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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Assessment of Delivery Accuracy in an Operational-Like Environment

In order to enable arrival management concepts and solutions in a Next Generation Air Transportation System (NextGen) environment, ground-based sequencing and scheduling functions were developed to support metering operations in the National Airspace System. These sequencing and scheduling tools are designed to assist air traffic controllers in developing an overall arrival strategy, from enroute down to the terminal area boundary. NASA developed a ground system concept and protoype capability called Terminal Sequencing and Spacing (TSAS) to extend metering operations into the terminal area to the runway. To demonstrate the use of these scheduling and spacing tools in an operational-like environment, the FAA, NASA, and MITRE conducted an Operational Integration Assessment (OIA) of a prototype TSAS system at the FAA's William J. Hughes Technical Center (WJHTC). This paper presents an analysis of the arrival management strategies utilized and delivery accuracy achieved during the OIA. The analysis demonstrates how en route preconditioning, in various forms, and schedule disruptions impact delivery accuracy. As the simulation spanned both enroute and terminal airspace, the use of Ground Interval Management - Spacing (GIM-S) enroute speed advisories was investigated. Delivery accuracy was measured as the difference between the Scheduled Time of Arrival (STA) and the Actual Time of Arrival (ATA). The delivery accuracy was computed across all runs conducted during the OIA, which included deviations from nominal operations which are known to commonly occur in real operations, such as schedule changes and missed approaches. Overall, 83% of all flights were delivered into the terminal airspace within +/- 30 seconds of their STA and 94% of flights were delivered within +/- 60 seconds. The meter fix delivery accuracy standard deviation was found to be between 36 and 55 seconds across all arrival procedures. The data also showed when schedule disruptions were excluded, the percentage of aircraft delivered within +/- 30 seconds was between 85 and 90% across the various arrival procedures at the meter fix. This paper illustrates the ability to meet new delivery accuracy requirements in an operational-like environment using operational systems and NATCA controller participants, while also including common events that might cause disruptions to the schedule and overall system.

Air Traffic Scheduling↗
NASA NTRS2019

Radiation Stability Evaluation of Protein-Based Nanopores for Mars and Europa Missions

Exploration of our Solar System has revealed a number of locations that are now habitable or could have supported life in the past. One approach to finding life involves detection of informational polymers like deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) that are definitive biosignatures for life as we know it. Alternatively, structural variants of DNA and RNA, collectively termed xenonucleic acids (XNAs) have been shown in the laboratory to behave similarly. Nanopore-based sequencers differ from traditional sequencing technologies in that they do not explicitly require synthesis of DNA before or during analysis. Because of this, nanopore sequencers have been used for the direct sequencing of RNA, and could be used for the detection and analysis of other charged polymers. Here we describe results of exposing the MinION hardware, flow cells, and key reagents to ionizing radiation at doses relevant to Mars and Europa missions (10 to 3000 silicon-equivalent gray).

Burton, Aaron S.↗
NASA NTRS2019

Radiation Tolerance of Nanopore Sequencing Technology for Life Detection on Mars and Europa

The search for life beyond Earth is a key motivator in space exploration. Informational polymers, like DNA and RNA, are key biosignatures for life as we know it. The MinION is a miniature DNA sequencer based on versatile nanopore technology that could be implemented on future planetary missions. A critical unanswered question is whether the MinION and its protein-based nanopores can withstand increased radiation exposure outside Earth’s shielding magnetic field. We evaluated the effects of ionizing radiation on the MinION platform – including flow cells, reagents, and hardware – and discovered limited performance loss when exposed to ionizing doses comparable to a mission to Mars. Targets with harsher radiation environments, like Europa, would require improved radiation resistance via additional shielding or design refinements.

Mark A. Sutton↗
NASA NTRS2006

Deep impact sequence planning using multi-mission adaptable planning tools with integrated spacecraft models

The Deep Impact mission was ambitious and challenging. JPL's well proven, easily adaptable multi-mission sequence planning tools combined with integrated spacecraft subsystem models enabled a small operations team to develop, validate, and execute extremely complex sequence-based activities within very short development times. This paper focuses on the core planning tool used in the mission, APGEN. It shows how the multi-mission design and adaptability of APGEN made it possible to model spacecraft subsystems as well as ground assets throughout the lifecycle of the Deep Impact project, starting with models of initial, high-level mission objectives, and culminating in detailed predictions of spacecraft behavior during mission-critical activities.

Seybold, Calina C.↗
NASA NTRS2017

Microbial Characteristics of ISS Environmental Surfaces

The microbiome of environmental surfaces from the International Space Station were characterized in order to examine the relationship to crew and hardware maintenance. The Microbial Observatory (ISS-MO) experiment generated a microbial census of ISS environments using advanced molecular microbial community analyses along with traditional culture-based methods. Since the “omics” methodologies generated an extensive microbial census, significant insights into spaceflight-induced changes in the populations of beneficial and/or potentially harmful microbes were gained. Surface samples were collected from several ISS surface locations from three flight opportunities, and were returned to Earth via the Soyuz TMA-14M or the Space X Dragon capsule. In addition to cultivation methods, viable microbial burden, iTag-based sequencing, and metagenome analyses were carried out. The cultivable microbial bioburden differed by location and sampling event. Exploring the ISS environmental microbiome revealed presence of opportunistic pathogens and antibiotic resistant microbes. Genes involved in ATP binding cassette transporters, two component systems, and beta-lactam resistance were among a diverse set of metabolic and genetic information processing pathways. Whole genome sequencing (WGS) of 50 ISS strains exhibiting resistance to various antibiotics was carried out. The antibiotic resistant genes deduced from the WGS were compared with the resistomes generated directly from the gene pool of the environmental samples. Two unique Aspergillus fumigatus strains isolated from the ISS were characterized and compared to the experimentally established clinical isolates Af293 and CEA10. A virulence assessment in a neutrophil-deficient larval zebrafish model of invasive aspergillosis indicated that both ISSFT-021 and IF1SW-F4 were significantly more lethal compared to Af293 and CEA10. The findings from this Environmental “Omics” project should be exploited to enhance human health and well-being of a closed system. In other words, the ISS-MO research aims to "translate" findings in fundamental research into medical practice (pathogen detection) and meaningful health outcomes (countermeasure development).

Perry, Jay↗
NASA NTRS2017

Autonomous Science Restart for the Planned Europa Mission with Lightweight Planning and Execution

In this paper we present MEXEC - a lightweight on-board planning and execution system that monitors spacecraft state to robustly respond to current conditions. In addition it projects the remaining plan forward in time to detect conflicts and revise the plan. Most current planetary missions use sequence based commanding from the ground,which limits the ability to respond to on-board state varying from planned for state. This results in planning for worst-case execution time, power utilization, data volume and other resources and leads to under utilization of the spacecraft capability. It also limits the ability to respond to faults. Due to the high radiation environment at Jupiter the probability of flight software resets is high. Therefore, of particular interest to the planned Europa Mission is the capability to restart the science plan after flight software resets. In this paper we present results from running Europa flyby scenarios with flight software resets in the Europa flight software test environment. Preliminary results with the prototype scenario show MEXEC takes less than a tenth of a second to respond to resets. The development was done as part of Europa-focused flight software, but MEXEC was designed to be applicable to landers and rovers as well.

Joshi, Rajeev↗
NASA NTRSDate not supplied

Enterococci in Space: Adaptation, Antibiotic Resistance, and Clinical Implications

Enterococci are gram-positive bacteria that originated when our ancient animal ancestors emerged from the oceans to live on land, and brought their gut flora with them. Enterococcus faecalis (EF) and Enterococcus faecium, are common human commensals and can harbor multidrug resistance. Both have been previously isolated from the International Space Station (ISS). Likely as a consequence of their evolutionary origins, enterococci show remarkable stress resistance within, but also outside, their human hosts. Their antibiotic resistance, coupled with tolerance to desiccation, starvation, and disinfection, make some EF strains potent pathogens in the built environment (e.g., hospitals), and a potential risk to crew health during space missions. Here we describe our planned flight studies, currently in development. Genomic Enumeration of Antibiotic Resistance in Space (GEARS) will characterize the frequency and genomic identity of antibiotic resistant organisms, including enterococci, on the ISS, and expand our future in-space sequencing-based diagnostic capabilities. Enterococcus Growth Advantage on ISS via Tn-seq (EnteroGAIT) will assess the evolutionary selective pressure of the space environment (microgravity, space radiation) using EF as a model system during a long-duration culture and persistence experiment. Adaptation & Evolution of Resilient Enterococcus in Space (AERES) will study existing and newly identified isolates to characterize the “natural” evolutionary history of EF on Earth and in space to reveal mechanisms of microbial adaption including, possibly, natural selection. Our work to date has identified that EF ISS isolates share virulence factors found in clinical strains and commensals, and revealed limitations of current pathogenicity assessment tools. While ISS isolates were, in some cases, multi-drug resistant, current data suggests these are largely commensal strains. Our work will further refine potential crew health risks and improve understanding of EF adaptation to the built environment, of great relevance on Earth where EF is the second leading cause of hospital acquired infection.

Jordan McKaig↗
NASA NTRS1994

Data compression of discrete sequence: A tree based approach using dynamic programming

A dynamic programming based approach for data compression of a ID sequence is presented. The compression of an input sequence of size N to that of a smaller size k is achieved by dividing the input sequence into k subsequences and replacing the subsequences by their respective average values. The partitioning of the input sequence is carried with the intention of reducing the mean squared error in the reconstructed sequence. The complexity involved in finding the partitions which would result in such an optimal compressed sequence is reduced by using the dynamic programming approach, which is presented.

Shivaram, Gurusrasad↗
NASA NTRS1986

Archaebacterial phylogeny: perspectives on the urkingdoms

Comparisons of complete 16S ribosomal RNA sequences have been used to confirm, refine and extend earlier concepts of archaebacterial phylogeny. The archaebacteria fall naturally into two major branches or divisions, I--the sulfur-dependent thermophilic archaebacteria, and II--the methanogenic archaebacteria and their relatives. Division I comprises a relatively closely related and phenotypically homogeneous collection of thermophilic sulfur-dependent species--encompassing the genera Sulfolobus, Thermoproteus, Pyrodictium and Desulfurococcus. The organisms of Division II, however, form a less compact grouping phylogenetically, and are also more diverse in phenotype. All three of the (major) methanogen groups are found in Division II, as are the extreme halophiles and two types of thermoacidophiles, Thermoplasma acidophilum and Thermococcus celer. This last species branches sufficiently deeply in the Division II line that it might be considered to represent a separate, third Division. However, both the extreme halophiles and Tp. acidophilum branch within the cluster of methanogens. The extreme halophiles are specifically related to the Methanomicrobiales, to the exclusion of both the Methanococcales and the Methanobacteriales. Tp. acidophilum is peripherally related to the halophile-Methanomicrobiales group. By 16S rRNA sequence measure the archaebacteria constitute a phylogenetically coherent grouping (clade), which excludes both the eubacteria and the eukaryotes--a conclusion that is supported by other sequence evidence as well. Alternative proposals for archaebacterial phylogeny, not based upon sequence evidence, are discussed and evaluated. In particular, proposals to rename (reclassify) various subgroups of the archaebacteria as new kingdoms are found wanting, for both their lack of proper experimental support and the taxonomic confusion they introduce.

NASA Discipline Exobiology↗
NASA NTRS1982

Computer constructed imagery of distant plasma interaction boundaries

Computer constructed sketches of plasma boundaries arising from the interaction between the solar wind and the magnetosphere can serve as both didactic and research tools. In particular, the structure of the earth's bow shock can be represented as a nonuniform surfce according to the instantaneous orientation of the IMF, and temporal changes in structural distribution can be modeled as a sequence of sketches based on observed sequences of spacecraft-based measurements. Viewed rapidly, such a sequence of sketches can be the basis for representation of plasma processes by computer animation.

Greenstadt, E. W.↗
NASA NTRS2003

The dynamics of herpesvirus and polyomavirus reactivation and shedding in healthy adults: a 14-month longitudinal study

Humans are infected with viruses that establish long-term persistent infections. To address whether immunocompetent individuals control virus reactivation globally or independently and to identify patterns of sporadic reactivation, we monitored herpesviruses and polyomaviruses in 30 adults, over 14 months. Epstein-Barr virus (EBV) DNA was quantitated in saliva and peripheral blood mononuclear cells (PBMCs), cytomegalovirus (CMV) was assayed in urine, and JC virus (JCV) and BK virus (BKV) DNAs were assayed in urine and PBMCs. All individuals shed EBV in saliva, whereas 67% had >or=1 blood sample positive for EBV. Levels of EBV varied widely. CMV shedding occurred infrequently but occurred more commonly in younger individuals (P<.03). JCV and BKV virurias were 46.7% and 0%, respectively. JCV shedding was age dependent and occurred commonly in individuals >or=40 years old (P<.03). Seasonal variation was observed in shedding of EBV and JCV, but there was no correlation among shedding of EBV, CMV, and JCV (P>.50). Thus, adults independently control persistent viruses, which display discordant, sporadic reactivations.

Non-NASA Center↗
NASA NTRS1991

A definition of the domains Archaea, Bacteria and Eucarya in terms of small subunit ribosomal RNA characteristics

The number of small subunit rRNA sequences is now great enough that the three domains Archaea, Bacteria and Eucarya (Woese et al., 1990) can be reliably defined in terms of their sequence "signatures". Approximately 50 homologous positions (or nucleotide pairs) in the small subunit rRNA characterize and distinguish among the three. In addition, the three can be recognized by a variety of nonhomologous rRNA characters, either individual positions and/or higher-order structural features. The Crenarchaeota and the Euryarchaeota, the two archaeal kingdoms, can also be defined and distinguished by their characteristic compositions at approximately fifteen positions in the small subunit rRNA molecule.

NASA Program Exobiology↗
NASA NTRS1990

PCR amplification of 16S rDNA from lyophilized cell cultures facilitates studies in molecular systematics

The sequence of the major portion of a Bacillus cycloheptanicus strain SCH(T) 16S rRNA gene is reported. This sequence suggests that B. cycloheptanicus is genetically quite distinct from traditional Bacillus strains (e.g., B. subtilis) and may be properly regarded as belonging to a different genus. The sequence was determined from DNA that was produced by direct amplification of ribosomal DNA from a lyophilized cell pellet with straightforward polymerase chain reaction (PCR) procedures. By obviating the need to revive cell cultures from the lyophile pellet, this approach facilitates rapid 16S rDNA sequencing and thereby advances studies in molecular systematics.

Non-NASA Center↗
NASA NTRS2000

Molecular cloning and characterization of a tomato cDNA encoding a systemically wound-inducible bZIP DNA-binding protein

Localized wounding of one leaf in intact tomato (Lycopersicon esculentum Mill.) plants triggers rapid systemic transcriptional responses that might be involved in defense. To better understand the mechanism(s) of intercellular signal transmission in wounded tomatoes, and to identify the array of genes systemically up-regulated by wounding, a subtractive cDNA library for wounded tomato leaves was constructed. A novel cDNA clone (designated LebZIP1) encoding a DNA-binding protein was isolated and identified. This clone appears to be encoded by a single gene, and belongs to the family of basic leucine zipper domain (bZIP) transcription factors shown to be up-regulated by cold and dark treatments. Analysis of the mRNA levels suggests that the transcript for LebZIP1 is both organ-specific and up-regulated by wounding. In wounded wild-type tomatoes, the LebZIP1 mRNA levels in distant tissue were maximally up-regulated within only 5 min following localized wounding. Exogenous abscisic acid (ABA) prevented the rapid wound-induced increase in LebZIP1 mRNA levels, while the basal levels of LebZIP1 transcripts were higher in the ABA mutants notabilis (not), sitiens (sit), and flacca (flc), and wound-induced increases were greater in the ABA-deficient mutants. Together, these results suggest that ABA acts to curtail the wound-induced synthesis of LebZIP1 mRNA.

Non-NASA Center↗
NASA NTRS2000

Arabidopsis chloroplast chaperonin 10 is a calmodulin-binding protein

Calcium regulates diverse cellular activities in plants through the action of calmodulin (CaM). By using (35)S-labeled CaM to screen an Arabidopsis seedling cDNA expression library, a cDNA designated as AtCh-CPN10 (Arabidopsis thaliana chloroplast chaperonin 10) was cloned. Chloroplast CPN10, a nuclear-encoded protein, is a functional homolog of E. coli GroES. It is believed that CPN60 and CPN10 are involved in the assembly of Rubisco, a key enzyme involved in the photosynthetic pathway. Northern analysis revealed that AtCh-CPN10 is highly expressed in green tissues. The recombinant AtCh-CPN10 binds to CaM in a calcium-dependent manner. Deletion mutants revealed that there is only one CaM-binding site in the last 31 amino acids of the AtCh-CPN10 at the C-terminal end. The CaM-binding region in AtCh-CPN10 has higher homology to other chloroplast CPN10s in comparison to GroES and mitochondrial CPN10s, suggesting that CaM may only bind to chloroplast CPN10s. Furthermore, the results also suggest that the calcium/CaM messenger system is involved in regulating Rubisco assembly in the chloroplast, thereby influencing photosynthesis. Copyright 2000 Academic Press.

NASA Discipline Plant Biology↗
NASA NTRS1999

Ionizing radiation-induced mutagenesis: radiation studies in Neurospora predictive for results in mammalian cells

Ionizing radiation was the first mutagen discovered and was used to develop the first mutagenicity assay. In the ensuing 70+ years, ionizing radiation became a fundamental tool in understanding mutagenesis and is still a subject of intensive research. Frederick de Serres et al. developed and used the Neurospora crassa ad-3 system initially to explore the mutagenic effects of ionizing radiation. Using this system, de Serres et al. demonstrated the dependence of the frequency and spectra of mutations induced by ionizing radiation on the dose, dose rate, radiation quality, repair capabilities of the cells, and the target gene employed. This work in Neurospora predicted the subsequent observations of the mutagenic effects of ionizing radiation in mammalian cells. Modeled originally on the mouse specific-locus system developed by William L. Russell, the N. crassa ad-3 system developed by de Serres has itself served as a model for interpreting the results in subsequent systems in mammalian cells. This review describes the primary findings on the nature of ionizing radiation-induced mutagenesis in the N. crassa ad-3 system and the parallel observations made years later in mammalian cells.

NASA Discipline Radiation Health↗
NASA NTRS1999

Cell and molecular biology of simian virus 40: implications for human infections and disease

Simian virus 40 (SV40), a polyomavirus of rhesus macaque origin, was discovered in 1960 as a contaminant of polio vaccines that were distributed to millions of people from 1955 through early 1963. SV40 is a potent DNA tumor virus that induces tumors in rodents and transforms many types of cells in culture, including those of human origin. This virus has been a favored laboratory model for mechanistic studies of molecular processes in eukaryotic cells and of cellular transformation. The viral replication protein, named large T antigen (T-ag), is also the viral oncoprotein. There is a single serotype of SV40, but multiple strains of virus exist that are distinguishable by nucleotide differences in the regulatory region of the viral genome and in the part of the T-ag gene that encodes the protein's carboxyl terminus. Natural infections in monkeys by SV40 are usually benign but may become pathogenic in immunocompromised animals, and multiple tissues can be infected. SV40 can replicate in certain types of simian and human cells. SV40-neutralizing antibodies have been detected in individuals not exposed to contaminated polio vaccines. SV40 DNA has been identified in some normal human tissues, and there are accumulating reports of detection of SV40 DNA and/or T-ag in a variety of human tumors. This review presents aspects of replication and cell transformation by SV40 and considers their implications for human infections and disease pathogenesis by the virus. Critical assessment of virologic and epidemiologic data suggests a probable causative role for SV40 in certain human cancers, but additional studies are necessary to prove etiology.

Review↗
NASA NTRS1998

Chimeric calcium/calmodulin-dependent protein kinase in tobacco: differential regulation by calmodulin isoforms

cDNA clones of chimeric Ca2+/calmodulin-dependent protein kinase (CCaMK) from tobacco (TCCaMK-1 and TCCaMK-2) were isolated and characterized. The polypeptides encoded by TCCaMK-1 and TCCaMK-2 have 15 different amino acid substitutions, yet they both contain a total of 517 amino acids. Northern analysis revealed that CCaMK is expressed in a stage-specific manner during anther development. Messenger RNA was detected when tobacco bud sizes were between 0.5 cm and 1.0 cm. The appearance of mRNA coincided with meiosis and became undetectable at later stages of anther development. The reverse polymerase chain reaction (RT-PCR) amplification assay using isoform-specific primers showed that both of the CCaMK mRNAs were expressed in anther with similar expression patterns. The CCaMK protein expressed in Escherichia coli showed Ca2+-dependent autophosphorylation and Ca2+/calmodulin-dependent substrate phosphorylation. Calmodulin isoforms (PCM1 and PCM6) had differential effects on the regulation of autophosphorylation and substrate phosphorylation of tobacco CCaMK, but not lily CCaMK. The evolutionary tree of plant serine/threonine protein kinases revealed that calmodulin-dependent kinases form one subgroup that is distinctly different from Ca2+-dependent protein kinases (CDPKs) and other serine/threonine kinases in plants.

NASA Discipline Plant Biology↗