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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Oxygen Reduction Reaction Measurements on Platinum Electrocatalysts Utilizing Rotating Disk Electrode Technique: I. Impact of Impurities, Measurement Protocols and Applied Corrections

The rotating disk electrode (RDE) technique is being extensively used as a screening tool to estimate the activity of novel PEMFC electrocatalysts synthesized in lab-scale (mg) quantities. Discrepancies in measured activity attributable to glassware and electrolyte impurity levels, as well as conditioning, protocols and corrections are prevalent in the literature. Moreover, the electrochemical response to a broad spectrum of commercially sourced perchloric acid and the effect of acid molarity on impurity levels and solution resistance were also assessed. Our findings reveal that an area specific activity (SA) exceeding 2.0 mA/cm 2 (20 mV/s, 25°C, 100 kPa, 0.1 M HClO 4 ) for polished poly-Pt is an indicator of impurity levels that do not impede the accurate measurement of the ORR activity of Pt based catalysts. After exploring various conditioning protocols to approach maximum utilization of the electrochemical area (ECA) and peak ORR activity without introducing catalyst degradation, an investigation of measurement protocols for ECA and ORR activity was conducted. Down-selected protocols were based on the criteria of reproducibility, duration of experiments, impurity effects and magnitude of pseudo-capacitive background correction. In sum, statistical reproducibility of ORR activity for poly-Pt and Pt supported on high surface area carbon was demonstrated.

14 SOLAR ENERGY↗
DOE OSTI2018

A Frequency Domain Multiplexing Technique for Multi-Channel Detector Instrumentation

Radiation detection often requires several detectors to be employed at once. Normally, each detector outputs a signal that must be transported, digitized, and stored. One common format for these signals is a finite, aperiodic pulse. Since the detector and data acquisition system are not necessarily physically close, transporting signals from several detectors to a central data acquisition system often requires the use of many cables. The technique presented here allows for the combination and later recovery of a number of analog detector signals using a single cable, by shifting their content to narrow bands in the frequency domain and summing them together into a single channel for transmission. The output is a linear combination of decaying sinusoids, whose peak frequencies and bandwidths in the frequency domain are controlled by inductor, resistor, and capacitor values in the circuit. By separating the outputs by several megahertz, and lowering the bandwidth to about 1 MHz, we can isolate each signal. The timing of the original input can be recovered by taking the inverse Fourier transform of the isolated peak and identifying the start time of the resulting single decaying sinusoid. The energy of the input signal is proportional to the square root of the integral of the corresponding power spectrum peak. We show that energy spectra can be reconstructed with minimal additions to energy resolution. We also show that coincidence timing measurements can be performed with an uncertainty smaller than 2 ns. The result is an N to 1 reduction in cabling, with obvious cost and complexity gains. Since most of the signal content exists only in a band around each peak frequency, noise outside of these bands does not impact the performance.

Belling, Samuel↗
NASA NTRS2002

Studies of Dust Emission as Measured by DIRBE and IRAS

The main activity supported by this grant was to make the dust reddening map more useful for optical and microwave astronomy, and to increase our understanding of interstellar dust in general. We completed all the major objectives of the proposal, and we are eagerly awaiting the launch of Space Infrared Telescope Facility (SIRTF) so that we can check one of our most controversial conclusions. According to the ADS abstract service, the above paper has been cited 895 times. A number of authors have claimed the SFD98 dust maps are miscalibrated, but recent work suggests that the calibration is correct. The primary goal of this ADP grant was to determine the microwave / sum-mm spectrum of interstellar dust emission by cross-correlating the Far Infrared Absolute Spectrophotometer (FIRAS) spectra with a model based on the SFD98 dust map. Because of temperature variation, large (factor of two) variations are observed in submillimeter / 100 micron ratio, so a careful accounting of dust temperature data, based on Diffuse Infrared Background Experiment (DIRBE) 100 and 240 micron channels, was required. Even this improvement was unable to reduce the chi(sup 2) per degree of freedom below 30. Further study revealed that a two-component model, with the two components having different (but reasonable) optical properties, achieved a decrease in chi(sup 2) to less than 2, five times better than the next best fit in the literature. The resulting model uses density and temperature estimates based on DIRBE data, with only four global parameters fit using the FIRAS data. This dramatic reduction in chi(sup 2) using only four fit parameters may indicate that the model is physically correct, but in any case, it is an acceptable phenomenological model. We have released the appropriate data and software on our website (http://astro.berkeley.edu/dust) to allow users to compute the interstellar dust emission between from 100-3000 GHz (or 100 micron 3 mm) with approx. 15% precision. The paper describing these efforts appeared in ApJ 524, 867. This paper has to date been cited 24 times.

Davis, Marc↗
DOE OSTI2014

Dose-to-water conversion for the backscatter-shielded EPID: A frame-based method to correct for EPID energy response to MLC transmitted radiation

Purpose: To develop a frame-by-frame correction for the energy response of amorphous silicon electronic portal imaging devices (a-Si EPIDs) to radiation that has transmitted through the multileaf collimator (MLC) and to integrate this correction into the backscatter shielded EPID (BSS-EPID) dose-to-water conversion model. Methods: Individual EPID frames were acquired using a Varian frame grabber and iTools acquisition software then processed using in-house software developed inMATLAB. For each EPID image frame, the region below the MLC leaves was identified and all pixels in this region were multiplied by a factor of 1.3 to correct for the under-response of the imager to MLC transmitted radiation. The corrected frames were then summed to form a corrected integrated EPID image. This correction was implemented as an initial step in the BSS-EPID dose-to-water conversion model which was then used to compute dose planes in a water phantom for 35 IMRT fields. The calculated dose planes, with and without the proposed MLC transmission correction, were compared to measurements in solid water using a two-dimensional diode array. Results: It was observed that the integration of the MLC transmission correction into the BSS-EPID dose model improved agreement between modeled and measured dose planes. In particular, the MLC correction produced higher pass rates for almost all Head and Neck fields tested, yielding an average pass rate of 99.8% for 2%/2 mm criteria. A two-sample independentt-test and fisher F-test were used to show that the MLC transmission correction resulted in a statistically significant reduction in the mean and the standard deviation of the gamma values, respectively, to give a more accurate and consistent dose-to-water conversion. Conclusions: The frame-by-frame MLC transmission response correction was shown to improve the accuracy and reduce the variability of the BSS-EPID dose-to-water conversion model. The correction may be applied as a preprocessing step in any pretreatment portal dosimetry calculation and has been shown to be beneficial for highly modulated IMRT fields.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1989

Rarefied-continuum gas dynamics transition for SUMS project

This program is to develop an analytic method for reducing SUMS data for the determination of the undisturbed atmosphere conditions ahead of the shuttle along its descending trajectory. It is divided into an internal flow problem, an external flow problem and their matching conditions. Since the existing method of Direct Simulation Monte Carlo (DSMC) failed completely for the internal flow problem, the emphasis is on the internal flow of a highly non-equilibrium, rarefied air through a short tube of a diameter much less than the gaseous mean free path. A two fluid model analysis of this internal flow problem has been developed and studied with typical results illustrated. A computer program for such an analysis and a technical paper published in Lecture Notes in Physics No. 323 (1989) are included as Appendices 3 and 4. A proposal for in situ determination of the surface accommodation coefficients sigma sub t and sigma e is included in Appendix 5 because of their importance in quantitative data reduction. A two fluid formulation for the external flow problem is included as Appendix 6 and a review article for AIAA on Hypersonic propulsion, much dependent on ambient atmospheric density, is also included as Appendix 7.

Cheng, Sin-I↗
NASA NTRS1984

Approaches to optimization of SS/TDMA time slot assignment

Reduction techniques for traffic matrices are explored in some detail. These matrices arise in satellite switched time-division multiple access (SS/TDMA) techniques whereby switching of uplink and downlink beams is required to facilitate interconnectivity of beam zones. A traffic matrix is given to represent that traffic to be transmitted from n uplink beams to n downlink beams within a TDMA frame typically of 1 ms duration. The frame is divided into segments of time and during each segment a portion of the traffic is represented by a switching mode. This time slot assignment is characterized by a mode matrix in which there is not more than a single non-zero entry on each line (row or column) of the matrix. Investigation is confined to decomposition of an n x n traffic matrix by mode matrices with a requirement that the decomposition be 100 percent efficient or, equivalently, that the line(s) in the original traffic matrix whose sum is maximal (called critical line(s)) remain maximal as mode matrices are subtracted throughout the decomposition process. A method of decomposition of an n x n traffic matrix by mode matrices results in a number of steps that is bounded by n(2) - 2n + 2. It is shown that this upper bound exists for an n x n matrix wherein all the lines are maximal (called a quasi doubly stochastic (QDS) matrix) or for an n x n matrix that is completely arbitrary. That is, the fact that no method can exist with a lower upper bound is shown for both QDS and arbitrary matrices, in an elementary and straightforward manner.

Wade, T. O.↗
DOE OSTI2018

Suppression of NLRP3 inflammasome attenuates stress-induced depression-like behavior in NLGN3-deficient mice

Highlights: • NLGN3 deletion attenuates stress-induced depression-like phenotype. • NLGN3 deficiency ameliorates neuron injury and glial cell activation. • NLGN3 knockout reduces NLRP3 inflammasome and NF-κB activity in cortex, hippocampus and amygdala. • NLGN3 knockdown alleviates inflammation in LPS-stimulated AST through NLRP3 inflammasome. Depression, regulated by central nervous system (CNS), is a significant inflammatory disorder. Neuroligin3 (NLGN3) has been implicated in brain functions. In the study, a chronic unpredictable mild stress (CUMS) model in wild type (WT) or NLGN3-knockout (KO) mice was established to explore the role of NLGN3 in regulating depression and to reveal the underlying molecular mechanism. The results indicated that NLGN3-knockout markedly reversed the loss of body weight, the reduction of sucrose consumption, the decrease of immobile time in the forced swimming tests (FST) and tail suspension tests (TST) induced by CUMS paradigm. CUMS up-regulated corticosterone (CORT) in serum, and down-regulated serotonin (5-HT), norepinephrine (NE) and brain-derived neurotrophic factor (BDNF) in hippocampus of mice, which were significantly reversed by NLGN3 deficiency. The results further demonstrated that NLGN3-knockout improved the degenerative neurons in cortex and hippocampus of CUMS-treated mice, accompanied with a significant decrease of ionized calciumbinding adapter molecule 1 (Iba-1) and glial fibrillary acidic protein (GFAP) expressions. Additionally, NLGN3-KO mice challenged with CUMS showed a significant reduction of pro-inflammatory cytokines and chemokine, including tumor necrosis factor-alpha (TNF-α), interleukin-18 (IL-18), interleukin-1 beta (IL-1β), interleukin-4 (IL-4), CC-chemokine ligand-1 (CCL-1) and CXC-chemokine ligand-1 (CXCL-1), in cortex, hippocampus and amygdala tissue samples. Western blot analysis suggested that NLGN3-knockout inhibited the activation of nod-like receptor protein 3 (NLRP3) inflammasome and its adaptor of apoptosis-associated speck like protein (ASC), and reduced the expression of Caspase-1, along with the inactivation of nuclear factor-κB (NF-κB) in CUMS-challenged mice. The role of NLGN3 in regulating depression in mice was confirmed in vitro using astrocytes stimulated by LPS that NLGN3 knockdown reduced LPS-induced inflammation. Importantly, the suppressive effects of NLGN3-knockdown on inflammatory response were reversed by NLRP3 or ASC over-expression in AST exposed to LPS. In sum, our findings indicated that suppressing NLGN3 played a potential antidepressant role in CUMS animal model by inactivating NLRP3 inflammasome, providing a new therapeutic avenue for depression.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Dynamic Household Vehicle Decision Modeling Considering Plug-in Electric Vehicles

Plug-in electric vehicles (PEVs) offer alternatives to traditional vehicles that rely on petroleum-based fuels. While PEV customers can enjoy significant reductions in fuel costs, they incur a larger capital cost than users of traditional vehicles because PEV technology is still maturing. Therefore, consumers adopting PEVs face a trade-off between fuel cost savings with environmental benefits and extra capital cost. It is thus crucial for policy makers and PEV manufacturers to understand people's vehicle decision-making process while considering their socio-economic and travel pattern characteristics as well as the built-environment factors. This paper presents a connected, two-stage, dynamic model of PEV adoption and vehicle-transaction decision-making. Two connected nested logit (NL) models are estimated. The upper level is a two-level NL model to predict choice of vehicle type between four fuel types: gasoline, diesel, hybrid gasoline-electric, and PEV. The lower level is an NL model of vehicle-transaction choice which accommodates four transaction decisions of buy, trade, dispose, and do nothing, while accounting for the log-sum from the vehicle-type choice model, and is estimated using two waves of a panel data set. We find that households with higher levels of income and education are more likely to adopt a PEV. We also found that primarily decision makers take into account the accessibility to charging stations as a critical factor in choosing PEVs.

Nazari, Fatemeh↗
DOE OSTI2014

EnergyFit Nevada (formerly known as the Nevada Retrofit Initiative) final report and technical evaluation

The EnergyFit Nevada (EFN) Better Buildings Neighborhood Program (BBNP, and referred to in this document as the EFN program) currently encourages Nevada residents to make whole-house energy-efficient improvements by providing rebates, financing, and access to a network of qualified home improvement contractors. The BBNP funding, consisting of 34 Energy Efficiency Conservation Block Grants (EECBG) and seven State Energy Program (SEP) grants, was awarded for a three-year period to the State of Nevada in 2010 and used for initial program design and implementation. By the end of first quarter in 2014, the program had achieved upgrades in 553 homes, with an average energy reduction of 32% per home. Other achievements included: Completed 893 residential energy audits and installed upgrades in 0.05% of all Nevada single-family homes1 Achieved an overall conversation rate of 38.1%2 7,089,089 kWh of modeled energy savings3 Total annual homeowner energy savings of approximately $525,7523 Efficiency upgrades completed on 1,100,484 square feet of homes3 $139,992 granted in loans to homeowners for energy-efficiency upgrades 29,285 hours of labor and $3,864,272 worth of work conducted by Nevada auditors and contractors4 40 contractors trained in Nevada 37 contractors with Building Performance Institute (BPI) certification in Nevada 19 contractors actively participating in the EFN program in Nevada 1 Calculated using 2012 U.S. Census data reporting 1,182,870 homes in Nevada. 2 Conversion rate through March 31, 2014, for all Nevada Retrofit Initiative (NRI)-funded projects, calculated using the EFN tracking database. 3 OptiMiser energy modeling, based on current utility rates. 4 This is the sum of $3,596,561 in retrofit invoice value and $247,711 in audit invoice value.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Optimal Traffic Signal Control Using Priority Metric Based on Real-Time Measured Traffic Information

Optimizing traffic control systems at traffic intersections can reduce network-wide fuel consumption as well as improve traffic flow. While traffic signals have conventionally been controlled based on predetermined schedules, various adaptive control systems have been developed recently using advanced sensors such as cameras, radars, and LiDARs. By utilizing rich traffic information enabled by the advanced sensors, more efficient or optimal traffic signal control is possible in response to varying traffic conditions. This paper proposes an optimal traffic signal control method to minimize network-wide fuel consumption utilizing real-time traffic information provided by advanced sensors. This new method employs a priority metric calculated by a weighted sum of various factors, including the total number of vehicles, total vehicle speed, vehicle waiting time, and road preference. Genetic Algorithm (GA) is used as a global optimization method to determine the optimal weights in the priority metric. In order to evaluate the effectiveness of the proposed method, a traffic simulation model is developed in a high-fidelity traffic simulation environment called SUMO, based on a real-world traffic network. The traffic flow within this model is simulated using actual measured traffic data from the traffic network, enabling a comprehensive assessment of the novel optimal traffic signal control method in realistic conditions. The simulation results show that the proposed priority metric-based real-time traffic signal control algorithm can significantly reduce network-wide fuel consumption compared to the conventional fixed-time control and coordinated actuated control methods that are currently used in the modeled network. Additionally, incorporating truck priority in the priority metric leads to further improvements in fuel consumption reduction.

47 OTHER INSTRUMENTATION↗
NASA NTRS1995

Joint ROSAT-Compton GRO observations of the X-ray bright Seyfert galaxy IC 4329A

We report a simultaneous ROSAT and Gamma Ray Observatory (GRO) observation of the X-ray-bright Seyfert galaxy IC 4329A. For the GRO Oriented Scintillation Spectrometer Experiment (OSSE) detector, we also present the sum of the data for this and earlier observations. The overall spectrum is very well described as a power law with an energy spectral index of approximately 1 absorbed at low energies plus a strong Compton reflection component, typical for Seyfert 1 galaxies. The low energy absorption can be well described by a sum of a neutral column density of approximately 3 x 10(exp 21)sq cm, most of which is associated with the edge-on galactic disk of IC 4329A, plus an edgelike feature at approximately 700 eV; this feature implies either complex absorption (due to additional ionized material, or due to a partial covering), or a soft excess. The data only weakly constrain the presence of a high-energy cutoff in the underlying power law; they are compatible with an exponential cutoff at any energy E(sub c) approximately greater than 100 keV. The relative steepness of the OSSE data, with the power-law energy index of 1.6 +/- 0.2, can be accounted for entirely by the contribution of the high-energy tail of the reflection component when E(sub c) approaches infinity. (We find that the definite cutoff at an energy E(sub c)approximately 130 keV suggested in the recently published analysis of the OSSE data for this subject is due to a data reduction error.) Including nonsimultaneous Ginga observations with 2 keV fluxes matching well that of ROSAT gives us likely broad-band X-ray/gamma-ray spectra of the object from approximately 0.1 keV up to several hundred keV. We also report the ROSAT spectrum of the companion object to the Seyfert galaxy, the elliptical galaxy IC 4329.

Madejski, G. M.↗
NASA NTRS2011

Benefit Assessment of the Precision Departure Release Capability Concept

A Precision Departure Release Capability concept is being evaluated by both the National Aeronautics and Space Administration and the Federal Aviation Administration as part of a larger goal of improving throughput, efficiency and capacity in integrated departure, arrival and surface operations. The concept is believed to have the potential of increasing flight efficiency and throughput by avoiding missing assigned slots and minimizing speed increase or path stretch to recover the slot. The main thrust of the paper is determining the impact of early and late departures from the departure runway when an aircraft has a slot assigned either at a meter fix or at the arrival airport. Results reported in the paper are for two scenarios. The first scenario considers flights out of Dallas/Fort Worth destined for Hartsfield-Jackson International Airport in Atlanta flying through the Meridian meter-fix in the Memphis Center with miles-in-trail constraints. The second scenario considers flights destined to George Bush Intercontinental/Houston Airport with specified airport arrival rate constraint. Results show that delay reduction can be achieved by allowing reasonable speed changes in scheduling. It was determined that the traffic volume between Dallas/Fort Worth and Atlanta via the Meridian fix is low and the departures times are spread enough that large departure schedule uncertainty can be tolerated. Flights can depart early or late within 90 minutes without accruing much more delay due to miles-in-trail constraint at the Meridian fix. In the Houston scenario, 808 arrivals from 174 airports were considered. Results show that delay experienced by the 16 Dallas/Fort Worth departures is higher if initial schedules of the remaining 792 flights are kept unaltered while they are rescheduled. Analysis shows that the probability of getting the initially assigned slot back after perturbation and rescheduling decreases with increasing standard deviation of the departure delay distributions. Results show that most Houston arrivals can be expected to be on time based on the assumed zero-mean Normal departure delay distributions achievable by Precision Departure Release Capability. In the current system, airport-departure delay, which is the sum of gate-departure delay and taxi-out delay, is observed at the airports. This delay acts as a bias, which can be reduced by Precision Departure Release Capability.

Palopo, Kee↗
NASA NTRS1986

Meal composition and plasma amino acid ratios: Effect of various proteins or carbohydrates, and of various protein concentrations

The effects of meals containing various proteins and carbohydrates, and of those containing various proportions of protein (0 percent to 20 percent of a meal, by weight) or of carbohydrate (0 percent to 75 percent), on plasma levels of certain large neutral amino acids (LNAA) in rats previously fasted for 19 hours were examined. Also the plasma tryptophan ratios (the ratio of the plasma trytophan concentration to the summed concentrations of the other large neutral amino acids) and other plasma amino acid ratios were calculated. (The plasma tryptophan ratio has been shown to determine brain tryptophan levels and, thereby, to affect the synthesis and release of the neurotransmitter serotonin). A meal containing 70 percent to 75 percent of an insulin-secreting carbohydrate (dextrose or dextrin) increased plasma insulin levels and the tryptophan ratio; those containing 0 percent or 25 percent carbohydrate failed to do so. Addition of as little as 5 percent casein to a 70 percent carbohydrate meal fully blocked the increase in the plasma tryptophan ratio without affecting the secretion of insulin - probably by contributing much larger quantities of the other LNAA than of tryptophan to the blood. Dietary proteins differed in their ability to suppress the carbohydrate-induced rise in the plasma tryptophan ratio. Addition of 10 percent casein, peanut meal, or gelatin fully blocked this increase, but lactalbumin failed to do so, and egg white did so only partially. (Consumption of the 10 percent gelatin meal also produced a major reduction in the plasma tyrosine ratio, and may thereby have affected brain tyrosine levels and catecholamine synthesis.) These observations suggest that serotonin-releasing neurons in brains of fasted rats are capable of distinguishing (by their metabolic effects) between meals poor in protein but rich in carbohydrates that elicit insulin secretion, and all other meals. The changes in brain serotonin caused by carbohydrate-rich, protein-poor meals may affect subsequent food choice and various serotonin-mediated behaviors.

Yokogoshi, Hidehiko↗
DOE OSTI2016

Determination of water equivalent content in fuel rods

In water-cooled reactors, hydriding failure of zircaloy cladding tubes can be easily caused by high content of total water in fuel rods. WEC, which is the water equivalent content within the cold space of a fuel rod, directly reflects the total water content of the fuel rod. A device measuring WEC has been designed, manufactured and tested. This extraction device is a hermetically sealed system consisting of six parts: the break-off part, the heating unit, the reduction unit, the sample storage part, the collecting unit and the gas flow system. Each part is connected to another one using a special connection, and the device's end part is connected to a gas chromatograph. The determination procedure can be briefly summarized as follows: first, a test fuel rod should be put into the sealed device after lathing two circular grooves on both ends, so that it can be easily broken at these points in the break-off part. Driven by carrier gas, water and hydrogen both contained in helium gas and absorbed on the rod in-wall pass over the hot uranium filament where water is converted into hydrogen. After being concentrated by the collecting unit, hydrogen flows into the gas chromatograph for measurement and data are calculated as total water content A. UO{sub 2} pellets in the test rod should be taken out from the sample storage part and the total hydrogen content of these pellets is determined according to ASTM C1457 standard, followed by its conversion into total water content B. Finally, the sum of A and B being divided by the free volume of the cold space within the test rod, gives the value of WEC.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

SU-G-BRA-17: Tracking Multiple Targets with Independent Motion in Real-Time Using a Multi-Leaf Collimator

Purpose: Multiple targets with large intrafraction independent motion are often involved in advanced prostate, lung, abdominal, and head and neck cancer radiotherapy. Current standard of care treats these with the originally planned fields, jeopardizing the treatment outcomes. A real-time multi-leaf collimator (MLC) tracking method has been developed to address this problem for the first time. This study evaluates the geometric uncertainty of the multi-target tracking method. Methods: Four treatment scenarios are simulated based on a prostate IMAT plan to treat a moving prostate target and static pelvic node target: 1) real-time multi-target MLC tracking; 2) real-time prostate-only MLC tracking; 3) correcting for prostate interfraction motion at setup only; and 4) no motion correction. The geometric uncertainty of the treatment is assessed by the sum of the erroneously underexposed target area and overexposed healthy tissue areas for each individual target. Two patient-measured prostate trajectories of average 2 and 5 mm motion magnitude are used for simulations. Results: Real-time multi-target tracking accumulates the least uncertainty overall. As expected, it covers the static nodes similarly well as no motion correction treatment and covers the moving prostate similarly well as the real-time prostate-only tracking. Multi-target tracking reduces >90% of uncertainty for the static nodal target compared to the real-time prostate-only tracking or interfraction motion correction. For prostate target, depending on the motion trajectory which affects the uncertainty due to leaf-fitting, multi-target tracking may or may not perform better than correcting for interfraction prostate motion by shifting patient at setup, but it reduces ∼50% of uncertainty compared to no motion correction. Conclusion: The developed real-time multi-target MLC tracking can adapt for the independently moving targets better than other available treatment adaptations. This will enable PTV margin reduction to minimize health tissue toxicity while remain tumor coverage when treating advanced disease with independently moving targets involved. The authors acknowledge funding support from the Australian NHMRC Australia Fellowship and NHMRC Project Grant No. APP1042375.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Passivation, conductivity, and selectivity in solar cell contacts: Concepts and simulations based on a unified partial-resistances framework

Passivation, conductivity, and selectivity are often acknowledged as the three requirements for optimal contacts to photovoltaic solar cells. Although there are generally accepted definitions and metrics for passivation and conductivity, a common understanding of the concept of selectivity is emerging only now. In this contribution, we present a generalized model of solar cell contacts based on the distinct lumped resistances encountered by electrons and holes traversing a contact, which we refer to as partial specific contact resistances. The relations between electron and hole partial current densities, quasi-Fermi level separation, and external voltage are derived from these partial specific contact resistances, leading to simple metrics for the aforementioned contact properties: the sum of the electron and hole resistances is a metric for passivation, their ratio is a metric for selectivity, and the majority-carrier resistance is a metric for conductivity. Using PC1D, we validate our model by simulating 10 500 cases of homojunction contacts to crystalline silicon solar cells, although our framework is material agnostic and can be equally applied to any other type of absorber. In these simulations, the hole contact and absorber are assumed to be ideal, whereas we vary the partial specific contact resistances in the electron contact by orders of magnitude by adjusting the electron and hole mobilities, their densities (through variations of the donor doping density), and the contact thickness. The simulations confirm the finding of the model that, when the contact fraction cannot be adjusted—as is the case with full-area contacts—combined passivation and conductivity are necessary and sufficient for optimal solar cell performance, and they imply selectivity. However, the reciprocal is not true: contacts can be selective but lack conductivity—causing a deleterious drop in fill factor—or can be selective but provide poor passivation—leading to a reduction in implied open-circuit voltage and, hence, actual open-circuit voltage. Furthermore, selectivity is a meaningful metric in the sole case of partial-area contacts, where the contact fraction can be adjusted arbitrarily.

14 SOLAR ENERGY↗
DOE OSTI2019

Comparison of CZT SPECT and conventional SPECT for assessment of contractile function, mechanical synchrony and myocardial scar in patients with heart failure

Aim: The aim of this study was to compare CZT-SPECT (CZT SPECT) to conventional SPECT (C-SPECT) in the assessment of left ventricular myocardial scar, contractile function, and mechanical synchrony in patients with heart failure (HF). Methods: Fifty-nine patients with HF who were referred for myocardial perfusion/metabolism imaging were enrolled. All patients underwent resting {sup 99m}Tc-MIBI gated myocardial perfusion imaging using a CZT SPECT camera and a C-SPECT camera, respectively, and {sup 18}F-FDG PET myocardial metabolism imaging within three days. Summed rest score (SRS) and total perfusion defect (TPD) (as indices of perfusion abnormality), left ventricular (LV), end diastolic volume (EDV), end systolic volume (ESV), and ejection fraction (EF) (as indices of LV systolic function), and histogram band width (BW) and standard deviation (SD) (as indices of mechanical synchrony) were analyzed by automated software while the perfusion/metabolism patterns were analyzed visually. Results: There was a good correlation between CZT SPECT and C-SPECT for SRS and TPD. CZT SPECT tended to underestimate SRS and TPD compared to C-SPECT. CZT-SPECT and C-SPECT showed excellent agreement in assessing the perfusion/metabolism pattern though a small proportion of normal segments (6.6%) identified by CZT/PET exhibited mismatch pattern on C-SPECT/PET. CZT SPECT also showed excellent correlation with C-SPECT in measuring EDV, ESV, and EF. Finally, BW and SD measured by CZT SPECT correlated well with C-SPECT but CZT SPECT tended to overestimate BW and SD compared to C-SPECT. Conclusion: CZT SPECT provided comparable data to C-SPECT for measuring LV scar, function and synchrony at a considerable reduction in imaging time. CZT SPECT holds a promise for comprehensive evaluation of myocardial performance in patients with HF.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Experimental Fuel Consumption Results from a Heterogeneous Four-Truck Platoon

Platooning has the potential to reduce greenhouse gas missions of heavy-duty vehicles. Prior platooning studies have chiefly focused on the fuel economy characteristics and three-truck platoons, and most have investigated aerodynamically homogeneous platoons with trucks of the same trim. For real world application and accurate return on investment for potential adopters, non-uniform platoons and the impacts of grade and disturbances on a platoon’s fuel economy must also be characterized. This study investigates the fuel economy of a heterogeneous four-truck platoon on a closed test track. Tests were run for one hour at a speed of 45 mph. The trucks used for this study are two 2015 Peterbilt 579’s with a Cummins ISX15 and a Paccar MX-13, and two 2009 Freightliner M915A5’s, one armored and the other unarmored. Many analysis methodologies were leveraged to describe and compare the fuel data, including lap-wise and track-segment analysis. The methodology for dividing the data into laps is described in detail. The influence of other factors beyond the aerodynamics of platooning is discussed. CAN fuel rate analysis showed excellent agreement with previous experimental trends for two and three-truck platoons. In general, the indicated fuel economy benefits in this study were 5-11% for following vehicles and 0-4% for the lead vehicle in platoon relative to their baseline fuel consumption. On a cumulative basis, all platoons saved fuel, ranging from 6% to 8% versus the sum of the standalone trucks’ fuel consumption. The practical implications of the fuel economy results are discussed, as well as avenues for future research. Introduction and Motivation platooning is controlled coordination of two or more vehicles in a convoy, sometimes called CACC (Coordinated or Cooperative Adaptive Cruise Control). The distance between vehicles in a platoon can be controlled tightly at no additional fatigue to the driver. Platooning vehicles can also respond quickly to braking events of the leader, much more quickly than the typical human driver’s reaction time of 1-1.5 s. Therefore, vehicles in a platoon can follow each other much more closely than would usually be considered a safe following distance under human operation. It is implied that under very close following conditions, platooning technology must be extremely robust before it is safe for wide-scale implementation. Platooning is under investigation as a fuel-saving technology. Close-following significantly reduces aerodynamic drag for both leading and trailing vehicles. According to the NRC in 2010, aerodynamic drag represents roughly half of a Class-8 truck’s on-highway fuel usage, meaning a 20% reduction in drag roughly equals a 10% reduction in fuel usage, if all other sources of energy loss remain equal (i.e. accessory, rolling resistance, drivetrain, braking). It is by aerodynamics that platooning saves fuel. At risk of oversimplifying the aerodynamics, following (or trailing) vehicles experience reduced wind velocity due to shielding, and the leading vehicles experience an increased aft pressure, especially at distances closer than 75’ (23 m).

greenhouse gas emissions, truck platoon, heavy-dut↗