Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “aberrations”

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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Modeling Space-Radiation Induced Chromosome Aberrations

Exposure to ionizing radiation is identified as one of the main hazards of space flight. Galactic cosmic rays (GCRs) are composed of energetic protons (87%), helium nuclei (12%) and high-charge and energy (HZE) ions. At the cellular scale, HZE ions have a pattern of energy deposition that depends on the ion linear energy transfer (LET), with high LET ions favoring the formation of complex DNA damages that induce chromosome aberrations (CAs). Understanding how physical (e.g., ion type and energy) and biological (e.g., cell type) parameters impact CA formation is required to assess space radiation risks such as carcinogenesis. The Monte Carlo tool RITCARD/RITRACKS [1,2] developed by NASA allows simulation of the transport of HZE ions and subsequent energy deposition at the cellular scale and models the creation of DNA double strand breaks (DSBs), DNA repair and formation of CAs. We used this radiation transport code to further understand how radiation quality and cell size affects CA formation.

Floriane Poignant↗
NASA NTRSDate not supplied

Monte Carlo Study of the Formation of Chromosome Aberrations by Direct Ion Traversal vs. Delta-Electrons

Space radiation constitutes a major risk for the safety of space travel. Galactic Cosmic Rays (GCRs) are made of high energy protons (87%), high energy helium ions (12%) and high-charge and energy (HZE) ions [1]. At a cellular scale, HZE ions display a characteristic pattern of energy deposition, known as the ion track, that correlates with the ion linear energy transfer (LET). These energy deposition events (ionizations/excitations) create DNA breaks that, if misrepaired, lead to the formation of chromosome aberrations (CAs). Compared to low-LET terrestrial radiations (X-rays and γ-rays), high LET ions are known to create complex, clustered DNA breaks that are particularly efficient at forming CAs. Indeed, ion tracks are usually described as a dense ionization core, where clustered breaks are formed, and a penumbra, made of low-LET δ-electrons that have sufficient energy to travel across many cells and induce breaks that are more homogeneously distributed. In this work, we investigated the formation of CAs, and separated them into two contributions (direct ion traversal of the nucleus vs.δ-electrons), to elucidate to which extent δ-electrons contribute to CA formation.

Floriane Poignant↗
DOE OSTI2014

Aberration-corrected X-ray spectrum imaging and Fresnel contrast to differentiate nanoclusters and cavities in helium-irradiated alloy 14YWT

Helium accumulation negatively impacts structural materials used in neutron-irradiated environments, such as fission and fusion reactors. Next-generation fission and fusion reactors will require structural materials, such as steels, resistant to large neutron doses yet see service temperatures in the range most affected by helium embrittlement. Previous work has indicated the difficulty of experimentally differentiating nanometer-sized helium bubbles from the Ti-Y-O rich nanoclustsers (NCs) in radiation-tolerant nanostructured ferritic alloys (NFAs). Because the NCs are expected to sequester helium away from grain boundaries and reduce embrittlement, experimental methods to study simultaneously the NC and bubble populations are needed. In this study, aberration-corrected scanning transmission electron microscopy (STEM) results combining high-collection-efficiency X-ray spectrum images (SIs), multivariate statistical analysis (MVSA), and Fresnel-contrast bright-field STEM imaging have been used for such a purpose. Results indicate that Fresnel-contrast imaging, with careful attention to TEM-STEM reciprocity, differentiates bubbles from NCs, and MVSA of X-ray SIs unambiguously identifies NCs. Therefore, combined Fresnel-contrast STEM and X-ray SI is an effective STEM-based method to characterize helium-bearing NFAs.

Miller, Michael K↗
DOE OSTI2016

Device and method for creating Gaussian aberration-corrected electron beams

Electron beam phase gratings have phase profiles that produce a diffracted beam having a Gaussian or other selected intensity profile. Phase profiles can also be selected to correct or compensate electron lens aberrations. Typically, a low diffraction order produces a suitable phase profile, and other orders are discarded.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Numerical Studies of Optimization and Aberration Correction Methods for the Preliminary Demonstration of the Parametric Ionization Cooling (PIC) Principle in the Twin Helix Muon Cooling Channel

Muon colliders have been proposed for the next generation of particle accelerators that study high-energy physics at the energy and intensity frontiers. In this paper we study a possible implementation of muon ionization cooling, Parametric-resonance Ionization Cooling (PIC), in the twin helix channel. The resonant cooling method of PIC offers the potential to reduce emittance beyond that achievable with ionization cooling with ordinary magnetic focusing. We examine optimization of a variety of parameters, study the nonlinear dynamics in the twin helix channel and consider possible methods of aberration correction.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Aberrated electron probes for magnetic spectroscopy with atomic resolution: Theory and practical aspects

It was recently proposed that electron magnetic circular dichroism (EMCD) can be measured in scanning transmission electron microscopy (STEM) with atomic resolution by tuning the phase distribution of a electron beam. Here, we describe the theoretical and practical aspects for the detection of out-of-plane and in-plane magnetization utilizing atomic size electron probes. Here we present the calculated optimized astigmatic probes and discuss how to achieve them experimentally.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

A Deep Exon Cryptic Splice Site Promotes Aberrant Intron Retention in a Von Willebrand Disease Patient

A translationally silent single nucleotide mutation in exon 44 (E44) of the von Willebrand factor (VWF) gene is associated with inefficient removal of intron 44 in a von Willebrand disease (VWD) patient. This intron retention (IR) event was previously attributed to reordered E44 secondary structure that sequesters the normal splice donor site. We propose an alternative mechanism: the mutation introduces a cryptic splice donor site that interferes with the function of the annotated site to favor IR. We evaluated both models using minigene splicing reporters engineered to vary in secondary structure and/or cryptic splice site content. Analysis of splicing efficiency in transfected K562 cells suggested that the mutation-generated cryptic splice site in E44 was sufficient to induce substantial IR. Mutations predicted to vary secondary structure at the annotated site also had modest effects on IR and shifted the balance of residual splicing between the cryptic site and annotated site, supporting competition among the sites. Further studies demonstrated that introduction of cryptic splice donor motifs at other positions in E44 did not promote IR, indicating that interference with the annotated site is context dependent. We conclude that mutant deep exon splice sites can interfere with proper splicing by inducing IR.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2000

High-LET radiation-induced aberrations in prematurely condensed G2 chromosomes of human fibroblasts

PURPOSE: To determine the number of initial chromatid breaks induced by low- or high-LET irradiations, and to compare the kinetics of chromatid break rejoining for radiations of different quality. MATERIAL AND METHODS: Exponentially growing human fibroblast cells AG1522 were irradiated with gamma-rays, energetic carbon (290MeV/u), silicon (490MeV/u) and iron (200 and 600 MeV/u). Chromosomes were prematurely condensed using calyculin A. Chromatid breaks and exchanges in G2 cells were scored. PCC were collected after several post-irradiation incubation times, ranging from 5 to 600 min. RESULTS: The kinetics of chromatid break rejoining following low- or high-LET irradiation consisted of two exponential components representing a rapid and a slow time constant. Chromatid breaks decreased rapidly during the first 10min after exposure, then continued to decrease at a slower rate. The rejoining kinetics were similar for exposure to each type of radiation. Chromatid exchanges were also formed quickly. Compared to low-LET radiation, isochromatid breaks were produced more frequently and the proportion of unrejoined breaks was higher for high-LET radiation. CONCLUSIONS: Compared with gamma-rays, isochromatid breaks were observed more frequently in high-LET irradiated samples, suggesting that an increase in isochromatid breaks is a signature of high-LET radiation exposure.

Non-NASA Center↗
DOE OSTI2014

Proteogenomic strategies for identification of aberrant cancer peptides using large-scale Next Generation Sequencing data

Cancer is driven by the acquisition of somatic DNA lesions. Distinguishing the early driver mutations from subsequent passenger mutations is key to molecular sub-typing of cancers, and the discovery of novel biomarkers. The availability of genomics technologies (mainly wholegenome and exome sequencing, and transcript sampling via RNA-seq, collectively referred to as NGS) have fueled recent studies on somatic mutation discovery. However, the vision is challenged by the complexity, redundancy, and errors in genomic data, and the difficulty of investigating the proteome using only genomic approaches. Recently, combination of proteomic and genomic technologies are increasingly employed. However, the complexity and redundancy of NGS data remains a challenge for proteogenomics, and various trade-offs must be made to allow for the searches to take place. This paperprovides a discussion of two such trade-offs, relating to large database search, and FDR calculations, and their implication to cancer proteogenomics. Moreover, it extends and develops the idea of a unified genomic variant database that can be searched by any mass spectrometry sample. A total of 879 BAM files downloaded from TCGA repository were used to create a 4.34 GB unified FASTA database which contained 2,787,062 novel splice junctions, 38,464 deletions, 1105 insertions, and 182,302 substitutions. Proteomic data from a single ovarian carcinoma sample (439,858 spectra) was searched against the database. By applying the most conservative FDR measure, we have identified 524 novel peptides and 65,578 known peptides at 1% FDR threshold. The novel peptides include interesting examples of doubly mutated peptides, frame-shifts, and non-sample-recruited mutations, which emphasize the strength of our approach.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

The Enlarged Fibroid Uterus: Aberrant Arterial Supply via the Omental Artery

Uterine artery embolization is considered a first-line therapy for symptomatic fibroids and is occasionally required to mitigate operative risk prior to total abdominal hysterectomy or myomectomy. We present a pictorial review of parasitized omental artery supply to the enlarged fibroid uterus in three patients undergoing preoperative uterine artery embolization. A detailed understanding of variant uterine blood supplies is crucial when performing fibroid embolization. Although omental artery supply to the fibroid uterus is an unusual finding, aortography to include mesenteric arteries may be necessary when anomalous blood supply to the enlarged fibroid uterus is suspected.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

E-beam manipulation of Si atoms on graphene edges with an aberration-corrected scanning transmission electron microscope

The burgeoning field of atomic-level material control holds great promise for future breakthroughs in quantum and memristive device manufacture and fundamental studies of atomic-scale chemistry. Realization of atom-by-atom control of matter represents a complex and ongoing challenge. Here, we explore the feasibility of controllable motion of dopant Si atoms at the edges of graphene via the sub-atomically focused electron beam in a scanning transmission electron microscope. Furthermore, we demonstrate that the graphene edges can be cleaned of Si atoms and then subsequently replenished from nearby source material. It is also shown how Si edge atoms may be “pushed” from the edge of a small hole into the bulk of the graphene lattice and from the bulk of the lattice back to the edge. This is accomplished through sputtering of the edge of the graphene lattice to bury or uncover Si dopant atoms. Finally, we demonstrate e-beam mediated hole healing and incorporation of dopant atoms. These experiments form an initial step toward general atomic-scale material control.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Aberrant localization of lamin B receptor (LBR) in cellular senescence in human cells

5-Bromodeoxyuridine (BrdU), a thymidine analogue, induces cellular senescence in mammalian cells. BrdU induces cellular senescence probably through the regulation of chromatin because BrdU destabilizes or disrupts nucleosome positioning and decondenses heterochromatin. Since heterochromatin is tethered to the nuclear periphery through the interaction with the nuclear envelope proteins, we examined the localization of the several nuclear envelope proteins such as lamins, lamin-interacting proteins, nuclear pore complex proteins, and nuclear transport proteins in senescent cells. We have shown here that lamin B receptor (LBR) showed a change in localization in both BrdU-induced and replicative senescent cells.

60 APPLIED LIFE SCIENCES↗