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The commensurate and incommensurate Haldane phases for the spin-1 bilinear-biquadratic model are investigated using the infinite matrix product state algorithm. The bipartite entanglement entropy can detect a transition point between the two phases. In both phases, the entanglement spectrum shows the double degeneracy. We calculate the nonlocal order parameter of the bond-centered inversion in both phases, which rapidly approaches a saturation value -1 as the segment length increases. The nonlocal order parameter of the bond-centered inversion with a saturation value -1 and the nonzero value string order indicate that the Haldane phase is a symmetry-protected topological phase. To distinguish the commensurate and incommensurate Haldane phases, the transversal spin correlation and corresponding momentum distribution of the structure factor are analyzed. As a result, the transversal spin correlations exhibit different decay forms in both phases.

The spectroscopic constants including equilibrium distance, harmonic frequency and binding energy of the ground state of the diatomic Ba-RG (RG = Kr, Xe, Rn) are studied by using the closed-shell coupled-cluster theory with spin–orbit coupling (SOC) at the singles, doubles, and non-iterative triples level [CCSD(T)] based on the two-component relativistic pseudo-potentials. The advantage of the adopted computational protocol is that the SOC is incorporated in the post-Hartree–Fock part (i.e. the couple-cluster iteration) which makes it possible to significantly improve the computational efficiency. The extrapolation to the complete basis set (CBS) limit is used to provide the most accurate computational values in the framework of the adopted theoretical approach. The computational values to the CBS limit show that the SOC effect decreases the equilibrium distance by 0.067 Å while the binding energy increases by 21.023 cm−1 for the heaviest Ba-Rn, but not significant in the Ba-Kr and Ba-Xe. To date, both experimental and theoretical spectroscopic constants for Ba-Rn are unavailable, the present work thus provides the reliable theoretical results of the ground state of Ba-Rn for the future investigations.

The high-temperature performance of 4H-SiC ultraviolet avalanche photodiodes (APDs) in both linear and Geiger modes is extensively investigated. During the temperature-dependent measurements, a fixed bias voltage is adopted for the device samples, which is much more practical and important for high-temperature applications. The results show that the fabricated 4H-SiC APDs are very stable and reliable at high temperatures. As the temperature increases from room temperature to 425 K, the dark current at 95% of the breakdown voltage increases slightly and remains lower than 40 pA. In Geiger mode, our 4H-SiC APDs can be self-quenched in a passive-quenching circuit, which is expected for high-speed detection systems. Moreover, an interesting phenomenon is observed for the first time: the single-photon detection efficiency shows a non-monotonic variation as a function of temperature. The physical mechanism of the variation in high-temperature performance is further analyzed. The results in this work can provide a fundamental reference for researchers in the field of 4H-SiC APD ultraviolet detectors.

The optimization of structural parameters in ejector design is a problem of optimization of multivariate nonlinear unsteady flow field, in this paper, the numerical model of the ejector is established by using the computational fluid dynamics (CFD) method. The CFD model is used to study the influence law of the structural parameters of the mixing section, diffuser section and fluid inlet of the ejector, optimize the structure of the ejector, and find out the best scheme for the structural optimization design of the hydrogen ejector, so as to broaden the available load range of the ejector.

To gain a better understanding of the mechanism governing arc dynamics in 3D gliding arc discharge (GAD) plasma, the spatio-temporal evolution of GAD was investigated in a reverse vortex flow by a novel reactor with ring (powered electrode, PE) and truncated cone (ground electrode, GE) electrodes. A newly underlying mechanism governing arc evolution in 3D GAD was gained with combination of flow field simulation, synchronous electrical characteristics, intensified charge coupled device images and high-speed photos. The spatio-temporal analysis indicates that, being different from the well-known ignition–gliding–extinction mechanism occurring in traditional GAD, the PE arc root glides continuously in the 3D GAD, but the GE arc root features jumps from the end of the gliding path to the beginning of the next one. By means of the jumping, the arc auto-sheds the caudal part of the arc and a new arc tail is simultaneously generated, rather than rebuilding a new arc channel back to the shortest electrode gap. With this special behavior of caudal autotomy and regeneration, the main part of the arc remains for each jump. This new insight improves the understanding of the discharge mechanism governing arc evolution in 3D GAD and provides a reference for optimization design of gliding arc plasma in a vortex flow.

The vibrational dynamics of the iron centres in 1D and 3D spin crossover Fe(II) 4-alkyl-urea triazole chains have been investigated by synchrotron based nuclear inelastic scattering. For the 1D system, the partial density of phonon states has been modelled with density functional theory methods. Furthermore, spin dependent iron ligand distances and vibrational modes were obtained. The previously introduced intramolecular cooperativity parameter H coop (Rackwitz et al, Phys. Chem. Chem. Phys. 2013, 15, 15450) has been determined to −31 kJ mol−1 for [Fe(n-Prtrzu)3(tosylate)2] and to +27 kJ mol−1 for [Fe(n-Prtrzu)3(BF4)2]. The change of sign in H coop is in line with the incomplete and gradual character of the spin transition for the former as well as with the sharp transition for the latter reported previously (Rentschler and von Malotki, Inorg. Chem., Act. 2008, 361, 3646). This effect can be ascribed to the networks of intramolecular interactions in the second coordination sphere of the polymer chains, depending on the spin state of the iron centres. In addition, we observe a decreased coupling and coherence when comparing the system which displays a sharp spin transition to the system with an incomplete soft transition by analyzing molecular modes involving a movement of the iron centres.

With the aim of understanding the arc behaviors of a gliding arc (GA) in a magnetic field, arc shape, voltage-current characteristics, plasma parameters, rotational frequency and force analysis of a GA in a magnetically-driven 3D GA reactor are investigated. Three modes, straight (S-arc), forward-bent (FB-arc) and reverse-bent (RB-arc) arcs are observed by moving the magnet axially. It is demonstrated that the arc mode depends on the magnetic field, but is independent of the discharge current. The GA is a glow-like discharge with similar plasma parameters in all the modes. The S-arc mode has the fastest rotational frequency and the highest gas-treated fraction, thus is the optimal for gas conversion (ammonia decomposition to hydrogen as a model reaction in this work). A criterion of the S-arc mode, that the azimuthal Lorentz force applied by the magnetic field is proportional to the square of the radial distance, is deduced from the force analysis. In addition, a method to calculate the arc rotational frequency based on the torque balance between the Lorentz and drag forces is set up to explain why the S-arc has the fastest rotational frequency, and the calculated values agree well with the experimental results.

As an intermedia between cold and thermal plasmas, warm plasma generated by gliding arc (GA) discharge possesses high conversions and high energy efficiencies for CO2 conversion. However, there is little understanding for the arc characteristics in CO2-based atmosphere and reaction mechanism of CO2 in GA plasma from experimental approach. For this purpose, a magnetically driven GA plasma with a constant length of arc is designed to study GA characteristics and reaction mechanism by changing H2/CO2 molar ratio (from pure CO2 to pure H2). In the entire range of H2/CO2 ratio, the arc channel shows a glow-like feature. The plasma parameters are arc temperature of 2200–3600 K, electron density of ~1.6 × 1014 cm−3 and electron temperature of ~3 eV. From pure CO2 to pure H2, arc diameter decreases from 1.3 to 0.6 mm, whereas rotational frequency increases from 20 to 64 Hz. Based upon the optical emission spectra of CO, OH, H and O species, chemluminescence spectra of CO and O recombination and CO production rate detected online by gas chromatographs, the reaction mechanism at low and high H2/CO2 molar ratios is disclosed.

The conventional double-probe technique was improved with a combination of self-powering and radio-frequency (RF) choking. RF perturbations in dual-frequency capacitively coupled discharge were effectively eliminated, as judged by the disappearance of self-bias on the probes. The improved technique was tested by spatially resolved measurements of the electron temperature and ion density in both the axial and radial directions of a dual-frequency capacitive plasma. The measured data in the axial direction were compared with simulation results, and they were excellently consistent with each other. The measured radial distributions of the ion density and electron temperature were influenced significantly by the lower frequency (LF) power. It was shown that superposition of the lower frequency to the higher frequency (HF) power shifted the maximum ion density from the radial center to the edge region, while the trend for the electron temperature profile was the opposite. The changing feature of the ion density distribution is qualitatively consistent with that of the optical emission intensity reported.

To deposit TiO2 films through plasma CVD, the partial pressure ratio of O2 to TiCl4 should be greater than the stoichiometric ratio (pO2/pTiCl4 > 1). However, this may lead to the formation of powder instead of film on the substrate when using volume dielectric barrier discharge (volume-DBD) at atmospheric pressure. In this study, by adding N2 into the working gas Ar, TiO2 photocatalytic films were successfully fabricated in the presence of excess O2 (pO2/pTiCl4 = 2.6) by using a wire-to-plate atmospheric-pressure volume-DBD. The tuning effect of N2 on the deposition of TiO2 film was studied in detail. The results showed that by increasing the N2 content, the deposition rate and particle size of the TiO2 film were reduced, and its photocatalytic activity was enhanced. The tuning mechanism of N2 is further discussed.

Non-thermal plasma at atmospheric pressure was explored for the preparation of polysilicon from SiCl4. The power supply sources of positive pulse and alternating current (8 kHz and 100 kHz) were compared for polysilicon preparation. The samples prepared by using the 100 kHz power source were crystalline silicon. The effects of H2 and SiCl4 volume fractions were investigated. The optical emission spectra showed that silicon species played an important role in polysilicon deposition

Local measurement of plasma radial uniformity was performed in a dual frequency capacitively coupled argon plasma (DF-CCP) reactor using an optical probe. The optical probe collects the light emission from a small separate volume in plasma, thus enabling to diagnose the plasma uniformity for different experimental parameters. Both the gas pressure and the low-frequency (LF) power have apparent effects on the radial uniformity of argon plasma. With the increase in either pressure or LF power, the emission profiles changed from a bell-shaped to a double-peak distribution. The influence of a fused-silica ring around the electrodes on the plasma uniformity was also studied using the optical probe. Possible reasons that result in nonuniform plasmas in our experiments are discussed.

A green process for the oxygen-free conversion of methane to high-concentration ethylene and hydrogen in a plasma-followed-by-catalyst (PFC) reactor is presented. Without any catalysts and with pure methane used as the feed gas, a stable kilohertz spark discharge leads to an acetylene yield of 64.1%, ethylene yield of 2.5% and hydrogen yield of 59.0% with 80.0% of methane conversion at a methane flow rate of 50 cm3/min and a specific input energy of 38.4 kJ/L. In the effluent gas from a stable kilohertz spark discharge reactor, the concentrations of acetylene, ethylene and hydrogen were 18.1%, 0.7% and 66.9%, respectively. When catalysts Pd-Ag/SiO2 were employed in the second stage with discharge conditions same as in the case of plasma alone, the PFC reactor provides an ethylene yield of 52.1% and hydrogen yield of 43.4%. The concentrations of ethylene and hydrogen in the effluent gas from the PFC reactor were found to be as high as 17.1% and 62.6%, respectively. Moreover, no acetylene was detected in the effluent gas. This means that a high concentration of ethylene and oxygen-free hydrogen can be co-produced directly from methane in the PFC reactor.

2H- and -phase monolayer MoTe2 films on highly oriented pyrolytic graphite are studied using scanning tunneling microscopy and spectroscopy (STM/STS). The phase transition of MoTe2 can be controlled by a post-growth annealing process, and the intermediate state during the phase transition is directly observed by STM. For 2H-MoTe2, inversion domain boundaries are presented as bright lines at high sample bias, but as dark lines at lower sample bias. The dI/dV mappings reveal the distinct distributions of electronic states between domain boundaries and interiors of domains. It should be noted that a 2 × 2 periodic structure is clearly discernable inside the domains, where the STS measurement shows a small dip of size ~150 meV at the vicinity of the Fermi level, indicating that the 2 × 2 periodic structure may be an incommensurate charge density wave. Moreover, a 4 × 4 periodic structure appears in 2H-MoTe2 grown at a higher substrate temperature.

Surface structures and properties of Sn islands grown on superconducting substrate 2H-NbSe2(0001) are studied using low temperature scanning tunneling microscopy or spectroscopy. The pure face-centered cubic (fcc) structure of Sn surface is obtained. Superconductivity is also detected on the fcc-Sn(111) surface, and the size of superconducting gap on the Sn surface is nearly the same as that on the superconducting substrate. Furthermore, phase transition occurs from fcc-Sn(111) to β-Sn(001) by keeping the sample at room temperature for a certain time. Due to the strain relaxation on the β-Sn islands, both the in-plane unit cell and out-of-plane structures distort, and the height of surface atoms varies periodically to form a universal ripple structure.

Near-infrared continuous wave cavity ring-down spectroscopy was applied to measure the OH radicals in dielectric barrier discharge plasmas, which play an important role in combustion systems, atmospheric chemistry and the removal of air pollutants by non-thermal plasmas. The P-branches of OH X2∏i ν″ = 2 ← ν″ = 0) bands were used for number density measurements. The OH number density and plasma temperature were determined for different applied voltages, gas pressures and concentrations of both oxygen and water. The temporal evolution of the OH number density was obtained by using the “time window method, which was used to extract individual ring-down times at different times in a half period of the sine wave applied voltage in dielectric barrier discharge plasmas.

HgTe (111) surface is comprehensively studied by scanning tunneling microscopy/spectroscopy (STS). In addition to the primitive (1 × 1) hexagonal lattice, six reconstructed surface structures are observed: (2 × 2), 2 × 1, 4 × 1, , and . The (2 × 2) reconstructed lattice maintains the primitive hexagonal symmetry, while the lattices of the other five reconstructions are rectangular. Moreover, the topographic features of the reconstruction are bias dependent, indicating that they have both topographic and electronic origins. The STSs obtained at different reconstructed surfaces show a universal dip feature with size ~100 mV, which may be attributed to the surface distortion. Our results reveal the atomic structure and complex reconstructions of the cleaved HgTe (111) surfaces, which paves the way to understand the rich properties of HgTe crystal.

A new type of external dynamic vibration absorber is designed to control the vibration at a specific frequency of the milling cutter during the milling process. The structural design of the dynamic vibration absorber and the selection of the corresponding parameters are conducted. The finite element model of the cutter is established and connected with the vibration absorber. The results of the harmonic response analysis of milling cutter before and after the installation of the vibration absorber are compared and show that the vibration absorber can reduce the vibration of the cutter at the resonant frequency, which means it has a good vibration damping performance. The vibration absorber has the advantages of simple structure, convenient frequency modulation and easy installation. This context lay the foundation of further application for damping cutter.

The electronic structures, one-photon absorption (OPA) and two-photon absorption (TPA) properties of the azulenylporphyrins and azulene-fused porphyrins have been comparatively studied by using DFT/B3LYP/6-31G(d) and the ZINDO/SDCI method. With the number of azulenyl groups increasing, the OPA wavelengths of all molecules are red-shifted in 400{600 nm and the two-photon absorption cross section is gradually enlarged. The azulene-fused structures facilitate an expanding conjugated area and increasing TPA cross section. The origin of TPA properties of studied compounds is studied with a two-level model. In summary, the azulene-fused porphyrins exhibit strong two-photon absorption.

In circadian rhythm generation, intercellular signaling factors are shown to play a crucial role in both sustaining intrinsic cellular rhythmicity and acquiring collective behaviours across a population of circadian neurons. However, the physical mechanism behind their role remains to be fully understood. In this paper, we propose an indirectly coupled multicellular model for the synchronization of Drosophila circadian oscillators combining both intracellular and intercellular dynamics. By simulating different experimental conditions, we find that such an indirect coupling way can synchronize both heterogeneous self-sustained circadian neurons and heterogeneous mutational damped circadian neurons. Moreover, they can also be entrained to ambient light-dark (LD) cycles depending on intercellular signaling.

We calculate the Casimir force at a finite cut-off Lambda by summing the forces induced by the all fluctuation modes. We show that the Casimir force is independent of the cut-off function in the limit L Lambda -> infinity. There is a correction in the order of (L Lambda)(-2), when L Lambda is finite and large. This correction becomes remarkable when L is comparable with the microscopic length scale Lambda(-1). It has been demonstrated that the Casimir force at a finite cut-off should be defined by summing forces of all fluctuation modes, instead of the derivative of Casimir energy with respect to L where an additional derivative of the cut-off function has been introduced.

Oxygen-free conversion of methane to ethylene was investigated in a two-stage plasma-followed-by-catalyst (PFC) reactor. In the absence of catalyst, pulsed spark discharges and pulsed corona discharges were compared for methane conversion. The results showed that methane was mainly converted to acetylene, but pulsed spark discharges exhibited distinct advantages over the pulsed corona discharges in methane conversion. Thereby, pulsed spark discharges were employed and followed by Ag-Pd/SiO2 catalyst for achieving ethylene as a target product in the PFC reactor. Using the PFC reactor, a steady single-pass ethylene yield of 57% was obtained at a rate of methane conversion of 74%.

An investigation on the structural stabilities and electronic properties of SrX (X = S, Se and Te) under high pressure is conducted using the first-principles calculation based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. Our results demonstrate that the sequence of the pressure-induced phase transition of the three compounds is the NaCl-type (B1) structure (Fm3m) to the CsCl-type (B2) structure (Pm3m). The phase transition and the metallization pressures are determined theoretically. The pressure effect on the optical properties is discussed. The results are compared with the previous calculations and experimental data.

By revealing the relationship between edge visibility and imaging parameters in in-line phase contrast imaging (PCI), we propose a method to quantitatively measure the contribution of absorption and phase shift from acquired images. We also prove that edge visibility will grow with the increasing source-object distance and object-detector distance. The result is validated by relative phase factor and by experiments conducted on a microfocus x-ray source. This method provides a new approach to evaluate in-line PCI images and is helpful for deciding imaging parameters.

Atomic hydrogen plays an important role in the chemical vapour deposition of diamond and other functional materials. This paper reports the experimental determinations of atomic hydrogen density in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry using Ar as an actinometer. At certain discharge conditions (ac 24 kHz, 28 kV of peak-to-peak voltage), the approximate hydrogen dissociation fractions calculated from the emission intensities with respect to electron temperatures obtained with the Langmuir probe, are decreased from 0.099 to 0.01 as the gas pressure increases from 2 to 4 Torr. The relative H atom mole fractions as a function of discharge parameters (spatial position and gas flow rate) have been investigated. It is shown that the discharge characteristics strongly depend on the spatial position but not on the gas flow rate. The influences of the above operating parameters on the emission intensities have been discussed.