An N-fold Darboux transformation with multi-parameters for the famous Belov–Chaltikian lattice is derived with the aid of the gauge transformation between the corresponding discrete 3×3 matrix spectra. By using the Darboux transformation and the reduction technique, new multi-soliton solutions for the Belov–Chaltikian lattice, which are proved to be of solitary features, are given in the exponential form.

The quantum adiabatic theorem is the basis of adiabatic quantum computation. However, the exact necessary and sufficient conditions for adiabatic evolution are still under debate. We discuss the adiabatic condition of a system undergoing a special evolution route, and obtain an explicit formula that is necessary and sufficient for the adiabatic evolution in this route. Based on this formula, we find that the traditional adiabatic condition is neither sufficient nor necessary. Finally, we show that no adiabatic process can occur even the evolution speed goes to 0 in some examples, which is surprising since the adiabatic theorem states that if the evolution of a system is slow enough, the adiabatic process could occur.

Considering the cosmological constant Λ as a thermodynamic pressure and its conjugate quantity as a thermodynamic volume as proposed by Kubiznak and Mann [J. High Energy Phys. 1207 (2012) 033], we discuss the critical behavior of charged AdS black hole in arbitrary dimensions d. In particular, we present a comparative study in terms of the spacetime dimension d and the displacement of critical points controlling the transition between the small and the large black holes. Such behaviors vary nicely in terms of d. Our result shows that the equation of state for a charged Reissner–Nordstrom AdS black hole predicts an universal number given by (2d?5)/(4d?8). The three-dimensional solution is also discussed.

A method of measuring laser frequency stability is proposed by using the spectral-hole-burning technique. The power spectra of the measured laser can be recorded as a spectral hole, and the engraving time of the spectral hole is mapped into the frequency of the measured laser. Frequency fluctuation can be expressed by spectral hole frequency variation with different engraving times. By using the proposed method, the frequency stability of the external-cavity diode laser is measured to be 2.22×10^{?9} with an integration time of 20 ms. The frequency stability measurement resolution reaches 14 kHz and the repetition rate is 50 Hz. Compared to the conventional method, it avoids the need for a high stability reference laser source.

In the design of resonators in low phase noise bulk acoustic wave (BAW) oscillators, maximization of quality factor is the primary target while energy trapping is not typically of concern. Analysis shows that although energy-trapping mode energy outside the electroded region decreases exponentially with distance away from the electrode edge of the wafer, the decaying wave will reflect at the wafer edge to the electroded region and generate a wave with same frequency but different phase which generates mutual modulation with resonant frequency. It is a source of phase noise and mainly affects the near-carrier-frequency phase noise. Two 120 MHz SC-cut 5^{th} overtone UM-1 crystals with similar dynamic equivalent parameters and different shunt capacitances are compared using the same circuit. Experimental results show that energy trapping also needs to be considered in the design of resonators in low phase noise BAW oscillators.

An atomic magnetometer based on optically detected magnetic resonance is investigated and demonstrated experimentally. We build an 894 nm external cavity diode laser which is frequency locked to the F=4→F'=3 transition of Cs D_{1} line with DAVLL spectroscopy. With the phase-locked loop, the frequency of the rf coils is actively locked to the Larmor frequency and the magnetometer tracks the magnetic field variations in a phase coherent manner. An ultimate sensitivity of 19 fT/Hz^{1/2} and an intrinsic sensitivity of 8.6 pT/Hz^{1/2} in the magnetic environment which is close to geomagnetic field have been achieved with the spatial resolution smaller than 2 cm.

The assignment of the meson nonet is phenomenologically analyzed in the framework of Regge phenomenology and meson-meson mixing. The mass of the partner of in the 1^{3}F_{4} meson nonet is determined to be 2167±27 MeV. The quarkonia content and the decay properties of the two isoscalar states of the 1^{3}F_{4} meson nonet are presented. The predictions can be tested by the BES-III experiment in the near future.

The equation of state (EOS) of cold and dense strongly interacting matter is crucial for better research of compact stars, i.e., neutron stars and quark stars. We generalize our improved quasi-particle model from finite temperature and zero chemical potential [Phys. Lett. B 711 (2012) 65] to the case of zero temperature and finite chemical potential to obtain an EOS of our improved quasi-particle model and then apply this EOS to study the structure of a quark star. The results are consistent with the most recent astronomical observational data.

LI Kuo-Ang, YE Yan-Lin, Heiko SCHEIT, Pieter DOORNENBAL, Satoshi TAKEUCHI, Nori AOI, Masafumi MATSUSHITA, Eri TAKESHITA, Tohru MOTOBAYASHI, Hiroyoshi SAKURAI, PANG Dan-Yang

Chin. Phys. Lett. 2012, 29 (10):
102301
.
DOI: 10.1088/0256-307X/29/10/102301

The first excited 2^{+} state (885 keV) of ^{32}Mg and its corresponding deformation parameter β_{2} are studied with proton inelastic scattering at 190 MeV/nucleon using in-beam γ technology with a thick target. Angular distributions of the inelastic scattering cross sections are analyzed with coupled-channel calculations. The deformation parameter β_{2}=0.41(3) obtained in this work agrees with the earlier experimental results obtained at lower beam energies. Our work demonstrates that the structure of unstable nuclei can be studied with proton inelastic scattering at high incident energies in the vicinity of 200 MeV/nucleon using thick targets.

We calculate the production of real photons originating from the photoproduction in relativistic pp collisions. The Weizs?cker–Williams approximation in the photoproduction is considered. Numerical results agree with the experimental data from the Relativistic Heavy Ion Collider and the Large Hadron Collider. We find that the modification of the photoproduction is more prominent in large transverse momentum regions.

The radiative and Auger decay processes of K-shell ionized Np ions are studied theoretically using the flexible atomic code (FAC). Relativistic effects, Breit interaction, QED corrections and nuclear finite mass and volume effects are considered systematically. The resulting calculated K x-rays and Auger spectra of Np are compared with the measured spectra emitted after the electron-capture (EC)-decay of mass-separated ^{237}Pu. The general consistency between theory and experiment is good; the relative intensities and relative positions of the peaks in the measured spectra are reproduced with good accuracy, in spite of the existence of different ways to produce the primary K-shell vacancy, enabling identification of the observed structure in the experimental spectra. We find that most of the radiative transition rates are greater than the Auger transition rates, and the latter decrease rapidly with the transfer of initial vacancies to the outer shell.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

A dual band planar antenna based on metamaterial transmission lines is presented for WLAN, WiMAX, and satellite system communication applications. This antenna is composed of an interdigital capacitor and a ground plane with triangular shaped slots on its top edges to broaden the impedance bandwidth. The measured bandwidth for 10 dB return loss is from 3.29 to 4.27 GHz and 5.04 to 9.8 GHz, covering the 5.2/5.8 GHz WLAN, 3.5/5.5 GHz WiMAX bands, and the X-band satellite communication systems at 7.4 GHz. The proposed antenna exhibits stable monopole-like radiation patterns and enough gains across the dual operating bands.

We investigate the dispersive and absorptive properties of an N-type four-level atomic system in three coherent fields, and consider the susceptibility mathematically. It is shown that the group velocity of the probe field exhibits sub- and super-luminal under some conditions, meanwhile the absorption coefficient keeps zero during the occurrence and transition process of sub- and super-luminal pulses.

Terahertz (THz) quantum well photodetectors (QWPs) are an extension of quantum well infrared photodetectors in the THz region. We construct an imaging system based on a THz QWP with a narrow response range from 3 THz to 6 THz. The peak responsivity of the THz QWP having background-limited performance is about 0.5 A/W, and the corresponding detectivity reaches 10^{11}cm?Hz^{1/2}/W at temperature of 4.2 K. We obtain the images of a concealed object by the imaging system and prove that THz QWPs have the potential for imaging applications.

We report the coherent resonant emission of the exciton state in a single InAs quantum dot, embedded in a planar optical microcavity. The quantum dot is excited by a laser beam from the cleaved sample edge, and the resonant fluorescence is collected in the direction perpendicular to the excitation laser beam, so the residual laser scattering can be deeply suppressed. This experimental setup enables us to observe Rabi oscillation and a Mollow triplet with Rabi energy up to about 27 μeV.

Polymeric semiconductors spin-coated onto the photoresist grating form discontinuously distributed flocci, which do not fill grating grooves with nanoscale widths. Thus, the polymer layer neither forms a continuous gain channel nor creates a waveguide that enhances the distributed feedback (DFB) mechanism provided by the grating structures. This is verified by the microscopic and spectroscopic investigations on the topographic surface of the polymer-covered grating as it is etched layer by layer using oxygen plasma. This gives more insights into the mechanisms involved in optically pumped polymer lasers and provides new guidance for constructing DFB lasers.

We propose a stable and high optical signal-to-noise ratio (OSNR) compound linear-cavity single-longitudinal-mode (SLM) erbium-doped silica fiber laser. It consists of three uniform fiber Bragg gratings (FBGs) and two fiber couplers to form a simple asymmetric four-cavity structure to select the longitudinal mode. The stable SLM operation at the wavelength of 1544.053 nm with a 3 dB bandwidth of 0.014 nm and an OSNR of ～60 dB was verified experimentally. Under laboratory conditions, a power fluctuation performance of less than 0.05 dB for 5 h and wavelength variation of less than 0.01 nm for about 150 min is demonstrated. Finally, the characteristic of laser output power as a function of pump power is investigated. The proposed system provides a simple and cost-effective approach to realize a stable SLM fiber laser.

We theoretically investigate the single photon transport in a coupled resonator waveguide embedded in a semiconductor quantum dot with a V-type system. The transmission and reflection amplitudes are obtained by using a discrete coordinates approach. It is shown that the photon transport properties can be controlled by the energy detuning between the two excited states of the V-type system, and the coupling strength between the photon and the V-type system. We also compare the single photon transport properties in the waveguide with sinusoidal and linear dispersion relations.

Blue-shifted dispersive waves (DWs) are efficiently generated from the red-shifted solitons by coupling the 120 fs pulses into the fundamental mode of the multi-knots of a photonic crystal fiber cladding. When the femtosecond pulses at the wavelength of 825 nm and the average power of 300 mW are coupled into knots 1–3, the conversion efficiency η_{DW} of 32% and bandwidth B_{DW} of 50 nm are obtained. The ultrashort pulses generated by the DWs can be tunable over the whole visible wavelength by adjusting the wavelengths of the pump pulses coupled into different knots. It can be believed that this widely wavelength-tunable ultrashort visible pulse source has important applications in ultrafast photonics and resonant Raman scattering.

A compressed terahertz imaging method using a terahertz time domain spectroscopy system (THz-TDSS) is suggested and demonstrated. In the method, a parallel THz wave with the beam diameter 4 cm from a usual THz-TDSS is used and a square shaped 2D echelon is placed in front of an imaged object. We confirm both in simulation and in experiment that only one terahertz time domain spectrum is needed to image the object. The image information is obtained from the compressed THz signal by deconvolution signal processing, and therefore the whole imaging time is greatly reduced in comparison with some other pulsed THz imaging methods. The present method will hopefully be used in real-time imaging.

A fiber-optic liquid-level sensor is proposed and experimentally demonstrated. It is a Mach–Zehnder interferometer (MZI) composed of a thin-core single-mode fiber (TCSMF) without coating sandwiched between two single-mode fibers (SMFs). The transmission spectrum properties of the MZI modified by liquid around the TCSMF are used for detecting the liquid level. It is found that the sensor exhibits an excellent linear relationship between the level and the shift of interference dip wavelength and its achieved sensitivities are 0.160 nm/mm and 0.288 nm/mm for liquid with an RI of 1.3330 and 1.3696, respectively. Employing the spectrum differential integration (SDI) method to analyze transmission spectra can increase the detecting resolution of the liquid level. Due to its advantages of an extremely easy fabrication process, high sensitivity and a large sensing range, the sensor is an ideal candidate for continuous liquid level sensing.

A novel structure based on a side-coupled cavity for optical wavelength demultiplexing is proposed and demonstrated numerically by using the two-dimensional finite element method. It is found that the transmission wavelength of each channel can be tuned by adjusting the geometrical parameters of the structure and the material filling the side-coupled cavity. Moreover, by introducing a reflection nanocavity, the value of the transmitted-peak can be improved significantly. The results of theoretical analysis and simulation are well consistent with each other.

We investigate the influence of the coherent effect on femtosecond time-resolved Z-scan measurements using a degenerate pump-probe Z-scan technique. The time response of the light-induced transient grating (LITG) of Bi_{2}O_{3}-B_{2}O_{3}-SiO_{2} (BI) glass shows a valley-peak variation, which has an obvious influence on the time-resolved Z-scan measurements. The valley-peak variation of the LITG signals with the delay time in BI glass is due to coherent transient energy transfer between positively chirped pump and probe pulses. The influence of the LITG effect on the closed-aperture time-resolved Z-scan measurements could be reduced by adjusting the position of the aperture transversely.

The velocity of sound in soap foams at high gas volume fractions is experimentally studied by using the time difference method. It is found that the sound velocities increase with increasing bubble diameter, and asymptotically approach to the value in air when the diameter is larger than 12.5 mm. We propose a simple theoretical model for the sound propagation in a disordered foam. In this model, the attenuation of a sound wave due to the scattering of the bubble wall is equivalently described as the effect of an additional length. This simplicity reasonably reproduces the sound velocity in foams and the predicted results are in good agreement with the experiments. Further measurements indicate that the increase of frequency markedly slows down the sound velocity, whereas the latter does not display a strong dependence on the solution concentration.

We present a photoacoustic imaging system for rapid high-resolution photoacoustic imaging of blood vessels based on an annular transducer array. The annular transducer array consists of 256 elements arranged along a 300° arc with a 50-mm radius of curvature, using piezocomposite technology for high sensitivity and high signal-to-noise ratio. An eight-channel data acquisition system is applied to capture the photoacoustic signals using multiplexing and a limited-view filtered back projection algorithm is used to reconstruct the photoacoustic images. The experiments with phantom and blood vessels of a chicken are performed and clear photoacoustic images are obtained. The results demonstrate that the photoacoustic imaging system using the annular transducer array holds the potential application in monitoring neovascularization in tumor angiogenesis.

Sound propagation in a wedge with perfectly reflecting boundaries is one of the few range-dependent problems with an analytical solution. Since sound propagation towards the wedge apex will be completely backscattered due to the perfectly reflecting boundaries, this test problem is an ideal benchmark for a full two-way solution to the wave equation. An analytical solution for sound propagation in a wedge with a pressure-release sea surface and a pressure-release bottom was presented by Buckingham et al. [J. Acoust. Soc. Am. 87 (1990) 1511]. The ideal wedge problem with a rigid bottom is also of great importance in underwater acoustics. We present an analytical solution to the problem with a wedge bounded above by a pressure-release sea surface and below by a rigid bottom, which may be used to provide informative means of investigating the sound field in depth-varying channels, and to establish the accuracy of numerical propagation models for which it is difficult to treat problems with a pressure-release bottom. A comparison of the analytical solution and the numerical solution recently proposed by Luo et al. [Chin. Phys. Lett. 29 (2012) 014302] is also presented, indicating that this numerical propagation model provides high accuracy.

The experimental investigation on transparent solid/solid (aluminum and plexiglas) interface leaky waves generated by a pulse laser and detected with a photoelastic effect technique is reported. Three waves, i.e., longitudinal head wave, leaky Rayleigh wave and leaky interface wave, are detected successfully. The leaky waves propagating along the 'weak bonding' interface are also measured. It is found that with the continuing epoxy solidification, the wave amplitude gradually decreases and the two leaky waves are more difficult to distinguish. The velocities of the detected interface wave are in good agreement with the theoretical calculation and the attenuation characteristics of the two leaky waves are also in accordance with the theoretical prediction.

The phenomenon of vibrational resonance in fractional-order anharmonic oscillators is investigated. Based on the method of separating slow and fast motions, the approximate solution of the response amplitude is obtained. Both analytical and numerical results show that not only the high-frequency signal but also the fractional-order damping can induce vibrational resonance. The present results provide a new way to control periodical signals in coupled systems.

Based on the impact of a desired following speed and safe distance on driving behaviour, we establish a cooperative car-following model (CCFM). The dynamics analysis results indicate that no unrealistic deceleration or collision occurs in the CCFM. Also, this model can describe the kinetic property in the processes of starting and braking. In addition, evolution of a small perturbation can be reproduced in a numerical simulation. Compared to the full velocity difference model (FVDM), the CCFM has a wider range of stability and a much smaller blocking region width. Meanwhile, the CCFM averts negative velocity, and is accordingly advanced compared with the comprehensive optimal velocity model (COVM). Moreover, the CCFM describes the deceleration process more smoothly than both the FVDM and COVM.

The inter-scale energy transfer process is one of the key issues in the multi-scale nature of turbulent flows. A direct numerical simulation of homogeneous isotropic turbulent flows is conducted and the energy transfer is studied in detail in spectral space. The band-to-band energy transfer function involving non-local triad interactions with large scale modes peaks sharply. The similarity of this non-local energy transfer function is observed in both the shape and the amplitude. In addition, the similarity is satisfied in both the inertial subrange and dissipation range, implying that it is a general property of turbulence. The amplitude is determined by wave numbers p and q independently in a power law, with the power rates ?3 and ?2, respectively.

The high resolution numerical perturbation (NP) algorithm is analyzed and tested using various convective-diffusion equations. The NP algorithm is constructed by splitting the second order central difference schemes of both convective and diffusion terms of the convective-diffusion equation into upstream and downstream parts, then the perturbation reconstruction functions of the convective coefficient are determined using the power-series of grid interval and eliminating the truncated errors of the modified differential equation. The important nature, i.e. the upwind dominance nature, which is the basis to ensuring that the NP schemes are stable and essentially oscillation free, is firstly presented and verified. Various numerical cases show that the NP schemes are efficient, robust, and more accurate than the original second order central scheme.

Steady non-similarity thermal boundary layer flow over a stretching flat plate is investigated. The velocity and temperature on the surface are assumed to vary with the distance. The energy equation is solved with the homotopy analysis method which is suitable for strongly non-linear problems. This approach is more general than the similarity methods and is valid in the whole spatial and temporal regions. The results are compared with the similarity solutions for special cases of velocity and temperature profiles on the wall. The effect of different parameters on the Nusselt number and temperature profiles is investigated.

Surface roughness is experimentally used to control the flat-plate boundary layer bypass transition induced by an upstream convected two-dimensional (2D) circular cylinder wake. It is shown that the later stage of this bypass transition is successfully postponed, at the price of accelerating the earlier transition stage. A regularisation process of the hairpin vortices, which are the dominant coherent structures to promote the transition process, are observed under the influence of roughness elements. Significant scale reduction and localisation of these hairpins are achieved, which enhances the possibility of a hairpin self-annihilation process. Therefore, the cascade to large-scale structures in the later transition stage might be impeded/weakened.

A self-learning fractal interpolation algorithm to construct synthetic fields with statistical properties close to real turbulence is proposed. Different from our previous work [Phys. Rev. E 84 (2011) 026328, 82 (2010) 036311], the position mapping and stretching factors between the adjacent large and small scales are learned from the initial information. Using this method, a turbulence-like field with K41 spectra and without dissipation is constructed well through a coarse grid velocity signal from one experiment's data. After filtering the interpolated signal appropriately, the probability distribution of velocity, velocity structure functions and the anomalous scaling law of the synthetic field are close to those of the original signal.

The wall-adapting local eddy-viscosity (WALE) and Vreman subgrid scale models for large eddy simulations are compared within the framework of a generalised lattice Boltzmann method. Fully developed turbulent flows near a flat wall are simulated with the two models for the shear (or friction) Reynolds number of 183.6. Compared to the direct numerical simulation (DNS), damped eddy viscosity in the vicinity of the wall and a correct velocity profile in the transitional region are achieved by both the models without dynamic procedures. The turbulent statistics, including, e.g., root-mean-square velocity fluctuations, also agree well with the DNS results. The comparison also shows that the WALE model predicts excellent damped eddy viscosity near the wall.

An improved Boltzmann plot method where the intensity is taken as the integral of the experimental spectrum within a special band for a cluster of a rotational line of R and Q branches is proposed. This method aims at deducing rotational and vibrational temperatures using CH radical A^{2}Δ→X^{2}Π band emission spectroscopy accurately. In addition, the data relative to the rotation lines of CH (A^{2}Δ→X^{2}Π) for both temperatures are assembled. The emission spectrum of CH (A^{2}Δ→X^{2}Π) at the inner cone of an acetylene-oxygen flame in a rich oxygen state is recorded and both of the temperatures are determined by the above-mentioned method. The values are recorded as 3141 K and 3097 K, for the rotational and vibrational temperatures, respectively. This result reveals that the equilibrium between the rotation and vibration states is achieved. A simple discussion for this method is also provided.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

A theoretical investigation is carried out to understand the basic features of ion-acoustic (IA) waves in an unmagnetised plasmas including cool ions, hot ions having a kappa distribution and kappa-distributed electrons, using small amplitude techniques. The effects of excess suprathermal ions, the ion temperature T_{i} and electron temperature T_{e} as well as the density ratio on the IA waves are studied. It is found that the suprathermality effects play an important role in the system, as the geometric characteristics of the IA solitons are found to be significantly affected through the ion and electron suprathermal index. In the presence of suprathermality effects, either polarity is in principle supported by this plasma model.

A conceptual design study of the HL-2M facility has shown that one can create not only a standard single-null divertor configuration on it, but also a second-order null (snowflake (SF)) configuration. For the SF divertor, the magnetic flux expansion closes to the separatrix and exceeds that of the standard configuration by more than a factor of 4 at the outer divertor. The heat load at the divertor targets of this innovative configuration has been investigated by using B2.5-Eirene. It is shown that the heat load it targets is different from that of the standard configuration. As a result of the magnetic flux expansion, the peak heat load reduces and does not concentrate on a small area near the separatrix. The heat load profile becomes flat as compared to the standard divertor. When the upstream density is 2.0×10^{19}/m^{3} with 10 MW heating power flowing into the SOL/divertor regions, the peak load at the outer divertor is 1.64 MW/m^{2} for the SF divertor, but it is 3.2 MW/m^{2} for the standard divertor, so the SF divertor can mitigate the heat load at the divertor targets when HL-2M operates at low plasma density and high heating power.

Experimental data obtained on audio frequency (100–10000 Hz) discharge in argon at four pressures 50, 60, 70, and 80 mTorr are presented. The data show significant changes of the discharge current waveform with frequency. These changes seem to be associated with the glow discharge profile and colour. An empirical model based on the assumption of a frequency-dependent breakdown voltage is used to describe the experimental data.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

In situ high pressure experiment of V_{2}O_{3} is carried out by means of synchrotron radiation angle dispersive x-ray diffraction with the diamond anvil cell technique up to about 42 GPa at room temperature. A reversible phase transition unreported previously is observed at above 31 GPa. The c-axis compressibility of corundum-type V_{2}O_{3} shows an abnormal behavior, i.e., the axial length increasing up to 9 GPa then decreasing at higher pressures, which could be attributed to the 3d electronic interaction. The results of compression for V_{2}O_{3} are described by the second-order Birch–Murnaghan equation of state with V_{0}=300.2(4) ?^{3} and B_{0}=255(9) GPa.

The colourless IaA-type gem-quality diamond crystals containing a high concentration of nitrogen (1500–1700 ppm) were successfully prepared by annealing the as-grown Ib-type N-doped diamonds at a high temperature and high pressure in China-type cubic anvil high-pressure apparatus. Experiments were carried out at pressures of 6.5–7.0 GPa and temperatures from 1900 K to 2100 K. Annealing treatment on high-level N-doped diamond crystals shows that the colour of the diamond crystals is obviously reduced from green to colourless after annealing treatment within 1 h at a higher temperature, which is induced by nitrogen aggregation in the diamond lattice indicated by infrared (IR) spectroscopy. It is further revealed that active energy of the nitrogen atom transforming from the dispersed form to the aggregated form is much lower than that in the standard Ib-type diamond crystals with nitrogen concentration less than 300 ppm. The colourless IaA-type diamond crystal prepared by annealing at 2100 K displays the same properties in IR spectra as the high-quality natural diamonds which are classified into the IaA type.

Zn_{0.95}Ni_{0.05}O and Zn_{0.90}Ni_{0.05}Al_{0.05}O compositions of nanocrystallites are synthesised using the well recognised auto-combustion technique. The x-ray diffraction patterns demonstrate the phase pure characteristic wurtzite-type crystal structure with space group P6_{3}mc in both the compositions. The elemental incorporation of Ni and Al contents into the ZnO structure is confirmed by energy dispersive x-ray analysis. The micrographs of scanning electron microscopy show an approximate ordered morphology. The electrical resistivity is observed to decrease with the rising temperature, depicting the characteristic semiconductor behaviour of the samples. The lower values of resistivity and ferromagnetic interactions in the Al-doped sample correspond to an increase of carrier's density. It is observed that the carrier mediated mechanism is mainly responsible for ferromagnetism in ZnO-based diluted magnetic semiconductors.

The creep damage in high temperature resistant titanium alloys Ti60 is measured using the nonlinear effect of an ultrasonic Lamb wave. The results show that the normalised acoustic nonlinearity of a Lamb wave exhibits a variation of the "increase-decrease" tendency as a function of the creep damage. The influence of microstructure evolution on the nonlinear Lamb wave propagation has been analyzed based on metallographic studies, which reveal that the normalised acoustic nonlinearity increases due to a rising of the precipitation volume fraction and the dislocation density in the early stage, and it decreases as a combined result of dislocation change and micro-void initiation in the material. The nonlinear Lamb wave exhibits the potential for the assessment of the remaining creep life in metals.

The magnetic anomaly associated with the premartensitic transformation (PT) in Heusler alloy Ni_{2}MnGa is investigated by using the Green's function technique based on the magnon-TA phonon interaction. The results of the numerical calculations suggest that the magnetic anomaly during the PT may originate from the strong magnon-TA phonon interaction, because this kind of coupling effect will destroy the magnetic ordering in some local zones and reduce the magnetization of the system. Magnon-magnon interaction plays a positive role in enhancing the magnetization and tends to reduce the PT temperature while this kind of interaction has little effect on the characteristic TA phonon-wavevector corresponding to the anomaly of spontaneous magnetization at the PT temperature.

Microstructure evolution in the surface layer of hydrogenated amorphous silicon (a-Si:H) film exposed to H_{2} plasma is investigated using grazing-incidence small-angle x-ray scattering and attenuated total reflection-Fourier transform infrared spectroscopy. Molecular hydrogen generated in the microvoids through H-abstraction reaction drives the evolution of the void shape from spherical to ellipsoidal as well as increases the average void volume and total void volume fraction. High-pressure H_{2} in the microvoid promotes the formation of a strained structure with high compressive stress within the a-Si:H film, which favours the generation of the SiH_{n} complex in the subsurface layer of the a-Si:H film by H insertion into strained Si–Si bonds.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

ZHANG Xu, LIU Bo, PENG Cheng, RAO Feng, ZHOU Xi-Lin, SONG San-Nian, WANG Liang-Yong, CHENG Yan, WU Liang-Cai, YAO Dong-Ning, SONG Zhi-Tang, FENG Song-Lin

Chin. Phys. Lett. 2012, 29 (10):
107201
.
DOI: 10.1088/0256-307X/29/10/107201

The results of adhesion improvement and SET-RESET operation voltage reduction for the GeN buffer layer are presented. It is found that the adhesive strength between the Ge_{2}Sb_{2}Te_{5}(GST) layer and the layer below could be increased at least 20 times, which is beneficial for solving the phase change material peeling issue in the fabrication process of phase change memory (PCM). Meanwhile, the RESET voltage of the PCM cell with a 3-nm-thick GeN buffer layer can be reduced from 3.5 V to 2.2 V. The GeN buffer layer will play an important role in high density and low power consumption PCM applications.

A novel controllable hybrid-anode AlGaN/GaN field-effect rectifier (HA-FER) with low operation voltage (LOV) is proposed. Its mechanism can be explained by the field-controlled energy band model. This model reveals that the electric field in the AlGaN layer alters the energy band to result in a variation of the two-dimensional electron gas (2DEG) at AlGaN/GaN interface; the field can be changed by the thickness d of the AlGaN layer and the applied bias. As the d reduces below the critical thickness, the 2DEG vanishes and then the channel is pinched off. Therefore, the threshold voltage of HA-FER can be designed as low as 0 V leading to LOV (<1 V). The analytical characteristic of the HA-FER is calculated and validated by the simulated results. These results also demonstrate that the forward properties of HA-FER are superior to the conventional SBD due to the high Schottky barrier.

We investigate the electronic structures of InGaN_{2} nanotubes (NTs) using first-principles calculations. It is found that all four types of InGaN_{2} NTs, with the same diameter, have similar stability. The total energy of the per unit InGaN_{2} NT depends on its diameter due to the curvature effect. The zigzag (armchair) InGaN_{2} NTs have direct (indirect) band gaps. The band gap increases for all of the InGaN_{2} NTs when their diameters increase. The valence band maximum (VBM) states of the InGaN_{2} NTs are p-like states localised around N atoms. The p-like VBM states in zigzag (armchair) InGaN_{2} NTs are perpendicular (parallel) to the tube axis.

We study electronic spin-polarised transport in a system composed of a quantum dot (QD) connected to one normal metal electrode and one ferromagnetic one. The electrical current of each spin component and the spin accumulation on the QD are calculated by using the nonequilibrium Green's function method. We find that in the Coulomb blockade regime, the current spin polarisation can reach 100% under a strong magnetic field. Meanwhile, the spin accumulation on the QD approaches to unit, and thus the dot is occupied by electrons of one certain spin orientation. The system can operate as a spin injector from a normal metal reservoir to a semiconductor material, and may find real usage in solid state quantum information processes.

We present experimental and numerical studies on the enhanced light narrow transmission through cascaded Au/SiO_{x}N_{y}/Au aperture arrays by varying the refractive index and thickness of SiO_{x}N_{y}. It is found that the enhancement as well as narrowing of the optical transmission originates from the coupling role of surface plasmon polaritons. The results indicate that the transmission enhancement is highly dependent on the refractive index and thickness of SiO_{x}N_{y}. A higher transmission efficiency and narrower peak are obtained in Au/SiO_{2.1}N_{0.3}/Au structure with a small refractive index (1.6) and thin thickness (0.2 μm).

The p-NiO thin film is prepared by radio frequency magnetron sputtering on the n-GaN/sapphire substrate to form p-NiO/n-GaN heterojunction diodes. The structural, optical and electrical properties of the p-NiO thin film are investigated. The results indicate that the NiO film has good crystal qualities and stable p-type conductivities. The current-voltage measurement of the p-NiO/n-GaN diode exhibits typical rectifying behaviour with a turn-on voltage of about 2.2 V. Under forward bias, a prominent ultraviolet emission centered at 375 nm is observed at room temperature. Furthermore, the mechanism of the light emission is discussed in terms of the band diagrams of the heterojunction in detail.

The electronic band structure and optical parameters of SnMg_{2}O_{4} are investigated by the first-principles technique based on a new potential approximation known as modified Becke–Johnson (mBJ). The direct band gap values by LDA, GGA and EV-GGA are underestimated significantly as compared to mBJ-GGA, which generally provides the results comparable to the experimental values. Similarly, the present band gap value (4.85 eV) using mBJ-GGA is greatly enhanced to the previous value by EV-GGA (2.823 eV). The optical parametric quantities (dielectric constant, index of refraction, reflectivity, optical conductivity and absorption coefficient) relying on the band structure are presented and examined. The first critical point (optical absorption's edge) in SnMg_{2}O_{4} occurs at about 4.85 eV. A strong absorption region is observed, extending between 5.4 eV to 25.0 eV. For SnMg_{2}O_{4}, static dielectric constant ε_{1}(0), static refractive index n(0), and the magnitude of the coefficient of reflectivity at zero frequency R(0) are 2.296, 1.515 and 0.0419, respectively. The optoelectronic properties indicate that this material can be successfully used in optical devices.

XIA Feng-Jin, WU Hao, FU Yue-Ju, XU Bo, YUAN Jie, ZHU Bei-Yi, QIU Xiang-Gang, CAO Li-Xin, LI Jun-Jie, JIN Ai-Zi, WANG Yu-Mei, LI Fang-Hua, LIU Bao-Ting, XIE Zhong, ZHAO Bai-Ru

Chin. Phys. Lett. 2012, 29 (10):
107402
.
DOI: 10.1088/0256-307X/29/10/107402

Oxide transistor is the basic device to construct the oxide electronic circuit that is the backing to develop integrated oxide electronics with high efficiency and low power consumption. By growing the perovskite oxide integrated layers and tailoring them to lead semiconducting functions at their interfaces, the development of oxide transistors may be able to perform. We realize a kind of p-i-n type integrated layers consisting of an n-type cuprate superconductor, p-type colossal magnetoresistance manganite, and a ferroelectric barrier (i). From this, bipolar transistors were fabricated at the back-to-back p-i-n junctions, for which the Schottky emission and p-n junction barriers, as well as the ferroelectric polarization, were integrated into the interfaces to control the transport properties; a preliminary but distinct current gain greater than 1.6 at input current of microampers order was observed. These results present a real possibility to date for developing bipolar all perovskite oxide transistors.

The formula for a magnetic fluid's apparent density is derived based on Bernoulli's equation of magnetic fluid, and the distribution of the magnetic fluid's apparent density is measured by the intelligent apparatus of measuring a magnetic fluid's apparent density in an applied perpendicular magnetic field. Magnetic particle chain-like alignments are observed by a transmission electron microscope (TEM). Without an applied magnetic field, the magnetic fluid's density is equal everywhere and the distribution of magnetic particles is homogeneous and unordered. When magnetic induction and magnetic induction gradient gather strength in an applied perpendicular magnetic field, the magnetic fluid's apparent density increases gradually, and more chain-like structures are formed and aligned with the direction of the magnetic field. The results of magnetic particle alignments are correspondent with the distribution of the magnetic fluid's apparent density. Both of them result from particle-particle interactions and particle-carrier liquid interactions, which are eventually controlled by the applied magnetic induction and magnetic induction gradient distribution.

The domain structure and magnetisation process in short glass-coated amorphous Fe_{45}Co_{20}Ni_{10}Si_{9}B_{16} microwires are investigated by analyzing the hysteresis loops measured by a vibrating sample magnetometer. Methods of calculating the thickness of the outer shell and the critical length to observe magnetic bistability have been established. The thickness of the outer shell is 2.3 μm and the critical length is 8.11 mm for a microwire with a metallic core diameter of 31.1 μm and a glass coat thickness of 10.6 μm. The experimental results demonstrate the reliability of this method to calculate the critical length.

Using a second-order helium-cooled superconducting quantum interference device gradiometer as the detector, ultra-low-field nuclear magnetic resonance (ULF-NMR) signals of protons are recorded in an urban environment without magnetic shielding. The homogeneity and stability of the measurement field are investigated. NMR signals of protons are studied at night and during working hours. The Larmor frequency variation caused by the fluctuation of the external magnetic field during daytime reaches around 5 Hz when performing multiple measurements for about 10 min, which seriously affects the results of averaging. In order to improve the performance of the averaged data, we suggest the use of a data processor, i.e. the so-called time-domain frequency correction (TFC). For a 50-times averaged signal spectrum, the signal-to-noise ratio is enhanced from 30 to 120 when applying TFC while preserving the NMR spectrum linewidth. The TFC is also applied successfully to the measurement data of the hetero-nuclear J-coupling in 2,2,2-trifluoroethanol.

The in-plane optical anisotropic properties of the non-polar a-plane GaN films grown by metal organic chemical vapour deposition are investigated by using polarised photoluminescence (PL), optical transmission and Raman scattering measurements. Through polarised PL and transmission spectra, the in-plane optical anisotropic properties of a-plane GaN film are found, which are attributed to the topmost valance band (at Γ point) split into three sub-bands under anisotropic strain. The PL spectra also exhibit that the light hole band moves up more rapidly than the spin-orbit crystal-field spilt-off hole band with the increasing in-plane anisotropic compressive strain. Raman scattering spectra under different configurations further indicate the in-plane anisotropy and the hexagonal crystalline structure of these a-plane GaN films.

Sb rich Ge_{2}Sb_{5}Te_{5} materials are investigated for use as the storage medium for high-speed phase change memory (PCM). Compared with conventional Ge_{2}Sb_{2}Te_{5}, Ge_{2}Sb_{5}Te_{5} films have a higher crystallisation temperature (～200°C), larger crystallisation activation energy (3.13 eV), and a better data retention ability (100.2°C for ten years). A reversible switching between set and reset states can be realised by an electric pulse as short as 5 ns for Ge_{2}Sb_{5}Te_{5}-based PCM cells, over 10 times faster than the Ge_{2}Sb_{2}Te_{5}-based one. In addition, Ge_{2}Sb_{2}Te_{5} shows a good endurance up to 3×10^{6} cycles with a resistance ratio of about three orders of magnitude. This work clearly reveals the highly promising potential of Ge_{2}Sb_{5}Te_{5} films for applications in high-speed PCM.

The modification of localised surface plasmons of photoluminescence properties of ZnO is studied. It is found that the ultraviolet emission is drastically enhanced, and the visible emission related to the defects is almost completely suppressed, after an Au layer of nanoparticles is deposited on the surface of ZnO island films. This pronounced change in PL spectra is attributed to the efficient electron transfer via the coupling of localised surface plasmons at the interface between the Au nanoparticle layer and ZnO films.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

screw-cone-like Zn_{2}GeO_{4}-ZnO particles with a base diameter of approximately 400 nm and a height of 400–800 nm or so were successfully synthesised by combustion oxidation of zinc and germanium powder at 960°C. No catalyst or carrier gases were used. XRD and SEM analyses reveal that Zn_{2}GeO_{4} and ZnO grew to parasitic crystals evenly in interaction with each other. EDS images exhibit the homogeneity of the distribution of Ge and Zn. The formation mechanism is discussed and attributed to the unique growth process of the screw-cone-like Zn_{2}GeO_{4}-ZnO particles and its vapour-solid (VS) growth mechanism. In addition, the Zn_{2}GeO_{4}-ZnO particles could tune the energy level structure of nano-tetrapod ZnO, which leads to the emission peak redshift from 376 nm to 435 nm and enhances the light emission intensity in the visible light region.

To verify the influence of the functional elements particular size for the radiation attenuation coefficients and mechanical properties radiation shielding material based on epoxy resin, we prepare two WO_{3}/E44 samples with different particular sizes of WO_{3} by a solidified forming approach. The linear attenuation coefficients of these samples are measured for γ-ray photo energies of 59.6, 121.8, and 344.1 keV, etc. using narrow beam transmission geometry. It is found that the linear attenuation coefficients would increase with the decreasing particle size of the WO_{3} in the epoxy resin based radiation shielding material. The theoretical values of the linear attenuation coefficients and mass attenuation are calculated using WinXcom, and good agreements between the experimental data and the theoretical values are observed. From the studies of the obtained results, it is reported that from the shielding point of view the nano-WO_{3} is more effective than micro-WO_{3} in the epoxy resin based radiation shielding material.

The effect of rare earth addition on thermal stability of Fe_{50?x}Cr_{15}Mo_{14}C_{15}B_{6}M_{x }(x=0, 2 and M=Y, Gd) is studied. Thermal and structural properties are measured using differential scanning calorimetry and x-ray diffraction, respectively. The microstructure is observed by using a scanning electron microscope, and chemical composition is checked by energy dispersive spectroscopy analysis. The effect of high temperature on the isothermal crystallization of Fe_{50?x}Cr_{15}Mo_{14}C_{15}B_{6}M_{x }(x=0, 2 and M=Y, Gd) bulk metallic glass and ribbons is investigated by high-temperature x-ray diffraction. It is found that the crystallization behavior of Fe_{50?x}Cr_{15}Mo_{14}C_{15}B_{6}M_{x}(x=0, 2 and M=Y, Gd) bulk metallic glass strongly depends on the annealing temperature. The different crystallization behavior is believed to be due to the different structures that the metallic glass possesses at different temperatures.

We investigate the evolution of cylindrical cellular detonation with different instabilities. The numerical results show that with decreasing initial temperature, detonation becomes more unstable and the cells of the cylindrical detonation tend to be irregular. For stable detonation, a divergence of cylindrical detonation cells is formed eventually due to detonation instability resulting from a curved detonation front. For mildly unstable detonation, local overdriven detonation occurs. The detonation cell diverges and its size decreases. For highly unstable detonation, locally driven detonation is more obvious and the front is highly wrinkled. As a result, the diverging cylindrical detonation cell becomes highly irregular.

A novel kind of AlInGaN ultraviolet (UV) light-emitting diode (LED) with an embedded AlN/Al_{0.3}Ga_{0.7}N distributed Bragg reflector (DBR) is proposed to enhance light extraction efficiency (LEE). The simulation technique we adopt to calculate the LEE of LEDs is based on the theory of spontaneous emission in a layered medium, the well-known mode-matching technique and the scattering matrix approach. The AlN/Al_{0.3}Ga_{0.7}N DBR was intentionally designed to have peak reflectivity at the LED emission wavelength and the optical properties of the DBR were simulated by using the transfer matrix method. A high LEE of 45.7% at 370 nm wavelength was predicted for a proposed AlInGaN UV LED consisting of 24 periods of the AlN/Al_{0.3}Ga_{0.7}N DBR, which is 1.5 times of that of the conventional AlInGaN UV LED. The investigation shows that the AlN/Al_{0.3}Ga_{0.7}N DBR grown on GaN templates with sapphire as a substrate by MOCVD can enhance the LEE effectively and would be very promising for the fabrication of high performance GaN-based UV LEDs.

The present research is devoted to the investigation of electron spin transmission through a nanoelectronic device. This device is modeled as nonmagnetic semiconductor quantum dot coupled to two diluted magnetic semiconductor leads. The spin transport characteristics through such a device are investigated under the effect of an ac-field of a wide range of frequencies. The present result shows a periodic oscillation of the conductance for both the cases of parallel and antiparallel spin alignment. These oscillations are due to Fano-resonance. Results for spin polarization and giant magneto-resistance show the coherency property. The present research might be useful for developing single spin-based quantum bits (qubits) required for quantum information processing and quantum spin-telecommunication.

Cell division must be tightly coupled to cell growth in order to maintain cell size, whereas the mechanisms of how initialization of mitosis is regulated by cell size remain to be elucidated. We develop a mathematical model of the cell cycle, which incorporates cell growth to investigate the dynamical properties of the size checkpoint in embryos of Xenopus laevis. We show that the size checkpoint is naturally raised from a saddle-node bifurcation, and in a mutant case, the cell loses its size control ability due to the loss of this saddle-node point.

We investigate how to assign link directions in a given complex network to enhance its controllability. Based on the node residual degree, a method of assigning link direction is proposed. Numerical simulation demonstrates that the method outperforms the random direction assignment method in enhancing the controllability of the network. Furthermore, robustness of control is also improved.

Fast magnetosonic (MS) waves have been suggested to contribute significantly to radiation belt electron dynamics via Landau resonance and transit time scattering. The corresponding quasi-linear diffusion coefficients in pitch angle, energy and particularly cross-pitch-angle-energy are calculated from the gyro-averaged test-particle simulations. It is found that the cross diffusion coefficient is an effective indicator to differentiate between the contributions of resonant and non-resonant mechanisms. Furthermore, the dependence of diffusion coefficients on the normal angle of MS waves are parametrically investigated. Numerical results show that the increasing normal angle can lead to the shrinking of the Landau resonance region and the expansion of the transit-time scattering region. With the increasing normal angle, the pitch angle diffusion coefficients decrease significantly (by about two orders of magnitude), while the other two diffusion coefficients have a relatively limited decrease (within one order of magnitude). For arbitrary normal angles, the magnitude of cross diffusion coefficients is comparable to the other diffusion coefficients, suggesting that the cross diffusion is indispensable in the kinetic simulation works.

We derive the first law of thermodynamics using the method proposed by Wald. Treating the entropy as Noether charge and comparing with the usual first law of thermodynamics, we obtain explicitly the expression of entropy which contains infinitely many non-local terms (i.e. the integral terms). We have proved, in general, that the first law of black hole thermodynamics is violated for f(R,T) gravity. However, there might exist some special cases in which the first law for f(R,T) gravity is recovered.