Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps, and recent advances in the synthesis, characterization, and device fabrication of the representative MoS$_2$, WS$_2$, WSe$_2$, and MoSe$_2$ TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer dependent. In this review, we discuss the basic lattice vibrations of monolayer, multilayer, and bulk TMDs, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica, and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin--orbit splitting, and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.Comment: 30 pages, 23 figure

SDSS J163459.82+204936.0: A Ringed Infrared-Luminous Quasar with Outflows in both Absorption and Emission Lines

SDSS J1634+2049 is a local (z = 0.1293) infrared-luminous quasar with LIR= 10^11.91 Lsun. We present a detailed multiwavelength study of both the host galaxy and the nucleus. The host galaxy demonstrates violent, obscured star formation activities with SFR ~ 140 Msun yr^-1, estimated from either the PAH emission or IR luminosity. The optical to NIR spectra exhibit a blueshifted narrow cuspy component in Hb, HeI5876,10830 and other emission lines consistently with an offset velocity of ~900 km/s, as well as additional blueshifting phenomena in high-ionization lines , while there exist blueshifted broad absorption lines (BALs) in NaID and HeI*3889,10830, indicative of the AGN outflows producing BALs and emission lines. Constrained mutually by the several BALs with CLOUDY, the physical properties of the absorption-line outflow are derived as follows: 10^4 < n_H <= 10^5 cm^-3, 10^-1.3 <= U <= 10^-0.7 and 10^22.5<= N_H <= 10^22.9 cm^-2 , similar to those derived for the emission-line outflows. The similarity suggests a common origin. Taking advantages of both the absorption lines and outflowing emission lines, we find that the outflow gas is located at a distance of 48 - 65 pc from the nucleus, and that the kinetic luminosity of the outflow is 10^44-10^46 erg s^-1. J1634+2049 has a off-centered galactic ring on the scale of ~ 30 kpc that is proved to be formed by a recent head-on collision by a nearby galaxy. Thus this quasar is a valuable object in the transitional phase emerging out of dust enshrouding as depicted by the co-evolution scenario.Comment: 13 figures, 6 tables; accepted for publication in Ap

Apply adsorption technology to solve the UV sensor instability of dynamic control on periodic counter current purification system

Cell culture media are a source of major nutrients that provide cell growth and synthesis of proteins. Researchers and suppliers use combine media components test continually in an attempt to find more suitable cell culture media for use in continuous cell culture processes. Commercial media components are a black box for downstream purification researchers who cannot predict the effects of their constituents on resin affinity, absorbability, even for interference with UV instrument. To more effectively utilize in dynamic continuous purification system, the loading product percentage of resin absorbability is typically controlled at 40-60% maximum binding capacity. It is often five times more than traditional batch purification. Therefore, the swing of UV percentage caused by color material in the bulk harvest is the key process parameter in the periodic counter current purification system. We compared different commercial quaternary ammonium adsorbent matrix (such as Stabilized Regenerated Cellulose, Agarose and Styrene Divinyl Benzene Copolymer) to observe their effects on the swing of the UV amplitude. The results show that agarose group has better de-coloration efficacy than the other two commercial quaternary ammonium groups. Please click Additional Files below to see the full abstract

Experimental study on a new type floating breakwater

In the article, a new type floating breakwater is proposed based on comparing the performance of different kinds of floating breakwater that include pontoon type breakwater, scrap tire breakwater, mat float type breakwater etc. The outstanding feature of the new type breakwater is that damping at bottom of breakwater can increase wave energy dissipation and decrease coefficient of wave transmission and reflection. The relative width and relative submergence depth (the ratio of width to wave length W/L and submergence depth to wave length D/L) on the performance of the breakwater are discussed based on a series of physical model test in flume. The relationship between critical transmission coefficient (Ct=0.5) and relative width is given by experiment. In the actual design and application process, the various parameters are not independent, so the relationship between transmission coefficient and different parameters is analyzed in this paper

Development and Evaluation of a Novel Four-Electrode Device System for Monitoring Skin Impedance

Qi, meridians, and acupoints are important issues in Chinese medicine. One of the theories claims that acupuncture points and meridians have unique electrical properties. The associations between acupuncture points or meridians and special electrical properties are still under debate. In the current study, we introduced and explained a device for this kind of research and evaluated the reliability of this device as well as effects of pressure, cleaning the skin by alcohol and exfoliation on electrical skin measurements. Fifteen subjects (10 female, 5 male) were recruited to participate in the study. An impedance meter based on the four-electrode technique was designed and fabricated specifically for this study. The effects of pressure, cleaning of the skin by alcohol, and exfoliation on electrical skin impedance were evaluated separately. The device repeatability was also evaluated 30 times in a 30 minutes period. Scale weight up to 200 grams, cleaning the skin with alcohol, and exfoliation didn't affect the performance of this device. The device performance didn&#8217;t change significantly during the 30 minutes measurement either. The new system we evaluated can be a reliable tool for researches on electrical skin impedance in acupuncture, as its performance is fairly stable even in the presence of various confounding factors such as various pressures on the probe, cleaning the skin with alcohol and exfoliation

Aquaporin 1, a potential therapeutic target for migraine with aura

The pathophysiology of migraine remains largely unknown. However, evidence regarding the molecules participating in the pathophysiology of migraine has been accumulating. Water channel proteins, known as aquaporins (AQPs), notably AQP-1 and AQP-4, appears to be involved in the pathophysiology of several neurological diseases. This review outlines newly emerging evidence indicating that AQP-1 plays an important role in pain signal transduction and migraine and could therefore serve as a potential therapeutic target for these diseases

Biomechanics Characteristics of New Type Artificial Hip Joint

The structure, geometrical shape and material are the three main parts of the prostheses. This research focuses on the geometrical shape analysis. The geometrical shape of human natural femoral head is similar to the ellipse, but, the artificial femoral head is rotundity shape. There is difference between ellipse and rotundity femoral head. Two models are developed and analyzed in this paper under same conditions used Finite element analysis method. Based on the calculation results, it is shown that the ellipse shape femoral head have the similar characteristics to the natural joint than rotundity model. The ellipse has the more lowness stress distribution area and more small distortion magnitude than rotundity shape artificial femoral head. It should have the more kind effect replace rotundity femoral head with ellipse shape artificial formal head. Keywords: hip joint; prosthesis design; finite element analysis; biomechanic

Polytypism and Unexpected Strong Interlayer Coupling of two-Dimensional Layered ReS2

The anisotropic two-dimensional (2D) van der Waals (vdW) layered materials, with both scientific interest and potential application, have one more dimension to tune the properties than the isotropic 2D materials. The interlayer vdW coupling determines the properties of 2D multi-layer materials by varying stacking orders. As an important representative anisotropic 2D materials, multilayer rhenium disulfide (ReS2) was expected to be random stacking and lack of interlayer coupling. Here, we demonstrate two stable stacking orders (aa and a-b) of N layer (NL, N>1) ReS2 from ultralow-frequency and high-frequency Raman spectroscopy, photoluminescence spectroscopy and first-principles density functional theory calculation. Two interlayer shear modes are observed in aa-stacked NL-ReS2 while only one interlayer shear mode appears in a-b-stacked NL-ReS2, suggesting anisotropic-like and isotropic-like stacking orders in aa- and a-b-stacked NL-ReS2, respectively. The frequency of the interlayer shear and breathing modes reveals unexpected strong interlayer coupling in aa- and a-b-NL-ReS2, the force constants of which are 55-90% to those of multilayer MoS2. The observation of strong interlayer coupling and polytypism in multi-layer ReS2 stimulate future studies on the structure, electronic and optical properties of other 2D anisotropic materials