Stellar Evolution in the Early Universe

Massive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this paper, we describe the strong impact of rotation induced mixing and mass loss at very low $Z$. The strong mixing leads to a significant production of primary nitrogen 14, carbon 13 and neon 22. Mass loss during the red supergiant stage allows the production of Wolf-Rayet stars, type Ib,c supernovae and possibly gamma-ray bursts (GRBs) down to almost Z=0 for stars more massive than 60 solar masses. Galactic chemical evolution models calculated with models of rotating stars better reproduce the early evolution of N/O, C/O and C12/C13. We calculated the weak s-process production induced by the primary neon 22 and obtain overproduction factors (relative to the initial composition, Z=1.e-6) between 100-1000 in the mass range 60-90.Comment: 8 pages, 4 figures, proceedings of IAU Symposium 255, "Low-Metallicity Star Formation: From the First stars to Dwarf Galaxies", L.K. Hunt, S. Madden & R. Schneider, ed

The new drift chamber of the MEG-II experiment, in search for lepton flavor violations

FORMATO LATEX The MEG experiment represents the state of the art in the search for the possible existence of the Charged Lepton Flavor Violating (CLFV) decay $\mu^+ \rightarrow e^+ \gamma$. This process is completely prohibited in the framework of the Minimal Standard Model (SM) of Particle Physics and practically forbidden also in the SM extensions including neutrino masses and oscillations, but is foreseen in many other extensions. The predicted Branching Ratios (BR) are not far from the current experimental sensitivities and the discovery of such a decay would be an indisputable proof of the existence of New Physics Beyond the Standard Model (BSM). The MEG collaboration has been presenting the final results of the experiment, exploiting the full statistics collected during the 2009-2013 data taking period at the Paul Scherrer Institut (PSI), which provides the most intense continuous low-energy muon beam in the world, up to $10^8$ $\mu^+$/s. The analysis of the complete data set, corresponding to a total number of $\approx 7.5 \times 10^{14}$ muons stopped in the target at $3 \times 10^{7}$ $\mu^+$/s, has resulted in the new best upper limit on the BR$(\mu^+ \rightarrow e^+ \gamma) \leq 4.2 \times 10^{-13}$ at $90\%$ Confidence Level (C.L.). This value is a factor of $\approx 30$ better than the previously published limit set by the MEGA experiment and lowers the former MEG limit on the BR$(\mu^+ \rightarrow e^+ \gamma) \leq 5.7 \times 10^{-13}$ at $90\%$ C.L. with the analysis of 2009-2011 data, corresponding to $\approx 3.6 \times 10^{14}$ stopped muons (half statistics). Although the MEG experiment detains the most stringent constraint on the $\mu^+ \rightarrow e^+ \gamma$ BR to date, it has reached its ultimate level of sensitivity, limited by the resolutions on the measurement of the kinematic variables of the two decay products. Therefore an upgrade (MEG-II) of the current experimental apparatus has been approved and is presently under construction. It aims at reaching a sensitivity enhancement of at least one order of magnitude compared to the final MEG results, in three years of data taking, by improving the detector figures of merit and the muon stopping rate. The items of the thesis are summarized in the following. After a brief theoretical introduction to Flavor Physics, with particular emphasis on the Lepton Flavor Violation (LFV) in the muon sector, an overview of the MEG experiment is presented. Starting from the experimental apparatus, the final MEG data analysis is described, ending with the presentation of the current best upper limit on the $\mu^+ \rightarrow e^+ \gamma$ BR. Afterwards, a detailed description of the MEG detectors upgrade is provided. It consists in improving the performance of the Liquid Xenon (LXe) calorimeter by enhancing its geometric acceptance and granularity through new photo-detectors (SiPM) and in developing and installing a new drift chamber, as well as a new positrons time detector (Timing Counter) featuring a scintillating multi-tiles configuration. The new drift chamber is designed to overcome the limitations of the MEG $e^+$ tracker and guarantee the proper operation at high rates with big detector stability. In fact, during the MEG-II data taking the muon rate on the stopping target will be more than doubled, up to $7 \times 10^7$ Hz. This also requires the design of a new trigger and DAQ electronics, capable of handling the increased number of readout channels, while maintaining a high bandwidth. A whole Chapter is dedicated to the main theme of the thesis: the MEG-II CYLindrical Drift CHamber (CYLDCH). It features a unique volume covering the whole azimuthal angle around the muon stopping target and a total length of $\approx 2$ meters which improves the geometric acceptance for signal positrons and allows the use of a new tracking procedure. It is designed to follow the $e^+$ tracks up to Timing Counter and to match the information provided by the two individual detectors in order to determine the positrons kinematic variables more accurately and minimize the background sources. The high-granularity of the new MEG-II CYLDCH is ensured by ten layers of drift cells defined by 13056 wires arranged in a stereo configuration and filled with a low-mass 85:15 Helium:Isobutane gas mixture. This minimizes the material budget in the sensitive volume, thus reducing the total radiation length down to $1.5 \times 10^{-3}$ X$_0$ and keeping the Multiple Coulomb Scattering (MCS) contribution to a minimum. Particular emphasis is put on the drift chamber geometry, focusing on the design and detector construction, which is a direct responsability of the MEG-II Pisa group. The CYLDCH assembly is performed in the San Piero a Grado (Pisa) facility of the Istituto Nazionale di Fisica Nucleare (INFN). In the next Chapter a description of a new Pattern Recognition (PR) algorithm for the new MEG-II CYLDCH is reported with the analysis of its performance in simulated experimental conditions near to that of the MEG-II data taking. Finally, in the following Chapter, the Track Fitting toolkit which will be used during the second phase of the MEG experiment is described, together with a study of the momentum and angular resolutions expected for MEG-II. At the end, possible further improvements and a brief review of the MEG-II experiment potentialities and expected time schedule will be presented in the conclusions

thermo structural analysis of components in ceramic material

Abstract The aim of this paper is the systematic study of thermo-structural behavior of ceramic components, in particular, mixtures of refractory materials with high thermal and mechanical performance. Using 3-point bending tests, the elastic modulus, ultimate stress and elongation was obtained; measured values, also thanks to the use of DIC optical technology, was correlated with the different thickness and specific weight values of the specimens used. In order to characterize the thermal behavior, thermal conductivity and specific heat were measured. The experimentally determined average values of such thermomechanical properties have been used in FEM thermo-mechanical models, developed using target geometries with shapes and sizes typical of manufactured ceramic products. In order to evaluate the goodness and the correctness of the developed models, some specimens having the the same shape of the target geometries used in FEM models have been tested at different load conditions and constraints

Modelling of Low-velocity Impacts on Composite Beams in Large Displacement

The paper provides an evaluation of the nonlinear dynamic response of a cantilever beam made of composite material subjected to low-velocity impacts. The structure is assumed to respond in a quasi-static manner and modelled by a continuous beam in large displacement with a lumped mass attached. First, an analytical model was developed to study the free vibrations of a beam, taking into account the nonlinearities due to large displacements and inertia. Then, the analytical findings were compared with experimental test data. The vibration of a real composite beam has been acquired through high-speed imaging technique. The displacements of the beam were extracted by digital image analysis; then, the nonlinear parameters of the analytical model were determined by the Fitting Time History technique. The results obtained by the analytical model and the experimental test are compared with numerical analysis. The validated analytical model was adapted to study a low-velocity impact; the lumped mass was associated with a rigid projectile, whose initial speed represents the impact velocity

Driving Hebbian plasticity over ventral premotor-motor projections transiently enhances motor resonance

Background: Making sense of others' actions relies on the activation of an action observation network (AON), which maps visual information about observed actions onto the observer's motor system. This motor resonance process manifests in the primary motor cortex (M1) as increased corticospinal excitability finely tuned to the muscles engaged in the observed action. Motor resonance in M1 is facilitated by projections from higher-order AON regions. However, whether manipulating the strength of AON-to-M1 connectivity affects motor resonance remains unclear. Methods: We used transcranial magnetic stimulation (TMS) in 48 healthy humans. Cortico-cortical paired associative stimulation (ccPAS) was administered over M1 and the ventral premotor cortex (PMv), a key AON node, to induce spike-timing-dependent plasticity (STDP) in the pathway connecting them. Single-pulse TMS assessed motor resonance during action observation. Results: Before ccPAS, action observation increased corticospinal excitability in the muscles corresponding to the observed movements, reflecting motor resonance in M1. Notably, ccPAS aimed at strengthening projections from PMv to M1 (PMv→M1) induced short-term enhancement of motor resonance. The enhancement specifically occurred with the ccPAS configuration consistent with forward PMv→M1 projections and dissipated 20 min post-stimulation; ccPAS administered in the reverse order (M1→PMv) and sham stimulation did not affect motor resonance. Conclusions: These findings provide the first evidence that inducing STDP to strengthen PMv input to M1 neurons causally enhances muscle-specific motor resonance in M1. Our study sheds light on the plastic mechanisms that shape AON functionality and demonstrates that exogenous manipulation of AON connectivity can influence basic mirror mechanisms that underlie social perception

Evolution and chemical and dynamical effects of high-mass stars

We review general characteristics of massive stars, present the main observable constraints that stellar models should reproduce. We discuss the impact of massive star nucleosynthesis on the early phases of the chemical evolution of the Milky Way (MW). We show that rotating models can account for the important primary nitrogen production needed at low metallicity. Interestingly such rotating models can also better account for other features as the variation with the metallicity of the C/O ratio. Damped Lyman Alpha (DLA) systems present similar characteristics as the halo of the MW for what concern the N/O and C/O ratios. Although in DLAs, the star formation history might be quite different from that of the halo, in these systems also, rotating stars (both massive and intermediate) probably play an important role for explaining these features. The production of primary nitrogen is accompanied by an overproduction of other elements as 13C, 22Ne and s-process elements. We show also how the observed variation with the metallicity of the number ratio of type Ibc to type II supernovae may be a consequence of the metallicity dependence of the line-driven stellar wind

congenital tuberculosis after in vitro fertilization presenting with endobronchial granuloma

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3-Methoxy-Phencyclidine Induced Psychotic Disorder: A Literature Review and an 18 F-FDG PET/CT Case Report

© 2024 by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/New Psychoactive Substances (NPS) are modifying the drug scenario worldwide and have become a public health concern because of their toxicological profiles and their harmful physical/psychological effects. 3-Methoxy-Phencyclidine (3-MeO-PCP), a non-competitive antagonist of glutamate N-methyl-D-aspartate (NMDA) receptors, belongs to the phencyclidine-like subfamily of arylcyclohexylamines and has gained attention for its toxic, sometimes fatal, effects. Despite several cases of intoxication and death reported in the literature, little is known about substance-induced psychotic disorders (SIP) and potential cognitive impairment following 3-MeO-PCP intake. This literature review aimed to summarize available evidence about 3-MeO-PCP mechanisms of action and physical and psychotropic effects and to spread preliminary findings about persistent psychotic symptoms and impaired cognitive functioning. Additionally, the case of an SIP is reported in a 29-year-old man with small oral intakes of 3-MeO-PCP over two weeks until a high dose ingestion. Psychometric and neuropsychological assessment and brain [18F]-fluorodeoxyglucose positron emission tomography integrated with computed tomography were used to support clinical description. Identifying and addressing the characteristic clinical features and neural substrates of NPS-induced psychoses might help clinicians with a more precise differentiation from other psychotic disorders. Although further studies are required, phenotyping the cognitive profile of NPS users might provide targets for tailored therapeutic approaches.Peer reviewe

Stellar Evolution in the Early Universe

Massive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this paper, we describe the strong impact of rotation induced mixing and mass loss at very low metallicity (Z). The strong mixing leads to a significant production of primary 14N, 13C and 22Ne. Mass loss during the red supergiant stage allows the production of Wolf-Rayet stars, type Ib,c supernovae and possibly gamma-ray bursts (GRBs) down to almost Z = 0 for stars more massive than 60 M. Galactic chemical evolution models calculated with models of rotating stars better reproduce the early evolution of N/O, C/O and 12C/13C. We calculated the weak s-process production induced by the primary 22Ne and obtain overproduction factors (relative to the initial composition, Z = 10−6) between 100-1000 in the mass range 60-90

The WaveDAQ integrated Trigger and Data Acquisition System for the MEG II experiment

The WaveDAQ is a newly-designed digitization Trigger and Data AcQuisition system (TDAQ) allowing Multi-gigasample waveform recording on a large amount of channels (up to 16384) by using the DRS4 analog switched capacitor array as downconverting ASIC. A high bandwidth, programmable input stage has been coupled with a bias generator to allow SiPM operation without need of any other external apparatus. The trigger generation is tightly coupled within the system to limit the required depth of the analog memory, allowing faster digitization speeds. This system has been designed for the MEG experiment upgrade but also proved to be highly scalable and already found other applications.Comment: This manuscript is for conference record of the 21st IEEE Real Time conference onl