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The static electric dipole polarizabilities of the ground state and n ≤ 3 excited states of a lithium atom embedded in a weekly coupled plasma environment are investigated as a function of the plasma screening radium. The plasma screening of the Coulomb interaction is described by the Debye-Huckel potential and the interaction between the valence electron and the atomic core is described by a model potential. The electron energies and wave functions for both the bound and continuum states are calculated by solving the Schrodinger equation numerically using the symplectic integrator. The oscillator strengths, partial-wave, and total static dipole polarizabilities of the ground state and n ≤ 3 excited states of the lithium atom are calculated. Comparison of present results with those of other authors, when available, is made. The results for the 2s ground state demonstrated that the oscillator strengths and the static dipole polarizabilities from np orbitals do not always increase or decrease with the plasma screening effect increasing, unlike that for hydrogen-like ions, especially for 2s→3p transition there is a zero value for both the oscillator strength and the static dipole polarizability for screening length D = 10.3106a0, which is associated with the Cooper minima. [ABSTRACT FROM AUTHOR]

This paper investigates the stochastic resonance (SR) phenomenon in an asymmetric system with coupling between multiplicative and additive noise when the coupling between two noise terms is coloured. The approximate expression of signal-to-noise ratio has been obtained by applying the two-state theory and SR exhibits in the bistable system. Moreover, the potential asymmetry r and cross-correlation strength l can weaken the SR phenomenon, while the cross-correlation time t can strengthen the SR phenomenon. [ABSTRACT FROM AUTHOR]

Acoustic characteristics of pulse detonation engine (PDE) sound propagating in enclosed space are numerically and experimentally investigated. The finite element software LS-DYNA is utilized to numerically simulate the PDE sound propagating in enclosed space. Acoustic measurement systems are established for testing the PDE sound in enclosed space, and the time-frequency characteristics of PDE sound in enclosed space are reported in detail. The experimental results show that the sound waveform of PDE sound in enclosed space are quite different from those in open space, and the reflection and superposition of PDE sound on the walls of enclosed space results in the sound pressure oscillating obviously. It is found that the peak sound pressure level (PSPL) and overall sound pressure level (OASPL) of PDE sound in enclosed space are higher than those in open space and their difference increases with the rise of propagation distance. The results of the duration of PDE sound indicate that the A duration of PDE sound in enclosed space is higher than that in open space except at measuring points located at 2-m and 5-m while the B duration is higher at each of all measuring points. Results show that the enclosed space has a great influence on the acoustic characteristic of PDE sound. This research is helpful in performing PDE experiments in enclosed laboratories to prevent the PDE sound from affecting the safety of laboratory environment, equipment, and staffs. [ABSTRACT FROM AUTHOR]

This paper presents a review of recent advances in quantum well and quantum cascade infrared photodetectors developed in Shanghai Institute of Technical Physics, Chinese Academy of Sciences (SITP/CAS). Firstly, the temperature- and bias-dependent photocurrent spectra of very long wavelength (VLW) GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are studied using spectroscopic measurements and corresponding theoretical calculations in detail. We confirm that the first excited state, which belongs to the quasi-bound state, can be converted into a quasi-continuum state induced by bias and temperature. Aided by band structure calculations, we propose a model of the double excited states that determine the working mechanism in VLW QWIPs. Secondly, we present an overview of a VLW QWIP focal plane array (FPA) with 320×256 pixels based on the bound to quasi-bound (BTQB) design. The technology of the manufacturing FPA based on the QWIP structures has been demonstrated. At the operating temperature of 45 K, the detectivity of QWIP FPA is larger than with a cutoff wavelength larger than . Finally, to meet the needs of space applications, we proposed a new long wavelength quantum cascade detector with a broadband detection ranging from to . With a pair of identical coupled quantum wells separated by a thin barrier, acting as absorption regions, the relative linewidth () of response can be dramatically broadened to 30.7%. It is shown that the spectral shape and linewidth can be tuned by the thickness of the thin barrier, while it is insensitive to the working temperature. The device can work above liquid nitrogen temperature with a peak responsivity of 63 mA/W and Johnson noise limited detectivity of . [ABSTRACT FROM AUTHOR]

Acoustic characteristics of a pulse detonation engine (PDE) with and without an ellipsoidal reflector are numerically and experimentally investigated. A two-dimensional (2D) non-splitting unstructured triangular mesh Euler solver based on the space-time conservation element and solution element (CE/SE) method is employed to simulate the flow field of a PDE. The numerical results clearly demonstrate the external flow field of the PDE. The effect of an ellipsoidal reflector on the flow field characteristic near the PDE exit is investigated. The formation process of reflected shock wave and reflected jet shock are reported in detail. An acoustic measurement system is established for the PDE acoustic testing. The experimental results show that the ellipsoidal reflector changes the sound waveform and directivity of PDE sound. The reflected shock wave and reflected jet shock result in two more positive pressure peaks in the sound waveform. The ellipsoidal reflector changes the directivity of PDE sound from 20° to 0°. It is found that the peak sound pressure level (PSPL) and overall sound pressure level (OASPL) each obtain an increment when the PDE is installed with a reflector. The maximum relative increase ratio of PSPL and OASPL are obtained at the focus point F2, whose values are 6.1% and 6.84% respectively. The results of the duration of the PDE sound indicate that the reflecting and focusing wave generated by the reflector result in the increment of A duration and B duration before and near focus point F2. Results show that the ellipsoidal reflector has a great influence on the acoustic characteristic of PDE sound. The research is helpful for understanding the influence of an ellipsoidal reflector on the formation and propagation process of PDE sound. [ABSTRACT FROM AUTHOR]

Strontium titanate (SrTiO is a promising n-type material for thermoelectric applications. However, its relatively high thermal conductivity limits its performance in efficiently converting heat into electrical power through thermoelectric effect. This work shows that the thermal conductivity of SrTiO can be effectively reduced by annealing treatments, through an integrated study of laser flash measurement, scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray absorption fine structure, and first-principles calculations. A phonon scattering model is proposed to explain the reduction of thermal conductivity after annealing. This work suggests a promising means to characterize and optimize the material for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Two types of flexible terahertz metamaterials were fabricated on polyethylene naphthalate (PEN) substrates. The unit cell of one type consists of two identical split-ring resonators (SRRs) that are arranged face-to-face (i.e., FlexMetaF); the unit cell of the other type has nothing different but is arranged back-to-back (i.e., FlexMetaB). FlexMetaF and FlexMetaB illustrate the similar transmission dips under zero strain because the excitation of fundamental inductive–capacitive (LC) resonance is mainly dependent on the geometric structure of individual SRR. However, if a gradually variant strain is applied to bend FlexMetaF and FlexMetaB, the new resonant peaks appear: in the case of FlexMetaF, the peaks are located at the lower frequencies; in the case of FlexMetaB, the peaks appear at the frequencies adjacent to the LC resonance. The origin and evolution of strain-induced resonances are studied. The origin is ascribed to the detuning effect and the different responses to strain from FlexMetaF and FlexMetaB are associated with the coupling effect. These findings may improve the understanding on flexible terahertz metamaterials and benefit their applications in flexible or curved devices. [ABSTRACT FROM AUTHOR]

The ionization process of B2+ by H+ impact is studied using the continuum-distorted-wave eikonal-initial-state (CDW-EIS) method and the modified free electron peak approximation (M-FEPA), respectively. Total, single-, and double-differential cross sections from 1s and 2s orbitals are presented for the energy range from 10 keV/u to 10 MeV/u. Comparison between the results from the two methods demonstrates that the total and single-differential cross sections for the high-energy incident projectile case can be well evaluated using the simple M-FEPA model. Moreover, the M-FEPA model reproduces the essential features of the binary-encounter (BE) bump in the double-differential cross sections. Thus, the BE ionization mechanism is discussed in detail by adopting the M-FEPA model. In particular, the double- and singledifferential cross sections from the 2s orbital show a high-energy hip, which is different from those from the 1s orbital. Based on Ref. [1], the Compton profiles of B2+ for 1s and 2s orbitals are given, and the hips in DDCS and SDCS from the 2s orbital are explained. [ABSTRACT FROM AUTHOR]

The optical-induced dielectric tunability properties of DAST crystal in THz range were experimentally demonstrated. The DAST crystal was grown by the spontaneous nucleation method (SNM) and characterized by infrared spectrum. With the optimum wavelength of the exciting optical field, the transmission spectra of the DAST crystal excited by 532 nm laser under different power were measured by terahertz time-domain spectroscopy (THz-TDS) at room temperature. The transmitted THz intensity reduction of 26 % was obtained at 0.68 THz when the optical field was up to 80 mW. Meanwhile, the variation of refractive index showed an approximate quadratic behavior with the exciting optical field, which was related to the internal space charge field of photorefractive phenomenon in the DAST crystal caused by the photogenerated carrier. A significant enhancement of 13.7 % for THz absorption coefficient occurred at 0.68 THz due to the photogenerated carrier absorption effect in the DAST crystal. [ABSTRACT FROM AUTHOR]

Migration of He atoms and growth of He bubbles in high angle twist grain boundaries (HAGBs) in tungsten (W) are investigated by atomic simulation method. The energy and free volume (FV) of grain boundary (GB) are affected by the density and structure of dislocation patterns in GB. The migration energy of the He atom between the neighboring trapping sites depends on free volume along the migration path at grain boundary. The region of grain boundary around the He bubble forms an ordered crystal structure when He bubble grows at certain grain boundaries. The He atoms aggregate on the grain boundary plane to form a plate-shape configuration. Furthermore, high grain boundary energy (GBE) results in a large volume of He bubble. Thus, the nucleation and growth of He bubbles in twist grain boundaries depend on the energy of grain boundary, the dislocation patterns and the free volume related migration path on the grain boundary plane. [ABSTRACT FROM AUTHOR]

The N and C doping effects on the crystal structures, electronic and optical properties of fluorite structure CeO2 have been investigated using the first-principles calculation. Co-doping these two elements results in the local lattice distortion and volume expansion of CeO2. Compared with the energy band structure of pure CeO2, some local energy levels appear in the forbidden band, which may facilitate the light absorption. Moreover, the enhanced photo-catalytic properties of CeO2 were explained through the absorption spectra and the selection rule of the band-to-band transitions. [ABSTRACT FROM AUTHOR]

Microwave-absorbing polymeric composites based on single-walled carbon nanotubes (SWNTs) are fabricated via a simple yet versatile method, and these SWNT—epoxy composites exhibit very impressive microwave absorption performances in a range of 2 GHz–18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT—epoxy composites (1.3-mm thickness) with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appropriate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix. [ABSTRACT FROM AUTHOR]

In this paper, we propose a controlled quantum state sharing scheme to share an arbitrary two-qubit state using a five-qubit cluster state and the Bell state measurement. In this scheme, the five-qubit cluster state is shared by a sender (Alice), a controller (Charlie), and a receiver (Bob), and the sender only needs to perform the Bell-state measurements on her particles during the quantum state sharing process, the controller performs a single-qubit projective measurement on his particles, then the receiver can reconstruct the arbitrary two-qubit state by performing some appropriate unitary transformations on his particles after he has known the measured results of the sender and the controller. [ABSTRACT FROM AUTHOR]