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At least 199 records · Page 11

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NASA NTRS1986

Enhancements to Sperry/NASTRAN

Reviewed is the enhancement to NASTRAN program performed by NUK (Nippon Univac Kaisha, Ltd.) added to Level 15.5. Features discussed include intermediate checkpoint-restart in triangular decomposition, I/O improvement, multibanked memory and new plate element. The first three improvements provide the capability to solve significantly large size problems, while the new elements release the analyst from the cumbersome work to constrain the singularities caused by the lack of stiffness of inplane rotation of old plate elements.

Koga, T.↗

NASA NTRS1986

X-29 flight - Acid test for design predictions

The X-29 flight test data are being disseminated to interested industrial and military users as fast as it becomes available. The aircraft is extensively instrumented with accelerometers and pressure sensors and optical sensors for measuring wing deflection. The thoroughness of preflight preparations permitted a rapid advance through initial test checkpoints, which have both confirmed many predictions and revealed several discrepancies. The flight envelope had been expanded to Mach 1.1 and an altitude of 40,000 ft by December 1985. Notably, the X-29 has provided in-flight data which could not be faithfully depicted in a simulator, e.g., flare procedures during landing, and has shown that the stability adjustments, although adequate for controlling the aircraft, are not rapid enough to offer a satisfactory margin of harmony. The tests are now being performed in the transonic regime, where supercritical airfoil and forward swept wing drag reduction become significant factors.

Putnam, T. W.↗

NASA NTRS1986

Ground-based time-guidance algorithm for control of airplanes in a time-metered air traffic control environment: A piloted simulation study

The rapidly increasing costs of flight operations and the requirement for increased fuel conservation have made it necessary to develop more efficient ways to operate airplanes and to control air traffic for arrivals and departures to the terminal area. One concept of controlling arrival traffic through time metering has been jointly studied and evaluated by NASA and ONERA/CERT in piloted simulation tests. From time errors attained at checkpoints, airspeed and heading commands issued by air traffic control were computed by a time-guidance algorithm for the pilot to follow that would cause the airplane to cross a metering fix at a preassigned time. These tests resulted in the simulated airplane crossing a metering fix with a mean time error of 1.0 sec and a standard deviation of 16.7 sec when the time-metering algorithm was used. With mismodeled winds representing the unknown in wind-aloft forecasts and modeling form, the mean time error attained when crossing the metering fix was increased and the standard deviation remained approximately the same. The subject pilots reported that the airspeed and heading commands computed in the guidance concept were easy to follow and did not increase their work load above normal levels.

Knox, C. E.↗

NASA NTRS1986

The cometary nucleus: Current concepts

Ideas concerning the nature of cometary nuclei as modified by observations of recent years, particularly by those of Halley's comet during the 1986 apparition are reviewed. The major trend is to increase the postulated dimensions of the nuclei and reduce their albedos. The Vega and Giotto missions establish an invaluable checkpoint with regard to comet nuclei. These and other observations are affecting opinions concerning many facets of cometary nature, origin, evolution, and decay.

Whipple, Fred L.↗

NASA NTRS1989

The Raid distributed database system

Raid, a robust and adaptable distributed database system for transaction processing (TP), is described. Raid is a message-passing system, with server processes on each site to manage concurrent processing, consistent replicated copies during site failures, and atomic distributed commitment. A high-level layered communications package provides a clean location-independent interface between servers. The latest design of the package delivers messages via shared memory in a configuration with several servers linked into a single process. Raid provides the infrastructure to investigate various methods for supporting reliable distributed TP. Measurements on TP and server CPU time are presented, along with data from experiments on communications software, consistent replicated copy control during site failures, and concurrent distributed checkpointing. A software tool for evaluating the implementation of TP algorithms in an operating-system kernel is proposed.

Bhargava, Bharat↗

NASA NTRS1989

Investigation of the applicability of a functional programming model to fault-tolerant parallel processing for knowledge-based systems

In a fault-tolerant parallel computer, a functional programming model can facilitate distributed checkpointing, error recovery, load balancing, and graceful degradation. Such a model has been implemented on the Draper Fault-Tolerant Parallel Processor (FTPP). When used in conjunction with the FTPP's fault detection and masking capabilities, this implementation results in a graceful degradation of system performance after faults. Three graceful degradation algorithms have been implemented and are presented. A user interface has been implemented which requires minimal cognitive overhead by the application programmer, masking such complexities as the system's redundancy, distributed nature, variable complement of processing resources, load balancing, fault occurrence and recovery. This user interface is described and its use demonstrated. The applicability of the functional programming style to the Activation Framework, a paradigm for intelligent systems, is then briefly described.

Harper, Richard↗

NASA NTRS1991

Analyzing the I/O behavior of supercomputer applications

Supercomputer applications of I/Os are classified here into three categories - required, checkpoint, and data staging - and it is shown how memory size and CPU speed are likely to affect each category. A data analysis shows that data staging I/O dominates when it is present. If an application requires data staging I/O, its read/write ratio is greater than one; otherwise, its read/write ratio is less than one. This information can be used to anticipate a program's I/O demands and thus reduce the load on the I/O system.

Miller, Ethan L.↗

NASA NTRS1994

Application of statistical process control and process capability analysis procedures in orbiter processing activities at the Kennedy Space Center

Successful ground processing at KSC requires that flight hardware and ground support equipment conform to specifications at tens of thousands of checkpoints. Knowledge of conformance is an essential requirement for launch. That knowledge of conformance at every requisite point does not, however, enable identification of past problems with equipment, or potential problem areas. This paper describes how the introduction of Statistical Process Control and Process Capability Analysis identification procedures into existing shuttle processing procedures can enable identification of potential problem areas and candidates for improvements to increase processing performance measures. Results of a case study describing application of the analysis procedures to Thermal Protection System processing are used to illustrate the benefits of the approaches described in the paper.

Safford, Robert R.↗

NASA NTRS1993

Progressive retry for software error recovery in distributed systems

In this paper, we describe a method of execution retry for bypassing software errors based on checkpointing, rollback, message reordering and replaying. We demonstrate how rollback techniques, previously developed for transient hardware failure recovery, can also be used to recover from software faults by exploiting message reordering to bypass software errors. Our approach intentionally increases the degree of nondeterminism and the scope of rollback when a previous retry fails. Examples from our experience with telecommunications software systems illustrate the benefits of the scheme.

Wang, Yi-Min↗

NASA NTRS1990

Fault-tolerant, embedded CLIPS applications

The enhancements to CLIPS4.3 presented in this paper provide an embedded CLIPS application with the ability to continue operation with minimal to no loss of information in the event of a hardware or a software failure. Given an arbitrary failure, the CLIPS application's environment (fact-list, agenda, and pattern matching network) will be reconstructed to the point at which the failure was experienced. The environment reconstruction is based on state files to which the application periodically checks environment information (fact-list and agenda). The routine for checkpointing the state of the application is as efficient as possible so that the overhead introduced to normal execution of the application is minimal. The only assumptions made by the CLIPS application are that it is running under an operating system that guarantees it access to uncorrupt state files and that the application will be automatically restarted should it terminate abnormally.

Hicks, Jaye↗

NASA NTRS1995

Software dependability in the Tandem GUARDIAN system

Based on extensive field failure data for Tandem's GUARDIAN operating system this paper discusses evaluation of the dependability of operational software. Software faults considered are major defects that result in processor failures and invoke backup processes to take over. The paper categorizes the underlying causes of software failures and evaluates the effectiveness of the process pair technique in tolerating software faults. A model to describe the impact of software faults on the reliability of an overall system is proposed. The model is used to evaluate the significance of key factors that determine software dependability and to identify areas for improvement. An analysis of the data shows that about 77% of processor failures that are initially considered due to software are confirmed as software problems. The analysis shows that the use of process pairs to provide checkpointing and restart (originally intended for tolerating hardware faults) allows the system to tolerate about 75% of reported software faults that result in processor failures. The loose coupling between processors, which results in the backup execution (the processor state and the sequence of events) being different from the original execution, is a major reason for the measured software fault tolerance. Over two-thirds (72%) of measured software failures are recurrences of previously reported faults. Modeling, based on the data, shows that, in addition to reducing the number of software faults, software dependability can be enhanced by reducing the recurrence rate.

Lee, Inhwan↗

NASA NTRS1995

Lidar measurements at Lauder, NZ

In March of 1994, the GSFC Stratospheric Ozone Lidar was deployed to the Network for the Detection of Stratospheric Change (NDSC) site at Lauder, NZ. This was in conjunction with a series of NASA ER-2 flights from Christchurch, NZ south to the Antarctic Circle. These flights were organized to study the chemistry of the stratosphere before, during and after the formation of the well-known 'ozone hole'. Lidar measurements were made at four different time periods corresponding to the times of the ER-2 flights. Lauder is situated nearly along the flight path as the aircraft flew south and so the lidar measurements provide a checkpoint for the ozone, aerosol and temperature instruments onboard the aircraft. Whenever the weather permitted, lidar measurements were made as near to dawn, prior to the flight, and as near to sunset, after the flight. This provided data as close to the aircraft transit time as possible. More than 70 individual lidar measurements were made, each consisting of a vertical profile of ozone, temperature, and aerosol. These were made over three different seasons and show seasonal variation. Of particular interest in the lidar data base is the wintertime stratospheric - mesospheric temperature profiles, which show large variations at the stratopause and also some significant wave activity.

McGee, Thomas J.↗

NASA NTRS1994

Reducing Interprocessor Dependence in Recoverable Distributed Shared Memory

Checkpointing techniques in parallel systems use dependency tracking and/or message logging to ensure that a system rolls back to a consistent state. Traditional dependency tracking in distributed shared memory (DSM) systems is expensive because of high communication frequency. In this paper we show that, if designed correctly, a DSM system only needs to consider dependencies due to the transfer of blocks of data, resulting in reduced dependency tracking overhead and reduced potential for rollback propagation. We develop an ownership timestamp scheme to tolerate the loss of block state information and develop a passive server model of execution where interactions between processors are considered atomic. With our scheme, dependencies are significantly reduced compared to the traditional message-passing model.

Janssens, Bob↗

NASA NTRS2002

Functional Characterization of G12, a Gene Required for Mitotic Progression during Gastrulation in Zebrafish

In a differential RNA display screen we have isolated a zebrafish gene, G12, for which homologs can only be found in DNA databases for vertebrates, but not invertebrates. This suggests that this is a gene required specifically in vertebrates. G12 expression is upregulated at mid-blastula transition (MBT). Morpholino inactivation of this gene by injection into 1-cell embryos results in mitotic defects and apoptosis shortly after MBT. Nuclei in morpholino treated embryos also display segregation defects. We have characterized the localization of this gene as a GFP fusion in live and fixed embryos. Overexpression of G12-GFP is non-toxic. Animals retain GFP expression for at least 7 days with no developmental defects, Interestingly in these animals G12-GFP is never detectable in blood cells though blood is present. In the deep cells of early embryos, G 12GFP is localized to nuclei and cytoskeletal elements in interphase and to the centrosome and spindle apparatus during mitosis. In the EVL, G12-GFP shows additional localization to the cell periphery, especially in mitosis. In the yolk syncytium, G12-GFP again localizes to nuclei and strongly to cytoplasmic microtubules of migrating nuclei at the YSL margin. Morpholinc, injection specifically into the YSL after cellularization blocks epiboly and nuclei of the YSL show mitotic defects while deep cells show no mitotic defects and continue to divide. Rescue experiments in which morpholino and G12-GFP RNA are co-injected indicate partial rescue by the G12-GFP. The rescue is cell autonomous; that is, regions of the embryo with higher G12-GFP expression show fewer mitotic defects. Spot 14, the human bomolog of G12, has been shown to be amplified in aggressive breast tumors. This finding, along with our functional and morphological data suggest that G12 and spot 14 are vertebrate-specific and may function either as mitotic checkpoints or as structural components of the spindle apparatus.

Reinsch, Sigrid↗

NASA NTRS2003

The TP53 dependence of radiation-induced chromosome instability in human lymphoblastoid cells

The dose and TP53 dependence for the induction of chromosome instability were examined in cells of three human lymphoblastoid cell lines derived from WIL2 cells: TK6, a TP53-normal cell line, NH32, a TP53-knockout created from TK6, and WTK1, a WIL2-derived cell line that spontaneously developed a TP53 mutation. Cells of each cell line were exposed to (137)Cs gamma rays, and then surviving clones were isolated and expanded in culture for approximately 35 generations before the frequency and characteristics of the instability were analyzed. The presence of dicentric chromosomes, formed by end-to-end fusions, served as a marker of chromosomal instability. Unexposed TK6 cells had low levels of chromosomal instability (0.002 +/- 0.001 dicentrics/cell). Exposure of TK6 cells to doses as low as 5 cGy gamma rays increased chromosome instability levels nearly 10-fold to 0.019 +/- 0.008 dicentrics/cell. There was no further increase in instability levels beyond 5 cGy. In contrast to TK6 cells, unexposed cultures of WTK1 and NH32 cells had much higher levels of chromosome instability of 0.034 +/- 0.007 and 0.041 +/- 0.009, respectively, but showed little if any effect of radiation on levels of chromosome instability. The results suggest that radiation exposure alters the normal TP53-dependent cell cycle checkpoint controls that recognize alterations in telomere structure and activate apoptosis.

Non-NASA Center↗

NASA NTRS2001

Response of thyroid follicular cells to gamma irradiation compared to proton irradiation. I. Initial characterization of DNA damage, micronucleus formation, apoptosis, cell survival, and cell cycle phase redistribution

The RBE of protons has been assumed to be equivalent to that of photons. The objective of this study was to determine whether radiation-induced DNA and chromosome damage, apoptosis, cell killing and cell cycling in organized epithelial cells was influenced by radiation quality. Thyroid-stimulating hormone-dependent Fischer rat thyroid cells, established as follicles, were exposed to gamma rays or proton beams delivered acutely over a range of physical doses. Gamma-irradiated cells were able to repair DNA damage relatively rapidly so that by 1 h postirradiation they had approximately 20% fewer exposed 3' ends than their counterparts that had been irradiated with proton beams. The persistence of free ends of DNA in the samples irradiated with the proton beam implies that either more initial breaks or a quantitatively different type of damage had occurred. These results were further supported by an increased frequency of chromosomal damage as measured by the presence of micronuclei. Proton-beam irradiation induced micronuclei at a rate of 2.4% per gray, which at 12 Gy translated to 40% more micronuclei than in comparable gamma-irradiated cultures. The higher rate of micronucleus formation and the presence of larger micronuclei in proton-irradiated cells was further evidence that a qualitatively more severe class of damage had been induced than was induced by gamma rays. Differences in the type of damage produced were detected in the apoptosis assay, wherein a significant lag in the induction of apoptosis occurred after gamma irradiation that did not occur with protons. The more immediate expression of apoptotic cells in the cultures irradiated with the proton beam suggests that the damage inflicted was more severe. Alternatively, the cell cycle checkpoint mechanisms required for recovery from such damage might not have been invoked. Differences based on radiation quality were also evident in the alpha components of cell survival curves (0.05 Gy(-1) for gamma rays, 0.12 Gy(-1) for protons), which suggests that the higher level of survival of gamma-irradiated cells could be attributed to the persistence of nonlethally irradiated thyrocytes and/or the capacity to repair damage more effectively than cells exposed to equal physical doses of protons. The final assessment in this study was radiation-induced cell cycle phase redistribution. Gamma rays and protons produced a similar dose-dependent redistribution toward a predominantly G(2)-phase population. From our cumulative results, it seems likely that a majority of the proton-irradiated cells would not continue to divide. In conclusion, these findings suggest that there are quantitative and qualitative differences in the biological effects of proton beams and gamma rays. These differences could be due to structured energy deposition from the tracks of primary protons and the associated high-LET secondary particles produced in the targets. The results suggest that a simple dose-equivalent approach to dosimetry may be inadequate to compare the biological responses of cells to photons and protons.

NASA Discipline Radiation Health↗

NASA NTRS2005

Transition Report for Dr. Ken Fernandez, NASA Marshall Space Flight Center

The primary objective proposed during my tenure with the NASA Administrator's Fellowship Program (NAFP) was the use of ROBOSIM, a NASA developed robot simulation software package, to introduce the first robotics class to the School of Engineering at Alabama A&M University. The students participating in the spring of 2004 chose as their class project a simulation of the Shuttle, the Shuttle Remote Manipulator System, and the inspection boom which may be used to inspect the Shuttle's tiles on-orbit. In addition to meeting this primary objective and fulfilling other activities that were required by NAFP participants, several other accomplishments are reported. Participation with the faculty of Alabama A&M in the planning and execution of the First and Second Annual Michael P. Anderson Memorial Summer Programs for minority high school students was completed. This program, funded by NASA, provided supervised "hands- on" group activities in various engineering disciplines, including robotics. A third major accomplishment during the NAFP tenure was the granting of a U.S. patent for the NASA 3-D Luggage Scanning System. International patents are also pending on this device. The device uses stereographic imaging similar to that used by NASA on the Mars Rover to enhance the contents of luggage and other items being inspected. It is believed that this device can greatly improve the efficiency and accuracy of security checkpoint screening.

Fernandez, Ken R.↗

NASA NTRS2005

NBS1 knockdown by small interfering RNA increases ionizing radiation mutagenesis and telomere association in human cells

Hypomorphic mutations which lead to decreased function of the NBS1 gene are responsible for Nijmegen breakage syndrome, a rare autosomal recessive hereditary disorder that imparts an increased predisposition to development of malignancy. The NBS1 protein is a component of the MRE11/RAD50/NBS1 complex that plays a critical role in cellular responses to DNA damage and the maintenance of chromosomal integrity. Using small interfering RNA transfection, we have knocked down NBS1 protein levels and analyzed relevant phenotypes in two closely related human lymphoblastoid cell lines with different p53 status, namely wild-type TK6 and mutated WTK1. Both TK6 and WTK1 cells showed an increased level of ionizing radiation-induced mutation at the TK and HPRT loci, impaired phosphorylation of H2AX (gamma-H2AX), and impaired activation of the cell cycle checkpoint regulating kinase, Chk2. In TK6 cells, ionizing radiation-induced accumulation of p53/p21 and apoptosis were reduced. There was a differential response to ionizing radiation-induced cell killing between TK6 and WTK1 cells after NBS1 knockdown; TK6 cells were more resistant to killing, whereas WTK1 cells were more sensitive. NBS1 deficiency also resulted in a significant increase in telomere association that was independent of radiation exposure and p53 status. Our results provide the first experimental evidence that NBS1 deficiency in human cells leads to hypermutability and telomere associations, phenotypes that may contribute to the cancer predisposition seen among patients with this disease.

Non-NASA Center↗