29,159 research outputs found
Judicially Compelled Disclosure of Researchers’ Data: A Judge’s View
Crabb looks at the approach one court has established to balance the demands of the legal system with the legitimate concerns of researchers
Women, migrant labor, and social change in Botswana
African Studies Center Working Paper No. 4
Probing spin dynamics and quantum relaxation in LiY0.998Ho0.002F4 via 19F NMR
We report measurements of 19F nuclear spin-lattice relaxation 1/T1 as a
function of temperature and external magnetic field in LiY0.998Ho0.002F4 single
crystal, a single-ion magnet exhibiting interesting quantum effects. The 19F
1/T1 is found to depend on the coupling with the diluted rare-earth (RE)
moments. Depending on the temperature range, a fast spin diffusion regime or a
diffusion limited regime is encountered. In both cases we find it possible to
use the 19F nucleus as a probe of the rare-earth spin dynamics. The results for
1/T1 show a behavior similar to that observed in molecular nanomagnets, a
result which we attribute to the discreteness of the energy levels in both
cases. At intermediate temperatures the lifetime broadening of the crystal
field split RE magnetic levels follows a T3 power law. At low temperature the
field dependence of 1/T1 shows peaks in correspondence to the critical magnetic
fields for energy level crossings (LC). The results can be explained by
inelastic scattering between the fluorine nuclear spins and the RE magnetic
levels. A key result of this study is that the broadening of the levels at LC
is found to be become extremely small at low temperatures, about 1.7 mT, a
value which is comparable to the weak dipolar fields at the RE lattice
positions. Thus, unlike the molecular magnets, decoherence effects are strongly
suppressed, and it may be possible to measure directly the level repulsions at
avoided level crossings.Comment: 21 pages, 5 figure
Critical Boolean networks with scale-free in-degree distribution
We investigate analytically and numerically the dynamical properties of
critical Boolean networks with power-law in-degree distributions. When the
exponent of the in-degree distribution is larger than 3, we obtain results
equivalent to those obtained for networks with fixed in-degree, e.g., the
number of the non-frozen nodes scales as with the system size .
When the exponent of the distribution is between 2 and 3, the number of the
non-frozen nodes increases as , with being between 0 and 2/3 and
depending on the exponent and on the cutoff of the in-degree distribution.
These and ensuing results explain various findings obtained earlier by computer
simulations.Comment: 5 pages, 1 graph, 1 sketch, submitte
Sensory Changes in Adults with Unilateral Transtibial Amputation
The purpose of this study was to describe the sensory changes in adults with unilateral transtibial amputation
(TTA), as any loss of sensation may have significant impact on the successful use of a prosthesis. Sensory modalities of light touch, deep pressure, vibration, and superficial pain (pinprick) were examined on the residual and contralateral limbs of 16 veterans with TTA. Six subjects demonstrated normal sensation on the contralateral limb and impaired sensation of superficial pain, vibration, and/or light touch on the residual limb. Superficial pain was the most frequently impaired sensation, and vibration and superficial pain sensation appeared to be age-dependent, with increased impairment observed in the elderly. Deep pressure sensation was intact in all subjects. These preliminary data suggest that although neither the amputation nor the prosthetic rehabilitation resulted in impaired deep pressure sensation, these two factors contributed to minimal impairment of light touch and vibration, and significant impairment of the superficial pain sensation
Resonant photon absorption in the low spin molecule V15
We report the first study of the micro-SQUID response of a molecular system
to electromagnetic radiation. The advantages of our micro-SQUID technique in
respect to pulsed electron paramagnetic resonance (EPR) techniques consist in
the possibility to perform time-resolved experiments (below 1 ns) on
submicrometer sizes samples (about 1000 spins) at low temperature (below 100
mK).
Resonant photon absorption in the GHz range was observed via low temperature
micro-SQUID magnetization measurements of the spin ground state S = 1/2 of the
molecular complex V15. The line-width essentially results from intra-molecular
hyperfine interaction. The results point out that observing Rabi oscillations
in molecular nanomagnets requires well isolated low spin systems and high
radiation power. Our first results open the way for time-resolved observations
of quantum superposition of spin-up and spin-down states in SMMs.Comment: 7 pages, 5 figure
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