Search results for "methods"
showing 10 items of 4526 documents
Dissociation mechanisms of cluster ions resolved using ab-initio molecular orbital calculations
2007
We have examined the cluster-size effect on fragments in the collision-induced dissociation (CID) of small boron clusters (B + n , n ≤ 8) by means of ab-initio molecular orbital (MO) calculation, for conditions representative of low-Z cationic clusters in plasma. Single cations B + (leaving B 0 n-1 ) are predominantly fragmented from small clusters B + n (n < 5) by low-energy collisions (<10 eV) with Xe atoms. With increasing the size n, beyond n = 5, B + n-1 (leaving B°) clusters are observed preferentially. This alternating trend in experiment has not been quantitatively explained by previous ab-initio MO calculations. We used a density functional method called B3LYP and basis functions 6…
Comparative ab initio calculations of SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) heterostructures
2016
Abstract Using a B3PW hybrid exchange–correlation functional within the density functional theory (DFT) we calculated from the first principles the electronic structure of BaTiO 3 /SrTiO 3 and PbZrO 3 /SrZrO 3 (0 0 1) interfaces. The optical band gap of both BaTiO 3 /SrTiO 3 and PbZrO 3 /SrZrO 3 (0 0 1) interfaces depends mostly from BaO or TiO 2 and SrO or ZrO 2 termination of the upper layer, respectively. Based on the results of our calculations we predict increase of the Ti–O and Zr–O chemical bond covalency near the SrTiO 3 /BaTiO 3 and SrZrO 3 /PbZrO 3 (0 0 1) interfaces as compared to the BaTiO 3 and PbZrO 3 bulk.
Proton-air cross section measurement with the ARGO-YBJ cosmic ray experiment
2009
The proton-air cross section in the energy range 1-100 TeV has been measured by the ARGO-YBJ cosmic ray experiment. The analysis is based on the flux attenuation for different atmospheric depths (i.e. zenith angles) and exploits the detector capabilities of selecting the shower development stage by means of hit multiplicity, density and lateral profile measurements at ground. The effects of shower fluctuations, the contribution of heavier primaries and the uncertainties of the hadronic interaction models, have been taken into account. The results have been used to estimate the total proton-proton cross section at center of mass energies between 70 and 500 GeV, where no accelerator data are …
Neutrino and dark radiation properties in light of recent CMB observations
2013
Recent cosmic microwave background measurements at high multipoles from the South Pole Telescope and from the Atacama Cosmology Telescope seem to disagree in their conclusions for the neutrino and dark radiation properties. In this paper we set new bounds on the dark radiation and neutrino properties in different cosmological scenarios combining the ACT and SPT data with the nine-year data release of the Wilkinson Microwave Anisotropy Probe (WMAP-9), baryon acoustic oscillation data, Hubble Telescope measurements of the Hubble constant, and supernovae Ia luminosity distance data. In the standard three massive neutrino case, the two high multipole probes give similar results if baryon acoust…
Constraints on the extremely-high energy cosmic neutrino flux with the IceCube 2008-2009 data
2011
We report on a search for extremely-high energy neutrinos with energies greater than $10^6$ GeV using the data taken with the IceCube detector at the South Pole. The data was collected between April 2008 and May 2009 with the half completed IceCube array. The absence of signal candidate events in the sample of 333.5 days of livetime significantly improves model independent limit from previous searches and allows to place a limit on the diffuse flux of cosmic neutrinos with an $E^{-2}$ spectrum in the energy range $2.0 \times 10^{6}$ $-$ $6.3 \times 10^{9}$ GeV to a level of $E^2 \phi \leq 3.6 \times 10^{-8}$ ${\rm GeV cm^{-2} sec^{-1}sr^{-1}}$.
Study of the electromagnetic background in the XENON100 experiment
2011
The XENON100 experiment, located at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off xenon nuclei. We present a comprehensive study of the predicted electronic recoil background coming from radioactive decays inside the detector and shield materials, and intrinsic contamination. Based on GEANT4 Monte Carlo simulations using a detailed geometry together with the measured radioactivity of all detector components, we predict an electronic recoil background in the WIMP-search energy range (0-100 keV) in the 30 kg fiducial mass of less than 10e-2 events/(kg-day-keV), co…
Lateral distribution of muons in IceCube cosmic ray events
2013
In cosmic ray air showers, the muon lateral separation from the center of the shower is a measure of the transverse momentum that the muon parent acquired in the cosmic ray interaction. IceCube has observed cosmic ray interactions that produce muons laterally separated by up to 400 m from the shower core, a factor of 6 larger distance than previous measurements. These muons originate in high pT (>2 GeV/c) interactions from the incident cosmic ray, or high-energy secondary interactions. The separation distribution shows a transition to a power law at large values, indicating the presence of a hard pT component that can be described by perturbative quantum chromodynamics. However, the ra…
Interaction position resolution simulations and in-beam measurements of the AGATA HPGe detectors
2011
WOS: 000290082600015
Search for gamma ray bursts with the ARGO-YBJ detector in scaler mode
2009
We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100 GeV in coincidence with the prompt emission detected by satellites using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R. China, 4300 m a.s.l.), active surface (about 6700 m**2 of Resistive Plate Chambers), and large field of view (about 2 sr, limited only by the atmospheric absorption), the ARGO-YBJ air shower detector is particularly suitable for the detection of unpredictable and short duration events such as GRBs. The search is carried out using the "single particle technique", i.e. counting all the …
Energy spectrum of cosmic protons and helium nuclei by a hybrid measurement at 4300 m a.s.l.
2014
The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured, below the so-called "knee", by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber (RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy resolution of about 25% is achieved throughout the whole energy range (100 TeV - 700 TeV). The observed energy spectrum is compatible with a single power law with index gamma=-2.63+/-0.06.