Search NASA⌕ Search

SEARCH · Search NASA

Results for “TOF”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Congruence of Clusters Defined By Whole Genome Sequencing and MALDI-TOF for Bacteria Isolated From Cleanrooms

Introduction: Oligotrophic conditions can render cleanrooms inhospitable to microbes. Despite these constraints, fungi and bacteria are frequently isolated from surfaces in astromaterials cleanrooms at the Johnson Space Center. Bacillus species are of particular concern because endospores belonging to this genus are resilient and can affect astromaterials. Current monitoring programs rely on 16S rRNA sequencing and the VITEK2 Compact system. These methods have limited power to resolve Bacillus species. Matrix-assisted laser desorption - time of flight mass spectrometry (MALDI-TOF MS), provides a rapid, low cost, method of identifying bacterial isolates and has a higher resolution than 16S rRNA sequencing, particularly for Bacillus species; however, few studies have compared this method to the industry gold standard, whole genome sequencing (WGS). Methods: Based on 16S rRNA classification, we selected 14 isolates for analysis with MALDI-TOF and WGS. Mass spectra were generated with MALDI-TOF MS and processed with custom scripts to identify clusters of closely related isolates and calculate a matrix of pairwise cosine similarity scores. Hybrid Illumina and Nanopore sequencing were used to generate draft genomes. Pairwise similarity scores were calculated from these genomes based on the average amino acid identity (AAI) predicted from single copy core genes. Congruence of clustering between these methods, was assessed by calculating adjusted Rand and Wallace coefficients. Results: Clusters of species generated from MALDI-TOF MS showed good agreement of phylotypes generated with WGS. Pairs of strains that were > 94% similar to each other in terms of predicted amino acid sequences consistently showed cosine similarities of mass spectra > 0.65 and, of the 9 clusters identified with WGS, 8 were identical with MALDI-TOF. This corresponds to an adjusted Rand index of 0.95 and a 95% confidence interval of 0.80 – 1.00 for adjusted Wallace coefficients. The only discordance was for a pair of isolates that were classified as Paenibacillus species. This pair showed relatively high similarity (0.84) in terms of MALDI-TOF MS but only 85% similarity in terms of AAI. Conclusion: This study shows that MALDI-TOF and WGS exhibit a similar ability to delineate Bacillus species isolated from cleanrooms and taxonomic units described by these two methods are consistent with one another. Since MALDI-TOF MS is low in cost and high in throughput, this approach appears to be an ideal option for routine microbial monitoring and identifying Bacillus species.

Farnaz Mazhari↗
NASA NTRS2021

Application of Whole Genome Sequencing and MALDI-TOF to the Identifcation of Bacillus Species Isolated from Cleanrooms at NASA Johnson Space Center

Astromaterial cleanrooms at NASA Johnson Space Center are built environments that hold samples, such as lunar rocks, from different space exploration missions. Bacillus sp. are frequently detected in routine microbial monitoring of these facilities. Since this, and related genera, can form endospores that can withstand harsh conditions, they could contaminate astromaterials. This could confound searches for extraterrestrial life. Whole genome sequencing (WGS) is widely used for identifying bacterial strains and tracking their source; however, WGS is expensive and time consuming. Matrix-assisted laser desorption ionization– time of flight mass spectrometry (MALDI-TOF) shows promise as a low-cost, rapid method of identifying strains of bacteria, but few studies have compared this proteomics method to WGS. To evaluate a high throughput method of tracking the source of contamination of this built environment, WGS and MALDI-TOF was conducted on 18 bacterial strains isolated from surfaces in astromaterials cleanrooms. WGS identified 14 Bacillus, 2 Paenibacillus, 1 Solibacillus and 1 Alcaligenes strains. These isolates showed similarity to strains commonly observed in spacecraft assembly cleanrooms at other facilities. Cluster analysis of mass spectra generated by MALDI-TOF grouped strains together that were greater than 94% similar to each other in terms of amino acid sequences of single copy core genes, as assessed by WGS. This suggests that MALDI-TOF and WGS results are consistent with each other and MALDI-TOF can rapidly identify strains of Bacillus sp. isolated from cleanroom environments with a resolution comparable to WGS. Based on phylogenomic analysis, these results also suggest the presence of a cosmopolitan class of Bacillus sp. that are more likely to be found in cleanrooms and similar built environments than in natural systems.

Farnaz Mazhari↗
NASA NTRSDate not supplied

Quick and Correlative TOF-SIMS Analysis of Dispersoid Content in Powder Feedstock and Printed Oxide Dispersion Strengthened Alloys

Oxide dispersion strengthening (ODS) of metal alloys, when combined with additive manufacturing (AM), can be used to solve high-temperature material application problems. The performance of ODS materials is dependent on nano-scale oxide being distributed uniformly throughout the metal matrix; a homogenous distribution is critical to the creep and yield strength. Therefore, quantifying and analyzing these oxide nanoparticles is essential for ODS alloy development. Assessing the chemistry and morphology of dispersoids in a material can be conducted using a variety of X-ray and electron-based methods. Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), which assesses chemical concentrations from ion masses, provides the necessary spatial resolution and avoids potential spectral overlap of all elements present. In this work, preparing ODS powder feedstock and Laser Powder Bed Fusion AM was conducted with a NiCoCr alloy and yttria dispersoid, mixed with a Resodyn resonance mixer and printed on an EOS M100 3D printer at NASA Glenn. TOF-SIMS was performed on a Physical Electronics NanoTOF TRIFT V TOF-SIMS at Case Western Reserve University. The TOF-SIMS results collected on the feedstock powder samples correspond to the qualitative interpretation of the homogeneity of the oxide coating on the metal powder from SEM images. This provides quantitative support to the qualitative microscopy images collected earlier in the process design phase. The variance in the yttrium distribution on the powder feedstock samples also correlated with the variance of the yttrium distribution detected in the printed samples. This correlation supported the hypothesis that an even coating of yttria on the metal powders contributes to an even distribution of yttria in the printed material.

Laura G. Wilson↗
NASA NTRS2002

MALDI TOF MS: An Exobiology Surface-Science Approach for Europa

If Europa is to be of primary exobiological interest, namely as a habitat for extant life, it is obvious that: (i) a hydrosphere must prevail beneath the cryosphere for a long time, (ii) internal energy sources must be present in a sufficient state of activity, and (iii) a reasonable technical means must be available for assessing if indeed life does exist in the hypothesized hydrosphere. This discussion focuses on technological issues, because the compounding evidence about Europa indicates that the first two are highly likely to be true. We present a consideration of time-of-flight mass spectroscopy (TOF MS) conducted in-situ on the cryosphere surface of Europa during a landed robotic mission. We assert that this is a reasonable technical means not only for exploring the composition of the cryosphere itself, but also for locating any biomolecular indicators of extant life brought to the surface through cryosphere activity. We also describe a MALDI (MAtrix Laser Desorption and Ionization) TOF MS system that we are constructing as a proof-of-concept prototype for conducting TOF MS measurements on Europa.

Gerakines, Perry A.↗
NASA NTRS2003

"DUST BUSTER" - A Single Photon Ionization TOF MS for Cometary Dusts

It is hard to predict the properties and composition of dust that will be returned by STARDUST from WED- 2. The most interesting but challenging case would be grains, pg to fg in weight, each carrying its own isotopic signature characteristic of its source zones in a variety of stars. How do we extract the maximum amount of science from such grains? Clearly, the best that can be accomplished is to measure every atom in each grain.Academia Sinica and Argonne National Laboratory (ANL) have entered into a collaboration to develop a SPI TOF MS instrument for analysis of stardust grains. A new instrument will be built at Academia Sinica based on the new TOF mass spectrometer design developed, built and operating at ANL. The instrument is intended for SPI TOF MS analysis of elements from Ca to Cu plus Li after first using SIMS to measure H, C, N, 0, Si, and S. There are still technical challenges facing the technique. We will need to improve submicrometer sample handling, avoid the effects of space charge, and increase the Mamie range of the detector. The most difficult obstacle to overcome may be the fact that the flux density of present high repetition rate, WV lasers is below the level needed to ensure full ionization (saturation) in the source region, which must be several mm in size to achieve the high useful yield needed for analysis of small stardust grains. A potential breakthrough effort is to exploit the novel free electron laser being pioneered at ANL. In principle, this FEL can reach ionization saturation and is tunable up to photon energies of 25 eV, which is higher than the ionization potential of any element.

Chen, C.-Y.↗
NASA NTRS2006

Spontaneous-Desorption Ionizer for a TOF-MS

A time-of-flight mass spectrometer (TOF-MS) like the one mentioned in the immediately preceding article has been retrofitted with an ionizer based on a surface spontaneous-desorption process. This ionizer includes an electron multiplier in the form of a microchannel plate (MCP). Relative to an ionizer based on a hot-filament electron source, this ionizer offers advantages of less power consumption and greater mechanical ruggedness. The current density and stability characteristics of the electron emission of this ionizer are similar to those of a filament-based ionizer. In tests of various versions of this ionizer in the TOF-MS, electron currents up to 100 nA were registered. Currents of microamperes or more - great enough to satisfy requirements in most TOFMS applications - could be obtained by use of MCPs different from those used in the tests, albeit at the cost of greater bulk. One drawback of this ionizer is that the gain of the MCP decreases as a function of the charge extracted thus far; the total charge that can be extracted over the operational lifetime is about 1 coulomb. An MCP in the ion-detector portion of the TOF-MS is subject to the same limitation.

Schultz, J. Albert↗
NASA NTRS2000

Elemental, Isotopic, and Organic Analysis on Mars with Laser TOF-MS

The in-depth landed exploration of Mars will require increasingly sophisticated robotic analytical tools for both in situ composition science [1] and reconnaissance for sample return [2]. Beyond dust, rock surfaces, and topsoil, samples must be accessed within rocks and ice, well below surface soil, and possibly in elevated deposit layers. A range of spatial scales will be studied, and for the most information-rich microscopic analyses, samples must be acquired, prepared, and positioned with high precision. In some cases samples must also be brought into a vacuum chamber. After expending such resources, it will be important to apply techniques that provide a wide range of information about the samples. Microscopy, mineralogy, and molecular/organic, elemental, and isotopic analyses are all needed, at a minimum, to begin to address the in situ goals at Mars. These techniques must work as an efficient suite to provide layers of data, each layer helping to determine if further analysis on a given sample is desired. In the spirit of broad-band and efficient data collection, we are developing miniature laser time-of-flight mass spectrometers (TOF-MS) for elemental, isotopic, and molecular/organic microanalysis of unprepared solid samples. Laser TOF-MS uses a pulsed laser to volatilize and ionize material from a small region on the sample. The laser energy and focus can be adjusted for atomic and molecular content, sampling area, and depth. Ions travel through the instrument and are detected at a sequence of times proportional to the square root of their mass-to- charge ratios. Thus, each laser pulse produces a complete mass spectrum (in less than 50 microseconds). These instruments can now be significantly miniaturized (potentially to the size of a soda can) without a loss in performance. This effort is reviewed here with an emphasis on applications to Mars exploration.

Brinckerhoff, W. B.↗
NASA NTRS2006

Hybrid Ion-Detector/Data-Acquisition System for a TOF-MS

A modified ion-detector/data-acquisition system has been devised to increase the dynamic range of a time-of-flight mass spectrometer (TOF-MS) that, previously, included a microchannel-plate detector and a data-acquisition system based on counting pulses and time-tagging them by use of a time-to-digital converter (TDC). The dynamic range of the TOF-MS was limited by saturation of the microchannel plate detector, which can handle no more than a few million counts per second. The modified system includes (1) a combined microchannel plate/discrete ion multiplier and (2) a hybrid data-acquisition system that simultaneously performs analog current or voltage measurements and multianode single-ion-pulse-counting time-of-flight measurements to extend the dynamic range of a TDC into the regime in which a mass peak comprises multiple ions arriving simultaneously at the detector. The multianode data are used to determine, in real time, whether the detector is saturated. When saturation is detected, the data-acquisition system selectively enables circuitry that simultaneously determines the ion-peak intensity by measuring the time profile of the analog current or voltage detector-output signal.

Burton, William D., Jr.↗
NASA NTRS2014

ToF-SIMS Investigation of the Effectiveness of Acid-Cleaning procedures for Genesis Solar Wind Collectors

ToF-SIMS images of Genesis sample surfaces contain an incredible amount of important information, but they also show that the crash-derived surface contamination has many components, presenting a challenge to cleaning. Within the variability, we have shown that there are some samples which appear to be clean to begin with, e.g. 60471, and some are more contaminated. Samples 60493 and 60500 are a part of a focused study of the effectiveness of aqua regia and/or sulfuric acid cleaning of small flight Si implanted with Li-6 using ToF-SIMS.

Goreva, Y. S.↗
NASA NTRS2017

Observations of VOC Emissions and Photochemical Products over US Oil- and Gas-Producing Regions Using High-Resolution H3O+ CIMS (PTR-ToF-MS)

VOCs (Volatile Organic Compounds) related to oil and gas extraction operations in the United States were measured by H3O (sup plus) chemical ionization time-of-flight mass spectrometry (H3O (sup plus) ToFCIMS/PTR-ToF-MS (Time of Flight Chemical Ionization Mass Spectrometry/Proton Transfer Reaction-Time of Flight-Mass Spectroscopy) from aircraft during the Shale Oil and Natural Gas Nexus (SONGNEX) campaign in March-April 2015. This work presents an overview of major VOC species measured in nine oil- and gas-producing regions, and a more detailed analysis of H3O (sup plus) ToF-CIMS measurements in the Permian Basin within Texas and New Mexico. Mass spectra are dominated by small photochemically produced oxygenates and compounds typically found in crude oil: aromatics, cyclic alkanes, and alkanes. Mixing ratios of aromatics were frequently as high as those measured downwind of large urban areas. In the Permian, the H3O (sup plus) ToF-CIMS measured a number of underexplored or previously unreported species, including aromatic and cycloalkane oxidation products, nitrogen heterocycles including pyrrole (C4H5N) and pyrroline (C4H7N), H2S, and a diamondoid (adamantane) or unusual monoterpene. We additionally assess the specificity of a number of ion masses resulting from H3O (sup plus) ion chemistry previously reported in the literature, including several new or alternate interpretations.

mass spectrometr↗
NASA NTRS1993

Multielement analysis of interplanetary dust particles using TOF-SIMS

Sections of three stratospheric particles (U2015G1, W7029*A27, and L2005P9) were analyzed with TOF-SIMS (Time Of Flight-Secondary Ion Mass Spectrometry) continuing our efforts to investigate the element distribution in interplanetary dust particles (IDP's) with high lateral resolution (approximately 0.2 micron), to examine possible atmospheric contamination effects, and to further explore the abilities of this technique for element analysis of small samples. The samples, previously investigated with SXRF (synchrotron X-ray fluorescence analysis), are highly enriched in Br (Br/Fe: 59 x CI, 9.2 x CI, and 116 x CI, respectively). U2015G1 is the IDP with the by far highest Zn/Fe-ratio (81 x CI) ever reported in chondritic particles.

Stephan, T.↗
NASA NTRS2006

TOF-SIMS Analysis of Crater Residues from Wild 2 Cometary on Stardust Aluminum Foil

Impact residues of cometary particles on aluminum foils from the Stardust mission were investigated with TOF-SIMS for their elemental and organic composition. The residual matter from comet 81P/Wild 2 shows a wide compositional range, from nearly monomineralic grains to polymict aggregates. Despite the comparably small analyzed sample volume, the average element composition of the investigated residues is similar to bulk CI chondritic values. Analysis of organic components in impact residues is complicated, due to fragmentation and alteration of the compounds during the impact process and by the presence of contaminants on the aluminum foils. Nevertheless, polycyclic aromatic hydrocarbons (PAHs) that are unambiguously associated with the impact residues were observed, and thus are most likely of cometary origin.

Leutner, Jan↗
NASA NTRSDate not supplied

Resolution of Maldi-Tof Compared to Whole Genome Sequencing for Identification of Bacillus Species Isolated From Cleanrooms at Nasa Johnson Space Center

The Astromaterials Acquisition and Curation Office at NASA Johnson Space Center maintains cleanrooms to archive extraterrestrial materials returned from space exploration missions. Compared to typical built environments, oligotrophic conditions make these facilities inhospitable to microbes. Despite these controls, bacteria and fungi are regularly cultured from these cleanrooms. In particular, Bacillus sp. are frequently isolated during routine microbial monitoring. Endospores associated with this genus can survive extreme environments, such as cleanrooms. This microbial contamination may affect the integrity of astromaterials.

Microbiology↗
NASA NTRS1974

Analytical tools and isolation of TOF events

Analytical tools are presented in two reports. The first is a probability analysis of the orbital distribution of events in relation to dust flux density observed in Pioneer 8 and 9 distributions. A distinction is drawn between asymmetries caused by random fluctuations and systematic variations, by calculating the probability of any particular asymmetry. The second article discusses particle trajectories for a repulsive force field. The force on a particle due to solar radiation pressure is directed along the particle's radius vector, from the sun, and is inversely proportional to its distance from the sun. Equations of motion which describe both solar radiation pressure and gravitational attraction are presented.

Wolf, H.↗