On the crack-tip stress singularity of interfacial cracks in transversely isotropic piezoelectric bimaterials

In this paper, characteristics of the interface crack-tip stress and electric displacement fields in transversely isotropic piezoelectric bimaterials are studied. The authors have proven, within the framework of the generalized Stroh formalism for piezoelectric bimaterials, that there is no coexistence of the parameters (oscillating) and κ (non-oscillating) in the interface crack-tip generalized stress field for all transversely isotropic piezoelectric bimaterials. This leads to the classification of piezoelectric bimaterials into one group that exhibits the oscillating property in the interface crack-tip generalized stress field and the other that does not. Fifteen (15) pair-combinations of six (6) piezoelectric materials PZT-4, PZT-5H, PZT-6B, PZT-7A, P-7, and BaTiO₃, which are commonly used in practice, are numerically analyzed in this study, and the results backup the above theoretical conclusions. Moreover, the associated eigenvectors for such material systems (with either =0 or κ=0) are also obtained numerically, and the result show that there still exist four linear independent associate eigenvectors for each bimaterial.     

Bulk heterojunction solar cells using thieno[3,4-c]pyrrole-4,6-dione and dithieno[3,2-b:2',3'-d]silole copolymer with a power conversion efficiency of 7.3%

A new alternating copolymer of dithienosilole and thienopyrrole-4,6-dione (PDTSTPD) possesses both a low optical bandgap (1.73 eV) and a deep highest occupied molecular orbital energy level (5.57 eV). The introduction of branched alkyl chains to the dithienosilole unit was found to be critical for the improvement of the polymer solubility. When blended with PC(71)BM, PDTSTPD exhibited a power conversion efficiency of 7.3% on the photovoltaic devices with an active area of 1 cm(2).     

Through-bond interactions and the localization of excited-state dynamics

The influence of through-bond interactions on nonadiabatic excited-state dynamics is investigated by time-resolved photoelectron spectroscopy (TRPES) and ab initio computation. We compare the dynamics of cyclohexa-1,4-diene, which exhibits a through-bond interaction known as homoconjugation (the electronic correlation between nonconjugated double bonds), with the nonconjugated cyclohexene. Each molecule was initially excited to a 3s Rydberg state using a 200 nm femtosecond pump pulse. The TRPES spectra of these molecules display similar structure and time constants on a subpicosecond time scale. Our ab initio calculations show that similar sets of conical intersections (a [1,2]- and [1,3]-hydrogen shift, as well as carbon-carbon bond cleavage) are energetically accessible to both molecules and that the geometry and orbital composition at the minimum energy crossing points to the ground state are directly analogous. These experimental and computational results suggest that the excited-state dynamics of cyclohexa-1,4-diene become localized at a single double bond and that the effects of through-bond interaction, dominant in the absorption spectrum, are absent in the excited-state dynamics. The notion of excited-state dynamics being localized at specific sites within the nuclear framework is analogous to the localization of light absorption by a subsystem within the molecule, designated a chromophore. We propose the utility of the analogous concept, denoted here as a dynamophore.     

Time-resolved photoelectron spectroscopy: from wavepackets to observables

Time-resolved photoelectron spectroscopy (TRPES) is a powerful tool for the study of intramolecular dynamics, particularly excited state non-adiabatic dynamics in polyatomic molecules. Depending on the problem at hand, different levels of TRPES measurements can be performed: time-resolved photoelectron yield; time- and energy-resolved photoelectron yield; time-, energy-, and angle-resolved photoelectron yield. In this pedagogical overview, a conceptual framework for time-resolved photoionization measurements is presented, together with discussion of relevant theory for the different aspects of TRPES. Simple models are used to illustrate the theory, and key concepts are further amplified by experimental examples. These examples are chosen to show the application of TRPES to the investigation of a range of problems in the excited state dynamics of molecules: from the simplest vibrational wavepacket on a single potential energy surface; to disentangling intrinsically coupled electronic and nuclear motions; to identifying the electronic character of the intermediate states involved in non-adiabatic dynamics by angle-resolved measurements in the molecular frame, the most complete measurement.     

Metallization of solid hydrogen: the challenge and possible solutions

The search for the means to convert molecular hydrogen to a metal under static conditions at high pressure is reviewed with emphasis on selected recent developments in both experimental studies and theoretical approaches. One approach suggested recently makes use of mixtures of hydrogen and suitable impurities. In these materials hydrogen is perturbed by impurities with the goal of obtaining the metallization of hydrogen at moderate pressures. This approach has also been extensively examined through the use of first-principles methods and we review this recently explored experimental approach and several theoretical studies that have provided an atomic-scale picture of the interaction of hydrogen with impurities under pressure. The objective of this novel approach is to help determine if metallization of hydrogen at pressures is attainable with currently available experimental techniques.     

Applications of high resolution spectroscopy to the identification of far-infrared laser emission from optically pumped13CH3OH

High-resolution infrared (IR) and far infrared (FIR) Fourier transform absorption spectra have been employed to investigate assignments of FIR laser lines reported from optically-pumped¹³CH₃OH. The spectroscopic measurements are used in conjunction with the reported IR pump and FIR laser frequencies to form closed combination loops for several systems, serving to confirm the assignments and in some cases to improve the accuracy of the FIR laser frequencies. Frequency predictions from combination differences are also presented for a number of potential new FIR laser lines.     

SIS junction as artificial line elements: A wide band matching scheme

A wide band tuning scheme for SIS junctions is suggested in which the junction capacitance is used as one element of a pisection artificial transmission line.     

Study of glassy microporous filters in the sodium borosilicate glasses with appropriate carriers

Summary DúThe aim of this work is to prepare a porous filter composed of two porous layers: macro-porous carrier and micro-porous sodium borosilicate (NBS) glass with TiO₂ additive (NBST glass), a Vycor-type glass. In the present work we prepared the macroporous support from the same material (NBST glass) as the upper microporous layer and then by sintering both parts to produce the required composite. This work introduces the results of experiments in the preparation of micro-porous filter on NBST glass base, laid on macro-porous carrier. After sintering of scrap NBST glass, porous samples were prepared to be used as carriers for micro-porous samples of phase-separated NBST glass. In other cases, the following carrier materials were used: a) frita SIMAX, b) Al₂O₃. The properties of the NBST glass and the changes in the glass structure with temperature were studied in order to determine the optimal sintering temperature of the prepared glasses. For the development of the sintered glasses, valuable information was obtained from heating microscopy (HM) and scanning electron microscopy (SEM) studies. The combination of the HM and SEM results with the measurements of the micro-hardness and density directed to the further study of the phase separated NBST glasses.     

Fluorescence studies on the conformation of litorin in solution and in the presence of model membranes

The conformation of the nonapeptide hormone litorin has been studied in buffer and in the presence of lipids, using static and dynamic fluorescence. The results obtained show that, in buffer, the hormone probably exists in a collection of flexible conformers, slowly interconverting between them. The marked changes observed in fluorescence spectra and lifetimes upon addition of dimyristoylphosphatidylserine vesicles clearly show that the peptide interacts with lipids assuming lipid specific conformations. Interestingly, no significative spectroscopic changes are produced by exposure to dimirystoylphosphatidylcholine vesicles both in the gel and liquid-christalline phases, suggesting a requirement for negatively charged lipids during the process of hormone-membrane interaction.