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Objective. The imaging photoplethysmography (IPPG), which is applied to heart rate measurement, is susceptible to interference caused by illumination variations during photography. To improve the accuracy, robustness, and real-time performance of IPPG, a new method combined with modified ensemble empirical mode decomposition (EEMD) and fast independent component analysis (FastICA) was proposed. Approach. On the modified EEMD, to reduce the error caused by the residual white noise of the algorithm, it was characterized by recurrently updating zero-mean white noise for ensemble averaging based on the standard deviation of the input signal. On the modified FastICA, its constructed nonlinear function was superseded by Huber’s approximation function to improve the robustness and running speed. Main results. Comparison experiments were conducted between the MAHNOB-HCI database and own collected data. In the hybrid natural light and computer screen light scenario, the mean absolute error (MAE) of heart rate amounted to 0.93 beats per minute and the correlation coefficient r reached 0.85. In the experiments of MAHNOB-HCI database, the MAE amounted to 6.03 beats per minute and the correlation coefficient r reached 0.75. Furthermore, the modified method decreased the running time by approximately ten times compared to the original algorithms. Significance. Various experimental results demonstrated that the proposed method significantly improves the accuracy, timeliness, and interference resistance.

In order to realize the smelting effect of high oxygen supply intensity in large and medium-sized converters, a new six hole oxygen lance nozzle with double angle, double flow and staggered double structure is designed in this paper, and the jet characteristics are compared with those of the traditional structure oxygen lance. According to the theory of fluid dynamics and the principle of similarity, the velocity attenuation of the centerline of the jet and the longitudinal section of the oxygen jet are tested by using the oxygen gun jet detection experimental system. The results show that the jet performance of the staggered double structure six hole oxygen lance nozzle is better than that of the traditional structure oxygen lance nozzle. When the ratio of large hole flow is 55%-65%, the angle of large hole is 12°-14°and the angle of small hole is 16°-18°, the ratio of hole flow plays a leading role in the size of jet velocity. The greater the flow distribution, the greater the jet velocity. Using staggered double structure six hole oxygen lance can improve the stirring force of the jet to the molten pool.

At present, Imaging Photoplethysmography (IPPG) has attracted extensive attention on heart rate measurement, because of its non-contact, non-invasive and safe characteristics. However, in reality, the IPPG signal is extremely feeble and susceptible to be submerged by ambient interference such as illumination. To this end, we propose a new IPPG signal processing approach to enhance the anti-interference capability of measuring heart rate through a modified EEMD algorithm with updated white-noise iterating. In the modified EEMD algorithm, based on the standard deviation of the input IPPG signal, zero-mean white noises are generated randomly for iterative ensemble averaging. Through this new method, the fault caused by the residual white noise of traditional EEMD is solved. Lastly, through the comparative experiments of our own acquisition statistics, the approach proposed by this paper has significantly improved the performance in terms of accuracy, timeliness and anti-interference under various scenarios. The mean absolute error reaches 1.4 beats per minute and the correlation coefficient r reaches 0.8089. In addition, the modified EEMD algorithm reduces the running time by more than 10 times compared to the original method, approximately 0.16s per time.

As one of the main indoor gas pollutants, formaldehyde gas (HCHO) seriously threatens human health and ranks second among toxic chemicals in China. In order to monitor the concentration of formaldehyde in the environment in real time, an online Quartz Crystal Microbalance (QCM) analyzing device based on FPGA is developed in this paper. This device is composed of QCM sensor module and FPGA signal processor. Firstly, graphene oxide film is prepared on QCM chip to adsorb formaldehyde, which causes the change of resonance frequency. Secondly, to monitor the quality of adsorbed formaldehyde through frequency change, FPGA signal processor is mainly integrated with Direct Digital Synthesis module, Analogue-to-Digital Conversion module, Low-Pass Filter module and Frequency Domain Analysis module. These modules have the characteristics of high speed, low power consumption and parallel processing, which provide the best solution for the online implementation of the analyzing device. Finally, the standard gas experiment shows that the device is feasible and reliable for the analysis of formaldehyde gas mass concentration, with a resolution of about 10 counts per 1% concentration.

We investigate high-fidelity multiple beam splitting in Hermitian and non-Hermitian symmetric coupled waveguides with one input and 2N output waveguide channels. In Hermitian systems, we realize adiabatically light splitting in resonant case based on the stimulated Raman adiabatic passage (STIRAP) and arbitrary proportion from the middle waveguide to outer waveguides in propagation coefficients mismatch case using shortcuts to adiabaticity (STA) technique. In non-Hermitian systems with even waveguides being dissipative, the compact and robust beam splitting can be achieved by eliminating the non-adiabatic coupling via the non-Hermitian STA method. We further verify the feasibility of our theoretical predictions by means of the beam propagation method (BPM). The suggested multiple beam splitters open new opportunities for the realization of on-chip high-bandwidth photonics with high fidelity in short distances., Accepted

With the progress of information technology, Internet of things (hereinafter referred to as IOT) technology has been applied to all walks of life, especially in oilfield construction. With the rapid development of IOT technology, the system will produce a lot of data, which also leads to the arrival of big data (hereinafter referred to as DB). Therefore, DB and IOT technology has become an important application in the construction of offshore smart oilfield. Through the IOT technology, enterprises can save production costs, which can also improve oil and gas production. Therefore, Internet technology can make the management of oilfield enterprises more transparent, which will realize the intelligent exploitation of offshore oil. Through the construction of Marine Intelligent oilfield, we can form an open system platform, which will realize the sharing of production process and data. Therefore, this paper first analyzes the important role of DB and IOT technology. Then, this paper analyzes the construction of offshore smart oilfield.

The manipulating of optical waves in a microcavity is essential to developing the integrated optical devices. Generally, the two eigenmodes in a whispering-gallery-mode (WGM) microcavity possess chiral symmetry. Here we show the chiral symmetry breaking is induced by the asymmetric backscattering of counter-propagating optical waves in a whispering-gallery-mode (WGM) microcavity with a cavity-made slot filled with atomic vapor. Through tuning the dispersion relation of the atomic vapor in the cavity-made slot, the chiral modes are continuously steered. The mode frequency splitting in the transmission and reflection spectra stem from the chiral symmetry breaking of the two eigenmodes. The displacement sensitivity of the proposed system in response to the length variation of cavity-made slot exhibits a high sensitivity value of 15.22 THz/nm.

Electron-positron plasma has attracted much attention recently due to their unique properties. In this paper, we study the acceleration of electron-positron plasma in a cone by using PIC method. The electrons and positrons will be scattered by transverse ponderomotive force during the interaction between laser and electron-positron plasma. A new scheme is proposed to obtain high-energy dense collimated electron-positron plasma by a hollow gold cone. Transverse scattered electrons and positrons are pinched in the gold cone. Both electrons and positrons can be accelerated by ponderomotive force continuously and a dense collimated electron-positron plasma is produced. The energy of electrons and positrons obtained in the cone is much higher than the upper limit of electron energy obtained by ponderomotive force acceleration. The high quality electron and positron beam has great potential value in further research.

With the rapid development of domestic economy, the process of urbanization is accelerating. According to the national unification and the national economic operation data released by the Planning Bureau in 2015, the urbanization population accounts for the total population 56.1% of the total. The rapid development of urbanization has promoted the economic and social development of the city. However, the development of urbanization brings about a series of urban problems as well as urban economy. For example, urban resources are increasingly tense, urban environment is becoming worse, and urban livelihood issues are becoming more and more serious. The more complicated. It is everyone’s wish to promote the harmony of life and improve the quality of life. How to reasonably apply computer big data technology to the construction of smart city has become an important topic for researcher significance to improve the employment rate to give full play to the role of counselors in employment guidance.

With the steady progress of China’s urbanization process, the smart city construction is also rising quietly. At the same time, the advent of the big data era has also provided new ideas for the construction and development of smart cities. In this paper, mainly the corresponding strategies for the construction and development of smart cities in the era of big data are proposed through the understanding of the features of smart cities and the positive role played by big data in the smart city construction.

Information interaction design leads the healthy development of smart city Information interaction design intersects with various disciplines and is related to “a kind of conscious information control activity”. It is committed to the reasonable control and arrangement of information, “it pays close attention to the whole process of information expression, processing, retrieval, identification and communication activities”, so as to achieve the effective, convenient and accurate information transmission.

Publish-subscribe middleware has been widely used in military, medical and other important industries because of its good characteristics of time and space decoupling. With the continuous expansion of the scale of distributed system application, the problems in distributed system testing, such as low efficiency and difficulty in fault positioning, are more prominent. In this paper, an automatic testing method is proposed, which is based on the characteristics of the publish-subscribe middleware systems. Based on an independent designed and implemented publish-subscribe system named BlueDCS, a corresponding automatic testing tool is developed. Application verification shows that the tool can well solve the aforementioned problems in distributed system testing.

We performed broadband terahertz (THz) time-domain spectroscopy measurements to study the photon-phonon interactions and frequency-resolved optical parameters of bulk ZnTe. Using laser-induced plasma as the source of THz radiation and a GaP bulk wafer as the sensor crystal, a broadband THz response of bulk ZnTe wafer with thickness of 0.1 millimeter within the frequency range from 0.1 to 7.5 THz was obtained. Comparing the measured photon absorption spectrum with phonon dispersion curves obtained from ab initio calculations, we identified the first- and second-order photon-phonon interactions of ZnTe crystal. The frequency-resolved optical parameters including the complex refractive index, dielectric response and conductivity of ZnTe crystal within the frequency range between 0.1 and 7.0 THz were derived from the measured THz transmitted field. By fitting the frequency dependent dielectric functions with the Lorentz oscillator model, a static permittivity of 10.5 along with a transverse optical phonon frequency of 5.9 THz and a phonon lifetime of 1.25 picosecond were obtained for ZnTe crystal.

Aiming at the problem of single measurement vector (SMV) OFDM signal delay estimation in complex environment, a sparse reconstruction off-grid delay estimation algorithm based on Bayesian automatic correlation determination (OGBARD) is proposed. The algorithm adopts Bayesian framework, from the perspective of further mining useful information, introduces asymmetric autocorrelation to determine a priori parameters and off-grid parameters, and integrates them into the parameter estimation process, which improves the delay estimation accuracy under SMV and low signal-to-noise ratio (SNR) condition. Firstly, based on the channel frequency response (CFR) estimation value of the OFDM signal physical layer protocol data unit, the algorithm constructs a sparse representation model with off-grid parameters, and then introduces the probability hypothesis of noise vector, off-grid parameters and sparse coefficient vector in the model. Finally, based on Bayesian inference, the expectation maximization (EM) algorithm is used to estimate the hyperparameters. Simulation experiments show that the proposed algorithm has better estimation performance than the comparison algorithm and is closer to the Cramer–Rao Bound (CRB).

We present femtosecond optical pump-terahertz probe studies on the ultrafast dynamical processes of photo-generated charge carriers in silicon photovoltaic cells with various nanostructured surfaces and doping densities. The pump-probe measurements provide direct insight on the lifetime of photo-generated carriers, frequency-dependent complex dielectric response along with photoconductivity of silicon photovoltaic cells excited by optical pump pulses. A lifetime of photo-generated carriers of tens of nanosecond is identified from the time-dependent pump-induced attenuation of the terahertz transmission. In addition, we find a large value of the imaginary part of the dielectric function and of the real part of the photoconductivity in silicon photovoltaic cells with micron length nanowires. We attribute these findings to the result of defect-enhanced electron–photon interactions. Moreover, doping densities of phosphorous impurities in silicon photovoltaic cells are also quantified using the Drude–Smith model with our measured frequency-dependent complex photoconductivities.

Self-injection and acceleration of monoenergetic electron beams from laser wakefield accelerators are first investigated in the highly relativistic regime, using 100 TW class, 27fs laser pulses. Quasi-monoenergetic multi-bunched beams with energies as high as multi-hundred MeV are observed with simultaneous measurements of side-scattering emissions that indicate the formation of self-channelling and self-injection of electrons into a plasma wake, referred to as a 'bubble'. The three-dimensional particle-in-cell simulations confirmed multiple self-injection of electron bunches into the bubble and their beam acceleration with gradient of 1.5GeV/cm.

We propose a geoacoustic inversion scheme employing a vector hydrophone array based on the fact that vector hydrophone can provide more acoustic field information than traditional pressure hydrophones. Firstly, the transmission loss of particle velocities is discussed. Secondly, the sediment sound speed is acquired by a matched-field processing (MFP) procedure, which is the optimization in combination of the pressure field and vertical particle velocity field. Finally, the bottom attenuation is estimated from the transmission loss difference between the vertical particle velocity and the pressure. The inversion method based on the vector hydrophone array mainly has two advantages: One is that the MFP method based on vector field can decrease the uncertain estimation of the sediment sound speed. The other is that the objective function based on the transmission loss difference has good sensitivity to the sediment attenuation and the inverted sediment attenuation is independent of source level. The validity of the inverted parameters is examined by comparison of the numerical results with the experimental data.

The resonant interminiband Zener tunneling rate between two minibands in the process of terahertz (THz) radiation has been calculated with Kane model for two structures of GaAs/Al0.3Ga0.7As superlattices with high electric field. From the theoretical results, it is found that Zener tunneling rate not only increases with the applied electric field F but also is very dependent on the width of the minibands and that of the gap between minibands. Without any fitting parameter, the calculated results agree well with the experimental data reported by Hirakawa and his co-workers. The results we obtained in this work demonstrate that the measured broadening in the spectra of terahertz emission and the observed oscillation in the intensity curve of terahertz emission in the high electric field region are indeed due to the resonant interminiband Zener tunneling. The good agreement with experimental results also indicates that Kane theory is good enough to model Zener tunneling rate when F is below 90 kV/cm in the system we worked on.

The transport properties of a homogenous perovskite oxide p-n junction composed of the p-type In-doped SrTiO3 and n-type Nb-doped SrTiO3 have been studied by solving one-dimensional steady-state carrier-transport equations based on the drift-diffusion model. The energy band profile, electric-field intensity, and charge density are obtained for the space charge region at various bias voltages. Furthermore, the rectifying characteristics of the I-V curves are calculated and analyzed as a function of doping density. The theoretical results are in good agreement with the experimental data, and more details in the understanding of transport mechanism for oxide p-n junctions have been gained.

The discovery of the essential difference of maximum ion energy for TW - ps laser plasma interaction compared with the 100 ns laser pulses [1] led to the theory of a skin layer model [2] where the control of prepulses suppressed the usual relativistic self-focusing. The subsequent generation of two nonlinear force driven blocks has been demonstrated experimentally and in extensive numerical studies where one block moves against the laser light and the other block into the irradiated target. These blocks of nearly solid state density DT plasma correspond to ion beam current densities [3] exceeding 1010 A/cm2 where the ion velocity can be chosen up to highly relativistic values. Using the results of the expected ignition of DT fuel by light ion beams, a self-sustained fusion reaction front may be generated even into uncompressed solid DT fuel similar to the Nuckolls-Wood [4] scheme where 10 kJ laser pulses produce 100 MJ fusion energy. This new and simplified scheme of laser-ICF needs and optimisation of the involved parameters.

Diffractive optical elements (DOEs) with spectrum separation and beam concentration (SSBC) functions have important applications in solar cell systems. With the SSBC DOEs, the sunlight radiation is divided into several wave bands so as to be effectively absorbed by photovoltaic materials with different band gaps. A new method is proposed for designing high-efficiency SSBC DOEs, which is physically simple, numerically fast, and universally applicable. The SSBC DOEs are designed by the new design method, and their performances are analyzed by the Fresnel diffraction integral method. The new design method takes two advantages over the previous design method. Firstly, the optical focusing efficiency is heightened by up to 10%. Secondly, focal positions of all the designed wavelengths can be designated arbitrarily and independently. It is believed that the designed SSBC DOEs should have practical applications to solar cell systems.

We present a self-consistent model calculation to study the influence of a radio-frequency surface acoustic wave (SAW) on the dynamic processes of photo-generated free carriers, excitons and trions in a 2D MoS2 flake with an odd number of layers. We found that the concentrations of excitons and trions decreased, while the lifetime of the free carriers increased when an external SAW field was applied. We attribute this phenomenon to the spatial separation of the electrons and holes, which are confined by a SAW-induced periodic type-II band-edge. We further studied the effect of the modulations on the spatiotemporal distributions of free carriers and excited quasiparticles by varying the amplitude and wavelength of the SAW field. We finally calculated the photoluminescent properties of the MoS2 flake under modulation of the SAW field and compared our results with those of recent experiments.

So far in the literature there mainly exist two quite different forms of the mass action law or the Saha equation modified to a two-temperature plasma. It has been shown in the present paper that the modified Saha equation deduced from the minimum Gibbs or Helmholtz free-energy principle is incorrect. The minimum Gibbs or Helmholtz free-energy principle, which is valid for a single-temperature system as a substitute of the maximum entropy principle in an isolated system, cannot be extended to the two-temperature plasma. A more rigorous thermodynamic derivation of the Saha equation modified to a two-temperature plasma system is presented based on the basic thermodynamic principle that the entropy of an isolated system will assume its maximum at the equilibrium state. It is pointed out that one has to pay close attention to the chemical potential expressions for the case of the two-temperature plasma, since any negligence may cause mistakes in the derivation of the two-temperature Saha equation.

We perform ab initio density functional theory calculations along with the frozen phonon approach to study the renormalization of the electronic structure of diamondoids induced by coupling to nuclear vibrations. We obtain an energy gap reduction between 0.1 and 0.3 eV across nine different diamondoids. The energy renormalization of the highest occupied molecular orbital state varies with the sizes and the symmetry of the diamondoids while that of the lowest unoccupied molecular orbital state is nearly constant. This behavior is explained using the localization of the electronic states. The energy gap renormalization is shown to originate mainly from bending C-H and rotation/shear H-C-H modes with frequencies between 800 and 1400 cm−1. We calculate the band gap renormalization due to excitonic effects using a screened configuration interaction approach and find excitonic binding energies of around 2 eV in excellent agreement with experiment for our largest diamondoids.

Two quite different Saha equations modified to a two-temperature plasma were proposed and employed in many literatures. In order to clear up this confusion phenomenon lasted for a few decades in the community of thermal plasma science and technology, this paper re-examines the thermodynamic derivation of the two-temperature Saha equations. It is pointed out that the modified Saha equation deduced by using the minimum Gibbs or Helmholtz free energy is incorrect for the two-temperature plasma. Instead, a more rigorous derivation is presented here from the basic thermodynamic principle that the entropy in an isolated system always assumes its maximum value at chemical equilibrium.

The frequency of the Rayleigh anomaly of a metallic grating varies with the refractive index of the surrounding medium. To employ this phenomenon in optical sensors it is essential that the feature, due to the Raleigh anomaly in the sensor’s optical response, is very distinct and stable. We study the reflectance of optical structures consisting of a metallic grating with a thin dielectric film on highly reflective silicon substrates in the terahertz (THz) range between 0.6 and 2 THz. A distinct reflectance peak due to the Rayleigh anomaly can only be observed if a dielectric spacer layer is inserted between the metallic grating and silicon substrate. The dielectric layer between the grating and substrate acts as a Fabry–Perot resonator with a low quality factor. Thus, the corresponding Fabry–Perot modes only couple weakly to the Rayleigh anomaly. At the frequency of the Rayleigh anomaly, the combined structure exhibits a distinct peak due to the Rayleigh anomaly, no matter whether there is a Fabry–Perot low or high reflection band at this frequency. In particular, the reflection background in the vicinity of the frequency of the Rayleigh anomaly is suppressed when the Rayleigh anomaly is in resonance with a Fabry–Perot low reflection band, whilst the Rayleigh reflectance peak itself is retained. The underlying physics is confirmed by a simple analytic model and by numerical calculations. This approach of optimizing the optical response of metallic gratings is important for the design of THz sensing devices based on Rayleigh anomalies.

We synthesize the homogenous graphene films on cheap industrial Cu foils using low pressure chemical vapor deposition. The quality and the number of layers of graphene are characterized by Raman spectra. Through carefully tuning the growth parameters, we find that the growth temperature, hydrocarbon concentration and the growth time can substantially affect the growth of high-quality graphene. Both single and bilayer large size homogenous graphenes have been synthesized in optimized growth conditions. The growth of graphene on Cu surface is found to be self ceasing in the bilayer graphene process with the low solubility of carbon in Cu. Furthermore, we have optimized the transfer process, and clear graphene films almost free from impurity are successfully transferred onto Si/SiO2 substrates. The field effect transistors of bilayer graphene are fabricated, which demonstrates a maximum hole (electron) mobility of 4300 cm2 V?1s?1 (1920 cm2V?1s?1) at room temperature.

A self-assembly method, named the angle controlled inclined deposition method, is developed for fabricating well-ordered silica and polystyrene colloidal crystals. A high-quality colloidal crystal with a flat and uniform surface over a large area can be produced rapidly using a minute quantity of suspension and without any additional equipment. By controlling the inclined angle, we can fabricate colloidal crystals with diverse numbers of layers. A colloidal crystal double-heterostructure (composed of three different colloidal photonic crystals) can be rapidly fabricated with this method. Both experimental and simulation results show that the photonic band gap of the double-heterostructure is not a simple superposition of that of the compositional colloidal crystals along the stacking direction.

Opto-thermionic refrigeration is an environment-friendly method. To improve the opto-thermionic refrigeration efficiency, a system with a perovskite oxide multilayer of p-BaTiO3/BaTiO3/SrTiO3/BaTiO3/n-BaTiO3 is proposed based on the model of opto-thermionic refrigeration. Because the Auger coefficient of SrTiO3 is two orders smaller than that of GaAs, the calculated refrigeration power of the p-BaTiO3/BaTiO3/SrTiO3/BaTiO3/n-BaTiO3 system is much higher than that of the p-AlGaAs/AlGaAs/GaAs/AlGaAs/n-AlGaAs system. A refrigeration power of as high as 39 Wc m −2 is obtained numerically in the p-BaTiO3/BaTiO3/SrTiO3/BaTiO3/n-BaTiO3 system, which suggests a potential application of the oxide structures in opto-thermionic refrigeration. (Some figures in this article are in colour only in the electronic version)

The transport property of the La0.7Sr03MnO3/Si heterostructure was investigated theoretically by applying the drift-diffusion model to the present system. A simple scenario of the semiconductor band and electric field at the interface region of the heterostructure with various bias voltages are presented. The good agreement between the self-consistent calculated results and the experimental data indicates that the proposed band picture is valid for the interpretation of the transport property of the p-n heterojunctions made of La0.7Sr0.3MnO3 and Si regardless of the complexity of the interface structures and multi-couplings among charge, spin, lattice and orbital of manganites.

We develop a comprehensive, elegant theory to explain terahertz (THz) emission from a superlattice over a wide range of applied electric field,which shows excellent agreement between theory andexperiment for a GaAs/Al{0.3}Ga{0.7As superlattice. Specifically we show that increasing electric field increases THz emission for low fields, then reduces emission for medium fields due to field-induced wave function localization, and then increases emission in the high field due to delocalization and Zener tunneling between minibands. Our theory shows that Zener tunneling resonances yield high THz emission intensities and points to superlattice design improvements., 10 pages, 3 figures