Effect Of Field Size Research Articles

A model-based algorithm to correct for the loss of backscatter in superficial X-ray radiation therapy

Dosimetry protocols for superficial X-rays prescribe the determination of kerma on the surface of a phantom through the use of a backscatter factor (Bw) that accounts for the effect of phantom scatter. Bw values corresponding to full-scatter phantoms are provided by these protocols. In practice, clinical situations arise wherein there is insufficient scattering material downstream, resulting in published Bw values that overestimate the amount of occurring scatter.To provide an accurate dose calculation the backscatter values need to be corrected for any reduction in scattered radiation. Estimating the change of Bw in situations with incomplete backscatter has previously been achieved by direct measurements or Monte Carlo modelling. For increasing the accuracy of clinical dosimetries, we developed a physical model to deduce an algorithm for calculating backscatter factors in situations with reduced downstream scattering medium. The predictions of the model were validated by comparison with published data, Monte Carlo simulations and film-based measurements for beams with a half-value layer of 0.8, 2 and 4 mm Al.Our algorithm accurately predicts the effect of partial scatter conditions with suitable precision. Its reliability, combined with the simplicity of calculation, makes this methodology suitable to be incorporated into routine clinical dosimetry. The algorithm’s underlying physical model provides an intuitive understanding of the effects of field size and beam energy on backscatter reduction, permitting a rational management of this effect.

The effect of SSD, Field size, Energy and Detector type for Relative Output Factor measurement in small photon beams as compared with Monte Carlo simulation

Abstract Introduction: Small fields photon dosimetry is associated with many problems. Using the right detector for measurement plays a fundamental role. This study investigated the measurement of relative output for small photon fields with different detectors. It was investigated for three-photon beam energies at SSDs of 90, 95, 100 and 110 cm. As a benchmark, the Monte Carlo simulation was done to calculate the relative output of these small photon beams for the dose in water. Materials and Methods: 6, 10 and 15 MV beams were delivered from a Synergy LINAC equipped with an Agility 160 multileaf collimator (MLC). A CC01 ion chamber, EFD-3G diode, PTW60019 microdiamond, EBT2 radiochromic film, and EDR2 radiographic film were used to measure the relative output of the linac. Measurements were taken in water for the CC01 ion chamber, EFD-3G diode, and the PTW60019. Films were measured in water equivalent RW3 phantom slabs. Measurements were made for 1 × 1, 2 × 2, 3 × 3, 4 × 4, 5 × 5 and a reference field of 10 × 10 cm2. Field sizes were defined at 100cm SSD. Relative output factors were also compared with Monte Carlo (MC) simulation of the LINAC and a water phantom model. The influence of voxel size was also investigated for relative output measurement. Results and Discussion: The relative output factor (ROF) increased with energy for all fields large enough to have lateral electronic equilibrium (LEE). This relation broke down as the field sizes decreased due to the onset of lateral electronic disequilibrium (LED). The high-density detector, PTW60019 gave the highest ROF for the different energies, with the less dense CC01 giving the lowest ROFs. Conclusion: These are results compared to MC simulation, higher density detectors give higher ROF values. Relative to water, the ROF measured with the air-chamber remained virtually unchanged. The ROFs, as measured in this study showed little variation due to increased SSDs. The effect of voxel size for the Monte Carlo calculations in water does not lead to significant ROF variation over the small fields studied.

Evaluation of electromagnetic and nuclear scattering models in GATE/Geant4 for proton therapy.

PurposeThe dose core of a proton pencil beam (PB) is enveloped by a low dose area reaching several centimeters off the central axis and containing a considerable amount of the dose. Adequate modeling of the different components of the PB profile is, therefore, required for accurate dose calculation. In this study, we experimentally validated one electromagnetic and two nuclear scattering models in GATE/Geant4 for dose calculation of proton beams in the therapeutic energy window (62–252 MeV) with and without range shifter (RaShi).MethodsThe multiple Coulomb scattering (MCS) model was validated by lateral dose core profiles measured for five energies at up to four depths from beam plateau to Bragg peak region. Nuclear halo profiles of single PBs were evaluated for three (62.4, 148.2, and 252.7 MeV) and two (97.4 and 124.7 MeV) energies, without and with RaShi, respectively. The influence of the dose core and nuclear halo on field sizes varying from 2–20 cm was evaluated by means of output factors (OFs), namely frame factors (FFs) and field size factors (FSFs), to quantify the relative increase of dose when increasing the field size.ResultsThe relative increase in the dose core width in the simulations deviated negligibly from measurements for depths until 80% of the beam range, but was overestimated by up to 0.2 mm in σ toward the end of range for all energies. The dose halo region of the lateral dose profile agreed well with measurements in the open beam configuration, but was notably overestimated in the deepest measurement plane of the highest energy or when the beam passed through the RaShi. The root‐mean‐square deviations (RMSDs) between the simulated and the measured FSFs were less than 1% at all depths, but were higher in the second half of the beam range as compared to the first half or when traversing the RaShi. The deviations in one of the two tested hadron physics lists originated mostly in elastic scattering. The RMSDs could be reduced by approximately a factor of two by exchanging the default elastic scattering cross sections for protons.ConclusionsGATE/Geant4 agreed satisfyingly with most measured quantities. MCS was systematically overestimated toward the end of the beam range. Contributions from nuclear scattering were overestimated when the beam traversed the RaShi or at the depths close to the end of the beam range without RaShi. Both, field size effects and calculation uncertainties, increased when the beam traversed the RaShi. Measured field size effects were almost negligible for beams up to medium energy and were highest for the highest energy beam without RaShi, but vice versa when traversing the RaShi.

Neutron Contamination Unexpected Dose in Varian LINAC

Introduction: Neutron contamination is very harmful for the patients receiving radiation therapy due to the high relative biological effect of neutrons. Medical linear accelerators head are made up of materials with high atomic numbers, and High-energy photons interaction with heavy materials can produce neutron contamination. In this study, neutron equivalent dose, neutron spectrum, and the effect of field size on neutron contamination dose is calculated by the FLUKA Monte Carlo code system. Materials and Methods: In this study, all parts of the Varian Clinac 2100 accelerator head’s elements, such as target, flattening filter, jaws, MLC, shields, primary and secondary collimators are simulated by the FLUKA code system. LINAC performance energy was considered 18MV and a water phantom with dimension of 140×140×35 cm3 was simulated for neutron dose calculation. To investigate the effect of field size on neutron contamination, larger treatment fields such as 10×10, 20×20, 30×30 and 40×40 was formed by the jaws, and the smaller ones like 1×1, 3×3 and 5×5 was formed by the MLC. Results: The results show that the Neutron contamination dose can be up to 2.54 mSv per 1Gy photon dose at isocenter. Neutron to photon dose ratio is 0.004 at isocenter and more than 8.6 in out-of-field areas. Furthermore, the neutron dose changes at the surface of the water phantom is only 15% that show the protective elements of the LINAC head are not able to control the neutron contamination flux. The most of neutron dose distribution is at the surface of the water phantom, So it can increases the secondary cancer risk in patients, including skin cancer. The effect of treatment field size on neutron contamination shows that the larger field size formed by the jaws contribute to higher in-field neutron dose, and using of smaller field size formed by the MLC, cause the lower in-field neutron dose. Conclusion: The neutron contamination dose can not be neglected, and the effective parameters in neutron contamination exasperation should be thoroughly investigated. Furthermore, the harmful effects of the neutron contamination should be minimized by the appropriate protective shields

Multi-path convolutional neural network for lung cancer detection

Lung cancer is the leading cause of death among cancer-related death. Like other cancers, the finest solution for lung cancer diagnosis and treatment is early screening. Automatic CAD system of lung cancer screening from Computed Tomography scan mainly involves two steps: detect all suspicious pulmonary nodules and evaluate the malignancy of the nodules. Recently, there are many works about the first step, but rare about the second step. Since the presence of pulmonary nodules does not absolutely specify cancer, the morphology of nodules such as shape, size, and contextual information has a sophisticated relationship with cancer, the screening of lung cancer needs a careful investigation on each suspicious nodule and integration of information of all nodules. We propose deep CNN architecture which differs from those traditionally used in computer vision to solve this problem. First, the suspicious nodules are generated with the modified version of U-Net and then the generated nodules become an input data for our model. The proposed model is a multi-path CNN which exploits both local features as well as more global contextual features simultaneously to automatically detect lung cancer. To this end, the model used three paths, each path employed different receptive field size which helps to model distant dependencies (short and long-range dependencies of the neighboring pixels). Then, to further upgrade our model performance, we concatenate features from the three paths. This balance the receptive field size effect and makes our model more adaptable to the variability of shape, size, and contextual information among nodules. Finally, we also introduce a retraining phase system that permits us to tackle difficulties related to the imbalance of image labels. Experimental results on Kaggle Data Science Bowl 2017 challenge shows that our model is better adaptable to the described inconsistency among nodules size and shape, and also obtained better detection results compared to the recently published state of the art methods.

Effect of Radiation Field Size and Dose on Local Control or Re-fracture Events after Post-Operative Radiation Following Intramedullary Nailing Procedures for Palliation of Bone Metastases

Pathologic fracture of long bones carries a heavy symptomatic burden in patients with metastatic malignancy. Standard therapy typically includes intramedullary nail placement to stabilize the bone, followed by palliative post-operative radiation therapy (PORT) to reduce the risk of re-fracture or local recurrence. The radiation dose and fields for this treatment approach have wide variation without uniform standards. We sought to estimate the distribution of PORT dose/fractionation, and field size, and estimate any potential association with the risk of re-fracture and/or local recurrence. We retrospectively analyzed patients treated at our institution with pathologic fractures of long bones, treated with intramedullary nailing of the femur, tibia, or humerus, followed by post-operative palliative radiation to that site. We stratified patients by radiation fractionation (single vs multi-fraction regimen) and by radiation field size (coverage of whole hardware [full-field] vs partial coverage of hardware [limited field]), to determine if these factors may be associated with the primary endpoint, which was defined as local re-fracture and/or local recurrence of disease within the long bone. Fisher’s exact test was used for statistical comparison due to the relative paucity of events. Eighty-six evaluable patients, treated between 2010 and 2017, were identified. Median patient age was 60 years. Median Karnofsky performance status was 70. Median follow up was 2.6 months (range, 2 weeks to 74 months). Radiation doses ranged from 8 – 30Gy, apart from one patient who received 45Gy in 3 Gy fractions. Thirty-six patients (42%) received 8 Gy in a single fraction, and fifty (58%) received multi-fraction treatment. Ten patients (12%) underwent limited field radiation, while 47 (55%) underwent full field radiation, and 29 (34%) were unevaluable for field size. Nine patients (10%) reached the primary endpoint of local recurrence and/or local refracture, consistent with historical comparison. On Fisher’s two-sided exact test, field size was not found to correlate with local recurrence/re-fracture (p=0.366). Local recurrence/re-fracture was also not significantly associated with multi-fraction radiation, compared to those who received 8 Gy in a single fraction, although was numerically worse in the multifraction group (p=0.073). Increased total dose beyond 8 Gy was not associated with improvement in local control. Similarly, irradiation of the entire hardware was not associated with improved rates of local control as compared to limited field radiation. Our findings suggest that single-fraction, limited-field palliative PORT may be sufficient to achieve adequate rates of local control, thereby allowing for expedient initiation of systemic therapy and minimal RT toxicity. Further evaluation is needed.

Surface Dose Measurements on an Indigenously Made Inhomogeneous Female Pelvic Phantom Using Metal-Oxide-Semiconductor-Field-Effect-Transistor Based Dosimetric System

Introduction: Megavoltage X-ray beams are used to treat cervix cancer due to their skin-sparing effect. Preferably, the radiation surface doses should be negligible; however, it increases due to electron contamination produced by various field parameters. Therefore, it is essential to provide proper knowledge about the effect of different field parameters on radiation doses. This study sought to find out the effect of various physical parameters on the surface doses. Materials and Methods: The effects of field size, source-to-surface distance, and open or acrylic block tray fields on surface doses were determined. Metal-Oxide-Semiconductor-Field-Effect-Transistor based dosimetric system was used for dose measurements for 6 MV photon beam. The directly measured radiation surface doses on pelvic phantom were compared to surface dose values computed by treatment planning system in the similar field parameters. Results: The measured results for the percentage depth dose (PDD0) in field size of 10x10 cm2 were 13.32%, 12.95% and 13.87% for open field and 36.87%, 36.31% and 35.88% for acrylic block tray field. In addition, the computed doses were 7.83%, 7.73% and 7.65% for open field and 16.33%, 16.12% and 15.88% for acrylic block tray field at 80 cm, 100 cm, and 120 cm SSDs, respectively. Conclusion: The surface dose increases along with the size of the field and decreases with increasing SSD. The surface doses in acrylic block tray fields were significantly higher than the open ones. The treatment planning system computed a lesser radiation doses in same field parameters.

A Gaze-Contingent Investigation of the Effect of Perceptual Field Size on Processing Identity and Expression of Faces

A Gaze-Contingent Investigation of the Effect of Perceptual Field Size on Processing Identity and Expression of Faces

Solar Hybrid Micro Gas Turbine Based on Turbocharger

The performance of solar hybrid Brayton cycle materialized by a micro-gas turbine based on a turbocharger is studied. The use of a turbocharger is aimed at investment cost reduction and construction simplification. Two configurations are investigated, namely hybrid and solar-only. Design aspects are discussed, in view of the requirement for minimizing the cost of electricity produced. A key parameter is the turbine inlet temperature and its effect on performance is investigated. The effect of heliostat field size is also investigated. Augmentation of the maximum temperature leads to better performance, as a result of higher cycle efficiency. Solar-only configuration features are compared with hybrid ones and the contribution of different cost components to the final electricity cost is discussed.

P125] First PDIP validation for stereotatic treatment control using FFF beams and EPID AS1000 on clinac

Objective Varian Medical System® proposes Portal dosimetry as an integrated solution to control modulated beam treatment. Among all Varian Electronic Portal Image Detectors (EPID), only the Portal Vision aS1200 allows verification of Flattening Filter-Free (FFF) treatment plans with PDIP algorithm. Many centers with a previous EPID, such as aS1000, are forced to use other methods for treatment verification. The purpose of this study is to verify the feasibility of setting up these controls by PDIP concerning the as1000 EPID model and modulated FFF beams performed on Varian Clinac. Materials/methods The EPID aS1000 response was studied for X6 FFF beams by analyzing SDD, linearity, field size, remanence and backscattering arm effects. PDIP algorithm was configured for pre-treatment verification of FFF beams at 1400 MU/min dose rate by placing the detector at SDD 150 cm to avoid saturation. The use of the Varian Portal Dosimetry software was validated using test plans provided by constructor. A retrospective study was carried out on 34 stereotactic treatment plans in VMAT X6 FFF corresponding to 140 beams. The plans were irradiated with the Varian Clinac 2300iX. Gamma analysis was performed on a Sun Nuclear ArcCheck® (Sun Nuclear, FL) plan control phantom. The gamma criteria of 2% 2 mm and 2.5% 2.5 mm for both global and local methods analysis were used. Results Dose linearity was within 0.99%. The backscattering arm effect results in asymmetries on the vertical dose profiles of 0.88 ± 0.36%. Integrated dose images had showed a remanence dose resulting on an overstatement of the dose of 0.38% at the maximum. The repeatability of the measurement showed mean dose deviations of 0.06 ± 0.17%. Conclusion The use of AS1000 and Clinac to measure FFF beams is a success. The locks due to the generation of the system have been lifted. The very complex and high dose field checks in VMAT type stereo allowed to validate the modeling. This solution saves measurement time, facilitates use, and improves spatial resolution which can be better than that in available 3D phantoms.

Validation of a virtual source model of medical linac for Monte Carlo dose calculation using multi-threaded Geant4

The use of phase space in medical linear accelerator Monte Carlo (MC) simulations significantly improves the execution time and leads to results comparable to those obtained from full calculations. The classical representation of phase space stores directly the information of millions of particles, producing bulky files. This paper presents a virtual source model (VSM) based on a reconstruction algorithm, taking as input a compressed file of roughly 800 kb derived from phase space data freely available in the International Atomic Energy Agency (IAEA) database. This VSM includes two main components; primary and scattered particle sources, with a specific reconstruction method developed for each. Energy spectra and other relevant variables were extracted from IAEA phase space and stored in the input description data file for both sources. The VSM was validated for three photon beams: Elekta Precise 6 MV/10 MV and a Varian TrueBeam 6 MV. Extensive calculations in water and comparisons between dose distributions of the VSM and IAEA phase space were performed to estimate the VSM precision. The Geant4 MC toolkit in multi-threaded mode (Geant4-[mt]) was used for fast dose calculations and optimized memory use. Four field configurations were chosen for dose calculation validation to test field size and symmetry effects, , , and for squared fields, and for an asymmetric rectangular field. Good agreement in terms of formalism, for 3%/3 mm and 2%/3 mm criteria, for each evaluated radiation field and photon beam was obtained within a computation time of 60 h on a single WorkStation for a 3 mm voxel matrix. Analyzing the VSM’s precision in high dose gradient regions, using the distance to agreement concept (DTA), showed also satisfactory results. In all investigated cases, the mean DTA was less than 1 mm in build-up and penumbra regions. In regards to calculation efficiency, the event processing speed is six times faster using Geant4-[mt] compared to sequential Geant4, when running the same simulation code for both. The developed VSM for 6 MV/10 MV beams widely used, is a general concept easy to adapt in order to reconstruct comparable beam qualities for various linac configurations, facilitating its integration for MC treatment planning purposes.

The field-size effect: Short motions look faster than long ones

Reducing the amount of motion information can surprisingly make motion look faster (e.g., motion behind Venetian blinds). We found that a textured pattern moving to the right at speeds ranging from 0.34 to 5.5°/s appeared to move 50% faster when viewed through a short (0.5°) compared with a long (4.5°) horizontal slot. Perceived speed varied inversely with the log of the slot length. We varied the length of rectangular apertures over a tenfold range and manipulated their size, shape, and orientation. We attribute the field-size effect mostly to landmarks provided by the ends of the slots, but we also examined temporal and spatial frequency and lateral inhibition of motion.

Shear Field Size Effect on Determining the Shear Modulus of Glulam beam

Research & Development in Material Science Shear Field Size Effect on Determining the Shear Modulus of Glulam beam Niaz Gharavi*, Murray MacCallum, Andrew MacIver, Ahmed Mohamed and Hexin Zhang School of Engineering and Built Environment, Edinburgh Napier University, UK *Corresponding author: Niaz Gharavi, School of Engineering and Built Environment, Edinburgh Napier University, 10 Colinton Road, EH10 5DT, UK Submission: February 13, 2018; Published: February 23, 2018 DOI: 10.31031/RDMS.2018.03.000575 ISSN: 2576-8840Volume3 Issue5

THE EXPERIMENTAL ASSESSMENT OF BUILD UP FACTOR AND ATTENUATION COEFFICIENT OF BRASS COMPENSATOR APPLIED IN INTENSITY-MODULATED RADIATION THERAPY (IMRT) FOR 6MV PHOTON BEAM

Introduction: Recent compensators are commonly applied in IMRT. The precise properties of applied compensators such as thickness, attenuation coefficient and build up factor are intensively important for IMRT calculations. Method: The brass compensator used for 6 MV photon beam was studied to estimate the relative effect of thickness and field size on IMRT calculations. Various field size together with several compensator thicknesses were examined. Result: The average reduction of effective attenuation coefficient (EAC), for the fields of 10A—10 cm2 to 20A—20 cm2, was 9.94%. By increasing the field size, EAC was decreased. The major reduction of EAC due to increasing field size was found to be 9.62%. The build up factor was increased by 2% to 21.8% respect to field size and compensator thickness. Also, the build up factor was increased by adding up the thickness. The rate of changes ranged from 24% to 48 %. Conclusion: The compensator thickness and field size are significantly important to calculate the effective attenuation coefficient and build up factor.

The ‘cutting away’ of potential secondary electron tracks explains the effects of beam size and detector wall density in small-field photon dosimetry

The well-known field-size dependent overresponse in small-field photon-beam dosimetry of solid-state detectors equipped with very thin sensitive volumes, such as the PTW microDiamond, cannot be caused by the photon and electron interactions within these sensitive layers because they are only a few micrometers thick. The alternative explanation is that their overresponse is caused by the combination of two effects, the modification of the secondary electron fluence profile (i) by a field size too small to warrant lateral secondary electron equilibrium and (ii) by the density-dependent electron ranges in the structural detector materials placed in front of or backing the sensitive layer. The present study aims at the numerical demonstration and visualization of this combined mechanism.The lateral fluence profiles of the secondary electrons hitting a 1 µm thick scoring layer were Monte-Carlo simulated by modelling their generation and transport in the upstream or downstream adjacent layers of thickness 0.6 mm and densities from 0.0012 to 3 g cm−3, whose atomic composition was constantly kept water-like. The scoring layer/adjacent layer sandwich was placed in an infinite water phantom irradiated by circular 60Co, 6 MV and 15 MV photon beams with diameters from 3 to 40 mm.The interpretation starts from the ideal case of lateral secondary electron equilibrium, where the Fano theorem excludes any density effect. If the field size is then reduced, electron tracks potentially originating from source points outside the field border will then be numerically ‘cut away’. This geometrical effect reduces the secondary electron fluence at the field center, but the magnitude of this reduction also varies with the density-dependent electron ranges in the adjacent layers. This combined mechanism, which strongly depends on the photon spectrum, explains the field size and material density effect on the response of detectors with very thin sensitive layers used in small-field photon-beam dosimetry.

Thermoeconomic assessment of a solar polygeneration plant for electricity, water, cooling and heating in high direct normal irradiation conditions

A thermoeconomic assessment of the joint production of electricity, fresh-water, cooling and heat for a solar polygeneration plant is carried out. The aims are to assess the actual cost of each product, to conduct a sensitivity analysis of investment, fuel cost and demand, and to evaluate the effects of solar field size and the sizing of thermal energy storage, for a polygeneration plant located in an area with high solar irradiation conditions and where there is demand for its production. The solar polygeneration plant is configured by a concentrated solar power (CSP) parabolic trough collector field with thermal energy storage and backup system, multi-effect distillation (MED) module, single-effect absorption refrigeration module, and process heat module. The solar polygeneration plant is simulated in a transient regime, in a representative location with high irradiation conditions, such as in northern Chile. Three configurations are investigated: two polygeneration schemes and one considering stand-alone systems. This study reveals that a solar polygeneration plant is more efficient and cost-effective than stand-alone plants for a zone with high irradiation conditions and proximity to consumption centers, such as mining industries, which require continuous operation and energy supply with fundamentally constant demand. Furthermore, according to northern Chilean market, solar polygeneration configurations are competitive regarding electricity, fresh-water, cooling and heat productions. Additionally, solar polygeneration plants can increase the economic profit by selling carbon credits and credits of renewable-energy quotas based on the Kyoto Protocol and Chilean legislation, respectively.

Evaluation of Therapeutic Properties of a Low Energy Electron Beam Plus Spoiler for Local Treatment of Mycosis Fungoides: A Monte Carlo Study

Background: When using low-energy electron beams for the treatment of skin lesions, such as Mycosis Fungoides (MF), a beam spoiler is used to decrease electron therapeutic depth (R90) while increasing the surface dose.Objective: The aim of this study was to evaluate the characteristics of a 5 MeV electron beam when using a spoiler for the local treatment of MF skin lesions by Monte Carlo (MC) simulation.Material and Methods: In this experimental study, a Siemens Primus treatment head and an acrylic spoiler, positioned at the end of applicator, were simulated using BEAMnrc, an EGSnrc user code. The modelled beam was validated by measurement using MP3-M water tank, Roos parallel plate chamber and Semi flex Chamber-31013 (all from PTW, Freiburg, Germany). For different spoiler thicknesses, dose distributions in water were calculated for 2 field sizes and were compared to those for the corresponding open fields.Results: For a 1.3 cm spoiler, therapeutic range changed from 1.5 cm (open field) to 0.5 cm and 0.4 cm for 10 × 10 cm2 and 20 × 20 cm2 field sizes, respectively. Maximum increase in penumbra width was 2.8 and 3.8 cm for 10 × 10 cm2 and 20 × 20 cm2 field sizes, respectively. Maximum increase in bremsstrahlung contamination was %2 in both field sizes.Conclusion: R90 decreased exponentially with increase in spoiler thickness. The effect of field size on penumbra was much larger for spoiled beam compared to the open beam. The results of this research can be applied to optimize the radiation treatment of MF patients in our hospital.

Experimental determination of stereotactic cone size and detector specific output correction factor

Objective: To investigate the effect of intermediate field size , volume of reference ionization chamber (IC) and normalization conditions on output factor measurement using small field detectors (SDs) and derive correction factors for active and passive detectors. Methods: Measurements were made on Novalis-Tx accelerator for 6 MV photon at 1000 MU min–1. Six active SDs, high resolution diodes (SFD, EDGE, PTW 60008), CC01 IC, PTW 60003 natural diamond, Exradin W1 plastic scintillator and two passive detectors (Al2O3:C nanoDot-OSLD and Gafchromic EBT3 films) were used for measurement from small circular cones having 4 to 15 mm diameter. Effect of the choice of ranging from 20 × 20mm2 to 40 × 40 mm2 and reference ICs (FC65, PPC40, CC13) volume on was investigated for all active SDs. Influence of direct normalization at reference field of 40 × 40mm2 or 100 × 100 mm2 and indirect normalization at 100 × 100 mm2 through using Daisy-chain strategy on was also investigated. was calculated as ratio of the of each SDs relative to Gafchromic EBT3. Results: For any combination of SDs and reference ICs, selection of of 40 × 40 mm2 will result in variation to within ±1.8%. Indirect normalization at 100 × 100 mm2 through of 40 × 40 mm2 and direct normalization at 40 × 40 mm2 showed comparable (≤2%) results for EDGE, PTW 60008 and CC01. Whereas, for PTW 60003 and Exradin W1 direct and indirect normalization at 100 × 100 mm2 agrees within −2%. measurement by SDs following Daisy-chain strategy shows deviation as large as 23% for 4 mm cone which reduces to <2% for cone size >10 mm except for nanoDot. The calculated is least for SFD (0.992–1.013) and largest for nanoDot (1.047–1.294) which reduces to 0.99–1.023 after correcting for volume averaging effect. The long-term standard uncertainty (k = 2, 95%CI) was largest for nanoDot (2.93%) and least for PTW60003 (0.11%). Conclusion: Medium size IC is less sensitive to and could be a better alternative to standard volume ICs. Minimum of 40 × 40 mm2 is suggested in Daisy-chain strategy. Different normalization conditions could lead to variation measured by same SD up to ±5%. varies largely with cone size and detector volume. Advances in knowledge: Comprehensive study of the influencing parameters and conditions on measurement from single data set and estimation of for newly emerging detectors.

Cotton Flower-visiting Insects in Small-scale Farm Fields in Mwachisompola, Zambia

Global declines in wild and managed pollinator species have increased the need to evaluate the current status of these populations and understand their needs for sustainability. Farming systems can be a useful place to examine the presence and activity of flower-visiting insects, because the blooming period of the crop provides a predictable floral resource which serves as an attractant to some species. The density and species richness of cotton flower-visiting insects were measured in five conservation and five conventional cotton fields in Mwachisompola, Zambia. Between the two farm types, density and species richness were not significantly different; however, only 33% of the total observed species were found within both farm systems. We found a significant negative relationship between species richness and field size regardless of farm type. Our results suggest that cotton fields attract both pollinator and predatory flower-visiting insects regardless of management, however more work is needed to better understand the effects of field size and surrounding natural areas.

Thermal conductivity of vitreous silica from molecular dynamics simulations: The effects of force field, heat flux and system size.

The thermal conductivity of vitreous silica is computed using the direct method in molecular dynamics simulations with three sets of empirical force fields, including the BKS, Teter, and ReaxFF, to investigate their performance in thermal characterization. Various heat flux and system sizes are used in the simulations to evaluate the statistical uncertainty and the finite-size effect. While all these potentials can reproduce realistic silica structures, the ReaxFF provides better agreement with experiments at 300 K than the BKS and Teter, which is due to its improved description of low-frequency vibrations. Increasing the heat flux and cross-sectional area tends to reduce the calculated standard deviation induced by thermal fluctuations, thus contributing to more accurate thermal conductivity predictions.