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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Long-Range Interaction between Molecules with Electronic Degeneracy: Beyond the Born–Oppenheimer Approximation

Long-range intermolecular interaction plays an essential role in (ultra)cold collisions. For monomers with degenerate electronic states, an accurate description of the long-range interaction can be challenging due to the potential breakdown of the Born–Oppenheimer approximation. In this work, we developed a general method to construct long-range interaction potential energy surfaces (IPESs) between arbitrary molecules using the degenerate perturbation theory of Schrödinger. To further simplify the application of this method, a group-theoretical method is introduced to identify nonzero components of electrostatic properties of monomers, especially for the nonlinear molecules. To demonstrate this approach, we report the long-range IPESs of the O( 3 P)–OH( 2 Π) and OH( 2 Π)–OH( 2 Π) systems. The excellent agreement with ab initio calculations in large separations, even near electronic degeneracies, confirms the accuracy of our approach. The method is expected to lay the groundwork for the accurate investigation of (ultra)cold collisional dynamics involving open-shell species.

ab initio calculations↗
DOE OSTI2014

Dielectric function in the NIR-VUV spectral range of (In{sub x}Ga{sub 1−x}){sub 2}O{sub 3} thin films

We determined the dielectric function of the alloy system (In{sub x}Ga{sub 1−x}){sub 2}O{sub 3} by spectroscopic ellipsometry in the wide spectral range from 0.5 eV to 8.5 eV and for In contents ranging from x = 0.02 to x = 0.61. The predicted optical transitions for binary, monoclinic β-Ga{sub 2}O{sub 3}, and cubic bcc-In{sub 2}O{sub 3} are well reflected by the change of the dielectric functions' lineshape as a function of the In content. In an intermediate composition range with phase-separated material (x ≈ 0.3…0.4), the lineshape differs considerably, which we assign to the presence of the high-pressure rhombohedral InGaO{sub 3}-II phase, which we also observe in Raman experiments in this range. By model analysis of the dielectric function, we derived spectra of the refractive index and the absorption coefficient and energy parameters of electronic band-band transitions. We discuss the sub-band gap absorption tail in relation to the influence of the In 4d orbitals on the valence bands. The data presented here provide a basis for a deeper understanding of the electronic properties of this technologically important material system and may be useful for device engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Cold and ultracold dynamics of the barrierless D{sup +} + H{sub 2} reaction: Quantum reactive calculations for ∼R{sup −4} long range interaction potentials

Quantum reactive and elastic cross sections and rate coefficients have been calculated for D{sup +} + H{sub 2} (v = 0, j = 0) collisions in the energy range from 10{sup −8} K (deep ultracold regime), where only one partial wave is open, to 150 K (Langevin regime) where many of them contribute. In systems involving ions, the ∼R{sup −4} behavior extends the interaction up to extremely long distances, requiring a special treatment. To this purpose, we have used a modified version of the hyperspherical quantum reactive scattering method, which allows the propagations up to distances of 10{sup 5} a{sub 0} needed to converge the elastic cross sections. Interpolation procedures are also proposed which may reduce the cost of exact dynamical calculations at such low energies. Calculations have been carried out on the PES by Velilla et al. [J. Chem. Phys. 129, 084307 (2008)] which accurately reproduces the long range interactions. Results on its prequel, the PES by Aguado et al. [J. Chem. Phys. 112, 1240 (2000)], are also shown in order to emphasize the significance of the inclusion of the long range interactions. The calculated reaction rate coefficient changes less than one order of magnitude in a collision energy range of ten orders of magnitude, and it is found in very good agreement with the available experimental data in the region where they exist (10-100 K). State-to-state reaction probabilities are also provided which show that for each partial wave, the distribution of HD final states remains essentially constant below 1 K.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Quantum phase transitions in long-range interacting hyperuniform spin chains in a transverse field

Hyperuniform states of matter are characterized by anomalous suppression of long-wavelength density fluctuations. While most of the interesting cases of disordered hyperuniformity are provided by complex many-body systems such as liquids or amorphous solids, classical spin chains with certain long-range interactions have been shown to demonstrate the same phenomenon. Such spin-chain systems are ideal models for exploring the effects of quantum mechanics on hyperuniformity. It is well-known that the transverse field Ising model shows a quantum phase transition (QPT) at zero temperature. Under the quantum effects of a transverse magnetic field, classical hyperuniform spin chains are expected to lose their hyperuniformity. High-precision simulations of these cases are complicated because of the presence of highly nontrivial long-range interactions. We perform an extensive analysis of these systems using density matrix renormalization group simulations to study the possibilities of phase transitions and the mechanism by which they lose hyperuniformity. Even for a spin chain of length 30, we see discontinuous changes in properties like the “τ order metric” of the ground state, the measure of hyperuniformity, and the second cumulant of the total magnetization along the x-direction, all suggestive of first-order QPTs. An interesting feature of the phase transitions in these disordered hyperuniform spin chains is that, depending on the parameter values, the presence of a transverse magnetic field may lead remarkably to an increase in the order of the ground state as measured by the “τ order metric,” even if hyperuniformity is lost. Therefore, it would be possible to design materials to target specific novel quantum behaviors in the presence of a transverse magnetic field. Our numerical investigations suggest that these spin chains can show no more than two QPTs. We further analyze the long-range interacting spin chains via the Jordan-Wigner mapping onto a system of spinless fermions, showing that under the pairwise-interaction approximation and a mean-field treatment, there can be at most two quantum phase transitions. Here, based on these numerical and theoretical explorations, we conjecture that for spin chains with long-range pair interactions that have convergent cosine transforms, there can be a maximum of two quantum phase transitions at zero temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Seed origin and warming constrain lodgepole pine recruitment, slowing the pace of population range shifts

Understanding how climate warming will affect the demographic rates of different ecotypes is critical to predicting shifts in species distributions. In this study, we present results from a common garden, climate change experiment in which we measured seedling recruitment of lodgepole pine, a widespread North American conifer that is also planted globally. Seeds from a low-elevation provenance had more than three-fold greater recruitment to their third year than seeds from a high-elevation provenance across sites within and above its native elevation range and across climate manipulations. Heating halved recruitment to the third year of both low- and high-elevation seed sources across the elevation gradient, while watering more than doubled recruitment, alleviating some of the negative effects of heating. Demographic models based on recruitment data from the climate manipulations and long-term observations of adult populations revealed that heating could effectively halt modeled upslope range expansion except when combined with watering. Simulating fire and rapid postfire forest recovery at lower elevations accelerated lodgepole pine expansion into the alpine, but did not alter final abundance rankings among climate scenarios. Regardless of climate scenario, greater recruitment of low-elevation seeds compensated for longer dispersal distances to treeline, assuming colonization was allowed to proceed over multiple centuries. In conclusion, our results show that ecotypes from lower elevations within a species’ range could enhance recruitment and facilitate upslope range shifts with climate change.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

EBT2 film as a depth-dose measurement tool for radiotherapy beams over a wide range of energies and modalities

Purpose: One of the fundamental parameters used for dose calculation is percentage depth-dose, generally measured employing ionization chambers. There are situations where use of ion chambers for measuring depth-doses is difficult or problematic. In such cases, radiochromic film might be an alternative. The EBT-2 model GAFCHROMIC film was investigated as a potential tool for depth-dose measurement in radiotherapy beams over a broad range of energies and modalities. Methods: Pieces of the EBT-2 model GAFCHROMIC EBT2 film were exposed to x-ray, electron, and proton beams used in radiotherapy. The beams employed for this study included kilovoltage x-rays (75 kVp), {sup 60}Co gamma-rays, megavoltage x-rays (18 MV), electrons (7 and 20 MeV), and pristine Bragg-peak proton beams (126 and 152 MeV). At each beam quality, film response was measured over the dose range of 0.4-8.0 Gy, which corresponds to optical densities ranging from 0.05 to 0.4 measured with a flat-bed document scanner. To assess precision in depth-dose measurements with the EBT-2 model GAFCHROMIC film, uncertainty in measured optical density was investigated with respect to variation in film-to-film and scanner-bed uniformity. Results: For most beams, percentage depth-doses measured with the EBT-2 model GAFCHROMIC film show an excellent agreement with those measured with ion chambers. Some discrepancies are observed in case of (i) kilovoltage x-rays at larger depths due to beam-hardening, and (ii) proton beams around Bragg-peak due to quenching effects. For these beams, an empirical polynomial correction produces better agreement with ion-chamber data. Conclusions: The EBT-2 model GAFCHROMIC film is an excellent secondary dosimeter for measurement of percentage depth-doses for a broad range of beam qualities and modalities used in radiotherapy. It offers an easy and efficient way to measure beam depth-dose data with a high spatial resolution.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2012

Development of array-type prompt gamma measurement system for in vivo range verification in proton therapy

Purpose: In vivo range verification is one of the most important parts of proton therapy to fully utilize its benefits delivering high radiation dose to tumor, while sparing the normal tissue with the so-called Bragg peak. Currently, however, range verification method is not used in clinics. The purpose of the present study is to optimize and evaluate the configuration of an array-type prompt gamma measurement system on determining distal dose edge for in vivo range verification of proton therapy. Methods: To effectively measure the prompt gammas against the background gammas, the Monte Carlo simulations with the MCNPX code were employed in optimizing the configuration of the measurement system, and the Monte Carlo method was also used to understand the effect of the background gammas, mainly neutron capture gammas, in the measured gamma distribution. To reduce the effect of the background gammas, the optimized energy window of 4-10 MeV in measuring the prompt gammas was employed. A parameterized source was used to maximize computation speed in the optimization study. A simplified test measurement system, using only one detector moving from one measurement location to the next, was constructed and applied to therapeutic proton beams of 80-220 MeV. For accurate determination of the distal dose edge, the sigmoidal curve-fitting method was applied to the measured distributions of the prompt gammas, and then, the location of the half-value between the maximum and minimum value in the curve-fitting was determined as the distal dose edge and compared with the beam range assessed by the proton dose distribution. Results: The parameterized source term employed in optimization process improved the calculation speed by up to {approx}300 times. The optimization study indicates that an array-type measurement system with 3, 2, 2, and 150 mm for scintillator thickness, slit width, septal thickness, and slit length, respectively, can effectively measure the prompt gamma distributions minimizing the contribution of background gammas. The present results show that a few hundred counts of prompt gammas can be easily obtained by measuring 10 s at each measurement location for proton beams of {approx}4 nA. The distal dose edges determined by the prompt gamma distribution are 5.45, 14.73, and 27.74 cm for proton beams of 5.17 (80 MeV), 14.99 (150 MeV), and 27.38 (220 MeV) cm, respectively. Conclusions: The results show that the array-type measurement system can measure prompt gamma distributions from a therapeutic proton beam within a short measurement time, and that the distal dose edge can be determined within a few millimeters of error without using any sophisticated analysis.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Universal relationships for the phonon spectra in BCC, FCC, and HCP crystals with a short-range interatomic interaction

The frequencies of the phonon branches that correspond to the vibrations of the close-packed atomic planes in bcc, fcc, and hcp crystals with short-range interatomic interaction are shown to be described by a universal relationship, which only contains two parameters for each branch, for any polarization {lambda}. These phonon branches correspond to the ({xi}, {xi}, 0) direction in bcc crystals, the ({xi}, {xi}, {xi}) direction in fcc crystals, and the (0, 0, {xi}) direction in hcp crystals. This universal relationship can only be violated by long-range interactions, namely, the interactions outside the sixth coordination shell in a bcc crystal, the fifth coordination shell in an fcc crystal, and the eleventh or tenth coordination shell in an hcp crystal. The effect of these long-range interactions for each phonon branch can be quantitatively characterized by certain parameters {Delta}{sub n{lambda}}, which are simply expressed in terms of the frequencies of three phonons of the branch. The values of these parameters are presented for all bcc, fcc, and hcp metals whose phonon spectra are measured. In most cases, the proposed relationships for the frequencies are found to be fulfilled accurate to several percent. In the cases where the {Delta}{sub n{lambda}} parameters are not small, they can give substantial information on the type and scale of long-range interaction effects in various metals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electrostatic Spectrograph for Different Ranges of Simultaneously Recorded Energies with a Discrete Combined External Electrode

We propose and study numerically a large-aperture electrostatic spectrograph consisting of the two coaxial electrodes, a cone-cylindrical electrode separated into several segments, and a small cylindrical electrode. The supply voltages providing sharp focusing of charged particle beams in the initial region of the spectrum for different ranges of simultaneously detected energies E{sub max}/E{sub min} = (25–100) are determined. Electron- optical parameters of the spectrograph in four energy ranges are calculated, with the electrical similarity principle being used for charged particles of medium and high energies. The resolution of the spectrograph for medium and high energies, E = (0.1–1)E{sub max}, is equal to (5–3) × 10{sup –3}. For small energies, E = (0.01–0.1)E{sub max}, the resolution worsens and varies within the (0.6–1.6) × 10{sup –2} range as the range of simultaneously recorded energies increases.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Tonopah Test Range Air Monitoring: CY2015 Meteorological, Radiological, and Airborne Particulate Observations

In 1963, the U.S. Department of Energy (DOE) (formerly the Atomic Energy Commission [AEC]), implemented Operation Roller Coaster on the Tonopah Test Range (TTR) and an adjacent area of the Nevada Test and Training Range (NTTR) (formerly the Nellis Air Force Range). The operation resulted in radionuclide-contaminated soils at the Clean Slate I, II, and III sites. This report documents observations made during ongoing monitoring of radiological, meteorological, and dust conditions at stations installed adjacent to Clean Slate I and Clean Slate III, and at the TTR Sandia National Laboratories (SNL) Range Operations Control (ROC) center. The primary objective of the monitoring effort is to determine if winds blowing across the Clean Slate sites are transporting particles of radionuclide-contaminated soil beyond the physical and administrative boundaries of the sites. Radionuclide assessment of airborne particulates in 2015 found the gross alpha and gross beta values of dust collected from the filters at the monitoring stations are consistent with background conditions. The meteorological and particle monitoring indicate that conditions for wind-borne contaminant movement exist at the Clean Slate sites and that, although the transport of radionuclide-contaminated soil by suspension has not been detected, movement by saltation is occurring.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Overcoming the Range Limitation of Medium-Duty Battery Electric Vehicles through the use of Hydrogen Fuel-Cells

Battery electric vehicles possess great potential for decreasing lifecycle costs in medium-duty applications, a market segment currently dominated by internal combustion technology. Characterized by frequent repetition of similar routes and daily return to a central depot, medium-duty vocations are well positioned to leverage the low operating costs of battery electric vehicles. Unfortunately, the range limitation of commercially available battery electric vehicles acts as a barrier to widespread adoption. This paper describes the National Renewable Energy Laboratory's collaboration with the U.S. Department of Energy and industry partners to analyze the use of small hydrogen fuel-cell stacks to extend the range of battery electric vehicles as a means of improving utility, and presumably, increasing market adoption. This analysis employs real-world vocational data and near-term economic assumptions to (1) identify optimal component configurations for minimizing lifecycle costs, (2) benchmark economic performance relative to both battery electric and conventional powertrains, and (3) understand how the optimal design and its competitiveness change with respect to duty cycle and economic climate. It is found that small fuel-cell power units provide extended range at significantly lower capital and lifecycle costs than additional battery capacity alone. And while fuel-cell range-extended vehicles are not deemed economically competitive with conventional vehicles given present-day economic conditions, this paper identifies potential future scenarios where cost equivalency is achieved.

08 HYDROGEN↗
DOE OSTI2017

Modeling Control Strategies and Range Impacts for Electric Vehicle Integrated Thermal Management Systems with MATLAB/Simulink

The National Renewable Energy Laboratory's (NREL's) CoolSim MATLAB/Simulink modeling framework was used to explore control strategies for an electric vehicle combined loop system. Three system variants of increased complexity and efficiency were explored: a glycol-based positive temperature coefficient heater (PTC), PTC with power electronics and electric motor (PEEM) waste heat recovery, and PTC with PEEM waste heat recovery plus heat pump versions. Additionally, the benefit of electric motor preheating was considered. A two-level control strategy was developed where the mode selection and component control were treated separately. Only the parameters typically available by vehicle sensors were used to control the system. The control approach included a mode selection algorithm and controllers for the compressor speed, cabin blower flow rate, coolant flow rate, and the front-end heat exchanger coolant bypass rate. The electric motor was bypassed by the cooling circuit until its temperature exceeded the coolant inlet temperature. The impact of these thermal systems on electric vehicle range during warmup was simulated for the Urban Dynamometer Driving Schedule (UDDS) and Highway Fuel Economy Test (HWFET2X) drive cycles weighted 45%/55% respectively. A range of ambient temperatures from -20 degrees C to +20 degrees C was considered. NREL's Future Automotive Systems Technology Simulator (FASTSim) vehicle modeling tool showed up to a 10.9% improvement in range for the full system over the baseline during warmup from cold soak. The full system with preheat showed up to 17% improvement in range.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2018

Range Extension Opportunities While Heating a Battery Electric Vehicle

The Kia Soul battery electric vehicle (BEV) is available with either a positive temperature coefficient (PTC) heater or an R134a heat pump (HP) with PTC heater combination (1). The HP uses both ambient air and waste heat from the motor, inverter, and on-board-charger (OBC) for its heat source. Hanon Systems, Hyundai America Technical Center, Inc. (HATCI) and the National Renewable Energy Laboratory jointly, with financial support from the U.S. Department of Energy, developed and proved-out technologies that extend the driving range of a Kia Soul BEV while maintaining thermal comfort in cold climates. Improved system configuration concepts that use thermal storage and waste heat more effectively were developed and evaluated. Range extensions of 5%-22% at ambient temperatures ranging from 5 degrees C to -18 degrees C were demonstrated. This paper reviews the three-year effort, including test data of the baseline and modified vehicles, resulting range extension, and recommendations for future actions.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1998

The cat vertebral column: stance configuration and range of motion

This study examined the configuration of the vertebral column of the cat during independent stance and in various flexed positions. The range of motion in the sagittal plane is similar across most thoracic and lumbar joints, with the exception of a lesser range at the transition region from thoracic-type to lumbar-type vertebrae. The upper thoracic column exhibits most of its range in dorsiflexion and the lower thoracic and lumbar in ventroflexion. Lateral flexion is limited to less than 5 degrees at all segments. The range in torsion is almost 180 degrees and occurs primarily in the midthoracic region, T4-T11. Contrary to the depiction in most atlases, the standing cat exhibits several curvatures, including a mild dorsiflexion in the lower lumbar segments, a marked ventroflexion in the lower thoracic and upper lumbar segments, and a profound dorsiflexion in the upper thoracic (above T9) and cervical segments. The curvatures are not significantly changed by altering stance distance but are affected by head posture. During stance, the top of the scapula lies well above the spines of the thoracic vertebrae, and the glenohumeral joint is just below the bodies of vertebrae T3-T5. Using a simple static model of the vertebral column in the sagittal plane, it was estimated that the bending moment due to gravity is bimodal with a dorsiflexion moment in the lower thoracic and lumbar region and a ventroflexion moment in the upper thoracic and cervical region. Given the bending moments and the position of the scapula during stance, it is proposed that two groups of scapular muscles provide the major antigravity support for the head and anterior trunk. Levator scapulae and serratus ventralis form the lateral group, inserting on the lateral processes of cervical vertebrae and on the ribs. The major and minor rhomboids form the medial group, inserting on the spinous tips of vertebrae from C4 to T4. It is also proposed that the hypaxial muscles, psoas major, minor, and quadratus lumborum could support the lumbar trunk during stance.

NASA Discipline Neuroscience↗
NASA NTRS2002

Short-range inverse-square law experiment in space

Newton's inverse-square law is a cornerstone of General Relativity. Its validity has been demonstrated to better than one part in thousand in ranges greater than 1 cm. The range below 1 mm has been left largely unexplored, due to the difficulties associated with designing sensitive short-range experiments. However, the theoretical rationale for testing Newton's law at ranges below 1 mm has become very strong recently.

inverse square law general relativity short range ↗
NASA NTRS2017

Design Guide for Aerodynamics Testing of Earth and Planetary Entry Vehicles in a Ballistic Range

The purpose of this manual is to aid in the design of an aerodynamics test of an earth or planetary entry capsule in a ballistic range. In this manual, much use is made of the results and experience gained in 50 years of ballistic range aerodynamics testing at the NASA Ames Research Center, and in particular, that gained in the last 27 years, while the author was working at NASA Ames. The topics treated herein include: Data to be obtained; flight data needed to design test; Reynolds number and dynamic similarity of flight trajectory and ballistic range test; capabilities of various ballistic ranges; Calculations of swerves due to average and oscillating lift and of drag-induced velocity decreases; Model and sabot design; materials, weights and stresses; Sabot separation; Launches at angle of attack and slapping with paper to produce pitch/yaw oscillations.

Test Design↗
NASA NTRS2021

Tropicalization of Temperate Ecosystems in North America: The Northward Range Expansion of Tropical Organisms in Response to Warming Winter Temperatures

Tropicalization is a term used to describe the transformation of temperate ecosystems by poleward-moving tropical organisms in response to warming temperatures. In North America, decreases in the frequency and intensity of extreme winter cold events are expected to allow the poleward range expansion of many cold-sensitive tropical organisms, sometimes at the expense of temperate organisms. Although ecologists have long noted the critical ecological role of winter cold temperature extremes in tropical–temperate transition zones, the ecological effects of extreme cold events have been understudied, and the influence of warming winter temperatures has too often been left out of climate change vulnerability assessments. Here, we examine the influence of extreme cold events on the northward range limits of a diverse group of tropical organisms, including terrestrial plants, coastal wetland plants, coastal fishes, sea turtles, terrestrial reptiles, amphibians, manatees, and insects. For these organisms, extreme cold events can lead to major physiological damage or landscape-scale mass mortality. Conversely, the absence of extreme cold events can foster population growth, range expansion, and ecological regime shifts. We discuss the effects of warming winters on species and ecosystems in tropical–temperate transition zones. In the 21st century, climate change-induced decreases in the frequency and intensity of extreme cold events are expected to facilitate the poleward range expansion of many tropical species. Our review highlights critical knowledge gaps for advancing understanding of the ecological implications of the tropicalization of temperate ecosystems in North America.

climate change↗
DOE OSTI2021

Whole-Voltage-Range Oxygen Redox in P2-Layered Cathode Materials for Sodium-Ion Batteries

Oxygen-redox of layer-structured metal-oxide cathodes has drawn great attention as an effective approach to break through the bottleneck of their capacity limit. However, reversible oxygen-redox can only be obtained in the high-voltage region (usually over 3.5 V) in current metal-oxide cathodes. Here, we realize reversible oxygen-redox in a wide voltage range of 1.5-4.5 V in a P2-layered Na 0.7 Mg 0.2 [Fe 0.2 Mn 0.6 $\square$0.2]O 2 cathode material, where intrinsic vacancies are located in transition-metal (TM) sites and Mg-ions are located in Na sites. Mg-ions in the Na layer serve as "pillars" to stabilize the layered structure during electrochemical cycling, especially in the high-voltage region. Intrinsic vacancies in the TM layer create the local configurations of "$\square$-O-$\square$", "Na-O-$\square$" and "Mg-O-$\square$" to trigger oxygen-redox in the whole voltage range of charge-discharge. Additionally, time-resolved techniques demonstrate that the P2 phase is well maintained in a wide potential window range of 1.5-4.5 V even at 10 C. It is revealed that charge compensation from Mn- and O-ions contributes to the whole voltage range of 1.5-4.5 V, while the redox of Fe-ions only contributes to the high-voltage region of 3.0-4.5 V. The orphaned electrons in the nonbonding 2p orbitals of O that point toward TM-vacancy sites are responsible for reversible oxygen-redox, and Mg-ions in Na sites suppress oxygen release effectively.

25 ENERGY STORAGE↗