Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN)
. Among the light elements produced during BBN
, ...deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of neutrino species permeating the early Universe. Although astronomical observations of primordial deuterium abundance have reached percent accuracy
, theoretical predictions
based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)
He reaction. Here we show that our improved cross-sections of this reaction lead to BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent analysis of the cosmic microwave background
. Improved cross-section data were obtained by exploiting the negligible cosmic-ray background deep underground at the Laboratory for Underground Nuclear Astrophysics (LUNA) of the Laboratori Nazionali del Gran Sasso (Italy)
. We bombarded a high-purity deuterium gas target
with an intense proton beam from the LUNA 400-kilovolt accelerator
and detected the γ-rays from the nuclear reaction under study with a high-purity germanium detector. Our experimental results settle the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances to probe the physics of the early Universe.
The OLYMPUS Collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, R_{2γ}, a direct measure of the contribution of hard two-photon ...exchange to the elastic cross section. In the OLYMPUS measurement, 2.01 GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of ≈20° to 80°. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved gas electron multiplier and multiwire proportional chamber detectors at 12°, as well as symmetric Møller or Bhabha calorimeters at 1.29°. A total integrated luminosity of 4.5 fb^{-1} was collected. In the extraction of R_{2γ}, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of R_{2γ}, presented here for a wide range of virtual photon polarization 0.456<ε<0.978, are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.
In this retrospective study, we examined the prevalence and spectrum of germline variants in selected cancer predisposition genes in 38 children and young adults with melanocytic lesions at St. Jude ...Children's Research Hospital. Diagnoses included malignant melanoma (n = 16; 42%), spitzoid melanoma (n = 16; 42%), uveal melanoma (n = 5; 13%), and malignant melanoma arising in a giant congenital melanocytic nevus (n = 1; 3%). Six patients (15.8%) harbored pathogenic germline variants: one with bi‐allelic PMS2 variants, one with a heterozygous 17q21.31 deletion, and one each with a pathogenic variant in TP53, BRIP1, ATM, or AXIN2. Overall, 15.8% of patients harbored a cancer‐predisposing genetic variant.
Background Obese subjects frequently show skin diseases. However, less attention has been paid to the impact of obesity on skin disorders until now.
Objective The purposes of this study are: to ...highlight the incidence of some dermatoses in obese subjects and to study the water barrier function of the obese skin using transepidermal water loss (TEWL).
Methods Sixty obese subjects and 20 normal weight volunteers were recruited. Obese group was further divided into three body mass index (BMI) classes: class I (BMI 30–34.9 kg/m2), class II (BMI 35–39.9 kg/m2) and class III (BMI 40 g/m2). All subjects attended dermatological examination for skin diseases. To assess barrier function, TEWL measurements were performed on the volar surface of the forearm using a tewameter.
Results The results of this study showed that: (i) obese subjects show a higher incidence of some dermatoses compared with normal‐weight controls; in addition the dermatoses are more, frequent as BMI increases; (ii) the rate of TEWL is lower in obese subjects, than in the normal‐weight subjects, particularly in patients with intra‐abdominal obesity.
Conclusion Specific dermatoses as skin tags, striae distensae and plantar hyperkeratosis, could be considered as a cutaneous stigma of severe obesity. The low permeability of the skin to evaporative water loss is observed in obese subjects compared with normal weight control. Although the physiological mechanisms are still unknown, this finding has not been previously described and we believe that this may constitute a new field in the research on obesity.
The accurate understanding and control of the time resolution of a scintillator–photodetector assembly are becoming more and more important in medical physics. The time-of-flight information in the ...positron emission tomography (TOF-PET) enhances in fact the signal-to-noise ratio of the reconstructed images. We present a custom-made Monte Carlo code investigating the role of all the parameters contributing to the time resolution. In particular, the single photoelectron response barely affects the best achievable time resolution. However, it plays a dominant role in reproducing the shape and features (rise time, amplitude) of the signal produced by the detection of a gamma ray. In such a way, it mostly determines the threshold for the best time resolution. We validated the Monte Carlo code by comparing its results with available measurements of time resolutions at various threshold levels in assemblies formed by small-size L(Y)SO and LuAG crystals coupled to Silicon photomultipliers (SiPM) and photomultiplier tubes (PMT).
Microscopic simulations may bring a better understanding of the response of gaseous detectors. Such simulations are computationally demanding, due to the modelling of the low energy processes and to ...the high segmentation required for the 2D/3D field maps. In MPGD such maps can be much more complex than those of traditional multiwire chambers, due to the heterogeneous materials and more involute geometries, which break the simplifying symmetries featured in the latter. In order to investigate the performance of the triple GEM 2-dimensional tracking chambers being developed for high luminosity experiments with the Super BigBite Spectrometer at Jefferson Laboratory, we have set up a flexible and rather effcient multistep simulation processor based on either ANSYS or GMSH+ELMER for 3D CAD and electrostatic field modelling and then combined to Garfield++. Potential systematic effects from the 3D CAD modellers, the mesh generators and the electrostatic field solvers have been estimated with dedicated simulations; once these effects have been assessed, the results of the multistep approach have been compared to a simplified whole GEM chamber model.
In this work graphitic structures were fabricated on high quality polycrystalline CVD diamond by using a UV laser beam (λ=193nm). Two different kinds of structures were realized on diamond to study ...the evolution from diamond to graphite at different irradiation conditions (spot like structures) and to study their electrical transport properties (strip like structures). The graphitic structures were characterized structurally and morphologically by micro-Raman spectroscopy and atomic force microscopy. The electrical properties were evaluated using the transmission line model. Finally, a full carbon detector was built and tested showing good nuclear detection properties.
When a diamond graphitization process is induced, for example by excimer laser which irradiates the diamond surface, two phenomena occur: diamond graphititization and graphite ablation. The figure shows the physical evolution of the average height of the graphitic spots obtained after laser-diamond interaction, at laser fluence of 5J/cm2, with respect to the number of pulses. The measurements were obtained by AFM investigations (zero level refers flat unirradiated diamond surface). For one and two pulses it dominates a swelling phenomenon which represents the diamond graphitization process (the swelling is due to different mass density between diamond and graphite phases), while for four and eight pulses the graphite ablation dominates generating crates with increasing depth. Display omitted
•The physical evolution of the diamond graphitization process was studied.•The characterizations of graphitization and ablation processes of diamond were made by AFM and micro-Raman investigations.•The realization and optimization of ohmic graphitic contacts on diamond surface were done.•The response of full carbon detector to an ionizing particle and estimation of its CCE were reported.
The observation of oxygen isotopes in giant stars sheds light on mixing processes operating in their interiors. Due to the very strong correlation between nuclear burning and mixing processes it is ...very important to reduce the uncertainty on the cross sections of the nuclear reactions that are involved. In this paper we focus our attention on the reaction O18(p,γ)19F. While the O18(p,α)15N channel is thought to be dominant, the (p,γ) channel can still be an important component in stellar burning in giants, depending on the low energy cross section. So far only extrapolations from higher-energy measurements exist and recent estimates vary by orders of magnitude. These large uncertainties call for an experimental reinvestigation of this reaction. We present a direct measurement of the O18(p,γ)19F cross section using a high-efficiency 4π BGO summing detector at the Laboratory for Underground Nuclear Astrophysics (LUNA). The reaction cross section has been directly determined for the first time from 140 keV down to 85 keV and the different cross section components have been obtained individually. The previously highly uncertain strength of the 90 keV resonance was found to be 0.53 ± 0.07 neV, three orders of magnitude lower than an indirect estimate based on nuclear properties of the resonant state and a factor of 20 lower than a recently established upper limit, excluding the possibility that the 90 keV resonance can contribute significantly to the stellar reaction rate.
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