2,951 research outputs found
Big Bang nucleosynthesis revisited via Trojan Horse Method measurements
Nuclear reaction rates are among the most important input for understanding
the primordial nucleosynthesis and therefore for a quantitative description of
the early Universe. An up-to-date compilation of direct cross sections of
2H(d,p)3H, 2H(d,n)3He, 7Li(p,alpha)4He and 3He(d,p)4He reactions is given.
These are among the most uncertain cross sections used and input for Big Bang
nucleosynthesis calculations. Their measurements through the Trojan Horse
Method (THM) are also reviewed and compared with direct data. The reaction
rates and the corresponding recommended errors in this work were used as input
for primordial nucleosynthesis calculations to evaluate their impact on the 2H,
3,4He and 7Li primordial abundances, which are then compared with observations.Comment: 22 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Technical Solutions and Standards Upgrade for Photovoltaic Systems Operated over 1500 Vdc
This paper deals with photovoltaic (PV) systems with operating voltage increased over the value 1500 V in DC, which represents the limit of the current solutions and the actual standard for the PV plant at utility-scale level. The increase of the DC voltage is aimed at reducing the cable energy losses, the number of components and to optimise the layout of the plants, increasing the competitiveness of Medium Voltage PV (MVPV) solutions with rated powers of hundreds of megawatt. The analysis carried out has identified the possible solutions to adopt in order to reach this target and has remarked that today the International Standards are not covering all the aspects of the technical solutions to be introduced in a MVPV plant. This paper indicates the key issues to be addressed by new Standards on some components in order to enable the deployment of MVPV solutions. Finally, the characteristics of an installation at 1500 V DC and some results of tests carried out on the isolation system of a 1500 V PV plant are discussed
Neoadjuvant therapy for breast cancer
Objective: To evaluate the frequency of neoadjuvant therapy (NT) in women with stage I–III breast cancer in Italy and whether it is influenced by biological characteristics, screening history, and geographic area. Methods: Data from the High Resolution Study conducted in 7 Italian cancer registries were used; they are a representative sample of incident cancers in the study period (2009–2013). Included were 3546 women aged <85 years (groups <50, 50–69, 70–64, and 75+) with stage I–III breast cancer at diagnosis who underwent surgery. Women were classified as receiving NT if they received chemotherapy, target therapy, and/or hormone therapy before the first surgical treatment. Logistic models were built to test the association with biological and contextual variables. Results: Only 8.2% of women (290 cases) underwent NT; the treatment decreases with increasing age (14.5% in age <50 and 2.2% in age 75+), is more frequent in women with negative receptors (14.8%), HER2-positive (15.7%), and triple-negative (15.6%). The multivariable analysis showed the probability of receiving NT is higher in stage III (odds ratio [OR] 3.83; 95% confidence interval [CI] 2.83–5.18), luminal B (OR 1.87; 95% CI 1.27–2.76), triple-negatives (OR 1.88; 95% CI 1.15–3.08), and in symptomatic cancers (OR 1.98; 95% CI 1.13–3.48). Use of NT varied among geographic areas: Reggio Emilia had the highest rates (OR 2.29; 95% CI 1.37–3.82) while Palermo had the lowest (OR 0.41; 95% CI 0.24–0.68). Conclusions: The use of NT in Italy is limited and variable. There are no signs of greater use in hospitals with more advanced care
Contact between the components of a knee prosthesis: numerical and experimental study
The aim of this work is the analysis of the contact area in a knee prosthesis using two different approaches. In particular, the interface between the femoral component and the polyethylene insert has been studied both numerically and experimentally. The interest in studying the contact area is related to the fact that the wear of the polyethylene insert, due to the high contact pressures, represents one of the major causes of failure of the total knee prosthesis. The possibility to evaluate the contact area at different loads and mutual position between femur and tibia is, therefore, of fundamental importance to study the service life of a prosthesis and to improve its performance. The finite element numerical approach has required the acquisition, through reverse engineering, and CAD modelling of the prosthetic components. Then the FEM simulations have been developed considering two different load conditions. In order to compare the calculated data, the same load configurations have been used for experimental tests based on ultrasonic method. In this case, some preliminary tests were required to calibrate the system depending on the particular characteristics of materials, geometries and surface finish of the prosthesis.The results show a good correlation between the data obtained with the two different approaches and, consequently, a good level of reliability of the procedures developed for the numerical and experimental evaluation of the contact area. The numerical procedure can be used to determine the area for different angles and loads, but especially in the design phase. The ultrasonic technique can be used to validate the numerical data
Pulsed Laser Deposition of two-dimensional ZnO nanocrystals on Au(111): Growth, surface structure and electronic properties
Two-dimensional (2D) ZnO structures have been deposited on the Au(111) surface by means of the pulsed laser deposition (PLD) technique. In situ scanning tunneling microscopy (STM) and spectroscopy (STS) measurements have been performed to characterize morphological, structural and electronic properties of 2D ZnO at the nanoscale. Starting from a sub-monolayer coverage, we investigated the growth of ZnO, identifying different atomic layers (up to the 5th). At low coverage, we observed single- and bi-layer nanocrystals, characterized by a surface moire pattern that is associated to a graphene-like ZnO structure.
By increasing the coverage, we revealed a morphological change starting from the 4th layer, which was attributed to a transition toward a bulk-like structure. Investigation of the electronic properties revealed the semiconducting character of 2D ZnO. We observed a dependence of the density of states (DOS) and, in particular, of the conduction band (CB) on the ZnO thickness, with a decreasing of the CB onset energy for increasing thickness. The CB DOS of 2D ZnO shows a step-like behaviour which may be interpreted as due to a 2D quantum confinement effect in ZnO atomic layer
Fabrication and Characterization of Molybdenum Tips for Scanning Tunneling Microscopy and Spectroscopy
We present a method for the preparation of bulk molybdenum tips for scanning Tunneling Microscopy and Spectroscopy (STM - STS) and we assess their potential in performing high resolution imaging and local spectroscop by measurements on different single crystal surfaces in UHV, namely Au(111), Si(111)-7x7 and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g. cobalt
Contact between the components of a knee prosthesis: numerical and experimental study
The aim of this work is the analysis of the contact area in a knee prosthesis using two different approaches. In particular, the interface between the femoral component and the polyethylene insert has been studied both numerically and experimentally. The interest in studying the contact area is related to the fact that the wear of the polyethylene insert, due to the high contact pressures, represents one of the major causes of failure of the total knee prosthesis. The possibility to evaluate the contact area at different loads and mutual position between femur and tibia is, therefore, of fundamental importance to study the service life of a prosthesis and to improve its performance. The finite element numerical approach has required the acquisition, through reverse engineering, and CAD modelling of the prosthetic components. Then the FEM simulations have been developed considering two different load conditions. In order to compare the calculated data, the same load configurations have been used for experimental tests based on ultrasonic method. In this case, some preliminary tests were required to calibrate the system depending on the particular characteristics of materials, geometries and surface finish of the prosthesis.The results show a good correlation between the data obtained with the two different approaches and, consequently, a good level of reliability of the procedures developed for the numerical and experimental evaluation of the contact area. The numerical procedure can be used to determine the area for different angles and loads, but especially in the design phase. The ultrasonic technique can be used to validate the numerical data
Trojan Horse as an indirect technique in nuclear astrophysics. Resonance reactions
The Trojan Horse method is a powerful indirect technique that provides
information to determine astrophysical factors for binary rearrangement
processes at astrophysically relevant energies by measuring
the cross section for the Trojan Horse reaction in
quasi-free kinematics. We present the theory of the Trojan Horse method for
resonant binary subreactions based on the half-off-energy-shell R matrix
approach which takes into account the off-energy-shell effects and initial and
final state interactions.Comment: 6 pages and 1 figur
Solving the large discrepancy between inclusive and exclusive measurements of the reaction cross section at astrophysical energies
A solution of the large discrepancy existing between inclusive and exclusive
measurements of the reaction
cross section at MeV is evaluated. This problem has profound
astrophysical relevance for this reaction is of great interest in Big-Bang and
r-process nucleosynthesis. By means of a novel technique, a comprehensive study
of all existing cross section
data is carried out, setting up a consistent picture in which all the inclusive
measurements provide the reliable value of the cross section. New unambiguous
signatures of the strong branch pattern non-uniformities, near the threshold of
higher excited levels, are presented and their possible
origin, in terms of the cluster structure of the involved excited states of
and nuclei, is discussed.Comment: 5 pages, 4 figures, 1 tabl
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