Search

Many irregular shaped high-rise buildings have been built for graceful demand of architecture or better amenity and ventilation in the world. In this study, a benchmark rectangular high-rise building model and six high-rise building models with various irregular shapes, including two T-shaped, two U-shaped, H-shaped and X-shaped, are tested in a boundary wind tunnel to investigate their wind loads characteristics. The coefficients, power spectral density and cross-correlation of base moments as well as local wind forces are analyzed and discussed in details. Based on the wind tunnel test results, it is founded that the effect of U-shape and H-shape on wind loads is negligible. The along-wind mean base moment coefficient of X-shaped model is increased by 10.0% in 90° wind direction. The wind force characteristics of T-shaped models are quite different from the benchmark model in many cases. The mean base moment coefficient of T-shaped 2 model is reduced by 18.6% in 0° wind direction. Larger mean lift forces and torques of T-shaped models are appeared and there is a certain correlation between along-wind and across-wind local wind forces in 90° wind direction.

In recent years, machine learning (ML) techniques have been used in various fields of engineering practice. In order to evaluate the feasibility of machine learning algorithms for prediction of wind-induced effects on high-rise buildings, four ML algorithms including ridge regression, decision tree, random forest and gradient boosting regression tree are adopted in this study to predict wind pressures on Commonwealth Advisory Aeronautical Research Council standard tall building. The gradient boosting regression tree model is proved to be well performed in predicting both mean wind pressures and fluctuating wind pressures. Compared to expensive wind tunnel tests and time-consuming computational fluid dynamic simulations, it is expected that the gradient boosting regression tree model is an efficient and economical alternative for predicting wind pressures on high-rise buildings.

Visible light response PAN@Ag-Ag2O/Sch (PAN@AS, schwertmannite and polyacrylonitrile abbreviated as Sch and PAN) nanofibers with different mass ratios were synthesized by electrospinning technology and pH-induced precipitation reaction. X-Ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy analysis showed that the formation of Ag-Ag2O/Sch heterojunction and Ag-Ag2O nanoparticles were evenly distributed on the surface of Sch. The prepared nanofibers have high oxidative removal performance for As(III) under visible light. In the PAN@AS0.10 system, the total As removal percent can reach 90.96% after 120 min irradiation at pH 4.0. The scavenger experiments confirmed that the main active substances of the PAN@AS0.10 system were h+ and •OH. The high oxidation and removal performance of the PAN@AS0.10 composite for As(III) was attributed to the effective separation of photogenerated electron-hole pairs and high adsorption capacity of Sch for As under acidic conditions. This research provides a new material for the oxidation and removal of pollutants in water [such as As(III)] and also provides a research basis for the preparation of recyclable photocatalysts.

Asphalt aging is a pivotal factor affecting the service performance of asphalt pavement. Previous studies often ignored the influence of ultraviolet radiation on asphalt aging. Coincidentally, there is no standard test method of photooxidation aging that can be applied to guide engineering practice. In this paper, the influence of ultraviolet aging on the composition, structure and properties of asphalt was studied by adopting Bert four-component method, Fourier transform infrared spectroscopy aned dynamic shear rheometer. Bert four-component method elaborates that the content of asphaltene increases and the content of aromatic component decreases after UV aging. Fourier transform infrared spectroscopy indicates that there are obvious peaks of carbonyl and sulfoxide groups after aging, the penetration of asphalt decreases while the softening point and viscosity increase. Moreover, the composite modulus of asphalt increases obviously at low temperature, but has little effect on the composite modulus at high temperature.

In this perspective, we outline that a space borne gravitational wave detector network combining LISA and Taiji can be used to measure the Hubble constant with an uncertainty less than 0.5% in ten years, compared with the network of the ground based gravitational wave detectors which can measure the Hubble constant within a 2% uncertainty in the next five years by the standard siren method. Taiji is a Chinese space borne gravitational wave detection mission planned for launch in the early 2030 s. The pilot satellite mission Taiji-1 has been launched in August 2019 to verify the feasibility of Taiji. The results of a few technologies tested on Taiji-1 are presented in this paper. Gravitational wave astronomy has opened the door to test general relativity and the effect of gravity in the Universe. The authors present the capabilities of an overlap between space gravitational wave detectors LISA and Taiji to constrain the Hubble constant to 0.5%, in 10 years, and what can be learned from the satellite pilot Taiji-1 launched in 2019.

Polyvinyl chloride materials used in cooling towers always lead to damage and low efficiency due to the hot and humid environment. This paper suggests a glass fiber reinforced material for a better performance. An optimal fractal distribution-of glass fibers in the composite matrix is experimentally obtained when the fractal dimensions are between 0.6 and 0.9.

Modern tall buildings are likely sensitive to wind excitations due to their increasing height and structural flexibility. Proper or optimal wind-resistant structural design of such high-rise buildings is required or sometimes necessary to meet the requirement of safety and serviceability. Combining a genetic algorithm (GA) with improved penalty function and calculation method for equivalent static wind loads (ESWLs), this paper presents an optimal procedure for the wind-resistant design of tall buildings, which aims to minimize the total weight of the designed building subject to the constraints of top acceleration and lateral drifts. A penalty function is utilized to deal with the implicit expressed constraints of optimization. The ESWLs can be instantaneously updated due to the change of structural dynamic properties during the optimal design process. A 60-story rectangular reinforced concrete frame structure with the same geometric shape of the CAARC standard tall building is adopted to verify the feasibility of the presented method. The example demonstrates that the proposed optimal design procedure is an effective tool for the wind-resistant optimal design of tall buildings.

Eight L-shaped rigid models with different geometric dimensions were tested at four typical terrain categories in a boundary wind tunnel to investigate the characteristics of wind pressures on L-shaped tall buildings. The effects including wind direction, turbulence intensity, and geometric dimension on the characteristics of wind pressures on L-shaped tall buildings were studied. Shape factors of each face under the unfavorable wind direction were summarized. Moreover, the power spectral densities, correlation coefficients, and coherence functions were analyzed in frequency domain. Based on the testing results, it is shown that the proposed exponential functions fit the measurements well. The objective of this study is to provide useful information for the wind-resistant design ofL-shaped tall buildings.

The space gravitational wave detection and drag free control requires the micro-thruster to have ultra-low thrust noise within 0.1 mHz–0.1 Hz, which brings a great challenge to calibration on the ground because it is impossible to shield any spurious couplings due to the asymmetry of torsion balance. Most thrusters dissipate heat during the test, making the rotation axis tilt and components undergo thermal drift, which is hysteretic and asymmetric for micro-Newton thrust measurement. With reference to LISA’s research and coming up with ideas inspired from proportional-integral-derivative (PID) control and multi-timescale (MTS), this paper proposes to expand the state space of temperature to be applied on the thrust prediction based on fine tree regression (FTR) and to subtract the thermal noise filtered by transfer function fitted with z-domain vector fitting (ZDVF). The results show that thrust variation of diurnal asymmetry in temperature is decoupled from 24 μN/Hz1/2 to 4.9 μN/Hz1/2 at 0.11 mHz. Additionally, 1 μN square wave modulation of electrostatic force is extracted from the ambiguous thermal drift background of positive temperature coefficient (PTC) heater. The PID-FTR validation is performed with experimental data in thermal noise decoupling, which can guide the design of thermal control and be extended to other physical quantities for noise decoupling.

The frictionless contact problem between an axisymmetric rigid indenter and a layered transversely isotropic medium with surface stresses is considered. The contact pressure is represented as a product of two series based on the solutions of the bulk material and the elastic surface. By using Hankel transforms, the coefficients in the product-series representation are determined by the normal displacement condition inside the contact area and the finite-pressure condition at the contact edge. Taking the spherical indentation as a specific example, the effectiveness of the solution procedure is verified for various contact scenarios. Comparing with the Green’s function method, this solution procedure is not only computationally efficient but also may give the contact pressure in its analytical form. For some specific problems, the effects of the material anisotropy and the layer thickness on the contact process with surface stresses are investigated.

For investigation of the effects of building corner modifications on reduction of wind loads on high-rise buildings, a benchmark square model and three corner modified models including recessed, chamfered and rounded are tested by pressure measurements in a boundary layer wind tunnel. Based on the experimental results, mean wind pressure coefficients, base moment coefficients, local wind force coefficients, power spectral densities and vertical correlation coefficients of the three corner modified models are discussed and compared with those of the square model to provide comprehensive evaluations of the effects of the aerodynamic treatments on reductions of the wind loads. This paper aims to provide useful information for the wind-resistant design of high-rise buildings.

This paper aims to systematically study the across-wind loads of rectangular-shaped tall buildings with aerodynamic modifications and propose refined mathematic models accordingly. This study takes the CAARC (Commonwealth Advisory Aeronautical Research Council) standard tall building as a benchmark model and conducts a series of pressure measurements on the benchmark model and four CAARC models with different round corner rates (5%, 10%, 15% and 20%) in a boundary layer wind tunnel to investigate the across-wind dynamic loads of the typical tall building with different corner modifications. Based on the experimental results of the five models, base moment coefficients, power spectral densities and vertical correlation coefficients of the across-wind loads are compared and discussed. The analyzed results shown that the across-wind aerodynamic performance of the tall buildings can be effectively improved as the rounded corner rate increases. Taking the corner round rate and terrain category as two basic variables, empirical formulas for estimating the across-wind dynamic loads of CAARC standard tall buildings with various rounded corners are proposed on the basis of the wind tunnel testing results. The accuracy and applicability of the proposed formulas are verified by comparisons between the empirical formulas and the experimental results.

The Hall Micro Thrusters (HMTs) use cold gas or accelerated plasma dual mode to provide ultra-precise spacecraft altitude control. They were operated in space for the first time as part of the demonstration payloads on Chinese Academy of Science’s (CASs) Taiji-1 spacecraft since September 2019. Hall Micro Thruster Assemblies (HMTAs) were the actuators in drag-free control, and will compensate the nonconservative force for gravity wave observatories. The HMTAs meet the requirements of operating at 5–100 [Formula: see text] N of thrust with 0.7 [Formula: see text] N resolution and [Formula: see text]0.6 [Formula: see text] N/Hz[Formula: see text] (0.01–1 Hz) noise to deliver the nanometer-level precision control as fast as 30 ms measured by Gravitational Reference Sensor (GRS). A transfer function model in z-domain was fit and used to filter HMTs cathode voltage to predict GRSs thrust noise response. Simulations of a single or dual-frequency disturbance and the corresponding compensation demonstrated that HMTAs could deliver the required thrust profile expected. The capability to meet the requirements of thruster noise in drag-free control is critical for future missions because the acceleration noise on test mass directly relates to the gravity wave signa l. Preliminary in-orbit verification of Taiji-1 has showed HMTAs’ great potential in future, and the data in the experiments are presented in this paper.

This paper takes CAARC standard tall building as example to investigate the effects of corner chamfers on the aerodynamic performance of tall buildings. Five rigid tall building models including CAARC standard tall building as benchmark model and four corner chamfered models with different modification rates from 5% to 20% are tested for pressure measurements in a boundary layer wind tunnel. Based on the experimental results, wind pressure coefficients, local wind force coefficients, base moment coefficients and their power spectral densities from the five models are compared and discussed. The results show that the aerodynamic performance of the tall building models can be effectively improved as the corner chamfer rate increases. The correlation factors for base moment coefficients and power spectral densities are proposed to assess the aerodynamic performance improvement. This paper aims to provide useful information for the wind-resistant optimal design of rectangular tall buildings.

Wind tunnel test of 1:500 rigid model of tall building with atrium was carried out. Based on the experimental results, characteristics of wind pressures on atrium facades and wind loads on the structure were investigated in detail. The results show that the formation of flow separation on the building top plays a critical role in the generation of wind pressures on the atrium facades. Meanwhile, wind pressure coefficient distributions on the atrium facades are found to be relatively uniform. Moreover, the horizontal and vertical correlations of pressure coefficient exhibit high at most locations on atrium facades. With the increasing of the opening ratio, the mean wind pressure coefficients first decreased and then stabilized, and the fluctuating wind pressure coefficients first decreased and then increased. A design guideline for the wind-resistant design of atrium facades was proposed, and the results predicted by the proposed guideline were in good agreement with those from the wind tunnel tests, indicating that the proposed guideline can be used in engineering applications. When the opening ratio is no more than 5.33%, the effect of the facade pressures within the atrium on the wind loads on the structure can be ignored. For such cases, the wind-resistant design for a tall building with atrium can refer to that of a similar shape tall building without atrium.

In this paper, flatwise tensile test (FWT) and modified double cantilever beam (DCB) experiment were conducted to investigated the debond fracture of sandwich plate with corrugated core. In the experiment, the crack always stays at the face/core interfacial. Tensile bond strength of face core can be given from the flatwise tensile test and we can get the mode I fracture toughness GIC from DCB tests. It is found that the trends of curves change greatly at the beginning, with the propagation of crack, load against open displacement curves change smoothly. In order to simulate the face/core failure of sandwich plate with corrugated core, the cohesive element model is used. Tensile strength and strain energy release rate measured by the experiments presented in this paper are used in as parameters for simulation of the debond fracture. By comparing with the experiment results, the model can express the face/core failure of sandwich plate with corrugated core validly.

In order to reveal the status of typhoon landfall in China coastal areas, the coastal areas and frequency of typhoon landing were compared with the statistical analysis in the paper for nearly 50 years; combined with the wind pressure of low-rise buildings under typhoon in China's coastal, structures damage of low-rise buildings were investigated. The results show that, the southwest coast of Guangdong landfall the largest number of typhoon landing, while the coastal areas of Fujian and Zhejiang have larger number of strong typhoons; turbulence great impact on surface air pressure; It was also found that the high suction pressure zones occurred around the windward roof edges at a wind azimuth of 450,and wind pressure along the roof corner just behind the roof ridge. The results of the present study are expected to be useful for the future development of a simple approximate formula for the low-rise buildings of the coastal area for design use.

Automatic modulation classification is very important in cognitive radio and communication reconnaissance systems. Two novel approaches for identifying the modulation format of general M-ary PSK signal are proposed, which are based on the phase entropy. Phase entropy of the first one is estimated in time domain with probability space partitioned into fixed dimensions. And for the second one, the frequency transform is first applied to the phase of the received signal and the entropy of the measured signal is then estimated. Based on a general hypothesis test, the entropies of different modulation signals are compared to classify them. The simulation results illustrate that the proposed algorithm has smaller computational complexity than existing classifier and the second one has better classification performance in low signal-to-noise ratio domain.

A three-arm Michelson–Fabry–Perot detector for gravitational waves is designed. It consists of three Michelson–Fabry–Perot interferometers, one for each pair of arms. The new detector can be used to confirm whether the gravitational waves are in general relativity polarization states and to set the strong constraints on non-GR gravitational wave polarization states. By the new detectors, the angular resolution of sources can be improved significantly. With the new detector, it is easier to search for and confirm a gravitational wave signal in the observation data.

Free electron laser (FEL) have been developed as tunable lasers over a wide range of wavelenths. Equipment in the region of 6-16 microns (1,660-630 cm-1) is available in the Beijing free electron laser erected by Institute of High Energy Physics, CAS. In this study we report first measurements of infrared-induced molecular change under irradiation by FEL of 9.414 microns and 6.228 microns, respectively. Taking o-amino-benzoic acid as an example, FTIR characterization indicates that the peak positions of both N-H and C=O stretching vibrations shift before and after the irradiation of FEL. It demonstrates that FEL induces the re-arrangement of H-bonds between COOH and NH2 by stimulating the vibration of carboxyl groups. It suggests that the presence of stable/metastable phases in the title compound.

We present a global analysis of latest solar and reactor neutrino data in the three-neutrino mixing scheme by using both the simple grid scanning and the Markov Chain Monte Carlo (MCMC) sampling methods. Accuracy and efficiency of the two sampling methods are compared and advantages of the latter are discussed. The fitting results of three oscillation parameters θ12, θ13 and [Formula: see text] are provided with both old and new evaluations of the reactor antineutrino flux. Possible correlation between the fitting parameters is also discussed.

By building the generalized Sigmoid function relationship between normalized step-size and the power of error signal, a novel variable step-size NLMS algorithm is proposed. It is proved that the step-size of NPVSS-NLMS changes as the new algorithm does when A=σv -m and B=2. The physical meanings of the parameters in this algorithm are explored. The theoretical analysis illustrate that this algorithm combine the virtues of NPVSS-NLMS and Sigmoid function, and it leads to faster convergence rate and lower final misalignment. The computer simulation results support the theoretical analysis.