Current-induced Kerr rotation spectra and reflectivity spectra of (Ga,Mn)As and p-GaAs are measured in the absence of the magnetic field via magneto-optic Kerr effect around the energy gap. The dependences of the Kerr rotation and the reflectivity on the laser wavelength show Lorentzian profile. The Kerr rotation depends linearly on the current, and the reflectivity depends linearly on the square of the current. The Kerr rotation of p-GaAs is much weaker than that of the (Ga,Mn)As, which indicates that the doping of Mn enhances the current-induced spin polarization. The dependences of the Kerr rotation and the reflectivity on temperature are also measured, both showing red shifts of their Lorentzian peaks, a familiar behavior as the absorption edge of GaAs. In addition, we observe the dependence of the Kerr signal on the polarizational direction of the incident beam.

: A microwave-modulated reflectance spectroscopy (MMRS) measurement system was constructed. This MMRS technique was used to identify a transition from holes in valence band to electrons in the ground subband (GS) of the two-dimensional electron system (2DES) formed in a GaAs/AlGaAs heterostructure sample. The temperature (T) dependence of the MMRS shows a blue shift of the energy gap with increasing T, while the magnetic field (B) dependence of the MMRS shows a red shift of the energy gap with increasing B. Both phenomena are attributed to the band-filling effect of holes in valence band in the GaAs/AlGaAs heterostructure. A theoretical simulation based on Kramers-Kronig relation was also presented which was similar with the experimental data.

Time-resolved Kerr rotation spectroscopy is used to determine the sign of the g factor of carriers in a semiconductor material, with the help of a rotatable magnetic field in the plane of the sample. The spin precession signal of carriers at a fixed time delay is measured as a function of the orientation of the magnetic field with a fixed strength B. The signal has a sine-like form and its phase determines the sign of the g factor of carriers. As a natural extension of previous methods to measure the (time-resolved) photoluminescence or time-resolved Kerr rotation signal as a function of the magnetic field strength with a fixed orientation, such a method gives the correct sign of the g factor of electrons in GaAs. Furthermore, the sign of carriers in a (Ga, Mn) As magnetic semiconductor is also found to be negative.

A time-resolved Kerr rotation system with a rotatable in-plane magnetic field has been constructed to study anisotropic spin relaxation of electrons in semiconductors. A permanent magnet magic ring is placed on top of a motor-driven rotation stage (RS) to create the rotatable in-plane magnetic field. The RS is placed on a second translation stage to vary the local magnetic field around a sample. The in-plane magnetic field in such a system varies from 0.05 to 0.95 T, with full-round 360° rotatablity, thus offering a convenient and low-cost way to study the anisotropy of spin dynamics in semiconductors. Its performance was demonstrated via measurement of the anisotropy of the spin dephasing time (SDT) of electrons in a two-dimensional electron system embedded in a GaAs/Al(0.35)Ga(0.65)As heterostructure. The SDT with B∥[110] was observed to be 10% larger than that with B∥[110], consistent with the results of others, which was measured via rotating sample.

Cluster, correlation, and multivariate regression analyses were used to rationalize the effects of grain composition, starch fine structure, and leaching characteristics on cooked rice texture (hardness and stickiness). The head rice grain composition of 23 U.S. long-grain cultivars was evaluated in terms of apparent amylose content, crude protein, and surface lipids. Starch samples were prepared by extraction with dilute alkali and amylopectin fine structure was characterized by high-performance anion-exchange chromatography with pulsed amperometric detection. Hardness and stickiness of head rice samples cooked in optimum water were measured with a texture analyzer. The amylose amylopectin ratio (AAR) of the material that leached out of the grains on cooking was evaluated by high-performance size-exclusion chromatography (HPSEC). Simple correlation and multivariate linear regression analyses pointed to AAR as the main indicator of cooked rice hardness and stickiness. Cluster analysis showed that the leached starch from soft-cooking, high-amylose cultivars (e.g., Jodon and L-202) generally had a higher proportion of amylopectin than amylose (AAR<1). In contrast, dry-cooking, high-amylose cultivars (e.g., Newrex and L-205) leached out starch with a higher proportion of amylose than amylopectin (AAR>1) during cooking. The amount of leached materials itself was also higher for the soft-cooking cultivars than the dry-cooking counterparts. Cultivar differences in leaching characteristics were attributed to variations in apparent amylose content, crude protein, and amylopectin chain-length distribution.

Chemometric tests were carried out to better understand the multidimensional facet of starch fine structure-relationship concerning gelatinization and pasting properties. With Ward's hierarchical cluster analysis 20 long-grain rice starch samples were sorted out into three clusters based on similarities in functional properties, particularly, paste peak (PV) and final viscosity (FV). The three clusters (arbitrarily named Clusters A, B, and C) exhibited a pasting profile trend of PVFV, respectively. Cluster A samples were also lower in peak temperature, range and enthalpy of gelatinization, and swelling power. These attributes were associated with higher amylose content (AM), beta-amylolysis limit, and percentage of B1 chains (DP13-24), but lower amylopectin weight-average molar mass (M-w) and percentage of A chains (DP6-12). A 5-variable linear discriminant function correctly predicted 85% of the Ward's cluster membership of the individual cultivars. The discriminant function included the variables A, B1, and B2 (DP25-36) chains, average chain length (ACL), and gyration radius (R-z). Fine structure variance was fully explained by a total of nine principal components, with the first three components cumulatively accounting for 74%. The leading variables included in the three rotated components pertained to amylopectin chain length distribution (A, B2, and B3+ or DP >= 37 chains, and ACL) and amylopectin molar mass (M-w, R-z, and polydispersity). AM and M-w were loaded most frequently in the 4-variable, best-fit linear regression models for predicting gelatinization and pasting properties. A combination of at least two fine structure variables controls the functionality of rice starch.

We report experimental results of the effect of Ka-band microwave on the spin dynamics of electrons in a two-dimensional electron system (2DES) in a GaAs/Al0.35Ga0.65As heterostructure via time-resolved Kerr rotation measurements. While the microwave reduces the transverse spin lifetime of electrons in the bulk GaAs, it significantly increases that in the 2DES, from 745 to 1213 ps, when its frequency is close to the Zeeman splitting of the electrons in the magnetic field. Such a microwave-enhanced spin lifetime is ascribed to the microwave-induced electron scattering which leads to a “motional narrowing” of spins via D’yakonov–Perel’ mechanism.