Heterogeneous Correction Research Articles

Comparison of Monte Carlo tally techniques for dosimetry in a transmission-type x-ray tube.

This study discussed comparing result accuracy and time cost under different tally methods using MCNP6 for a novel transmission x-ray tube which was designed for the Auger electron yield with specific material (e.g. iodine). The assessment included photon spectrum, percent depth dose, mass-energy absorption coefficient corresponding to air and water, and figure of merit comparison. The mean energy of in-air phantom was from 41.8 keV (0 mm) to 40.9 keV (100 mm), and the mean energy of in-water phantom was from 41.41 keV (0 mm) to 45.2 keV (100 mm). The specific dose conversion factors based mass-energy absorption coefficient corresponding to different materials was established and the difference was less than 2% for the dose conversion of FMESH comparing to measurement data. FMESH had better figure of merit (FOM) than the F6 tally for the dose parameter assessment, which mean the dose calculation that focused on the superficial region could be assessed with more calculation efficiency by FMESH tally for this novel transmission x-ray tube. The results of this study could help develop treatment planning system (TPS) to quickly obtain the calculated data for phase space data establishment and heterogeneous correction under different physical condition settings.

Experimental validation of absorbed dose-to-medium calculation algorithms in heterogeneous media.

Objective.The aim of this work was to determine heterogeneous correction factors h[fclin,frefQclinQref]m,wdetto validate absorbed dose-to-medium Dm,fclinm,Qclincalculation algorithms from detector readings. The impact of detector orientation perpendicular and parallel to the beam central axis on the correction factors was also investigated.Approach.The h[fclin,frefQclinQref]m,wdetfactors were calculated for four types of detectors (PTW PinPoint T31016, PTW microDiamond T60016, PTW microSilicon T60023 and EBT3 film) placed in different media (cortical bone, lung, Teflon, adipose tissue and RW3) for the 6 MV energy beam with a 10x10 cm2field size. These corrections were then applied to the detector measurements performed at different depths in heterogeneous phantoms.Main results.The h[fclin,frefQclinQref]m,wdetfactors mainly depended on the media and slightly on the type of detector. Considering all detectors, the largest corrections were found in high-density media with values ranging from 0.911 to 0.934 in cortical bone. For comparison, the corrections in other media were closer to unity with values from 0.966 (lung and RW3) to 0.991 (adipose tissue). Except for the PinPoint T31016, detector orientation-dependence was observed especially in high-density media. A good agreement (≤ 1.5%) was found between Dm,fclinm,Qclincalculations and the detector readings corrected with the h[fclin,frefQclinQref]m,wdetfactor for all studied heterogeneous phantoms.SignificanceThis paper could serve as an initial guideline for medical physicists involved in the validation of the advanced type-b dose calculation algorithms reporting Dm,fclinm,Qclin. To our knowledge, this is the first study to assess the impact of the orientation of different detectors in heterogeneous media. The orientation dependence of the detector response observed in water may not reflect what is observed in heterogeneous media, especially in high-density media. The knowledge of the h[fclin,frefQclinQref]m,wdetfactors becomes mandatory for accurate interpretation of detector readings and comparisons with Dm,fclinm,Qclincalculations.

Heterogeneous InSAR Tropospheric Correction Based on Local Texture Correlation

Heterogeneous InSAR Tropospheric Correction Based on Local Texture Correlation

Transient expression of an adenine base editor corrects the Hutchinson-Gilford progeria syndrome mutation and improves the skin phenotype in mice

Hutchinson-Gilford progeria syndrome (HGPS) is a rare premature ageing disorder caused by a point mutation in the LMNA gene (LMNA c.1824 C > T), resulting in the production of a detrimental protein called progerin. Adenine base editors recently emerged with a promising potential for HGPS gene therapy. However adeno-associated viral vector systems currently used in gene editing raise concerns, and the long-term effects of heterogeneous mutation correction in highly proliferative tissues like the skin are unknown. Here we use a non-integrative transient lentiviral vector system, expressing an adenine base editor to correct the HGPS mutation in the skin of HGPS mice. Transient adenine base editor expression corrected the mutation in 20.8-24.1% of the skin cells. Four weeks post delivery, the HGPS skin phenotype was improved and clusters of progerin-negative keratinocytes were detected, indicating that the mutation was corrected in both progenitor and differentiated skin cells. These results demonstrate that transient non-integrative viral vector mediated adenine base editor expression is a plausible approach for future gene-editing therapies.

Testing for the Bidirectional Relationship Between FDI in Services and Trade in Services: Evidence from Emerging Economies

We examine the two-way links between foreign direct investments (FDI) in services and trade in services for 26 emerging economies from 2003 to 2015 using sectoral and sectoral disaggregated FDI data. Within a multivariate framework, we use panel unit root tests, recently developed heterogeneous panel cointegration and panel vector error correction model (VECM). Our results confirmed the cointegrating relationship between trade in services, FDI in services, financial services FDI and nonfinancial services FDI. We find the existence of long-run unidirectional causality from trade in services to FDI in services. However, the disaggregated analysis shows a bidirectional link between nonfinancial services FDI and trade in services in the short run. Still, there is no causality between financial services FDI and trade in services both in the short run and long run. The result also shows the evidence of unidirectional causality running from trade in services to nonfinancial services FDI in the long run. It implies that sectoral decomposition matters in the FDI–trade nexus in emerging economies. JEL Codes: G20, F14, G20, F23

The Influence of Heterogeneity on Lunar Irradiance Based on Multiscale Analysis

The Moon is a stable light source for the radiometric calibration of satellite sensors. It acts as a diffuse panel that reflects sunlight in all directions, however, the lunar surface is heterogeneous due to its topography and different mineral content and chemical composition at different locations, resulting in different optical properties. In order to perform radiometric calibration using the Moon, a lunar irradiance model using different observation geometry is required. Currently, two lunar irradiance models exist, namely, the Robotic Lunar Observatory (ROLO) and the Miller and Turner 2009 (MT2009). The ROLO lunar irradiance model is widely used as the radiometric standard for on-orbit sensors. The MT2009 lunar irradiance model is popular for remote sensing at night, however, the original version of the MT2009 lunar irradiance model takes less consideration of the heterogeneous lunar surface and lunar topography. Since the heterogeneity embedded in the lunar surface is the key to the improvement of the lunar irradiance model, this study analyzes the influence of the heterogeneous surface on the irradiance of moonlight based on model data at different scales. A heterogeneous correction factor is defined to describe the impact of the heterogeneous lunar surface on lunar irradiance. On the basis of the analysis, the following conclusions can be made. First, the influence of heterogeneity in the waning hemisphere is greater than that in waxing hemisphere under all 32 wavelengths of the ROLO filters. Second, the influence of heterogeneity embedded in the lunar surface exerts less impact on lunar irradiance at lower resolution. Third, the heterogeneous correction factor is scale independent. Finally, the lunar irradiance uncertainty introduced by topography is very small and decreases as the resolution of model data decreases due to the loss of topographic information.

Reliability of 3D memories using Orthogonal Latin Square codes

Radiation is a cause of errors in electronics systems, especially on those deployed in space. Memories can suffer from different radiation effects including Single Event Upsets and Multiple Cell Upsets. These effects produce corruption of data and may cause a system malfunction. 3D die-stacked memories have been designed to increase bandwidth, reduce latency and limit power consumption. The shielding characteristic of the 3D structure causes a heterogeneous fault tolerance behaviour of the system where some of the inner dies are invulnerable while the outer dies require different protection levels. Orthogonal Latin Square codes are a class of error correcting codes that are modular and can provide different error correction degrees depending on the number of parity bits used. This paper proposed a solution based on current standards to provide dynamic and heterogeneous error correction capabilities to a 3D memory. To do so, Orthogonal Latin Square codes are used.

Who is Picking Up the Child from Day Care?: Understanding the Intrahousehold Dynamics in Drop-Off and Pickup Allocation for Households with Dependent Children

This paper presents a joint model for the allocation of drop-off and pickup responsibilities and the choice of the day care location for two-adult households with dependent children. This analysis aims to capture the trade-offs that occur at the household level in the selection of both day care location and drop-off and pickup responsibility allocation. The paper uses a stochastic frontier modeling approach to predict feasible locations for each possible allocation pair. The frontier model predicts the maximum distance an individual would be willing to travel within a time budget constraint. This travel time prediction is then applied to each individual for generating feasible location sets given two endogenous anchor points. The paper then presents a joint econometric-choice model of task allocation and day care location with heterogeneous sampling correction factors for each possible allocation. Captured within the model are the choice of who performs the drop-off and pickup activities and the eventual location that is selected for day care. The model structure provides key insights into both the choice to use day care and the allocation of drop-off and pickup responsibilities.

Analysis and improvement of Brinkman lattice Boltzmann schemes: bulk, boundary, interface. Similarity and distinctness with finite elements in heterogeneous porous media.

This work focuses on the numerical solution of the Stokes-Brinkman equation for a voxel-type porous-media grid, resolved by one to eight spacings per permeability contrast of 1 to 10 orders in magnitude. It is first analytically demonstrated that the lattice Boltzmann method (LBM) and the linear-finite-element method (FEM) both suffer from the viscosity correction induced by the linear variation of the resistance with the velocity. This numerical artefact may lead to an apparent negative viscosity in low-permeable blocks, inducing spurious velocity oscillations. The two-relaxation-times (TRT) LBM may control this effect thanks to free-tunable two-rates combination Λ. Moreover, the Brinkman-force-based BF-TRT schemes may maintain the nondimensional Darcy group and produce viscosity-independent permeability provided that the spatial distribution of Λ is fixed independently of the kinematic viscosity. Such a property is lost not only in the BF-BGK scheme but also by "partial bounce-back" TRT gray models, as shown in this work. Further, we propose a consistent and improved IBF-TRT model which vanishes viscosity correction via simple specific adjusting of the viscous-mode relaxation rate to local permeability value. This prevents the model from velocity fluctuations and, in parallel, improves for effective permeability measurements, from porous channel to multidimensions. The framework of our exact analysis employs a symbolic approach developed for both LBM and FEM in single and stratified, unconfined, and bounded channels. It shows that even with similar bulk discretization, BF, IBF, and FEM may manifest quite different velocity profiles on the coarse grids due to their intrinsic contrasts in the setting of interface continuity and no-slip conditions. While FEM enforces them on the grid vertexes, the LBM prescribes them implicitly. We derive effective LBM continuity conditions and show that the heterogeneous viscosity correction impacts them, a property also shared by FEM for shear stress. But, in contrast with FEM, effective velocity conditions in LBM give rise to slip velocity jumps which depend on (i) neighbor permeability values, (ii) resolution, and (iii) control parameter Λ, ranging its reliable values from Poiseuille bounce-back solution in open flow to zero in Darcy's limit. We suggest an "upscaling" algorithm for Λ, from multilayers to multidimensions in random extremely dispersive samples. Finally, on the positive side for LBM besides its overall versatility, the implicit boundary layers allow for smooth accommodation of the flat discontinuous Darcy profiles, quite deficient in FEM.

Simulation and experimental verification of a hydrodynamic model for a dual fluidized Bed gasifier

We propose a revised 2-D energy-minimization multi-scale (EMMS) model based on a two-fluid model to perform the hydrodynamic character analysis of a pilot-scale full-loop dual fluidized bed gasifier (DFBG), which consists of a riser, a cyclone with a down-comer, a bubbling fluidized bed (BFB), and a loop-seal. The EMMS model is used to analyze the interaction force between the gas and solid phases in the DFBG. For comparison, O'Brien & Syamlal's drag heterogeneous force coefficient correction is also analyzed. The instantaneous particle profiles are described by the calculated results. The local and overall flow characteristics are determined by the solids concentration under different fluidization conditions. The effects of the gas velocities in the riser and the recycle gas velocities in the U loop seal on the axial solids concentration and solids circulation profiles, as well as the flow heterogeneity in sub-zones of the riser are investigated. The numerical results are in good agreement with the experimental data, indicating that the EMMS model is appropriate to simulate the heterogeneous gas–solids two-phase flow in DFBG.

Short-run and long-run effects of exchange rate change on trade balance: Evidence from China and its trading partners

As one of largest exporting countries in the world, China has experienced a large amount of trade surpluses for the past decade. However, a growing criticism has been focused on the manipulation of Chinese Yuan (RMB) exchange rate by the Chinese government. While China implemented the exchange rate reform policy in July 2005, the question, whether its currency is undervalued remains as a debatable issue. Different from previous studies by focusing on individual trading partners, this paper tests the short-run J-Curve hypothesis and long-run trade balance effect of real exchange rate between China and its eighteen major trading partners using a panel dataset over the 2005–2009 period. We adopt the methodologies of panel cointegration test, fully modified OLS for heterogeneous cointegrated panel (panel FMOLS) and panel error correction model (panel ECM) to investigate the above examination. Our empirical results lend support to the inverted J-curve hypothesis between China and its trading partners. However, we find that a real appreciation of RMB has a decreasing long-run effect on China's trade balance in only three of the eighteen trading partners, while it has an increasing long-run effect in five of the eighteen trading partners. These mixed findings, therefore, lead to the empirical evidence that the real appreciation of RMB has no overall long-run impact on China's trade balance.

Geometric Integration of Heterogeneous Models for Multisatellite Image Positioning

With the wider availability of more and more images acquired from various satellites, the integration of different orientation models for different sensors has become an important task in order to maintain geometrical consistency. This study combines two heterogeneous geometric correction models, namely, direct georeferencing and the rational function model for multisatellite image positioning. Two types of adjustment models, collocation-based block adjustment (CBBA) and collocation-aided block adjustment (CABA), are proposed to reach the goal. The former is based on the concept that the adjustment is first performed on individual images, and then, all images are integrated. Discrepancies are compensated for by least squares collocation (LSC). The latter method entails simultaneous adjustment of the two heterogeneous models followed by LSC. Experimental results indicate that the proposed method can significantly improve the geometric accuracy as well as reduce geometric discrepancies between images. We also demonstrate that CABA is slightly better than CBBA.

SU‐E‐T‐444: Feasibility Study of In‐Vivo Transit Dosimetry for IMRT Patients

Purpose: The ultimate goal of IMRT QA should be to verify that the correct dose has been delivered to the patient. The purpose of this study is to evaluate for feasibility and reliability of volumetric transit dosimetry as a routine in‐vivo dosimetry method during the actual patient treatment for different sites. Methods: To evaluate volumetric transit dosimetry for IMRT delivery, prostate, H&N and lung IMRT cases were selected. During patient treatment, the EPID imager was extended to collect transit radiation through the patient. Collected transit dose images are imported and reconstructed as a volumetric dose distribution using the Dosimetry Check (Math Resolutions LLC, Maryland, USA) Exit Dose module. Dosimetry Check program to compare to the reconstructed volumetric dose including tissue heterogeneous correction from the transit EPID images. Also, to investigate the influence of daily setup or anatomy change, multiple transit dosimetry measurements were performed on different treatment days up to 5 fractions for prostate case. In addition, patientˈs verification plan was generated on a homogeneous CIRS IMRT phantom to verify the absolute dose and transit dosimetry algorithm check. Collected QA results were evaluated with 1) gamma passing rate (3 mm DTA and 3% dose) comparing calculated dose from exit dosimetry and treatment planning system (TPS) dose prediction, 2) difference of absolute point dose from exit dosimetry module compared to ion chamber measurements in the phantom. Results: The current implementation shows promise at predicting point doses from exit dose images acquired during patient treatment. However, 3D dose distributions calculated from exit dose images are not consistent in their agreement with the planned dose distribution. Conclusions: Further study is needed to explain the differences. Areas to consider include offsets in imager position, differences in dose calculation algorithm, couch attenuation effects and anatomy changes.

SU‐E‐T‐676: Dosimetric Dependence on Variations of the Lung Density and Geometry: A Monte Carlo Evaluation Using Virtual Dynamic Heterogeneous Phantom

Purpose: This Monte Carlo study investigates the dosimetry of the lung—soft tissue interface under different lung geometries using virtual dynamic heterogeneous phantoms. Methods: 6 and 18 MV photon beams (field sizes = 4×4 and 10×10 cm2), produced by a Varian 21EX linac were used. Three lung phantoms namely slab, column and cube representing different lung geometries were irradiated by the photon beams. The lung volume and density were varied in five phases mimicking the lung motion in breathing. The lung density was set to 0.15, 0.2, 0.25, 0.3 and 0.35 g/cc corresponding to phases 1 to 5 with the lung volume changed while keeping the lung mass constant. Relative depth doses and beam profiles for each phantom in the five phases were calculated using the DOSXYZnrc. Results: Our results show that there is obvious dosimetric variation around the lung—soft tissue interface among the five phases in the three lung phantoms. This is due to the positional and density change of the interface. Interpolation was done to register all dose distributions in the five phases to one in order to compare with the dosimetry of a static lung phantom (e.g. only phase 3 with lung density = 0.25 g/cc). Dose deviation was found to be about ±5%, when a breathing lung with changes of volume and density was considered. Moreover, the deviation is more significant for photon beams of relatively higher energy (18 MV) and smaller field size (4×4 cm2). Conclusions: Through Monte Carlo studies of lung heterogeneous correction, we concluded that more realistic dosimetry may be acquired by considering a virtual dynamic phantom to mimic the breathing motion. The accuracy of the lung motion can further be improved by increasing the number of phase and applying weight factor to each phase in the breathing cycle.

放射線治療計画ＣＴにおけるＣＴ値―電子密度変換方法に関する調査

To obtain heterogeneous corrections, it is necessary to convert computed tomography (CT) values into electron density. However, differences in the current conversion tables of the method of acquisition for each institution are not clear. Therefore, we sent a questionnaire survey to 200 radiotherapy institutions in the Kanto area regarding heterogeneous correction data acquisition. When these conversion tables were created, many institutions used phantoms for conversion, and 85% of institutions borrowed them from the factories. On the other hand, some institutions used the factory values as the other conversion method. In the conversion tables of the various institutions, we recognized large differences between institutions, in that relative electronic density (Rel.ED) was greater than 1.0. When we assumed the CT value of bone to be 793 HU, the mean relative electron density at 120 kV was 1.46+/-0.09, with a minimum of 1.36 and maximum of 1.82. We have recognized the need to create guidelines detailing these methods of evaluation.

New panel results on cointegration of international health expenditure and GDP

This article tests for existence of cointegration between health expenditure and GDP using data from 25 OECD countries for the period 19607ndash;1997. The empirical modelling is based on a heterogeneous bivariate vector error correction panel model that allows for trending data as well as intercepts and trends in the cointegrating relations. Univariate country-by-country and panel unit root tests generally fail to reject the null of a unit root in the health expenditure and GDP variables. Country-by-country results based on the Johansen multivariate likelihood-based inference indicate somewhat mixed results on country-specific cointegration with a rank of one found for 12 countries and a rank of zero for the remaining 13 countries. Application of a new panel test for cointegration rank with higher power than the individual tests indicates that health expenditure and GDP are cointegrated around linear trends.

Transmission based heterogeneous attenuation correction of myocardial perfusion scans in comparison to dedicated emission equipment

Transmission based heterogeneous attenuation correction of myocardial perfusion scans in comparison to dedicated emission equipment

新しい 3 次元不均質補正線量分布計算 : Modified Equivalent TMR Method : (第二報) ビーム中心軸外の線量計算

A new three-dimensional (3-D) computation algorithm, "Modified equivalent TMR method", for photon beam dose calculation considering the heterogeneous correction has been developed. This algorithm in based on the modified equivalent TAR method that was proposed by Inamura et al. The modified equivalent TMR method has two calculation modes; the scatter mode which takes account for the 3-D contribution of scattered radiation and the non-scatter mode which doesn't. The dose distributions on off-central axis can be obtained from a approximate expression using the penumbra factor suggested by Shribastava and Cunningham. The purpose of this study is to evaluate the accuracy of dose computations using of this new algorithm. The accuracy is compared with both calculations and measurements on off-central axis for Cobalt-60 gamma rays and 10MV photon beams for various geometries and field sizes. Using the modified equivalent TMR method, we could show that the accuracy of 3-D dose computation on off-central axis with the scatter mode in unit-density phantom agreed with measured the data within 6%. For rectangular and irregular fields, this algorithm based on the scatter mode is accurate to a satisfactory lenel, while calculations on the off-central axis within the low density medium used two algorithm are inadequate in situation of electron disequilibrium, in particular near the beam edge. To satisfy the routine clinical needs of radiation therapy, it is highly desirable to develop a satisfactory approximation to situation of electron disequilibrium. In particular with present-day computers, it may take days of computation to obtain an accurate dose distribution in a single inhomogeneous medium. For new calculating algorithm that we have been developed, it may be applied with a suitable accuracy and reasonable computation time except for the electron disequilibrium regions.

Saccharification of concentrated brewing bagasse slurries with dilute sulfuric acid for producing acetone–butanol by Clostridium acetobutylicum

A comprehensive kinetic study of the acid hydrolysis of concentrated brewing bagasse slurries was performed. The use of the simple series reaction model was found to be suitable when a "heterogeneous correction" (pseudosubstrate-inhibition) is taken into account in slurries with low liquid-to-biomass ratios. Rate constants are shown to be dependent not only on temperature and acid concentration but essentially also on the initial biomass concentration. Actual rate constants, activation energies, and acid and substrate reaction orders are reported for xylan, arabinan, and alpha-glucan acid saccharification. There is a threshold acid loading necessary to overcome the 80% conversion, but no threshold has been found to overcome the "neutralizing" property of cellulosic materials. Reversible acid capture from brewing bagasse has been postulated. The highest monosccharide concentration into hydrolyzates has been found (65 g/L) after 10 h treatment, but economic considerations led us to treat a mean-concentrated slurry (156 g/L) with 0.3M H(2)SO(4) at 96 degrees C, thus obtaining 45.5 g/L monosaccharides in 5 h with 50% less furfural content. After pH regulation only, growth of Clostridium acetobutylicum has been obtained, although complete sugar comsumption has not been achieved. Experiments are now underway to reach complete digestion and to investigate the increase of enzymic accessibility into residual substrate rich in cellulose.