48 research outputs found
Enhancement of fusion rates due to quantum effects in the particles momentum distribution in nonideal media
This study concerns a situation when measurements of the nonresonant
cross-section of nuclear reactions appear highly dependent on the environment
in which the particles interact. An appealing example discussed in the paper is
the interaction of a deuteron beam with a target of deuterated metal Ta. In
these experiments, the reaction cross section for d(d,p)t was shown to be
orders of magnitude greater than what the conventional model predicts for the
low-energy particles. In this paper we take into account the influence of
quantum effects due to the Heisenberg uncertainty principle for particles in a
non-ideal medium elastically interacting with the medium particles. In order to
calculate the nuclear reaction rate in the non-ideal environment we apply both
the Monte Carlo technique and approximate analytical calculation of the Feynman
diagram using nonrelativistic kinetic Green's functions in the medium which
correspond to the generalized energy and momentum distribution functions of
interacting particles. We show a possibility to reduce the 12-fold integral
corresponding to this diagram to a fivefold integral. This can significantly
speed up the computation and control accuracy. Our calculations show that
quantum effects significantly influence reaction rates such as p +7Be, 3He
+4He, p +7Li, and 12C +12C. The new reaction rates may be much higher than the
classical ones for the interior of the Sun and supernova stars. The possibility
to observe the theoretical predictions under laboratory conditions is
discussed
Possibility of quantitative T2-mapping MRI of cartilage near metal in high tibial osteotomy: A human cadaver study
T2-mapping is a widely used quantitative MRI technique in osteoarthritis research. An important challenge for its application in the context of high tibial osteotomy (HTO) is the presence of metallic fixation devices. In this study, we evaluated the possibility of performing T2-mapping after a HTO, by assessing the extent of magnetic susceptibility artifacts and the influence on T2 relaxation times caused by two commonly used fixation devices. T2-mapping with a 3D fast spin-echo sequence at three Tesla was performed on 11 human cadaveric knee joints before and after implantation of a titanium plate and screws (n = 5) or cobalt chrome staples (n = 6). Mean T2 relaxation times were calculated in six cartila
Separating the Early Universe from the Late Universe: cosmological parameter estimation beyond the black box
We present a method for measuring the cosmic matter budget without
assumptions about speculative Early Universe physics, and for measuring the
primordial power spectrum P*(k) non-parametrically, either by combining CMB and
LSS information or by using CMB polarization. Our method complements currently
fashionable ``black box'' cosmological parameter analysis, constraining
cosmological models in a more physically intuitive fashion by mapping
measurements of CMB, weak lensing and cluster abundance into k-space, where
they can be directly compared with each other and with galaxy and Lyman alpha
forest clustering. Including the new CBI results, we find that CMB measurements
of P(k) overlap with those from 2dF galaxy clustering by over an order of
magnitude in scale, and even overlap with weak lensing measurements. We
describe how our approach can be used to raise the ambition level beyond
cosmological parameter fitting as data improves, testing rather than assuming
the underlying physics.Comment: Replaced to match accepted PRD version. Refs added. Combined CMB data
and window functions at http://www.hep.upenn.edu/~max/pwindows.html or from
[email protected]. 18 figs, 19 journal page
Two-component spike nanoparticle vaccine protects macaques from SARS-CoV-2 infection
Brouwer et al. present preclinical evidence in support of a COVID-19 vaccine candidate, designed as a self-assembling two-component protein nanoparticle displaying multiple copies of the SARS-CoV-2 spike protein, which induces strong neutralizing antibody responses and protects from high-dose SARS-CoV-2 challenge.The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is continuing to disrupt personal lives, global healthcare systems, and economies. Hence, there is an urgent need for a vaccine that prevents viral infection, transmission, and disease. Here, we present a two-component protein-based nanoparticle vaccine that displays multiple copies of the SARS-CoV-2 spike protein. Immunization studies show that this vaccine induces potent neutralizing antibody responses in mice, rabbits, and cynomolgus macaques. The vaccine-induced immunity protects macaques against a high-dose challenge, resulting in strongly reduced viral infection and replication i
Ionentemperaturmessungen an ASDEX mit verbesserter Fusions-Protonen- und -Tritonen-Diagnostik
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Ionenenergietransport in elektronengeheizten Entladungen am Tokamak ASDEX
In the present work conducted at the TOKAMAK experiment ASDEX (axial symmetrical divertor experiment) an optimization of the neutral particle diagnostics was carried out in order to derive reliable ion temperatures from the neutral particle flux, and to establish radial profiles for all important discharge scenaria. Separating high-energetic and non-thermal contributions, relative errors in ion temperature determination could be limited to #+-# 10%, excluding at the same time systematic errors. Based on these experimental and theoretical studies, the local ion energy transport has been analyzed. Results are in line with the basic equations of the neoclassic theory. (WEN)SIGLEAvailable from TIB Hannover: RA 71(III/198) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Statistical analysis of the global energy confinement time #tau#_E in Ohmic discharges in the ASDEX tokamak
In ohmic discharges in all tokamaks at low plasma densities the global energy confinement time #tau#_E increases almost linearly with the density (LOC, Linear Ohmic Confinement). In tokamaks with sufficiently large dimensions #tau#_E saturates at a critical density (ASDEX: anti n_e#approx#3x10"1"9 m"-"3) and is nearly constant at higher densities (SOC, Saturated Ohmic Confinement). In the same density region some experiments report a further confinement regime for deuterium discharges in which #tau#_E exceeds the saturated value and is further increased (IOC, Improved Ohmic Confinement). There the global energy confinement time roughly behaves as in the LOC regime. For both the LOC and the SOC regimes an isotope effect, i.e. the dependence of #tau#_E on the ion mass, is reported as an additional aspect of the ohmic energy confinement. A statistical analysis is performed to identify the parameters which are responsible for the properties of the energy confinement in these discharges in ASDEX. Contrary to earlier reports on confinement time scalings in ASDEX OH, only discharges with a full experimental description of kinetic electron and ion parameters, i.e. profiles of densities, temperatures and Z_e_f_f, are used to evaluate the energy contents of both species. By means of statistics it is shown that the characteristics of #tau#_E are mainly caused by the behaviour of the electron energy flux and the ohmic input power. The ion energy flux, however, does not play a significant role. Furthermore, the IOC regime is explained as a continuation of the low-density LOC regime. Both effects, the isotope effect and the density dependence of #tau#_E, are caused by the features of the electron energy transport. (orig.)30 refs.Available from TIB Hannover: RA 71(205) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman