The Efficiency of UVC Radiation in the Inactivation of
Listeria monocytogenes on Beef-Agar Food Models.

PubMed

Hamidi-Oskouei, Amir M; James, Christian; James, Stephen

2015-06-01

The aim of this study is to evaluate the effect of meat content and surface smoothness on the deactivation of Listeria monocytogenes in beef-agar food models achieved by shortwave ultraviolet (UVC) light. Food models with various meat contents were made using chopped beef slices and agar solution. Prepared models together with a Listeria selective agar (LSA) plate and a slice of cooked beef were inoculated with L. monocytogenes and then exposed to UVC light. Population of Listeria reduced to below the level of detection on the LSA plates. As the content of beef in the beef-agar models increased, more L. monocytogenes cells survived. Survival was greatest on the treated cooked slice of beef. To better understand the effect of surface irregularities, a white light interferometer was used to analyse the surface smoothness of beef-agar media and LSA plates. No correlation was observed between the surface roughness of seven out of nine types of produced beef-agar media and the degree of inactivation resulting from UVC radiation at the given dose, whereas, less bacterial cells were killed as beef content of the food models increased. The findings of the current study show that the chemical composition of the treated sample also plays an important role in pathogen resistance and survival, meaning that two samples with similar surface irregularities but different chemical composition might produce very different inactivation results when exposed to UVC light.

The Efficiency of UVC Radiation in the Inactivation of
Listeria monocytogenes on Beef-Agar Food Models

PubMed Central

James, Christian; James, Stephen

2015-01-01

Summary The aim of this study is to evaluate the effect of meat content and surface smoothness on the deactivation of Listeria monocytogenes in beef-agar food models achieved by shortwave ultraviolet (UVC) light. Food models with various meat contents were made using chopped beef slices and agar solution. Prepared models together with a Listeria selective agar (LSA) plate and a slice of cooked beef were inoculated with L. monocytogenes and then exposed to UVC light. Population of Listeria reduced to below the level of detection on the LSA plates. As the content of beef in the beef-agar models increased, more L. monocytogenes cells survived. Survival was greatest on the treated cooked slice of beef. To better understand the effect of surface irregularities, a white light interferometer was used to analyse the surface smoothness of beef-agar media and LSA plates. No correlation was observed between the surface roughness of seven out of nine types of produced beef-agar media and the degree of inactivation resulting from UVC radiation at the given dose, whereas, less bacterial cells were killed as beef content of the food models increased. The findings of the current study show that the chemical composition of the treated sample also plays an important role in pathogen resistance and survival, meaning that two samples with similar surface irregularities but different chemical composition might produce very different inactivation results when exposed to UVC light. PMID:27904353

Extended local similarity analysis (eLSA) of microbial community and other time series data with replicates.

PubMed

Xia, Li C; Steele, Joshua A; Cram, Jacob A; Cardon, Zoe G; Simmons, Sheri L; Vallino, Joseph J; Fuhrman, Jed A; Sun, Fengzhu

2011-01-01

The increasing availability of time series microbial community data from metagenomics and other molecular biological studies has enabled the analysis of large-scale microbial co-occurrence and association networks. Among the many analytical techniques available, the Local Similarity Analysis (LSA) method is unique in that it captures local and potentially time-delayed co-occurrence and association patterns in time series data that cannot otherwise be identified by ordinary correlation analysis. However LSA, as originally developed, does not consider time series data with replicates, which hinders the full exploitation of available information. With replicates, it is possible to understand the variability of local similarity (LS) score and to obtain its confidence interval. We extended our LSA technique to time series data with replicates and termed it extended LSA, or eLSA. Simulations showed the capability of eLSA to capture subinterval and time-delayed associations. We implemented the eLSA technique into an easy-to-use analytic software package. The software pipeline integrates data normalization, statistical correlation calculation, statistical significance evaluation, and association network construction steps. We applied the eLSA technique to microbial community and gene expression datasets, where unique time-dependent associations were identified. The extended LSA analysis technique was demonstrated to reveal statistically significant local and potentially time-delayed association patterns in replicated time series data beyond that of ordinary correlation analysis. These statistically significant associations can provide insights to the real dynamics of biological systems. The newly designed eLSA software efficiently streamlines the analysis and is freely available from the eLSA homepage, which can be accessed at http://meta.usc.edu/softs/lsa.

Extended local similarity analysis (eLSA) of microbial community and other time series data with replicates

PubMed Central

2011-01-01

Background The increasing availability of time series microbial community data from metagenomics and other molecular biological studies has enabled the analysis of large-scale microbial co-occurrence and association networks. Among the many analytical techniques available, the Local Similarity Analysis (LSA) method is unique in that it captures local and potentially time-delayed co-occurrence and association patterns in time series data that cannot otherwise be identified by ordinary correlation analysis. However LSA, as originally developed, does not consider time series data with replicates, which hinders the full exploitation of available information. With replicates, it is possible to understand the variability of local similarity (LS) score and to obtain its confidence interval. Results We extended our LSA technique to time series data with replicates and termed it extended LSA, or eLSA. Simulations showed the capability of eLSA to capture subinterval and time-delayed associations. We implemented the eLSA technique into an easy-to-use analytic software package. The software pipeline integrates data normalization, statistical correlation calculation, statistical significance evaluation, and association network construction steps. We applied the eLSA technique to microbial community and gene expression datasets, where unique time-dependent associations were identified. Conclusions The extended LSA analysis technique was demonstrated to reveal statistically significant local and potentially time-delayed association patterns in replicated time series data beyond that of ordinary correlation analysis. These statistically significant associations can provide insights to the real dynamics of biological systems. The newly designed eLSA software efficiently streamlines the analysis and is freely available from the eLSA homepage, which can be accessed at http://meta.usc.edu/softs/lsa. PMID:22784572

Continuous monitoring of evapotranspiration (ET) overview of LSA-SAF evapotranspiration products

NASA Astrophysics Data System (ADS)

Arboleda, A.; Ghilain, N.; Gellens-Meulenberghs, F.

2017-10-01

Evapotranspiration (ET) is the flux of water between the surface (vegetation, soil and water bodies) and the atmosphere. Monitoring this water loss may be of crucial importance for applications in hydrology, agriculture, water use efficiency studies and drought monitoring. We introduce one of the few satellite-based operational evapotranspiration products, generated continuously and in near real-time over Europe, Africa and part of South America. The ET products (30 minutes and daily) are generated at the EUMETSAT's Satellite Application Facility on Land Surface Analysis (LSA-SAF) operations centre (http://landsaf.ipma.pt). Following our commitments to our user's community, we are continuously looking for new ways to improve the product. To accomplish this, the feedback from users and potential users of the products is of great interest. In this contribution we present the ET products characteristics and recent improvements gained thanks to the inclusion in our ET algorithm of new variables derived from Earth observation by MSG SEVIRI. We show examples of the ET products and we highlight their potential in droughts detection and monitoring. Some examples of possible applications are presented to invite users and researchers to explore the possibilities offered by LSA-SAF evapotranspiration products.

Concurrent validity of the Swedish version of the life-space assessment questionnaire.

PubMed

Fristedt, Sofi; Kammerlind, Ann-Sofi; Bravell, Marie Ernsth; Fransson, Eleonor I

2016-11-08

The Life-Space Assessment (LSA), developed in the USA, is an instrument focusing on mobility with respect to reaching different areas defined as life-spaces, extending from the room where the person sleeps to mobility outside one's hometown. A newly translated Swedish version of the LSA (LSA-S) has been tested for test-retest reliability, but the validity remains to be tested. The purpose of the present study was to examine the concurrent validity of the LSA-S, by comparing and correlating the LSA scores to other measures of mobility. The LSA was included in a population-based study of health, functioning and mobility among older persons in Sweden, and the present analysis comprised 312 community-dwelling participants. To test the concurrent validity, the LSA scores were compared to a number of other mobility-related variables, including the Short Physical Performance Battery (SPPB) as well as "stair climbing", "transfers", "transportation", "food shopping", "travel for pleasure" and "community activities". The LSA total mean scores for different levels of the other mobility-related variables, and measures of correlation were calculated. Higher LSA total mean scores were observed with higher levels of all the other mobility related variables. Most of the correlations between the LSA and the other mobility variables were large (r = 0.5-1.0) and significant at the 0.01 level. The LSA total score, as well as independent life-space and assistive life-space correlated with transportation (0.63, 0.66, 0.64) and food shopping (0.55, 0.58, 0.55). Assistive life-space also correlated with SPPB (0.47). With respect to maximal life-space, the correlations with the mobility-related variables were generally lower (below 0.5), probably since this aspect of life-space mobility is highly influenced by social support and is not so dependent on the individual's own physical function. LSA was shown to be a valid measure of mobility when using the LSA total, independent LS or assistive LSA.

A critical analysis of the internal logic in the Life-Space Assessment (LSA) composite score and suggested solutions.

PubMed

Siordia, Carlos

2016-06-01

An individual's ability to live independently is commonly measured in health research interested in identifying risk factors associated with disablement processes. In order to inform clinical practice, population research has attempted to identify the contraction of "lived-space" by using various survey instruments. Studies assessing habitual movements over the environment with the Life-Space Assessment (LSA) survey instrument should carefully consider how the LSA Composite Score (LSA-CS) is computed. Until now, no publication has carefully delineated the assumptions guiding the internal logic used in the computation of the LSA-CS. Because the internal logic of the LSA may need further justification, a non-data-editing scoring algorithm should be considered. Compute LSA-CS by only using non-edited data. Paper first delineates the logic guiding the algorithm used in the formation of the LSA-CS and explains how the scoring creates and changes participant responses when they conflict with its internal logic. An easy-to-use SAS® 9.3 program for estimating a Non-Data-Edited LSA-CS (NDE-LSA-CS) is also presented. Researchers interested in assessing lived-space should carefully consider if the internal logic of the LSA-CS is warranted. Clinicians should know it is important to understand the strengths and weaknesses of outcome measures used when deciding on whether to apply the results of research to direct clinical practice. © The Author(s) 2015.

Extragenital Lichen Sclerosus et Atrophicus

PubMed Central

Ganesan, Leelavathy; Parmar, Heena; Das, Jayanta Kr; Gangopadhyay, Asok

2015-01-01

Lichen sclerosus et atrophicus (LSA) is a chronic inflammatory dermatosis with anogenital and extragenital presentations. Extragenital lichen sclerosus is most common on the neck, shoulders and upper trunk. Linear lesions are uncommon in LSA. We report a case of linear extragenital LSA involving forehead and scalp, along with grouped white papules of LSA in the right side of the back in a postmenopausal woman. The patient showed atypical clinical presentation of LSA in face which clinically mimicked ‘en coup de sabre’ as seen in morphea, but other clinical features suggested the diagnosis of LSA and the histopathological findings confirmed it. PMID:26288432

Life-Space Assessment scale to assess mobility: validation in Latin American older women and men.

PubMed

Curcio, Carmen-Lucia; Alvarado, Beatriz E; Gomez, Fernando; Guerra, Ricardo; Guralnik, Jack; Zunzunegui, Maria Victoria

2013-10-01

The Life-Space Assessment (LSA) instrument of the University of Alabama and Birmingham study is a useful and innovative measure of mobility in older populations. The purpose of this article was to assess the reliability, construct and convergent validity of the LSA in Latin American older populations. In a cross-sectional study, a total of 150 women and 150 men, aged 65-74 years, were recruited from seniors' community centers in Manizales, Colombia and Natal, Brazil. The LSA questionnaire summarizes where people travel (5 levels from room to places outside of town), how often and any assistance needed. Four LSA variables were obtained according to the maximum life space achieved and the level of independence. As correlates of LSA, education, perception of income sufficiency, depression, cognitive function, and functional measures (objective and subjectively measured) were explored. The possible modifying effect of the city on correlates of LSA was examined. Reliability for the composite LSA score was substantial (ICC = 0.70; 95 % CI 0.49-0.83) in Manizales. Average levels of LSA scores were higher in those with better functional performance and those who reported less mobility difficulties. Low levels of education, insufficient income, depressive symptoms, and low scores of cognitive function were all significantly related to lower LSA scores. Women in both cities were more likely to be restricted to their neighborhood and had lower LSA scores. This study provides evidence for the validity of LSA in two Latin American populations. Our results suggest that LSA is a good measure of mobility that reflects the interplay of physical functioning with gender and the social and physical environment.

Lsa63, a newly identified surface protein of Leptospira interrogans binds laminin and collagen IV.

PubMed

Vieira, Monica L; de Morais, Zenaide M; Gonçales, Amane P; Romero, Eliete C; Vasconcellos, Silvio A; Nascimento, Ana L T O

2010-01-01

Leptospira interrogans is the etiological agent of leptospirosis, a zoonotic disease that affects populations worldwide. We have identified in proteomic studies a protein that is encoded by the gene LIC10314 and expressed in virulent strain of L. interrogans serovar Pomona. This protein was predicted to be surface exposed by PSORT program and contains a p83/100 domain identified by BLAST analysis that is conserved in protein antigens of several strains of Borrelia and Treponema spp. The proteins containing this domain have been claimed antigen candidates for serodiagnosis of Lyme borreliosis. Thus, we have cloned the LIC10314 and expressed the protein in Escherichia coli BL21-SI strain by using the expression vector pAE. The recombinant protein tagged with N-terminal hexahistidine was purified by metal-charged chromatography and characterized by circular dichroism spectroscopy. This protein is conserved among several species of pathogenic Leptospira and absent in the saprophytic strain L. biflexa. We confirm by liquid-phase immunofluorescence assays with living organisms that this protein is most likely a new surface leptospiral protein. The ability of the protein to mediate attachment to ECM components was evaluated by binding assays. The leptospiral protein encoded by LIC10314, named Lsa63 (Leptospiral surface adhesin of 63kDa), binds strongly to laminin and collagen IV in a dose-dependent and saturable fashion. In addition, Lsa63 is probably expressed during infection since it was recognized by antibodies of serum samples of confirmed-leptospirosis patients in convalescent phase of the disease. Altogether, the data suggests that this novel identified surface protein may be involved in leptospiral pathogenesis. 2009 The British Infection Society. Published by Elsevier Ltd. All rights reserved.

Feelings of worthlessness, traumatic experience, and their comorbidity in relation to lifetime suicide attempt in community adults with major depressive disorder.

PubMed

Jeon, Hong Jin; Park, Jong-Ik; Fava, Maurizio; Mischoulon, David; Sohn, Jee Hoon; Seong, Sujeong; Park, Jee Eun; Yoo, Ikki; Cho, Maeng Je

2014-09-01

Major depressive disorder (MDD) and traumatic experience are independent risk factors for lifetime suicide attempt (LSA). However, the relationships between trauma history and depressive symptomatology as they relate to LSA are not fully understood. A total of 12,532 adults, randomly selected through one-person-per-household method, completed a face-to-face interview using the Korean version of Composite International Diagnostic Interview (K-CIDI) and a questionnaire for LSA (response rate 80.2%). Among 825 subjects with MDD, 141 subjects reported an LSA (17.1%). LSAs were significantly greater in those who had experienced any trauma than in those who had not (χ(2)=34.66, p<0.0001). Multivariate logistic regression showed that only feelings of worthlessness were significantly associated with LSA among 20 depression symptoms in individuals with MDD (AOR=3.08, 95% CI 1.70-5.60). Feelings of worthlessness was associated with LSA in those who had experienced serious trauma (AOR=5.02, 95% CI 3.35-7.52), but not in those who had not. Serious traumas associated with LSA included military combat, witnessing a violent crime, rape or sexual assault, a bad beating, being threatened by others, and learning about traumas to others. Serious trauma showed no significant association with LSA in those who did not have feelings of worthlessness. PTSD was a comorbidity that showed the highest odds ratio with LSA in individuals with MDD. Feelings of worthlessness are more strongly associated with LSA than other depression symptoms in individuals with MDD, and it is significantly associated with LSA in those who experienced serious trauma but not in those who did not. Copyright © 2014 Elsevier B.V. All rights reserved.

Identification of ABC transporter genes conferring combined pleuromutilin-lincosamide-streptogramin A resistance in bovine methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci.

PubMed

Wendlandt, Sarah; Kadlec, Kristina; Feßler, Andrea T; Schwarz, Stefan

2015-06-12

The aim of this study was to investigate the genetic basis of combined pleuromutilin-lincosamide-streptogramin A resistance in 26 unrelated methicillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative staphylococci (CoNS) from dairy cows suffering from mastitis. The 26 pleuromutilin-resistant staphylococcal isolates were screened for the presence of the genes vga(A), vga(B), vga(C), vga(E), vga(E) variant, sal(A), vmlR, cfr, lsa(A), lsa(B), lsa(C), and lsa(E) by PCR. None of the 26 isolates carried the genes vga(B), vga(C), vga(E), vga(E) variant, vmlR, cfr, lsa(A), lsa(B), or lsa(C). Two Staphylococcus haemolyticus and single Staphylococcus xylosus, Staphylococcus lentus, and Staphylococcus hominis were vga(A)-positive. Twelve S. aureus, two Staphylococcus warneri, as well as single S. lentus and S. xylosus carried the lsa(E) gene. Moreover, single S. aureus, S. haemolyticus, S. xylosus, and Staphylococcus epidermidis were positive for both genes, vga(A) and lsa(E). The sal(A) gene was found in a single Staphylococcus sciuri. All ABC transporter genes were located in the chromosomal DNA, except for a plasmid-borne vga(A) gene in the S. epidermidis isolate. The genetic environment of the lsa(E)-positive isolates was analyzed using previously described PCR assays. Except for the S. warneri and S. xylosus, all lsa(E)-positive isolates harbored a part of the previously described enterococcal multiresistance gene cluster. This is the first report of the novel lsa(E) gene in the aforementioned bovine CoNS species. This is also the first identification of the sal(A) gene in a S. sciuri from a case of bovine mastitis. Moreover, the sal(A) gene was shown to also confer pleuromutilin resistance. Copyright © 2015 Elsevier B.V. All rights reserved.

The potential of latent semantic analysis for machine grading of clinical case summaries.

PubMed

Kintsch, Walter

2002-02-01

This paper introduces latent semantic analysis (LSA), a machine learning method for representing the meaning of words, sentences, and texts. LSA induces a high-dimensional semantic space from reading a very large amount of texts. The meaning of words and texts can be represented as vectors in this space and hence can be compared automatically and objectively. A generative theory of the mental lexicon based on LSA is described. The word vectors LSA constructs are context free, and each word, irrespective of how many meanings or senses it has, is represented by a single vector. However, when a word is used in different contexts, context appropriate word senses emerge. Several applications of LSA to educational software are described, involving the ability of LSA to quickly compare the content of texts, such as an essay written by a student and a target essay. An LSA-based software tool is sketched for machine grading of clinical case summaries written by medical students.

Analysis of lysergic acid amide in human serum and urine after ingestion of Argyreia nervosa seeds.

PubMed

Paulke, Alexander; Kremer, Christian; Wunder, Cora; Toennes, Stefan W

2012-08-01

The ergot alkaloid lysergic acid amide (LSA) is a secondary plant constituent in a number of plants, but it is mainly present in considerable amounts in Convolvulaceae, like Argyreia nervosa. Due to its close structural similarity to lysergic acid diethylamide, LSA is considered as psychedelic and therefore promoted as so-called "legal high" in various internet forums. During a human behavioral study with orally administered seeds of A. nervosa, blood and urine samples were obtained. The present study describes the validation of a sensitive and robust high performance liquid chromatography method with fluorescence detection, which was applied to the study samples. The limit of detection (LOD) and lower limit of quantification in human serum were 0.05 and 0.17 ng/mL, respectively, and in urine, the LOD was 0.15 ng/mL. Intra- and interday precision and accuracy were below 15 % relative standard deviation with a bias better than ±15 %. No conversion of LSA to its epimer iso-LSA was noted during analyses. The LSA concentrations in the authentic human serum samples were in the range of 0.66 to 3.15 ng/mL approximately 2 h after ingestion. In urine, LSA could be found 1-24 h after ingestion; after 48 h, no LSA could be detected. The LSA epimer iso-LSA was also detected in serum and urine in varying ratios. In conclusion, LSA serum levels in the low nanogram per milliliter range correlated with severe vegetative adverse effects (nausea, weakness, fatigue, tremor, blood pressure elevation) and a psychosis-like state, which led to study termination.

Operational evapotranspiration based on Earth observation satellites

NASA Astrophysics Data System (ADS)

Gellens-Meulenberghs, Françoise; Ghilain, Nicolas; Arboleda, Alirio; Barrios, Jose-Miguel

2016-04-01

Geostationary satellites have the potential to follow fast evolving atmospheric and Earth surface phenomena such those related to cloud cover evolution and diurnal cycle. Since about 15 years, EUMETSAT has set up a network named 'Satellite Application Facility' (SAF, http://www.eumetsat.int/website/home/Satellites/GroundSegment/Safs/index.html) to complement its ground segment. The Land Surface Analysis (LSA) SAF (http://landsaf.meteo.pt/) is devoted to the development of operational products derived from the European meteorological satellites. In particular, an evapotranspiration (ET) product has been developed by the Royal Meteorological Institute of Belgium. Instantaneous and daily integrated results are produced in near real time and are freely available respectively since the end of 2009 and 2010. The products cover Europe, Africa and the Eastern part of South America with the spatial resolution of the SEVIRI sensor on-board Meteosat Second Generation (MSG) satellites. The ET product algorithm (Ghilain et al., 2011) is based on a simplified Soil-Vegetation-Atmosphere transfer (SVAT) scheme, forced with MSG derived radiative products (LSA SAF short and longwave surface fluxes, albedo). It has been extensively validated against in-situ validation data, mainly FLUXNET observations, demonstrating its good performances except in some arid or semi-arid areas. Research has then been pursued to develop an improved version for those areas. Solutions have been found in reviewing some of the model parameterizations and in assimilating additional satellite products (mainly vegetation indices and land surface temperature) into the model. The ET products will be complemented with related latent and sensible heat fluxes, to allow the monitoring of land surface energy partitioning. The new algorithm version should be tested in the LSA-SAF operational computer system in 2016 and results should become accessible to beta-users/regular users by the end of 2016/early 2017. In parallel, research has been started to investigate ET downscaling to a finer spatial scale. A first step is focusing on the assimilation into the algorithm of vegetation products derived from polar satellites. MODIS and SPOT-VEG products have been investigated to prepare the exploitation of the new Proba-V derived vegetation products that should become part the Copernicus Land Monitoring Service portfolio. Furthermore, an ongoing specific project is dedicated to the study of ET in wetlands allowing to concentrate research on relationship between ET, vegetation characteristics and ecosystem health. In the future, the launch of the Meteosat Third Generation satellite will motivate new developments in the framework of LSA-SAF. The present contribution will give an overview of above mentioned operational products and related ongoing research activities. LSA-SAF research at RMI is co-funded by EUMETSAT and Belgian Federal Science Policy/ESA through their Prodex funding program (contract C4000110695). Exploratory research on multi-mission EO exploitation has been allowed thanks to grants of Belgian Federal Science Policy (CB/34/18, SR/34/163, SR/00/301).

A newly identified protein of Leptospira interrogans mediates binding to laminin.

PubMed

Longhi, Mariana T; Oliveira, Tatiane R; Romero, Eliete C; Gonçales, Amane P; de Morais, Zenaide M; Vasconcellos, Silvio A; Nascimento, Ana L T O

2009-10-01

Pathogenic Leptospira is the aetiological agent of leptospirosis, a life-threatening disease that affects populations worldwide. The search for novel antigens that could be relevant in host-pathogen interactions is being pursued. These antigens have the potential to elicit several activities, including adhesion. This study focused on a hypothetical predicted lipoprotein of Leptospira, encoded by the gene LIC12895, thought to mediate attachment to extracellular matrix (ECM) components. The gene was cloned and expressed in Escherichia coli BL21 Star (DE3)pLys by using the expression vector pAE. The recombinant protein tagged with N-terminal hexahistidine was purified by metal-charged chromatography and characterized by circular dichroism spectroscopy. The capacity of the protein to mediate attachment to ECM components was evaluated by binding assays. The leptospiral protein encoded by LIC12895, named Lsa27 (leptospiral surface adhesin, 27 kDa), bound strongly to laminin in a dose-dependent and saturable fashion. Moreover, Lsa27 was recognized by antibodies from serum samples of confirmed leptospirosis specimens in both the initial and the convalescent phases of the disease. Lsa27 is most likely a surface protein of Leptospira as revealed in liquid-phase immunofluorescence assays with living organisms. Taken together, these data indicate that this newly identified membrane protein is expressed during natural infection and may play a role in mediating adhesion of L. interrogans to its host.

Long-Lasting Sound-Evoked Afterdischarge in the Auditory Midbrain.

PubMed

Ono, Munenori; Bishop, Deborah C; Oliver, Douglas L

2016-02-12

Different forms of plasticity are known to play a critical role in the processing of information about sound. Here, we report a novel neural plastic response in the inferior colliculus, an auditory center in the midbrain of the auditory pathway. A vigorous, long-lasting sound-evoked afterdischarge (LSA) is seen in a subpopulation of both glutamatergic and GABAergic neurons in the central nucleus of the inferior colliculus of normal hearing mice. These neurons were identified with single unit recordings and optogenetics in vivo. The LSA can continue for up to several minutes after the offset of the sound. LSA is induced by long-lasting, or repetitive short-duration, innocuous sounds. Neurons with LSA showed less adaptation than the neurons without LSA. The mechanisms that cause this neural behavior are unknown but may be a function of intrinsic mechanisms or the microcircuitry of the inferior colliculus. Since LSA produces long-lasting firing in the absence of sound, it may be relevant to temporary or chronic tinnitus or to some other aftereffect of long-duration sound.

Life-Space Assessment questionnaire: Novel measurement properties for Brazilian community-dwelling older adults.

PubMed

Simões, Maria do Socorro Mp; Garcia, Isabel Ff; Costa, Lucíola da Cm; Lunardi, Adriana C

2018-05-01

The Life-Space Assessment (LSA) assesses mobility from the spaces that older adults go, and how often and how independent they move. Despite its increased use, LSA measurement properties remain unclear. The aim of the present study was to analyze the content validity, reliability, construct validity and interpretability of the LSA for Brazilian community-dwelling older adults. In this clinimetric study we analyzed the measurement properties (content validity, reliability, construct validity and interpretability) of the LSA administered to 80 Brazilian community-dwelling older adults. Reliability was analyzed by Cronbach's alpha (internal consistency), intraclass correlation coefficients and 95% confidence interval (reproducibility), and standard error of measurement (measurement error). Construct validity was analyzed by Pearson's correlations between the LSA and accelerometry (time in inactivity and moderate-to-vigorous activities), and interpretability was analyzed by determination of the minimal detectable change, and floor and ceiling effects. The LSA met the criteria for content validity. The Cronbach's alpha was 0.92, intraclass correlation coefficient was 0.97 (95% confidence interval 0.95-0.98) and standard error of measurement was 4.12. The LSA showed convergence with accelerometry (negative correlation with time in inactivity and positive correlation with time in moderate to vigorous activities), the minimal detectable change was 0.36 and we observed no floor or ceiling effects. The LSA showed adequate reliability, validity and interpretability for life-space mobility assessment of Brazilian community-dwelling older adults. Geriatr Gerontol Int 2018; 18: 783-789. © 2018 Japan Geriatrics Society.

49 CFR 173.427 - Transport requirements for low specific activity (LSA) Class 7 (radioactive) materials and...

Code of Federal Regulations, 2010 CFR

2010-10-01

... package (IP-1, IP-2 or IP-3; § 173.411), subject to the limitations of Table 6; (2) In a DOT Specification... use shipment 1. LSA-I: Solid IP-1 IP-1 Liquid IP-1 IP-2 2. LSA-II: Solid IP-2 IP-2 Liquid and gas IP-2 IP-3 3. LSA-III IP-2 IP-3 4. SCO-I IP-1 IP-1 5. SCO-II IP-2 IP-2 [69 FR 3676, Jan. 26, 2004; 69 FR...

49 CFR 173.427 - Transport requirements for low specific activity (LSA) Class 7 (radioactive) materials and...

Code of Federal Regulations, 2011 CFR

2011-10-01

... package (IP-1, IP-2 or IP-3; § 173.411), subject to the limitations of Table 6; (2) In a DOT Specification... use shipment 1. LSA-I: Solid IP-1 IP-1 Liquid IP-1 IP-2 2. LSA-II: Solid IP-2 IP-2 Liquid and gas IP-2 IP-3 3. LSA-III IP-2 IP-3 4. SCO-I IP-1 IP-1 5. SCO-II IP-2 IP-2 [69 FR 3676, Jan. 26, 2004; 69 FR...

Comparison between three adjuvants for a vaccine against canine leishmaniasis: In vitro evaluation of macrophage killing ability.

PubMed

Trotta, T; Fasanella, A; Scaltrito, D; Gradoni, L; Mitolo, V; Brandonisio, O; Acquafredda, A; Panaro, M A

2010-03-01

The aim of this study was to evaluate, in terms of dog macrophage killing ability in vitro, a vaccine based on Leishmania infantum promastigote soluble antigen (LSA) formulated with three different adjuvants (BCG, AdjuPrime, MPL/TDM/CWS). A significant increase of the macrophage killing ability was observed in dogs vaccinated with LSA+MPL/TDM/CWS after 1 month from vaccination. A similar increase of macrophage parasitocidal ability was present only after 5 months in dogs vaccinated with LSA+BCG or LSA+AdjuPrime. In all dogs the augmented killing percentage was still present after 12 months from vaccination. Therefore, in particular LSA+MPL/TDM/CWS vaccine seems promising for further studies in dogs. 2009 Elsevier Ltd. All rights reserved.

Aerosol Emissions from Great Lakes Harmful Algal Blooms

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

May, Nathaniel W.; Olson, Nicole E.; Panas, Mark

In freshwater lakes, harmful algal blooms (HABs) of Cyanobacteria (blue-green algae) produce toxins that impact human health. However, little is known about the chemical species present in lake spray aerosol (LSA) produced from wave-breaking in freshwater HABs. In this study, a laboratory LSA generator produced aerosols from freshwater samples collected from Lake Michigan and Lake Erie during HAB and non-bloom conditions. Particles were analyzed for size and chemical composition by single particle mass spectrometry, electron microscopy, and fluorescence microscopy, with three distinct types of LSA identified with varying levels of organic carbon and biological material associated with calcium salts. LSAmore » autofluorescence increases with blue-green algae concentration, showing that organic molecules of biological origin are incorporated in LSA from HABs. The number fraction of LSA with biological mass spectral markers also increases with particle diameter (greater than 0.5 μm), showing that HABs have size-dependent impacts on aerosol composition. The highest number fraction of LSA enriched in organic carbon were observed in particles less than 0.5 μm in diameter. Understanding the transfer of organic and biogenic material from freshwater to the atmosphere via LSA particles is crucial for determining health and climate effects due to HABs.« less

Leptospiral outer membrane protein microarray, a novel approach to identification of host ligand-binding proteins.

PubMed

Pinne, Marija; Matsunaga, James; Haake, David A

2012-11-01

Leptospirosis is a zoonosis with worldwide distribution caused by pathogenic spirochetes belonging to the genus Leptospira. The leptospiral life cycle involves transmission via freshwater and colonization of the renal tubules of their reservoir hosts. Infection requires adherence to cell surfaces and extracellular matrix components of host tissues. These host-pathogen interactions involve outer membrane proteins (OMPs) expressed on the bacterial surface. In this study, we developed an Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 OMP microarray containing all predicted lipoproteins and transmembrane OMPs. A total of 401 leptospiral genes or their fragments were transcribed and translated in vitro and printed on nitrocellulose-coated glass slides. We investigated the potential of this protein microarray to screen for interactions between leptospiral OMPs and fibronectin (Fn). This approach resulted in the identification of the recently described fibronectin-binding protein, LIC10258 (MFn8, Lsa66), and 14 novel Fn-binding proteins, denoted Microarray Fn-binding proteins (MFns). We confirmed Fn binding of purified recombinant LIC11612 (MFn1), LIC10714 (MFn2), LIC11051 (MFn6), LIC11436 (MFn7), LIC10258 (MFn8, Lsa66), and LIC10537 (MFn9) by far-Western blot assays. Moreover, we obtained specific antibodies to MFn1, MFn7, MFn8 (Lsa66), and MFn9 and demonstrated that MFn1, MFn7, and MFn9 are expressed and surface exposed under in vitro growth conditions. Further, we demonstrated that MFn1, MFn4 (LIC12631, Sph2), and MFn7 enable leptospires to bind fibronectin when expressed in the saprophyte, Leptospira biflexa. Protein microarrays are valuable tools for high-throughput identification of novel host ligand-binding proteins that have the potential to play key roles in the virulence mechanisms of pathogens.

Use of Language Sample Analysis by School-Based SLPs: Results of a Nationwide Survey

ERIC Educational Resources Information Center

Pavelko, Stacey L.; Owens, Robert E., Jr.; Ireland, Marie; Hahs-Vaughn, Debbie L.

2016-01-01

Purpose: This article examines use of language sample analysis (LSA) by school-based speech-language pathologists (SLPs), including characteristics of language samples, methods of transcription and analysis, barriers to LSA use, and factors affecting LSA use, such as American Speech-Language-Hearing Association certification, number of years'…

Effectiveness of Automated Chinese Sentence Scoring with Latent Semantic Analysis

ERIC Educational Resources Information Center

Liao, Chen-Huei; Kuo, Bor-Chen; Pai, Kai-Chih

2012-01-01

Automated scoring by means of Latent Semantic Analysis (LSA) has been introduced lately to improve the traditional human scoring system. The purposes of the present study were to develop a LSA-based assessment system to evaluate children's Chinese sentence construction skills and to examine the effectiveness of LSA-based automated scoring function…

46 CFR 148.04-1 - Radioactive material, Low Specific Activity (LSA).

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 5 2010-10-01 2010-10-01 false Radioactive material, Low Specific Activity (LSA). 148... § 148.04-1 Radioactive material, Low Specific Activity (LSA). (a) Authorized materials are limited to: (1) Uranium or thorium ores and physical or chemical concentrates of such ores; (2) Uranium metal...

Long-Lasting Sound-Evoked Afterdischarge in the Auditory Midbrain

PubMed Central

Ono, Munenori; Bishop, Deborah C.; Oliver, Douglas L.

2016-01-01

Different forms of plasticity are known to play a critical role in the processing of information about sound. Here, we report a novel neural plastic response in the inferior colliculus, an auditory center in the midbrain of the auditory pathway. A vigorous, long-lasting sound-evoked afterdischarge (LSA) is seen in a subpopulation of both glutamatergic and GABAergic neurons in the central nucleus of the inferior colliculus of normal hearing mice. These neurons were identified with single unit recordings and optogenetics in vivo. The LSA can continue for up to several minutes after the offset of the sound. LSA is induced by long-lasting, or repetitive short-duration, innocuous sounds. Neurons with LSA showed less adaptation than the neurons without LSA. The mechanisms that cause this neural behavior are unknown but may be a function of intrinsic mechanisms or the microcircuitry of the inferior colliculus. Since LSA produces long-lasting firing in the absence of sound, it may be relevant to temporary or chronic tinnitus or to some other aftereffect of long-duration sound. PMID:26867811

Is the Life Space Assessment applicable to a palliative care population? Its relationship to measures of performance and quality of life.

PubMed

Phillips, Jane Louise; Lam, Lawrence; Luckett, Tim; Agar, Meera; Currow, David

2014-06-01

The spatial environments that palliative care patients frequent for business and leisure constrict as their disease progresses and their physical functioning deteriorates. Measuring a person's movement within his or her own environment is a clinically relevant and patient-centered outcome because it measures function in a way that reflects actual and not theoretical participation. This exploratory study set out to test whether the Life-Space Assessment (LSA) would correlate with other commonly used palliative care outcome measures of function and quality of life. The baseline LSA, Australia-modified Karnofsky Performance Status Scale (AKPS), and the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 15-Palliative (EORTC QLQ-C15-PAL) scores from two large clinical trials were used to calculate correlation coefficients between the measures. Convergent validity analysis was undertaken by comparing LSA scores between participants with higher (≥70) and lower (≤60) AKPS scores. The LSA was correlated significantly and positively with the AKPS, with a moderate correlation coefficient of 0.54 (P<0.001). There was a significant weak negative correlation between the LSA and the EORTC QLQ-C15-PAL, with a small coefficient of -0.22 (P=0.027), but a strong correlation between the LSA and the EORTC QLQ-C15-PAL item related to independent activities of daily living (r=-0.654, P<0.01). A significant difference in the LSA score between participants with higher (≥70) and lower (≤60) AKPS scores t(97)=-4.35, P<0.001) was found. The LSA appears applicable to palliative care populations given the convergent validity and capacity of this instrument to differentiate a person's ability to move through life-space zones by performance status. Further research is required to validate and apply the LSA within community palliative care populations. Copyright © 2014 U.S. Cancer Pain Relief Committee. Published by Elsevier Inc. All rights reserved.

[Psychoactive effects of 'legal high': About lysergic acid amide (LSA)].

PubMed

Ponté, Camille; Lapeyre-Mestre, Maryse

2017-10-01

Lysergic acid amide (LSA) is a natural psychoactive substance consumed as a psychedelic drug. In 2016, 4 cases were reported to the Toulouse Addictovigilance Centre, resulting in unintended psychic effects and led to a hospitalisation in 2 cases. Other cases of serious LSA intoxication are published, including a death. It is important to inform about the risks related to LSA consumption, a substance which is freely available and sometimes hidden behind various plant names. Copyright © 2017 Société française de pharmacologie et de thérapeutique. Published by Elsevier Masson SAS. All rights reserved.

46 CFR 148.300 - Radioactive materials.

Code of Federal Regulations, 2011 CFR

2011-10-01

... radioactive materials defined in 49 CFR 173.403 as Low Specific Activity Material, LSA-1, or Surface... 7 material (radioactive) listed in Table 148.10 of this part must be surveyed after the completion of off-loading by a qualified person using appropriate radiation detection instruments. Such holds...

Lifetime suicidal ideation and attempt in adults with full major depressive disorder versus sustained depressed mood.

PubMed

Yoo, Hye Jin; Hong, Jin Pyo; Cho, Maeng Je; Fava, Maurizio; Mischoulon, David; Heo, Jung-Yoon; Kim, Kiwon; Jeon, Hong Jin

2016-10-01

Major depressive disorder (MDD) is a well-known risk factor for suicidality, but depressed mood has been used non-specifically to describe the emotional state. We sought to compare influence of MDD versus sustained depressed mood on suicidality. A total of 12,532 adults, randomly selected through the one-person-per-household method, completed a face-to-face interview using the Korean version of Composite International Diagnostic Interview (K-CIDI) and a questionnaire for lifetime suicidal ideation (LSI) and lifetime suicidal attempt (LSA). Of 12,361 adults, 565 were assessed as 'sustained depressed mood group' having depressed mood for more than two weeks without MDD (4.6%), and 810 adults were assessed as having full MDD (6.55%) which consisted of 'MDD with depressed mood group' (6.0%) and 'MDD without depressed mood group' (0.5%). The MDD with depressed mood group showed higher odds ratios for LSI and LSA than the sustained depressed mood group. Contrarily, no significant differences were found in LSI and LSA between the MDD group with and without depressed mood. MDD showed significant associations with LSI (AOR=2.83, 95%CI 2.12-3.78) and LSA (AOR=2.17, 95%CI 1.34-3.52), whereas sustained depressed mood showed significant associations with neither LSI nor LSA after adjusting for MDD and other psychiatric comorbidities. Interaction effect of sustained depressed mood with MDD was significant for LSI but not for LSA. Sustained depressed mood was not related to LSI and LSA after adjusting for psychiatric comorbidities, whereas MDD was significantly associated with both LSI and LSA regardless of the presence of sustained depressed mood. Copyright © 2016 Elsevier B.V. All rights reserved.

Survivin inhibition via EZN-3042 in canine lymphoma and osteosarcoma.

PubMed

Shoeneman, J K; Ehrhart, E J; Charles, J B; Thamm, D H

2016-06-01

Canine lymphoma (LSA) and osteosarcoma (OS) have high mortality rates and remain in need of more effective therapeutic approaches. Survivin, an inhibitor of apoptosis (IAP) family member protein that inhibits apoptosis and drives cell proliferation, is commonly elevated in human and canine cancer. Survivin expression is a negative prognostic factor in dogs with LSA and OS, and canine LSA and OS cell lines express high levels of survivin. In this study, we demonstrate that survivin downregulation in canine LSA and OS cells using a clinically applicable locked nucleic acid antisense oligonucleotide (EZN-3042, Enzon Pharmaceuticals, Piscataway Township, NJ, USA) inhibits growth, induces apoptosis and enhances chemosensitivity in vitro, and inhibits survivin transcription and protein production in orthotopic canine OS xenografts. Our findings strongly suggest that survivin-directed therapies might be effective in treatment of canine LSA and OS and support evaluation of EZN-3042 in dogs with cancer. © 2014 John Wiley & Sons Ltd.

Left subclavian artery revascularization in zone 2 thoracic endovascular aortic repair is associated with lower stroke risk across all aortic diseases.

PubMed

Bradshaw, Rhiannon J; Ahanchi, S Sadie; Powell, Obie; Larion, Sebastian; Brandt, Colin; Soult, Michael C; Panneton, Jean M

2017-05-01

The best management strategy for the left subclavian artery (LSA) in pathologic processes of the aorta requiring zone 2 thoracic endovascular aortic repair (TEVAR) remains controversial. We compared LSA coverage with or without revascularization as well as the different means of LSA revascularization. A retrospective chart review was conducted of patients with any aortic diseases who underwent zone 2 TEVAR deployment from 2007 to 2014. Primary end points included 30-day stroke and 30-day spinal cord injury (SCI). Secondary end points were 30-day procedure-related reintervention, freedom from aorta-related reintervention, aorta-related mortality, and all-cause mortality. We identified 96 patients with zone 2 TEVAR who met our inclusion criteria. The mean age of the patients was 62 years, with 61.5% male. Diseases included acute aortic dissections (n = 25), chronic aortic dissection with aneurysmal degeneration (n = 22), primary aortic aneurysms (n = 21), penetrating aortic ulcers/intramural hematomas (n = 17), and traumatic aortic injuries (n = 11). Strategies for the LSA included coverage with revascularization (n = 54) or without revascularization (n = 42). Methods of LSA revascularization included laser fenestration with stenting (n = 33) and surgical revascularization: transposition (n = 10) or bypass (n = 11). Of the 54 patients with LSA revascularization, 44 (81.5%) underwent LSA intervention at the time of TEVAR and 10 (18.5%) at a mean time of 33 days before TEVAR (range, 4-63 days). For the entire cohort, the overall incidence of 30-day stroke was 7.3%; of 30-day SCI, 2.1%; and of procedure-related reintervention, 5.2%. At a mean follow-up of 24 months (range, 1-79 months), aorta-related reintervention was 15.6%, aorta-related mortality was 12.5%, and all-cause mortality was 29.2%. The 30-day stroke rate was highest for LSA coverage without revascularization (6/42 [14.3%]) compared with any form of LSA revascularization (1/54 [1.9%]; P = .020), with no difference between LSA interventions done synchronously with TEVAR (1/44 [2.3%]) vs metachronously with TEVAR (0/10 [0%]; P = .63). There was no significant difference in 30-day SCI in LSA coverage without revascularization (2/42 [4.8%]) vs with revascularization (0/54 [0%]; P = .11). There was no difference in aorta-related reintervention, aorta-related mortality, or all-cause mortality in coverage without revascularization (5/42 [11.9%], 6/42 [14.3%], and 14/42 [33.3%]) vs with revascularization (10/54 [18.5%; P = .376], 6/54 [11.1%; P = .641], and 14/54 [25.9%; P = .43], respectively). After univariate and multivariable analysis, we identified LSA coverage without revascularization as associated with a higher rate of 30-day stroke (hazard ratio, 17.2; 95% confidence interval, 1.3-220.4; P = .029). Our study suggests that coverage of the LSA without revascularization increases the risk of stroke and possibly SCI. Copyright © 2016 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.

Latent semantic analysis cosines as a cognitive similarity measure: Evidence from priming studies.

PubMed

Günther, Fritz; Dudschig, Carolin; Kaup, Barbara

2016-01-01

In distributional semantics models (DSMs) such as latent semantic analysis (LSA), words are represented as vectors in a high-dimensional vector space. This allows for computing word similarities as the cosine of the angle between two such vectors. In two experiments, we investigated whether LSA cosine similarities predict priming effects, in that higher cosine similarities are associated with shorter reaction times (RTs). Critically, we applied a pseudo-random procedure in generating the item material to ensure that we directly manipulated LSA cosines as an independent variable. We employed two lexical priming experiments with lexical decision tasks (LDTs). In Experiment 1 we presented participants with 200 different prime words, each paired with one unique target. We found a significant effect of cosine similarities on RTs. The same was true for Experiment 2, where we reversed the prime-target order (primes of Experiment 1 were targets in Experiment 2, and vice versa). The results of these experiments confirm that LSA cosine similarities can predict priming effects, supporting the view that they are psychologically relevant. The present study thereby provides evidence for qualifying LSA cosine similarities not only as a linguistic measure, but also as a cognitive similarity measure. However, it is also shown that other DSMs can outperform LSA as a predictor of priming effects.

Risk burdens of modifiable risk factors incorporating lipoprotein (a) and low serum albumin concentrations for first incident acute myocardial infarction

PubMed Central

Yang, Qin; He, Yong-Ming; Cai, Dong-Ping; Yang, Xiang-Jun; Xu, Hai-Feng

2016-01-01

Risk burdens of modifiable risk factors incorporating lipoprotein (a) (Lp(a)) and low serum albumin (LSA) concentrations for first incident acute myocardial infarction (AMI) haven’t been studied previously. Cross-sectional study of 1552 cases and 6125 controls was performed for identifying the association of risk factors with first incident AMI and their corresponding population attributable risks (PARs). Modifiable risk factors incorporating LSA and Lp(a) accounted for up to 92% of PAR for first incident AMI. Effects of these risk factors were different in different sexes across different age categories. Overall, smoking and LSA were the 2 strongest risk factors, together accounting for 64% of PAR for first incident AMI. After multivariable adjustment, Lp(a) and LSA accounted for 19% and 41%, respectively, and together for more than a half (54%) of PAR for first incident AMI. Modifiable risk factors incorporating LSA and Lp(a) have accounted for an overwhelmingly large proportion of the risk of first incident AMI, indicating most first incident AMI is preventable. The knowledge of risk burdens for first incident AMI incorporating Lp (a) and LSA may be beneficial for further reducing first incident AMI from a new angle. PMID:27748452

An index-based algorithm for fast on-line query processing of latent semantic analysis

PubMed Central

Li, Pohan; Wang, Wei

2017-01-01

Latent Semantic Analysis (LSA) is widely used for finding the documents whose semantic is similar to the query of keywords. Although LSA yield promising similar results, the existing LSA algorithms involve lots of unnecessary operations in similarity computation and candidate check during on-line query processing, which is expensive in terms of time cost and cannot efficiently response the query request especially when the dataset becomes large. In this paper, we study the efficiency problem of on-line query processing for LSA towards efficiently searching the similar documents to a given query. We rewrite the similarity equation of LSA combined with an intermediate value called partial similarity that is stored in a designed index called partial index. For reducing the searching space, we give an approximate form of similarity equation, and then develop an efficient algorithm for building partial index, which skips the partial similarities lower than a given threshold θ. Based on partial index, we develop an efficient algorithm called ILSA for supporting fast on-line query processing. The given query is transformed into a pseudo document vector, and the similarities between query and candidate documents are computed by accumulating the partial similarities obtained from the index nodes corresponds to non-zero entries in the pseudo document vector. Compared to the LSA algorithm, ILSA reduces the time cost of on-line query processing by pruning the candidate documents that are not promising and skipping the operations that make little contribution to similarity scores. Extensive experiments through comparison with LSA have been done, which demonstrate the efficiency and effectiveness of our proposed algorithm. PMID:28520747

"Inclusive working life in Norway": a registry-based five-year follow-up study.

PubMed

Foss, Line; Gravseth, Hans Magne; Kristensen, Petter; Claussen, Bjørgulf; Mehlum, Ingrid Sivesind; Skyberg, Knut

2013-07-08

In 2001, the Norwegian authorities and major labour market partners signed an agreement regarding 'inclusive working life' (IW), whereby companies that participate are committed to reducing sickness absence. Our main aim was to determine the effect of the IW program and work characteristics by gender on long-term (>8 weeks) sickness absence (LSA). Self-reported data on work characteristics from the Oslo Health Study were linked to registry-based data on IW status, education and LSA. From 2001-2005, 10,995 participants (5,706 women and 5,289 men) aged 30, 40, 45 and 60 years were followed. A Cox regression was used to compute hazard ratios (HR) for LSA risk. The cohort was divided into an IW group (2,733 women and 2,058 men) and non-IW group (2,973/3,231). 43.2% and 41.6% of women and 22.3%/24.3% of men (IW / non-IW, respectively) experienced at least one LSA. In a multivariate model, statistically significant risk factors for LSA were low education (stronger in men), shift work/night work or rotating hours (strongest in men in the non-IW group), and heavy physical work or work involving walking and lifting (men only and stronger in the non-IW group). Among men who engaged in shift work, the LSA risk was significantly lower in the IW group. Our results could suggest that IW companies that employ many men in shift work have implemented relevant efforts for reducing sickness absence. However, this study could not demonstrate a significant effect of the IW program on the overall LSA risk.

Behavioral and autonomic responses to acute restraint stress are segregated within the lateral septal area of rats.

PubMed

Reis, Daniel G; Scopinho, América A; Guimarães, Francisco S; Corrêa, Fernando M A; Resstel, Leonardo B M

2011-01-01

The Lateral Septal Area (LSA) is involved with autonomic and behavior responses associated to stress. In rats, acute restraint (RS) is an unavoidable stress situation that causes autonomic (body temperature, mean arterial pressure (MAP) and heart rate (HR) increases) and behavioral (increased anxiety-like behavior) changes in rats. The LSA is one of several brain regions that have been involved in stress responses. The aim of the present study was to investigate if the neurotransmission blockade in the LSA would interfere in the autonomic and behavioral changes induced by RS. Male Wistar rats with bilateral cannulae aimed at the LSA, an intra-abdominal datalogger (for recording internal body temperature), and an implanted catheter into the femoral artery (for recording and cardiovascular parameters) were used. They received bilateral microinjections of the non-selective synapse blocker cobalt chloride (CoCl(2), 1 mM/ 100 nL) or vehicle 10 min before RS session. The tail temperature was measured by an infrared thermal imager during the session. Twenty-four h after the RS session the rats were tested in the elevated plus maze (EPM). Inhibition of LSA neurotransmission reduced the MAP and HR increases observed during RS. However, no changes were observed in the decrease in skin temperature and increase in internal body temperature observed during this period. Also, LSA inhibition did not change the anxiogenic effect induced by RS observed 24 h later in the EPM. The present results suggest that LSA neurotransmission is involved in the cardiovascular but not the temperature and behavioral changes induced by restraint stress.

An index-based algorithm for fast on-line query processing of latent semantic analysis.

PubMed

Zhang, Mingxi; Li, Pohan; Wang, Wei

2017-01-01

Latent Semantic Analysis (LSA) is widely used for finding the documents whose semantic is similar to the query of keywords. Although LSA yield promising similar results, the existing LSA algorithms involve lots of unnecessary operations in similarity computation and candidate check during on-line query processing, which is expensive in terms of time cost and cannot efficiently response the query request especially when the dataset becomes large. In this paper, we study the efficiency problem of on-line query processing for LSA towards efficiently searching the similar documents to a given query. We rewrite the similarity equation of LSA combined with an intermediate value called partial similarity that is stored in a designed index called partial index. For reducing the searching space, we give an approximate form of similarity equation, and then develop an efficient algorithm for building partial index, which skips the partial similarities lower than a given threshold θ. Based on partial index, we develop an efficient algorithm called ILSA for supporting fast on-line query processing. The given query is transformed into a pseudo document vector, and the similarities between query and candidate documents are computed by accumulating the partial similarities obtained from the index nodes corresponds to non-zero entries in the pseudo document vector. Compared to the LSA algorithm, ILSA reduces the time cost of on-line query processing by pruning the candidate documents that are not promising and skipping the operations that make little contribution to similarity scores. Extensive experiments through comparison with LSA have been done, which demonstrate the efficiency and effectiveness of our proposed algorithm.

Computerized summary scoring: crowdsourcing-based latent semantic analysis.

PubMed

Li, Haiying; Cai, Zhiqiang; Graesser, Arthur C

2017-11-03

In this study we developed and evaluated a crowdsourcing-based latent semantic analysis (LSA) approach to computerized summary scoring (CSS). LSA is a frequently used mathematical component in CSS, where LSA similarity represents the extent to which the to-be-graded target summary is similar to a model summary or a set of exemplar summaries. Researchers have proposed different formulations of the model summary in previous studies, such as pregraded summaries, expert-generated summaries, or source texts. The former two methods, however, require substantial human time, effort, and costs in order to either grade or generate summaries. Using source texts does not require human effort, but it also does not predict human summary scores well. With human summary scores as the gold standard, in this study we evaluated the crowdsourcing LSA method by comparing it with seven other LSA methods that used sets of summaries from different sources (either experts or crowdsourced) of differing quality, along with source texts. Results showed that crowdsourcing LSA predicted human summary scores as well as expert-good and crowdsourcing-good summaries, and better than the other methods. A series of analyses with different numbers of crowdsourcing summaries demonstrated that the number (from 10 to 100) did not significantly affect performance. These findings imply that crowdsourcing LSA is a promising approach to CSS, because it saves human effort in generating the model summary while still yielding comparable performance. This approach to small-scale CSS provides a practical solution for instructors in courses, and also advances research on automated assessments in which student responses are expected to semantically converge on subject matter content.

Outcomes of Thoracic Endovascular Aortic Repair and Subclavian Revascularization Techniques

PubMed Central

Zamor, Kimberly C; Eskandari, Mark K; Rodriguez, Heron E; Ho, Karen J; Morasch, Mark D; Hoel, Andrew W

2015-01-01

Background Practice guidelines regarding management of the left subclavian artery (LSA) during thoracic endovascular aortic repair (TEVAR) are based on low quality evidence and there is limited literature that addresses optimal revascularization techniques. The purpose of this study is to compare outcomes of LSA coverage during TEVAR and revascularization techniques. Study Design We performed a single-center retrospective cohort study from 2001–2013. Patients were categorized by LSA revascularization and by revascularization technique, carotid-subclavian bypass (CSB) or subclavian-carotid transposition (SCT). Thirty-day and mid-term stroke, spinal cord ischemia, vocal cord paralysis, upper extremity ischemia, primary patency of revascularization, and mortality were compared. Results Eighty patients underwent TEVAR with LSA coverage, 25% (n=20) were unrevascularized and the remaining patients underwent CSB (n=22, 27.5%) or SCT (n=38, 47.5%). Mean follow-up time was 24.9 months. Comparisons between unrevascularized and revascularized patients were significant for a higher rate of 30-day stroke (25% vs. 2%, p=0.003) and upper extremity ischemia (15% vs. 0%, p=0.014). However, there was no difference in 30-day or mid-term rates of spinal cord ischemia, vocal cord paralysis, or mortality. There were no statistically significant differences in 30-day or midterm outcomes for CSB vs. SCT. Primary patency of revascularizations was 100%. Survival analysis comparing unrevascularized vs. revascularized LSA, was statistically significant for freedom from stroke and upper extremity ischemia, p=0.02 and p=0.003, respectively. After adjustment for advanced age, urgency and coronary artery disease, LSA revascularization was associated with lower rates of peri-operative adverse events (OR 0.23, p=0.034). Conclusions During TEVAR, LSA coverage without revascularization is associated with an increased risk of stroke and upper extremity ischemia. When LSA coverage is required during TEVAR, CSB and SCT are equally acceptable options. PMID:25872688

Analogous Three-Dimensional Constructive Interference in Steady State Sequences Enhance the Utility of Three-Dimensional Time of Flight Magnetic Resonance Angiography in Delineating Lenticulostriate Arteries in Insular Gliomas: Evidence from a Prospective Clinicoradiologic Analysis of 48 Patients.

PubMed

Rao, Arun S; Thakar, Sumit; Sai Kiran, Narayanam Anantha; Aryan, Saritha; Mohan, Dilip; Hegde, Alangar S

2018-01-01

Three-dimensional (3D) time of flight (TOF) imaging is the current gold standard for noninvasive, preoperative localization of lenticulostriate arteries (LSAs) in insular gliomas; however, the utility of this modality depends on tumor intensity. Over a 3-year period, 48 consecutive patients with insular gliomas were prospectively evaluated. Location of LSAs and their relationship with the tumor were determined using a combination of contrast-enhanced coronal 3D TOF magnetic resonance angiography and coronal 3D constructive interference in steady state (CISS) sequences. These findings were analyzed with respect to extent of tumor resection and early postoperative motor outcome. Tumor was clearly visualized in 29 (60.4%) patients with T1-hypointense tumors using 3D TOF and in all patients using CISS sequences. Using combined 3D TOF and CISS, LSA-tumor interface was well seen in 47 patients, including all patients with T1-heterointense or T1-isointense tumors. Extent of resection was higher in the LSA-pushed group compared with the LSA-encased group. In the LSA-encased group, 6 (12.5%) patients developed postoperative hemiparesis; 2 (4.2%) cases were attributed to LSA injury. Contrast-enhanced 3D TOF can delineate LSAs in almost all insular gliomas but is limited in identifying the LSA-tumor interface. This limitation can be overcome by addition of analogous CISS sequences that delineate the LSA-tumor interface regardless of tumor intensity. Combined 3D TOF and 3D CISS is a useful tool for surgical planning and safer resections of insular tumors and may have added surgical relevance when included as an intraoperative adjunct. Copyright © 2017 Elsevier Inc. All rights reserved.

Design and use of multiple blade slurry sawing in a production atmosphere

NASA Technical Reports Server (NTRS)

Lynah, F. P., Jr.; Ross, J. B.

1982-01-01

The technique and uses of the multiple blade slurry (MBS) saw are considered. Multiple bands of steel are arranged in a frame and the frame is reciprocated with the steel bands to a workpiece, while simultaneously applying abrasive at the point of contact. The blades wear slots in the workpiece and progress through the piece resulting in several parts of wafers. The transition to MBA from diamond slicing is justified by savings resulting from minimized kerf losses, minimized subsurface damage, and improved surface quality off the saw. This allows wafering much closer to finished thickness specifications. The current state of the art MBS technology must be significantly improved if the low cost solar array (LSA) goals are to be attained. It is concluded that although MBS will never be the answer to every wafering requirement, the economical production of wafers to LSA project specifications will be achieved.

Exploring MEDLINE Space with Random Indexing and Pathfinder Networks

PubMed Central

Cohen, Trevor

2008-01-01

The integration of disparate research domains is a prerequisite for the success of the translational science initiative. MEDLINE abstracts contain content from a broad range of disciplines, presenting an opportunity for the development of methods able to integrate the knowledge they contain. Latent Semantic Analysis (LSA) and related methods learn human-like associations between terms from unannotated text. However, their computational and memory demands limits their ability to address a corpus of this size. Furthermore, visualization methods previously used in conjunction with LSA have limited ability to define the local structure of the associative networks LSA learns. This paper explores these issues by (1) processing the entire MEDLINE corpus using Random Indexing, a variant of LSA, and (2) exploring learned associations using Pathfinder Networks. Meaningful associations are inferred from MEDLINE, including a drug-disease association undetected by PUBMED search. PMID:18999236

Exploring MEDLINE space with random indexing and pathfinder networks.

PubMed

Cohen, Trevor

2008-11-06

The integration of disparate research domains is a prerequisite for the success of the translational science initiative. MEDLINE abstracts contain content from a broad range of disciplines, presenting an opportunity for the development of methods able to integrate the knowledge they contain. Latent Semantic Analysis (LSA) and related methods learn human-like associations between terms from unannotated text. However, their computational and memory demands limits their ability to address a corpus of this size. Furthermore, visualization methods previously used in conjunction with LSA have limited ability to define the local structure of the associative networks LSA learns. This paper explores these issues by (1) processing the entire MEDLINE corpus using Random Indexing, a variant of LSA, and (2) exploring learned associations using Pathfinder Networks. Meaningful associations are inferred from MEDLINE, including a drug-disease association undetected by PUBMED search.

A statistical model that predicts the length from the left subclavian artery to the celiac axis; towards accurate intra aortic balloon sizing.

PubMed

Parissis, Haralabos; Soo, Alan; Leotsinidis, Michalis; Dougenis, Dimitrios

2011-08-09

Ideally the length of the Intraaortic balloon membrane (22-27.5 cm) should match to the distance from the left subclavian artery (LSA) to the celiac axis (CA), (LSA - CA). By being able to estimate this distance, better guidance regarding IABP sizing could be recommended. Internal aortic lengths and demographic values were collected from a series of 40 cadavers during autopsy. External somatometric measurements were also obtained.There were 23 males and 17 females. The mean age was 73.1+/-13.11 years, weight 56.75+/-12.51 kg and the height 166+/-9.81 cm. Multiple regression analysis revealed the following predictor variables (R2 > 0.70) for estimating the length from LSA to CA: height (standardized coefficient (SRC) = 0.37, p = 0.004), age (SRC = 0.35, p < 0.001), sex (SRC = 0.21, p = 0.088) and the distance from the jugular notch to trans-pyloric plane (SRC = 0.61, p < 0.001). If LSA-CA < 21.9 cm use 34 cc IABP & if LSA-CA > 26.3 cm use 50 cc IABP. However if LSA-CA = 21.9- 26.3 cm use 40 cc, but be aware that it could be "aortic length-balloon membrane length" mismatching. Routinely, IABP size selection is being dictated by the patient's height. Inevitably, this leads to pitfalls. We reported a mathematical model of accurate intraaortic balloon sizing, which is easy to be applied and has a high predictive value.

Lifetime Sexual Assault and Sexually Transmitted Infections Among Women Veterans.

PubMed

Goyal, Vinita; Mengeling, Michelle A; Booth, Brenda M; Torner, James C; Syrop, Craig H; Sadler, Anne G

2017-07-01

Women veterans report a high prevalence of sexual assault. Unfortunately, there are limited data on the reproductive health sequelae faced by these women. Our objective was to evaluate the association between completed lifetime sexual assault (LSA) and sexually transmitted infections (STIs) among a cohort of women veterans, adjusting for sexual risk behaviors. We conducted a retrospective study among women veterans aged 51 years or younger who enrolled for care at two Veterans Administration (VA) healthcare sites between 2000 and 2008. Participants completed a telephone interview assessing reproductive health and sexual violence history. We compared the frequencies of past STI diagnoses among those who had and had not experienced LSA. We used logistic regression to assess the effect of sexual assault with history of an STI diagnosis after adjusting for age, sexual risk behaviors, and substance abuse treatment. Among 996 women veterans, a history of STIs was reported by 32%, including a lifetime history of gonorrhea (5%), chlamydia (15%), genital herpes infection (8%), and human papillomavirus infection (15%), not mutually exclusive; 51% reported LSA. Women with a history of LSA were significantly more likely to report a history of STIs (unadjusted odds ratio [OR] 1.91, 95% confidence interval [CI] 1.45-2.50; adjusted OR 1.49, 95% CI 1.07-2.08). Women veterans who have experienced LSA are at increased risk for lifetime STI diagnoses. To adequately address the reproductive health needs of the growing population of women veterans, STI risk assessments should include queries of military service and LSA histories.

Singularity analysis based on wavelet transform of fractal measures for identifying geochemical anomaly in mineral exploration

NASA Astrophysics Data System (ADS)

Chen, Guoxiong; Cheng, Qiuming

2016-02-01

Multi-resolution and scale-invariance have been increasingly recognized as two closely related intrinsic properties endowed in geofields such as geochemical and geophysical anomalies, and they are commonly investigated by using multiscale- and scaling-analysis methods. In this paper, the wavelet-based multiscale decomposition (WMD) method was proposed to investigate the multiscale natures of geochemical pattern from large scale to small scale. In the light of the wavelet transformation of fractal measures, we demonstrated that the wavelet approximation operator provides a generalization of box-counting method for scaling analysis of geochemical patterns. Specifically, the approximation coefficient acts as the generalized density-value in density-area fractal modeling of singular geochemical distributions. Accordingly, we presented a novel local singularity analysis (LSA) using the WMD algorithm which extends the conventional moving averaging to a kernel-based operator for implementing LSA. Finally, the novel LSA was validated using a case study dealing with geochemical data (Fe2O3) in stream sediments for mineral exploration in Inner Mongolia, China. In comparison with the LSA implemented using the moving averaging method the novel LSA using WMD identified improved weak geochemical anomalies associated with mineralization in covered area.

Inkjet-Printed In-Ga-Zn Oxide Thin-Film Transistors with Laser Spike Annealing

NASA Astrophysics Data System (ADS)

Huang, Hang; Hu, Hailong; Zhu, Jingguang; Guo, Tailiang

2017-07-01

Inkjet-printed In-Ga-Zn oxide (IGZO) thin-film transistors (TFTs) have been fabricated at low temperature using laser spike annealing (LSA) treatment. Coffee-ring effects during the printing process were eliminated to form uniform IGZO films by simply increasing the concentration of solute in the ink. The impact of LSA on the TFT performance was studied. The field-effect mobility, threshold voltage, and on/off current ratio were greatly influenced by the LSA treatment. With laser scanning at 1 mm/s for 40 times, the 30-nm-thick IGZO TFT baked at 200°C showed mobility of 1.5 cm2/V s, threshold voltage of -8.5 V, and on/off current ratio >106. Our findings demonstrate the feasibility of rapid LSA treatment of low-temperature inkjet-printed oxide semiconductor transistors, being comparable to those obtained by conventional high-temperature annealing.

Latent morpho-semantic analysis : multilingual information retrieval with character n-grams and mutual information.

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

Bader, Brett William; Chew, Peter A.; Abdelali, Ahmed

We describe an entirely statistics-based, unsupervised, and language-independent approach to multilingual information retrieval, which we call Latent Morpho-Semantic Analysis (LMSA). LMSA overcomes some of the shortcomings of related previous approaches such as Latent Semantic Analysis (LSA). LMSA has an important theoretical advantage over LSA: it combines well-known techniques in a novel way to break the terms of LSA down into units which correspond more closely to morphemes. Thus, it has a particular appeal for use with morphologically complex languages such as Arabic. We show through empirical results that the theoretical advantages of LMSA can translate into significant gains in precisionmore » in multilingual information retrieval tests. These gains are not matched either when a standard stemmer is used with LSA, or when terms are indiscriminately broken down into n-grams.« less

Visualization of lenticulostriate arteries at 3T: Optimization of slice-selective off-resonance sinc pulse-prepared TOF-MRA and its comparison with flow-sensitive black-blood MRA.

PubMed

Okuchi, Sachi; Okada, Tomohisa; Fujimoto, Koji; Fushimi, Yasutaka; Kido, Aki; Yamamoto, Akira; Kanagaki, Mitsunori; Dodo, Toshiki; Mehemed, Taha M; Miyazaki, Mitsue; Zhou, Xiangzhi; Togashi, Kaori

2014-06-01

To optimize visualization of lenticulostriate artery (LSA) by time-of-flight (TOF) magnetic resonance angiography (MRA) with slice-selective off-resonance sinc (SORS) saturation transfer contrast pulses and to compare capability of optimal TOF-MRA and flow-sensitive black-blood (FSBB) MRA to visualize the LSA at 3T. This study was approved by the local ethics committee, and written informed consent was obtained from all the subjects. TOF-MRA was optimized in 20 subjects by comparing SORS pulses of different flip angles: 0, 400°, and 750°. Numbers of LSAs were counted. The optimal TOF-MRA was compared to FSBB-MRA in 21 subjects. Images were evaluated by the numbers and length of visualized LSAs. LSAs were significantly more visualized in TOF-MRA with SORS pulses of 400° than others (P < .003). When the optimal TOF-MRA was compared to FSBB-MRA, the visualization of LSA using FSBB (mean branch numbers 11.1, 95% confidence interval (CI) 10.0-12.1; mean total length 236 mm, 95% CI 210-263 mm) was significantly better than using TOF (4.7, 95% CI 4.1-5.3; 78 mm, 95% CI 67-89 mm) for both numbers and length of the LSA (P < .0001). LSA visualization was best with 400° SORS pulses for TOF-MRA but FSBB-MRA was better than TOF-MRA, which indicates its clinical potential to investigate the LSA on a 3T magnetic resonance imaging. Copyright © 2014 AUR. Published by Elsevier Inc. All rights reserved.

Frontal delta-beta cross-frequency coupling in high and low social anxiety: An index of stress regulation?

PubMed

Poppelaars, Eefje S; Harrewijn, Anita; Westenberg, P Michiel; van der Molen, Melle J W

2018-05-17

Cross-frequency coupling (CFC) between frontal delta (1-4 Hz) and beta (14-30 Hz) oscillations has been suggested as a candidate neural correlate of social anxiety disorder, a disorder characterized by fear and avoidance of social and performance situations. Prior studies have used amplitude-amplitude correlation (AAC) as a CFC measure and hypothesized it as a candidate neural mechanism of affective control. However, using this metric has yielded inconsistent results regarding the direction of CFC, and the functional significance of coupling strength is uncertain. To offer a better understanding of CFC in social anxiety, we compared frontal delta-beta AAC with phase-amplitude coupling (PAC) - a mechanism for information transfer through neural circuits. Twenty high socially anxious (HSA) and 32 low socially anxious (LSA) female undergraduates participated in a social performance task (SPT). Delta-beta PAC and AAC were estimated during the resting state, as well as the anticipation and recovery conditions. Results showed significantly more AAC in LSA than HSA participants during early anticipation, as well as significant values during all conditions in LSA participants only. PAC did not distinguish between LSA and HSA participants, and instead was found to correlate with state nervousness during early anticipation, but in LSA participants only. Together, these findings are interpreted to suggest that delta-beta AAC is a plausible neurobiological index of adaptive stress regulation and can distinguish between trait high and low social anxiety during stress, while delta-beta PAC might be sensitive enough to reflect mild state anxiety in LSA participants.

DEVELOPMENT OF A CERAMIC TAMPER INDICATING SEAL: SRNL CONTRIBUTIONS

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

Krementz, D.; Brinkman, K.; Martinez-Rodriguez, M.

2013-06-03

Savannah River National Laboratory (SRNL) and Sandia National Laboratories (SNL) are collaborating on development of a Ceramic Seal, also sometimes designated the Intrinsically Tamper Indicating Ceramic Seal (ITICS), which is a tamper indicating seal for international safeguards applications. The Ceramic Seal is designed to be a replacement for metal loop seals that are currently used by the IAEA and other safeguards organizations. The Ceramic Seal has numerous features that enhance the security of the seal, including a frangible ceramic body, protective and tamper indicating coatings, an intrinsic unique identifier using Laser Surface Authentication, electronics incorporated into the seal that providemore » cryptographic seal authentication, and user-friendly seal wire capture. A second generation prototype of the seal is currently under development whose seal body is of Low Temperature Co-fired Ceramic (LTCC) construction. SRNL has developed the mechanical design of the seal in an iterative process incorporating comments from the SNL vulnerability review team. SRNL is developing fluorescent tamper indicating coatings, with recent development focusing on optimizing the durability of the coatings and working with a vendor to develop a method to apply coatings on a 3-D surface. SRNL performed a study on the effects of radiation on the electronics of the seal and possible radiation shielding techniques to minimize the effects. SRNL is also investigating implementation of Laser Surface Authentication (LSA) as a means of unique identification of each seal and the effects of the surface coatings on the LSA signature.« less

Your Laptop to the Rescue: Using the Child Language Data Exchange System Archive and CLAN Utilities to Improve Child Language Sample Analysis.

PubMed

Ratner, Nan Bernstein; MacWhinney, Brian

2016-05-01

In this article, we review the advantages of language sample analysis (LSA) and explain how clinicians can make the process of LSA faster, easier, more accurate, and more insightful than LSA done "by hand" by using free, available software programs such as Computerized Language Analysis (CLAN). We demonstrate the utility of CLAN analysis in studying the expressive language of a very large cohort of 24-month-old toddlers tracked in a recent longitudinal study; toddlers in particular are the most likely group to receive LSA by clinicians, but existing reference "norms" for this population are based on fairly small cohorts of children. Finally, we demonstrate how a CLAN utility such as KidEval can now extract potential normative data from the very large number of corpora now available for English and other languages at the Child Language Data Exchange System project site. Most of the LSA measures that we studied appear to show developmental profiles suggesting that they may be of specifically higher value for children at certain ages, because they do not show an even developmental trajectory from 2 to 7 years of age. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

Higher mobility scores in patients with cystic fibrosis are associated with better lung function.

PubMed

Thobani, Aneesha; Alvarez, Jessica A; Blair, Shaina; Jackson, Kaila; Gottlieb, Eric R; Walker, Seth; Tangpricha, Vin

2015-01-01

The purpose of this study was to determine whether mobility and physical activity were associated with lung function in adults with cystic fibrosis (CF). This was a prospective cohort observational study in an urban, academic, specialized care center. Participants were ambulatory, nonhospitalized adults with CF. Mobility was assessed monthly by the Life-Space Assessment (LSA) questionnaire and quarterly by pedometer. Lung function was assessed by spirometry. Twenty-seven subjects participated. Subjects recorded mean pedometer steps of 20,213 ± 11,331 over three days and FEV1% predicted of 77.48% ± 22.60% over one year. The LSA score at enrollment was correlated with initial pedometer steps (r = 0.42 and P = 0.03), and mean LSA score over one year was correlated with mean number of steps (r = 0.51 and P = 0.007). LSA mobility and pedometer scores were correlated with FEV1% predicted at enrollment and throughout the study. Mobility and physical activity measured by LSA questionnaire and pedometer are positively associated with lung function in adults with CF. This study confirms the importance of mobility and physical activity and supports the utility of a simple office-based questionnaire as a measure of mobility in adults with CF.

Chemiluminescent labels released from long spacer arm-functionalized magnetic particles: a novel strategy for ultrasensitive and highly selective detection of pathogen infections.

PubMed

Yang, Haowen; Liang, Wenbiao; He, Nongyue; Deng, Yan; Li, Zhiyang

2015-01-14

Previously, the unique advantages provided by chemiluminescence (CL) and magnetic particles (MPs) have resulted in the development of many useful nucleic acid detection methods. CL is highly sensitive, but when applied to MPs, its intensity is limited by the inner filter-like effect arising from excess dark MPs. Herein, we describe a modified strategy whereby CL labels are released from MPs to eliminate this negative effect. This approach relies on (1) the magnetic capture of target molecules on long spacer arm-functionalized magnetic particles (LSA-MPs), (2) the conjugation of streptavidin-alkaline phosphatase (SA-AP) to biotinylated amplicons of target pathogens, (3) the release of CL labels (specifically, AP tags), and (4) the detection of the released labels. CL labels were released from LSA-MPs through LSA ultrasonication or DNA enzymolysis, which proved to be the superior method. In contrast to conventional MPs, LSA-MPs exhibited significantly improved CL detection, because of the introduction of LSA, which was made of water-soluble carboxymethylated β-1,3-glucan. Detection of hepatitis B virus with this technique revealed a low detection limit of 50 fM, high selectivity, and excellent reproducibility. Thus, this approach may hold great potential for early stage clinical diagnosis of infectious diseases.

Photocopy of photograph (original negative in possession of LSA Associates, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph (original negative in possession of LSA Associates, Irvine, California) Dana Privett, Photographer, August 1982 WEST (REAR), LOOKING EAST - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

Photocopy of photograph (original negative in possession of LSA Associates, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph (original negative in possession of LSA Associates, Irvine, California) Dana Privett, Photographer, August 1982 EAST (FRONT), LOOKING WEST - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

Copy Photograph (original negative in possession of LSA Associates, Irvine, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Copy Photograph (original negative in possession of LSA Associates, Irvine, California) Rebecca Conard, Photographer, January 1989 STORAGE SHED, WEST (FRONT), LOOKING EAST - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

Photocopy of photograph (original negative in possession of LSA Associates, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph (original negative in possession of LSA Associates, Irvine, California) Rebecca Conard, Photographer, January 1989 NORTH SIDE, FROM (REAR) LOOKING SOUTHEAST - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

Photocopy of photograph (original negative in possession of LSA Associates, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph (original negative in possession of LSA Associates, Irvine, California) Rebecca Conard, Photographer, January 1989 SOUTH SIDE AND YARD, FACING NORTHEAST - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

Photocopy of photograph (original negative in possession of LSA Associates, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph (original negative in possession of LSA Associates, Irvine, California) Rebecca Conard, Photographer, January 1989 WINDOW DETAIL, NORTH SIDE, LOOKING SOUTH - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

The interpretation of dream meaning: Resolving ambiguity using Latent Semantic Analysis in a small corpus of text.

PubMed

Altszyler, Edgar; Ribeiro, Sidarta; Sigman, Mariano; Fernández Slezak, Diego

2017-11-01

Computer-based dreams content analysis relies on word frequencies within predefined categories in order to identify different elements in text. As a complementary approach, we explored the capabilities and limitations of word-embedding techniques to identify word usage patterns among dream reports. These tools allow us to quantify words associations in text and to identify the meaning of target words. Word-embeddings have been extensively studied in large datasets, but only a few studies analyze semantic representations in small corpora. To fill this gap, we compared Skip-gram and Latent Semantic Analysis (LSA) capabilities to extract semantic associations from dream reports. LSA showed better performance than Skip-gram in small size corpora in two tests. Furthermore, LSA captured relevant word associations in dream collection, even in cases with low-frequency words or small numbers of dreams. Word associations in dreams reports can thus be quantified by LSA, which opens new avenues for dream interpretation and decoding. Copyright © 2017 Elsevier Inc. All rights reserved.

Amatchmethod Based on Latent Semantic Analysis for Earthquakehazard Emergency Plan

NASA Astrophysics Data System (ADS)

Sun, D.; Zhao, S.; Zhang, Z.; Shi, X.

2017-09-01

The structure of the emergency plan on earthquake is complex, and it's difficult for decision maker to make a decision in a short time. To solve the problem, this paper presents a match method based on Latent Semantic Analysis (LSA). After the word segmentation preprocessing of emergency plan, we carry out keywords extraction according to the part-of-speech and the frequency of words. Then through LSA, we map the documents and query information to the semantic space, and calculate the correlation of documents and queries by the relation between vectors. The experiments results indicate that the LSA can improve the accuracy of emergency plan retrieval efficiently.

Photocopy of photograph (original negative in possession of LSA Associates, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph (original negative in possession of LSA Associates, Irvine, California) Beth Padon, photographer, 1985 WEST (REAR) IN RELATION TO GARAGE, LOOKING NORTH - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

Photocopy of photograph (original negative in possession of LSA Associates, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph (original negative in possession of LSA Associates, Irvine, California) Rebecca Conard, Photographer, January 1989 EAST (FRONT) AND NORTH SIDE, LOOKING SOUTHWEST - Irvine Ranch Agricultural Headquarters, Boyd Tenant House, Southeast of Intersection of San Diego & Santa Ana Freeways, Irvine, Orange County, CA

Grounding Collaborative Learning in Semantics-Based Critiquing

ERIC Educational Resources Information Center

Cheung, William K.; Mørch, Anders I.; Wong, Kelvin C.; Lee, Cynthia; Liu, Jiming; Lam, Mason H.

2007-01-01

In this article we investigate the use of latent semantic analysis (LSA), critiquing systems, and knowledge building to support computer-based teaching of English composition. We have built and tested an English composition critiquing system that makes use of LSA to analyze student essays and compute feedback by comparing their essays with…

49 CFR 173.468 - Test for LSA-III material.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 2 2014-10-01 2014-10-01 false Test for LSA-III material. 173.468 Section 173.468 Transportation Other Regulations Relating to Transportation PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION HAZARDOUS MATERIALS REGULATIONS SHIPPERS-GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS Class 7 ...

49 CFR 173.468 - Test for LSA-III material.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 2 2011-10-01 2011-10-01 false Test for LSA-III material. 173.468 Section 173.468 Transportation Other Regulations Relating to Transportation PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION HAZARDOUS MATERIALS REGULATIONS SHIPPERS-GENERAL REQUIREMENTS FOR SHIPMENTS AND PACKAGINGS Class 7 ...

Argyreia nervosa (Burm. f.): receptor profiling of lysergic acid amide and other potential psychedelic LSD-like compounds by computational and binding assay approaches.

PubMed

Paulke, Alexander; Kremer, Christian; Wunder, Cora; Achenbach, Janosch; Djahanschiri, Bardya; Elias, Anderson; Schwed, J Stefan; Hübner, Harald; Gmeiner, Peter; Proschak, Ewgenij; Toennes, Stefan W; Stark, Holger

2013-07-09

The convolvulacea Argyreia nervosa (Burm. f.) is well known as an important medical plant in the traditional Ayurvedic system of medicine and it is used in numerous diseases (e.g. nervousness, bronchitis, tuberculosis, arthritis, and diabetes). Additionally, in the Indian state of Assam and in other regions Argyreia nervosa is part of the traditional tribal medicine (e.g. the Santali people, the Lodhas, and others). In the western hemisphere, Argyreia nervosa has been brought in attention as so called "legal high". In this context, the seeds are used as source of the psychoactive ergotalkaloid lysergic acid amide (LSA), which is considered as the main active ingredient. As the chemical structure of LSA is very similar to that of lysergic acid diethylamide (LSD), the seeds of Argyreia nervosa (Burm. f.) are often considered as natural substitute of LSD. In the present study, LSA and LSD have been compared concerning their potential pharmacological profiles based on the receptor binding affinities since our recent human study with four volunteers on p.o. application of Argyreia nervosa seeds has led to some ambiguous effects. In an initial step computer-aided in silico prediction models on receptor binding were employed to screen for serotonin, norepinephrine, dopamine, muscarine, and histamine receptor subtypes as potential targets for LSA. In addition, this screening was extended to accompany ergotalkaloids of Argyreia nervosa (Burm. f.). In a verification step, selected LSA screening results were confirmed by in vitro binding assays with some extensions to LSD. In the in silico model LSA exhibited the highest affinity with a pKi of about 8.0 at α1A, and α1B. Clear affinity with pKi>7 was predicted for 5-HT1A, 5-HT1B, 5-HT1D, 5-HT6, 5-HT7, and D2. From these receptors the 5-HT1D subtype exhibited the highest pKi with 7.98 in the prediction model. From the other ergotalkaloids, agroclavine and festuclavine also seemed to be highly affine to the 5-HT1D-receptor with pKi>8. In general, the ergotalkaloids of Argyreia nervosa seem to prefer serotonin and dopamine receptors (pKi>7). However, with exception of ergometrine/ergometrinine only for 5-HT3A, and histamine H2 and H4 no affinities were predicted. Compared to LSD, LSA exhibited lower binding affinities in the in vitro binding assays for all tested receptor subtypes. However, with a pKi of 7.99, 7.56, and 7.21 a clear affinity for 5-HT1A, 5-HT2, and α2 could be demonstrated. For DA receptor subtypes and the α1-receptor the pKi ranged from 6.05 to 6.85. Since the psychedelic activity of LSA in the recent human study was weak and although LSA from Argyreia nervosa is often considered as natural exchange for LSD, LSA should not be regarded as LSD-like psychedelic drug. However, vegetative side effects and psychotropic effects may be triggered by serotonin or dopamine receptor subtypes. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Characterization of Novel OmpA-Like Protein of Leptospira interrogans That Binds Extracellular Matrix Molecules and Plasminogen

PubMed Central

Oliveira, Rosane; de Morais, Zenaide Maria; Gonçales, Amane Paldes; Romero, Eliete Caló; Vasconcellos, Silvio Arruda; Nascimento, Ana L. T. O.

2011-01-01

Leptospira interrogans is the etiological agent of leptospirosis, a zoonotic disease of human and veterinary concern. The identification of novel proteins that mediate host-pathogen interactions is important for understanding the bacterial pathogenesis as well as to identify protective antigens that would help fight the disease. We describe in this work the cloning, expression, purification and characterization of three predicted leptospiral membrane proteins, LIC10258, LIC12880 (Lp30) and LIC12238. We have employed Escherichia coli BL21 (SI) strain as a host expression system. Recently, we have identified LIC12238 as a plasminogen (PLG)-binding receptor. We show now that Lp30 and rLIC10258 are also PLG-receptors of Leptospira, both exhibiting dose-dependent and saturating binding (K D, 68.8±25.2 nM and 167.39±60.1 nM, for rLIC10258 and rLIC12880, respectively). In addition, LIC10258, which is a novel OmpA-like protein, binds laminin and plasma fibronectin ECM molecules and hence, it was named Lsa66 (Leptospiral surface adhesin of 66 kDa). Binding of Lsa66 to ECM components was determined to be specific, dose-dependent and saturable, with a K D of 55.4±15.9 nM to laminin and of 290.8±11.8 nM to plasma fibronectin. Binding of the recombinant proteins to PLG or ECM components was assessed by using antibodies against each of the recombinant proteins obtained in mice and confirmed by monoclonal anti-polyhistidine antibodies. Lsa66 caused partial inhibition on leptospiral adherence to immobilized ECM and PLG. Moreover, this adhesin and rLIC12238 are recognized by antibodies in serum samples of confirmed leptospirosis cases. Thus, Lsa66 is a novel OmpA-like protein with dual activity that may promote the attachment of Leptospira to host tissues and may contribute to the leptospiral invasion. To our knowledge, this is the first leptospiral protein with ECM and PLG binding properties reported to date. PMID:21755014

Characterization of novel OmpA-like protein of Leptospira interrogans that binds extracellular matrix molecules and plasminogen.

PubMed

Oliveira, Rosane; de Morais, Zenaide Maria; Gonçales, Amane Paldes; Romero, Eliete Caló; Vasconcellos, Silvio Arruda; Nascimento, Ana L T O

2011-01-01

Leptospira interrogans is the etiological agent of leptospirosis, a zoonotic disease of human and veterinary concern. The identification of novel proteins that mediate host-pathogen interactions is important for understanding the bacterial pathogenesis as well as to identify protective antigens that would help fight the disease. We describe in this work the cloning, expression, purification and characterization of three predicted leptospiral membrane proteins, LIC10258, LIC12880 (Lp30) and LIC12238. We have employed Escherichia coli BL21 (SI) strain as a host expression system. Recently, we have identified LIC12238 as a plasminogen (PLG)-binding receptor. We show now that Lp30 and rLIC10258 are also PLG-receptors of Leptospira, both exhibiting dose-dependent and saturating binding (K(D), 68.8±25.2 nM and 167.39±60.1 nM, for rLIC10258 and rLIC12880, respectively). In addition, LIC10258, which is a novel OmpA-like protein, binds laminin and plasma fibronectin ECM molecules and hence, it was named Lsa66 (Leptospiral surface adhesin of 66 kDa). Binding of Lsa66 to ECM components was determined to be specific, dose-dependent and saturable, with a K(D) of 55.4±15.9 nM to laminin and of 290.8±11.8 nM to plasma fibronectin. Binding of the recombinant proteins to PLG or ECM components was assessed by using antibodies against each of the recombinant proteins obtained in mice and confirmed by monoclonal anti-polyhistidine antibodies. Lsa66 caused partial inhibition on leptospiral adherence to immobilized ECM and PLG. Moreover, this adhesin and rLIC12238 are recognized by antibodies in serum samples of confirmed leptospirosis cases. Thus, Lsa66 is a novel OmpA-like protein with dual activity that may promote the attachment of Leptospira to host tissues and may contribute to the leptospiral invasion. To our knowledge, this is the first leptospiral protein with ECM and PLG binding properties reported to date.

Concomitant morphea and lichen sclerosus et atrophicus in the same plaque at the site of intramuscular drug injection: an interesting case presentation.

PubMed

Arif, Tasleem; Adil, Mohammad; Amin, Syed Suhail; Mahtab, Alam

2018-06-01

Morphea and lichen sclerosus et atrophicus (LSA) are two diseases that show considerable clinical and histopathological similarity and have been known to coexist in the same patient. Whether the two conditions are different entities or part of the same spectrum has been a topic of debate. This article describes a very rare and interesting case of concomitant morphea and LSA in a 50-year-old female in the same plaque following intramuscular drug injection in the deltoid region of the right arm. The coexistence of morphea and LSA in the same lesion has rarely been reported, thus compelling us to report this case.

The relationship between gender segregation in the workplace and long-term sickness absence in Sweden.

PubMed

Bryngelson, Anna; Bacchus Hertzman, Jennie; Fritzell, Johan

2011-08-01

The aim of the study is to investigate whether the gender composition in workplaces is related to long-term sickness absence (LSA). We start off with Kanter's theory on ''tokenism,'' suggesting an increased risk of stress among minority groups (tokens), which, in turn, might increase the risk of ill health and LSA. The dataset consists of information obtained from the Swedish level of Living Survey (LNU) and the Swedish Establishment Survey (APU), linked to register-based data from the Swedish Social Insurance Agency. The longitudinal data is representative for the Swedish population and consists of 496 women and 566 men, aged 20-55 at baseline. Our study group consisted of employed persons in 1991 and we analyze, by means of piecewise constant intensity regressions, the first entry into LSA with a follow-up period of nine years. Compared with women in gender-integrated workplaces, women's risk of LSA is most elevated at both extremely male-dominated (0-20% females) and extremely female-dominated workplaces (80-100% females), although the result among women in the most male-dominated group did not reach statistical significance at the 5% level. Men's risk seems less varied by gender composition. The present study suggests that the gender composition in the workplace has an impact on the risk of LSA, especially among women. Our findings lend no support for Kanter's theory on the effects of being a token. Most likely, women's and men's different status positions have an impact on the different associations found.

Simultaneous separation and purification of flavonoids and oleuropein from Olea europaea L. (olive) leaves using macroporous resin.

PubMed

Li, Chen; Zheng, Yuanyuan; Wang, Xiaofei; Feng, Shilan; Di, Duolong

2011-12-01

This study developed a feasible process to simultaneously separate and purify polyphenols, including flavonoids and oleuropein, from the leaves of Olea europaea L. Macroporous resins were used as the separation and purification materials. The performance and separation capabilities of eight resins (D101, DM130, HPD450, LSA-21, LSA-40, 07C, LSD001 and HPD600) were systematically evaluated. The contents of target polyphenols in different extracts were determined using ultraviolet (for flavonoids) and high-performance liquid chromatographic (for oleuropein) methods. The static adsorption and desorption results showed that resin LSA-21 had better adsorption properties among the eight resins. Influential factors such as extraction method, pH value of feeding solution, desorption solution, adsorption kinetics and adsorption isotherm, etc. to the extraction and purification of these polyphenols were successively investigated on resin LSA-21. The target flavonoids and oleuropein were selectively purified using resin LSA-21. Compared with the contents in raw leaves, the contents of total flavonoids and oleuropein in the final purified products were increased 13.2-fold (from 16 to 211 g kg(-1) ) and 7.5-fold (from 120 to 902 g kg(-1) ) with recovery yields of 87.9% and 85.6%, respectively. This extraction and purification method could be used in the large-scale enrichment or purification of flavonoids, oleuropein and other polyphenols from O. europaea L. leaves or other herbal materials in industrial, food processing and medical manufacture. Copyright © 2011 Society of Chemical Industry.

Multichannel biomedical time series clustering via hierarchical probabilistic latent semantic analysis.

PubMed

Wang, Jin; Sun, Xiangping; Nahavandi, Saeid; Kouzani, Abbas; Wu, Yuchuan; She, Mary

2014-11-01

Biomedical time series clustering that automatically groups a collection of time series according to their internal similarity is of importance for medical record management and inspection such as bio-signals archiving and retrieval. In this paper, a novel framework that automatically groups a set of unlabelled multichannel biomedical time series according to their internal structural similarity is proposed. Specifically, we treat a multichannel biomedical time series as a document and extract local segments from the time series as words. We extend a topic model, i.e., the Hierarchical probabilistic Latent Semantic Analysis (H-pLSA), which was originally developed for visual motion analysis to cluster a set of unlabelled multichannel time series. The H-pLSA models each channel of the multichannel time series using a local pLSA in the first layer. The topics learned in the local pLSA are then fed to a global pLSA in the second layer to discover the categories of multichannel time series. Experiments on a dataset extracted from multichannel Electrocardiography (ECG) signals demonstrate that the proposed method performs better than previous state-of-the-art approaches and is relatively robust to the variations of parameters including length of local segments and dictionary size. Although the experimental evaluation used the multichannel ECG signals in a biometric scenario, the proposed algorithm is a universal framework for multichannel biomedical time series clustering according to their structural similarity, which has many applications in biomedical time series management. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Bi-criteria travelling salesman subtour problem with time threshold

NASA Astrophysics Data System (ADS)

Kumar Thenepalle, Jayanth; Singamsetty, Purusotham

2018-03-01

This paper deals with the bi-criteria travelling salesman subtour problem with time threshold (BTSSP-T), which comes from the family of the travelling salesman problem (TSP) and is NP-hard in the strong sense. The problem arises in several application domains, mainly in routing and scheduling contexts. Here, the model focuses on two criteria: total travel distance and gains attained. The BTSSP-T aims to determine a subtour that starts and ends at the same city and visits a subset of cities at a minimum travel distance with maximum gains, such that the time spent on the tour does not exceed the predefined time threshold. A zero-one integer-programming problem is adopted to formulate this model with all practical constraints, and it includes a finite set of feasible solutions (one for each tour). Two algorithms, namely, the Lexi-Search Algorithm (LSA) and the Tabu Search (TS) algorithm have been developed to solve the BTSSP-T problem. The proposed LSA implicitly enumerates the feasible patterns and provides an efficient solution with backtracking, whereas the TS, which is metaheuristic, will give the better approximate solution. A numerical example is demonstrated in order to understand the search mechanism of the LSA. Numerical experiments are carried out in the MATLAB environment, on the different benchmark instances available in the TSPLIB domain as well as on randomly generated test instances. The experimental results show that the proposed LSA works better than the TS algorithm in terms of solution quality and, computationally, both LSA and TS are competitive.

German National Proficiency Scales in Biology: Internal Structure, Relations to General Cognitive Abilities and Verbal Skills

ERIC Educational Resources Information Center

Kampa, Nele; Köller, Olaf

2016-01-01

National and international large-scale assessments (LSA) have a major impact on educational systems, which raises fundamental questions about the validity of the measures regarding their internal structure and their relations to relevant covariates. Given its importance, research on the validity of instruments specifically developed for LSA is…

Evaluation of Mathematical Self-Explanations with LSA in a Counterintuitive Problem of Probabilities

ERIC Educational Resources Information Center

Guiu, Jordi Maja

2012-01-01

In this paper different type of mathematical explanations are presented in relation to the mathematical problem of probabilities Monty Hall (card version) and the computational tool Latent Semantic Analyses (LSA) is used. At the moment the results in the literature about this computational tool to study texts show that this technique is…

Plenary Speeches: Applied Linguists without Borders

ERIC Educational Resources Information Center

Tarone, Elaine

2013-01-01

Until 1989, the American Association for Applied Linguistics (AAAL) could have been viewed as an interest group of the Linguistics Society of America (LSA); AAAL met in two designated meeting rooms as a subsection of the LSA conference. In 1991, I was asked to organize the first independent meeting of AAAL in New York City, with the help of…

Airborne Salmonella and Listeria associated with Irish commercial beef, sheep and pig plants.

PubMed

Okraszewska-Lasica, Wioletta; Bolton, D J; Sheridan, J J; McDowell, D A

2014-06-01

Air samples from lairage, hide/fleece pulling or dehairing/scraping, evisceration and chilling areas in commercial beef, sheep and pig plants were examined for Salmonella spp. and Listeria monocytogenes, by impaction or sedimentation onto selective (Brilliant Green Agar, BSA; Listeria Selective Agar, LSA) and non-selective (Plate Count Agar, PCA) media. Both pathogens were frequently detected in all three plants. Improved recoveries were achieved by combining sedimentation, and broth based resuscitation, suggesting cell injury. Salmonella were recovered from all three plants, with the highest counts on BGA in the pig plant. The most common serotypes were S. Typhimurium in the beef/sheep plants and S. Derby in the pig plant. Very low counts of L. monocytogenes (e.g. 2.6CFUm(2)) were detected at hide removal on LSA sedimentation plates in the beef plant. These included serogroup 1/2a-3a and 1/2b-3b-7. Pathogen counts in the three plants were generally very low, suggesting that air is unlikely to be a significant source of carcass or plant surface contamination. Copyright © 2014 Elsevier Ltd. All rights reserved.

Association between Body Condition Score and Cancer Prognosis in Dogs with Lymphoma and Osteosarcoma.

PubMed

Romano, F R; Heinze, C R; Barber, L G; Mason, J B; Freeman, L M

2016-07-01

In humans and rodents obesity appears to promote some cancers by increasing incidence, tumor aggressiveness, recurrence, and fatality. However, the relationship between obesity and cancer in dogs has not been thoroughly evaluated. Whether body condition score (BCS) at the time of lymphoma (LSA) or osteosarcoma (OSA) diagnosis in dogs is predictive of survival time (ST) or progression-free interval (PFI). We hypothesized that an overweight body state at the time of cancer diagnosis would be associated with negative outcomes. Dogs with LSA (n = 270) and OSA (n = 54) diagnosed and treated between 2000 and 2010. Retrospective case review. Signalment, body weight, BCS, cancer diagnosis and treatment, relevant clinicopathologic values, and survival data were collected. Dogs were grouped by BCS (underweight, ideal, and overweight) and ST and PFI were compared. Overall, 5.5% of dogs were underweight, 54.0% were ideal weight, and 40.4% were overweight at diagnosis. Underweight dogs with LSA had shorter ST (P = .017) than ideal or overweight dogs. BCS was not associated with ST for OSA (P = .474). Progression-free interval did not differ among BCS categories for either cancer. Obesity was not associated with adverse outcomes among dogs with LSA or OSA in this retrospective study; however, being underweight at the time of diagnosis of LSA was associated with shorter survival. More research is needed to elucidate the relationship between excessive body weight and cancer development and progression in dogs. Copyright © 2016 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.

Involvement of the Lateral Septal Area in the Expression of Fear Conditioning to Context

ERIC Educational Resources Information Center

Reis, Daniel G.; Scopinho, America A.; Guimaraes, Francisco S.; Correa, Fernando M. A.; Resstel, Leonardo B. M.

2010-01-01

Considering the evidence that the lateral septal area (LSA) modulates defensive responses, the aim of the present study is to verify if this structure is also involved in contextual fear conditioning responses. Neurotransmission in the LSA was reversibly inhibited by bilateral microinjections of cobalt chloride (CoCl[subscript 2], 1 mM) 10 min…

Exploring dangerous neighborhoods: Latent Semantic Analysis and computing beyond the bounds of the familiar

PubMed Central

Cohen, Trevor; Blatter, Brett; Patel, Vimla

2005-01-01

Certain applications require computer systems to approximate intended human meaning. This is achievable in constrained domains with a finite number of concepts. Areas such as psychiatry, however, draw on concepts from the world-at-large. A knowledge structure with broad scope is required to comprehend such domains. Latent Semantic Analysis (LSA) is an unsupervised corpus-based statistical method that derives quantitative estimates of the similarity between words and documents from their contextual usage statistics. The aim of this research was to evaluate the ability of LSA to derive meaningful associations between concepts relevant to the assessment of dangerousness in psychiatry. An expert reference model of dangerousness was used to guide the construction of a relevant corpus. Derived associations between words in the corpus were evaluated qualitatively. A similarity-based scoring function was used to assign dangerousness categories to discharge summaries. LSA was shown to derive intuitive relationships between concepts and correlated significantly better than random with human categorization of psychiatric discharge summaries according to dangerousness. The use of LSA to derive a simulated knowledge structure can extend the scope of computer systems beyond the boundaries of constrained conceptual domains. PMID:16779020

Sensitivity Analysis for Probabilistic Neural Network Structure Reduction.

PubMed

Kowalski, Piotr A; Kusy, Maciej

2018-05-01

In this paper, we propose the use of local sensitivity analysis (LSA) for the structure simplification of the probabilistic neural network (PNN). Three algorithms are introduced. The first algorithm applies LSA to the PNN input layer reduction by selecting significant features of input patterns. The second algorithm utilizes LSA to remove redundant pattern neurons of the network. The third algorithm combines the proposed two and constitutes the solution of how they can work together. PNN with a product kernel estimator is used, where each multiplicand computes a one-dimensional Cauchy function. Therefore, the smoothing parameter is separately calculated for each dimension by means of the plug-in method. The classification qualities of the reduced and full structure PNN are compared. Furthermore, we evaluate the performance of PNN, for which global sensitivity analysis (GSA) and the common reduction methods are applied, both in the input layer and the pattern layer. The models are tested on the classification problems of eight repository data sets. A 10-fold cross validation procedure is used to determine the prediction ability of the networks. Based on the obtained results, it is shown that the LSA can be used as an alternative PNN reduction approach.

Metallic-thin-film instability with spatially correlated thermal noise.

PubMed

Diez, Javier A; González, Alejandro G; Fernández, Roberto

2016-01-01

We study the effects of stochastic thermal fluctuations on the instability of the free surface of a flat liquid metallic film on a solid substrate. These fluctuations are represented by a stochastic noise term added to the deterministic equation for the film thickness within the long-wave approximation. Unlike the case of polymeric films, we find that this noise, while remaining white in time, must be colored in space, at least in some regimes. The corresponding noise term is characterized by a nonzero correlation length, ℓ_{c}, which, combined with the size of the system, leads to a dimensionless parameter β that accounts for the relative importance of the spatial correlation (β∼ℓ_{c}^{-1}). We perform the linear stability analysis (LSA) of the film both with and without the noise term and find that for ℓ_{c} larger than some critical value (depending on the system size), the wavelength of the peak of the spectrum is larger than that corresponding to the deterministic case, while for smaller ℓ_{c} this peak corresponds to smaller wavelength than the latter. Interestingly, whatever the value of ℓ_{c}, the peak always approaches the deterministic one for larger times. We compare LSA results with the numerical simulations of the complete nonlinear problem and find a good agreement in the power spectra for early times at different values of β. For late times, we find that the stochastic LSA predicts well the position of the dominant wavelength, showing that nonlinear interactions do not modify the trends of the early linear stages. Finally, we fit the theoretical spectra to experimental data from a nanometric laser-melted copper film and find that at later times, the adjustment requires smaller values of β (larger space correlations).

Metallic-thin-film instability with spatially correlated thermal noise

NASA Astrophysics Data System (ADS)

Diez, Javier A.; González, Alejandro G.; Fernández, Roberto

2016-01-01

We study the effects of stochastic thermal fluctuations on the instability of the free surface of a flat liquid metallic film on a solid substrate. These fluctuations are represented by a stochastic noise term added to the deterministic equation for the film thickness within the long-wave approximation. Unlike the case of polymeric films, we find that this noise, while remaining white in time, must be colored in space, at least in some regimes. The corresponding noise term is characterized by a nonzero correlation length, ℓc, which, combined with the size of the system, leads to a dimensionless parameter β that accounts for the relative importance of the spatial correlation (β ˜ℓc-1 ). We perform the linear stability analysis (LSA) of the film both with and without the noise term and find that for ℓc larger than some critical value (depending on the system size), the wavelength of the peak of the spectrum is larger than that corresponding to the deterministic case, while for smaller ℓc this peak corresponds to smaller wavelength than the latter. Interestingly, whatever the value of ℓc, the peak always approaches the deterministic one for larger times. We compare LSA results with the numerical simulations of the complete nonlinear problem and find a good agreement in the power spectra for early times at different values of β . For late times, we find that the stochastic LSA predicts well the position of the dominant wavelength, showing that nonlinear interactions do not modify the trends of the early linear stages. Finally, we fit the theoretical spectra to experimental data from a nanometric laser-melted copper film and find that at later times, the adjustment requires smaller values of β (larger space correlations).

The secret life of pronouns: flexibility in writing style and physical health.

PubMed

Campbell, R Sherlock; Pennebaker, James W

2003-01-01

Numerous disclosure studies have demonstrated that individuals randomly assigned to write about emotional topics evidence improved physical health compared with those who write about superficial topics. The writing samples from three previously published studies of 74 first-year students, 50 upper-division students, and 59 maximum-security prisoners were reanalyzed using Latent Semantic Analysis (LSA) to explore possible relationships of writing content and style to changes in frequency of physician visits following the disclosure intervention. LSA revealed that flexibility in the use of common words-particularly personal pronouns--when writing about traumatic memories was related to positive health outcomes. The findings point to the importance of the role of discussing the self and social relationships in writing and, at the same time, to the remarkable potential of techniques such as LSA.

NASA Supportability Engineering Implementation Utilizing DoD Practices and Processes

NASA Technical Reports Server (NTRS)

Smith, David A.; Smith, John V.

2010-01-01

The Ares I design and development program made the determination early in the System Design Review Phase to utilize DoD ILS and LSA approach for supportability engineering as an integral part of the system engineering process. This paper is to provide a review of the overall approach to design Ares-I with an emphasis on a more affordable, supportable, and sustainable launch vehicle. Discussions will include the requirements development, design influence, support concept alternatives, ILS and LSA planning, Logistics support analyses/trades performed, LSA tailoring for NASA Ares Program, support system infrastructure identification, ILS Design Review documentation, Working Group coordination, and overall ILS implementation. At the outset, the Ares I Project initiated the development of the Integrated Logistics Support Plan (ILSP) and a Logistics Support Analysis process to provide a path forward for the management of the Ares-I ILS program and supportability analysis activities. The ILSP provide the initial planning and coordination between the Ares-I Project Elements and Ground Operation Project. The LSA process provided a system engineering approach in the development of the Ares-I supportability requirements; influence the design for supportability and development of alternative support concepts that satisfies the program operability requirements. The LSA planning and analysis results are documented in the Logistics Support Analysis Report. This document was required during the Ares-I System Design Review (SDR) and Preliminary Design Review (PDR) review cycles. To help coordinate the LSA process across the Ares-I project and between programs, the LSA Report is updated and released quarterly. A System Requirement Analysis was performed to determine the supportability requirements and technical performance measurements (TPMs). Two working groups were established to provide support in the management and implement the Ares-I ILS program, the Integrated Logistics Support Working Group (ILSWG) and the Logistics Support Analysis Record Working Group (LSARWG). The Ares I ILSWG is established to assess the requirements and conduct, evaluate analyses and trade studies associated with acquisition logistic and supportability processes and to resolve Ares I integrated logistics and supportability issues. It established a strategic collaborative alliance for coordination of Logistics Support Analysis activates in support of the integrated Ares I vehicle design and development of logistics support infrastructure. A Joint Ares I - Orion LSAR Working Group was established to: 1) Guide the development of Ares-I and Orion LSAR data and serve as a model for future Constellation programs, 2) Develop rules and assumptions that will apply across the Constellation program with regards to the program's LSAR development, and 3) Maintain the Constellation LSAR Style Guide.

Surface modification of high temperature iron alloys

DOEpatents

Park, Jong-Hee

1995-01-01

A method and article of manufacture of a coated iron based alloy. The method includes providing an iron based alloy substrate, depositing a silicon containing layer on the alloy surface while maintaining the alloy at a temperature of about 700.degree. C.-1200.degree. C. to diffuse silicon into the alloy surface and exposing the alloy surface to an ammonia atmosphere to form a silicon/oxygen/nitrogen containing protective layer on the iron based alloy.

Surface modification of high temperature iron alloys

DOEpatents

Park, J.H.

1995-06-06

A method and article of manufacture of a coated iron based alloy are disclosed. The method includes providing an iron based alloy substrate, depositing a silicon containing layer on the alloy surface while maintaining the alloy at a temperature of about 700--1200 C to diffuse silicon into the alloy surface and exposing the alloy surface to an ammonia atmosphere to form a silicon/oxygen/nitrogen containing protective layer on the iron based alloy. 13 figs.

Development and Validation of the Life Sciences Assessment: A Measure of Preschool Children's Conceptions of Basic Life Sciences

ERIC Educational Resources Information Center

Maherally, Uzma Nooreen

2014-01-01

The purpose of this study was to develop and validate a science assessment tool termed the Life Sciences Assessment (LSA) in order to assess preschool children's conceptions of basic life sciences. The hypothesis was that the four sub-constructs, each of which can be measured through a series of questions on the LSA, will make a significant…

The Use of a Context-Based Information Retrieval Technique

DTIC Science & Technology

2009-07-01

provided in context. Latent Semantic Analysis (LSA) is a statistical technique for inferring contextual and structural information, and previous studies...WAIS). 10 DSTO-TR-2322 1.4.4 Latent Semantic Analysis LSA, which is also known as latent semantic indexing (LSI), uses a statistical and...1.4.6 Language Models In contrast, natural language models apply algorithms that combine statistical information with semantic information. Semantic

Cross-language information retrieval using PARAFAC2.

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

Bader, Brett William; Chew, Peter; Abdelali, Ahmed

A standard approach to cross-language information retrieval (CLIR) uses Latent Semantic Analysis (LSA) in conjunction with a multilingual parallel aligned corpus. This approach has been shown to be successful in identifying similar documents across languages - or more precisely, retrieving the most similar document in one language to a query in another language. However, the approach has severe drawbacks when applied to a related task, that of clustering documents 'language-independently', so that documents about similar topics end up closest to one another in the semantic space regardless of their language. The problem is that documents are generally more similar tomore » other documents in the same language than they are to documents in a different language, but on the same topic. As a result, when using multilingual LSA, documents will in practice cluster by language, not by topic. We propose a novel application of PARAFAC2 (which is a variant of PARAFAC, a multi-way generalization of the singular value decomposition [SVD]) to overcome this problem. Instead of forming a single multilingual term-by-document matrix which, under LSA, is subjected to SVD, we form an irregular three-way array, each slice of which is a separate term-by-document matrix for a single language in the parallel corpus. The goal is to compute an SVD for each language such that V (the matrix of right singular vectors) is the same across all languages. Effectively, PARAFAC2 imposes the constraint, not present in standard LSA, that the 'concepts' in all documents in the parallel corpus are the same regardless of language. Intuitively, this constraint makes sense, since the whole purpose of using a parallel corpus is that exactly the same concepts are expressed in the translations. We tested this approach by comparing the performance of PARAFAC2 with standard LSA in solving a particular CLIR problem. From our results, we conclude that PARAFAC2 offers a very promising alternative to LSA not only for multilingual document clustering, but also for solving other problems in cross-language information retrieval.« less

Catabolism of N-Acetylneuraminic Acid, a Fitness Function of the Food-Borne Lactic Acid Bacterium Lactobacillus sakei, Involves Two Newly Characterized Proteins

PubMed Central

Chaillou, Stéphane; Zagorec, Monique; Champomier-Vergès, Marie-Christine

2013-01-01

In silico analysis of the genome sequence of the meat-borne lactic acid bacterium (LAB) Lactobacillus sakei 23K has revealed a repertoire of potential functions related to the adaptation of this bacterium to the meat environment. Among these functions, the ability to use N-acetyl-neuraminic acid (NANA) as a carbon source could provide a competitive advantage for growth on meat in which this amino sugar is present. In this work, we proposed to analyze the functionality of a gene cluster encompassing nanTEAR and nanK (nanTEAR-nanK). We established that this cluster encoded a pathway allowing transport and early steps of the catabolism of NANA in this genome. We also demonstrated that this cluster was absent from the genome of other L. sakei strains that were shown to be unable to grow on NANA. Moreover, L. sakei 23K nanA, nanT, nanK, and nanE genes were able to complement Escherichia coli mutants. Construction of different mutants in L. sakei 23K ΔnanR, ΔnanT, and ΔnanK and the double mutant L. sakei 23K Δ(nanA-nanE) made it possible to show that all were impaired for growth on NANA. In addition, two genes located downstream from nanK, lsa1644 and lsa1645, are involved in the catabolism of sialic acid in L. sakei 23K, as a L. sakei 23K Δlsa1645 mutant was no longer able to grow on NANA. All these results demonstrate that the gene cluster nanTEAR-nanK-lsa1644-lsa1645 is indeed involved in the use of NANA as an energy source by L. sakei. PMID:23335758

Assessment of lumbosacral kyphosis in spondylolisthesis: a computer-assisted reliability study of six measurement techniques

PubMed Central

Glavas, Panagiotis; Mac-Thiong, Jean-Marc; Parent, Stefan; de Guise, Jacques A.

2008-01-01

Although recognized as an important aspect in the management of spondylolisthesis, there is no consensus on the most reliable and optimal measure of lumbosacral kyphosis (LSK). Using a custom computer software, four raters evaluated 60 standing lateral radiographs of the lumbosacral spine during two sessions at a 1-week interval. The sample size consisted of 20 normal, 20 low and 20 high grade spondylolisthetic subjects. Six parameters were included for analysis: Boxall’s slip angle, Dubousset’s lumbosacral angle (LSA), the Spinal Deformity Study Group’s (SDSG) LSA, dysplastic SDSG LSA, sagittal rotation (SR), kyphotic Cobb angle (k-Cobb). Intra- and inter-rater reliability for all parameters was assessed using intra-class correlation coefficients (ICC). Correlations between parameters and slip percentage were evaluated with Pearson coefficients. The intra-rater ICC’s for all the parameters ranged between 0.81 and 0.97 and the inter-rater ICC’s were between 0.74 and 0.98. All parameters except sagittal rotation showed a medium to large correlation with slip percentage. Dubousset’s LSA and the k-Cobb showed the largest correlations (r = −0.78 and r = −0.50, respectively). SR was associated with the weakest correlation (r = −0.10). All other parameters had medium correlations with percent slip (r = 0.31–0.43). All measurement techniques provided excellent inter- and intra-rater reliability. Dubousset’s LSA showed the strongest correlation with slip grade. This parameter can be used in the clinical setting with PACS software capabilities to assess LSK. A computer-assisted technique is recommended in order to increase the reliability of the measurement of LSK in spondylolisthesis. PMID:19015898

Surface composition of alloys

NASA Astrophysics Data System (ADS)

Sachtler, W. M. H.

1984-11-01

In equilibrium, the composition of the surface of an alloy will, in general, differ from that of the bulk. The broken-bond model is applicable to alloys with atoms of virtually equal size. If the heat of alloy formation is zero, the component of lower heat of atomization is found enriched in the surface. If both partners have equal heats of sublimination, the surface of a diluted alloy is enriched with the minority component. Size effects can enhance or weaken the electronic effects. In general, lattice strain can be relaxed by precipitating atoms of deviating size on the surface. Two-phase alloys are described by the "cherry model", i.e. one alloy phase, the "kernel" is surrounded by another alloy, the "flesh", and the surface of the outer phase, the "skin" displays a deviating surface composition as in monophasic alloys. In the presence of molecules capable of forming chemical bonds with individual metal atoms, "chemisorption induced surface segregation" can be observed at low temperatures, i.e. the surface becomes enriched with the metal forming the stronger chemisorption bonds.

Review of the MDF-LSA 100 Spray Decontamination System

DTIC Science & Technology

2011-12-01

decontamination technology. In October 2000, SNL received funding from the U.S. Department of Energy’s and National Nuclear Security Administration’s...UNCLASSIFIED DSTO-GD-0662 The MDF-LSA 200 is supplied or created as a foam, liquid or aerosol. The foam can be sprayed from handheld canisters . When the foam...DSTO Publications Repository http://dspace.dsto.defence.gov.au/dspace/ 14. RELEASE AUTHORITY Chief, Human Protection and Performance

Reflective Random Indexing and indirect inference: a scalable method for discovery of implicit connections.

PubMed

Cohen, Trevor; Schvaneveldt, Roger; Widdows, Dominic

2010-04-01

The discovery of implicit connections between terms that do not occur together in any scientific document underlies the model of literature-based knowledge discovery first proposed by Swanson. Corpus-derived statistical models of semantic distance such as Latent Semantic Analysis (LSA) have been evaluated previously as methods for the discovery of such implicit connections. However, LSA in particular is dependent on a computationally demanding method of dimension reduction as a means to obtain meaningful indirect inference, limiting its ability to scale to large text corpora. In this paper, we evaluate the ability of Random Indexing (RI), a scalable distributional model of word associations, to draw meaningful implicit relationships between terms in general and biomedical language. Proponents of this method have achieved comparable performance to LSA on several cognitive tasks while using a simpler and less computationally demanding method of dimension reduction than LSA employs. In this paper, we demonstrate that the original implementation of RI is ineffective at inferring meaningful indirect connections, and evaluate Reflective Random Indexing (RRI), an iterative variant of the method that is better able to perform indirect inference. RRI is shown to lead to more clearly related indirect connections and to outperform existing RI implementations in the prediction of future direct co-occurrence in the MEDLINE corpus. 2009 Elsevier Inc. All rights reserved.

A social ecological approach to understanding correlates of lifetime sexual assault among sexual minority women in Toronto, Canada: results from a cross-sectional internet-based survey

PubMed Central

Logie, C. H.; Alaggia, R.; Rwigema, M. J.

2014-01-01

Stigma, discrimination and violence contribute to health disparities among sexual minorities. Lesbian, bisexual and queer (LBQ) women experience sexual violence at similar or higher rates than heterosexual women. Most research with LBQ women, however, has focused on measuring prevalence of sexual violence rather than its association with health outcomes, individual, social and structural factors. We conducted a cross-sectional online survey with LBQ women in Toronto, Canada. Multivariate logistic regression analyses were conducted to assess correlates of lifetime sexual assault (LSA). Almost half (42%) of participants (n = 415) reported experiences of LSA. Participants identifying as queer were more likely to have experienced LSA than those identifying as lesbian. When controlling for socio-demographic characteristics, experiencing LSA was associated with higher rates of depression, sexually transmitted infections (STIs), receiving an STI test, belief that healthcare providers were not comfortable with their LBQ sexual orientation, and sexual stigma (overall, perceived and enacted). A history of sexual violence was associated with lower: self-rated health, overall social support, family social support and self-esteem. This research highlights the salience of a social ecological framework to inform interventions for health promotion among LBQ women and to challenge sexual stigma and sexual violence. PMID:24412812

Method for welding beryllium

DOEpatents

Dixon, Raymond D.; Smith, Frank M.; O'Leary, Richard F.

1997-01-01

A method is provided for joining beryllium pieces which comprises: depositing aluminum alloy on at least one beryllium surface; contacting that beryllium surface with at least one other beryllium surface; and welding the aluminum alloy coated beryllium surfaces together. The aluminum alloy may be deposited on the beryllium using gas metal arc welding. The aluminum alloy coated beryllium surfaces may be subjected to elevated temperatures and pressures to reduce porosity before welding the pieces together. The aluminum alloy coated beryllium surfaces may be machined into a desired welding joint configuration before welding. The beryllium may be an alloy of beryllium or a beryllium compound. The aluminum alloy may comprise aluminum and silicon.

Method for welding beryllium

DOEpatents

Dixon, R.D.; Smith, F.M.; O`Leary, R.F.

1997-04-01

A method is provided for joining beryllium pieces which comprises: depositing aluminum alloy on at least one beryllium surface; contacting that beryllium surface with at least one other beryllium surface; and welding the aluminum alloy coated beryllium surfaces together. The aluminum alloy may be deposited on the beryllium using gas metal arc welding. The aluminum alloy coated beryllium surfaces may be subjected to elevated temperatures and pressures to reduce porosity before welding the pieces together. The aluminum alloy coated beryllium surfaces may be machined into a desired welding joint configuration before welding. The beryllium may be an alloy of beryllium or a beryllium compound. The aluminum alloy may comprise aluminum and silicon. 9 figs.

Evaluation of Surface Roughness and Tensile Strength of Base Metal Alloys Used for Crown and Bridge on Recasting (Recycling).

PubMed

Agrawal, Amit; Hashmi, Syed W; Rao, Yogesh; Garg, Akanksha

2015-07-01

Dental casting alloys play a prominent role in the restoration of the partial dentition. Casting alloys have to survive long term in the mouth and also have the combination of structure, molecules, wear resistance and biologic compatibility. According to ADA system casting alloys were divided into three groups (wt%); high noble, Noble and predominantly base metal alloys. To evaluate the mechanical properties such as tensile strength and surface roughness of the new and recast base metal (nickel-chromium) alloys. Recasting of the base metal alloys derived from sprue and button, to make it reusable has been done. A total of 200 test specimens were fabricated using specially fabricated jig of metal and divided into two groups- 100 specimens of new alloy and 100 specimens of recast alloys, which were tested for tensile strength on universal testing machine and surface roughness on surface roughness tester. Tensile strength of new alloy showed no statistically significant difference (p-value>0.05) from recast alloy whereas new alloy had statistically significant surface roughness (Maximum and Average surface roughness) difference (p-value<0.01) as compared to recast alloy. Within the limitations of the study it is concluded that the tensile strength will not be affected by recasting of nickel-chromium alloy whereas surface roughness increases markedly.

Successful use of Gamma Knife surgery in a distal lenticulostriate artery aneurysm intervention.

PubMed

Lan, ZhiGang; Li, Jin; You, Chao; Chen, Jing

2012-02-01

We report a case of a 21-year-old woman who underwent radiosurgical treatment of a distal lenticulostriate artery (LSA) aneurysm. Twenty-two months after treatment, repeat angiography demonstrated patency of the parent vessel and complete obliteration of the aneurysm. Our case implies that Gamma Knife surgery (GKS) might serve as an alternative microinvasive technique in the treatment of LSA aneurysms, making this procedure a potential addition to present methods.

Computational methods to extract meaning from text and advance theories of human cognition.

PubMed

McNamara, Danielle S

2011-01-01

Over the past two decades, researchers have made great advances in the area of computational methods for extracting meaning from text. This research has to a large extent been spurred by the development of latent semantic analysis (LSA), a method for extracting and representing the meaning of words using statistical computations applied to large corpora of text. Since the advent of LSA, researchers have developed and tested alternative statistical methods designed to detect and analyze meaning in text corpora. This research exemplifies how statistical models of semantics play an important role in our understanding of cognition and contribute to the field of cognitive science. Importantly, these models afford large-scale representations of human knowledge and allow researchers to explore various questions regarding knowledge, discourse processing, text comprehension, and language. This topic includes the latest progress by the leading researchers in the endeavor to go beyond LSA. Copyright © 2010 Cognitive Science Society, Inc.

Computer assessment of interview data using latent semantic analysis.

PubMed

Dam, Gregory; Kaufmann, Stefan

2008-02-01

Clinical interviews are a powerful method for assessing students' knowledge and conceptualdevelopment. However, the analysis of the resulting data is time-consuming and can create a "bottleneck" in large-scale studies. This article demonstrates the utility of computational methods in supporting such an analysis. Thirty-four 7th-grade student explanations of the causes of Earth's seasons were assessed using latent semantic analysis (LSA). Analyses were performed on transcriptions of student responses during interviews administered, prior to (n = 21) and after (n = 13) receiving earth science instruction. An instrument that uses LSA technology was developed to identify misconceptions and assess conceptual change in students' thinking. Its accuracy, as determined by comparing its classifications to the independent coding performed by four human raters, reached 90%. Techniques for adapting LSA technology to support the analysis of interview data, as well as some limitations, are discussed.

Study of laser heated propulsion devices. Part 1: Evaluation of laser devices, fuels and energy coupling mechanisms

NASA Technical Reports Server (NTRS)

Hofer, O. C.

1982-01-01

Closed cycle, CW waveform and short wavelength laser devices are desirable characteristics for laser propulsion. The choice of specific wavelengths for hydrogen fuel affects the operational conditions under which a laser supported absorption (LSA) wave is initiated and maintained. The mechanisms of initiating and maintaining LSA waves depend on the wavelength of the laser. Consequently, the shape and size of the hot core plasma is also dependent on wavelength and pressure. Detailed modeling of these mechanisms must be performed before their actual significance can be ascertained. Inverse bremsstrahlung absorption mechanism is the dominant mechanism for coupling energy into the plasma, but other mechanisms which are wavelength dependent can dictate the LSA wave plasma initiation and maintenance conditions. Multiphoton mechanisms become important at visible or shorter wavelengths. These are important mechanisms in creating the initial H2 gas breakdown and supplying the precursor electrons required to sustain the plasma.

Effect of surface roughness on the in vitro degradation behaviour of a biodegradable magnesium-based alloy

NASA Astrophysics Data System (ADS)

Walter, R.; Kannan, M. Bobby; He, Y.; Sandham, A.

2013-08-01

In this study, the in vitro degradation behaviour of AZ91 magnesium alloy with two different surface finishes was investigated using electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF). The polarisation resistance (Rp) of the rough surface alloy immersed in SBF for 3 h was ~30% lower as compared to that of the smooth surface alloy. After 12 h immersion in SBF, the Rp values for both the surface finishes decreased and were also similar. However, localised degradation occurred sooner, and to a noticeably higher severity in the rough surface alloy as compared to the smooth surface alloy.

Land Surface Albedo From EPS/AVHRR : Method For Retrieval and Validation

NASA Astrophysics Data System (ADS)

Jacob, G.

2015-12-01

The scope of Land Surface Analysis Satellite Applications Facility (LSA-SAF) is to increase benefit from EUMETSAT Satellites (MSG and EPS) data by providing added value products for the meteorological and environmental science communities with main applications in the fields of climate modelling, environmental management, natural hazards management, and climate change detection. The MSG/SEVIRI daily albedo product is disseminated operationally by the LSA-SAF processing centre based in Portugal since 2009. This product so-called MDAL covers Europe and Africa includes in the visible, near infrared and shortwave bands at a resolution of 3km at the equator. Recently, an albedo product at 1km so-called ETAL has been built from EPS/AVHRR observations in order to primarily MDAL product outside the MSG disk, while ensuring a global coverage. The methodology is common to MSG and EPS data and relies on the inversion of the BRDF (Bidirectional Reflectance Distribution Function) model of Roujean et al. On a given target, ETAL products exploits the variability of viewing angles whereas MDAL looks at the variations of solar illumination. The comparison of ETAL albedo product against MODIS and MSG/SEVIRI products over the year 2015 is instructive in many ways and shows in general a good agreement between them. The dispersion may be accounted by different factors that will be explained The additional information provided by EPS appears to be particularly beneficial for high latitudes during winter and for snow albedo.

Evaluation of Surface Roughness and Tensile Strength of Base Metal Alloys Used for Crown and Bridge on Recasting (Recycling)

PubMed Central

Hashmi, Syed W.; Rao, Yogesh; Garg, Akanksha

2015-01-01

Background Dental casting alloys play a prominent role in the restoration of the partial dentition. Casting alloys have to survive long term in the mouth and also have the combination of structure, molecules, wear resistance and biologic compatibility. According to ADA system casting alloys were divided into three groups (wt%); high noble, Noble and predominantly base metal alloys. Aim To evaluate the mechanical properties such as tensile strength and surface roughness of the new and recast base metal (nickel-chromium) alloys. Materials and Methods Recasting of the base metal alloys derived from sprue and button, to make it reusable has been done. A total of 200 test specimens were fabricated using specially fabricated jig of metal and divided into two groups- 100 specimens of new alloy and 100 specimens of recast alloys, which were tested for tensile strength on universal testing machine and surface roughness on surface roughness tester. Results Tensile strength of new alloy showed no statistically significant difference (p-value>0.05) from recast alloy whereas new alloy had statistically significant surface roughness (Maximum and Average surface roughness) difference (p-value<0.01) as compared to recast alloy. Conclusion Within the limitations of the study it is concluded that the tensile strength will not be affected by recasting of nickel-chromium alloy whereas surface roughness increases markedly. PMID:26393194

Three MMIC Amplifiers for the 120-to-200 GHz Frequency Band

NASA Technical Reports Server (NTRS)

Samoska, Lorene; Schmitz, Adele

2009-01-01

Closely following the development reported in the immediately preceding article, three new monolithic microwave integrated circuit (MMIC) amplifiers that would operate in the 120-to-200-GHz frequency band have been designed and are under construction at this writing. The active devices in these amplifiers are InP high-electron-mobility transistors (HEMTs). These amplifiers (see figure) are denoted the LSLNA150, the LSA200, and the LSA185, respectively. Like the amplifiers reported in the immediately preceding article, the LSLNA150 (1) is intended to be a prototype of low-noise amplifiers (LNAs) to be incorporated into spaceborne instruments for sensing cosmic microwave background radiation and (2) has potential for terrestrial use in electronic test equipment, passive millimeter-wave imaging systems, radar receivers, communication receivers, and systems for detecting hidden weapons. The HEMTs in this amplifier were fabricated according to 0.08- m design rules of a commercial product line of InP HEMT MMICs at HRL Laboratories, LLC, with a gate geometry of 2 fingers, each 15 m wide. On the basis of computational simulations, this amplifier is designed to afford at least 15 dB of gain, with a noise figure of no more than about 6 dB, at frequencies from 120 to 160 GHz. The measured results of the amplifier are shown next to the chip photo, with a gain of 16 dB at 150 GHz. Noise figure work is ongoing. The LSA200 and the LSA185 are intended to be prototypes of transmitting power amplifiers for use at frequencies between about 180 and about 200 GHz. These amplifiers have also been fabricated according to rules of the aforesaid commercial product line of InP HEMT MMICs, except that the HEMTs in these amplifiers are characterized by a gate geometry of 4 fingers, each 37 m wide. The measured peak performance of the LSA200 is characterized by a gain of about 1.4 dB at a frequency of 190 GHz; the measured peak performance of the LSA185 is characterized by a gain of about 2.7 dB at a frequency of 181 GHz. The measured gain results of each chip are shown next to their respective photos.

Neural correlates of anticipation and processing of performance feedback in social anxiety.

PubMed

Heitmann, Carina Y; Peterburs, Jutta; Mothes-Lasch, Martin; Hallfarth, Marlit C; Böhme, Stephanie; Miltner, Wolfgang H R; Straube, Thomas

2014-12-01

Fear of negative evaluation, such as negative social performance feedback, is the core symptom of social anxiety. The present study investigated the neural correlates of anticipation and perception of social performance feedback in social anxiety. High (HSA) and low (LSA) socially anxious individuals were asked to give a speech on a personally relevant topic and received standardized but appropriate expert performance feedback in a succeeding experimental session in which neural activity was measured during anticipation and presentation of negative and positive performance feedback concerning the speech performance, or a neutral feedback-unrelated control condition. HSA compared to LSA subjects reported greater anxiety during anticipation of negative feedback. Functional magnetic resonance imaging results showed deactivation of medial prefrontal brain areas during anticipation of negative feedback relative to the control and the positive condition, and medial prefrontal and insular hyperactivation during presentation of negative as well as positive feedback in HSA compared to LSA subjects. The results indicate distinct processes underlying feedback processing during anticipation and presentation of feedback in HSA as compared to LSA individuals. In line with the role of the medial prefrontal cortex in self-referential information processing and the insula in interoception, social anxiety seems to be associated with lower self-monitoring during feedback anticipation, and an increased self-focus and interoception during feedback presentation, regardless of feedback valence. © 2014 Wiley Periodicals, Inc.

Middle and Later Stone Age chronology of Kisese II rockshelter (UNESCO World Heritage Kondoa Rock-Art Sites), Tanzania.

PubMed

Tryon, Christian A; Lewis, Jason E; Ranhorn, Kathryn L; Kwekason, Amandus; Alex, Bridget; Laird, Myra F; Marean, Curtis W; Niespolo, Elizabeth; Nivens, Joelle; Mabulla, Audax Z P

2018-01-01

The archaeology of East Africa during the last ~65,000 years plays a central role in debates about the origins and dispersal of modern humans, Homo sapiens. Despite the historical importance of the region to these discussions, reliable chronologies for the nature, tempo, and timing of human behavioral changes seen among Middle Stone Age (MSA) and Later Stone Age (LSA) archaeological assemblages are sparse. The Kisese II rockshelter in the Kondoa region of Tanzania, originally excavated in 1956, preserves a ≥ 6-m-thick archaeological succession that spans the MSA/LSA transition, with lithic artifacts such as Levallois and bladelet cores and backed microliths, the recurrent use of red ochre, and >5,000 ostrich eggshell beads and bead fragments. Twenty-nine radiocarbon dates on ostrich eggshell carbonate make Kisese II one of the most robust chronological sequences for understanding archaeological change over the last ~47,000 years in East Africa. In particular, ostrich eggshell beads and backed microliths appear by 46-42 ka cal BP and occur throughout overlying Late Pleistocene and Holocene strata. Changes in lithic technology suggest an MSA/LSA transition that began 39-34.3 ka, with typical LSA technologies in place by the Last Glacial Maximum. The timing of these changes demonstrates the time-transgressive nature of behavioral innovations often linked to the origins of modern humans, even within a single region of Africa.

A social ecological approach to understanding correlates of lifetime sexual assault among sexual minority women in Toronto, Canada: results from a cross-sectional internet-based survey.

PubMed

Logie, C H; Alaggia, R; Rwigema, M J

2014-08-01

Stigma, discrimination and violence contribute to health disparities among sexual minorities. Lesbian, bisexual and queer (LBQ) women experience sexual violence at similar or higher rates than heterosexual women. Most research with LBQ women, however, has focused on measuring prevalence of sexual violence rather than its association with health outcomes, individual, social and structural factors. We conducted a cross-sectional online survey with LBQ women in Toronto, Canada. Multivariate logistic regression analyses were conducted to assess correlates of lifetime sexual assault (LSA). Almost half (42%) of participants (n = 415) reported experiences of LSA. Participants identifying as queer were more likely to have experienced LSA than those identifying as lesbian. When controlling for socio-demographic characteristics, experiencing LSA was associated with higher rates of depression, sexually transmitted infections (STIs), receiving an STI test, belief that healthcare providers were not comfortable with their LBQ sexual orientation, and sexual stigma (overall, perceived and enacted). A history of sexual violence was associated with lower: self-rated health, overall social support, family social support and self-esteem. This research highlights the salience of a social ecological framework to inform interventions for health promotion among LBQ women and to challenge sexual stigma and sexual violence. © The Author 2014. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Voluntary and involuntary childlessness in female veterans: associations with sexual assault.

PubMed

Ryan, Ginny L; Mengeling, Michelle A; Booth, Brenda M; Torner, James C; Syrop, Craig H; Sadler, Anne G

2014-08-01

To assess associations between lifetime sexual assault and childlessness in female veterans. Cross-sectional, computer-assisted telephone interview study. Two Midwestern Veterans Administration (VA) medical centers. A total of 1,004 women aged ≤52 years, VA-enrolled between 2000 and 2008. None. Sociodemographic variables, reproductive history and care utilization, and mental health. A total of 620 veterans (62%) reported at least one attempted or completed sexual assault in their lifetime (LSA). Veterans with LSA more often self-reported a history of pregnancy termination (31% vs. 19%) and infertility (23% vs. 12%), as well as sexually transmitted infection (42% vs. 27%), posttraumatic stress disorder (32% vs. 10%), and postpartum dysphoria (62% vs. 44%). Lifetime sexual assault was independently associated with termination and infertility in multivariate models; sexually transmitted infection, posttraumatic stress disorder, and postpartum dysphoria were not. The LSA by period of life was as follows: 41% of participants in childhood, 15% in adulthood before the military, 33% in military, and 13% after the military (not mutually exclusive). Among the 511 who experienced a completed LSA, 23% self-reported delaying or foregoing pregnancy because of their assault. This study demonstrated associations between sexual assault history and pregnancy termination, delay or avoidance (voluntary childlessness), and infertility (involuntary childlessness) among female veterans. Improved gender-specific veteran medical care must attend to these reproductive complexities. Copyright © 2014 American Society for Reproductive Medicine. All rights reserved.

Characteristics and outcomes of older adults with long-standing versus late-onset asthma.

PubMed

Herscher, Michael L; Wisnivesky, Juan P; Busse, Paula J; Hanania, Nicola A; Sheng, Tianyun; Wolf, Michael S; Federman, Alex D

2017-04-01

To examine the effect of age of onset on clinical characteristics and outcomes in a cohort of older patients with long-standing (LSA) and late-onset asthma (LOA). In all, 452 patients 60 years of age and older with persistent asthma were recruited. We defined LOA as asthma developing at age 40 or later and LSA as developing before age 40. We compared airway obstruction as assessed by spirometry, as well as asthma control using the Asthma Control Questionnaire (ACQ), quality of life using the Mini Asthma Quality of Life Questionnaire (AQLQ), and asthma-related emergency department visits and hospitalizations among patients with LSA vs. LOA. Patients with LOA, were less likely to have FEV 1 <70% of predicted (23% vs. 40%, p = 0.0002), to have FEV 1 /FVC<0.7 (27% vs. 38%, p = 0.01), or to have been intubated in the past (5% vs. 14%, p = 0.0007), and were also less likely to report a history of allergic conditions (64% vs 76%, p = 0.007). There was no significant difference in the level of asthma control, quality of life, or health care utilization. Older adults with LOA have different clinical and physiological characteristics and outcomes compared to those with LSA. Some of these differences may represent sequelae of longstanding disease, however LOA may also represent a different clinical phenotype that could influence management approaches.

Laser Surface Alloying of Copper, Manganese, and Magnesium with Pure Aluminum Substrate

NASA Astrophysics Data System (ADS)

Jiru, Woldetinsay G.; Sankar, M. Ravi; Dixit, Uday S.

2016-03-01

Laser surface alloying is one of the recent technologies used in the manufacturing sector for improving the surface properties of the metals. Light weight materials like aluminum alloys, titanium alloys, and magnesium alloys are used in the locomotive, aerospace, and structural applications. In the present work, an experimental study was conducted to improve the surface hardness of commercially pure aluminum plate. CO2 laser is used to melt pre-placed powders of pure copper, manganese, and magnesium. Microstructure of alloyed surface was analyzed using optical microscope. The best surface alloying was obtained at the optimum values of laser parameters, viz., laser power, scan speed, and laser beam diameter. In the alloyed region, microhardness increased from 30 HV0.5 to 430 HV0.5, while it was 60 HV0.5 in the heat-affected region. Tensile tests revealed some reduction in the strength and total elongation due to alloying. On the other hand, corrosion resistance improved.

Andesites of the 2009 eruption of Redoubt Volcano, Alaska

USGS Publications Warehouse

Coombs, Michelle L.; Sisson, Thomas W.; Bleick, Heather A.; Henton, Sarah M.; Nye, Christopher J.; Payne, Allison; Cameron, Cheryl E.; Larsen, Jessica F.; Wallace, Kristi; Bull, Katharine F.

2013-01-01

Crystal-rich andesites that erupted from Redoubt Volcano in 2009 range from 57.5 to 62.5 wt.% SiO2 and have phenocryst and phenocryst-melt relations consistent with staging in the upper crust. Early explosive products are low-silica andesites (LSA, < 58 wt.% SiO2) that ascended from deeper crustal levels during or before the 6 months of precursory activity, but a broad subsequent succession to more evolved and cooler products, and predominantly effusive dome growth, are interpreted to result from progressive mobilization and mixing with differentiated magmas tapped from pre-2009 Redoubt intrusions at ~ 3–6 km depth. Initial explosions on March 23–28 ejected predominantly LSA with a uniform phenocryst assemblage of high-Al amphibole, ~ An70 plagioclase, ortho- and clinopyroxene, FeTi oxides (890 to 960 °C), and traces of magmatic sulfide. Melt in the dominant microlite-poor LSA was compositionally uniform dacite (67–68 wt.% SiO2) but ranged to rhyolite with greater microlite growth. Minor amounts of intermediate- to high-silica andesite (ISA, HSA; 59–62.5 wt.% SiO2) also erupted during the early explosions and most carried rhyolitic melt (72–74 wt.% SiO2). A lava dome grew following the initial tephra-producing events but was destroyed by an explosion on April 4. Ejecta from the April 4 explosion consists entirely of ISA and HSA, as does a subsequent lava dome that grew April 4–July 1; LSA was absent. Andesites from the April 4 event and from the final dome had pre-eruptive temperatures of 725–840 °C (FeTi oxides) and highly evolved matrix liquids (77–80 wt.% SiO2), including in rare microlite-free pyroclasts. ISA has mixed populations of phenocrysts suggesting it is a hybrid between HSA and LSA. The last lavas from the 2009 eruption, effused May 1–July 1, are distinctly depleted in P2O5, consistent with low temperatures and high degrees of crystallization including apatite.Plagioclase–melt hygrometry and comparison to phase equilibrium experiments are consistent with pre-eruptive storage of all three magma types at 100–160 MPa (4–6 km depth), if they were close to H2O-saturation, coincident with the locus of shallow syn-eruptive seismicity. Deeper storage would be indicated if the magmas were CO2-rich. Relatively coarse-grained clinopyroxene-rich reaction rims on many LSA amphibole phenocrysts may result from slow ascent to, or storage at, depths shallow enough for the onset of appreciable H2O exsolution, consistent with pre-eruptive staging in the uppermost crust. We interpret that the 2009 LSA ascended from depth during the 8 or more months prior to the first eruption, but that the magma stalled and accumulated in the upper crust where its phenocryst rim and melt compositions were established. Ascent of LSA through stagnant mushy intrusions residual from earlier Redoubt activity mobilized differentiated magma pockets and interstitial liquids represented by HSA, and as LSA–HSA hybrids represented by ISA, that fed the subsequently erupted lava domes.

Editor's Choice - Incidence of Stroke Following Thoracic Endovascular Aortic Repair for Descending Aortic Aneurysm: A Systematic Review of the Literature with Meta-analysis.

PubMed

von Allmen, R S; Gahl, B; Powell, J T

2017-02-01

Stroke is an increasingly recognised complication following thoracic endovascular aortic repair (TEVAR). The aim of this study was to systematically synthesise the published data on perioperative stroke incidence during TEVAR for patients with descending thoracic aneurysmal disease and to assess the impact of left subclavian artery (LSA) coverage on stroke incidence. A systematic review of English and German articles on perioperative (in-hospital or 30 day) stroke incidence following TEVAR for descending aortic aneurysm was performed, including studies with ≥50 cases, using MEDLINE and EMBASE (2005-2015). The pooled prevalence of perioperative stroke with 95% CI was estimated using random effect analysis. Heterogeneity was examined using I 2 statistic. Of 215 studies identified, 10 were considered suitable for inclusion. The included studies enrolled a total of 2594 persons (61% male) between 1997 and 2014 with a mean weighted age of 71.8 (95% CI 71.1-73.6) years. The pooled prevalence for stroke was 4.1% (95% CI 2.9-5.5) with moderate heterogeneity between studies (I 2  = 49.8%, p = .04). Five studies reported stroke incidences stratified by the management of the LSA, that is uncovered versus covered and revascularised versus covered and not-revascularised. In cases where the LSA remained uncovered, the pooled stroke incidence was 3.2% (95% CI 1.0-6.5). There was, however, an indication that stroke incidence increased following LSA coverage, to 5.3% (95% CI 2.6-8.6) in those with a revascularisation and 8.0% (95% CI 4.1-12.9) in those without revascularisation. Stroke incidence is an important morbidity after TEVAR, and probably increases if the LSA is covered during the procedure, particularly in those without revascularisation. Copyright © 2016 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.

Structured Analysis/Design - LSA Task 101, Early Logistic Support Analysis Strategy, Subtask 101.2.1, Develop Early LSA Strategy

DTIC Science & Technology

1990-07-01

replacing "logic diagrams" or "flow charts") to aid in coordinating the functions to be performed by a computer program and its associated Inputs...ADDRESS (City, State, and ZIP Code) 10. SOURCE OF FUNDING NUMBERS PROGRAM PROJECT ITASK IWORK UNIT ELEMENT NO. NO. NO. ACCESSION NO. 11. TITLE...the analysis. Both the logical model and detailed procedures are used to develop the application software programs which will be provided to Government

Report of the Joint Industry - DoD Task Force on Computer Aided Logistic Support (CALS). Volume 2. Report of Policy and Legal Constraints Subgroup.

DTIC Science & Technology

1985-06-01

via the LSA process, to determine the best mix of support resource requirements. The data elements required for the LSA process would reside in an...homework. (ii) Policy to deal matrix digital data format/delivery defintion to replace paper world definitions in our current contractive procedures...2.2.2.1 NAPLPS. (North American Presentation Level Protocol Syntax) was developed for the videotex market during 1981-82, based on a series of

Structured Analysis and Structured Design for the Logistic Support Analysis (LSA) Task 303 Evaluation of Alternatives and Trade-Off Analysis, LSA Subtask 303.2.2, Trade-Off Between Support System Alternatives and System/Equipment Alternatives

DTIC Science & Technology

1991-01-01

Field 3. Training and Training Devices: a. Factory training b. Instructor and key personnel training c. New equipment training plan d. New equipment...12345678901234567990123456789012345678901234567890123456789� 1. 0016 10 SUPPOR2AILITY ALTEIIIVE TRADE-OFF ANALISIS . 4. + 4" + 4. 4. 4 2. C1.0 111.0 N2.0 1.0 INITIATE

Structured Analysis of the Logistics Support Analysis (LSA) Task, and Integrated Logistic Support (ILS) Element, ’Standardization and Interoperability (S and I)’.

DTIC Science & Technology

1988-11-01

system, using graphic techniques which enable users, analysts, and designers to get a clear and common picture of the system and how its parts fit...boxes into hierarchies suitable for computer implementation. ŗ. Structured Design uses tools, especially graphic ones, to render systems readily...LSA, PROCESSES, DATA FLOWS, DATA STORES, EX"RNAL ENTITIES, OVERALL SYSTEMS DESIGN PROCESS, over 19, ABSTRACT (Continue on reverse if necessary and

Automated Logistics Support Analysis Tool, Version 1.0 User’s Manual, LSA Task 101, Early LSA Strategy

DTIC Science & Technology

1991-05-01

US AMCCOM INTEGRATED LOGISTIC SUPPORT OFFICE AMSMC-LSP ROCK ISLAND, IL by AMERICAN POWER JET COMPANY RIDGEFIELD, NJ ARLINGTON, VA WILLIAMSBURG, VA ST...the American Power Jet (APJ) Company , under contract to HQs AMCCOM. A major goal of the project is to unify the military and contractor approach to...and should be addressed to: George Chernowitz AMERICAN POWER JET COMPANY 705 Grand Avenue Ridgefield, New Jersey 07657 Phone: (201) 945-8203 TABLE OF

Large space antenna communications systems: Integrated Langley Research Center/Jet Propulsion Laboratory technology development activities. 1: Introduction

NASA Technical Reports Server (NTRS)

Campbell, T. G.

1983-01-01

The Jet Propulsion Laboratory and the Langley Research Center have been developing technology related to large space antennas (LSA) during the past several years. The need for a communication system research program became apparent during the recent studies for the Land Mobile Satellite System. This study indicated the need for additional research in (1) electromagnetic analysis methods, (2) design and development of multiple beam feed systems, and (3) the measurement methods for LSA reflectors.

Surface modification of Ni–Ti alloys for stent application after magnetoelectropolishing

PubMed Central

Musaramthota, Vishal; Munroe, Norman; Datye, Amit; Dua, Rupak; Haider, Waseem; McGoron, Anthony; Rokicki, Ryszard

2015-01-01

The constant demand for new implant materials and the multidisciplinary design approaches for stent applications have expanded vastly over the past decade. The biocompatibility of these implant materials is a function of their surface characteristics such as morphology, surface chemistry, roughness, surface charge and wettability. These surface characteristics can directly influence the material's corrosion resistance and biological processes such as endothelialization. Surface morphology affects the thermodynamic stability of passivating oxides, which renders corrosion resistance to passivating alloys. Magnetoelectropolishing (MEP) is known to alter the morphology and composition of surface films, which assist in improving corrosion resistance of Nitinol alloys. This work aims at analyzing the surface characteristics of MEP Nitinol alloys by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The wettability of the alloys was determined by contact angle measurements and the mechanical properties were assessed by Nanoindentation. Improved mechanical properties were observed with the addition of alloying elements. Cyclic potentiodynamic polarization tests were performed to determine the corrosion susceptibility. Further, the alloys were tested for their cytotoxicity and cellular growth with endothelial cells. Improved corrosion resistance and cellular viability were observed with MEP surface treated alloys. PMID:25746243

Compensation for occupational diseases by chemical agents in Korea.

PubMed

Kwon, Soon-Chan; Roh, Soo-Yong; Lee, Ji-Hoon; Kim, Eun-A

2014-06-01

Investigation into the frequency of compensation for occupational diseases (ODs) caused by hazardous chemicals revealed an important opportunity for the improvement and further development of occupational health and safety systems in Korea. In response to concerns after outbreaks of disease due to chemical exposure, specific criteria for recognition of ODs were established and included in the Enforcement Decree of the Labor Standard Act (LSA) and the Industrial Accident Compensation Insurance Act (IACIA) on June 28, 2013. However, the original versions of the LSA and IACIA contain several limitations. First, the criteria was listed inconsistently according to the symptoms or signs of acute poisoning. Second, all newly recognized hazardous chemicals and chemicals recognized as hazardous by the International Labor Organization (ILO) were not included in the LSA and IACIA. Although recent amendments have addressed these shortcomings, future amendments should strive to include all chemicals listed by the ILO and continuously add newly discovered hazardous chemicals as they are introduced into the workplace.

The semantic representation of prejudice and stereotypes.

PubMed

Bhatia, Sudeep

2017-07-01

We use a theory of semantic representation to study prejudice and stereotyping. Particularly, we consider large datasets of newspaper articles published in the United States, and apply latent semantic analysis (LSA), a prominent model of human semantic memory, to these datasets to learn representations for common male and female, White, African American, and Latino names. LSA performs a singular value decomposition on word distribution statistics in order to recover word vector representations, and we find that our recovered representations display the types of biases observed in human participants using tasks such as the implicit association test. Importantly, these biases are strongest for vector representations with moderate dimensionality, and weaken or disappear for representations with very high or very low dimensionality. Moderate dimensional LSA models are also the best at learning race, ethnicity, and gender-based categories, suggesting that social category knowledge, acquired through dimensionality reduction on word distribution statistics, can facilitate prejudiced and stereotyped associations. Copyright © 2017 Elsevier B.V. All rights reserved.

Latent semantic analysis.

PubMed

Evangelopoulos, Nicholas E

2013-11-01

This article reviews latent semantic analysis (LSA), a theory of meaning as well as a method for extracting that meaning from passages of text, based on statistical computations over a collection of documents. LSA as a theory of meaning defines a latent semantic space where documents and individual words are represented as vectors. LSA as a computational technique uses linear algebra to extract dimensions that represent that space. This representation enables the computation of similarity among terms and documents, categorization of terms and documents, and summarization of large collections of documents using automated procedures that mimic the way humans perform similar cognitive tasks. We present some technical details, various illustrative examples, and discuss a number of applications from linguistics, psychology, cognitive science, education, information science, and analysis of textual data in general. WIREs Cogn Sci 2013, 4:683-692. doi: 10.1002/wcs.1254 CONFLICT OF INTEREST: The author has declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website. © 2013 John Wiley & Sons, Ltd.

Combination of Bleomycin and Cytosine Arabinoside Chemotherapy for Relapsed Canine Lymphoma.

PubMed

Batschinski, Karen; Dervisis, Nikolaos; Kitchell, Barbara; Newman, Rebecca; Erfourth, Todd

A retrospective study was performed to evaluate response rate, time to progression, and toxicity of a bleomycin and cytosine arabinoside (Bleo/Cytarabine) combination protocol for dogs with relapsed lymphoma (LSA). Dogs diagnosed with LSA and previously treated with chemotherapy were included in the study. A total of 20 dogs met the inclusion criteria, and 19 were evaluable for response. Bleomycin was administered subcutaneously on days 1 and 8 and cytosine arabinoside was administered subcutaneously on days 1-5 of a 21-day cycle. The median number of chemotherapy drugs given prior to the administration of Bleo/Cytarabine was 8.5. A total of 23 cycles of Bleo/Cytarabine were administered. The overall response rate was 36.8% (7 of 19 dogs had a partial response). The median time to progression was 15 days. Three dogs developed grade 3 thrombocytopenia and one dog had a grade 4 neutropenia. Bleo/Cytarabine had minor activity when used as a rescue therapy for pretreated LSA patients.

Effects of surface poisons on the oxidation of binary alloys

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

Hagan, P.S.; Polizzotti, R.S.; Luckman, G.

1985-10-01

A system of reaction-diffusion equations describing the oxidation of binary alloys in environments containing small amounts of surface poisons is analyzed. These poisons reduce the oxygen flux into the alloy, which causes the alloy to oxidize in two stages.During the initial stage, the oxidation reaction occurs in a stationary boundary layer at the alloy surface. Consequently, a thin zone containing a very high concentration of the metal oxide is created at the alloy surface. During the second stage, the oxidation reaction occurs in a moving boundary layer. This leads to a Stefan problem, which is analyzed by using asymptotic andmore » numerical techniques. By comparing the solutions to those of alloys in unpoisoned environments, it is concluded that surface poisons can lead to the formation of protective external oxide scales in alloys which would not normally form such scales. 11 references.« less

The role of electro-explosion alloying with titanium diboride and treatment with pulsed electron beam in the surface modification of VT6 alloy

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

Konovalov, Sergey, E-mail: konovserg@gmail.com; Gromov, Victor, E-mail: gromov@physics.sibsiu.ru; Kobzareva, Tatyana

The paper presents the results of the investigation of VT6 titanium alloy subjected to electro-explosion alloying with TiB{sub 2} and irradiation with pulsed electron beam. It was established that electro-explosion alloying resulted in a high level of roughness of the surface layer with high adhesion of the modified layer and matrix. Further irradiation of the material with electron beam resulted in the smoothing of the surface of alloying and formation of a porous structure with various scale levels in the surface layer. It was also established that the energetic exposure causes the formation of a gradient structure with a changingmore » elemental composition along the direction from the surface of alloying.« less

Effect of a microstructure and surface hydrogen alloying of a VT6 alloy on diffusion welding

NASA Astrophysics Data System (ADS)

Senkevich, K. S.; Skvortsova, S. V.; Kudelina, I. M.; Knyazev, M. I.; Zasypkin, V. V.

2014-01-01

The effect of a structural type (lamellar, fine, gradient) and additional surface alloying with hydrogen on the diffusion bonding of titanium alloy VT6 samples is studied. It is shown that the surface alloying of VT6 alloy parts with hydrogen allows one to decrease the diffusion welding temperature by 50-100°C, to obtain high-quality pore-free bonding, and to remove the "structural" boundary between materials to be welded that usually forms during welding of titanium alloys with a lamellar structure.

Correlation of serum biomarkers (TSA & LSA) and epithelial dysplasia in early diagnosis of oral precancer and oral cancer.

PubMed

Sawhney, Hemant; Kumar, C Anand

Oral cancer is currently the most frequent cause of cancer-related deaths, which is usually preceded by oral pre-cancerous lesions and conditions. Altered glycosylation of glycoconjugates, such as sialic acid, fucose, etc. are amongst the important molecular changes that accompany malignant transformation. The purpose of our study was to evaluate usefulness of serum Total Sialic Acid (TSA) and serum Lipid-Bound Sialic Acid (LSA) as markers of oral precancerous lesions and histopathologically correlating them with grades of epithelial dysplasia. Blood samples were collected from 50 patients with oral precancer (Leukoplakia & OSMF), 25 patients with untreated oral cancer and 25 healthy subjects. Serum sialic acid (total and lipid bound) levels were measured spectrophotometrically. Tissue samples from all the patients were evaluated for dysplasia. Serum levels of total and lipid bound sialic acid were significantly elevated in patients with oral precancer and cancer when compared with healthy subjects. Analysis of variance test documented that there is progressive rise in serum levels of sialic acid with the degree of dysplastic changes in oral precancer patients. We observed positive correlation between serum levels of the markers and the extent of malignant disease (TNM Clinical staging) as well as histopathological grades. The results suggested that serum levels of TSA and LSA progressively increases with grades of dysplasia in precancerous groups and cancer group, when compared with healthy controls. These glycoconjugates, especially LSA has the clinical utility in indicating a premalignant change.

Middle and Later Stone Age chronology of Kisese II rockshelter (UNESCO World Heritage Kondoa Rock-Art Sites), Tanzania

PubMed Central

Ranhorn, Kathryn L.; Kwekason, Amandus; Alex, Bridget; Laird, Myra F.; Marean, Curtis W.; Niespolo, Elizabeth; Nivens, Joelle; Mabulla, Audax Z. P.

2018-01-01

The archaeology of East Africa during the last ~65,000 years plays a central role in debates about the origins and dispersal of modern humans, Homo sapiens. Despite the historical importance of the region to these discussions, reliable chronologies for the nature, tempo, and timing of human behavioral changes seen among Middle Stone Age (MSA) and Later Stone Age (LSA) archaeological assemblages are sparse. The Kisese II rockshelter in the Kondoa region of Tanzania, originally excavated in 1956, preserves a ≥ 6-m-thick archaeological succession that spans the MSA/LSA transition, with lithic artifacts such as Levallois and bladelet cores and backed microliths, the recurrent use of red ochre, and >5,000 ostrich eggshell beads and bead fragments. Twenty-nine radiocarbon dates on ostrich eggshell carbonate make Kisese II one of the most robust chronological sequences for understanding archaeological change over the last ~47,000 years in East Africa. In particular, ostrich eggshell beads and backed microliths appear by 46–42 ka cal BP and occur throughout overlying Late Pleistocene and Holocene strata. Changes in lithic technology suggest an MSA/LSA transition that began 39–34.3 ka, with typical LSA technologies in place by the Last Glacial Maximum. The timing of these changes demonstrates the time-transgressive nature of behavioral innovations often linked to the origins of modern humans, even within a single region of Africa. PMID:29489827

Surface characterization of hydrogen charged and uncharged alpha-2 and gamma titanium aluminide alloys using AES and REELS

NASA Technical Reports Server (NTRS)

Shanabarger, M. R.

1990-01-01

The surfaces of selected uncharged and hydrogen charged alpha-2 and gamma titanium aluminide alloys with Nb additions were characterized by Auger electron (AES) and reflected electron energy loss (REELS) spectroscopy. The alloy surfaces were cleaned before analysis at room temperature by ion sputtering. The low energy (500 eV) ion sputtering process preferentially sputtered the surface concentration. The surface concentrations were determined by comparing AES data from the alloys with corresponding data from elemental references. No differences were observed in the Ti or Nb Auger spectra for the uncharged and hydrogen charged alloys, even though the alpha-2 alloy had 33.4 atomic percent dissolved hydrogen. Also, no differences were observed in the AES spectra when hydrogen was adsorbed from the gas phase. Bulk plasmon energy shifts were observed in all alloys. The energy shifts were induced either by dissolved hydrogen (alpha-2 alloy) or hydrogen adsorbed from the gas phase (alpha-2 and gamma alloys). The adsorption induced plasmon energy shifts were greatest for the gamma alloy and cp-Ti metal.

Kinetic model of mass transfer through gas liquid interface in laser surface alloying

NASA Astrophysics Data System (ADS)

Gnedovets, A. G.; Portnov, O. M.; Smurov, I.; Flamant, G.

1997-02-01

In laser surface alloying from gas atmosphere neither surface concentration nor the flux of the alloying elements are known beforehand. They should be determined from the combined solution of heat and mass transfer equations with an account for the kinetics of interaction of a gas with a melt. Kinetic theory description of mass transfer through the gas-liquid interface is applied to the problem of laser surface alloying of iron from the atmosphere of molecular nitrogen. The activation nature of gas molecules dissociation at the surface is considered. It is shown that under pulsed-periodic laser action the concentration profiles of the alloying element have maxima situated close to the surface of the metal. The efficiency of surface alloying increases steeply under laser-plasma conditions which results in the formation of highly supersaturated gas solutions in the metal.

Surface Nb-ALLOYING on 0.4C-13Cr Stainless Steel: Microstructure and Tribological Behavior

NASA Astrophysics Data System (ADS)

Yu, Shengwang; You, Kai; Liu, Xiaozhen; Zhang, Yihui; Wang, Zhenxia; Liu, Xiaoping

2016-02-01

0.4C-13Cr stainless steel was alloyed with niobium using double glow plasma surface alloying and tribological properties of Nb-alloyed steel such as hardness, friction and wear were measured. Effects of the alloying temperature on microstructure and the tribological behavior of the alloyed steel were investigated compared with untreated steel. Formation mechanisms of Nb-alloyed layers and increased wear resistance were also studied. The result shows that after surface Nb-alloying treatment, the 0.4C-13Cr steel exhibits a diffusion adhesion at the alloyed layer/substrate interface and improved tribological property. The friction coefficient of Nb-alloyed steel is decreased by about 0.3-0.45 and the wear rate after Nb-alloying is only 2-5% of untreated steel.

Surface Segregation in Multicomponent Systems: Modeling of Surface Alloys and Alloy Surfaces

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John; Noebe, Ronald D.; Good, Brian; Honecy, Frank S.; Abel, Phillip

1999-01-01

The study of surface segregation, although of great technological importance, has been largely restricted to experimental work due to limitations associated with theoretical methods. However, recent improvements in both first-particle and semi-empirical methods are opening, the doors to an array of new possibilities for surface scientists. We apply one of these techniques, the Bozzolo, Ferrante and Smith (BFS) method for alloys, which is particularly suitable for complex systems, to several aspects of the computational modeling of surfaces and segregation, including alloy surface segregation, structure and composition of alloy surfaces, and the formation of surface alloys. We conclude with the study of complex NiAl-based binary, ternary and quaternary thin films (with Ti, Cr and Cu additions to NiAl). Differences and similarities between bulk and surface compositions are discussed, illustrated by the results of Monte Carlo simulations. For some binary and ternary cases, the theoretical predictions are compared to experimental results, highlighting the accuracy and value of this developing theoretical tool.

Modification of the titanium alloy surface in electroexplosive alloying with boron carbide and subsequent electron-beam treatment

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

Gromov, Victor E., E-mail: gromov@physics.sibsiu.ru; Budovskikh, Evgeniy A., E-mail: budovskikh-ea@physics.sibsiu.ru; Bashchenko, Lyudmila P., E-mail: gromov@physics.sibsiu.ru

2015-10-27

The modification of the VT6 titanium alloy surface in electroexplosion alloying with plasma being formed in titanium foil with a weighed powder of boron carbide with subsequent irradiation by a pulsed electron beam has been carried out. An electroexplosive alloying zone of a thickness up to 50 μm with a gradient structure is found to form. The subsequent electron-beam treatment of the alloying zone results in smoothing of the alloying surface and is accompanied by the formation of the multilayer structure with alternating layers of various alloying degree at a depth of 30 μm.

First Principles Calculations of Transition Metal Binary Alloys: Phase Stability and Surface Effects

NASA Astrophysics Data System (ADS)

Aspera, Susan Meñez; Arevalo, Ryan Lacdao; Shimizu, Koji; Kishida, Ryo; Kojima, Kazuki; Linh, Nguyen Hoang; Nakanishi, Hiroshi; Kasai, Hideaki

2017-06-01

The phase stability and surface effects on binary transition metal nano-alloy systems were investigated using density functional theory-based first principles calculations. In this study, we evaluated the cohesive and alloying energies of six binary metal alloy bulk systems that sample each type of alloys according to miscibility, i.e., Au-Ag and Pd-Ag for the solid solution-type alloys (SS), Pd-Ir and Pd-Rh for the high-temperature solid solution-type alloys (HTSS), and Au-Ir and Ag-Rh for the phase-separation (PS)-type alloys. Our results and analysis show consistency with experimental observations on the type of materials in the bulk phase. Varying the lattice parameter was also shown to have an effect on the stability of the bulk mixed alloy system. It was observed, particularly for the PS- and HTSS-type materials, that mixing gains energy from the increasing lattice constant. We furthermore evaluated the surface effects, which is an important factor to consider for nanoparticle-sized alloys, through analysis of the (001) and (111) surface facets. We found that the stability of the surface depends on the optimization of atomic positions and segregation of atoms near/at the surface, particularly for the HTSS and the PS types of metal alloys. Furthermore, the increase in energy for mixing atoms at the interface of the atomic boundaries of PS- and HTSS-type materials is low enough to overcome by the gain in energy through entropy. These, therefore, are the main proponents for the possibility of mixing alloys near the surface.

Auger electron spectroscopy study of surface segregation in the binary alloys copper-1 atomic percent indium, copper-2 atomic percent tin, and iron-6.55 atomic percent silicon

NASA Technical Reports Server (NTRS)

Ferrante, J.

1973-01-01

Auger electron spectroscopy was used to examine surface segregation in the binary alloys copper-1 at. % indium, copper-2 at. % tin and iron-6.55 at. % silicon. The copper-tin and copper-indium alloys were single crystals oriented with the /111/ direction normal to the surface. An iron-6.5 at. % silicon alloy was studied (a single crystal oriented in the /100/ direction for study of a (100) surface). It was found that surface segregation occurred following sputtering in all cases. Only the iron-silicon single crystal alloy exhibited equilibrium segregation (i.e., reversibility of surface concentration with temperature) for which at present we have no explanation. McLean's analysis for equilibrium segregation at grain boundaries did not apply to the present results, despite the successful application to dilute copper-aluminum alloys. The relation of solute atomic size and solubility to surface segregation is discussed. Estimates of the depth of segregation in the copper-tin alloy indicate that it is of the order of a monolayer surface film.

Electro and Magneto-Electropolished Surface Micro-Patterning on Binary and Ternary Nitinol

PubMed Central

Munroe, Norman; McGoron, Anthony

2012-01-01

In this study, an Atomic Force Microscopy (AFM) roughness analysis was performed on non-commercial Nitinol alloys with Electropolished (EP) and Magneto-Electropolished (MEP) surface treatments and commercially available stents by measuring Root-Mean-Square (RMS), Average Roughness (Ra), and Surface Area (SA) values at various dimensional areas on the alloy surfaces, ranging from (800 × 800 nm) to (115 × 115μm), and (800 × 800 nm) to (40 × 40 μm) on the commercial stents. Results showed that NiTi-Ta 10 wt% with an EP surface treatment yielded the highest overall roughness, while the NiTi-Cu 10 wt% alloy had the lowest roughness when analyzed over (115 × 115 μm). Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis revealed unique surface morphologies for surface treated alloys, as well as an aggregation of ternary elements Cr and Cu at grain boundaries in MEP and EP surface treated alloys, and non-surface treated alloys. Such surface micro-patterning on ternary Nitinol alloys could increase cellular adhesion and accelerate surface endothelialization of endovascular stents, thus reducing the likelihood of in-stent restenosis and provide insight into hemodynamic flow regimes and the corrosion behavior of an implantable device influenced from such surface micro-patterns. PMID:22754200

Structured Analysis of the Logistic Support Analysis (LSA) Task, and Integrated Logistic Support (ILS) Element, LSA Subtask 301.2.4.2, Reliability Centered Maintenance (RCM)

DTIC Science & Technology

1988-06-01

Di’Lt. ibu601’. I j I o; DTIC Qt.ALTTY I ,2,1 4 AMERICAN POWER JET COMPANY RIDGEFIELD, NJ FALLS CHURCH...The logic is applied to each reparable item in the system/equipment. When the components have been analyzed, an overall system/equipment analysis is...in the AMSDL as applicable to the referenced DIDs of interest. 5. Apply staff experience in logistics support analysis to assure that the intent of the

Biocompatibility enhancement of rare earth magnesium alloy by laser surface processing

NASA Astrophysics Data System (ADS)

Nie, Shilin; Wang, Yuqing; Liu, Haifeng; Guan, Yingchun

2018-01-01

Although magnesium and magnesium alloys are considered biocompatible and biodegradable, insufficient biocompatibility in body fluid environment is still the major drawback of magnesium alloys for their successful applications as biodegradable orthopaedic implants. In this work, magnesium alloy surface with both enhanced corrosion resistance and better cell adhesion property was directly fabricated by laser surface processing. Laser surface melting was used to improve corrosion resistance of Mg-6Gd-0.6Ca alloy. After laser surface melting, laser surface texturing was utilized on melted surface for better cell adhesion property. The corrosion resistance of laser-treated and as-received samples were evaluated using electrochemical technique. The effect of laser surface treatment on phase and microstructure evolution was evaluated using scanning electron microscopy, optical microscopy and X-ray diffraction. This work investigated the effect of laser treatment on cell distribution across the surface of magnesium alloy substrates. Osteoblast was cultured on the laser-treated surface and as-received surface. Cell morphology was observed with a scanning electron microscopy, and cell viability was evaluated by optical density measurement.

Laser Surface Alloying of Aluminum for Improving Acid Corrosion Resistance

NASA Astrophysics Data System (ADS)

Jiru, Woldetinsay Gutu; Sankar, Mamilla Ravi; Dixit, Uday Shanker

2018-04-01

In the present study, laser surface alloying of aluminum with magnesium, manganese, titanium and zinc, respectively, was carried out to improve acid corrosion resistance. Laser surface alloying was conducted using 1600 and 1800 W power source using CO2 laser. Acid corrosion resistance was tested by dipping the samples in a solution of 2.5% H2SO4 for 200 h. The weight loss due to acid corrosion was reduced by 55% for AlTi, 41% for AlMg alloy, 36% for AlZn and 22% for AlMn alloy. Laser surface alloyed samples offered greater corrosion resistance than the aluminum substrate. It was observed that localized pitting corrosion was the major factor to damage the surface when exposed for a long time. The hardness after laser surface alloying was increased by a factor of 8.7, 3.4, 2.7 and 2 by alloying with Mn, Mg, Ti and Zn, respectively. After corrosion test, hardness was reduced by 51% for AlTi sample, 40% for AlMg sample, 41.4% for AlMn sample and 33% for AlZn sample.

Role of alloying elements in adhesive transfer and friction of copper-base alloys

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1978-01-01

Sliding friction experiments were conducted in a vacuum with binary-copper alloy riders sliding against a conventional bearing-steel surface with normal residual oxides present. The binary alloys contained 1 atomic percent of various alloying elements. Auger spectroscopy analysis was used to monitor the adhesive transfer of the copper alloys to the bearing-steel surface. A relation was found to exist between adhesive transfer and the reaction potential and free energy of formation of the alloying element in the copper. The more chemically active the element and the more stable its oxide, the greater was the adhesive transfer and wear of the copper alloy. Transfer occurred in all the alloys except copper-gold after relatively few (25) passes across the steel surface.

[The effect of epigallocatechin gallate (EGCG) on the surface properties of nickel-chromium dental casting alloys after electrochemical corrosion].

PubMed

Qiao, Guang-yan; Zhang, Li-xia; Wang, Jue; Shen, Qing-ping; Su, Jian-sheng

2014-08-01

To investigate the effect of epigallocatechin gallate (EGCG) on the surface properties of nickel-chromium dental alloys after electrochemical corrosion. The surface morphology and surface structure of nickel-chromium dental alloys were examined by stereomicroscope and scanning electron microscopy before and after electrochemical tests in 0 g/L and 1.0 g/L EGCG artificial saliva. The surface element component and chemical states of nickel-chromium dental alloys were analyzed by X-ray photoelectron spectrograph after electrochemical tests in 0 g/L and 1.0 g/L EGCG artificial saliva. More serious corrosion happened on the surface of nickel-chromium alloy in 1.0 g/L EGCG artificial saliva than in 0 g/L EGCG. The diameters of corrosion pits were smaller, and the dendrite structure of the alloy surface was not affected in 0 g/L EGCG. While the diameters of corrosion pits were larger, the dendritic interval of the alloy surface began to merge, and the dendrite structure was fuzzy in 1.0 g/L EGCG. In addition, the O, Ni, Cr, Be, C and Mo elements were detected on the surface of nickel-chromium alloys after sputtered for 120 s in 0 g/L EGCG and 1.0 g/L EGCG artificial saliva after electrochemical corrosion, and the surface oxides were mainly NiO and Cr(2)O(3). Compared with 0 g/L EGCG artificial saliva, the content of O, NiO and Cr(2)O(3) were lower in 1.0 g/L EGCG. The results of surface morphology and the corrosion products both show that the corrosion resistance of nickel-chromium alloys become worse and the oxide content of corrosion products on the surface reduce in 1.0 g/L EGCG artificial saliva.

The structure and mechanical properties of AlMg5Si2Mn alloy after surface alloying by the use of fiber laser

NASA Astrophysics Data System (ADS)

Pakieła, Wojciech; Tanski, Tomasz; Pawlyta, Mirosława; Pakieła, Katarzyna; Brytan, Zbigniew; Sroka, Marek

2018-03-01

Laser surface treatment is successfully applied to increase hardness as well as corrosion and wear resistance in light alloys such as aluminum or magnesium. The laser surface remelting also can be used to repair superficial cracks, voids or porosity caused by the mechanical impact, metallurgical process as well as the corrosive environment on the surface of the aluminum alloy. The purpose of this paper was to investigate the influence of a fiber laser surface treatment on the structure and properties of the EN AC AlMg5Si2Mn alloy. The goal of this investigation was to increase the hardness and improve tribological properties of the aluminum alloy surface as a result of the conducted laser surface treatment. During laser processing, the top surface of the aluminum alloy was enriched with Cr and Ni particles. The grain size of the applied particles was approximately about 60-130 m. The Cr-Ni powder has been introduced in the molten pool using vacuum feeder at a constant rate of 4.5 g/min. For surface remelting we used square laser beam at a size 3 × 3 mm and with the power of 3.0 kW. The linear laser scan rate of the beam was set at 0.5 m/min. Argon was used to protect the liquid metal alloy during surface treatment. Application of the laser treatment on aluminum alloy has enabled to obtain much harder as well as better wear resistant material compared to the untreated EN AC AlMg5Si2Mn.

Effect of Fe- and Si-Enriched Secondary Precipitates and Surface Roughness on Pore Formation on Aluminum Plate Surfaces During Anodizing

NASA Astrophysics Data System (ADS)

Zhu, Yuanzhi; Wang, Shizhi; Yang, Qingda; Zhou, Feng

2014-09-01

Two twin roll casts (TRCs) and one hot rolled (HR) AA 1235 aluminum alloy plates with different microstructures are prepared. The plates were electrolyzed in a 1.2 wt% HCl solution with a voltage of 21 V and a current of 1.9 mA. The shape, size, and number of pores formed on the surfaces of these plates were analyzed and correlated with the microstructures of the plates. It is found that pores are easier to form on the alloy plates containing subgrains with a lower dislocation density inside the subgrains, rather than along the grain boundaries. Furthermore, Fe- and Si-enriched particles in the AA1235 aluminum alloys lead to the formation of pores on the surface during electrolyzing; the average precipitate sizes of 4, 3.5, and 2 μm in Alloy 1#, Alloy 2# and Alloy 3# result in the average pore sizes of 3.78, 2.76, and 1.9 μm on the surfaces of the three alloys, respectively; The G.P zone in the alloy also facilitates the surface pore formation. High-surface roughness enhances the possibility of entrapping more lubricants into the plate surface, which eventually blocks the formation of the pores on the surface of the aluminum plates in the following electrolyzing process.

Ab initio investigation of the surface properties of austenitic Fe-Ni-Cr alloys in aqueous environments

NASA Astrophysics Data System (ADS)

Rák, Zs.; Brenner, D. W.

2017-04-01

The surface energetics of two austenitic stainless steel alloys (Type 304 and 316) and three Ni-based alloys (Alloy 600, 690, and 800) are investigated using theoretical methods within the density functional theory. The relative stability of the low index surfaces display the same trend for all alloys; the most closely packed orientation and the most stable is the (111), followed by the (100) and the (110) surfaces. Calculations on the (111) surfaces using various surface chemical and magnetic configurations reveal that Ni has the tendency to segregate toward the surface and Cr has the tendency to segregate toward the bulk. The magnetic frustration present on the (111) surfaces plays an important role in the observed segregation tendencies of Ni and Cr. The stability of the (111) surfaces in contact with aqueous solution are evaluated as a function of temperature, pH, and concentration of aqueous species. The results indicate that the surface stability of the alloys decrease with temperature and pH, and increase slightly with concentration. Under conditions characteristic to an operating pressurized water reactor, the Ni-based alloy series appears to be of better quality than the stainless steel series with respect to corrosion resistance and release of aqueous species when in contact with aqueous solutions.

Cerebral Perforating Artery Disease : Characteristics on High-Resolution Magnetic Resonance Imaging.

PubMed

Liang, Jianye; Liu, Yiyong; Xu, Xiaoshuang; Shi, Changzheng; Luo, Liangping

2018-03-23

Our aims were to evaluate the feasibility of high-resolution magnetic resonance imaging (HR-MRI) for displaying the cerebral perforating arteries in normal subjects and to discuss the value of HR-MRI for detecting the causes of infarctions in the territory of the lenticulostriate artery (LSA). Included in this study were 31 healthy subjects and 28 patients who had infarctions in the territory supplied by the LSA. The T1-weighted imaging (T1WI), T2WI, diffusion-weighted imaging (DWI), and HR-MRI, including 3‑dimensional time-of-flight magnetic resonance angiography (3D-TOF-MRA) and 3D fast spin-echo T1WI (namely CUBE T1 in GE Healthcare), were applied on a 3-Tesla scanner. The numbers and route of the perforating arteries on both sides were independently confirmed on HR-MRI by two physicians. The Wilcoxon test was used to compare the differences. The numbers of perforating arteries in healthy subjects observed on 3D-TOF-MRA were as follows: numbers of the bilateral recurrent artery of Heubner (RAH) ranged from 0-3 (median 1), numbers of the left LSA ranged from 0-7 (median 3), numbers of the right LSA ranged from 0-5 (median 3), numbers of the bilateral anterior choroidal artery ranged from 1-2 (median 1) and the numbers of the bilateral thalamoperforating artery ranged from 1-2 (median 1). In the patients with lenticulostriate infarctions, the numbers of LSAs on the affected side were lower than on the opposite and ipsilateral sides in the healthy subjects. The results were statistically significant. An abnormality of the RAH may lead to a centrum semiovale infarct pattern, whereas an abnormality of the LSA is associated with a corona radiata infarct pattern. The use of HR 3D-TOF-MRA and CUBE T1 had unique advantages in displaying the tiny perforating arteries in vivo. Moreover, effective recognition of the associated cerebral perforating artery and infarct patterns may enhance our understanding of the mechanism of stroke in patients with lenticulostriate infarctions.

Plasma surface tantalum alloying on titanium and its corrosion behavior in sulfuric acid and hydrochloric acid

NASA Astrophysics Data System (ADS)

Wei, D. B.; Chen, X. H.; Zhang, P. Z.; Ding, F.; Li, F. K.; Yao, Z. J.

2018-05-01

An anti-corrosion Ti-Ta alloy coating was prepared on pure titanium surface by double glow plasma surface alloying technology. Electrochemical corrosion test was applied to test the anti-corrosion property of Ti-Ta alloy layer. The microstructure and the phase composition of Ti-Ta alloy coating were detected before and after corrosion process by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results showed that the Ta-Ti alloy layer has a thickness of about 13-15 μm, which is very dense without obvious defects such as pores or cracks. The alloy layer is composed mainly of β-Ta and α-Ti. The Ta alloy layer improves the anti-corrosion property of pure titanium. A denser and more durable TiO2 formed on the surface Ta-Ti alloy layer after immersing in strong corrosive media may account for the excellent corrosion resistant.

Synthesis and characterization of Ag-doped TiO2 nanotubes on Ti-6Al-4V and Ti-6Al-7Nb alloy

NASA Astrophysics Data System (ADS)

Ulfah, Ika Maria; Bachtiar, Boy M.; Murnandityas, Arnita Rut; Slamet

2018-05-01

The present paper is focused on comparative behavior of nanotubes growth on Ti-6Al-4V and Ti-6Al-7Nb alloy using electrochemical anodization method. These alloys were anodized in electrolytes solution containing glycerol, water and 0.5wt.% of NH4F. Silver-doped TiO2 nanotubes were synthesized using photo-assisted deposition (PAD) at various Ag loading concentration in 0.05 M, 0.10 M, and 0.15 M. The phase composition and morphological characteristics were investigated by XRD and FESEM/EDX, respectively. The surface wettability was measured by contact angle meter. The results showed that TiO2 nanotubes can be grown on these surface alloys. XRD profiles revealed crystal formation of anatase, rutile and Ag on these surface alloys. According to FESEM images, the average nanotube diameter of Ti-6Al-4V alloy and Ti-6Al-7Nb alloy are 134 nm and 120 nm, respectively. EDX-Mapping analysis showed that Ag desposited over surface of TiO2 nanotubes. The surface wettability indicated hydrophilicity properties on Ti-4Al-4V alloy and Ti-6Al-7Nb alloy surface. This study may contribute to the development of silver-doped TiO2 nanotubes on Ti-6Al-4V alloy and Ti-6Al-7Nb alloy can be considered in various photocatalytic applications such as biomedical devicesdue to photocatalytic mechanism and antibacterial ability.

Determination of community structure through deconvolution of PLFA-FAME signature of mixed population.

PubMed

Dey, Dipesh K; Guha, Saumyen

2007-02-15

Phospholipid fatty acids (PLFAs) as biomarkers are well established in the literature. A general method based on least square approximation (LSA) was developed for the estimation of community structure from the PLFA signature of a mixed population where biomarker PLFA signatures of the component species were known. Fatty acid methyl ester (FAME) standards were used as species analogs and mixture of the standards as representative of the mixed population. The PLFA/FAME signatures were analyzed by gas chromatographic separation, followed by detection in flame ionization detector (GC-FID). The PLFAs in the signature were quantified as relative weight percent of the total PLFA. The PLFA signatures were analyzed by the models to predict community structure of the mixture. The LSA model results were compared with the existing "functional group" approach. Both successfully predicted community structure of mixed population containing completely unrelated species with uncommon PLFAs. For slightest intersection in PLFA signatures of component species, the LSA model produced better results. This was mainly due to inability of the "functional group" approach to distinguish the relative amounts of the common PLFA coming from more than one species. The performance of the LSA model was influenced by errors in the chromatographic analyses. Suppression (or enhancement) of a component's PLFA signature in chromatographic analysis of the mixture, led to underestimation (or overestimation) of the component's proportion in the mixture by the model. In mixtures of closely related species with common PLFAs, the errors in the common components were adjusted across the species by the model.

Lysergic acid amide as chemical marker for the total ergot alkaloids in rye flour - Determination by high-performance thin-layer chromatography-fluorescence detection.

PubMed

Oellig, Claudia

2017-07-21

Ergot alkaloids are generally determined by high-performance liquid chromatography (HPLC) coupled to fluorescence detection (FLD) or mass selective detection, analyzing the individual compounds. However, fast and easy screening methods for the determination of the total ergot alkaloid content are more suitable, since for monitoring only the sum of the alkaloids is relevant. The herein presented screening uses lysergic acid amide (LSA) as chemical marker, formed from ergopeptine alkaloids, and ergometrine for the determination of the total ergot alkaloids in rye with high-performance thin-layer chromatography-fluorescence detection (HPTLC-FLD). An ammonium acetate buffered extraction step was followed by liquid-liquid partition for clean-up before the ergopeptine alkaloids were selectively transformed to LSA and analyzed by HPTLC-FLD on silica gel with isopropyl acetate/methanol/water/25% ammonium hydroxide solution (80:10:3.8:1.1, v/v/v/v) as the mobile phase. The enhanced native fluorescence of LSA and unaffected ergometrine was used for quantitation without any interfering matrix. Limits of detection and quantitation were 8 and 26μg LSA/kg rye, which enables the determination of the total ergot alkaloids far below the applied quality criterion limit for rye. Close to 100% recoveries for different rye flours at relevant spiking levels were obtained. Thus, reliable results were guaranteed, and the fast and efficient screening for the total ergot alkaloids in rye offers a rapid alternative to the HPLC analysis of the individual compounds. Copyright © 2017 Elsevier B.V. All rights reserved.

Life-Space Assessment and Physical Activity Scale for the Elderly: validity of proxy informant responses.

PubMed

Cavanaugh, James T; Crawford, Kelley

2014-08-01

To validate the administration of the Life-Space Assessment (LSA) and Physical Activity Scale for the Elderly (PASE) surveys to proxy informants, as would be necessary when measuring long-term outcomes in acutely ill, hospitalized older adults who are initially incapacitated but eventually return to the community. Cross-sectional study. General community. Convenience sample of dyads (N=40) composed of an ambulatory older adult and a familiar companion. Dyads completed the LSA and PASE surveys on 1 occasion. Companions based their responses on the recent mobility and physical activity of the older adult. Paired total scores for each instrument. At a group level, the difference between older adult and companion mean scores for each instrument was not significant (P>.05). Standardized mean difference values were small (d<0.1). Paired scores were significantly yet moderately associated: intraclass correlation coefficient(1,1)=.84 to .88; P<.01. Difference in scores was not associated with time spent together (P>.05) or older adult gait speed (P>.05). At an individual level, older adults and companions agreed more closely on the LSA than on the PASE. However, disagreement in excess of estimated measurement error occurred in 40% of the dyads for the LSA and in none of the dyads for the PASE. Older adults and companions collectively provided similar responses on each instrument. Nonetheless, varying levels of agreement within individual dyads suggested that proxy responses should be considered carefully. Implications for clinical research and practice research are discussed. Copyright © 2014 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

Creating poly(ethylene glycol) film on the surface of NiTi alloy by gamma irradiation

NASA Astrophysics Data System (ADS)

Yu, Hongyan; Yan, Jin; Ma, Huiling; Zeng, Xinmiao; Liu, Yang; Zhao, Xinqing

2015-07-01

NiTi alloy has been extensively utilized as biomaterials owing to its unique shape memory effect, superelasticity and biocompatibility. However, concern with the toxic and allergic responses of nickel potentially releasing from implants stimulated lots of researches of modification on NiTi alloy surface. Creating chemical bond attachment of bioorganic film on NiTi alloy surface could effectively inhibit Ni releasing and obtain bioactive functions for further application. In this work, to get a bioorganic surface, NiTi alloy was modified with poly(ethylene glycol) (PEG) film by gamma ray induced grafting or crosslinking. X-ray diffraction (XRD) spectrum, water contact angle geometer and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the NiTi surface. The results indicated that PEG was covalent bonded on NiTi alloy surface. Fluorescence microscope (FM) images for morphology of 1 day osteoblast culture on the PEG coated NiTi surface showed that PEG could improve cell proliferation on NiTi surface. Our work offers a way to introduce a bioorganic metal surface by gamma irradiation.

Zr/ZrC modified layer formed on AISI 440B stainless steel by plasma Zr-alloying

NASA Astrophysics Data System (ADS)

Shen, H. H.; Liu, L.; Liu, X. Z.; Guo, Q.; Meng, T. X.; Wang, Z. X.; Yang, H. J.; Liu, X. P.

2016-12-01

The surface Zr/ZrC gradient alloying layer was prepared by double glow plasma surface alloying technique to increase the surface hardness and wear resistance of AISI 440B stainless steel. The microstructure of the Zr/ZrC alloying layer formed at different alloying temperatures and times as well as its formation mechanism were discussed by using scanning electron microscopy, glow discharge optical emission spectrum, X-ray diffraction and X-ray photoelectron spectroscopy. The adhesive strength, hardness and tribological property of the Zr/ZrC alloying layer were also evaluated in the paper. The alloying surface consists of the Zr-top layer and ZrC-subsurface layer which adheres strongly to the AISI 440B steel substrate. The thickness of the Zr/ZrC alloying layer increases gradually from 16 μm to 23 μm with alloying temperature elevated from 900 °C to 1000 °C. With alloying time from 0.5 h to 4 h, the alloyed depth increases from 3 μm to 30 μm, and the ZrC-rich alloyed thickness vs time is basically parabola at temperature of 1000 °C. Both the hardness and wear resistance of the Zr/ZrC alloying layer obviously increase compared with untreated AISI 440B steel.

Surface modification of Ti alloy by electro-explosive alloying and electron-beam treatment

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

Gromov, Victor, E-mail: gromov@physics.sibsiu.ru; Kobzareva, Tatiana, E-mail: kobzarevatanya@mail.ru; Budovskikh, Evgeniy, E-mail: budovskih-ea@physics.sibsiu.ru

2016-01-15

By methods of modern physical metallurgy the analysis of structure phase states of titanium alloy VT6 is carried out after electric explosion alloying with boron carbide and subsequent irradiation by pulsed electron beam. The formation of an electro-explosive alloying zone of a thickness up to 50 µm, having a gradient structure, characterized by decrease in the concentration of carbon and boron with increasing distance to the treatable surface has been revealed. Subsequent electron-beam treatment of alloying zone leads to smoothing of the alloying area surface and is accompanied by the multilayer structure formation at the depth of 30 µm withmore » alternating layers with different alloying degrees having the structure of submicro - and nanoscale level.« less

Wear mechanisms and improvements of wear resistance in cobalt-chromium alloy femoral components in artificial total knee joints

NASA Astrophysics Data System (ADS)

Que, Like

Wear is one of the major causes of artificial total knee arthroplasty (TKA) failure. Wear debris can cause adverse reactions to the surrounding tissue which can ultimately lead to loosening of the prosthesis. The wear behavior of UHMWPE tibial components have been studied extensively, but relatively little attention has been paid to the CoCrMo femoral component. The goal of the present study was to investigate the wear mechanisms of CoCrMo femoral components, to study the effect of CoCrMo alloy surface roughness on the wear of UHMWPE, and to determine the effect of heat treatments on the wear resistance of the CoCrMo implant alloys. The surface roughness of twenty-seven retrieved CoCrMo femoral components was analyzed. A multiple station wear testing machine and a wear fixture attached to an MTS 858 bionix system were built and used for in vitro wear studies of the CoCrMo/UHMWPE bearing couple. Solution and aging treatments were applied to the CoCrMo alloys. A white light interference surface profilometer (WLISP) and a scanning electron microscope (SEM) were used to measure the surface roughness and to study wear mechanisms of CoCrMo alloy. An optical microscope was used for alloy microstructure study. X-ray diffraction tests were performed to identify alloy phase transformation after aging. The micro-structure, hardness, and wear resistance of the alloys were studied. Surface roughness was used to quantify alloy wear, and the minimum number of surface roughness measurements required to obtain a reliable and repeatable characterization of surface roughness for a worn alloy surface was determined. The surfaces of the retrieved CoCrMo femoral components appeared to be damaged by metal particles embedded in the UHMWPE tibial component and metal-on-metal wear due to UHMWPE tibial component through-wear. Surface roughness of the femoral components was not correlated with patient age, weight, sex, or length of implantation. In vitro wear tests showed that when the CoCrMo alloy surface roughness was higher than 0.022 mum Ra (surface roughness average), UHMWPE wear increased with increasing CoCrMo alloy surface roughness. Bone and poly(methyl methacrylate) (PMMA) bone cement abrasive particles created scratches on the alloy via a ploughing mechanism, and resulted in significantly rougher surfaces than controls without particles (P < 0.01). Solution treatments at 1230sp°C and 1245sp°C reduced the hardness and wear resistance of the as-cast F75 CoCrMo alloy. Aging at 700sp°C caused recrystallization of the forged F799 alloy and improved wear resistance. Thermo-mechanical treatments have the potential to increase the lifetime of artificial joints by increasing the wear resistance of CoCrMo components.

Surface modifications of hydrogen storage alloy by heavy ion beams with keV to MeV irradiation energies

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Tokuhira, Shinnosuke; Uchida, Hirohisa; Ohshima, Takeshi

2015-12-01

This study deals with the effect of surface modifications induced from keV to MeV heavy ion beams on the initial reaction rate of a hydrogen storage alloy (AB5) in electrochemical process. The rare earth based alloys like this sample alloy are widely used as a negative electrode of Ni-MH (Nickel-Metal Hydride) battery. We aimed to improve the initial reaction rate of hydrogen absorption by effective induction of defects such as vacancies, dislocations, micro-cracks or by addition of atoms into the surface region of the metal alloys. Since defective layer near the surface can easily be oxidized, the conductive oxide layer is formed on the sample surface by O+ beams irradiation, and the conductive oxide layer might cause the improvement of initial reaction rate of hydriding. This paper demonstrates an effective surface treatment of heavy ion irradiation, which induces catalytic activities of rare earth oxides in the alloy surface.

Corrosion resistance and durability of superhydrophobic surface formed on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution.

PubMed

Ishizaki, Takahiro; Masuda, Yoshitake; Sakamoto, Michiru

2011-04-19

The corrosion resistant performance and durability of the superhydrophobic surface on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution were investigated using electrochemical and contact angle measurements. The durability of the superhydrophobic surface in corrosive 5 wt% NaCl aqueous solution was elucidated. The corrosion resistant performance of the superhydrophobic surface formed on magnesium alloy was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the superhydrophobic surface considerably improved the corrosion resistant performance of magnesium alloy AZ31. American Society for Testing and Materials (ASTM) standard D 3359-02 cross cut tape test was performed to investigate the adhesion of the superhydrophobic film to the magnesium alloy surface. The corrosion formation mechanism of the superhydrophobic surface formed on the magnesium alloy was also proposed. © 2011 American Chemical Society

Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1983-01-01

An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.

Extended local similarity analysis (eLSA) reveals unique associations between bacterial community structure and odor emission during pig carcasses decomposition.

PubMed

Ki, Bo-Min; Ryu, Hee Wook; Cho, Kyung-Suk

2018-02-22

Soil burial and composting methods have been widely used for the disposal of pig carcasses. The relationship between bacterial community structure and odor emission was examined using extended local similarity analysis (eLSA) during the degradation of pig carcasses in soil and compost. In soil, Hyphomicrobium, Niastella, Rhodanobacter, Polaromonas, Dokdonella and Mesorhizobium were associated with the emission of sulfur-containing odors such as hydrogen sulfide, methyl mercaptan and dimethyl disulfide. Sphingomonas, Rhodanobacter, Mesorhizobium, Dokdonella, Leucobacter and Truepera were associated with the emission of nitrogen-containing odors including ammonia and trimetylamine. In compost, however, Carnobacteriaceae, Lachnospiaceae and Clostridiales were highly correlated with the emission of sulfur-containing odors, while Rumincoccaceae was associated with the emission of nitrogen-containing odors. The emission of organic acids was closely related to Massilia, Sphaerobacter and Bradyrhizobiaceae in soil, but to Actinobacteria, Sporacetigenium, Micromonosporaceae and Solirubrobacteriales in compost. This study suggests that network analysis using eLSA is a useful strategy for exploring the mechanisms of odor emission during biodegradation of pig carcasses.

On the selection of ordinary differential equation models with application to predator-prey dynamical models.

PubMed

Zhang, Xinyu; Cao, Jiguo; Carroll, Raymond J

2015-03-01

We consider model selection and estimation in a context where there are competing ordinary differential equation (ODE) models, and all the models are special cases of a "full" model. We propose a computationally inexpensive approach that employs statistical estimation of the full model, followed by a combination of a least squares approximation (LSA) and the adaptive Lasso. We show the resulting method, here called the LSA method, to be an (asymptotically) oracle model selection method. The finite sample performance of the proposed LSA method is investigated with Monte Carlo simulations, in which we examine the percentage of selecting true ODE models, the efficiency of the parameter estimation compared to simply using the full and true models, and coverage probabilities of the estimated confidence intervals for ODE parameters, all of which have satisfactory performances. Our method is also demonstrated by selecting the best predator-prey ODE to model a lynx and hare population dynamical system among some well-known and biologically interpretable ODE models. © 2014, The International Biometric Society.

Seasonal and solar cycle dependence of F3-layer near the southern crest of the equatorial ionospheric anomaly

NASA Astrophysics Data System (ADS)

Fagundes, P. R.; Klausner, V.; Bittencourt, J. A.; Sahai, Y.; Abalde, J. R.

2011-08-01

The occurrence of an additional F3-layer has been reported at Brazilian, Indian and Asian sectors by several investigators. In this paper, we report for the first time the seasonal variations of F3-layer carried out near the southern crest of the equatorial ionospheric anomaly (EIA) at São José dos Campos (23.2°S, 45.0°W; dip latitude 17.6°S - Brazil) as a function of solar cycle. The period from September 2000 to August 2001 is used as representative of high solar activity (HSA) and the period from January 2006 to December 2006 as representative of low solar activity (LSA). This investigation shows that during HSA there is a maximum occurrence of F3-layer during summer time and a minimum during winter time. However, during LSA, there is no seasonal variation in the F3-layer occurrence. Also, the frequency of occurrence of the F3-layer during HSA is 11 times more than during LSA.

Modification of surface properties of copper-refractory metal alloys

DOEpatents

Verhoeven, John D.; Gibson, Edwin D.

1993-10-12

The surface properties of copper-refractory metal (CU-RF) alloy bodies are modified by heat treatments which cause the refractory metal to form a coating on the exterior surfaces of the alloy body. The alloys have a copper matrix with particles or dendrites of the refractory metal dispersed therein, which may be niobium, vanadium, tantalum, chromium, molybdenum, or tungsten. The surface properties of the bodies are changed from those of copper to that of the refractory metal.

Laser surface modification of Ti and TiC coatings on magnesium alloy

NASA Astrophysics Data System (ADS)

Kim, J. M.; Lee, S. G.; Park, J. S.; Kim, H. G.

2014-12-01

In order to enhance the surface properties of magnesium alloy, a highly intense laser surface melting process following plasma spraying of Ti or TiC on AZ31 alloy were employed. When laser surface melting was applied to Ti coated magnesium alloy, the formation of fine Ti particle dispersed surface layer on the substrate occurred. The corrosion potential of the AZ31 alloy with Ti dispersed surface was significantly increased in 3.5 wt % NaCl solution. Additionally, an improved hardness was observed for the laser treated specimens as compared to the untreated AZ31 alloy. Laser melting process following plasma thermal deposition was also applied for obtaining in situ TiC coating layer on AZ31 alloy. The TiC coating layer could be successfully formed via in situ reaction between pure titanium and carbon powders. Incomplete TiC formation was observed in the plasma sprayed specimen, while completely transformed TiC layer was found after post laser melting process. It was also confirmed that the laser post treatment induced enhanced adhesion strength between the coating and the substrate.

Effects of ultraviolet irradiation on bonding strength between Co-Cr alloy and citric acid-crosslinked gelatin matrix.

PubMed

Inoue, Motoki; Sasaki, Makoto; Katada, Yasuyuki; Taguchi, Tetsushi

2014-02-01

Novel techniques for creating a strong bond between polymeric matrices and biometals are required. We immobilized polymeric matrices on the surface of biometal for drug-eluting stents through covalent bond. We performed to improve the bonding strength between a cobalt-chromium alloy and a citric acid-crosslinked gelatin matrix by ultraviolet irradiation on the surface of cobalt-chromium alloy. The ultraviolet irradiation effectively generated hydroxyl groups on the surface of the alloy. The bonding strength between the gelatin matrix and the alloy before ultraviolet irradiation was 0.38 ± 0.02 MPa, whereas it increased to 0.48 ± 0.02 MPa after ultraviolet irradiation. Surface analysis showed that the citric acid derivatives occurred on the surface of the cobalt-chromium alloy through ester bond. Therefore, ester bond formation between the citric acid derivatives active esters and the hydroxyl groups on the cobalt-chromium alloy contributed to the enhanced bonding strength. Ultraviolet irradiation and subsequent immobilization of a gelatin matrix using citric acid derivatives is thus an effective way to functionalize biometal surfaces.

Atomistic Method Applied to Computational Modeling of Surface Alloys

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo H.; Abel, Phillip B.

2000-01-01

The formation of surface alloys is a growing research field that, in terms of the surface structure of multicomponent systems, defines the frontier both for experimental and theoretical techniques. Because of the impact that the formation of surface alloys has on surface properties, researchers need reliable methods to predict new surface alloys and to help interpret unknown structures. The structure of surface alloys and when, and even if, they form are largely unpredictable from the known properties of the participating elements. No unified theory or model to date can infer surface alloy structures from the constituents properties or their bulk alloy characteristics. In spite of these severe limitations, a growing catalogue of such systems has been developed during the last decade, and only recently are global theories being advanced to fully understand the phenomenon. None of the methods used in other areas of surface science can properly model even the already known cases. Aware of these limitations, the Computational Materials Group at the NASA Glenn Research Center at Lewis Field has developed a useful, computationally economical, and physically sound methodology to enable the systematic study of surface alloy formation in metals. This tool has been tested successfully on several known systems for which hard experimental evidence exists and has been used to predict ternary surface alloy formation (results to be published: Garces, J.E.; Bozzolo, G.; and Mosca, H.: Atomistic Modeling of Pd/Cu(100) Surface Alloy Formation. Surf. Sci., 2000 (in press); Mosca, H.; Garces J.E.; and Bozzolo, G.: Surface Ternary Alloys of (Cu,Au)/Ni(110). (Accepted for publication in Surf. Sci., 2000.); and Garces, J.E.; Bozzolo, G.; Mosca, H.; and Abel, P.: A New Approach for Atomistic Modeling of Pd/Cu(110) Surface Alloy Formation. (Submitted to Appl. Surf. Sci.)). Ternary alloy formation is a field yet to be fully explored experimentally. The computational tool, which is based on the BFS (Bozzolo, Ferrante, and Smith) method for the calculation of the energetics, consists of a small number of simple PCbased computer codes that deal with the different aspects of surface alloy formation. Two analysis modes are available within this package. The first mode provides an atom-by-atom description of real and virtual stages 1. during the process of surface alloying, based on the construction of catalogues of configurations where each configuration describes one possible atomic distribution. BFS analysis of this catalogue provides information on accessible states, possible ordering patterns, and details of island formation or film growth. More importantly, it provides insight into the evolution of the system. Software developed by the Computational Materials Group allows for the study of an arbitrary number of elements forming surface alloys, including an arbitrary number of surface atomic layers. The second mode involves large-scale temperature-dependent computer 2. simulations that use the BFS method for the energetics and provide information on the dynamic processes during surface alloying. These simulations require the implementation of Monte-Carlo-based codes with high efficiency within current workstation environments. This methodology capitalizes on the advantages of the BFS method: there are no restrictions on the number or type of elements or on the type of crystallographic structure considered. This removes any restrictions in the definition of the configuration catalogues used in the analytical calculations, thus allowing for the study of arbitrary ordering patterns, ultimately leading to the actual surface alloy structure. Moreover, the Monte Carlo numerical technique used for the large-scale simulations allows for a detailed visualization of the simulated process, the main advantage of this type of analysis being the ability to understand the underlying features that drive these processes. Because of the simplicity of the BFS method for e energetics used in these calculations, a detailed atom-by-atom analysis can be performed at any point in the simulation, providing necessary insight on the details of the process. The main objective of this research program is to develop a tool to guide experimenters in understanding and interpreting often unexpected results in alloy formation experiments. By reducing the computational effort without losing physical accuracy, we expect that powerful simulation tools will be developed in the immediate future, which will allow material scientists to easily visualize and analyze processes at a level not achievable experimentally.

Ab initio atomistic thermodynamics study on the oxidation mechanism of binary and ternary alloy surfaces

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

Liu, Shi-Yu, E-mail: buaasyliu@gmail.com; Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong; Liu, Shiyang

Utilizing a combination of ab initio density-functional theory and thermodynamics formalism, we have established the microscopic mechanisms for oxidation of the binary and ternary alloy surfaces and provided a clear explanation for the experimental results of the oxidation. We construct three-dimensional surface phase diagrams (SPDs) for oxygen adsorption on three different Nb-X(110) (X = Ti, Al or Si) binary alloy surfaces. On the basis of the obtained SPDs, we conclude a general microscopic mechanism for the thermodynamic oxidation, that is, under O-rich conditions, a uniform single-phase SPD (type I) and a nonuniform double-phase SPD (type II) correspond to the sustainedmore » complete selective oxidation and the non-sustained partial selective oxidation by adding the X element, respectively. Furthermore, by revealing the framework of thermodynamics for the oxidation mechanism of ternary alloys through the comparison of the surface energies of two separated binary alloys, we provide an understanding for the selective oxidation behavior of the Nb ternary alloy surfaces. Using these general microscopic mechanisms, one could predict the oxidation behavior of any binary and multi-component alloy surfaces based on thermodynamics considerations.« less

Fabrication of the micro/nano-structure superhydrophobic surface on aluminum alloy by sulfuric acid anodizing and polypropylene coating.

PubMed

Wu, Ruomei; Liang, Shuquan; Liu, Jun; Pan, Anqiang; Yu, Y; Tang, Yan

2013-03-01

The preparation of the superhydrophobic surface on aluminum alloy by anodizing and polypropylene (PP) coating was reported. Both the different anodizing process and different PP coatings of aluminum alloy were investigated. The effects of different anodizing conditions, such as electrolyte concentration, anodization time and current on the superhydrophobic surface were discussed. By PP coating after anodizing, a good superhydrophobic surface was facilely fabricated. The optimum conditions for anodizing were determined by orthogonal experiments. After the aluminium-alloy was grinded with 600# sandpaper, pretreated by 73 g/L hydrochloric acid solution at 1 min, when the concentration of sulfuric acid was 180 g/L, the concentration of oxalic acid was 5 g/L, the concentration of potassium dichromate was 10 g/L, the concentration of chloride sodium was 50 g/L and 63 g/L of glycerol, anodization time was 20 min, and anodization current was 1.2 A/dm2, anodization temperature was 30-35 degrees C, the best micro-nanostructure aluminum alloy films was obtained. On the other hand, the PP with different concentrations was used to the PP with different concentrations was used to coat the aluminum alloy surface after anodizing. The results showed that the best superhydrophobicity was achieved by coating PP, and the duration of the superhydrophobic surface was improved by modifying the coat the aluminum alloy surface after anodizing. The results showed that the best superhydrophobicity was surface with high concentration PP. The morphologies of micro/nano-structure superhydrophobic surface were further confirmed by scanning electron microscope (SEM). The material of PP with the low surface free energy combined with the micro/nano-structures of the surface resulted in the superhydrophobicity of the aluminum alloy surface.

The evaluation of serum total sialic acid and lipid-bound sialic acid levels in chronically exposed rats to 7,12-dimethylbenz(a)anthracene and fluoride

NASA Astrophysics Data System (ADS)

Oto, Gokhan; Ekin, Suat; Uyar, Hasan; Ozdemir, Hulya; Yıldız, Damla; Karakuş, Yagmur

2017-04-01

In this study, changes in serum total sialic acid (TSA) and lipid-bound sialic acid (LSA) levels were examined in chronically exposed rats to 7,12-dimethylbenz(a)anthracene (DMBA) and fluoride. This study demonstrated that the TSA, LSA levels increased more in DMBA-treated groups compared to the fluoride treated groups. The result obtained has shown that the harmful effect of DMBA which is also causing more cell membrane damage on human and animal health should be taken into consideration.

Relating Chemical and Topographical Modification of Materials to Macroscopic Adhesion

DTIC Science & Technology

2011-11-14

CFRP, T800H/3900-2) and titanium alloy (Ti- 6Al - 4V ) surfaces are presented, before and after surface treatment, using a number of surface...Experimental: Titanium alloy (Ti- 6Al - 4V , an alloy consisting of 90% titanium , 6% aluminum and 4% vanadium, 0.063" thick) was purchased from...spectrum indicates a dramatic decrease in oxygen content and a concomitant increase in titanium metal alloy (Ti- 6Al - 4V ) at the surface. This

Plasma Spray for Difficult-To-Braze Alloys

NASA Technical Reports Server (NTRS)

Brennan, A.

1982-01-01

Nickel plating on surfaces makes brazing easier for some alloys. Sometimes nickel plating may not be feasible because of manufacturing sequence, size of hardware, or lack of suitable source for nickel plating. Alternative surface preparation in such cases is to grit-blast surface lightly and then plasma-spray 1 1/2 to 2 mils of fine nickel powder or braze-alloy material directly on surface. Powder is sprayed from plasma gun, using argon as carrier gas to prevent oxidation of nickel or braze alloy.

Derivation of global vegetation biophysical parameters from EUMETSAT Polar System

NASA Astrophysics Data System (ADS)

García-Haro, Francisco Javier; Campos-Taberner, Manuel; Muñoz-Marí, Jordi; Laparra, Valero; Camacho, Fernando; Sánchez-Zapero, Jorge; Camps-Valls, Gustau

2018-05-01

This paper presents the algorithm developed in LSA-SAF (Satellite Application Facility for Land Surface Analysis) for the derivation of global vegetation parameters from the AVHRR (Advanced Very High Resolution Radiometer) sensor on board MetOp (Meteorological-Operational) satellites forming the EUMETSAT (European Organization for the Exploitation of Meteorological Satellites) Polar System (EPS). The suite of LSA-SAF EPS vegetation products includes the leaf area index (LAI), the fractional vegetation cover (FVC), and the fraction of absorbed photosynthetically active radiation (FAPAR). LAI, FAPAR, and FVC characterize the structure and the functioning of vegetation and are key parameters for a wide range of land-biosphere applications. The algorithm is based on a hybrid approach that blends the generalization capabilities offered by physical radiative transfer models with the accuracy and computational efficiency of machine learning methods. One major feature is the implementation of multi-output retrieval methods able to jointly and more consistently estimate all the biophysical parameters at the same time. We propose a multi-output Gaussian process regression (GPRmulti), which outperforms other considered methods over PROSAIL (coupling of PROSPECT and SAIL (Scattering by Arbitrary Inclined Leaves) radiative transfer models) EPS simulations. The global EPS products include uncertainty estimates taking into account the uncertainty captured by the retrieval method and input errors propagation. A sensitivity analysis is performed to assess several sources of uncertainties in retrievals and maximize the positive impact of modeling the noise in training simulations. The paper discusses initial validation studies and provides details about the characteristics and overall quality of the products, which can be of interest to assist the successful use of the data by a broad user's community. The consistent generation and distribution of the EPS vegetation products will constitute a valuable tool for monitoring of earth surface dynamic processes.

Gas-tungsten arc welding of aluminum alloys

DOEpatents

Frye, Lowell D.

1984-01-01

A gas-tungsten arc welding method for joining together structures formed of aluminum alloy with these structures disposed contiguously to a heat-damagable substrate of a metal dissimilar to the aluminum alloy. The method of the present invention is practiced by diamond machining the fay surfaces of the aluminum alloy structures to provide a mirror finish thereon having a surface roughness in the order of about one microinch. The fay surfaces are aligned and heated sufficiently by the tungsten electrode to fuse the aluminum alloy contiguous to the fay surfaces to effect the weld joint. The heat input used to provide an oxide-free weld is significantly less than that required if the fay surfaces were prepared by using conventional chemical and mechanical practices.

"Electroless" E-Coating for Magnesium Alloys

NASA Astrophysics Data System (ADS)

Song, Guang-Ling

By utilizing the unique electrochemistry of Mg, a thin organic film can rapidly be deposited on the surface of a Mg alloy by dipping the Mg alloy in a cathodic E-coating bath solution without applying a current or potential. The self-deposited coating is selectively formed on Mg alloy surfaces. Although the "electroless" E-coating pre-film is relatively thin, it can offer sufficient corrosion protection for Mg alloys in a chloride-containing environment. The stability of the film can be significantly improved after curing. The corrosion resistance of the substrate Mg alloy has an important effect on the corrosion protection performance of the coating. The coating is more protective on a corrosion resistant Mg alloy than on a non-corrosion resistant Mg substrate. The coating protection performance is also influenced by the substrate surface condition or pre-treatment process. Wet cleaning + heat-treatment may be a cost-effective surface preparation/treatment for the "electroless" E-coating in industrial applications.

Method for improve x-ray diffraction determinations of residual stress in nickel-base alloys

DOEpatents

Berman, Robert M.; Cohen, Isadore

1990-01-01

A process for improving the technique of measuring residual stress by x-ray diffraction in pieces of nickel-base alloys which comprises covering part of a predetermined area of the surface of a nickel-base alloy with a dispersion, exposing the covered and uncovered portions of the surface of the alloy to x-rays by way of an x-ray diffractometry apparatus, making x-ray diffraction determinations of the exposed surface, and measuring the residual stress in the alloy based on these determinations. The dispersion is opaque to x-rays and serves a dual purpose since it masks off unsatisfactory signals such that only a small portion of the surface is measured, and it supplies an internal standard by providing diffractogram peaks comparable to the peaks of the nickel alloy so that the alloy peaks can be very accurately located regardless of any sources of error external to the sample.

Laser surface alloying on aluminum and its alloys: A review

NASA Astrophysics Data System (ADS)

Chi, Yiming; Gu, Guochao; Yu, Huijun; Chen, Chuanzhong

2018-01-01

Aluminum and its alloys have been widely used in aerospace, automotive and transportation industries owing to their excellent properties such as high specific strength, good ductility and light weight. Surface modification is of crucial importance to the surface properties of aluminum and its alloys since high coefficient of friction, wear characteristics and low hardness have limited their long term performance. Laser surface alloying is one of the most effective methods of producing proper microstructure by means of non-equilibrium solidification which results from rapid heating and cooling. In this paper, the influence of different processing parameters, such as laser power and scanning velocity is discussed. The developments of various material systems including ceramics, metals or alloys, and metal matrix composites (MMCs) are reviewed. The microstructure, hardness, wear properties and other behaviors of laser treated layer are analyzed. Besides, the existing problems during laser surface treatment and the corresponding solutions are elucidated and the future developments are predicted.

Surface tension of substantially undercooled liquid Ti-Al alloy

NASA Astrophysics Data System (ADS)

Zhou, K.; Wang, H. P.; Chang, J.; Wei, B.

2010-06-01

It is usually difficult to undercool Ti-Al alloys on account of their high reactivity in the liquid state. This results in a serious scarcity of information on their thermophysical properties in the metastable state. Here, we report on the surface tension of a liquid Ti-Al alloy under high undercooling condition. By using the electromagnetic levitation technique, a maximum undercooling of 324 K (0.19 T L) was achieved for liquid Ti-51 at.% Al alloy. The surface tension of this alloy, which was determined over a broad temperature range 1429-2040 K, increases linearly with the enhancement of undercooling. The experimental value of the surface tension at the liquidus temperature of 1753 K is 1.094 N m-1 and its temperature coefficient is -1.422 × 10-4 N m-1 K-1. The viscosity, solute diffusion coefficient and Marangoni number of this liquid Ti-Al alloy are also derived from the measured surface tension.

Enhancement of biocompatibility of nickel-titanium by laser surface modification technology

NASA Astrophysics Data System (ADS)

Ng, Ka Wai

Nickel Titanium is a relatively new biomaterial that has attracted research interest for biomedical application. The good biocompatibility with specific functional properties of shape memory effect and superelasticity creates a smart material for medical applications. However, there are still concerns on nickel ion release of this alloy if it is going to be implanted for a long time. Nickel ion is carcinogenic and also causes allergic response and degeneration of muscle tissue. The subsequent release of Ni+ ions into the body system is fatal for the long term application of this alloy in the human body. To improve the long term biocompatibility and corrosion properties of NiTi, different surface treatment techniques have been investigated but no optimum technique has been established yet. This project will investigate the feasibility of applying laser surface alloying technique to improve the corrosion resistance and biocompatibility of NiTi in simulated body fluid condition. This thesis summarizes the result of laser surface modification of NiTi with Mo, Nb and Co using CO2 laser. The modified layer, which is free of microcracks and pores, acts as physical barrier to reduce nickel release and enhance the surface properties. The hardness values of the Mo-alloyed NiTi, Nb-alloyed NiTi and Co-alloyed NiTi surface were found to be three to four times harder than the NiTi substrate. Corrosion polarization tests also showed that the alloyed NiTi are significantly more resistant than the NiTi alloy. The release of Ni ions can be greatly reduced after laser surface alloying NiTi with Mo, Nb and Co. The improvement in wettability characteristics, the growth of the apatite on the specimen's surface and the adhesion of cell confirm the good biocompatibility after laser surface alloying. It is concluded that laser surface alloying is one of the potential technique not only to improve the corrosion resistance with low nickel release rate, but also retain the good biocompatibility of NiTi. The technique can be applied to bone fixation plates or implants with relatively large surface area. The results of this project are significant as they add new knowledge on the surface modification of NiTi for long term implant application.

The prevalence of sexual assault against people who identify as Gay, Lesbian or Bisexual in the United States: A systematic review

PubMed Central

Rothman, Emily F.; Exner, Deinera; Baughman, Allyson

2011-01-01

This article systematically reviews 75 studies that examine the prevalence of sexual assault victimization among gay or bisexual (GB) men, and lesbian or bisexual (LB) women, in the United States. All studies were published between 1989 and 2009 and report the results of quantitative research. The authors reviewed the reported prevalence of lifetime sexual assault victimization (LSA), and where available, childhood sexual assault (CSA), adult sexual assault (ASA), intimate partner sexual assault (IPSA), and hate crime-related sexual assault (HC). The studies were grouped into those that used a probability or census sampling technique (n=25) and those that used a non-probability or “community-based” sampling technique (n=50). A total of 139,635 GLB respondents participated in the underlying studies reviewed. Prevalence estimates of LSA ranged from 15.6–85.0% for LB women, and 11.8–54.0% for GB men. Considering the median estimates derived from the collective set of studies reviewed, LB women were more likely to report CSA, ASA, LSA and IPSA than GB men, whereas GB men were more likely to report HC than LB women. Across all studies, the highest estimates reported were for LSA of LB women (85%), CSA of LB women (76.0%), and CSA of GB men (59.2%). With some exceptions, studies using non-probability samples reported higher sexual assault prevalence rates than did population-based or census sample studies. The challenges of assessing sexual assault victimization with GLB populations are discussed, as well as the implications for practice, policy and future research. PMID:21247983

Reverse engineering a gene network using an asynchronous parallel evolution strategy

PubMed Central

2010-01-01

Background The use of reverse engineering methods to infer gene regulatory networks by fitting mathematical models to gene expression data is becoming increasingly popular and successful. However, increasing model complexity means that more powerful global optimisation techniques are required for model fitting. The parallel Lam Simulated Annealing (pLSA) algorithm has been used in such approaches, but recent research has shown that island Evolutionary Strategies can produce faster, more reliable results. However, no parallel island Evolutionary Strategy (piES) has yet been demonstrated to be effective for this task. Results Here, we present synchronous and asynchronous versions of the piES algorithm, and apply them to a real reverse engineering problem: inferring parameters in the gap gene network. We find that the asynchronous piES exhibits very little communication overhead, and shows significant speed-up for up to 50 nodes: the piES running on 50 nodes is nearly 10 times faster than the best serial algorithm. We compare the asynchronous piES to pLSA on the same test problem, measuring the time required to reach particular levels of residual error, and show that it shows much faster convergence than pLSA across all optimisation conditions tested. Conclusions Our results demonstrate that the piES is consistently faster and more reliable than the pLSA algorithm on this problem, and scales better with increasing numbers of nodes. In addition, the piES is especially well suited to further improvements and adaptations: Firstly, the algorithm's fast initial descent speed and high reliability make it a good candidate for being used as part of a global/local search hybrid algorithm. Secondly, it has the potential to be used as part of a hierarchical evolutionary algorithm, which takes advantage of modern multi-core computing architectures. PMID:20196855

Modelling of Surfaces. Part 2: Metallic Alloy Surfaces Using the BFS Method

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John; Kobistek, Robert J.

1994-01-01

Using BFS, a new semiempirical method for alloys, we study the surface structure of fcc ordered binary alloys. We concentrate on the calculation of surface energies and surface relaxations for the L1(sub 0) and L1(sub 2) ordered structures. Different terminations of the low-index faces are studied. Also, we present results for the interlayer relaxations for planes close to the surface, revealing different relaxations for atoms of different species producing a rippled surface layer.

Calculation of the surface tension of liquid Ga-based alloys

NASA Astrophysics Data System (ADS)

Dogan, Ali; Arslan, Hüseyin

2018-05-01

As known, Eyring and his collaborators have applied the structure theory to the properties of binary liquid mixtures. In this work, the Eyring model has been extended to calculate the surface tension of liquid Ga-Bi, Ga-Sn and Ga-In binary alloys. It was found that the addition of Sn, In and Bi into Ga leads to significant decrease in the surface tension of the three Ga-based alloy systems, especially for that of Ga-Bi alloys. The calculated surface tension values of these alloys exhibit negative deviation from the corresponding ideal mixing isotherms. Moreover, a comparison between the calculated results and corresponding literature data indicates a good agreement.

Gas-tungsten arc welding of aluminum alloys

DOEpatents

Frye, L.D.

1982-03-25

The present invention is directed to a gas-tungsten arc welding method for joining together structures formed of aluminum alloy with these structures disposed contiguously to a heat-damagable substrate of a metal dissimilar to the aluminum alloy. The method of the present invention is practiced by diamond machining the fay surfaces of the aluminum alloy structures to profice a mirror finish thereon having a surface roughness in the order of about one microinch. The fay surface are aligned and heated sufficiently by the tungsten electrode to fuse the aluminum alloy continguous to the fay surfaces to effect the weld joint. The heat input used to provide an oxide-free weld is significantly less than that required if the fay surfaces were prepared by using conventional chemical and mechanical practices.

Laser surface processing on sintered PM alloys

NASA Astrophysics Data System (ADS)

Reiter, Wilfred; Daurelio, Giuseppe; Ludovico, Antonio D.

1997-08-01

Usually the P.M. alloys are heat treated like case hardening, gas nitriding or plasma nitriding for a better wear resistance of the product surface. There is an additional method for gaining better tribological properties and this is the surface hardening (or remelting or alloying) of the P.M. alloy by laser treatment on a localized part of the product without heating the whole sample. This work gives a cured experimentation about the proper sintering powder alloys for laser surface processing from the point of view of wear, fatigue life and surface quality. As concerns the materials three different basic alloy groups with graduated carbon contents were prepared. Regarding these sintered powder alloys one group holds Fe, Mo and C and other group holds Fe, Ni, Mo and C and the last one holds Fe, Ni, Cu, Mo and C contents. Obviously each group has a different surface hardness, different porosity distribution, different density and diverse metallurgical structures (pearlite or ferrite-pearlite, etc.). ON the sample surfaces a colloidal graphite coating, in different thicknesses, has been sprayed to increase laser energy surface absorption. On some other samples a Mo coating, in different thicknesses, has been produced (on the bulk alloy) by diverse deposition techniques (D.C. Sputtering, P.V.D. and Flame Spraying). Only a few samples have a Mo coating and also an absorber coating, that is a bulk material- Mo and a colloidal graphite coating. All these sintered alloys have been tested by laser technology; so that, many laser working parameters (covering gas, work-speed, focussed and defocussed spot, rastered and integrated beam spots, square and rectangular beam shapes and so on) have been experimented for two different processes at constant laser power and at constant surface temperature (by using a temperature surface sensor and a closed controlled link). For all experiments a transverse fast axial flow CO2 2.5 kW c.w. laser source has been employed.

Study on Composition, Microstructure and Wear Behavior of Fe-B-C Wear-Resistant Surfacing Alloys

NASA Astrophysics Data System (ADS)

Zhuang, Minghui; Li, Muqin; Wang, Jun; Ma, Zhen; Yuan, Shidan

2017-12-01

Fe-B-C alloy layers with various microstructures were welded on Q235 steel plates using welding powders/H08Mn2Si and welding wires composite surfacing technology. The relationship existing between the chemical composition, microstructure and wear resistance of the surfacing alloy layers was investigated by scanning electron microscopy, x-ray diffraction, electron backscatter diffraction and wear tests. The results demonstrated that the volume fractions and morphologies of the microstructures in the surfacing alloy layers could be controlled by adjusting the boron and carbon contents in the welding powders, which could further regulate the wear resistance of the surfacing alloy layers. The typical microstructures of the Fe-B-C surfacing alloy layers included dendritic Fe, rod-like Fe2B, fishbone-like Fe2B and daisy-like Fe3(C, B). The wear resistance of the alloy layers with various morphologies differed. The wear resistance order of the different microstructures was: rod-like Fe2B > fishbone-like Fe2B > daisy-like Fe3(C, B) > dendritic Fe. A large number of rod-like Fe2B with high microhardness could be obtained at the boron content of 5.70 5.90 wt.% and the carbon content of 0.50 0.60wt.%. The highest wear resistance of the Fe-B-C alloy layers reached the value of 24.1 g-1, which demonstrates the main microscopic cutting wear mechanism of the Fe-B-C alloy layers.

In vitro biocompatibility of the surface ion modified NiTi alloy

NASA Astrophysics Data System (ADS)

Gudimova, Ekaterina Yu.; Meisner, Ludmila L.; Lotkov, Aleksander I.; Matveeva, Vera A.; Meisner, Stanislav N.; Matveev, Andrey L.; Shabalina, Olga I.

2016-11-01

This paper presents the results of the chemical, topographic and structural properties of the NiTi alloy surface and their changes after surface treatments by ion implantation techniques with use of ions Ta+ and Si+. The influence of physicochemical properties of the surface ion modified NiTi alloy was studied on in vitro cultured mesenchymal stem cells of the rats' bone marrow. It is shown that the ion surface modification improves histocompatibility of the NiTi alloy and leads to increase of proliferative activity of mesenchymal stem cells on its surface. It was experimentally found that a major contribution to viability improvement mesenchymal stem cells of rat marrow has the chemical composition and the microstructure of the surface area.

Electronic structure studies of a clock-reconstructed Al/Pd(1 0 0) surface alloy

NASA Astrophysics Data System (ADS)

Kirsch, Janet E.; Tainter, Craig J.

We have employed solid-state Fenske-Hall band structure calculations to examine the electronic structure of Al/Pd(1 0 0), a surface alloy that undergoes a reconstruction, or rearrangement, of the atoms in the top few surface layers. Surface alloys are materials that consist primarily of a single elemental metal, but which have a bimetallic surface composition that is only a few atomic layers in thickness. The results of this study indicate that reconstruction into a clock configuration simultaneously optimizes the intralayer bonding within the surface plane and the bonding between the first and second atomic layers. These results also allow us to examine the fundamental relationship between the electronic and physical structures of this reconstructed surface alloy.

Cleavage crystallography of liquid metal embrittled aluminum alloys

NASA Technical Reports Server (NTRS)

Reynolds, A. P.; Stoner, G. E.

1991-01-01

The crystallography of liquid metal-induced transgranular cleavage in six aluminum alloys having a variety of microstructures has been determined via Laue X-ray back reflection. The cleavage crystallography was independent of alloy microstructure, and the cleavage plane was 100-plane oriented in all cases. It was further determined that the cleavage crystallography was not influenced by alloy texture. Examination of the fracture surface indicated that there was not a unique direction of crack propagation. In addition, the existence of 100-plane cleavage on alloy 2024 fracture surfaces was inferred by comparison of secondary cleavage crack intersection geometry on the 2024 surfaces with the geometry of secondary cleavage crack intersections on the test alloys.

Functionalization of biodegradable magnesium alloy implants with alkylphosphonate self-assembled films.

PubMed

Grubač, Z; Metikoš-Huković, M; Babić, R; Rončević, I Škugor; Petravić, M; Peter, R

2013-05-01

Mg and Mg-alloys are promising materials for biodegradable implants. In order to slowdown the Mg-alloy (AZ91D) degradation and enhance its biocompatibility, the alloy surface was modified with alkylphosphonate self-assembling films. The binding configuration and the structural organization of alkylphosphonate monolayers on the Mg-alloy surface were investigated using contact angle measurements, FTIR, and XPS. Combination of FTIR and XPS data indicated the presence of several different bonding modes (mono-, di-, and tri dentate) of phosphonate head groups with the alloy surface. The existence of well organized and ordered self-assembled alkylphosphonate monolayers with good barrier protecting properties in a physiological solution is a key step in the development of biocompatible Mg-alloy implants. Copyright © 2013 Elsevier B.V. All rights reserved.

Software Package Completed for Alloy Design at the Atomic Level

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo H.; Noebe, Ronald D.; Abel, Phillip B.; Good, Brian S.

2001-01-01

As a result of a multidisciplinary effort involving solid-state physics, quantum mechanics, and materials and surface science, the first version of a software package dedicated to the atomistic analysis of multicomponent systems was recently completed. Based on the BFS (Bozzolo, Ferrante, and Smith) method for the calculation of alloy and surface energetics, this package includes modules devoted to the analysis of many essential features that characterize any given alloy or surface system, including (1) surface structure analysis, (2) surface segregation, (3) surface alloying, (4) bulk crystalline material properties and atomic defect structures, and (5) thermal processes that allow us to perform phase diagram calculations. All the modules of this Alloy Design Workbench 1.0 (ADW 1.0) are designed to run in PC and workstation environments, and their operation and performance are substantially linked to the needs of the user and the specific application.

Ab initio surface properties of Ag-Sn alloys: implications for lead-free soldering.

PubMed

Saleh, Gabriele; Xu, Chen; Sanvito, Stefano

2018-02-07

Ag and Sn are the major components of solder alloys adopted to assemble printed circuit boards. The qualities that make them the alloys of choice for the modern electronic industry are related to their physical and chemical properties. For corrosion resistance and solderability, surface properties are particularly important. Yet, atomic-level information about the surfaces of these alloys is not known. Here we fill this gap by presenting an extensive ab initio investigation of composition, energetics, structure and reactivity of Ag-Sn alloy surfaces. The structure and stability of various surfaces is evaluated, and the main factors determining the energetics of surface formation are uncovered. Oxygen and sulphur chemisorptions are studied and discussed in the framework of corrosion tendency, an important issue for printed circuit boards. Adsorption energy trends are rationalized based on the analysis of structural and electronic features.

Surface tension modelling of liquid Cd-Sn-Zn alloys

NASA Astrophysics Data System (ADS)

Fima, Przemyslaw; Novakovic, Rada

2018-06-01

The thermodynamic model in conjunction with Butler equation and the geometric models were used for the surface tension calculation of Cd-Sn-Zn liquid alloys. Good agreement was found between the experimental data for limiting binaries and model calculations performed with Butler model. In the case of ternary alloys, the surface tension variation with Cd content is better reproduced in the case of alloys lying on vertical sections defined by high Sn to Zn molar fraction ratio. The calculated surface tension is in relatively good agreement with the available experimental data. In addition, the surface segregation of liquid ternary Cd-Sn-Zn and constituent binaries has also been calculated.

The fractography of casting alloys

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

Powell, G.W.

1994-10-01

Several types of casting alloys were fractured using various loading modes (uniaxial tension, bending, impact, and torsion, and cyclic stressing), and the corresponding mechanical properties were determined. The unetched and etched fracture surfaces and the microstructures were examined using conventional techniques. The types of casting alloys that were the subjects f these investigations include gray iron, ductile iron, cast steel, and aluminum-base alloys (A380, A356, and 319). The fractographic studies have yielded these generalizations regarding the topography of the fracture surfaces. In the case of low-ductility alloys such as gray iron and the aluminum-base alloys, the tensile edge of amore » fracture surface produced by a stress system with a strong bending-moment component has a highly irregular contour, whereas the compressive edge of the fracture surface is quite straight and parallel to the bend axis. On the other hand, the periphery of a fracture surface produced by uniaxial tension has a completely irregular contour. The fracture surface produced by cyclic loading of a gray iron does not display any macroscopic evidence (such as a thumb nail) of the loading mode. However, the fracture surface of each of the other casting alloys displays clear, macroscopic evidence of failure induced by fatigue. The aluminum-base alloys fracture completely within the interdendritic region of the microstructure when subjected to monotonic loading by uniaxial tension or bending, whereas a fatigue crack propagates predominantly through the primary crystals of the microstructure.« less

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

Wulfmeyer, Volker; Turner, David

The Land-Atmosphere Feedback Experiment (LAFE; pronounced “la-fey”) deploys several state-of-the-art scanning lidar and remote sensing systems to the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility’s Southern Great Plains (SGP) site. These instruments will augment the ARM instrument suite in order to collect a data set for studying feedback processes between the land surface and the atmosphere. The novel synergy of remote-sensing systems will be applied for simultaneous measurements of land-surface fluxes and horizontal and vertical transport processes in the atmospheric convective boundary layer (CBL). The impact of spatial inhomogeneities of the soil-vegetation continuum on land-surface-atmospheremore » (LSA) feedback will be studied using the scanning capability of the instrumentation. The time period of the observations is August 2017, because large differences in surface fluxes between different fields and bare soil can be observed, e.g., pastures versus fields where the wheat has already been harvested. The remote sensing system synergy will consist of three components: 1) The SGP water vapor and temperature Raman lidar (SRL), the SGP Doppler lidar (SDL), and the National Center for Atmospheric Research (NCAR) water vapor differential absorption lidar (DIAL) (NDIAL) mainly in vertical staring modes to measure mean profiles and gradients of moisture, temperature, and horizontal wind. They will also measure profiles of higher-order turbulent moments in the water vapor and wind fields and profiles of the latent heat flux. 2) A novel scanning lidar system synergy consisting of the National Oceanic and Atmospheric Administration (NOAA) High-Resolution Doppler lidar (HRDL), the University of Hohenheim (UHOH) water-vapor differential absorption lidar (UDIAL), and the UHOH temperature Raman lidar (URL). These systems will perform coordinated range-height indicator (RHI) scans from just above the canopy level to the lower troposphere, including the interfacial layer of the CBL. The optimal azimuth is to the ENE of the SGP central facility, which takes advantage of both changes in the surface elevation and different crop types planted along that path. 3) The University of Wisconsin Space Science and Engineering Center Portable Atmospheric Research Center (SPARC) and the University of Oklahoma Collaborative Lower Atmospheric Mobile Profiling System (CLAMPS) operating two vertically pointing atmospheric emitted radiance interferometers (AERIs) and two Doppler lidar (DL) systems scanning cross track to the central RHI for determining the surface friction velocity and the horizontal variability of temperature, moisture, and wind. Thus, both the variability of surface fluxes and CBL dynamics and thermodynamics over the SGP site will be studied for the first time. The combination of these three components will enable us to estimate both the divergence of the latent heat profile and the advection of moisture. Thus, the moisture budget in the SGP domain can be studied. Furthermore, the simultaneous measurements of surface and entrainment fluxes as well as the daily cycle of the CBL thermodynamic state will provide a unique data set for characterizing LSA interaction in dependence of large-scale and local conditions such as soil moisture and the state of the vegetation. The measurements will also be applied for the development of improved parameterizations of surface fluxes and turbulence in the CBL. The latter is possible because mean profiles, gradients, higher-order moments, and fluxes are measured simultaneously. The results will be used for the verification of simulations of LSA feedback in large-eddy simulation (LES) and mesoscale models, which are planned for the SGP site. Due to the strong connection between the pre-convective state of the CBL and the formation of clouds and precipitation, this new generation of experiments will strongly contribute to the improvement of their representation in weather, climate, and earth system models.« less

Outstanding resistance and passivation behaviour of new Fe-Co metal-metal glassy alloys in alkaline media

PubMed Central

Al-Harbi, Albandaree K.

2018-01-01

The electrochemical behavior of the oxide layers on two metal-metal glassy alloys, Fe78Co9Cr10Mo2Al1 (VX9)and Fe49Co49V2 (VX50) (at.%), were studied using electrochemical techniques including electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) measurements. The morphology and composition of the alloy surfaces were investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion rate and surface roughness of both alloys increased as the concentration of NaOH in aqueous solution was raised. The presence of some protective elements in the composition of the alloys led to the formation of a spontaneous passive layer on the alloy surface. The higher resistance values of both alloys were associated with the magnitude of the dielectric properties of the passive films formed on their surfaces. Both alloys are classified as having outstanding resistance to corrosion, which results from the formation of a passive film that acts as an efficient barrier to corrosion in alkaline solution. PMID:29337992

Outstanding resistance and passivation behaviour of new Fe-Co metal-metal glassy alloys in alkaline media.

PubMed

Emran, Khadijah M; Al-Harbi, Albandaree K

2018-01-01

The electrochemical behavior of the oxide layers on two metal-metal glassy alloys, Fe78Co9Cr10Mo2Al1 (VX9)and Fe49Co49V2 (VX50) (at.%), were studied using electrochemical techniques including electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) measurements. The morphology and composition of the alloy surfaces were investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion rate and surface roughness of both alloys increased as the concentration of NaOH in aqueous solution was raised. The presence of some protective elements in the composition of the alloys led to the formation of a spontaneous passive layer on the alloy surface. The higher resistance values of both alloys were associated with the magnitude of the dielectric properties of the passive films formed on their surfaces. Both alloys are classified as having outstanding resistance to corrosion, which results from the formation of a passive film that acts as an efficient barrier to corrosion in alkaline solution.

Performance assessment of femoral knee components made from cobalt-chromium alloy and oxidized zirconium.

PubMed

Brandt, J-M; Guenther, L; O'Brien, S; Vecherya, A; Turgeon, T R; Bohm, E R

2013-12-01

The surface characteristics of the femoral component affect polyethylene wear in modular total knee replacements. In the present retrieval study, the surface characteristics of cobalt-chromium (CoCr) alloy and oxidized zirconium (OxZr) femoral components were assessed and compared. Twenty-six retrieved CoCr alloy femoral components were matched with twenty-six retrieved OxZr femoral components for implantation period, body-mass index, patient gender, implant type, and polyethylene insert thickness. The surface damage on the retrieved femoral components was evaluated using a semi-quantitative assessment method, scanning electron microscopy, and contact profilometry. The retrieved CoCr alloy femoral components showed less posterior surface gouging than OxZr femoral components; however, at a higher magnification, the grooving damage features on the retrieved CoCr alloy femoral components confirmed an abrasive wear mechanism. The surface roughness values Rp, Rpm, and Rpk for the retrieved CoCr alloy femoral components were found to be significantly higher than those of the retrieved OxZr femoral components (p≤0.031). The surface roughness values were higher on the medial condyles than on the lateral condyles of the retrieved CoCr alloy femoral components; such a difference was not observed on the retrieved OxZr femoral components. The surface roughness of CoCr alloy femoral components increased while the surface roughness of the OxZr femoral components remained unchanged after in vivo service. Therefore, the OxZr femoral components' resistance to abrasive wear may enable lower polyethylene wear and ensure long-term durability in vivo. Level IV. Crown Copyright © 2013. Published by Elsevier B.V. All rights reserved.

German National Proficiency Scales in Biology: Internal Structure, Relations to General Cognitive Abilities and Verbal Skills

PubMed Central

KÖLLER, OLAF

2016-01-01

ABSTRACT National and international large‐scale assessments (LSA) have a major impact on educational systems, which raises fundamental questions about the validity of the measures regarding their internal structure and their relations to relevant covariates. Given its importance, research on the validity of instruments specifically developed for LSA is still sparse, especially in science and its subdomains biology, chemistry, and physics. However, policy decisions for the improvement of educational quality based on LSA can only be helpful if valid information on students’ achievement levels is provided. In the present study, the nature of the measurement instruments based on the German Educational Standards in Biology is examined. On the basis of data from 3,165 students in Grade 10, we present dimensional analyses and report the relationship between different subdimensions of biology literacy and cognitive covariates such as general cognitive abilities and verbal skills. A theory‐driven two‐dimensional model fitted the data best. Content knowledge and scientific inquiry, two subdimensions of biology literacy, are highly correlated and show differential correlational patterns to the covariates. We argue that the underlying structure of biology should be incorporated into curricula, teacher training and future assessments. PMID:27818532

Morphological and Hemodynamic Discriminators for Rupture Status in Posterior Communicating Artery Aneurysms

PubMed Central

Karmonik, Christof; Fang, Yibin; Xu, Jinyu; Yu, Ying; Cao, Wei; Liu, Jianmin; Huang, Qinghai

2016-01-01

Background and Purpose The conflicting findings of previous morphological and hemodynamic studies on intracranial aneurysm rupture may be caused by the relatively small sample sizes and the variation in location of the patient-specific aneurysm models. We aimed to determine the discriminators for aneurysm rupture status by focusing on only posterior communicating artery (PCoA) aneurysms. Materials and Methods In 129 PCoA aneurysms (85 ruptured, 44 unruptured), clinical, morphological and hemodynamic characteristics were compared between the ruptured and unruptured cases. Multivariate logistic regression analysis was performed to determine the discriminators for rupture status of PCoA aneurysms. Results While univariate analyses showed that the size of aneurysm dome, aspect ratio (AR), size ratio (SR), dome-to-neck ratio (DN), inflow angle (IA), normalized wall shear stress (NWSS) and percentage of low wall shear stress area (LSA) were significantly associated with PCoA aneurysm rupture status. With multivariate analyses, significance was only retained for higher IA (OR = 1.539, p < 0.001) and LSA (OR = 1.393, p = 0.041). Conclusions Hemodynamics and morphology were related to rupture status of intracranial aneurysms. Higher IA and LSA were identified as discriminators for rupture status of PCoA aneurysms. PMID:26910518

Morphological and Hemodynamic Discriminators for Rupture Status in Posterior Communicating Artery Aneurysms.

PubMed

Lv, Nan; Wang, Chi; Karmonik, Christof; Fang, Yibin; Xu, Jinyu; Yu, Ying; Cao, Wei; Liu, Jianmin; Huang, Qinghai

2016-01-01

The conflicting findings of previous morphological and hemodynamic studies on intracranial aneurysm rupture may be caused by the relatively small sample sizes and the variation in location of the patient-specific aneurysm models. We aimed to determine the discriminators for aneurysm rupture status by focusing on only posterior communicating artery (PCoA) aneurysms. In 129 PCoA aneurysms (85 ruptured, 44 unruptured), clinical, morphological and hemodynamic characteristics were compared between the ruptured and unruptured cases. Multivariate logistic regression analysis was performed to determine the discriminators for rupture status of PCoA aneurysms. While univariate analyses showed that the size of aneurysm dome, aspect ratio (AR), size ratio (SR), dome-to-neck ratio (DN), inflow angle (IA), normalized wall shear stress (NWSS) and percentage of low wall shear stress area (LSA) were significantly associated with PCoA aneurysm rupture status. With multivariate analyses, significance was only retained for higher IA (OR = 1.539, p < 0.001) and LSA (OR = 1.393, p = 0.041). Hemodynamics and morphology were related to rupture status of intracranial aneurysms. Higher IA and LSA were identified as discriminators for rupture status of PCoA aneurysms.

Successful Resection of a Growing Distal Medial Lenticulostriate Artery Pseudoaneurysm Presenting with Isolated Intraventricular Hemorrhage.

PubMed

Sato, Yosuke; Ando, Kazuhiro; Kawaguchi, Makoto; Kakinuma, Kenichi

2017-10-01

Distal medial lenticulostriate artery (LSA) aneurysms associated with isolated intraventricular hemorrhage (IVH) are extremely rare. We report a very rare case of the isolated IVH due to the rupture of the distal medial LSA pseudoaneurysm that was not visible at the initial angiography but later emerged and grew. A 61-year-old woman with a history of hypertension had sudden onset of severe headache and mild consciousness disturbance. The computed tomography scan revealed the IVH, but the initial angiographies showed no evidence of aneurysm. The follow-up magnetic resonance imaging revealed that an intraventricular mass, arising from the right distal medial LSA, emerged and grew into the right anterior horn. Considering the risk of rebleeding, we resected the mass lesion via the transsulcal transventricular approach. The postoperative imaging showed complete obliteration of the mass lesion. Histopathological analysis indicated the pseudoaneurysm. The patient was discharged without any neurological deficit. The careful and repetitive follow-up imaging should be done in the cases with isolated IVH even if the initial image evaluations are unrevealing. The transsulcal transventricular approach can be the most minimally invasive surgical option for intraventricular lesion. Copyright © 2017 National Stroke Association. Published by Elsevier Inc. All rights reserved.

German National Proficiency Scales in Biology: Internal Structure, Relations to General Cognitive Abilities and Verbal Skills.

PubMed

Kampa, Nele; Köller, Olaf

2016-09-01

National and international large-scale assessments (LSA) have a major impact on educational systems, which raises fundamental questions about the validity of the measures regarding their internal structure and their relations to relevant covariates. Given its importance, research on the validity of instruments specifically developed for LSA is still sparse, especially in science and its subdomains biology, chemistry, and physics. However, policy decisions for the improvement of educational quality based on LSA can only be helpful if valid information on students' achievement levels is provided. In the present study, the nature of the measurement instruments based on the German Educational Standards in Biology is examined. On the basis of data from 3,165 students in Grade 10, we present dimensional analyses and report the relationship between different subdimensions of biology literacy and cognitive covariates such as general cognitive abilities and verbal skills. A theory-driven two-dimensional model fitted the data best. Content knowledge and scientific inquiry, two subdimensions of biology literacy, are highly correlated and show differential correlational patterns to the covariates. We argue that the underlying structure of biology should be incorporated into curricula, teacher training and future assessments.

F3-layer and MSTIDs under the equatorial ionospheric anomaly crest

NASA Astrophysics Data System (ADS)

Fagundes, Paulo Roberto; Klausner, Virginia; Sahai, Yogeshwar; Bittencourt, Jose A.; Abalde Guede, Jose Ricardo

We present F3-layer and medium-scale traveling ionospheric disturbances (MSTIDs) observa-tions from a digital ionosonde installed at São José dos Campos (23.2° S, 45.0° W; dip latitude a 17.6° S), under the southern crest of the equatorial ionization anomaly (EIA) region. In this study we have used ionospheric data from September 2000 to August 2001 representing high solar activity (HSA) and ionospheric data from January 2006 to December 2006 representing low solar activity (LSA) to study the F3-layer characteristics at low latitude. The present investigation shows that the F3-layer occurrence is very larger during HSA as compared with during LSA. Also, during HSA there is a clear seasonal variation with maximum occurrence during January, February, November and December (summer months in South America) and minimum during May, June, July and August (winter months in South America). However, there is no clear seasonal variation in occurrence characteristics of F3-layer during LSA. Since, our previous work and present observations show that MSTIDs occurrences have similar re-sponse to the solar cycle; therefore, we suggest that both F3-layer and MSTIDs have strong connection.

Determination of the Average Native Background and the Light-Induced EPR Signals and their Variation in the Teeth Enamel Based on Large-Scale Survey of the Population.

PubMed

Ivannikov, Alexander I; Khailov, Artem M; Orlenko, Sergey P; Skvortsov, Valeri G; Stepanenko, Valeri F; Zhumadilov, Kassym Sh; Williams, Benjamin B; Flood, Ann B; Swartz, Harold M

2016-12-01

The aim of the study is to determine the average intensity and variation of the native background signal amplitude (NSA) and of the solar light-induced signal amplitude (LSA) in electron paramagnetic resonance (EPR) spectra of tooth enamel for different kinds of teeth and different groups of people. These values are necessary for determination of the intensity of the radiation-induced signal amplitude (RSA) by subtraction of the expected NSA and LSA from the total signal amplitude measured in L-band for in vivo EPR dosimetry. Variation of these signals should be taken into account when estimating the uncertainty of the estimated RSA. A new analysis of several hundred EPR spectra that were measured earlier at X-band in a large-scale examination of the population of the Central Russia was performed. Based on this analysis, the average values and the variation (standard deviation, SD) of the amplitude of the NSA for the teeth from different positions, as well as LSA in outer enamel of the front teeth for different population groups, were determined. To convert data acquired at X-band to values corresponding to the conditions of measurement at L-band, the experimental dependencies of the intensities of the RSA, LSA and NSA on the m.w. power, measured at both X and L-band, were analysed. For the two central upper incisors, which are mainly used in in vivo dosimetry, the mean LSA annual rate induced only in the outer side enamel and its variation were obtained as 10 ± 2 (SD = 8) mGy y -1 , the same for X- and L-bands (results are presented as the mean ± error of mean). Mean NSA in enamel and its variation for the upper incisors was calculated at 2.0 ± 0.2 (SD = 0.5) Gy, relative to the calibrated RSA dose-response to gamma radiation measured under non-power saturation conditions at X-band. Assuming the same value for L-band under non-power saturating conditions, then for in vivo measurements at L-band at 25 mW (power saturation conditions), a mean NSA and its variation correspond to 4.0 ± 0.4 (SD = 1.0) Gy. © Crown copyright 2016.

Determination of the Average Native Background and the Light-Induced EPR Signals and their Variation in the Teeth Enamel Based on Large-Scale Survey of the Population

PubMed Central

Ivannikov, Alexander I.; Khailov, Artem M.; Orlenko, Sergey P.; Skvortsov, Valeri G.; Stepanenko, Valeri F.; Zhumadilov, Kassym Sh.; Williams, Benjamin B.; Flood, Ann B.; Swartz, Harold M.

2016-01-01

The aim of the study is to determine the average intensity and variation of the native background signal amplitude (NSA) and of the solar light-induced signal amplitude (LSA) in electron paramagnetic resonance (EPR) spectra of tooth enamel for different kinds of teeth and different groups of people. These values are necessary for determination of the intensity of the radiation-induced signal amplitude (RSA) by subtraction of the expected NSA and LSA from the total signal amplitude measured in L-band for in vivo EPR dosimetry. Variation of these signals should be taken into account when estimating the uncertainty of the estimated RSA. A new analysis of several hundred EPR spectra that were measured earlier at X-band in a large-scale examination of the population of the Central Russia was performed. Based on this analysis, the average values and the variation (standard deviation, SD) of the amplitude of the NSA for the teeth from different positions, as well as LSA in outer enamel of the front teeth for different population groups, were determined. To convert data acquired at X-band to values corresponding to the conditions of measurement at L-band, the experimental dependencies of the intensities of the RSA, LSA and NSA on the m.w. power, measured at both X and L-band, were analysed. For the two central upper incisors, which are mainly used in in vivo dosimetry, the mean LSA annual rate induced only in the outer side enamel and its variation were obtained as 10 ± 2 (SD = 8) mGy y−1, the same for X- and L-bands (results are presented as the mean ± error of mean). Mean NSA in enamel and its variation for the upper incisors was calculated at 2.0 ± 0.2 (SD = 0.5) Gy, relative to the calibrated RSA dose–response to gamma radiation measured under non-power saturation conditions at X-band. Assuming the same value for L-band under non-power saturating conditions, then for in vivo measurements at L-band at 25 mW (power saturation conditions), a mean NSA and its variation correspond to 4.0 ± 0.4 (SD = 1.0) Gy. PMID:27412516

Method for improving x-ray diffraction determinations of residual stress in nickel-base alloys

DOEpatents

Berman, R.M.; Cohen, I.

1988-04-26

A process for improving the technique of measuring residual stress by x-ray diffraction in pieces of nickel-base alloys is discussed. Part of a predetermined area of the surface of a nickel-base alloy is covered with a dispersion. This exposes the covered and uncovered portions of the surface of the alloy to x-rays by way of an x-ray diffractometry apparatus, making x-ray diffraction determinations of the exposed surface, and measuring the residual stress in the alloy based on these determinations. The dispersion is opaque to x-rays and serves a dual purpose, since it masks off unsatisfactory signals such that only a small portion of the surface is measured, and it supplies an internal standard by providing diffractogram peaks comparable to the peaks of the nickel alloy so that the alloy peaks can be very accurately located regardless of any sources of error external to the sample. 2 figs.

The influence of alloy composition on residual stresses in heat treated aluminium alloys

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

Robinson, J.S., E-mail: jeremy.robinson@ul.ie; Redington, W.

The as quenched properties of eight different heat treatable aluminium alloys are related to residual stress magnitudes with the objective being to establish if there is a relationship between the residual stress and the as quenched alloy hardness and strength. Near surface residual stresses were assessed with X-ray diffraction using both the established sin{sup 2}ψ method and the more recent cos α technique. Through thickness residual stresses were also characterised using neutron diffraction. The alloys were chosen to encompass a wide range of strengths. The low to medium strength alloys were 6060 and 6082, medium to high strength 2618A, 2014A,more » 7075, 7010 and two variants of 7449, while the very high strength alloy was the powder metallurgy alloy N707. To assess the as quenched strength, dynamic hardness and tensile properties were determined from samples tested immediately after quenching to minimise the influence of precipitation hardening by natural aging. In addition, hot hardness measurements were made in situ on samples cooled to simulate quench paths. Within the experimental constraints of the investigation, the distribution of residual stress through the thickness was found to follow the same pattern for all the alloys investigated, varying from tensile in the interior to surface compression. The influence of alloy strength was manifested as a change in the observed residual stress magnitudes, and surface residual stresses were found to vary linearly with as quenched hardness and strength. - Highlights: • As quenched aluminium alloys contain high magnitude residual stresses. • Surface is compressive balance by a tensile core. • As quenched surface residual stress is linear function of alloy strength. • In situ hot hardness demonstrates rapid change in intrinsic hardness during rapid cooling.« less

Surface structure and electrochemical characteristics of Ti-V-Cr bcc-type solid solution alloys sintered with Ni

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

Tsuji, Yoichiro; Yamamoto, Osamu; Matsuda, Hiromu

2000-07-01

Ti-V-Cr bcc-type solid solution alloys can absorb a large amount of hydrogen and be applied to active materials of the negative electrode in Ni-MH batteries. However, because of the insolubility of Ni into these alloys, the electrochemical characteristics like discharge capacity and cycle life were poor. In order to increase the discharge capacity of hydrogen absorbing alloy electrodes, Ti-V-Cr bcc-type alloy powders were sintered with Ni in order to form Ni contained surface layer on the alloy surface. As sintering temperature rose up, the surface composition changed from TiNi to Ti{sub 2}Ni. TiNi surface layer showed better electrochemical characteristics. Formore » the Ni adding method, Ni electroless plating was preferred because of good adhesion. As a result of optimized conditions, a discharge capacity of 570 mAh/g and an improvement of cycle life were achieved.« less

Development of casting investment preventing blackening of noble metal alloys Part 2. Application of developed investment for type 4 gold alloy.

PubMed

Nakai, Akira; Kakuta, Kiyoshi; Goto, Shin-ichi; Kato, Katuma; Yara, Atushi; Ogura, Hideo

2003-09-01

The objective of this study was to evaluate the efficacy of the developed investment for the prevention of blackening of a cast Type 4 gold and to analyze the oxides on its surface in relation to the blackening of the alloy. The experimental investments were prepared using a gypsum-bonded investment in which boron (B) or aluminum (Al) was added as a reducing agent. A Type 4 gold alloy was cast into the mold made of the prepared investment. The effect of the additives was evaluated from the color difference (deltaE*) between the as-cast surface and the polished surface of the cast specimen. B and Al were effective to prevent the blackening of a Type 4 gold alloy and the color of the as-cast surface approached that of the polished surface with increasing B and Al content. The prevention of the blackening of the gold alloy can be achieved by restraining the formation of CuO.

Adsorption of methanol, ethanol and water on well-characterized PtSn surface alloys

NASA Astrophysics Data System (ADS)

Panja, Chameli; Saliba, Najat; Koel, Bruce E.

1998-01-01

Adsorption and desorption of methanol (CH 3OH), ethanol (C 2H 5OH) and water on Pt(111) and two, ordered, PtSn alloys has been studied primarily using temperature-programmed desorption (TPD) mass spectroscopy. The two alloys studied were the {p(2 × 2) Sn}/{Pt(111) } and (√3 × √3) R30° {Sn}/{Pt(111) } surface alloys prepared by vapor deposition of Sn on Pt(111), with θSn = 0.25 and 0.33, respectively. All three molecules are weakly bonded and reversibly adsorbed under UHV conditions on all three surfaces, molecularly desorbing during TPD without any decomposition. The two PtSn surface alloys were found to chemisorb both methanol and ethanol slightly more weakly than on the Pt(111) surface. The desorption activation energies measured by TPD, and hence the adsorption energies, of both methanol and ethanol progressively decrease as the surface concentration of Sn increases, compared with Pt(111). The decreased binding energy leads one to expect a lower reactivity for these alcohols on the two alloys. The sticking coefficients and the monolayer coverages of these alcohols on the two alloys were identical to that on Pt(111) at 100 K, independent of the amount of Sn present in the surface layer. Alloying Sn in Pt(111) also slightly weakens the adsorption energy of water. Water clusters are formed even at low coverages on all three surfaces, eventually forming a water bilayer prior to the formation of a condensed ice phase. These results are relevant to a molecular-level explanation for the reactivity of Sn-promoted Pt surfaces that have been used in the electro-oxidation of simple organic molecules.

Influence of charged defects on the interfacial bonding strength of tantalum- and silver-doped nanograined TiO2.

PubMed

Azadmanjiri, Jalal; Wang, James; Berndt, Christopher C; Kapoor, Ajay; Zhu, De Ming; Ang, Andrew S M; Srivastava, Vijay K

2017-05-17

A nano-grained layer including line defects was formed on the surface of a Ti alloy (Ti alloy , Ti-6Al-4V ELI). Then, the micro- and nano-grained Ti alloy with the formation of TiO 2 on its top surface was coated with a bioactive Ta layer with or without incorporating an antibacterial agent of Ag that was manufactured by magnetron sputtering. Subsequently, the influence of the charged defects (the defects that can be electrically charged on the surface) on the interfacial bonding strength and hardness of the surface system was studied via an electronic model. Thereby, material systems of (i) Ta coated micro-grained titanium alloy (Ta/MGTi alloy ), (ii) Ta coated nano-grained titanium alloy (Ta/NGTi alloy ), (iii) TaAg coated micro-grained titanium alloy (TaAg/MGTi alloy ) and (iv) TaAg coated nano-grained titanium alloy (TaAg/NGTi alloy ) were formed. X-ray photoelectron spectroscopy was used to probe the electronic structure of the micro- and nano-grained Ti alloy , and so-formed heterostructures. The thin film/substrate interfaces exhibited different satellite peak intensities. The satellite peak intensity may be related to the interfacial bonding strength and hardness of the surface system. The interfacial layer of TaAg/NGTi alloy exhibited the highest satellite intensity and maximum hardness value. The increased bonding strength and hardness in the TaAg/NGTi alloy arises due to the negative core charge of the dislocations and neighbor space charge accumulation, as well as electron accumulation in the created semiconductor phases of larger band gap at the interfacial layer. These two factors generate interfacial polarization and enhance the satellite intensity. Consequently, the interfacial bonding strength and hardness of the surface system are improved by the formation of mixed covalent-ionic bonding structures around the dislocation core area and the interfacial layer. The bonding strength relationship by in situ XPS on the metal/TiO 2 interfacial layer may be examined with other noble metals and applied in diverse fields.

In vitro metal ion release and biocompatibility of amorphous Mg67Zn28Ca5 alloy with/without gelatin coating.

PubMed

Chan, W Y; Chian, K S; Tan, M J

2013-12-01

Amorphous zinc-rich Mg-Zn-Ca alloys have exhibited good tissue compatibility and low hydrogen evolution in vivo. However, suboptimal cell-surface interaction on magnesium alloy surface observed in vitro could lead to reduced integration with host tissue for regenerative purpose. This study aims to improve cell-surface interaction of amorphous Mg67Zn28Ca5 alloy by coating a gelatin layer by electrospinning. Coated/uncoated alloys were immersed and extracted for 3 days under different CO2. The immersion results showed that pH and metal ion release in the alloy extracts were affected by gelatin coating and CO2, suggesting their roles in alloy biocorrosion and a mechanism has been proposed for the alloy-CO2 system with/without coating. Cytotoxicity results are evident that gelatin-coated alloy with 2-day crosslinking not only exhibited no indirect cytotoxicity, but also supported attachment of L929 and MG63 cell lines around/on the alloy with high viability. Therefore, amorphous Mg67Zn28Ca5 alloy coated with gelatin by electrospinning technique provides a useful method to improve alloy biocompatibility. © 2013 Elsevier B.V. All rights reserved.

Precipitation Modeling in Nitriding in Fe-M Binary System

NASA Astrophysics Data System (ADS)

Tomio, Yusaku; Miyamoto, Goro; Furuhara, Tadashi

2016-10-01

Precipitation of fine alloy nitrides near the specimen surface results in significant surface hardening in nitriding of alloyed steels. In this study, a simulation model of alloy nitride precipitation during nitriding is developed for Fe-M binary system based upon the Kampmann-Wagner numerical model in order to predict variations in the distribution of precipitates with depth. The model can predict the number density, average radius, and volume fraction of alloy nitrides as a function of depth from the surface and nitriding time. By a comparison with the experimental observation in a nitrided Fe-Cr alloy, it was found that the model can predict successfully the observed particle distribution from the surface into depth when appropriate solubility of CrN, interfacial energy between CrN and α, and nitrogen flux at the surface are selected.

Surface integrity and corrosion performance of biomedical magnesium-calcium alloy processed by hybrid dry cutting-finish burnishing.

PubMed

Salahshoor, M; Li, C; Liu, Z Y; Fang, X Y; Guo, Y B

2018-02-01

Biodegradable magnesium-calcium (MgCa) alloy is a very attractive orthopedic biomaterial compared to permanent metallic alloys. However, the critical issue is that MgCa alloy corrodes too fast in the human organism. Compared to dry cutting, the synergistic dry cutting-finish burnishing can significantly improve corrosion performance of MgCa0.8 (wt%) alloy by producing a superior surface integrity including good surface finish, high compressive hook-shaped residual stress profile, extended strain hardening in subsurface, and little change of grain size. A FEA model was developed to understand the plastic deformation of MgCa materials during burnishing process. The measured polarization curves, surface micrographs, and element distributions of the corroded surfaces by burnishing show an increasing and uniform corrosion resistance to simulated body fluid. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fracture surface analysis of a quenched (α+β)-metastable titanium alloy

NASA Astrophysics Data System (ADS)

Illarionov, A. G.; Stepanov, S. I.; Demakov, S. L.

2017-12-01

Fracture surface analysis is conducted by means of SEM for VT16 titanium alloy specimens solution-treated at temperatures ranging from 700 to 875 °C, water-quenched and subjected to tensile testing. A cup and cone shape failure and dimple microstructure of the fracture surface indicates the ductile behavior of the alloy. Dimple dimensions correlated with the β-grain size of the alloy in quenched condition. The fracture area (namely, the size; the cup and cone shape) depends on the volume fraction of the primary α-phase in the quenched sample. However, the fracture surface changes considerably when the strain-induced β-αʺ-transformation takes place during tensile testing, resulting in the increase of alloy ductility.

A Study on Factors Affecting the Degradation of Magnesium and a Magnesium-Yttrium Alloy for Biomedical Applications

PubMed Central

Johnson, Ian; Liu, Huinan

2013-01-01

Controlling degradation of magnesium or its alloys in physiological saline solutions is essential for their potential applications in clinically viable implants. Rapid degradation of magnesium-based materials reduces the mechanical properties of implants prematurely and severely increases alkalinity of the local environment. Therefore, the objective of this study is to investigate the effects of three interactive factors on magnesium degradation, specifically, the addition of yttrium to form a magnesium-yttrium alloy versus pure magnesium, the metallic versus oxide surfaces, and the presence versus absence of physiological salt ions in the immersion solution. In the immersion solution of phosphate buffered saline (PBS), the magnesium-yttrium alloy with metallic surface degraded the slowest, followed by pure magnesium with metallic or oxide surfaces, and the magnesium-yttrium alloy with oxide surface degraded the fastest. However, in deionized (DI) water, the degradation rate showed a different trend. Specifically, pure magnesium with metallic or oxide surfaces degraded the slowest, followed by the magnesium-yttrium alloy with oxide surface, and the magnesium-yttrium alloy with metallic surface degraded the fastest. Interestingly, only magnesium-yttrium alloy with metallic surface degraded slower in PBS than in DI water, while all the other samples degraded faster in PBS than in DI water. Clearly, the results showed that the alloy composition, presence or absence of surface oxide layer, and presence or absence of physiological salt ions in the immersion solution all influenced the degradation rate and mode. Moreover, these three factors showed statistically significant interactions. This study revealed the complex interrelationships among these factors and their respective contributions to degradation for the first time. The results of this study not only improved our understanding of magnesium degradation in physiological environment, but also presented the key factors to consider in order to satisfy the degradation requirements for next-generation biodegradable implants and devices. PMID:23799028

A new method for promoting adhesion between precious metal alloys and dental adhesives.

PubMed

Ohno, H; Araki, Y; Endo, K

1992-06-01

A new, simple method of modifying the adherend metal surface by a liquid Ga-Sn alloy (Adlloy) was applied to dental precious and base-metal alloys for adhesion with 4-META adhesive resin. Adhesions of 4-META resin to three other surface states--as-polished, oxidized at high temperature, and electroplated tin--were also performed for comparison with the adhesion on Adlloy-modified surfaces. Bond strength measurements were made, and the durability against water at the adhering interface was evaluated. The Adlloy-modified gold alloys (Type IV and 14 K) and silver-based alloys (Ag-Pd and Ag-Cu) showed not only high bond strengths but also excellent water durability at the adhesion interface. Surface modification by Adlloy, however, did not affect adhesion to Ag-In-Zn and base-metal (SUS, Co-Cr, and Ni-Cr) alloys. Adhesion to the tin-electroplated specimens was comparable with that to the Adlloy-modified specimens.

Oxygen-Barrier Coating for Titanium

NASA Technical Reports Server (NTRS)

Clark, Ronald K.; Unnam, Jalaiah

1987-01-01

Oxygen-barrier coating for titanium developed to provide effective and low-cost means for protecting titanium alloys from oxygen in environment when alloys used in high-temperature mechanical or structural applications. Provides protective surface layer, which reduces extent of surface oxidation of alloy and forms barrier to diffusion of oxygen, limiting contamination of substrate alloy by oxygen. Consists of submicron layer of aluminum deposited on surface of titanium by electron-beam evaporation, with submicron layer of dioxide sputtered onto aluminum to form coat.

Corrosion of Mg alloy AZ91D in the presence of living cells.

PubMed

Seuss, F; Seuss, S; Turhan, M C; Fabry, B; Virtanen, S

2011-11-01

Mg and Mg alloys are of interest for biodegradable implants as they readily corrode in biological fluids, and dissolved Mg ions are nontoxic. Even though it is well known that Mg dissolution leads to pH increase in the surroundings, the effect of the corrosion-induced alkalization on the biological environment has not been studied in detail. We therefore explored the interactions between corrosion-induced pH increase and cell growth on Mg alloy AZ91D surface. Cell adhesion and spreading on the alloy surface is unimpeded initially. However, with time a large fraction of cells de-adhere. We attribute this to the observed increase of the pH in the cell culture medium in the process of alloy dissolution. Cytotoxicity tests with HeLa cells grown on glass surfaces confirm that cell death increases with increasing alkalinity of the cell culture medium. We also show that a the cells that adhere on the Mg alloy surface act as a corrosion-blocking surface layer. In consequence, a slower pH increase in the medium takes place when the alloy surface is covered with cells. Electrochemical impedance spectroscopy measurements (EIS) verify that a cell layer slows down the corrosion process. 2011 Wiley Periodicals, Inc.

In vitro bioactivity investigations of Ti-15Mo alloy after electrochemical surface modification.

PubMed

Kazek-Kęsik, Alicja; Kuna, Karolina; Dec, Weronika; Widziołek, Magdalena; Tylko, Grzegorz; Osyczka, Anna M; Simka, Wojciech

2016-07-01

Titanium and its aluminum and vanadium-free alloys have especially great potential for medical applications. Electrochemical surface modification improves their surface bioactivity and stimulates osseointegration process. In this work, the effect of plasma electrolytic oxidation of the β-type alloy Ti-15Mo surface on its bioactivity is presented. Bioactivity of the modified alloy was investigated by immersion in simulated body fluid (SBF). Biocompatibility of the modified alloys were tested using human bone marrow stromal cells (hBMSC) and wild intestinal strains (DV/A, DV/B, DV/I/1) of Desulfovibrio desulfuricans bacteria. The particles of apatite were formed on the anodized samples. Human BMSC cells adhered well on all the examined surfaces and expressed ALP, collagen, and produced mineralized matrix as determined after 10 and 21 days of culture. When the samples were inoculated with D. desulfuricans bacteria, only single bacteria were visible on selected samples. There were no obvious changes in surface morphology among samples. Colonization and bacterial biofilm formation was observed on as-ground sample. In conclusion, the surface modification improved the Ti-15Mo alloy bioactivity and biocompatibility and protected surface against colonization of the bacteria. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 903-913, 2016. © 2015 Wiley Periodicals, Inc.

Effect of Cu Alloying on S Poisoning of Ni Surfaces and Nanoparticle Morphologies Using Ab-Initio Thermodynamics Calculations.

PubMed

Kim, Ji-Su; Kim, Byung-Kook; Kim, Yeong-Cheol

2015-10-01

We investigated the effect of Cu alloying on S poisoning of Ni surfaces and nanoparticle morphologies using ab-initio thermodynamics calculations. Based on the Cu segregation energy and the S adsorption energy, the surface energy and nanoparticle morphology of pure Ni, pure Cu, and NiCu alloys were evaluated as functions of the chemical potential of S and the surface orientations of (100), (110), and (111). The constructed nanoparticle morphology was varied as a function of chemical potential of S. We find that the Cu added to Ni for NiCu alloys is strongly segregated into the top surface, and increases the S tolerance of the NiCu nanoparticles.

Ductile and brittle transition behavior of titanium alloys in ultra-precision machining.

PubMed

Yip, W S; To, S

2018-03-02

Titanium alloys are extensively applied in biomedical industries due to their excellent material properties. However, they are recognized as difficult to cut materials due to their low thermal conductivity, which induces a complexity to their deformation mechanisms and restricts precise productions. This paper presents a new observation about the removal regime of titanium alloys. The experimental results, including the chip formation, thrust force signal and surface profile, showed that there was a critical cutting distance to achieve better surface integrity of machined surface. The machined areas with better surface roughness were located before the clear transition point, defining as the ductile to brittle transition. The machined area at the brittle region displayed the fracture deformation which showed cracks on the surface edge. The relationship between depth of cut and the ductile to brittle transaction behavior of titanium alloys in ultra-precision machining(UPM) was also revealed in this study, it showed that the ductile to brittle transaction behavior of titanium alloys occurred mainly at relatively small depth of cut. The study firstly defines the ductile to brittle transition behavior of titanium alloys in UPM, contributing the information of ductile machining as an optimal machining condition for precise productions of titanium alloys.

Surface improvement and biocompatibility of TiAl 24Nb 10 intermetallic alloy using rf plasma nitriding

NASA Astrophysics Data System (ADS)

Abd El-Rahman, A. M.; Maitz, M. F.; Kassem, M. A.; El-Hossary, F. M.; Prokert, F.; Reuther, H.; Pham, M. T.; Richter, E.

2007-09-01

The present work describes the surface improvement and biocompatibility of TiAl 24Nb 10 intermetallic alloy using rf plasma nitriding. The nitriding process was carried out at different plasma power from 400 W to 650 W where the other plasma conditions were fixed. Grazing incidence X-ray diffractometry (GIXRD), Auger electron spectroscopy (AES), tribometer and a nanohardness tester were employed to characterize the nitrided layer. Further potentiodynamic polarization method was used to describe the corrosion behavior of the un-nitrided and nitrided alloy. It has been found that the Vickers hardness (HV) and corrosion resistance values of the nitrided layers increase with increasing plasma power while the wear rates of the nitrided layers reduce by two orders of magnitude as compared to those of the un-nitrided layer. This improvement in surface properties of the intermetallic alloy is due to formation of a thin modified layer which is composed of titanium nitride in the alloy surface. Moreover, all modified layers were tested for their sustainability as a biocompatible material. Concerning the application area of biocompatibility, the present treated alloy show good surface properties especially for the nitrided alloy at low plasma power of 400 W.

The effect of metallic oxide deposition on the electrochemical behaviour of Al-Zn-Mg-Sn alloy in natural tropical seawater

NASA Astrophysics Data System (ADS)

Din Yati, M. S.; Nazree Derman, Mohd; Isa, M. C.; Y Ahmad, M.; Yusoff, N. H. N.; Muhammad, M. M.; Nain, H.

2014-06-01

The potential of aluminium alloys as anode materials in cathodic protection system has been explored and a significant improvement has been achieved. However, for marine application, it is quite difficult to maintain continuous activation process due to passivation behavior of aluminum alloys. Therefore, to choose the best activation mechanism for aluminium alloy in marine environment, it has to be considered from various points such as alloy composition and surface treatment. This paper report the effect of metallic ruthenium oxide (RuO2) deposition on the surface of as-cast Al-Zn-Mg-Sn alloy and to study the effect of its presence on the electrochemical behavior using direct current (DC) electrochemical polarization and current capacity measurement. The morphology and topography of corroded surface were studied by the aid of scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM) respectively. Results from this study showed that the presence of intermetallic compound (Mg2Sn) and also mixed metal oxide compound (Al2O3 and RuO2) on the alloy surface has been very useful in improving electrochemical reaction and charge transfer activities in chloride containing solution. This study also showed that RuO2 catalytic coating applied on the surface of Al-Zn-Mg-Sn alloy has slightly increased the corrosion current density compared to Al-Zn-Mg-Sn without RuO2. The corrosion morphology and topography of corroded surface of Al-Zn-Mg-Sn alloy deposited with RuO2 was found more uniform corrosion attack with the formation of porous and fibrous mud-like crack on outer layer. Based on surface morphology and 3D topographic studies, these features were believed to facilitate ionic species adsorption and diffusion through corrosion product layer at solution-alloy interface. Deposited RuO2 films also was found to increase of current efficiency by more than 10%.

Effects of self-assembly of 3-phosphonopropionic acid, 3-aminopropyltrimethoxysilane and dopamine on the corrosion behaviors and biocompatibility of a magnesium alloy.

PubMed

Pan, Chang-Jiang; Hou, Yu; Wang, Ya-Nan; Gao, Fei; Liu, Tao; Hou, Yan-Hua; Zhu, Yu-Fu; Ye, Wei; Wang, Ling-Ren

2016-10-01

Magnesium based alloys are attracting tremendous interests as the novel biodegradable metallic biomaterials. However, the rapid in vivo degradation and the limited surface biocompatibility restrict their clinical applications. Surface modification represents one of the important approaches to control the corrosion rate of Mg based alloys and to enhance the biocompatibility. In the present study, in order to improve the corrosion resistance and surface biocompatibility, magnesium alloy (AZ31B) was modified by the alkali heating treatment followed by the self-assembly of 3-phosphonopropionic acid, 3-aminopropyltrimethoxysilane (APTMS) and dopamine, respectively. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectra (XPS) indicated that the molecules were successfully immobilized on the magnesium alloy surface by the self-assembly. An excellent hydrophilic surface was obtained after the alkali heating treatment and the water contact angle increased to some degree after the self-assembly of dopamine, APTMS and 3-phosphonopropionic acid, however, the hydrophilicity of the modified samples was better than that of the pristine magnesium substrate. Due to the formation of the passivation layer after the alkali heating treatment, the corrosion resistance of the magnesium alloy was obviously improved. The corrosion rate further decreased to varying degrees after the self-assembly surface modification. The blood compatibility of the pristine magnesium was significantly improved after the surface modification. The hemolysis rate was reduced from 56% of the blank magnesium alloy to 18% of the alkali heating treated sample and the values were further reduced to about 10% of dopamine-modified sample and 7% of APTMS-modified sample. The hemolysis rate was below 5% for the 3-phosphonopropionic acid modified sample. As compared to the pristine magnesium alloy, fewer platelets were attached and activated on the modified surfaces and the activated partial thromboplastin times (APTT) were prolonged to some degree. Furthermore, the modified samples showed good cytocompatibility. Endothelial cells exhibited the improved proliferative profiles in terms of CCK-8 assay as compared to those on the pristine magnesium alloy. The modified samples showed better endothelial cell adhesion and spreading than the pristine magnesium alloy. Taking all these results into consideration, the method of this study can be used to modify the magnesium alloy surface to improve the corrosion resistance and biocompatibility simultaneously. Copyright © 2016 Elsevier B.V. All rights reserved.

Stability of Fe-Cr alloy interconnects under CH 4-H 2O atmosphere for SOFCs

NASA Astrophysics Data System (ADS)

Horita, Teruhisa; Xiong, Yueping; Yamaji, Katsuhiko; Sakai, Natsuko; Yokokawa, Harumi

The chemical stability of Fe-Cr alloys (ZMG232 and SUS430) was examined under humidified CH 4 gases at 1073 K to simulate the real anode atmosphere in SOFC operation. Surface microstructure change and oxide scale layer formation were observed on the oxidized Fe-Cr alloy surfaces. The main reaction products were Mn-Cr-(Fe) spinels for both alloys. Secondary ion mass spectrometry (SIMS) was applied to measure the elemental distribution of minor and major elements around the oxide scale/alloy interface. A high concentration of Mn on the oxide scale surface suggested the fast diffusion of Mn in the oxide scale to form the spinels. Annealing in CH 4-H 2O made the oxide scale thicker with duration time on the alloy surface. The parabolic growth rates ( kp) of oxide scale layer were evaluated from the thickness of oxide scales by secondary ion mass spectrometry (SIMS) depth profiles, which were calculated to the following: kp=6.25×10 -6 μm 2/s for SUS430 and kp=4.42×10 -6 μm 2/s for ZMG232. The electrical conductivity of oxidized alloys showed the semi-conductor temperature dependence for both alloys. The electrical conductivity of oxidized ZMG232 alloy was higher than that of oxidized SUS430.

The influence of various cooling rates during laser alloying on nodular iron surface layer

NASA Astrophysics Data System (ADS)

Paczkowska, Marta; Makuch, Natalia; Kulka, Michał

2018-06-01

The results of research referring to modification of the nodular iron surface layer by laser alloying with cobalt were presented. The aim of this study was to analyze the possibilities of cobalt implementation into the surface layer of nodular iron in various laser heat treatment conditions (by generating different cooling rates of melted surface layer). The modified surface layer of nodular iron was analyzed with OM, SEM, TEM, XRD, EDS and Vickers microhardness tester. The modified surface layer of nodular iron after laser alloying consisted of: the alloyed zone (melted with cobalt), the transition zone and the hardened zone from solid state. The alloyed zone was characterized by higher microstructure homogeneity - in contrast to the transition and the hardened zones. All the alloyed zones contained a dendritic microstructure. Dendrites consisted of martensite needles and retained austenite. Cementite was also detected. It was stated, that due to similar dimension of iron and cobalt atoms, their mutual replacement in the crystal lattice could occur. Thus, formation of phases based on α solution: Co-Fe (44-1433) could not be excluded. Although cobalt should be mostly diluted in solid solutions (because of its content in the alloyed zone), the other newly formed phases as Co (ε-hex.), FeC and cobalt carbides: Co3C, CoC0.25 could be present in the alloyed zones as a result of unique microstructure creation during laser treatment. Pearlite grains were observed in the zone, formed using lower power density of the laser beam and its longer exposition time. Simply, such conditions resulted in the cooling rate which was lower than critical cooling rate. The alloyed zones, produced at a higher cooling rate, were characterized by better microstructure homogeneity. Dendrites were finer in this case. This could result from a greater amount of crystal nuclei appearing at higher cooling rate. Simultaneously, the increased amount of γ-Fe and Fe3C precipitates was expected in the alloyed zone formed at higher cooling rates. The hardness of nodular iron surface layer, alloyed with cobalt, was up to 4-times higher than the hardness of core material. The hardness of alloyed zones strongly depended on laser treatment conditions. In the case of lower cooling rate, lower hardness was observed due to more coarse-grained microstructure and a presence of pearlite. The hardness of the alloyed zone increased (from 850 to 950HV0.1) together with the increasing cooling rate (from 2 · 103 to nearly 9 · 103 °C/s). Laser treatment enabled a formation of surface layers on nodular iron, alloyed with cobalt. The microstructure of such a surface layer could be controlled by the laser processing parameters. High hardness and fine microstructure of the laser-alloyed nodular iron with cobalt should result in higher resistance to wear, corrosion and even (due to effect of cobalt addition) elevated temperatures during operation conditions of machine parts.

Fabrication of the superhydrophobic surface on aluminum alloy by anodizing and polymeric coating

NASA Astrophysics Data System (ADS)

Liu, Wenyong; Luo, Yuting; Sun, Linyu; Wu, Ruomei; Jiang, Haiyun; Liu, Yuejun

2013-01-01

We reported the preparation of the superhydrophobic surface on aluminum alloy via anodizing and polymeric coating. Both the different anodizing processes and different polymeric coatings of aluminum alloy were investigated. The effects of different anodizing conditions, such as electrolyte concentration, anodization time and current on the superhydrophobic surface were discussed. The results showed that a good superhydrophobic surface was facilely fabricated by polypropylene (PP) coating after anodizing. The optimum conditions for anodizing were determined by orthogonal experiments. When the concentration of oxalic acid was 10 g/L, the concentration of NaCl was 1.25 g/L, anodization time was 40 min, and anodization current was 0.4 A, the best superhydrophobic surface on aluminum alloy with the contact angle (CA) of 162° and the sliding angle of 2° was obtained. On the other hand, the different polymeric coatings, such as polystyrene (PS), polypropylene (PP) and polypropylene grafting maleic anhydride (PP-g-MAH) were used to coat the aluminum alloy surface after anodizing. The results showed that the superhydrophobicity was most excellent by coating PP, while the duration of the hydrophobic surface was poor. By modifying the surface with the silane coupling agent before PP coating, the duration of the superhydrophobic surface was improved. The morphologies of the superhydrophobic surface were further confirmed by optical microscope (OM) and scanning electron microscope (SEM). Combined with the material of PP with the low surface free energy, the micro/nano-structures of the surface resulted in the superhydrophobicity of the aluminum alloy surface.

Impact of Surface Potential on Apatite Formation in Ti Alloys Subjected to Acid and Heat Treatments

PubMed Central

Yamaguchi, Seiji; Hashimoto, Hideki; Nakai, Ryusuke; Takadama, Hiroaki

2017-01-01

Titanium metal (Ti) and its alloys are widely used in orthopedic and dental fields. We have previously shown that acid and heat treatment was effective to introduce bone bonding, osteoconduction and osteoinduction on pure Ti. In the present study, acid and heat treatment with or without initial NaOH treatment was performed on typical Ti-based alloys used in orthopedic and dental fields. Dynamic movements of alloying elements were developed, which depended on the kind of treatment and type of alloy. It was found that the simple acid and heat treatment enriched/remained the alloying elements on Ti–6Al–4V, Ti–15Mo–5Zr–3Al and Ti–15Zr–4Nb–4Ta, resulting in neutral surface charges. Thus, the treated alloys did not form apatite in a simulated body fluid (SBF) within 3 days. In contrast, when the alloys were subjected to a NaOH treatment prior to an acid and heat treatment, alloying elements were selectively removed from the alloy surfaces. As a result, the treated alloys became positively charged, and formed apatite in SBF within 3 days. Thus, the treated alloys would be useful in orthopedic and dental fields since they form apatite even in a living body and bond to bone. PMID:28946646

Bioactivity of Ti-6Al-4V alloy implants treated with ibandronate after the formation of the nanotube TiO2 layer.

PubMed

Moon, So-Hee; Lee, Seung-Jae; Park, Il-Song; Lee, Min-Ho; Soh, Yun-Jo; Bae, Tae-Sung; Kim, Hyung-Seop

2012-11-01

Nanostructure surface of titanium implants treated with anodic oxidation, heat, and bisphosphonates, has been introduced to improve osseointegration of the implants. However, no information could be found about the efficiency of these approaches on Ti-6Al-4V alloy surfaces. This study examined the drug loading capacity of anodized nanotubular Ti-6Al-4V alloy surfaces in vitro as well as the bone response to surface immobilized bisphosphonates (BPs) on anodized nanotubular Ti-6Al-4V alloy surface in tibiae of rats. Ti-6Al-4V alloy titanium was divided into two groups: (1) control group (nontreated); (2) test group (anodized, heat-, and bisphosphonate-treated group). In vitro, amount of the drug released from the both groups' specimens was examined; all samples were 1 × 2 cm in size. In vivo, the 10 implants were placed inside of tibias of five rats. After 4 weeks, the bone response of the implants was evaluated using a removal torque test, and measuring bone contact and bone area. In addition, the surfaces of the extracted implants were observed by FE-SEM and EDS. In vitro, the drug loading capacity of the Ti-6Al-4V alloy surfaces was enhanced by anodizing surface modification. The values of the removal torque, bone contact, and bone area were significantly higher in the test group (p < 0.05). Furthermore, according to the EDS analysis, the amounts of Ca and P on the surface of the extracted implants were higher in the test group. Within the limits of this experiment, results of this research demonstrated that bisphosphonate-treated Ti-6Al-4V alloy implants with nanotubular surfaces have positive effects in bone-to-implant contact. Copyright © 2012 Wiley Periodicals, Inc.

Stress-corrosion behavior of aluminum-lithium alloys in aqueous salt environments

NASA Technical Reports Server (NTRS)

Pizzo, P. P.; Galvin, R. P.; Nelson, H. G.

1984-01-01

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg; two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Stress-corrosion behavior of aluminum-lithium alloys in aqueous environments

NASA Technical Reports Server (NTRS)

Pizzo, P. P.; Galvin, R. P.; Nelson, H. G.

1983-01-01

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Optimum surface roughness prediction for titanium alloy by adopting response surface methodology

NASA Astrophysics Data System (ADS)

Yang, Aimin; Han, Yang; Pan, Yuhang; Xing, Hongwei; Li, Jinze

Titanium alloy has been widely applied in industrial engineering products due to its advantages of great corrosion resistance and high specific strength. This paper investigated the processing parameters for finish turning of titanium alloy TC11. Firstly, a three-factor central composite design of experiment, considering the cutting speed, feed rate and depth of cut, are conducted in titanium alloy TC11 and the corresponding surface roughness are obtained. Then a mathematic model is constructed by the response surface methodology to fit the relationship between the process parameters and the surface roughness. The prediction accuracy was verified by the one-way ANOVA. Finally, the contour line of the surface roughness under different combination of process parameters are obtained and used for the optimum surface roughness prediction. Verification experimental results demonstrated that material removal rate (MRR) at the obtained optimum can be significantly improved without sacrificing the surface roughness.

Diffusion and surface alloying of gradient nanostructured metals

PubMed Central

Lu, Ke

2017-01-01

Gradient nanostructures (GNSs) have been optimized in recent years for desired performance. The diffusion behavior in GNS metals is crucial for understanding the diffusion mechanism and relative characteristics of different interfaces that provide fundamental understanding for advancing the traditional surface alloying processes. In this paper, atomic diffusion, reactive diffusion, and surface alloying processes are reviewed for various metals with a preformed GNS surface layer. We emphasize the promoted atomic diffusion and reactive diffusion in the GNS surface layer that are related to a higher interfacial energy state with respect to those in relaxed coarse-grained samples. Accordingly, different surface alloying processes, such as nitriding and chromizing, have been modified significantly, and some diffusion-related properties have been enhanced. Finally, the perspectives on current research in this field are discussed. PMID:28382244

Containerless Measurement of Thermophysical Properties of Ti-Zr-Ni Alloys

NASA Technical Reports Server (NTRS)

Hyers, Robert; Bradshaw, Richard C.; Rogers, Jan C.; Rathz, Thomas J.; Lee, Geun W.; Gangopadhyay, Anup K.; Kelton, Kenneth F.

2004-01-01

The surface tension, viscosity, density, and thermal expansion of Ti-Zr-Ni alloys were measured for a number of compositions by electrostatic levitation methods. Containerless methods greatly reduce heterogeneous nucleation, increasing access to the undercooled liquid regime at finite cooling rates. The density and thermal expansion are measured optically, while the surface tension and viscosity are measured by the oscillating drop method. The measured alloys include compositions which form a metastable quasicrystal phase from the undercooled liquid, and alloys close to the composition of several multi-component bulk metallic glass-forming alloys. Measurements of surface tension show behavior typical of transition metals at high temperature, but a sudden decrease in the deeply undercooled liquid for alloys near the quasicrystal-forming composition range, but not for compositions which form the solid-solution phase first.

Influence of laser parameters in surface texturing of Ti6Al4V and AA2024-T3 alloys

NASA Astrophysics Data System (ADS)

Ahuir-Torres, J. I.; Arenas, M. A.; Perrie, W.; de Damborenea, J.

2018-04-01

Laser texturing can be used for surface modification of metallic alloys in order to improve their properties under service conditions. The generation of textures is determined by the relationship between the laser processing parameters and the physicochemical properties of the alloy to be modified. In the present work the basic mechanism of dimple generation is studied in two alloys of technological interest, titanium alloy Ti6Al4V and aluminium alloy AA2024-T3. Laser treatment was performed using a pulsed solid state Nd: Vanadate (Nd: YVO4) laser with a pulse duration of 10 ps, operating at a wavelength of 1064 nm and 5 kHz repetition rate. Dimpled surface geometries were generated through ultrafast laser ablation while varying pulse energy between 1 μJ and 20 μJ/pulse and with pulse numbers from 10 to 200 pulses per spot. In addition, the generation of Laser Induced Periodic Surface Structures (LIPSS) nanostructures in both alloys, as well as the formation of random nanostructures in the impact zones are discussed.

The influence of laser alloying on the structure and mechanical properties of AlMg5Si2Mn surface layers

NASA Astrophysics Data System (ADS)

Pakieła, W.; Tański, T.; Brytan, Z.; Labisz, K.

2016-04-01

The goal of this paper was focused on investigation of microstructure and properties of surface layer produced during laser surface treatment of aluminium alloy by high-power fibre laser. The performed laser treatment involves remelting and feeding of Inconel 625 powder into the aluminium surface. As a base metal was used aluminium alloy AlMg5Si2Mn. The Inconel powder was injected into the melt pool and delivered by a vacuum feeder at a constant rate of 4.5 g/min. The size of Inconel alloying powder was in the range 60-130 µm. In order to remelt the aluminium alloy surface, the fibre laser of 3 kW laser beam power has been used. The linear laser scan rate of the beam was set 0.5 m/min. Based on performed investigations, it was possible to obtain the layer consisting of heat-affected zone, transition zone and remelted zone, without cracks and defects having much higher hardness value compared to the non-alloyed material.

Molybdeno-Aluminizing of Powder Metallurgy and Wrought Ti and Ti-6Al-4V alloys by Pack Cementation process

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

Tsipas, Sophia A., E-mail: stsipas@ing.uc3m.es; Go

Wear and high temperature oxidation resistance of some titanium-based alloys needs to be enhanced, and this can be effectively accomplished by surface treatment. Molybdenizing is a surface treatment where molybdenum is introduced into the surface of titanium alloys causing the formation of wear-resistant surface layers containing molybdenum, while aluminizing of titanium-based alloys has been reported to improve their high temperature oxidation properties. Whereas pack cementation and other surface modification methods have been used for molybdenizing or aluminizing of wrought and/or cast pure titanium and titanium alloys, such surface treatments have not been reported on titanium alloys produced by powder metallurgymore » (PM). Also a critical understanding of the process parameters for simultaneous one step molybdeno-aluminizing of titanium alloys by pack cementation and the predominant mechanism for this process have not been reported. The current research work describes the surface modification of titanium and Ti-6Al-4V prepared by PM by molybdeno-aluminizing and analyzes thermodynamic aspects of the deposition process. Similar coatings are also deposited to wrought Ti-6Al-4V and compared. Characterization of the coatings was carried out using scanning electron microscopy and x-ray diffraction. For both titanium and Ti-6Al-4V, the use of a powder pack containing ammonium chloride as activator leads to the deposition of molybdenum and aluminium into the surface but also introduces nitrogen causing the formation of a thin titanium nitride layer. In addition, various titanium aluminides and mixed titanium aluminium nitrides are formed. The appropriate conditions for molybdeno-aluminizing as well as the phases expected to be formed were successfully determined by thermodynamic equilibrium calculations. - Highlights: •Simultaneous co-deposition of Mo-Al onto powder metallurgy and wrought Ti alloy •Thermodynamic calculations were used to optimize deposition conditions •External TiN and internal a Mo-rich layer on all alloy substrates •Titanium aluminides and Ti-Al mixed nitrides are formed on Ti-6Al-4V •The presence of Al and V alloying elements modifies the diffusion of Mo.« less

Wear of carbide inserts with complex surface treatment when milling nickel alloy

NASA Astrophysics Data System (ADS)

Fedorov, Sergey; Swe, Min Htet; Kapitanov, Alexey; Egorov, Sergey

2018-03-01

One of the effective ways of strengthening hard alloys is the creating structure layers on their surface with the gradient distribution of physical and mechanical properties between the wear-resistant coating and the base material. The article discusses the influence of the near-surface layer which is modified by low-energy high-current electron-beam alloying and the upper anti-friction layer in a multi-component coating on the wear mechanism of the replaceable multifaceted plates in the dry milling of the difficult to machine nickel alloys.

Surface Characterization of New Biomaterials

NASA Astrophysics Data System (ADS)

Minciuna, M. G.; Vizureanu, P.; Abdullah, M. M. B.; Achitei, D. C.; Istrate, B.; Cimpoesu, R.; Focsaneanu, S. C.

2017-06-01

This paper presents the characterization of new alloys CoCrMoSi6, CoCrMoSi7, CoCrMoSi10, in terms of hardness determinations, fractographic analysis and surface analysis. The original version of the alloy was obtained by casting process in a vacuum arc furnace. Experimental results obtained from this study confirms that by increasing content of silicon, the mechanical properties are superior and the positive results obtained at surface studies favoring the formation of compounds, that lead to the reduction of alloying grade for α solid solution and the plasticity of the alloys.

First-principles study of the surface properties of U-Mo system

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

Mei, Zhi-Gang; Liang, Linyun; Yacout, Abdellatif M.

U-Mo alloys are promising fuels for future high-performance research reactors with low enriched uranium. Surface properties, such as surface energy, are important inputs for mesoscale simulations (e.g., phase field method) of fission gas bubble behaviors in irradiated nuclear fuels. The lack of surface energies of U-Mo alloys prevents an accurate modeling of the morphology of gas bubbles and gas bubble-induced fuel swelling. To this end, we study the surface properties of U-Mo system, including bcc Mo, alpha-U, gamma-U, and gamma U-Mo alloys. All surfaces up to a maximum Miller index of three and two are calculated for cubic Mo andmore » gamma-U and non-cubic alpha-U, respectively. The equilibrium crystal shapes of bcc Mo, alpha-U and gamma-U are constructed using the calculated surface energies. The dominant surface orientations and the area fraction of each facet are determined from the constructed equilibrium crystal shape. The disordered gamma U-Mo alloys are simulated using the Special Quasirandom Structure method. The (1 1 0) and (1 0 0) surface energies of gamma U-7Mo and U-10Mo alloys are predicted to lie between those of gamma-U and bcc Mo, following a linear combination of the two constituents' surface energies. To better compare with future measurements of surface energies, the area fraction weighted surface energies of alpha-U, gamma-U and gamma U-7Mo and U-10Mo alloys are also predicted. (C) 2017 Published by Elsevier B.V.« less

Iron-based alloys with corrosion resistance to oxygen-sulfur mixed gases

DOEpatents

Natesan, K.

1992-11-17

An iron-based alloy with improved performance with exposure to oxygen-sulfur mixed gases with the alloy containing about 9--30 wt. % Cr and a small amount of Nb and/or Zr implanted on the surface of the alloy to diffuse a depth into the surface portion, with the alloy exhibiting corrosion resistance to the corrosive gases without bulk addition of Nb and/or Zr and without heat treatment at temperatures of 1000--1100 C. 7 figs.

Iron-based alloys with corrosion resistance to oxygen-sulfur mixed gases

DOEpatents

Natesan, Krishnamurti

1992-01-01

An iron-based alloy with improved performance with exposure to oxygen-sulfur mixed gases with the alloy containing about 9-30 wt. % Cr and a small amount of Nb and/or Zr implanted on the surface of the alloy to diffuse a depth into the surface portion, with the alloy exhibiting corrosion resistance to the corrosive gases without bulk addition of Nb and/or Zr and without heat treatment at temperatures of 1000.degree.-1100.degree. C.

A Case Study on Sepsis Using PubMed and Deep Learning for Ontology Learning.

PubMed

Arguello Casteleiro, Mercedes; Maseda Fernandez, Diego; Demetriou, George; Read, Warren; Fernandez Prieto, Maria Jesus; Des Diz, Julio; Nenadic, Goran; Keane, John; Stevens, Robert

2017-01-01

We investigate the application of distributional semantics models for facilitating unsupervised extraction of biomedical terms from unannotated corpora. Term extraction is used as the first step of an ontology learning process that aims to (semi-)automatic annotation of biomedical concepts and relations from more than 300K PubMed titles and abstracts. We experimented with both traditional distributional semantics methods such as Latent Semantic Analysis (LSA) and Latent Dirichlet Allocation (LDA) as well as the neural language models CBOW and Skip-gram from Deep Learning. The evaluation conducted concentrates on sepsis, a major life-threatening condition, and shows that Deep Learning models outperform LSA and LDA with much higher precision.

Thermophysical Property Measurements of Silicon-Transition Metal Alloys

NASA Technical Reports Server (NTRS)

Banish, R. Michael; Erwin, William R.; Sansoucie, Michael P.; Lee, Jonghyun; Gave, Matthew A.

2014-01-01

Metals and metallic alloys often have high melting temperatures and highly reactive liquids. Processing reactive liquids in containers can result in significant contamination and limited undercooling. This is particularly true for molten silicon and it alloys. Silicon is commonly termed "the universal solvent". The viscosity, surface tension, and density of several silicon-transition metal alloys were determined using the Electrostatic Levitator system at the Marshall Space Flight Center. The temperature dependence of the viscosity followed an Arrhenius dependence, and the surface tension followed a linear temperature dependence. The density of the melts, including the undercooled region, showed a linear behavior as well. Viscosity and surface tension values were obtain for several of the alloys in the undercooled region.

Lattice matched semiconductor growth on crystalline metallic substrates

DOEpatents

Norman, Andrew G; Ptak, Aaron J; McMahon, William E

2013-11-05

Methods of fabricating a semiconductor layer or device and said devices are disclosed. The methods include but are not limited to providing a metal or metal alloy substrate having a crystalline surface with a known lattice parameter (a). The methods further include growing a crystalline semiconductor alloy layer on the crystalline substrate surface by coincident site lattice matched epitaxy. The semiconductor layer may be grown without any buffer layer between the alloy and the crystalline surface of the substrate. The semiconductor alloy may be prepared to have a lattice parameter (a') that is related to the lattice parameter (a). The semiconductor alloy may further be prepared to have a selected band gap.

Molecular dynamics simulation study of nanoscale passive oxide growth on Ni-Al alloy surfaces at low temperatures

NASA Astrophysics Data System (ADS)

Sankaranarayanan, Subramanian K. R. S.; Ramanathan, Shriram

2008-08-01

Oxidation kinetics of Ni-Al (100) alloy surface is investigated at low temperatures (300-600 K) and at different gas pressures using molecular dynamics (MD) simulations with dynamic charge transfer between atoms. Monte Carlo simulations employing the bond order simulation model are used to generate the surface segregated minimum energy initial alloy configurations for use in the MD simulations. In the simulated temperature-pressure-composition regime for Ni-Al alloys, we find that the oxide growth curves follow a logarithmic law beyond an initial transient regime. The oxidation rates for Ni-Al alloys were found to decrease with increasing Ni composition. Structure and dynamical correlations in the metal/oxide/gas environments are used to gain insights into the evolution and morphology of the growing oxide film. Oxidation of Ni-Al alloys is characterized by the absence of Ni-O bond formation. Oxide films formed on the various simulated metal surfaces are amorphous in nature and have a limiting thickness ranging from ˜1.7nm for pure Al to 1.1 nm for 15% Ni-Al surfaces. Oxide scale analysis indicates significant charge transfer as well as variation in the morphology and structure of the oxide film formed on pure Al and 5% Ni-Al alloy. For oxide scales thicker than 1 nm, the oxide structure in case of pure Al exhibits a mixed tetrahedral (AlO4˜37%) and octahedral (AlO6˜19%) environment, whereas the oxide scale on Ni-Al alloy surface is almost entirely composed of tetrahedral environment (AlO4˜60%) with very little AlO6 (<1%) . The oxide growth kinetic curves are fitted to Arrhenius-type plots to get an estimate of the activation energy barriers for metal oxidation. The activation energy barrier for oxidation on pure Al was found to be 0.3 eV lower than that on 5% Ni-Al surface. Atomistic observations as well as calculated dynamical correlation functions indicate a layer by layer growth on pure Al, whereas a transition from an initial island growth mode (<75ps) to a layer by layer mode (>100ps) occurs in case of 5% Ni-Al alloy. The oxide growth on both pure Al and Ni-Al alloy surfaces occurs by inward anion and outward cation diffusions. The cation diffusion in both the cases is similar, whereas the anion diffusion in case of 5% Ni-Al is 25% lower than pure Al, thereby resulting in reduced self-limiting thickness of oxide scale on the alloy surface. The simulation findings agree well with previously reported experimental observations of oxidation on Ni-Al alloy surface.

Surface alloying of aluminum with molybdenum by high-current pulsed electron beam

NASA Astrophysics Data System (ADS)

Xia, Han; Zhang, Conglin; Lv, Peng; Cai, Jie; Jin, Yunxue; Guan, Qingfeng

2018-02-01

The surface alloying of pre-coated molybdenum (Mo) film on aluminum (Al) substrate by high-current pulsed electron beam (HCPEB) was investigated. The microstructure and phase analysis were conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that Mo particles were dissolved into Al matrix to form alloying layer, which was composed of Mo, Al and acicular or equiaxed Al5Mo phases after surface alloying. Meanwhile, various structure defects such as dislocation loops, high-density dislocations and dislocation walls were observed in the alloying surface. The corrosion resistance was tested by using potentiodynamic polarization curves and electrochemical impedance spectra (EIS). Electrochemical results indicate that all the alloying samples had better corrosion resistance in 3.5 wt% NaCl solution compared to initial sample. The excellent corrosion resistance is mainly attributed to the combined effect of the structure defects and the addition of Mo element to form a more stable passive film.

Laser Nitriding of the Newly Developed Ti-20Nb-13Zr at.% Biomaterial Alloy to Enhance Its Mechanical and Corrosion Properties in Simulated Body Fluid

NASA Astrophysics Data System (ADS)

Hussein, M. A.; Kumar, A. Madhan; Yilbas, Bekir S.; Al-Aqeeli, N.

2017-11-01

Despite the widespread application of Ti alloy in the biomedical field, surface treatments are typically applied to improve its resistance to corrosion and wear. A newly developed biomedical Ti-20Nb-13Zr at.% alloy (TNZ) was laser-treated in nitrogen environment to improve its surface characteristics with corrosion protection performance. Surface modification of the alloy by laser was performed through a Nd:YAG laser. The structural and surface morphological alterations in the laser nitrided layer were investigated by XRD and a FE-SEM. The mechanical properties have been evaluated using nanoindentation for laser nitride and as-received samples. The corrosion protection behavior was estimated using electrochemical corrosion analysis in a physiological medium (SBF). The obtained results revealed the production of a dense and compact film of TiN fine grains (micro-/nanosize) with 9.1 µm below the surface. The mechanical assessment results indicated an improvement in the modulus of elasticity, hardness, and resistance of the formed TiN layer to plastic deformation. The electrochemical analysis exhibited that the surface protection performance of the laser nitrided TNZ substrates in the SBF could be considerably enhanced compared to that of the as-received alloy due to the presence of fine grains in the TiN layer resulting from laser nitriding. Furthermore, the untreated and treated Ti-20Nb-13Zr alloy exhibited higher corrosion resistance than the CpTi and Ti6Al4V commercial alloys. The improvements in the surface hardness and corrosion properties of Ti alloy in a simulated body obtained using laser nitriding make this approach a suitable candidate for enhancing the properties of biomaterials.

Sporicidal efficacy of thermal-sprayed copper alloy coating.

PubMed

Shafaghi, Romina; Mostaghimi, Javad; Pershin, Valerian; Ringuette, Maurice

2017-05-01

Approximately 200 000 Canadians acquire healthcare-associated bacterial infections each year and several-fold more acquire food-borne bacterial illnesses. Bacterial spores are particularly problematic because they can survive on surfaces for several months. Owing to its sporicidal activity, copper alloy sheet metal is sometimes used in hospital settings, but its widespread use is limited by cost and incompatibility with complex furniture and instrument designs and topographies. A potential alternative is the use of thermal spray technology to coat surfaces with copper alloys. We compared the sporicidal activity of thermally sprayed copper alloy on stainless steel with that of copper alloy sheet metal against Bacillus subtilis spores. Spores remained intact for at least 1 week on uncoated stainless steel, whereas spore fragmentation was initiated within 2 h of exposure to either copper surface. Less than 15% of spores were viable 2 h after exposure to either copper surface, as compared with stainless steel. By day 7, only degraded spores and petal-like nanoflowers were present on the copper surfaces. Nanoflowers, which are laminar arrangements of thin crystal sheets composed of carbon - copper phosphate, appeared to be derived from the degraded spores. Altogether, these results indicate that a thermal-sprayed copper alloy coating on stainless steel provides sporicidal activity similar to that afforded by copper alloy sheet metal.

Fire danger rating over Mediterranean Europe based on fire radiative power derived from Meteosat

NASA Astrophysics Data System (ADS)

Pinto, Miguel M.; DaCamara, Carlos C.; Trigo, Isabel F.; Trigo, Ricardo M.; Feridun Turkman, K.

2018-02-01

We present a procedure that allows the operational generation of daily forecasts of fire danger over Mediterranean Europe. The procedure combines historical information about radiative energy released by fire events with daily meteorological forecasts, as provided by the Satellite Application Facility for Land Surface Analysis (LSA SAF) and the European Centre for Medium-Range Weather Forecasts (ECMWF). Fire danger is estimated based on daily probabilities of exceedance of daily energy released by fires occurring at the pixel level. Daily probability considers meteorological factors by means of the Canadian Fire Weather Index (FWI) and is estimated using a daily model based on a generalized Pareto distribution. Five classes of fire danger are then associated with daily probability estimated by the daily model. The model is calibrated using 13 years of data (2004-2016) and validated against the period of January-September 2017. Results obtained show that about 72 % of events releasing daily energy above 10 000 GJ belong to the extreme class of fire danger, a considerably high fraction that is more than 1.5 times the values obtained when using the currently operational Fire Danger Forecast module of the European Forest Fire Information System (EFFIS) or the Fire Risk Map (FRM) product disseminated by the LSA SAF. Besides assisting in wildfire management, the procedure is expected to help in decision making on prescribed burning within the framework of agricultural and forest management practices.

Chemical, electronic, and magnetic structure of LaFeCoSi alloy: Surface and bulk properties

NASA Astrophysics Data System (ADS)

Lollobrigida, V.; Basso, V.; Borgatti, F.; Torelli, P.; Kuepferling, M.; Coïsson, M.; Olivetti, E. S.; Celegato, F.; Tortora, L.; Stefani, G.; Panaccione, G.; Offi, F.

2014-05-01

We investigate the chemical, electronic, and magnetic structure of the magnetocaloric LaFeCoSi compound with bulk and surface sensitive techniques. We put in evidence that the surface retains a soft ferromagnetic behavior at temperatures higher than the Curie temperature of the bulk due to the presence of Fe clusters at the surface only. This peculiar magnetic surface effect is attributed to the exchange interaction between the ferromagnetic Fe clusters located at the surface and the bulk magnetocaloric alloy, and it is used here to monitor the magnetic properties of the alloy itself.

Membrane Lipid Peroxidation in Copper Alloy-Mediated Contact Killing of Escherichia coli

PubMed Central

Hong, Robert; Kang, Tae Y.; Michels, Corinne A.

2012-01-01

Copper alloy surfaces are passive antimicrobial sanitizing agents that kill bacteria, fungi, and some viruses. Studies of the mechanism of contact killing in Escherichia coli implicate the membrane as the target, yet the specific component and underlying biochemistry remain unknown. This study explores the hypothesis that nonenzymatic peroxidation of membrane phospholipids is responsible for copper alloy-mediated surface killing. Lipid peroxidation was monitored with the thiobarbituric acid-reactive substances (TBARS) assay. Survival, TBARS levels, and DNA degradation were followed in cells exposed to copper alloy surfaces containing 60 to 99.90% copper or in medium containing CuSO4. In all cases, TBARS levels increased with copper exposure levels. Cells exposed to the highest copper content alloys, C11000 and C24000, exhibited novel characteristics. TBARS increased immediately at a very rapid rate but peaked at about 30 min. This peak was associated with the period of most rapid killing, loss in membrane integrity, and DNA degradation. DNA degradation is not the primary cause of copper-mediated surface killing. Cells exposed to the 60% copper alloy for 60 min had fully intact genomic DNA but no viable cells. In a fabR mutant strain with increased levels of unsaturated fatty acids, sensitivity to copper alloy surface-mediated killing increased, TBARS levels peaked earlier, and genomic DNA degradation occurred sooner than in the isogenic parental strain. Taken together, these results suggest that copper alloy surface-mediated killing of E. coli is triggered by nonenzymatic oxidative damage of membrane phospholipids that ultimately results in the loss of membrane integrity and cell death. PMID:22247141

Energy-Efficient Transmissions for Remote Wireless Sensor Networks: An Integrated HAP/Satellite Architecture for Emergency Scenarios

PubMed Central

Dong, Feihong; Li, Hongjun; Gong, Xiangwu; Liu, Quan; Wang, Jingchao

2015-01-01

A typical application scenario of remote wireless sensor networks (WSNs) is identified as an emergency scenario. One of the greatest design challenges for communications in emergency scenarios is energy-efficient transmission, due to scarce electrical energy in large-scale natural and man-made disasters. Integrated high altitude platform (HAP)/satellite networks are expected to optimally meet emergency communication requirements. In this paper, a novel integrated HAP/satellite (IHS) architecture is proposed, and three segments of the architecture are investigated in detail. The concept of link-state advertisement (LSA) is designed in a slow flat Rician fading channel. The LSA is received and processed by the terminal to estimate the link state information, which can significantly reduce the energy consumption at the terminal end. Furthermore, the transmission power requirements of the HAPs and terminals are derived using the gradient descent and differential equation methods. The energy consumption is modeled at both the source and system level. An innovative and adaptive algorithm is given for the energy-efficient path selection. The simulation results validate the effectiveness of the proposed adaptive algorithm. It is shown that the proposed adaptive algorithm can significantly improve energy efficiency when combined with the LSA and the energy consumption estimation. PMID:26404292

Energy-Efficient Transmissions for Remote Wireless Sensor Networks: An Integrated HAP/Satellite Architecture for Emergency Scenarios.

PubMed

Dong, Feihong; Li, Hongjun; Gong, Xiangwu; Liu, Quan; Wang, Jingchao

2015-09-03

A typical application scenario of remote wireless sensor networks (WSNs) is identified as an emergency scenario. One of the greatest design challenges for communications in emergency scenarios is energy-efficient transmission, due to scarce electrical energy in large-scale natural and man-made disasters. Integrated high altitude platform (HAP)/satellite networks are expected to optimally meet emergency communication requirements. In this paper, a novel integrated HAP/satellite (IHS) architecture is proposed, and three segments of the architecture are investigated in detail. The concept of link-state advertisement (LSA) is designed in a slow flat Rician fading channel. The LSA is received and processed by the terminal to estimate the link state information, which can significantly reduce the energy consumption at the terminal end. Furthermore, the transmission power requirements of the HAPs and terminals are derived using the gradient descent and differential equation methods. The energy consumption is modeled at both the source and system level. An innovative and adaptive algorithm is given for the energy-efficient path selection. The simulation results validate the effectiveness of the proposed adaptive algorithm. It is shown that the proposed adaptive algorithm can significantly improve energy efficiency when combined with the LSA and the energy consumption estimation.

Late Pleistocene age and archaeological context for the hominin calvaria from GvJm-22 (Lukenya Hill, Kenya)

PubMed Central

Tryon, Christian A.; Crevecoeur, Isabelle; Faith, J. Tyler; Ekshtain, Ravid; Nivens, Joelle; Patterson, David; Mbua, Emma N.; Spoor, Fred

2015-01-01

Kenya National Museums Lukenya Hill Hominid 1 (KNM-LH 1) is a Homo sapiens partial calvaria from site GvJm-22 at Lukenya Hill, Kenya, associated with Later Stone Age (LSA) archaeological deposits. KNM-LH 1 is securely dated to the Late Pleistocene, and samples a time and region important for understanding the origins of modern human diversity. A revised chronology based on 26 accelerator mass spectrometry radiocarbon dates on ostrich eggshells indicates an age range of 23,576–22,887 y B.P. for KNM-LH 1, confirming prior attribution to the Last Glacial Maximum. Additional dates extend the maximum age for archaeological deposits at GvJm-22 to >46,000 y B.P. (>46 kya). These dates are consistent with new analyses identifying both Middle Stone Age and LSA lithic technologies at the site, making GvJm-22 a rare eastern African record of major human behavioral shifts during the Late Pleistocene. Comparative morphometric analyses of the KNM-LH 1 cranium document the temporal and spatial complexity of early modern human morphological variability. Features of cranial shape distinguish KNM-LH 1 and other Middle and Late Pleistocene African fossils from crania of recent Africans and samples from Holocene LSA and European Upper Paleolithic sites. PMID:25730861

Impact of the De-Alloying Kinetics and Alloy Microstructure on the Final Morphology of De-Alloyed Meso-Porous Metal Films

PubMed Central

Lin, Bao; Kong, Lingxue; Hodgson, Peter D.; Dumée, Ludovic F.

2014-01-01

Nano-textured porous metal materials present unique surface properties due to their enhanced surface energy with potential applications in sensing, molecular separation and catalysis. In this paper, commercial alloy foils, including brass (Cu85Zn15 and Cu70Zn30) and white gold (Au50Ag50) foils have been chemically de-alloyed to form nano-porous thin films. The impact of the initial alloy micro-structure and number of phases, as well as chemical de-alloying (DA) parameters, including etchant concentration, time and solution temperature on the final nano-porous thin film morphology and properties were investigated by electron microscopy (EM). Furthermore, the penetration depth of the pores across the alloys were evaluated through the preparation of cross sections by focus ion beam (FIB) milling. It is demonstrated that ordered pores ranging between 100 nm and 600 nm in diameter and 2–5 μm in depth can be successfully formed for the range of materials tested. The microstructure of the foils were obtained by electron back-scattered diffraction (EBSD) and linked to development of pits across the material thickness and surface during DA. The role of selective etching of both noble and sacrificial metal phases of the alloy were discussed in light of the competitive surface etching across the range of microstructures and materials tested. PMID:28344253

Effect of Composition of Alloys of Tin-Sodium Systems on Surface Tension

NASA Astrophysics Data System (ADS)

Alchagirov, B. B.; Kyasova, O. Kh.

2018-07-01

The results are presented from investigating the surface tensions of tin-sodium systems, along with original experimental data on the concentration dependences of the surface tensions of 19 tin-based sodium alloys obtained for samples of enhanced purity in a range of compositions with contents of 0.06 to 5.00 at % Na at T = 573 K. It is established that adding small amounts of sodium to tin greatly reduces the surface tensions of the studied melts. Calculations of sodium adsorption in alloys with tin show there is a maximum on the adsorption curve that corresponds to alloys with contents of around 1.5 at % Na in Sn.

Surface Segregation in Ternary Alloys

NASA Technical Reports Server (NTRS)

Good, Brian; Bozzolo, Guillermo H.; Abel, Phillip B.

2000-01-01

Surface segregation profiles of binary (Cu-Ni, Au-Ni, Cu-Au) and ternary (Cu-Au-Ni) alloys are determined via Monte Carlo-Metropolis computer simulations using the BFS method for alloys for the calculation of the energetics. The behavior of Cu or Au in Ni is contrasted with their behavior when both are present. The interaction between Cu and Au and its effect on the segregation profiles for Cu-Au-Ni alloys is discussed.

A survey of some metallographic etching reagents for restoration of obliterated engraved marks on aluminium-silicon alloy surfaces.

PubMed

Uli, Norjaidi; Kuppuswamy, R; Amran, Mohd Firdaus Che

2011-05-20

A brief survey to assess the sensitivity and efficacy of some common etching reagents for revealing obliterated engraved marks on Al-Si alloy surfaces is presented. Experimental observations have recommended use of alternate swabbing of 10% NaOH and 10% HNO(3) on the obliterated surfaces for obtaining the desired results. The NaOH etchant responsible for bringing back the original marks resulted in the deposition of some dark coating that has masked the recovered marks. The coating had been well removed by dissolving it in HNO(3) containing 10-20% acid. However, the above etching procedure was not effective on aluminium (99% purity) and Al-Zn-Mg-Cu alloy surfaces. Also the two reagents (i) immersion in 10% aq. phosphoric acid and (ii) alternate swabbing of 60% HCl and 40% NaOH suggested earlier for high strength Al-Zn-Mg-Cu alloys [23] were quite ineffective on Al-Si alloys. Thus different aluminium alloys needed different etching treatments for successfully restoring the obliterated marks. Al-Si alloys used in casting find wide applications especially in the manufacture of engine blocks of motor vehicles. Hence, the results presented in this paper are of much relevance in serial number restoration problems involving this alloy. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.

Taphonomic and paleoecological change in the large mammal sequence from Boomplaas Cave, western Cape, South Africa.

PubMed

Faith, J Tyler

2013-12-01

Excavations conducted by H.J. Deacon in the 1970s at Boomplaas Cave (BPA) uncovered a stratified sequence of Middle Stone Age (MSA) and Later Stone Age (LSA) deposits spanning the last >65,000 years. This study provides the first comprehensive and integrated taphonomic and paleoecological analysis of the BPA large mammals, with a focus on its implications for understanding human adaptations and environmental changes in southern Africa's Cape Floristic Region (CFR), an area that features prominently in understanding modern human origins. Taphonomic data indicate a complex history of human, carnivore, and raptor accumulation of the large mammal assemblage. The anthropogenic signal is largely absent from the bottom of the sequence (>65,000 years ago), intermediate in MSA and LSA assemblages from ~50,000 to 20,000 years ago, and strong in LSA deposits post-dating the Last Glacial Maximum (LGM). When viewed in the broader CFR context, the inferred occupation history of BPA is consistent with the hypothesis that both MSA and LSA human populations were concentrated on the submerged coastline from ~60,000 to ~20,000 years ago. Intensive occupation following the LGM parallels an apparent increase in regional population densities, which may have been driven in part by rising sea levels. The BPA ungulate assemblage is characterized by the rise and decline of a taxonomically diverse grazing community, which peaks during the LGM. These changes are not correlated with taphonomic shifts, meaning that they are likely driven by environmental factors, namely the expansion and contraction of grassland habitats. Changes in ungulate diversity indicate that effective precipitation was highest during the LGM, corresponding with an intensified winter rainfall system. This is consistent with recent arguments that the LGM in this region may not have been extremely harsh and arid. Copyright © 2013 Elsevier Ltd. All rights reserved.

Safety and Efficacy of a Genetic Vaccine Targeting Telomerase Plus Chemotherapy for the Therapy of Canine B-Cell Lymphoma

PubMed Central

Gavazza, Alessandra; Lubas, George; Fridman, Arthur; Peruzzi, Daniela; Impellizeri, Joseph A.; Luberto, Laura; Marra, Emanuele; Roscilli, Giuseppe; Ciliberto, Gennaro

2013-01-01

Abstract Client-owned pet dogs represent exceptional translational models for advancement of cancer research because they reflect the complex heterogeneity observed in human cancer. We have recently shown that a genetic vaccine targeting dog telomerase reverse transcriptase (dTERT) and based on adenovirus DNA electro-gene-transfer (Ad/DNA-EGT) technology can induce strong cell-mediated immune responses against this tumor antigen and increase overall survival of dogs affected by B-cell lymphosarcoma (LSA) in comparison with historical controls when combined with a cyclophosphamide, vincristine, and prednisone (COP) chemotherapy regimen. Here, we have conducted a double-arm clinical trial with an extended number of LSA patients, measured the antigen-specific immune response, and evaluated potential toxic effects of the immunotherapy along with a follow-up of patients survival for 3.5 years. The immune response was measured by enzyme-linked immunospot assay. The expression of dTERT was quantified by quantitative polymerase chain reaction. Changes in hematological parameters, local/systemic toxicity or organic dysfunction and fever were monitored over time during the treatment. dTERT-specific cell-mediated immune responses were induced in almost all treated animals. No adverse effects were observed in any dog patient that underwent treatment. The overall survival time of vaccine/COP-treated dogs was significantly increased over the COP-only cohort (>76.1 vs. 29.3 weeks, respectively, p<0.0001). There was a significant association between dTERT expression levels in LSA cells and overall survival among vaccinated patients. In conclusion, Ad/DNA-EGT-based cancer vaccine against dTERT in combination with COP chemotherapy is safe and significantly prolongs the survival of LSA canine patients. These data confirm the therapeutic efficacy of dTERT vaccine and support the evaluation of this approach for other cancer types as well as the translation of this approach to human clinical trials. PMID:23902422

Surface functionalization of Cu-Ni alloys via grafting of a bactericidal polymer for inhibiting biocorrosion by Desulfovibrio desulfuricans in anaerobic seawater.

PubMed

Yuan, S J; Liu, C K; Pehkonen, S O; Bai, R B; Neoh, K G; Ting, Y P; Kang, E T

2009-01-01

A novel surface modification technique was developed to provide a copper nickel alloy (M) surface with bactericidal and anticorrosion properties for inhibiting biocorrosion. 4-(chloromethyl)-phenyl tricholorosilane (CTS) was first coupled to the hydroxylated alloy surface to form a compact silane layer, as well as to confer the surface with chloromethyl functional groups. The latter allowed the coupling of 4-vinylpyridine (4VP) to generate the M-CTS-4VP surface with biocidal functionality. Subsequent surface graft polymerization of 4VP, in the presence of benzoyl peroxide (BPO) initiator, from the M-CTS-4VP surface produced the poly(4-vinylpyridine) (P(4VP)) grafted surface, or the M-CTS-P(4VP) surface. The pyridine nitrogen moieties on the M-CTS-P(4VP) surface were quaternized with hexylbromide to produce a high concentration of quaternary ammonium groups. Each surface functionalization step was ascertained by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurements. The alloy with surface-quaternized pyridinium cation groups (N+) exhibited good bactericidal efficiency in a Desulfovibrio desulfuricans-inoculated seawater-based modified Barr's medium, as indicated by viable cell counts and fluorescence microscopy (FM) images of the surface. The anticorrosion capability of the organic layers was verified by the polarization curve and electrochemical impedance spectroscopy (EIS) measurements. In comparison, the pristine (surface hydroxylated) Cu-Ni alloy was found to be readily susceptible to biocorrosion under the same environment.

A parametric study of surface roughness and bonding mechanisms of aluminum alloys with epoxies: a molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Timilsina, Rajendra; Termaath, Stephanie

The marine environment is highly aggressive towards most materials. However, aluminium-magnesium alloys (Al-Mg, specifically, 5xxx series) have exceptionally long service life in such aggressive marine environments. For instance, an Al-Mg alloy, AA5083, is extensively used in naval structures because of its good mechanical strength, formability, seawater corrosion resistance and weldability. However, bonding mechanisms of these alloys with epoxies in a rough surface environment are not fully understood yet. It requires a rigorous investigation at molecular or atomic levels. We performed a molecular dynamics simulation to study an adherend surface preparation and surface bonding mechanisms of Al-Mg alloy (AA5083) with different epoxies by developing several computer models. Various distributions of surface roughness are introduced in the models and performed molecular dynamics simulations. Formation of a beta phase (Al3Mg2) , microstructures, bonding energies at the interface, bonding strengths and durability are investigated. Office of Naval Research.

The fabrication and hydrophobic property of micro-nano patterned surface on magnesium alloy using combined sparking sculpture and etching route

NASA Astrophysics Data System (ADS)

Wu, Yunfeng; Wang, Yaming; Liu, Hao; Liu, Yan; Guo, Lixin; Jia, Dechang; Ouyang, Jiahu; Zhou, Yu

2016-12-01

Magnesium alloy with micro-nano structure roughness surface, can serve as the loading reservoirs of medicine capsule and industrial lubricating oil, or mimic 'lotus leaf' hydrophobic surface, having the potential applications in medical implants, automobile, aerospace and electronic products, etc. Herein, we propose a novel strategy to design a micro-nano structure roughness surface on magnesium alloy using combined microarc sparking sculpture and etching in CrO3 aqueous solution. A hydrophobic surface (as an applied example) was further fabricated by chemical decorating on the obtained patterned magnesium alloy surface to enhance the corrosion resistance. The results show that the combined micro-nano structure of 7-9 μm diameter big pores insetting with nano-scale fine pores was duplicated after etched the sparking sculptured 'over growth' oxide regions towards the magnesium substrate. The micro-nano structure surface was chemically decorated using AgNO3 and stearic acid, which enables the contact angle increased from 60° to 146.8°. The increasing contact angle is mainly attributed to the micro-nano structure and the chemical composition. The hydrophobic surface of magnesium alloy improved the corrosion potential from -1.521 V of the bare magnesium to -1.274 V. Generally, the sparking sculpture and then etching route demonstrates a low-cost, high-efficacy method to fabricate a micro-nano structure hydrophobic surface on magnesium alloy. Furthermore, our research on the creating of micro-nano structure roughness surface and the hydrophobic treatment can be easily extended to the other metal materials.

Laser polishing of additive manufactured Ti alloys

NASA Astrophysics Data System (ADS)

Ma, C. P.; Guan, Y. C.; Zhou, W.

2017-06-01

Laser-based additive manufacturing has attracted much attention as a promising 3D printing method for metallic components in recent years. However, surface roughness of additive manufactured components has been considered as a challenge to achieve high performance. In this work, we demonstrate the capability of fiber laser in polishing rough surface of additive manufactured Ti-based alloys as Ti-6Al-4V and TC11. Both as-received surface and laser-polished surfaces as well as cross-section subsurfaces were analyzed carefully by White-Light Interference, Confocal Microscope, Focus Ion Beam, Scanning Electron Microscopy, Energy Dispersive Spectrometer, and X-ray Diffraction. Results revealed that as-received Ti-based alloys with surface roughness more than 5 μm could be reduce to less than 1 μm through laser polishing process. Moreover, microstructure, microhardness and wear resistance of laser-polished zone was investigated in order to examine the thermal effect of laser polishing processing on the substrate of additive manufactured Ti alloys. This proof-of-concept process has the potential to effectively improve the surface roughness of additive manufactured metallic alloy by local polishing method without damage to the substrate.

Surface tension measurement of undercooled liquid Ni-based multicomponent alloys

NASA Astrophysics Data System (ADS)

Chang, J.; Wang, H. P.; Zhou, K.; Wei, B.

2012-09-01

The surface tensions of liquid ternary Ni-5%Cu-5%Fe, quaternary Ni-5%Cu-5%Fe-5%Sn and quinary Ni-5%Cu-5%Fe-5%Sn-5%Ge alloys were determined as a function of temperature by the electromagnetic levitation oscillating drop method. The maximum undercoolings obtained in the experiments are 272 (0.15T L), 349 (0.21T L) and 363 K (0.22T L), respectively. For all the three alloys, the surface tension decreases linearly with the rise of temperature. The surface tension values are 1.799, 1.546 and 1.357 N/m at their liquidus temperatures of 1719, 1644 and 1641 K. Their temperature coefficients are -4.972 × 10-4, -5.057 × 10-4 and -5.385 × 10-4 N/m/K. It is revealed that Sn and Ge are much more efficient than Cu and Fe in reducing the surface tension of Ni-based alloys. The addition of Sn can significantly enlarge the maximum undercooling at the same experimental condition. The viscosity of the three undercooled liquid alloys was also derived from the surface tension data.

Characterization and corrosion study of NiTi laser surface alloyed with Nb or Co

NASA Astrophysics Data System (ADS)

Ng, K. W.; Man, H. C.; Yue, T. M.

2011-02-01

The interest in NiTi alloys for medical applications has been steadily growing in recent years because of its biocompatibility, superelasticity and shape memory characteristics. However, the high Ni content in NiTi alloys is still a concern for its long-term applications in the human body. The release of Ni ion into the human body might cause serious problems, as Ni is capable of eliciting toxic and allergic responses. In view of this, surface modification to reduce the surface content of Ni and to improve the corrosion resistance, both of which would reduce Ni release, is an important step in the development of NiTi implants. In the present study, NiTi was surface alloyed with Nb or Co by laser processing. The fine dendritic structure characteristic of laser processing has been described in terms of rapid solidification. The amount of surface elemental Ni was reduced to 10% and 35% for the Nb-alloyed and Co-alloyed layer, respectively. The corrosion resistance in Hanks' solution (a simulated body fluid) was increased as evidenced by a reduced passive current density and a higher pitting potential for both the Nb- and Co-alloyed specimens. The composition and hardness profiles along the depth of the modified layer were correlated with the distribution of the dendrites. The microhardness of the alloyed layers was around 700-800 Hv, which was about four times that of the untreated NiTi specimens.

Surface modification of titanium and titanium alloys by ion implantation.

PubMed

Rautray, Tapash R; Narayanan, R; Kwon, Tae-Yub; Kim, Kyo-Han

2010-05-01

Titanium and titanium alloys are widely used in biomedical devices and components, especially as hard tissue replacements as well as in cardiac and cardiovascular applications, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet all of the clinical requirements. Therefore, to improve the biological, chemical, and mechanical properties, surface modification is often performed. In view of this, the current review casts new light on surface modification of titanium and titanium alloys by ion beam implantation. (c) 2010 Wiley Periodicals, Inc.

Improving tribological properties of Ti-5Zr-3Sn-5Mo-15Nb alloy by double glow plasma surface alloying

NASA Astrophysics Data System (ADS)

Guo, Lili; Qin, Lin; Kong, Fanyou; Yi, Hong; Tang, Bin

2016-12-01

Molybdenum, an alloying element, was deposited and diffused on Ti-5Zr-3Sn-5Mo-15Nb (TLM) substrate by double glow plasma surface alloying technology at 900, 950 and 1000 °C. The microstructure, composition distribution and micro-hardness of the Mo modified layers were analyzed. Contact angles on deionized water and wear behaviors of the samples against corundum balls in simulated human body fluids were investigated. Results show that the surface microhardness is significantly enhanced after alloying and increases with treated temperature rising, and the contact angles are lowered to some extent. More importantly, compared to as-received TLM alloy, the Mo modified samples, especially the one treated at 1000 °C, exhibit the significant improvement of tribological properties in reciprocating wear tests, with lower specific wear rate and friction coefficient. To conclude, Mo alloying treatment is an effective approach to obtain excellent comprehensive properties including optimal wear resistance and improved wettability, which ensure the lasting and safety application for titanium alloys as the biomedical implants.

Controlling Heterogeneous Catalysis of Water Dissociation Using Cu-Ni Bimetallic Alloy Surfaces: A Quantum Dynamics Study.

PubMed

Ray, Dhiman; Ghosh, Smita; Tiwari, Ashwani Kumar

2018-06-07

Copper-Nickel bimetallic alloys are emerging heterogeneous catalysts for water dissociation which is the rate determining step of industrially important Water Gas Shift (WGS) reaction. Yet, the detailed quantum dynamics studies of water-surface scattering in literature are limited to pure metal surfaces. We present here, a three dimensional wave-packet dynamics study of water dissociation on Cu-Ni alloy surfaces, using a pseudo diatomic model of water on a London-Eyring-Polanyi-Sato (LEPS) potential energy surface in order to study the effect of initial vibration, rotation and orientation of water molecule on reactivity. For all the chosen surfaces reactivity increases significantly with vibrational excitation. In general, for lower vibrational states the reactivity increases with increasing rotational excitation but it decreases in higher vibrational states. Molecular orientation strongly affects reactivity by helping the molecule to align along the reaction path at higher vibrational states. For different alloys, the reaction probability follows the trend of barrier heights and the surfaces having all Ni atoms in the uppermost layer are much more reactive than the ones with Cu atoms. Hence the nature of the alloy surface and initial quantum state of the incoming molecule significantly influence the reactivity in surface catalyzed water dissociation.

Surface characterization of implant materials c.p. Ti, Ti-6Al-7Nb and Ti-6Al-4V with different pretreatments.

PubMed

Sittig, C; Textor, M; Spencer, N D; Wieland, M; Vallotton, P H

1999-01-01

The biocompatibility of commercially pure titanium and its alloys is closely related to their surface properties, with both the composition of the protecting oxide film and the surface topography playing an important role. Surfaces of commercially pure titanium and of the two alloys Ti-6Al-7Nb and Ti-6Al-4V (wt %) have been investigated following three different pretreatments: polishing, nitric acid passivation and pickling in nitric acid-hydrogen fluoride. Nitric acid treatment is found to substantially reduce the concentration of surface contaminants present after polishing. The natural 4-6 nm thick oxide layer on commercially pure titanium is composed of titanium oxide in different oxidation states (TiO2, Ti2O3 and TiO), while for the alloys, aluminium and niobium or vanadium are additionally present in oxidized form (Al2O3, Nb2O5 or V-oxides). The concentrations of the alloying elements at the surface are shown to be strongly dependent on the pretreatment process. While pickling increases the surface roughness of both commercially pure titanium and the alloys, different mechanisms appear to be involved. In the case of commercially pure titanium, the dissolution rate depends on grain orientation, whereas in the case of the two alloys, selective alpha-phase dissolution and enrichment of the beta-phase appears to occur. Copyright 1999 Kluwer Academic Publishers

Hierarchical Pd-Sn alloy nanosheet dendrites: an economical and highly active catalyst for ethanol electrooxidation.

PubMed

Ding, Liang-Xin; Wang, An-Liang; Ou, Yan-Nan; Li, Qi; Guo, Rui; Zhao, Wen-Xia; Tong, Ye-Xiang; Li, Gao-Ren

2013-01-01

Hierarchical alloy nanosheet dendrites (ANSDs) are highly favorable for superior catalytic performance and efficient utilization of catalyst because of the special characteristics of alloys, nanosheets, and dendritic nanostructures. In this paper, we demonstrate for the first time a facile and efficient electrodeposition approach for the controllable synthesis of Pd-Sn ANSDs with high surface area. These synthesized Pd-Sn ANSDs exhibit high electrocatalytic activity and superior long-term cycle stability toward ethanol oxidation in alkaline media. The enhanced electrocataytic activity of Pd-Sn ANSDs may be attributed to Pd-Sn alloys, nanosheet dendrite induced promotional effect, large number of active sites on dendrite surface, large surface area, and good electrical contact with the base electrode. Because of the simple implement and high flexibility, the proposed approach can be considered as a general and powerful strategy to synthesize the alloy electrocatalysts with high surface areas and open dendritic nanostructures.

Manufacturing of Fe-Mn-C surface alloys by Nd:YAG and CO2 laser processing

NASA Astrophysics Data System (ADS)

Pelletier, Jean-Marc.; Pilloz, Michel; Sallamand, P.; Malau, V.; Grevey, Dominique F.; Vannes, A. B.

1996-09-01

In order to obtain a good behavior in dynamic conditions, it is often necessary to manufacture surface alloys with conflicting properties, for example a high ductility combined with a high hardness or a high yield stress. Iron- base alloys with appropriated contents of manganese and carbon can be candidates for such requirements. Particular alloys, known as Hadfield steels, are of major interest. By using either Nd-YAG or CO2 lasers, and by either injection of specific powder or remelting of a predeposited layer with a suitable composition, sound surface layers have been manufactured on steels with either a low or a high carbon content. These coatings with an austenitic structure have an elevated yield stress. After a presentation of the experimental procedures, the new surface alloys are characterized by using metallurgical observations, chemical analysis and mechanical tests.

Hierarchical Pd-Sn Alloy Nanosheet Dendrites: An Economical and Highly Active Catalyst for Ethanol Electrooxidation

PubMed Central

Ding, Liang-Xin; Wang, An-Liang; Ou, Yan-Nan; Li, Qi; Guo, Rui; Zhao, Wen-Xia; Tong, Ye-Xiang; Li, Gao-Ren

2013-01-01

Hierarchical alloy nanosheet dendrites (ANSDs) are highly favorable for superior catalytic performance and efficient utilization of catalyst because of the special characteristics of alloys, nanosheets, and dendritic nanostructures. In this paper, we demonstrate for the first time a facile and efficient electrodeposition approach for the controllable synthesis of Pd-Sn ANSDs with high surface area. These synthesized Pd-Sn ANSDs exhibit high electrocatalytic activity and superior long-term cycle stability toward ethanol oxidation in alkaline media. The enhanced electrocataytic activity of Pd-Sn ANSDs may be attributed to Pd-Sn alloys, nanosheet dendrite induced promotional effect, large number of active sites on dendrite surface, large surface area, and good electrical contact with the base electrode. Because of the simple implement and high flexibility, the proposed approach can be considered as a general and powerful strategy to synthesize the alloy electrocatalysts with high surface areas and open dendritic nanostructures. PMID:23383368

60NiTi Alloy for Tribological and Biomedical Surface Engineering Applications

NASA Astrophysics Data System (ADS)

Ingole, Sudeep

2013-06-01

60NiTi is an alloy with 60 wt% of nickel (Ni) and 40 wt% of titanium (Ti). This alloy was developed in the 1950s at the Naval Ordnance Laboratory (NOL) along with 55NiTi (55 wt% of Ni and 45 wt% of Ti). Both of these alloys exhibit the shape memory effect to different extents. The unique properties of 60NiTi, which are suitable for surface engineering (tribological) applications, are enumerated here. With appropriate heat treatment, this alloy can achieve high hardness (between Rc 55 and Rc 63). It has very good corrosion resistance and is resilient. Machinable before its final heat treatment, this alloy can be ground to fine surface finish and to tight dimensions. At one time, due to the popularity and wider applications of 55NiTi, the study of 60NiTi suffered. Recently, 60NiTi alloy gained some technological advantages due to advanced materials synthesis processes and progress in surface engineering. A feasibility study of 60NiTi bearings for space application has shown promise for its further development and suitability for other tribological applications. This report focuses on an overview of the properties and potential tribological and biomedical applications of 60NiTi.

Facile formation of biomimetic color-tuned superhydrophobic magnesium alloy with corrosion resistance.

PubMed

Ishizaki, Takahiro; Sakamoto, Michiru

2011-03-15

The design of color-tuned magnesium alloy with anticorrosive properties and damping capacity was created by means of a simple and inexpensive method. The vertically self-aligned nano- and microsheets were formed on magnesium alloy AZ31 by a chemical-free immersion process in ultrapure water at a temperature of 120 °C, resulting in the color expression. The color changed from silver with metallic luster to some specific colors such as orange, green, and orchid, depending on the immersion time. The color-tuned magnesium alloy showed anticorrosive performance and damping capacity. In addition, the colored surface with minute surface textures was modified with n-octadecyltrimethoxysilane (ODS), leading to the formation of color-tuned superhydrophobic surfaces. The corrosion resistance of the color-tuned superhydrophobic magnesium alloy was also investigated using electrochemical potentiodynamic measurements. Moreover, the color-tuned superhydrophobic magnesium alloy showed high hydrophobicity not just for pure water but also for corrosive liquids, such as acidic, basic, and some aqueous salt solutions. In addition, the American Society for Testing and Materials (ASTM) standard D 3359-02 cross cut tape test was performed to investigate the adhesion of the color-tuned superhydrophobic film to the magnesium alloy surface.

Inhibiting the corrosion of MNZh 5-1 alloy in neutral solutions of 5-chloro-1,2,3-benzotrialzol

NASA Astrophysics Data System (ADS)

Kuznetsov, Yu. I.; Agafonkina, M. O.; Andreeva, N. P.; Arkhipushkin, I. A.; Kazansky, L. P.

2017-11-01

The adsorption and protective properties of 5-chloro-1,2,3-benzotriazol (5-chloro-BTA) are studied in relation to MNZh 5-1 alloy in a chloride borate buffer solution with pH 7.4. It is shown that this inhibitor can stabilize the passive state of the alloy at a concentration of 0.12 mmol/g. The adsorption of 5-chloro-BTA on a surface of MNZh 5-1 alloy is polymolecular; the free energy of adsorption is about 80 kJ/mol. The advantages of adsorption and protective properties of 5-chloro-BTA compared to BTA on both MNZh 5-1 alloy and the metals contained in the alloy (Ni, Cu) are shown. XPS data indicate a 5-chloro-BTA monolayer formed on the surface of the alloy. This monolayer was composed of inhibitor molecules, which are normally oriented toward a surface and are not removed during ultrasonic washing of the electrode.

Effects of Cr Content and Surface Finishes on Oxidation Behaviors of Austenitic Fe-Cr-Ni Alloys Exposed in Supercritical Water (SCW)

NASA Astrophysics Data System (ADS)

Xing, Bo

The scope of this work was to characterize the corrosion resistance of candidate austenitic alloys in supercritical water for the use of the fuel cladding material within the Canadian supercritical water-cooled reactor (SCWR) concept. A series of Commercial austenitic stainless steels (SS) and alloys were exposed to supercritical water for different exposure times up to 500 hours. Two surface finishes were applied - a coarse grinding with 120 grit abrasive or polishing with either 1200 grit or 0.05 microm alumina suspension. Gravimetric measurements and electron microscopy techniques were used to evaluate the oxidation behaviors of tested alloys. The superior corrosion resistance of alloy 310S was benefited from a critical Cr content of 25 wt.%. The surface finish played a significant role to vary the oxidation behavior of alloys containing slightly less than the critical Cr content. However, Oxide exfoliation was observed on low Cr content alloys.

Structural Evolution of a Ni Alloy Surface During High-Temperature Oxidation

DOE PAGES

Oleksak, Richard P.; Carney, Casey S.; Holcomb, Gordon R.; ...

2017-11-20

We show that considerable structural transformations occur at a Ni alloy surface during the transient stages of high-temperature oxidation. This was demonstrated by exposing the alloy to high-temperature CO 2 for short times at both atmospheric and supercritical pressures. A protective Cr-rich oxide layer formed after only 5 min at 700 °C and persisted for longer exposures up to 500 h. Voids formed and grew over time by the condensation of metal vacancies generated during oxidation, while the alloy surface recrystallized after sufficient oxidation had occurred. The oxygen potential established at the oxide/alloy interface led to oxidation along the newlymore » formed grain boundaries as well as adjacent to and inside of the voids. Al, the most stable oxide-former and present at low concentration in the alloy, was preferentially oxidized in these regions. Furthermore, the results provide an improved understanding of the internal oxidation of Al and its role in enhancing scale adhesion for this class of Ni alloys.« less

Microstructure and corrosion resistance of sputter-deposited titanium-chromium alloy coatings

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

Landolt, D.; Robyr, C.; Mettraux, P.

1998-10-01

Titanium, chromium, and titanium-chromium alloy coatings were sputter-deposited to study their corrosion behaviors in relation to microstructure and composition. Silicon substrates were used to study the effect of alloying on intrinsic corrosion resistance of the coating materials, and brass substrates were used to study the effect of alloying on the penetrating porosity of the coatings. Corrosion behavior was characterized using linear sweep voltammetry. The crystal structure of the coatings was examined by x-ray diffraction (XRD) and the microstructure by scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) was used to estimate the real surface area of the coatings. Results showedmore » alloying of titanium with chromium greatly influenced microstructure of the coatings. Alloying led to deposits of higher apparent density and, in some cases, to an x-ray amorphous structure. Alloy coatings showed significantly lower corrosion currents than the constituting metals. The effect was attributed to a smoother surface topography. When corrected of differences in real surface area, the intrinsic corrosion rate of the alloy coatings did not differ significantly from that of the constituting metals. Alloy coatings deposited on brass exhibited a lower porosity than titanium or chromium metal coatings produced under identical conditions.« less

Biodegradable magnesium alloys for orthopaedic applications: A review on corrosion, biocompatibility and surface modifications.

PubMed

Agarwal, Sankalp; Curtin, James; Duffy, Brendan; Jaiswal, Swarna

2016-11-01

Magnesium (Mg) and its alloys have been extensively explored as potential biodegradable implant materials for orthopaedic applications (e.g. Fracture fixation). However, the rapid corrosion of Mg based alloys in physiological conditions has delayed their introduction for therapeutic applications to date. The present review focuses on corrosion, biocompatibility and surface modifications of biodegradable Mg alloys for orthopaedic applications. Initially, the corrosion behaviour of Mg alloys and the effect of alloying elements on corrosion and biocompatibility is discussed. Furthermore, the influence of polymeric deposit coatings, namely sol-gel, synthetic aliphatic polyesters and natural polymers on corrosion and biological performance of Mg and its alloy for orthopaedic applications are presented. It was found that inclusion of alloying elements such as Al, Mn, Ca, Zn and rare earth elements provides improved corrosion resistance to Mg alloys. It has been also observed that sol-gel and synthetic aliphatic polyesters based coatings exhibit improved corrosion resistance as compared to natural polymers, which has higher biocompatibility due to their biomimetic nature. It is concluded that, surface modification is a promising approach to improve the performance of Mg-based biomaterials for orthopaedic applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Investigation Of A Tin-Lithium Alloy As A Liquid Plasma-Facing Material

NASA Astrophysics Data System (ADS)

Sandefur, Heather; Ruzic, David; Kolasinski, Robert; Buchenauer, Dean; Sandia National Laboratories Collaboration; University of Illinois Collaboration

2017-10-01

Sn-Li is a low melting-point alloy that has been identified as a material with favorable performance in plasma material interaction studies. While lithium is a low Z material with a demonstrated ability to absorb impinging ions, pure lithium is plagued by high evaporation rates in the liquid phase. The Sn-Li alloy is a more stable alternative that provides a lower rate of evaporative flux due to the high vapor pressure of tin. In the liquid phase, the bulk segregation of lithium to the surface of the material has also been observed. While the alloy is of considerable interest, little data has been collected on its surface chemistry in a plasma environment. In order to expand the existing body of knowledge in this area, samples of an 80 percent Sn-20 percent Li alloy were prepared and analyzed in order to assess the surface composition and degree of lithium segregation in the liquid phase. The Angle-Resolved Ion Energy Spectrometer (ARIES) at Sandia National Laboratories was used to probe the surfaces of the alloy using the low energy ion scattering method. The lithium coverage at the surface was measured, and the material's affinity for hydrogen chemisorption was investigated.

Reciprocal interaction between dental alloy biocorrosion and Streptococcus mutans virulent gene expression.

PubMed

Zhang, Songmei; Qiu, Jing; Ren, Yanfang; Yu, Weiqiang; Zhang, Fuqiang; Liu, Xiuxin

2016-04-01

Corrosion of dental alloys is a major concern in dental restorations. Streptococcus mutans reduces the pH in oral cavity and induces demineralization of the enamel as well as corrosion of restorative dental materials. The rough surfaces of dental alloys induced by corrosion enhance the subsequent accumulation of plaque. In this study, the corrosion process of nickel-chromium (Ni-Cr) and cobalt-chromium (Co-Cr) alloys in a nutrient-rich medium containing S. mutans was studied using inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS) and electrochemical corrosion test. Our results showed that the release of Ni and Co ions increased, particularly after incubation for 3 days. The electrochemical corrosion results showed a significant decrease in the corrosion resistance (Rp) value after the alloys were immersed in the media containing S. mutans for 3 days. Correspondingly, XPS revealed a reduction in the relative dominance of Ni, Co, and Cr in the surface oxides after the alloys were immersed in the S. mutans culture. After removal of the biofilm, the pre-corroded alloys were re-incubated in S. mutans medium, and the expressions of genes associated with the adhesion and acidogenesis of S. mutans, including gtfBCD, gbpB, fif and ldh, were evaluated by detecting the mRNA levels using real-time reverse transcription polymerase chain reaction (RT-PCR). We found that the gtfBCD, gbpB, ftf and Idh expression of S. mutans were noticeably increased after incubation with pre-corroded alloys for 24 h. This study demonstrated that S. mutans enhanced the corrosion behavior of the dental alloys, on the other hand, the presence of corroded alloy surfaces up-regulated the virulent gene expression in S. mutans. Compared with smooth surfaces, the rough corroded surfaces of dental alloys accelerated the bacteria-adhesion and corrosion process by changing the virulence gene expression of S. mutans.

Alloyed surfaces: New substrates for graphene growth

NASA Astrophysics Data System (ADS)

Tresca, C.; Verbitskiy, N. I.; Fedorov, A.; Grüneis, A.; Profeta, G.

2017-11-01

We report a systematic ab-initio density functional theory investigation of Ni(111) surface alloyed with elements of group IV (Si, Ge and Sn), demonstrating the possibility to use it to grow high quality graphene. Ni(111) surface represents an ideal substrate for graphene, due to its catalytic properties and perfect matching with the graphene lattice constant. However, Dirac bands of graphene growth on Ni(111) are completely destroyed due to the strong hybridization between carbon pz and Ni d orbitals. Group IV atoms, namely Si, Ge and Sn, once deposited on Ni(111) surface, form an ordered alloyed surface with √{ 3} ×√{ 3} -R30° reconstruction. We demonstrate that, at variance with the pure Ni(111) surface, alloyed surfaces effectively decouple graphene from the substrate, resulting unstrained due to the nearly perfect lattice matching and preserves linear Dirac bands without the strong hybridization with Ni d states. The proposed surfaces can be prepared before graphene growth without resorting on post-growth processes which necessarily alter the electronic and structural properties of graphene.

Effect of different alloyed layers on the high temperature oxidation behavior of newly developed Ti 2AlNb-based alloys

NASA Astrophysics Data System (ADS)

Wu, Hongyan; Zhang, Pingze; Zhao, Haofeng; Wang, Ling; Xie, Aigen

2011-01-01

The application of titanium aluminide orthorhombic alloys (O-phase alloys) as potential materials in aircraft and jet engines was limited by their poor oxidation resistance at high temperature. The Ti 2AlNb-based alloys were chromised (Cr), chromium-tungstened (Cr-W) and nickel-chromised (Ni-Cr) by the double glow plasma surface alloying process to improve their high temperature oxidation resistance. The discontinuous oxidative behavior of Cr, Cr-W and Ni-Cr alloyed layers on Ti 2AlNb-based alloy at 1093 K was explored in this study. After exposing at 1093 K, the TiO 2 layer was formed on the bare alloy and accompanied by the occurrence of crack, which promoted oxidation rate. The oxidation behavior of Ti 2AlNb-based alloys was improved by surface alloying due to the formation of protective Al 2O 3 scale or continuous and dense NiCr 2O 4 film. The Ni-Cr alloyed layer presented the best high-temperature oxidation resistance among three alloyed layers.

Effects of recasting on the biocompatibility of a Ni-Cr alloy.

PubMed

Zhang, Chang Yuan; Cheng, Hui; Lin, Dong Hong; Zheng, Ming; Ozcan, Mutlu; Zhao, Wei; Yu, Hao

2012-01-01

To evaluate the effects of recasting on the biocompatibility of a commercially available Ni-Cr alloy. The alloy tested was cast and subsequently recast four more times. For each cast condition, 24 disk shaped specimens were fabricated (5 mm in diameter, 0.5 mm in thickness). All the recasting was performed without adding new alloy. After the first cast and following each recast, the surface composition and microstructure of the alloy were determined using an X-ray fluorescence spectrometer and optical microscope, respectively. The in vitro cytotoxicity and in vivo mucous irritation potential of the cast and recast Ni-Cr alloy were investigated. The results were statistically analysed at the significance level of 0.05. Recasting neither yielded to cytotoxicity or to changes in the surface composition of the Ni-Cr alloy tested. However, an increase in impurities and porosity of the surface structure was observed with recasting. Also, the segregation of the impurities to grain boundaries was evident after multiple castings. After the fourth recast, the alloys showed significantly greater mucosal irritation than the control. After fourth recast, the alloy of this type may contribute to mucosal inflammation. Furthermore, there is a need for diverse methods addressing different biological endpoints for the evaluation of dental alloys.

Biocompatibility of the micro-patterned NiTi surface produced by femtosecond laser

NASA Astrophysics Data System (ADS)

Liang, Chunyong; Wang, Hongshui; Yang, Jianjun; Li, Baoe; Yang, Yang; Li, Haipeng

2012-11-01

Biocompatibility of the micro-patterned NiTi surface produced by femtosecond laser (FSL) was studied in this work. The surface characteristics of the laser treated NiTi alloys were investigated by scanning electron microscopy (SEM), atom force microscopy (AFM), X-ray diffractometry (XRD) and X-ray photoelectron spectrum (XPS). The biocompatibility was evaluated by in vitro cell culture test. The results showed that, grooves, ripples, which covered by nanoparticles were formed on the sample surfaces, and the Ni/Ti ratio on the alloy surface increased with increasing laser energy. The crystal structure was not changed by laser treatment. However, the cell culture test proved that the micro-patterns induced by FSL were beneficial to improve the biocompatibility of NiTi alloys: the growth of osteoblasts oriented along the grooves, a large amount of synapses and filopodias were formed due to the ripples, holes and nanoparticles on the alloy surface, and the proliferation rate and alkaline phosphatase (ALP) content of cells were increased after FSL treatment. However, due to the toxicity of Ni ions on cell growth, the NiTi alloy surface should not be treated by laser fluence of more than 3.82 J/cm2 to obtain the ideal biocompatibility.

Performance Improvement of V-Fe-Cr-Ti Solid State Hydrogen Storage Materials in Impure Hydrogen Gas.

PubMed

Ulmer, Ulrich; Oertel, Daria; Diemant, Thomas; Bonatto Minella, Christian; Bergfeldt, Thomas; Dittmeyer, Roland; Behm, R Jürgen; Fichtner, Maximilian

2018-01-17

Two approaches of engineering surface structures of V-Ti-based solid solution hydrogen storage alloys are presented, which enable improved tolerance toward gaseous oxygen (O 2 ) impurities in hydrogen (H 2 ) gas. Surface modification is achieved through engineering lanthanum (La)- or nickel (Ni)-rich surface layers with enhanced cyclic stability in an H 2 /O 2 mixture. The formation of a Ni-rich surface layer does not improve the cycling stability in H 2 /O 2 mixtures. Mischmetal (Mm, a mixture of La and Ce) agglomerates are observed within the bulk and surface of the alloy when small amounts of this material are added during arc melting synthesis. These agglomerates provide hydrogen-transparent diffusion pathways into the bulk of the V-Ti-Cr-Fe hydrogen storage alloy when the remaining oxidized surface is already nontransparent for hydrogen. Thus, the cycling stability of the alloy is improved in an O 2 -containing hydrogen environment as compared to the same alloy without addition of Mm. The obtained surface-engineered storage material still absorbs hydrogen after 20 cycles in a hydrogen-oxygen mixture, while the original material is already deactivated after 4 cycles.

Fabrication of superhydrophobic surface with improved corrosion inhibition on 6061 aluminum alloy substrate

NASA Astrophysics Data System (ADS)

Li, Xuewu; Zhang, Qiaoxin; Guo, Zheng; Shi, Tian; Yu, Jingui; Tang, Mingkai; Huang, Xingjiu

2015-07-01

This work has developed a simple and low-cost method to render 6061 aluminum alloy surface superhydrophobicity and excellent corrosion inhibition. The superhydrophobic aluminum alloy surface has been fabricated by hydrochloric acid etching, potassium permanganate passivation and fluoroalkyl-silane modification. Meanwhile, the effect of the etching and passivation time on the wettability and corrosion inhibition of the fabricated surface has also been investigated. Results show that with the etching time of 6 min and passivation time of 180 min the fabricated micro/nano-scale terrace-like hierarchical structures accompanying with the nanoscale coral-like network bulge structures after being modified can result in superhydrophobicity with a water contact angle (CA) of 155.7°. Moreover, an extremely weak adhesive force to droplets as well as an outstanding self-cleaning behavior of the superhydrophobic surface has also been proved. Finally, corrosion inhibition in seawater of the as-prepared aluminum alloy surface is characterized by potentiodynamic polarization curves and electrochemical impedance spectroscopy. Evidently, the fabricated superhydrophobic surface attained an improved corrosion inhibition efficiency of 83.37% compared with the traditional two-step processing consisting of etching and modification, which will extend the further applications of aluminum alloy especially in marine engineering fields.

Influence of Primary Water Chemistry on Oxides Formed on Alloy 600 and Alloy 690

NASA Astrophysics Data System (ADS)

Devine, Thomas M.

The results of in situ SERS investigations of Alloys' 600 and 690 surface films were combined with the results of a number of ex situ studies conducted by other researchers who used a variety of experimental techniques. Comparing the results of different investigations revealed the surface films' composition and microstructure were most sensitive to alloy composition and the concentrations of aqueous metal cations (especially Fe+2).

The Nature of Surface Oxides on Corrosion-Resistant Nickel Alloy Covered by Alkaline Water

PubMed Central

2010-01-01

A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline water layers are on the alloy surface in order to account for the relative inertness of the nickel alloy in corrosive environments. PMID:20672134

Surface amorphization of NiTi alloy induced by Ultrasonic Nanocrystal Surface Modification for improved mechanical properties.

PubMed

Ye, Chang; Zhou, Xianfeng; Telang, Abhishek; Gao, Hongyu; Ren, Zhencheng; Qin, Haifeng; Suslov, Sergey; Gill, Amrinder S; Mannava, S R; Qian, Dong; Doll, Gary L; Martini, Ashlie; Sahai, Nita; Vasudevan, Vijay K

2016-01-01

We report herein the effects of Ultrasonic Nano-crystal Surface Modification (UNSM), a severe surface plastic deformation process, on the microstructure, mechanical (hardness, wear), wettability and biocompatibility properties of NiTi shape memory alloy. Complete surface amorphization of NiTi was achieved by this process, which was confirmed by X-ray diffraction and high-resolution transmission electron microscopy. The wear resistance of the samples after UNSM processing was significantly improved compared with the non-processed samples due to increased surface hardness of the alloy by this process. In addition, cell culture study demonstrated that the biocompatibility of the samples after UNSM processing has not been compromised compared to the non-processed sample. The combination of high wear resistance and good biocompatibility makes UNSM an appealing process for treating alloy-based biomedical devices. Copyright © 2015 Elsevier Ltd. All rights reserved.

Method for Surface Texturing Titanium Products

NASA Technical Reports Server (NTRS)

Banks, Bruce A. (Inventor)

1998-01-01

The present invention teaches a method of producing a textured surface upon an arbitrarily configured titanium or titanium alloy object for the purpose of improving bonding between the object and other materials such as polymer matrix composites and/or human bone for the direct in-growth of orthopaedic implants. The titanium or titanium alloy object is placed in an electrolytic cell having an ultrasonically agitated solution of sodium chloride therein whereby a pattern of uniform "pock mark" like pores or cavities are produced upon the object's surface. The process is very cost effective compared to other methods of producing rough surfaces on titanium and titanium alloy components. The surface textures produced by the present invention are etched directly into the parent metal at discrete sites separated by areas unaffected by the etching process. Bonding materials to such surface textures on titanium or titanium alloy can thus support a shear load even if adhesion of the bonding material is poor.

Analysis of Surface and Bulk Behavior in Ni-Pd Alloys

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Noebe, Rondald D.

2003-01-01

The most salient features of the surface structure and bulk behavior of Ni-Pd alloys have been studied using the BFS method for alloys. Large-scale atomistic simulations were performed to investigate surface segregation profiles as a function of temperature, crystal face, and composition. Pd enrichment of the first layer was observed in (111) and (100) surfaces, and enrichment of the top two layers occurred for (110) surfaces. In all cases, the segregation profile shows alternate planes enriched and depleted in Pd. In addition, the phase structure of bulk Ni-Pd alloys as a function of temperature and composition was studied. A weak ordering tendency was observed at low temperatures, which helps explain the compositional oscillations in the segregation profiles. Finally, based on atom-by-atom static energy calculations, a comprehensive explanation for the observed surface and bulk features will be presented in terms of competing chemical and strain energy effects.

The corrosivity and passivity of sputtered Mg-Ti alloys

DOE PAGES

Song, Guang -Ling; Unocic, Kinga A.; Meyer, III, Harry M.; ...

2015-11-30

Our study explored the possibility of forming a “stainless” Mg–Ti alloy. The electrochemical behavior of magnetron-sputtered Mg–Ti alloys was measured in a NaCl solution, and the surface films on the alloys were examined by XPS, SEM and TEM. Increased corrosion resistance was observed with increased Ti content in the sputtered Mg–Ti alloys, but passive-like behavior was not reached until the Ti level (atomic %) was higher than the Mg level. Moreover, the surface film that formed on sputtered Mg–Ti based alloys in NaCl solution was thick, discontinuous and non-protective, whereas a thin, continuous and protective Mg and Ti oxide filmmore » was formed on a sputtered Ti–Mg based alloy.« less

Atomically Visualizing Elemental Segregation-Induced Surface Alloying and Restructuring

DOE PAGES

Zou, Lianfeng; Li, Jonathan; Zakharov, Dmitri; ...

2017-12-01

Using in situ transmission electron microscopy that spatially and temporally resolves the evolution of the atomic structure in the surface and subsurface regions, we Find that the surface segregation of Au atoms in a Cu(Au) solid solution results in the nucleation and growth of a (2 × 1) missing-row reconstructed, half-unit-cell thick L1 2 Cu 3Au(110) surface alloy. Our in situ electron microscopy observations and atomistic simulations demonstrate that the (2 × 1) reconstruction of the Cu 3Au(110) surface alloy remains as a stable surface structure as a result of the favored Cu-Au diatom configuration.

Investigation on wear resistance and corrosion resistance of electron beam cladding co-alloy coating on Inconel617

NASA Astrophysics Data System (ADS)

Liu, Hailang; Zhang, Guopei; Huang, Yiping; Qi, Zhengwei; Wang, Bo; Yu, Zhibiao; Wang, Dezhi

2018-04-01

To improve surface properties of Inconel 617 alloy (referred to as 617 alloy), co-alloy coating metallurgically bonded to substrate was prepared on the surface of 617 alloy by electron beam cladding. The microstructure, phase composition, microhardness, tribological properties and corrosion resistance of the coatings were investigated. The XRD results of the coatings reinforced by co-alloy (Co800) revealed the presence of γ-Co, CoCx and Cr23C6 phase as matrix and new metastable phases of Cr2Ni3 and Co3Mo2Si. These hypoeutectic structures contain primary dendrites and interdendritic eutectics. The metallurgical bonding forms well between the cladding layer and the matrix of 617 alloy. In most studied conditions, the co-alloy coating displays a better hardness, tribological performance, i.e., lower coefficient of frictions and wear rates, corrosion resistance in 1 mol L‑1 HCl solution, than the 617 alloy.

Surface segregation in HAYNES 230 alloy

NASA Astrophysics Data System (ADS)

Pop, D.; Wolski, K.

2006-12-01

The surface segregation in the Ni-based alloy HAYNES 230 was studied by Auger Electron Spectroscopy and X-ray Photoelectron Spectroscopy between 400 and 1100 °C. The qualitative variations of the surface contents of S, P, W, Mo, N, Si, and Mn were determined as a function of annealing temperature and time. It was found that at 925 °C the maximum coverage of sulphur at the alloy surface is in the range 0.06-0.15 monolayers. Chromium evaporation from the HAYNES 230 surface under UHV conditions is clearly evidenced for annealing at 1100 °C.

The use of computational thermodynamics for the determination of surface tension and Gibbs-Thomson coefficient of multicomponent alloys

NASA Astrophysics Data System (ADS)

Ferreira, D. J. S.; Bezerra, B. N.; Collyer, M. N.; Garcia, A.; Ferreira, I. L.

2018-04-01

The simulation of casting processes demands accurate information on the thermophysical properties of the alloy; however, such information is scarce in the literature for multicomponent alloys. Generally, metallic alloys applied in industry have more than three solute components. In the present study, a general solution of Butler's formulation for surface tension is presented for multicomponent alloys and is applied in quaternary Al-Cu-Si-Fe alloys, thus permitting the Gibbs-Thomson coefficient to be determined. Such coefficient is a determining factor to the reliability of predictions furnished by microstructure growth models and by numerical computations of solidification thermal parameters, which will depend on the thermophysical properties assumed in the calculations. The Gibbs-Thomson coefficient for ternary and quaternary alloys is seldom reported in the literature. A numerical model based on Powell's hybrid algorithm and a finite difference Jacobian approximation has been coupled to a Thermo-Calc TCAPI interface to assess the excess Gibbs energy of the liquid phase, permitting liquidus temperature, latent heat, alloy density, surface tension and Gibbs-Thomson coefficient for Al-Cu-Si-Fe hypoeutectic alloys to be calculated, as an example of calculation capabilities for multicomponent alloys of the proposed method. The computed results are compared with thermophysical properties of binary Al-Cu and ternary Al-Cu-Si alloys found in the literature and presented as a function of the Cu solute composition.

In Vivo Neural Recording and Electrochemical Performance of Microelectrode Arrays Modified by Rough-Surfaced AuPt Alloy Nanoparticles with Nanoporosity

PubMed Central

Zhao, Zongya; Gong, Ruxue; Zheng, Liang; Wang, Jue

2016-01-01

In order to reduce the impedance and improve in vivo neural recording performance of our developed Michigan type silicon electrodes, rough-surfaced AuPt alloy nanoparticles with nanoporosity were deposited on gold microelectrode sites through electro-co-deposition of Au-Pt-Cu alloy nanoparticles, followed by chemical dealloying Cu. The AuPt alloy nanoparticles modified gold microelectrode sites were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and in vivo neural recording experiment. The SEM images showed that the prepared AuPt alloy nanoparticles exhibited cauliflower-like shapes and possessed very rough surfaces with many different sizes of pores. Average impedance of rough-surfaced AuPt alloy nanoparticles modified sites was 0.23 MΩ at 1 kHz, which was only 4.7% of that of bare gold microelectrode sites (4.9 MΩ), and corresponding in vitro background noise in the range of 1 Hz to 7500 Hz decreased to 7.5 μVrms from 34.1 μVrms at bare gold microelectrode sites. Spontaneous spike signal recording was used to evaluate in vivo neural recording performance of modified microelectrode sites, and results showed that rough-surfaced AuPt alloy nanoparticles modified microelectrode sites exhibited higher average spike signal-to-noise ratio (SNR) of 4.8 in lateral globus pallidus (GPe) due to lower background noise compared to control microelectrodes. Electro-co-deposition of Au-Pt-Cu alloy nanoparticles combined with chemical dealloying Cu was a convenient way for increasing the effective surface area of microelectrode sites, which could reduce electrode impedance and improve the quality of in vivo spike signal recording. PMID:27827893

The \

NASA Astrophysics Data System (ADS)

Stoilova, N. I.; Van der Jeugt, J.

2018-04-01

When the relative commutation relations between a set of m parafermions and n parabosons are of ‘relative parafermion type’, the underlying algebraic structure is the classical orthosymplectic Lie superalgebra (LSA) \

Enhancement of wear and corrosion resistance of beta titanium alloy by laser gas alloying with nitrogen

NASA Astrophysics Data System (ADS)

Chan, Chi-Wai; Lee, Seunghwan; Smith, Graham; Sarri, Gianluca; Ng, Chi-Ho; Sharba, Ahmed; Man, Hau-Chung

2016-03-01

The relatively high elastic modulus coupled with the presence of toxic vanadium (V) in Ti6Al4V alloy has long been a concern in orthopaedic applications. To solve the problem, a variety of non-toxic and low modulus beta-titanium (beta-Ti) alloys have been developed. Among the beta-Ti alloy family, the quaternary Ti-Nb-Zr-Ta (TNZT) alloys have received the highest attention as a promising replacement for Ti6Al4V due to their lower elastic modulus and outstanding long term stability against corrosion in biological environments. However, the inferior wear resistance of TNZT is still a problem that must be resolved before commercialising in the orthopaedic market. In this work, a newly developed laser surface treatment technique was employed to improve the surface properties of Ti-35.3Nb-7.3Zr-5.7Ta alloy. The surface structure and composition of the laser-treated TNZT surface were examined by grazing incidence X-ray diffraction (GI-XRD) and X-ray photoelectron spectroscopy (XPS). The wear and corrosion resistance were evaluated by pin-on-plate sliding test and anodic polarisation test in Hanks' solution. The experimental results were compared with the untreated (or base) TNZT material. The research findings showed that the laser surface treatment technique reported in this work can effectively improve the wear and corrosion resistance of TNZT.

The underlying biological mechanisms of biocompatibility differences between bare and TiN-coated NiTi alloys.

PubMed

Lifeng, Zhao; Yan, Hong; Dayun, Yang; Xiaoying, Lü; Tingfei, Xi; Deyuan, Zhang; Ying, Hong; Jinfeng, Yuan

2011-04-01

TiN coating has been demonstrated to improve the biocompatibility of bare NiTi alloys; however, essential biocompatibility differences between NiTi alloys before and after TiN coating are not known so far. In this study, to explore the underlying biological mechanisms of biocompatibility differences between them, the changes of bare and TiN-coated NiTi alloys in surface chemical composition, morphology, hydrophilicity, Ni ions release, cytotoxicity, apoptosis, and gene expression profiles were compared using energy-dispersive spectroscopy, scanning electron microscopy, contact angle, surface energy, Ni ions release analysis, the methylthiazoltetrazolium (MTT) method, flow cytometry and microarray methods, respectively. Pathways binding to networks and real-time polymerase chain reaction (PCR) were employed to analyze and validate the microarray data, respectively. It was found that, compared with the bare NiTi alloys, TiN coating significantly decreased Ni ions content on the surfaces of the NiTi alloys and reduced the release of Ni ions from the alloys, attenuated the inhibition of Ni ions to the expression of genes associated with anti-inflammatory, and also suppressed the promotion of Ni ions to the expression of apoptosis-related genes. Moreover, TiN coating distinctly improved the hydrophilicity and uniformity of the surfaces of the NiTi alloys, and contributed to the expression of genes participating in cell adhesion and other physiological activities. These results indicate that the TiN-coated NiTi alloys will help overcome the shortcomings of NiTi alloys used in clinical application currently, and can be expected to be a replacement of biomaterials for a medical device field.

Electrochemical synthesis of a surface-porous Mg70.5Al29.5 eutectic alloy in a neutral aqueous NaCl solution

NASA Astrophysics Data System (ADS)

Yang, Feng; Li, Yong-gang; Wei, Ying-hui; Wei, Huan; Yan, Ze-ying; Hou, Li-feng

2018-03-01

A surface-porous Mg-Al eutectic alloy was fabricated at room temperature via electrochemical dealloying in a neutral, aqueous 0.6 M NaCl solution by controlling the applied potential and processing duration. Selective dissolution occurred on the alloy surface. The surface-porous formation mechanism is governed by the selective dissolution of the α-Mg phase, which leaves the Mg17Al12 phase as the porous layer framework. The pore characteristics (morphology, size, and distribution) of the dealloyed samples are inherited from the α-Mg phases of the precursor Mg70.5Al29.5 (at.%) alloy. Size control in the porous layer can be achieved by regulating the synthesis parameters.

Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

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

Puli, Ramesh, E-mail: rameshpuli2000@gmail.com; Janaki Ram, G.D.

2012-12-15

Friction surfacing involves complex thermo-mechanical phenomena. In this study, the nature of dynamic recrystallization in friction surfaced austenitic stainless steel AISI 316L coatings was investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the alloy 316L undergoes discontinuous dynamic recrystallization under conditions of moderate Zener-Hollomon parameter during friction surfacing. - Highlights: Black-Right-Pointing-Pointer Dynamic recrystallization in alloy 316L friction surfaced coatings is examined. Black-Right-Pointing-Pointer Friction surfacing leads to discontinuous dynamic recrystallization in alloy 316L. Black-Right-Pointing-Pointer Strain rates in friction surfacing exceed 400 s{sup -1}. Black-Right-Pointing-Pointer Estimated grain size matches well with experimental observations in 316L coatings.

The atomic level structure of the TiO(2)-NiTi interface.

PubMed

Nolan, M; Tofail, S A M

2010-09-07

The biocompatibility of NiTi shape memory alloys (SMA) has made possible applications in invasive and minimally invasive biomedical devices. The NiTi intermetallic alloy spontaneously forms a thin passive layer of TiO(2), which provides its biocompatibility. The oxide layer is thought to form as Ti in the alloy reacts with oxygen. In this paper, we study the details of the oxide-alloy interface. The atomic model is the (110) NiTi surface interfaced with the (100) rutile TiO(2) surface; this combination provides the best lattice match of alloy and oxide. When the interface forms, static minimisations and molecular dynamics show that there is no migration of atoms between the alloy and the oxide. In the alloy there are some notable structural relaxations. We find that a columnar structure appears in which alternating long and short Ni-Ti bonds are present in each surface and subsurface plane into the fourth subsurface layer. The oxide undergoes some structural changes as a result of terminal oxygen coordinating to Ti in the NiTi surface. The electronic structure shows that Ti(3+) species are present at the interface, with Ti(4+) in the bulk of the oxide layer and that the metallic character of the alloy is unaffected by the interaction with oxygen, all of which is consistent with experiment. A thermodynamic analysis is used to examine the stability of different possible structures-a perfect interface and one with Ti and O vacancies. We find that under conditions typical of oxidation and shape memory treatments, the most stable interface structure is that with Ti vacancies in the alloy surface, leaving an Ni-rich layer, consistent with the experimental findings for this interface.

Study of the effects of implantation on the high Fe-Ni-Cr and Ni-Cr-Al alloys

NASA Technical Reports Server (NTRS)

Ribarsky, M. W.

1985-01-01

A theoretical study of the effects of implantation on the corrosion resistance of Fe-Ni-Cr and Ni-Cr-Al alloys was undertaken. The purpose was to elucidate the process by which corrosion scales form on alloy surfaces. The experiments dealt with Ni implanted with Al, exposed to S at high temperatures, and then analyzed using scanning electron microscopy, scanning Auger spectroscopy and X-ray fluorescence spectroscopy. Pair bonding and tight-binding models were developed to study the compositions of the alloys and as a result, a new surface ordering effect was found which may exist in certain real alloys. With these models, the behavior of alloy constituents in the presence of surface concentrations of O or S was also studied. Improvements of the models to take into account the important effects of long- and short-range ordering were considered. The diffusion kinetics of implant profiles at various temperatures were investigated, and it was found that significant non-equilibrium changes in the profiles can take place which may affect the implants' performance in the presence of surface contaminants.

Influence of silicon on friction and wear of iron-cobalt alloys

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Brainard, W. A.

1972-01-01

Sliding friction and wear experiments were conducted with ternary ordered alloys of iron and cobalt containing various amounts of silicon to 5 weight percent. The friction and wear of these alloys were compared to those for binary iron-cobalt alloys in the ordered and disordered states and to those for the conventionally used bearing material, 440-C. Environments in which experiments were conducted included air, argon, and 0.25percent stearic acid in hexadecane. Results indicate that a ternary iron - cobalt - 5-percent-silicon alloy exhibits lower friction and wear than the simple binary iron-cobalt alloy. It exhibits lower wear than 440-C in all three environments. Friction was lower for the alloy in argon than in air. Auger analysis of the surface of the ternary alloy indicated segregation of silicon at the surface as a result of sliding.

Method for laser welding a fin and a tube

DOEpatents

Fuerschbach, Phillip W.; Mahoney, A. Roderick; Milewski, John O

2001-01-01

A method of laser welding a planar metal surface to a cylindrical metal surface is provided, first placing a planar metal surface into approximate contact with a cylindrical metal surface to form a juncture area to be welded, the planar metal surface and cylindrical metal surface thereby forming an acute angle of contact. A laser beam, produced, for example, by a Nd:YAG pulsed laser, is focused through the acute angle of contact at the juncture area to be welded, with the laser beam heating the juncture area to a welding temperature to cause welding to occur between the planar metal surface and the cylindrical metal surface. Both the planar metal surface and cylindrical metal surface are made from a reflective metal, including copper, copper alloys, stainless steel alloys, aluminum, and aluminum alloys.

Stable biomimetic super-hydrophobic engineering materials.

PubMed

Guo, Zhiguang; Zhou, Feng; Hao, Jingcheng; Liu, Weimin

2005-11-16

We describe a simple and inexpensive method to produce super-hydrophobic surfaces on aluminum and its alloy by oxidation and chemical modification. Water or aqueous solutions (pH = 1-14) have contact angles of 168 +/- 2 and 161 +/- 2 degrees on the treated surfaces of Al and Al alloy, respectively. The super-hydrophobic surfaces are produced by the cooperation of binary structures at micro- and nanometer scales, thus reducing the energies of the surfaces. Such super-hydrophobic properties will greatly extend the applications of aluminum and its alloy as lubricating materials.

Dispersoid reinforced alloy powder and method of making

DOEpatents

Anderson, Iver E [Ames, IA; Terpstra, Robert L [Ames, IA

2012-06-12

A method of making dispersion-strengthened alloy particles involves melting an alloy having a corrosion and/or oxidation resistance-imparting alloying element, a dispersoid-forming element, and a matrix metal wherein the dispersoid-forming element exhibits a greater tendency to react with a reactive species acquired from an atomizing gas than does the alloying element. The melted alloy is atomized with the atomizing gas including the reactive species to form atomized particles so that the reactive species is (a) dissolved in solid solution to a depth below the surface of atomized particles and/or (b) reacted with the dispersoid-forming element to form dispersoids in the atomized particles to a depth below the surface of said atomized particles. The atomized alloy particles are solidified as solidified alloy particles or as a solidified deposit of alloy particles. Bodies made from the dispersion strengthened alloy particles, deposit thereof, exhibit enhanced fatigue and creep resistance and reduced wear as well as enhanced corrosion and/or oxidation resistance at high temperatures by virtue of the presence of the corrosion and/or oxidation resistance imparting alloying element in solid solution in the particle alloy matrix.

Dispersoid reinforced alloy powder and method of making

DOEpatents

Anderson, Iver E.; Terpstra, Robert L.

2010-04-20

A method of making dispersion-strengthened alloy particles involves melting an alloy having a corrosion and/or oxidation resistance-imparting alloying element, a dispersoid-forming element, and a matrix metal wherein the dispersoid-forming element exhibits a greater tendency to react with a reactive species acquired from an atomizing gas than does the alloying element. The melted alloy is atomized with the atomizing gas including the reactive species to form atomized particles so that the reactive species is (a) dissolved in solid solution to a depth below the surface of atomized particles and/or (b) reacted with the dispersoid-forming element to form dispersoids in the atomized particles to a depth below the surface of said atomized particles. The atomized alloy particles are solidified as solidified alloy particles or as a solidified deposit of alloy particles. Bodies made from the dispersion strengthened alloy particles, deposit thereof, exhibit enhanced fatigue and creep resistance and reduced wear as well as enhanced corrosion and/or oxidation resistance at high temperatures by virtue of the presence of the corrosion and/or oxidation resistance imparting alloying element in solid solution in the particle alloy matrix.

Nano-Nucleation Characteristic of Cu-Ag Alloy Directly Electrodeposited on W Diffusion Barrier for Microelectronic Device Interconnect.

PubMed

Kim, Kang O; Kim, Sunjung

2016-05-01

Cu-Ag alloy interconnect is promising for ultra-large-scale integration (ULSI) microelectronic system of which device dimension keeps shrinking. In this study, seedless electrodeposition of Cu-Ag alloy directly on W diffusion barrier as interconnect technology is presented in respect of nano-nucleation control. Chemical equilibrium state of electrolyte was fundamentally investigated according to the pH of electrolyte because direct nano-nucleation of Cu-Ag alloy on W surface is challenging. Chelation behavior of Cu2+ and Ag+ ions with citrate (Cit) and ammonia ligands was dependent on the pH of electrolyte. The amount and kind of Cu- and Ag-based complexes determine the deposition rate, size, elemental composition, and surface morphology of Cu-Ag alloy nano-nuclei formed on W surface.

High temperature thrust chamber for spacecraft

NASA Technical Reports Server (NTRS)

Chazen, Melvin L. (Inventor); Mueller, Thomas J. (Inventor); Kruse, William D. (Inventor)

1998-01-01

A high temperature thrust chamber for spacecraft (20) is provided herein. The high temperature thrust chamber comprises a hollow body member (12) having an outer surface and an internal surface (16) defining the high temperature chamber (10). The body member (12) is made substantially of rhenium. An alloy (18) consisting of iridium and at least alloying metal selected of the group consisting of rhodium, platinum and palladium is deposited on at least a portion of the internal surface (16) of the body member (12). The iridium and the alloying metal are electrodeposited onto the body member (12). A HIP cycle is performed upon the body member (12) to cause the coating of iridium and the alloying metal to form the alloy (18) which protects the body member (12) from oxidation.

Vacuum Levels Needed to Simulate Internal Fatigue Crack Growth in Titanium Alloys and Nickel-Base Superalloys Thermaodynamic Conditioners (Preprint)

DTIC Science & Technology

2012-08-01

AFRL-RX-WP-TP-2012-0412 VACUUM LEVELS NEEDED TO SIMULATE INTERNAL FATIGUE CRACK GROWTH IN TITANIUM ALLOYS AND NICKEL - BASE SUPERALLOYS...LEVELS NEEDED TO SIMULATE INTERNAL FATIGUE CRACK GROWTH IN TITANIUM ALLOYS AND NICKEL - BASE SUPERALLOYS: THERMAODYNAMIC CONSIDERATIONS (PREPRINT) 5a...have examined fatigue growth of surface cracks in vacuum to simulate sub-surface growth in Ti- alloys and Ni - base superalloys. Even with the highest

Fabrication of dopamine-modified hyaluronic acid/chitosan multilayers on titanium alloy by layer-by-layer self-assembly for promoting osteoblast growth

NASA Astrophysics Data System (ADS)

Zhang, Xinming; Li, Zhaoyang; Yuan, Xubo; Cui, Zhenduo; Yang, Xianjin

2013-11-01

The bare inert surface of titanium (Ti) alloy typically causes early failures in implants. Layer-by-layer self-assembly is one of the simple methods for fabricating bioactive multilayer coatings on titanium implants. In this study, a dopamine-modified hyaluronic acid/chitosan (DHA/CHI) bioactive multilayer was built on the surface of Ti-24Nb-2Zr (TNZ) alloy. Zeta potential oscillated between -2 and 17 mV for DHA- and CHI-ending layers during the assembly process, respectively. The DHA/CHI multilayer considerably decreased the contact angle and dramatically improved the wettability of TNZ alloy. Atomic force microscopy results revealed a rough surface on the original TNZ alloy, while the surface became smoother and more homogeneous after the deposition of approximately 5 bilayers (TNZ/(DHA/CHI)5). X-ray photoelectron spectroscopy analysis indicated that the TNZ/(DHA/CHI)5 sample was completely covered by polyelectrolytes. Pre-osteoblast MC3T3-E1 cells were cultured on the original TNZ alloy and TNZ/(DHA/CHI)5 to evaluate the effects of DHA/CHI multilayer on osteoblast proliferation in vitro. The proliferation of osteoblasts on TNZ/(DHA/CHI)5 was significantly higher than that on the original TNZ alloy. The results of this study indicate that the proposed technique improves the biocompatibility of TNZ alloy and can serve as a potential modification method in orthopedic applications.

Surface Composition of NiPd Alloys

NASA Technical Reports Server (NTRS)

Noebe, Ronald D.; Khalil, Joe; Bozzolo, Guillermo; Gray, Hugh R. (Technical Monitor)

2002-01-01

Surface segregation in Ni-Pd alloys has been studied using the BFS method for alloys. Not only does the method predict an oscillatory segregation profile but it also indicates that the number of Pd-enriched surface planes can vary as a function of orientation. The segregation profiles were computed as a function of temperature, crystal face, and composition. Pd enrichment of the first layer is observed in (111) and (100) surfaces, and enrichment of the top two layers occurs for (110) surfaces. In all cases, the segregation profile shows oscillations that are actually related to weak ordering tendencies in the bulk. An atom-by-atom analysis was performed to identify the competing mechanisms leading to the observed surface behaviors. Large-scale atomistic simulations were also performed to investigate the temperature dependence of the segregation profiles as well as for analysis of the bulk structures. Finally, the observed surface behaviors are discussed in relation to the bulk phase structure of Ni-Pd alloys, which exhibit a tendency to weakly order.

Albumin adsorption on CoCrMo alloy surfaces

NASA Astrophysics Data System (ADS)

Yan, Yu; Yang, Hongjuan; Su, Yanjing; Qiao, Lijie

2015-12-01

Proteins can adsorb on the surface of artificial joints immediately after being implanted. Although research studying protein adsorption on medical material surfaces has been carried out, the mechanism of the proteins’ adsorption which affects the corrosion behaviour of such materials still lacks in situ observation at the micro level. The adsorption of bovine serum albumin (BSA) on CoCrMo alloy surfaces was studied in situ by AFM and SKPFM as a function of pH and the charge of CoCrMo alloy surfaces. Results showed that when the specimens were uncharged, hydrophobic interaction could govern the process of the adsorption rather than electrostatic interaction, and BSA molecules tended to adsorb on the surfaces forming a monolayer in the side-on model. Results also showed that adsorbed BSA molecules could promote the corrosion process for CoCrMo alloys. When the surface was positively charged, the electrostatic interaction played a leading role in the adsorption process. The maximum adsorption occurred at the isoelectric point (pH 4.7) of BSA.

Surface modification of an Mg-1Ca alloy to slow down its biocorrosion by chitosan.

PubMed

Gu, X N; Zheng, Y F; Lan, Q X; Cheng, Y; Zhang, Z X; Xi, T F; Zhang, D Y

2009-08-01

The surface morphologies before and after immersion corrosion test of various chitosan-coated Mg-1Ca alloy samples were studied to investigate the effect of chitosan dip coating on the slowdown of biocorrosion. It showed that the corrosion resistance of the Mg-Ca alloy increased after coating with chitosan, and depended on both the chitosan molecular weight and layer numbers of coating. The Mg-Ca alloy coated by chitosan with a molecular weight of 2.7 x 10(5) for six layers has smooth and intact surface morphology, and exhibits the highest corrosion resistance in a simulated body fluid.

Surface thermodynamic stability, electronic and magnetic properties in various (001) surfaces of Zr2CoSn Heusler alloy

NASA Astrophysics Data System (ADS)

Yang, Yan; Feng, Zhong-Ying; Zhang, Jian-Min

2018-05-01

The spin-polarized first-principles are used to study the surface thermodynamic stability, electronic and magnetic properties in various (001) surfaces of Zr2CoSn Heusler alloy, and the bulk Zr2CoSn Heusler alloy are also discussed to make comparison. The conduction band minimum (CBM) of half-metallic (HM) bulk Zr2CoSn alloy is contributed by ZrA, ZrB and Co atoms, while the valence band maximum (VBM) is contributed by ZrB and Co atoms. The SnSn termination is the most stable surface with the highest spin polarizations P = 77.1% among the CoCo, ZrCo, ZrZr, ZrSn and SnSn terminations of the Zr2CoSn (001) surface. In the SnSn termination of the Zr2CoSn (001) surface, the atomic partial density of states (APDOS) of atoms in the surface, subsurface and third layers are much influenced by the surface effect and the total magnetic moment (TMM) is mainly contributed by the atomic magnetic moments of atoms in fourth to ninth layers.

Galvanic corrosion behavior of orthodontic archwire alloys coupled to bracket alloys.

PubMed

Iijima, Masahiro; Endo, Kazuhiko; Yuasa, Toshihiro; Ohno, Hiroki; Hayashi, Kazuo; Kakizaki, Mitsugi; Mizoguchi, Itaru

2006-07-01

The purpose of this study was to provide a quantitative assessment of galvanic corrosion behavior of orthodontic archwire alloys coupled to orthodontic bracket alloys in 0.9% NaCl solution and to study the effect of surface area ratios. Two common bracket alloys, stainless steels and titanium, and four common wire alloys, nickel-titanium (NiTi) alloy, beta-titanium (beta-Ti) alloy, stainless steel, and cobalt-chromium-nickel alloy, were used. Three different area ratios, 1:1, 1:2.35, and 1:3.64, were used; two of them assumed that the multibracket appliances consists of 14 brackets and 0.016 inch of round archwire or 0.016 x 0.022 inch of rectangular archwire. The galvanic current was measured for 3 successive days using zero-impedance ammeter. When the NiTi alloy was coupled with Ti (1:1, 1:2.35, and 1:3.64 of the surface area ratio) or beta-Ti alloy was coupled with Ti (1:2.35 and 1:3.64 of the surface area ratio), Ti initially was the anode and corroded. However, the polarity reversed in 1 hour, resulting in corrosion of the NiTi or beta-Ti. The NiTi alloy coupled with SUS 304 or Ti exhibited a relatively large galvanic current density even after 72 hours. It is suggested that coupling SUS 304-NiTi and Ti-NiTi may remarkably accelerate the corrosion of NiTi alloy, which serves as the anode. The different anode-cathode area ratios used in this study had little effect on galvanic corrosion behavior.

Surface treatments for controlling corrosion rate of biodegradable Mg and Mg-based alloy implants

PubMed Central

Uddin, M S; Hall, Colin; Murphy, Peter

2015-01-01

Due to their excellent biodegradability characteristics, Mg and Mg-based alloys have become an emerging material in biomedical implants, notably for repair of bone as well as coronary arterial stents. However, the main problem with Mg-based alloys is their rapid corrosion in aggressive environments such as human bodily fluids. Previously, many approaches such as control of alloying materials, composition and surface treatments, have been attempted to regulate the corrosion rate. This article presents a comprehensive review of recent research focusing on surface treatment techniques utilised to control the corrosion rate and surface integrity of Mg-based alloys in both in vitro and in vivo environments. Surface treatments generally involve the controlled deposition of thin film coatings using various coating processes, and mechanical surfacing such as machining, deep rolling or low plasticity burnishing. The aim is to either make a protective thin layer of a material or to change the micro-structure and mechanical properties at the surface and sub-surface levels, which will prevent rapid corrosion and thus delay the degradation of the alloys. We have organised the review of past works on coatings by categorising the coatings into two classes—conversion and deposition coatings—while works on mechanical treatments are reviewed based on the tool-based processes which affect the sub-surface microstructure and mechanical properties of the material. Various types of coatings and their processing techniques under two classes of coating and mechanical treatment approaches have been analysed and discussed to investigate their impact on the corrosion performance, biomechanical integrity, biocompatibility and cell viability. Potential challenges and future directions in designing and developing the improved biodegradable Mg/Mg-based alloy implants were addressed and discussed. The literature reveals that no solutions are yet complete and hence new and innovative approaches are required to leverage the benefit of Mg-based alloys. Hybrid treatments combining innovative biomimetic coating and mechanical processing would be regarded as a potentially promising way to tackle the corrosion problem. Synergetic cutting-burnishing integrated with cryogenic cooling may be another encouraging approach in this regard. More studies focusing on rigorous testing, evaluation and characterisation are needed to assess the efficacy of the methods. PMID:27877829

From Laboratory Research to a Clinical Trial

PubMed Central

Michels, Harold T.; Keevil, C. William; Salgado, Cassandra D.; Schmidt, Michael G.

2015-01-01

Objective: This is a translational science article that discusses copper alloys as antimicrobial environmental surfaces. Bacteria die when they come in contact with copper alloys in laboratory tests. Components made of copper alloys were also found to be efficacious in a clinical trial. Background: There are indications that bacteria found on frequently touched environmental surfaces play a role in infection transmission. Methods: In laboratory testing, copper alloy samples were inoculated with bacteria. In clinical trials, the amount of live bacteria on the surfaces of hospital components made of copper alloys, as well as those made from standard materials, was measured. Finally, infection rates were tracked in the hospital rooms with the copper components and compared to those found in the rooms containing the standard components. Results: Greater than a 99.9% reduction in live bacteria was realized in laboratory tests. In the clinical trials, an 83% reduction in bacteria was seen on the copper alloy components, when compared to the surfaces made from standard materials in the control rooms. Finally, the infection rates were found to be reduced by 58% in patient rooms with components made of copper, when compared to patients' rooms with components made of standard materials. Conclusions: Bacteria die on copper alloy surfaces in both the laboratory and the hospital rooms. Infection rates were lowered in those hospital rooms containing copper components. Thus, based on the presented information, the placement of copper alloy components, in the built environment, may have the potential to reduce not only hospital-acquired infections but also patient treatment costs. PMID:26163568

Effect of surface oxidation on thermomechanical behavior of NiTi shape memory alloy wire

NASA Astrophysics Data System (ADS)

Ng, Ching Wei; Mahmud, Abdus Samad

2017-12-01

Nickel titanium (NiTi) alloy is a unique alloy that exhibits special behavior that recovers fully its shape after being deformed to beyond elastic region. However, this alloy is sensitive to any changes of its composition and introduction of inclusion in its matrix. Heat treatment of NiTi shape memory alloy to above 600 °C leads to the formation of the titanium oxide (TiO2) layer. Titanium oxide is a ceramic material that does not exhibit shape memory behaviors and possess different mechanical properties than that of NiTi alloy, thus disturbs the shape memory behavior of the alloy. In this work, the effect of formation of TiO2 surface oxide layer towards the thermal phase transformation and stress-induced deformation behaviors of the NiTi alloy were studied. The NiTi wire with composition of Ti-50.6 at% Ni was subjected to thermal oxidation at 600 °C to 900 °C for 30 and 60 minutes. The formation of the surface oxide layers was characterized by using the Scanning Electron Microscope (SEM). The effect of surface oxide layers with different thickness towards the thermal phase transformation behavior was studied by using the Differential Scanning Calorimeter (DSC). The effect of surface oxidation towards the stress-induced deformation behavior was studied through the tensile deformation test. The stress-induced deformation behavior and the shape memory recovery of the NiTi wire under tensile deformation were found to be affected marginally by the formation of thick TiO2 layer.

Nitriding of super alloys for enhancing physical properties

DOEpatents

Purohit, Ankur

1986-01-01

The invention teaches the improvement of certain super alloys by exposing the alloy to an atmosphere of elemental nitrogen at elevated temperatures in excess of 750.degree. C. but less than 1150.degree. C. for an extended duration, viz., by nitriding the surface of the alloy, to establish barrier nitrides of the order of 25-100 micrometers thickness. These barrier nitrides appear to shield the available oxidizing metallic species of the alloy for up to a sixfold improved resistance against oxidation and also appear to impede egress of surface dislocations for increased fatigue and creep strengths.

Oxide compounds on Ni-Cr alloys.

PubMed

Baran, G R

1984-11-01

Five Ni-Cr alloys were studied in order to identify the compounds formed on the alloy surface during oxidation under conditions similar to those encountered during dental laboratory procedures prior to application of porcelain. After the alloys were oxidized, the films covering the surfaces were removed with the aid of a Br-methanol solution. X-ray diffraction was used to analyze the compounds formed. Oxides of nearly all elements contained by the alloys were found after low-temperature (650 degrees C) oxidation, while NiO and particularly Cr2O3 were predominant after oxidation at high temperatures (1000 degrees C).

Density functional theory simulation of titanium migration and reaction with oxygen in the early stages of oxidation of equiatomic NiTi alloy.

PubMed

Nolan, Michael; Tofail, Syed A M

2010-05-01

The biocompatibility of NiTi shape memory alloys (SMA) has made possible applications in self-expandable cardio-vascular stents, stone extraction baskets, catheter guide wires and other invasive and minimally invasive biomedical devices. The NiTi intermetallic alloy spontaneously forms a thin passive layer of TiO(2), which provides its biocompatibility. The oxide layer is thought to form as the Ti in the alloy surface reacts with oxygen, resulting in a depletion of Ti in the subsurface region - experimental evidence indicates formation of a Ni-rich layer below the oxide film. In this paper, we study the initial stages of oxide growth on the (110) surface of the NiTi alloy to understand the formation of alloy/oxide interface. We initially adsorb atomic and molecular oxygen on the (110) surface and then successively add O(2) molecules, up to 2 monolayer of O(2). Oxygen adsorption always results in a large energy gain. With atomic oxygen, Ti is pulled out of the surface layer leaving behind a Ni-rich subsurface region. Molecular O(2), on the other hand adsorbs dissociatively and pulls a Ti atom farther out of the surface layer. The addition of further O(2) up to 1 monolayer is also dissociative and results in complete removal of Ti from the initial surface layer. When further O(2) is added up to 2 monolayer, Ti is pulled even further out of the surface and a single thin layer of composition O-Ti-O is formed. The electronic structure shows that the metallic character of the alloy is unaffected by interaction with oxygen and formation of the oxide layer, consistent with the oxide layer being a passivant. Copyright 2010 Elsevier Ltd. All rights reserved.

Sandblasting and silica-coating of dental alloys: volume loss, morphology and changes in the surface composition.

PubMed

Kern, M; Thompson, V P

1993-05-01

Silica-coating alloys improves chemo-mechanical bonding. Sandblasting is recommended as pretreatment to thermal silica-coating or as part of a tribochemical silica-coating process. This study evaluated the effects of sandblasting and coating techniques on volume loss, surface morphology and compositional changes in noble (AuAgCu) and base alloys (NiCr and CoCr). Volume loss was statistically significantly higher in the noble as compared to the base alloys but does not seem to be critical for the clinical fit of restorations. Embedded alumina particles were found in all alloys after sandblasting and the alumina content increased to a range of 14 to 37 wt% as measured by EDS. Following tribochemical silica-coating, a layer of small silica particles remained on the surface, increasing the silica content to between 12 and 20 wt%. Ultrasonic cleaning removed loose alumina or silica particles from the surface, resulting in only slight decreases in alumina or silica contents, thus suggesting firm attachment of the major part of alumina and silica to the alloy surface. Clinically, ultrasonic cleaning of sandblasted and tribochemically silica-coated alloys might improve resin bonding as loose surface particles are removed without relevant changes in composition. Silica content following thermal silica-coating treatment increased only slightly from the sandblasted specimen. The silica layer employed by these silica-coating methods differs widely in both morphology and thickness. These results provide a basis for explanation of adhesive failure modes in bond strength tests which will possibly optimize resin bonding. Further research is needed to characterize the outermost surface layers after these treatments and the exact location of adhesive failures.

Surface control alloy substrates and methods of manufacture therefor

DOEpatents

Fritzemeier, Leslie G.; Li, Qi; Rupich, Martin W.; Thompson, Elliott D.; Siegal, Edward J.; Thieme, Cornelis Leo Hans; Annavarapu, Suresh; Arendt, Paul N.; Foltyn, Stephen R.

2004-05-04

Methods and articles for controlling the surface of an alloy substrate for deposition of an epitaxial layer. The invention includes the use of an intermediate layer to stabilize the substrate surface against oxidation for subsequent deposition of an epitaxial layer.

Bimetallic alloy electrocatalysts with multilayered platinum-skin surfaces

DOEpatents

Stamenkovic, Vojislav R.; Wang, Chao; Markovic, Nenad M.

2016-01-26

Compositions and methods of preparing a bimetallic alloy having enhanced electrocatalytic properties are provided. The composition comprises a PtNi substrate having a surface layer, a near-surface layer, and an inner layer, where the surface layer comprises a nickel-depleted composition, such that the surface layer comprises a platinum skin having at least one atomic layer of platinum.

Prediction of Phase Separation of Immiscible Ga-Tl Alloys

NASA Astrophysics Data System (ADS)

Kim, Yunkyum; Kim, Han Gyeol; Kang, Youn-Bae; Kaptay, George; Lee, Joonho

2017-06-01

Phase separation temperature of Ga-Tl liquid alloys was investigated using the constrained drop method. With this method, density and surface tension were investigated together. Despite strong repulsive interactions, molar volume showed ideal mixing behavior, whereas surface tension of the alloy was close to that of pure Tl due to preferential adsorption of Tl. Phase separation temperatures and surface tension values obtained with this method were close to the theoretically calculated values using three different thermodynamic models.

Surface modification of biodegradable magnesium and its alloys for biomedical applications

PubMed Central

Tian, Peng; Liu, Xuanyong

2015-01-01

Magnesium and its alloys are being paid much attention recently as temporary implants, such as orthopedic implants and cardiovascular stents. However, the rapid degradation of them in physiological environment is a major obstacle preventing their wide applications to date, which will result in rapid mechanical integrity loss or even collapse of magnesium-based implants before injured tissues heal. Moreover, rapid degradation of the magnesium-based implants will also cause some adverse effects to their surrounding environment, such as local gas cavity around the implant, local alkalization and magnesium ion enrichment, which will reduce the integration between implant and tissue. So, in order to obtain better performance of magnesium-based implants in clinical trials, special alloy designs and surface modifications are prerequisite. Actually, when a magnesium-based implant is inserted in vivo, corrosion firstly happens at the implant-tissue interface and the biological response to implant is also determined by the interaction at this interface. So the surface properties, such as corrosion resistance, hemocompatibility and cytocompatibility of the implant, are critical for their in vivo performance. Compared with alloy designs, surface modification is less costly, flexible to construct multi-functional surface and can prevent addition of toxic alloying elements. In this review, we would like to summarize the current investigations of surface modifications of magnesium and its alloys for biomedical application. The advantages/disadvantages of different surface modification methods are also discussed as a suggestion for their utilization. PMID:26816637

Surface, corrosion and biocompatibility aspects of Nitinol as an implant material.

PubMed

Shabalovskaya, Svetlana A

2002-01-01

The present review surveys studies on physical-chemical properties and biological response of living tissues to NiTi (Nitinol) carried out recently, aiming at an understanding of the place of this material among the implant alloys in use. Advantages of shape memory and superelasticity are analyzed in respect to functionality of implants in the body. Various approaches to surface treatment, sterilization procedures, and resulting surface conditions are analyzed. A review of corrosion studies conducted both on wrought and as-cast alloys using potentiodynamic and potentiostatic techniques in various corrosive media and in actual body fluids is also given. The parameters of localized and galvanic corrosion are presented. The corrosion behavior is analyzed with respect to alloy composition, phase state, surface treatment, and strain and compared to that of conventional implant alloys. Biocompatibility of porous Nitinol, Ni release and its effect on living cells are analyzed based on understanding of the surface conditions and corrosion behavior. Additionally, the paper offers a brief overview of the comparative toxicity of metals, components of commonly used medical alloys, indicating that the biocompatibility profile of Nitinol is conducive to present in vivo applications.

Effects of surface treatments and bonding types on the interfacial behavior of fiber metal laminate based on magnesium alloy

NASA Astrophysics Data System (ADS)

Zhang, Xi; Ma, Quanyang; Dai, Yu; Hu, Faping; Liu, Gang; Xu, Zouyuan; Wei, Guobing; Xu, Tiancai; Zeng, Qingwen; Xie, Weidong

2018-01-01

Fiber metal laminates based on magnesium alloys (MgFML) with different surface treatments and different bonding types were tested and analyzed. By using dynamic contact angle measurement and scanning electron microscopy (SEM), it was found that phosphating treatment can significantly improve the surface energy and wettability of magnesium alloy, and the surface energy of phosphated magnesium alloy was approximately 50% higher than that of abraded-only magnesium alloy. The single cantilever beam (SCB) test showed that the interfacial fracture energies of directly bonded MgFMLs based on abraded-only magnesium and abraded + phosphated magnesium were 650 J/m2 and 1030 J/m2, respectively, whereas the interfacial fracture energies of indirectly bonded MgFMLs were 1650 J/m2 and 2260 J/m2, respectively. Phosphating treatment and modified polypropylene interleaf were observed to improve the tensile strength and interfacial fracture toughness of MgFML. In addition, the rougher surface was more conducive to enhance the bonding strength and interfacial fracture toughness of MgFML.

Graphene coating on the surface of CoCrMo alloy enhances the adhesion and proliferation of bone marrow mesenchymal stem cells.

PubMed

Zhang, Qi; Li, Kewen; Yan, Jinhong; Wang, Zhuo; Wu, Qi; Bi, Long; Yang, Min; Han, Yisheng

2018-03-18

The objective was to investigate whether a graphene coating could improve the surface bioactivity of a cobalt-chromium-molybdenum-based alloy (CoCrMo). Graphene was produced by chemical vapor deposition and transferred to the surface of the CoCrMo alloy using an improved wet transfer approach. The morphology of the samples was observed, and the adhesion force and stabilization of graphene coating were analyzed by a nanoscratch test and ultrasonication test. In an in vitro study, the adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) cultured on the samples were quantified via an Alamar Blue assay and cell counting kit-8 (CCK-8) assay. The results showed that it is feasible to apply graphene to modify the surface of a CoCrMo alloy, and the enhancement of the adhesion and proliferation of BMSCs was also shown in the present study. In conclusion, graphene exhibits considerable potential for enhancing the surface bioactivity of CoCrMo alloy. Copyright © 2018 Elsevier Inc. All rights reserved.

Development of casting investment preventing blackening of noble metal alloys part 1. Application of developed investment for Ag-Pd-Cu-Au alloy.

PubMed

Kakuta, Kiyoshi; Nakai, Akira; Goto, Shin-ichi; Wakamatsu, Yasushi; Yara, Atushi; Miyagawa, Yukio; Ogura, Hideo

2003-03-01

The objective of this study is to develop a casting investment that prevents the blackening of the cast surface of noble metal alloys. The experimental investments were prepared using a gypsum-bonded investment in which the metallic powders such as boron (B), silicon (Si), aluminum (Al) and titanium (Ti) were added as oxidizing agents. An Ag-Pd-Cu-Au alloy was cast into the mold made of the prepared investment. The effect of the addition of each metal powder was evaluated from the color difference between the as-cast surface and the polished surface of the cast specimen. The color of the as-cast surface approached that of the polished surface with increasing B and Al content. A lower mean value in the color difference was obtained at 0.25-1.00 mass% B content. B and Al are useful as an additive in a gypsum-bonded investment to prevent the blackening of an Ag-Pd-Cu-Au alloy. The effects of Si and Ti powder addition could not be found.

Thermal migration of alloying agents in aluminium

NASA Astrophysics Data System (ADS)

Cooil, S. P.; Mørtsell, E. A.; Mazzola, F.; Jorge, M.; Wenner, S.; Edmonds, M. T.; Thomsen, L.; Klemm, H. W.; Peschel, G.; Fuhrich, A.; Prieto, M.; Schmidt, Th; Miwa, J. A.; Holmestad, R.; Wells, J. W.

2016-11-01

The in situ thermal migration of alloying agents in an Al-Mg-Si-Li alloy is studied using surface sensitive photo-electron and electron diffraction/imaging techniques. Starting with the preparation of an almost oxide free surface (oxide thickness = 0.1 nm), the relative abundance of alloying agents (Mg, Li and Si) at the surface are recorded at various stages of thermal annealing, from room temperature to melting (which is observed at 550 ◦C). Prior to annealing, the surface abundances are below the detection limit ≪1%, in agreement with their bulk concentrations of 0.423% Si, 0.322% Mg and 0.101% Li (atomic %). At elevated temperatures, all three alloying agents appear at drastically increased concentrations (13.3% Si, 19.7% Mg and 45.3% Li), but decrease again with further elevation of the annealing temperature or after melting. The temperature at which the migration occurs is species dependent, with Li migration occurring at significantly higher temperatures than Si and Mg. The mechanism of migration also appears to be species dependent with Li migration occurring all over the surface but Mg migration being restricted to grain boundaries.

Method of protecting the surface of a substrate. [by applying aluminide coating

NASA Technical Reports Server (NTRS)

Gedwill, M. A. (Inventor); Grisaffe, S. J.

1974-01-01

The surface of a metallic base system is initially coated with a metallic alloy layer that is ductile and oxidation resistant. An aluminide coating is then applied to the metallic alloy layer. The chemistry of the metallic alloy layer is such that the oxidation resistance of the subsequently aluminized outermost layer is not seriously degraded.

Microstructures of tribologically modified surface layers in two-phase alloys

NASA Astrophysics Data System (ADS)

Figueroa, C. G.; Ortega, I.; Jacobo, V. H.; Ortiz, A.; Bravo, A. E.; Schouwenaars, R.

2014-08-01

When ductile alloys are subject to sliding wear, small increments of plastic strain accumulate into severe plastic deformation and mechanical alloying of the surface layer. The authors constructed a simple coaxial tribometer, which was used to study this phenomenon in wrought Al-Sn and cast Cu-Mg-Sn alloys. The first class of materials is ductile and consists of two immiscible phases. Tribological modification is observed in the form of a transition zone from virgin material to severely deformed grains. At the surface, mechanical mixing of both phases competes with diffusional unmixing. Vortex flow patterns are typically observed. The experimental Cu-Mg-Sn alloys are ductile for Mg-contents up to 2 wt% and consist of a- dendrites with a eutectic consisting of a brittle Cu2Mg-matrix with α-particles. In these, the observations are similar to the Al-Sn Alloys. Alloys with 5 wt% Mg are brittle due to the contiguity of the eutectic compound. Nonetheless, under sliding contact, this compound behaves in a ductile manner, showing mechanical mixing of a and Cu2Mg in the top layers and a remarkable transition from a eutectic to cellular microstructure just below, due to severe shear deformation. AFM-observations allow identifying the mechanically homogenized surface layers as a nanocrystalline material with a cell structure associated to the sliding direction.

Effect of Various Material Properties on the Adhesive Stage of Fretting

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1974-01-01

Various properties of metals and alloys were studied with respect to their effect on the initial stage of the fretting process, namely adhesion. Crystallographic orientation, crystal structure, interfacial binding energies of dissimiliar metal, segregation of alloy constituents and the nature and structure of surface films were found to influence adhesion. High atomic density, low surface energy grain orientations exhibited lower adhesion than other orientations. Knowledge of interfacial surface binding energies assists in predicting adhesive transfer and wear. Selective surface segregation of alloy constituents accomplishes both a reduction in adhesion and improved surface oxidation characteristics. Equivalent surface coverages of various adsorbed species indicate that some are markedly more effective in inhibiting adhesion than others.

Substrate effect on the growth of Sn thin films

NASA Astrophysics Data System (ADS)

Chakraborty, Suvankar; Menon, Krishnakumar S. R.

2018-05-01

Growth of tin (Sn) on Ag(001), Ag(111) and W(110) substrate has been studied at elevated temperatures (473 K) using x-ray photoemission spectroscopy (XPS) and low energy electron diffraction (LEED). For Sn growth on silver substrates, it is noticed that both Sn 3d and Ag 3d core-level spectra shift in the higher binding energy direction due to the formation of surface alloy with the substrate. In both cases, surface alloy finally transforms into bulk alloy finally reaching bulk Sn value. For Sn growth on W(110) only Sn 3d core-level spectra shift in the higher binding energy direction due to surface core-level effect whereas no shift for tungsten core-level was noticed confirming no alloy formation. Sn is incorporated into the surface of substrate silver layer by removing every alternate or every third silver atoms to relieve the surface tensile stress as confirmed by LEED. On the other hand, tungsten being hard, Sn forms an overlayer structure by sitting in different energetically available positions rather than forming an alloy as energetically also it is not possible. Sn forms alloy with soft substrate silver and form overlayer films with tungsten. These studies are important in understanding the growth mechanism of Sn films on metal substrates.

Cerium Addition Improved the Dry Sliding Wear Resistance of Surface Welding AZ91 Alloy

PubMed Central

Zhao, Zhihao; Zhu, Qingfeng; Wang, Gaosong; Tao, Kai

2018-01-01

In this study, the effects of cerium (Ce) addition on the friction and wear properties of surface welding AZ91 magnesium alloys were evaluated by pin-on-disk dry sliding friction and wear tests at normal temperature. The results show that both the friction coefficient and wear rate of surfacing magnesium alloys decreased with the decrease in load and increase in sliding speed. The surfacing AZ91 alloy with 1.5% Ce had the lowest friction coefficient and wear rate. The alloy without Ce had the worst wear resistance, mainly because it contained a lot of irregularly shaped and coarse β-Mg17Al12 phases. During friction, the β phase readily caused stress concentration and thus formed cracks at the interface between β phase and α-Mg matrix. The addition of Ce reduced the size and amount of Mg17Al12, while generating Al4Ce phase with a higher thermal stability. The Al-Ce phase could hinder the grain-boundary sliding and migration and reduced the degree of plastic deformation of subsurface metal. Scanning electron microscopy observation showed that the surfacing AZ91 alloy with 1.5% Ce had a total of four types of wear mechanism: abrasion, oxidation, and severe plastic deformation were the primary mechanisms; delamination was the secondary mechanism. PMID:29415492

Effect of Aluminum Coating on the Surface Properties of Ti-(~49 at. pct) Ni Alloy

NASA Astrophysics Data System (ADS)

Sinha, Arijit; Khan, Gobinda Gopal; Mondal, Bholanath; Majumdar, Jyotsna Dutta; Chattopadhyay, Partha Protim

2015-08-01

Stable porous layer of mixed Al2O3 and TiO2 has been formed on the Ti-(~49 at. pct) Ni alloy surface with an aim to suppress leaching of Ni from the alloy surface in contact with bio-fluid and to enhance the process of osseointegration. Aluminum coating on the Ni-Ti alloy surface prior to the anodization treatment has resulted in enhancement of depth and uniformity of pores. Thermal oxidation of the anodized aluminum-coated Ni-Ti samples has exhibited the formation of Al2O3 and TiO2 phases with dense porous structure. The nanoindentation and nanoscratch measurements have indicated a remarkable improvement in the hardness, wear resistance, and adhesiveness of the porous aluminum-coated Ni-Ti sample after thermal oxidation.

Friction and surface chemistry of some ferrous-base metallic glasses

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

The friction properties of some ferrous-base metallic glasses were measured both in argon and in vacuum to a temperature of 350 C. The alloy surfaces were also analyzed with X-ray photoelectron spectroscopy to identify the compounds and elements present on the surface. The results of the investigation indicate that even when the surfaces of the amorphous alloys, or metallic glasses, are atomically clean, bulk contaminants such as boric oxide and silicon dioxide diffuse to the surfaces. Friction measurements in both argon and vacuum indicate that the alloys exhibit higher coefficients of friction in the crystalline state than they do in the amorphous state.

Superhydrophobic aluminum alloy surfaces by a novel one-step process.

PubMed

Saleema, N; Sarkar, D K; Paynter, R W; Chen, X-G

2010-09-01

A simple one-step process has been developed to render aluminum alloy surfaces superhydrophobic by immersing the aluminum alloy substrates in a solution containing NaOH and fluoroalkyl-silane (FAS-17) molecules. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements have been performed to characterize the morphological features, chemical composition and superhydrophobicity of the surfaces. The resulting surfaces provided a water contact angle as high as ∼162° and a contact angle hysteresis as low as ∼4°. The study indicates that it is possible to fabricate superhydrophobic aluminum surfaces easily and effectively without involving the traditional two-step processes.

Pitting and Bending Fatigue Evaluations of a New Case-Carburized Gear Steel

NASA Technical Reports Server (NTRS)

Krantz, Timothy; Tufts, Brian

2007-01-01

The power density of a gearbox is an important consideration for many applications and is especially important for gearboxes used on aircraft. One approach to improving power density of gearing is to improve the steel properties by design of the alloy. The alloy tested in this work was designed to be case-carburized with surface hardness of Rockwell C66 after hardening. Test gear performance was evaluated using surface fatigue tests and single-tooth bending fatigue tests. The performance of gears made from the new alloy was compared to the performance of gears made from two alloys currently used for aviation gearing. The new alloy exhibited significantly better performance in surface fatigue testing, demonstrating the value of the improved properties in the case layer. However, the alloy exhibited lesser performance in single-tooth bending fatigue testing. The fracture toughness of the tested gears was insufficient for use in aircraft applications as judged by the behavior exhibited during the single tooth bending tests. This study quantified the performance of the new alloy and has provided guidance for the design and development of next generation gear steels.

Wettability of magnesium based alloys

NASA Astrophysics Data System (ADS)

Ornelas, Victor Manuel

The premise of this project was to determine the wettability behavior of Mg-based alloys using three different liquids. Contact angle measurements were carried out along with utilizing the Zisman method for obtaining values for the critical surface tension. Adhesion energy values were also found through the use of the Young-Dupre equation. This project utilized the Mg-based alloy Mg-2Zn-2Gd with supplemented alpha-Minimum Essential Medium (MEM), Phosphate Buffer Saline solution (PBS), and distilled water. These three liquids are commonly used in cell cultivation and protein adsorption studies. Supplemented alpha-MEM consisted of alpha-MEM, fetal bovine serum, and penicillin-streptomycin. Mg-2Zn-2Gd was used because of observed superior mechanical properties and better corrosion resistance as compared to conventional Mg-alloys. These attractive properties have made it possible for this alloy to be used in biomedical devices within the human body. However, the successful use of this alloy system in the human body requires knowledge in the response of protein adsorption on the alloy surface. Protein adsorption depends on many parameters, but one of the most important factors is the wettability behavior at the surface.

A vanadium alloy for the application in a liquid metal blanket of a fusion reactor

NASA Astrophysics Data System (ADS)

Borgstedt, H. U.; Grundmann, M.; Konys, J.; Perić, Z.

1988-07-01

The vanadium alloy V3Ti1Si has been corrosion tested in liquid lithium and the eutectic alloy Pb-17Li at 550°C. This alloy has a comparable corrosion resistance to the alloy V15Cr5Ti in lithium. In this molten metal it is superior to stainless steel AISI 316. In the Pb-17Li melt it is even superior to martensitic steels. The alloy has only a weak tendency to be dissolved. It is sensitive to an exchange of non-metallic elements, which causes the formation of a hardened surface layer. These chemical effects are influenced by the mass and surface ratios of the vanadium alloy to the molten metals and other structural materials. These ratios are unfavorable in the two test loops. The effects might be less pronounced in a vanadium alloy/liquid metal fusion reactor blanket.

Influence of UFG structure formation on mechanical and fatigue properties in Ti-6Al-7Nb alloy

NASA Astrophysics Data System (ADS)

Polyakova, V. V.; Anumalasetty, V. N.; Semenova, I. P.; Valiev, R. Z.

2014-08-01

Ultrafine-grained (UFG) Ti alloys have potential applications in osteosynthesis and orthopedics due to high bio-compatibility and increased weight-to- strength ratio. In current study, Ti6Al7Nb ELI alloy is processed through equal channel angular pressing-conform (ECAP-Conform) and subsequent thermomechanical processing to generate a UFG microstructure. The fatigue properties of UFG alloys are compared to coarse grained (CG) alloys. Our study demonstrates that the UFG alloys with an average grain size of ~180 nm showed 35% enhancement of fatigue endurance limit as compared to coarse-grained alloys. On the fracture surfaces of the UFG and CG samples fatigue striations and dimpled relief were observed. However, the fracture surface of the UFG sample looks smoother; fewer amounts of secondary micro-cracks and more ductile rupture were also observed, which testifies to the good crack resistance in the UFG alloy after high-cyclic fatigue tests.

Oxidation and emittance of superalloys in heat shield applications

NASA Technical Reports Server (NTRS)

Wiedemann, K. E.; Clark, R. K.; Unnam, J.

1986-01-01

Recently developed superalloys that form alumina coatings have a high potential for heat shield applications for advanced aerospace vehicles at temperatures above 1095C. Both INCOLOY alloy MA 956 (of the Inco Alloys International, Inc.), an iron-base oxide-dispersion-strengthened alloy, and CABOT alloy No. 214 (of the Cabot Corporation), an alumina-forming nickel-chromium alloy, have good oxidation resistance and good elevated temperature strength. The oxidation resistance of both alloys has been attributed to the formation of a thin alumina layer (alpha-Al2O3) at the surface. Emittance and oxidation data were obtained for simulated Space Shuttle reentry conditions using a hypersonic arc-heated wind tunnel. The surface oxides and substrate alloys were characterized using X-ray diffraction and scanning and transmission electron microscopy with an energy-dispersive X-ray analysis unit. The mass loss and emittance characteristics of the two alloys are discussed.

Electrochemical Performance Estimation of Anodized AZ31B Magnesium Alloy as Function of Change in the Current Density

NASA Astrophysics Data System (ADS)

Girón, L.; Aperador, W.; Tirado, L.; Franco, F.; Caicedo, J. C.

2017-08-01

The anodized AZ31B magnesium alloys were synthesized via electrodeposition processes. The aim of this work was to determine the electrochemical behavior of magnesium alloys by using anodized alloys as a protective coating. The anodized alloys were characterized by x-ray diffraction, exhibiting the crystallography orientation for Mg and MgO phases. The x-ray photoelectron spectroscopy was used to determine the chemical composition of anodized magnesium alloys. By using electrochemical impedance spectroscopy and Tafel curves, it was possible to estimate the electrochemical behavior of anodized AZ31B magnesium alloys in Hank's balanced salt solution (HBSS). Scanning electron microscopy was performed to analyze chemical changes and morphological surface changes on anodized Mg alloys due to the reaction in HBSS/anodized magnesium surface interface. Electrochemical behavior in HBSS indicates that the coatings may be a promising material for biomedical industry.

Etching Behavior of Aluminum Alloy Extrusions

NASA Astrophysics Data System (ADS)

Zhu, Hanliang

2014-11-01

The etching treatment is an important process step in influencing the surface quality of anodized aluminum alloy extrusions. The aim of etching is to produce a homogeneously matte surface. However, in the etching process, further surface imperfections can be generated on the extrusion surface due to uneven materials loss from different microstructural components. These surface imperfections formed prior to anodizing can significantly influence the surface quality of the final anodized extrusion products. In this article, various factors that influence the materials loss during alkaline etching of aluminum alloy extrusions are investigated. The influencing variables considered include etching process parameters, Fe-rich particles, Mg-Si precipitates, and extrusion profiles. This study provides a basis for improving the surface quality in industrial extrusion products by optimizing various process parameters.

Learning by stimulation avoidance: A principle to control spiking neural networks dynamics

PubMed Central

Sinapayen, Lana; Ikegami, Takashi

2017-01-01

Learning based on networks of real neurons, and learning based on biologically inspired models of neural networks, have yet to find general learning rules leading to widespread applications. In this paper, we argue for the existence of a principle allowing to steer the dynamics of a biologically inspired neural network. Using carefully timed external stimulation, the network can be driven towards a desired dynamical state. We term this principle “Learning by Stimulation Avoidance” (LSA). We demonstrate through simulation that the minimal sufficient conditions leading to LSA in artificial networks are also sufficient to reproduce learning results similar to those obtained in biological neurons by Shahaf and Marom, and in addition explains synaptic pruning. We examined the underlying mechanism by simulating a small network of 3 neurons, then scaled it up to a hundred neurons. We show that LSA has a higher explanatory power than existing hypotheses about the response of biological neural networks to external simulation, and can be used as a learning rule for an embodied application: learning of wall avoidance by a simulated robot. In other works, reinforcement learning with spiking networks can be obtained through global reward signals akin simulating the dopamine system; we believe that this is the first project demonstrating sensory-motor learning with random spiking networks through Hebbian learning relying on environmental conditions without a separate reward system. PMID:28158309

Learning by stimulation avoidance: A principle to control spiking neural networks dynamics.

PubMed

Sinapayen, Lana; Masumori, Atsushi; Ikegami, Takashi

2017-01-01

Learning based on networks of real neurons, and learning based on biologically inspired models of neural networks, have yet to find general learning rules leading to widespread applications. In this paper, we argue for the existence of a principle allowing to steer the dynamics of a biologically inspired neural network. Using carefully timed external stimulation, the network can be driven towards a desired dynamical state. We term this principle "Learning by Stimulation Avoidance" (LSA). We demonstrate through simulation that the minimal sufficient conditions leading to LSA in artificial networks are also sufficient to reproduce learning results similar to those obtained in biological neurons by Shahaf and Marom, and in addition explains synaptic pruning. We examined the underlying mechanism by simulating a small network of 3 neurons, then scaled it up to a hundred neurons. We show that LSA has a higher explanatory power than existing hypotheses about the response of biological neural networks to external simulation, and can be used as a learning rule for an embodied application: learning of wall avoidance by a simulated robot. In other works, reinforcement learning with spiking networks can be obtained through global reward signals akin simulating the dopamine system; we believe that this is the first project demonstrating sensory-motor learning with random spiking networks through Hebbian learning relying on environmental conditions without a separate reward system.

Generalized stacking fault energies of alloys.

PubMed

Li, Wei; Lu, Song; Hu, Qing-Miao; Kwon, Se Kyun; Johansson, Börje; Vitos, Levente

2014-07-02

The generalized stacking fault energy (γ surface) provides fundamental physics for understanding the plastic deformation mechanisms. Using the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation, we calculate the γ surface for the disordered Cu-Al, Cu-Zn, Cu-Ga, Cu-Ni, Pd-Ag and Pd-Au alloys. Studying the effect of segregation of the solute to the stacking fault planes shows that only the local chemical composition affects the γ surface. The calculated alloying trends are discussed using the electronic band structure of the base and distorted alloys.Based on our γ surface results, we demonstrate that the previous revealed 'universal scaling law' between the intrinsic energy barriers (IEBs) is well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning measure parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability.

The behaviour of entrainment defects formed in commercial purity Mg alloy cast under a cover gas of SF6

NASA Astrophysics Data System (ADS)

Li, T.; Griffiths, W. D.

2016-03-01

In the casting of light alloys, the oxidised film on the melt surface can be folded due to surface turbulence, thus forming entrainment defects that have a significant negative effect on the mechanical properties of castings. Previous researchers reported that the surface film of Mg alloys formed in an atmosphere containing SF6 had a complicated structure composed of MgO and MgF2. The work reported here aims to investigate the behaviour of entrainment defects formed in magnesium alloys protected by SF6-containing atmospheres. Tensile test bars of commercial purity Mg were cast in an unsealed environment under a cover gas of pure SF6. 34Scanning electron microscopy (SEM) of the fracture surface of the test bars indicated entrainment defects that consisted of symmetrical films containing MgO, but also sulphur and fluorine. The results of these examinations of the symmetrical films were used to infer the potential formation and development of entrainment defects in commercial purity Mg alloy.

New oxidation treatment of NiTi shape memory alloys to obtain Ni-free surfaces and to improve biocompatibility.

PubMed

Michiardi, A; Aparicio, C; Planell, J A; Gil, F J

2006-05-01

Various oxidation treatments were applied to nearly equiatomic NiTi alloys so as to form a Ni-free protective oxide on the surface. Sample surfaces were analyzed by X-ray Photoelectron Spectroscopy, and NiTi transformation temperatures were determined by differential scanning calorimetry (DSC) before and after the surface treatment. An ion release experiment was carried out up to one month of immersion in SBF for both oxidized and untreated surfaces. The results show that oxidation treatment in a low-oxygen pressure atmosphere leads to a high surface Ti/Ni ratio, a very low Ni surface concentration and a thick oxide layer. This oxidation treatment does not significantly affect the shape memory properties of the alloy. Moreover, the oxide formed significantly decreases Ni release into exterior medium comparing with untreated surfaces. As a consequence, this new oxidation treatment could be of great interest for biomedical applications, as it could minimize sensitization and allergies and improve biocompatibility and corrosion resistance of NiTi shape memory alloys. (c) 2005 Wiley Periodicals, Inc.

Surface modification by electrolytic plasma processing for high Nb-TiAl alloys

NASA Astrophysics Data System (ADS)

Gui, Wanyuan; Hao, Guojian; Liang, Yongfeng; Li, Feng; Liu, Xiao; Lin, Junpin

2016-12-01

Metal surface modification by electrolytic plasma processing (EPP) is an innovative treatment widely commonly applied to material processing and pretreatment process of coating and galvanization. EPP involves complex processes and a great deal of parameters, such as preset voltage, current, solution temperature and processing time. Several characterization methods are presented in this paper for evaluating the micro-structure surfaces of Ti45Al8Nb alloys: SEM, EDS, XRD and 3D topography. The results showed that the oxide scale and other contaminants on the surface of Ti45Al8Nb alloys can be effectively removed via EPP. The typical micro-crater structure of the surface of Ti45Al8Nb alloys were observed by 3D topography after EPP to find that the mean diameter of the surface structure and roughness value can be effectively controlled by altering the processing parameters. The mechanical properties of the surface according to nanomechanical probe testing exhibited slight decrease in microhardness and elastic modulus after EPP, but a dramatic increase in surface roughness, which is beneficial for further processing or coating.

Surface modification of CoCr alloy using varying concentrations of phosphoric and phosphonoacetic acids: albumin and fibrinogen adsorption, platelet adhesion, activation, and aggregation studies.

PubMed

Thiruppathi, Eagappanath; Larson, Mark K; Mani, Gopinath

2015-01-01

CoCr alloy is commonly used in various cardiovascular medical devices for its excellent physical and mechanical properties. However, the formation of blood clots on the alloy surfaces is a serious concern. This research is focused on the surface modification of CoCr alloy using varying concentrations (1, 25, 50, 75, and 100 mM) of phosphoric acid (PA) and phosphonoacetic acid (PAA) to generate various surfaces with different wettability, chemistry, and roughness. Then, the adsorption of blood plasma proteins such as albumin and fibrinogen and the adhesion, activation, and aggregation of platelets with the various surfaces generated were investigated. Contact angle analysis showed PA and PAA coatings on CoCr provided a gradient of hydrophilic surfaces. FTIR showed PA and PAA were covalently bound to CoCr surface and formed different bonding configurations depending on the concentrations of coating solutions used. AFM showed the formation of homogeneous PA and PAA coatings on CoCr. The single and dual protein adsorption studies showed that the amount of albumin and fibrinogen adsorbed on the alloy surfaces strongly depend on the type of PA and PAA coatings prepared by different concentrations of coating solutions. All PA coated CoCr showed reduced platelet adhesion and activation when compared to control CoCr. Also, 75 and 100 mM PA-CoCr showed reduced platelet aggregation. For PAA coated CoCr, no significant difference in platelet adhesion and activation was observed between PAA coated CoCr and control CoCr. Thus, this study demonstrated that CoCr can be surface modified using PA for potentially reducing the formation of blood clots and improving the blood compatibility of the alloy.

Stability of Phosphonic Self Assembled Monolayers (SAMs) on Cobalt Chromium (Co-Cr) Alloy under Oxidative conditions

PubMed Central

Bhure, Rahul; Abdel-Fattah, Tarek M.; Bonner, Carl; Hall, Felicia; Mahapatro, Anil

2011-01-01

Cobalt Chromium (Co-Cr) alloys has been widely used in the biomedical arena for cardiovascular, orthopedic and dental applications. Surface modification of the alloy allows us to tailor the interfacial properties to address critical challenges of Co-Cr alloy in medical applications. Self assembled monolayers (SAMs) of Octadecylphosphonic acid (ODPA) have been used to form thin films on the oxide layer of the Co-Cr alloy surface by solution deposition technique. The SAMs formed were investigated for their stability to oxidative conditions of ambient laboratory environment over periods of 1, 3, 7 and 14 days. The samples were then characterized for their stability using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Contact Angle Measurements. Detailed high energy XPS elemental scans confirmed the presence of the phosphonic monolayer after oxidative exposure which suggested that the SAMs were firmly attached to the oxide layer of Co-Cr alloy. AFM images gave topographical data of the surface and showed islands of SAMs on Co-Cr alloy surface, before and after SAM formation and also over the duration of the oxidative exposure. Contact angle measurements confirmed the hydrophobicity of the surface over 14 days. Thus the SAMs were found to be stable for the duration of the study. These SAMs could be subsequently tailored by modifying the terminal functional groups and could be used for various potential biomedical applications such as drug delivery, biocompatibility and tissue integration PMID:21603056

Surface damage mitigation of TC4 alloy via micro arc oxidation for oil and gas exploitation application: Characterizations of microstructure and evaluations on surface performance

NASA Astrophysics Data System (ADS)

Xie, Ruizhen; Lin, Naiming; Zhou, Peng; Zou, Jiaojuan; Han, Pengju; Wang, Zhihua; Tang, Bin

2018-04-01

Because of its excellent corrosion resistance, high specific strength and high tensile strength, TC4 titanium alloys used as petroleum tubes have received wide interest from material engineers after many technical investigations and estimations. However, because of its low surface hardness values, high coefficient of friction and poor wear resistance, the TC4 alloy is seldom adopted in tribological-related engineering components. In this work, micro-arc oxidation (MAO) coatings were fabricated on TC4 alloys in NaAlO2 and (NaPO3)6 electrolytes with and without ultrasonic assistance. The microstructural characterizations of the produced MAO coatings were investigated. Comparative estimations of electrochemical corrosion in CO2-saturated simulated oilfield brine and tribological behaviours on MAO coatings and TC4 alloys were conducted. The results showed that the introduction of ultrasound increased the thickness of the MAO coatings. The thickness increased by 34% and 15% in the NaAlO2 and (NaPO3)6 electrolytes, respectively. There was no significant discrepancy in phase constitutions when the MAO processes were conducted with and without ultrasonic assistance. Both MAO coatings obtained with and without ultrasonic assistance were found to improve the corrosion and wear resistance of the TC4 alloy. MAO treatments made it possible to ensure the working surface of a TC4 alloy with an enhanced surface performance for oil and gas exploitation applications.

Effect of alloy addition and growth conditions on the formation of Mg-based bioabsorbable thin films

NASA Astrophysics Data System (ADS)

Pursel, Sean M.; Petrilli, John D.; Horn, Mark W.; Shaw, Barbara A.

2008-08-01

Magnesium is an essential mineral in the human body and has recently been studied as a bioabsorbable material for use in cardiac stents. New areas of application can be found in bone plates, bone screws, and orthopedic implants. Magnesium alone has a corrosion rate much too high for use in such applications and has been alloyed with various elements to improve corrosion resistance. The use of vapor deposition to create Mg alloys for the above applications has not been attempted although certain properties of non-equilibrium alloys, namely corrosion resistance, can be improved. Using vapor deposition the characterization of the growth of magnesium alloy thin films has been done utilizing various alloying elements, substrate temperatures, post-deposition treatments, and substrate positions. The results point towards a growth mode controlled by crystallization of the Mg. Mg Sculptured thin films (STFs) are used to demonstrate these effects and potential solutions while also providing a route to control nanoscale surface morphology to enhance cell growth, cell attachment, and absorption properties. The results of the study are presented in terms of x-ray diffraction data, microscopy analysis of growth evolution, and corrosion testing. This magnesium alloy research utilizes a dual source deposition method that has also provided insight about some of the growth modes of other alloy STFs. Engineering of surface morphology using dip coatings and etching has been used in biomedical materials to enhance certain application specific surface properties. STF technology potentially provides a path to merge the advantages of non-equilibrium alloy formation and engineering nanoscale surface morphology.

Effect of abrasive water jet on the structure of the surface layer of Al-Mg alloy

NASA Astrophysics Data System (ADS)

Tabatchikova, T. I.; Tereshchenko, N. A.; Yakovleva, I. L.; Gudnev, N. Z.

2017-09-01

Optical, scanning, and transmission electron microscopy methods, and X-ray diffraction analysis have been used to study the changes in the structure and the microhardness in the surface layer of the Al-Mg (5.8-6.8 wt %) alloy after water jet cutting. The dislocation density, the sizes of coherent scattering regions, and microdistortions have been determined. The transformation of the fine structure has been revealed in the displacement from the alloy volume to the abrasive-waterjet cutting surface.

Surface modification of a biodegradable magnesium alloy with phosphorylcholine (PC) and sulfobetaine (SB) functional macromolecules for reduced thrombogenicity and acute corrosion resistance.

PubMed

Ye, Sang-Ho; Jang, Yong-Seok; Yun, Yeo-Heung; Shankarraman, Venkat; Woolley, Joshua R; Hong, Yi; Gamble, Lara J; Ishihara, Kazuhiko; Wagner, William R

2013-07-02

Siloxane functionalized phosphorylcholine (PC) or sulfobetaine (SB) macromolecules (PCSSi or SBSSi) were synthesized to act as surface modifying agents for degradable metallic surfaces to improve acute blood compatibility and slow initial corrosion rates. The macromolecules were synthesized using a thiol-ene radical photopolymerization technique and then utilized to modify magnesium (Mg) alloy (AZ31) surfaces via an anhydrous phase deposition of the silane functional groups. X-ray photoelectron spectroscopy surface analysis results indicated successful surface modification based on increased nitrogen and phosphorus or sulfur composition on the modified surfaces relative to unmodified AZ31. In vitro acute thrombogenicity assessment after ovine blood contact with the PCSSi and SBSSi modified surfaces showed a significant decrease in platelet deposition and bulk phase platelet activation compared with the control alloy surfaces. Potentiodynamic polarization and electrochemical impedance spectroscopy data obtained from electrochemical corrosion testing demonstrated increased corrosion resistance for PCSSi- and SBSSi-modified AZ31 versus unmodified surfaces. The developed coating technique using PCSSi or SBSSi showed promise in acutely reducing both the corrosion and thrombotic processes, which would be attractive for application to blood contacting devices, such as vascular stents, made from degradable Mg alloys.

Effects of conventional welding and laser welding on the tensile strength, ultimate tensile strength and surface characteristics of two cobalt-chromium alloys: a comparative study.

PubMed

Madhan Kumar, Seenivasan; Sethumadhava, Jayesh Raghavendra; Anand Kumar, Vaidyanathan; Manita, Grover

2012-06-01

The purpose of this study was to evaluate the efficacy of laser welding and conventional welding on the tensile strength and ultimate tensile strength of the cobalt-chromium alloy. Samples were prepared with two commercially available cobalt-chromium alloys (Wironium plus and Diadur alloy). The samples were sectioned and the broken fragments were joined using Conventional and Laser welding techniques. The welded joints were subjected to tensile and ultimate tensile strength testing; and scanning electron microscope to evaluate the surface characteristics at the welded site. Both on laser welding as well as on conventional welding technique, Diadur alloy samples showed lesser values when tested for tensile and ultimate tensile strength when compared to Wironium alloy samples. Under the scanning electron microscope, the laser welded joints show uniform welding and continuous molt pool all over the surface with less porosity than the conventionally welded joints. Laser welding is an advantageous method of connecting or repairing cast metal prosthetic frameworks.

Growth of Au on Ni(110): A Semiempirical Modeling of Surface Alloy Phases

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ibanez-Meier, Rodrigo; Ferrante, John

1995-01-01

Recent experiments using scanning tunneling microscopy show evidence for the formation of surface alloys of otherwise immiscible metals. Such is the case for Au deposited in Ni(110), where experiments by Pleth Nielsen el al.indicate that at low Au coverage (less than 0. 5 ML), Au atoms replace Ni atoms in the surface layer forming a surface alloy while the Ni atoms form islands on the surface. In this paper, we present results of a theoretical modeling of this phenomenon using the recently developed Bozzolo-Ferrante-Smith method for alloys. We provide results of an extensive analysis of the growth process that strongly support the conclusions drawn from the experiment: at very low coverages, there is a tendency for dimer formation on the overlayer, which later exchange positions with Ni atoms in the surface layer, thus accounting for the large number of substituted dimers. Ni island formation as well as other alternative short-range-order patterns are discussed.

SURFACE HARDENING OF TITANIUM BY TREATMENT IN MOLTEN BORAX

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

Minkevich, A.N.; Shul'ga, Yu.N.

1957-01-01

The surface hardening of titanium and titanium alloys by treatment in molten borax was investigated. Commercial titanium, a titanium-tungsten alloy, and an aluminum-chromium-titanium alloy were used for the experiments. To prevent oxidation of the titanium and to protect the surface, electro-chemical protection was applied, the current density being 0.1 amp/cm/sup 2/ and the the specimens were coated with a thin layer of borax. The results showed that treatment in molten borax is an effective method of increasing surface hardness. However, the strength, mmalleabiltiy, and toughness of the hardness increase is discussed. (J.S.R.)

First-principles surface interaction studies of aluminum-copper and aluminum-copper-magnesium secondary phases in aluminum alloys

NASA Astrophysics Data System (ADS)

da Silva, Thiago H.; Nelson, Eric B.; Williamson, Izaak; Efaw, Corey M.; Sapper, Erik; Hurley, Michael F.; Li, Lan

2018-05-01

First-principles density functional theory-based calculations were performed to study θ-phase Al2Cu, S-phase Al2CuMg surface stability, as well as their interactions with water molecules and chloride (Cl-) ions. These secondary phases are commonly found in aluminum-based alloys and are initiation points for localized corrosion. Density functional theory (DFT)-based simulations provide insight into the origins of localized (pitting) corrosion processes of aluminum-based alloys. For both phases studied, Cl- ions cause atomic distortions on the surface layers. The nature of the distortions could be a factor to weaken the interlayer bonds in the Al2Cu and Al2CuMg secondary phases, facilitating the corrosion process. Electronic structure calculations revealed not only electron charge transfer from Cl- ions to alloy surface but also electron sharing, suggesting ionic and covalent bonding features, respectively. The S-phase Al2CuMg structure has a more active surface than the θ-phase Al2Cu. We also found a higher tendency of formation of new species, such as Al3+, Al(OH)2+, HCl, AlCl2+, Al(OH)Cl+, and Cl2 on the S-phase Al2CuMg surface. Surface chemical reactions and resultant species present contribute to establishment of local surface chemistry that influences the corrosion behavior of aluminum alloys.

Technological capabilities of surface layers formation on implant made of Ti-6Al-4V ELI alloy.

PubMed

Kiel-Jamrozik, Marta; Szewczenko, Janusz; Basiaga, Marcin; Nowińska, Katarzyna

2015-01-01

The aim of the presented research was to find a combination of surface modification methods of implants made of the Ti-6Al-4V ELI alloy, that lead to formation of effective barrier for metallic ions that may infiltrate into solution. To this end, the following tests were carried out: roughness measurement, the voltamperometric tests (potentiodynamic and potentiostatic), and the ion infiltration test. The electropolishing process resulted in the lowering of surface roughness in comparison with mechanical treatment of the surface layer. The anodization process and steam sterilization increased corrosion resistance regardless of the mechanical treatment or electropolishing. The crevice corrosion tests revealed that independent of the modification method applied, the Ti-6Al-4V ELI alloy has excellent crevice corrosion resistance. The smallest quantity of ions infiltrated to the solution was observed for surface modification consisting in the mechanical treatment and anodization with the potential of 97 V. Electric parameters deter- mined during studies were the basis for effectiveness estimation of particular surface treatment methods. The research has shown that the anodization process significantly influences the pitting corrosion resistance of the Ti-6Al-4V ELI alloy independent of the previous surface treatment methods (mechanical and electrochemical). The surface layer after such modification is a protective barrier for metallic ions infiltrated to solution and protects titanium alloy against corrosive environment influence.

Process for manufacturing a lithium alloy electrochemical cell

DOEpatents

Bennett, William R.

1992-10-13

A process for manufacturing a lithium alloy, metal sulfide cell tape casts slurried alloy powders in an organic solvent containing a dissolved thermoplastic organic binder onto casting surfaces. The organic solvent is then evaporated to produce a flexible tape removable adhering to the casting surface. The tape is densified to increase its green strength and then peeled from the casting surface. The tape is laminated with a separator containing a lithium salt electrolyte and a metal sulfide electrode to form a green cell. The binder is evaporated from the green cell at a temperature lower than the melting temperature of the lithium salt electrolyte. Lithium alloy, metal sulfide and separator powders may be tape cast.

Thermophysical properties of a highly superheated and undercooled Ni-Si alloy melt

NASA Astrophysics Data System (ADS)

Wang, H. P.; Cao, C. D.; Wei, B.

2004-05-01

The surface tension of superheated and undercooled liquid Ni-5 wt % Si alloy was measured by an electromagnetic oscillating drop method over a wide temperature range from 1417 to 1994 K. The maximum undercooling of 206 K (0.13TL) was achieved. The surface tension of liquid Ni-5 wt % Si alloy is 1.697 N m-1 at the liquidus temperature 1623 K, and its temperature coefficient is -3.97×10-4 N m-1 K-1. On the basis of the experimental data of surface tension, the other thermophysical properties such as the viscosity, the solute diffusion coefficient, and the density of liquid Ni-5 wt % Si alloy were also derived.

Dispersoid reinforced alloy powder and method of making

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

Anderson, Iver E.; Terpstra, Robert L.

A method of making dispersion-strengthened alloy particles involves melting an alloy having a corrosion and/or oxidation resistance-imparting alloying element, a dispersoid-forming element, and a matrix metal wherein the dispersoid-forming element exhibits a greater tendency to react with a reactive species acquired from an atomizing gas than does the alloying element. The melted alloy is atomized with the atomizing gas including the reactive species to form atomized particles so that the reactive species is (a) dissolved in solid solution to a depth below the surface of atomized particles and/or (b) reacted with the dispersoid-forming element to form dispersoids in the atomizedmore » particles to a depth below the surface of said atomized particles. The atomized alloy particles are solidified as solidified alloy particles or as a solidified deposit of alloy particles. Bodies made from the dispersion strengthened alloy particles, deposit thereof, exhibit enhanced fatigue and creep resistance and reduced wear as well as enhanced corrosion and/or oxidation resistance at high temperatures by virtue of the presence of the corrosion and/or oxidation resistance imparting alloying element in solid solution in the particle alloy matrix.« less

Dispersoid reinforced alloy powder and method of making

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

Anderson, Iver E.; Terpstra, Robert L.

2017-10-10

A method of making dispersion-strengthened alloy particles involves melting an alloy having a corrosion and/or oxidation resistance-imparting alloying element, a dispersoid-forming element, and a matrix metal wherein the dispersoid-forming element exhibits a greater tendency to react with a reactive species acquired from an atomizing gas than does the alloying element. The melted alloy is atomized with the atomizing gas including the reactive species to form atomized particles so that the reactive species is (a) dissolved in solid solution to a depth below the surface of atomized particles and/or (b) reacted with the dispersoid-forming element to form dispersoids in the atomizedmore » particles to a depth below the surface of said atomized particles. The atomized alloy particles are solidified as solidified alloy particles or as a solidified deposit of alloy particles. Bodies made from the dispersion strengthened alloy particles, deposit thereof, exhibit enhanced fatigue and creep resistance and reduced wear as well as enhanced corrosion and/or oxidation resistance at high temperatures by virtue of the presence of the corrosion and/or oxidation resistance imparting alloying element in solid solution in the particle alloy matrix.« less

Investigation of passive films formed on the surface of alloy 690 in borate buffer solution

NASA Astrophysics Data System (ADS)

Jinlong, Lv; Tongxiang, Liang; Chen, Wang; Wenli, Guo

2015-10-01

The passive film formed on the surface of the alloy 690 in borate buffer solution was studied by potentiodynamic curves and electrochemical impedance spectroscopy. With the increasing of the passivation potential, the corrosion resistance of the alloy 690 reduced. Moreover, the corrosion resistance of the passive film was the lowest in the vicinity of 0.6 VSCE. These results were supported by XPS and Mott-Schottky analyses. The corrosion resistance of the alloy 690 increased with the increasing of passivated potential in borate buffer solution with chloride ion. The chloride ion decreased corrosion resistance of the alloy 690 according to point defect model.

Self-assembly of bimetallic AuxPd1-x alloy nanoparticles via dewetting of bilayers through the systematic control of temperature, thickness, composition and stacking sequence

NASA Astrophysics Data System (ADS)

Kunwar, Sundar; Pandey, Puran; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-03-01

Bimetallic alloy nanoparticles (NPs) are attractive materials for various applications with their morphology and elemental composition dependent optical, electronic, magnetic and catalytic properties. This work demonstrates the evolution of AuxPd1-x alloy nanostructures by the solid-state dewetting of sequentially deposited bilayers of Au and Pd on sapphire (0001). Various shape, size and configuration of AuxPd1‑x alloy NPs are fabricated by the systematic control of annealing temperature, deposition thickness, composition as well as stacking sequence. The evolution of alloy nanostructures is attributed to the surface diffusion, interface diffusion between bilayers, surface and interface energy minimization, Volmer-Weber growth model and equilibrium configuration. Depending upon the temperature, the surface morphologies evolve with the formation of pits, grains and voids and gradually develop into isolated semi-spherical alloy NPs by the expansion of voids and agglomeration of Au and Pd adatoms. On the other hand, small isolated to enlarged elongated and over-grown layer-like alloy nanostructures are fabricated due to the coalescence, partial diffusion and inter-diffusion with the increased bilayer thickness. In addition, the composition and stacking sequence of bilayers remarkably affect the final geometry of AuxPd1‑x nanostructures due to the variation in the dewetting process. The optical analysis based on the UV–vis-NIR reflectance spectra reveals the surface morphology dependent plasmonic resonance, scattering, reflection and absorption properties of AuxPd1‑x alloy nanostructures.

Corrosion behavior of cast Ti-6Al-4V alloyed with Cu.

PubMed

Koike, Marie; Cai, Zhuo; Oda, Yutaka; Hattori, Masayuki; Fujii, Hiroyuki; Okabe, Toru

2005-05-01

It has recently been found that alloying with copper improved the inherently poor grindability and wear resistance of titanium. This study characterized the corrosion behavior of cast Ti-6Al-4V alloyed with copper. Alloys (0.9 or 3.5 mass % Cu) were cast with the use of a magnesia-based investment in a centrifugal casting machine. Three specimen surfaces were tested: ground, sandblasted, and as cast. Commercially pure titanium and Ti-6Al-4V served as controls. Open-circuit potential measurement, linear polarization, and potentiodynamic cathodic polarization were performed in aerated (air + 10% CO(2)) modified Tani-Zucchi synthetic saliva at 37 degrees C. Potentiodynamic anodic polarization was conducted in the same medium deaerated by N(2) + 10% CO(2). Polarization resistance (R(p)), Tafel slopes, and corrosion current density (I(corr)) were determined. A passive region occurred for the alloy specimens with ground and sandblasted surfaces, as for CP Ti. However, no passivation was observed on the as-cast alloys or on CP Ti. There were significant differences among all metals tested for R(p) and I(corr) and significantly higher R(p) and lower I(corr) values for CP Ti compared to Ti-6Al-4V or the alloys with Cu. Alloying up to 3.5 mass % Cu to Ti-6Al-4V did not change the corrosion behavior. Specimens with ground or sandblasted surfaces were superior to specimens with as-cast surfaces. (c) 2005 Wiley Periodicals, Inc.

Scapulothoracic Muscle Activity during Use of a Wall Slide Device (WSD), a Comparison with the General Wall Push up Plus

PubMed Central

Park, Se-yeon; Ahn, Tae-kyung; Eom, Ji-hwan; Youn, Hyun-ji; Kim, In-kwang; Yoo, Won-gyu

2014-01-01

[Purpose] The purpose of this study was to evaluate the effect of the wall slide device on activation of the scapulothoracic musculature. [Subjects] We recruited 15 healthy male subjects. [Methods] The subjects performed the general wall push-up plus (WPUP) and the wall slide with device (WSD) exercises. During the exercises, the muscle activities of the upper and lower trapezius (UT, LT), middle and lower serratus anterior (MSA, LSA), and pectoralis major (PM) were measured. [Results] The normalized muscle activity data of the WSD were significantly higher in UT, MSA and LSA than the WPUP. [Conclusion] Our results suggest that exercise using the WSD can more effectively activate the scapulothoracic musculature than the general WPUP. PMID:25013271

LSA silicon material task closed-cycle process development

NASA Technical Reports Server (NTRS)

Roques, R. A.; Wakefield, G. F.; Blocher, J. M., Jr.; Browning, M. F.; Wilson, W.

1979-01-01

The initial effort on feasibility of the closed cycle process was begun with the design of the two major items of untested equipment, the silicon tetrachloride by product converter and the rotary drum reactor for deposition of silicon from trichlorosilane. The design criteria of the initial laboratory equipment included consideration of the reaction chemistry, thermodynamics, and other technical factors. Design and construction of the laboratory equipment was completed. Preliminary silicon tetrachloride conversion experiments confirmed the expected high yield of trichlorosilane, up to 98 percent of theoretical conversion. A preliminary solar-grade polysilicon cost estimate, including capital costs considered extremely conservative, of $6.91/kg supports the potential of this approach to achieve the cost goal. The closed cycle process appears to have a very likely potential to achieve LSA goals.

F3-LAYER Seasonal Variations Near the Southern Crest of the Equatorial Ionospheric Anomaly as a Function of Solar Cycle

NASA Astrophysics Data System (ADS)

Fagundes, P. R.; Klausner, V.; Bittencourt, J. A.; Sahai, Y.; Abalde, J. R.

2011-12-01

The occurrence of an additional F3-layer has been reported at Brazilian, Indian and Asian sectors by several investigators. In this paper, we report F3-layer seasonal variations carried out at São José dos Campos (23.2 S, 45.0 W; dip latitude 17.6 S), near the southern crest of the equatorial ionospheric anomaly (EIA), Brazil, as a function of solar cycle. The period from September 2000 to August 2001 is used as representative of high solar activity (HSA) and the period from January 2006 to December 2006 as representative of low solar activity (LSA). This investigation shows that the frequency of occurrence of the F3-layer during HSA is 11 times more than during LSA.

Quantifying Narrative Ability in Autism Spectrum Disorder: A Computational Linguistic Analysis of Narrative Coherence

PubMed Central

Losh, Molly; Gordon, Peter C.

2014-01-01

Autism Spectrum Disorder (ASD) is characterized by difficulties with social communication and functioning, and ritualistic/repetitive behaviors (American Psychiatric Association, 2013). While substantial heterogeneity exists in symptom expression, impairments in language discourse skills, including narrative, are universally observed (Tager-Flusberg, Paul, & Lord, 2005). This study applied a computational linguistic tool, Latent Semantic Analysis (LSA), to objectively characterize narrative performance in ASD across two narrative contexts differing in interpersonal and cognitive demands. Results indicated that individuals with ASD produced narratives comparable in semantic content to those from controls when narrating from a picture book, but produced narratives diminished in semantic quality in a more demanding narrative recall task. Results are discussed in terms of the utility of LSA as a quantitative, objective, and efficient measure of narrative ability. PMID:24915929

Large space antennas: A systems analysis case history

NASA Technical Reports Server (NTRS)

Keafer, Lloyd S. (Compiler); Lovelace, U. M. (Compiler)

1987-01-01

The value of systems analysis and engineering is aptly demonstrated by the work on Large Space Antennas (LSA) by the NASA Langley Spacecraft Analysis Branch. This work was accomplished over the last half-decade by augmenting traditional system engineering, analysis, and design techniques with computer-aided engineering (CAE) techniques using the Langley-developed Interactive Design and Evaluation of Advanced Spacecraft (IDEAS) system. This report chronicles the research highlights and special systems analyses that focused the LSA work on deployable truss antennas. It notes developmental trends toward greater use of CAE techniques in their design and analysis. A look to the future envisions the application of improved systems analysis capabilities to advanced space systems such as an advanced space station or to lunar and Martian missions and human habitats.

Biocompatibility and characterization of a Kolsterised® medical grade cobalt-chromium-molybdenum alloy

PubMed Central

Conti, Malcolm Caligari; Karl, Andreas; Wismayer, Pierre Schembri; Buhagiar, Joseph

2014-01-01

High failure rates of cobalt-chromium-molybdenum (Co-Cr-Mo) metal-on-metal hip prosthesis were reported by various authors, probably due to the alloy's limited hardness and tribological properties. This thus caused the popularity of the alloy in metal-on-metal hip replacements to decrease due to its poor wear properties when compared with other systems such as ceramic-on-ceramic. S-phase surface engineering has become an industry standard when citing surface hardening of austenitic stainless steels. This hardening process allows the austenitic stainless steel to retain its corrosion resistance, while at the same time also improving its hardness and wear resistance. By coupling S-phase surface engineering, using the proprietary Kolsterising® treatment from Bodycote Hardiff GmbH, that is currently being used mainly on stainless steel, with Co-Cr-Mo alloys, an improvement in hardness and tribological characteristics is predicted. The objective of this paper is to analyze the biocompatibility of a Kolsterised® Co-Cr-Mo alloy, and to characterize the material surface in order to show the advantages gained by using the Kolsterised® material relative to the original untreated alloy, and other materials. This work has been performed on 3 fronts including; Material characterization, “In-vitro” corrosion testing, and Biological testing conforming to BS EN ISO 10993–18:2009 - Biological evaluation of medical devices. Using these techniques, the Kolsterised® cobalt-chromium-molybdenum alloys were found to have good biocompatibility and an augmented corrosion resistance when compared with the untreated alloy. The Kolsterised® samples also showed a 150% increase in surface hardness over the untreated material thus predicting better wear properties. PMID:24451266

Biocompatibility and characterization of a Kolsterised(®) medical grade cobalt-chromium-molybdenum alloy.

PubMed

Conti, Malcolm Caligari; Karl, Andreas; Wismayer, Pierre Schembri; Buhagiar, Joseph

2014-01-01

High failure rates of cobalt-chromium-molybdenum (Co-Cr-Mo) metal-on-metal hip prosthesis were reported by various authors, probably due to the alloy's limited hardness and tribological properties. This thus caused the popularity of the alloy in metal-on-metal hip replacements to decrease due to its poor wear properties when compared with other systems such as ceramic-on-ceramic. S-phase surface engineering has become an industry standard when citing surface hardening of austenitic stainless steels. This hardening process allows the austenitic stainless steel to retain its corrosion resistance, while at the same time also improving its hardness and wear resistance. By coupling S-phase surface engineering, using the proprietary Kolsterising(®) treatment from Bodycote Hardiff GmbH, that is currently being used mainly on stainless steel, with Co-Cr-Mo alloys, an improvement in hardness and tribological characteristics is predicted. The objective of this paper is to analyze the biocompatibility of a Kolsterised(®) Co-Cr-Mo alloy, and to characterize the material surface in order to show the advantages gained by using the Kolsterised(®) material relative to the original untreated alloy, and other materials. This work has been performed on 3 fronts including; Material characterization, "In-vitro" corrosion testing, and Biological testing conforming to BS EN ISO 10993-18:2009 - Biological evaluation of medical devices. Using these techniques, the Kolsterised(®) cobalt-chromium-molybdenum alloys were found to have good biocompatibility and an augmented corrosion resistance when compared with the untreated alloy. The Kolsterised(®) samples also showed a 150% increase in surface hardness over the untreated material thus predicting better wear properties.

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

Alkhaldi, H. S.; Department of Physics in Jubail Education college, Dammam University, Dammam 1982; Kremer, F.

The development of porosity in single-crystal germanium and silicon-germanium alloys (c-Si{sub 1−x} Ge{sub x}) of (100) orientation was studied under bombardment with 140 keV Ge{sup −} ions over a wide range of temperatures (−180 to 400 °C) and ion fluences up to 1 × 10{sup 18} ions/cm{sup 2}. The surface swelling and morphology were investigated using multi-characterization techniques including optical profilometry, transmission electron microscopy, and scanning electron microscopy. The initiation of porosity and the evolution of the near-surface microstructure strongly depend on the ion fluence, the irradiation temperature, and the stoichiometry of the substrate. Significant results and new findings include: (i) the fact that,more » over the entire temperature and stoichiometry range, porosity is only developed once the substrate is rendered amorphous; (ii) with increasing Si content in the alloy, the onset of porosity is pushed to higher fluences; (iii) porosity is observed for Si contents in the alloy up to 23% but not higher under the irradiation conditions used; and (iv) in all cases the initiation of porosity was observed to occur at the surface of the amorphous alloy above a threshold fluence. This last result strongly suggests that the mechanism for initiation of porosity is via preferential vacancy segregation and clustering at the surface of the amorphous alloy. Particularly at elevated temperatures, preferential sputtering of the Si-Ge atomic species in the alloy also plays an important role in developing the surface topography and porosity in alloys. Such effects are discussed along with the implications of our results for mechanisms of porosity in Ge and its alloys.« less

Copper-acrylic enamel serves as lubricant for cold drawing of refractory metals

NASA Technical Reports Server (NTRS)

Beane, C.; Karasek, F.

1966-01-01

Acrylic enamel spray containing metallic copper pigment lubricates refractory metal tubing during cold drawing operations so that the tubing surface remains free from scratches and nicks and does not seize in the die. Zirconium alloys, zirconium, tantalum alloys, niobium alloys, vanandium alloys and titanium alloys have been drawn using this lubricant.

Shear strengths of a gallium alloy bonded to human enamel following nine different surface treatments.

PubMed

Claire, J; Williams, P T

2001-03-01

Gallium and indium-containing alloys have demonstrated an ability to wet and bond to many types of materials including enamel. The purpose of this study was to evaluate and compare the bond strengths of a gallium-and-indium-containing alloy and a dental amalgam to human enamel surfaces. A flat enamel bonding surface was created by slicing recently extracted human molars with a 180-grit diamond wheel. Cylinders of amalgam or a gallium-indium alloy were bonded to the as-cut surfaces or to as-cut surfaces that had been pumiced, air-abraded or acid-etched for various times. Before testing, samples were stored under different conditions (100% humidity, immersed in water, thermocycled). The shear-bond strength was determined using a crosshead speed of 0.1 mm x min(-1). Sample size was 10. Data was subjected to ANOVA and a post-hoc Tukey's test. The bond strength of amalgam to enamel was zero. The bond strength of the gallium-indium alloy ranged between 6.5 MPa (10s etch with 10% phosphoric acid) and 4.2 MPa (pumiced enamel). Acid-etching significantly increased the bond strength (P>0.0001) The bond strength was not significantly affected by the type of mechanical surface preparation, storage conditions, thermocycling, etching times or acid concentrations. Bonding, particularly chemical bonding, suggests a greater potential for better wetting and therefore better sealing of a cavity. Since microleakage of restorations is one of the principal causes of restoration failure, materials that can bond may in turn posses enhanced resistance to microleakage and ultimately, resistance to restoration failure. The gallium-indium alloy evaluated in this study may be such an alloy.

Upregulation of cell proliferation via Shc and ERK1/2 MAPK signaling in SaOS-2 osteoblasts grown on magnesium alloy surface coating with tricalcium phosphate.

PubMed

Jiang, Tianlong; Guo, Lei; Ni, Shenghui; Zhao, Yuyan

2015-04-01

Magnesium (Mg) alloys have been demonstrated to be viable orthopedic implants because of mechanical and biocompatible properties similar to natural bone. In order to improve its osteogenic properties, a porous β-tricalcium phosphate (β-TCP) was coated on the Mg-3AI-1Zn alloy by alkali-heat treatment technique. The human bone-derived cells (SaOS-2) were cultured on (β-TCP)-Mg-3AI-1Zn in vitro, and the osteoblast response, the morphology and the elements on this alloy surface were investigated. Also, the regulation of key intracellular signalling proteins was investigated in the SaOS-2 cells cultured on alloy surface. The results from scanning electron microscope and immunofluorescence staining demonstrated that (β-TCP)-Mg-3AI-1Zn induced significant osteogenesis. SaOS-2 cell proliferation was improved by β-TCP coating. Moreover, the (β-TCP)-Mg-3AI-1Zn surface induced activation of key intracellular signalling proteins in SaOS-2 cells. We observed an enhanced activation of Src homology and collagen (Shc), a common point of integration between bone morphogenetic protein 2, and the Ras/mitogen-activated protein kinase (MAPK) pathway. ERK1/2 MAP kinase activation was also upregulated, suggesting a role in mediating osteoblastic cell interactions with biomaterials. The signalling pathway involving c-fos (member of the activated protein-1) was also shown to be upregulated in osteoblasts cultured on the (β-TCP)-Mg-3AI-1Zn. These results suggest that β-TCP coating may contribute to successful osteoblast function on Mg alloy surface. (β-TCP)-Mg-3AI-1Zn may upregulate cell proliferation via Shc and ERK1/2 MAPK signaling in SaOS-2 osteoblasts grown on Mg alloy surface.

Advances in aluminum anodizing

NASA Technical Reports Server (NTRS)

Dale, K. H.

1969-01-01

White anodize is applied to aluminum alloy surfaces by specific surface preparation, anodizing, pigmentation, and sealing techniques. The development techniques resulted in alloys, which are used in space vehicles, with good reflectance values and excellent corrosive resistance.

The surface alloying effect of silicon in a binary NiTi-base alloy on the corrosion resistance and biocompatibility of the material

NASA Astrophysics Data System (ADS)

Psakhie, S. G.; Lotkov, A. I.; Meisner, L. L.; Meisner, S. N.; Matveeva, V. A.

2013-02-01

The corrosion resistance behavior and cytotoxicity of binary NiTi-base alloy specimens subjected to surface modification by silicon ion beams and the proliferative ability of mesenchymal stem cells of rat marrow on an ion-implanted surface of the alloy have been studied. The silicon ion beam processing of specimen surfaces is shown to bring about a nearly two-fold improvement in the corrosion resistance of the material to attack by aqueous solutions of NaCl (artificial body fluid) and human plasma and a drastic decrease in the nickel concentration after immersion of the specimens into the solutions for ˜3400 and ˜6000 h, respectively (for the artificial plasma solution, a nearly 20-fold decrease in the Ni concentration is observed.)

Editors' Choice—Electrochemically Active Surface Area Measurement of Aged Pt Alloy Catalysts in PEM Fuel Cells by CO Stripping

DOE PAGES

Garrick, Taylor R.; Moylan, Thomas E.; Carpenter, Michael K.; ...

2016-12-13

The use of hydrogen adsorption/desorption (HAD) is a convenient method to measure the Pt surface area of a catalyst. However, it was shown that electrochemical charges measured by this technique can underestimate the Pt surface area by up to a factor of two for small Pt nanoparticles or Pt alloy nanoparticles. Electrooxidation of CO, so-called CO stripping, has been shown to be more accurate. Yet measurements of CO stripping in MEAs are scarce, especially on high activity alloy catalysts. In this study we investigated CO stripping and the ratio between Pt surface areas measured by CO and by HAD onmore » several Pt and Pt alloy catalysts. The effects on these measurements of temperature and catalyst aging by voltage cycling are discussed.« less

Editors' Choice—Electrochemically Active Surface Area Measurement of Aged Pt Alloy Catalysts in PEM Fuel Cells by CO Stripping

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

Garrick, Taylor R.; Moylan, Thomas E.; Carpenter, Michael K.

The use of hydrogen adsorption/desorption (HAD) is a convenient method to measure the Pt surface area of a catalyst. However, it was shown that electrochemical charges measured by this technique can underestimate the Pt surface area by up to a factor of two for small Pt nanoparticles or Pt alloy nanoparticles. Electrooxidation of CO, so-called CO stripping, has been shown to be more accurate. Yet measurements of CO stripping in MEAs are scarce, especially on high activity alloy catalysts. In this study we investigated CO stripping and the ratio between Pt surface areas measured by CO and by HAD onmore » several Pt and Pt alloy catalysts. The effects on these measurements of temperature and catalyst aging by voltage cycling are discussed.« less

Surface characteristics, corrosion and bioactivity of chemically treated biomedical grade NiTi alloy.

PubMed

Chembath, Manju; Balaraju, J N; Sujata, M

2015-11-01

The surface of NiTi alloy was chemically modified using acidified ferric chloride solution and the characteristics of the alloy surface were studied from the view point of application as a bioimplant. Chemically treated NiTi was also subjected to post treatments by annealing at 400°C and passivation in nitric acid. The surface of NiTi alloy after chemical treatment developed a nanogrid structure with a combination of one dimensional channel and two dimensional network-like patterns. From SEM studies, it was found that the undulations formed after chemical treatment remained unaffected after annealing, while after passivation process the undulated surface was filled with oxides of titanium. XPS analysis revealed that the surface of passivated sample was enriched with oxides of titanium, predominantly TiO2. The influence of post treatment on the corrosion resistance of chemically treated NiTi alloy was monitored using Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS) in Phosphate Buffered Saline (PBS) solution. In the chemically treated condition, NiTi alloy exhibited poor corrosion resistance due to the instability of the surface. On the other hand, the breakdown potential (0.8V) obtained was highest for the passivated samples compared to other surface treated samples. During anodic polarization, chemically treated samples displayed dissolution phenomenon which was predominantly activation controlled. But after annealing and passivation processes, the behavior of anodic polarization was typical of a diffusion controlled process which confirmed the enhanced passivity of the post treated surfaces. The total resistance, including the porous and barrier layer, was in the range of mega ohms for passivated surfaces, which could be attributed to the decrease in surface nickel content and formation of compact titanium oxide. The passivated sample displayed good bioactivity in terms of hydroxyapatite growth, noticed after 14days immersion in Hanks' solution. Copyright © 2015 Elsevier B.V. All rights reserved.

The inflammatory cytokine effect of Pam3CSK4 TLR2 agonist alone or in combination with Leishmania infantum antigen on ex-vivo whole blood from sick and resistant dogs.

PubMed

Martínez-Orellana, Pamela; Quirola-Amores, Paulina; Montserrat-Sangrà, Sara; Ordeix, Laura; Llull, Joan; Álvarez-Fernández, Alejandra; Solano-Gallego, Laia

2017-03-13

A wide spectrum of clinical manifestations and immune responses exist in canine L. infantum infection. Ibizan hounds are more "resistant" to disease than other dog breeds. Recognition of pathogen-associated molecule patterns by toll like receptors (TLRs) rapidly triggers a variety of anti-microbial immune responses through the induction of pro-inflammatory cytokines such as TNF-α and IL-6 which may play an important role in controlling Leishmania infection. The main objective of this study was to investigate and compare the effect of a TLR2 agonist (TLR2a) alone or in combination with L. infantum antigen (LSA) on ex vivo whole blood cytokine production from healthy seronegative IFN-γ non-producer dogs from an area of low in canine leishmaniosis endemicity (n = 11); sick seropositive dogs with low production of IFN-γ (n = 17) and healthy seronegative or low positive Ibizan hounds with a predominant IFN-γ production (n = 21) from a highly endemic area. Whole blood was stimulated with medium alone (Ø), LSA, concanavalin A, TLR2 (Pam3CSK4) receptor agonist (Ø + TLR2a) and TLR2a and LSA (LSA + TLR2a) for 48 h. Supernatants were harvested for measurement of canine TNF-α and IL-6 cytokines by ELISA. A significant increase of TNF-α was found in the supernatants of stimulated blood from all groups (Ø + TLR2a and LSA + TLR2a) when compared with medium alone. A similar pattern was observed for IL-6. Interestingly, a significant increase of TNF-α production was only observed when stimulation with LSA + TLR2a was compared with TLR2a alone in Ibizan hounds. A significant increase of TNF-α production was observed with stimulation of LSA + TLR2a when compared with LSA in all groups. Significantly higher concentrations of TNF-α and IL-6 were detected in Ibizan hounds, especially for the Ø + TLR2a and LSA + TLR2a treatments compared with other groups. This study demonstrated that TLR2a alone enhances the production of the inflammatory cytokines TNF-α and IL-6 in sick, "resistant" and healthy non-infected dogs. In addition, a combination of LSA+TLR2a promoted a synergistic pro-inflammatory effect with TNF-α in Ibizan hounds but not in seropositive sick dogs and seronegative healthy dogs. These findings might suggest the importance of Pam3CSK4 as a possible immunomodulator for CanL.

Corrosion behaviour of laser-cleaned AA7024 aluminium alloy

NASA Astrophysics Data System (ADS)

Zhang, F. D.; Liu, H.; Suebka, C.; Liu, Y. X.; Liu, Z.; Guo, W.; Cheng, Y. M.; Zhang, S. L.; Li, L.

2018-03-01

Laser cleaning has been considered as a promising technique for the preparation of aluminium alloy surfaces prior to joining and welding and has been practically used in the automotive industry. The process is based on laser ablation to remove surface contaminations and aluminium oxides. However the change of surface chemistry and oxide status may affect corrosion behaviour of aluminium alloys. Until now, no work has been reported on the corrosion characteristics of laser cleaned metallic surfaces. In this study, we investigated the corrosion behaviour of laser-cleaned AA7024-T4 aluminium alloy using potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The results showed that the laser-cleaned surface exhibited higher corrosion resistance in 3.5 wt.% NaCl solution than as-received hot-rolled alloy, with significant increase in impedance and decrease in capacitance, while SVET revealed that the active anodic points appeared on the as-received surface were not presented on the laser-cleaned surfaces. Such corrosion behaviours were correlated to the change of surface oxide status measured by glow discharge optical emission spectrometry (GDOES) and X-ray photoelectron spectroscopy (XPS). It was suggested that the removal of the original less protective oxide layer consisting of MgO and MgAl2O4 on the as-received surfaces and the newly formed more protective oxide layer containing mainly Al2O3 and MgO by laser cleaning were responsible for the improvement of the corrosion performance.

Superhydrophobic surface prepared by micro-milling and WEDM on aluminum alloy

NASA Astrophysics Data System (ADS)

Yanling, Wan; Jian, Yang; Huadong, Yu

2018-06-01

To simulate the hydrophobic microstructure of rice leaf surface, high-speed precision micro-milling machine was used to fabricate micro groove array structure on the surface of aluminum alloy. The micro-and nanostructure was constructed on the surface of the grooved convex platform by Wire Cut Electrical Discharge Machining (WEDM). The surface morphology and hydrophobic properties of the aluminum alloy microstructures fabricated by two processing methods were observed respectively, and the hydrophobic mechanism was analyzed. The results show that the contact angle was effectively improved from 49° up to 158.4° in the vertical direction, and 146.7° in the parallel direction. The change of surface wettability from hydrophilic to hydrophobic was realized. By comparison, the micro-and nanostructure fabricated by WEDM had improved the hydrophobic stability of the aluminum alloy surface while enlarging the contact Angle, and the micro-milling groove structure further amplified the contact angle and greatly reduced the contact area of the water droplet, it was also observed that the drop took longer to completely spread on the sample after WEDM.

Comparison of the effect of different surface treatments on the bond strength of different cements with nickel chromium metal alloy: An in vitro study

PubMed Central

Kapoor, Saumya; Balakrishnan, Dhanasekar

2017-01-01

Background For success of any indirect metal restoration, a strong bond between cement and the intaglio surface of metal is imperative. The aim of this study is to evaluate and compare the effect of different surface treatment on the tensile and shear bond strength of different cements with nickel–chromium alloy. Material and Methods 120 premolars were sectioned horizontally parallel to the occlusal surface to expose the dentin. Wax patterns were fabricated for individual tooth followed by casting them in nickel chromium alloy. 60 samples were tested for tensile bond strength, and the remaining 60 for shear bond strength. The samples were divided into three groups (of 20 samples each) as per the following surface treatment: oxidation only, oxidation and sandblasting, or oxidation, sandblasting followed by application of alloy primer. Each group was subdivided into 2 subgroups of 10 samples each, according to the bonding cement i.e RM-GIC and resin cement. Samples were subjected to thermocycling procedure followed by evaluation of bond strength. Results Two-way analyses of variance (ANOVA) was performed to compare the means of tensile and shear bond strength across type of surface treatment and cement, followed by post hoc parametric analysis. For all tests ‘p’ value of less than 0.05 was considered statistically significant. Conclusions The surface treatment of oxidation and sandblasting followed by application of alloy primer offered the maximum tensile and shear bond strength for both RM GIC and resin cement. Resin cement exhibited greater tensile and shear bond strength than RM-GIC for all the three surface treatment methods. Key words:Resin cement, resin modified glass ionomer cement, oxidation, sandblasting, alloy primer, tensile bond strength, shear bond strength, universal testing machine. PMID:28828160

The microstructure of the surface layer of magnesium laser alloyed with aluminum and silicon

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

Dziadoń, Andrzej

2016-08-15

The surface layer under analysis was formed as a result of diffusion bonding of a thin AlSi20 plate to a magnesium substrate followed by laser melting. Depending on the process parameters, the laser beam melted the AlSi20 plate only or the AlSi20 plate and a layer of the magnesium surface adjacent to it. Two types of microstructure of the remelted layer were thus analyzed. If the melting zone was limited to the AlSi20 plate, the microstructure of the surface layer was typical of a rapidly solidified hypereutectic Al–Si alloy. Since, however, the liquid AlSi20 reacted with the magnesium substrate, themore » following intermetallic phases formed: Al{sub 3}Mg{sub 2}, Mg{sub 17}Al{sub 12} and Mg{sub 2}Si. The microstructure of the modified surface layer of magnesium was examined using optical, scanning electron and transmission electron microscopy. The analysis of the surface properties of the laser modified magnesium revealed that the thin layer has a microstructure of a rapidly solidified Al–Si alloy offering good protection against corrosion. By contrast, the surface layer containing particles of intermetallic phases was more resistant to abrasion but had lower corrosion resistance than the silumin type layer. - Highlights: •A CO{sub 2} laser was used for surface alloying of Mg with AlSi20. •Before alloying, an AlSi20 plate was diffusion bonded with the Mg substrate. •The process parameters affected the alloyed layer microstructure and properties. •With melting limited to AlSi20, the layer had a structure of rapidly solidified AlSi20. •Mg–Al and Mg–Si phases were present when both the substrate and the plate were melted.« less

Delivery of paclitaxel from cobalt–chromium alloy surfaces without polymeric carriers

PubMed Central

Mani, Gopinath; Macias, Celia E.; Feldman, Marc D.; Marton, Denes; Oh, Sunho; Agrawal, C. Mauli

2014-01-01

Polymer-based carriers are commonly used to deliver drugs from stents. However, adverse responses to polymer coatings have raised serious concerns. This research is focused on delivering drugs from stents without using polymers or any carriers. Paclitaxel (PAT), an anti-restenotic drug, has strong adhesion towards a variety of material surfaces. In this study, we have utilized such natural adhesion property of PAT to attach these molecules directly to cobalt–chromium (Co–Cr) alloy, an ultra-thin stent strut material. Four different groups of drug coated specimens were prepared by directly adding PAT to Co–Cr alloy surfaces: Group-A (PAT coated, unheated, and ethanol cleaned); Group-B (PAT coated, heat treated, and ethanol cleaned); Group-C (PAT coated, unheated, and not ethanol cleaned); and Group-D (PAT coated, heat treated and not ethanol cleaned). In vitro drug release of these specimens was investigated using high performance liquid chromatography. Groups A and B showed sustained PAT release for up to 56 days. A simple ethanol cleaning procedure after PAT deposition can remove the loosely bound drug crystals from the alloy surfaces and thereby allowing the remaining strongly bound drug molecules to be released at a sustained rate. The heat treatment after PAT coating further improved the stability of PAT on Co–Cr alloy and allowed the drug to be delivered at a much slower rate, especially during the initial 7 days. The specimens which were not cleaned in ethanol, Groups C and D, showed burst release. PAT coated Co–Cr alloy specimens were thoroughly characterized using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. These techniques were collectively useful in studying the morphology, distribution, and attachment of PAT molecules on Co–Cr alloy surfaces. Thus, this study suggests the potential for delivering paclitaxel from Co–Cr alloy surfaces without using any carriers. PMID:20398928

The surface variation of Ti-14Al-21Nb as a function of temperature under ultrahigh vacuum conditions

NASA Technical Reports Server (NTRS)

Lee, W. S.; Sankaran, S. N.; Outlaw, R. A.; Clark, R. K.

1990-01-01

The effect of temperature, at conditions of ultrahigh vacuum, on the surface composition of the Ti-14Al-21Nb (in wt pct) alloy was investigated in samples heated to 1000 C in 100 C increments. Results of AES spectroscopy revealed that the Ti-14Al-21Nb alloy surface is extremely sensitive to temperature. At 300 C, the carbon and oxygen began to rapidly dissolve into the alloy, and at 600 C, bulk S segregated to the surface. The variation in the surface composition was extensive and different over the temperature range studied, indicating that there may be substantial changes in the hydrogen transport.

[Studies on high temperature oxidation of noble metal alloys for dental use. (III) On high temperature oxidation resistance of noble metal alloys by adding small amounts of alloying elements. (author's transl)].

PubMed

Ohno, H

1976-11-01

The previous report pointed out the undesirable effects of high temperature oxidation on the casting. The influence of small separate additions of Zn, Mg, Si, Be and Al on the high temperature oxidation of the noble metal alloys was examined. These alloying elements were chosen because their oxide have a high electrical resistivity and they have much higher affinity for oxygen than Cu. The casting were oxidized at 700 degrees C for 1 hour in air. The results obtained were as follows: 1. The Cu oxides are not observed on the as-cast surface of noble metal alloys containing small amounts of Zn, Mg, Si, Be, and Al. The castings have gold- or silver-colored surface. 2. After heating of the unpolished and polished castings, the additions of Si, Be and Al are effective in preventing oxidation of Cu in the 18 carats gold alloys. Especially the golden surface is obtained by adding Be and Al. But there is no oxidation-resistance on the polished castings in the alloys containing Zn and Mg. 3. The zinc oxide film formed on the as-cast specimen is effective in preventing of oxidation Cu in 18 carats gold alloys. 4. It seems that the addition of Al is most available in dental application.

Influence of artificial biological fluid composition on the biocorrosion of potential orthopedic Mg-Ca, AZ31, AZ91 alloys.

PubMed

Gu, X N; Zheng, Y F; Chen, L J

2009-12-01

The electrochemical behavior of potential orthopedic Mg-Ca, AZ31 and AZ91 alloys was studied in Hank's solution, Dulbecco's Modified Eagle's Medium (DMEM) and serum-containing medium (DMEM adding 10% fetal bovine serum (DMEM+FBS)) over a 7 day immersion period. The biocorrosion of the above three alloys for various immersion time intervals was investigated by linear polarization and electrochemical impedance spectroscopy (EIS). After 7 day immersion, potentiodynamic polarization tests were carried out and the surface morphologies of experimental samples were examined by scanning electron microscopy (SEM) observation complemented by energy-disperse spectrometer (EDS) analysis. It was shown that the corrosion of magnesium alloys was influenced by the composition of the solution. The results indicated that chloride ion could reduce the corrosion resistance and the hydrocarbonate ions could induce rapid surface passivation. The adsorbed amino acid on the experimental magnesium alloys' surface increased their polarization resistance and reduced current densities. The influence of the serum protein on corrosion was found to be associated with the magnesium alloy compositions. A Mg-Ca alloy exhibited an increased corrosion rate in the presence of serum protein. An AZ31 alloy showed an increased corrosion rate in DMEM+FBS in the initial 3 day immersion and the corrosion rate decreased thereafter. An AZ91 alloy, with high Al content, showed a reduced corrosion rate with the addition of FBS into DMEM.

In vitro and in vivo corrosion evaluation of nickel-chromium- and copper-aluminum-based alloys.

PubMed

Benatti, O F; Miranda, W G; Muench, A

2000-09-01

The low resistance to corrosion is the major problem related to the use of copper-aluminum alloys. This in vitro and in vivo study evaluated the corrosion of 2 copper-aluminum alloys (Cu-Al and Cu-Al-Zn) compared with a nickel-chromium alloy. For the in vitro test, specimens were immersed in the following 3 corrosion solutions: artificial saliva, 0.9% sodium chloride, and 1.0% sodium sulfide. For the in vivo test, specimens were embedded in complete dentures, so that one surface was left exposed. The 3 testing sites were (1) close to the oral mucosa (partial self-cleaning site), (2) surface exposed to the oral cavity (self-cleaning site), and (3) specimen bottom surface exposed to the saliva by means of a tunnel-shaped perforation (non-self-cleaning site). Almost no corrosion occurred with the nickel-chromium alloy, for either the in vitro or in vivo test. On the other hand, the 2 copper-aluminum-based alloys exhibited high corrosion in the sulfide solution. These same alloys also underwent high corrosion in non-self-cleaning sites for the in vivo test, although minimal attack was observed in self-cleaning sites. The nickel-chromium alloy presented high resistance to corrosion. Both copper-aluminum alloys showed considerable corrosion in the sulfide solution and clinically in the non-self-cleaning site. However, in self-cleaning sites these 2 alloys did not show substantial corrosion.

Surface Modification of NiTi Alloy via Cathodic Plasma Electrolytic Deposition and its Effect on Ni Ion Release and Osteoblast Behaviors

NASA Astrophysics Data System (ADS)

Yan, Ying; Cai, Kaiyong; Yang, Weihu; Liu, Peng

2013-07-01

To reduce Ni ion release and improve biocompatibility of NiTi alloy, the cathodic plasma electrolytic deposition (CPED) technique was used to fabricate ceramic coating onto a NiTi alloy surface. The formation of a coating with a rough and micro-textured surface was confirmed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. An inductively coupled plasma mass spectrometry test showed that the formed coating significantly reduced the release of Ni ions from the NiTi alloy in simulated body fluid. The influence of CPED treated NiTi substrates on the biological behaviors of osteoblasts, including cell adhesion, cell viability, and osteogenic differentiation function (alkaline phosphatase), was investigated in vitro. Immunofluorescence staining of nuclei revealed that the CPED treated NiTi alloy was favorable for cell growth. Osteoblasts on CPED modified NiTi alloy showed greater cell viability than those for the native NiTi substrate after 4 and 7 days cultures. More importantly, osteoblasts cultured onto a modified NiTi sample displayed significantly higher differentiation levels of alkaline phosphatase. The results suggested that surface functionalization of NiTi alloy with ceramic coating via the CPED technique was beneficial for cell proliferation and differentiation. The approach presented here is useful for NiTi implants to enhance bone osseointegration and reduce Ni ion release in vitro.

Laser irradiation of Mg-Al-Zn alloy: Reduced electrochemical kinetics and enhanced performance in simulated body fluid.

PubMed

Florian, David C; Melia, Michael A; Steuer, Fritz W; Briglia, Bruce F; Purzycki, Michael K; Scully, John R; Fitz-Gerald, James M

2017-05-11

As a lightweight metal with mechanical properties similar to natural bone, Mg and its alloys are great prospects for biodegradable, load bearing implants. However, rapid degradation and H 2 gas production in physiological media has prevented widespread use of Mg alloys. Surface heterogeneities in the form of intermetallic particles dominate the corrosion response. This research shows that surface homogenization significantly improved the biological corrosion response observed during immersion in simulated body fluid (SBF). The laser processed Mg alloy exhibited a 50% reduction in mass loss and H 2 evolution after 24 h of immersion in SBF when compared to the wrought, cast alloy. The laser processed samples exhibited increased wettability as evident from wetting angle studies, further suggesting improved biocompatibility. Electrochemical analysis by potentiodynamic polarization measurements showed that the anodic and cathodic kinetics were reduced following laser processing and are attributed to the surface chemical homogeneity.

Solid solution lithium alloy cermet anodes

DOEpatents

Richardson, Thomas J.

2013-07-09

A metal-ceramic composite ("cermet") has been produced by a chemical reaction between a lithium compound and another metal. The cermet has advantageous physical properties, high surface area relative to lithium metal or its alloys, and is easily formed into a desired shape. An example is the formation of a lithium-magnesium nitride cermet by reaction of lithium nitride with magnesium. The reaction results in magnesium nitride grains coated with a layer of lithium. The nitride is inert when used in a battery. It supports the metal in a high surface area form, while stabilizing the electrode with respect to dendrite formation. By using an excess of magnesium metal in the reaction process, a cermet of magnesium nitride is produced, coated with a lithium-magnesium alloy of any desired composition. This alloy inhibits dendrite formation by causing lithium deposited on its surface to diffuse under a chemical potential into the bulk of the alloy.

Iron-based alloy and nitridation treatment for PEM fuel cell bipolar plates

DOEpatents

Brady, Michael P [Oak Ridge, TN; Yang, Bing [Oak Ridge, TN; Maziasz, Philip J [Oak Ridge, TN

2010-11-09

A corrosion resistant electrically conductive component that can be used as a bipolar plate in a PEM fuel cell application is composed of an alloy substrate which has 10-30 wt. % Cr, 0.5 to 7 wt. % V, and base metal being Fe, and a continuous surface layer of chromium nitride and vanadium nitride essentially free of base metal. A oxide layer of chromium vanadium oxide can be disposed between the alloy substrate and the continuous surface nitride layer. A method to prepare the corrosion resistant electrically conductive component involves a two-step nitridization sequence by exposing the alloy to a oxygen containing gas at an elevated temperature, and subsequently exposing the alloy to an oxygen free nitrogen containing gas at an elevated temperature to yield a component where a continuous chromium nitride layer free of iron has formed at the surface.

Activation characteristics of multiphase Zr-based hydrogen storage alloys for Ni/MH rechargeable batteries

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

Lee, H.; Lee, S.M.; Lee, J.Y.

1999-10-01

AB{sub 2} type Zr-based Laves phase alloys have been studied for possible use as negative electrodes of Ni/MH batteries with high hydrogen storage capacity. However, these alloys have the serious problem of slow activation owing to the formation of surface oxide films. To overcome this problem, alloys with multiphase microstructures have been developed. These alloys become electrochemically active via the creation of micropores by the dissolution of soluble oxide components such as vanadium oxide. However, this phenomenon has been described based only on changes in the chemical composition of the oxide layer. In the present study, this phenomenon is approachedmore » with respect to interactions between the constituent phases. An electrochemical analysis of constituent phases showed that the second phase, resulting in localized Ni-rich pits on the alloy surface. The presence of microcracks at the periphery of the Ni-rich pits after 30 h exposure to KOH electrolyte implies that hydrogen is absorbed preferentially at Ni-rich pits, thereby forming a large active surface area. However, such multiphase alloys have poor cycle durability due to the persistent dissolution of components in the second phase. Through Cr substitution, the authors have developed a family of durable alloys to prevent this unwanted dissolution from the second phase.« less

Evaluation of the new TAMZ titanium alloy for dental cast application.

PubMed

Zhang, Y M; Guo, T W; Li, Z C

2000-12-01

To reveal the potential of the new titanium alloy as dental prosthodontic materials. Dental castings of TAMZ alloy were investigated in the casting machine specially designed for titanium. A mesh pattern was used to count the castability value. The mechanical properties were measured by means of a universal testing machine. Optical micrography was done on the exposed cross-section of TAMZ alloy casting. From the surface to the inner part the Knoop hardness in reacted layer of TAMZ alloy casting was measured. The structure and elemental analyses of the reacted layer were made by SEM and element line scanning observation. The castability value (Cv = 98%) and the tensile test (sigma b = 850 Mpa, sigma 0.2 = 575 Mpa, delta = 7.33%) data were collected. The castings microstructure showed main alpha phase and small beta phase. Knoop hardness in the surface reacted layer was greater than that in the inner part. From the SEM and element line scanning observation, there are three different layers in the surface reacted layer of the TAMZ alloy castings, and higher level of element of O, Al, Si and Zr were found in the reacted layer while the Si permeated deeper than others. TAMZ alloy can be accepted as a material for dental alloy in prosthodontics.

Mg-MOF-74/MgF2 Composite Coating for Improving the Properties of Magnesium Alloy Implants: Hydrophilicity and Corrosion Resistance

PubMed Central

Liu, Wei; Yan, Zhijie; Ma, Xiaolu; Geng, Tie; Wu, Haihong

2018-01-01

Surface modification on Mg alloys is highly promising for their application in the field of bone repair. In this study, a new metal–organic framework/MgF2 (Mg-MOF-74/MgF2) composite coating was prepared on the surface of AZ31B Mg alloy via pre-treatment of hydrofluoric acid and in situ hydrothermal synthesis methods. The surface topography of the composite coating is compact and homogeneous, and Mg-MOF-74 has good crystallinity. The corrosion resistance of this composite coating was investigated through Tafel polarization test and immersion test in simulated body fluid at 37 °C. It was found that Mg-MOF-74/MgF2 composite coating significantly slowed down the corrosion rate of Mg alloy. Additionally, Mg-MOF-74/MgF2 composite coating expresses super-hydrophilicity with the water contact angle of nearly 0°. In conclusion, on the basis of MgF2 anticorrosive coating, the introduction of Mg-MOF-74 further improves the biological property of Mg alloys. At last, we propose that the hydrophilicity of the composite coating is mainly owing to the large number of hydroxyl groups, the high specific surface area of Mg-MOF-74, and the rough coating produced by Mg-MOF-74 particles. Hence, Mg-MOF-74 has a great advantage in enhancing the hydrophilicity of Mg alloy surface. PMID:29518933

Mg-MOF-74/MgF₂ Composite Coating for Improving the Properties of Magnesium Alloy Implants: Hydrophilicity and Corrosion Resistance.

PubMed

Liu, Wei; Yan, Zhijie; Ma, Xiaolu; Geng, Tie; Wu, Haihong; Li, Zhongyue

2018-03-07

Surface modification on Mg alloys is highly promising for their application in the field of bone repair. In this study, a new metal-organic framework/MgF₂ (Mg-MOF-74/MgF₂) composite coating was prepared on the surface of AZ31B Mg alloy via pre-treatment of hydrofluoric acid and in situ hydrothermal synthesis methods. The surface topography of the composite coating is compact and homogeneous, and Mg-MOF-74 has good crystallinity. The corrosion resistance of this composite coating was investigated through Tafel polarization test and immersion test in simulated body fluid at 37 °C. It was found that Mg-MOF-74/MgF₂ composite coating significantly slowed down the corrosion rate of Mg alloy. Additionally, Mg-MOF-74/MgF₂ composite coating expresses super-hydrophilicity with the water contact angle of nearly 0°. In conclusion, on the basis of MgF₂ anticorrosive coating, the introduction of Mg-MOF-74 further improves the biological property of Mg alloys. At last, we propose that the hydrophilicity of the composite coating is mainly owing to the large number of hydroxyl groups, the high specific surface area of Mg-MOF-74, and the rough coating produced by Mg-MOF-74 particles. Hence, Mg-MOF-74 has a great advantage in enhancing the hydrophilicity of Mg alloy surface.

Enhanced in vitro biocompatibility of ultrafine-grained biomedical NiTi alloy with microporous surface

NASA Astrophysics Data System (ADS)

Zheng, C. Y.; Nie, F. L.; Zheng, Y. F.; Cheng, Y.; Wei, S. C.; Valiev, R. Z.

2011-08-01

Bulk ultrafine-grained Ni 50.8Ti 49.2 alloy (UFG-NiTi) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study, and to further improve its surface biocompatibility, surface modification techniques including sandblasting, acid etching and alkali treatment were employed to produce either irregularly roughened surface or microporous surface or hierarchical porous surface with bioactivity. The effect of the above surface treatments on the surface roughness, wettability, corrosion behavior, ion release, apatite forming ability and cytocompatibility of UFG-NiTi alloy were systematically investigated with the coarse-grained NiTi alloy as control. The pitting corrosion potential ( Epit) was increased from 393 mV (SCE) to 704 mV (SCE) with sandblasting and further increased to 1539 mV (SCE) with following acid etching in HF/HNO 3 solution. All the above surface treatment increased the apatite forming ability of UFG-NiTi in varying degrees when soaked them in simulated body fluid (SBF). Meanwhile, both sandblasting and acid etching could promote the cytocompatibility for osteoblasts: sandblasting enhanced cell attachment and acid etching increased cell proliferation. The different corrosion behavior, apatite forming ability and cellular response of UFG-NiTi after different surface modifications are attributed to the topography and wettability of the resulting surface oxide layer.

Brush Plating of Nickel-Tungsten Alloy for Engineering Application

DTIC Science & Technology

2012-08-01

ASETS Defense ‘12 1 Brush Plating of Nickel-Tungsten Alloy for Engineering Application Zhimin Zhong & Sid Clouser Report Documentation Page Form...COVERED 00-00-2012 to 00-00-2012 4. TITLE AND SUBTITLE Brush Plating of Nickel-Tungsten Alloy for Engineering Application 5a. CONTRACT NUMBER...6 Surface morphology Visual appearance, scanning electron and optical microscope images. Smooth, fine grained, micro- cracked surface morphology

Consolidation of Surface Coatings by Friction Stir Techniques

DTIC Science & Technology

2010-09-01

alloy samples were plasma sprayed with a Titanium-Nickel-Chrome coating or a Titanium coating. Single and multiple pass experiments were performed...based coatings onto the Aluminum alloy surface. Results showed that the most successful results were accomplished using a flat, pinless tool, with...properties. Aluminum alloy samples were plasma sprayed with a Titanium-Nickel-Chrome coating or a Titanium coating. Single and multiple pass experiments

NiTi shape-memory alloy oxidized in low-temperature plasma with carbon coating: Characteristic and a potential for cardiovascular applications

NASA Astrophysics Data System (ADS)

Witkowska, Justyna; Sowińska, Agnieszka; Czarnowska, Elżbieta; Płociński, Tomasz; Borowski, Tomasz; Wierzchoń, Tadeusz

2017-11-01

Surface layers currently produced on NiTi alloys do not meet all the requirements for materials intended for use in cardiology. Plasma surface treatments of titanium and its alloys under glow discharge conditions make it possible to produce surface layers, such as TiN or TiO2, which increases corrosion resistance and biocompatibility. The production of layers on NiTi alloys with the same properties, and maintaining their shape memory and superelasticity features, requires the use of low-temperature processes. At the same time, since it is known that the carbon-based layers could prevent excessive adhesion and aggregation of platelets, we examined the composite a-CNH + TiO2 type surface layer produced by means of a hybrid method combining oxidation in low-temperature plasma and Radio Frequency Chemical Vapor Deposition (RFCVD) processes. Investigations have shown that this composite layer increases the corrosion resistance of the material, and both the low degree of roughness and the chemical composition of the surface produced lead to decreased platelet adhesion and aggregation and proper endothelialization, which could extend the range of applications of NiTi shape memory alloys.

Surface compositional variations of Mo-47Re alloy as a function of temperature

NASA Technical Reports Server (NTRS)

Hoekje, S. J.; Outlaw, R. A.; Sankaran, S. N.

1993-01-01

Molybdenum-rhenium alloys are candidate materials for the National Aero-Space Plane (NASP) as well as for other applications in generic hypersonics. These materials are expected to be subjected to high-temperature (above 1200 C) casual hydrogen (below 50 torr), which could potentially degrade the material strength. Since the uptake of hydrogen may be controlled by the contaminant surface barriers, a study of Mo-47Re was conducted to examine the variations in surface composition as a function of temperature from 25 C to 1000 C. Pure molybdenum and rhenium were also examined and the results compared with those for the alloy. The analytical techniques employed were Auger electron spectroscopy, electron energy loss spectroscopy, ion scattering spectroscopy, and x ray photoelectron spectroscopy. The native surface was rich in metallic oxides that disappeared at elevated temperatures. As the temperature increased, the carbon and oxygen disappeared by 800 C and the surface was subsequently populated by the segregation of silicon, presumably from the grain boundaries. The alloy readily chemisorbed oxygen, which disappeared with heating. The disappearance temperature progressively increased for successive dosings. When the alloy was exposed to 800 torr of hydrogen at 900 C for 1 hour, no hydrogen interaction was observed.

[A surface reacted layer study of titanium-zirconium alloy after dental casting].

PubMed

Zhang, Y; Guo, T; Li, Z; Li, C

2000-10-01

To investigate the influence of the mold temperature on the surface reacted layer of Ti-Zr alloy castings. Ti-Zr alloy was casted into a mold which was made of a zircon (ZrO2.SiO2) for inner coating and a phosphate-bonded material for outer investing with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was casted separately. The surface roughness of the castings was calculated by instrument of smooth finish (China). From the surface to the inner part the Knoop hardness and thickness in reacted layer of Ti-Zr alloy casting was measured. The structure of the surface reacted layer was analysed by SEM. Elemental analyses of the interfacial zone of the casting was made by element line scanning observation. The surface roughness of the castings was increased significantly with the mold temperature increasing. At a higher mold temperature the Knoop hardness of the reactive layer was increased. At the three mold temperature the outmost surface was very hard, and microhardness data decreased rapidly where they reached constant values. The thickness was about 85 microns for castings at room temperature and 300 degrees C, 105 microns for castings at 600 degrees C. From the SEM micrograph of the Ti-Zr alloy casting, the surface reacted layer could be divided into three different layers. The first layer was called non-structure layer, which thickness was about 10 microns for room temperature group, 20 microns for 300 degrees C and 25 microns for 600 degrees C. The second layer was characterized by coarse-grained acicular crystal, which thickness was about 50 microns for three mold temperatures. The third layer was Ti-Zr alloy. The element line scanning showed non-structure layer with higher level of element of O, Al, Si and Zr, The higher the mold temperature during casting, the deeper the Si permeating and in the second layer the element Si could also be found. The mold temperature is one of the major factors influencing to casting quality. In order to reduce the surface reacted layer of Ti-Zr alloy castings, the lower mold temperature and the investment without Si should be chosen.

Layer Protecting the Surface of Zirconium Used in Nuclear Reactors.

PubMed

Ashcheulov, Petr; Skoda, Radek; Skarohlíd, Jan; Taylor, Andrew; Fendrych, Frantisek; Kratochvílová, Irena

2016-01-01

Zirconium alloys have very useful properties for nuclear facilities applications having low absorption cross-section of thermal electrons, high ductility, hardness and corrosion resistance. However, there is also a significant disadvantage: it reacts with water steam and during this (oxidative) reaction it releases hydrogen gas, which partly diffuses into the alloy forming zirconium hydrides. A new strategy for surface protection of zirconium alloys against undesirable oxidation in nuclear reactors by polycrystalline diamond film has been patented- Czech patent 305059: Layer protecting the surface of zirconium alloys used in nuclear reactors and PCT patent: Layer for protecting surface of zirconium alloys (Patent Number: WO2015039636-A1). The zirconium alloy surface was covered by polycrystalline diamond layer grown in plasma enhanced chemical vapor deposition apparatus with linear antenna delivery system. Substantial progress in the description and understanding of the polycrystalline diamond/ zirconium alloys interface and material properties under standard and nuclear reactors conditions (irradiation, hot steam oxidation experiments and heating-quenching cycles) was made. In addition, process technology for the deposition of protective polycrystalline diamond films onto the surface of zirconium alloys was optimized. Zircaloy2 nuclear fuel pins were covered by 300 nm thick protective polycrystalline diamond layer (PCD) using plasma enhanced chemical vapor deposition apparatus with linear antenna delivery system. The polycrystalline diamond layer protects the zirconium alloy surface against undesirable oxidation and consolidates its chemical stability while preserving its functionality. PCD covered Zircaloy2 and standard Zircaloy2 pins were for 30 min. oxidized in 1100°C hot steam. Under these conditions α phase of zirconium changes to β phase (more opened for oxygen/hydrogen diffusion). PCD anticorrosion protection of Zircaloy nuclear fuel assemblies can significantly prolong lifetime of Zirconium alloy in nuclear reactors even above Zirconium phase transition temperatures. Even after ion beam irradiation (10 dpa, 3 MeV Fe(2+)) the diamond film still shows satisfactory structural integrity with both sp(3) and sp(2) carbon phases. Zircaloy2 under the carbon-based protective layer after hot steam oxidation test differed from the original Zircaloy2 material composition only very slightly, proving that the diamond coating increases the material resistance to high temperature oxidation. Zirconium alloys nuclear fuel pins' surfaces were covered by compact and homogeneous polycrystalline diamond layers consisting of sp(3) and sp(2) carbon phases with a high crystalline diamond content and low roughness. Diamond withstands very high temperatures, has excellent thermal conductivity and low chemical reactivity, it does not degrade over time and (important for the nuclear fuel cladding) being pure carbon, it has perfect neutron cross-section properties. Moreover, polycrystalline diamond layers consisting of crystalline (sp(3)) and amorphous (sp(2)) carbon phases could have suitable thermal expansion. Zirconium alloys coated with polycrystalline diamond film are protected against undesirable changes and processes. Further, the polycrystalline diamond layer prevents the reaction between the alloy surface and water vapor. During such reaction, water molecules dissociate and initiate formation of zirconium dioxide and hydrogen, accompanied by the release of large amount of heat. Thus the protective layer prevents the formation of hydrogen and the release of reaction heat. Few relevant patents to the topic have been reviewed and cited.

Comparison of the tensile bond strength of high-noble, noble, and base metal alloys bonded to enamel.

PubMed

Sen, D; Nayir, E; Pamuk, S

2000-11-01

Although the bond strengths of various resin composite luting materials have been reported in the literature, the evaluation of these systems with various cast alloys of different compositions has not been completely clarified. To evaluate the tensile bond strength of sandblasted high-noble, noble, and base metal alloys bonded to etched enamel by 2 different bonding agents of different chemical composition: Panavia-Ex (BIS-GMA) and Super-Bond (4-META acrylic). Flat enamel surfaces were prepared on buccal surfaces of 60 extracted noncarious human incisors. Teeth were divided into 3 groups of 20 each. Twenty circular disks of 5 mm diameter were prepared for casting for each group. Group I was cast with a high-noble, group II with a noble, and group III with a base metal alloy. The surfaces of the disks were sandblasted with 250 microm Al(2)O(3). Ten disks of each group were bonded to exposed enamel surfaces with Super-Bond and 10 disks with Panavia-Ex as recommended by the manufacturer. The tensile bond strength was measured with an Instron universal testing machine with a crosshead speed of 0.5 mm/min until failure occurred. Two-way ANOVA was used to evaluate the results. The differences in bond strengths of Super-Bond and Panavia-Ex with different alloys were not significant. The highest bond strengths were obtained in base metal alloys, followed by noble and high-noble alloys. These results were significant. Panavia-Ex and Super-Bond exhibited comparable tensile bond strengths. For both luting agents, the highest bond strengths were achieved with base metal alloys and the lowest with high-noble alloys.

Microstructure and mechanical characteristics of gradient structured Cu and Cu alloys processed by surface mechanical attrition treatment

NASA Astrophysics Data System (ADS)

Hu, XZ; Cheng, LP; Chen, HL; Yin, Z.; Zhang, Z.; Shu, BP; Gong, YL; Zhu, XK

2017-05-01

Cu-Al-Zn alloys with different stacking fault energy (SFE) were processed by surface mechanical attrition treatment (SMAT) at cryogenic temperature (CT), mechanical properties of gradient structured Cu-Al-Zn alloys were investigated in this study. Al and Zn content in alloys, which result in the decrease of SFE, can contribute to the increase in strength. Cu-4.5wt%Al-14.3wt%Zn alloy with the lower SFE shows that the strength increased, the ductility did not decrease significantly with increasing processing time, and the strength can be improved by a thicker gradient structure (GS) layer. The better combination of strength and ductility was achieved in Cu-4.5wt%Al-14.3wt%Zn alloy with lower SFE.

Proximity-interference wake-induced vibration at subcritical Re: Mechanism analysis using a linear dynamic model

NASA Astrophysics Data System (ADS)

Li, Xintao; Zhang, Weiwei; Gao, Chuanqiang

2018-03-01

Wake-induced vibration (WIV) contains rich and complex phenomena due to the flow interference between cylinders. The aim of the present study is to gain physical insight into the intrinsic dynamics of WIV via linear stability analysis (LSA) of the fluid-structure interaction (FSI) system. A reduced-order-model-based linear dynamic model, combined with the direct computational fluid dynamics/computational structural dynamics simulation method, is adopted to investigate WIV in two identical tandem cylinders at low Re. The spacing ratio L/D, with L as the center-to-center distance and D as the diameter of cylinders, is selected as 2.0 to consider the effect of proximity flow interference. Results show that extensive WIV along with the vortex shedding could occur at subcritical Re conditions due to the instability of one coupled mode (i.e., coupled mode I, CM-I) of the FSI system. The eigenfrequency of CM-I transfers smoothly from close to the reduced natural frequency of structure to the eigenfrequency of uncoupled wake mode as the reduced velocity U* increases. Thus, CM-I characterizes as the structure mode (SM) at low U*, while it characterizes as the wake mode (WM) at large U*. Mode conversion of CM-I is the primary cause of the "frequency transition" phenomenon observed in WIV responses. Furthermore, LSA indicates that there exists a critical mass ratio mcr*, below which no upper instability boundary of CM-I exists (Uup p e r *→∞ ). The unbounded instability of CM-I ultimately leads to the "infinite WIV" phenomenon. The neutral stability boundaries for WIV in the (Re, U*) plane are determined through LSA. It is shown that the lowest Re possible for WIV regarding the present configuration is R el o w e s t≈34 . LSA accurately captures the dynamics of WIV at subcritical Re and reveals that it is essentially a fluid-elastic instability problem. This work lays a good foundation for the investigation of WIV at supercritical high Re and gives enlightenment to the understanding of more complex WIV phenomena therein.

General anesthesia versus segmental thoracic or conventional lumbar spinal anesthesia for patients undergoing laparoscopic cholecystectomy.

PubMed

Yousef, Gamal T; Lasheen, Ahmed E

2012-01-01

Laparoscopic cholecystectomy became the standard surgery for gallstone disease because of causing less postoperative pain, respiratory compromise and early ambulation. This study was designed to compare spinal anesthesia, (segmental thoracic or conventional lumbar) vs the gold standard general anesthesia as three anesthetic techniques for healthy patients scheduled for elective laparoscopic cholecystectomy, evaluating intraoperative parameters, postoperative recovery and analgesia, complications as well as patient and surgeon satisfaction. A total of 90 patients undergoing elective laparoscopic cholecystectomy, between January 2010 and May 2011, were randomized into three equal groups to undergo laparoscopic cholecystectomy with low-pressure CO2 pneumoperitoneum under segmental thoracic (TSA group) or conventional lumbar (LSA group) spinal anesthesia or general anesthesia (GA group). To achieve a T3 sensory level we used (hyperbaric bupivacaine 15 mg, and fentanyl 25 mg at L2/L3) for LSAgroup, and (hyperbaric bupivacaine 7.5 mg, and fentanyl 25 mg at T10/T11) for TSAgroup. Propofol, fentanyl, atracurium, sevoflurane, and tracheal intubation were used for GA group. Intraoperative parameters, postoperative recovery and analgesia, complications as well as patient and surgeon satisfaction were compared between the three groups. All procedures were completed laparoscopically by the allocated method of anesthesia with no anesthetic conversions. The time for the blockade to reach T3 level, intraoperative hypotensive and bradycardic events and vasopressor use were significantly lower in (TSA group) than in (LSA group). Postoperative pain scores as assessed throughout any time, postoperative right shoulder pain and hospital stay was lower for both (TSA group) and (LSA group) compared with (GA group). The higher degree of patients satisfaction scores were recorded in patients under segmental TSA. The present study not only confirmed that both segmental TSA and conventional lumber spinal anesthesia (LSA) are safe and good alternatives to general anesthesia (GA) in healthy patients undergoing laparoscopic cholecystectomy but also showed better postoperative pain control of both spinal techniques when compared with general anesthesia. Segmental TSA provides better hemodynamic stability, lesser vasopressor use and early ambulation and discharge with higher degree of patient satisfaction making it excellent for day case surgery compared with conventional lumbar spinal anesthesia.

The Effect of High Temperature Corrosion on Mechanical Behavior of a GAMMA-TiAl Alloy

NASA Astrophysics Data System (ADS)

Zhao, Wenyue; Ma, Yue; Gong, Shengkai

The mechanical properties of Ti-48Al-2Cr-2Nb alloy were discussed after the high temperature corrosion tests carried out with salt mixture of 75wt. % Na2SO4 and 25wt. % NaCl at 800°C. The microstructure of the alloy after corrosion was observed by SEM and the fracture behavior of the corroded and uncorroded alloys was investigated by means of the three-point bending tests. It has been shown that the corrosion path was mainly along the lamellar structure and rough surface with a large number of corrosion pits formed during the high temperature corrosion. The experimental results also indicated that the bearing capacity of bending fracture descended evidently due to the molten salt corrosion at high temperature, which only had remarkable effects on the surface state of the alloy. The microcracks inside the alloy always propagated along the phase interfaces and grain boundaries while the corrosion pits on salt-deposited surface became the main crack initiation location in corroded alloy. The stress concentration caused by corrosion was considered as the essential reason of the property reduction, which decreased the energy barrier of crack nucleation and shortened the incubation period.

First principles study of surface stability and segregation of PdRuRh ternary metal alloy system

NASA Astrophysics Data System (ADS)

Aspera, Susan Meñez; Arevalo, Ryan Lacdao; Nakanishi, Hiroshi; Kasai, Hideaki

2018-05-01

The recognized importance on the studies of alloyed materials is due to the high possibility of forming designer materials that caters to different applications. In any reaction and application, the stability and configuration of the alloy combination are important. In this study, we analyzed the surface stability and segregation of ternary metal alloy system PdRuRh through first principles calculation using density functional theory (DFT). We considered the possibility of forming phases as observed in the binary combinations of elements, i.e., completely miscible, and separating phases. With that, the model we analyzed for the ternary metal alloy slabs considers forming complete atomic miscibility, segregation of each component, and segregation of one component with mixing of the two other. Our results show that for the ternary combination of Pd, Rh and Ru, the Pd atoms have high tendency to segregate at the surface, while due to the high tendency of Ru and Rh to mix, core formation of a mixed RuRh is possible. Also, we determined that the trend of stability in the binary alloy system is a good determinant of stability in the ternary alloy system.

Evolution of Nickel-titanium Alloys in Endodontics.

PubMed

Ounsi, Hani F; Nassif, Wadih; Grandini, Simone; Salameh, Ziad; Neelakantan, Prasanna; Anil, Sukumaran

2017-11-01

To improve clinical use of nickel-titanium (NiTi) endodontic rotary instruments by better understanding the alloys that compose them. A large number of engine-driven NiTi shaping instruments already exists on the market and newer generations are being introduced regularly. While emphasis is being put on design and technique, manufacturers are more discreet about alloy characteristics that dictate instrument behavior. Along with design and technique, alloy characteristics of endodontic instruments is one of the main variables affecting clinical performance. Modification in NiTi alloys is numerous and may yield improvements, but also drawbacks. Martensitic instruments seem to display better cyclic fatigue properties at the expense of surface hardness, prompting the need for surface treatments. On the contrary, such surface treatments may improve cutting efficiency but are detrimental to the gain in cyclic fatigue resistance. Although the design of the instrument is vital, it should in no way cloud the importance of the properties of the alloy and how they influence the clinical behavior of NiTi instruments. Dentists are mostly clinicians rather than engineers. With the advances in instrumentation design and alloys, they have an obligation to deal more intimately with engineering consideration to not only take advantage of their possibilities but also acknowledge their limitations.

Study the formation of porous surface layer for a new biomedical titanium alloy

NASA Astrophysics Data System (ADS)

Talib Mohammed, Mohsin; Diwan, Abass Ali; Ali, Osamah Ihsan

2018-03-01

In the present work, chemical treatment using hydrogen peroxide (H2O2) oxidation and subsequent thermal treatment was applied to create a uniform porous layer over the surface of a new metastable β-Ti alloy. The results revealed that this oxidation treatment can create a stable ultrafine porous film over the oxidized surface. This promoted the electrochemical characteristics of H2O2-treated Ti-Zr-Nb (TZN) alloy system, presenting nobler corrosion behavior in simulated body fluid (SBF) comparing with untreated sample.

Experimental study of modification mechanism at a wear-resistant surfacing

NASA Astrophysics Data System (ADS)

Dema, R. R.; Amirov, R. N.; Kalugina, O. B.

2018-01-01

In the study, a simulation of the crystallization process was carried out for the deposition of the near-eutectic structure alloys with inoculants presence in order to reveal the regularities of the inoculant effect and parameters of the process mode simulating surfacing on the structure of the crystallization front and on the nucleation rate and kinetics of growth of equiaxed crystallites of primary phases occurring in the volume of the melt. The simulation technique of primary crystallization of alloys similar to eutectic alloys in the presence of modifiers is offered. The possibility of fully eutectic structure during surfacing of nominal hypereutectic alloys of type white cast irons in wide range of deviations from the nominal composition is revealed.

The effect of surface oxide layer on the rate of hydrogen emission from aluminum and its alloys in a high vacuum

NASA Technical Reports Server (NTRS)

Makarova, V. I.; Zyabrev, A. A.

1979-01-01

The influence of surface oxide layers on the kinetics of hydrogen emission at the high vacuum of 10 to the minus 8th power torr was investigated at temperatures from 20 to 450 C using samples of pure AB00 aluminum and the cast alloy AMg. Cast and deformed samples of AMts alloy were used to study the effect of oxide film thickness on the rate of hydrogen emission. Thermodynamic calculations of the reactions of the generation and dissociation of aluminum oxide show that degasification at elevated temperatures (up to 600 C) and high vacuum will not reduce the thickness of artificially-generated surface oxide layers on aluminum and its alloys.

Surface phenomena of hydroxyapatite film on the nanopore formed Ti-29Nb-xZr alloy by anodization for bioimplants.

PubMed

Kim, Eun-Ju; Jeong, Yong-Hoon; Choe, Han-Cheol

2013-03-01

In this study, surface phenomena of hydroxyapatite (HA) film on the nanopore formed Ti-29Nb-xZr alloy by anodization for bioimplants have been investigated by electron beam physical vapor deposition (EB-PVD), field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), potentiostat and contact angle. The microstructure of Ti-29Nb-xZr alloys exhibited equiaxed structure and alpha" phase decreased, whereas beta phase increased as Zr content increased. The increment of Zr contents in HA coated nanotubular Ti-29Nb-xZr alloys showed good corrosion potential in 0.9% NaCI solution. The wettability of HA coated nanotubular surface was higher than that of non-coated samples.

Method for fabricating laminated uranium composites

DOEpatents

Chapman, L.R.

1983-08-03

The present invention is directed to a process for fabricating laminated composites of uranium or uranium alloys and at least one other metal or alloy. The laminated composites are fabricated by forming a casting of the molten uranium with the other metal or alloy which is selectively positioned in the casting and then hot-rolling the casting into a laminated plate in or around which the casting components are metallurgically bonded to one another to form the composite. The process of the present invention provides strong metallurgical bonds between the laminate components primarily since the bond disrupting surface oxides on the uranium or uranium alloy float to the surface of the casting to effectively remove the oxides from the bonding surfaces of the components.

Wear Characteristic of Stellite 6 Alloy Hardfacing Layer by Plasma Arc Surfacing Processes

PubMed Central

Zhou, Xiaowei

2017-01-01

The microstructure and wear resistance of Stellite 6 alloy hardfacing layer at two different temperatures (room temperature and 300°C) were investigated by plasma arc surfacing processes on Q235 Steel. Tribological test was conducted to characterize the wear property. The microstructure of Stellite 6 alloy coating mainly consists of α-Co and (Cr, Fe)7C3 phases. The friction coefficient of Stellite 6 alloys fluctuates slightly under different loads at 300°C. The oxide layer is formed on the coating surface and serves as a special lubricant during the wear test. Abrasive wear is the dominant mechanism at room temperature, and microploughing and plasticity are the key wear mechanisms at 300°C. PMID:29359005

Reversible brazing process

DOEpatents

Pierce, Jim D.; Stephens, John J.; Walker, Charles A.

1999-01-01

A method of reversibly brazing surfaces together. An interface is affixed to each surface. The interfaces can be affixed by processes such as mechanical joining, welding, or brazing. The two interfaces are then brazed together using a brazing process that does not defeat the surface to interface joint. Interfaces of materials such as Ni-200 can be affixed to metallic surfaces by welding or by brazing with a first braze alloy. The Ni-200 interfaces can then be brazed together using a second braze alloy. The second braze alloy can be chosen so that it minimally alters the properties of the interfaces to allow multiple braze, heat and disassemble, rebraze cycles.

Nanostructured Platinum Alloys for Use as Catalyst Materials

NASA Technical Reports Server (NTRS)

Narayan, Sri R. (Inventor); Hays, Charles C. (Inventor)

2015-01-01

A series of binary and ternary Pt-alloys, that promote the important reactions for catalysis at an alloy surface; oxygen reduction, hydrogen oxidation, and hydrogen and oxygen evolution. The first two of these reactions are essential when applying the alloy for use in a PEMFC.

Nanostructured Platinum Alloys for Use as Catalyst Materials

NASA Technical Reports Server (NTRS)

Hays, Charles C. (Inventor); Narayan, Sri R. (Inventor)

2013-01-01

A series of binary and ternary Pt-alloys, that promote the important reactions for catalysis at an alloy surface; oxygen reduction, hydrogen oxidation, and hydrogen and oxygen evolution. The first two of these reactions are essential when applying the alloy for use in a PEMFC.

INFLUENCE OF THE KRAMER EFFECT ON ADSORPTION ON METALS.

DTIC Science & Technology

ADSORPTION, *ALLOYS, *FILMS, *METALS, *PROCESSING, ACIDS, ALCOHOLS , CYCLOHEXANES, EXCHANGE REACTIONS , FATTY ACIDS, HEAT TREATMENT , LEAD ALLOYS...LINOLENIC ACID, MACHINING , MEASUREMENT, MONOMOLECULAR FILMS, OLEIC ACID, SURFACES, TIN ALLOYS, WATER

Blanch Resistant and Thermal Barrier NiAl Coating Systems for Advanced Copper Alloys

NASA Technical Reports Server (NTRS)

Raj, Sai V. (Inventor)

2005-01-01

A method of forming an environmental resistant thermal barrier coating on a copper alloy is disclosed. The steps include cleansing a surface of a copper alloy, depositing a bond coat on the cleansed surface of the copper alloy, depositing a NiAl top coat on the bond coat and consolidating the bond coat and the NiAl top coat to form the thermal barrier coating. The bond coat may be a nickel layer or a layer composed of at least one of copper and chromium-copper alloy and either the bond coat or the NiAl top coat or both may be deposited using a low pressure or vacuum plasma spray.

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

DOE PAGES

Jayaraman, T. V.; Meka, V. M.; Jiang, X.; ...

2018-01-09

Here we investigated the ambient temperature structural properties (thickness, width, microstructure, and lattice parameter), and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties—saturation magnetization (M S) and intrinsic coercivity (H CI)—of rapidly-solidified (melt-spun) Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbonsmore » ranged between ~15 and 60 μm and 500–800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). The wheel surface speed showed an insignificant effect on M S while increased silicon content resulted in a decreasing trend in M S. Elevated temperature evaluation of the magnetization (M-T curves at ~7.96 kA/m) in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from that of the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The M S for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 to 900 K). While H CI increased with the increase in temperature for all the wheel surface speed and composition combination, its nature of increase is distinct for Fe-8 wt.% Si alloy ribbons compared to Fe-3 & 5 wt.% Si alloys ribbons. Finally, it appears that rapidly-solidified Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) while the Fe-8 wt.% Si alloy ribbons are comprised primarily of disordered phase along with minor constituents of an ordered phase.« less

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

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

Jayaraman, T. V.; Meka, V. M.; Jiang, X.

Here we investigated the ambient temperature structural properties (thickness, width, microstructure, and lattice parameter), and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties—saturation magnetization (M S) and intrinsic coercivity (H CI)—of rapidly-solidified (melt-spun) Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbonsmore » ranged between ~15 and 60 μm and 500–800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). The wheel surface speed showed an insignificant effect on M S while increased silicon content resulted in a decreasing trend in M S. Elevated temperature evaluation of the magnetization (M-T curves at ~7.96 kA/m) in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from that of the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The M S for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 to 900 K). While H CI increased with the increase in temperature for all the wheel surface speed and composition combination, its nature of increase is distinct for Fe-8 wt.% Si alloy ribbons compared to Fe-3 & 5 wt.% Si alloys ribbons. Finally, it appears that rapidly-solidified Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) while the Fe-8 wt.% Si alloy ribbons are comprised primarily of disordered phase along with minor constituents of an ordered phase.« less

Adsorption of oxygen on low-index surfaces of the TiAl{sub 3} alloy

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

Latyshev, A. M.; Bakulin, A. V.; Kulkova, S. E., E-mail: kulkova@ms.tsc.ru

Method of the projector augmented waves in the plane-wave basis within the generalized-gradient approximation for the exchange-correlation functional has been used to study oxygen adsorption on (001), (100), and (110) low-index surfaces of the TiAl{sub 3} alloy. It has been established that the sites that are most energetically preferred for the adsorption of oxygen are hollow (H) positions on the (001) surface and bridge (B) positions on the (110) and (100) surfaces. Structural and electronic factors that define their energy preference have been discussed. Changes in the atomic and electronic structure of subsurface layers that occur as the oxygen concentrationmore » increases to three monolayers have been analyzed. It has been shown that the formation of chemical bonds of oxygen with both components of the alloy leads to the appearance of states that are split-off from the bottoms of their valence bands, which is accompanied by the formation of a forbidden gap at the Fermi level and by a weakening of the Ti–Al metallic bonds in the alloy. On the Al-terminated (001) and (110) surfaces, the oxidation of aluminum dominates over that of titanium. On the whole, the binding energy of oxygen on the low-index surfaces with a mixed termination is higher than that at the aluminum-terminated surface. The calculation of the diffusion of oxygen in the TiAl{sub 3} alloy has shown that the lowest barriers correspond to the diffusion between tetrahedral positions in the (001) plane; the diffusion of oxygen in the [001] direction occurs through octahedral and tetrahedral positions. An increase in the concentration of aluminum in the alloy favors a reduction in the height of the energy barriers as compared to the corresponding barriers in the γ-TiAl alloy.« less

Corrosion and wear properties of laser surface modified NiTi with Mo and ZrO 2

NASA Astrophysics Data System (ADS)

Ng, K. W.; Man, H. C.; Yue, T. M.

2008-08-01

Because of its biocompatibility, superelasticity and shape memory characteristics, NiTi alloys have been gaining immense interest in the medical field. However, there is still concern on the corrosion resistance of this alloy if it is going to be implanted in the human body for a long time. Titanium is not toxic but nickel is carcinogenic and is implicated in various reactions including allergic response and degeneration of muscle tissue. Debris from wear and the subsequent release of Ni + ions due to corrosion in the body system are fatal issues for long-term application of this alloy in the human body. This paper reports the corrosion and wear properties of laser surface modified NiTi using Mo and ZrO 2 as surface alloying elements, respectively. The modified layers which are free from microcracks and porosity, act as both physical barrier to nickel release and enhance the bulk properties, such as hardness, wear resistance, and corrosion resistance. The electrochemical performance of the surface modified alloy was studied in Hanks' solution. Electrochemical impedance spectroscopy was measured.

Structure and properties of nitrided surface layer produced on NiTi shape memory alloy by low temperature plasma nitriding

NASA Astrophysics Data System (ADS)

Czarnowska, Elżbieta; Borowski, Tomasz; Sowińska, Agnieszka; Lelątko, Józef; Oleksiak, Justyna; Kamiński, Janusz; Tarnowski, Michał; Wierzchoń, Tadeusz

2015-04-01

NiTi shape memory alloys are used for bone and cardiological implants. However, on account of the metallosis effect, i.e. the release of the alloy elements into surrounding tissues, they are subjected to various surface treatment processes in order to improve their corrosion resistance and biocompatibility without influencing the required shape memory properties. In this paper, the microstructure, topography and morphology of TiN surface layer on NiTi alloy, and corrosion resistance, both before and after nitriding in low-temperature plasma at 290 °C, are presented. Examinations with the use of the potentiodynamic and electrochemical impedance spectroscopy methods were carried out and show an increase of corrosion resistance in Ringer's solution after glow-discharge nitriding. This surface titanium nitride layer also improved the adhesion of platelets and the proliferation of osteoblasts, which was investigated in in vitro experiments with human cells. Experimental data revealed that nitriding NiTi shape memory alloy under low-temperature plasma improves its properties for bone implant applications.

Oxidation- and Creep-Enhanced Fatigue of Haynes 188 Alloy-Oxide Scale System Under Simulated Pulse Detonation Engine Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.

2002-01-01

The development of the pulse detonation engine (PDE) requires robust design of the engine components that are capable of enduring harsh detonation environments. In this study, a high cycle thermal fatigue test rig was developed for evaluating candidate PDE combustor materials using a CO2 laser. The high cycle thermal fatigue behavior of Haynes 188 alloy was investigated under an enhanced pulsed laser test condition of 30 Hz cycle frequency (33 ms pulse period, and 10 ms pulse width including 0.2 ms pulse spike). The temperature swings generated by the laser pulses near the specimen surface were characterized by using one-dimensional finite difference modeling combined with experimental measurements. The temperature swings resulted in significant thermal cyclic stresses in the oxide scale/alloy system, and induced extensive surface cracking. Striations of various sizes were observed at the cracked surfaces and oxide/alloy interfaces under the cyclic stresses. The test results indicated that oxidation and creep-enhanced fatigue at the oxide scale/alloy interface was an important mechanism for the surface crack initiation and propagation under the simulated PDE condition.

Microstructure of rapidly solidified Nb-based pre-alloyed powders for additive manufacturing

NASA Astrophysics Data System (ADS)

Guo, Yueling; Jia, Lina; Kong, Bin; Zhang, Shengnan; Zhang, Fengxiang; Zhang, Hu

2017-07-01

For powder-based additive manufacturing, sphere-shaped Nb-37Ti-13Cr-2Al-1Si pre-alloyed powders were prepared by plasma rotating electrode processing (PREP). The microstructure, surface oxidation and microhardness of the pre-alloyed powders were systematically investigated. Results showed that the main phases were Nb solid solution (Nbss) and Cr2Nb. The Cr2Nb phases were further determined using transmission electron microscopy (TEM). Fine dendrite structures were observed in the as-fabricated pre-alloyed powders, which transformed to large grains after heat treatment (HT) at 1450 °C for 3 h. With the increase of powder size, the secondary dendrite arm spacing (SDAS) increased and the microhardness (HV) decreased. A clean powder surface free of oxide particles was obtained by PREP and an oxide layer with 9.39 nm in thickness was generated on the powder surface. Compared with Cr- and Nb-oxides, more Ti-oxides were formed on outmost powder surface with a higher content of Ti (up to 47.86 at.%). The differences upon the microstructure and microhardness of the pre-alloyed powders with different sizes were discussed.

High-mass heterogeneous cluster formation by ion bombardment of the ternary alloy Au 7Cu 5Al 4

DOE PAGES

Zinovev, Alexander V.; King, Bruce V.; Veryovkin, Igor V.; ...

2016-02-04

The ternary alloy Au 7Cu 5Al 4 was irradiated with 0.1–10 keV Ar + and the surface composition analyzed using laser sputter neutral mass spectrometry. Ejected clusters containing up to seven atoms, with masses up to 2000 amu, were observed. By monitoring the signals from sputtered clusters, the surface composition of the alloy was seen to change with 100 eV Ar + dose, reaching equilibrium after 10 nm of the surface was eroded, in agreement with TRIDYN simulation and indicating that the changes were due to preferential sputtering of Al and Cu. Ejected gold containing clusters were found to increasemore » markedly in intensity while aluminum containing clusters decreased in intensity as a result of Ar sputtering. Such an effect was most pronounced for low energy (<1 keV) Ar + sputtering and was consistent with TRIDYN simulations of the depth profiling. As a result, the component sputter yields from the ternary alloy were consistent with previous binary alloy measurements but showed greater Cu surface concentrations than expected from TRIDYN simulations.« less

Surface alloying in Sn/Au(111) at elevated temperature

NASA Astrophysics Data System (ADS)

Sadhukhan, Pampa; Singh, Vipin Kumar; Rai, Abhishek; Bhattacharya, Kuntala; Barman, Sudipta Roy

2018-04-01

On the basis of x-ray photoelectron spectroscopy, we show that when Sn is deposited on Au(111) single crystal surface at a substrate temperature TS=373 K, surface alloying occurs with the formation of AuSn phase. The evolution of the surface structure and the surface morphology has been studied by low energy electron diffraction and scanning tunneling microscopy, respectively as a function of Sn coverage and substrate temperatures.

Surface modification of a biodegradable magnesium alloy with phosphorylcholine (PC) and sulfobetaine (SB) functional macromolecules for reduced thrombogenicity and acute corrosion resistance

PubMed Central

Ye, Sang-Ho; Jang, Yong-Seok; Yun, Yeo-Heung; Shankarraman, Venkat; Woolley, Joshua R.; Hong, Yi; Gamble, Lara J.; Ishihara, Kazuhiko; Wagner, William R.

2013-01-01

Siloxane functionalized phosphorylcholine (PC) or sulfobetaine (SB) macromolecules (PCSSi or SBSSi) were synthesized to act as surface modifying agents for degradable metallic surfaces to improve acute blood compatibility and slow initial corrosion rates. The macromolecules were synthesized using a thiol-ene radical photopolymerization technique and then utilized to modify magnesium (Mg) alloy (AZ31) surfaces via an anhydrous phase deposition of the silane functional groups. X-ray photoelectron spectroscopy surface analysis results indicated successful surface modification based on increased nitrogen and phosphorus or sulfur composition on the modified surfaces relative to unmodified AZ31. In vitro acute thrombogenicity assessment after ovine blood contact with the PCSSi and SBSSi modified surfaces showed a significant decrease in platelet deposition and bulk phase platelet activation compared with the control alloy surfaces. Potentiodynamic polarization and electrochemical impedance spectroscopy data obtained from electrochemical corrosion testing demonstrated increased corrosion resistance for PCSSi and SBSSi modified AZ31 versus unmodified surfaces. The developed coating technique using PCSSi or SBSSi showed promise in acutely reducing both the corrosion and thrombotic processes, which would be attractive for application to blood contacting devices, such as vascular stents, made from degradable Mg alloys. PMID:23705967

LSA: Low-cost Solar Array project

NASA Technical Reports Server (NTRS)

1978-01-01

Topics discussed include silicon material processing; large-area silicon sheet development; encapsulation materials testing and development; project engineering and operations activities, and manufacturing techniques. The steps taken to integrate these efforts, are described.

Electronic structure of BaO/W cathode surfaces

NASA Technical Reports Server (NTRS)

Muller, Wolfgang

1989-01-01

The local electronic structure of the emissive layer of barium dispenser thermionic cathodes is investigated theoretically using the relativistic scattered-wave approach. The interaction of Ba and O with W, Os, and W-Os alloy surfaces is studied with atomic clusters modeling different absorption environments representative of B- and M-type cathodes. Ba is found to be strongly oxidized, while O and the metal substrate are in a reduced chemical state. The presence of O enhances the surface dipole and Ba binding energy relative to Ba on W. Model results for W-Os alloy substrates show only relatively small changes in Ba and O for identical geometries, but very large charge redistributions inside the substrate, which are attributed to the electronegativity difference between Os and W. If Os is present in the surface layer, the charge transfer from Ba to the substrate and the Ba binding energy increase relative to W. Explanations are offered for the improved electron emission from alloy surfaces and the different emission enhancement for different alloy substrates.

Application of Taguchi method to optimization of surface roughness during precise turning of NiTi shape memory alloy

NASA Astrophysics Data System (ADS)

Kowalczyk, M.

2017-08-01

This paper describes the research results of surface quality research after the NiTi shape memory alloy (Nitinol) precise turning by the tools with edges made of polycrystalline diamonds (PCD). Nitinol, a nearly equiatomic nickel-titanium shape memory alloy, has wide applications in the arms industry, military, medicine and aerospace industry, and industrial robots. Due to their specific properties NiTi alloys are known to be difficult-to-machine materials particularly by using conventional techniques. The research trials were conducted for three independent parameters (vc, f, ap) affecting the surface roughness were analyzed. The choice of parameter configurations were performed by factorial design methods using orthogonal plan type L9, with three control factors, changing on three levels, developed by G. Taguchi. S/N ratio and ANOVA analyses were performed to identify the best of cutting parameters influencing surface roughness.

Preparation of Copper and Chromium Alloyed Layers on Pure Titanium by Plasma Surface Alloying Technology

NASA Astrophysics Data System (ADS)

He, Xiaojing; Li, Meng; Wang, Huizhen; Zhang, Xiangyu; Tang, Bin

2015-05-01

Cu-Cr alloyed layers with different Cu and Cr contents on pure titanium were obtained by means of plasma surface alloying technology. The microstructure, chemical composition and phase composition of Cu-Cr alloyed layers were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. The experimental results demonstrate that the alloyed layers are bonded strongly to pure titanium substrate and consist of unbound Ti, CuTi, Cu3Ti, CuTi3 and Cr2Ti. The thickness of Cu5Cr5 and Cu7Cr3 alloyed layer are about 18 μm and 28 μm, respectively. The antibacterial properties against gram-negative Escherichia coli (E.coli, ATCC10536) and gram-positive Staphylococcus aureus (S. aureus, ATCC6538) of untreated pure titanium and Cu-Cr alloyed specimen were investigated by live/dead fluorescence staining method. The study shows that Cu-Cr alloyed layers exhibit excellent antibacterial activities against both E.coli and S.aureus within 24 h, which may be attributed to the formation of Cu-containing phases.

Monomolecular Silane Coatings on Magnesium/Aluminium Fuels

DTIC Science & Technology

1991-07-01

iii SUMMARY The aim of this project was to investigate the curing reaction between CTBN and magnesium/aluminium ailoy surfaces. A dispersion of...performing rheoloqacai experiments with these coated magnesium particles and CTBN . Surface analysis ot the alloys show a nigh percentage of magnesium...Rheoloq’cai analysis of these alloys dispersed 40% w/w in CTBN show increasing rates of change in viscosity with time for each alloy with increasing nominal

A study on alkaline heat treated Mg-Ca alloy for the control of the biocorrosion rate.

PubMed

Gu, X N; Zheng, W; Cheng, Y; Zheng, Y F

2009-09-01

To reduce the biocorrosion rate by surface modification, Mg-Ca alloy (1.4wt.% Ca content) was soaked in three alkaline solutions (Na(2)HPO(4), Na(2)CO(3) and NaHCO(3)) for 24h, respectively, and subsequently heat treated at 773K for 12h. Scanning electron microscopy and energy-dispersive spectroscopy results revealed that magnesium oxide layers with the thickness of about 13, 9 and 26microm were formed on the surfaces of Mg-Ca alloy after the above different alkaline heat treatments. Atomic force microscopy showed that the surfaces of Mg-Ca alloy samples became rough after three alkaline heat treatments. The in vitro corrosion tests in simulated body fluid indicated that the corrosion rates of Mg-Ca alloy were effectively decreased after alkaline heat treatments, with the following sequence: NaHCO(3) heated

Micro and Nano Laser Pulses for Melting and Surface Alloying of Aluminum with Copper

NASA Astrophysics Data System (ADS)

Hamoudi, Walid K.; Ismail, Raid A.; Sultan, Fatima I.; Jaleel, Summayah

2017-03-01

In the present work, the use of microsecond and nanosecond laser pulses to alloy copper in aluminum is presented. In the first run, high purity (99.999%) copper thin film was thermally evaporated over (99.9%) purity, 300 μm aluminum sheet. Thereafter, surface alloying was performed using (1-3) 500 μs, (0.1-1.5) Joule Nd: YAG laser pulses; operating at 1060 nm wavelength. Hard homogeneous alloyed zone was obtained at depths between 60 and 110 μm below the surface. In the second run, 9 ns laser pulses from Q-switched Nd: YAG laser operating at 1060 nm was employed to melt/alloy Al-Cu sheets. The resulted alloyed depth, after using 20 laser pulses, was 199.22 μm for Al over Cu samples and 419.61 μm for Cu over Al samples. X-ray diffraction and fluorescence analysis revealed the formation of Cu2Al2, CuAl2 and δ- Al4Cu9 phases with percentage depended on laser energy and copper layer thicknesses.

Metal release rate from AISI 316L stainless steel and pure Fe, Cr and Ni into a synthetic biological medium--a comparison.

PubMed

Herting, G; Wallinder, I Odnevall; Leygraf, C

2008-09-01

Metal release rates from stainless steel grade 316L were investigated in artificial lysosomal fluid (ALF), simulating a human inflammatory cell response. The main focus was placed on release rates of main alloying elements using graphite furnace atomic absorption spectroscopy, and changes in surface oxide composition by means of X-ray photoelectron spectroscopy. To emphasise that alloys and pure metals possess totally different intrinsic properties, comparative studies were performed on the pure alloying constituents: iron, nickel and chromium. Significant differences in release rates were observed due to the presence of a passive surface film on stainless steel. Iron and nickel were released at rates more than 300 times lower from the 316L alloy compared with the pure metals whereas the release rate of chromium was similar. Iron was preferentially released compared with nickel and chromium. Immersion in ALF resulted in the gradual enrichment of chromium in the surface film, a small increase of nickel, and the reduction of oxidized iron with decreasing release rates of alloy constituents as a result. As expected, released metals from stainless steel grade 316L were neither in proportion to the bulk alloy composition nor to the surface film composition.

Dynamic oxidation behavior of TD-NiCr alloy with different surface pretreatments

NASA Technical Reports Server (NTRS)

Young, C. T.; Tenney, D. R.; Herring, H. W.

1975-01-01

Oxidation tests of TD-NiCr alloy with different surface pretreatments were conducted in a Mach-5 arc-jet at 1200 C and 0.002 lb/sec flowing air environment. The mechanisms responsible for the observed oxidation behavior are examined. The presence of atomic oxygen in the air stream plays a significant role in determining the oxidation characteristic of the alloy. The rate of Cr2O3 vaporization by formation of volatile CrO3 is greatly enhanced by the flowing conditions. The typical microstructure of oxides formed in the dynamic tests consists of an external layer of NiO with a porous mushroom-type morphology, an intermediate layer of NiO and Cr2O3 oxide mixture, and a continuous inner layer of Cr2O3 in contact with the Cr-depleted alloy substrate. Three basic processes underlying the formation of mushroom-type NiO are identified and discussed. The oxidation rate is determined by the rate of vaporization of NiO. Surface pretreatment has a significant effect on the oxidation behavior of the alloy in the early stage of oxidation, but becomes less important as exposure time increases. Mechanical polishing induces surface recrystallization, but promotes the concurrence of external growth of NiO and internal oxidation of the alloy in the dynamic atmosphere.

Surface modification and its role in the preparation of FeSi gradient alloys with good magnetic property and ductility

NASA Astrophysics Data System (ADS)

Yu, Haiyuan; Bi, Xiaofang

2018-04-01

Realization of the effective Si penetration at a lower processing temperature is a challenge, but of significance in reducing the strict requirements for the equipment and realizing cost-cutting in production. In this work, we have modified the surface microstructure of Fe-3 wt%Si alloy by using surface mechanical attrition treatment. The modified surface microstructure is characteristic of nanocrystalline, which is found to significantly enhance the efficiency of subsequent Si penetration into the alloy, and successively leading to the decrease of penetration temperature up to 200 °C. As a consequence, the Si gradient distribution across thickness can be readily controlled by changing penetration time, and FeSi alloys with various gradients are prepared by chemical vapor deposition along with subsequent annealing process. The dependence of magnetic and mechanical properties on Si gradient for demonstrates that the increase of Si gradient reduces core losses, especially at higher frequencies, and meanwhile improves ductility of FeSi alloys as well. The mechanism underlying the effect of Si gradient is clarified by combining magnetostriction measurement and domain structure observations. This work provides a facile and effective way for achieving gradient FeSi alloys with good magnetic property and ductility.

Using sewage sludge pyrolytic gas to modify titanium alloy to obtain high-performance anodes in bio-electrochemical systems

NASA Astrophysics Data System (ADS)

Gu, Yuan; Ying, Kang; Shen, Dongsheng; Huang, Lijie; Ying, Xianbin; Huang, Haoqian; Cheng, Kun; Chen, Jiazheng; Zhou, Yuyang; Chen, Ting; Feng, Huajun

2017-12-01

Titanium is under consideration as a potential stable bio-anode because of its high conductivity, suitable mechanical properties, and electrochemical inertness in the operating potential window of bio-electrochemical systems; however, its application is limited by its poor electron-transfer capacity with electroactive bacteria and weak ability to form biofilms on its hydrophobic surface. This study reports an effective and low-cost way to convert a hydrophobic titanium alloy surface into a hydrophilic surface that can be used as a bio-electrode with higher electron-transfer rates. Pyrolytic gas of sewage sludge is used to modify the titanium alloy. The current generation, anodic biofilm formation surface, and hydrophobicity are systematically investigated by comparing bare electrodes with three modified electrodes. Maximum current density (15.80 A/m2), achieved using a modified electrode, is 316-fold higher than that of the bare titanium alloy electrode (0.05 A/m2) and that achieved by titanium alloy electrodes modified by other methods (12.70 A/m2). The pyrolytic gas-modified titanium alloy electrode can be used as a high-performance and scalable bio-anode for bio-electrochemical systems because of its high electron-transfer rates, hydrophilic nature, and ability to achieve high current density.

The Effect of Coatings on the Wear Behavior of Ti6Al4V Alloy Used in Biomedical Applications

NASA Astrophysics Data System (ADS)

Danışman, Ş.; Odabas, D.; Teber, M.

2018-01-01

The properties expected from implant materials are biocompatibility, long service life and wear resistance. The wear resistance of the implant materials varies according to the type of implant, usage area and the movement. The ability of implant material to be more compatible with biological tissues and to increase the useful life depends on the surface properties. Today many different kind of surface modification techniques are applying on medical and dental implant surfaces to improve surface specifications and wear resistance. In this study TiN, TiAlN, TiCN coatings were applied on Ti6Al4V alloy used as implant material by reactive magnetron sputtering method. The wear resistances of uncoated Ti6Al4V alloy and TiN, TiAlN, TiCN coatings were investigated at room temperature under dry conditions. The wear resistance at different load and different sliding rates were compared using an wear tester. The wear losses, wear track widths and friction coefficients of coated and uncoated Ti6Al4V alloys are taken into account for comparison. The results show that a significant improvement in wear resistance of the alloy with the coating is achieved and TiN-coated Ti6Al4V alloy has the highest wear resistance.

Estimating surface reflectance from Himawari-8/AHI reflectance channels Using 6SV

NASA Astrophysics Data System (ADS)

Lee, Kyeong-sang; Choi, Sungwon; Seo, Minji; Seong, Noh-hun; Han, Kyung-soo

2017-04-01

TOA (Top Of Atmospheric) reflectance observed by satellite is modified by the influence of atmosphere such as absorbing and scattering by molecular and gasses. Removing TOA reflectance attenuation which is caused by the atmospheric is essential. surface reflectance with compensated atmospheric effects used as important input data for land product such as Normalized Difference Vegetation Index (NDVI), Land Surface Albedo (LSA) and etc. In this study, we Second Simulation of a Satellite Signal in the Solar Spectrum Vector (6SV) Radiative Transfer Model (RTM) for atmospheric correction and estimating surface reflectance from Himawari-8/Advanced Himawari Imager (AHI) reflectance channels. 6SV has the advantage that it has high accuracy by performing the atmospheric correction by dividing the width of the satellite channel by 2.5 nm, but it is slow to use in the operation. So, we use LUT approach to reduce the computation time and avoid the intensive calculation required for retrieving surface reflectance. Estimated surface reflectance data were compared with PROBA-V S1 data to evaluate the accuracy. As a result Root Mean Square Error (RMSE) and bias were about 0.05 and -0.02. It is considered that this error is due to the difference of angle component and Spectral Response Function (SRF) of each channel.

Surface properties of liquid In-Zn alloys

NASA Astrophysics Data System (ADS)

Pstruś, J.; Moser, Z.; Gąsior, W.

2011-02-01

The measurements of surface tension and density of zinc, indium and liquid In-Zn alloys containing 0.9, 0.85, 0.75, 0.70, 0.60, 0.40, 0.25 and 0.10 mole fraction of In were carried out using the method of maximum pressure in gaseous bubbles (MBP) as well as dilatometric technique. The technique of sessile drop was additionally applied in the measurements of surface tension for pure indium and zinc. The measurements were performed at temperature range 474-1151 K. The isotherms of surface tension calculated based on Butler's equation at 700 and 1100 K corresponded well with the experimental values for zinc content lower than 0.6 mole fraction. The surface tension calculated for alloys of higher zinc concentrations (0.6 < XZn < 0.95) had a positive value of the surface tension temperature coefficient (dσ/dT), which did not coincide with the experimental results. The density as well as molar volume of liquid In-Zn alloys showed almost identical behaviour like the ideal solutions. The observed little deviations were contained within assessed experimental errors.

Effect of SMAT on microstructural and mechanical properties of AA2024

NASA Astrophysics Data System (ADS)

Tadge, Prashant; Sasikumar, C.

2016-05-01

In recent days surface mechanical attrition treatment (SMAT) had attracted the attention of researchers as it produces a nano-crystalline surface with improved mechanical properties. In the present study Al-4%Cu alloy used in automobile and aerospace application is subjected to surface mechanical attrition treatment using steel shots. The microstructural changes introduced on the surface of the Al alloy was investigated using Scanning Electron Microscopy (SEM). The secondary phases formed during the SMAT process is been investigated using EDX and XRD analysis. The effects of SMAT on the mechanical properties were analyzed using a tensile testing. The SMA treatment had resulted in severe plastic deformation of the surface, thereby yielded a nanocrystalline surface with a grain size of 30 to 50 nm. Further, it is also found that the SMAT produced ultra nanocrystalline particles of Cu2Al dispersed uniformly into α-Al matrix. These microstructural changes had resulted in considerable change in the mechanical properties of these alloys. The tensile strength of these alloys had increased from ˜212 MPa to 303 MPa while the fracture toughness increased up to 28% in 10 minutes of SMAT.

Phosphonic acid functionalization of nanostructured Ni-W coatings on steel

NASA Astrophysics Data System (ADS)

Orrillo, P. A.; Ribotta, S. B.; Gassa, L. M.; Benítez, G.; Salvarezza, R. C.; Vela, M. E.

2018-03-01

The functionalization of nanocrystalline Ni-W coatings, formed by galvanostatic pulsed electrodeposition on steel, by thermal treatment of octadecylphosphonic acid self-assembled on the oxidized alloy surface is studied by Raman spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy, AFM and electrochemical techniques. Results show that this procedure preserves the surface topography and the optimum mechanical properties of the alloy. More importantly, it turns the alloy surface highly hydrophobic and markedly improves its corrosion resistance, in particular to pitting corrosion in aggressive solutions containing chloride anions. The ability of the phosphonate layer to improve surface properties arises from the barrier properties introduced by the hydrocarbon chains and the strong bonds between the phosphonate head and the underlying surface oxides.

46 CFR 160.156-1 - Scope.

Code of Federal Regulations, 2012 CFR

2012-10-01

... APPROVAL LIFESAVING EQUIPMENT Rescue Boats and Fast Rescue Boats (SOLAS) § 160.156-1 Scope. This subpart... fast rescue boat, complying with SOLAS and the IMO LSA Code, for use on waters other than protected...

46 CFR 160.156-1 - Scope.

Code of Federal Regulations, 2013 CFR

2013-10-01

... APPROVAL LIFESAVING EQUIPMENT Rescue Boats and Fast Rescue Boats (SOLAS) § 160.156-1 Scope. This subpart... fast rescue boat, complying with SOLAS and the IMO LSA Code, for use on waters other than protected...

46 CFR 160.156-1 - Scope.

Code of Federal Regulations, 2014 CFR

2014-10-01

... APPROVAL LIFESAVING EQUIPMENT Rescue Boats and Fast Rescue Boats (SOLAS) § 160.156-1 Scope. This subpart... fast rescue boat, complying with SOLAS and the IMO LSA Code, for use on waters other than protected...

Modulation of Morphology and Optical Property of Multi-Metallic PdAuAg and PdAg Alloy Nanostructures.

PubMed

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-05-16

In this work, the evolution of PdAg and PdAuAg alloy nanostructures is demonstrated on sapphire (0001) via the solid-state dewetting of multi-metallic thin films. Various surface configurations, size, and arrangements of bi- and tri-metallic alloy nanostructures are fabricated as a function of annealing temperature, annealing duration, film thickness, and deposition arrangements such as bi-layers (Pd/Ag), tri-layers (Pd/Au/Ag), and multi-layers (Pd/Au/Ag × 5). Specifically, the tri-layers film shows the gradual evolution of over-grown NPs, voids, wiggly nanostructures, and isolated PdAuAg alloy nanoparticles (NPs) along with the increased annealing temperature. In contrast, the multi-layers film with same thickness show the enhanced dewetting rate, which results in the formation of voids at relatively lower temperature, wider spacing, and structural regularity of alloy NPs at higher temperature. The dewetting enhancement is attributed to the increased number of interfaces and reduced individual layer thickness, which aid the inter-diffusion process at the initial stage. In addition, the time evolution of the Pd 150 nm /Ag 80 nm bi-layer films at constant temperature show the wiggly-connected and isolated PdAg alloy NPs. The overall evolution of alloy NPs is discussed based on the solid-state dewetting mechanism in conjunction with the diffusion, inter-diffusion, alloying, sublimation, Rayleigh instability, and surface energy minimization. Depending upon their surface morphologies, the bi- and tri-metallic alloy nanostructures exhibit the dynamic reflectance spectra, which show the formation of dipolar (above 700 nm) and quadrupolar resonance peaks (~ 380 nm) and wide dips in the visible region as correlated to the localized surface plasmon resonance (LSPR) effect. An absorption dip is readily shifted from ~ 510 to ~ 475 nm along with the decreased average size of alloy nanostructures.

Modulation of Morphology and Optical Property of Multi-Metallic PdAuAg and PdAg Alloy Nanostructures

NASA Astrophysics Data System (ADS)

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-05-01

In this work, the evolution of PdAg and PdAuAg alloy nanostructures is demonstrated on sapphire (0001) via the solid-state dewetting of multi-metallic thin films. Various surface configurations, size, and arrangements of bi- and tri-metallic alloy nanostructures are fabricated as a function of annealing temperature, annealing duration, film thickness, and deposition arrangements such as bi-layers (Pd/Ag), tri-layers (Pd/Au/Ag), and multi-layers (Pd/Au/Ag × 5). Specifically, the tri-layers film shows the gradual evolution of over-grown NPs, voids, wiggly nanostructures, and isolated PdAuAg alloy nanoparticles (NPs) along with the increased annealing temperature. In contrast, the multi-layers film with same thickness show the enhanced dewetting rate, which results in the formation of voids at relatively lower temperature, wider spacing, and structural regularity of alloy NPs at higher temperature. The dewetting enhancement is attributed to the increased number of interfaces and reduced individual layer thickness, which aid the inter-diffusion process at the initial stage. In addition, the time evolution of the Pd150 nm/Ag80 nm bi-layer films at constant temperature show the wiggly-connected and isolated PdAg alloy NPs. The overall evolution of alloy NPs is discussed based on the solid-state dewetting mechanism in conjunction with the diffusion, inter-diffusion, alloying, sublimation, Rayleigh instability, and surface energy minimization. Depending upon their surface morphologies, the bi- and tri-metallic alloy nanostructures exhibit the dynamic reflectance spectra, which show the formation of dipolar (above 700 nm) and quadrupolar resonance peaks ( 380 nm) and wide dips in the visible region as correlated to the localized surface plasmon resonance (LSPR) effect. An absorption dip is readily shifted from 510 to 475 nm along with the decreased average size of alloy nanostructures.

Surface Tension and Viscosity of SCN and SCN-acetone Alloys at Melting Points and Higher Temperatures Using Surface Light Scattering Spectrometer

NASA Technical Reports Server (NTRS)

Tin, Padetha; deGroh, Henry C., III.

2003-01-01

Succinonitrile has been and is being used extensively in NASA's Microgravity Materials Science and Fluid Physics programs and as well as in several ground-based and microgravity studies including the Isothermal Dendritic Growth Experiment (IDGE). Succinonitrile (SCN) is useful as a model for the study of metal solidification, although it is an organic material, it has a BCC crystal structure and solidifies dendriticly like a metal. It is also transparent and has a low melting point (58.08 C). Previous measurements of succinonitrile (SCN) and alloys of succinonitrile and acetone surface tensions are extremely limited. Using the Surface Light Scattering technique we have determined non invasively, the surface tension and viscosity of SCN and SCN-Acetone Alloys at different temperatures. This relatively new and unique technique has several advantages over the classical methods such as, it is non invasive, has good accuracy and measures the surface tension and viscosity simultaneously. The accuracy of interfacial energy values obtained from this technique is better than 2% and viscosity about 10 %. Succinonitrile and succinonitrile-acetone alloys are well-established model materials with several essential physical properties accurately known - except the liquid/vapor surface tension at different elevated temperatures. We will be presenting the experimentally determined liquid/vapor surface energy and liquid viscosity of succinonitrile and succinonitrile-acetone alloys in the temperature range from their melting point to around 100 C using this non-invasive technique. We will also discuss about the measurement technique and new developments of the Surface Light Scattering Spectrometer.

A demographic perspective on the Middle to Later Stone Age transition from Nasera rockshelter, Tanzania

PubMed Central

Tryon, Christian A.; Faith, J. Tyler

2016-01-01

Increased population density is among the proposed drivers of the behavioural changes culminating in the Middle to Later Stone Age (MSA–LSA) transition and human dispersals from East Africa, but reliable archaeological measures of demographic change are lacking. We use Late Pleistocene–Holocene lithic and faunal data from Nasera rockshelter (Tanzania) to show progressive declines in residential mobility—a variable linked to population density—and technological shifts, the latter associated with environmental changes. These data suggest that the MSA–LSA transition is part of a long-term pattern of changes in residential mobility and technology that reflect human responses to increased population density, with dispersals potentially marking a complementary response to larger populations. This article is part of the themed issue ‘Major transitions in human evolution’. PMID:27298469

A comparison of methods to quantify the in-season training load of professional soccer players.

PubMed

Scott, Brendan R; Lockie, Robert G; Knight, Timothy J; Clark, Andrew C; Janse de Jonge, Xanne A K

2013-03-01

To compare various measures of training load (TL) derived from physiological (heart rate [HR]), perceptual (rating of perceived exertion [RPE]), and physical (global positioning system [GPS] and accelerometer) data during in-season field-based training for professional soccer. Fifteen professional male soccer players (age 24.9 ± 5.4 y, body mass 77.6 ± 7.5 kg, height 181.1 ± 6.9 cm) were assessed in-season across 97 individual training sessions. Measures of external TL (total distance [TD], the volume of low-speed activity [LSA; <14.4 km/h], high-speed running [HSR; >14.4 km/h], very high-speed running [VHSR; >19.8 km/h], and player load), HR and session-RPE (sRPE) scores were recorded. Internal TL scores (HR-based and sRPE-based) were calculated, and their relationships with measures of external TL were quantified using Pearson product-moment correlations. Physical measures of TD, LSA volume, and player load provided large, significant (r = .71-.84; P < .01) correlations with the HR-based and sRPE-based methods. Volume of HSR and VHSR provided moderate to large, significant (r = .40-.67; P < .01) correlations with measures of internal TL. While the volume of HSR and VHSR provided significant relationships with internal TL, physical-performance measures of TD, LSA volume, and player load appear to be more acceptable indicators of external TL, due to the greater magnitude of their correlations with measures of internal TL.

[Differential diagnosis of hypercalcemia--a retrospective study of 46 dogs].

PubMed

Uehlinger, P; Glaus, T; Hauser, B; Reusch, C

1998-01-01

The case records of 46 dogs with hypercalcemia were studied retrospectively. The most common cause of hypercalcemia was malignancy, of which the majority were diagnosed as having lymphosarcoma (LSA, n = 23). Interestingly only 15 had palpable lymphadenopathy. Other neoplasia were apocrine adenocarcinoma of the anal sac (n = 4), mammary adenocarcinoma (n = 2), anaplastic carcinoma (n = 1), and malignant histiocytosis (n = 1). Non-neoplastic reasons for hypercalcemia were hypoadrenocorticism (n = 5), acute renal failure (n = 2), chronic renal failure (n = 2), hypervitaminosis D (n = 1), and primary hyperparathyroidism (n = 1). In 4 cases no definitive diagnosis could be obtained. Moderate to marked hyperphosphatemia and azotemia was found in all dogs with primary renal failure and in 4 of 5 dogs with hypoadrenocorticism. In contrast only 4 of 31 dogs with neoplasia showed (mild) hyperphosphatemia and 20 showed mild to moderate azotemia. Elevated PTH levels were found in dogs with primary chronic renal failure and with primary hyperparathyroidism, but also in one dog with neoplasia. Low PTH concentrations were measured in the dog with hypervitaminosis D and in 8 cases with neoplasia. Additional three cases with neoplasia had values in the reference range. 1. The most common cause of hypercalcemia is LSA. Absence of palpable lymphadenopathy does not exclude LSA and further diagnostic steps may be necessary 2. The combination of moderate to marked hyperphosphatemia suggests primary renal failure or hypoadrenocorticism. 3. An elevated PTH level is consistent with primary hyperparathyroidism, but does not exclude other causes of hypercalcemia.

Look who's judging-Feedback source modulates brain activation to performance feedback in social anxiety.

PubMed

Peterburs, Jutta; Sandrock, Carolin; Miltner, Wolfgang H R; Straube, Thomas

2016-06-01

It is as yet unknown if behavioral and neural correlates of performance monitoring in socially anxious individuals are affected by whether feedback is provided by a person or a computer. This fMRI study investigated modulation of feedback processing by feedback source (person vs. computer) in participants with high (HSA) (N=16) and low social anxiety (LSA) (N=16). Subjects performed a choice task in which they were informed that they would receive positive or negative feedback from a person or the computer. Subjective ratings indicated increased arousal and anxiety in HSA versus LSA, most pronounced for social and negative feedback. FMRI analyses yielded hyperactivation in ventral medial prefrontal cortex (vmPFC)/anterior cingulate cortex (ACC) and insula for social relative to computer feedback, and in mPFC/ventral ACC for positive relative to negative feedback in HSA as compared to LSA. These activation patterns are consistent with increased interoception and self-referential processing in social anxiety, especially during processing of positive feedback. Increased ACC activation in HSA to positive feedback may link to unexpectedness of (social) praise as posited in social anxiety disorder (SAD) psychopathology. Activation in rostral ACC showed a reversed pattern, with decreased activation to positive feedback in HSA, possibly indicating altered action values depending on feedback source and valence. The present findings corroborate a crucial role of mPFC for performance monitoring in social anxiety. Copyright © 2016 Elsevier Inc. All rights reserved.

Self-disintegrating Raney metal alloys

DOEpatents

Oden, Laurance L.; Russell, James H.

1979-01-01

A method of preparing a Raney metal alloy which is capable of self-disintegrating when contacted with water vapor. The self-disintegrating property is imparted to the alloy by incorporating into the alloy from 0.4 to 0.8 weight percent carbon. The alloy is useful in forming powder which can be converted to a Raney metal catalyst with increased surface area and catalytic activity.

Effect of surface reaction layer on grindability of cast titanium alloys.

PubMed

Ohkubo, Chikahiro; Hosoi, Toshio; Ford, J Phillip; Watanabe, Ikuya

2006-03-01

The purpose of this study was to investigate the effect of the cast surface reaction layer on the grindability of titanium alloys, including free-machining titanium alloy (DT2F), and to compare the results with the grindability of two dental casting alloys (gold and Co-Cr). All titanium specimens (pure Ti, Ti-6Al-4V and DT2F) were cast using a centrifugal casting machine in magnesia-based investment molds. Two specimen sizes were used to cast the titanium metals so that the larger castings would be the same size as the smaller gold and Co-Cr alloy specimens after removal of the surface reaction layer (alpha-case). Grindability was measured as volume loss ground from a specimen for 1 min using a handpiece engine with a SiC abrasive wheel at 0.1 kgf and four circumferential wheel speeds. For the titanium and gold alloys, grindability increased as the rotational speed increased. There was no statistical difference (p>0.05) in grindability for all titanium specimens either with or without the alpha-case. Of the titanium metals tested, Ti-6 Al-4V had the greatest grindability at higher speeds, followed by DT2F and CP Ti. The grindability of the gold alloy was similar to that of Ti-6 Al-4V, whereas the Co-Cr alloy had the lowest grindability. The results of this study indicated that the alpha-case did not significantly affect the grindability of the titanium alloys. The free-machining titanium alloy had improved grindability compared to CP Ti.

Microstructure, Surface Characterization, and Electrochemical Behavior of New Ti-Zr-Ta-Ag Alloy in Simulated Human Electrolyte

NASA Astrophysics Data System (ADS)

Vasilescu, Cora; Drob, Silviu Iulian; Osiceanu, Petre; Moreno, Jose Maria Calderon; Prodana, Mariana; Ionita, Daniela; Demetrescu, Ioana; Marcu, Maria; Popovici, Ion Alexandru; Vasilescu, Ecaterina

2017-01-01

A new Ti-20Zr-5Ta-2Ag alloy was elaborated and characterized regarding its microstructure, its native passive film composition and thickness, its surface wettability, its electrochemical behavior in Ringer solution of different pH values, and its ion release. The new alloy has a bi-phase, α + β, acicular, homogeneous microstructure (scanning electron microscopy (SEM)). Its native passive film (12-nm thicknesses) consists of the protective TiO2, ZrO2, and Ta2O5 oxides, Ti and Ta suboxides, and metallic Ag (X-ray photoelectron spectroscopy (XPS) data). The alloy possesses high hydrophilic properties. The main electrochemical parameters of the new alloy are superior to those of Ti as a result of the beneficial influence of Zr, Ta, and Ag alloying elements, which reinforce its native passive film. Electrochemical impedance spectroscopy (EIS) spectra in Ringer solutions for the new alloy displayed better values of impedances and phase angles, proving a more insulate passive film than that on the Ti surface. The main corrosion parameters for the new Ti-20Zr-5Ta-2Ag alloy are more favorable by about 25 to 38 times than those of Ti, confirming extremely resistant passive film. The new Ti-20Zr-5Ta-2Ag alloy releases into Ringer solution low quantities of Ti4+, Zr4+ metallic ions (inductively coupled plasma-mass spectroscopy (ICP-MS)). The Ag+ ions are released in low quantity, conferring to this alloy's low antibacterial activity. All experimental results show that the new Ti-20Zr-5Ta-2Ag alloy fulfills the requirements for biocompatibility, corrosion resistance, and antibacterial protection.