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DOE OSTI2014

Systematic investigation on topological properties of layered GaS and GaSe under strain

The topological properties of layered β-GaS and ε-GaSe under strain are systematically investigated by ab initio calculations with the electronic exchange-correlation interactions treated beyond the generalized gradient approximation (GGA). Based on the GW method and the Tran-Blaha modified Becke-Johnson potential approach, we find that while ε-GaSe can be strain-engineered to become a topological insulator, β-GaS remains a trivial one even under strong strain, which is different from the prediction based on GGA. The reliability of the fixed volume assumption rooted in nearly all the previous calculations is discussed. By comparing to strain calculations with optimized inter-layer distance, we find that the fixed volume assumption is qualitatively valid for β-GaS and ε-GaSe, but there are quantitative differences between the results from the fixed volume treatment and those from more realistic treatments. This work indicates that it is risky to use theoretical approaches like GGA that suffer from the band gap problem to address physical properties, including, in particular, the topological nature of band structures, for which the band gap plays a crucial role. In the latter case, careful calibration against more reliable methods like the GW approach is strongly recommended.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2017

Efficient Scalable Parallel Higher Order Direct MoM-SIE Method With Hierarchically Semiseparable Structures for 3-D Scattering

A novel fast scalable parallel algorithm is proposed for the solution of large 3-D scattering problems based on: 1) the double (geometrical and current-approximation) higher order (DHO) method of moments (MoM) in the surface integral equation (SIE) formulation and 2) a direct solver for dense linear systems utilizing hierarchically semiseparable (HSS) structures. Namely, an HSS matrix representation is used for compression, factorization, and solution of the system matrix. In addition, a rank-revealing QR decomposition for memory compression is used, with a stopping criterion in terms of the relative rank tolerance value. One method for geometrical preprocessing of the scatterers based on the cobblestone distance sorting technique is employed in order to enhance the HSS algorithm accuracy and parallelization. Numerical examples show how the accuracy of the DHO HSS-MoM-SIE method is easily controllable by using the relative tolerance for the matrix compression. Furthermore, the examples demonstrate low memory consumption, as well as much faster simulation time, when compared to the direct LU decomposition. The method enables dramatically faster monostatic scattering computations than iterative solvers and reduced number of unknowns when compared to low-order discretizations. Finally, great scalability of the algorithm is demonstrated on more than one thousand processes.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2015

Feasibility and robustness of dose painting by numbers in proton therapy with contour-driven plan optimization

Purpose: To prove the ability of protons to reproduce a dose gradient that matches a dose painting by numbers (DPBN) prescription in the presence of setup and range errors, by using contours and structure-based optimization in a commercial treatment planning system. Methods: For two patients with head and neck cancer, voxel-by-voxel prescription to the target volume (GTV{sub PET}) was calculated from {sup 18}FDG-PET images and approximated with several discrete prescription subcontours. Treatments were planned with proton pencil beam scanning. In order to determine the optimal plan parameters to approach the DPBN prescription, the effects of the scanning pattern, number of fields, number of subcontours, and use of range shifter were separately tested on each patient. Different constant scanning grids (i.e., spot spacing = Δx = Δy = 3.5, 4, and 5 mm) and uniform energy layer separation [4 and 5 mm WED (water equivalent distance)] were analyzed versus a dynamic and automatic selection of the spots grid. The number of subcontours was increased from 3 to 11 while the number of beams was set to 3, 5, or 7. Conventional PTV-based and robust clinical target volumes (CTV)-based optimization strategies were considered and their robustness against range and setup errors assessed. Because of the nonuniform prescription, ensuring robustness for coverage of GTV{sub PET} inevitably leads to overdosing, which was compared for both optimization schemes. Results: The optimal number of subcontours ranged from 5 to 7 for both patients. All considered scanning grids achieved accurate dose painting (1% average difference between the prescribed and planned doses). PTV-based plans led to nonrobust target coverage while robust-optimized plans improved it considerably (differences between worst-case CTV dose and the clinical constraint was up to 3 Gy for PTV-based plans and did not exceed 1 Gy for robust CTV-based plans). Also, only 15% of the points in the GTV{sub PET} (worst case) were above 5% of DPBN prescription for robust-optimized plans, while they were more than 50% for PTV plans. Low dose to organs at risk (OARs) could be achieved for both PTV and robust-optimized plans. Conclusions: DPBN in proton therapy is feasible with the use of a sufficient number subcontours, automatically generated scanning patterns, and no more than three beams are needed. Robust optimization ensured the required target coverage and minimal overdosing, while PTV-approach led to nonrobust plans with excessive overdose. Low dose to OARs can be achieved even in the presence of a high-dose escalation as in DPBN.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2016

Squeeze flow between a sphere and a textured wall

The motion of a millimetric sphere, translating in a viscous fluid towards a wettable textured wall, is investigated experimentally. The textures consist of square arrays of cylindrical or square micro-pillars, the height, width, and spacing of which are varied, keeping the periodicity small compared to the sphere radius. An interferometric device is used to measure the sphere vertical displacement, for distances between the sphere and the base of the pillars smaller than 0.1 sphere radius, and with a resolution of 200 nm. At a given distance from the top of the pillars, the sphere velocity is found to be significantly larger than the corresponding velocity for a smooth solid wall. A squeeze flow model of two adjacent fluid layers is developed in the lubrication approximation, one fluid layer having an effective viscosity that reflects the viscous dissipation through the array of pillars. The pressure field in the gap between the sphere and the textured surface is then used to obtain the drag force on the sphere and hence its velocity. Adjustment of the model to the velocity measurements yields the effective viscosity for a given texture. Finally, a correlation between the effective viscosity and the geometry of the pillar array is proposed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

THE BOLOCAM GALACTIC PLANE SURVEY. XII. DISTANCE CATALOG EXPANSION USING KINEMATIC ISOLATION OF DENSE MOLECULAR CLOUD STRUCTURES WITH {sup 13}CO(1-0)

We present an expanded distance catalog for 1710 molecular cloud structures identified in the Bolocam Galactic Plane Survey (BGPS) version 2, representing a nearly threefold increase over the previous BGPS distance catalog. We additionally present a new method for incorporating extant data sets into our Bayesian distance probability density function (DPDF) methodology. To augment the dense-gas tracers (e.g., HCO{sup +}(3-2), NH{sub 3}(1,1)) used to derive line-of-sight velocities for kinematic distances, we utilize the Galactic Ring Survey (GRS) {sup 13}CO(1-0) data to morphologically extract velocities for BGPS sources. The outline of a BGPS source is used to select a region of the GRS {sup 13}CO data, along with a reference region to subtract enveloping diffuse emission, to produce a line profile of {sup 13}CO matched to the BGPS source. For objects with a HCO{sup +}(3-2) velocity, ≈95% of the new {sup 13}CO(1-0) velocities agree with that of the dense gas. A new prior DPDF for kinematic distance ambiguity (KDA) resolution, based on a validated formalism for associating molecular cloud structures with known objects from the literature, is presented. We demonstrate this prior using catalogs of masers with trigonometric parallaxes and H II regions with robust KDA resolutions. The distance catalog presented here contains well-constrained distance estimates for 20% of BGPS V2 sources, with typical distance uncertainties ≲ 0.5 kpc. Approximately 75% of the well-constrained sources lie within 6 kpc of the Sun, concentrated in the Scutum-Centaurus arm. Galactocentric positions of objects additionally trace out portions of the Sagittarius, Perseus, and Outer arms in the first and second Galactic quadrants, and we also find evidence for significant regions of interarm dense gas.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Thermoelectric properties of IV–VI-based heterostructures and superlattices

Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature in the directions perpendicular to the doping planes, yet no improvement on the values of ZT is found when compared to bulk PbTe. For the PbTe/SnTe/PbTe heterostructures, the calculated S presents good agreement with recent experimental data, and an anisotropic behavior is observed for low carrier concentrations (n<10{sup 18} cm{sup −3}). A large value of ZT{sub ||} (parallel to the growth direction) of 3.0 is predicted for n=4.7×10{sup 18} cm{sup −3} and T=700 K, whereas ZT{sub p} (perpendicular to the growth direction) is found to peak at 1.5 for n=1.7×10{sup 17} cm{sup −3}. Both electrical conductivity enhancement and thermal conductivity reduction are analyzed. - Graphical abstract: Figure of merit for PbTe/SnTe/PbTe heterostructure along the [0 0 1] direction, P.D. Borges, J.E. Petersen, L. Scolfaro, H.W. Leite Alves, T.H. Myers, Improved thermoelectric properties of IV–VI-based heterostructures and superlattices. - Highlights: • Thermoelectric properties of IV–VI-based heterostructures and superlattices. • High figure of merit is predicted for the PbTe/SnTe/PbTe heterostructure. • Nanotechnology has an important role for the development of thermoelectric devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

X-ray-selected galaxy groups in Boötes

We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Boötes survey. We used follow-up Chandra observations to better define the group sample and their X-ray properties. Group redshifts were measured from the AGN and Galaxy Evolution Survey spectroscopic data. We used photometric data from the NOAO Deep Wide Field Survey to estimate the group richness (N {sub gals}) and the optical luminosity (L {sub opt}). Our final sample comprises 32 systems at z < 1.75 with 14 below z = 0.35. For these 14 systems, we estimate velocity dispersions (σ {sub gr}) and perform a virial analysis to obtain the radii (R {sub 200} and R {sub 500}) and total masses (M {sub 200} and M {sub 500}) for groups with at least 5 galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity (L{sub X} ). We examine the performance of the group properties σ{sub gr}, L {sub opt}, and L{sub X} , as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Boötes sample and comparing these with samples from the literature, we find a break in the L{sub X} -M {sub 500} relation at approximately M {sub 500} = 5 × 10{sup 13} M {sub ☉} (for M {sub 500} > 5 × 10{sup 13} M {sub ☉}, M{sub 500}∝L{sub X}{sup 0.61±0.02}, while for M {sub 500} ≤ 5 × 10{sup 13} M {sub ☉}, M{sub 500}∝L{sub X}{sup 0.44±0.05}). Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions, and projection effects that reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our cluster/group luminosity function estimates, eROSITA will identify ∼1800 groups (L{sub X} = 10{sup 41}-10{sup 43} erg s{sup –1}) within a distance of 200 Mpc. Since groups lie in large-scale filaments, this group sample will map the large-scale structure of the local universe.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2026

Predicting U 3 O 8 powder processing conditions: An AI/ML approach analyzing deep learning embeddings of SEM micrographs

High-resolution SEM images of uranium-oxide powders encode micro- and nanoscale clues to their synthesis route and calcination temperature. We trained a ResNet-50 model on 11 commercial-scale U₃O₈ classes, ammonium diuranate (ADU) or uranyl peroxide (H₂O₂) precursors calcined at temperatures ranging from 400 to 750 °C and added a 256-D projection head before the classifier to analyze the learned representation. The best of eight seeds reached 92.4 % accuracy on reserved testing data, but our focus is the structure of the embedding space rather than the accuracy and labels. We quantify class relatedness in the original 256-D space using centroid similarity and distributional distances, and we use Uniform Manifold Approximation Projection (UMAP) for visualization. ‘Unknown’ images from different preparation methods, SEM operators, and from the literature localized near the expected classes under a nearest-centroid analysis without retraining, as well as clustered in similar UMAP space. In conclusion, this embedding-centered workflow complements black-box classification by providing quantitative, similarity-based comparisons of U₃O₈ morphologies and reduces storage space by up to 98 % for image data used in millisecond vector search comparisons.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Artificial intelligence “sees” split electrons

Chemical bonds between atoms are stabilized by the exchange-correlation (xc) energy, a quantum-mechanical effect in which “social distancing” by electrons lowers their electrostatic repulsion energy. Kohn-Sham density functional theory (DFT) states that the electron density determines this xc energy, but the density functional must be approximated. Furthermore, this is usually done by satisfying exact constraints of the exact functional (making the approximation predictive), by fitting to data (making it interpolative), or both. Two exact constraints—the ensemble-based piecewise linear variation of the total energy with respect to fractional electron number and fractional electron z-component of spin —require hard-to-control nonlocality. On page 1385 of this issue, Kirkpatrick et al. have taken a big step toward more accurate predictions for chemistry through the machine learning of molecular data plus the fractional charge and spin constraints, expressed as data that a machine can learn.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Sparse Approximate Multifrontal Factorization with Butterfly Compression for High-Frequency Wave Equations

In this work, we present a fast and approximate multifrontal solver for large-scale sparse linear systems arising from finite-difference, finite-volume or finite-element discretization of high-frequency wave equations. The proposed solver leverages the butterfly algorithm and its hierarchical matrix extension for compressing and factorizing large frontal matrices via graph-distance guided entry evaluation or randomized matrix-vector multiplication-based schemes. Complexity analysis and numerical experiments demonstrate $\mathcal{O}(N\log^2 N)$ computation and $\mathcal{O}(N)$ memory complexity when applied to an $N\times N$ sparse system arising from 3D high-frequency Helmholtz and Maxwell problems.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2014

SU-F-BRF-09: A Non-Rigid Point Matching Method for Accurate Bladder Dose Summation in Cervical Cancer HDR Brachytherapy

Purpose: To propose and validate a deformable point matching scheme for surface deformation to facilitate accurate bladder dose summation for fractionated HDR cervical cancer treatment. Method: A deformable point matching scheme based on the thin plate spline robust point matching (TPSRPM) algorithm is proposed for bladder surface registration. The surface of bladders segmented from fractional CT images is extracted and discretized with triangular surface mesh. Deformation between the two bladder surfaces are obtained by matching the two meshes' vertices via the TPS-RPM algorithm, and the deformation vector fields (DVFs) characteristic of this deformation is estimated by B-spline approximation. Numerically, the algorithm is quantitatively compared with the Demons algorithm using five clinical cervical cancer cases by several metrics: vertex-to-vertex distance (VVD), Hausdorff distance (HD), percent error (PE), and conformity index (CI). Experimentally, the algorithm is validated on a balloon phantom with 12 surface fiducial markers. The balloon is inflated with different amount of water, and the displacement of fiducial markers is benchmarked as ground truth to study TPS-RPM calculated DVFs' accuracy. Results: In numerical evaluation, the mean VVD is 3.7(±2.0) mm after Demons, and 1.3(±0.9) mm after TPS-RPM. The mean HD is 14.4 mm after Demons, and 5.3mm after TPS-RPM. The mean PE is 101.7% after Demons and decreases to 18.7% after TPS-RPM. The mean CI is 0.63 after Demons, and increases to 0.90 after TPS-RPM. In the phantom study, the mean Euclidean distance of the fiducials is 7.4±3.0mm and 4.2±1.8mm after Demons and TPS-RPM, respectively. Conclusions: The bladder wall deformation is more accurate using the feature-based TPS-RPM algorithm than the intensity-based Demons algorithm, indicating that TPS-RPM has the potential for accurate bladder dose deformation and dose summation for multi-fractional cervical HDR brachytherapy. This work is supported in part by the National Natural ScienceFoundation of China (no 30970866 and no 81301940)

60 APPLIED LIFE SCIENCES↗

DOE OSTI2013

SMA OBSERVATIONS OF CLASS 0 PROTOSTARS: A HIGH ANGULAR RESOLUTION SURVEY OF PROTOSTELLAR BINARY SYSTEMS

We present high angular resolution 1.3 mm and 850 {mu}m dust continuum data obtained with the Submillimeter Array toward 33 Class 0 protostars in nearby clouds (distance < 500 pc), which represents so far the largest survey toward protostellar binary/multiple systems. The median angular resolution in the survey is 2.''5, while the median linear resolution is approximately 600 AU. Compact dust continuum emission is observed from all sources in the sample. Twenty-one sources in the sample show signatures of binarity/multiplicity, with separations ranging from 50 AU to 5000 AU. The numbers of singles, binaries, triples, and quadruples in the sample are 12, 14, 5, and 2, respectively. The derived multiplicity frequency (MF) and companion star fraction (CSF) for Class 0 protostars are 0.64 {+-} 0.08 and 0.91 {+-} 0.05, respectively, with no correction for completeness. The derived MF and CSF in this survey are approximately two times higher than the values found in the binary surveys toward Class I young stellar objects, and approximately three (for MF) and four (for CSF) times larger than the values found among main-sequence stars, with a similar range of separations. Furthermore, the observed fraction of high-order multiple systems to binary systems in Class 0 protostars (0.50 {+-} 0.09) is also larger than the fractions found in Class I young stellar objects (0.31 {+-} 0.07) and main-sequence stars ({<=}0.2). These results suggest that binary properties evolve as protostars evolve, as predicted by numerical simulations. The distribution of separations for Class 0 protostellar binary/multiple systems shows a general trend in which CSF increases with decreasing companion separation. We find that 67% {+-} 8% of the protobinary systems have circumstellar mass ratios below 0.5, implying that unequal-mass systems are preferred in the process of binary star formation. We suggest an empirical sequential fragmentation picture for binary star formation, based on this work and existing lower resolution single-dish observations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

THE DYNAMICAL EVOLUTION OF LOW-MASS HYDROGEN-BURNING STARS, BROWN DWARFS, AND PLANETARY-MASS OBJECTS FORMED THROUGH DISK FRAGMENTATION

Theory and simulations suggest that it is possible to form low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) via disk fragmentation. As disk fragmentation results in the formation of several bodies at comparable distances to the host star, their orbits are generally unstable. Here, we study the dynamical evolution of these objects. We set up the initial conditions based on the outcomes of the smoothed-particle hydrodynamics simulations of Stamatellos and Whitworth, and for comparison we also study the evolution of systems resulting from lower-mass fragmenting disks. We refer to these two sets of simulations as set 1 and set 2, respectively. At 10 Myr, approximately half of the host stars have one companion left, and approximately 22% (set 1) to 9.8% (set 2) of the host stars are single. Systems with multiple secondaries in relatively stable configurations are common (about 30% and 44%, respectively). The majority of the companions are ejected within 1 Myr with velocities mostly below 5 km s{sup −1}, with some runaway escapers with velocities over 30 km s{sup −1}. Roughly 6% (set 1) and 2% (set 2) of the companions pair up into very low-mass binary systems, resulting in respective binary fractions of 3.2% and 1.2%. The majority of these pairs escape as very low-mass binaries, while others remain bound to the host star in hierarchical configurations (often with retrograde inner orbits). Physical collisions with the host star (0.43 and 0.18 events per host star for set 1 and set 2, respectively) and between companions (0.08 and 0.04 events per host star for set 1 and set 2, respectively) are relatively common and their frequency increases with increasing disk mass. Our study predicts observable properties of very low-mass binaries, low-mass hierarchical systems, the BD desert, and free-floating BDs and PMOs in and near young stellar groupings, which can be used to distinguish between different formation scenarios of very low-mass stars, BDs, and PMOs.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

Temporal multispectral and 3D analysis of Cerro de Pasco, Peru

Mining operations across the world often lead to contamination of land, water resources, ecosystems and in some cases, entire communities.Results of recent health and ground sampling studies revealed extensive lead contamination within the populace and around the City of Cerro de Pasco, Peru. Tailings excavated from a large open pit zinc mine in the center of the city have been aggregated in four large stockpiles within close proximity to neighborhoods, schools, and hospitals. Visual comparison of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) imagery from 2001 and Sentinel-2 imagery from 2018 suggests a size increase in one tailing stockpile in particular near the neighborhood of Paragsha. Due to ongoing mining efforts, the hypothesis motivating the work presented here is that Pb-bearing minerals would be detectable through multispectral analysis, an increase in Pb mineral percent abundance would be observed and tailing stockpile volume would be detectable between 2001 and 2016. This hypothesis is tested using Spectral Angle Mapper (SAM), Adaptive Coherence Estimator (ACE), and Jeffries-Matusita distance calculation on ASTER (2001) and Sentinel-2 (2018) VNIR and SWIR bands. Volume and area estimate of tailing stockpiles were calculated using a photogrammetrically derived point cloud. SAM detected the presence of five Pb-bearing minerals around Cerro de Pasco and Paragsha. The results of the temporal SAM analysis displayed an increase of approximately 17% of Pb-bearing minerals around the greater Cerro de Pasco city area and approximately 11% for the neighborhood of Paragsha. Jeffries-Matusita distance results suggest clear correlation between contamination sources and affected locations. Total tailing stockpile volume was measured to be approximately 200,300,000 m 3 . Volume for Pile 4 was estimated to have increased by approximately 46,000,000 m 3 between 2001 and 2018. Lastly, these presented results will hopefully inspire and guide future remote sensing campaigns, perhaps involving a UAV or aircraft-based hyperspectral instrument.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2015

X-RAY AND RADIO OBSERVATIONS OF THE MASSIVE STAR-FORMING REGION IRAS 20126+4104

We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6 cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17′ × 17′ ACIS-I field, and a total of 13 radio sources within the 9.′2 primary beam at 4.9 GHz. Among these observtions are the first 6 cm detections of the central sources reported by Hofner et al., namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-ray sources had 6 cm counterparts. Based on an NIR color–color analysis and on the Besançon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2 pc from the massive protostar.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

SU-E-T-774: Use of a Scintillator-Mirror-Camera System for the Measurement of MLC Leakage Radiation with the CyberKnife M6 System

Purpose: A technique using a scintillator-mirror-camera system to measure MLC leakage was developed to provide an efficient alternative to film dosimetry while maintaining high spatial resolution. This work describes the technique together with measurement uncertainties. Methods: Leakage measurements were made for the InCise™ MLC using the Logos XRV-2020A device. For each measurement approximately 170 leakage and background images were acquired using optimized camera settings. Average background was subtracted from each leakage frame before filtering the integrated leakage image to replace anomalous pixels. Pixel value to dose conversion was performed using a calibration image. Mean leakage was calculated within an ROI corresponding to the primary beam, and maximum leakage was determined by binning the image into overlapping 1mm x 1mm ROIs. 48 measurements were performed using 3 cameras and multiple MLC-linac combinations in varying beam orientations, with each compared to film dosimetry. Optical and environmental influences were also investigated. Results: Measurement time with the XRV-2020A was 8 minutes vs. 50 minutes using radiochromic film, and results were available immediately. Camera radiation exposure degraded measurement accuracy. With a relatively undamaged camera, mean leakage agreed with film measurement to ≤0.02% in 92% cases, ≤0.03% in 100% (for maximum leakage the values were 88% and 96%) relative to reference open field dose. The estimated camera lifetime over which this agreement is maintained is at least 150 measurements, and can be monitored using reference field exposures. A dependency on camera temperature was identified and a reduction in sensitivity with distance from image center due to optical distortion was characterized. Conclusion: With periodic monitoring of the degree of camera radiation damage, the XRV-2020A system can be used to measure MLC leakage. This represents a significant time saving when compared to the traditional film-based approach without any substantial reduction in accuracy.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2024

Scale sensitivity of ethanol production via consolidated bioprocessing with consideration of feedstock cost

We examine feedstock cost and minimum selling price for ethanol production from corn stover as a function of scale, stover yield, participation rate, and price incentives for two conversion technologies: a conventional base case featuring thermochemical pretreatment with added cellulase, and an advanced case featuring consolidated bioprocessing with cotreatment (C-CBP). Delivered feedstock cost ranged from $\$85$ Mg −1 at small (10 million gallons year −1 or ~38 million L year −1 ) scale with high yield and participation rates to $\$124$ Mg −1 at large scale (60 million gallons year −1 or 227 million L year −1 ) and low yield and participation rates. The minimum ethanol selling price (MESP) was approximately twofold lower for the advanced case compared with the base case. The payback period was several times lower for the advanced case compared with the base case, with increasing disparity at smaller scales, and was highly sensitive to ethanol price supports. For both C-CBP and the conventional processing paradigm, MESP decreased with increasing scale, indicating that the cost penalty due to higher feedstock transport distances was more than outweighed by lower capital costs. However, the cost penalty for operation at small scale, expressed in $ gallon −1 ethanol, is lower for C-CBP than for the conventional paradigm by roughly twofold. Particularly for initial applications of C-CBP, we speculate that this cost penalty will likely be modest compared with the anticipated benefits of small-scale operation such as increased opportunity to use existing infrastructure, easier plant siting and supply chain establishment, and lower total investment required.

biorefinery scale↗

DOE OSTI2020

Analytical Investigation of the Role of Lateral Mixing in the Evolution of Nonprecipitating Cumulus. Part I: Developing Clouds

Evolution of nonprecipitating cumulus clouds (Cu) at the developing stage under the influence of lateral entrainment and mixing is studied analytically using a minimalistic analytical model. We present a model of an ascending cloud volume (a model of developing Cu) whose structure is determined by the processes of droplet diffusion growth/evaporation and entrainment mixing in the horizontal direction. Spatial and time changes of liquid water content, the adiabatic fraction, droplet concentration, and the mean volume droplet radius are calculated. It is shown that the existence of a nondiluted core in a growing cumulus cloud significantly depends on the cloud width and vertical velocity. While at the updraft velocity of 2 m s −1 the core of a 400-m-wide cloud becomes diluted at distances of a few hundred meters above cloud base, the core of a cloud of 1000-m width remains nondiluted at distances up to 1500 m above cloud base. The explanation of this result is simple: the increase in cloud width and the decrease in the updraft velocity increase the time during which the cloud is diluted due to mixing. Since lateral mixing synchronously decreases both the cloud water content and droplet concentration, the variation of the mean volume droplet radius is low inside the cloud. The approximate quantitative condition for cloud formation in updraft is derived. It is shown that a cloud can arise when its vertical velocity exceeds a critical value. To produce clouds, narrow turbulent plumes should ascend at higher velocity as compared to wider plumes. High humidity of the environment air is favorable for formation of clouds from plumes. The comparison of the obtained results with previously published observational data indicates a reasonable agreement. The results can be useful for parameterization purposes.

54 ENVIRONMENTAL SCIENCES↗