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Compared with the traditional solution, the microgrid (MG) employed capacitive coupling inverters (CCIs) with higher reactive power capacity can effectively reduce the probability of low voltage. However, because of the special coupling structure, different power flow control methods will greatly affect the cost and operation efficiency of the CCI. A multi‐layer and timescale optimal power flow control considering inverter‐layer is therefore proposed in this paper. Firstly, the power output characteristics of CCI are analyzed, and the power flow control model of CCI with an energy storage unit is established. Secondly, an optimal control method on different timescales was proposed. By coordinating the active power output and the reserved charging state margin of the energy storage unit, the CCI‐MG reactive power regulation with the most economical and minimum loss was realized, so as to achieve long‐term voltage stability and dynamic satisfaction of load demands. Furthermore, the optimal power flow control of CCI is proposed. The simulation results show that the proposed method can effectively realize the optimal control of active and reactive power of MG, and also improve the voltage stability of AC bus under the economical operation of CCI. [ABSTRACT FROM AUTHOR]

Recognition of partial discharge (PD) patterns is essential for insulation diagnosis of covered conductors in overhead lines. Current research has not sufficiently addressed the complex background noise in real environments, and most detection methods depend primarily on feature engineering or deep learning, suggesting potential for improvement in accuracy and efficiency. This has led the authors to propose a PD pattern recognition algorithm that integrates feature selection and deep learning. This algorithm incorporates the design of a discrete wavelet denoising function specifically tailored to the characteristics of PD for data preprocessing. It employs Bayesian optimization algorithms and light gradient boosting machines for characterizing corona discharge features. Furthermore, it develops multi‐scale clustering features and phase‐resolved features for feature fusion, and constructs insightful features based on the light gradient boosting machine. Finally, a novel deep learning model is formulated, demonstrating exceptional detection performance for early faults in covered conductors. Experimental results show that this algorithm attains an Matthews correlation coefficient score of 0.814, a 13.2% improvement over the baseline algorithm's 0.719, and a speed increase of 39.18%. The final accuracy amounts to 97.85%. This algorithm demonstrates exceptional performance in detecting early insulation faults in conductors. [ABSTRACT FROM AUTHOR]

Background: Online adaptive radiotherapy (ART) involves the development of adaptable treatment plans that consider patient anatomical data obtained right prior to treatment administration, facilitated by cone‐beam computed tomography guided adaptive radiotherapy (CTgART) and magnetic resonance image‐guided adaptive radiotherapy (MRgART). To ensure accuracy of these adaptive plans, it is crucial to conduct calculation‐based checks and independent verification of volumetric dose distribution, as measurement‐based checks are not practical within online workflows. However, the absence of comprehensive, efficient, and highly integrated commercial software for secondary dose verification can impede the time‐sensitive nature of online ART procedures. Purpose: The main aim of this study is to introduce an efficient online quality assurance (QA) platform for online ART, and subsequently evaluate it on Ethos and Unity treatment delivery systems in our clinic. Methods: To enhance efficiency and ensure compliance with safety standards in online ART, ART2Dose, a secondary dose verification software, has been developed and integrated into our online QA workflow. This implementation spans all online ART treatments at our institution. The ART2Dose infrastructure comprises four key components: an SQLite database, a dose calculation server, a report generator, and a web portal. Through this infrastructure, file transfer, dose calculation, report generation, and report approval/archival are seamlessly managed, minimizing the need for user input when exporting RT DICOM files and approving the generated QA report. ART2Dose was compared with Mobius3D in pre‐clinical evaluations on secondary dose verification for 40 adaptive plans. Additionally, a retrospective investigation was conducted utilizing 1302 CTgART fractions from ten treatment sites and 1278 MRgART fractions from seven treatment sites to evaluate the practical accuracy and efficiency of ART2Dose in routine clinical use. Results: With dedicated infrastructure and an integrated workflow, ART2Dose achieved gamma passing rates that were comparable to or higher than those of Mobius3D. Additionally, it significantly reduced the time required to complete pre‐treatment checks by 3–4 min for each plan. In the retrospective analysis of clinical CTgART and MRgART fractions, ART2Dose demonstrated average gamma passing rates of 99.61 ± 0.83% and 97.75 ± 2.54%, respectively, using the 3%/2 mm criteria for region greater than 10% of prescription dose. The average calculation times for CTgART and MRgART were approximately 1 and 2 min, respectively. Conclusion: Overall, the streamlined implementation of ART2Dose notably enhances the online ART workflow, offering reliable and efficient online QA while reducing time pressure in the clinic and minimizing labor‐intensive work. [ABSTRACT FROM AUTHOR]

With the advantages of the low cost of transmission lines and high efficiency, the DC microgrid has become a rising star in the low‐voltage network. However, multi‐source and multi‐transformation characteristics in DC microgrids will lead to the existence of various forms of ripple generation sources in the system. The existence of a large amount of ripple not only directly cause the reduction of power quality of DC microgrids, but also decreases the accuracy of electricity billing. It is vital to achieving accurate ripple detection for the reliable power supply of the DC microgrid. A DC‐side ripple detection method, which combines the Whale Optimization Algorithm (WOA), Variational Modal Decomposition (VMD), and Hilbert Transform (HT), is therefore investigated and proposed here. Firstly, the sample entropy (SampEn) is used as the fitness function, applied the whale optimization algorithm, is to determine the optimal decomposition scale and penalty factor, of the variational modal decomposition; then, the ripple‐containing DC signal is decomposed into a series of eigenmodal components (imf) by the optimized variational modal decomposition algorithm. Finally, the Hilbert Transform is performed to obtain the amplitude and frequency of the ripple components. To prove the effectiveness, the proposed method is compared with the conventional Empirical Mode Decomposition (EMD) and the VMD algorithm, by testing simulated DC signals without and with noise. Results show that the proposed method has higher accuracy and noise robustness than the EMD and VMD algorithms. [ABSTRACT FROM AUTHOR]

As renewable power penetration gradually increases in hierarchical distribution networks, certain regions have started to lack the ability to consume. How to improve the consumption capacity of a hierarchical distribution network through optimal dispatching has become a hot topic in the current research on distribution system operation. Firstly, the article makes an accurate and rapid assessment of the consumption capacity of the station area through the limit scenario analysis method; secondly, based on the assessment results, the main network renewable power sources are prioritized for consumption, while the main network and the station area; thirdly, the main network renewable power sources are prioritized for consumption, considering the assessment results while the main network and the station area reach the optimal power flow simultaneously through a multi‐layer dispatching model. Then, through the flexible interconnection system, load balancing and energy optimization are performed for unconsumed distributed generation (DG) and incomplete energy storage system (ESS) in the station area to further improve the efficiency of renewable energy. Finally, the effectiveness of the proposed model is verified by simulation tests. [ABSTRACT FROM AUTHOR]

Drug‐resistant bacteria and highly infectious viruses are among the major global threats affecting the human health. There is an immediate need for novel strategies to tackle this challenge. Copper‐based nanoparticles (CBNPs) have exhibited a broad antimicrobial capacity and are receiving increasing attention in this context. In this review, we describe the functionalization of CBNPs, elucidate their antibacterial and antiviral activity as well as applications, and briefly review their toxicity, biodistribution, and persistence. The limitations of the current study and potential solutions are also shortly discussed. The review will guide the rational design of functional nanomaterials for antimicrobial application. This article is categorized under:Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease [ABSTRACT FROM AUTHOR]

Snap bean (Phaseolus vulgaris L.) is the vegetable form of common bean, and regarded as one of the most important and commonly consumed products in the world. In this study, 221 snap bean core accessions mostly from China were characterized the genetic diversity, gene pool identity, and relationships using 30 microsatellite markers, and concurrently evaluated for phenotype traits and phaseolin patterns. A total of 140 alleles were detected with an average of 4.67 per locus. The polymorphic information content ranged from 0.215 to 0.823, with an average of 0.488. Nei's genetic distances between accessions ranged from 0 to 0.9999, with an average of 0.6143. In those Chinese snap beans, structure analysis proved the existence of a high proportion of hybrid accessions except for identification of Andean and Mesoamerican gene pools. Neighbor‐joining clustering and principal coordinate analysis based microsatellite markers were similar in explaining the extent of diversity with both revealed Andean and Mesoamerican gene pools, which were divided into seven subgroups. Four of those subgroups, including one arising from introgression, were identified as belonging to the Andean gene pool, which likely represented Nueva Granada and Peru races. Other three subgroups were identified as belonging to the Mesoamerican gene pool, which likely represented the Mesoamerican race, owing to their close association with the control genotype. The diversity index of the qualitative traits was 0.80 to 1.88, with the average value of 1.20, while the diversity of the quantitative traits was ranked as 100‐seed weight (H′ = 1.98) > pod length (H′ = 1.90). Six principal components explained 69.13% of the total variation. Eight phaseolin patterns were identified in the 221 accessions. This study demonstrated the gene pool, as well as geographical, diversity of snap bean germplasms in China. The substantial diversity level is important for the utilization and conservation of snap bean, as well as future breeding programs. Core Ideas: The distinction in snap bean of China has blurred between Andean and Mesoamerican pools for obvious introgression.The combination of microsatellites, phaseolin, and phenotypic traits is effectively evaluated for genetic diversity.Phaseolin can separate two gene pools but not be well detected population structure and new variation. [ABSTRACT FROM AUTHOR]

The elemental analysis in disease diagnosis and biomedicine screening generally aims at alleviating the difficulties of sample pretreatment techniques, elucidating the distribution and speciation information of elements in bio‐samples as well as elevating resolution of multidimensional elemental profiling. The integration of microfluidic techniques with inductively coupled plasma mass spectrometry (ICP‐MS) has been demonstrated to possess great potential in these aspects due to the versatile microstructure design, rapid sample pretreatment, extremely low sample consumption, and high‐sensitivity/high‐throughput elemental detection capability. Herein, an overview of the advancements in microfluidic‐based ICP‐MS for precise biological elemental determination is provided. A few microfluidic approaches for multiplex and effective manipulation of clinical samples followed by detection with ICP‐MS are highlighted, that is, high spatiotemporal resolution sampling, high‐purity elemental microextraction device, and high signal‐to‐noise ratio elemental analysis. In addition, other front‐end techniques are discussed for converting various types of samples into a suitable form for detection, for example, laser ablation and time of flight MS. The opportunities and outstanding challenges of microfluidic‐based ICP‐MS elemental investigations in clinical diagnosis and biomedical studies are also depicted. [ABSTRACT FROM AUTHOR]

Purpose: Many radiotherapy modalities can deliver concentrated radiation in the form of spots, such as Gamma Knife (GK), GammaPod (GP), intensity‐modulated proton therapy, and brachytherapy, and can be generalized as spot‐based treatments. These treatments have a great therapeutic advantage of creating potent target dose while sparing the surrounding normal tissues. However, global optimization to determine the spot positions, shapes, and intensities is an intractable combinatorial problem for any real 3D problem. The conventional approach adopts heuristic spot selection and intensity optimization in a sequential manner to mitigate the problem complexity. In this work, we propose a novel framework that enables global optimization of spot‐based treatment planning. Methods: The framework is based on kernel decomposition (KD) dose calculation, which models each spot dose as a scaled shift‐invariant kernel, with the reference kernels and scales pre‐calculated. During optimization, the framework incorporates Fast Fourier Transform (FFT) for objective and derivative evaluations and accommodates all spot candidates in optimization search with a temporal complexity of O(N3log N) as opposed to O(N6) complexity in the conventional beamlet framework for volume dimensions of N × N × N. We demonstrated the FFT framework using simulations with different objectives. The framework's planning performance was illustrated using clinical GK and GP cases. Results: Pre‐processing involves only a small number of reference kernels and a scale map for the KD model with marginal spatial and temporal overheads. For simulations with 512 × 512 image dimensions, plan optimization finished in ∼2 seconds with FFT, whereas it took 100× longer with the beamlet approach. For clinical cases, the FFT attained solutions within a minute with improved plan quality compared to clinical plans: better conformity and less integral dose because of using a global fine search space for optimal spots. Conclusions: The scaled shift‐invariance and FFT framework opens a new paradigm for spot‐based treatment planning, as it can substantially reduce both the spatial and temporal complexities. The framework makes global optimization for spot‐based treatment planning clinically feasible. [ABSTRACT FROM AUTHOR]

Purpose: Adaptive radiotherapy (ART), especially online ART, effectively accounts for positioning errors and anatomical changes. One key component of online ART process is accurately and efficiently delineating organs at risk (OARs) and targets on online images, such as cone beam computed tomography (CBCT). Direct application of deep learning (DL)‐based segmentation to CBCT images suffered from issues such as low image quality and limited available contour labels for training. To overcome these obstacles to online CBCT segmentation, we propose a registration‐guided DL (RgDL) segmentation framework that integrates image registration algorithms and DL segmentation models. Methods: The RgDL framework is composed of two components: image registration and RgDL segmentation. The image registration algorithm transforms/deforms planning contours that were subsequently used as guidance by the DL model to obtain accurate final segmentations. We had two implementations of the proposed framework—Rig‐RgDL (Rig for rigid body) and Def‐RgDL (Def for deformable)—with rigid body (RB) registration or deformable image registration (DIR) as the registration algorithm, respectively, and U‐Net as the DL model architecture. The two implementations of RgDL framework were trained and evaluated on seven OARs in an institutional clinical head‐and‐neck dataset. Results: Compared to the baseline approaches using the registration or the DL alone, RgDLs achieved more accurate segmentation, as measured by higher mean Dice similarity coefficients (DSCs) and other distance‐based metrics. Rig‐RgDL achieved a DSC of 84.5% on seven OARs on average, higher than RB or DL alone by 4.5% and 4.7%. The average DSC of Def‐RgDL was 86.5%, higher than DIR or DL alone by 2.4% and 6.7%. The inference time required by the DL model component to generate final segmentations of seven OARs was less than 1 s in RgDL. By examining the contours from RgDLs and DL case by case, we found that RgDL was less susceptible to image artifacts. We also studied how the performances of RgDL and DL vary with the size of the training dataset. The DSC of DL dropped by 12.1% as the number of training data decreased from 22 to 5, whereas RgDL only dropped by 3.4%. Conclusion: By incorporating the patient‐specific registration guidance to a population‐based DL segmentation model, RgDL framework overcame the obstacles associated with online CBCT segmentation, including low image quality and insufficient training data, and achieved better segmentation accuracy than baseline methods. The resulting segmentation accuracy and efficiency show promise for applying this RgDL framework for online ART. [ABSTRACT FROM AUTHOR]

Purpose: To develop a method that can extend dose from two isodose surfaces (isosurfaces) to the entire patient volume, and to demonstrate its application in radiotherapy plan isodose tuning. Methods: We hypothesized that volumetric dose distribution can be extended from two isosurfaces—the 100% isosurface and a reference isosurface—with the distances to these two surfaces (L100${L_{100}}$ and Lref${L_{{\rm{ref}}}}$) as extension variables. The extension function is modeled by a three‐dimensional lookup table (LUT), where voxel dose values from clinical plans are binned by three indexes: L100${L_{100}}$, Lref${L_{{\rm{ref}}}}$, and Dref${D_{{\rm{ref}}}}$ (reference dose level). The mean and standard deviation of voxel doses in each bin are calculated and stored in LUT. Volumetric dose extension is performed voxel‐wisely by indexing the LUT with the L100${L_{100}}$, Lref${L_{{\rm{ref}}}}$, and Dref${D_{{\rm{ref}}}}$ of each query voxel. The mean dose stored in the corresponding bin is filled into the query voxel as extended dose, and the standard deviation be filled voxel‐wisely as the uncertainty of extension result. We applied dose extension in isodose tuning, which aims to tune volumetric dose distribution by isosurface dragging. We adopted extended dose as an approximate dose estimation, and combined it with dose correction strategy to achieve accurate dose tuning. Results: We collected 32 post‐operative prostate volumetric‐modulated arc therapy (VMAT) cases and built the LUT and its associated uncertainties from the doses of 27 cases. The dose extension method was tested on five cases, whose dose distributions were defined as ground truth (GT). We extended the doses from 100% and 50% GT isosurfaces to the entire volume, and evaluated the accuracy of extended doses. The 5 mm/5% gamma passing rate (GPR) of extended doses are 92.0%. The mean error is 4.5%, which is consistent to the uncertainty estimated by LUT. The dose difference in 90.5% of voxels is within two sigma and 97.5% in three sigma. The calculation time is less than 2 seconds. To simulate plan isodose tuning, we optimized a dose with less sparing on rectum (than GT dose) and defined it as a "base dose"—the dose awaiting isosurface dragging. In front‐end, the simulated isodose tuning is conducted as such that the base dose was given to plan tuner, and its 50% isosurface would be dragged to the desired position (position of 50% isosurface in GT dose). In back‐end, the output of isodose tuning is obtained by (1) extending dose from the desired isosurfaces and viewed the extended dose as an approximate dose, (2) obtaining a correction map from the base dose, and (3) applying the correction map to the extended dose. The accuracy of output—extended dose with correction—was 97.2% in GPR (3 mm/3%) and less than 1% in mean dose difference. The total calculation time is less than 2 seconds, which allows for interactive isodose tuning. Conclusions: We developed a dose extension method that generates volumetric dose distribution from two surfaces. The application of dose extension is in interactive isodose tuning. The distance‐based LUT fashion and correction strategy guarantee the computation efficiency and accuracy in isodose tuning. [ABSTRACT FROM AUTHOR]

Purpose: Pre‐calculation of accurate dose deposition kernels for treatment planning of spot‐based radiotherapies, such as Gamma Knife (GK) and Gamma Pod (GP), can be very time‐consuming and may require large data storage with an enormous number of possible spots. We proposed a novel kernel decomposition (KD) model to address accurate and fast (real‐time) dose calculation with reduced data storage requirements for spot‐based treatment planning. The application of the KD model was demonstrated for clinical GK and GP radiotherapy platforms. Methods: The dose deposition kernel at each spot (shot position) is modeled as the product of a shift‐invariant kernel based on a reference kernel and spatially variant scale factor. The reference kernel, one for each collimator, is defined at the center of the commissioning phantom for GK and at the center of the treatment target for GP and calculated using the Monte Carlo (MC) method. The spatially variant scale factor is defined as the ratio of the mean tissue maximum ratio (TMR) at the candidate shot position to that at the reference kernel position, and the mean TMR map is calculated within the entire volume through parallel beam ray tracing on the density image followed by averaging over all source directions. The proposed KD dose calculations were compared with the MC method and with the GK and GP treatment planning system (TPS) computations for various shot positions and collimator sizes utilizing a phantom and 14 and 12 clinical plans for GK and GP, respectively. Results: For the phantom study, the KD Gamma index (3%/1 mm) passing rates were greater than 99% (median 100%) relative to the MC doses, except for the shots close to the boundary. The passing rates dropped below 90% for 8 mm (16 mm) shots positioned within ∼1 cm (∼2 cm) of the boundary. For the clinical GK plans, the KD Gamma passing rates were greater than 99% (median 100%) compared to the MC and greater than 92% (median 99%) compared to the TPS. For the clinical GP plans, the KD Gamma passing rates were greater than 95% (median 98%) compared to the MC and greater than 91% (median 97%) compared to the TPS. The scale factors were calculated in sub‐seconds with GPU implementation and only need to be calculated once before treatment plan optimization. The calculation of the dose kernel was also within sub‐seconds without requiring beam‐by‐beam calculation commonly done in the TPS. Conclusion: The proposed model can provide an accurate dose and enables real‐time dose and derivative calculations by kernel shifting and scaling without pre‐calculating or requiring large data storage for GK and GP dose deposition kernels during treatment planning. This model could be useful for spot‐based radiotherapy treatment planning by allowing an efficient global fine search for optimal spots. [ABSTRACT FROM AUTHOR]

The similar material research method was adopted in this research to study the generation and migration law of dust in the process of discharge. The study result shows that the relation between the dust concentration and discharge rate in the unloading area is c = 6.622(Mpr)0.37348 for real conditions derived from similar materials experiment, which can be verified mutually with the numerical simulation result. When the natural air flow in real conditions increased to 1.89 m/s, the dust concentration reached the maximum value, and then, the dust diffusion rate accelerated and the dust concentration decreased. The smaller the ore particle size, the larger the area of interaction with the air, and the larger the dust concentration. An increase of the ore moisture content can reduce the dust concentration and keep the dust concentration at a low level. Additionally, the moisture content of the ore powder without hardening was 4.17–8%. As the height of the intermediate mine heap increased, the dust produced by both falling and impact decreased, and the dust concentration decreased. The dust removal effect of installing the seal cover was verified. The research results can provide a reference for dust control of an intermediate mine heap. [ABSTRACT FROM AUTHOR]

Purpose: Stereotactic radiosurgery (SRS) has become a primary treatment for multiple brain metastases (BM) but may require distribution of BMs over several sessions to make delivery time and radiation toxicity manageable. Contrasting to equal fraction dose in conventional fractionation, distributed SRS delivers full dose to a subset of BMs in each session while avoiding adjacent BMs in the same session to reduce toxicity from overlapping radiation. However, current clinical treatment planning for distributed SRS relies on manual BM assignment, which can be tedious and error prone. This work describes a novel approach to automate the distribution of BM in the Gamma Knife (GK) clinical workflow. Methods: We represent each BM as an electrostatic field of the same polarity that exerts repulsive forces on other BMs in the same session. This representation naturally leads to separation of close BMs into different sessions to lower the potential energy. Indeed, the BM distribution problem can be formulated as minimization of the total potential energy from all treatment sessions subject to delivery time constraints in mixed‐integer quadratic programming (MIQP). We retrospectively studied eight clinical GK cases of multiple BM and compared the automated MIQP solution with clinically used BM distribution to demonstrate the efficacy of the proposed approach. Results: With the problem size equal to the number of BMs times the number of sessions, this MIQP can be solved in a minute on a personal workstation. The MIQP solution effectively separated BMs for a given number of treatment sessions and evened out the delivery time distribution among sessions. Compared to the clinically used manual BM distributions in paired t‐test for a similar range of delivery time variation, the automated BM distributions had lower energy objectives (range of decrease: [11% 89%]; median: 25%; P=.073), more uniformly distributed treatment volumes (range of decrease for the normalized standard deviation of volume distribution: [0.02 0.95]; median: 0.16; P=.013), more scattered BMs in each treatment session (range of increase for the mean minimum BM distance: [0 14] mm; median: 6 mm; P=.008), and lower overall V12 (range of decrease: [0.0 1.6] cc; median: 0.2 cc; P=.052). Moreover, without distribution, that is, with all BMs treated in the same session, V12 was substantially larger compared to both manual and automated BM distributions; the increase ranged from 0.1 to 16.6 cc with a median of 1.3 cc. Conclusions: The proposed approach models the clinical practice and provides an efficient solution for optimal selection of BM subsets for distributed SRS. Further evaluations are underway to establish this approach as a tool for improving clinical workflow and to facilitate systematic study on the benefits of distributed SRS treatments. [ABSTRACT FROM AUTHOR]

Underground cables such as pipe-type cables are widely used in urban power industry. In this study, an advanced thin-wire model of the pipe-type cables is 3D FDTD simulations. In this model, the multi-conductor cables are represented with two-level transmission line equations. A stabilising technique with a 1D spatial low-pass filter is proposed to maintain computational stability. Frequency-dependent losses are fully considered by using a vector-fitting technique. The proposed thin-wire model is validated with the multi-conductor transmission line theory analytically and the traditional FDTD method numerically. Good agreements are observed. It is found that the simulation maintains stability for 360,000-time steps. Compared to the traditional FDTD method, the memory space and computation time of the proposed model can be reduced by 73% and 98%, respectively. Induced lightning currents in a cable connection station are analysed. It is found that, without considering soil ionisation and soil stratification, the peak current in the metallic armour is 1.54 times as much as the one with considering these non-linear effects. It can be reduced by 9.04% and 18.6% if the cable is buried at depths of 1 m and 1.5 m, compared with the case of a 0.5 m buried depth. [ABSTRACT FROM AUTHOR]

Summary: As the network gradually penetrates into all aspects of life, the transportation system as the most network‐specific field, its security management issues need to be innovative from the traditional aspects. Therefore, this paper attempts to analyze the traffic network from the perspective of vulnerability. First, starting from the conceptual framework of vulnerability, the process of the concept of vulnerability is gradually complicated. At the same time, the main points of vulnerability analysis at each level are defined. Secondly, the analysis model is constructed on two aspects of network vulnerability: station and community. The concept of station vulnerability, which is similar to the traditional vulnerability analysis, is proposed in this paper. Considering the interrelationship between the indicators, the ANP method is used to construct the evaluation model. However, in the community area, the concept of regional vulnerability is proposed, which is based on the community structure of complex networks. Finally, the actual vulnerability analysis was carried out with the Beijing Subway as an example. The result of the calculation not only can obtain important stations that need to be controlled but also divide the lines in the network structure into suitable communities. This improves the collaboration between the subway system and other functional entities in society. [ABSTRACT FROM AUTHOR]

Studies show that intense lightning discharges can perturb nighttime lower ionosphere through induced electromagnetic fields. We report here new evidence that every lightning stroke, regardless of intensity, has an impact on both daytime and nighttime lower ionosphere. Through analysis of thousands of negative cloud‐to‐ground lightning strokes in southern China, we find that skywave features of a lightning sferic are closely related to its source intensity. Variations with increasing lightning intensity show a higher reflectivity from nighttime ionosphere but a larger time delay from daytime ionosphere. It also shows that the ionosphere recovers from the lightning impact in a time shorter than tens of milliseconds. This suggests that there exists a direct and fast nonlinear coupling between lightning‐generated electromagnetic fields and lower ionosphere, making the ionospheric response to a lightning stroke dependent of the lightning intensity. A candidate mechanism for this is the Joule heating effect, but it needs future studies. Key Points: The skywave features of lightning sferics versus the lightning source peak currents have been investigated based on observationsIt shows that a stronger lightning sferic gets a higher reflectivity from the ionosphere in nighttime but a larger phase delay in daytimeThis is the first strong evidence that a lightning stroke can produce a fast impact on the lower ionosphere even during daytime [ABSTRACT FROM AUTHOR]

An approach for retrieving the leader channel charge density, leader current, ambient electric field, and space charge along a leader channel path from ground observations with a complicated ground condition was presented. With this approach, properties of two downward positive leaders (DPL1 and DPL2) struck at high‐rise buildings were studied based on electric and optical measurements made on the roof of a 100 m high building in Guangzhou, China. It shows that the leader‐produced electric field on the roof of the 100 m high building was about 4 times of that on flat ground. The 2‐D speed for both leaders showed a general increasing trend as the leader going down, in the range of 1.8 to 32.3 × 105 and 1.7 to 46.9 × 105 m/s, respectively. The channel line charge density for both leaders showed firstly a sharp increasing trend and then a decreasing trend as the leader going down, in the range of 0.4 to 8.6 and 0.4 to 15.2 mC/m, respectively. The current of the two leaders varied in the range of 0.7 to 5.4 and 0.7 to 4.6 kA, respectively. The ambient electric field (downward is positive) for both leaders showed an alternating polarity along the leader path, in the range of −120 to +176 and −250 to +180 kV/m, respectively. The space charge for both leaders showed also an alternating polarity along the leader path, in the range of −12.3 to +4.2 and −13.9 to +7.8 nC/m3, respectively, which may reflect the in‐cloud electric structure and the corona charge distribution between the cloud and ground. Key Points: An approach for getting the leader charge, ambient electric field, and space charge along a leader path from ground measurements is proposedProperties of two downward positive leaders struck to high‐rise buildings are investigated with the proposed approachResults show that the leader path and charge transfer are closely related to the ambient electric field and space charge distributions [ABSTRACT FROM AUTHOR]

This work aimed to establish a fast and accurate method to detect glioma by combining surface‐enhanced Raman scattering (SERS) and mathematical analysis. At first, 785‐nm laser was selected as the optimum laser to acquire Raman spectra of human brain tissue. Second, it was verified that Raman data in the range of 1,200–1,600 cm−1 could improve the performance of classifier. Based on the analytical results of 1,200–1,600 cm−1 data, the sensitivity and specificity of partial least square (PLS) analysis and back‐propagation neural network (BPNN) were as high as 100%, whereas the sensitivity and specificity of support vector machine (SVM) were 96% and 100%, respectively. Among them, PLS was more potential in the detection of glioma, because of its lower computational cost compared with SVM and BPNN. Moreover, the correlation between observed Raman peaks and 2‐hydroxyglutarate (2HG; 512, 790, 1,204, 1,302, and 1,463 cm−1) was observed, suggesting 2HG as a potential marker of glioma using its Raman spectroscopic signatures. After all, SERS combining with mathematical analysis could be a promising tool for the accurate detection of glioma. [ABSTRACT FROM AUTHOR]

Recent measurements of narrow bipolar lightning events (NBEs) by very high frequency (VHF) radio interferometer have resolved the dynamic development of this special lightning process with submicrosecond time resolution, and showed that the fast positive breakdown (FPB) process is responsible for initiating at least some lightning flashes. In this study, with a newly built and deployed VHF interferometer system, we analyzed 31 intracloud lightning flash initiation events during three thunderstorms at short range from the interferometer. These events separate into two distinct classes that can be identified based on the time scale and the occurrence contexts of the first detectable VHF emissions from the flash. One class has features completely consistent with previously reported FPB events and is associated with continuous VHF emissions of 10–20 μs duration. Downward motion of the FPB region centroid merged continuously into the development of the subsequent upward negative leaders. But the majority of the lightning flashes analyzed began with ultrashort, submicrosecond duration, isolated pulses of VHF emission with no identifiable FPB signatures between these pulses and the leader development. These short VHF pulses begin typically a few hundred microseconds before the upward leader developes and are located at the same position where the leader eventually begins. We suggest that the FPB process is responsible for initiating some but not all lightning flashes, and the extremely short pulse‐like VHF emissions play a role in initiating those flashes without any FPB process. Key Points: Lightning initiation processes imaged at close range with a new VHF broadband interferometer can be classified into two different groupsThe first is the reported fast positive breakdown, with 10–20 μs continuous VHF bursts that merge continuously into upward negative leadersThe second is a kind of isolated short VHF pulses of typical duration <0.5 μs that begin hundreds of microseconds prior to upward negative leader [ABSTRACT FROM AUTHOR]

The lightning sferic has been shown to be a valuable radio signal for detecting perturbations of the lower ionosphere caused by the lightning activity itself and by other terrestrial and space events (Shao et al., 2012, https://doi.org/10.1038/ngeo1668). Adding to many existing methods, we have recently proposed an improved ray theory (RT) model for investigating the lightning sferic transmission in the Earth‐ionosphere waveguide (Qin et al., 2017, https://doi.org/10.1002/2016JD025599). In the present study, a further modification to the RT model was made to increase its accuracy in modeling the lightning sferic in a broader frequency band and a larger distance range. The modification included two aspects: a new incident angle finding technique and a novel method for deriving the high‐order hop series. To quantitatively evaluate the effectiveness of the modification, a comparative study of this modified RT model with its previous version and the full‐wave finite difference time domain model was carried out. The results showed that this modified RT model did better than its previous version and was in close agreement with the full‐wave finite difference time domain method in modeling the lightning sferic in frequencies bands lower to 3, 5, and 7 kHz for distances up to 500, 800, and 1,000 km, respectively. Key Points: New modifications to the ray theory (RT) model for simulating lightning sferics in the Earth‐ionosphere waveguide (EIWG) were madeThe modified RT model was then compared with the finite difference time domain (FDTD) method in modeling lightning sferics under various conditionsThe results show that the RT model is well consistent with the FDTD model in modeling lightning sferics in frequencies lower to 3 kHz and in ranges up to 1,000 km [ABSTRACT FROM AUTHOR]

Purpose: The flattening filter (FF) has traditionally been used to flatten beams or create uniform fields in conformal and intensity‐modulated radiation therapy (IMRT) but reduces the dose rate. Many studies have confirmed improvement in delivery efficiency by removing the FF, also known as flattening filter free (FFF), especially for small field stereotactic body radiation therapy (SBRT); but it is unclear if large treatment fields still favor the FFF beam. We propose a novel, unified approach to quantify delivery efficiency of the FFF and flattened beams. Methods: We modeled the FF effect by inverse conical filters and systematically studied delivery efficiency (beam‐on time, BOT) by varying the filter thickness, including the FF and FFF mode. We formulated the BOT of different beams for any arbitrary fluence map in linear programming to solve the optimal inverse conical filter that minimizes the BOT. One‐dimensional optimal filters of minimum BOT were also derived in closed form for conical fluence to gain insight for arbitrary clinical fluence maps. We evaluated the BOT of the FFF beam and flattened beam for conformal treatment fields of various dimensions ranging from 5 cm × 5 cm to 25 cm × 25 cm. We also analyzed the BOT for 698 clinical IMRT prostate fluence maps of field size 10 cm × 10 cm, 17 head‐and‐neck fluence maps of field size 15 cm × 15 cm, and additional realistic test data from 90° rotation and up to 40 cm × 40 cm enlargement of these clinical fluence maps, which were all initially generated with flattened beams. Results: The FFF beam minimized the BOT for A field size less than 20 cm in single leaf pair cases and for conformal fields of dimension less than 20 cm × 20 cm. The FFF beam also minimized the BOT for all tested prostate and head‐and‐neck cases. The median BOT ratios of the FFF beam to the flattened beam were 0.56 and 0.61 for prostate and head‐and‐neck cases, respectively. The FFF beam minimized the BOT for field size up to 30 cm × 30 cm and had similar BOTs to those of the flattened beam for field size greater than 30 cm × 30 cm in those clinically realistic test data. Conclusion: The filter modeling and BOT calculation enable us to quantify delivery efficiency of the FFF beam and flattened beam in a unified approach. The FFF beam minimized the BOT both theoretically and in simulations for all clinically relevant field sizes and fluence maps in IMRT. The results for conformal fields imply that the FFF beam requires less BOT than the flattened beam for volumetric modulated arc therapy (VMAT) treatments. The delivery efficiency consideration favors the FFF beam in intensity‐modulated treatments and may eventually lead to removal of the FF in all future linear accelerator head designs. [ABSTRACT FROM AUTHOR]

Abstract: On 19 August 2012, the Imager of Sprites and Upper Atmospheric Lightning on board the FORMOSAT‐2 satellite captured a sequence of seven blue discharges within 1 min that emanated from a parent thunderstorm over Lake Taihu in East China. The analysis of lightning activity produced in the thunderstorm indicates that at least six of these events occurred in association with negative narrow bipolar events (NBEs) that were concurrent with the blue discharge by less than 1 ms, and negative cloud‐to‐ground occurred within 6 s before each blue discharge, which is in agreement with the modeling presented by Krehbiel et al. (2008). Therefore, the frequent occurrence of negative cloud‐to‐ground could provide the favorable condition for the production of blue discharges, and negative NBEs are probably the initial event of blue discharges. The detection of negative NBEs might provide a convenient approach to detect the occurrence of blue discharges as lightning bolt shooting upward from the top of energetic thunderstorms. [ABSTRACT FROM AUTHOR]

Abstract: Electron therapy is widely used to treat shallow tumors because of its characteristic sharp dose fall‐off beyond a certain range. A customized cutout is typically applied to block radiation to normal tissues. Determining the final monitor unit (MU) for electron treatment requires an output factor for the cutout, which is usually generated by measurement, especially for highly irregular cutouts. However, manual measurement requires a lengthy quality assurance process with possible errors. This work presents an accurate and efficient cutout output factor prediction model, convolution‐based modified Clarkson integration (CMCI), to replace patient‐specific output factor measurement. Like the Clarkson method, we decompose the field into basic sectors. Unlike the Clarkson integration method, we use annular sectors for output factor estimation. This decomposition method allows calculation via convolution. A 2D distribution of fluence is generated, and the output factor at any given point can be obtained. We applied our method to 10 irregularly shaped cutouts for breast patients for 6E, 9E, and 15E beams and compared the results with measurements and the electron Monte Carlo (eMC) calculation using the Eclipse planning system. While both the CMCI and eMC methods showed good agreement with chamber measurements and film measurements in relative distributions at the nominal source to surface distance (SSD) of 100 cm, eMC generated larger errors than the CMCI method at extended SSDs, with up to −9.28% deviations from the measurement for 6E beam. At extended SSD, the mean absolute errors of our method relative to measurements were 0.92 and 1.14, while the errors of eMC were 1.42 and 1.79 for SSD 105 cm and 110 cm, respectively. These results indicate that our method is more accurate than eMC, especially for low‐energy beams, and can be used for MU calculation and as a QA tool for electron therapy. [ABSTRACT FROM AUTHOR]

Abstract: By using the data of lightning detection and ranging system at the Kennedy Space Center, the temporal fractal and correlation of interevent time series of lightning flash sequences in thunderstorms have been investigated with Allan factor (AF), Fano factor (FF), and detrended fluctuation analysis (DFA) methods. AF, FF, and DFA methods are powerful tools to detect the time‐scaling structures and correlations in point processes. Totally 40 thunderstorms with distinguishing features of a single‐cell storm and apparent increase and decrease in the total flash rate were selected for the analysis. It is found that the time‐scaling exponents for AF (αAF) and FF (αFF) analyses are 1.62 and 0.95 in average, respectively, indicating a strong time correlation of the lightning flash sequences. DFA analysis shows that there is a crossover phenomenon—a crossover timescale (τc) ranging from 54 to 195 s with an average of 114 s. The occurrence of a lightning flash in a thunderstorm behaves randomly at timescales <τc but shows strong time correlation at scales >τc. Physically, these may imply that the establishment of an extensive strong electric field necessary for the occurrence of a lightning flash needs a timescale >τc, which behaves strongly time correlated. But the initiation of a lightning flash within a well‐established extensive strong electric field may involve the heterogeneities of the electric field at a timescale <τc, which behave randomly. [ABSTRACT FROM AUTHOR]

A downward lightning flash usually starts with a downward leader and an upward connecting leader followed by an upward return stroke. It is the preceding leader that governs the following return stroke property. Besides, the return stroke property evolves with height and time. These two aspects, however, are not well addressed in most existing return stroke models. In this paper, we present a leader-return stroke consistent model based on the time domain electric field integral equation, which is a growth and modification of Kumar's macroscopic model. The model is further extended to simulate the optical and electromagnetic emissions of a return stroke by introducing a set of equations relating the return stroke current and conductance to the optical and electromagnetic emissions. With a presumed leader initiation potential, the model can then simulate the temporal and spatial evolution of the current, charge transfer, channel size, and conductance of the return stroke, furthermore the optical and electromagnetic emissions. The model is tested with different leader initiation potentials ranging from −10 to −140 MV, resulting in different return stroke current peaks ranging from 2.6 to 209 kA with different return stroke speed peaks ranging from 0.2 to 0.8 speed of light and different optical power peaks ranging from 4.76 to 248 MW/m. The larger of the leader initiation potential, the larger of the return stroke current and speed. Both the return stroke current and speed attenuate exponentially as it propagates upward. All these results are qualitatively consistent with those reported in the literature. [ABSTRACT FROM AUTHOR]

Total electron content (TEC) computed from the network of Global Positioning System over Hong Kong area known as Hong Kong Sat-Ref-network has been used to study perturbation in the ionosphere from thunder storm activity. Data for geomagnetic quiet day ( Kp < 4, on 1 April 2014) have been analyzed. The lightning activity was measured from Total Lightning sensor LS8000 over/around the Hong Kong region. Deviation in vertical TEC (DTEC) and the rate of change of TEC index (ROTI) have been derived and compared for lightning day of 1 April 2014 and nonlightning day of 7 April 2014. An analysis showed reduction in TEC during evening hour (up to 1245 UT), whereas an enhancement during nighttime hour on the lightning day is observed. The variations in DTEC during nonlightning day are found to be insignificant in comparison to that during the lightning day. The ionospheric perturbation in TEC has been noticed up to a distance around ~500 km and more from the lightning center. ROTI is found to vary from 3 to 60 total electron content unit (TECU)/min (1 TECU = 1016 el m−2) on the day of thunderstorm activity, whereas ROTI is insignificant on nonlightning days. Signature of density bubbles in slant TEC data and periodicities (10-100 min) in DTEC data are observed. For the same pseudorandom numbers (1, 10, 13, 23, and 28) strong amplitude scintillations are also observed at a close by station. Amplitude scintillations are proposed to be caused by plasma bubbles. The results are tentatively explained by thunderstorm-induced electric fields and gravity waves. [ABSTRACT FROM AUTHOR]

Purpose: Conventional step-and-shoot intensity modulated radiation therapy leaf sequencing methods, where a nonhomogeneous fluence map is converted to a set of apertures and associated intensities, assume that target fluence is stratified into a fixed number of discrete levels and/or aperture leaf positions are restricted to a discrete set of locations. These assumptions induce a deviation from the planned fluence map and/or reduce the feasible region of potential plans, respectively. A continuous leaf optimization (CLO) framework is developed as a postprocessing methodology to improve upon conventional leaf sequencing so that the resulting plan avoids these two main drawbacks. Methods: The CLO model directly represents leaf positions and aperture intensities with continuous variables with the goal of reproducing some target fluence profile. Fluence through leaf edges is modeled using the error function, and continuous fluence is approximated using a 0.1 mm discretization across the aperture opening. Conventional leaf sequencing methods provide feasible solutions to the CLO model, and a first-order descent algorithm is used to converge onto a locally optimal solution. Results: As a proof-of-concept, the authors test this framework on 1D (single leaf pair) fluence maps. The CLO model was applied to conventional leaf sequencing and direct aperture optimization solutions. Consistent improvements to existing leaf sequencing methods were found when tested on 232 generated instances of potential target fluence. In addition to improvements in matching the target fluence, the CLO model was able to keep MUs at similar values to the initial conventional sequence. Conclusions: The CLO model can improve upon existing leaf sequencing methods by avoiding the restrictions of fluence stratification and discretized leaf positions. This study lays the foundation for future models and solution methodologies that can incorporate continuous leaf positions explicitly into the treatment planning model. [ABSTRACT FROM AUTHOR]

Adenosine triphosphate-binding cassette (ABC) transporters, including ABCB, ABCC and ABCG families represent general biological defenses against environmental toxicants in varieties of marine and freshwater organisms, but their physiological functions at differential developmental stages of zebrafish embryos remain undefined. In this work, functional expressions of typical ABC transporters including P-glycoprotein (Pgp), multiresistance associated protein 1 (Mrp1) and Mrp2 were studied in zebrafish embryos at 4, 24, 48 and 72 h post-fertilization (hpf). As a result, both the gene expressions and activities of Pgp and Mrps increased with the development of embryos. Correspondingly, 4-72 hpf embryos exhibited an increased tolerance to the toxicity caused by cadmium chloride (CdCl2) and β-naphthoflavone (BNF) with time. Such a correlation was assumed caused by the involvement of ABC transporters in the detoxification of chemicals. In addition, the assumption was supported by the fact that model efflux inhibitors of Pgp and Mrps such as reversine 205 and MK571 significantly inhibited the efflux of toxicants and increased the toxicity of Cd and BNF in zebrafish embryos. Moreover, exposure to CdCl2 and BNF induced the gene expressions of Pgp and Mrp1 in 72 hpf embryos. Thus, functional expressions of Pgp and Mrps increased with the development of zebrafish embryos, which could cause an increasing tolerance of zebrafish embryos to CdCl2 and BNF. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel adsorbent was developed by coating yttrium hydroxide precipitate layer on cellulose fibre. This material takes up ca. 98% of 5 µg·L−1 As(III) and As(V) at low pH (pH<7), while a favorable selectivity for As(V) was achieved within pH 11-12. In practice, a mini-column packed with Y(OH)3 precipitate layer coated cellulose fibre particles was incorporated into a sequential injection system for selective uptake of arsenate at pH 11.5. The retained arsenate was afterwards recovered with 50 µL of 0.8 mol·L−1 NaOH solution as eluent, followed by hydride generation in a reaction medium of 2.0 mol·L−1 HCl and 1.0% NaBH4 solution ( W/ V, in 0.5% NaOH) after pre-reduction of arsenate to arsenite by KI-ascorbic acid (5%, W/ V), with detection by atomic fluorescence spectrometry. Total inorganic arsenic was quantitatively taken up at pH 6.0 by following the same procedure and arsenic speciation was performed by difference. With a sample volume of 1.0 mL, an enrichment factor of 16.4 was derived with a detection limit of 17 ng·L−1 within a linear range of 0.05-2.0 µg·L−1. A relative standard deviation (RSD) of 2.6% (0.5 µg·L−1, n=11) was achieved. The procedure was validated by analyzing arsenic in a certified reference material GBW 09101 (human hair), and speciation of inorganic arsenic in natural water samples. The entire process requires no organic solvents, thus Y(OH)3 coated cellulose fibre provides a green adsorbent. [ABSTRACT FROM AUTHOR]

Purpose: The graphic processing unit (GPU) based TomoTherapy convolution/superposition(C/S) dose engine (GPU dose engine) achieves a dramatic performance improvement over the traditional CPU-cluster based TomoTherapy dose engine (CPU dose engine). Besides the architecture difference between the GPU and CPU, there are several algorithm changes from the CPU dose engine to the GPU dose engine. These changes made the GPU dose slightly different from the CPU-cluster dose. In order for the commercial release of the GPU dose engine, its accuracy has to be validated. Methods: Thirty eight TomoTherapy phantom plans and 19 patient plans were calculated with both dose engines to evaluate the equivalency between the two dose engines. Gamma indices (Γ) were used for the equivalency evaluation. The GPU dose was further verified with the absolute point dose measurement with ion chamber and film measurements for phantom plans. Monte Carlo calculation was used as a reference for both dose engines in the accuracy evaluation in heterogeneous phantom and actual patients. Results: The GPU dose engine showed excellent agreement with the current CPU dose engine. The majority of cases had over 99.99% of voxels with Γ(1%, 1 mm) < 1. The worst case observed in the phantom had 0.22% voxels violating the criterion. In patient cases, the worst percentage of voxels violating the criterion was 0.57%. For absolute point dose verification, all cases agreed with measurement to within ±3% with average error magnitude within 1%. All cases passed the acceptance criterion that more than 95% of the pixels have Γ(3%, 3 mm) < 1 in film measurement, and the average passing pixel percentage is 98.5%-99%. The GPU dose engine also showed similar degree of accuracy in heterogeneous media as the current TomoTherapy dose engine. Conclusions: It is verified and validated that the ultrafast TomoTherapy GPU dose engine can safely replace the existing TomoTherapy cluster based dose engine without degradation in dose accuracy. [ABSTRACT FROM AUTHOR]

Purpose: The longitudinal dose ripple on the off-axis caused by helical radiation delivery, such as the TomoTherapy system, has been observed, and its relation with respect to pitch has been studied with empirically found optimal pitches, 0.86/n, by Kissick et al. [Med. Phys. 32, 1414-1423 (2005)]. This ripple artifact referred to as the thread effect is periodic in nature and is caused by various periodic factors. In this work, the factors that cause the thread effect were unveiled, including jaw profile divergence, the inverse square law, attenuation, and the cone effect, and their impact on the thread effect were studied. Methods: Mathematical formulation for individual and combined factors were set up. Based on theoretical analysis and simulations, optimal pitches that result in local minima of the ripple amplitude with respect to the jaw width and off-axis distance were identified and verified. The effectiveness of optimization in reducing the thread effect were also studied. Results: Analysis and simulation based on the square-shaped jaw profiles well characterize the thread effect. Simulations based on the real jaw profiles show reduced ripples and very good agreement of optimal pitches compared with those based on the square profiles. The optimal pitches were found to have little jaw width dependence, except for the real jaw profile of small width (1.05 cm). The optimal pitches for the real jaw profile of width 1.05 cm are unidentifiable except for the largest ones, due to the relative smoothness of the jaw profile. With optimized intensity modulation, the thread effect can be largely suppressed. For real jaw profiles, the optimal pitches with or without dose optimization do not change much. The numbers 0.86/n found by Kissick et al. well approximate the optimal pitches for off-axis distance of 5 cm. However, optimal pitches are not universal for different off-axis distances: they decrease as the off-axis distance increases. Conclusions: The thread effect can be well explained by the proposed model. Optimization can largely reduce the thread effect. However, an optimal pitch reduces the ripple much easier especially when optimization is limited by many constraints. The optimal pitches predicted by the proposed model could be used as a reference for pitch selection regardless the tumor is at large or small off-axis distance. [ABSTRACT FROM AUTHOR]

Purpose: To obtain accurate x-ray source profile measurements using a slit-collimator, the slit-collimator should have a narrow width, large height, and be positioned near the source. However, these conditions may not always be met. In this paper, the authors provide a detailed analysis of the slit measurement geometry and the relationship between the slit parameters and the measured x-ray source profile. The slit model allows the use of a shorter and more easily available slit-collimator, while accurate source profile measurements can still be obtained. Methods: Measurements were performed with a variety of slit widths and/or slit to source distances. The relationship derived between the slit parameters and the measured profile was used to determine the true focal spot profile through a least square fit of the profile data. The model was verified by comparing the predicted profiles at a variety of slit-collimator parameters with the measured results on the TomoTherapy Hi-Art system. Results: Both the treatment beam and the imaging beam were measured. For treatment mode, it was found that a source consisting of one Gaussian with a 0.75 mm full-width-half-maximum (FWHM) and 72% peak amplitude and a second Gaussian with a 2.27 mm FWHM and 18% peak amplitude matched measurement profiles. The overall source profile has a FWHM of 0.93 mm, but with a higher amplitude in the tail region than a single Gaussian. For imaging mode, the source consists of one Gaussian with a 0.68 mm FWHM and 82% peak amplitude and a second Gaussian with a 1.83 mm FWHM and 18% peak amplitude. The overall source profile has a FWHM of 0.77 mm. Conclusions: Our study of the focal spot measurement using slit-collimators showed that accurate source profile measurements can be achieved through fitting of measurement results at different slit widths and source-to-slit distances (SSD). Quantitative measurements of the TomoTherapy linac focal spot showed that the source distribution could be better described with a model consisting of two Gaussian components rather than a single Gaussian model as assumed in previous studies. [ABSTRACT FROM AUTHOR]

Purpose: Several dynamic techniques are introduced to speed up TomoTherapy® delivery and improve longitudinal conformity. These techniques include dynamic jaws, dynamic couch, and their combinations.Methods: In general, dynamic jaws techniques allow jaws to move during a treatment. On the one hand, the jaws open wide to increase efficiency and thus reduce beam-on time. On the other hand, the jaws can close and follow the target border when sharp penumbra is required near the superior and inferior borders of tumor sites, which results in improved longitudinal dose conformity. The main purpose of the dynamic couch technique is to move the couch as fast as possible at variable speed to reduce beam-on time. Delivering most conformal dose as fast as possible requires a combination of dynamic jaws and dynamic couch techniques (DJDC). Motions of the jaws and couch are determined from the longitudinal fluence profile, which is calculated from an optimized leaf sinogram of small jaw width regular delivery or running start and stop delivery (RSS). We focused on RSS and DJDC in this study and also discussed other delivery techniques.Results: Several conceptual cases are simulated to compare different delivery techniques. The results show that beam-on time can be reduced by about 60% compared to regular delivery with a 2.5 cm jaw width (REG 2.5 cm) for these cases and arbitrary longitudinal fluence profiles can be delivered. Two clinical cases, a prostate and a head-and-neck case, with different delivery techniques are calculated. The results show that plan quality yielded by DJDC with a maximum 5.0 cm jaw width is overall comparable to or better than that of the existing REG 2.5 cm.Conclusions: The DVH comparisons show better critical structure avoidance with the dynamic techniques. At the same time, beam-on time is reduced by about one half compared to REG 2.5 cm. Dynamic delivery techniques provide users more tools to speed up delivery and/or improve plan quality. [ABSTRACT FROM AUTHOR]

Purpose: Collapsed-cone convolution/superposition (CCCS) dose calculation is the workhorse for IMRT dose calculation. The authors present a novel algorithm for computing CCCS dose on the modern graphic processing unit (GPU). Methods: The GPU algorithm includes a novel TERMA calculation that has no write-conflicts and has linear computation complexity. The CCCS algorithm uses either tabulated or exponential cumulative-cumulative kernels (CCKs) as reported in literature. The authors have demonstrated that the use of exponential kernels can reduce the computation complexity by order of a dimension and achieve excellent accuracy. Special attentions are paid to the unique architecture of GPU, especially the memory accessing pattern, which increases performance by more than tenfold. Results: As a result, the tabulated kernel implementation in GPU is two to three times faster than other GPU implementations reported in literature. The implementation of CCCS showed significant speedup on GPU over single core CPU. On tabulated CCK, speedups as high as 70 are observed; on exponential CCK, speedups as high as 90 are observed. Conclusions: Overall, the GPU algorithm using exponential CCK is 1000-3000 times faster over a highly optimized single-threaded CPU implementation using tabulated CCK, while the dose differences are within 0.5% and 0.5 mm. This ultrafast CCCS algorithm will allow many time-sensitive applications to use accurate dose calculation. [ABSTRACT FROM AUTHOR]

Purpose: The equivalent field size (EFS) method is widely used to estimate dose of nonstandard fields, such as elongated or arbitrary shaped fields, for both central axis and off axis points. However, its application is limited to fluence maps with uniform intensity. In this work, we propose a generalized EFS (GEFS) for nonuniform fluence maps and present a formula for GEFS-based dose calculation. Methods: A parallel-beam dose table (PDT) consisting of central axis dose of circular fields of various diameters at various depths is used to define scatter contributions, based on which we calculate GEFS of any given fluence map. Such obtained GEFS, together with the radiological depth and PDT, is used to determine the dose at the point of interest. We tested GEFS-based dose calculation on a water phantom for both uniform and nonuniform fluence maps and compared the results with those by the collapsed cone convolution/superposition (CCCS) method. Results: For all test cases, the gamma index is less than 1 based on the 3%/1 mm criteria for more than 96% of the calculated points. Larger discrepancies mainly occur along the field edges in the buildup region. Conclusions: A generalized equivalent field size for nonuniform fluence maps was proposed and its application in calculating dose at any point was presented and verified through comparison with the CCCS method. [ABSTRACT FROM AUTHOR]

Two initial upward positive leaders (UPLs) in upward negative flashes initiated from a 356‐m‐tall tower were observed with a high‐speed camera, an electric field sensor, and a magnetic field sensor. Although the waveforms of electric fields measured were saturated, both camera images and magnetic fields showed that the two UPLs had obvious stepwise characteristics in their upward moving stage. The magnetic fields associated with the UPLs were characterized by a series of fast‐changing bipolar impulses superimposed on a slowly increasing continuous component as the leaders moved upward, which were well corresponding to the light intensity changes of their high‐speed camera images. The 2‐D step length and step extension speed of the two leaders were estimated in the range of 0.5–3 m and 1.1–9.4 × 105 m/s, respectively. The radius of the leader luminous channel as a function of time and height was also estimated. The channel radius showed first a stable increasing trend in the leader upward moving stage and then 4–5 times of shrinking and expanding processes after the leader connected the cloud. The channel expanding and shrinking speeds were in the range of 2–9 × 104 m/s. Particularly, the channel radius showed an obvious increasing trend with the increase of the height all the time, which was in the range of 2.8–3.5 m when around the tower tip and of 5.6–8.4 m when at 24 m high above the tower tip. Such a feature of the channel radius is in good agreement with the concept of leader corona sheath in literature. Key Points: Two upward positive stepped leaders initiated from a tall tower were analyzed based on magnetic field and high‐speed camera measurementsThe leader step length and step extension speed were found in the range of 0.5–3 m and 105–106 m/s, respectivelyThe leader channel had an expanding and shrinking feature and an increasing trend with height in the range of 2–10 m [ABSTRACT FROM AUTHOR]