Ultra-High Aggregate Bandwidth Two-Dimensional Multiple-Wavelength Diode Laser Arrays

DTIC Science & Technology

1993-12-09

during the growth of the cavity spacer region using the fact that the molecular beam epitaxy growth of GaAs is highly sensitive to the substrate... molecular beam epitaxy (MBE) crystal growth, the GaAs growth rate is highly sensitive to the substrate temperature above 650"C (2], a GaAs/AIGaAs... epitaxial growth technique to make reproducible and repeatable multi-wavelength VCSEL arrays. Our approach to fabricate the spatially graded layer

Functional interrogation of non-coding DNA through CRISPR genome editing

PubMed Central

Canver, Matthew C.; Bauer, Daniel E.; Orkin, Stuart H.

2017-01-01

Methodologies to interrogate non-coding regions have lagged behind coding regions despite comprising the vast majority of the genome. However, the rapid evolution of clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing has provided a multitude of novel techniques for laboratory investigation including significant contributions to the toolbox for studying non-coding DNA. CRISPR-mediated loss-of-function strategies rely on direct disruption of the underlying sequence or repression of transcription without modifying the targeted DNA sequence. CRISPR-mediated gain-of-function approaches similarly benefit from methods to alter the targeted sequence through integration of customized sequence into the genome as well as methods to activate transcription. Here we review CRISPR-based loss- and gain-of-function techniques for the interrogation of non-coding DNA. PMID:28288828

Short intronic repeat sequences facilitate circular RNA production

PubMed Central

Liang, Dongming

2014-01-01

Recent deep sequencing studies have revealed thousands of circular noncoding RNAs generated from protein-coding genes. These RNAs are produced when the precursor messenger RNA (pre-mRNA) splicing machinery “backsplices” and covalently joins, for example, the two ends of a single exon. However, the mechanism by which the spliceosome selects only certain exons to circularize is largely unknown. Using extensive mutagenesis of expression plasmids, we show that miniature introns containing the splice sites along with short (∼30- to 40-nucleotide) inverted repeats, such as Alu elements, are sufficient to allow the intervening exons to circularize in cells. The intronic repeats must base-pair to one another, thereby bringing the splice sites into close proximity to each other. More than simple thermodynamics is clearly at play, however, as not all repeats support circularization, and increasing the stability of the hairpin between the repeats can sometimes inhibit circular RNA biogenesis. The intronic repeats and exonic sequences must collaborate with one another, and a functional 3′ end processing signal is required, suggesting that circularization may occur post-transcriptionally. These results suggest detailed and generalizable models that explain how the splicing machinery determines whether to produce a circular noncoding RNA or a linear mRNA. PMID:25281217

Burst annealing of high temperature GaAs solar cells

NASA Technical Reports Server (NTRS)

Brothers, P. R.; Horne, W. E.

1991-01-01

One of the major limitations of solar cells in space power systems is their vulnerability to radiation damage. One solution to this problem is to periodically heat the cells to anneal the radiation damage. Annealing was demonstrated with silicon cells. The obstacle to annealing of GaAs cells was their susceptibility to thermal damage at the temperatures required to completely anneal the radiation damage. GaAs cells with high temperature contacts and encapsulation were developed. The cells tested are designed for concentrator use at 30 suns AMO. The circular active area is 2.5 mm in diameter for an area of 0.05 sq cm. Typical one sun AMO efficiency of these cells is over 18 percent. The cells were demonstrated to be resistant to damage after thermal excursions in excess of 600 C. This high temperature tolerance should allow these cells to survive the annealing of radiation damage. A limited set of experiments were devised to investigate the feasibility of annealing these high temperature cells. The effect of repeated cycles of electron and proton irradiation was tested. The damage mechanisms were analyzed. Limitations in annealing recovery suggested improvements in cell design for more complete recovery. These preliminary experiments also indicate the need for further study to isolate damage mechanisms. The primary objective of the experiments was to demonstrate and quantify the annealing behavior of high temperature GaAs cells. Secondary objectives were to measure the radiation degradation and to determine the effect of repeated irradiation and anneal cycles.

Functional interrogation of non-coding DNA through CRISPR genome editing.

PubMed

Canver, Matthew C; Bauer, Daniel E; Orkin, Stuart H

2017-05-15

Methodologies to interrogate non-coding regions have lagged behind coding regions despite comprising the vast majority of the genome. However, the rapid evolution of clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing has provided a multitude of novel techniques for laboratory investigation including significant contributions to the toolbox for studying non-coding DNA. CRISPR-mediated loss-of-function strategies rely on direct disruption of the underlying sequence or repression of transcription without modifying the targeted DNA sequence. CRISPR-mediated gain-of-function approaches similarly benefit from methods to alter the targeted sequence through integration of customized sequence into the genome as well as methods to activate transcription. Here we review CRISPR-based loss- and gain-of-function techniques for the interrogation of non-coding DNA. Copyright © 2017 Elsevier Inc. All rights reserved.

Length and sequence heterogeneity in 5S rDNA of Populus deltoides.

PubMed

Negi, Madan S; Rajagopal, Jyothi; Chauhan, Neeti; Cronn, Richard; Lakshmikumaran, Malathi

2002-12-01

The 5S rRNA genes and their associated non-transcribed spacer (NTS) regions are present as repeat units arranged in tandem arrays in plant genomes. Length heterogeneity in 5S rDNA repeats was previously identified in Populus deltoides and was also observed in the present study. Primers were designed to amplify the 5S rDNA NTS variants from the P. deltoides genome. The PCR-amplified products from the two accessions of P. deltoides (G3 and G48) suggested the presence of length heterogeneity of 5S rDNA units within and among accessions, and the size of the spacers ranged from 385 to 434 bp. Sequence analysis of the non-transcribed spacer (NTS) revealed two distinct classes of 5S rDNA within both accessions: class 1, which contained GAA trinucleotide microsatellite repeats, and class 2, which lacked the repeats. The class 1 spacer shows length variation owing to the microsatellite, with two clones exhibiting 10 GAA repeat units and one clone exhibiting 16 such repeat units. However, distance analysis shows that class 1 spacer sequences are highly similar inter se, yielding nucleotide diversity (pi) estimates that are less than 0.15% of those obtained for class 2 spacers (pi = 0.0183 vs. 0.1433, respectively). The presence of microsatellite in the NTS region leading to variation in spacer length is reported and discussed for the first time in P. deltoides.

Purα Repaired Expanded Hexanucleotide GGGGCC Repeat Noncoding RNA-Caused Neuronal Toxicity in Neuro-2a Cells.

PubMed

Shen, Jianying; Zhang, Yu; Zhao, Shi; Mao, Hong; Wang, Zhongjing; Li, Honglian; Xu, Zihui

2018-05-01

Expanded hexanucleotide GGGGCC repeat in a noncoding region of C9ORF72 is the most common cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). However, its molecular pathogenesis remains unclear. In our previous study, the expanded GGGGCC repeats have been shown to be sufficient to cause neurodegeneration. In order to investigate the further role of expanded GGGGCC repeats in the neuron, the normal r(GGGGCC) 3 and mutant-type expanded r(GGGGCC) 30 expression vectors were transfected into Neuro-2a cells. Cell proliferation, dendrite development, and the proteins' levels of microtubule-associated protein-2 (MAP2) and cyclin-dependent kinase-5 (CDK5) were used to evaluate the cell toxicity of GGGGCC repeats on Neuro-2a cells. The results were shown that expression of expanded GGGGCC repeats caused neuronal cell toxicity in Neuro-2a cells, enhanced the expression of pMAP2 and pCDK5. Moreover, overexpression of Purα repaired expanded GGGGCC repeat-inducing neuronal toxicity in Neuro-2a cells and reduced the expression of pMAP2 and pCDK5. In all, our findings suggested that the expanded GGGGCC repeats might cause neurodegeneration through destroyed neuron cells. And the GGGGCC repeat-induced neuronal cell toxicity was inhibited by upregulation of Purα. We inferred that Purα inhibits expanded GGGGCC repeat-inducing neurodegeneration, which might reveal a novel mechanism of neurodegenerative diseases ALS and FTD.

Short intronic repeat sequences facilitate circular RNA production.

PubMed

Liang, Dongming; Wilusz, Jeremy E

2014-10-15

Recent deep sequencing studies have revealed thousands of circular noncoding RNAs generated from protein-coding genes. These RNAs are produced when the precursor messenger RNA (pre-mRNA) splicing machinery "backsplices" and covalently joins, for example, the two ends of a single exon. However, the mechanism by which the spliceosome selects only certain exons to circularize is largely unknown. Using extensive mutagenesis of expression plasmids, we show that miniature introns containing the splice sites along with short (∼ 30- to 40-nucleotide) inverted repeats, such as Alu elements, are sufficient to allow the intervening exons to circularize in cells. The intronic repeats must base-pair to one another, thereby bringing the splice sites into close proximity to each other. More than simple thermodynamics is clearly at play, however, as not all repeats support circularization, and increasing the stability of the hairpin between the repeats can sometimes inhibit circular RNA biogenesis. The intronic repeats and exonic sequences must collaborate with one another, and a functional 3' end processing signal is required, suggesting that circularization may occur post-transcriptionally. These results suggest detailed and generalizable models that explain how the splicing machinery determines whether to produce a circular noncoding RNA or a linear mRNA. © 2014 Liang and Wilusz; Published by Cold Spring Harbor Laboratory Press.

Simple Sequence Repeats in Escherichia coli: Abundance, Distribution, Composition, and Polymorphism

PubMed Central

Gur-Arie, Riva; Cohen, Cyril J.; Eitan, Yuval; Shelef, Leora; Hallerman, Eric M.; Kashi, Yechezkel

2000-01-01

Computer-based genome-wide screening of the DNA sequence of Escherichia coli strain K12 revealed tens of thousands of tandem simple sequence repeat (SSR) tracts, with motifs ranging from 1 to 6 nucleotides. SSRs were well distributed throughout the genome. Mononucleotide SSRs were over-represented in noncoding regions and under-represented in open reading frames (ORFs). Nucleotide composition of mono- and dinucleotide SSRs, both in ORFs and in noncoding regions, differed from that of the genomic region in which they occurred, with 93% of all mononucleotide SSRs proving to be of A or T. Computer-based analysis of the fine position of every SSR locus in the noncoding portion of the genome relative to downstream ORFs showed SSRs located in areas that could affect gene regulation. DNA sequences at 14 arbitrarily chosen SSR tracts were compared among E. coli strains. Polymorphisms of SSR copy number were observed at four of seven mononucleotide SSR tracts screened, with all polymorphisms occurring in noncoding regions. SSR polymorphism could prove important as a genome-wide source of variation, both for practical applications (including rapid detection, strain identification, and detection of loci affecting key phenotypes) and for evolutionary adaptation of microbes.[The sequence data described in this paper have been submitted to the GenBank data library under accession numbers AF209020–209030 and AF209508–209518.] PMID:10645951

Identification of common, unique and polymorphic microsatellites among 73 cyanobacterial genomes.

PubMed

Kabra, Ritika; Kapil, Aditi; Attarwala, Kherunnisa; Rai, Piyush Kant; Shanker, Asheesh

2016-04-01

Microsatellites also known as Simple Sequence Repeats are short tandem repeats of 1-6 nucleotides. These repeats are found in coding as well as non-coding regions of both prokaryotic and eukaryotic genomes and play a significant role in the study of gene regulation, genetic mapping, DNA fingerprinting and evolutionary studies. The availability of 73 complete genome sequences of cyanobacteria enabled us to mine and statistically analyze microsatellites in these genomes. The cyanobacterial microsatellites identified through bioinformatics analysis were stored in a user-friendly database named CyanoSat, which is an efficient data representation and query system designed using ASP.net. The information in CyanoSat comprises of perfect, imperfect and compound microsatellites found in coding, non-coding and coding-non-coding regions. Moreover, it contains PCR primers with 200 nucleotides long flanking region. The mined cyanobacterial microsatellites can be freely accessed at www.compubio.in/CyanoSat/home.aspx. In addition to this 82 polymorphic, 13,866 unique and 2390 common microsatellites were also detected. These microsatellites will be useful in strain identification and genetic diversity studies of cyanobacteria.

ChloroSSRdb: a repository of perfect and imperfect chloroplastic simple sequence repeats (cpSSRs) of green plants

PubMed Central

Kapil, Aditi; Rai, Piyush Kant; Shanker, Asheesh

2014-01-01

Simple sequence repeats (SSRs) are regions in DNA sequence that contain repeating motifs of length 1–6 nucleotides. These repeats are ubiquitously present and are found in both coding and non-coding regions of genome. A total of 534 complete chloroplast genome sequences (as on 18 September 2014) of Viridiplantae are available at NCBI organelle genome resource. It provides opportunity to mine these genomes for the detection of SSRs and store them in the form of a database. In an attempt to properly manage and retrieve chloroplastic SSRs, we designed ChloroSSRdb which is a relational database developed using SQL server 2008 and accessed through ASP.NET. It provides information of all the three types (perfect, imperfect and compound) of SSRs. At present, ChloroSSRdb contains 124 430 mined SSRs, with majority lying in non-coding region. Out of these, PCR primers were designed for 118 249 SSRs. Tetranucleotide repeats (47 079) were found to be the most frequent repeat type, whereas hexanucleotide repeats (6414) being the least abundant. Additionally, in each species statistical analyses were performed to calculate relative frequency, correlation coefficient and chi-square statistics of perfect and imperfect SSRs. In accordance with the growing interest in SSR studies, ChloroSSRdb will prove to be a useful resource in developing genetic markers, phylogenetic analysis, genetic mapping, etc. Moreover, it will serve as a ready reference for mined SSRs in available chloroplast genomes of green plants. Database URL: www.compubio.in/chlorossrdb/ PMID:25380781

ChloroSSRdb: a repository of perfect and imperfect chloroplastic simple sequence repeats (cpSSRs) of green plants.

PubMed

Kapil, Aditi; Rai, Piyush Kant; Shanker, Asheesh

2014-01-01

Simple sequence repeats (SSRs) are regions in DNA sequence that contain repeating motifs of length 1-6 nucleotides. These repeats are ubiquitously present and are found in both coding and non-coding regions of genome. A total of 534 complete chloroplast genome sequences (as on 18 September 2014) of Viridiplantae are available at NCBI organelle genome resource. It provides opportunity to mine these genomes for the detection of SSRs and store them in the form of a database. In an attempt to properly manage and retrieve chloroplastic SSRs, we designed ChloroSSRdb which is a relational database developed using SQL server 2008 and accessed through ASP.NET. It provides information of all the three types (perfect, imperfect and compound) of SSRs. At present, ChloroSSRdb contains 124 430 mined SSRs, with majority lying in non-coding region. Out of these, PCR primers were designed for 118 249 SSRs. Tetranucleotide repeats (47 079) were found to be the most frequent repeat type, whereas hexanucleotide repeats (6414) being the least abundant. Additionally, in each species statistical analyses were performed to calculate relative frequency, correlation coefficient and chi-square statistics of perfect and imperfect SSRs. In accordance with the growing interest in SSR studies, ChloroSSRdb will prove to be a useful resource in developing genetic markers, phylogenetic analysis, genetic mapping, etc. Moreover, it will serve as a ready reference for mined SSRs in available chloroplast genomes of green plants. Database URL: www.compubio.in/chlorossrdb/ © The Author(s) 2014. Published by Oxford University Press.

Systematic analysis of coding and noncoding DNA sequences using methods of statistical linguistics

NASA Technical Reports Server (NTRS)

Mantegna, R. N.; Buldyrev, S. V.; Goldberger, A. L.; Havlin, S.; Peng, C. K.; Simons, M.; Stanley, H. E.

1995-01-01

We compare the statistical properties of coding and noncoding regions in eukaryotic and viral DNA sequences by adapting two tests developed for the analysis of natural languages and symbolic sequences. The data set comprises all 30 sequences of length above 50 000 base pairs in GenBank Release No. 81.0, as well as the recently published sequences of C. elegans chromosome III (2.2 Mbp) and yeast chromosome XI (661 Kbp). We find that for the three chromosomes we studied the statistical properties of noncoding regions appear to be closer to those observed in natural languages than those of coding regions. In particular, (i) a n-tuple Zipf analysis of noncoding regions reveals a regime close to power-law behavior while the coding regions show logarithmic behavior over a wide interval, while (ii) an n-gram entropy measurement shows that the noncoding regions have a lower n-gram entropy (and hence a larger "n-gram redundancy") than the coding regions. In contrast to the three chromosomes, we find that for vertebrates such as primates and rodents and for viral DNA, the difference between the statistical properties of coding and noncoding regions is not pronounced and therefore the results of the analyses of the investigated sequences are less conclusive. After noting the intrinsic limitations of the n-gram redundancy analysis, we also briefly discuss the failure of the zeroth- and first-order Markovian models or simple nucleotide repeats to account fully for these "linguistic" features of DNA. Finally, we emphasize that our results by no means prove the existence of a "language" in noncoding DNA.

[Comparative organization and the origin of noncoding regulatory RNA genes from X-chromosome inactivation center of human and mouse].

PubMed

Kolesnikov, N N; Elisafenko, E A

2010-10-01

After the radiation of primates and rodents, the evolution of X-chromosome inactivation centers in human and mouse (XIC/Xic) followed two different directions. Human XIC followed the pathway towards transposon accumulation (the repeat proportion in the center constitutes 72%), especially LINEs, which prevail in the center. On the contrary, mouse Xic eliminated long repeats and accumulated species-specific SIN Es (the repeat proportion in the center constitutes 35%). The mechanism underlying inactivation of one of the X chromosomes in female mammals appeared on the basis of trasnsposons. The key gene of the inactivation process, XIST/Xist, similarly to other long noncoding RNA genes, like TSIX/Tsix, JPX/Jpx, and FTX/Ftx, was formed with the involvement of different transposon sequences. Furthermore, two clusters ofmicroRNA genes from inactivation center originated from L2 [1]. In mouse, one of such clusters has been preserved in the form of microRNA pseudogenes. Thus, long ncRNA genes and microRNAs appeared during the period of transposable elements expansion in this locus, 140 to 105 Myr ago, after the radiation of marsupials and placental mammal lineages.

Chimeric mitochondrial minichromosomes of the human body louse, Pediculus humanus: evidence for homologous and non-homologous recombination.

PubMed

Shao, Renfu; Barker, Stephen C

2011-02-15

The mitochondrial (mt) genome of the human body louse, Pediculus humanus, consists of 18 minichromosomes. Each minichromosome is 3 to 4 kb long and has 1 to 3 genes. There is unequivocal evidence for recombination between different mt minichromosomes in P. humanus. It is not known, however, how these minichromosomes recombine. Here, we report the discovery of eight chimeric mt minichromosomes in P. humanus. We classify these chimeric mt minichromosomes into two groups: Group I and Group II. Group I chimeric minichromosomes contain parts of two different protein-coding genes that are from different minichromosomes. The two parts of protein-coding genes in each Group I chimeric minichromosome are joined at a microhomologous nucleotide sequence; microhomologous nucleotide sequences are hallmarks of non-homologous recombination. Group II chimeric minichromosomes contain all of the genes and the non-coding regions of two different minichromosomes. The conserved sequence blocks in the non-coding regions of Group II chimeric minichromosomes resemble the "recombination repeats" in the non-coding regions of the mt genomes of higher plants. These repeats are essential to homologous recombination in higher plants. Our analyses of the nucleotide sequences of chimeric mt minichromosomes indicate both homologous and non-homologous recombination between minichromosomes in the mitochondria of the human body louse. Copyright © 2010 Elsevier B.V. All rights reserved.

Mediator directs co-transcriptional heterochromatin assembly by RNA interference-dependent and -independent pathways.

PubMed

Oya, Eriko; Kato, Hiroaki; Chikashige, Yuji; Tsutsumi, Chihiro; Hiraoka, Yasushi; Murakami, Yota

2013-01-01

Heterochromatin at the pericentromeric repeats in fission yeast is assembled and spread by an RNAi-dependent mechanism, which is coupled with the transcription of non-coding RNA from the repeats by RNA polymerase II. In addition, Rrp6, a component of the nuclear exosome, also contributes to heterochromatin assembly and is coupled with non-coding RNA transcription. The multi-subunit complex Mediator, which directs initiation of RNA polymerase II-dependent transcription, has recently been suggested to function after initiation in processes such as elongation of transcription and splicing. However, the role of Mediator in the regulation of chromatin structure is not well understood. We investigated the role of Mediator in pericentromeric heterochromatin formation and found that deletion of specific subunits of the head domain of Mediator compromised heterochromatin structure. The Mediator head domain was required for Rrp6-dependent heterochromatin nucleation at the pericentromere and for RNAi-dependent spreading of heterochromatin into the neighboring region. In the latter process, Mediator appeared to contribute to efficient processing of siRNA from transcribed non-coding RNA, which was required for efficient spreading of heterochromatin. Furthermore, the head domain directed efficient transcription in heterochromatin. These results reveal a pivotal role for Mediator in multiple steps of transcription-coupled formation of pericentromeric heterochromatin. This observation further extends the role of Mediator to co-transcriptional chromatin regulation.

¹H, ¹³C, ¹⁵N and ³¹P chemical shift assignments of a human Xist RNA A-repeat tetraloop hairpin essential for X-chromosome inactivation.

PubMed

Duszczyk, Malgorzata M; Sattler, Michael

2012-04-01

Initiation of X-chromosome inactivation in female mammals depends on the non-coding RNA Xist. We have solved the NMR structure of a 14-nucleotide hairpin with a novel AUCG tetraloop fold from a Xist A-repeat that is essential for silencing. The (1)H, (13)C, (15)N and (31)P chemical shift assignments are reported.

The complete mitochondrial genome of Pomacea canaliculata (Gastropoda: Ampullariidae).

PubMed

Zhou, Xuming; Chen, Yu; Zhu, Shanliang; Xu, Haigen; Liu, Yan; Chen, Lian

2016-01-01

The mitochondrial genome of Pomacea canaliculata (Gastropoda: Ampullariidae) is the first complete mtDNA sequence reported in the genus Pomacea. The total length of mtDNA is 15,707 bp, which containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a 359 bp non-coding region. The A + T content of the overall base composition of H-strand is 71.7% (T: 41%, C: 12.7%, A: 30.7%, G: 15.6%). ATP6, ATP8, CO1, CO2, ND1-3, ND5, ND6, ND4L and Cyt b genes begin with ATG as start codon, CO3 and ND4 begin with ATA. ATP8, CO2-3, ND4L, ND2-6 and Cyt b genes are terminated with TAA as stop codon, ATP6, ND1, and CO1 end with TAG. A long non-coding region is found and a 23 bp repeat unit repeat 11 times in this region.

Noncoding copy-number variations are associated with congenital limb malformation.

PubMed

Flöttmann, Ricarda; Kragesteen, Bjørt K; Geuer, Sinje; Socha, Magdalena; Allou, Lila; Sowińska-Seidler, Anna; Bosquillon de Jarcy, Laure; Wagner, Johannes; Jamsheer, Aleksander; Oehl-Jaschkowitz, Barbara; Wittler, Lars; de Silva, Deepthi; Kurth, Ingo; Maya, Idit; Santos-Simarro, Fernando; Hülsemann, Wiebke; Klopocki, Eva; Mountford, Roger; Fryer, Alan; Borck, Guntram; Horn, Denise; Lapunzina, Pablo; Wilson, Meredith; Mascrez, Bénédicte; Duboule, Denis; Mundlos, Stefan; Spielmann, Malte

2017-10-12

PurposeCopy-number variants (CNVs) are generally interpreted by linking the effects of gene dosage with phenotypes. The clinical interpretation of noncoding CNVs remains challenging. We investigated the percentage of disease-associated CNVs in patients with congenital limb malformations that affect noncoding cis-regulatory sequences versus genes sensitive to gene dosage effects.MethodsWe applied high-resolution copy-number analysis to 340 unrelated individuals with isolated limb malformation. To investigate novel candidate CNVs, we re-engineered human CNVs in mice using clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing.ResultsOf the individuals studied, 10% harbored CNVs segregating with the phenotype in the affected families. We identified 31 CNVs previously associated with congenital limb malformations and four novel candidate CNVs. Most of the disease-associated CNVs (57%) affected the noncoding cis-regulatory genome, while only 43% included a known disease gene and were likely to result from gene dosage effects. In transgenic mice harboring four novel candidate CNVs, we observed altered gene expression in all cases, indicating that the CNVs had a regulatory effect either by changing the enhancer dosage or altering the topological associating domain architecture of the genome.ConclusionOur findings suggest that CNVs affecting noncoding regulatory elements are a major cause of congenital limb malformations.Genetics in Medicine advance online publication, 12 October 2017; doi:10.1038/gim.2017.154.

Improved PCR-Based Detection of Soil Transmitted Helminth Infections Using a Next-Generation Sequencing Approach to Assay Design.

PubMed

Pilotte, Nils; Papaiakovou, Marina; Grant, Jessica R; Bierwert, Lou Ann; Llewellyn, Stacey; McCarthy, James S; Williams, Steven A

2016-03-01

The soil transmitted helminths are a group of parasitic worms responsible for extensive morbidity in many of the world's most economically depressed locations. With growing emphasis on disease mapping and eradication, the availability of accurate and cost-effective diagnostic measures is of paramount importance to global control and elimination efforts. While real-time PCR-based molecular detection assays have shown great promise, to date, these assays have utilized sub-optimal targets. By performing next-generation sequencing-based repeat analyses, we have identified high copy-number, non-coding DNA sequences from a series of soil transmitted pathogens. We have used these repetitive DNA elements as targets in the development of novel, multi-parallel, PCR-based diagnostic assays. Utilizing next-generation sequencing and the Galaxy-based RepeatExplorer web server, we performed repeat DNA analysis on five species of soil transmitted helminths (Necator americanus, Ancylostoma duodenale, Trichuris trichiura, Ascaris lumbricoides, and Strongyloides stercoralis). Employing high copy-number, non-coding repeat DNA sequences as targets, novel real-time PCR assays were designed, and assays were tested against established molecular detection methods. Each assay provided consistent detection of genomic DNA at quantities of 2 fg or less, demonstrated species-specificity, and showed an improved limit of detection over the existing, proven PCR-based assay. The utilization of next-generation sequencing-based repeat DNA analysis methodologies for the identification of molecular diagnostic targets has the ability to improve assay species-specificity and limits of detection. By exploiting such high copy-number repeat sequences, the assays described here will facilitate soil transmitted helminth diagnostic efforts. We recommend similar analyses when designing PCR-based diagnostic tests for the detection of other eukaryotic pathogens.

Impact of Noncoding Satellite Repeats on Pancreatic Cancer Metastasis

DTIC Science & Technology

2015-11-01

in 2D and Xenografts . B) Panel of cancer cell lines grown in 2D or 3D culture. 5 cancers (Fig. 3). We have completed RNA-seq analysis of 2D and 3D...reverse transcribed (RT) as a means to expand these regions in tumor genomes. We evaluated the presence of HSATII RT products by treating xenograft small...specific for satellite repeats in human cells. These RNA derived DNAs (rdDNA) are found in primary tumors, xenografts , and tumorspheres in large

A Trio of Human Molecular Genetics PCR Assays

ERIC Educational Resources Information Center

Reinking, Jeffrey L.; Waldo, Jennifer T.; Dinsmore, Jannett

2013-01-01

This laboratory exercise demonstrates three different analytical forms of the polymerase chain reaction (PCR) that allow students to genotype themselves at four different loci. Here, we present protocols to allow students to a) genotype a non-coding polymorphic Variable Number of Tandem Repeat (VNTR) locus on human chromosome 5 using conventional…

DDM1 represses noncoding RNA expression and RNA-directed DNA methylation in heterochromatin.

PubMed

Tan, Feng; Lu, Yue; Jiang, Wei; Zhao, Yu; Wu, Tian; Zhang, Ruoyu; Zhou, Dao-Xiu

2018-05-24

Cytosine methylation of DNA, which occurs at CG, CHG, and CHH (H=A, C, or T) sequences in plants, is a hallmark for epigenetic repression of repetitive sequences. The chromatin remodeling factor DECREASE IN DNA METHYLATION1 (DDM1) is essential for DNA methylation, especially at CG and CHG sequences. However, its potential role in RNA-directed DNA methylation (RdDM) and in chromatin function is not completely understood in rice (Oryza sativa). In this work, we used high-throughput approaches to study the function of rice DDM1 (OsDDM1) in RdDM and the expression of non-coding RNA (ncRNA). We show that loss of function of OsDDM1 results in ectopic CHH methylation of transposable elements and repeats. The ectopic CHH methylation was dependent on rice DOMAINS REARRANGED METHYLTRANSFERASE2 (OsDRM2), a DNA methyltransferase involved in RdDM. Mutations in OsDDM1 lead to decreases of histone H3K9me2 and increases in the levels of heterochromatic small RNA (sRNA) and long noncoding RNA (lncRNA). In particular, OsDDM1 was found to be essential to repress transcription of the two repetitive sequences, Centromeric Retrotransposons of Rice1 (CRR1) and the dominant centromeric CentO repeats. These results suggest that OsDDM1 antagonizes RdDM at heterochromatin and represses tissue-specific expression of ncRNA from repetitive sequences in the rice genome. {copyright, serif} 2018 American Society of Plant Biologists. All rights reserved.

The primary structures of two yeast enolase genes. Homology between the 5' noncoding flanking regions of yeast enolase and glyceraldehyde-3-phosphate dehydrogenase genes.

PubMed

Holland, M J; Holland, J P; Thill, G P; Jackson, K A

1981-02-10

Segments of yeast genomic DNA containing two enolase structural genes have been isolated by subculture cloning procedures using a cDNA hybridization probe synthesized from purified yeast enolase mRNA. Based on restriction endonuclease and transcriptional maps of these two segments of yeast DNA, each hybrid plasmid contains a region of extensive nucleotide sequence homology which forms hybrids with the cDNA probe. The DNA sequences which flank this homologous region in the two hybrid plasmids are nonhomologous indicating that these sequences are nontandemly repeated in the yeast genome. The complete nucleotide sequence of the coding as well as the flanking noncoding regions of these genes has been determined. The amino acid sequence predicted from one reading frame of both structural genes is extremely similar to that determined for yeast enolase (Chin, C. C. Q., Brewer, J. M., Eckard, E., and Wold, F. (1981) J. Biol. Chem. 256, 1370-1376), confirming that these isolated structural genes encode yeast enolase. The nucleotide sequences of the coding regions of the genes are approximately 95% homologous, and neither gene contains an intervening sequence. Codon utilization in the enolase genes follows the same biased pattern previously described for two yeast glyceraldehyde-3-phosphate dehydrogenase structural genes (Holland, J. P., and Holland, M. J. (1980) J. Biol. Chem. 255, 2596-2605). DNA blotting analysis confirmed that the isolated segments of yeast DNA are colinear with yeast genomic DNA and that there are two nontandemly repeated enolase genes per haploid yeast genome. The noncoding portions of the two enolase genes adjacent to the initiation and termination codons are approximately 70% homologous and contain sequences thought to be involved in the synthesis and processing messenger RNA. Finally there are regions of extensive homology between the two enolase structural genes and two yeast glyceraldehyde-3-phosphate dehydrogenase structural genes within the 5- noncoding portions of these glycolytic genes.

DNA topoisomerase 1α promotes transcriptional silencing of transposable elements through DNA methylation and histone lysine 9 dimethylation in Arabidopsis.

PubMed

Dinh, Thanh Theresa; Gao, Lei; Liu, Xigang; Li, Dongming; Li, Shengben; Zhao, Yuanyuan; O'Leary, Michael; Le, Brandon; Schmitz, Robert J; Manavella, Pablo A; Manavella, Pablo; Li, Shaofang; Weigel, Detlef; Pontes, Olga; Ecker, Joseph R; Chen, Xuemei

2014-07-01

RNA-directed DNA methylation (RdDM) and histone H3 lysine 9 dimethylation (H3K9me2) are related transcriptional silencing mechanisms that target transposable elements (TEs) and repeats to maintain genome stability in plants. RdDM is mediated by small and long noncoding RNAs produced by the plant-specific RNA polymerases Pol IV and Pol V, respectively. Through a chemical genetics screen with a luciferase-based DNA methylation reporter, LUCL, we found that camptothecin, a compound with anti-cancer properties that targets DNA topoisomerase 1α (TOP1α) was able to de-repress LUCL by reducing its DNA methylation and H3K9me2 levels. Further studies with Arabidopsis top1α mutants showed that TOP1α silences endogenous RdDM loci by facilitating the production of Pol V-dependent long non-coding RNAs, AGONAUTE4 recruitment and H3K9me2 deposition at TEs and repeats. This study assigned a new role in epigenetic silencing to an enzyme that affects DNA topology.

Whole-genome sequencing reveals a coding non-pathogenic variant tagging a non-coding pathogenic hexanucleotide repeat expansion in C9orf72 as cause of amyotrophic lateral sclerosis.

PubMed

Herdewyn, Sarah; Zhao, Hui; Moisse, Matthieu; Race, Valérie; Matthijs, Gert; Reumers, Joke; Kusters, Benno; Schelhaas, Helenius J; van den Berg, Leonard H; Goris, An; Robberecht, Wim; Lambrechts, Diether; Van Damme, Philip

2012-06-01

Motor neuron degeneration in amyotrophic lateral sclerosis (ALS) has a familial cause in 10% of patients. Despite significant advances in the genetics of the disease, many families remain unexplained. We performed whole-genome sequencing in five family members from a pedigree with autosomal-dominant classical ALS. A family-based elimination approach was used to identify novel coding variants segregating with the disease. This list of variants was effectively shortened by genotyping these variants in 2 additional unaffected family members and 1500 unrelated population-specific controls. A novel rare coding variant in SPAG8 on chromosome 9p13.3 segregated with the disease and was not observed in controls. Mutations in SPAG8 were not encountered in 34 other unexplained ALS pedigrees, including 1 with linkage to chromosome 9p13.2-23.3. The shared haplotype containing the SPAG8 variant in this small pedigree was 22.7 Mb and overlapped with the core 9p21 linkage locus for ALS and frontotemporal dementia. Based on differences in coverage depth of known variable tandem repeat regions between affected and non-affected family members, the shared haplotype was found to contain an expanded hexanucleotide (GGGGCC)(n) repeat in C9orf72 in the affected members. Our results demonstrate that rare coding variants identified by whole-genome sequencing can tag a shared haplotype containing a non-coding pathogenic mutation and that changes in coverage depth can be used to reveal tandem repeat expansions. It also confirms (GGGGCC)n repeat expansions in C9orf72 as a cause of familial ALS.

Comparison of simple sequence repeats in 19 Archaea.

PubMed

Trivedi, S

2006-12-05

All organisms that have been studied until now have been found to have differential distribution of simple sequence repeats (SSRs), with more SSRs in intergenic than in coding sequences. SSR distribution was investigated in Archaea genomes where complete chromosome sequences of 19 Archaea were analyzed with the program SPUTNIK to find di- to penta-nucleotide repeats. The number of repeats was determined for the complete chromosome sequences and for the coding and non-coding sequences. Different from what has been found for other groups of organisms, there is an abundance of SSRs in coding regions of the genome of some Archaea. Dinucleotide repeats were rare and CG repeats were found in only two Archaea. In general, trinucleotide repeats are the most abundant SSR motifs; however, pentanucleotide repeats are abundant in some Archaea. Some of the tetranucleotide and pentanucleotide repeat motifs are organism specific. In general, repeats are short and CG-rich repeats are present in Archaea having a CG-rich genome. Among the 19 Archaea, SSR density was not correlated with genome size or with optimum growth temperature. Pentanucleotide density had an inverse correlation with the CG content of the genome.

A-to-I editing of coding and non-coding RNAs by ADARs

PubMed Central

Nishikura, Kazuko

2016-01-01

Adenosine deaminases acting on RNA (ADARs) convert adenosine to inosine in double-stranded RNA. This A-to-I editing occurs not only in protein-coding regions of mRNAs, but also frequently in non-coding regions that contain inverted Alu repeats. Editing of coding sequences can result in the expression of functionally altered proteins that are not encoded in the genome, whereas the significance of Alu editing remains largely unknown. Certain microRNA (miRNA) precursors are also edited, leading to reduced expression or altered function of mature miRNAs. Conversely, recent studies indicate that ADAR1 forms a complex with Dicer to promote miRNA processing, revealing a new function of ADAR1 in the regulation of RNA interference. PMID:26648264

Complete mitochondrial genome of the whiter-spotted flower chafer, Protaetia brevitarsis (Coleoptera: Scarabaeidae).

PubMed

Kim, Min Jee; Im, Hyun Hwak; Lee, Kwang Youll; Han, Yeon Soo; Kim, Iksoo

2014-06-01

Abstract The complete nucleotide sequences of the mitochondrial genome from the whiter-spotted flower chafer, Protaetia brevitarsis (Coleoptera: Scarabaeidae), was determined. The 20,319-bp long circular genome is the longest among completely sequenced Coleoptera. As is typical in animals, the P. brevitarsis genome consisted of two ribosomal RNAs, 22 transfer RNAs, 13 protein-coding genes and one A + T-rich region. Although the size of the coding genes was typical, the non-coding A + T-rich region was 5654 bp, which is the longest in insects. The extraordinary length of this region was composed of 28,117-bp tandem repeats and 782-bp tandem repeats. These repeat sequences were encompassed by three non-repeat sequences constituting 1804 bp.

Comparative sequence analysis of the X-inactivation center region in mouse, human, and bovine.

PubMed

Chureau, Corinne; Prissette, Marine; Bourdet, Agnès; Barbe, Valérie; Cattolico, Laurence; Jones, Louis; Eggen, André; Avner, Philip; Duret, Laurent

2002-06-01

We have sequenced to high levels of accuracy 714-kb and 233-kb regions of the mouse and bovine X-inactivation centers (Xic), respectively, centered on the Xist gene. This has provided the basis for a fully annotated comparative analysis of the mouse Xic with the 2.3-Mb orthologous region in human and has allowed a three-way species comparison of the core central region, including the Xist gene. These comparisons have revealed conserved genes, both coding and noncoding, conserved CpG islands and, more surprisingly, conserved pseudogenes. The distribution of repeated elements, especially LINE repeats, in the mouse Xic region when compared to the rest of the genome does not support the hypothesis of a role for these repeat elements in the spreading of X inactivation. Interestingly, an asymmetric distribution of LINE elements on the two DNA strands was observed in the three species, not only within introns but also in intergenic regions. This feature is suggestive of important transcriptional activity within these intergenic regions. In silico prediction followed by experimental analysis has allowed four new genes, Cnbp2, Ftx, Jpx, and Ppnx, to be identified and novel, widespread, complex, and apparently noncoding transcriptional activity to be characterized in a region 5' of Xist that was recently shown to attract histone modification early after the onset of X inactivation.

Complete Genome Sequences of Four Isolates of Plutella xylostella Granulovirus.

PubMed

Spence, Robert J; Noune, Christopher; Hauxwell, Caroline

2016-06-30

Granuloviruses are widespread pathogens of Plutella xylostella L. (diamondback moth) and potential biopesticides for control of this global insect pest. We report the complete genomes of four Plutella xylostella granulovirus isolates from China, Malaysia, and Taiwan exhibiting pairs of noncoding, homologous repeat regions with significant sequence variation but equivalent length. Copyright © 2016 Spence et al.

CRISPR/Cas9-mediated noncoding RNA editing in human cancers.

PubMed

Yang, Jie; Meng, Xiaodan; Pan, Jinchang; Jiang, Nan; Zhou, Chengwei; Wu, Zhenhua; Gong, Zhaohui

2018-01-02

Cancer is characterized by multiple genetic and epigenetic alterations, including a higher prevalence of mutations of oncogenes and/or tumor suppressors. Mounting evidences have shown that noncoding RNAs (ncRNAs) are involved in the epigenetic regulation of cancer genes and their associated pathways. The clustered regularly interspaced short palindromic repeats (CRISPR)-associated nuclease 9 (CRISPR/Cas9) system, a revolutionary genome-editing technology, has shed light on ncRNA-based cancer therapy. Here, we briefly introduce the classifications and mechanisms of CRISPR/Cas9 system. Importantly, we mainly focused on the applications of CRISPR/Cas9 system as a molecular tool for ncRNA (microRNA, long noncoding RNA and circular RNA, etc.) editing in human cancers, and the novel techniques that are based on CRISPR/Cas9 system. Additionally, the off-target effects and the corresponding solutions as well as the challenges toward CRISPR/Cas9 were also evaluated and discussed. Long- and short-ncRNAs have been employed as targets in precision oncology, and CRISPR/Cas9-mediated ncRNA editing may provide an excellent way to cure cancer.

Live-cell imaging of budding yeast telomerase RNA and TERRA.

PubMed

Laprade, Hadrien; Lalonde, Maxime; Guérit, David; Chartrand, Pascal

2017-02-01

In most eukaryotes, the ribonucleoprotein complex telomerase is responsible for maintaining telomere length. In recent years, single-cell microscopy techniques such as fluorescent in situ hybridization and live-cell imaging have been developed to image the RNA subunit of the telomerase holoenzyme. These techniques are now becoming important tools for the study of telomerase biogenesis, its association with telomeres and its regulation. Here, we present detailed protocols for live-cell imaging of the Saccharomyces cerevisiae telomerase RNA subunit, called TLC1, and also of the non-coding telomeric repeat-containing RNA TERRA. We describe the approach used for genomic integration of MS2 stem-loops in these transcripts, and provide information for optimal live-cell imaging of these non-coding RNAs. Copyright © 2016 Elsevier Inc. All rights reserved.

Comparison of small molecules and oligonucleotides that target a toxic, non-coding RNA.

PubMed

Costales, Matthew G; Rzuczek, Suzanne G; Disney, Matthew D

2016-06-01

Potential RNA targets for chemical probes and therapeutic modalities are pervasive in the transcriptome. Oligonucleotide-based therapeutics are commonly used to target RNA sequence. Small molecules are emerging as a modality to target RNA structures selectively, but their development is still in its infancy. In this work, we compare the activity of oligonucleotides and several classes of small molecules that target the non-coding r(CCUG) repeat expansion (r(CCUG)(exp)) that causes myotonic dystrophy type 2 (DM2), an incurable disease that is the second-most common cause of adult onset muscular dystrophy. Small molecule types investigated include monomers, dimers, and multivalent compounds synthesized on-site by using RNA-templated click chemistry. Oligonucleotides investigated include phosphorothioates that cleave their target and vivo-morpholinos that modulate target RNA activity via binding. We show that compounds assembled on-site that recognize structure have the highest potencies amongst small molecules and are similar in potency to a vivo-morpholino modified oligonucleotide that targets sequence. These studies are likely to impact the design of therapeutic modalities targeting other repeats expansions that cause fragile X syndrome and amyotrophic lateral sclerosis, for example. Copyright © 2016. Published by Elsevier Ltd.

Endogenous siRNAs and noncoding RNA-derived small RNAs are expressed in adult mouse hippocampus and are up-regulated in olfactory discrimination training.

PubMed

Smalheiser, Neil R; Lugli, Giovanni; Thimmapuram, Jyothi; Cook, Edwin H; Larson, John

2011-01-01

We previously proposed that endogenous siRNAs may regulate synaptic plasticity and long-term gene expression in the mammalian brain. Here, a hippocampal-dependent task was employed in which adult mice were trained to execute a nose-poke in a port containing one of two simultaneously present odors in order to obtain a reward. Mice demonstrating olfactory discrimination training were compared to pseudo-training and nose-poke control groups; size-selected hippocampal RNA was subjected to Illumina deep sequencing. Sequences that aligned uniquely and exactly to the genome without uncertain nucleotide assignments, within exons or introns of MGI annotated genes, were examined further. The data confirm that small RNAs having features of endogenous siRNAs are expressed in brain; that many of them derive from genes that regulate synaptic plasticity (and have been implicated in neuropsychiatric diseases); and that hairpin-derived endo-siRNAs and the 20- to 23-nt size class of small RNAs show a significant increase during an early stage of training. The most abundant putative siRNAs arose from an intronic inverted repeat within the SynGAP1 locus; this inverted repeat was a substrate for dicer in vitro, and SynGAP1 siRNA was specifically associated with Argonaute proteins in vivo. Unexpectedly, a dramatic increase with training (more than 100-fold) was observed for a class of 25- to 30-nt small RNAs derived from specific sites within snoRNAs and abundant noncoding RNAs (Y1 RNA, RNA component of mitochondrial RNAse P, 28S rRNA, and 18S rRNA). Further studies are warranted to characterize the role(s) played by endogenous siRNAs and noncoding RNA-derived small RNAs in learning and memory.

Virulence Phenotypes of Legionella pneumophila Associated with Noncoding RNA lpr0035

PubMed Central

Jayakumar, Deepak; Early, Julie V.

2012-01-01

The Philadelphia-1 strain of Legionella pneumophila, the causative organism of Legionnaires' disease, contains a recently discovered noncoding RNA, lpr0035. lpr0035 straddles the 5′ chromosomal junction of a 45-kbp mobile genetic element, pLP45, which can exist as an episome or integrated in the bacterial chromosome. A 121-bp deletion was introduced in strain JR32, a Philadelphia-1 derivative. The deletion inactivated lpr0035, removed the 49-bp direct repeat at the 5′ junction of pLP45, and locked pLP45 in the chromosome. Intracellular multiplication of the deletion mutant was decreased by nearly 3 orders of magnitude in Acanthamoeba castellanii amoebae and nearly 2 orders of magnitude in J774 mouse macrophages. Entry of the deletion mutant into amoebae and macrophages was decreased by >70%. The level of entry in both hosts was restored to that in strain JR32 by plasmid copies of two open reading frames immediately downstream of the 5′ junction and plasmid lpr0035 driven by its endogenous promoter. When induced from a tac promoter, plasmid lpr0035 completely reversed the intracellular multiplication defect in macrophages but was without effect in amoebae. These data are the first evidence of a role for noncoding RNA lpr0035, which has homologs in six other Legionella genomes, in entry of L. pneumophila into amoebae and macrophages and in host-specific intracellular multiplication. The data also demonstrate that deletion of a direct-repeat sequence restricts the mobility of pLP45 and is a means of studying the role of pLP45 mobility in Legionella virulence phenotypes. PMID:22966048

Novel variants of the 5S rRNA genes in Eruca sativa.

PubMed

Singh, K; Bhatia, S; Lakshmikumaran, M

1994-02-01

The 5S ribosomal RNA (rRNA) genes of Eruca sativa were cloned and characterized. They are organized into clusters of tandemly repeated units. Each repeat unit consists of a 119-bp coding region followed by a noncoding spacer region that separates it from the coding region of the next repeat unit. Our study reports novel gene variants of the 5S rRNA genes in plants. Two families of the 5S rDNA, the 0.5-kb size family and the 1-kb size family, coexist in the E. sativa genome. The 0.5-kb size family consists of the 5S rRNA genes (S4) that have coding regions similar to those of other reported plant 5S rDNA sequences, whereas the 1-kb size family consists of the 5S rRNA gene variants (S1) that exist as 1-kb BamHI tandem repeats. S1 is made up of two variant units (V1 and V2) of 5S rDNA where the BamHI site between the two units is mutated. Sequence heterogeneity among S4, V1, and V2 units exists throughout the sequence and is not limited to the noncoding spacer region only. The coding regions of V1 and V2 show approximately 20% dissimilarity to the coding regions of S4 and other reported plant 5S rDNA sequences. Such a large variation in the coding regions of the 5S rDNA units within the same plant species has been observed for the first time. Restriction site variation is observed between the two size classes of 5S rDNA in E. sativa.(ABSTRACT TRUNCATED AT 250 WORDS)

The primary transcriptome of the marine diazotroph Trichodesmium erythraeum IMS101

NASA Astrophysics Data System (ADS)

Pfreundt, Ulrike; Kopf, Matthias; Belkin, Natalia; Berman-Frank, Ilana; Hess, Wolfgang R.

2014-08-01

Blooms of the dinitrogen-fixing marine cyanobacterium Trichodesmium considerably contribute to new nitrogen inputs into tropical oceans. Intriguingly, only 60% of the Trichodesmium erythraeum IMS101 genome sequence codes for protein, compared with ~85% in other sequenced cyanobacterial genomes. The extensive non-coding genome fraction suggests space for an unusually high number of unidentified, potentially regulatory non-protein-coding RNAs (ncRNAs). To identify the transcribed fraction of the genome, here we present a genome-wide map of transcriptional start sites (TSS) at single nucleotide resolution, revealing the activity of 6,080 promoters. We demonstrate that T. erythraeum has the highest number of actively splicing group II introns and the highest percentage of TSS yielding ncRNAs of any bacterium examined to date. We identified a highly transcribed retroelement that serves as template repeat for the targeted mutation of at least 12 different genes by mutagenic homing. Our findings explain the non-coding portion of the T. erythraeum genome by the transcription of an unusually high number of non-coding transcripts in addition to the known high incidence of transposable elements. We conclude that riboregulation and RNA maturation-dependent processes constitute a major part of the Trichodesmium regulatory apparatus.

Microwave Characterization of the GaAs MESFET and Development of a Low Noise Microwave Amplifier.

DTIC Science & Technology

1979-12-01

investigation. Comparison of measured scattering parameters with those predicted by this model pro - vide a useful check for the validity of the model. B. Device...tuning co-nditions can be changed and their effects measured without changing the setup con - figuration. Gain or noise figure measurements are selected by...lines. The coaxial sections then transition to precision, sexless 7 mm (type APC-7) con - nectors, which provide highly repeatable connections, and a

Formation of a parallel-stranded DNA homoduplex by d(GGA) repeat oligonucleotides.

PubMed Central

Suda, T; Mishima, Y; Asakura, H; Kominami, R

1995-01-01

The GGA9-H molecules consisting of a double helical stretch followed by a single-stranded 3'-terminal overhang of nine GGA sequence repeats exhibited a gel mobility-shifted band in a concentration-dependent manner, suggestive of the intermolecular complex formation. The position of the shifted band in a gel was almost identical to that of the Y-shaped dimer marker of the same molecular weight that had the two double-helices at one side. This suggests that GGA9-H dimerizes in a parallel orientation without the formation of four-stranded hairpin structure. Since the GGA9-H homoduplex was stably formed at pH 4, 7 and 9, the formation does not require protonation or deprotonation of the N1 position of adenines. Neither does it require the N7 group of guanines responsible for Hoogsteen base pairing from the methylation interference and modification studies. Modification of the N7 group of guanines with dimethyl sulfate (DMS) did not inhibit the association and also the N7 group in the homoduplex was not protected from DMS. On the other hand, the GAA9-H having the G to A base substitution did not show such an association with either GGA9-H or GAA9-H. These results suggest that the homoduplex formation may be due to G.G base pairing through non-Hoogsteen hydrogen bonds. Images PMID:7479009

Photoelectrolytic production of hydrogen using semiconductor electrodes

NASA Technical Reports Server (NTRS)

Byvik, C. E.; Walker, G. H.

1976-01-01

Experimental data for the photoelectrolytic production of hydrogen using GaAs photoanodes was presented. Four types of GaAs anodes were investigated: polished GaAs, GaAs coated with gold, GaAs coated with silver, and GaAs coated with tin. The maximum measured efficiency using a tungsten light source was 8.9 percent for polished GaAs electrodes and 6.3 percent for tin coated GaAs electrodes.

New technologies accelerate the exploration of non-coding RNAs in horticultural plants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Degao; Mewalal, Ritesh; Hu, Rongbin

Non-coding RNAs (ncRNAs), that is, RNAs not translated into proteins, are crucial regulators of a variety of biological processes in plants. While protein-encoding genes have been relatively well-annotated in sequenced genomes, accounting for a small portion of the genome space in plants, the universe of plant ncRNAs is rapidly expanding. Recent advances in experimental and computational technologies have generated a great momentum for discovery and functional characterization of ncRNAs. Here we summarize the classification and known biological functions of plant ncRNAs, review the application of next-generation sequencing (NGS) technology and ribosome profiling technology to ncRNA discovery in horticultural plants andmore » discuss the application of new technologies, especially the new genome-editing tool clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) systems, to functional characterization of plant ncRNAs.« less

Mitochondrial genomes of parasitic flatworms.

PubMed

Le, Thanh H; Blair, David; McManus, Donald P

2002-05-01

Complete or near-complete mitochondrial genomes are now available for 11 species or strains of parasitic flatworms belonging to the Trematoda and the Cestoda. The organization of these genomes is not strikingly different from those of other eumetazoans, although one gene (atp8) commonly found in other phyla is absent from flatworms. The gene order in most flatworms has similarities to those seen in higher protostomes such as annelids. However, the gene order has been drastically altered in Schistosoma mansoni, which obscures this possible relationship. Among the sequenced taxa, base composition varies considerably, creating potential difficulties for phylogeny reconstruction. Long non-coding regions are present in all taxa, but these vary in length from only a few hundred to approximately 10000 nucleotides. Among Schistosoma spp., the long non-coding regions are rich in repeats and length variation among individuals is known. Data from mitochondrial genomes are valuable for studies on species identification, phylogenies and biogeography.

New technologies accelerate the exploration of non-coding RNAs in horticultural plants

PubMed Central

Liu, Degao; Mewalal, Ritesh; Hu, Rongbin; Tuskan, Gerald A; Yang, Xiaohan

2017-01-01

Non-coding RNAs (ncRNAs), that is, RNAs not translated into proteins, are crucial regulators of a variety of biological processes in plants. While protein-encoding genes have been relatively well-annotated in sequenced genomes, accounting for a small portion of the genome space in plants, the universe of plant ncRNAs is rapidly expanding. Recent advances in experimental and computational technologies have generated a great momentum for discovery and functional characterization of ncRNAs. Here we summarize the classification and known biological functions of plant ncRNAs, review the application of next-generation sequencing (NGS) technology and ribosome profiling technology to ncRNA discovery in horticultural plants and discuss the application of new technologies, especially the new genome-editing tool clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) systems, to functional characterization of plant ncRNAs. PMID:28698797

Reptiles and mammals have differentially retained long conserved noncoding sequences from the amniote ancestor.

PubMed

Janes, D E; Chapus, C; Gondo, Y; Clayton, D F; Sinha, S; Blatti, C A; Organ, C L; Fujita, M K; Balakrishnan, C N; Edwards, S V

2011-01-01

Many noncoding regions of genomes appear to be essential to genome function. Conservation of large numbers of noncoding sequences has been reported repeatedly among mammals but not thus far among birds and reptiles. By searching genomes of chicken (Gallus gallus), zebra finch (Taeniopygia guttata), and green anole (Anolis carolinensis), we quantified the conservation among birds and reptiles and across amniotes of long, conserved noncoding sequences (LCNS), which we define as sequences ≥500 bp in length and exhibiting ≥95% similarity between species. We found 4,294 LCNS shared between chicken and zebra finch and 574 LCNS shared by the two birds and Anolis. The percent of genomes comprised by LCNS in the two birds (0.0024%) is notably higher than the percent in mammals (<0.0003% to <0.001%), differences that we show may be explained in part by differences in genome-wide substitution rates. We reconstruct a large number of LCNS for the amniote ancestor (ca. 8,630) and hypothesize differential loss and substantial turnover of these sites in descendent lineages. By contrast, we estimated a small role for recruitment of LCNS via acquisition of novel functions over time. Across amniotes, LCNS are significantly enriched with transcription factor binding sites for many developmental genes, and 2.9% of LCNS shared between the two birds show evidence of expression in brain expressed sequence tag databases. These results show that the rate of retention of LCNS from the amniote ancestor differs between mammals and Reptilia (including birds) and that this may reflect differing roles and constraints in gene regulation.

Reptiles and Mammals Have Differentially Retained Long Conserved Noncoding Sequences from the Amniote Ancestor

PubMed Central

Janes, D.E.; Chapus, C.; Gondo, Y.; Clayton, D.F.; Sinha, S.; Blatti, C.A.; Organ, C.L.; Fujita, M.K.; Balakrishnan, C.N.; Edwards, S.V.

2010-01-01

Many noncoding regions of genomes appear to be essential to genome function. Conservation of large numbers of noncoding sequences has been reported repeatedly among mammals but not thus far among birds and reptiles. By searching genomes of chicken (Gallus gallus), zebra finch (Taeniopygia guttata), and green anole (Anolis carolinensis), we quantified the conservation among birds and reptiles and across amniotes of long, conserved noncoding sequences (LCNS), which we define as sequences ≥500 bp in length and exhibiting ≥95% similarity between species. We found 4,294 LCNS shared between chicken and zebra finch and 574 LCNS shared by the two birds and Anolis. The percent of genomes comprised by LCNS in the two birds (0.0024%) is notably higher than the percent in mammals (<0.0003% to <0.001%), differences that we show may be explained in part by differences in genome-wide substitution rates. We reconstruct a large number of LCNS for the amniote ancestor (ca. 8,630) and hypothesize differential loss and substantial turnover of these sites in descendent lineages. By contrast, we estimated a small role for recruitment of LCNS via acquisition of novel functions over time. Across amniotes, LCNS are significantly enriched with transcription factor binding sites for many developmental genes, and 2.9% of LCNS shared between the two birds show evidence of expression in brain expressed sequence tag databases. These results show that the rate of retention of LCNS from the amniote ancestor differs between mammals and Reptilia (including birds) and that this may reflect differing roles and constraints in gene regulation. PMID:21183607

Complete mitochondrial genome of the Tyto longimembris (Strigiformes: Tytonidae).

PubMed

Xu, Peng; Li, Yankuo; Miao, Lujun; Xie, Guangyong; Huang, Yan

2016-07-01

The complete mitochondrial genome of Tyto longimembris has been determined in this study. It is 18,466 bp in length and consists of 13 protein-coding genes, 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes and a non-coding control region (D-loop). The overall base composition of the heavy strand of the T. longimembris mitochondrial genome is A: 30.1%, T: 23.5%, C: 31.8% and G: 14.6%. The structure of control region should be characterized by a region containing tandem repeats as two definitely separated clusters of tandem repeats were found. This study provided an important data set for phylogenetic and taxonomic analyses of Tyto species.

Genomic Editing of Non-Coding RNA Genes with CRISPR/Cas9 Ushers in a Potential Novel Approach to Study and Treat Schizophrenia

PubMed Central

Zhuo, Chuanjun; Hou, Weihong; Hu, Lirong; Lin, Chongguang; Chen, Ce; Lin, Xiaodong

2017-01-01

Schizophrenia is a genetically related mental illness, in which the majority of genetic alterations occur in the non-coding regions of the human genome. In the past decade, a growing number of regulatory non-coding RNAs (ncRNAs) including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) have been identified to be strongly associated with schizophrenia. However, the studies of these ncRNAs in the pathophysiology of schizophrenia and the reverting of their genetic defects in restoration of the normal phenotype have been hampered by insufficient technology to manipulate these ncRNA genes effectively as well as a lack of appropriate animal models. Most recently, a revolutionary gene editing technology known as Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated nuclease 9 (Cas9; CRISPR/Cas9) has been developed that enable researchers to overcome these challenges. In this review article, we mainly focus on the schizophrenia-related ncRNAs and the use of CRISPR/Cas9-mediated editing on the non-coding regions of the genomic DNA in proving causal relationship between the genetic defects and the pathophysiology of schizophrenia. We subsequently discuss the potential of translating this advanced technology into a clinical therapy for schizophrenia, although the CRISPR/Cas9 technology is currently still in its infancy and immature to put into use in the treatment of diseases. Furthermore, we suggest strategies to accelerate the pace from the bench to the bedside. This review describes the application of the powerful and feasible CRISPR/Cas9 technology to manipulate schizophrenia-associated ncRNA genes. This technology could help researchers tackle this complex health problem and perhaps other genetically related mental disorders due to the overlapping genetic alterations of schizophrenia with other mental illnesses. PMID:28217082

Antibody-mediated enzyme replacement therapy targeting both lysosomal and cytoplasmic glycogen in Pompe disease.

PubMed

Yi, Haiqing; Sun, Tao; Armstrong, Dustin; Borneman, Scott; Yang, Chunyu; Austin, Stephanie; Kishnani, Priya S; Sun, Baodong

2017-05-01

Pompe disease is characterized by accumulation of both lysosomal and cytoplasmic glycogen primarily in skeletal and cardiac muscles. Mannose-6-phosphate receptor-mediated enzyme replacement therapy (ERT) with recombinant human acid α-glucosidase (rhGAA) targets the enzyme to lysosomes and thus is unable to digest cytoplasmic glycogen. Studies have shown that anti-DNA antibody 3E10 penetrates living cells and delivers "cargo" proteins to the cytosol or nucleus via equilibrative nucleoside transporter ENT2. We speculate that 3E10-mediated ERT with GAA will target both lysosomal and cytoplasmic glycogen in Pompe disease. A fusion protein (FabGAA) containing a humanized Fab fragment derived from the murine 3E10 antibody and the 110 kDa human GAA precursor was constructed and produced in CHO cells. Immunostaining with an anti-Fab antibody revealed that the Fab signals did not co-localize with the lysosomal marker LAMP2 in cultured L6 myoblasts or Pompe patient fibroblasts after incubation with FabGAA. Western blot with an anti-GAA antibody showed presence of the 150 kDa full-length FabGAA in the cell lysates, in addition to the 95- and 76 kDa processed forms of GAA that were also seen in the rhGAA-treated cells. Blocking of mannose-6-phosphate receptor with mannose-6-phosphate markedly reduced the 95- and the 76 kDa forms but not the 150 kDa form. In GAA-KO mice, FabGAA achieved similar treatment efficacy as rhGAA at an equal molar dose in reducing tissue glycogen contents. Our data suggest that FabGAA retains the ability of rhGAA to treat lysosomal glycogen accumulation and has the beneficial potential over rhGAA to reduce cytoplasmic glycogen storage in Pompe disease. FabGAA can be delivered to both the cytoplasm and lysosomes in cultured cells. FabGAA equally reduced lysosomal glycogen accumulation as rhGAA in GAA-KO mice. FabGAA has the beneficial potential over rhGAA to clear cytoplasmic glycogen. This study suggests a novel antibody-enzyme fusion protein therapy for Pompe disease.

Complete mitochondrial genome of the larch hawk moth, Sphinx morio (Lepidoptera: Sphingidae).

PubMed

Kim, Min Jee; Choi, Sei-Woong; Kim, Iksoo

2013-12-01

The larch hawk moth, Sphinx morio, belongs to the lepidopteran family Sphingidae that has long been studied as a family of model insects in a diverse field. In this study, we describe the complete mitochondrial genome (mitogenome) sequences of the species in terms of general genomic features and characteristic short repetitive sequences found in the A + T-rich region. The 15,299-bp-long genome consisted of a typical set of genes (13 protein-coding genes, 2 rRNA genes, and 22 tRNA genes) and one major non-coding A + T-rich region, with the typical arrangement found in Lepidoptera. The 316-bp-long A + T-rich region located between srRNA and tRNA(Met) harbored the conserved sequence blocks that are typically found in lepidopteran insects. Additionally, the A + T-rich region of S. morio contained three characteristic repeat sequences that are rarely found in Lepidoptera: two identical 12-bp repeat, three identical 5-bp-long tandem repeat, and six nearly identical 5-6 bp long repeat sequences.

De novo transcriptome sequencing reveals a considerable bias in the incidence of simple sequence repeats towards the downstream of 'Pre-miRNAs' of black pepper.

PubMed

Joy, Nisha; Asha, Srinivasan; Mallika, Vijayan; Soniya, Eppurathu Vasudevan

2013-01-01

Next generation sequencing has an advantageon transformational development of species with limited available sequence data as it helps to decode the genome and transcriptome. We carried out the de novo sequencing using illuminaHiSeq™ 2000 to generate the first leaf transcriptome of black pepper (Piper nigrum L.), an important spice variety native to South India and also grown in other tropical regions. Despite the economic and biochemical importance of pepper, a scientifically rigorous study at the molecular level is far from complete due to lack of sufficient sequence information and cytological complexity of its genome. The 55 million raw reads obtained, when assembled using Trinity program generated 2,23,386 contigs and 1,28,157 unigenes. Reports suggest that the repeat-rich genomic regions give rise to small non-coding functional RNAs. MicroRNAs (miRNAs) are the most abundant type of non-coding regulatory RNAs. In spite of the widespread research on miRNAs, little is known about the hair-pin precursors of miRNAs bearing Simple Sequence Repeats (SSRs). We used the array of transcripts generated, for the in silico prediction and detection of '43 pre-miRNA candidates bearing different types of SSR motifs'. The analysis identified 3913 different types of SSR motifs with an average of one SSR per 3.04 MB of thetranscriptome. About 0.033% of the transcriptome constituted 'pre-miRNA candidates bearing SSRs'. The abundance, type and distribution of SSR motifs studied across the hair-pin miRNA precursors, showed a significant bias in the position of SSRs towards the downstream of predicted 'pre-miRNA candidates'. The catalogue of transcripts identified, together with the demonstration of reliable existence of SSRs in the miRNA precursors, permits future opportunities for understanding the genetic mechanism of black pepper and likely functions of 'tandem repeats' in miRNAs.

Impact of Noncoding Satellite Repeats on Pancreatic Cancer Metastasis

DTIC Science & Technology

2014-09-01

nucleoside reverse transcriptase inhibitor ddC as a small molecule inhibitor of HSATII reverse transcription. Initial data indicates there are anti...proliferative effects of ddC in cancer cell lines. We will evaluate ddC and anti-sense locked nucleic acids as methods for inhibiting this process and...of these hybrids, we tested the effect of the nucleoside analog RT inhibitor (NRTI) 2’,3’-dideoxycytidine ( ddC ) in COLO205 cells (Fig. 2e). Notably

The complete mitochondrial genome of the Giant Manta ray, Manta birostris.

PubMed

Hinojosa-Alvarez, Silvia; Díaz-Jaimes, Pindaro; Marcet-Houben, Marina; Gabaldón, Toni

2015-01-01

The complete mitochondrial genome of the giant manta ray (Manta birostris), consists of 18,075 bp with rich A + T and low G content. Gene organization and length is similar to other species of ray. It comprises of 13 protein-coding genes, 2 rRNAs genes, 23 tRNAs genes and 1 non-coding sequence, and the control region. We identified an AT tandem repeat region, similar to that reported in Mobula japanica.

Comparative Sequence Analysis of the X-Inactivation Center Region in Mouse, Human, and Bovine

PubMed Central

Chureau, Corinne; Prissette, Marine; Bourdet, Agnès; Barbe, Valérie; Cattolico, Laurence; Jones, Louis; Eggen, André; Avner, Philip; Duret, Laurent

2002-01-01

We have sequenced to high levels of accuracy 714-kb and 233-kb regions of the mouse and bovine X-inactivation centers (Xic), respectively, centered on the Xist gene. This has provided the basis for a fully annotated comparative analysis of the mouse Xic with the 2.3-Mb orthologous region in human and has allowed a three-way species comparison of the core central region, including the Xist gene. These comparisons have revealed conserved genes, both coding and noncoding, conserved CpG islands and, more surprisingly, conserved pseudogenes. The distribution of repeated elements, especially LINE repeats, in the mouse Xic region when compared to the rest of the genome does not support the hypothesis of a role for these repeat elements in the spreading of X inactivation. Interestingly, an asymmetric distribution of LINE elements on the two DNA strands was observed in the three species, not only within introns but also in intergenic regions. This feature is suggestive of important transcriptional activity within these intergenic regions. In silico prediction followed by experimental analysis has allowed four new genes, Cnbp2, Ftx, Jpx, and Ppnx, to be identified and novel, widespread, complex, and apparently noncoding transcriptional activity to be characterized in a region 5′ of Xist that was recently shown to attract histone modification early after the onset of X inactivation. [The sequence data described in this paper have been submitted to the EMBL data library under accession nos. AJ421478, AJ421479, AJ421480, and AJ421481. Online supplemental data are available at http://pbil.univ-lyon1.fr/datasets/Xic2002/data.html and www.genome.org.] PMID:12045143

Comprehensive analysis of gene expression patterns in Friedreich's ataxia fibroblasts by RNA sequencing reveals altered levels of protein synthesis factors and solute carriers

PubMed Central

Li, Yanjie; Lu, Yue; Lin, Kevin; Hauser, Lauren A.; Lynch, David R.

2017-01-01

ABSTRACT Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disease usually caused by large homozygous expansions of GAA repeat sequences in intron 1 of the frataxin (FXN) gene. FRDA patients homozygous for GAA expansions have low FXN mRNA and protein levels when compared with heterozygous carriers or healthy controls. Frataxin is a mitochondrial protein involved in iron–sulfur cluster synthesis, and many FRDA phenotypes result from deficiencies in cellular metabolism due to lowered expression of FXN. Presently, there is no effective treatment for FRDA, and biomarkers to measure therapeutic trial outcomes and/or to gauge disease progression are lacking. Peripheral tissues, including blood cells, buccal cells and skin fibroblasts, can readily be isolated from FRDA patients and used to define molecular hallmarks of disease pathogenesis. For instance, FXN mRNA and protein levels as well as FXN GAA-repeat tract lengths are routinely determined using all of these cell types. However, because these tissues are not directly involved in disease pathogenesis, their relevance as models of the molecular aspects of the disease is yet to be decided. Herein, we conducted unbiased RNA sequencing to profile the transcriptomes of fibroblast cell lines derived from 18 FRDA patients and 17 unaffected control individuals. Bioinformatic analyses revealed significantly upregulated expression of genes encoding plasma membrane solute carrier proteins in FRDA fibroblasts. Conversely, the expression of genes encoding accessory factors and enzymes involved in cytoplasmic and mitochondrial protein synthesis was consistently decreased in FRDA fibroblasts. Finally, comparison of genes differentially expressed in FRDA fibroblasts to three previously published gene expression signatures defined for FRDA blood cells showed substantial overlap between the independent datasets, including correspondingly deficient expression of antioxidant defense genes. Together, these results indicate that gene expression profiling of cells derived from peripheral tissues can, in fact, consistently reveal novel molecular pathways of the disease. When performed on statistically meaningful sample group sizes, unbiased global profiling analyses utilizing peripheral tissues are critical for the discovery and validation of FRDA disease biomarkers. PMID:29125828

Processing of double-R-loops in (CAG)·(CTG) and C9orf72 (GGGGCC)·(GGCCCC) repeats causes instability

PubMed Central

Reddy, Kaalak; Schmidt, Monika H.M.; Geist, Jaimie M.; Thakkar, Neha P.; Panigrahi, Gagan B.; Wang, Yuh-Hwa; Pearson, Christopher E.

2014-01-01

R-loops, transcriptionally-induced RNA:DNA hybrids, occurring at repeat tracts (CTG)n, (CAG)n, (CGG)n, (CCG)n and (GAA)n, are associated with diseases including myotonic dystrophy, Huntington's disease, fragile X and Friedreich's ataxia. Many of these repeats are bidirectionally transcribed, allowing for single- and double-R-loop configurations, where either or both DNA strands may be RNA-bound. R-loops can trigger repeat instability at (CTG)·(CAG) repeats, but the mechanism of this is unclear. We demonstrate R-loop-mediated instability through processing of R-loops by HeLa and human neuron-like cell extracts. Double-R-loops induced greater instability than single-R-loops. Pre-treatment with RNase H only partially suppressed instability, supporting a model in which R-loops directly generate instability by aberrant processing, or via slipped-DNA formation upon RNA removal and its subsequent aberrant processing. Slipped-DNAs were observed to form following removal of the RNA from R-loops. Since transcriptionally-induced R-loops can occur in the absence of DNA replication, R-loop processing may be a source of repeat instability in the brain. Double-R-loop formation and processing to instability was extended to the expanded C9orf72 (GGGGCC)·(GGCCCC) repeats, known to cause amyotrophic lateral sclerosis and frontotemporal dementia, providing the first suggestion through which these repeats may become unstable. These findings provide a mechanistic basis for R-loop-mediated instability at disease-associated repeats. PMID:25147206

New PAH gene promoter KLF1 and 3'-region C/EBPalpha motifs influence transcription in vitro.

PubMed

Klaassen, Kristel; Stankovic, Biljana; Kotur, Nikola; Djordjevic, Maja; Zukic, Branka; Nikcevic, Gordana; Ugrin, Milena; Spasovski, Vesna; Srzentic, Sanja; Pavlovic, Sonja; Stojiljkovic, Maja

2017-02-01

Phenylketonuria (PKU) is a metabolic disease caused by mutations in the phenylalanine hydroxylase (PAH) gene. Although the PAH genotype remains the main determinant of PKU phenotype severity, genotype-phenotype inconsistencies have been reported. In this study, we focused on unanalysed sequences in non-coding PAH gene regions to assess their possible influence on the PKU phenotype. We transiently transfected HepG2 cells with various chloramphenicol acetyl transferase (CAT) reporter constructs which included PAH gene non-coding regions. Selected non-coding regions were indicated by in silico prediction to contain transcription factor binding sites. Furthermore, electrophoretic mobility shift assay (EMSA) and supershift assays were performed to identify which transcriptional factors were engaged in the interaction. We found novel KLF1 motif in the PAH promoter, which decreases CAT activity by 50 % in comparison to basal transcription in vitro. The cytosine at the c.-170 promoter position creates an additional binding site for the protein complex involving KLF1 transcription factor. Moreover, we assessed for the first time the role of a multivariant variable number tandem repeat (VNTR) region located in the 3'-region of the PAH gene. We found that the VNTR3, VNTR7 and VNTR8 constructs had approximately 60 % of CAT activity. The regulation is mediated by the C/EBPalpha transcription factor, present in protein complex binding to VNTR3. Our study highlighted two novel promoter KLF1 and 3'-region C/EBPalpha motifs in the PAH gene which decrease transcription in vitro and, thus, could be considered as PAH expression modifiers. New transcription motifs in non-coding regions will contribute to better understanding of the PKU phenotype complexity and may become important for the optimisation of PKU treatment.

Complete sequence and gene organization of the mitochondrial genome of Asio flammeus (Strigiformes, strigidae).

PubMed

Zhang, Yanan; Song, Tao; Pan, Tao; Sun, Xiaonan; Sun, Zhonglou; Qian, Lifu; Zhang, Baowei

2016-07-01

The complete sequence of the mitochondrial genome was determined for Asio flammeus, which is distributed widely in geography. The length of the complete mitochondrial genome was 18,966 bp, containing 2 rRNA genes, 22 tRNA genes, 13 protein-coding genes (PCGs), and 1 non-coding region (D-loop). All the genes were distributed on the H-strand, except for the ND6 subunit gene and eight tRNA genes which were encoded on the L-strand. The D-loop of A. flammeus contained many tandem repeats of varying lengths and repeat numbers. The molecular-based phylogeny showed that our species acted as the sister group to A. capensis and the supported Asio was the monophyletic group.

Correction of the enzymatic and functional deficits in a model of Pompe disease using adeno-associated virus vectors.

PubMed

Fraites, Thomas J; Schleissing, Mary R; Shanely, R Andrew; Walter, Glenn A; Cloutier, Denise A; Zolotukhin, Irene; Pauly, Daniel F; Raben, Nina; Plotz, Paul H; Powers, Scott K; Kessler, Paul D; Byrne, Barry J

2002-05-01

Pompe disease is a lysosomal storage disease caused by the absence of acid alpha-1,4 glucosidase (GAA). The pathophysiology of Pompe disease includes generalized myopathy of both cardiac and skeletal muscle. We sought to use recombinant adeno-associated virus (rAAV) vectors to deliver functional GAA genes in vitro and in vivo. Myotubes and fibroblasts from Pompe patients were transduced in vitro with rAAV2-GAA. At 14 days postinfection, GAA activities were at least fourfold higher than in their respective untransduced controls, with a 10-fold increase observed in GAA-deficient myotubes. BALB/c and Gaa(-/-) mice were also treated with rAAV vectors. Persistent expression of vector-derived human GAA was observed in BALB/c mice up to 6 months after treatment. In Gaa(-/-) mice, intramuscular and intramyocardial delivery of rAAV2-Gaa (carrying the mouse Gaa cDNA) resulted in near-normal enzyme activities. Skeletal muscle contractility was partially restored in the soleus muscles of treated Gaa(-/-) mice, indicating the potential for vector-mediated restoration of both enzymatic activity and muscle function. Furthermore, intramuscular treatment with a recombinant AAV serotype 1 vector (rAAV1-Gaa) led to nearly eight times normal enzymatic activity in Gaa(-/-) mice, with concomitant glycogen clearance as assessed in vitro and by proton magnetic resonance spectroscopy.

Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

NASA Astrophysics Data System (ADS)

Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

2004-09-01

In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Albert G. Baca; Edwin J. Heller; Gregory C. Frye-Mason

High sensitivity acoustic wave chemical microsensors are being developed on GaAs substrates. These devices take advantage of the piezoelectric properties of GaAs as well as its mature microelectronics fabrication technology and nascent micromachining technology. The design, fabrication, and response of GaAs SAW chemical microsensors are reported. Functional integrated GaAs SAW oscillators, suitable for chemical sensing, have been produced. The integrated oscillator requires 20 mA at 3 VK, operates at frequencies up to 500 MHz, and occupies approximately 2 mmz. Discrete GaAs sensor components, including IC amplifiers, SAW delay lines, and IC phase comparators have been fabricated and tested. A temperaturemore » compensation scheme has been developed that overcomes the large temperature dependence of GaAs acoustic wave devices. Packaging issues related to bonding miniature flow channels directly to the GaAs substrates have been resolved. Micromachining techniques for fabricating FPW and TSM microsensors on thin GaAs membranes are presented and GaAs FPW delay line performance is described. These devices have potentially higher sensitivity than existing GaAs and quartz SAW sensors.« less

Nitridation of porous GaAs by an ECR ammonia plasma

NASA Astrophysics Data System (ADS)

Naddaf, M.; Hullavarad, S. S.; Ganesan, V.; Bhoraskar, S. V.

2006-02-01

The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 °C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 °C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

Microprocessor design for GaAs technology

NASA Astrophysics Data System (ADS)

Milutinovic, Veljko M.

Recent advances in the design of GaAs microprocessor chips are examined in chapters contributed by leading experts; the work is intended as reading material for a graduate engineering course or as a practical R&D reference. Topics addressed include the methodology used for the architecture, organization, and design of GaAs processors; GaAs device physics and circuit design; design concepts for microprocessor-based GaAs systems; a 32-bit GaAs microprocessor; a 32-bit processor implemented in GaAs JFET; and a direct coupled-FET-logic E/D-MESFET experimental RISC machine. Drawings, micrographs, and extensive circuit diagrams are provided.

Systematic discovery of Xist RNA binding proteins

PubMed Central

Chu, Ci; Zhang, Qiangfeng Cliff; da Rocha, Simão Teixeira; Flynn, Ryan A.; Bharadwaj, Maheetha; Calabrese, J. Mauro; Magnuson, Terry; Heard, Edith; Chang, Howard Y.

2015-01-01

Summary Noncoding RNAs (ncRNAs) function with associated proteins to effect complex structural and regulatory outcomes. To reveal the composition and dynamics of specific noncoding RNA- protein complexes (RNPs) in vivo, we developed comprehensive identification of RNA-binding proteins by mass spectrometry (ChIRP-MS). ChIRP-MS analysis of four ncRNAs captures key protein interactors, including a U1-specific link to the 3′ RNA processing machinery. Xist, an essential lncRNA for X-chromosome inactivation (XCI), interacts with 81 proteins from chromatin modification, nuclear matrix, and RNA remodeling pathways. The Xist RNA-protein particle assembles in two steps coupled with the transition from pluripotency to differentiation. Specific interactors include HnrnpK that participates in Xist-mediated gene silencing and histone modifications, but not Xist localization and Drosophila Split ends homolog Spen that interacts via the A-repeat domain of Xist and is required for gene silencing. Thus, Xist lncRNA engages with proteins in a modular and developmentally controlled manner to coordinate chromatin spreading and silencing. PMID:25843628

Complete Sequence of the mitochondrial genome of the tapeworm Hymenolepis diminuta: Gene arrangements indicate that platyhelminths are eutrochozoans

DOE Office of Scientific and Technical Information (OSTI.GOV)

von Nickisch-Rosenegk, Markus; Brown, Wesley M.; Boore, Jeffrey L.

2001-01-01

Using ''long-PCR'' we have amplified in overlapping fragments the complete mitochondrial genome of the tapeworm Hymenolepis diminuta (Platyhelminthes: Cestoda) and determined its 13,900 nucleotide sequence. The gene content is the same as that typically found for animal mitochondrial DNA (mtDNA) except that atp8 appears to be lacking, a condition found previously for several other animals. Despite the small size of this mtDNA, there are two large non-coding regions, one of which contains 13 repeats of a 31 nucleotide sequence and a potential stem-loop structure of 25 base pairs with an 11-member loop. Large potential secondary structures are identified also formore » the non-coding regions of two other cestode mtDNAs. Comparison of the mitochondrial gene arrangement of H. diminuta with those previously published supports a phylogenetic position of flatworms as members of the Eutrochozoa, rather than being basal to either a clade of protostomes or a clade of coelomates.« less

Recurrence of 49-base decamers, nonomers, and octamers within mouse C mu gene of Ig heavy chain and its primordial building block.

PubMed Central

Yazaki, A; Ohno, S

1983-01-01

Within the published 2,168-base-long mouse C mu gene of Ig heavy chain consisting of four coding and four noncoding segments, 2 base decamers, 8 nonomers, and 39 octamers recurred. Recurring base heptamers (about 100) and hexamers (about 350) were simply too numerous to merit individual identification. In spite of extensive overlaps between these recurring base decamers to hexamers, they occupied nearly the entire length of mouse Ig C mu gene. As with other genes of the beta-sheet-forming beta 2-microglobulin family, the Ig C mu gene (flanking and intervening noncoding sequences included) is not a unique sequence but rather it is degenerate repeats of the 45-base-long primordial building-block sequence uniquely its own. This primordial building block must originally have specified the 15-amino-acid-residue-long primordial arm of beta-sheet-forming loops, the characteristics of the beta 2-microglobulin family of polypeptides. PMID:6403948

The complete mitochondrial genome of the green lizard Lacerta viridis viridis (Reptilia: Lacertidae) and its phylogenetic position within squamate reptiles.

PubMed

Böhme, M U; Fritzsch, G; Tippmann, A; Schlegel, M; Berendonk, T U

2007-06-01

For the first time the complete mitochondrial genome was sequenced for a member of Lacertidae. Lacerta viridis viridis was sequenced in order to compare the phylogenetic relationships of this family to other reptilian lineages. Using the long-polymerase chain reaction (long PCR) we characterized a mitochondrial genome, 17,156 bp long showing a typical vertebrate pattern with 13 protein coding genes, 22 transfer RNAs (tRNA), two ribosomal RNAs (rRNA) and one major noncoding region. The noncoding region of L. v. viridis was characterized by a conspicuous 35 bp tandem repeat at its 5' terminus. A phylogenetic study including all currently available squamate mitochondrial sequences demonstrates the position of Lacertidae within a monophyletic squamate group. We obtained a narrow relationship of Lacertidae to Scincidae, Iguanidae, Varanidae, Anguidae, and Cordylidae. Although, the internal relationships within this group yielded only a weak resolution and low bootstrap support, the revealed relationships were more congruent with morphological studies than with recent molecular analyses.

Deep sequencing reveals unique small RNA repertoire that is regulated during head regeneration in Hydra magnipapillata.

PubMed

Krishna, Srikar; Nair, Aparna; Cheedipudi, Sirisha; Poduval, Deepak; Dhawan, Jyotsna; Palakodeti, Dasaradhi; Ghanekar, Yashoda

2013-01-07

Small non-coding RNAs such as miRNAs, piRNAs and endo-siRNAs fine-tune gene expression through post-transcriptional regulation, modulating important processes in development, differentiation, homeostasis and regeneration. Using deep sequencing, we have profiled small non-coding RNAs in Hydra magnipapillata and investigated changes in small RNA expression pattern during head regeneration. Our results reveal a unique repertoire of small RNAs in hydra. We have identified 126 miRNA loci; 123 of these miRNAs are unique to hydra. Less than 50% are conserved across two different strains of Hydra vulgaris tested in this study, indicating a highly diverse nature of hydra miRNAs in contrast to bilaterian miRNAs. We also identified siRNAs derived from precursors with perfect stem-loop structure and that arise from inverted repeats. piRNAs were the most abundant small RNAs in hydra, mapping to transposable elements, the annotated transcriptome and unique non-coding regions on the genome. piRNAs that map to transposable elements and the annotated transcriptome display a ping-pong signature. Further, we have identified several miRNAs and piRNAs whose expression is regulated during hydra head regeneration. Our study defines different classes of small RNAs in this cnidarian model system, which may play a role in orchestrating gene expression essential for hydra regeneration.

Deep sequencing reveals unique small RNA repertoire that is regulated during head regeneration in Hydra magnipapillata

PubMed Central

Krishna, Srikar; Nair, Aparna; Cheedipudi, Sirisha; Poduval, Deepak; Dhawan, Jyotsna; Palakodeti, Dasaradhi; Ghanekar, Yashoda

2013-01-01

Small non-coding RNAs such as miRNAs, piRNAs and endo-siRNAs fine-tune gene expression through post-transcriptional regulation, modulating important processes in development, differentiation, homeostasis and regeneration. Using deep sequencing, we have profiled small non-coding RNAs in Hydra magnipapillata and investigated changes in small RNA expression pattern during head regeneration. Our results reveal a unique repertoire of small RNAs in hydra. We have identified 126 miRNA loci; 123 of these miRNAs are unique to hydra. Less than 50% are conserved across two different strains of Hydra vulgaris tested in this study, indicating a highly diverse nature of hydra miRNAs in contrast to bilaterian miRNAs. We also identified siRNAs derived from precursors with perfect stem–loop structure and that arise from inverted repeats. piRNAs were the most abundant small RNAs in hydra, mapping to transposable elements, the annotated transcriptome and unique non-coding regions on the genome. piRNAs that map to transposable elements and the annotated transcriptome display a ping–pong signature. Further, we have identified several miRNAs and piRNAs whose expression is regulated during hydra head regeneration. Our study defines different classes of small RNAs in this cnidarian model system, which may play a role in orchestrating gene expression essential for hydra regeneration. PMID:23166307

The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study.

PubMed

Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

2014-01-01

First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.

CRISPRDetect: A flexible algorithm to define CRISPR arrays.

PubMed

Biswas, Ambarish; Staals, Raymond H J; Morales, Sergio E; Fineran, Peter C; Brown, Chris M

2016-05-17

CRISPR (clustered regularly interspaced short palindromic repeats) RNAs provide the specificity for noncoding RNA-guided adaptive immune defence systems in prokaryotes. CRISPR arrays consist of repeat sequences separated by specific spacer sequences. CRISPR arrays have previously been identified in a large proportion of prokaryotic genomes. However, currently available detection algorithms do not utilise recently discovered features regarding CRISPR loci. We have developed a new approach to automatically detect, predict and interactively refine CRISPR arrays. It is available as a web program and command line from bioanalysis.otago.ac.nz/CRISPRDetect. CRISPRDetect discovers putative arrays, extends the array by detecting additional variant repeats, corrects the direction of arrays, refines the repeat/spacer boundaries, and annotates different types of sequence variations (e.g. insertion/deletion) in near identical repeats. Due to these features, CRISPRDetect has significant advantages when compared to existing identification tools. As well as further support for small medium and large repeats, CRISPRDetect identified a class of arrays with 'extra-large' repeats in bacteria (repeats 44-50 nt). The CRISPRDetect output is integrated with other analysis tools. Notably, the predicted spacers can be directly utilised by CRISPRTarget to predict targets. CRISPRDetect enables more accurate detection of arrays and spacers and its gff output is suitable for inclusion in genome annotation pipelines and visualisation. It has been used to analyse all complete bacterial and archaeal reference genomes.

Guanidinoacetic acid loading affects plasma γ-aminobutyric acid in healthy men.

PubMed

Ostojic, Sergej M; Stojanovic, Marko

2015-08-01

Guanidinoacetic acid (GAA), a precursor of creatine and an innovative dietary agent, activates γ-amino butyric acid (GABA) receptors yet clinical effects of dietary GAA on GABA metabolism are currently unknown. The main aim of this pilot research was to investigate whether GAA loading affected peripheral GABA homeostasis in healthy humans. Eight healthy male volunteers aged 22-25 years were randomized in a double-blind design to receive either GAA (three grams daily) or placebo by oral administration for 3 weeks. At baseline and after 3 weeks participants provided fasting blood samples for free plasma levels of GABA, GAA, creatine and glutamine. Following 3 weeks of intervention, plasma GABA level dropped significantly in participants receiving 3 g of GAA per day as compared to the placebo (P = 0.03). GAA loading significantly decreased plasma GABA by 88.8 nmol/L (95% confidence interval; 5.4-172.1) after 3 weeks of intervention as compared to the baseline (P = 0.03). GAA intervention positively affected both plasma GAA and creatine (P < 0.05), while no effects of intervention were reported for plasma glutamine. Results indicate that supplemental GAA affects peripheral GABA metabolism, and potentially down-regulates GABA synthesis in peripheral tissues. Possible GABAergic action of dietary GAA adds to the safety profile of this novel dietary supplement.

Establishment and Maintenance of Primary Fibroblast Repositories for Rare Diseases-Friedreich's Ataxia Example.

PubMed

Li, Yanjie; Polak, Urszula; Clark, Amanda D; Bhalla, Angela D; Chen, Yu-Yun; Li, Jixue; Farmer, Jennifer; Seyer, Lauren; Lynch, David; Butler, Jill S; Napierala, Marek

2016-08-01

Friedreich's ataxia (FRDA) represents a rare neurodegenerative disease caused by expansion of GAA trinucleotide repeats in the first intron of the FXN gene. The number of GAA repeats in FRDA patients varies from approximately 60 to <1000 and is tightly correlated with age of onset and severity of the disease symptoms. The heterogeneity of Friedreich's ataxia stresses the need for a large cohort of patient samples to conduct studies addressing the mechanism of disease pathogenesis or evaluate novel therapeutic candidates. Herein, we report the establishment and characterization of an FRDA fibroblast repository, which currently includes 50 primary cell lines derived from FRDA patients and seven lines from mutation carriers. These cells are also a source for generating induced pluripotent stem cell (iPSC) lines by reprogramming, as well as disease-relevant neuronal, cardiac, and pancreatic cells that can then be differentiated from the iPSCs. All FRDA and carrier lines are derived using a standard operating procedure and characterized to confirm mutation status, as well as expression of FXN mRNA and protein. Consideration and significance of creating disease-focused cell line and tissue repositories, especially in the context of rare and heterogeneous disorders, are presented. Although the economic aspect of creating and maintaining such repositories is important, the benefits of easy access to a collection of well-characterized cell lines for the purpose of drug discovery or disease mechanism studies overshadow the associated costs. Importantly, all FRDA fibroblast cell lines collected in our repository are available to the scientific community.

Establishment and Maintenance of Primary Fibroblast Repositories for Rare Diseases—Friedreich's Ataxia Example

PubMed Central

Li, Yanjie; Polak, Urszula; Clark, Amanda D.; Bhalla, Angela D.; Chen, Yu-Yun; Li, Jixue; Farmer, Jennifer; Seyer, Lauren; Lynch, David

2016-01-01

Friedreich's ataxia (FRDA) represents a rare neurodegenerative disease caused by expansion of GAA trinucleotide repeats in the first intron of the FXN gene. The number of GAA repeats in FRDA patients varies from approximately 60 to <1000 and is tightly correlated with age of onset and severity of the disease symptoms. The heterogeneity of Friedreich's ataxia stresses the need for a large cohort of patient samples to conduct studies addressing the mechanism of disease pathogenesis or evaluate novel therapeutic candidates. Herein, we report the establishment and characterization of an FRDA fibroblast repository, which currently includes 50 primary cell lines derived from FRDA patients and seven lines from mutation carriers. These cells are also a source for generating induced pluripotent stem cell (iPSC) lines by reprogramming, as well as disease-relevant neuronal, cardiac, and pancreatic cells that can then be differentiated from the iPSCs. All FRDA and carrier lines are derived using a standard operating procedure and characterized to confirm mutation status, as well as expression of FXN mRNA and protein. Consideration and significance of creating disease-focused cell line and tissue repositories, especially in the context of rare and heterogeneous disorders, are presented. Although the economic aspect of creating and maintaining such repositories is important, the benefits of easy access to a collection of well-characterized cell lines for the purpose of drug discovery or disease mechanism studies overshadow the associated costs. Importantly, all FRDA fibroblast cell lines collected in our repository are available to the scientific community. PMID:27002638

C9orf72 BAC Transgenic Mice Display Typical Pathologic Features of ALS/FTD.

PubMed

O'Rourke, Jacqueline G; Bogdanik, Laurent; Muhammad, A K M G; Gendron, Tania F; Kim, Kevin J; Austin, Andrew; Cady, Janet; Liu, Elaine Y; Zarrow, Jonah; Grant, Sharday; Ho, Ritchie; Bell, Shaughn; Carmona, Sharon; Simpkinson, Megan; Lall, Deepti; Wu, Kathryn; Daughrity, Lillian; Dickson, Dennis W; Harms, Matthew B; Petrucelli, Leonard; Lee, Edward B; Lutz, Cathleen M; Baloh, Robert H

2015-12-02

Noncoding expansions of a hexanucleotide repeat (GGGGCC) in the C9orf72 gene are the most common cause of familial amyotrophic lateral sclerosis and frontotemporal dementia. Here we report transgenic mice carrying a bacterial artificial chromosome (BAC) containing the full human C9orf72 gene with either a normal allele (15 repeats) or disease-associated expansion (∼100-1,000 repeats; C9-BACexp). C9-BACexp mice displayed pathologic features seen in C9orf72 expansion patients, including widespread RNA foci and repeat-associated non-ATG (RAN) translated dipeptides, which were suppressed by antisense oligonucleotides targeting human C9orf72. Nucleolin distribution was altered, supporting that either C9orf72 transcripts or RAN dipeptides promote nucleolar dysfunction. Despite early and widespread production of RNA foci and RAN dipeptides in C9-BACexp mice, behavioral abnormalities and neurodegeneration were not observed even at advanced ages, supporting the hypothesis that RNA foci and RAN dipeptides occur presymptomatically and are not sufficient to drive neurodegeneration in mice at levels seen in patients. Copyright © 2015 Elsevier Inc. All rights reserved.

Performance and temperature dependencies of proton irradiated n/p and p/n GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

n/p homojunction GaAs cells are found to be more radiation resistant than p/n heteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increased temperature dependency of maximum power for the GaAs n/p cells is attributed to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

Performance and temperature dependencies of proton irradiated n/p GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

The n/p homojunction GaAs cell is found to be more radiation resistant than p/nheteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increase temperature dependency of maximum power for the GaAs n/p cells is attributed largely to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

Creatine metabolism and safety profiles after six-week oral guanidinoacetic acid administration in healthy humans.

PubMed

Ostojic, Sergej M; Niess, Barbara; Stojanovic, Marko; Obrenovic, Milos

2013-01-01

Guanidinoacetic acid (GAA) is a natural precursor of creatine, yet the potential use of GAA as a nutritional additive for restoring creatine availability in humans has been limited by unclear efficacy and safety after exogenous GAA administration. The present study evaluated the effects of orally administered GAA on serum and urinary GAA, creatine and creatinine concentration, and on the occurrence of adverse events in healthy humans. Twenty-four healthy volunteers were randomized in a double-blind design to receive either GAA (2.4 grams daily) or placebo (PLA) by oral administration for 6 weeks. www.clinicaltrials.gov, identification number NCT01133899. Serum creatine and creatinine increased significantly from before to after administration in GAA-supplemented participants (P < 0.05). The proportion of participants who reported minor side effects was 58.3% in the GAA group and 45.5% in the placebo group (P = 0.68). A few participants experienced serum creatine levels above 70 µmol/L. Exogenous GAA is metabolized to creatine, resulting in a significant increase of fasting serum creatine after intervention. GAA had an acceptable side-effects profile with a low incidence of biochemical abnormalities.

Creatine Metabolism and Safety Profiles after Six-Week Oral Guanidinoacetic Acid Administration in Healthy Humans

PubMed Central

Ostojic, Sergej M.; Niess, Barbara; Stojanovic, Marko; Obrenovic, Milos

2013-01-01

Objectives; Guanidinoacetic acid (GAA) is a natural precursor of creatine, yet the potential use of GAA as a nutritional additive for restoring creatine availability in humans has been limited by unclear efficacy and safety after exogenous GAA administration. The present study evaluated the effects of orally administered GAA on serum and urinary GAA, creatine and creatinine concentration, and on the occurrence of adverse events in healthy humans. Methods and Results; Twenty-four healthy volunteers were randomized in a double-blind design to receive either GAA (2.4 grams daily) or placebo (PLA) by oral administration for 6 weeks. Clinical trial registration: www.clinicaltrials.gov, identification number NCT01133899. Serum creatine and creatinine increased significantly from before to after administration in GAA-supplemented participants (P < 0.05). The proportion of participants who reported minor side effects was 58.3% in the GAA group and 45.5% in the placebo group (P = 0.68). A few participants experienced serum creatine levels above 70 µmol/L. Conclusion; Exogenous GAA is metabolized to creatine, resulting in a significant increase of fasting serum creatine after intervention. GAA had an acceptable side-effects profile with a low incidence of biochemical abnormalities. PMID:23329885

Gate Drain Underlapped-PNIN-GAA-TFET for Comprehensively Upgraded Analog/RF Performance

NASA Astrophysics Data System (ADS)

Madan, Jaya; Chaujar, Rishu

2017-02-01

This work integrates the merits of gate-drain underlapping (GDU) and N+ source pocket on cylindrical gate all around tunnel FET (GAA-TFET) to form GDU-PNIN-GAA-TFET. It is analysed that the source pocket located at the source-channel junction narrows the tunneling barrier width at the tunneling junction and thereby enhances the ON-state current of GAA-TFET. Further, it is obtained that the GDU resists the extension of carrier density (built-up under the gated region) towards the drain side (under the underlapped length), thereby suppressing the ambipolar current and reducing the parasitic capacitances of GAA-TFET. Consequently, the amalgamated merits of both engineering schemes are obtained in GDU-PNIN-GAA-TFET that thus conquers the greatest challenges faced by TFET. Thus, GDU-PNIN-GAA-TFET results in an up-gradation in the overall performance of GAA-TFET. Moreover, it is realised that the RF figure of merits FOMs such as cut-off frequency (fT) and maximum oscillation frequency (fMAX) are also considerably improved with integration of source pocket on GAA-TFET. Thus, the improved analog and RF performance of GDU-PNIN-GAA-TFET makes it ideal for low power and high-speed applications.

Disease-associated repeat instability and mismatch repair.

PubMed

Schmidt, Monika H M; Pearson, Christopher E

2016-02-01

Expanded tandem repeat sequences in DNA are associated with at least 40 human genetic neurological, neurodegenerative, and neuromuscular diseases. Repeat expansion can occur during parent-to-offspring transmission, and arise at variable rates in specific tissues throughout the life of an affected individual. Since the ongoing somatic repeat expansions can affect disease age-of-onset, severity, and progression, targeting somatic expansion holds potential as a therapeutic target. Thus, understanding the factors that regulate this mutation is crucial. DNA repair, in particular mismatch repair (MMR), is the major driving force of disease-associated repeat expansions. In contrast to its anti-mutagenic roles, mammalian MMR curiously drives the expansion mutations of disease-associated (CAG)·(CTG) repeats. Recent advances have broadened our knowledge of both the MMR proteins involved in disease repeat expansions, including: MSH2, MSH3, MSH6, MLH1, PMS2, and MLH3, as well as the types of repeats affected by MMR, now including: (CAG)·(CTG), (CGG)·(CCG), and (GAA)·(TTC) repeats. Mutagenic slipped-DNA structures have been detected in patient tissues, and the size of the slip-out and their junction conformation can determine the involvement of MMR. Furthermore, the formation of other unusual DNA and R-loop structures is proposed to play a key role in MMR-mediated instability. A complex correlation is emerging between tissues showing varying amounts of repeat instability and MMR expression levels. Notably, naturally occurring polymorphic variants of DNA repair genes can have dramatic effects upon the levels of repeat instability, which may explain the variation in disease age-of-onset, progression and severity. An increasing grasp of these factors holds prognostic and therapeutic potential. Copyright © 2015 Elsevier B.V. All rights reserved.

Origin and enhancement of the 1.3 μm luminescence from GaAs treated by ion-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2013-09-01

GaAs and GaAs based materials have outstanding optoelectronic properties and are widely used as light emitting media in devices. Many approaches have been applied to GaAs to generate luminescence at 0.88, 1.30, and 1.55 μm which are transmission windows of optical fibers. In this paper, we present the photoluminescence at 1.30 μm from deep level defects in GaAs treated by ion-implantation and flash lamp annealing (FLA). Such emission, which exhibits superior temperature stability, can be obtained from FLA treated virgin GaAs as well as doped GaAs. Indium-doping in GaAs can greatly enhance the luminescence. By photoluminescence, Raman measurements, and positron annihilation spectroscopy, we conclude that the origin of the 1.30 μm emission is from transitions between the VAs-donor and X-acceptor pairs.

GaAs shallow-homojunction solar cells

NASA Technical Reports Server (NTRS)

Fan, J. C. C.

1981-01-01

The feasibility of fabricating space resistant, high efficiency, light weight, low cost GaAs shallow homojunction solar cells for space application is investigated. The material preparation of ultrathin GaAs single crystal layers, and the fabrication of efficient GaAs solar cells on bulk GaAs substrates are discussed. Considerable progress was made in both areas, and conversion efficiency about 16% AMO was obtained using anodic oxide as a single layer antireflection coating. A computer design shows that even better cells can be obtained with double layer antireflection coating. Ultrathin, high efficiency solar cells were obtained from GaAs films prepared by the CLEFT process, with conversion efficiency as high as 17% at AMI from a 10 micrometers thick GaAs film. A organometallic CVD was designed and constructed.

Comparison and correlation of Simple Sequence Repeats distribution in genomes of Brucella species

PubMed Central

Kiran, Jangampalli Adi Pradeep; Chakravarthi, Veeraraghavulu Praveen; Kumar, Yellapu Nanda; Rekha, Somesula Swapna; Kruti, Srinivasan Shanthi; Bhaskar, Matcha

2011-01-01

Computational genomics is one of the important tools to understand the distribution of closely related genomes including simple sequence repeats (SSRs) in an organism, which gives valuable information regarding genetic variations. The central objective of the present study was to screen the SSRs distributed in coding and non-coding regions among different human Brucella species which are involved in a range of pathological disorders. Computational analysis of the SSRs in the Brucella indicates few deviations from expected random models. Statistical analysis also reveals that tri-nucleotide SSRs are overrepresented and tetranucleotide SSRs underrepresented in Brucella genomes. From the data, it can be suggested that over expressed tri-nucleotide SSRs in genomic and coding regions might be responsible in the generation of functional variation of proteins expressed which in turn may lead to different pathogenicity, virulence determinants, stress response genes, transcription regulators and host adaptation proteins of Brucella genomes. Abbreviations SSRs - Simple Sequence Repeats, ORFs - Open Reading Frames. PMID:21738309

Advances in clinical and molecular understanding of the FMR1 premutation and fragile X-associated tremor/ataxia syndrome

PubMed Central

Hagerman, Randi; Hagerman, Paul

2014-01-01

Summary Fragile X syndrome, the leading heritable form of cognitive impairment, is caused by epigenetic silencing of the fragile X (FMR1) gene consequent to large expansions (>200 repeats) of a non-coding CGG-repeat element. Smaller, “premutation” expansions (55–200 repeats) can give rise to a family of neurodevelopmental (ADHD, autism spectrum disorder, seizure disorder) and neurodegenerative (FXTAS) clinical phenotypes through an entirely distinct molecular mechanism involving increased FMR1 mRNA production and toxicity. Basic cellular, animal, and human studies have helped to elucidate the underlying RNA toxicity mechanism, while clinical research is providing a more nuanced picture of the spectrum of clinical involvement. Whereas advances on both mechanistic and clinical fronts are driving new approaches to targeted treatment, two important issues/needs are emerging: to define the extent to which the mechanisms contributing to FXTAS also contribute to other neurodegenerative and medical disorders, and to redefine FXTAS in light of its differing presentations and associated features. PMID:23867198

Excitation and De-Excitation Mechanisms of Er-Doped GaAs and A1GaAs.

DTIC Science & Technology

1992-12-01

AD-A258 814 EXCITATION AND DE -EXCITATION MECHANISMS OF Er-DOPED GaAs AND A1GaAs DISSERTATION David W. Elsaesser, Captain, USAF DTICY. ft £ICTE’’ )AN...0 8 1993U -o Wo- .%Approved for public release; Distribution unlimited 93 1 04 022 AFIT/DS/ENP/92-5 EXCITATION AND DE -EXCITATION MECHANISMS OF Er...public release; Distribution unlimited AFIT/DS/ENP/92D-005 EXCITATION AND DE -EXCITATION MECHANISMS OF Er-DOPED GaAs AND A1GaAs 4 toFlor -- David W

Luminescence and Electroluminescence of Nd, Tm and Yb Doped GaAs and some II-Vi Compounds

DTIC Science & Technology

1994-02-28

from the bandgap discontinuity (as was proposed in my publications [1,2]). Also, by using superlattice structure A1GaAs / GaAs: Er / AlGaAs, we could...n ipact ightemiting evic 10 3. The AlGaAs/GaAs: Er/A1GaAs superlattice structure. For the first time we designed the unipolar n’ - superlattice - n...structure as shown in Figure 5. The GaAs: Er/Alo.45Gao.55As superlattice was grown by MBE on an n’ GaAs: Si substrate. It consisted of 60 periods of

Heteroepitaxial growth of GaAs on (100) Ge/Si using migration enhanced epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanoto, H.; Loke, W. K.; Yoon, S. F.

In this paper, heteroepitaxial growth of GaAs on nominal (100) Ge/Si substrate was investigated. The root-mean square surface roughness of the sample where the first few monolayers of the GaAs were nucleated by migration enhanced epitaxy (MEE) is four times smaller compared to the sample without such a process, indicating better surface planarity. From the (004) x-ray diffraction rocking curve measurement, the full width at half maximum of the GaAs layer nucleated by MEE is 40% lower compared to that of the GaAs layer without such a process, indicating better crystal quality. Furthermore, it was found that the sample wheremore » the GaAs layer was nucleated by MEE experienced early relaxation. As the MEE process promotes two-dimensional growth, the GaAs layer where nucleation was initiated by such a process has fewer islandlike formations. This leads to a pseudomorphically grown GaAs layer, which experiences higher strain compared to the GaAs layer with more islandlike formations, where most relaxation occurs on the free surface of the islands. Therefore, for the same layer thickness, the GaAs layer on (100) Ge/Si substrate where nucleation was initiated by MEE relaxed first.« less

The Mitochondrial Cytochrome Oxidase Subunit I Gene Occurs on a Minichromosome with Extensive Heteroplasmy in Two Species of Chewing Lice, Geomydoecus aurei and Thomomydoecus minor

PubMed Central

Pietan, Lucas L.; Spradling, Theresa A.

2016-01-01

In animals, mitochondrial DNA (mtDNA) typically occurs as a single circular chromosome with 13 protein-coding genes and 22 tRNA genes. The various species of lice examined previously, however, have shown mitochondrial genome rearrangements with a range of chromosome sizes and numbers. Our research demonstrates that the mitochondrial genomes of two species of chewing lice found on pocket gophers, Geomydoecus aurei and Thomomydoecus minor, are fragmented with the 1,536 base-pair (bp) cytochrome-oxidase subunit I (cox1) gene occurring as the only protein-coding gene on a 1,916–1,964 bp minicircular chromosome in the two species, respectively. The cox1 gene of T. minor begins with an atypical start codon, while that of G. aurei does not. Components of the non-protein coding sequence of G. aurei and T. minor include a tRNA (isoleucine) gene, inverted repeat sequences consistent with origins of replication, and an additional non-coding region that is smaller than the non-coding sequence of other lice with such fragmented mitochondrial genomes. Sequences of cox1 minichromosome clones for each species reveal extensive length and sequence heteroplasmy in both coding and noncoding regions. The highly variable non-gene regions of G. aurei and T. minor have little sequence similarity with one another except for a 19-bp region of phylogenetically conserved sequence with unknown function. PMID:27589589

GaAs VLSI technology and circuit elements for DSP

NASA Astrophysics Data System (ADS)

Mikkelson, James M.

1990-10-01

Recent progress in digital GaAs circuit performance and complexity is presented to demonstrate the current capabilities of GaAs components. High density GaAs process technology and circuit design techniques are described and critical issues for achieving favorable complexity speed power and cost tradeoffs are reviewed. Some DSP building blocks are described to provide examples of what types of DSP systems could be implemented with present GaAs technology. DIGITAL GaAs CIRCUIT CAPABILITIES In the past few years the capabilities of digital GaAs circuits have dramatically increased to the VLSI level. Major gains in circuit complexity and power-delay products have been achieved by the use of silicon-like process technologies and simple circuit topologies. The very high speed and low power consumption of digital GaAs VLSI circuits have made GaAs a desirable alternative to high performance silicon in hardware intensive high speed system applications. An example of the performance and integration complexity available with GaAs VLSI circuits is the 64x64 crosspoint switch shown in figure 1. This switch which is the most complex GaAs circuit currently available is designed on a 30 gate GaAs gate array. It operates at 200 MHz and dissipates only 8 watts of power. The reasons for increasing the level of integration of GaAs circuits are similar to the reasons for the continued increase of silicon circuit complexity. The market factors driving GaAs VLSI are system design methodology system cost power and reliability. System designers are hesitant or unwilling to go backwards to previous design techniques and lower levels of integration. A more highly integrated system in a lower performance technology can often approach the performance of a system in a higher performance technology at a lower level of integration. Higher levels of integration also lower the system component count which reduces the system cost size and power consumption while improving the system reliability. For large gate count circuits the power per gate must be minimized to prevent reliability and cooling problems. The technical factors which favor increasing GaAs circuit complexity are primarily related to reducing the speed and power penalties incurred when crossing chip boundaries. Because the internal GaAs chip logic levels are not compatible with standard silicon I/O levels input receivers and output drivers are needed to convert levels. These I/O circuits add significant delay to logic paths consume large amounts of power and use an appreciable portion of the die area. The effects of these I/O penalties can be reduced by increasing the ratio of core logic to I/O on a chip. DSP operations which have a large number of logic stages between the input and the output are ideal candidates to take advantage of the performance of GaAs digital circuits. Figure 2 is a schematic representation of the I/O penalties encountered when converting from ECL levels to GaAs

GaAs Monolithic Microwave Subsystem Technology Base

DTIC Science & Technology

1980-01-01

To provide a captive source of reliable, high-quality GaAs substrates, a new crystal growth and substrate preparation facility which utilizes a high...Symp. GaAs and Related Compounds, Inst. Phys. Conf. Ser. 24, 6. 20. Wood, Woodcock and Harris (1978) GaAs and Related Compounds, Inst. Phys. Conf

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1979-01-01

The optimization of space processing of GaAs is described. The detailed compositional, structural, and electronic characterization of GaAs on a macro- and microscale and the relationships between growth parameters and the properties of GaAs are among the factors discussed. The key parameters limiting device performance are assessed.

GaAs thin films and methods of making and using the same

DOEpatents

Boettcher, Shannon; Ritenour, Andrew; Boucher, Jason; Greenaway, Ann

2016-06-14

Disclosed herein are embodiments of methods for making GaAs thin films, such as photovoltaic GaAs thin films. The methods disclosed herein utilize sources, precursors, and reagents that do not produce (or require) toxic gas and that are readily available and relatively low in cost. In some embodiments, the methods are readily scalable for industrial applications and can provide GaAs thin films having properties that are at least comparable to or potentially superior to GaAs films obtained from conventional methods.

GaAs High Breakdown Voltage Front and Back Side Processed Schottky Detectors for X-Ray Detection

DTIC Science & Technology

2007-11-01

front and back side processed, unintentionally doped bulk gallium -arsenic (GaAs) Schottky detectors and determined that GaAs detectors with a large...a few materials that fulfill these requirements are gallium -arsenic (GaAs) and cadmium-zinc-tellurium (CdZnTe or CZT). They are viable alternative...Whitehill, C.; Pospíšil, S.; Wilhem, I.; Doležal, Z.; Juergensen, H.; Heuken, M. Development of low-pressure vapour -phase epitaxial GaAs for medical imaging

Joint services electronics program

NASA Astrophysics Data System (ADS)

Flynn, George W.; Osgood, Richard M., Jr.

1988-05-01

Several milestones have been reached in GaAs research. The first active GaAs device, a 1 micrometer channel width MESFET, has been made at Columbia. This device is a basic building block in the GaAs CCD program. GaAs surface studies have also born fruit. UV light has been found to oxidize rapidly the surface of GaAs in an UHV environment containing traces of water vapor and O2. The mechanism appears to be related to the generation of hot photocarriers.

NONCODE v2.0: decoding the non-coding.

PubMed

He, Shunmin; Liu, Changning; Skogerbø, Geir; Zhao, Haitao; Wang, Jie; Liu, Tao; Bai, Baoyan; Zhao, Yi; Chen, Runsheng

2008-01-01

The NONCODE database is an integrated knowledge database designed for the analysis of non-coding RNAs (ncRNAs). Since NONCODE was first released 3 years ago, the number of known ncRNAs has grown rapidly, and there is growing recognition that ncRNAs play important regulatory roles in most organisms. In the updated version of NONCODE (NONCODE v2.0), the number of collected ncRNAs has reached 206 226, including a wide range of microRNAs, Piwi-interacting RNAs and mRNA-like ncRNAs. The improvements brought to the database include not only new and updated ncRNA data sets, but also an incorporation of BLAST alignment search service and access through our custom UCSC Genome Browser. NONCODE can be found under http://www.noncode.org or http://noncode.bioinfo.org.cn.

Inverted repeat Alu elements in the human lincRNA-p21 adopt a conserved secondary structure that regulates RNA function

PubMed Central

Chillón, Isabel; Pyle, Anna M.

2016-01-01

LincRNA-p21 is a long intergenic non-coding RNA (lincRNA) involved in the p53-mediated stress response. We sequenced the human lincRNA-p21 (hLincRNA-p21) and found that it has a single exon that includes inverted repeat Alu elements (IRAlus). Sense and antisense Alu elements fold independently of one another into a secondary structure that is conserved in lincRNA-p21 among primates. Moreover, the structures formed by IRAlus are involved in the localization of hLincRNA-p21 in the nucleus, where hLincRNA-p21 colocalizes with paraspeckles. Our results underscore the importance of IRAlus structures for the function of hLincRNA-p21 during the stress response. PMID:27378782

Selected missense mutations impair frataxin processing in Friedreich ataxia.

PubMed

Clark, Elisia; Butler, Jill S; Isaacs, Charles J; Napierala, Marek; Lynch, David R

2017-08-01

Frataxin (FXN) is a highly conserved mitochondrial protein. Reduced FXN levels cause Friedreich ataxia, a recessive neurodegenerative disease. Typical patients carry GAA repeat expansions on both alleles, while a subgroup of patients carry a missense mutation on one allele and a GAA repeat expansion on the other. Here, we report that selected disease-related FXN missense mutations impair FXN localization, interaction with mitochondria processing peptidase, and processing. Immunocytochemical studies and subcellular fractionation were performed to study FXN import into the mitochondria and examine the mechanism by which mutations impair FXN processing. Coimmunoprecipitation was performed to study the interaction between FXN and mitochondrial processing peptidase. A proteasome inhibitor was used to model traditional therapeutic strategies. In addition, clinical profiles of subjects with and without point mutations were compared in a large natural history study. FXN I 154F and FXN G 130V missense mutations decrease FXN 81-210 levels compared with FXN WT , FXN R 165C , and FXN W 155R , but do not block its association with mitochondria. FXN I 154F and FXN G 130V also impair FXN maturation and enhance the binding between FXN 42-210 and mitochondria processing peptidase. Furthermore, blocking proteosomal degradation does not increase FXN 81-210 levels. Additionally, impaired FXN processing also occurs in fibroblasts from patients with FXN G 130V . Finally, clinical data from patients with FXN G 130V and FXN I 154F mutations demonstrates a lower severity compared with other individuals with Friedreich ataxia. These data suggest that the effects on processing associated with FXN G 130V and FXN I 154F mutations lead to higher levels of partially processed FXN, which may contribute to the milder clinical phenotypes in these patients.

TFIIS-Dependent Non-coding Transcription Regulates Developmental Genome Rearrangements

PubMed Central

Maliszewska-Olejniczak, Kamila; Gruchota, Julita; Gromadka, Robert; Denby Wilkes, Cyril; Arnaiz, Olivier; Mathy, Nathalie; Duharcourt, Sandra; Bétermier, Mireille; Nowak, Jacek K.

2015-01-01

Because of their nuclear dimorphism, ciliates provide a unique opportunity to study the role of non-coding RNAs (ncRNAs) in the communication between germline and somatic lineages. In these unicellular eukaryotes, a new somatic nucleus develops at each sexual cycle from a copy of the zygotic (germline) nucleus, while the old somatic nucleus degenerates. In the ciliate Paramecium tetraurelia, the genome is massively rearranged during this process through the reproducible elimination of repeated sequences and the precise excision of over 45,000 short, single-copy Internal Eliminated Sequences (IESs). Different types of ncRNAs resulting from genome-wide transcription were shown to be involved in the epigenetic regulation of genome rearrangements. To understand how ncRNAs are produced from the entire genome, we have focused on a homolog of the TFIIS elongation factor, which regulates RNA polymerase II transcriptional pausing. Six TFIIS-paralogs, representing four distinct families, can be found in P. tetraurelia genome. Using RNA interference, we showed that TFIIS4, which encodes a development-specific TFIIS protein, is essential for the formation of a functional somatic genome. Molecular analyses and high-throughput DNA sequencing upon TFIIS4 RNAi demonstrated that TFIIS4 is involved in all kinds of genome rearrangements, including excision of ~48% of IESs. Localization of a GFP-TFIIS4 fusion revealed that TFIIS4 appears specifically in the new somatic nucleus at an early developmental stage, before IES excision. RT-PCR experiments showed that TFIIS4 is necessary for the synthesis of IES-containing non-coding transcripts. We propose that these IES+ transcripts originate from the developing somatic nucleus and serve as pairing substrates for germline-specific short RNAs that target elimination of their homologous sequences. Our study, therefore, connects the onset of zygotic non coding transcription to the control of genome plasticity in Paramecium, and establishes for the first time a specific role of TFIIS in non-coding transcription in eukaryotes. PMID:26177014

Comparison of photoemission characteristics between square and circular wire array GaAs photocathodes.

PubMed

Deng, Wenjuan; Peng, Xincun; Zou, Jijun; Wang, Weilu; Liu, Yun; Zhang, Tao; Zhang, Yijun; Zhang, Daoli

2017-11-10

Two types of negative electron affinity gallium arsenide (GaAs) wire array photocathodes were fabricated by reactive ion etching and inductively coupled plasma etching of bulk GaAs material. High density GaAs wire arrays with high periodicity and good morphology were verified using scanning electron microscopy, and photoluminescence spectra confirmed the wire arrays had good crystalline quality. Reflection spectra showed that circular GaAs wire arrays had superior light trapping compared with square ones. However, after Cs/O activation, the square GaAs wire array photocathodes showed enhanced spectral response. The integral sensitivity of the square wire array photocathodes was approximately 2.8 times that of the circular arrays.

Integration of GaAs vertical-cavity surface emitting laser on Si by substrate removal

NASA Astrophysics Data System (ADS)

Yeh, Hsi-Jen J.; Smith, John S.

1994-03-01

The successful integration of strained quantum well InGaAs vertical-cavity surface-emitting lasers (VCSELs) on both Si and Cu substrates was described using a GaAs substrate removal technique. The GaAs VCSEL structure was metallized and bonded to the Si substrate after growth. The GaAs substrate was then removed by selective chemical wet etching. Finally, the bonded GaAs film metallized on the top (emitting) side and separate lasers were defined. This is the first time a VCSEL had been integrated on a Si substrate with its substrate removed. The performance enhancement of GaAs VCSELs bonded on good thermal conductors are demonstrated.

De novo Transcriptome Sequencing Reveals a Considerable Bias in the Incidence of Simple Sequence Repeats towards the Downstream of ‘Pre-miRNAs’ of Black Pepper

PubMed Central

Joy, Nisha; Asha, Srinivasan; Mallika, Vijayan; Soniya, Eppurathu Vasudevan

2013-01-01

Next generation sequencing has an advantageon transformational development of species with limited available sequence data as it helps to decode the genome and transcriptome. We carried out the de novo sequencing using illuminaHiSeq™ 2000 to generate the first leaf transcriptome of black pepper (Piper nigrum L.), an important spice variety native to South India and also grown in other tropical regions. Despite the economic and biochemical importance of pepper, a scientifically rigorous study at the molecular level is far from complete due to lack of sufficient sequence information and cytological complexity of its genome. The 55 million raw reads obtained, when assembled using Trinity program generated 2,23,386 contigs and 1,28,157 unigenes. Reports suggest that the repeat-rich genomic regions give rise to small non-coding functional RNAs. MicroRNAs (miRNAs) are the most abundant type of non-coding regulatory RNAs. In spite of the widespread research on miRNAs, little is known about the hair-pin precursors of miRNAs bearing Simple Sequence Repeats (SSRs). We used the array of transcripts generated, for the in silico prediction and detection of ‘43 pre-miRNA candidates bearing different types of SSR motifs’. The analysis identified 3913 different types of SSR motifs with an average of one SSR per 3.04 MB of thetranscriptome. About 0.033% of the transcriptome constituted ‘pre-miRNA candidates bearing SSRs’. The abundance, type and distribution of SSR motifs studied across the hair-pin miRNA precursors, showed a significant bias in the position of SSRs towards the downstream of predicted ‘pre-miRNA candidates’. The catalogue of transcripts identified, together with the demonstration of reliable existence of SSRs in the miRNA precursors, permits future opportunities for understanding the genetic mechanism of black pepper and likely functions of ‘tandem repeats’ in miRNAs. PMID:23469176

Comparative Analysis of the Complete Plastomes of Apostasia wallichii and Neuwiedia singapureana (Apostasioideae) Reveals Different Evolutionary Dynamics of IR/SSC Boundary among Photosynthetic Orchids.

PubMed

Niu, Zhitao; Pan, Jiajia; Zhu, Shuying; Li, Ludan; Xue, Qingyun; Liu, Wei; Ding, Xiaoyu

2017-01-01

Apostasioideae, consists of only two genera, Apostasia and Neuwiedia , which are mainly distributed in Southeast Asia and northern Australia. The floral structure, taxonomy, biogeography, and genome variation of Apostasioideae have been intensively studied. However, detailed analyses of plastome composition and structure and comparisons with those of other orchid subfamilies have not yet been conducted. Here, the complete plastome sequences of Apostasia wallichii and Neuwiedia singapureana were sequenced and compared with 43 previously published photosynthetic orchid plastomes to characterize the plastome structure and evolution in the orchids. Unlike many orchid plastomes (e.g., Paphiopedilum and Vanilla ), the plastomes of Apostasioideae contain a full set of 11 functional NADH dehydrogenase ( ndh ) genes. The distribution of repeat sequences and simple sequence repeat elements enhanced the view that the mutation rate of non-coding regions was higher than that of coding regions. The 10 loci- ndhA intron, matK-5'trnK , clpP-psbB , rps8-rpl14 , trnT-trnL , 3'trnK-matK , clpP intron , psbK-trnK , trnS-psbC , and ndhF-rpl32 -that had the highest degrees of sequence variability were identified as mutational hotspots for the Apostasia plastome. Furthermore, our results revealed that plastid genes exhibited a variable evolution rate within and among different orchid genus. Considering the diversified evolution of both coding and non-coding regions, we suggested that the plastome-wide evolution of orchid species was disproportional. Additionally, the sequences flanking the inverted repeat/small single copy (IR/SSC) junctions of photosynthetic orchid plastomes were categorized into three types according to the presence/absence of ndh genes. Different evolutionary dynamics for each of the three IR/SSC types of photosynthetic orchid plastomes were also proposed.

Comparative Analysis of the Complete Plastomes of Apostasia wallichii and Neuwiedia singapureana (Apostasioideae) Reveals Different Evolutionary Dynamics of IR/SSC Boundary among Photosynthetic Orchids

PubMed Central

Niu, Zhitao; Pan, Jiajia; Zhu, Shuying; Li, Ludan; Xue, Qingyun; Liu, Wei; Ding, Xiaoyu

2017-01-01

Apostasioideae, consists of only two genera, Apostasia and Neuwiedia, which are mainly distributed in Southeast Asia and northern Australia. The floral structure, taxonomy, biogeography, and genome variation of Apostasioideae have been intensively studied. However, detailed analyses of plastome composition and structure and comparisons with those of other orchid subfamilies have not yet been conducted. Here, the complete plastome sequences of Apostasia wallichii and Neuwiedia singapureana were sequenced and compared with 43 previously published photosynthetic orchid plastomes to characterize the plastome structure and evolution in the orchids. Unlike many orchid plastomes (e.g., Paphiopedilum and Vanilla), the plastomes of Apostasioideae contain a full set of 11 functional NADH dehydrogenase (ndh) genes. The distribution of repeat sequences and simple sequence repeat elements enhanced the view that the mutation rate of non-coding regions was higher than that of coding regions. The 10 loci—ndhA intron, matK-5′trnK, clpP-psbB, rps8-rpl14, trnT-trnL, 3′trnK-matK, clpP intron, psbK-trnK, trnS-psbC, and ndhF-rpl32—that had the highest degrees of sequence variability were identified as mutational hotspots for the Apostasia plastome. Furthermore, our results revealed that plastid genes exhibited a variable evolution rate within and among different orchid genus. Considering the diversified evolution of both coding and non-coding regions, we suggested that the plastome-wide evolution of orchid species was disproportional. Additionally, the sequences flanking the inverted repeat/small single copy (IR/SSC) junctions of photosynthetic orchid plastomes were categorized into three types according to the presence/absence of ndh genes. Different evolutionary dynamics for each of the three IR/SSC types of photosynthetic orchid plastomes were also proposed. PMID:29046685

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

NASA Technical Reports Server (NTRS)

Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

1988-01-01

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

Design optimization of GaAs betavoltaic batteries

NASA Astrophysics Data System (ADS)

Chen, Haiyanag; Jiang, Lan; Chen, Xuyuan

2011-06-01

GaAs junctions are designed and fabricated for betavoltaic batteries. The design is optimized according to the characteristics of GaAs interface states and the diffusion length in the depletion region of GaAs carriers. Under an illumination of 10 mCi cm-2 63Ni, the open circuit voltage of the optimized batteries is about ~0.3 V. It is found that the GaAs interface states induce depletion layers on P-type GaAs surfaces. The depletion layer along the P+PN+ junction edge isolates the perimeter surface from the bulk junction, which tends to significantly reduce the battery dark current and leads to a high open circuit voltage. The short circuit current density of the optimized junction is about 28 nA cm-2, which indicates a carrier diffusion length of less than 1 µm. The overall results show that multi-layer P+PN+ junctions are the preferred structures for GaAs betavoltaic battery design.

Lateral epitaxial overgowth of GaAs by organometallic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Gale, R. P.; Mcclelland, R. W.; Fan, J. C. C.; Bozler, C. O.

1982-01-01

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than five have been obtained. The lateral growth is due to surface-kinetic control for the two-dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 microns thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

LEC GaAs for integrated circuit applications

NASA Technical Reports Server (NTRS)

Kirkpatrick, C. G.; Chen, R. T.; Homes, D. E.; Asbeck, P. M.; Elliott, K. R.; Fairman, R. D.; Oliver, J. D.

1984-01-01

Recent developments in liquid encapsulated Czochralski techniques for the growth of semiinsulating GaAs for integrated circuit applications have resulted in significant improvements in the quality and quantity of GaAs material suitable for device processing. The emergence of high performance GaAs integrated circuit technologies has accelerated the demand for high quality, large diameter semiinsulating GaAs substrates. The new device technologies, including digital integrated circuits, monolithic microwave integrated circuits and charge coupled devices have largely adopted direct ion implantation for the formation of doped layers. Ion implantation lends itself to good uniformity and reproducibility, high yield and low cost; however, this technique also places stringent demands on the quality of the semiinsulating GaAs substrates. Although significant progress was made in developing a viable planar ion implantation technology, the variability and poor quality of GaAs substrates have hindered progress in process development.

Supernormal hardness increase of dilute Ga(As, N) thin films

NASA Astrophysics Data System (ADS)

Berggren, Jonas; Hanke, Michael; Luna, Esperanza; Trampert, Achim

2017-03-01

Hardness of epitaxial GaAs1-xNx films on GaAs(001) with different film thicknesses, varying from 80 to 700 nm, and nitrogen compositions x between zero (pure GaAs) and 0.031, were studied by means of nano-indentation. As a result, a disproportionate and monotonic increase by 17% in hardness was proved in the dilute range from GaAs to GaAs0.969N0.031. We are tracing this observation to solid solution strengthening, an extrinsic effect based on dislocation pinning due to interstitial nitrogen. On the other hand, intrinsic effects related to different electronegativities of As and N (i.e., altered bonding conditions) could be ruled out. Furthermore, in tensilely strained GaAs1-xNx layers, the appearance of cracks acts as the main strain relieving mechanism. A correlation between cracking and hardness reduction is investigated and discussed as a further relaxation pathway.

Transposon-driven transcription is a conserved feature of vertebrate spermatogenesis and transcript evolution.

PubMed

Davis, Matthew P; Carrieri, Claudia; Saini, Harpreet K; van Dongen, Stijn; Leonardi, Tommaso; Bussotti, Giovanni; Monahan, Jack M; Auchynnikava, Tania; Bitetti, Angelo; Rappsilber, Juri; Allshire, Robin C; Shkumatava, Alena; O'Carroll, Dónal; Enright, Anton J

2017-07-01

Spermatogenesis is associated with major and unique changes to chromosomes and chromatin. Here, we sought to understand the impact of these changes on spermatogenic transcriptomes. We show that long terminal repeats (LTRs) of specific mouse endogenous retroviruses (ERVs) drive the expression of many long non-coding transcripts (lncRNA). This process occurs post-mitotically predominantly in spermatocytes and round spermatids. We demonstrate that this transposon-driven lncRNA expression is a conserved feature of vertebrate spermatogenesis. We propose that transposon promoters are a mechanism by which the genome can explore novel transcriptional substrates, increasing evolutionary plasticity and allowing for the genesis of novel coding and non-coding genes. Accordingly, we show that a small fraction of these novel ERV-driven transcripts encode short open reading frames that produce detectable peptides. Finally, we find that distinct ERV elements from the same subfamilies act as differentially activated promoters in a tissue-specific context. In summary, we demonstrate that LTRs can act as tissue-specific promoters and contribute to post-mitotic spermatogenic transcriptome diversity. © 2017 The Authors. Published under the terms of the CC BY 4.0 license.

Noncoding origins of anthropoid traits and a new null model of transposon functionalization

PubMed Central

del Rosario, Ricardo C.H.; Rayan, Nirmala Arul

2014-01-01

Little is known about novel genetic elements that drove the emergence of anthropoid primates. We exploited the sequencing of the marmoset genome to identify 23,849 anthropoid-specific constrained (ASC) regions and confirmed their robust functional signatures. Of the ASC base pairs, 99.7% were noncoding, suggesting that novel anthropoid functional elements were overwhelmingly cis-regulatory. ASCs were highly enriched in loci associated with fetal brain development, motor coordination, neurotransmission, and vision, thus providing a large set of candidate elements for exploring the molecular basis of hallmark primate traits. We validated ASC192 as a primate-specific enhancer in proliferative zones of the developing brain. Unexpectedly, transposable elements (TEs) contributed to >56% of ASCs, and almost all TE families showed functional potential similar to that of nonrepetitive DNA. Three L1PA repeat-derived ASCs displayed coherent eye-enhancer function, thus demonstrating that the “gene-battery” model of TE functionalization applies to enhancers in vivo. Our study provides fundamental insights into genome evolution and the origins of anthropoid phenotypes and supports an elegantly simple new null model of TE exaptation. PMID:25043600

Transcription of tandemly repetitive DNA: functional roles.

PubMed

Biscotti, Maria Assunta; Canapa, Adriana; Forconi, Mariko; Olmo, Ettore; Barucca, Marco

2015-09-01

A considerable fraction of the eukaryotic genome is made up of satellite DNA constituted of tandemly repeated sequences. These elements are mainly located at centromeres, pericentromeres, and telomeres and are major components of constitutive heterochromatin. Although originally satellite DNA was thought silent and inert, an increasing number of studies are providing evidence on its transcriptional activity supporting, on the contrary, an unexpected dynamicity. This review summarizes the multiple structural roles of satellite noncoding RNAs at chromosome level. Indeed, satellite noncoding RNAs play a role in the establishment of a heterochromatic state at centromere and telomere. These highly condensed structures are indispensable to preserve chromosome integrity and genome stability, preventing recombination events, and ensuring the correct chromosome pairing and segregation. Moreover, these RNA molecules seem to be involved also in maintaining centromere identity and in elongation, capping, and replication of telomere. Finally, the abnormal variation of centromeric and pericentromeric DNA transcription across major eukaryotic lineages in stress condition and disease has evidenced the critical role that these transcripts may play and the potentially dire consequences for the organism.

Immunochromatographic strip assay for detection of bioactive Ganoderma triterpenoid, ganoderic acid A in Ganoderma lingzhi.

PubMed

Sakamoto, Seiichi; Kikkawa, Nao; Kohno, Toshitaka; Shimizu, Kuniyoshi; Tanaka, Hiroyuki; Morimoto, Satoshi

2016-10-01

Ganoderic acid A (GAA) is one of the major Ganoderma triterpenes produced by medicinal mushroom belonging to the genus Ganoderma (Ganodermataceae). Due to its interesting pharmacological activities, Ganoderma species have been traditionally used in China for the treatment of various diseases. Herein, we developed a colloidal gold-based immunochromatographic strip assay (ICA) for the rapid detection of GAA using highly specific monoclonal antibody against GAA (MAb 12A) conjugated with gold nanoparticles. Using the developed ICA, the detection of GAA can be completed within 15min after dipping the test strip into an analyte solution with the limit of detection (LOD) for GAA of ~500ng/mL. In addition, this system makes it possible to perform a semi-quantitative analysis of GAA in Ganoderma lingzhi, where high reliability was evaluated by enzyme-linked immunosorbent assay (ELISA). The newly developed ICA can potentially be applied to the standardization of Ganoderma using GAA as an index because GAA is major triterpenoid present much in the mushroom. Copyright © 2016. Published by Elsevier B.V.

MicroRNAs in CAG trinucleotide repeat expansion disorders: an integrated review of the literature.

PubMed

Dumitrescu, Laura; Popescu, Bogdan O

2015-01-01

MicroRNAs are small RNAs involved in gene silencing. They play important roles in transcriptional regulation and are selectively and abundantly expressed in the central nervous system. A considerable amount of the human genome is comprised of tandem repeating nucleotide streams. Several diseases are caused by above-threshold expansion of certain trinucleotide repeats occurring in a protein-coding or non-coding region. Though monogenic, CAG trinucleotide repeat expansion disorders have a complex pathogenesis, various combinations of multiple coexisting pathways resulting in one common final consequence: selective neurodegeneration. Mutant protein and mutant transcript gain of toxic function are considered to be the core pathogenic mechanisms. The profile of microRNAs in CAG trinucleotide repeat disorders is scarcely described, however microRNA dysregulation has been identified in these diseases and microRNA-related intereference with gene expression is considered to be involved in their pathogenesis. Better understanding of microRNAs functions and means of manipulation promises to offer further insights into the pathogenic pathways of CAG repeat expansion disorders, to point out new potential targets for drug intervention and to provide some of the much needed etiopathogenic therapeutic agents. A number of disease-modifying microRNA silencing strategies are under development, but several implementation impediments still have to be resolved. CAG targeting seems feasible and efficient in animal models and is an appealing approach for clinical practice. Preliminary human trials are just beginning.

Current Research on Non-Coding Ribonucleic Acid (RNA).

PubMed

Wang, Jing; Samuels, David C; Zhao, Shilin; Xiang, Yu; Zhao, Ying-Yong; Guo, Yan

2017-12-05

Non-coding ribonucleic acid (RNA) has without a doubt captured the interest of biomedical researchers. The ability to screen the entire human genome with high-throughput sequencing technology has greatly enhanced the identification, annotation and prediction of the functionality of non-coding RNAs. In this review, we discuss the current landscape of non-coding RNA research and quantitative analysis. Non-coding RNA will be categorized into two major groups by size: long non-coding RNAs and small RNAs. In long non-coding RNA, we discuss regular long non-coding RNA, pseudogenes and circular RNA. In small RNA, we discuss miRNA, transfer RNA, piwi-interacting RNA, small nucleolar RNA, small nuclear RNA, Y RNA, single recognition particle RNA, and 7SK RNA. We elaborate on the origin, detection method, and potential association with disease, putative functional mechanisms, and public resources for these non-coding RNAs. We aim to provide readers with a complete overview of non-coding RNAs and incite additional interest in non-coding RNA research.

The emergence of noncoding RNAs as Heracles in autophagy.

PubMed

Zhang, Jian; Wang, Peiyuan; Wan, Lin; Xu, Shouping; Pang, Da

2017-06-03

Macroautophagy/autophagy is a catabolic process that is widely found in nature. Over the past few decades, mounting evidence has indicated that noncoding RNAs, ranging from small noncoding RNAs to long noncoding RNAs (lncRNAs) and even circular RNAs (circRNAs), mediate the transcriptional and post-transcriptional regulation of autophagy-related genes by participating in autophagy regulatory networks. The differential expression of noncoding RNAs affects autophagy levels at different physiological and pathological stages, including embryonic proliferation and differentiation, cellular senescence, and even diseases such as cancer. We summarize the current knowledge regarding noncoding RNA dysregulation in autophagy and investigate the molecular regulatory mechanisms underlying noncoding RNA involvement in autophagy regulatory networks. Then, we integrate public resources to predict autophagy-related noncoding RNAs across species and discuss strategies for and the challenges of identifying autophagy-related noncoding RNAs. This article will deepen our understanding of the relationship between noncoding RNAs and autophagy, and provide new insights to specifically target noncoding RNAs in autophagy-associated therapeutic strategies.

Reflection high energy electron diffraction and reflectance difference studies of surface anisotropy in InGaAs chemical beam epitaxy on flat and vicinal (001) GaAs

NASA Astrophysics Data System (ADS)

Junno, B.; Paulsson, G.; Miller, M.; Samuelson, L.

1994-03-01

InGaAs quantum wells (QWs) were grown in a chemical beam epitaxy (CBE) machine with trimethylindium (TMI), triethylgallium (TEG) and tertiarybutylarsine (TBA) as precursors. Growth was monitored in-situ by reflectance difference (RD) and reflection high energy electron diffraction (RHEED), on both flat and vicinal (2° off in the <111> A direction) (001)GaAs substrates. The RD was monitored at 632.8 nm. At this wavelength the RD signal from a GaAs surface is primarily related to the absorption by Ga dimers. When InGaAs had been grown, both the average RD signal and the amplitude of the RD oscillations for the subsequent growth of GaAs increased significantly, compared to GaAs growth on GaAs. This In influence was found to persist even after the growth of 20-30 ML of pure GaAs. As a result we were able to monitor growth oscillations with RD and RHEED simultaneously during growth of quantum wells of InGaAs in GaAs. As a conclusion to these observations we suggest that the group III dimer bond concentration, detected in the RD signal, increases.

First tests of Timepix detectors based on semi-insulating GaAs matrix of different pixel size

NASA Astrophysics Data System (ADS)

Zaťko, B.; Kubanda, D.; Žemlička, J.; Šagátová, A.; Zápražný, Z.; Boháček, P.; Nečas, V.; Mora, Y.; Pichotka, M.; Dudák, J.

2018-02-01

In this work, we have focused on Timepix detectors coupled with the semi-insulating GaAs material sensor. We used undoped bulk GaAs material with the thickness of 350 μm. We prepared and tested four pixelated detectors with 165 μm and 220 μm pixel size with two versions of technology preparation, without and with wet chemically etched trenches around each pixel. We have carried out adjustment of GaAs Timepix detectors to optimize their performance. The energy calibration of one GaAs Timepix detector in Time-over-threshold mode was performed with the use of 241Am and 133Ba radioisotopes. We were able to detect γ-photons with the energy up to 160 keV. The X-ray imaging quality of GaAs Timepix detector was tested with X-ray source using various samples. After flat field we obtained very promising imaging performance of tested GaAs Timepix detectors.

Formation and photoluminescence of GaAs1-xNx dilute nitride achieved by N-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2014-07-01

In this paper, we present the fabrication of dilute nitride semiconductor GaAs1-xNx by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1 = 0.38% and ximp2 = 0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs1-xNx samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1 = 0.38% and ximp2 = 0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.

Giant and reversible enhancement of the electrical resistance of GaAs1-xNx by hydrogen irradiation

NASA Astrophysics Data System (ADS)

Alvarez, J.; Kleider, J.-P.; Trotta, R.; Polimeni, A.; Capizzi, M.; Martelli, F.; Mariucci, L.; Rubini, S.

2011-08-01

The electrical properties of untreated and hydrogen-irradiated GaAs1-xNx are investigated by conductive-probe atomic force microscopy (CP-AFM). After hydrogen irradiation, the resistance R of GaAs1-xNx increases by more than three orders of magnitude while that of a N-free GaAs reference slightly decreases. Thermal annealing at 550 °C of H-irradiated GaAs1-xNx restores the pristine electrical properties of the as-grown sample thus demonstrating that this phenomenon is fully reversible. These effects are attributed to the nitrogen-hydrogen complexes that passivate N in GaAs1-xNx (thus restoring the energy gap of N-free GaAs) and, moreover, reduce the carrier scattering time by more than one order of magnitude. This opens up a route to the fabrication of planar conductive/resistive/conductive heterostructures with submicrometer spatial resolution, which is also reported here.

Prediction of dislocation generation during Bridgman growth of GaAs crystals

NASA Technical Reports Server (NTRS)

Tsai, C. T.; Yao, M. W.; Chait, Arnon

1992-01-01

Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

Prediction of dislocation generation during Bridgman growth of GaAs crystals

NASA Astrophysics Data System (ADS)

Tsai, C. T.; Yao, M. W.; Chait, Arnon

1992-11-01

Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1984-01-01

The crystal growth, device processing and device related properties and phenomena of GaAs are investigated. Our GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor materials (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; (3) investigation of electronic properties and phenomena controlling device applications and device performance. The ground based program is developed which would insure successful experimentation with and eventually processing of GaAs in a near zero gravity environment.

Effect of guanidinoacetic acid supplementation on live performance, meat quality, pectoral myopathies and blood parameters of male broilers fed corn-based diets with or without poultry by-products.

PubMed

Córdova-Noboa, H A; Oviedo-Rondón, E O; Sarsour, A H; Barnes, J; Sapcota, D; López, D; Gross, L; Rademacher-Heilshorn, M; Braun, U

2018-04-13

Creatine is a nitrogenous compound naturally occurring in animal tissues and is obtained from dietary animal protein or de novo synthesis from guanidinoacetic acid (GAA). The dietary supply of this semi-essential nutrient could be adversely compromised when feeding purely vegetable-based diets. The objective of this experiment was to evaluate the effects of GAA supplementation in broilers fed corn-based diets with or without the inclusion of poultry by-products (PBP) on live performance, carcass and cut up yields, meat quality, pectoral muscle myopathies, differential blood count, blood clinical chemistry, serum GAA and its metabolites. The treatments consisted of PBP inclusion in the diets at 0 and 5%, with or without GAA supplementation (0 or 0.06%). A total of 1,280 one-d-old male Ross 708 broiler chicks were randomly placed in 64 floor pens with 16 replicates per treatment combination. At 0, 14, 35, 48, and 55 d, pen BW and feed intake were recorded. BW gain and FCR were calculated at the end of each phase. Individual BW was obtained at 55 d and one broiler per pen was selected for blood collection. Additionally, four broilers per pen were selected (including the chicken for blood collection) for processing. Data were analyzed as a randomized complete block design in a 2 × 2 factorial arrangement with PBP and GAA supplementation as main effects. An improvement (P < 0.05) on FCR of 0.019 (g:g) was detected at 55 d due to GAA supplementation. The probability of having breast meat with low severity of wooden breast (score 2) was increased (P < 0.05) by GAA inclusion in diets without PBP. An interaction effect (P < 0.05) was detected on GAA concentration in blood. The supplementation with GAA and PBP inclusion resulted in higher (P < 0.05) GAA serum concentration. Generally, meat quality parameters were not affected by GAA. In conclusion, GAA supplementation improved FCR regardless of dietary PBP and reduced wooden breast severity by increasing score 2 in diets without PBP.

The ratio of glycated albumin to hemoglobin A1c measured in IFCC units accurately represents the glycation gap.

PubMed

Akatsuka, Junya; Mochizuki, Mie; Musha, Ikuma; Ohtake, Akira; Kobayashi, Kisho; Kikuchi, Toru; Kikuchi, Nobuyuki; Kawamura, Tomoyuki; Urakami, Tatsuhiko; Sugihara, Shigetaka; Hoshino, Tadao; Amemiya, Shin

2015-01-01

The glycation gap (G-gap: difference between measured hemoglobin A1c [A1C] and the value predicted by its regression on the fructosamine level) is stable and associated with diabetic complications. Measuring A1C level in International Federation of Clinical Chemistry (IFCC) units (A1C-SI; mmol/mol) and National Glycohemoglobin Standardization Program units (A1C-NGSP; %) and using glycated albumin (GA) level instead of fructosamine level for calculating the G-gap, we investigated whether the G-gap is better represented by GA/A1C ratio if expressed in SI units (GA/A1C-SI ratio) rather than in NGSP units (GA/A1C-% ratio). We examined 749 Japanese children with type 1 diabetes using simultaneous GA and A1C measurements. Of these, 369 patients were examined more than five times to assess the consistency of the G-gap and the GA/A1C ratio within individuals. The relationship of GA/A1C-% ratio to the corresponding A1C-NGSP was stronger than that of GA/A1C-SI ratio to A1C-IFCC. At enrollment, the inverse relationship between the GA/A1C-SI ratio and G-gap was highly significant (R(2) = 0.95) compared with that between the GA/A1C-% ratio and G-gap (R(2) = 0.69). A highly significant inverse relationship was also observed between the mean GA/A1C-SI ratio and the mean G-gaps obtained individually over time (R(2) = 0.95) compared with that using the corresponding A1C-NGSP (R(2) = 0.67). We conclude that the G-gap is better represented by the GA/A1C-SI ratio. We propose the use of mean GA/A1C-SI ratios easily obtained individually over time as reference values in Japanese children with type 1 diabetes (6.75 ± 0.60 [means ± SD]).

Expansion of the Spinocerebellar Ataxia Type 10 (SCA10) Repeat in a Patient with Sioux Native American Ancestry

PubMed Central

Liu, Jilin; McFarland, Karen N.; Landrian, Ivette; Hutter, Diane; Teive, Hélio A. G.; Rasmussen, Astrid; Mulligan, Connie J.; Ashizawa, Tetsuo

2013-01-01

Spinocerebellar ataxia type 10 (SCA10), an autosomal dominant cerebellar ataxia, is caused by the expansion of the non-coding ATTCT pentanucleotide repeat in the ATAXIN 10 gene. To date, all cases of SCA10 are restricted to patients with ancestral ties to Latin American countries. Here, we report on a SCA10 patient with Sioux Native American ancestry and no reported Hispanic or Latino heritage. Neurological exam findings revealed impaired gait with mild, age-consistent cerebellar atrophy and no evidence of epileptic seizures. The age at onset for this patient, at 83 years of age, is the latest documented for SCA10 patients and is suggestive of a reduced penetrance allele in his family. Southern blot analysis showed an SCA10 expanded allele of 1400 repeats. Established SNPs surrounding the SCA10 locus showed a disease haplotype consistent with the previously described “SCA10 haplotype”. This case suggests that the SCA10 expansion represents an early mutation event that possibly occurred during the initial peopling of the Americas. PMID:24278426

Major satellite repeat RNA stabilize heterochromatin retention of Suv39h enzymes by RNA-nucleosome association and RNA:DNA hybrid formation.

PubMed

Velazquez Camacho, Oscar; Galan, Carmen; Swist-Rosowska, Kalina; Ching, Reagan; Gamalinda, Michael; Karabiber, Fethullah; De La Rosa-Velazquez, Inti; Engist, Bettina; Koschorz, Birgit; Shukeir, Nicholas; Onishi-Seebacher, Megumi; van de Nobelen, Suzanne; Jenuwein, Thomas

2017-08-01

The Suv39h1 and Suv39h2 histone lysine methyltransferases are hallmark enzymes at mammalian heterochromatin. We show here that the mouse Suv39h2 enzyme differs from Suv39h1 by containing an N-terminal basic domain that facilitates retention at mitotic chromatin and provides an additional affinity for major satellite repeat RNA. To analyze an RNA-dependent interaction with chromatin, we purified native nucleosomes from mouse ES cells and detect that Suv39h1 and Suv39h2 exclusively associate with poly-nucleosomes. This association was attenuated upon RNaseH incubation and entirely lost upon RNaseA digestion of native chromatin. Major satellite repeat transcripts remain chromatin-associated and have a secondary structure that favors RNA:DNA hybrid formation. Together, these data reveal an RNA-mediated mechanism for the stable chromatin interaction of the Suv39h KMT and suggest a function for major satellite non-coding RNA in the organization of an RNA-nucleosome scaffold as the underlying structure of mouse heterochromatin.

Precise small molecule recognition of a toxic CUG RNA repeat expansion

PubMed Central

Rzuczek, Suzanne G; Colgan, Lesley A; Nakai, Yoshio; Cameron, Michael D; Furling, Denis; Yasuda, Ryohei; Disney, Matthew D

2017-01-01

Excluding the ribosome and riboswitches, developing small molecules that selectively target RNA is a longstanding problem in chemical biology. A typical cellular RNA is difficult to target because it has little tertiary, but abundant secondary structure. We designed allele-selective compounds that target such an RNA, the toxic noncoding repeat expansion (r(CUG)exp) that causes myotonic dystrophy type 1 (DM1). We developed several strategies to generate allele-selective small molecules, including non-covalent binding, covalent binding, cleavage and on-site probe synthesis. Covalent binding and cleavage enabled target profiling in cells derived from individuals with DM1, showing precise recognition of r(CUG)exp. In the on-site probe synthesis approach, small molecules bound adjacent sites in r(CUG)exp and reacted to afford picomolar inhibitors via a proximity-based click reaction only in DM1-affected cells. We expanded this approach to image r(CUG)exp in its natural context. PMID:27941760

Precise small-molecule recognition of a toxic CUG RNA repeat expansion.

PubMed

Rzuczek, Suzanne G; Colgan, Lesley A; Nakai, Yoshio; Cameron, Michael D; Furling, Denis; Yasuda, Ryohei; Disney, Matthew D

2017-02-01

Excluding the ribosome and riboswitches, developing small molecules that selectively target RNA is a longstanding problem in chemical biology. A typical cellular RNA is difficult to target because it has little tertiary, but abundant secondary structure. We designed allele-selective compounds that target such an RNA, the toxic noncoding repeat expansion (r(CUG) exp ) that causes myotonic dystrophy type 1 (DM1). We developed several strategies to generate allele-selective small molecules, including non-covalent binding, covalent binding, cleavage and on-site probe synthesis. Covalent binding and cleavage enabled target profiling in cells derived from individuals with DM1, showing precise recognition of r(CUG) exp . In the on-site probe synthesis approach, small molecules bound adjacent sites in r(CUG) exp and reacted to afford picomolar inhibitors via a proximity-based click reaction only in DM1-affected cells. We expanded this approach to image r(CUG) exp in its natural context.

Nezha, a novel active miniature inverted-repeat transposable element in cyanobacteria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou Fengfeng; Tran Thao; Xu Ying

2008-01-25

Miniature inverted-repeat transposable elements (MITEs) were first identified in plants and exerted extensive proliferations throughout eukaryotic and archaeal genomes. But very few MITEs have been characterized in bacteria. We identified a novel MITE, called Nezha, in cyanobacteria Anabaena variabilis ATCC 29413 and Nostoc sp. PCC 7120. Nezha, like most previously known MITEs in other organisms, is small in size, non-coding, carrying TIR and DR signals, and of potential to form a stable RNA secondary structure, and it tends to insert into A+T-rich regions. Recent transpositions of Nezha were observed in A. variabilis ATCC 29413 and Nostoc sp. PCC 7120, respectively.more » Nezha might have proliferated recently with aid from the transposase encoded by ISNpu3-like elements. A possible horizontal transfer event of Nezha from cyanobacteria to Polaromonas JS666 is also observed.« less

Biological significance of long non-coding RNA FTX expression in human colorectal cancer.

PubMed

Guo, Xiao-Bo; Hua, Zhu; Li, Chen; Peng, Li-Pan; Wang, Jing-Shen; Wang, Bo; Zhi, Qiao-Ming

2015-01-01

The purpose of this study was to determine the expression of long non-coding RNA (lncRNA) FTX and analyze its prognostic and biological significance in colorectal cancer (CRC). A quantitative reverse transcription PCR was performed to detect the expression of long non-coding RNA FTX in 35 pairs of colorectal cancer and corresponding noncancerous tissues. The expression of long non-coding RNA FTX was detected in 187 colorectal cancer tissues and its correlations with clinicopathological factors of patients were examined. Univariate and multivariate analyses were performed to analyze the prognostic significance of Long Non-coding RNA FTX expression. The effects of long non-coding RNA FTX expression on malignant phenotypes of colorectal cancer cells and its possible biological significances were further determined. Long non-coding RNA FTX was significantly upregulated in colorectal cancer tissues, and low long non-coding RNA FTX expression was significantly correlated with differentiation grade, lymph vascular invasion, and clinical stage. Patients with high long non-coding RNA FTX showed poorer overall survival than those with low long non-coding RNA FTX. Multivariate analyses indicated that status of long non-coding RNA FTX was an independent prognostic factor for patients. Functional analyses showed that upregulation of long non-coding RNA FTX significantly promoted growth, migration, invasion, and increased colony formation in colorectal cancer cells. Therefore, long non-coding RNA FTX may be a potential biomarker for predicting the survival of colorectal cancer patients and might be a molecular target for treatment of human colorectal cancer.

Understanding and Curing Structural Defects in Colloidal GaAs Nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, Vishwas; Liu, Wenyong; Janke, Eric M.

2017-02-22

Nearly three decades since the first report on the synthesis of colloidal GaAs nanocrystals (NCs), the preparation and properties of this material remain highly controversial. Traditional synthetic routes either fail to produce the GaAs phase or result in materials that do not show expected optical properties such as excitonic transitions. In this work, we demonstrate a variety of synthetic routes toward crystalline GaAs NCs. By using a combination of Raman, EXAFS and transient absorption spectroscopies, we conclude that unusual optical properties of 2 colloidal GaAs NCs can be related to the presence of vacancies and lattice disorder. We introduce novelmore » molten salt based annealing approach to alleviate these structural defects and show the emergence of size-dependent excitonic transitions in colloidal GaAs quantum dots.« less

Creatine synthesis: production of guanidinoacetate by the rat and human kidney in vivo.

PubMed

Edison, Erica E; Brosnan, Margaret E; Meyer, Christian; Brosnan, John T

2007-12-01

A fraction of the body's creatine and creatine phosphate spontaneously degrades to creatinine, which is excreted by the kidneys. In humans, this amounts to approximately 1-2 g/day and demands a comparable rate of de novo creatine synthesis. This is a two-step process in which l-arginine:glycine amidinotransferase (AGAT) catalyzes the conversion of glycine and arginine to ornithine and guanidinoacetate (GAA); guanidinoacetate methyltransferase (GAMT) then catalyzes the S-adenosylmethionine-dependent methylation of GAA to creatine. AGAT is found in the kidney and GAMT in the liver, which implies an interorgan movement of GAA from the kidney to the liver. We studied the renal production of this metabolite in both rats and humans. In control rats, [GAA] was 5.9 microM in arterial plasma and 10.9 microM in renal venous plasma for a renal arteriovenous (A-V) difference of -5.0 microM. In the rat, infusion of arginine or citrulline markedly increased renal GAA production but infusion of glycine did not. Rats fed 0.4% creatine in their diet had decreased renal AGAT activity and mRNA, an arterial plasma [GAA] of 1.5 microM, and a decreased renal A-V difference for GAA of -0.9 microM. In humans, [GAA] was 2.4 microM in arterial plasma, with a renal A-V difference of -1.1 microM. These studies show, for the first time, that GAA is produced by both rat and human kidneys in vivo.

Rescue of Pompe disease in mice by AAV-mediated liver delivery of secretable acid α-glucosidase

PubMed Central

Puzzo, Francesco; Colella, Pasqualina; Biferi, Maria G.; Bali, Deeksha; Paulk, Nicole K.; Vidal, Patrice; Collaud, Fanny; Simon-Sola, Marcelo; Charles, Severine; Hardet, Romain; Leborgne, Christian; Meliani, Amine; Cohen-Tannoudji, Mathilde; Astord, Stephanie; Gjata, Bernard; Sellier, Pauline; van Wittenberghe, Laetitia; Vignaud, Alban; Boisgerault, Florence; Barkats, Martine; Laforet, Pascal; Kay, Mark A.; Koeberl, Dwight D.; Ronzitti, Giuseppe; Mingozzi, Federico

2018-01-01

Glycogen storage disease type II or Pompe disease is a severe neuromuscular disorder caused by mutations in the lysosomal enzyme, acid α-glucosidase (GAA), which result in pathological accumulation of glycogen throughout the body. Enzyme replacement therapy is available for Pompe disease; however, it has limited efficacy, has high immunogenicity, and fails to correct pathological glycogen accumulation in nervous tissue and skeletal muscle. Using bioinformatics analysis and protein engineering, we developed transgenes encoding GAA that could be expressed and secreted by hepatocytes. Then, we used adeno-associated virus (AAV) vectors optimized for hepatic expression to deliver the GAA transgenes to Gaa knockout (Gaa−/−) mice, a model of Pompe disease. Therapeutic gene transfer to the liver rescued glycogen accumulation in muscle and the central nervous system, and ameliorated cardiac hypertrophy as well as muscle and respiratory dysfunction in the Gaa−/− mice; mouse survival was also increased. Secretable GAA showed improved therapeutic efficacy and lower immunogenicity compared to nonengineered GAA. Scale-up to nonhuman primates, and modeling of GAA expression in primary human hepatocytes using hepatotropic AAV vectors, demonstrated the therapeutic potential of AAV vector–mediated liver expression of secretable GAA for treating pathological glycogen accumulation in multiple tissues in Pompe disease. PMID:29187643

Three-dimensional lattice rotation in GaAs nanowire growth on hydrogen-silsesquioxane covered GaAs (001) using molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Tran, Dat Q.; Pham, Huyen T.; Higashimine, Koichi; Oshima, Yoshifumi; Akabori, Masashi

2018-05-01

We report on crystallographic behaviors of inclined GaAs nanowires (NWs) self-crystallized on GaAs (001) substrate. The NWs were grown on hydrogen-silsesquioxane (HSQ) covered substrates using molecular beam epitaxy (MBE). Commonly, the epitaxial growth of GaAs < 111>B (B-polar) NWs is prominently observed on GaAs (001); however, we yielded a remarkable number of epitaxially grown GaAs < 111>A (A-polar) NWs in addition to the majorly obtained B-polar NWs. Such NW orientations are always accompanied by a typical inclined angle of 35° from (001) plane. NWs with another inclined angle of 74° were additionally observed and attributed to be < 111>-oriented, not in direct epitaxial relation with the substrate. Such 74° NWs' existence is related to first-order three-dimensional (3D) lattice rotation taking place at the very beginning of the growth. It turns out that spatially 60° lattice rotation around < 111> directions at GaAs seeds is essentially in charge of A- and B-polar 74° NWs. Transmission electron microscope observations reveal a high density of twinning in the B-polar NWs and twin-free characteristic in the A-polar NWs.

Photoelectrochemical Water Oxidation by GaAs Nanowire Arrays Protected with Atomic Layer Deposited NiO x Electrocatalysts

NASA Astrophysics Data System (ADS)

Zeng, Joy; Xu, Xiaoqing; Parameshwaran, Vijay; Baker, Jon; Bent, Stacey; Wong, H.-S. Philip; Clemens, Bruce

2018-02-01

Photoelectrochemical (PEC) hydrogen production makes possible the direct conversion of solar energy into chemical fuel. In this work, PEC photoanodes consisting of GaAs nanowire (NW) arrays were fabricated, characterized, and then demonstrated for the oxygen evolution reaction (OER). Uniform and periodic GaAs nanowire arrays were grown on a heavily n-doped GaAs substrates by metal-organic chemical vapor deposition selective area growth. The nanowire arrays were characterized using cyclic voltammetry and impedance spectroscopy in a non-aqueous electrochemical system using ferrocene/ferrocenium (Fc/Fc+) as a redox couple, and a maximum oxidation photocurrent of 11.1 mA/cm2 was measured. GaAs NW arrays with a 36 nm layer of nickel oxide (NiO x ) synthesized by atomic layer deposition were then used as photoanodes to drive the OER. In addition to acting as an electrocatalyst, the NiO x layer served to protect the GaAs NWs from oxidative corrosion. Using this strategy, GaAs NW photoanodes were successfully used for the oxygen evolution reaction. This is the first demonstration of GaAs NW arrays for effective OER, and the fabrication and protection strategy developed in this work can be extended to study any other nanostructured semiconductor materials systems for electrochemical solar energy conversion.

Inverted thermal conversion - GaAs, a new alternative material for integrated circuits

NASA Technical Reports Server (NTRS)

Lagowski, J.; Gatos, H. C.; Kang, C. H.; Skowronski, M.; Ko, K. Y.

1986-01-01

A new type of GaAs is developed which exhibits inverted thermal conversion (ITC); i.e., it converts from conducting to semiinsulating upon annealing at about 850 C. In device fabrication, its low resistivity prior to high-temperature processing differentiates ITC GaAs from the standard semiinsulating GaAs. The ITC characteristics are obtained through control of the concentration of the midgap donor EL2 based on heat treatment and crystal-growth modification. Thus EL2 does not exist in the conducting state of ITC GaAs. Conversion to the semiinsulating state during 850 C annealing is caused by the formation of EL2.

Characteristics of GaAs with inverted thermal conversion

NASA Technical Reports Server (NTRS)

Kang, C. H.; Lagowski, J.; Gatos, H. C.

1987-01-01

GaAs crystals exhibiting inverted thermal conversion (ITC) of resistivity were investigated in conjunction with standard semiinsulating (SI) GaAs regarding characteristics important in device processing. It was established that dislocation density and Si implant activation are unaffected by transformation to the ITC state. However, in ITC GaAs the controlled increase of the EL2 (native midgap donor) concentration during annealing makes it possible to attain resistivities one order of magnitude greater (e.g., about 10 to the 9th ohm cm of 300 K) than those attained in standard SI GaAs (e.g., 10 to the 7th-10 to the 8th ohm cm).

Investigation of a Quadruplex-Forming Repeat Sequence Highly Enriched in Xanthomonas and Nostoc sp.

PubMed

Rehm, Charlotte; Wurmthaler, Lena A; Li, Yuanhao; Frickey, Tancred; Hartig, Jörg S

2015-01-01

In prokaryotes simple sequence repeats (SSRs) with unit sizes of 1-5 nucleotides (nt) are causative for phase and antigenic variation. Although an increased abundance of heptameric repeats was noticed in bacteria, reports about SSRs of 6-9 nt are rare. In particular G-rich repeat sequences with the propensity to fold into G-quadruplex (G4) structures have received little attention. In silico analysis of prokaryotic genomes show putative G4 forming sequences to be abundant. This report focuses on a surprisingly enriched G-rich repeat of the type GGGNATC in Xanthomonas and cyanobacteria such as Nostoc. We studied in detail the genomes of Xanthomonas campestris pv. campestris ATCC 33913 (Xcc), Xanthomonas axonopodis pv. citri str. 306 (Xac), and Nostoc sp. strain PCC7120 (Ana). In all three organisms repeats are spread all over the genome with an over-representation in non-coding regions. Extensive variation of the number of repetitive units was observed with repeat numbers ranging from two up to 26 units. However a clear preference for four units was detected. The strong bias for four units coincides with the requirement of four consecutive G-tracts for G4 formation. Evidence for G4 formation of the consensus repeat sequences was found in biophysical studies utilizing CD spectroscopy. The G-rich repeats are preferably located between aligned open reading frames (ORFs) and are under-represented in coding regions or between divergent ORFs. The G-rich repeats are preferentially located within a distance of 50 bp upstream of an ORF on the anti-sense strand or within 50 bp from the stop codon on the sense strand. Analysis of whole transcriptome sequence data showed that the majority of repeat sequences are transcribed. The genetic loci in the vicinity of repeat regions show increased genomic stability. In conclusion, we introduce and characterize a special class of highly abundant and wide-spread quadruplex-forming repeat sequences in bacteria.

Investigation of a Quadruplex-Forming Repeat Sequence Highly Enriched in Xanthomonas and Nostoc sp.

PubMed Central

Rehm, Charlotte; Wurmthaler, Lena A.; Li, Yuanhao; Frickey, Tancred; Hartig, Jörg S.

2015-01-01

In prokaryotes simple sequence repeats (SSRs) with unit sizes of 1–5 nucleotides (nt) are causative for phase and antigenic variation. Although an increased abundance of heptameric repeats was noticed in bacteria, reports about SSRs of 6–9 nt are rare. In particular G-rich repeat sequences with the propensity to fold into G-quadruplex (G4) structures have received little attention. In silico analysis of prokaryotic genomes show putative G4 forming sequences to be abundant. This report focuses on a surprisingly enriched G-rich repeat of the type GGGNATC in Xanthomonas and cyanobacteria such as Nostoc. We studied in detail the genomes of Xanthomonas campestris pv. campestris ATCC 33913 (Xcc), Xanthomonas axonopodis pv. citri str. 306 (Xac), and Nostoc sp. strain PCC7120 (Ana). In all three organisms repeats are spread all over the genome with an over-representation in non-coding regions. Extensive variation of the number of repetitive units was observed with repeat numbers ranging from two up to 26 units. However a clear preference for four units was detected. The strong bias for four units coincides with the requirement of four consecutive G-tracts for G4 formation. Evidence for G4 formation of the consensus repeat sequences was found in biophysical studies utilizing CD spectroscopy. The G-rich repeats are preferably located between aligned open reading frames (ORFs) and are under-represented in coding regions or between divergent ORFs. The G-rich repeats are preferentially located within a distance of 50 bp upstream of an ORF on the anti-sense strand or within 50 bp from the stop codon on the sense strand. Analysis of whole transcriptome sequence data showed that the majority of repeat sequences are transcribed. The genetic loci in the vicinity of repeat regions show increased genomic stability. In conclusion, we introduce and characterize a special class of highly abundant and wide-spread quadruplex-forming repeat sequences in bacteria. PMID:26695179

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

NASA Astrophysics Data System (ADS)

Zhou, Xu-Liang; Pan, Jiao-Qing; Yu, Hong-Yan; Li, Shi-Yan; Wang, Bao-Jun; Bian, Jing; Wang, Wei

2014-12-01

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm-2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

A new assay for fast, reliable CRIM status determination in infantile-onset Pompe disease.

PubMed

Wang, Zhaohui; Okamoto, Patricia; Keutzer, Joan

2014-02-01

Pompe disease is caused by a deficiency of acid α-glucosidase (GAA; EC, 3.2.1.20), and the infantile-onset form is rapidly fatal if left untreated. However, recombinant human GAA (rhGAA) enzyme replacement therapy (ERT) extends survival for infantile Pompe patients. Although cross-reactive immunologic material (CRIM)-negative patients, who lack detectable endogenous GAA, mount an immune response to rhGAA that renders the therapy ineffective, timely induction of immune tolerance in these patients may improve clinical outcomes. Previously, CRIM status has been determined by Western blot analysis in cultured skin fibroblasts, a process that can take a few weeks. We present a blood-based CRIM assay that can yield results within 48 to 72 h. Results from this assay have been confirmed by GAA Western blot analysis in fibroblasts or by GAA sequencing in a small number of Pompe disease patients. Rapid classification of CRIM status will assist in identifying the most effective treatment course and minimizing treatment delays in patients with infantile-onset Pompe disease. © 2013.

Biological significance of long non-coding RNA FTX expression in human colorectal cancer

PubMed Central

Guo, Xiao-Bo; Hua, Zhu; Li, Chen; Peng, Li-Pan; Wang, Jing-Shen; Wang, Bo; Zhi, Qiao-Ming

2015-01-01

The purpose of this study was to determine the expression of long non-coding RNA (lncRNA) FTX and analyze its prognostic and biological significance in colorectal cancer (CRC). A quantitative reverse transcription PCR was performed to detect the expression of long non-coding RNA FTX in 35 pairs of colorectal cancer and corresponding noncancerous tissues. The expression of long non-coding RNA FTX was detected in 187 colorectal cancer tissues and its correlations with clinicopathological factors of patients were examined. Univariate and multivariate analyses were performed to analyze the prognostic significance of Long Non-coding RNA FTX expression. The effects of long non-coding RNA FTX expression on malignant phenotypes of colorectal cancer cells and its possible biological significances were further determined. Long non-coding RNA FTX was significantly upregulated in colorectal cancer tissues, and low long non-coding RNA FTX expression was significantly correlated with differentiation grade, lymph vascular invasion, and clinical stage. Patients with high long non-coding RNA FTX showed poorer overall survival than those with low long non-coding RNA FTX. Multivariate analyses indicated that status of long non-coding RNA FTX was an independent prognostic factor for patients. Functional analyses showed that upregulation of long non-coding RNA FTX significantly promoted growth, migration, invasion, and increased colony formation in colorectal cancer cells. Therefore, long non-coding RNA FTX may be a potential biomarker for predicting the survival of colorectal cancer patients and might be a molecular target for treatment of human colorectal cancer. PMID:26629053

Dynamics of reflection high-energy electron diffraction intensity oscillations during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates

NASA Astrophysics Data System (ADS)

Yen, M. Y.; Haas, T. W.

1990-06-01

We have observed intensity oscillations in reflection high-energy electron diffraction during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates. These oscillations only exist over a narrow range of growth conditions and their behavior is strongly dependent on the migration kinetics of group III and the molecular dissociative reaction of group V elements.

Multilayer self-organization of InGaAs quantum wires on GaAs surfaces

NASA Astrophysics Data System (ADS)

Wang, Zhiming M.; Kunets, Vasyl P.; Xie, Yanze Z.; Schmidbauer, Martin; Dorogan, Vitaliy G.; Mazur, Yuriy I.; Salamo, Gregory J.

2010-12-01

Molecular-Beam Epitaxy growth of multiple In 0.4Ga 0.6As layers on GaAs (311)A and GaAs (331)A has been investigated by Atomic Force Microscopy and Photoluminescence. On GaAs (311)A, uniformly distributed In 0.4Ga 0.6As quantum wires (QWRs) with wider lateral separation were achieved, presenting a significant improvement in comparison with the result on single layer [H. Wen, Z.M. Wang, G.J. Salamo, Appl. Phys. Lett. 84 (2004) 1756]. On GaAs (331)A, In 0.4Ga 0.6As QWRs were revealed to be much straighter than in the previous report on multilayer growth [Z. Gong, Z. Niu, Z. Fang, Nanotechnology 17 (2006) 1140]. These observations are discussed in terms of the strain-field interaction among multilayers, enhancement of surface mobility at high temperature, and surface stability of GaAs (311)A and (331)A surfaces.

Wafer-scale layer transfer of GaAs and Ge onto Si wafers using patterned epitaxial lift-off

NASA Astrophysics Data System (ADS)

Mieda, Eiko; Maeda, Tatsuro; Miyata, Noriyuki; Yasuda, Tetsuji; Kurashima, Yuichi; Maeda, Atsuhiko; Takagi, Hideki; Aoki, Takeshi; Yamamoto, Taketsugu; Ichikawa, Osamu; Osada, Takenori; Hata, Masahiko; Ogawa, Arito; Kikuchi, Toshiyuki; Kunii, Yasuo

2015-03-01

We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.

Formation of embedded plasmonic Ga nanoparticle arrays and their influence on GaAs photoluminescence

NASA Astrophysics Data System (ADS)

Kang, M.; Jeon, S.; Jen, T.; Lee, J.-E.; Sih, V.; Goldman, R. S.

2017-07-01

We introduce a novel approach to the seamless integration of plasmonic nanoparticle (NP) arrays into semiconductor layers and demonstrate their enhanced photoluminescence (PL) efficiency. Our approach utilizes focused ion beam-induced self-assembly of close-packed arrays of Ga NPs with tailorable NP diameters, followed by overgrowth of GaAs layers using molecular beam epitaxy. Using a combination of PL spectroscopy and electromagnetic computations, we identify a regime of Ga NP diameter and overgrown GaAs layer thickness where NP-array-enhanced absorption in GaAs leads to enhanced GaAs near-band-edge (NBE) PL efficiency, surpassing that of high-quality epitaxial GaAs layers. As the NP array depth and size are increased, the reduction in spontaneous emission rate overwhelms the NP-array-enhanced absorption, leading to a reduced NBE PL efficiency. This approach provides an opportunity to enhance the PL efficiency of a wide variety of semiconductor heterostructures.

Biochemical, molecular, and clinical diagnoses of patients with cerebral creatine deficiency syndromes.

PubMed

Comeaux, Matthew S; Wang, Jing; Wang, Guoli; Kleppe, Soledad; Zhang, Victor Wei; Schmitt, Eric S; Craigen, William J; Renaud, Deborah; Sun, Qin; Wong, Lee-Jun

2013-07-01

Cerebral creatine deficiency syndromes (CCDS) are a group of inborn errors of creatine metabolism that involve AGAT and GAMT for creatine biosynthesis disorders and SLC6A8 for creatine transporter (CT1) deficiency. Deficiencies in the three enzymes can be distinguished by intermediate metabolite levels, and a definitive diagnosis relies on the presence of deleterious mutations in the causative genes. Mutations and unclassified variants were identified in 41 unrelated patients, and 22 of these mutations were novel. Correlation of sequencing and biochemical data reveals that using plasma guanidinoacetate (GAA) as a biomarker has 100% specificity for both AGAT and GAMT deficiencies, but AGAT deficiency has decreased sensitivity in this assay. Furthermore, the urine creatine:creatinine ratio is an effective screening test with 100% specificity in males suspected of having creatine transporter deficiency. This test has a high false-positive rate due to dietary factors or dilute urine samples and lacks sensitivity in females. We conclude that biochemical screening for plasma GAA and measuring of the urine creatine:creatinine ratio should be performed for suspected CCDS patients prior to sequencing. Also, based on the results of this study, we feel that sequencing should only be considered if a patient has abnormal biochemical results on repeat testing. Copyright © 2013 Elsevier Inc. All rights reserved.

Cytogenetic and molecular markers for detecting Aegilops uniaristata chromosomes in a wheat background.

PubMed

Gong, Wenping; Li, Guangrong; Zhou, Jianping; Li, Genying; Liu, Cheng; Huang, Chengyan; Zhao, Zhendong; Yang, Zujun

2014-09-01

Aegilops uniaristata has many agronomically useful traits that can be used for wheat breeding. So far, a Triticum turgidum - Ae. uniaristata amphiploid and one set of Chinese Spring (CS) - Ae. uniaristata addition lines have been produced. To guide Ae. uniaristata chromatin transformation from these lines into cultivated wheat through chromosome engineering, reliable cytogenetic and molecular markers specific for Ae. uniaristata chromosomes need to be developed. Standard C-banding shows that C-bands mainly exist in the centromeric regions of Ae. uniaristata but rarely at the distal ends. Fluorescence in situ hybridization (FISH) using (GAA)8 as a probe showed that the hybridization signal of chromosomes 1N-7N are different, thus (GAA)8 can be used to identify all Ae. uniaristata chromosomes in wheat background simultaneously. Moreover, a total of 42 molecular markers specific for Ae. uniaristata chromosomes were developed by screening expressed sequence tag - sequence tagged site (EST-STS), expressed sequence tag - simple sequence repeat (EST-SSR), and PCR-based landmark unique gene (PLUG) primers. The markers were subsequently localized using the CS - Ae. uniaristata addition lines and different wheat cultivars as controls. The cytogenetic and molecular markers developed herein will be helpful for screening and identifying wheat - Ae. uniaristata progeny.

Self-assembled InAs quantum dot formation on GaAs ring-like nanostructure templates

PubMed Central

Strom, NW; Wang, Zh M; AbuWaar, ZY; Mazur, Yu I; Salamo, GJ

2007-01-01

The evolution of InAs quantum dot (QD) formation is studied on GaAs ring-like nanostructures fabricated by droplet homo-epitaxy. This growth mode, exclusively performed by a hybrid approach of droplet homo-epitaxy and Stransky-Krastanor (S-K) based QD self-assembly, enables one to form new QD morphologies that may find use in optoelectronic applications. Increased deposition of InAs on the GaAs ring first produced a QD in the hole followed by QDs around the GaAs ring and on the GaAs (100) surface. This behavior indicates that the QDs prefer to nucleate at locations of high monolayer (ML) step density.

Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

PubMed Central

Ohno, Takeo; Oyama, Yutaka

2012-01-01

In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE), in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor. PMID:27877466

GaAs Computer Technology

DTIC Science & Technology

1992-01-07

AD-A259 259 FASTC-ID FOREIGN AEROSPACE SCIENCE AND TECHNOLOGY CENTER GaAs COMPUTER TECHNOLOGY (1) by Wang Qiao-yu 93-00999 Distrir bution t,,,Nm ted...FASTC- ID(RS)T-0310-92 HUMAN TRANSLATION FASTC-ID(RS)T-0310-92 7 January 1993 GaAs COMPUTER TECHNOLOGY (1) By: Wang Qiao-yu English pages: 6 Source...the best quality copy available. j C] " ------ GaAs Computer Technology (1) Wang Qiao-yu (Li-Shan Microelectronics Institute) Abstract: The paper

GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Juang, Bor-Chau, E-mail: bcjuang@ucla.edu; Laghumavarapu, Ramesh B.; Foggo, Brandon J.

There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAsmore » substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.« less

Gallium Arsenide welded panel technology for advanced spaceflight applications

NASA Technical Reports Server (NTRS)

Lillington, D. R.; Gillanders, M. S.; Garlick, G. F. J.; Cavicchi, B. T.; Glenn, G. S.; Tobin, S. P.

1989-01-01

A significant impediment to the widespread use of GaAs solar cells in space is the cost and weight of the GaAs substrate. In order to overcome these problems, Spectrolab is pursuing thin cell technologies encompassing both liquid phase epitaxy (LPE) GaAs on GaAs and MOCVD GaAs on Ge cells. Spectrolab's experience in the manufacture of 4 to 6 mil 2 cm x 4 cm GaAs cells on a LPE production line is discussed. By thinning the cells at a late state of processing, production yields comparable to 12 mil cells have been achieved. Data are presented showing that GaAs cells can be welded without degradation and have achieved minimum average efficiencies of 18 percent AM0, 28 C with efficiencies up to 20 percent. Spectrolab, in conjunction with Spire Corporation has also been pursuing GaAs on Ge cell technology in support of larger area lighter weight power systems. Data are presented showing that individual 2 cm x 2 cm, 8 mil cell efficiencies up to 21.7 percent have been achieved. Efficiencies up to 24 percent AM0 will be possible by optimizing the GaAs/Ge interface. Cells have been welded without degradation using silver interconnects and have been laid down on an aluminum honeycomb/graphite facesheet substrate to produce a small coupon. The efficiency was 18.1 percent at AM0, 28 C.

Sulfur doping of GaAs with (NH4)2Sx solution

NASA Astrophysics Data System (ADS)

Lee, Jong-Lam

1999-01-01

A novel technique for sulfur doping to GaAs was demonstrated. The surface of GaAs was treated with (NH4)2Sx solution, subsequent to annealing using either furnace or rapid thermal processing. Sulfur atoms adsorbed at the surface of GaAs during the (NH4)2Sx treatment diffuse into GaAs during the annealing. The diffusion profiles of sulfur in both types of annealing treatments show a concave shape from the GaAs surface. Diffusion constants of sulfur determined using the Boltzmann-Matano technique increase with the decrease of sulfur concentration via the depth from the surface of GaAs. This suggests that immobile sulfur donor SAs+ forms at the near surface interacts with a Ga divacancy, and results in the production of mobile As interstitials, IAs. The IAs moves fast toward the inside of GaAs and kickout the SAs+ donor, producing a fast diffusing species of interstitial S atoms. The diffusion coefficients of sulfur determined are 2.5×10-14 cm2/s at 840 °C and 5×10-12 cm2/s at 900 °C. The sulfur doping technique is applied to the fabrication of metal-semiconductor field-effect transistors (MESFETs). The MESFETs with 1.0 μm gate length exhibit transconductance of 190 mS/mm, demonstrating the applicability of this technique to the formation of active channel layer of MESFETs.

Supplementation of guanidinoacetic acid to broiler diets: effects on performance, carcass characteristics, meat quality, and energy metabolism.

PubMed

Michiels, J; Maertens, L; Buyse, J; Lemme, A; Rademacher, M; Dierick, N A; De Smet, S

2012-02-01

Creatine, (CREA) a central constituent in energy metabolism, is obtained from dietary animal protein or de novo synthesis from guanidinoacetic acid (GAA). Especially in all-vegetable diets, supplemental CREA or GAA may restore the CREA availability in tissues, and hence, improve performance. In this study, 768 one-d-old male Ross 308 broilers were assigned to 1 of 4 diets: negative control, all-vegetable corn-soybean-based; negative control supplemented with either 0.6 or 1.2 g of GAA per kilogram of feed; and positive control (60, 30, and 30 g/kg of fish meal in the starter, grower, and finisher diets, respectively). Each treatment was replicated in 6 pens of 32 birds each. At the end of the grower period (d 26), 2 birds per pen were euthanized for metabolic measurements. Four broilers per pen were selected at slaughter age (d 39) to determine carcass characteristics and meat quality. Compared with the negative control, GAA supplementation resulted in an improved gain:feed ratio (P < 0.05) and ADG (P < 0.05; + 2.7 and + 2.2% for GAA at 0.6 and 1.2 g/kg, respectively) throughout the entire period. Breast meat yield was higher for the GAA diets compared with that of the negative control birds (P < 0.05; 30.6 vs. 29.4%) and was comparable with that of the positive control birds (30.2%). With regard to meat quality, lower ultimate pH values, higher cooking and press fluid losses, and higher color L* values were observed for the GAA diets compared with those of the negative control diet (P < 0.05). These effects were small, however. The GAA and CREA levels in breast meat were lower and higher, respectively, in GAA-fed birds compared with those of the control birds (P < 0.01). The diets did not affect plasma metabolic traits, except that plasma insulin-like growth factor I concentrations were almost twice as high in animals fed 1.2 g/kg of GAA compared with those of all other treatments. The GAA included in all-vegetable diets improved animal performance for the whole rearing period and increased breast meat yield.

Noncoding origins of anthropoid traits and a new null model of transposon functionalization.

PubMed

del Rosario, Ricardo C H; Rayan, Nirmala Arul; Prabhakar, Shyam

2014-09-01

Little is known about novel genetic elements that drove the emergence of anthropoid primates. We exploited the sequencing of the marmoset genome to identify 23,849 anthropoid-specific constrained (ASC) regions and confirmed their robust functional signatures. Of the ASC base pairs, 99.7% were noncoding, suggesting that novel anthropoid functional elements were overwhelmingly cis-regulatory. ASCs were highly enriched in loci associated with fetal brain development, motor coordination, neurotransmission, and vision, thus providing a large set of candidate elements for exploring the molecular basis of hallmark primate traits. We validated ASC192 as a primate-specific enhancer in proliferative zones of the developing brain. Unexpectedly, transposable elements (TEs) contributed to >56% of ASCs, and almost all TE families showed functional potential similar to that of nonrepetitive DNA. Three L1PA repeat-derived ASCs displayed coherent eye-enhancer function, thus demonstrating that the "gene-battery" model of TE functionalization applies to enhancers in vivo. Our study provides fundamental insights into genome evolution and the origins of anthropoid phenotypes and supports an elegantly simple new null model of TE exaptation. © 2014 del Rosario et al.; Published by Cold Spring Harbor Laboratory Press.

Identification of antisense long noncoding RNAs that function as SINEUPs in human cells.

PubMed

Schein, Aleks; Zucchelli, Silvia; Kauppinen, Sakari; Gustincich, Stefano; Carninci, Piero

2016-09-20

Mammalian genomes encode numerous natural antisense long noncoding RNAs (lncRNAs) that regulate gene expression. Recently, an antisense lncRNA to mouse Ubiquitin carboxyl-terminal hydrolase L1 (Uchl1) was reported to increase UCHL1 protein synthesis, representing a new functional class of lncRNAs, designated as SINEUPs, for SINE element-containing translation UP-regulators. Here, we show that an antisense lncRNA to the human protein phosphatase 1 regulatory subunit 12A (PPP1R12A), named as R12A-AS1, which overlaps with the 5' UTR and first coding exon of the PPP1R12A mRNA, functions as a SINEUP, increasing PPP1R12A protein translation in human cells. The SINEUP activity depends on the aforementioned sense-antisense interaction and a free right Alu monomer repeat element at the 3' end of R12A-AS1. In addition, we identify another human antisense lncRNA with SINEUP activity. Our results demonstrate for the first time that human natural antisense lncRNAs can up-regulate protein translation, suggesting that endogenous SINEUPs may be widespread and present in many mammalian species.

The long non-coding RNA HOTTIP enhances pancreatic cancer cell proliferation, survival and migration.

PubMed

Cheng, Yating; Jutooru, Indira; Chadalapaka, Gayathri; Corton, J Christopher; Safe, Stephen

2015-05-10

HOTTIP is a long non-coding RNA (lncRNA) transcribed from the 5' tip of the HOXA locus and is associated with the polycomb repressor complex 2 (PRC2) and WD repeat containing protein 5 (WDR5)/mixed lineage leukemia 1 (MLL1) chromatin modifying complexes. HOTTIP is expressed in pancreatic cancer cell lines and knockdown of HOTTIP by RNA interference (siHOTTIP) in Panc1 pancreatic cancer cells decreased proliferation, induced apoptosis and decreased migration. In Panc1 cells transfected with siHOTTIP, there was a decrease in expression of 757 genes and increased expression of 514 genes, and a limited gene analysis indicated that HOTTIP regulation of genes is complex. For example, Aurora kinase A, an important regulator of cell growth, is coregulated by MLL and not WDR5 and, in contrast to previous studies in liver cancer cells, HOTTIP does not regulate HOXA13 but plays a role in regulation of several other HOX genes including HOXA10, HOXB2, HOXA11, HOXA9 and HOXA1. Although HOTTIP and the HOX-associated lncRNA HOTAIR have similar pro-oncogenic functions, they regulate strikingly different sets of genes in Panc1 cells and in pancreatic tumors.

Long noncoding RNA UPAT promotes colon tumorigenesis by inhibiting degradation of UHRF1

PubMed Central

Taniue, Kenzui; Kurimoto, Akiko; Sugimasa, Hironobu; Nasu, Emiko; Takeda, Yasuko; Iwasaki, Kei; Nagashima, Takeshi; Okada-Hatakeyama, Mariko; Oyama, Masaaki; Kozuka-Hata, Hiroko; Hiyoshi, Masaya; Kitayama, Joji; Negishi, Lumi; Kawasaki, Yoshihiro; Akiyama, Tetsu

2016-01-01

Many long noncoding RNAs (lncRNAs) are reported to be dysregulated in human cancers and play critical roles in tumor development and progression. Furthermore, it has been reported that many lncRNAs regulate gene expression by recruiting chromatin remodeling complexes to specific genomic loci or by controlling transcriptional or posttranscriptional processes. Here we show that an lncRNA termed UPAT [ubiquitin-like plant homeodomain (PHD) and really interesting new gene (RING) finger domain-containing protein 1 (UHRF1) Protein Associated Transcript] is required for the survival and tumorigenicity of colorectal cancer cells. UPAT interacts with and stabilizes the epigenetic factor UHRF1 by interfering with its β-transducin repeat-containing protein (TrCP)–mediated ubiquitination. Furthermore, we demonstrate that UHRF1 up-regulates Stearoyl-CoA desaturase 1 and Sprouty 4, which are required for the survival of colon tumor cells. Our study provides evidence for an lncRNA that regulates protein ubiquitination and degradation and thereby plays a critical role in the survival and tumorigenicity of tumor cells. Our results suggest that UPAT and UHRF1 may be promising molecular targets for the therapy of colon cancer. PMID:26768845

Design and fabrication of GaAs OMIST photodetector

NASA Astrophysics Data System (ADS)

Kang, Xuejun; Lin, ShiMing; Liao, Qiwei; Gao, Junhua; Liu, Shi'an; Cheng, Peng; Wang, Hongjie; Zhang, Chunhui; Wang, Qiming

1998-08-01

We designed and fabricated GaAs OMIST (Optical-controlled Metal-Insulator-Semiconductor Thyristor) device. Using oxidation of AlAs layer that is grown by MBE forms the Ultra- Thin semi-Insulating layer (UTI) of the GAAS OMIST. The accurate control and formation of high quality semi-insulating layer (AlxOy) are the key processes for fabricating GaAs OMIST. The device exhibits a current-controlled negative resistance region in its I-V characteristics. When illuminated, the major effect of optical excitation is the reduction of the switching voltage. If the GaAs OMIST device is biased at a voltage below its dark switching voltage Vs, sufficient incident light can switch OMIST from high impedance low current 'off' state to low impedance high current 'on' state. The absorbing material of OMIST is GaAS, so if the wavelength of incident light within 600 to approximately 850 nm can be detected effectively. It is suitable to be used as photodetector for digital optical data process. The other attractive features of GaAs OMIST device include suitable conducted current, switching voltage and power levels for OEIC, high switch speed and high sensitivity to light or current injection.

Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

PubMed

Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

2012-07-01

Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

Non coding RNAs in vascular disease - from basic science to clinical applications: Scientific update from the Working Group of Myocardial Function of the European Society of Cardiology

PubMed

Fiedler, Jan; Baker, Andrew H; Dimmeler, Stefanie; Heymans, Stephane; Mayr, Manuel; Thum, Thomas

2018-05-23

Non-coding RNAs are increasingly recognized not only as regulators of various biological functions but also as targets for a new generation of RNA therapeutics and biomarkers. We hereby review recent insights relating to non-coding RNAs including microRNAs (e.g. miR-126, miR-146a), long non-coding RNAs (e.g. MIR503HG, GATA6-AS, SMILR) and circular RNAs (e.g. cZNF292) and their role in vascular diseases. This includes identification and therapeutic use of hypoxia-regulated non-coding RNAs and endogenous non-coding RNAs that regulate intrinsic smooth muscle cell signalling, age-related non-coding RNAs and non-coding RNAs involved in the regulation of mitochondrial biology and metabolic control. Finally, we discuss non-coding RNA species with biomarker potential.

Medium energy proton radiation damage to (AlGa)As-GaAs solar cells

NASA Technical Reports Server (NTRS)

Loo, R. Y.; Kamath, G. S.; Knechtli, R. C.

1982-01-01

The performance of (AlGa)As-GaAs solar cells irradiated by medium energy 2, 5, and 10 MeV protons was evaluated. The Si cells without coverglass and a number of GaAs solar cells with 12 mil coverglass were irradiated simultaneously with bare GaAs cells. The cell degradation is directly related to the penetration of depth of protons with GaAs. The influence of periodic and continuous thermal annealing on the GaAs solar cells was investigated.

Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

NASA Technical Reports Server (NTRS)

Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

2003-01-01

NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

Alternatives to Arsine: The Atmospheric Pressure Organometallic Chemical Vapor Deposition Growth of GaAs Using Triethylarsenic.

DTIC Science & Technology

1987-08-15

SUPPLEMENTARY NOTATION 17. COSATI CODES 18 SUBJECT TERMS (Corinue on reverse if necessary and identify by block number) FIELD GROUP SUB-GROUP Epitaxy GaAs 9...Zr leiK m I141’ FIGURES 1 . Effect of Growth Parameters on Residual Doping Type ................... 7 2. Photoluminescence Spectrum of a GaAs Epilayer... 1 3 Successful homoepitaxial growth of high purity, unintentionally doped GaAs epilayers by organometallic chemical vapor deposition (OMCVD) has

New Passivation Methods of GaAs.

DTIC Science & Technology

1980-01-01

Fabrication of Thin Nitride Layers on GaAs 33 - 35 CHAPTER 7 Passivation of InGaAsP 36 - 37 CHAPTER 8 Emulsions on GaAs Surfaces 38 - 42 APPENDIX...not yet given any useful results. The deposition of SiO2 by using emulsions is pursued and first results on the possibility of GaAs doping are...glycol-tartaric acid based aqueous solution was used in order to anodically oxidise the gate notch after the source and drain ohmic contacts were formed

Insulators for Pb(1-x)Sn(x)Te

NASA Technical Reports Server (NTRS)

Tsuo, Y. H.; Sher, A.

1981-01-01

Thin films of LaF3 were e-gun and thermally deposited on several substrates. The e-gun deposited films are fluorine deficient, have high ionic conductivities that persist to 77 K, and high effective dielectric constants. The thermally deposited material tends to be closer to stoichiometric, and have higher effective breakdown field strengths. Thermally deposited LaF3 films with resistivities in excess of 10 to the 12th power ohms - cm were deposited on metal coated glass substrates. The LaF3 films were shown to adhere well to PbSnTe, surviving repeated cycles between room temperature and 77 K. The LaF3 films on GaAs were also studied.

Investigation of ZnSe-coated silicon substrates for GaAs solar cells

NASA Technical Reports Server (NTRS)

Huber, Daniel A.; Olsen, Larry C.; Dunham, Glen; Addis, F. William

1993-01-01

Studies are being carried out to determine the feasibility of using ZnSe as a buffer layer for GaAs solar cells grown on silicon. This study was motivated by reports in the literature indicating ZnSe films had been grown by metallorganic chemical vapor deposition (MOCVD) onto silicon with EPD values of 2 x 10(exp 5) cm(sup -2), even though the lattice mismatch between silicon and ZnSe is 4.16 percent. These results combined with the fact that ZnSe and GaAs are lattice matched to within 0.24 percent suggest that the prospects for growing high efficiency GaAs solar cells onto ZnSe-coated silicon are very good. Work to date has emphasized development of procedures for MOCVD growth of (100) ZnSe onto (100) silicon wafers, and subsequent growth of GaAs films on ZnSe/Si substrates. In order to grow high quality single crystal GaAs with a (100) orientation, which is desirable for solar cells, one must grow single crystal (100) ZnSe onto silicon substrates. A process for growth of (100) ZnSe was developed involving a two-step growth procedure at 450 C. Single crystal, (100) GaAs films were grown onto the (100) ZnSe/Si substrates at 610 C that are adherent and specular. Minority carrier diffusion lengths for the GaAs films grown on ZnSe/Si substrates were determined from photoresponse properties of Al/GaAs Schottky barriers. Diffusion lengths for n-type GaAs films are currently on the order of 0.3 microns compared to 2.0 microns for films grown simultaneously by homoepitaxy.

The non-coding RNA landscape of human hematopoiesis and leukemia.

PubMed

Schwarzer, Adrian; Emmrich, Stephan; Schmidt, Franziska; Beck, Dominik; Ng, Michelle; Reimer, Christina; Adams, Felix Ferdinand; Grasedieck, Sarah; Witte, Damian; Käbler, Sebastian; Wong, Jason W H; Shah, Anushi; Huang, Yizhou; Jammal, Razan; Maroz, Aliaksandra; Jongen-Lavrencic, Mojca; Schambach, Axel; Kuchenbauer, Florian; Pimanda, John E; Reinhardt, Dirk; Heckl, Dirk; Klusmann, Jan-Henning

2017-08-09

Non-coding RNAs have emerged as crucial regulators of gene expression and cell fate decisions. However, their expression patterns and regulatory functions during normal and malignant human hematopoiesis are incompletely understood. Here we present a comprehensive resource defining the non-coding RNA landscape of the human hematopoietic system. Based on highly specific non-coding RNA expression portraits per blood cell population, we identify unique fingerprint non-coding RNAs-such as LINC00173 in granulocytes-and assign these to critical regulatory circuits involved in blood homeostasis. Following the incorporation of acute myeloid leukemia samples into the landscape, we further uncover prognostically relevant non-coding RNA stem cell signatures shared between acute myeloid leukemia blasts and healthy hematopoietic stem cells. Our findings highlight the importance of the non-coding transcriptome in the formation and maintenance of the human blood hierarchy.While micro-RNAs are known regulators of haematopoiesis and leukemogenesis, the role of long non-coding RNAs is less clear. Here the authors provide a non-coding RNA expression landscape of the human hematopoietic system, highlighting their role in the formation and maintenance of the human blood hierarchy.

Morphology- and orientation-controlled gallium arsenide nanowires on silicon substrates.

PubMed

Ihn, Soo-Ghang; Song, Jong-In; Kim, Tae-Wook; Leem, Dong-Seok; Lee, Takhee; Lee, Sang-Geul; Koh, Eui Kwan; Song, Kyung

2007-01-01

GaAs nanowires were epitaxially grown on Si(001) and Si(111) substrates by using Au-catalyzed vapor-liquid-solid (VLS) growth in a solid source molecular beam epitaxy system. Scanning electron microscopy analysis revealed that almost all the GaAs nanowires were grown along <111> directions on both Si substrates for growth conditions investigated. The GaAs nanowires had a very uniform diameter along the growth direction. X-ray diffraction data and transmission electron microscopy analysis revealed that the GaAs<111> nanowires had a mixed crystal structure of the hexagonal wurtzite and the cubic zinc-blende. Current-voltage characteristics of junctions formed by the epitaxially grown GaAs nanowires and the Si substrate were investigated by using a current-sensing atomic force microscopy.

Advances in gallium arsenide monolithic microwave integrated-circuit technology for space communications systems

NASA Technical Reports Server (NTRS)

Bhasin, K. B.; Connolly, D. J.

1986-01-01

Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. In this paper, current developments in GaAs MMIC technology are described, and the status and prospects of the technology are assessed.

Real-time detection of laser-GaAs interaction process

NASA Astrophysics Data System (ADS)

Jia, Zhichao; Li, Zewen; Lv, Xueming; Ni, Xiaowu

2017-05-01

A real-time method based on laser scattering technology was used to detect the interaction process of GaAs with a 1080 nm laser. The detector collected the scattered laser beam from the GaAs wafer. The main scattering sources were back surface at first, later turn into front surface and vapor, so scattering signal contained much information of the interaction process. The surface morphologies of GaAs with different irradiation times were observed using an optical microscope to confirm occurrence of various phenomena. The proposed method is shown to be effective for the real-time detection of GaAs. By choosing a proper wavelength, the scattering technology can be promoted in detection of thicker GaAs wafer or other materials.

Long-term radiation effects on GaAs solar cell characteristics

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.; Doviak, M. J.

1978-01-01

This report investigates preliminary design considerations which should be considered for a space experiment involving Gallium Arsenide (GaAs) solar cells. The electron radiation effects on GaAs solar cells were conducted in a laboratory environment, and a statistical analysis of the data is presented. In order to augment the limited laboratory data, a theoretical investigation of the effect of radiation on GaAs solar cells is also developed. The results of this study are empirical prediction equations which can be used to estimate the actual damage of electrical characteristics in a space environment. The experimental and theoretical studies also indicate how GaAs solar cell parameters should be designed in order to withstand the effects of electron radiation damage.

Crystal Growth of Device Quality Gaas in Space

NASA Technical Reports Server (NTRS)

Gatos, H. C.

1985-01-01

The GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and (3) investigation of electronic properties and phenomena controlling device applications and device performance. This effort is aimed at the essential ground-based program which would insure successful experimentation with and eventually processing of GaAs in near zero gravity environment. It is believed that this program addresses in a unique way materials engineering aspects which bear directly on the future exploitation of the potential of GaAs and related materials in device and systems applications.

Study of sulfur bonding on gallium arsenide (100) surfaces using supercritical fluid extraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cabauy, P.; Darici, Y.; Furton, K.G.

1995-12-01

In the last decades Gallium Arsenide (GaAs) has been considered the semiconductor that will replace silicon because of its direct band gap and high electron mobility. Problems with GaAs Fermi level pinning has halted its widespread use in the electronics industry. The formation of oxides on GaAs results in a high density of surface states that effectively pin the surface Fermi level at the midgap. Studies on sulfur passivation have eliminated oxidation and virtually unpinned the Fermi level on the GaAs surface. This has given rise to interest in sulfur-GaAs bonds. In this presentation, we will discuss the types ofmore » sulfur bonds extracted from a sulfur passivated GaAs (100) using Supercritical Fluid (CO2) Extraction (SFE). SFE can be a valuable tool in the study of chemical speciations on semiconductor surfaces. The variables evaluated to effectively study the sulfur species from the GaAs surface include passivation techniques, supercritical fluid temperatures, densities, and extraction times.« less

Theoretical and experimental study of highly textured GaAs on silicon using a graphene buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alaskar, Yazeed; Arafin, Shamsul; Lin, Qiyin

2015-09-01

A novel heteroepitaxial growth technique, quasi-van der Waals epitaxy, promises the ability to deposit three-dimensional GaAs materials on silicon using two-dimensional graphene as a buffer layer by overcoming the lattice and thermal expansion mismatch. In this study, density functional theory (DFT) simulations were performed to understand the interactions at the GaAs/graphene hetero-interface as well as the growth orientations of GaAs on graphene. To develop a better understanding of the molecular beam epitaxy-grown GaAs films on graphene, samples were characterized by x-ray diffraction (..theta..-2..theta.. scan, ..omega..-scan, grazing incidence XRD and pole figure measurement) and transmission electron microscopy. The realizations of smoothmore » GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using this deposition technique are a milestone towards an eventual demonstration of the epitaxial growth of GaAs on silicon, which is necessary for integrated photonics application.« less

Late-onset Pompe disease: what is the prevalence of limb-girdle muscular weakness presentation?

PubMed

Lorenzoni, Paulo José; Kay, Cláudia Suemi Kamoi; Higashi, Nádia Sugano; D'Almeida, Vânia; Werneck, Lineu Cesar; Scola, Rosana Herminia

2018-04-01

Pompe disease is an inherited disease caused by acid alpha-glucosidase (GAA) deficiency. A single center observational study aimed at assessing the prevalence of late-onset Pompe disease in a high-risk Brazilian population, using the dried blood spot test to detect GAA deficiency as a main screening tool. Dried blood spots were collected for GAA activity assay from 24 patients with "unexplained" limb-girdle muscular weakness without vacuolar myopathy in their muscle biopsy. Samples with reduced enzyme activity were also investigated for GAA gene mutations. Of the 24 patients with dried blood spots, one patient (4.2%) showed low GAA enzyme activity (NaG/AaGIA: 40.42; %INH: 87.22%). In this patient, genetic analysis confirmed two heterozygous mutations in the GAA gene (c.-32-13T>G/p.Arg854Ter). Our data confirm that clinicians should look for late-onset Pompe disease in patients whose clinical manifestation is an "unexplained" limb-girdle weakness even without vacuolar myopathy in muscle biopsy.

n-Type Doping of Vapor-Liquid-Solid Grown GaAs Nanowires.

PubMed

Gutsche, Christoph; Lysov, Andrey; Regolin, Ingo; Blekker, Kai; Prost, Werner; Tegude, Franz-Josef

2011-12-01

In this letter, n-type doping of GaAs nanowires grown by metal-organic vapor phase epitaxy in the vapor-liquid-solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 10(17) cm(-3) to 2 × 10(18) cm(-3). The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal-insulator-semiconductor field-effect transistor devices.

Formation of two-dimensionally confined superparamagnetic (Mn, Ga)As nanocrystals in high-temperature annealed (Ga, Mn)As/GaAs superlattices.

PubMed

Sadowski, Janusz; Domagala, Jaroslaw Z; Mathieu, Roland; Kovacs, Andras; Dłużewski, Piotr

2013-05-15

The annealing-induced formation of (Mn, Ga)As nanocrystals in (Ga, Mn)As/GaAs superlattices was studied by x-ray diffraction, transmission electron microscopy and magnetometry. The superlattice structures with 50 Å thick (Ga, Mn)As layers separated by 25, 50 and 100 Å thick GaAs spacers were grown by molecular beam epitaxy at low temperature (250 °C), and then annealed at high temperatures of 400, 560 and 630 °C. The high-temperature annealing causes decomposition to a (Ga, Mn)As ternary alloy and the formation of (Mn, Ga)As nanocrystals inside the GaAs matrix. The nanocrystals are confined in the planes that were formerly occupied by (Ga, Mn)As layers for the up to 560 °C annealing and diffuse throughout the GaAs spacer layers at 630 °C annealing. The two-dimensionally confined nanocrystals exhibit a superparamagnetic behavior which becomes high-temperature ferromagnetism (~350 K) upon diffusion.

ZnSe Window Layers for GaAs and GaInP2 Solar Cells

NASA Technical Reports Server (NTRS)

Olsen, Larry C.

1997-01-01

This report concerns studies of the use of n-type ZnSe as a window layer for n/p GaAs and GaInP2 solar cells. Emphasis was placed in this phase of the project on characterizing the interface between n-type ZnSe films grown on epi-GaAs films grown onto single crystal GaAs. Epi-GaAs and heteroepitaxial ZnSe films were grown by MOCVD with a Spire 50OXT Reactor. After growing epitaxial GaAs films on single crystal GaAs wafers, well-oriented crystalline ZnSe films were grown by MOCVD. ZnSe films were grown with substrate temperatures ranging from 250 C to 450 C. Photoluminescence studies carried out by researchers at NASA Lewis determined that the surface recombination velocity at a GaAs surface was significantly reduced after the deposition of a heteroepitaxial layer of ZnSe. The optimum temperature for ZnSe deposition appears to be on the order of 350 C.

Reflection high energy electron diffraction study of nitrogen plasma interactions with a GaAs (100) surface

NASA Astrophysics Data System (ADS)

Hauenstein, R. J.; Collins, D. A.; Cai, X. P.; O'Steen, M. L.; McGill, T. C.

1995-05-01

Effect of a nitrogen electron-cyclotron-resonance (ECR) microwave plasma on near-surface composition, crystal structure, and morphology of the As-stabilized GaAs (100) surface is investigated with the use of digitally image-processed in situ reflection high energy electron diffraction. Nitridation is performed on molecular beam epitaxially (MBE) grown GaAs surfaces near 600 °C under typical conditions for ECR microwave plasma-assisted MBE growth of GaN films on GaAs. Brief plasma exposures (≊3-5 s) are shown to result in a specular, coherently strained, relatively stable, GaN film approximately one monolayer in thickness, which can be commensurately overgrown with GaAs while longer exposures (up to 1 min) result in incommensurate zincblende epitaxial GaN island structures. Specular and nonspecular film formations are explained in terms of N-for-As surface and subsurface anion exchange reactions, respectively. Commensurate growth of ultrathin buried GaN layers in GaAs is achieved.

Non-Invasive Optical Characterization of Defects in Gallium Arsenide.

NASA Astrophysics Data System (ADS)

Cao, Xuezhong

This work is concerned with the development of a non-invasive comprehensive defect analysis system based on computer-assisted near infrared (NIR) microscopy. Focus was placed on the development of software for quantitative image analysis, contrast enhancement, automated defects density counting, and two-dimensional defect density mapping. Bright field, dark field, phase contrast, and polarized light imaging modes were explored for the analysis of striations, precipitates, decorated and undecorated dislocations, surface and subsurface damage, and local residual strain in GaAs wafers. The origin of the contrast associated with defect image formation in NIR microscopy was analyzed. The local change in the index of refraction about a defect was modelled as a mini-lens. This model can explain reversal of image contrast for dislocations in heavily doped n-type GaAs during defocusing. Defect structures in GaAs crystals grown by the conventional liquid encapsulated Czochralski (LEC) method are found to differ significantly from those grown by the horizontal Bridgman (HB) or vertical gradient freeze (VGF) method. Dislocation densities in HB and VGF GaAs are one to two orders of magnitude lower compared to those in conventional LEC GaAs. The dislocations in HB and VGF GaAs remain predominantly on the {111}/<1 |10> primary slip system and tend to form small-angle subboundaries. Much more complicated dislocation structures are found in conventional LEC GaAs. Dislocation loops, dipoles, and helices were observed, indicating strong interaction between dislocations and point defects in these materials. Precipitates were observed in bulk GaAs grown by the LEC, HB, and VGF methods. Precipitation was found to occur predominantly along dislocation lines, however, discrete particles were also observed in dislocation-free regions of the GaAs matrix. The size of discrete precipitates is much smaller than that of the precipitates along dislocations. Quenching after high temperature annealing at 1150^ circC was found effective in dissolving the precipitates but glide dislocations are generated during the quenching process. STEM/EDX analysis showed that the precipitates are essentially pure arsenic in both undoped and doped GaAs. NIR phase contrast transmission microscopy was found to be very sensitive in detecting surface and subsurface damage on commercial GaAs wafers. Wafers from a number of GaAs manufacturers were examined. It was shown that some GaAs wafers exhibit perfect surface quality, but in many instances they exhibit, to various extents, subsurface damage. Computer-assisted NIR transmission microscopy in a variety of modes is found to be a rapid and non-invasive technique suitable for wafer characterization in a fabline environment. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.).

SEMICONDUCTOR TECHNOLOGY: GaAs surface wet cleaning by a novel treatment in revolving ultrasonic atomization solution

NASA Astrophysics Data System (ADS)

Zaijin, Li; Liming, Hu; Ye, Wang; Ye, Yang; Hangyu, Peng; Jinlong, Zhang; Li, Qin; Yun, Liu; Lijun, Wang

2010-03-01

A novel process for the wet cleaning of GaAs surface is presented. It is designed for technological simplicity and minimum damage generated within the GaAs surface. It combines GaAs cleaning with three conditions consisting of (1) removal of thermodynamically unstable species and (2) surface oxide layers must be completely removed after thermal cleaning, and (3) a smooth surface must be provided. Revolving ultrasonic atomization technology is adopted in the cleaning process. At first impurity removal is achieved by organic solvents; second NH4OH:H2O2:H2O = 1:1:10 solution and HCl: H2O2:H2O = 1:1:20 solution in succession to etch a very thin GaAs layer, the goal of the step is removing metallic contaminants and forming a very thin oxidation layer on the GaAs wafer surface; NH4OH:H2O = 1:5 solution is used as the removed oxide layers in the end. The effectiveness of the process is demonstrated by the operation of the GaAs wafer. Characterization of the oxide composition was carried out by X-ray photoelectron spectroscopy. Metal-contamination and surface morphology was observed by a total reflection X-ray fluorescence spectroscopy and atomic force microscope. The research results show that the cleaned surface is without contamination or metal contamination. Also, the GaAs substrates surface is very smooth for epitaxial growth using the rotary ultrasonic atomization technology.

Temporal and Spatial Post-Transcriptional Regulation of Zebrafish Tie1 mRNA by Long Noncoding RNA During Brain Vascular Assembly.

PubMed

Chowdhury, Tamjid A; Koceja, Chris; Eisa-Beygi, Shahram; Kleinstiver, Benjamin P; Kumar, Suresh N; Lin, Chien-Wei; Li, Keguo; Prabhudesai, Shubhangi; Joung, J Keith; Ramchandran, Ramani

2018-05-03

Tie1 (tyrosine kinase containing immunoglobulin and epidermal growth factor homology 1), an endothelial and hematopoietic cell-specific receptor tyrosine kinase, is an important regulator of angiogenesis and critical for maintaining vascular integrity. The post-transcriptional regulation of tie1 mRNA expression is not understood, but it might partly explain Tie1's differential expression pattern in endothelium. Following up on our previous work that identified natural antisense transcripts from the tie1 locus- tie1 antisense ( tie1AS ), which regulates tie1 mRNA levels in zebrafish-we attempted to identify the mechanism of this regulation. Through in vitro and in vivo ribonucleoprotein binding studies, we demonstrated that tie1AS long noncoding RNA interacts with an RNA binding protein-embryonic lethal and abnormal vision Drosophila-like 1 (Elavl1)-that regulates tie1 mRNA levels. When we disrupted the interaction between tie1AS and Elavl1 by using constitutively active antisense morpholino oligonucleotides or photoactivatable morpholino oligonucleotides, tie1 mRNA levels increased between 26 and 31 hours post-fertilization, particularly in the head. This increase correlated with dilation of primordial midbrain channels, smaller eyes, and reduced ventricular space. We also observed these phenotypes when we used CRISPR (clustered regularly interspaced short palindromic repeats)-mediated CRISPRi (CRISPR-mediated interference) to knock down tie1AS . Treatment of the morpholino oligonucleotide-injected embryos with a small molecule that decreased tie1 mRNA levels rescued all 3 abnormal phenotypes. We identified a novel mode of temporal and spatial post-transcriptional regulation of tie1 mRNA. It involves long noncoding RNA, tie1AS, and Elavl1 (an interactor of tie1AS ). © 2018 American Heart Association, Inc.

Targeting Non-Coding RNAs in Plants with the CRISPR-Cas Technology is a Challenge yet Worth Accepting.

PubMed

Basak, Jolly; Nithin, Chandran

2015-01-01

Non-coding RNAs (ncRNAs) have emerged as versatile master regulator of biological functions in recent years. MicroRNAs (miRNAs) are small endogenous ncRNAs of 18-24 nucleotides in length that originates from long self-complementary precursors. Besides their direct involvement in developmental processes, plant miRNAs play key roles in gene regulatory networks and varied biological processes. Alternatively, long ncRNAs (lncRNAs) are a large and diverse class of transcribed ncRNAs whose length exceed that of 200 nucleotides. Plant lncRNAs are transcribed by different RNA polymerases, showing diverse structural features. Plant lncRNAs also are important regulators of gene expression in diverse biological processes. There has been a breakthrough in the technology of genome editing, the CRISPR-Cas9 (clustered regulatory interspaced short palindromic repeats/CRISPR-associated protein 9) technology, in the last decade. CRISPR loci are transcribed into ncRNA and eventually form a functional complex with Cas9 and further guide the complex to cleave complementary invading DNA. The CRISPR-Cas technology has been successfully applied in model plants such as Arabidopsis and tobacco and important crops like wheat, maize, and rice. However, all these studies are focused on protein coding genes. Information about targeting non-coding genes is scarce. Hitherto, the CRISPR-Cas technology has been exclusively used in vertebrate systems to engineer miRNA/lncRNAs, but it is still relatively unexplored in plants. While briefing miRNAs, lncRNAs and applications of the CRISPR-Cas technology in human and animals, this review essentially elaborates several strategies to overcome the challenges of applying the CRISPR-Cas technology in editing ncRNAs in plants and the future perspective of this field.

ALUminating the Path of Atherosclerosis Progression: Chaos Theory Suggests a Role for Alu Repeats in the Development of Atherosclerotic Vascular Disease.

PubMed

Hueso, Miguel; Cruzado, Josep M; Torras, Joan; Navarro, Estanislao

2018-06-12

Atherosclerosis (ATH) and coronary artery disease (CAD) are chronic inflammatory diseases with an important genetic background; they derive from the cumulative effect of multiple common risk alleles, most of which are located in genomic noncoding regions. These complex diseases behave as nonlinear dynamical systems that show a high dependence on their initial conditions; thus, long-term predictions of disease progression are unreliable. One likely possibility is that the nonlinear nature of ATH could be dependent on nonlinear correlations in the structure of the human genome. In this review, we show how chaos theory analysis has highlighted genomic regions that have shared specific structural constraints, which could have a role in ATH progression. These regions were shown to be enriched with repetitive sequences of the Alu family, genomic parasites that have colonized the human genome, which show a particular secondary structure and are involved in the regulation of gene expression. Here, we show the impact of Alu elements on the mechanisms that regulate gene expression, especially highlighting the molecular mechanisms via which the Alu elements alter the inflammatory response. We devote special attention to their relationship with the long noncoding RNA (lncRNA); antisense noncoding RNA in the INK4 locus ( ANRIL ), a risk factor for ATH; their role as microRNA (miRNA) sponges; and their ability to interfere with the regulatory circuitry of the (nuclear factor kappa B) NF-κB response. We aim to characterize ATH as a nonlinear dynamic system, in which small initial alterations in the expression of a number of repetitive elements are somehow amplified to reach phenotypic significance.

Activity-Dependent Human Brain Coding/Noncoding Gene Regulatory Networks

PubMed Central

Lipovich, Leonard; Dachet, Fabien; Cai, Juan; Bagla, Shruti; Balan, Karina; Jia, Hui; Loeb, Jeffrey A.

2012-01-01

While most gene transcription yields RNA transcripts that code for proteins, a sizable proportion of the genome generates RNA transcripts that do not code for proteins, but may have important regulatory functions. The brain-derived neurotrophic factor (BDNF) gene, a key regulator of neuronal activity, is overlapped by a primate-specific, antisense long noncoding RNA (lncRNA) called BDNFOS. We demonstrate reciprocal patterns of BDNF and BDNFOS transcription in highly active regions of human neocortex removed as a treatment for intractable seizures. A genome-wide analysis of activity-dependent coding and noncoding human transcription using a custom lncRNA microarray identified 1288 differentially expressed lncRNAs, of which 26 had expression profiles that matched activity-dependent coding genes and an additional 8 were adjacent to or overlapping with differentially expressed protein-coding genes. The functions of most of these protein-coding partner genes, such as ARC, include long-term potentiation, synaptic activity, and memory. The nuclear lncRNAs NEAT1, MALAT1, and RPPH1, composing an RNAse P-dependent lncRNA-maturation pathway, were also upregulated. As a means to replicate human neuronal activity, repeated depolarization of SY5Y cells resulted in sustained CREB activation and produced an inverse pattern of BDNF-BDNFOS co-expression that was not achieved with a single depolarization. RNAi-mediated knockdown of BDNFOS in human SY5Y cells increased BDNF expression, suggesting that BDNFOS directly downregulates BDNF. Temporal expression patterns of other lncRNA-messenger RNA pairs validated the effect of chronic neuronal activity on the transcriptome and implied various lncRNA regulatory mechanisms. lncRNAs, some of which are unique to primates, thus appear to have potentially important regulatory roles in activity-dependent human brain plasticity. PMID:22960213

Cancer-linked satellite 2 DNA hypomethylation does not regulate Sat2 non-coding RNA expression and is initiated by heat shock pathway activation.

PubMed

Tilman, Gaëlle; Arnoult, Nausica; Lenglez, Sandrine; Van Beneden, Amandine; Loriot, Axelle; De Smet, Charles; Decottignies, Anabelle

2012-08-01

Epigenetic dysfunctions, including DNA methylation alterations, play major roles in cancer initiation and progression. Although it is well established that gene promoter demethylation activates transcription, it remains unclear whether hypomethylation of repetitive heterochromatin similarly affects expression of non-coding RNA from these loci. Understanding how repetitive non-coding RNAs are transcriptionally regulated is important given that their established upregulation by the heat shock (HS) pathway suggests important functions in cellular response to stress, possibly by promoting heterochromatin reconstruction. We found that, although pericentromeric satellite 2 (Sat2) DNA hypomethylation is detected in a majority of cancer cell lines of various origins, DNA methylation loss does not constitutively hyperactivate Sat2 expression, and also does not facilitate Sat2 transcriptional induction upon heat shock. In melanoma tumor samples, our analysis revealed that the HS response, frequently upregulated in tumors, is probably the main determinant of Sat2 RNA expression in vivo. Next, we tested whether HS pathway hyperactivation may drive Sat2 demethylation. Strikingly, we found that both hyperthermia and hyperactivated RasV12 oncogene, another potent inducer of the HS pathway, reduced Sat2 methylation levels by up to 27% in human fibroblasts recovering from stress. Demethylation occurred locally on Sat2 repeats, resulting in a demethylation signature that was also detected in cancer cell lines with moderate genome-wide hypomethylation. We therefore propose that upregulation of Sat2 transcription in response to HS pathway hyperactivation during tumorigenesis may promote localized demethylation of the locus. This, in turn, may contribute to tumorigenesis, as demethylation of Sat2 was previously reported to favor chromosomal rearrangements.

Mutations in the Norrie disease gene.

PubMed

Schuback, D E; Chen, Z Y; Craig, I W; Breakefield, X O; Sims, K B

1995-01-01

We report our experience to date in mutation identification in the Norrie disease (ND) gene. We carried out mutational analysis in 26 kindreds in an attempt to identify regions presumed critical to protein function and potentially correlated with generation of the disease phenotype. All coding exons, as well as noncoding regions of exons 1 and 2, 636 nucleotides in the noncoding region of exon 3, and 197 nucleotides of 5' flanking sequence, were analyzed for single-strand conformation polymorphisms (SSCP) by polymerase chain reaction (PCR) amplification of genomic DNA. DNA fragments that showed altered SSCP band mobilities were sequenced to locate the specific mutations. In addition to three previously described submicroscopic deletions encompassing the entire ND gene, we have now identified 6 intragenic deletions, 8 missense (seven point mutations, one 9-bp deletion), 6 nonsense (three point mutations, three single bp deletions/frameshift) and one 10-bp insertion, creating an expanded repeat in the 5' noncoding region of exon 1. Thus, mutations have been identified in a total of 24 of 26 (92%) of the kindreds we have studied to date. With the exception of two different mutations, each found in two apparently unrelated kindreds, these mutations are unique and expand the genotype database. Localization of the majority of point mutations at or near cysteine residues, potentially critical in protein tertiary structure, supports a previous protein model for norrin as member of a cystine knot growth factor family (Meitinger et al., 1993). Genotype-phenotype correlations were not evident with the limited clinical data available, except in the cases of larger submicroscopic deletions associated with a more severe neurologic syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

A screen for nuclear transcripts identifies two linked noncoding RNAs associated with SC35 splicing domains

PubMed Central

Hutchinson, John N; Ensminger, Alexander W; Clemson, Christine M; Lynch, Christopher R; Lawrence, Jeanne B; Chess, Andrew

2007-01-01

Background Noncoding RNA species play a diverse set of roles in the eukaryotic cell. While much recent attention has focused on smaller RNA species, larger noncoding transcripts are also thought to be highly abundant in mammalian cells. To search for large noncoding RNAs that might control gene expression or mRNA metabolism, we used Affymetrix expression arrays to identify polyadenylated RNA transcripts displaying nuclear enrichment. Results This screen identified no more than three transcripts; XIST, and two unique noncoding nuclear enriched abundant transcripts (NEAT) RNAs strikingly located less than 70 kb apart on human chromosome 11: NEAT1, a noncoding RNA from the locus encoding for TncRNA, and NEAT2 (also known as MALAT-1). While the two NEAT transcripts share no significant homology with each other, each is conserved within the mammalian lineage, suggesting significant function for these noncoding RNAs. NEAT2 is extraordinarily well conserved for a noncoding RNA, more so than even XIST. Bioinformatic analyses of publicly available mouse transcriptome data support our findings from human cells as they confirm that the murine homologs of these noncoding RNAs are also nuclear enriched. RNA FISH analyses suggest that these noncoding RNAs function in mRNA metabolism as they demonstrate an intimate association of these RNA species with SC35 nuclear speckles in both human and mouse cells. These studies show that one of these transcripts, NEAT1 localizes to the periphery of such domains, whereas the neighboring transcript, NEAT2, is part of the long-sought polyadenylated component of nuclear speckles. Conclusion Our genome-wide screens in two mammalian species reveal no more than three abundant large non-coding polyadenylated RNAs in the nucleus; the canonical large noncoding RNA XIST and NEAT1 and NEAT2. The function of these noncoding RNAs in mRNA metabolism is suggested by their high levels of conservation and their intimate association with SC35 splicing domains in multiple mammalian species. PMID:17270048

Long Noncoding RNA-Associated Transcriptomic Changes in Resiliency or Susceptibility to Depression and Response to Antidepressant Treatment

PubMed Central

Roy, Bhaskar; Wang, Qingzhong; Dwivedi, Yogesh

2018-01-01

Abstract Background Recent emergence of long noncoding RNAs in regulating gene expression and thereby modulating physiological functions in brain has manifested their possible role in psychiatric disorders. In this study, the roles of long noncoding RNAs in susceptibility and resiliency to develop stress-induced depression and their response to antidepressant treatment were examined. Methods Microarray-based transcriptome-wide changes in long noncoding RNAs were determined in hippocampus of male Holtzman rats who showed susceptibility (learned helplessness) or resiliency (nonlearned helplessness) to develop depression. Changes in long noncoding RNA expression were also ascertained after subchronic administration of fluoxetine to learned helplessness rats. Bioinformatic and target prediction analyses (cis- and trans-acting) and qPCR-based assays were performed to decipher the functional role of altered long noncoding RNAs. Results Group-wise comparison showed an overrepresented class of long noncoding RNAs that were uniquely associated with nonlearned helplessness or learned helplessness behavior. Chromosomal mapping within the 5-kbp flank region of the top 20 dysregulated long noncoding RNAs in the learned helplessness group showed several target genes that were regulated through cis- or trans-actions, including Zbtb20 and Zfp385b from zinc finger binding protein family. Genomic context of differentially expressed long noncoding RNAs showed an overall blunted response in the learned helplessness group regardless of the long noncoding RNA classes analyzed. Gene ontology exhibited the functional clustering for anatomical structure development, cellular architecture modulation, protein metabolism, and cellular communications. Fluoxetine treatment reversed learned helplessness-induced changes in many long noncoding RNAs and target genes. Conclusions The involvement of specific classes of long noncoding RNAs with distinctive roles in modulating target gene expression could confer the role of long noncoding RNAs in resiliency or susceptibility to develop depression with a reciprocal response to antidepressant treatment. PMID:29390069

Approaches to Fungal Genome Annotation

PubMed Central

Haas, Brian J.; Zeng, Qiandong; Pearson, Matthew D.; Cuomo, Christina A.; Wortman, Jennifer R.

2011-01-01

Fungal genome annotation is the starting point for analysis of genome content. This generally involves the application of diverse methods to identify features on a genome assembly such as protein-coding and non-coding genes, repeats and transposable elements, and pseudogenes. Here we describe tools and methods leveraged for eukaryotic genome annotation with a focus on the annotation of fungal nuclear and mitochondrial genomes. We highlight the application of the latest technologies and tools to improve the quality of predicted gene sets. The Broad Institute eukaryotic genome annotation pipeline is described as one example of how such methods and tools are integrated into a sequencing center’s production genome annotation environment. PMID:22059117

Electrode pattern design for GaAs betavoltaic batteries

NASA Astrophysics Data System (ADS)

Haiyang, Chen; Jianhua, Yin; Darang, Li

2011-08-01

The sensitivities of betavoltaic batteries and photovoltaic batteries to series and parallel resistance are studied. Based on the study, an electrode pattern design principle of GaAs betavoltaic batteries is proposed. GaAs PIN junctions with and without the proposed electrode pattern are fabricated and measured under the illumination of 63Ni. Results show that the proposed electrode can reduce the backscattering and shadowing for the beta particles from 63Ni to increase the GaAs betavoltaic battery short circuit currents effectively but has little impact on the fill factors and ideal factors.

Lightweight, Light-Trapped, Thin GaAs Solar Cells for Spacecraft Applications.

DTIC Science & Technology

1995-10-05

improve the efficiency of this type of cell. 2 The high efficiency and light weight of the cover glass supported GaAs solar cell can have a significant...is a 3-mil cover glass and 1-mil silicone adhesive on the front surface of the GaAs solar cell. Power Output 3000 400 -{ 2400 { N 300 S18200 W/m2...the ultra-thin, light-trapped GaAs solar ceill 3. Incorporate light trapping. 0 external quantum efficiency at 850 nm increased by 5.2% 4. Develop

GaAs core--shell nanowires for photovoltaic applications.

PubMed

Czaban, Josef A; Thompson, David A; LaPierre, Ray R

2009-01-01

We report the use of Te as an n-type dopant in GaAs core-shell p-n junction nanowires for use in photovoltaic devices. Te produced significant change in the morphology of GaAs nanowires grown by the vapor-liquid-solid process in a molecular beam epitaxy system. The increase in radial growth of nanowires due to the surfactant effect of Te had a significant impact on the operating characteristics of photovoltaic devices. A decrease in solar cell efficiency occurred when the Te-doped GaAs growth duration was increased.

Monolithic high voltage nonlinear transmission line fabrication process

DOEpatents

Cooper, Gregory A.

1994-01-01

A process for fabricating sequential inductors and varactor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varactor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process.

The transcriptional activator GaaR of Aspergillus niger is required for release and utilization of d- galacturonic acid from pectin

DOE PAGES

Alazi, Ebru; Niu, Jing; Kowalczyk, Joanna E.; ...

2016-05-13

We identified the d-galacturonic acid (GA)-responsive transcriptional activator GaaR of the saprotrophic fungus, Aspergillus niger, which was found to be essential for growth on GA and polygalacturonic acid (PGA). Growth of the ΔgaaR strain was reduced on complex pectins. Genome-wide expression analysis showed that GaaR is required for the expression of genes necessary to release GA from PGA and more complex pectins, to transport GA into the cell, and to induce the GA catabolic pathway. Residual growth of ΔgaaR on complex pectins is likely due to the expression of pectinases acting on rhamnogalacturonan and subsequent metabolism of the monosaccharides othermore » than GA.« less

Resonant electronic Raman scattering of below-gap states in molecular-beam epitaxy grown and liquid-encapsulated Czochralski grown GaAs

NASA Astrophysics Data System (ADS)

Fluegel, B.; Rice, A. D.; Mascarenhas, A.

2018-05-01

Resonant electronic Raman (ER) scattering is used to compare the below-gap excitations in molecular-beam epitaxially grown GaAs and in undoped semi-insulating GaAs substrates. The measurement geometry was designed to eliminate common measurement artifacts caused by the high optical transmission below the fundamental absorption edge. In epitaxial GaAs, ER is a clear Raman signal from the two-electron transitions of donors, eliminating an ambiguity encountered in previous results. In semi-insulating GaAs, ER occurs in a much broader dispersive band well below the bound exciton energies. The difference in the two materials may be due to the occupation of the substrate acceptor states in the presence of the midgap state EL2.

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Hidetoshi, E-mail: hsuzuki@cc.miyazaki-u.ac.jp; Nakata, Yuka; Takahasi, Masamitu

2016-03-15

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain sizemore » was smaller for all film thicknesses.« less

Electrodeposition of Metal on GaAs Nanowires

NASA Astrophysics Data System (ADS)

Liu, Chao; Einabad, Omid; Watkins, Simon; Kavanagh, Karen

2010-10-01

Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60^oC. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field.

Comparisons of single event vulnerability of GaAs SRAMS

NASA Astrophysics Data System (ADS)

Weatherford, T. R.; Hauser, J. R.; Diehl, S. E.

1986-12-01

A GaAs MESFET/JFET model incorporated into SPICE has been used to accurately describe C-EJFET, E/D MESFET and D MESFET/resistor GaAs memory technologies. These cells have been evaluated for critical charges due to gate-to-drain and drain-to-source charge collection. Low gate-to-drain critical charges limit conventional GaAs SRAM soft error rates to approximately 1E-6 errors/bit-day. SEU hardening approaches including decoupling resistors, diodes, and FETs have been investigated. Results predict GaAs RAM cell critical charges can be increased to over 0.1 pC. Soft error rates in such hardened memories may approach 1E-7 errors/bit-day without significantly reducing memory speed. Tradeoffs between hardening level, performance and fabrication complexity are discussed.

Influence of arsenic flow on the crystal structure of epitaxial GaAs grown at low temperatures on GaAs (100) and (111)A substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B.; Klimov, E. A.; Vasiliev, A. L.

The influence of arsenic flow in a growth chamber on the crystal structure of GaAs grown by molecular-beam epitaxy at a temperature of 240°C on GaAs (100) and (111)A substrates has been investigated. The flow ratio γ of arsenic As4 and gallium was varied in the range from 16 to 50. GaAs films were either undoped, or homogeneously doped with silicon, or contained three equidistantly spaced silicon δ-layers. The structural quality of the annealed samples has been investigated by transmission electron microscopy. It is established for the first time that silicon δ-layers in “low-temperature” GaAs serve as formation centers ofmore » arsenic precipitates. Their average size, concentration, and spatial distribution are estimated. The dependence of the film structural quality on γ is analyzed. Regions 100–150 nm in size have been revealed in some samples and identified (by X-ray microanalysis) as pores. It is found that, in the entire range of γ under consideration, GaAs films on (111)A substrates have a poorer structural quality and become polycrystalline beginning with a thickness of 150–200 nm.« less

Mutual anti-oxidative effect of gossypol acetic acid and gossypol-iron complex on hepatic lipid peroxidation in male rats.

PubMed

El-Sharaky, A S; Wahby, M M; Bader El-Dein, M M; Fawzy, R A; El-Shahawy, I N

2009-11-01

Gossypol displays anticancer behavior and anti-fertility in males. Male rats were treated with either gossypol acetic acid (GAA) or gossypol-iron complex (GIC). Serum alanine transaminase (ALT) activity elevated of GAA. However, GIC-treated animals showed a decrease in hepatic glutathione (GSH) content with increased malondialdehyde (MDA) content. Whereas, GSH-Px specific activity increased in GAA group. GAA and GIC induce significant increases in the hepatic NEFA with remarkable decrease in the total saturated fatty acids with a significant increase of PUFA. Lipid peroxidation is inhibited by gossypol, which shield lipids against oxidative damage. Phenols are oxidized to phenoxy radicals, which do not permit anti-oxidation due to resonance stabilization. GAA stimulate hydroxyl radicals (()OH) generation and DNA damage. GAA and GIC produce increase in lipid peroxidation as proved by a steep rise in thiobarbituric acid reactive species (TBARS). Controversy of specificity of TBARS towards compounds other than MDA was reported. If TBARS increased, more specific assay to be employed. Assay of lipid classes and fatty acids pattern, reveled the significance of the technique in assessment of lipid peroxidation in tissues. GAA and GIC were powerful inhibitors of lipid peroxidation and exhibit pro- and antioxidant behavior, with less toxicity of GIC.

Chemical beam epitaxy of GaAs1-xNx using MMHy and DMHy precursors, modeled by ab initio study of GaAs(100) surfaces stability over As2, H2 and N2

NASA Astrophysics Data System (ADS)

Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

2017-06-01

Using ab initio calculations, a simple model for GaAs1-xNx vapor-phase epitaxy on (100) surface of GaAs was created. By studying As2 and H2 molecules adsorptions and As/N atom substitutions on (100) GaAs surfaces, we obtain a relative stability diagram of all stable surfaces under varying As2, H2, and N2 conditions. We previously proved that this model could describe the vapor-phase epitaxy of GaAs1-x Nx with simple, fully decomposed, precursors. In this paper, we show that in more complex reaction conditions using monomethylhydrazine (MMHy), and dimethylhydrazine (DMHy), it is still possible to use our model to obtain an accurate description of the temperature and pressure stability domains for each surfaces, linked to chemical beam epitaxy (CBE) growth conditions. Moreover, the different N-incorporation regimes observed experimentally at different temperature can be explain and predict by our model. The use of MMHy and DMHy precursors can also be rationalized. Our model should then help to better understand the conditions needed to obtain an high quality GaAs1-xNx using vapor-phase epitaxy.

Noncoding sequence classification based on wavelet transform analysis: part I

NASA Astrophysics Data System (ADS)

Paredes, O.; Strojnik, M.; Romo-Vázquez, R.; Vélez Pérez, H.; Ranta, R.; Garcia-Torales, G.; Scholl, M. K.; Morales, J. A.

2017-09-01

DNA sequences in human genome can be divided into the coding and noncoding ones. Coding sequences are those that are read during the transcription. The identification of coding sequences has been widely reported in literature due to its much-studied periodicity. Noncoding sequences represent the majority of the human genome. They play an important role in gene regulation and differentiation among the cells. However, noncoding sequences do not exhibit periodicities that correlate to their functions. The ENCODE (Encyclopedia of DNA elements) and Epigenomic Roadmap Project projects have cataloged the human noncoding sequences into specific functions. We study characteristics of noncoding sequences with wavelet analysis of genomic signals.

Performance, meat quality, and pectoral myopathies of broilers fed either corn or sorghum based diets supplemented with guanidinoacetic acid.

PubMed

Córdova-Noboa, H A; Oviedo-Rondón, E O; Sarsour, A H; Barnes, J; Ferzola, P; Rademacher-Heilshorn, M; Braun, U

2018-04-13

One experiment was conducted to evaluate the effects of guanidinoacetic acid (GAA) supplementation in broilers fed corn or sorghum-based diets on live performance, carcass and cut up yields, meat quality, and pectoral myopathies. The treatments consisted of corn or sorghum-based diets with or without the addition of GAA (600 g/ton). A total of 800 one-d-old male Ross 708 broiler chicks were randomly placed in 40 floor pens with 10 replicates (20 birds per pen) per each of the four treatments. At hatch, 14, 35, and 50 d, BW and feed intake were recorded. BW gain and FCR were calculated at the end of each phase. Four broilers per pen were selected and slaughtered at 51d and 55d of age to determine carcass and cut up yields, meat quality and myopathies (spaghetti muscle, white striping, and wooden breast) severity in the Pectoralis major. Data were analyzed as a randomized complete block design in a 2 × 2 factorial arrangement with grain type and GAA supplementation as main effects. At 50 d, diets containing GAA improved (P < 0.01) FCR (1.682 vs. 1.724 g: g) independently of grain type. At 55 d, broilers fed corn diets with GAA had higher breast meat yield (P < 0.05) compared to corn without GAA. Drip and cook loss, and shear force (Warner-Bratzler) were not affected (P > 0.05) by GAA supplementation at any slaughter ages. However, GAA decreased (P < 0.05) the ultimate pH at 51 and 55 d in breast meat samples compared to unsupplemented diets. At 51 d, broilers supplemented with GAA had double (P < 0.05) breast meat fillets without wooden breast (score 1) compared with broilers fed non-supplemented diets, therefore reducing the severity of this myopathy. In conclusion, GAA supplementation improved broiler live performance in broilers raised up to 50 d independently of grain source, increased breast meat yield in corn-based diets and reduced the severity of wooden breast myopathy.

Inheritance patterns of ATCCT repeat interruptions in spinocerebellar ataxia type 10 (SCA10) expansions.

PubMed

Landrian, Ivette; McFarland, Karen N; Liu, Jilin; Mulligan, Connie J; Rasmussen, Astrid; Ashizawa, Tetsuo

2017-01-01

Spinocerebellar ataxia type 10 (SCA10), an autosomal dominant cerebellar ataxia disorder, is caused by a non-coding ATTCT microsatellite repeat expansion in the ataxin 10 gene. In a subset of SCA10 families, the 5'-end of the repeat expansion contains a complex sequence of penta- and heptanucleotide interruption motifs which is followed by a pure tract of tandem ATCCT repeats of unknown length at its 3'-end. Intriguingly, expansions that carry these interruption motifs correlate with an epileptic seizure phenotype and are unstable despite the theory that interruptions are expected to stabilize expanded repeats. To examine the apparent contradiction of unstable, interruption-positive SCA10 expansion alleles and to determine whether the instability originates outside of the interrupted region, we sequenced approximately 1 kb of the 5'-end of SCA10 expansions using the ATCCT-PCR product in individuals across multiple generations from four SCA10 families. We found that the greatest instability within this region occurred in paternal transmissions of the allele in stretches of pure ATTCT motifs while the intervening interrupted sequences were stable. Overall, the ATCCT interruption changes by only one to three repeat units and therefore cannot account for the instability across the length of the disease allele. We conclude that the AT-rich interruptions locally stabilize the SCA10 expansion at the 5'-end but do not completely abolish instability across the entire span of the expansion. In addition, analysis of the interruption alleles across these families support a parsimonious single origin of the mutation with a shared distant ancestor.

GaAs1-xBix/GaNyAs1-y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics.

PubMed

Broderick, Christopher A; Jin, Shirong; Marko, Igor P; Hild, Konstanze; Ludewig, Peter; Bushell, Zoe L; Stolz, Wolfgang; Rorison, Judy M; O'Reilly, Eoin P; Volz, Kerstin; Sweeney, Stephen J

2017-04-19

The potential to extend the emission wavelength of photonic devices further into the near- and mid-infrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs 1-x Bi x /GaN y As 1-y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 µm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs 0.967 Bi 0.033 /GaN 0.062 As 0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 μm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for long-wavelength applications.

GaAs1-xBix/GaNyAs1-y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics

NASA Astrophysics Data System (ADS)

Broderick, Christopher A.; Jin, Shirong; Marko, Igor P.; Hild, Konstanze; Ludewig, Peter; Bushell, Zoe L.; Stolz, Wolfgang; Rorison, Judy M.; O'Reilly, Eoin P.; Volz, Kerstin; Sweeney, Stephen J.

2017-04-01

The potential to extend the emission wavelength of photonic devices further into the near- and mid-infrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs1-xBix/GaNyAs1-y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 µm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 μm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for long-wavelength applications.

Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Ha, Minh Thien Huu; Hoang Huynh, Sa; Binh Do, Huy; Nguyen, Tuan Anh; Luc, Quang Ho; Chang, Edward Yi

2017-08-01

High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1  ×  106 cm-2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.

GaAs1−xBix/GaNyAs1−y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics

PubMed Central

Broderick, Christopher A.; Jin, Shirong; Marko, Igor P.; Hild, Konstanze; Ludewig, Peter; Bushell, Zoe L.; Stolz, Wolfgang; Rorison, Judy M.; O’Reilly, Eoin P.; Volz, Kerstin; Sweeney, Stephen J.

2017-01-01

The potential to extend the emission wavelength of photonic devices further into the near- and mid-infrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs1−xBix/GaNyAs1−y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 µm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 μm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for long-wavelength applications. PMID:28422129

Partners in crime: bidirectional transcription in unstable microsatellite disease.

PubMed

Batra, Ranjan; Charizanis, Konstantinos; Swanson, Maurice S

2010-04-15

Nearly two decades have passed since the discovery that the expansion of microsatellite trinucleotide repeats is responsible for a prominent class of neurological disorders, including Huntington disease and fragile X syndrome. These hereditary diseases are characterized by genetic anticipation or the intergenerational increase in disease severity accompanied by a decrease in age-of-onset. The revelation that the variable expansion of simple sequence repeats accounted for anticipation spawned a number of pathogenesis models and a flurry of studies designed to reveal the molecular events affected by these expansions. This work led to our current understanding that expansions in protein-coding regions result in extended homopolymeric amino acid tracts, often polyglutamine or polyQ, and deleterious protein gain-of-function effects. In contrast, expansions in noncoding regions cause RNA-mediated toxicity. However, the realization that the transcriptome is considerably more complex than previously imagined, as well as the emerging regulatory importance of antisense RNAs, has blurred this distinction. In this review, we summarize evidence for bidirectional transcription of microsatellite disease genes and discuss recent suggestions that some repeat expansions produce variable levels of both toxic RNAs and proteins that influence cell viability, disease penetrance and pathological severity.

Major satellite repeat RNA stabilize heterochromatin retention of Suv39h enzymes by RNA-nucleosome association and RNA:DNA hybrid formation

PubMed Central

Velazquez Camacho, Oscar; Galan, Carmen; Swist-Rosowska, Kalina; Ching, Reagan; Gamalinda, Michael; Karabiber, Fethullah; De La Rosa-Velazquez, Inti; Engist, Bettina; Koschorz, Birgit; Shukeir, Nicholas; Onishi-Seebacher, Megumi; van de Nobelen, Suzanne; Jenuwein, Thomas

2017-01-01

The Suv39h1 and Suv39h2 histone lysine methyltransferases are hallmark enzymes at mammalian heterochromatin. We show here that the mouse Suv39h2 enzyme differs from Suv39h1 by containing an N-terminal basic domain that facilitates retention at mitotic chromatin and provides an additional affinity for major satellite repeat RNA. To analyze an RNA-dependent interaction with chromatin, we purified native nucleosomes from mouse ES cells and detect that Suv39h1 and Suv39h2 exclusively associate with poly-nucleosomes. This association was attenuated upon RNaseH incubation and entirely lost upon RNaseA digestion of native chromatin. Major satellite repeat transcripts remain chromatin-associated and have a secondary structure that favors RNA:DNA hybrid formation. Together, these data reveal an RNA-mediated mechanism for the stable chromatin interaction of the Suv39h KMT and suggest a function for major satellite non-coding RNA in the organization of an RNA-nucleosome scaffold as the underlying structure of mouse heterochromatin. DOI: http://dx.doi.org/10.7554/eLife.25293.001 PMID:28760199

Construction of a self-cloning sake yeast that overexpresses alcohol acetyltransferase gene by a two-step gene replacement protocol.

PubMed

Hirosawa, I; Aritomi, K; Hoshida, H; Kashiwagi, S; Nishizawa, Y; Akada, R

2004-07-01

The commercial application of genetically modified industrial microorganisms has been problematic due to public concerns. We constructed a "self-cloning" sake yeast strain that overexpresses the ATF1 gene encoding alcohol acetyltransferase, to improve the flavor profile of Japanese sake. A constitutive yeast overexpression promoter, TDH3p, derived from the glyceraldehyde-3-phosphate dehydrogenase gene from sake yeast was fused to ATF1; and the 5' upstream non-coding sequence of ATF1 was further fused to TDH3p-ATF1. The fragment was placed on a binary vector, pGG119, containing a drug-resistance marker for transformation and a counter-selection marker for excision of unwanted DNA. The plasmid was integrated into the ATF1 locus of a sake yeast strain. This integration constructed tandem repeats of ATF1 and TDH3p-ATF1 sequences, between which the plasmid was inserted. Loss of the plasmid, which occurs through homologous recombination between either the TDH3p downstream ATF1 repeats or the TDH3p upstream repeat sequences, was selected by growing transformants on counter-selective medium. Recombination between the downstream repeats led to reversion to a wild type strain, but that between the upstream repeats resulted in a strain that possessed TDH3p-ATF1 without the extraneous DNA sequences. The self-cloning TDH3p-ATF1 yeast strain produced a higher amount of isoamyl acetate. This is the first expression-controlled self-cloning industrial yeast.

Interpolative modeling of GaAs FET S-parameter data bases for use in Monte Carlo simulations

NASA Technical Reports Server (NTRS)

Campbell, L.; Purviance, J.

1992-01-01

A statistical interpolation technique is presented for modeling GaAs FET S-parameter measurements for use in the statistical analysis and design of circuits. This is accomplished by interpolating among the measurements in a GaAs FET S-parameter data base in a statistically valid manner.

Influence of GaAs substrate properties on the congruent evaporation temperature

NASA Astrophysics Data System (ADS)

Spirina, A. A.; Nastovjak, A. G.; Shwartz, N. L.

2018-03-01

High-temperature annealing of GaAs(111)A and GaAs(111)B substrates under Langmuir evaporation conditions was studied using Monte Carlo simulation. The maximal value of the congruent evaporation temperature was estimated. The congruent evaporation temperature was demonstrated to be dependent on the surface orientation and concentration of surface defects.

Nanostructuring-induced modification of optical properties of p-GaAs (1 0 0)

NASA Astrophysics Data System (ADS)

Naddaf, M.; Saloum, S.

2009-10-01

A pulsed anodic etching method has been utilized for nanostructuring of p-type GaAs (1 0 0) surface, using HCl-based solution as electrolyte. The resulting porous GaAs layer is characterized by atomic force microscopy (AFM), room temperature photoluminescence (PL), Raman spectroscopy and optical reflectance measurements. AFM imaging reveals that the porous GaAs layer is consisted of a pillar-like of few nm in width distributed between more-reduced size nanostructures. In addition to the “infrared” PL band of un-etched GaAs, a strong “green” PL band is observed in the etched sample. The broad visible PL band of a high-energy (3.82 eV) excitation is found to compose of two PL band attributed to excitons confinement in two different sizes distribution of GaAs nanocrystals. The quantum confinement effects in GaAs nanocrystallites is also evidenced from Raman spectroscopy through the pronounced appearance of the transverse optical (TO) phonon line in the spectra of the porous sample. Porosity-induced a significant reduction of the specular reflection, in the spectral range (400-800 nm), is also demonstrated.

In-situ ellipsometric studies of optical and surface properties of GaAs(100) at elevated temperatures

NASA Technical Reports Server (NTRS)

Yao, Huade; Snyder, Paul G.

1991-01-01

A rotating-polarizer ellipsometer was attached to an ultrahigh vacuum (UHV) chamber. A GaAs(100) sample was introduced into the UHV chamber and heated at anumber of fixed elevated temperatures, without arsenic overpressure. In-situ spectroscopic ellipsometric (SE) measurements were taken, through a pair of low-strain quartz windows, to monitor the surface changes and measure the pseudodielectric functions at elevated temperatures. Real-time data from GaAs surface covered with native oxide showed clearly the evolution of oxide desorption at approximately 580 C. In addition, surface degradation was found before and after the oxide desorption. An oxide free and smooth GaAs surface was obtained by depositing an arsenic protective coating onto a molecular beam epitaxy grown GaAs surface. The arsenic coating was evaporated immediately prior to SE measurements. A comparison showed that our room temperature data from this GaAs surface, measured in the UHV, are in good agreement with those in the literature obtained by wet-chemical etching. The surface also remained clean and smooth at higher temperatures, so that reliable temperature-dependent dielectric functions were obtained.

High-efficiency thin-film GaAs solar cells, phase2

NASA Technical Reports Server (NTRS)

Yeh, Y. C. M.

1981-01-01

Thin GaAs epi-layers with good crystallographic quality were grown using a (100) Si-substrate on which a thin Ge epi-interlayer was grown by CVD from germane. Both antireflection-coated metal oxide semiconductor (AMOS) and n(+)/p homojunction structures were studied. The AMOS cells were fabricated on undoped-GaAs epi-layers deposited on bulk poly-Ge substrates using organo-metallic CVD film-growth, with the best achieved AM1 conversion efficiency being 9.1%. Both p-type and n(+)-type GaAs growth were optimized using 50 ppm dimethyl zinc and 1% hydrogen sulfide, respectively. A direct GaAs deposition method in fabricating ultra-thin top layer, epitaxial n(+)/p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed to produce large area (1 sq/cm) cells, with 19.4% AM1 conversion efficiency achieved. Additionally, an AM1 conversion efficiency of 18.4% (17.5% with 5% grid coverage) was achieved for a single crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer.

The comparison between gallium arsenide and indium gallium arsenide as materials for solar cell performance using Silvaco application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zahari, Suhaila Mohd; Norizan, Mohd Natashah; Mohamad, Ili Salwani

2015-05-15

The work presented in this paper is about the development of single and multilayer solar cells using GaAs and InGaAs in AM1.5 condition. The study includes the modeling structure and simulation of the device using Silvaco applications. The performance in term of efficiency of Indium Gallium Arsenide (InGaAs) and GaAs material was studied by modification of the doping concentration and thickness of material in solar cells. The efficiency of the GaAs solar cell was higher than InGaAs solar cell for single layer solar cell. Single layer GaAs achieved an efficiency about 25% compared to InGaAs which is only 2.65% ofmore » efficiency. For multilayer which includes both GaAs and InGaAs, the output power, P{sub max} was 8.91nW/cm² with the efficiency only 8.51%. GaAs is one of the best materials to be used in solar cell as a based compared to InGaAs.« less

Spin-lattice relaxation of optically polarized nuclei in p -type GaAs

NASA Astrophysics Data System (ADS)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Cherbunin, R. V.; Sokolov, P. S.; Yakovlev, D. R.; Bayer, M.; Suter, D.; Kavokin, K. V.

2018-04-01

Spin-lattice relaxation of the nuclear spin system in p -type GaAs is studied using a three-stage experimental protocol including optical pumping and measuring the difference of the nuclear spin polarization before and after a dark interval of variable length. This method allows us to measure the spin-lattice relaxation time T1 of optically pumped nuclei "in the dark," that is, in the absence of illumination. The measured T1 values fall into the subsecond time range, being three orders of magnitude shorter than in earlier studied n -type GaAs. The drastic difference is further emphasized by magnetic-field and temperature dependencies of T1 in p -GaAs, showing no similarity to those in n -GaAs. This unexpected behavior finds its explanation in the spatial selectivity of the optical pumping in p -GaAs, that is only efficient in the vicinity of shallow donors, together with the quadrupole relaxation of nuclear spins, which is induced by electric fields within closely spaced donor-acceptor pairs. The developed theoretical model explains the whole set of experimental results.

Growth and characteristics of p-type doped GaAs nanowire

NASA Astrophysics Data System (ADS)

Li, Bang; Yan, Xin; Zhang, Xia; Ren, Xiaomin

2018-05-01

The growth of p-type GaAs nanowires (NWs) on GaAs (111) B substrates by metal-organic chemical vapor deposition (MOCVD) has been systematically investigated as a function of diethyl zinc (DEZn) flow. The growth rate of GaAs NWs was slightly improved by Zn-doping and kink is observed under high DEZn flow. In addition, the I–V curves of GaAs NWs has been measured and the p-type dope concentration under the II/III ratio of 0.013 and 0.038 approximated to 1019–1020 cm‑3. Project supported by the National Natural Science Foundation of China (Nos. 61376019, 61504010, 61774021) and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), China (Nos. IPOC2017ZT02, IPOC2017ZZ01).

Monolithic high voltage nonlinear transmission line fabrication process

DOEpatents

Cooper, G.A.

1994-10-04

A process for fabricating sequential inductors and varistor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varistor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process. 6 figs.

Comparative study of textured and epitaxial ZnO films

NASA Astrophysics Data System (ADS)

Ryu, Y. R.; Zhu, S.; Wrobel, J. M.; Jeong, H. M.; Miceli, P. F.; White, H. W.

2000-06-01

ZnO films were synthesized by pulsed laser deposition (PLD) on GaAs and α-Al 2O 3 substrates. The properties of ZnO films on GaAs and α-Al 2O 3 have been investigated to determine the differences between epitaxial and textured ZnO films. ZnO films on GaAs show very strong emission features associated with exciton transitions as do ZnO films on α-Al 2O 3, while the crystalline structural qualities for ZnO films on α-Al 2O 3 are much better than those for ZnO films on GaAs. The properties of ZnO films are studied by comparing highly oriented, textured ZnO films on GaAs with epitaxial ZnO films on α-Al 2O 3 synthesized along the c-axis.

Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

NASA Technical Reports Server (NTRS)

Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

1987-01-01

GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

Two-Photon Pumped Synchronously Mode-Locked Bulk GaAs Laser

NASA Astrophysics Data System (ADS)

Cao, W. L.; Vaucher, A. M.; Ling, J. D.; Lee, C. H.

1982-04-01

Pulses 7 picoseconds or less in duration have been generated from a bulk GaAs crystal by a synchronous mode-locking technique. The GaAs crystal was optically pumped by two-photon absorption of the emission from a mode-locked Nd:glass laser. Two-photon absorption as the means of excitation increases the volume of the gain medium by increasing the pene-tration depth of the pump intensity, enabling generation of intra-cavity pulses with peak power in the megawatt range. Tuning of the wavelength of the GaAs emission is achieved by varying the temperature. A tuning range covering 840 nm to 885 nm has been observed over a temperature range from 97°K to 260°K. The intensity of the GaAs emission has also been observed to decrease as the temperature of the crystal is increased.

High power cascaded mid-infrared InAs/GaSb light emitting diodes on mismatched GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Provence, S. R., E-mail: sydney-provence@uiowa.edu; Ricker, R.; Aytac, Y.

2015-09-28

InAs/GaSb mid-wave, cascaded superlattice light emitting diodes are found to give higher radiance when epitaxially grown on mismatched GaAs substrates compared to lattice-matched GaSb substrates. Peak radiances of 0.69 W/cm{sup 2}-sr and 1.06 W/cm{sup 2}-sr for the 100 × 100 μm{sup 2} GaSb and GaAs-based devices, respectively, were measured at 77 K. Measurement of the recombination coefficients shows the shorter Shockley-Read-Hall recombination lifetime as misfit dislocations for growth on GaAs degrade the quantum efficiency only at low current injection. The improved performance on GaAs was found to be due to the higher transparency and improved thermal properties of the GaAs substrate.

Resonant electronic Raman scattering of below-gap states in molecular-beam epitaxy grown and liquid-encapsulated Czochralski grown GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fluegel, B.; Rice, A. D.; Mascarenhas, A.

Resonant electronic Raman (ER) scattering is used to compare the below-gap excitations in molecular-beam epitaxially grown GaAs and in undoped semi-insulating GaAs substrates. The measurement geometry was designed to eliminate common measurement artifacts caused by the high optical transmission below the fundamental absorption edge. In epitaxial GaAs, ER is a clear Raman signal from the two-electron transitions of donors, eliminating an ambiguity encountered in previous results. In semi-insulating GaAs, ER occurs in a much broader dispersive band well below the bound exciton energies. Furthermore, the difference in the two materials may be due to the occupation of the substrate acceptormore » states in the presence of the midgap state EL2.« less

All-optical switching in GaAs microdisk resonators by a femtosecond pump-probe technique through tapered-fiber coupling.

PubMed

Lin, Yen-Chih; Mao, Ming-Hua; Lin, You-Ru; Lin, Hao-Hsiung; Lin, Che-An; Wang, Lon A

2014-09-01

We demonstrate ultrafast all-optical switching in GaAs microdisk resonators using a femtosecond pump-probe technique through tapered-fiber coupling. The temporal tuning of the resonant modes resulted from the refractive index change due to photoexcited carrier density variation inside the GaAs microdisk resonator. Transmission through the GaAs microdisk resonator can be modulated by more than 10 dB with a switching time window of 8 ps in the switch-off operation using pumping pulses with energies as low as 17.5 pJ. The carrier lifetime was fitted to be 42 ps, much shorter than that of the bulk GaAs, typically of the order of nanoseconds. The above observation indicates that the surface recombination plays an important role in increasing the switching speed.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1983-01-01

GaAs device technology has recently reached a new phase of rapid advancement, made possible by the improvement of the quality of GaAs bulk crystals. At the same time, the transition to the next generation of GaAs integrated circuits and optoelectronic systems for commercial and government applications hinges on new quantum steps in three interrelated areas: crystal growth, device processing and device-related properties and phenomena. Special emphasis is placed on the establishment of quantitative relationships among crystal growth parameters-material properties-electronic properties and device applications. The overall program combines studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and investigation of electronic properties and phenomena controlling device applications and device performance.

Room temperature lasing of GaAs quantum wire vertical-cavity surface-emitting lasers grown on (7 7 5) B GaAs substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Higuchi, Y.; Osaki, S.; Kitada, T.; Shimomura, S.; Takasuka, Y.; Ogura, M.; Hiyamizu, S.

2006-06-01

Self-organized GaAs/(GaAs) 4(AlAs) 2 quantum wires (QWRs) grown on (7 7 5) B-oriented GaAs substrates by molecular beam epitaxy have been applied to an active region of vertical-cavity surface-emitting lasers (VCSELs). The (7 7 5) B GaAs QWR-VCSEL with an aperture diameter of 3 μm lased at a wavelength of 765 nm with a threshold current of 0.38 mA at room temperature. This is the first demonstration of laser operation of the QWR-VCSEL by current injection. The light output was linearly polarized in the direction parallel to the QWRs due to the optical anisotropy of the self-organized (7 7 5) B GaAs QWRs.

An expanding universe of noncoding RNAs between the poles of basic science and clinical investigations.

PubMed

Weil, Patrick P; Hensel, Kai O; Weber, David; Postberg, Jan

2016-03-01

The Keystone Symposium 'MicroRNAs and Noncoding RNAs in Cancer', Keystone, CO, USA, 7-12 June 2015 Since the discovery of RNAi, great efforts have been undertaken to unleash the potential biomedical applicability of small noncoding RNAs, mainly miRNAs, involving their use as biomarkers for personalized diagnostics or their usability as active agents or therapy targets. The research's focus on the noncoding RNA world is now slowly moving from a phase of basic discoveries into a new phase, where every single molecule out of many hundreds of cataloged noncoding RNAs becomes dissected in order to investigate these molecules' biomedical relevance. In addition, RNA classes neglected before, such as long noncoding RNAs or circular RNAs attract more attention. Numerous timely results and hypotheses were presented at the 2015 Keystone Symposium 'MicroRNAs and Noncoding RNAs in Cancer'.

Energy utilisation of broiler chickens in response to guanidinoacetic acid supplementation in diets with various energy contents.

PubMed

Ale Saheb Fosoul, Sayed Sadra; Azarfar, Arash; Gheisari, Abbasali; Khosravinia, Heshmatollah

2018-07-01

This experiment was conducted to investigate the effects of guanidinoacetic acid (GAA) on productive performance, intestinal morphometric features, blood parameters and energy utilisation in broiler chickens. A total of 390 male broiler chicks (Ross 308) were assigned to six dietary treatments based on a factorial arrangement (2×3) across 1-15 and 15-35-d periods. Experimental treatments consisted of two basal diets with standard (STD; starter: 12·56 MJ/kg and grower: 12·97 MJ/kg) and reduction (LME; starter: 11·93 MJ/kg and grower: 12·33 MJ/kg) of apparent metabolisable energy (AME) requirement of broiler chickens each supplemented with 0, 0·6 and 1·2 g/kg GAA. Supplemental 1·2 g/kg GAA decreased the negative effects of feed energy reduction on weight gain across starter, growing and the entire production phases (P<0·05). Energy retention as fat and total energy retention were increased when birds received LME diets supplemented with 1·2 g/kg GAA (P<0·05). Net energy for production (NEp) and total heat production increased in birds fed LME diets containing 1·2 g/kg GAA (P<0·05). A significant correlation was observed between dietary NEp and weight gain of broilers (r 0·493; P=0·0055), whereas this relationship was not seen with AME. Jejunal villus height and crypt depth were lower in birds fed LME diets (P<0·05). Serum concentration of creatinine increased in broilers fed LME diets either supplemented with 1·2 g/kg GAA or without GAA supplementation (P<0·05). Supplemental GAA improved performance of chickens fed LME diet possibly through enhanced dietary NEp. The NEp could be preferred over the AME to assess response of broiler chickens to dietary GAA supplementation.

Impact of dislocation densities on n+/p and p+/n junction GaAs diodes and solar cells on SiGe virtual substrates

NASA Astrophysics Data System (ADS)

Andre, C. L.; Wilt, D. M.; Pitera, A. J.; Lee, M. L.; Fitzgerald, E. A.; Ringel, S. A.

2005-07-01

Recent experimental measurements have shown that in GaAs with elevated threading dislocation densities (TDDs) the electron lifetime is much lower than the hole lifetime [C. L. Andre, J. J. Boeckl, D. M. Wilt, A. J. Pitera, M. L. Lee, E. A. Fitzgerald, B. M. Keyes, and S. A. Ringel, Appl. Phys. Lett. 84, 3884 (2004)]. This lower electron lifetime suggests an increase in depletion region recombination and thus in the reverse saturation current (J0 for an n+/p diode compared with a p+/n diode at a given TDD. To confirm this, GaAs diodes of both polarities were grown on compositionally graded Ge /Si1-xGex/Si (SiGe) substrates with a TDD of 1×106cm-2. It is shown that the ratio of measured J0 values is consistent with the inverse ratio of the expected lifetimes. Using a TDD-dependent lifetime in solar cell current-voltage models we found that the Voc, for a given short-circuit current, also exhibits a poorer TDD tolerance for GaAs n+/p solar cells compared with GaAs p+/n solar cells. Experimentally, the open-circuit voltage (Voc) for the n+/p GaAs solar cell grown on a SiGe substrate with a TDD of ˜1×106cm-2 was ˜880mV which was significantly lower than the ˜980mV measured for a p+/n GaAs solar cell grown on SiGe at the same TDD and was consistent with the solar cell modeling results reported in this paper. We conclude that p+/n polarity GaAs junctions demonstrate superior dislocation tolerance than n+/p configured GaAs junctions, which is important for optimization of lattice-mismatched III-V devices.

Phosphine Functionalization GaAs(111)A Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Traub, M.; Biteen, J; Michalak, D

Phosphorus-functionalized GaAs surfaces have been prepared by exposure of Cl-terminated GaAs(111)A surfaces to triethylphosphine (PEt3) or trichlorophosphine (PCl3), or by the direct functionalization of the native-oxide terminated GaAs(111)A surface with PCl3. The presence of phosphorus on each functionalized surface was confirmed by X-ray photoelectron spectroscopy. High-resolution, soft X-ray photoelectron spectroscopy was used to evaluate the As and Ga 3d regions of such surfaces. On PEt3 treated surfaces, the Ga 3d spectra exhibited a bulk Ga peak as well as peaks that were shifted to 0.35, 0.92 and 1.86 eV higher binding energy. These peaks were assigned to residual Cl-terminated Gamore » surface sites, surficial Ga2O and surficial Ga2O3, respectively. For PCl3-treated surfaces, the Ga 3d spectra displayed peaks ascribable to bulk Ga(As), Ga2O, and Ga2O3, as well as a peak shifted 0.30 eV to higher binding energy relative to the bulk signal. A peak corresponding to Ga(OH)3, observed on the Cl-terminated surface, was absent from all of the phosphine-functionalized surfaces. After reaction of the Cl-terminated GaAs(111)A surface with PCl3 or PEt3, the As 3d spectral region was free of As oxides and As0. Although native oxide-terminated GaAs surfaces were free of As oxides after reaction with PCl3, such surfaces contained detectable amounts of As0. Photoluminescence measurements indicted that phosphine-functionalized surfaces prepared from Cl-terminated GaAs(111)A surfaces had better electrical properties than the native-oxide capped GaAs(111)A surface, while the native-oxide covered surface treated with PCl3 showed no enhancement in PL intensity.« less

Facts and updates about cardiovascular non-coding RNAs in heart failure.

PubMed

Thum, Thomas

2015-09-01

About 11% of all deaths include heart failure as a contributing cause. The annual cost of heart failure amounts to US $34,000,000,000 in the United States alone. With the exception of heart transplantation, there is no curative therapy available. Only occasionally there are new areas in science that develop into completely new research fields. The topic on non-coding RNAs, including microRNAs, long non-coding RNAs, and circular RNAs, is such a field. In this short review, we will discuss the latest developments about non-coding RNAs in cardiovascular disease. MicroRNAs are short regulatory non-coding endogenous RNA species that are involved in virtually all cellular processes. Long non-coding RNAs also regulate gene and protein levels; however, by much more complicated and diverse mechanisms. In general, non-coding RNAs have been shown to be of great value as therapeutic targets in adverse cardiac remodelling and also as diagnostic and prognostic biomarkers for heart failure. In the future, non-coding RNA-based therapeutics are likely to enter the clinical reality offering a new treatment approach of heart failure.

Noncoding RNAs in human intervertebral disc degeneration: An integrated microarray study.

PubMed

Liu, Xu; Che, Lu; Xie, Yan-Ke; Hu, Qing-Jie; Ma, Chi-Jiao; Pei, Yan-Jun; Wu, Zhi-Gang; Liu, Zhi-Heng; Fan, Li-Ying; Wang, Hai-Qiang

2015-09-01

Accumulating evidence indicates that noncoding RNAs play important roles in a multitude of biological processes. The striking findings of miRNAs (microRNAs) and lncRNAs (long noncoding RNAs) as members of noncoding RNAs open up an exciting era in the studies of gene regulation. More recently, the reports of circRNAs (circular RNAs) add fuel to the noncoding RNAs research. Human intervertebral disc degeneration (IDD) is a main cause of low back pain as a disabling spinal disease. We have addressed the expression profiles if miRNAs, lncRNAs and mRNAs in IDD (Wang et al., J Pathology, 2011 and Wan et al., Arthritis Res Ther, 2014). Furthermore, we thoroughly analysed noncoding RNAs, including miRNAs, lncRNAs and circRNAs in IDD using the very same samples. Here we delineate in detail the contents of the aforementioned microarray analyses. Microarray and sample annotation data were deposited in GEO under accession number GSE67567 as SuperSeries. The integrated analyses of these noncoding RNAs will shed a novel light on coding-noncoding regulatory machinery.

Probability of twin formation on self-catalyzed GaAs nanowires on Si substrate

PubMed Central

2012-01-01

We attempted to control the incorporation of twin boundaries in self-catalyzed GaAs nanowires (NWs). Self-catalyzed GaAs NWs were grown on a Si substrate under various arsenic pressures using molecular beam epitaxy and the vapor-liquid-solid method. When the arsenic flux is low, wurtzite structures are dominant in the GaAs NWs. On the other hand, zinc blende structures become dominant as the arsenic flux rises. We discussed this phenomenon on the basis of thermodynamics and examined the probability of twin-boundary formation in detail. PMID:23043754

Photovoltaic Properties of p-Doped GaAs Nanowire Arrays Grown on n-Type GaAs(111)B Substrate

PubMed Central

2010-01-01

We report on the molecular beam epitaxy growth of Au-assisted GaAs p-type-doped NW arrays on the n-type GaAs(111)B substrate and their photovoltaic properties. The samples are grown at different substrate temperature within the range from 520 to 580 °C. It is shown that the dependence of conversion efficiency on the substrate temperature has a maximum at the substrate temperature of 550 °C. For the best sample, the conversion efficiency of 1.65% and the fill factor of 25% are obtained. PMID:20672038

Formation of a pn junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Leon, R. P.; Bailey, S. G.; Mazaris, G. A.; Williams, W. D.

1986-01-01

A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using MOCVD. A wet chemical etching process was used to expose the intersecting (111)Ga and (-1 -1 1)Ga planes with 6-micron periodicity. Charge-collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.

Technology requirements for GaAs photovoltaic arrays

NASA Technical Reports Server (NTRS)

Scott-Monck, J.; Rockey, D.

1981-01-01

An analysis based on percent GaAs solar cell weight and cost is performed to assess the utility of this cell for future space missions. It is shown that the GaAs substrate cost and the end-of-life (EOL) advantage the cell can provide over the space qualified silicon solar cell are the dominant factors determining potential use. Examples are presented to show that system level advantages resulting from reduction in solar panel area may warrant the use of GaAs at its current weight and projected initial cost provided the EOL advantage over silicon is at least 20 percent.

High efficiency epitaxial GaAs/GaAs and GaAs/Ge solar cell technology using OM/CVD

NASA Technical Reports Server (NTRS)

Wang, K. L.; Yeh, Y. C. M.; Stirn, R. J.; Swerdling, S.

1980-01-01

A technology for fabricating high efficiency, thin film GaAs solar cells on substrates appropriate for space and/or terrestrial applications was developed. The approach adopted utilizes organometallic chemical vapor deposition (OM-CVD) to form a GaAs layer epitaxially on a suitably prepared Ge epi-interlayer deposited on a substrate, especially a light weight silicon substrate which can lead to a 300 watt per kilogram array technology for space. The proposed cell structure is described. The GaAs epilayer growth on single crystal GaAs and Ge wafer substrates were investigated.

Epitaxial growth of quantum rods with high aspect ratio and compositional contrast

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, L. H.; Patriarche, G.; Fiore, A.

2008-12-01

The epitaxial growth of quantum rods (QRs) on GaAs was investigated. It was found that GaAs thickness in the GaAs/InAs superlattice used for QR formation plays a key role in improving the QR structural properties. Increasing the GaAs thickness results in both an increased In compositional contrast between the QRs and surrounding layer, and an increased QR length. QRs with an aspect ratio of up to 10 were obtained, representing quasiquantum wires in a GaAs matrix. Due to modified confinement and strain potential, such nanostructure is promising for controlling gain polarization.

Strand invasion structures in the inverted repeat of Candida albicans mitochondrial DNA reveal a role for homologous recombination in replication.

PubMed

Gerhold, Joachim M; Aun, Anu; Sedman, Tiina; Jõers, Priit; Sedman, Juhan

2010-09-24

Molecular recombination and transcription are proposed mechanisms to initiate mitochondrial DNA (mtDNA) replication in yeast. We conducted a comprehensive analysis of mtDNA from the yeast Candida albicans. Two-dimensional agarose gel electrophoresis of mtDNA intermediates reveals no bubble structures diagnostic of specific replication origins, but rather supports recombination-driven replication initiation of mtDNA in yeast. Specific species of Y structures together with DNA copy number analyses of a C. albicans mutant strain provide evidence that a region in a mainly noncoding inverted repeat is predominantly involved in replication initiation via homologous recombination. Our further findings show that the C. albicans mtDNA forms a complex branched network that does not contain detectable amounts of circular molecules. We provide topological evidence for recombination-driven mtDNA replication initiation and introduce C. albicans as a suitable model organism to study wild-type mtDNA maintenance in yeast. Copyright © 2010 Elsevier Inc. All rights reserved.

Failure Mechanisms of GaAs Transistors - A Literature Survey

DTIC Science & Technology

1990-03-01

doping profile cannot be as sharp as with epitaxial methods. This is the result of the statistics of the implantation and the general diffusion that...Speed GaAs Logic Gates 5.1 GaAs PLANAR TRANSITOR STRUCTURES USED IN IC’S Some planar transistor structures used in IC’s with examples of the

Laser Induced Electrodeposition on Polyimide and GaAs Substrates

DTIC Science & Technology

1983-10-01

6 3.1 Laser Gold Plating on Undoped Ga As Substrate ........... 6 3.1.1 Deposit Formation...22 iv LIST OF ILLUSTRATIONS Figure Page 1. Experimental Set-Up . . . . . .................. 4 2. Laser Gold Pla’ting Undoped GaAs (100...9 3. Laser Gold Plating Undoped GaAs (100) Deposit Resistance Measurement ......................... .10 4. Laser Gold Plating on Polyimide

Dietary guanidinoacetic acid increases brain creatine levels in healthy men.

PubMed

Ostojic, Sergej M; Ostojic, Jelena; Drid, Patrik; Vranes, Milan; Jovanov, Pavle

2017-01-01

Guanidinoacetic acid (GAA) is an experimental dietary additive that might act as a creatine source in tissues with high-energy requirements. In this case study, we evaluated brain levels of creatine in white matter, gray matter, cerebellum, and thalamus during 8 wk oral GAA administration in five healthy men and monitored the prevalence and severity of side effects of the intervention. Volunteers were supplemented daily with 36 mg/kg body weight (BW) of GAA for the first 4 wk of the intervention; afterward GAA dosage was titrated ≤60 mg/kg BW of GAA daily. At baseline, 4, and 8 wk, the participants underwent brain magnetic resonance spectroscopy, clinical chemistry studies, and open-ended questionnaire for side-effect prevalence and severity. Brain creatine levels increased in similar fashion in cerebellum, and white and gray matter after GAA supplementation, with an initial increase of 10.7% reported after 4 wk, and additional upsurge (7.7%) from the weeks 4 to 8 follow-up (P < 0.05). Thalamus creatine levels decreased after 4 wk for 6.5% (P = 0.02), and increased nonsignificantly after 8 wk for 8% (P = 0.09). GAA induced an increase in N-acetylaspartate levels at 8-wk follow-up in all brain areas evaluated (P < 0.05). No participants reported any neurologic adverse event (e.g., seizures, tingling, convulsions) during the intervention. Supplemental GAA led to a region-dependent increase of the creatine pool in the human brain. This might be relevant for restoring cellular bioenergetics in disorders characterized by low brain creatine and functional enzymatic machinery for creatine synthesis, including neurodegenerative diseases, brain tumors, or cerebrovascular disease. Copyright © 2016 Elsevier Inc. All rights reserved.

Lettuce Costunolide Synthase (CYP71BL2) and Its Homolog (CYP71BL1) from Sunflower Catalyze Distinct Regio- and Stereoselective Hydroxylations in Sesquiterpene Lactone Metabolism*

PubMed Central

Ikezawa, Nobuhiro; Göpfert, Jens Christian; Nguyen, Don Trinh; Kim, Soo-Un; O'Maille, Paul E.; Spring, Otmar; Ro, Dae-Kyun

2011-01-01

Sesquiterpene lactones (STLs) are terpenoid natural products possessing the γ-lactone, well known for their diverse biological and medicinal activities. The occurrence of STLs is sporadic in nature, but most STLs have been isolated from plants in the Asteraceae family. Despite the implication of the γ-lactone group in many reported bioactivities of STLs, the biosynthetic origins of the γ-lactone ring remains elusive. Germacrene A acid (GAA) has been suggested as a central precursor of diverse STLs. The regioselective (C6 or C8) and stereoselective (α or β) hydroxylation on a carbon of GAA adjacent to its carboxylic acid at C12 is responsible for the γ-lactone formation. Here, we report two cytochrome P450 monooxygenases (P450s) capable of catalyzing 6α- and 8β-hydroxylation of GAA from lettuce and sunflower, respectively. To identify these P450s, sunflower trichomes were isolated to generate a trichome-specific transcript library, from which 10 P450 clones were retrieved. Expression of these clones in a yeast strain metabolically engineered to synthesize substrate GAA identified a P450 catalyzing 8β-hydroxylation of GAA, but the STL was not formed by spontaneous lactonization. Subsequently, we identified the closest homolog of the GAA 8β-hydroxylase from lettuce and discovered 6α-hydroxylation of GAA by the recombinant enzyme. The resulting 6α-hydroxy-GAA spontaneously undergoes a lactonization to yield the simplest form of STL, costunolide. Furthermore, we demonstrate the milligram per liter scale de novo synthesis of costunolide using the lettuce P450 in an engineered yeast strain, an important advance that will enable exploitation of STLs. Evolution and homology models of these two P450s are discussed. PMID:21515683

Biocompatibility and calcification of bovine pericardium employed for the construction of cardiac bioprostheses treated with different chemical crosslink methods.

PubMed

Jorge-Herrero, Eduardo; Fonseca, Carlos; Barge, Alexandra P; Turnay, Javier; Olmo, Nieves; Fernández, Pilar; Lizarbe, María A; García Páez, José M

2010-05-01

The use of biological materials in the construction of bioprostheses requires the application of different chemical procedures to improve the durability of the material without producing any undesirable effects. A number of crosslinking methods have been tested in biological tissues composed mainly of collagen. The aim of this study was to evaluate the in vitro biocompatibility, the mechanical properties, and in vivo calcification of chemically modified bovine pericardium using glutaraldehyde acetals (GAAs) in comparison with glutaraldehyde (GA) treatment. Homsy's tests showed that the most cytotoxic treatment is GA whereas GAA treatments showed lower cytotoxicity. Regarding the mechanical properties of the modified materials, no significant differences in stress at rupture were detected among the different treatments. Zeta-Potential showed higher negative values for GA treatment (-4.9 +/- 0.6 mV) compared with GAA-0.625% (-2.2 +/- 0.5 mV) and GAA-1% (-2.2 +/- 0.4 mV), which presented values similar to native tissue. Similar results were obtained for calcium permeability coefficients which showed the highest values for GA treatment (0.12 +/- 0.02 mm(2)/min), being significantly lower for GAA treatments or non-crosslinked pericardium. These results confirmed the higher propensity of the GA-treated tissues for attraction of calcium cations and were in good agreement with the calcification degree obtained after 60 days implantation into young rats, which was significantly higher for the GA group (22.70 +/- 20.80 mg/g dry tissue) compared with GAA-0.625% and GAA-1% groups (0.49 +/- 0.28 mg/g dry tissue and 3.51 +/- 3.27 mg/g dry tissue, respectively; P < 0.001). In conclusion, GAA treatments can be considered a promising alternative to GA treatment.

Reveglucosidase alfa (BMN 701), an IGF2-Tagged rhAcid α-Glucosidase, Improves Respiratory Functional Parameters in a Murine Model of Pompe Disease.

PubMed

Peng, Jeffrey; Dalton, Jill; Butt, Mark; Tracy, Kristin; Kennedy, Derek; Haroldsen, Peter; Cahayag, Rhea; Zoog, Stephen; O'Neill, Charles A; Tsuruda, Laurie S

2017-02-01

Pompe disease is a rare neuromuscular disorder caused by an acid α-glucosidase (GAA) deficiency resulting in glycogen accumulation in muscle, leading to myopathy and respiratory weakness. Reveglucosidase alfa (BMN 701) is an insulin-like growth factor 2-tagged recombinant human acid GAA (rhGAA) that enhances rhGAA cellular uptake via a glycosylation-independent insulin-like growth factor 2 binding region of the cation-independent mannose-6-phosphate receptor (CI-MPR). The studies presented here evaluated the effects of Reveglucosidase alfa treatment on glycogen clearance in muscle relative to rhGAA, as well as changes in respiratory function and glycogen clearance in respiratory-related tissue in a Pompe mouse model (GAA tm1Rabn /J). In a comparison of glycogen clearance in muscle with Reveglucosidase alfa and rhGAA, Reveglucosidase alfa was more effective than rhGAA with 2.8-4.7 lower EC 50 values, probably owing to increased cellular uptake. The effect of weekly intravenous administration of Reveglucosidase alfa on respiratory function was monitored in Pompe and wild-type mice using whole body plethysmography. Over 12 weeks of 20-mg/kg Reveglucosidase alfa treatment in Pompe mice, peak inspiratory flow (PIF) and peak expiratory flow (PEF) stabilized with no compensation in respiratory rate and inspiratory time during hypercapnic and recovery conditions compared with vehicle-treated Pompe mice. Dose-related decreases in glycogen levels in both ambulatory and respiratory muscles generally correlated to changes in respiratory function. Improvement of murine PIF and PEF were similar in magnitude to increases in maximal inspiratory and expiratory pressure observed clinically in late onset Pompe patients treated with Reveglucosidase alfa (Byrne et al., manuscript in preparation). Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.

The complete chloroplast genome of Cinnamomum camphora and its comparison with related Lauraceae species.

PubMed

Chen, Caihui; Zheng, Yongjie; Liu, Sian; Zhong, Yongda; Wu, Yanfang; Li, Jiang; Xu, Li-An; Xu, Meng

2017-01-01

Cinnamomum camphora , a member of the Lauraceae family, is a valuable aromatic and timber tree that is indigenous to the south of China and Japan. All parts of Cinnamomum camphora have secretory cells containing different volatile chemical compounds that are utilized as herbal medicines and essential oils. Here, we reported the complete sequencing of the chloroplast genome of Cinnamomum camphora using illumina technology. The chloroplast genome of Cinnamomum camphora is 152,570 bp in length and characterized by a relatively conserved quadripartite structure containing a large single copy region of 93,705 bp, a small single copy region of 19,093 bp and two inverted repeat (IR) regions of 19,886 bp. Overall, the genome contained 123 coding regions, of which 15 were repeated in the IR regions. An analysis of chloroplast sequence divergence revealed that the small single copy region was highly variable among the different genera in the Lauraceae family. A total of 40 repeat structures and 83 simple sequence repeats were detected in both the coding and non-coding regions. A phylogenetic analysis indicated that Calycanthus is most closely related to Lauraceae , both being members of Laurales , which forms a sister group to Magnoliids . The complete sequence of the chloroplast of Cinnamomum camphora will aid in in-depth taxonomical studies of the Lauraceae family in the future. The genetic sequence information will also have valuable applications for chloroplast genetic engineering.

The Glycine-Alanine Dipeptide Repeat from C9orf72 Hexanucleotide Expansions Forms Toxic Amyloids Possessing Cell-to-Cell Transmission Properties.

PubMed

Chang, Yu-Jen; Jeng, U-Ser; Chiang, Ya-Ling; Hwang, Ing-Shouh; Chen, Yun-Ru

2016-03-04

Hexanucleotide expansions, GGGGCC, in the non-coding regions of the C9orf72 gene were found in major frontotemporal lobar dementia and amyotrophic lateral sclerosis patients (C9FTD/ALS). In addition to possible RNA toxicity, several dipeptide repeats (DPRs) are translated through repeat-associated non-ATG-initiated translation. The DPRs, including poly(GA), poly(GR), poly(GP), poly(PR), and poly(PA), were found in the brains and spinal cords of C9FTD/ALS patients. Among the DPRs, poly(GA) is highly susceptible to form cytoplasmic inclusions, which is a characteristic of C9FTD/ALS. To elucidate DPR aggregation, we used synthetic (GA)15 DPR as a model system to examine the aggregation and structural properties in vitro. We found that (GA)15 with 15 repeats fibrillates rapidly and ultimately forms flat, ribbon-type fibrils evidenced by transmission electron microscopy and atomic force microscopy. The fibrils are capable of amyloid dye binding and contain a characteristic cross-β sheet structure, as revealed by x-ray scattering. Furthermore, using neuroblastoma cells, we demonstrated the neurotoxicity and cell-to-cell transmission property of (GA)15 DPR. Overall, our results show the structural and toxicity properties of GA DPR to facilitate future DPR-related therapeutic development. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Voltage-selective bidirectional polarization and coherent rotation of nuclear spins in quantum dots.

PubMed

Takahashi, R; Kono, K; Tarucha, S; Ono, K

2011-07-08

We propose and demonstrate that the nuclear spins of the host lattice in GaAs double quantum dots can be polarized in either of two opposite directions, parallel or antiparallel to an external magnetic field. The direction is selected by adjusting the dc voltage. This nuclear polarization manifests itself by repeated controlled electron-nuclear spin scattering in the Pauli spin-blockade state. Polarized nuclei are also controlled by means of nuclear magnetic resonance. This Letter confirms that the nuclear spins in quantum dots are long-lived quantum states with a coherence time of up to 1 ms, and may be a promising resource for quantum-information processing such as quantum memories for electron spin qubits.

Temporal behavior of RHEED intensity oscillations during molecular beam epitaxial growth of GaAs and AlGaAs on (111)B GaAs substrates

NASA Astrophysics Data System (ADS)

Yen, Ming Y.; Haas, T. W.

1990-10-01

We present the temporal behavior of intensity oscillations in reflection high-energy electron diffraction (RHEED) during molecular beam epitaxial (MBE) growth of GaAs and A1GaAs on (1 1 1)B GaAs substrates. The RHEED intensity oscillations were examined as a function of growth parameters in order to provide the insight into the dynamic characteristics and to identify the optimal condition for the two-dimensional layer-by-layer growth. The most intense RHEED oscillation was found to occur within a very narrow temperature range which seems to optimize the surface migration kinetics of the arriving group III elements and the molecular dissodiative reaction of the group V elements. The appearance of an initial transient of the intensity upon commencement of the growth and its implications are described.

Structure of high-index GaAs surfaces - the discovery of the stable GaAs(2511) surface

NASA Astrophysics Data System (ADS)

Jacobi, K.; Geelhaar, L.; Márquez, J.

We present a brief overview of surface structures of high-index GaAs surfaces, putting emphasis on recent progress in our own laboratory. By adapting a commercial scanning tunneling microscope (STM) to our molecular beam epitaxy and ultra high vacuum analysis chamber system, we have been able to atomically resolve the GaAs( {1} {1} {3})B(8 ×1), (114)Aα2(2×1), (137), (3715), and (2511) surface structures. In cooperation with P. Kratzer and M. Scheffler from the Theory Department of the Fritz-Haber Institute we determined the structure of some of these surfaces by comparing total-energy calculations and STM image simulations with the atomically resolved STM images. We present the results for the {112}, {113}, and {114} surfaces. Then we describe what led us to proceed into the inner parts of the stereographic triangle and to discover the hitherto unknown stable GaAs(2511) surface.

Nanoepitaxy of GaAs on a Si(001) substrate using a round-hole nanopatterned SiO2 mask.

PubMed

Hsu, Chao-Wei; Chen, Yung-Feng; Su, Yan-Kuin

2012-12-14

GaAs is grown by metal-organic vapor-phase epitaxy on a 55 nm round-hole patterned Si substrate with SiO(2) as a mask. The threading dislocations, which are stacked on the lowest energy facet plane, move along the SiO(2) walls, reducing the number of dislocations. The etching pit density of GaAs on the 55 nm round-hole patterned Si substrate is about 3.3 × 10(5) cm(-2). Compared with the full width at half maximum measurement from x-ray diffraction and photoluminescence spectra of GaAs on a planar Si(001) substrate, those of GaAs on the 55 nm round-hole patterned Si substrate are reduced by 39.6 and 31.4%, respectively. The improvement in material quality is verified by transmission electron microscopy, field-emission scanning electron microscopy, Hall measurements, Raman spectroscopy, photoluminescence, and x-ray diffraction studies.

Passively Q-switched, intracavity frequency-doubled YVO{sub 4}/Nd : YVO{sub 4}/KTP green laser with a GaAs saturable absorber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shang Gao

2015-11-30

A diode-pumped, passively Q-switched, intracavity frequency-doubled YVO{sub 4}/Nd : YVO{sub 4}/KTP green laser is realised using a GaAs saturable absorber. Two pieces of GaAs wafers are employed in the experiment. In using a 400-μm-thick GaAs wafer and an incident pump power of 10.5 W, the maximum output power of the passively Q-switched green laser is 362 mW at a pulse repetition rate of 84 kHz and a pulse duration of 2.5 ns. When use is made of a 700-mm-thick GaAs wafer, the minimum pulse duration is 1.5 ns at a repetition rate of 67 kHz, pulse energy of 4.18 μJmore » and peak power of 2.8 kW. (control of laser radiation parameters)« less

Photon counting microstrip X-ray detectors with GaAs sensors

NASA Astrophysics Data System (ADS)

Ruat, M.; Andrä, M.; Bergamaschi, A.; Barten, R.; Brückner, M.; Dinapoli, R.; Fröjdh, E.; Greiffenberg, D.; Lopez-Cuenca, C.; Lozinskaya, A. D.; Mezza, D.; Mozzanica, A.; Novikov, V. A.; Ramilli, M.; Redford, S.; Ruder, C.; Schmitt, B.; Shi, X.; Thattil, D.; Tinti, G.; Tolbanov, O. P.; Tyazhev, A.; Vetter, S.; Zarubin, A. N.; Zhang, J.

2018-01-01

High-Z sensors are increasingly used to overcome the poor efficiency of Si sensors above 15 keV, and further extend the energy range of synchrotron and FEL experiments. Detector-grade GaAs sensors of 500 μm thickness offer 98% absorption efficiency at 30 keV and 50% at 50 keV . In this work we assess the usability of GaAs sensors in combination with the MYTHEN photon-counting microstrip readout chip developed at PSI. Different strip length and pitch are compared, and the detector performance is evaluated in regard of the sensor material properties. Despite increased leakage current and noise, photon-counting strips mounted with GaAs sensors can be used with photons of energy as low as 5 keV, and exhibit excellent linearity with energy. The charge sharing is doubled as compared to silicon strips, due to the high diffusion coefficient of electrons in GaAs.

Strain relaxation in epitaxial GaAs/Si (0 0 1) nanostructures

NASA Astrophysics Data System (ADS)

Kozak, Roksolana; Prieto, Ivan; Arroyo Rojas Dasilva, Yadira; Erni, Rolf; Skibitzki, Oliver; Capellini, Giovanni; Schroeder, Thomas; von Känel, Hans; Rossell, Marta D.

2017-11-01

Crystal defects, present in 100 nm GaAs nanocrystals grown by metal organic vapour phase epitaxy on top of (0 0 1)-oriented Si nanotips (with a tip opening 50-90 nm), have been studied by means of high-resolution aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. The role of 60° perfect, 30° and 90° Shockley partial misfit dislocations (MDs) in the plastic strain relaxation of GaAs on Si is discussed. Formation conditions of stair-rod dislocations and coherent twin boundaries in the GaAs nanocrystals are explained. Also, although stacking faults are commonly observed, we show here that synthesis of GaAs nanocrystals with a minimum number of these defects is possible. On the other hand, from the number of MDs, we have to conclude that the GaAs nanoparticles are fully relaxed plastically, such that for the present tip sizes no substrate compliance can be observed.

Optimization of solar cells for air mass zero operation and a study of solar cells at high temperatures

NASA Technical Reports Server (NTRS)

Hovel, H. J.; Vernon, S. M.

1982-01-01

The power to weight ratio of GaAs cells can be reduced by fabricating devices using thin GaAs films on low density substrate materials (silicon, glass, plastics). A graphoepitaxy technique was developed which uses fine geometric patterns in the substrate to affect growth. Initial substrates were processed by etching 25 microns deep grooves into 100 oriented wafers; fine-grained polycrystalline GaAs layers 25-50 microns thick were then deposited on these and recrystallization was performed, heating the substrates to above the GaAs melting point in ASH3 atmosphere, resulting in large grain regrowth oriented along the groove dimensions. Experiments with smaller groove depths and spacings were initially encouraging; single large GaAs grains would totally cover one and often two groove fields of 14 groove each spanning several hundred microns. Dielectric coatings on the grooved substrates were also used to modify the growth.

Low-temperature photoluminescence study of thin epitaxial GaAs films on Ge substrates

NASA Astrophysics Data System (ADS)

Brammertz, Guy; Mols, Yves; Degroote, Stefan; Motsnyi, Vasyl; Leys, Maarten; Borghs, Gustaaf; Caymax, Matty

2006-05-01

Thin epitaxial GaAs films, with thickness varying from 140 to 1000 nm and different Si doping levels, were grown at 650 °C by organometallic vapor phase epitaxy on Ge substrates and analyzed by low-temperature photoluminescence (PL) spectroscopy. All spectra of thin GaAs on Ge show two different structures, one narrow band-to-band (B2B) structure at an energy of ~1.5 eV and a broad inner-band-gap (IB) structure at an energy of ~1.1 eV. Small strain in the thin GaAs films causes the B2B structure to be separated into a light-hole and a heavy-hole peak. At 2.5 K the good structural quality of the thin GaAs films on Ge can be observed from the narrow excitonic peaks. Peak widths of less than 1 meV are measured. GaAs films with thickness smaller than 200 nm show B2B PL spectra with characteristics of an n-type doping level of approximately 1018 at./cm3. This is caused by heavy Ge diffusion from the substrate into the GaAs at the heterointerface between the two materials. The IB structure observed in all films consists of two Gaussian peaks with energies of 1.04 and 1.17 eV. These deep trapping states arise from Ge-based complexes formed within the GaAs at the Ge-GaAs heterointerface, due to strong diffusion of Ge atoms into the GaAs. Because of similarities with Si-based complexes, the peak at 1.04 eV was identified to be due to a GeGa-GeAs complex, whereas the peak at 1.17 eV was attributed to the GeGa-VGa complex. The intensity of the IB structure decreases strongly as the GaAs film thickness is increased. PL intensity of undoped GaAs films containing antiphase domains (APDs) is four orders of magnitude lower than for similar films without APDs. This reduction in intensity is due to the electrically active Ga-Ga and As-As bonds at the boundaries between the different APDs. When the Si doping level is increased, the PL intensity of the APD-containing films is increased again as well. A film containing APDs with a Si doping level of ~1018 at./cm3 has only a factor 10 reduced intensity. We tentatively explain this observation by Si or Ge clustering at antiphase boundaries, which eliminates the effects of the Ga-Ga and As-As bonds. This assumption is confirmed by the fact that, at 77 K, the ratio between the intensity of the IB peak at 1.17 eV to the intensity of the peak at 1.04 eV is smaller than 1.4 for all films containing APDs, whereas it is larger than 1.4 for all films without APDs. This shows stronger clustering of Si or Ge in the material with APDs. For future electronic applications, Ge diffusion into the GaAs will have to be reduced. PL analysis will be a rapid tool for studying the Ge diffusion into the GaAs thin films.

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2013 CFR

2013-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2012 CFR

2012-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2010 CFR

2010-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2014 CFR

2014-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2011 CFR

2011-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

Panel fabrication utilizing GaAs solar cells

NASA Technical Reports Server (NTRS)

Mardesich, N.

1984-01-01

The development of the GaAs solar cells for space applications is described. The activities in the fabrication of GaAs solar panels are outlined. Panels were fabricated while introducing improved quality control, soldering laydown and testing procedures. These panels include LIPS II, San Marco Satellite, and a low concentration panel for Rockwells' evaluation. The panels and their present status are discussed.

Implementation and Performance of GaAs Digital Signal Processing ASICs

NASA Technical Reports Server (NTRS)

Whitaker, William D.; Buchanan, Jeffrey R.; Burke, Gary R.; Chow, Terrance W.; Graham, J. Scott; Kowalski, James E.; Lam, Barbara; Siavoshi, Fardad; Thompson, Matthew S.; Johnson, Robert A.

1993-01-01

The feasibility of performing high speed digital signal processing in GaAs gate array technology has been demonstrated with the successful implementation of a VLSI communications chip set for NASA's Deep Space Network. This paper describes the techniques developed to solve some of the technology and implementation problems associated with large scale integration of GaAs gate arrays.

Research on gallium arsenide diffused junction solar cells

NASA Technical Reports Server (NTRS)

Borrego, J. M.; Ghandi, S. K.

1984-01-01

The feasibility of using bulk GaAs for the fabrication of diffused junction solar cells was determined. The effects of thermal processing of GaAs was studied, and the quality of starting bulk GaAs for this purpose was assessed. These cells are to be made by open tube diffusion techniques, and are to be tested for photovoltaic response under AMO conditions.

Characterisation of semi-insulating GaAs

NASA Technical Reports Server (NTRS)

Walukiewicz, W.; Pawlowicz, L.; Lagowski, J.; Gatos, H. C.

1982-01-01

Hole and electron mobilities as functions of temperature and ionised impurity concentration are calculated for GaAs. It is shown that these calculations, when used to analyse electrical properties of semi-insulating GaAs, enable an assessment of the Fermi energy position and ionised impurity concentration to be made. In contrast to previous work, the analysis does not require any phenomenological assumptions.

Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

NASA Technical Reports Server (NTRS)

Kang, C. H.; Kondo, K.; Lagowski, J.; Gatos, H. C.

1987-01-01

Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

High Frequency GaAs Bulk Acousto-Optic Devices For Modulators And Frequency Shifters At 1.3um And 1.5um In Fiber-Optics

NASA Astrophysics Data System (ADS)

Soos, J. I.; Rosemeier, R. G.

1989-02-01

The edge of a transmission window for a GaAs Bragg cell starts about lum, which allows this material to be used for infrared fiber-optic applications, especially at 1.3um and 1.5um. The single crystal of GaAs is acoustically anisotropic and has the highest figure of merit, M2, along <111> direction for a longitudinal mode sound wave. Recently, Brimrose has designed and fabricated an acousto-optic modulator from GaAs operating at a carrier frequency of 2.3 GHz with a diffraction efficiency of 4%/RF watt.

Epitaxial lateral overgrowth of GaAs: effect of doping on LPE growth behaviour

NASA Astrophysics Data System (ADS)

Zytkiewicz, Z. R.; Dobosz, D.; Pawlowska, M.

1999-05-01

Results of epitaxial lateral overgrowth (ELO) of GaAs on (001) GaAs substrates by liquid phase epitaxy are reported. We show that by introducing Si, Sn or Te impurities to the Ga-As solution the vertical growth rate is reduced while the lateral growth rate is significantly enhanced, which leads to a growth habit modification. Furthermore, the impurity incorporation into the growing layer is different on the upper and side surfaces of the ELO, reflecting the fundamental differences between the lateral and vertical growth modes. This phenomenon can be applied for studying the temporal development of ELO layers.

Noncoding RNAs of the Ultrabithorax Domain of the Drosophila Bithorax Complex

PubMed Central

Pease, Benjamin; Borges, Ana C.; Bender, Welcome

2013-01-01

RNA transcripts without obvious coding potential are widespread in many creatures, including the fruit fly, Drosophila melanogaster. Several noncoding RNAs have been identified within the Drosophila bithorax complex. These first appear in blastoderm stage embryos, and their expression patterns indicate that they are transcribed only from active domains of the bithorax complex. It has been suggested that these noncoding RNAs have a role in establishing active domains, perhaps by setting the state of Polycomb Response Elements A comprehensive survey across the proximal half of the bithorax complex has now revealed nine distinct noncoding RNA transcripts, including four within the Ultrabithorax transcription unit. At the blastoderm stage, the noncoding transcripts collectively span ∼75% of the 135 kb surveyed. Recombination-mediated cassette exchange was used to invert the promoter of one of the noncoding RNAs, a 23-kb transcript from the bxd domain of the bithorax complex. The resulting animals fail to make the normal bxd noncoding RNA and show no transcription across the bxd Polycomb Response Element in early embryos. The mutant flies look normal; the regulation of the bxd domain appears unaffected. Thus, the bxd noncoding RNA has no apparent function. PMID:24077301

Analysis of conserved noncoding DNA in Drosophila reveals similar constraints in intergenic and intronic sequences.

PubMed

Bergman, C M; Kreitman, M

2001-08-01

Comparative genomic approaches to gene and cis-regulatory prediction are based on the principle that differential DNA sequence conservation reflects variation in functional constraint. Using this principle, we analyze noncoding sequence conservation in Drosophila for 40 loci with known or suspected cis-regulatory function encompassing >100 kb of DNA. We estimate the fraction of noncoding DNA conserved in both intergenic and intronic regions and describe the length distribution of ungapped conserved noncoding blocks. On average, 22%-26% of noncoding sequences surveyed are conserved in Drosophila, with median block length approximately 19 bp. We show that point substitution in conserved noncoding blocks exhibits transition bias as well as lineage effects in base composition, and occurs more than an order of magnitude more frequently than insertion/deletion (indel) substitution. Overall, patterns of noncoding DNA structure and evolution differ remarkably little between intergenic and intronic conserved blocks, suggesting that the effects of transcription per se contribute minimally to the constraints operating on these sequences. The results of this study have implications for the development of alignment and prediction algorithms specific to noncoding DNA, as well as for models of cis-regulatory DNA sequence evolution.

Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

NASA Astrophysics Data System (ADS)

Clayburn, Nathan; Dreiling, Joan; McCarter, James; Ryan, Dominic; Poelker, Matt; Gay, Timothy

2012-06-01

GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35%. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5%. [4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).

Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE.

PubMed

Skibitzki, Oliver; Prieto, Ivan; Kozak, Roksolana; Capellini, Giovanni; Zaumseil, Peter; Arroyo Rojas Dasilva, Yadira; Rossell, Marta D; Erni, Rolf; von Känel, Hans; Schroeder, Thomas

2017-03-01

We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO 2 -mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.

IMPATT Diodes Based on 〈111〉, 〈100〉, and 〈110〉 Oriented GaAs: A Comparative Study to Search the Best Orientation for Millimeter-Wave Atmospheric Windows

PubMed Central

Banerjee, Bhadrani; Tripathi, Anvita; Das, Adrija; Singh, Kumari Alka; Banerjee, J. P.

2015-01-01

The authors have carried out the large-signal (L-S) simulation of double-drift region (DDR) impact avalanche transit time (IMPATT) diodes based on 〈111〉, 〈100〉, and 〈110〉 oriented GaAs. A nonsinusoidal voltage excited (NSVE) L-S simulation technique is used to investigate both the static and L-S performance of the above-mentioned devices designed to operate at millimeter-wave (mm-wave) atmospheric window frequencies, such as 35, 94, 140, and 220 GHz. Results show that 〈111〉 oriented GaAs diodes are capable of delivering maximum RF power with highest DC to RF conversion efficiency up to 94 GHz; however, the L-S performance of 〈110〉 oriented GaAs diodes exceeds their other counterparts while the frequency of operation increases above 94 GHz. The results presented in this paper will be helpful for the future experimentalists to choose the GaAs substrate of appropriate orientation to fabricate DDR GaAs IMPATT diodes at mm-wave frequencies. PMID:27347524

Electrical and Optical Characterization of Sputtered Silicon Dioxide, Indium Tin Oxide, and Silicon Dioxide/Indium Tin Oxide Antireflection Coating on Single-Junction GaAs Solar Cells

PubMed Central

Ho, Wen-Jeng; Lin, Jian-Cheng; Liu, Jheng-Jie; Bai, Wen-Bin; Shiao, Hung-Pin

2017-01-01

This study characterized the electrical and optical properties of single-junction GaAs solar cells coated with antireflective layers of silicon dioxide (SiO2), indium tin oxide (ITO), and a hybrid layer of SiO2/ITO applied using Radio frequency (RF) sputtering. The conductivity and transparency of the ITO film were characterized prior to application on GaAs cells. Reverse saturation-current and ideality factor were used to evaluate the passivation performance of the various coatings on GaAs solar cells. Optical reflectance and external quantum efficiency response were used to evaluate the antireflective performance of the coatings. Photovoltaic current-voltage measurements were used to confirm the efficiency enhancement obtained by the presence of the anti-reflective coatings. The conversion efficiency of the GaAs cells with an ITO antireflective coating (23.52%) exceeded that of cells with a SiO2 antireflective coating (21.92%). Due to lower series resistance and higher short-circuit current-density, the carrier collection of the GaAs cell with ITO coating exceeded that of the cell with a SiO2/ITO coating. PMID:28773063

Long non-coding RNA AK096174 promotes cell proliferation and invasion in gastric cancer by regulating WDR66 expression.

PubMed

Zhang, Yeqian; Yu, Site; Zhang, Zizhen; Zhao, Gang; Xu, Jia

2018-05-01

Gastric cancer is one of the major causes of cancer death worldwide; however, the mechanism of carcinogenesis is complex and poorly understood. Long noncoding RNA (lncRNA) have been reported to be involved in the development of multiple cancers. Here we identified a novel lncRNA, AK096174, which was upregulated and associated with tumorigenesis, tumor size, metastasis, and poor prognosis in gastric cancer. Our data showed that AK096174 was highly expressed in the gastric cancer tissues and cell lines (SGC-7901, AGS, BGC-823, MGC-803), and patients with higher AK096174 expression had a poorer prognosis and shorter overall survival. AK096174 knockdown inhibited the proliferation, migration and invasiveness in SGC-7901 and BGC-823 cells, whereas AK096174 overexpression had the promoting effects. Furthermore, mechanistic investigation showed that AK096174 positively correlated with the expression of WD repeat-containing protein 66 (WDR66) gene at the translational level. Knockdown of WRD66 attenuated the positive impact of AK096174 in gastric cancer cells. The findings of this study establish a function for AK096174 in gastric cancer progression and suggest it may serve as a potential target for gastric cancer therapy in the future. ©2018 The Author(s).

The long non-coding RNA HOTTIP enhances pancreatic cancer cell proliferation, survival and migration

PubMed Central

Cheng, Yating; Jutooru, Indira; Chadalapaka, Gayathri; Corton, J. Christopher; Safe, Stephen

2015-01-01

HOTTIP is a long non-coding RNA (lncRNA) transcribed from the 5′ tip of the HOXA locus and is associated with the polycomb repressor complex 2 (PRC2) and WD repeat containing protein 5 (WDR5)/mixed lineage leukemia 1 (MLL1) chromatin modifying complexes. HOTTIP is expressed in pancreatic cancer cell lines and knockdown of HOTTIP by RNA interference (siHOTTIP) in Panc1 pancreatic cancer cells decreased proliferation, induced apoptosis and decreased migration. In Panc1 cells transfected with siHOTTIP, there was a decrease in expression of 757 genes and increased expression of 514 genes, and a limited gene analysis indicated that HOTTIP regulation of genes is complex. For example, Aurora kinase A, an important regulator of cell growth, is coregulated by MLL and not WDR5 and, in contrast to previous studies in liver cancer cells, HOTTIP does not regulate HOXA13 but plays a role in regulation of several other HOX genes including HOXA10, HOXB2, HOXA11, HOXA9 and HOXA1. Although HOTTIP and the HOX-associated lncRNA HOTAIR have similar pro-oncogenic functions, they regulate strikingly different sets of genes in Panc1 cells and in pancreatic tumors. PMID:25912306

Reduction of myeloid-derived suppressor cells and lymphoma growth by a natural triterpenoid.

PubMed

Radwan, Faisal F Y; Hossain, Azim; God, Jason M; Leaphart, Nathan; Elvington, Michelle; Nagarkatti, Mitzi; Tomlinson, Stephen; Haque, Azizul

2015-01-01

Lymphoma is a potentially life threatening disease. The goal of this study was to investigate the therapeutic potential of a natural triterpenoid, Ganoderic acid A (GA-A) in controlling lymphoma growth both in vitro and in vivo. Here, we show that GA-A treatment induces caspase-dependent apoptotic cell death characterized by a dose-dependent increase in active caspases 9 and 3, up-regulation of pro-apoptotic BIM and BAX proteins, and a subsequent loss of mitochondrial membrane potential with release of cytochrome c. In addition to GA-A's anti-growth activity, we show that lower doses of GA-A enhance HLA class II-mediated antigen (Ag) presentation and CD4+ T cell recognition of lymphoma cells in vitro. The therapeutic relevance of GA-A treatment was also tested in vivo using the EL4 syngeneic mouse model of metastatic lymphoma. GA-A-treatment significantly prolonged survival of EL4 challenged mice and decreased tumor metastasis to the liver, an outcome accompanied by a marked down-regulation of STAT3 phosphorylation, reduction myeloid-derived suppressor cells (MDSCs), and enhancement of cytotoxic CD8+ T cells in the host. Thus, GA-A not only selectively induces apoptosis in lymphoma cells, but also enhances cell-mediated immune responses by attenuating MDSCs, and elevating Ag presentation and T cell recognition. The demonstrated therapeutic benefit indicates that GA-A is a candidate for future drug design for the treatment of lymphoma. © 2014 Wiley Periodicals, Inc.

The mitochondrial genome of Pomacea maculata (Gastropoda: Ampullariidae).

PubMed

Yang, Qianqian; Liu, Suwen; Song, Fan; Li, Hu; Liu, Jinpeng; Liu, Guangfu; Yu, Xiaoping

2016-07-01

The golden apple snail, Pomacea maculata Perry, 1810 (Gastropoda: Ampullariidae) is one of the most serious invasive alien species from the native range of South America. The mitochondrial genome of P. maculata (15 516 bp) consists of 37 genes (13 protein-coding genes, two rRNAs, and 22 tRNAs) and a non-coding region with a 16 bp repeat unit. Most mitochondrial genes of P. maculata are distributed on the H-strand, except eight tRNA genes, which are encoded on the L-strand. A phylogenetic analysis showed that there was a close relationship between P. maculata and another invasive golden apple snail species, Pomacea canaliculata (Lamarck, 1822).

2009 Epigenetics Gordon Research Conference (August 9 - 14, 2009)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeanie Lee

Epigenetics refers to the study of heritable changes in genome function that occur without a change in primary DNA sequence. The 2009 Gordon Conference in Epigenetics will feature discussion of various epigenetic phenomena, emerging understanding of their underlying mechanisms, and the growing appreciation that human, animal, and plant health all depend on proper epigenetic control. Special emphasis will be placed on genome-environment interactions particularly as they relate to human disease. Towards improving knowledge of molecular mechanisms, the conference will feature international leaders studying the roles of higher order chromatin structure, noncoding RNA, repeat elements, nuclear organization, and morphogenic evolution. Traditionalmore » and new model organisms are selected from plants, fungi, and metazoans.« less

Experimental investigation of millimeter-wave GaAs TED oscillators cooled to cryogenic temperatures

NASA Astrophysics Data System (ADS)

Rydberg, Anders; Kollberg, Erik

1988-03-01

The output power and operating (bias) point for 80-100-GHz GaAs TED oscillators have been investigated for temperatures between 300 and 40 K. It is shown experimentally that the power can be increased by as much as nearly four times by cooling the oscillator. The thermal design of the oscillator was studied for GaAs and InP TED oscillators.

Mechanisms of p53-Mediated Apoptosis

DTIC Science & Technology

2007-03-01

Bonnet, P. Dikkes, A. Sharpe, F. McKeon, and D. Caput. 2000. p73-deficient mice have neurological, pheromonal and inflammatory defects but lack...TTT TTG GAA A-3’ and HDAC1-si- CR-R: 5’-AGC TTT TCC AAA AAG CAG ATG CAG AGA TTC AAC TCT CTT GAA GTT GAA TCT CTG CAT CTG CGG G-3’ with HDAC1 targeting

[Relevance of long non-coding RNAs in tumour biology].

PubMed

Nagy, Zoltán; Szabó, Diána Rita; Zsippai, Adrienn; Falus, András; Rácz, Károly; Igaz, Péter

2012-09-23

The discovery of the biological relevance of non-coding RNA molecules represents one of the most significant advances in contemporary molecular biology. It has turned out that a major fraction of the non-coding part of the genome is transcribed. Beside small RNAs (including microRNAs) more and more data are disclosed concerning long non-coding RNAs of 200 nucleotides to 100 kb length that are implicated in the regulation of several basic molecular processes (cell proliferation, chromatin functioning, microRNA-mediated effects, etc.). Some of these long non-coding RNAs have been associated with human tumours, including H19, HOTAIR, MALAT1, etc., the different expression of which has been noted in various neoplasms relative to healthy tissues. Long non-coding RNAs may represent novel markers of molecular diagnostics and they might even turn out to be targets of therapeutic intervention.

Use of a corrugated surface to enhance radiation tolerance in a GaAs solar cell

NASA Technical Reports Server (NTRS)

Leon, Rosa P.; Piszczor, Michael F., Jr.

1985-01-01

The use of a corrugated surface on a GaAs solar cell and its effects on radiation resistance were studied. A compute code was developed to determine the performance of the cell for various geometric parameters. The large optical absorption coefficient of GaAs allows grooves to be only 4-5 micrometers deep. Using accepted material parameters for GaAs solar cells the theoretical performances were compared for various corrugated cells before and after minority carrier diffusion length degradation. The total power output was maximized for both n(+)/p and p(+)/n cells. Optimum values of 1.0-1.5 and 5.0 micrometers for groove and ridge widths respectively were determined.

4-GHz counters bring synthesizers up to speed

NASA Astrophysics Data System (ADS)

Lee, F.; Miller, R.

1984-06-01

The availability of digital IC counters built on GaAs makes direct frequency division in microwave synthesizers possible. Four GHz is the highest clock rate achievable in production designs. These devices have the ability to drive TTL/CMOS logic, and the counter can be connected directly to single-chip frequency synthesizers controllers. A complete microwave sythesizer is formed by two chips and a voltage-controlled oscillator (VCO). The advantages of GaAs are discussed along with flip-flop basics, aspects of device fabrication, and the characteristics of GaAs MESAFETs. Attention is given to a GaAs prescaler usable for direct conversion, four kinds of flip-flops in a divide-by-two mode, and seven-stage binary ripple counters.

GaAs Solar Cell Radiation Handbook

NASA Technical Reports Server (NTRS)

Anspaugh, B. E.

1996-01-01

The handbook discusses the history of GaAs solar cell development, presents equations useful for working with GaAs solar cells, describes commonly used instrumentation techniques for assessing radiation effects in solar cells and fundamental processes occurring in solar cells exposed to ionizing radiation, and explains why radiation decreases the electrical performance of solar cells. Three basic elements required to perform solar array degradation calculations: degradation data for GaAs solar cells after irradiation with 1 MeV electrons at normal incidence; relative damage coefficients for omnidirectional electron and proton exposure; and the definition of the space radiation environment for the orbit of interest, are developed and used to perform a solar array degradation calculation.

Nanoscale Semiconductor Electronics

DTIC Science & Technology

2015-02-25

GaAs into Ga2O3 . Compared with LHO along the Al0.98Ga0.02As layer, however, the vertical oxidation into the GaAs capping is very slow. Its rate is...Then, NH4NO3 reacts with GaAs and results in Ga2O3 and As2O3. The oxidation rate is critically affected by pH and temperature. A high oxidation rate...shrinkage 500 nm Al0.98Ga0.02As Semi-insulating GaAs(001) 100 nm n+-GaAs Al2O3 100 nm SiO2 Ga2O3 n+-GaAs stripe ~20‐25 m LHO condition Temperature

Noncoding sequence classification based on wavelet transform analysis: part II

NASA Astrophysics Data System (ADS)

Paredes, O.; Strojnik, M.; Romo-Vázquez, R.; Vélez-Pérez, H.; Ranta, R.; Garcia-Torales, G.; Scholl, M. K.; Morales, J. A.

2017-09-01

DNA sequences in human genome can be divided into the coding and noncoding ones. We hypothesize that the characteristic periodicities of the noncoding sequences are related to their function. We describe the procedure to identify these characteristic periodicities using the wavelet analysis. Our results show that three groups of noncoding sequences, each one with different biological function, may be differentiated by their wavelet coefficients within specific frequency range.

Hyperhomocysteinemia induced by guanidinoacetic acid is effectively suppressed by choline and betaine in rats.

PubMed

Setoue, Minoru; Ohuchi, Seiya; Morita, Tatsuya; Sugiyama, Kimio

2008-07-01

Rats were fed 25% casein (25C) diets differing in choline levels (0-0.5%) with and without 0.5% guanidinoacetic acid (GAA) or 0.75% L-methionine for 7 d to determine the effects of dietary choline level on experimental hyperhomocysteinemia. The effects of dietary choline (0.30%) and betaine (0.34%) on GAA- and methionine-induced hyperhomocysteinemia were also compared. Dietary choline suppressed hyperhomocysteinemia induced by GAA, but not by methionine, in a dose-dependent manner. GAA-induced enhancement of the plasma homocysteine concentration was suppressed by choline and betaine to the same degree, but the effects of these compounds were relatively small on methionine-induced hyperhomocysteinemia. Dietary supplementation with choline and betaine significantly increased the hepatic betaine concentration in rats fed a GAA diet, but not in rats fed a methionine diet. These results indicate that choline and betaine are effective at relatively low levels in reducing plasma homocysteine, especially under the condition of betaine deficiency without a loading of homocysteine precursor.

Creatine metabolism: detection of creatine and guanidinoacetate in saliva of healthy subjects.

PubMed

Martínez, Lidia D; Bezard, Miriam; Brunotto, Mabel; Dodelson de Kremer, Raquel

2016-04-01

Creatine (Cr) plays an important role in storage and transmission of phosphate-bound energy. Cerebral creatine deficiency syndromes comprise three inherited defects in Cr biosynthesis and transport. The aim of this study was to investigate whether Cr and Guanidinoacetate (GAA) can be detected in saliva of healthy subjects and to establish the relationship between salivary and plasma levels of these molecules. An adapted gas chromatography (GC) method is described for the quantification of Cr and GAA biomarkers in saliva. Reference values were established for GAA and Cr in saliva. These values were age dependent (p= 0.001). No difference between genders was observed. We detected a difference between GAA and Cr concentrations in saliva and in plasma. The GC method for simultaneous determination of GAA and Cr in human saliva is fast, reliable, sensitive, non-invasive and precise to use as a biochemical approach in early detection of cerebral creatine deficiency syndromes. Sociedad Argentina de Investigación Odontológica.

Response of GaAs charge storage devices to transient ionizing radiation

NASA Astrophysics Data System (ADS)

Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

GaAs MOEMS Technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

SPAHN, OLGA B.; GROSSETETE, GRANT D.; CICH, MICHAEL J.

2003-03-01

Many MEMS-based components require optical monitoring techniques using optoelectronic devices for converting mechanical position information into useful electronic signals. While the constituent piece-parts of such hybrid opto-MEMS components can be separately optimized, the resulting component performance, size, ruggedness and cost are substantially compromised due to assembly and packaging limitations. GaAs MOEMS offers the possibility of monolithically integrating high-performance optoelectronics with simple mechanical structures built in very low-stress epitaxial layers with a resulting component performance determined only by GaAs microfabrication technology limitations. GaAs MOEMS implicitly integrates the capability for radiation-hardened optical communications into the MEMS sensor or actuator component, a vitalmore » step towards rugged integrated autonomous microsystems that sense, act, and communicate. This project establishes a new foundational technology that monolithically combines GaAs optoelectronics with simple mechanics. Critical process issues addressed include selectivity, electrochemical characteristics, and anisotropy of the release chemistry, and post-release drying and coating processes. Several types of devices incorporating this novel technology are demonstrated.« less

Photoluminescence upconversion at GaAs /InGa P2 interfaces driven by a sequential two-photon absorption mechanism

NASA Astrophysics Data System (ADS)

Hylton, N. P.; Hinrichsen, T. F.; Vaquero-Stainer, A. R.; Yoshida, M.; Pusch, A.; Hopkinson, M.; Hess, O.; Phillips, C. C.; Ekins-Daukes, N. J.

2016-06-01

This paper reports on the results of an investigation into the nature of photoluminescence upconversion at GaAs /InGa P2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGa P2 material, arising from partial ordering of the InGa P2 . We also observed the excitation of a two-dimensional electron gas at the GaAs /InGa P2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron gas at the GaAs /InGa P2 interface, suggesting that charge accumulation at the interface can play a crucial role in the upconversion process.

Temperature effect on the coupling between coherent longitudinal phonons and plasmons in n -type and p -type GaAs

NASA Astrophysics Data System (ADS)

Hu, Jianbo; Zhang, Hang; Sun, Yi; Misochko, Oleg V.; Nakamura, Kazutaka G.

2018-04-01

The coupling between longitudinal optical (LO) phonons and plasmons plays a fundamental role in determining the performance of doped semiconductor devices. In this work, we report a comparative investigation into the dependence of the coupling on temperature and doping in n - and p -type GaAs by using ultrafast coherent phonon spectroscopy. A suppression of coherent oscillations has been observed in p -type GaAs at lower temperature, strikingly different from n -type GaAs and other materials in which coherent oscillations are strongly enhanced by cooling. We attribute this unexpected observation to a cooling-induced elongation of the depth of the depletion layer which effectively increases the screening time of the surface field due to a slow diffusion of photoexcited carriers in p -type GaAs. Such an increase breaks the requirement for the generation of coherent LO phonons and, in turn, LO phonon-plasmon coupled modes because of their delayed formation in time.

Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching

PubMed Central

2014-01-01

In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface. PMID:24495647

Millimeter-wave monolithic diode-grid frequency multiplier

NASA Technical Reports Server (NTRS)

Maserjian, Joseph (Inventor)

1990-01-01

A semiconductor diode structure useful for harmonic generation of millimeter or submillimeter wave radiation from a fundamental input wave is fabricated on a GaAs substrate. A heavily doped layer of n(sup ++) GaAs is produced on the substrate and then a layer of intrinsic GaAs on said heavily doped layer on top of which a sheet of heavy doping (++) is produced. A thin layer of intrinsic GaAs grown over the sheet is capped with two metal contacts separated by a gap to produce two diodes connected back to back through the n(sup ++) layer for multiplication of frequency by an odd multiple. If only one metal contact caps the thin layer of intrinsic GaAs, the second diode contact is produced to connect to the n(sup ++) layer for multiplication of frequency by an even number. The odd or even frequency multiple is selected by a filter. A phased array of diodes in a grid will increase the power of the higher frequency generated.

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

NASA Astrophysics Data System (ADS)

Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

2018-05-01

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

GaSb and GaSb/AlSb Superlattice Buffer Layers for High-Quality Photodiodes Grown on Commercial GaAs and Si Substrates

NASA Astrophysics Data System (ADS)

Gutiérrez, M.; Lloret, F.; Jurczak, P.; Wu, J.; Liu, H. Y.; Araújo, D.

2018-05-01

The objective of this work is the integration of InGaAs/GaSb/GaAs heterostructures, with high indium content, on GaAs and Si commercial wafers. The design of an interfacial misfit dislocation array, either on GaAs or Si substrates, allowed growth of strain-free devices. The growth of purposely designed superlattices with their active region free of extended defects on both GaAs and Si substrates is demonstrated. Transmission electron microscopy technique is used for the structural characterization and plastic relaxation study. In the first case, on GaAs substrates, the presence of dopants was demonstrated to reduce several times the threading dislocation density through a strain-hardening mechanism avoiding dislocation interactions, while in the second case, on Si substrates, similar reduction of dislocation interactions is obtained using an AlSb/GaSb superlattice. The latter is shown to redistribute spatially the interfacial misfit dislocation array to reduce dislocation interactions.

Study on the high-power semi-insulating GaAs PCSS with quantum well structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luan, Chongbiao; Wang, Bo; Huang, Yupeng

A high-power semi-insulating GaAs photoconductive semiconductor switch (PCSS) with quantum well structure was fabricated. The AlGaAs layer was deposited on the surface of the GaAs material, and the reflecting film and the antireflection film have been made on the surface of the GaAs and AlGaAs, respectively. When the prepared PCSS worked at a bias voltage of 9.8 kV and triggered by a laser pulse with an incident optical energy of 5.4 mJ, a wavelength of 1064 nm and an optical pulse width of 25 ns, the on-state resistance of the AlGaAs/GaAs PCSS was only 0.45 Ω, and the longevity ofmore » the AlGaAs/GaAs PCSS was larger than 10{sup 6} shots. The results show that this structure reduces the on-state resistance and extends the longevity of the GaAs PCSS.« less

Idiopathic Parkinson’s disease phenotype related to C9ORF72 repeat expansions: contribution of the neuropsychological assessment

PubMed Central

2013-01-01

Background Expanded GGGGCC hexanucleotide repeats in the non-coding region of the C9ORF72 gene was recently identified as being responsible for over 40% of the cases of amyotrophic lateral sclerosis associated with frontotemporal lobar degeneration, in various extrapyramidal syndromes including supranuclear gaze palsy and corticobasal degeneration, and in addition, has been found to be a rare genetic cause of isolated Parkinsonism. To our knowledge, there is no published data concerning the neuropsychological evaluation of patients diagnosed with idiopathic Parkinson’s disease related with C9ORF72 repeat expansions. Case presentation We report the results of the comprehensive neuropsychological evaluation in a newly described case in the literature (the sixth) of a patient presenting isolated idiopathic Parkinson’s disease associated with C9ORF72 repeat expansions. The decrease in the patient’s prefrontal functions resulted in a slight decrease in global efficiency. These abnormalities did not appear to be different, with respect to the deficit observed and the intensity of the cognitive impairment, from those classically observed in cases of sporadic idiopathic Parkinson’s disease. Our patient also exhibited a significant impairment in visual gnosis. Conclusions If confirmed in other patients, visuoperceptive deficits in idiopathic Parkinson’s disease could represent a red flag that should prompt the clinician to perform addition diagnostic procedures. A thorough neuropsychological assessment may prove to be useful for detecting idiopathic Parkinson’s disease in patients who are suspected of having repeat abnormalities of C9ORF72 expansions. PMID:23987827

Hb Beograd [beta121(GH4)Glu-->Val, GAA-->GTA] in the Turkish population.

PubMed

Atalay, Ayfer; Koyuncu, Hasan; Köseler, Aylin; Ozkan, Anzel; Atalay, Erol O

2007-01-01

Hb Beograd [beta121(GH4)Glu-->Val, GAA-->GTA] is a rare variant first reported in Yugoslavia and then in Turkey, Australia and New Zealand. We report two further unrelated cases from Turkey. The importance of identifying Hb Beograd at the molecular level, especially in regions where Hb D-Los Angeles [beta121(GH4)Glu-->Gln, GAA-->CAA] is prevalent, is emphasized.

Paths to light trapping in thin film GaAs solar cells.

PubMed

Xiao, Jianling; Fang, Hanlin; Su, Rongbin; Li, Kezheng; Song, Jindong; Krauss, Thomas F; Li, Juntao; Martins, Emiliano R

2018-03-19

It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.

Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable III–V photovoltaics

DOE PAGES

Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; ...

2014-09-01

The high balance-of-system costs of photovoltaic (PV) installations indicate that reductions in cell $/W costs alone are likely insufficient for PV electricity to reach grid parity unless energy conversion efficiency is also increased. Technologies which yield both high-efficiency cells (>25%) and maintain low costs are needed. GaAs and related III-V semiconductors are used in the highest-efficiency single- and multi-junction photovoltaics, but the technology is too expensive for non-concentrated terrestrial applications. This is due in part to the difficulty of scaling the metal-organic chemical vapor deposition (MOCVD) process, which relies on expensive reactors and employs toxic and pyrophoric gas-phase precursors suchmore » as arsine and trimethyl gallium, respectively. In this study, we describe GaAs films made by an alternative close-spaced vapor transport (CSVT) technique which is carried out at atmospheric pressure and requires only bulk GaAs, water vapor, and a temperature gradient in order to deposit crystalline films with similar electronic properties to that of GaAs deposited by MOCVD. CSVT is similar to the vapor transport process used to deposit CdTe thin films and is thus a potentially scalable low-cost route to GaAs thin films.« less

HfO2 Gate Dielectric on (NH4)2S Passivated (100) GaAs Grown by Atomic Layer Deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.T.; /Stanford U., Materials Sci. Dept.; Sun, Y.

2007-09-28

The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH{sub 4}){sub 2}S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As{sub 2}O{sub 3} formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out-diffusion into the hafnia film were observed after a 450 C post-deposition anneal, and may be the origins for the electrically active defects. Transmission electron microscopymore » cross section images showed thicker HfO{sub 2} films for a given precursor exposure on S-treated GaAs versus the non-treated sample. In addition, the valence-band and the conduction-band offsets at the HfO{sub 2}/GaAs interface were deduced to be 3.18 eV and a range of 0.87-0.97 eV, respectively. It appears that HCl+(NH{sub 4})2{sub S} treatments provide a superior chemical passivation for GaAs and initial surface for ALD deposition.« less

Improvement in etching rate for epilayer lift-off with surfactant

NASA Astrophysics Data System (ADS)

Wu, Fan-Lei; Horng, Ray-Hua; Lu, Jian-Heng; Chen, Chun-Li; Kao, Yu-Cheng

2013-03-01

In this study, the GaAs epilayer is quickly separated from GaAs substrate by epitaxial lift-off (ELO) process with mixture etchant solution. The HF solution mixes with surfactant as mixture etchant solution to etch AlAs sacrificial layer for the selective wet etching of AlAs sacrificial layer. Addiction surfactants etchant significantly enhance the etching rate in the hydrofluoric acid etching solution. It is because surfactant provides hydrophilicity to change the contact angle with enhances the fluid properties of the mixture etchant between GaAs epilayer and GaAs substrate. Arsine gas was released from the etchant solution because the critical reaction product in semiconductor etching is dissolved arsine gas. Arsine gas forms a bubble, which easily displaces the etchant solution, before the AlAs layer was undercut. The results showed that acetone and hydrofluoric acid ratio of about 1:1 for the fastest etching rate of 13.2 μm / min. The etching rate increases about 4 times compared with pure hydrofluoric acid, moreover can shorten the separation time about 70% of GaAs epilayer with GaAs substrate. The results indicate that etching ratio and stability are improved by mixture etchant solution. It is not only saving the epilayer and the etching solution exposure time, but also reducing the damage to the epilayer structure.

Reaction mechanism of guanidinoacetate methyltransferase, concerted or step-wise.

PubMed

Zhang, Xiaodong; Bruice, Thomas C

2006-10-31

We describe a quantum mechanics/molecular mechanics investigation of the guanidinoacetate methyltransferase catalyzed reaction, which shows that proton transfer from guanidinoacetate (GAA) to Asp-134 and methyl transfer from S-adenosyl-L-methionine (AdoMet) to GAA are concerted. By self-consistent-charge density functional tight binding/molecular mechanics, the bond lengths in the concerted mechanism's transition state are 1.26 A for both the OD1 (Asp-134)-H(E) (GAA) and H(E) (GAA)-N(E) (GAA) bonds, and 2.47 and 2.03 A for the S8 (AdoMet)-C9 (AdoMet) and C9 (AdoMet)-N(E) (GAA) bonds, respectively. The potential-energy barrier (DeltaE++) determined by single-point B3LYP/6-31+G*//MM is 18.9 kcal/mol. The contributions of the entropy (-TDeltaS++) and zero-point energy corrections Delta(ZPE)++ by normal mode analysis are 2.3 kcal/mol and -1.7 kcal/mol, respectively. Thus, the activation enthalpy of this concerted mechanism is predicted to be DeltaH++ = DeltaE++ plus Delta(ZPE)++ = 17.2 kcal/mol. The calculated free-energy barrier for the concerted mechanism is DeltaG++ = 19.5 kcal/mol, which is in excellent agreement with the value of 19.0 kcal/mol calculated from the experimental rate constant (3.8 +/- 0.2.min(-1)).

Monte Carlo simulation to calculate the rate of 137Cs gamma rays dispersion in gallium arsenide compound

NASA Astrophysics Data System (ADS)

Haider, F. A.; Chee, F. P.; Abu Hassan, H.; Saafie, S.

2017-01-01

Radiation effects on Gallium Arsenide (GaAs) have been tested by exposing samples to Cesium-137 (137Cs) gamma rays. Gallium Arsenide is a basic photonic material for most of the space technology communication, and, therefore, lends itself for applications where this is of concern. Monte Carlo simulations of interaction between direct ionizing radiation and GaAs structure have been performed in TRIM software, being part of SRIM 2011 programming package. An adverse results shows that energy dose does not govern the displacement of atoms and is dependent on the changes of incident angles and thickness of the GaAs target element. At certain thickness of GaAs and incident angle of 137Cs ion, the displacement damage is at its highest value. From the simulation result, it is found that if the thickness of the GaAs semiconductor material is small compared to the projected range at that particular incident energy, the energy loss in the target GaAs will be small. Hence, when the depth of semiconductor material is reduced, the range of damage in the target also decreased. However, the other factors such as quantum size effect, the energy gap between the conduction and valence band must also be taken into consideration when the dimension of the device is diminished.

Manipulation of morphology and structure of the top of GaAs nanowires grown by molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Li, Lixia; Pan, Dong; Yu, Xuezhe; So, Hyok; Zhao, Jianhua

2017-10-01

Self-catalyzed GaAs nanowires (NWs) are grown on Si (111) substrates by molecular-beam epitaxy. The effect of different closing sequences of the Ga and As cell shutters on the morphology and structural phase of GaAs NWs is investigated. For the sequences of closing the Ga and As cell shutters simultaneously or closing the As cell shutter 1 min after closing the Ga cell shutter, the NWs grow vertically to the substrate surface. In contrast, when the As cell shutter is closed first, maintaining the Ga flux is found to be critical for the following growth of GaAs NWs, which can change the growth direction from [111] to < 11\\bar{1}> . The evolution of the morphology and structural phase transition at the tips of these GaAs NWs confirm that the triple-phase-line shift mode is at work even for the growth with different cell shutter closing sequences. Our work will provide new insights for better understanding of the growth mechanism and realizing of the morphology and structure control of the GaAs NWs. Project supported partly by the MOST of China (No. 2015CB921503), the National Natural Science Foundation of China (Nos. 61504133, 61334006, 61404127), and Youth Innovation Promotion Association, CAS (No. 2017156).

Ab initio study of GaAs(100) surface stability over As2, H2 and N2 as a model for vapor-phase epitaxy of GaAs1-xNx

NASA Astrophysics Data System (ADS)

Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

2015-12-01

GaAs(100) c(4×4) surfaces were examined by ab initio calculations, under As2, H2 and N2 gas mixed conditions as a model for GaAs1-xNx vapor-phase epitaxy (VPE) on GaAs(100). Using a simple model consisting of As2 and H2 molecules adsorptions and As/N atom substitutions, it was shown to be possible to examine the crystal growth behavior considering the relative stability of the resulting surfaces against the chemical potential of As2, H2 and N2 gases. Such simple model allows us to draw a picture of the temperature and pressure stability domains for each surfaces that can be linked to specific growth conditions, directly. We found that, using this simple model, it is possible to explain the different N-incorporation regimes observed experimentally at different temperatures, and to predict the transition temperature between these regimes. Additionally, a rational explanation of N-incorporation ratio for each of these regimes is provided. Our model should then lead to a better comprehension and control of the experimental conditions needed to realize a high quality VPE of GaAs1-xNx.

Immunotoxicity of gallium arsenide on antigen presentation: comparative study of intratracheal and intraperitoneal exposure routes.

PubMed

Hartmann, Constance B; Harrison, M Travis; McCoy, Kathleen L

2005-01-01

Gallium arsenide (GaAs) is a semiconductor utilized in electronics and computer industries. GaAs exposure of animals causes local inflammation and systemic immune suppression. Mice were administered 2 to 200 mg/kg GaAs. On day 5, intratracheal instillation increased lung weights in a dose-dependent manner and induced pulmonary inflammation exemplified by mononuclear cell infiltration and mild epithelial hyperplasia. No fibrosis, pneumocyte hyperplasia, proteinosis, or bronchial epithelial damage was observed in the lungs. Splenic cellularity and composition were unaffected. GaAs' effect on antigen presentation by macrophages was similar after intratracheal and intraperitoneal exposure, although the lowest observable adverse effect levels differed. Macrophages from the exposure site displayed an enhanced ability to activate an antigen-specific CD4(+) helper T-cell hybridoma compared with vehicle controls, whereas splenic macrophages were defective in this function. The chemical's impact on peritoneal macrophages depended on the exposure route. GaAs exposure augmented thiol cathepsins B and L activities in macrophages from the exposure site, but decreased proteolytic activities in splenic macrophages. Alveolar macrophages had increased expression of major histocompatibility complex (MHC) Class II molecules, whereas MHC Class II expression on splenic and peritoneal macrophages was unaffected. Modified thiol cathepsin activities statistically correlated with altered efficiency of antigen presentation, whereas MHC Class II expression did not. Our study is the first one to examine the functional capability of alveolar macrophages after intratracheal GaAs instillation. Therefore, thiol cathepsins may be potential target molecules by which GaAs exposure modulates antigen presentation.

Growth and Characterisation of GaAs/AlGaAs Core-shell Nanowires for Optoelectronic Device Applications

NASA Astrophysics Data System (ADS)

Jiang, Nian

III-V semiconductor nanowires have been investigated as key components for future electronic and optoelectronic devices and systems due to their direct band gap and high electron mobility. Amongst the III-V semiconductors, the planar GaAs material system has been extensively studied and used in industries. Accordingly, GaAs nanowires are the prime candidates for nano-scale devices. However, the electronic performance of GaAs nanowires has yet to match that of state-of-the-art planar GaAs devices. The present deficiency of GaAs nanowires is typically attributed to the large surface-to- volume ratio and the tendency for non-radiative recombination centres to form at the surface. The favoured solution of this problem is by coating GaAs nanowires with AlGaAs shells, which replaces the GaAs surface with GaAs/AlGaAs interface. This thesis presents a systematic study of GaAs/AlGaAs core-shell nanowires grown by metal organic chemical vapour deposition (MOCVD), including understanding the growth, and characterisation of their structural and optical properties. The structures of the nanowires were mainly studied by scanning electron microscopy and transmis- sion electron microscopy (TEM). A procedure of microtomy was developed to prepare the cross-sectional samples for the TEM studies. The optical properties were charac- terised by photoluminescence (PL) spectroscopy. Carrier lifetimes were measured by time-resolved PL. The growth of AlGaAs shell was optimised to obtain the best optical properties, e.g. the strongest PL emission and the longest minority carrier lifetimes. (Abstract shortened by ProQuest.).

Analysis of GAA/TTC DNA triplexes using nuclear magnetic resonance and electrospray ionization mass spectrometry.

PubMed

Mariappan, S V Santhana; Cheng, Xun; van Breemen, Richard B; Silks, Louis A; Gupta, Goutam

2004-11-15

The formation of a GAA/TTC DNA triplex has been implicated in Friedreich's ataxia. The destabilization of GAA/TTC DNA triplexes either by pH or by binding to appropriate ligands was analyzed by nuclear magnetic resonance (NMR) and positive-ion electrospray mass spectrometry. The triplexes and duplexes were identified by changes in the NMR chemical shifts of H8, H1, H4, 15N7, and 15N4. The lowest pH at which the duplex is detectable depends upon the overall stability and the relative number of Hoogsteen C composite function G to T composite function A basepairs. A melting pH (pHm) of 7.6 was observed for the destabilization of the (GAA)2T4(TTC)2T4(CTT)2 triplex to the corresponding Watson-Crick duplex and the T4(CTT)2 overhang. The mass spectrometric analyses of (TTC)6.(GAA)6 composite function(TTC)6 triplex detected ions due to both triplex and single-stranded oligonucleotides under acidic conditions. The triplex ions disappeared completely at alkaline pH. Duplex and single strands were detectable only at neutral and alkaline pH values. Mass spectrometric analyses also showed that minor groove-binding ligands berenil, netropsin, and distamycin and the intercalating ligand acridine orange destabilize the (TTC)6.(GAA)6 composite function (TTC)6 triplex. These NMR and mass spectrometric methods may function as screening assays for the discovery of agents that destabilize GAA/TTC triplexes and as general methods for the characterization of structure, dynamics, and stability of DNA and DNA-ligand complexes.

Phase I/II Trial of Adeno-Associated Virus–Mediated Alpha-Glucosidase Gene Therapy to the Diaphragm for Chronic Respiratory Failure in Pompe Disease: Initial Safety and Ventilatory Outcomes

PubMed Central

Smith, Barbara K.; Collins, Shelley W.; Conlon, Thomas J.; Mah, Cathryn S.; Lawson, Lee Ann; Martin, Anatole D.; Fuller, David D.; Cleaver, Brian D.; Clément, Nathalie; Phillips, Dawn; Islam, Saleem; Dobjia, Nicole

2013-01-01

Abstract Pompe disease is an inherited neuromuscular disease caused by deficiency of lysosomal acid alpha-glucosidase (GAA) leading to glycogen accumulation in muscle and motoneurons. Cardiopulmonary failure in infancy leads to early mortality, and GAA enzyme replacement therapy (ERT) results in improved survival, reduction of cardiac hypertrophy, and developmental gains. However, many children have progressive ventilatory insufficiency and need additional support. Preclinical work shows that gene transfer restores phrenic neural activity and corrects ventilatory deficits. Here we present 180-day safety and ventilatory outcomes for five ventilator-dependent children in a phase I/II clinical trial of AAV-mediated GAA gene therapy (rAAV1-hGAA) following intradiaphragmatic delivery. We assessed whether rAAV1-hGAA results in acceptable safety outcomes and detectable functional changes, using general safety measures, immunological studies, and pulmonary functional testing. All subjects required chronic, full-time mechanical ventilation because of respiratory failure that was unresponsive to both ERT and preoperative muscle-conditioning exercises. After receiving a dose of either 1×1012 vg (n=3) or 5×1012 vg (n=2) of rAAV1-hGAA, the subjects' unassisted tidal volume was significantly larger (median [interquartile range] 28.8% increase [15.2–35.2], p<0.05). Further, most patients tolerated appreciably longer periods of unassisted breathing (425% increase [103–851], p=0.08). Gene transfer did not improve maximal inspiratory pressure. Expected levels of circulating antibodies and no T-cell-mediated immune responses to the vector (capsids) were observed. One subject demonstrated a slight increase in anti-GAA antibody that was not considered clinically significant. These results indicate that rAAV1-hGAA was safe and may lead to modest improvements in volitional ventilatory performance measures. Evaluation of the next five patients will determine whether earlier intervention can further enhance the functional benefit. PMID:23570273

Study of subband electronic structure of Si δ-doped GaAs using magnetotransport measurements in tilted magnetic fields

NASA Astrophysics Data System (ADS)

Li, G.; Hauser, N.; Jagadish, C.; Antoszewski, J.; Xu, W.

1996-06-01

Si δ-doped GaAs grown by metal organic vapor phase epitaxy (MOVPE) is characterized using magnetotransport measurements in tilted magnetic fields. Angular dependence of the longitudinal magnetoresistance (Rxx) vs the magnetic field (B) traces in tilted magnetic fields is used to examine the existence of a quasi-two-dimensional electron gas. The subband electron densities (ni) are obtained applying fast Fourier transform (FFT) analysis to the Rxx vs B trace and using mobility spectrum (MS) analysis of the magnetic field dependent Hall data. Our results show that (1) the subband electron densities remain roughly constant when the tilted magnetic field with an angle <30° measured from the Si δ-doped plane normal is ramped up to 13 T; (2) FFT analysis of the Rxx vs B trace and MS analysis of the magnetic field dependent Hall data both give the comparable results on subband electron densities of Si δ-doped GaAs with low δ-doping concentration, however, for Si δ-doped GaAs with very high δ-doping concentration, the occupation of the lowest subbands cannot be well resolved in the MS analysis; (3) the highest subband electron mobility reported to date of 45 282 cm2/s V is observed in Si δ-doped GaAs at 77 K in the dark; and (4) the subband electron densities of Si δ-doped GaAs grown by MOVPE at 700 °C are comparable to those grown by MBE at temperatures below 600 °C. A detailed study of magnetotransport properties of Si δ-doped GaAs in the parallel magnetic fields is then carried out to further confirm the subband electronic structures revealed by FFT and MS analysis. Our results are compared to theoretical calculation previously reported in literature. In addition, influence of different cap layer structures on subband electronic structures of Si δ-doped GaAs is observed and also discussed.

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

NASA Astrophysics Data System (ADS)

Chen, C.-H.; Gösele, U. M.; Tan, T. Y.

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species SiGa+ and as shallow acceptor species SiAs-. The solubility of SiAs- is much lower than that of SiGa+ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is SiGa+ which will convert into SiAs- in accordance with their solubilities and that the point defect species governing the diffusion of SiGa+ are triply-negatively-charged Ga vacancies VGa3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n+-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently.

Crosstalk between the Notch signaling pathway and non-coding RNAs in gastrointestinal cancers

PubMed Central

Pan, Yangyang; Mao, Yuyan; Jin, Rong; Jiang, Lei

2018-01-01

The Notch signaling pathway is one of the main signaling pathways that mediates direct contact between cells, and is essential for normal development. It regulates various cellular processes, including cell proliferation, apoptosis, migration, invasion, angiogenesis and metastasis. It additionally serves an important function in tumor progression. Non-coding RNAs mainly include small microRNAs, long non-coding RNAs and circular RNAs. At present, a large body of literature supports the biological significance of non-coding RNAs in tumor progression. It is also becoming increasingly evident that cross-talk exists between Notch signaling and non-coding RNAs. The present review summarizes the current knowledge of Notch-mediated gastrointestinal cancer cell processes, and the effect of the crosstalk between the three major types of non-coding RNAs and the Notch signaling pathway on the fate of gastrointestinal cancer cells. PMID:29285185

High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

NASA Technical Reports Server (NTRS)

Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.

2005-01-01

III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge/GeSi/Si substrate show nearly identical I-V characteristics in both forward and reverse bias regions. External quantum efficiencies of AlGaAs/GaAs cell structures grown on Ge/GeSi/Si and Ge substrates demonstrated nearly identical photoresponse, which indicates that high lifetimes, diffusion lengths and efficient minority carrier collection is maintained after complete cell processing.

Fabrication, testing and reliability modeling of copper/titanium-metallized GaAs MESFETs and HEMTs for low-noise applications

NASA Astrophysics Data System (ADS)

Feng, Ting

Today, GaAs based field effect transistors (FETs) have been used in a broad range of high-speed electronic military and commercial applications. However, their reliability still needs to be improved. Particularly the hydrogen induced degradation is a large remaining issue in the reliability of GaAs FETs, because hydrogen can easily be incorporated into devices during the crystal growth and virtually every device processing step. The main objective of this research work is to develop a new gate metallization system in order to reduce the hydrogen induced degradation from the gate region for GaAs based MESFETs and HEMTs. Cu/Ti gate metallization has been introduced into the GaAs MESFETs and HEMTs in our work in order to solve the hydrogen problem. The purpose of the use of copper is to tie up the hydrogen atoms and prevent hydrogen penetration into the device active region as well as to keep a low gate resistance for low noise applications. In this work, the fabrication technology of GaAs MESFETs and AlGaAs/GaAs HEMTs with Cu/Ti metallized gates have been successfully developed and the fabricated Cu/Ti FETs have shown comparable DC performance with similar Au-based GaAs FETs. The Cu/Ti FETs were subjected to temperature accelerated testing at NOT under 5% hydrogen forming gas and the experimental results show the hydrogen induced degradation has been reduced for the Cu/Ti FETs compared to commonly used AuPtTi based GaAs FETs. A long-term reliability testing for Cu/Ti FETs has also been carried out at 200°C and up to 1000hours and testing results show Cu/Ti FETs performed with adequate reliability. The failure modes were found to consist of a decrease in drain saturation current and pinch-off voltage and an increase in source ohmic contact resistance. Material characterization tools including Rutherford backscattering spectroscopy and a back etching technique were used in Cu/Ti GaAs FETs, and pronounced gate metal copper in-diffusion and intermixing compounds at the interface between the gate and GaAs channel layer were found. A quantifying gate sinking degradation model was developed in order to extend device physics models to reliability testing results of Cu/Ti GaAs FETs. The gate sinking degradation model includes the gate metal and hydrogen in-diffusion effect, decrease of effective channel due to the formation of interfacial compounds, decrease of electron mobility due to the increase of in-diffused impurities, and donor compensation from in-diffused metal impurity acceptors or hydrogen passivation. A variational charge control model was applied to simulate and understand the degradation mechanisms of Cu/Ti HEMTs, including hydrogen induced degradation due to the neutralization of donors. The degradation model established in this study is also applicable to other Au or Al metallized GaAs FETs for understanding the failure mechanisms induced by gate sinking and hydrogen neutralization of donors and con-elating the device physics model with reliability testing results.

The paradox of MHC-DRB exon/intron evolution: alpha-helix and beta-sheet encoding regions diverge while hypervariable intronic simple repeats coevolve with beta-sheet codons.

PubMed

Schwaiger, F W; Weyers, E; Epplen, C; Brün, J; Ruff, G; Crawford, A; Epplen, J T

1993-09-01

Twenty-one different caprine and 13 ovine MHC-DRB exon 2 sequences were determined including part of the adjacent introns containing simple repetitive (gt)n(ga)m elements. The positions for highly polymorphic DRB amino acids vary slightly among ungulates and other mammals. From man and mouse to ungulates the basic (gt)n(ga)m structure is fixed in evolution for 7 x 10(7) years whereas ample variations exist in the tandem (gt)n and (ga)m dinucleotides and especially their "degenerated" derivatives. Phylogenetic trees for the alpha-helices and beta-pleated sheets of the ungulate DRB sequences suggest different evolutionary histories. In hoofed animals as well as in humans DRB beta-sheet encoding sequences and adjacent intronic repeats can be assembled into virtually identical groups suggesting coevolution of noncoding as well as coding DNA. In contrast alpha-helices and C-terminal parts of the first DRB domain evolve distinctly. In the absence of a defined mechanism causing specific, site-directed mutations, double-recombination or gene-conversion-like events would readily explain this fact. The role of the intronic simple (gt)n(ga)m repeat is discussed with respect to these genetic exchange mechanisms during evolution.

Evolutionary Dynamics of Microsatellite Distribution in Plants: Insight from the Comparison of Sequenced Brassica, Arabidopsis and Other Angiosperm Species

PubMed Central

Shi, Jiaqin; Huang, Shunmou; Fu, Donghui; Yu, Jinyin; Wang, Xinfa; Hua, Wei; Liu, Shengyi; Liu, Guihua; Wang, Hanzhong

2013-01-01

Despite their ubiquity and functional importance, microsatellites have been largely ignored in comparative genomics, mostly due to the lack of genomic information. In the current study, microsatellite distribution was characterized and compared in the whole genomes and both the coding and non-coding DNA sequences of the sequenced Brassica, Arabidopsis and other angiosperm species to investigate their evolutionary dynamics in plants. The variation in the microsatellite frequencies of these angiosperm species was much smaller than those for their microsatellite numbers and genome sizes, suggesting that microsatellite frequency may be relatively stable in plants. The microsatellite frequencies of these angiosperm species were significantly negatively correlated with both their genome sizes and transposable elements contents. The pattern of microsatellite distribution may differ according to the different genomic regions (such as coding and non-coding sequences). The observed differences in many important microsatellite characteristics (especially the distribution with respect to motif length, type and repeat number) of these angiosperm species were generally accordant with their phylogenetic distance, which suggested that the evolutionary dynamics of microsatellite distribution may be generally consistent with plant divergence/evolution. Importantly, by comparing these microsatellite characteristics (especially the distribution with respect to motif type) the angiosperm species (aside from a few species) all clustered into two obviously different groups that were largely represented by monocots and dicots, suggesting a complex and generally dichotomous evolutionary pattern of microsatellite distribution in angiosperms. Polyploidy may lead to a slight increase in microsatellite frequency in the coding sequences and a significant decrease in microsatellite frequency in the whole genome/non-coding sequences, but have little effect on the microsatellite distribution with respect to motif length, type and repeat number. Interestingly, several microsatellite characteristics seemed to be constant in plant evolution, which can be well explained by the general biological rules. PMID:23555856

Regulation of mammalian cell differentiation by long non-coding RNAs

PubMed Central

Hu, Wenqian; Alvarez-Dominguez, Juan R; Lodish, Harvey F

2012-01-01

Differentiation of specialized cell types from stem and progenitor cells is tightly regulated at several levels, both during development and during somatic tissue homeostasis. Many long non-coding RNAs have been recognized as an additional layer of regulation in the specification of cellular identities; these non-coding species can modulate gene-expression programmes in various biological contexts through diverse mechanisms at the transcriptional, translational or messenger RNA stability levels. Here, we summarize findings that implicate long non-coding RNAs in the control of mammalian cell differentiation. We focus on several representative differentiation systems and discuss how specific long non-coding RNAs contribute to the regulation of mammalian development. PMID:23070366

Basic mechanisms study for MIS solar cell structures on GaAs

NASA Technical Reports Server (NTRS)

Fonash, S. J.

1978-01-01

The solar cell structure examined is the MIS configuration on (n) GaAs. The metal room temperature oxide/(n) GaAs materials system was studied. Metals with electronegativities varying from 2.4 (Au) to 1.5 (Al) were used as the upper electrode. The thinnest metallization that did not interfere with the measurement techniques (by introducing essentially transmission line series resistance problems across a device) was used. Photovoltaic response was not optimized.

GaAs homojunction solar cell development

NASA Technical Reports Server (NTRS)

Flood, D. J.; Swartz, C. K.; Hart, R. E., Jr.

1980-01-01

The Lincoln Laboratory n(+)/p/p(+) GaAs shallow homojunction cell structure was successfully demonstrated on 2 by 2 cm GaAs substrates. Air mass zero efficiencies of the seven cells produced to date range from 13.6 to 15.6 percent. Current voltage (I-V) characteristics, spectral response, and measurements were made on all seven cells. Preliminary analysis of 1 MeV electron radiation damage data indicate excellent radiation resistance for these cells.

Peroxiredoxins: A Model for a Self-Assembling Nanoscale System

DTIC Science & Technology

2014-08-24

specific primers was: Forward: 5’ – GGC AGC GGC GCG ATG CCC GGC ATG GAA – 3’ Reverse: 5’ – GAA AGC TGG GTG CTA CTC CCC CCT TGC CT – 3’ The bold...8217 Reverse: 5’ – GGGG AC CAC TTT GTA CAA GAA AGC TGG GTG – 3’ The bold section introduces the attB sites to the linear fragment produced by reaction 1

Investigation of the fabrication mechanism of self-assembled GaAs quantum rings grown by droplet epitaxy.

PubMed

Tong, C Z; Yoon, S F

2008-09-10

We have directly imaged the formation of a GaAs quantum ring (QR) using droplet epitaxy followed by annealing in arsenic ambient. Based on the atomic force micrograph measurement and the analysis of surface energy, we determine that the formation of self-assembled GaAs QRs is due to the gallium atom's diffusion and crystallization driven by the gradient of surface energy. The phenomenon that GaAs is etched by the gallium droplets is reported and analyzed. It has been demonstrated that the epitaxy layers, such as AlAs and InGaP, can be used as the etching stop layer and hence can be used to control the shape and height of the QRs.

Ferromagnetic thin films

DOEpatents

Krishnan, K.M.

1994-12-20

A ferromagnetic [delta]-Mn[sub 1[minus]x]Ga[sub x] thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4[+-]0.05. 7 figures.

Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.; Wu, Y.

1988-01-01

A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

Electric field effects on the optical properties of buckled GaAs monolayer

NASA Astrophysics Data System (ADS)

Bahuguna, Bhagwati Prasad; Saini, L. K.; Sharma, Rajesh O.

2018-04-01

Buckled GaAs monolayer has a direct band gap semiconductor with energy gap of 1.31 eV in the absence of electric field. When we applied transverse electric field, the value of band gap decreases with increasing of electric field strength. In our previous work [1], it is observed that the buckled GaAs monolayer becomes metallic at 1.3 V/Å. In the present work, we investigate the optical properties such as photon energy-dependent dielectric functions, extinction coefficient, refractive index, absorption spectrum and reflectivity of buckled GaAs monolayer in the semiconducting phase i.e. absence of external electric field and metallic phase i.e. presence of external electric field using density functional theory.

Monolithic optical integrated control circuitry for GaAs MMIC-based phased arrays

NASA Technical Reports Server (NTRS)

Bhasin, K. B.; Ponchak, G. E.; Kascak, T. J.

1985-01-01

Gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) show promise in phased-array antenna applications for future space communications systems. Their efficient usage will depend on the control of amplitude and phase signals for each MMIC element in the phased array and in the low-loss radiofrequency feed. For a phased array contining several MMIC elements a complex system is required to control and feed each element. The characteristics of GaAs MMIC's for 20/30-GHz phased-array systems are discussed. The optical/MMIC interface and the desired characteristics of optical integrated circuits (OIC's) for such an interface are described. Anticipated fabrication considerations for eventual full monolithic integration of optical integrated circuits with MMIC's on a GaAs substrate are presented.

Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

NASA Technical Reports Server (NTRS)

Kashkarov, P. K.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

1983-01-01

An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

Length measurement and spatial orientation reconstruction of single nanowires.

PubMed

Prestopino, Giuseppe; Orsini, Andrea; Falconi, Christian; Bietti, Sergio; Verona-Rinati, Gianluca; Caselli, Federica; Bisegna, Paolo

2018-06-27

The accurate determination of the geometrical features of quasi one-dimensional nanostructures is mandatory for reducing errors and improving repeatability in the estimation of a number of geometry-dependent properties in nanotechnology. In this paper a method for the reconstruction of length and spatial orientation of single nanowires is presented. Those quantities are calculated from a sequence of scanning electron microscope images taken at different tilt angles using a simple 3D geometric model. The proposed method is evaluated on a collection of scanning electron microscope images of single GaAs nanowires. It is validated through the reconstruction of known geometric features of a standard reference calibration pattern. An overall uncertainty of about 1% in the estimated length of the nanowires is achieved. © 2018 IOP Publishing Ltd.

Uncommon features in Cuban families affected with Friedreich ataxia.

PubMed

Cruz-Mariño, Tania; González-Zaldivar, Yanetza; Laffita-Mesa, Jose Miguel; Almaguer-Mederos, Luis; Aguilera-Rodríguez, Raul; Almaguer-Gotay, Dennis; Rodríguez-Labrada, Roberto; Canales-Ochoa, Nalia; Macleod, Patrick; Velázquez-Pérez, Luis

2010-03-19

This report describes two families who presented with autosomal recessive ataxia. By means of Polymerase Chain Reaction (PCR) molecular testing we identified expansions in the gene encoding Frataxin (FTX) that is diagnostic of Friedreich ataxia. A history of reproductive loss in the two families, prominent scoliosis deformity preceding the onset of ataxic gait, the presence of a sensitive axonal neuropathy, as well as the common origin of ancestors are unusual features of these families. These cases illustrate the importance of molecular diagnosis in patients with a recessive ataxia. The origin of the expanded gene and the GAA repeat size in the normal population are issues to be further investigated. The molecular diagnosis of Friedreich ataxia is now established in Cuba. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.

Translation of dipeptide repeat proteins from the C9ORF72 expanded repeat is associated with cellular stress.

PubMed

Sonobe, Yoshifumi; Ghadge, Ghanashyam; Masaki, Katsuhisa; Sendoel, Ataman; Fuchs, Elaine; Roos, Raymond P

2018-08-01

Expansion of a hexanucleotide repeat (HRE), GGGGCC, in the C9ORF72 gene is recognized as the most common cause of familial amyotrophic lateral sclerosis (FALS), frontotemporal dementia (FTD) and ALS-FTD, as well as 5-10% of sporadic ALS. Despite the location of the HRE in the non-coding region (with respect to the main C9ORF72 gene product), dipeptide repeat proteins (DPRs) that are thought to be toxic are translated from the HRE in all three reading frames from both the sense and antisense transcript. Here, we identified a CUG that has a good Kozak consensus sequence as the translation initiation codon. Mutation of this CTG significantly suppressed polyglycine-alanine (GA) translation. GA was translated when the G 4 C 2 construct was placed as the second cistron in a bicistronic construct. CRISPR/Cas9-induced knockout of a non-canonical translation initiation factor, eIF2A, impaired GA translation. Transfection of G 4 C 2 constructs induced an integrated stress response (ISR), while triggering the ISR led to a continuation of translation of GA with a decline in conventional cap-dependent translation. These in vitro observations were confirmed in chick embryo neural cells. The findings suggest that DPRs translated from an HRE in C9ORF72 aggregate and lead to an ISR that then leads to continuing DPR production and aggregation, thereby creating a continuing pathogenic cycle. Copyright © 2018 Elsevier Inc. All rights reserved.

A Novel Terminal-Repeat Retrotransposon in Miniature (TRIM) Is Massively Expressed in Echinococcus multilocularis Stem Cells

PubMed Central

Koziol, Uriel; Radio, Santiago; Smircich, Pablo; Zarowiecki, Magdalena; Fernández, Cecilia; Brehm, Klaus

2015-01-01

Taeniid cestodes (including the human parasites Echinococcus spp. and Taenia solium) have very few mobile genetic elements (MGEs) in their genome, despite lacking a canonical PIWI pathway. The MGEs of these parasites are virtually unexplored, and nothing is known about their expression and silencing. In this work, we report the discovery of a novel family of small nonautonomous long terminal repeat retrotransposons (also known as terminal-repeat retrotransposons in miniature, TRIMs) which we have named ta-TRIM (taeniid TRIM). ta-TRIMs are only the second family of TRIM elements discovered in animals, and are likely the result of convergent reductive evolution in different taxonomic groups. These elements originated at the base of the taeniid tree and have expanded during taeniid diversification, including after the divergence of closely related species such as Echinococcus multilocularis and Echinococcus granulosus. They are massively expressed in larval stages, from a small proportion of full-length copies and from isolated terminal repeats that show transcriptional read-through into downstream regions, generating novel noncoding RNAs and transcriptional fusions to coding genes. In E. multilocularis, ta-TRIMs are specifically expressed in the germinative cells (the somatic stem cells) during asexual reproduction of metacestode larvae. This would provide a developmental mechanism for insertion of ta-TRIMs into cells that will eventually generate the adult germ line. Future studies of active and inactive ta-TRIM elements could give the first clues on MGE silencing mechanisms in cestodes. PMID:26133390

Genome-wide DNA methylation patterns in LSH mutant reveals de-repression of repeat elements and redundant epigenetic silencing pathways

PubMed Central

Yu, Weishi; McIntosh, Carl; Lister, Ryan; Zhu, Iris; Han, Yixing; Ren, Jianke; Landsman, David; Lee, Eunice; Briones, Victorino; Terashima, Minoru; Leighty, Robert; Ecker, Joseph R.

2014-01-01

Cytosine methylation is critical in mammalian development and plays a role in diverse biologic processes such as genomic imprinting, X chromosome inactivation, and silencing of repeat elements. Several factors regulate DNA methylation in early embryogenesis, but their precise role in the establishment of DNA methylation at a given site remains unclear. We have generated a comprehensive methylation map in fibroblasts derived from the murine DNA methylation mutant Hells−/− (helicase, lymphoid specific, also known as LSH). It has been previously shown that HELLS can influence de novo methylation of retroviral sequences and endogenous genes. Here, we describe that HELLS controls cytosine methylation in a nuclear compartment that is in part defined by lamin B1 attachment regions. Despite widespread loss of cytosine methylation at regulatory sequences, including promoter regions of protein-coding genes and noncoding RNA genes, overall relative transcript abundance levels in the absence of HELLS are similar to those in wild-type cells. A subset of promoter regions shows increases of the histone modification H3K27me3, suggesting redundancy of epigenetic silencing mechanisms. Furthermore, HELLS modulates CG methylation at all classes of repeat elements and is critical for repression of a subset of repeat elements. Overall, we provide a detailed analysis of gene expression changes in relation to DNA methylation alterations, which contributes to our understanding of the biological role of cytosine methylation. PMID:25170028

Long Noncoding RNA H19 Inhibits Cell Viability, Migration, and Invasion Via Downregulation of IRS-1 in Thyroid Cancer Cells

PubMed Central

Wang, Peng; Xu, Weimin; Liu, Haixia; Bu, Qingao; Sun, Diwen

2017-01-01

Thyroid cancer is a common endocrine gland malignancy which exhibited rapid increased incidence worldwide in recent decades. This study was aimed to investigate the role of long noncoding RNA H19 in thyroid cancer. Long noncoding RNA H19 was overexpressed or knockdown in thyroid cancer cells SW579 and TPC-1, and the expression of long noncoding RNA H19 was detected by real-time polymerase chain reaction. The cell viability, migration, and invasion were determined by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide assay, Transwell assay, and wound healing assay, respectively. Furthermore, cell apoptosis was analyzed by flow cytometry, and expressions of some factors that were related to phosphatidyl inositide 3-kinases/protein kinase B and nuclear factor κB signal pathway were measured by Western blotting. This study revealed that cell viability and migration/invasion of SW579 and TPC-1 were significantly decreased by long noncoding RNA H19 overexpression compared with the control group (P < .05), whereas cell apoptosis was statistically increased (P < .001). Meanwhile, cell viability and migration/invasion were significantly increased after long noncoding RNA H19 knockdown (P < .05). Furthermore, long noncoding RNA H19 negatively regulated the expression of insulin receptor substrate 1 and thus effect on cell proliferation and apoptosis. Insulin receptor substrate 1 regulated the activation of phosphatidyl inositide 3-kinases/AKT and nuclear factor κB signal pathways. In conclusion, long noncoding RNA H19 could suppress cell viability, migration, and invasion via downregulation of insulin receptor substrate 1 in SW579 and TPC-1 cells. These results suggested the important role of long noncoding RNA H19 in thyroid cancer, and long noncoding RNA H19 might be a potential target of thyroid cancer treatment. PMID:29332545

Non-coding cancer driver candidates identified with a sample- and position-specific model of the somatic mutation rate

PubMed Central

Juul, Malene; Bertl, Johanna; Guo, Qianyun; Nielsen, Morten Muhlig; Świtnicki, Michał; Hornshøj, Henrik; Madsen, Tobias; Hobolth, Asger; Pedersen, Jakob Skou

2017-01-01

Non-coding mutations may drive cancer development. Statistical detection of non-coding driver regions is challenged by a varying mutation rate and uncertainty of functional impact. Here, we develop a statistically founded non-coding driver-detection method, ncdDetect, which includes sample-specific mutational signatures, long-range mutation rate variation, and position-specific impact measures. Using ncdDetect, we screened non-coding regulatory regions of protein-coding genes across a pan-cancer set of whole-genomes (n = 505), which top-ranked known drivers and identified new candidates. For individual candidates, presence of non-coding mutations associates with altered expression or decreased patient survival across an independent pan-cancer sample set (n = 5454). This includes an antigen-presenting gene (CD1A), where 5’UTR mutations correlate significantly with decreased survival in melanoma. Additionally, mutations in a base-excision-repair gene (SMUG1) correlate with a C-to-T mutational-signature. Overall, we find that a rich model of mutational heterogeneity facilitates non-coding driver identification and integrative analysis points to candidates of potential clinical relevance. DOI: http://dx.doi.org/10.7554/eLife.21778.001 PMID:28362259

The Inescapable Influence of Noncoding RNAs in Cancer

PubMed Central

Adams, Brian D.; Anastasiadou, Eleni; Esteller, Manel; He, Lin; Slack, Frank J.

2015-01-01

This report summarizes information presented at the 2015 Keystone Symposium on “MicroRNAs and Noncoding RNAs in Cancer”. Nearly two decades after the discovery of the first microRNA (miRNA), the role of noncoding RNAs in developmental processes and the mechanisms behind their dysregulation in cancer has been steadily elucidated. Excitingly, miRNAs have begun making their way into the clinic to combat disease such a hepatitis C, and various forms of cancer. Therefore, at this Keystone meeting novel findings were presented that enhance our view on how small and long noncoding RNAs control developmental timing and oncogenic processes. Recurring themes included, 1) how miRNAs can be differentially processed, degraded, and regulated by ribonucleoprotein (RNP) complexes, 2) how particular miRNA genetic networks that control developmental process, when disrupted, can result in cancer disease, 3) the technologies available to therapeutically deliver RNA to combat diseases such as cancer, and 4) the elucidation of the mechanism of actions for long noncoding RNAs, currently a poorly understood class of noncoding RNA. During the meeting there was an emphasis on presenting unpublished findings, and the breadth of topics covered reflected how inescapable the influence of noncoding RNAs are in development and cancer. PMID:26567137

Genomic Sequence around Butterfly Wing Development Genes: Annotation and Comparative Analysis

PubMed Central

Conceição, Inês C.; Long, Anthony D.; Gruber, Jonathan D.; Beldade, Patrícia

2011-01-01

Background Analysis of genomic sequence allows characterization of genome content and organization, and access beyond gene-coding regions for identification of functional elements. BAC libraries, where relatively large genomic regions are made readily available, are especially useful for species without a fully sequenced genome and can increase genomic coverage of phylogenetic and biological diversity. For example, no butterfly genome is yet available despite the unique genetic and biological properties of this group, such as diversified wing color patterns. The evolution and development of these patterns is being studied in a few target species, including Bicyclus anynana, where a whole-genome BAC library allows targeted access to large genomic regions. Methodology/Principal Findings We characterize ∼1.3 Mb of genomic sequence around 11 selected genes expressed in B. anynana developing wings. Extensive manual curation of in silico predictions, also making use of a large dataset of expressed genes for this species, identified repetitive elements and protein coding sequence, and highlighted an expansion of Alcohol dehydrogenase genes. Comparative analysis with orthologous regions of the lepidopteran reference genome allowed assessment of conservation of fine-scale synteny (with detection of new inversions and translocations) and of DNA sequence (with detection of high levels of conservation of non-coding regions around some, but not all, developmental genes). Conclusions The general properties and organization of the available B. anynana genomic sequence are similar to the lepidopteran reference, despite the more than 140 MY divergence. Our results lay the groundwork for further studies of new interesting findings in relation to both coding and non-coding sequence: 1) the Alcohol dehydrogenase expansion with higher similarity between the five tandemly-repeated B. anynana paralogs than with the corresponding B. mori orthologs, and 2) the high conservation of non-coding sequence around the genes wingless and Ecdysone receptor, both involved in multiple developmental processes including wing pattern formation. PMID:21909358

Differential effects of temperature and glucose on glycogenolytic enzymes in tissues of rainbow trout (Oncorhynchus mykiss).

PubMed

Bolinger, Mark T; Rodnick, Kenneth J

2014-05-01

The pathways and regulatory mechanisms of glycogenolysis remain relatively unexplored in non-mammalian vertebrates, especially poikilotherms. We studied the temperature sensitivity and inhibition of glycogenolytic enzymes in liver, ventricle, and white muscle of rainbow trout acclimated to 14 °C. Glycogen phosphorylase (GP) and acid α-glucosidase (GAA) activities were measured in homogenates of tissues at physiological temperatures (4, 14, and 24 °C), and in the presence of allosteric inhibitor, glucose. Higher GP versus GAA activity in all three tissues suggested a predominance of phosphorolytic glycogenolysis over the lysosomal glucosidic pathway. GP activities at 14 °C were ~2-fold higher in the ventricle and white muscle versus the liver and selectively increased by AMP in striated muscle. Conversely, the activities of GAA and lysosomal marker acid phosphatase were 8- to 10-fold higher in the liver compared with the ventricle and white muscle. Thermal sensitivity (Q10) was increased for GP in all tissues below 14 °C and decreased in striated muscle in the absence of AMP above 14 °C. GAA had lower Q10 values than GP below 14 °C, and, unlike GP, Q10s for GAA were not different between tissues or affected by temperature. Both GP (in the absence of AMP) and GAA were inhibited by glucose in a dose-dependent manner, with the lowest IC50 values observed in the white muscle (1.4 and 6.3 mM, respectively). In conclusion, despite comparatively low kinetic potential, lysosomal GAA might facilitate glycogenolysis at colder body temperatures in striated muscle and intracellular glucose could limit phosphorolytic and glucosidic glycogenolysis in multiple tissues of the rainbow trout. Copyright © 2014 Elsevier Inc. All rights reserved.

Guanidinoacetate and creatine plus creatinine assessment in physiologic fluids: an effective diagnostic tool for the biochemical diagnosis of arginine:glycine amidinotransferase and guanidinoacetate methyltransferase deficiencies.

PubMed

Carducci, Claudia; Birarelli, Maurizio; Leuzzi, Vincenzo; Carducci, Carla; Battini, Roberta; Cioni, Giovanni; Antonozzi, Italo

2002-10-01

Disorders of creatine metabolism arise from genetic alterations of arginine:glycine amidinotransferase (AGAT), guanidinoacetate methyltransferase (GAMT), and the creatine transporter. We developed a strategy for the detection of AGAT and GAMT defects by measurement of guanidinoacetate (GAA) and creatine plus creatinine (Cr+Crn) in biological fluids. Three patients with AGAT deficiency from the same pedigree and their eight relatives, as well as a patient affected by a GAMT defect and his parents were analyzed by a new HPLC procedure in comparison with 90 controls. The method, which uses precolumn derivatization with benzoin, separation with a reversed-phase column, and fluorescence detection, has shown good precision and sensitivity and requires minimal sample handling. In the three AGAT patients, plasma GAA was 0.01-0.04 micro mol/L [mean (SD) for neurologically normal controls was 1.16 (0.59) micromol/L], Cr+Crn was 15-29 micro mol/L [reference limit in our laboratory, 79 (38) micromol/L]. Urinary GAA was 2.4-5.8 micro mol/L [reference, 311 (191) micromol/L], and Cr+Crn was 2.1-3.3 mmol/L [reference, 9.9 (4.1) mmol/L]. We found a smaller decrease in GAA and Cr+Crn in some carriers of an AGAT defect. In the patient with GAMT deficiency, plasma and urine GAA was increased (18.6 and 1783 micromol/L, respectively), and Cr+Crn was decreased in plasma (10.7 micromol/L) and urine (2.1 mmol/L). GAA was increased in the parents' plasmas and in the mother's urine. The assessment of GAA is a new tool for the detection of both GAMT and AGAT deficiencies.

GaAs QWIP Array Containing More Than a Million Pixels

NASA Technical Reports Server (NTRS)

Jhabvala, Murzy; Choi, K. K.; Gunapala, Sarath

2005-01-01

A 1,024 x 1,024-pixel array of quantum-well infrared photodetectors (QWIPs) has been built on a 1.8 x 1.8- cm GaAs chip. In tests, the array was found to perform well in detecting images at wavelengths from 8 to 9 m in operation at temperatures between 60 and 70 K. The largest-format QWIP prior array that performed successfully in tests contained 512 x 640 pixels. There is continuing development effort directed toward satisfying actual and anticipated demands to increase numbers of pixels and pixel sizes in order to increase the imaging resolution of infrared photodetector arrays. A 1,024 x 1,024-pixel and even larger formats have been achieved in the InSb and HgCdTe material systems, but photodetector arrays in these material systems are very expensive and manufactured by fewer than half a dozen large companies. In contrast, GaAs-photodetector-array technology is very mature, and photodetectors in the GaAs material system can be readily manufactured by a wide range of industrial technologists, by universities, and government laboratories. There is much similarity between processing in the GaAs industry and processing in the pervasive silicon industry. With respect to yield and cost, the performance of GaAs technology substantially exceeds that of InSb and HgCdTe technologies. In addition, GaAs detectors can be designed to respond to any portion of the wavelength range from 3 to about 16 micrometers - a feature that is very desirable for infrared imaging. GaAs QWIP arrays, like the present one, have potential for use as imaging sensors in infrared measuring instruments, infrared medical imaging systems, and infrared cameras.

Rare-earth gate oxides for GaAs MOSFET application

NASA Astrophysics Data System (ADS)

Kwon, Kwang-Ho; Yang, Jun-Kyu; Park, Hyung-Ho; Kim, Jongdae; Roh, Tae Moon

2006-08-01

Rare-earth oxide films for gate dielectric on n-GaAs have been investigated. The oxide films were e-beam evaporated on S-passivated GaAs, considering interfacial chemical bonding state and energy band structure. Rare-earth oxides such as Gd 2O 3, (Gd xLa 1- x) 2O 3, and Gd-silicate were employed due to high resistivity and no chemical reaction with GaAs. Structural and bonding properties were characterized by X-ray photoemission, absorption, and diffraction. The electrical characteristics of metal-oxide-semiconductor (MOS) diodes were correlated with material properties and energy band structures to guarantee the feasibility for MOS field effect transistor (FET) application. Gd 2O 3 films were grown epitaxially on S-passivated GaAs (0 0 1) at 400 °C. The passivation induced a lowering of crystallization temperature with an epitaxial relationship of Gd 2O 3 (4 4 0) and GaAs (0 0 1). A better lattice matching relation between Gd 2O 3 and GaAs substrate was accomplished by the substitution of Gd with La, which has larger ionic radius. The in-plane relationship of (Gd xLa 1- x) 2O 3 (4 4 0) with GaAs (0 0 1) was found and the epitaxial films showed an improved crystalline quality. Amorphous Gd-silicate film was synthesized by the incorporation of SiO 2 into Gd 2O 3. These amorphous Gd-silicate films excluded defect traps or current flow path due to grain boundaries and showed a relatively larger energy band gap dependent on the contents of SiO 2. Energy band parameters such as Δ EC, Δ EV, and Eg were effectively controlled by the film composition.

Interpretation of acid α-glucosidase activity in creatine kinase elevation: A case of Becker muscular dystrophy.

PubMed

Oitani, Yoshiki; Ishiyama, Akihiko; Kosuga, Motomichi; Iwasawa, Kentaro; Ogata, Ayako; Tanaka, Fumiko; Takeshita, Eri; Shimizu-Motohashi, Yuko; Komaki, Hirofumi; Nishino, Ichizo; Okuyama, Torayuki; Sasaki, Masayuki

2018-05-16

Diagnosis of Pompe disease is sometimes challenging because it exhibits clinical similarities to muscular dystrophy. We describe a case of Becker muscular dystrophy (BMD) with a remarkable reduction in activity of the acid α-glucosidase (GAA) enzyme, caused by a combination of pathogenic mutation and polymorphism variants resulting in pseudodeficiency in GAA. The three-year-old boy demonstrated asymptomatic creatine kinase elevation. Neither exon deletion nor duplication was detected on multiplex ligation-dependent probe amplification (MLPA) of DMD. GAA enzyme activity in both dried blood spots and lymphocytes was low, at 11.7% and 7.7% of normal, respectively. However, genetic analysis of GAA detected only heterozygosity for a nonsense mutation (c.118C > T, p.Arg40 ∗ ). Muscle pathology showed no glycogen deposits and no high acid phosphatase activity. Hematoxylin-eosin staining detected scattered regenerating fibers; the fibers were faint and patchy on immunochemistry staining of dystrophin. The amount of dystrophin protein was reduced to 11.8% of normal, on Western blotting analysis. Direct sequencing analysis of DMD revealed hemizygosity for a nonsense mutation (c.72G > A, p.Trp24 ∗ ). The boy was diagnosed with BMD, despite remarkable reduction in GAA activity; further, he demonstrated heterozygosity for [p.Gly576Ser; p.Glu689Lys] polymorphism variants that indicated pseudodeficiency on another allele in GAA. Pseudodeficiency alleles are detected in approximately 4% of the Asian population; these demonstrate low activity of acid α-glucosidase (GAA), similar to levels found in Pompe disease. Clinicians should be careful in their interpretations of pseudodeficiency alleles that complicate diagnosis in cases of elevated creatine kinase. Copyright © 2018 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.

Investigation of the interface characteristics of Y2O3/GaAs under biaxial strain, triaxial strain, and non-strain conditions

NASA Astrophysics Data System (ADS)

Shi, Li-Bin; Liu, Xu-Yang; Dong, Hai-Kuan

2016-09-01

We investigate the interface behaviors of Y2O3/GaAs under biaxial strain, triaxial strain, and non-strain conditions. This study is performed by first principles calculations based on density functional theory (DFT). First of all, the biaxial strain is realized by changing the lattice constants in ab plane. Averaged electrostatic potential (AEP) is aligned by establishing Y2O3 and GaAs (110) surfaces. The band offsets of Y2O3/GaAs interface under biaxial strain are investigated by generalized gradient approximation and Heyd-Scuseria-Ernzerhof (HSE) functionals. The interface under biaxial strain is suitable for the design of metal oxide semiconductor (MOS) devices because the valence band offsets (VBO) and conduction band offsets (CBO) are larger than 1 eV. Second, the triaxial strain is applied to Y2O3/GaAs interface by synchronously changing the lattice constants in a, b, and c axis. The band gaps of Y2O3 and GaAs under triaxial strain are investigated by HSE functional. We compare the VBO and CBO under triaxial strain with those under biaxial strain. Third, in the absence of lattice strain, the formation energies, charge state switching levels, and migration barriers of native defects in Y2O3 are assessed. We investigate how they will affect the MOS device performance. It is found that VO+2 and Oi-2 play a very dangerous role in MOS devices. Finally, a direct tunneling leakage current model is established. The model is used to analyze current and voltage characteristics of the metal/Y2O3/GaAs.

Birth, coming of age and death: The intriguing life of long noncoding RNAs.

PubMed

Samudyata; Castelo-Branco, Gonçalo; Bonetti, Alessandro

2018-07-01

Mammalian genomes are pervasively transcribed, with long noncoding RNAs being the most abundant fraction. Recent studies have highlighted the central role played by these transcripts in several physiological and pathological processes. Despite several metabolic features shared between coding and noncoding transcripts, these two classes of RNAs exhibit multiple differences regarding their biogenesis and processing. Here we review such distinctions, focusing on the unique features of specific long noncoding RNAs. Copyright © 2017 Elsevier Ltd. All rights reserved.

Scaling behavior of GaAs and GaMnAs quantum rings grown by droplet epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Placidi, E.; Dipartimento di Fisica, Universita di Roma 'Tor Vergata,' via della Ricerca Scientifica 1, 00133 Roma Italy; Arciprete, F.

2012-10-01

The transition from the liquid phase of Ga droplets to the formation of GaAs and GaMnAs quantum rings has been studied as a function of temperature. We show that different aggregation processes involve the GaAs (GaMnAs) island and the droplet formation. Furthermore, the aspect ratio of the islands exhibits an anomalous scaling law related to a tendency to aggregate in the vertical direction.

Activities of the Solid State Physics Research Institute

NASA Technical Reports Server (NTRS)

1984-01-01

Three research programs are reviewed. These programs are muon spin rotation, studies of annealing in gallium arsenide and Hall effect studies in semiconductors. The muon spin rotation work centers around the development of a facility at the Alternating Gradient Synchrotron of BNL. Studies of annealing in GaAs concerns itself with the measurement of depolarization in GaAs. The Hall effect studies of proton damaged semiconductors provide new information on the nature of defects and dislocations in GaAs.

New dynamic FET logic and serial memory circuits for VLSI GaAs technology

NASA Technical Reports Server (NTRS)

Eldin, A. G.

1991-01-01

The complexity of GaAs field effect transistor (FET) very large scale integration (VLSI) circuits is limited by the maximum power dissipation while the uniformity of the device parameters determines the functional yield. In this work, digital GaAs FET circuits are presented that eliminate the DC power dissipation and reduce the area to 50% of that of the conventional static circuits. Its larger tolerance to device parameter variations results in higher functional yield.

A model for proton-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Walker, G. H.; Outlaw, R. A.; Stock, L. V.

1982-01-01

A simple model for proton radiation damage in GaAs heteroface solar cells is developed. The model includes the effects of spatial nonuniformity of low energy proton damage. Agreement between the model and experimental proton damage data for GaAs heteroface solar cells is satisfactory. An extension of the model to include angular isotropy, as is appropriate for protons in space, is shown to result in significantly less cell damage than for normal proton incidence.

Extraordinary Transmission in the UV Range from Sub-wavelength Slits on Semiconductors

DTIC Science & Technology

2010-03-01

M. Scalora, G. D’Aguanno, N. Mattiucci, M. J. Bloemer, J. W. Haus and A. M. Zheltikov, "Negative refraction of ultrashort electromagnetic pulses...a GaAs Substrate We consider a single layer of a GaAs having the linear dispersion profile taken from Palik’s handbook of optical constants [11...wavelength to investigate the relationship between the extraordinary transmission regime and the dispersion peculiarities of GaAs. As Fig.6 shows, the

Highly efficient single-junction GaAs thin-film solar cell on flexible substrate.

PubMed

Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

2016-07-20

There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination.

Arsenic moiety in gallium arsenide is responsible for neuronal apoptosis and behavioral alterations in rats.

PubMed

Flora, Swaran J S; Bhatt, Kapil; Mehta, Ashish

2009-10-15

Gallium arsenide (GaAs), an intermetallic semiconductor finds widespread applications in high frequency microwave and millimeter wave, and ultra fast supercomputers. Extensive use of GaAs has led to increased exposure to humans working in semiconductor industry. GaAs has the ability to dissociate into its constitutive moieties at physiological pH and might be responsible for the oxidative stress. The present study was aimed at evaluating, the principle moiety (Ga or As) in GaAs to cause neurological dysfunction based on its ability to cause apoptosis, in vivo and in vitro and if this neuronal dysfunction translated to neurobehavioral changes in chronically exposed rats. Result indicated that arsenic moiety in GaAs was mainly responsible for causing oxidative stress via increased reactive oxygen species (ROS) and nitric oxide (NO) generation, both in vitro and in vivo. Increased ROS further caused apoptosis via mitochondrial driven pathway. Effects of oxidative stress were also confirmed based on alterations in antioxidant enzymes, GPx, GST and SOD in rat brain. We noted that ROS induced oxidative stress caused changes in the brain neurotransmitter levels, Acetylcholinesterase and nitric oxide synthase, leading to loss of memory and learning in rats. The study demonstrates for the first time that the slow release of arsenic moiety from GaAs is mainly responsible for oxidative stress induced apoptosis in neuronal cells causing behavioral changes.

Photoelectron and Auger electron diffraction studies of a sulfur-terminated GaAs(001)-(2×6) surface

NASA Astrophysics Data System (ADS)

Shimoda, M.; Tsukamoto, S.; Koguchi, N.

1998-01-01

Core-level X-ray photoelectron diffraction (XPD) and Auger electron diffraction (AED) have been applied to investigate the sulfur-terminated GaAs(001)-(2×6) surface. No forward scattering peaks were found in the XPD pattern of S 2s emission, indicating that adsorbed S atoms form a single layer on the GaAs substrate. In accordance with the zincblende structure of GaAs, the AED patterns of Ga L 3M 45M 45 and As L 3M 45M 45 emission almost coincide with each other, if one of the emissions is rotated by 90° around the [001] direction. This fact suggests that the diffraction patterns mainly reflect the structure of the bulk GaAs crystal. In order to investigate the surface structure, AED patterns in large polar angles were analyzed with single scattering cluster (SSC) calculations. The best result was obtained with a model cluster where the S-S bond length was set at 0.28 nm, 30% shorter than the corresponding length of the ideal (1×1) structure, and the adsorption height was set at 0.12-0.13 nm, 10% shorter than the ideal interlayer distance of GaAs(001) planes. These values are in good agreement with the results of STM measurements. A modulation of the inter-dimer distance was also found, suggesting the existence of missing dimers.

Reaction mechanism of guanidinoacetate methyltransferase, concerted or step-wise

PubMed Central

Zhang, Xiaodong; Bruice, Thomas C.

2006-01-01

We describe a quantum mechanics/molecular mechanics investigation of the guanidinoacetate methyltransferase catalyzed reaction, which shows that proton transfer from guanidinoacetate (GAA) to Asp-134 and methyl transfer from S-adenosyl-l-methionine (AdoMet) to GAA are concerted. By self-consistent-charge density functional tight binding/molecular mechanics, the bond lengths in the concerted mechanism's transition state are 1.26 Å for both the OD1 (Asp-134)–HE (GAA) and HE (GAA)–NE (GAA) bonds, and 2.47 and 2.03 Å for the S8 (AdoMet)–C9 (AdoMet) and C9 (AdoMet)–NE (GAA) bonds, respectively. The potential-energy barrier (ΔE‡) determined by single-point B3LYP/6–31+G*//MM is 18.9 kcal/mol. The contributions of the entropy (−TΔS‡) and zero-point energy corrections Δ(ZPE)‡ by normal mode analysis are 2.3 kcal/mol and −1.7 kcal/mol, respectively. Thus, the activation enthalpy of this concerted mechanism is predicted to be ΔH‡ = ΔE‡ + Δ(ZPE)‡ = 17.2 kcal/mol. The calculated free-energy barrier for the concerted mechanism is ΔG‡ = 19.5 kcal/mol, which is in excellent agreement with the value of 19.0 kcal/mol calculated from the experimental rate constant (3.8 ± 0.2·min−1). PMID:17053070

Development of a 1K x 1K GaAs QWIP Far IR Imaging Array

NASA Technical Reports Server (NTRS)

Jhabvala, M.; Choi, K.; Goldberg, A.; La, A.; Gunapala, S.

2003-01-01

In the on-going evolution of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have developed a 1,024 x 1,024 (1K x1K), 8.4-9 microns infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using the Rockwell TCM 8050 silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). The finished hybrid is thinned at the Jet Propulsion Lab. Prior to this development the largest format array was a 512 x 640 FPA. We have integrated the 1K x 1K array into an imaging camera system and performed tests over the 40K-90K temperature range achieving BLIP performance at an operating temperature of 76K (f/2 camera system). The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. In this paper we will present the first results of our 1K x 1K QWIP array development including fabrication methodology, test data and our imaging results.

Imaging of single magnetic dopants in III-V semiconductor hosts

NASA Astrophysics Data System (ADS)

Koenraad, Paul; Celebi, Cem; Silov, Andrei; Yakunin, Andrei; Tang, Jian-Ming; Flatte, Michael; Kaminska, Maria

2007-03-01

We present room-temperature cross-sectional scanning tunneling microscopy (STM) topographic measurements of the acceptor state wave function for Mn dopants in InP and compare with measurements for the nonmagnetic dopants Zn and Cd as well as with previous results for Mn in GaAs[1]. We find a strongly anisotropic ``bow-tie'' shape for the Mn acceptor state wave function in InP, similar to Mn in GaAs, which has a binding energy of 210 meV (compared to 113 meV for Mn in GaAs). The shape for Mn in InP is more symmetric with respect to the 001 plane than Mn in GaAs, which agrees with a general trend for the magnetic and nonmagnetic acceptor state symmetry as a function of acceptor binding energy. We present a new theoretical model based on the surface strain of GaAs (110) that explains why the 001-plane asymmetry of acceptor states seen in STM measurements is much larger than expected from bulk calculations. [1] A. M. Yakunin, et al., Phys. Rev. Lett. 92, 216806 (2004).

DFT algorithms for bit-serial GaAs array processor architectures

NASA Technical Reports Server (NTRS)

Mcmillan, Gary B.

1988-01-01

Systems and Processes Engineering Corporation (SPEC) has developed an innovative array processor architecture for computing Fourier transforms and other commonly used signal processing algorithms. This architecture is designed to extract the highest possible array performance from state-of-the-art GaAs technology. SPEC's architectural design includes a high performance RISC processor implemented in GaAs, along with a Floating Point Coprocessor and a unique Array Communications Coprocessor, also implemented in GaAs technology. Together, these data processors represent the latest in technology, both from an architectural and implementation viewpoint. SPEC has examined numerous algorithms and parallel processing architectures to determine the optimum array processor architecture. SPEC has developed an array processor architecture with integral communications ability to provide maximum node connectivity. The Array Communications Coprocessor embeds communications operations directly in the core of the processor architecture. A Floating Point Coprocessor architecture has been defined that utilizes Bit-Serial arithmetic units, operating at very high frequency, to perform floating point operations. These Bit-Serial devices reduce the device integration level and complexity to a level compatible with state-of-the-art GaAs device technology.

Electrophilic surface sites as precondition for the chemisorption of pyrrole on GaAs(001) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruhn, Thomas; Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V., Albert-Einstein-Str.9, 12489 Berlin; Fimland, Bjørn-Ove

We report how the presence of electrophilic surface sites influences the adsorption mechanism of pyrrole on GaAs(001) surfaces. For this purpose, we have investigated the adsorption behavior of pyrrole on different GaAs(001) reconstructions with different stoichiometries and thus different surface chemistries. The interfaces were characterized by x-ray photoelectron spectroscopy, scanning tunneling microscopy, and by reflectance anisotropy spectroscopy in a spectral range between 1.5 and 5 eV. On the As-rich c(4 × 4) reconstruction that exhibits only nucleophilic surface sites, pyrrole was found to physisorb on the surface without any significant modification of the structural and electronic properties of the surface. Onmore » the Ga-rich GaAs(001)-(4 × 2)/(6 × 6) reconstructions which exhibit nucleophilic as well as electrophilic surface sites, pyrrole was found to form stable covalent bonds mainly to the electrophilic (charge deficient) Ga atoms of the surface. These results clearly demonstrate that the existence of electrophilic surface sites is a crucial precondition for the chemisorption of pyrrole on GaAs(001) surfaces.« less

Surface segregation and the Al problem in GaAs quantum wells

NASA Astrophysics Data System (ADS)

Chung, Yoon Jang; Baldwin, K. W.; West, K. W.; Shayegan, M.; Pfeiffer, L. N.

2018-03-01

Low-defect two-dimensional electron systems (2DESs) are essential for studies of fragile many-body interactions that only emerge in nearly-ideal systems. As a result, numerous efforts have been made to improve the quality of modulation-doped AlxGa1 -xAs /GaAs quantum wells (QWs), with an emphasis on purifying the source material of the QW itself or achieving better vacuum in the deposition chamber. However, this approach overlooks another crucial component that comprises such QWs, the AlxGa1 -xAs barrier. Here we show that having a clean Al source and hence a clean barrier is instrumental to obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the 2DES in GaAs QWs declines as the thickness or Al content of the AlxGa1 -xAs barrier beneath the QW is increased, which we attribute to the surface segregation of oxygen atoms that originate from the Al source. This conjecture is supported by the improved mobility in the GaAs QWs as the Al cell is cleaned out by baking.

Design of quantum efficiency measurement system for variable doping GaAs photocathode

NASA Astrophysics Data System (ADS)

Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

2008-03-01

To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

Covalent attachment of TAT peptides and thiolated alkyl molecules on GaAs surfaces.

PubMed

Cho, Youngnam; Ivanisevic, Albena

2005-07-07

Four TAT peptide fragments were used to functionalize GaAs surfaces by adsorption from solution. In addition, two well-studied alkylthiols, mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT) were utilized as references to understand the structure of the TAT peptide monolayer on GaAs. The different sequences of TAT peptides were employed in recognition experiments where a synthetic RNA sequence was tested to verify the specific interaction with the TAT peptide. The modified GaAs surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). AFM studies were used to compare the surface roughness before and after functionalization. XPS allowed us to characterize the chemical composition of the GaAs surface and conclude that the monolayers composed of different sequences of peptides have similar surface chemistries. Finally, FT-IRRAS experiments enabled us to deduce that the TAT peptide monolayers have a fairly ordered and densely packed alkyl chain structure. The recognition experiments showed preferred interaction of the RNA sequence toward peptides with high arginine content.

Enhancement of conductance of GaAs sub-microwires under external stimuli

NASA Astrophysics Data System (ADS)

Qu, Xianlin; Deng, Qingsong; Zheng, Kun

2018-03-01

Semiconductors with one dimension on the micro-nanometer scale have many unique physical properties that are remarkably different from those of their bulk counterparts. Moreover, changes in the external field will further modulate the properties of the semiconductor micro-nanomaterials. In this study, we used focused ion beam technology to prepare freestanding ⟨111⟩-oriented GaAs sub-microwires from a GaAs substrate. The effects of laser irradiation and bending or buckling deformation induced by compression on the electrical transport properties of an individual GaAs sub-microwire were studied. The experimental results indicate that both laser irradiation and bending deformation can enhance their electrical transport properties, the laser irradiation resulted in a conductance enhancement of ˜30% compared to the result with no irradiation, and in addition, bending deformation changed the conductance by as much as ˜180% when the average strain was approximately 1%. The corresponding mechanisms are also discussed. This study provides beneficial insight into the fabrication of electronic and optoelectronic devices based on GaAs micro/nano-wires.

A new structure for comparing surface passivation materials of GaAs solar cells

NASA Technical Reports Server (NTRS)

Desalvo, Gregory C.; Barnett, Allen M.

1989-01-01

The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described.

Structures, Properties and Defects of SrTiO3/GaAs Hetero-interfaces

NASA Astrophysics Data System (ADS)

Hong, Liang; Bhatnagar, Kunal; Droopad, Ravi; Öğüt, Serdar; Klie, Robert

SrTiO3 thin film can be epitaxially grown on GaAs substrate and used as a platform for growing other oxides to create functional metal-oxide-semiconductor devices, where a high-quality SrTiO3/GaAs interface is essential. We studied the structural and electronic properties of SrTiO3/GaAs hetero-interfaces at atomic level using scanning transmission electron microscopy and first-principles calculations. Our results suggest the preferred termination of GaAs (001) is significantly dependent on the oxygen concentration in the first oxide layer. The favorable interface structure is characterized as oxygen-deficient SrO in contact with arsenic and is observed in both experiment and simulation. The electronic properties are calculated and found to be tunable by interfacial defects such as oxygen, gallium and arsenic vacancies. This work was supported by the National Science Foundation (Grant No. DMR-1408427). This work made use of instruments in the Electron Microscopy Service and the High Performance Computing Clusters at University of Illinois at Chicago.

InGaAs quantum dots grown on B-type high index GaAs substrates: surface morphologies and optical properties

NASA Astrophysics Data System (ADS)

Liang, B. L.; Wang, Zh M.; Mazur, Yu I.; Strelchuck, V. V.; Holmes, K.; Lee, J. H.; Salamo, G. J.

2006-06-01

We systematically investigated the correlation between morphological and optical properties of InGaAs self-assembled quantum dots (QDs) grown by solid-source molecular beam epitaxy on GaAs (n 11)B (n = 9, 8, 7, 5, 3, 2) substrates. Remarkably, all InGaAs QDs on GaAs(n 11)B under investigation show optical properties superior to those for ones on GaAs(100) as regards the photoluminescence (PL) linewidth and intensity. The morphology for growth of InGaAs QDs on GaAs (n 11)B, where n = 9, 8, 7, 5, is observed to have a rounded shape with a higher degree of lateral ordering than that on GaAs(100). The optical property and the lateral ordering are best for QDs grown on a (511)B substrate surface, giving a strong correlation between lateral ordering and PL optical quality. Our results demonstrate the potential for high quality InGaAs QDs on GaAs(n 11)B for optoelectronic applications.

Genome-scale deletion screening of human long non-coding RNAs using a paired-guide RNA CRISPR library

PubMed Central

Zhu, Shiyou; Li, Wei; Liu, Jingze; Chen, Chen-Hao; Liao, Qi; Xu, Ping; Xu, Han; Xiao, Tengfei; Cao, Zhongzheng; Peng, Jingyu; Yuan, Pengfei; Brown, Myles; Liu, Xiaole Shirley; Wei, Wensheng

2017-01-01

CRISPR/Cas9 screens have been widely adopted to analyse coding gene functions, but high throughput screening of non-coding elements using this method is more challenging, because indels caused by a single cut in non-coding regions are unlikely to produce a functional knockout. A high-throughput method to produce deletions of non-coding DNA is needed. Herein, we report a high throughput genomic deletion strategy to screen for functional long non-coding RNAs (lncRNAs) that is based on a lentiviral paired-guide RNA (pgRNA) library. Applying our screening method, we identified 51 lncRNAs that can positively or negatively regulate human cancer cell growth. We individually validated 9 lncRNAs using CRISPR/Cas9-mediated genomic deletion and functional rescue, CRISPR activation or inhibition, and gene expression profiling. Our high-throughput pgRNA genome deletion method should enable rapid identification of functional mammalian non-coding elements. PMID:27798563

Noncoding Genomics in Gastric Cancer and the Gastric Precancerous Cascade: Pathogenesis and Biomarkers

PubMed Central

Garcia-Bloj, Benjamin; Fry, Jacqueline; Wichmann, Ignacio

2015-01-01

Gastric cancer is the fifth most common cancer and the third leading cause of cancer-related death, whose patterns vary among geographical regions and ethnicities. It is a multifactorial disease, and its development depends on infection by Helicobacter pylori (H. pylori) and Epstein-Barr virus (EBV), host genetic factors, and environmental factors. The heterogeneity of the disease has begun to be unraveled by a comprehensive mutational evaluation of primary tumors. The low-abundance of mutations suggests that other mechanisms participate in the evolution of the disease, such as those found through analyses of noncoding genomics. Noncoding genomics includes single nucleotide polymorphisms (SNPs), regulation of gene expression through DNA methylation of promoter sites, miRNAs, other noncoding RNAs in regulatory regions, and other topics. These processes and molecules ultimately control gene expression. Potential biomarkers are appearing from analyses of noncoding genomics. This review focuses on noncoding genomics and potential biomarkers in the context of gastric cancer and the gastric precancerous cascade. PMID:26379360

2-D Structure of the A Region of Xist RNA and Its Implication for PRC2 Association

PubMed Central

Maenner, Sylvain; Blaud, Magali; Fouillen, Laetitia; Savoye, Anne; Marchand, Virginie; Dubois, Agnès; Sanglier-Cianférani, Sarah; Van Dorsselaer, Alain; Clerc, Philippe; Avner, Philip; Visvikis, Athanase; Branlant, Christiane

2010-01-01

In placental mammals, inactivation of one of the X chromosomes in female cells ensures sex chromosome dosage compensation. The 17 kb non-coding Xist RNA is crucial to this process and accumulates on the future inactive X chromosome. The most conserved Xist RNA region, the A region, contains eight or nine repeats separated by U-rich spacers. It is implicated in the recruitment of late inactivated X genes to the silencing compartment and likely in the recruitment of complex PRC2. Little is known about the structure of the A region and more generally about Xist RNA structure. Knowledge of its structure is restricted to an NMR study of a single A repeat element. Our study is the first experimental analysis of the structure of the entire A region in solution. By the use of chemical and enzymatic probes and FRET experiments, using oligonucleotides carrying fluorescent dyes, we resolved problems linked to sequence redundancies and established a 2-D structure for the A region that contains two long stem-loop structures each including four repeats. Interactions formed between repeats and between repeats and spacers stabilize these structures. Conservation of the spacer terminal sequences allows formation of such structures in all sequenced Xist RNAs. By combination of RNP affinity chromatography, immunoprecipitation assays, mass spectrometry, and Western blot analysis, we demonstrate that the A region can associate with components of the PRC2 complex in mouse ES cell nuclear extracts. Whilst a single four-repeat motif is able to associate with components of this complex, recruitment of Suz12 is clearly more efficient when the entire A region is present. Our data with their emphasis on the importance of inter-repeat pairing change fundamentally our conception of the 2-D structure of the A region of Xist RNA and support its possible implication in recruitment of the PRC2 complex. PMID:20052282

NASA seeking high-power 60-GHz IMPATT diodes

NASA Technical Reports Server (NTRS)

Haugland, E. J.

1984-01-01

Recent progress in the development of high-power 60 GHz GaAs IMPATT diodes for communication links with high-data-rate satellites is discussed. One of the advantages of GaAs over Si as the material for the diodes are that GaAs is likely to have a higher output and efficiency than Si despite recent advances in Si technology. It is therefore in GaAs technology that research is currently concentrating. Some of the design strategies of the various companies working on the technology are described, including a pill process, MOCVD growth, and the use of diethy zinc as a dopant. Reliability testing of the diodes will be performed by NASA. Some of the alternatives to solid state amplifiers are discussed, including optical and traveling wave tube technology (TWT).

Stacking InAs quantum dots over ErAs semimetal nanoparticles on GaAs (0 0 1) using molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Zhang, Yuanchang; Eyink, Kurt G.; Grazulis, Lawrence; Hill, Madelyn; Peoples, Joseph; Mahalingam, Krishnamurthy

2017-11-01

Hybrid nanostructures are known to elicit an enhanced optical response. We study the directed alignment of ErAs metal nanoparticle (NP) and InAs quantum dot (QD) using molecular beam eptaxy (MBE) in a GaAs matrix. Due to high surface free energy caused by the crystal structure difference, overgrowth of an ErAs NP with GaAs forms a depression that condenses subsequent InAs adatoms to form an inverted QD self-aligned to the underlying ErAs NP. The ErAs NP growth, GaAs overgrowth, and InAs QD deposition were carefully controlled and studied with transmission electron microscopy (TEM) and atomic force microscopy (AFM) to investigate their effects on the QD-NP alignment.

Interface demarcation in GaAs by current pulsing

NASA Technical Reports Server (NTRS)

Matthiesen, D. H.; Kafalas, J. A.; Duchene, G. A.; Bellows, A. H.

1990-01-01

GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

Rugged spin-polarized electron sources based on negative electron affinity GaAs photocathode with robust Cs2Te coating

NASA Astrophysics Data System (ADS)

Bae, Jai Kwan; Cultrera, Luca; DiGiacomo, Philip; Bazarov, Ivan

2018-04-01

Photocathodes capable of providing high intensity and highly spin-polarized electron beams with long operational lifetimes are of great interest for the next generation nuclear physics facilities like Electron Ion Colliders. We report on GaAs photocathodes activated by Cs2Te, a material well known for its robustness. GaAs activated by Cs2Te forms Negative Electron Affinity, and the lifetime for extracted charge is improved by a factor of 5 compared to that of GaAs activated by Cs and O2. The spin polarization of photoelectrons was measured using a Mott polarimeter and found to be independent from the activation method, thereby shifting the paradigm on spin-polarized electron sources employing photocathodes with robust coatings.

Photoluminescence emission from GaAs nanodisks in GaAs/AlGaAs nanopillar arrays fabricated by neutral beam etching

NASA Astrophysics Data System (ADS)

Ohori, Daisuke; Fukuyama, Atsuhiko; Sakai, Kentaro; Higo, Akio; Thomas, Cedric; Samukawa, Seiji; Ikari, Tetsuo

2017-05-01

GaAs quantum nanodisks (QNDs) in nanopillar (NP) arrays are considered to be an attractive candidate for photonic device applications. We report a damageless fabrication technique that can be used to produce large-area lattice-matched GaAs/AlGaAs heterostructure NP arrays through the use of a bio-template and neutral beam etching. We have successfully realized GaAs QNDs in NPs owing to nanoscale iron oxide masks included in poly(ethylene glycol)-decorated ferritin protein shells. We observed for first time the photoluminescence emission from as-etched GaAs QNDs and confirmed quantum confinement by quantum mechanical calculation. Our methodology is vital for high-efficiency pillar-based optoelectronic devices such as NP laser diodes.

Nanoheteroepitaxy of gallium arsenide on strain-compliant silicon-germanium nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chin, Hock-Chun; Gong, Xiao; Yeo, Yee-Chia

Heterogeneous integration of high-quality GaAs on Si-based substrates using a selective migration-enhanced epitaxy (MEE) of GaAs on strain-compliant SiGe nanowires was demonstrated for the first time. The physics of compliance in nanoscale heterostructures was captured and studied using finite-element simulation. It is shown that nanostructures can provide additional substrate compliance for strain relief and therefore contribute to the formation of defect-free GaAs on SiGe. Extensive characterization using scanning electron microscopy and cross-sectional transmission electron microscopy was performed to illustrate the successful growth of GaAs on SiGe nanowire. Raman and Auger electron spectroscopy measurements further confirmed the quality of the GaAsmore » grown and the high growth selectivity of the MEE process.« less

Heterojunction photovoltaics using GaAs nanowires and conjugated polymers.

PubMed

Ren, Shenqiang; Zhao, Ni; Crawford, Samuel C; Tambe, Michael; Bulović, Vladimir; Gradecak, Silvija

2011-02-09

We demonstrate an organic/inorganic solar cell architecture based on a blend of poly(3-hexylthiophene) (P3HT) and narrow bandgap GaAs nanowires. The measured increase of device photocurrent with increased nanowire loading is correlated with structural ordering within the active layer that enhances charge transport. Coating the GaAs nanowires with TiO(x) shells passivates nanowire surface states and further improves the photovoltaic performance. We find that the P3HT/nanowire cells yield power conversion efficiencies of 2.36% under white LED illumination for devices containing 50 wt % of TiO(x)-coated GaAs nanowires. Our results constitute important progress for the use of nanowires in large area solution processed hybrid photovoltaic cells and provide insight into the role of structural ordering in the device performance.

Modeling of phase velocity and frequency spectrum of guided Lamb waves in piezoelectric-semiconductor multilayered structures made of AlAs and GaAs

NASA Astrophysics Data System (ADS)

Othmani, Cherif; Takali, Farid; Njeh, Anouar

2017-11-01

Modeling of guided Lamb waves propagation in piezoelectric-semiconductor multilayered structures made of AlAs and GaAs is evaluated in this paper. Here, the Legendre polynomial method is used to calculate dispersion curves, frequency spectrum and field distributions of guided Lamb waves propagation modes in AlAs, GaAs, AlAs/GaAs and AlAs/GaAs/AlAs-1/2/1 structures. In fact, formulations are given for open-circuit surface. Consequently, the polynomial method is numerically stable according to the total number of layers and the frequency range. This analysis is meaningful for the applications of the piezoelectric-semiconductor multilayered structures made of AlAs and GaAs such as in novel acoustic devices.

Doping assessment in GaAs nanowires.

PubMed

Goktas, N Isik; Fiordaliso, E M; LaPierre, R R

2018-06-08

Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p-n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs was studied. The GaAs NWs were grown on (111) Si by molecular beam epitaxy using the self-assisted method. The dopant incorporation in the self-assisted GaAs NWs was investigated using Raman spectroscopy, photoluminescence, secondary ion mass spectrometry and electron holography. Be-doped NWs showed similar carrier concentration as compared to thin film (TF) standards. However, Te-doped NWs showed at least a one order of magnitude lower carrier concentration as compared to TF standards. Dopant incorporation mechanisms in NWs are discussed.

GaAs quantum dots in a GaP nanowire photodetector

NASA Astrophysics Data System (ADS)

Kuyanov, P.; McNamee, S. A.; LaPierre, R. R.

2018-03-01

We report the structural, optical and electrical properties of GaAs quantum dots (QDs) embedded along GaP nanowires. The GaP nanowires contained p-i-n junctions with 15 consecutively grown GaAs QDs within the intrinsic region. The nanowires were grown by molecular beam epitaxy using the self-assisted vapor-liquid-solid process. The crystal structure of the NWs alternated between twinned ZB and WZ as the composition along the NW alternated between the GaP barriers and the GaAs QDs, respectively, leading to a polytypic structure with a periodic modulation of the NW sidewall facets. Photodetector devices containing QDs showed absorption beyond the bandgap of GaP in comparison to nanowires without QDs. Voltage-dependent measurements suggested a field emission process of carriers from the QDs.

Microwave GaAs Integrated Circuits On Quartz Substrates

NASA Technical Reports Server (NTRS)

Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

1994-01-01

Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

Effects of ultrathin oxides in conducting MIS structures on GaAs

NASA Technical Reports Server (NTRS)

Childs, R. B.; Ruths, J. M.; Sullivan, T. E.; Fonash, S. J.

1978-01-01

Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

Quantum-confinement effects on conduction band structure of rectangular cross-sectional GaAs nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanaka, H., E-mail: tanaka@semicon.kuee.kyoto-u.ac.jp; Morioka, N.; Mori, S.

2014-02-07

The conduction band structure and electron effective mass of GaAs nanowires with various cross-sectional shapes and orientations were calculated by two methods, a tight-binding method and an effective mass equation taking the bulk full-band structure into account. The effective mass of nanowires increases as the cross-sectional size decreases, and this increase in effective mass depends on the orientations and substrate faces of nanowires. Among [001], [110], and [111]-oriented rectangular cross-sectional GaAs nanowires, [110]-oriented nanowires with wider width along the [001] direction showed the lightest effective mass. This dependence originates from the anisotropy of the Γ valley of bulk GaAs. Themore » relationship between effective mass and bulk band structure is discussed.« less

Gettering of donor impurities by V in GaAs and the growth of semi-insulating crystals

NASA Technical Reports Server (NTRS)

Ko, K. Y.; Lagowski, J.; Gatos, H. C.

1989-01-01

Vanadium added to the GaAs melt getters shallow donor impurities (Si and S) and decreases their concentration in the grown crystals. This gettering is driven by chemical reactions in the melt rather than in the solid. Employing V gettering, reproducibly semi-insulating GaAs were grown by horizontal Bridgman and liquid-encapsulated Czochralski techniques, although V did not introduce any midgap energy levels. The compensation mechanism in these crystals was controlled by the balance between the native midgap donor EL2 and residual shallow acceptors. Vanadium gettering contributed to the reduction of the concentration of shallow donors below the concentration of acceptors. The present findings clarify the long-standing controversy on the role of V in achieving semi-insulating GaAs.

Nitride surface passivation of GaAs nanowires: impact on surface state density.

PubMed

Alekseev, Prokhor A; Dunaevskiy, Mikhail S; Ulin, Vladimir P; Lvova, Tatiana V; Filatov, Dmitriy O; Nezhdanov, Alexey V; Mashin, Aleksander I; Berkovits, Vladimir L

2015-01-14

Surface nitridation by hydrazine-sulfide solution, which is known to produce surface passivation of GaAs crystals, was applied to GaAs nanowires (NWs). We studied the effect of nitridation on conductivity and microphotoluminescence (μ-PL) of individual GaAs NWs using conductive atomic force microscopy (CAFM) and confocal luminescent microscopy (CLM), respectively. Nitridation is found to produce an essential increase in the NW conductivity and the μ-PL intensity as well evidence of surface passivation. Estimations show that the nitride passivation reduces the surface state density by a factor of 6, which is of the same order as that found for GaAs/AlGaAs nanowires. The effects of the nitride passivation are also stable under atmospheric ambient conditions for six months.

Doping assessment in GaAs nanowires

NASA Astrophysics Data System (ADS)

Isik Goktas, N.; Fiordaliso, E. M.; LaPierre, R. R.

2018-06-01

Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p–n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs was studied. The GaAs NWs were grown on (111) Si by molecular beam epitaxy using the self-assisted method. The dopant incorporation in the self-assisted GaAs NWs was investigated using Raman spectroscopy, photoluminescence, secondary ion mass spectrometry and electron holography. Be-doped NWs showed similar carrier concentration as compared to thin film (TF) standards. However, Te-doped NWs showed at least a one order of magnitude lower carrier concentration as compared to TF standards. Dopant incorporation mechanisms in NWs are discussed.

High-throughput screens in mammalian cells using the CRISPR-Cas9 system.

PubMed

Peng, Jingyu; Zhou, Yuexin; Zhu, Shiyou; Wei, Wensheng

2015-06-01

As a powerful genome-editing tool, the clustered regularly interspaced short palindromic repeats (CRISPR)-clustered regularly interspaced short palindromic repeats-associated protein 9 (Cas9) system has been quickly developed into a large-scale function-based screening strategy in mammalian cells. This new type of genetic library is constructed through the lentiviral delivery of single-guide RNA collections that direct Cas9 or inactive dead Cas9 fused with effectors to interrogate gene function or regulate gene transcription in targeted cells. Compared with RNA interference screening, the CRISPR-Cas9 system demonstrates much higher levels of effectiveness and reliability with respect to both loss-of-function and gain-of-function screening. Unlike the RNA interference strategy, a CRISPR-Cas9 library can target both protein-coding sequences and regulatory elements, including promoters, enhancers and elements transcribing microRNAs and long noncoding RNAs. This powerful genetic tool will undoubtedly accelerate the mechanistic discovery of various biological processes. In this mini review, we summarize the general procedure of CRISPR-Cas9 library mediated functional screening, system optimization strategies and applications of this new genetic toolkit. © 2015 FEBS.

Non-coding RNAs and Berberine: A new mechanism of its anti-diabetic activities.

PubMed

Chang, Wenguang

2017-01-15

Type 2 Diabetes (T2D) is a metabolic disease with high mortality and morbidity. Non-coding RNAs, including small and long non-coding RNAs, are a novel class of functional RNA molecules that regulate multiple biological functions through diverse mechanisms. Studies in the last decade have demonstrated that non-coding RNAs may represent compelling therapeutic targets and play important roles in regulating the course of insulin resistance and T2D. Berberine, a plant-based alkaloid, has shown promise as an anti-hyperglycaemic, anti-hyperlipidaemic agent against T2D. Previous studies have primarily focused on a diverse array of efficacy end points of berberine in the pathogenesis of metabolic syndromes and inflammation or oxidative stress. Currently, an increasing number of studies have revealed the importance of non-coding RNAs as regulators of the anti-diabetic effects of berberine. The regulation of non-coding RNAs has been associated with several therapeutic actions of berberine in T2D progression. Thus, this review summarizes the anti-diabetic mechanisms of berberine by focusing on its role in regulating non-coding RNA, thus demonstrating that berberine exerts global anti-diabetic effects by targeting non-coding RNAs and that these effects involve several miRNAs, lncRNAs and multiple signal pathways, which may enhance the current understanding of the anti-diabetic mechanism actions of berberine and provide new pathological targets for the development of berberine-related drugs. Copyright © 2016 Elsevier B.V. All rights reserved.

High energy proton radiation damage to (AlGa)As-G aAs solar cells

NASA Technical Reports Server (NTRS)

Loo, R.; Goldhammer, L.; Kamath, S.; Knechtli, R. C.

1979-01-01

Twelve 2 + 2 sq cm (AlGa)As-GaAs solar cells were fabricated and were subjected to 15.4 and 40 MeV of proton irradiation. The results showed that the GaAs cells degrade considerably less than do conventional and developmental K7 silicon cells. The detailed characteristics of the GaAs and silicon cells, both before and after irradiation, are described. Further optimization of the GaAs cells seems feasible, and areas for future work are suggested.

Large Signal Modeling and Analysis of the GaAs MESFET.

DTIC Science & Technology

1986-07-09

various dimensions and physical parameters. A powerful computer aided design system can be developed by automating the circuit element and parameter...circuit model of the GaAs MESFET to aid in the designs of microwave MESFET circuits. The circuit elements of this model are obtained either directly...34. -. ’ Abstract The purpose of this work is to develop a large signal signal lumped circuit model of the GaAs MESFET to aid In the designs of microwave MESFET

Ferromagnetic GaAs structures with single Mn delta-layer fabricated using laser deposition.

PubMed

Danilov, Yuri A; Vikhrova, Olga V; Kudrin, Alexey V; Zvonkov, Boris N

2012-06-01

The new technique combining metal-organic chemical vapor epitaxy with laser ablation of solid targets was used for fabrication of ferromagnetic GaAs structures with single Mn delta-doped layer. The structures demonstrated anomalous Hall effect, planar Hall effect, negative and anisotropic magnetoresistance in temperature range of 10-35 K. In GaAs structures with only single Mn delta-layer (without additional 2D hole gas channel or quantum well) ferromagnetism was observed for the first time.

Study of Carbon Nanotubes as Etching Masks and Related Applications in the Surface Modification of GaAs-based Light-Emitting Diodes.

PubMed

Jin, Yuanhao; Li, Qunqing; Chen, Mo; Li, Guanhong; Zhao, Yudan; Xiao, Xiaoyang; Wang, Jiaping; Jiang, Kaili; Fan, Shoushan

2015-09-02

The surface modification of LEDs based on GaAs is realized by super-aligned multiwalled carbon nanotube (SACNT) networks as etching masks. The surface morphology of SACNT networks is transferred to the GaAs. It is found that the light output power of LEDs based on GaAs with a nanostructured surface morphology is greatly enhanced with the electrical power unchanged. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

NASA Technical Reports Server (NTRS)

Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

1988-01-01

The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

Advanced GaAs Process Modeling. Volume 1

DTIC Science & Technology

1989-05-01

COSATI CODES 18 . SUBJECT TERMS (Continue on reverse if necessary and identify by block number) FIELD GROUP SUB-GROUP Gallium Arsenide, MESFET, Process...Background 9 3.2 Model Calculations 10 3.3 Conclusions 17 IV. ION-IMPLANTATION INTO GaAs PROFILE DETERMINATION 18 4.1 Ion Implantation Profile...Determination in GaAs 18 4.1.1. Background 18 4.1.2. Experimental Measurements 20 4.1.3. Results 22 4.1.3.1 Ion-Energy Dependence 22 4.1.3.2. Tilt and Rotation

GaAsP Top Solar Cells for Increased Solar Conversion Efficiency

DTIC Science & Technology

1989-01-01

responsible for high surface recombination in devices made from that material. Inorganic sulfide films have been used on GaAs to reduce surface recom...same time, Hamaker et al [2] demonstrated less radiation damage in 1.93 eV AlGaAs solar cells than GaAs counterparts. In very recent results on...material. Yablonovitch and coworkers [25] have used inorganic sulfide films on GaAs to reduce surface recombination rates to that of the nearly ideal AlGaAs

The circulating transcriptome as a source of non-invasive cancer biomarkers: concepts and controversies of non-coding and coding RNA in body fluids

PubMed Central

Fernandez-Mercado, Marta; Manterola, Lorea; Larrea, Erika; Goicoechea, Ibai; Arestin, María; Armesto, María; Otaegui, David; Lawrie, Charles H

2015-01-01

The gold standard for cancer diagnosis remains the histological examination of affected tissue, obtained either by surgical excision, or radiologically guided biopsy. Such procedures however are expensive, not without risk to the patient, and require consistent evaluation by expert pathologists. Consequently, the search for non-invasive tools for the diagnosis and management of cancer has led to great interest in the field of circulating nucleic acids in plasma and serum. An additional benefit of blood-based testing is the ability to carry out screening and repeat sampling on patients undergoing therapy, or monitoring disease progression allowing for the development of a personalized approach to cancer patient management. Despite having been discovered over 60 years ago, the clear clinical potential of circulating nucleic acids, with the notable exception of prenatal diagnostic testing, has yet to translate into the clinic. The recent discovery of non-coding (nc) RNA (in particular micro(mi)RNAs) in the blood has provided fresh impetuous for the field. In this review, we discuss the potential of the circulating transcriptome (coding and ncRNA), as novel cancer biomarkers, the controversy surrounding their origin and biology, and most importantly the hurdles that remain to be overcome if they are really to become part of future clinical practice. PMID:26119132

cDNA cloning of the human peroxisomal enoyl-CoA hydratase: 3-Hydroxyacyl-CoA dehydrogenase bifunctional enzyme and localization to chromosome 3q26. 3-3q28: A free left Alu arm is inserted in the 3[prime] noncoding region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoefler, G.; Forstner, M.; Hulla, W.

1994-01-01

Enoyl-CoA hydratase:3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme is one of the four enzymes of the peroxisomal, [beta]-oxidation pathway. Here, the authors report the full-length human cDNA sequence and the localization of the corresponding gene on chromosome 3q26.3-3q28. The cDNA sequence spans 3779 nucleotides with an open reading frame of 2169 nucleotides. The tripeptide SKL at the carboxy terminus, known to serve as a peroxisomal targeting signal, is present. DNA sequence comparison of the coding region showed an 80% homology between human and rat bifunctional enzyme cDNA. The 3[prime] noncoding sequence contains 117 nucleotides homologous to an Alu repeat. Based on sequence comparison,more » they propose that these nucleotides are a free left Alu arm with 86% homology to the Alu-J family. RNA analysis shows one band with highest intensity in liver and kidney. This cDNA will allow in-depth studies of molecular defects in patients with defective peroxisomal bifunctional enzyme. Moreover, it will also provide a means for studying the regulation of peroxisomal [beta]-oxidation in humans. 33 refs., 5 figs.« less

A family of long intergenic non-coding RNA genes in human chromosomal region 22q11.2 carry a DNA translocation breakpoint/AT-rich sequence

PubMed Central

2018-01-01

FAM230C, a long intergenic non-coding RNA (lincRNA) gene in human chromosome 13 (chr13) is a member of lincRNA genes termed family with sequence similarity 230. An analysis using bioinformatics search tools and alignment programs was undertaken to determine properties of FAM230C and its related genes. Results reveal that the DNA translocation element, the Translocation Breakpoint Type A (TBTA) sequence, which consists of satellite DNA, Alu elements, and AT-rich sequences is embedded in the FAM230C gene. Eight lincRNA genes related to FAM230C also carry the TBTA sequences. These genes were formed from a large segment of the 3’ half of the FAM230C sequence duplicated in chr22, and are specifically in regions of low copy repeats (LCR22)s, in or close to the 22q.11.2 region. 22q11.2 is a chromosomal segment that undergoes a high rate of DNA translocation and is prone to genetic deletions. FAM230C-related genes present in other chromosomes do not carry the TBTA motif and were formed from the 5’ half region of the FAM230C sequence. These findings identify a high specificity in lincRNA gene formation by gene sequence duplication in different chromosomes. PMID:29668722

Activity of the Rhodopseudomonas palustris p-coumaroyl-homoserine lactone-responsive transcription factor RpaR.

PubMed

Hirakawa, Hidetada; Oda, Yasuhiro; Phattarasukol, Somsak; Armour, Christopher D; Castle, John C; Raymond, Christopher K; Lappala, Colin R; Schaefer, Amy L; Harwood, Caroline S; Greenberg, E Peter

2011-05-01

The Rhodopseudomonas palustris transcriptional regulator RpaR responds to the RpaI-synthesized quorum-sensing signal p-coumaroyl-homoserine lactone (pC-HSL). Other characterized RpaR homologs respond to fatty acyl-HSLs. We show here that RpaR functions as a transcriptional activator, which binds directly to the rpaI promoter. We developed an RNAseq method that does not require a ribosome depletion step to define a set of transcripts regulated by pC-HSL and RpaR. The transcripts include several noncoding RNAs. A footprint analysis showed that purified His-tagged RpaR (His(6)-RpaR) binds to an inverted repeat element centered 48.5 bp upstream of the rpaI transcript start site, which we mapped by S1 nuclease protection and primer extension analyses. Although pC-HSL-RpaR bound to rpaI promoter DNA, it did not bind to the promoter regions of a number of RpaR-regulated genes not in the rpaI operon. This indicates that RpaR control of these other genes is indirect. Because the RNAseq analysis allowed us to track transcript strand specificity, we discovered that there is pC-HSL-RpaR-activated antisense transcription of rpaR. These data raise the possibility that this antisense RNA or other RpaR-activated noncoding RNAs mediate the indirect activation of genes in the RpaR-controlled regulon.

Mining and gene ontology based annotation of SSR markers from expressed sequence tags of Humulus lupulus

PubMed Central

Singh, Swati; Gupta, Sanchita; Mani, Ashutosh; Chaturvedi, Anoop

2012-01-01

Humulus lupulus is commonly known as hops, a member of the family moraceae. Currently many projects are underway leading to the accumulation of voluminous genomic and expressed sequence tag sequences in public databases. The genetically characterized domains in these databases are limited due to non-availability of reliable molecular markers. The large data of EST sequences are available in hops. The simple sequence repeat markers extracted from EST data are used as molecular markers for genetic characterization, in the present study. 25,495 EST sequences were examined and assembled to get full-length sequences. Maximum frequency distribution was shown by mononucleotide SSR motifs i.e. 60.44% in contig and 62.16% in singleton where as minimum frequency are observed for hexanucleotide SSR in contig (0.09%) and pentanucleotide SSR in singletons (0.12%). Maximum trinucleotide motifs code for Glutamic acid (GAA) while AT/TA were the most frequent repeat of dinucleotide SSRs. Flanking primer pairs were designed in-silico for the SSR containing sequences. Functional categorization of SSRs containing sequences was done through gene ontology terms like biological process, cellular component and molecular function. PMID:22368382

[Myotonic dystrophies: clinical presentation, pathogenesis, diagnostics and therapy].

PubMed

Finsterer, Josef; Rudnik-Schöneborn, S

2015-01-01

The autosomal-dominant myotonic dystrophies dystrophia myotonica type-1 (DM1, Curschmann-Steinert disease) and dystrophia myotonica type-2 (DM2, proximal myotonic myopathy (PROMM)), are, contrary to the non-dystrophic myotonias, progressive multisystem disorders. DM1 and DM2 are the most frequent of the muscular dystrophies. In both diseases the skeletal muscle is the most severely affected organ (weakness, wasting, myotonia, myalgia). Additionally, they manifest in the eye, heart, brain, endocrine glands, gastrointestinal tract, skin, skeleton, and peripheral nerves. Phenotypes of DM1 may be classified as congenital, juvenile, classical, or late onset. DM2 is a disorder of the middle or older age and usually has a milder course compared to DM1. DM1 is due to a CTG-repeat expansion > 50 repeats in the non-coding 3' UTR of the DMPK-gene. DM2 is caused by a CCTG-repeat expansion to 75 - 11 000 repeats in intron-1 of the CNBP/ZNF9 gene. Mutant pre-mRNAs of both genes aggregate within the nucleus (nuclear foci), which sequester RNA-binding proteins and result in an abnormal protein expression via alternative splicing in downstream effector genes (toxic RNA diseases). Other mechanisms seem to play an additional pathogenetic role. Clinical severity of DM1 increases from generation to generation (anticipation). The higher the repeat expansion the more severe the DM1 phenotype. In DM2 severity of symptoms and age at onset do not correlate with the expansion size. Contrary to DM2, there is a congenital form and anticipation in DM1. © Georg Thieme Verlag KG Stuttgart · New York.

Analysis of Two Cosmid Clones from Chromosome 4 of Drosophila melanogaster Reveals Two New Genes Amid an Unusual Arrangement of Repeated Sequences

PubMed Central

Locke, John; Podemski, Lynn; Roy, Ken; Pilgrim, David; Hodgetts, Ross

1999-01-01

Chromosome 4 from Drosophila melanogaster has several unusual features that distinguish it from the other chromosomes. These include a diffuse appearance in salivary gland polytene chromosomes, an absence of recombination, and the variegated expression of P-element transgenes. As part of a larger project to understand these properties, we are assembling a physical map of this chromosome. Here we report the sequence of two cosmids representing ∼5% of the polytenized region. Both cosmid clones contain numerous repeated DNA sequences, as identified by cross hybridization with labeled genomic DNA, BLAST searches, and dot matrix analysis, which are positioned between and within the transcribed sequences. The repetitive sequences include three copies of the mobile element Hoppel, one copy of the mobile element HB, and 18 DINE repeats. DINE is a novel, short repeated sequence dispersed throughout both cosmid sequences. One cosmid includes the previously described cubitus interruptus (ci) gene and two new genes: that a gene with a predicted amino acid sequence similar to ribosomal protein S3a which is consistent with the Minute(4)101 locus thought to be in the region, and a novel member of the protein family that includes plexin and met–hepatocyte growth factor receptor. The other cosmid contains only the two short 5′-most exons from the zinc-finger-homolog-2 (zfh-2) gene. This is the first extensive sequence analysis of noncoding DNA from chromosome 4. The distribution of the various repeats suggests its organization is similar to the β-heterochromatic regions near the base of the major chromosome arms. Such a pattern may account for the diffuse banding of the polytene chromosome 4 and the variegation of many P-element transgenes on the chromosome. PMID:10022978

The ZnSe(110) puzzle - Comparison with GaAs(110)

NASA Technical Reports Server (NTRS)

Duke, C. B.; Paton, A.; Kahn, A.; Tu, D.-W.

1984-01-01

The surface structure of monocrystalline ZnSe(110) and of 4-5-nm-thick ZnSe(110) layers epitaxially grown on GaAs(110) is investigated by means of elastic LEED and AES; the results are analyzed using the computer programs and R-factor methods of Duke et al. (1981 and 1983), presented in graphs and tables, and compared to those for GaAs(110). Significant differences are attributed to bond-length-conserving outward rotation of Se and inward rotation of Zn in the top layer, with an angle of 4 deg between the actual plane of the cation-anion chain and the truncated bulk surface. The R intensities measured for ZnSe(110) and GaAs(110) are given as Rx = 0.22 and RI = 0.21 and Rx = 0.24 and RI = 0.16, respectively.

Multi-shell spherical GaAs /AlxGa1-x As quantum dot shells-size distribution as a mechanism to generate intermediate band energy levels

NASA Astrophysics Data System (ADS)

Rodríguez-Magdaleno, K. A.; Pérez-Álvarez, R.; Martínez-Orozco, J. C.; Pernas-Salomón, R.

2017-04-01

In this work the generation of an intermediate band of energy levels from multi-shell spherical GaAs /AlxGa1-x As quantum dot shells-size distribution is reported. Within the effective mass approximation the electronic structure of a GaAs spherical quantum-dot surrounded by one, two and three shells is studied in detail using a numerically stable transfer matrix method. We found that a shells-size distribution characterized by continuously wider GaAs domains is a suitable mechanism to generate the intermediate band whose width is also dependent on the Aluminium concentration x. Our results suggest that this effective mechanism can be used for the design of wider intermediate band than reported in other quantum systems with possible solar cells enhanced performance.

Growth studies at bulk III-Vs by image processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donecker, J.; Hempel, G.; Kluge, J.

1996-12-01

The patterns of inhomogeneities in GaAs and InP are studied by scattering and diffraction of light. An adapted version of laser scattering tomography is used for observations with short exposure times and large fields. The information about the three-dimensional distribution of the scatterers in GaAs are evaluated by video travels through the crystal and images of intensities added in interesting directions. Near-infrared transmission and striation distance mapping act like special data compression techniques due to their optical principles. In general, columnar extension of cellular patterns and striations could not be detected in s.i. GaAs. Long-range correlations exist for lineages andmore » slip lines. The comparison with the behavior of striations in doped InP cannot confirm the idea that cellular patterns in GaAs originate from constitutional supercooling during solidification.« less

InGaN working electrodes with assisted bias generated from GaAs solar cells for efficient water splitting.

PubMed

Liu, Shu-Yen; Sheu, J K; Lin, Yu-Chuan; Chen, Yu-Tong; Tu, S J; Lee, M L; Lai, W C

2013-11-04

Hydrogen generation through water splitting by n-InGaN working electrodes with bias generated from GaAs solar cell was studied. Instead of using an external bias provided by power supply, a GaAs-based solar cell was used as the driving force to increase the rate of hydrogen production. The water-splitting system was tuned using different approaches to set the operating points to the maximum power point of the GaAs solar cell. The approaches included changing the electrolytes, varying the light intensity, and introducing the immersed ITO ohmic contacts on the working electrodes. As a result, the hybrid system comprising both InGaN-based working electrodes and GaAs solar cells operating under concentrated illumination could possibly facilitate efficient water splitting.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baidus, N. V.; Kukushkin, V. A., E-mail: vakuk@appl.sci-nnov.ru; Zvonkov, B. N.

As a result of theoretical and experimental analyses, the parameters of heterostructures with InAs quantum dots in a GaAs matrix are determined, which provide the development of high-speed and efficient plasmon-polariton near-infrared light-emitting Schottky diodes based on such structures. The quantum dots should be arranged on a heavily doped (to a dopant concentration of 10{sup 19} cm{sup –3}) GaAs buffer layer and be separated from the metal by a thin (10–30 nm thick) undoped GaAs cap layer. The interface between the metal (e.g., gold) and GaAs provides the efficient scattering of surface plasmon-polaritons to ordinary photons if it contains inhomogeneitiesmore » shaped as metal-filled cavities with a characteristic size of ~30 nm and a surface concentration above 10{sup 10} cm{sup –2}.« less

Progress toward thin-film GaAs solar cells using a single-crystal Si substrate with a Ge interlayer

NASA Technical Reports Server (NTRS)

Yeh, Y. C. M.; Wang, K. L.; Zwerdling, S.

1982-01-01

Development of a technology for fabricating light-weight, high-efficiency, radiation-resistant solar cells for space applications is reported. The approaches currently adopted are to fabricate shallow homojunction n(+)/p as well as p/n AlGaAs-heteroface GaAs solar cells by organometallic chemical vapor deposition (OM-CVD) on single-crystal Si substrates using in each case, a thin Ge epi-interlayer first grown by CVD. This approach maintains the advantages of the low specific gravity of Si as well as the high efficiency and radiation-resistant properties of the GaAs solar cell which can lead to greatly improved specific power for a solar array. The growth of single-crystal GaAs epilayers on Ge epi-interlayers on Si substrates is investigated. Related solar cell fabrication is reviewed.

The 20 GHz spacecraft FET solid state transmitter

NASA Technical Reports Server (NTRS)

1983-01-01

The engineering development of a solid state transmitter amplifier operating in the 20 GHz frequency band using GaAs field effect transistors (FETs) was detailed. The major efforts include GaAs FET device development, single-ended amplifier stage, balanced amplifier stage, cascaded stage and radial combiner designs, and amplifier integration and test. A multistage GaAs FET amplifier capable of 8.2 W CW output over the 17.9 to 19.1 GHz frequency band was developed. The GaAs FET devices developed represent state of the art FET power device technology. Further device improvements are necessary to increase the bandwidth to 2.5 GHz, improve dc-to-RF efficiency, and increase power capability at the device level. Higher power devices will simplify the amplifier combining scheme, reducing the size and weight of the overall amplifier.

Structural and electronic properties of isovalent boron atoms in GaAs

NASA Astrophysics Data System (ADS)

Krammel, C. M.; Nattermann, L.; Sterzer, E.; Volz, K.; Koenraad, P. M.

2018-04-01

Boron containing GaAs, which is grown by metal organic vapour phase epitaxy, is studied at the atomic level by cross-sectional scanning tunneling microscopy (X-STM) and spectroscopy (STS). In topographic X-STM images, three classes of B related features are identified, which are attributed to individual B atoms on substitutional Ga sites down to the second layer below the natural {110} cleavage planes. The X-STM contrast of B atoms below the surface reflects primarily the structural modification of the GaAs matrix by the small B atoms. However, B atoms in the cleavage plane have in contrast to conventional isovalent impurities, such as Al and In, a strong influence on the local electronic structure similar to donors or acceptors. STS measurements show that B in the GaAs {110} surfaces gives rise to a localized state short below the conduction band (CB) edge while in bulk GaAs, the B impurity state is resonant with the CB. The analysis of BxGa1-xAs/GaAs quantum wells reveals a good crystal quality and shows that the incorporation of B atoms in GaAs can be controlled along the [001] growth direction at the atomic level. Surprisingly, the formation of the first and fourth nearest neighbor B pairs, which are oriented along the <110 > directions, is strongly suppressed at a B concentration of 1% while the third nearest neighbor B pairs are found more than twice as often than expected for a completely spatially random pattern.

Photo-recovery of electron-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Meulenberg, Andrew

1995-01-01

The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has produced some unexpected and important results. Two results, independent of the coverslide coatings, are of particular importance in terms of the predictability of GaAs solar-array lifetime in space: ( 1) The GaAs/Ge solar cells used for this series of tests displayed a much higher radiation degradation than that predicted based on JPL Solar Cell Radiation Handbook data. Covered cells degraded more in Isc than did bare cells. Short-term illumination at 60 C did not produce significant recovery (-1%) of the radiation damage. (2) However, electron radiation damage to these GaAs solar celIs anneals at 40 C when exposed to approximately 1 sun AM0 UV light sources for extended periods. The effect appears to be roughly linear with time (-1% of lsc per 1000 UVSH), is large (greater than or equal to 3%), and has not yet saturated (at 3000 hours). This photo-recovery of radiation damage to GaAs solar cells is a new effect and potentially important to the spacecraft community. The figure compares the effects of extended UV on irradiated and unirradiated GaAs solar cells with INTELSAT-6 Si cells. The effect and its generality, the extent of and conditions for photo-recovery, and the implications of such recovery for missions in radiation environments have not yet been determined.

Ab initio-based approach to structural change of compound semiconductor surfaces during MBE growth

NASA Astrophysics Data System (ADS)

Ito, Tomonori; Akiyama, Toru; Nakamura, Kohji

2009-01-01

Phase diagrams of GaAs and GaN surfaces are systematically investigated by using our ab initio-based approach in conjunction with molecular beam epitaxy (MBE). The phase diagrams are obtained as a function of growth parameters such as temperature and beam equivalent pressure (BEP). The versatility of our approach is exemplified by the phase diagram calculations for GaAs(0 0 1) surfaces, where the stable phases and those phase boundaries are successfully determined as functions of temperature and As 2 and As 4 BEPs. The initial growth processes are clarified by the phase diagram calculations for GaAs(1 1 1)B-(2×2). The calculated results demonstrate that the As-trimer desorption on the GaAs(1 1 1)B-(2×2) with Ga adatoms occurs beyond 500-700 K while the desorption without Ga adatoms does beyond 800-1000 K. This self-surfactant effect induced by Ga adsorption crucially affects the initial growth of GaAs on the GaAs(1 1 1)B-(2×2). Furthermore, the phase diagram calculations for GaN(0 0 0 1) suggests that Ga adsorption or desorption during GaN MBE growth can easily change the pseudo-(1×1) to the (2×2)-Ga via newly found (1×1) and vice versa. On the basis of this finding, the possibility of ghost island formation during MBE growth is discussed.

Reduction of Myeloid-derived Suppressor Cells and Lymphoma Growth by a Natural Triterpenoid

PubMed Central

Radwan, Faisal F. Y.; Hossain, Azim; God, Jason M.; Leaphart, Nathan; Elvington, Michelle; Nagarkatti, Mitzi; Tomlinson, Stephen; Haque, Azizul

2016-01-01

Lymphoma is a potentially life threatening disease. The goal of this study was to investigate the therapeutic potential of a natural triterpenoid, Ganoderic acid A (GA-A) in controlling lymphoma growth both in vitro and in vivo. Here, we show that GA-A treatment induces caspase-dependent apoptotic cell death characterized by a dose-dependent increase in active caspases 9 and 3, up-regulation of pro-apoptotic BIM and BAX proteins, and a subsequent loss of mitochondrial membrane potential with release of cytochrome c. In addition to GA-A’s anti-growth activity, we show that lower doses of GA-A enhance HLA class II-mediated antigen presentation and CD4+ T cell recognition of lymphoma in vitro. The therapeutic relevance of GA-A treatment was also tested in vivo using the EL4 syngeneic mouse model of metastatic lymphoma. GA-A-treatment significantly prolonged survival of EL4 challenged mice and decreased tumor metastasis to the liver, an outcome accompanied by a marked down-regulation of STAT3 phosphorylation, reduction myeloid-derived suppressor cells (MDSCs), and enhancement of cytotoxic CD8+ T cells in the host. Thus, GA-A not only selectively induces apoptosis in lymphoma cells, but also enhances cell-mediated immune responses by attenuating MDSCs, and elevating Ag presentation and T cell recognition. The demonstrated therapeutic benefit indicates that GA-A is a candidate for future drug design for the treatment of lymphoma. PMID:25142864

Bacterial Expression of a Single-Chain Variable Fragment (scFv) Antibody against Ganoderic Acid A: A Cost-Effective Approach for Quantitative Analysis Using the scFv-Based Enzyme-Linked Immunosorbent Assay.

PubMed

Yusakul, Gorawit; Nuntawong, Poomraphie; Sakamoto, Seiichi; Ratnatilaka Na Bhuket, Pahweenvaj; Kohno, Toshitaka; Kikkawa, Nao; Rojsitthisak, Pornchai; Shimizu, Kuniyoshi; Tanaka, Hiroyuki; Morimoto, Satoshi

2017-01-01

Due to the highly specific binding between an antibody and its target, superior analytical performances was obtained by immunoassays for phytochemical analysis over conventional chromatographic techniques. Here, we describe a simple method for producing a functional single-chain variable fragment (scFv) antibody against ganoderic acid A (GAA), a pharmacologically active metabolite from Ganoderma lingzhi. The Escherichia coli BL21(DE3) strain produced a large amount of anti-GAA scFv. However, in vitro refolding steps, which partially recovered the reactivity of the scFv, were required. Interestingly, the functional scFv was expressed as a soluble and active form in the cytoplasm of an engineered E. coli SHuffle ® strain. Purified anti-GAA scFv, which yielded 2.56 mg from 1 L of culture medium, was obtained from simple and inexpensive procedures for expression and purification. The anti-GAA scFv-based indirect competitive enzyme-linked immunosorbent assay (icELISA) exhibited high sensitivity (linearity: 0.078-1.25 µg/mL) with precision (CV: ≤6.20%) and reliability (recovery: 100.1-101.8%) for GAA determination. In summary, the approach described here is an inexpensive, simple, and efficient expression system that extends the application of anti-GAA scFv-based immunoassays. In addition, when in vitro refolding steps can be skipped, the cost and complexity of scFv antibody production can be minimized.

Heavy Chronic Intermittent Ethanol Exposure Alters Small Noncoding RNAs in Mouse Sperm and Epididymosomes.

PubMed

Rompala, Gregory R; Mounier, Anais; Wolfe, Cody M; Lin, Qishan; Lefterov, Iliya; Homanics, Gregg E

2018-01-01

While the risks of maternal alcohol abuse during pregnancy are well-established, several preclinical studies suggest that chronic preconception alcohol consumption by either parent may also have significance consequences for offspring health and development. Notably, since isogenic male mice used in these studies are not involved in gestation or rearing of offspring, the cross-generational effects of paternal alcohol exposure suggest a germline-based epigenetic mechanism. Many recent studies have demonstrated that the effects of paternal environmental exposures such as stress or malnutrition can be transmitted to the next generation via alterations to small noncoding RNAs in sperm. Therefore, we used high throughput sequencing to examine the effect of preconception ethanol on small noncoding RNAs in sperm. We found that chronic intermittent ethanol exposure altered several small noncoding RNAs from three of the major small RNA classes in sperm, tRNA-derived small RNA (tDR), mitochondrial small RNA, and microRNA. Six of the ethanol-responsive small noncoding RNAs were evaluated with RT-qPCR on a separate cohort of mice and five of the six were confirmed to be altered by chronic ethanol exposure, supporting the validity of the sequencing results. In addition to altered sperm RNA abundance, chronic ethanol exposure affected post-transcriptional modifications to sperm small noncoding RNAs, increasing two nucleoside modifications previously identified in mitochondrial tRNA. Furthermore, we found that chronic ethanol reduced epididymal expression of a tRNA methyltransferase, Nsun2 , known to directly regulate tDR biogenesis. Finally, ethanol-responsive sperm tDR are similarly altered in extracellular vesicles of the epididymis (i.e., epididymosomes), supporting the hypothesis that alterations to sperm tDR emerge in the epididymis and that epididymosomes are the primary source of small noncoding RNAs in sperm. These results add chronic ethanol to the growing list of paternal exposures that can affect small noncoding RNA abundance and nucleoside modifications in sperm. As small noncoding RNAs in sperm have been shown to causally induce heritable phenotypes in offspring, additional research is warranted to understand the potential effects of ethanol-responsive sperm small noncoding RNAs on offspring health and development.

Heavy Chronic Intermittent Ethanol Exposure Alters Small Noncoding RNAs in Mouse Sperm and Epididymosomes

PubMed Central

Rompala, Gregory R.; Mounier, Anais; Wolfe, Cody M.; Lin, Qishan; Lefterov, Iliya; Homanics, Gregg E.

2018-01-01

While the risks of maternal alcohol abuse during pregnancy are well-established, several preclinical studies suggest that chronic preconception alcohol consumption by either parent may also have significance consequences for offspring health and development. Notably, since isogenic male mice used in these studies are not involved in gestation or rearing of offspring, the cross-generational effects of paternal alcohol exposure suggest a germline-based epigenetic mechanism. Many recent studies have demonstrated that the effects of paternal environmental exposures such as stress or malnutrition can be transmitted to the next generation via alterations to small noncoding RNAs in sperm. Therefore, we used high throughput sequencing to examine the effect of preconception ethanol on small noncoding RNAs in sperm. We found that chronic intermittent ethanol exposure altered several small noncoding RNAs from three of the major small RNA classes in sperm, tRNA-derived small RNA (tDR), mitochondrial small RNA, and microRNA. Six of the ethanol-responsive small noncoding RNAs were evaluated with RT-qPCR on a separate cohort of mice and five of the six were confirmed to be altered by chronic ethanol exposure, supporting the validity of the sequencing results. In addition to altered sperm RNA abundance, chronic ethanol exposure affected post-transcriptional modifications to sperm small noncoding RNAs, increasing two nucleoside modifications previously identified in mitochondrial tRNA. Furthermore, we found that chronic ethanol reduced epididymal expression of a tRNA methyltransferase, Nsun2, known to directly regulate tDR biogenesis. Finally, ethanol-responsive sperm tDR are similarly altered in extracellular vesicles of the epididymis (i.e., epididymosomes), supporting the hypothesis that alterations to sperm tDR emerge in the epididymis and that epididymosomes are the primary source of small noncoding RNAs in sperm. These results add chronic ethanol to the growing list of paternal exposures that can affect small noncoding RNA abundance and nucleoside modifications in sperm. As small noncoding RNAs in sperm have been shown to causally induce heritable phenotypes in offspring, additional research is warranted to understand the potential effects of ethanol-responsive sperm small noncoding RNAs on offspring health and development. PMID:29472946

Identification and Functional Prediction of Large Intergenic Noncoding RNAs (lincRNAs) in Rainbow Trout (Oncorhynchus mykiss)

USDA-ARS?s Scientific Manuscript database

Long noncoding RNAs (lncRNAs) have been recognized in recent years as key regulators of diverse cellular processes. Genome-wide large-scale projects have uncovered thousands of lncRNAs in many model organisms. Large intergenic noncoding RNAs (lincRNAs) are lncRNAs that are transcribed from intergeni...

Role of non-coding RNAs in non-aging-related neurological disorders.

PubMed

Vieira, A S; Dogini, D B; Lopes-Cendes, I

2018-06-11

Protein coding sequences represent only 2% of the human genome. Recent advances have demonstrated that a significant portion of the genome is actively transcribed as non-coding RNA molecules. These non-coding RNAs are emerging as key players in the regulation of biological processes, and act as "fine-tuners" of gene expression. Neurological disorders are caused by a wide range of genetic mutations, epigenetic and environmental factors, and the exact pathophysiology of many of these conditions is still unknown. It is currently recognized that dysregulations in the expression of non-coding RNAs are present in many neurological disorders and may be relevant in the mechanisms leading to disease. In addition, circulating non-coding RNAs are emerging as potential biomarkers with great potential impact in clinical practice. In this review, we discuss mainly the role of microRNAs and long non-coding RNAs in several neurological disorders, such as epilepsy, Huntington disease, fragile X-associated ataxia, spinocerebellar ataxias, amyotrophic lateral sclerosis (ALS), and pain. In addition, we give information about the conditions where microRNAs have demonstrated to be potential biomarkers such as in epilepsy, pain, and ALS.

Statistical properties of DNA sequences

NASA Technical Reports Server (NTRS)

Peng, C. K.; Buldyrev, S. V.; Goldberger, A. L.; Havlin, S.; Mantegna, R. N.; Simons, M.; Stanley, H. E.

1995-01-01

We review evidence supporting the idea that the DNA sequence in genes containing non-coding regions is correlated, and that the correlation is remarkably long range--indeed, nucleotides thousands of base pairs distant are correlated. We do not find such a long-range correlation in the coding regions of the gene. We resolve the problem of the "non-stationarity" feature of the sequence of base pairs by applying a new algorithm called detrended fluctuation analysis (DFA). We address the claim of Voss that there is no difference in the statistical properties of coding and non-coding regions of DNA by systematically applying the DFA algorithm, as well as standard FFT analysis, to every DNA sequence (33301 coding and 29453 non-coding) in the entire GenBank database. Finally, we describe briefly some recent work showing that the non-coding sequences have certain statistical features in common with natural and artificial languages. Specifically, we adapt to DNA the Zipf approach to analyzing linguistic texts. These statistical properties of non-coding sequences support the possibility that non-coding regions of DNA may carry biological information.

The expanding universe of noncoding RNAs.

PubMed

Hannon, G J; Rivas, F V; Murchison, E P; Steitz, J A

2006-01-01

The 71st Cold Spring Harbor Symposium on Quantitative Biology celebrated the numerous and expanding roles of regulatory RNAs in systems ranging from bacteria to mammals. It was clearly evident that noncoding RNAs are undergoing a renaissance, with reports of their involvement in nearly every cellular process. Previously known classes of longer noncoding RNAs were shown to function by every possible means-acting catalytically, sensing physiological states through adoption of complex secondary and tertiary structures, or using their primary sequences for recognition of target sites. The many recently discovered classes of small noncoding RNAs, generally less than 35 nucleotides in length, most often exert their effects by guiding regulatory complexes to targets via base-pairing. With the ability to analyze the RNA products of the genome in ever greater depth, it has become clear that the universe of noncoding RNAs may extend far beyond the boundaries we had previously imagined. Thus, as much as the Symposium highlighted exciting progress in the field, it also revealed how much farther we must go to understand fully the biological impact of noncoding RNAs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bagraev, N. T., E-mail: Bagraev@mail.ioffe.ru; Chaikina, E. I.; Danilovskii, E. Yu.

The sulfur passivation of the semi-insulating GaAs bulk (SI GaAs) grown in an excess phase of arsenic is used to observe the transition from the Coulomb blockade to the weak localization regime at room temperature. The I–V characteristics of the SI GaAs device reveal nonlinear behavior that appears to be evidence of the Coulomb blockade process as well as the Coulomb oscillations. The sulfur passivation of the SI GaAs device surface results in enormous transformation of the I–V characteristics that demonstrate the strong increase of the resistance and Coulomb blockade regime is replaced by the electron tunneling processes. The resultsmore » obtained are analyzed within frameworks of disordering SI GaAs surface that is caused by inhomogeneous distribution of the donor and acceptor anti-site defects which affects the conditions of quantum- mechanical tunneling. Weak localization processes caused by the preservation of the Fermi level pinning are demonstrated by measuring the negative magnetoresistance in weak magnetic fields at room temperature. Finally, the studies of the magnetoresistance at higher magnetic fields reveal the h/2e Aharonov–Altshuler–Spivak oscillations with the complicated behavior due to possible statistical mismatch of the interference paths in the presence of different microdefects.« less

GaAs Photovoltaics on Polycrystalline Ge Substrates

NASA Technical Reports Server (NTRS)

Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

2007-01-01

High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

Raman scattering studies of strain effects in (100) and (311)B GaAs1-xBix epitaxial layers

NASA Astrophysics Data System (ADS)

Steele, J. A.; Lewis, R. A.; Henini, M.; Lemine, O. M.; Alkaoud, A.

2013-11-01

We report room-temperature Raman studies of strained (100) and (311)B GaAs1-xBix epitaxial layers for x ≤ 0.039. The Raman spectra exhibit a two-mode behavior, as well as disorder-activated GaAs-like phonons. The experimental results show that the GaAs-like LO(Γ) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs (˜293 cm-1) with the alloyed Bi fraction x and the introduced in-plane lattice strain ɛ∥, by ΔωLO=Δωalloy-Δωstrain. X-ray diffraction measurements are used to determine x and ɛ∥ allowing Δωalloy to be decoupled and is estimated to be -12(±4) cm-1/x for (100) GaAs1-xBix. ΔωLO is measured to be roughly double for samples grown on (311)B-oriented substrates to that of (100) GaAs. This large difference in redshift is accounted for by examining the Bi induced strain, effects from alloying, and defects formed during high-index (311)B crystal growth.

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions

NASA Astrophysics Data System (ADS)

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-01

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

Effects of doping impurity and growth orientation on dislocation generation in GaAs crystals grown from the melt: A qualitative finite-element study

NASA Astrophysics Data System (ADS)

Zhu, X. A.; Tsai, C. T.

2000-09-01

Dislocations in gallium arsenide (GaAs) crystals are generated by excessive thermal stresses induced during the crystal growth process. The presence of dislocations has adverse effects on the performance and reliability of the GaAs-based devices. It is well known that dislocation density can be significantly reduced by doping impurity atoms into a GaAs crystal during its growth process. A viscoplastic constitutive equation that couples the microscopic dislocation density with the macroscopic plastic deformation is employed in a crystallographic finite element model for calculating the dislocation density generated in the GaAs crystal during its growth process. The dislocation density is considered as an internal state variable and the drag stress caused by doping impurity is included in this constitutive equation. A GaAs crystal grown by the vertical Bridgman process is adopted as an example to study the influences of doping impurity and growth orientation on dislocation generation. The calculated results show that doping impurity can significantly reduce the dislocation density generated in the crystal. The level of reduction is also influenced by the growth orientation during the crystal growth process.

Core-level photoemission investigation of atomic-fluorine adsorption on GaAs(110)

NASA Astrophysics Data System (ADS)

McLean, A. B.; Terminello, L. J.; McFeely, F. R.

1989-12-01

The adsorption of atomic F on the cleaved GaAs(110) surface has been studied with use of high-resolution core-level photoelectron spectroscopy by exposing the GaAs(110) surfaces to XeF2, which adsorbs dissociatively, leaving atomic F behind. This surface reaction produces two chemically shifted components in the Ga 3d core-level emission which are attributed to an interfacial monofluoride and a stable trifluoride reaction product, respectively. The As 3d core level develops only one chemically shifted component and from its exposure-dependent behavior it is attributed to an interfacial monofluoride. Least-squares analysis of the core-level line shapes revealed that (i) the F bonds to both the anion and the cation , (ii) the GaF3 component (characteristic of strong interfacial reaction) and the surface core-level shifted component (characteristic of a well ordered, atomically clean surface) are present together over a relatively large range of XeF2 exposures, and (iii) it is the initial disruption of the GaAs(110) surface that is the rate-limiting step in this surface reaction. These results are compared with similar studies of Cl and O adsorption on GaAs(110).

Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

NASA Astrophysics Data System (ADS)

Louarn, K.; Claveau, Y.; Marigo-Lombart, L.; Fontaine, C.; Arnoult, A.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

2018-04-01

In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm‑2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions.

PubMed

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-25

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

Self-catalyzed GaAs nanowires on silicon by hydride vapor phase epitaxy.

PubMed

Dong, Zhenning; André, Yamina; Dubrovskii, Vladimir G; Bougerol, Catherine; Leroux, Christine; Ramdani, Mohammed R; Monier, Guillaume; Trassoudaine, Agnès; Castelluci, Dominique; Gil, Evelyne

2017-03-24

Gold-free GaAs nanowires on silicon substrates can pave the way for monolithic integration of photonic nanodevices with silicon electronic platforms. It is extensively documented that the self-catalyzed approach works well in molecular beam epitaxy but is much more difficult to implement in vapor phase epitaxies. Here, we report the first gallium-catalyzed hydride vapor phase epitaxy growth of long (more than 10 μm) GaAs nanowires on Si(111) substrates with a high integrated growth rate up to 60 μm h -1 and pure zincblende crystal structure. The growth is achieved by combining a low temperature of 600 °C with high gaseous GaCl/As flow ratios to enable dechlorination and formation of gallium droplets. GaAs nanowires exhibit an interesting bottle-like shape with strongly tapered bases, followed by straight tops with radii as small as 5 nm. We present a model that explains the peculiar growth mechanism in which the gallium droplets nucleate and rapidly swell on the silicon surface but then are gradually consumed to reach a stationary size. Our results unravel the necessary conditions for obtaining gallium-catalyzed GaAs nanowires by vapor phase epitaxy techniques.

Effect of thermal annealing on the photoluminescence of structures with InGaAs/GaAs quantum wells and a low-temperature GaAs layer δ-doped with Mn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalentyeva, I. L.; Vikhrova, O. V., E-mail: istery@rambler.ru; Danilov, Yu. A.

2016-11-15

The effects of isochronal thermal annealing (at 325–725°C) on the radiative properties of InGaAs/GaAs nanoheterostructures containing a low-temperature GaAs layer δ-doped with Mn grown by laser deposition are studied. A decrease in the photoluminescence intensity and increase in the ground transition energy are observed upon thermal impact for quantum wells located near the low-temperature GaAs layer. The distribution of Mn atoms in the initial and annealed structures is obtained by secondary-ion mass spectrometry. A qualitative model of the observed effects of thermal annealing on the radiative properties of the structures is discussed; this model takes into account two main processes:more » diffusion of point defects (primarily gallium vacancies) from the GaAs coating layer deep into the structure and Mn diffusion in both directions by the dissociation mechanism. Magnetization studies show that, as a result of thermal annealing, an increase in the proportion of the ferromagnetic phase at room temperature (presumably, MnAs clusters) in the low-temperature GaAs coating layer takes place.« less

Modified energetics and growth kinetics on H-terminated GaAs (110)

NASA Astrophysics Data System (ADS)

Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

2013-10-01

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

Isolating GaSb membranes grown metamorphically on GaAs substrates using highly selective substrate removal etch processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavrova, Olga; Balakrishnan, Ganesh

2017-02-24

The etch rates of NH 4OH:H 2O 2 and C 6H 8O 7:H 2O 2 for GaAs and GaSb have been investigated to develop a selective etch for GaAs substrates and to isolate GaSb epilayers grown on GaAs. The NH 4OH:H 2O 2 solution has a greater etch rate differential for the GaSb/GaAs material system than C 6H 8O 7:H 2O 2 solution. The selectivity of NH 4OH:H 2O 2 for GaAs/GaSb under optimized etch conditions has been observed to be as high as 11471 ± 1691 whereas that of C 6H 8O 7:H 2O 2 has been measured upmore » to 143 ± 2. The etch contrast has been verified by isolating 2 μm thick GaSb epi-layers that were grown on GaAs substrates. GaSb membranes were tested and characterized with high-resolution X-Ray diffraction (HR-XRD) and atomic force microscopy (AFM).« less

A comparison of GaAs and Si hybrid solar power systems

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.; Roberts, A. S., Jr.

1977-01-01

Five different hybrid solar power systems using silicon solar cells to produce thermal and electric power are modeled and compared with a hybrid system using a GaAs cell. Among the indices determined are capital cost per unit electric power plus mechanical power, annual cost per unit electric energy, and annual cost per unit electric plus mechanical work. Current costs are taken to be $35,000/sq m for GaAs cells with an efficiency of 15% and $1000/sq m for Si cells with an efficiency of 10%. It is shown that hybrid systems can be competitive with existing methods of practical energy conversion. Limiting values for annual costs of Si and GaAs cells are calculated to be 10.3 cents/kWh and 6.8 cents/kWh, respectively. Results for both systems indicate that for a given flow rate there is an optimal operating condition for minimum cost photovoltaic output. For Si cell costs of $50/sq m optimal performance can be achieved at concentrations of about 10; for GaAs cells costing 1000/sq m, optimal performance can be obtained at concentrations of around 100. High concentration hybrid systems offer a distinct cost advantage over flat systems.

Growth mechanism of GaAs1-xSbx ternary alloy thin film on MOCVD reactor using TMGa, TDMAAs and TDMASb

NASA Astrophysics Data System (ADS)

Suhandi, A.; Tayubi, Y. R.; Arifin, P.

2016-04-01

Metal Organic Chemical Vapor Deposition (MOCVD) is a method for growing a solid material (in the form of thin films, especially for semiconductor materials) using vapor phase metal organic sources. Studies on the growth mechanism of GaAs1-xSbx ternary alloy thin solid film in the range of miscibility-gap using metal organic sources trimethylgallium (TMGa), trisdimethylaminoarsenic (TDMAAs), and trisdimethylaminoantimony (TDMASb) on MOCVD reactor has been done to understand the physical and chemical processes involved. Knowledge of the processes that occur during alloy formation is very important to determine the couple of growth condition and growth parameters are appropriate for yield high quality GaAs1-xSbx alloy. The mechanism has been studied include decomposition of metal organic sources and chemical reactions that may occur, the incorporation of the alloy elements forming and the contaminants element that are formed in the gown thin film. In this paper presented the results of experimental data on the growth of GaAs1-xSbx alloy using Vertical-MOCVD reactor to demonstrate its potential in growing GaAs1-xSbx alloy in the range of its miscibility gap.

Effects of surface passivation on twin-free GaAs nanosheets.

PubMed

Arab, Shermin; Chi, Chun-Yung; Shi, Teng; Wang, Yuda; Dapkus, Daniel P; Jackson, Howard E; Smith, Leigh M; Cronin, Stephen B

2015-02-24

Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30- to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 × 10(5) to 2.7 × 10(4) cm/s with passivation.

Accelerated life testing and temperature dependence of device characteristics in GaAs CHFET devices

NASA Technical Reports Server (NTRS)

Gallegos, M.; Leon, R.; Vu, D. T.; Okuno, J.; Johnson, A. S.

2002-01-01

Accelerated life testing of GaAs complementary heterojunction field effect transistors (CHFET) was carried out. Temperature dependence of single and synchronous rectifier CHFET device characteristics were also obtained.

Cathodoluminescence Characterization of Ion Implanted GaAs.

DTIC Science & Technology

1980-03-01

technique that can be used to characterize the semiconductor device "in situ" before further processing can save the Air Force valuable time as well...Patterson Air Force Base,Ohio i! i ill i I ;Wow AFIT/DS/PH/80- I.i1I LEVELOO CATHODOLUMINESCENCE CHARACTERIZATION OF ION IPLANTED GaAs D I SSERUrAT ION...CATODOLUMINESCENCE CHARACTERIZATION .’ a .... OF ION IMPLANTED GaAs’ - .. .. Dtriy’ t’ c:’/ A’: t 1. - Cc;-,P by an i’or Milton L one B.S., M.S. Major USAF Approved

Guanidinoacetic acid versus creatine for improved brain and muscle creatine levels: a superiority pilot trial in healthy men.

PubMed

Ostojic, Sergej M; Ostojic, Jelena; Drid, Patrik; Vranes, Milan

2016-09-01

In this randomized, double-blind, crossover trial, we evaluated whether 4-week supplementation with guanidinoacetic acid (GAA) is superior to creatine in facilitating creatine levels in healthy men (n = 5). GAA (3.0 g/day) resulted in a more powerful rise (up to 16.2%) in tissue creatine levels in vastus medialis muscle, middle-cerebellar peduncle, and paracentral grey matter, as compared with creatine (P < 0.05). These results indicate that GAA as a preferred alternative to creatine for improved bioenergetics in energy-demanding tissues.

Fabrication of p(+)-n junction GaAs solar cells by a novel method

NASA Technical Reports Server (NTRS)

Ghandhi, S. K.; Mathur, G.; Rode, H.; Borrego, J. M.

1984-01-01

A novel method for making p(+)-n diffused junction GaAs solar cells, with the formation of a diffusion source, an anti-reflective coating, and a protective cover glass in a single chemical-vapor deposition operation is discussed. Consideration is given to device fabrication and to solar-cell characteristics. The advantages of the technique are that the number of process steps is kept to an absolute minimum, the fabrication procedure is low-cost, and the GaAs surface is protected during the entire operation.

Status of high polarization DC high voltage Gallium Arsenide photoelectron guns

DOE Office of Scientific and Technical Information (OSTI.GOV)

M. Poelker, P. Adderley, J. Brittian, J. Clark, J. Grames, J. Hansknecht, J. McCarter, M. Stutzman, R. Suleiman, K. Surles-Law

2008-01-01

Users receive very high beam polarization from reliable GaAs photoelectron guns at facilities worldwide. Satisfaction with beam quality (and a number of lab closures) has reduced the level of polarized source R&D from the heyday of 1990s. However, new experiments and new accelerators proposals including high current unpolarized machines, require GaAs photoguns with capabilities that exceed today's state of the art. This submission describes the capabilities of today's high- polarization DC high voltage GaAs photoguns and discusses issues that must be addressed to meet new demands.

Amplification in Double Heterostructure GaAs Lasers.

DTIC Science & Technology

1981-03-15

done, for example, in the book by Siegman . When the laser signal which is to be amplified is a single mode, it is important to include the possibility...k A’AD-A097 862 AEROSPACE CORP EL SEGUNDO CA ELECTRONICS RESEARCH LAP) P 5 20/5 I AMPLIFICATION IN DOUBLE HETEROSTRUCTURE GAAS LASERS .(U IMAR al E...GARMIRE, M CHANG F04701-80-C-0081I UNCLASSIFIED TR GO81(6930 03)-2 SD-TA8-30 NL Amplification in Double Heterostructure GaAs Lasers E. GARMIRE nd M

Low temperature growth and electrical characterization of insulators for GaAs MISFETS

NASA Technical Reports Server (NTRS)

Borrego, J. M.; Ghandhi, S. K.

1981-01-01

Progress in the low temperature growth of oxides and layers on GaAs and the detailed electrical characterization of these oxides is reported. A plasma anodization system was designed, assembled, and put into operation. A measurement system was assembled for determining capacitance and conductance as a function of gate voltage for frequencies in the range from 1 Hz to 1 MHz. Initial measurements were carried out in Si-SiO2 capacitors in order to test the system and in GaAs MIS capacitors abricated using liquid anodization.

Radiation testing of GaAs on CRRES and LIPS experiment

NASA Technical Reports Server (NTRS)

Trumble, T. M.; Masloski, K.

1984-01-01

The radiation damage of solar cells has become a prime concern to the U.S. Air Force due to longer satellite lifetime requirements. Flight experiments were undertaken on the Navy Living Plume Shield (LPS) satellite and the NASA/Air Force Combined Release and Radiation Effects Satellite (CRRES) to complement existing radiation testing. Each experiment, the rationale behind it, and its approach and status are presented. The effect of space radiation on gallium arsenide (GaAs) solar cells was the central parameter investigated. Specifications of the GaAs solar cells are given.

Single crystal and polycrystalline GaAs solar cells using AMOS technology

NASA Technical Reports Server (NTRS)

Stirn, R. J.; Yeh, Y. C. M.

1976-01-01

A description is given of current technology for fabricating single AMOS (antireflection-coated metal oxide semiconductor) solar cells, with attention given to thermal, plasma, and anodic oxidation, native oxide stripping, and X-ray photoelectron spectroscopy results. Some preliminary results are presented on the chemistry and electrical characterization of such cells, and the characteristics of cells fabricated on sliced polycrystalline GaAs wafers are examined. Consideration is also given to the recrystallization of evaporated Ge films for use as low-cost substrates for polycrystalline GaAs solar cells.

Arsine flow requirement for the flow modulation growth of high purity GaAs using adduct-grade triethylgallium

NASA Astrophysics Data System (ADS)

Pitts, B. L.; Emerson, D. T.; Shealy, J. R.

1992-10-01

Using arsine and triethylgallium with flow modulation, organometallic vapor phase epitaxy can produce high purity GaAs layers with V/III molar ratios near unity. We have estimated that under appropriate growth conditions the arsine incorporation efficiency into epitaxial GaAs can exceed 30%. The arsine flow requirement for obtaining good morphology has been identified over a range of substrate temperatures using adduct-grade triethylgallium. The process described reduces the environmental impact and life safety risk of the hydride based organometallic vapor phase epitaxial method.

GaAs Surface Passivation for Device Applications.

DTIC Science & Technology

1981-12-01

Ga203.’" . QI. a) / b) x 2.5 •• 24 21 18 As3d a) b) x 2. / 0 II 2 46 43 40 BINDING ENERGY (eV) Fig. 3 XPS spectra from a Ga2O3 covered GaAs surface of Ga...wU 24 21 Gas 18 SAs3d As2O3 ) .. 46 43 40 BINDING ENERGY (e) Fig. 4 XPS spectra from a AsJ03- Ga2O3 covered GaAs surface of Ga 3d (upper panel) and As

High efficiency thin-film GaAs solar cells

NASA Technical Reports Server (NTRS)

Stirn, R. J.

1977-01-01

Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

GaAs photoconductive semiconductor switch

DOEpatents

Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

1998-01-01

A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

Deep levels in H-irradiated GaAs1-xNx (x < 0.01) grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Shafi, M.; Mari, R. H.; Khatab, A.; Henini, M.; Polimeni, A.; Capizzi, M.; Hopkinson, M.

2011-12-01

Dilute nitride GaAs1-xNx layers have been grown by molecular beam epitaxy with nitrogen concentration ranging from 0.2% to 0.8%. These samples have been studied before and after hydrogen irradiation by using standard deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS techniques. The activation energy, capture cross section and density of the electron traps have been estimated and compared with results obtained in N-free as-grown and H-irradiated bulk GaAs.

Gallium arsenide processing for gate array logic

NASA Technical Reports Server (NTRS)

Cole, Eric D.

1989-01-01

The development of a reliable and reproducible GaAs process was initiated for applications in gate array logic. Gallium Arsenide is an extremely important material for high speed electronic applications in both digital and analog circuits since its electron mobility is 3 to 5 times that of silicon, this allows for faster switching times for devices fabricated with it. Unfortunately GaAs is an extremely difficult material to process with respect to silicon and since it includes the arsenic component GaAs can be quite dangerous (toxic) especially during some heating steps. The first stage of the research was directed at developing a simple process to produce GaAs MESFETs. The MESFET (MEtal Semiconductor Field Effect Transistor) is the most useful, practical and simple active device which can be fabricated in GaAs. It utilizes an ohmic source and drain contact separated by a Schottky gate. The gate width is typically a few microns. Several process steps were required to produce a good working device including ion implantation, photolithography, thermal annealing, and metal deposition. A process was designed to reduce the total number of steps to a minimum so as to reduce possible errors. The first run produced no good devices. The problem occurred during an aluminum etch step while defining the gate contacts. It was found that the chemical etchant attacked the GaAs causing trenching and subsequent severing of the active gate region from the rest of the device. Thus all devices appeared as open circuits. This problem is being corrected and since it was the last step in the process correction should be successful. The second planned stage involves the circuit assembly of the discrete MESFETs into logic gates for test and analysis. Finally the third stage is to incorporate the designed process with the tested circuit in a layout that would produce the gate array as a GaAs integrated circuit.

Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si

NASA Technical Reports Server (NTRS)

Lao, Pudong; Tang, Wade C.; Rajkumar, K. C.; Guha, S.; Madhukar, A.; Liu, J. K.; Grunthaner, F. J.

1990-01-01

The quality of GaAs thin films grown via MBE under pulsed excimer laser irradiation on Si substrates is examined in both laser-irradiated and nonirradiated areas using Raman scattering, Rayleigh scattering, and by photoluminescence (PL), as a function of temperature, and by TEM. The temperature dependence of the PL and Raman peak positions indicates the presence of compressive stress in the thin GaAs films in both laser-irradiated and nonirradiated areas. This indicates incomplete homogeneous strain relaxation by dislocations at the growth temperature. The residual compressive strain at the growth temperature is large enough such that even with the introduction of tensile strain arising from the difference in thermal expansion coefficients of GaAs and Si, a compressive strain is still present at room temperature for these thin GaAs/Si films.

The 20 GHz solid state transmitter design, impatt diode development and reliability assessment

NASA Technical Reports Server (NTRS)

Picone, S.; Cho, Y.; Asmus, J. R.

1984-01-01

A single drift gallium arsenide (GaAs) Schottky barrier IMPATT diode and related components were developed. The IMPATT diode reliability was assessed. A proof of concept solid state transmitter design and a technology assessment study were performed. The transmitter design utilizes technology which, upon implementation, will demonstrate readiness for development of a POC model within the 1982 time frame and will provide an information base for flight hardware capable of deployment in a 1985 to 1990 demonstrational 30/20 GHz satellite communication system. Life test data for Schottky barrier GaAs diodes and grown junction GaAs diodes are described. The results demonstrate the viability of GaAs IMPATTs as high performance, reliable RF power sources which, based on the recommendation made herein, will surpass device reliability requirements consistent with a ten year spaceborne solid state power amplifier mission.

GaAs and 3-5 compound solar cells status and prospects for use in space

NASA Technical Reports Server (NTRS)

Flood, D. J.; Brinker, D. J.

1984-01-01

Gallium arsenide solar cells equal or supass the best silicon solar cells in efficiency, radiation resistance, annealability, and in the capability to produce usable power output at elevated temperatures. NASA has been involved in a long range research and development program to capitalize on these manifold advantages, and to explore alternative III-V compounds for additional potential improvements. The current status and future prospects for research and development in this area are reviewed and the progress being made toward development of GaAs cells suitable for variety of space missions is discussed. Cell types under various stages of development include n(+)/p shallow homojunction thin film GaAs cells, x100 concentration ratio p/n and n/p GaAs small area concentrator cells, mechanically-stacked, two-junction tandem cells, and three-junction monolithic cascade cells, among various other cell types.

Segregation effects during solidification in weightless melts. [effects of evaporation and solidification on crystalization

NASA Technical Reports Server (NTRS)

Li, C.

1975-01-01

Computer programs are developed and used in the study of the combined effects of evaporation and solidification in space processing. The temperature and solute concentration profiles during directional solidification of binary alloys with surface evaporation were mathematically formulated. Computer results are included along with an econotechnical model of crystal growth. This model allows: prediction of crystal size, quality, and cost; systematic selection of the best growth equipment or alloy system; optimization of growth or material parameters; and a maximization of zero-gravity effects. Segregation in GaAs crystals was examined along with vibration effects on GaAs crystal growth. It was found that a unique segregation pattern and strong convention currents exist in GaAs crystal growth. Some beneficial effects from vibration during GaAs growth were discovered. The implications of the results in space processing are indicated.

Spectrally resolved localized states in GaAs 1– xBi x

DOE PAGES

Christian, Theresa M.; Alberi, Kirstin; Beaton, Daniel A.; ...

2017-02-01

In this study, the role of localized states and their influence on the broader band structure remains a crucial question in understanding the band structure evolution in GaAs 1-xBi x. Here in this work, we present clear spectroscopic observations of recombination at several localized states in GaAs 1-xBi x. Sharp and recognizable photoluminescence features appear in multiple samples and redshift as a function of GaBi fraction between x = 0.16% and 0.4% at a linearized rate of 34 meV per % Bi, weaker than the redshift associated with band-to-band recombination. Interpreting these results in terms of radiative recombination between localizedmore » holes and free electrons sheds light on the relative movement of the conduction band minimum and the characteristics of localized bismuth-related trap states in GaAs 1-xBi x alloys.« less

Growth rate dependence of boron incorporation into BxGa1-xAs layers

NASA Astrophysics Data System (ADS)

Detz, H.; MacFarland, D.; Zederbauer, T.; Lancaster, S.; Andrews, A. M.; Schrenk, W.; Strasser, G.

2017-11-01

This work provides a comprehensive study of the incorporation behavior of B in growing GaAs under molecular beam epitaxy conditions. Structural characterization of superlattices revealed a strong dependence of the BAs growth rate on the GaAs growth rate used. In general, higher GaAs growth rates lead to a higher apparent BAs growth rate, although lower B cell temperatures showed saturation behavior. Each B cell temperature requires a minimum GaAs growth rate for producing smooth films. The B incorporation into single thick layers was found to be reduced to 75-80% compared to superlattice structures. The p-type carrier densities in 1000 nm thick layers were found to be indirectly proportional to the B content. Furthermore, 500 nm thick BxGa1-xAs layers showed significantly lower carrier concentrations, indicating B segregation on the surface during growth of thicker layers.

Fermi level pinning at epitaxial Si on GaAs(100) interfaces

NASA Astrophysics Data System (ADS)

Silberman, J. A.; de Lyon, T. J.; Woodall, J. M.

1991-12-01

GaAs Schottky barrier contacts and metal-insulator-semiconductor structures that include thin epitaxial Si interfacial layers operate in a manner consistent with an unpinned Fermi level at the GaAs interface. These findings raise the question of whether this effect is an intrinsic property of the epitaxial GaAs(100)-Si interface. We have used x-ray photoemission spectroscopy to monitor the Fermi level position during in situ growth of thin epitaxial Si layers. In particular, films formed on heavily doped n- and p-type substrates were compared so as to use the large depletion layer fields available with high impurity concentration as a field-effect probe of the interface state density. The results demonstrate that epitaxial bonding at the interface alone is insufficient to eliminate Fermi level pinning, indicating that other mechanisms affect the interfacial charge balance in the devices that utilize Si interlayers.

Applications of ultrashort laser pulses in science and technology; Proceedings of the Meeting, The Hague, Netherlands, Mar. 12, 13, 1990

NASA Technical Reports Server (NTRS)

Antonetti, Andre (Editor)

1990-01-01

Topics discussed are on the generation of high-intensity femtosecond lasers, the high-repetition and infrared femtosecond pulses, and physics of semiconductors and applications. Papers are presented on the femtosecond pulse generation at 193 nm; the generation of intense subpicosecond and femtosecond pulses; intense tunable subpicosecond and femtosecond pulses in the visible and infrared, generated by optical parametric oscillators; a high-efficiency high-energy optical amplifier for femtosecond pulses; and the generation of solitons, periodic pulsing, and nonlinearities in GaAs. Other papers are on ultrafast relaxation dynamics of photoexcited carriers in GaAs, high-order optical nonlinear susceptibilities of transparent glasses, subnanosecond risetime high-power pulse generation using photoconductive bulk GaAs devices, femtosecond studies of plasma formation in crystalline and amorphous silicon, and subpicosecond dynamics of hot carrier relaxation in InP and GaAs.

Germanium- and tellurium-doped GaAs for non-alloyed p-type and n-type ohmic contacts

NASA Astrophysics Data System (ADS)

Park, Joongseo; Barnes, Peter A.; Lovejoy, Michael L.

1995-08-01

Epitaxial ohmic contacts to GaAs were grown by liquid phase epitaxy. Heavily Ge-doped GaAs was grown to prepare ohmic contacts to p-GaAs while Te was used for the n-type contacts. Hall measurements were carried out for the samples grown from melts in which the mole fraction of Ge was varied between 1.55 atomic % and 52.2 atomic %, while the Te mole fractions varied between 0.03% and 0.5%. Specific contact resistance, rc, as low as rcp=2.9×10-6 ohm-cm 2 for Ge doping of p=(Na-Nd)=6.0×1019 holes/cm3 was measured for p-contacts and rcn=9.6×10-5 ohm-cm2 was measured for Te doping of n=(Nd-Na)=8.9×1018 electrons/cm3 for GaAs metallized with non-alloyed contacts of Ti/Al.

Type I band alignment in GaAs{sub 81}Sb{sub 19}/GaAs core-shell nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, T.; Key Laboratory of Advanced Display and System Application, Shanghai University, 149 Yanchang Road, Shanghai 200072; Wei, M. J.

2015-09-14

The composition and band gap of the shell that formed during the growth of axial GaAs/GaAs{sub 81}Sb{sub 19}/ GaAs heterostructure nanowires have been investigated by transmission electron microscopy combined with energy dispersion spectroscopy, scanning tunneling spectroscopy, and density functional theory calculations. On the GaAs{sub 81}Sb{sub 19} intermediate segment, the shell is found to be free of Sb (pure GaAs shell) and transparent to the tunneling electrons, despite the (110) biaxial strain that affects its band gap. As a result, a direct measurement of the core band gap allows the quantitative determination of the band offset between the GaAs{sub 81}Sb{sub 19}more » core and the GaAs shell and identifies it as a type I band alignment.« less

Nanoscale Footprints of Self-Running Gallium Droplets on GaAs Surface

PubMed Central

Wu, Jiang; Wang, Zhiming M.; Li, Alvason Z.; Benamara, Mourad; Li, Shibin; Salamo, Gregory J.

2011-01-01

In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001) surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems. PMID:21673965

Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shang-Hua; Jarrahi, Mona; Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095

2015-09-28

We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more thanmore » 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.« less

Transient GaAs plasmonic metasurfaces at terahertz frequencies

DOE PAGES

Yang, Yuanmu; Kamaraju, N.; Campione, Salvatore; ...

2016-12-09

Here we demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron–phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to moremore » complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. In conclusion, the platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.« less

Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

NASA Technical Reports Server (NTRS)

Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

1987-01-01

Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

NASA Technical Reports Server (NTRS)

Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

1987-01-01

Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMICs to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMICs is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

Nitride passivation reduces interfacial traps in atomic-layer-deposited Al2O3/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Aoki, T.; Fukuhara, N.; Osada, T.; Sazawa, H.; Hata, M.; Inoue, T.

2014-07-01

Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al2O3. This AlN passivation incorporated nitrogen at the Al2O3/GaAs interface, improving the capacitance-voltage (C-V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C-V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (Dit). The Dit was reduced over the entire GaAs band gap. In particular, these devices exhibited Dit around the midgap of less than 4 × 1012 cm-2eV-1, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1985-01-01

The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

Fabrication of GaAs symmetric pyramidal mesas prepared by wet-chemical etching using AlAs interlayer

NASA Astrophysics Data System (ADS)

Kicin, S.; Cambel, V.; Kuliffayová, M.; Gregušová, D.; Kováčová, E.; Novák, J.; Kostič, I.; Förster, A.

2002-01-01

We present a wet-chemical-etching method developed for the preparation of GaAs four-sided pyramid-shaped mesas. The method uses a fast lateral etching of AlAs interlayer that influences the cross-sectional profiles of etched structures. We have tested the method using H3PO4:H2O2:H2O etchant for the (100) GaAs patterning. The sidewalls of the prepared pyramidal structures together with the (100) bottom facet formed the cross-sectional angles 25° and 42° for mask edges parallel, resp. perpendicular to {011} cleavage planes. For mask edges turned in 45° according to the cleavage planes, 42° cross-sectional angles were obtained. Using the method, symmetric and more than 10-μm-high GaAs "Egyptian" pyramids with smooth tilted facets were prepared.

Structural and optical properties of GaAs(100) with a thin surface layer doped with chromium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V., E-mail: paul@phys.vsu.ru; Fedyukin, A. V.; Arsentyev, I. N.

The aim of this study is to explore the structural and optical properties of single-crystal GaAs(100) doped with Cr atoms by burning them into the substrate at high temperatures. The diffusion of chromium into single-crystal GaAs(100) substrates brings about the formation of a thin (~20–40 μm) GaAs:Cr transition layer. In this case, chromium atoms are incorporated into the gallium-arsenide crystal lattice and occupy the regular atomic sites of the metal sublattice. As the chromium diffusion time is increased, such behavior of the dopant impurity yields changes in the energy structure of GaAs, a decrease in the absorption at free chargemore » carriers, and a lowering of the surface recombination rate. As a result, the photoluminescence signal from the sample is significantly enhanced.« less

Effect of ZnSe/GaAs interface treatment in ZnSe quality control for optoelectronic device applications

DOE PAGES

Park, Kwangwook; Beaton, Daniel; Steirer, Kenneth X.; ...

2017-01-27

Here, we investigate the role of interface initiation conditions on the growth of ZnSe/GaAs heterovalent heterostructures. ZnSe epilayers were grown on a GaAs surface with various degrees of As-termination and the application of either a Zn or Se pre-treatment. Structural analysis revealed that Zn pre-treatment of an As-rich GaAs surface suppresses Ga 2Se 3 formation at the interface and promotes the growth of high crystal quality ZnSe. This is confirmed with low-temperature photoluminescence. However, moderation of Ga-Se bonding through a Se pre-treatment of an As-rich GaAs surface can prevent excessive intermixing at the interface and promote excitonic emission in themore » underlying GaAs layer. These results provide guidance on how best to prepare heterovalent interfaces for various applications.« less

Outdoor Performance of a Thin-Film Gallium-Arsenide Photovoltaic Module

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silverman, T. J.; Deceglie, M. G.; Marion, B.

2013-06-01

We deployed a 855 cm2 thin-film, single-junction gallium arsenide (GaAs) photovoltaic (PV) module outdoors. Due to its fundamentally different cell technology compared to silicon (Si), the module responds differently to outdoor conditions. On average during the test, the GaAs module produced more power when its temperature was higher. We show that its maximum-power temperature coefficient, while actually negative, is several times smaller in magnitude than that of a Si module used for comparison. The positive correlation of power with temperature in GaAs is due to temperature-correlated changes in the incident spectrum. We show that a simple correction based on precipitablemore » water vapor (PWV) brings the photocurrent temperature coefficient into agreement with that measured by other methods and predicted by theory. The low operating temperature and small temperature coefficient of GaAs give it an energy production advantage in warm weather.« less

Oxygen in GaAs - Direct and indirect effects

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Skowronski, M.; Pawlowicz, L.; Lagowski, J.

1984-01-01

Oxygen has profound effects on the key electronic properties and point defects of GaAs crystals. Thus, when added in the growth system, it decreases the free electron concentration and enhances the concentration of deep donors in the resulting crystals. Both of these effects are highly beneficial for achieving semi-insulating material and have been utilized for that purpose. They have been attributed to the tendency of oxygen to getter silicon impurities during crystal growth. Only recently, it has been found that oxygen in GaAs introduces also a midgap level, ELO, with essentially the same activation energy as EL2 but with four times greater electron capture cross section. The present report reassesses the electrical and optical properties of the midgap levels in GaAs crystals grown by the horizontal Bridgman (HB) and the Czochralski-LEC techniques. Emphasis is placed on the identification of the specific effects of ELO.

EBIC spectroscopy - A new approach to microscale characterization of deep levels in semi-insulating GaAs

NASA Technical Reports Server (NTRS)

Li, C.-J.; Sun, Q.; Lagowski, J.; Gatos, H. C.

1985-01-01

The microscale characterization of electronic defects in (SI) GaAs has been a challenging issue in connection with materials problems encountered in GaAs IC technology. The main obstacle which limits the applicability of high resolution electron beam methods such as Electron Beam-Induced Current (EBIC) and cathodoluminescence (CL) is the low concentration of free carriers in semiinsulating (SI) GaAs. The present paper provides a new photo-EBIC characterization approach which combines the spectroscopic advantages of optical methods with the high spatial resolution and scanning capability of EBIC. A scanning electron microscope modified for electronic characterization studies is shown schematically. The instrument can operate in the standard SEM mode, in the EBIC modes (including photo-EBIC and thermally stimulated EBIC /TS-EBIC/), and in the cathodo-luminescence (CL) and scanning modes. Attention is given to the use of CL, Photo-EBIC, and TS-EBIC techniques.

Growth of GaAs crystals from the melt in a partially confined configuration

NASA Technical Reports Server (NTRS)

Gatos, Harry C.; Lagowski, Jacek

1988-01-01

The experimental approach was directed along two main goals: (1) the implementation of an approach to melt growth in a partially confined configuration; and (2) the investigation of point defect interaction and electronic characteristics as related to thermal treatment following solidification and stoichiometry. Significant progress was made along both fronts. Crystal growth of GaAs in triangular ampuls was already carried out successfully and consistent with the model. In fact, pronounced surface tension phenomena which cannot be observed in ordinary confinement system were identified and should premit the assessment of Maragoni effects prior to space processing. Regarding thermal treatment, it was discovered that the rate of cooling from elevated temperatures is primarily responsible for a whole class of defect interactions affecting the electronic characteristics of GaAs and that stoichiometry plays a critical role in the quality of GaAs.

Negative differential velocity in ultradilute GaAs1-xNx alloys

NASA Astrophysics Data System (ADS)

Vogiatzis, N.; Rorison, J. M.

2011-04-01

We present theoretical results on steady state characteristics in bulk GaAs1-xNx alloys (x ≤ 0.2) using the single electron Monte-Carlo method. Two approaches have been used; the first assumes a GaAs band with a strong nitrogen scattering resonance and the second uses the band anti-crossing model, in which the localized N level interacts with the GaAs band strongly perturbing the conduction band. In the first model we observe two negative differential velocity peaks, the lower one associated with nitrogen scattering while the higher one with polar optical phonon emission accounting for the nonparabolicity effect. In the second model one negative differential velocity peak is observed associated with polar optical phonon emission. Good agreement with experimental low field mobility is obtained from the first model. We also comment on the results from both Models when the intervalley Г → L transfer is accounted for.

E+ Transition in GaAs1-xNx and GaAs1-xBix Due to Isoelectronic-Impurity-Induced Perturbation of the Conduction Band

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fluegel, B.; Mascarenhas, A.; Ptak, A. J.

2007-01-01

An above-band-gap transition E{sub +} is experimentally observed in the dilute GaAs{sub 1-x}Bi{sub x} alloy. Precise measurements at very low dilutions are made of the above-band-gap transition E{sub +} that is observed in GaAs{sub 1-x}N{sub x}, making it possible to compare the behavior of the different isoelectronic traps Bi and N in the common host GaAs with respect to their perturbation to the host electronic structure. We suggest that the origin of the E{sub +} level observed in GaAs is not the isolated isoelectronic impurity level N{sub x}, as is presumed in the band-anticrossing model, but rather the isoelectronic-impurity-induced perturbationmore » of the conduction band L{sub 6}{sup c}.« less