25,753 research outputs found
Symmetries and Triplet Dispersion in a Modified Shastry-Sutherland Model for SrCu_2(BO_3)_2
We investigate the one-triplet dispersion in a modified Shastry-Sutherland
Model for SrCu_2(BO_3)_2 by means of a series expansion about the limit of
strong dimerization. Our perturbative method is based on a continuous unitary
transformation that maps the original Hamiltonian to an effective, energy
quanta conserving block diagonal Hamiltonian H_{eff}. The dispersion splits
into two branches which are nearly degenerated. We analyse the symmetries of
the model and show that space group operations are necessary to explain the
degeneracy of the dispersion at k=0 and at the border of the magnetic Brillouin
zone. Moreover, we investigate the behaviour of the dispersion for small |k|
and compare our results to INS data.Comment: 9 pages, 8 figures accepted by J. Phys.: Condens. Matte
Large scale Gd-beta-diketonate based organic liquid scintillator production for antineutrino detection
Over the course of several decades, organic liquid scintillators have formed
the basis for successful neutrino detectors. Gadolinium-loaded liquid
scintillators provide efficient background suppression for electron
antineutrino detection at nuclear reactor plants. In the Double Chooz reactor
antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded
scintillator is utilized for the first time. Its large scale production and
characterization are described. A new, light yield matched metal-free companion
scintillator is presented. Both organic liquids comprise the target and "Gamma
Catcher" of the Double Chooz detectors.Comment: 16 pages, 4 figures, 5 table
Large scale Gd-beta-diketonate based organic liquid scintillator production for antineutrino detection
Over the course of several decades, organic liquid scintillators have formed
the basis for successful neutrino detectors. Gadolinium-loaded liquid
scintillators provide efficient background suppression for electron
antineutrino detection at nuclear reactor plants. In the Double Chooz reactor
antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded
scintillator is utilized for the first time. Its large scale production and
characterization are described. A new, light yield matched metal-free companion
scintillator is presented. Both organic liquids comprise the target and "Gamma
Catcher" of the Double Chooz detectors.Comment: 16 pages, 4 figures, 5 table
Formation Rates of Black Hole Accretion Disk Gamma-Ray Bursts
While many models have been proposed for GRBs, those currently favored are
all based upon the formation of and/or rapid accretion into stellar mass black
holes. We present population synthesis calculations of these models using a
Monte Carlo approach in which the many uncertain parameters intrinsic to such
calculations are varied. We estimate the event rate for each class of model as
well as the propagation distance for those having significant delay between
formation and burst production, i.e., double neutron star (DNS) mergers and
black hole-neutron star (BH/NS) mergers. For reasonable assumptions regarding
the many uncertainties in population synthesis, we calculate a daily event rate
in the universe for i) merging neutron stars: ~100/day; ii) neutron-star black
hole mergers: ~450/day; iii) collapsars: ~10,000/day; iv) helium star black
hole mergers: ~1000/day; and v) white dwarf black hole mergers: ~20/day. The
range of uncertainty in these numbers however, is very large, typically two to
three orders of magnitude. These rates must additionally be multiplied by any
relevant beaming factor and sampling fraction (if the entire universal set of
models is not being observed). Depending upon the mass of the host galaxy, half
of the DNS and BH/NS mergers will happen within 60kpc (for a Milky-Way massed
galaxy) to 5Mpc (for a galaxy with negligible mass) from the galactic center.
Because of the delay time, neutron star and black hole mergers will happen at a
redshift 0.5 to 0.8 times that of the other classes of models. Information is
still lacking regarding the hosts of short hard bursts, but we suggest that
they are due to DNS and BH/NS mergers and thus will ultimately be determined to
lie outside of galaxies and at a closer mean distance than long complex bursts
(which we attribute to collapsars).Comment: 57 pages total, 23 figures, submitted by Ap
Large scale Gd-beta-diketonate based organic liquid scintillator production for antineutrino detection
Over the course of several decades, organic liquid scintillators have formed
the basis for successful neutrino detectors. Gadolinium-loaded liquid
scintillators provide efficient background suppression for electron
antineutrino detection at nuclear reactor plants. In the Double Chooz reactor
antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded
scintillator is utilized for the first time. Its large scale production and
characterization are described. A new, light yield matched metal-free companion
scintillator is presented. Both organic liquids comprise the target and "Gamma
Catcher" of the Double Chooz detectors.Comment: 16 pages, 4 figures, 5 table
Photospheric Emission in the Joint GBM and Konus Prompt Spectra of GRB 120323A
GRB 120323A is a very intense short Gamma Ray Burst (GRB) detected
simultaneously during its prompt gamma-ray emission phase with the Gamma-ray
Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope and the Konus
experiment on board the Wind satellite. GBM and Konus operate in the keV--MeV
regime, however, the GBM range is broader both toward the low and the high
parts of the gamma-ray spectrum. Analysis of such bright events provide a
unique opportunity to check the consistency of the data analysis as well as
cross-calibrate the two instruments. We performed time-integrated and coarse
time-resolved spectral analysis of GRB 120323A prompt emission. We conclude
that the analyses of GBM and Konus data are only consistent when using a
double-hump spectral shape for both data sets; in contrast, the single-hump of
the empirical Band function, traditionally used to fit GRB prompt emission
spectra, leads to significant discrepancies between GBM and Konus analysis
results. Our two-hump model is a combination of a thermal-like and a
non-thermal component. We interpret the first component as a natural
manifestation of the jet photospheric emission.Comment: 7 pages of article (3 figures and 1 table) + 3 pages of Appendix (3
figures). Submitted to ApJ on 2017 March 2
Tensile and Shear Experiments using Polypropylene/Polyethylene Foils at different Temperatures
An experimental campaign on a thermo-plastic copolymer of polypropylene/polyethylene (PP/PE) serves to investigate the rate- and temperature-dependence of the material. Isothermal tensile and shear experiments for four different constant displacement-rates and temperatures (−10 ◦C - 120 ◦C) are conducted, monitored by means of a Digital Image Correlation (DIC) system. The tensile experiments are carried out within the large deformation range, where localization phenomena are observed. This requires the application of a full-field deformation analysis system to develop stress-stretch (strain) diagrams, which are necessary with regard to aspects of constitutive modeling. In addition to these experiments, a modified three-rail shear tool was designed in order to investigate the shear behavior of PP/PE. Apart from the rate-dependence, the relaxation behavior is investigated for both tensile and shear load conditions by means of multi-step relaxation tests at different temperatures in order to obtain indications about the equilibrium stress state of the material
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