Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “common references”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3

Wildfire Segmentation From Remotely Sensed Data Using Quantum-Compatible Conditional Vector Quantized-Variational Autoencoders

Wildfires represent a critical environmental hazard with multifaceted implications for ecosystems, communities, and public health [1]. The escalating frequency and intensity of wildfires globally have intensified the urgency for robust segmentation methodologies to facilitate effective mitigation, response, and recovery strategies [2]. Accurate wildfire segmentation is pivotal for delineating fire boundaries, assessing progression patterns, and prioritizing resource allocation during emergency scenarios. Furthermore, precise segmentation enables stakeholders, including policymakers, environmental scientists, and emergency responders, to formulate evidence-based strategies, thereby minimizing socio-economic disruptions and ecological degradation. Consequently, advancing wildfire segmentation techniques through innovative technological interventions remains a paramount research imperative. Although foundational in wildfire segmentation, traditional deterministic models exhibit inherent limitations that compromise their efficacy in dynamic and uncertain environments. These models often operate on rigid algorithms prioritizing deterministic classifications, thereby overlooking the inherent complexities and uncertainties associated with wildfire behavior and satellite data variability. Such deterministic frameworks tend to produce oversimplified representations that fail to capture the intricate nuances of evolving fire dynamics, spatial heterogeneity, and environmental interactions [1]. Consequently, the deterministic approach’s propensity for uncertainty collapsing [1, 3] hampers the accuracy, reliability, and applicability of segmentation outcomes in real-world scenarios. Contrastingly, stochastic models offer a more nuanced and adaptable framework for wildfire segmentation. By integrating probabilistic elements into the modeling paradigm, stochastic approaches, particularly probabilistic approaches such as variational auto encoders (VAEs) [4], facilitate comprehensive uncertainty assessment, enabling researchers to quantify and incorporate uncertainties into segmentation outcomes effectively. This probabilistic nature empowers stochastic models to encapsulate variability, account for data inconsistencies, and adapt to evolving environmental conditions, enhancing segmentation accuracy, reliability, and robustness. Embracing stochastic methodologies thus catalyzes advancements in wildfire science by fostering a more holistic, adaptive, and resilient segmentation framework. Despite VAEs demonstrating significant promise in various applications, they come with inherent limitations that have garnered attention within the machine learning community. One of the primary drawbacks lies in their reliance on static priors, which essentially assume a fixed distribution for latent variables, thereby limiting the model’s flexibility to capture complex data structures effectively [5]. This static nature leads to suboptimal representations, especially when dealing with complex and high-dimensional data. Additionally, VAEs often struggle with generating sharp and realistic samples, a phenomenon commonly referred to as mode collapse [5, 7, 6]. Furthermore, the optimization process in VAEs, which involves balancing the reconstruction loss and the regularization term, can sometimes be challenging to fine-tune [7]. In recent efforts to address these shortcomings, alternative approaches like Vector Quantized Variational Auto encoders(VQ-VAEs) [7], address the challenges by incorporating discrete latent variables and leveraging techniques that enhance the quality and diversity of generated samples while maintaining efficient training dynamics. VQ-VAEs propose a dynamic prior distribution generation mechanism that diverges from the static priors commonly associated with traditional VAEs. This dynamic approach allows for more adaptive and context-aware latent variable representations, thereby potentially capturing complex data structures more effectively. Unlike autoregressive prior models such as PixelCNN, which, despite their ability to model dependencies across data dimensions, suffer from significant computational inefficiencies and lack flexibility in handling diverse datasets. In our work, we propose to use a generative quantum-compatible approach to help alleviate the shortcomings of autoregressive prior model in VQ-VAEs. Restricted Boltzmann Machines (RBMs) are a viable alternative prior model that can learn prior distributions in a faster and more flexible manner. In this research endeavor, we meticulously curate a state-of-the-art dataset leveraging satellite MODIS data in conjunction with VIIRS fire masks, derived from Fire Radiative Power (FRP), thereby encapsulating diverse wildfire scenarios and environmental contexts. We developed a conditional VQ-VAE architecture with the RBM prior model that is trained in a supervised manner for segmenting wildfire masks. This innovative approach synergistically harnesses deep learning capabilities, enabling the generation of segmentation maps characterized by heightened precision, granularity, and contextual relevance. Furthermore, replacing the autoregressive prior learning method proposed by the original VQ-VAE with a prior density approximation via quantum-compatible RBM facilitates expedited inference processes, augments flexibility in prior sampling, optimizes computational efficiency and establishes a groundbreaking benchmark in wildfire segmentation methodologies.

quantum machine learning↗

Independence of Environmental and Mechanical Damages on Silicone Adhesive Stored in a Thermo-Oxidative Environment

Abstract Elastomeric polymer materials hold a special place in today’s industrial sectors with respect to structural application needs. Low quality materials are detrimental to industries like aerospace, and automotive engineering. Assessment of the durability of elastomers for structural applications has been of much interest among the literary circles for decades and new materials keep outperforming the existing ones. Polymeric adhesives are one of the most abundantly used materials in these industries. All polymeric materials get damaged when in contact with aggressive environments in presence of high temperature and oxygen. Commonly referred to as thermo-oxidation, this environment exposes the material to heat and oxidation reactions in presence of oxygen. Resultantly, during service life, the damage to the polymer matrix is primarily caused by two factors: mechanical damage and environmental aging. Environmental aging is an irreversible phenomenon caused by changes in the molecular structure while mechanical damage maintains the shape of the polymer matrix, and the deterioration is mostly due to polymer chain mobility. Environmental aging can be caused by a single environmental agent or by a synergized impact of several environmental elements. Increasing temperature is found to be proportional to decreasing tensile strength and toughness of material. The rate and extent of degradation can be accessed by scrutinizing the changes in constitutive behavior of material through mechanical and chemical properties. Accelerated thermal aging is among the most common modes of process related degradation, leading generally to chain scission, and crosslinking phenomena and reduced resistance to fracture stress, and strain. In this experimental study, our goal is to separate the environmental degradation from mechanical damage. A silicone-based adhesive was aged in thermo-oxidative at (0%RH) aging environment. The damage and decay mechanisms have been used to draw a distinction between environmental degradation and mechanical damage. Material characterization included uniaxial tensile test (failure and cyclic) and scanning electron microscopy (SEM) tests on as-received and aged samples. Aging was conducted at three different temperatures (60°C, 80°C and 95°C) and six different exposure durations (1, 3, 10, 30, 90 and 200 days). This work confirms that environmental damage is superposed on top of the mechanical damage, and thus, they are separable. The total mechanical and environmental damage is a synergized effect of all exposure conditions and parameters involved i.e., aging time, temperature, and oxygen. The chemistry and mechanics of the polymer degradation were found to be in good agreement with each other.

Alazhary, Sharif↗

Integration of the Back End of the Nuclear Fuel Cycle

Management of spent nuclear fuel and high-level radioactive waste consists of three main phases – storage, transportation, and disposal – commonly referred to as the back end of the nuclear fuel cycle. Current practice for commercial spent nuclear fuel management in the United States (US) includes temporary storage of spent fuel in both pools and dry storage systems at operating or shutdown nuclear power plants. Storage pools are filling to their operational capacity, and management of the approximately 2,200 metric tons of spent fuel newly discharged each year requires transferring older and cooler spent fuel from pools into dry storage. Unless a repository becomes available that can accept spent fuel for permanent disposal, projections indicate that the US will have approximately 136,000 metric tons of spent fuel in dry storage systems by mid-century, when the last plants in the current reactor fleet are decommissioned. Current designs for dry storage systems rely on large multi-assembly canisters, the most common of which are so-called “dual-purpose canisters” (DPCs). DPCs are certified for both storage and transportation, but are not designed or licensed for permanent disposal. The large capacity (greater number of spent fuel assemblies) of these canisters can lead to higher canister temperatures, which can delay transportation and/or complicate disposal. This current management practice, in which the utilities continue loading an ever-increasing inventory of larger DPCs, does not emphasize integration among storage, transportation, and disposal. This lack of integration does not cause safety issues, but it does lead to a suboptimal system that increases costs, complicates storage and transportation operations, and limits options for permanent disposal. This paper describes strategies for improving integration of management practices in the US across the entire back end of the nuclear fuel cycle. The complex interactions between storage, transportation, and disposal make a single optimal solution unlikely. However, efforts to integrate various phases of nuclear waste management can have the greatest impact if they begin promptly and continue to evolve throughout the remaining life of the current fuel cycle. A key factor that influences the path forward for integration of nuclear waste management practices is the identification of the timing and location for a repository. The most cost-effective path forward would be to open a repository by mid-century with the capability to directly dispose of DPCs without repackaging the spent fuel into disposalready canisters. Options that involve repackaging of spent fuel from DPCs into disposalready canisters or that delay the repository opening significantly beyond mid-century could add 10s of billions of dollars to the total system life cycle cost.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Exhaust Nozzle for a Multitube Detonative Combustion Engine

An improved type of exhaust nozzle has been invented to help optimize the performances of multitube detonative combustion engines. The invention is applicable to both air-breathing and rocket engines used to propel some aircraft and spacecraft, respectively. In a detonative combustion engine, thrust is generated through the expulsion of combustion products from a detonation process in which combustion takes place in a reaction zone coupled to a shock wave. The combustion releases energy to sustain the shock wave, while the shock wave enhances the combustion in the reaction zone. The coupled shockwave/reaction zone, commonly referred to as a detonation, propagates through the reactants at very high speed . typically of the order of several thousands of feet per second (of the order of 1 km/s). The very high speed of the detonation forces combustion to occur very rapidly, thereby contributing to high thermodynamic efficiency. A detonative combustion engine of the type to which the present invention applies includes multiple parallel cylindrical combustion tubes, each closed at the front end and open at the rear end. Each tube is filled with a fuel/oxidizer mixture, and then a detonation wave is initiated at the closed end. The wave propagates rapidly through the fuel/oxidizer mixture, producing very high pressure due to the rapid combustion. The high pressure acting on the closed end of the tube contributes to forward thrust. When the detonation wave reaches the open end of the tube, it produces a blast wave, behind which the high-pressure combustion products are expelled from the tube. The process of filling each combustion tube with a detonable fuel/oxidizer mixture and then producing a detonation repeated rapidly to obtain repeated pulses of thrust. Moreover, the multiple combustion tubes are filled and fired in a repeating sequence. Hence, the pressure at the outlet of each combustion tube varies cyclically. A nozzle of the present invention channels the expansion of the pulsed combustion gases from the multiple combustion tubes into a common exhaust stream, in such a manner as to enhance performance in two ways: (1) It reduces the cyclic variations of pressure at the outlets of the combustion tubes so as to keep the pressure approximately constant near the optimum level needed for filling the tubes, regardless of atmospheric pressure at the altitude of operation; and (2) It maximizes the transfer of momentum from the exhaust gas to the engine, thereby maximizing thrust. The figure depicts a typical engine equipped with a nozzle according to the invention. The nozzle includes an interface section comprising multiple intake ports that couple the outlets of the combustion tubes to a common plenum. Proceeding from its upstream to its downstream end, the interface section tapers to a larger cross-sectional area for flow. This taper fosters expansion of the exhaust gases flowing from the outlets of the combustion tubes and contributes to the desired equalization of exhaust combustion pressure. The cross-sectional area for flow in the common plenum is greater than, or at least equal to, the combined cross-sectional flow areas of the combustor tubes. In the common plenum, the exhaust streams from the individual combustion tubes mix to form a single compound subsonic exhaust stream. Downstream of the common plenum is the throat that tapers to a smaller flow cross section. In this throat, the exhaust gases become compressed to form a compound sonic gas stream. Downstream of the throat is an expansion section, which typically has a bell or a conical shape. (The expansion section can be truncated or even eliminated in the case of an air-breathing engine.) After entering the expansion section, the exhaust gases expand rapidly from compound sonic to compound supersonic speeds and are then vented to the environment. The basic invention admits of numerous variations. For example, the combustion tubes can be arranged around the central axin a symmetrical or asymmetrical pattern other than the one shown in the figure. For another example, the flow cross-sectional area(s) of one or more of the intake ports in the interface section, of the common plenum, the throat, and/or the expansion section can be varied, either symmetrically or asymmetrically, to adjust dynamics of the exhaust stream or to direct the thrust vector away from the central axis.

Bratkovich, Thomas E.↗

Human Stability While Exercising on a VIS Device in Zero Gravity

BACKGROUND: A Vibration Isolation and Stabilization (VIS) system is being designed for use with the European Enhanced Exploration Exercise Device (E4D) [1]. The exercise bar is attached to cables that extend and retract through openings in the E4D platform, which the subject stands on while exercising. Since the E4D is mounted on a moving VIS device, the whole system moves under the subject’s feet. While tension in the cables does help stabilize a crew member in 0g by bracing him or her against the moving platform, flexible cables do not offer full support against falling. This raises the question of whether various exercises that are successfully performed in 1g on a stationary device can be performed without losing balance in 0g on a moving device. Quantifying stability conditions and establishing stability requirements for exercise countermeasure systems is a long-standing challenge and this work helped to inform this specific need for integrated E4D/VIS flight project development. METHODS AND RESULTS: A simplified stability analysis can be attempted based on platform accelerations generated by the VIS device simulation. In this type of analysis, the subject is conceived as standing on the platform in 0g while being held down to it by the tension in the cables. If the sideways acceleration of the platform is such that the cables cannot generate a sufficient moment relative to, e.g., the heels or the toes of the subject to overcome the tipping moment from the inertial forces on the accelerated subject’s body, the subject becomes unstable. This approach, which we refer to as the ‘static’ approximation, indicated failure of all the exercises that were considered in the comprehensive VIS analysis of the E4D. It was realized, however, that platform accelerations are not externally imposed but are themselves induced by the motion of the subject’s body during exercise, and a model calculation confirmed that this drastically altered the tipping moment on the subject, with the potential to even switch the direction in which the body would tip over. This made it imperative to consider in a coupled manner both the motion of the exercising subject’s body and the induced VIS platform motion while considering stability. The coupled dynamics requirement was met by the VIS simulation incorporating time-dependent human mass properties atop the platform and driven by the inertial forces from the prescribed subject motion relative to the platform based on motion-capture recorded human trajectories in 1g on a stationary E4D [2]. To analyze simulation results, a stability criterion was also needed. We do not know how to account for the human ‘control system’ that would take visual and vestibular cues as inputs as the platform moves in 0g. We thus chose to follow an approach we had previously used to analyze the dynamic feasibility of performing a task in lunar gravity along the human body trajectory recorded in 1g [3]. In this approach, one analyzes the center of pressure (COP) between the shoes and the ground (or platform) and checks if the COP remains within the convex hull of the footprints on the ground (or platform), commonly referred to as base of support (BOS). Since pressure is vertical and, in the absence of foot restraints, positive, the COP going outside the BOS indicates that the trajectory recorded in 1g is not dynamically feasible in microgravity and/or on the moving platform of the device. The outcome of the COP-based analysis was that some of the key exercises, especially the deadlift and the back squat exercises, were found to be dynamically feasible for at least some number of the exercise cycles, this number increasing with the cable tension. While this type of stability analysis does not account for the likely alteration of the exercise trajectory from its 1g form in space, it does show that there exist at least some realistic trajectories that pass the dynamic feasibility criterion. This adds confidence that, with further adjustment by the subject of the exercise form in 0g on a moving device, a number of exercises can be performed without losing balance.

D Frenkel↗

Medical Devices Assess, Treat Balance Disorders

You may have heard the phrase as difficult as walking and chewing gum as a joking way of referring to something that is not difficult at all. Just walking, however, is not all that simple physiologically speaking. Even standing upright is an undertaking requiring the complex cooperation of multiple motor and sensory systems including vision, the inner ear, somatosensation (sensation from the skin), and proprioception (the sense of the body s parts in relation to each other). The compromised performance of any of these elements can lead to a balance disorder, which in some form affects nearly half of Americans at least once in their lifetimes, from the elderly, to those with neurological or vestibular (inner ear) dysfunction, to athletes with musculoskeletal injuries, to astronauts returning from space. Readjusting to Earth s gravity has a significant impact on an astronaut s ability to balance, a result of the brain switching to a different "model" for interpreting sensory input in normal gravity versus weightlessness. While acclimating, astronauts can experience headaches, motion sickness, and problems with perception. To help ease the transition and study the effects of weightlessness on the body, NASA has conducted many investigations into post-flight balance control, realizing this research can help treat patients with balance disorders on Earth as well. In the 1960s, the NASA-sponsored Man Vehicle Laboratory at the Massachusetts Institute of Technology (MIT) studied the effects of prolonged space flight on astronauts. The lab s work intrigued MIT doctoral candidate Lewis Nashner, who began conducting NASA-funded research on human movement and balance under the supervision of Dr. Larry Young in the MIT Department of Aeronautics and Astronautics. In 1982, Nashner s work resulted in a noninvasive clinical technique for assessing the cooperative systems that allow the body to balance, commonly referred to as computerized dynamic posturography (CDP). CDP employs a series of dynamic protocols to isolate and assess balance function deficiencies. The technology was based on Nashner s novel, engineering-inspired concept of balance as an adaptable collaboration between multiple sensory and motor systems. CDP proved useful not only for examining astronauts, but for anyone suffering from balance problems. Today, CDP is the standard medical tool for objectively evaluating balance control.

Source record↗

Environmental Stress Testing of the Single Sample Cylinder: A Proven Consensus Standard for Internal Gas Analysis (IGA) or Residual Gas Analysis (RGA)

In August 2008, Schuessler Consulting was contracted by NASA GSFC in support of the NASA Electronic Parts and Packaging (NEPP) program to perform two separate studies on moisture laden air in a stainless steel cylinder that had been designed to become a consensus standard for Test Method 1018. This Test Method was originally released for hybrids under Mil. Std. 883 but was quickly utilized on other microelectronic devices under the auspice of Mil. Std. 750. The cylinder had subsequently been fabricated for the 750 community. It was back-filled with moist air and subsequently analyzed over a period of time under a previous NASA contract. It had been shown that moisture in the 4000 - 5000 ppm range could be analyzed rather precisely with a mass spectrometer, commonly referred to as a Residual Gas Analyzer (RGA). The scope of this study was to ascertain if the composition and precision varied as a function of thermal shock at sub-zero temperatures and whether there was consensus when the standard was submitted to other RGA units. It was demonstrated and published that the consensus standard would yield precise RGA data for moisture within +/- 1% when optimized for a given RGA unit. It has been subsequently shown in this study at Oneida Research Services, that sub-zero storage did not affect that precision when a well-defined protocol for the analysis was followed. The consensus standard was taken to a second facility for analysis where it was found that moisture adsorption on the transfer lines caused precision to drop to +/- 12%. The Single Sample Cylinder (SSC) is a one liter stainless steel cylinder with associated sampling valves and has considerable weight and volume. But this considerable size allows for approximately 300 gas samples of the same composition to be delivered to any RGA unit. Lastly, a smaller cylinder, approximately 75 cc, of a second consensus standard was fabricated and tested with a different mix of fixed gases where moisture was kept in the 100 ppm range. This second standard has the potential of providing 30 gaseous samples and can be readily shipped to any analytical facility that desires to generate comparison RGA data. A series of comparison residual gas analyses was performed at the Honeywell Federal Manufacturing & Technologies facility in the National Nuclear Facility Administration s plant in Kansas City to complete this project. It was shown that improvements in the precision of a given RGA unit can be done by controlling the cycle time for each analysis and increasing analysis temperatures to minimize moisture adsorption. It was also found that a "one time event" in the subzero storage of the large SSC did not effect the units ability to continuously supply precise samples of the same chemistry, however the "event" caused a permanent +8% shift in the reported value of the moisture content. Lastly, a set of SSC RGA results was plotted on a common graph with DSCC "correlation study" RGA data. The result demonstrates the ability of the SSC to remove many of the individual variances that single, individual samples introduce. The consensus standards are now in storage at Oneida Research Services, one of the DSCC certified houses that does RGA to Military Standards, where they await future studies. The analytical data and the operational parameters of the instruments used are provided in the following discussion. Limitations and suggested means for improvement of both precision and accuracy are provided.

Schuessler, Philipp WH↗

Development of a Numerical Model of Hypervelocity Impact into a Pressurized Composite Overwrapped Pressure Vessel

As the outlook for space exploration becomes more ambitious and spacecraft travel deeper into space than ever before, it is increasingly important that propulsion systems perform reliably within the space environment. The increased reliability compels designers to increase design margin at the expense of system mass, which contrasts with the need to limit vehicle mass to maximize payload. Such are the factors that motivate the integration of high specific strength composite materials in the construction of pressure vessels commonly referred to as composite overwrapped pressure vessels (COPV). The COPV consists of a metallic liner for the inner shell of the COPV that is stiff, negates fluid permeation and serves as the anchor for composite laminates or filaments, but the liner itself cannot contain the stresses from the pressurant it contains. The compo-site-fiber reinforced polymer (CFRP) is wound around the liner using a combination of hoop (circumferential) and helical orientations. Careful consideration of wrap orientation allows the composite to evenly bear structural loading and creates the COPV's characteristic high strength to weight ratio. As the CFRP overwrap carries most of the stresses induced by pressurization, damage to the overwrap can affect mission duration, mission success and potentially cause loss-of-vehicle/loss-of-crew. For this reason, it is critical to establish a fundamental understanding of the mechanisms involved in the failure of a stressed composite such as that of the COPV. One of the greatest external threats to the integrity of a spacecraft's COPV is an impact from the meteoroid and orbital debris environments (MMOD). These impacts, even from submillimeter particles, generate extremely high stress states in the CFRP that can damage numerous fibers. As a result of this possibility, initial assumptions in survivability analysis for some human-rated NASA space-craft have assumed that any alteration of the vessel due to impact is considered a catastrophic failure. This assumption is conservative and made due to lack of knowledge on the level of allow-able damage to the composite overwrap that can be sustained and still allow successful completion of the mission. To quantify the allowable damage level to the composite overwrap involves assessing stress redistribution following damage as well as evaluating possible time-dependent mechanisms involved in the COPV response to an impact event. Limited published work in this subject has shown that COPV can withstand at least some level of damage due to high energy impacts. These observations have been confirmed and expanded upon in recent experimental research performed by NASA. This research has demonstrated that there is not only robustness in a COPV to compensate for CFRP damage, but has also identified two significant failure modes for pressurized COPV. The lowest threshold failure mode involves the perforation of the vessel, and the highest threshold failure mode is the catastrophic rupture. While both of these failure modes mean a loss of the COPV, system robustness affords some tolerance to the venting as opposed to the more catastrophic rupture. As a consequence, it is necessary to understand the conditions that result in the transition between these failure modes. The aforementioned experimental research has been performed in both the unpressurized and pressurized condition to identify the damage level that triggered the failure thresh-old. This COPV test program was sponsored by the NASA Engineering and Safety Center (NESC), and tests were performed at NASA White Sands Test Facility (WSTF). Planning and coordination were provided by NASA JSC Hypervelocity Impact Technology (HVIT) group, and the COPVs were provided by the ISS Program. Unpressurized testing has been conducted at the pressure of the vacuum test chamber, while, the pressurized testing has been conducted at 290 +/- 10 bar (4,200  100 psi) using nitrogen as the pressurizing gas, which corresponds to the design pressure for the target COPV. In this research, spherical aluminum projectiles with varying diameter has been chosen as the impactor. For the unpressurized COPV, the dependence of penetration up to the dependence of hole size in the liner has been obtained as a function of impact conditions. For the pressurized research, the dependence of penetration up to rupture has been obtained as a function of im-pact conditions. Two representative post-test photographs of the failed COPV's from a nor-mal impact into the COPV surface are shown in Fig. 1. These images display the dramatic difference between failure modes, venting (Fig. 1a) and rupture (Fig. 1b). For venting, liner perforation, severed composite fibers/tows and ply delamination are commonly observed damage characteristics of this COPV failure mode. In the case of rupture, the COPV typically experienced a separation of its domed regions and severe break-up of the cylindrical region. Fully understanding the transition from venting to rupture experimentally is costly and potentially unachievable for conditions that cannot be generated in the laboratory. These shortcomings have motivated the performance of three-dimensional numerical simulations to expand the existing experimental database. These simulations have been carried out with the nonlinear-structural-dynamics, analysis-tool, CTH. A typical pressure contour plot from an impact simulation of an entire COPV is shown in Fig. 2. To generate the COPV stress state without initiating a shock wave, the pressure in the simulated COPV is ramped up to the final pressure over a millisecond prior to impact of the projectile with nitrogen gas. Figure 2a shows the system in this initial condition. After one millisecond, a projectile is initiated into the simulation and impacts the COPV. Figure 2b shows the system after this impact. In the figure, the onset of venting is represented as the change in pressure (μbar), red to green, at the perforation site. Also seen in the figure is the eroded projectile that had passed into the COPV vessel with the generated shock wave in the pressurant propagating just ahead of the material. In this paper, pertinent experimental details and the development of the material constitutive models necessary for this work along with the efforts to validate their use are dis-cussed. The simulation results are presented and compared with the NASA experimental observations. While work is on-going from this effort, early observations pertinent to the failure threshold are presented.

Garcia, M. A.↗

Appropriate “marginal” farmlands for second‐generation biofuel crops in North Carolina

Abstract Current research on bioenergy crops shows that perennial grasses can yield substantial amounts of dry biomass with relatively low inputs of water and fertilizer. In order to minimize competition with food production, it has been suggested that bioenergy crops could be directed to land areas less suitable for commodity crops, commonly referred to as “marginal” lands. These are land units with inherent limitations to vegetative growth and production, which may be due to several factors (soil physical and chemical properties, climatic conditions, etc.). However the term “marginal” is an adjective with imprecise meaning, and objective criteria for determining “marginal” lands for siting bioenergy crops are necessary. Here we propose that such criteria may be based on soil survey classifications and realistic yield estimates, and we show an example of its use to justify site selection for bioenergy crops in different regions of North Carolina.

09 BIOMASS FUELS↗

Self‐Consistent Convolutional Density Functional Approximations: Application to Adsorption at Metal Surfaces

The exchange-correlation (XC) functional in density functional theory is used to approximate multi-electron interactions. A plethora of different functionals are available, but nearly all are based on the hierarchy of inputs commonly referred to as “Jacob's ladder.” This paper introduces an approach to construct XC functionals with inputs from convolutions of arbitrary kernels with the electron density, providing a route to move beyond Jacob's ladder. We derive the variational derivative of these functionals, showing consistency with the generalized gradient approximation (GGA), and provide equations for variational derivatives based on multipole features from convolutional kernels. A proof-of-concept functional, PBEq, which generalizes the PBEα framework with mathematical equation being a spatially-resolved function of the monopole of the electron density, is presented and implemented. It allows a single functional to use different GGAs at different spatial points in a system, while obeying PBE constraints. Analysis of the results underlines the importance of error cancellation and the XC potential in data-driven functional design. After testing on small molecules, bulk metals, and surface catalysts, the results indicate that this approach is a promising route to simultaneously optimize multiple properties of interest.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Gas–Phase Preparation of the 14π Hückel Polycyclic Aromatic Anthracene and Phenanthrene Isomers (C 14 H 10 ) via the Propargyl Addition–BenzAnnulation (PABA) Mechanism

Polycyclic aromatic hydrocarbons (PAHs) imply the missing link between resonantly stabilized free radicals and carbonaceous nanoparticles, commonly referred to as soot particles in combustion systems and interstellar grains in deep space. Whereas gas phase formation pathways to the simplest PAH – naphthalene (C 10 H 8 ) – are beginning to emerge, reaction pathways leading to the synthesis of the 14π Hückel aromatic PAHs anthracene and phenanthrene (C 14 H 10 ) are still incomplete. Here, by utilizing a chemical microreactor in conjunction with vacuum ultraviolet (VUV) photoionization (PI) of the products followed by detection of the ions in a reflectron time-of-flight mass spectrometer (ReTOF-MS), the reaction between the 1'- and 2'-methylnaphthyl radicals (C 11 H 9 •) with the propargyl radical (C 3 H 3 •) accesses anthracene (C 14 H 10 ) and phenanthrene (C 14 H 10 ) via the Propargyl Addition–BenzAnnulation (PABA) mechanism in conjunction with a hydrogen assisted isomerization. Furthermore, the preferential formation of the thermodynamically less stable anthracene isomer compared to phenanthrene suggests a kinetic, rather than a thermodynamics control of the reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Multi-channel direct detection of light dark matter: theoretical framework

We present a unified theoretical framework for computing spin-independent direct detection rates via various channels relevant for sub-GeV dark matter — nuclear re- coils, electron transitions and single phonon excitations. Despite the very different physics involved, in each case the rate factorizes into the particle-level matrix element squared, and an integral over a target material- and channel-specific dynamic structure factor. We show how the dynamic structure factor can be derived in all three cases following the same procedure, and extend previous results in the literature in several aspects. For electron transitions, we incorporate directional dependence and point out anisotropic target materials with strong daily modulation in the scattering rate. For single phonon excitations, we present a new derivation of the rate formula from first principles for generic spin-independent couplings, and include the first calculation of phonon excitation through electron couplings. We also discuss the interplay between single phonon excitations and nuclear recoils, and clarify the role of Umklapp processes, which can dominate the single phonon production rate for dark matter heavier than an MeV. Our results highlight the complementarity between various search channels in probing different kinematic regimes of dark matter scattering, and provide a common reference to connect dark matter theories with ongoing and future direct detection experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

A Review of Global Radioxenon Background Research and Issues

Among the most important problems for the world-wide nuclear explosion monitoring is the interference of naturally occurring and man-made radionuclides. The International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) frequently detects these interferences using sensitive radionuclide measurement equipment. We commonly refer to the presence of radionuclides that are relevant to the CTBT but do not originate from a nuclear explosion as “background”. Backgrounds are highest near the sources but are known to have regional and global effects on the IMS. This review paper summarizes much of the relevant work in the area of background and discusses issues of interest for nuclear explosion detection.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗

Fundamentals on dependence of volume on pressure and temperature

The common wisdom that volume decreases with pressure and increases with temperature is analyzed in terms of Hillert nonequilibrium thermodynamics in the present work. It is shown that the derivative of volume to pressure in a stable system is always negative, i.e., volume decreases with the increase of pressure, when all other natural variables of the system are kept constant. This originates from the stability requirement that the conjugate variables, such as volume and negative pressure, must change in the same direction in a stable system. Consequently, since volume and temperature are not conjugate variables, they do not have to change in the same direction and thus do change in opposite directions in both natural and man-made systems. It is shown that the decrease of volume with the increase of temperature, commonly referred as negative thermal expansion (NTE) in the literature, originates from the statistical competitions of configurations in the system when the volumes of metastable configurations are smaller than that of the ground-state configuration. As a result, it is demonstrated that the zentropy theory can concisely explain and accurately predict NTE based on the density functional theory without fitting parameters.

36 MATERIALS SCIENCE↗

Life Cycle Analysis of Thermoelectric Power Generation in the United States

In this article, the basics of performing a life cycle analysis of thermoelectric power generation are discussed, with three examples of life cycle greenhouse gas (GHG) balances for thermoelectric power generation forms: coal, natural gas, and nuclear. The final section compares multiple electricity generation methods in the United States. Results are presented on the basis of 1 megawatt-hour (MWh) of electricity delivered to the end user. Environmental life cycle results for greenhouse gas (GHG) emissions are presented as carbon dioxide equivalents, based on 100-year global warming potentials (GWPs) established by the 6th Assessment Report from the Intergovernmental Panel on Climate Change in 2021, commonly referred to as AR6 GWP values (IPCC, 2021). Additional details on other environmental life cycle impacts from non-GHG emissions to air, emissions to water, solid waste generation, and land use are available on the Department of Energy, National Energy Technology Laboratory’s Life Cycle Analysis website: www.netl.doe.gov/LCA.

Cutshaw, Ashley↗

Non-destructive simulation of node defects in additively manufactured lattice structures

Additive Manufacturing (AM), commonly referred to as 3D printing, offers the ability to not only fabricate geometrically complex lattice structures but parts in which lattice topologies in-fill volumes bounded by complex surface geometries. However, current AM processes produce defects on the strut and node elements which make up the lattice structure. This creates an inherent difference between the as-designed and as-fabricated geometries, which negatively affects predictions (via numerical simulation) of the lattice’s mechanical performance. Although experimental and numerical analysis of an AM lattice’s bulk structure, unit cell and struts have been performed, there exists almost no research data on the mechanical response of the individual as-manufactured lattice node elements. Here we propose a methodology that, for the first time, allows non-destructive quantification of the mechanical response of node elements within an as-manufactured lattice structure. A custom-developed tool is used to extract and classify each individual node geometry from micro-computed tomography scans of an AM fabricated lattice. Voxel-based finite element meshes are generated for numerical simulation and the mechanical response distribution is compared to that of the idealised computer-aided design model. The method demonstrates compatibility with Uncertainty Quantification methods that provide opportunities for efficient prediction of a population of nodal responses from sampled data. Overall, the non-destructive and automated nature of the node extraction and response evaluation is promising for its application in qualification and certification of additively manufactured lattice structures.

36 MATERIALS SCIENCE↗

Acceleration of Glass Alteration Rates Induced by Zeolite Seeds at Controlled pH

As the glass-water reaction proceeds, certain glass compositions undergo a delayed acceleration in the alteration rate – a phenomenon that is commonly referred to as Stage III behavior – which generally coincides with zeolite formation. However, studying Stage III in the laboratory is difficult because the time scale required to observe Stage III behavior can vary from months to several years, and the solution conditions that initiate this acceleration remain poorly understood. Consequently, the development of a corrosion test method capable of quantifying Stage III rates in a timely manner would be of great benefit to both the scientific community and policy makers concerned with nuclear waste disposal. In this work, we induced and measured the acceleration in the corrosion rate of the AFCI glass by seeding static corrosion tests with zeolite Na-P2 at fixed pH90°C values ranging from 9.5 to 11.5. The induced Stage III rates increased linearly with increasing pH and were measured to be between the forward and residual rates of AFCI. Tests designed to compare induced Stage III rates obtained for different seeding times showed that the induced Stage III rates were faster in the absence of an alteration layer. In summary, the use of the seeded test method allows for a conservative quantification of Stage III rates in a relatively short, one-month time period.

Neeway, James J.↗

Effect of an oxide layer on high velocity impact of tantalum particles characterized using molecular dynamics

Micro-cold spray, also commonly referred to as the aerosol deposition method or vacuum kinetic spraying, is a process for depositing nanostructured films of metals and ceramics by impacting solid nanoparticles at high velocity onto a substrate at room temperature and at low pressures. Tantalum films deposited by micro-cold spray are desirable because tantalum is non-reactive to certain molten metals and can therefore serve as a non-reactive barrier coating. However, unlike most other metals deposited by micro-cold spray, tantalum quickly forms an oxide layer when exposed to air. In the deposition of films using traditional cold spray with much larger particles, native oxides must fracture for particle–substrate bonding to occur. Furthermore, the fraction of the particle that is oxidized in micro-cold spray and the strain rates experienced by the particles upon impact are both much larger than in cold spray, suggesting that the role of the oxide on film deposition may be distinct. The effect of this oxide layer on particle deformation and adherence to a substrate under high strain rates is studied using molecular dynamics simulations. The effect of oxide layer thickness, particle diameter, and impact velocity are examined.

42 ENGINEERING↗