Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field.

Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots. The strong interaction of a single, optically injected electron spin with the nuclear spins acts as a stabilizing, effective magnetic field (Knight field) on the nuclei. We optically tune the Knight field amplitude and direction. In combination with a small transverse magnetic field, we are able to control the longitudinal and transverse components of the nuclear spin polarization in the absence of lattice strain--that is, in dots with strongly reduced static nuclear quadrupole effects, as reproduced by our model calculations.

Effect of Pauli blockade on spin-dependent diffusion in a degenerate electron gas.

Spin-polarized transport of photoelectrons in bulk, p-type GaAs is investigated in the Pauli blockade regime. In contrast to usual spin diffusion processes in which the spin polarization decreases with distance traveled due to spin relaxation, images of the polarized photoluminescence reveal a spin-filter effect in which the spin polarization increases during transport over the first 2 µm from 26% to 38%. This is shown to be a direct consequence of the Pauli principle and the associated quantum degeneracy pressure which results in a spin-dependent increase in the minority carrier diffusion constants and mobilities. The central role played by the quantum degeneracy pressure is confirmed via the observation of a spin-dependent increase in the photoelectron volume and a spin-charge coupling description of this is presented.

Circularly polarized luminescence microscopy for the imaging of charge and spin diffusion in semiconductors.

Room temperature electronic diffusion is studied in 3 µm thick epitaxial p(+) GaAs lift-off films using a novel circularly polarized photoluminescence microscope. The method is equivalent to using a standard optical microscope and provides a contactless means to measure both the charge (L) and spin (L(s)) diffusion lengths simultaneously. The measured values of L and L(s) are in excellent agreement with the spatially averaged polarization and a sharp reduction in these two quantities (L from 21.3 to 1.2 µm and L(s) from 1.3 to 0.8 µm) is found with increasing surface recombination velocity. Outward diffusion results in a factor of 10 increase in the polarization at the excitation spot. The range of materials to which the technique can be applied, as well as a comparison with other existing methods for the measurement of spin diffusion, is discussed.

Upper extremity hemodynamic changes after radial artery harvest for coronary artery bypass grafting.

Twenty-seven patients were studied with arterial duplex, photoplethysmography, segmental pressures, and pulse volume recordings both preoperatively and following radial artery harvesting. The average number of days to the follow-up visit was 66. Preoperative and postoperative data were compared using the matched Student's t-test. There were no significant changes between preoperative and postoperative pressures in the brachial, radial, and ulnar arteries, and thumb, index, long, ring, or little fingers. Pressure changes in the thumb and index finger approached but did not achieve a statistical difference. Peak systolic velocity (PSV), end diastolic velocity (EDV), and resistive index (RI) in the distal ulnar artery changed significantly between preoperative and postoperative measurements. PSV changed from 0.50 +/- 0.05 m/sec to 0.67 +/- 0.04 m/sec (p = 0.02); EDV changed from 0.03 +/- 0.03 m/sec to -0.10 +/- 0.05 m/sec (p = 0.05); and RI changed from 0.97 +/- 0. 05 to 1.13 +/- 0.05 (p = 0.02). Palmar arch evaluations revealed significant changes at rest and with ulnar compression between preoperative and postoperative measurements: (1) at rest EDV changed from 0.03 +/- 0.02 m/sec to -0.05 +/- 0.02 m/sec (p < 0.01); (2) at rest RI changed from 0.96 +/- 0.05 to 1.12 +/- 0.05 (p = 0.01); (3) with ulnar compression the PSV changed from 0.23 +/- 0.05 m/sec to 0. 005 +/- 0.01 m/sec (p < 0.01); and (4) with ulnar compression the RI changed from 0.82 +/- 0.11 to 0.27 +/- 0.12 (p < 0.01). Eight patients had a variety of complaints at the follow-up visit, the majority being numbness and tingling. No patients reported symptoms of claudication or rest pain at the follow-up visit. The data suggest that while statistically significant changes in velocity and arterial resistance do occur, patients seem to tolerate radial artery harvesting without clinical consequences. The ideal method of preoperative evaluation remains to be determined.

Infectibility of endovascular stents following antibiotic prophylaxis or after arterial wall incorporation.

BACKGROUND: Case reports of endovascular stent infection have been accumulating in the last several years. We sought to determine if prophylactic antibiotics would prevent stent/artery complex infections in a swine model if given before a bacterial challenge at the time of stent placement and 4 weeks following deployment. We also investigated whether arterial wall incorporation protected the stent against infection without antibiotic prophylaxis. METHODS: Balloon expandable Palmaz stents were placed in the iliac arteries of 42 swine. At the same time, angioplasty was performed on the contralateral iliac artery as a control. In group A, prophylactic cefazolin was given to 12 swine at the time of stent deployment followed by an intraaortic bacterial challenge of Staphylococcus aureus. In group B, 10 swine received prophylactic cefazolin followed by intravenous S aureus 4 weeks after iliac stenting and angioplasty. In group C, 3 months following iliac stent placement and angioplasty an intravenous bacterial challenge was administered with S aureus. All swine were euthanized, and the iliac stent/artery complex and the contralateral angioplastied iliac artery were harvested and sent for culture and pathology. Experimental groups were compared with results from our previously published swine infection model using the Fisher's exact test. P values were considered significant if less than 0.05. RESULTS: Group A: Two of the 12 (17%) stent/artery complexes in the antibiotic treatment group had positive cultures. This compares with 7 of 10 (70%) in the control group (P = 0.016). In addition, there was one infection in an angioplastied vessel contralateral to one of the two stent infections. Molecular strain typing verified that the positive cultures were the same strain that was used to challenge the animals. No vessel thrombosis occurred in the stented arteries even in the presence of infection. Group B: One of 10 (10%) stented iliac arteries had a culture positive infection. This compares with 7 of 14 (50%) positive cultures in the control group (P = 0.04). In addition, one angioplastied vessel did have mild S aureus growth on culture. Both positive cultures were verified to be the same as the injected strain by molecular strain typing. There were no thrombosed or occluded vessels. Group C: One of 15 patent stents had growth of S aureus on culture and evidence of acute inflammation on histopathologic examination. The stent infection rate of 1 of 15 (7%) patent stents in this study was significantly less than the infection rates with bacterial challenge at placement (7 of 10, 70%; P < 0.01) and at 1 month postplacement (7 of 14, 50%; P = 0.0142). Five stents occluded without evidence of infectious cause. CONCLUSIONS: The results of this study support a recommendation that antibiotic prophylaxis should be used at the time of arterial stent placement and early after placement at times of anticipated bacteremia, but indefinite prophylaxis may be unnecessary due to arterial wall incorporation of the stent.

Evaluation of lidocaine as an analgesic when added to hypertonic saline for sclerotherapy.

PURPOSE: The efficacy of sclerosing agents for the treatment of telangiectasias and reticular veins is well established. The injection of these agents is often associated with pain, and it is not uncommon for sclerotherapists to include lidocaine with the sclerosants in an attempt to reduce the pain associated with treatment. However, there are concerns that this may reduce the overall efficacy of the treatment because of dilution of the sclerosant. Patient comfort and overall outcome associated with treatment using HS with lidocaine (LIDO) versus that using HS alone was compared. METHODS: Forty-two patients were prospectively entered into the study and randomized blindly to sclerotherapy with 23.4% HS or 19% LIDO. Study subjects and treating physicians were blinded to the injection solution used. Injection sites were chosen for veins ranging in size from 0.1 to 3 mm. Photographs of the area to be treated were taken, and the patients rated their pain. They were then observed at regular intervals for four months, and clinical data was collected. Thirty-five subjects completed the full follow-up period, and photographs of the injected area were taken again. Three investigators blinded to the treatment assignment then evaluated the photographs and scored the treatment efficacy according to a standardized system. RESULTS: In the HS group, 61.9% (13 of 21) patients rated their pain as none or mild, whereas 90.5% (19 of 21) of patients in the LIDO group had no or mild discomfort. This difference is significant, with a P value of.034. There was no difference in the overall efficacy of treatment between the two groups. The groups had similar rates of vein thrombosis and skin necrosis. CONCLUSION: Although lidocaine is often used with sclerosing agents, there are no previous reports in the literature to evaluate its effectiveness in reducing the pain experienced by the patient. In this study, patients receiving LIDO experienced significantly less discomfort at the time of injection than patients who received HS alone. There were no differences in the effectiveness of treatment or in the incidence of complications between the two groups.

HIV/AIDS and the legislature: an international comparison.

This paper examines the legislative response to the AIDS epidemic. It goes beyond a mere overview and tries to give an insight into the chronology of the legislative reaction as well as its contents. For this, the legal instruments of 217 jurisdictions were analyzed. A global chronological pattern of legislative reaction could be observed. Concerning the contents of legislation, legislatures seem to combine the public health interests with the interests, rights and responsibilities of individuals. This insight into the legislative reaction to AIDS can help us to predict and understand legislative responses to future epidemics.

[Can weight gain during weaning from smoking be limited using nicotine gum?]. / Peut-on limiter la prise de poids chez les fumeurs lors du sevrage tabagique en utilisant la gomme à la nicotine?

One hundred subjects smoking more than 20 cigarettes per day were divided into two groups allocated at random to either nicotine gum or a placebo gum. Forty-eight subjects stopped smoking, irrespective of the treatment received. The magnitude of weight gain after given up smoking and the benefits of nicotine gum were evaluated. Weight gain was found to increase in ex-smokers compared with persistent smokers, but the increase was less pronounced in subjects who chewed nicotine than in those who chewed the placebo, although the difference was not statistically significant. However, enough gum must be chewed for the appetite and feeling of hunger to be reduced.