Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “passive structures”

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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Unconventional colloidal aggregation in chiral bacterial baths

Abstract When in equilibrium, thermal forces agitate molecules, which then diffuse, collide and bind to form materials. However, the space of accessible structures in which micron-scale particles can be organized by thermal forces is limited, owing to the slow dynamics and metastable states. Active agents in a passive fluid generate forces and flows, forming a bath with active fluctuations. Two unanswered questions are whether those active agents can drive the assembly of passive components into unconventional states and which material properties they will exhibit. Here we show that passive, sticky beads immersed in a bath of swimmingEscherichia colibacteria aggregate into unconventional clusters and gels that are controlled by the activity of the bath. We observe a slow but persistent rotation of the aggregates that originates in the chirality of theE. coliflagella and directs aggregation into structures that are not accessible thermally. We elucidate the aggregation mechanism with a numerical model of spinning, sticky beads and reproduce quantitatively the experimental results. We show that internal activity controls the phase diagram and the structure of the aggregates. Overall, our results highlight the promising role of active baths in designing the structural and mechanical properties of materials with unconventional phases.

Physics↗
DOE OSTI2015

Structural stability and electronic properties of InSb nanowires: A first-principles study

Using first-principles calculations, we investigate the structural stability and electronic properties of InSb nanowires (NWs). The results show that, in contrast to the bulk InSb phase, wurtzite (WZ) NWs are more stable than zinc-blende (ZB) NWs when the NW diameter is smaller than 10 nm. Nonpassivated ZB and WZ NWs are found to be metallic and semiconducting, respectively. After passivation, both ZB and WZ NWs exhibit direct-gap semiconductor character, and the band gap magnitude of the NWs strongly depends on the suppression of surface states by the charge-compensation ability of foreign atoms to surface atoms. Moreover, the carrier mobility of the NW can be strengthened by halogen passivation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2016

NASA and ESA Collaboration on Alternative to Nitric Acid Passivation: Parameter Optimization of Citric Acid Passivation for Stainless Steel Alloys

National Aeronautics and Space Administration (NASA) Headquarters chartered the Technology Evaluation for Environmental Risk Mitigation Principal Center (TEERM) to coordinate agency activities affecting pollution prevention issues identified during system and component acquisition and sustainment processes. The primary objectives of NASA TEERM are to: Reduce or eliminate the use of hazardous materials or hazardous processes at manufacturing, remanufacturing, and sustainment locations. Avoid duplication of effort in actions required to reduce or eliminate hazardous materials through joint center cooperation and technology sharing. Corrosion is an extensive problem that affects the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). The damaging effects of corrosion result in steep costs, asset downtime affecting mission readiness, and safety risks to personnel. Consequently, it is vital to reduce corrosion costs and risks in a sustainable manner. NASA and ESA have numerous structures and equipment that are fabricated from stainless steel. The standard practice for protection of stainless steel is a process called passivation. Passivation is defined by The American Heritage Dictionary of the English Language as to treat or coat (a metal) in order to reduce the chemical reactivity of its surface. Passivation works by forming a shielding outer (metal oxide) layer that reduces the impact of destructive environmental factors such as air or water. Consequently, this process necessitates a final product that is very clean and free of iron and other contaminants. Typical passivation procedures call for the use of nitric acid; however, there are a number of environmental, worker safety, and operational issues associated with its use. Citric acid is an alternative to nitric acid for the passivation of stainless steels. Citric acid offers a variety of benefits including increased safety for personnel, reduced environmental impact, and reduced operational cost. The primary objective of this effort is to qualify citric acid as an environmentally-preferable alternative to nitric acid for the passivation of stainless steel alloys. While citric acid use has become more prominent in industry, there is little evidence that citric acid is a technically sound passivation agent, especially for the unique and critical applications encountered by NASA and ESA.

citric acid passivation↗
NASA NTRS1993

Design, analysis, and testing of high frequency passively damped struts

Objectives of the research are: (1) to develop design requirements for damped struts to stabilize control system in the high frequency cross-over and spill-over range; (2) to design, fabricate and test viscously damped strut and viscoelastically damped strut; (3) to verify accuracy of design and analysis methodology of damped struts; and (4) to design and build test apparatus, and develop data reduction algorithm to measure strut complex stiffness. In order to meet the stringent performance requirements of the SPICE experiment, the active control system is used to suppress the dynamic responses of the low order structural modes. However, the control system also inadvertently drives some of the higher order modes unstable in the cross-over and spill-over frequency range. Passive damping is a reliable and effective way to provide damping to stabilize the control system. It also improves the robustness of the control system. Damping is designed into the SPICE testbed as an integral part of the control-structure technology.

Yiu, Y. C.↗
NASA NTRS1990

Remote measurements of the structure of midwest thunderstorm tops and anvils from high altitude aircraft

Results are presented from observations by a visible and IR scanning radiometer, a scanning passive microwave radiometer, and a nadir-viewing cloud lidar system (CLS), carried out from ER-2 overflights for two midwest severe weather events both of which presented following phenomena: (1) a group of severe thunderstorms which later transformed into a linear mesoscale convective system, and (2) a severe thunderstorm which produced large hail. Most of the aircraft in situ and remote measurements pointed to a deep subsidence region and gravity waves downstream of the overshooting cloud tops. The observations do not support a radiative explanation for the warm areas in the anvil.

Heymsfield, Gerald M.↗
DOE OSTI2012

Fuel Pond Sludge - Lessons Learned from Initial De-sludging of Sellafield's Pile Fuel Storage Pond - 12066

The Pile Fuel Storage Pond (PFSP) at Sellafield was built and commissioned between the late 1940's and early 1950's as a storage and cooling facility for irradiated fuel and isotopes from the two Windscale Pile reactors. The pond was linked via submerged water ducts to each reactor, where fuel and isotopes were discharged into skips for transfer along the duct to the pond. In the pond the fuel was cooled then de-canned underwater prior to export for reprocessing. The plant operated successfully until it was taken out of operation in 1962 when the First Magnox Fuel Storage Pond took over fuel storage and de-canning operations on the site. The pond was then used for storage of miscellaneous Intermediate Level Waste (ILW) and fuel from the UK's Nuclear Programme for which no defined disposal route was available. By the mid 1970's the import of waste ceased and the plant, with its inventory, was placed into a passive care and maintenance regime. By the mid 1990s, driven by the age of the facility and concern over the potential challenge to dispose of the various wastes and fuels being stored, the plant operator initiated a programme of work to remediate the facility. This programme is split into a number of key phases targeted at sustained reduction in the hazard associated with the pond, these include: - Pond Preparation: Before any remediation work could start the condition of the pond had to be transformed from a passive store to a plant capable of complex retrieval operations. This work included plant and equipment upgrades, removal of redundant structures and the provision of a effluent treatment plant for removing particulate and dissolved activity from the pond water. - Canned Fuel Retrieval: Removal of canned fuel, including oxide and carbide fuels, is the highest priority within the programme. Handling and export equipment required to remove the canned fuel from the pond has been provided and treatment routes developed utilising existing site facilities to allow the fuel to be reprocessed or conditioned for long term storage. - Sludge Retrieval: In excess of 300 m{sup 3} of sludge has accumulated in the pond over many years and is made up of debris arising from fuel and metallic corrosion, wind blown debris and bio-organic materials. The Sludge Retrieval Project has provided the equipment necessary to retrieve the sludge, including skip washer and tipper machines for clearing sludge from the pond skips, equipment for clearing sludge from the pond floor and bays, along with an 'in pond' corral for interim storage of retrieved sludge. Two further projects are providing new plant processing routes, which will initially store and eventually passivate the sludge. - Metal Fuel Retrieval: Metal Fuel from early Windscale Pile operations and various other sources is stored within the pond; the fuel varies considerably in both form and condition. A retrieval project is planned which will provide fuel handling, conditioning, sentencing and export equipment required to remove the metal fuel from the pond for export to on site facilities for interim storage and disposal. - Solid Waste Retrieval: A final retrieval project will provide methods for handling, retrieval, packaging and export of the remaining solid Intermediate Level Waste within the pond. This includes residual metal fuel pieces, fuel cladding (Magnox, aluminium and zircaloy), isotope cartridges, reactor furniture, and miscellaneous activated and contaminated items. Each of the waste streams requires conditioning to allow it to be and disposed of via one of the site treatment plants. - Pond Dewatering and Dismantling: Delivery of the above projects will allow operations to progressively remove the radiological inventory, thereby reducing the hazard/risk posed by the plant. This will then allow subsequent dewatering of the pond and dismantling of the structure. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Progress in Fast Modular Reactor Conceptual Design

The Fast Modular Reactor (FMR) is a 100-MW(thermal) gas-cooled fast reactor being developed by General Atomics Electromagnetic System with the goal of developing a FMR for flexible and dispatchable power to the U.S. electricity market in the mid-2030s. The conceptual design aims to develop and verify simplified design features. These include an inert helium gas coolant, pellet-loaded fuel rods, installations with air cooling as ultimate heat sink, and small and passive heat removal systems. The goal is to ensure the development of a safe, maintainable, cost-effective, and distributed nuclear energy-generating station. The baseline technologies selected to achieve this goal are a helium coolant that is an inert gas with no chemical reaction with structural components, not activated, single phase, enabling high-temperature operation and a high thermal efficiency Brayton cycle; conventional uranium dioxide (UO 2 ) fuel, which is the most widely used and well-known fuel material, capable of high burnup (100 MWd/kg) and a long fuel life; and silicon carbide composite (SiGA®) cladding and internal structures that are chemically inert in the helium environment, exceptionally radiation tolerant, and being derisked by accident tolerant fuel technology development. Further, the reactor was specifically designed with passive safety features, including high-temperature in-core materials and a reactor vessel cooling system consisting of cooling panels of naturally circulating water. The passive safety of the core was confirmed for the depressurized loss-of–forced cooling accident, which showed the peak cladding temperature at ~1600°C during the transient, which is below the current design limit of 1800°C. The conceptual design of the FMR has been conducted for the reactor system, vessel system, generator and turbomachine, instrumentation and control, residual heat removal system, plant service system, and containment, as well as pre-application licensing documents.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2021

Finite-size correction for slab supercell calculations of materials with spontaneous polarization

Abstract The repeated slab approach has become a de facto standard to accurately describe surface properties of materials by density functional theory calculations with periodic boundary conditions. For materials exhibiting spontaneous polarization, we show that the conventional scheme of passivation with pseudo hydrogen is unable to realize a charge-neutral surface. The presence of a net surface charge induces via Gauss’s law a macroscopic electric field through the slab and results in poor size convergence with respect to the thickness of the slab. We propose a modified passivation method that accounts for the effect of spontaneous polarization, describes the correct bulk limits and boosts convergence with respect to slab thickness. The robustness, reliability, and superior convergence of energetics and electronic structure achieved by the proposed method are demonstrated using the example of polar ZnO surfaces.

Chemistry↗
DOE OSTI2024

Dry etching of epitaxial InGaAs/InAlAs/InAlGaAs structures for fabrication of photonic integrated circuits

A dry etching process to transfer the pattern of a photonic integrated circuit design for high-speed laser communications is described. The laser stack under consideration is a 3.2-µm-thick InGaAs/InAlAs/InAlGaAs epitaxial structure grown by molecular beam epitaxy. The etching was performed using Cl2-based inductively-coupled-plasma and reactive-ion-etching (ICP-RIE) reactors. Four different recipes are presented in two similar ICP-RIE reactors, with special attention paid to the etched features formed with various hard mask compositions, in-situ passivations, and process temperatures. The results indicate that it is possible to produce high-aspect-ratio features with sub-micron separation on this multilayer structure. Additionally, the results of the etching highlight the tradeoffs involved with the corresponding recipes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

An Engineered Multifunctional Composite for Passive Sensing, Power Harvesting, and In Situ Damage Identification with Enhanced Mechanical Performance

A multifunctional fiber-reinforced composite with passive self-sensing, energy-harvesting, and damage detection capabilities is presented. In this work, barium titanate piezoelectric microparticles are deposited on basalt fibers by a scalable, low-cost, environmentally friendly continuous feed-through process. The resulting composite derives a superior interlaminar shear strength from the microparticle-modified fiber–matrix interfaces. The composite also demonstrates passive self-sensing capabilities that produce electrical signals proportional to various dynamic loading events. Vibration and strain-controlled experiments are performed on composite beams to quantify the sensitivity and power output as a function of input acceleration and strain. Furthermore, these composite-generated electrical signals are used to identify in situ damage initiation for structural health monitoring to inform composite damage prior to structural failure. In brief, this truly multifunctional composite simultaneously displays a sensitivity of 0.5–2.6 mV g -1 at a resolution of 0.045–0.20g (g = gravitational acceleration), energy harvesting in the range of nW cc -1 , and prediction of early damage by exhibiting 0.017–1.17 mV peaks in voltage–time history profiles while assuring ≈20% improved interlaminar shear strength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Nanomechanical properties of platinum thin films synthesized by atomic layer deposition

The nanomechanical properties of Pt thin films grown on Si (100) using atomic layer deposition (ALD) were investigated using nanoindentation. Recently, atomic layer deposition (ALD) has successfully demonstrated the capability to deposit ultra-thin films of platinum (Pt). Using (methylcyclopentadienyl) trimethylplatinum (MeCpPtMe3) as chemical platinum precursor and oxygen (O2) as the oxidizing agent, the ALD synthesis of Pt can be achieved with high conformity and excellent film uniformity. The ALD process window for Pt films was experimentally established in the temperature range between 270 °C and 320 °C, where the sheet conductance was constant over that temperature range, indicating stable ALD Pt film growth rate. ALD growth of Pt films exhibits very poor nucleation and adhesion characteristics on bare Si surfaces when the native oxide was removed by 2% HF etch. Pt adhesion improves for thermally oxidized Si wafers and for Si wafers covered with native oxide. Three ALD Pt films deposited at 800, 900, and 1000 ALD deposition cycles were tested for the structural and mechanical properties. Additionally, the sample with 900 ALD deposition cycles was further annealed in forming gas (95% N2 and 5% H2) at 450 °C for 30 min in order to passivate dangling bonds in the grain boundaries of the polycrystalline Pt film. Cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscope (SEM) were employed to characterize the films' surface structure and morphology. Nanoindentation technique was used to evaluate the hardness and modulus of the ALD Pt films of various film thicknesses. The results indicate that the films depict comparable hardness and modulus results; however, the 800 and 1000 ALD deposition cycles films without forming gas annealing experienced significant amount of pileup, whereas the 900 ALD deposition cycles sample annealed in forming gas resulted in a smaller pileup.

Mamun, M.A.↗
DOE OSTI2015

Rossby-Khantadze electromagnetic planetary waves driven by sheared zonal winds in the E-layer ionosphere

Nonlinear simulations of electromagnetic Rossby and Khantadze planetary waves in the presence of a shearless and sheared zonal flows in the weakly ionized ionospheric E-layer are carried out. The simulations show that the nonlinear action of the vortex structures keeps the solitary character in the presence of shearless zonal winds as well as the ideal solutions of solitary vortex in the absence of zonal winds. In the presence of sheared zonal winds, the zonal flows result in breaking into separate multiple smaller pieces. A passively convected scalar field is shown to clarify the transport associated with the vortices. The work shows that the zonal shear flows provide an energy source into the vortex structure according to the shear rate of the zonal winds.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Proximity operations considerations affecting spacecraft design

Proximity operations can be defined as the maneuvering of two or more spacecraft within 1 nautical mile range, with relative velocity less than 10 feet per second. The passive vehicle is nontranslating and should provide for maintenance of the desired approach attitude. It must accommodate the active (translating) vehicle induced structural loads and performance characteristics (mating hardware tolerances), and support sensor compatibility (transponder, visual targets, etc.). The active vehicle must provide adequate sensor systems (relative state information, field-of-view, redundancy), flight control hardware (thruster sizing, minimal cross-coupling, performance margins, redundancy) and software (reconfigurable, attitude/rate modes, translation and rotation fine control authority) characteristic, and adequate non-propulsive consumables such as power. Operational concerns must be considered. These include the following: (1) the desired approach trajectory and relative orientation; (2) the active vehicle thruster plume effects (forces, torques, contamination) on the passive vehicle; and (3) procedures for contingencies such as loss of communications, sensor or propulsion failures, and target vehicle loss of control.

Staas, Steven K.↗
DOE OSTI2021

Enhanced Diffusive Transport in Fluctuating Porous Media

Mass transport within porous structures is a ubiquitous process in biological, geological, and technological systems. Despite the importance of these phenomena, there is no comprehensive theory that describes the complex and diverse transport behavior within porous environments. While the porous matrix itself is generally considered a static and passive participant, many porous environments are in fact dynamic, with fluctuating walls, pores that open and close, and dynamically changing cross-links. While diffusion has been measured in fluctuating structures, notably in model biological systems, it is rarely possible to isolate the effect of fluctuations because of the absence of control experiments involving an identical static counterpart, and it is generally impossible to observe the dynamics of the structure. In this paper, we present a direct comparison of the diffusion of nanoparticles of various sizes within a trackable, fluctuating porous matrix and a geometrically equivalent static matrix, in conditions spanning a range of regimes from obstructed to highly confined. The experimental system comprised a close-packed layer of colloidal spheres that were either immobilized to a planar surface or allowed to fluctuate locally, within the space defined by their nearest neighbors. Interestingly, the effective long-time diffusion coefficient was approximately 35–65% greater in the fluctuating porous matrix than in the static one (depending on the size of the nanoparticle probes), regardless of the geometric regime. This was explained by considering the enhancing effects of matrix fluctuations on the short-time diffusion coefficient and cooperative “gate-opening” motions of matrix particles and nanoparticle probes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Applications of Doppler-free saturation spectroscopy for edge physics studies (invited)

Doppler-free saturation spectroscopy provides a very powerful method to obtain detailed information about the electronic structure of the atom through measurement of the spectral line profile. This is achieved through a significant decrease in the Doppler broadening and essentially an elimination of the instrument broadening inherent to passive spectroscopic techniques. In this paper we present the technique and associated physics of Doppler-free saturation spectroscopy in addition to how one selects the appropriate transition. Simulations of H{sub δ} spectra are presented to illustrate the increased sensitivity to both electric field and electron density measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Phase evolution of conversion-type electrode for lithium ion batteries

Batteries with conversion-type electrodes exhibit higher energy storage density but suffer much severer capacity fading than those with the intercalation-type electrodes. The capacity fading has been considered as the result of contact failure between the active material and the current collector, or the breakdown of solid electrolyte interphase layer. Here, using a combination of synchrotron X-ray absorption spectroscopy and in situ transmission electron microscopy, we investigate the capacity fading issue of conversion-type materials by studying phase evolution of iron oxide composited structure during later-stage cycles, which is found completely different from its initial lithiation. The accumulative internal passivation phase and the surface layer over cycling enforce a rate-limiting diffusion barrier for the electron transport, which is responsible for the capacity degradation and poor rate capability. This work directly links the performance with the microscopic phase evolution in cycled electrode materials and provides insights into designing conversion-type electrode materials for applications.

25 ENERGY STORAGE↗
DOE OSTI2016

Size-dependent forced PEG partitioning into channels: VDAC, OmpC, and α-hemolysin

Significance With consequences for the selective partitioning of large molecules in cells, polymer partitioning into nanopores is instructive for single-molecule sensing as well as for polymer-assisted transport and packaging. Here we detect and analyze not only passive but also forced size-dependent partitioning of binary mixtures of differently sized PEGs. We probe three structurally different channels exhibiting forced partitioning that can be understood conceptually as well as quantitatively within a “polymers-pushing-polymers” model, allowing good estimates for the size-dependent pore penetration energy differences. Beyond proof of concept, forced partitioning in cells can now be recognized and used as a new tool for molecule-selective transport and active osmotically regulated packaging.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microbial community assembly differs across minerals in a rhizosphere microcosm

Mineral–associated microbes drive many critical soil processes, including mineral weathering, soil aggregation and cycling of mineral–sorbed organic matter. To investigate the interactions between soil minerals and microbes in the rhizosphere, we incubated three types of minerals (ferrihydrite, kaolinite and quartz) and a native soil mineral fraction near roots of a common Californian annual grass, Avena barbata , growing in its resident soil. We followed microbial colonization of these minerals for up to 2.5 months – the plant's lifespan. Bacteria and fungi that colonized mineral surfaces during this experiment differed across mineral types and differed from those in the background soil, implying that microbial colonization was the result of processes in addition to passive movement with water to mineral surfaces. Null model analysis revealed that dispersal limitation was a dominant factor structuring mineral–associated microbial communities for all mineral types. Once bacteria arrived at a mineral surface, capacity for rapid growth appeared important, as ribosomal copy number was significantly correlated with relative enrichment on minerals. Glomeromycota (a phylum associated with arbuscular mycorrhizal fungi) appeared to preferentially associate with ferrihydrite surfaces. In conclusion, the mechanisms enabling the colonization of soil minerals may be foundational in shaping the overall soil microbiome composition and development of persistent organic matter in soils.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗