Efficient designs for mean estimation in multilevel populations and test norming

A crucial step in the research process is the choice of the design of the study because a poorly designed study can have serious consequences for science (e.g. biased or unreliable results) and society (e.g. a waste of resources or bad decisions in health and education based on invalid research conclusions). This thesis deals with the design of two types of studies: surveys for mean estimation in multilevel populations (e.g. estimation of average alcohol consumption by students grouped in schools), and normative studies for estimating reference values for psychological test scores and questionnaires (e.g. to measure patients’ symptoms). Both types of studies are of practical importance: results from surveys can help policymakers, and reference values are used by clinicians or educators to assess individuals. Thus, averages and reference values must be estimated with the highest possible precision, but without wasting resources (i.e. time and money). Hence, the main objective of this thesis is to provide guidelines for planning both types of studies to achieve precise estimates using minimum resources

Management of gynecomastia in patients with different body types: Considerations on 312 consecutive treated cases

Abstract BACKGROUND: Gynecomastia is a common finding in male subjects which incidence varies widely in the world population. In adolescents, it is frequently temporary but, if it becomes persistent, it generates considerable embarrassment, inducing the patients to seek surgical consultation. Even in patients with good body contour, gynecomastia creates even greater distress considering the special attention given by these subjects to their physical appearance. The authors present their experience in the treatment of gynecomastia comparing different body types of patients with the aim to investigate dissimilar expectations, needs and surgical outcomes thus optimizing the management of the pathological condition, achieving high levels of agreement and reducing unsatisfied patients arising from cosmetic surgery. MATERIALS AND METHODS: Between January 2007 and January 2015, 312 selected patients have been treated surgically for gynecomastia. Patients were grouped according to their physical aspect: 97 were classified as high muscle mass body type (group A), 106 as normal (group B) and 109 as overweight patients (group C). All of them were adults ranging in age between 18 and 52 years. Follow-up ranged from 12 to 60 months. In all cases, an excision of the gland in the form of a subcutaneous mastectomy was performed; the most common surgical access was in the inferior part of the areola. RESULTS: No breast cancers were found at the histological examinations. Also, no skin or areola necrosis have been referred, and no recurrence of gynecomastia disorder has been reported. Six cases of seroma (limited to the fatty gynecomastia) and 3 cases of hematomas (requiring immediate surgical revision) were found. Although the patients in group B resulted more distressed by the disorder, higher levels of postoperative satisfaction were recorded in this group. CONCLUSIONS: The study demonstrates the importance of the different management of the same disorder according to the different patients' expectations, related to the different body type. Our experience demonstrated that most of the cases did not require extensive skin incisions, reducing the risk of unpleasant scars and that direct excision of glandular tissue ensures stable and satisfactory results

Crystal growth from a supersaturated melt: relaxation of the solid-liquid dynamic stiffness

We discuss the growth process of a crystalline phase out of a metastable over-compressed liquid that is brought into contact with a crystalline substrate. The process is modeled by means of molecular dynamics. The particles interact via the Lennard-Jones potential and their motion is locally thermalized by Langevin dynamics. We characterize the relaxation process of the solid-liquid interface, showing that the growth speed is maximal for liquid densities above the solid coexistence density, and that the structural properties of the interface rapidly converge to equilibrium-like properties. In particular, we show that the off-equilibrium dynamic stiffness can be extracted using capillary wave theory arguments, even if the growth front moves fast compared to the typical diffusion time of the compressed liquid, and that the dynamic stiffness converges to the equilibrium stiffness in times much shorter than the diffusion time

Generation of sub-ion scale magnetic holes from electron shear flow instabilities in plasma turbulence

Magnetic holes (MHs) are coherent structures associated with strong magnetic field depressions in magnetized plasmas. They are observed in many astrophysical environments at a wide range of scales but their origin is still under debate. In this work we investigate the formation of sub-ion scale MHs using a fully kinetic 2D simulation of plasma turbulence initialized with parameters typical of the Earth's magnetosheath. Our analysis shows that the turbulence is capable of generating sub-ion scale MHs from large scale fluctuations via the following mechanism: first, the nonlinear large scale dynamics spontaneously leads to the development of thin and elongated electron velocity shears; these structures then become unstable to the electron Kelvin-Helmholtz instability and break up into small scale electron vortices; the electric current carried by these vortices locally reduces the magnetic field, inducing the formation of sub-ion scale MHs. The MHs thus produced exhibit features consistent with satellite observations and with previous numerical studies. We finally discuss the kinetic properties of the observed sub-ion scale MHs, showing that they are characterized by complex non-Maxwellian electron velocity distributions exhibiting anisotropic and agyrotropic features.Comment: Submitted to AP

On the relations between discrete and continuous dynamics in C2

E’ noto che in dimensione complessa uno, un germe di diffeomorfismo tangente all’identità ha una dinamica “a fiore” vicino ad un punto fisso, i.e. esistono regioni attrattive e repulsive che si alternano attorno al punto fisso. In questa tesi si studia la dinamica di germi di diffeomorfismi in C2. Lavori recenti di Abate, Bracci , Tovena e Hakim suggerscono una struttura analoga anche per mappe tangenti all’identità in dimensione due. Le tecniche usate sono molto vicine a quelle utilizzate da Camacho e Sad per provare l’esistenza di separatrici passanti attraverso una singolarità di un campo di vettori olomorfo. In una direzione, si sono studiate le relazioni esistenti tra mappe e campi di vettori. Si costruisce un metodo per associare, sotto certe ipotesi, ad una mappa un campo di vettori (formale) che preserva le proprietà dinamiche della mappa. Nell’altra direzione si è studiata l’esistenza e il numero di curve paraboliche i.e. regioni attrattive, per mappe tangenti all’identità con un punto fisso o una curva di punti fissi