7,537 research outputs found
Analysing powers for the reaction and for np elastic scattering from 270 to 570 MeV
The analysing power of the reaction for neutron energies between threshold and 570 MeV has been determined
using a transversely polarised neutron beam at PSI. The reaction has been
studied in a kinematically complete measurement using a time-of-flight
spectrometer with large acceptance. Analysing powers have been determined as a
function of the c.m. pion angle in different regions of the proton-proton
invariant mass. They are compared to other data from the reactions and . The np elastic scattering analysing power was determined as a
by-product of the measurements.Comment: 12 pages, 6 figures, subitted to EPJ-
The reaction from threshold up to 570 MeV
The reaction has been studied in a
kinematically complete measurement with a large acceptance time-of-flight
spectrometer for incident neutron energies between threshold and 570 MeV. The
proton-proton invariant mass distributions show a strong enhancement due to the
pp() final state interaction. A large anisotropy was found in the
pion angular distributions in contrast to the reaction . At small energies, a large forward/backward asymmetry has been
observed. From the measured integrated cross section , the isoscalar cross section has been extracted.
Its energy dependence indicates that mainly partial waves with Sp final states
contribute. Note: Due to a coding error, the differential cross sections as shown in Fig. 9 are too small by a factor of two, and
inn Table 3 the differential cross sections
are too large by a factor of . The integrated cross sections and all
conclusions remain unchanged. A corresponding erratum has been submitted and
accepted by European Physics Journal.Comment: 18 pages, 16 figure
Polarised target for Drell-Yan experiment in COMPASS at CERN, part I
In the polarised Drell-Yan experiment at the COMPASS facility in CERN pion
beam with momentum of 190 GeV/c and intensity about pions/s interacted
with transversely polarised NH target. Muon pairs produced in Drel-Yan
process were detected. The measurement was done in 2015 as the 1st ever
polarised Drell-Yan fixed target experiment. The hydrogen nuclei in the
solid-state NH were polarised by dynamic nuclear polarisation in 2.5 T
field of large-acceptance superconducting magnet. Large helium dilution
cryostat was used to cool the target down below 100 mK. Polarisation of
hydrogen nuclei reached during the data taking was about 80 %. Two oppositely
polarised target cells, each 55 cm long and 4 cm in diameter were used.
Overview of COMPASS facility and the polarised target with emphasis on the
dilution cryostat and magnet is given. Results of the polarisation measurement
in the Drell-Yan run and overviews of the target material, cell and dynamic
nuclear polarisation system are given in the part II.Comment: 4 pages, 2 figures, Proceedings of the 22nd International Spin
Symposium, Urbana-Champaign, Illinois, USA, 25-30 September 201
Hard X-ray variability of the black-hole candidate GRO J0422+32 during its 1992 outburst
We have studied the hard X-ray variability of the soft X-ray transient GRO
J0422+32 with BATSE in the 20-100 keV energy band. Our analysis covers 180 days
following the first X-ray detection of the source on 1992 August 5, fully
covering its primary and secondary X-ray outburst. We computed power density
spectra (PDSs) in the 20-50, 50-100, and 20-100 keV energy bands, in the
frequency interval 0.002-0.488 Hz. The PDSs of GRO J0422+32 are approximately
flat up to a break frequency, and decay as a power law above, with index ~1.
The canonical anticorrelation between the break frequency and the power density
at the break, observed in Cyg X-1 and other BHCs in the low state, is not
observed in the PDSs of GRO J0422+32. We compare our results with those of
similar variability studies of Cyg X-1. The relation between the spectral slope
and the amplitude of the X-ray variations of GRO J0422+32 is similar to that of
Cyg X-1; however, the relation between the hard X-ray flux and the amplitude of
its variation is opposite to what has been found in Cyg X-1. Phase lags between
the X-ray flux variations of GRO J0422+32 at high and low photon energies,
could only be derived during the first 30 days of its outburst. During this
period, the variations in the 50-100 keV lag those in the 20-50 keV energy band
by an approximately constant phase difference of 0.039(3) rad in the frequency
interval 0.02-0.20 Hz.Comment: 33 pages, including 14 postscript figures, AASTEX. To appear in ApJ
1999, March 1, vol. 513 #
Algorithmic Interpretations of Fractal Dimension
We study algorithmic problems on subsets of Euclidean space of low fractal dimension. These spaces are the subject of intensive study in various branches of mathematics, including geometry, topology, and measure theory. There are several well-studied notions of fractal dimension for sets and measures in Euclidean space. We consider a definition of fractal dimension for finite metric spaces which agrees with standard notions used to empirically estimate the fractal dimension of various sets. We define the fractal dimension of some metric space to be the infimum delta>0, such that for any eps>0, for any ball B of radius r >= 2eps, and for any eps-net N, we have |B cap N|=O((r/eps)^delta).
Using this definition we obtain faster algorithms for a plethora of classical problems on sets of low fractal dimension in Euclidean space. Our results apply to exact and fixed-parameter algorithms, approximation schemes, and spanner constructions. Interestingly, the dependence of the performance of these algorithms on the fractal dimension nearly matches the currently best-known dependence on the standard Euclidean dimension. Thus, when the fractal dimension is strictly smaller than the ambient dimension, our results yield improved solutions in all of these settings.
We remark that our definition of fractal definition is equivalent up to constant factors to the well-studied notion of doubling dimension.
However, in the problems that we consider, the dimension appears in the exponent of the running time, and doubling dimension is not precise enough for capturing the best possible such exponent for subsets of Euclidean space. Thus our work is orthogonal to previous results on spaces of low doubling dimension; while algorithms on spaces of low doubling dimension seek to extend results from the case of low dimensional Euclidean spaces to more general metric spaces, our goal is to obtain faster algorithms for special pointsets in Euclidean space
Resistivity study of the pseudogap phase for (Hg,Re) - 1223 superconductors
The pseudogap phase above the critical temperature of high
superconductors (HTSC) presents different energy scales and it is currently a
matter of intense study. The complexity of the HTSC normal state requires very
accurate measurements with the purpose of distinguishing different types of
phenomena. Here we have performed systematically studies through electrical
resistivity () measurements by several different current densities in
order to obtain an optimal current for each sample. This approach allows to
determine reliable values of the pseudogap temperature , the layer
coupling temperature between the superconductor layers , the
fluctuation temperature and the critical temperature as
function of the doping . The interpretation of these different temperature
scales allows to characterize possible scenarios for the (Hg,Re) - 1223 normal
state. This method, described in detail here, and used to derive the
(Hg,Re)-1223 phase diagram is general and can be applied to any HTSC.Comment: 31 pages, 12 figures, Latex; 25 pages, LaTeX; 11 figures; rewrited
section II and III; added 18 reference; rewrited title, added discussion
sectio
Flexible n-i-p thin film silicon solar cells on polyimide foils with textured ZnO:Ga back reflector
In thin film silicon solar cells on opaque substrates in n-i-p deposition sequence where the textured transparent conductive oxide (TCO) layer serves as a back reflector, one can independently optimize the morphology of the TCO layer without compromise on transparency and conductivity of this layer and further adjust the electro-optical properties of the back contact by using additional layers on top of the textured TCO. In the present work, we use this strategy to obtain textured back reflectors for solar cells in n-i-p deposition sequence on non-transparent flexible plastic foils. Gallium doped ZnO (ZnO:Ga) films were deposited on polyimide substrates by DC magnetron sputtering at a temperature of 200 °C. A wet-chemical etching step was performed by dipping the ZnO:Ga covered foil into a diluted HCl solution. The textured ZnO:Ga is then coated with a highly reflective Ag/ZnO double layer. On this back reflector, we develop thin film silicon solar cells with a microcrystalline silicon absorber layer. The current density for the cell with the textured ZnO:Ga layer is ~ 23 mA/cm2, 4 mA/cm2 higher than the one without such layer, and a maximum efficiency of 7.5% is obtained for a 1 cm2 cell.Fundação para a Ciência e a Tecnologia (FCT
John Schuster, Descartes-agonistes: Physico-mathematics, method and corpuscular-mechanism, 1618–1633
We report on a 10 ks simultaneous Chandra/HETG-NuSTAR observation of the
Bursting Pulsar, GRO J1744-28, during its third detected outburst since
discovery and after nearly 18 years of quiescence. The source is detected up to
60 keV with an Eddington persistent flux level. Seven bursts, followed by dips,
are seen with Chandra, three of which are also detected with NuSTAR. Timing
analysis reveals a slight increase in the persistent emission pulsed fraction
with energy (from 10% to 15%) up to 10 keV, above which it remains constant.
The 0.5-70 keV spectra of the persistent and dip emission are the same within
errors, and well described by a blackbody (BB), a power-law with an exponential
rolloff, a 10 keV feature, and a 6.7 keV emission feature, all modified by
neutral absorption. Assuming that the BB emission originates in an accretion
disc, we estimate its inner (magnetospheric) radius to be about 4x10^7 cm,
which translates to a surface dipole field B~9x10^10 G. The Chandra/HETG
spectrum resolves the 6.7 keV feature into (quasi-)neutral and highly ionized
Fe XXV and Fe XXVI emission lines. XSTAR modeling shows these lines to also
emanate from a truncated accretion disk. The burst spectra, with a peak flux
more than an order of magnitude higher than Eddington, are well fit with a
power-law with an exponential rolloff and a 10~keV feature, with similar fit
values compared to the persistent and dip spectra. The burst spectra lack a
thermal component and any Fe features. Anisotropic (beamed) burst emission
would explain both the lack of the BB and any Fe components.Comment: 15 pages, 11 figures, Accepted in Ap
Magnetic Field-Induced Condensation of Triplons in Han Purple Pigment BaCuSiO
Besides being an ancient pigment, BaCuSiO is a quasi-2D magnetic
insulator with a gapped spin dimer ground state. The application of strong
magnetic fields closes this gap creating a gas of bosonic spin triplet
excitations called triplons. The topology of the spin lattice makes
BaCuSiO an ideal candidate for studying the Bose-Einstein condensation
of triplons as a function of the external magnetic field, which acts as a
chemical potential. In agreement with quantum Monte Carlo numerical
simulations, we observe a distinct lambda-anomaly in the specific heat together
with a maximum in the magnetic susceptibility upon cooling down to liquid
Helium temperatures.Comment: published on August 20, 200
Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6
Results of high resolution x-ray diffraction experiments are presented for
single crystals of the spin gap compound BaCuSiO in the temperature
range from 16 to 300 K. The data show clear evidence of a transition from the
room temperature tetragonal phase into an incommensurately modulated
orthorhombic structure below 100 K. This lattice modulation is
characterized by a resolution limited wave vector {\bf
q}=(0,0.13,0) and its 2 and 3 harmonics. The phase
transition is first order and exhibits considerable hysteresis. This
observation implies that the spin Hamiltonian representing the system is more
complex than originally thought.Comment: 4 pages, 4 figure
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