stato infine ideato un cinematismo in grado di soddisfar le specifiche richieste dalle prove utilizzando gli attuatori elettrici attualmente presenti sul mercato

Los juglares, cornamusas del diablo : las repercusiones iconográficas de la condena de los entretenedores

Los juglares fueron condenados por los escritores cristianos durante toda la época medieval. La transformación del aspecto natural, considerada como un pecado contra Dios, implicó una reprobación particular contra los acróbatas, danzadores y contorsionistas. Estas tipologías de juglares han sido frecuentemente representadas en la iconografía del los siglos xiii y xiv, en las esculturas de las iglesias así como en las miniaturas de los manuscritos. Los múltiples documentos figurativos muestran en diversa manera y grado las repercusiones de estas condenas, con una frecuente asimilación entre los juglares y los animales mas torpes y despreciables, como el mono, que hacen de intermediarios entre los hombres y el diablo. Instrumentos degenerados del demonio, los entretenedores deshonran la dignidad de la naturaleza humana y entonces son representados como seres deformes, bestiales y demoníacos.Throughout the Middle Ages, Christian writers condemned jesters because of the ways in which they contorted and thus altered their bodies. Considered sins against God, these practices engendered particular disapproval of acrobats, dancers, and contortionists. These types of jesters appear frequently in 13th and 14th century iconography in the form of carved reliefs found in churches and miniatures encountered in manuscripts. These diverse figurative documents display the repercussions of scholarly condemnations in various ways and degrees, especially by means of frequent associations between jesters and the baser and more despicable animals, such as apes, seen as playing an intermediate role between humans and the devil. As degenerated instruments of the devil, such entertainers dishonoured human dignity and were therefore represented as deformed, bestial, and demonic creatures

Brain, images and imagination: how the brain represents the world

The present work aims to describe the main results obtained from the neuroimaging studies on the study of those cognitive processes related to imaging and imagination. A brief excursus on the development of modern neuroimaging techniques presents the methodological background of the many studies. The relationship between sight, blindness and conceptual representation is explored. Research has shown that the ventro-temporal cortex is responsible for recognizing the surrounding environment, to distinguish an object from a face and, in general, objects’ categorization. This area is responsible of imagery in both sighted and blind people, being its morpho-functional organization independent of the visual experience. It follows that a very precise classification of all categories of objects could be obtained in the human brain, and it is supported by a distributed cortical representation independent from the sensorial modality. The last part of the paper presents a series of studies, in which the study of imagery was related to aggressivity. The prefrontal cortex is deactivated when an individual imagines himself becoming aggressive, being this effect more relevant in females than in males. As a conclusion, the neuroscientific approach produced important results in the definition of what imagery is, and showed its relevance to the study of how mind and brain work

The Parody of Musical Instruments in Medieval Iconography

El vasto campo de la iconografía musical durante la Edad Media debe ocuparse necesariamente de las ricas y sorprendentes imágenes que se encuentran en algunos manuscritos occidentales y que muestran una proliferación de criaturas que tocan y se contorsionan a menudo inspiradas por exóticas reminiscencias. En los marginalia del siglo xiv puede descubrirse un tema interesante y desconcertante a la vez, la parodia de los entretenedores: hombres híbridos que tocan la viola con pinzas, sirenas o monos tocando con mandíbulas y así sucesivamente. La difusión que tuvo este tema en la iconografía medieval se ha relacionado con una finalidad satírica dirigida a los entretenedores profesionales, condenados muchas veces por los escritores. Instrumentos extraños hechos con objetos cotidianos como parrillas y ruecas, o animales exóticos como los pavos reales se mezclan en el grotesco submundo de los marginalia, en las que el noble arte de la música es a menudo reemplazado por los ruidos cacofónicos que sugiere el diablo.The vast field of musical iconography during the Middle Ages must necessarily deal with the rich and surprising imagery of western manuscripts, showing a fanciful proliferation of playing creatures and bizarre deformations, sometimes inspired by exotic suggestions. In marginal miniatures of 14th century we can discover an interesting and puzzling topic: the parody of entertainers, with hybrid men playing a vielle with tongs, mermaids or apes playing jawbones and so on. The spreading of this topic in medieval iconography is linked to a satirical purpose aimed at professional entertainers, harshly condemned by Christian writers. Strange instruments made out of everyday objects like grills and distaffs, or ‘exotic’ animals like peacocks, mingle in the grotesque underworld of marginal miniatures, in which the noble art of music is often replaced by the cacophonous noises suggested by the devil