1,891 research outputs found
Investigation of Gravitational Lens Mass Models
We have previously reported the discovery of strong gravitational lensing by
faint elliptical galaxies using the WFPC2 on HST and here we investigate their
potential usefulness in putting constraints on lens mass models. We compare
various ellipsoidal surface mass distributions, including those with and
without a core radius, as well as models in which the mass distributions are
assumed to have the same axis ratio and orientation as the galaxy light. We
also study models which use a spherical mass distribution having various
profiles, both empirical and following those predicted by CDM simulations.
These models also include a gravitational shear term. The model parameters and
associated errors have been derived by 2-dimensional analysis of the observed
HST WFPC2 images. The maximum likelihood procedure iteratively converges
simultaneously on the model for the lensing elliptical galaxy and the lensed
image components. The motivation for this study was to distinguish between
these mass models with this technique. However, we find that, despite using the
full image data rather than just locations and integrated magnitudes, the
lenses are fit equally well with several of the mass models. Each of the mass
models generates a similar configuration but with a different magnification and
cross-sectional area within the caustic, and both of these latter quantities
govern the discovery probability of lensing in the survey. These differences
contribute to considerable cosmic scatter in any estimate of the cosmological
constant using gravitational lenses.Comment: 10 pages with 6 embedded figures, tentatively scheduled to be
published in the July 2001 issue of The Astronomical Journal. For additional
information see http://mds.phys.cmu.edu/lense
Differential cross sections for pion charge exchange on the proton at 27.5 MeV
We have measured pion single charge exchange differential cross sections on
the proton at 27.5 MeV incident kinetic energy in the center of
momentum angular range between and . The extracted cross
sections are compared with predictions of the standard pion-nucleon partial
wave analysis and found to be in excellent agreement.Comment: ReVTeX v3.0 with aps.sty, 23 pages in e-print format, 7 PostScript
Figures and 4 Tables, also available via anonymous ftp at
ftp://helena.phys.virginia.edu/pub/preprints/scx.p
Parity Violation in Neutron Resonances in 107,109Ag
Parity nonconservation (PNC) was studied in p-wave resonances in Ag by measuring the helicity dependence of the neutron total cross section. Transmission measurements on natural Ag were performed in the energy range 32 to 422 eV with the time-of-flight method at the Manuel Lujan Neutron Scattering Center at Los Alamos National Laboratory. A total of 15 p-wave neutron resonances were studied in 107Ag and ninep-wave resonances in 109Ag. Statistically significant asymmetries were observed for eight resonances in 107Ag and for four resonances in109Ag. An analysis treating the PNC matrix elements as random variables yields a weak spreading width of Îw=(2.67-1.21+2.65)Ă10-7âeV for107Ag and Îw=(1.30-0.74+2.49)Ă10-7âeV for 109Ag
Parity Violation in Neutron Resonances in 115In
Parity nonconservation (PNC) was studied in p-wave resonances in indium by measuring the helicity dependence of the neutron total cross section in the neutron energy range 6.0â316 eV with the time-of-flight method at LANSCE. A total of 36 p-wave neutron resonances were studied in 115In, and statistically significant asymmetries were observed for nine cases. An analysis treating the PNC matrix elements as random variables yields a weak matrix element of M=(0.67-0.12+0.16)âmeV and a weak spreading width of Îw=(1.30-0.43+0.76)Ă10-7âeV
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[Arctic] Greenland ice sheet [in âState of the Climate in 2012â]
Melting at the surface of the Greenland Ice Sheet set new records for extent and melt index (i.e., the number of days on which melting occurred multiplied by the area where melting was detected) for the period 1979â2012, according to passive microwave observations (e.g., Tedesco 2007, 2009; Mote and Anderson 1995). Melt extent reached ~97% of the ice sheet surface during a rare, ice-sheet-wide event on 11â12 July (Fig. 5.13a; Nghiem et al. 2012). This was almost four times greater than the average melt extent for 1981â2010. The 2012 standardized melting index (SMI, defined as the melting index minus its average and divided by its standard deviation) was +2.4, almost twice the previous record of about +1.3 set in 2010
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Equation of State Measurements in Liquid Deuterium to 70 Gpa
Using intense magnetic pressure, a method was developed to launch flyer plates to velocities in excess of 20 km/s. This technique was used to perform plate-impact, shock wave experiments on cryogenic liquid deuterium (LD{sub 2}) to examine its high-pressure equation of state (EOS). Using an impedance matching method, Hugoniot measurements were obtained in the pressure range of 30-70 GPa. The results of these experiments disagree with previously reported Hugoniot measurements of LD{sub 2} in the pressure range above {approx}40 GPa, but are in good agreement with first principles, ab-initio models for hydrogen and its isotopes
Para-adventure: A hyper-dynamic problem for the inclusive coach
Recent research has recognized sports coaching as complex, chaotic, and cognitively taxing for coaches. Against this backdrop, the present paper explores challenges faced by high-level coaches working with disabled performers. Specifically, it seeks to understand how coaches create mental models of performance in adventure sports and para-canoe. Five coaches were purposively sampled and underwent a semi-structured interview. A thematic analysis revealed conceptualizing the mental model as being mechanically-related for all and as including a social construction within the para-canoe coaches. Reflection on the coaching process and on personal characteristics were perceived as important to individualized inclusive coaching. Coach training should particularly emphasize the need for critical judgment and decision making skills within a similarly oriented social structure of coaches and support staff where applicable
NH4-Smectite, a Potential Source of N Compounds (NO) in SAM Analyses
Recent detection of nitrate by Curiosity's Sample Analysis at Mars (SAM) instrument suite in Gale Crater sediments on Mars at abundances up to ~600 mg/kg indicates that nitrogen fixation processes occurred in early Martian history. But little is known about other possible N reservoirs on Mars, including those that may contain reduced forms of fixed N (i.e., NH3, NH4+) in the mantle, crust and sediments. Specifically, fixed nitrogen (i.e. NH3, NH4+, NOx or N that is chemically bound to either inorganic or organic molecules and can be released by hydrolysis to form NH3 or NH4+) is useful to terrestrial living organisms Therefore, understanding whether reduced N compounds such as NH4+ are present in surface materials is important to assess habitability in the Martian environment. While these species generally have short photochemical lifetimes, nitrogen in this form may be sequestered and stabilized in the soil by inclusion of NH4+ in certain phyllosilicates
Strangeness enhancements at central rapidity in 40 A GeV/c Pb-Pb collisions
Results are presented on neutral kaon, hyperon and antihyperon production in
Pb-Pb and p-Be interactions at 40 GeV/c per nucleon. The enhancement pattern
follows the same hierarchy as seen in the higher energy data - the enhancement
increases with the strangeness content of the hyperons and with the centrality
of collision. The centrality dependence of the Pb-Pb yields and enhancements is
steeper at 40 than at 158 A GeV/c. The energy dependence of strangeness
enhancements at mid-rapidity is discussed.Comment: 15 pages, 10 figures and 3 tables. Presented at International
Conference on Strangeness in Quark Matter (SQM2009), Buzios, Rio de Janeiro,
Brazil, 27 Sept - 2 Oct 2009. Submitted to J.Phys.G: Nucl.Part.Phys, one
reference adde
Centrality dependence of the expansion dynamics in Pb-Pb collisions at 158 A GeV/c
Two-particle correlation functions of negatively charged hadrons from Pb-Pb
collisions at 158 GeV/c per nucleon have been measured by the WA97 experiment
at the CERN SPS. A Coulomb correction procedure that assumes an expanding
source has been implemented. Within the framework of an expanding thermalized
source model the size and dynamical state of the collision fireball at
freeze-out have been reconstructed as a function of the centrality of the
collision. Less central collisions exhibit a different dynamics than central
ones: both transverse and longitudinal expansion velocities are slower, the
expansion duration is shorter and the system freezes out showing smaller
dimensions and higher temperature.Comment: 22 pages, 11 figures, Te
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