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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

SGP Merged Aerosol Size Distribution (CPC+SMPS+APS)

Five years (2009-2013) of data from three instrument at the SGP site were merged in order to create a new aerosol size distribution dataset. Data from the scanning mobility particle sizer (SMPS), part of the TDMA system, were combined with size distribution data from the aerodynamic particle sizer (APS). The merged size distribution from those two instruments spanned the diameter (mobility) size range between ~12 nm and ~14 um with 215 bins (Collins 2010). Total aerosol number concentrations from a TSI 3010 condensation particle counter (CPC) were then used to adjust and constrain the SMPS+APS size distributions and to extend the size distribution down to ~7 nm. Collins, D: Tandem Differential Mobility Analyzer/Aerodynamic Particular Sizer (APS) Handbook. DOE ARM Climate Research Facility. DOE/SC-ARM-TR-090, 2010.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

black carbon mass loading, size distribution for CACTI - ground site

The Single-Particle Soot Photometer (SP2, Droplet Mea- surement Technologies) is an instrument that measures, in situ, the time-dependent scattering and incandescence signals produced by individual BC-containing particles as they travel through a continuous-wave laser beam. Any particle traversing the laser beam will scatter light, and the BC component of a BC-containing particle will absorb some of the laser energy until its temperature is raised to the point at which it incandesces (hereafter we adopt the standard terminology of the SP2 community and denote any substance determined by the SP2 to be BC as refractory black carbon (rBC)). The scattering signal provides information on particle size, and the incandescence signal is used for counting rBC-containing particles and yields the mass of the rBC component within each particle (obtained via calibration). Hence, the SP2 can determine size-resolved number and mass concentrations of rBC-containing particles and thus provides information on the rBC particle population-based mixing states within ambient aerosols rBC concentration is reported at STP conditions Time resolution: 1-min Uncertainty: ~ 30% SP2 Unit: 25 Location: Ascension Island, British Territory Location: 7° 56' S, 14° 25' W" SP2_dateTime: UTC rBC concentration is in units of ng/m^3 - dry air. Mass Equivalent Diameters [MED] used for size distribution (SP2_min; SP2_geo; and SP2_max) are in units of micrometers dN/dlogDp counts for a given size bin (SP2_geo) listed as 'SP2_cnts_0…SP2_cnts_199'. Column naming convention: 'SP2_cnts_X' are the number of particles in bin number _X. , where _X is the row number within the 'SP2_geo' size bin column that contains the mass equivalent diameter (e.g., SP2_cnts_0 = 0.01 microns; SP2_cnts_10 = 0.060 microns, etc…). The dN/dlogDp data is time-resolved where a given row is associated with the timestamp for that row. Note that the rBC column length is one field shorter than the SP2_datetime column. Last time field is not relevant to the rBC time series (see comment below on length of SP2_datetime column) Lengths for SP2_max; SP2_min; SP2_geo are one field longer then the number of SP2_cnts_XX columns . This is to provide bounds for image plots (if desired). Length for SP2_datetime is one field longer than that length of the SP2_cnts_XX columns This is to provide bounds for image plots (if desired) SP2 Calibration: Fullerene soot with corrrection applied for particle density as a function of particle size. No correction for OC content in Fullerene (recent study on SP2 sensitivity to differing black carbon types reports that non-refractory material content for fullerene soot is about 20%). Comments and/or requests are to be directed to Art Sedlacek (sedlacek@bnl.gov)

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

HISCALE: Best Estimate Aerosol Size Distribution by airborne measurements

The data were collected during the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE, http://www.arm.gov/campaigns/aaf2016hiscale) field campaign as part of ARM Aerial Facility (AAF) deployment. The ARM Aerial Facility Gulfstream-1 was deployed at Bartlesville, OK, for two intensive observation periods from April 23 through May 22 and from August 27 through September 25, 2016. The G-1 aircraft performed 38 (17+21) research flights over the ARM Southern Great Plains (SGP) Atmospheric Observatory to measure atmospheric turbulence, cloud water content and drop size distributions, aerosol precursor gases, aerosol chemical composition and size distributions. The current data set presents Best Estimate Aerosol Size Distribution: a merged aerosol size distribution composed of the data from 4 sensors: two aerosol spectrometers (FIMS and PCASP) and two cloud probes (CAS and FCDP). Aerosol chemical composition, measured by the Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS), was used to estimate aerosol refractive index (RI) required for correction of the equivalent optical size into geometric size

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

ACE-ENA: Best Estimate Aerosol Size Distribution by airborne measurements

These data were collected during the Aerosol and Cloud Experiments in the Eastern North Atlantic field campaign as part of ARM Aerial Facility deployment (ACE-ENA, https://www.arm.gov/research/campaigns/aaf2017ace-ena). The ARM Aerial Facility Gulfstream-1 was deployed at Lajes Air Base (IATA: TER, ICAO: LPLA), on Terceira Island in the Azores, Portugal, for the two Intensive Observation Periods from June 20 through July 22, 2017 (IOP#1) and from January 11 through February 22, 2018 (IOP#2). The G-1 aircraft performed 20+19 research flights over the ARM Eastern North Atlantic (ENA) site and Atlantic Ocean to measure atmospheric turbulence, cloud water content and drop size distributions, aerosol precursor gases, aerosol chemical composition and size distributions. The current data set presents Best Estimate Aerosol Size Distribution: a merged aerosol size distribution composed of the data from 4 sensors: two aerosol spectrometers (FIMS and PCASP) and two cloud probes (CAS and FCDP). Aerosol chemical composition, measured by the Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS), was used to estimate aerosol refractive index (RI) required for correction of the equivalent optical size into geometric size.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1992

Size of metallic and polyethylene debris particles in failed cemented total hip replacements

Reports of differing failure rates of total hip prostheses made of various metals prompted us to measure the size of metallic and polyethylene particulate debris around failed cemented arthroplasties. We used an isolation method, in which metallic debris was extracted from the tissues, and a non-isolation method of routine preparation for light and electron microscopy. Specimens were taken from 30 cases in which the femoral component was of titanium alloy (10), cobalt-chrome alloy (10), or stainless steel (10). The mean size of metallic particles with the isolation method was 0.8 to 1.0 microns by 1.5 to 1.8 microns. The non-isolation method gave a significantly smaller mean size of 0.3 to 0.4 microns by 0.6 to 0.7 microns. For each technique the particle sizes of the three metals were similar. The mean size of polyethylene particles was 2 to 4 microns by 8 to 13 microns. They were larger in tissue retrieved from failed titanium-alloy implants than from cobalt-chrome and stainless-steel implants. Our results suggest that factors other than the size of the metal particles, such as the constituents of the alloy, and the amount and speed of generation of debris, may be more important in the failure of hip replacements.

Non-NASA Center↗
DOE OSTI2018

EXTINCTION DROPLET SIZING MEASUREMENTS IN DIESEL RELEVANT SPRAYS

A new diagnostic for the quantification of Sauter Mean Diameter (SMD) in high-pressure fuel sprays has been recently developed using combined optical and x-ray measurements at the Georgia Institute of Technology and Argonne National Laboratory, respectively. This diagnostic utilizes liquid scattering extinction measurements from diffuse back-illumination (DBI) imaging, conducted at Georgia Tech, and liquid absorption measurements from x-ray radiography, conducted at Argonne’s Advanced Photon Source. The new diagnostic, entitled the Scattering Absorption Measurement Ratio (SAMR), quantifies two-dimensional distributions of path-integrated SMD, enabling construction of the spatial history of drop size development within practical fuel sprays. This technique offers unique benefits over conventional drop-sizing methods in that it can be more robust in optically dense regions of the spray, while also providing high spatial resolution of the corresponding droplet field. The spatially-resolved SMD measurements that result from the SAMR diagnostic will be especially valuable to the engine modeling community for the quantitative validation of spray submodels in engine CFD codes. The methodology for quantification of SMD distributions using the SAMR technique has been previously introduced. This thesis aims to extend the initial development of the SAMR technique by presenting in detail: the experimental methodologies used in the SAMR technique, including the development of an ideal DBI setup for this technique; the data processing methodologies developed by the author; two-dimensional Sauter Mean Diameter measurements within diesel sprays for various experimental conditions; a summary of the various sources of measurement uncertainty; an assessment for how the sources of uncertainty affect the quantified SMD; and paths to improve the technique moving forward. The SMD results show that for low ambient density conditions droplets decrease in size as radial and axial position increases. For high ambient density conditions, however, the droplets show a stable size near the spray centerline and steadily increase in size as distance from the centerline increases. Additionally, this work provides 2-D droplet sizing maps which are particularly useful for model validation.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2018

EXTINCTION DROPLET SIZING MEASUREMENTS IN DIESEL RELEVANT SPRAYS

A new diagnostic for the quantification of Sauter Mean Diameter (SMD) in high-pressure fuel sprays has been recently developed using combined optical and x-ray measurements at the Georgia Institute of Technology and Argonne National Laboratory, respectively. This diagnostic utilizes liquid scattering extinction measurements from diffuse back-illumination (DBI) imaging, conducted at Georgia Tech, and liquid absorption measurements from x-ray radiography, conducted at Argonne’s Advanced Photon Source. The new diagnostic, entitled the Scattering Absorption Measurement Ratio (SAMR), quantifies two-dimensional distributions of path-integrated SMD, enabling construction of the spatial history of drop size development within practical fuel sprays. This technique offers unique benefits over conventional drop-sizing methods in that it can be more robust in optically dense regions of the spray, while also providing high spatial resolution of the corresponding droplet field. The spatially-resolved SMD measurements that result from the SAMR diagnostic will be especially valuable to the engine modeling community for the quantitative validation of spray submodels in engine CFD codes. The methodology for quantification of SMD distributions using the SAMR technique has been previously introduced. This thesis aims to extend the initial developmen of SAMR technique by presenting in detail: the experimental methodologies used in the SAMR technique, including the development of an ideal DBI setup for this technique; the data processing methodologies developed by the author; two-dimensional Sauter Mean Diameter measurements within diesel sprays for various experimental conditions; a summary of the various sources of measurement uncertainty; an assessment for how the sources of uncertainty affect the quantified SMD; and paths to improve the technique moving forward. The SMD results show that for low ambient density conditions droplets decrease in size as radial and axial position increases. For high ambient density conditions, however, the droplets show a stable size near the spray centerline and steadily increase in size as distance from the centerline increases. Additionally, this work provides 2-D droplet sizing maps which are particularly useful for model validation.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2016

Manufacture of large grain size of Gd{sub 2}O{sub 3}-UO{sub 2} pellets adding Al(OH){sub 3}

In order to improve the utilization of nuclear fuel, reduce the cost of fuel cycle and improve the economics and flexibility of nuclear power plant in the latest light-water reactors, designers usually adopt the operation strategy of high burnup, long cycle, low leakage, such as using burnable poison fuel in nuclear reactors. So the Gd{sub 2}O{sub 3}-UO{sub 2} pellets is widely used as burnable poison fuel. Pellets is harmful for the running of nuclear reactor if the grain size is too large or too small. Generally, the grain size of Gd{sub 2}O{sub 3}-UO{sub 2} pellets can be called big grain pellets if the grain size is larger than 10 μm. In order to get big grain Gd{sub 2}O{sub 3}-UO{sub 2} pellets, researcher usually adopt grain growth agent to increase the grain size of pellets, this article research the rule of density, pore and grain size of Gd{sub 2}O{sub 3}-UO{sub 2} pellets by adding Al(OH){sub 3}. Al(OH){sub 3} breaks down Al{sub 2}O{sub 3} and H{sub 2}O which can increase the spread of the cation in the lattice, which cause the growth of grain in Gd{sub 2}O{sub 3}-UO{sub 2} pellets. Besides, it also determines the process route of average grain size of more than 10 μm in pellets.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Acoustic Monitor for Particle Size and Bed Friction in a Carbonate Fluidized Bed at High Temperature - 18014

Previous work has shown that acoustic spectra of fluidized bed pressure fluctuations show many useful bed properties [1-3]. This current work further explores the use of acoustic monitors for an 18' diameter, 66-74'' height fluidized bed at >640 deg. C. This process denitrates and agglomerates an injected sodium/aluminum nitrate aqueous simulant and produces at steady-state a denitrated product of 200-300 micron sodium carbonate/aluminate particles. The fluidized bed shows characteristic acoustic resonances around 1-2 Hz in the FFT (Fast Fourier Transform) of pressure fluctuations for each of three taps at fluidized bed heights of 12'', 39'', and 58''. The acoustic resonance spectra depend on a bed friction that once calibrated, monitors the HMPD (harmonic mass mean particle diameter or Sauter mean diameter) along with other important bed properties. This fluidized bed operates at high temperature with an evolving HMPD that can be steady state with an appropriate superficial spatial velocity (SSV). The acoustic FFT integrated power spectrum, IPS, of pressure fluctuations represents the bed-friction damped RMS (root mean square) pressure fluctuations at each tap. The transition from a static to fluidized bed at each bed height occurs when the damped bed RMS pressure fluctuations are greater than the static head (the FFT zero Hz designated zero Hz proportional to FFT zero Hz) at that bed height. A bed will de-fluidize and become static at a bed height when bed friction completely dampens the RMS pressure fluctuations, which occurs for decreasing particle size among other factors. The ratio IPS/zero Hz then provides a continuous monitor of bed friction damping as well as particle size as the HMPD. Since HMPD and bed friction damping are both very important parameters for fluidized particle beds, the acoustic HMPD and bed friction damping both provide very useful monitors for fluidized bed operation. Such acoustic monitors have shown that they are especially sensitive to the presence of very fine particles in the bed of less than 50 microns diameter. Acoustic monitors for particle size and bed friction damping will be very useful in any fluidized bed, especially fluidized beds where particle size changes. The fluidized bed friction damping depends on many other bed properties besides particle size such as bed height, density, SSV, void fraction, gas viscosity, and fluidization scheme and so acoustic bed friction should also be useful for monitoring other bed properties besides particle size. In fact, the change in the static bed friction slope with SSV upon fluidization follows the Ergun function and reveals a minimum fluidization velocity for each HMPD. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Effect of Particle Size Upon Pt/SiO 2 Catalytic Cracking of n-Dodecane Under Supercritical Conditions: in situ SAXS and XANES Studies

The endothermic cracking and dehydrogenation of n-dodecane is investigated over well-defined nanometer size platinum catalysts supported on SiO 2 to study the particle size effects in the catalytic cracking reaction, with simultaneous in situ monitoring of the particle size and oxidation state of the working catalysts by in situ SAXS (small angle X-ray scattering) and XAS (X-ray absorption spectroscopy). The selectivity toward olefins products was found dominant in the 1 nm size platinum catalysts, whereas paraffins are dominant in the 2 nm catalysts. This reveals a strong correlation between catalytic performance and catalyst size as well as the stability of the nanoparticles in supercritical condition of n-dodecane. The presented results suggest that controlling the size and geometric structure of platinum nanocatalysts could lead to a fundamentally new level of understanding of nanoscale materials by monitoring the catalysts in realistic reaction conditions.

Nanocatalysis↗
DOE OSTI2024

Ability of x‐ray computed tomography to resolve critical flaw size in laser‐based, paste stereolithography ceramic printing of alumina

Abstract Complex alumina parts were printed using vat photopolymerization (VPP), which is a stereolithography‐based additive manufacturing (AM) technique used to shape ceramic preforms, or green parts. The critical flaw size was determined using classical fracture mechanics techniques. The strength and fracture toughness were measured and compared to flaws detected in x‐ray computed tomography (XCT or CT) distributions as well as the fracture surfaces. The strength was lower compared traditionally made alumina, and that is due to layering effects, slurry defects, and printing defects. The critical flaw size from fracture mechanics was 206 µm. XCT has high enough resolution to detect the critical flaw size and much smaller features, where the average flaw size observed in CT scans was around 80–100 µm. The fracture surfaces indicate that flaws causing failure are larger than that of the critical flaw size (∼300 µm), but fracture surfaces do not show definitive features compared to traditionally made ceramics. Since XCT can observe flaws smaller than the critical flaw size, this method can be used as a screening technique.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Decreasing transmembrane segment length greatly decreases perfringolysin O pore size

Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakage assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

The Effect of Grain Size on the Strain Hardening Behavior for Extruded ZK61 Magnesium Alloy

The effects of grain size on the tensile and compressive strain hardening behaviors for extruded ZK61 alloys have been investigated by uniaxial tensile and compressive tests along the extrusion directions. Cylindrical tension and compression specimens of extruded ZK61 alloys with various sized grain were fabricated by annealing treatments. Tensile and compressive tests at ambient temperature were conducted at a strain rate of 0.5 × 10{sup −3} s{sup −1}. The results indicate that both tensile strain hardening and compressive strain hardening of ZK61 alloys with different grain sizes have an athermal regime of dislocation accumulation in early deformation. The threshold stress value caused dynamic recovery is predominantly related to grain size in tensile strain hardening, but the threshold stress values for different grain sizes are almost identical in compressive strain hardening. There are obvious transition points on the tensile strain hardening curves which indicate the occurrence of dynamic recrystallization (DRX). The tensile strain hardening rate of the coarse-grained alloy obviously decreases faster than that of fine-grained alloys before DRX and the tensile strain hardening curves of different grain sizes basically tend to parallel after DRX. The compressive strain hardening rate of the fine-grained alloy obviously increases faster than that of coarse-grained alloy for twin-induced strain hardening, but compressive strain hardening curves also tend to parallel after twinning is exhausted.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Relationship between Grain Size and Sample Thickness on the Creep-Rupture Performance of Thin Metallic Sheets of INCONEL Alloy 740H

A study was conducted on INCONEL® alloy 740H® to examine the role of grain size and sheet thickness on the alloy’s creep-rupture behavior. Three different starting sheet thicknesses were utilized and multiple heat-treatment conditions anticipated for compact heat exchanger (CHX) manufacturing were applied to produce a range of grain sizes. Creep-rupture testing was conducted at 750 °C for times up to about 6000 h and the results were compared to wrought databases. The data show that both creep strength and ductility were important factors in the overall creep performance of the sheets. Reductions in performance were observed due either to accelerated creep when grain size was fine or loss of rupture ductility when grain sizes approached the sheet thickness. Some combinations of heat-treatment and thickness were able to produce typical expected wrought creep properties. Historically a ‘rule-of-thumb’ requirement for creep testing suggests 3-5 grains per sample minimum dimension to ensure homogeneous behavior. This research shows that to ensure representative wrought creep performance (i.e. no effect of sample size), the sample minimum cross-section should be 10 times the average ASTM grain size. Statistical analysis of the microstructures suggests the population of larger grains as a controlling feature in creep failure.

14 SOLAR ENERGY↗
DOE OSTI2022

Wet-chemical synthesis of Li7P3S11 with tailored particle size for solid state electrolytes

The small-size solid-state electrodes (SSEs) with high Li+ conductivity play an important role in reducing the interfacial resistance between electrode materials and SSEs and defects between SSEs. As one of the most conductive sulfide based ionic conductors, scalable synthesis of Li7P3S11 with controllable particle sizes is highly desired but rarely reported. Here, we report a facile wet-chemical synthesis method to prepare Li7P3S11 SSEs with variable sizes for all-solid-state lithium batteries (ASSLBs). By fully dissolving 70Li2S-30P2S5 precursors in ethyl acetate solution, the particle size of Li7P3S11 can be manipulated into as small as ~110 nm and high Li+ conductivity of 1.05 mS cm-1 can be achieved. A systematical mechanistic study of solvent effects suggests that the controlled particle sizes are attributed to the excellent solvability and low binding energy of ethyl acetate solvent toward solutes. Moreover, this generic method can be extended to the facilely synthesis of Li3PS4 nanoparticles with an average size of ~200 nm and high Li+ conductivity of 0.1 mS cm-1.

Zhou, Jianbin↗
DOE OSTI2013

Influence of heteroanion and ammonium cation size on the composition and gas-phase fragmentation of polyoxovanadates

This paper describes the results of a systematic experimental investigation of the influence of different size cationic ammonium ligands and heteroanions on the composition, ionic charge state and gas-phase fragmentation pathways of anionic polyoxovanadates synthesized in solution. Four separate solutions of olyoxometalates (POMs) were prepared using all possible combinations of the tetraethylammonium [(C2H5)4N+] ligand, chloride (Cl-) heteroanion, tetrabutylammonium [(C4H9)4N+] ligand and acetate (CH3CO2-) heteroanion. Employing electrospray ionization combined with high-resolution mass spectrometry (ESI-MS) we demonstrate that POM solutions synthesized using the small [(C2H5)4N+] ligand and Cl-heteroanion are composed predominately of large doubly and triply charged chlorine containing clusters with a size distribution centered at fourteen vanadium atoms. POM solutions prepared using the Cl- anion and [(C4H9)4N+] ligand are shown to contain slightly larger clusters with fifteen and sixteen vanadium atoms, thereby indicating that the size of the cationic ammonium ligand exerts only a weak influence on the polymerization of polyoxovanadates. POM solutions prepared using (C2H5)4NCl and (C4H9)4NCl also produced peaks consistent with the attachment of one and two ammonium cations to the larger clusters. Solutions prepared using the large CH3CO2 - heteroanion, in contrast, are demonstrated to contain much smaller singly and doubly *Manuscript Click here to view linked References 2 charged clusters with a size distribution centered at six vanadium atoms. In addition, while incorporation of one and two ammonium ligands into the smaller clusters was observed, no POMs containing the CH3CO2 - heteroanion were identified. The gas-phase fragmentation pathways of representative POMs containing one and two ammonium ligands were examined using collision induced dissociation (CID) and mass spectrometry. Similar primary fragmentation pathways involving partial loss of a ligand -[(CxHy)3N+ x = 2,4; y = 5,9] were observed for clusters containing both one and two ligands largely independent of the size, composition and charge state of the precursor ion. The [(C4H9)4N+] ligand was found to exhibit stronger interactions with the core of the POMs resulting in higher abundances of fragment ions containing (C4H9) units compared to (C2H5) units from [(C2H5)4N+]. These results provide fundamental insight into the interactions between anionic metal oxide clusters, heteroanions and cationic ammonium ligands that are responsible for the size and composition controlled synthesis of POMs in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Unraveling the implications of finite specimen size on the interpretation of dynamic experiments for polycrystalline aluminum through direct numerical simulations

Normal and Pressure-shear plate impact (NPI and PSPI) experiments are popular experimental techniques for studying the mean-field macroscopic behavior of polycrystalline metals under high-rate dynamic loading. However, since both configurations rely upon geometry for subjecting the specimen to high strain rates, these experiments often involve a limited specimen size. Moreover, because of the inherent heterogeneities present within polycrystalline metals, it is difficult to ascertain if the size of the specimen and/or regions where measurements are made are sufficiently large for making representative inferences about the mean-field macroscopic properties from single-point velocity measurements. In the present study, we quantify the expected measurement variability on observable point measurements in NPI and PSPI experiments by carrying out direct numerical simulations (DNS) of statistically representative polycrystalline microstructures subjected to dynamic compression and compression-shear loading. In particular, we consider the role of specific material heterogeneities (e.g. the grain-to-grain difference in size, crystallographic orientation) on dispersion in the normal and transverse particle velocity records and on local fluctuations in key state variables (e.g. velocity, accumulated plastic strain) by incorporating these effects directly into a representative synthetic microstructure geometry and crystalline description of pure polycrystalline aluminum. The form of the present study is a large parametric investigation, consisting of ten ensembles of one hundred simulations. Each of the thousand simulations reflects a randomly realized synthetic microstructure in one of five cases of decreasing average grain size for the two loading configurations. Our analysis of the DNS results demonstrates that for both of these experimental configurations, the grain size directly correlates with the coefficient of variation (CV) in simulated point measurements, showing a convergent decrease in CV to zero (i.e. particle velocity record approaches the mean-field value) with decreasing grain size. Remarkably, the magnitude of variations in the particle velocity record is shown to be largest where the deviatoric stresses are most significant. In the case of NPI, this occurs at the elastic and plastic wavefront, whereas, in the case of PSPI, the magnitude of fluctuations are approximately constant throughout the experimental window time. The reasoning for the scatter in particle velocity due to the heterogeneous microstructure is demonstrated to be dependent on the mechanisms for accommodating deformation and on the interaction of reflection waves generated at sites of heterogeneities occurring at the scale of grains. Lastly, we develop a power-law description for the magnitude of scattering versus characteristic length, which provides a statistical framework for assessing the required number of grains per characteristic specimen dimension for minimizing scatter within these two experimental configurations (NPI, PSPI).

36 MATERIALS SCIENCE↗
DOE OSTI2012

Hypofractionated Whole-Breast Radiation Therapy: Does Breast Size Matter?

Purpose: To evaluate the effects of breast size on dose-volume histogram parameters and clinical toxicity in whole-breast hypofractionated radiation therapy using intensity modulated radiation therapy (IMRT). Materials and Methods: In this retrospective study, all patients undergoing breast-conserving therapy between 2005 and 2009 were screened, and qualifying consecutive patients were included in 1 of 2 cohorts: large-breasted patients (chest wall separation >25 cm or planning target volume [PTV] >1500 cm{sub 3}) (n=97) and small-breasted patients (chest wall separation <25 cm and PTV <1500 cm{sub 3}) (n=32). All patients were treated prone or supine with hypofractionated IMRT to the whole breast (42.4 Gy in 16 fractions) followed by a boost dose (9.6 Gy in 4 fractions). Dosimetric and clinical toxicity data were collected and analyzed using the R statistical package (version 2.12). Results: The mean PTV V95 (percentage of volume receiving >= 95% of prescribed dose) was 90.18% and the mean V105 percentage of volume receiving >= 105% of prescribed dose was 3.55% with no dose greater than 107%. PTV dose was independent of breast size, whereas heart dose and maximum point dose to skin correlated with increasing breast size. Lung dose was markedly decreased in prone compared with supine treatments. Radiation Therapy Oncology Group grade 0, 1, and 2 skin toxicities were noted acutely in 6%, 69%, and 25% of patients, respectively, and at later follow-up (>3 months) in 43%, 57%, and 0% of patients, respectively. Large breast size contributed to increased acute grade 2 toxicity (28% vs 12%, P=.008). Conclusions: Adequate PTV coverage with acceptable hot spots and excellent sparing of organs at risk was achieved by use of IMRT regardless of treatment position and breast size. Although increasing breast size leads to increased heart dose and maximum skin dose, heart dose remained within our institutional constraints and the incidence of overall skin toxicity was comparable to that reported in the literature. Taken together, these data suggest that hypofractionated radiation therapy using IMRT is a viable and appropriate therapeutic modality in large-breasted patients.

62 RADIOLOGY AND NUCLEAR MEDICINE↗