Changing exchange bias in spin valves with an electric current

We show that a high-density electric current, injected from a point contact into an exchange-biased spin valve, systematically changes the exchange bias. The bias can either increase or decrease depending upon the current direction. This observation is not readily explained by the well-known spin-transfer torque effect in ferromagnetic metal circuits, but could be evidence for the recently predicted current-induced torques in antiferromagnetic metals.     

Magnetic properties of chalcogenide spinel CuCr2Se4 nanocrystals

The magnetic properties of chalcogenide spinel CuCr₂Se₄ nanocrystals have been studied as a function of crystallite size (15-30 nm). A solution-based method is used for the facile synthesis of the nanocrystals with good size control. They have close to cubic morphology with a narrow size distribution and exhibit superparamagnetic behavior at room temperature. The Curie temperature and saturation magnetization of the nanocrystals are lower as compared with the bulk and decrease with decreasing nanocrystal size. A similar trend is observed in the paramagnetic state for the Curie-Weiss temperature and effective magnetic moment. The low temperature magnetization behavior can be qualitatively explained by spin glass dynamics.     

Modified epoxy-novolac block cooligomers

New thermoreactive polymers with predefined properties are prepared for the case of modification of an epoxy-novolac block cooligomer by high-molecular-weight polymers (rubbers, polyvinylbutyral, polyamide, and polyimide), depending on the synthetic conditions and processing regimes.     

Fe vibrational spectroscopy of myoglobin and cytochrome f

The Fe vibrational density of states (VDOS) has been determined for the heme proteins deoxymyoglobin, metmyoglobin, and cytochrome f in the oxidized and reduced states, using nuclear resonance vibrational spectroscopy (NRVS). For cytochrome f in particular, the NRVS spectrum is compared with multiwavelength resonance Raman spectra to identify those Raman modes with significant Fe displacement. Modes not seen by Raman due to optical selection rules appear in the NRVS spectrum. The mean Fe force constant extracted from the VDOS illustrates how Fe dynamics varies among these four monoheme proteins, and is correlated with oxidation and spin state trends seen in model heme compounds. The protein's contribution to Fe motion is dominant at low frequencies, where coupling to the backbone tightly constrains Fe displacements in cytochrome f, in contrast to enhanced heme flexibility in myoglobin.     

Weak exponential stability of stochastic differential equations

In this paper we introduce weak exponential stability of stochastic differential equations. In particular, we introduce weak exponential stability in mean, weak exponential asymptotical stability in mean and weak uniform asymptotical stability in mean. We also derive some results related to the above concepts     

Heterocyclic reactive mesogens: synthesis, characterisation and mesomorphic behaviour

Novel heterocyclic and photopolymerizable liquid crystalline materials (reactive mesogens) with smectic phases have been synthesized and characterized. A selection of heterocyclic rings, such as benzothiazole, benzothiadiazole and pyrimidine, has been incorporated into the aromatic core to control the electrochemical/luminescence properties and the structural geometry. Particular emphasis is focused on structure-property relationships, in which the variation of molecular structure and its subsequent effect on the liquid crystalline transition temperatures have been investigated.     

On the question of short-period oscillations of the collector voltage during transverse electron focusing

Giant short-period oscillations during transverse electron focusing at high emitter voltages have been observed in bismuth samples with a superlattice on the surface. A model is proposed which explains the onset of the oscillations, their position on the magnetic-field scale, and their intensification and shift along the magnetic-field scale with increasing current (this shift depending on the direction of current flow) and which can also account for the absence of oscillations in fields which are multiples of the field of the first oscillation. In this model the oscillations are attributed to the appearance of resonant surface (edge) states and their contribution to the electron transport. Pis'ma Zh. éksp. Teor. Fiz. 68, No. 12, 887–892 (25 December 1998)     

Toward the use of surface modified activated carbon in speciation: selective preconcentration of selenite and selenate in environmental waters

This paper describes a novel application of tetrabutylammonium hydroxide-modified activated carbon (AC-TBAH) to the speciation of ultra-trace Se(IV) and Se(VI) using LC-ICP-DRC-MS. The anion exchange functionality was immobilized onto the AC surface enables selective preconcentration of inorganic Se anions in a wide range of working pHs. Simultaneous retention and elution of both analytes, followed by subsequent analysis with LC-ICP-DRC-MS, allows to accomplish speciation analysis in natural samples without complicated redox pre-treatment. The laboratory-made column of immobilized AC (0.4 g of sorbent packed in a 6 mL syringe barrel) has achieved analyte enrichment factors of 76 and 93, respectively, for Se(IV) and Se(VI), thus proving its superior preconcentration efficiency and selectivity over common AC. The considerable enhancement in sensitivity achieved by using the preconcentration column has improved the method's detection limits to 1.9-2.2 ng L(-1), which is a 100-fold improvement compared with direct injection. The analyte recoveries from heavily polluted river matrix were between 95.3 and 107.7% with less than 5.0% RSD. The robustness of the preconcentration and speciation method was validated by analysis of natural waters collected from rivers and reservoirs in Hong Kong. The modified AC material is hence presented as a low-cost yet robust substitute for conventional anion exchange resins for routine applications.     

Laser Simulations of the Destructive Impact of Nuclear Explosions on Hazardous Asteroids

We present the results of preliminary experiments at laser facilities in which the processes of the undeniable destruction of stony asteroids (chondrites) in space by nuclear explosions on the asteroid surface are simulated based on the principle of physical similarity. We present the results of comparative gasdynamic computations of a model nuclear explosion on the surface of a large asteroid and computations of the impact of a laser pulse on a miniature asteroid simulator confirming the similarity of the key processes in the fullscale and model cases. The technology of fabricating miniature mockups with mechanical properties close to those of stony asteroids is described. For mini-mockups 4–10 mm in size differing by the shape and impact conditions, we have made an experimental estimate of the energy threshold for the undeniable destruction of a mockup and investigated the parameters of its fragmentation at a laser energy up to 500 J. The results obtained confirm the possibility of an experimental determination of the criteria for the destruction of asteroids of various types by a nuclear explosion in laser experiments. We show that the undeniable destruction of a large asteroid is possible at attainable nuclear explosion energies on its surface.