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This paper analysis the characteristics of two kinds of ant colony algorithm, some kind of aircraft structure dynamic optimization design model is established, based on the analysis of the model, two kinds of ant colony algorithm are combined with optimization calculation method respectively, the two kinds of ant colony algorithm is studied in the aircraft structure optimization design, the calculation results indicate that improved ant colony algorithm is scientific and feasible, it can effectively solve the optimization problems of aerobat and other structures.

Ant colony algorithm is a kind of bionic intelligent algorithm, which is suitable for combinatorial optimization. The principle and calculation flow of ant colony algorithm is discussed in this paper, how to use improved ant colony algorithm to solve the optimization problem of truss structure is analyzed, the optimization problem of 13-bar truss structure is calculated. The results show that ant colony algorithm has certain advantages in solving the structural optimization problem with discrete design variables.

The 500kV transmission line is exposed to the outdoor for a long time. It is affected by complex climate charge change and other factors which leads to line connection parts bolt loosening, wire breaking and fixture damage and other line failures. In order to ensure the stable transmission of electric energy, power operators need to wear shielding suits and work in the high-risk and high-voltage environment. Use of electric power operation robot instead of manual operation is an effective way to liberate maintenance staff labor. But robots still have some problems such as low degree of automation and low efficiency of power operation. Machine vision detection technology in recent years has been widely used in major areas including deep learning as emerging visual detection technology shows excellent performance. In this paper, the vision detection algorithm is studied respectively for the bolt fastening end working device and wire repairing end working device of the live transmission line robot to improve the operating efficiency of the robot.

Two-dimensional (2D) van der Waals material is a focus of research for its widespread application in optoelectronics, memories, and spintronics. The ternary compound Nb2SiTe4 is a van der Waals semiconductor with excellent air stability and small cleavage energy, which is suitable for preparing a few layers counterpart to explore novel properties. Here, properties of bulk Nb2SiTe4 with large in-plane electrical anisotropy are demonstrated. It is found that hole carriers dominate at a temperature above 45 K with a carrier active energy of 31.3 meV. The carrier mobility measured at 100 K is about 213 cm2⋅V−1⋅s−1 in bulk Nb2SiTe4, higher than the reported results. In a thin flake Nb2SiTe4, the resistivity ratio between the crystalline axes of a and b is reaching about 47.3 at 2.5 K, indicating that there exists a large anisotropic transport behavior in their basal plane. These novel transport properties provide accurate information for modulating or utilizing Nb2SiTe4 for electronic device applications.

The goal of this study is to develop a generalized source model (GSM) for accurate Monte Carlo dose simulations of CT scans based solely on the measurement data without a priori knowledge of scanner specifications. The proposed generalized source model consists of an extended circular source located at x-ray target level with its energy spectrum, source distribution and fluence distribution derived from a set of measurement data conveniently available in the clinic. Specifically, the central axis percent depth dose (PDD) curves measured in water and the cone output factors measured in air were used to derive the energy spectrum and the source distribution respectively with a Levenberg-Marquardt algorithm. The in-air film measurement of fan-beam dose profiles at fixed gantry was back-projected to generate the fluence distribution of the source model. A benchmarked Monte Carlo user code was used to simulate the dose distributions in water with the developed source model as beam input. The feasibility and accuracy of the proposed source model was tested on a GE LightSpeed and a Philips Brilliance Big Bore multi-detector CT (MDCT) scanners available in our clinic. In general, the Monte Carlo simulations of the PDDs in water and dose profiles along lateral and longitudinal directions agreed with the measurements within 4%/1mm for both CT scanners. The absolute dose comparison using two CTDI phantoms (16 cm and 32 cm in diameters) indicated a better than 5% agreement between the Monte Carlo-simulated and the ion chamber-measured doses at a variety of locations for the two scanners. Overall, this study demonstrated that a generalized source model can be constructed based only on a set of measurement data and used for accurate Monte Carlo dose simulations of patients’ CT scans, which would facilitate patient-specific CT organ dose estimation and cancer risk management in the diagnostic and therapeutic radiology.

At present, total station or gnss-rtk is often used in mine ecological environment restoration survey, which has the disadvantages of high intensity, long cycle and high cost. In particular, the problems of landslide and collapse in abandoned mines bring potential safety hazards to the surveying and mapping personnel. The traditional surveying and mapping results are 2D graphics, and the information of topography and geological disasters is not intuitive, which brings inconvenience to the design of ecological environment restoration scheme. In order to meet the actual needs of mine ecological restoration, UAV incline photogrammetry technology is applied in the survey and mapping, scheme design and construction management stages of mine ecological environment restoration. The research results show that UAV incline photogrammetry technology can realize: ensure the safety of technical personnel, make the survey and mapping more efficient; make the mine environment information more intuitive, vivid and vivid, which is conducive to the formulation of ecological restoration plan, dynamic grasp of construction progress, and make mine ecological restoration more accurate.

With the continuous development of science and technology, computer software and network information technology are also developing, computer graphics technology has been widely used in various fields. With the continuous improvement of people’s living standard, all kinds of interior design emerge in endlessly, and the quality requirements of interior design have gradually changed. More and more design institutions use computer technology to improve the contents of interior design, so as to continuously improve the quality and efficiency of interior design, and make interior design more standardized and scientific and technological. This paper introduces the computer drawing technology and the concrete application and method in interior design, in order to improve the working method, improve the level of interior design and realize the leapfrog development of interior design in the future work and life.

Terraces are an effective and common mode of mountain agriculture. Issues such as water resource storage and drainage, structural stability, impact on the conservation of soil and water, and their adaptive and influencing mechanism to the natural and social environment are important technical engineering issues in the creation and operation of terraces creating. Moreover, these issues are also the key topics in heritage research. Covering a total area of 6,416 hectares, Ziquejie Terraces located in South China is built on hills with an altitude of 460–1,540 m and a surface slope of 25°–40°. Owing to its 1,000-year history and simple but systematic irrigation and drainage system, Ziquejie Terraces has been included in The World List of ICID Heritage Irrigation Structure in 2014 as a unique type of agricultural irrigation. A systematic analysis has been conducted on its creation, influences on the ecological environment and human society, components and characteristics of irrigation and drainage system in the terraces area, and scientific and cultural values as a heritage area. Through such analysis, a traditional pattern of mountain agricultural development has been revealed under the population pressure and mechanism of background adaptation and environment response. The creation of Ziquejie Terraces has specific natural conditions. As an example of overall planning and exploitation of water and land resources, Ziquejie Terraces reflect ancient Chinese philosophy that the simplest projects could afford the largest comprehensive benefits. The successful experiences of Ziquejie Terraces should be used as reference of modern agricultural development in mountainous areas.

Using the newly-developed solid ionic gating technique, we measure the electrical transport property of a thin-flake NbSe2 superconductor (T c = 6.67 K) under continuous Li intercalation and electron doping. It is found that the charge-density-wave transition is suppressed, while at the same time a carrier density, decreasing from 7 × 1014 cm–2 to 2 × 1014 cm–2 also occurs. This tunable capability in relation to carrier density is 70%, which is 5 times larger than that found using the liquid ionic gating method [Phys. Rev. Lett. 117 (2016) 106801]. Meanwhile, we find that the scattering type of conduction electrons transits to the s–d process, which may be caused by the change of the occupied states of 4d-electrons in Nb under the condition of Li intercalation. Simultaneously, we observe a certain decrement of electron-phonon coupling (EPC), based on the electron-phonon scattering model, in the high temperature range. Based on data gathered from in situ measurements, we construct a full phase diagram of carrier density, EPC and T c in the intercalated NbSe2 sample, and qualitatively explain the variation of T c within the BCS framework. It is our opinion that the in situ solid ionic gating method provides a direct route to describing the relationship between carrier density and superconductivity, which is helpful in promoting a clearer understanding of electronic phase competition in transition metal dichalcogenides.

Due to the high cost and low real-time reliability of low-voltage distribution network topology checking by manual field verification, an online verification method based on revised Pearson correlation coefficient with error expectation values and KNN algorithm is proposed. Firstly, the Pearson correlation coefficient with error expectation values is used to judge the similarity between the user’s voltage curve and the transformer substation voltage curve, then the user with incorrect household relationship is found to perform re-verification. For performing re-verification, the user sample set is generated based on the data of GIS system and the Technical Guidelines for Distribution Network Planning and Design, and the K-Nearest Neighbor (KNN) algorithm is used to find out the correct station to which area the user belongs. Finally, based on the results of the manual field verification, the correctness of the algorithm verification is judged.

The topology of the distribution network often changes during routine maintenance and expansion. In addition, the real-time measurement data and the number of configured sensors is limited, and the switch state lacks of real-time telemetry, which causes the topology generator to often fail to obtain actual structure of distribution network. At present, the common topology identification methods are not well adapted to the above characteristics of the distribution network. Therefore, in order to avoid the state estimation distortion of the distribution network caused by serious errors in the distribution network topology, a new topology identification method is proposed. The method determines the possible topologies based on the matching loop power and performs state estimation on the possible topologies based on the common measured values. According to the state evaluation result and the measured value, thereby based on the highest matching degree, it is determined that the topology is a trusted topology, that is, an actual topology. The proposed method realizes the quantitative evaluation of the topology, simplifies the topology identification process, and reduces the computational complexity of the topology identification process. Finally, the effectiveness and practicality of the method are verified through related cases.

Silicone rubber foam (SiF) with EG/HPCTP was prepared by high-temperature vulcanization. The flame retardancy of SiF was evaluated using the LOI (limiting oxygen index), UL-94, cone calorimetry test (CCT), thermogravimetric analysis (TGA), and mechanical properties. The results showed that EG/HPCTP could improve the LOI of SiF, and the SiF could pass the UL-94 V-0 rating. Compared with pristine SiF, EG/HPCTP could reduce the total heat release rate (THR), heat release rate (PHRR). Digital images of the char residues showed that the HPCTP was beneficial to promote the strength of SiF with EG. TGA showed that the branched decomposition temperature and main chain pyrolysis temperature of SiF were delayed. Mechanical properties analysis showed that EG and HPCTP could improve the mechanical properties of SiF. These indicated that the addition of EG/HPCTP was a good approach to prepare high effective flame-retarding SiF.

Coal mining in Peixian County, Jiangsu Province has a long history, and the surface subsidence of mining area is obvious. To better grasp the characteristics of long time-series surface subsidence in of mining area, this paper uses SBAS method fusing distributed scattererst to process 14 Sentinel-1A images ranging from October 2016 to April 2017, and obtains the deformation field caused by mining in Zhangshuanglou(ZSL) mine. The results show that SBAS method based on distributed object fusion can effectively monitor the surface subsidence. The maximum subsidence of Zhangshuanglou mining area reached - 209.3 mm in the period from October 2016 to April 2017, and there is a trend of gradual increase of surface subsidence. It needs to be early-warning through time series observation.

To reduce the difficulty of the epitaxy caused by multiple quantum well infrared photodetector (QWIP) with tunnel compensation structure, an improved structure is proposed. In the new structure, the superlattices are located between the tunnel junction and the barrier as the infrared absorption region, eliminating the effect of doping concentration on the well width in the original structure. Theoretical analysis and experimental verification of the new structure are carried out. The experimental sample is a two-cycle device, each cycle contains a tunnel junction, a superlattice infrared absorption region and a thick barrier. The photosurface of the detector is 200 × 200 μm2 and the light is optically coupled by 45° oblique incidence. The results show that the optimal operating voltage of the sample is –1.1 V, the dark current is 2.99 × 10–8 A, and the blackbody detectivity is 1.352 × 108 cm·Hz1/2·W–1 at 77 K. Our experiments show that the new structure can work normally.

Bi2O2Se thin film could be one of the promising material candidates for the next-generation electronic and optoelectronic applications. However, the performance of Bi2O2Se thin film-based device is not fully explored in the photodetecting area. Considering the fact that the electrical properties such as carrier mobility, work function, and energy band structure of Bi2O2Se are thickness-dependent, the in-plane Bi2O2Se homojunctions consisting of layers with different thicknesses are successfully synthesized by the chemical vapor deposition (CVD) method across the terraces on the mica substrates, where terraces are created in the mica surface layer peeling off process. In this way, effective internal electrical fields are built up along the Bi2O2Se homojunctions, exhibiting diode-like rectification behavior with an on/off ratio of 102, what is more, thus obtained photodetectors possess highly sensitive and ultrafast features, with a maximum photoresponsivity of 2.5 A/W and a lifetime of 4.8 μs. Comparing with the Bi2O2Se uniform thin films, the photo-electric conversion efficiency is greatly improved for the in-plane homojunctions.

We have identified a new superconductor Pd3Te2 based on pure phase samples. Electrical resistivity, magnetic susceptibility and specific heat measurements confirm that Pd3Te2 is a bulk superconductor at 2.2 K. The value of Ginzburg–Landau parameter is larger than 1/√2, suggesting type-II superconductivity. Meanwhile, the analysis of specific heat indicates that Pd3Te2 is a fully-gapped superconductor with electron-phonon coupling constant λ e-p = 0.58, which features a BCS weakly coupling case. According to our theoretical calculations, the superconductivity is related to the states of hybridization of Pd d states and Te p states at the Fermi level. Our results reveal that superconductivity can occur in five coordinated palladium tellurides.

Heavy electron-doped FeSe-derived materials have attracted attention due to their uncommon electronic structures with only ‘electron pockets’, and they are different from other iron-based superconductors. Here, we report the crystal structures, superconductivities and normal state properties of two new Li-doped FeSe-based materials, i.e., Li0.15(C3H10N2)0.32FeSe (P-4) and Li x (C3H10N2)0.32FeSe (P4/nmm, 0.25 < x < 0.4 ) with superconducting transition temperatures ranging from 40 K to 46 K. The determined crystal structures reveal a coupling between Li concentration and the orientation of 1,3-diaminopropane molecules within the largely expanded FeSe layers. Superconducting fluctuations appear in the resistivity of the two superconductors and are fitted in terms of the quasi two-dimensional (2D) Lawrence–Doniach model. The existence of a crossing point and scaling behavior in the T-dependence of diamagnetic response also suggests that the two superconductors belong to the quasi-2D system. Interestingly, with the increase of temperature, a sign of Hall coefficient (R H) reversing from negative to positive is observed at ∼185 K in both phases, suggesting that ‘hole pockets’ emerge in these electron-doped FeSe materials. First principle calculations indicate that the increase in FeSe layer distance will lift up a ‘hole band’ associated with d x 2 − y 2 character and increase the hole carriers. Our findings suggest that the increase in two dimensionalities may lead to the sign-reversal Hall resistivity in Li x (C3H10N2)0.32FeSe at high temperature.

The aim of this study is to investigate the imaging dose to red bone marrow (RBM) and the associated leukaemia risks attributable to pelvic kilo-voltage cone beam computed tomography (kVCBCT) scans in image-guided radiation therapy (IGRT). The RBM doses of 42 patients (age 2.7-86.4 years) were calculated using Monte Carlo simulations. The trabecular spongiosa was segmented to substitute RBM rather than the whole bone. Quantitative correlations between anthropometric variables such as age, physical bone density (PBD) and RBM dose were established. Personalized leukaemia risk was evaluated using an improved Boice model which included the age-associated RBM involvement. An incremental leukaemia risk of 29%-82% (mean = 45%) was found to be associated with 40 pelvic kVCBCT scans in the subject group used in a typical external beam radiation therapy course. Higher risks were observed in children. Due to the enhanced photoelectric effect in high atomic number materials, PBD was observed to strongly affect the RBM dose. Considerable overestimations (9%-42%, mean = 28%) were observed if the whole bone doses were used as surrogates of RBM doses. The personalized estimation of RBM dose and associated leukaemia risk caused by pelvic kVCBCT scans is clinically feasible with the proposed empirical models. Higher radiogenic cancer risks are associated with repeated kVCBCT scans in IGRT of cancer patients, especially children.

A two-dimensional mathematical model was developed to investigate the effects of dielectric barrier discharge (DBD) plasma on CH4-air mixtures combustion at atmospheric pressure. Considering the physical and chemical processes of plasma-assisted combustion (PAC), plasma discharge, heat transfer and turbulent were simultaneously coupled into simulation of PAC. This coupling model consists of DBD kinetic model and methane combustion model. By comparing simulations and the original reference's results, a high-accuracy of this model was validated. In addition, the effects of PAC actuation parameters on combustion characteristics were studied. Numerical simulations show that with an inlet airflow velocity of 10 m s−1, a CH4-air mixtures' equivalence ratio of 0.5, an applied voltage of 10 kV, a frequency of 1200 kHz, compared to conventional combustion (CC), the highest flame temperature rises by 32 K; outlet temperature distribution coefficient drops by 2.3%; the maximum net reaction rate of CH4 and H2O increase by 11.22% and 12.80% respectively; the maximum CO emission index decreases by 14.61%; the mixing region turbulence mixing time reduces by 89 ms.

The nitrogen dimer as both a fundamental building unit in designing a new type of nitrides, and a material gene associated with high electrical and thermal conductivities is investigated by first principles calculations. The results indicate that the predicted SiN 4 is structurally stable and reasonably energy-favored with a striking feature in its band structure that exhibits free electron-like energy dispersions. It possesses a high electrical conductivity (5.07 × 105 S/cm) and a high thermal conductivity (371 W/m⋅K) comparable to copper. The validity is tested by isostructural AlN 4 and SiC 4. It is demonstrated that the nitrogen dimers can supply a high density of delocalized electrons in this new type of nitrides.

The goal of this work is to present a systematic Monte Carlo validation study on the clinical implementation of the enhanced dynamic wedges (EDWs) into the Pinnacle(3) (Philips Medical Systems, Fitchburg, WI) treatment planning system (TPS) and QA procedures for patient plan verification treated with EDWs. Modeling of EDW beams in the Pinnacle(3) TPS, which employs a collapsed-cone convolution superposition (CCCS) dose model, was based on a combination of measured open-beam data and the 'Golden Segmented Treatment Table' (GSTT) provided by Varian for each photon beam energy. To validate EDW models, dose profiles of 6 and 10 MV photon beams from a Clinac 2100 C/D were measured in virtual water at depths from near-surface to 30 cm for a wide range of field sizes and wedge angles using the Profiler 2 (Sun Nuclear Corporation, Melbourne, FL) diode array system. The EDW output factors (EDWOFs) for square fields from 4 to 20 cm wide were measured in virtual water using a small-volume Farmer-type ionization chamber placed at a depth of 10 cm on the central axis. Furthermore, the 6 and 10 MV photon beams emerging from the treatment head of Clinac 2100 C/D were fully modeled and the central-axis depth doses, the off-axis dose profiles and the output factors in water for open and dynamically wedged fields were calculated using the Monte Carlo (MC) package EGS4. Our results have shown that (1) both the central-axis depth doses and the off-axis dose profiles of various EDWs computed with the CCCS dose model and MC simulations showed good agreement with the measurements to within 2%/2 mm; (2) measured EDWOFs used for monitor-unit calculation in Pinnacle(3) TPS agreed well with the CCCS and MC predictions within 2%; (3) all the EDW fields satisfied our validation criteria of 1% relative dose difference and 2 mm distance-to-agreement (DTA) with 99-100% passing rate in routine patient treatment plan verification using MapCheck 2D diode array.

Timothy Jorgensen's Strange Glow relates a brief history of our dealings with radiation, tracking the most important events and profiling the most pioneering researchers in the field.

This paper investigates a quality assurance (QA) phantom specially designed to verify the accuracy of dose distributions and monitor units (MU) calculated by clinical treatment planning optimization systems and by the Monte Carlo method for intensity-modulated radiotherapy (IMRT). The QA phantom is a PMMA cylinder of 30 cm diameter and 40 cm length with various bone and lung inserts. A procedure (and formalism) has been developed to measure the absolute dose to water in the PMMA phantom. Another cylindrical phantom of the same dimensions, but made of water, was used to confirm the results obtained with the PMMA phantom. The PMMA phantom was irradiated by 4, 6 and 15 MV photon beams and the dose was measured using an ionization chamber and compared to the results calculated by a commercial inverse planning system (CORVUS, NOMOS, Sewickley, PA) and by the Monte Carlo method. The results show that the dose distributions calculated by both CORVUS and Monte Carlo agreed to within 2% of dose maximum with measured results in the uniform PMMA phantom for both open and intensity-modulated fields. Similar agreement was obtained between Monte Carlo calculations and measured results with the bone and lung heterogeneity inside the PMMA phantom while the CORVUS results were 4% different. The QA phantom has been integrated as a routine QA procedure for the patient's IMRT dose verification at Stanford since 1999.

A Monte Carlo user code, MCDOSE, has been developed for radiotherapy treatment planning (RTP) dose calculations. MCDOSE is designed as a dose calculation module suitable for adaptation to host RTP systems. MCDOSE can be used for both conventional photon/electron beam calculation and intensity modulated radiotherapy (IMRT) treatment planning. MCDOSE uses a multiple-source model to reconstruct the treatment beam phase space. Based on Monte Carlo simulated or measured beam data acquired during commissioning, source-model parameters are adjusted through an automated procedure. Beam modifiers such as jaws, physical and dynamic wedges, compensators, blocks, electron cut-outs and bolus are simulated by MCDOSE together with a 3D rectilinear patient geometry model built from CT data. Dose distributions calculated using MCDOSE agreed well with those calculated by the EGS4/DOSXYZ code using different beam set-ups and beam modifiers. Heterogeneity correction factors for layered-lung or layered-bone phantoms as calculated by both codes were consistent with measured data to within 1%. The effect of energy cut-offs for particle transport was investigated. Variance reduction techniques were implemented in MCDOSE to achieve a speedup factor of 10-30 compared to DOSXYZ.

This work presents a reconfigurable mixed-signal system-on-chip (SoC), which integrates switched-capacitor-based field programmable analog arrays (FPAA), analog-to-digital converter (ADC), digital-to-analog converter, digital down converter , digital up converter, 32-bit reduced instruction-set computer central processing unit (CPU) and other digital IPs on a single chip with 0.18 μm CMOS technology. The FPAA intellectual property could be reconfigured as different function circuits, such as gain amplifier, divider, sine generator, and so on. This single-chip integrated mixed-signal system is a complete modern signal processing system, occupying a die area of 7 × 8 mm 2 and consuming 719 mW with a clock frequency of 150 MHz for CPU and 200 MHz for ADC/DAC. This SoC chip can help customers to shorten design cycles, save board area, reduce the system power consumption and depress the system integration risk, which would afford a big prospect of application for wireless communication.

Three dimensional (3D) divertor particle flux footprints induced by the lower hybrid wave (LHW) have been systematically investigated in the EAST superconducting tokamak during the recent experimental campaign. We find that the striated particle flux (SPF) peaks away from the strike point (SP) closely fit the pitch of the edge magnetic field line for different safety factors q 95, as predicted by a field line tracing code taking into account the helical current filaments (HCFs) in the scrape-off-layer (SOL). As LHW power increases, it requires the fuelling to be increased e.g. by super molecular beam injection (SMBI), to maintain a similar plasma density, which may be attributed to the pump-out effect due to LHW, and may thus be beneficial for EAST steady state operations. The 3D SPF structure is observed with a LHW power threshold (P LHW ~ 0.9 MW). The ratio of the particle fluxes between SPF and outer strike point (OSP), i.e. , increases with the LHW power. Upon transition to divertor detachment, the particle flux at the main OSP decreases, as expected, however, the particle flux at SPF continues increasing, in contrast to the RMP-induced striations that vanish with increasing divertor density. In addition, we also find that the in–out asymmetry of the 3D particle flux footprint pattern exhibits a clear dependence on the toroidal field direction (B × ∇ B ↓ and B × ∇ B↑). Experiments using neon impurity seeding show a promising capability in 3D particle and heat flux control on EAST. LHW-induced particle and heat flux striations are also present in the H-mode plasmas, reducing the peak heat flux and erosion at the main strike point, thus facilitating long-pulse operation with a new steady-state H-mode over 60 s being recently achieved in EAST.

When the underground coal mine gob area has been sealed due to the coal spontaneous combustion, under the low oxygen and potentially high temperature environment, the CO concentration could drop sharply and disappear quickly. But it could rise rapidly after re-opening. These indicate that the disappearance is the only index for coal burnt out. In order to find a way how let CO disappear, experiments have been conducted using the newly developed experiment setup for three samples, raw, watered and bacteria-free coal sample. The CO and CO2 concentration have been monitored and analyzed. The results show the bacteria in the coal do consume CO and increase the chance of CO transfer to CO2. These results reveal how let CO disappear in a sealed zone from a new aspect. And the accuracy was improved when used gas index to determine combustion status for coal spontaneous combustion.

A method for deriving the electron and photon energy spectra from electron beam central axis percentage depth dose (PDD) curves has been investigated. The PDD curves of 6, 12 and 20 MeV electron beams obtained from the Monte Carlo full phase space simulations of the Varian linear accelerator treatment head have been used to test the method. We have employed a 'random creep' algorithm to determine the energy spectra of electrons and photons in a clinical electron beam. The fitted electron and photon energy spectra have been compared with the corresponding spectra obtained from the Monte Carlo full phase space simulations. Our fitted energy spectra are in good agreement with the Monte Carlo simulated spectra in terms of peak location, peak width, amplitude and smoothness of the spectrum. In addition, the derived depth dose curves of head-generated photons agree well in both shape and amplitude with those calculated using the full phase space data. The central axis depth dose curves and dose profiles at various depths have been compared using an automated electron beam commissioning procedure. The comparison has demonstrated that our method is capable of deriving the energy spectra for the Varian accelerator electron beams investigated. We have implemented this method in the electron beam commissioning procedure for Monte Carlo electron beam dose calculations.

We have investigated the tongue-and-groove effect on the IMRT dose distributions for a Varian MLC. We have compared the dose distributions calculated using the intensity maps with and without the tongue-and-groove effect. Our results showed that, for one intensity-modulated treatment field, the maximum tongue-and-groove effect could be up to 10% of the maximum dose in the dose distributions. For an IMRT treatment with multiple gantry angles (or = 5), the difference between the dose distributions with and without the tongue-and-groove effect was hardly visible, less than 1.6% for the two typical clinical cases studied. After considering the patient setup errors, the dose distributions were smoothed with reduced and insignificant differences between plans with and without the tongue-and-groove effect. Therefore, for a multiple-field IMRT plan (or = 5), the tongue-and-groove effect on the IMRT dose distributions will be generally clinically insignificant due to the smearing effect of individual fields. The tongue-and-groove effect on an IMRT plan with small number of fields (5) will vary depending on the number of fields in a plan (coplanar or non-coplanar), the MLC leaf sequences and the patient setup uncertainty, and may be significant (5% of maximum dose) in some cases, especially when the patient setup uncertainty is small (or = 2 mm).

A new EGS4/PRESTA Monte Carlo user code, MCDOSE, has been developed as a routine dose calculation tool for radiotherapy treatment planning. It is suitable for both conventional and intensity modulated radiation therapy. Two important features of MCDOSE are the inclusion of beam modifiers in the patient simulation and the implementation of several variance reduction techniques. Before this tool can be used reliably for clinical dose calculation, it must be properly validated. The validation for beam modifiers has been performed by comparing the dose distributions calculated by MCDOSE and the well-benchmarked EGS4 user codes BEAM and DOSXYZ. Various beam modifiers were simulated. Good agreement in the dose distributions was observed. The differences in electron cutout factors between the results of MCDOSE and measurements were within 2%. The accuracy of MCDOSE with various variance reduction techniques was tested by comparing the dose distributions in different inhomogeneous phantoms with those calculated by DOSXYZ without variance reduction. The agreement was within 1.0%. Our results demonstrate that MCDOSE is accurate and efficient for routine dose calculation in radiotherapy treatment planning, with or without beam modifiers.

This work investigates the feasibility of optimizing energy- and intensity-modulated electron beams for radiation therapy. A multileaf collimator (MLC) specially designed for modulated electron radiotherapy (MERT) was investigated both experimentally and by Monte Carlo simulations. An inverse-planning system based on Monte Carlo dose calculations was developed to optimize electron beam energy and intensity to achieve dose conformity for target volumes near the surface. The results showed that an MLC with 5 mm leaf widths could produce complex field shapes for MERT. Electron intra- and inter-leaf leakage had negligible effects on the dose distributions delivered with the MLC, even at shallow depths. Focused leaf ends reduced the electron scattering contributions to the dose compared with straight leaf ends. As anticipated, moving the MLC position toward the patient surface reduced the penumbra significantly. There were significant differences in the beamlet distributions calculated by an analytic 3-D pencil beam algorithm and the Monte Carlo method. The Monte Carlo calculated beamlet distributions were essential to the accuracy of the MERT dose distribution in cases involving large air gaps, oblique incidence and heterogeneous treatment targets (at the tissue-bone and bone-lung interfaces). To demonstrate the potential of MERT for target dose coverage and normal tissue sparing for treatment of superficial targets, treatment plans for a hypothetical treatment were compared using photon beams and MERT.

The in–out divertor asymmetry in the Experimental Advanced Superconducting Tokamak (EAST), as manifested by particle fluxes measured by the divertor triple Langmuir probe arrays, is significantly enhanced during type-I edge localized modes (ELMs), favoring the inner divertor in lower single null (LSN) for the normal toroidal field (B t) direction, i.e. with the ion B × ∇ B direction towards the lower X-point, while the in–out asymmetry is reversed when the ion B × ∇ B is directed away from the lower X-point. The plasma flow measured by the Mach probe at the outer midplane is in the ion Pfirsch–Schlüter (PS) flow direction, opposite to both B × ∇ B and E × B drifts, i.e. towards the inner divertor for normal B t, and the outer divertor for reverse B t, consistent with the observed in–out divertor asymmetry in particle fluxes. Since the particle source from an ELM event is predominantly located near the outer midplane, this new finding suggests a critical role of the PS flow in driving the in–out divertor asymmetry. The divertor asymmetry during type-III ELMs exhibits a similar trend to that during type-I ELMs. Strong in–out divertor asymmetry is also present during inter-ELM and ELM-free phases for the normal field direction, i.e. with more particle flux to the lower inner divertor target, but the peak particle flux merely becomes more symmetric, or slightly reversed, for reverse B t, i.e. reversed B × ∇ B drift direction.

Far-field properties dependent on array scale, separation, element width and emitted wavelength are systematically analyzed theoretically and experimentally. An array model based on the finite-difference method is established to simulate the far-field profile of the coherent arrays. Some important conclusions are obtained. To achieve a higher quality beam, it is necessary to decrease separation between elements, or to increase the element width. Higher brightness can be achieved in the array with larger scale. Emitted wavelength also has an influence on the far-field profile. These analyses can be extended to the future design of coherent vertical cavity surface emitting laser arrays.

The performance of the oxide-confined surface-relief (SR) structure vertical-cavity surface-emitting laser (VCSEL) is simulated and analyzed by using the three-dimensional finite-difference time-domain (FDTD) method. The impacts of the device structure parameters on the far-field characteristics are researched. A single-fundamental-mode SR VCSEL with an oxide-aperture of 15 ?m is designed and produced. The single-mode power of the VCSEL is 5mW, the threshold current is 2.5 mA, far-field divergent angles range from 7.8? to 10.8? and the side-mode suppression ratio is over 30 dB. The optical and electrical properties of the device are in agreement with the results of FDTD simulation, which shows that the SR technology can effectively suppress the higher-order-mode lasing, and make the SR VCSEL work in a single mode under a larger oxide aperture.