Low-temperature dielectric and impedance properties of SrSn0.2Ti0.8O3 ceramics

Depeng Wang,Ruifeng Niu,Liqi Cui,Weitian Wang 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.3

Tin-doped and undoped perovskite SrTiO3 ceramics were synthesized by solid-state reaction method using SrCO3, TiO2 andSnO2 powders as raw materials. When the samples sintered at 1400 ℃, the SrSn0.2Ti0.8O3 and SrTiO3 ceramics all crystallizedin cubic structures. The lattice parameters of SrSn0.2Ti0.8O3 are slightly larger than that of SrTiO3 due to the bigger size ofSn4+ ions. The frequency-dependent dielectric and impedance properties of SrSn0.2Ti0.8O3 ceramics were investigated in thetemperature range of 300-100 K. The obtained value of low-temperature dielectric permittivity is larger than 10000, and thatof dielectric loss is lower than 0.018 at f = 1 kHz. The impedance spectra were used to show the grains and grain boundarieseffects in SrSn0.2Ti0.8O3 ceramics. The calculated electrical conductivity demonstrates the semiconductor properties of theprepared samples. The results indicate that SrSn0.2Ti0.8O3 ceramics have potential applications in dielectric and electronicdevices.

Unusual Electrical Transport Characteristic of the SrSnO3/Nb-Doped SrTiO3 Heterostructure

Depeng Wang,Ruifeng Niu,Liqi Cui,Weitian Wang 한국재료학회 2023 한국재료학회지 Vol.33 No.6

An all-perovskite oxide heterostructure composed of SrSnO3/Nb-doped SrTiO3 was fabricated using the pulsed laser deposition method. In-plane and out-of-plane structural characterization of the fabricated films were analyzed by x-ray diffraction with θ-2θ scans and φ scans. X-ray photoelectron spectroscopy measurement was performed to check the film’s composition. The electrical transport characteristic of the heterostructure was determined by applying a pulsed dc bias across the interface. Unusual transport properties of the interface between the SrSnO3 and Nb-doped SrTiO3 were investigated at temperatures from 100 to 300 K. A diodelike rectifying behavior was observed in the temperature-dependent current-voltage (IV) measurements. The forward current showed the typical IV characteristics of p-n junctions or Schottky diodes, and were perfectly fitted using the thermionic emission model. Two regions with different transport mechanism were detected, and the boundary curve was expressed by ln I = -1.28V - 13. Under reverse bias, however, the temperature- dependent IV curves revealed an unusual increase in the reverse-bias current with decreasing temperature, indicating tunneling effects at the interface. The Poole-Frenkel emission was used to explain this electrical transport mechanism under the reverse voltages.

Experimental investigation on the dielectric and impedance properties of indium doped titanium dioxide ceramics

Liqi Cui,Ruifeng Niu,Depeng Wang,Weitian Wang 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.2

Single-phased indium doped titanium dioxide (Ti1-xInxO2, x=0~5%) ceramics were synthesized by using solid-state reactionmethod in this study. The doping effect on the dielectric and impedance properties was investigated in a broad frequency rangefrom 102 Hz to 106 Hz. The observed dielectric behavior can be ascribed to the Universal Dielectric Response. In higherfrequency field, the dielectric permittivity varies slightly with the doping concentration x. However, the measured dielectricconstant increases significantly with the increase of doping concentration within lower frequency range. The charged grainboundarycores originated from the doping trivalent ion can be used to explain the results.

Reentry Risk and Safety Assessment of Spacecraft Debris Based on Machine Learning

Hu Gao,Zhihui Li,Depeng Dang,Jingfan Yang,Ning Wang 한국항공우주학회 2024 International Journal of Aeronautical and Space Sc Vol.25 No.1

Uncontrolled spacecraft will disintegrate and generate a large amount of debris in the reentry process. Ablative debris may cause potential risks to the safety of human life and property on the ground. Therefore, predicting the landing points of spacecraft debris and forecasting the degree of risk of waste to human life and property is very important. In view that it is difficult to predict the reentry process and the reentry point in advance, the debris generated from reentry disintegration may cause ground damage for the uncontrolled space vehicle on the expiration of service. In this paper, we adopt the object-oriented approach to consider the spacecraft and its disintegrated components as consisting of simple basic geometric models and introduce three machine learning models: the support vector regression (SVR), decision tree regression (DTR), and multilayer perceptron (MLP) to predict the velocity, longitude, and latitude of spacecraft debris landing points for the first time. Then, we compare the prediction accuracy of the three models. Furthermore, we define the reentry risk and the degree of danger, and we calculate the risk level for each spacecraft debris and make warnings accordingly. The experimental results show that the proposed method can obtain high-accuracy prediction results in at least 10 s and make safety-level warning more real-time.

Effect of A- and B-site doping on the low-temperature dielectric and impedance properties of BaTiO3-based ceramics

Niu Ruifeng,Wang Depeng,Cui Liqi,Wang Weitian 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.6

In this work, two series of BaTiO3-based ceramics, Ba1-xSrxTiO3 (x=0, 0.2, 0.4, 0.6, 0.8) and BaTi1-xTaxO3 (x=0.03, 0.06, 0.075, 0.09, 0.1), were synthesized by using standard solid-state reaction method. Frequency-dependent dielectric and impedance properties were investigated in low temperature range of 300–100 K. The changes in dielectric properties of Ba1-xSrxTiO3 are believed to originate from the phase transition due to the diferent A-site Sr2+ doping concentration. The local electron-pinned defect-dipole efect is responsible for the enhancement of dielectric constant observed in B-site Ta5+ doped BaTi1-xTaxO3 ceramics. The complex impedance analysis was used to discern the temperature and frequency dependence of grains and grain boundaries responses. The results suggest the application of A- and B-site doped BaTiO3 ceramics in the feld of dielectric devices at low temperatures.

An Advanced Algorithm for Image Resolution Enhancement Technique in both Wavelet and Spatial Domain

Pann Ei San,Fengchun Tian,Depeng Liu,Ran Liu 보안공학연구지원센터 2014 International Journal of Hybrid Information Techno Vol.7 No.5

Optimum synthesis of esomeprazole catalyzed by Rhodococcus rhodochrous ATCC 4276 through response surface methodology

Yuanyuan Zhang,Qiuxiang Zhao,Hui Tang,Huiling Li,Depeng Li,Zhiyong Wang,Xin Gao,Fanye Wang 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.5

Enantiopure esomeprazole is an important drug in the treatment of gastric ulcer. The asymmetric sulfoxidation of omeprazole thioether was catalyzed by immobilized cells of a mutant of Rhodococcus rhodocrous ATCC 4276 to synthesize esomeprazole. The bioreaction was carried out in a biphasic system (chloroform-water), at a high substrate concentration (200mM), and optimized using response surface methodology (RSM). The optimal yield of esomeprazole obtained was 94.8% with e.e. (>99%) without the formation of the sulfone form as a byproduct, under the optimal conditions: the concentration of immobilized cells, 283.5 g/L, the incubation temperature, 37.05 oC, and pH of phosphate buffer, 7.35, respectively. A quadratic polynomial model was developed with R2 of 0.9998, which indicates that the model predicts the observed data with very high accuracy. The mutant exhibited a high enantioselective activity and substrate and product tolerance. The small size of immobilized cell beads (0.5-1 mm) creates a large reaction interface. The aerated flask provides enough oxygen for a high concentration of cells. The significant improvement of substrate tolerance may mainly be attributed to employing the chloroform-water biphasic system because organic substrates may be partitioned in the organic phase, eliminating potential damage and inhibition to cells. Based on the above, the asymmetric sulfoxidation catalyzed by immobilized bacterial cells is therefore more promising for efficient synthesis of chiral sulfoxides.

Exploiting Multi-Hop Relaying to Overcome Blockage in Directional mmWave Small Cells

Yong Niu,Chuhan Gao,Yongliang Ma,Li Su,Depeng Jin 한국통신학회 2016 Journal of communications and networks Vol.18 No.3

With vast amounts of spectrum available in themillimeter wave (mmWave) band, small cells at mmWave frequenciesdensely deployed underlying the conventional homogeneousmacrocell network have gained considerable interest fromacademia, industry, and standards bodies. Due to high propagationloss at higher frequencies, mmWave communications are inherentlydirectional, and concurrent transmissions (spatial reuse)under low inter-link interference can be enabled to significantlyimprove network capacity. On the other hand, mmWave linksare easily blocked by obstacles such as human body and furniture. In this paper, we develop a multi-hop relaying transmission(MHRT) scheme to steer blocked flows around obstacles by establishingmulti-hop relay paths. In MHRT, a relay path selectionalgorithm is proposed to establish relay paths for blocked flowsfor better use of concurrent transmissions. After relay path selection,we use a multi-hop transmission scheduling algorithm to computenear-optimal schedules by fully exploiting the spatial reuse. Through extensive simulations under various traffic patterns andchannel conditions, we demonstrate MHRT achieves superior performancein terms of network throughput and connection robustnesscompared with other existing protocols, especially under seriousblockage conditions. The performance ofMHRT with differenthop limitations is also simulated and analyzed for a better choiceof the maximum hop number in practice.

Surfactant-stripped naphthalocyanines for multimodal tumor theranostics with upconversion guidance cream

Zhang, Yumiao,Hong, Hao,Sun, Boyang,Carter, Kevin,Qin, Yiru,Wei,Wang, Depeng,Jeon, Mansik,Geng, Jumin,Nickles, Robert J.,Chen, Guanying,Prasad, Paras N.,Kim, Chulhong,Xia, Jun,Cai, Weibo,Lovell, Jonat The Royal Society of Chemistry 2017 Nanoscale Vol.9 No.10

<P>Surfactant-stripped, nanoformulated naphthalocyanines (nanonaps) can be formed with Pluronic F127 and low temperature membrane processing, resulting in dispersed frozen micelles with extreme contrast in the near infrared region. Here, we demonstrate that nanonaps can be used for multifunctional cancer theranostics. This includes lymphatic mapping and whole tumor photoacoustic imaging following intradermal or intravenous injection in rodents. Without further modification, pre-formed nanonaps were used for positron emission tomography and passively accumulated in subcutaneous murine tumors. Because the nanonaps used absorb light beyond the visible range, a topical upconversion skin cream was developed for anti-tumor photothermal therapy with laser placement that can be guided by the naked eye.</P>

A GPU-Accelerated Hydrodynamic Model for Urban Rainstorm Inundation Simulation: A Case Study in China

Hao Han,Jingming Hou,Zongxue Xu,Haixiao Jing,Jiahui Gong,Depeng Zuo,Bingyao Li,Shaoxiong Yang,Yongde Kang,Run Wang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.3

Frequent urban rainstorm inundations can cause serious damages to human life and social economy. Reliable simulation of urban rainstorm inundation is an effective approach for performing flood risk analysis to reduce losses. In this work, a full 2D high-performance hydrodynamic model for urban rainstorm inundation simulation based on Graphic Processing Unit (GPU) was developed. The idealized V-shape catchment and sponge city district of Fengxi New City were selected as the study areas to assess performance of the model. The model was validated against analytical benchmark results of the idealized V-catchment test which show good agreement between the modelled flow and analytical solutions. The model was then applied to simulate actual urban rainstorm inundation process under measured rainfall. The results indicated that the model can be applied to high-resolution urban region simulations. Specifically, the validation results indicated that the proposed model had a good performance, with an accepted error of less than 15%. When applied to compute the Fengxi New city under design rainstorms with different annual return periods of 1, 5, 10, 20, 50, and 100 years, it was found that the model effectively evaluated the temporal and spatial variation process of urban inundation, and quantitatively investigated flood risks according to the water depth change. The model has been substantially accelerated on GPU to quickly predict urbaninundation. The accuracy and rapid simulation speed of the model were verified based on the actual study area. Therefore, the proposed model can help to predict the dynamic processes of urban flood inundation and thus reduce flood inundation disasters. This is essential for future optimal sponge urban construction planning in China.