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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Enhanced Deuteron Coalescence Probability in Jets

The transverse-momentum ($p_T$) spectra and coalescence parameters $B_2$ of (anti)deuterons are measured in p-p collisions at $\sqrt{s}=13$ $\text{TeV}$ for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest $p_T$ in the event ($p^{lead}_T > 5 GeV/c$) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the $B^{Jet}_2$ is not reproduced by the models, which instead give a decreasing trend.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

WE-H-BRA-02: Radiobiological Modeling of Tumor Control Probability (TCP) and Radiation-Induced Pneumonitis (RP) for Lung Cancer Patients Treated with Monte Carlo-Based Lung SBRT

Purpose: To present radiobiological modeling of TCP using tumor size-adjusted BED(s-BED)and PTV(D99) to lung SBRT patients treated with X-ray Voxel Monte Carlo(XVMC) algorithm, apply parameterized Lyman-NTCP model to predict grade-2 RP and subsequently, compare with clinical outcomes/observations. Methods: Dosimetric parameters and clinical follow-up for XVMC-based lung-SBRT patients were retrospectively evaluated. Patients were treated at Novalis-TX with hybrid(2 non-coplanar partial-arcs plus 3–6 static-beams)plan using HD-MLC/6MV-SRS-beam.For TCP,s-BED modelling was utilized: TCP=EXP[sBED-TCD50]/k/(1.0+EXP[sBED-TCD50]/k), where k=31Gy corresponding to TCD50=0Gy and s-BED was defined as BED10 minus 10 times the tumor diameter(in centimeters)by Ohri et al.(IJROBP,2012). For 2-yr local-control, we used more-realistic MC-computed PTVD99 as a predictive parameter, s-BED(D99).Due to relatively shorter median follow-up interval(12-months),Kaplan-Meier curves were generated to estimate 2-yr observed local-control and compared to predicted-rate by TCP modeling. For NTCP, we employed parameterized Lyman-NTCP model utilizing normal-lung DVH and α/β=3Gy fitted to predict grade-2 RP after lung-SBRT. Results: Total 108 patients (137 tumors) treated for 35–70Gy in 3–5 fractions, either primary-lung(n=74)or metastatic-lung(n=53)tumors were included.F or the given prescription dose with MC-computed MUs, 2-yr local-control rates with s-BED(D99) was 87±8%. Kaplan-Meier generated observed local-control rate at 2-yr was 87.5%,suggesting that PTV(D99) could be a potential predictor (p-value=0.38). Observed vs predicted TCP for primary-lung tumors and metastatic tumors were 97% vs 88±7% and 94% vs 86±9%.NTCP model predicted well for symptomatic-RP with predicted vs observed (3±5% vs 2%). Radiographic and clinically significant RP was observed in 13% and 2% of patients. Higher rates of radiographic change were observed in patients who received >50Gy compared to ≤50Gy(24% vs 10%). Conclusion: Utilizing MC-computed PTVD99, our TCP results were well correlated with clinical outcome. The predicted grade-2 RP rate was comparable to clinical observations. Clinical application of these radiobiological models may potentially allow for target dose escalation and/or lung-toxicity reduction. Further validation of these radiobiological models with longer follow up interval for large cohorts of lung-SBRT patients is anticipated.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Probable Decay Modes at Limits of Nuclear Stability of the Superheavy Nuclei

The modes of decay for the even–even isotopes of superheavy nuclei of Z = 118 and 120 with neutron number 160 ≤ N ≤ 204 are investigated in the framework of the axially deformed relativistic mean field model. The asymmetry parameter η and the relative neutron–proton asymmetry of the surface to the center (R{sub η}) are estimated from the ground state density distributions of the nucleus. We analyze the resulting asymmetry parameter η and the relative neutron–proton asymmetry R{sub η} of the density play a crucial role in the mode(s) of decay and its half-life. Moreover, the excess neutron richness on the surface, facets a superheavy nucleus for β{sup −} decays.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Probability and Cumulative Density Function Methods for the Stochastic Advection-Reaction Equation

We present a cumulative density function (CDF) method for the probabilistic analysis of $d$-dimensional advection-dominated reactive transport in heterogeneous media. We employ a probabilistic approach in which epistemic uncertainty on the spatial heterogeneity of Darcy-scale transport coefficients is modeled in terms of random fields with given correlation structures. Our proposed CDF method employs a modified Large-Eddy-Diffusivity (LED) approach to close and localize the nonlocal equations governing the one-point PDF and CDF of the concentration field, resulting in a $(d + 1)$ dimensional PDE. Compared to the classsical LED localization, the proposed modified LED localization explicitly accounts for the mean-field advective dynamics over the phase space of the PDF and CDF. To illustrate the accuracy of the proposed closure, we apply our CDF method to one-dimensional single-species reactive transport with uncertain, heterogeneous advection velocities and reaction rates modeled as random fields.

advection-reaction equation↗
DOE OSTI2023

A Generalization of Threshold-Based and Probability-Based Models of Information Diffusion

Diffusion of information through complex networks is of interest in studies such as propagation prediction and influence maximization, both of which have applications in viral marketing and rumor controlling. There are a variety of information diffusion models, all of which simulate the adoption and spread of information over time. However, there is a lack of understanding of whether, despite their conceptual differences, these models represent the same underlying generative structures. For instance, if two different models utilize different conceptual mechanisms, but generate the same results, does the choice of model matter? A classification of diffusion of information models is developed based on the neighbor knowledge of the model infection requirement and the stochasticity of the model. This classification allows for the identification of models that fall into each respective category. The study involves the analysis of the following agent-based models on directed scale-free networks: (1) a linear absolute threshold model (LATM), (2) a linear fractional threshold model (LTFM), (3) the independent cascade model (ICM), (4) Bass-Rand-Rust model (BRRM) (5) a stochastic linear absolute threshold model (SLATM) (6) a stochastic fractional threshold model (SLFTM), and (7) Dodds–Watts model (DWM). Through the execution of simulations and analysis of the experimental results, the distinctive properties of each model are identified. Our analysis reveals that similarity in conceptual design does not imply similarity in behavior concerning speed, final state of nodes and edges, and sensitivity to parameters. Therefore, we highlight the importance of considering the unique behavioral characteristics of each model when selecting a suitable information diffusion model for a particular application.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Long-Period, Long-Duration Seismic Events and Their Probable Role in Reservoir Stimulation and Stage Productivity

Hydraulic fracturing is a well-established technique to extract gas or liquid hydrocarbons from low-permeability formations like shale and tight gas reservoirs. Diffusion of hydrofracturing fluid outward from the stimulated fractures into the target formation produces slip across preexisting fractures and other discontinuities in the rock. Microseismic events recorded by downhole seismic monitoring arrays are a manifestation of associated deformation. Recent investigations suggest that the total cumulative seismic moment of microearthquakes during hydraulic fracturing is only a small portion of the total seismic energy release expected for the fluid volume injected into the formation. These observations suggest that other sources of energy release (such as inelastic deformation), contemporaneous with microseismicity, should be considered as relevant to the hydraulic fracturing process. Recent observations on long period, long duration (LPLD) seismic events suggest that slow slip emission along weaknesses that are misaligned with respect to the present-day stress field are likely an important mechanism of deformation and should be better understood and quantified in reservoir stimulations. In Morgantown, West Virginia, we carried out seismic monitoring of hydraulic fracturing activity using an array of five broadband, three-component surface seismometers. Using this network, we identified 89 high-amplitude, impulsive events and 436 long period, long duration (LPLD) events, with highly emergent waveform characteristics. In these interpreted LPLD events, we observed a significant concentration of energy in the 0.8-3 Hz frequency range. During hydraulic fracturing, LPLD events were found to occur most frequently when the pumping pressure and rate were at or near maximum values. As the main purpose of hydraulic fracturing is to stimulate oil and gas production from the less permeable reservoir, we compared the relative production contribution per stage to the frequency of occurrence of suspected LPLD events. We found positive correlation between the frequency of LPLD events and stage-by-stage gas production, highlighting the potential contribution of slow deformation processes and its effectiveness in the reservoir stimulation.

58 GEOSCIENCES↗