Enhanced sensitivity in detection of Kerr rotation by double modulation and time averaging based on Allan variance

Experiments in spintronics necessarily involve the detection of spin polarization. The sensitivity of this detection becomes an important factor to consider when extending the low temperature studies on semiconductor spintronic devices to room temperature, where the spin signal is weaker. In pump-probe experiments, which optically inject and detect spins, the sensitivity is often improved by using a photoelastic modulator (PEM) for lock-in detection. However, spurious signals can arise if diode lasers are used as optical sources in such experiments, along with a PEM. In this work, we eliminated the spurious electromagnetic coupling of the PEM onto the probe diode laser, by the double modulation technique. We also developed a test for spurious modulated interference in the pump-probe signal, due to the PEM. Besides, an order of magnitude enhancement in the sensitivity of detection of spin polarization by Kerr rotation, to 3x10(-8) rad was obtained by using the concept of Allan variance to optimally average the time series data over a period of 416 s. With these improvements, we are able to experimentally demonstrate at room temperature, photoinduced steady-state spin polarization in bulk GaAs. Thus, the advances reported here facilitate the use of diode lasers with a PEM for sensitive pump-probe experiments. They also constitute a step toward detection of spin-injection in Si at room temperature.

X-ray studies of crystalline complexes involving amino acids. II. The crystal structure of L-arginine L-glutamate

Abstract is not available.

Simplified theory of optical nonlinearities in spin-polarized semiconductors

The spin degree of freedom is largely disregarded in existing theories of the density-dependent optical properties of an interacting electron-hole plasma in quasiequilibrium. Here, we extended the pair equation, which is applicable to a bulk semiconductor at elevated temperatures, to calculate optical nonlinearities due to a spin-polarized plasma. We obtained agreement with recent circular dichroism data in laser-excited GaAs by using the plasma density alone as the fitting parameter. The simplicity of our theory, based on the analytical pair-equation formula, makes it ideal for conveniently modelling absorption in a carrier spin-polarized semiconductor.

Quasiequilibrium optical nonlinearities from spin-polarized carriers in GaAs

Semiconductor Bloch equations, which microscopically describe the dynamics of a Coulomb interacting, spin-unpolarized electron-hole plasma, can be solved in two limits: the coherent and the quasiequilibrium regimes. These equations have been recently extended to include the spin degree of freedom and used to explain spin dynamics in the coherent regime. In the quasiequilibrium limit, one solves the Bethe-Salpeter equation in a two-band model to describe how optical absorption is affected by Coulomb interactions within a spin unpolarized plasma of arbitrary density. In this work, we modified the solution of the Bethe-Salpeter equation to include spin polarization and light holes in a three-band model, which allowed us to account for spin-polarized versions of many-body effects in absorption. The calculated absorption reproduced the spin-dependent, density-dependent, and spectral trends observed in bulk GaAs at room temperature, in a recent pump-probe experiment with circularly polarized light. Hence, our results may be useful in the microscopic modeling of density-dependent optical nonlinearities due to spin-polarized carriers in semiconductors.

Rationalizing the effects of amino acid side chain, pyridine, and imidazole on the assembly and reversible disassembly of a octanuclear Cu(III) complex

This paper reports the observation of a reversible disassembly process for a previously reported octanuclear Cu(II) complex with imidazole. To identify the factors responsible for the process, five Cu(II) complexes of different nuclearity with different amino acid-derived tetradentate ligands were structurally characterized. The results show that the coordination geometry preference of Cu(II), the tendency of imidazole to act as in-plane ligand, and H-bonding played important role in the formation and disassembly of the octanuclear complex. A general scheme describing the effect of different amino acid side arms, solvents, and exogenous ligands on the nuclearity of the Cu(II) complexes has been presented. The crystals of the complexes also showed formation of multifaceted networks in the resulting complexes.

Simplified theory of optical nonlinearities in spin-polarized bulk GaAs

Apart from their intrinsic physical interest, spin-polarized many-body effects are expected to be important to the working of spintronic devices. A vast literature exists on the effects of a spin-unpolarized electron-hole plasma on the optical properties of a semiconductor. Here, we include the spin degree of freedom to model optical absorption of circularly polarized light by spin-polarized bulk GaAs. Our model is easy to implement and does not require elaborate numerics, since it is based on the closed-form analytical pair-equation formula that is valid in 3d. The efficacy of our approach is demonstrated by a comparison with recent experimental data.

Simplified theory of optical nonlinearities in spin-polarized bulk GaAs

Apart from their intrinsic physical interest, spin-polarized many-body effects are expected to be important to the working of spintronic devices. A vast literature exists on the effects of a spin-unpolarized electron-hole plasma on the optical properties of a semiconductor. Here, we include the spin degree of freedom to model optical absorption of circularly polarized light by spin-polarized bulk GaAs. Our model is easy to implement and does not require elaborate numerics, since it is based on the closed-form analytical pair-equation formula that is valid in 3d. The efficacy of our approach is demonstrated by a comparison with recent experimental data.

A simple and rapid method for quantification of hapten specific antibodies

A sensitive and simple method for quantification of antibodies against small molecules is described using DNP-lysozyme as the enzyme conjugate. The anti-DNP antiserum was raised against DNP-bovin serum albumin conjugate. Anti-DNP antibody or its monovalent fragment (Fab) reduced the enzyme activity of DNP-lysozyme conjugate in a concentration-dependent manner. The inhibition of enzyme activity is a specific measure of the antibody and Fab content of the sample. The specificity of the reaction was assessed by reduction of antibody-induced inhibition by DNP-lysine. The ability of DNP-lysine to reduce the antibody-induced inhibition of DNP-lysozyme activity also makes possible a sensitive assay for DNP-lysine.

Shelter from the storm? Use and misuse of coastal vegetation bioshields for managing natural disasters

Vegetated coastal ecosystems provide goods and services to billions of people. In the aftermath of a series of recent natural disasters, including the Indian Ocean Tsunami, Hurricane Katrina and Cyclone Nargis, coastal vegetation has been widely promoted for the purpose of reducing the impact of large storm surges and tsunami. In this paper, we review the use of coastal vegetation as a "bioshield" against these extreme events. Our objective is to alter bioshield policy and reduce the long-term negative consequences for biodiversity and human capital. We begin with an overview of the scientific literature, in particular focusing on studies published since the Indian Ocean Tsunami in 2004 and discuss the science of wave attenuation by vegetation. We then explore case studies from the Indian subcontinent and evaluate the detrimental impacts bioshield plantations can have upon native ecosystems, drawing a distinction between coastal restoration and the introduction of exotic species in inappropriate locations. Finally, we place bioshield policies into a political context, and outline a new direction for coastal vegetation policy and research.

Shelter from the storm? Use and misuse of coastal vegetation bioshields for managing natural disasters

Vegetated coastal ecosystems provide goods and services to billions of people.In the aftermath of a series of recent natural disasters, including the Indian Ocean Tsunami, Hurricane Katrina and Cyclone Nargis, coastal vegetation has been widely promoted for the purpose of reducing the impact of large storm surges and tsunami. In this paper, we review the use of coastal vegetation as a ``bioshield'' against these extreme events. Our objective is to alter bioshield policy and reduce the long-term negative consequences for biodiversity and human capital. We begin with an overview of the scientific literature, in particular focusing on studies published since the Indian Ocean Tsunami in 2004 and discuss the science of wave attenuation by vegetation. We then explore case studies from the Indian subcontinent and evaluate the detrimental impacts bioshield plantations can have upon native ecosystems, drawing a distinction between coastal restoration and the introduction of exotic species in inappropriate locations. Finally, we place bioshield policies into a political context, and outline a new direction for coastal vegetation policy and research.

Studies on non-specific interference due to serum in the avidin-biotin microELISA for monkey chorionic gonadotropin and a method for its elimination

A study has been carried out on the non-specific interference due to serum in the avidin biotin micro-ELISA for monkey chorionic gonadotropin. Results suggest that it is not due to any proteolytic activity in the serum, but immunoglobulin or associated factors interfering at the level of antigen-antibody interaction. This interference was eliminated by heating samples at 60°C for 30 min.

Antibodies raised against denatured DNA bind to double-stranded DNA

Antibodies raised against denatured DNA complexed with methylated bovine serum albumin have been reported to react with ssDNA but not with dsDNA. Using a highly sensitive avidin-biotin microELISA, we report that such antibodies also bind to dsDNA. Antibodies which reacted with ssDNA and dsDNA were found to be IgG type. The antibodies did not react with tRNA and rRNA. The binding of antibodies to dsDNA was partially inhibited dy individual deoxyribonucleotides. ssDNA as well as dsDNA inhibited the binding of antibodies to dsDNA. The binding of these antibodies to supercoiled and relaxed forms of pBR322 DNA was demonstrated by gel retardation assay. The cross-reaction with ssDNA was observed even after affinity purification on native DNA-cellulose. The antibodies were also shown to bind to poly(dA-dT)·poly(dA-dT)

Effect of La modification on antiferroelectricity and dielectric phase transition in sol-gel grown PbZrO3 thin films

Antiferroelectricity of sol-gel grown pure and La modified PbZrO3 thin films, with a maximum extent of 6 mol%, has been characterized by temperature dependent P-E hysteresis loops within the applied electric field of 60 MV/m. It has been seen that on extent of La modification electric field induced phase transformation can be altered and at 40 degrees C its maximum value has been observed at +/- 38 MV/m on 6 mol% modifications whereas the minimum value is +/- 22 MV/m on 1 mol%. On La modification the variation of electric field induced phase transformations at 40 degrees C has been correlated with the temperature of ntiferroelectric phase condensation on cooling. The critical electric fields for saturated P-E hysteresis loops have been defined from field dependent maximum polarizations and their variations on La modification show a similar trend as found in their dielectric phase transition temperatures. (C) 2010 Elsevier Ltd. All rights reserved.

Gas Sensing Characteristics of Superconducting Cuprates

Gas sensing characteristics of YBa2Cu3O7−δ, La2−x SrxCuO4, and Bi2Y1−xCaxSr2Cu2O8 have been examined. La2−x SrxCuO4 (x = 0.075), and Bi2YSr2Cu2O8 are found to show good sensitivity (≈10 ppm) to ethyl alcohol and such vapours.