Optical properties of (TTF) (TCNQ) in the visible and infrared

Polarized optical studies of single crystals and polycrystalline compactions of the organic salt (TTF) (TCNQ) are reported. Metallic behavior is observed for light polarized parallel to the conducting axis. The plasma edge occurs at 1.4 μm with metallic reflection observed in the i.r. The plasma frequency $\text{(}\text{h}\text{?}\text{ω}{}_{\mathrm{p}}\text{=}\text{1.2eV}\text{)}$ leads to an optical effective mass $\text{m}{}^1\text{=}\text{5}\text{m}{}_{\mathrm{e}}$ implying a tight-binding transfer integral of 0.1 eV in agreement with estimates obtained from other measurements. The scattering time, τ, as determined from the shape of the reflectance curve, yields a room temperature metallic conductivity of 10³(Ω-cm)^-1 in good agreement with the measured d.c. value. An estimate of the dimensionless electron-phonon coupling constant is obtained from the measured value of τ,λ_ph?1.3. The strong anisotropic absorption in the visible portion of the spectrum is attributed to interband transitions.     

Charge transport at mid-gap in trans-(CH)x: An electrochemical study

Electrochemical studies demonstrate that ～300 ppm of charge (equal to the number of neutral solitons in undoped $\text{trans}$-(CH)_x) is removed at mid-gap. These charges are transported through the polyacetylene electrode via hopping among states at the center of the energy gap, in agreement with Kivelson's theory. From analysis of the data, we have been able to determine the soliton creation energy, E_s ? 0.5eV, which is in good agreement with the theoretical value, E_s = (2/π)Δ.     

Anomalous electrical properties of linear chain mercury compounds

The electrical resistivity of Hg_2.86AsF₆ has been studied as a function of temperature. At room temperature, the resistivity along the chain direction is 10^?4 Ω-cm with an anisotropy of about 10². This incommensurate linear chain system remains metallic at low temperatures with resistance ratio ?_ab(300 K)/ ?_ab(1.4 K) ? 3000 and still increasing with no apparent sign of residual resistivity. A large anisotropic magnetic field dependence of the resistivity is observed below 30 K. Near 4 K, the c-axis resistance drops abruptly more than three orders of magnitude, apparently to zero, while ?_ab is continuous. The c-axis transition is suppressed in a small magnetic field.     

Constraints on nucleon decay via invisible modes from the Sudbury Neutrino Observatory

Data from the Sudbury Neutrino Observatory have been used to constrain the lifetime for nucleon decay to "invisible" modes, such as n-->3nu. The analysis was based on a search for gamma rays from the deexcitation of the residual nucleus that would result from the disappearance of either a proton or neutron from 16O. A limit of tau(inv)>2 x 10(29) yr is obtained at 90% confidence for either neutron- or proton-decay modes. This is about an order of magnitude more stringent than previous constraints on invisible proton-decay modes and 400 times more stringent than similar neutron modes.     

High sensitivity search for nu;e's from the sun and other sources at KamLAND

Data corresponding to a KamLAND detector exposure of 0.28 kton yr has been used to search for nu;(e)'s in the energy range 8.3相似文献   

Numerical continuation of degenerate homoclinic orbits in planar systems

In this paper we develop numerical algorithms for the continuationof degenerate homoclinic connections in planar systems. We considerthe case where the equilibrium point has zero trace and twocases of higher-order degeneracies. The method we propose isable to continue homoclinic connections of order up to codimension-four.Application of the algorithm to four examples supports its validityand demonstrates its usefulness.     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

Detection of telomerase activity in high concentration of cell lysates using primer-modified gold nanoparticles

Although the telomeric repeat amplification protocol (TRAP) has served as a powerful assay for detecting telomerase activity, its use has been significantly limited when performed directly in complex, interferant-laced samples. In this work, we report a modification of the TRAP assay that allows the detection of high-fidelity amplification of telomerase products directly from concentrated cell lysates. Briefly, we covalently attached 12 nm gold nanoparticles (AuNPs) to the telomere strand (TS) primer, which is used as a substrate for telomerase elongation. These TS-modified AuNPs significantly reduce polymerase chain reaction (PCR) artifacts (such as primer dimers) and improve the yield of amplified telomerase products relative to the traditional TRAP assay when amplification is performed in concentrated cell lysates. Specifically, because the TS-modified AuNPs eliminate most of the primer-dimer artifacts normally visible at the same position as the shortest amplified telomerase PCR product apparent on agarose gels, the AuNP-modified TRAP assay exhibits excellent sensitivity. Consequently, we observed a 10-fold increase in sensitivity for cancer cells diluted 1000-fold with somatic cells. It thus appears that the use of AuNP-modified primers significantly improves the sensitivity and specificity of the traditional TRAP assay and may be an effective method by which PCR can be performed directly in concentrated cell lysates.