Structural characterization of opal-based photonic crystals in the visible range

For structural characterization of periodic three-dimensional systems with submicron-scale lattice parameters (optical photonic crystals), is analogous to the use of visible light of x-rays. It is shown that specular reflectance and transmittance spectra of opal do indeed yield information on the lattice period and structural perfection of photonic crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 648–650 (April 1998)     

Heat transport over nonmagnetic lithium chains in LiCuVO<Subscript>4</Subscript>, a new one-dimensional superionic conductor

The thermal conductivity of three single-crystal samples of the quasi-one-dimensional spin system of LiCuVO₄ with different concentrations of defects (primarily, vacancies on the lithium sublattice) was measured along the crystallographic a axis (along the nonmagnetic lithium chains) in the temperature interval 5–300 K. An increase in thermal conductivity from that of the crystal lattice was revealed for T>150–200 K. This increase can be accounted for only by assuming LiCuVO₄ to be a superionic conductor. This assumption was confirmed by measuring its electrical conductivity in the temperature interval 300–500 K. Li⁺ ions move over vacancies on the lithium sublattice (conducting channels) and act as charge carriers in LiCuVO₄. It is shown that LiCuVO₄ is a fairly good superionic conductor with application potential.     

Ensemble of asymmetric quantum dots in a cavity as a terahertz laser source

The possibility of establishing a terahertz laser generation at a transition between the dressed states formed by the interaction of an intense optical field with an ensemble of asymmetric quantum dots (QDs) in a high-Q terahertz cavity is discussed. It has been shown that the population inversion in the system of dressed states is achieved owing to spontaneous relaxation of the excited state of the QDs. The set of Maxwell–Bloch equations for the difference between dressed-state populations, polarization, and population of the cavity mode has been analyzed in the mean-field approximation. The lasing conditions have been clarified and the possibility of controlling the terahertz radiation intensity has been studied, including the case of an inhomogeneously broadened ensemble of QDs.     

Rotons in a hybrid Bose-Fermi system

We calculate the spectrum of elementary excitations in a two-dimensional exciton condensate in the vicinity of a two-dimensional electron gas. We show that attraction of excitons due to their scattering with free electrons may lead to formation of a roton minimum. The energy of this minimum may go below the ground state energy which manifests breaking of the superfluidity. The Berezinsky-Kosterlitz-Thouless phase transition temperature decreases due to the exciton-exciton attraction mediated by electrons.     

泥沙输运模拟综述——现状及其发展趋势

随着流体力学中数值方法的飞速发展,计算模型已经成为研究流体运动,泥沙输运和不同环境(诸如河流,湖泊及沿海地区)中相应污染物归趋过程等方面非常有吸引力的工具,在过去的30多年里,发展了许多计算水动力学/泥沙输运模型.文章追溯当前具有代表性的(一维、二维、三维)模型的发展历程,描述他们各自的特点,优势及局限,力图作为对模型方面感兴趣读者的第一指南,同时也为大家讨论模型的局限性,未来的发展趋势和研究需求方面搭建一个平台.给出了模型的表达,时空特性,水动力学和沉积物的耦合方式,处理非恒定流,推移质和悬移质,泥沙交换过程,泥沙类型(粘性或非粘性)及非均匀泥沙输运的能力.总结了不同模型的应用实例,读者可以运用这些例子作为研究模型设置,模型率定及模型验证的参考.给出了选择泥沙输运模型应遵循的原则,模型输入及率定方面存在的问题及改进的途径.探讨了现有水动力学/泥沙输运模型在处理复杂湍流,泥沙携带,流动与输沙耦合,非均匀泥沙,离散和扩散系数,河岸来沙处理等方面的局限性及改进的方向.最后,对基于多相流思想的泥沙输运模型及其它一些交叉性问题作了评述与展望.     

Entangled photon pairs produced by a quantum dot strongly coupled to a microcavity

We show theoretically that entangled photon pairs can be produced on demand through the biexciton decay of a quantum dot strongly coupled to the modes of a photonic crystal. The strong coupling allows us to tune the energy of the mixed exciton-photon (polariton) eigenmodes and to overcome the natural splitting existing between the exciton states coupled with different linear polarizations of light. Polariton states are moreover well protected against dephasing due to their lifetime of ten to a hundred times shorter than that of a bare exciton. Our analysis shows that the scheme proposed is achievable with the present technology.     

Polariton spin beats in semiconductor quantum well microcavities

Time-resolved Kerr (Faraday) rotation experiments allow for the observation of polariton spin beats in both InGaAs and CdMnTe quantum well (QW) microcavities. The existence of these beats is an unambiguous manifestation of the coherent energy exchange between exciton and photon components of polariton states created by a circularly polarized and spectrally wide femtosecond laser pulse. The polariton states are also shown to be split into a linearly polarized doublet. This splitting is responsible for the polarization transfer between linearly and circularly polarized states. In a highest-quality sample, the resulting spin dynamics could be detected.     

Possible molecular effect related to the reception of low-intensity IR radiation: Role of Src-kinase

The patch-clamp technique has been used to demonstrate that low-intensity IR irradiation affects the effective charge of the activation gating system of slow sodium channels in the nociceptive neuron membrane. IR photons are absorbed by ATP molecules bound to Na⁺,K⁺-ATPase at their hydrolysis site. Na⁺,K⁺-ATPase is a transducer of signal that is further delivered to slow sodium channels and cell genome. It is demonstrated that the irradiation does not modulate the response of a sensory neuron in the presence of PP2, an inhibitor of Src-kinase. The results show that Src-kinase is a series unit involved in the intracellular cascade processes triggered by low-intensity radiation of CO₂ laser.     

Linear expansion coefficient of the SiC/Si biomorphic composite

In the temperature range 100–650 K, the linear expansion coefficient β was measured for the SiC/Si biomorphic composite, a new cellular ecoceramic fabricated from a porous cellular carbon matrix prepared through pyrolysis of wood (white eucalyptus) in an argon ambient with subsequent infiltration of molten Si into the channels of the matrix and the formation of 3C-SiC. The SiC/Si samples studied had an “excess” ～30% volume concentration of Si and a porosity of ～13–15%. The measurements were conducted on samples cut along (β_∥) and across (β_⊥) the tree growth direction. The measured values of β(T) of SiC/Si are compared with literature data available for the linear expansion coefficients of Si and 3C-SiC.