4,991 research outputs found
Optical Properties of the DIRC Fused Silica Cherenkov Radiator
The DIRC is a new type of Cherenkov detector that is successfully operating
as the hadronic particle identification system for the BABAR experiment at
SLAC. The fused silica bars that serve as the DIRC's Cherenkov radiators must
transmit the light over long optical pathlengths with a large number of
internal reflections. This imposes a number of stringent and novel requirements
on the bar properties. This note summarizes a large amount of R&D that was
performed both to develop specifications and production methods and to
determine whether commercially produced bars could meet the requirements. One
of the major outcomes of this R&D work is an understanding of methods to select
radiation hard and optically uniform fused silica material. Others include
measurement of the wavelength dependency of the internal reflection
coefficient, and its sensitivity to surface contaminants, development of
radiator support methods, and selection of good optical glue.Comment: 36 pages, submitted to Nuclear Instruments and Methods
Diffusion versus linear ballistic accumulation: different models but the same conclusions about psychological processes?
Quantitative models for response time and accuracy are increasingly used as tools to draw conclusions about psychological processes. Here we investigate the extent to which these substantive conclusions depend on whether researchers use the Ratcliff diffusion model or the Linear Ballistic Accumulator model. Simulations show that the models agree on the effects of changes in the rate of information accumulation and changes in non-decision time, but that they disagree on the effects of changes in response caution. In fits to empirical data, however, the models tend to agree closely on the effects of an experimental manipulation of response caution. We discuss the implications of these conflicting results, concluding that real manipulations of caution map closely, but not perfectly to response caution in either model. Importantly, we conclude that inferences about psychological processes made from real data are unlikely to depend on the model that is used
Temperature-dependent properties of the magnetic order in single-crystal BiFeO3
We report neutron diffraction and magnetization studies of the magnetic order
in multiferroic BiFeO3. In ferroelectric monodomain single crystals, there are
three magnetic cycloidal domains with propagation vectors equivalent by
crystallographic symmetry. The cycloid period slowly grows with increasing
temperature. The magnetic domain populations do not change with temperature
except in the close vicinity of the N{\P}eel temperature, at which, in
addition, a small jump in magneti- zation is observed. No evidence for the
spin-reorientation transitions proposed in previous Raman and dielectric
studies is found. The magnetic cycloid is slightly anharmonic for T=5 K. The
an- harmonicity is much smaller than previously reported in NMR studies. At
room temperature, a circular cycloid is observed, within errors. We argue that
the observed anharmonicity provides important clues for understanding
electromagnons in BiFeO3.Comment: In Press at PR
Freezing Injury of Seed Corn
The object of the investigations in this bulletin has been to determine the conditions under which freezing injury may occur to seed corn; to indicate, if possible, the vital changes in the embryo resulting in such injury; and to point out ways by which seed corn of strong vitality and satisfactory yielding capacity may be obtained
Spin and Lattice Structure of Single Crystal SrFe2As2
We use neutron scattering to study the spin and lattice structure on single
crystals of SrFe2As2, the parent compound of the FeAs based superconductor
(Sr,K)Fe2As2. We find that SrFe2As2 exhibits an abrupt structural phase
transitions at 220K, where the structure changes from tetragonal with lattice
parameters c > a = b to orthorhombic with c > a > b. At almost the same
temperature, Fe spins in SrFe2As2 develop a collinear antiferromagnetic
structure along the orthorhombic a-axis with spin direction parallel to this
a-axis. These results are consistent with earlier work on the RFeAsO (R = rare
earth elements) families of materials and on BaFe2As2, and therefore suggest
that static antiferromagnetic order is ubiquitous for the parent compound of
these FeAs-based high-transition temperature superconductors.Comment: 14 pages with 4 figure
Combinations of Earth Orientation Measurements: SPACE2011, COMB2011, and POLE2011
Independent Earth orientation measurements taken by the space-geodetic techniques of lunar and satellite laser ranging, very long baseline interferometry, and the Global Positioning System have been combined using a Kalman filter. The resulting combined Earth orientation series, SPACE2011, consists of values and uncertainties for Universal Time, polar motion, and their rates that span from September 28, 1976, to July 13, 2012, at daily intervals and is available in versions with epochs given at either midnight or noon. The space-geodetic measurements used to generate SPACE2011 have then been combined with optical astrometric measurements to form two additional combined Earth orientation series: (1) COMB2011, consisting of values and uncertainties for Universal Time, polar motion, and their rates that span from January 20, 1962, to July 13, 2012, at daily intervals and which are also available in versions with epochs given at either midnight or noon; and (2) POLE2011, consisting of values and uncertainties for polar motion and its rate that span from January 20, 1900, to June 21, 2012, at 30.4375-day intervals
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