First Results in the Search for Dark Sectors at NA64 with the CERN SPS High Energy Muon Beam.

We report the first search for dark sectors performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super Proton Synchrotron with a momentum of 160 GeV/c are directed to an active target. The signal signature consists of a single scattered muon with momentum <80 GeV/c in the final state, accompanied by missing energy, i.e., no detectable activity in the downstream calorimeters. For a total dataset of (1.98±0.02)×10^{10} muons on target, no event is observed in the expected signal region. This allows us to set new limits on the remaining (m_{Z^{'}},g_{Z^{'}}) parameter space of a new Z^{'} (L_{µ}-L_{τ}) vector boson which could explain the muon (g-2)_{µ} anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal dark matter relic abundance. Our results pave the way to explore dark sectors and light dark matter with muon beams in a unique and complementary way to other experiments.

Search for Light Dark Matter with NA64 at CERN.

Thermal dark matter models with particle χ masses below the electroweak scale can provide an explanation for the observed relic dark matter density. This would imply the existence of a new feeble interaction between the dark and ordinary matter. We report on a new search for the sub-GeV χ production through the interaction mediated by a new vector boson, called the dark photon A^{'}, in collisions of 100 GeV electrons with the active target of the NA64 experiment at the CERN SPS. With 9.37×10^{11} electrons on target collected during 2016-2022 runs NA64 probes for the first time the well-motivated region of parameter space of benchmark thermal scalar and fermionic dark matter models. No evidence for dark matter production has been found. This allows us to set the most sensitive limits on the A^{'} couplings to photons for masses m_{A^{'}}≲0.35 GeV, and to exclude scalar and Majorana dark matter with the χ-A^{'} coupling α_{D}≤0.1 for masses 0.001≲m_{χ}≲0.1 GeV and 3m_{χ}≤m_{A^{'}}.

Reversible alteration of calcium dynamics in cardiomyocytes during acute hypoxia transient in a microfluidic platform.

Heart disease is the leading cause of mortality in western countries. Apart from congenital and anatomical alterations, ischemia is the most common agent causing myocardial damage. During ischemia, a sudden decrease in oxygen concentration alters cardiomyocyte function and compromises cell survival. The calcium handling machinery, which regulates the main functional features of a cardiomyocyte, is heavily compromised during acute hypoxic events. Alterations in calcium dynamics have been linked to both short- and long-term consequences of ischemia, ranging from arrhythmias to heart failure. In this perspective, we aimed at investigating the calcium dynamics in functional cardiomyocytes during the early phase of a hypoxic event. For this purpose, we developed a microfluidic system specifically designed for controlling fast oxygen concentration dynamics through a gas micro-exchanger allowing in line analysis of intracellular calcium concentration by confocal microscopy. Experimental results show that exposure of Fluo-4 loaded neonatal rat cardiomyocytes to hypoxic conditions induced changes in intracellular Ca(2+) transients. Such behavior was reversible and was detected for hypoxic levels below 5% of oxygen partial pressure. The observed changes in Ca(2+) dynamics were mimicked using specific L-type Ca(2+) channel antagonists, suggesting that alterations in calcium channel function occur at low oxygen levels. Reversible alteration in ion channel function, that takes place in response to changes in cellular oxygen, might represent an adaptive mechanism of cardiopreservation during ischemia.

[Release of metals from metal-on-metal hip prostheses]. / Rilascio di metalli da protesi d'anca metallo-su-metallo.

The present study examined blood and urinary concentrations of Cr and Co in 30 patients with metal-on-metal hip prostheses without signs of wear and 6 patients with prosthetic bearing and clear signs of wear and metallosis. The determination in biological fluids showed in patients with not signs of wear the geometric mean concentration of metals only modestly increased (CoS 0.5 microg/l, CoU 5.7 microg/l, CrS 0.8 microg/l, CrU 3.4 microg/l) compared to the reference values, while the wear caused a significant increase in the concentration of both Co (CoS 94.6 microg/l, CoU 334.5 microg/l) and Cr (CrS 57.7 microg/l, CrU 89.4 microg/I). As the results, the not functioning implants are a risks to the patients and are associated with high levels of metals in biological fluids. Currently, the patients with metallosis had not signs and symptoms associated with metal toxicity, but high concentrations could to cause kidney, peripheral nervous system, heart, and thyroid damage.

Quantum transport in GaN/AlN double-barrier heterostructure nanowires.

We investigate electronic transport in n-i-n GaN nanowires with and without AlN double barriers. The nanowires are grown by catalyst-free, plasma-assisted molecular beam epitaxy enabling abrupt GaN/AlN interfaces as well as longitudinal n-type doping modulation. At low temperature, transport in n-i-n GaN nanowires is dominated by the Coulomb blockade effect. Carriers are confined in the undoped middle region, forming single or multiple islands with a characteristic length of approximately 100 nm. The incorporation of two AlN tunnel barriers causes confinement to occur within the GaN dot in between. In the case of a 6 nm thick dot and 2 nm thick barriers, we observe characteristic signatures of Coulomb-blockaded transport in single quantum dots with discrete energy states. For thinner dots and barriers, Coulomb-blockade effects do not play a significant role while the onset of resonant tunneling via the confined quantum levels is accompanied by a negative differential resistance surviving up to approximately 150 K.

Hybrid superconductor-semiconductor devices made from self-assembled SiGe nanocrystals on silicon.

The epitaxial growth of germanium on silicon leads to the self-assembly of SiGe nanocrystals by a process that allows the size, composition and position of the nanocrystals to be controlled. This level of control, combined with an inherent compatibility with silicon technology, could prove useful in nanoelectronic applications. Here, we report the confinement of holes in quantum-dot devices made by directly contacting individual SiGe nanocrystals with aluminium electrodes, and the production of hybrid superconductor-semiconductor devices, such as resonant supercurrent transistors, when the quantum dot is strongly coupled to the electrodes. Charge transport measurements on weakly coupled quantum dots reveal discrete energy spectra, with the confined hole states displaying anisotropic gyromagnetic factors and strong spin-orbit coupling with pronounced dependences on gate voltage and magnetic field.

[Prevalence of hepatitis virus A, B, and C markers according to the geographic origin of medical students]. / Prevalenza dei marcatori dell'epatite (A, B e C) in relazione alla provenienza geografica degli studenti dei corsi di laurea in medicina.

Antibodies against viral hepatitis A, B and C were evaluated in 221 students of graduate courses of the Medical School of Padua University born in countries different from Italy. Data were compared with those measured in 362 students born in Veneto Region and 87 students born in Centre-Southern Italy. The results showed a high, significant prevalence of positive antibodies against hepatitis A in students from Africa (94.7%), Asia (60.9%), Centre-Southern America (60.9%) and East Europe (52.7%); in Italy, the prevalence was significant in student from Centre-Southern Italy (19.5%). A high prevalence of hepatitis B antibodies was observed in 33.3% of Africa students (two subjects HBsAg positive), in 22.6% of students from East Europe (five subjects HBsAg positive) and in 12.5% of Asian and Centre-Southern American students (one HBeAg positive). Finally, infection with hepatitis C is sporadic and without a significant geographic distribution (three subjects only).

[Prevalence of virus hepatitis B markers among medical students]. / Prevalenza dei marcatori dell'epatite B negli studenti dei corsi di laurea in medicina.

Healthcare workers are a category of subjects at risk of infections higher than general population, though the introduction of vaccination against hepatitis B generally reduced this risk. In the present research, 2137 students of graduate course for health professions were subdivide in two age classes: 25 years old or younger and older than 25 years old according to the vaccination strategy defined by the law 165/91. A high number of students (82.3%) appeared immune against hepatitis B virus, whereas 16.7% were negative. About 30% of negative subjects declared vaccination. Females and subjects 25 years old or younger showed a significantly higher prevalence of anti-HBsAg antibodies (p < 0.001) than males and older subjects respectively. The obtained results show the need to evaluate the immunity status of the healthcare workers in training with the aim to reduce the number of susceptible subjects.

A complex phosphodiesterase system controls beta-adrenoceptor signalling in cardiomyocytes.

beta-Adrenergic signalling mediates the positive inotropic effect of catecholamines on cardiomyocytes, mainly through cAMP generation and subsequent activation of PKA (protein kinase A). Given the large diversity of PKA targets within cardiac cells, a precisely regulated and confined activity of such signalling pathways is essential for the specificity of response. PDEs (phosphodiesterases) constitute the only cAMP-degrading mechanism and are expressed in the cardiomyocyte in at least 5 family variants. Each PDE family is characterized by unique functional properties and contributes to a cAMP-degrading system enabling the modulation of PKA activity in a stimulus-dependent fashion.

Imaging the cAMP-dependent signal transduction pathway.

In recent years, the development of new technologies based on the green fluorescent protein and FRET (fluorescence resonance energy transfer) has introduced a new perspective in the study of cAMP signalling. Real-time imaging of fluorescent biosensors is making it possible to visualize cAMP dynamics directly as they happen in intact, living cells, providing important and original insights for our understanding of the spatiotemporal organization of the cAMP/PKA (protein kinase A) signalling pathway.