Women, migrant labor, and social change in Botswana

African Studies Center Working Paper No. 4

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

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

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

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

Contralateral inhibition of click- and chirp-evoked human compound action potentials

Cochlear outer hair cells (OHC) receive direct efferent feedback from the caudal auditory brainstem via the medial olivocochlear (MOC) bundle. This circuit provides the neural substrate for the MOC reflex, which inhibits cochlear amplifier gain and is believed to play a role in listening in noise and protection from acoustic overexposure. The human MOC reflex has been studied extensively using otoacoustic emissions (OAE) paradigms; however, these measurements are insensitive to subsequent “downstream” efferent effects on the neural ensembles that mediate hearing. In this experiment, click- and chirp-evoked auditory nerve compound action potential (CAP) amplitudes were measured electrocochleographically from the human eardrum without and with MOC reflex activation elicited by contralateral broadband noise. We hypothesized that the chirp would be a more optimal stimulus for measuring neural MOC effects because it synchronizes excitation along the entire length of the basilar membrane and thus evokes a more robust CAP than a click at low to moderate stimulus levels. Chirps produced larger CAPs than clicks at all stimulus intensities (50–80 dB ppeSPL). MOC reflex inhibition of CAPs was larger for chirps than clicks at low stimulus levels when quantified both in terms of amplitude reduction and effective attenuation. Effective attenuation was larger for chirp- and click-evoked CAPs than for click-evoked OAEs measured from the same subjects. Our results suggest that the chirp is an optimal stimulus for evoking CAPs at low stimulus intensities and for assessing MOC reflex effects on the auditory nerve. Further, our work supports previous findings that MOC reflex effects at the level of the auditory nerve are underestimated by measures of OAE inhibition

First-principles Calculations of Engineered Surface Spin Structures

The engineered spin structures recently built and measured in scanning tunneling microscope experiments are calculated using density functional theory. By determining the precise local structure around the surface impurities, we find the Mn atoms can form molecular structures with the binding surface, behaving like surface molecular magnets. The spin structures are confirmed to be antiferromagnetic, and the exchange couplings are calculated within 8% of the experimental values simply by collinear-spin GGA+U calculations. We can also explain why the exchange couplings significantly change with different impurity binding sites from the determined local structure. The bond polarity is studied by calculating the atomic charges with and without the Mn adatoms