Photon tunneling in a frustrated total internal reflection structure with a lossy indefinite metamaterial barrier

We study the phenomenon of photon tunneling through a frustrated total internal reflection structure with a dispersive lossy indefinite metamaterial barrier. The tunneling coefficient, lateral shift, and tunneling time for different incident light waves through the barrier are obtained by employing the stationary-phase approximation. The properties of tunneling time and lateral shift are discussed for different metamaterial parameters. It is shown that negative lateral shift and tunneling time can appear in the cutoff and always cutoff metamaterials. The lateral shift can be enhanced by adjusting the light frequency, the barrier thickness, and the permittivity or permeability of the indefinite metamaterial. In addition, it is found that the lateral shift can be resonantly amplified due to the weak loss of the indefinite metamaterial slab. The Hartman effects of the lateral shift and tunneling time are also demonstrated. PACS 42.50.Ct; 42.25.Bs; 73.43.Jn; 73.40.Gk; 42.70.Qs     

Influence of nonlinear dispersion on modulation instability of coherent and partially coherent ultrashort pulses in metamaterials

The combination of dispersive magnetic permeability with nonlinear polarization leads to a series of nonlinear dispersion terms in the propagation equations for ultrashort pulses in metamaterials. Here we present an investigation of modulation instability (MI) of both coherent and partially coherent ultrashort pulses in metamaterials to identify the role of nonlinear dispersion in pulse propagation. The Wigner–Moyal equation for partially coherent ultrashort pulses and the nonlinear dispersion relation for MI in metamaterials are derived. Combining the standard MI theory with the unique properties of the metamaterial, the influence of the controllable first-order nonlinear dispersion, namely self-steepening, and the second-order nonlinear dispersion on both coherent and partially coherent MI, in both negative-index and positive-index regions of the metamaterial for all physically possible cases is analyzed in detail. For the first time to our knowledge, we demonstrate that the role of the second-order nonlinear dispersion in MI is equivalent to that of group-velocity dispersion (GVD) to some extent, and thus due to the role of the second-order nonlinear dispersion, MI may appear in the otherwise impossible cases, such as in the normal GVD regime. PACS 42.25.Kb; 42.65.Sf; 78.20.Ci     

Characterization of MoO<Subscript>3</Subscript> nanobelt cathode for Li-battery applications

Molybdenum trioxide (MoO₃) and PPy_xMoO₃ (x=0.5 and 1) nanobelts were obtained by the simple hydrothermal process from MoO₃ sol. The morphology and structure of the samples were characterized using X-ray diffractometry (XRD), Fourier transformation infrared spectroscopy (FTIR), Raman spectra, SEM and AFM. The results show that the H atoms in polypyrrole are H-bonded with the O atoms in the Mo=O bonds of MoO₃ nanobelts. Using the electrolyte, we fabricated electrochemical cells with a configuration of Li/(LiPF₆+EC+DMC)/(MoO₃+acetyleneblack+PTFE) and studied discharge profiles. PACS 81.07.BC; 81.05.Je; 82.47.Aa; 82.45.Fk; 82.45.Gj     

Nd0.67Sr0.33MnOy(Y＜3.0)中的自旋相关电致电阻效应

用固相反应法制备系列Nd0.67Sr0.33MnOy(y=3.00-2.80)多晶样品.样品输运性质表现出自旋相关电致电阻特征.对氧含量等于化学计量样品,在测量温度范围内电阻不随负载电流变化,I-V曲线符合线性欧姆定律.对氧含量低于化学计量样品,当高于某一特征温度时,电阻变化符合线性欧姆定律;但低于这一特征温度时,电阻大小与负载电流有关,I-V曲线偏离线性规律;在绝缘体-导体相转变点附近,样品电阻随负载电流增大而迅速减小,表现出巨大电致电阻效应.对于y=2.85样品,当电流从1μA增加到30μA时,电致电阻接近80%.这种自旋相关的电致电阻行为与氧含量和界面有很大关系.     

The aggregation behavior of O-carboxymethylchitosan in dilute aqueous solution

O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.     

Negative differential conductance and hot phonons in suspended nanotube molecular wires

Freely suspended metallic single-walled carbon nanotubes (SWNTs) exhibit reduced current carrying ability compared to those lying on substrates, and striking negative differential conductance at low electric fields. Theoretical analysis reveals significant self-heating effects including electron scattering by hot nonequilibrium optical phonons. Electron transport characteristics under strong self-heating are exploited for the first time to probe the thermal conductivity of individual SWNTs (approximately 3600 W m-1 K-1 at T=300 K) up to approximately 700 K, and reveal a 1/T dependence expected for umklapp phonon scattering at high temperatures.     

Hydrogenation of single-walled carbon nanotubes

Towards the development of a useful mechanism for hydrogen storage, we have studied the hydrogenation of single-walled carbon nanotubes with atomic hydrogen using core-level photoelectron spectroscopy and x-ray absorption spectroscopy. We find that atomic hydrogen creates C-H bonds with the carbon atoms in the nanotube walls, and such C-H bonds can be completely broken by heating to 600 degrees C. We demonstrate approximately 65 +/- 15 at % hydrogenation of carbon atoms in the single-walled carbon nanotubes, which is equivalent to 5.1 +/- 1.2 wt % hydrogen capacity. We also show that the hydrogenation is a reversible process.     

Quantum critical scaling and the origin of non-fermi-liquid behavior in Sc1-xUxPd3

We used inelastic neutron scattering to study magnetic excitations of Sc1-xUxPd3 for U concentrations (x=0.25, 0.35) near the spin glass quantum critical point (QCP). The excitations are spatially incoherent, broad in energy (E=variant Planck's over 2piomega), and follow omega/T scaling at all wave vectors investigated. Since similar omega/T scaling has been observed for UCu5-xPdx and CeCu6-xAux near the antiferromagnetic QCP, we argue that the observed non-Fermi-liquid behavior in these f-electron materials arises from the critical phenomena near a T=0 K phase transition, irrespective of the nature of the transition.     

Two-dimensional cross-spectral correlation analysis and its application to time-resolved Fourier transform emission spectra of transient radicals

A spectral analysis method, based on the generalized two-dimensional (2D) vibrational spectra correlation analysis, is developed for deciphering the correlation among the spectral peaks of two different spectra. This 2D cross-spectral correlation (2DCSC) analysis is aimed at revealing the vibrational features associated with a common species in two spectra, each obtained from a system containing multiple species with at least one common species. The cross-spectral correlation is based on the premise that the spectral features of the same species should have the same time and frequency responses toward similar perturbations. The effectiveness of the cross-spectral correlation analysis is first illustrated with model systems, with spectral peaks decaying linearly or exponentially with time, before being applied to analyzing time-resolved emission spectra obtained, by a Fourier transform IR spectrometer, for samples consisting of the vibrationally excited transient cyanooxomethyl radical (OCCN). 2DCSC among the three different sets of time-resolved spectra collected following the photodissociation of three different precursor molecules of OCCN, respectively, allows the identification of the CN and CO stretching modes of this radical.     

Role of ion pairing in anionic additive effects on the separation of cationic drugs in reversed-phase liquid chromatography

Mobile phase additives can significantly affect the separation of cationic drugs in reversed-phase liquid chromatography (RPLC). Although there are many applications for anionic additives in RPLC separations, the retention mechanism of basic drugs in the presence of inorganic and highly hydrophilic anionic species in the mobile phase is not at all well understood. Two major retention mechanisms by which anionic additives can influence the retention of cations are: (1) ion pair formation in the mobile phase with subsequent retention of the neutral ion pair; (2) pre-sorption of anionic additives on the stationary phase followed by "dynamic ion-exchange" or "electrostatic interaction" with the analytes. Because the use of ion pair chromatography in the separation of proteins, peptides, and basic drugs is rapidly increasing, understanding the retention mechanism involved is becoming more important, especially for the smaller commonly used hydrophilic anionic additives (e.g., formate HCOO, chloride Cl-, trifluoroacetate CF3COO-, perchlorate ClO4-, and hexafluorophosphate PF6-). In this work, we compared various anionic additives in light of their effects on the retention of basic drugs. As did many others we found that the addition of anionic additives (Cl-, CF3COO-, ClO4-, PF6-) profoundly influences the retention of basic drugs. In order to explain the data and differentiate the mechanisms by which the anionic additives perturb the chromatography, we used ion pair formation constants independently measured by capillary electrophoresis (CE) under the mobile phase conditions (pH, solvent composition) identical to those used in chromatography. Agreement between the predicted and experimental chromatographic data under various conditions was evaluated. Under specific circumstances (e.g., pH, stationary phase, and nature of anionic additive), we conclude that the ion pair mechanism is more important than the dynamic ion-exchange and at other conditions it remains a significant contribution.