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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Development and performance assessment of a Plasma Focus electron beam generator for Intra-Operative Radiation Therapy

Ceccolini, Elisa <1983> 11 May 2012 (has links)
The Plasma Focus is a device designed to generate a plasma sheet between two coaxial electrodes by means of a high voltage difference. The plasma is then driven to collapse into a “pinch”, where thermonuclear conditions prevail. During the “pinch phase” charged particles are emitted, with two main components: an ion beam peaked forward and an electron beam directed backward. The electron beam emitted backward by Plasma Focus devices is being investigated as a radiation source for medical applications, using it to produce x-rays by interaction with appropriate targets (through bremsstrahlung and characteristic emission). A dedicated Plasma Focus device, named PFMA-3 (Plasma Focus for Medical Applications number 3), has been designed, put in operation and tested by the research groups of the Universities of Bologna and Ferrara. The very high dose rate (several gray per discharge, in less than 1 µs) is a peculiarity of this device that has to be investigated, as it might modify the relative biological effectiveness (RBE). Aim of this Ph.D. project was to investigate the main physical properties of the low-energy x-ray beams produced by a Plasma Focus device and their potential medical applications to IORT treatments. It was necessary to develop the optimal geometrical configuration; to evaluate the x-rays produced and their dose deposited; to estimate the energy electron spectrum produced in the “pinch phase”; to study an optimal target for the conversion of the x-rays; to conduct simulations to study the physics involved; and in order to evaluate the radio-biological features of the beam, cell holders had to be developed for both irradiations and cell growth conditions. / Il Plasma Focus è un dispositivo progettato per generare una guaina di plasma tra due elettrodi coassiali attraverso un’ elevata differenza di potenziale. Il plasma viene accelerato e compresso in un “pinch”, dove avvengono reazioni termonucleari. Durante la fase del “pinch” sono emesse particelle cariche, con due componenti principali: un fascio di ioni diretto in avanti e un fascio retroemesso di elettroni. Si pensa di utilizzare il fascio retroemesso di elettroni prodotto dal Plasma Focus come sorgente di radiazioni per applicazioni medicali, producendo raggi X attraverso l’interazione con un target appropriato (tramite emissione prodotta per bremsstrahlung o caratteristica). Il Plasma Focus, PFMA-3 (Plasma Focus per Applicazioni Mediche numero 3), è stato progettato, messo in opera e testato dai gruppi di ricerca delle università di Bologna e di Ferrara. L’alto rateo di dose (diversi gray per scarica, in meno di 1 µs) è una particolarità del dispositivo che deve essere analizzata, perché potrebbe modificarne l’efficacia biologica relativa (RBE). Scopo di questo progetto di dottorato è stato studiare le principali proprietà fisiche del fascio di raggi X a bassa energia prodotti dal Plasma Focus e le loro potenzialità mediche per i trattamenti IORT. E’ stato necessario determinare la configurazione geometrica ottimale, valutare i raggi X prodotti e la dose da questi depositata, stimare lo spettro energetico degli elettroni prodotti nella fase di “pinch”, studiare un target ottimale per la conversione in raggi X, condurre simulazioni per studiare la fisica coinvolta e per valutare l’efficacia radio-biologica del fascio, sviluppare porta-campioni utilizzati sia per la crescita delle cellule, sia per gli irraggiamenti di quest’ultime.
142

Fast and accurate numerical solutions in some problems of particle and radiation transport: synthetic acceleration for the method of short characteristics, Doppler-broadened scattering kernel, remote sensing of the cryosphere

Previti, Alberto <1985> 23 May 2014 (has links)
The aim of this work is to present various aspects of numerical simulation of particle and radiation transport for industrial and environmental protection applications, to enable the analysis of complex physical processes in a fast, reliable, and efficient way. In the first part we deal with speed-up of numerical simulation of neutron transport for nuclear reactor core analysis. The convergence properties of the source iteration scheme of the Method of Characteristics applied to be heterogeneous structured geometries has been enhanced by means of Boundary Projection Acceleration, enabling the study of 2D and 3D geometries with transport theory without spatial homogenization. The computational performances have been verified with the C5G7 2D and 3D benchmarks, showing a sensible reduction of iterations and CPU time. The second part is devoted to the study of temperature-dependent elastic scattering of neutrons for heavy isotopes near to the thermal zone. A numerical computation of the Doppler convolution of the elastic scattering kernel based on the gas model is presented, for a general energy dependent cross section and scattering law in the center of mass system. The range of integration has been optimized employing a numerical cutoff, allowing a faster numerical evaluation of the convolution integral. Legendre moments of the transfer kernel are subsequently obtained by direct quadrature and a numerical analysis of the convergence is presented. In the third part we focus our attention to remote sensing applications of radiative transfer employed to investigate the Earth's cryosphere. The photon transport equation is applied to simulate reflectivity of glaciers varying the age of the layer of snow or ice, its thickness, the presence or not other underlying layers, the degree of dust included in the snow, creating a framework able to decipher spectral signals collected by orbiting detectors. / Questo lavoro si propone di presentare diversi aspetti della simulazione numerica del trasporto di particelle e di radiazione per applicazioni industriali e di protezione ambientale, per consentire l'analisi di processi fisici complessi in modo veloce, affidabile ed efficiente. Nella prima parte è trattata la velocizzazione della simulazione numerica del trasporto di neutroni per l'analisi del nocciolo di un reattore nucleare. Le proprietà di convergenza della source iteration del Metodo delle Caratteristiche applicate a geometrie strutturate eterogenee sono state migliorate per mezzo della Boundary Projection Acceleration, consentendo lo studio di geometrie 2D e 3D con la teoria del trasporto senza omogeneizzazione spaziale. Le prestazioni computazionali sono state verificate tramite il benchmark C5G7 2D e 3D, mostrando una sensibile riduzione del numero di iterazioni e del tempo di calcolo. La seconda parte è dedicata allo studio dello scattering elastico dei neutroni con isotopi pesanti in funzione della temperatura vicino alla zona termica. È presentato il calcolo numerico della convoluzione Doppler del kernel di scattering elastico col modello gas per una generale sezione d'urto dipendente dall'energia e per una generica legge di scattering nel sistema del centro di massa. L'intervallo di integrazione è stata ottimizzato utilizzando un cutoff numerico, consentendo una valutazione numerica più veloce dell'integrale. I momenti di Legendre del kernel di trasferimento sono successivamente ottenuti per quadratura diretta e validati tramite un'analisi numerica della convergenza. La terza parte è focalizzata alle applicazioni di telerilevamento del trasferimento radiativo per indagini sulla criosfera terrestre. L'equazione del trasporto per fotoni è applicata per simulare la riflettività dei ghiacciai a diverse età dello strato di neve o ghiaccio, al suo spessore, alla presenza o meno di altri strati sottostanti, al grado di polvere inclusa nella neve, creando un sistema in grado di decifrare segnali spettrali raccolti dai rivelatori orbitanti.
143

Zr(IV)-Assisted Peptide Hydrolysis

Kassai, Miki 06 August 2007 (has links)
The development of new reagents to efficiently cleave peptides and proteins has become increasingly important for protein structural studies and other applications. However, this has proved to be a very challenging task due to the extreme stability of the peptide amide bond. Transition metal complexes cleave proteins and peptides through either oxidative or hydrolytic pathways. However, hydrolytic cleavage is preferred over oxidative cleavage, because the latter process produces irreversibly modified peptide fragments. Metal-assisted peptide hydrolysis is introduced in Chapter I. The metals Ce(IV), Co(II), Co(III), Cu(II), Fe(III), Mo(IV), Ni(II), Pd(II), Pt(II), Zn(II), and Zr(IV) are described as promising non-enzymatic hydrolysis reagents. In Chapter II, Zr(IV)-assisted hydrolysis of the dipeptide Gly-Gly and of its N- and C- blocked analogs is described. The highest levels of cleavage were observed at pH values ranging from 4.4 to 4.7. When the pH was raised to ~ 7.0, hydrolysis yields were decreased and amounts of zirconium precipitation were increased proportionately. Zirconium(IV)-assisted peptide hydrolysis in the presence of 4,13-diaza-18-crown-6 is reported in Chapter III. The goal of this work was to use an azacrown ether to reduce Zr(IV) precipitation and enhance levels of hydrolysis at neutral pH. An experiment in which 16 glycine containing dipeptides were hydrolyzed by Zr(IV) and by Zr(IV)/4,13-diaza-18-crown-6 indicated that 4,13-diaza-18-crown-6 markedly enhanced the reactivity of Zr(IV) under near physiological conditions. Because Zr(IV) precipitation was not reduced in these reactions, we proposed that hydrolysis of peptides by Zr(IV)/4,13-diaza-18-crown-6 might be heterogeneous in nature. In Chapter IV, seventeen macrocyclic and open-chain Zr(IV) ligands were compared in order to gain mechanistic insights that would enable hydrolysis yields at neutral pH to be further improved. While the macrocyclic ligands 4,13-diaza-18-crown-6 and 4,10-trioxa-7,13-diazacyclopentadecane tended to produce higher levels of Zr(IV)-assisted dipeptide cleavage, it was not necessary to have a ring structure to enhance Zr(IV) reactivity. With respect to the open-chain ligands, the potential ability to form multiple chelate rings appeared to coincide with reduced levels of Zr(IV) precipitation as well as with reduced levels of dipeptide hydrolysis. In Chapter V, a summary of our results and conclusions is presented.
144

Die adäquate strafrechtliche Sanktion bei Delinquenz nicht nach Jugendstrafrecht verurteilter Heranwachsender und Jungerwachsener ab 21 Jahren /

Schwerin, Hartmut von. January 1997 (has links) (PDF)
Univ., Diss.--Mainz, 1997.
145

The biographies and identities of the young Polish immigrants in Germany after 1989

Waniek, Katarzyna Malgorzata. Unknown Date (has links) (PDF)
Magdeburg, University, Diss., 2007.
146

Interferenzanfälligkeit bei kognitiven Leistungen im Altersvergleich eine kritische Betrachtung von Modellebene und Empirie /

Titz, Cora. January 2005 (has links) (PDF)
Göttingen, Universiẗat, Diss., 2005. / Erscheinungsjahr an der Haupttitelstelle: 2004.
147

A comprehensive global 3D model of d18O in atmospheric CO2

Cuntz, Matthias. Unknown Date (has links) (PDF)
University, Diss., 2002--Heidelberg.
148

Entwicklung und trägerarme 18F-Markierung selektiver Inhibitoren des Serotonin-Transporters

Stoll, Timo. Unknown Date (has links) (PDF)
Universiẗat, Diss., 2004--Köln.
149

Fairness, rationality and integration : success factors towards a new organizational model

January 1996 (has links)
Toshihiro Nishiguchi. / Originally published in the Working paper series of the MIT International Motor Vehicle Program. / Includes bibliographical references (p. 19-20).
150

Personer med schizofreni och deras upplevelser av mötet med sjuksköterskan : en beskrivande litteraturstudie

Björn, Daniella, Holm, Rebecca January 2018 (has links)
Bakgrund: Psykisk ohälsa existerar i hela världen och år 2016 uppgav 16 % av den svenska befolkningen att de led av nedsatt psykiskt välbefinnande. Enligt WHO (World Health Organisation) lider 21 miljoner personer världen över av schizofreni. Cirka 30 000-40 000 personer i Sverige har i dagsläget diagnosen schizofreni och årligen beräknas 1200-1500 personer insjukna i psykos. Syfte: Syftet med denna studie var att beskriva hur personer (från 18+ år) med schizofreni inom öppen- och slutenvården upplever mötet med sjuksköterskan samt att beskriva den metodologiska aspekten av de inkluderade artiklarnas undersökningsgrupp. Metod: En litteraturstudie med en deskriptiv design. Sökningarna av artiklarna genomfördes i Cinahl, PubMed och PsycINFO. Båda författarna granskade artiklarna objektivt. Huvudresultat: Resultatet presenterades med hjälp av tre rubriker, tillgänglighet, relation och förväntningar. Tillgänglighet, där visades att mer tid önskas med sjuksköterskan för att uppnå ett gott möte. Under relation framkom varierande resultat där både en god samt en dålig relation beskrivs i mötet med sjuksköterskor. Förväntningar där patienterna uttryckte sina förväntningar på sjuksköterskan innan och vid mötet. Slutsats: Patienter som i mötet med sjuksköterskan upplevde en god relation, gavs tid samt fick sina förväntningar uppfyllda var mer tillfredsställd med vården. Mer forskning kring patientens upplevelser i mötet med sjuksköterskan behövs.

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