Observation of forbidden phonons and dark excitons by resonance Raman scattering in few-layer WS2_2

The optical properties of the two-dimensional (2D) crystals are dominated by tightly bound electron-hole pairs (excitons) and lattice vibration modes (phonons). The exciton-phonon interaction is fundamentally important to understand the optical properties of 2D materials and thus help develop emerging 2D crystal based optoelectronic devices. Here, we presented the excitonic resonant Raman scattering (RRS) spectra of few-layer WS$_2$ excited by 11 lasers lines covered all of A, B and C exciton transition energies at different sample temperatures from 4 to 300 K. As a result, we are not only able to probe the forbidden phonon modes unobserved in ordinary Raman scattering, but also can determine the bright and dark state fine structures of 1s A exciton. In particular, we also observed the quantum interference between low-energy discrete phonon and exciton continuum under resonant excitation. Our works pave a way to understand the exciton-phonon coupling and many-body effects in 2D materials.Comment: 14 pages, 11 figure

The microwave spectrum and structure of the methanol⋅SO2 complex

The rotational spectra of nine isotopomers of the methanol⋅sulfur dioxide van der Waals complex were observed with a pulsed molecular beam Fourier transform microwave spectrometer. Each rotational transition is split into an A‐state (m=0) and an E‐state (m=±1) transition due to methyl top internal rotation effects. The A and E transitions show an additional inversion splitting ranging from a MHz to a few tens of MHz in seven of the isotopomers. The inversion splitting is absent in the two S16O18O isotopomers. The center frequencies of the inversion doublets were used in a simultaneous fit of both the A‐ and E‐state transitions, producing rotational constants which allowed a complete determination of the structure of the complex. Analysis of the moments of inertia indicate that the complex has a stacked structure. The center of mass distance between the two monomers is 3.08(5) Å. The effective torsional barrier height is V3=128.6(1) cm−1 based on the assumption that the methyl group rotates against a heavy frame. The dipole moment is μT=1.94(3) D. The inversion motion is discussed based on effects on the splitting associated with isotopic substitution and the transition dipole direction. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71010/2/JCPSA6-103-15-6440-1.pd

Disrupting long-range polar order with an electric field

lectric fields are known to favor long-range polar order through the aligning of electric dipoles in relation to Coulomb\u27s force. Therefore, it would be surprising to observe a disordered polar state induced from an ordered state by electric fields. Here we show such an unusual phenomenon in a polycrystalline oxide where electric fields induce a ferroelectric-to-relaxor phase transition. The nonergodic relaxor phase with disordered dipoles appears as an intermediate state under electric fields during polarization reversal of the ferroelectric phase. Using the phenomenological theory, the underlying mechanism for this unexpected behavior can be attributed to the slow kinetics of the ferroelectric-to-relaxor phase transition, as well as its competition against domain switching during electric reversal. The demonstrated material could also serve as a model system to study the transient stages in first-order phase transitions; the slow kinetics does not require the use of sophisticated ultrafast tools

The microwave spectrum, structure, and large amplitude motions of the methylacetylene⋅SO2 complex

Rotational spectra of five isotopomers of the methylacetylene⋅SO2 (MA⋅SO2) van der Waals complex have been observed with a Fourier transform microwave spectrometer. Each species showed two sets of rotational transitions, one associated with the A (m=0) and the other with the E (m=±1) methyl group internal rotation states. The rotational transitions of the isotopomers with S 16O2 and the doubly substituted S 18O2 also showed inversion splitting ranging from tens of kHz to a few MHz. This splitting was absent in the S 16O 18O isotopomers. The spectra of these species have been assigned and fit, yielding rotational constants, which allowed a complete determination of the structure of the complex. The SO2 was found to sit above the carbon–carbon triple bond, with one of the S–O bonds roughly parallel to the symmetry axis of methylacetylene. The centers‐of‐mass distance between the two monomers was determined to be 3.382(10) Å. The center frequencies of the inversion doublets (or quartets) were used in a fit of both the A and the E transitions; the barrier hindering the internal rotation of the methyl group was determined to be 62.8(5) cm−1. Based on the dependence of the inversion splitting on the transition dipole direction and isotopic substitution, the inversion motion was identified as an ‘‘in plane’’ wagging of the SO2 relative to methylacetylene. A pure inversion splitting of 3.11 MHz (free from rotation) was extracted from the A‐state spectrum of the normal species, from which an inversion barrier height of about 63 cm−1 was estimated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69904/2/JCPSA6-101-8-6512-1.pd

Effect of the Ratio of Materials Used in Fermented Total Mixed Ration on the Aerobic Stability of the TMR Compared with a Mixed-Silage

Fermented Total Mixed Ration (TMR) is an important forage for livestock, but if it has a high content of protein, the aerobic stability is poor (Wang, 2008). There is little published information about the aerobic stability of fermented TMR. This experiment was undertaken to study the effects of the ratio of materials used in TMR and mixed-silage on the pH, the numbers of lactobacillus, mould and yeast, and the temperature of the fermented TMR and mix-silage after opening

Interaction Dynamics Between Ferroelectric and Antiferroelectric Domains in a PbZrO3-Based Ceramic

The antiferroelectric-ferroelectric phase transition in PbZrO3-based oxides is of both fundamental and practical importance. In ceramics in which such a transition readily occurs, the antiferroelectric and the ferroelectric phases often coexist in individual grains with a coherent interphase interface. In this work, the electric biasing in situ transmission electron microscopy technique is employed to directly observe a unique microstructural dynamic when ferroelectric and antiferroelectric domains are driven by a moderate electric field to interact. It is found that, under monotonic loading, the ferroelectric domain grows until it is blocked by the ferroelectric-antiferroelectric interface. At the same time, a kink is formed on the interface at the contact point. The interaction of the growing domain with the interface is interpreted in terms of depolarization field-assisted phase transition, which is supported by our phase-field simulation. Upon further bipolar cycling, the ferroelectric domain becomes less mobile and no longer reaches the ferroelectric-antiferroelectric interface, indicative of electric fatigue of the ferroelectric phase

An Epidemiological Study of Concomitant Use of Chinese Medicine and Antipsychotics in Schizophrenic Patients: Implication for Herb-Drug Interaction

Background: Herb-drug interactions are an important issue in drug safety and clinical practice. The aim of this epidemiological study was to characterize associations of clinical outcomes with concomitant herbal and antipsychotic use in patients with schizophrenia. Methods and Findings: In this retrospective, cross-sectional study, 1795 patients with schizophrenia who were randomly selected from 17 psychiatric hospitals in China were interviewed face-to-face using a structured questionnaire. Association analyses were conducted to examine correlates between Chinese medicine (CM) use and demographic, clinical variables, antipsychotic medication mode, and clinical outcomes. The prevalence of concomitant CM and antipsychotic treatment was 36.4% [95% confidence interval (95% CI) 34.2%-38.6%]. Patients using concomitant CM had a significantly greater chance of improved outcomes than non-CM use (61.1% vs. 34.3%, OR = 3.44, 95% CI 2.80-4.24). However, a small but significant number of patients treated concomitantly with CM had a greater risk of developing worse outcomes (7.2% vs. 4.4%, OR = 2.06, 95% CI 2.06-4.83). Significant predictors for concomitant CM treatment-associated outcomes were residence in urban areas, paranoid psychosis, and exceeding 3 months of CM use. Herbal medicine regimens containing Radix Bupleuri, Fructus Gardenia, Fructus Schisandrae, Radix Rehmanniae, Akebia Caulis, and Semen Plantaginis in concomitant use with quetiapine, clozapine, and olanzepine were associated with nearly 60% of the risk of adverse outcomes. Conclusions: Concomitant herbal and antipsychotic treatment could produce either beneficial or adverse clinical effects in schizophrenic population. Potential herb-drug pharmacokinetic interactions need to be further evaluated. © 2011 Zhang et al.published_or_final_versio

An Updated Search of Steady TeV γ−\gamma-Ray Point Sources in Northern Hemisphere Using the Tibet Air Shower Array

Using the data taken from Tibet II High Density (HD) Array (1997 February-1999 September) and Tibet-III array (1999 November-2005 November), our previous northern sky survey for TeV $\gamma-$ray point sources has now been updated by a factor of 2.8 improved statistics. From $0.0^{\circ}$ to $60.0^{\circ}$ in declination (Dec) range, no new TeV $\gamma-$ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV $\gamma-$ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level (C.L.), the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.Comment: This paper has been accepted by hepn