782 research outputs found
Spin Echo Decay in a Stochastic Field Environment
We derive a general formalism with which it is possible to obtain the time
dependence of the echo size for a spin in a stochastic field environment. Our
model is based on ``strong collisions''. We examine in detail three cases
where: (I) the local field is Ising-like, (II) the field distribution is
continuous and has a finite second moment, and (III) the distribution is
Lorentzian. The first two cases show a T2 minimum effect and are exponential in
time cubed for short times. The last case can be approximated by a
phenomenological stretched exponential.Comment: 11 pages + 3 postscript figure
Procedures for the salvage and necropsy of the dugong (dugong dugon)
This manual provides a detailed guide for dugong (Dugong dugon) carcass handling and
necropsy procedures. It is intended to be used as a resource and training guide for anyone
involved in dugong incidents, including management officers, biologists, parks and wildlife
field staff, and veterinarians and pathologists who may lack dugong expertise. Because of the
wide range of professionals this book is targeting, information and the use of technical terms is
necessarily extensive. Section 8 provides definitions of various terms used and italicised
throughout the text
Nuclear spin-spin coupling in La_{2-x}Sr_{x}CuO_{4} studied by stimulated echo decay
We have performed copper NQR experiments in high temperature superconductors
YBa_{2}Cu_{4}O_{8}, YBa_{2}Cu_{3}O_{7}, and La_{2-x}Sr_{x}CuO_{4} (x=0.12 and
0.15), using the stimulated echo technique. The stimulated echo intensity is
analyzed by a model that includes the spin-lattice relaxation process (T_ {1
}-process) and the fluctuating local field due to nuclear spin-spin coupling.
The model gives quantitative account of the experimental results in Y-based
compounds using the known values of 1/T_{1} and 1/T_{2G}, the gaussian decay
rate of the spin echo intensity. The same model applied to LSCO enables us to
extract the value of T_{2G}. Our results indicate that T_{1}T/T_{2G} is
independent of temperature, implying that the dynamic exponent is one in
La_{2-x}Sr_{x}CuO_{4}.Comment: 14 pages, 11 fugures, The bibliography field is correcte
Procedures for the salvage and necropsy of the Dugong (Dugong Dugon)-second edition 2007
This manual provides a detailed guide for dugong (Dugong dugon) carcass handling and
necropsy procedures. It is intended to be used as a resource and training guide for anyone
involved in dugong incidents including management officers, biologists, parks and wildlife field
staff, and veterinarians and pathologists who may lack dugong expertise. Because of the wide
range of professionals this book is targeting, information and the use of technical terms is
extensive. Section 8.0 provides definitions of various terms used which are italicised throughout
the text
Spectroscopy of P using the one-proton knockout reaction
The structure of P was studied with a one-proton knockout reaction
at88~MeV/u from a S projectile beam at NSCL. The rays from
thedepopulation of excited states in P were detected with GRETINA,
whilethe P nuclei were identified event-by-event in the focal plane of
theS800 spectrograph. The level scheme of P was deduced up to 7.5 MeV
using coincidences. The observed levels were attributed to
protonremovals from the -shell and also from the deeply-bound
orbital.The orbital angular momentum of each state was derived from the
comparisonbetween experimental and calculated shapes of individual
(-gated)parallel momentum distributions. Despite the use of different
reactions andtheir associate models, spectroscopic factors, , derived
from theS knockout reaction agree with those obtained earlier
fromS(,\nuc{3}{He}) transfer, if a reduction factor , as
deducedfrom inclusive one-nucleon removal cross sections, is applied to the
knockout transitions.In addition to the expected proton-hole configurations,
other states were observedwith individual cross sections of the order of
0.5~mb. Based on their shiftedparallel momentum distributions, their decay
modes to negative parity states,their high excitation energy (around 4.7~MeV)
and the fact that they were notobserved in the (,\nuc{3}{He}) reaction, we
propose that they may resultfrom a two-step mechanism or a nucleon-exchange
reaction with subsequent neutronevaporation. Regardless of the mechanism, that
could not yet be clarified, thesestates likely correspond to neutron core
excitations in \nuc{35}{P}. Thisnewly-identified pathway, although weak, offers
the possibility to selectivelypopulate certain intruder configurations that are
otherwise hard to produceand identify.Comment: 5 figures, 1 table, accepted for publication in Physical Review
Magnetic field independence of the spin gap in YBa_2Cu_3O_{7-delta}
We report, for magnetic fields of 0, 8.8, and 14.8 Tesla, measurements of the
temperature dependent ^{63}Cu NMR spin lattice relaxation rate for near
optimally doped YBa_2Cu_3O_{7-delta}, near and above T_c. In sharp contrast
with previous work we find no magnetic field dependence. We discuss
experimental issues arising in measurements of this required precision, and
implications of the experiment regarding issues including the spin or pseudo
gap.Comment: 4 pages, 3 figures, as accepted for publication in Physical Review
Letter
Triplet energy differences and the low lying structure of Ga 62
Background: Triplet energy differences (TED) can be studied to yield information on isospin-non-conserving interactions in nuclei.
Purpose: The systematic behavior of triplet energy differences (TED) of T=1, J\u3c0=2+ states is examined. The A=62 isobar is identified as having a TED value that deviates significantly from an otherwise very consistent trend. This deviation can be attributed to the tentative assignments of the pertinent states in Ga62 and Ge62.
Methods: An in-beam \u3b3-ray spectroscopy experiment was performed to identify excited states in Ga62 using Gamma-Ray Energy Tracking In-Beam Nuclear Array with the S800 spectrometer at NSCL using a two-nucleon knockout approach. Cross-section calculations for the knockout process and shell-model calculations have been performed to interpret the population and decay properties observed.
Results: Using the systematics as a guide, a candidate for the transition from the T=1, 2+ state is identified. However, previous work has identified similar states with different J\u3c0 assignments. Cross-section calculations indicate that the relevant T=1, 2+ state should be one of the states directly populated in this reaction.
Conclusions: As spins and parities were not measurable, it is concluded that an unambiguous identification of the first T=1, 2+ state is required to reconcile our understanding of TED systematics
First-Order Melting and Dynamics of Flux Lines in a Model for YBaCuO
We have studied the statics and dynamics of flux lines in a model for YBCO,
using both Monte Carlo simulations and Langevin dynamics. For a clean system,
both approaches yield the same melting curve, which is found to be weakly first
order with a heat of fusion of about per vortex pancake at a
field of The time averaged magnetic field distribution
experienced by a fixed spin is found to undergo a qualitative change at
freezing, in agreement with NMR and experiments. Melting in the
clean system is accompanied by a proliferation of free disclinations which show
a clear B-dependent 3D-2D crossover from long disclination lines parallel to
the c-axis at low fields, to 2D ``pancake'' disclinations at higher fields.
Strong point pins produce a logarithmical relaxation which results from
slow annealing out of disclinations in disordered samples.Comment: 31 pages, latex, revtex, 12 figures available upon request, No major
changes to the original text, but some errors in the axes scale for Figures 6
and 7 were corrected(new figures available upon request), to be published in
Physical Review B, July 199
Low-lying level structure of Cu and its implications on the rp process
The low-lying energy levels of proton-rich Cu have been extracted
using in-beam -ray spectroscopy with the state-of-the-art -ray
tracking array GRETINA in conjunction with the S800 spectrograph at the
National Superconducting Cyclotron Laboratory at Michigan State University.
Excited states in Cu serve as resonances in the
Ni(p,)Cu reaction, which is a part of the rp-process in
type I x-ray bursts. To resolve existing ambiguities in the reaction Q-value, a
more localized IMME mass fit is used resulting in ~keV. We derive
the first experimentally-constrained thermonuclear reaction rate for
Ni(p,)Cu. We find that, with this new rate, the
rp-process may bypass the Ni waiting point via the Ni(p,)
reaction for typical x-ray burst conditions with a branching of up to
40. We also identify additional nuclear physics uncertainties that
need to be addressed before drawing final conclusions about the rp-process
reaction flow in the Ni region.Comment: 8 pages, accepted for Phys. Rev.
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