Giant spin Seebeck effect in a non-magnetic material.

The spin Seebeck effect is observed when a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material, where it gets converted into a measurable voltage. It has been previously observed with a magnitude of microvolts per kelvin in magnetically ordered materials, ferromagnetic metals, semiconductors and insulators. Here we describe a signal in a non-magnetic semiconductor (InSb) that has the hallmarks of being produced by the spin Seebeck effect, but is three orders of magnitude larger (millivolts per kelvin). We refer to the phenomenon that produces it as the giant spin Seebeck effect. Quantizing magnetic fields spin-polarize conduction electrons in semiconductors by means of Zeeman splitting, which spin-orbit coupling amplifies by a factor of ∼25 in InSb. We propose that the giant spin Seebeck effect is mediated by phonon-electron drag, which changes the electrons' momentum and directly modifies the spin-splitting energy through spin-orbit interactions. Owing to the simultaneously strong phonon-electron drag and spin-orbit coupling in InSb, the magnitude of the giant spin Seebeck voltage is comparable to the largest known classical thermopower values.

Optical control of internal electric fields in band gap-graded InGaN nanowires.

InGaN nanowires are suitable building blocks for many future optoelectronic devices. We show that a linear grading of the indium content along the nanowire axis from GaN to InN introduces an internal electric field evoking a photocurrent. Consistent with quantitative band structure simulations we observe a sign change in the measured photocurrent as a function of photon flux. This negative differential photocurrent opens the path to a new type of nanowire-based photodetector. We demonstrate that the photocurrent response of the nanowires is as fast as 1.5 ps.

Observation of the spin-Seebeck effect in a ferromagnetic semiconductor.

Reducing the heat generated in traditional electronics is a chief motivation for the development of spin-based electronics, called spintronics. Spin-based transistors that do not strictly rely on the raising or lowering of electrostatic barriers can overcome scaling limits in charge-based transistors. Spin transport in semiconductors might also lead to dissipation-less information transfer with pure spin currents. Despite these thermodynamic advantages, little experimental literature exists on the thermal aspects of spin transport in solids. A recent and surprising exception was the discovery of the spin-Seebeck effect, reported as a measurement of a redistribution of spins along the length of a sample of permalloy (NiFe) induced by a temperature gradient. This macroscopic spatial distribution of spins is, surprisingly, many orders of magnitude larger than the spin diffusion length, which has generated strong interest in the thermal aspects of spin transport. Here, the spin-Seebeck effect is observed in a ferromagnetic semiconductor, GaMnAs, which allows flexible design of the magnetization directions, a larger spin polarization, and measurements across the magnetic phase transition. This effect is observed even in the absence of longitudinal charge transport. The spatial distribution of spin currents is maintained across electrical breaks, highlighting the local nature of this thermally driven effect.

Spin-seebeck effect: a phonon driven spin distribution.

Here we report on measurements of the spin-Seebeck effect in GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.

Coherent spin manipulation without magnetic fields in strained semiconductors.

A consequence of relativity is that in the presence of an electric field, the spin and momentum states of an electron can be coupled; this is known as spin-orbit coupling. Such an interaction opens a pathway to the manipulation of electron spins within non-magnetic semiconductors, in the absence of applied magnetic fields. This interaction has implications for spin-based quantum information processing and spintronics, forming the basis of various device proposals. For example, the concept of spin field-effect transistors is based on spin precession due to the spin-orbit coupling. Most studies, however, focus on non-spin-selective electrical measurements in quantum structures. Here we report the direct measurement of coherent electron spin precession in zero magnetic field as the electrons drift in response to an applied electric field. We use ultrafast optical techniques to spatiotemporally resolve spin dynamics in strained gallium arsenide and indium gallium arsenide epitaxial layers. Unexpectedly, we observe spin splitting in these simple structures arising from strain in the semiconductor films. The observed effect provides a flexible approach for enabling electrical control over electron spins using strain engineering. Moreover, we exploit this strain-induced field to electrically drive spin resonance with Rabi frequencies of up to approximately 30 MHz.

Zero-field optical manipulation of magnetic ions in semiconductors.

Controlling and monitoring individual spins is desirable for building spin-based devices, as well as implementing quantum information processing schemes. As with trapped ions in cold gases, magnetic ions trapped on a semiconductor lattice have uniform properties and relatively long spin lifetimes. Furthermore, diluted magnetic moments in semiconductors can be strongly coupled to the surrounding host, permitting optical or electrical spin manipulation. Here we describe the zero-field optical manipulation of a few hundred manganese ions in a single gallium arsenide quantum well. Optically created mobile electron spins dynamically generate an energy splitting of the ion spins and enable magnetic moment orientation solely by changing either photon helicity or energy. These polarized manganese spins precess in a transverse field, enabling measurements of the spin lifetimes. As the magnetic ion concentration is reduced and the manganese spin lifetime increases, coherent optical control and readout of single manganese spins in gallium arsenide should be possible.

A Net Sink for Atmospheric CH3Br in the East Pacific Ocean.

Surface waters along a cruise track in the East Pacific Ocean were undersaturated in methyl bromide (CH(3)Br) in most areas except for coastal and upwelling regions, with saturation anomalies ranging from + 100 percent in coastal waters to -50 percent in open ocean areas, representing a regionally weighted mean of -16 (-13 to -20) percent. The partial lifetime of atmospheric CH(3)Br with respect to calculated oceanic degradation along this cruise track is 3.0 (2.9 to 3.6) years. The global, mean dry mole fraction of CH3Br in the atmosphere was 9.8 +/- 0.6 parts per trillion, with an interhemispheric ratio of 1.31 +/- 0.08. These data indicate that approximately 8 percent (0.2 parts per trillion) of the observed interhemispheric difference in atmospheric CH3Br could be attributed to an uneven global distribution of oceanic sources and sinks.

Chemiluminescence in a macrophage cell line modulated by biological response modifiers.

We have studied a murine macrophage cell line, J774, and found these cells capable of a zymosan-triggered chemiluminescent oxidative burst. Such activity was enhanced by preincubation with Corynebacterium parvum (CP), bacillus Calmette-Guerin, and lipopolysaccharide (LPS). Under similar conditions, CP and LPS were shown to enhance J774-mediated tumor cell lysis. We have also demonstrated that murine interferon alpha + beta rendered J774 cells more sensitive to the actions of CP and LPS. These results indicate that J774 cells may be useful for the in vitro evaluation of biological response modifiers as well as the study of oxygen radical production by macrophages.

The effect of lactation on the mineral distribution profile of the rat femur by single photon absorptiometry.

The distribution of bone mineral in excised femurs from lactating and nonlactating control rats was localized and quantitated using single photon absorptiometry. Bone mineral content was measured proximodistally in nine sequential 0.32 cm increments along the femur length and then plotted as a function of the distance from the proximal end of the femur. The plots described a mineral distribution profile and revealed that bone loss following lactation was site specific, being greater in the metaphyseal regions (23-36%) than in the diaphyseal area (14-20%). The change in total bone mineral of femur caused by lactation was estimated by integrating the mineral distribution profile plots. The 28% lower bone mineral determined by this method was in close agreement with the 27% difference determined from femur dry weight measurements. Reproducibility of measurements with 10 repositionings of a single femur was within 4% at all but the 2 most distal sites. Variation in the estimated total bone mineral was 1.3%.

Modulation of hematoporphyrin derivative-sensitized phototherapy with corynebacterium parvum in murine transitional cell carcinoma.

The interaction of photodynamic therapy (PDT) with hematoporphyrin derivative (Hpd) and immunotherapy with Corynebacterium parvum (CP) was studied in a murine transitional cell carcinoma (MBT-2) model. C3H/He mice were transplanted subcutaneously in the hind limb with 2.5 X 10(5) tumor cells. One day after transplantation, mice were randomized into groups to receive saline (control), PDT, CP 25 micrograms, CP 250 micrograms, CP 25 micrograms + PDT, and CP 250 micrograms + PDT. PDT was administered by intraperitoneal (IP) injection of Hpd (12.5 micrograms/g body weight), followed twenty-four hours later by photoirradiation. CP was given intralesionally at the same time as IP injection of Hpd (24 hours before photoirradiation). A low dose of CP (25 micrograms) was shown to enhance the effect of PDT while PDT reduced the benefit obtained with high dose of CP (250 micrograms). In a second series of experiments, CP (250 micrograms) treatment after photoirradiation was shown to give significantly greater benefit than CP treatment before photoirradiation. The study thus indicates that the effectiveness of combined immunophototherapy is dependent on the sequence of the combination and its intricate relationship with the dosage of CP. The enhancement of PDT by low dose of CP in this model suggests the usefulness of this combined immunophototherapy in enhancing tumor control and in lessening deleterious side effects.

The proteinuria of diabetic nephropathy.

The results of an investigation into the nature of the proteinuria of diabetic nephropathy are described. Proteinuria increases quantitatively with deteriorating renal function but there is no consistent qualitative change; even with small amounts of proteinuria the selectivity may be poor and the proportion of albumin to the total excretion constant. These and other findings are discussed in relation to the possible pathogenesis of the glomerular dysfunction in diabetic nephropathy.

Studies on the acute toxicity primary irritancy and genotoxic potential of 1,3,5-triacryloylhexahydro-s-triazine (TAHT).

TAHT (1,3,5-triacryloylhexahydro-s-triazine), a reactive chemical coupling agent, was highly toxic following a single peroral dose of an aqueous suspension (10% w/v) to Wistar rats, or following application of TAHT in dichloromethane (DCM) solution (10% w/v) to covered skin of New Zealand rabbits. It was moderately toxic when applied dermally as an aqueous paste. Ocular contact with 25 mg of TAHT in a 5% aqueous suspension, or of 0.5 mg of TAHT in a 10% (w/v) solution in DCM, produced severe corneal damage, iritis and blepharo-conjunctivitis. A 30-min exposure of uncovered rabbit skin to 1 mg of TAHT in a 10% (w/v) aqueous suspension produced only slight skin irritation. However, 24-h exposures to TAHT on covered skin produced erythema, edema, ecchymoses, scabs, and death depending upon dosage and vehicle. In vitro genotoxicity studies revealed no positive effects upon gene mutations (HGPRT locus) or on sister chromatid exchanges (SCEs) of CHO cells exposed to TAHT with and without a rat-liver S9 metabolic activation system. TAHT did not increase the levels of [3H]thymidine incorporation in a test for unscheduled DNA synthesis with primary rat hepatocytes. In contrast, substantial increases in the number of chromosome breaks and rearrangements were observed in chromosome preparations used for the SCE analyses. The clastogenic activity of TAHT was confirmed in an in vitro chromosome aberration test with CHO cells. Treatment-related increases in chromosome breakage were observed at two independent sampling times and positive effects did not depend upon the presence or absence of a metabolic activation system. Clastogenic activity of TAHT was also demonstrated in vivo in a micronucleus test using mouse peripheral polychromatic erythrocytes. Significant, treatment-related increases in micronucleated polychromatic erythrocytes were obtained at two of three sampling times. The high degree of mammalian toxicity, severe eye irritancy and the in vitro and in vivo clastogenicity indicate that TAHT should be handled as a hazardous material using suitable caution and protective equipment.

Difficulties associated with the development and licensing of vaccines for protection against bio-warfare and bio-terrorism.

Today there is an increasing need to license vaccines for the protection of individuals against bio-warfare and bio-terrorism. While the need is apparent, the actual road to developing, producing and licensing such vaccines successfully is as yet undefined. Bio-defence vaccine candidates may come from several sources. They may come from vaccines that were previously licensed but are no longer in production, vaccines that are currently in an IND status, vaccines currently licensed in foreign countries, and newer vaccines currently under development. The issues that apply to the development and licensing of these vaccines can be defined by currently accepted standards for manufacture, and the requirement to demonstrate safety and efficacy to a level that gives the scientific and medical community, regulatory agencies, users and the public at large confidence. Requirements for manufacturing and demonstration of safety will be consistent with vaccines being developed for traditional purposes. However, demonstration of efficacy will be more difficult. Because field trials for these vaccines are generally not feasible and the conduct of human challenge studies is generally considered unethical, the demonstration of efficacy will need to be based on existing efficacy data, a thorough understanding of both the disease's pathogenesis and mechanism of protection, the ability to identify surrogate markers for efficacy, and the use of the proposed FDA "animal rule".

Evaluation of intravenous administration of concentrated immunoglobulin G to colostrum-deprived foals.

Ten foals of various breeds were deprived of colostrum from birth to 36 hours of age, then were allotted to 2 groups. Foals of group 1 (n = 6) were given 20 g (200 ml) of purified equine IgG IV in a 10% solution, and foals of group 2 (n = 4) were given 30 g (300 ml) of the same preparation. Total administration time for each 10 g of IgG in 100 ml was approximately 10 minutes. Serum IgG concentration in foals was assessed prior to, between 24 and 48 hours, and at 7 and 14 days after IgG administration. Between 24 and 48 hours after IgG administration, mean serum IgG concentration in group-1 foals was 425 mg/dl (range, 350 to 480 mg/dl). Mean body weight for this group of foals was 50.3 kg (range, 43.3 to 54.7 kg). For group-2 foals, mean serum IgG concentration was 768 mg/dl (range, 640 to 920 mg/dl) between 24 and 48 hours after administration of IgG. Foals of this group had mean body weight of 43.2 kg (range, 36.5 to 47.5 kg). Serum IgG concentration in group-2 foals at 24 to 48 hours was significantly (P = 0.005) greater than that in group-1 foals. Mean total IgG recovery at 24 to 48 hours, calculated on the basis of 94.5 ml of plasma volume/kg of body weight, was approximately 100%. Values of IgG measured in all foals 1 and 2 weeks after administration of the IgG concentrate were equivalent to values expected after normal decay of passively acquired IgG.(ABSTRACT TRUNCATED AT 250 WORDS)

Onset of Ferromagnetism in Low-Doped Ga1-xMnxAs.

We develop a quantitatively predictive theory for impurity-band ferromagnetism in the low-doping regime of Ga1-xMnxAs. We compare it with measurements of a series of samples whose compositions span the transition from paramagnetic insulating to ferromagnetic conducting behavior. The theoretical Curie temperatures depend sensitively on the local fluctuations in the Mn-hole binding energy, which originate from Mn disorder and As antisite defects. The experimentally determined hopping energy is an excellent predictor of the Curie temperature, in agreement with the theory.

Suppression of spin relaxation in submicron InGaAs wires.

We investigate electron-spin dynamics in narrow two-dimensional n-InGaAs channels as a function of the channel width. The spin relaxation times increase with decreasing channel width, in accordance with recent theoretical predictions based on the dimensionally constrained D'yakonov-Perel' mechanism. Surprisingly, the suppression of the relaxation rate, which is anticipated for the one-dimensional limit, is observed for widths that are an order of magnitude larger than the electron mean free path. We find the spin precession length and the channel width to be the relevant length scales for interpreting these results.

Generating spin currents in semiconductors with the spin Hall effect.

We investigate electrically induced spin currents generated by the spin Hall effect in GaAs structures that distinguish edge effects from spin transport. Using Kerr rotation microscopy to image the spin polarization, we demonstrate that the observed spin accumulation is due to a transverse bulk electron spin current, which can drive spin polarization nearly 40 microns into a region in which there is minimal electric field. Using a model that incorporates the effects of spin drift, we determine the transverse spin drift velocity from the magnetic field dependence of the spin polarization.

Enhancement of spin coherence using Q-factor engineering in semiconductor microdisc lasers.

Semiconductor microcavities offer unique means of controlling light-matter interactions in confined geometries, resulting in a wide range of applications in optical communications and inspiring proposals for quantum information processing and computational schemes. Studies of spin dynamics in microcavities, a new and promising research field, have revealed effects such as polarization beats, stimulated spin scattering and giant Faraday rotation. Here, we study the electron spin dynamics in optically pumped GaAs microdisc lasers with quantum wells and interface-fluctuation quantum dots in the active region. In particular, we examine how the electron spin dynamics are modified by the stimulated emission in the discs, and observe an enhancement of the spin-coherence time when the optical excitation is in resonance with a high-quality (Q approximately 5,000) lasing mode. This resonant enhancement, contrary to expectations from the observed trend in the carrier-recombination time, is then manipulated by altering the cavity design and dimensions. In analogy with devices based on excitonic coherence, this ability to engineer coherent interactions between electron spins and photons may provide new pathways towards spin-dependent quantum optoelectronics.

Antiferromagnetic s-d exchange coupling in GaMnAs.

Measurements of coherent electron spin dynamics in Ga1-xMnxAs/Al0.4Ga0.6As quantum wells with 0.0006%

The comparative acute toxicity and primary irritancy of the monohexyl ethers of ethylene and diethylene glycol.

Ethylene glycol monohexyl ether (EGHE) and diethylene glycol monohexyl ether (DGHE) are glycol ethers used as industrial solvents and coating materials, and whose acute handling hazards were investigated. Acute peroral LD50 values in the rat were for EGHE 1.67 ml/kg (males) and 0.83 ml/kg (females), and for DGHE 4.92 ml/kg (males) and 3.73 ml/kg (females). Acute percutaneous LD50 values in the rabbit were for EGHE 0.81 ml/kg (males) and 0.93 ml/kg (females), and for DGHE 2.14 ml/kg (males) and 2.37 ml/kg (females). There were neither deaths nor signs of toxicity or irritancy during or following a 6-hr exposure of rats to a statically generated substantially saturated vapor atmosphere from either EGHE or DGHE at ambient temperature. Occluded dermal application with 0.5 ml test material for 4-hr in rabbits produced moderate inflammation of several days duration, and half of the animals developed necrosis; with DGHE there was minor erythema and edema of about 24-hr duration. In the more demanding conditions of the acute percutaneous toxicity study (24-hr occlusions with up to 4.0 ml/kg) both EGHE and DGHE produced persistent erythema, edema, necrosis, and ecchymoses. Rabbit eye irritation studies showed severe effects (conjunctivitis and corneal injury) with both EGHE and DGHE. The major acute handling hazards with both EGHE and DGHE are by swallowing, sustained skin contact, and splash contamination of the eye.