Time Refraction of Spin Waves.

We present an experimental study of time refraction of spin waves (SWs) propagating in microscopic waveguides under the influence of time-varying magnetic fields. Using space- and time-resolved Brillouin light scattering microscopy, we demonstrate that the broken translational symmetry along the time coordinate results in a loss of energy conservation for SWs and thus allows for a broadband and controllable shift of the SW frequency. With an integrated design of SW waveguide and microscopic current line for the generation of strong, nanosecond-long, magnetic field pulses, a conversion efficiency up to 39% of the carrier SW frequency is achieved, significantly larger compared to photonic systems. Given the strength of the magnetic field pulses and its strong impact on the SW dispersion relation, the effect of time refraction can be quantified on a length scale comparable to the SW wavelength. Furthermore, we utilize time refraction to excite SW bursts with pulse durations in the nanosecond range and a frequency shift depending on the pulse polarity.

Large Spin-Wave Bullet in a Ferrimagnetic Insulator Driven by the Spin Hall Effect.

Because of its transverse nature, spin Hall effects (SHE) provide the possibility to excite and detect spin currents and magnetization dynamics even in magnetic insulators. Magnetic insulators are outstanding materials for the investigation of nonlinear phenomena and for novel low power spintronics applications because of their extremely low Gilbert damping. Here, we report on the direct imaging of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the ferrimagnetic insulator Y_{3}Fe_{5}O_{12} based on the excitation and detection by SHEs. The driven spin dynamics in Y_{3}Fe_{5}O_{12} is directly imaged by spatially resolved microfocused Brillouin light scattering spectroscopy. Previously, ST-FMR experiments assumed a uniform precession across the sample, which is not valid in our measurements. A strong spin-wave localization in the center of the sample is observed indicating the formation of a nonlinear, self-localized spin-wave "bullet".

Universal method for separating spin pumping from spin rectification voltage of ferromagnetic resonance.

We develop a method for universally resolving the important issue of separating spin pumping from spin rectification signals in bilayer spintronics devices. This method is based on the characteristic distinction of spin pumping and spin rectification, as revealed in their different angular and field symmetries. It applies generally for analyzing charge voltages in bilayers induced by the ferromagnetic resonance (FMR), independent of FMR line shape. Hence, it solves the outstanding problem that device-specific microwave properties restrict the universal quantification of the spin Hall angle in bilayer devices via FMR experiments. Furthermore, it paves the way for directly measuring the nonlinear evolution of spin current generated by spin pumping. The spin Hall angle in a Py/Pt bilayer is thereby directly measured as 0.021±0.015 up to a large precession cone angle of about 20°.

Unanticipated proximity behavior in ferromagnet-superconductor heterostructures with controlled magnetic noncollinearity.

Magnetization noncollinearity in ferromagnet-superconductor (F/S) heterostructures is expected to enhance the superconducting transition temperature (T(c)) according to the domain-wall superconductivity theory, or to suppress T(c) when spin-triplet Cooper pairs are explicitly considered. We study the proximity effect in F/S structures where the F layer is a Sm-Co/Py exchange-spring bilayer and the S layer is Nb. The exchange-spring contains a single, controllable and quantifiable domain wall in the Py layer. We observe an enhancement of superconductivity that is nonmonotonic as the Py domain wall is increasingly twisted via rotating a magnetic field, different from theoretical predictions. We have excluded magnetic fields and vortex motion as the source of the nonmonotonic behavior. This unanticipated proximity behavior suggests that new physics is yet to be captured in the theoretical treatments of F/S systems containing noncollinear magnetization.

Thermoelectric detection of spin waves.

We report on the thermoelectric detection of spin waves in Permalloy stripes via the anomalous Nernst effect. Spin waves are locally excited by a dynamic magnetic field generated from a microwave current flowing in a coplanar waveguide placed on top of a Permalloy stripe, which acts as a waveguide for spin waves. Electric contacts at the ends of the Permalloy stripe measure a dc voltage generated along the stripe. Magnetic field sweeps for different applied microwave frequencies reveal, with a remarkable signal-to-noise ratio, an electric voltage signature characteristic of spin-wave excitations. The symmetry of the signal with respect to the applied magnetic field direction indicates that the anomalous Nernst effect is responsible; Seebeck effects, anisotropic magnetoresistance, and voltages due to spin-motive forces are excluded. The dissipation of spin waves causes local heating that drains into the substrate, giving rise to a temperature gradient perpendicular to the sample plane, resulting in the anomalous Nernst voltage.

Direct determination of energy level alignment and charge transport at metal-Alq3 interfaces via ballistic-electron-emission spectroscopy.

Using ballistic-electron-emission spectroscopy (BEES), we directly determined the energy barrier for electron injection at clean interfaces of Alq(3) with Al and Fe to be 2.1 and 2.2 eV, respectively. We quantitatively modeled the sub-barrier BEES spectra with an accumulated space charge layer, and found that the transport of nonballistic electrons is consistent with random hopping over the injection barrier.

Surface spin flip probability of mesoscopic Ag wires.

Spin relaxation in mesoscopic Ag wires in the diffusive transport regime is studied via nonlocal spin valve and Hanle effect measurements performed on Permalloy/Ag lateral spin valves. The ratio between momentum and spin relaxation times is not constant at low temperatures. This can be explained with the Elliott-Yafet spin relaxation mechanism by considering the momentum surface relaxation time as being temperature dependent. We present a model to separately determine spin flip probabilities for phonon, impurity and surface scattering and find that the spin flip probability is highest for surface scattering.

Quantifying spin Hall angles from spin pumping: experiments and theory.

Spin Hall effects intermix spin and charge currents even in nonmagnetic materials and, therefore, ultimately may allow the use of spin transport without the need for ferromagnets. We show how spin Hall effects can be quantified by integrating Ni{80}Fe{20}|normal metal (N) bilayers into a coplanar waveguide. A dc spin current in N can be generated by spin pumping in a controllable way by ferromagnetic resonance. The transverse dc voltage detected along the Ni{80}Fe{20}|N has contributions from both the anisotropic magnetoresistance and the spin Hall effect, which can be distinguished by their symmetries. We developed a theory that accounts for both. In this way, we determine the spin Hall angle quantitatively for Pt, Au, and Mo. This approach can readily be adapted to any conducting material with even very small spin Hall angles.

Negative nonlocal resistance in mesoscopic gold Hall bars: absence of the giant spin Hall effect.

We report the observation of negative nonlocal resistances in multiterminal mesoscopic gold Hall bar structures whose characteristic dimensions are larger than the electron mean-free path. Our results can only be partially explained by a classical diffusive model of the nonlocal transport, and are not consistent with a recently proposed model based on spin Hall effects. Instead, our analysis suggests that a quasiballistic transport mechanism is responsible for the observed negative nonlocal resistance. Based on the sensitivity of our measurements and the spin Hall effect model, we find an upper limit for the spin Hall angle in gold of 0.023 at 4.5 K.

Complex patterns in a simple system.

Numerical simulations of a simple reaction-diffusion model reveal a surprising variety of irregular spatiotemporal patterns. These patterns arise in response to finite-amplitude perturbations. Some of them resemble the steady irregular patterns recently observed in thin gel reactor experiments. Others consist of spots that grow until they reach a critical size, at which time they divide in two. If in some region the spots become overcrowded, all of the spots in that region decay into the uniform background.

An investigation of models of the IP3R channel in Xenopus oocyte.

We consider different models of inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R) channels in order to fit nuclear membrane patch clamp data of the stationary open probability, mean open time, and mean close time of channels in the Xenopus oocyte. Our results indicate that rather than to treat the tetrameric IP(3)R as four independent and identical subunits, one should assume sequential binding-unbinding processes of Ca(2+) ions and IP(3) messengers. Our simulations also favor the assumption that a channel opens through a conformational transition from a close state to an active state.

Regulatory constraints for the transport of samples and compliance with the World Organisation for Animal Health (OIE) standards for biosecurity and biocontainment.

The International Regulations for transport of infectious substances, including diagnostic specimens, are based on the United Nations Model Regulations and are the standard for transport by all means of transportation including air transport; the International Air Transport Association (IATA) regulation specifically addresses air shipment. In 2005 and 2006 there were major improvements in the procedures for shipping infectious substances. These substances are divided into Category A, which includes primarily cultures of the more pathogenic agents and Category B, all the other substances. Category A shipments must have a Dangerous Goods Certificate and meet other requirements. Category B shipments, which include most diagnostic tissue specimens, do not. These regulations specifically exempt certain substances, including those that have been neutralized or inactivated to destroy pathogens and samples from "normal" animals. The packaging requirements help insure that biocontainment is maintained during shipment to protect the shipper and the environment. The packaging requirements and the shipping procedures provide a chain of custody and assist in supporting biosecurity. The more stringent Category A requirements provide increased biocontainment and biosecurity safeguards for these potentially more dangerous substances. In addition, National requirements, such as import permits and the US select agent requirements, provide an added measure of biocontainment and biosecurity.

Transportation of reagents, reference materials and samples: the international perspective.

The International Regulations for the transport of infectious substances, which could include reagents, reference material and samples, are based on the 13th revision of the United Nations Model Regulations and are the standard for transport of infectious substances by all means of transportation. The 13th revision, effective January 2005 and further amended in March and July 2005, made major improvements in these shipping regulations. They specifically exempt certain substances, including those that have been neutralized or inactivated to destroy any pathogens and samples from "normal" animals. Infectious substances are divided into Category A, which includes primarily cultures of the more pathogenic agents and Category B, which includes all other substances that do not meet the Category A criteria. Tissue specimens, submitted for diagnosis, are included in Category B. Category A shipments must have a Dangerous Goods Certificate and meet other requirements; Category B shipments do not. The National requirements, such as import permits, and certain airline restrictions must also be met.

Myocardial depressant effects of sodium acetate.

Sodium acetate produced a direct, dose-related decrease in myocardial contractile force in the dog and isolated rabbit papillary muscle. In the dog, there was also a decrease in blood pressure which was attributed primarily to the fall in contractile force. However, sodium acetate was found to have weak vasodilator properties as shown by the decreases in hind-limb perfusion pressure.

Sequential measurement of beta 2-microglobulin levels, p24 antigen levels, and antibody titers following transplantation of a human immunodeficiency virus-infected kidney allograft.

A renal allograft recipient developed symptoms suggestive of AIDS. Serological studies revealed that the donor was positive for human immunodeficiency virus (HIV). Retrospective testing of stored sequential serum samples showed that the recipient was negative for HIV pretransplant; anti-p24 and anti-p41 antibodies appeared 10 and 49 days posttransplant, respectively. The recipient's serum beta 2-microglobulin levels were elevated 14 days posttransplant, with normal renal function, 35 days before the detection of anti-p24 antibody. p24 Antigen was detected for the first time 21 days posttransplant. In addition to p24 antigen, elevated serum beta 2-microglobulins may be a useful marker for HIV infection prior to seroconversion.

Increased monoclonal antibody ascites production in mice primed with Freund's incomplete adjuvant.

The production of monoclonal antibodies is conveniently achieved by propagation of antibody-secreting hybridoma cells as ascites tumours in mice. With a view to improve production and minimise animal usage, the choice of primer (pristane or Freund's incomplete adjuvant (FIA] and the effect of sex of mouse (female vs. uncastrated male) upon antibody yields were compared. The volume of ascitic fluid harvested from 134 FIA-primed mice was 697 ml, which was significantly (P less than 0.02) greater than the 343 ml collected from 116 pristane-primed mice. Moreover, FIA-primed mice required tapping for only 11 days (90% in 7 days) compared to the 17 days needed for pristane-primed mice. While there was little difference between the mean IgG1 concentration (as determined by enzyme immunoassay) of both ascites pools (4.9 mg/ml compared to 4.6 mg/ml), the volume differences equated to yields of 25.5 mg/mouse and 13.5 mg/mouse respectively. The FIA-primed mice were also shown to produce on average more (P less than 0.02) ascites per day. There was no significant difference found between the yield of monoclonal antibodies obtained from either uncastrated males (22.1 mg/mouse) or females (23.1 mg/mouse). The use of FIA to prime mice for the in vivo production of monoclonal antibodies should improve the yield to over 20 mg/mouse, thereby reducing the number of mice required.

Surface plasmon resonance: a study of the effect of biotinylation on the selection of antibodies for use in immunoassays.

Surface plasmon resonance is a valuable optical phenomenon for monitoring biomolecular interactions in real time. In this project anti-mouse-Fc was coupled to the carboxymethyl dextran coating on the surface of a CM5 sensor chip (BIAcore) using amine coupling. Monoclonal antibodies (MAbs) to Luteinizing Hormone (LH) were then captured on this surface in the correct orientation for binding. LH (500 IU/l) was injected over the surface and the subsequent binding and dissociation events were monitored. The resulting optical response curves allowed fast analysis of the binding interactions of eight selected MAbs. It was possible to develop a two-site immunometric assay for LH using a pair of these MAbs. The effect of biotinylating the MAbs, using various biotin:antibody coupling ratios, on their subsequent binding to both LH and avidin conjugated alkaline phosphatase was also investigated. This approach has allowed rapid evaluation of the effect of changes in both reagent and reaction conditions on immunoassay performance and appears to be a valuable adjunct to immunosensor and immunoassay development.

Albumin uptake by renal lymphatics with and without obstruction of the renal vein.

Experiments involving injection of radio-iodinated albumin into the left renal arteries or left ureters of dogs indicate that the renal lymphatics are capable of a major contribution in returning to the circulation albumin (or other large molecules) escaping from renal capillaries. I131-albumin was injected into the jugular vein of controls or into the left renal artery or in retrograde manner into the left ureter of female dogs. Experimental groups included those with no obstruction, occlusion of left renal veins or left renal lymphatics, or both. Collections were made from the right femoral artery, both renal veins, thoracic duct and both ureters at frequent intervals for 2 to 4 hours. Data analysis included I131 concentration, specific activity, rate of recovery and selected ratios. After renal arterial injection, the percentage of I131 recovered in thoracic duct lymph of dogs without renal venous obstruction was 5 to 10 times that recovered in those that received injections into the jugular vein. In dogs with renal venous obstruction, recovery from the thoracic duct was 10 to 1,000 times that in control dogs. Most of the differences occurred during the first hour, after which time as recirculation and redistribution occurred the rates of appearance in thoracic duct lymph in each group were similar. The differences in the ratios of concentration in thoracic duct lymph to concentration in femoral arterial blood were also much greater when the renal vein was obstructed than in dogs with no obstruction. The greater return of albumin through the thoracic duct in those with impeded renal venous outflow was probably related to both sequestered concentration and increased intrarenal pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of cyclo (His-Pro) to exhibit natriuretic activity.

Administration of exogenous cyclo (His-Pro) to dogs has been reported to elicit natriuresis. In contrast, our data fail to show any natriuretic activity of cyclo (His-Pro) in dogs or rats. The possible reasons underlying this discrepancy are discussed.

Comparison of effects of cyanide and acetylcholine on renal hemodynamics and sodium excretion.

The present study compared the effects of acetylcholine to cyanide under the same experimental conditions of renal clearance in anesthetized dogs. Since cyanide is one of the few drugs for which the mechanism of action is known (cytotoxic hypoxia), some insight may be gained into the renal effects of acetylcholine since both produce direct natriuresis and diuresis. Infusion of 0.2 microgram/kg/min of acetylcholine and 12.0 microgram/kg/min of sodium cyanide into the left renal artery resulted in similar effects, i.e., increased fractional excretion of sodium, potassium, calcium, and magnesium. These effects were immediate and ipsilateral. Both agents increased the renal plasma flow to the same extent. In addition, regression plots of the relation between changes in sodium excretion and changes in renal plasma flow were similar for both agents. The pattern of similar renal functional changes suggested that acetylcholine is not a mere renal vasodilator but that its action is also medicated through alterations on direct transport of ions.