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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

On the theory of current passage via an ideal insulator

An analytic solution to the problem of current passage via an ideal insulator in the case of monopolar hole injection has been found. The current-voltage (J-V) characteristics have been obtained for the first time in a broad range of parameters (insulator length, hole concentrations at boundaries, temperature, etc.) and applied voltages. It is shown that the Mott-Gurney quadratic J-V relation is valid only in a certain interval of currents between J{sub 1} and J{sub 2}. For J < J{sub 1}, the current linearly depends on voltage V to within V{sup 3} terms. A new mode has been found for J > J{sub 2}, where the J-V characteristic also becomes linear because the insulator is completely filled with injected holes. The integration constants are determined in the entire range of parameters and currents. Analytic expressions for the spatial electric-field and hole-concentration distributions are derived.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Metal–Insulator Transition in the Presence of Van Hove Singularities for Bipartite Lattices

We have considered the phase diagram of the ground state for the t–t' Hubbard model with half-filling of the band. The criterion for the metal–insulator transition has been formulated using the analytic expansion in transfer integral t' and in direct antiferromagnetic gap Δ. For a square lattice, there exists an interval of t' values for which the metal–insulator transition is of the first order due to the existence of the Van Hove singularity. For simple and body-centered cubic lattices, a transition occurring from the insulator antiferromagnetic state to the antiferromagnetic metal phase is a second-order transition followed by a transition to paramagnetic metal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Spin-polarized currents in the tunnel contact of a normal conductor and a two-dimensional topological insulator

The spin filtering of electrons tunneling from the edge states of a two-dimensional topological insulator into a normal conductor under a magnetic field (external or induced due to proximity to a magnetic insulator) is studied. Calculations are performed for a tunnel contact of finite length between the topological insulator and an electronic multimode quantum strip. It is shown that the flow of tunneling electrons is split in the strip, so that spin-polarized currents arise in its left and right branches. These currents can be effectively controlled by the contact voltage and the chemical potential of the system. The presence of a magnetic field, which splits the spin subbands of the electron spectrum in the strip, gives rise to switching of the spin current between the strip branches.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Features of high-frequency measurements of the impedance of metal-insulator-semiconductor structures with an ultrathin oxide

The possibilities of using the data of high-frequency measurements of the impedance of metal-oxide-semiconductor structures with an ultrathin insulating layer for determining the parameters of the semiconductor and the tunneling characteristics of the insulator are considered. If the accuracy of the experiment makes it possible to record both the active and reactive impedance components, the thickness of the surface depletion layer, the resistance of the semiconductor base portion, the differential tunnel conductivity of the insulating layer, and the differential tunneling-stimulated current of the generation of electron-hole pairs are calculated using the values of the capacitance and conduction of the structure measured at two frequencies. In the case, where the values of the active component of the impedance is beyond the accuracy of measurements, analysis of the parameters is possible upon four-frequency organization of the experiment from the values of only the capacitances with an increased accuracy of their measurements. A test for the necessary accuracy of data of such an experiment is formulated. If the test fails, it is possible to determine only the capacitance of the surface depletion layer in the semiconductor and, in this case, it is sufficient to implement only the single-frequency experiment.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Semi-insulating 4H-SiC layers formed by the implantation of high-energy (53 MeV) argon ions into n-type epitaxial films

It is shown that 9-μm-thick semi-insulating surface layers can be formed in moderately doped n-type silicon carbide (donor concentration 2 × 10{sup 16} cm{sup –3}) via the comparatively low-dose (7 × 10{sup 11} cm{sup –2}) implantation of high-energy (53 MeV) argon ions. The free-carrier removal rate is estimated at ~10{sup 4} cm{sup –1}. The resistivity of the semi-insulator is no less than 7 × 10{sup 12} Ω cm. Analysis of the monopolar current of electron injection into the semi-insulator shows that the impurity-conductivity compensation is due to radiation induced defects pinning the equilibrium Fermi level at a depth of 1.16 eV below the conduction-band bottom. The density of defect states at the Fermi level is 2.7 × 10{sup 16} cm{sup 2} eV{sup –1}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Metal–Insulator Phase Transition in Iron-Doped Vanadium Dioxide Thin Films

The electrical conductivity of polycrystalline V{sub (1 –} {sub x)}Fe{sub x}O{sub 2} films has been investigated in a wide temperature range, which covers both the metal and insulator phase regions. It is shown that with an increase in the iron concentration the metal–insulator phase transition shifts toward lower temperatures, while the temperature range of the transition in doped samples additionally broadens as compared with pure VO{sub 2}. To explain the temperature dependence of the electrical conductivity of the V{sub (1 –} {sub x)}Fe{sub x}O{sub 2} insulator phase, a hopping conductivity model has been used, which takes into account the effect of thermal vibrations of atoms on the resonance integral. The values of parameter ε have been calculated as a function of the degree of VO{sub 2} doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Metal–Insulator Phase Transition in Tungsten-Doped Vanadium Dioxide Thin Films

The electrical conductivity of thin polycrystalline V{sub (1 –} {sub x)}W{sub x}O{sub 2} has been studied in a wide temperature range, which covers the regions of both the metallic and insulator phases. An increase in the tungsten concentration is shown to shift the metal–insulator phase transition toward lower temperatures, while the temperature range of the coexistence of the phases monotonically increases as the impurity concentration increases. The temperature dependence of the conductivity of the insulator phase of V{sub (1 –} {sub x)}W{sub x}O{sub 2} is explained using the hopping conduction model that takes into account the influence of thermal vibrations of atoms on the resonance integral. Parameter ε in the dependence on the level of doping VO{sub 2} has been calculated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Metal–Insulator Phase Transition in Thin Films of a Nickel-Doped Vanadium Dioxide

The electrical conductivity of thin polycrystalline VNi{sub x}O{sub 2} films has been studied in a wide range of temperatures, which covers the regions of both metallic and insulator phase. It is shown that the metal–insulator phase transition temperature decreases as the nickel concentration increases, and the temperature range of coexistence of the phases increases monotonically. The temperature dependence of the conductivity of the insulating VNi{sub x}O{sub 2} phase is explained using the hopping conduction model that takes into account the influence of thermal atomic vibrations on the resonance integral. Parameter ε has been calculated as a function of the doping level of VO{sub 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Regulation of β-cell death by ADP-ribosylhydrolase ARH3 via lipid signaling in insulitis

Lipids are regulators of insulitis and β-cell death in type 1 diabetes development, but the underlying mechanisms are poorly understood. Here, we investigated how the islet lipid composition and downstream signaling regulate β-cell death. We performed lipidomics using three models of insulitis: human islets and EndoC-βH1 β cells treated with the pro-inflammatory cytokines interlukine-1β and interferon-γ, and islets from pre-diabetic non-obese mice. We also performed mass spectrometry and fluorescence imaging to determine the localization of lipids and enzyme in islets. RNAi, apoptotic assay, and qPCR were performed to determine the role of a specific factor in lipid-mediated cytokine signaling. Across all three models, lipidomic analyses showed a consistent increase of lysophosphatidylcholine species and phosphatidylcholines with polyunsaturated fatty acids and a reduction of triacylglycerol species. Imaging assays showed that phosphatidylcholines with polyunsaturated fatty acids and their hydrolyzing enzyme phospholipase PLA2G6 are enriched in islets. In downstream signaling, omega-3 fatty acids reduce cytokine-induced β-cell death by improving the expression of ADP-ribosylhydrolase ARH3. The mechanism involves omega-3 fatty acid-mediated reduction of the histone methylation polycomb complex PRC2 component Suz12, upregulating the expression of Arh3, which in turn decreases cell apoptosis. Our data provide insights into the change of lipidomics landscape in β cells during insulitis and identify a protective mechanism by omega-3 fatty acids.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Performance Evaluation of Gray-box and Machine Learning Models of a Thermal Energy Storage System with Active Insulation

An interior partition wall integrated with active thermal storage and a dynamic insulation system was built and then installed in an office building in Oak Ridge, Tennessee, TN. This smart wall, termed the Empower Wall, was equipped with embedded pipes in the building envelope core component and an additional pipe network enclosing rigid insulation to switch on and off the active insulation dynamically. The performance of the wall's contribution to cooling load reduction under different parameters has been investigated in previous publications. Aiming to be deployed into model predictive control and other optimization methods, simplified and reliable models for the developed wall and the room accommodating it are required. They are needed to characterize the properties and thermal response of both Empower Wall and building envelope, which form an essential component for accurate indoor temperature or cooling/heating demand prediction. In this study, simplified gray-box and regression models as well as machine learning model were developed and the performance of them were compared and analyzed.

Cui, Borui↗
DOE OSTI2013

Humidity effects on wire insulation breakdown strength.

Methods for the testing of the dielectric breakdown strength of insulation on metal wires under variable humidity conditions were developed. Two methods, an ASTM method and the twisted pair method, were compared to determine if the twisted pair method could be used for determination of breakdown strength under variable humidity conditions. It was concluded that, although there were small differences in outcomes between the two testing methods, the non-standard method (twisted pair) would be appropriate to use for further testing of the effects of humidity on breakdown performance. The dielectric breakdown strength of 34G copper wire insulated with double layer Poly-Thermaleze/Polyamide-imide insulation was measured using the twisted pair method under a variety of relative humidity (RH) conditions and exposure times. Humidity at 50% RH and below was not found to affect the dielectric breakdown strength. At 80% RH the dielectric breakdown strength was significantly diminished. No effect for exposure time up to 140 hours was observed at 50 or 80%RH.

Appelhans, Leah↗
DOE OSTI2013

High Reliability R-10 Windows Using Vacuum Insulating Glass Units

The objective of this effort was for EverSealed Windows (“EverSealed” or “ESW”) to design, assemble, thermally and environmentally test and demonstrate a Vacuum Insulating Glass Unit (“VIGU” or “VIG”) that would enable a whole window to meet or exceed the an R-10 insulating value (U-factor ≤ 0.1). To produce a VIGU that could withstand any North American environment, ESW believed it needed to design, produce and use a flexible edge seal system. This is because a rigid edge seal, used by all other know VIG producers and developers, limits the size and/or thermal environment of the VIG to where the unit is not practical for typical IG sizes and cannot withstand severe outdoor environments. The rigid-sealed VIG’s use would be limited to mild climates where it would not have a reasonable economic payback when compared to traditional double-pane or triple-pane IGs. ESW’s goals, in addition to achieving a sufficiently high R-value to enable a whole window to achieve R-10, included creating a VIG design that could be produced for a cost equal to or lower than a traditional triple-pane IG (low-e, argon filled). ESW achieved these goals. EverSealed produced, tested and demonstrated a flexible edge-seal VIG that had an R-13 insulating value and the edge-seal system durability to operate reliably for at least 40 years in the harshest climates of North America.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2016

Construction Guidelines for High R-Value Walls without Exterior Rigid Insulation

High R-value wall assemblies (R-40 and above) are gaining popularity in the market due to programs such as the U.S. Department of Energy Zero Energy Ready Home program, Passive House, Net Zero Energy Home challenges in several states, and highly incentivized retrofit programs. In response to this demand, several builders have successfully used double-wall systems to achieve higher R-values in thicker, framed walls. To builders of conventional stick-framed homes, often one of the most appealing features of double-wall systems is that there are very few new exterior details. Exterior sheathings, structural bracings, house wraps or building paper, window and door flashings, and siding attachments are usually identical to good details in conventional framed-wall systems. However, although the details in double-wall systems are very similar to those in conventional stick framing, there is sometimes less room for error. Several studies have confirmed colder temperatures of exterior sheathing in high R-value wall assemblies that do not have exterior rigid foam insulation. These colder temperatures can lead to increased chances for condensation from air exfiltration, and they have the potential to result in moisture-related problems (Straube and Smegal 2009, Arena 2014, Ueno 2015). The information presented in this guide is intended to reduce the risk of failure in these types of assemblies, increase durability, and reduce material brought to landfills due to failures and resulting decay. Although this document focuses on double-wall framing techniques, the majority of the information about how to properly construct and finish high R-value assemblies is applicable to all wall assemblies that do not have foam insulation installed on the exterior of the structural sheathing. The techniques presented have been shown through field studies to reduce the likelihood of mold growth and moisture-related damage and are intended for builders, framing contractors, architects, and consultants involved in designing and building super-insulated homes. The information is applicable to both new construction and gut-rehabilitation projects in Climate Zones 5 and higher.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

Optical Manipulation and Detection of Emergent Phenomena in Topological Insulators

The three-dimensional topological insulator (TI) is a new quantum phase of matter that exhibits quantum-Hall-like properties, even in the absence of an external magnetic field. These materials are insulators in the bulk but have a topologically protected conducting state at the surface. Charge carriers on these surface states behave like a two-dimensional gas of massless helical Dirac fermions for which the spin is ideally locked perpendicular to the momentum. The purpose of this project is to probe the unique collective electronic behaviors of topological insulators by developing and using advanced time resolved spectroscopic techniques with state-of-the-art temporal and spatial resolutions. The nature of these materials requires development of specialized ultrafast techniques (such as time resolved ARPES that also has spin detection capability, ultrafast electron diffraction that has sub-100 fs time resolution and THz magneto-spectroscopy). The focus of this report is to detail our achievements in terms of establishing state of the art experimental facilities. Below, we will describe achievements under this award for the entire duration of five years. We will focus on detailing the development of ultrafast technqiues here. The details of the science that was done with these technqiues can be found in the publications referencing this grant.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Monitoring of Unvented Roofs with Fibrous Insulation, Diffusion Vents, and Interior Vapor Control in a Cold Climate

Unvented roof assemblies have been accepted in North American building codes since 2007; code-compliant construction calls for a minimum thickness of “air-impermeable insulation” (based on climate zone) to avoid cold-weather condensation and moisture risks. This is typically implemented with polyurethane spray foam insulation; however, negatives of this material include high first cost and possible adverse environmental impacts. Implementing unvented roofs in a moisture-safe manner with air-permeable fibrous fill insulations (e.g., fiberglass or cellulose) could potentially reduce the first cost of unvented roof designs, allowing for more widespread use. Building unvented roofs in a cost-effective, airtight, and moisture-safe manner opens up options for high-performance house designers and builders.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Interlaminar Fracture Toughness Testing of Nb3Sn Insulation Systems

Epoxy cracking has been the main suspected contributor to training in Nb3Sn magnets for some time, as it leads to energy release and magnet quenching. Cracking in a superconducting composite can occur from several modes, and the likelihood of these modes is not well understood. Failure has been observed between insulation systems and the superconducting cable itself rather than within the cable or insulation. To target the behavior at the interface, samples have been fabricated and tested for mode I fracture toughness in an adapted version of ASTM D5528. This work seeks to better characterize the fracture toughness of this interface to better understand how to model and design insulation systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Inexpensive Superinsulation for Cryogenic and Highly Insulating Applications (CRADA Final Report)

This effort will use our novel insulation formed into effective “solid” (as compared to powder) insulating panels and/or wraps to demonstrate important technical achievements including scaling appropriate crosslinking to directly and cost effectively address vacuum insulated panel (VIP) applications and cryogenic component wrapping to help reduce energy use. This project will improve and scale-up processes (from 3” diameter disks) to make larger samples (e.g., 12” x 12” x 1”) Wow, cfor external evaluation and testing.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Ultra-clear Aerogels for Insulated Glass in Refrigeration Doors (CRADA Final Report)

Display refrigerators commonly employ glass doors to provide product visibility; however, these doors exhibit significantly poorer thermal insulation than solid doors, resulting in increased heat transfer and higher energy consumption. To address this limitation, this project investigated the use of silica aerogel as a transparent insulating medium for refrigerator glass doors, with the objective of enhancing thermal performance without compromising visual clarity. In Phase I of the project, we assessed the feasibility of silica aerogel insulation through laboratory and full-scale studies, including material characterization, durability testing, and heat transfer measurements, along with the development and performance evaluation of prototype glass doors under realistic operating conditions. In Phase II, the project focused on scaling the technology toward practical deployment. This included scaling up the manufacturing process to achieve a surface area roughly 20 times larger for commercial applications, developing full-scale prototypes that integrated silica aerogel into standard display refrigerator doors, and conducting field evaluations to assess thermal performance, energy savings, and operational durability under real-world conditions.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗