Ultraviolet Properties of the Spinless, One-Particle Yukawa Model

We consider the one-particle sector of the spinless Yukawa model, which describes the interaction of a nucleon with a real field of scalar massive bosons (neutral mesons). The nucleon as well as the mesons have relativistic dispersion relations. In this model we study the dependence of the nucleon mass shell on the ultraviolet cut-off $\Lambda$. For any finite ultraviolet cut-off the nucleon one-particle states are constructed in a bounded region of the energy-momentum space. We identify the dependence of the ground state energy on $\Lambda$ and the coupling constant. More importantly, we show that the model considered here becomes essentially trivial in the limit $\Lambda\to\infty$ regardless of any (nucleon) mass and self-energy renormalization. Our results hold in the small coupling regime.Comment: 30 pages, typos corrected, references extende

Renormalized Electron Mass in Nonrelativistic QED

Within the framework of nonrelativistic QED, we prove that, for small values of the coupling constant, the energy function, E_|P|, of a dressed electron is twice differentiable in the momentum P in a neighborhood of P = 0. Furthermore, (E_|P|)" is bounded from below by a constant larger than zero. Our results are proven with the help of iterative analytic perturbation theory

The Mass Shell of the Nelson Model without Cut-Offs

The massless Nelson model describes non-relativistic, spinless quantum particles interacting with a relativistic, massless, scalar quantum field. The interaction is linear in the field. We analyze the one particle sector. First, we construct the renormalized mass shell of the non-relativistic particle for an arbitrarily small infrared cut-off that turns off the interaction with the low energy modes of the field. No ultraviolet cut-off is imposed. Second, we implement a suitable Bogolyubov transformation of the Hamiltonian in the infrared regime. This transformation depends on the total momentum of the system and is non-unitary as the infrared cut-off is removed. For the transformed Hamiltonian we construct the mass shell in the limit where both the ultraviolet and the infrared cut-off are removed. Our approach is constructive and leads to explicit expansion formulae which are amenable to rigorously control the S-matrix elements.Comment: explanations added, typos correcte

Effective Dynamics of a Tracer Particle Interacting with an Ideal Bose Gas

We study a system consisting of a heavy quantum particle, called tracer particle, coupled to an ideal gas of light Bose particles, the ratio of masses of the tracer particle and a gas particle being proportional to the gas density. All particles have non-relativistic kinematics. The tracer particle is driven by an external potential and couples to the gas particles through a pair potential. We compare the quantum dynamics of this system to an effective dynamics given by a Newtonian equation of motion for the tracer particle coupled to a classical wave equation for the Bose gas. We quantify the closeness of these two dynamics as the mean-field limit is approached (gas density $\to\infty$). Our estimates allow us to interchange the thermodynamic with the mean-field limit.Comment: 27 pages, typos corrected, a few more explanations adde

Dynamics of Sound Waves in an Interacting Bose Gas

We consider a non-relativistic quantum gas of $N$ bosonic atoms confined to a box of volume $\Lambda$ in physical space. The atoms interact with each other through a pair potential whose strength is inversely proportional to the density, $\rho=\frac{N}{\Lambda}$, of the gas. We study the time evolution of coherent excitations above the ground state of the gas in a regime of large volume $\Lambda$ and small ratio $\frac{\Lambda}{\rho}$. The initial state of the gas is assumed to be close to a \textit{product state} of one-particle wave functions that are approximately constant throughout the box. The initial one-particle wave function of an excitation is assumed to have a compact support independent of $\Lambda$. We derive an effective non-linear equation for the time evolution of the one-particle wave function of an excitation and establish an explicit error bound tracking the accuracy of the effective non-linear dynamics in terms of the ratio $\frac{\Lambda}{\rho}$. We conclude with a discussion of the dispersion law of low-energy excitations, recovering Bogolyubov's well-known formula for the speed of sound in the gas, and a dynamical instability for attractive two-body potentials.Comment: 42 page

Epidemiology, prevention and control of oral diseases in pediatric subjects

Caries and periodontal diseases are a neglected epidemic by millions of Italians who suffer unnecessarily from them. Both diseases are preventable and the combination of high prevalence, high morbidity and relative inattention from the National Health Service (NHS), makes caries and periodontal disease a significant public health problem. In this perspective, the World Health Organization and the University of Milan have promoted a national epidemiological study aimed at a sample of 4, 6 and 12-years-old students from schools in the North, Central and South of Italy. The study provides for the administration of a questionnaire to parents and a dental examination carried out at school by dentists trained by the WHO. In our town the epidemiological study planning and the survey were carried out by professors of the School of Specialization in "Pediatric Dentistry" (Prof. G. Giuliana and Prof. G. Pizzo) supported by specialist dentists from the same School, calibrated according to the WHO methodology. The survey was carried out between 2017 and 2019 involving 2701 children attending schools in the 8 districts of the town. The parents were sent a letter which explained the nature of the survey and contained a pre-printed form for the issue of informed consent to participate in the survey with a questionnaire regarding the family nuclear, the oral hygiene and eating habits of the minor and the child's previous dental experiences. The ICDAS (International Caries Detection and Assessment System) was used to detect the prevalence of carious lesions. The dentist used for each child visited a dental mirror and the CPI (Community Periodontal Index) index for periodontal assessment. Preliminary results showed that 25.3% of 12-years-old students had gingival bleeding and 41.1% had tartar. The caries index (ICDAS) shows us that as early as 4 years, 20% of children have initial carious lesions, 37% have dentine caries and that 34.38% have highly destructive caries. At 12 years, 34.95% had initial carious lesions, 46% had cavities that already affected dentin and that 42.44% had highly destructive cavities. The exigence to implement a program of prevention / early treatment of caries/gingivitis in pediatric subjects living in Palermo, since the first months of child's life, was born from the data analysis. The project "Un sorriso per 54 tutti i bambini", carried out at the U.O. of "Pediatric Dentistry" of Policlinico Paolo Giaccone in Palermo, was therefore finalised in order to 1) improve efficiency and effectiveness in the promotion of the oral health of minors, through the creation of a preventive / assistance route of significant social health impact; 2) assess the effectiveness of the preventive methodologies adopte

Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations

Laterolateral teleradiography of the skull as a screening method for OSA/OSAS, in patients in orthodontic treatment

Aim: Obstructive sleep apnea syndrome (OSAS) is the most common type of sleep apnea and it is caused by complete or partial obstruction of the upper airway. Adenotonsillar hypertrophy, obesity, cranio-facial anomalies and neuromuscular diseases are the main risk factors for the development of OSAS in the pediatric age. Specially several studies identify the relationship between respiratory disorders in sleep and obesity, and, in particular, between OSAS and obesity, designing a prevalence of OSAS among obese subjects between 14 and 78%. The diagnosis of OSAS in the child is of great importance as it can lead to neurocognitive and behavioral complications, growth retardation, systemic arterial hypertension, pulmonary hypertension, cardiovascular disease and metabolism. The WHO (World Health Organization) has established the new criteria for the classification of Obesity on the basis of BMI and the risk of comorbidities, identifying a moderate risk for underweight subjects, a very low risk for normal weights and an increased risk from severe to severe for overweight and obese individuals respectively. According to that the aim of this study is to evaluate the correlation between obstructive sleep apnea syndrome and cephalometric variables in children considering age and BMI. Materials and methods: Children aged 7–10 years and 11-14 years with no genetic syndrome, previous otorhinolaryngologic or orthodontic therapy treatments are being selected from our Departments of Paediatric Dentistry, University of Palermo, and from the Department of Orthodontics, University of Messina (Italy). All patients so far recruited and visited for orthodontic problems were in mixed or early permanent dentition phase, with the first upper molars fully erupted and presented to the history of several symptoms of Osas, such as recurring episodes of shallow or paused breathing during sleep, waking up frequently to urinate, morning headaches, memory or learning problems and not be able to concentrate or feeling irritable. Dental records and lateral cephalometric radiographs were obtained for all of the patients and than they have been subjected to paediatric, otolaryngology and polysomnography visits. Subject with a positive diagnosis of Osas were studied and they were divided in group based on their BMI. In all groups the inter-molar distance in dental records was measured, and the cephalometric traces have been calculated. As reported by the study by Galeotti et al. the cephalometric measurements analysed are S-PNS, ad1-PNS, and ad2-PNS for the nasopharynx; p-pp and pa for oropharynx; H-H’ for the Hyoid bone; SNA for the maxilla; SNB;ANB and Go-Me for the mandible; S-Go, N-Me and P-A for facial Height; SN for cranial base; SN-MP and PP-MP for the typology, and angle ArGoMe for Growth prevision. At the time that children are still in the way of recruitment the results may not yet be defined; however it is necessary to emphasize the importance of the study, because in the child respiratory disturbances in the sleep, and in particular the OSAS, are often underestimated, despite representing the third place between the threats of health after the smoke and the excess of weight

Diffuse radio emission in the complex merging galaxy cluster Abell 2069

Galaxy clusters with signs for a recent merger show in many cases extended diffuse radio features. This emission originates from relativistic electrons which suffer synchrotron losses due to the intra-cluster magnetic field. The mechanisms of the particle acceleration and the properties of the magnetic field are still poorly understood. We search for diffuse radio emission in galaxy clusters. Here, we study the complex galaxy cluster Abell 2069, for which X-ray observations indicate a recent merger. We investigate the cluster's radio continuum emission by deep Westerbork Synthesis Radio Telescope (WSRT) observations at 346 MHz and a Giant Metrewave Radio Telescope (GMRT) observation at 322 MHz. We find an extended diffuse radio feature roughly coinciding with the main component of the cluster. We classify this emission as a radio halo and estimate its lower limit flux density to 25 +/- 9 mJy. Moreover, we find a second extended diffuse source located at the cluster's companion and estimate its flux density to 15 +/- 2 mJy. We speculate that this is a small halo or a mini-halo. If true, this cluster is the first example of a double-halo in a single galaxy cluster.Comment: 6 pages, 3 figures, accepted for publication in A&

Stream dynamics between 1 AU and 2 AU: A detailed comparison of observations and theory

A radial alignment of three solar wind stream structures observed by IMP-7 and -8 (at 1.0 AU) and Voyager 1 and 2 (in the range 1.4 to 1.8 AU) in late 1977 is presented. It is demonstrated that several important aspects of the observed dynamical evolution can be both qualitatively and quantitatively described with a single-fluid 2-D MHD numerical model of quasi-steady corotating flow, including accurate prediction of: (1) the formation of a corotating shock pair at 1.75 AU in the case of a simple, quasi-steady stream; (2) the coalescence of the thermodynamic and magnetic structures associated with the compression regions of two neighboring, interacting, corotating streams; and (3) the dynamical destruction of a small (i.e., low velocity-amplitude, short spatial-scale) stream by its overtaking of a slower moving, high-density region associated with a preceding transient flow. The evolution of these flow systems is discussed in terms of the concepts of filtering and entrainment