Angle-resolved reflectance and surface plasmonics of the MAX phases

We investigate theoretically the optical response of bulk samples and thin films of the MAX phase materials, accounting for their large electrical anisotropy. We reveal the unusual behavior of the reflection and transmission spectra as a function of the incidence angle and predict the effect of the inverse total internal reflection. We also investigate the behavior of the surface plasmon modes in bulk samples and thin films and analyze the difference between MAX materials and conventional metals.     

同步荧光光谱法测定石油中的晕苯

用苯做溶剂对原油样品进行逐级稀释,恒波长同步荧光法对原油样品中晕苯进行定性、定量分析。分别从溶剂选择、波长差、狭缝宽度等参数对其测定的光谱条件进行优化。实验结果表明：用苯为溶剂、Δλ=6nm,狭缝宽度为2.5nm,为原油样品中晕苯的最佳测试条件。所建立方法测定晕苯的线性范围为0.5—100μg/mL,校准曲线的相关系数r大于0.99,相对标准偏差小于3%（n=5）。该法分析快速、准确,对石化工厂中对原油样品中晕苯的快速检测具有一定的应用价值。     

Electrical conductivity and permittivity of the one-dimensional superionic conductor LiCuVO<Subscript>4</Subscript>

The electrical conductivity σ^a and permittivities ?^a, ?^b, and ?^c of a LiCuVO₄ single crystal have been measured along the a, b, and c crystallographic axes, respectively, in the temperature range 300–390 K at a frequency of 10³ Hz. The temperature dependences σ(T) and ?(T) were found to be typical for superionics.     

Interference of coherent polariton beams in microcavities: polarization-controlled optical gates

We demonstrate, theoretically and experimentally, a polarization-controlled optical gate based on a degenerate polariton-polariton scattering process occurring in semiconductor microcavities. Because of the interference between coherent polaritons, this process is observed in the case of polaritons generated from two collinearly polarized coherent pump beams. On the contrary, if the beams are cross polarized, the scattering is suppressed.     

Interpreting early land management through compound specific stable isotope analyses of archaeological soils

Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd.     

Spatial coherence of polaritons in a 1D channel

We analyze time evolution of spatial coherence of a polariton ensemble in a quantum wire (1D channel) under constant uniform resonant pumping. Using the theoretical approach based on the Lindblad equation for a one-particle density matrix, which takes into account the polariton-phonon and excitonexciton interactions, we study the behavior of the first-order coherence function g ¹ for various pump intensities and temperatures in the range of 1–20 K. Bistability and hysteresis in the dependence of the first-order coherence function on the pump intensity is demonstrated.     

Non-Volatile Threshold Adaptive Transistors with Embedded RRAM

We propose a novel nonvolatile threshold adaptive transistor （TAT） for neuromorphic circuits. The threshold adaptive transistor is achieved by embedding a resistive random-access memory （RRAM） material stack between the gate electrode and gate dielectric. During operation, the embedded RRAM device is kept at a high resistance state, which makes it act as a nonvolatile capacitor. The threshold could be nonlinearly adjusted by the voltage pulses applied on the gate of the transistor. We quantitatively estimate the range of the capacitance variation of the RRAM device. The threshold voltage of the TAT is simulated and shows expected variation. The simulated output of an inverter using a TAT shows a nonlinear adaptive behavior.     

Electrical and thermoelectric properties of the SiC/Si biomorphic composite at high temperatures

The electrical resistivity ρ and the thermopower coefficient α of a SiC/Si biomorphic composite fabricated from a porous carbon matrix [prepared through pyrolysis of wood (white eucalyptus)] by infiltrating molten Si into the empty channels of the matrix were measured in the temperature ranges 100–950 and 100–750 K, respectively. Silicon reacts chemically with the carbon of the matrix to produce 3C-SiC, which, in combination with the excess Si unreacted with carbon, forms the SiC/Si biomorphic composite. The SiC/Si samples studied had a concentration of “excess” Si of ～30 vol % and a porosity of ～13–15 vol %. Measurements of ρ were carried out on samples cut either along (ρ_∥) or across (ρ_⊥) the tree growth direction, and α was measured on a sample cut along the tree growth direction.     

Spin depolarization and a metal-insulator transition in a two-dimensional system in zero magnetic field

The conditions for spontaneous spin polarization in a two-dimensional system in a zero magnetic field are considered in the case of a partial filling of the lower quantum-well subbands when the energy of exchange interaction of charge carriers exceeds their kinetic energy. The critical density above which the two-dimensional gas of charge carriers undergoes complete spin depolarization is determined in the Hartree-Fock approximation. It is assumed that this process can be due to a transition of the two-dimensional gas to a metallic state.     

Uniaxial exchange flows of two Bingham fluids in a cylindrical duct

Buoyancy driven flows of two Bingham fluids in an inclined ductare considered, providing a simplified model for many oilfieldcementing processes. The flows studied are near-uniaxial andstratified, with the heavy fluid moving down the incline, displacingthe lighter fluid upwards. Existence and uniqueness resultsare obtained for quite general flows and for those which satisfyan axial flow rate constraint. Parametric dependence of thesolutions on the axial pressure gradient is studied. Flows whichsatisfy a zero net axial flow constraint result from an axialpressure gradient which minimizes the viscous dissipation, butnot the plastic dissipation. A regularization method is usedto compute solutions to these problems for (more or less) arbitraryfluid-fluid interfaces and duct-cross sections. Examples relatedto a number of practical applications are presented.