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1

Application of polymerase chain reaction-denaturing gradient gel electrophoresis for comparison of direct and indirect extraction methods of soil DNA used for microbial community fingerprinting  

Microsoft Academic Search

We used polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) to compare bacterial community patterns\\u000a obtained with target DNA extracted from a soil by direct and indirect methods. For this purpose, two direct extraction methods,\\u000a i.e. cell lysis by bead beating and cell disruption by grinding in liquid N, and two indirect methods, i.e. cell extraction\\u000a followed by DNA extraction, and

J. Kozdrój; J. D. van Elsas

2000-01-01

2

Polymerase chain reaction denaturing gradient gel electrophoresis analysis of the N2-fixing bacterial diversity in soil under Acacia tortilis ssp. raddiana and Balanites aegyptiaca in the dryland part of Senegal.  

PubMed

Denaturing gradient gel electrophoresis (DGGE) of amplified nifH gene fragments was used to study the diazotrophic community of soil samples under Acacia tortilis ssp. raddiana (legume tree) and Balanites aegyptiaca (non-legume tree), two dominant plant species growing naturally in the dryland part of Senegal. Samples were taken along transects from the stem up to 10 m distance from it, at depths of 0-0.25 m and 0.25-0.50 m. Sampling was done in the dry season (25 June 1999) and in the rainy season (28 August 1999). The community structure and diversity of the bacterial groups from the different samples was analysed further using different techniques, such as statistical analysis and diversity index evaluation of the band patterns. Diazotrophic diversity was lower under B. aegyptiaca than under A. tortilis ssp. raddiana. Multidimensional scaling (MDS) analysis and ANOSIM tests showed a significant effect of the tree on the diazotroph assemblages. SIMPER analysis showed that the major elements responsible for the dissimilarity are a member of the genus Sinorhizobium, which is characteristic of the samples taken under A. tortilis ssp. raddiana and a member of the cluster Bradyrhizobium for the samples taken under B. aegyptiaca. Forty-four major bands were partially sequenced, yielding 33 different nifH sequences, which were used in phylogenetic reconstructions. Most sequences were affiliated with the alpha- beta- and gamma-proteobacteria. Five nifH sequences were identical to those of Pseudomonas stutzeri, and one sequence showed 100% similarity to that of Azotobacter vinelandii. Four bands were affiliated with the Cyanobacteria and a single one with the Firmicutes. For both trees, there were also clear differences between the samples taken in the dry and rainy seasons. Only for the samples taken under A. tortilis ssp. raddiana was a significant difference found between the two sampling depths. PMID:15008817

Demba Diallo, Moudjahidou; Willems, Anne; Vloemans, Nele; Cousin, Sylvie; Vandekerckhove, Tom T; de Lajudie, Philippe; Neyra, Marc; Vyverman, Wim; Gillis, Monique; Van der Gucht, Katleen

2004-04-01

3

Tracking the composition and dominant components of the microbial community via polymerase chain reaction-denaturing gradient gel electrophoresis and fluorescence in situ hybridization during vermiconversion for liquid-state excess sludge stabilization.  

PubMed

To quantitatively explore the microbial community modified by earthworms, a vermifilter (VF, with earthworms) and a conventional biofilter (BF, without earthworms) were continuously operated to stabilize excess sludge. The results demonstrated a positive role imposed by earthworms on compositions and dominant components of microbial community in the VF. For one thing, the phyla Actinobacteria and Acidobacteria were only detected in the VF, which might explain for the higher Shannon index of bacteria in the VF (H=2.58) than that in the BF (H=1.99). For another, the total proportion of dominant bacteria in the VF increased by 23% compared to the BF. Moreover, quantification analysis explicitly noted that the dominant bacteria in VF were ?-proteobacteria (27±2%) and ?-proteobacteria (24±1%) while that in BF was Bacteroidetes (21±1%). In conclusion, stimulated by earthworms, a unique microbial community developed in the VF, thus improving the stabilization of excess sludge. PMID:24971951

Xu, Ting; Xing, Meiyan; Yang, Jian; Lv, Baoyi; Duan, Ting; Nie, Jing

2014-09-01

4

Analysis of kimchi microflora using denaturing gradient gel electrophoresis  

Microsoft Academic Search

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technique was used to determine the microfloral composition during the fermentation of kimchi, a traditional Korean fermented vegetable food. The kimchi was fermented at 10 °C or 20 °C for 30 or 20 days, respectively. DGGE of the partially amplified 16S rDNA was performed and the most intense bands sequenced. The application

Jung-Sook Lee; Gun-Young Heo; Jun Won Lee; Yun-Jung Oh; Jeong A Park; Yong-Ha Park; Yu-Ryang Pyun; Jong Seog Ahn

2005-01-01

5

Diversity analysis of lactic acid bacteria in Korean rice wines by culture-independent method using PCR-denaturing gradient gel electrophoresis  

Microsoft Academic Search

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was used to determine the presence and\\u000a diversity of lactic acid bacteria (LAB) in takju, a traditional Korean rice wine. Bacterial DNAs were extracted from 15 commercial rice wines and amplicons of partial 16S\\u000a rRNA genes were separated by DGGE and intense bands were sequenced. Lactobacillus (Lb.) paracasei, Lb. plantarum, and

So-Young Kim; Ki-Seon Yoo; Ji Eun Kim; Ji-Sun Kim; Jee Yun Jung; Qing Jin; Hyun-Ju Eom; Nam Soo Han

2010-01-01

6

Extraordinarily low density of hepatitis C virus estimated by sucrose density gradient centrifugation and the polymerase chain reaction  

Microsoft Academic Search

The genomic RNA of hepatitis C virus (HCV) in the plasma of volunteer blood donors was detected by using the polymerase chain reaction in a fraction of density 1-08 g\\/ml from sucrose density gradient equilibrium centrifugation. When the fraction was treated with the detergent NP40 and recentrifuged in sucrose, the HCV RNA banded at 1.25g\\/ml. Assuming that NP40 removed a

Hideaki Miyamoto; Hiroaki Okamoto; Koei Sato; Takeshi Tanaka; Shunji Mishiro

1992-01-01

7

Thermal denaturation of double-stranded nucleic acids: prediction of temperatures critical for gradient gel electrophoresis and polymerase chain reaction.  

PubMed Central

A program is described which calculates the thermal stability and the denaturation behaviour of double-stranded DNAs and RNAs up to a length of 1000 base pairs. The algorithm is based on recursive generation of conditional and a priori probabilities for base stacking. Output of the program may be compared directly to experimental results; thus the program may be used to optimize the nucleic acid fragments, the primers and the experimental conditions prior to experiments like polymerase chain reactions, temperature-gradient gel electrophoresis, denaturing-gradient gel electrophoresis and hybridizations. The program is available in three versions; the first version runs interactively on VAXstations producing graphics output directly, the second is implemented as part of the HUSAR package at GENIUSnet, the third runs on any computer producing text output which serves as input to available graphics programs. Images

Steger, G

1994-01-01

8

Comparison of bacterial community changes in fermenting kimchi at two different temperatures using a denaturing gradient gel electrophoresis analysis.  

PubMed

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technique followed by sequencing of the 16S rDNA fragments eluted from the bands of interest on denaturing gradient gels was used to monitor changes in the bacterial microflora of two commercial kimchi, salted cabbage, and ingredient mix samples during 30 days of fermentation at 4°C and 10°C. Leuconostoc (Lc.) was the dominant lactic acid bacteria (LAB) over Lactobacillus (Lb.) species at 4°C. Weissella confusa was detected in the ingredient mix and also in kimchi samples throughout fermentation in both samples at 4°C and 10°C. Lc. gelidum was detected as the dominant LAB at 4°C in both samples. The temperature affected the LAB profile of kimchi by varing the pH, which was primarily caused by the temperature-dependent competition among different LAB species in kimchi. At 4°C, the sample variations in pH and titratable acidity were more conspicuous owing to the delayed growth of LAB. Temperature affected only initial decreases in pH and initial increases in viable cell counts, but affected both the initial increases and final values of titratable acidity. The initial microflora in the kimchi sample was probably determined by the microflora of the ingredient mix, not by that of the salted cabbage. The microbial distributions in the samples used in this study resembled across the different kimchi samples and the different fermentation temperatures as the numbers of LAB increased and titratable acidity decreased. PMID:23314371

Hong, Yeun; Yang, Hee-Seok; Chang, Hae-Choon; Kim, Hae-Yeong

2013-01-01

9

Changes in community structure of sediment bacteria along the Florida coastal everglades marsh-mangrove-seagrass salinity gradient.  

PubMed

Community structure of sediment bacteria in the Everglades freshwater marsh, fringing mangrove forest, and Florida Bay seagrass meadows were described based on polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) patterns of 16S rRNA gene fragments and by sequencing analysis of DGGE bands. The DGGE patterns were correlated with the environmental variables by means of canonical correspondence analysis. There was no significant trend in the Shannon-Weiner index among the sediment samples along the salinity gradient. However, cluster analysis based on DGGE patterns revealed that the bacterial community structure differed according to sites. Not only were these salinity/vegetation regions distinct but the sediment bacteria communities were consistently different along the gradient from freshwater marsh, mangrove forest, eastern-central Florida Bay, and western Florida Bay. Actinobacteria- and Bacteroidetes/Chlorobi-like DNA sequences were amplified throughout all sampling sites. More Chloroflexi and members of candidate division WS3 were found in freshwater marsh and mangrove forest sites than in seagrass sites. The appearance of candidate division OP8-like DNA sequences in mangrove sites distinguished these communities from those of freshwater marsh. The seagrass sites were characterized by reduced presence of bands belonging to Chloroflexi with increased presence of those bands related to Cyanobacteria, gamma-Proteobacteria, Spirochetes, and Planctomycetes. This included the sulfate-reducing bacteria, which are prevalent in marine environments. Clearly, bacterial communities in the sediment were different along the gradient, which can be explained mainly by the differences in salinity and total phosphorus. PMID:19705193

Ikenaga, Makoto; Guevara, Rafael; Dean, Amanda L; Pisani, Cristina; Boyer, Joseph N

2010-02-01

10

Selection of single chain fragment variables with direct coating of aflatoxin B1 to enzyme-linked immunosorbent assay plates.  

PubMed

Most selections of antihapten recombinant antibodies from antibody libraries were against hapten-carrier conjugates, which are different from free haptens in antigen specificity and often mislead the screening due to immunodominant epitopes in carriers. In the present study, aflatoxin B(1) (AFB(1)) was directly coated to enzyme-linked immunosorbent assay (ELISA) plates and anti-AFB(1) single chain fragment variables (scFvs) were selected with the AFB(1)-coated plates. Compared to the selection against AFB(1)-bovine serum albumin conjugate (31 positives out of 46 random clones), the isolated scFvs against AFB(1) (44 positives out of 46 random clones) showed higher specificities for AFB(1). The clone H4 with K(D) of 9.8 x 10(-11) M to AFB(1)-BSA and K(D) of 1.2 x 10(-12) to AFB1 was sequenced. In addition, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was applied to describe the biopanning for the first time. Our research presents a quick and robust selection technique for antihapten recombinant antibody from large naive libraries. PMID:19764785

Yang, Lian; Ding, Husheng; Gu, Zhennan; Zhao, Jianxin; Chen, Haiqin; Tian, Fengwei; Chen, Yong Q; Zhang, Hao; Chen, Wei

2009-10-14

11

Polymerase Chain Reaction and Denaturing Gradient Gel Electrophoresis Monitoring of Fecal Bifidobacterium Populations in a Prebiotic and Probiotic Feeding Trial  

Microsoft Academic Search

A culture-independent approach based on genus-specific PCR and denaturing gradient gel electrophoresis (DGGE) was used to monitor qualitative changes in fecal bifidobacterial communities in a human feeding trial. DNA was extracted directly from feces and bifidobacterial 16S rDNA sequences were amplified using genus-specific PCR. The PCR fragments were subsequently separated in a sequence-specific manner by DGGE in order to obtain

Reetta M. Satokari; Elaine E. Vaughan; Antoon D. L. Akkermans; Maria Saarela; Willem M. de Vos

2001-01-01

12

Culture-based and denaturing gradient gel electrophoresis analysis of the bacterial community structure from the intestinal tracts of earthworms(Eisenia fetida).  

PubMed

The bacterial communities in the intestinal tracts of earthworm were investigated by culture-dependent and - independent approaches. In total, 72 and 55 pure cultures were isolated from the intestinal tracts of earthworms under aerobic and anaerobic conditions, respectively. Aerobic bacteria were classified as Aeromonas (40%), Bacillus (37%), Photobacterium (10%), Pseudomonas (7%), and Shewanella (6%). Anaerobic bacteria were classified as Aeromonas (52%), Bacillus (27%), Shewanella (12%), Paenibacillus (5%), Clostridium (2%), and Cellulosimicrobium (2%). The dominant microorganisms were Aeromonas and Bacillus species under both aerobic and anaerobic conditions. In all, 39 DNA fragments were identified by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis. Aeromonas sp. was the dominant microorganism in feeds, intestinal tracts, and casts of earthworms. The DGGE band intensity of Aeromonas from feeds, intestinal tracts, and casts of earthworms was 12.8%, 14.7%, and 15.1%, respectively. The other strains identified were Bacillus, Clostridium, Enterobacter, Photobacterium, Pseudomonas, Shewanella, Streptomyces, uncultured Chloroflexi bacterium, and uncultured bacterium. These results suggest that PCR-DGGE analysis was more efficient than the culture-dependent approach for the investigation of bacterial diversity and the identification of unculturable microorganisms. PMID:21952364

Hong, Sung Wook; Kim, In Su; Lee, Ju Sam; Chung, Kun Sub

2011-09-01

13

Heavy metal concentrations in a soil–plant–snail food chain along a terrestrial soil pollution gradient  

Microsoft Academic Search

We investigated concentrations of Zn, Cu, Cd and Pb in the compartments of a soil-plant (Urtica dioica)-snail (Cepaea nemoralis) food chain in four polluted locations in the Biesbosch floodplains, the Netherlands, and two reference locations. Total soil metal concentrations in the polluted locations were 4–20 times higher than those in the reference locations. Positive relationships between the generally low leaf

M. J. M. Notten; A. J. P. Oosthoek; J. Rozema; R. Aerts

2005-01-01

14

Analysis of microbial diversity on deli slicers using polymerase chain reaction and denaturing gradient gel electrophoresis technologies.  

PubMed

Cross-contamination of pathogenic and spoilage bacteria from food-contact surfaces to food products is a serious public health issue. Bacteria may survive and attach to food-contact surfaces by residual food components and/or background bacteria which may subsequently transfer to other food products. Deli slicers, generally used for slicing ready-to-eat products, can serve as potential sources for considerable bacterial transfer. The objective of this study was to assess the extent and distribution of microbial diversity of deli slicers by identification of pathogenic and background bacteria. Slicer-swab samples were collected from restaurants in Arkansas and Texas in the United States. Ten surface areas for each slicer were swabbed using sterile sponges. Denaturing gradient gel electrophoresis (DGGE) was applied to investigate the fingerprint of samples, and each band was further identified by sequence analysis. Pseudomonads were identified as the dominant bacteria followed by Enterobacteriaceae family, and lactic acid bacteria such as Lactococcus lactis and Streptococcus thermophilus were also found. Bacterial distribution was similar for all surface areas, while the blade guard exhibited the greatest diversity. This study provides a profile of the microbial ecology of slicers using DGGE to develop more specific sanitation practices and to reduce cross-contamination during slicing. PMID:23121623

Koo, O K; Mertz, A W; Akins, E L; Sirsat, S A; Neal, J A; Morawicki, R; Crandall, P G; Ricke, S C

2013-02-01

15

A gradient Markov chain Monte Carlo algorithm for computing multivariate maximum likelihood estimates and posterior distributions: mixture dose-response assessment.  

PubMed

Multivariate probability distributions, such as may be used for mixture dose-response assessment, are typically highly parameterized and difficult to fit to available data. However, such distributions may be useful in analyzing the large electronic data sets becoming available, such as dose-response biomarker and genetic information. In this article, a new two-stage computational approach is introduced for estimating multivariate distributions and addressing parameter uncertainty. The proposed first stage comprises a?gradient Markov chain Monte Carlo?(GMCMC) technique to find Bayesian posterior mode estimates (PMEs) of parameters, equivalent to maximum likelihood estimates (MLEs) in the absence of subjective information. In the second stage, these estimates are used to initialize a Markov chain Monte Carlo (MCMC) simulation, replacing the conventional burn-in period to allow convergent simulation of the full joint Bayesian posterior distribution and the corresponding unconditional multivariate distribution (not conditional on uncertain parameter values). When the distribution of parameter uncertainty is such a Bayesian posterior, the unconditional distribution is termed?predictive. The method is demonstrated by finding conditional and unconditional versions of the recently proposed emergent dose-response function (DRF). Results are shown for the five-parameter common-mode and seven-parameter dissimilar-mode models, based on published data for eight benzene-toluene dose pairs. The common mode conditional DRF is obtained with a 21-fold reduction in data requirement versus MCMC. Example common-mode unconditional DRFs are then found using synthetic data, showing a 71% reduction in required data. The approach is further demonstrated for a PCB 126-PCB 153 mixture. Applicability is analyzed and discussed. Matlab(®) computer programs are provided. PMID:21906114

Li, Ruochen; Englehardt, James D; Li, Xiaoguang

2012-02-01

16

Application of PCR-Denaturing-Gradient Gel Electrophoresis (DGGE) Method to Examine Microbial Community Structure in Asparagus Fields with Growth Inhibition due to Continuous Cropping  

PubMed Central

Growth inhibition due to continuous cropping of asparagus is a major problem; the yield of asparagus in replanted fields is low compared to that in new fields, and missing plants occur among young seedlings. Although soil-borne disease and allelochemicals are considered to be involved in this effect, this is still controversial. We aimed to develop a technique for the biological field diagnosis of growth inhibition due to continuous cropping. Therefore, in this study, fungal community structure and Fusarium community structure in continuously cropped fields of asparagus were analyzed by polymerase chain reaction/denaturing-gradient gel electrophoresis (PCR-DGGE). Soil samples were collected from the Aizu region of Fukushima Prefecture, Japan. Soil samples were taken from both continuously cropped fields of asparagus with growth inhibition and healthy neighboring fields of asparagus. The soil samples were collected from the fields of 5 sets in 2008 and 4 sets in 2009. We were able to distinguish between pathogenic and non-pathogenic Fusarium by using Alfie1 and Alfie2GC as the second PCR primers and PCR-DGGE. Fungal community structure was not greatly involved in the growth inhibition of asparagus due to continuous cropping. By contrast, the band ratios of Fusarium oxysporum f. sp. asparagi in growth-inhibited fields were higher than those in neighboring healthy fields. In addition, there was a positive correlation between the band ratios of Fusarium oxysporum f. sp. asparagi and the ratios of missing asparagus plants. We showed the potential of biological field diagnosis of growth inhibition due to continuous cropping of asparagus using PCR-DGGE.

Urashima, Yasufumi; Sonoda, Takahiro; Fujita, Yuko; Uragami, Atsuko

2012-01-01

17

NIF optics phase gradient specification.  

National Technical Information Service (NTIS)

A root-mean-square (rms) phase gradient specification seems to allow a good connection between the NIF optics quality and focal spot requirements. Measurements on Beamlet optics individually, and as a chain, indicate they meet the assumptions necessary to...

J. Auerbach J. Hunt K. Manes L. Lawson W. Williams

1997-01-01

18

Evaluation of repetitive extragenic palindromic-polymerase chain reaction and denatured gradient gel electrophoresis in identifying Salmonella serotypes isolated from processed turkeys.  

PubMed

The current study was conducted to determine the usefulness of 2 molecular techniques, automated repetitive extragenic palindromic-PCR (REP-PCR) and denaturing gradient gel electrophoresis (DGGE), to identify Salmonella serotypes of poultry origin. Salmonella continues to be a foodborne pathogen of principal concern in the United States. The interspersed conserved repetitive sequence of the bacterial genome and the 16-23S rDNA intergenic spacer region were amplified for REP-PCR and DGGE, respectively. Fifty-four Salmonella isolates from 2 turkey processing plants (A and B) were used for this comparison. Serotypes consisted of Brandenburg, Derby, Hadar, and Typhimurium, with n=6, 21, 12, and 15, respectively. The REP-PCR was fully automated, whereas DGGE was run on an acrylamide gel and the image was captured digitally. Both dendrograms were created using the unweighted pair group method with arithmetic average. There were more variations in percentage similarity in DGGE when compared with REP-PCR. The banding patterns were more distinct and uniform in the REP-PCR group than with DGGE. The results from the REP-PCR were generated within 1 h, whereas the DGGE required approximately 1 d to run. These data suggest that DGGE and REP-PCR are useful tools for identifying Salmonella serotypes isolated from poultry production or processing environments. In addition, REP-PCR is more rapid, may have a higher discriminatory power, but may be less cost-effective than DGGE. However, more research may be needed to validate this argument. Both DGGE and REP-PCR displayed high sensitivity in discriminating among Salmonella serotypes and either method could be considered as an alternative to more expensive and time-consuming conventional antibody-based serotyping methodologies. PMID:20460676

Anderson, P N; Hume, M E; Byrd, J A; Hernandez, C; Stevens, S M; Stringfellow, K; Caldwell, D J

2010-06-01

19

Geothermal Gradients  

NSDL National Science Digital Library

In this problem set the students use two different equations to calculate a conductive geothermal gradient using a spreadsheet program like Excel. Once they have the geothermal gradient plotted, they are asked to experiment with and comment on the model by changing parameters (e.g. mantle heat flow, thermal conductivity). There is a mix of specific, fill in the blank questions and open-ended questions. This problem set helps develop quantitative problem solving skills using a spreadsheet as a tool, and forces students to think about thermal constraints during igneous and metamorphic processes.

Davidson, Cameron

20

The ecological distribution and comparative photobiology of symbiotic dinoflagellates from reef corals in Belize: Potential implications for coral bleaching  

Microsoft Academic Search

The photobiology and distribution of dinoflagellates in the genus Symbiodinium was investigated for eight common reef coral species over a depth range of 1-25 m on a coral reef in Belize. The genetic identification of symbionts using polymerase chain reaction-denaturing gradient electrophoresis of the internal transcribed spacer 2 region revealed marked differences in host specificity and depth zonation for certain

Mark E. Warner; Todd C. LaJeunesse; Jennifer D. Robison; Rebecca M. Thur

2006-01-01

21

Food Chains  

NSDL National Science Digital Library

In this project, you will discover the way food chains function by viewing four different types of food chains and designing your favorite one. How is the flow of energy traced through a food chain? Use your cluster organizer to record information for four different food chains and what the consumers, 1st level consumers, 2nd level consumers, and 3rd level consumers are and what they eat. Begin by viewing ecosystems: Introduction to Ecosystems Now that you know what an ...

Hammond, Ms.

2009-10-21

22

Association of Thioautotrophic Bacteria with Deep-Sea Sponges  

Microsoft Academic Search

We investigated microorganisms associated with a deep-sea sponge, Characella sp. (Pachastrellidae) collected at a hydrothermal vent site (686 m depth) in the Sumisu Caldera, Ogasawara Island chain,\\u000a Japan, and with two sponges, Pachastrella sp. (Pachastrellidae) and an unidentified Poecilosclerida sponge, collected at an oil seep (572 m depth) in the Gulf of Mexico,\\u000a using polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE) directed

Miyuki Nishijima; Dhugal J. Lindsay; Junko Hata; Aoi Nakamura; Hiroaki Kasai; Yuji Ise; Charles R. Fisher; Yoshihiro Fujiwara; Masaru Kawato; Tadashi Maruyama

2010-01-01

23

Modelling the Bicoid gradient.  

PubMed

Morphogen gradients provide embryonic tissues with positional information by inducing target genes at different concentration thresholds and thus at different positions. The Bicoid morphogen gradient in Drosophila melanogaster embryos has recently been analysed quantitatively, yet how it forms remains a matter of controversy. Several biophysical models that rely on production, diffusion and degradation have been formulated to account for the observed dynamics of the Bicoid gradient, but no one model can account for all its characteristics. Here, we discuss how existing data on this gradient fit the various proposed models and what aspects of gradient formation these models fail to explain. We suggest that knowing a few additional parameters, such as the lifetime of Bicoid, would help to identify and develop better models of Bicoid gradient formation. PMID:20570935

Grimm, Oliver; Coppey, Mathieu; Wieschaus, Eric

2010-07-01

24

Gradient Estimation Revitalized  

Microsoft Academic Search

We investigate the use of a Fourier-domain derivative error kernel to quantify the error incurred while estimating the gradient of a function from scalar point samples on a regular lattice. We use the error kernel to show that gradient reconstruction quality is significantly enhanced merely by shifting the reconstruction kernel to the centers of the principal lattice directions. Additionally, we

Usman R. Alim; Torsten Möller; Laurent Condat

2010-01-01

25

Gradient index metamaterials  

Microsoft Academic Search

Metamaterials---artificially structured materials with tailored electromagnetic response---can be designed to have properties difficult or impossible to achieve with traditional materials fabrication methods. Here we present a structured metamaterial, based on conducting split ring resonators (SRRs), which has an effective index of refraction with a constant spatial gradient. We experimentally confirm the gradient by measuring the deflection of a microwave beam

D. R. Smith; J. J. Mock; A. F. Starr; D. Schurig

2005-01-01

26

Gradient Driven Fluctuations  

NASA Technical Reports Server (NTRS)

We have worked with our collaborators at the University of Milan (Professor Marzio Giglio and his group-supported by ASI) to define the science required to measure gradient driven fluctuations in the microgravity environment. Such a study would provide an accurate test of the extent to which the theory of fluctuating hydrodynamics can be used to predict the properties of fluids maintained in a stressed, non-equilibrium state. As mentioned above, the results should also provide direct visual insight into the behavior of a variety of fluid systems containing gradients or interfaces, when placed in the microgravity environment. With support from the current grant, we have identified three key systems for detailed investigation. These three systems are: 1) A single-component fluid to be studied in the presence of a temperature gradient; 2) A mixture of two organic liquids to be studied both in the presence of a temperature gradient, which induces a steady-state concentration gradient, and with the temperature gradient removed, but while the concentration gradient is dying by means of diffusion; 3) Various pairs of liquids undergoing free diffusion, including a proteidbuffer solution and pairs of mixtures having different concentrations, to allow us to vary the differences in fluid properties in a controlled manner.

Cannell, David

2005-01-01

27

Fluctuation Effects on Phase Behavior of Gradient Copolymer Systems  

NASA Astrophysics Data System (ADS)

We consider the effect of sequence polydispersity on fluctuation induced shift in order-disorder transition (ODT) temperature for symmetric systems of gradient copolymers. Using single chain in mean field simulations, a systematic change in scaling prediction for shift in ODT with Ginzburg parameter is reported. We demonstrate that gradient strength and overall blockiness of sequences has a significant impact on shift in ODT temperature. The weak gradient copolymers having high compositional polydispersity mimic random copolymers whereas, strong gradient copolymers possess inherent blockiness and are close to diblock copolymers. The blockiness parameter has a minimal impact on shift in ODT in strong gradient copolymers. Also, ternary blends of homopolymer/gradient copolymer are investigated to capture effect of compositional polydispersity on phase diagram and formation of microemulsion structures.

Pandav, Gunja; Ganesan, Venkat

2013-03-01

28

Type of automatic gradienter  

NASA Astrophysics Data System (ADS)

Aiming at the requirement that some kinds of big dynamo- electric equipments such as a dam gate of hydro-power plant or a elevator have to keep their balance in the process of being lifted and dropped, a novel and precise gradienter with high resolution and short response time is presented in this article. In this gradienter, the respective hydraulic pressure method is adopted.

Li, Shaohui; He, Liang; Zhang, Gang; Zhang, Zhipeng

2000-05-01

29

Phylogenetic diversity of sediment bacteria in the northern Bering Sea  

Microsoft Academic Search

The bacterial diversity in sediments from the northern Bering Sea was investigated by culture-independent approaches. Community\\u000a fingerprint analysis by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) revealed that sediment\\u000a at two deep stations (DBSE and DBS1, >400 m in depth) harbored a bacterial community distinct from the sediments collected\\u000a at shallow stations (<150 m in depth) on the continental shelf. Three 16S

Yinxin ZengYang; Yang Zou; Bo Chen; Jacqueline M. Grebmeier; Huirong Li; Yong Yu; Tianling Zheng

2011-01-01

30

Bacterial diversity dynamics in a long-term petroleum-contaminated soil  

Microsoft Academic Search

Bacterial diversity dynamics were investigated in the soil samples in different distances and depths from\\/at a long-term petroleum-contaminated site. Microbial activity in the soil samples showed ATP values closely correlated with organic matter content (OC) and total petroleum hydrocarbon (TPH). Bacterial community diversity (H) and evenness (J) using PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) and PCR-T-RFLP (terminal restriction fragment

Eun-Hee Lee; Sang Hyon Lee; Kyung-Suk Cho

2011-01-01

31

Identification of new Mamu-DRB alleles using DGGE and direct sequencing  

Microsoft Academic Search

Rhesus macaques represent important animal models for biomedical research. The ability to identify macaque major histocompatibility\\u000a complex (Mhc) alleles is crucial for fully understanding these models of autoimmune and infectious disease. Here we describe a rapid and\\u000a unambiguous way to distinguish DRB alleles in the rhesus macaque using the polymerase chain reaction, denaturing gradient gel electrophoresis (DGGE), and direct\\u000a sequencing.

L. A. Knapp; Luis F. Cadavid; Mary E. Eberle; Stuart J. Knechtle; Ronald E. Bontrop; David I. Watkins

1997-01-01

32

Succession and phylogenetic profile of eukaryotic communities in the composting process of rice straw estimated by PCR-DGGE analysis  

Microsoft Academic Search

The succession and phylogenetic profile of eukaryotic communities during the composting process of rice straw (RS) were studied by applying polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis followed by sequencing of 18S rDNA. Principal component analysis and cluster analysis of the DGGE band patterns of eukaryotic communities resulted in exactly the same grouping as found with phospholipid fatty acid

Vita Ratri Cahyani; Kazuo Matsuya; Susumu Asakawa; Makoto Kimura

2004-01-01

33

Analysis of bacteria communities in an up-flow fixed-bed (UFB) bioreactor for treating sulfide in hydrocarbon wastewater  

Microsoft Academic Search

An up-flow fixed-bed (UFB) bioreactor with patented functional polyurethane foam (FPUF) carriers was used to treat sulfide in hydrocarbon wastewater. Community compositions of autotrophic and heterotrophic bacteria were analyzed by polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE). DGGE results showed that a relatively stable bacterial community composed of heterotrophic and autotrophic bacteria formed in the bioreactor by the end of

Guodong Ji; Bo Liao; Huchun Tao; Zhihong Lei

2009-01-01

34

Profling of microbial communities in a bioreactor for treating hydrocarbon-sulfde-containing wastewater  

Microsoft Academic Search

A technology of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was used to profle the structure and dynamic changes of microbial communities in a bioreactor for treating hydrocarbon-sulfde-containing (HSC) wastewater. The results showed that the heterotrophic genus of Acinetobacter and the autotrophic genera of Thiobacillus and Thiomonas could survive well in all of three operating conditions. Some special genera were

Bo LIAO; Guodong JI; Liqiu CHENG

2008-01-01

35

Molecular analysis of fungal communities of biodegradable plastics in two Japanese soils  

Microsoft Academic Search

This study aimed to elucidate the microbial communities responsible for the decomposition of poly-(?-caprolactone) (PCL), poly-(butylene succinate) (PBS), poly-(butylene succinate and adipate) (PBSA) and poly-lactide (PLA) in two soils using a culture-independent, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method with subsequent sequencing of the main DGGE bands. The PCL, PBS and PBSA films were considerably degraded within 50 days at

Masahiro Kamiya; Susumu Asakawa; Makoto Kimura

2007-01-01

36

Bulk soil and rhizosphere bacterial community PCR–DGGE profiles and ?-galactosidase activity as indicators of biological quality in soils contaminated by heavy metals and cultivated with Silene vulgaris (Moench) Garcke  

Microsoft Academic Search

The biological quality of two heavy metal contaminated soils (soil C: Typic Calcixerept, pH 8.3 and soil H: Typic Haploxeraf, pH 7.3) was investigated after growing the metal-tolerant plant Silene vulgaris (Moench) Garcke for two vegetative periods. The activity of the enzyme ?-galactosidase, which is sensitive to the presence of contaminants in soil, and the polymerase chain reaction-denaturing gradient gel

M. J. Martínez-Iñigo; A. Pérez-Sanz; I. Ortiz; J. Alonso; R. Alarcón; P. García; M. C. Lobo

2009-01-01

37

Microbiological study of lactic acid bacteria in kefir grains by culture-dependent and culture-independent methods  

Microsoft Academic Search

Lactic acid bacteria (LAB) in different original kefir grains were first assessed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) by a culture-dependent way, and were further confirmed by DNA sequencing techniques. Results indicated that a combined method of cultivation with PCR-DGGE and subsequent DNA sequencing could successfully identify four LAB strains from three kefir grains from Taiwan (named Hsinchu,

Hsi-Chia Chen; Sheng-Yao Wang; Ming-Ju Chen

2008-01-01

38

High gradient superconducting quadrupoles  

SciTech Connect

Prototype superconducting quadrupoles with a 5 cm aperture and gradient of 16 kG/cm have been built and tested as candidate magnets for the final focus at SLC. The magnets are made from NbTi Tevatron style cable with 10 inner and 14 outer turns per quadrant. Quench performance and multipole data are presented. Design and data for a low current, high gradient quadrupole, similar in cross section but wound with a cable consisting of five insulated conductors are also discussed.

Lundy, R.A.; Brown, B.C.; Carson, J.A.; Fisk, H.E.; Hanft, R.H.; Mantsch, P.M.; McInturff, A.D.; Remsbottom, R.H.

1987-07-01

39

Electron temperature gradient turbulence.  

PubMed

The first toroidal, gyrokinetic, electromagnetic simulations of small scale plasma turbulence are presented. The turbulence considered is driven by gradients in the electron temperature. It is found that electron temperature gradient (ETG) turbulence can induce experimentally relevant thermal losses in magnetic confinement fusion devices. For typical tokamak parameters, the transport is essentially electrostatic in character. The simulation results are qualitatively consistent with a model that balances linear and secondary mode growth rates. Significant streamer-dominated transport at long wavelengths occurs because the secondary modes that produce saturation become weak in the ETG limit. PMID:11136051

Dorland, W; Jenko, F; Kotschenreuther, M; Rogers, B N

2000-12-25

40

Electron Temperature Gradient Turbulence  

SciTech Connect

The first toroidal, gyrokinetic, electromagnetic simulations of small scale plasma turbulence are presented. The turbulence considered is driven by gradients in the electron temperature. It is found that electron temperature gradient (ETG) turbulence can induce experimentally relevant thermal losses in magnetic confinement fusion devices. For typical tokamak parameters, the transport is essentially electrostatic in character. The simulation results are qualitatively consistent with a model that balances linear and secondary mode growth rates. Significant streamer-dominated transport at long wavelengths occurs because the secondary modes that produce saturation become weak in the ETG limit.

Dorland, W.; Jenko, F.; Kotschenreuther, M.; Rogers, B. N.

2000-12-25

41

HIGH GRADIENT INDUCTION ACCELERATOR  

SciTech Connect

A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is stimulated by the desire for compact flash x-ray radiography sources. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be described. Progress in applying this technology to several applications will be reviewed.

Caporaso, G J; Sampayan, S; Chen, Y; Blackfield, D; Harris, J; Hawkins, S; Holmes, C; Krogh, M; Nelson, S; Nunnally, W; Paul, A; Poole, B; Rhodes, M; Sanders, D; Selenes, K; Sullivan, J; Wang, L; Watson, J

2007-06-21

42

Markov Chains  

NSDL National Science Digital Library

This website, created by Everett F. Carter of Taygeta Scientific Inc., discusses Markov chains, transition probabilities, and the transition probability matrix. The website is simple, but is still a good resource to demonstrate these principles. Its use of mathematical formulas, intertwined with the text, allows the user to interact with both simultaneously. Overall, this is a good website for anyone interested in statistics.

Carter, Everett F.

2008-12-26

43

Control over wettability via surface modification of porous gradients  

NASA Astrophysics Data System (ADS)

The control over surface wettability is of concern for a number of important applications including chromatography, microfluidics, biomaterials, low-fouling coatings and sensing devices. Here, we report the ability to tailor wettability across a surface using lateral porous silicon (pSi) gradients. Lateral gradients made by anodisation of silicon using an asymmetric electrode configuration showed a lateral distribution of pore sizes, which decreased with increasing distance from the electrode. Pore sizes were characterised using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Pore diameters ranged from micrometres down to less than 10 nanometres. Chemical surface modification of the pSi gradients was employed in order to produce gradients with different wetting or non-wetting properties. Surface modifications were achieved via silanisation of oxidised pSi surfaces introducing functionalities including polyethylene glycol, terminal amine and fluorinated hydrocarbon chains. Surface modifications were characterised using infrared spectroscopy. Sessile drop water contact angle measurements were used to probe the wettability in regions of different pore size across the gradient. For the fluorinated gradients, a comparison of equilibrium and dynamic contact angle measurement was undertaken. The fluorinated surface chemistry produced gradients with wettabilities ranging from hydrophobic to near super-hydrophobic whereas pSi gradients functionalised with polyethylene glycol showed graded hydrophilicity. In all cases investigated here, changes in pore size across the gradient had a significant effect on wettability.

Khung, Y. L.; Cole, M. A.; McInnes, S. J. P.; Voelcker, N. H.

2007-12-01

44

Manipulating the Gradient  

ERIC Educational Resources Information Center

We introduce a cooperative learning, group lab for a Calculus III course to facilitate comprehension of the gradient vector and directional derivative concepts. The lab is a hands-on experience allowing students to manipulate a tangent plane and empirically measure the effect of partial derivatives on the direction of optimal ascent. (Contains 7…

Gaze, Eric C.

2005-01-01

45

Gradient Refractive Index Lenses.  

ERIC Educational Resources Information Center

Describes the nature of gradient refractive index (GRIN) lenses, focusing on refraction in these materials, focal length of a thin Wood lens, and on manufacturing of such lenses. Indicates that GRIN lenses of small cross section are in limited production with applications suggested for optical communication and photocopying fields. (JN)

Morton, N.

1984-01-01

46

Chain Gang  

NASA Technical Reports Server (NTRS)

6 August 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a chain of clustered and battered craters. These were formed by secondary impact. That is, somewhere to the south (beyond the bottom of this image), a large impact crater formed. When this occurred, material ejected from the crater was thrown tens to hundreds of kilometers away. This material then impacted the martian surface, forming clusters and chains of smaller craters.

Location near: 15.8oN, 35.6oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Northern Spring

2006-01-01

47

Markov Chains  

NSDL National Science Digital Library

S.O.S. Mathematics is your free resource for math review material from algebra to differential equations. The perfect study site for high school, college students and adult learners. Get help to do your homework, refresh your memory, or prepare for a test. This page focuses on the ideas behind Markov chains. This is a wonderful resource for anyone wanting to learn more about statistics.

Khamsi, Mohamed A.

2008-12-25

48

Markov Chains  

NSDL National Science Digital Library

Created by Lewis Blake for the Connected Curriculum Project, the purposes of this module are to introduce the concepts of transition matrices and Markov chains; to provide motivation for the definition of matrix multiplication in the context of an interesting application; and to lay the groundwork for applied problems that can be solved later with eigenvalues and eigenvectors. This is part of a larger collection of learning modules hosted by Duke University.

Blake, Lewis

2010-06-01

49

Toward fractional gradient elasticity  

NASA Astrophysics Data System (ADS)

The use of an extension of gradient elasticity through the inclusion of spatial derivatives of fractional order to describe the power law type of non-locality is discussed. Two phenomenological possibilities are explored. The first is based on the Caputo fractional derivatives in one dimension. The second involves the Riesz fractional derivative in three dimensions. Explicit solutions of the corresponding fractional differential equations are obtained in both cases. In the first case, stress equilibrium in a Caputo elastic bar requires the existence of a nonzero internal body force to equilibrate it. In the second case, in a Riesz-type gradient elastic continuum under the action of a point load, the displacement may or may not be singular depending on the order of the fractional derivative assumed.

Tarasov, Vasily E.; Aifantis, Elias C.

2014-05-01

50

Polymer brush gradients grafted from plasma-polymerized surfaces.  

PubMed

A new method for generating a surface density gradient of polymer chains is presented. A substrate-independent polymer deposition technique was used to coat materials with a chemical gradient based on plasma copolymerization of 1,7-octadiene and allylamine. This provided a uniform chemical gradient to which initiators for atom transfer radical polymerization (ATRP) were immobilized. After surface-initiated atom transfer radical polymerization (SI-ATRP), poly(2-hydroxyethyl methacrylate) (PHEMA) chains were grafted from the surface and the measured thickness profiles provided direct evidence for how surface crowding provides an entropic driving force resulting in chain extension away from the surface. Film thicknesses were found to increase with the position along the gradient surface, reflecting the gradual transition from collapsed to more extended surface-tethered polymer chains as the grafting density increased. The method described is novel in that the approach provides covalent linkages from the polymer coating to the substrate and is not limited to a particular surface chemistry of the starting material. PMID:24967529

Coad, Bryan R; Bilgic, Tugba; Klok, Harm-Anton

2014-07-22

51

Markov Chains  

NSDL National Science Digital Library

Created by Kyle Siegrist of the University of Alabama-Huntsville, this is an online, interactive lesson on Markov chains. The author provides examples, exercises, and applets to introduce the subject. More specifically, the lesson covers: recurrence, transience, periodicity, time reversal, as well as invariant and limiting distributions. In addition, the author has provided links to external resources for further research. Overall, this is a great resource for those interested in this statistical process. It provides basic examples to introduce the topic, but also provides a more in-depth study to further challenge students.

Siegrist, Kyle

2009-03-02

52

Charge gradient microscopy  

PubMed Central

Here we present a simple and fast method to reliably image polarization charges using charge gradient microscopy (CGM). We collected the current from the grounded CGM probe while scanning a periodically poled lithium niobate single crystal and single-crystal LiTaO3 thin film on the Cr electrode. We observed current signals at the domains and domain walls originating from the displacement current and the relocation or removal of surface charges, which enabled us to visualize the ferroelectric domains at a scan frequency above 78 Hz over 10 ?m. We envision that CGM can be used in high-speed ferroelectric domain imaging and piezoelectric energy-harvesting devices.

Hong, Seungbum; Tong, Sheng; Park, Woon Ik; Hiranaga, Yoshiomi; Cho, Yasuo; Roelofs, Andreas

2014-01-01

53

Charge gradient microscopy.  

PubMed

Here we present a simple and fast method to reliably image polarization charges using charge gradient microscopy (CGM). We collected the current from the grounded CGM probe while scanning a periodically poled lithium niobate single crystal and single-crystal LiTaO3 thin film on the Cr electrode. We observed current signals at the domains and domain walls originating from the displacement current and the relocation or removal of surface charges, which enabled us to visualize the ferroelectric domains at a scan frequency above 78 Hz over 10 ?m. We envision that CGM can be used in high-speed ferroelectric domain imaging and piezoelectric energy-harvesting devices. PMID:24760831

Hong, Seungbum; Tong, Sheng; Park, Woon Ik; Hiranaga, Yoshiomi; Cho, Yasuo; Roelofs, Andreas

2014-05-01

54

Tectorial Membrane Stiffness Gradients  

PubMed Central

The mammalian inner ear processes sound with high sensitivity and fine resolution over a wide frequency range. The underlying mechanism for this remarkable ability is the “cochlear amplifier”, which operates by modifying cochlear micromechanics. However, it is largely unknown how the cochlea implements this modification. Although gradual improvements in experimental techniques have yielded ever-better descriptions of gross basilar membrane vibration, the internal workings of the organ of Corti and of the tectorial membrane have resisted exploration. Although measurements of cochlear function in mice with a gene mutation for ?-tectorin indicate the tectorial membrane's key role in the mechanoelectrical transformation by the inner ear, direct experimental data on the tectorial membrane's physical properties are limited, and only a few direct measurements on tectorial micromechanics are available. Using the hemicochlea, we are able to show that a tectorial membrane stiffness gradient exists along the cochlea, similar to that of the basilar membrane. In artificial perilymph (but with low calcium), the transversal and radial driving point stiffnesses change at a rate of –4.0 dB/mm and ?4.9 dB/mm, respectively, along the length of the cochlear spiral. In artificial endolymph, the stiffness gradient for the transversal component was –3.4 dB/mm. Combined with the changes in tectorial membrane dimensions from base to apex, the radial stiffness changes would be able to provide a second frequency-place map in the cochlea. Young's modulus, which was obtained from measurements performed in the transversal direction, decreased by ?2.6 dB/mm from base to apex.

Richter, Claus-Peter; Emadi, Gulam; Getnick, Geoffrey; Quesnel, Alicia; Dallos, Peter

2007-01-01

55

Nanoparticle manipulation by thermal gradient  

PubMed Central

A method was proposed to manipulate nanoparticles through a thermal gradient. The motion of a fullerene molecule enclosed inside a (10, 10) carbon nanotube with a thermal gradient was studied by molecular dynamics simulations. We created a one-dimensional potential valley by imposing a symmetrical thermal gradient inside the nanotube. When the temperature gradient was large enough, the fullerene sank into the valley and became trapped. The escaping velocities of the fullerene were evaluated based on the relationship between thermal gradient and thermophoretic force. We then introduced a new way to manipulate the position of nanoparticles by translating the position of thermostats with desirable thermal gradients. Compared to nanomanipulation using a scanning tunneling microscope or an atomic force microscope, our method for nanomanipulation has a great advantage by not requiring a direct contact between the probe and the object.

2012-01-01

56

Nanoparticle manipulation by thermal gradient.  

PubMed

A method was proposed to manipulate nanoparticles through a thermal gradient. The motion of a fullerene molecule enclosed inside a (10, 10) carbon nanotube with a thermal gradient was studied by molecular dynamics simulations. We created a one-dimensional potential valley by imposing a symmetrical thermal gradient inside the nanotube. When the temperature gradient was large enough, the fullerene sank into the valley and became trapped. The escaping velocities of the fullerene were evaluated based on the relationship between thermal gradient and thermophoretic force. We then introduced a new way to manipulate the position of nanoparticles by translating the position of thermostats with desirable thermal gradients. Compared to nanomanipulation using a scanning tunneling microscope or an atomic force microscope, our method for nanomanipulation has a great advantage by not requiring a direct contact between the probe and the object. PMID:22364240

Wei, Ning; Wang, Hui-Qiong; Zheng, Jin-Cheng

2012-01-01

57

Gradient index in borate glasses  

NASA Astrophysics Data System (ADS)

A number of aluminum-borate glasses has been developed for producing gradient index glasses by exchanging. Both positive and negative axial gradient were fabricated in the glasses by exchange of Li+ for Na+ and Na+ for Li+, respectively. Index change to 0.03 and gradient index Abble number larger than +100 were achieved. The diffusion coefficients of Na+ and Li+ in borate glasses were calculated by fitting the profiles of refractive index to complimentary error function.

Sun, Yunan; Kindred, Douglas S.; Moore, Duncan T.

1994-08-01

58

Reduced gradient bubble model.  

PubMed

An approach to decompression modeling, the reduced gradient bubble model (RGBM), is developed from the critical phase hypothesis. The phase limit is introduced, extended, and applied within bubble-nucleation theory proposed by Yount. Much is different in the RGBM algorithm, on both theoretical and applied sides, with a focus on permissible bubble excesses rather than just dissolved gas buildup, something of a departure from traditional models. Overall, the approach is conservative, with changes in parameter settings affording flexibility. Marginal profiles permitted by tables and meters are restricted by the bubble algorithm. Highlighted features of the conservative algorithm include: (1) reduced no-stop time limits from the varying-permeability model (VPM); (2) short safety stops (or shallow swimming ascents) in the 10-20 feet of sea water (fsw) zone; (3) ascent and descent rates of 60 fsw/min, or slower; (4) restricted repetitive exposures, particularly beyond 100 fsw, based on reduced permissible bubble excess; (5) restricted spike (shallow-to-deep) exposures based on excitation of additional micronuclei; (6) restricted multi-day activity based on regeneration of micronuclei; (7) consistent treatment of altitude diving within model framework; (8) algorithm linked to bubble-nucleation theory and experiment. Coupled to medical reports about the long term effects of breathing pressurized gases and shortcomings in dissolved gas models, conservative modeling seems prudent. PMID:2276850

Wienke, B R

1990-11-01

59

Fast image processing on chain board of inverted tooth chain  

NASA Astrophysics Data System (ADS)

Discussed ordinary image processing technology of inverted tooth chain board, including noise reduction, image segmentation, edge detection and contour extraction etc.. Put forward a new kind of sub-pixel arithmetic for edge orientation of circle. The arithmetic first did edge detection to image by Canny arithmetic, so as to enhance primary orientation precision of edge, then calculated gradient direction, and then interpolated gradient image (image that was detected by Sobel arithmetic) along gradient direction, last obtained sub-pixel orientation of edge. Performed two kinds of least-square fitting methods for line edge to getting its sub-pixel orientation, from analysis and experiments, the orientation error of improved least-square linear fitting method was one quarter of ordinary least-square linear fitting error under small difference of orientation time. The sub-pixel orientation of circle made resolution of CCD increase 42 tines, which enhanced greatly orientation precision of image edge. For the need of quick on-line inspection next step, integrated the whole environment containing image preprocess, Hough conversion of line, setting orientation & direction of image, sub-pixel orientation of line and circle, output of calculation result. The whole quick processing course performed without operator, processing tine of single part is less than 0.3 second. The sub-pixel orientation method this paper posed fits precision orientation of image, and integration calculation method ensure requirement of quick inspection, and lays the foundations for on-line precision visual measurement of image.

Liu, Qing-min; Li, Guo-fa

2007-11-01

60

Height and gradient from shading  

Microsoft Academic Search

The method described here for recovering the shape of a surface from a shaded image can deal with complex, wrinkled surfaces. Integrability can be enforced easily because both surface height and gradient are represented (A gra- dient field is integrable if it is the gradient of some surface height function). The robustness of the method stems in part from linearization

Berthold K. P. Horn

1990-01-01

61

Geothermal gradient map of Colorado  

SciTech Connect

Reported bottom hole temperatures (BHT) were taken from 12,000 oil and gas wells provided by the Colorado Oil and Gas Conservation Commission files. Average annual surface temperatures were subtracted from the BHT and then divided by the depth to give a gradient. To eliminate as many sources of error as possible, the gradient values were averaged for each township and contoured.

Repplier, F.N.; Fargo, R.L.

1981-01-01

62

Metallicity Gradients in Elliptical Galaxies  

NASA Technical Reports Server (NTRS)

The study of metalicity gradients is an examination of the relics of the first epoch of star formation and, thus, another issue that metallicity gradients can address is the relationship between chemical and dynamical evolution during the initial phase of star formation.

Hanlan, Patricia C.; Schombert, James M.; Barsony, Mary; Rakos, Karl D.

1993-01-01

63

Edge dislocation in gradient elasticity  

Microsoft Academic Search

The present paper is a natural continuation of the authors` previous work where they have considered the screw dislocation in gradient elasticity. They consider two dislocation configurations: a separate edge dislocation and a dipole of edge dislocations. The gradient solutions presented have been obtained by two different ways, i.e., in total displacements and in elastic strains with both leading to

M. Yu. Gutkin; E. C. Aifantis

1997-01-01

64

Empirical equation estimates geothermal gradients  

SciTech Connect

An empirical equation can estimate geothermal (natural) temperature profiles in new exploration areas. These gradients are useful for cement slurry and mud design and for improving electrical and temperature log interpretation. Downhole circulating temperature logs and surface outlet temperatures are used for predicting the geothermal gradients.

Kutasov, I.M. (MultiSpectrum Technologies, Santa Monica, CA (United States))

1995-01-02

65

Rapid Gradient-Echo Imaging  

PubMed Central

Gradient echo sequences are widely used in magnetic resonance imaging (MRI) for numerous applications ranging from angiography to perfusion to functional MRI. Compared with spin-echo techniques, the very short repetition times of gradient-echo methods enable very rapid 2D and 3D imaging, but also lead to complicated “steady states.” Signal and contrast behavior can be described graphically and mathematically, and depends strongly on the type of spoiling: fully balanced (no spoiling), gradient spoiling, or RF-spoiling. These spoiling options trade off between high signal and pure T1 contrast while the flip angle also affects image contrast in all cases, both of which can be demonstrated theoretically and in image examples. As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography.

Hargreaves, Brian

2012-01-01

66

Gradient elution in capillary electrochromatography  

SciTech Connect

In analogy to pressure-driven gradient techniques in high-performance liquid chromatography, a system has been developed for delivering electroosmotically-driven solvent gradients for capillary electrochromatography (CEC). Dynamic gradients with sub-mL/min flow rates are generated by merging two electroosmotic flows that are regulated by computer-controlled voltages. These flows are delivered by two fused-silica capillary arms attached to a T-connector, where they mix and then flow into a capillary column that has been electrokinetically packed with 3-mm reversed-phase particles. The inlet of one capillary arm is placed in a solution reservoir containing one mobile phase and the inlet of the other is placed in a second reservoir containing a second mobile phase. Two independent computer-controlled programmable high-voltage power supplies (0-50 kV)--one providing an increasing ramp and the other providing a decreasing ramp--are used to apply variable high-voltage potentials to the mobile phase reservoirs to regulate the electroosmotic flow in each arm. The ratio of the electroosmotic flow rates between the two arms is changed with time according to the computer-controlled voltages to deliver the required gradient profile to the separation column. Experiments were performed to confirm the composition of the mobile phase during a gradient run and to determine the change of the composition in response to the programmed voltage profile. To demonstrate the performance of electroosmotically-driven gradient elution in CEC, a mixture of 16 polycyclic aromatic hydrocarbons (PAHs) was separated in less than 90 minutes. This gradient technique is expected to be well-suited for generating not only solvent gradients in CEC, but also other types of gradients such as pH- and ionic-strength gradients in capillary electrokinetic separations and analyses.

Anex, D.; Rakestraw, D.J. [Sandia National Labs., Livermore, CA (United States); Yan, Chao; Dadoo, R.; Zare, R.N. [Stanford Univ., CA (United States). Dept. of Chemistry

1997-08-01

67

The energy flow of discrete extended gradient systems  

NASA Astrophysics Data System (ADS)

We study the energy flow of spatially discrete, extended gradient systems (infinite lattices), allowing the total energy to be infinite and considering formally gradient dynamics. We show that in spatial dimensions 1,2, the flow is for almost all times arbitrarily close to the set of equilibria, and in dimensions ?3, the size of the set with non-equilibrium dynamics for a positive density of times is two dimensions less than the space dimension. The theory applies to first- and second-order dynamics of elastic chains in a periodic or polynomial potential, chains with interactions beyond the nearest neighbour, deterministic dynamics of spin glasses, the discrete complex Ginzburg-Landau equation, and others. In particular, we apply the theory to show the existence of coarsening dynamics for a class of generalized Frenkel-Kontorova models in bistable potential.

Slijep?evi?, Siniša

2013-07-01

68

Gradient zone boundary control in salt gradient solar ponds  

DOEpatents

A method and apparatus for suppressing zone boundary migration in a salt gradient solar pond includes extending perforated membranes across the pond at the boundaries, between the convective and non-convective zones, the perforations being small enough in size to prevent individual turbulence disturbances from penetrating the hole, but being large enough to allow easy molecular diffusion of salt thereby preventing the formation of convective zones in the gradient layer. The total area of the perforations is a sizable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

Hull, John R. (Downers Grove, IL)

1984-01-01

69

Exponentiated Gradient Versus Gradient Descent for Linear Predictors  

Microsoft Academic Search

We consider two algorithms for on-line prediction based on a linear model. The algorithms are the well-known gradient descent (GD) algorithm and a new algorithm, which we call EG±. They both maintain a weight vector using simple updates. For the GD algorithm, the update is based on subtracting the gradient of the squared error made on a prediction. The EG±algorithm

Jyrki Kivinen; Manfred K. Warmuth

1997-01-01

70

High field gradient particle accelerator  

DOEpatents

A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications is disclosed. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle. 10 figs.

Nation, J.A.; Greenwald, S.

1989-05-30

71

High field gradient particle accelerator  

DOEpatents

A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle.

Nation, John A. (Ithaca, NY) [Ithaca, NY; Greenwald, Shlomo (Haifa, IL) [Haifa, IL

1989-01-01

72

Heat transport in quantum harmonic chains with Redfield baths  

NASA Astrophysics Data System (ADS)

We provide an explicit method for solving general markovian master equations for quadratic bosonic Hamiltonians with linear bath operators. As an example we consider a onedimensional quantum harmonic oscillator chain coupled to thermal reservoirs at both ends of the chain. We derive an analytic solution of the Redfield master equation for homogeneous harmonic chain and recover classical results, namely, vanishing temperature gradient and constant heat current in the thermodynamic limit. In the case of the disordered gapped chains we observe universal heat current scaling independent of the bath spectral function, the system-bath coupling strength, and the boundary conditions.

Žunkovi?, Bojan; Prosen, Tomaž

2012-08-01

73

Generalized gradient and contour program  

USGS Publications Warehouse

This program computes estimates of gradients, prepares contour maps, and plots various sets of data provided by the user on the CalComp plotters. The gradients represent the maximum rates of change of a real variable Z=f(X,Y) with respect to the twodimensional rectangle on which the function is defined. The contours are lines of equal Z values. The program also plots special line data sets provided by the user.

Hellman, Marshall Strong

1972-01-01

74

Control in bioreactors showing gradients  

Microsoft Academic Search

In large-scale bioreactors gradients often occur as a result of non-ideal mixing. This phenomenon complicates design and control of large-scale bioreactors. Gradients in the oxygen concentration can be modeled with a two-compartment model of the liquid phase. Application of this model had been suggested for the control of the dissolved oxygen concentration with a batch gluconic acid fermentation process as

S. R. Weijers; G. Honderd; K. Ch. A. M. Luyben

1990-01-01

75

Jet Stream and Horizontal Temperature Gradients  

NSDL National Science Digital Library

This applet explores the relationship between wind speed, jet streams and temperature gradients. The text explains jet streams and polar front jets and their relationship to temperature gradients. Questions about pressure gradients and wind are also provided.

Ackerman, Steve; Whittaker, Tom

76

Effects of compositional polydispersity on gradient copolymer melts  

NASA Astrophysics Data System (ADS)

The phase behavior of gradient copolymers is studied theoretically using random phase approximation (RPA) and self-consistent field theory (SCFT), focusing on the effects of monomer sequence distribution, or compositional polydispersity, of the polymer chains. The stability of the disordered phase is examined using RPA analysis, whereas the ordered phases of the system are studied using SCFT calculations. It is discovered that the critical domain spacing increases and the disorder-order transition temperature moves to higher values with the increase of the compositional polydispersity. SCFT results reveal that, depending on the value of the degree of segregation, structural change due to the different chain-to-chain monomer sequence distribution is controlled by two different mechanisms.

Jiang, Run; Wang, Zheng; Yin, Yuhua; Li, Baohui; Shi, An-Chang

2013-02-01

77

Estimation of coastal density gradients  

NASA Astrophysics Data System (ADS)

Density gradients in coastal regions with significant freshwater input are large and variable and are a major control of nearshore circulation. However their measurement is difficult, especially where the gradients are largest close to the coast, with significant uncertainties because of a variety of factors - spatial and time scales are small, tidal currents are strong and water depths shallow. Whilst temperature measurements are relatively straightforward, measurements of salinity (the dominant control of spatial variability) can be less reliable in turbid coastal waters. Liverpool Bay has strong tidal mixing and receives fresh water principally from the Dee, Mersey, Ribble and Conwy estuaries, each with different catchment influences. Horizontal and vertical density gradients are variable both in space and time. The water column stratifies intermittently. A Coastal Observatory has been operational since 2002 with regular (quasi monthly) CTD surveys on a 9 km grid, an situ station, an instrumented ferry travelling between Birkenhead and Dublin and a shore-based HF radar system measuring surface currents and waves. These measurements are complementary, each having different space-time characteristics. For coastal gradients the ferry is particularly useful since measurements are made right from the mouth of Mersey. From measurements at the in situ site alone density gradients can only be estimated from the tidal excursion. A suite of coupled physical, wave and ecological models are run in association with these measurements. The models, here on a 1.8 km grid, enable detailed estimation of nearshore density gradients, provided appropriate river run-off data are available. Examples are presented of the density gradients estimated from the different measurements and models, together with accuracies and uncertainties, showing that systematic time series measurements within a few kilometres of the coast are a high priority. (Here gliders are an exciting prospect for detailed regular measurements to fill this gap.) The consequences for and sensitivity of circulation estimates are presented using both numerical and analytic models.

Howarth, M. J.; Palmer, M. R.; Polton, J. A.; O'Neill, C. K.

2012-04-01

78

Laser amplifier chain  

DOEpatents

A laser amplifier chain has a plurality of laser amplifiers arranged in a chain to sequentially amplify a low-power signal beam to produce a significantly higher-power output beam. Overall efficiency of such a chain is improved if high-gain, low efficiency amplifiers are placed on the upstream side of the chain where only a very small fraction of the total pumped power is received by the chain and low-gain, high-efficiency amplifiers are placed on the downstream side where a majority of pumping energy is received by the chain. 6 figs.

Hackel, R.P.

1992-10-20

79

Laser amplifier chain  

DOEpatents

A laser amplifier chain has a plurality of laser amplifiers arranged in a chain to sequentially amplify a low-power signal beam to produce a significantly higher-power output beam. Overall efficiency of such a chain is improved if high-gain, low efficiency amplifiers are placed on the upstream side of the chain where only a very small fraction of the total pumped power is received by the chain and low-gain, high-efficiency amplifiers are placed on the downstream side where a majority of pumping energy is received by the chain.

Hackel, Richard P. (Livermore, CA)

1992-01-01

80

Dielectric gradient metasurface optical elements.  

PubMed

Gradient metasurfaces are two-dimensional optical elements capable of manipulating light by imparting local, space-variant phase changes on an incident electromagnetic wave. These surfaces have thus far been constructed from nanometallic optical antennas, and high diffraction efficiencies have been limited to operation in reflection mode. We describe the experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum. Ultrathin gratings, lenses, and axicons have been realized by patterning a 100-nanometer-thick Si layer into a dense arrangement of Si nanobeam antennas. The use of semiconductors can broaden the general applicability of gradient metasurfaces, as they offer facile integration with electronics and can be realized by mature semiconductor fabrication technologies. PMID:25035488

Lin, Dianmin; Fan, Pengyu; Hasman, Erez; Brongersma, Mark L

2014-07-18

81

Nuclear Chain Reaction  

NSDL National Science Digital Library

This simulation shows a chain reaction. The visitor can introduce a neutron and observe how it produces an additional reaction or escapes. The chain reaction can be paused in order to analyze the process.

Bauer, W. (Wolfgang), 1959-

2011-11-29

82

Denaturing gradient gel electrophoresis (DGGE).  

PubMed

Denaturing Gradient Gel Electrophoresis (DGGE) is a technique used to separate short- to medium-length DNA fragments based on their melting characteristics. It has been used frequently for identifying single-nucleotide polymorphisms without the need for DNA sequencing and as a molecular fingerprinting method for complex ecosystem communities, in particular in conjunction with amplification of microbial 16S rRNA genes. Here, the principles of DGGE, based on partial DNA strand separation at a given position in a gradient of chemical denaturant, are described, and an example protocol, optimized for fingerprinting of 200-300 bp fragments of bacterial 16S rRNA genes, is given. PMID:23913290

Strathdee, Fiona; Free, Andrew

2013-01-01

83

Templating Surfaces with Gradient Assemblies  

SciTech Connect

One of the most versatile and widely used methods of forming surfaces with position-dependent wettability is that conceived by Chaudhury and Whitesides more than a decade ago. In this paper we review several projects that utilize this gradient-forming methodology for: controlled of deposition of self-assembled monolayers on surfaces, generating arrays of nanoparticles with number density gradients, probing the mushroom-to-brush transition in surface-anchored polymers, and controlling the speed of moving liquid droplets on surfaces.

Genzer,J.

2005-01-01

84

Oxidation in a temperature gradient  

SciTech Connect

The effects of a temperature gradient and heat flux on point defect diffusion in protective oxide scales were examined. Irreversible thermodynamics were used to expand Fick's first law of diffusion to include a heat flux term--a Soret effect. Oxidation kinetics were developed for the oxidation of cobalt and for nickel doped with chromium. Research in progress is described to verify the effects of a heat flux by oxidizing pure cobalt in a temperature gradient above 800 C, and comparing the kinetics to isothermal oxidation. The tests are being carried out in the new high temperature gaseous corrosion and corrosion/erosion facility at the Albany Research Center.

Holcomb, Gordon R.; Covino, Bernard S., Jr.; Russell, James H.

2001-01-01

85

Dislocations in second strain gradient elasticity  

Microsoft Academic Search

A second strain gradient elasticity theory is proposed based on first and second gradients of the strain tensor. Such a theory is an extension of first strain gradient elasticity with double stresses. In particular, the strain energy depends on the strain tensor and on the first and second gradient terms of it. Using a simplified but straightforward version of this

Markus Lazar; Gérard A. Maugin; Elias C. Aifantis

2006-01-01

86

Effect of Gradient Sequencing on Copolymer Order?Disorder Transitions: Phase Behavior of Styrene/n-Butyl Acrylate Block and Gradient Copolymers  

SciTech Connect

We investigate the effect of gradient sequence distribution in copolymers on order-disorder transitions, using rheometry and small-angle X-ray scattering to compare the phase behavior of styrene/n-butyl acrylate (S/nBA) block and gradient copolymers. Relative to block sequencing, gradient sequencing increases the molecular weight necessary to induce phase segregation by over 3-fold, directly consistent with previous predictions from theory. Results also suggest the existence of both upper and lower order-disorder transitions in a higher molecular weight S/nBA gradient copolymer, made accessible by the shift in order-disorder temperatures from gradient sequencing. The combination of transitions is speculated to be inaccessible in S/nBA block copolymer systems due to their overlap at even modest molecular weights and also their location on the phase diagram relative to the polystyrene glass transition temperature. Finally, we discuss the potential impacts of polydispersity and chain-to-chain monomer sequence variation on gradient copolymer phase segregation.

Mok, Michelle M.; Ellison, Christopher J.; Torkelson, John M. (NWU); (UMM)

2012-11-14

87

Food Chain Game  

NSDL National Science Digital Library

In this outdoor game, learners role play populations linked in a food chain. The resource suggests a chain with plant, grasshopper, frog, and hawk, but other food chains can be role-played, for example plankton, anchovy, salmon, sea lion. The more "animals" (learners!) the merrier for this active game.

Science, Lawrence H.

1979-01-01

88

Measuring supply chain performance  

Microsoft Academic Search

The process of choosing appropriate supply chain performance measures is difficult due to the complexity of these systems. The paper presents an overview and evaluation of the performance measures used in supply chain models and also presents a framework for the selection of performance measurement systems for manufacturing supply chains. Three types of performance measures are identified as necessary components

Benita M. Beamon

1999-01-01

89

Algorithm for Image Retrieval Based on Edge Gradient Orientation Statistical Code  

PubMed Central

Image edge gradient direction not only contains important information of the shape, but also has a simple, lower complexity characteristic. Considering that the edge gradient direction histograms and edge direction autocorrelogram do not have the rotation invariance, we put forward the image retrieval algorithm which is based on edge gradient orientation statistical code (hereinafter referred to as EGOSC) by sharing the application of the statistics method in the edge direction of the chain code in eight neighborhoods to the statistics of the edge gradient direction. Firstly, we construct the n-direction vector and make maximal summation restriction on EGOSC to make sure this algorithm is invariable for rotation effectively. Then, we use Euclidean distance of edge gradient direction entropy to measure shape similarity, so that this method is not sensitive to scaling, color, and illumination change. The experimental results and the algorithm analysis demonstrate that the algorithm can be used for content-based image retrieval and has good retrieval results.

Zeng, Jiexian; Zhao, Yonggang; Li, Weiye

2014-01-01

90

Added stresses because of the presence of FENE-P bead spring chains in a random velocity field  

Microsoft Academic Search

FENE-P bead spring chains unravel in the presence of large enough velocity gradients. In a turbulent flow, this can result in intermittent added stresses and exchanges of energy between the chains and the fluid, whose magnitudes depend on the degree of unravelling and on the orientations of the bead spring chains. These effects are studied by calculating the average behaviour

Heshmat Massah; Thomas J. Hanratty

1997-01-01

91

Arizona's Salt Gradient Solar Pond.  

National Technical Information Service (NTIS)

The research project for designing and constructing a salt gradient solar pond within the State of Arizona was requested by the Arizona Solar Energy Commission during a period when an oil embargo was still a possibility. The project was built at the Gray ...

J. B. Hauskins F. Mancini R. Kolaja

1987-01-01

92

Assessing hue constancy using gradients  

Microsoft Academic Search

The lack of blue hue constancy has been identified as a significant shortcoming of the CIELAB color space. The CIECAM97s, CIELUV, IPT and MLab color spaces have been proposed as alternatives to CIELAB. Color gradients with fixed anchor values were used as stimuli in a visual experiment. This allowed an efficient comparison of the hue constancy of different color spaces.

Nathan Moroney

1999-01-01

93

Assessing hue constancy using gradients  

Microsoft Academic Search

The lack of blue hue constancy has been identified as a significant shortcoming of the CIELAB color space. The CIECAM97s, CIELUV, IPT and MLab color spaces have been proposed as alternatives to CIELAB. Color gradients with fixed anchor values were used as stimuli in a visual experiment. This allowed an efficient comparison of the hue constancy of different color spaces.

Nathan Moroney

2000-01-01

94

HORIZONTAL GRADIENT SIGNATURE OF MOROCCO  

Microsoft Academic Search

The grid of the anomalies of the horizontal gradient of the field of gravity of Morocco represents the varia- tions of the field of gravity ascribable to the side variations of density in the earth's crust and the higher coat, which reflect variations of composition and thickness. The systematic gravimetric cartography in Morocco is very recent and always continues. All

BOUGUER ANOMALY; SAAD BAKKALI; TAOUFIK MOURABIT

95

Texture gradient based watershed segmentation  

Microsoft Academic Search

The watershed transform is a well established tool for the segmentation of images. However, watershed segmentation is often not effective for textured regions that are perceptually homogeneous. Such regions are usually inaccurately over-segmented with no reference to any texture changes. We now introduce a novel concept of “texture gradient” implemented using a non-decimated complex wavelet transform. A novel marker location

P. R. Hill; C. N. Canagarajah; D. R. Bull

2002-01-01

96

HIGH GRADIENT MAGNETIC PARTICULATE COLLECTION  

EPA Science Inventory

This paper describes the initial phases of an evaluation of high gradient magnetic separation (HGMS) as a potential method of fine particle collection from industrial stack gases. HGMS is a relatively new separation technique that has been shown to be capable of removing small, w...

97

The thermodynamics of gradient elastoplasticity  

NASA Astrophysics Data System (ADS)

A thermomechanical framework for the modelling of gradient plasticity is developed within the range of linear strains. Full anisotropy is considered. Special focus is given to the restrictions imposed by the Clausius-Duhem inequality. A rather general example gives a complete anisotropic model and shows its thermodynamic consistency. This is finally particularized for the isotropic case by using isotropic tensor-function representations.

Bertram, Albrecht; Forest, Samuel

2014-05-01

98

Does the Bicoid gradient matter?  

PubMed

The generation and interpretation of positional information are key processes in developmental systems. In this issue, Chen et al. report discoveries made in the Drosophila embryo that give new insights into how positional information can be produced by patterning gradients. PMID:22541424

Roth, Siegfried; Lynch, Jeremy

2012-04-27

99

Improved generalized gradient approximation for positron states in solids  

NASA Astrophysics Data System (ADS)

Several first-principles calculations of positron-annihilation characteristics in solids have added gradient corrections to the local-density approximation within the theory by Arponen and Pajanne [Ann. Phys. (NY) 121, 343 (1979), 10.1016/0003-4916(79)90101-5] since this theory systematically overestimates the annihilation rates. As a further remedy, we propose to use gradient corrections for other local-density approximation schemes based on perturbed hypernetted chain and on quantum Monte Carlo results. Our calculations for various metals and semiconductors show that the proposed schemes generally improve the positron lifetimes when they are confronted with experiment. We also compare the resulting positron affinities in solids with data from slow-positron measurements.

Kuriplach, Jan; Barbiellini, Bernardo

2014-04-01

100

General lattice model of gradient elasticity  

NASA Astrophysics Data System (ADS)

In this paper, new lattice model for the gradient elasticity is suggested. This lattice model gives a microstructural basis for second-order strain-gradient elasticity of continuum that is described by the linear elastic constitutive relation with the negative sign in front of the gradient. Moreover, the suggested lattice model allows us to have a unified description of gradient models with positive and negative signs of the strain gradient terms. Possible generalizations of this model for the high-order gradient elasticity and three-dimensional case are also suggested.

Tarasov, Vasily E.

2014-02-01

101

High gradient directional solidification furnace  

NASA Astrophysics Data System (ADS)

A high gradient directional solidification furnace is disclosed which includes eight thermal zones throughout the length of the furnace. In the hot end of the furnace, furnace elements provide desired temperatures. These elements include Nichrome wire received in a grooved tube which is encapsulated y an outer alumina core. A booster heater is provided in the hot end of the furnace which includes toroidal tungsten/rhenium wire which has a capacity to put heat quickly into the furnace. An adiabatic zone is provided by an insulation barrier to separate the hot end of the furnace from the cold end. The old end of the furnace is defined by additional heating elements. A heat transfer plate provides a means by which heat may be extracted from the furnace and conducted away through liquid cooled jackets. By varying the input of heat via the booster heater and output of heat via the heat transfer plate, a desired thermal gradient profile may be provided.

Aldrich, B. R.; Whitt, W. D.

1985-10-01

102

Gradient elution in microchannel electrochromatography.  

PubMed

There is great interest in using microfluidic channels packed with a stationary phase for chemical separations of complex mixtures. A key advantage of such techniques is the use of electroosmotic flow (EOF), controlled simply by applying electrical potentials between reservoirs. A disadvantage for this technique, however, is a lack of compatibility with gradient elution separations. This limitation arises from the dependence of EOF velocity on run buffer content (including the concentration of organic modifier). Here, we introduce a method for implementing gradient elution in electrochromatography in which multiple run buffers are velocity-matched, such that the elution profile resembles that found in conventional HPLC. This method is driven entirely with EOF, meaning that pumps, valves, and pressure fittings are not required. The method was validated by application to separations of peptide standards and protein digests. These results suggest that microfluidic electrochromatography may be compatible with a wide range of applications that have previously been unexplored. PMID:19438263

Watson, Michael W L; Mudrik, Jared M; Wheeler, Aaron R

2009-05-15

103

High gradient directional solidification furnace  

NASA Technical Reports Server (NTRS)

A high gradient directional solidification furnace is disclosed which includes eight thermal zones throughout the length of the furnace. In the hot end of the furnace, furnace elements provide desired temperatures. These elements include Nichrome wire received in a grooved tube which is encapsulated y an outer alumina core. A booster heater is provided in the hot end of the furnace which includes toroidal tungsten/rhenium wire which has a capacity to put heat quickly into the furnace. An adiabatic zone is provided by an insulation barrier to separate the hot end of the furnace from the cold end. The old end of the furnace is defined by additional heating elements. A heat transfer plate provides a means by which heat may be extracted from the furnace and conducted away through liquid cooled jackets. By varying the input of heat via the booster heater and output of heat via the heat transfer plate, a desired thermal gradient profile may be provided.

Aldrich, B. R.; Whitt, W. D. (inventor)

1985-01-01

104

THE GRADIENT OF VASCULAR PERMEABILITY  

PubMed Central

A mounting gradient of permeability exists along the capillaries of frog muscle. In chicken muscle on the other hand none has been demonstrated; but the close-knit vascularization is arranged in duplicate in such manner that the blood runs in opposite directions through the capillaries of nearly adjacent fibres. In a flight muscle of the pigeon there exists in addition to this artifice what appears to be a special collecting system of venous capillaries. In the mammalian diaphragm indications of such a system are also to be found, and a gradient of capillary permeability like that in the other skeletal muscles is probably present. These vascular conditions are briefly considered in terms of function.

Smith, Frederick; Rous, Peyton

1931-01-01

105

Investigation of internal pressure gradients generated in electrokinetic flows with axial conductivity gradients  

Microsoft Academic Search

Field amplified sample stacking (FASS) is used to increase sample concentrations in electrokinetic flows. The technique uses\\u000a conductivity gradients to establish a non-uniform electric field that accumulates ions within a conductivity gradient, and\\u000a can be readily integrated with capillary electrophoresis. Conductivity gradients also cause gradients in near-wall electroosmotic\\u000a flow velocities. These velocity gradients generate internal pressure gradients that drive secondary,

Shankar Devasenathipathy; Rajiv Bharadwaj; Juan G. Santiago

2007-01-01

106

Analysis of mutations using PCR and denaturing gradient gel electrophoresis  

SciTech Connect

Denaturing gradient gel electrophoresis (DGGE) separates DNA molecules based on primary sequence. Under the appropriate conditions, all base pair (bp) substitutions, frameshifts, and deletions less than about 10 bp can be resolved from the wild type sequence using DGGE. Polymerase chain reaction (PCR) permits facile amplification of a given region of the genome. The authors have combined PCR and DGGE to: (1) localize mutations in the X-linked human androgen receptor gene; (2) analyze thousands of thioguanine-resistant mutants simultaneously; (3) examine the fidelity of several DNA polymerases used in PCR.

Cariello, N.F.; Swenberg, J.A. (Univ. of North Carolina, Chapel Hill (United States) Duke Univ., Durham, NC (United States)); DeBellis, A.; Skopek, T.R. (Univ. of North Carolina, Chapel Hill (United States))

1991-01-01

107

Stellar Population Gradients in WLM  

NASA Astrophysics Data System (ADS)

WLM is one of the most isolated galaxies in the Local Group. From archival HST frames, we look for population gradients using star count ratios from distinct regions of the Color-Magnitude diagram. We find clear evidence for a central concentration of the younger stars. This scenario supports the two-component disk/halo-like structure suggested for dwarf irregular galaxies (Martinez-Delgado, Gallart & Aparicio, 1999).

Noriega-Mendoza, H.; Holtzman, J.

2001-12-01

108

Programming the gradient projection algorithm  

NASA Technical Reports Server (NTRS)

The gradient projection method of numerical optimization which is applied to problems having linear constraints but nonlinear objective functions is described and analyzed. The algorithm is found to be efficient and thorough for small systems, but requires the addition of auxiliary methods and programming for large scale systems with severe nonlinearities. In order to verify the theoretical results a digital computer is used to simulate the algorithm.

Hargrove, A.

1983-01-01

109

Generalized Gradient Approximation Made Simple  

Microsoft Academic Search

Generalized gradient approximations (GGA's) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91

John P. Perdew; Kieron Burke; Matthias Ernzerhof

1996-01-01

110

General probabilistic chain teleportation  

NASA Astrophysics Data System (ADS)

We have investigated different strategies for chain teleportation of a d-level quantum state (qu dit-state) with the non-maximally entangled channels. The total success probabilities of chain teleportation protocols, the separate chain teleportation protocol (SCTP) and the global chain teleportation protocol (GCTP) are calculated. In the SCTP the errors are corrected between every step while in the GCTP the errors are corrected only at the end. The result shows that the GCTP is more efficient than the SCTP. Nevertheless, the error-correction of the GCTP will become more complicated with the increase of the node number. For keeping away from this inconvenience of the GCTP, we have presented an eclectic strategy, the piecewise chain teleportation protocol (PCTP) to balance the efficiency and maneuverability of chain teleportation.

Wang, Meiyu; Yan, Fengli

2011-05-01

111

Bt corn plants and their straw have no apparent impact on soil microbial communities  

Microsoft Academic Search

Polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) and sequences of the 16S and 18S rRNA genes were\\u000a used to access the effects of actively growing Bacillus thuringiensis (Bt) corn Pioneer 34B24 and Nongda 1246*1482, and plant straw (leaves plus stalks) of Bt hybrid Pioneer 34B24 and Nongda 61 on soil bacterial and fungal communities. Two-way indicator species analysis (TWINSPAN®),\\u000a and

Fengxiao Tan; Jianwu Wang; Yuanjiao Feng; Guoliang Chi; Hailan Kong; Huifeng Qiu; Suling Wei

2010-01-01

112

Neuron Chain Tag  

NSDL National Science Digital Library

In this outdoor activity, learners play a game of Tag to discover how neurons attach themselves to each other to form a chain. The game starts with one learner who is "it" and represents the first neuron. When "it" tags another player, the tagger player must hold the hand of "it" and work together to form a long a chain. The game ends when all the players are part of the neuron chain.

Yoshioka, Melissa

2009-01-01

113

Gradient Copolymers Yield Uniquely Broad Glass Transition Temperatures in Comparison with Block Copolymers and Polymer Blends  

NASA Astrophysics Data System (ADS)

Gradient copolymers, which can be made by controlled radical polymerization or ring-opening metathesis polymerization, are distinct from random and block copolymer because of the gradient in comonomer composition along the copolymer backbone. As a result of this gradient along the chain, in the ordered lamellar state gradient copolymers are believed to exhibit a sinusoidal composition profile that is distinct from the ``square-wave'' composition profile observed in ordered lamellar block copolymers. This difference in the manner in which the local composition varies in the ordered state leads to dramatic differences in the glass transition behavior of gradient copolymers and block copolymers and similarly between gradient copolymers and polymer blends. Five gradient copolymer systems have been examined allowing for study of the effects of the enthalpic incompatibility of the comonomer units, the Tg differences among the homopolymers, and hydrogen bonding effects leading to random copolymers exhibiting higher Tgs than those found in block copolymers. We show via differential scanning calorimetry and dynamic mechanical analysis that single, continuous Tg breadths as large as 70-100 K are possible in gradient copolymers.

Kim, Jungki; Mok, Michelle M.; Wong, Christopher L. H.; Sandoval, Robert W.; Torkelson, John M.

2007-03-01

114

Geothermal Gradient MAP of the United States.  

National Technical Information Service (NTIS)

A geothermal gradient map is needed in order to determine the hot dry rock (HDR) geothermal resource of the United States. Based on published and unpublished data (including new measurements) the HDR program will produce updated gradient maps annually, to...

A. Kron G. Heiken

1980-01-01

115

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2010 CFR

...within that estuary. The downstream migration of the salinity gradient can...circulation pattern can cause the upstream migration of the salinity gradient displacing...maximim sedimentation zone. This migration may affect those organisms...

2010-07-01

116

Ion Temperature Gradient Driven Drift Cyclotron Instabilities.  

National Technical Information Service (NTIS)

The role of ion temperature gradient driven drift cyclotron instabilities in both mirror machines and tokamaks is examined. Destabilizing temperature gradient modifications to the drift cyclotron loss cone mode are found to exist even when the loss cone i...

P. J. Catto R. E. Aamodt

1977-01-01

117

Mining Top-K Multidimensional Gradients  

Microsoft Academic Search

Several business applications such as marketing basket analysis, clickstream analysis, fraud detection and churning migration analysis demand gradient data analysis. By employing gradient data analysis one is able to identify trends, outliers and answering \\

Ronnie Alves; Orlando Belo; Joel Ribeiro

2007-01-01

118

Experiments and theory in strain gradient elasticity  

Microsoft Academic Search

Conventional strain-based mechanics theory does not account for contributions from strain gradients. Failure to include strain gradient contributions can lead to underestimates of stresses and size-dependent behaviors in small-scale structures. In this paper, a new set of higher-order metrics is developed to characterize strain gradient behaviors. This set enables the application of the higher-order equilibrium conditions to strain gradient elasticity

D. C. C. Lam; F. Yang; A. C. M. Chong; J. Wang; P. Tong

2003-01-01

119

Gradient elasticity and nonstandard boundary conditions  

Microsoft Academic Search

Gradient elasticity for a second gradient model is addressed within a suitable thermodynamic framework apt to account for nonlocality. The pertinent thermodynamic restrictions upon the gradient constitutive equations are derived, which are shown to include, besides the field (differential) stress–strain laws, a set of nonstandard boundary conditions. Consistently with the latter thermodynamic requirements, a surface layer with membrane stresses is

Castrenze Polizzotto

2003-01-01

120

Structural analysis of gradient elastic components  

Microsoft Academic Search

The present study investigates the size effects in the problems of cantilever beam bending and cracked bar tension within the gradient elasticity framework. Analytical solutions for metrics that characterize both the normalized stiffness and toughness are derived. It is found that the gradient elastic beam exhibits a significantly stiffer but also more brittle response, while the gradient cracked bar exhibits

A. E. Giannakopoulos; K. Stamoulis

2007-01-01

121

Finite element analysis with staggered gradient elasticity  

Microsoft Academic Search

In this article, staggered gradient elasticity formulations are studied. Firstly, the standard equations of classical elasticity are considered. Afterwards, a set of Helmholtz equations associated with the theory of gradient elasticity is solved to handle the gradient dependence. Due to the two-step nature of the algorithms, C0-continuous interpolation functions suffice and finite element discretisations are straightforward and efficient. Different versions

Harm Askes; Irene Morata; Elias C. Aifantis

2008-01-01

122

Polydopamine gradients by oxygen diffusion controlled autoxidation.  

PubMed

We report a simple and facile protocol to fabricate mussel-inspired polydopamine (PDA) gradients on different surfaces. An oxygen diffusion phenomenon was used for dopamine autoxidation to form thickness gradients of PDA on different substrates. These PDA gradients showed gradual changes in thickness, roughness, wettability and light transmittance. PMID:24088788

Yang, Hao-Cheng; Wu, Qing-Yun; Wan, Ling-Shu; Xu, Zhi-Kang

2013-11-18

123

Global supply chain management  

Microsoft Academic Search

The ability of organizations to effectively compete in the global marketplace is contingent on identifying and selecting an adequate number of qualified global managers. Nowhere is the shortage of managerial talent more evident than in the management of global supply chains. The complex and vexing set of problems facing global supply chain managers makes the task of selecting an adequate

Michael G Harvey; R. Glenn Richey

2001-01-01

124

Global Supply Chain Design  

Microsoft Academic Search

I review principles and methods of global supply chain design, especially from two viewpoints, in this paper. The first perspective is focused on the practitioner who is interested in an overview of the key concepts and applications of supply chain design within a global context. The second theme of this paper is to assess opportunities for research to extend supply

Terry P. Harrison

2001-01-01

125

Chain model of electrorheology  

SciTech Connect

We develop a chain model of an electrorheological fluid in steady and oscillatory shear. This model is based on a balance of hydrodynamic and electrostatic forces and focuses on the mechanical stability of chains. With this model we compute the shape and orientation of an unconfined dipolar chain in steady shear as a function of the shear rate and electric field, and show that this leads to the expected shear-thinning viscosity. We then demonstrate that chains confined by electrodes are unstable in some Mason number regimes. The chain model is extended to the case of oscillatory shear by including a kinetic equation for the aggregation and fragmentation of chains. The resultant chain dynamics is found to be strongly nonlinear, as is the rheology. Finally, we consider the effect of local field corrections and long range interactions on the bare dipolar interaction force and derive a self-consistent pair interaction force that demonstrates that the maximum orientation of a chain in shear depends strongly on the dielectric contrast. {copyright} {ital 1996 American Institute of Physics.}

Martin, J.E.; Anderson, R.A. [Research and Exploratory Technology Division, Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States)] [Research and Exploratory Technology Division, Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States)

1996-03-01

126

Coordinated supply chain management  

Microsoft Academic Search

Historically, the three fundamental stages of the supply chain, procurement, production and distribution, have been managed independently, buffered by large inventories. Increasing competitive pressures, and market globalization are forcing firms to develop supply chains that can quickly respond to customer needs. To remain competitive, these firms must reduce operating costs while continuously improving customer service. With recent advances in communications

Douglas J. Thomas; Paul M. Griffin

1996-01-01

127

Supply chain contract evolution  

Microsoft Academic Search

Summary This paper draws together theories from organisational and neo-institutional literatures to address the evolution of supply chain contracts. Using a longitudinal case study of the Norwegian State Railways, we examine how firms move through the stages in an inter-organisational process of supply chain contract evolution and how they can cooperate to ensure efficiency and equity in their contractual relationship.

Tim Coltman; Kathrine Bru; Nidthida Perm-Ajchariyawong; Timothy M. Devinney; Gabriel R. G. Benito

2009-01-01

128

Oxygen Gradients in the Microcirculation  

PubMed Central

Early in the last century August Krogh embarked on a series of seminal studies to understand the connection between tissue metabolism and mechanisms by which the cardiovascular system supplied oxygen to meet those needs. Krogh recognized that oxygen was supplied from blood to the tissues by passive diffusion and that the most likely site for oxygen exchange was the capillary network. Studies of tissue oxygen consumption and diffusion coefficient, coupled with anatomical studies of capillarity in various tissues, led him to formulate a model of oxygen diffusion from a single capillary. Fifty years after the publication of this work, new methods were developed which allowed the direct measurement of oxygen in and around microvessels. These direct measurements have confirmed the predictions by Krogh and have led to extensions of his ideas resulting in our current understanding of oxygenation within the microcirculation. Developments during the last 40 years are reviewed, including studies of oxygen gradients in arterioles, capillaries, venules, microvessel wall and surrounding tissue. These measurements were made possible by the development and use of new methods to investigate oxygen in the microcirculation, so mention is made of oxygen microelectrodes, microspectrophotometry of haemoglobin and phosphorescence quenching microscopy. Our understanding of oxygen transport from the perspective of the microcirculation has gone from a consideration of oxygen gradients in capillaries and tissue to the realization that oxygen has the ability to diffuse from any microvessel to another location under the conditions that there exists a large enough PO2 gradient and that the permeability for oxygen along the intervening pathway is sufficient.

Pittman, Roland N.

2010-01-01

129

Gradient-index contact lens  

NASA Astrophysics Data System (ADS)

A gradient-index (GRIN) contact lens (CL) is proposed to decrease spherical aberration and to increase the diopter. A plastic radial GRIN rod was successfully obtained by using the vapor-phase diffusion copolymerization technique. The resulting index distribution of the GRIN rod was almost parabolic against the distance from the center axis, and the Delta n value was -0.030. The GRIN CL was prepared by grinding and polishing the rod. It is theoretically and experimentally concluded that using the radial GRIN material can significantly improve the optical properties of CL's.

Koike, Yasuhiro; Asakawa, Akihiko; Wu, Shang Pin; Nihei, Eisuke

1995-08-01

130

Generalized Gradient Approximation Made Simple  

SciTech Connect

Generalized gradient approximations (GGA{close_quote}s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. {copyright} {ital 1996 The American Physical Society.}

Perdew, J.P.; Burke, K.; Ernzerhof, M. [Department of Physics and Quantum Theory Group, Tulane University, New Orleans, Louisiana 70118 (United States)] [Department of Physics and Quantum Theory Group, Tulane University, New Orleans, Louisiana 70118 (United States)

1996-10-01

131

Gradient magnetic binary alloy nanowire  

NASA Astrophysics Data System (ADS)

CoNi gradient binary-alloy nanowires are prepared in porous anodic aluminum oxide (AAO) template via electrodeposition. The coercivity and remanence of the nanowires are of high anisotropy due to the axial deposition of the magnetic compositions. The magnetocrystalline anisotropy and crystalline structure of the nanowires show dependence on the treatment of the annealing process that may reduce the anisotropy and improve the squareness. The difference in intensity of the effective anisotropic field with easy magnetization direction along the wire axis is responsible for different variation of the magnetic properties which is dominated by the competition between shape anisotropy and magnetocrystalline anisotropy.

Zeng, Min; Yang, Haozhe; Liu, Jue; Yu, Ronghai

2014-05-01

132

Protein gradient films of fibroin and gelatine.  

PubMed

Gradients are a natural design principle in biological systems that are used to diminish stress concentration where materials of differing mechanical properties connect. An interesting example of a natural gradient material is byssus, which anchors mussels to rocks and other hard substrata. Building upon previous work with synthetic polymers and inspired by byssal threads, protein gradient films are cast using glycerine-plasticized gelatine and fibroin exhibiting a highly reproducible and smooth mechanical gradient, which encompasses a large range of modulus from 160 to 550?MPa. The reproducible production of biocompatible gradient films represents a first step towards medical applications. PMID:23894133

Claussen, Kai U; Lintz, Eileen S; Giesa, Reiner; Schmidt, Hans-Werner; Scheibel, Thomas

2013-10-01

133

Extraordinary strain hardening by gradient structure  

PubMed Central

Gradient structures have evolved over millions of years through natural selection and optimization in many biological systems such as bones and plant stems, where the structures change gradually from the surface to interior. The advantage of gradient structures is their maximization of physical and mechanical performance while minimizing material cost. Here we report that the gradient structure in engineering materials such as metals renders a unique extra strain hardening, which leads to high ductility. The grain-size gradient under uniaxial tension induces a macroscopic strain gradient and converts the applied uniaxial stress to multiaxial stresses due to the evolution of incompatible deformation along the gradient depth. Thereby the accumulation and interaction of dislocations are promoted, resulting in an extra strain hardening and an obvious strain hardening rate up-turn. Such extraordinary strain hardening, which is inherent to gradient structures and does not exist in homogeneous materials, provides a hitherto unknown strategy to develop strong and ductile materials by architecting heterogeneous nanostructures.

Wu, XiaoLei; Jiang, Ping; Chen, Liu; Yuan, Fuping; Zhu, Yuntian T.

2014-01-01

134

Supply chain assessment methodology.  

PubMed

This article describes an assessment methodology based on the supply chain proficiency model that can be used to set realistic supply chain objectives. The assessment centers on a business model that identifies the logical stages of supply chain proficiency as measured against a comprehensive set of business characteristics. For each characteristic, an enterprise evolves from one stage to the next. The magnitude of change inherent in moving forward usually prohibits skipping stages. Although it is possible to be at different stages for each characteristic, it is usually desirable to maintain balance. PMID:11183381

Topor, E

2000-08-01

135

SCIENCE MATTERS KEY CHAIN  

NSDL National Science Digital Library

Brushed nickel key chain commemorating the launch of the new Science Matters initiative. Limited edition. All proceeds from the sale of this item go to fund the John Glenn Center for Science Education.

1900-01-01

136

Heavy Chain Diseases  

MedlinePLUS

... Multimedia Table Index In This Topic Blood Disorders Plasma Cell Disorders Heavy Chain Diseases Back to Top ... Blood Vessels Platelet Disorders White Blood Cell Disorders Plasma Cell Disorders Leukemias Lymphomas Myeloproliferative Disorders Spleen Disorders ...

137

Food Chains and Webs  

NSDL National Science Digital Library

In this activity, learners investigate feeding relationships. Learners complete a food web and then make a mobile to represent a food chain. Use this activity to talk about predator/prey relationships and ecosystems.

Council, Biotechnology A.

2012-06-26

138

Polymerase Chain Reaction  

NSDL National Science Digital Library

This interactive activity adapted from the University of Nebraska's Library of Crop Technologies depicts steps in the polymerase chain reaction (PCR) technique and explains how it is used to efficiently copy sections of DNA for analysis.

Foundation, Wgbh E.

2009-12-07

139

Food Chains: Nature's Restaurant  

NSDL National Science Digital Library

In these life science activities, students will participate in field observations of living things & do research of animals they observe to create a food chain & present it to the class. Students will participate in a food web simulation game.

Schaffran, Jane

140

Wnt Secretion and Gradient Formation  

PubMed Central

Concentration gradients formed by the lipid-modified morphogens of the Wnt family are known for their pivotal roles during embryogenesis and adult tissue homeostasis. Wnt morphogens are also implicated in a variety of human diseases, especially cancer. Therefore, the signaling cascades triggered by Wnts have received considerable attention during recent decades. However, how Wnts are secreted and how concentration gradients are formed remains poorly understood. The use of model organisms such as Drosophila melanogaster has provided important advances in this area. For instance, we have previously shown that the lipid raft-associated reggie/flotillin proteins influence Wnt secretion and spreading in Drosophila. Our work supports the notion that producing cells secrete Wnt molecules in at least two pools: a poorly diffusible one and a reggie/flotillin-dependent highly diffusible pool which allows morphogen spreading over long distances away from its source of production. Here we revise the current views of Wnt secretion and spreading, and propose two models for the role of the reggie/flotillin proteins in these processes: (i) reggies/flotillins regulate the basolateral endocytosis of the poorly diffusible, membrane-bound Wnt pool, which is then sorted and secreted to apical compartments for long-range diffusion, and (ii) lipid rafts organized by reggies/flotillins serve as “dating points” where extracellular Wnt transiently interacts with lipoprotein receptors to allow its capture and further spreading via lipoprotein particles. We further discuss these processes in the context of human breast cancer. A better understanding of these phenomena may be relevant for identification of novel drug targets and therapeutic strategies.

Solis, Gonzalo P.; Luchtenborg, Anne-Marie; Katanaev, Vladimir L.

2013-01-01

141

Ligase Chain Reaction  

Microsoft Academic Search

\\u000a Nucleic acid amplification technologies have greatly facilitated medical diagnostics for genetic and infectious diseases through\\u000a the exquisite sensitivity and specificity associated with these methods. Polymerase chain reaction (PCR) (see\\u000a Chapter 6) ushered in these technologies and was soon accompanied by numerous newly developed amplification techniques, including\\u000a ligase chain reaction (LCR). These nucleic acid amplification techniques result in the exponential increase

Carla Osiowy

142

Green Supply Chain Management  

Microsoft Academic Search

\\u000a In this chapter, we will discuss some of the fundamental aspects of Green Supply Chain Management (GrSCM). First, GrSCM, its\\u000a origins, advantages, barriers, and initiatives will be discussed. Next, we will review green design, green operations, green\\u000a procurement, and GrSCM frameworks. Finally, the role of governments and international organizations in promoting and developing\\u000a green supply chain practices will be analyzed

Ehsan Nikbakhsh

143

AC field induced cell membrane temperature gradients  

NASA Astrophysics Data System (ADS)

While generally inducing minimal heating in many biomedical applications, electric fields may still induce significant temperature gradients, particularly for pulses of short duration and AC (sinusoidal) fields of high frequency, such as microwaves. This paper extends a recent analysis of temperature gradients across a biological cell and membrane for single pulses [(A. L. Garner, et al., J. Appl. Phys. 113, 214701 (2013).] to multiple pulses or AC fields where the time between the two pulses, or the period for AC signals, is shorter than the thermal diffusion time. We calculate profiles of the induced temperature changes and gradients across a biological cell for AC wave of different frequencies and show that the location of the peak temperature and gradient shifts toward the center of the cell during subsequent half-waves. Higher frequency fields induce higher temperature gradients with the temperature gradient shifts toward the center of the cell for subsequent cycles.

Garner, Allen L.; Deminsky, Maxim; Neculaes, V. Bogdan; Potapkin, Boris

2014-03-01

144

Controllable growth of gradient porous structures.  

PubMed

Cocontinuous phase structures of immiscible polymers can be developed under appropriate melt-blending conditions. Because of the presence of interfacial tension, such cocontinuous structures start to coarsen when heated to a temperature higher than the melting/softening temperature of both phases. In this study, a method for controllable growth of gradient porous structures utilizing variable coarsening rates in a gradient temperature field was investigated. The phase structure coarsens at a higher rate in higher temperature regions but at a slower rate in lower temperature regions, resulting in the generation of a gradient phase morphology. Subsequent dissolution of one phase in the binary blend yields a gradient porous structure made of the remaining polymer component. A polystyrene/poly(lactic acid) (PLA) blend was used as a model system. By designing proper thermal boundary conditions and introducing different thermal gradients during annealing, different types of gradient porous structures of PLA were created. PMID:19354280

Yao, Donggang; Zhang, Wei; Zhou, Jack G

2009-05-11

145

Temperature gradient sensor based on CNT composite  

NASA Astrophysics Data System (ADS)

This work describes fabrication and investigation of thin film temperature gradient sensor based on the composite of carbon nano-tubes (CNT) and polymer adhesive. The dependences of the voltage, current and Seebeck coefficient of the sensor upon gradient of temperature were measured. It was observed that with increase of temperature gradient, the voltage and current of the sensor increase while the Seebeck coefficient decreases.

Karimov, Khasan S.; Abid, ?uhammad; Saleem, Muhammad; Akhmedov, Khakim M.; Bashir, Muhammad M.; Shafique, Umar; Ali, Muhammad M.

2014-08-01

146

The Jet Stream and Horizontal Temperature Gradients  

NSDL National Science Digital Library

Dramatic temperature shifts, in which warm, autumn days turn unbearably cold in what seems like minutes, are almost always ushered in by powerful winds. These temperature differences (or temperature gradients) between air masses are what actually causes the wind. This set of interactive graphs, adapted from the University of Wisconsin-Madison, allows users to control the temperature gradient between two air masses and view the effects that changes in the temperature gradient have on wind speed.

147

Stellar population gradients in brightest cluster galaxies  

NASA Astrophysics Data System (ADS)

We present the stellar population and velocity dispersion gradients for a sample of 24 brightest cluster galaxies (BCGs) in the nearby Universe for which we have obtained high quality long-slit spectra at the Gemini telescopes. With the aim of studying the possible connection between the formation of the BCGs and their host clusters, we explore the relations between the stellar population gradients and properties of the host clusters, as well as the possible connections between the stellar population gradients and other properties of the galaxies. We find mean stellar population gradients (negative ?[Z/H]/log r gradient of - 0.285 +/- 0.064; small positive ?log(age)/log r gradient of +0.069 +/- 0.049; and null ?[E/Fe]/log r gradient of -0.008 +/- 0.032), that are consistent with those of normal massive elliptical galaxies. However, we find a trend between metallicity gradients and velocity dispersion (with a negative slope of - 1.616 +/- 0.539), that is not found for the most massive ellipticals. Furthermore, we find trends between the metallicity gradients and K-band luminosities (with a slope of 0.173 +/- 0.081) as well as the distance from the BCG to the X-ray peak of the host cluster (with a slope of - 7.546 +/- 2.752). The latter indicates a possible relation between the formation of the cluster and that of the central galaxy.

Loubser, S. I.; Sánchez-Blázquez, P.

2013-07-01

148

Nanofiber Scaffold Gradients for Interfacial Tissue Engineering  

PubMed Central

We have designed a 2-spinnerette device that can directly electrospin nanofiber scaffolds containing a gradient in composition that can be used to engineer interfacial tissues such as ligament and tendon. Two types of nanofibers are simultaneously electrospun in an overlapping pattern to create a nonwoven mat of nanofibers containing a composition gradient. The approach is an advance over previous methods due to its versatility - gradients can be formed from any materials that can be electrospun. A dye was used to characterize the 2-spinnerette approach and applicability to tissue engineering was demonstrated by fabricating nanofibers with gradients in amorphous calcium phosphate nanoparticles (nACP). Adhesion and proliferation of osteogenic cells (MC3T3-E1 murine pre-osteoblasts) on gradients was enhanced on the regions of the gradients that contained higher nACP content yielding a graded osteoblast response. Since increases in soluble calcium and phosphate ions stimulate osteoblast function, we measured their release and observed significant release from nanofibers containing nACP. The nanofiber-nACP gradients fabricated herein can be applied to generate tissues with osteoblast gradients such as ligaments or tendons. In conclusion, these results introduce a versatile approach for fabricating nanofiber gradients that can have application for engineering graded tissues.

Ramalingam, Murugan; Young, Marian F.; Thomas, Vinoy; Sun, Limin; Chow, Laurence C.; Tison, Christopher K.; Chatterjee, Kaushik; Miles, William C.; Simon, Carl G.

2012-01-01

149

Structured electrodeposition in magnetic gradient fields  

NASA Astrophysics Data System (ADS)

Electrodeposition in superimposed magnetic gradient fields is a new and promising method of structuring metal deposits while avoiding masking techniques. The magnetic properties of the ions involved, their concentrations, the electrochemical deposition parameters, and the amplitude of the applied magnetic gradient field determine the structure generated. This structure can be thicker in regions of high magnetic field gradients. It can also be free-standing or inversely structured. The complex mechanism of structured electrodeposition of metallic layers in superimposed magnetic gradient fields was studied by different experimental methods, by analytical methods and by numerical simulation and will be discussed comprehensively.

Uhlemann, Margitta; Tschulik, Kristina; Gebert, Annett; Mutschke, Gerd; Fröhlich, Jochen; Bund, Andreas; Yang, Xuegeng; Eckert, Kerstin

2013-03-01

150

Effects of Sequence Distribution, Concentration and pH on Gradient and Block Copolymer Micelle Formation in Solution  

NASA Astrophysics Data System (ADS)

Gradient copolymers are a relatively new class of materials with a gradual change in comonomer composition along the copolymer chain length, which have exhibited unique material properties in comparison to random and block copolymers. Here we extend this architecture to amphiphilic systems that form micelles in solvent, as the effect of a nonuniform comonomer sequence distribution is expected to strongly influence critical aggregation phenomena. Utilizing pyrene as a fluorescence probe, we determined that gradient copolymers present an intermediate critical aggregation concentration in comparison to analogous block and random copolymers. The effect of gradient architecture on a pH-sensitive copolymer was also investigated, concluding that gradient sequencing significantly impacts the solubility and critical aggregation pH when compared to block and random copolymers of similar composition, providing further evidence that gradient architectures introduce a powerful means of tuning properties between block and random copolymers.

Marrou, Stephen; Kim, Jungki; Wong, Christopher; Torkelson, John

2011-03-01

151

Chain formation and chain dynamics in a dilute magnetorheological fluid.  

PubMed

Magnetorheological fluids are suspensions of magnetizable particles that reversibly change from liquid to solid when subjected to a magnetic field. A field-induced structure of dipolar chains is responsible for these changes. Our work aimed at understanding chain dynamics and the kinetics of chain formation by using dynamic light scattering. Chain length is determined by measurement of the diffusion coefficient. Chain-length growth shows a Smoluchowski behavior. PMID:18264283

Hagenbüchle, M; Liu, J

1997-10-20

152

Oscillator Chain Model  

NSDL National Science Digital Library

The EJS Oscillator Chain model shows a one-dimensional linear array of coupled harmonic oscillators with fixed ends. This model can be used to study the propagation of waves in a continuous medium and the vibrational modes of a crystalline lattice. The Ejs model shown here contains 31 coupled oscillators equally spaced within the interval [0, 2 pi] with fixed ends. Ejs Oscillator Chain model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_mech_osc_OscillatorChain.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for classical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang

2008-11-06

153

Supply-Chain Optimization Template  

NASA Technical Reports Server (NTRS)

The Supply-Chain Optimization Template (SCOT) is an instructional guide for identifying, evaluating, and optimizing (including re-engineering) aerospace- oriented supply chains. The SCOT was derived from the Supply Chain Council s Supply-Chain Operations Reference (SCC SCOR) Model, which is more generic and more oriented toward achieving a competitive advantage in business.

Quiett, William F.; Sealing, Scott L.

2009-01-01

154

Microinstabilities in weak density gradient tokamak systems  

SciTech Connect

A prominent characteristic of auxiliary-heated tokamak discharges which exhibit improved (''H-mode type'') confinement properties is that their density profiles tend to be much flatter over most of the plasma radius. Depsite this favorable trend, it is emphasized here that, even in the limit of zero density gradient, low-frequency microinstabilities can persist due to the nonzero temperature gradient.

Tang, W.M.; Rewoldt, G.; Chen, L.

1986-04-01

155

CISLUNAR GEOMAGNETIC TAIL GRADIENT IN 1967  

Microsoft Academic Search

In this letter, the geomagnetic tail field gradient during the summers of 1966 and 1967 is examined for secular change. We use data from Ames magnetometers on Explorers 33 and 35. The 1967 data are compared with the earlier published 1966. Explorer 33 results [Mihalo. v et al., 1968]. Secular change of the tail field magnitude gradient is not found

J. D. Mihalov; C. P. Sonett

1968-01-01

156

Density gradients in Galactic planetary nebulae  

Microsoft Academic Search

Certain hydrodynamic models of planetary nebulae (PNe) suggest that their shells possess appreciable radial density gradients. However, the observational evidence for such gradients is far from clear. On the one hand, Taylor et al. claim to find evidence for radio spectral indices 0.6 < alpha < 1.8, a trend which is taken to imply a variation ne ~ r-2 in

J. P. Phillips

2007-01-01

157

Cell migration: sinking in a gradient.  

PubMed

How chemoattractant gradients form and persist in complex tissues is a key question in cell migration. Two studies now show that CXCR7 acts as a sink in the migrating zebrafish lateral line primordium to generate SDF1 gradients. PMID:24405672

Moissoglu, Konstadinos; Majumdar, Ritankar; Parent, Carole A

2014-01-01

158

Gradient algorithms for designing predictive vector quantizers  

Microsoft Academic Search

A predictive vector quantizer (PVQ) is a vector extension of a predictive quantizer. It consists of two parts: a conventional memoryless vector quantizer (VQ) and a vector predictor. Two gradient algorithms for designing a PVQ are developed in this paper: the steepest descent (SD) algorithm and the stochastic gradient (SG) algorithm. Both have the property of improving the quantizer and

PAO-CHI CHANG; ROBERT M. GRAY

1986-01-01

159

Sonic Gradient Index Lens in Water.  

National Technical Information Service (NTIS)

We study the acoustic scattering properties of a phononic crystal designed to behave as a gradient index lens in water, both experimentally and theoretically. The gradient index lens is designed using a square lattice of stainless-steel cylinders based on...

D. Torrent G. J. Orris L. Cai M. Nicholas T. P. Martin

2010-01-01

160

Velocity gradients in a turbulent jet flow  

Microsoft Academic Search

We present a selection of results from experiments on an air turbulent jet flow, which included measurements of all the three velocity components and their nine gradients with the emphasis on the properties of invariant quantities related to velocity gradients (enstrophy, dissipation, enstrophy generation, etc.). This has been achieved by a 21 hot wire probe (5 arrays x 4 wires

E. Kit; A. Tsinober; T. Dracos

1993-01-01

161

Factor-multiple Chains  

NSDL National Science Digital Library

This problem offers opportunities for students to reinforce their understanding of factors and multiples and provides them the chance to justify their solutions. The goal is for the students to create number chains of four whole numbers that can range from 2 to 100 and each consecutive number is a multiple of the previous number. The Teachers' Notes page offers suggestions for implementation, key discussion questions, ideas for extension and support, and a link to a spreadsheet for students to experiment with placing numbers in specific boxes in the chain.

2007-04-01

162

Solitons in Granular Chains  

SciTech Connect

The authors consider a chain of elastic (Hertzian) grains that repel upon contact according to the potential V = a{delta}{sup u}, u > 2, where {delta} is the overlap between the grains. They present numerical and analytical results to show that an impulse initiated at an end of a chain of Hertzian grains in contact eventually propagates as a soliton for all n > 2 and that no solitons are possible for n {le} 2. Unlike continuous, they find that colliding solitons in discrete media initiative multiple weak solitons at the point of crossing.

Manciu, M.; Sen, S.; Hurd, A.J.

1999-04-12

163

Oscillator Chain JS Model  

NSDL National Science Digital Library

The EJS Oscillator Chain model shows a one-dimensional linear array of coupled harmonic oscillators with fixed ends. This model can be used to study the propagation of waves in a continuous medium and the vibrational modes of a crystalline lattice. The Ejs model shown here contains 31 coupled oscillators equally spaced within the interval [0, 2 pi] with fixed ends. The Oscillator Chain JS Model was developed using the Easy Java Simulations (Ejs) version 5. It is distributed as a ready-to-run html page and requires only a browser with JavaScript support.

Christian, Wolfgang

2013-08-25

164

Volcanoes, Plates, and Chains  

NSDL National Science Digital Library

In this lesson students will discover how seamounts in the Axial-Cobb-Eikelberg-Patton chain were formed. They will learn about the processes that form seamounts, describe the movement of tectonic plates in the Gulf of Alaska region and explain the types of volcanic activity that might be associated with these movements, and describe how a combination of hotspot activity and tectonic plate movement could produce the arrangement of seamounts observed in this chain. This hands-on activity uses online data resources and includes: focus questions, learning objectives, teaching time, audio/visual materials needed, background information, learning procedures, evaluations, extensions, as well as resources and student handouts.

165

Density Gradient Stabilization of Electron Temperature Gradient Driven Turbulence in a Spherical Tokamak  

SciTech Connect

In this letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k??s ?10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of two decrease in the plasma effective thermal diffusivity.

Ren, Y; Mazzucato, E; Guttenfelder, W; Bell, R E; Domier, C W; LeBlanc, B P; Lee, K C; Luhmann Jr, N C; Smith, D R

2011-03-21

166

Adhesion and friction properties of polymer brushes on rough surfaces: a gradient approach.  

PubMed

The effect of nanoscale surface roughness on the lubrication properties of a polymer brush in a good solvent has been investigated. Friction and adhesion forces were measured by means of polyethylene colloidal-probe AFM across a 12 nm silica particle gradient before and after the adsorption of a poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) polymer brush. The adsorption and conformation of the polymer chains were studied with multiple transmission and reflection infrared (MTR-IR) spectroscopy. The results show that prior to the adsorption of PLL-g-PEG on the gradient surface, the friction is high at the smooth end of the gradient while it decreases toward the rough end. Moreover, there is a direct correlation between friction and adhesion. Upon adsorption of the brushes, adhesion vanishes. In this case, a higher frictional force between the PEG-coated particle gradient substrate and the polyethylene sphere is observed at the rough end of the gradient in comparison to the smooth end. In spite of the increased adsorbed mass of PLL-g-PEG at the rough end of the gradient, theory and simulations show that the high curvature of the nanoparticles leads to a less swollen PEG brush in comparison to PEG brushes adsorbed on a planar surface, resulting in a lower repulsion, which can explain the observed increase in friction with particle density. PMID:24266663

Ramakrishna, Shivaprakash N; Espinosa-Marzal, Rosa M; Naik, Vikrant V; Nalam, Prathima C; Spencer, Nicholas D

2013-12-10

167

Approximate error conjugation gradient minimization methods  

DOEpatents

In one embodiment, a method includes selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, calculating an approximate error using the subset of rays, and calculating a minimum in a conjugate gradient direction based on the approximate error. In another embodiment, a system includes a processor for executing logic, logic for selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, logic for calculating an approximate error using the subset of rays, and logic for calculating a minimum in a conjugate gradient direction based on the approximate error. In other embodiments, computer program products, methods, and systems are described capable of using approximate error in constrained conjugate gradient minimization problems.

Kallman, Jeffrey S

2013-05-21

168

MRI gradient coils with reduced neural stimulation  

US Patent & Trademark Office Database

A novel approach to the design of gradient coils for MRI is introduced which takes into account from the start the effects of induced E-fields and hence currents in a patient subjected to time dependent magnetic field gradients. The approach has led to conceptually novel designs of gradient coils which comprise distributions of electrodes or tessellae placed around the basic coil structure. When properly energised the electrode arrays are able, in the simplest case, to reduce the maximum E-field experienced by the patient by approximately a factor of three over that experienced with a standard fingerprint or distributed transverse gradient coil, the comparison being done for the same gradient strength, same coil diameter and same ROI.

2009-07-21

169

On the strain gradient bending deformations  

NASA Astrophysics Data System (ADS)

Bending deformations are reviewed in the context of strain gradient linear elasticity, considering the complete set of strain gradient components. It is well understood that conventional bending deformations depend on the collective uniaxial extension of axial fibers resulting in the dependence on the curvature of the neutral geometry of various (linear or surface) structures. Nevertheless, the deformation of each fiber depends not only on the local curvature of the neutral geometry but also on the distance of the fiber from the neutral axis. Hence, the strain gradient tensor of the conventional bending strain should include not only components along the neutral axis but also those on the transverse direction. The problems of bending and buckling, along with geometrically non-linear and post-critical behavior, are reviewed in the context of strain gradient elasticity considering not only conventional bending strain but also the complete components of the strain gradient.

Lazopoulos, Konstantinos A.; Lazopoulos, Anastasios K.

2013-04-01

170

A compartmental model for the bicoid gradient.  

PubMed

The anterior region of the Drosophila embryo is patterned by the concentration gradient of the homeodomain transcription factor bicoid (Bcd). The Bcd gradient was the first identified morphogen gradient and continues to be a subject of intense research at multiple levels, from the mechanisms of RNA localization in the oocyte to the evolution of the Bcd-mediated patterning events in multiple Drosophila species. Critical assessment of the mechanisms of the Bcd gradient formation requires biophysical models of the syncytial embryo. Most of the proposed models rely on reaction-diffusion equations, but their formulation and applicability at high nuclear densities is a nontrivial task. We propose a straightforward alternative in which the syncytial blastoderm is approximated by a periodic arrangement of well-mixed compartments: a single nucleus and an associated cytoplasmic region. We formulate a compartmental model, constrain its parameters by experimental data, and demonstrate that it provides an adequate description of the Bcd gradient dynamics. PMID:20580703

Kavousanakis, Michail E; Kanodia, Jitendra S; Kim, Yoosik; Kevrekidis, Ioannis G; Shvartsman, Stanislav Y

2010-09-01

171

Induced population gradients in galaxy merger remnants  

NASA Technical Reports Server (NTRS)

We use numerical models to investigate the nature of induced population gradients in merger remnants. As noted by White, we find that the population mixing in stellar-dynamical mergers is rather moderate, leading to metallicity gradients in the remnant that are closely tied to gradients in the progenitor galaxies. Furthermore, the resultant metallicity gradients are poorly fitted by power laws, showing significant nonlinearities within an effective radius. If constant metallicity bulges are added to the progenitor disks, the strong relation between final and initial metallicity gradients is diluted, but the final gradients are still not well fitted by power laws. Detailed studies of the shape of the metallicity gradients in elliptical galaxies should help determine the degree to which stellar-dynamical mergers have contributed to the population of present-day ellipticals. We also consider the effects of centrally concentrated starbursts on metallicity gradients. Using simple models for metallicity enhancement, we find that addition of a metal-rich starburst population can reproduce the magnitude and shape of metallicity gradients observed in elliptical galaxies. However, even in such cases the metallicity gradients in the merger remnant should steepen significantly beyond an effective radius. Modelling such merger-induced starbursts with population synthesis techniques, we find that if the starburst is characterized by solar metallicity, it should be detectable as a bluing of the nuclear regions for several Gyr. However, if the starburst is metal-rich, the reddening effects of higher metallicity makes the broad-band signature of the starburst much more difficult to detect.

Mihos, J. Christopher; Hernquist, Lars

1994-01-01

172

A novel method for RNA extraction from Andosols using casein and its application to amoA gene expression study in soil.  

PubMed

The lack of a universal method to extract RNA from soil hinders the progress of studies related to nitrification in soil, which is an important step in the nitrogen cycle. It is particularly difficult to extract RNA from certain types of soils such as Andosols (volcanic ash soils), which is the dominant agricultural soil in Japan, because of RNA adsorption by soil. To obtain RNA from these challenging soils to study the bacteria involved in nitrification, we developed a soil RNA extraction method for gene expression analysis. Autoclaved casein was added to an RNA extraction buffer to recover RNA from soil, and high-quality RNA was successfully extracted from eight types of agricultural soils that were significantly different in their physicochemical characteristics. To detect bacterial ammonia monooxygenase subunit A gene (amoA) transcripts, bacterial genomic DNA and messenger RNA were co-extracted from two different types of Andosols during incubation with ammonium sulfate. Polymerase chain reaction-denaturing gradient gel electrophoresis and reverse transcription polymerase chain reaction-denaturing gradient gel electrophoresis analyses of amoA in soil microcosms revealed that only few amoA, which had the highest similarities to those in Nitrosospira multiformis, were expressed in these soils after treatment with ammonium sulfate, although multiple amoA genes were present in the soil microcosms examined. PMID:22993110

Wang, Yong; Nagaoka, Kazunari; Hayatsu, Masahito; Sakai, Yoriko; Tago, Kanako; Asakawa, Susumu; Fujii, Takeshi

2012-11-01

173

TSP Ejection Chains  

Microsoft Academic Search

We identify ejection chain methods for the traveling salesman problem based on a special reference structure for generating constructions related to alternating paths. Computational tests show that the method performs very effectively, obtaining generally better solutions than improved versions of the Lin-Kernighan method within the same time frame. Our approach, which currently has a simple tabu search guidance component at

Erwin Pesch; Fred Glover

1997-01-01

174

Analysis of Synfire Chains  

Microsoft Academic Search

The biological implications of synfire chain neural networks are explored by studying twoidealized models. In the first a network model is proposed with binary firing neurons and parallelupdating. This model can be solved exactly in the thermodynamic limit using mean field theory.An explicit equation for the capacity is obtained. In the second model the synchrony of thepulse of activity along

M. Herrmann; J. a. Hertz; A. Prügel-bennett

1995-01-01

175

Franchising the supply chain  

Microsoft Academic Search

Many firms have used information technology systems to eliminate or reduce inventory. Supply chain management integrates the supplier, distributor, and customer logistic requirements into a single system. The goal of this paper is to develop a model where a company can utilize an established wholesale or service network and create franchises to reduce operating costs. This model drives the traditional

Mark C. Chiang; Irina Ilovici

2004-01-01

176

The Agile Supply Chain  

Microsoft Academic Search

Turbulent and volatile markets are becoming the norm as life cycles shorten and global economic and competitive forces create additional uncertainty. The risk attached to lengthy and slow-moving logistics “pipelines” has become unsustainable, forcing organizations to look again at how their supply chains are structured and managed. This paper suggests that the key to survival in these changed conditions is

Martin Christopher

2000-01-01

177

Supply chain dynamics  

Microsoft Academic Search

The application of system dynamics models to supply chains is reviewed. The most profitable area for system modelling and design concerns the demand amplification which is frequently observed in the medium-term operation of individual businesses, which behaviour is one manifestation of the Law of Industrial Dynamics. One cause of this amplification is the time delay incurred by both ‘value-added’ and

D. R. TOWILL

1991-01-01

178

Assessment of microbial populations in methyl ethyl ketone degrading biofilters by denaturing gradient gel electrophoresis  

Microsoft Academic Search

Denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction-amplified genes coding for 16S rRNA was used to assess differences in bacterial community structure as a function of spatial location along the height of two biofilters used to treat a model waste gas stream containing methyl ethyl ketone (MEK). One of the laboratory-scale biofilters was operated as a conventional continuous-flow

C. Li; W. M. Moe

2004-01-01

179

Atom Transfer Radical Copolymerization of Gradient Copolymers of HEMA/DMAEMA with Arbitrary Composition Profiles  

NASA Astrophysics Data System (ADS)

Gradient copolymers represent a new class of statistical copolymers where a non-uniform composition profile is controllably introduced along the length of the polymer chain. Gradient copolymers have thermal and mechanical properties that are different from random or block copolymers having the same average composition. Due to synthetic limitations, however, the introduction of arbitrary composition profiles remains challenging. Here, we demonstrate the ability to controllably introduce arbitrary composition profiles along copolymers of 2-hydroxyethyl methacrylate (HEMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) by atom transfer radical copolymerization in a semi-batch reactor. Using gas chromatography to monitor monomer consumption, we have constructed a kinetic model which we use as a basis to synthesize copolymers with linear and parabolic composition profiles. The overall DMAEMA content and molecular weight of these gradient copolymers were determined using nuclear magnetic resonance spectroscopy and size exclusion chromatography, respectively, and both show good agreement with our model's predictions.

Gallow, Keith; Loo, Yueh-Lin

2009-03-01

180

Extraordinary strain hardening by gradient structure.  

PubMed

Gradient structures have evolved over millions of years through natural selection and optimization in many biological systems such as bones and plant stems, where the structures change gradually from the surface to interior. The advantage of gradient structures is their maximization of physical and mechanical performance while minimizing material cost. Here we report that the gradient structure in engineering materials such as metals renders a unique extra strain hardening, which leads to high ductility. The grain-size gradient under uniaxial tension induces a macroscopic strain gradient and converts the applied uniaxial stress to multiaxial stresses due to the evolution of incompatible deformation along the gradient depth. Thereby the accumulation and interaction of dislocations are promoted, resulting in an extra strain hardening and an obvious strain hardening rate up-turn. Such extraordinary strain hardening, which is inherent to gradient structures and does not exist in homogeneous materials, provides a hitherto unknown strategy to develop strong and ductile materials by architecting heterogeneous nanostructures. PMID:24799688

Wu, XiaoLei; Jiang, Ping; Chen, Liu; Yuan, Fuping; Zhu, Yuntian T

2014-05-20

181

BIOMIMETIC GRADIENT HYDROGELS FOR TISSUE ENGINEERING  

PubMed Central

During tissue morphogenesis and homeostasis, cells experience various signals in their environments, including gradients of physical and chemical cues. Spatial and temporal gradients regulate various cell behaviours such as proliferation, migration, and differentiation during development, inflammation, wound healing, and cancer. One of the goals of functional tissue engineering is to create microenvironments that mimic the cellular and tissue complexity found in vivo by incorporating physical, chemical, temporal, and spatial gradients within engineered three-dimensional (3D) scaffolds. Hydrogels are ideal materials for 3D tissue scaffolds that mimic the extracellular matrix (ECM). Various techniques from material science, microscale engineering, and microfluidics are used to synthesise biomimetic hydrogels with encapsulated cells and tailored microenvironments. In particular, a host of methods exist to incorporate micrometer to centimetre scale chemical and physical gradients within hydrogels to mimic the cellular cues found in vivo. In this review, we draw on specific biological examples to motivate hydrogel gradients as tools for studying cell–material interactions. We provide a brief overview of techniques to generate gradient hydrogels and showcase their use to study particular cell behaviours in two-dimensional (2D) and 3D environments. We conclude by summarizing the current and future trends in gradient hydrogels and cell–material interactions in context with the long-term goals of tissue engineering.

Sant, Shilpa; Hancock, Matthew J.; Donnelly, Joseph P.; Iyer, Dharini; Khademhosseini, Ali

2011-01-01

182

Pure phase encode magnetic field gradient monitor  

NASA Astrophysics Data System (ADS)

Numerous methods have been developed to measure MRI gradient waveforms and k-space trajectories. The most promising new strategy appears to be magnetic field monitoring with RF microprobes. Multiple RF microprobes may record the magnetic field evolution associated with a wide variety of imaging pulse sequences. The method involves exciting one or more test samples and measuring the time evolution of magnetization through the FIDs. Two critical problems remain. The gradient waveform duration is limited by the sample T2?, while the k-space maxima are limited by gradient dephasing. The method presented is based on pure phase encode FIDs and solves the above two problems in addition to permitting high strength gradient measurement. A small doped water phantom (1-3 mm droplet, T1, T2, T2? < 100 ?s) within a microprobe is excited by a series of closely spaced broadband RF pulses each followed by FID single point acquisition. Two trial gradient waveforms have been chosen to illustrate the technique, neither of which could be measured by the conventional RF microprobe measurement. The first is an extended duration gradient waveform while the other illustrates the new method's ability to measure gradient waveforms with large net area and/or high amplitude. The new method is a point monitor with simple implementation and low cost hardware requirements.

Han, Hui; MacGregor, Rodney P.; Balcom, Bruce J.

2009-12-01

183

Heat conduction in one-dimensional aperiodic quantum Ising chains  

NASA Astrophysics Data System (ADS)

The heat conductivity of nonperiodic quantum Ising chains whose ends are connected with heat baths at different temperatures are studied numerically by solving the Lindblad master equation. The chains are subjected to a uniform transverse field h, while the exchange coupling Jm between the nearest-neighbor spins takes the two values JA and JB arranged in Fibonacci, generalized Fibonacci, Thue-Morse, and period-doubling sequences. We calculate the energy-density profile and energy current of the resulting nonequilibrium steady states to study the heat-conducting behavior of finite but large systems. Although these nonperiodic quantum Ising chains are integrable, it is clearly found that energy gradients exist in all chains and the energy currents appear to scale as the system size ~N?. By increasing the ratio of couplings, the exponent ? can be modulated from ?>-1 to ?<-1 corresponding to the nontrivial transition from the abnormal heat transport to the heat insulator. The influences of the temperature gradient and the magnetic field to heat conduction have also been discussed.

Li, Wenjuan; Tong, Peiqing

2011-03-01

184

Heat conduction in one-dimensional aperiodic quantum Ising chains.  

PubMed

The heat conductivity of nonperiodic quantum Ising chains whose ends are connected with heat baths at different temperatures are studied numerically by solving the Lindblad master equation. The chains are subjected to a uniform transverse field h, while the exchange coupling J{m} between the nearest-neighbor spins takes the two values J{A} and J{B} arranged in Fibonacci, generalized Fibonacci, Thue-Morse, and period-doubling sequences. We calculate the energy-density profile and energy current of the resulting nonequilibrium steady states to study the heat-conducting behavior of finite but large systems. Although these nonperiodic quantum Ising chains are integrable, it is clearly found that energy gradients exist in all chains and the energy currents appear to scale as the system size ~N{?}. By increasing the ratio of couplings, the exponent ? can be modulated from ? > -1 to ? < -1 corresponding to the nontrivial transition from the abnormal heat transport to the heat insulator. The influences of the temperature gradient and the magnetic field to heat conduction have also been discussed. PMID:21517475

Li, Wenjuan; Tong, Peiqing

2011-03-01

185

CSF gradients for amino acid neurotransmitters.  

PubMed Central

Amino acid concentrations were measured in CSF samples obtained by lumbar puncture in 51 patients, cervical puncture in 16 patients, spinal drains in nine patients, ventricular taps in five patients and from below a spinal block in six patients. There was evidence of a rostrocaudal gradient for GABA and taurine and a reverse gradient for alanine and asparagine. Lumbar CSF glycine concentrations rose with increasing age whilst GABA concentrations fell. Women had significantly lower concentrations of asparagine and glutamine and elevated taurine compared to men. The influence of biological factors and gradients must be taken into account before the interpretation of changes in CSF amino acid concentrations.

Crawford, P M; Lloyd, K G; Chadwick, D W

1988-01-01

186

Microbatch macromolecular crystallization on a thermal gradient  

NASA Astrophysics Data System (ADS)

We can exploit the temperature dependence of protein solubility in a blind search for optimal crystallization conditions by conducting experiments on thermal gradients. A microbatch technique coupled with a specially constructed thermal gradient allows us to conduct polythermal experiments over the range 6-30°C using as little as 7 ?l of solution. The crystallization vessel is a micropipette commonly used in blood testing labs. As many as 150 simultaneous experiments can be conducted on a gradient machined out of a 200×250×25 mm aluminium plate.

Luft, Joseph R.; Rak, Dawn M.; DeTitta, George T.

1999-01-01

187

Colour Gradients in Clusters of Galaxies  

NASA Astrophysics Data System (ADS)

We investigate the environmental effects (interactions/mergers, ram preasure stripping) in clusters of galaxies by means of colour gradients. These effects affect the photometrical properties of clusters, enhancing the fraction of blue galaxies (Butcher-Oemler effect). In this paper we determine the colour gradients frac{d(B-V)}{dR} in 13 clusters of galaxies, with redshifts 0.198 < = z < = 0.81, and investigate their cosmological dependence. The problem of colour evolution of galaxies in clusters, the connexion between the colour gradients and the Butcher-Oemler effect are also discussed.

Suran, M. D.; Popescu, N. A.

188

Inertial dynamics of chains: slack, stress, and convective instabilities  

NASA Astrophysics Data System (ADS)

Inertial chains may be thought of as one-dimensional incompressible/inextensible fluids or solids moving in three dimensions. Incompressibility is enforced by a stress screened by the chain's curvature (slack). The nature of the stress--- tensile or compressive, uniform or spatially varying--- governs the stability of the motion. The most stable motions, characterized by a uniform tensile stress, belong to a wide class that includes travelling waves of curvature and torsion. Convective instabilities exist in the presence of stress gradients; we present a striking example from a tabletop experiment involving a growing arch in a straightening chain. This work adds to a large body of literature on locally arc length preserving dynamics of curves arising in the study of thin objects such as elastic rods, vortex filaments, and oceanic jets.

Hanna, James; Santangelo, Christian

2011-11-01

189

Tractus Fossae Pit Chain  

NASA Technical Reports Server (NTRS)

29 January 2004 This January 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a chain of pits formed in a trough of the Tractus Fossae region near 24.1oN, 103.4oW. The troughs are graben, which are formed by faults cutting rock as the crust is stretched and extended, in this case toward the east and toward the west (right and left). As the rocks broke and moved along the fault lines that create the sharp cliffs on either side of the troughs, some materials between the trough walls collapsed along the fault trend to form the chain of pits. The picture covers an area approximately 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

2004-01-01

190

Cross-contact chain  

NASA Technical Reports Server (NTRS)

A system is provided for use with wafers that include multiple integrated circuits that include two conductive layers in contact at multiple interfaces. Contact chains are formed beside the integrated circuits, each contact chain formed of the same two layers as the circuits, in the form of conductive segments alternating between the upper and lower layers and with the ends of the segments connected in series through interfaces. A current source passes a current through the series-connected segments, by way of a pair of current tabs connected to opposite ends of the series of segments. While the current flows, voltage measurements are taken between each of a plurality of pairs of voltage tabs, the two tabs of each pair connected to opposite ends of an interface that lies along the series-connected segments. A plot of interface conductances on normal probability chart enables prediction of the yield of good integrated circuits from the wafer.

Lieneweg, U. (inventor)

1986-01-01

191

Cross-contact chain  

NASA Technical Reports Server (NTRS)

A system is provided for use with wafers that include multiple integrated circuits that include two conductive layers in contact at multiple interfaces. Contact chains are formed beside the integrated circuits, each contact chain formed of the same two layers as the circuits, in the form of conductive segments alternating between the upper and lower layers and with the ends of the segments connected in series through interfaces. A current source passes a current through the series-connected segments, by way of a pair of current tabs connected to opposite ends of the series of segments. While the current flows, voltage measurements are taken between each of a plurality of pairs of voltage tabs, the two tabs of each pair connected to opposite ends of an interface that lies along the series-connected segments. A plot of interface conductances on a normal probability chart, enables prediction of the yield of good integrated circuits from the wafer.

Lieneweg, Udo (Inventor)

1988-01-01

192

On the interplanetary cosmic ray latitudinal gradient  

NASA Technical Reports Server (NTRS)

Results are presented from measurements, from 1983 to 1990, of the temporal history of the latitudinal and radial gradients of cosmic ray particles with E greater than 70-MeV. The data used include measurements obtained by the Voyager 2 and Pioneer 10 spacecraft near the heliographic equatorial plane, and from Pioneer 11 and Voyager 1 at average latitudes of 16 deg and 30 deg, respectively. Using the data from Pioneer 11 and Voyager 1 at different altitudes, the altitude dependence of the 26-day-average differential cosmic ray latitudinal gradient was deduced. The gradient was found to be a strong function of latitude when the tilt angle approached zero and became essentially independent of latitude for tilt angles above 30 deg. The relationship between the latitudinal and radial gradients was used to estimate the perpendicular diffusion coefficient for E greater than 7-MeV particles.

Lockwood, J. A.; Webber, W. R.

1992-01-01

193

Axon chemotaxis: Nature's most sensitive gradient detector?  

NASA Astrophysics Data System (ADS)

Axonal chemotaxis plays an important role in wiring up the developing and regenerating nervous system, but little is known about the mechanisms by which axons responsd to molecular gradients. We have developed a new assay that allows measurement of the long-term response of axons to gradients of controllable shape in a three-dimensional gel. We show that axons are among the most sensitive chemical gradient detecting devices yet discovered, capable of responding to concentration differences that average less than one molecule across the growth cone, the sensing structure at the tip of the developing axon (Rosoff et al, Nat. Neurosci., 7:678- 682, 2004). We also present a theoretical model of axonal response to gradients in the presence of stochastic receptor binding that quantitatively matches the experimental data.

Urbach, Jeffrey

2005-03-01

194

Compact High Gradient Pulsed Magnetic Quadrupole.  

National Technical Information Service (NTIS)

A design for a high gradient, low inductance pulsed quadrupole magnet is presented. The magnet is a circular current dominated design with a circular iron return yoke. Conductor angles are determined by a method of direct multipole elimination which theor...

D. Shuman A. Faltens Y. Kajiyama M. Kireeff-Covo P. Seidl

2005-01-01

195

Accuracy of Gravity Gradients at Elevations.  

National Technical Information Service (NTIS)

Formulas are derived for the computation of accuracy of the three components of gravity disturbance gradient at elevations as determined from surface anomalies. The earth is replaced by its tangent plane. (Author)

E. Groten

1965-01-01

196

Continuous spray forming of functionally gradient materials  

SciTech Connect

Researchers at Plasma Processes Inc. have produced a Functional Gradient Material (FGM) through advanced vacuum plasma spray processing for high heat flux applications. Outlined in this paper are the manufacturing methods used to develop a four component functional gradient material of copper, tungsten, boron, and boron nitride. The FGM was formed with continuous gradients and integral cooling channels eliminating bondlines and providing direct heat transfer from the high temperature exposed surface to a cooling medium. Metallurgical and x-ray diffraction analyses of the materials formed through innovative VPS (vacuum plasma spray) processing are also presented. Applications for this functional gradient structural material range from fusion reactor plasma facing components to missile nose cones to boilers.

McKechnie, T.N.; Richardson, E.H.

1995-12-01

197

Continuous spray forming of functionally gradient materials.  

National Technical Information Service (NTIS)

Researchers at Plasma Processes Inc. have produced a Functional Gradient Material (FGM) through advanced vacuum plasma spray processing for high heat flux applications. Outlined in this paper are the manufacturing methods used to develop a four component ...

T. N. McKechnie E. H. Richardson

1995-01-01

198

Impurity gradients and high efficiency solar cells  

NASA Technical Reports Server (NTRS)

One potential means of improving the efficiency of solar cells especially after space irradiation is to incorporate built-in fields into the device through the use of impurity doping gradients. A detailed numerical calculation of solar cell performance has been used to study various types of doping gradients. In general, the predicted improvements in performance have been less than previously reported due to various device effects such as, high injection and the dependence of lifetime on doping density.

Fang, C. R.; Hauser, J. R.

1977-01-01

199

Polarized electrons from high-gradient guns  

SciTech Connect

To take advantage of the lower emittance associated with extraction fields >> 10 MV/m, a number of technological hurdles must be overcome before photocathodes appropriate for generating polarized electrons can be utilized in high-gradient guns. Both rf guns and very fast ultra-high gradient ({ge} 1 GV/m) diode guns are anticipated. The known problems--some of which may be more than just technical--are delineated, and the present status of relevant research is reviewed.

Clendenin, J.E.; Mulhollan, G.A.

1998-09-01

200

Pressure Gradient Evolution and Substorm Onset  

NASA Astrophysics Data System (ADS)

Near-Earth current disruption (NECD) and substorm current wedge (SCW) formation are two related key phenomena for substorm onset. They are believed to be in close association with evolution of pressure gradient near the inner edge of plasma sheet. In the past, a few attempts have been made to investigate the pressure gradient in the late growth phase based on one- or two-spacecraft observations (e.g. , Korth et al., 1991; Pu et al., 1992; Shiokawa et al., 1998; Xing et al., 2010, 2011,etc). In this paper, with linearization assumption in the inner-probe region, we use THEMIS three-probe measurements to estimate the pressure gradient near the inner edge of the equatorward and duskward (dawnward) plasma sheet where pressure gradient in the Z-direction is almost vanished. We therefore can roughly get the two-dimensional pressure gradient in the X- and Y-direction simultaneously. Our observations indicate that the pressure gradients in both the X- and Y-direction enhance right after (within one minute) substorm onset. The enhanced pressure gradient in the Y-direction is duskward (dawnward) when the probes are in the duskside (dawnside) of the enhanced earthward flow in the growth phase. The enhanced dawn-dusk pressure gradients can drive downward field-aligned current (FAC) on the dawnside and upward FAC on the duskside, thus make contributions to the NECD and formation of SCW. THEMIS in situ data and all-sky auroral images for two events are presented, followed by a brief discussion.

Zhonghua, Y.; Pu, Z.; Cao, X.; Nishimura, T.; Zhang, H.; Fu, S.; Xie, L.; Guo, R.

2011-12-01

201

Impurity transport in temperature gradient driven turbulence  

NASA Astrophysics Data System (ADS)

In the present paper, the transport of impurities driven by trapped electron (TE) mode turbulence is studied. Non-linear (NL) gyrokinetic simulations using the code GENE are compared with results from quasilinear (QL) gyrokinetic simulations and a computationally efficient fluid model. The main focus is on model comparisons for electron temperature gradient driven turbulence regarding the sign of the convective impurity velocity (pinch) and the impurity density gradient R/LnZ (peaking factor) for zero impurity flux. In particular, the scaling of the impurity peaking factors with impurity charge Z and with driving temperature gradient is investigated and compared with results for the more studied ion temperature gradient (ITG) driven turbulence. The question of helium ash removal in TE mode turbulence is also investigated. In addition, the impurity peaking is compared to the main ion peaking obtained by a self-consistent fluid calculation of the density gradients corresponding to zero particle fluxes. For the scaling of the peaking factor with impurity charge Z, a weak dependence is obtained from NL GENE and fluid simulations. The QL GENE results show a stronger dependence for low Z impurities and overestimates the peaking factor by up to a factor of two in this region. As in the case of ITG dominated turbulence, the peaking factors saturate as Z increases, at a level much below neoclassical predictions. The scaling with Z is, however, weak or reversed as compared to the ITG case. The results indicate that TE mode turbulence is as efficient as ITG turbulence at removing He ash, with DHe/?eff>1.0. The scaling of impurity peaking with the background temperature gradients is found to be weak in the NL GENE and fluid simulations. The QL results are also here found to significantly overestimate the peaking factor for low Z values. For the parameters considered, the background density gradient for zero particle flux is found to be slightly larger than the corresponding impurity zero flux gradient.

Skyman, A.; Nordman, H.; Strand, P.

2012-03-01

202

Recognizing faces defined by texture gradients  

Microsoft Academic Search

Texture gradients can reveal surface orientation in a manner similar to shape from shading, and therefore provide an important\\u000a cue for object recognition. In this study, we tested whether a complex 3-D object, such as a face, can be identified from\\u000a texture gradients alone. The stimuli were laserscanned faces for which the texture element was a fractal-noise pattern mapped\\u000a onto

Chang Hong Liu; Charles A. Collin; Reza Farivar; Avi Chaudhuri

2005-01-01

203

Improved Scalable Hash Chain Traversal  

Microsoft Academic Search

\\u000a Yaron Sella recently proposed a scalable version of Jakobsson’s algorithm to traverse a hash chain of size n. Given the hash chain and a computation limit m (k=m+1 and b=kÖ{n}b=\\\\sqrt[k]{n}), Sella’s algorithm traverses the hash chain using a total of kb memory. We improve the memory usage to k(b-1). Because efficient hash chain traversal algorithms are aimed at devices with

Sung-ryul Kim

2003-01-01

204

Immunoglobulin heavy chain binding protein  

Microsoft Academic Search

Pre-B lymphocytes, and hybridomas derived from them, synthesize immunoglobulin heavy (IgH) chain in the absence of light (L) chain1. In the Abelson virus transformed line 18-81, which is representative of the pre-B cell stage, we observed that at least some of the H-chains are bound to a protein other than L-chain. Here we show that the protein (which we term

Ingrid G. Haas; Matthias Wabl

1983-01-01

205

Advances in Supply Chain Simulation  

Microsoft Academic Search

The lecture aims to provide an insight into modern approaches to simulation-based analysis of supply chains. It gives an overview of using modeling and simulation (M&S) for facing different types of activities in supply chain management. In particular, different issues are considered, starting with new criticality such as: green logistics; supply chain resilience; sustainable logistics; logistics security; logistics safety; logistics

Agostino G. Bruzzone; Yuri Merkuryev

2009-01-01

206

The Supply Chain Management Processes  

Microsoft Academic Search

Increasingly, supply chain management is being recognized as the management of key business processes across the network of organizations that comprise the supply chain. While many have recognized the benefits of a process approach to managing the business and the supply chain, most are vague about what processes are to be considered, what sub-processes and activities are contained in each

Keely L. Croxton; Sebastián J. García-Dastugue; Douglas M. Lambert; Dale S. Rogers

2001-01-01

207

Investigation of internal pressure gradients generated in electrokinetic flows with axial conductivity gradients  

NASA Astrophysics Data System (ADS)

Field amplified sample stacking (FASS) is used to increase sample concentrations in electrokinetic flows. The technique uses conductivity gradients to establish a non-uniform electric field that accumulates ions within a conductivity gradient, and can be readily integrated with capillary electrophoresis. Conductivity gradients also cause gradients in near-wall electroosmotic flow velocities. These velocity gradients generate internal pressure gradients that drive secondary, dispersive flows. This dispersion leads to a significant reduction in the efficiency of sample stacking. This paper presents an experimental investigation of internally generated pressure gradients in FASS using micron-resolution particle image velocimetry (?PIV). We measure velocity fields of particles seeded into an electrokinetic FASS flow field in a glass microchannel with a single buffer-buffer interface. ?PIV allows for the direct quantification of local, instantaneous pressure gradients by analyzing the curvature of velocity profiles. Measurements show internally generated pressure-driven velocities on the order of 1mm/s for a typical applied electric field of 100 V/cm and a conductivity ratio of 10. A one-dimensional (1D) analytical model for the temporal development of the internal pressure gradient generation is proposed which is useful in estimating general trends in flow dynamics.

Devasenathipathy, Shankar; Bharadwaj, Rajiv; Santiago, Juan G.

2007-12-01

208

One Step ATRP Initiator Immobilization on Surfaces Leading to Gradient-Grafted Polymer Brushes.  

PubMed

A method is described that allows potentially any surface to be functionalized covalently with atom transfer radical polymerization (ATRP) initiators derived from ethyl-2-bromoisobutyrl bromide in a single step. In addition, the initiator surface density was variable and tunable such that the thickness of polymer chain grafted from the surface varied greatly on the surfaces providing examples, across the surface of a substrate, of increased chain stretching due to the entropic nature of crowded polymer chains leading toward polymer brushes. An initiator gradient of increasing surface density was deposited by plasma copolymerization of an ATRP initiator (ethyl 2-bromoisobutyrate) and a non-ATRP reactive diluent molecule (ethanol). The deposited plasma polymer retained its chemical ability to surface-initiate polymerization reactions as exemplified by N,N'-dimethyl acrylamide and poly(ethylene glycol) methyl ether methacrylate polymerizations, illustrating linear and bottle-brush-like chains, respectively. A large variation in graft thickness was observed from the low to high chain-density side suggesting that chains were forced to stretch away from the surface interface-a consequence of entropic effects resulting from increased surface crowding. The tert-butyl bromide group of ethyl 2-bromoisobutyrate is a commonly used initiator in ATRP, so a method for covalent linkage to any substrate in a single step desirably simplifies the multistep surface activation procedures currently used. PMID:24783968

Coad, Bryan R; Styan, Katie E; Meagher, Laurence

2014-05-28

209

Swarm SCARF Dedicated Lithospheric Field Inversion chain  

NASA Astrophysics Data System (ADS)

The forthcoming Swarm satellite mission is a constellation of three satellites dedicated to the study of the geomagnetic field. The orbital characteristics of the mission, which includes a pair of satellites flying side by side, has prompted new efforts in data processing and modeling. A consortium of several research institutions has been selected by the European Space Agency (ESA) to provide a number of Level-2 data products which will be made available to the scientific community. Within this framework, specific tools have been tailor-made to better recover the lithospheric magnetic field contribution. These tools take advantage of gradient properties measured by the lower pair of Swarm satellites and rely on a regional modeling scheme designed to better detect signatures of small spatial scales. We report on a processing chain specifically designed for the Swarm mission. Using an End-to-End simulation, we show that the tools developed are operational. The chain generates a model that meets the primary scientific objectives of the Swarm mission. We also discuss refinements that could also be implemented during the Swarm operational phase to further improve lithospheric field models and reach unprecedented spatial resolution.

Thébault, E.; Vigneron, P.; Maus, S.; Chulliat, A.; Sirol, O.; Hulot, G.

2013-11-01

210

Radiology's value chain.  

PubMed

A diagnostic radiology value chain is constructed to define its main components, all of which are vulnerable to change, because digitization has caused disaggregation of the chain. Some components afford opportunities to improve productivity, some add value, while some face outsourcing to lower labor cost and to information technology substitutes, raising commoditization risks. Digital image information, because it can be competitive at smaller economies of scale, allows faster, differential rates of technological innovation of components, initiating a centralization-to-decentralization technology trend. Digitization, having triggered disaggregation of radiology's professional service model, may soon usher in an information business model. This means moving from a mind-set of "reading images" to an orientation of creating and organizing information for greater accuracy, faster speed, and lower cost in medical decision making. Information businesses view value chain investments differently than do small professional services. In the former model, producing a better business product will extend image interpretation beyond a radiologist's personal fund of knowledge to encompass expanding external imaging databases. A follow-on expansion with integration of image and molecular information into a report will offer new value in medical decision making. Improved interpretation plus new integration will enrich and diversify radiology's key service products, the report and consultation. A more robust, information-rich report derived from a "systems" and "computational" radiology approach will be facilitated by a transition from a professional service to an information business. Under health care reform, radiology will transition its emphasis from volume to greater value. Radiology's future brightens with the adoption of a philosophy of offering information rather than "reads" for decision making. Staunchly defending the status quo via turf wars is unlikely to constitute a forward-looking, competitive strategy. PMID:22438447

Enzmann, Dieter R

2012-04-01

211

Musical Markov Chains  

NASA Astrophysics Data System (ADS)

A system for using dice to compose music randomly is known as the musical dice game. The discrete time MIDI models of 804 pieces of classical music written by 29 composers have been encoded into the transition matrices and studied by Markov chains. Contrary to human languages, entropy dominates over redundancy, in the musical dice games based on the compositions of classical music. The maximum complexity is achieved on the blocks consisting of just a few notes (8 notes, for the musical dice games generated over Bach's compositions). First passage times to notes can be used to resolve tonality and feature a composer.

Volchenkov, Dima; Dawin, Jean René

212

Polymer chain dynamics under nanoscopic confinements.  

PubMed

It is shown that the confinement of polymer melts in nanopores leads to chain dynamics dramatically different from bulk behavior. This so-called corset effect occurs both above and below the critical molecular mass and induces the dynamic features predicted for reptation. A spinodal demixing technique was employed for the preparation of linear poly(ethylene oxide) (PEO) confined to nanoscopic strands that are in turn embedded in a quasi-solid and impenetrable methacrylate matrix. Both the molecular weight of the PEO and the mean diameter of the strands were varied to a certain degree. The chain dynamics of the PEO in the molten state was examined with the aid of field-gradient NMR diffusometry (time scale, 10(-2)-10(0) s) and field-cycling NMR relaxometry (time scale, 10(-9)-10(-4) s). The dominating mechanism for translational displacements probed in the nanoscopic strands by either technique is shown to be reptation. On the time scale of spin-lattice relaxation time measurements, the frequency dependence signature of reptation (i.e., T1 approximately nu(3/4)) showed up in all samples. A "tube" diameter of only 0.6 nm was concluded to be effective on this time scale even when the strand diameter was larger than the radius of gyration of the PEO random coils. This corset effect is traced back to the lack of the local fluctuation capacity of the free volume in nanoscopic confinements. The confinement dimension is estimated at which the crossover from confined to bulk chain dynamics is expected. PMID:15833611

Kimmich, Rainer; Fatkullin, Nail; Mattea, Carlos; Fischer, Elmar

2005-02-01

213

Age and metallicity gradients in fossil ellipticals  

NASA Astrophysics Data System (ADS)

Context. Fossil galaxy groups are speculated to be old and highly evolved systems of galaxies that formed early in the universe and had enough time to deplete their L? galaxies through successive mergers of member galaxies, building up one massive central elliptical, but retaining the group X-ray halo. Aims: Considering that fossils are the remnants of mergers in ordinary groups, the merger history of the progenitor group is expected to be imprinted in the fossil central galaxy (FCG). We present for the first time radial gradients of single-stellar population (SSP) ages and metallicites in a sample of FCGs to constrain their formation scenario. We also measure line-strength gradients for the strongest absorption features in these galaxies. Methods: We took deep spectra with the long-slit spectrograph ISIS at the William Herschel Telescope (WHT) for six FCGs. The obtained spectra are fit with Pegase HR SSP models within the full-spectrum fitting package ULySS yielding SSP ages and metallicities of the stellar populations. We measure radial gradients of SSP ages and metallicities along the major axes. Lick indices are measured for the strongest absorption features to determine line-strength gradients and compare with the full-spectrum fitting results. Results: Our sample comprises some of the most massive galaxies in the universe exhibiting an average central velocity dispersion of ?0 = 271 ± 28 km s-1. Metallicity gradients are throughout negative with comparatively flat slopes of ?[Fe/H] = -0.19 ± 0.08 while age gradients are found to be insignificant (?age = 0.00 ± 0.05). All FCGs lie on the fundamental plane, suggesting that they are virialised systems. We find that gradient strengths and central metallicities are similar to those found in cluster ellipticals of similar mass. Conclusions: The comparatively flat metallicity gradients with respect to those predicted by monolithic collapse (?Z = -0.5) suggest that fossils are indeed the result of multiple major mergers. Hence we conclude that fossils are not "failed groups" that formed with a top-heavy luminosity function. The low scatter of gradient slopes suggests a similar merging history for all galaxies in our sample. Figures 3 and 4 are available in electronic form at http://www.aanda.orgReduced spectra are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/553/A99

Eigenthaler, P.; Zeilinger, W. W.

2013-05-01

214

Granular chain between asymmetric boundaries and the quasiequilibrium state  

NASA Astrophysics Data System (ADS)

Some 30 years have passed since we learned that any velocity perturbation develops into a propagating solitary wave in a granular chain, and over a decade has passed since we learned that these solitary waves break and reform upon collision, leaving behind small secondary solitary waves. The production of the latter eventually precipitates the quasiequilibrium state characterized by large energy fluctuations in dissipation-free granular systems. Here we present dynamical simulations on the effects of soft boundaries on solitary wave interaction in granular chains held between fixed walls. We show that at short time scales, a gradient in the distribution of kinetic energy between the boundaries is indeed sustained. At long times, however, such a gradient gets obliterated and there is no measurable difference between the average kinetic energies of the particles adjacent to walls. Our findings suggest that (i) the quasiequilibrium state can effectively erase small gradients of the average kinetic energies of the particles adjacent to walls in a system, (ii) Boltzmann distribution of grain speeds is realized in the system of interest, and (iii) time and space averages yield the same result, thus suggesting that the system is ergodic.

Ávalos, Edgar; Sen, Surajit

2014-05-01

215

Gradient algorithm applied to laboratory quantum control  

SciTech Connect

The exploration of a quantum control landscape, which is the physical observable as a function of the control variables, is fundamental for understanding the ability to perform observable optimization in the laboratory. For high control variable dimensions, trajectory-based methods provide a means for performing such systematic explorations by exploiting the measured gradient of the observable with respect to the control variables. This paper presents a practical, robust, easily implemented statistical method for obtaining the gradient on a general quantum control landscape in the presence of noise. In order to demonstrate the method's utility, the experimentally measured gradient is utilized as input in steepest-ascent trajectories on the landscapes of three model quantum control problems: spectrally filtered and integrated second harmonic generation as well as excitation of atomic rubidium. The gradient algorithm achieves efficiency gains of up to approximately three times that of the standard genetic algorithm and, as such, is a promising tool for meeting quantum control optimization goals as well as landscape analyses. The landscape trajectories directed by the gradient should aid in the continued investigation and understanding of controlled quantum phenomena.

Roslund, Jonathan; Rabitz, Herschel [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)

2009-05-15

216

Shaping a morphogen gradient for positional precision.  

PubMed

Morphogen gradients, which provide positional information to cells in a developing tissue, could in principle adopt any nonuniform profile. To our knowledge, how the profile of a morphogen gradient affects positional precision has not been well studied experimentally. Here, we compare the positional precision provided by the Drosophila morphogenetic protein Bicoid (Bcd) in wild-type (wt) embryos with embryos lacking an interacting cofactor. The Bcd gradient in the latter case exhibits decreased positional precision around mid-embryo compared with its wt counterpart. The domain boundary of Hunchback (Hb), a target activated by Bcd, becomes more variable in mutant embryos. By considering embryo-to-embryo, internal, and measurement fluctuations, we dissect mathematically the relevant sources of fluctuations that contribute to the error in positional information. Using this approach, we show that the defect in Hb boundary positioning in mutant embryos is directly reflective of an altered Bcd gradient profile with increasing flatness toward mid-embryo. Furthermore, we find that noise in the Bcd input signal is dominated by internal fluctuations but, due to time and spatial averaging, the spatial precision of the Hb boundary is primarily affected by embryo-to-embryo variations. Our results demonstrate that the positional information provided by the wt Bcd gradient profile is highly precise and necessary for patterning precision. PMID:20682246

He, Feng; Saunders, Timothy E; Wen, Ying; Cheung, David; Jiao, Renjie; ten Wolde, Pieter Rein; Howard, Martin; Ma, Jun

2010-08-01

217

[Amyloid light chain amyloidosis].  

PubMed

Abstract Primary amyloid light chain (AL) amyloidosis is the most common and most aggressive form of systemic amyloidosis. In AL amyloidosis, the products of free light chains (FLCs) of monoclonal amyloidogenic plasma cells deposit in the heart, kidneys, liver, gastrointestinal tract, autonomic nerve systems, and soft tissues, consequently leading to progressive disability and organ failure. Tissue biopsy (mainly bone marrow and subcutaneous fat aspirate) staining with Congo red to demonstrate amyloid deposits is required for diagnosis. Autologous stem cell transplant is the preferred treatment method; however, only 25% of patients are eligible. Non-transplant candidates can be offered melphalan-dexamethasone or clinical trials of new agents (thalidomide, lenalidomide, and bortezomib), which have been shown to improve survival. N-terminal pro-brain natriuretic peptide (>1800 ng/l), cardiac troponin T (>0.025 ng/ml), and dFLC (>180 mg/l) are known poor prognostic factors. Late diagnosis remains a major obstacle for initiating effective therapy while organ dysfunction is still recoverable. PMID:24998824

Suzuki, Kenshi; Shimizu, Toshiko

2014-07-01

218

Chain and local dynamics of polyisoprene as probed by experiments and computer simulations  

Microsoft Academic Search

The dynamics of designed short polyisoprene (PI) chains in the melt is investigated on a wide temperature window using dielectric relaxation spectroscopy and pulsed field gradient nuclear magnetic resonance (NMR). At high temperatures, molecular dynamics (MD) simulations performed using two different models (an explicit atom model and a united atom one) capture very well the dynamic properties documented experimentally. Structures

M. Doxastakis; D. N. Theodorou; G. Fytas; F. Kremer; R. Faller; F. Müller-Plathe; N. Hadjichristidis

2003-01-01

219

Application of denaturing gradient gel electrophoresis (DGGE) and temperature gradient gel electrophoresis (TGGE) in microbial ecology  

Microsoft Academic Search

Here, the state of the art of the application of denaturing gradient gel electrophoresis (DGGE) and temperature gradient gel electrophoresis (TGGE) in microbial ecology will be presented. Furthermore, the potentials and limitations of these techniques will be discussed, and it will be indicated why their use in ecological studies has become so important.

Gerard Muyzer; Kornelia Smalla

1998-01-01

220

Application of denaturing gradient gel electrophoresis (DGGE) and temperature gradient gel electrophoresis (TGGE) in microbial ecology  

Microsoft Academic Search

Here, the state of the art of the application of denaturing gradient gel electrophoresis (DGGE) and temperature gradient gel electrophoresis (TGGE) in microbial ecology will be presented. Furthermore, the potentials and limitations of these techniques will be discussed, and it will be indicated why their use in ecological studies has become so important. Abbreviations: ARDRA - amplified ribosomal DNA restriction

Gerard Muyzer; Kornelia Smalla

1998-01-01

221

Influence of elastic gradient profiles on dynamically loaded functionally graded materials: cracks along the gradient  

Microsoft Academic Search

The effect of different elastic gradient profiles on the fracture behavior of dynamically loaded functionally graded materials (FGM) having cracks parallel to the elastic gradient is studied numerically. Finite element analyses of FGM and homogeneous beams are used to examine crack tip responses to low velocity, symmetric impact loading on the uncracked edge of the beams. Elastic description of FGMs

C.-E. Rousseau; H. V. Tippur

2001-01-01

222

Variable gradient permanent-magnet quadrupole lenses  

SciTech Connect

Rare earth (RE) permanent-magnet quadrupoles (PMQs) have been used for many applications in particle accelerators. They have the advantage over electromagnets of being lightweight and reliable. One difficulty associated with PMQs is that the quadrupole gradient is not easily adjusted. Over a certain range, the magnetization of RE magnets is a reversible function of temperature. We have developed a scheme to use this property to make variable gradient PMQs. The field gradient changes required for tuning are typically on the order of a few percent. For many RE magnets, this requires temperature changes of a few tens of degrees centigrade and is accomplished by actively heating or cooling the quadrupoles. 8 refs., 7 figs.

O'Shea, P.G.; Zaugg, T.J.; Maggs, R.G.; Schafstall, P.; Dyson, J.E.

1989-01-01

223

Gradient Dynamics for Turbulent Space Plasmas  

NASA Astrophysics Data System (ADS)

The local topology of the streamlines and magnetic lines of the plasma often determines important phenomena occurring in space physics. Since field line local topology may be transparently described through field gradients (Vieillefosse, Physica 125 A, 150, 1984), it is appealing to reformulate plasma dynamics using the gradients of the velocity and magnetic field as dynamical variables. In this work we present an attempt in this direction: the velocity gradient dynamics, well explored in Hydrodynamics, is here extended to the magnetic variables of MHD. Furthermore, the Probability Distribution Functions of the defined quantities are investigated for a real turbulent space plasma: statistical aspects of topological variables are indeed expected to be extremely relevant in the turbulent regime, where a stochastic field scenario is, in practice, taking place.

Materassi, Massimo; Consolini, Giuseppe

2014-05-01

224

Water Potential Gradient in a Tall Sequoiadendron  

PubMed Central

With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about ?0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees.

Tobiessen, Peter; Rundel, Philip W.; Stecker, R. E.

1971-01-01

225

Recovering gradients from sparsely observed functional data  

PubMed Central

The recovery of gradients of sparsely observed functional data is a challenging ill-posed inverse problem. Given observations of smooth curves (e.g., growth curves) at isolated time points, the aim is to provide estimates of the underlying gradients (or growth velocities). To address this problem, we develop a Bayesian inversion approach that models the gradient in the gaps between the observation times by a tied-down Brownian motion, conditionally on its values at the observation times. The posterior mean and covariance kernel of the growth velocities are then found to have explicit and computationally tractable representations in terms of quadratic splines. The hyperparameters in the prior are specified via nonparametric empirical Bayes, with the prior precision matrix at the observation times estimated by constrained ?1 minimization. The infinitessimal variance of the Brownian motion prior is selected by cross-validation. The approach is illustrated using both simulated and real data examples.

Loez-Pintado, Sara; McKeague, Ian W.

2013-01-01

226

Relativistic klystrons for high-gradient accelerators  

SciTech Connect

Experimental work is being performed by collaborators at LLNL, SLAC, and LBL to investigate relativistic klystrons as a possible rf power source for future high-gradient accelerators. We have learned how to overcome or previously reported problem of high power rf pulse shortening and have achieved peak rf power levels of 330 MW using an 11.4-GHz high-gain tube with multiple output structures. In these experiments the rf pulse is of the same duration as the beam current pulse. In addition, experiments have been performed on two short sections of a high-gradient accelerator using the rf power from a relativistic klystron. An average accelerating gradient of 84 MV/m has been achieved with 80-MW of rf power.

Westenskow, G.A.; Aalberts, D.P.; Boyd, J.K.; Deis, G.A.; Houck, T.L.; Orzechowski, T.J.; Ryne, R.D.; Yu, S.S. (Lawrence Livermore National Lab., CA (USA)); Allen, M.A.; Callin, R.S.; Deruyter, H.; Eppley, K.R.; Fant, K.S.; Fowkes, W.R.; Hoag, H.A.; Koontz, R.F.; Lavine, T.L.; Loew, G.A.; Miller, R.H.; Ruth, R.D.; Vlieks, A.E.; Wang, J.W. (Stanford Linear Accelerator Center, Menlo Park, CA (USA)); Haimson, J.; Mecklen

1990-09-05

227

Ceramic transactions: Functionally gradient materials. Volume 34  

SciTech Connect

A functionally gradient material (FGM) is a composite that smoothly transitions from one material at one surface to another material at the opposite surface. Metals and ceramics are usually the materials that are combined in a controlled manner to optimize a specific property. The First International Symposium on Functionally Gradient Materials was held in Sendai, Japan, in August 1990. Contained in the present volume are the Proceedings of the Second International Symposium on Functionally Gradient Materials, presented at the Third International Ceramic Science and Technology Congress, held in San Francisco, CA, November 1-4, 1992. The papers presented here are divided into eight sections: the concept of FGM; mathematical modeling; methods of fabrication; material evaluation; applications; joining processes in FGM; process characterization; and design considerations. Separate abstracts are provided for each of the 54 papers.

Holt, J.B.; Koizumi, Mitsue; Hirai, Toshio; Munir, Z.A. (eds.)

1993-01-01

228

Shadowgraph Study of Gradient Driven Fluctuations  

NASA Technical Reports Server (NTRS)

A fluid or fluid mixture, subjected to a vertical temperature and/or concentration gradient in a gravitational field, exhibits greatly enhanced light scattering at small angles. This effect is caused by coupling between the vertical velocity fluctuations due to thermal energy and the vertically varying refractive index. Physically, small upward or downward moving regions will be displaced into fluid having a refractive index different from that of the moving region, thus giving rise to the enhanced scattering. The scattered intensity is predicted to vary with scattering wave vector q, as q(sup -4), for sufficiently large q, but the divergence is quenched by gravity at small q. In the absence of gravity, the long wavelength fluctuations responsible for the enhanced scattering are predicted to grow until limited by the sample dimensions. It is thus of interest to measure the mean-squared amplitude of such fluctuations in the microgravity environment for comparison with existing theory and ground based measurements. The relevant wave vectors are extremely small, making traditional low-angle light scattering difficult or impossible because of stray elastically scattered light generated by optical surfaces. An alternative technique is offered by the shadowgraph method, which is normally used to visualize fluid flows, but which can also serve as a quantitative tool to measure fluctuations. A somewhat novel shadowgraph apparatus and the necessary data analysis methods will be described. The apparatus uses a spatially coherent, but temporally incoherent, light source consisting of a super-luminescent diode coupled to a single-mode optical fiber in order to achieve extremely high spatial resolution, while avoiding effects caused by interference of light reflected from the various optical surfaces that are present when using laser sources. Results obtained for a critical mixture of aniline and cyclohexane subjected to a vertical temperature gradient will be presented. The sample was confined between two horizontal parallel sapphire plates with a vertical spacing of 1 mm. The temperatures of the sapphire plates were controlled by independent circulating water loops that used Peltier devices to add or remove heat from the room air as required. For a mixture with a temperature gradient, two effects are involved in generating the vertical refractive index gradient, namely thermal expansion and the Soret effect, which generates a concentration gradient in response to the applied temperature gradient. For the aniline/cyclohexane system, the denser component (aniline) migrates toward the colder surface. Consequently, when heating from above, both effects result in the sample density decreasing with altitude and are stabilizing in the sense that no convective motion occurs regardless of the magnitude of the applied temperature gradient. The Soret effect is strong near a binary liquid critical point, and thus the dominant effect is due to the induced concentration gradient. The results clearly show the divergence at low q and the predicted gravitational quenching. Results obtained for different applied temperature gradients at varying temperature differences from the critical temperature, clearly demonstrate the predicted divergence of the thermal diffusion ratio. Thus, the more closely the critical point is approached, the smaller becomes the temperature gradient required to generate the same signal. Two different methods have been used to generate pure concentration gradients. In the first, a sample cell was filled with a single fluid, ethylene glycol, and a denser miscible fluid, water, was added from below thus establishing a sharp interface to begin the experiment. As time went on the two fluids diffused into each other, and large amplitude fluctuations were clearly observed at low q. The effects of gravitational quenching were also evident. In the second method, the aniline/cyclohexane sample was used, and after applying a vertical temperature gradient for several hours, the top and bottom temperatures were set equal and the thermal

Cannell, David; Nikolaenko, Gennady; Giglio, Marzio; Vailati, Alberto; Croccolo, Fabrizio; Meyer, William

2002-01-01

229

Doping of Semiconducting Atomic Chains  

NASA Technical Reports Server (NTRS)

Due to the rapid progress in atom manipulation technology, atomic chain electronics would not be a dream, where foreign atoms are placed on a substrate to form a chain, and its electronic properties are designed by controlling the lattice constant d. It has been shown theoretically that a Si atomic chain is metallic regardless of d and that a Mg atomic chain is semiconducting or insulating with a band gap modified with d. For electronic applications, it is essential to establish a method to dope a semiconducting chain, which is to control the Fermi energy position without altering the original band structure. If we replace some of the chain atoms with dopant atoms randomly, the electrons will see random potential along the chain and will be localized strongly in space (Anderson localization). However, if we replace periodically, although the electrons can spread over the chain, there will generally appear new bands and band gaps reflecting the new periodicity of dopant atoms. This will change the original band structure significantly. In order to overcome this dilemma, we may place a dopant atom beside the chain at every N lattice periods (N > 1). Because of the periodic arrangement of dopant atoms, we can avoid the unwanted Anderson localization. Moreover, since the dopant atoms do not constitute the chain, the overlap interaction between them is minimized, and the band structure modification can be made smallest. Some tight-binding results will be discussed to demonstrate the present idea.

Toshishige, Yamada; Kutler, Paul (Technical Monitor)

1997-01-01

230

METALLICITY GRADIENTS OF THICK DISK DWARF STARS  

SciTech Connect

We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 {+-} 0.010 (-0.125 {+-} 0.008) dex kpc{sup -1} using an isochrone (photometric) distance determination in the range 1 kpc <|Z| < 3 kpc, which is the vertical height range most consistent with the thick disk of our Galaxy. In the radial direction, we find metallicity gradients between +0.02 and +0.03 dex kpc{sup -1} for bins in the vertical direction between 1 kpc <|Z| < 3 kpc. Both of these results agree with similar values determined from other populations of stars, but this is the first time a radial metallicity gradient for the thick disk has been found at these vertical heights. We are also able to separate thin and thick disk stars based on kinematic and spatial probabilities in the vertical height range where there is significant overlap of these two populations. This should aid further studies of the metallicity gradients of the disk for vertical heights lower than those studied here but above the solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.

Carrell, Kenneth; Chen Yuqin; Zhao Gang, E-mail: carrell@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2012-12-01

231

GOCE Gravity Gradients in an Orbital Aspect  

NASA Astrophysics Data System (ADS)

This work includes a study of the possibility of the Gravity Field and Steady-State Ocean Circulation Explorer Mission (GOCE) satellite orbit improvement using gravity gradient observations. The orbit improvement is performed by a dedicated software package, called Orbital Computation System (OCS), which is based on the classical least squares method. In an iterative process, the corrections to the initial state vector components of the satellite are estimated, using dynamical models describing gravitational perturbations. An important component implemented in the OCS package is the Cowell 8th order numerical integration procedure, which directly generates the satellite orbit. Taking into account the GOCE real and simulated gravity gradients, different variants of solution of the orbit improvement process were obtained. The improved orbits were compared to the GOCE reference orbits (Precise Science Orbits of the GOCE satellite delivered by the European Space Agency) using the root mean squares (RMS) of the differences between the satellite positions on the improved orbits and on the reference ones. The comparison between the improved orbits and the reference ones was performed with respect to the inertial reference frame (IRF) at J2000.0 epoch. RMS values for the solutions based on the real gravity gradients measurements are at a level of hundreds of kilometers and more. This means that the orbit improvement using the real gravity gradients is ineffective. However, all solutions using the simulated gravity gradients, have RMS values below the threshold determined by RMS values for the computed orbits (without the improvement). The most promising results have been achieved here in the case of improving of short orbital arcs with the lengths from a few to tens of minutes. For these short arcs, RMS values reach the level of centimeters, which is close to the accuracy of Precise Science Orbit of GOCE satellite. Additional research have provided requirements for the effective orbit improvement in terms of the accuracy and spectral content of measured gravity gradients.

Bobojc, Andrzej; Drozyner, Andrzej

2014-05-01

232

Stereo transparency and the disparity gradient limit  

NASA Technical Reports Server (NTRS)

Several studies (Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient >1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6' and the other with uncrossed disparity of 6', vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent-disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai-Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.

McKee, Suzanne P.; Verghese, Preeti

2002-01-01

233

High pressure liquid chromatographic gradient mixer  

DOEpatents

A gradient mixer which effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum "band-broadening".

Daughton, Christian G. (San Pablo, CA); Sakaji, Richard H. (El Cerrito, CA)

1985-01-01

234

High-pressure liquid chromatographic gradient mixer  

DOEpatents

A gradient mixer effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum band-broadening.

Daughton, C.G.; Sakaji, R.H.

1982-09-08

235

Short wavelength ion temperature gradient turbulence  

SciTech Connect

The ion temperature gradient (ITG) mode in the high wavenumber regime (k{sub y}{rho}{sub s}>1), referred to as short wavelength ion temperature gradient mode (SWITG) is studied using the nonlinear gyrokinetic electromagnetic code GENE. It is shown that, although the SWITG mode may be linearly more unstable than the standard long wavelength (k{sub y}{rho}{sub s}<1) ITG mode, nonlinearly its contribution to the total thermal ion heat transport is found to be low. We interpret this as resulting from an increased zonal flow shearing effect on the SWITG mode suppression.

Chowdhury, J.; Ganesh, R. [Institute for Plasma Research, Bhat, Gandhinagar (India); Brunner, S.; Lapillonne, X.; Villard, L. [CRPP, Association EURATOM-Confederation Suisse, EPFL, 1015 Lausanne (Switzerland); Jenko, F. [Max-Planck-Institut fuer Plasmaphysik Boltzmannstr. 2, D-85748 Garching (Germany)

2012-10-15

236

Surface-Bound Soft Matter Gradients  

SciTech Connect

This feature article describes the progress realized over the past half century in the field of surface-bound gradient structures created on or from soft materials (oligomers and/or polymers), or those enabling the study of the behavior of soft materials. By highlighting our work in the field and accounting for the contribution of other groups, we emphasize the exceptional versatility of gradient assemblies in facilitating fast screening of physicochemical phenomena, acting as 'recording media' for monitoring a process, and playing a key role in the design and fabrication of surface-bound molecular and macromolecular motors capable of directing a transport phenomenon.

Genzer,J.; Bhat, R.

2008-01-01

237

Critique of the vertical gradient of gravity  

NASA Technical Reports Server (NTRS)

Growing interest in high precision studies of the Earth's gravitational field warrant a critical review of precision requirements to yield useful results. Several problems are now under consideration. All of these problems involve, more or less, the precise value of the vertical gradients of gravity. The principle conclusion from this review is that the essential absence of Free Air Vertical Gravity Gradient control and actual values of gravimeter calibrations require serious attention. Large errors in high topography on official published gravity maps also cannot be ignored.

Hammer, Sigmund

1989-01-01

238

Gradient elution for micellar electrokinetic capillary chromatography  

SciTech Connect

A method for performing gradient elution in micellar electrokinetic capillary chromatography is developed. The influence of temperature and mobile phase organic solvent concentration on capacity factors is presented and attributed to changes in phase ratio and solute distribution coefficient. Solvent programming is more effective than temperature programming at adjusting retention due to its greater influence on distribution coefficient. As anticipated, phase ratio changes could not be exploited due to concomitant losses in column efficiency. A stepwise solvent gradient involving increasing concentrations of 2-propanol and Triton-X-100 is used for the separation of a test mixture of derivatized amines.

Balchunas, A.T.; Sepaniak, M.J.

1988-04-01

239

Design of spherical symmetric gradient index lenses  

NASA Astrophysics Data System (ADS)

Spherical symmetric refractive index distributions also known as Gradient Index lenses such as the Maxwell-Fish-Eye (MFE), the Luneburg or the Eaton lenses have always played an important role in Optics. The recent development of the technique called Transformation Optics has renewed the interest in these gradient index lenses. For instance, Perfect Imaging within the Wave Optics framework has recently been proved using the MFE distribution. We review here the design problem of these lenses, classify them in two groups (Luneburg moveable-limits and fixed-limits type), and establish a new design techniques for each type of problem.

Miñano, Juan C.; Grabovi?ki?, Dejan; Benítez, Pablo; González, Juan C.; Santamaría, Asunción

2012-10-01

240

Reduced acoustic cloaks based on temperature gradients  

NASA Astrophysics Data System (ADS)

This letter presents the design of a reduced acoustic cloak that uses a temperature gradient in order to obtain sound speeds larger than in air. The cloak consists of a circular acoustic crystal made of ten concentric layers of rigid cylinders whose surfaces are heated or cooled in order to get the temperature gradient needed for cloaking behavior. The total pressure field produced by the scattering of sound waves impinging this complex structure is computed and it is shown how acoustic waves are bent in a way similar to that predicted for perfect cloaking devices.

García-Chocano, Victor M.; Torrent, Daniel; Sánchez-Dehesa, José

2012-08-01

241

Critical gradient response of the Weiland model  

NASA Astrophysics Data System (ADS)

The success the Weiland model has had in reproducing modulation experiments prompted this in-depth investigation into its behaviour as a critical gradient model (CGM). The critical gradient properties of the Weiland model is examined analytically and numerically and compared with the empirical CGM commonly used in experiment. A simplified Weiland CGM is derived in which the height-above-threshold dependence is not necessarily linear. Simultaneously, the validity of the empirical CGM was examined. It is shown that an effective threshold, which is higher than the instability threshold, can be obtained if pinches influence the diffusivity.

Asp, E.; Weiland, J.; Garbet, X.; Parail, V.; Strand, P.; JET EFDA contributors, the

2007-08-01

242

Relativistic klystron research for high gradient accelerators  

SciTech Connect

Relativistic klystrons are being developed as a power source for high gradient accelerator applications which include large linear electron--positron colliders, compact accelerators, and FEL sources. We have attained 200MW peak power at 11.4 GHz from a relativistic klystron, and 140 MV/m longitudinal gradient in a short 11.4 GHz accelerator section. We report here on the design of our first klystrons, the results of our experiments so far, and some of our plans for the near future. 5 refs., 7 figs.

Allen, M.A.; Callin, R.S.; Deruyter, H.; Eppley, K.R.; Fowkes, W.R.; Herrmannsfeldt, W.B.; Higo, T.; Hoag, H.A.; Lavine, T.L.; Lee, T.G.

1988-06-01

243

Short wavelength ion temperature gradient turbulence  

NASA Astrophysics Data System (ADS)

The ion temperature gradient (ITG) mode in the high wavenumber regime (ky?s>1), referred to as short wavelength ion temperature gradient mode (SWITG) is studied using the nonlinear gyrokinetic electromagnetic code GENE. It is shown that, although the SWITG mode may be linearly more unstable than the standard long wavelength (ky?s<1) ITG mode, nonlinearly its contribution to the total thermal ion heat transport is found to be low. We interpret this as resulting from an increased zonal flow shearing effect on the SWITG mode suppression.

Chowdhury, J.; Brunner, S.; Ganesh, R.; Lapillonne, X.; Villard, L.; Jenko, F.

2012-10-01

244

17 GHz High Gradient Accelerator Research  

SciTech Connect

This is a report on the MIT High Gradient Accelerator Research program which has included: Operation of the 17 GHz, 25 MeV MIT/Haimson Research Corp. electron accelerator at MIT, the highest frequency, stand-alone accelerator in the world; collaboration with members of the US High Gradient Collaboration, including the design and test of novel structures at SLAC at 11.4 GHz; the design, construction and testing of photonic bandgap structures, including metallic and dielectric structures; the investigation of the wakefields in novel structures; and the training of the next generation of graduate students and postdoctoral associates in accelerator physics.

Temkin, Richard J. [MIT] [MIT; Shapiro, Michael A. [MIT] [MIT

2013-07-10

245

Airfoil optimization with efficient gradient calculations  

NASA Technical Reports Server (NTRS)

The viscous airfoil design analysis code XFOIL was extended to allow optimization using conformal mapping coefficients as design variables. The optimization technique used was the Steepest Descent method applied to a Penalty Function. The gradients of the aerodynamic variables with respect to the design variables were cheaply calculated as by-products of XFOIL's integral boundary layer Newton solver. The speed of the optimization process further increased by updating the Newton system boundary layer variables after each optimization step using the available gradient information. Two examples are presented.

Sorensen, Thomas

1991-01-01

246

On some applications of gradient elasticity to composite materials  

Microsoft Academic Search

Some applications of the gradient theory of elasticity to composite materials are discussed. A brief introduction to gradient theory is given and some mathematical aspects are provided. Of particular importance is a constitutive equation of a higher-order strain gradient theory, and a particular form of gradient theory for which the Ru–Aifantis theorem holds. Applications include a fiber pullout from a

L. Teneketzis Tenek; E. C. Aifantis

2001-01-01

247

Design, engineering, and manufacturing aspects of gradient index optical components  

Microsoft Academic Search

The fifth order aberration coefficients for gradient index lenses derived using Lagrangian methods are discussed. The aberrations of lenses containing spherical gradients are considered. The radius of curvature of the gradient is demonstrated to be an extra degree of freedom. The fabrication process of gradient materials is studied and models are devised for describing the refractive index, spectral, and mechanical

S. D. Fantone

1979-01-01

248

Stability and Nuclear Dynamics of the Bicoid Morphogen Gradient  

Microsoft Academic Search

SUMMARY Patterning in multicellular organisms results from spatial gradients in morphogen concen- tration, but the dynamics of these gradients remain largely unexplored. We characterize, through in vivo optical imaging, the develop- ment and stability of the Bicoid morphogen gradient in Drosophila embryos that express a Bicoid-eGFP fusion protein. The gradient is established rapidly (? 1 hr after fertilization), with nuclear

Thomas Gregor; Eric F. Wieschaus; Alistair P. McGregor; William Bialek; David W. Tank

2007-01-01

249

Polymerase chain reaction  

SciTech Connect

This paper discusses the polymerase chain reaction (PCR) an in-vitro method of amplifying DNA sequences. Beginning with DNA of any origin- bacterial, viral, plant, or animal- PCR can increase the amount of a DNA sequence hundreds of millions to billions of times. The procedure can amplify a targeted sequence even when it makes up less than one part in a million of the total initial sample. PCR is an enzymatic process that is carried out in discrete cycles of amplification, each of which can double the amount of target DNA in the sample. Thus, n cycles can produce 2{sup n} times as much target as was present to begin with. This paper discusses how PCR has had an impact on molecular biology, human genetics, infectious and genetic disease diagnosis, forensic science, and evolutionary biology.

Arnhelm, N. (Univ. of Southern California, CA (US)); Levenson, C.H. (Cetus Corp. (US))

1990-10-01

250

NNSA TRITIUM SUPPLY CHAIN  

SciTech Connect

Savannah River Site plays a critical role in the Tritium Production Supply Chain for the National Nuclear Security Administration (NNSA). The entire process includes: • Production of Tritium Producing Burnable Absorber Rods (TPBARs) at the Westinghouse WesDyne Nuclear Fuels Plant in Columbia, South Carolina • Production of unobligated Low Enriched Uranium (LEU) at the United States Enrichment Corporation (USEC) in Portsmouth, Ohio • Irradiation of TPBARs with the LEU at the Tennessee Valley Authority (TVA) Watts Bar Reactor • Extraction of tritium from the irradiated TPBARs at the Tritium Extraction Facility (TEF) at Savannah River Site • Processing the tritium at the Savannah River Site, which includes removal of nonhydrogen species and separation of the hydrogen isotopes of protium, deuterium and tritium.

Wyrick, Steven [Savannah River National Laboratory, Aiken, SC, USA; Cordaro, Joseph [Savannah River National Laboratory, Aiken, SC, USA; Founds, Nanette [National Nuclear Security Administration, Albuquerque, NM, USA; Chambellan, Curtis [National Nuclear Security Administration, Albuquerque, NM, USA

2013-08-21

251

Translocation of a Polymer Chain across a Nanopore: A Brownian Dynamics Simulation Study  

NASA Technical Reports Server (NTRS)

We carried out Brownian dynamics simulation studies of the translocation of single polymer chains across a nanosized pore under the driving of an applied field (chemical potential gradient). The translocation process can be either dominated by the entropic barrier resulted from restricted motion of flexible polymer chains or by applied forces (or chemical gradient across the wall), we focused on the latter case in our studies. Calculation of radius of gyrations at the two opposite sides of the wall shows that the polymer chains are not in equilibrium during the translocation process. Despite this fact, our results show that the one-dimensional diffusion and the nucleation model provide an excellent description of the dependence of average translocation time on the chemical potential gradients, the polymer chain length and the solvent viscosity. In good agreement with experimental results and theoretical predictions, the translocation time distribution of our simple model shows strong non-Gaussian characteristics. It is observed that even for this simple tubelike pore geometry, more than one peak of translocation time distribution can be generated for proper pore diameter and applied field strengths. Both repulsive Weeks-Chandler-Anderson and attractive Lennard-Jones polymer-nanopore interaction were studied, attraction facilitates the translocation process by shortening the total translocation time and dramatically improve the capturing of polymer chain. The width of the translocation time distribution was found to decrease with increasing temperature, increasing field strength, and decreasing pore diameter.

Tian, Pu; Smith, Grant D.

2003-01-01

252

A novel aerobic respiratory chain-linked NADH oxidase system in Zymomonas mobilis.  

PubMed Central

Membrane vesicles prepared from Zymomonas mobilis oxidized NADH exclusively, whereas deamino-NADH was little oxidized. In addition, the respiratory chain-linked NADH oxidase system exhibited only a single apparent Km value of approximately 66 microM for NADH. The NADH oxidase was highly sensitive to the respiratory chain inhibitor 2-heptyl-4-hydroxyquinoline-N-oxide. However, the NADH:quinone oxidoreductase was not sensitive to 2-heptyl-4-hydroxyquinoline-N-oxide and was highly resistant to another respiratory chain inhibitor, rotenone. Electron transfer from NADH to oxygen generated a proton electrochemical gradient (inside positive) in inside-out membrane vesicles. In contrast, electron transfer from NADH to ubiquinone-1 generated no electrochemical gradient. These findings indicate that Z. mobilis possesses only NADH:quinone oxidoreductase lacking the energy coupling site.

Kim, Y J; Song, K B; Rhee, S K

1995-01-01

253

Differentiation Rules: The Chain Rule  

NSDL National Science Digital Library

Recognize composite functions, including their inner and outer components; decompose composite functions into compositions of elementary functions;differentiate compositions of functions using the chain rule

Freeze, Michael

2003-01-21

254

Restart procedures for the conjugate gradient method  

Microsoft Academic Search

The conjugate gradient method is particularly useful for minimizing functions of very many variables because it does not require the storage of any matrices. However the rate of convergence of the algorithm is only linear unless the iterative procedure is “restarted” occasionally. At present it is usual to restart everyn or (n + 1) iterations, wheren is the number of

M. J. D. Powell

1977-01-01

255

Plasma density gradient measurement using laser deflection  

Microsoft Academic Search

For a given chord through a plasma, changes in the line integrated index of refraction as a result of a transverse density gradient can be observed by measuring the angle of deflection of a laser beam. In contrast to laser interferometers, this method of density profile measurement places modest requirements on laser quality and alignment procedures, allowing measurements to be

Samuel J. E. Brockington; Robert D. Horton; David Q. Hwang; Russell W. Evans; Stephen J. Howard; Y. C. Francis Thio

2005-01-01

256

Multi-gradient drilling method and system  

DOEpatents

A multi-gradient system for drilling a well bore from a surface location into a seabed includes an injector for injecting buoyant substantially incompressible articles into a column of drilling fluid associated with the well bore. Preferably, the substantially incompressible articles comprises hollow substantially spherical bodies.

Maurer, William C. (Houston, TX); Medley, Jr., George H. (Spring, TX); McDonald, William J. (Houston, TX)

2003-01-01

257

Globally Convergent Hybrid Conjugate Gradient Methods.  

National Technical Information Service (NTIS)

Two hybrid conjugate gradient methods are presented. The first hybrid, Hybrid 1, uses the Polak-Ribiere beta as long as it is positive and less than or equal to that of Fletcher-Reeves and uses the Fletcher-Reeves beta instead, otherwise. This condition e...

D. Touati-ahmed C. Storey

1986-01-01

258

Optimizing the readout of morphogen gradients  

NASA Astrophysics Data System (ADS)

In multicellular organisms, the initial patterns of gene expression are regulated by spatial gradients of biochemical factors, known as morphogen gradients. Because of biochemical noise in the morphogen gradients there are associated spatial errors in the positions of target gene patterns. Using a simple single morphogen and/or single target gene model, we use propagation of error analysis to derive a condition on the amount of morphogen that needs to be produced in order to have precise spatial patterning of the target. We find that there is an optimal morphogen gradient profile that requires the least amount of morphogen to be produced. Experimental results for the Bicoid-Hunchback system in early Drosophila development are consistent with the predictions of this analysis. We also discuss our results in the context of recent work that analyzed this system using mutual information as an organizing principle, and show that minimizing the amount of morphogen produced also leads to a near optimal flow of information between input and target.

Emberly, Eldon

2008-04-01

259

On causality of the gradient elasticity models  

Microsoft Academic Search

This paper is concerned with causality of the gradient elasticity models of heterogeneous materials. As a rule, these models are not strictly causal since they allow an infinite speed of energy transfer by means of either propagating or transient evanescent waves. A discussion is presented in this paper of both physical and mathematical implications of this fact. This discussion is

A. V. Metrikine

2006-01-01

260

Gradient formation of boride layers by borocarburizing  

NASA Astrophysics Data System (ADS)

In this study borocarburizing was used for the formation of gradient boride layers. The microstructure, microhardness profiles and the low-cycle fatigue strength during radial compression of carburized, borided and borocarburized layer have been compared. The gradient borocarburized layers, formed by boriding of previously carburized substrate, are characterized by two zones in diffusion layer: iron borides zone and carburized zone. After borocarburizing the iron borides show a tendency towards a loss of the needle-like nature. The hardness gradient between iron borides and low-carbon substrate is reduced. The microhardness beneath the iron borides decreases to 900 HV in carburized zone and next gradually decreases to 400-450 HV in the core of steel. The highest resistance to low-cycle fatigue during radial compression has been observed in case of carburized and through hardened layer. The fatigue strength of gradient boride layer (borocarburized and through hardened) is a little lower. The typical borided and through hardened layer is characterized by the lowest resistance to low-cycle fatigue during radial compression. The profiles of stresses after boriding and borocarburizing have been compared. The obtained profile of stresses and the lower values of tensile stresses at the surface can be the reason for higher frictional wear resistance of borocarburized layers and for higher fatigue strength of these layers, too.

Kulka, M.; Pertek, A.

2008-06-01

261

Histograms of Oriented Gradients for Human Detection  

Microsoft Academic Search

We study the question of feature sets for robust visual ob- ject recognition, adopting linear SVM based human detec- tion as a test case. After reviewing existing edge and gra- dient based descriptors, we show experimentally that grids of Histograms of Oriented Gradient (HOG) descriptors sig- nicantly outperform existing feature sets for human detec- tion. We study the inuence of

Navneet Dalal; Bill Triggs

2005-01-01

262

Convergence Properties of Gradient Descent Noise Reduction  

Microsoft Academic Search

Gradient descent noise reduction is a technique that attempts to recover the true signal, or trajectory, from noisy observations of a non-lin ear dynamical system for which the dynamics are known. This paper provides the first ri gorous proof that the algorithm will recover the original trajectory for a broad c lass of dynamical sys- tems under certain conditions. The

David Ridout; Kevin Judd

263

Magnetic Control of Concentration Gradient in Microgravity  

NASA Technical Reports Server (NTRS)

A report describes a technique for rapidly establishing a fluid-concentration gradient that can serve as an initial condition for an experiment on solutal instabilities associated with crystal growth in microgravity. The technique involves exploitation of the slight attractive or repulsive forces exerted on most fluids by a magnetic-field gradient. Although small, these forces can dominate in microgravity and therefore can be used to hold fluids in position in preparation for an experiment. The magnetic field is applied to a test cell, while a fluid mixture containing a concentration gradient is prepared by introducing an undiluted solution into a diluting solution in a mixing chamber. The test cell is then filled with the fluid mixture. Given the magnetic susceptibilities of the undiluted and diluting solutions, the magnetic-field gradient must be large enough that the magnetic force exceeds both (1) forces associated with the flow of the fluid mixture during filling of the test cell and (2) forces imposed by any residual gravitation and fluctuations thereof. Once the test cell has been filled with the fluid mixture, the magnetic field is switched off so that the experiment can proceed, starting from the proper initial conditions.

Leslie, Fred; Ramachandran, Narayanan

2005-01-01

264

Gradient Vector Flow Fast Geodesic Active Contours  

Microsoft Academic Search

This paper proposes a new front propagation flow for boundary extraction. The proposed framework is inspired by the geodesic active contour model and leads to a paradigm that is relatively free from the initial curve po- sition. Towards this end, it makes use of a recently in- troduced external boundary force, the gradient vector field that refers to a spatial

Nikos Paragios; Olivier Mellina-gottardo; Visvanathan Ramesh

2001-01-01

265

On-chip temperature gradient interaction chromatography.  

PubMed

This paper reports the first integrated microelectromechanical system (MEMS) HPLC chip that consists of a parylene high-pressure LC column, an electrochemical sensor, a resistive heater and a thermal-isolation structure for on-chip temperature gradient interaction chromatography application. The separation column was 8 mm long, 100 microm wide, 25 microm high and was packed with 5 microm sized, C18-coated beads using conventional slurry-packing technique. A novel parylene-enhanced, air-gap thermal isolation technology was used to reduce heater power consumption by 58% and to reduce temperature rise in the off-column area by 67%. The fabricated chip consumed 400 mW when operated at 100 degrees C. To test the chromatography performance of the fabricated system, a mixture of derivatized amino acids was chosen for separation. A temporal temperature gradient scanning from 25 to 65 degrees C with a ramping rate of 3.6 degrees C/min was applied to the column during separation. Successful chromatographic separation of derivatized amino acids was carried out using our chip. Compared with conventional temperature gradient HPLC system which incorporates "macro oven" to generate temporal temperature gradient on the column, our chip's thermal performance, i.e., power consumption and thermal response, is greatly improved without sacrificing chromatography quality. PMID:16569585

Shih, Chi-Yuan; Chen, Yang; Xie, Jun; He, Qing; Tai, Yu-Chong

2006-04-14

266

Density Gradient Columns for Chemical Displays.  

ERIC Educational Resources Information Center

Procedures for preparing density gradient columns for chemical displays are presented. They include displays illustrating acid-base reactions, metal ion equilibria, and liquid density. The lifetime of these metastable displays is surprising, some lasting for months in display cabinets. (JN)

Guenther, William B.

1986-01-01

267

Stability of Morphogen Gradients & Movement of Molecules  

NSDL National Science Digital Library

A 23 minute QuickTime movie of Nobel Laureate Eric Wieschaus lecture describing the processes that help a fruit fly embryo create morphogen gradients required for normal development. This second part looks at quantitation of maternal protein bicoid and the genes that respond to it. Related lectures cover pattern formation and evolution of patterning.

iBioSeminars (American Society for Cell Biology)

2009-02-05

268

Microfluidic high gradient magnetic cell separation  

Microsoft Academic Search

Separation of blood cells by native susceptibility and by the selective attachment of magnetic beads has recently been demonstrated on microfluidic devices. We discuss the basic principles of how forces are generated via the magnetic susceptibility of an object and how microfluidics can be combined with micron-scale magnetic field gradients to greatly enhance in principle the fractionating power of magnetic

David W. Inglis; Robert Riehn; James C. Sturm; Robert H. Austin

2006-01-01

269

Moving Forward: Mechanisms of Chemoattractant Gradient Sensing  

NSDL National Science Digital Library

Cells use an internal compass to sense the direction of chemoattractant gradients. This is used to bias pseudopod extension at the front of the cell and to orient cell polarization. Recent studies have highlighted the important roles played by phosphoinositide-3,4,5-triphosphate and small G proteins, but many questions remain.

PhD Jonathan Franca-Koh (Johns Hopkins University School of Medicine Department of Cell Biology); PhD Peter N. Devreotes (Johns Hopkins University School of Medicine Department of Cell Biology)

2004-10-01

270

High-gradient continuous-casting furnace  

NASA Technical Reports Server (NTRS)

High gradient allows rapid growth rates in directionally-solidified eutectic alloys. Furnace design permits cost reductions in directional solidification process through its increased solidification rates, which reduces melt/mold interaction. It produces structural engineering materials for any application requiring properties directionally-solidified eutectic materials.

Scheuermann, C. M.; Flemings, M. C.; Neff, M. A.; Rickinson, B. A.; Young, K. P.

1979-01-01

271

HOT PRESSING WITH A TEMPERATURE GRADIENT  

Microsoft Academic Search

A method is described for producing powder metal compacts with a high ; length to width ratio, which are of substantially uniform density. The process ; consists in arranging a heating coil around the die and providing a temperature ; gradient along the length of the die with the highest temperature at the point of ; the compact farthest away

Hausner

1958-01-01

272

Latitudinal temperature gradients and climate change  

Microsoft Academic Search

The effects of a change in the latitudinal sea surface temperature gradient are investigated in several GCM experiments. Sea surface temperatures are increased\\/decreased in the tropics and polar regions, with little change in the global average surface air temperature. Then the experiments are repeated with colder\\/warmer conditions globally. Expectations generated from these runs are compared with the resulting climate changes

D. Rind

1998-01-01

273

Uranium Distribution along the Salinity Gradient  

NASA Astrophysics Data System (ADS)

Uranium distribution has been examined in the estuarine waters of the Keum River, Korea. Water samples were collected along a salinity gradient, range from 0.2 to 31.5 psu. Dissolved uranium in the samples has been extracted by C-18 SPE cartridge after pre-treatment. Extraction of uranium by C-18 cartridge after complexation with APDC/DDDC shows about 90 % recovery. After concentration of sample onto C-18 cartridge, uranium complex has been sequentially extracted by 50 % and 100 % acetonitrile, respectively. Result shows good recovery efficiency at low pH (2.5 _ 3.0) during the pre-treatment of sample which was presumably related with destabilization of uranium-carbonate complex. In the estuary, uranium shows typical conservative behavior along the salinity gradient. The current result substantiates earlier reports that uranium is conservatively transported from the river to the ocean. Most of dissolved trace metals, except cadmium, decreased with increasing salinity in the estuary. Dissolved organic carbon also decreased along the salinity gradient. Copper was rapidly removed during the mixing with seawaters as a result of organic matter flocculation. Dissolved molybdenum, vanadium and uranium distribution in the estuary showed similarities that those concentration increase along the salinity gradient.

Yoon, C.; Yoon, H.; Seo, J.; Lee, J.; Chung, K.

2006-12-01

274

Pressure Gradient Boundary Layers With Eventual Separation  

NASA Astrophysics Data System (ADS)

Using the similarity analysis for turbulent boundary layer with pressure gradient by Castillo and George(Castillo, L. and George, W.K.,``Similarity Analysis for Turbulent Boundary Layer with Pressure Gradient: out flow,'' AIAA Journal, Vol.39,2001) it will be shown that the outer part of adverse pressure gradient turbulent boundary layers tends to remain in equilibrium similarity, even near (and sometimes past) separation. Thus such boundary layers are characterized by a single pressure parameter, ?_? =frac? ? U_? ^2d? /dxfracdP_? dx, and its value appears to be the same for all adverse pressure gradient flows; i.e., ?_? ? 0.22. Using this pressure parameter and the momentum integral boundary layer equation, it is possible to show that the shape factor at separation must have a single value, H_sep ? 2.5. Both the conditions for equilibrium similarity and the value of H_sep are shown to be in reasonable agreement with a variety of experimental estimates.

Wang, Xia; Castillo, Luciano; George, William K.

2001-11-01

275

Detection of nanoparticles using optical gradient forces  

Microsoft Academic Search

We present a detection scheme for nanoscale particles based on the gradient force and torque near a tightly focused laser beam. The focus affects the path of nanoparticles passing by and a quadrant detector records the particle trajectory. A feedback system continuously adjusts the laser power and thereby prevents the particles from being trapped. Particle size and shape can be

Filipp V. Ignatovich; Achim Hartschuh; Lukas Novotny

2003-01-01

276

Ocean thermal gradient hydraulic power plant.  

PubMed

Solar energy stored in the oceans may be used to generate power by exploiting ploiting thermal gradients. A proposed open-cycle system uses low-pressure steam to elevate vate water, which is then run through a hydraulic turbine to generate power. The device is analogous to an air lift pump. PMID:17813707

Beck, E J

1975-07-25

277

Gradient Adaptive Image Restoration and Enhancement  

Microsoft Academic Search

in Proc. IEEE Int'l Conf. on Image Processing (ICIP), pp 2893-2896, 2006 Various methods have been proposed for image enhancement and restoration. The main difculty is how to enhance the structures uniformly while suppressing the noise without arti- facts. In this paper, we tackle this problem in the gradient do- main instead of the traditional intensity domain. By enhanc- ing

Hongcheng Wangt; Yunqiang Chen; Tong Fang; Jason Tyan; Narendra Ahuja

2006-01-01

278

Stress gradients in titanium nitride thin films  

Microsoft Academic Search

Titanium nitride films, as used for hard coatings, were deposited on silicon wafers by reactive unbalanced magnetron sputtering. For thinner films we find a higher compressive average residual stress than for thicker films. In the paper it is shown that this reduction in average stress is not due to relaxation, but to a stress gradient in the film. Experiments in

R. Machunze; G. C. A. M. Janssen

2008-01-01

279

Snakes, shapes, and gradient vector flow  

Microsoft Academic Search

Snakes, or active contours, are used extensively in computer vision and image processing applications, particularly to locate object boundaries. Problems associated with initializa- tion and poor convergence to boundary concavities, however, have limited their utility. This paper presents a new external force for active contours, largely solving both problems. This external force, which we call gradient vector flow (GVF), is

Chenyang Xu; Jerry L. Prince

1998-01-01

280

Joining of Tungsten Armor Using Functional Gradients  

SciTech Connect

The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

John Scott O'Dell

2006-12-31

281

Subspace learning from image gradient orientations.  

PubMed

We introduce the notion of subspace learning from image gradient orientations for appearance-based object recognition. As image data are typically noisy and noise is substantially different from Gaussian, traditional subspace learning from pixel intensities very often fails to estimate reliably the low-dimensional subspace of a given data population. We show that replacing pixel intensities with gradient orientations and the ?? norm with a cosine-based distance measure offers, to some extend, a remedy to this problem. Within this framework, which we coin Image Gradient Orientations (IGO) subspace learning, we first formulate and study the properties of Principal Component Analysis of image gradient orientations (IGO-PCA). We then show its connection to previously proposed robust PCA techniques both theoretically and experimentally. Finally, we derive a number of other popular subspace learning techniques, namely, Linear Discriminant Analysis (LDA), Locally Linear Embedding (LLE), and Laplacian Eigenmaps (LE). Experimental results show that our algorithms significantly outperform popular methods such as Gabor features and Local Binary Patterns and achieve state-of-the-art performance for difficult problems such as illumination and occlusion-robust face recognition. In addition to this, the proposed IGO-methods require the eigendecomposition of simple covariance matrices and are as computationally efficient as their corresponding ?? norm intensity-based counterparts. Matlab code for the methods presented in this paper can be found at http://ibug.doc.ic.ac.uk/resources. PMID:22271825

Tzimiropoulos, Georgios; Zafeiriou, Stefanos; Pantic, Maja

2012-12-01

282

Immobilized streptavidin gradients as bioconjugation platforms.  

PubMed

Surface density gradients of streptavidin (SAV) were created on solid surfaces and demonstrated functionality as a bioconjugation platform. The surface density of immobilized streptavidin steadily increased in one dimension from 0 to 235 ng cm(-2) over a distance of 10 mm. The density of coupled protein was controlled by its immobilization onto a polymer surface bearing a gradient of aldehyde group density, onto which SAV was covalently linked using spontaneous imine bond formation between surface aldehyde functional groups and primary amine groups on the protein. As a control, human serum albumin was immobilized in the same manner. The gradient density of aldehyde groups was created using a method of simultaneous plasma copolymerization of ethanol and propionaldehyde. Control over the surface density of aldehyde groups was achieved by manipulating the flow rates of these vapors while moving a mask across substrates during plasma discharge. Immobilized SAV was able to bind biotinylated probes, indicating that the protein retained its functionality after being immobilized. This plasma polymerization technique conveniently allows virtually any substrate to be equipped with tunable protein gradients and provides a widely applicable method for bioconjugation to study effects arising from controllable surface densities of proteins. PMID:22235975

Coad, Bryan R; Vasilev, Krasimir; Diener, Kerrilyn R; Hayball, John D; Short, Robert D; Griesser, Hans J

2012-02-01

283

Gradient methods for geophysical image inversions  

SciTech Connect

This paper presents a conjugate-gradient algorithm adapted to solve the linear equations, Ax = b, arising from simulated electromagnetic geophysical data. Four test cases are considered, and reconstructions are obtained that compare favorably with those obtained using the standard ART algorithms.

Frank, M.S.; Balanis, C.A.

1986-09-01

284

THERMODYNAMICAL ASPECTS OF IMPLICIT GRADIENT DAMAGE  

Microsoft Academic Search

A gradient damage formulation for quasi-brittle damage is derived from a nonstandard expression for the free energy potential. In contrast with many existing approaches, the nonstandard terms are related to the kinematics of the problem and therefore come into play already in the elastic regime. Following the argument that the second law of thermodynamics need only be satisfied globally for

R. H. J. PEERLINGS; M. G. D. GEERS

285

Supply chain risk in an uncertain global supply chain environment  

Microsoft Academic Search

The breadth and scope of supply chain risks have broadened significantly in recent years. Even prior to the 2001 terrorist attacks, the creep of risks and uncertainties were widening with increased globalization, widening political reach by leading countries, and the rise of market producing and consuming economies. This article raises some essential supply chain questions as well as some that

Jack Barry

2004-01-01

286

Plasma protein adsorption and platelet adhesion onto comb-like PEO gradient surfaces.  

PubMed

Comb-like polyethylene oxide (PEO) surfaces were prepared on low-density polyethylene (PE). The comb-like PEO chain density was changed gradually along the sample lengths by corona discharge treatment with gradually increasing power and the following graft copolymerization of poly(ethylene glycol) monomethacrylate macromers (PEO-MA). The macromers with different PEO repeat unit, 1, 5, and 10, were used. The prepared comb-like PEO gradient surfaces were characterized by water contact angle, Fourier transform infrared spectroscopy in the attenuated total reflectance mode, and electron spectroscopy for chemical analysis. All these measurements indicated that the PEO chains are grafted on the PE surface with gradually increasing density of PEO. Plasma protein adsorption and platelet adhesion on the PEO gradient surfaces decreased with increasing PEO chain length and surface density. As observed by scanning electron microscopy, PEO10-MA-grafted surface with high PEO density was very effective in preventing protein adsorption and platelet adhesion and did not activate the platelets. PMID:8978659

Lee, J H; Jeong, B J; Lee, H B

1997-01-01

287

How Entangled Polymer Chains Relax  

NASA Astrophysics Data System (ADS)

It will be shown through a series of experiments with selectively deuterated model polymers that stress relaxation occurs through a mechanical percolation process which permits large clusters of entangled polymers to stress relax before their conformations are fully relaxed. We find that: (a) Reptating homopolymer chains with molecular weight M >> Mc appear to be non-Reptating as their ends and centers relax at the same rate in a Rouse-like manner during percolation. (b) The mechanical relaxation time .?(M) is related to the Reptation time Tr˜ M^3 by .?(M) = Tr[(1-Mc/M) Me/Mc]^2, which is the origin of the viscosity behaving as .?˜M^3.4 (c) During stress relaxation, the random coil dimensions Rg(//) and Rg(.) are significantly not relaxed when the stress and birefringence relax to zero. (d) Matrix molecular weight P effects on relaxation time .?(M) of the probe chain M are as follows: When the probe chain M>>P, the matrix P-chains percolate and Rouse-like dynamics is observed for the M-Reptating chains with .?(M) ˜ P^1M^2. (e) When the matrix P>>M, percolation does not occur for the M-chain and the relaxation time of the probe chain .?(M) ˜ P^oM^3 is in accord with DeGennes Reptation theory. These results clearly suggest that current notions of polymer rheology involving chain end fluctuation and constraint release need to be reconsidered. .

Wool, Richard

2010-03-01

288

Building an efficient supply chain.  

PubMed

Realizing at last that supply chain management can produce efficiencies and save costs, hospitals are beginning to adopt practices from other industries, such as the concept of extended supply chains, to improve product flow. They're also investing in enterprise planning resource software, radio frequency identification and other technologies, using quality data to drive standardization and streamlining processes. PMID:16225319

Scalise, Dagmara

2005-08-01

289

Commutation relations and Markov chains  

Microsoft Academic Search

It is shown that the combinatorics of commutation relations is well suited for analyzing the convergence rate of certain Markov chains. Examples studied include random walk on irreducible representations, a local random walk on partitions whose stationary distribution is the Ewens distribution, and some birth-death chains.

Jason Fulman

2007-01-01

290

Synfire Chains and Catastrophic Interference  

Microsoft Academic Search

The brain must be capable of achieving extraordinarily precise sub-millisecond timing with imprecise neural hardware. We discuss how this might be possible using synfire chains (Abeles, 1991) and present a synfire chain learning algorithm for a sparsely-distributed network of spiking neurons (Sougné, 1999). Surprisingly, we show that this learning is not subject to catastrophic interference, a problem that plagues many

Jacques P. Sougné; Robert M. French

291

Chain Migration of Neuronal Precursors  

Microsoft Academic Search

In the brain of adult mice, cells that divide in the subventricular zone of the lateral ventricle migrate up to 5 millimeters to the olfactory bulb where they differentiate into neurons. These migrating cells were found to move as chains through a well-defined pathway, the rostral migratory stream. Electron microscopic analysis of serial sections showed that these chains contained only

Carlos Lois; Jose-Manuel Garcia-Verdugo; Arturo Alvarez-Buylla

1996-01-01

292

Can a franchise chain coordinate?  

Microsoft Academic Search

In today's business landscape, the familiar traditional corporation has been augmented by new species, such as joint ventures, strategic alliances, and franchise chains. The properties of these new species, termed hybrid forms, are distinctly different from the traditional corporation. In this paper, we examine whether one hybrid form, the franchise chain, can coordinate elements of the marketing mix (price, quality,

Steven C. Michael

2002-01-01

293

Do franchised chains advertise enough?  

Microsoft Academic Search

Evidence from the research literature and the trade press suggests that advertising is a common source of controversy among channel partners in franchised chains. A theoretical explanation for this controversy is that investment in an asset will be less when that asset is shared. Hybrid organizational forms such as franchised chains share a brand name among the franchisor and its

Steven C Michael

1999-01-01

294

Supply chain design and analysis  

Microsoft Academic Search

For years, researchers and practitioners have primarily investigated the various processes within manufacturing supply chains individually. Recently, however, there has been increasing attention placed on the performance, design, and analysis of the supply chain as a whole. This attention is largely a result of the rising costs of manufacturing, the shrinking resources of manufacturing bases, shortened product life cycles, the

Benita M. Beamon

1998-01-01

295

Verifying the Hanging Chain Model  

ERIC Educational Resources Information Center

The wave equation with variable tension is a classic partial differential equation that can be used to describe the horizontal displacements of a vertical hanging chain with one end fixed and the other end free to move. Using a web camera and TRACKER software to record displacement data from a vibrating hanging chain, we verify a modified version…

Karls, Michael A.

2013-01-01

296

Regulating Railways in Logistics Chains  

Microsoft Academic Search

ailways contain natural monopoly components in their track infrastructure. Hence, like most infrastructure industries in Australia, they are subject to economic regulation to prevent abuses of monopoly power. Railways also form part of logistics chains and, as such, their ability to abuse market power depends upon the characteristics of those chains. Third party access regimes presently apply to the whole

Nick Wills-Johnson

2007-01-01

297

Issues in Supply Chain Management  

Microsoft Academic Search

Successful supply chain management requires cross-functional integration and marketing must play a critical role. The challenge is to determine how to successfully accomplish this integration. We present a framework for supply chain management as well as questions for how it might be implemented and questions for future research. Case studies conducted at several companies and involving multiple members of supply

Douglas M Lambert; Martha C Cooper

2000-01-01

298

Permanently Linked, Rigid, Magnetic Chains.  

National Technical Information Service (NTIS)

One aspect of the present invention relates to a permanently linked, rigid, magnetic chain of particles prepared by sol-gel methods. A second aspect of the present invention relates to a method of preparing a permanently linked, rigid, magnetic chain of p...

H. Singh T. A. Hatton

2004-01-01

299

Characterization of imaging gradients in diffusion tensor imaging  

NASA Astrophysics Data System (ADS)

For obtaining a complete model the diffusion tensor imaging (DTI) method is derived in a new linear algebraic framework in order to include the effect of all of the magnetic field gradients on the MRI signal. In the framework, the coefficient matrix of the estimation equations consists of the sum of three matrices corresponding to diffusion gradients, imaging gradients and the cross-terms between them. The derivations demonstrate that there exists modeling incongruities originating from the choice of phase-encoding gradient magnitude and the read-out gradient affecting the entirety of the signal sample points. These reflect on the cross-terms and the imaging gradient coefficient matrix, revealing the DTI's inadequacy for the inclusion of imaging gradients. The linear algebraic framework mitigates the inadequacy by the utilization of center-symmetric gradient schemes. The observations are verified by the experimental results obtained from an isotropic phantom using several existing diffusion gradient schemes.

Özcan, Alpay

2010-11-01

300

Thermodynamics of Dipolar Chain Systems  

NASA Astrophysics Data System (ADS)

The thermodynamics of a quantum system of layers containing perpendicularly oriented dipolar molecules is studied within an oscillator approximation for both bosonic and fermionic species. The system is assumed to be built from chains with one molecule in each layer. We consider the effects of the intralayer repulsion and quantum statistical requirements in systems with more than one chain. Specifically, we consider the case of two chains and solve the problem analytically within the harmonic Hamiltonian approach which is accurate for large dipole moments. The case of three chains is calculated numerically. Our findings indicate that thermodynamic observables, such as the heat capacity, can be used to probe the signatures of the intralayer interaction between chains. This should be relevant for near future experiments on polar molecules with strong dipole moments.

Armstrong, J. R.; Zinner, N. T.; Fedorov, D. V.; Jensen, A. S.

2013-05-01

301

Abundance gradients in spiral discs: is the gradient inversion at high redshift real?  

NASA Astrophysics Data System (ADS)

We compute the abundance gradients along the disc of the Milky Way by means of the two-infall model: in particular, the gradients of oxygen and iron and their temporal evolution. First, we explore the effects of several physical processes which influence the formation and evolution of abundance gradients. They are (i) the inside-out formation of the disc, (ii) a threshold in the gas density for star formation, (iii) a variable star formation efficiency along the disc, (iv) radial flows and their speed and (v) different total surface mass density (gas plus stars) distributions for the halo. We are able to reproduce at best the present day gradients of oxygen and iron if we assume an inside-out formation, no threshold gas density, a constant efficiency of star formation along the disc and radial gas flows. It is particularly important the choice of the velocity pattern for radial flows and the combination of this velocity pattern with the surface mass density distribution in the halo. Having selected the best model, we then explore the evolution of abundance gradients in time and find that the gradients in general steepen in time and that at redshift z ˜ 3 there is a gradient inversion in the inner regions of the disc, in the sense that at early epochs the oxygen abundance decreases towards the Galactic Centre. This effect, which has been observed, is naturally produced by our models if an inside-out formation of the disc and a constant star formation efficiency are assumed. The inversion is due to the fact that in the inside-out formation a strong infall of primordial gas, contrasting chemical enrichment, is present in the innermost disc regions at early times. The gradient inversion remains also in the presence of radial flows, either with constant or variable speed in time, and this is a new result.

Mott, A.; Spitoni, E.; Matteucci, F.

2013-11-01

302

Optimisation of gradient elution with serially-coupled columns. Part I: Single linear gradients.  

PubMed

A mixture of compounds often cannot be resolved with a single chromatographic column, but the analysis can be successful using columns of different nature, serially combined through zero-dead volume junctions. In previous work (JCA 1281 (2013) 94), we developed an isocratic approach that optimised simultaneously the mobile phase composition, stationary phase nature and column length. In this work, we take the challenge of implementing optimal linear gradients for serial columns to decrease the analysis time for compounds covering a wide polarity range. For this purpose, five ACE columns of different selectivity (three C18 columns of different characteristics, a cyano and a phenyl column) were combined, aimed to resolve a mixture of 15 sulphonamides using acetonitrile-water gradients. A gradient predictive system, based on numerical integration, was built to simulate chromatograms under linear gradient profiles. Two approaches were compared: the optimisation of the combination of columns pre-selecting the gradient profile, developed by De Beer et al. (Anal. Chem. 82 (2010) 1733), and the optimisation of the gradient program after pre-selecting the column combination using isocratic elution, developed for this work. Several refinements concerning the gradient delays along the solute migration and peak half-width modelling were included to improve the realism of the predictions. Pareto plots (expressed as analysis time versus predicted global resolution) assisted in the selection of the best separation conditions. The massive computation time in the gradient optimisation, once the column combination was optimised, was reduced to ca. 3min by using genetic algorithms. PMID:24891161

Ortiz-Bolsico, C; Torres-Lapasió, J R; García-Alvarez-Coque, M C

2014-07-11

303

Magnon localization and Bloch oscillations in finite Heisenberg spin chains in an inhomogeneous magnetic field.  

PubMed

We study the localization of magnon states in finite defect-free Heisenberg spin-1/2 ferromagnetic chains placed in an inhomogeneous magnetic field with a constant spatial gradient. Continuous transformation from the extended magnon states to the localized Wannier-Zeeman states in a finite spin chain placed in an inhomogeneous field is described both analytically and numerically. We describe for the first time the non-monotonic dependence of the energy levels of magnons, both long and short wavelength, on the magnetic field gradient, which is a consequence of magnon localization in a finite spin chain. We show that, in contrast to the destruction of the magnon band and the establishment of the Wannier-Stark ladder in a vanishingly small field gradient in an infinite chain, the localization of magnon states at the chain ends preserves the memory of the magnon band. Essentially, the localization at the lower- or higher-field chain end resembles the localization of the positive- or negative-effective-mass band quasiparticles. We also show how the beat dynamics of coherent superposition of extended spin waves in a finite chain in a homogeneous or weakly inhomogeneous field transforms into magnon Bloch oscillations of the superposition of localized Wannier-Zeeman states in a strongly inhomogeneous field. We provide a semiclassical description of the magnon Bloch oscillations and show that the correspondence between the quantum and semiclassical descriptions is most accurate for Bloch oscillations of the magnon coherent states, which are built from a coherent superposition of a large number of the nearest-neighbour Wannier-Zeeman states. PMID:23709517

Kosevich, Yuriy A; Gann, Vladimir V

2013-06-19

304

Latitudinal gradients in intraspecific ecological diversity.  

PubMed

The increase in the number of species with decreasing latitude is a striking pattern of global biodiversity. An important feature of studies of this pattern up to now has been the focus on species as the fundamental unit of interest, neglecting potential within-species ecological diversity. Here, we took a new perspective on this topic by measuring the degree to which individuals within populations differ in niche attributes across a latitudinal gradient (range: 54.01° S to 69.12° N). We show that 156 populations of 76 species across a wide range of vertebrate and invertebrate animal taxa contain more ecologically diverse assemblages of individuals towards lower latitudes. Our results add a new level of complexity to our understanding of global patterns of biodiversity and suggest the possibility that niche variation is partly responsible for the latitudinal gradients of species diversity. PMID:24335269

Araújo, Márcio S; Costa-Pereira, Raul

2013-01-01

305

The latitudinal biodiversity gradient through deep time.  

PubMed

Today, biodiversity decreases from equatorial to polar regions. This is a fundamental pattern governing the distribution of extant organisms, the understanding of which is critical to predicting climatically driven biodiversity loss. However, its causes remain unresolved. The fossil record offers a unique perspective on the evolution of this latitudinal biodiversity gradient (LBG), providing a dynamic system in which to explore spatiotemporal diversity fluctuations. Deep-time studies indicate that a tropical peak and poleward decline in species diversity has not been a persistent pattern throughout the Phanerozoic, but is restricted to intervals of the Palaeozoic and the past 30 million years. A tropical peak might characterise cold icehouse climatic regimes, whereas warmer greenhouse regimes display temperate diversity peaks or flattened gradients. PMID:24139126

Mannion, Philip D; Upchurch, Paul; Benson, Roger B J; Goswami, Anjali

2014-01-01

306

Automated apparatus for producing gradient gels  

DOEpatents

Apparatus for producing a gradient gel which serves as a standard medium for a two-dimensional analysis of proteins, the gel having a density gradient along its height formed by a variation in gel composition, with the apparatus including first and second pumping means each including a plurality of pumps on a common shaft and driven by a stepping motor capable of providing small incremental changes in pump outputs for the gel ingredients, the motors being controlled, by digital signals from a digital computer, a hollow form or cassette for receiving the gel composition, means for transferring the gel composition including a filler tube extending near the bottom of the cassette, adjustable horizontal and vertical arms for automatically removing and relocating the filler tube in the next cassette, and a digital computer programmed to automatically control the stepping motors, arm movements, and associated sensing operations involving the filling operation.

Anderson, N.L.

1983-11-10

307

Spectral Simulations Incorporating Gradient Coherence Selection  

NASA Astrophysics Data System (ADS)

Computer-aided methods can considerably simplify the use of the product operator formalism for theoretical analysis of NMR phenomena, which otherwise becomes unwieldy for anything but simple spin systems and pulse sequences. In this report, two previously available programming approaches using symbolic algebra (J. Shriver, Concepts Magn. Reson. 4, 1-33, 1992) and numerical simulation using object-oriented programming (S. A. Smith, T. O. Levante, B. H. Meier, and R. R. Ernst, J. Magn. Reson. A 106, 75-105, 1994) have been extended to include the use of gradient operators for simulation of spatially localized NMR spectroscopy and gradient coherence selection. These methods are demonstrated using an analysis of the response of an AX 3 spin system to the STEAM pulse sequence and verified with experimental measurements on lactate.

Young, Karl; Matson, Gerald B.; Govindaraju, Varanavasi; Maudsley, Andrew A.

1999-09-01

308

Self-similar dynamics of morphogen gradients.  

PubMed

Morphogen gradients are concentration fields of molecules acting as spatial regulators of cell differentiation in developing tissues and play a fundamental role in various aspects of embryonic development. We discovered a family of self-similar solutions in a canonical class of nonlinear reaction-diffusion models describing the formation of morphogen gradients. These solutions are realized in the limit of infinitely high production rate at the tissue boundary and are given by the product of the steady state concentration profile and a function of the diffusion similarity variable. We solved the boundary value problem for the similarity profile numerically and analyzed the implications of the discovered self-similarity on the dynamics of morphogenetic patterning. PMID:22181184

Muratov, Cyrill B; Gordon, Peter V; Shvartsman, Stanislav Y

2011-10-01

309

Advanced pneumatic method for gradient flow analysis  

NASA Astrophysics Data System (ADS)

Pneumatic 5-hole probes are widely known reliable sensors for the analysis of three-dimensional flow fields. Since the accuracy of such measurements depends strongly on the volume of the probe and the gradients in the flow, a miniature spherical five-hole-probe with an improved analysis method was developed. With the new method, the complete physically reasonable angle measurement range can be used now by introducing modified calibration functions. A dimensionless examination of the flow around spheres shows the independence of the calibration functions within a wide range of flow velocities. Misrepresentations in flows with high gradients caused by the volume of the probe are estimated by a geometry based correction method. The quality of the method is analyzed by an extensive error calculation. Results of measurements in a three-dimensional model combustor are discussed.

Glahn, A.; Hallmann, M.; Jeckel, R.; Wittig, S.

1993-08-01

310

Temperature Gradient Driven Lasing and Stimulated Cooling  

NASA Astrophysics Data System (ADS)

A laser can be understood as a thermodynamic engine converting heat to a coherent single mode field close to Carnot efficiency. To achieve lasing, spectral shaping of the excitation light is used to generate a higher effective temperature on the pump than on the gain transition. Here, using a toy model of a quantum well structure with two suitably designed tunnel-coupled wells kept at different temperatures, we predict that lasing can also occur on an actual spatial temperature gradient between the pump and gain regions. Gain and narrow band laser emission require a sufficiently large temperature gradient and resonator quality. Lasing appears concurrent with amplified heat flow between the reservoirs and points to a new form of stimulated solid state cooling. In addition, such a mechanism could reduce intrinsic heating and thus extend the operating regime of quantum cascade lasers by substituting phonon emission driven injection by a phonon absorption step.

Sandner, K.; Ritsch, H.

2012-11-01

311

Electron profile stiffness and critical gradient studies  

NASA Astrophysics Data System (ADS)

Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in ?Te. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/LC ~ 3 m-1 was identified at ?=0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -?Te, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/LT above the threshold.

DeBoo, J. C.; Petty, C. C.; White, A. E.; Burrell, K. H.; Doyle, E. J.; Hillesheim, J. C.; Holland, C.; McKee, G. R.; Rhodes, T. L.; Schmitz, L.; Smith, S. P.; Wang, G.; Zeng, L.

2012-08-01

312

Hydrodynamic gradient expansion in gauge theory plasmas.  

PubMed

We utilize the fluid-gravity duality to investigate the large order behavior of hydrodynamic gradient expansion of the dynamics of a gauge theory plasma system. This corresponds to the inclusion of dissipative terms and transport coefficients of very high order. Using the dual gravity description, we calculate numerically the form of the stress tensor for a boost-invariant flow in a hydrodynamic expansion up to terms with 240 derivatives. We observe a factorial growth of gradient contributions at large orders, which indicates a zero radius of convergence of the hydrodynamic series. Furthermore, we identify the leading singularity in the Borel transform of the hydrodynamic energy density with the lowest nonhydrodynamic excitation corresponding to a 'nonhydrodynamic' quasinormal mode on the gravity side. PMID:23745858

Heller, Michal P; Janik, Romuald A; Witaszczyk, Przemys?aw

2013-05-24

313

A mesh gradient technique for numerical optimization  

NASA Technical Reports Server (NTRS)

A class of successive-improvement optimization methods in which directions of descent are defined in the state space along each trial trajectory are considered. The given problem is first decomposed into two discrete levels by imposing mesh points. Level 1 consists of running optimal subarcs between each successive pair of mesh points. For normal systems, these optimal two-point boundary value problems can be solved by following a routine prescription if the mesh spacing is sufficiently close. A spacing criterion is given. Under appropriate conditions, the criterion value depends only on the coordinates of the mesh points, and its gradient with respect to those coordinates may be defined by interpreting the adjoint variables as partial derivatives of the criterion value function. In level 2, the gradient data is used to generate improvement steps or search directions in the state space which satisfy the boundary values and constraints of the given problem.

Willis, E. A., Jr.

1973-01-01

314

Geothermal temperature gradient core drill, Santiam Pass  

SciTech Connect

DOE is proposing to share in the cost of drilling a 3000-ft core hole to evaluate temperature gradients, subsurface geology and the geothermal potential of an area in the Cascade Mountains. The proposed core hole will be located in the Deschutes National Forest in Oregon, near Santiam Pass. The proposed action has been described in the Environmental Assessment (EA) for Geothermal Temperature Gradient Core Drill Santiam Pass Area (No. OR-050-9-51) prepared by the US Bureau of Land Management (BLM). DOE has determined that the BLM EA adequately addresses the impacts of the proposal and is hereby adopting the EA in partial fulfillment of its NEPA responsibilities. Based upon a review of the EA and an independent analysis, DOE has concluded that the proposed corehole drilling project does not constitute a major federal action significantly affecting the quality of the human environment within the meaning of NEPA. Therefore, an environmental impact statement will not be prepared.

Not Available

1989-01-01

315

Electron profile stiffness and critical gradient studies  

SciTech Connect

Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in {nabla}T{sub e}. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/L{sub C} {approx} 3 m{sup -1} was identified at {rho}=0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -{nabla}T{sub e}, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/L{sub T} above the threshold.

DeBoo, J. C.; Petty, C. C.; Burrell, K. H.; Smith, S. P. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); White, A. E. [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Doyle, E. J.; Hillesheim, J. C.; Rhodes, T. L.; Schmitz, L.; Wang, G.; Zeng, L. [University of California-Los Angeles, Los Angeles, California 90095-7099 (United States); Holland, C. [University of California-San Diego, La Jolla, California 92093-0417 (United States); McKee, G. R. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2012-08-15

316

Ecological gradients within a Pennsylvanian mire forest  

USGS Publications Warehouse

Pennsylvanian coals represent remains of the earliest peat-forming rain forests, but there is no current consensus on forest ecology. Localized studies of fossil forests suggest intermixture of taxa (heterogeneity), while, in contrast, coal ball and palynological analyses imply the existence of pronounced ecological gradients. Here, we report the discovery of a spectacular fossil forest preserved over ???1000 ha on top of the Pennsylvanian (Desmoinesian) Herrin (No. 6) Coal of Illinois, United States. The forest was abruptly drowned when fault movement dropped a segment of coastal mire below sea level. In the largest study of its kind to date, forest composition is statistically analyzed within a well-constrained paleogeographic context. Findings resolve apparent conflicts in models of Pennsylvanian mire ecology by confirming the existence of forest heterogeneity at the local scale, while additionally demonstrating the emergence of ecological gradients at landscape scale. ?? 2007 The Geological Society of America.

DiMichele, W. A.; Falcon-Lang, H. J.; Nelson, W. J.; Elrick, S. D.; Ames, P. R.

2007-01-01

317

Program predicts reservoir temperature and geothermal gradient  

SciTech Connect

This paper reports that a Fortran computer program has been developed to determine static formation temperatures (SFT) and geothermal gradient (GG). A minimum of input data (only two shut-in temperature logs) is required to obtain the values of SFT and GG. Modeling of primary oil production and designing enhanced oil recovery (EOR) projects requires knowing the undisturbed (static) reservoir temperature. Furthermore, the bottom hole circulating temperature (BHCT) is an important factor affecting a cement's thickening time, rheological properties, compressive strength, development, and set time. To estimate the values of BHCT, the geothermal gradient should be determined with accuracy. Recently we obtained an approximate analytical solution which describes the shut-in temperature behavior.

Kutasov, I.M.

1992-06-01

318

Voltammetry under a Controlled Temperature Gradient  

PubMed Central

Electrochemical measurements are generally done under isothermal conditions. Here we report on the application of a controlled temperature gradient between the working electrode surface and the solution. Using electrochemical sensors prepared on ceramic materials with extremely high specific heat conductivity, the temperature gradient between the electrode and solution was applied here as a second driving force. This application of the Soret phenomenon increases the mass transfer in the Nernst layer and enables more accurate control of the electrode response enhancement by a combination of diffusion and thermal diffusion. We have thus studied the effect of Soret phenomenon by cyclic voltammetry measurements in ferro/ferricyanide. The time dependence of sensor response disappears when applying the Soret phenomenon, and the complicated shape of the cyclic voltammogram is replaced by a simple exponential curve. We have derived the Cotrell-Soret equation describing the steady-state response with an applied temperature difference.

Krejci, Jan; Sajdlova, Zuzana; Krejci, Jan; Marvanek, Tomas

2010-01-01

319

Designing superhydrophobic surfaces using fluorosilsesquioxane-urethane hybrid and porous silicon gradients  

NASA Astrophysics Data System (ADS)

Here we describe a new class of near superhydrophobic surfaces formed using fluorinated polyhedral oligosilsesquioxane (FluoroPOSS) urethane hybrids and porous silicon gradients (pSi). We demonstrate that the surface segregation behavior of the hydrophobic fluoro component can be controlled by the type and nature of chain extender of the urethane and resultant hydrophobic association via intra or intermolecular aggregation. The surface film formed exhibits near superhydrophobicity. This work has significant potential for applications in antifouling and self-cleaning coatings, biomedical devices, microfluidic systems and tribological surfaces.

Kannan, Aravindaraj G.; McInnes, Steven J. P.; Choudhury, Namita R.; Dutta, Naba K.; Voelcker, Nicolas H.

2008-12-01

320

Hepatic Venous Pressure Gradient: Worth Another Look?  

Microsoft Academic Search

Portal hypertension is one of the most important complications of chronic liver disease and accounts for significant morbidity\\u000a and mortality. Measurement of the hepatic venous pressure gradient (HVPG) is a simple, invasive, and reproducible method of\\u000a assessing portal venous pressure. Measurement of HVPG provides the clinician an estimate of the degree of intrahepatic portal\\u000a flow resistance, guides therapy for variceal

Sameer Parikh

2009-01-01

321

Pathway selection by pulsed field gradients.  

PubMed

A method for pathway selection in a multiple spin-echo pulse sequence applying crusher gradients before and after each pi pulse, to dephase unwanted pathways, is described. This method selects the only pathway that would contribute to the measurable signal if the pi pulses were perfect (1,-1,1,-1, em leader ). Good pathway selection is essential in pulse programming, especially when the CPMG condition is not met. An interactive applet was also developed to deal with these calculations. PMID:12210921

Rodriguez, Ignacio; Perez de Alejo, Rigoberto; Ruiz-Cabello, Jesus

2002-09-01

322

High gradient magnetic separation: Theory versus experiment  

Microsoft Academic Search

The experimental performance of a high gradient magnetic separator has been previously reported by other workers in some detail for a CuO\\/Al2O3slurry. Less detailed results were also reported for slurries of Mn2O3, Al, and ?-Fe2O3particles with Al2O3representing a 20:1 range in particle sizes and a 200:1 range in magnetic susceptibility. Examination of these results indicates that many layers of particles

F. Luborsky; B. Drummond

1975-01-01

323

High gradient accelerators for linear light sources  

SciTech Connect

Ultra-high gradient radio frequency linacs powered by relativistic klystrons appear to be able to provide compact sources of radiation at XUV and soft x-ray wavelengths with a duration of 1 picosecond or less. This paper provides a tutorial review of the physics applicable to scaling the present experience of the accelerator community to the regime applicable to compact linear light sources. 22 refs., 11 figs., 21 tabs.

Barletta, W.A.

1988-09-26

324

A gentle Hessian for efficient gradient descent  

Microsoft Academic Search

Several second-order optimization methods for gradient descent algorithms have been proposed over the years, but they usually need to compute the inverse of the Hessian of the cost function (or an approximation of this inverse) during training. In most cases, this leads to an O(n2) cost in time and space per iteration, where n is the number of parameters, which

Ronan Collobert; Samy Bengio

2004-01-01

325

Gradient Vector Flow Fast Geometric Active Contours  

Microsoft Academic Search

Abstract—In this paper, we propose an edge-driven bidirectional geometric flow for boundary extraction. To this end, we combine the geodesic active contour flow [3] and the gradient vector flow external force for snakes,[25]. The resulting motion equation is considered within a level set formulation [19], can deal with topological changes,and important shape deformations. An efficient numerical,schema,is used for the flow

Nikos Paragios; Olivier Mellina-gottardo; Visvanathan Ramesh

2003-01-01

326

Characterization of transport in microfluidic gradient generators  

Microsoft Academic Search

We present a two-dimensional model that describes the concentration profile of a class of previously reported microfluidic\\u000a devices which are of particular interest in cellular taxis research. The devices generate stable concentration gradients by\\u000a mixing and dividing two or more external inputs into a large number of discrete streams. This study focuses specifically on\\u000a modeling the confluence of the discrete

Bryan R. Gorman; John P. Wikswo

2008-01-01

327

Parametric study of salt gradient solar ponds  

SciTech Connect

A mathematical model for efficiency of a salt gradient solar pond is described. Heat losses from the bottom of the pond have been calculated, and the results for the effective thermal conductivity with the thicknesses of various insulating materials have been presented. The effect of the ground thermal resistance on the efficiency of the pond for different values of ..delta..T/S/sup 0/ are also shown.

Beniwal, R.S.; Saxena, N.S.; Bhandari, R.C.

1986-02-01

328

Exploration of very high gradient cavities  

SciTech Connect

Several of the 9-cell ILC cavities processed at Jlab within ongoing ILC R&D program have shown interesting behavior at high fields, such as mode mixing and sudden field emission turn-on during quench. Equipped with thermometry and oscillating superleak transducer (OST) system for quench detection, we couple our RF measurements with local dissipation measurements. In this contribution we report on our findings with high gradient SRF cavities.

Grigory Eremeev

2011-07-01

329

Laminate delamination due to thermal gradients  

SciTech Connect

Flaw-induced delamination of orthotropic laminates subject to through-thickness temperature gradients is analyzed. A crack-like flaw impedes heat flow through the laminate, producing thermal stresses and crack tip stress intensities. The focus is on delamination cracks which propagate under steady-state conditions. The steady-state analysis becomes accurate for a crack whose length is about one laminate thickness. Moreover, the analysis provides realistic fail-safe criteria for excluding delamination.

Hutchinson, J.W.; Lu, T.J. [Harvard Univ., Cambridge, MA (United States). Div. of Applied Sciences

1995-10-01

330

Observation of a Gradient Catastrophe Generating Solitons  

SciTech Connect

We investigate the propagation of a dark beam in a defocusing medium in the strong nonlinear regime. We observe for the first time a shock fan filled with noninteracting one-dimensional gray solitons that emanates from a gradient catastrophe developing around a null of the optical intensity. This scenario turns out to be very robust, persisting also when the material nonlocal response averages the nonlinearity over dimensions much larger than the emerging soliton filaments.

Conti, Claudio [Research Center SOFT INFM-CNR, Universita di Roma 'La Sapienza', P. A. Moro 2, 00185 Roma (Italy); Fratalocchi, Andrea; Peccianti, Marco [Research Center SOFT INFM-CNR, Universita di Roma 'La Sapienza', P. A. Moro 2, 00185 Roma (Italy); Centro Studi e Ricerche 'Enrico Fermi', Via Panisperna 89/A, 00184 Roma (Italy); Ruocco, Giancarlo [Research Center SOFT INFM-CNR, Universita di Roma 'La Sapienza', P. A. Moro 2, 00185 Roma (Italy); Dipartimento di Fisica, Universita di Roma 'La Sapienza', P. A. Moro 2, 00185 Roma (Italy); Trillo, Stefano [Research Center SOFT INFM-CNR, Universita di Roma 'La Sapienza', P. A. Moro 2, 00185 Roma (Italy); Dipartimento di Ingegneria, Universita di Ferrara, Via Saragat 1, 44100 Ferrara (Italy)

2009-02-27

331

Cosmic ray gradients in the outer heliosphere  

NASA Technical Reports Server (NTRS)

Launched in 1972 and 1973 respectively, the Pioneer 10 and 11 spacecraft are now probing the outer heliosphere on their final escape from the sun. The data in this paper extend for almost an entire solar cycle from launch to early 1983, when Pioneer 10 was at a heliocentric distance of 29 AU and Pioneer 11, 13 AU. The UCSD instruments on board were used to study the gradient, and to look at the time and spatial variations of the cosmic ray intensities.

Fillius, W.; Wake, B.; Ip, W.-H.; Axford, I.

1983-01-01

332

Diffusion weighted vertical gradient and spin echo.  

PubMed

In this work, diffusion weighting and parallel imaging is combined with a vertical gradient and spin echo data readout. This sequence was implemented and evaluated on healthy volunteers using a 1.5 and a 3 T whole-body MR system. As the vertical gradient and spin echo trajectory enables a higher k-space velocity in the phase-encoding direction than single-shot echo planar imaging, the geometrical distortions are reduced. When combined with parallel imaging such as generalized autocalibrating partially parallel acquisition, the geometric distortions are reduced even further, while also keeping the minimum echo time reasonably low. However, this combination of a diffusion preparation and multiple refocusing pulses during the vertical gradient and spin echo readout, generally violates the Carr-Purcell-Meiboom-Gill condition, which leads to interferences between echo pathways. To suppress the stimulated echo pathway, refocusing pulses with a sharper slice profiles and an odd/even crusher variation scheme were implemented and evaluated. Being a single-shot acquisition technique, the reconstructed images are robust to rigid-body head motion and spatially varying brain motion, both of which are common sources of artifacts in diffusion MRI. PMID:23008151

Engström, Mathias; Bammer, Roland; Skare, Stefan

2012-12-01

333

Fast computation of satellite gravitational gradient.  

NASA Astrophysics Data System (ADS)

The computation of the Earth's potential function at high order and degree with the method of Cunningham (1970) causes overflow most of the time. The normalized method can eliminate the overflows, but leads to formulae much more involved than those in Cunningham's method; besides, the programming is more complex and the computer time required larger. The method presented has the following features: each component of the satellite gravitational gradient can be computed; the formulae are short and easy to be programmed; the method is much quicker than the normalization method and can be carried out with a microcomputer, without overflow even in the case of Earth's spherical harmonics of order and degree as high as 1025 or higher. This method satisfies the present demand to compute the satellite gravitational gradient with high accuracy. Furthermore, the authors present formulae for the fast computation, without overflow, of the gravitational gradient corresponding to Earth's spherical harmonics up to order and degree of 3170×3170 or higher.

Lin, Qinchang; Yuan, Lin

1998-07-01

334

Efficient gradient computation for dynamical models.  

PubMed

Data assimilation is a fundamental issue that arises across many scales in neuroscience - ranging from the study of single neurons using single electrode recordings to the interaction of thousands of neurons using fMRI. Data assimilation involves inverting a generative model that can not only explain observed data but also generate predictions. Typically, the model is inverted or fitted using conventional tools of (convex) optimization that invariably extremise some functional - norms, minimum descriptive length, variational free energy, etc. Generally, optimisation rests on evaluating the local gradients of the functional to be optimized. In this paper, we compare three different gradient estimation techniques that could be used for extremising any functional in time - (i) finite differences, (ii) forward sensitivities and a method based on (iii) the adjoint of the dynamical system. We demonstrate that the first-order gradients of a dynamical system, linear or non-linear, can be computed most efficiently using the adjoint method. This is particularly true for systems where the number of parameters is greater than the number of states. For such systems, integrating several sensitivity equations - as required with forward sensitivities - proves to be most expensive, while finite-difference approximations have an intermediate efficiency. In the context of neuroimaging, adjoint based inversion of dynamical causal models (DCMs) can, in principle, enable the study of models with large numbers of nodes and parameters. PMID:24769182

Sengupta, B; Friston, K J; Penny, W D

2014-09-01

335

Resolution requirements for velocity gradients in turbulence  

NASA Technical Reports Server (NTRS)

Since high resolution numerical simulations of turbulent flows, or experiments at high Reynolds numbers, represent a substantial investment in resources, the estimation of the minimum resolution required for the study of a given property has been the subject of continued interest. Different properties require, in general, different resolutions, and the present paper is dedicated to the requirements for the measurement of the probability distribution functions of the velocity gradients and, in particular, of their low order moments. The deviation of these quantities from the values corresponding to a Gaussian distribution was one of the first indications of the presence of Reynolds number-dependent intermittency and has been the object of recent interest as numerical simulations have become able to explore the distribution of gradients in the low Reynolds number range, while new experiments have extended the range to increasingly high Reynolds numbers. We will use progressive filtering of the results of numerical simulations of isotropic turbulence as a model for the effect of a sensor of finite size. The numerical issues will be addressed first to ensure that the simulations are fully resolved from the point of view of the velocity gradients. This will also give us an estimate for the numerical resolution required for the different quantities.

Jimenez, Javier

1994-01-01

336

Crosswind Shear Gradient Affect on Wake Vortices  

NASA Technical Reports Server (NTRS)

Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.

Proctor, Fred H.; Ahmad, Nashat N.

2011-01-01

337

SPEAR3 Gradient Dipole Core Fabrication  

SciTech Connect

Traditional means of core fabrication are to glue the laminations or weld them to form the yoke structure. These means result in good yoke assemblies for shorter (<0.6m) magnets. However, because of weld distortions or mechanical strength limitations, welding and/or gluing techniques are difficult to gain high mechanical precision for longer cores. The SPEAR3 gradient dipoles are up to 1.45m long and require distortions of <0.05mm. Therefore, the SPEAR3 gradient dipole core design incorporated an assembly technique, originally devised for the PEPII insertion quadrupoles and later adapted for the ALS gradient magnets. This technique involved fabricating a rigid frame for the core, precisely stacking and compressing the laminations using hydraulic jacks and granite surfaces and straight edges, and fixing the laminations in the frame by filling the grooves between the laminations and frame using steel loaded epoxy. Although this technique has been used in the past, it has never been fully described and published. This paper is written to provide a detailed description of the procedure and to present measurement data demonstrating the mechanical precision and stiffness of the resulting product.

Li, Nanyang

2003-07-29

338

High magnetic gradient environment causes alterations of cytoskeleton and cytoskeleton-associated genes in human osteoblasts cultured in vitro  

NASA Astrophysics Data System (ADS)

The effects of a high magnetic gradient environment (HMGE) on the cytoskeletal architecture and genes associated with the cytoskeleton in osteoblasts (MC3T3-E1 and MG-63 cells) were investigated using confocal microscopy, real-time polymerase chain reaction (PCR) and atomic force microscopy (AFM). The findings showed that, under diamagnetic levitation conditions, the architecture and average height of the cytoskeleton and surface roughness in osteoblasts were dramatically altered. HMGE affects cytoskeleton arrangement and cytoskeleton-associated gene expression.

Qian, A. R.; Yang, P. F.; Hu, L. F.; Zhang, W.; Di, S. M.; Wang, Z.; Han, J.; Gao, X.; Shang, P.

2010-09-01

339

Quantitative thermal gradient imaging of biological surfaces  

NASA Astrophysics Data System (ADS)

Heat production in biological systems is an obligate consequence of the chemical thermodynamics of the living state. Various cellular and systemic mechanisms exist of the dissipation (or conservation) of this net heat production in a basically aqueous environment to various exchange surfaces. Besides fundamental conduction, and radiation, convective modes of heat transfer are particularly significant, the latter often establishing steady-state thermal gradients particularly at normal or experimental exchange surfaces. Considering the relatively high specific heat of water and the low level of heat generation, the magnitude of such gradients are small and this require methods with sensitivity < 0.1 degree(s)C, with reasonable time response, and ones adaptable to quantitative spatial mapping. To that end, we have developed a calibration procedure and protocols employing a variety of thermotropic liquid crystal (TLC) formats which can quantitatively map both cellular and tissue surface gradients in a reproducible manner. TLC's used in a quantitative mode have the extreme temperature resolution required for basic biological studies, as well as application where altered cellular metabolism and/or vascular flow patterns are manifested as thermal changes in the spatial thermogram. This paper provides preliminary data on the application of the above protocols for the assessment of the dynamic changes in the thermal gradient pattern on the left-ventricular surface of supported, experimental heart preparations. Accordingly, after initial capture of the calibrated TLC images onto videotape using a multichannel plate intensifier (together with A/D conversion of physiological signals), single frame digitization allows for exact quantitative correlations of changes in the thermogram with hemodynamic parameters throughout the cardiac cycles with a time resolution of approximately equals 33 msec. The type of information obtained has potential value in clinical cardiac diagnosis (ie. coronary artery disease, by-pass assessment, etc.) and other biological applications where altered flow and/or heat production leads to changing surface gradients (ie thrombosis, embolism, tumor cell heat production, etc.) which can now be accurately and quantitatively mapped by the use of TLC's.

Swanson, Curtis J.; Wingard, Christopher J.

1991-03-01

340

Association with BiP and aggregation of class II MHC molecules synthesized in the absence of invariant chain.  

PubMed Central

Class II molecules of the major histocompatibility complex (MHC) are composed of two polymorphic glycoprotein chains (alpha and beta), that associate in the ER with a third, non-polymorphic glycoprotein known as the invariant chain (Ii). We have examined the relationship between the intracellular transport and physico-chemical characteristics of various combinations of murine alpha, beta and Ii chains. Biochemical and morphological analyses of transfected fibroblasts expressing class II MHC chains show that both unassembled alpha and beta chains, as well as a large fraction of alpha+beta complexes synthesized in the absence of Ii chain, are retained in the ER in association with the immunoglobulin heavy chain binding protein, BiP. Analyses by sedimentation velocity on sucrose gradients show that most incompletely assembled class II MHC species exist as high molecular weight aggregates in both transfected fibroblasts and spleen cells from mice carrying a disruption of the Ii chain gene. This is in contrast to the sedimentation properties of alpha beta Ii complexes from normal mice, which migrate as discrete, stoichiometric complexes of M(r) approximately 200,000-300,000. These observations suggest that assembly with the Ii chain prevents accumulation of aggregated alpha and beta chains in the ER, which might relate to the known ability of the Ii chain to promote exit of class II MHC molecules from the ER. Images

Bonnerot, C; Marks, M S; Cosson, P; Robertson, E J; Bikoff, E K; Germain, R N; Bonifacino, J S

1994-01-01

341

Computation of Turbulent Wake Flows in Variable Pressure Gradient.  

National Technical Information Service (NTIS)

Transport aircraft performance is strongly in uencedectiveness of high-lift systems. Developing wakes generated by the airfoil elements are subjected to strong pressure gradients and can thicken very rapidly, ects of various pressure gradients on developi...

N. Duquesne J. R. Carlson C. L. Rumsey

2004-01-01

342

Concentration Gradient Detection by Near-Infrared Diode Laser Interferometry.  

National Technical Information Service (NTIS)

Concentration gradient detection is performed with a diode laser system which probes the associated refractive index gradient (RIG). The detector has excellent potential for both High Performance Liquid Chromatography (HPLC) and Flow Injection Analysis (F...

D. O. Hancock

1988-01-01

343

Calculation of vertical temperature gradients in heated rooms.  

National Technical Information Service (NTIS)

This paper deals with a simple model which predicts the vertical temperature gradient in a heated room. The gradient is calculated from a dimensionless temperature profile which is determined by two room air temperatures only, the mean temperature in the ...

H. Overby M. Steen-Thoede

1990-01-01

344

Mathematical characterisation of the transduction chain in growth cone pathfinding.  

PubMed

Axon guidance by graded diffusible ligands plays an important role in the developing nervous system. Concentration gradients induce an asymmetric localisation of molecules in the axon tip, the growth cone, and the consequent internal polarised signalling pathway leads to rearrangement of the growth cone cytoskeleton and, ultimately, to motility. Here the authors provide a mathematical description of the growth cone transduction chain as a series of functional boxes characterised by input/output relations. The model relies on the assumption that the characteristic time of independent concentration measures by growth cone receptors, the characteristic time of growth cone internal reorganisation preceding motion and the characteristic time needed for a discernible axon turning belong to separated scales. The results give insight into the deterministic against stochastic regime of internal growth cone functions that are not readily accessible from experimental observations, pointing out a substantial equilibrium of the two contributions. The mathematical model predicts the decrease of the coefficient of variation of the signal moving down the functional chain leading to motion. Moreover, possible mechanisms that allow for buffering against noise are highlighted. These results have an interest also for the more experimentally minded reader, since they can be used to predict sample sizes for detecting significant differences in benchmark gradient assays. PMID:18537455

Aletti, G; Causin, P

2008-05-01

345

Some observations on the regularizing field for gradient damage models  

Microsoft Academic Search

Summary Gradient enhanced material models can potentially preserve well-posedness of incremental boundary value problems also after the onset of strain softening. Gradient dependent constitutive relations are rooted in the assumption that some scalar or tensor field, which appears in the yield function, has to be enriched by adding a term involving its second-order gradient field. For gradient-dependent plasticity this term

G. Borino; R. de Borst

2000-01-01

346

Pore-pressure gradients, stresses, and induced earthquakes  

Microsoft Academic Search

In the theory of poroelasticity, spatial gradients in pore-pressure enter the equilibrium equations in the same way as distributed body forces. Pore-pressure gradients are thus associated with poroelastic stresses in the same way that temperature gradients associated with thermoelastic stresses. The author has suggested that pore-pressure gradients caused by pumping are responsible for earthquakes near some oil and gas fields.

Segall

1992-01-01

347

Bibliometric Application of Markov Chains.  

ERIC Educational Resources Information Center

A rudimentary description of Markov Chains is presented in order to introduce its use to describe and to predict authors' movements among subareas of the discipline of ethnomusicology. Other possible applications are suggested. (Author)

Pao, Miranda Lee; McCreery, Laurie

1986-01-01

348

Side-Chain Liquid-Crystalline Polyphosphazenes.  

National Technical Information Service (NTIS)

Polyphosphazenes represent a new approach to the design and synthesis of side-chain liquid crystal polymers. Polyphosphazenes are inorganic main-chain polymers consisting of alternating phosphorus-nitrogen atoms in the main chain with two substituents att...

R. E. Singler R. A. Willingham C. Noel C. Friedrich L. Bosio

1990-01-01

349

Bioenergy supply chains and stakeholders  

Microsoft Academic Search

What are the management challenges and opportunities of bio-energy chains for both running their business efficiently and\\u000a effectively and fostering the relationships with most relevant external stakeholders? This question is approached by systematically\\u000a reviewing papers at the interface of bio-energy and supply chain or logistics issues. The review conducted as content analysis\\u000a is based on an analytic framework that conceives

Stefan Gold

2011-01-01

350

Cosmic ray gradients in the heliosphere and particle drifts  

NASA Technical Reports Server (NTRS)

K-coronameter, solar wind, and neutron monitor data are used to estimate the latitudinal gradient of protons of approximately 5 GeV in the heliosphere at 1 AU during 1965 and 1975. The reversal of sign of the gradient between 1965 and 1975 and the strong positive latitudinal gradient in 1975 predicted by models in which drifts are dominant are not observed.

Newkirk, G., Jr.; Lockwood, J. A.

1981-01-01

351

Direct Numerical Simulation of a Turbulent Flow with Pressure Gradients  

NASA Astrophysics Data System (ADS)

Flows with favorable pressure gradient (FPG) and adverse pressure gradient (APG) are of great importance practically and theoretically. In practice, many industrial applications, especially aerodynamics, involve flows with pressure gradients and separation. In theory, wall shear stress does not dominate this type of flow[8].Much remains not understood.

Wei, Liang; Pollard, Andrew

352

Learning sparse gradients for variable selection and dimension reduction  

Microsoft Academic Search

Variable selection and dimension reduction are two commonly adopted approaches for high-dimensional data analysis, but have traditionally been treated separately. Here we propose an integrated approach, called sparse gradient learning (SGL), for variable selection and dimension reduction via learning the gradients of the prediction function directly from samples. By imposing a sparsity constraint on the gradients, variable selection is achieved

Gui-Bo Ye; Xiaohui Xie

2010-01-01

353

Cracks in gradient elastic bodies with surface energy  

Microsoft Academic Search

In the present paper the effect of higher order gradients on the structure of line-crack tips is determined. In particular we introduce in the constitutive equations of the linear deformation of an elastic solid a volumetric energy term, which includes the contribution of the strain gradient, and a surface energy gradient dependent term and then determine the effect of these

G. Exadaktylos; I. Vardoulakis; E. Aifantis

1996-01-01

354

Defects in gradient micropolar elasticity—I: screw dislocation  

Microsoft Academic Search

A gradient micropolar elasticity is proposed based on first gradients of distortion and bend-twist tensors for an isotropic micropolar medium. This theory is an extension of the theory of micropolar elasticity with couple stresses together with gradient elasticity in a way that in addition to hyper stresses, hyper couple stresses also appear. In particular, the strain energy, besides its dependence

Markus Lazar; Gérard A. Maugin

2004-01-01

355

Induced charge electro-osmotic concentration gradient generator  

Microsoft Academic Search

Biomolecule gradients play an important role in the understanding of various biological processes. Typically, biological cells are exposed to linear and nonlinear concentration gradients and their response is studied for understanding cell growth, cell migration, and cell differentiation mechanisms. Recent studies have demonstrated the use of microfluidic devices for precise and stable concentration gradient generation. However, most of the reported

Mranal Jain; Anthony Yeung; K. Nandakumar

2010-01-01

356

Effects of pressure gradients on turbulent premixed flames  

Microsoft Academic Search

In most practical situations, turbulent premixed flames are ducted and, accordingly, subjected to externally imposed pressure gradients. These pressure gradients may induce strong modifications of the turbulent flame structure because of buoyancy effects between heavy cold fresh and light hot burnt gases. In the present work, the influence of a constant acceleration, inducing large pressure gradients, on a premixed turbulent

Denis Veynante; Thierry Poinsot

1997-01-01

357

Forest gradient response in Sierran landscapes: the physical template  

Microsoft Academic Search

Vegetation pattern on landscapes is the manifestation of physical gradients, biotic response to these gradients, and disturbances. Here we focus on the physical template as it governs the distribution of mixed-conifer forests in California's Sierra Nevada. We extended a forest simulation model to examine montane environmental gradients, emphasizing factors affecting the water balance in these summer-dry landscapes. The model simulates

Dean L. Urban; Carol Miller; Patrick N. Halpin; Nathan L. Stephenson

2000-01-01

358

Temperature Gradients and Clear-Air Turbulence Probabilities  

Microsoft Academic Search

From the end of October 1973 to the beginning of January 1974, Continental Airlines operated one of its Boeing 747 aircraft with special instrumentation for the study of clear-air turbulence (CAT). The observations were compared with satellite-derived radiance gradients, conventional temperature gradients from analyzed maps, and temperature gradients obtained from a Rosemount total air temperature sensor on the plane. The

Morris A. Bender; Hans A. Panofsky; C. A. Peslen

1976-01-01

359

Electric Charge Transfer Associated with Temperature Gradients in Ice  

Microsoft Academic Search

The development of electric potentials in ice crystals under the influence of temperature gradients is investigated both theoretically and experimentally. The maintenance of a steady temperature gradient across a piece of ice is accompanied by concentration gradients of H^+ and OH^- ions; because of the much greater mobility of H^+ ions, these diffuse more rapidly into the colder part of

J. Latham; B. J. Mason

1961-01-01

360

Master equation simulation analysis of immunostained Bicoid morphogen gradient  

Microsoft Academic Search

BACKGROUND: The concentration gradient of Bicoid protein which determines the developmental pathways in early Drosophila embryo is the best characterized morphogen gradient at the molecular level. Because different developmental fates can be elicited by different concentrations of Bicoid, it is important to probe the limits of this specification by analyzing intrinsic fluctuations of the Bicoid gradient arising from small molecular

Yu Feng Wu; Ekaterina Myasnikova; John Reinitz

2007-01-01

361

Gravity gradient preliminary investigations, part 2: Lunar tidal gravity gradients and stresses (exhibit C)  

NASA Technical Reports Server (NTRS)

Preliminary analysis of the gravity gradients associated with gravity tides on the moon caused by the earth indicates that the relative changes in the gradients are very irregular, and large, and about 15 times greater than those experienced on earth. Thus gradients, in preference to gravity tides themselves, may well be an important key in correlating tide effects with lunar transient events and moonquakes, and also in determining triggering mechanisms for crustal movement and faulting. Preliminary analysis of lunar crustal stresses and strains caused by lunar gravity tides indicates that these factors may be more direct causative agents or triggering mechanisms. In particular, the cubic dilation undergoes relatively large changes and is about 11 times greater on the moon than on earth. Thus it should be correspondingly more important.

Houston, M. H.; Thompson, L. G. D.

1971-01-01

362

Biogeochemistry of a temperate forest nitrogen gradient  

USGS Publications Warehouse

Wide natural gradients of soil nitrogen (N) can be used to examine fundamental relationships between plant–soil–microbial N cycling and hydrologic N loss, and to test N-saturation theory as a general framework for understanding ecosystem N dynamics. We characterized plant production, N uptake and return in litterfall, soil gross and net N mineralization rates, and hydrologic N losses of nine Douglas-fir (Pseudotsuga menziesii) forests across a wide soil N gradient in the Oregon Coast Range (USA). Surface mineral soil N (0–10 cm) ranged nearly three-fold from 0.29% to 0.78% N, and in contrast to predictions of N-saturation theory, was linearly related to 10-fold variation in net N mineralization, from 8 to 82 kg N·ha?1·yr?1. Net N mineralization was unrelated to soil C:N, soil texture, precipitation, and temperature differences among sites. Net nitrification was negatively related to soil pH, and accounted for ?1·yr?1. Aboveground net primary production per unit net N mineralization varied inversely with soil N, suggesting progressive saturation of plant N demands at high soil N. Hydrologic N losses were dominated by dissolved organic N at low-N sites, with increased nitrate loss causing a shift to dominance by nitrate at high-N sites, particularly where net nitrification exceeded plant N demands. With the exception of N mineralization patterns, our results broadly support the application of the N-saturation model developed from studies of anthropogenic N deposition to understand N cycling and saturation of plant and microbial sinks along natural soil N gradients. This convergence of behavior in unpolluted and polluted forest N cycles suggests that where future reductions in deposition to polluted sites do occur, symptoms of N saturation are most likely to persist where soil N content remains elevated.

Perakis, Steven S.; Sinkhorn, Emily R.

2011-01-01

363

Spin Gradient Demagnetization Cooling of Ultracold Atoms  

SciTech Connect

We demonstrate a new cooling method in which a time-varying magnetic field gradient is applied to an ultracold spin mixture. This enables preparation of isolated spin distributions at positive and negative effective spin temperatures of {+-}50 pK. The spin system can also be used to cool other degrees of freedom, and we have used this coupling to cool an apparently equilibrated Mott insulator of rubidium atoms to 350 pK. These are the lowest temperatures ever measured in any system. The entropy of the spin mixture is in the regime where magnetic ordering is expected.

Medley, Patrick; Weld, David M.; Miyake, Hirokazu; Pritchard, David E.; Ketterle, Wolfgang [MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2011-05-13

364

Biogeochemistry of a temperate forest nitrogen gradient.  

PubMed

Wide natural gradients of soil nitrogen (N) can be used to examine fundamental relationships between plant-soil-microbial N cycling and hydrologic N loss, and to test N-saturation theory as a general framework for understanding ecosystem N dynamics. We characterized plant production, N uptake and return in litterfall, soil gross and net N mineralization rates, and hydrologic N losses of nine Douglas-fir (Pseudotsuga menziesii) forests across a wide soil N gradient in the Oregon Coast Range (U.S.A.). Surface mineral soil N (0-10 cm) ranged nearly three-fold from 0.29% to 0.78% N, and in contrast to predictions of N-saturation theory, was linearly related to 10-fold variation in net N mineralization, from 8 to 82 kg N.ha(-1) x yr(-1). Net N mineralization was unrelated to soil C:N, soil texture, precipitation, and temperature differences among sites. Net nitrification was negatively related to soil pH, and accounted for <20% of net N mineralization at low-N sites, increasing to 85-100% of net N mineralization at intermediate- and high-N sites. The ratio of net: gross N mineralization and nitrification increased along the gradient, indicating progressive saturation of microbial N demands at high soil N. Aboveground N uptake by plants increased asymptotically with net N mineralization to a peak of approximately 35 kg N.ha(-1) x yr(-1). Aboveground net primary production per unit net N mineralization varied inversely with soil N, suggesting progressive saturation of plant N demands at high soil N. Hydrologic N losses were dominated by dissolved organic N at low-N sites, with increased nitrate loss causing a shift to dominance by nitrate at high-N sites, particularly where net nitrification exceeded plant N demands. With the exception of N mineralization patterns, our results broadly support the application of the N-saturation model developed from studies of anthropogenic N deposition to understand N cycling and saturation of plant and microbial sinks along natural soil N gradients. This convergence of behavior in unpolluted and polluted forest N cycles suggests that where future reductions in deposition to polluted sites do occur, symptoms of N saturation are most likely to persist where soil N content remains elevated. PMID:21870622

Perakis, Steven S; Sinkhorn, Emily R

2011-07-01

365

Alternating-Gradient Photodetector For Far Infrared  

NASA Technical Reports Server (NTRS)

Proposed detector of photons of wavelengths in range of 30 to 200 micrometer made of alternating layers of lightly and heavily negatively doped germanium. Formed in sequence by conventional chemical-vapor deposition. Alternating-gradient structure enhances collection of photogenerated charge carriers while suppressing dark current, thus achieving high detectivity. Alternating layers of n+ and n- germanium provides high detectivity in far-infrared spectral region. Also possible to make similar structures with positive doping and with other semiconductors as silicon or gallium arsenide to obtain various spectral response.

Overhauser, Albert W.; Maserjian, Joseph

1989-01-01

366

New challenges in biogeochemical gradient research  

NASA Astrophysics Data System (ADS)

At a recent workshop focusing on biogeochemical gradients predominantly in groundwater and sediments, 32 North American and German scientists discussed research needs in three areas including (1) redox and microbes; (2) contaminants, isotopes, and fluxes; and (3) instruments, monitoring, and modeling.The presentation topics at the workshop at the Eberhard Karls University of Tübingen in Germany ranged from new concepts for monitoring contaminant attenuation, microgradients, microbial and abiotic recycling of iron and arsenic, porous media characterization, modeling in marine and groundwater environments, and stable isotope as well as radioisotope techniques.

Barth, Johannes A. C.; Kappler, Andreas; Piepenbrink, Matthias; Werth, Charles; Regenspurg, Simona; Semprini, Lewis; Slater, Gregory F.; Schüth, Christoph; Grathwohl, Peter

367

A Compact High Gradient Pulsed Magnetic Quadpole  

SciTech Connect

A design for a high gradient, low inductance pulsed quadrupole magnet is presented. The magnet is a circular current dominated design with a circular iron return yoke. Conductor angles are determined by a method of direct multipole elimination which theoretically eliminates the first four higher order multipole field components. Coils are fabricated from solid round film-insulated conductor, wound as a single layer ''non-spiral bedstead'' coil having a diagonal leadout entirely within one upturned end. The coils are wound and stretched straight in a special winder, then bent in simple fixtures to form the upturned ends.

Shuman, D.; Faltens, A.; Kajiyama, Y.; Kireeff-Covo, M.; Seidl, P.

2005-07-05

368

New techniques for studying calcium gradients  

NASA Technical Reports Server (NTRS)

Improved techniques for detecting and manipulating spatial gradients of cytosolic free Ca(2+) concentrations (Ca(2)) sub i and intracellular stores are discussed. Three areas of progress are: (1) development of new fluorescent indicators for Ca(2+) that are the first to be suitable for measuring Ca(2+)) sub i and its inhomogeneities in individual cells; (2) invention of photolabile chelators which shift irreversibly from high to low affinity for Ca(2+) upon illumination, permitting light-controlled jumps in (Ca(2+)) sub i; and (3) fixation methods to trap dynamic intraorganellar Ca stores in a form readily visible by electron microscopy.

Tsien, R. Y.

1985-01-01

369

Linear chains and chain-like fractals from electrostatic heteroaggregation.  

PubMed

The internal structure of materials prepared by aggregation of oppositely charged polystyrene spheres (electrostatic heteroaggregation) is investigated by static light scattering, optical microscopy, and Brownian dynamics simulation. Light scattering indicates ultralow mass fractal dimensions, as low as 1.2. Such low fractal dimensions, approaching the theoretical limit of a linear object, imply a chaining mechanism. Optical micrographs reveal linear chains with the particle charge alternating down the chains. Brownian dynamics simulation gives additional support for a chaining mechanism. For the polystyrene system (120-nm primary particle diameters), the fractal dimension is found to increase from 1.2 to 1.7 as the background electrolyte is increased. In terms of electrostatic screening, the results match those reported recently for larger polystyrene spheres. The low fractal dimensions appear to represent a crossover from linear chains to a structure of diffusion-limited aggregates; however, experiments under density-neutral conditions imply that sedimentation plays an important role in the formation of ultralow fractal dimensions. The practical implication is that microcomposites with a locally uniform distribution of starting materials and almost any degree of branching can be prepared from oppositely charged particles. PMID:12742045

Kim, Anthony Y; Hauch, Kip D; Berg, John C; Martin, James E; Anderson, Robert A

2003-04-01

370

Temperature gradient effects in electromigration using an extended transition probability model and temperature gradient free tests. I. Transition probability model  

Microsoft Academic Search

Temperature gradient effects incorporated in electromigration are examined via the movement of vacancies. To explain the movement of metal ions or vacancies, an extended transition probability model with temperature gradients and vacancy concentration gradients is compared with the usual drift-diffusion model including the equation of continuity and the Einstein relationship. The self-consistent constant vacancy source boundary condition for repeated SWEAT

Kim Jonggook; V. C. Tyree; C. R. Crowell

1999-01-01

371

Interferometric measurement of the refractive-index gradient distribution in gradient-index optical blanks  

NASA Astrophysics Data System (ADS)

A new interferometric method for measuring the refractive-index distribution in a plane-parallel section cut from a gradient-index lens blank is described. A standard double-pass interferometric scheme modified to provide a single pass of the beam through the investigated gradient-index sample is used. The two-dimensional variation of the refractive index in dimensions transverse to the sample surface is measured with an accuracy of better than 1 \\times 10-4. interferometry, nondestructive testing, refractometry, optical properties, index of refraction.

Gerasimova, L. A.

1996-06-01

372

Effect of Temperature Gradient on Thick Film Selective Emitter Emittance  

NASA Technical Reports Server (NTRS)

A temperature gradient across a thick (greater than or equal to .1 mm) film selective emitter will produce a significant reduction in the spectral emittance from the no temperature gradient case. Thick film selective emitters of rare earth doped host materials such as yttrium-aluminum-garnet (YAG) are examples where temperature gradient effects are important. In this paper a model is developed for the spectral emittance assuming a linear temperature gradient across the film. Results of the model indicate that temperature gradients will result in reductions the order of 20% or more in the spectral emittance.

Chubb, Donald L.; Good, Brian S.; Clark, Eric B.; Chen, Zheng

1997-01-01

373

Controlled mobility of unmanned aircraft chains to optimize network capacity in realistic communication environments  

NASA Astrophysics Data System (ADS)

This dissertation presents a decentralized gradient-based mobility control algorithm for the formation and maintenance of an optimal end-to-end communication chain using a team of unmanned aircraft acting as communication relays. With the use of unmanned aircraft (UA) as communication relays, a common mode of operation is to form a communication relay chain between a lead exploring node (which may be ground based or another UA) and a control station. In this type of operation the lead node is typically deployed to explore (sense) a remote region of interest that is beyond direct radio frequency (RF) communication range, or out of line-of-sight, to the control station. To provide non-line-of-sight service, and extend the communication range of the lead node, unmanned aircraft acting as communication relays are deployed in a convoy fashion behind the lead vehicle to form a cascaded relay chain. The focus of this work is the use of the mobility of a fixed number of relay aircraft to maximize the capacity of a directed communication chain from a source node to a destination node. Local objective functions are presented that use the signal-to-noise-and-interference ratio (SNIR) of neighbor communication links as inputs to maximize the end-to-end capacity of packet-based and repeater-type network chains. An adaptive gradient-based SNIR controller using the local objective function can show significant improvement in the capacity of the communication chain that is not possible with range-based controllers, or static deployment strategies, in RF environments containing unknown localized noise sources and terrain effects. Since the SNIR field is unknown, an online estimate of the SNIR field gradient is formed using methods of Stochastic Approximation from the orbital motion of the aircraft tracking a control point. Flight demonstrations using the Networked Unmanned Aircraft System Command, Control and Communications testbed were conducted to validate the controller presented herein. Results from flight experiments show that mobility of unmanned aircraft, following locally estimated SNIR gradients, can be used to form a locally optimized communication chain by driving the aircraft to locations that improve the end-to-end capacity of the chain over that of a range-based controller or a static deployment algorithm.

Dixon, Cory

374

METALLICITY GRADIENTS AND GAS FLOWS IN GALAXY PAIRS  

SciTech Connect

We present the first systematic investigation into the metallicity gradients in galaxy close pairs. We determine the metallicity gradients for eight galaxies in close pairs using H II region metallicities obtained with high signal-to-noise multi-slit observations with the Keck LRIS Spectrograph. We show that the metallicity gradients in close pairs are significantly shallower than gradients in isolated spiral galaxies such as the Milky Way, M83, and M101. These observations provide the first solid evidence that metallicity gradients in interacting galaxies are systematically different from metallicity gradients in isolated spiral galaxies. Our results suggest that there is a strong relationship between metallicity gradients and the gas dynamics in galaxy interactions and mergers.

Kewley, Lisa J.; Rupke, David; Jabran Zahid, H. [Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Hilo, HI 96822 (United States); Geller, Margaret J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Barton, Elizabeth J., E-mail: kewley@ifa.hawaii.ed [University of California, Irvine, CA 92697 (United States)

2010-09-20

375

Bacterial chemotaxis in linear and nonlinear steady microfluidic gradients  

PubMed Central

Diffusion-based microfluidic devices can generate steady, arbitrarily shaped chemical gradients without requiring fluid flow and are ideal for studying chemotaxis of free-swimming cells such as bacteria. However, if microfluidic gradient generators are to be used to systematically study bacterial chemotaxis, it is critical to evaluate their performance with actual quantitative chemotaxis tests. We characterize and compare three diffusion-based gradient generators by confocal microscopy and numerical simulations, select an optimal design and apply it to chemotaxis experiments with Escherichia coli in both linear and nonlinear gradients. Comparison of the observed cell distribution along the gradients with predictions from an established mathematical model shows very good agreement, providing the first quantification of chemotaxis of free-swimming cells in steady nonlinear microfluidic gradients and opening the door to bacterial chemotaxis studies in gradients of arbitrary shape.

Ahmed, Tanvir; Shimizu, Thomas S.; Stocker, Roman

2010-01-01

376

Shape optimization of pressure gradient microphones  

NASA Technical Reports Server (NTRS)

Recently developed finite element computer programs were utilized to investigate the influence of the shape of a body on its scattering field with the aim of determining the optimal shape for a Pressure Gradient Microphone (PGM). Circular cylinders of various aspect ratios were evaluated to choose the length to diameter ratio best suited for a dual element PGM application. Alterations of the basic cylindrical shape by rounding the edges and recessing at the centerline were also studied. It was found that for a + or - 1 db deviation from a linear pressure gradient response, a circular cylinder of aspect ratio near 0.5 was most suitable, yielding a useful upper frequency corresponding to ka = 1.8. The maximum increase in this upper frequency limit obtained through a number of shape alterations was only about 20 percent. An initial experimental evaluation of a single element cylindrical PGM of aspect ratio 0.18 utilizing a piezoresistive type sensor was also performed and is compared to the analytical results.

Norum, T. D.; Seiner, J. M.

1977-01-01

377

Gradient navigation model for pedestrian dynamics  

NASA Astrophysics Data System (ADS)

We present a microscopic ordinary differential equation (ODE)-based model for pedestrian dynamics: the gradient navigation model. The model uses a superposition of gradients of distance functions to directly change the direction of the velocity vector. The velocity is then integrated to obtain the location. The approach differs fundamentally from force-based models needing only three equations to derive the ODE system, as opposed to four in, e.g., the social force model. Also, as a result, pedestrians are no longer subject to inertia. Several other advantages ensue: Model-induced oscillations are avoided completely since no actual forces are present. The derivatives in the equations of motion are smooth and therefore allow the use of fast and accurate high-order numerical integrators. At the same time, the existence and uniqueness of the solution to the ODE system follow almost directly from the smoothness properties. In addition, we introduce a method to calibrate parameters by theoretical arguments based on empirically validated assumptions rather than by numerical tests. These parameters, combined with the accurate integration, yield simulation results with no collisions of pedestrians. Several empirically observed system phenomena emerge without the need to recalibrate the parameter set for each scenario: obstacle avoidance, lane formation, stop-and-go waves, and congestion at bottlenecks. The density evolution in the latter is shown to be quantitatively close to controlled experiments. Likewise, we observe a dependence of the crowd velocity on the local density that compares well with benchmark fundamental diagrams.

Dietrich, Felix; Köster, Gerta

2014-06-01

378

A selection of high gradient cavity experiments  

SciTech Connect

In the two years since the 7th SRF workshop, a variety of cavity tests have been carried out with the objective to reproducibly achieve surface electric rf fields above 40 MV/m with no or only very little electron loading. This paper reports about a collection of tests on single cell and multi-cell cavities, which received standard surface treatments such as buffered chemical polishing and high pressure ultrapure water rinsing, but no heat treatments. Often the cavities were limited by quenches, posting a limit of 700 to 1,000 Oersted on achievable peak magnetic fields of high purity niobium RRR values between 200 and 250. In a seamless single cell cavity fabricated by V. Palmieri of INFN Legnaro by spinning, a very promising gradient of E{sub acc}=25 MV/m was measured. In collaboration with CERN, several tests on sputtering niobium prepared at CERN were also carried out, and accelerating gradients up to 25 MV/m were achieved. A single cell cavity, electron beam welded after electrochemical buffing, showed only good performance--E{sub p} > 50 MV/m--after the removal of more than 100 {micro}m of material. However, this cavity showed rather heavy Q disease even when cooled down rapidly; the Q degradation could be partially reversed by diffusing the oxygen from an anodized Nb{sub 2}O{sub 5} layer into the niobium by heating the cavity in-situ at T=250 C.

Peter Kneisel

1998-01-01

379

Nappe emplacement under lateral pressure gradient  

NASA Astrophysics Data System (ADS)

New thin viscous approximation is under development specifically targeted to model spontaneous initiation and tens of kilometers horizontal displacement of tectonic nappes. Nappes are few kilometers thing and tens of kilometers long rock units trusted towards foreland often preserving internal lithological consistency and laying at near horizontal position at the end of the emplacement. Significant shear stresses and deviation of principal stresses from vertical is required to explain this very peculiar strain localization style from mechanical point of view. There is also a need for the explanation of their common appearances in most collisional settings. Both pure shear thin sheet and flexural models kinematically eliminate nappes formation. Spreading viscous sheet models, such as used to model glaciers, are also not applicable as the direction of motion is upward, against gravity. The reason for this discrepancy is the hydrostatic pressure approximation of the gravity-driven spreading models. Actually, the thin sheet approximation is not sensitive to the assumptions made on pressure profile. Lateral non-lithostatic pressure gradient-driven viscous sheet model is appropriate for modeling of nappes. In turn, significant non-lithostatic pressure must be supported by flexural rigidity of overlying and underlying units. Lateral gradients of this non-lithostatic pressure are responsible for the significant shear stress and, therefore, deviation of principal stress from vertical.

Podladchikov, Yury; Schmalholz, Stefan

2014-05-01

380

Intergenerational and socioeconomic gradients of child obesity.  

PubMed

Can the rise in obesity among children be attributed to the intergenerational transmission of parental influences? Does this trend affect the influence of parent's socioeconomic status on obesity? This paper documents evidence of an emerging social gradient of obesity in pre-school children resulting from a combination of both socio-economic status and less intensive childcare associated with maternal employment, when different forms of intergenerational transmission are controlled for. We also estimate and decompose income related inequalities in child obesity. We take advantage of a uniquely constructed dataset from Spain that contains records form 13,358 individuals for a time period (years 2003-2006) in which a significant spike in the growth of child obesity was observed. Our results suggest robust evidence of both socioeconomic and intergenerational gradients. Results are suggestive of a high income effect in child obesity, alongside evidence that income inequalities have doubled in just three years with a pure income effect accounting for as much as 72-66% of these income inequality estimates, even when intergenerational transmission is accounted for. Although, intergenerational transmission does not appear to be gender specific, when accounted for, mother's labour market participation only explains obesity among boys but not among girls. Hence, it appears income and parental influences are the central determinants of obesity among children. PMID:23906118

Costa-Font, Joan; Gil, Joan

2013-09-01

381

Magnetic Advection due to Diffusivity Gradients  

NASA Astrophysics Data System (ADS)

We have derived the advection of magnetic fields in plasmas, due to gradients in diffusivity, for a completely general case. Magnetic diffusivity is proportional to electrical resistivity. Where the value of this parameter is high, it is well known that magnetic fields can leak (or diffuse) rapidly into (or out) of the plasma. Where gradients are high, i.e. the diffusivity changes rapidly in space, magnetic fields can experience enhanced advection. We derive this phenomenon rigorously, and discuss its implications, e.g. for the solar dynamo. We also find that this magnetic advection can be expressed in terms of a diffusion equation within the induction equation, making its computational implementation especially simple. We present results of simulations of the effect generated with a magnetohydrodynamic model. We are grateful to Tom Bogdan for discussions about the mathematical derivation, and to Neal Hurlburt for the use of his MHD code. This work was supported in part by Evergreen's Sponsored Research Program, and by NSF grant 0807651. We are grateful to HAO/NCAR in Boulder, CO and Lockheed Martin Solar and Astrophysics Lab in Palo Alto, CA for their support during the performance of this work.

Zita, E. J.

2011-01-01

382

The multigrid preconditioned conjugate gradient method  

NASA Technical Reports Server (NTRS)

A multigrid preconditioned conjugate gradient method (MGCG method), which uses the multigrid method as a preconditioner of the PCG method, is proposed. The multigrid method has inherent high parallelism and improves convergence of long wavelength components, which is important in iterative methods. By using this method as a preconditioner of the PCG method, an efficient method with high parallelism and fast convergence is obtained. First, it is considered a necessary condition of the multigrid preconditioner in order to satisfy requirements of a preconditioner of the PCG method. Next numerical experiments show a behavior of the MGCG method and that the MGCG method is superior to both the ICCG method and the multigrid method in point of fast convergence and high parallelism. This fast convergence is understood in terms of the eigenvalue analysis of the preconditioned matrix. From this observation of the multigrid preconditioner, it is realized that the MGCG method converges in very few iterations and the multigrid preconditioner is a desirable preconditioner of the conjugate gradient method.

Tatebe, Osamu

1993-01-01

383

From supply chain to demand chain: the role of lead time reduction in improving demand chain performance  

Microsoft Academic Search

To improve demand chain performance, is it better for parties in a supply chain to focus first on lead time reduction, or instead concentrate on improving the transfer of demand information upstream in the chain? Even though the theory of supply and demand chain management suggests that lead time reduction is an antecedent to the use of market mediation (i.e.,

Suzanne de Treville; Roy D. Shapiro; Ari-Pekka Hameri

2004-01-01

384

Pumpernickel Valley Geothermal Project Thermal Gradient Wells  

SciTech Connect

The Pumpernickel Valley geothermal project area is located near the eastern edge of the Sonoma Range and is positioned within the structurally complex Winnemucca fold and thrust belt of north-central Nevada. A series of approximately north-northeast-striking faults related to the Basin and Range tectonics are superimposed on the earlier structures within the project area, and are responsible for the final overall geometry and distribution of the pre-existing structural features on the property. Two of these faults, the Pumpernickel Valley fault and Edna Mountain fault, are range-bounding and display numerous characteristics typical of strike-slip fault systems. These characteristics, when combined with geophysical data from Shore (2005), indicate the presence of a pull-apart basin, formed within the releasing bend of the Pumpernickel Valley – Edna Mountain fault system. A substantial body of evidence exists, in the form of available geothermal, geological and geophysical information, to suggest that the property and the pull-apart basin host a structurally controlled, extensive geothermal field. The most evident manifestations of the geothermal activity in the valley are two areas with hot springs, seepages, and wet ground/vegetation anomalies near the Pumpernickel Valley fault, which indicate that the fault focuses the fluid up-flow. There has not been any geothermal production from the Pumpernickel Valley area, but it was the focus of a limited exploration effort by Magma Power Company. In 1974, the company drilled one exploration/temperature gradient borehole east of the Pumpernickel Valley fault and recorded a thermal gradient of 160oC/km. The 1982 temperature data from five unrelated mineral exploration holes to the north of the Magma well indicated geothermal gradients in a range from 66 to 249oC/km for wells west of the fault, and ~283oC/km in a well next to the fault. In 2005, Nevada Geothermal Power Company drilled four geothermal gradient wells, PVTG-1, -2, -3, and -4, and all four encountered geothermal fluids. The holes provided valuable water geochemistry, supporting the geothermometry results obtained from the hot springs and Magma well. The temperature data gathered from all the wells clearly indicates the presence of a major plume of thermal water centered on the Pumpernickel Valley fault, and suggests that the main plume is controlled, at least in part, by flow from this fault system. The temperature data also defines the geothermal resource with gradients >100oC/km, which covers an area a minimum of 8 km2. Structural blocks, down dropped with respect to the Pumpernickel Valley fault, may define an immediate reservoir. The geothermal system almost certainly continues beyond the recently drilled holes and might be open to the east and south, whereas the heat source responsible for the temperatures associated with this plume has not been intersected and must be at a depth greater than 920 meters (depth of the deepest well – Magma well). The geological and structural setting and other characteristics of the Pumpernickel Valley geothermal project area are markedly similar to the portions of the nearby Dixie Valley geothermal field. These similarities include, among others, the numerous, unexposed en echelon faults and large-scale pull-apart structure, which in Dixie Valley may host part of the geothermal field. The Pumpernickel Valley project area, for the majority of which Nevada Geothermal Power Company has geothermal rights, represents a geothermal site with a potential for the discovery of a relatively high temperature reservoir suitable for electric power production. Among locations not previously identified as having high geothermal potential, Pumpernickel Valley has been ranked as one of four sites with the highest potential for electrical power production in Nevada (Shevenell and Garside, 2003). Richards and Blackwell (2002) estimated the total heat loss and the preliminary production capacity for the entire Pumpernickel Valley geothermal system to be at 35MW. A more conservative estimate, for

Z. Adam Szybinski

2006-01-01

385

Polymer chains in four dimensions  

NASA Astrophysics Data System (ADS)

We investigate analytically the asymptotic logarithmic behavior in four dimensions ( d = 4) of very long continuous polymer chains with excluded volume, described by the two-parameter Edwards model. Using renormalization theory, we calculate directly all the connected partition functions LN of N polymer chains in this model, and obtain their logarithmic expression, including the subleading order. To first order, they are found in the universal form LN ˜ S 2( N-1) ( ln S) hNwithhN = {1}/{4}(2- N) , and where S is the Brownian area of the chains, given in terms of their Brownian radius ° R, by ° R2 = dS. The partition functions L1, L2, L3, L4, and the averageend-to-end square distance R2, and square radius of gyration RG2 are calculated up to logarithmic sub-subleading order. The virial expansion in 4d of the osmotic pressure is obtained. For semi-dilute solutions, the logarithmic correction to Edwards' tree approximation for the osmotic pressure is calculated, and we find the new result ?? ? C2/?ln C, where C is the monomer concentration. We give in 4d a set of geometrical quantities, characterizing a single chain: the form factor, the average 2 nth power R[2 n] of the end-to-end distance, the average 2 nth radius of gyration RG[2 n] , and their universal ratio. We also consider in 4d the probability distribution for the internal distances inside a chain.

Duplantier, Bertrand

1986-10-01

386

Influence of petroleum deposit geometry on local gradient of electron acceptors and microbial catabolic potential.  

PubMed

A field survey was conducted following the Deepwater Horizon blowout and it was noted that resulting coastal petroleum deposits possessed distinct geometries, ranging from small tar balls to expansive horizontal oil sheets. A subsequent laboratory study evaluated the effect of oil deposit geometry on localized gradients of electron acceptors and microbial community composition, factors that are critical to accurately estimating biodegradation rates. One-dimensional top-flow sand columns with 12-h simulated tidal cycles compared two contrasting geometries (isolated tar "balls" versus horizontal "sheets") relative to an oil-free control. Significant differences in the effluent dissolved oxygen and sulfate concentrations were noted among the columns, indicating presence of anaerobic zones in the oiled columns, particularly in the sheet condition. Furthermore, quantification of genetic markers of terminal electron acceptor and catabolic processes via quantitative polymerase chain reaction of dsrA (sulfate-reduction), mcrA (methanogenesis), and cat23 (oxygenation of aromatics) genes in column cores suggested more extensive anaerobic conditions induced by the sheet relative to the ball geometry. Denaturing gradient gel electrophoresis similarly revealed that distinct gradients of bacterial communities established in response to the different geometries. Thus, petroleum deposit geometry impacts local dominant electron acceptor conditions and may be a key factor for advancing attenuation models and prioritizing cleanup. PMID:22574781

Singh, Gargi; Pruden, Amy; Widdowson, Mark A

2012-06-01

387

GradientOptimizer: An open-source graphical environment for calculating optimized gradients in reversed-phase liquid chromatography.  

PubMed

We here present GradientOptimizer, an intuitive, lightweight graphical user interface to design nonlinear gradients for separation of peptides by reversed-phase liquid chromatography. The software allows to calculate three types of nonlinear gradients, each of them optimizing a certain retention time distribution of interest. GradientOptimizer is straightforward to use, requires minimum processing of the input files, and is supported under Windows, Linux, and OS X platforms. The software is open-source and can be downloaded under an Apache 2.0 license at https://github.com/statisticalbiotechnology/NonlinearGradientsUI. PMID:24700534

Moruz, Luminita; Käll, Lukas

2014-06-01

388

Modeling of polypeptide chains as C alpha chains, C alpha chains with C beta, and C alpha chains with ellipsoidal lateral chains.  

PubMed

In an effort to reduce the number of degrees of freedom necessary to describe a polypeptide chain we analyze the statistical behavior of polypeptide chains when represented as C alpha chains, C alpha chains with C beta atoms attached, and C alpha chains with rotational ellipsoids as models of side chains. A statistical analysis on a restricted data set of 75 unrelated protein structures is performed. The comparison of the database distributions with those obtained by model calculation on very short polypeptide stretches allows the dissection of local versus nonlocal features of the distributions. The database distribution of the bend angles of polypeptide chains of pseudo bonded C alpha atoms spans a restricted range of values and shows a bimodal structure. On the other hand, the torsion angles of the C alpha chain may assume almost all possible values. The distribution is bimodal, but with a much broader probability distribution than for bend angles. The C alpha - C beta vectors may be taken as representative of the orientation of the lateral chain, as the direction of the bond is close to the direction of the vector joining C alpha to the ad hoc defined center of the "steric mass" of the side chain. Interestingly, both the bend angle defined by C alpha i-C alpha i+1-C beta i+1 and the torsional angle offset of the pseudo-dihedral C alpha i-C alpha i+1-C alpha i+2-C beta i+2 with respect to C alpha i-C alpha i+1-C alpha i+2-C alpha i+3 span a limited range of values. The latter results show that it is possible to give a more realistic representation of polypeptide chains without introducing additional degrees of freedom, i.e., by just adding to the C alpha chain a C beta with given side-chain properties. However, a more realistic description of side chains may be attained by modeling side chains as rotational ellipsoids that have roughly the same orientation and steric hindrance. To this end, we define the steric mass of an atom as proportional to its van der Waals volume and we calculate the side-chain inertia ellipsoid assuming that the steric mass of each atom is uniformly distributed within its van der Waals volume. Finally, we define the rotational ellipsoid representing the side chain as the uniform density ellipsoid possessing the same rotationally averaged inertia tensor of the side chain. The statistics of ellipsoid parameters support the possibility of representing a side chain via an ellipsoid, independently of the local conformation. To make this description useful for molecular modeling we describe ellipsoid-ellipsoid interactions via a Lennard-Jones potential that preserves the repulsive core of the interacting ellipsoids and takes into account their mutual orientation. Tests are performed for two different forms of the interaction potential on a set of high-resolution protein structures. Results are encouraging, in view of the drastic simplifications that were introduced. PMID:8785277

Fogolari, F; Esposito, G; Viglino, P; Cattarinussi, S

1996-03-01

389

Macrophage response to methacrylate conversion using a gradient approach.  

PubMed

Incomplete conversion, an ongoing challenge facing photopolymerized methacrylate-based polymers, affects leachables as well as the resulting polymer network. As novel polymers and composites are developed, methods to efficiently screen cell response to these materials and their properties, including conversion, are needed. In this study, an in vitro screening methodology was developed to assess cells cultured directly on cross-linked polymer networks. A gradient in methacrylate double bond conversion was used to increase the experimental throughput. A substrate of 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl] propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) was prepared with a conversion ranging from 43.0% to 61.2%. Substrates aged for 7 days had no significant differences in surface roughness or hydrophilicity as a function of conversion. Leachables were detectable for at least 7 days using UV absorption, but their global cytotoxicity was insignificant after 5 days of aging. Thus, RAW 264.7 macrophage-like cells were cultured on aged substrates to evaluate the cell response to conversion, with possible contributions from the polymer network and local leachables. Conversions of 45% and 50% decreased viability (via calcein/ethidium staining) and increased apoptosis (via annexin-V staining). No significant changes (p>0.05) in tumor necrosis factor-alpha and interleukin-1beta gene expression, as measured by quantitative, real-time reverse transcription-polymerase chain reaction, were seen as conversion increased. Thus, conversions greater than 50% are recommended for equimolar BisGMA/TEGDMA. The ability to distinguish cell response as a function of conversion is useful as an initial biological screening platform to optimize dental polymers. PMID:17140868

Lin, Nancy J; Bailey, LeeAnn O; Becker, Matthew L; Washburn, Newell R; Henderson, Lori A

2007-03-01

390

Precise Nanoelectronics with Adatom Chains  

NASA Technical Reports Server (NTRS)

Adatom chains on an atomically regulated substrate will be building components in future precise nanoelectronics. Adatoms need to be secured with chemical bonding, but then electronic isolation between the adatom and substrate systems is not guaranteed. A one-dimensional model shows that good isolation with existence of surface states is expected on an s-p crossing substrate such as Si, Ge, or GaAs, reflecting the bulk nature of the substrate. Isolation is better if adatoms are electronically similar to the substrate atoms, and can be manipulated by hydrogenation. Chain structures with group IV adatoms with two chemical bonds, or group III adatoms with one chemical bond, are semiconducting, reflecting the surface nature of the substrate. These structures are unintentionally doped due to the charge transfer across the chemical bonds. Physical properties of adatom chains have to be determined for the unified adatom-substrate system.

Yamada, Toshishige

1999-01-01

391

Ligand chain length conveys thermochromism.  

PubMed

Thermochromic properties of a series of non-ionic copper compounds have been reported. Herein, we demonstrate that Cu(ii) ion with straight-chain primary amine (A) and alpha-linolenic (fatty acid, AL) co-jointly exhibit thermochromic properties. In the current case, we determined that thermochromism becomes ligand chain length-dependent and at least one of the ligands (A or AL) must be long chain. Thermochromism is attributed to a balanced competition between the fatty acids and amines for the copper(ii) centre. The structure-property relationship of the non-ionic copper compounds Cu(AL)2(A)2 has been substantiated by various physical measurements along with detailed theoretical studies based on time-dependent density functional theory. It is presumed from our results that the compound would be a useful material for temperature-sensor applications. PMID:24943491

Ganguly, Mainak; Panigrahi, Sudipa; Chandrakumar, K R S; Sasmal, Anup Kumar; Pal, Anjali; Pal, Tarasankar

2014-08-14

392

Decision models in global supply chain management  

Microsoft Academic Search

Integrative decision making is key to effective supply chain management (SCM). This article examines five illustrative supply chain decision models that demonstrate the importance of integrating the decisions across the supply chain. The models that are discussed illustrate the diversity of analytical approaches and their usefulness in managing global supply chain issues. The paper identifies potential areas of additional research

Ram Narasimhan; Santosh Mahapatra

2004-01-01

393

Chain teleportation via partially entangled states  

NASA Astrophysics Data System (ADS)

We investigate chain teleportation with some nonmaximally entangled channels. The efficiencies of two chain teleportation protocols, the separate chain teleportation protocol (SCTP) and the global chain teleportation protocol (GCTP), are calculated. In SCTP the errors are corrected between every step while in GCTP the errors are corrected only at the end. We show that GCTP is more efficient than SCTP.

Wang, M. Y.; Yan, F. L.

2009-07-01

394

Chain Stores, Consumer Mobility, and Market Structure  

Microsoft Academic Search

Homogeneous products are often sold by chains and locals but the chains charge higher prices. We explain this pricing pattern as well as the empirical fact that chains became increasingly dominant at the same time as consumer mobility increased: Consumers bear setup costs whenever they visit a firm for the first time. A chain operating stores in all locations insures

Simon Loertscher; Yves Schneider

2011-01-01

395

Integrating environmental management and supply chain strategies  

Microsoft Academic Search

The decisions related to managing the supply chain and supply chain strategy are already considered important in many organizations. As more executives adopt envi- ronmental practices, supply chain strategies will only increase in importance. In this paper, we review how companies develop environmental supply chain strategies. Our interviews with companies from The United States, The United Kingdom, Japan and Korea,

Robert Handfield; Robert Sroufe; Steven Walton

2005-01-01

396

Supply chain contract under product cost disruption  

Microsoft Academic Search

Supply chain contracts, as the effective supply chain coordination mechanism, have been extensively investigated in the literature under the stationary setting. We consider a supply chain involving one supplier and one retailer in which a revenue-sharing contract is adopted. Though the supply chain can obtain coordination under the stationary setting using this contract, but emergent and unforeseeable accidents maybe occur,

Caihong Sun; Hui Yu

2005-01-01

397

Finite sample effect in temperature gradient focusing.  

PubMed

Temperature gradient focusing (TGF) is a new and promising equilibrium gradient focusing method which can provide high concentration factors for improved detection limits in combination with high-resolution separation. In this technique, temperature-dependent buffer chemistry is employed to generate a gradient in the analyte electrophoretic velocity. By the application of a convective counter-flow, a zero-velocity point is created within a microchannel, at which location the ionic analytes accumulate or focus. In general, the analyte concentration is small when compared with buffer ion concentrations, such that the focusing mechanism works in the ideal, linearized regime. However, this presumption may at times be violated due to significant sample concentration growth or the use of a low-concentration buffer. Under these situations the sample concentration becomes non-negligible and can induce strong nonlinear interactions with buffer ions, which eventually lead to peak shifting and distortion, and the loss of detectability and resolution. In this work we combine theory, simulation, and experimental data to present a detailed study on nonlinear sample-buffer interactions in TGF. One of the key results is the derivation of a generalized Kohlrausch regulating function (KRF) that is valid for systems in which the electrophoretic mobilities are not constant but vary spatially. This generalized KRF greatly facilitates analysis, allowing reduction of the problem to a single equation describing sample concentration evolution, and is applicable to other problems with heterogeneous electrophoretic mobilities. Using this sample evolution equation we have derived an understanding of the nonlinear peak deformation phenomenon observed experimentally in TGF. We have used numerical simulations to validate our theory and to quantitatively predict TGF. Our simulation results demonstrate excellent agreement with experimental data, and also indicate that the proper inclusion of Taylor dispersion is important for the accurate modeling of TGF. This work is an important first step towards the understanding and prediction of the more complex, nonlinear, and multi-species interactions which often occur in on-chip electrophoretic assays such as TGF. PMID:18497919

Lin, Hao; Shackman, Jonathan G; Ross, David

2008-06-01

398

Leading a supply chain turnaround.  

PubMed

Just five years ago, salespeople at Whirlpool were in the habit of referring to their supply chain organization as the "sales disablers." Now the company excels at getting products to the right place at the right time--while managing to keep inventories low. How did that happen? In this first-person account, Reuben Slone, Whirlpool's vice president of Global Supply Chain, describes how he and his colleagues devised the right supply chain strategy, sold it internally, and implemented it. Slone insisted that the right focal point for the strategy was the satisfaction of consumers at the end of the supply chain. Most supply chain initiatives do the opposite: They start with the realities of a company's manufacturing base and proceed from there. Through a series of interviews with trade customers large and small, his team identified 27 different capabilities that drove industry perceptions of Whirlpool's performance. Knowing it was infeasible to aim for world-class performance across all of them, Slone weighed the costs of excelling at each and found the combination of initiatives that would provide overall competitive advantage. A highly disciplined project management office and broad training in project management were key to keeping work on budget and on benefit. Slone set an intense pace--three "releases" of new capabilities every month--that the group maintains to this day. Lest this seem like a technology story, however, Slone insists it is just as much a "talent renaissance." People are proud today to be part of Whirlpool's supply chain organization, and its new generation of talent will give the company a competitive advantage for years to come. PMID:15559580

Slone, Reuben E

2004-10-01

399

Supply chain management practices in toy supply chains  

Microsoft Academic Search

Purpose – Innovative products usually experience highly unpredictable and variable demand. This is especially valid for the volatile and seasonal toy industry, which produces high obsolete inventory, lost sales and markdown. In such a volatile industry, what supply chain management (SCM) practices are applicable and effective? This study seeks to explore SCM practices, and identify practical and theoretical gaps in

Chee Yew Wong; Jan Stentoft Arlbjørn; John Johansen

2005-01-01

400

Gradients of meteorological parameters in convective and nonconvective areas  

NASA Technical Reports Server (NTRS)

Horizontal gradients of geopotential height, temperature, and wind speed were computed at the 850-, 700-, 500-, and 200-mb levels. Mixing ratio gradients also were computed, but only for the 850-, 700-, and 500-mb levels. Rawinsonde data was provided at 3- to 6-h intervals. Cumulative frequency distributions and statistical parameters showed that the variability and magnitude of the gradients decreased as the gradients were computed over progressively longer distances. Most frequency distributions were positively skewed, and the standard deviations of the gradient distributions were roughly half as large as the means. An examination of the differences of gradients observed in convective and nonconvective areas was made after convective areas were determined objectively using Manually Digitized Radar data. The gradients of height, wind speed, and mixing ratio at 850 mb were larger in convective than nonconvective areas. No general relationship held for the meteorological variables at other levels. Intensive examination of the gradients observed near squall lines revealed typical gradient patterns and trends in the magnitudes of the gradients associated with convective systems.

Mccown, M. S.; Scoggins, J. R.

1977-01-01

401

Gradient estimation in dendritic reinforcement learning  

PubMed Central

We study synaptic plasticity in a complex neuronal cell model where NMDA-spikes can arise in certain dendritic zones. In the context of reinforcement learning, two kinds of plasticity rules are derived, zone reinforcement (ZR) and cell reinforcement (CR), which both optimize the expected reward by stochastic gradient ascent. For ZR, the synaptic plasticity response to the external reward signal is modulated exclusively by quantities which are local to the NMDA-spike initiation zone in which the synapse is situated. CR, in addition, uses nonlocal feedback from the soma of the cell, provided by mechanisms such as the backpropagating action potential. Simulation results show that, compared to ZR, the use of nonlocal feedback in CR can drastically enhance learning performance. We suggest that the availability of nonlocal feedback for learning is a key advantage of complex neurons over networks of simple point neurons, which have previously been found to be largely equivalent with regard to computational capability.

2012-01-01

402

Collimation testing using coherent gradient sensing  

NASA Astrophysics Data System (ADS)

In the present communication, an application of coherent gradient sensing (CGS) for collimation testing of an optical beam has been proposed. In the path of the beam to be tested, a set of two identical linear Ronchi gratings is introduced. The diffracted orders from the two gratings traveling in the same direction are isolated using spatial filtering arrangement. The resulting laterally sheared wavefronts carry information regarding the defocusing errors. The grating rotation mechanism has been incorporated for collimation setting. The results of experimental investigation are presented. Improved accuracy and precision has been achieved because the requirement of maintaining the grating separation to be equal to self-imaging distance as in Talbot interferometry has been alleviated.

Dhanotia, Jitendra; Prakash, Shashi

2011-09-01

403

Molecular evolution and the latitudinal biodiversity gradient  

PubMed Central

Species density is higher in the tropics (low latitude) than in temperate regions (high latitude) resulting in a latitudinal biodiversity gradient (LBG). The LBG must be generated by differential rates of speciation and/or extinction and/or immigration among regions, but the role of each of these processes is still unclear. Recent studies examining differences in rates of molecular evolution have inferred a direct link between rate of molecular evolution and rate of speciation, and postulated these as important drivers of the LBG. Here we review the molecular genetic evidence and examine the factors that might be responsible for differences in rates of molecular evolution. Critical to this is the directionality of the relationship between speciation rates and rates of molecular evolution.

Dowle, E J; Morgan-Richards, M; Trewick, S A

2013-01-01

404

Experimental demonstration of gradient index plasmonics  

NASA Astrophysics Data System (ADS)

Plasmonics is an emerging field essential for bridging nanoelectronics and diffraction-limited photonics. One central objective of plasmonics research is modifying the propagation of surface plasmon polaritons (SPPs) in order to implement diverse functionalities in the context of two-dimensional optics. Here, we demonstrate an effective approach to manipulate SPPs by adiabatically tailoring the topology of a dielectric layer adjacent to a metal surface using grey-scale lithography. In such a way, we are able to continuously modify the propagation constant of SPPs, analogous to traditional gradient index optics. Applying this method, we design and experimentally demonstrate two different devices: a plasmonic Luneburg lens to focus SPPs and a plasmonic Eaton lens to bend SPPs.ootnotetextT. Zentgraf*, Y. Liu*, M. H. Mikkelsen*, J. Valentine, X. Zhang, Submitted, (2010) Our approach has the potential to achieve low-loss functional plasmonic elements and provides a scheme to realize more complex structures using transformation optics.

Mikkelsen, Maiken H.; Zentgraf, Thomas; Liu, Yongmin; Valentine, Jason; Zhang, Xiang

2011-03-01

405

Constant field gradient planar coupled cavity structure  

DOEpatents

A cavity structure having at least two opposing planar housing members spaced apart to accommodate the passage of a particle beam through the structure between the members. Each of the housing members have a plurality of serially aligned hollows defined therein, and also passages, formed in the members, which interconnect serially adjacent hollows to provide communication between the hollows. The opposing planar housing members are spaced and aligned such that the hollows in one member cooperate with corresponding hollows in the other member to form a plurality of resonant cavities aligned along the particle beam within the cavity structure. To facilitate the obtaining of a constant field gradient within the cavity structure, the passages are configured so as to be incrementally narrower in the direction of travel of the particle beam. In addition, the spacing distance between the opposing housing members is configured to be incrementally smaller in the direction of travel of the beam.

Kang, Yoon W. (Naperville, IL); Kustom, Robert L. (Oswego, IL)

1999-01-01

406

Constant field gradient planar coupled cavity structure  

DOEpatents

A cavity structure is disclosed having at least two opposing planar housing members spaced apart to accommodate the passage of a particle beam through the structure between the members. Each of the housing members have a plurality of serially aligned hollows defined therein, and also passages, formed in the members, which interconnect serially adjacent hollows to provide communication between the hollows. The opposing planar housing members are spaced and aligned such that the hollows in one member cooperate with corresponding hollows in the other member to form a plurality of resonant cavities aligned along the particle beam within the cavity structure. To facilitate the obtaining of a constant field gradient within the cavity structure, the passages are configured so as to be incrementally narrower in the direction of travel of the particle beam. In addition, the spacing distance between the opposing housing members is configured to be incrementally smaller in the direction of travel of the beam. 16 figs.

Kang, Y.W.; Kustom, R.L.

1999-07-27

407

Gradient coupling in isolated intestinal cells  

SciTech Connect

Work with isolated intestinal cells summarized below shows that: (1) an answer to the energetic adequacy question for Na/sup +/-dependent transport systems cannot be provided unless solute fluxes by all routes are taken into account; (2) the conventional view of transport efficiency is in fact a measure of membrane leakiness to solute rather than a measure of innate efficiency for the Na/sup +/-dependent carrier; (3) uncontrolled sugar-induced changes in membrane potential introduce a systematic error in measurements of the Na/sup +/:sugar coupling stoichiometry; (4) with appropriate control of the membrane potential the measured coupling ratio is 2 Na/sup +/ per sugar molecule; and (5) a 2:1 coupling ratio allows for theoretical maximum sugar gradients of several hundred fold via a mechanism sharply dependent on the membrane potential.

Kimmich, G.A.

1981-08-01

408

A gradient model for Timoshenko nanobeams  

NASA Astrophysics Data System (ADS)

The elastostatic problem of a Timoshenko nanobeam is formulated by a new constitutive behaviour of gradient-type. Unlike previous approaches which directly substitute the expression of the nonlocal stress into the classical equilibrium equations, the proposed model starts from a nonlocal thermodynamic formulation. A suitable definition of the expression for the internal energy provides the variational formulation of Timoshenko nanobeams in terms of rotations and transverse displacements so that a higher-order system of ordinary differential equations is consistently obtained with the corresponding boundary conditions. Different from other nonlocal models, the solutions indicate that the stiffness of nanobeams is significantly increased at smaller scales due to size effects. The solutions corresponding to local models are perfectly obtained as a special case of the nonlocal ones.

Marotti de Sciarra, Francesco; Barretta, Raffaele

2014-08-01

409

Gradient estimation in dendritic reinforcement learning.  

PubMed

We study synaptic plasticity in a complex neuronal cell model where NMDA-spikes can arise in certain dendritic zones. In the context of reinforcement learning, two kinds of plasticity rules are derived, zone reinforcement (ZR) and cell reinforcement (CR), which both optimize the expected reward by stochastic gradient ascent. For ZR, the synaptic plasticity response to the external reward signal is modulated exclusively by quantities which are local to the NMDA-spike initiation zone in which the synapse is situated. CR, in addition, uses nonlocal feedback from the soma of the cell, provided by mechanisms such as the backpropagating action potential. Simulation results show that, compared to ZR, the use of nonlocal feedback in CR can drastically enhance learning performance. We suggest that the availability of nonlocal feedback for learning is a key advantage of complex neurons over networks of simple point neurons, which have previously been found to be largely equivalent with regard to computational capability. PMID:22657827

Schiess, Mathieu; Urbanczik, Robert; Senn, Walter

2012-01-01

410

Plasma density gradient measurement using laser deflection  

SciTech Connect

For a given chord through a plasma, changes in the line integrated index of refraction as a result of a transverse density gradient can be observed by measuring the angle of deflection of a laser beam. In contrast to laser interferometers, this method of density profile measurement places modest requirements on laser quality and alignment procedures, allowing measurements to be conducted with short coherence length commercial laser diodes and segmented photodiode detectors. A prototype implementation of this scheme has been constructed and tested on the compact toroid injection experiment (CTIX). At densities comparable to magnetic fusion plasmas, laser deflections in the nanoradian range were measured. By assuming a particular density profile, a sensitivity of {approx}10{sup 12} cm{sup -3}/nrad was obtained. This produced estimates of CTIX peak density in reasonable agreement with conventional interferometry data. The final goal of this diagnostic is a simple, reliable, array deployable density profile diagnostic.

Brockington, Samuel J.E.; Horton, Robert D.; Hwang, David Q.; Evans, Russell W.; Howard, Stephen J.; Thio, Y.C. Francis [Department of Electrical and Computer Engineering, University of California at Davis, Davis, California (United States); Department of Applied Science, University of California at Davis, Livermore, California (United States); Office of Fusion Energy Sciences, SC-24/Germantown Building, U S. Department of Energy, 1000 Independence Avenue, SW, Washington, DC 20585-1290 (United States)

2005-06-15

411

The Curlometer and Other Gradient Based Methods  

NASA Astrophysics Data System (ADS)

The magnetic field measurements on the four Cluster spacecraft can be combined to produce a determination of the electric current density, j, point by point in time, from Ampere's law, i.e., through an estimate of the curl of the magnetic field, B, assuming the displacement current may be neglected (an assumption nearly always true in space plasmas). This combination of spatial gradients is named the Curlometer technique, first introduced by Dunlop et al. [1988], and first used on Cluster measurements by Dunlop et al. [2002b]. Although estimates of current density from single and dual spacecraft have been attempted in the past [e.g. van Allen and Adnan, 1992] (a simple 1-D current layer, sampled from an individual spacecraft, can at least give an estimate of the current magnitude), these estimates also depend on accurate knowledge of relative orientation and motion in order to obtain positions within a current layer (the finite region where the cur- rent density is distributed). The Curlometer technique independently estimates the current vector at each time in the data stream and can be understood in a number of different ways, as outlined in Chapters 12, 14, 15, and 16 of ISSI SR-001. In using the Curlometer, a clear understanding of the associated caveats is important, the main one being that only linear estimates of B and B can be made. Multi-spacecraft analysis also depends upon temporal behaviour, and most methods assume some degree of stationarity in their interpretation. The Curlometer is an important part of the analysis of spatial gradients as measured by four spacecraft, and this general problem was addressed in part in ISSI SR- 001. A number of additional methods have since been introduced which are also based on the use of spatial gradients and we also deal briefly with these below, or reference them. The four Cluster spacecraft fly in an evolving configuration, which repeats every or- bit (apart from minor perturbations), but which has been changed at intervals during the mission to cover a large range of spacecraft separation distances (100-10,000 km) at the magnetopause and in the magnetotail. The results presented here therefore have been con- firmed over a variety of spatial scales, and have been used in a number of different investigations, and below we list those papers that have used the technique in these circumstances. Through these studies, an understanding of the applicability of the method has developed. For example, the thickness of a planar current layer can be accurately estimated from its magnetic profile at each spacecraft and the corresponding boundary crossing times; the latter also giving a determination of boundary motion relative to the Cluster array, which scales the corresponding current profile through the current layer. The estimate of electric current density can be representative even when the configuration of Cluster spacecraft approaches the thickness of the current layer and minimum variance analysis on the Curlometer measurements can estimate the current normal. The other gradient methods can be used to calculate a number of other properties, such as the dimensionality of the structure.

Dunlop, Malcolm W.; Eastwood, Jonathan P.

412

Gradient Measurements of Nitrous Acid (hono)  

NASA Astrophysics Data System (ADS)

Nitrous acid (HONO) plays an important role in photochemical air pollution due to its photodissociation by solar UV radiation into hydroxyl radicals and thus significantly enhances photooxidation processes. Furthermore, HONO is an important indoor pol- lutant, which can react with amines leading to nitrosamines, which are known to be carcinogenic. Despite its importance in atmospheric chemistry the mechanisms lead- ing to HONO formation are still not completely understood at present. Although it is commonly proposed that HONO is formed by heterogeneous processes, i.e. by the conversion of NO2 on wet surfaces, it is still under discussion whether HONO produc- tion is dominated by the surface of particles or by the ground surface. Simultaneous vertical profile measurements of HONO, the precursor NO2 and the aerosol surface area, which could answer this question are not available at present. Accordingly, in the present study night-time HONO, NO2 and particle surface area gradients in the altitude range 10-190 m were measured on the meteorological tower at the Forschungszentrum Karlsruhe/Germany using a new, very sensitive HONO in- strument (LOPAP), a commercial NOx monitor and a SMPS system. For all gradient measurements during the campaign it was observed that the [HONO]/[NO2] ratio decreased with increasing altitude. In contrast, the particle sur- face area was found to be more or less constant. Accordingly, no correlation between the [HONO]/[NO2] ratio and the particle surface area was observed showing that HONO formation was dominated by processes on ground surfaces and that signifi- cant HONO formation on particle surfaces could be excluded for the measurement site.

Kleffmann, J.; Kurtenbach, R.; Lörzer, J.; Wiesen, P.; Kalthoff, N.; Vogel, B.; Vogel, H.

413

High-gradient compact linear accelerator  

DOEpatents

A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter.

Carder, Bruce M. (205 Rogue River Hwy., Gold Hill, OR 97525)

1998-01-01

414

High-gradient compact linear accelerator  

DOEpatents

A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter. 10 figs.

Carder, B.M.

1998-05-26

415

Subduction Plate Characterization from GOCE Gravity Gradients  

NASA Astrophysics Data System (ADS)

The study of subduction zones, i.e. regions where one tectonic plate moves under another and sinks into the mantle, is a fundamental topic in many Earth related sciences. Among others it is required in tectonophysics to model Earthquakes, it is useful in petrology and it is a basic information to study the Earth crust by means of gravity observations. In the present work the possibility of characterizing a subduction zone by exploiting GOCE gravity gradients is investigated. In particular GOCE along orbit-filtered gravity gradients are first reduced for the effect of the oceans, ice sheets and sediments. After that, the subduction zone is approximately delimited and for the observation points falling in this zone, the effect of ';a normal crust', i.e. a crust without subduction anomalies, is estimated by kriging extrapolating the surrounding residual signal. A further reduction for this normal crust effect is performed, thus isolating the gravitational effect of the subducting crust. By using a simulated annealing procedure, the isolated signal is finally fitted with the gravitational effect of a dipping prism, characterized by a set of parameters defining the prism position, size and its dipping and striking angles. The whole procedure has been firstly tested on a close-loop scenario to assess the performance of the simulating annealing algorithm in detecting the parameters used to generate the reference signal; then the procedure has been applied to real data to study the Tonga subduction. The close-loop simulation has shown the good efficiency of the proposed approach that is able of estimating the unknown prism parameters with a relative accuracy lower than 10% even in presence of noise. As for the Tonga subduction, the estimated model seems to confirm the geometry already proposed in literature.

Mansi, A. H.; Reguzzoni, M.; Sampietro, D.

2013-12-01

416

Molecular Simulation of Main-Chain and Side-Chain Liquid Crystalline Polymers  

Microsoft Academic Search

Main-chain liquid crystalline polymers (LCP) have a rigid polymer chain or rigid groups at intervals within the chain. The rigid groups cause the overall polymer chain to be elongated form the normal random coil configuration. Modelling can be performed on a single molecule and after energy minimisation and molecular dynamics, the ratio of the chain length to diameter can be

Dumitru Pavel; Jolanta Lagowski; Robert Shanks; Xiangen Han

2004-01-01

417

Closing Loops in Supply Chain Management: Designing Reverse Supply Chains for End-of-Life Vehicles  

Microsoft Academic Search

Closed-loop supply chain management is the extension of forward supply chains with a reverse supply chain (reverse logistics) and is concerned with the integration of key business processes to create additional value for all players in the forward and the reverse supply chain. Traditional supply chains aim at optimization of customer service and costs until the point of sales; closed-loop

H. M. le Blanc

2006-01-01

418

A global supply chain framework  

Microsoft Academic Search

The relationship between supply chain competencies and performance has been somewhat elusive. The 21st Century Logistics framework, developed at Michigan State University is currently assessed as to its global relevance, particularly relating to performance. A sample of U.S. firms is compared to a sample of Australian and New Zealand firms to assess the robustness of the framework across different business

David J Closs; Diane A Mollenkopf

2004-01-01

419

The linked dipole chain MC  

SciTech Connect

We are working on a full-scale Monte Carlo simulation program [1] for describing e-p collisions. This MC is based on the Linked Dipole Chain (LDC) model which, in turn, is a modification and generalization of the CCFM model. Here I will start by explaining the basic model, then describe the MC-implementation and finish with some preliminary results.

Kharraziha, Hamid [Department of Theoretical Physics, Lund University (Sweden)

1997-04-20

420

Spin chains and string theory  

Microsoft Academic Search

Recently, an impressive agreement was found between anomalous dimen- sions of certain operators in N = 4 SYM and rotating strings with two angular mo- menta in the bulk of AdS5 × S5. A one-loop field theory computation, which involves solving a Heisenberg chain by means of the Bethe ansatz agrees with the large angular momentum limit of a rotating

Martin Kruczenski

421

Theory of localized synfire chain  

Microsoft Academic Search

Neuron is a noisy information processing unit and conventional view is that information in the cortex is carried on the rate of neurons spike emission. More recent studies on the activity propagation through the homogeneous network have demonstrated that signals can be transmitted with millisecond fidelity; this model is called the Synfire chain and suggests the possibility of the spatio-temporal

Kosuke Hamaguchi; Masato Okada; Kazuyuki Aihara

2004-01-01

422

Gumdrop Chains and Shrinky Necklaces  

NSDL National Science Digital Library

In this activity, learners thread gumdrops together to make a model of a polymer. Then they thread the chains together to mimic crosslinks, and discover how crosslinked polymers act differently than uncrosslinked ones. Use this activity to illustrate about the various structures of polymers.

Watkiss, Gina

2003-01-01

423

Theory of Disordered Ising Chains.  

National Technical Information Service (NTIS)

The disordered Ising chain is considered. It is shown that for zero magnetic field the replicas method of Edwards and Anderson is exact and requires a specific type of fluctuation of the interaction parameters, excluding the spin-glass state. Linear renor...

I. Z. Kostadinov I. V. Petrov T. Sariisky

1977-01-01

424

Order estimation of Markov chains  

Microsoft Academic Search

We describe estimatorsn(X0,X1,...,Xn), which when applied to an unknown stationary process taking values from a countable al- phabet X, converge almost surely to k in case the process is a k-th order Markov chain and to infinity otherwise.

Gusztáv Morvai; Benjamin Weiss

2005-01-01

425

Chain-Ring Coding Method.  

National Technical Information Service (NTIS)

The article considers a coding method on the basis of a binary code, with which correcting properties are obtained without using a large number of supplementary digits. The method is based on the formation of a chain-ring group sequence possessing the fol...

I. A. Nabiev M. S. Granovskii

1968-01-01

426

Verifying Continuous Time Markov Chains  

Microsoft Academic Search

. We present a logical formalism for expressing properties ofcontinuous time Markov chains. The semantics for such properties ariseas a natural extension of previous work on discrete time Markov chainsto continuous time. The major result is that the verification problemis decidable; this is shown using results in algebraic and transcendentalnumber theory.IntroductionRecent work on formal verification has addressed systems with stochastic

Adnan Aziz; Kumud Sanwal; Vigyan Singhal; Robert K. Brayton

1996-01-01

427

Convection driven generation of long-range material gradients  

PubMed Central

Natural materials exhibit anisotropy with variations in soluble factors, cell distribution, and matrix properties. The ability to recreate the heterogeneity of the natural materials is a major challenge for investigating cell-material interactions and for developing biomimetic materials. Here we present a generic fluidic approach using convection and alternating flow to rapidly generate multi-centimeter gradients of biomolecules, polymers, beads and cells and cross-gradients of two species in a microchannel. Accompanying theoretical estimates and simulations of gradient growth provide design criteria over a range of material properties. A poly(ethyleneglycol) hydrogel gradient, a porous collagen gradient and a composite material with a hyaluronic acid/gelatin cross-gradient were generated with continuous variations in material properties and in their ability to regulate cellular response. This simple yet generic fluidic platform should prove useful for creating anisotropic biomimetic materials and high-throughput platforms for investigating cell-microenvironment interaction.

Du, Yanan; Hancock, Matthew J.; He, Jiankang; Villa-Uribe, Jose; Wang, Ben; Cropek, Donald M.; Khademhosseini, Ali

2009-01-01

428

Advantage of nonlinear axial gradients in optical design  

NASA Astrophysics Data System (ADS)

Recent advances in axial gradient material fabrication via the diffusion of glass plates has opened the door to a wide variety of optical design applications incorporating entire lenses of gradient index material. A proprietary software-driven process developed at LightPath Technologies Inc. creates gradient index glass by fusing together a stack of discrete glass plates, where each constituent plate has a distinctive composition and desired optical properties. LightPath's ability to prescribe large optical index changes (up to 0.47) throughout a glass substrate of virtually any diameter and thickness (macro gradient), invokes an interesting question: what are the properties of a solid gradient index lens and how can these properties be used most efficiently and effectively? This paper reports on a parametric study of third order spherical aberration vs. shape factor, for a macro gradient F/3 singlet lens whose index varies by +/- 0.4 in linear, quadratic and cubic profiles.

Manhart, Paul K.; Castle, Kenneth R.; Ruda, Mitchell C.; Stuhlinger, Tilman W.

1993-11-01

429

Design of a High Thermal Gradient Bridgman Furnace  

NASA Technical Reports Server (NTRS)

The Advanced Automated Directional Solidification Furnace (AADSF) is a Bridgman-Stockbarger microgravity processing facility, designed and manifested to first fly aboard the second United States Microgravity Payload (USMP-2) Space Shuttle mission. The AADSF was principally designed to produce high axial thermal gradients, and is particularly suitable for metals solidification experiments, including non-dilute alloys. To accommodate a wider range of experimental conditions, the AADSF is equipped with a reconfigurable gradient zone. The overall design of the AADSF and the relationship between gradient zone design and furnace performance are described. Parametric thermal analysis was performed and used to select gradient zone design features that fulfill the high thermal gradient requirements of the USMP-2 experiment. The thermal model and analytical procedure, and parametric results leading to the first flight gradient zone configuration, are presented. Performance for the USMP-2 flight experiment is also predicted, and analysis results are compared to test data.

LeCroy, J. E.; Popok, D. P.

1994-01-01

430

COMPARISON OF GKS CALCULATED CRITICAL ION TEMPERATURE GRADIENTS AND ITG GROWTH RATES TO DIII-D MEASURED GRADIENTS AND DIFFUSIVITIES  

SciTech Connect

OAK-B135 The gyrokinetic equations predict that various drift type waves or modes can be unstable in a tokamak. For some of these modes, such as the ion temperature gradient (ITG) mode and the electron temperature gradient mode, there exists a critical gradient, above which the mode is unstable. Since the existence of unstable modes can cause increased transport, plasmas which are centrally heated tend to increase in temperature gradient until the modes become unstable. Under some conditions the increased transport can fix the gradient at the critical value. here they present a comparison between the measured ion temperature gradients and the critical gradient as calculated by a gyrokinetic linear stability (GKS) code. They also present the maximum linear growth rate as calculated by this code for comparison to experimentally derived transport coefficients. The results show that for low confinement mode (L-mode) discharges, the measured ion temperature gradient is significantly greater than the GKS calculated critical gradient over a large region of the plasma. This is the same region of the plasma where the ion thermal diffusivity is large. For high confinement mode (H-mode) discharges the ion temperature gradient is closer to the critical gradient, but often still greater than the critical gradient over some region. For the best H-mode discharges, the ion temperature is less than or equal to the critical gradient over the whole plasma. In general they find that the position in the plasma where the ion thermal diffusivity starts to increase rapidly is where the maximum linear growth rate is greater than the E x B shearing rate.

BAKER,DR; STAEBLER,GM; PETTY,CC; GREENFIELD,CM; LUCE,TC

2003-04-01

431

Parameter inference for discretely observed stochastic kinetic models using stochastic gradient descent  

PubMed Central

Background Stochastic effects can be important for the behavior of processes involving small population numbers, so the study of stochastic models has become an important topic in the burgeoning field of computational systems biology. However analysis techniques for stochastic models have tended to lag behind their deterministic cousins due to the heavier computational demands of the statistical approaches for fitting the models to experimental data. There is a continuing need for more effective and efficient algorithms. In this article we focus on the parameter inference problem for stochastic kinetic models of biochemical reactions given discrete time-course observations of either some or all of the molecular species. Results We propose an algorithm for inference of kinetic rate parameters based upon maximum likelihood using stochastic gradient descent (SGD). We derive a general formula for the gradient of the likelihood function given discrete time-course observations. The formula applies to any explicit functional form of the kinetic rate laws such as mass-action, Michaelis-Menten, etc. Our algorithm estimates the gradient of the likelihood function by reversible jump Markov chain Monte Carlo sampling (RJMCMC), and then gradient descent method is employed to obtain the maximum likelihood estimation of parameter values. Furthermore, we utilize flux balance analysis and show how to automatically construct reversible jump samplers for arbitrary biochemical reaction models. We provide RJMCMC sampling algorithms for both fully observed and partially observed time-course observation data. Our methods are illustrated with two examples: a birth-death model and an auto-regulatory gene network. We find good agreement of the inferred parameters with the actual parameters in both models. Conclusions The SGD method proposed in the paper presents a general framework of inferring parameters for stochastic kinetic models. The method is computationally efficient and is effective for both partially and fully observed systems. Automatic construction of reversible jump samplers and general formulation of the likelihood gradient function makes our method applicable to a wide range of stochastic models. Furthermore our derivations can be useful for other purposes such as using the gradient information for parametric sensitivity analysis or using the reversible jump samplers for full Bayesian inference. The software implementing the algorithms is publicly available at http://cbcl.ics.uci.edu/sgd

2010-01-01

432

Molecular theories for chain fluids  

NASA Astrophysics Data System (ADS)

In this work, we derive two molecular models for chain molecules: (1)a hard-sphere model for binary mixtures; and (2)a variational theory for Lennard- Jones fluids. The ultimate objective is a practical engineering equation of state for real fluids to satisfy the industry's escalating demand for physical properties. Molecular models are supplanting empirical correlations because today's rigorous and competitive engineering climate demands accurate properties over ever-broadening ranges. Classical empirical correlations, such as Peng-Robinson, are becoming inadequate for today's sophisticated design tools, which now rely heavily on data bases and process simulators. Their primary disadvantage, in addition to the palpable dangers of extrapolation, is their inability to capture molecular structure. Molecular models, conversely, offer a offer theoretical framework which does capture the molecular structure so essential for characterizing chain molecules prevalent in petroleum, polymer and other industries. They comprise two broad categories: discontinuous and continuous. A simple example of the former is hard-spheres; of the latter is Lennard-Jones (LJ) fluids. In the first part of this work, we extend Chiew's [27, 28, 30] hard-sphere particle-particle framework to binary mixtures and derive average intermolecular correlation functions. Simulation data is presented and compared with theory. Lennard-Jones potentials are introduced, in the second part of this work, to overcome the limitations of hard- sphere theory, mainly its discontinuous nature and inability to account for attractive forces. The Helmholtz energy and pressure for single-component LJ chains were derived using variational perturbation theory. The reference system, comprising freely-jointed tangent hard- sphere-chains was solved in the PY approximation. The optimal segment diameter in the hard-sphere-chain reference was then found by minimizing the free energy through the Gibbs-Bogoliubov inequality. The optimal diameter depends on chain length, density and temperature. The theory exhibits excellent agreement with Monte Carlo (MC) simulation, over a wide range of conditions, without adjustable parameters. In a parallel work, we extended the variational theory to mixtures. Simulation data were obtained for binary LJ chain mixtures for a range of temperatures, chain lengths, and chain fractions, as well as LJ energy (3ij) and size (sij) parameters. Six physical systems were studied: 4- mer/4-mer, 4-mer/8-mer, and 8-mer/8-mer mixtures with 321/311 of 1.0 and 1.2, and s21/s11 of 1.0 and 1.5. All six systems were simulated at segment densities of 0.2, 0.4 and 0.8, reduced temperatures (T*) of 4 and 8 with chain fractions of 0, .2, .4, .6, .8, and 1. Good agreement is obtained between simulation and theory over a range of parameters and conditions.

O'Lenick, Richard

433

On the role of strain gradients in adiabatic shear banding  

Microsoft Academic Search

Summary The effect of higher order strain gradients on adiabatic shear banding is investigated by considering the simple shearing of a heat conducting thermoviscoplastic material with a gradient-dependent flow stress. The competition between the gradient-dependent plastic flow and heat conduction and their influence on the shear band width and structure are examined. Two internal length scales, i.e., the deformation internal

H. T. Zhu; H. M. Zbib

1995-01-01

434

Comparison of genetic algorithms with conjugate gradient methods  

NASA Technical Reports Server (NTRS)

Genetic algorithms for mathematical function optimization are modeled on search strategies employed in natural adaptation. Comparisons of genetic algorithms with conjugate gradient methods, which were made on an IBM 1800 digital computer, show that genetic algorithms display superior performance over gradient methods for functions which are poorly behaved mathematically, for multimodal functions, and for functions obscured by additive random noise. Genetic methods offer performance comparable to gradient methods for many of the standard functions.

Bosworth, J. L.; Foo, N. Y.; Zeigler, B. P.

1972-01-01

435

Effects of pressure gradients on turbulent premixed flames  

NASA Technical Reports Server (NTRS)

The influence of a constant acceleration on a turbulent premixed flame is studied by direct numerical simulation. This acceleration induces a mean pressure gradient across the flame brush, leading to a modification of the turbulent flame structure due to differential buoyancy mechanisms between heavy cold fresh and light hot burnt gases. Such a pressure gradient may be encountered in practical applications in ducted flames. A favorable pressure gradient, i.e. the pressure decreases from unburnt to burnt gases, is found to decrease the flame wrinkling, the flame brush thickness, and the turbulent flame speed. A favorable pressure gradient also promotes counter-gradient turbulent transport. On the other hand, adverse pressure gradients tend to increase the flame brush thickness and turbulent flame speed, and promote classical gradient turbulent transport. The balance equation for the turbulent flux of the Favre averaged progress variable is also analyzed. The first results show that the fluctuating pressure term, cannot be neglected as generally assumed in models. Simple models assuming that a high mean pressure gradient may only be balanced by the cross-dissipation term seem too approximate. This analysis has to be continued to compare simulation data and closure schemes proposed for the transport equation. The analysis developed by Veynante et al.(1995) has been extended to imposed acceleration and mean pressure gradients. A simple model for the turbulent flux is proposed and validated from simulation data. Then, a modified criterion is derived to delineate between counter-gradient and gradient turbulent diffusion. In fact, counter-gradient diffusion may occur in most practical applications, especially for ducted flames.

Veynante, D.; Poinsot, T.

1995-01-01

436

Effects of pressure gradients on turbulent premixed flames  

NASA Astrophysics Data System (ADS)

In most practical situations, turbulent premixed flames are ducted and, accordingly, subjected to externally imposed pressure gradients. These pressure gradients may induce strong modifications of the turbulent flame structure because of buoyancy effects between heavy cold fresh and light hot burnt gases. In the present work, the influence of a constant acceleration, inducing large pressure gradients, on a premixed turbulent flame is studied using direct numerical simulations.

Veynante, Denis; Poinsot, Thierry

1997-12-01

437

Gradient descent algorithms for quantile regression with smooth approximation  

Microsoft Academic Search

Gradient based optimization methods often converge quickly to a local optimum. However, the check loss function used by quantile\\u000a regression model is not everywhere differentiable, which prevents the gradient based optimization methods from being applicable.\\u000a As such, this paper introduces a smooth function to approximate the check loss function so that the gradient based optimization\\u000a methods could be employed for

Songfeng Zheng

438

Subaortic stenosis revisited: the importance of the dynamic pressure gradient.  

PubMed

Brachfeld and Gorlin's revised concept of subaortic stenosis derived from their recognition that the large magnitudes of the pressure gradients were incompatible with the relatively mild anatomic lesions found at surgery in 3 of their patients, and the rapidity of their arterial pulse upstroke. They proposed that a gradient caused by a superimposed systolic stenosis was responsible for the large pressure gradients and the overestimation of the severity of the discrete subaortic stenosis (DSAS). A fourth patient had no anatomic cause for the pressure gradient, and findings compatible with hypertrophic cardiomyopathy (HCM). All 4 patients had septal hypertrophy which they felt was instrumental in the brisk pulse contour and dynamic gradients across the outflow tract. In the ensuing decades, imaging techniques have been developed which permit detailed studies of ventricular ejection patterns in dynamic gradients associated with HCM and DSAS. These studies have been interpreted variously. The prevailing view is that there is a dynamic obstruction that increases progressively in severity during systole, as proposed by Brachfeld and Gorlin. An opposing view is that dynamic gradients can occur in the absence of any hindrance to ejection, and that these gradients instead result from rapid and complete emptying of the ventricle. Regardless of their cause, dynamic gradients are often superimposed upon gradients caused by DSAS and valvar aortic stenosis, leading to exaggerated estimates of severity. These dynamic gradients are uncovered when the anatomic cause of stenosis is removed, and seemingly increase the postoperative morbidity. A greater understanding of the significance of dynamic gradients and the mechanism(s) responsible for them should lead to more rational management of DSAS and HCM in the future. PMID:8231790

Criley, J M; Siegel, R J

1993-11-01

439

Vehicle detection combining gradient analysis and AdaBoost classification  

Microsoft Academic Search

This paper presents a real-time vision-based vehicle's rear detection system using gradient based methods and Adaboost classification, for ACC applications. Our detection algorithm consists of two main steps: gradient driven hypothesis generation and appearance based hypothesis verification. In the hypothesis generation step, possible target locations are hypothesized. This step uses an adaptive range-dependant threshold and symmetry for gradient maxima localization.

Ayoub Khammari; Fawzi Nashashibi; Yotam Abramson; Claude Laurgeau

2005-01-01

440

Supply chain challenges. building relationships.  

PubMed

Supply chain management is all about software and systems, right? Put in the best technology, sit back, and watch as your processes run smoothly and the savings roll in? Apparently not. When HBR convened a panel of leading thinkers in the field of supply chain management, technology was not top of mind. People and relationships were the dominant issues of the day. The opportunities and problems created by globalization, for example, are requiring companies to establish relationships with new types of suppliers. The ever-present pressure for speed and cost containment is making it even more important to break down stubbornly high internal barriers and establish more effective cross-functional relationships. The costs of failure have never been higher. The leading supply chain performers are applying new technology, new innovations, and process thinking to far greater advantage than the laggards, reaping tremendous gains in all the variables that affect shareholder value: cost, customer service, asset productivity, and revenue generation. And the gap between the leaders and the losers is growing in almost every industry. This roundtable gathered many of the leading thinkers and doers in the field of supply chain management, including practitioners Scott Beth of Intuit, Sandra Morris of Intel, and Chris Gopal of Unisys. David Burt of the University of San Diego and Stanford's Hau Lee bring the latest research from academia. Accenture's William Copacino and the Warren Company's Robert Porter Lynch offer the consultant's perspectives. Together, they take a wide-ranging view of such topics as developing talent, the role of the chief executive, and the latest technologies, exploring both the tactical and the strategic in the current state of supply chain management. PMID:12858712

Beth, Scott; Burt, David N; Copacino, William; Gopal, Chris; Lee, Hau L; Lynch, Robert Porter; Morris, Sandra

2003-07-01

441

Control of Hydrogen Photoproduction by the Proton Gradient Generated by Cyclic Electron Flow in Chlamydomonas reinhardtii[W  

PubMed Central

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H2 production is a transitory phenomenon under most natural conditions, often viewed as a safety valve protecting the photosynthetic electron transport chain from overreduction. From the colony screening of an insertion mutant library of the unicellular green alga Chlamydomonas reinhardtii based on the analysis of dark-light chlorophyll fluorescence transients, we isolated a mutant impaired in cyclic electron flow around photosystem I (CEF) due to a defect in the Proton Gradient Regulation Like1 (PGRL1) protein. Under aerobiosis, nonphotochemical quenching of fluorescence (NPQ) is strongly decreased in pgrl1. Under anaerobiosis, H2 photoproduction is strongly enhanced in the pgrl1 mutant, both during short-term and long-term measurements (in conditions of sulfur deprivation). Based on the light dependence of NPQ and hydrogen production, as well as on the enhanced hydrogen production observed in the wild-type strain in the presence of the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, we conclude that the proton gradient generated by CEF provokes a strong inhibition of electron supply to the hydrogenase in the wild-type strain, which is released in the pgrl1 mutant. Regulation of the trans-thylakoidal proton gradient by monitoring pgrl1 expression opens new perspectives toward reprogramming the cellular metabolism of microalgae for enhanced H2 production.

Tolleter, Dimitri; Ghysels, Bart; Alric, Jean; Petroutsos, Dimitris; Tolstygina, Irina; Krawietz, Danuta; Happe, Thomas; Auroy, Pascaline; Adriano, Jean-Marc; Beyly, Audrey; Cuine, Stephan; Plet, Julie; Reiter, Ilja M.; Genty, Bernard; Cournac, Laurent; Hippler, Michael; Peltier, Gilles

2011-01-01

442

Recent progress in macro axial gradient index optics (it's time to rethink gradients)  

NASA Astrophysics Data System (ADS)

Lenses whose material is represented by a line on the glass map (nd equals f((upsilon) d)), as opposed by a point, like homogeneous glass, open the door to a wide variety of optical design applications incorporating entire lenses of axial gradient refractive material (GRADIUM). This material essentially gives bi-aspheric performance to lenses with spherical surfaces and exhibits a controlled gradient in both index and dispersion. Thus, the applications for this material range from the simple singlet lens used for laser applications, in which spherical aberration is eliminated, to complex multi-element lens systems where improved overall performance is desired. The fusion/diffusion process that produces this material, is surprisingly simple, repeatable, and applicable to mass production. The advantage of GRADIUM and its accessibility in commercially available lens design programs, (ZEMAX, CODE V and OSLO), provides optical designers with the opportunity to push performance further than with conventional optics.

Manhart, Paul K.; Xu, Xiaojie

1995-08-01

443

A Gradient-generating Microfluidic Device for Cell Biology  

PubMed Central

The fabrication and operation of a gradient-generating microfluidic device for studying cellular behavior is described. A microfluidic platform is an enabling experimental tool, because it can precisely manipulate fluid flows, enable high-throughput experiments, and generate stable soluble concentration gradients. Compared to conventional gradient generators, poly(dimethylsiloxane) (PDMS)-based microfluidic devices can generate stable concentration gradients of growth factors with well-defined profiles. Here, we developed simple gradient-generating microfluidic devices with three separate inlets. Three microchannels combined into one microchannel to generate concentration gradients. The stability and shape of growth factor gradients were confirmed by fluorescein isothyiocyanate (FITC)-dextran with a molecular weight similar to epidermal growth factor (EGF). Using this microfluidic device, we demonstrated that fibroblasts exposed to concentration gradients of EGF migrated toward higher concentrations. The directional orientation of cell migration and motility of migrating cells were quantitatively assessed by cell tracking analysis. Thus, this gradient-generating microfluidic device might be useful for studying and analyzing the behavior of migrating cells.

Chung, Bong Geun; Manbachi, Amir; Saadi, Wajeeh; Lin, Francis; Jeon, Noo Li; Khademhosseini, Ali

2007-01-01

444

Gradient index plasmonic ring resonator with high extinction ratio  

NASA Astrophysics Data System (ADS)

We propose and investigate a compact gradient index plasmonic ring resonator (Grin PRR) with strong light confinement and extinction ratio based on finite element method (FEM). Theoretical simulation reveals that the change of index gradient influences the resonant frequency, Q factor and the mode volume. Significantly, it is demonstrated that the extinction ratio of Grin PRR can be optimized by varying the index gradient for any radius. Index gradient can enhance extinction ratio at settled size, so this structure has both high extinction ratio and smaller size footprint. It could be very promising for the high-density optical integration.

Zhou, Zidong; He, Pengbin; Xu, Jinyou; Zhuang, Xiujuan; Li, Yunyun; Pan, Anlian

2014-02-01

445

A gradient-generating microfluidic device for cell biology.  

PubMed

The fabrication and operation of a gradient-generating microfluidic device for studying cellular behavior is described. A microfluidic platform is an enabling experimental tool, because it can precisely manipulate fluid flows, enable high-throughput experiments, and generate stable soluble concentration gradients. Compared to conventional gradient generators, poly(dimethylsiloxane) (PDMS)-based microfluidic devices can generate stable concentration gradients of growth factors with well-defined profiles. Here, we developed simple gradient-generating microfluidic devices with three separate inlets. Three microchannels combined into one microchannel to generate concentration gradients. The stability and shape of growth factor gradients were confirmed by fluorescein isothyiocyanate (FITC)-dextran with a molecular weight similar to epidermal growth factor (EGF). Using this microfluidic device, we demonstrated that fibroblasts exposed to concentration gradients of EGF migrated toward higher concentrations. The directional orientation of cell migration and motility of migrating cells were quantitatively assessed by cell tracking analysis. Thus, this gradient-generating microfluidic device might be useful for studying and analyzing the behavior of migrating cells. PMID:18989442

Chung, Bong Geun; Manbachi, Amir; Saadi, Wajeeh; Lin, Francis; Jeon, Noo Li; Khademhosseini, Ali

2007-01-01

446

Bias in the Gradient Sensing Response of Chemotactic Cells  

PubMed Central

We apply linear-stability theory and perform perturbation studies to better characterize, and to generate new experimental predictions from, a model of chemotactic gradient sensing in eukaryotic cells. The model uses reaction-diffusion equations to describe 3? phosphoinositide signaling and its regulation at the plasma membrane. It demonstrates a range of possible gradient-sensing mechanisms and captures such characteristic behaviors as strong polarization in response to static gradients, adaptation to differing mean levels of stimulus, and plasticity in response to changing gradients. An analysis of the stability of polarized steady-state solutions indicates that the model is most sensitive to off-axis perturbations. This biased sensitivity is reflected in responses to localized external stimuli as well, and leads to a clear experimental prediction, namely, that a cell which is polarized in a background gradient will be most sensitive to transient point-source stimuli lying within a range of angles that are oblique with respect to the polarization axis. Stimuli at angles below this range will elicit responses whose directions overshoot the stimulus angle, while responses to stimuli applied at larger angles will undershoot the stimulus angle. We argue that such a bias is likely to be a general feature of gradient sensing in highly motile cells, particularly if they are optimized to respond to small gradients. Finally, an angular bias in gradient sensing might lead to preferred turn angles and zigzag movements of cells moving up chemotactic gradients, as has been noted under certain experimental conditions.

Skupsky, Ron; McCann, Colin; Nossal, Ralph; Losert, Wolfgang

2009-01-01

447

DGPS Positioning Improvement by Utilizing the Ionospheric Horizontal Gradient Factor  

NASA Astrophysics Data System (ADS)

The ionospheric horizontal gradient is the variation of electron density with latitude and longitude which can cause the azimuthal deviation of the Global Positioning System (GPS) ray path. The effect of an ionospheric horizontal gradient is more pronounced in the low-latitude region (equatorial) and mid-auroral (trough) or polar regions than at mid-latitudes. In this paper, the positioning improvement in differential GPS (DGPS) by mitigating the ionospheric horizontal gradient has been shown. This ionospheric horizontal gradient factor was obtained from ionospheric tomographic images or contour of Total Electron Content (TEC) from Rutherford Appleton Laboratory (RAL) in the United Kingdom (UK). Since the factor of ionospheric horizontal gradient from RAL UK's TEC contour correlates very well with the factor of ionospheric horizontal gradient from the International Reference Ionosphere (IRI), so the factor of ionospheric horizontal gradient for the ionosphere over the equatorial region was determined from IRI. Then, this factor will be used to show DGPS positioning improvement over the equatorial region. By using the same linear gradient method approach, a significant amount of positioning improvement (15 cm) has been shown over the equatorial region for the DGPS by mitigating the ionospheric horizontal gradient.

Nagarajoo, K.

2011-03-01

448

Demonstration of the elusive concentration-gradient paramagnetic force.  

PubMed

Using classical electrochemistry, it is demonstrated that the concentration-gradient paramagnetic force, FnablaC, is a body force proportional to |B|2 acting parallel to the concentration gradient of electrogenerated radicals. FnablaC can balance gravity, holding volumes of solution wherein mass transfer continues to take place by diffusion. In contrast to usual levitation forces, FnablaC does not depend on field gradients and may be present even in homogeneous magnetic fields. Understanding the properties of FnablaC is relevant to magnetic confinement and levitation and is speculated even to propulsion with objects having permanent susceptibility gradients. PMID:15810811

Leventis, Nicholas; Dass, Amala

2005-04-13

449

Analysis of bacteria communities in an up-flow fixed-bed (UFB) bioreactor for treating sulfide in hydrocarbon wastewater.  

PubMed

An up-flow fixed-bed (UFB) bioreactor with patented functional polyurethane foam (FPUF) carriers was used to treat sulfide in hydrocarbon wastewater. Community compositions of autotrophic and heterotrophic bacteria were analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). DGGE results showed that a relatively stable bacterial community composed of heterotrophic and autotrophic bacteria formed in the bioreactor by the end of experiment, which ensured 92-100% sulfide removal efficiencies. Furthermore, autotrophic genera of Thiobacillus and Thiomonas, as well as those of the heterotrophic genus of Acinetobacter survived and exhibited high sulfide oxidation activity under all three operational conditions. Different special genera were also observed under each operational condition, such as the halophilic genus of Nesterenkonia. In addition, a new genus of sulfide oxidation bacteria was found in the bioreactor, which had the ability to synthesize cytoplasm from organic compounds. These genera have wide applications for the treatment of sulfide in hydrocarbon wastewater. PMID:19559604

Ji, Guodong; Liao, Bo; Tao, Huchun; Lei, Zhihong

2009-11-01

450

Profiling of microbial communities in a bioreactor for treating hydrocarbon-sulfide-containing wastewater.  

PubMed

A technology of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was used to profile the structure and dynamic changes of microbial communities in a bioreactor for treating hydrocarbon-sulfide-containing (HSC) wastewater. The results showed that the heterotrophic genus of Acinetobacter and the autotrophic genera of Thiobacillus and Thiomonas could survive well in all of three operating conditions. Some special genera were also observed with changes of micro-ecoenvironment in the reactor, such as the halophilic genus of Nesterenkonia. Further, a new genus was found in the reactor, which was likely to have the ability to degrade sulfide and hydrocarbon at the same time. All of these detected and the new found genera have widely applicable potential in the treatment of HSC wastewater. PMID:18817065

Liao, Bo; Ji, Guodong; Cheng, Liqiu

2008-01-01

451

Sequential sludge digestion after diverse pre-treatment conditions: Sludge removal, methane production and microbial community changes.  

PubMed

A lab-scale sequential sludge digestion process which consists of a mesophilic anaerobic digester (MAD) and a thermophilic aerobic digester (TAD) was developed. Thermal, thermal-alkaline and long-term alkaline pre-treatments were applied to the feed sludge to examine their effects on sludge removal and methane production. Especially after thermal-alkaline pre-treatment, high COD removal was maintained; methane production rate was also drastically increased by improving the hydrolysis step of sludge degradation. Polymerase chain reaction-denaturing gel gradient electrophoresis indicated that bacterial communities were represented by three phyla (Firmicutes, Proteobacteria, Actinobacteria) and that Clostridium straminisolvens was the major bacterial species in MAD. Quantitative real-time PCR results indicated that Methanosaeta concilli was the major archaeal species in MAD, and that Ureibacillus sp. was the most abundant bacterial species in TAD. PMID:24768888

Park, Sang Kyu; Jang, Hyun Min; Ha, Jeong Hyub; Park, Jong Moon

2014-06-01

452

Stationary chemical gradients for concentration gradient-based separation and focusing in nanofluidic channels.  

PubMed

Previous work has demonstrated the simultaneous concentration and separation of proteins via a stable ion concentration gradient established within a nanochannel ( Inglis Angew. Chem., Int. Ed. 2001 , 50 , 7546 - 7550 ). To gain a better understanding of how this novel technique works, we here examine experimentally and numerically how the underlying electric potential controlled ion concentration gradients can be formed and controlled. Four nanochannel geometries are considered. Measured fluorescence profiles, a direct indicator of ion concentrations within the Tris-fluorescein buffer solution, closely match depth-averaged fluorescence profiles calculated from the simulations. The simulations include multiple reacting species within the fluid bulk and surface wall charge regulation whereby the deprotonation of silica-bound silanol groups is governed by the local pH. The three-dimensional system is simulated in two dimensions by averaging the governing equations across the (varying) nanochannel width, allowing accurate numerical results to be generated for the computationally challenging high aspect ratio nanochannel geometries. An electrokinetic circuit analysis is incorporated to directly relate the potential drop across the (simulated) nanochannel to that applied across the experimental chip device (which includes serially connected microchannels). The merit of the thick double layer, potential-controlled concentration gradient as a particle focusing and separation tool is discussed, linking this work to the previously presented protein trapping experiments. We explain why stable traps are formed when the flow is in the opposite direction to the concentration gradient, allowing particle separation near the low concentration end of the nanochannel. We predict that tapered, rather than straight nanochannels are better at separating particles of different electrophoretic mobilities. PMID:24725102

Hsu, Wei-Lun; Inglis, David W; Jeong, Helen; Dunstan, David E; Davidson, Malcolm R; Goldys, Ewa M; Harvie, Dalton J E

2014-05-13

453

Chain Release Behavior of Gellan Gels  

NASA Astrophysics Data System (ADS)

The chain release behavior from gellan gels was studied by immersing the gel into water and monitoring the mass loss as a function of time. Concentration of released gellan in the external solution was determined for gels of different sizes using phenol-sulfuric acid method. The chain release process became faster with increasing total surface area and volume. However the concentration of released chain normalized by surface area and volume suggests that the chain release itself is governed not only by the ionic effect and the amount of unassociated chains in gel but other factors such as osmotic pressure may play an important role on the chain release from the gels. The diffusion coefficient was estimated from the chain release process which is in the same order of magnitude reported for an isolated gellan chain by light scattering. Rheological measurements also suggest that the unassociated gellan chains are released out when immersed in pure water while unassociated chains are restricted to release out when immersed in salt solution due to the intrusion of cations which is responsible for further association of the unassociated gellan chains being in agreement with the previously published results. The elastic modulus of gels was increased by immersion of gels in water and in salt solutions, which can be attributed as the stiffening of network chains due to gel swelling and the conversion from free and unassociated chains into network chains, respectively, leading to an increase in elastic modulus with time.

Hossain, Khandker S.; Nishinari, Katsuyoshi

454

3-D radial gravity gradient inversion  

NASA Astrophysics Data System (ADS)

We have presented a joint inversion of all gravity-gradient tensor components to estimate the shape of an isolated 3-D geological body located in subsurface. The method assumes the knowledge about the depth to the top and density contrast of the source. The geological body is approximated by an interpretation model formed by an ensemble of vertically juxtaposed 3-D right prisms, each one with known thickness and density contrast. All prisms forming the interpretation model have a polygonal horizontal cross-section that approximates a depth slice of the body. Each polygon defining a horizontal cross-section has the same fixed number of vertices, which are equally spaced from 0° to 360° and have their horizontal locations described in polar coordinates referred to an arbitrary origin inside the polygon. Although the number of vertices forming each polygon is known, the horizontal coordinates of these vertices are unknown. To retrieve a set of juxtaposed depth slices of the body, and consequently, its shape, our method estimates the radii of all vertices and the horizontal Cartesian coordinates of all arbitrary origins defining the geometry of all polygons describing the horizontal cross-sections of the prisms forming the interpretation model. To obtain a stable estimate that fits the observed data, we impose constraints on the shape of the estimated body. These constraints are imposed through the well-known zeroth- and first-order Tikhonov regularizations allowing, for example, the estimate of vertical or dipping bodies. If the data do not have enough in-depth resolution, the proposed inverse method can obtain a set of stable estimates fitting the observed data with different maximum depths. To analyse the data resolution and deal with this possible ambiguity, we plot the ?2-norm of the residuals (s) against the estimated volume (vp) produced by a set of estimated sources having different maximum depths. If this s × vp curve (s as a function of vp) shows a well-defined minimum of s, the data have enough resolution to recover the shape of the body entirely. Conversely, if the observed data do not have enough resolution, some estimates with different maximum depths produce practically the same minimum value of s on the s × vp curve. In this case, the best estimate among a suite of estimates producing equally data fits is the one fitting the gravity-gradient data and producing the minima of both the source's bottom depth and volume. The histograms of the residuals can be used to quantify and remove systematic errors in the data. After removing these errors, we confirmed the ability of our method to recover the source geometry entirely (or its upper part only), if the data have sufficient (or insufficient) in-depth resolution. By inverting the gravity-gradient data from a survey over the Vinton salt dome (Louisiana, USA) with a density contrast of 0.55 g cm-3, we estimated a massive cap rock whose maximum depth attains 460 ± 10 m and its shallowest portion is elongated in the northeast-southwest direction.

Oliveira, Vanderlei C.; Barbosa, Valéria C. F.

2013-11-01

455

Data Supply Chain Management: Supply Chain Management for Incentive and Risk-based Assured Information Sharing.  

National Technical Information Service (NTIS)

In this paper we introduce the notion of data supply chain management and draw parallels between supply chain management and developing a data product. Then we discuss information sharing in supply chain management and discuss risks and incentives for inf...

B. Thuraisingham

2011-01-01

456

Protein side chain modeling with orientation-dependent atomic force fields derived by series expansions.  

PubMed

We describe the development of new force fields for protein side chain modeling called optimized side chain atomic energy (OSCAR). The distance-dependent energy functions (OSCAR-d) and side-chain dihedral angle potential energy functions were represented as power and Fourier series, respectively. The resulting 802 adjustable parameters were optimized by discriminating the native side chain conformations from non-native conformations, using a training set of 12,000 side chains for each residue type. In the course of optimization, for every residue, its side chain was replaced by varying rotamers, whereas conformations for all other residues were kept as they appeared in the crystal structure. Then, the OSCAR-d were multiplied by an orientation-dependent function to yield OSCAR-o. A total of 1087 parameters of the orientation-dependent energy functions (OSCAR-o) were optimized by maximizing the energy gap between the native conformation and subrotamers calculated as low energy by OSCAR-d. When OSCAR-o with optimized parameters were used to model side chain conformations simultaneously for 218 recently released protein structures, the prediction accuracies were 88.8% for ?(1) , 79.7% for ?(1 + 2) , 1.24 Å overall root mean square deviation (RMSD), and 0.62 Å RMSD for core residues, respectively, compared with the next-best performing side-chain modeling program which achieved 86.6% for ?(1) , 75.7% for ?(1 + 2) , 1.40 Å overall RMSD, and 0.86 Å RMSD for core residues, respectively. The continuous energy functions obtained in this study are suitable for gradient-based optimization techniques for protein structure refinement. A program with built-in OSCAR for protein side chain prediction is available for download at http://sysimm.ifrec.osaka-u.ac.jp/OSCAR/. PMID:21374632

Liang, Shide; Zhou, Yaoqi; Grishin, Nick; Standley, Daron M

2011-06-01

457

Wave Propagation in Rectangular Nanoplates Based on Strain Gradient Theory with One Gradient Parameter with Considering Initial Stress  

NASA Astrophysics Data System (ADS)

In this paper, on the basis of gradient elasticity theory with one gradient parameter, wave propagation in rectangular nanoplates is studied. In the governing equation, the influences of initial stresses and elastic foundation are also considered. An analytical approach is used to solve the governing equation. The effects of different parameters such as gradient parameter on the circular and cut-off frequencies are presented. One can see that the initial stress and gradient parameter play an important role in investigating the wave propagation in nanoplates.

Nami, Mohammad Rahim; Janghorban, Maziar

2014-01-01

458

Nonunique steady states in the disordered harmonic chain.  

PubMed

The heat transport in disordered harmonic chains (DHCs) with arbitrary heat baths is studied, based on a general formulation developed by Dhar [Phys. Rev. Lett. 86, 5882 (2001)]. The obtained temperature profile of a steady state is very unusual for any heat bath: (i) it is not unique, but dependent on the initial condition; (ii) it may be highly nonlinear, even though the temperature difference of the two ends of the system is in zero limit, and the temperature gradient inverted Delta T is not inversely proportional to the system size; and (iii) when a DHC is coupled to two thermostats with the same temperature, the temperature of the system is still not uniform. The localized higher frequency normal modes induced by the mass disorders are responsible for these strange properties. PMID:12513272

Zhou, Xin; Chen, Hu; Iwamoto, Mitsumasa

2002-12-01

459

Gradient drift eigenmodes in the equatorial electrojet  

NASA Technical Reports Server (NTRS)

The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the denisty and electrostatic potential perturbations is solved numerically by a relaxation technique. Under some approximations, the fourth-order system can be shown to reduce to a second-order differential equation for the perturbed potential or density. The latter is solved using a shooting technique and provides initial guesses for numerical solutions to the full problem. It is shown that the linear growth rate peaks for kilometer-scale waves, contrary to the findings of recent initial-value studies. This occurs because the equilibrium velocity shear is much more effective as a damping mechanism for short-wavelength modes than it is for the longer, kilometer-scale modes. These results provide a natural qualitative explanation for the observed dominance of kilometer-scale structures in the daytime electrojet spectrum.

Wang, X.-H.; Bhattacharjee, A.

1994-01-01

460

Gradient drift eigenmodes in the equatorial electrojet  

SciTech Connect

The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the density and electrostatic potential perturbations is solved numerically by a relaxation technique. Under some approximations, the fourth-order system can be shown to reduce to a second-order differential equation for the perturbed potential or density. The latter is solved using a shooter technique and provides initial guesses for numerical solutions to the full problem. It is shown that the linear growth rate peaks for kilometer-scale waves, contrary to the findings of recent initial-value studies. This occurs because the equilibrium velocity shear is much more effective as a damping mechanism for short-wavelength modes than it is for the longer, kilometer-scale modes. These results provide a natural qualitative explanation for the observed dominance of kilometer-scale structures in the daytime electrojet spectrum. 27 refs., 9 figs.

Wang, X.H.; Bhattacharjee, A. [Univ. of Iowa, Iowa City, IA (United States)

1994-07-01

461

Metallicity gradients in early-type galaxies  

NASA Technical Reports Server (NTRS)

A study of medium-to-bright early-type galaxies in six bandpasses from 3500 A to 2.2 microns is presented in order to quantify their colors and color gradients and relate these to metallicity and properties of the underlying stellar population. The Stromgren filter system chosen makes it possible to introduce a new calibration to the Mg(2) system from the present narrow-band v - y indices. A comparison is presented of narrow-band colors centered on particular spectral features vs a color dominated by the mean temperature of the giant branch (i.e., J - K) to test the effects of light vs heavy element abundances on knowledge of the total system metallicity, Z, and the effects of reddening. A good correlation is found between v - y and Mg(2); it provides a connection between one light element metallicity indicator (v - y centers on the CN blend) and another, Mg. The color-magnitude relations for all five optical and near-IR colors are shown. The strongest correlation exists for the metallicity colors, v - y and J - K.

Schombert, James M.; Hanlan, Patricia C.; Barsony, Mary; Rakos, Karl D.

1993-01-01

462

Environmental causes for plant biodiversity gradients.  

PubMed Central

One of the most pervasive patterns observed in biodiversity studies is the tendency for species richness to decline towards the poles. One possible explanation is that high levels of environmental energy promote higher species richness nearer the equator. Energy input may set a limit to the number of species that can coexist in an area or alternatively may influence evolutionary rates. Within flowering plants (angiosperms), families exposed to a high energy load tend to be both more species rich and possess faster evolutionary rates, although there is no evidence that one drives the other. Specific environmental effects are likely to vary among lineages, reflecting the interaction between biological traits and environmental conditions in which they are found. One example of this is demonstrated by the high species richness of the iris family (Iridaceae) in the Cape of South Africa, a likely product of biological traits associated with reproductive isolation and the steep ecological and climatic gradients of the region. Within any set of conditions some lineages will tend to be favoured over others; however, the identity of these lineages will fluctuate with a changing environment, explaining the highly labile nature of diversification rates observed among major lineages of flowering plants.

Davies, T Jonathan; Barraclough, Timothy G; Savolainen, Vincent; Chase, Mark W

2004-01-01

463

Microfluidic multi-analyte gradient generator  

PubMed Central

A microfluidic device was developed to produce temporal concentration gradients of multiple analytes. Four on-chip pumps del