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High spatial and temporal current resolution velocities were measured by use of an acoustic Doppler velocimeter (ADV) in the tidal bottom layer of North Passage Deep water Navigational Channel (DNC) of Yangtze Estuary in China. And the vertical profiles of mean velocity were measured by using a pulse-coherent acoustic Doppler profiler (PC-ADP). The measured data show the vertical profiles of mean velocity are almost logarithmic. For discussing, the turbulent kinetic energy (TKE) method based on the velocity for ADVs-based is chosen and a new logarithmic profile (LP) method ignoring the influence of complex variation of the parameter Z 0 is suggested to estimate the bed shear stresses respectively. The calculated results show that the bed shear stresses estimated by LP method are larger than the ones estimated by TKE method mostly in Yangtze estuary. At the moment of ebb peak, the maximum error can be about twice occurring and the error of ebb tide is almost greater than the one of flood tide. These phenomena are explained in this study by the deduction of formula for steady and unsteady flow. It is concluded that the vertical logarithmic profile of velocities will be influenced by unsteady flow and there is not the same bed shear stress even if there is the same logarithmic velocity profile in vertical. Generally, this has led to a necessary adjustment of the drag coefficient Cd of steady flow in flow model to avoid overestimating the bed stress for unsteady flow in estuary based on the observed data.

In-situ Cu-based composites have been investigated extensively over the past decades because of their good conductivity and high strength. The preparation technologies of in-situ Cu-based composites mainly include casting of Cu alloys, initial heat treatment, hot deformation, cold deformation, intermediate and final heat treatment. This paper primarily researched the effect of thermo-mechanical processing such as initial heat treatment, hot deformation, cold deformation, intermediate and final heat treatments on the property and microstructure of in-situ Cu-based composites, analyzed the main role and mechanism of each thermo-mechanical processing, summarized the related research work and achievements, and prospected the future main research directions of the thermo-mechanical processing for in-situ Cu-based composites.

With the development of China’s economy, pollution has become more and more serious, so total pollution control has become a priority for governments at all levels. The center of total pollutant emission reduction is to formulate scientific and reasonable pollutant emission reduction policies based on the forecast of pollutant emission in the next few years. According to the national requirements, the emissions of four pollutants, namely sulfur dioxide, nitrogen oxide, ammonia nitrogen and chemical oxygen demand, need to be counted. The research objective of this paper is to establish a combined model applicable to the emission prediction of sulfur dioxide, nitrogen oxide, ammonia nitrogen and chemical oxygen demand by analyzing the impact of population factors and industrial distribution on pollutant emissions and combining the grey system theory and neural network theory. According to the characteristics of pollutant discharge in a certain city, a pollutant discharge prediction model based on GM (1,1), GM (0,4) and BP neural network is proposed.

A biomimetic underwater robot was designed utilizing ionic polymer-metal composite (IPMC) artificial muscles. The actuators were controlled by thermal and electrical inputs, taking advantage of both the shape-memory and electromechanical behavior of the material, to achieve multiple swimming modes in the proposed robot. The design was inspired by the pectoral fish swimming modes, such as stingrays, knifefish, and cuttlefish. The robot was actuated by two soft fins which consisted of multiple embedded IPMC actuators connected with an Eco-Flex membrane. Through electromechanical actuation, a traveling wave was generated on the soft fin. The deformation and the blocking force of the IPMCs on the fin were measured to characterize the actuators. An experimental setup was also designed in a flow channel to measure the thrust force of the robot under different frequencies and travelling wave numbers in a captive state. Experiments determined a peak thrusting force of 12 mN at a frequency of 0.5 Hz and wave number of 1,a nd twisting deformations of 30o were obtained. Additionally, shape-memory was utilized to change the swimming mode of the robot from Gymnotiform to Mobuliform. The designed underwater robot utilizes IPMC materials with multi-input control, enabling high deformability, with available maneuverability and agility in future studies.

Density flows frequently occur in nature and some of them have caused serious consequences, such as sedimentation and saline water intrusion. In order to control density flows, the method like placing an obstacle has been proposed. In this paper, the influence of the height and position of obstacle and the salinity difference on the behaviors of lock-exchange density flow was studied experimentally by using high-speed camera and laser particle image velocimetry (PIV) technique. The experiments were conducted in a plexiglass flume whose height, width and depth were 1.8 m, 0.22 m and 0.3 m respectively. Besides, the bottom of the flume is smooth. The flume was separated by one board and the left side of the flume was filled by fresh water while the right side of the flume was filled by salt water. After the board was lifted, the salt water flow into the fresh water and formed a density flow. Obstacles were placed 0.05 m and 0.25 m away from the gate respectively. The velocity and flow field were measured by using the PIV technique. The results indicated that the existence of obstacles blocked the progress of density flow and the propagation distance of density current in the case without obstacle was much longer than the other one which contained obstacle. Additionally, it was observed that when the density flow was crossing over one obstacle, a re-acceleration process was happening at the head of the current, and the maximum velocity caused by this process was larger than the maximum velocity without obstacles. Besides, by comparing the obstacle and non-obstacle situations, the body velocity of density flow was greatly reduced at the front of obstacle. However, the effect of different obstacle positions on the maximum velocity of the head of density flow is not significant.

Based on the passing data and floating car data (FCD) collected by the traffic police of Shenzhen Public Security Bureau, China. A dynamic Bayesian network (DBN) model is constructed to describe the change and dissipation of road congestion. The prediction model of road congestion diffusion is established by integrating Internet traffic data and FCD data. To provide a theoretical basis for solving urban traffic congestion, the experimental results show that the prediction results coincide with the actual state of the Internet road conditions, which proves the feasibility and practicability of the prediction method.

The multiple-shape-memory ionic polymer–metal composite (MSM-IPMC) actuator can demonstrate complex 3D deformation. The MSM-IPMC has two distinct characteristics, which are the electromechanical actuation effect and the thermal-mechanical shape memory effect. The bending, twisting, and oscillating motions of the actuator could be controlled simultaneously or separately by means of thermal-mechanical and electromechanical transduction. In this study, a theoretical model for the MSM-IPMC was developed and experimentally investigated. Based on previous studies on the electromechanical actuation effect of ionic polymer–metal composite (IPMC), a comprehensive physics-based model of MSM-IPMC which couples the actuation effect and the multiple shape memory effect was developed. To verify the model, an MSM-IPMC sample was prepared and used in experimental testing. The simulation results were shown to be in good agreement with the experimental results obtained. The multiple shape memory and recovery rate of three different polymers, namely the Nafion, Aquivion and GEFC of different ions, which are the hydrogen, lithium and sodium, were also tested. Based on the results, it is shown that all the polymers demonstrate the multiple shape memory effect with varying amounts of programmable shapes. The ion type was shown to have an influence on the broad glass transition range of the polymers, which in turn dictated the number of possible programmable shapes for each membrane. The current study is beneficial for the better understanding of the multiple shape memory effect of MSM-IPMC.

Using a special property of dynamic complementary-suppression-modulated transmission (DCSMT) in the bacteriorhodopsin (bR) film, we have demonstrated an all-optical time-delay relay. To extend our work, the relationship between the delay time of the all-optical time-delay relay and parameters of a bR film is numerically studied. We show how the delay time changes with the product of concentration and thickness (PCT) of a bR film. Furthermore, the shortest and longest delay times are given for the relay of 'switch off'. The saturable delay time and maximum delay-time of 'switch on' are also given. How the wavelengths (632.8, 568, 533 and 412 nm) and intensities of the illuminating light influence the delay time is also discussed. The simulation results are useful for optimizing the design of all-optical time-delay relays.

A new quantum optical mechanism to realize simultaneously negative electric permittivity and magnetic permeability is suggested. In order to obtain a negative permeability, we choose a proper atomic configuration that can dramatically enhance the contribution of the magnetic-dipole allowed transition via the atomic phase coherence. It is shown that the atomic system chosen with proper optical parameters can give rise to striking electromagnetic responses (leading to a negative refractive index) and that the atomic vapour becomes a left-handed medium in an optical frequency band. Differing from the previous schemes of artificial composite metamaterials (based on classical electromagnetic theory) to achieve the left-handed materials, which consist of anisotropic millimetre-scale composite structure units, the left-handed atomic vapour presented here is isotropic and homogeneous at the atomic-scale level. Such an advantage may be valuable in realizing the superlens (and hence perfect image) with left-handed atomic vapour.

A new scheme for realizing a nonadiabatic conditional geometric phase shift via a noncoplanar (coiled) fibre system is presented. It is shown that the effective Hamiltonian that describes the interaction of polarized photons with a fibre medium is just the Wang-Matsumoto type of Hamiltonian. This, therefore, means that the coiled fibre system may be an ideal implementation for realizing the nonadiabatic geometric phase gates involved in the topological quantum computation. A remarkable feature of the present method is that it can automatically meet the conditions and requirements proposed in the Wang-Matsumoto nuclear magnetic resonance (NMR) scheme: specifically, (i) in the coiled fibre system, the dynamical phase of photon wavefunction caused by the interaction Hamiltonian automatically vanishes; (ii) the Wang-Matsumoto requirement for the parameters in the Wang-Matsumoto NMR Hamiltonian can be exactly satisfied automatically in such a fibre system; and (iii) the conditional initial state can be easily achieved by manipulating the initial wave vector of polarized photons.

We study the quantum-vacuum geometric phases resulting from the vacuum fluctuation of photon fields in Tomita-Chiao-Wu noncoplanar curved fibre system, and suggest a scheme to test the potential existence of such vacuum effect. Since the signs of the quantum-vacuum geometric phases of left- and right- handed (LRH) circularly polarized light are just opposite, the total geometric phases at vacuum level is inescapably absent in the fibre experiments performed previously by other authors. By using the present approach where the fibre made of gyroelectric media is employed, the quantum-vacuum geometric phases of LRH light cannot be exactly cancelled, and may therefore be achieved test experimentally., Comment: 3 pages, Latex

The contribution of self-induced charge currents of metamaterial media to photon effective rest mass is discussed in detail in the present paper. We concern ourselves with two kinds of photon effective rest mass, i.e., the frequency-dependent and frequency-independent effective rest mass. Based on these two definitions, we calculate the photon effective rest mass in the left-handed medium and the 2TDLM media, the latter of which is described by the so-called two time derivative Lorentz material (2TDLM) model. Additionally, we concentrate primarily on the torque, which is caused by the interaction between self-induced charge currents in dilute plasma (e.g., the secondary cosmic rays) and interstellar magnetic fields (ambient cosmic magnetic vector potentials), acting on the torsion balance of the rotating torsion balance experiment.

The connections between the anti-shielding effect, negative absolute temperature and superluminal light propagation in both the instantaneously reversed electric field and the left-handed media are considered in the present paper. The instantaneous inversion of the exterior electric field may cause the electric dipoles into the state of negative absolute temperature and therefore give rise to a negative effective mass term of electromagnetic field (i. e., the electromagnetic field propagating inside the negative-temperature medium will acquire an imaginary rest mass), which is said to result in the potential superluminality effect of light propagation in this anti-shielding dielectric. In left-handed media, such phenomena may also arise., Comment: 9 pages, Latex

Quantum technology establishes a foundation for secure communication via quantum key distribution (QKD). In the last two decades, the rapid development of QKD makes a global quantum communication network feasible. In order to construct this network, it is economical to consider small-sized and low-cost QKD payloads, which can be assembled on satellites with different sizes, such as space stations. Here we report an experimental demonstration of space-to-ground QKD using a small-sized payload, from Tiangong-2 space lab to Nanshan ground station. The 57.9-kg payload integrates a tracking system, a QKD transmitter along with modules for synchronization, and a laser communication transmitter. In the space lab, a 50 MHz vacuum + weak decoy-state optical source is sent through a reflective telescope with an aperture of 200 mm. On the ground station, a telescope with an aperture of 1200 mm collects the signal photons. A stable and high-transmittance communication channel is set up with a high-precision bidirectional tracking system, a polarization compensation module, and a synchronization system. When the quantum link is successfully established, we obtain a key rate over 100 bps with a communication distance up to 719 km. Together with our recent development of QKD in daylight, the present demonstration paves the way towards a practical satellite-constellation-based global quantum secure network with small-sized QKD payloads.

In recent years, spectral X-ray imaging using photon counting detectors (PCDs) becomes a hot topic in the field. For a PCD, each individual incident photon with different energies is analyzed and assigned to different energy channels according to pre-set thresholds respectively. Thus, the data from an energy channel carry spectral information. Because of the influence of pulse pileup, charge sharing and other physical effects, energy calibration of PCDs is a piece of challenging work. Various energy calibration methods of PCDs have been researched. Most of them demand extensive work with additional sources or equipments. In this work, we propose a novel approach for energy calibration by using only one monochromatic source. We use iterative optimization method to fully excavate and utilize the data. The method requires fewer experiments than other common-used calibration methods. Moreover, the charge sharing effect is implicitly taken into account in this method which is an important factor in the calibration of pixel detectors. We validated our method with radioactive sources. The resulting energy spectrum matched well as expected.

Quantum random number generators adopting single photon detection have been restricted due to the non-negligible dead time of avalanche photodiodes (APDs). We propose a new approach based on an APD array to improve the generation rate of random numbers significantly. This method compares the detectors' responses to consecutive optical pulses and generates the random sequence. We implement a demonstration experiment to show its simplicity, compactness and scalability. The generated numbers are proved to be unbiased, post-processing free, ready to use, and their randomness is verified by using the national institute of standard technology statistical test suite. The random bit generation efficiency is as high as 32.8% and the potential generation rate adopting the 32 × 32 APD array is up to tens of Gbits/s.

A series of blue organic light-emitting diodes with electron or hole blocking interlayer are fabricated. Different structures of blocking interlayers can influence the position of the recombination zone due to the fact that they confine carriers in different ways. We find that the double hole blocking interlayer structure can balance carrier injection more effectively. Its power and current efficiency are more stable and the current efficiency value is 30.2 cd/A at 1000 cd/m2. Decreasing the thicknesses of the emitting layer and interlayers is in favor of the power efficiency. The performance of the device is also affected by changing the interlayer position when we use hole and electron blocking material as interlayers simultaneously.

In an effort to explore the application possibility of composite films in ignition field, Al/CuO was fabricated on semiconductor bridge (SCB) chip by ion beam sputtering technique. Surface morphology and elemental composition of the composite films were analysed by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Spatial size and duration of the products was detected with the open-air combustion experiment. The results showed that the prepared composite films surface is smooth, flat, and uniform. Element weight ratio meets the design requirements. And the chemical reaction of the Al/CuO nCFs improves output performances of ignition chip.

A strongly confined acoustic surface wave is an acoustic eigenstate localized on an interface between an ordinary acoustic medium and an acoustic metamaterial with negative effective dynamical mass ...

In this paper, we study the thrust performance of a biomimetic robotic swimmer that uses ionic polymer–metal composite (IPMC) as a flexible actuator in viscous and inertial flow, for a comprehensive understanding of IPMC swimmers at different scales. A hydrodynamic model based on the elongated body theory was developed. Based on image analysis, the parameters of the model were identified and simulation results were obtained. To obtain the hydrodynamic thrust performance of the robotic swimmer, we implemented a novel experimental apparatus. Systematic tests were conducted in the servo towing system to measure the self-propelled speed and thrust efficiency under different actuation of IPMC. The undulatory motions of the IPMC swimmer were identified. Experimental results demonstrated that the theoretical model can accurately predict the speed and thrust efficiency of the robotic swimmer. When the Reynolds number of the robotic swimmer was reduced to approximately 0.1%, its speed and thrust efficiency were reduced by 95.22% and 87.33% respectively. It was concluded that the robotic swimmer has a low speed and thrust efficiency when it swims in a viscous flow. Generally, the thrust performance of the robotic swimmer is determined by the kinematics and Reynolds number. In addition, the optimal actuation frequency for the thrust efficiency is greater in a viscous fluid. These results may contribute to a better understanding of the swimming performance of IPMC actuated swimmers in a distinct flow regime (viscous and inertial regime).

A spin-connection gravitational gauge theory with a spin-affine connection as its fundamental dynamical variable is suggested in the framework of vierbein formulation. The functional integral approach to the interaction between complex scalar matter fields and a heavy intermediate coupling field is considered, where the Einstein field equation appears as a first-integral solution to the low-energy spin-connection gauge field equation of Yang–Mills type. The most intriguing characteristics of the present scheme include: (i) the gravitational constant originates from the low-energy propagator of the heavy coupling field that mediates the gravitation between the matter fields and the spin-connection gauge field; (ii) the large cosmological constant resulting from the quantum vacuum energy actually makes no gravitational contribution since the spin-connection gauge field equation is a third-order differential equation of the metric, and an integration constant of the first-integral solution serves as an effective cosmological constant that would cause the cosmic accelerated expansion. The present mechanism for interpreting the nonzero but small cosmological constant provides a new insight into the cosmological constant problem.

The evolutional optical behaviours (turn-on dynamics) of a four-level N-configuration atomic system are considered based on the transient solution to the equations of motion of atomic probability amplitudes. It is shown that the quantum interference between the signal and control fields can lead to the controllable absorption and transparency properties of the atomic vapour. One of the most remarkable properties of the present scheme is that the absorption (or transmittance) of the probe light in the atomic vapour depends on the intensity ratio of the signal field to the control field, and thus the tunable optical features (transparency or opaqueness to the probe light) can be realized by tuning the quantum interferences between the signal and control fields. The present mechanism can be applicable to designs of some new photonic and quantum optical devices such as logic and functional devices as well as optical switches. Two typical photonic logic gates (NOT and NOR gates) designed based on the tunable four-level optical responses are presented as illustrative examples.

The evolutional optical behaviours (turn-on dynamics) of a four-level double-control tripod-configuration (electromagnetically induced transparency) system are considered based on the transient s ...

The possibility of the backward waves and negative refractive indices of the gyrotropic chiral materials is studied, and the impedances of the eigenmodes are derived. Since the gyrotropic parameters in the permittivity and permeability tensors favour the realization of the negative refractive index in the gyrotropic chiral material, the negatively refracting medium can be achieved even far off the resonances of the permittivity and permeability. A potential effect of the field quantization in a compact subwavelength cavity resonator containing the gyrotropic chiral material is suggested.