Design of small-scale gradient coils in magnetic resonance imaging by using the topology optimization method
Practical security of continuous-variable quantum key distribution under finite-dimensional effect of multi-dimensional reconciliation
Bogoliubov excitations in a Bose-Hubbard model on a hyperhoneycomb lattice
We study the topological properties of Bogoliubov excitation modes in a Bose-Hubbard model of three-dimensional (3D) hyperhoneycomb lattices. For the non-interacting case, there exist nodal loop excitations in the Bloch bands. As the on-site repulsive interaction increases, the system is first driven into the superfluid phase and then into the Mott-insulator phase. In both phases, the excitation bands exhibit robust nodal-loop structures and bosonic surface states. From a topology point of view, these nodal-loop excitation modes may be viewed as a permanent fingerprint left in the Bloch bands.
Stochastic resonance in an under-damped bistable system driven by harmonic mixing signal
Chaos generation by a hybrid integrated chaotic semiconductor laser
A new control method based on the lattice hydrodynamic model considering the double flux difference
Optimization of pick-up coils for weakly damped SQUID gradiometers
Using the HgxMg(1-x) Te ternary compound as a room temperature photodetector: The electronic structure, charge transport, and response function of the energetic electromagnetic radiation
Precise calibration of zero-crossing temperature and drift of an ultralow expansion cavity with a clock transition spectrum
Modulation of multiphoton resonant high-order harmonic spectra driven by two frequency-comb fields
Delay time dependence of wave packet motion and population transfer of four-level K2 molecule in pump-pump-probe pulses
Analysis of the fractal intrinsic quality in the ionization of Rydberg helium and lithium atoms
Electron-impact single ionizaiton for W4+ and W5+
Polarization and exchange effects in elastic scattering of electron with atoms and ions
Optical Stark deceleration of neutral molecules from supersonic expansion with a rotating laser beam
Influence of cutting off position of plasma filament formed by two-color femtosecond laser on terahertz generation
Confinement of Bloch surface waves in a graphene-based one-dimensional photonic crystal and sensing applications
Propagation properties of chirped Airy vortex beams with x-polarization through uniaxial crystals
Fabry-Pérot resonance coupling associated exceptional points in a composite grating structure
Broadband achromatic phase retarder based on metal-multilayer dielectric grating
Influence of moderate-to-strong anisotropic non-Kolmogorov turbulence on intensity fluctuations of a Gaussian-Schell model beam in marine atmosphere
Wideband linear-to-circular polarization conversion realized by a transmissive anisotropic metasurface
Passive ranging and a three-dimensional imaging system through wavefront coding
Scattering of a single photon in a one-dimensional coupled resonator waveguide with a Λ-type emitter assisted by an additional cavity
We analyze the transport property of a single photon in a one-dimensional coupled resonator waveguide coupled with a Λ-type emitter assisted by an additional cavity. The reflection and transmission coefficients of the inserted photon are obtained by the stationary theory. It is shown that the polarization state of the inserted photon can be converted with high efficiency. This study may inspire single-photon devices for scalable quantum memory.
Modulation and mechanism of ultrafast transient spectroscopy based on dimethylamino-carbaldehyde derivatives
Microparticle collection for water purification based on laser-induced convection
Lasing properties of a Yb ion in tetragonal LuPO4 and LuVO4 isomorphic crystals: A comparative study
High-power ultraviolet 278-nm laser from fourth-harmonic generation of an Nd: YAG amplifier in CsB3O5 crystal
Development of an injection-seeded single-frequency laser by using the phase modulated technique
Probing the structure of multi-center molecules with odd-even high harmonics
Nonlinear spectral cleaning effect in cross-polarized wave generation
The underlying mechanism of the spectral cleaning effect of the cross-polarized wave (XPW) generation process was theoretically investigated. This study shows that the spectral noise of an input spectrum can be removed in the XPW generation process and that the spectral cleaning effect depends on the characteristics of the input pulses, such as the chirp and Fourier-transform-limited duration of the initial pulse, and the modulation amplitude and frequency of the spectral noise. Though these factors codetermine the output spectrum of the XPW generation process, the spectral cleaning effect is mainly affected by the initial pulse chirp. The smoothing of the spectrum in the XPW generation process leads to a significant enhancement of the coherent contrast.
Light-scattering model for aerosol particles with irregular shapes and inhomogeneous compositions using a parallelized pseudo-spectral time-domain technique
Structural, vibrational, optical, photoluminescence, thermal, dielectric, and mechanical studies on zinc (tris) thiourea sulfate single crystal: A noticeable effect of organic dye
Experimental demonstration of narrow-band rugate minus filters using rapidly alternating deposition technology
Guiding properties of proton-implanted Nd3+-doped phosphate glass waveguides
An analytical variational method for the biased quantum Rabi model in the ultra-strong coupling regime
An analytical variational method for the ground state of the biased quantum Rabi model in the ultra-strong coupling regime is presented. This analytical variational method can be obtained by a unitary transformation or alternatively by assuming the form of the ground state wave function. The key of the method is to introduce a variational parameter λ, which can be determined by minimizing the energy functional. Using this method, we calculate the physical observables with high accuracy in comparison with the numerical exact ones. Our method evidently improves over the widely used general rotating-wave approximation (GRWA) in both qualitative and quantitative aspects.
Generation of narrowband Lamb waves based on the Michelson interference technique
Reconstruction model for temperature and concentration profiles of soot and metal-oxide nanoparticles in a nanofluid fuel flame by using a CCD camera
This paper presents a numerical study on the simultaneous reconstruction of temperature and volume fraction fields of soot and metal-oxide nanoparticles in an axisymmetric nanofluid fuel sooting flame based on the radiative energy images captured by a charge-coupled device (CCD) camera. The least squares QR decomposition method was introduced to deal with the reconstruction inverse problem. The effects of ray numbers and measurement errors on the reconstruction accuracy were investigated. It was found that the reconstruction accuracies for volume fraction fields of soot and metal-oxide nanoparticles were easily affected by the measurement errors for radiation intensity, whereas only the metal-oxide volume fraction field reconstruction was more sensitive to the measurement error for the volume fraction ratio of metal-oxide nanoparticles to soot. The results show that the temperature, soot volume fraction, and metal-oxide nanoparticles volume fraction fields can be simultaneously and accurately retrieved for exact and noisy data using a single CCD camera.
Accurate quantification of hydration number for polyethylene glycol molecules Hot!
Hydration water can even decide the physicochemical properties of hydrated organic molecules. However, by far the most important hydration number for organic molecules, in particular polyethylene glycol which we are concerned with here, usually suffers from a large discrepancy. Here, we provide a scheme for accurate and unambiguous quantification of the hydration number based on the universal water-content dependence of glass transition temperature for aqueous solutions, testified by experimental results for polyethylene glycol molecules of a molar weight ranging from 200 to 20000. Moreover, we also clarify the fundamental misunderstanding lying in the definition and quantification of hydration water for PEG molecules in the literature, therein the hydration number for PEG in water-rich solutions has been determined at a critical concentration, across which the properties of the solution display obviously distinct water-content dependence.
Upstream ion wave excitation in an ion-beam-plasma system
Plasma normal modes in ion-beam-plasma systems were experimentally investigated previously only for the waves propagating in the downstream (along the beam) direction. In this paper, the ion wave excitation and propagation in the upstream (against the beam) direction in an ion-beam-plasma system were experimentally studied in a double plasma device. The waves were launched by applying a ramp voltage to a negatively biased excitation grid. Two kinds of wave signals were detected, one is a particle signal composed of burst ions and the other is an ion-acoustic signal arising from the background plasma. These signals were identified by the dependence of the signal velocities on the characteristics of the ramp voltage. The velocity of the burst ion signal increases with the decrease of the rise time and the increase of the peak-to-peak amplitude of the applied ramp voltage while that of the ion-acoustic signal is independent of these parameters. By adjusting these parameters such that the burst ion velocity approaches to the ion-acoustic velocity, the wave-particle interaction can be observed.
Characteristic plume morphologies of atmospheric Ar and He plasma jets excited by a pulsed microwave hairpin resonator
Analysis of Landau damping in radially inhomogeneous plasma column
A miniaturized 2.45 GHz ECR ion source at Peking University
A miniaturized 2.45 GHz permanent magnet electron cyclotron resonance (PMECR) ion source, which has the ability of producing a tens-mA H+ beam, has been built and tested at Peking University (PKU). Its plasma chamber dimension is Φ 30 mm×40 mm and the whole size of the ion source is Φ 180 mm×130 mm. This source has a unique structure with the whole source body embedded into the extraction system. It can be operated in both continuous wave (CW) mode and pulse mode. In the CW mode, more than 20 mA hydrogen ion beam at 40 kV can be obtained with the microwave power of 180 W and about 1 mA hydrogen ion beam is produced with a microwave power of 10 W. In the pulse mode, more than 50 mA hydrogen ion beam with a duty factor of 10% can be extracted when the peak microwave power is 1800 W.
Coupling between velocity and interface perturbations in cylindrical Rayleigh-Taylor instability
Synchrotron radiation intensity and energy of runaway electrons in EAST tokamak
Sterilization of mycete attached on the unearthed silk fabrics by an atmospheric pressure plasma jet
The sterilization of the simulated unearthed silk fabrics using an atmospheric pressure plasma jet (APPJ) system employing Ar/O2 or He/O2 plasma to inactivate the mycete attached on the silk fabrics is reported. The effects of the APPJ characteristics (particularly the gas type and discharge power) on the fabric strength, physical-chemical structures, and sterilizing efficiency were investigated. Experimental results showed that the Ar/O2 APPJ plasma can inactivate the mycete completely within 4.0 min under a discharge power of 50.0 W. Such an APPJ treatment had negligible impact on the mechanical strength of the fabric and the surface chemical characteristics. Moreover, the Ar ions, O and OH radicals were shown to play important roles on the sterilization of the mycete attached on the unearthed silk fabrics.
Compression behavior and phase transition of β-Si3N4 under high pressure
The compressibility and pressure-induced phase transition of β-Si3N4 were investigated by using an angle dispersive x-ray diffraction technique in a diamond anvil cell at room temperature. Rietveld refinements of the x-ray powder diffraction data verified that the hexagonal structure (with space group P63/m, Z=2 formulas per unit cell) β-Si3N4 remained stable under high pressure up to 37 GPa. Upon increasing pressure, β-Si3N4 transformed to δ-Si3N4 at about 41 GPa. The initial β-Si3N4 was recovered as the pressure was released to ambient pressure, implying that the observed pressure-induced phase transformation was reversible. The pressure-volume data of β-Si3N4 was fitted by the third-order Birch-Murnaghan equation of state, which yielded a bulk modulus K0=273(2) GPa with its pressure derivative K'0=4 (fixed) and K0=278(2) GPa with K'0=5. Furthermore, the compressibility of the unit cell axes (a and c-axes) for the β-Si3N4 demonstrated an anisotropic property with increasing pressure.
Ab initio molecular dynamics study on the local structures in Ce70Al30 and La70Al30 metallic glasses
Ab initio molecular dynamics simulations were performed to investigate the effect of similar elements on the short-to medium-range atomic packing features in Ce70Al30 and La70Al30 glass-forming alloys. 4f electrons of Ce element in Ce70Al30 alloy were properly treated in electronic calculations. The local atomic structures in both alloys are qualitatively similar. However, the local environments of Al atoms in Ce70Al30 alloy show fluctuation with temperature in the cooling process, which could result from 4f electrons of Ce elements. Surprisingly, the medium-range atomic packing features of Al atoms in both MGs are quite different, although Ce and La elements are similar. These findings are useful for understanding the enhanced glass-forming ability by similar element substitution in RE-based MGs from a medium-range structure perspective.
Fine structures of defect cores induced by elastic anisotropy and biaxiality in hybrid alignment nematics
Facile and controllable synthesis of molybdenum disulfide quantum dots for highly sensitive and selective sensing of copper ions
Molybdenum disulfide quantum dots (MoS2 QDs) were synthesized via a hydrothermal method using sodium molybdate and cysteine as molybdenum and sulfur sources, respectively. The optimal hydrothermal time was studied. Furthermore, the as synthesized water-soluble MoS2 QDs were used as a fluorescence probe for the sensitive and selective detection of copper ions. The fluorescence of the MoS2 QDs was quenched after the addition of copper ions; the reason may be that the transfer of the excited electron from QDs to copper ions leads to the reduction of the radiative recombination. The fluorescence quenching of MoS2 QDs is linearly dependent on the copper ions concentration ranging from 0.1 μM to 600 μM, the limit of detection is 0.098 μM, which is much lower than that of existing methods. Moreover, the MoS2 QDs show highly selectivity towards the detection of copper ions.
Polycrystalline cubic boron nitride prepared with cubic-hexagonal boron nitride under high pressure and high temperature
Effect of pressure on the elastic properties and optoelectronic behavior of Zn4B6O13: First-principles investigation
Thermoelectric properties of lower concentration K-doped Ca3Co4O9 ceramics
Spin depolarization dynamics of WSe2 bilayer
Generalized Drude model and electromagnetic screening in metals and superconductors
Electromagnetic screening is studied from the perspective of fluid mechanics by generalizing the Drude theory, which unifies three known results:Thomas-Fermi screening of the longitudinal field in both metals and superconductors, the skin effect of the transverse field in metals, and the Meissner effect in superconductors. In the special case of superfluid electrons, we slightly generalize the London equations to incorporate the longitudinal electric fields. Moreover, regarding the experiments, our study points out that the dynamical measurement may overestimate the superfluid density.
Vortex pinning and rectification effect in a nanostructured superconducting film with a square array of antidot triplets
Fabrication of Tl2Ba2CaCu2O8 superconducting films without thallium pellets
Interfacial effect on the reverse of magnetization and ultrafast demagnetization in Co/Ni bilayers with perpendicular magnetic anisotropy
Estimation of vector static magnetic field by a nitrogen-vacancy center with a single first-shell 13C nuclear (NV-13C) spin in diamond
Experimental investigation of vector static magnetic field detection using an NV center with a single first-shell 13C nuclear spin in diamond
Effect of O-O bonds on p-type conductivity in Ag-doped ZnO twin grain boundaries
Effect of oxygen content on dielectric characteristics of Cr-doped LaTiOx
Spin-current pump in silicene Hot!
We report a theoretical study of pumped spin currents in a silicene-based pump device, where two time-dependent staggered potentials are introduced through the perpendicular electric fields and a magnetic insulator is considered in between the two pumping potentials to magnetize the Dirac electrons. It is shown that giant spin currents can be generated in the pump device because the pumping can be optimal for each transport mode, the pumping current is quantized. By controlling the relevant parameters of the device, both pure spin currents and fully spin-polarized currents can be obtained. Our results may shed a new light on the generation of pumped spin currents in Dirac-electron systems.
Theoretical study on the lasing plasmon of a split ring for label-free detection of single molecules and single nanoparticles
Controlling flexural waves in thin plates by using transformation acoustic metamaterials
Band offset and electronic properties at semipolar plane AlN(1101)/diamond heterointerface
Phase transition of a diblock copolymer and homopolymer hybrid system induced by different properties of nanorods
Theoretical investigation on the excited state intramolecular proton transfer in Me2N substituted flavonoid by the time-dependent density functional theory method
Time-dependent density functional theory (TDDFT) method is used to investigate the details of the excited state intramolecular proton transfer (ESIPT) process and the mechanism for temperature effect on the Enol*/Keto* emission ratio for the Me2N-substited flavonoid (MNF) compound. The geometric structures of the S0 and S1 states are denoted as the Enol, Enol*, and Keto*. In addition, the absorption and fluorescence peaks are also calculated. It is noted that the calculated large Stokes shift is in good agreement with the experimental result. Furthermore, our results confirm that the ESIPT process happens upon photoexcitation, which is distinctly monitored by the formation and disappearance of the characteristic peaks of infrared (IR) spectra involved in the proton transfer and in the potential energy curves. Besides, the calculations of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) reveal that the electronegativity change of proton acceptor due to the intramolecular charge redistribution in the S1 state induces the ESIPT. Moreover, the thermodynamic calculation for the MNF shows that the Enol*/Keto* emission ratio decreasing with temperature increasing arises from the barrier lowering of ESIPT.
Theoretical investigation of tunable polarized broadband terahertz radiation from magnetized gas plasma
The mechanism of terahertz (THz) pulse generation with a static magnetic field imposed on a gas plasma is theoretically investigated. The investigation demonstrates that the static magnetic field alters the electron motion during the optical field ionization of gas, leading to a two-dimensional asymmetric acceleration process of the ionized electrons. Simulation results reveal that elliptically or circularly polarized broadband THz radiation can be generated with an external static magnetic field imposed along the propagation direction of the two-color laser. The polarization of the THz radiation can be tuned by the strength of the external static magnetic field.
Equivalent magnetic dipole method used to design gradient coil for unilateral magnetic resonance imaging
The conventional magnetic resonance imaging (MRI) equipment cannot measure large volume samples nondestructively in the engineering site for its heavy weight and closed structure. In order to realize the mobile MRI, this study focuses on the design of gradient coil of unilateral magnet. The unilateral MRI system is used to image the local area above the magnet. The current density distribution of the gradient coil cannot be used as a series of superconducting nuclear magnetic resonance gradient coils, because the region of interest (ROI) and the wiring area of the unilateral magnet are both cylindrical side arc surfaces. Therefore, the equivalent magnetic dipole method is used to design the gradient coil, and the algorithm is improved for the special case of the wiring area and the ROI, so the X and Y gradient coils are designed. Finally, a flexible printed circuit board (PCB) is used to fabricate the gradient coil, and the magnetic field distribution of the ROI is measured by a Gauss meter, and the measured results match with the simulation results. The gradient linearities of x and y coils are 2.82% and 3.56%, respectively, less than 5% of the commercial gradient coil requirement.
Application of millimeter-sized polymer cylindrical lens array concentrators in solar cells
A unique method is proposed to encapsulate solar cells and improve their power conversion efficiency by using a millimeter-sized cylindrical lens array concentrator. Millimeter-sized epoxy resin polymer (ERP) cylindrical lens array concentrators are fabricated by the soft imprint technique based on polydimethylsiloxane stamps. The photovoltaic measurements show that millimeter-sized ERP cylindrical lens array concentrators can considerably improve the power conversion efficiency of silicon solar cells. The validity of the proposed method is proved by the coupled optical and electrical simulations. The designed solar cell devices with the advantages of high-efficiency and convenient cleaning are very useful in practical applications.
Efficient ternary organic solar cells with high absorption coefficient DIB-SQ as the third component
A series of organic solar cells (OSCs) are prepared with PTB7:PC71 BM as the host materials and DIB-SQ as the third component. The power conversion efficienty (PCE) of OSCs can be improved from 6.79% to 7.92% by incorporating 6 wt% DIB-SQ into donors, resulting from the enhanced short circuit current density (JSC) and fill factor (FF). The increased JSC of the optimized ternary OSCs should be attributed to the enhanced photon harvesting of teranry active layer by incorporating DIB-SQ. Meanwhile, FF of the optimized ternary OSCs should be due to the optimied phase separation. The open circuit voltage (VOC) of tenray OSCs can be maintained at a constant of 0.75 V, indicating that all photogenerated holes willl be transported along the channels formed by PTB7.
Simultaneous estimation of aerosol optical constants and size distribution from angular light-scattering measurement signals
Simulation of a torrential rainstorm in Xinjiang and gravity wave analysis