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In this paper, we construct an alternative proof for the long-time behavior of large-data classical solutions to the 2D semi-dissipative Boussinesq equations without thermal diffusion on a bounded domain subject to the stress-free boundary conditions, which was previously studied in Doering et al (2018 Physica D 376/7 144–59). To demonstrate the effectiveness of the new approach, we study the long-time behavior of large-data classical solutions to the initial-boundary value problem of a related model with density variance and subject to the no-flow boundary condition, for which the analytic technique utilized in Doering et al (2018 Physica D 376/7 144–59) is not directly accessible.

Heavy crude oil is a type of crude oil that has high viscosity, which leads to poor fluidity. In this paper, a 532 nm laser was employed to reduce the oil viscosity at low current. The voltage, temperature and the viscosity will change under laser irradiation. Under laser irradiation, the photon energy was absorbed by liquid and converted into heat energy, leading to the temperature rise. Furthermore, the rise in temperature led to breaking of the hydrogen bonds, which resulted in the drop in the viscosity v. Due to the thermal effect induced by the laser, the variation of viscosity Δv was closely related to the laser irradiation position. The results of the experiments suggest that laser technology could be applied to characterize the viscosity change in crude oil under laser irradiation.

Two-dimensional (2D) melting is a fundamental research topic in condensed matter physics, which can also provide guidance on fabricating new functional materials. Nevertheless, our understanding of 2D melting is still far from being complete due to existence of possible complicate transition mechanisms and absence of effective analysis methods. Here, using Monte Carlo simulations, we investigate 2D melting of 60° rhombs which melt from two different surface-fully-coverable crystals, a complex hexagonal crystal (cHX) whose primitive cell contains three rhombs, and a simple rhombic crystal (RB) whose primitive cell contains one rhomb. The melting of both crystals shows a sequence of solid, hexatic in molecular orientation (Hmo), and isotropic phases which obey the Berezinskii–Kosterlitz–Thouless–Halperin–Nelson–Young (BKTHNY) theory. However, local polymorphic configuration (LPC) based analysis reveals different melting mechanisms: the cHX–Hmo transition is driven by the proliferation of point-like defects during which defect-associated LPCs are generated sequentially, whereas the RB–Hmo transition is driven by line defects where defect-associated LPCs are generated simultaneously. These differences result in the observed different solid–Hmo transition points which are ϕ A = 0.812 for the cHX–Hmo and ϕ A = 0.828 for the RB–Hmo. Our work will shed light on the initial-crystal-dependence of 2D melting behavior.

The Stellar Abundances and Galactic Evolution Survey (SAGES) is a multi-band photometric survey focused on estimation of stellar atmospheric parameters and interstellar extinction. In this paper we have derived photonic passbands for the intermediate-band u and v filters of the SAGES photometric system. The derived photonic passbands have been compared with those of the u and v filters of the Strömgren and SkyMapper systems. Synthetic photometry based on the derived photonic passbands could reproduce the observations very well. We have also derived observed, model-free extinction coefficients for the SAGES u and v bands (as well as the Pan-STARRS grizy bands) using the “standard pair” method. The derived reddening coefficients have been compared with those predicted by the extinction laws. Variations of reddening coefficients with effective temperatures and color excesses of B–V given by Schlegel et al. (E(B−V)SFD) have been investigated. No obvious trends or significant variations with effective temperatures have been found, but reddening coefficients for all the colors exhibit declining trends with increasing E(B−V)SFD, with typical relative variations of twenty-some percent from E(B − V)SFD ∼ 0 to 1.

Isolated attosecond pulse generation in argon is theoretically investigated for different gas pressures and medium lengths. The output of attosecond pulse is effectively enhanced by using a longer gas medium with optimized pressure. The peak intensity of the attosecond pulse by using 6 mm gas medium is doubled compared with that of 1–3 mm gas cell, which is usually used in the experiment. Our simulation shows that the distortion of the driving laser waveform and the absorption are the main factors that limit the output of the attosecond pulse for the long gas medium. Optimized generation condition could be found by balancing the medium length and pressure.

Previous Monte Carlo simulations have shown that ordered tetratic phases can emerge in a dense two-dimensional Brownian system of rotationally asymmetric hard kites having 90° internal angles. However, there have been no experimental investigations yet to compare with these simulation results. Here, we have fabricated two types of micron-sized kites having internal angles of 72°–90°–108°–90° and 72°–99°–90°–99°, respectively, and we have experimentally studied their phase behavior in two-dimensional systems. Interestingly and in contrast to the Monte Carlo simulations, the experimental results show a phase sequence of isotropic fluid-hexagonal rotator crystal-square crystal as the area fraction ϕ A increases for both types of kites. The observed square crystal displays not only a quasi-long-range translational order but also (quasi-)long-range 4-fold bond- and molecular-orientational order; these characteristics confirm that tetratic order can emerge even in dense Brownian systems of rotationally asymmetric particles. A model based on local polymorphic configurations (LPCs) is proposed to understand the origin of the square lattice order in these dense kite systems. The results in this study provide a new route to realize custom-designed self-assembly of colloids by controlling LPCs.

The internal environment of the passenger compartment directly affects the mental state of the driver and passengers. The research on the thermal comfort of the passenger compartment has become an important topic in the automotive industry. This paper used computational fluid dynamics method to study the thermal environment of the passenger compartment and the thermal comfort of the human body under different air outlets. Predictive mean vote model and equivalent temperature model were used for calculation. The influence of solar radiation on the velocity and temperature field in the passenger compartment was considered in the simulation process, and the correctness of the simulation results was verified by the cooling performance experiment of air conditioning. The results showed that the position of the air outlet had a great influence on the driver’s thermal comfort. When the air outlet was on the driver’s side, the driver’s thermal comfort was the best.

In recent years, high-brightness picosecond lasers have been widely used in high-end precision processing, spectroscopy and high harmonic generation. To obtain higher power and excellent beam quality, it is an ideal solution to add a high-gain amplifier to the back end of the high-stability picosecond fiber or solid seed. In this article, a fiber-solid hybrid end-pumped Nd:YVO4 picosecond laser system with high beam quality is demonstrated. The influence of the self-developed picosecond fiber seed output characteristics on solid amplifiers has been studied in detail, including the energy, repetition rate and spectrum. After two-stage traveling wave amplifiers, the maximum 155 μJ single pulse energy is obtained with 20 kHz repetition rate, and the corresponding peak power reaches 14.9 MW with 10.4 ps pulse duration. Meanwhile, the beam quality factors under the maximum 18.4 W average power are measured to be M x 2 = 1.27 and M y 2 = 1.25, respectively.

A convolutional neural network is employed to retrieve the time-domain envelop and phase of few-cycle femtosecond pulses from transient-grating frequency-resolved optical gating (TG-FROG) traces. We use theoretically generated TG-FROG traces to complete supervised trainings of the convolutional neural networks, then use similarly generated traces not included in the training dataset to test how well the networks are trained. Accurate retrieval of such traces by the neural network is realized. In our case, we find that networks with exponential linear unit (ELU) activation function perform better than those with leaky rectified linear unit (LRELU) and scaled exponential linear unit (SELU). Finally, the issues that need to be addressed for the retrieval of experimental data by this method are discussed.

It is well known that Hawking radiation can be treated as a quantum tunneling process of particles from the event horizon of black hole. In this paper, we attempt to apply the massive vector bosons tunneling method to study the Hawking radiation from the non-rotating and rotating dilaton black holes. Starting with the Proca field equation that govern the dynamics of massive vector bosons, we derive the tunneling probabilities and radiation spectrums of the emitted vector bosons from the static spherical symmetric dilatonic black hole, the rotating Kaluza—Klein black hole, and the rotating Kerr—Sen black hole. Comparing the results with the blackbody spectrum, we satisfactorily reproduce the Hawking temperatures of these dilaton black holes, which are consistent with the previous results in the literature.

We investigate the massive vector particles' Hawking radiation from the neutral rotating Anti-de Sitter (AdS) black holes in conformal gravity by using the tunneling method. It is well known that the dynamics of massive vector particles are governed by the Proca field equation. Applying WKB approximation to the Proca equation, the tunneling probabilities and radiation spectrums of the emitted particles are derived. Hawking temperature of the neutral rotating AdS black holes in conformal gravity is recovered, which is consistent with the previous result in the literature.

This paper has investigated the distributed attitude regulation problem for multiple spacecrafts on the basis of the leader-follower architecture. In this paper, a control scheme based on the distributed fixed-time observer is proposed. To be specific, with the condition that some following spacecraft can’t obtain the leader’s attitude, a distributed attitude observer is introduced for estimating the leader’s attitude. By using the distributed observer, this issue will be transformed into an attitude tracking control problem for a single spacecraft. It is proved that the proposed distributed observer is in the sense of the fixed-time stability. Finally, simulation results illustrate that the proposed distributed observer is effective.

In recent years, there has been a variety of improved collaborative filtering methods, which promote accuracy of recommendation by analysing too much user or item information like individual characteristics, application scenarios and so on. This increases the time complexity of the algorithm and leads to low efficiency of recommendation. Therefore, how to improve the quality of recommendation through analysing a small amount of effective information has attracted more attention in the research of collaborative filtering methods. This paper proposes a collaborative filtering method based on expected utility from the perspective of the economic significance of user rating. Firstly, the method establishes the corresponding similarity criterion and calculates the similarity between users or items by scoring expectation. Then, the nearest neighbour set is calculated and the final prediction is got. Finally, our method is validated by the experimental results using movielens-1m data set. The results show that the collaborative filtering method proposed in this paper is simpler and more feasible compared with the traditional IBCF, KNN and other mainstream methods, and can improve the efficiency and quality effectively of recommendation only using less information. This work has significance both in theoretical research and practical application value.

We investigate the quantitative behaviour of one-dimensional classical solutions for a hyperbolic-parabolic system describing repulsive chemotaxis. It is shown that classical solutions to the Cauchy problem always exist globally in time for large initial perturbations around constant equilibrium states. We prove rigorously the chemo-repulsion collapse scenario and show that all solutions converge to the attractive ground states as time approaches infinity. Moreover explicit decay rates of the perturbations are computed under some mild conditions on the initial data. The proof is established via a novel Lp-based energy method. We also obtain a frequency-dependent stretched-exponential decay rate by using a new Fourier method which can be of independent interest.

The idea of word embedding is based on the semantic distribution hypothesis of linguist Harris (1954), who believes that words with the same semantics are distributed in similar contexts. The learning of word embedding is a crucial technology in natural language processing. In recent years, cross-language word vectors have received more and more attention. Cross-language Word vectors can transfer knowledge between different languages. Most importantly, this transfer can occur between rich-resource and low-resource languages. This paper uses the Tibetan-Chinese Wikipedia corpus to train monolingual word vectors. Based on the Tibetan-Chinese bilingual translations, we use the supervised method in the MUSE library to train the Tibetan-Chinese bilingual cross-language word embeddings. In the experiment, we evaluate the result of word representation on the standard lexical semantic evaluation task. The results show that the method has a certain improvement in the semantic representation of the word embedding.

We utilized a set of fused silica thin plates to broaden the spectrum of 1 kHz, 30 fs Ti:sapphire amplified laser pulses to an octave. Following the compression by chirped mirror pairs, the generated few-cycle pulses were focused onto an argon filled gas cell. We detected high order harmonics corresponding to a train of 209 as pulses, characterized by the reconstruction of attosecond beating by interference of two-photon transition (RABITT) technique. Compared with the conventional attosecond pulse trains, the broad harmonics in such pulse trains cover more energy range, so it is more efficient in studying some typical cases, such as resonances, with frequency resolved RABITT. As the solid thin plates can support high power supercontinuum generation, it is feasible to tailor the spectrum to have different central wavelength and spectral width, which will make the RABITT source work in different applications.

We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to 2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation (DFG) in β-barium borate crystal (β-BBO) and passively carrier-envelope-phase (CEP) stabilized. The DFG is induced by few-cycle pulses initiated from spectral broadening in multiple thin plates driven by a Ti: sapphire chirped-pulse amplifier. Furthermore, a numerical simulation is developed to estimate the conversion efficiency and output spectrum of the DFG. Our results show that the pulses from the DFG have the potential for seeding intense mid-infrared (MIR) laser generation and amplification to study strong-field physics and attosecond science.

The collaborative filtering recommendation system has been widely used in E-commerce as a relatively successful recommendation system. At present, the focus of collaborative filtering recommendation research is mainly on how to improve the accuracy of recommendation by improving the recommendation algorithm. However, in real world, the user’s rating behaviour is not perfectly rational. It is no odd that there is deviation of rating to any a given item for a user in real evaluation. In this case, what it means for the improvement of collaborative filtering recommendation methods, and how they performed when we use the commonly used quality metrics to evaluate the collaborative filtering recommendation methods? In view of these problems, this paper presupposes that the user’s rating behaviour is a bounded rational behaviour, and based on the normality hypothesis of rating error, introduces a simulated rating experiment innovatively to analyse the effect that rating prediction can achieve in sense of the commonly used quality metrics. This study is of significance for the research and application of collaborative filtering recommendation technology.

The new generation of power grid dispatching control system draws on the cloud computing concept for reference, adopts a new overall architecture of “physically distributed and logically uniform”. It applies a large number of new technologies, enhances the relevance of various applications of the new system, and rapidly expands the application data scale, making the operation and maintenance of the power grid dispatching control system increasingly complicated. At present, the State Grid Corporation of China is carrying out research on operation and maintenance technology of dispatching control system based on historical big data mining. In the face of the collection and aggregation of a large number of operation history data and operation indexes of dispatching control system, the traditional relational database is facing great challenges. This paper discusses the data storage technology supporting big data, and through analyzing the characteristics of big data storage and the existing typical databases of NO SQL and NewSQL, puts forward a data storage technology that can meet the needs of mass operation and maintenance data storage and high-speed access of the new generation of power grid dispatching control system.

Accurate and rapid detection in remote sensing images is of great significance in military navigation, environmental monitoring, and civil applications. Due to the small object detection problem of remote sensing images, higher requirements and challenges are put forward for object detection technology. In recent years, the one-stage object detector and the two-stage object detector based on convolutional neural network have made great achievements in the field of image classification and detection. The one-stage object detector is generally superior to the two-stage object detector in detection speed, but the detection accuracy is inferior to the two-stage target detector. In this paper, YOLOv3 is used as a one- stage target detector for small aircraft detection of remote sensing images. We chose appropriate anchors to cover the size distribution in our experimental data by using dimension clusters. The experimental results show that YOLOv3 not only exceeds the conventional one-stage object detector in speed, but also well match the accuracy of the two-stage object detector. The YOLOv3 achieved excellent detection accuracy and low processing time at the same time for small aircraft detection.

Bio-inspired noise reduction based on the silent flight characteristics of the owl is an effective passive aerodynamic noise control method. Inspired by the silent flight of owls, this paper investigates trailing edge noise control of the NACA 0012 airfoil by using a brush-serrated coupling bionic structure at chord based Reynolds numbers ranging from Rec =6×105 to Rec =1.2×106. Preliminary experimental results showed that the proposed brush-serrated coupling bionic structure can not only avoid low-frequency vortex shedding tonal noise caused by single serrated trailing edges, but also reduce noise emission in a wider frequency range, which can be widely used in aerodynamic noise control.

The flexible bearing is an important component and installed in the harmonic driver which transmits motion by elastic characteristics of flexible parts. The rings of the flexible bearing are forced to deform by the wave generator of harmonic driver in its unique working condition different from normal bearings. A large bending stress is generated in the both rings of the flexible bearing after assembly deformation in addition to the contact stress of normal bearings. And, the meshing state of the internal gear of the driver will also be affected greatly. In the present research, a statically indeterminate model is proposed by combining theory of normal bearings with mechanics of materials to solve the deformation characteristics and internal force state of the flexible bearing under the wave generator. The results show that the error of mathematical model is within 6.7%.

As a relatively successful recommendation system, the collaborative filtering recommendation system (CFRS) has been widely used in e-commerce. However, the current CFRS is mainly based on mainstream or popular products to recommending similar items for users and is less efficiency in recommend the so called "Long Tail" products to meet the individual needs of users. Based on the Item-based system filtering recommendation algorithm, this paper proposes a collaborative filtering recommendation algorithm that implements long tail recommendation by using the item rating probability matrix and item rating reliability. Compared with the traditional collaborative filtering algorithm, the experimental result based on MovieLens 1M dataset shows that the proposed algorithm can deal with the data sparsity problem better, and is better for producing recommendation for the long tail products effect, and furthermore, it shows stability to a certain extent in producing recommendations under different situations of data sparseness.

A model of total transfer capability (TTC) for the AC/DC system with multi-terminal voltage source converter DC (VSC-MTDC) system is set up in this paper. As the load and generator power in traditional continuation power flow (CPF) algorithm increased with equal proportion, a novel continuous power flow approach based on economic operation of power grid is proposed. In the method, taking the minimum generation cost as the goal, the distribution of generator output is optimized by economic dispatching based on linear programming method, which can avoid the defects of some existing methods that caused by the piecewise linearization of incremental ratio of generator consumption curve. The distribution of load increment and the parameters of VSC control modes are optimized by mathematical optimization method to minimize the network loss, which can get the TTC under economic conditions. Finally, cases study based on modified IEEE 9-node system and modified IEEE 30-node system verify the rationality and effectiveness of the proposed methods.

With the rapid development of deep learning, great breakthroughs have been made in the field of object detection. In this article, the deep learning algorithm is applied to the detection of daily objects, and some progress has been made in this direction. Compared with traditional object detection methods, the daily objects detection method based on deep learning is faster and more accurate. The main research work of this article: 1. collect a small data set of daily objects; 2. in the TensorFlow framework to build different models of object detection, and use this data set training model; 3. the training process and effect of the model are improved by fine-tuning the model parameters.

The side-illumination-enhanced photovoltaic effect has been studied in La0.9Sr0.1MnO3/Si heterojunctions fabricated by laser molecular beam epitaxy. When a He–Ne laser illuminated the La0.9Sr0.1MnO3 film surface, a stable photovoltage was produced and the responsivity is ~0.17 mV mW−1. An enhancement of the photovoltaic effect occurred when the La0.9Sr0.1 MnO3/Si interface was illuminated directly by side illumination, and the steady responsivity reached ~6.87 mV mW−1. This work demonstrates an effective way to improve the photovoltaic responsivity of the perovskite oxide heterojunctions.

Transient photo-induced voltage characteristics have been studied in La0.9Sr0.1MnO3 films on vicinal cut SrTiO3 (0 0 1) substrates. The as-received thin films are epitaxially grown on the substrates and predominated by a single ( 1 01)-oriented growth. Under irradiation of a 308 nm laser pulse the voltage signal is pulsed and the response time agrees with the laser pulse width. The dependence of the voltage peak on the tilting angles from 0 degrees to 45 degrees is further measured. For the c-axis tilt angle, the largest signal does not appear at 45 degrees and the optimum choice is similar to 30 degrees.

We report on the infrared laser-induced photovoltaic effect of a heterostructure comprising a n-ZnO film with an electron concentration of 1.6 x 10(21) cm(-3) and a MgB2 film with a high carrier concentration of 1.8 x 10(23) cm(-3) at room temperature. Current-voltage characteristics of the structures have good rectifying diode-like behaviour. An open-circuit photovoltage of 10 ns rise time and 20 ns full width at half-maximum was observed under the illumination of a 1.064 mu m pulsed laser for a duration of 25 ps. When the junction was irradiated by a 10.6 mu m CO2 laser pulse for 60 ns, a transient photovoltaic signal of similar to 27 mV occurred with a rise time of similar to 60 ns. A possible mechanism of the observed phenomena is discussed based on the laser-induced hot carrier photovoltaic effect.

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.

As a compact and burgeoning alternative to synchrotron radiation and free-electron lasers, high harmonic generation has proven its superiority in static and time-resolved XUV spectroscopy for the past two decades and has recently gained many interests and successes in generating soft X-ray emissions covering the biologically important water window spectral region. Unlike synchrotron and free-electron sources, which suffer from relatively long pulse width or large time jitter, soft X-ray sources from high harmonic generation could offer attosecond time resolution and be synchronized with their driving field to investigate time-resolved near edge absorption spectroscopy, which could reveal rich structural and dynamical information of the interrogated samples. In this paper, we review recent progresses on generating and characterizing attosecond light sources in the water window region. We show our development of an energetic, two-cycle, carrier-envelope phase stable laser source at 1.7~$\mu$m and our achievement in producing a 53~attosecond soft X-ray pulse covering the carbon K-edge in the water window. Such source paves the ways for the next generation X-ray spectroscopy with unprecedented temporal resolution.

We have used a variety of different applied fields to control the density, growth, and structure of colloidal crystals. Gravity exerts a body force proportional to the buoyant mass and in equilibrium produces a height-dependent concentration profile. A similar body force can be obtained with electric fields on charged particles (electrophoresis), a temperature gradient on all particles, or an electric field gradient on uncharged particles (dielectrophoresis). The last is particularly interesting since its magnitude and sign can be changed by tuning the applied frequency. We study these effects in bulk (making 'dielectrophoretic bottles' or traps), to control concentration profiles during nucleation and growth and near surfaces. We also study control of non-spherical and optically anisotropic particles with the light field from laser tweezers.

We demonstrate efficient generation of continuous spectrum centered at 400 nm from solid thin plates. By frequency doubling of 0.8 mJ, 30 fs Ti:sapphire laser pulses with a BBO crystal, 0.2 mJ, 33 fs laser pulses at 400 nm are generated. Focusing the 400-nm pulses into 7 thin fused silica plates, we obtain 0.15 mJ continuous spectrum covering 350–450 nm. After compressing by 3 pairs of chirped mirrors, 0.12 mJ, 8.6 fs pulses are achieved. To the best of our knowledge, this is the first time that sub-10-fs pulses centered at 400 nm are generated by solid thin plates, which shows that spectral broadening in solid-state materials works not only at 800 nm but also at different wavelengths.

This paper presents an effective sequential approach based on weight modification for VSC-MTDC power system state estimation, called weight modification sequential method. The proposed approach simplifies the AC/DC system state estimation algorithm through modifying the weight of state quantity to keep the matrix dimension constant. The weight modification sequential method can also make the VSC-MTDC system state estimation calculation results more ccurate and increase the speed of calculation. The effectiveness of the proposed weight modification sequential method is demonstrated and validated in modified IEEE 14 bus system.

In terms of the evaluation of the diffusion-controlled adsorption and diffused rate, a mathematical model was built on the basis of the double-exponential kinetics model and terahertz amplitude in this letter. The double-exponential-THz model described the two-step mechanism controlled by diffusion. A rapid step involves external and internal diffusion, followed by a slow step controlled by intraparticle diffusion. The concentration gradient of the molecules promoted the organic molecules rapidly diffusing to the external surface of adsorbent. The solute molecules then transferred across the liquid film. Intraparticle diffusion began and was determined by the molecular sizes, as well as affinities between organics and activated carbon.

This paper presents an effective approach for state estimation in power systems that include multi-terminal voltage source converter based high voltage direct current (VSC-MTDC), called improved adaptive weighting function method. The proposed approach is simplified in which the VSC-MTDC system is solved followed by the AC system. Because the new state estimation method only changes the weight and keeps the matrix dimension unchanged. Accurate and fast convergence of AC/DC system can be realized by adaptive weight function method. This method also provides the technical support for the simulation analysis and accurate regulation of AC/DC system. Both the oretical analysis and numerical tests verify practicability, validity and convergence of new method.