Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “current sheet”

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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Split-cross-bridge resistor for testing for proper fabrication of integrated circuits

An electrical testing structure and method is described whereby a test structure is fabricated on a large scale integrated circuit wafer along with the circuit components and has a van der Pauw cross resistor in conjunction with a bridge resistor and a split bridge resistor, the latter having two channels each a line width wide, corresponding to the line width of the wafer circuit components, and with the two channels separated by a space equal to the line spacing of the wafer circuit components. The testing structure has associated voltage and current contact pads arranged in a two by four array for conveniently passing currents through the test structure and measuring voltages at appropriate points to calculate the sheet resistance, line width, line spacing, and line pitch of the circuit components on the wafer electrically.

Buehler, M. G.↗
NASA NTRS1992

Is there a near-Earth neutral line?

The high correlation between magnetic activity and the interplanetary magnetic field provides strong evidence that magnetic reconnection causes substorms. Rapid changes in magnetospheric configuration following a southward turning suggest that nightside reconnection is delayed relative to the dayside. The near Earth neutral line model postulates that it begins in the near Earth plasma sheet near midnight at expansion onset. Evidence supporting this model is reviewed. Observations of current disruption near synchronous orbit were recently interpreted as proof that reconnection is not necessary in the expansion phase, and that nightside reconnection is a recovery phase phenomenon. Problems with magnetic field mapping make this conclusion premature. Furthermore, the spatial distribution of delays in plasmoid signatures are incompatible with such a late start. Speculation is made concerning a mechanism whereby current disruption might be caused by an x-line that forms further from the Earth in the late growth phase.

Mcpherron, Robert L.↗
NASA NTRS2003

Leasing as a Source of Finance by the Major US Airlines: Hidden Debt and its Changes Over Time

This paper updates prior research on aircraft leasing and contrasts the findings of current data with prior results. Usage of leases by air carriers is a means to lessen the impact of financial obligations from fleet purchases. The study revisits two previous studies, one in 1969 and one in 1991, which is analyzed the incidence of leases by major air carriers. The current study updates these past studies to consider air carriers current usage of leases. Additionally, since operating leases are not reflected in the balance sheets of airlines, operating lease information was capitalized using a present value of future operating lease payments. Then, financial debt burden ratios were computed to determine the impact from the capitalization of lease information. The usage of operating leases increased, significantly from the first study to the 1991 study, and this trend continues. The incidence of leasing, the classification of leases as operating, and the percentage of operating leases to total fleet have all increased for the majority of the airlines reviewed. When operating lease data were capitalized, debt ratios weakened, providing further evidence of deterioration in the financial health of air carriers.

Gritta, Richard D.↗
NASA NTRS2005

Three Dimensional Rover/Lander/Orbiter Mission-Planning (3D-ROMPS) System: A Modern Approach to Mission Planning

NASA's current mission planning system is based on point design, two-dimensional display, spread sheets, and report technology. This technology does not enable engineers to analyze the results of parametric studies of missions plans. This technology will not support the increased observational complexity and data volume of missions like Cassini, Mars Reconnaissance Orbiter (MRO), Mars Science Laboratory (MSL), and Mars Sample Return (MSR). The goal of the 3D-ROMPS task has been to establish a set of operational mission planning and analysis tools in the Image Processing Laboratory (IPL) Mission Support Area (MSA) that will respond to engineering requirements for planning future Solar System Exploration (SSE) missions using a three-dimensional display.

Scharfe, Nathan D.↗
DOE OSTI2024

Medical Imaging Equipment Energy Efficiency

The energy use of medical imaging equipment (MIE) in healthcare facilities is estimated to be about 5% of total site energy use. MIE energy use is only expected to increase as technology advances and more patients seek services from MIE, enabling more facilities to install additional MIE. Healthcare organizations need reliable information regarding comprehensive energy use or lifetime energy costs with which to make energy-efficient MIE procurement decisions, and there are currently no MIE energy or efficiency standards in the United States (U.S.). This fact sheet provides background on MIE energy consumption, key terms, and guidance on why and how to meter MIE, helping stakeholders make informed decisions to enhance their facility's performance.

ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION↗
NASA NTRS2015

Characterization of Hybrid CNT Polymer Matrix Composites

Carbon nanotubes (CNTs) have been studied extensively since their discovery and demonstrated at the nanoscale superior mechanical, electrical and thermal properties in comparison to micro and macro scale properties of conventional engineering materials. This combination of properties suggests their potential to enhance multi-functionality of composites in regions of primary structures on aerospace vehicles where lightweight materials with improved thermal and electrical conductivity are desirable. In this study, hybrid multifunctional polymer matrix composites were fabricated by interleaving layers of CNT sheets into Hexcel® IM7/8552 prepreg, a well-characterized toughened epoxy carbon fiber reinforced polymer (CFRP) composite. The resin content of these interleaved CNT sheets, as well as ply stacking location were varied to determine the effects on the electrical, thermal, and mechanical performance of the composites. The direct-current electrical conductivity of the hybrid CNT composites was characterized by in-line and Montgomery four-probe methods. For [0](sub 20) laminates containing a single layer of CNT sheet between each ply of IM7/8552, in-plane electrical conductivity of the hybrid laminate increased significantly, while in-plane thermal conductivity increased only slightly in comparison to the control IM7/8552 laminates. Photo-microscopy and short beam shear (SBS) strength tests were used to characterize the consolidation quality of the fabricated laminates. Hybrid panels fabricated without any pretreatment of the CNT sheets resulted in a SBS strength reduction of 70 percent. Aligning the tubes and pre-infusing the CNT sheets with resin significantly improved the SBS strength of the hybrid composite To determine the cause of this performance reduction, Mode I and Mode II fracture toughness of the CNT sheet to CFRP interface was characterized by double cantilever beam (DCB) and end notch flexure (ENF) testing, respectively. Results are compared to the control IM7/8552 laminate.

Grimsley, Brian W.↗
NASA NTRS1978

Bismaleimide resins for flame resistant honeycomb sandwich panels

Bismaleimide resins are prime candidates for nonflammable aircraft interior panels. Three resin types with different structures and processing characteristics were formulated. Resin M 751 was used to fabricate 100 kg of glass fabric prepregs which were used for the preparation of face sheets for honeycomb sandwich panels. Prepreg characteristics and curing cycles for laminate fabrication are provided. In order to advance beyond the current solvent resin technology for fibre and fabric impregnation, a hot melt solvent-less resin system was prepared and characterized. Preliminary tests were performed to develop a wet bonding process for the fabrication of advanced sandwich honeycomb panels by use of polybismaleimide glass fabric face sheets and polybismaleimide Nomex honeycomb core. B-stage material was used for both the core and the face sheet, providing flatwise tensile properties equivalent to those obtained by the state-of-the-art 3-step process which includes an epoxy adhesive resin.

Stenzenberger, H. D.↗
NASA NTRS1982

Observations of large electric fields near the plasmasheet boundary by ISEE-1

Large electric field spikes of up to about 80 mV/m, at distances of seven to 23 earth radii, were detected within one minute of encountering the high-altitude plasma sheet boundary, as identified by energetic particle detectors. If these high-altitude events, whose strong electric fields occur in enhanced low-frequency turbulence and field-aligned current flow regions and are individually well-correlated with small-scale gradients in particle fluxes and small-scale currents, are mappings of the low-altitude electrostatic shocks, these data may be taken as evidence that poleward auroral field lines map to the boundary of the plasma sheet.

Cattell, C. A.↗
NASA NTRS1995

Directly Deposited Current Collecting Grids for Alkali Metal Thermal-to-Electric Converter Electrodes

Current collection in porous thin film electrodes on solid electrolytes has been improved by using thick film grids to decrease sheet and contact resistance in RhW and PtW electrodes. The grids are directly deposited on the solid electrolyte either by sputter- or photodeposition, and the electrode deposited over the grid. Comparison of the performance of electrodes having such underlying grids with that of electrodes without such grids has shown performance, as measured by current or power produced, to be improved by 10-30% in electrodes with grids.

Ryan, M. A.↗
NASA NTRS1995

Directly Deposited Current Collecting Grids for AMTEC Electrodes

Current collection in porous thin film electrodes on solid electrolytes has been improved by using thick film grids to decrease sheet and contact resistance in RhW and PtW electrodes. The grids are directly deposited on the solid electrolyte, either by sputter or photodepostion, and the electrode is deposited over the grid. Comparison of the performance of electrodes having such underlying grids with that of electodes without such grids has shown performance, as measured by current or power produced, to be improved by 10-30% in electrodes with grids.

Ryan, M. A.↗
NASA NTRS2011

Modeling the Superstorm in November 2003

The superstorm on 20.21 November 2003 was the largest geomagnetic storm in solar cycle 23 as measured by Dst, which attained a minimum value of .422 nT. We have simulated this storm to understand how particles originating from the solar wind and ionosphere get access to the magnetosphere and how the subsequent transport and energization processes contribute to the buildup of the ring current. The global electromagnetic configuration and the solar wind H+ distribution are specified by the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamics model. The outflow of H+ and O+ ions from the ionosphere are also considered. Their trajectories in the magnetosphere are followed by a test-particle code. The particle distributions at the inner plasma sheet established by the LFM model and test-particle calculations are then used as boundary conditions for a ring current model. Our simulations reproduce the rapid decrease of Dst during the storm main phase and the fast initial phase of recovery. Shielding in the inner magnetosphere is established at early main phase. This shielding field lasts several hours and then breaks down at late main phase. At the peak of the storm, strong penetration of ions earthward to L shell of 1.5 is revealed in the simulation. It is surprising that O+ is significant but not the dominant species in the ring current in our calculation for this major storm. It is very likely that substorm effects are not well represented in the models and O+ energization is underestimated. Ring current simulation with O+ energy density at the boundary set comparable to Geotail observations produces excellent agreement with the observed symH. As expected in superstorms, ring current O+ is the dominant species over H+ during the main to mid-recovery phase of the storm.

Fok, Mei-Ching↗
NASA NTRS1984

Origin of the Greenland Ice Sheet

A climate model resolving the seasonal cycle and the two horizontal dimensions was developed and applied to several problems of current interest. Models of this type are useful when for various reasons a general circulation model experiment is not warranted or not feasible. For example, in cases where the signal to natural variability is small it may be advantageous to first consider such a statistical dynamical model because extremely long runs may be necessary in the application. In this case the simpler statistical dynamical model serves as a pilot study device. The model developed is a thermodynamic model whose solution yields the equilibrium seasonal cycle for the surface temperature field over the globe. The model is essentially a statement of the conservation of heat energy for individual columns of the earth atmosphere system. Various terms such as the infrared radiation flux to space are parameterized with earth radiation budget data from satellites such as Nimbus 6. The primary agent modulating the seasonal cycle amplitude is the heat capacity per unit area which is a strong function of surface type -- ocean surface can store 60 times more heat per unit time than land. By adjusting its few empirical parameters the model can be brought into remarkable agreement with the observed seasonal cycle. The model is then very useful for looking at the dependence of the seasonal cycle of the temperature on such externally defined variables as the Earth's orbital elements (eccentricity, tilt, precession of equinoxes) or the configuration of land-sea geography which can be changed by continental drift.

North, G. R.↗
NASA NTRS1999

Monolithic Cu-Cr-Nb Alloys for High Temperature, High Heat Flux Applications

Work during the prior four years of this grant has resulted in significant advances in the development of Cu-8 Cr4 Nb and related Cu-Cr-Nb alloys. The alloys are nearing commercial use in the Reusable Launch Vehicle (RLV) where they are candidate materials for the thrust cell liners of the aerospike engines being developed by Rocketdyne. During the fifth and final year of the grant, it is proposed to complete development of the design level database of mechanical and thermophysical properties and transfer it to NASA Glenn Research Center and Rocketdyne. The database development work will be divided into three main areas: Thermophysical Database Augmentation, Mechanical Testing and Metallography and Fractography. In addition to the database development, work will continue that is focussed on the production of alternatives to the powder metallurgy alloys currently used. Exploration of alternative alloys will be aimed at both the development of lower cost materials and higher performance materials. A key element of this effort will be the use of Thermo-Calc software to survey the solubility behavior of a wide range of alloying elements in a copper matrix. The ultimate goals would be to define suitable alloy compositions and processing routes to produce thin sheets of the material at either a lower cost, or, with improved mechanical and thermal properties compared to the current Cu-Cr-Nb powder metallurgy alloys.

Ellis, David L.↗
DOE OSTI2021

Assessing Global Ocean Circulation Sensitivity to Changes in Antarctic Ice Discharge

The principal goal of this research is to assess how projected increases in meltwater discharge and iceberg calving from the Antarctic Ice Sheet will impact climate in the next 250 years. In short, the sensitivity of the global ocean circulation and climate, and in particular the Atlantic Meridional Overturning Circulation (AMOC), to large increases in iceberg calving and meltwater discharges to the Southern Ocean are poorly understood. The requirement to investigate this topic is heightened by growing evidence that the West Antarctic Ice Sheet (WAIS) is vulnerable to rapid retreat and collapse through marine-ice-sheet-instability (MISI) on multidecadal-to-centennial timescales. Future model simulations of the AIS show the potential for rapid ice sheet retreat in the next 50 – 300 years, with such a collapse associated with the discharge of enormous volumes of ice and meltwater to the Southern Ocean. This project uses a combination of an ice sheet/shelf model and a fully coupled (ocean-atmosphere-seaice) model (CESM 1.2) to explore the sensitive of global climate to future changes in runoff from the Antarctic continent under future greenhouse gas emissions scenarios IPCC RCP4.5 and 8.5. Overall, accounting for Antarctic meltwater reduces the projected global mean anthropogenic greenhouse warming by up to 2 deg C. during peak WAIS collapse and by ~1 deg. for most of the simulation. In addition, the increased meltwater contribution raises sub-surface ocean temperatures at the Antarctic ice sheet margin by more than 1ºC, such that the ice shelf basal melt rates increase beyond those currently projected. In contrast, the model predicts a strong cooling of both the surface air and ocean temperatures over the Southern Ocean that results in a massive expansion and thickening of the perennial sea-ice. The slow-down in anthropogenic warming also results in the onset of ice-free conditions in the Arctic being delayed in the model by several decades, and the projected slowdown in the AMOC to reduce.

58 GEOSCIENCES↗
DOE OSTI2024

DEPRECATED - State Policies and Programs for Community Solar (2024 Q3 Update)

This data set is no longer current – The most current data and all historical data sets can be found at https://data.nlr.gov/submissions/249 The purpose of this dataset is to summarize current community solar policies and low-income stipulations by state in the United States as of June 2024. The "State_Program" sheet summarizes the key policy details for each state. This list has been reviewed, but errors may exist, and the list may not be comprehensive. NREL invites input to update or add to the database. To submit updates, additions, or corrections please find contact information on the current data set page linked above.

14 SOLAR ENERGY↗
NASA NTRS1971

Ignition of Fuel Vapors Beneath Titanium Aircraft Skins Exposed to Lightning

Hot-spot and puncture ignition of fuel vapors by simulated lightning discharges was studied experimentally. The influences of skin coating, skin structure, discharge polarity, skin thickness, discharge current level, and current duration were measured and interpreted. Ignition thresholds are reported for titanium alloy constructed as sheets, sheets coated with sealants, and sandwich skins. Results indicated that the ignition threshold charge transfer for coated sheets, honeycomb, and truss skins is respectively about 200%, 400%, 800% that of bare alloy sheet of .102 cm (.040 in.)-thickness. It was found that hot-spot ignition can occur well after termination of the arc, and that sandwich materials allow ignition only if punctured.

Kosvic, T. C.↗
NASA NTRS1976

Cyclotron side-band emissions from ring-current electrons

The paper examines temporal variations in electron energy spectra and pitch-angle distributions during a VLF-emission event observed by Explorer 45 in the main phase of a magnetic storm. It is noted that the observed event occurred outside the plasmasphere on the night side of the magnetosphere and that the dusk-side plasmapause had a double structure during the event. It is found that the VLF emissions consisted of two frequency bands, corresponding to the whistler and electrostatic modes, and that there was a sharp band of 'missing emissions' along frequencies equal to half the equatorial electron gyrofrequency. A peculiar pitch-angle distribution for high-energy electrons (50 to 350 keV) is noted. It is concluded that the VLF-producing particles were enhanced low-energy (about 5 keV) ring-current electrons which penetrated into the night side of the magnetosphere from the magnetotail plasma sheet and which drifted eastward after encountering the steep gradient of the geomagnetic field.

Maeda, K.↗
NASA NTRS1998

Fracture Analysis of the FAA/NASA Wide Stiffened Panels

This paper presents the fracture analyses conducted on the FAA/NASA stiffened and unstiffened panels using the STAGS (STructural Analysis of General Shells) code with the critical crack-tip-opening angle (CTOA) fracture criterion. The STAGS code with the "plane-strain" core option was used in all analyses. Previous analyses of wide, flat panels have shown that the high-constraint conditions around a crack front, like plane strain, has to be modeled in order for the critical CTOA fracture criterion to predict wide panel failures from small laboratory tests. In the present study, the critical CTOA value was determined from a wide (unstiffened) panel with anti-buckling guides. The plane-strain core size was estimated from previous fracture analyses and was equal to about the sheet thickness. Rivet flexibility and stiffener failure was based on methods and criteria, like that currently used in industry. STAGS and the CTOA criterion were used to predict load-against-crack extension for the wide panels with a single crack and multiple-site damage cracking at many adjacent rivet holes. Analyses were able to predict stable crack growth and residual strength with a few percent (5%) of stiffened panel tests results but over predicted the buckling failure load on a unstiffened panel with a single crack by 10%.

Seshadri, B. R.↗