Alcuni aspetti della quantizzazione dell'oscillatore armonico

Scopo principale della tesi è quello di presentare alcuni aspetti quantistici di un siste- ma fisico intermedio fra la buca infinita di potenziale e l’oscillatore armonico: una buca di potenziale con le pareti elastiche. Per questo tipo di potenziale si determinano le autofunzioni dell’energia attraverso l’u- tilizzo di equazioni differenziali di Kummer, Whittaker o Weber. Si determina inoltre lo spettro energetico di tale sistema sotto forma di un’equazione trascendente, e ne si analizza il comportamento sotto determinati limiti, dapprima in approssimazione zero e successivamente in prima approssimazione. Segue una breve trattazione sul propagatore quantistico e sulla sua forma in approssi- mazione semiclassica fornita dalla formula di Pauli - van Vleck - Morette, completa di alcuni esempi di calcolo esplicito relativo a semplici potenziali che presentano analogie con il potenziale in oggetto, e di confronti fra le forme esatte di tali propagatori e le loro approssimazioni semiclassiche. È calcolato infine anche il propagatore quantistico per la buca di potenziale con pareti elastiche, nella sua forma semiclassica

Interacting Bose-Fermi mixtures in optical lattices

In this thesis, we investigate mixtures of quantum degenerate Bose and Fermi gases of neutral atoms in threedimensional optical lattices. Feshbach resonances allow to control interspecies interactions in these systems precisely, by preparing suitable combinations of internal atomic states and applying external magnetic fields. This way, the system behaviour can be tuned continuously from mutual transparency to strongly interacting correlated phases, up to the stability boundary.rnThe starting point for these investigations is the spin-polarized fermionic band insulator. The properties of this non-interacting system are fully determined by the Pauli exclusion principle for the occupation of states in the lattice. A striking demonstration of the latter can be found in the antibunching of the density-density correlation of atoms released from the lattice. If bosonic atoms are added to this system, isolated heteronuclear molecules can be formed on the lattice sites via radio-frequency stimulation. The efficiency of this process hints at a modification of the atom number distribution over the lattice caused by interspecies interaction.rnIn the following, we investigate systems with tunable interspecies interaction. To this end, a method is developed which allows to assess the various contributions to the system Hamiltonian both qualitatively and quantitatively by following the quantum phase diffusion of the bosonic matter wave.rnBesides a modification of occupation number statistics, these measurements show a significant renormalization of the bosonic Hubbard parameters. The final part of the thesis considers the implications of this renormalization effect on the many particle physics in the mixture. Here, we demonstrate how the quantum phase transition from a bosonic superfluid to a Mott insulator state is shifted towards considerably shallower lattices due to renormalization.

Il metodo di Hartree-Fock

Il metodo Hartree-Fock permette di determinare approssimativamente la funzione d'onda e l'energia per atomi a più elettroni in uno stato stazionario. Più in generale, si applica a sistemi quantistici a N-corpi, per studiare, ad esempio, gli elettroni nelle molecole e nei solidi. Il punto di partenza di questo metodo è il modello della particella indipendente; sotto questa ipotesi, ogni elettrone del sistema è descritto dalla propria funzione d'onda. Il contributo di D. R. Hartree allo studio della struttura di atomi complessi consiste nell'aver formulato le equazioni per le funzioni d'onda dei singoli elettroni usando argomentazioni intuitive e nell'avere inoltre proposto, per la loro risoluzione, una procedura iterativa basata sul requisito di autoconsistenza. La generalizzazione del suo metodo, che tiene conto del requisito di antisimmetria imposto dal principio di esclusione di Pauli, fu formulata da V. A. Fock e J. C. Slater. Con tale tecnica si assume che la funzione d'onda totale a N-elettroni sia un determinante di Slater, ovvero un prodotto antisimmetrico di orbitali relativi a singoli elettroni. Il determinante di Slater ottimale si ottiene usando il metodo variazionale per individuare i migliori spin-orbitali.

Comparison of cartilage histopathology assessment systems on human knee joints at all stages of osteoarthritis development

To compare the MANKIN and OARSI cartilage histopathology assessment systems using human articular cartilage from a large number of donors across the adult age spectrum representing all levels of cartilage degradation.

Systemic prokinetic pharmacologic treatment for postoperative adynamic ileus following abdominal surgery in adults

BACKGROUND: Postoperative adynamic bowel atony interferes with recovery following abdominal surgery. Prokinetic pharmacologic drugs are widely used to accelerate postoperative recovery. OBJECTIVES: To evaluate the benefits and harms of systemic acting prokinetic drugs to treat postoperative adynamic ileus in patients undergoing abdominal surgery. SEARCH STRATEGY: Trials were identified by computerised searches of the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, and the Cochrane Colorectal Cancer Group specialised register. The reference lists of included trials and review articles were tracked and authors contacted. SELECTION CRITERIA: Randomised controlled parallel-group trials (RCT) comparing the effect of systemically acting prokinetic drugs against placebo or no intervention. DATA COLLECTION AND ANALYSIS: Four reviewers independently extracted the data and assessed trial quality. Trial authors were contacted for additional information if needed. MAIN RESULTS: Thirty-nine RCTs met the inclusion criteria contributing a total of 4615 participants. Most trials enrolled a small number of patients and showed moderate to poor (reporting of) methodological quality, in particular regarding allocation concealment and intention-to-treat analysis. Fifteen systemic acting prokinetic drugs were investigated and ten comparisons could be summarized. Six RCTs support the effect of Alvimopan, a novel peripheral mu receptor antagonist. However, the trials do not meet reporting guidelines and the drug is still in an investigational stage. Erythromycin showed homogenous and consistent absence of effect across all included trials and outcomes. The evidence is insufficient to recommend the use of cholecystokinin-like drugs, cisapride, dopamine-antagonists, propranolol or vasopressin. Effects are either inconsistent across outcomes, or trials are too small and often of poor methodological quality. Cisapride has been withdrawn from the market due to adverse cardiac events in many countries. Intravenous lidocaine and neostigmine might show a potential effect, but more evidence on clinically relevant outcomes is needed. Heterogeneity among included trials was seen in 10 comparisons. No major adverse drug effects were evident. AUTHORS' CONCLUSIONS: Alvimopan may prove to be beneficial but proper judgement needs adherence to reporting standards. Further trials are needed on intravenous lidocaine and neostigmine. The remaining drugs can not be recommended due to lack of evidence or absence of effect.

Assessment of splanchnic blood flow using magnetic resonance imaging

BACKGROUND AND AIMS: The splanchnic circulation has an important function in the body under both physiological and pathophysiological conditions. Despite its importance, no reliable noninvasive procedures for estimating splanchnic circulation have been established. The aim of this study was to evaluate MRI as a tool for assessing intra-abdominal blood flows of the aorta, portal vein (VPO) and the major intestinal and hepatic vessels. METHODS: In nine healthy volunteers, the proximal aorta (AOP) and distal abdominal aorta (AOD), superior mesenteric artery (SAM), celiac trunk (CTR), hepatic arteries (common and proper hepatic arteries, AHC and AHP, respectively), and VPO were localized on contrast-enhanced magnetic resonance angiography images. Volumetric flow was measured using a two-dimensional cine echocardiogram-gated phase contrast technique. Measurements were taken before and 30 min after continuous intravenous infusion of somatostatin (250 microg/h) and were independently evaluated by two investigators. RESULTS: Blood flow measured by MRI in the VPO, SAM, AOP, AHP, and CTR significantly decreased after drug infusion. Flows in the AOD and AHC showed a tendency to decrease (P>0.05). Interrater agreement on flows in MRI was very good for large vessels (VPO, AOP, and AOD), with a concordance correlation coefficient of 0.94, as well as for smaller vessels such as the CTR, AHC, AHP, and SAM (concordance correlation coefficient =0.78). CONCLUSION: Somatostatin-induced blood flow changes in the splanchnic region were reliably detected by MRI. MRI may be useful for the noninvasive assessment of blood flow changes in the splanchnic region.

Influence of Information and Instructions on Human Behavior in Tunnel Accidents: A Virtual Reality Study

Human behavior is a major factor modulating the consequences of road tunnel accidents. We investigated the effect of information and instruction on drivers' behavior as well as the usability of virtual environments to simulate such emergency situations. Tunnel safety knowledge of the general population was assessed using an online questionnaire, and tunnel safety behavior was investigated in a virtual reality experiment. Forty-four participants completed three drives through a virtual road tunnel and were confronted with a traffic jam, no event, and an accident blocking the road. Participants were randomly assigned to a control group (no intervention), an informed group who read a brochure containing safety information prior to the tunnel drives, or an informed and instructed group who read the same brochure and received additional instructions during the emergency situation. Informed participants showed better and quicker safety behavior than the control group. Self-reports of anxiety were assessed three times during each drive. Anxiety was elevated during and after the emergency situation. The findings demonstrate problematic safety behavior in the control group and that knowledge of safety information fosters adequate behavior in tunnel emergencies. Enhanced anxiety ratings during the emergency situation indicate external validity of the virtual environment.

Beyond the tree of texts: Building an empirical model of scribal variation through graph analysis of texts and stemmata

Stemmatology, or the reconstruction of the transmission history of texts, is a field that stands particularly to gain from digital methods. Many scholars already take stemmatic approaches that rely heavily on computational analysis of the collated text (e.g. Robinson and O’Hara 1996; Salemans 2000; Heikkilä 2005; Windram et al. 2008 among many others). Although there is great value in computationally assisted stemmatology, providing as it does a reproducible result and allowing access to the relevant methodological process in related fields such as evolutionary biology, computational stemmatics is not without its critics. The current state-of-the-art effectively forces scholars to choose between a preconceived judgment of the significance of textual differences (the Lachmannian or neo-Lachmannian approach, and the weighted phylogenetic approach) or to make no judgment at all (the unweighted phylogenetic approach). Some basis for judgment of the significance of variation is sorely needed for medieval text criticism in particular. By this, we mean that there is a need for a statistical empirical profile of the text-genealogical significance of the different sorts of variation in different sorts of medieval texts. The rules that apply to copies of Greek and Latin classics may not apply to copies of medieval Dutch story collections; the practices of copying authoritative texts such as the Bible will most likely have been different from the practices of copying the Lives of local saints and other commonly adapted texts. It is nevertheless imperative that we have a consistent, flexible, and analytically tractable model for capturing these phenomena of transmission. In this article, we present a computational model that captures most of the phenomena of text variation, and a method for analysis of one or more stemma hypotheses against the variation model. We apply this method to three ‘artificial traditions’ (i.e. texts copied under laboratory conditions by scholars to study the properties of text variation) and four genuine medieval traditions whose transmission history is known or deduced in varying degrees. Although our findings are necessarily limited by the small number of texts at our disposal, we demonstrate here some of the wide variety of calculations that can be made using our model. Certain of our results call sharply into question the utility of excluding ‘trivial’ variation such as orthographic and spelling changes from stemmatic analysis.