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1

Microbial Community Analysis During Composting of Digested Sludge and Sawdust by Using Quinone Profile and Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis  

Microsoft Academic Search

Microbial community structure during the composting of digested sewage sludge and sawdust was analyzed by a combination of quinone profile and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The change in total quinine content (TQ) indicated that microbial biomass reached a peak followed by a decrease, whereas the divergence of quinine (DQ) showed that the microbial community diversity increased continuously

Lijuan Yang; Mengchun Gao; Fangyuan Liang; Chao Qin

2009-01-01

2

Appropriate Chicken Sample Size for Identifying the Composition of Broiler Intestinal Microbiota Affected by Dietary Antibiotics, Using the Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis Technique  

Microsoft Academic Search

The bacterial microbiota in the broiler gas- trointestinal tract are crucial for chicken health and growth. Their composition can vary among individual birds. To evaluate the composition of chicken microbiota in response to environmental disruption accurately, 4 dif- ferent pools made up of 2, 5, 10, and 15 individuals were used to determine how many individuals in each pool were

H. Zhou; J. Gong; J. T. Brisbin; H. Yu; B. Sanei; P. Sabour; S. Sharif

2007-01-01

3

Methanogenic archaeal communities developed in paddy fields in the Kojima Bay polder, estimated by denaturing gradient gel electrophoresis, real-time PCR and sequencing analyses  

Microsoft Academic Search

Methanogenic archaeal communities inhabiting the paddy field soils in the Kojima Bay polder were investigated using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), real-time PCR and sequencing analyses. Soil samples of the plow and subsoil layers were collected in 2006 from four paddy fields that were reclaimed between 1692 and 1954. The DGGE band patterns of the targeted 16S rRNA

Takeshi Watanabe; Vita Ratri Cahyani; Jun Murase; Eiji Ishibashi; Makoto Kimura; Susumu Asakawa

2009-01-01

4

Carotenoids in a food chain along a pollution gradient.  

PubMed

Carotenoids are synthesized by plants, therefore insects and birds must obtain them from their diet. They function in pigmentation and as antioxidants. We studied the carotenoid profiles in a model food chain (plant-insect-bird) in an air pollution gradient to find out whether heavy metal pollution affects the transfer of carotenoids across the trophic levels. Birch leaves showed higher beta-carotene and, one of the birch species (Betula pendula), higher total carotenoids levels in the polluted area. There was no difference in the lutein concentration of caterpillars' food source, birch leaves, between the study areas. Autumnal moth larvae accumulated lutein more efficiently than beta-carotene while sawfly larvae accumulated beta-carotene over lutein. Because of different antioxidant profiles in different leaf chewing insects their sensitivity to pollution stress may differ. The lutein concentration of plasma and feathers of Great tit nestlings did not differ along the pollution gradient. The lack of difference in lutein concentration of autumnal moth larvae along pollution gradient may partly explain the lutein concentrations of Great tit nestlings, since the abundance of autumnal moth larvae peak during the nestling phase of Great tit. The lutein concentration of autumnal moth larvae was positively associated to circulating plasma lutein level of Great tit indicating the importance of carotenoid rich diet during the nestling phase. In addition, the higher the plasma lutein concentration the more lutein was deposited to feathers, irrespective of the other possible functions of lutein in nestlings. We found that carotenoid levels differed between the polluted and the unpolluted area especially at lower levels of food chain: in birches and in caterpillars. PMID:18789813

Sillanpää, Saila; Salminen, Juha-Pekka; Lehikoinen, Esa; Toivonen, Eija; Eeva, Tapio

2008-09-13

5

Detonation ignition from a temperature gradient for a two-step chain-branching kinetics model  

NASA Astrophysics Data System (ADS)

The evolution from a linear temperature gradient to a detonation is investigated for combustible materials whose chemistry is governed by chain-branching kinetics, using a combination of high-activation-temperature asymptotics and numerical simulations. A two-step chemical model is used, which captures the main properties of detonations in chain-branching fuels. The first step is a thermally neutral induction time, representing chain initiation and branching, which has a temperature-sensitive Arrhenius form of the reaction rate. At the end of the induction time is a transition point where the fuel is instantaneously converted into chain-radicals. The second step is the main exothermic reaction, representing chain termination, assumed to be temperature insensitive. Emphasis is on comparing and contrasting the results with previous studies that used simple one-step kinetics. It is shown that the largest temperature gradient for which a detonation can be successfully ignited depends on the heat release rate of the main reaction. The slower the heat release compared to the initial induction time, the shallower the gradient has to be for successful ignition. For example, when the rate of heat release is moderate or slow on the initial induction time scale, it was found that the path of the transition point marking the end of the induction stage should move supersonically, in which case its speed is determined only by the initial temperature gradient. For steeper gradients such that the transition point propagates subsonically from the outset, the rate of heat release must be very high for a detonation to be ignited. Detonation ignition for the two-step case apparently does not involve the formation of secondary shocks, unlike some cases when one-step kinetics is used.

Sharpe, Gary J.; Short, Mark

2003-02-01

6

Mutations of the G sup s. alpha. -subunit gene in Albright hereditary osteodystrophy detected by denaturing gradient gel electrophoresis  

SciTech Connect

Affected members of most kindreds with Albright hereditary osteodystrophy have a partial deficiency of functional G{sub s}, the guanine nucleotide-binding protein that stimulates adenylyl cyclase. By use of the polymerase chain reaction to amplify genomic fragments with the attachment of a high-melting G+C-rich region (GC clamp) and analysis of these fragments by denaturing gradient gel electrophoresis, heterozygous mutations in the G{sub s} {alpha}-subunit at the donor splice junction of intron 10 and a coding frameshift created by a single base deletion within exon 10. The findings illustrate the heterogeneity of genetic defects in Albright hereditary osteodystrophy and the usefulness of the polymerase chain reaction-denaturing gradient gel electrophoresis method to search rapidly for mutations in a large candidate gene.

Weinstein, L.S.; Friedman, E.; Collins, R.M.; Spiegel, A.M.; Gejman, P.V.; Kadowaki, Takashi; Gershon, E.S. (National Inst. of Health, Bethesda, MD (United States))

1990-11-01

7

Quantification of HIV1 proviral DNA and analysis of genomic diversity by polymerase chain reaction and temperature gradient gel electrophoresis  

Microsoft Academic Search

A competitive polymerase chain reaction\\/temperature gradient gel electrophoresis (PCR\\/TGGE) protocol was developed for exact quantification of HIV-1 proviral DNA copy numbers in clinical samples. An internal standard (ST) that differs from wildtype-sequences only by a single base exchange was used as a competitor in PCR. Quantification of HIV-1 target sequences was achieved by coamplification of defined copy numbers of ST

Ulrike Wieland; Helge Suhr; Bernd Salzberger; Hans J. Eggers; Rüdiger W. Braun; Joachim E. Kühn

1996-01-01

8

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

9

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

10

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

11

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

2012-11-21

12

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

PubMed

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 concentrations and the soil concentrations were found for Zn only (r2 = 0.20). Bioaccumulation of Zn, Cu and Cd was observed in the snail tissues. We found positive relationships between the snail and leaf concentrations for all metals (range r2 = 0.19-0.46). The relationships between soil and snail concentrations were also positive, except for Cu (range r2 = 0.15-0.33). These results suggest transfer of metals to C. nemoralis snails from U. dioica leaves and from the soil. Metal transfer from polluted leaves to C. nemoralis is more important than transfer from the soil. PMID:16005127

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

2005-11-01

13

Quantitative determination of human cytomegalovirus target sequences in peripheral blood leukocytes by nested polymerase chain reaction and temperature gradient gel electrophoresis  

Microsoft Academic Search

A competitive nested PCR-temperature gradient gel electrophoresis protocol (nPCR\\/TGGE) has been es- tablished for the quantification of human cytomegalo- virus (HCMV) target sequences. The measurement was achieved by co-amplification of a defined copy number of an internal standard (st) and separation of st and wild- type (wt) amplimers by temperature gradient gel electro- phoresis (TGGE). The number of HCMV target

P. Schafer; Riidiger W. Braun; K. Mohring; Karsten Henco; Jie Kang; Thomas Wendland; J. E. Kuhn

1993-01-01

14

Detection of Clonal T-Cell Receptor ? Gene Rearrangements in Early Mycosis Fungoides\\/Sezary Syndrome by Polymerase Chain Reaction and Denaturing Gradient Gel Electrophoresis (PCR\\/DGGE)  

Microsoft Academic Search

We used a gene amplification strategy to analyze T-cell receptor (TCR) gene rearrangements in 185 specimens, including mycosis fungoides\\/Sezary syndrome (MF\\/SS), other cutaneous neoplasms, inflammatory dermatoses, reactive lymphoid tissues,and normal skin. Genomic DNA was extracted from lesional tissues and rearrangements of the TCR-? chain gene were amplified using the polymerase chain reaction (PCR) with primers specific for rearrangements involving V?1-8

Gary S. Wood; Rosnn M. Tung; Andreas C. Heaffner; Carol F. Crooks; Shaoyi Liao; Rachaci Orozco; Hendrik Veelken; Marshall E. Kadin; Howard Koh; Peter Heald; Raymond L. Barnhill; Jeffrey Sklar

1994-01-01

15

Phase Behavior of Gradient Copolymer Solution  

NASA Astrophysics Data System (ADS)

We study the behavior of amphiphilic linear gradient copolymer chains under poor solvent conditions. Using Bond Fluctuation model and parallel tempering algorithm, we explore qualitative behavior of this class of polymers with varying gradient strength; which is the largest difference in the instantaneous composition along the polymer chain. Under poor solvent conditions, the chains collapse to form micelles. We find a linear dependence of hydrophilic to hydrophobic transition temperature on gradient strength. Systematic analysis of these clusters reveals a strong dependence of micelle properties on gradient strength. Also, we discuss our results with reference to recent experiments on synthesis and cloud point depression in gradient copolymers confirming gradient strength as key parameter in tuning micelle properties.

Pandav, Gunja; Gallow, Keith; Loo, Yueh-Lin; Ganesan, Venkat

2012-02-01

16

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

17

Irradiance gradients  

SciTech Connect

A new method for improving the accuracy of a diffuse interreflection calculation is introduced in a ray tracing context. The information from a hemispherical sampling of the luminous environment is interpreted in a new way to predict the change in irradiance as a function of position and surface orientation. The additional computation involved is modest and the benefit is substantial. An improved interpolation of irradiance resulting from the gradient calculation produces smoother, more accurate renderings. This result is achieved through better utilization of ray samples rather than additional samples or alternate sampling strategies. Thus, the technique is applicable to a variety of global illumination algorithms that use hemicubes or Monte Carlo sampling techniques.

Ward, G.J. [Lawrence Berkeley Lab., CA (United States)]|[Ecole Polytechnique Federale, Lausanne (Switzerland); Heckbert, P.S. [Carnegie-Mellon Univ., Pittsburgh, PA (United States). School of Computer Science]|[Technische Hogeschool Delft (Netherlands). Dept. of Technical Mathematics and Informatics

1992-04-01

18

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

19

Effects of fertilization on bacterial community structure and function in a black soil of Dehui region estimated by Biolog and PCR-DGGE methods  

Microsoft Academic Search

Soil microbial community structure and function are commonly used as indicators for soil quality and fertility. In this paper, the bacterial community structure and function in a black soil of Dehui region influenced by fertilization were investigated by Biolog and PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) methods. Biolog examination showed that substrate richness and catabolic diversities of bacterial communities

Wang Guanghua; Liu Junjie; Qi Xiaoning; Jin Jian; Wang Yang; Liu Xiaobing

2008-01-01

20

Characterization of microbial community structure of anaerobic baffled reactor-integrated oxidation ditch-biological aerated filter for landfill leachate treatment  

Microsoft Academic Search

To provide microbial evidence for technique improvement of anaerobic baffled reactor (ABR) - integrated oxidation ditch - biological aerated filter (BAF) combined processes for landfill leachate treatment, microbial community structure of the treatment system under different recycle ratios were investigated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) combined with sequencing and phylogenetic analysis. The results indicated that, under high

Yudong Xu; Xiaofang Chen

2011-01-01

21

Bacterial Community Structure and Diversity in a Black Soil as Affected by Long-Term Fertilization *1 *1 Project supported by the Heilongjiang Provincial Natural Science Funds for Distinguished Young Scholars, China (No. JC200622), the Heilongjiang Provincial Natural Science Foundation of China (No. C2004-17), and the National “Eleventh Five Years Plan” Key Project on Science and Technology of China (No. 2006BAD25B05)  

Microsoft Academic Search

Black soil (Mollisol) is one of the main soil types in northeastern China. Biolog and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) methods were used to examine the influence of various fertilizer combinations on the structure and function of the bacterial community in a black soil collected from Harbin, Heilongjiang Province. Biolog results showed that substrate richness and catabolic diversity

Dan WEI; Qian YANG; Jun-Zheng ZHANG; Shuang WANG; Xue-Li CHEN; Xi-Lin ZHANG; Wei-Qun LI

2008-01-01

22

Chains Within Chains  

Microsoft Academic Search

The literature on franchising has largely ignored one of its distinguishing features: the ownership of multiple units by a single franchisee. Based on the findings of an in-depth field study, this article argues that multi-unit franchisees outperform single unit franchisees in meeting several important management challenges facing chain organizations, which helps explain the prevalence of this form of franchising.

Jeffrey L. Bradach

1995-01-01

23

Gradient sensing during chemotaxis.  

PubMed

Eukaryotic cells have the ability to sense chemoattractant gradients and to migrate toward the sources of attractants. The chemical gradient-guided cell movement is referred to as chemotaxis. Chemoattractants are detected by members of G-protein-coupled receptors (GPCRs) that link to heterotrimeric G-proteins. The GPCR/G-protein sensing machinery is able to translate external chemoattractants fields into intercellular cues, which direct reorganization of the actin cytoskeleton that drives cell movement. Here, I review our current understanding of the formation of chemoattractant gradients in vivo, the GPCR-mediated gradient sensing, and the sophisticated signaling network that guides the function of the actin cytoskeleton. PMID:23880435

Jin, Tian

2013-07-20

24

Scalar Field Gradient Model  

NSDL National Science Digital Library

The Scalar Field Gradient Model displays the gradient of a scalar field using a numerical approximation to the partial derivatives. This simple teaching model also shows how to display and model scalar and vector fields using the EJS. The EJS Scalar Field Gradient 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_math_ScalarFieldGradient.jar file will run the program if Java is installed.

Christian, Wolfgang

2009-03-14

25

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

26

Macroscopic singlet states for gradient magnetometry  

NASA Astrophysics Data System (ADS)

We present a method for measuring magnetic field gradients with macroscopic singlet states realized with ensembles of spin-j particles. While the singlet state is completely insensitive to homogeneous magnetic fields, the variance of its collective spin components is highly sensitive to field gradients. We compute the dynamics of this variance analytically for a chain of spins and also for an ensemble of particles with a given density distribution. We find an upper bound on how precisely the field gradient can be estimated from the measured data. Based on our calculations, differential magnetometry can be carried out with cold atomic ensembles using a multipartite singlet state obtained via spin squeezing. On the other hand, comparing the metrological properties of the experimentally prepared state to that of the ideal singlet can be used as further evidence that a singlet state has indeed been created.

Urizar-Lanz, Iñigo; Hyllus, Philipp; Egusquiza, Iñigo Luis; Mitchell, Morgan W.; Tóth, Géza

2013-07-01

27

Density gradient quantum similarity  

NASA Astrophysics Data System (ADS)

Computation of density gradient quantum similarity integrals is analyzed, while comparing such integrals with overlap density quantum similarity measures. Gradient quantum similarity corresponds to another kind of numerical similarity assessment between a pair of molecular frames, which contrarily to the usual up to date quantum similarity definitions are not measures, that is: strictly positive definite integrals. As the density gradient quantum similarity integrals are defined as scalar products of three real functions, they appear to possess a richer structure than the corresponding positive definite density overlap quantum similarity measures, while preserving the overall similarity trends, when the molecular frames are relatively moved in three dimensional space. Numerical results within the atomic shell approximation (ASA) framework are presented as simple examples showing the new performances of the gradient density quantum similarity.

Carbó-Dorca, Ramon; Mercado, Luz Dary

2012-12-01

28

Gradient enhanced spectroscopy  

NASA Astrophysics Data System (ADS)

This paper provides a brief overview of the personal recollections of the authors regarding their contributions to the introduction of shielded gradient technology into NMR spectroscopy during the late 1980s and early 1990s. It provides some background into early probe design and details some of the early technical progress with the use of shielded magnetic field gradients for coherence selection in high resolution NMR and describes the developments at General Electric, the National Institutes of Health, Georgetown University and Johns Hopkins University School of Medicine that ultimately led to this technology becoming commonplace in modern NMR spectroscopy. Most of this early technical work was published in the Journal of Magnetic Resonance.

van Zijl, Peter C.; Hurd, Ralph E.

2011-12-01

29

Gradient-Index Optics.  

National Technical Information Service (NTIS)

SAIC has performed an effort to advance the state of the art in gradient-index (GRIN) nanolayered polymer optics. The goal of this study was to take significant risks off the table with regard to practical high-performance GRIN optical designs. The DARPA ...

N. Shatz

2010-01-01

30

Gradient Armor System.  

National Technical Information Service (NTIS)

The patent application describes an armor system comprising a ceramic matrix having a gradient of fine ductile metallic particles dispersed therein in an amount of from 0.0% commencing at the front or impact surface of the armor to about 2 to 15% by volum...

M. L. Wilkins A. C. Holt C. F. Cline K. E. Fromschner

1970-01-01

31

Power from salinity gradients  

Microsoft Academic Search

A large source of energy exists at the interface between water bodies of different salinities. Two techniques, pressure-retarded osmosis and reverse electrodialysis, appear to be promising entrees into this energy source. Although the present cost of membranes suitable to these methods is too high, a research and development effort should make this salinity gradient energy competitive with other energy sources.

G Wick

1978-01-01

32

Effect of different salt adaptation strategies on the microbial diversity, activity, and settling of nitrifying sludge in sequencing batch reactors  

Microsoft Academic Search

The effect of salinity on the activity of nitrifying bacteria, floc characteristics, and microbial community structure accessed\\u000a by fluorescent in situ hybridization and polymerase chain reaction–denaturing gradient gel electrophoresis techniques was\\u000a investigated. Two sequencing batch reactors (SRB1 and SBR2) treating synthetic wastewater were subjected to increasing salt concentrations. In SBR1, four salt concentrations (5, 10, 15, and 20 g NaCl\\/L) were

João Paulo Bassin; Robbert Kleerebezem; Gerard Muyzer; Alexandre Soares Rosado; Mark C. M. van Loosdrecht; Marcia Dezotti

2011-01-01

33

Polycyclic Aromatic Hydrocarbon-Induced Structural Shift of Bacterial Communities in Mangrove Sediment  

Microsoft Academic Search

Mangrove sediment is well known for its susceptibility to anthropogenic pollution, including polycyclic aromatic hydrocarbons\\u000a (PAHs), but knowledge of the sediment microbial community structure with regards to exposure to PAHs is limited. The study\\u000a aims to assess the effects of PAHs on the bacterial community of mangrove sediment using both 16s rDNA polymerase chain reaction-denaturing\\u000a gradient gel electrophoresis (PCR-DGGE) and

Hong Wei Zhou; Ada H. Y. Wong; Richard M. K. Yu; Yong Doo Park; Yuk Shan Wong; Nora F. Y. Tam

2009-01-01

34

Culture-independent and -dependent methods to investigate the diversity of planktonic bacteria in the northern Bering Sea  

Microsoft Academic Search

Planktonic bacteria are abundant in the Bering Sea. However, very little is known about their diversity and the roles of various\\u000a bacteria in the ocean. Bacterioplankton diversity in the northern Bering Sea was investigated using a combination of molecular\\u000a and cultivation-based methods. Community fingerprint analysis using polymerase chain reaction-denaturing gradient gel electrophoresis\\u000a revealed an apparent difference in the bacterioplankton community

Yinxin Zeng; Yang Zou; Jacqueline M. Grebmeier; Jianfeng He; Tianling Zheng

35

The impact of grassland management regime on the community structure of selected bacterial groups in soils  

Microsoft Academic Search

The impact of long-term grassland management regimes on microbial community structure in soils was assessed using multivariate analysis of polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) banding patterns of selected bacterial groups and PLFA (phospholipid fatty acid) profiling. The management regimes assessed were inorganic nitrogen (N) fertiliser application and soil drainage. PCR–DGGE profiles of the eubacteria, actinomycetes, ammonia oxidisers and

Christopher D Clegg; Roger D. L Lovell; Philip J Hobbs

2003-01-01

36

Effect of long-term herbicide applications on the bacterial community structure and function in an agricultural soil  

Microsoft Academic Search

Little is known about the chronic effect of herbicides on the soil microbial community, with most studies focusing on acute impacts. In this study, we investigated the effect of 20 years of atrazine and metolachlor application on the community structure, abundance and function of bacterial groups in the bulk soil of a maize monoculture. Group-specific PCR-DGGE (polymerase chain reaction-denaturing gradient

Dave Seghers; Dirk Reheul; Robert Bulcke; Steven D Siciliano; Willy Verstraete; Eva M Top

2003-01-01

37

Comprehensive study on dynamics of microbial community in Anaerobic-Oxic-Oxic process using PCR-DGGE, gas chromatography analysis, and dehydrogenase activity assays  

Microsoft Academic Search

This study was conducted to evaluate the relationship between the function of microbes and the change in their communities\\u000a during the treatment of coking wastewater using a bio-fluidized bed Anaerobic-Oxic-Oxic (A\\/O\\/O) process. Polymerase chain\\u000a reaction denaturing gradient gel electrophoresis (PCR-DGGE), Gas Chromatography (GC) analysis, and the triphenyl-tetrazolium\\u000a chloride (TTC) dehydrogenase activity test (TTC test) were simultaneously conducted to analyze the

Sheng Zhou; Chaohai Wei; Chaodeng Liao; Haizhen Wu

2010-01-01

38

Bacterial community structures in MBRs treating municipal wastewater: Relationship between community stability and reactor performance  

Microsoft Academic Search

Bacterial community structures in pilot-scale conventional membrane bioreactors (CMBRs) and hybrid MBRs (HMBRs) which were combined with pre-coagulation\\/sedimentation were analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and fluorescence in situ hybridization (FISH) techniques. The results were compared with the community structure in a full-scale activated sludge (AS) process treating the same municipal wastewater. The Dice index (Cs) of

Yuki Miura; Mirian Noriko Hiraiwa; Tsukasa Ito; Takanori Itonaga; Yoshimasa Watanabe; Satoshi Okabe

2007-01-01

39

Spatiotemporal development of the bacterial community in a tubular longitudinal microbial fuel cell  

Microsoft Academic Search

The spatiotemporal development of a bacterial community in an exoelectrogenic biofilm was investigated in sucrose-fed longitudinal\\u000a tubular microbial fuel cell reactors, consisting of two serially connected modules. The proportional changes in the microbial\\u000a community composition were assessed by polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) and DNA sequencing\\u000a in order to relate them to the performance and stability of the

Jung Rae Kim; Nelli J. Beecroft; John R. Varcoe; Richard M. Dinsdale; Alan J. Guwy; Robert C. T. Slade; Alfred Thumser; Claudio Avignone-Rossa; Giuliano C. Premier

2011-01-01

40

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

41

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

42

Tetracycline susceptibility of the ingested Lactobacillus acidophilus LaCH-5 and Bifidobacterium animalis subsp. lactis Bb12 strains during antibiotic\\/probiotic intervention  

Microsoft Academic Search

We investigated the effects of oral therapy with doxycycline, a tetracycline group antibiotic, on the gastrointestinal (GI) survival and tetracycline susceptibility of probiotic strains Lactobacillus acidophilus LaCH-5 and Bifidobacterium animalis subsp. lactis Bb-12. In addition, the influence of doxycycline therapy on the diversity of the predominant faecal microbiota was evaluated by polymerase chain reaction—denaturing gradient gel electrophoresis (PCR-DGGE). Faecal samples

Maria Saarela; Johanna Maukonen; Atte von Wright; Terttu Vilpponen-Salmela; Andrea J. Patterson; Karen P. Scott; Heikki Hämynen; Jaana Mättö

2007-01-01

43

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

44

Aerobic metabolism of vitamin E by marine bacteria: Interaction with free radical oxidation (autoxidation) processes  

Microsoft Academic Search

The degradation of vitamin E by aerobic bacterial communities, isolated from marine sediment and microbial mat samples, was investigated. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) profiles and cloning\\/sequencing experiments revealed that biodegradation of vitamin E in sediments is mainly carried out by strains belonging to the genera Idiomarina and Bacillus, for which the DGGE pattern matched the pattern obtained

Jean-François Rontani; Mina Nassiry; Sophie Guasco; Abdelkrim Mouzdahir; Patricia Bonin

2008-01-01

45

Community analysis of arbuscular mycorrhizal fungi associated with Ammophila arenaria in Dutch coastal sand dunes  

Microsoft Academic Search

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) approach for the detection and characterization of arbuscular mycorrhizal fungi (AMF) 18S ribosomal DNA (rDNA) was developed and applied to the study of AMF communities associated with the main sand-stabilizing plant species of the Dutch sand dunes, marram. grass (Ammophila arenaria, L.). DNA was extracted directly from plant roots, soil or isolated

George A. Kowalchuk; Francisco A. de Souza; Johannes A. van Veen

2002-01-01

46

The biophysical model for accuracy of cellular sensing spatial gradients of multiple chemoattractants.  

PubMed

Spatial gradients of surrounding chemoattractants are the key factors in determining the directionality of eukaryotic cell movement. Thus, it is important for cells to accurately measure the spatial gradients of surrounding chemoattractants. Here, we study the precision of sensing the spatial gradients of multiple chemoattractants using cooperative receptor clusters. Cooperative receptors on cells are modeled as an Ising chain of Monod-Wyman-Changeux clusters subject to multiple chemical-gradient fields to study the physical limits of multiple chemoattractants spatial gradients sensing. We found that eukaryotic cells cannot sense each chemoattractant gradient individually. Instead, cells can only sense a weighted sum of surrounding chemical gradients. Moreover, the precision of sensing one chemical gradient is signicantly affected by coexisting chemoattractant concentrations. These findings can provide a further insight into the role of chemoattractants in immune response and help develop novel treatments for inflammatory diseases. PMID:24104469

Chang, Qiang; Zuo, Li

2013-10-08

47

The biophysical model for accuracy of cellular sensing spatial gradients of multiple chemoattractants  

NASA Astrophysics Data System (ADS)

Spatial gradients of surrounding chemoattractants are the key factors in determining the directionality of eukaryotic cell movement. Thus, it is important for cells to accurately measure the spatial gradients of surrounding chemoattractants. Here, we study the precision of sensing the spatial gradients of multiple chemoattractants using cooperative receptor clusters. Cooperative receptors on cells are modeled as an Ising chain of Monod–Wyman–Changeux clusters subject to multiple chemical-gradient fields to study the physical limits of multiple chemoattractants spatial gradients sensing. We found that eukaryotic cells cannot sense each chemoattractant gradient individually. Instead, cells can only sense a weighted sum of surrounding chemical gradients. Moreover, the precision of sensing one chemical gradient is signicantly affected by coexisting chemoattractant concentrations. These findings can provide a further insight into the role of chemoattractants in immune response and help develop novel treatments for inflammatory diseases.

Chang, Qiang; Zuo, Li

2013-10-01

48

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

49

High Performance Liquid Cbromatographic Separation of Globin Chains on a Large-Pore C4 Column  

Microsoft Academic Search

Excellent resolution of human and baboon globin chains may be obtained by HPLC on a Vydac large-pore C4 column. The procedure is rapid and uses a gradient between aqueous trifluoroacetic acid and trifluoroacetic acid in acetonitrile. The common human ? chains are easily separable from each other as are some ?- and ?-chain variants from the normal chains and from

Joan B. Shelton; J. Roger Shelton; W. A. Schroeder

1984-01-01

50

Gradient echo MRI  

PubMed Central

Background: Recent studies have demonstrated that gradient echo (GRE) MRI sequences are as accurate as CT for the detection of intracerebral hemorrhage (ICH) in the context of acute stroke. However, many physicians who currently read acute stroke imaging studies may be unfamiliar with interpretation of GRE images. Methods: An NIH Web-based training program was developed including a pretest, tutorial, and posttest. Physicians involved in the care of acute stroke patients were encouraged to participate. The tutorial covered acute, chronic, and mimic hemorrhages as they appear on CT, diffusion-weighted imaging, and GRE sequences. Ability of users to identify ICH presence, type, and age on GRE was compared from the pretest to posttest timepoint. Results: A total of 104 users completed the tutorial. Specialties represented included general radiology (42%), general neurology (16%), neuroradiology (15%), stroke neurology (14%), emergency medicine (1%), and other (12%). Median overall score improved pretest to posttest from 66.7% to 83.3%, p < 0.001. Improvement by category was as follows: acute ICH, 66.7%–100%, p < 0.001; chronic ICH, 33.3%–66.7%, p < 0.001; ICH negatives/mimics, 100%–100%, p = 0.787. Sensitivity for identification of acute hemorrhage improved from 68.2% to 96.4%. Conclusions: Physicians involved in acute stroke care achieved significant improvement in gradient echo (GRE) hemorrhage interpretation after completing the NIH GRE MRI tutorial. This indicates that a Web-based tutorial may be a viable option for the widespread education of physicians to achieve an acceptable level of diagnostic accuracy at reading GRE MRI, thus enabling confident acute stroke treatment decisions. GLOSSARY AHA/ASA = American Heart Association/American Stroke Association; CME = continuing medical education; DWI = diffusion-weighted imaging; GRE = gradient echo; ICH = intracerebral hemorrhage; tPA = tissue plasminogen activator.

Copenhaver, B R.; Shin, J; Warach, S; Butman, J A.; Saver, J L.; Kidwell, C S.

2009-01-01

51

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

52

Speciation along environmental gradients  

NASA Astrophysics Data System (ADS)

Traditional discussions of speciation are based on geographical patterns of species ranges. In allopatric speciation, long-term geographical isolation generates reproductively isolated and spatially segregated descendant species. In the absence of geographical barriers, diversification is hindered by gene flow. Yet a growing body of phylogenetic and experimental data suggests that closely related species often occur in sympatry or have adjacent ranges in regions over which environmental changes are gradual and do not prevent gene flow. Theory has identified a variety of evolutionary processes that can result in speciation under sympatric conditions, with some recent advances concentrating on the phenomenon of evolutionary branching. Here we establish a link between geographical patterns and ecological processes of speciation by studying evolutionary branching in spatially structured populations. We show that along an environmental gradient, evolutionary branching can occur much more easily than in non-spatial models. This facilitation is most pronounced for gradients of intermediate slope. Moreover, spatial evolutionary branching readily generates patterns of spatial segregation and abutment between the emerging species. Our results highlight the importance of local processes of adaptive divergence for geographical patterns of speciation, and caution against pitfalls of inferring past speciation processes from present biogeographical patterns.

Doebeli, Michael; Dieckmann, Ulf

2003-01-01

53

Scanning temperature gradient focusing.  

PubMed

Temperature gradient focusing (TGF) is a recently developed technique for the simultaneous concentration and electrophoretic separation of ionic analytes in microfluidic channels. One drawback to TGF as it has previously been described is the limited peak capacity; only a small number of analyte peaks (approximately 2-3) can be simultaneously focused and separated. In this paper, we report on a variation of the TGF method whereby the bulk flow rate is varied over time so that a large number of analytes can be sequentially focused, moved past a fixed detection point, and flushed to waste. In addition to improved peak capacity, the detection limits of the scanning TGF method can be adjusted on-the-fly, as needed for different samples. Finally, scanning TGF provides a technique by which high-resolution, high-peak-capacity electrophoretic separations can be performed in simple, straight, and short microfluidic channels. PMID:17037919

Hoebel, Stacey J; Balss, Karin M; Jones, Barbara J; Malliaris, Constantin D; Munson, Matthew S; Vreeland, Wyatt N; Ross, David

2006-10-15

54

Gradient index polymer optics  

NASA Astrophysics Data System (ADS)

The design, fabrication, and properties of one of a new class of gradient-index lenses are reported. The lens is an f/2.25 GRIN singlet based on a nanolayered polymer composite material, designed to correct for spherical aberration. The light gathering and focusing properties of the polymer lens are compared to a homogeneous BK7 glass singlet with a similar f-number. The modulation transfer function of the polymer GRIN lens exceeded that of the homogeneous glass lens at all spatial frequencies and was as much as 3 times better at 5 cyc/mm. The weight of the polymer lens was approximately an order of magnitude less than the homogeneous glass lens.

Beadie, G.; Fleet, E.; Rosenberg, A.; Lane, Paul A.; Shirk, James S.; Kamdar, A. R.; Ponting, M.; Hiltner, A.; Baer, E.

2008-08-01

55

Conjugate gradient Mojette reconstruction  

NASA Astrophysics Data System (ADS)

Iterative methods are now recognized as powerful tools to solve inverse problems such as tomographic reconstruction. In this paper, the main goal is to present a new reconstruction algorithm made from two components. An iterative algorithm, namely the Conjugate Gradient (CG) method, is used to solve the tomographic problem in the least square (LS) sense for our specific discrete Mojette geometry. The results are compared (with the same geometry) to the corresponding Mojette Filtered Back Projection (FBP) method. In the fist part of the paper, we recall the discrete geometry used to define the projection M and backprojection M* operators. In the second part, the CG algorithm is presented within the context of the Mojette geometry. Noise is then added onto these Mojette projections with respect to the sampling and reconstructions are performed. Finally the Toeplitz block Toeplitz (TBT) character of M*M is demonstrated.

Servieres, Myriam; Idier, Jerome; Normand, Niccolas; Guedon, Jean-Pierre

2005-04-01

56

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

57

Anisotropic Ion Temperature Gradient Instabilities  

Microsoft Academic Search

The effects of anisotropic temperature gradient and collisions on the ion-temperature-gradient (ITG) instabilities have been investigated by using kinetic theory. In the slab limit, the ITG mode is driven unstable by coupling between the transit resonance and ion temperature gradients. While eta_{rm i|} (eta_{rm i| } equiv partiallnT_ {i|}\\/partiallnn, where T_{rm i|} is the perpendicular ion temperature and n is

Hao Song

1994-01-01

58

Gradient elution in capillary electrochromatography  

Microsoft Academic Search

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

D. S. Anex; D. J. Rakestraw; Chao Yan; R. Dadoo; R. N. Zare

1997-01-01

59

Gradient waveform synthesis for magnetic propulsion using MRI gradient coils  

NASA Astrophysics Data System (ADS)

Navigating an untethered micro device in a living subject is of great interest for both diagnostic and therapeutic applications. Magnetic propulsion of an untethered device carrying a magnetic core in it is one of the promising methods to navigate the device. MRI gradients coils are thought to be suitable for navigating the device since they are capable of magnetic propulsion in any direction while providing magnetic resonance images. For precise navigation of the device, especially in the peripheral region of the gradient coils, the concomitant gradient fields, as well as the linear gradient fields in the main magnetic field direction, should be considered in driving the gradient coils. For simple gradient coil configurations, the Maxwell coil in the z-direction and the Golay coil in the x- and y-directions, we have calculated the magnetic force fields, which are not necessarily the same as the conventional linear gradient fields of MRI. Using the calculated magnetic force fields, we have synthesized gradient waveforms to navigate the device along a desired path.

Han, B. H.; Park, S.; Lee, S. Y.

2008-09-01

60

Gradient waveform synthesis for magnetic propulsion using MRI gradient coils.  

PubMed

Navigating an untethered micro device in a living subject is of great interest for both diagnostic and therapeutic applications. Magnetic propulsion of an untethered device carrying a magnetic core in it is one of the promising methods to navigate the device. MRI gradients coils are thought to be suitable for navigating the device since they are capable of magnetic propulsion in any direction while providing magnetic resonance images. For precise navigation of the device, especially in the peripheral region of the gradient coils, the concomitant gradient fields, as well as the linear gradient fields in the main magnetic field direction, should be considered in driving the gradient coils. For simple gradient coil configurations, the Maxwell coil in the z-direction and the Golay coil in the x- and y-directions, we have calculated the magnetic force fields, which are not necessarily the same as the conventional linear gradient fields of MRI. Using the calculated magnetic force fields, we have synthesized gradient waveforms to navigate the device along a desired path. PMID:18695296

Han, B H; Park, S; Lee, S Y

2008-08-11

61

Interphases of chain molecules: Monolayers and lipid bilayer membranes  

PubMed Central

Using the lattice model for a liquid, we treat the packing of short-chain molecules in interphases such as bilayer membranes. The constant density in the interphase imposes intermolecular constraints on the configurations of the flexible chains. The statistical theory here presented predicts a diffuse distribution of chain ends near the bilayer midplane; no adjustable parameters are required. Inasmuch as some of the chains terminate relatively near the polar interface, the number of chains reaching deeper planar layers is diminished. Consequently, configurational freedom increases with depth. This is the source of the well-known disorder gradient.

Dill, Ken A.; Flory, Paul J.

1980-01-01

62

Tumbling dynamics of isolated polymer chains in strong shear flows and the effects of chain resolution  

NASA Astrophysics Data System (ADS)

Using Brownian dynamics simulations, without hydrodynamic and excluded volume interactions, on polymer chain models encompassing a wide range of resolutions, we present a detailed investigation on the behavior of isolated chains in shear flow. We find a highly non-monotonic behavior for all models, with chain compression occurring at ultra-high shear rates that is consistent with the recent simulation studies. However, results obtained using highly refined models, with resolutions lower than a Kuhn step, reveal that this transition is an artifact of the level of chain discretization. Also, our results clearly indicate that, at high shear rates, the chain thickness in the shear-gradient direction is independent of the chain length, which differ from previously reported scaling law. We show that the chain thickness is fixed by the distance a sub-section of the chain can diffuse in the shear-gradient direction before convection stretches it out and suppresses further diffusion. Simple physical arguments are then used to derive the correct scaling laws for the coil width and the tumbling time at high shear rates. We believe that our findings presented here will provide the foundation for a better understanding of this basic problem in polymer dynamics.

Larson, Ronald; Saha Dalal, Indranil; Albaugh, Alex; Hoda, Nazish

2012-02-01

63

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

64

Geothermal gradient map of Colorado  

Microsoft Academic Search

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

F. N. Repplier; R. L. Fargo

1981-01-01

65

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

66

Multilayer High-Gradient Insulators  

SciTech Connect

Multilayer High-Gradient Insulators are vacuum insulating structures composed of thin, alternating layers of dielectric and metal. They are currently being developed for application to high-current accelerators and related pulsed power systems. This paper describes some of the High-Gradient Insulator research currently being conducted at Lawrence Livermore National Laboratory.

Harris, J R

2006-08-16

67

Growth kinetics of colloidal chains and labyrinths  

NASA Astrophysics Data System (ADS)

Particles interacting by a combination of isotropic short-range attraction and long-range repulsion have been shown to form complex phases despite the apparent simplicity of the interparticle potential. Using computer simulations we study the behavior of two-dimensional systems of colloids with such an interaction, focusing on how area fraction and repulsion range at fixed repulsion gradient may be used to tune the resulting kinetics and nonequilibrium structure. While the short-range attraction leads to aggregation, the long-range repulsion encourages growth of chains of particles due to repulsive intercluster interactions. Depending on area fraction/repulsion range we observe chain labyrinths, chain-compact aggregate coexistence, and connected networks of chains. The kinetics of cluster growth displays a sequence of connected networks and disconnected cluster or chain systems with increasing repulsion range, indicating the competing roles of connectivity of growing chains and repulsion-driven breakup of chains into compact aggregates. Chain-dominated systems show approximately logarithmic coarsening at late time that we interpret as the result of chains performing random walks in the randomly fluctuating potential landscape created by their neighbors, a situation reminiscent of glassy systems.

Haw, Mark D.

2010-03-01

68

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

69

Gradient elution in capillary electrochromatography.  

PubMed

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 submicroliter per minute 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-?m 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) [Formula: see text] one providing an increasing ramp and the other providing a decreasing ramp [Formula: see text] 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 was separated in less than 90 min. 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. PMID:21619344

Yan, C; Dadoo, R; Zare, R N; Rakestraw, D J; Anex, D S

1996-09-01

70

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

71

Interactions of Bubbles in a Temperature Gradient.  

NASA Astrophysics Data System (ADS)

A theoretical and experimental investigation of the hydrodynamic interactions of bubbles in the presence of a temperature gradient has been performed. Both theory and experiment correspond to motion at negligible values of the Reynolds and Peclet numbers so that convective transport of momentum and energy is unimportant. In the theoretical models, the thermocapillary migration of a small chain of spherical bubbles in an unbounded fluid possessing a uniform temperature gradient is investigated. The line of bubble centers is permitted to be either parallel or perpendicular to the direction of the undisturbed temperature gradient. The governing equations are solved by a truncated -series, boundary-collocation technique. Results are presented which demonstrate the impact of the presence of other bubbles on a test bubble. Also, features of the flow topology in the fluid are explored. A pairwise-additive approximation is presented, and is found to perform well except for relatively small separations. The migration of a pair of gas bubbles in an unbounded fluid subject to the combined action of gravity and a downward temperature gradient also is investigated theoretically. The solution for the case when the line-of-centers is oriented arbitrarily with respect to the gravity vector is constructed by superposing solutions of the axisymmetric and asymmetric problems. In the axisymmetric problem, it is found that a pair of unequal bubbles can reach a stable critical separation at which both bubbles move at the same velocity, if the smaller bubble is on top of the larger one; at an appropriate balance of the relative strengths of the gravitational and thermocapillary forces, such a pair of bubbles also can reach a motionless state. Flow structures are illustrated via streamlines. Experiments are performed to measure the velocities of individual members of a pair of air bubbles in a silicone oil under isothermal conditions as well as in a downward temperature gradient. Three situations are investigated: motion driven by buoyancy, motion dominated by thermocapillarity, and motion when the gravitational force and the thermocapillary force on the larger bubble of the pair are comparable. The experimental results are found to be in good agreement with theoretical predictions from the method of reflections which gives the simplest form with results indistinguishable from those based on the boundary collocation technique within the experimental uncertainty. When the gravitational force is slightly smaller than the thermocapillary force on the larger bubble in the pair, the larger bubble moves downward but the smaller bubble nearby is found to move upward. This counter-intuitive behavior is actually consistent with expectation, and an explanation is given.

Wei, Huailiang

72

Optimum gradient of mountain paths.  

PubMed

By combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained predictions. PMID:8594031

Minetti, A E

1995-11-01

73

Development of Temporal Temperature Gradient Electrophoresis for Characterising Methanogen Diversity  

Microsoft Academic Search

Temporal temperature gradient electrophoretic (TTGE) analysis of 16S rDNA sequences was optimized to monitor the methanogen\\u000a population present in water and sediments of a small eutrophic lake, Priest Pot, in the English Lake district. The production\\u000a of nonrepresentative TTGE profiles due to the generation of polymerase chain reaction (PCR) artifacts initially proved problematical.\\u000a The use of a proofreading polymerase in

Julie Earl; Roger W. Pickup; Donald A. Ritchie; Clive Edwards

2005-01-01

74

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2013 CFR

...26 2013-07-01 2013-07-01 false Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2013-07-01

75

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2010 CFR

...24 2010-07-01 2010-07-01 false Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2010-07-01

76

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2010 CFR

...24 2009-07-01 2009-07-01 false Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2009-07-01

77

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

78

Templating Surfaces with Gradient Assemblies  

Microsoft Academic Search

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 [Science256, 1539 (1992)]. 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

Jan Genzer

2005-01-01

79

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

80

Health supply chain management.  

PubMed

This chapter gives an educational overview of: * The actual application of supply chain practice and disciplines required for service delivery improvement within the current health environment. * A rationale for the application of Supply Chain Management (SCM) approaches to the Health sector. * The tools and methods available for supply chain analysis and benchmarking. * Key supply chain success factors. PMID:20407173

Zimmerman, Rolf; Gallagher, Pat

2010-01-01

81

Planar gradient index photonic metamaterials  

NASA Astrophysics Data System (ADS)

Metamaterials operating at optical frequencies, referred to as optical or photonic metamaterials, require features fabricated at a subwavelength scale from 50 nm to 1000nm. In this work a planar gradient index metamaterial is designed and demonstrated at optical frequencies by numerical simulation through a finite-difference time domain method in conjunction with an electromagnetic retrieval technique. We confirm the gradient by simulating the deflection of a light beam passing through a multilayer silver (Ag) and magnesium fluoride (MgF2) slab featured with specially designed nano-rectangular holes. The planar gradient index photonic metamaterials we propose can be fabricated by available nano-fabrication technologies. Optical tests can be performed since the designs are also based on the consideration of the frequency range available for evaluation.

Wu, Zhuoyuan; Yönak, Serdar

2011-09-01

82

Subpixel registration with gradient correlation.  

PubMed

We address the problem of subpixel registration of images assumed to be related by a pure translation. We present a method which extends gradient correlation to achieve subpixel accuracy. Our scheme is based on modeling the dominant singular vectors of the 2-D gradient correlation matrix with a generic kernel which we derive by studying the structure of gradient correlation assuming natural image statistics. Our kernel has a parametric form which offers flexibility in modeling the functions obtained from various types of image data. We estimate the kernel parameters, including the unknown subpixel shifts, using the Levenberg-Marquardt algorithm. Experiments with LANDSAT and MRI data show that our scheme outperforms recently proposed state-of-the-art phase correlation methods. PMID:21118776

Tzimiropoulos, Georgios; Argyriou, Vasileios; Stathaki, Tania

2010-11-29

83

THE GRADIENT OF VASCULAR PERMEABILITY  

PubMed Central

A steeply mounting gradient of permeability is demonstrable along the meshwork of capillaries which connects the arterioles and venules of the skin of the frog. The venules incorporated in the meshwork are even more permeable than the capillary meshes giving into them. The presence of the gradient under such differing conditions as exist along frog and mammalian capillaries enables one to rule out certain factors which might be invoked to explain it; and it is not explainable in terms of those influences generally recognized as conditioning exchange between the blood and tissues. Not improbably it results from a structural differentiation along the capillary.

Rous, Peyton; Smith, Frederick

1931-01-01

84

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

85

Multilayer High-Gradient Insulators  

SciTech Connect

High voltage systems operated in vacuum require insulating materials to maintain spacing between conductors held at different potentials, and may be used to maintain a nonconductive vacuum boundary. Traditional vacuum insulators generally consist of a single material, but insulating structures composed of alternating layers of dielectric and metal can also be built. These ''High-Gradient Insulators'' have been experimentally shown to withstand higher voltage gradients than comparable conventional insulators. As a result, they have application to a wide range of high-voltage vacuum systems where compact size is important. This paper describes ongoing research on these structures, as well as the current theoretical understanding driving this work.

Harris, J R; Anaya, R M; Blackfield, D; Chen, Y -; Falabella, S; Hawkins, S; Holmes, C; Paul, A C; Sampayan, S; Sanders, D M; Watson, J A; Caporaso, G J; Krogh, M

2006-11-15

86

Superlinear Convergence of Conjugate Gradients  

Microsoft Academic Search

We give a theoretical explanation for superlinear convergence behavior observed while solving large symmetric systems of equations using the Conjugate Gradient method, or other Krylov subspace methods. We present a new bound on the relative error after n iterations. This bound is valid in an asymptotic sense, when the size N of the system grows together with the number of

Bernhard Beckermann; Arno B. J. Kuijlaars

1999-01-01

87

Policy Gradient Methods for Robotics  

Microsoft Academic Search

The aquisition and improvement of motor skills and control policies for robotics from trial and error is of essential importance if robots should ever leave precisely pre-structured environments. However, to date only few existing reinforcement learning methods have been scaled into the domains of high- dimensional robots such as manipulator, legged or humanoid robots. Policy gradient methods remain one of

Jan Peters; Stefan Schaal

2006-01-01

88

Shape reconstruction from gradient data  

Microsoft Academic Search

We present a novel method for reconstructing the shape of an object from measured gradient data. A certain class of optical sensors does not measure the shape of an object, but its local slope. These sensors display several advantages, including high information efficiency, sensitivity, and robustness. For many applications, however, it is necessary to acquire the shape, which must be

Svenja Ettl; Juergen Kaminski; Markus C. Knauer; Gerd Haeusler

2008-01-01

89

Long pendulums in gravitational gradients  

Microsoft Academic Search

Previous results for long pendulums above a spherical Earth are generalized for arbitrary non-uniform gravitational fields in the limit of small oscillation. As is the case for the previous results, gravitational gradients are multiplied by the length of the string even though the string is assumed massless. The effect is shown to arise from the constraint on the motion imposed

B H Suits

2006-01-01

90

Variable metric conjugate gradient methods  

SciTech Connect

1.1 Motivation. In this paper we present a framework that includes many well known iterative methods for the solution of nonsymmetric linear systems of equations, Ax = b. Section 2 begins with a brief review of the conjugate gradient method. Next, we describe a broader class of methods, known as projection methods, to which the conjugate gradient (CG) method and most conjugate gradient-like methods belong. The concept of a method having either a fixed or a variable metric is introduced. Methods that have a metric are referred to as either fixed or variable metric methods. Some relationships between projection methods and fixed (variable) metric methods are discussed. The main emphasis of the remainder of this paper is on variable metric methods. In Section 3 we show how the biconjugate gradient (BCG), and the quasi-minimal residual (QMR) methods fit into this framework as variable metric methods. By modifying the underlying Lanczos biorthogonalization process used in the implementation of BCG and QMR, we obtain other variable metric methods. These, we refer to as generalizations of BCG and QMR.

Barth, T.; Manteuffel, T.

1994-07-01

91

AGENT NAVIGATION USING POTENTIAL FIELDS AND FORWARD CHAINING  

Microsoft Academic Search

Key Results: Increasingly competent heuristics produce the novel Forward Chaining heuristic, allowing navigation past obstacle configurations that are impossible for traditional potential field methods. How does the work advance the state-of-the-art?: Gradient based potential field navigation heuristics cannot overcome the Local Minimum Problem. Forward Chaining overcomes the LMP and allows successful navigation in most 2D environments. Motivation (problems addressed): To

Graeme Bell; Michael Weir

92

Corrosion in a temperature gradient  

SciTech Connect

High temperature corrosion limits the operation of equipment used in the Power Generation Industry. Some of the more destructive corrosive attack occurs on the surfaces of heat exchangers, boilers, and turbines where the alloys are subjected to large temperature gradients that cause a high heat flux through the accumulated ash, the corrosion product, and the alloy. Most current and past corrosion research has, however, been conducted under isothermal conditions. Research on the thermal-gradient-affected corrosion of various metals and alloys is currently being studied at the Albany Research Center’s SECERF (Severe Environment Corrosion and Erosion Research Facility) laboratory. The purpose of this research is to verify theoretical models of heat flux effects on corrosion and to quantify the differences between isothermal and thermal gradient corrosion effects. The effect of a temperature gradient and the resulting heat flux on corrosion of alloys with protective oxide scales is being examined by studying point defect diffusion and corrosion rates. Fick’s first law of diffusion was expanded, using irreversible thermodynamics, to include a heat flux term – a Soret effect. Oxide growth rates are being measured for the high temperature corrosion of cobalt at a metal surface temperature of 900ºC. Corrosion rates are also being determined for the high temperature corrosion of carbon steel boiler tubes in a simulated waste combustion environment consisting of O2, CO2, N2, and water vapor. Tests are being conducted both isothermally and in the presence of a temperature gradient to verify the effects of a heat flux and to compare to isothermal oxidation.

Covino, Bernard S., Jr.; Holcomb, Gordon R.; Cramer, Stephen D.; Bullard, Sophie J.; Ziomek-Moroz, Margaret; White, M.L. (Convanta)

2003-01-01

93

Thermalization and temperature distribution in a driven ion chain  

NASA Astrophysics Data System (ADS)

We study thermalization and non-equilibrium dynamics in a dissipative quantum many-body system --- a chain of ions with two points of the chain driven by thermal bath under different temperature. Instead of a simple linear temperature gradient as one expects from the classical heat diffusion process, the temperature distribution in the ion chain shows surprisingly rich patterns, which depend on the ion coupling rate to the bath, the location of the driven ions, and the dissipation rates of the other ions in the chain. We discuss implementation issues and show these unusual temperature distribution patterns in the ion chain can be quantitatively tested through experimental observation. A direct application is continuous sympathetic cooling in a scalable trapped ion quantum computer. We demonstrate the architecture how the ion chain can be maintained cooled efficiently to guarantee high-fidelity computation.

Lin, Guin-Dar; Duan, Luming

2010-03-01

94

Application of a food chain model to polychlorinated biphenyl contamination of the lobster and winter flounder food chains in New Bedford Harbor  

Microsoft Academic Search

As part of a Remedial Investigation\\/Feasibility Study for the New Bedford Harbor Superfund site a model of polychlorinated biphenyls (PCBs) in the lobster and winter flounder food chains was developed. This model successfully reproduces tri-, tetra-, penta-, and hexachlorobiphenyl concentrations observed at all levels of the food chain and across the 2 order of magnitude concentration gradient in the system.

John P. Connolly

1991-01-01

95

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

96

Gradient-based image deconvolution  

NASA Astrophysics Data System (ADS)

Image restoration and deconvolution from blurry and noisy observation is known to be ill-posed. To stabilize the recovery, total variation (TV) regularization is often utilized for its beneficial edge in preserving the image's property. We take a different approach of TV regularization for image restoration. We first recover horizontal and vertical differences of images individually through some successful deconvolution algorithms. We restore horizontal and vertical difference images separately so that each is more sparse or compressible than the corresponding original image with a TV measure. Then we develop a novel deconvolution method that recovers the horizontal and vertical gradients, respectively, and then estimate the original image from these gradients. Various experiments that compare the effectiveness of the proposed method against the traditional TV methods are presented. Experimental results are provided to show the improved performance of our method for deconvolution problems.

Huang, Heyan; Yang, Hang; Ma, Siliang

2013-01-01

97

Regulation of the mitochondrial proton gradient by cytosolic Ca²? signals.  

PubMed

Mitochondria convert the energy stored in carbohydrate and fat into ATP molecules that power enzymatic reactions within cells, and this process influences cellular calcium signals in several ways. By providing ATP to calcium pumps at the plasma and intracellular membranes, mitochondria power the calcium gradients that drive the release of Ca²? from stores and the entry of Ca²? across plasma membrane channels. By taking up and subsequently releasing calcium ions, mitochondria determine the spatiotemporal profile of cellular Ca²? signals and the activity of Ca²?-regulated proteins, including Ca²? entry channels that are themselves part of the Ca²? circuitry. Ca²? elevations in the mitochondrial matrix, in turn, activate Ca²?-dependent enzymes that boost the respiratory chain, increasing the ability of mitochondria to buffer calcium ions. Mitochondria are able to encode and decode Ca²? signals because the respiratory chain generates an electrochemical gradient for protons across the inner mitochondrial membrane. This proton motive force (?p) drives the activity of the ATP synthase and has both an electrical component, the mitochondrial membrane potential (??(m)), and a chemical component, the mitochondrial proton gradient (?pH(m)). ??(m) contributes about 190 mV to ?p and drives the entry of Ca²? across a recently identified Ca²?-selective channel known as the mitochondrial Ca²? uniporter. ?pH(m) contributes ~30 mV to ?p and is usually ignored or considered a minor component of mitochondria respiratory state. However, the mitochondrial proton gradient is an essential component of the chemiosmotic theory formulated by Peter Mitchell in 1961 as ?pH(m) sustains the entry of substrates and metabolites required for the activity of the respiratory chain and drives the activity of electroneutral ion exchangers that allow mitochondria to maintain their osmolarity and volume. In this review, we summarize the mechanisms that regulate the mitochondrial proton gradient and discuss how thermodynamic concepts derived from measurements in purified mitochondria can be reconciled with our recent findings that mitochondria have high proton permeability in situ and that ?pH(m) decreases during mitochondrial Ca²? elevations. PMID:22526460

Poburko, Damon; Demaurex, Nicolas

2012-04-24

98

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

99

Financial supply chain management  

Microsoft Academic Search

To effectively manage a supply chain, we should no longer focus on physical flow and informational flow only, but also the financial flow. The financial supply chain management (FSCM) extracts capital tied to the raw material, work-in-process, inventory in transit, and accounts receivable (accounts payable). In this paper we review a set of supply chain financing solutions tailored by the

Miao He; Changrui Ren; Bing Shao; Qinhua Wang; Jin Dong

2010-01-01

100

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

101

Mitigating Supply Chain Vulnerability  

Microsoft Academic Search

Competitive pressures are forcing companies to adopt practices and supply chain structures that will produce high quality, reliable, reasonably priced products with continuously shorter lead times. In order to meet these goals, companies are utilizing flatter organizational structures and narrower supply chains. Flatter structures and narrower supply chains typically reap the benefits of reduced coordination costs and improved organizational efficiencies.

Brian D. Neureuther; George Kenyon

2009-01-01

102

Primordial vorticity and gradient expansion  

NASA Astrophysics Data System (ADS)

The evolution equations of the vorticities of the electrons, ions and photons in a pre-decoupling plasma are derived, in a fully inhomogeneous geometry, by combining the general relativistic gradient expansion and the drift approximation within the Adler-Misner-Deser decomposition. The vorticity transfer between the different species is discussed in this novel framework and a set of general conservation laws, connecting the vorticities of the three-component plasma with the magnetic field intensity, is derived. After demonstrating that a source of large-scale vorticity resides in the spatial gradients of the geometry and of the electromagnetic sources, the total vorticity is estimated to lowest order in the spatial gradients and by enforcing the validity of the momentum constraint. By acknowledging the current bounds on the tensor to scalar ratio in the (minimal) tensor extension of the ?CDM paradigm, the maximal comoving magnetic field induced by the total vorticity turns out to be, at most, of the order of 10-37 G over the typical comoving scales ranging between 1 and 10 Mpc. While the obtained results seem to be irrelevant for seeding a reasonable galactic dynamo action, they demonstrate how the proposed fully inhomogeneous treatment can be used for the systematic scrutiny of pre-decoupling plasmas beyond the conventional perturbative expansions.

Giovannini, Massimo; Rezaei, Zahra

2012-02-01

103

Development Value Chains Meet Business Supply Chains: The concept of Global Value Chains unraveled  

Microsoft Academic Search

Value chain promotion is considered a key element of private sector development strategies and pro-poor growth. However, (value) chain concepts are rather complex and unclear. this paper unravels the concept of global value chains and studies the diversity of key value chain-related (supply chain, commodity chain, value chain) approaches. To this aim, we reviewed academic literature and donor agencies' reports,

Sarah Drost; Jeroen van Wijk; Sietze Vellema

2011-01-01

104

Gravity gradient preprocessing at the GOCE HPF  

Microsoft Academic Search

One of the products derived from the GOCE observations are the gravity gradients. These gravity gradients are provided in the Gradiometer Reference Frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. In order to use these gravity gradients for application in Earth sciences and gravity field analysis, additional pre-processing needs to be done, including corrections for

J. Bouman; S. Rispens; T. Gruber; E. Schrama; P. Visser; C. C. Tscherning; M. Veicherts

2009-01-01

105

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

2013-10-15

106

Online learning via congregational gradient descent  

Microsoft Academic Search

We propose and analyse a populational version of stepwise gradient descent suitable for a wide range of learning problems. The algorithm is motivated by genetic algorithms which update a population of solutions rather than just a single representative as is typical for gradient descent. This modification of traditional gradient descent (as used, for example, in the backpropogation algorithm) avoids getting

Kim L. Blackmore; Robert C. Williamson; Iven M. Y. Mareels; William A. Sethares

1997-01-01

107

Gradient domain high dynamic range compression  

Microsoft Academic Search

We present a new method for rendering high dynamic range images on conventional displays. Our method is conceptually simple, computationally efficient, robust, and easy to use. We manipulate the gradient field of the luminance image by attenuating the magnitudes of large gradients. A new, low dynamic range image is then obtained by solving a Poisson equation on the modified gradient

Raanan Fattal; Dani Lischinski; Michael Werman

2002-01-01

108

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

2013-07-25

109

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

110

Shape reconstruction from gradient data  

SciTech Connect

We present a generalized method for reconstructing the shape of an object from measured gradient data. A certain class of optical sensors does not measure the shape of an object but rather its local slope. These sensors display several advantages, including high information efficiency, sensitivity, and robustness. For many applications, however, it is necessary to acquire the shape, which must be calculated from the slopes by numerical integration. Existing integration techniques show drawbacks that render them unusable in many cases. Our method is based on an approximation employing radial basis functions. It can be applied to irregularly sampled, noisy, and incomplete data, and it reconstructs surfaces both locally and globally with high accuracy.

Ettl, Svenja; Kaminski, Juergen; Knauer, Markus C.; Haeusler, Gerd

2008-04-20

111

Interhemispheric thermal gradient and tropical Pacific climate  

NASA Astrophysics Data System (ADS)

We explore the impact of interhemispheric thermal gradients forcing on the tropical Pacific ocean-atmosphere climate in an intermediate coupled model. The equatorial zonal sea surface temperature (SST) gradient strengthens with an increased northward interhemispheric thermal gradient, the increase arising from earlier onset and later retreat of the seasonal cold tongue, and intensification during the peak cold season. When the mean interhemispheric thermal gradient is reversed, the central equatorial Pacific SST annual cycle abruptly reverses in phase, with its cold season in Mar-May rather than Sep-Nov. While startling, this response is consistent with a prevailing hypothesis that ties the cold tongue SST annual cycle phase to the hemispheric mean asymmetry of the Intertropical Convergence Zone. El Niño-Southern Oscillation activity is also sensitive to the interhemispheric thermal gradient, with peak activity occurring when the mean gradient is small, reducing rapidly as the mean gradient increases in either direction.

Chiang, John C. H.; Fang, Yue; Chang, P.

2008-07-01

112

Nanooptics of gradient dielectric films  

SciTech Connect

The propagation of light through subwave photonic barriers formed by dielectric nanofilms with the refractive indices changing across the films according to the specified law n(z) is considered. Generalised Fresnel formulae depending on the gradient and profile curvature of the refractive index and describing reflection and transmission of such inhomogeneous films are found. For the specified material and thickness, the optical properties of such nanofilms can change from total transmission to total reflection by producing a technologically controlled profile n(z). The obtained results are based on exact analytic solutions of Maxwell's equations for new multiparametric models of inhomogeneous dielectric media. The possibility of producing new subwave dispersion elements, whose action is based on the dependence of the reflection and transmission spectra of gradient photonic barriers on their local dispersion determined by the shape and geometrical parameters of the profile n(z), is shown. The schemes are considered for producing such spectra in the visible and IR regions with the help of periodic nanostructures containing subwave photonic barriers with the normal and anomalous nonlocal dispersion. (nanostructures)

Shvartsburg, Aleksandr B; Agranat, Mikhail B; Chefonov, O V [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow (Russian Federation)

2009-10-31

113

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

114

The Value Chain  

NSDL National Science Digital Library

From Industry Week, The Value Chain is an online publication providing up-to-date information, articles, and resources on value chain management (VCM), a theory of management that considers every step of manufacturing a product, from raw materials "right down to disposing of the packaging after use." Along with feature articles and columns about value chain management, the site also contains a FAQ, which offers excellent basic advice about VCM, a New Roundup Weblog of breaking VCM news, and short research pieces.

115

Differential gradient separation of cells  

US Patent & Trademark Office Database

A device and method in which cells of a heterogeneous population are separated through a column partially packed with antibody coated beads. The antibody coated beads may be placed in a gradient fashion such that each layer binds to and selects a subset of cells from the entire sample population. A lipoaspirate fluid, or other fluid containing cells, may be brought through the column by positive pressure on the specimen bag side and negative pressure at the base of the column with a vacuum line and waste trap. The column may then be inverted and irrigated internally with a wash buffer to remove unhomogenized macroscopic tissue material and unbound residual cells. The column may be closed at the ends and shaken and/or washed with an enzymatic buffer. Cells may be removed from the device with an elution buffer.

2012-10-09

116

Assessing hue constancy using gradients  

NASA Astrophysics Data System (ADS)

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. The results show that IPT, MLab and CIECAM97s are better than CIELUV and CIELAB in the blue regions of color space. There are minimal differences between the color spaces for other hue angles. However, there are still differences in lightness and chroma for the different color spaces that should be further investigated. Finally, the blue constancy of CIELAB is considerably improved by converting to Hunt-Pointer-Estevez cone fundamentals before applying the standard CIELAB equations.

Moroney, Nathan

1999-12-01

117

Integrable hydrodynamic chains  

Microsoft Academic Search

A new approach for derivation of Benney-type moment chains and integrable hydrodynamic type systems is presented. New integrable hydrodynamic chains are constructed; all their hydrodynamical reductions are described and integrated. New (2+1) integrable hydrodynamic type systems are found.

Maxim V. Pavlov

2003-01-01

118

Chain Reaction Polymerization.  

ERIC Educational Resources Information Center

The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

McGrath, James E.

1981-01-01

119

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.

120

Latitudinal temperature gradients and climate change  

NASA Astrophysics Data System (ADS)

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 in a doubled CO2 experiment and show overall agreement. Results show that the latitudinal temperature gradient governs the Hadley cell intensity, eddy energy properties, and eddy transports other than latent heat. The global mean temperature governs moisture and cloud cover, Hadley cell extent, and total rainfall. The degree of tropical and subtropical moisture changes depend on both the latitudinal gradient and the mean temperature. The Aleutian low is particularly sensitive to gradient changes, while the Icelandic low (and therefore the Greenland ice core region) is not, possibly due to orographically induced constraints in the North Atlantic. The results are then compared with paleoclimate evidence to deduce what has happened to latitudinal gradients and climate in the past. It is estimated that low-latitude temperature gradients similar to today's may have occurred in the Mesozoic and in the Little Ice Age; reduced gradients were more likely in the Pliocene, Eocene, Younger Dryas, and Last Glacial Maximum. At higher latitudes, warm climates likely had reduced temperature gradients, and cold climates increased gradients. Observed equator to pole gradients were increased in the 1980s relative to the 1950s, and the simulated climate changes consistent with observations include warming of Alaska and Asia, drying in the subtropics, and moisture variability in the United States. Assignment of causes to past latitudinal gradient changes is problematic due to uncertainties concerning CO2 and ocean heat transports, but tentative conclusions based on this analysis support the likelihood of a future, higher-CO2 climate exhibiting a large low-latitude gradient and ample precipitation at middle latitudes.

Rind, D.

1998-03-01

121

Nanofiber scaffold gradients for interfacial tissue engineering.  

PubMed

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. PMID:22286209

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

2012-01-27

122

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

123

Self-Assembling Gradient Copolymers of Vinylimidazol and (Acrylic)ibuprofen With Anti-Inflammatory and Zinc Chelating Properties.  

PubMed

Novel gradient copolymers of hydrophilic 1-vinylimidazol and hydrophobic methacrylic derivative of ibuprofen prepared by free radical polymerization are described. The heterogeneous distribution of monomeric units along the polymeric chains leads to a gradient distribution of the hydrophobic and hydrophilic sequences responsible of nanoparticles formation through a self-assembling mechanism, capable of tune the water permeation due to the ionizable imidazole moieties and their gradient profile along the macromolecules, exhibiting pH and composition dependent effect in terms of diameter, zeta potential, acid-base buffering, ibuprofen release and chelating capacities, responsible of matrix metalloproteinase dysfunction showing anti-inflammatory activity in a nitric oxide inhibition assay. PMID:23836487

Suárez, Patricia; Rojo, Luis; González-Gómez, Alvaro; Román, Julio San

2013-07-08

124

SUMO chains: polymeric signals.  

PubMed

Ubiquitin and ubiquitin-like proteins are conjugated to a wide variety of target proteins that play roles in all biological processes. Target proteins are conjugated to ubiquitin monomers or to ubiquitin polymers that form via all seven internal lysine residues of ubiquitin. The fate of these target proteins is controlled in a chain architecture-dependent manner. SUMO (small ubiquitin-related modifier) shares the ability of ubiquitin to form chains via internal SUMOylation sites. Interestingly, a SUMO-binding site in Ubc9 is important for SUMO chain synthesis. Similar to ubiquitin-polymer cleavage by USPs (ubiquitin-specific proteases), SUMO chain formation is reversible. SUMO polymers are cleaved by the SUMO proteases SENP6 [SUMO/sentrin/SMT3 (suppressor of mif two 3)-specific peptidase 6], SENP7 and Ulp2 (ubiquitin-like protease 2). SUMO chain-binding proteins including ZIP1, SLX5/8 (synthetic lethal of unknown function 5/8), RNF4 (RING finger protein 4) and CENP-E (centromere-associated protein E) have been identified that interact non-covalently with SUMO chains, thereby regulating target proteins that are conjugated to SUMO multimers. SUMO chains play roles in replication, in the turnover of SUMO targets by the proteasome and during mitosis and meiosis. Thus signalling via polymers is an exciting feature of the SUMO family. PMID:20074033

Vertegaal, Alfred C O

2010-02-01

125

Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios  

Microsoft Academic Search

By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (Fp\\/r and Gp\\/r), magic pulsed field gradient (MPFG) ratios for the prepare (Gp\\/Fp) and the read (Gr\\/Fr) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the

Petrik Galvosas; Frank Stallmach; Jörg Kärger

2004-01-01

126

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

127

Density gradient stabilization of electron temperature gradient driven turbulence in a spherical tokamak.  

PubMed

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 2 decrease in the plasma effective thermal diffusivity. PMID:21599377

Ren, Y; Kaye, S M; Mazzucato, E; Guttenfelder, W; Bell, R E; Domier, C W; LeBlanc, B P; Lee, K C; Luhmann, N C; Smith, D R; Yuh, H

2011-04-22

128

An Inexpensive Digital Gradient Controller for HPLC.  

ERIC Educational Resources Information Center

|Use of gradient elution techniques in high performance liquid chromatography (HPLC) is often essential for direct separation of complex mixtures. Since most commercial controllers have features that are of marginal value for instructional purposes, a low-cost controller capable of illustrating essential features of gradient elution was developed.…

Brady, James E.; Carr, Peter W.

1983-01-01

129

An Inexpensive Digital Gradient Controller for HPLC.  

ERIC Educational Resources Information Center

Use of gradient elution techniques in high performance liquid chromatography (HPLC) is often essential for direct separation of complex mixtures. Since most commercial controllers have features that are of marginal value for instructional purposes, a low-cost controller capable of illustrating essential features of gradient elution was developed.…

Brady, James E.; Carr, Peter W.

1983-01-01

130

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

131

Accelerated gradient methods for networked optimization  

Microsoft Academic Search

This paper explores the use of accelerated gra- dient methods in networked optimization. Optimal algorithm parameters and associated convergence rates are derived for distributed resource allocation and consensus problems, and the practical performance of the accelerated gradient algorithms are shown to outperform alternatives in the literature. Since the optimal parameters for the accelerated gradient method depends on upper and lower

Euhanna Ghadimi; Mikael Johansson; Iman Shames

2011-01-01

132

Automated Apparatus for Producing Gradient Gels.  

National Technical Information Service (NTIS)

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...

N. L. Anderson

1983-01-01

133

Biopotential amplifier for potential gradient measurements  

Microsoft Academic Search

This work proposes a bio-potential amplifier suitable for measurements from an electric potential gradient sensor, in electro-encephalography (EEG). The sensor is an array made by three electrodes placed on the vertices of an equilateral triangle of reduced size. Measuring the gradient requires small separation between electrodes hence, very low amplitude signals, of a few ?V, are obtained. Therefore, it is

Enrique M Spinelli; Carlos H Muravchik

2007-01-01

134

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

135

CARS thermometry in high temperature gradients  

Microsoft Academic Search

CARS is an effective non-intrusive technique for measuring gas temperature in combustion environments. In regions of high temperature gradient, however, the CARS signal is complicated by contributions from gas at different temperature. This paper examines theoretically the uncertainty associated with CARS thermometry in steep temperature gradients. In addition, the work compares the temperature predicted from CARS with the adiabatic mixed

J. Y. Zhu; D. Dunn-Rankin

1993-01-01

136

Molecular daisy chains.  

PubMed

This tutorial review summarizes the progress made towards mechanically interlocked daisy chains. Such materials can be seen as a further development in polymer science, where the conventional covalent interlinking bonds are replaced by supramolecular binding concepts. Materials in which the mechanical bond is an integral part of the polymeric backbone are expected to possess unique macroscopic properties and are therefore the synthetic aim in an ever growing research community. After introducing general considerations about daisy chains, the most common analytic methods to get insight into the aggregation behaviour of such self-complementary monomers are presented. Cyclodextrins/aromatic rods, crown ethers/cationic rods and pillararenes/alkyl chains are systems used to achieve daisy chain-like molecular arrays. By comparison of the reported systems, conclusions about an improved structural design are drawn. PMID:22983207

Rotzler, Jürgen; Mayor, Marcel

2012-09-17

137

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

138

Chain or Web?  

NSDL National Science Digital Library

This reference provides a brief description of marine food webs. It presents food web terminology, explains the relationship between food chains and food webs, and introduces the concept of microbial loops.

139

Polarisation effects in gradient nano-optics  

NASA Astrophysics Data System (ADS)

The spectra of reflection of s- and p-polarised waves from gradient nanocoatings at arbitrary angles of incidence are found within the framework of two exactly solvable models of such coatings. To use the detected spectra in the visible and IR ranges, for different frequencies and coating thicknesses we present the wave reflection coefficients as functions of dimensionless frequencies related to the refractive index gradient of the coating material. It is shown that reflection from the gradient coatings in question is an order of magnitude weaker than reflection from uniform coatings, other parameters of radiation and the reflection system being equal. We report a new exactly solvable model illustrating the specific effect of gradient film optics - the possibility of non-reflective propagation of an s-wave through such a film (an analogue of the Brewster effect). The prospects are shown for the use of gradient nanostructures with different refractive index profiles to fabricate broadband non-reflective coatings.

Erokhin, N. S.; Zueva, Yu M.; Shvartsburg, A. B.

2013-09-01

140

Gradient-enhanced FAWSETS perfusion measurements  

NASA Astrophysics Data System (ADS)

This work describes the use of custom-built gradients to enhance skeletal muscle perfusion measurements acquired with a previously described arterial spin labeling technique known as FAWSETS (flow-driven arterial water stimulation with elimination of tissue signal). Custom-built gradients provide active control of the static magnetic field gradient on which FAWSETS relies for labeling. This allows selective, 180° modulations of the phase of the perfusion component of the signal. Phase cycling can then be implemented to eliminate all extraneous components leaving a signal that exclusively reflects capillary-level perfusion. Gradient-enhancement substantially reduces acquisition time and eliminates the need to acquire an ischemic signal to quantify perfusion. This removes critical obstacles to application of FAWSETS in organs other than skeletal muscle and makes the measurements more desirable for clinical environments. The basic physical principles of gradient-enhancement are demonstrated in flow phantom experiments and in vivo utility is demonstrated in rat hind limb during stimulated exercise.

Marro, Kenneth I.; Lee, Donghoon; Hyyti, Outi M.

2005-08-01

141

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

142

Ideal chain (entropic elasticity)  

NSDL National Science Digital Library

In the first video segment, we present a cartoon model of a weighted chain, which can be regarded as an approximation for a polymer under tension (e.g. a strand of DNA being stretched out using optical tweezers). The Hamiltonian and partition function for this system are described in the second segment. Finally, in the third segment, we calculate the average energy and elongation of the chain.

Liao, David

143

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

144

Dynamic supply chain scheduling  

Microsoft Academic Search

Based on a combination of fundamental results of modern optimal program control theory and operations research, an original\\u000a approach to supply chain scheduling is developed in order to answer the challenges of dynamics, uncertainty, and adaptivity.\\u000a Both supply chain schedule generation and execution control are represented as an optimal program control problem in combination\\u000a with mathematical programming and interpreted as

D. Ivanov; B. Sokolov

145

Stratospheric Balloon Gradient Geomagnetic Measurements  

NASA Astrophysics Data System (ADS)

The study of the interior structure of the Earth and laws of its evolution is one of the most difficult problems of natural science. Among the geophysical fields the anomaly magnetic field is one of the most informational in questions of the Earth's crust structure. Many important parameters of an environment are expedient for measuring at lower altitudes, than satellite ones. So, one of the alternatives is stratospheric balloon survey. The balloon flight altitudes cover the range from 20 to 50 km. At such altitudes there are steady zone air flows due to which the balloon flight trajectories can be of any direction, including round-the-world (round-the-pole). One of the examples of such sounding system have been designed, developed and maintained at IZMIRAN during already about 20 years. This system consists of three instrumental con-tainers uniformly placed along a vertical 6 km line. System allows measuring a module and vertical gradient of the geomagnetic field along the whole flight trajectory and so one's name is -stratospheric balloon magnetic gradiometer (SMBG). The GPS-receivers, located in each instrumental container, fix the flight coordinates to within several tens meters. Data trans-mission is carried out by Globalstar satellite link. The obtained data are used in solving the problems of deep sounding of the Earth's crust magnetic structure -an extraction of magnetic anomalies, determination of a depth of bedding of magnetoactive rocks and others. The developed launching technology, deployment in flight, assembly, data processing, transfer and landing the containers with the equipment can be used for other similar problems of monitoring and sounding an environment. Useful flight weights of each instrumental container may be reaching 50 kg. More than ten testing flights (1986-2009) at stratospheric altitudes (20-30 km) have proven the reliability of this system.

Filippov, Sergey; Tsvetkov, Yury

146

Dynamics of Cloud Point Transitions in Dilute Solutions of Gradient Copolymers with Prescribed Gradient Strengths  

NASA Astrophysics Data System (ADS)

We have investigated dilute solutions of gradient copolymers comprising hydroxyethyl methacrylate and dimethylaminoethyl methacrylate with different gradient strengths undergoing their cloud point transitions. The gradient strength defines the maximum difference in instantaneous compositions along the polymer backbone. Isothermal dynamic light scattering tracks the fractions of unimers and aggregates with which the half times characterizing this transition can be quantified. We find the temperature dependence of this transition to depend on gradient strength, ranging from -2.22 decades/^oC for a random copolymer to -0.75 decades/^oC for a gradient copolymer of comparable molecular weight and overall composition but a gradient strength of 0.52. The progressively shallower temperature dependence of this transition with increasing gradient strength suggests of a nucleation and growth mechanism of aggregate formation.

Gallow, Keith; Loo, Yueh-Lin

2011-03-01

147

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

148

Hot Corrosion in a Temperature Gradient  

SciTech Connect

Hot corrosion is the accelerated attack of materials at elevated temperatures that is induced by a thin film of fused salt. Many materials that experience hot corrosion are exposed to high heat fluxes and temperature gradients. The hot corrosion of metals can be described by the dissolution of a protective metal oxide into the fused salt and the subsequent precipitation of the metal oxide in a non-protective form. Rapp and Goto have established a criterion for the sustained hot corrosion of a pure metal that the solubility gradient of the protective oxide in the salt film must be negative at the oxide/salt interface. The influence of a temperature gradient on the metal oxide solubility gradient (and the predicted hot corrosion susceptibility) is discussed. Solubility data for NiO and Na{sub 2}SO{sub 4} are used to illustrate the effects of a temperature gradient. The effects of a temperature gradient were determined by examining various combinations of dissolution reactions, oxidants, and transport kinetics. Based on these results, and the thinness of the molten salt films, temperature gradients are not expected to be of importance to hot corrosion fluxing mechanisms.

Holcomb, G.R.

1999-04-01

149

Seismic velocity gradients in the upper mantle  

SciTech Connect

The radial velocity gradients for P- and S- waves in the upper mantle are of considerable interest for petrological studies of the upper mantle but are difficult to constrain directly. Comparison of three different styles of velocity model, constructed within a common parameterization to give a good fit to the travel times of P- and S-waves to 30{degree}, provide a useful framework for constructing bounds on the radial gradients. For depths from 250-1,000 km a somewhat subjective set of bounds are suggested for the velocity gradients and velocity contrasts at the major discontinuities in an average mantle. One of the most significant factors affecting the estimation of radial gradients is the presence of small-scale heterogeneity in the mantle. Modest heterogeneity, around 1 percent perturbations on scale lengths of about 300 km, can give rise to horizontal velocity gradients which can overwhelm the radial gradients in the shallower parts of the mantle and still be a quarter of the size of the radial gradients at greater depths. However such scales of heterogeneity are unlikely to simulate the presence of additional upper mantle discontinuities for ray paths travelling near vertical.

Kennett, B.L.N.

1991-06-01

150

Hot Corrosion in a Temperature Gradient  

SciTech Connect

Hot corrosion is the accelerated attack of materials at elevated temperatures that is induced by a thin film of fused salt. Many materials that experience hot corrosion are exposed to high heat fluxes and temperature gradients. The hot corrosion of metals can be described by the dissolution of a protective metal oxide into the fused salt and the subsequent precipitation of the metal oxide in a non-protective form. Rapp and Goto have established a criterion for the sustained hot corrosion of a pure metal that the solubility gradient of the protective oxide in the salt film must be negative at the oxide/salt interface. The influence of a temperature gradient on the metal oxide solubility gradient (and the predicted hot corrosion susceptibility) is discussed. Solubility data for NiO in Na{sub 2}SO{sub 4} are used to illustrate the effects of a temperature gradient. The effects of a temperature gradient were determined by examining various combinations of dissolution reactions, oxidants, and transport kinetics. Based on these results, and the thinness of the molten salt films, temperature gradients are not expected to be of importance to hot corrosion fluxing mechanisms.

Holcomb, G.R.

2000-08-01

151

Pure phase encode magnetic field gradient monitor.  

PubMed

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 T(2)*, 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, T(1), T(2), T(2)* < 100 micros) 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. PMID:19815435

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

2009-09-17

152

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

153

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

154

Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios  

NASA Astrophysics Data System (ADS)

By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (Fp/r and Gp/r), magic pulsed field gradient (MPFG) ratios for the prepare (Gp/Fp) and the read (Gr/Fr) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the cases where the background field gradients may change during the z-store interval of the pulse sequence. These MPFG ratios depend only on the timing of the pulsed gradients in the pulse sequence and allow a convenient experimental approach to background gradient suppression in NMR diffusion studies with heterogeneous systems, where the local properties of the (internal) background gradients are often unknown. If the pulsed field gradients are centered in the ?-intervals between the ? and ?/2 rf pulses, these two MPFG ratios coincide to ?=Gp/r/Fp/r=1-8/[1+(1/3)(?/?)2]. Since the width of the pulsed field gradients (?) is bounded by 0<=?<=?, ? can only be in the range of 5<=-?<=7. The predicted suppression of the unwanted cross terms is demonstrated experimentally using time-dependent external gradients which are controlled in the NMR experiment as well as spatially dependent internal background gradients generated by the magnetic properties of the sample itself. The theoretical and experimental results confirm and extend the approach of Sun et al. (J. Magn. Reson. 161 (2003) 168), who recently introduced a 13-interval type PFG NMR sequence with two asymmetric pulsed magnetic field gradients suitable to suppress unwanted cross terms with spatially dependent background field gradients.

Galvosas, Petrik; Stallmach, Frank; Kärger, Jörg

2004-02-01

155

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

156

Assessment of Microbial Populations Dynamics in a Blue Cheese by Culturing and Denaturing Gradient Gel Electrophoresis  

Microsoft Academic Search

The composition and development of microbial population during the manufacture and ripening of two batches of a blue-veined\\u000a cheese was examined by culturing and polymerase chain reaction (PCR) denaturing gradient gel electrophoresis (DGGE) (PCR–DGGE).\\u000a Nine selective and\\/or differential media were used to track the cultivable populations of total and indicator microbial groups.\\u000a For PCR–DGGE, the V3 hyper variable region of

Ángel Alegría; Renata González; Mario Díaz; Baltasar Mayo

2011-01-01

157

High-gradient two-beam accelerator structure  

NASA Astrophysics Data System (ADS)

A novel cavity structure is described that could be the basis for a two-beam, high-gradient, accelerator. Versions of the structure could be used for acceleration of beams of electrons, positrons, muons, protons, or heavier ions; with either electron or proton drive beams. The structure embodies cavities that are excited in several harmonically related eigenmodes, such that rf fields reach their peak values only during small portions of each basic rf period. This feature could help raise breakdown and pulse heating thresholds. The two-beam accelerator structure comprises chains of these cavities. In this configuration, no transfer elements are needed to couple rf energy from the drive beam to the accelerated beam, since both beams traverse the same cavities. Purposeful cavity detuning is used to provide much smaller deceleration for a high-current drive beam, than acceleration for a low-current accelerated beam, i.e., to provide a high transformer ratio. A self-consistent theory is presented to calculate idealized acceleration gradient, transformer ratio, and efficiency for energy transfer from the drive beam to the accelerated beam, for either parallel or antiparallel motion of the beams. The theory has been cast in dimensionless quantities so as to facilitate optimization with respect to efficiency, acceleration gradient, or transformer ratio, and to illuminate the interdependence of these parameters. Means for dramatically shortening the structure fill time are also described. However, no beam dynamics analysis is presented, so the range of parameters within which this new acceleration concept can be used will remain uncertain until it is established that stable beam transport along the structure using an appropriate focusing system is possible.

Kazakov, S. Yu; Kuzikov, S. V.; Jiang, Y.; Hirshfield, J. L.

2010-07-01

158

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

159

Polar Chains and Webs  

NSDL National Science Digital Library

In this activity students will put into practice the evaluation component of the scientific method while comparing and contrasting the similarities and differences of the food chains and webs of polar animal life. Students will learn about classification and ecology through the real life experiences and connections of professionals who have been in the field. Through developing skills in teamwork and planning, this activity will allow students to understand the similarities and differences of the Arctic and Antarctic regions, their animal life and the food chains and webs supporting them. Students will: locate the Arctic region and Antarctica on globes and maps; identify similarities and differences in their animal life; and show and explain the food chain of a specific species and the food web of that species while discussing their interrelationships.

Kolb, Sandra; Griffith, Rick

160

Pictish chains and Welsh forgeries  

Microsoft Academic Search

The Pictish silver chains can be shown to be 12 in number, and not 10 as often stated. The evidence of a Welsh chronicle that the chains were royal insignia is worthless, because the chronicle is an 18th- century forgery. PICTISH CHAINS A striking feature of Pictish art is the series of massive silver chains found at locations from Inverness

Andrew Breeze

161

Supply chain management - SMEs approach  

Microsoft Academic Search

The supply chain management is implemented in various business functions. Most of the originators of supply chain are the large organizations. The objectives of supply chain implementation are the cost reduction that yielded the higher profits, good partnership management, etc. The negotiation is the part of supply chain activity. The large organization has more negotiation over their small supplier but

P. Udomleartprasert; C. Jungthirapanich; C. Sommechai

2003-01-01

162

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

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

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

165

Density Gradient Analysis of Suspended Matter.  

National Technical Information Service (NTIS)

Development of a simple and inexpensive density gradient centrifugation method, utilizing silica soils, for separating and isolating various fractions of suspended matter and bottom sediments was begun. There is presently no effective means for fractionat...

A. W. Knight

1983-01-01

166

Lightness and brightness over spatial illumination gradients.  

PubMed

We extended our studies of lightness and brightness in complex scenes to cathode-ray-tube simulations of an array of 35 gray reflective patches under spatially varying illuminants. There were three illuminance profiles, an abrupt step, a linear gradient, and a simulation of side illumination, with nine steepnesses of each. In half the sessions observers adjusted a test patch at one end of the illumination gradient in order to match the lightness of a standard patch at the other end of the gradient. In the remaining sessions they matched the brightness of the test patch to that of the standard. For all three illuminance profiles the lightnesses of the patches matched when they had approximately the same simulated reflectance; i.e., there was excellent lightness constancy even though the illuminance gradients were clearly visible. PMID:2231104

Arend, L E; Goldstein, R

1990-10-01

167

Density-gradient-corrected embedded atom method  

NASA Astrophysics Data System (ADS)

Through detailed comparisons between embedded atom method (EAM) and first-principles calculations for Al, we find that EAM tends to fail when there are large electron-density gradients present. We attribute the observed failures to the violation of the uniform density approximation (UDA) underlying EAM. To remedy the insufficiency of UDA, we propose a gradient-corrected EAM model which introduces gradient corrections to the embedding function in terms of exchange correlation and kinetic energies. Based on the perturbation theory of “quasiatoms” and density-functional theory, the embedding function captures the essential physics missing in UDA and paves the way for developing more transferable EAM potentials. With Voter-Chen EAM potential as an example, we show that the gradient corrections can significantly improve the transferability of the potential.

Wu, Gang; Lu, Gang; García-Cervera, Carlos J.; E, Weinan

2009-01-01

168

Pumpernickel Valley Geothermal Project Thermal Gradient Wells.  

National Technical Information Service (NTIS)

This report documents the drilling operations and presents the technical results and information obtained from the thermal gradient wells in the Pumpernickel Valley geothermal project area near Winnemucca, in north-central Nevada. The report incorporates ...

2006-01-01

169

Electron temperature gradient instability in toroidal plasmas  

NASA Astrophysics Data System (ADS)

Electron temperature gradient (ETG) driven instability in toroidal plasmas is studied with gyrokinetic theory. The full electron kinetics including finite Larmor radius effects, toroidal (curvature and magnetic gradient) drift motion ?D, and transit k?v?, is considered. The upgraded numerical scheme for solving the integral eigenvalue equations allows the study of both growing and damping modes, and thus direct calculation of critical gradient. A systematic parameter study is carried out for low ?(=plasma pressure/magnetic pressure) circular flux surface equilibria. The basic characteristics of the modes are discussed. The scaling of the critical gradient with respect to toroidicity and to the ratio of electron temperature over ion temperature is obtained. Estimation for the transport induced by the modes is given.

Dong, J. Q.; Sanuki, H.; Itoh, K.; Chen, Liu

2002-11-01

170

Bioanalytical separations using electric field gradient techniques.  

PubMed

The field of separations science will be strongly impacted by new electric-field-gradient-based strategies. Many new capabilities are being developed with analytical targets ranging from particles to small molecules, and soot to living cells. Here we review the emerging area of electric field gradient techniques, dividing the large variety of techniques by the target of separation. In doing so, we have contributions using dielectrophoresis, electric field gradient focusing (including dynamic, true moving bed, and pulsed field), electrocapture and electrophoretic focusing, temperature gradient focusing, and focusing with centrifugal force. We cover the literature from the start of 2007 to June 2008, along with some introductory discussions. Even with the relatively short time frame, this young and dynamic field of inquiry produced some 100 contributions describing new and unique techniques and several new applications. PMID:19197905

Meighan, Michelle M; Staton, Sarah J R; Hayes, Mark A

2009-03-01

171

Isogeometric analysis of 2D gradient elasticity  

NASA Astrophysics Data System (ADS)

In the present contribution the concept of isogeometric analysis is extended towards the numerical solution of the problem of gradient elasticity in two dimensions. In gradient elasticity the strain energy becomes a function of the strain and its derivative. This assumption results in a governing differential equation which contains fourth order derivatives of the displacements. The numerical solution of this equation with a displacement-based finite element method requires the use of C 1-continuous elements, which are mostly limited to two dimensions and simple geometries. This motivates the implementation of the concept of isogeometric analysis for gradient elasticity. This NURBS based interpolation scheme naturally includes C 1 and higher order continuity of the approximation of the displacements and the geometry. The numerical approach is implemented for two-dimensional problems of linear gradient elasticity and its convergence behavior is studied.

Fischer, Paul; Klassen, Markus; Mergheim, Julia; Steinmann, Paul; Müller, Ralf

2011-03-01

172

Cosmic ray gradients in the outer heliosphere.  

NASA Astrophysics Data System (ADS)

Pioneer 10 and 11 spacecraft are now probing the outer heliosphere. The authors have used the UCSD instruments on board 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.

1983-08-01

173

Stability of gradient semigroups under perturbations  

NASA Astrophysics Data System (ADS)

In this paper we prove that gradient-like semigroups (in the sense of Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) are gradient semigroups (possess a Lyapunov function). This is primarily done to provide conditions under which gradient semigroups, in a general metric space, are stable under perturbation exploiting the known fact (see Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) that gradient-like semigroups are stable under perturbation. The results presented here were motivated by the work carried out in Conley (1978 Isolated Invariant Sets and the Morse Index (CBMS Regional Conference Series in Mathematics vol 38) (RI: American Mathematical Society Providence)) for groups in compact metric spaces (see also Rybakowski (1987 The Homotopy Index and Partial Differential Equations (Universitext) (Berlin: Springer)) for the Morse decomposition of an invariant set for a semigroup on a compact metric space).

Aragão-Costa, E. R.; Caraballo, T.; Carvalho, A. N.; Langa, J. A.

2011-07-01

174

Tearing modes with pressure gradient effect in pair plasmas  

SciTech Connect

The general dispersion relation of tearing mode with pressure gradient effect in pair plasmas is derived analytically. If the pressure gradients of positron and electron are not identical in pair plasmas, the pressure gradient has significant influence at tearing mode in both collisionless and collisional regimes. In collisionless regime, the effects of pressure gradient depend on its magnitude. For small pressure gradient, the growth rate of tearing mode is enhanced by pressure gradient. For large pressure gradient, the growth rate is reduced by pressure gradient. The tearing mode can even be stabilized if pressure gradient is large enough. In collisional regime, the growth rate of tearing mode is reduced by the pressure gradient. While the positron and electron have equal pressure gradient, tearing mode is not affected by pressure gradient in pair plasmas.

Cai Huishan; Li Ding; Zheng Jian [Key Laboratory of Basic Plasma Physics, School of Science, CAS, University of Science and Technology of China, Hefei 230026 (China)

2009-04-15

175

Infinite-Horizon Policy-Gradient Estimation  

Microsoft Academic Search

Gradient-based approaches to direct policy search in reinforcement learning have received much recent attention as a means to solve problems of partial observability and to avoid some of the problems associated with policy degradation in value-function methods. In this paper we intro- duce , a simulation-based algorithm for generating a biased estimate of the gradient of the average reward in

Jonathan Baxter; Peter L. Bartlett

2001-01-01

176

Advanced High Gradient RF Structure Development  

SciTech Connect

Multi-mode accelerating structures aimed at increasing accelerating gradient are described. Such structures operating in several resonant, equidistantly-spaced, axisymmetric, TM-like eigenmodes allow reduction of exposure time to surface fields, reduction of high-field areas and reduction of those fields which are responsible for electron emission. These effects are planned for use in studying the physics of RF breakdown phenomenon with the goal of designing new high-gradient accelerating structures.

Kuzikov, S. V. [Institute of Applied Physics, Russian Academy of Sciences, 46 Ulyanov St., Nizhny Novgorod, 603950 (Russian Federation); Omega-P, Inc., 258 Bradley St., New Haven, CT 06510 (United States); Kazakov, S. Yu. [Omega-P, Inc., 258 Bradley St., New Haven, CT 06510 (United States); Fermi National Accelerator Laboratory, Batavia, IL (United States); Jiang, Y. [Yale University, New Haven, CT (United States); Plotkin, M. E.; Vikharev, A. A. [Institute of Applied Physics, Russian Academy of Sciences, 46 Ulyanov St., Nizhny Novgorod, 603950 (Russian Federation); Hirshfield, J. L. [Omega-P, Inc., 258 Bradley St., New Haven, CT 06510 (United States); Yale University, New Haven, CT (United States)

2010-11-04

177

Preparing nanoparticle assemblies with number density gradients  

Microsoft Academic Search

We report on preparing assemblies of gold nanoparticles with gradient in number densities on flat silica-covered substrates. The methodology consists of : i) first forming a molecular gradient of amino groups (-NH2) on the substrate by vapor deposition of amine-terminated silane molecules, followed by ii) attachment of gold nanoparticles to -NH2 functional groups by immersing the substrate in a colloidal

Rajendra Bhat; Daniel Fischer; Jan Genzer

2002-01-01

178

Biopotential amplifier for potential gradient measurements  

Microsoft Academic Search

This work proposes a bio-potential amplifier suitable for measurements from an electric potential gradient sensor, in electro-encephalography (EEG). The sensor is an array made by three electrodes placed on the vertices of an equilateral triangle of reduced size. Measuring the gradient requires small separation between electrodes hence, very low amplitude signals, of a few muV, are obtained. Therefore, it is

Andrea N. Bermúdez; Enrique M. Spinelli; Carlos H. Muravchik

2007-01-01

179

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

180

Interplay between transport barriers and density gradient  

SciTech Connect

The present paper addresses two critical issues of zonal flows: the evidence of control parameters of their driving term, namely the Reynolds stress, and how they back-react on turbulence and transport. Kinetic nonlinear simulations are performed with the GYSELA code [V. Grandgirard et al., J. Comput. Phys. (to be published)], which models the slab branch of the ion temperature gradient driven instability in the four-dimensional drift-kinetic regime. First, the numerical results show that the gradient of the guiding center density, related to the general potential vorticity, is stabilizing both linearly, by increasing the instability threshold, and nonlinearly, by activating zonal flows. Accordingly, the Reynolds stress is found to scale like L{sub {omega}}{sup -2} in the quasilinear regime, L{sub {omega}} being the gradient length of the guiding center density. Second, the local temperature gradient appears to increase linearly with the curvature of the zonal flows, regardless of its sign. Such behavior agrees qualitatively with a perturbative theory. Indeed, while linear eigenmodes are localized at the maximum of the temperature gradient in the absence of zonal flows, they tend to be expelled if both exhibit a maximum at the same location. In this case, the reduction mechanism of the turbulent transport results from the ability of large zonal flow curvatures to render strong temperature gradients stable with respect to perturbations.

Sarazin, Y.; Grandgirard, V.; Dif-Pradalier, G.; Garbet, X.; Ghendrih, Ph. [Association Euratom-CEA, CEA/DSM/DRFC Centre de Cadarache, 13108 Saint-Paul-Lez-Durance (France)

2006-09-15

181

Supply chains and terrorism  

Microsoft Academic Search

On the morning of September 11th, 2001 the United States and the Western world entered a new era - one in which indiscriminate terrorist acts of all kinds must be expected. Many, if not most, of the expected consequences of the new era will be reflected in supply chain management challenges: relations with suppliers and customers, transportation difficulties and revised

Yossi Sheffi

182

Breaking the Chains  

ERIC Educational Resources Information Center

|In 1792 more than 350,000 people in Britain signed a petition calling for an end to the slave trade. It was, writes historian Adam Hochschild in his book "Bury the Chains," "the first time in history that a large number of people became outraged, and stayed outraged for many years, over someone else's rights". In 1807--after 15 years of…

Stanistreet, Paul

2007-01-01

183

INTERACTING QUANTUM SPIN CHAINS  

SciTech Connect

A brief review of recent advances in neutron scattering studies of low-dimensional quantum magnets is followed by a particular example. The separation of single-particle and continuum states in the weakly-coupled S = l/2 chains system BaCu{sub 2}Si{sub 2}O{sub 7} is described in some detail.

ZHELUDEV,A.

2001-09-09

184

Knowledge value chain  

Microsoft Academic Search

Introduces the knowledge value chain model as a knowledge management (KM) framework. The model consists of knowledge infrastructure (knowledge worker recruitment, knowledge storage capacity, customer\\/supplier relationship and CKO and management), the process of KM (knowledge acquisition, knowledge innovation, knowledge protection, knowledge integration, and knowledge dissemination), and the interaction among those components resulting in knowledge performance. Further to the discussion of

Ching Chyi Lee; Jie Yang

2000-01-01

185

Atwood's Heavy Chain  

ERIC Educational Resources Information Center

|While perusing various websites in search of a more challenging lab for my students, I came across a number of ideas where replacing the string in an Atwood's machine with a simple ball chain like the kind found in lamp pulls created an interesting system to investigate. The replacement of the string produced a nice nonuniform acceleration, but…

Beeken, Paul

2011-01-01

186

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

187

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

188

Atwood's Heavy Chain  

ERIC Educational Resources Information Center

While perusing various websites in search of a more challenging lab for my students, I came across a number of ideas where replacing the string in an Atwood's machine with a simple ball chain like the kind found in lamp pulls created an interesting system to investigate. The replacement of the string produced a nice nonuniform acceleration, but…

Beeken, Paul

2011-01-01

189

Supply chain quality.  

PubMed

As the development of complex manufacturing models and virtual companies become more prevalent in today's growing global markets, it is increasingly important to support the relationships between manufacturer and supplier. Utilising these relationships will ensure that supply chains operate more effectively and reduce costs, risks and time-to-market time frames, whilst maintaining product quality. PMID:20058652

Feary, Simon

190

The Leadership Value Chain  

Microsoft Academic Search

There is little question that leadership is vital to organizational effectiveness; however, there is a lack of comprehensive models of the processes and intervening factors that explain the link between individual leaders and organizational performance. This article concerns an evidence-based framework, the leadership value chain, that traces the characteristics of individual leaders to their leadership style; leadership style to effect

Robert B. Kaiser; Darren V. Overfield

2010-01-01

191

Handling supply chains  

Microsoft Academic Search

Delves into supply chains - and possible effects of Y2K on them - and their possible complex nature. Includes discussion on US retailer Home Depot and Toyota's UK plant. Contends that more and more organizations are considering stockpiling in lean systems, for example the USA has already built up 2-3 months supply of petrol in reserve as a precautionary measure.

T Kippenberger

1999-01-01

192

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{sub perpendicular{rho}s} < or approx. 10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of 2 decrease in the plasma effective thermal diffusivity.

Ren, Y.; Kaye, S. M.; Mazzucato, E.; Guttenfelder, W.; Bell, R. E.; LeBlanc, B. P. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Domier, C. W.; Lee, K. C.; Luhmann, N. C. Jr. [University of California at Davis, Davis, California 95616 (United States); Smith, D. R. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Yuh, H. [Nova Photonics, Inc., Princeton, New Jersey 08540 (United States)

2011-04-22

193

Intersegmental coordination of the leech swimming rhythm. I. Roles of cycle period gradient and coupling strength.  

PubMed

The isolated leech nervous system generates a metachronally coordinated rhythmic output that is the neuronal correlate of swimming activity. We investigated two factors that contribute to intersegmental coordination: the swim-cycle periods expressed by segmental ganglia and the strength of neuronal coupling between ganglia. To determine the regional variation in swim-cycle periods, we severed both of the lateral intersegmental connectives. We left intact the median connective, which conveys tonic excitation but little phasic information. We obtained a reduction in intersegmental coupling strength by severing a single lateral intersegmental connective. Cycle periods were manipulated by cooling restricted sections of the nerve cord. Our experiments revealed an anterior-posterior gradient of cycle periods in ganglia of the isolated nerve cord; that is, chains of ganglia obtained from the anterior nerve cord exhibited longer cycle periods than those obtained from the posterior end of the cord. This gradient extends posteriorly to approximately ganglion 12 and may reverse posterior to ganglion 13. Increasing local cycle periods by cooling restricted sections of the nerve cord caused delay in activity cycles in the cooled ganglia, relative to the cycles of ganglia at the control temperature. This finding demonstrates that the observed gradient in cycle period provides for smaller intersegmental phase lags than would occur if there were no period gradients. Reduction of coupling strength by severing a lateral connective led to altered phase relationships across the lesion, both at the motor and oscillator levels. For those ganglion chains in which the anterior ganglia had greater periods, the reduced coupling led to reduced or even reversed phase relationships across the lesion but left unchanged the phase lag between the ends of the chain. In contrast, reduced coupling between halves of a chain in which the posterior ganglia had greater cycle periods led to increased phase lags across the lesion and between the ends. These altered phase relationships arise from a relative increase in the contribution of period differences when coupling strength is decreased. We conclude that the anterior-to-posterior progression of neuronal activity in the isolated leech nerve cord during swimming activity is provided by the intersegmental coupling signals. Furthermore, the period gradient expressed in our preparations acts to provide for smaller phase lags than would be generated by these coupling signals in the absence of such a gradient.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:4087042

Pearce, R A; Friesen, W O

1985-12-01

194

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

195

Gradient system characterization by impulse response measurements with a dynamic field camera.  

PubMed

This work demonstrates a fast, sensitive method of characterizing the dynamic performance of MR gradient systems. The accuracy of gradient time-courses is often compromised by field imperfections of various causes, including eddy currents and mechanical oscillations. Characterizing these perturbations is instrumental for corrections by pre-emphasis or post hoc signal processing. Herein, a gradient chain is treated as a linear time-invariant system, whose impulse response function is determined by measuring field responses to known gradient inputs. Triangular inputs are used to probe the system and response measurements are performed with a dynamic field camera consisting of NMR probes. In experiments on a whole-body MR system, it is shown that the proposed method yields impulse response functions of high temporal and spectral resolution. Besides basic properties such as bandwidth and delay, it also captures subtle features such as mechanically induced field oscillations. For validation, measured response functions were used to predict gradient field evolutions, which was achieved with an error below 0.2%. The field camera used records responses of various spatial orders simultaneously, rendering the method suitable also for studying cross-responses and dynamic shim systems. It thus holds promise for a range of applications, including pre-emphasis optimization, quality assurance, and image reconstruction. PMID:22499483

Vannesjo, Signe J; Haeberlin, Maximilan; Kasper, Lars; Pavan, Matteo; Wilm, Bertram J; Barmet, Christoph; Pruessmann, Klaas P

2012-04-12

196

Improving the accuracy of pulsed field gradient NMR diffusion experiments: Correction for gradient non-uniformity  

NASA Astrophysics Data System (ADS)

Pulsed field gradient NMR is a well-established technique for the determination of self-diffusion coefficients. However, a significant source of systematic error exists in the spatial variation of the applied pulsed field gradient. Non-uniform pulsed field gradients cause the decay of peak amplitudes to deviate from the expected exponential dependence on gradient squared. This has two undesirable effects: the apparent diffusion coefficient will deviate from the true value to an extent determined by the choice of experimental parameters, and the error estimated by the nonlinear least squares fitting will contain a significant systematic contribution. In particular, the apparent diffusion coefficient determined by exponential fitting of the diffusional attenuation of NMR signals will depend both on the exact pulse widths used and on the range of gradient amplitudes chosen. These problems can be partially compensated for if experimental attenuation data are fitted to a function corrected for the measured spatial dependence of the gradient and signal strength. This study describes a general alternative to existing methods for the calibration of NMR diffusion measurements. The dominant longitudinal variation of the pulsed field gradient amplitude and the signal strength are mapped by measuring pulsed field gradient echoes in the presence of a weak read gradient. These data are then used to construct a predicted signal decay function for the whole sample, which is parameterised as the exponential of a power series. Results are presented which compare diffusion coefficients obtained using the new calibration method with previous literature values.

Connell, Mark A.; Bowyer, Paul J.; Adam Bone, P.; Davis, Adrian L.; Swanson, Alistair G.; Nilsson, Mathias; Morris, Gareth A.

2009-05-01

197

Assessment of bacterial community structure in soil by polymerase chain reaction and denaturing gradient gel electrophoresis  

Microsoft Academic Search

Bacterial community structure was studied in a Flevo silt loam (FSL) soil microplot, as well as in 15 other soils, by using DNA extraction followed by molecular fingerprinting. Total community DNA was extracted and purified by a direct method, which yielded amplifiable DNA of high molecular weight for all soils. A variable region of the 16S rRNA gene was then

Antonio Gelsomino; Anneke C Keijzer-Wolters; Giovanni Cacco; Jan Dirk van Elsas

1999-01-01

198

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

199

The innovation value chain.  

PubMed

The challenges of coming up with fresh ideas and realizing profits from them are different for every company. One firm may excel at finding good ideas but may have weak systems for bringing them to market. Another organization may have a terrific process for funding and rolling out new products and services but a shortage of concepts to develop. In this article, Hansen and Birkinshaw caution executives against using the latest and greatest innovation approaches and tools without understanding the unique deficiencies in their companies' innovation systems. They offer a framework for evaluating innovation performance: the innovation value chain. It comprises the three main phases of innovation (idea generation, conversion, and diffusion) as well as the critical activities performed during those phases (looking for ideas inside your unit; looking for them in other units; looking for them externally; selecting ideas; funding them; and promoting and spreading ideas companywide). Using this framework, managers get an end-to-end view of their innovation efforts. They can pinpoint their weakest links and tailor innovation best practices appropriately to strengthen those links. Companies typically succumb to one of three broad "weakest-link" scenarios. They are idea poor, conversion poor, or diffusion poor. The article looks at the ways smart companies - including Intuit, P&G, Sara Lee, Shell, and Siemens- modify the best innovation practices and apply them to address those organizations' individual needs and flaws. The authors warn that adopting the chain-based view of innovation requires new measures of what can be delivered by each link in the chain. The approach also entails new roles for employees "external scouts" and "internal evangelists," for example. Indeed, in their search for new hires, companies should seek out those candidates who can help address particular weaknesses in the innovation value chain. PMID:17580654

Hansen, Morten T; Birkinshaw, Julian

2007-06-01

200

Backward chaining rule induction  

Microsoft Academic Search

Exploring the vast number of possible feature interactions in domains such as gene expression microarray data is an onerous task. We describe Backward-Chaining Rule Induction (BCRI) as a semi-supervised mechanism for biasing the search for IF-THEN rules that express plausible feature interactions. BCRI adds to a relatively limited tool-chest of hypothesis generation software and is an alternative to purely unsupervised

Douglas H. Fisher; Mary E. Edgerton; Zhihua Chen; Lianhong Tang; Lewis Frey

2006-01-01

201

The Antarctic Food Chain  

NSDL National Science Digital Library

This lesson plan introduces students to the animals of Antarctica and to the Antarctic food chain. Students will draw pictures of a variety of animals and attach the pictures to a wall collage. They will then listen to or read statements about the diet of each animal and draw arrows to show which animals eat which other animals. Students will end up with a food web that illustrates the importance of krill to the Antarctic ecosystem.

202

Optimization of Water Resources Systems by the Gradient Projection and the Conjugate Gradient Methods.  

National Technical Information Service (NTIS)

The gradient projection and the conjugate gradient methods are applied to the optimization of complex water resources systems. The most important advantages of these approaches are that they can be used to solve nonlinear problems with a large number of i...

E. S. Lee S. Wazirrudin

1970-01-01

203

Linear polyubiquitin chains  

PubMed Central

The ubiquitin conjugation system regulates a wide variety of biological phenomena, including protein degradation and signal transduction, by regulating protein function via polyubiquitin conjugation in most cases. Several types of polyubiquitin chains exist in cells, and the type of polyubiquitin chain conjugated to a protein seems to determine how that protein is regulated. We identified a novel linear polyubiquitin chain and the ubiquitin-protein ligase complex that assembles it, designated LUBAC. Both were shown to have crucial roles in the canonical NF?B activation pathway. This year, three groups, including our laboratory, identified SHARPIN as a new subunit of LUBAC. Of great interest, Sharpin was identified as a causative gene of chronic proliferative dermatitis in mice (cpdm), which is characterized by numerous inflammatory symptoms including chronic dermatitis, arthritis and immune disorders. Deletion of SHARPIN drastically reduces the amount of LUBAC and attenuates signal-induced NF?B activation. The pleomorphic symptoms of cpdm mice suggest that LUBAC-mediated NF?B activation may play critical roles in mammals and be involved in various disorders. A forward look into the linear polyubiquitin research is also discussed.

2011-01-01

204

Folding of polyglutamine chains  

NASA Astrophysics Data System (ADS)

Long polyglutamine chains have been associated with a number of neurodegenerative diseases. These include Huntington's disease, where expanded polyglutamine (PolyQ) sequences longer than 36 residues are correlated with the onset of symptoms. In this paper we study the folding pathway of a 54-residue PolyQ chain into a ?-helical structure. Transition path sampling Monte Carlo simulations are used to generate unbiased reactive pathways between unfolded configurations and the folded ?-helical structure of the polyglutamine chain. The folding process is examined in both explicit water and an implicit solvent. Both models reveal that the formation of a few critical contacts is necessary and sufficient for the molecule to fold. Once the primary contacts are formed, the fate of the protein is sealed and it is largely committed to fold. We find that, consistent with emerging hypotheses about PolyQ aggregation, a stable ?-helical structure could serve as the nucleus for subsequent polymerization of amyloid fibrils. Our results indicate that PolyQ sequences shorter than 36 residues cannot form that nucleus, and it is also shown that specific mutations inferred from an analysis of the simulated folding pathway exacerbate its stability.

Chopra, Manan; Reddy, Allam S.; Abbott, N. L.; de Pablo, J. J.

2008-10-01

205

Trace gas retrieval including horizontal gradients  

NASA Astrophysics Data System (ADS)

The development of a software package for the retrieval of vertical trace gas profiles from limb sounding measurements led to the analysis of the radiometric effects of inhomogeneous distributions of pressure, temperature and/or trace gases within simulated atmospheric layers as seen by a limb sounding instrument. These inhomogeneities called "horizontal gradients" affect the radiance measured by the instrument and — if unaccounted for - will degrade the retrieval quality of vertical pressure, temperature and/or trace gas profiles. On the other hand, if the retrieval of the vertical profiles is able to support the determination of horizontal gradients and if sufficient additional external knowledge about these gradients is available, then this offers an opportunity to retrieve vertical temperature and trace gas profiles with high accuracy. Several examples will demonstrate typical cases where the use of optimal estimation techniques including a priori knowledge of profiles and covariance data will deliver high quality results.

Kemnitzer, H.; Hilgers, S.; Schwarz, G.; Steck, T.; Clarmann, T. v.; Höpfner, M.; Ressel, K.

206

Shadowgraph Study of Gradient Driven Fluctuations  

NASA Astrophysics Data System (ADS)

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-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 gradie

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

2002-11-01

207

Texturing of REBCO using temperature gradient.  

SciTech Connect

Isothermal melt texturing is currently a well-established technique for manufacturing superconducting materials with high trapped magnetic field and levitation forces. For conductor applications, however, a temperature gradient needs to be employed in order to align the oriented domains with the a-b planes where the current will be flowing over long lengths. Melt-textured Y-123 bars of length 100 mm with Jc values of 70,000 A/cm2 at 77 K in self-field have been routinely manufactured by directional solidification. The presence of temperature gradient also lends itself to faster texturing rates. Recently, Ag-clad Yb-123 tapes made by the powder-in-tube process were successfully melt textured in the presence of a temperature gradient and controlled oxygen partial pressure. These tapes exhibit the potential to be an alternative to BSCCO tapes, for relatively high temperature and magnetic field applications.

Salama, K.; Athur, S. P.; Balachandran, U.; Energy Technology; Univ. of Houston

2001-01-01

208

Using Spatial Gradients to Model Localization Phenomena  

SciTech Connect

We present the final report on a Laboratory-Directed Research and Development project, Using Spatial Gradients to Model Localization Phenomena, performed during the fiscal years 1996 through 1998. The project focused on including spatial gradients in the temporal evolution equations of the state variables that describe hardening in metal plasticity models. The motivation was to investigate the numerical aspects associated with post-bifurcation mesh dependent finite element solutions in problems involving damage or crack propagation as well as problems in which strain Localizations occur. The addition of the spatial gradients introduces a mathematical length scale that eliminates the mesh dependency of the solution. In addition, new experimental techniques were developed to identify the physical mechanism associated with the numerical length scale.

D.J.Bammann; D.Mosher; D.A.Hughes; N.R.Moody; P.R.Dawson

1999-07-01

209

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

210

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

211

Stream function optimization for gradient coil design.  

PubMed

This work presents a method applied to the design of short self-shielded gradient coils of cylindrical geometry. The method uses a hybrid technique that combines the simulated annealing and target field methods to optimize the standard stream functions. The optimized stream functions were parameterized using a few degrees of freedom to reduce the computing time. The optima stream function parameters are given for easy coil design purposes. The proposed approach is compared to the target field method. The main advantage of the present method over the target field method is its ability to enlarge the homogeneous gradient volume. In addition, the designs of short coils based on this approach have shown lower inductance than the coil design based on the target field method. The fast-simulated annealing technique presented in this work enables the gradient coil optimization in less than 3 min of computing time. Magn Reson Med 45:505-512, 2001. PMID:11241710

Tomasi, D

2001-03-01

212

Marine microbes see a sea of gradients.  

PubMed

Marine bacteria influence Earth's environmental dynamics in fundamental ways by controlling the biogeochemistry and productivity of the oceans. These large-scale consequences result from the combined effect of countless interactions occurring at the level of the individual cells. At these small scales, the ocean is surprisingly heterogeneous, and microbes experience an environment of pervasive and dynamic chemical and physical gradients. Many species actively exploit this heterogeneity, while others rely on gradient-independent adaptations. This is an exciting time to explore this frontier of oceanography, but understanding microbial behavior and competition in the context of the water column's microarchitecture calls for new ecological frameworks, such as a microbial optimal foraging theory, to determine the relevant trade-offs and global consequences of microbial life in a sea of gradients. PMID:23118182

Stocker, Roman

2012-11-01

213

Metamaterials with gradient negative index of refraction.  

PubMed

We propose a new metamaterial with a gradient negative index of refraction, which can focus a collimated beam of light coming from a distant object. A slab of the negative refractive index metamaterial has a focal length that can be tuned by changing the gradient of the negative refractive index. A thin metal film pierced with holes of appropriate size or spacing between them can be used as a metamaterial with the gradient negative index of refraction. We use finite-difference time-domain calculations to show the focusing of a plane electromagnetic wave passing through a system of equidistantly spaced holes in a metal slab with decreasing diameters toward the edges of the slab. PMID:17912287

Pinchuk, Anatoliy O; Schatz, George C

2007-10-01

214

Noise Reduction in Surface Reconstruction from a Given Gradient Field  

Microsoft Academic Search

We present a gradient space technique for noise reduction in surfaces reconstructed from a noisy gradient field. We first analyze the error sources in the recovered gradient field of a surface using a three-image photometric stereo method. Based on this analysis, we propose an additive noise model to describe the errors in the surface gradient estimates. We then use a

Bilge Karaçali; Wesley E. Snyder

2004-01-01

215

Density gradient expansion of correlation functions  

NASA Astrophysics Data System (ADS)

We present a general scheme based on nonlinear response theory to calculate the expansion of correlation functions such as the pair-correlation function or the exchange-correlation hole of an inhomogeneous many-particle system in terms of density derivatives of arbitrary order. We further derive a consistency condition that is necessary for the existence of the gradient expansion. This condition is used to carry out an infinite summation of terms involving response functions up to infinite order from which it follows that the coefficient functions of the gradient expansion can be expressed in terms of the local density profile rather than the background density around which the expansion is carried out. We apply the method to the calculation of the gradient expansion of the one-particle density matrix to second order in the density gradients and recover in an alternative manner the result of Gross and Dreizler [Gross and Dreizler, Z. Phys. AZPAADB0340-219310.1007/BF01413038 302, 103 (1981)], which was derived using the Kirzhnits method. The nonlinear response method is more general and avoids the turning point problem of the Kirzhnits expansion. We further give a description of the exchange hole in momentum space and confirm the wave vector analysis of Langreth and Perdew [Langreth and Perdew, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.21.5469 21, 5469 (1980)] for this case. This is used to derive that the second-order gradient expansion of the system averaged exchange hole satisfies the hole sum rule and to calculate the gradient coefficient of the exchange energy without the need to regularize divergent integrals.

van Leeuwen, Robert

2013-04-01

216

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

217

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

218

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

219

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

220

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

221

Implementing supply chain quality management  

Microsoft Academic Search

This paper describes a strategic framework for the development of supply chain quality management (SCQM). The framework integrates both vision- and gap-driven change approaches to evaluate not only the implementation gaps but also their potential countermeasures. Based on literature review, drivers of supply chain quality are identified. They are: supply chain competence, critical success factors (CSF), strategic components, and SCQ

Chu-Hua Kuei; Christian N. Madu; Chinho Lin

2008-01-01

222

Supply chain collaboration: what's happening?  

Microsoft Academic Search

Purpose – Collaboration has been referred to as the driving force behind effective supply chain management and may be the ultimate core capability. However, there is a fairly widespread belief that few firms have truly capitalized on its potential. A study was undertaken to assess the current level of supply chain collaboration and identify best practice. Design\\/methodology\\/approach – Supply chain

Soonhong Min; Anthony S. Roath; Patricia J. Daugherty; Stefan E. Genchev; Haozhe Chen; Aaron D. Arndt; R. Glenn Richey

2005-01-01

223

Somali Basin, Chain Ridge, and Origin of the Northern Somali Basin Gravity and Geoid Low.  

National Technical Information Service (NTIS)

The Northern Somali Basin, located between Chain Ridge and the Horn of Africa north of 4 deg N, is characterized by a distinct 5-m geoid low and by large negative gravity anomalies. Boundaries of the basin are marked by steep gradients in both gravity and...

J. R. Cochran

1988-01-01

224

Monte Carlo without chains  

SciTech Connect

A sampling method for spin systems is presented. The spin lattice is written as the union of a nested sequence of sublattices, all but the last with conditionally independent spins, which are sampled in succession using their marginals. The marginals are computed concurrently by a fast algorithm; errors in the evaluation of the marginals are offset by weights. There are no Markov chains and each sample is independent of the previous ones; the cost of a sample is proportional to the number of spins (but the number of samples needed for good statistics may grow with array size). The examples include the Edwards-Anderson spin glass in three dimensions.

Chorin, Alexandre J.

2007-12-12

225

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

226

COAL CLEANING BY HIGH GRADIENT MAGNETIC SEPARATION  

Microsoft Academic Search

Results of experimental work on HGMS coal c leaning will be presented with emphasis on the r elation between cleaning results and coal characteristics. I INTRODUCTION High Gradient Magnetic Separation (HGMS) is a particle separation technique which is based on the differences in the magnetic properties of the particles. A survey of the principles, theory, experimental work and applications has

C. P. van Driel; J. Sikkenga; C. B. W. Kerkdijk

1984-01-01

227

Hot Corrosion in a Temperature Gradient  

Microsoft Academic Search

Hot corrosion is the accelerated attack of materials at elevated temperatures that is induced by a thin film of fused salt. Many materials that experience hot corrosion are exposed to high heat fluxes and temperature gradients. The hot corrosion of metals can be described by the dissolution of a protective metal oxide into the fused salt and the subsequent precipitation

Gordon Holcomb

1999-01-01

228

Hot Corrosion in a Temperature Gradient  

Microsoft Academic Search

Hot corrosion is the accelerated attack of materials at elevated temperatures that is induced by a thin film of fused salt. Many materials that experience hot corrosion are exposed to high heat fluxes and temperature gradients. The hot corrosion of metals can be described by the dissolution of a protective metal oxide into the fused salt and the subsequent precipitation

G. R. Holcomb

2000-01-01

229

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

230

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

231

Gradient elution for micellar electrokinetic capillary chromatography  

Microsoft Academic Search

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,

Anthony T. Balchunas; Michael J. Sepaniak

1988-01-01

232

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

233

Learning to Learn Using Gradient Descent  

Microsoft Academic Search

Abstract: This paper introduces the application of gradient descentmethods to meta-learning. The concept of \\\\meta-learning", i.e. of a systemthat improves or discovers a learning algorithm, has been of interestin machine learning for decades because of its appealing applications.

Sepp Hochreiter; A. Steven Younger; Peter R. Conwell

2001-01-01

234

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

235

Escalation of polymerization in a thermal gradient  

PubMed Central

For the emergence of early life, the formation of biopolymers such as RNA is essential. However, the addition of nucleotide monomers to existing oligonucleotides requires millimolar concentrations. Even in such optimistic settings, no polymerization of RNA longer than about 20 bases could be demonstrated. How then could self-replicating ribozymes appear, for which recent experiments suggest a minimal length of 200 nt? Here, we demonstrate a mechanism to bridge this gap: the escalated polymerization of nucleotides by a spatially confined thermal gradient. The gradient accumulates monomers by thermophoresis and convection while retaining longer polymers exponentially better. Polymerization and accumulation become mutually self-enhancing and result in a hyperexponential escalation of polymer length. We describe this escalation theoretically under the conservative assumption of reversible polymerization. Taking into account the separately measured thermophoretic properties of RNA, we extrapolate the results for primordial RNA polymerization inside a temperature gradient in pores or fissures of rocks. With a dilute, nanomolar concentration of monomers the model predicts that a pore length of 5 cm and a temperature difference of 10 K suffice to polymerize 200-mers of RNA in micromolar concentrations. The probability to generate these long RNAs is raised by a factor of >10600 compared with polymerization in a physical equilibrium. We experimentally validate the theory with the reversible polymerization of DNA blocks in a laser-driven thermal trap. The results confirm that a thermal gradient can significantly enlarge the available sequence space for the emergence of catalytically active polymers.

Mast, Christof B.; Schink, Severin; Gerland, Ulrich; Braun, Dieter

2013-01-01

236

Biogeographical gradients in galling species richness  

Microsoft Academic Search

Five hypotheses were invoked to account for variation in galling species number per location on plants of different structural complexity, namely herbs, shrubs, and trees, both in Brazil and USA. The hypotheses were: 1) the altitudinal\\/latitudinal gradient hypothesis; 2) the harsh environment hypothesis; 3) the plant species richness hypothesis; 4) the host plant area hypothesis; 5) the plant structural complexity

G. Wilson Fernandes; Peter W. Price

1988-01-01

237

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

238

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

239

Preparing nanoparticle assemblies with number density gradients  

NASA Astrophysics Data System (ADS)

We report on preparing assemblies of gold nanoparticles with gradient in number densities on flat silica-covered substrates. The methodology consists of : i) first forming a molecular gradient of amino groups (-NH2) on the substrate by vapor deposition of amine-terminated silane molecules, followed by ii) attachment of gold nanoparticles to -NH2 functional groups by immersing the substrate in a colloidal gold solution. Experiments using atomic force microscopy (AFM) reveal that the number density of nanoparticles on the substrate varies gradually as a function of the position on the substrate. Near edge x-ray absorption fine structure (NEXAFS) studies confirm that the decrease of the nanoparticle density is associated with the decrease of the number of the -NH2 groups anchored to the substrate. We demonstrate that the number density and spatial distribution of the nanoparticles within the gradients can be tuned by contolling the vapor diffusion of silane molecules. In addition we show that this simple methodology can be further extended to create "double gradients" of nanoparticles.

Bhat, Rajendra; Fischer, Daniel; Genzer, Jan

2002-03-01

240

Social dimensions of gradients in urban ecosystems  

Microsoft Academic Search

Urban ecosystems are complex mosaics in which the biophysical characteristics are transformed over time by a concentrated, diverse set of human activities. Understanding their complexity requires the continuing development of interdisciplinary approaches. The use of gradient approaches has pointed towards the need to examine in greater detail the roles of human influences. In this paper, I propose the addition of

Kirstin Dow

2000-01-01

241

Phase Retrieval Using Conjugate Gradient Minimization  

Microsoft Academic Search

A new algorithm for phase retrieval from the Fourier modulus is presented. The technique differs from the iterative transform algorithm in both the choice of error metric and the use of a conjugate gradient minimization research. Results are presented for noisy simulated data and also for measured photon-limited data.

1991-01-01

242

Visual detectability gradients: effect of illiteracy.  

PubMed

When subjects are required to detect a target pattern presented simultaneously with a number of similar non-target patterns in a brief exposure, marked differences of target detectability are observed as a function of the spatial location of the target (Efron, Yund, & Nichols, 1987, 1990a, b, c; Yund, Efron & Nichols, 1990a, b, c). These differences in detectability as a function of retinal locus, referred to collectively as a "detectability gradient," have been attributed to a central serial processing mechanism, which scans the decaying neural representation of the image. There also is evidence suggesting that, at least in some circumstances, this gradient may be influenced by the direction in which subjects normally read (Heron, 1957; Mishkin & Forgays, 1952; Efron et al., 1987). The object of the present experiment was to determine whether the detectability gradient obtained with the non-linguistic stimuli used in our previous experiments would differ as a function of previous reading experience. The experiment was performed on a group of 60 illiterate subjects and on a socioeconomic-matched group of 60 literate subjects. While the overall accuracy of target detection was identical in the two groups, there were significant differences between the detectability gradients of the literate and illiterate subjects. The nature of these differences indicates that reading, or learning to read, causes the scanning mechanisms of literate subjects to adopt more consistent scan paths, from subject to subject, than they would have adopted without this reading experience. PMID:1781980

Ostrosky-Solis, F; Efron, R; Yund, E W

1991-09-01

243

Optimal well placement using an adjoint gradient  

Microsoft Academic Search

In the process of reservoir development, one wishes to drill wells at optimal locations so that more hydrocarbons can be extracted at a lower cost. Because well locations in a reservoir simulator are commonly treated as discrete variables (well gridblock indices), standard implementations of gradient-based optimization are not applicable for optimal well placement, so optimization is commonly done with a

Kai Zhang; Gaoming Li; Albert C. Reynolds; Jun Yao; Liming Zhang

2010-01-01

244

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

245

Predicted fitness changes along an environmental gradient  

Microsoft Academic Search

Summary The relations between enzyme activity and the intensity of selection across an environmental gradient are investigated usingEscherichia coli growing on mixed resources. Experimental results demonstrate that the direction and intensity of natural selection can be predicted solely from a knowledge of the underlying biochemistry, physiology and ecology of the organism. Ecological theory, based on the logistic equation, is unable

Daniel E. Dykhuizen; Antony M. Dean

1994-01-01

246

Pure phase encode magnetic field gradient monitor  

Microsoft Academic Search

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

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

2009-01-01

247

Interpolation of Deflections from Horizontal Gravity Gradients.  

National Technical Information Service (NTIS)

The report gives the computational processor and the results of a test on the interpolation of deflections from horizontal gravity gradients measured by means of a torsion balance. First, the theory of such an interpolation is given together with the desc...

J. Badekas I. I. Mueller

1967-01-01

248

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

249

Morphogen gradients in vertebrate limb development  

Microsoft Academic Search

The developing limb is an excellent model for pattern formation in vertebrate embryos. Signalling by the polarizing region controls limb pattern across the antero-posterior axis of the chick limb. It was suggested first on theoretical grounds that signalling by the polarizing region could involve a morphogen gradient. Embryological manipulations provided evidence consistent with this model and, more recently, signalling molecules

Cheryll Tickle

1999-01-01

250

Value chain analysis: an approach to supply chain improvement in agri-food chains  

Microsoft Academic Search

Purpose – To develop an innovative methodology to apply lean value chain improvement techniques to a complete supply chain for a food product from farm to consumer. Design\\/methodology\\/approach – Action research based on a UK case study involving farmers, a food processor and a major retailer. Findings – Value stream analysis (VCA) highlights significant opportunities to improve supply chain performance,

David H. Taylor

2005-01-01

251

Social class gradients in health during adolescence  

PubMed Central

Study objective: To review existing data on social class gradients in adolescent health and to examine whether such gradients exist in new data concerning US adolescents. Design: Review of relevant publications and unpublished data; regression analyses using adolescent self reported health status data to determine whether there are gradients by social class, using three classes categorised by adolescent reported parental work status and education. Participants: Adolescents of ages 11–17. Main results: Findings from the literature indicate the presence of social class gradients in some but not all aspects of adolescent health. Results from new data showed social class gradients in several domains of health and in profiles of health. The likelihood of being satisfied with one's health, of being more resilient (better family involvement, better problem solving, more physical activity, better home safety), having higher school achievement, and of being in the best health profiles were significantly and progressively greater as social class rose. Moreover, the probability of being in the poorest health profile type group was progressively higher as social class declined. Conclusions: The review of existing data and the new findings support the existence of social class gradients in satisfaction with one's health, in resilience to health threats, in school achievement, and in being in the best health overall (as manifested by the health profiles composed of four major domains of health). The study had two especially notable findings: (1) the paucity of studies using the same or similar indicators, and (2) the consistent existence of social class gradients in characteristics related to subsequent health, particularly intake of nutritional foods and physical activity. The sparseness of existing data and the different aspects of health investigated in the relatively few studies underscore the need for (1) the development of conceptual models specifically focused on adolescent health and social class; (2) additional inquiry into the measurement of social class and adolescent perceptions of class; (3) inclusion of contextual variables in study design; and (4) longitudinal cohort studies to better understand the specific determinants of health during adolescence.

Starfield, B; Riley, A; Witt, W; Robertson, J

2002-01-01

252

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 sizeable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

Hull, J.R.

1982-09-29

253

GPS, GNSS, and Ionospheric Density Gradients  

NASA Astrophysics Data System (ADS)

Ionospheric density and density gradients affect GNSS signals in two ways. They can introduce ranging errors or irregularities that form on the density gradients producing scintillation. Here we focus on the issue of ranging errors. There are two approaches to mitigating ranging errors produced by ionospheric density gradients which can be 20-30 m during major magnetic storms. The first approach is to use a reference receiver(s) to determine the ionospheric contribution to ranging errors. The ranging error is then transmitted to the user for correction within the mobile receiver. This approach is frequently referred to as differential GPS and, when multiple reference receivers are used, the system is referred to as an augmentation system. This approach is vulnerable to ionospheric gradients depending on the reference receiver spacing(s) and latency in applying the correction within the mobile receiver. The second approach is to transmit navigation signals at two frequencies and then use the relative delay between the two signals to both estimate the ranging error and calculate the correct range. Currently the dual frequency technique is used by US military receivers with an encryption key and some civilian receivers which must be stationary and average over times long compared to those required for navigation. However, the technology of space based radio navigation is changing. GPS will soon be a system with three frequencies and multiple codes. Furthermore Europe, Russia, and China are developing independent systems to complement and compete with GPS while India and Japan are developing local systems to enhance GPS performance in their regions. In this talk we address two questions. How do density gradients affect augmentation systems including the social consequences and will the new GPS/GNSS systems with multiple civilian frequencies be able to remove ionospheric errors. The answers are not at all clear.

Kintner, P. M.; O'Hanlon, B.; Humphreys, T. E.

2009-12-01

254

Translocation of a polymer chain across a nanopore: A Brownian dynamics simulation study  

NASA Astrophysics Data System (ADS)

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.

2003-12-01

255

A technique for preparing protein gradients on polymeric surfaces: effects on PC12 pheochromocytoma cells.  

PubMed

A technique for preparing micropatterns and gradients of proteins on polymeric substrates has been developed in this work. Peroxides were generated on the substrate surface by UV preirradiation and they initiated graft polymerization of acrylic acid (AA) onto the surface upon a second UV irradiation. Micropatterns and gradients of poly(acrylic acid) (PAA) were formed when the substrate was placed under or moved with respect to a photomask during UV preirradiation. Protein micropatterns and gradients were fabricated on the surface by covalently linking to the carboxyl groups on PAA chains. To test cell response to the protein gradient surfaces, PC12 pheochromocytoma cells were cultured on laminin-bound substrates in serum-free medium supplemented with nerve growth factor (NGF). It is found that both the attachment and neurite outgrowth behaviors of PC12 cells were dependent on the surface laminin density. However, the unreacted carboxyl groups on the polymer surface negatively affected PC12 cells. This weakened the positive influence from laminin. PMID:15522750

Li, Bin; Ma, Yuexia; Wang, Shu; Moran, Peter M

2005-05-01

256

Characterization of imaging gradients in diffusion tensor imaging.  

PubMed

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. PMID:20810298

Özcan, Alpay

2010-08-13

257

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

258

NMR imaging analogue of the individual qubit operations in superconducting flux-qubit chains  

NASA Astrophysics Data System (ADS)

A solid-state quantum computer conventionally requires the control lines for each qubit to operate individually. This makes quantum circuits complicated, especially in multi-qubit systems. Here we propose a simple single-qubit operation in a superconducting flux-qubit chain without control lines in an analogy of the Nuclear Magnetic Resonance (NMR) imaging technique. A superconducting flux qubit can be regarded as an artificial atom with spin 1/2 that can be manipulated by an external magnetic field. To identify the location of each qubit in the qubit chain, a static field gradient is introduced along the qubit chain. This magnetic field gradient causes differences in the Zeeman frequencies of each separate qubit. This allows a large number of distinct qubits to be individually addressed. Single-qubit operations are then possible when the external electromagnetic frequency is adjusted to the resulting energy-level separation of the target qubit.

Fujii, Toshiyuki; Matsuo, Shigemasa; Hatakenaka, Noriyuki

2009-02-01

259

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

260

Cross-term-compensated pulsed-gradient stimulated echo MR with asymmetric gradient pulse lengths  

NASA Astrophysics Data System (ADS)

The magic asymmetric gradient stimulated echo (MAGSTE) sequence developed to compensate background-gradient cross-terms in the preparation and readout interval independently, assumes identical lengths for the two gradient pulses applied in each interval. However, this approach is rather inefficient if some extra delay time is present in one half of an interval, e.g. as required for special RF excitations or spatial encoding prior to the stimulated echo in MR imaging. Therefore, a generalized version of the sequence is presented that considers different gradient pulse lengths within an interval. It is shown theoretically that (i) for any pulse lengths a “magic” amplitude ratio exists which ensures the desired cross-term compensation in each interval and that (ii) prolonging one of the gradients can deliver a considerably higher diffusion weighting efficiency. These results are confirmed in MR imaging experiments on phantoms and in vivo in the human brain at 3 T using an echo-planar trajectory. In the examples shown, typically 10 times higher b values can be achieved or an echo time reduction with a 40% signal gain in brain white matter. Thus, in case of asymmetric timing requirements, the generalized MAGSTE sequence with different gradient pulse lengths may help to overcome signal-to-noise limitations in diffusion weighted MR.

Finsterbusch, Jürgen

2008-07-01

261

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

262

Atwood's Heavy Chain  

NASA Astrophysics Data System (ADS)

While perusing various websites in search of a more challenging lab for my students, I came across a number of ideas where replacing the string in an Atwood's machine1 with a simple ball chain like the kind found in lamp pulls created an interesting system to investigate. The replacement of the string produced a nice nonuniform acceleration, but one that my AP® students found difficult to analyze given their current math background. As the year progressed, we began to explore the importance of work and its utility in making predictions on systems that did not lend themselves to easy analysis using Newtonian mechanics. The effort made it apparent that the heavy rope Atwood's machine would make a perfect system for investigation using the lessons gained from work and energy.

Beeken, Paul

2011-11-01

263

Dynamics of Oscillator Chains  

NASA Astrophysics Data System (ADS)

The Fermi-Pasta-Ulam (FPU) nonlinear oscillator chain has proved to be a seminal system for investigating problems in nonlinear dynamics. First proposed as a nonlinear system to elucidate the foundations of statistical mechanics, the initial lack of confirmation of the researchers expectations eventually led to a number of profound insights into the behavior of high-dimensional nonlinear systems. The initial numerical studies, proposed to demonstrate that energy placed in a single mode of the linearized chain would approach equipartition through nonlinear interactions, surprisingly showed recurrences. Although subsequent work showed that the origin of the recurrences is nonlinear resonance, the question of lack of equipartition remained. The attempt to understand the regularity bore fruit in a profound development in nonlinear dynamics: the birth of soliton theory. A parallel development, related to numerical observations that, at higher energies, equipartition among modes could be approached, was the understanding that the transition with increasing energy is due to resonance overlap. Further numerical investigations showed that time-scales were also important, with a transition between faster and slower evolution. This was explained in terms of mode overlap at higher energy and resonance overlap at lower energy. Numerical limitations to observing a very slow approach to equipartition and the problem of connecting high-dimensional Hamiltonian systems to lower dimensional studies of Arnold diffusion, which indicate transitions from exponentially slow diffusion along resonances to power-law diffusion across resonances, have been considered. Most of the work, both numerical and theoretical, started from low frequency (long wavelength) initial conditions.

Lichtenberg, Allan J.; Livi, Roberto; Pettini, Marco; Ruffo, Stefano

264

Sulfation of the bikunin chondroitin sulfate chain determines heavy chain·hyaluronan complex formation.  

PubMed

Inter-?-trypsin inhibitor (I?I) is a complex comprising two heavy chains (HCs) that are covalently bound by an ester bond to chondroitin sulfate (CS), which itself is attached to Ser-10 of bikunin. I?I is essential for the trans-esterification of HCs onto hyaluronan (HA). This process is important for the stabilization of HA-rich matrices during ovulation and some inflammatory processes. Bikunin has been isolated previously by anion exchange chromatography with a salt gradient up to 0.5 M NaCl and found to contain unsulfated and 4-sulfated CS disaccharides. In this study, bikunin-containing fractions in plasma and urine were separated by anion exchange chromatography with a salt gradient of 0.1-1.0 M NaCl, and fractions were analyzed for their reactivity with the 4-sulfated CS linkage region antibody (2B6). The fractions that reacted with the 2B6 antibody (0.5-0.8 M NaCl) were found to predominantly contain sulfated CS disaccharides, including disulfated disaccharides, whereas the fractions that did not react with this antibody (0.1-0.5 M NaCl) contained unsulfated and 4-sulfated CS disaccharides. I?I in the 0.5-0.8 M NaCl plasma fraction was able to promote the trans-esterification of HCs to HA in the presence of TSG-6, whereas the 0.1-0.5 M NaCl fraction had a much reduced ability to transfer HC proteins to HA, suggesting that the CS containing 4-sulfated linkage region structures and disulfated disaccharides are involved in the HC transfer. Furthermore, these data highlight that the structure of the CS attached to bikunin is important for the transfer of HC onto HA and emphasize a specific role of CS chain sulfation. PMID:23801333

Lord, Megan S; Day, Anthony J; Youssef, Peter; Zhuo, Lisheng; Watanabe, Hideto; Caterson, Bruce; Whitelock, John M

2013-06-25

265

Towards a supply chain analysis framework  

Microsoft Academic Search

Coordination between supply chain organizations on strategic, tactical and operation levels leads to more effective and efficient supply chains. For a supply chain coordination process a systems approach together with broad understanding of relevant supply chain management issues is necessary. Supply chain managers must speak the same language and be able to gain mutual understanding of possible supply chain problems.

M. W. Ludema

2008-01-01

266

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

267

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

268

Density Gradients at and Near the Plasmapause  

NASA Astrophysics Data System (ADS)

We explore density gradients observed at and near the plasmapause using spacecraft potential data from the EFI instruments on the five THEMIS spacecraft. The plasmasphere boundary is an important region in the inner magnetosphere for wave growth, decay, and propagation. Through waves which occur there, low energy particles couple to the highest energy particles thereby connecting the entire particle population in inner magnetosphere. We present here statistics on the structure, size, location, and occurrence of plasma density gradients and their relation to geomagnetic activity. The THEMIS mission and its five spacecraft in orbits of different periods present an idea platform to study the plasmasphere boundary region, providing different local time traversals with a variety of revisit times needed to separate spatial and temporal structure.

Larsen, B. A.; Spence, H. E.; Bonnell, J. W.

2009-12-01

269

Responding to chemical gradients: bacterial chemotaxis.  

PubMed

Chemotaxis allows bacteria to follow gradients of nutrients and other environmental stimuli. The bacterium Escherichia coli performs chemotaxis via a run-and-tumble strategy in which sensitive temporal comparisons lead to a biased random walk, with longer runs in the preferred gradient direction. The chemotaxis network of E. coli has developed over the years into one of the most thoroughly studied model systems for signal transduction and behavior, yielding general insights into such properties of cellular networks as signal amplification, signal integration, and robustness. Despite its relative simplicity, the operation of the E. coli chemotaxis network is highly refined and evolutionarily optimized at many levels. For example, recent studies revealed that the network adjusts its signaling properties dependent on the extracellular environment, apparently to optimize chemotaxis under particular conditions. The network can even utilize potentially detrimental stochastic fluctuations in protein levels and reaction rates to maximize the chemotactic performance of the population. PMID:22169400

Sourjik, Victor; Wingreen, Ned S

2011-12-09

270

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

271

Hydrodynamic Gradient Expansion in Gauge Theory Plasmas  

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

272

Gradient Moment Compensated Magnetic Resonance Spectroscopic Imaging  

PubMed Central

Spectroscopic imaging applications outside of the brain can suffer from artifacts due to inherent long scan times and susceptibility to motion. A fast spectroscopic imaging sequence has been devised with reduced sensitivity to motion. The sequence uses oscillating readout gradients and acquires k-space data in a spiral out–in fashion, which allows fast k-space coverage. We show that a spiral out–in readout acquisition is characterized by small gradient moments, reducing sensitivity to motion-induced artifacts. Data are acquired comparing the sequence to normal phase encoded spectroscopic imaging and conventional spiral spectroscopic imaging protocols. In addition, in vivo data are acquired from the liver, demonstrating potential usage as a multivoxel fat/water spectroscopic imaging tool. Results indicate that in the presence of motion, ghosting effects are reduced while metabolite signal increases of approximately 10% can be achieved.

Kim, Dong-Hyun; Gu, Meng; Spielman, Daniel M.

2010-01-01

273

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

274

Anisotropic gradients in the upper mantle  

SciTech Connect

Pn amplitudes in some widely spaced sets of orthogonal marine refraction lines on young oceanic crust are greater in the fast direction than in the slow direction. This is inconsistent with the predicted amplitude behavior for simple head waves, but can be explained by an increase in anisotropy with depth. It appears that these gradients are due to increasing olivine crystal orientation, although changes in the relative abundance of two anisotropic minerals without variable tectonization could also account for the observations. Depth variation of tectonization most probably indicates very high temperature gradients at the Moho. This would imply a substantial amount of convective heat transport in the whole oceanic crust near mid-ocean rises.

Garmany, J.

1981-09-01

275

Ecological gradients within a Pennsylvanian mire forest  

SciTech Connect

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.

DiMichele, W.A.; Falcon-Lang, H.J.; Nelson, W.J.; Brick, S.D.; Ames, P.R. [Smithsonian Institute, Washington, DC (United States)

2007-05-15

276

Spontaneous wrinkle branching by gradient stiffness  

NASA Astrophysics Data System (ADS)

The concept of coherency loss is proposed to understand wrinkle branching as a pathway toward hierarchical wrinkling pattern formation in a compressed film-substrate system with gradient stiffness of the film or substrate. A simple model indicates that the wrinkle branching arises when the characteristic length of the stiffness inhomogeneity zone is larger than the coherency persistent length, which depends on the amplitude of the stiffness inhomogeneity. Numerical simulations of nonlinear wrinkles based on the model of the Föppl-von Kármán plate on compliant substrates show how regulating the size and amplitude of the stiffness inhomogeneities results in branched wrinkles in striking agreement with the existing observations. The paper reveals the origin of such kinds of branched wrinkles and may provide a guideline for controllable hierarchical wrinkles by patterning the stiffness gradient.

Ni, Yong; Yang, Dong; He, Linghui

2012-09-01

277

MAGNETIC ADVECTION DUE TO DIFFUSIVITY GRADIENTS  

NASA Astrophysics Data System (ADS)

We derive and discuss an important source of advection of magnetic fields in plasmas, for a completely general case. Magnetic diffusivity is proportional to electrical resistivity: where the value this parameter is high, it is well known that magnetic fields can leak (or diffuse) rapidly into (or out) of the plasma. Magnetohydrodynamic lore has it that where gradients, or changes in space, of the value of the diffusivity are high, magnetic fields can have enhanced flow (or advection). We derive this phenomenon rigorously, compare our results to other work in the literature, and discuss its implications, especially for kinematic dynamos. As an extra mathematical bonus, we find that the magnetic advection due to diffusivity gradients can be expressed in terms of a diffusion equation within the induction equation, making its computational implementation especially simple.

Zita, E. J.

2009-12-01

278

Thermal fracture of functionally gradient ceramics  

NASA Astrophysics Data System (ADS)

An edge crack in a strip of functionally gradient ceramics (FGC) is studied under thermal loading conditions. Two FGC materials are considered, i.e., one with a spatial variation of shear modulus and the other with a spatial variation of thermal conductivity. Thermal stress intensity factors (TSIF) are numerically calculated based on singular integral equations derived for the dislocation density along the crack faces. It is shown that: (a) for the FGC with a graded shear modulus, the TSIF are reduced for crack lengths longer than l c b and remain approximately the same as those of a homogeneous material for shorter crack lengths, where l c is about 0.065 and b is the width of the strip; and (b) for the FGC with a thermal conductivity gradient, the TSIF are generally lower compared with those for the bonded two-layer material.

Jin, Zhi-He; Mai, Yiu-Wing

1996-05-01

279

Temperature gradient driven lasing and stimulated cooling.  

PubMed

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. PMID:23215382

Sandner, K; Ritsch, H

2012-11-07

280

Enhanced gradient for training restricted Boltzmann machines.  

PubMed

Restricted Boltzmann machines (RBMs) are often used as building blocks in greedy learning of deep networks. However, training this simple model can be laborious. Traditional learning algorithms often converge only with the right choice of metaparameters that specify, for example, learning rate scheduling and the scale of the initial weights. They are also sensitive to specific data representation. An equivalent RBM can be obtained by flipping some bits and changing the weights and biases accordingly, but traditional learning rules are not invariant to such transformations. Without careful tuning of these training settings, traditional algorithms can easily get stuck or even diverge. In this letter, we present an enhanced gradient that is derived to be invariant to bit-flipping transformations. We experimentally show that the enhanced gradient yields more stable training of RBMs both when used with a fixed learning rate and an adaptive one. PMID:23148412

Cho, Kyunghyun; Raiko, Tapani; Ilin, Alexander

2012-11-13

281

Colloidal attraction induced by a temperature gradient.  

PubMed

Colloidal crystals are of extreme importance for applied research and for fundamental studies in statistical mechanics. Long-range attractive interactions, such as capillary forces, can drive the spontaneous assembly of such mesoscopic ordered structures. However, long-range attractive forces are very rare in the colloidal realm. Here we report a novel strong, long-ranged attraction induced by a thermal gradient in the presence of a wall. By switching the thermal gradient on and off, we can rapidly and reversibly form stable hexagonal 2D crystals. We show that the observed attraction is hydrodynamic in nature and arises from thermally induced slip flow on particle surfaces. We used optical tweezers to measure the force law directly and compare it to an analytical prediction based on Stokes flow driven by Marangoni-like forces. PMID:19265405

Di Leonardo, R; Ianni, F; Ruocco, G

2009-04-21

282

Self-organization of intracellular gradients during mitosis  

PubMed Central

Gradients are used in a number of biological systems to transmit spatial information over a range of distances. The best studied are morphogen gradients where information is transmitted over many cell lengths. Smaller mitotic gradients reflect the need to organize several distinct events along the length of the mitotic spindle. The intracellular gradients that characterize mitosis are emerging as important regulatory paradigms. Intracellular gradients utilize intrinsic auto-regulatory feedback loops and diffusion to establish stable regions of activity within the mitotic cytosol. We review three recently described intracellular mitotic gradients. The Ran GTP gradient with its elaborate cascade of nuclear transport receptors and cargoes is the best characterized, yet the dynamics underlying the robust gradient of Ran-GTP have received little attention. Gradients of phosphorylation have been observed on Aurora B kinase substrates both before and after anaphase onset. In both instances the phosphorylation gradient appears to result from a soluble gradient of Aurora B kinase activity. Regulatory properties that support gradient formation are highlighted. Intracellular activity gradients that regulate localized mitotic events bare several hallmarks of self-organizing biologic systems that designate spatial information during pattern formation. Intracellular pattern formation represents a new paradigm in mitotic regulation.

2010-01-01

283

Statistical Methods in Markov Chains  

Microsoft Academic Search

This paper is an expository survey of the mathematical aspects of statistical inference as it applies to finite Markov chains, the problem being to draw inferences about the transition probabilities from one long, unbroken observation $\\\\{x_1, x_2, \\\\cdots, x_n\\\\}$ on the chain. The topics covered include Whittle's formula, chi-square and maximum-likelihood methods, estimation of parameters, and multiple Markov chains. At

Patrick Billingsley

1961-01-01

284

Numerical investigation of monopole chains  

NASA Astrophysics Data System (ADS)

We present numerical results for chains of SU(2) BPS monopoles constructed from Nahm data. The long chain limit reveals an asymmetric behaviour transverse to the periodic direction, with the asymmetry becoming more pronounced at shorter separations. This analysis is motivated by a search for semiclassical finite temperature instantons in the 3D SU(2) Georgi-Glashow model, but it appears that in the periodic limit the instanton chains either have logarithmically divergent action or wash themselves out.

Dunne, Gerald V.; Khemani, Vishesh

2005-10-01

285

Gravity gradient modeling using gravity and DEM  

Microsoft Academic Search

A model of the gravity gradient tensor at aircraft altitude is developed from the combination of ground gravity anomaly data\\u000a and a digital elevation model. The gravity data are processed according to various operational solutions to the boundary-value\\u000a problem (numerical integration of Stokes’ integral, radial-basis splines, and least-squares collocation). The terrain elevation\\u000a data are used to reduce free-air anomalies to

Lizhi Zhu; Christopher Jekeli

2009-01-01

286

Relaxation of Star Clusters and Color Gradients  

NASA Astrophysics Data System (ADS)

The collapse of stellar systems with initially little or no velocity dispersion leads to efficient relaxation and orbit mixing, and, presumably, a loss of memor y of the initial conditions. However for aspherical mass profiles, such as axisymmetric spheroids, cold collapse does not always erase memory of the initial distribution. Thus if colour gradients are observed in young, relaxed star clusters, they may well have originated from an initial stellar distributi on in space biased with respect to mass.

Boily, C.

287

Cosmic ray gradients in the outer heliosphere  

NASA Astrophysics Data System (ADS)

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.

Walker, F.; Wake, B.; Ip, W.-H.; Axford, I.

1983-08-01

288

On numerical analysis of conjugate gradient method  

Microsoft Academic Search

The goal of this paper is to make a trial for evaluating the computational efficiency of the conjugate gradient method and\\u000a to discuss some practical aspects important for the user in solving large and sparse systems of linear equations arising from\\u000a the discretization of boundary value problems for elliptic partial differential equations. The solution efficiency of different\\u000a algorithms of the

Z. I. Wo?nicki

1993-01-01

289

DC CHARACTERIZATION OF HIGH GRADIENT MULTILAYER INSULATORS  

SciTech Connect

We have developed a novel insulator concept that involves the use of alternating layers of conductors and insulators with periods less than 1 mm. We have demonstrated that these structures perform 2 to 5 times better than conventional insulators in long pulse, short pulse, and alternating polarity applications. We present new testing results showing exceptional behavior at DC, with gradients in excess of 110kV/cm in vacuum.

Watson, J A; Caporaso, G J; Sampayan, S E; Sanders, D M; Krogh, M L

2005-05-26

290

Pedestrian Detection Using Gradient Local Binary Patterns  

NASA Astrophysics Data System (ADS)

In recent years, local pattern based features have attracted increasing interest in object detection and recognition systems. Local Binary Pattern (LBP) feature is widely used in texture classification and face detection. But the original definition of LBP is not suitable for human detection. In this paper, we propose a novel feature named gradient local binary patterns (GLBP) for human detection. In this feature, original 256 local binary patterns are reduced to 56 patterns. These 56 patterns named uniform patterns are used for generating a 56-bin histogram. And gradient value of each pixel is set as the weight which is always same in LBP based features in histogram calculation to computing the values in 56 bins for histogram. Experiments are performed on INRIA dataset, which shows the proposal GLBP feature is discriminative than histogram of orientated gradient (HOG), Semantic Local Binary Patterns (S-LBP) and histogram of template (HOT). In our experiments, the window size is fixed. That means the performance can be improved by boosting methods. And the computation of GLBP feature is parallel, which make it easy for hardware acceleration. These factors make GLBP feature possible for real-time pedestrian detection.

Jiang, Ning; Xu, Jiu; Goto, Satoshi

291

The spinor Boltzmann equation beyond gradient approximation  

NASA Astrophysics Data System (ADS)

In this paper, we generalize the spinor Boltzmann equation in order to describe the spin-polarized transport in magnetic multilayers beyond gradient approximation, because the usual gradient approximation, hence the quantum Boltzmann equation based on it, is only suitable for the systems whose potentials vary slowly with respect to time and position. In our derivation, we do not adopt the gradient approximation to simplify those convolutions concerning with Fourier transformations, we just deal with them by the way given by Wigner [E. Wigner, Phys. Rev. 40, 749 (1932)], which assures the final quantum Boltzmann equation can be applied to the system with rapid varying potential. Then we illustrate it by the spin-polarized transport in magnetic multilayers in which the potential have sudden jumps at the interfaces, and apply the generalized spinor Boltzmann equation to the entire magnetic multilayers, it avoids to connect the distribution functions of different layers by matching conditions as usual. We also study the quantum corrections for the distribution function, the equations satisfied by the zero-order distribution function and the first order quantum correction are exhibited.

Wang, Zheng-Chuan

2013-05-01

292

Gradient expansion, curvature perturbations, and magnetized plasmas  

SciTech Connect

The properties of magnetized plasmas are always investigated under the hypothesis that the relativistic inhomogeneities stemming from the fluid sources and from the geometry itself are sufficiently small to allow for a perturbative description prior to photon decoupling. The latter assumption is hereby relaxed and predecoupling plasmas are described within a suitable expansion where the inhomogeneities are treated to a given order in the spatial gradients. It is argued that the (general relativistic) gradient expansion shares the same features of the drift approximation, customarily employed in the description of cold plasmas, so that the two schemes are physically complementary in the large-scale limit and for the low-frequency branch of the spectrum of plasma modes. The two-fluid description, as well as the magnetohydrodynamical reduction, is derived and studied in the presence of the spatial gradients of the geometry. Various solutions of the coupled system of evolution equations in the anti-Newtonian regime and in the quasi-isotropic approximation are presented. The relation of this analysis to the so-called separate universe paradigm is outlined. The evolution of the magnetized curvature perturbations in the nonlinear regime is addressed for the magnetized adiabatic mode in the plasma frame.

Giovannini, Massimo [Department of Physics, Theory Division, CERN, 1211 Geneva 23 (Switzerland); INFN, Section of Milan-Bicocca, 20126 Milan (Italy); Rezaei, Zahra [Department of Physics, Theory Division, CERN, 1211 Geneva 23 (Switzerland); Isfahan University of Technology, Department of Physics, 84154 Isfahan (Iran, Islamic Republic of)

2011-04-15

293

Phosphorescent imaging of oxygen gradients in tissues  

NASA Astrophysics Data System (ADS)

Until recently, the ability to measure the changing oxygen gradients in perfused tissues in response to metabolic demand, has been limited to point-measurements and/or averaged A-V oxygen differences during perfusion using oxygen electrodes. With the recent introduction of novel phosphorescent probes specifically quenched by oxygen, the ability to spacially map oxygen gradients in real-time may offer new insights into the dynamics of microvascular design and supply. Accordingly, this paper provides initial image data on Langendorff perfused rat hearts wherein the relative change in phosphorescent intensity of Pd-meso-tetra(4- carboxyphenyl)phorphine (2micrometers ) as the reporter probe, is quantitatively related to spacial oxygen gradients as seen on the left-ventricle during changing gassing conditions. Digital image analysis (frame advance), after proper calibration and alignment, provides images which can be usefully interpreted. Clinical applications of such emerging technologies could have wide-spread diagnostic applications not only as applied to the coronary bed, but other tissue surfaces displaying various degrees of aschemia and/or hypoxia.

Swanson, Curtis J.; Kitakis, F.

1995-08-01

294

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

295

Domain Formation in Model Membranes Studied by Pulsed-Field Gradient-NMR: The Role of Lipid Polyunsaturation  

Microsoft Academic Search

The effects of increased unsaturation in the sn-2 fatty acyl chain of phosphatidylcholines (PCs) on the lipid lateral diffusion have been investigated by pulsed-field gradient NMR. Macroscopically oriented bilayers containing a monosaturated PC, egg sphingomyelin, and cholesterol (CHOL) have been studied at temperatures between 0°C and 60°C, and the number of double bonds in the PC was one, two, four,

Andrey Filippov; Greger Orädd; Göran Lindblom

2007-01-01

296

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

297

Non-singular dislocation loops in gradient elasticity  

NASA Astrophysics Data System (ADS)

Using gradient elasticity, we give in this Letter the non-singular fields produced by arbitrary dislocation loops in isotropic media. We present the 'modified' Mura, Peach-Koehler and Burgers formulae in the framework of gradient elasticity theory.

Lazar, Markus

2012-04-01

298

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

2013-05-24

299

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

NASA Astrophysics Data System (ADS)

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.

Kosevich, Yuriy A.; Gann, Vladimir V.

2013-06-01

300

Temperature-gradient zone recrystallization of semiconductor materials  

NASA Astrophysics Data System (ADS)

The physicomechanical principles of the temperature-gradient zone recrystallization of semiconductor materials are reviewed. In particular, attention is given to the methods and equipment for producing liquid zones, kinetics of temperature-gradient zone recrystallization, component distribution in a solid solution layer grown by zone recrystallization, and impurity distribution. Finally, applications of temperature-gradient zone recrystallization in semiconductor technology are discussed.

Lozovskii, Vladimir Nikolaevich; Lunin, Leonid Sergeevich; Popov, Viktor Pavlovich

301

GRADIENT BASED SPECTRAL PEAK LOCATION FOR NOISE ROBUST SPEECH RECOGNITION  

Microsoft Academic Search

In this paper a gradient-based algorithm for finding spectral peak locations is presented. The algorithm makes use of gradient and acceleration locations in the spectrogram for locating the peaks. Use of frequency gradients and accelerations locate peaks. The results are then interpolated to yield a smooth peak envelope. The method is evaluated in the aurora framework. A first pass locates

Penny Hix

302

Estimation of gradients from sparse data by universal kriging  

Microsoft Academic Search

The determination of a gradient, or directional derivative, of a spatial variable is a common problem in many Earth science applications. For hydraulic heads, for example, the gradient defines the direction of the groundwater flow and is used in solving groundwater flow and transport equations. Kriging provides a methodology for estimating gradients directly from experimental data without the need to

Eulogio Pardo-Igúzquiza; Mario Chica-Olmo

2004-01-01

303

Ant Activity along Moisture Gradients in a Neotropical Forest1  

Microsoft Academic Search

Insect activity often tracks moisture gradients. We studied ant activity, size, and diversity along three moisture gradients in a Panamanian rain forest. Ant activity at baits increased by 25 percent from the dry to the wet season, and . 200 percent on a topographical gradient from a ravine to an exposed plateau. Activity varied little from day to night. Three

Michael Kaspari; Michael D. Weiser

2000-01-01

304

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

305

Nitrification and nitrate reductase activity along a secondary successional gradient  

Microsoft Academic Search

The control of nitrification was studied in a secondary successional gradient on Nantucket Island, MA. It was hypothesized that 1) variability in nitrification along the gradient is controlled by litter primary and secondary chemistry, and 2) differences in nitrate availability along the gradient are reflected in potential nitrate assimilation rates in plant tissue. Nitrification varied significantly (ppSchizachyrium scoparium). Although there

C. Barford; K. Lajtha

1992-01-01

306

Zoom lens design using gradient-index lenses  

Microsoft Academic Search

A zoom lens system using gradient-index lenses was studied to realize a compact video camera. This study investigates the relationship between the total index change and the amount of aberration correction in order to effectively apply existing gradient-index lenses to the zoom lenses. In addition, it examines how the effective dispersion of the gradient affects the chromatic aberrations while zooming.

Masaharu Deguchi; Duncan T. Moore; Douglas S. Kindred

1994-01-01

307

Characterization of imaging gradients in diffusion tensor imaging  

Microsoft Academic Search

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

Alpay Özcan

2010-01-01

308

HYBRID MANEUVER FOR GRADIENT SEARCH WITH MULTIPLE COORDINATED AUVs  

Microsoft Academic Search

This work presents a hybrid maneuver for gradient search with multiple AUV's. The mission consists in following a gradient field in order to locate the source of a hydrothermal vent or underwater freshwater source. The formation gradient search exploits the environment structuring by the phenomena to be studied. The ingredients for coordination are the payload data collected by each vehicle

Alfredo Martins; José Miguel Almeida; Eduardo Silva; Fernando Lobo Pereira

309

Le gradient géothermique profond du Maroc : détermination et cartographie  

Microsoft Academic Search

Mots clés : Maroc, gradient géothermique, forage pétrolier, BHT, DST, anomalie thermique, hydrodynamisme. The deep geothermal gradient of Morocco : determination and cartography. Abstract. The aim of this study is to establish a geothermal gradient map of Morocco, by using thermal data obtained from petroleum exploration wells. Both the corrected bottom-hole temperatures (BHT) and the drill-stem test temperatures (DST) were

Yassine ZARHLOULE

310

Positive and negative generalization gradients obtained after equivalent training conditions  

Microsoft Academic Search

Positive and negative gradients were compared on the dimension of angular orientation (tilt) following discrimination training with the presence of a vertical line being positive and its absence being negative for one group of pigeons, and the opposite discrimination for another group. The gradients were initially very similar in form, although the negative gradient became flatter in the course of

Werner K. Honig; C. Alan Boneau; K. R. Burstein; H. S. Pennypacker

1963-01-01

311

Histogram of oriented gradient detector with color-invariant gradients in Gaussian color space  

NASA Astrophysics Data System (ADS)

The histogram of oriented gradients has been proven to be a successful method of object detection, especially for pedestrian detection in images and videos. However, the question of how to make maximal use of color information for gradient calculation has not been thoroughly investigated. We propose a simple yet effective adaption that uses a combination of grayscale-based gradient and color-invariant-based gradients (after Geusebroek et al.) to replace the original gradient definition. Our experiments show that such a combination achieves a 30% reduction in miss rate, using the same experiment setting and the same evaluation criteria as Dalal et al. We have also measured the trade-off between the performance and computational cost by using a more sophisticated quadratic kernel instead of a linear kernel. While it can reduce the miss rate further by 10% to 20%, using a quadratic kernel can take as much as 70 times more running time for the original (Dalal et al. 2006) dataset.

Lei, Zhen; Fang, Tao; Li, Deren

2010-10-01

312

The Use of Ethylene Glycol to Evaluate Gradient Performance in Gradient-Intensive Diffusion MR Sequences  

PubMed Central

Imaging a phantom of known dimensions is a widely used and simple method for calibrating MRI gradient strength. However, full-range characterization of gradient response is not achievable using this approach. Measurement of the apparent diffusion coefficient of a liquid with known diffusivity allows for calibration of gradient amplitudes across a wider dynamic range. An important caveat is that the temperature-dependence of the liquid’s diffusion characteristics must be known, and the temperature of the calibration phantom must be recorded. In this report we demonstrate that the diffusion coefficient of ethylene glycol is well-described by Arrhenius-type behavior across the typical range of ambient MRI magnet temperatures. Because of ethylene glycol’s utility as an NMR chemical-shift thermometer, the same 1H MR spectroscopy measurements that are used for gradient calibration also simultaneously “report” the sample temperature. The high viscosity of ethylene glycol makes it well-suited for assessing gradient performance in demanding diffusion-weighted imaging and spectroscopy sequences.

Spees, William M.; Song, Sheng-Kwei; Garbow, Joel R.; Neil, Jeffrey J.; Ackerman, Joseph J.H.

2011-01-01

313

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

314

Organising for supply chain management  

Microsoft Academic Search

Many companies have introduced the supply chain function in their organisation. Little attention, however, is devoted to the way the supply chain function is organised, e.g. the range of responsibilities it has, the position it occupies in the hierarchy and the skills it requires. The literature on this is scarce. This paper provides initial benchmarking data on company decisions regarding

Robert Boute; Roland Van Dierdonck; Ann Vereecke

2011-01-01

315

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

316

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

317

Agent Simulation of Chain Bankruptcy  

Microsoft Academic Search

We have conducted an agent-based simulation of chain bankruptcy. The propagation of credit risk on a network, i.e., chain bankruptcy, is the key to nderstanding largesized bankruptcies. In our model, decrease of revenue by the loss of accounts payable is modeled by an interaction term, and bankruptcy is defined as a capital deficit. Model parameters were estimated using financial data

Yuichi Ikeda; Yoshi Fujiwara; Wataru Souma; Hideaki Aoyama; Hiroshi Iyetomi

2007-01-01

318

Discount Chains and Brand Policy  

Microsoft Academic Search

Retail chains are observed in many industries. The question addressed here is whether retail chains can exploit buyer power by excluding some brands. In a theoretical model with two differentiated producers and a single retailer, the authors show that a retailer will require exclusivity (exclude a brand) if the brands are sufficiently symmetric in demand potential. Exclusivity will increase welfare

Tommy Staahl Gabrielsen; Lars Sorgard

1999-01-01

319

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

320

Developing sustainable food supply chains.  

PubMed

This paper reviews the opportunities available for food businesses to encourage consumers to eat healthier and more nutritious diets, to invest in more sustainable manufacturing and distribution systems and to develop procurement systems based on more sustainable forms of agriculture. The important factors in developing more sustainable supply chains are identified as the type of supply chain involved and the individual business attitude to extending responsibility for product quality into social and environmental performance within their own supply chains. Interpersonal trust and working to standards are both important to build more sustainable local and many conserved food supply chains, but inadequate to transform mainstream agriculture and raw material supplies to the manufactured and commodity food markets. Cooperation among food manufacturers, retailers, NGOs, governmental and farmers' organizations is vital in order to raise standards for some supply chains and to enable farmers to adopt more sustainable agricultural practices. PMID:17766237

Smith, B Gail

2008-02-27

321

GOCE Gravity Gradients: A New Satellite Observable  

NASA Astrophysics Data System (ADS)

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) is one of the flagships in ESA's Living Planet Programme. With the help of the on-board, very precise gravitational gradiometer the Earth's gravity field is to be determined with unprecedented accuracy. The gradiometer measures gravity field differences that are contained in six gravity gradient (GG) tensor components. Because of the instrument characteristics, four out of six tensor elements are very accurate, whereas the other two are less accurate. We will concentrate on the noise characteristics of the accurate GGs by a spectral analysis of the residuals of a semi-analytical gravity field solution for the first measurement phase (November - December 2009). Formal errors of spherical harmonic coefficients are estimated in a semi-analytical way by means of a GOCE combined gravity field solution. In addition they are then compared with formal errors of recent GOCE-only models. As in the measured GG tensor there are two less accurate components the rotation of the GG tensor from the instrument frame to a local Earth related frame is not straightforward. A possible solution is to replace the less accurate components with model gradients. We will discuss the trade-off between measured and model GGs and assess the information content of the rotated gradients in diferent local frames, specifically the local north- oriented frame and the local orbital frame. Furthermore we will present a quality assessment of the GOCE GGs over time. We will show that the errors of Vxx and Vxz are constant over time, but that the errors in Vyy increase after each calibration event, which is due to a drift in the differential scale factor associated with Vyy. Finally, the Vzz error level seems to have decreased by 25% after the switch from CPU A to B in February 2010.

Murböck, M.; Pail, R.; Fuchs, M.; Bouman, J.

2011-07-01

322

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

323

Galactic abundance gradients from Cepheids. On the iron abundance gradient around 10-12 kpc  

NASA Astrophysics Data System (ADS)

Context: Classical Cepheids are excellent tracers of intermediate-mass stars, since their distances can be estimated with very high accuracy. In particular, they can be adopted to trace the chemical evolution of the Galactic disk. Aims: Homogeneous iron abundance measurements for 33 Galactic Cepheids located in the outer disk together with accurate distance determinations based on near-infrared photometry are adopted to constrain the Galactic iron gradient beyond 10 kpc. Methods: Iron abundances were determined using high resolution Cepheid spectra collected with three different observational instruments: ESPaDOnS@CFHT, Narval@TBL and FEROS@2.2m ESO/MPG telescope. Cepheid distances were estimated using near-infrared (J,H,K-band) period-luminosity relations and data from SAAO and the 2MASS catalog. Results: The least squares solution over the entire data set indicates that the iron gradient in the Galactic disk presents a slope of -0.052±0.003 textrm {dex kpc}-1 in the 5-17 kpc range. However, the change of the iron abundance across the disk seems to be better described by a linear regime inside the solar circle and a flattening of the gradient toward the outer disk (beyond 10 kpc). In the latter region the iron gradient presents a shallower slope, i.e. -0.012±0.014 textrm {dex kpc}-1. In the outer disk (10-12 kpc) we also found that Cepheids present an increase in the spread in iron abundance. Current evidence indicates that the spread in metallicity depends on the Galactocentric longitude. Finally, current data do not support the hypothesis of a discontinuity in the iron gradient at Galactocentric distances of 10-12 kpc. Conclusions: The occurrence of a spread in iron abundance as a function of the Galactocentric longitude indicates that linear radial gradients should be cautiously treated to constrain the chemical evolution across the disk.

Lemasle, B.; François, P.; Piersimoni, A.; Pedicelli, S.; Bono, G.; Laney, C. D.; Primas, F.; Romaniello, M.

2008-11-01

324

Interaction intensity and importance along two stress gradients: adding shape to the stress-gradient hypothesis.  

PubMed

The stress-gradient hypothesis (SGH) predicts that the community-wide prevalence of positive interactions, relative to negative interactions, is greater under more severe environmental conditions. Because the frequency of positive and negative interactions within a community is the aggregate of multiple pair-wise interactions, one approach to testing the SGH is to examine how pair-wise interactions vary along severity gradients. While the SGH suggests that the net outcome of an interaction should monotonically become more positive with increasing environmental severity, recent studies have suggested that the severity-interaction relationship (SIR) may rather be unimodal. We tested which of the proposed shapes of the SIR best fits the variation in the interaction between two species along two types of severity gradients on sub-Antarctic Marion Island. This was done by comparing the performance of the grass Agrostis magellanica in the presence and absence of the cushion plant Azorella selago, along both species' entire altitudinal ranges (transects spanning 4-8 km), and along a shorter (transect = 0.4 km) wind exposure gradient. Along the altitudinal transects the relative intensity, but not the absolute intensity or the importance, of the Azorella selago-Agrostis magellanica interaction increased with altitude, consistently forming a plateau-shaped SIR with a positive asymptote. Thus, while the performance of Agrostis magellanica was negatively affected by Azorella selago at low altitudes, the grass benefited from growing on the cushion plant under greater environmental severity. Along the wind exposure gradient the intensity of the interaction also became more positive with increasing environmental severity for most performance measures. This suggests that the switch from a net negative to a net positive interaction can occur across both short and long distances. Therefore, this study provides strong evidence for a plateau-shaped SIR, and confirms that the SIR is unimodal along the particular non-resource severity gradients of this study. PMID:19902260

le Roux, Peter Christiaan; McGeoch, Melodie A

2009-11-10

325

Complex surface concentration gradients by stenciled "electro click chemistry".  

PubMed

Complex one- or two-dimensional concentration gradients of alkynated molecules are produced on azidized conducting polymer substrates by stenciled "electro click chemistry". The latter describes the local electrochemical generation of catalytically active Cu(I) required to complete a "click reaction" between alkynes and azides at room temperature. A stencil on the counter electrode defines the shape and multiplicity of the gradient(s) on the conducting polymer substrate, while the specific reaction conditions control gradient steepness and the maximum concentration deposited. Biologically active ligands including cell binding peptides are patterned in gradients by this method without losing their biological function or the conductivity of the polymer. PMID:20860406

Hansen, Thomas S; Lind, Johan U; Daugaard, Anders E; Hvilsted, Søren; Andresen, Thomas L; Larsen, Niels B

2010-10-19

326

Biomimetic Approaches to Control Soluble Concentration Gradients in Biomaterials  

PubMed Central

Soluble concentration gradients play a critical role in controlling tissue formation during embryonic development. The importance of soluble signaling in biology has motivated engineers to design systems that allow precise and quantitative manipulation of gradient formation in vitro. Engineering techniques have increasingly moved to the third dimension in order to provide more physiologically relevant models to study the biological role of gradient formation and to guide strategies for controlling new tissue formation for therapeutic applications. This review provides an overview of efforts to design biomimetic strategies for soluble gradient formation, with a focus on microfluidic techniques and biomaterials approaches for moving gradient generation to the third dimension.

Nguyen, Eric H.; Schwartz, Michael P.

2013-01-01

327

Stereo vision with distance and gradient recognition  

NASA Astrophysics Data System (ADS)

Robot vision technology is needed for the stable walking, object recognition and the movement to the target spot. By some sensors which use infrared rays and ultrasonic, robot can overcome the urgent state or dangerous time. But stereo vision of three dimensional space would make robot have powerful artificial intelligence. In this paper we consider about the stereo vision for stable and correct movement of a biped robot. When a robot confront with an inclination plane or steps, particular algorithms are needed to go on without failure. This study developed the recognition algorithm of distance and gradient of environment by stereo matching process.

Kim, Soo-Hyun; Kang, Suk-Bum; Yang, Tae-Kyu

2007-12-01

328

PET regularization by envelope guided conjugate gradients  

SciTech Connect

The authors propose a new way to iteratively solve large scale ill-posed problems and in particular the image reconstruction problem in positron emission tomography by exploiting the relation between Tikhonov regularization and multiobjective optimization to obtain iteratively approximations to the Tikhonov L-curve and its corner. Monitoring the change of the approximate L-curves allows us to adjust the regularization parameter adaptively during a preconditioned conjugate gradient iteration, so that the desired solution can be reconstructed with a small number of iterations.

Kaufman, L. [Lucent Technologies, Murray Hill, NJ (United States); Neumaier, A. [Univ. of Vienna (Austria). Inst. fuer Mathematik

1996-06-01

329

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

330

High gradient experiments on NLCTA accelerator structures  

SciTech Connect

This paper presents new results of high-gradient studies performed on a 1.8 m traveling-wave accelerator section with detuned high-order deflecting modes. This structure was designed initially for studies of detuned structures and will be installed in the Next Linear Collider Test Accelerator (NLCTA). The paper describes the test set-up in the Accelerator Structure Test Area (ASTA) including electron gun, prebuncher, pre-accelerator, spectrometer, Faraday cups, 200 MW SLED-II power compression system, Magic-T type phase shifters and attenuators. Rf processing, detailed dark current analysis, radiation problems, and beam acceleration measurements are discussed.

Wang, J.W.; Eichner, J.P.; Fant, K.H. [and others

1996-08-01

331

Radial oxygen gradients over rat cortex arterioles  

Microsoft Academic Search

Purpose  We present the results of the visualisation of radial oxygen gradients in rats’ cortices and their potential use in neurocritical\\u000a management.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  PO2 maps of the cortex of ten sedated, intubated and controlled ventilated Wistar rats were obtained with a camera (SensiMOD,\\u000a PCO, Kelheim, Germany). Those pictures were analysed and edited by a custom-made software. A virtual matrix, designed to evaluate

Michael Galler; Stefan Moritz; Gregor Liebsch; Chris Woertgen; Alexander Brawanski; Jan Warnat

2010-01-01

332

Supply chain finance: applying finance theory to supply chain management to enhance finance in supply chains  

Microsoft Academic Search

It is now accepted that logistics and supply chain management (SCM) have great potential for improving bottom line results. This paper proposes a framework for investigating the financial issues in logistics and SCM and shows that taking a supply chain perspective on financial issues offers great opportunities for SCM professionals. SCM can not only contribute to improvements in sales, cost

Moritz Leon Gomm

2010-01-01

333

The effect of concomitant gradient fields on diffusion tensor imaging.  

PubMed

Concomitant gradient fields are transverse magnetic field components that are necessarily present to satisfy Maxwell's equations when magnetic field gradients are utilized in magnetic resonance imaging. They can have deleterious effects that are more prominent at lower static fields and/or higher gradient strengths. In diffusion tensor imaging schemes that employ large gradients that are not symmetric about a refocusing radiofrequency pulse (unlike Stejskal-Tanner, which is symmetric), concomitant fields may cause phase accrual that could corrupt the diffusion measurement. Theory predicting the error from this dephasing is described and experimentally validated for both Reese twice-refocused and split gradient single spin-echo diffusion gradient schemes. Bias in apparent diffusion coefficient values was experimentally found to worsen with distance from isocenter and with increasing duration of gradient asymmetry in both a phantom and in the brain. The amount of error from concomitant gradient fields depends on many variables, including the diffusion gradient pattern, pulse sequence timing, maximum effective gradient amplitude, static magnetic field strength, voxel size, slice distance from isocenter, and partial Fourier fraction. A prospective correction scheme that can reduce concomitant gradient errors is proposed and verified for diffusion imaging. PMID:22851517

Baron, C A; Lebel, R M; Wilman, A H; Beaulieu, C

2012-01-03

334

Thermocapillary migration of a small chain of bubbles  

NASA Astrophysics Data System (ADS)

The quasistatic thermocapillary migration of a chain of two or three spherical bubbles in an unbounded fluid possessing a uniform temperature gradient is investigated in the limit of vanishing Reynolds and Peclet numbers. The line of bubble centers is permitted to be either parallel or perpendicular to the direction of the undisturbed temperature gradient. The governing equations are solved by a truncated-series, boundary-collocation technique. Results are presented which demonstrate the impact of the presence of other bubbles on a test bubble. In the three-bubble case, a simple pairwise-additive approximation is constructed from the reflections solution, and found to perform well except when the bubbles are close to each other. Also, features of the flow topology in the fluid are explored. Separated reverse flow wakes are found in the axisymmetric problem, and other interesting structures are noted for the case in which the line of centers is perpendicular to the applied temperature gradient. The observed flow structure is shown to be the result of superposition of simpler basic flows.

Wei, Huailiang; Subramanian, R. S.

1993-07-01

335

Droplet microfluidics driven by gradients of confinement  

PubMed Central

The miniaturization of droplet manipulation methods has led to drops being proposed as microreactors in many applications of biology and chemistry. In parallel, microfluidic methods have been applied to generate monodisperse emulsions for applications in the pharmaceuticals, cosmetics, and food industries. To date, microfluidic droplet production has been dominated by a few designs that use hydrodynamic forces, resulting from the flowing fluids, to break drops at a junction. Here we present a platform for droplet generation and manipulation that does not depend on the fluid flows. Instead, we use devices that incorporate height variations to subject the immiscible interfaces to gradients of confinement. The resulting curvature imbalance along the interface causes the detachment of monodisperse droplets, without the need for a flow of the external phase. Once detached, the drops are self-propelled due to the gradient of surface energy. We show that the size of the drops is determined by the device geometry; it is insensitive to the physical fluid properties and depends very weakly on the flow rate of the dispersed phase. This allows us to propose a geometric theoretical model that predicts the dependence of droplet size on the geometric parameters, which is in agreement with experimental measurements. The approach presented here can be applied in a wide range of standard applications, while simplifying the device operations. We demonstrate examples for single-droplet operations and high-throughput generation of emulsions, all of which are performed in simple and inexpensive devices.

Dangla, Remi; Kayi, S. Cagri; Baroud, Charles N.

2013-01-01

336

Gradientes de abundâncias em galáxias espirais  

NASA Astrophysics Data System (ADS)

Gradientes de abundâncias obtidos através de observações de regiões H II têm um papel importante no estudo de formação e evolução de galáxias espirais. Determinações diretas de abundâncias somente são obtidas quando linhas de emissão sensíveis à temperatura eletrônica (e.g., [O III]l4363) são detectadas. Infelizmente estas linhas são fracas ou não observadas em regiões H II de baixa excitação. Nestes casos métodos empíricos são utilizados para estimar as abundâncias químicas. Entretanto, diferentes métodos têm produzido diferentes estimativas de gradientes de abundâncias. Neste trabalho, nós construímos modelos de fotoionização com o objetivo de descrever diagramas de diagnósticos construídos com dados publicados de algumas galáxias espirais normais e barradas. Comparações entre nossas estimativas de abundâncias e de outros métodos mostram que quando não há acordo entre eles, nossos modelos superestimam as abundâncias de O/H e N/H por um fator de 0.3 dex em relação a estimativas diretas de abundâncias, e por fator de 0.2 dex em relação a outros métodos empíricos. A origem da produção de nitrogênio nas galáxias estudadas é discutida.

Dors, O. L.., Jr.; Copetti, M. V. F.

2003-08-01

337

Doubly diffusive linear stability with nonconstant gradients  

NASA Astrophysics Data System (ADS)

The effect of variable stratification on thelinear bifurcations of a doubly diffusive plane parallel layer are examined numerically by expanding in a Fourier series. Because the motivation is analysis of solar pond stability, a Prandtl number of 7 and ratio of diffusivities of 1/80 is used in the study, with (large) solute Rayleigh numbers (Rs) ranging from 10,000 to 10 to the 12th power. Stratification of solute is a cubic antisymmetric about midlayer; because temprature has a higher diffusivity, it is given a linear stratification. The numerical results approach Walton's perturbation solution at large Rs, but differ significantly at smaller Rs (10 to the 8th power). While both exchange of stabilities and overstable modes display n expected tendency to localize about the point of minimum solute gradient, the overstable modes behave in oder, nonintuitive, ways. Localization, if extreme enough, can even stabilize small sublayers of reversed salinity gradient. Above Rs = 10 to the 12th power, computations become prohibitively expensive as a continuous spectrum is approached.

Zangrando, F.; Bertram, L.

1984-06-01

338

Resistivity gradient driven versus drift wave turbulence  

NASA Astrophysics Data System (ADS)

Drift wave and rippling mode turbulences are investigated numerically in a 2-D slab, using the full fluid electron dynamical system from which both spring. Non-adiabatic electron dynamics capable of free energy access from temperature and density gradients are localized in the vicinity of the resonant surface, either by resistive dissipation/thermal conduction or by 'rippling', i.e. coupling of temperature and electrostatic potential fluctuations by the equilibrium current. Which type of turbulence prevails, self-organized drift wave or instability driven rippling mode, is determined solely by the competition between these two localization mechanisms. Because the localization is through linear terms, the regime boundary between the two types of turbulence is precisely where the linear theory of Hassam and Drake (Phys. Fluids 26 (1983) 133) says it is. And since even the most collisional edge plasmas in tokamaks such as ASDEX or TFTR are firmly ensconced within the drift wave regime, it is concluded that 'resistivity gradient driven turbulence' has no relevance to present or future tokamak experiments. Non-linearly self-sustaining collisional drift wave turbulence, on the other hand, remains viable

Scott, B. D.

1992-05-01

339

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

340

Droplet microfluidics driven by gradients of confinement.  

PubMed

The miniaturization of droplet manipulation methods has led to drops being proposed as microreactors in many applications of biology and chemistry. In parallel, microfluidic methods have been applied to generate monodisperse emulsions for applications in the pharmaceuticals, cosmetics, and food industries. To date, microfluidic droplet production has been dominated by a few designs that use hydrodynamic forces, resulting from the flowing fluids, to break drops at a junction. Here we present a platform for droplet generation and manipulation that does not depend on the fluid flows. Instead, we use devices that incorporate height variations to subject the immiscible interfaces to gradients of confinement. The resulting curvature imbalance along the interface causes the detachment of monodisperse droplets, without the need for a flow of the external phase. Once detached, the drops are self-propelled due to the gradient of surface energy. We show that the size of the drops is determined by the device geometry; it is insensitive to the physical fluid properties and depends very weakly on the flow rate of the dispersed phase. This allows us to propose a geometric theoretical model that predicts the dependence of droplet size on the geometric parameters, which is in agreement with experimental measurements. The approach presented here can be applied in a wide range of standard applications, while simplifying the device operations. We demonstrate examples for single-droplet operations and high-throughput generation of emulsions, all of which are performed in simple and inexpensive devices. PMID:23284169

Dangla, Rémi; Kayi, S Cagri; Baroud, Charles N

2013-01-02

341

Manufacturing supply chain applications 1: decision support tool - supply chain  

Microsoft Academic Search

We present a currently developed Decision Support Tool - Supply Chain (DST-SC). This is specialized domain oriented tool, which is an extension of the general purpose, UML-RT Hybrid Simulation kernel of AnyLogic by XJ Technologies. DST-SC allows high degree of flexibility with respect to the supply chain functionality being modeled, has the ability to handle large complex problems, and offers

Christian Wartha; Momtchil Peev; Andrei Borshchev; Alexei Filippov

2002-01-01

342

Dispersion-free linear chains  

SciTech Connect

General formulas are given for the masses and spring constants of one-dimensional finite chains with linear dispersion relations, examples of which were given by Herrmann and Schmaelzle in 1981 in their discussion of a well-known collision apparatus. The mathematical similarity to the problem of a Boson in a constant magnetic field is shown. The explicit formulas make a study of the continuum limit possible. This is shown to be related to the system of uniform rods studied by Bayman in 1976. Examples are given of chains with quadratic dispersion relations. Resonances that give singularities in the interaction time are discovered in certain chains of elastic spheres.

Reinsch, M. (Department of Physics, University of California at Berkeley, Berkeley, California 94720 (United States))

1994-03-01

343

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

344

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

2012-05-17

345

The Great Chain of Being  

Microsoft Academic Search

This essay presents a brief summary of the great chain of being, as historically conceived and as it is reappearing in modern evolutionary and system theories. It particularly addresses the misconception that the notion of \\

Ken Wilber

1993-01-01

346

Configurational Correlation in Chain Molecules.  

National Technical Information Service (NTIS)

Although the potentials affecting the rotation about a skeletal bond in a chain molecule such as polymethylene (PM) usually depend only on rotations of immediately adjoining bonds, the interdependence of rotational states may be transmitted over greater d...

R. L. Jernigan P. J. Flory

1968-01-01

347

Hoists, Chain and Wire Rope.  

National Technical Information Service (NTIS)

The Engineering Test Procedure describes test methods and techniques for evaluating the technical performance and characteristics of Hoists (Chain and Wire Rope Types), and for determining their suitability for service use by the U. S. Army. (Author)

1970-01-01

348

A Drug Supply Chain Example  

Center for Drug Evaluation (CDER)

Text Version... Pharmacy or Hospital Patient (Primary) Wholesaler Distributor Repackager (Secondary) A Drug Supply Chain Example From Supplier to Patient More results from www.fda.gov/downloads/drugs/drugsafety

349

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

350

Osteoradionecrosis of the ossicular chain  

SciTech Connect

Osteoradionecrosis of the temporal bone is a well-known sequela of radiotherapy for neoplasms at the base of the skull. Presenting symptoms include otalgia, chronic aural drainage, and hearing loss, which can be conductive, sensorineural, or mixed. The conductive component has been hypothesized to be caused by radionecrosis of the ossicular chain. This case report documents the existence of osteoradionecrosis of the ossicular chain in a 10-year-old boy operated on for resection of extensive osteoradionecrosis of the temporal bone.

Kveton, J.F.; Sotelo-Avila, C.

1986-11-01

351

Driven Diatomic Oscillator Chain Model  

NSDL National Science Digital Library

The Driven Diatomic Oscillator Chain model displays a one-dimensional diatomic chain of coupled harmonic oscillators with one end driven by an external force and the other end attached to a sliding rod shock absorber. The mass and Stoke's Law damping for the shock absorber are chosen to eliminate reflections at the driving frequency. The frequency of the driving force and the masses can be changed using the text boxes provided. You can change the initial position of the masses by dragging individual oscillators. You can also change the number of oscillators in the chain. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Driven Diatomic 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_osc_chains_OscillatorChainDrivenDiatomic.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 Newtonian mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang

2008-07-05

352

Force cycles and force chains.  

PubMed

We examine the coevolution of N cycles and force chains as part of a broader study which is designed to quantitatively characterize the role of the laterally supporting contact network to the evolution of force chains. Here, we elucidate the rheological function of these coexisting structures, especially in the lead up to failure. In analogy to force chains, we introduce the concept of force cycles: N cycles whose contacts each bear above average force. We examine their evolution around force chains in a discrete element simulation of a dense granular material under quasistatic biaxial loading. Three-force cycles are shown to be stabilizing structures that inhibit relative particle rotations and provide strong lateral support to force chains. These exhibit distinct behavior from other cycles. Their population decreases rapidly during the initial stages of the strain-hardening regime-a trend that is suddenly interrupted and reversed upon commencement of force chain buckling prior to peak shear stress. Results suggest that the three-force cycles are called upon for reinforcements to ward off failure via shear banding. Ultimately though, the resistance to buckling proves futile; buckling wins under the combined effects of dilatation and increasing compressive load. The sudden increase in three-force cycles may thus be viewed as an indicator of imminent failure via shear bands. PMID:20365363

Tordesillas, Antoinette; Walker, David M; Lin, Qun

2010-01-13

353

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

354

A matrix analysis of conjugate gradient algorithms  

SciTech Connect

This paper explores the relationships between the conjugate gradient algorithms Orthodir, Orthomin, and Orthores. To facilitate this exploration, a matrix formulation for each algorithm is given. It is shown that Orthodir directly computes a Hessenberg matrix H{sub k} at step k. Orthores also computes a Hessenberg matrix, G{sub k}, which is similar to a Hessenberg matrix obtained from H{sub k} by perturbing its last column. (This perturbation vanishes at convergence.) Orthomin, on the other hand, computes a UL and LU factorization of the perturbed H{sub k} and G{sub k}, respectively. The breakdown of Orthomin and Orthores are interpreted in terms of these underlying matrix factorizations. A connection with Lanczos algorithms is also examined, as is the special case of B-normal(1) matrices (for which efficient three-term CG algorithms exist).

Ashby, S.F. [Lawrence Livermore National Lab., CA (United States); Gutknecht, M.H. [Eidgenoessische Technische Hochschule, Zurich (Switzerland)

1993-04-01

355

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

356

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

2012-02-15

357

Tryptic digest mapping by gradient capillary electrochromatography.  

PubMed

A high performance liquid chromatography (HPLC) system complemented with T-split, capillary detection cell and a high voltage power supply was used for peptide mapping by gradient electrochromatography and nanoliquid chromatography (nano-LC). With capillary columns of 100 microm ID, 6 cm packed with octadecylated 1.5 microm silica particles, the typical analysis time was approximately 10-15 min. The resolution of a tryptic digest of cytochrome c obtained by electrochromatography at 100 kV/m was superior compared to the analysis by nano-LC. Bubble formation caused by Joule heating at currents up to 100 microA was successfully suppressed by using a resistor capillary of 25 microm ID connected to the outlet of the packed column. PMID:10065962

Behnke, B; Metzger, J W

1999-01-01

358

Terrestrial refraction and vertical temperature gradient  

NASA Astrophysics Data System (ADS)

An assessment of the techniques and accuracy of current observations of coefficient of terrestrial refraction, including its diurnal and seasonal variations, is presented. One methodology has employed 1924 measurements of vertical angles between two geodetic stations with either one-way or line refraction techniques. The stations were 15 km apart and at heights of 177 and 361 m. Additional data has been gathered from adjustments of trigonometric leveling traverses with vertical angle capability, using stations 4 km apart. Another network featured lines of 4-23 km, with measurements repeated 12-60 hours sequentially. Mention is also given to measuring light attenuation and evaluation of the vertical refraction angle from the variance of the angle of arrival fluctuations. Formulas for modeling the vertical temperature gradient are discussed.

Mavridis, L. N.

359

Formulating viscous hydrodynamics for large velocity gradients  

SciTech Connect

Viscous corrections to relativistic hydrodynamics, which are usually formulated for small velocity gradients, have recently been extended from Navier-Stokes formulations to a class of treatments based on Israel-Stewart equations. Israel-Stewart treatments, which treat the spatial components of the stress-energy tensor {tau}{sub ij} as dynamical objects, introduce new parameters, such as the relaxation times describing nonequilibrium behavior of the elements {tau}{sub ij}. By considering linear response theory and entropy constraints, we show how the additional parameters are related to fluctuations of {tau}{sub ij}. Furthermore, the Israel-Stewart parameters are analyzed for their ability to provide stable and physical solutions for sound waves. Finally, it is shown how these parameters, which are naturally described by correlation functions in real time, might be constrained by lattice calculations, which are based on path-integral formulations in imaginary time.

Pratt, Scott [Department of Physics and Astronomy, Michigan State University East Lansing, Michigan 48824-1321 (United States)

2008-02-15

360

Ultrasonic wave propagation in temperature gradients  

SciTech Connect

Ultrasonic methods are being developed for sensing and control of high temperature material processes such as welding and solidification. One of the problems in these methods is the distortion of the sound field caused by the change in material properties due to temperature gradients. This paper describes a ray-tracing method for calculating the effects of temperature on ultrasonic propagation in such systems. In the ray-tracing method, the material is conceptually divided into a number of plane layers. The fraction at each layer boundary is calculated from Snell's law using the sound speeds determined from the temperatures of the adjacent layers. The time required for an ultrasonic pulse to traverse each layer is also calculated, allowing the determination of the total time along a particular path. The method is applied to calculating the time of arrival of echoes from various interfaces around a molten weld pool.

Johnson, J.A.; Carlson, N.M.; Lott, L.A.

1987-09-01

361

Electron temperature gradient scale at collisionless shocks.  

PubMed

Shock waves are ubiquitous in space and astrophysics. They transform directed flow energy into thermal energy and accelerate energetic particles. The energy repartition is a multiscale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. While large scale features of ion heating are known, the electron heating and smaller scale fields remain poorly understood. We determine for the first time the scale of the electron temperature gradient via electron distributions measured in situ by the Cluster spacecraft. Half of the electron heating coincides with a narrow layer several electron inertial lengths (c/?(pe)) thick. Consequently, the nonlinear steepening is limited by wave dispersion. The dc electric field must also vary over these small scales, strongly influencing the efficiency of shocks as cosmic ray accelerators. PMID:22181889

Schwartz, Steven J; Henley, Edmund; Mitchell, Jeremy; Krasnoselskikh, Vladimir

2011-11-14

362

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

363

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.

364

High Gradient Wakefields in Dielectric Loaded Structures  

SciTech Connect

Dielectric loaded wakefield structures have potential to be used as high gradient accelerator components. Using the high current drive beam at the Argonne Wakefield Accelerator Facility, we employed cylindrical dielectric loaded wakefield structures to generate accelerating fields of up to 86 MV/m, at 10 GHz. Short electron bunches of up to 86 nC are used to drive these fields, either as single bunches or as bunch trains. The structures consist of cylindrical ceramic tubes (cordierite) with a dielectric constant of 4.76, inserted into cylindrical copper waveguides. These standing-wave structures have a field probe near the outer diameter of the dielectric, in order to sample the RF fields generated by the electron bunches. Monitoring the field probe signal serves to verify the absence of electric breakdown in the structures. MAFIA simulations are used to calculate the amplitude of the fields generated by the traversing electrons bunches.

Conde, M. E.; Franchini, F.; Gai, W.; Konecny, R.; Liu, W.; Power, J. G.; Yusof, Z. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Antipov, S.; Gao, F.; Wang, H. [Illinois Institute of Technology, 3300 South Federal Street, Chicago, IL 60616 (United States); Jing, C. [Euclid TechLabs, 5900 Harper Road, Solon, OH 44139 (United States)

2006-11-27

365

Higher-order force gradient symplectic algorithms  

PubMed

We show that a recently discovered fourth order symplectic algorithm, which requires one evaluation of force gradient in addition to three evaluations of the force, when iterated to higher order, yielded algorithms that are far superior to similarly iterated higher order algorithms based on the standard Forest-Ruth algorithm. We gauge the accuracy of each algorithm by comparing the step-size independent error functions associated with energy conservation and the rotation of the Laplace-Runge-Lenz vector when solving a highly eccentric Kepler problem. For orders 6, 8, 10, and 12, the new algorithms are approximately a factor of 10(3), 10(4), 10(4), and 10(5) better. PMID:11138177

Chin; Kidwell

2000-12-01

366

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

367

Strain gradient plasticity theory applied to machining  

NASA Astrophysics Data System (ADS)

Machining is the most common manufacturing process. A good behaviour law is necessary in the simulation of machining processes (analytical and finite element modeling). Usually, commonly used behaviour laws such as Jonhson-Cook can bring unsatisfactory results especially for high strain and large deformation processes. Significant differences can appear between experimental and simulation results. The aim of this paper is to present the choices made regarding the behaviour law in this context. This study develops a large deformation strain-gradient theoretical framework with hypothesis linked to metal cutting processes. The theoretical framework has the potential of expressing moments at the tool tip as they were observed in experiments. It will be shown that the theory has the capability of interpreting the complex phenomena found in machining and more particularly in high speed machining.

Royer, Raphael; Laheurte, Raynald; Darnis, Philippe; Gérard, Alain; Cahuc, Olivier

2011-05-01

368

Diffusion effects in gradient echo memory  

NASA Astrophysics Data System (ADS)

We study the effects of diffusion on a ?-gradient echo memory, which is a coherent optical quantum memory, using thermal gases. The efficiency of this memory is high for short storage time, but decreases exponentially due to decoherence as the storage time is increased. We study the effects of both longitudinal and transverse diffusion in this memory system, and give both analytical and numerical results that are in good agreement. Our results show that diffusion has a significant effect on the efficiency. Further, we suggest ways to reduce these effects to improve storage efficiency. We also report on a mechanism by which the rate of expansion of the transverse width of the beam is reduced compared to the naive expectation of diffusive effects, as observed in recent experiments.

Luo, X.-W.; Hope, J. J.; Hillman, B.; Stace, T. M.

2013-06-01

369

Gradient Sensitivity Kernels for Structural Analysis  

NASA Astrophysics Data System (ADS)

In recent years there has been considerable emphasis on the calculation of sensitivity kernels for Earth structure for different types of seismological information. The basis of such results has been a first order Born approximation in terms of variations in wavespeeds or density. Such a model requires scattering to produce travel time changes, with non-intuitive consequences such as lack of sensitivity along a ray path. A different class of sensitivity kernels can be developed by working with velocity gradients through a integration by parts. The resulting kernels do not depend on localized scattering. In particular they restore the sensitivity near the turning point of a ray that has been successfully employed for many years in seismic interpretation. For a 1-D inversion, such `quelling' is required to remove singularities and there are major benefits in 3-D as well since attention is focused on those regions where there are changes in structure.

Kennett, B. L.; Sambridge, M. S.

2006-12-01

370

Spatially Resolved Solid-State (1)H NMR for Evaluation of Gradient-Composition Polymeric Libraries.  

PubMed

Polyurethane libraries consisting of films with composition gradients of aliphatic polyisocyanate and hydroxy-terminated polyacrylate resin were characterized using methods of (1)H NMR microimaging (i.e., magnetic resonance imaging, (MRI)) and solid-state NMR. Molecular mobilities and underlying structural information were extracted as a function of the relative content of each of the two components. Routine NMR microimaging using the spin-echo sequence only allows investigations of transverse relaxation of magnetization at echo times >2 ms. A single-exponential decay was found, which is likely due to free, noncross-linked polymer chains. The mobility of these chains decreases with increasing content of the aliphatic polyisocyanate. The concept of a 1D NMR profiler is introduced as a novel modality for library screening, which allows the convenient measurement of static solid-state NMR spectra as a function of spatial location along a library sample that is repositioned in the rf coil between experiments. With this setup the complete transverse relaxation function was measured using Bloch decays and spin echoes. For all positions within the gradient-composition film, relaxation data consisted of at least three components that were attributed to a rigid highly cross-linked resin, an intermediate cross-linked but mobile constituent, and the highly mobile free polymer chains (the latter is also detectable by MRI). Analysis of this overall relaxation function measured via Bloch decays and spin echoes revealed only minor changes in the mobilities of the individual fractions. Findings with respect to the most mobile components are consistent with the results obtained by NMR microimaging. The major effect is the significant increase in the rigid-component fraction with the addition of the hydroxy-terminated polyacrylate resin. PMID:22676634

Leisen, Johannes; Gomez, Ismael J; Roper, John A; Meredith, J Carson; Beckham, Haskell W

2012-06-20

371

Thermoacoustic mixture separation with an axial temperature gradient  

SciTech Connect

The theory of thermoacoustic mixture separation is extended to include the effect of a nonzero axial temperature gradient. The analysis yields a new term in the second-order mole flux that is proportional to the temperature gradient and to the square of the volumetric velocity and is independent of the phasing of the wave. Because of this new term, thermoacoustic separation stops at a critical temperature gradient and changes direction above that gradient. For a traveling wave, this gradient is somewhat higher than that predicted by a simple four-step model. An experiment tests the theory for temperature gradients from 0 to 416 K/m in 50-50 He-Ar mixtures.

Geller, Drew W [Los Alamos National Laboratory; Swift, Gregory A [Los Alamos National Laboratory

2008-01-01

372

Gradient-dependent deformation of two-phase single crystals  

Microsoft Academic Search

In this work, a gradient- and rate-dependent crystallographic formulation is proposed to investigate the macroscopic behaviour of two-phase single crystals. The slip-system-based constitutive formulation relies on strain-gradient concepts to account for the additional strengthening mechanism associated with the deformation gradients within a single crystal with a high volume fraction of dispersed inclusions. The resulting total slip resistance in each active

E. P. Busso; F. T. Meissonnier; N. P. O'Dowd

2000-01-01

373

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

374

Aligning incentives in supply chains.  

PubMed

Most companies don't worry about the behavior of their supply chain partners. Instead, they expect the supply chain to work efficiently without interference, as if guided by Adam Smith's famed invisible hand. In their study of more than 50 supply networks, V.G. Narayanan and Ananth Raman found that companies often looked out for their own interests and ignored those of their network partners. Consequently, supply chains performed poorly. Those results aren't shocking when you consider that supply chains extend across several functions and many companies, each with its own priorities and goals. Yet all those functions and firms must pull in the same direction for a chain to deliver goods and services to consumers quickly and cost-effectively. According to the authors, a supply chain works well only if the risks, costs, and rewards of doing business are distributed fairly across the network. In fact, misaligned incentives are often the cause of excess inventory, stock-outs, incorrect forecasts, inadequate sales efforts, and even poor customer service. The fates of all supply chain partners are interlinked: If the firms work together to serve consumers, they will all win. However, they can do that only if incentives are aligned. Companies must acknowledge that the problem of incentive misalignment exists and then determine its root cause and align or redesign incentives. They can improve alignment by, for instance, adopting revenue-sharing contracts, using technology to track previously hidden information, or working with intermediaries to build trust among network partners. It's also important to periodically reassess incentives, because even top-performing networks find that changes in technology or business conditions alter the alignment of incentives. PMID:15559449

Narayanan, V G; Raman, Ananth

2004-11-01

375

Maintaining Optimal Communication Chains in Robotic Sensor Networks using Mobility Control  

Microsoft Academic Search

This paper presents a decentralized mobility control algorithm for the formation and maintenance of an optimal cascaded communication\\u000a chain between a lead sensor-equipped robot and a control station, using a team of robotic vehicles acting as communication\\u000a relays in an unknown and dynamic RF environment. The gradient-based controller presented uses measurements of the signal-to-noise\\u000a ratio (SNR) field of neighbor communication

Cory Dixon; Eric W. Frew

2009-01-01

376

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

377

Magnetic reconnection with pressure gradient effect in compressible electron magnetohydrodynamics  

SciTech Connect

The general dispersion relation of the tearing mode with charge separation and pressure gradient effects in the whistler frequency is analytically derived in the framework of electron magnetohydrodynamics (EMHD). It is shown that pressure gradient effect enhances the growth rate, and makes the EMHD tearing mode drift. The growth rate of the EMHD tearing mode is significantly affected by the pressure gradient effect in the large pressure gradient limit. Furthermore, in this limit, the growth rate in the compressible EMHD fluid is much different from that in the incompressible EMHD fluid.

Cai Huishan; Li Ding [CAS Key Laboratory of Basic Plasma Physics, School of Science, University of Science and Technology of China, Hefei 230026 (China)

2008-04-15

378

Sequential annealing gradient Gamma-Knife radiosurgery optimization  

NASA Astrophysics Data System (ADS)

Simulated annealing and gradient methods are commonly employed for inverse planning of radiotherapy delivery schemes. Annealing is effective in finding an approximation of the global solution, suffering from slow late convergence and in some cases poor dose homogeneity. Gradient methods converge well but not necessarily to the global minimum. We explored simulated annealing followed by gradient optimization to improve on either method alone, using radiosurgery as the model system. Simulated annealing and gradient inverse planning programs using the same objective function were adapted for radiosurgical optimization. The objective function chosen is a least-squares dose-matching function, with differential weighting of tissues. A simple test target allowing local minima in the objective function was evaluated. Two hundred trials using the gradient method were done. The gradient method approximated the global solution only 12% of the time, commonly finding a local minimum. The annealing-gradient technique converged to the global minimum in 78 out of 80 trials, more efficiently than annealing alone. Dose homogeneity was improved. In conclusion, sequential annealing-gradient optimization can improve on either method alone. The technique may be extensible to radiotherapy inverse planning in general, with benefit expected for problems characterized by slow gradient method convergence and local minima.

Ove, Roger; Popple, Richard

2003-07-01

379

Two-dimensional reconfigurable gradient index memory metasurface  

NASA Astrophysics Data System (ADS)

Creation and control of spatial gradients in electromagnetic properties is a central theme underlying optical device design. In this work, we demonstrate that through modification of the spatial and temporal distribution of current, we can obtain increased control over the shape of these gradients. We are able to write spatially sharp gradients with ~50% change in the index of refraction over length scales of only a few wavelengths as observed through diffraction limited terahertz spectroscopy. Furthermore, we assess the potentials for such gradients for beam-steering applications.

Goldflam, M. D.; Driscoll, T.; Barnas, D.; Khatib, O.; Royal, M.; Marie Jokerst, N.; Smith, D. R.; Kim, Bong-Jun; Seo, Giwan; Kim, Hyun-Tak; Basov, D. N.

2013-06-01

380

Planar molecular and macromolecular gradients: preparation and properties  

NASA Astrophysics Data System (ADS)

We present a method for fabricating polymer brushes with a gradual variation of grafting density on solid substrates. The technique for generating such structures consists of: i) deposition of a molecular gradient of polymerization initiator on the solid substrate, and ii) polymerization from the substrate bound initiator centers ("grafting from"). We describe the preparation of gradient polymer brushes of poly(acryl amide) on silica-covered substrates. We show that the polymer density within the gradient polymer brush can be tuned by: i) varying the properties of the initiator gradient (i.e., evaporation time and temperature) and by ii) adjusting the polymerization time and the concentration of the acryl amide monomer.

Genzer, Jan; Wu, Tao; Efimenko, Kirill

2002-03-01

381

?-Conjugated Copolymers of Thiophene: Effect of Chain Architecture on the Physical and Optoelectronic Properties for Photovoltaic Applications  

NASA Astrophysics Data System (ADS)

We found that polymer chain architecture strongly influences phase separation capabilities of the donor-acceptor blend in bulk heterojunction organic photovoltaic devices. Ni-catalyzed controlled polymerization was utilized to access new conjugated copolymers of 3-hexylthiophene and 3-(hexyloxy)methylthiophene, two donor polymers. Monomer sequence was controlled along the copolymer chain by the rate of addition of the comonomers, to achieve diblock, random and gradient copolymer chain architectures. This allowed us to study the effect of copolymer sequence of polythiophene based copolymer/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend on the structure, nanoscale morphology and local charge transport properties using conductive and photoconductive atomic force microscopy. The gradient configuration showed the largest phase separation behavior with PCBM.

Amonoo, Jojo; Glynos, Emmanouil; Chen, Chelsea; Li, Anton; Locke, Jonas; McNeil, Anne; Green, Peter

2012-02-01

382

Two heavy chains of 21S dynein from sea urchin sperm flagella.  

PubMed

The biochemical properties of 21S dynein derived from sea urchin sperm flagella and of its components dissociated by low salt treatment were studied. SDS-urea gel electrophoresis and two-dimensional gel electrophoresis showed that the 21S dynein preparation contains two distinct heavy chains. These two heavy chains, termed A alpha and A beta, had apparently the same molecular weight of 500,000 but showed different mobilities on SDS-urea gels. The isoelectric points of A alpha and A beta heavy chains were 5.7 and 5.2, respectively, in the presence of urea. Proteolytic digestion patterns of these two heavy chains were clearly different, but the amino acid compositions were similar. Low salt treatment and sucrose density gradient centrifugation could partially separate the components of 21S dynein into two fractions: the one with larger sedimentation coefficient contained the A alpha heavy chain, and the other with smaller sedimentation coefficient contained the A beta heavy chain and three intermediate chains. These two fractions showed distinctly different kinetic properties, and thus may play different roles in dynein-microtubule interaction. PMID:2935525

Yano-Toyoshima, Y

1985-09-01

383

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

384

CH abundance gradient in TMC-1  

NASA Astrophysics Data System (ADS)

Aims: The aim of this study is to examine if the well-known chemical gradient in TMC-1 is reflected in the amount of rudimentary forms of carbon available in the gas-phase. As a tracer we use the CH radical which is supposed to be well correlated with carbon atoms and simple hydrocarbon ions. Methods: We observed the 9-cm ?-doubling lines of CH along the dense filament of TMC-1. The CH column densities were compared with the total H2 column densities derived using the 2MASS NIR data and previously published SCUBA maps and with OH column densities derived using previous observations with Effelsberg. We also modelled the chemical evolution of TMC-1 adopting physical conditions typical of dark clouds using the UMIST Database for Astrochemistry gas-phase reaction network to aid the interpretation of the observed OH/CH abundance ratios. Results: The CH column density has a clear peak in the vicinity of the cyanopolyyne maximum of TMC-1. The fractional CH abundance relative to H2 increases steadily from the northwestern end of the filament where it lies around 1.0 × 10-8, to the southeast where it reaches a value of 2.0 × 10-8. The OH and CH column densities are well correlated, and we obtained OH/CH abundance ratios of ~16-20. These values are clearly larger than what has been measured recently in diffuse interstellar gas and is likely to be related to C to CO conversion at higher densities. The good correlation between CH and OH can be explained by similar production and destruction pathways. We suggest that the observed CH and OH abundance gradients are mainly due to enhanced abundances in a low-density envelope which becomes more prominent in the southeastern part and seems to continue beyond the dense filament. Conclusions: An extensive envelope probably signifies an early stage of dynamical evolution, and conforms with the detection of a large CH abundance in the southeastern part of the cloud. The implied presence of other simple forms of carbon in the gas phase provides a natural explanation for the observation of "early-type" molecules in this region. This publication is based on observations with the 100-m telescope of the Max-Planck-Institute für Radioastronomie (MPIfR) at Effelsberg.

Suutarinen, A.; Geppert, W. D.; Harju, J.; Heikkilä, A.; Hotzel, S.; Juvela, M.; Millar, T. J.; Walsh, C.; Wouterloot, J. G. A.

2011-07-01

385

Geothermal gradient and heat flow data in and around Japan (I): Appraisal of heat flow from geothermal gradient data  

NASA Astrophysics Data System (ADS)

We published a CD-ROM "Geothermal Gradient and Heat Flow Data in and around Japan" (Tanaka et al., 2004a), which includes values of heat flow and geothermal gradient data. This compilation was intended to improve the understanding of variations in the thermal regime in and around Japan. Our current knowledge of the heat flow distribution can be increased by including information derived from geothermal gradient data contained in this compilation. In southern Kyushu, the pattern of heat flow is significantly modified by incorporation of estimates of heat flow from geothermal gradient data.

Tanaka, A.; Yamano, M.; Yano, Y.; Sasada, M.

2004-12-01

386

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

387

Information Transfer in Supply Chain Management  

Microsoft Academic Search

The paper deals with integration of supply chains and specifically concentrates on the importance of distribution of information among various companies in the chain. It summarizes the most im- portant concepts of supply chain management. Both technological changes and organizational improvements are essential for effective integration of supply chains. Therefore the paper shows how business process modelling can be used

Peter Trkman; Mojca Indihar Stemberger; Jurij Jaklic

388

Indicators of energy efficiency of supply chains  

Microsoft Academic Search

Energy issues have become increasingly important in supply chain management (SCM). Traditionally, the focus of the environmental impacts of SCM has been on transport chains, which are key functions in logistics. Therefore, many of the relevant measures to evaluate the energy efficiency of supply chains are related to transport chains and mileage. In order to affect transport demand and total

Hanna Kalenoja; Erika Kallionpää; Jarkko Rantala

2011-01-01

389

Supply Chain Dynamics Under the Sustainable Development  

Microsoft Academic Search

Supply chain dynamics is the key issues in supply chain management. To explain supply chain dynamics under the sustainable development, the paper will focus on its classic behavior: the inventory variance and bullwhip effect. A simple system dynamics model of an initial\\/closed loop supply chain system is investigated. Particularly, the effect of remanufacture, remanufacturing lead-time and the return rate on

Lizhen Huang; Yongping Liu

2008-01-01

390

Single chain Fab (scFab) fragment  

Microsoft Academic Search

BACKGROUND: The connection of the variable part of the heavy chain (VH) and and the variable part of the light chain (VL) by a peptide linker to form a consecutive polypeptide chain (single chain antibody, scFv) was a breakthrough for the functional production of antibody fragments in Escherichia coli. Being double the size of fragment variable (Fv) fragments and requiring

Michael Hust; Thomas Jostock; Christian Menzel; Bernd Voedisch; Anja Mohr; Mariam Brenneis; Martina I Kirsch; Doris Meier; Stefan Dübel

2007-01-01

391

On non-reversible Markov chains  

Microsoft Academic Search

. Reversibility is a sufficient but not necessary condition forMarkov chains for use in Markov chain Monte Carlo simulation. It is necessaryto select a Markov chain that has a pre-specified distribution asits unique stationary distribution. There are many Markov chains thathave such property. We give guidelines on how to rank them based onthe asymptotic variance of the estimates they produce.

Charles J. Geyer; Antonietta Mira

392

Conformation of Adsorbed Polymeric Chain. II  

Microsoft Academic Search

By developing the theoretical treatment of an isolated polymeric chain at an interface, which is based on a three-dimensional random walk on a simple cubic lattice, the average number of segments in the tail of a polymeric chain k¯0 and the average number of trains per polymeric chain m¯ are calculated in the limit in which the chain length n

Kinsi Motomura; Ryohei Matuura

1969-01-01

393

Supply chain risk mitigation: modeling the enablers  

Microsoft Academic Search

Purpose – Supply chain risk management assumes importance in the wake of organizations understanding that their risk susceptibility is dependent on other constituents of their supply chain. The purpose of this paper is to present an approach to effective supply chain risk mitigation by understanding the dynamics between various enablers that help to mitigate risk in a supply chain. Design\\/methodology\\/approach

Mohd Nishat Faisal; D. K. Banwet; Ravi Shankar

2006-01-01

394

Chain and network science: A research framework  

Microsoft Academic Search

In this first article of the Journal on Chain and Network Science the base-line is set for a discussion on contents and scope of chain and network theory. Chain and network research is clustered into four main 'streams': Network theory, social capital theory, supply chain management and business economics and organizational theory. Furthermore a research agenda is formulated. The article

Jacques H. Trienekens; George Beers

2001-01-01

395

Polymerase Chain Reaction and Reverse Transcription-Polymerase Chain Reaction  

Microsoft Academic Search

\\u000a Polymerase chain reaction (PCR) enables one to determine if a specific needle is present in a haystack, and it can be used\\u000a as a step toward the characterization of the needle. It is a quick, powerful, inexpensive DNA amplification technique that\\u000a has become a fundamental tool in molecular pathology.

Dwight Oliver

396

Reconciling supply chain vulnerability, risk and supply chain management  

Microsoft Academic Search

Supply chain vulnerability has become a fashionable area of management research. The purpose of this paper is to provide a critique of the extant canon and to review of the positioning of research in the field, together with literature drawn from several relevant and overlapping fields of research and practice. The aim is to foster a more explicit understanding of

H. Peck

2006-01-01

397

Differential evolution Markov chain with snooker updater and fewer chains  

SciTech Connect

Differential Evolution Markov Chain (DE-MC) is an adaptive MCMC algorithm, in which multiple chains are run in parallel. Standard DE-MC requires at least N=2d chains to be run in parallel, where d is the dimensionality of the posterior. This paper extends DE-MC with a snooker updater and shows by simulation and real examples that DE-MC can work for d up to 50--100 with fewer parallel chains (e.g. N=3) by exploiting information from their past by generating jumps from differences of pairs of past states. This approach extends the practical applicability of DE-MC and is shown to be about 5--26 times more efficient than the optimal Normal random walk Metropolis sampler for the 97.5% point of a variable from a 25--50 dimensional Student T{sub 3} distribution. In a nonlinear mixed effects model example the approach outperformed a block-updater geared to the specific features of the model.

Vrugt, Jasper A [Los Alamos National Laboratory; Ter Braak, Cajo J F [NON LANL

2008-01-01

398

Polymers are Chains (K-2)  

NSDL National Science Digital Library

In this activity, learners make a paper model of a polymer, then make Silly Putty, an actual polymer. For the model, learners make chains of paper dolls and color them in different ways to represent different types of monomers. The doll stencil is not included, but can be improvised. Shaking the chains in a bag simulates making the polymer. For the Silly Putty, learners mix saturated borax with Elmer's glue. There are two versions of this activity, one written for grades K-2, one for 3-6, with the older version including some additional materials testing, and some variation in the Silly Putty mixture.

Shaw, Maisie; Gomez, Maria

2009-01-01

399

Optical bistability in spaser chains  

NASA Astrophysics Data System (ADS)

Optical bistability of a spaser and criteria of its appearance are studied theoretically. The effective transmission coefficient of a spaser is calculated. This allows for considering a "mirrorless" spaser bistability in the same way as that of a nonlinear Fabry-Perot cavity. It is shown that at sufficiently high losses in a spaser, due to the bistability, kink waves may propagate along a one-dimensional chain of spasers. This wave propagates even if the pumping is below the threshold of spasing. At low losses in spaser, quasiperiodic dissipative structures emerge in the spaser chain. The dynamics of the origin of such structures has a self-assembling character.

Pukhov, A. A.; Andrianov, E. S.; Vinogradov, A. P.; Dorofeenko, A. V.; Lisyansky, A. A.

2012-09-01

400

Climatic gradients of arms race coevolution.  

PubMed

In nature, spatiotemporally dynamic coevolutionary processes play major roles in the foundation and maintenance of biodiversity. Here, we examined the arms race coevolution involving a seed-eating weevil with a long snout and its camellia plant host with a thick fruit coat (pericarp) throughout the marked climatic gradient observed across the Japanese islands. Results demonstrated that female weevils, which bored holes through camellia pericarps to lay eggs into seeds, had evolved much longer snouts than males, especially in areas in which Japanese camellia pericarps were very thick. The thickness of the plant pericarp was heritable, and the camellia plant evolved a significantly thicker pericarp on islands with the weevil than on islands without it. Across populations with weevils, resource allocation to plant defense increased with increasing annual mean temperature or annual precipitation, thereby geographically differentiating the evolutionary and ecological interactions between the two species. Given that the coevolutionary relationship exhibited appreciable variation across a relatively small range of annual mean temperatures, ongoing global climatic change can dramatically alter the coevolutionary process, thereby changing the ecological interaction between these species. PMID:21508604

Toju, Hirokazu; Abe, Harue; Ueno, Saneyoshi; Miyazawa, Yoshiyuki; Taniguchi, Fumiya; Sota, Teiji; Yahara, Tetsukazu

2011-05-01

401

Cubic Gradient-Based Material Interfaces.  

PubMed

Multi-fluid simulations often create volume fraction data, representing fluid volumes per region or cell of a fluid data set. Accurate and visually realistic extraction of fluid boundaries is a challenging and essential task for efficient analysis of multi-fluid data. In this work we present a new material interface reconstruction method for such volume fraction data. Within each cell of the data set, our method utilizes a gradient field approximation based on trilinearly blended Coons-patches to generate a volume-fraction function, representing the change in volume fractions over the cells. A continuously varying isovalue field is applied to this function to produce a smooth interface that preserves the given volume fractions well. Further, the method allows user-controlled balance between volume accuracy and physical plausibility of the interface. The method works on two- and three-dimensional Cartesian grids, and handles multiple materials. Calculations are performed locally and utilize only the one-ring of cells surrounding a given cell, allowing visualizations of the material interfaces to be easily generated on a GPU or in a large-scale distributed parallel environment. Our results demonstrate the robustness, accuracy and flexibility of the developed algorithms. PMID:23420219

Prilepov, Iuri; Obermaier, Harald; Deines, Eduard; Garth, Christoph; Joy, Kenneth I

2013-02-13

402

Environmental inequality and circulatory disease mortality gradients  

PubMed Central

Study objective: Studies in Europe and North America have reported that living in a disadvantaged neighbourhood is associated with an increased incidence of coronary heart disease. The aim of this study was to test the hypotheses that exposure to traffic and air pollution might account for some of the socioeconomic differences in mortality rates in a city where residents are covered by universal health insurance. Design: Cohort mortality study. Individual postal codes used to derive: (1) socioeconomic status from census data; (2) mean air pollution levels from interpolation between governmental monitoring stations; (3) proximity to traffic from the geographical information system. Analysis conducted with Cox proportional hazards models. Setting: Hamilton Census Metropolitan Area, Ontario, Canada, on the western tip of Lake Ontario (population about 480 000). Participants: 5228 people, aged 40 years or more, identified from register of lung function laboratory at an academic respirology clinic between 1985 and 1999. Main results: Circulatory disease (cardiovascular and stroke) mortality rates were related to measures of neighbourhood deprivation. Circulatory disease mortality rates were also associated with indices of long term ambient pollution at the subjects' residences (relative risk 1.06, 1.00 to 1.13) and with proximity to traffic (relative risk 1.40, 1.08 to 1.81). Subjects in more deprived neighbourhoods had greater exposure to ambient particulate and gaseous pollutants and to traffic. Conclusions: At least some of the observed social gradients in circulatory mortality arise from inequalities in environmental exposure to background and traffic air pollutants.

Finkelstein, M.; Jerrett, M.; Sears, M.

2005-01-01

403

Velocity Gradient Maps Directly Measured by PLF  

NASA Astrophysics Data System (ADS)

Flows are macroscopically classified as laminar or turbulent due to their velocity distributions, nevertheless most chemical and biological phenomena are yield or enhanced by intermolecular orientation and microscopic turbulence. Here was studied a 100micra liquid sheet produced by a slit nozzle, both flowing freely into air and over a borosilicate surface (roughness bellow 5nm), ranging from 17 to 36Re (143 to 297cm/s, similar to muscles and brain blood flow). Mono ethylene glycol was used either pure, or with sodium alkyl benzene sulfated (ABS) surfactant (24.5mol/L, submicellar), or with poly(ethylene oxide) (PEO) (1409ppm, 4millions aw). Velocity gradients were directly measured by 514nm polarized laser induced fluorescence (PLF) with R6G as probe. Intermolecular alignment (IA) maps were obtained all over the flow (about 1,950 points, 0.02mm2 precision). The free jet average IA has increased 57% when flowing over borosilicate. With ABS, the IA increased, suggesting wall drag reduction. With PEO the IA decreases due to solvent intermolecular forces attenuation, generating wider turbulent areas. PLF proved to be an excellent method to evaluate IA within liquid thin flows. Chosen solute additions permits IA control over wide regions.

Quintella, Cristina M.; Gonçalves, Cristiane C.; Lima, Angelo Mv; Pepe, Iuri M.

2000-11-01

404

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

405

Plasma collective modes driven by velocity gradients  

SciTech Connect

Collisional modes driven by shear in the plasma flow velocity V{sub {parallel}}, parallel to the magnetic field, are shown to exist over significant scale distances while subject to the constraints imposed by gradients in the transverse velocity V{sub E} {proportional to} E {times} B. These constraints make the modes localized over finite distances around the surfaces where V{sub E} reaches a maximum or a minimum. Composite modes that can be constructed as a sequence or a superposition of these elementary normal modes can be excited in regions where the transverse velocity acquires a plateau type of profile that is assumed to be formed after macroscopic Kelvin-Helmholtz modes associated with the shear of V{sub E} have reached their saturation stage. Thus a significant rate of longitudinal plasma momentum transport in the transverse direction to the magnetic field can be produced. The relevance of this analysis to the fluctuations observed in the auroral F region is discussed.

Basu, B. (Air Force Geophysics Lab., Bedford, MA (USA)); Coppi, B. (Massachusetts Inst. of Tech., Cambridge (USA))

1990-12-01

406

Self-Assembled Monolayers with Molecular Gradients  

NASA Astrophysics Data System (ADS)

In recent years, biosensors and sensor arrays have developed into very important analytical tools, which found applications in many fields such as pharmaceutical (high-throughput) screening, medical diagnosis, or industrial process control. One of the major challenges for material research is the preparation of appropriate sensor surfaces, providing an interface with a high sensitivity and selectivity toward a given analyte. This chapter discusses some straightforward and flexible approaches to study structure and/or composition-function relationships and response characteristics of polymeric and molecular sensor materials. The controlled continuous deposition of self-assembled monolayers (SAMs), e.g. of substituted thiols or silanes, paves the way for the generation of molecular gradients on solid surfaces. These are useful for the preparation of interfaces with spatially controlled chemical composition and/ or physical properties. These tools can help to improve the selectivity and specificity of surfaces for biosensors and biochips. They can also be utilized for the study of fundamental protein adsorption and exchange phenomena.

Schäferling, Michael; Riepl, Michael; Liedberg, Bo

407

Analytical gradients for LEDO-DFT  

NASA Astrophysics Data System (ADS)

We present an implementation of the limited expansion of diatomic overlap density functional theory (LEDO-DFT) including the determination of analytical gradients in the TURBOMOLE program package. LEDO-DFT is a recently developed formalism in the framework of Kohn-Sham density functional theory exhibiting a formal scaling behaviour with N being the number of basis functions. Numerical results obtained with the Ahlrichs split valence plus polarization basis set (SVP) and a preliminary auxiliary basis set for a test set of small molecules demonstrate the accuracy of electronic energies, structural parameters and harmonic frequencies. Compared to the corresponding full Kohn-Sham model, the total energies are typically affected by 10-3au and the computed structure parameters by 0.1pm in bond distances and 0.1° in bond angles. Harmonic frequencies coincide within a few wavenumbers. Larger deviations can be attributed to deficiencies in the preliminary auxiliary basis set. Results for linear alkanes suggest that LEDO-DFT should be very suitable for electronic structure calculations of large molecular systems.

Götz, Andreas W.; Kollmar, Christian; Hess, Bernd A.

2005-01-01

408

Two and three-dimensional numerical analysis of gradient and parasitic gradient fields of a three-channel surface gradient coil for magnetic resonance imaging  

Microsoft Academic Search

For many organ-specific magnetic resonance imaging (MRI) applications, surface gradient coils (SGCs) offer an attractive alternative to the whole-body gradient coils presently employed in MR scanners. This investigation develops a 2D and 3D numerical analysis and design strategy based on the magnetic scalar and vector potentials to obtain the field strength and field linearity within a localized imaging area. It

Funan Shi; Reinhold Ludwig

1996-01-01

409

Vine species diversity across environmental gradients in northwestern México  

Microsoft Academic Search

The presence of vines has been described as a distinctive feature of tropical forests. However, vine species diversity exhibits trends across environmental gradients that are not well documented. Here we use a latitudinal and a rainfall gradient along the Pacific slope of México to explore the influence of environmental factors on vine species diversity. A total of 630 vines species

Francisco Molina-Freaner; Reyna Castillo Gámez; Clara Tinoco-Ojanguren; Alejandro E. V. Castellanos

2004-01-01

410

Chromatic aberrations of radial gradient-index lenses. I. Theory.  

PubMed

Chromatic effects of radial gradient-index materials have been analyzed, and several important conclusions have been derived in terms of material dispersion data. The use of Buchdahl dispersion data, both for base glass materials and ion-exchange pairs, provides some simple relationships for chromatic aberration and helps in selecting suitable materials for producing achromatic radial gradient-index lenses. PMID:21085210

Krishna, K S; Sharma, A

1996-03-01

411

Prediction of fracture gradients from log derived elastic moduli  

Microsoft Academic Search

Thirty-five measured fracture gradients in 10 fields are included in this study. The procedure utilizes all plugback operations from open hole, both into surface pipe and production strings or liners. Sonic and density logs have been obtained where possible from wells in the fields with measured breakdown gradients. Unfortunately, offshore logistics, risks, costs, and particularly hole conditions in highly deviated,

L. A. MacPherson; L. N. Berry

1972-01-01

412

Video Fingerprinting Based on Centroids of Gradient Orientations  

Microsoft Academic Search

Fingerprints are feature vectors that can uniquely characterize the video signal. The goal of a video fingerprinting system is to judge whether two videos have the same contents by measuring distance between fingerprints extracted from the videos. In this paper, a novel video fingerprinting method based on the centroids of gradient orientations is proposed. The centroid of gradient orientations is

Sunil Lee; Chang D. Yoo

2006-01-01

413

The effect of ordering on preconditioned conjugate gradients  

Microsoft Academic Search

We investigate the effect of the ordering of the unknowns on the convergence of the preconditioned conjugate gradient method. We examine a wide range of ordering methods including nested dissection, minimum degree, and red-black and consider preconditionings without fill-in. We show empirically that there can be a significant difference in the number of iterations required by the conjugate gradient method

Iain S. Duff; Gérard A. Meurant

1989-01-01

414

Azimuthal pressure gradient as driving force of substorm currents  

Microsoft Academic Search

We have studied the azimuthal pressure gradient in the central plasma sheet during substorms using plasma and magnetic field data obtained by the AMPTE\\/IRM satellite at nightside in radial distances of 9-15 RE. The pressure gradient is statistically estimated for the interval when the magnetic field shows a dipolar configuration (elevation angle >45°). It is found that by this criterion,

K. Shiokawa; G. Haerendel; W. Baumjohann

1998-01-01

415

Magnetic reconnection with pressure gradient effect in compressible electron magnetohydrodynamics  

Microsoft Academic Search

The general dispersion relation of the tearing mode with charge separation and pressure gradient effects in the whistler frequency is analytically derived in the framework of electron magnetohydrodynamics (EMHD). It is shown that pressure gradient effect enhances the growth rate, and makes the EMHD tearing mode drift. The growth rate of the EMHD tearing mode is significantly affected by the

Huishan Cai; Ding Li

2008-01-01

416

New Roles for Lysosomal Trafficking in Morphogen Gradient Sensing  

NSDL National Science Digital Library

The way in which cells recognize their position in a gradient of morphogen controls differentiation during embryogenesis. New findings indicate that the rate at which internalized morphogen receptors are trafficked to lysosomes is key to the accurate and precise sensing of morphogen gradients and the appropriate initiation of differentiation programs during development.

Elena Rainero (Beatson Institute for Cancer Research;Integrin Cell Biology Laboratory REV); Jim C. Norman (Beatson Institute for Cancer Research;Integrin Cell Biology Laboratory REV)

2011-05-03

417

Application of Sobolev gradient method to Poisson–Boltzmann system  

Microsoft Academic Search

The idea of a weighted Sobolev gradient, introduced and applied to singular differential equations in [1], is extended to a Poisson–Boltzmann system with discontinuous coefficients. The technique is demonstrated on fully nonlinear and linear forms of the Poisson– Boltzmann equation in one, two, and three dimensions in a finite difference setting. A comparison between the weighted gradient and FAS multigrid

Abdul Majid; Sultan Sial

2010-01-01

418

Mechanism-based strain gradient plasticity— I. Theory  

Microsoft Academic Search

A mechanism-based theory of strain gradient plasticity (MSG) is proposed based on a multiscale framework linking the microscale notion of statistically stored and geometrically necessary dislocations to the mesoscale notion of plastic strain and strain gradient. This theory is motivated by our recent analysis of indentation experiments which strongly suggest a linear dependence of the square of plastic flow stress

H. Gao; Y. Huang; W. D. Nix; J. W. Hutchinson

1999-01-01

419

The Optimal Reward Baseline for Gradient-Based Reinforcement Learning  

Microsoft Academic Search

There exist a number of reinforcement learning algorithms which learn by climbing the gradient of expected reward. Their long-run convergence has been proved, even in partially observable en- vironments with non-deterministic actions, and without the need for a system model. How- ever, the variance of the gradient estimator has been found to be a significant practical problem. Recent approaches have

Lex Weaver; Nigel Tao

2001-01-01

420

Computer Subroutines for Analytic Rotation by Two Gradient Methods.  

ERIC Educational Resources Information Center

|Two computer subroutine packages for the analytic rotation of a factor matrix, A(p x m), are described. The first program uses the Flectcher (1970) gradient method, and the second uses the Polak-Ribiere (Polak, 1971) gradient method. The calculations in both programs involve the optimization of a function of free parameters. The result is a…

van Thillo, Marielle

421

Second generation high gradient quadrupoles for the LHC interaction regions  

Microsoft Academic Search

Conceptual designs of large-aperture high-gradient Nb3Sn quadrupoles, suitable for use in a second generation LHC interaction region, are presented. A quadrupole with a 90 mm coil aperture and the same 200 T\\/m gradient as in the current LHC IR is technically feasible and would allow ?*=0.25 in to be achieved, doubling the LHC luminosity

T. Sen; J. Strait; A. V. Zlobin

2001-01-01

422

The electric field gradient in heavy rare earth metals  

Microsoft Academic Search

Estimates of the electric field gradient in heavy rare earth metals have been evaluated from experimental hyperfine interaction data. In addition, the magnetic hyperfine fields are analyzed. In the metals the effective radial integrals r-3>4f of the magnetic and quadrupole hyperfine interaction are reduced at most by 10% compared with the free ion values. The electric field gradients due to

J. Pelzl; Fachbereich Physik

1972-01-01

423

Cryptosporidium parvum: oocysts purification using potassium bromide discontinuous gradient  

Microsoft Academic Search

Cryptosporidiumparvum oocysts were purified using a discontinuous potassium bromide density gradient, composed by three solutions of 6, 16 and 28% (w\\/v) KBr in Tris–EDTA buffer. Fecal samples containing oocysts were washed to diminish interfering lipids and applied to the gradient. After centrifugation, oocysts can be easily aspirated from a clear band, diluted and washed by centrifugation in phosphate buffer to

Emilio Entrala; Jose-Manuel Molina-Molina; Maria-José Rosales-Lombardo; Manuel Sánchez-Moreno; Carmen Mascaró-Lazcano

2000-01-01

424

Gradient Well-Formedness across the Morpheme Boundary  

ERIC Educational Resources Information Center

|Recent theories of phonology hold that phonotactic well-formedness may be gradient, with some legal structures being more well-formed than others. Linguistic and psycholinguistic research has demonstrated that "within" morphemes, speakers encode both categorical (*n/Onset) and gradient (st/Onset greater than sin/Onset) phonotactic restrictions.…

Goldberg, Ariel M.

2010-01-01

425

Control over wettability via surface modification of porous gradients  

Microsoft Academic Search

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

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

2007-01-01

426

Gradient limitations in room temperature and superconducting acceleration structures  

SciTech Connect

Accelerating gradient is a key parameter of the accelerating structure in large linac facilities, like future Linear Collider. In room temperature accelerating structures the gradient is limited mostly by breakdown phenomena, caused by high surface electric fields or pulse surface heating. High power processing is a necessary procedure to clean surface and improve the gradient. In the best tested X-band structures the achieved gradient is exceed 100 MV/m in of {approx}200 ns pulses for breakdown rate of {approx} 10{sup -7}. Gradient limit depends on number of factors and no one theory which can explain all sets of experimental results and predict gradient in new accelerating structure. In paper we briefly overview the recent experimental results of breakdown studies, progress in understanding of gradient limitations and scaling laws. Although superconducting rf technology has been adopted throughout the world for ILC, it has frequently been difficult to reach the predicted performance in these structures due to a number of factors: multipactoring, field emission, Q-slope, thermal breakdown. In paper we are discussing all these phenomena and the ways to increase accelerating gradient in SC cavity, which are a part of worldwide R&D program.

Solyak, N.A.; /Fermilab

2008-10-01

427

Influence of transport properties in electric field gradient focusing.  

PubMed

Miniaturized devices for electric field gradient focusing (EFGF) were developed that consist of a cylindrical separation channel surrounded by an acrylic-based polymer hydrogel. The ionic transport properties of the hydrogel enable the manipulation of the electric field inside the separation channel. A changing cross-section design was used in which the hydrogel is shaped such that an electric field gradient is established in the separation channel. One of the challenges with this type of EFGF device has been that experimental resolution between protein analytes is lower than theoretically predicted. In order to investigate this phenomenon, a mathematical transport model was developed using FEMLAB. Model results and experimental observations showed that the reduced performance was caused by concentration gradients formed in the EFGF channel, and that these concentration gradients were the result of an imbalance in cation transport between the open separation channel and the hydrogel. Removing acidic impurities from the monomers that form the hydrogel reduced this tendency and improved the resolution. These transport-induced concentration gradients can be used to establish electric field gradients that may be useful for sample pre-concentration. Both the results of simulation and experiments demonstrate how transport-induced concentration gradients lead to the establishment of electric field gradients. PMID:17481644

Humble, Paul H; Harb, John N; Tolley, H Dennis; Woolley, Adam T; Farnsworth, Paul B; Lee, Milton L

2007-04-13

428

Arm classification and velocity gradients in spiral galaxies  

Microsoft Academic Search

On the basis of published rotation curves, velocity gradients are compiled for 94 galaxies. A significant correlation is found in this sample of galaxies between their gradients and arm classes (as given by Elmegreen and Elmegreen, 1982); galaxies with steeper curves tend to have a flocculent arm structure, and galaxies with flatter curves tend to have a grand design morphology.

A. Biviano; M. Girardi; G. Giuricin; F. Mardirossian; M. Mezzetti

1991-01-01

429

Dissociation of Diatomic Molecule by Speed-Gradient Feedback Control  

Microsoft Academic Search

New method for dissociation of diatomic molecule based on nonperiodic excitation generated by speed-gradient feedback control mechanism is proposed. The speed-gradient algorithm does not depend on the shape of the potential energy of molecule. It is shown that the feedback control is more ecien t then methods based on constant frequency and linear chirping excitations. Eciency of the proposed method

Fradkov Alexander; Krivtsov Anton

430

Stress release structures for actuator beams with a stress gradient  

Microsoft Academic Search

Stress release structures are introduced in fixed-fixed beams or membranes for releasing average stress. The influence of a stress gradient on the initial deformation of a fixed-fixed beam with stress release structures is studied in this paper. The objective is to obtain actuator beams that are insensitive to both the average stress and the stress gradient. The target application for

G. Klaasse; R. Puers; H. A. C. Tilmans

2007-01-01

431

Velocity Gradient Calibration of Jar-Test Equipment  

Microsoft Academic Search

During a study to determine mixing intensity, four groups of jars-test systems were utilized and mean velocity gradient, turbulent gross drag coefficient, and Reynolds and Power numbers were calculated. It was concluded that the same G, or mean velocity gradient, values could be produced by impellers of different shapes as long as projected areas were the same.

Ruey J. Lai; H. E. Hudson Jr.; J. E. Singley

1975-01-01

432

Simplest magnetometer configuration scheme to measure magnetic field gradient tensor  

Microsoft Academic Search

Due to geomagnetic anomaly strength can't be separated from magnetic field data, underwater vehicle localization based on geomagnetic anomaly needs vehicle draft depth information. For this localization method, we conclude that the simplest configuration be seven single-axis vector magnetometers to measure magnetic dipole gradients. The essential conditions and optimal measurement matrix of magnetic gradient tensor are analyzed, and a kind

Huang Yu; Sun Feng; Hao Yan-ling

2010-01-01

433

A scaled conjugate gradient algorithm for fast supervised learning  

Microsoft Academic Search

A supervised learning algorithm (Scaled Conjugate Gradient, SCG) with superlinear convergence rate is introduced. The algorithm is based upon a class of optimization techniques well known in numerical analysis as the Conjugate Gradient Methods. SCG uses second order information from the neural network but requires only O(N) memory usage, where N is the number of weights in the network. The

Martin Fodslette Møller

1993-01-01

434

Remote Sensing of Radiation Stress Gradients From Optical Imagery  

Microsoft Academic Search

Radiation stress, the excess momentum due to the presence of waves, is a function of wave energy. Thus, as waves break in the surf zone, gradients in radiation stress are created with this excess momentum providing a force that is typically of order 102 dynes\\/cm2, several orders of magnitude greater than wind forcing. These gradients drive all nearshore currents and

J. R. Killian; R. A. Holman

2002-01-01

435

Computer Subroutines for Analytic Rotation by Two Gradient Methods.  

ERIC Educational Resources Information Center

Two computer subroutine packages for the analytic rotation of a factor matrix, A(p x m), are described. The first program uses the Flectcher (1970) gradient method, and the second uses the Polak-Ribiere (Polak, 1971) gradient method. The calculations in both programs involve the optimization of a function of free parameters. The result is a…

van Thillo, Marielle

436

Gradient Intra Prediction for Coding of Computer Animated Videos  

Microsoft Academic Search

The increasing interest in computer animations initiated the need of efficient coding for such applications. This paper proposes two gradient based approaches to improve the efficiency of Intra Prediction. Taking advantage of a special property of computer animations, namely the gradient distribution of intensity on object surfaces, the devised methods provided a better performance over H.264\\/AVC. According to the simulations,

Xiang Li; Norbert Oertel; André Kaup

2006-01-01

437

Rotation therapy using a novel high-gradient filter  

SciTech Connect

A rotation therapy technique developed for treatment of head and neck tumors produced a sharp dose gradient between the target volume and the organ at risk, the medulla spinalis. To produce this effect, a specially designed high-gradient filter was placed in the photon beam.

Lax, I.; Brahme, A.

1982-11-01

438

Toroidal drift modes driven by ion pressure gradients  

NASA Astrophysics Data System (ADS)

Ion pressure gradient-driven drift modes are analyzed for their parametric dependence on the shear, the toroidal aspect ratio, and the pressure gradient using the ballooning toroidal mode theory. An approximate formula for the anomalous ion thermal conductivity is derived for the turbulent regime.

Horton, W., Jr.; Choi, D.-I.; Tang, W. M.

1981-06-01

439

Toroidal drift modes driven by ion pressure gradients  

Microsoft Academic Search

Ion pressure gradient-driven drift modes are analyzed for their parametric dependence on the shear, the toroidal aspect ratio, and the pressure gradient using the ballooning toroidal mode theory. An approximate formula for the anomalous ion thermal conductivity is derived for the turbulent regime.

Wendell Horton; Duk-In Choi; W. M. Tang

1981-01-01

440

Kinetic effects on the toroidal ion pressure gradient drift mode  

Microsoft Academic Search

The question of the threshold of the ion pressure gradient drift mode in toroidal geometry is examined from the drift-kinetic equation retaining the grad-B and curvature drift resonances of the ions with the mode. Analytic criteria for the onset of the instability are derived which exhibit the parametric dependence on toroidicity, pressure gradient and perpendicular wavenumber.

P. Terry; W. Anderson; W. Horton

1982-01-01

441

Temperature Gradient Vacuum Furnace for Diffusion Studies to 2000°C  

Microsoft Academic Search

An rf induction-heated furnace has been designed that produces a stable linear temperature gradient greater than 1000° C?cm and a maximum specimen temperature of 2000°C. Methods of measuring temperature in a temperature gradient have been evaluated and the performance of the furnace and its power requirements are discussed.

R. O. Meyer; J. C. Voglewede

1971-01-01

442

Magnetic field and gradient analysis around matrix for HGMS  

Microsoft Academic Search

A High Gradient Magnetic Separator (HGMS) uses matrix to make high magnetic field gradient so that ferro- or para-magnetic particles can be attracted to them by high magnetic force. These matrixes are usually composed of stainless wires having high magnetization characteristics. This paper deals with superconducting HGMS which is aimed for purifying wastewater by using stainless steel matrix. Background magnetic

S. K. Baik; D. W. Ha; R. K. Ko; J. M. Kwon

2010-01-01

443

Anomalous plasma transport due to electron temperature gradient instability  

Microsoft Academic Search

The collisionless drift wave instability driven by an electron temperature inhomogeneity (electron temperature gradient instability) and the enhanced transport processes associated with it are studied using a two-and-a-half dimensional particle simulation code. The simulation results show that quasilinear diffusion in phase space is an important mechanism for the saturation of the electron temperature gradient instability. Also, the instability yields partical

S. Tokuda; T. Kamimura; H. Ito

1979-01-01

444

Pore-Pressure and Fracture-Gradient Predictions  

Microsoft Academic Search

Drillers must, as far as possible, avoid kicks, wellbore instability, and loss of circulation through fractures, usually by selecting an appropriate mud weight. Knowledge of formation pore pressure and fracture gradient is essential for selection of a safe range of mud weights. This paper reports on predictions of pore-pressure and fracture gradients so that the proper range of mud weights

Marc Lesage; Peter Hall; John Pearson; Marc Thiercelin

1991-01-01

445

The role of temperature gradients in residential copper pipe corrosion  

Microsoft Academic Search

Experiments were conducted to determine the effect of sustained temperature gradients of ?20 °C on copper pipe corrosion under stagnant conditions in simulated potable water. An apparatus was constructed to (1) apply realistic temperature gradients to the pipes, (2) monitor copper release to the water, and (3) measure thermogalvanic currents between the warm and cold sections of pipe. The orientation

Jason C Rushing; Marc Edwards

2004-01-01

446

Dynamic Analysis for Inductance Gradient of Rail Gun  

Microsoft Academic Search

A simplified rail gun model is established and three dimensional finite element method of electromagnetic (EM) field is used to analyze the model parameters. The parameters include: inductance gradient, resistance gradient, magnetic induction intensity, magnetic force etc. The simulation result indicates that the load of rail gun may be equivalent to the nonlinear resistance, inductance and back electromotive force.

Yudong Yang; Kui Jin

2010-01-01

447

On bending of strain gradient elastic micro-plates  

Microsoft Academic Search

Bending of strain gradient elastic thin plates is studied, adopting Kirchhoff’s theory of plates. Simple linear strain gradient elastic theory with surface energy is employed. The governing plate equation with its boundary conditions are derived through a variational method. It turns out that new terms are introduced, indicating the importance of the cross-section area in bending of thin plates. Those

K. A. Lazopoulos

2009-01-01

448

Achieving consumer focus in supply chains  

Microsoft Academic Search

Purpose – Supply chain performance is two-dimensional: efficiency and effectiveness. The purpose of this paper is to further define and explore the demarcation between supply chain effectiveness and supply chain efficiency. Design\\/methodology\\/approach – A case-study research method is adopted in this paper. This contribution discusses an approach for the improvement of supply chain effectiveness, i.e. Supply Chain Kano-QFD. Findings –

Keivan Zokaei; Peter Hines

2007-01-01

449

Probing Electron Temperature Critical Gradients in Experiment and Simulation  

NASA Astrophysics Data System (ADS)

In DIII-D, localized electron cyclotron heating (ECH) is used to probe the critical gradient of, and onset of stiffness in, the electron temperature Te profile. While keeping the total injected ECH power constant, the deposition profile was varied to investigate the relationship between the Te gradient and the electron power balance heat flux. A critical temperature gradient was observed, above which both the heat diffusivity and the Te fluctuations increase sharply. To compare to modeling, efforts have been made to produce the most realistic equilibrium reconstructions by using kinetic pressure constraints and motional Stark effect measurements of the local magnetic pitch. With these reconstructions, the gyrokinetic stability codes GYRO and TGLF predict that there is a critical Te gradient, similar to the experimentally observed gradient, above which electron modes exist and whose growth rates dominate over the ion growth rates.

Smith, S. P.; Luce, T. C.; Deboo, J. C.; Petty, C. C.; Burrell, K. H.; Waltz, R. E.; Staebler, G. M.; Candy, J.; Holland, C.; Meneghini, O.; White, A. E.; Rhodes, T. L.; Schmitz, L.; Doyle, E. J.; Hillesheim, J. C.; Wang, G.; Zeng, L.; McKee, G. R.; Yan, Z.

2012-10-01

450

Directional swimming in bacteria: active and passive gradient responses  

NASA Astrophysics Data System (ADS)

The ability to swim directionally is paramount for bacteria, in their quest for nutrients and favorable microhabitats. This ability depends on both active and passive responses to gradients. Here we bring an example from each case, based on novel microfluidic experiments that quantify the swimming behavior of bacteria. First, we describe their active response to oxygen gradients - or aerotaxis - and show the unexpected consequences of competing oxygen gradients with nutrient gradients. Then, we present the first observations of directional swimming by bacteria in response to fluid velocity gradients - or rheotaxis. Combining experiments with mathematical modeling we demonstrate that, unlike in larger organisms such as fish, rheotaxis in bacteria is passive, resulting from a previously undetected torque that originates from the chirality of the bacterial flagellum.

Stocker, Roman

2012-02-01

451

Tailoring magnetic field gradient design to magnet cryostat geometry.  

PubMed

Eddy currents induced within a magnetic resonance imaging (MRI) cryostat bore during pulsing of gradient coils can be applied constructively together with the gradient currents that generate them, to obtain good quality gradient uniformities within a specified imaging volume over time. This can be achieved by simultaneously optimizing the spatial distribution and temporal pre-emphasis of the gradient coil current, to account for the spatial and temporal variation of the secondary magnetic fields due to the induced eddy currents. This method allows the tailored design of gradient coil/magnet configurations and consequent engineering trade-offs. To compute the transient eddy currents within a realistic cryostat vessel, a low-frequency finite-difference time-domain (FDTD) method using total-field scattered-field (TFSF) scheme has been performed and validated. PMID:17945575

Trakic, A; Liu, F; Lopez, H S; Wang, H; Crozier, S

2006-01-01

452

Acceleration and radiation processes in controlled gradient gas jets  

NASA Astrophysics Data System (ADS)

The controlled gradient gas jet was designed, constructed and tested at the Naval Research Laboratory. The gas jet is using a laser generated shock wave to control the density gradient between vacuum and neutral gas. The length scale of the density gradient is fully controlled by the strength of the shock wave and can be varied continuously from under 10 ?m in case of strong shock to a 100 ?m for a weak shock wave. To verify the experimental results a simulation was run to model the system using a three-dimensional hydrodynamic code, SPARC, developed at the Naval Research Laboratory. Controlling the gas density gradient is important for electrons and protons acceleration, as well as for optical transition radiation generation. Experiments on using the controlled gradient gas jet and preliminary results on electron acceleration will be presented.

Kaganovich, Dmitri; Helle, Mike; Gordon, Daniel; Xie, Frank; Ting, Antonio

2011-11-01

453

Calibration and correction of the device measuring magnetic gradient tensor  

NASA Astrophysics Data System (ADS)

Generally, four three-axis magnetometers (TAMs) are used to measure magnetic gradient tensor. But the measurement precision of magnetic gradient tensor is tightly connected with the imperfect performance of sensors such as non-orthogonality, different scale factors and biases among sensitive axes, misalignment between different TAMs. It is necessary to calibrate and correct the measurement device to obtain precise magnetic gradient tensor. A mathematical model for calibration of the device measuring magnetic gradient tensor is established, and the calibration algorithm and its steps based on functional link artificial neural network (FLANN) and least-squares method (LSM) are proposed. The numerical simulations prove the effectiveness and good convergence of calibration algorithm, which can improve remarkably the measurement precision of magnetic gradient tensor.

Huang, Yu; Wu, Li-hua

454

Isolation and characterization of a novel dynein that contains C and A heavy chains from sea urchin sperm flagellar axonemes.  

PubMed

A novel dynein (C/A dynein), which is composed of C and A heavy chains, two intermediate chains and several light chains, was isolated from sea urchin sperm flagella. The C/A dynein was released by the treatment with 0.7 M NaCl plus 5 mM ATP from the axonemes depleted of outer arm 21 S dynein. Sedimentation coefficient of this dynein was estimated by sucrose density gradient centrifugation to be 22-23 S. The C/A dynein particle appeared to be composed of three distinct domains; two globular head domains and one rod domain as seen by negative staining electron microscopy. The mobility of 'A' heavy chain of C/A dynein on SDS-gel electrophoresis was similar to that of A heavy chains (A alpha and A beta) of 21 S dynein. However, UV-cleavage patterns of C and A heavy chains of C/A dynein were different from those of A heavy chains of 21 S dynein. Furthermore, an antiserum raised against A heavy chain of C/A dynein did not crossreact with A heavy chains of 21 S dynein. Under the conditions in which the C/A dynein was released, some of inner arms were removed concomitantly from axonemes as observed by electron microscopy. These results suggested that C/A dynein is a component of the inner arms. PMID:8207066

Yokota, E; Mabuchi, I

1994-02-01

455

Remarks on food chain dynamics  

Microsoft Academic Search

The main modes of behavior of a food chain model composed of logistic prey and Holling type II predator and superpredator are discussed in this paper. The study is carried out through bifurcation analysis, alternating between a normal form approach and numerical continuation. The two-parameter bifurcation diagram of the model contains Hopf, fold, and transcritical bifurcation curves of equilibria as

S Rinaldi

1996-01-01

456

Remarks on food chain dynamics  

Microsoft Academic Search

The main modes of behavior of a food chain model, composed of logistic prey and Holling type II predator and superpredator, are discussed in this paper. The study is carried out through bifurcation analysis, alternating between a normal form approach and numerical continuation. The two-parameter bifurcation diagram of the model contains Hopf, fold and transcritical bifurcation curves of equilibria as

Yu. a. Kuznetsov; S. Rinaldi

1995-01-01

457

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

458

Chains and the Common Ground  

Microsoft Academic Search

In this paper we provide a description of how the iterated specific use of an indefinite NP can lead to the establishment of referential chains across dialogues and dialogue participants. We describe how they introduce discourse referents, how they are related to the common ground, and how this common ground can be represented by the dialogue participants. Of central concern

Anton Benz

459

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

460

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

461

Using Gagne's Chain in OJT.  

National Technical Information Service (NTIS)

This report discusses Gagne's Chain which is a taxonomy which can used as a tool to identify trainee deficiencies encountered during On-the-Job Training. It also assists in the development of effective training strategies for the training of deficient beh...

F. E. Fetters

1993-01-01

462

The causal chain of loyalty  

Microsoft Academic Search

Loyalty is considered as a key concept in the establishment and maintenance of long term relationships. In this work in progress communication, a theoretical framework is proposed on the basis of the relationship marketing paradigm and commitment trust theory. Loyalty is conceived according to Oliver (1997) as a causal chain composed by cognitive loyalty, affective loyalty, conative loyalty and action

Manel KHADRAOUI; Jamel-Eddine GHARBI; Michel Plaisent

463

An ARIMA Supply Chain Model  

Microsoft Academic Search

This paper presents a multistage supply chain model that is based on Autoregressive Integrated Moving Average (ARIMA) time-series models. Given an ARIMA model of consumer demand and the lead times at each stage, it is shown that the orders and inventories at each stage are also ARIMA, and closed-form expressions for these models are given. The paper also discusses the

Kenneth Gilbert

2005-01-01

464

Text Summarization Using Lexical Chains  

Microsoft Academic Search

Text summarization addresses both the problem of selecting the most important portions of text and the problem of generating coherent summaries. We present in this paper the summarizer of the University of Lethbridge at DUC 2001, which is based on an efficient use of lexical chains.

Meru Brunn; Yllias Chali; Christopher J. Pinchak

2001-01-01

465

Bridging organization theory and supply chain management: The case of best value supply chains  

Microsoft Academic Search

Rivalry is increasingly being contested at the supply chain level of analysis. Rather than competing “firm versus firm,” today's organizations are battling “supply chain versus supply chain.” Within this context, best value supply chains are emerging as a means to create competitive advantages and superior performance. While traditional supply chains often focus primarily on one key outcome such as speed

David J. Ketchen; G. Tomas M. Hult

2007-01-01

466

Gravitational Gradients at Satellite Altitudes in Global Geophysical Studies  

NASA Astrophysics Data System (ADS)

Due to the ESA's satellite mission GOCE launched in March 2009, gravitational gradients sampled along the orbital trajectory approximately 250 km above the Earth's surface have become available. Since 2010, gravitational gradients have routinely been applied in geodesy for the derivation of global Earth's gravitational models provided in terms of fully normalized coefficients in a spherical harmonic series representation of the Earth's gravitational potential. However, in geophysics, gravitational gradients observed by spaceborne instruments have still been applied relatively seldom. This contribution describes their possible geophysical applications in structural studies where gravitational gradients observed at satellite altitudes are compared with those derived by a spectral forward modeling technique using available global models of selected Earth's mass components as input data. In particular, GOCE gravitational gradients are interpreted in terms of a superposition principle of gravitation as combined gravitational effects generated by a homogeneous reference ellipsoid of revolution, mean topographic and ice mass density distributions, depth-dependent mass density contrasts within bathymetry and lateral mass density anomalies with sediments and crustal layers. Respective gravitational effects are one by one removed from gravitational gradients observed at approximately 250 km elevation above ground. Removing respective gravitational gradients from observed gravitational gradients gradually reveals problematic geographic areas with model deficiencies. For the full interpretation of observed gravitational gradients, deficiencies of CRUST2.0 must be corrected and effects of deeper laying mass anomalies not included in the study considered. These findings are confirmed by parameters describing spectral properties of the gravitational gradients. The methodology can be applied for validating Earth's gravitational models and for constraining crustal models in the development phase.

Novák, Pavel; Tenzer, Robert

2013-09-01

467

An axoplasmic myosin with a calmodulin-like light chain.  

PubMed Central

Organelles in the axoplasm from the squid giant axon move along exogenous actin filaments toward their barbed ends. An approximately 235-kDa protein, the only band recognized by a pan-myosin antibody in Western blots of isolated axoplasmic organelles, has been previously proposed to be a motor for these movements. Here, we purify this approximately 235-kDa protein (p235) from axoplasm and demonstrate that it is a myosin, because it is recognized by a pan-myosin antibody and has an actin-activated Mg-ATPase activity per mg of protein 40-fold higher than that of axoplasm. By low-angle rotary shadowing, p235 differs from myosin II and it does not form bipolar filaments in low salt. The amino acid sequence of a 17-kDa protein that copurifies with p235 shows that it is a squid optic lobe calcium-binding protein, which is more similar by amino acid sequence to calmodulin (69% identity) than to the light chains of myosin II (33% identity). A polyclonal antibody to this light chain was raised by using a synthetic peptide representing the calcium binding domain least similar to calmodulin. We then cloned this light chain by reverse transcriptase-PCR and showed that this antibody recognizes the bacterially expressed protein but not brain calmodulin. In Western blots of sucrose gradient fractions, the 17-kDa protein is found in the organelle fraction, suggesting that it is a light chain of the p235 myosin that is also associated with organelles. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4

Bearer, E L; DeGiorgis, J A; Jaffe, H; Medeiros, N A; Reese, T S

1996-01-01

468

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

469

Hydraulic gradient control for groundwater contaminant removal  

USGS Publications Warehouse

The Rocky Mountain Arsenal near Denver, Colarado, U.S.A., is used as a realistic setting for a hypothetical test of a procedure that plans the hydraulic stabilization and removal of a groundwater contaminant plume. A two-stage planning procedure successfully selects the best wells and their optimal pumping/recharge schedules to contain the plume while a well or system of wells within the plume removes the contaminated water. In stage I, a combined groundwater flow and solute transport model is used to simulate contaminant removal under an assumed velocity field. The result is the approximated plume boundary location as a function of time. In stage II, a linear program, which includes a groundwater flow model as part of the set of constraints, determines the optimal well selection and their optimal pumping/recharge schedules by minimizing total pumping and recharge. The simulation-management model eliminates wells far from the plume perimeter and activates wells near the perimeter as the plume decreases in size. This successfully stablizes the hydraulic gradient during aquifer cleanup.The Rocky Mountain Arsenal near Denver, Colorado, USA, is used as a realistic setting for a hypothetical test of a procedure that plans the hydraulic stabilization and removal of a groundwater contaminant plume. A two-stage planning procedure successfully selects the best wells and their optimal pumping/recharge schedules to contain the plume while a well or system of wells within the plume removes the contaminated water. In stage I, a combined groundwater flow and solute transport model is used to simulate contaminant removal under an assumed velocity field. The result is the approximated plume boundary location as a function of time. In stage II, a linear program, which includes a groundwater flow model as part of the set of constraints, determines the optimal well selection and their optimal pumping/recharge schedules by minimizing total pumping and recharge. Refs.

Fisher, Atwood, D.; Gorelick, S. M.

1985-01-01

470

Molecular mechanisms for generating transmembrane proton gradients.  

PubMed

Membrane proteins use the energy of light or high energy substrates to build a transmembrane proton gradient through a series of reactions leading to proton release into the lower pH compartment (P-side) and proton uptake from the higher pH compartment (N-side). This review considers how the proton affinity of the substrates, cofactors and amino acids are modified in four proteins to drive proton transfers. Bacterial reaction centers (RCs) and photosystem II (PSII) carry out redox chemistry with the species to be oxidized on the P-side while reduction occurs on the N-side of the membrane. Terminal redox cofactors are used which have pKas that are strongly dependent on their redox state, so that protons are lost on oxidation and gained on reduction. Bacteriorhodopsin is a true proton pump. Light activation triggers trans to cis isomerization of a bound retinal. Strong electrostatic interactions within clusters of amino acids are modified by the conformational changes initiated by retinal motion leading to changes in proton affinity, driving transmembrane proton transfer. Cytochrome c oxidase (CcO) catalyzes the reduction of O2 to water. The protons needed for chemistry are bound from the N-side. The reduction chemistry also drives proton pumping from N- to P-side. Overall, in CcO the uptake of 4 electrons to reduce O2 transports 8 charges across the membrane, with each reduction fully coupled to removal of two protons from the N-side, the delivery of one for chemistry and transport of the other to the P-side. PMID:23507617

Gunner, M R; Amin, Muhamed; Zhu, Xuyu; Lu, Jianxun

2013-03-16

471

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

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Markov chains and embedded Markov chains in geology  

Microsoft Academic Search

Geological data are structured as first-order, discrete-state discrete-time Markov chains in two main ways. In one, observations are spaced equally in time or space to yield transition probability matrices with nonzero elements in the main diagonal; in the other, only state transitions are recorded, to yield matrices with diagonal elements exactly equal to zero. The mathematical differences in these two