分类： 物理学 >> 核物理学 提交时间： 2023-09-03
摘要： The gradient element of the aperture gradient map is utilized directly to generate the aperture shape without modulation. This process can be likened to choosing the direction of negative gradient descent for the generic aperture shape optimization. The negative-gradient descent direction is more suitable under local conditions and has a slow convergence rate. To overcome these limitations, this study introduced conjugate gradients into aperture shape optimization based on gradient modulation. First, the aperture gradient map of the current beam was obtained for the proposed aperture shape optimization method, and the gradients of the aperture gradient map were modulated using conjugate gradients to form a modulated gradient map. The aperture shape was generated based on the modulated gradient map. The proposed optimization method does not change the optimal solution of the original optimization problem but changes the iterative search direction when generating the aperture shape. The performance of the proposed method was verified using cases of head and neck cancer, and prostate cancer. The optimization results indicate that the proposed optimization method better protects the organs at risk and rapidly reduces the objective function value by ensuring a similar dose distribution to the planning target volume. Compared to the contrasting methods, the normal tissue complication probability obtained by the proposed optimization method decreased by up to 4.61%, and the optimization time of the proposed method decreased by 5.26% on average for ten cancer cases. The effectiveness and acceleration of the proposed method were verified through comparative experiments. According to the comparative experiments, the results indicate that the proposed optimization method is more suitable for clinical applications. It is feasible for the aperture shape optimization involving the proposed method.
分类： 物理学 >> 核物理学 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Optimization of the inverse planning becomes critical because it follows the invention of intensity modulated radiotherapy (IMRT) to shorten the previous trial-and-error treatment process and increase efficiency. In this paper, the inverse planning is used to direct aperture optimization in the ARTS (Accurate/Advanced Radiotherapy System). The objective function was quadratic, both tolerance and dose-volume constraint types are supported. The memory efficient conjugate gradient algorithm is used to cope with its large data. Furthermore, to fully exploit the solution space, a shortest path sub-procedure is coupled into the whole algorithm, thus giving further possibility decreasing the objective function. Two clinical cases are tested, indicating that the applicability of this algorithm is promising to clinical usage.
分类： 计算机科学 >> 计算机软件 提交时间： 2021-06-29
摘要： Evolution is the driving force behind the evolution of biological intelligence. Learning is the driving force behind human civilization. The combination of evolution and learning can form an entire natural world. Now, reinforcement learning has shown significant effects in many places. However, Currently, researchers in the field of optimization algorithms mainly focus on evolution strategies. And there is very little research on learning. Inspired by these ideas, this paper proposes a new particle swarm optimization algorithm Reinforcement learning based Ensemble particle swarm optimizer (RLEPSO) that combines reinforcement learning. The algorithm uses reinforcement learning for pre-training in the design phase to automatically find a more effective combination of parameters for the algorithm to run better and Complete optimization tasks faster. Besides, this algorithm integrates two robust particle swarm variants. And it sets the weight parameters for different algorithms to better adapt to the solution requirements of a variety of different optimization problems, which significantly improves the robustness of the algorithm. RLEPSO makes a certain number of sub-swarms to increase the probability of finding the global optimum and increasing the diversity of particle swarms. This proposed RLEPSO is evaluated on an optimization test functions benchmark set (CEC2013) with 28 functions and compared with other eight particle swarm optimization variants, including three state-of-the-art optimization algorithms. The results show that RLEPSO has better performance and outperforms all compared algorithms.
分类： 力学 >> 基础力学 提交时间： 2017-08-08
摘要： In this work, analytical solutions to the single scattering of SH waves by a cylindrical fiber with two specific radially gradient interphase layers are supported based on the method proposed by P.A. Martin (Martin 2002, JASA). In the first case, 1) shear modulus μ(r)=e^2βrand the square of wave number, k^2 , is a linear function of 1/r, and 2) μ(r)=e^(-βr^2 ) and k^2 is a linear function of r^2. For example, analytical solutions to single scattering of SH waves by a Sic fiber with the above two interphase layers embedded in aluminum are presented. The calculated scattering cross sections are compared with values obtained from an approximate method (dividing the continuous varying layer into multiple homogeneous sub-layers). The two methods yield similar results. The contribution of this work benefits the validation of various numerical methods used in the inhomogeneous media.
分类： 物理学 >> 核物理学 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： DNA origami technique, a breakthrough in DNA nanotechnology, has been widely used to prepare complex DNA nanostructures with nanoscale addressability. However, the purity and yield are generally the bottleneck to application of DNA nanostructures, and current methods for purifying DNA origami nanostructures in large quantities are time-consuming and laborious. This study aims to develop a scalable, cost-effective and contamination-free method of purifying DNA origami nanostructures. We employ an effective and convenient purification approach to purify planar rectangle DNA origami structures through rate-zonal centrifugation. By subjecting DNA origami samples to high centrifugal force in a density gradient media of glycerol, well-folded nanostructures and by-products are separated successfully, which are confirmed by agarose gel electrophoresis and atomic force microscopy (AFM). This method will aid the production of pure rectangle DNA origami nanostructures in large quantity.
分类： 物理学 >> 核物理学 提交时间： 2023-12-28
摘要： Radio frequency quadrupoles (RFQs), which are crucial components of proton injectors, significantly affect the performance of proton accelerator facilities. An RFQ with a high frequency of 714 MHz dedicated to compact proton injectors for medical applications is designed in this study. The RFQ is designed to accelerate proton beams from 50 keV to 4 MeV within a short length of 2 m and can be matched closely with the downstream drift tube linac to capture more particles through a preliminary optimization. To develop an advanced RFQ, challenging techniques, including fabrication and tuning method, must be evaluated and verified using a prototype. An aluminium prototype is derived from the conceptual design of the RFQ and then redesigned to confirm the radio frequency performance, fabrication procedure, and feasibility of the tuning algorithm. Eventually, a new tuning algorithm based on the response matrix and least-squares method is developed, which yields favorable results based on the prototype, i.e., the errors of the dipole and quadrupole components reduced to a low level after several tuning iterations. Benefiting from the conceptual design and techniques obtained from the prototype, the formal mechanical design of the 2-m RFQ is ready for the next manufacturing step.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Recently we measured with the Modified Three Gradient Method (MTGM) [1, 2] the beam emittance of an injector constructed in 2012, which was designed to provide a 2.4 kA, 2.6 MeV electron beam. The MTGM is a non-intercept indirect method, which is based on the three gradient type measurements of beam profiles and subsequent data processing which helps to get the least square solution to the beam emittance. Beam profiles under different currents of guiding coil are measured using Cerenkov radiation given off by a piece of quartz glass in the beam tube, which is recorded with a CCD camera. MTGM Code is developed to realize the data fitting as well as beam transport simulation, in which both the matrix method and the numerical solution of root-mean-square beam envelope equation are used. The error is also analyzed.
分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2025-02-25
Yin, Ziang
Zhang, Yaru
Kang, Zhe
Zhang, Xianggang
Liu, Jinbo
Liu, Kejin
Sun, Zhengyi
Jie, Wangqi
Zhao, Qinhua
Wang, Tao
摘要： Cadmium telluride (CdTe), which has a high average atomic number and a unique band structure, is a leadingmaterial for room-temperature X/γ-ray detectors. Resistivity and mobility are the two most importantproperties of detector-grade CdTe single crystals. However, despite decades of research, the fabrication ofhigh-resistivity and high-mobility CdTe single crystals faces persistent challenges, primarily because the stoichiometriccomposition cannot be well controlled owing to the high volatility of Cd under high-temperatureconditions. This volatility introduces Te inclusions and cadmium vacancies (VCd) into the as-grown CdTe ingot,which significantly degrades the device performance. In this study, we successfully obtained detector-gradeCdTe single crystals by simultaneously employing a Cd reservoir and chlorine (Cl) dopants via a vertical gradientfreeze (VGF) method. By installing a Cd reservoir, we can maintain the Cd pressure under the crystalgrowth conditions, thereby preventing the accumulation of Te in the CdTe ingot. Additionally, the existenceof the Cl dopant helps improve the CdTe resistivity by minimizing VCd density through the formation of anacceptor complex (ClTe-VCd)−1. The crystalline quality of the obtained CdTe(Cl) was evidenced by a reductionin large Te inclusions, high optical transmission (60%), and a sharp absorption edge (1.456 eV). Thepresence of substitutional Cl dopants, known as Cl+ Te, simultaneously supports the record high resistivity of1.5 × 1010 Ω · c meter and remarkable electron mobility of 1075±88 cm2 V−1 s−1 simultaneously, has beenconfirmed by photoluminescence spectroscopy. Moreover, using our crystals, we fabricated a planar detectorwith μτe of (1.11 ± 0.04) × 10−4 cm2/V, which performed with a decent radiation-detection feature. Thisstudy demonstrates that the vapor-pressure-controlled VGF method is a viable technical route for fabricatingdetector-grade CdTe crystals.
分类： 核科学技术 >> 粒子加速器 分类： 物理学 >> 核物理学 提交时间： 2024-12-15
Jin-Fang Chen
Yue Zong
Xiao-Yun Pu
Sheng-Wang Xiang
Shuai Xing
Zheng Li
Xu-Ming Liu
Yan-Fei Zhai
Xiao-Wei Wu
Yong-Zhou He
Ling-Ling Gong
Ji-Dong Zhang
Shan-Shan Cao
Wen-Ding Fan
Bin-Tuan Zhang
Kai Xu
Yi-Bo Yu
Guang-Hua Chen
Li-Jun Lu
Ya-Wei Huang
摘要： We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process. During continuous wave horizontal testing, these cavities achieved unprecedented average intrinsic quality factors of 4.0 × 1010 at 20 MV/m and 3.2 × 1010 at 29 MV/m, with no instances of field emission. The cryomodule demonstrates near-complete preservation of ultra-high-quality factors and ultra-high accelerating gradients from vertical to horizontal testing, marking a significant milestone in continuous-wave superconducting radio-frequency accelerator technology. This letter presents the cryomodule development experience, including cavity preparation, cryomodule assembly, degaussing, fast cooldown, and performance testing.
分类： 生物学 >> 植物学 >> 植物生态学和植物地理学 提交时间： 2025-03-18 合作期刊: 《干旱区科学》
摘要： Under current climate warming, the growth resilience of plantation forests after extreme droughts has garnered increasing attention. Platycladus orientalis Linn. is an evergreen tree species commonly used for afforestation, and the stability of P. orientalis plantation forests in the Loess Hilly region directly affects the ecological and environmental security of the entire Loess Plateau of China. However, systematic analyses of the growth resilience of P. orientalis plantation forests after extreme droughts along precipitation gradients remain scarce. In this study, we collected tree ring samples of P. orientalis along a precipitation gradient (255, 400, and 517 mm) from 2021 to 2023 and used dendroecological methods to explore the growth resilience of P. orientalis to drought stress on the Loess Plateau. Our findings revealed that the growth resilience of P. orientalis increased with increasing precipitation, enabling the trees to recover to the pre-drought growth levels. In regions with low precipitation (255 mm), the plantation forests were more sensitive to extreme droughts, struggling to recover to previous growth levels, necessitating conditional artificial irrigation. In regions with medium precipitation (400 mm), the growth of P. orientalis was significantly limited by drought stress and exhibited some recovery ability after extreme droughts, therefore warranting management through rainwater harvesting and conservation measures. Conversely, in regions with high precipitation (517 mm), the impacts of extreme droughts on P. orientalis plantation forests were relatively minor. This study underscored the need for targeted strategies tailored to different precipitation conditions rather than a "one-size-fits-all" approach to utilize precipitation resources effectively and maximize the ecological benefits of plantation forests. The findings will help maintain the stability of plantation forests and improve their ecosystem service functions in arid and semi-arid areas.
分类： 地球科学 >> 地理学 提交时间： 2021-04-22 合作期刊: 《干旱区科学》
摘要： Bacteria in desert soil have unique phylogeny and important ecological functions, and their responses to changes in precipitation need further attention. However, relevant studies have mainly focused on the surface soil, and studies on the responses of bacteria at different soil depths to variations in precipitation are rare. Thus, we used 16S rDNA high-throughput sequencing to investigate the changes in soil bacterial distribution along a mean annual precipitation gradient (50–150 mm) in the Alxa Desert, China, and compared the variation characteristics in the surface soil layer (0–10 cm) and subsurface soil layer (10–20 cm). Results showed that soil bacterial communities significantly changed along the precipitation gradient in both soil layers. However, the subsurface soil layer could support bacterial communities with higher diversity and closer internal relationships but more internal competition than the surface soil layer. Additionally, compared with the surface soil layer, variations in diversity and co-occurrence patterns in the subsurface soil layer were more in line with the changes in the mean annual precipitation, while bacterial community structure was less variable in the subsurface soil layer. Compared with the mean annual precipitation, soil moisture had little influence on the structure and diversity of soil bacterial community but had a high correlation with intercommunity connectivity. Therefore, soil moisture might play a complex role in mediating environmental conditions and soil bacterial community characteristics. Due to the different responses of surface and subsurface soil bacteria to the changes in precipitation, it is necessary to distinguish different soil layers when predicting the trends in desert soil bacterial conditions associated with precipitation, and prediction of subsurface soil bacteria may be more accurate.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-15
摘要： A widely appreciated aspect of developmental robustness is pattern formation in proportion to size. But how such scaling features emerge dynamically remains poorly understood. Here we generate a data set of the expression profiles of six gap genes in Drosophila melanogaster embryos that differ significantly in size. Expression patterns exhibit size-dependent dynamics both spatially and temporally. We uncover a dynamic emergence of under-scaling in the posterior, accompanied by reduced expression levels of gap genes near the middle of large embryos. Simulation results show that a size-dependent Bicoid gradient input can lead to reduced Kruppel expression that can have long-range and dynamic effects on gap gene expression in the posterior. Thus, for emergence of scaled patterns, the entire embryo may be viewed as a single unified dynamic system where maternally derived size-dependent information interpreted locally can be propagated in space and time as governed by the dynamics of a gene regulatory network.
分类： 数学 >> 计算数学 提交时间： 2024-01-04
摘要： This paper presents error analysis of stabilizer free weak Galerkin finite element method (SFWG-FEM) for a second order elliptic equation with low regularity solutions. The standard error analysis of SFWG-FEM requires additional regularity on solutions, such as H^2-regularity for the second-order convergence. However, if the solutions are in H^{1+s} with 0< s < 1, numerical experiments show that the SFWG-FEM is also effective and stable with the (1+s)-order convergence rate, so we develop a theoretical analysis for it. We introduce a standard H^{2} finite element approximation for the elliptic problem, and then we apply the SFWG-FEM to approach this smooth approximating finite element solution. Finally, we establish the error analysis for SFWG-FEM with low regularity in both discrete H^1-norm and standard L^2-norm. The (P_{k}(T),P_{k-1}(e), P_{k+1}(T) ^d) elements with dimensions of space d = 2,3 are employed and the numerical examples are tested to confirm the theory.
分类： 地球科学 >> 地理学 提交时间： 2021-07-23 合作期刊: 《干旱区科学》
摘要： The accurate simulation and prediction of runoff in alpine glaciated watersheds is of increasing importance for the comprehensive management and utilization of water resources. In this study, long short-term memory (LSTM), a state-of-the-art artificial neural network algorithm, is applied to simulate the daily discharge of two data-sparse glaciated watersheds in the Tianshan Mountains in Central Asia. Two other classic machine learning methods, namely extreme gradient boosting (XGBoost) and support vector regression (SVR), along with a distributed hydrological model (Soil and Water Assessment Tool (SWAT) and an extended SWAT model (SWAT_Glacier) are also employed for comparison. This paper aims to provide an efficient and reliable method for simulating discharge in glaciated alpine regions that have insufficient observed meteorological data. The two typical basins in this study are the main tributaries (the Kumaric and Toxkan rivers) of the Aksu River in the south Tianshan Mountains, which are dominated by snow and glacier meltwater and precipitation. Our comparative analysis indicates that simulations from the LSTM shows the best agreement with the observations. The performance metrics Nash-Sutcliffe efficiency coefficient (NS) and correlation coefficient (R2) of LSTM are higher than 0.90 in both the training and testing periods in the Kumaric River Basin, and NS and R2 are also higher than 0.70 in the Toxkan River Basin. Compared to classic machine learning algorithms, LSTM shows significant advantages over most evaluating indices. XGBoost also has high NS value in the training period, but is prone to overfitting the discharge. Compared with the widely used hydrological models, LSTM has advantages in predicting accuracy, despite having fewer data inputs. Moreover, LSTM only requires meteorological data rather than physical characteristics of underlying data. As an extension of SWAT, the SWAT_Glacier model shows good adaptability in discharge simulation, outperforming the original SWAT model, but at the cost of increasing the complexity of the model. Compared with the oftentimes complex semi-distributed physical hydrological models, the LSTM method not only eliminates the tedious calibration process of hydrological parameters, but also significantly reduces the calculation time and costs. Overall, LSTM shows immense promise in dealing with scarce meteorological data in glaciated catchments.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-02 合作期刊: 《热科学学报》
摘要： In this paper the theoretical model is built for ZEpHyR (ZARM Experimental Hybrid Rocket) main engine which is being developed at ZARM institute, Bremen, Germany. The theoretical model is used to estimate the temperature of exhaust gas. The Conjugate Gradient Method (CGM) with Adjoint Problem for Function Estimation iterative technique is used to solve the Inverse Heat Conduction Problem (IHCP) to estimate the heat flux and internal wall temperature at the throat section of the nozzle. Bartz equation is used to calculate the convective heat transfer coefficient. The exhaust gas temperature is determined using the estimated heat flux, the wall temperature at internal surface of nozzle and the heat transfer coefficient. The accuracy of CGM iterative scheme to solve the IHCP is also investigated and its results are presented.
分类： 生物学 >> 生态学 提交时间： 2023-06-13 合作期刊: 《干旱区科学》
摘要：The dead fuel moisture content (DFMC) is the key driver leading to fire occurrence. Accurately estimating the DFMC could help identify locations facing fire risks, prioritise areas for fire monitoring, and facilitate timely deployment of fire-suppression resources. In this study, the DFMC and environmental variables, including air temperature, relative humidity, wind speed, solar radiation, rainfall, atmospheric pressure, soil temperature, and soil humidity, were simultaneously measured in a grassland of Ergun City, Inner Mongolia Autonomous Region of China in 2021. We chose three regression models, i.e., random forest (RF) model, extreme gradient boosting (XGB) model, and boosted regression tree (BRT) model, to model the seasonal DFMC according to the data collected. To ensure accuracy, we added time-lag variables of 3 d to the models. The results showed that the RF model had the best fitting effect with an R2 value of 0.847 and a prediction accuracy with a mean absolute error score of 4.764% among the three models. The accuracies of the models in spring and autumn were higher than those in the other two seasons. In addition, different seasons had different key influencing factors, and the degree of influence of these factors on the DFMC changed with time lags. Moreover, time-lag variables within 44 h clearly improved the fitting effect and prediction accuracy, indicating that environmental conditions within approximately 48 h greatly influence the DFMC. This study highlights the importance of considering 48 h time-lagged variables when predicting the DFMC of grassland fuels and mapping grassland fire risks based on the DFMC to help locate high-priority areas for grassland fire monitoring and prevention.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
Zhang, QJ [Zhang, Qiuju][ 1 ]
Li, BH [Li, Baihai][ 1,2 ]
Wang, HY [Wang, Houyuan][ 1 ]
Suo, YG [Suo, Yange][ 1 ]
Chen, L [Chen, Liang][ 1 ]
摘要： In the present work, we investigated the structural and catalytic properties of a prototype system Pt-doped CaTiO3 by means of first principles calculations. We paid particular attention to the aggregation and penetration of Pt on different surfaces of CaTiO3, and subsequent CO oxidation by surface oxygen atoms on Pt-doped CaTiO3. Our calculations indicate that CO oxidation can potentially take place when Pt is doped on the first layer of CaTiO3(001). The activation barriers are calculated to be 0.20–0.45 eV. The possibly induced O vacancy on the surface will produce a magnetic behavior by breaking the spin density symmetry due to one Pt–O bond cleavage. Our study is expected to provide an insight into the catalytic behavior of Pt ions in Pt-doped perovskite toward the oxidation of exhaust gas.
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