Optical-phonon transport and localization in periodic and Fibonacci polar-semiconductor superlattices

A transfer-matrix formalism is employed to study optical-phonon transport in a macroscopic continuum model for both periodic and Fibonacci polar-semiconductor superlattices. A phonon bandgap with subband structures is obtained for the periodic superlattices. However, in the Fibonacci superlattices, there is a spectrum trifurcation and self-similarity. The LO phonon localization length is calculated from which we confirm the existence of complete exponential localization of LO phonons.     

The microwave spectrum of HCN dimer

The microwave spectrum of the hydrogen-bonded HCN dimer was observed over the range 28–93 GHz. Improved values of the spectral parameters B = 1788.214(16) MHz, D_J = 2.582(16) kHz were obtained. The electric dipole moment was found to be 6.0(15) D (2.0(5) × 10^?29 cm).     

Microwave spectrum and structure of cyanamide: Semirigid bender treatment

An extensive study of the microwave spectrum of cyanamide has been undertaken, the analysis being based in part on semirigidbender calculations by the methods of Bunker and Szalay. Inversion lines of NH₂CN, $\text{K}{}_{\mathrm{?1}}\text{= 2}{}^{\mathrm{a}}\text{Q}$ branches and a number of vibrational satellites of the J = 2?1 transition were observed. A two-vibrational-state Hamiltonian was used to fit simultaneously the 0⁺ and 0^? microwave data and yielded rotational constants X, Y, Z, D_J, D_JK, d₁, H_JK as well as the inversion splitting and the μ_yz-connecting matrix element. Vibrational satellite data of seven isotopic species and infrared frequencies of NH₂CN were included in the semirigid bender calculations: The NCN spine is nonlinear by ca. 5° in the equilibrium structure of the molecule. Also, $\text{r}{}_{\mathrm{<mtext>NH</mtext>}}\text{A}\text{?}\text{= 0.9994 + 0.0144?}{}^2$; <HNH/2 = 60.39° ? 0.1134?²; $\text{r}{}_{\mathrm{<mtext>NC</mtext>}}\text{A}\text{?}\text{= 1.3301 + 0.0327?}{}^2$ (? is the inversion angle in rad); $\text{r}{}_{\mathrm{<mtext>CN</mtext>}}\text{= 1.1645}\text{A}\text{?}$ fixed. The inclusion of the NC bond flexing was necessary in order to reproduce the observed vibrational satellite patterns of NH₂CN, NHDCN, and ND₂CN. The barrier to inversion of the amino group is 510 ± 6 cm^?1 with minima at ±45.0 ±0.2°. The inversion dipole moment is 0.91 ± 0.02 Debye.     

The Initial Value Problem in Relativistic Plasma

The Landau problem in relativistic plasma is considered in detail. It is shown how all modes in the plasma arise through proper treatment of the inverse Laplace transforms without imposition of any external conditions. A correct derivation of the asymptotic behavior of the electric field is included and estimates of the contribution of more rapidly decaying Landau modes are made analytically and are compared with numerical computations.     

A note on the acoustic sensitivity of microphone windscreens

Measurements have been made of the changes in the sensitivity of an outdoor microphone system when it is mounted with a B and K windscreen, type U A 0082. The measurements were made using both dry and wet windscreens in order to determine the magnitude of the change in system sensitivity for measurement conditions consistent with dry and wet weather, respectively.It is concluded that the standard practice of neglecting the effect of the windscreen on the system sensitivity will not appreciably affect the accuracy of traffic-noise measurement.     

Langmuir Wave Phase Velocity in Unneutralized Beams

We investigate the dispersion relation for long wavelength slow Langmuir waves in a relativistic particle beam propagating along a strong magnetic guide field in an evacuated metallic waveguide. For a large class of beam radial profiles, wave phase velocity drops to zero with infinite slope as beam current approaches the space-charge limit. This result is of importance to certain collective ion acceleration proposals.     

交通产业链上企业工程项目成本控制的影响因素研究

一些企业以轨道交通产业为纽带形成了交通产业链,轨道交通产业链上的企业要注重对相关工程项目实施全过程中的成本控制.从产业链的视角出发,围绕财务指标、内部业务流程指标、客户指标、学习与成长能力指标这4个方面,构建了评价指标体系和成本控制指标体系.运用层次分析法和模糊综合评价法进行评价和分析,找出了影响轨道交通产业链上企业工程项目成本控制的主要因素.研究表明,有55%的人认为财务指标、内部业务流程指标、客户指标、学习与成长能力指标这4个因素对轨道交通工程项目成本控制的影响较大.     

Formula for the absorption coefficient for multi-wall nanotubes

We present a formalism for calculating the absorption coefficient of a pair of coaxial tubules. A spatially nonlocal, dynamical self-consistent field theory is obtained by calculating the electrostatic potential produced by the charge density fluctuations as well as the external electric field. There are peaks in the absorption spectrum arising from plasma excitations corresponding either to plasmon or particle-hole modes. In this Letter, we numerically calculate the plasmon contribution to the absorption spectrum when an external electric field is applied. The number of peaks depends on the radius of the inner as well as outer tubule. The height of each peak is determined by the plasmon wavelength and energy. For a chosen wave number, the most energetic plasmon has the highest peak corresponding to the largest oscillator strength of the excited modes. Some of the low-frequency plasmon modes have such weak coupling to an external electric field that they are not seen on the same scale as the modes with larger energy of excitation. We plot the peak positions of the plasmon excitations for a pair of coaxial tubules. The coupled modes on the two tubules are split by the Coulomb interaction. The energies of the two highest plasmon branches increase with the radius of the outer tubule. On the contrary, the lowest modes decrease in energy as this radius is increased. No effects due to inter-tubule hopping are included in these calculations.     

Millimetre wave spectroscopy of PANHs: phenanthridine

The pure rotational spectrum of phenanthridine (C(13)H(9)N), a small polycyclic aromatic nitrogen heterocycle (PANH), has been measured from 48 to 85 GHz employing Stark modulated millimetre wave absorption spectroscopy of a supersonic rotationally cold molecular beam. Initial survey search scans were guided by rotational constants obtained through quantum chemical calculations performed at the B3LYP/cc-pVTZ level of theory. Close agreement--to well within 1%--is found between the calculated equilibrium and experimentally derived ground state rotational constants. From the moments of inertia a substantial negative inertial defect of Delta = -0.4688(44) amu Angstroms(2) is obtained which can be explained by the presence of several energetically low-lying out-of-plane vibrational modes. Corresponding density functional theory calculations of harmonic fundamental frequencies indeed yield four such low frequency modes with values as low as 96 cm(-1). The data presented here will also be useful for deep radio astronomical searches for PANHs employing large radio telescopes.     

Microfluidic systems to examine intercellular coupling of pairs of cardiac myocytes

In this paper we describe a microfluidic environment that enables us to explore cell-to-cell signalling between longitudinally linked primary heart cells. We have chosen to use pairs (or doublets) of cardiac myocyte as a model system, not only because of the importance of cell-cell signalling in the study of heart disease but also because the single cardiomyocytes are both mechanically and electrically active and their synchronous activation due to the intercellular coupling within the doublet can be readily monitored on optical and electrical recordings. Such doublets have specialised intercellular contact structures in the form of the intercalated discs, comprising the adhesive junction (fascia adherens and macula adherens or desmosome) and the connecting junction (known as gap junction). The latter structure enables adjacent heart cells to share ions, second messengers and small metabolites (<1 kDa) between them and thus provides the structural basis for the synchronous (syncytical) behaviour of connected cardiomyocytes. Using the unique environment provided by the microfluidic system, described in this paper, we explore the local ionic conditions that enable the propagation of Ca(2+) waves between two heart cells. We observe that the ability of intracellular Ca(2+) waves to traverse the intercalated discs is dependent on the relative concentrations of diastolic Ca(2+) in the two adjacent cells. These experiments rely upon our ability to independently control both the electrical stimulation of each of the cells (using integrated microelectrodes) and to rapidly change (or switch) the local concentrations of ions and drugs in the extracellular buffer within the microfluidic channel (using a nanopipetting system). Using this platform, it is also possible to make simultaneous optical recordings (including fluorescence and cell contraction) to explore the effect of drugs on one or both cells, within the doublet.