Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Charge divider”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Decentralized Control Synthesis for Air Traffic Management in Urban Air Mobility

Urban air mobility (UAM) refers to air transportation services within an urban area, often in an on-demand fashion. We study air traffic management (ATM) for vehicles in a UAM fleet, while guaranteeing system safety requirements such as traffic separation. Existing ATM methods for unmanned aerial systems, such as UAS traffic management, utilize alternative approaches which do not provide strict safety guarantees. No established infrastructure exists for providing ATM at scale for UAM. We provide a decentralized, hierarchical approach for UAM ATM that allows for scalability to high traffic densities as well as providing theoretical guarantees of correctness with respect to user-provided safety specifications. Our main contributions are two-fold. First, we propose a novel UAM ATM architecture that divides the control authority between vertihubs that are each in charge of all UAM vehicles in their local airspace. Each vertihub also contains a number of vertiports that are in charge of UAM vehicle takeoffs and landings. The resulting architecture is decentralized and hierarchical, which not only enables scalability, but also robustness in the event of any individual vertihub or vertiport no longer being operational. Second, we provide a contract-based correct-by-construction reactive synthesis approach that provably guarantees safety properties with respect to user-provided specifications in linear temporal logic. We demonstrate the approach on large-volume UAM air traffic data.

Urban Air Mobility↗
NASA NTRS1994

An acoustic charge transport imager for high definition television applications

The primary goal of this research is to develop a solid-state television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels/frame. This imager will offer an order of magnitude improvements in speed over CCD designs and will allow for monolithic imagers operating from the IR to UV. The technical approach of the project focuses on the development of the three basic components of the imager and their subsequent integration. The camera chip can be divided into three distinct functions: (1) image capture via an array of avalanche photodiodes (APD's); (2) charge collection, storage, and overflow control via a charge transfer transistor device (CTD); and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the optimization of each of these component devices. In addition to the development of each of the three distinct components, work towards their integration and manufacturability is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail.

Hunt, W. D.↗
NASA NTRS1994

An acoustic charge transport imager for high definition television applications

The primary goal of this research is to develop a solid-state high definition television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels per frame. This imager offers an order of magnitude improvement in speed over CCD designs and will allow for monolithic imagers operating from the IR to the UV. The technical approach of the project focuses on the development of the three basic components of the imager and their integration. The imager chip can be divided into three distinct components: (1) image capture via an array of avalanche photodiodes (APD's), (2) charge collection, storage and overflow control via a charge transfer transistor device (CTD), and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the development of manufacturable designs for each of these component devices. In addition to the development of each of the three distinct components, work towards their integration is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail in Sections 2-4.

Hunt, W. D.↗
NASA NTRS1980

Simulation of spacecraft charging environments by monoenergetic beams

To simulate the distributed spectra of plasmas in space, the differential current density spectrum of the plasma was divided into a number of energy bands and the beam energy and current were calculated for each band to provide a piecewise reproduction of the distributed spectrum. Beam energies and current densities were chosen to match the velocity moments of the plasma distribution function. The velocity moments are averages related to physical quantities such as particle density, flux, pressure, and energy flux, and have been used extensively to characterize the measured properties of plasmas in space. Combinations of one, two, and three beams were found to match two to six velocity moments of Maxwellian distributions. A computational model was used to compare the charging of a spacecraft by plasmas with distributed spectra and by monoenergetic beams.

Halverson, W.↗
NASA NTRS2004

Monitoring the Hazards of Silicic Volcanoes with Remote Sensing

This report details the final progress on the Solid Earth and Natural Hazards project: Monitoring of Hazards of Silicic Volcanoes with Remote Sensing (SENH99-0000-0159). The original award went to Arizona State University (ASU) with Dr. Jonathan Fink as the P.I. and Dr. Michael Ramsey as the Co-I. In May 2000, Dr. Ramsey left ASU to take a tenure-track faculty position at the University of Pittsburgh. The principle investigators and NASA Headquarters agreed to split the grant award at the HQ level and therefore avoid the double overhead charges that would arise from a university subcontract. The objectives of the science were divided, and coordinated yearly progress reports have been submitted from each University. This report details the final progress on work carried out at Arizona State. A report by Dr. Ramsey at the University of Pittsburgh has already been submitted. The work from both institutions is closely related and this report will reflect that connection.

Fink, Jonathan↗
NASA NTRS1996

Application of Hybrid Optimization-Expert System for Optimal Power Management on Board Space Power Station

The space power system has two sources of energy: photo-voltaic blankets and batteries. The optimal power management problem on-board has two broad operations: off-line power scheduling to determine the load allocation schedule of the next several hours based on the forecast of load and solar power availability. The nature of this study puts less emphasis on speed requirement for computation and more importance on the optimality of the solution. The second category problem, on-line power rescheduling, is needed in the event of occurrence of a contingency to optimally reschedule the loads to minimize the 'unused' or 'wasted' energy while keeping the priority on certain type of load and minimum disturbance of the original optimal schedule determined in the first-stage off-line study. The computational performance of the on-line 'rescheduler' is an important criterion and plays a critical role in the selection of the appropriate tool. The Howard University Center for Energy Systems and Control has developed a hybrid optimization-expert systems based power management program. The pre-scheduler has been developed using a non-linear multi-objective optimization technique called the Outer Approximation method and implemented using the General Algebraic Modeling System (GAMS). The optimization model has the capability of dealing with multiple conflicting objectives viz. maximizing energy utilization, minimizing the variation of load over a day, etc. and incorporates several complex interaction between the loads in a space system. The rescheduling is performed using an expert system developed in PROLOG which utilizes a rule-base for reallocation of the loads in an emergency condition viz. shortage of power due to solar array failure, increase of base load, addition of new activity, repetition of old activity etc. Both the modules handle decision making on battery charging and discharging and allocation of loads over a time-horizon of a day divided into intervals of 10 minutes. The models have been extensively tested using a case study for the Space Station Freedom and the results for the case study will be presented. Several future enhancements of the pre-scheduler and the 'rescheduler' have been outlined which include graphic analyzer for the on-line module, incorporating probabilistic considerations, including spatial location of the loads and the connectivity using a direct current (DC) load flow model.

Momoh, James↗
NASA NTRS1999

Model Experiments and Model Descriptions

The Second Workshop on Stratospheric Models and Measurements Workshop (M&M II) is the continuation of the effort previously started in the first Workshop (M&M I, Prather and Remsberg [1993]) held in 1992. As originally stated, the aim of M&M is to provide a foundation for establishing the credibility of stratospheric models used in environmental assessments of the ozone response to chlorofluorocarbons, aircraft emissions, and other climate-chemistry interactions. To accomplish this, a set of measurements of the present day atmosphere was selected. The intent was that successful simulations of the set of measurements should become the prerequisite for the acceptance of these models as having a reliable prediction for future ozone behavior. This section is divided into two: model experiment and model descriptions. In the model experiment, participant were given the charge to design a number of experiments that would use observations to test whether models are using the correct mechanisms to simulate the distributions of ozone and other trace gases in the atmosphere. The purpose is closely tied to the needs to reduce the uncertainties in the model predicted responses of stratospheric ozone to perturbations. The specifications for the experiments were sent out to the modeling community in June 1997. Twenty eight modeling groups responded to the requests for input. The first part of this section discusses the different modeling group, along with the experiments performed. Part two of this section, gives brief descriptions of each model as provided by the individual modeling groups.

Jackman, Charles H.↗
NASA NTRS1995

Cross sections for the production of energetic cations by electron impact on N2 and CO2

Dissociative ionization cross sections for the production of singly charged energetic ions by electron impact on N2 and CO2 have been measured. The ions were divided into two groups: one with energies less than 1 eV and the other with energies greater than 1 eV. The ions detected were N+ from N2 and C+, O+, and CO+ from CO2. The electron impact energy range, and cross section data on ions is given.

energetic cations↗
NASA NTRS2012

Simple Cell Balance Circuit

A method has been developed for continuous cell voltage balancing for rechargeable batteries (e.g. lithium ion batteries). A resistor divider chain is provided that generates a set of voltages representing the ideal cell voltage (the voltage of each cell should be as if the cells were perfectly balanced). An operational amplifier circuit with an added current buffer stage generates the ideal voltage with a very high degree of accuracy, using the concept of negative feedback. The ideal voltages are each connected to the corresponding cell through a current- limiting resistance. Over time, having the cell connected to the ideal voltage provides a balancing current that moves the cell voltage very close to that ideal level. In effect, it adjusts the current of each cell during charging, discharging, and standby periods to force the cell voltages to be equal to the ideal voltages generated by the resistor divider. The device also includes solid-state switches that disconnect the circuit from the battery so that it will not discharge the battery during storage. This solution requires relatively few parts and is, therefore, of lower cost and of increased reliability due to the fewer failure modes. Additionally, this design uses very little power. A preliminary model predicts a power usage of 0.18 W for an 8-cell battery. This approach is applicable to a wide range of battery capacities and voltages.

Johnson, Steven D.↗
NASA NTRS2011

CMOS Imager Has Better Cross-Talk and Full-Well Performance

A complementary metal oxide/semiconductor (CMOS) image detector now undergoing development is designed to exhibit less cross-talk and greater full-well capacity than do prior CMOS image detectors of the same type. Imagers of the type in question are designed to operate from low-voltage power supplies and are fabricated by processes that yield device features having dimensions in the deep submicron range. Because of the use of low supply potentials, maximum internal electric fields and depletion widths are correspondingly limited. In turn, these limitations are responsible for increases in cross-talk and decreases in charge-handling capacities. Moreover, for small pixels, lateral depletion cannot be extended. These adverse effects are even more accentuated in a back-illuminated CMOS imager, in which photogenerated charge carriers must travel across the entire thickness of the device. The figure shows a partial cross section of the structure in the device layer of the present developmental CMOS imager. (In a practical imager, the device layer would sit atop either a heavily doped silicon substrate or a thin silicon oxide layer on a silicon substrate, not shown here.) The imager chip is divided into two areas: area C, which contains readout circuits and other electronic circuits; and area I, which contains the imaging (photodetector and photogenerated-charge-collecting) pixel structures. Areas C and I are electrically isolated from each other by means of a trench filled with silicon oxide. The electrical isolation between areas C and I makes it possible to apply different supply potentials to these areas, thereby enabling optimization of the supply potential and associated design features for each area. More specifically, metal oxide semiconductor field-effect transistors (MOSFETs) that are typically included in CMOS imagers now reside in area C and can remain unchanged from established designs and operated at supply potentials prescribed for those designs, while the dopings and the lower supply potentials in area I can be tailored to optimize imager performance. In area I, the device layer includes an n+ -doped silicon layer on which is grown an n-doped silicon layer. A p-doped silicon layer is grown on top of the n -doped layer. The total imaging device thickness is the sum of the thickness of the n+, n, and p layers. A pixel photodiode is formed between a surface n+ implant, a p implant underneath it, the aforementioned p layer, and the n and n+ layers. Adjacent to the diode is a gate for transferring photogenerated charges out of the photodiode and into a floating diffusion formed by an implanted p+ layer on an implanted n-doped region. Metal contact pads are added to the back-side for providing back-side bias.

Pain, Bedabrata↗
NASA NTRS2011

The Super-TIGER Instrument to Probe Galactic Cosmic Ray Origins

Super-TIGER (Super Trans-Iron Galactic Element Recorder) is under construction for the first of two planned Antarctic long-duration balloon flights in December 2012. This new instrument will measure the abundances of ultra-heavy elements (30Zn and heavier), with individual element resolution, to provide sensitive tests of the emerging model of cosmic-ray origins in OB associations and models of the mechanism for selection of nuclei for acceleration. Super-TIGER builds on the techniques of TIGER, which produced the first well-resolved measurements of elemental abundances of the elements 31Ga, 32Ge, and 34Se. Plastic scintillators together with acrylic and silica-aerogel Cherenkov detectors measure particle charge. Scintillating-fiber hodoscopes track particle trajectories. Super-TIGER has an active area of 5.4 sq m, divided into two independent modules. With reduced material thickness to decrease interactions, its effective geometry factor is approx.6.4 times larger than TIGER, allowing it to measure elements up to 42Mo with high statistical precision, and make exploratory measurements up to 56Ba. Super-TIGER will also accurately determine the energy spectra of the more abundant elements from l0Ne to 28Ni between 0.8 and 10 GeV/nucleon to test the hypothesis that microquasars or other sources could superpose spectral features. We will discuss the implications of Super-TIGER measurements for the study of cosmic-ray origins and will present the measurement technique, design, status, and expected performance, including numbers of events and resolution. Details of the hodoscopes, scintillators, and Cherenkov detectors will be given in other presentations at this conference.

Mitchell, John W.↗
NASA NTRS1979

NASCAP modelling of high-voltage power system interactions with space charged-particle environments

A simple space power system operating in geosynchronous orbit was analyzed. This system consisted of two solar array wings and a central body. Each solar array wing was considered to be divided into three regions operating at 2000 volts. The center body was considered to be an electrical ground with the array voltages both positive and negative relative to ground. The system was analyzed for both a normal environment and a moderate geomagnetic substorm environment. Initial results indicate a high probability of arcing at the interconnects on the negative operating voltage wing. The dielectric strength of the substrate may be exceeded giving rise to breakdown in the bulk of the material. The geomagnetic substorm did not seem to increase the electrical gradients at the interconnects on the negative operating voltage wing but did increase the gradients on the positive operating voltage wing which could result in increased coupling current losses.

Stevens, N. J.↗
NASA NTRS1973

Calculation of energy deposition distributions for simple geometries

When high-energy charged particles pass through a thin detector, the ionization energy loss in that detector is subject to fluctuations or straggling which must be considered in interpreting the data. Under many conditions, which depend upon the charge and energy of the incident particle and the detector geometry, the ionization energy lost by the particle is significantly different from the energy deposited in the detector. This problem divides naturally into a calculation of the energy loss that results in excitation and low-energy secondary electrons which do not travel far from their production points, and a calculation of energy loss that results in high-energy secondary electrons which can escape from the detector. The first calculation is performed using a modification of the Vavilov energy loss distribution. A cutoff energy is introduced above which all electrons are ignored and energy transferred to low energy particles is assumed to be equivalent to the energy deposited by them. For the second calculation, the trajectory of the primary particle is considered as a source of secondary high-energy electrons. The electrons from this source are transported using Monte Carlo techniques and multiple scattering theory, and the energy deposited by them in the detector is calculated. The results of the two calculations are then combined to predict the energy deposition distribution. The results of these calculations are used to predict the charge resolution of parallel-plate pulse ionization chambers that are being designed to measure the charge spectrum of heavy nuclei in the galactic cosmic-ray flux.

Watts, J. W., Jr.↗
NASA NTRS1993

Milling dynamics. I - Attritor dynamics: Results of a cinematographic study

The motions of grinding media and powder in an attritor canister were studied by means of filming the agitated charge and frame-by-frame scrutiny of the footage. In conjunction with auxiliary experiments, this permitted semiquantitative analysis of the milling action. In particular, the mill can be divided into several regions characterized by different balances between direct impacts and rolling/sliding of the grinding media. Simple calculations suggest that impacts are more capable of effecting mechanical alloying (MA) than are rolling or sliding events in an attritor. Powder circulation within an operating mill was also investigated. Based on the results and the accompanying analysis, concepts for improved attritor design are presented.

Rydin, R. W.↗
NASA NTRS1975

Energy spectra and charge states of H, He, and heavy ions observed in the earth's magnetosheath and magnetotail

Observations of pulses of H, He, and heavy ions of energies greater than 0.12 MeV per charge in the magnetotail and in the magnetosheath are reported. It was found that the relative ion abundances were about 9:1:0.04, their differential energy spectra were about 1 divided by the fourth power of E, and their atomic electrons were almost completely stripped. These results suggest that they were low-energy 'quiet-time' cosmic rays accelerated within the magnetotail and the magnetosheath to the observed energies.

Fan, C. Y.↗
NASA NTRS1994

Planar varactor frequency multiplier devices with blocking barrier

The invention relates to planar varactor frequency multiplier devices with a heterojunction blocking barrier for near millimeter wave radiation of moderate power from a fundamental input wave. The space charge limitation of the submillimeter frequency multiplier devices of the BIN(sup +) type is overcome by a diode structure comprising an n(sup +) doped layer of semiconductor material functioning as a low resistance back contact, a layer of semiconductor material with n-type doping functioning as a drift region grown on the back contact layer, a delta doping sheet forming a positive charge at the interface of the drift region layer with a barrier layer, and a surface metal contact. The layers thus formed on an n(sup +) doped layer may be divided into two isolated back-to-back BNN(sup +) diodes by separately depositing two surface metal contacts. By repeating the sequence of the drift region layer and the barrier layer with the delta doping sheet at the interfaces between the drift and barrier layers, a plurality of stacked diodes is formed. The novelty of the invention resides in providing n-type semiconductor material for the drift region in a GaAs/AlGaAs structure, and in stacking a plurality of such BNN(sup +) diodes stacked for greater output power with and connected back-to-back with the n(sup +) GaAs layer as an internal back contact and separate metal contact over an AlGaAs barrier layer on top of each stack.

Lieneweg, Udo↗
NASA NTRS1973

Evaluation of ERTS-1 imagery for mapping Quaternary deposits and landforms in the Great Plains and Midwest

The author has identified the following significant results. Maps at 1:1 million scale exemplifying the first phase of the investigation (which consists of the identification and mapping of landform and land use characteristics and surficial geologic materials directly from the ERTS-1 images without use of additional data) were prepared. For areas that have not been mapped at 1:500,000 or larger scales, maps will provide the first moderately detailed information on landform features and surficial materials. Much of the information mapped is significant for exploration and development of ground (and, locally, petroleum) and for applications in engineering and environmental geology, including land use planning. Analysis of drainage patterns, stream-divide relations and land use patterns has revealed several possible moraine-controlled divices of middle and early Pleistocene age. One is an extension of the Cedar Bluffs moraine of southeastern Nebraska. Another of these divides may correspond to the terminus of Nebraska drift in the Kansas City study area. The trends of parts of various ancient filled valleys also have been identified by analysis of charges in width of the present stream valleys. The alinements of certain segments of stream valleys in Kansas and Missouri appear to be controlled by regional faults or other structural features.

Morrison, R. B.↗
NASA NTRS1987

Revised NASA axially symmetric ring model for coupled-cavity traveling-wave tubes

A versatile large-signal, two-dimensional computer program is used by NASA to model coupled-cavity travelling-wave tubes (TWTs). In this model, the electron beam is divided into a series of disks, each of which is further divided into axially symmetric rings which can expand and contract. The trajectories of the electron rings and the radiofrequency (RF) fields are determined from the calculated axial and radial space-charge, RF, and magnetic forces as the rings pass through a sequence of cavities. By varying electrical and geometric properties of individual cavities, the model is capable of simulating severs, velocity tapers, and voltage jumps. The calculated electron ring trajectories can be used in designing magnetic focusing and multidepressed collectors. The details of using the program are presented, and results are compared with experimental data.

Wilson, Jeffrey D.↗