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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Non-Markovian dynamics of quantum open systems embedded in a hybrid environment

Quantum systems of interest are typically coupled to several quantum channels (more generally environments). In this paper, we develop an exact stochastic Schrödinger equation for an open quantum system coupled to a hybrid environment containing both bosonic and fermionic particles. Such a stochastic differential equation may be obtained directly from a microscopic model through employing a classical complex Gaussian noise and a non-commutative fermionic noise to simulate the hybrid bath. As an immediate application of our developed stochastic approach, we show that the evolution of the reduced density matrix can be derived by taking the average over both the bosonic noise and the fermionic noise. Three specific examples are given in this paper to illustrate that the hybrid quantum trajectory is fully consistent with the standard quantum mechanics. Our examples also shed new light on the special features exhibited by the fermionic bath and bosonic bath. - Highlights: • Exact dynamic equation for quantum open system coupled to a hybrid bath is derived. • The equation is consistent with standard quantum mechanics. • The dynamic equation derived is useful in exploring non-Markovian features.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Potential landscape and flux field theory for turbulence and nonequilibrium fluid systems

Highlights: •The notion of nonequilibrium trinity based on detailed balance breaking is proposed. •Nonequilibrium trinity captures the nonequilibrium irreversible nature of turbulence. •Nonequilibrium trinity leads to the potential-flux form of stochastic fluid dynamics. •Energy flux in turbulence energy cascade is connected to nonequilibrium trinity. •The four-fifths law of turbulence is a manifestation of nonequilibrium trinity. -- Abstract: Turbulence is a paradigm for far-from-equilibrium systems without time reversal symmetry. To capture the nonequilibrium irreversible nature of turbulence and investigate its implications, we develop a potential landscape and flux field theory for turbulent flow and more general nonequilibrium fluid systems governed by stochastic Navier–Stokes equations. We find that equilibrium fluid systems with time reversibility are characterized by a detailed balance constraint that quantifies the detailed balance condition. In nonequilibrium fluid systems with nonequilibrium steady states, detailed balance breaking leads directly to a pair of interconnected consequences, namely, the non-Gaussian potential landscape and the irreversible probability flux, forming a ‘nonequilibrium trinity’. The nonequilibrium trinity characterizes the nonequilibrium irreversible essence of fluid systems with intrinsic time irreversibility and is manifested in various aspects of these systems. The nonequilibrium stochastic dynamics of fluid systems including turbulence with detailed balance breaking is shown to be driven by both the non-Gaussian potential landscape gradient and the irreversible probability flux, together with the reversible convective force and the stochastic stirring force. We reveal an underlying connection of the energy flux essential for turbulence energy cascade to the irreversible probability flux and the non-Gaussian potential landscape generated by detailed balance breaking. Using the energy flux as a center of connection, we demonstrate that the four-fifths law in fully developed turbulence is a consequence and reflection of the nonequilibrium trinity. We also show how the nonequilibrium trinity can affect the scaling laws in turbulence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Analogue stochastic gravity in strongly-interacting Bose–Einstein condensates

Collective modes propagating in a moving superfluid are known to satisfy wave equations in a curved space–time, with a metric determined by the underlying superflow. We use the Keldysh technique in a curved space–time to develop a quantum geometric theory of fluctuations in superfluid hydrodynamics. This theory relies on a “quantized” generalization of the two-fluid description of Landau and Khalatnikov, where the superfluid component is viewed as a quasi-classical field coupled to a normal component — the collective modes/phonons representing a quantum bath. This relates the problem in the hydrodynamic limit to the “quantum friction” problem of Caldeira–Leggett type. By integrating out the phonons, we derive stochastic Langevin equations describing a coupling between the superfluid component and phonons. These equations have the form of Euler equations with additional source terms expressed through a fluctuating stress–energy tensor of phonons. Conceptually, this result is similar to stochastic Einstein equations that arise in the theory of stochastic gravity. We formulate the fluctuation–dissipation theorem in this geometric language and discuss possible physical consequences of this theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

An average stochastic approach to two-body dissipation in finite fermion systems

We present average stochastic time-dependent Hartree–Fock (ASTDHF) as a theory for efficient handling of incoherent dynamical correlations in finite fermion systems at fully quantum-mechanical level. The basic time evolution is given by time-dependent mean-field theory. The two-body collisions beyond mean-field propagation are evaluated stochastically in an incoherent ensemble of mean-field states as was done in the previously developed STDHF. The new, and time saving, feature in ASTDHF is that it employs one common mean field throughout the whole ensemble. A detailed presentation of ASTDHF is given and extensive comparison with STDHF and other approaches to dissipation are discussed. ASTDHF is found to be a very efficient approach for well bound systems where mean-field fluctuations remain small.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Quasielastic neutron scattering in biology: Theory and applications

Neutrons scatter quasielastically from stochastic, diffusive processes, such as overdamped vibrations, localized diffusion and transitions between energy minima. In biological systems, such as proteins and membranes, these relaxation processes are of considerable physical interest. We review here recent methodological advances and applications of quasielastic neutron scattering (QENS) in biology, concentrating on the role of molecular dynamics simulation in generating data with which neutron profiles can be unambiguously interpreted. We examine the use of massively-parallel computers in calculating scattering functions, and the application of Markov state modeling. The decomposition of MD-derived neutron dynamic susceptibilities is described, and the use of this in combination with NMR spectroscopy. We discuss dynamics at very long times, including approximations to the infinite time mean-square displacement and nonequilibrium aspects of single-protein dynamics. Lastly, we examine how neutron scattering and MD can be combined to provide information on lipid nanodomains.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

Trehalose as an indicator of desiccation stress in Drosophila melanogaster larvae: A potential marker of anhydrobiosis

Highlights: Black-Right-Pointing-Pointer First report confirming anhydrobiosis in Drosophila melanogaster larvae. Black-Right-Pointing-Pointer Trehalose synthesis and accumulation in larvae that hydrolyzed on rehydration. Black-Right-Pointing-Pointer Trehalose synthesis in concert with the enzymes involved in trehalose metabolism. Black-Right-Pointing-Pointer Inhibition of trehalose hydrolysis in presence of a specific trehalase inhibitor. Black-Right-Pointing-Pointer Trehalose proposed as a reliable marker for biomonitoring of climate change studies. -- Abstract: In the current scenario of global climate change, desiccation is considered as one of the major environmental stressors for the biota exposed to altered levels of ambient temperature and humidity. Drosophila melanogaster, a cosmopolitan terrestrial insect has been chosen as a humidity-sensitive bioindicator model for the present study since its habitat undergoes frequent stochastic and/or seasonally aggravated dehydration regimes. We report here for the first time the occurrence of anhydrobiosis in D. melanogaster larvae by subjecting them to desiccation stress under laboratory conditions. Larvae desiccated for ten hours at <5% relative humidity could enter anhydrobiosis and could revive upon rehydration followed by resumption of active metabolism. As revealed by FTIR and HPLC analyzes, our findings strongly indicated the synthesis and accumulation of trehalose in the desiccating larvae. Biochemical measurements pointed out the desiccation-responsive trehalose metabolic pathway that was found to be coordinated in concert with the enzymes trehalose 6-phosphate synthase and trehalase. Further, an inhibitor-based experimental approach using deoxynojirimycin, a specific trehalase inhibitor, demonstrated the pivotal role of trehalose in larval anhydrobiosis of D. melanogaster. We therefore propose trehalose as a potential marker for the assessment of anhydrobiosis in Drosophila. The present findings thus add to the growing list of novel biochemical markers in specific bioindicator organisms for fulfilling the urgent need of environmental biomonitoring of climate change.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Functional characterization of a rice de novo DNA methyltransferase, OsDRM2, expressed in Escherichia coli and yeast

Highlights: ► A rice de novo DNA methyltransferase OsDRM2 was cloned. ► In vitro methylation activity of OsDRM2 was characterized with Escherichia coli. ► Assays of OsDRM2 in vivo methylation were done with Saccharomyces cerevisiae. ► OsDRM2 methylation activity is not preferential to any type of cytosine context. ► The activity of OsDRM2 is independent of RdDM pathway. - Abstract: DNA methylation of cytosine nucleotides is an important epigenetic modification that occurs in most eukaryotic organisms and is established and maintained by various DNA methyltransferases together with their co-factors. There are two major categories of DNA methyltransferases: de novo and maintenance. Here, we report the isolation and functional characterization of a de novo methyltransferase, named OsDRM2, from rice (Oryza sativa L.). The full-length coding region of OsDRM2 was cloned and transformed into Escherichia coli and Saccharomyces cerevisiae. Both of these organisms expressed the OsDRM2 protein, which exhibited stochastic de novo methylation activity in vitro at CG, CHG, and CHH di- and tri-nucleotide patterns. Two lines of evidence demonstrated the de novo activity of OsDRM2: (1) a 5′-CCGG-3′ containing DNA fragment that had been pre-treated with OsDRM2 protein expressed in E. coli was protected from digestion by the CG-methylation-sensitive isoschizomer HpaII; (2) methylation-sensitive amplified polymorphism (MSAP) analysis of S. cerevisiae genomic DNA from transformants that had been introduced with OsDRM2 revealed CG and CHG methylation levels of 3.92–9.12%, and 2.88–6.93%, respectively, whereas the mock control S. cerevisiae DNA did not exhibit cytosine methylation. These results were further supported by bisulfite sequencing of the 18S rRNA and EAF5 genes of the transformed S. cerevisiae, which exhibited different DNA methylation patterns, which were observed in the genomic DNA. Our findings establish that OsDRM2 is an active de novo DNA methyltransferase gene with conserved activity in both prokaryotic and eukaryotic non-host species.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Biophysical and biological meanings of healthspan from C. elegans cohort

Highlights: • We focus on a third factor, noise, as well as on genetic and environmental factors. • C. elegans fed a healthy food had an extended healthspan as compared to those fed a conventional diet. • An amplification of ATP noise was clearly evident from around the onset of biodemographic aging. • The extension of timing of noise amplification may contribute to effectively extending the healthspan. • The same mechanism of the mean lifespan extension in C. elegans may be realized in humans. - Abstract: Lifespan among individuals ranges widely in organisms from yeast to mammals, even in an isogenic cohort born in a nearly uniform environment. Needless to say, genetic and environmental factors are essential for aging and lifespan, but in addition, a third factor or the existence of a stochastic element must be reflected in aging and lifespan. An essential point is that lifespan or aging is an unpredictable phenomenon. The present study focuses on elucidating the biophysical and biological meanings of healthspan that latently indwells a stochastic nature. To perform this purpose, the nematode Caenorhabditis elegans served as a model animal. C. elegans fed a healthy food had an extended healthspan as compared to those fed a conventional diet. Then, utilizing this phenomenon, we clarified a mechanism of healthspan extension by measuring the single-worm ATP and estimating the ATP noise (or the variability of the ATP content) among individual worms and by quantitatively analyzing biodemographic data with the lifespan equation that was derived from a fluctuation theory.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Aberrant increase of NMR signal in hydrogen exchange experiments. Observation and explanation

Hydrogen exchange (HX) NMR spectroscopy is widely used for monitoring structure, stability and dynamics of proteins at the level of individual residues. The stochastic replacement of protons by deuterons typically leads to an exponential decrease of the NMR signals. However, an unusual signal increase was observed in HX of several amides for T4 lysozyme L99A. This effect can be attributed to peak sharpening as a result of reduced dipolar relaxation from proximal amide protons that experience more rapid hydrogen/deuterium (H/D) exchange. The behavior was specifically observed at the termini of secondary structure elements, where large differences in protection against H/D exchange are observed. This effect is expected to be more widespread in NMR HX studies, and is important for the accurate determination of protection factors. - Highlights: • Unusual NMR signal increase in hydrogen/deuterium exchange experiments. • The suppression of the effect of dipole-dipole interactions leads to peak sharpening and NMR signal increase. • Taking the effects of dipole-dipole interactions into account improves analysis of hydrogen exchange in general.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Theoretical estimate of the effect of thermal agitation on ribosome motion generated by stochastic microswimming

The effect of thermal agitation on ribosome motion is evaluated through the Péclet number, assuming that the ribosome is self-propelled along the mRNA during protein synthesis by a swimming stroke consisting of a cycle of stochastically-generated ribosome configurations involving its two subunits. The ribosome velocity probability distribution function is obtained, giving an approximately normal distribution. Its mean and variance together with an estimate of the in vivo free diffusion coefficient of the ribosome and using only configuration changes of small size, give a Péclet number similar to motor proteins and microorganisms. These results suggest the feasibility of the stochastic microswimming hypothesis to explain ribosome motion. - Highlights: • Hypothesis: the ribosome swims along the mRNA during protein synthesis. • How can withstand the thermal agitation of the particles in the surrounding fluid? • The Péclet number Pe is calculated estimating the in vivo diffusion coefficient. • With small size deformations the ribosome has speeds similar to motor proteins. • Similar Pe values for the ribosome and the motor proteins mean feasible hypothesis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Bimodal expression of yeast GAL genes is controlled by a long non-coding RNA and a bifunctional galactokinase

Bimodality in gene expression can generate phenotypic heterogeneity facilitating fitness and growth of isogenic cell populations in suboptimal environments. We investigated the mechanism by which, in conditions of limiting galactose, yeast cell populations activate GAL genes in a bimodal fashion with a cell fraction expressing GAL genes (ON), while the rest subpopulation is kept at the non-expressing (OFF) state. We show that a long non-coding RNA (GAL10-ncRNA) crossing the bidirectional GAL1-10 promoter, decreases the rate by which single cells commit transition to the ON state without affecting the rate of GAL transcription per se in ON cells. This is accomplished by repressing stochastic expression of the bifunctional Gal1p galactokinase, which besides its enzymatic activity acts as an essential inducer of the system under those conditions. We show that once single cells switch to the ON state, the GAL10-ncRNA effect is overridden by accumulating Gal1p levels sufficient to feedback positively on Gal4p, and not by the active transcription of GAL10 that occurs in opposite direction relative to that of GAL10-ncRNA. Conversely, GAL10-ncRNA does not influence transition of ON cells, where Gal4p is active, back to the OFF state. Our model suggests that the functional interplay between GAL10-ncRNA transcription, stochastic Gal1p expression and Gal1p positive feedback on Gal4p constitutes a novel molecular switch mechanism dictating the commitment of individual cells for either metabolic state. - Highlights: • Stochastic transcription of the Gal1p galactokinase creates bimodality in GAL expression. • GAL10-ncRNA controls GAL bimodality by repressing Gal1p. • GAL10-ncRNA repression is overridden by the inducing activity of Gal1p itself.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Seawater sea-sand engineered/strain-hardening cementitious composites (ECC/SHCC): Assessment and modeling of crack characteristics

Highlights: • A probabilistic model was proposed to model the crack width evolution of SS-ECC at different strain levels. • The Weibull distribution fit the crack width distribution better than the log-normal distribution. • A 5-D representation was proposed to assess the SS-ECC by considering both cracking and mechanical performance. • Larger sea-sand size and lower fiber dosage led to larger crack widths in SS-ECC under the same tensile strain. • 18-mm PE fiber led to larger crack widths in SS-ECC at strain >2%, due to a large fraction of fiber rupture. Seawater sea-sand Engineered Cementitious Composites (SS-ECC) is a new version of ECC for marine constructions facing the scarcity of freshwater and river/manufactured sand. This study aims to assess and model the crack characteristics of SS-ECC, which are critical for its applications with non-corrosive reinforcements. The influence of sea-sand size, fiber length and fiber dosage on the crack characteristics of SS-ECC was explored. A five-dimensional representation was proposed to assess the overall performance of SS-ECC, by comprehensively considering both the crack characteristics (i.e., crack width and its variation) and the mechanical properties (i.e., compressive and tensile properties). A probabilistic model was also proposed to describe the stochastic nature and evolution of crack width, and it can be used to estimate the critical tensile strain on SS-ECC for a given crack-width limit and cumulative probability. The findings and proposed methods can facilitate the design of SS-ECC in marine and coastal structures.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Flow-flame interactions causing acoustically coupled heat release fluctuations in a thermo-acoustically unstable gas turbine model combustor

A detailed analysis of the flow-flame interactions associated with acoustically coupled heat-release rate fluctuations was performed for a 10 kW, CH{sub 4}/air, swirl stabilized flame in a gas turbine model combustor exhibiting self-excited thermo-acoustic oscillations at 308 Hz. High-speed stereoscopic particle image velocimetry, OH planar laser induced fluorescence, and OH* chemiluminescence measurements were performed at a sustained repetition rate of 5 kHz, which was sufficient to resolve the relevant combustor dynamics. Using spatio-temporal proper orthogonal decomposition, it was found that the flow-field contained several simultaneous periodic motions: the reactant flux into the combustion chamber periodically oscillated at the thermo-acoustic frequency (308 Hz), a helical precessing vortex core (PVC) circumscribed the burner nozzle at 515 Hz, and the PVC underwent axial contraction and extension at the thermo-acoustic frequency. The global heat release rate fluctuated at the thermo-acoustic frequency, while the heat release centroid circumscribed the combustor at the difference between the thermo-acoustic and PVC frequencies. Hence, the three-dimensional location of the heat release fluctuations depended on the interaction of the PVC with the flame surface. This motivated the compilation of doubly phase resolved statistics based on the phase of both the acoustic and PVC cycles, which showed highly repeatable periodic flow-flame configurations. These include flames stabilized between the inflow and inner recirculation zone, large-scale flame wrap-up by the PVC, radial deflection of the inflow by the PVC, and combustion in the outer recirculation zones. Large oscillations in the flame surface area were observed at the thermo-accoustic frequency that significantly affected the total heat-release oscillations. By filtering the instantaneous reaction layers at different scales, the importance of the various flow-flame interactions affecting the flame area was determined. The greatest contributor was large-scale elongation of the reaction layers associated with the fluctuating reactant flow rate, which accounted for approximately 50% of the fluctuations. The remaining 50% was distributed between fine scale stochastic corrugation and large-scale corrugation due to the PVC. (author)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Modelling cycle to cycle variations in an SI engine with detailed chemical kinetics

This paper presents experimental results and a new computational model that investigate cycle to cycle variations (CCV) in a spark ignition (SI) engine. An established stochastic reactor model (SRM) previously used to examine homogeneous charge compression ignition (HCCI) combustion has been extended by spark initiation, flame propagation and flame termination sub-models in order to simulate combustion in SI engines. The model contains a detailed chemical mechanism but relatively short computation times are achieved. The flame front is assumed to be spherical and centred at the spark location, and a pent roof and piston bowl geometry are accounted for. The model is validated by simulating the pressure profile and emissions from an iso-octane fuelled single cylinder research engine that showed low CCV. The effects of key parameters are investigated. Experimental results that show cycle to cycle fluctuations in a four-cylinder naturally aspirated gasoline fuelled SI engine are presented. The model is then coupled with GT-Power, a one-dimensional engine simulation tool, which is used to simulate the breathing events during a multi-cycle simulation. This allows an investigation of the cyclic fluctuations in peak pressure. The source and magnitude of nitric oxide (NO) emissions produced by different cycles are then investigated. It was found that faster burning cycles result in increased NO emissions compared with cycles that have a slower rate of combustion and that more is produced in the early stages of combustion compared with later in the cycle. The majority of NO was produced via the thermal mechanism just after combustion begins. (author)

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2012

The impacts of population change on carbon emissions in China during 1978-2008

This study examines the impacts of population size, population structure, and consumption level on carbon emissions in China from 1978 to 2008. To this end, we expanded the stochastic impacts by regression on population, affluence, and technology model and used the ridge regression method, which overcomes the negative influences of multicollinearity among independent variables under acceptable bias. Results reveal that changes in consumption level and population structure were the major impact factors, not changes in population size. Consumption level and carbon emissions were highly correlated. In terms of population structure, urbanization, population age, and household size had distinct effects on carbon emissions. Urbanization increased carbon emissions, while the effect of age acted primarily through the expansion of the labor force and consequent overall economic growth. Shrinking household size increased residential consumption, resulting in higher carbon emissions. Households, rather than individuals, are a more reasonable explanation for the demographic impact on carbon emissions. Potential social policies for low carbon development are also discussed. - Highlights: Black-Right-Pointing-Pointer We examine the impacts of population change on carbon emissions in China. Black-Right-Pointing-Pointer We expand the STIRPAT model by containing population structure factors in the model. Black-Right-Pointing-Pointer The population structure includes age structure, urbanization level, and household size. Black-Right-Pointing-Pointer The ridge regression method is used to estimate the model with multicollinearity. Black-Right-Pointing-Pointer The population structure plays a more important role compared with the population size.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Research on impacts of population-related factors on carbon emissions in Beijing from 1984 to 2012

Carbon emissions related to population factors have aroused great attention around the world. A multitude of literature mainly focused on single demographic impacts on environmental issues at the national level, and comprehensive studies concerning population-related factors at a city level are rare. This paper employed STIRPAT (Stochastic Impacts by Regression on Population, Affluence and Technology) model incorporating PLS (Partial least squares) regression method to examine the influence of population-related factors on carbon emissions in Beijing from 1984 to 2012. Empirically results manifest that urbanization is the paramount driver. Changes in population age structure have significantly positive impacts on carbon emissions, and shrinking young population, continuous expansion of working age population and aging population will keep on increasing environmental pressures. Meanwhile, shrinking household size and expanding floating population boost the discharge of carbon emissions. Besides, per capita consumption is an important contributor of carbon emissions, while industry energy intensity is the main inhibitory factor. Based upon these findings and the specific circumstances of Beijing, policies such as promoting clean and renewable energy, improving population quality and advocating low carbon lifestyles should be enhanced to achieve targeted emissions reductions. - Highlights: • We employed the STIRPAT model to identify population-related factors of carbon emissions in Beijing. • Urbanization is the paramount driver of carbon emissions. • Changes in population age structure exert significantly positive impacts on carbon emissions. • Shrinking household size, expanding floating population and improving consumption level increase carbon emissions. • Industry energy intensity decreases carbon emissions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Distribution System Segmented Model Simplification with Independent Dynamically Changing End-Use Loads

With more emerging technologies in power distribution systems, to support quasi-static time-series (QSTS) simulation over short time frames, accurately modeling the dynamic behavior of end-use load under various conditions is im- portant. However, time and cost can be a burden for the QSTS simulation of thousands of houses representing dynamic load behaviors on large distribution feeders. There are two main contributions of this paper in order to reduce the QSTS simulation complexity. First, the paper presents a method to stochasti- cally model the dynamic behavior of end-use load for QSTS simulations. Second, using the stochastically modeled load behavior as an input to a distribution sys- tem, and building on our previous QSTS simulation simplification/acceleration method that relies on uniform load behavior, this paper presents a segment substitution approach for the simplification of distribution system models with independent dynamically changing end-use loads. Our numerical results show that compared to GridLAB-D, a software tool that simulates end-use load be- havior through physical models, the proposed stochastic modeling approach achieved an 89.3% simulation time reduction for end-use loads, while accurately capturing the temporally changing total load behavior. Moreover, the QSTS simulation of a large test distribution system through OpenDSS showed that the proposed simplification method decreased the feeder simulation time by a factor of three at less than 0.3% voltage error. Compared to our previous method with independent dynamic loads, the voltage error is reduced by a factor of four.

Power distribution system modeling, stochastic pro↗
DOE OSTI2016

Stochastic Predictions of Cell Kill During Stereotactic Ablative Radiation Therapy: Do Hypoxia and Reoxygenation Really Matter?

Purpose: To simulate stereotactic ablative radiation therapy on hypoxic and well-oxygenated in silico tumors, incorporating probabilistic parameter distributions and linear-quadratic versus linear-quadratic-cubic methodology and the evaluation of optimal fractionation schemes using biological effective dose (BED{sub α/β=10} {sub or} {sub 3}) comparisons. Methods and Materials: A temporal tumor growth and radiation therapy algorithm simulated high-dose external beam radiation therapy using stochastic methods. Realistic biological proliferative cellular hierarchy and pO{sub 2} histograms were incorporated into the 10{sup 8}-cell tumor model, with randomized radiation therapy applied during continual cell proliferation and volume-based gradual tumor reoxygenation. Dose fractions ranged from 6-35 Gy, with predictive outcomes presented in terms of the total doses (converted to BED) required to eliminate all cells that could potentially regenerate the tumor. Results: Well-oxygenated tumor control BED{sub 10} outcomes were not significantly different for high-dose versus conventional radiation therapy (BED{sub 10}: 79-84 Gy; Equivalent Dose in 2 Gy fractions with α/β of 10: 66-70 Gy); however, total treatment times decreased from 7 down to 1-3 weeks. For hypoxic tumors, an additional 28 Gy (51 Gy BED{sub 10}) was required, with BED{sub 10} increasing with dose per fraction due to wasted dose in the final fraction. Fractions of 9 Gy compromised well for total treatment time and BED, with BED{sub 10}:BED{sub 3} of 84:176 Gy for oxic and 132:278 Gy for non-reoxygenating hypoxic tumors. Initial doses of 12 Gy followed by 6 Gy further increased the therapeutic ratio. When delivering ≥9 Gy per fraction, applying reoxygenation and/or linear-quadratic-cubic cell survival both affected tumor control doses by a significant 1-2 fractions. Conclusions: The complex temporal dynamics of tumor oxygenation combined with probabilistic cell kinetics in the modeling of radiation therapy requires sophisticated stochastic modeling to predict tumor cell kill. For stereotactic ablative radiation therapy, high doses in the first week followed by doses that are more moderate may be beneficial because a high percentage of hypoxic cells could be eradicated early while keeping the required BED{sub 10} relatively low and BED{sub 3} toxicity to tolerable levels.

62 RADIOLOGY AND NUCLEAR MEDICINE↗