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1

Synthesis of alpha-amino acids  

DOEpatents

A method is described for synthesizing alpha amino acids proceeding through novel intermediates of the formulas: R[sub 1]R[sub 2]C(OSOCl)CN, R[sub 1]R[sub 2]C(Cl)CN and [R[sub 1]R[sub 2]C(CN)O][sub 2]SO wherein R[sub 1] and R[sub 2] are each selected from hydrogen monovalent substituted and unsubstituted hydrocarbon radicals of 1 to 10 carbon atoms. The use of these intermediates allows the synthesis steps to be exothermic and results in an overall synthesis method which is faster than the synthesis methods of the prior art. No Drawings

Davis, J.W. Jr.

1983-01-25

2

alpha-Amino-beta-hydroxy-gamma-lactam for constraining peptide Ser and Thr residue conformation.  

PubMed

Alpha-amino-beta-hydroxy-gamma-lactam 1 is a peptide mimic in which the Ser/Thr residue omega-, psi-, and chi-dihedral angle geometry all are constrained by the 5-membered lactam ring. Lactams 1 were made by employing N-(Fmoc)oxiranylglycine 3 as a bis-electrophile in TFE with cat. BzOH to sequentially alkylate and acylate a variety of amino acid derivatives in one pot. Solid-phase synthesis of beta-hydroxy-gamma-lactam 8, an analogue of the IL-1 modulator 101.10, was achieved using this method for studying Ser/Thr geometry. PMID:20225885

St-Cyr, Daniel J; Jamieson, Andrew G; Lubell, William D

2010-04-16

3

An efficient preparation of N-methyl-alpha-amino acids from N-nosyl-alpha-amino acid phenacyl esters.  

PubMed

In this paper we describe a simple and efficient solution-phase synthesis of N-methyl-N-nosyl-alpha-amino acids and N-Fmoc-N-methyl-alpha-amino acids. This represents a very important application in peptide synthesis to obtain N-methylated peptides in both solution and solid phase. The developed methodology involves the use of N-nosyl-alpha-amino acids with the carboxyl function protected as a phenacyl ester and the methylating reagent diazomethane. An important aspect of this synthetic strategy is the possibility to selectively deprotect the carboxyl function or alternatively both amino and carboxyl moieties by using the same reagent with a different molar excess and under mild conditions. Furthermore, the adopted procedure keeps unchanged the acid-sensitive side chain protecting groups used in Fmoc-based synthetic strategies. PMID:20121053

Leggio, Antonella; Belsito, Emilia Lucia; De Marco, Rosaria; Liguori, Angelo; Perri, Francesca; Viscomi, Maria Caterina

2010-03-01

4

Scaleable catalytic asymmetric Strecker syntheses of unnatural alpha-amino acids  

Microsoft Academic Search

alpha-Amino acids are the building blocks of proteins and are widely used as components of medicinally active molecules and chiral catalysts. Efficient chemo-enzymatic methods for the synthesis of enantioenriched alpha-amino acids have been developed, but it is still a challenge to obtain non-natural amino acids. Alkene hydrogenation is broadly useful for the enantioselective catalytic synthesis of many classes of amino

Stephan J. Zuend; Matthew P. Coughlin; Mathieu P. Lalonde; Eric N. Jacobsen

2009-01-01

5

Expedient synthesis of threo-beta-hydroxy-alpha-amino acid derivatives: phenylalanine, tyrosine, histidine, and tryptophan.  

PubMed

An expedient synthesis of enantiomerically pure threo-beta-hydroxy-alpha-amino acid derivatives of phenylalanine, tyrosine, histidine, and tryptophan is described. The NBS-mediated radical bromination of the N,N-di-tert-butoxycarbonyl protected alpha-amino acids and subsequent treatment with silver nitrate in acetone provided the trans-oxazolidinones predominantly. Cesium carbonate catalyzed hydrolysis then generated the beta-hydroxy amino acid derivatives in excellent overall yield. PMID:16930077

Crich, David; Banerjee, Abhisek

2006-09-01

6

Structural Characterization of a Pentapeptide Derived from a Novel Carbohydrate [alpha]-Amino Acid  

SciTech Connect

Subsequent to our previous report describing several novel carbohydrate {alpha}-amino acid dipeptides (and the structural characterization of one of those), and their extension to higher peptides, a synchrotron radiation study of one of those - a pentapeptide - showing its structure to be a well-defined helical array in each of two independent molecules, stabilized by internal hydrogen bonds, is reported.

Scaffidi, Adrian; Skelton, Brian W.; Stick, Robert V.; White, Allan H. (UWA)

2008-06-30

7

Action of some Water-soluble Poly-alpha-Amino-Acids on Bacteria  

Microsoft Academic Search

SOME of the antibiotics formed by fungi and bacteria have been found to consist of alpha-amino-acids linked by peptide bonds1. The recent work of Bloom, Watson, Cromartie and their associates2 showed that even the cells of higher animals may, in certain circumstances, for example, in infection with anthrax, excrete antibacterial substances of peptide nature. These facts encouraged us to study

E. Katchalski; L. Bichovski-Slomnitzki; B. E. Volcani

1952-01-01

8

Adsorption of alpha amino acids at the water/goethite interface.  

PubMed

The adsorption of amino acids onto mineral surfaces plays an important role in a wide range of areas, e.g., low-temperature aqueous geochemistry, bone formation and protein-bone interactions. In this work, the adsorption of three alpha aminoacids (sarcosine, MIDA and EDDA) onto goethite (alpha-FeOOH) was studied as a function of pH and background electrolyte concentration at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The results showed that adsorption of alpha amino acids were strongly dependent on the functionality and structure of the ligands. No adsorption was detected for the zwitterionic sarcosine indicating that simple alpha amino acids without other ionizable and/or functional groups display insignificant affinity for mineral surfaces such as goethite. With respect to the more complex amino acids, which are surface reactive, the number and relative positions of carboxylate and amine groups determine the types of surface interactions. These interactions range from non-specific outer-sphere to specific inner-sphere interactions as shown by the MIDA and EDDA results, respectively. The results presented herein suggest that isomerically-selective adsorption might only occur for amino acids that are capable of specific surface interactions, either through site-specific hydrogen bonding or inner-sphere complexation. PMID:18155715

Norén, Katarina; Loring, John S; Persson, Per

2007-12-05

9

Molecular Basis of Prodrug Activation by Human Valacyclovirase, an [alpha]-Amino Acid Ester Hydrolase  

SciTech Connect

Chemical modification to improve biopharmaceutical properties, especially oral absorption and bioavailability, is a common strategy employed by pharmaceutical chemists. The approach often employs a simple structural modification and utilizes ubiquitous endogenous esterases as activation enzymes, although such enzymes are often unidentified. This report describes the crystal structure and specificity of a novel activating enzyme for valacyclovir and valganciclovir. Our structural insights show that human valacyclovirase has a unique binding mode and specificity for amino acid esters. Biochemical data demonstrate that the enzyme hydrolyzes esters of {alpha}-amino acids exclusively and displays a broad specificity spectrum for the aminoacyl moiety similar to tricorn-interacting aminopeptidase F1. Crystal structures of the enzyme, two mechanistic mutants, and a complex with a product analogue, when combined with biochemical analysis, reveal the key determinants for substrate recognition; that is, a flexible and mostly hydrophobic acyl pocket, a localized negative electrostatic potential, a large open leaving group-accommodating groove, and a pivotal acidic residue, Asp-123, after the nucleophile Ser-122. This is the first time that a residue immediately after the nucleophile has been found to have its side chain directed into the substrate binding pocket and play an essential role in substrate discrimination in serine hydrolases. These results as well as a phylogenetic analysis establish that the enzyme functions as a specific {alpha}-amino acid ester hydrolase. Valacyclovirase is a valuable target for amino acid ester prodrug-based oral drug delivery enhancement strategies.

Lai, Longsheng; Xu, Zhaohui; Zhou, Jiahai; Lee, Kyung-Dall; Amidon, Gordon L. (Michigan)

2008-07-08

10

Asymmetric Synthesis of alpha-Amino Phosphonic Acids by Diastereoselective Addition of Trimethyl Phosphite onto Chiral Oxazolidines(1).  

PubMed

A simple and general asymmetric synthesis of alpha-amino phosphonic acids is described. The method involves the highly selective addition of trialkyl phosphite onto various chiral oxazolidines. Oxazaphosphorinanes thus obtained with an excellent diastereoselectivity furnish the corresponding (S)-alpha-substituted amino phosphonic acids in good overall yields and high ee (77-->97%) after simple deprotection. PMID:11667216

Maury, Catherine; Gharbaoui, Tawfik; Royer, Jacques; Husson, Henri-Philippe

1996-05-31

11

Enantioseparation of alpha-amino acids on an 18-crown-6-tetracarboxylic acid-bonded silica by capillary electrochromatography.  

PubMed

(-)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid-bonded silica was used as the chiral stationary phase in capillary electrochromatography (CEC) for enantioseparation of some alpha-amino acids. Separation data in CEC were measured in mobile phases of varying pH, and composition of methanol and buffer, and compared with those in capillary liquid chromatography (CLC). In CEC better enantioseparation was generally obtained in the eluent of lower pH, higher buffer concentration and intermediate MeOH content, usually at the expense of analysis time. CEC showed generally better enantioselectivity and resolutions than CLC for the amino acids investigated. PMID:20060534

Lee, Taeho; Lee, Wonjae; Hyun, Myung Ho; Park, Jung Hag

2010-01-04

12

Site-selective methylation of N(beta)-nosyl hydrazides of N-nosyl protected alpha-amino acids.  

PubMed

The methylation reaction of N(beta)-nosyl hydrazides of N-nosyl protected alpha-amino acids by using diazomethane shows a controlled regiochemical trend and makes it possible to obtain the corresponding products methylated at specific positions depending on the amount of diazomethane used. The observed selectivity is closely connected with the different acidity of sulfonyl hydrazide, sulfonamide, and acyl hydrazine protons present in the analyzed substrates. The reactivity order of these three diverse reactive sites is supported by theoretical calculations. The hydrazine derivatives considered in this work belong to a class of compounds with interesting biological activity and of great interest in organic synthesis. PMID:20405869

De Marco, Rosaria; Leggio, Antonella; Liguori, Angelo; Marino, Tiziana; Perri, Francesca; Russo, Nino

2010-05-21

13

Quantitation of fourteen urinary alpha-amino acids using isobutane gas chromatography chemical ionization mass spectrometry with 13C amino acids as internal standards.  

PubMed

Isobutane chemical ionization gas chromatography mass spectometry of the N-trifluoroacetyl-carboxy-n-butyl ester derivatives of amino acids, using a commercial per-13C-amino acid mixture as internal standards, provided a sensitive and specific method for quantitative analysis of fourteen urinary alpha-amino acids. A computer controlled quadrupole mass spectrometer was used in a selected ion monitoring mode to record the ion current due to the protonated molecular ions of each alpha-amino acid/13C analogue pair. BASIC programmes located peak maxima, and using previously established standard curves, calculated the amino acid content on the bases of both peak height and peak area ratios. Duplicate amino acid analyses are possible on 5 microliter of urine. Instrumental analysis required 25 minutes, automated data processing 10 minutes, and sample preparation 2 hours. Detection limits approached 1 ng with a typical mean standard deviation of 2% for the instrumental analysis. PMID:6452181

Finlayson, P J; Christopher, R K; Duffield, A M

1980-10-01

14

Determination of the enantiomers of alpha-hydroxy- and alpha-amino acids in capillary electrophoresis with contactless conductivity detection.  

PubMed

The enantiomers of the anions of five alpha-hydroxy acids, namely lactic acid, alpha-hydroxybutyric acid, 2-hydroxycaproic acid, 2-hydroxyoctanoic acid and 2-hydroxydecanoic acid, as well as the two alpha-amino acids aspartic acid and glutamic acid, were baseline separated and detected by CE with contactless conductivity detection. Vancomycin was employed as chiral selector and could be used with conductivity detection without having to resort to a partial filling protocol as needed when this reagent is used with UV absorbance measurements. The procedure was successfully applied to the determination of the lactic acid enantiomers in samples of milk and yogurt. Linearity was achieved in the concentration range of 10-500 micromol/L with good correlation coefficients (0.9993 and 0.9990 for L- and D-lactic acid, respectively). The LODs (3 S/N) for L- and D-lactic acid were determined as 2.8 and 2.4 micromol/L, respectively. PMID:20496346

Pormsila, Worapan; Gong, Xiao Yang; Hauser, Peter C

2010-06-01

15

alpha-Hydroxy and alpha-amino acids under possible Hadean, volcanic origin-of-life conditions.  

PubMed

To test the theory of a chemoautotrophic origin of life in a volcanic, hydrothermal setting, we explored mechanisms for the buildup of bio-organic compounds by carbon fixation on catalytic transition metal precipitates. We report the carbon monoxide-dependent formation of carbon-fixation products, including an ordered series of alpha-hydroxy and alpha-amino acids of the general formula R-CHA-COOH (where R is H, CH3,C2H5,orHOCH2 and A is OH or NH2) by carbon fixation at 80 degrees to 120 degrees C, catalyzed by nickel or nickel,iron precipitates with carbonyl, cyano, and methylthio ligands as carbon sources, with or without sulfido ligands. Calcium or magnesium hydroxide was added as a pH buffer. The results narrow the gap between biochemistry and volcanic geochemistry and open a new gateway for the exploration of a volcanic, hydrothermal origin of life. PMID:17068257

Huber, Claudia; Wächtershäuser, Günter

2006-10-27

16

Organization of genes responsible for the stereospecific conversion of hydantoins to alpha-amino acids in Arthrobacter aurescens DSM 3747.  

PubMed

Arthrobacter aurescens DSM 3747 hydrolyzes stereospecifically 5'-monosubstituted hydantoins to alpha-amino acids. The genes involved in hydantoin utilization (hyu) were isolated on an 8.7-kb DNA fragment, and by DNA sequence analysis eight ORFs were identified. The hyu gene cluster includes four genes: hyuP encoding a putative transport protein, the hydantoin racemase gene hyuA, the hydantoinase gene hyuH, and the carbamoylase gene hyuC. The four genes are transcribed in the same direction. Upstream of hyuP and in opposite orientation to the hyu genes, three ORFs were found showing similarities to cytochrome P450 monooxygenase (ORF1, incomplete), to membrane proteins (ORF2), and to ferredoxin (ORF3). ORF8 was found downstream of hyuC and again in opposite orientation to the hyu genes. The gene product of ORF8 displayed similarities to the LacI/GalR family of transcriptional regulators. Reverse transcriptase PCR experiments and Northern blot analysis revealed that the genes hyuPAHC are coexpressed in A. aurescens after induction with 3-N-CH3-IMH. The expression of the hyu operon was not regulated by the putative regulator ORF8 as shown by gene disruption and mobility-shift experiments. PMID:11511866

Wiese, A; Syldatk, C; Mattes, R; Altenbuchner, J

2001-09-01

17

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels lacking the N-terminal domain.  

PubMed

Ionotropic glutamate receptor (iGluR) subunits contain a approximately 400-residue extracellular N-terminal domain ("X domain"), which is sequence-related to bacterial amino acid-binding proteins and to class C G-protein-coupled receptors. The X domain has been implicated in the assembly, transport to the cell surface, allosteric ligand binding, and desensitization in various members of the iGluR family, but its actual role in these events is poorly characterized. We have studied the properties of homomeric alpha-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA)-selective GluR-D glutamate receptors carrying N-terminal deletions. Our analysis indicates that, surprisingly, transport to the cell surface, ligand binding properties, agonist-triggered channel activation, rapid desensitization, and allosteric potentiation by cyclothiazide can occur normally in the complete absence of the X domain (residues 22-402). The relatively intact ligand-gated channel function of a homomeric AMPA receptor in the absence of the X domain indirectly suggests more subtle roles for this domain in AMPA receptors, e.g. in the assembly of heteromeric receptors and in synaptic protein interactions. PMID:12393905

Pasternack, Arja; Coleman, Sarah K; Jouppila, Annukka; Mottershead, David G; Lindfors, Maria; Pasternack, Michael; Keinänen, Kari

2002-10-21

18

Glutamate Regulates Intracellular Calcium and Gene Expression in Oligodendrocyte Progenitors through the Activation of DL-alpha-Amino-3- Hydroxy5Methyl4-Isoxazolepropionic Acid Receptors  

Microsoft Academic Search

Oligodendrocytes and their progenitors (O-2A) express functional kainate- and DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-preferring glutamate receptors. The physiological consequences of activation of these receptors were studied in purified rat cortical O-2A progenitors and in the primary oligodendrocyte cell line CG-4. Changes in the mRNA levels of a set of immediate early genes were studied and were correlated to intracellular Ca2+ concentration, as

Mario Pende; Lynne A. Holtzclaw; Joseph L. Curtis; James T. Russell; Vittorio Gallo

1994-01-01

19

Catalytic enantioselective synthesis of 18F-fluorinated alpha-amino acids under phase-transfer conditions using (S)-NOBIN.  

PubMed

We describe a new method for the asymmetric synthesis of [(18)F]fluorinated aromatic alpha-amino acids (FAA) under phase transfer conditions using achiral glycine derivative NiPBPGly and (S)-NOBIN as a novel substrate/catalyst pair. The key alkylation step proceeds under mild conditions. Substituted [(18)F]fluorobenzylbromides were prepared using nucleophilic [(18)F]fluoride and were used as alkylation agents. Two important FAA, 2-[(18)F]fluoro-L-tyrosine (2-FTYR) and 6-[(18)F]fluoro-L-3,4-dihydroxyphenylalanine (6-FDOPA), were synthesized with an ee of 92 and 96%, respectively. The total synthesis time was 110-120 min and radiochemical yields (d.c.) were 25+/-6% for 2-FTYR and 16+/-5% for 6-FDOPA. PMID:15219278

Krasikova, R N; Zaitsev, V V; Ametamey, S M; Kuznetsova, O F; Fedorova, O S; Mosevich, I K; Belokon, Y N; Vyskocil, S; Shatik, S V; Nader, M; Schubiger, P A

2004-07-01

20

Chromatographic separation of enantiomers of non-protein alpha-amino acids after derivatization with Marfey's reagent and its four variants.  

PubMed

Some non-protein alpha-amino acids were derivatized with 1-fluoro-2,4-dinitrophenyl-5-L-alaninamide (Marfey's reagent, MR, FDNP-L-Ala-NH(2),) and four of its structural variants FDNP-L-Phe-NH(2), FDNP-L-Val-NH(2), FDNP-L-Leu-NH(2) and FDNP-L-Pro-NH(2). The resultant diastereomers were separated by normal and reversed phase thin layer chromatography (TLC) and reversed phase HPLC. In normal phase TLC, best resolution was obtained with solvent combination of phenol-water (3:1) while in reversed phase TLC mixtures of acetonitrile with triethylammonium phosphate buffer were found successful for resolution of diastereomers. The separation behavior of diastereomers prepared with different reagents was compared. The diastereomers of most of the amino acids prepared with FDNP-L-Leu-NH(2) were best separated while those prepared with FDNP-L-Pro-NH(2) failed to separate in most of the cases. The diastereomers were also separated on a reversed phase C(8) column with gradient elution using mixture of aqueous-trifluoroacetic acid (TFA) and acetonitrile and with detection at 340 nm. The effects of TFA concentration, flow rate and run time on HPLC separation were studied. PMID:18612776

Bhushan, R; Kumar, Virender; Tanwar, Shivani

2008-07-09

21

Asymmetric synthesis of alpha-amino acids: preparation and alkylation of monocyclic iminolactones derived from alpha-methyl trans-cinnamaldehyde.  

PubMed

Two novel chiral monocyclic iminolactones 14a and 14b have been prepared. The chiral auxiliary 12 was obtained from alpha-methyl-trans-cinnamaldehyde through reduction, methylation, Sharpless asymmetric dihydroxylation, and oxidation in 87% overall yield. Esterification of compound 12 with the respective protected amino acids followed by deprotection and cyclization provided the corresponding iminolactones, each in 82% overall yield. Alkylation of the iminolactone 14a afforded the alpha-methyl-alpha,alpha-disubstituted products 15 and 16 in good yields (78-99%) and excellent diastereoselectivity (de >98%). Alkylations of the iminolactone 14b furnished the alpha-benzyl-alpha,alpha-disubstituted products 15a, 16b, 17, and 18 in good yields (51-86%) but moderate diastereoselectivities (43-56%). When HMPA or DMPU was used as a cosolvent, the rate of alkylation of the iminolactone 14b was accelerated with improved yields (56-99%) and diastereoselectivities (50-83%). Hydrolysis of the dialkylated iminolactones yielded the alpha,alpha-disubstituted alpha-amino acids in good yields (80-98%) and high enantiomeric excesses (98-99%) with good recovery of compound 12 (83-92%). PMID:18783273

Lu, Ta-Jung; Lin, Cheng-Kun

2008-12-19

22

Iron-bleomycin-deoxyribonucleic acid system. Evidence of deoxyribonucleic acid interaction with the alpha-amino group of the beta-aminoalanine moiety.  

PubMed

The Fe(III) complex of bleomycin (BLM) is, at pH 4, in the high-spin form. At pH 7, the coordination of the alpha-amino group of the beta-aminoalanine moiety of BLM converts it to a low-spin species: BLM X Fe(III) X alpha NH2. The conversion of the high-spin species to the low-spin one can also take place at pH 4 (i) by addition of ligands L such as N3-, S2O3(2-), and SCN- or (ii) through interaction with DNA. Moreover, the addition, at pH 7, of DNA to BLM X Fe(III) that has been previously complexed with one of these ligands L displaces this latter from its position. These results suggest that (i) the ligand L occupies the same site of coordination as the alpha-amino group and (ii) an interaction occurs between the beta-aminoalanine moiety of BLM and DNA that lowers the pKd of the alpha-amino group, promoting its coordination to iron. PMID:6197995

Albertini, J P; Garnier-Suillerot, A

1984-01-01

23

Synthesis and characterization of a lipidic alpha amino acid: solubility and interaction with serum albumin and lipid bilayers.  

PubMed

The lipidic ?-amino acid with 11 carbons in the alkyl lateral chain (?-aminotridecanoic acid) was synthesized via multicomponent hydroformylation/Strecker reaction, which is a greener synthetic approach to promote this transformation relative to previously described methods. Its solubility and aggregation behavior in aqueous solutions was characterized, as well as the interaction with lipid bilayers. Lipidic amino acids are very promising molecules in the development of prodrugs with increased bioavailability due to the presence of the two polar functional groups and nonpolar alkyl chain. They are also biocompatible surfactants that may be used in the food and pharmaceutical industry. In this work we have conjugated the lipidic amino acid with a fluorescent polar group (7-nitrobenz-2-oxa-1,3-diazol-4-yl), to mimic drug conjugates, and its association with serum proteins and lipid bilayers was characterized. The results obtained indicate that conjugates of polar molecules with lipidic ?-amino acid, via covalent attachment to the amine group, have a relatively high solubility in aqueous solutions due to their negative global charge. They bind to serum albumin with intermediate affinity and show a very high partition coefficient into lipid bilayers in the liquid-disordered state. The attachment of the polar group to the lipidic amino acid increased strongly the aqueous solubility of the amphiphile, although the partition coefficient into lipid membranes was not significantly reduced. Conjugation of polar drugs with lipidic amino acids is therefore an efficient approach to increase their affinity for biomembranes. PMID:23477590

Filipe, Hugo A L; Coreta-Gomes, Filipe M; Velazquez-Campoy, Adrian; Almeida, Ana R; Peixoto, Andreia F; Pereira, Mariette M; Vaz, Winchil L C; Moreno, Maria J

2013-03-26

24

Glutamate regulates intracellular calcium and gene expression in oligodendrocyte progenitors through the activation of DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors.  

PubMed Central

Oligodendrocytes and their progenitors (O-2A) express functional kainate- and DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-preferring glutamate receptors. The physiological consequences of activation of these receptors were studied in purified rat cortical O-2A progenitors and in the primary oligodendrocyte cell line CG-4. Changes in the mRNA levels of a set of immediate early genes were studied and were correlated to intracellular Ca2+ concentration, as measured by fura-2 Ca2+ imaging. Both in CG-4 and in cortical O-2A progenitors, basal mRNA levels of NGFI-A were much higher than c-fos, c-jun, or jun-b. Glutamate, kainate, and AMPA greatly increased NGFI-A mRNA and protein by activation of membrane receptors in a Ca(2+)-dependent fashion. Agonists at non-N-methyl-D-aspartate receptors promoted transmembrane Ca2+ influx through voltage-dependent channels as well as kainate and/or AMPA channels. The influx of Ca2+ ions occurring through glutamate-gated channels was sufficient by itself to increase the expression of NGFI-A mRNA. AMPA receptors were found to be directly involved in intracellular Ca2+ and NGFI-A mRNA regulation, because the effects of kainate were greatly enhanced by cyclothiazide, an allosteric modulator that selectively suppresses desensitization of AMPA but not kainate receptors. Our results indicate that glutamate acting at AMPA receptors regulates immediate early gene expression in cells of the oligodendrocyte lineage by increasing intracellular calcium. Consequently, modulation of these receptor channels may have immediate effects at the genomic level and regulate oligodendrocyte development at critical stages. Images

Pende, M; Holtzclaw, L A; Curtis, J L; Russell, J T; Gallo, V

1994-01-01

25

Dehydration of (R)-2-hydroxyacyl-CoA to enoyl-CoA in the fermentation of alpha-amino acids by anaerobic bacteria.  

PubMed

Several clostridia and fusobacteria ferment alpha-amino acids via (R)-2-hydroxyacyl-CoA, which is dehydrated to enoyl-CoA by syn-elimination. This reaction is of great mechanistic interest, since the beta-hydrogen, to be eliminated as proton, is not activated (pK 40-50). A mechanism has been proposed, in which one high-energy electron acts as cofactor and transiently reduces the electrophilic thiol ester carbonyl to a nucleophilic ketyl radical anion. The 2-hydroxyacyl-CoA dehydratases are two-component systems composed of an extremely oxygen-sensitive component A, an activator, and component D, the actual dehydratase. Component A, a homodimer with one [4Fe-4S]cluster, transfers an electron to component D, a heterodimer with 1-2 [4Fe-4S]clusters and FMN, concomitant with hydrolysis of two ATP. From component D the electron is further transferred to the substrate, where it facilitates elimination of the hydroxyl group. In the resulting enoxyradical the beta-hydrogen is activated (pK14). After elimination the electron is handed-over to the next incoming substrate without further hydrolysis of ATP. The helix-cluster-helix architecture of component A forms an angle of 105 degrees, which probably opens to 180 degrees upon binding of ATP resembling an archer shooting arrows. Therefore we designated component A as 'Archerase'. Here, we describe 2-hydroxyglutaryl-CoA dehydratase from Acidaminococcus fermentans, Clostridium symbiosum and Fusobacterium nucleatum, 2-phenyllactate dehydratase from Clostridium sporogenes, 2-hydroxyisocaproyl-CoA dehydratase from Clostridium difficile, and lactyl-CoA dehydratase from Clostridium propionicum. A relative of the 2-hydroxyacyl-CoA dehydratases is benzoyl-CoA reductase from Thauera aromatica. Analogous but unrelated archerases are the iron proteins of nitrogenase and bacterial protochlorophyllide reductase. In anaerobic organisms, which do not oxidize 2-oxo acids, a second energy-driven electron transfer from NADH to ferredoxin, the electron donor of component A, has been established. The transfer is catalysed by a membrane-bound NADH-ferredoxin oxidoreductase driven by an electrochemical Na(+)-gradient. This enzyme is related to the Rnf proteins involved in Rhodobacter capsulatus nitrogen fixation. PMID:15374661

Kim, Jihoe; Hetzel, Marc; Boiangiu, Clara Dana; Buckel, Wolfgang

2004-10-01

26

Positive modulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors in prefrontal cortical pyramidal neurons by a novel allosteric potentiator.  

PubMed

Positive modulators of glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors can enhance cognitive function in several species. The present experiments compared the actions of a novel biarylpropylsulfonamide compound, LY404187, with the prototypical benzoylpiperidine, 1-(quinoxalin-6-ylcarbonyl)-piperidine (CX516), on AMPA receptors of prefrontal cortex (PFC) pyramidal neurons. LY404187 (0.03-10 microM) selectively enhanced glutamate-evoked currents through AMPA receptor/channels of acutely isolated pyramidal neurons with considerably greater potency (EC50 = 1.3 +/- 0.3 microM) and efficacy (Emax = 45.3 +/- 8.0-fold increase) than did CX516 (EC50 = 2.8 +/- 0.9 mM; Emax = 4.8 +/- 1.4-fold increase). Both LY404187 and CX516 increased the potency of the glutamate concentration-response profile by 6- and 3-fold, respectively. Rapid perfusion experiments demonstrated that LY404187 produced a marked suppression in the magnitude but no change in the kinetics of receptor desensitization; whereas CX516 produced little change in the degree and a modest deceleration of the desensitization process. In PFC slices, both spontaneous and stimulus-evoked AMPA receptor-mediated excitatory postsynaptic potentials were enhanced by nanomolar concentrations of LY404187. Voltage-sensitive N-methyl-D-aspartate (NMDA) receptor-dependent synaptic responses also were indirectly augmented as a consequence of greater postsynaptic depolarization. Consistent with the in vitro data, LY404187 was 1000-fold more potent than CX516 in enhancing the probability of discharge of PFC neurons in response to stimulation of glutamatergic afferents from hippocampus in vivo. This potentiation by LY404187 was reduced by both selective AMPA (LY300168, 1 mg/kg, i.v.) and NMDA (LY235959, 5 mg/kg, i.v.) receptor antagonists. Collectively, these results demonstrate that LY404187 is an extremely potent and centrally active potentiator of native AMPA receptors and has a unique mechanism of action. The therapeutic implications of AMPA receptor potentiators are discussed. PMID:11408529

Baumbarger, P J; Muhlhauser, M; Zhai, J; Yang, C R; Nisenbaum, E S

2001-07-01

27

Coordination of biologically important alpha-amino acids to calcium(II) at high pH: insights from crystal structures of calcium alpha-aminocarboxylates.  

PubMed

A series of calcium alpha-aminocarboxylates was prepared by refluxing aqueous solutions/suspensions of calcium hydroxide and the respective alpha-amino acid. The colorless, crystalline hydrates Ca(gly)2.H2O (1), Ca(ala)2.3H2O (2), Ca(val)2.H2O (3), Ca(leu)2.3H2O (4), Ca(met)2.nH2O (5, n approximately 2), and Ca(pro)2.H2O (6) have been isolated in yields between 29 and 67% (gly- = glycinate, ala- = rac-alaninate, val- = rac-valinate, leu- = rac-leucinate, met- = rac-methioninate, pro- = rac-prolinate). The compounds 1-6 are readily soluble in water. The 0.10 M solutions have ca. pH 10-11 which is consistent with a noticeable degree of dissociation. The 13C NMR spectra of 1-6 in D2O were measured, and their comparison with those of the corresponding tetramethylammonium alpha-aminocarboxylates point to carboxylate coordination in solution, but no indication of nitrogen coordination was found. Infrared spectra of 1-6 gave similar results for the solid state. Complete single-crystal X-ray structure analyses of 1-4 and preliminary ones of 5 and 6, however, revealed that all aminocarboxylate ligands are N,O-chelating. Crystals of 2 consist of mononuclear complexes, while the other five compounds form three different types of one-dimensional coordination polymers. Structural diversity is also observed with the binding modes of the aminocarboxylate ligands and the calcium environment. Besides terminal aminocarboxylate coordination, there are three different types of aminocarboxylate bridges. The calcium ions are seven- or eight-coordinate in N2O5 and N2O6 coordination environments, respectively; one or three water molecules are part of the first ligand sphere of each metal ion. The crystal structures support conjectures about the existence of the yet undetected solution species [Cax(aa)2x(H2O)n] (aa- = alpha-aminocarboxylate). For example, x = 1 is realized in crystalline [Ca(ala)2(H2O)3] (2), and in 4 [Ca2(leu)4(H2O)4] complexes (x = 2) are linked to infinite chains by bridging aqua ligands. PMID:17257025

Fox, Stefan; Büsching, Insa; Barklage, Walter; Strasdeit, Henry

2007-02-01

28

Molecular cloning and expression of the hyu genes from Microbacterium liquefaciens AJ 3912, responsible for the conversion of 5-substituted hydantoins to alpha-amino acids, in Escherichia coli.  

PubMed

A DNA fragment from Microbacterium liquefaciens AJ 3912, containing the genes responsible for the conversion of 5-substituted-hydantoins to alpha-amino acids, was cloned in Escherichia coli and sequenced. Seven open reading frames (hyuP, hyuA, hyuH, hyuC, ORF1, ORF2, and ORF3) were identified on the 7.5 kb fragment. The deduced amino acid sequence encoded by the hyuA gene included the N-terminal amino acid sequence of the hydantoin racemase from M. liquefaciens AJ 3912. The hyuA, hyuH, and hyuC genes were heterologously expressed in E. coli; their presence corresponded with the detection of hydantoin racemase, hydantoinase, and N-carbamoyl alpha-amino acid amido hydrolase enzymatic activities respectively. The deduced amino acid sequences of hyuP were similar to those of the allantoin (5-ureido-hydantoin) permease from Saccharomyces cerevisiae, suggesting that hyuP protein might function as a hydantoin transporter. PMID:16116274

Suzuki, Shun'ichi; Takenaka, Yasuhiro; Onishi, Norimasa; Yokozeki, Kenzo

2005-08-01

29

Contributions of the histidine side chain and the N-terminal alpha-amino group to the binding thermodynamics of oligopeptides to nucleic acids as a function of pH.  

PubMed

Interactions of histidine with nucleic acid phosphates and histidine pK(a) shifts make important contributions to many protein-nucleic acid binding processes. To characterize these phenomena in simplified systems, we quantified binding of a histidine-containing model peptide HWKK ((+)NH(3)-His-Trp-Lys-Lys-NH(2)) and its lysine analogue KWKK ((+)NH(3)-Lys-Trp-Lys-Lys-NH(2)) to a single-stranded RNA model, polyuridylate (polyU), by changes in tryptophan fluorescence as a function of salt concentration and pH. For both HWKK and KWKK, equilibrium binding constants, K(obs), and magnitudes of log-log salt derivatives, SK(obs) identical with (partial differential logK(obs)/partial differential log[Na(+)]), decreased with increasing pH in the manner expected for a titration curve model in which deprotonation of the histidine and alpha-amino groups weakens binding and reduces its salt-dependence. Fully protonated HWKK and KWKK exhibit the same K(obs) and SK(obs) within uncertainty, and these SK(obs) values are consistent with limiting-law polyelectrolyte theory for +4 cationic oligopeptides binding to single-stranded nucleic acids. The pH-dependence of HWKK binding to polyU provides no evidence for pK(a) shifts nor any requirement for histidine protonation, in stark contrast to the thermodynamics of coupled protonation often seen for these cationic residues in the context of native protein structure where histidine protonation satisfies specific interactions (e.g., salt-bridge formation) within highly complementary binding interfaces. The absence of pK(a) shifts in our studies indicates that additional Coulombic interactions across the nonspecific-binding interface between RNA and protonated histidine or the alpha-amino group are not sufficient to promote proton uptake for these oligopeptides. We present our findings in the context of hydration models for specific vs nonspecific nucleic acid binding. PMID:20108951

Ballin, Jeff D; Prevas, James P; Ross, Christina R; Toth, Eric A; Wilson, Gerald M; Record, M Thomas

2010-03-01

30

Determinants of antagonist binding at the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit, GluR-D. Role of the conserved arginine 507 and glutamate 727 residues.  

PubMed

Previous structural and mutagenesis studies indicate that the invariant alpha-amino and alpha-carboxyl groups of glutamate receptor agonists are engaged in polar interactions with oppositely charged, conserved arginine and glutamate residues in the ligand-binding domain of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor. To examine the role of these residues (R507 and E727 in the GluR-D subunit) in the discrimination between agonists and antagonists, we analyzed the ligand-binding properties of homomeric GluR-D and its soluble ligand-binding domain with mutations at these positions. Filter-binding assays using [3H]AMPA, an agonist, and [3H]Ro 48-8587, a high-affinity antagonist, as radioligands revealed that even a conservative mutation at R507 (R507K) resulted in the complete loss of both agonist and antagonist binding. In contrast, a negative charge at position 727 was necessary for agonist binding, whereas the isosteric mutation, E727Q, abolished all agonist binding but retained high-affinity binding for [3H]Ro 48-8587, displaceable by 7,8-dinitroquinoxaline-2,3-dione. Competition binding studies with antagonists representing different structural classes in combination with ligand docking experiments suggest that the role of E727 is antagonist-specific, ranging from no interaction to weak electrostatic interactions involving indirect and direct hydrogen bonding with the antagonist molecule. These results underline the importance of ion pair interaction with E727 for agonist activity and suggest that an interaction with R507, but not with E727, is essential for antagonist binding. PMID:12473122

Jouppila, Annukka; Pentikäinen, Olli T; Settimo, Luca; Nyrönen, Tommi; Haapalahti, Jukka-Pekka; Lampinen, Milla; Mottershead, David G; Johnson, Mark S; Keinänen, Kari

2002-12-01

31

Discrimination between agonists and antagonists by the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid-selective glutamate receptor. A mutation analysis of the ligand-binding domain of GluR-D subunit.  

PubMed

The crystal structures of the ligand-binding core of the agonist complexes of the glutamate receptor-B (GluR-B) subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-selective glutamate receptor indicate that the distal anionic group of agonist molecules are stabilized by interactions with an N-terminal region of an alpha-helix (helix F) in the lobe 2 ("domain 2," Armstrong, N., and Gouaux, E. (2000) Neuron 28, 165-181) of the two-lobed ligand-binding domain. We used site-directed mutagenesis to further analyze the role of this region in the recognition of both agonists and antagonists by the AMPA receptor. Wild-type and mutated versions of the ligand-binding domain of GluR-D were expressed in insect cells as secreted soluble polypeptides and subjected to binding assays using [(3)H]AMPA, an agonist, and [(3)H]Ro 48-8587 (9-imidazol-1-yl-8-nitro-2,3,5,6-tetrahydro[1,2,4]triazolo[1,5-c] quinazoline-2,5-dione), a high affinity AMPA receptor antagonist, as radioligands. Single alanine substitutions at residues Leu-672 and Thr-677 severely affected the affinities for all agonists, as seen in ligand competition assays, whereas similar mutations at residues Asp-673, Ser-674, Gly-675, Ser-676, and Lys-678 selectively affected the binding affinities of one or two of the agonists. In striking contrast, the binding affinities of [(3)H]Ro 48-8587 and of another competitive antagonist, 6,7-dinitroquinoxaline-2,3-dione, were not affected by any of these alanine mutations, suggesting the absence of critical side-chain interactions. Together with ligand docking experiments, our results indicate a selective engagement of the side chains of the helix F region in agonist binding, and suggest that conformational changes involving this region may play a critical role in receptor activation. PMID:12167621

Lampinen, Milla; Settimo, Luca; Pentikainen, Olli T; Jouppila, Annukka; Mottershead, David G; Johnson, Mark S; Keinanen, Kari

2002-08-07

32

Synthesis and anticonvulsant evaluation of N-Cbz-alpha-amino-N-alkoxysuccinimides.  

PubMed

In previous studies for the development of new anticonvulsants, we found that N-Cbz-alpha-amino-N-alkylsuccinimides exhibited significant anticonvulsant activities in the Maximal electroshock seizure (MES) and Pentylenetetrazole induced seizure (PTZ) tests, and also their anticonvulsant activities were dependent on the N-alkyl substituents existent in their structures. Based on these estimations, N-Cbz-alpha-amino-N-hydroxysuccinimide and various N-Cbz-alpha-amino-N-alkoxysuccinimides were prepared in order to develop more active anticonvulsants and to examine the effects of N-hydoxy or N-alkoxy groups on their anticonvulsant activities. The (R)- or (S)-N-Cbz-alpha-amino-N-hydroxysuccinimide and N-Cbz-alpha-amino-N-alkoxysuccinimides were prepared from the corresponding (R)- or (S)-N-Cbz-aspartic acid through the known synthetic procedures. Their anticonvulsant activities in the MES and PTZ test were evaluated. All of these compounds except 3a showed significant anticonvulsant activities against the PTZ test, but these compounds were not active in the MES test. The most active compound in the PTZ test was (R)-N-Cbz-alpha-amino-N-benzyloxysuccinimide (ED50=62.5 mg/kg). In addition, the anticonvulsant activities of these compounds were dependent on their N-substited groups. The order of anticonvulsant activity against the PTZ test, as judged from the ED50 values for (R) series was N-benzyloxy > N-hydroxy > N-isopropoxy > N-methoxy > N-ethoxy; for the (S) series N-ethoxy > N-benzyloxy > N-methoxy > N-isopropoxy. PMID:15089029

Byun, Aesun; Kim, Minjeong; Choi, Jongwon; Moon, Kyung Ho; Lee, Chung Kyu; Park, Minsoo

2004-03-01

33

Synthesis and anticonvulsant evaluations of N-cbz-alpha-amino-N-alkoxyglutarimides.  

PubMed

In our previous studies for the development of new anticonvulsant of broad spectrum, we found that N-cbz-alpha-aminoglutarimides showed significant anticonvulsant activities of broad spectrum enough to be recommended for the new anticonvulsants and their anticonvulsant activities were dependent on their imide substituent groups. Based on these results, various N-cbz-alpha-amino-N-alkoxyglutarimides, where the imide N-H was substituted with the hydroxy and alkoxy group, were prepared and evaluated for their anticonvulsant activities using the Maximal electroshock seizure (MES) and Pentylenetetrazole induced seizure (PTZ) tests and also the rotorod test. A series of (R) or (S)-N-cbz-alpha-amino-N-alkoxyglutarimides could be prepared from the corresponding (R) or (S)-N-cbz-glutamic acid following the usual synthetic procedure. Among them, (R)-N-cbz-alpha-amino-N-hydroxyglutarimide (ED50=86.25 mg/kg) was most active in the MES test. In the case of the PTZ test, (R)-N-cbz-alpha-amino-N-benzyloxyglutarimide (ED50=62.5 mg/kg) was most active. Among the tested compounds, 2a-c, 3a, and 3b showed anticonvulsant activities in the MES and PTZ test. All of the tested compounds, except 2f and 3f, showed significant anticonvulsant activities in the MES or PTZ test. In addition, the neurotoxicities of these compounds were comparable to other anticonvulsant drugs. PMID:15022714

Kim, Minjeong; Byun, Aesun; Choi, Jongwon; Moon, Kyung Ho; Lee, Chung Kyu; Park, Minsoo

2004-02-01

34

Conformational choices for the stereochemically constrained gamma-amino acid residue gabapentin: theoretical studies and correlation with experimental results.  

PubMed

Gabapentin (1-aminomethylcyclohexaneacetic acid, Gpn) is an achiral, conformationally constrained gamma amino acid residue. A survey of available crystal structures of Gpn peptides reveals that the torsion angles about the C(gamma)-C(beta) (theta(1)) and C(beta)-C(alpha) (theta(2)) bonds are overwhelmingly limited to gauche, gauche (g(+)g(+)/g(-)g(-)) conformations. The Gpn residue forms C(7) and C(9) hydrogen bonds in which the donor and acceptor atoms come from the flanking peptide units. In combination with alpha amino acid residues alphagamma and gammaalpha segments can adopt C(12) hydrogen bonded structures. The conformational choices available to the Gpn residue have been probed using energy calculations, adopting a grid search strategy. Ramachandran phi-psi maps have been constructed for fixed values of theta(1) and theta(2), corresponding to the gauche and trans conformations. The sterically allowed and energetically favorable regions of conformational space have been defined and experimental observations compared. C(7) and C(9) hydrogen bonded conformational families have been identified using a grid search approach in which theta(1) and theta(2) values are varied over a range of +/-10 degrees about ideal values at 1 degrees intervals. The theoretical analysis together with experimental observations for 59 Gpn residues from 35 crystal structures permits definition of the limited range of conformational possibilities at this gamma amino acid residue. PMID:19384987

Vasudev, Prema G; Chatterjee, Sunanda; Ramakrishnan, Chandrasekharan; Shamala, Narayanaswamy; Balaram, Padmanabhan

2009-01-01

35

Hybrid peptide design. Hydrogen bonded conformations in peptides containing the stereochemically constrained gamma-amino acid residue, gabapentin.  

PubMed

The crystal structure of 12 peptides containing the conformationally constrained 1-(aminomethyl)cyclohexaneacetic acid, gabapentin (Gpn), are reported. In all the 39 Gpn residues conformationally characterized so far, the torsion angles about the Calpha-Cbeta and Cbeta-Cgamma bonds are restricted to the gauche conformation (+/-60 degrees ). The Gpn residue is constrained to adopt folded conformations resulting in the formation of intramolecularly hydrogen-bonded structures even in short peptides. The peptides Boc-Ac6c-Gpn-OMe 1 and Boc-Gpn-Aib-Gpn-Aib-OMe 2 provide examples of C7 conformation; peptides Boc-Gpn-Aib-OH 3, Boc-Ac6c-Gpn-OH 4, Boc-Val-Pro-Gpn-OH 5, Piv-Pro-Gpn-Val-OMe 6, and Boc-Gpn-Gpn-Leu-OMe 7 provide examples of C9 conformation; peptide Boc-Ala-Aib-Gpn-Aib-Ala-OMe 8 provides an example of C12 conformation and peptides Boc-betaLeu-Gpn-Val-OMe 9 and Boc-betaPhe-Gpn-Phe-OMe 10 provide examples of C13 conformation. Gpn peptides provide examples of backbone expanded mimetics for canonical alpha-peptide turns like the gamma (C7) and the beta (C10) turns. The hybrid betagamma sequences provide an example of a mimetic of the C13 alpha-turn formed by three contiguous alpha-amino acid residues. Two examples of folded tripeptide structures, Boc-Gpn-betaPhe-Leu-OMe 11 and Boc-Aib-Gpn-betaPhg-NHMe 12, lacking internal hydrogen bonds are also presented. An analysis of available Gpn residue conformations provides the basis for future design of folded hybrid peptides. PMID:17348653

Vasudev, Prema G; Ananda, Kuppanna; Chatterjee, Sunanda; Aravinda, Subrayashastry; Shamala, Narayanaswamy; Balaram, Padmanabhan

2007-03-10

36

Hybrid polypeptides: gabapentin as a stereochemically constrained ?-amino acid residue.  

PubMed

The design of folded structures in peptides containing the higher homologues of ?-amino acid residues requires the restriction of the range of local conformational choices. In ?-amino acids stereochemically constrained residues like ?,?-dialkylated residue, aminoisobutyric acid (Aib), and D-Proline ((D)Pro) have proved extremely useful in the design of helices and hairpins in short peptides. Extending this approach, backbone substitution and cyclization are anticipated to be useful in generating conformationally constrained ?- and ?-residues. This brief review provides a survey of work on hybrid peptide sequences concerning the conformationally constrained ?-amino acid residue 1-aminomethyl cyclohexane acetic acid, gabapentin (Gpn). This achiral, ?,?-disubstituted, ?-residue strongly favors gauche-gauche conformations about the C(?)-C(?) (?(2)) and C(?)-C(?) (?(1)) bonds, facilitating local folding. The Gpn residue can adopt both C(7) (NH(i)?CO(i)) and C(9) (CO(i-1)?NH(i+1)) hydrogen bonds which are analogous to the C(5) and C(7) (?-turn) conformations at ?-residues. In conjunction with adjacent residues, Gpn may be used in ?? and ?? segments to generate C(12) hydrogen bonded conformations which may be considered as expanded analogs of conventional ?-turns. The structural characterization of C(12) helices, C(12)/C(10) helices with mixed hydrogen bond directionalities and ?-hairpins incorporating Gpn residues at the turn segment is illustrated. PMID:20564041

Balaram, Padmanabhan

2010-01-01

37

Highly selective addition of chiral, sulfonimidoyl substituted bis(allyl)titanium complexes to N-sulfonyl alpha-imino esters: asymmetric synthesis of gamma,delta-unsaturated alpha-amino acids bearing a chiral, electron-withdrawing nucleofuge at the delta-position.  

PubMed

Selective addition of the chiral, sulfonimidoyl substituted bis(allyl)titanium complexes 5a-d, which are configurationally labile in regard to the Calpha-atoms, to N-toluenesulfonyl (Ts)-, N-2-trimethylsilylethanesulfonyl (SES)-, and N-tert-butylsulfonyl (Bus) alpha-imino ester (9a-c) in the presence of Ti(OiPr)(4) and ClTi(OiPr)(3) afforded with high regio- and diastereoselectivities in good yields the (syn, E)-configured beta-alkyl-gamma,delta-unsaturated alpha-amino acid derivatives 2a-g, which carry a chiral, electron-withdrawing nucleofuge at the delta-position and a cyclohexyl, an isopropyl, a phenyl, and a methyl group at the beta-position. Addition of the cyclic bis(allyl)titanium complex 14 to N-Bus alpha-imino ester 9c afforded with similar high regio- and diastereoselectivities the (E)- and (Z)-configured amino acid derivatives (E)-8 and (Z)-8. Reaction of complexes 5a-d with alpha-imino esters 9a-c in the presence of Ti(OiPr)(4) occurs stepwise to give first the mono(allyl)titanium complexes containing 2a-g as ligands, which react in the presence of ClTi(OiPr)(3) with a second molecule of 9a-c with formation of two molecules of 2a-g. Formation of (S,R,E)-configured homoallylic amines 2a-g entails Si,Re,E processes of alpha-imino esters 9a-c with the (R,R)-configured bis(allyl)titanium complexes (R,R)-5a-d and (R)-configured mono(allyl)titanium complexes (R)-17a-d, both of which are most likely in rapid equilibrium with their (S,S)-diastereomers and (S)-diastereomers, respectively. Interestingly, in the reaction of 5a-d with aldehydes, the (S,S)-configured complexes (S,S)-5a-d are the ones which react faster. Reaction of the N-titanated amino acid derivatives Ti-2a and Ti-2b with N-Ts alpha-imino ester 9a led to the highly diastereoselective formation of imidazolidinones 15a and 15b, respectively. Cleavage of the sulfonamide group of the N-Bus amino acid derivative 2d with CF(3)SO(3)H gave quantitatively the sulfonimidoyl functionalized amino acid H-2d. A Ni-catalyzed cross-coupling reaction of the amino acid derivative 2e with ZnPh(2) led to a substitution of the sulfonimidoyl group by a phenyl group and furnished the enantiomerically pure protected alpha-amino acid Bus-1. Two new N-sulfonyl alpha-imino esters, the SES and the Bus alpha-imino esters 9b and 9c, respectively, have been synthesized from the corresponding sulfonamides by the Kresze method in medium to good yields. The N-SES alpha-imino ester 9b and the N-Bus alpha-imino ester 9c should find many synthetic applications, in particular, in cases where the N-Ts alpha-imino ester 9a had been used before. PMID:12083933

Schleusner, Marcel; Gais, Hans-Joachim; Koep, Stefan; Raabe, Gerhard

2002-07-01

38

Structure of subtilosin A, a cyclic antimicrobial peptide from Bacillus subtilis with unusual sulfur to alpha-carbon cross-links: formation and reduction of alpha-thio-alpha-amino acid derivatives.  

PubMed

The complete primary and three-dimensional solution structures of subtilosin A (1), a bacteriocin from Bacillus subtilis, were determined by multidimensional NMR studies on peptide produced using isotopically labeled [(13)C,(15)N]medium derived from Anabaena sp. grown on sodium [(13)C]bicarbonate and [(15)N]nitrate. Additional samples of 1 were also generated by separate incorporations of [U-(13)C,(15)N]-L-phenylalanine and [U-(13)C,(15)N]-L-threonine using otherwise unlabeled media. The results demonstrate that in addition to having a cyclized peptide backbone (amide between N and C termini), three cross-links are formed between the sulfurs of Cys13, Cys7, and Cys4 and the alpha-positions of Phe22, Thr28, and Phe31, respectively. The stereochemistry of all residues in 1 except for the three modified ones was confirmed to be L by complete desulfurization with nickel boride, acid hydrolysis to the constituent amino acids, and conversion of these to the corresponding pentafluoropropanamide isopropyl esters for chiral GC MS analysis. The stereochemistry at the modified residues was determined by subjecting each of the eight possible stereoisomers of 1 to eight rounds of ARIA structure calculations, starting with the same NMR peak files and assignments. The stereoisomer with the l stereochemistry at Phe22 (alpha-R) and d stereochemistry at Thr28 (alpha-S) and Phe31 (alpha-S) (LDD isomer) fit the NMR data, giving the lowest energy family of structures with the best rmsd. Thus, biochemical formation of the unusual thio links proceeds with net retention of configuration at Phe22, and inversion at Thr28 and Phe31. Model amino acid derivatives bearing a sulfide moiety at the alpha-carbon were synthesized by reaction of the corresponding alpha-alkoxy compounds with benzyl thiol and SnCl(4). Separation of their pure stereoisomers and desulfurization with nickel boride demonstrated that the reduction of such compounds proceeds with epimerization, in contrast to the previously reported retention of stereochemistry for analogous reaction of steroidal sulfides. However, desulfurization of subtilosin A to cyclic peptide 14, which is inactive as an antimicrobial agent, occurs with inversion of stereochemistry at the alpha-carbons of Phe22 and Thr28 and with 4:1 retention at Phe31. This indicates that the desulfurization reaction proceeds via an N-acyl imine and that the structure of the surrounding peptide controls the geometry of reduction. Posttranslational linkage of a thiol to the alpha-carbon of an amino acid residue is unprecedented in ribosomally synthesized peptides or proteins, and very rare in secondary metabolites. Subtilosin A (1) represents a new class of bacteriocins. PMID:15035610

Kawulka, Karen E; Sprules, Tara; Diaper, Christopher M; Whittal, Randy M; McKay, Ryan T; Mercier, Pascal; Zuber, Peter; Vederas, John C

2004-03-30

39

Minimal genome encoding proteins with constrained amino acid repertoire  

PubMed Central

Minimal bacterial gene set comprises the genetic elements needed for survival of engineered bacterium on a rich medium. This set is estimated to include 300–350 protein-coding genes. One way of simplifying an organism with such a minimal genome even further is to constrain the amino acid content of its proteins. In this study, comparative genomics approaches and the results of gene knockout experiments were used to extrapolate the minimal gene set of mollicutes, and bioinformatics combined with the knowledge-based analysis of the structure-function relationships in these proteins and their orthologs, paralogs and analogs was applied to examine the challenges of completely replacing the rarest residue, cysteine. Among several known functions of cysteine residues, their roles in the active centers of the enzymes responsible for deoxyribonucleoside synthesis and transfer RNA modification appear to be crucial, as no alternative chemistry is known for these reactions. Thus, drastic reduction of the content of the rarest amino acid in a minimal proteome appears to be possible, but its complete elimination is challenging.

Tsoy, Olga; Yurieva, Marina; Kucharavy, Andrey; O'Reilly, Mary; Mushegian, Arcady

2013-01-01

40

Betidamino acids: versatile and constrained scaffolds for drug discovery.  

PubMed Central

Betidamino acids (a contraction of "beta" position and "amide") are N'-monoacylated (optionally, N'-monoacylated and N-mono- or N,N'-dialkylated) aminoglycine derivatives in which each N'acyl/alkyl group may mimic naturally occurring amino acid side chains or introduce novel functionalities. Betidamino acids are most conveniently generated on solid supports used for the synthesis of peptides by selective acylation of one of the two amino functions of orthogonally protected aminoglycine(s) to generate the side chain either prior to or after the elongation of the main chain. We have used unresolved Nalpha-tert-butyloxycarbonyl-N'alpha-fluorenylmethoxycarbonyl++ + aminoglycine, and Nalpha-(Nalpha-methyl)-tert-butyloxycarbonyl-N'alpha-fluo renylmethoxycarbonyl aminoglycine as the templates for the introduction of betidamino acids in Acyline [Ac-D2Nal-D4Cpa-D3Pal-Ser-4Aph(Ac)-D4Aph(A c)-Leu-Ilys-Pro-DAla-NH2, where 2Nal is 2-naphthylalanine, 4Cpa is 4-chlorophenylalanine, 3Pal is 3-pyridylalanine, Aph is 4-aminophenylalanine, and Ilys is Nepsilon-isopropyllysine], a potent gonadotropin-releasing hormone antagonist, in order to test biocompatibility of these derivatives. Diasteremneric peptides could be separated in most cases by reverse-phase HPLC. Biological results indicated small differences in relative potencies (<5-fold) between the D and L nonalkylated betidamino acid-containing Acyline derivatives. Importantly, most betide diastereomers were equipotent with Acyline. In an attempt to correlate structure and observed potency, Ramachandran-type plots were calculated for a series of betidamino acids and their methylated homologs. According to these calculations, betidamino acids have access to a more limited and distinct number of conformational states (including those associated with alpha-helices, beta-sheets, or turn structures), with deeper minima than those observed for natural amino acids.

Rivier, J E; Jiang, G; Koerber, S C; Porter, J; Simon, L; Craig, A G; Hoeger, C A

1996-01-01

41

Phosphorus constrains accelerated nitrogen cycling in limed acidic forests  

NASA Astrophysics Data System (ADS)

Anthropogenic deposition can increase phosphorus (P) limitation by abiotic and biotic means. Soil acidification can remove P from available pools and nitrogen (N) deposition can increase the demand for P. We reason that chronic acidic deposition is promoting P limitation in acidic hardwood forests and thereby altering N cycling. The objectives of this study were to investigate the interactive influence of P availability and soil pH on N and P cycling and availability to determine if the response varies between two physiographic regions experiencing similar chronic acidic deposition. We addressed these objectives by experimentally manipulating soil pH, P, or both in strongly acidic glaciated and unglaciated hardwood forests in eastern Ohio, USA. Our results suggest complex interactions between P, soil pH, and the N cycle. Glaciated soils were found to be more N-saturated with nitrification rates 18 times greater than in unglaciated soils. Elevating pH, with or without added P, doubled nitrification rates in glaciated soils. For unglaciated soils, raising pH increased nitrification 10-fold, but increased nitrification only 5-fold in combination with P. This result suggests raising soil pH lowered the demand of soil N, or directly stimulated nitrifying activity, and that increasing P availability could limit N availability. To various degrees, readily available P was geochemically or biologically immobilized in all treatments, suggesting chronic P deficiency in these ecosystems. Phosphorus immobilization decreased as soil pH was elevated, but elevated P either had no effect (glaciated) or doubled P immobilization rates (unglaciated). These results suggest that raising soil pH reduces microbial P limitation for phosphate, whereas adding P appears to make phosphate scarcer. We suggest that P plays an important role in N transformations and cycling, but appears more important in unglaciated soils than in glaciated soils. Chronic soil acidification may have a greater impact on P limitation than N deposition because P immobilization was not greater in relatively N-rich, glaciated soils. Thus, ecosystem responses to anthropogenic deposition will not be universal, but instead will be sensitive to initial biogeochemical conditions.

Deforest, J. L.; Shaw, A. N.; Kluber, L. A.; Burke, D. J.; Carrino-Kyker, S. R.; Smemo, K. A.

2011-12-01

42

Synthesis and preliminary biological evaluation of new alpha-amino amide anticonvulsants incorporating a dextromethorphan moiety.  

PubMed

Dextromethorphan 1 is an effective neuroprotectant in animal models of epilepsy and ischemia but showed side-effects during clinical trials limiting its potential use in a clinical setting. Here we describe the enantioselective and enantiospecific syntheses and the initial in vitro and in vivo biological evaluation of new hybrid structures between 1 and a previously disclosed alpha-amino amide anticonvulsant (3). PMID:10406642

Pevarello, P; Traquandi, G; Bonsignori, A; McArthur, R A; Maj, R; Caccia, C; Salvati, P; Varasi, M

1999-07-01

43

Oxygen Consumption Constrains Food Intake in Fish Fed Diets Varying in Essential Amino Acid Composition  

PubMed Central

Compromisation of food intake when confronted with diets deficient in essential amino acids is a common response of fish and other animals, but the underlying physiological factors are poorly understood. We hypothesize that oxygen consumption of fish is a possible physiological factor constraining food intake. To verify, we assessed the food intake and oxygen consumption of rainbow trout fed to satiation with diets which differed in essential amino acid (methionine and lysine) compositions: a balanced vs. an imbalanced amino acid diet. Both diets were tested at two water oxygen levels: hypoxia vs. normoxia. Trout consumed 29% less food under hypoxia compared to normoxia (p<0.001). Under both hypoxia and normoxia trout significantly reduced food intake by 11% and 16% respectively when fed the imbalanced compared to the balanced amino acid diet. Oxygen consumption of the trout per unit body mass remained identical for both diet groups not only under hypoxia but also under normoxia (p>0.05). This difference in food intake between diets under normoxia together with the identical oxygen consumption supports the hypothesis that food intake in fish can be constrained by a set-point value of oxygen consumption, as seen here on a six-week time scale.

Saravanan, Subramanian; Geurden, Inge; Figueiredo-Silva, A. Claudia; Nusantoro, Suluh; Kaushik, Sadasivam; Verreth, Johan; Schrama, Johan W.

2013-01-01

44

Constraining protein sequence space: four amino acid alphabets are sufficient to recapitulate lambda repressor multimerization.  

PubMed

Nucleic acid polymers selected from random sequence space constitute an enormous array of catalytic, diagnostic and therapeutic molecules. Despite the fact that proteins are robust polymers with far greater chemical and physical diversity, success in unlocking protein sequence space remains elusive. We have devised a combinatorial strategy for accessing nucleic acid sequence space corresponding to proteins comprising selected amino acid alphabets. Using the SynthOMIC approach (synthesis of ORFs by multimerizing in-frame codons), representative libraries comprising four amino acid alphabets were fused in-frame to the lambda repressor DNA-binding domain to provide an in vivo selection for self-interacting proteins that re-constitute lambda repressor function. The frequency of self-interactors as a function of amino acid composition ranged over five orders of magnitude, from approximately 6% of clones in a library comprising the amino acid residues LARE to approximately 0.6 in 10(6) in the MASH library. Sequence motifs were evident by inspection in many cases, and individual clones from each library presented substantial sequence identity with translated proteins by BLAST analysis. We posit that the SynthOMIC approach represents a powerful strategy for creating combinatorial libraries of open reading frames that distils protein sequence space on the basis of three inherent properties: it supports the use of selected amino acid alphabets, eliminates redundant sequences and locally constrains amino acids. PMID:17931656

Maillet, Daniel S; Drummond, James T

2007-09-12

45

Evaluation of the interaction of protein alpha-amino groups with M(II) by immobilized metal ion affinity chromatography.  

PubMed

The adsorption properties of various peptides and proteins, lacking histidyl groups, on immobilized Cu(II), Ni(II), Zn(II) and Co(II) ions are described; at pH 6 and below they were little retarded. At higher pH the retention became pronounced for iminodiacetate (IDA)-Cu(II) gel. This effect seems to be related to the presence of a terminal alpha-amino group; in the absence of this group the retention of the protein was largely eliminated. At pH 8.5 a terminal alpha-amino group is adsorbed as strongly as a histidyl group. IDA-Ni(II), IDA-Zn(II) and IDA-Co(II) gels display little or no attraction for the terminal alpha-amino group of a protein. PMID:1379250

Andersson, L; Sulkowski, E

1992-06-26

46

Inhibition of CO2 Combination and Reduction of the Bohr Effect in Haemoglobin chemically modified at its alpha-Amino Groups  

Microsoft Academic Search

Blocking of the alpha-amino groups by cyanate inhibits the uptake of CO2 by haemoglobin. It also inhibits the influence which changes in pCO2 at constant pH normally have on the oxygen affinity and on the Bohr effect. Blocking the alpha-amino groups of the alpha chain reduces the alkaline Bohr effect by 25 per cent.

J. V. Kilmartin; L. ROSSI-BERNARDI

1969-01-01

47

Reduction of Acute Alcoholic Intoxication by Alpha Amino Acids: Glycine and Serine.  

National Technical Information Service (NTIS)

The ability of glycine and of serine to protect rats from ethanol induced motor impairment was determined by pretreating the animals with these drugs, administering ethanol 30 minutes later, and evaluating the rats' performance on a rotor-rod test at 30 m...

K. Blum J. E. Wallace R. Friedman

1973-01-01

48

Dioxaphosphorinane-Constrained Nucleic Acid Dinucleotides as Tools for Structural Tuning of Nucleic Acids  

PubMed Central

We describe a rational approach devoted to modulate the sugar-phosphate backbone geometry of nucleic acids. Constraints were generated by connecting one oxygen of the phosphate group to a carbon of the sugar moiety. The so-called dioxaphosphorinane rings were introduced at key positions along the sugar-phosphate backbone allowing the control of the six-torsion angles ? to ? defining the polymer structure. The syntheses of all the members of the D-CNA family are described, and we emphasize the effect on secondary structure stabilization of a couple of diastereoisomers of ?,?-D-CNA exhibiting wether B-type canonical values or not.

Catana, Dan-Andrei; Renard, Brice-Loic; Maturano, Marie; Payrastre, Corinne; Tarrat, Nathalie; Escudier, Jean-Marc

2012-01-01

49

Synthesis and biophysical evaluation of 2',4'-constrained 2'O-methoxyethyl and 2',4'-constrained 2'O-ethyl nucleic acid analogues.  

PubMed

We have recently shown that combining the structural elements of 2'O-methoxyethyl (MOE) and locked nucleic acid (LNA) nucleosides yielded a series of nucleoside modifications (cMOE, 2',4'-constrained MOE; cEt, 2',4'-constrained ethyl) that display improved potency over MOE and an improved therapeutic index relative to that of LNA antisense oligonucleotides. In this report we present details regarding the synthesis of the cMOE and cEt nucleoside phosphoramidites and the biophysical evaluation of oligonucleotides containing these nucleoside modifications. The synthesis of the cMOE and cEt nucleoside phosphoramidites was efficiently accomplished starting from inexpensive commercially available diacetone allofuranose. The synthesis features the use of a seldom used 2-naphthylmethyl protecting group that provides crystalline intermediates during the synthesis and can be cleanly deprotected under mild conditions. The synthesis was greatly facilitated by the crystallinity of a key mono-TBDPS-protected diol intermediate. In the case of the cEt nucleosides, the introduction of the methyl group in either configuration was accomplished in a stereoselective manner. Ring closure of the 2'-hydroxyl group onto a secondary mesylate leaving group with clean inversion of stereochemistry was achieved under surprisingly mild conditions. For the S-cEt modification, the synthesis of all four (thymine, 5-methylcytosine, adenine, and guanine) nucleobase-modified phosphoramidites was accomplished on a multigram scale. Biophysical evaluation of the cMOE- and cEt-containing oligonucleotides revealed that they possess hybridization and mismatch discrimination attributes similar to those of LNA but greatly improved resistance to exonuclease digestion. PMID:20136157

Seth, Punit P; Vasquez, Guillermo; Allerson, Charles A; Berdeja, Andres; Gaus, Hans; Kinberger, Garth A; Prakash, Thazha P; Migawa, Michael T; Bhat, Balkrishen; Swayze, Eric E

2010-03-01

50

?,?-D-Constrained Nucleic Acids Are Strong Terminators of Thermostable DNA Polymerases in Polymerase Chain Reaction  

PubMed Central

(SC5?, RP) ?,?-D- Constrained Nucleic Acids (CNA) are dinucleotide building blocks that can feature either B-type torsional angle values or non-canonical values, depending on their 5?C and P absolute stereochemistry. These CNA are modified neither on the nucleobase nor on the sugar structure and therefore represent a new class of nucleotide with specific chemical and structural characteristics. They promote marked bending in a single stranded DNA so as to preorganize it into a loop-like structure, and they have been shown to induce rigidity within oligonucleotides. Following their synthesis, studies performed on CNA have only focused on the constraints that this family of nucleotides introduced into DNA. On the assumption that bending in a DNA template may produce a terminator structure, we investigated whether CNA could be used as a new strong terminator of polymerization in PCR. We therefore assessed the efficiency of CNA as a terminator in PCR, using triethylene glycol phosphate units as a control. Analyses were performed by denaturing gel electrophoresis and several PCR products were further analysed by sequencing. The results showed that the incorporation of only one CNA was always skipped by the polymerases tested. On the other hand, two CNA units always stopped proofreading polymerases, such as Pfu DNA polymerase, as expected for a strong replication terminator. Non-proofreading enzymes, e.g. Taq DNA polymerase, did not recognize this modification as a strong terminator although it was predominantly stopped by this structure. In conclusion, this first functional use of CNA units shows that these modified nucleotides can be used as novel polymerization terminators of proofreading polymerases. Furthermore, our results lead us to propose that CNA and their derivatives could be useful tools for investigating the behaviour of different classes of polymerases.

Maheo, Sabrina; Gross, Gregori; Bodin, Pierre; Teissie, Justin; Escudier, Jean-Marc; Paquereau, Laurent

2011-01-01

51

Characterization of renal tubular apical efflux of zonampanel, an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor antagonist, in humans.  

PubMed

1. Zonampanel, a novel alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor antagonist, is mainly excreted unchanged via renal tubular secretion. The renal apical transport transport of zonampanel was examined in this study using HEK293 cells expressing human organic anion transporter 4 (OAT4/SLC22A11), and membrane vesicles prepared from Sf-9 insect cells expressing human multidrug resistance-associated protein 2 (MRP2/ABCC2), MRP4 (ABCC4), and breast cancer resistance protein (BCRP/ABCG2). 2. Glutaric acid, a model dicarboxylate, trans-stimulated the uptake of [(14)C]zonampanel by OAT4, suggesting that zonampanel was transported by OAT4 via an exchange with dicarboxylate. Considering the endogenous dicarboxylate gradient, OAT4 seems to transport zonampanel in the direction of reabsorption rather than secretion. For MRP2, MRP4, and BCRP, zonampanel selectively inhibited the activity of MRP4 (K(i) = 41.3 microM). Marked transport of [(14)C]zonampanel was observed only for MRP4 (K(m) = 33.7 microM). 3. In conclusion, the data indicate that MRP4 was the apical efflux transporter that contributed to the active renal tubular secretion of zonampanel in humans, in concert with the apical reabsorption transporter OAT4 and basolateral uptake transporters. PMID:18609448

Minematsu, T; Hashimoto, T; Usui, T; Kamimura, H

2008-09-01

52

Synthesis of conformationally constrained ?-amino acid derivatives using ethyl isocyanoacetate as glycine equivalent  

Microsoft Academic Search

Some novel cyclic ?-amino acid derivatives are prepared under solid-liquid phase-transfer catalytic conditions. Some of these amino acids prepared here are not directly accessible by the known methods.

Sambasivarao Kotha; Enugurthi Brahmachary

1997-01-01

53

Transformation of some hydroxy amino acids to other amino acids.  

PubMed

It has been observed that beta-hydroxy-alpha-amino acids are transformed into other amino acids, when heated in dilute solutions with phosphorous acid, phosphoric acid or their ammonium salts. It has been shown that as in the case of previously reported glycine-aldehyde reactions, glycine also reacts with acetone to give beta-hydroxyvaline under prebiologically feasible conditions. It is suggested, therefore, that the formation of beta-hydroxy-alpha-amino acids and their transformation to other amino acids may have been a pathway for the synthesis of amino acids under primitive earth conditions. PMID:1208100

Choughuley, A S; Subbaraman, A S; Kazi, Z A; Chadha, M S

1975-10-01

54

Thiopeptide synthesis. {alpha}-amino thionoacid derivatives of nitrobenzotriazole as thioacylating agents  

SciTech Connect

There has been considerable interest recently in the synthesis and properties of thiopeptides in which the -CSNH- group replaces one or more peptide bonds. These modified peptides have demonstrated increased activity in vivo as biological response modifiers, neuro-effectors, and immunomodulators due to the stability of their thioamide bonds toward enzymatic degradation as compared to that of their oxygenated counterpart. Synthetic routes employed to prepare these thiopeptides included replacement of oxygen by sulfur using P{sub 4}S{sub 10} or Lawesson`s phosphetane disulfide reagent, and thioesters or dithioesters of N-protected amino acids. Several procedures also have been reported for monothionation of peptides using N-protected amino monothioacids and benzotriazolyloxytris(pyrrolidino) phosphonium hexafluorophosphate (PYBOP) and some of its derivatives. Unfortunately, these methods displayed lack of reaction site specificity, low yields and purity because of side reactions, and loss of enantiomeric integrity in the final product, apparently because of racemization induced by the thioacylating agents. Recently, major improvement was described for the site specific incorporation of thioamide linkages into a growing peptide under mild conditions using thioacylbenzimidazolinones of amino acid derivatives as thioacylating agents. This method proceeds with about 2% loss of enantiomeric purity, as demonstrated by HPLC analysis of the reaction product 10a, formed in reaction with {alpha}-methylbenzylamine. This procedure, although superior to previous methods, still suffers from the formation of benzimidazole 2 as a significant byproduct, and the overall yield for the four-step process was only about 20%. Furthermore, recent attempt to use this procedure failed due to the limited reactivity of the benzimidazolinone 4 as a thioacylating agent. To overcome these limitations, the authors have developed a new method for thiopeptide synthesis. 12 refs.

Shalaby, M.A.; Grote, C.W.; Rapoport, H. [Lawrence Berkeley National Lab., CA (United States)

1996-12-13

55

Gabapentin: a stereochemically constrained gamma amino acid residue in hybrid peptide design.  

PubMed

Nature has used the all-alpha-polypeptide backbone of proteins to create a remarkable diversity of folded structures. Sequential patterns of 20 distinct amino acids, which differ only in their side chains, determine the shape and form of proteins. Our understanding of these specific secondary structures is over half a century old and is based primarily on the fundamental elements: the Pauling alpha-helix and beta-sheet. Researchers can also generate structural diversity through the synthesis of polypeptide chains containing homologated (omega) amino acid residues, which contain a variable number of backbone atoms. However, incorporating amino acids with more atoms within the backbone introduces additional torsional freedom into the structure, which can complicate the structural analysis. Fortunately, gabapentin (Gpn), a readily available bulk drug, is an achiral beta,beta-disubstituted gamma amino acid residue that contains a cyclohexyl ring at the C(beta) carbon atom, which dramatically limits the range of torsion angles that can be obtained about the flanking C-C bonds. Limiting conformational flexibility also has the desirable effect of increasing peptide crystallinity, which permits unambiguous structural characterization by X-ray diffraction methods. This Account describes studies carried out in our laboratory that establish Gpn as a valuable residue in the design of specifically folded hybrid peptide structures. The insertion of additional atoms into polypeptide backbones facilitates the formation of intramolecular hydrogen bonds whose directionality is opposite to that observed in canonical alpha-peptide helices. If hybrid structures mimic proteins and biologically active peptides, the proteolytic stability conferred by unusual backbones can be a major advantage in the area of medicinal chemistry. We have demonstrated a variety of internally hydrogen-bonded structures in the solid state for Gpn-containing peptides, including the characterization of the C(7) and C(9) hydrogen bonds, which can lead to ribbons in homo-oligomeric sequences. In hybrid alphagamma sequences, distinct C(12) hydrogen-bonded turn structures support formation of peptide helices and hairpins in longer sequences. Some peptides that include the Gpn residue have hydrogen-bond directionality that matches alpha-peptide helices, while others have the opposite directionality. We expect that expansion of the polypeptide backbone will lead to new classes of foldamer structures, which are thus far unknown to the world of alpha-polypeptides. The diversity of internally hydrogen-bonded structures observed in hybrid sequences containing Gpn shows promise for the rational design of novel peptide structures incorporating hybrid backbones. PMID:19572698

Vasudev, Prema G; Chatterjee, Sunanda; Shamala, Narayanaswamy; Balaram, Padmanabhan

2009-10-20

56

Structure-based design of a highly constrained nucleic acid analogue: improved duplex stabilization by restricting sugar pucker and torsion angle ?.  

PubMed

Dual conformational restriction: a new, highly constrained modification of the ?-L-locked nucleic acid (?-L-LNA) scaffold that locks the sugar furanose ring in an N-type configuration and also restricts rotation around torsion angle ? was synthesized. This new modification increases the thermostability of an oligonucleotide duplex compared to using a single mode of constraint alone. PMID:22915274

Hanessian, Stephen; Schroeder, Benjamin R; Giacometti, Robert D; Merner, Bradley L; Ostergaard, Michael; Swayze, Eric E; Seth, Punit P

2012-08-22

57

Insertion of multiple alpha-amino gamma-lactam (Agl) residues into a peptide sequence by solid-phase synthesis on synphase lanterns.  

PubMed

The insertion of lactams into peptide analogs can enhance potency and improve receptor selectivity. The synthesis of lactam-bridged peptide sequences has been accomplished by a solid-phase approach on SynPhase lanterns using cyclic (R)- and (S)-oxathiazinane ester (2) to annulate the amino lactam residue onto the peptide chain. Parallel synthesis of alpha-amino gamma-lactam analogs of the allosteric modulator of IL-1 receptor 101.10 (D-Arg-D-Tyr-D-Thr-D-Val-D-Glu-D-Leu-D-Ala: rytvela) was performed by split-mix chemistry on the lanterns. In particular, the double insertion of alpha-amino gamma-lactams in the same peptide sequence has been accomplished by this effective method for the solid-supported combinatorial synthesis of lactam-bridged peptides. Peptides bearing an Agl residue exhibited curve shapes indicative of turn conformations in their circular dichroism spectra. PMID:20225301

Ronga, Luisa; Jamieson, Andrew G; Beauregard, Kim; Quiniou, Christiane; Chemtob, Sylvain; Lubell, William D

2010-01-01

58

Evidence for a Dual Role of an Active Site Histidine in [alpha]-Amino-[beta]-carboxymuconate-[epsilon]-semialdehyde Decarboxylase  

SciTech Connect

The previously reported crystal structures of {alpha}-amino-{beta}-carboxymuconate-{epsilon}-semialdehyde decarboxylase (ACMSD) show a five-coordinate Zn(II)(His){sub 3}(Asp)(OH{sub 2}) active site. The water ligand is H-bonded to a conserved His228 residue adjacent to the metal center in ACMSD from Pseudomonas fluorescens (PfACMSD). Site-directed mutagenesis of His228 to tyrosine and glycine in this study results in a complete or significant loss of activity. Metal analysis shows that H228Y and H228G contain iron rather than zinc, indicating that this residue plays a role in the metal selectivity of the protein. As-isolated H228Y displays a blue color, which is not seen in wild-type ACMSD. Quinone staining and resonance Raman analyses indicate that the blue color originates from Fe(III)-tyrosinate ligand-to-metal charge transfer. Co(II)-substituted H228Y ACMSD is brown in color and exhibits an electron paramagnetic resonance spectrum showing a high-spin Co(II) center with a well-resolved {sup 59}Co (I = 7/2) eight-line hyperfine splitting pattern. The X-ray crystal structures of as-isolated Fe-H228Y (2.8 {angstrom}) and Co-substituted (2.4 {angstrom}) and Zn-substituted H228Y (2.0 {angstrom} resolution) support the spectroscopic assignment of metal ligation of the Tyr228 residue. The crystal structure of Zn-H228G (2.6 {angstrom}) was also determined. These four structures show that the water ligand present in WT Zn-ACMSD is either missing (Fe-H228Y, Co-H228Y, and Zn-H228G) or disrupted (Zn-H228Y) in response to the His228 mutation. Together, these results highlight the importance of His228 for PfACMSD's metal specificity as well as maintaining a water molecule as a ligand of the metal center. His228 is thus proposed to play a role in activating the metal-bound water ligand for subsequent nucleophilic attack on the substrate.

Huo, Lu; Fielding, Andrew J.; Chen, Yan; Li, Tingfeng; Iwaki, Hiroaki; Hosler, Jonathan P.; Chen, Lirong; Hasegawa, Yoshie; Que, Jr., Lawrence; Liu, Aimin (GSU); (Kansai); (UMMC); (UMM)

2012-10-09

59

Design, synthesis, and application of azabicyclo[X.Y.0]alkanone amino acids as constrained dipeptide surrogates and peptide mimics.  

PubMed

Azabicyclo[X.Y.0]alkanone amino acids are challenging synthetic targets and useful tools for studying structure-activity relationships of native peptide ligands. They have been employed to increase potency and stability in conformationally rigid enzyme inhibitors and receptor ligands. Since last reviewed in 1997, activity in their synthesis and application has increased significantly and access is now available to a wider diversity of these peptide mimics. This review focuses on recent syntheses of these heterocyclic amino acids and their application in the investigation of biologically active peptides and peptide mimics. PMID:15795926

Cluzeau, Jérôme; Lubell, William D

2005-01-01

60

GluR2-free alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors intensify demyelination in experimental autoimmune encephalomyelitis.  

PubMed

We adopted a genetic approach to test the importance of edited GluR2-free, Ca(2+)-permeable, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors in the pathophysiology of experimental autoimmune encephalomyelitis, an inflammatory demyelinative disorder resembling multiple sclerosis. Initial studies showed that oligodendroglial lineage cells from mice lacking functional copies of the gene encoding the GluR3 AMPA receptor subunit (Gria3) had a diminished capacity to assemble edited GluR2-free AMPA receptors, and were resistant to excitotoxicity in vitro. Neurological deficits and spinal cord demyelination elicited by immunization with myelin oligodendrocyte glycoprotein peptide were substantially milder in these Gria3 mutant mice than in their wild-type littermates. These results support the hypothesis that oligodendroglial excitotoxicity mediated by AMPA receptors that do not contain edited GluR2 subunits contributes to demyelination in experimental autoimmune encephalomyelitis, and suggest that inhibiting these Ca(2+)-permeable AMPA receptors would be therapeutic in multiple sclerosis. PMID:17472701

Bannerman, Peter; Horiuchi, Makoto; Feldman, Daniel; Hahn, Ashleigh; Itoh, Aki; See, Jill; Jia, Zheng Ping; Itoh, Takayuki; Pleasure, David

2007-05-01

61

TGF-? and retinoic acid induce miR-10a, which targets Bcl-6 and constrains helper T cell plasticity  

PubMed Central

Distinct CD4+ T cell subsets are critical for host defense and immunoregulation. While these subsets can behave as terminally differentiated lineages, elements of plasticity are increasingly recognized. MicroRNAs are one factor that controls stability and plasticity. Herein, we report that miR-10a was highly expressed in naturally-occurring regulatory T (Treg) cells and induced by retinoic acid and TGF-? in inducible Treg cells. By simultaneously targeting Bcl-6 and a co-repressor, Ncor2, miR-10a attenuated phenotypic conversion of inducible Treg cells to follicular helper T cells. miR-10a also limited TH17 differentiation and therefore represents a new factor that can fine tune plasticity and fate decision of helper T cells.

Takahashi, Hayato; Kanno, Tomohiko; Nakayamada, Shingo; Hirahara, Kiyoshi; Sciume, Giuseppe; Muljo, Stefan A.; Kuchen, Stefan; Casellas, Rafael; Wei, Lai; Kanno, Yuka; O'Shea, John J.

2012-01-01

62

Concepts and schemes for the re-engineering of physical protein modules: generating nanodevices via targeted replacements with constrained amino acids  

NASA Astrophysics Data System (ADS)

Physically building complex multi-molecular structures from naturally occurring biological macromolecules has aroused a great deal of interest. Here we focus on nanostructures composed of re-engineered, natural 'foldamer' building blocks. Our aim is to provide some of the underlying concepts and schemes for crafting structures utilizing such conformationally relatively stable molecular components. We describe how, via chemical biology strategies, it is further possible to chemically manipulate the foldamer building blocks toward specific shape-driven structures, which in turn could be used toward potential-designed functions. We outline the criteria in choosing candidate foldamers from the vast biological repertoire, and how to enhance their stability through selected targeted replacements by non-proteinogenic conformationally constrained amino acids. These approaches combine bioinformatics, high performance computations and mathematics with synthetic organic chemistry. The resulting artificially engineered self-organizing molecular scale structures take advantage of nature's nanobiology toolkit and at the same time improve on it, since their new targeted function differs from that optimized by evolution. The major challenge facing nanobiology is to be able to exercise fine control over the performance of these target-specific molecular machines.

Alemán, Carlos; Zanuy, David; Jiménez, Ana I.; Cativiela, Carlos; Haspel, Nurit; Zheng, Jie; Casanovas, Jordi; Wolfson, Haim; Nussinov, Ruth

2006-03-01

63

Design of novel neurokinin 1 receptor antagonists based on conformationally constrained aromatic amino acids and discovery of a potent chimeric opioid agonist-neurokinin 1 receptor antagonist.  

PubMed

A screening of conformationally constrained aromatic amino acids as base cores for the preparation of new NK1 receptor antagonists resulted in the discovery of three new NK1 receptor antagonists, 19 [Ac-Aba-Gly-NH-3',5'-(CF(3))(2)-Bn], 20 [Ac-Aba-Gly-NMe-3',5'-(CF(3))(2)-Bn], and 23 [Ac-Tic-NMe-3',5'-(CF(3))(2)-Bn], which were able to counteract the agonist effect of substance P, the endogenous ligand of NK1R. The most active NK1 antagonist of the series, 20 [Ac-Aba-Gly-NMe-3',5'-(CF(3))(2)-Bn], was then used in the design of a novel, potent chimeric opioid agonist-NK1 receptor antagonist, 35 [Dmt-D-Arg-Aba-Gly-NMe-3',5'-(CF(3))(2)-Bn], which combines the N terminus of the established Dmt(1)-DALDA agonist opioid pharmacophore (H-Dmt-D-Arg-Phe-Lys-NH(2)) and 20, the NK1R ligand. The opioid component of the chimeric compound 35, that is, Dmt-D-Arg-Aba-Gly-NH(2) (36), also proved to be an extremely potent and balanced ? and ? opioid receptor agonist with subnanomolar binding and in vitro functional activity. PMID:21413804

Ballet, Steven; Feytens, Debby; Buysse, Koen; Chung, Nga N; Lemieux, Carole; Tumati, Suneeta; Keresztes, Attila; Van Duppen, Joost; Lai, Josephine; Varga, Eva; Porreca, Frank; Schiller, Peter W; Vanden Broeck, Jozef; Tourwé, Dirk

2011-03-17

64

Design of novel neurokinin 1 receptor antagonists based on conformationally constrained aromatic amino acids and discovery of a potent chimeric opioid agonist-neurokinin 1 receptor antagonist  

PubMed Central

A screening of conformationally constrained aromatic amino acids as base cores for the preparation of new NK1 receptor antagonists resulted in the discovery of three new NK1 receptor antagonists, 19 [Ac-Aba-Gly-NH-3?,5?-(CF3)2-Bn], 20 [Ac-Aba-Gly-NMe-3?,5?-(CF3)2-Bn] and 23 [Ac-Tic-NMe-3?,5?-(CF3)2-Bn], which were able to counteract the agonist effect of substance P, the endogenous ligand of NK1R. The most active NK1 antagonist of the series, 20 [Ac-Aba-Gly-NMe-3?,5?-(CF3)2-Bn], was then used in the design of a novel, potent chimeric opioid agonist-NK1 receptor antagonist, 35 [Dmt-D-Arg-Aba-Gly-NMe-3?,5?-(CF3)2-Bn], which combines the N-terminus of the established Dmt1-DALDA agonist opioid pharmacophore (H-Dmt-D-Arg-Phe-Lys-NH2) and 20, the NK1R ligand. The opioid component of the chimeric compound 35, i.e. Dmt-D-Arg-Aba-Gly-NH2 36, also proved to be an extremely potent and balanced ?- and ? opioid receptor agonist with subnanomolar binding and in vitro functional activity.

Ballet, Steven; Feytens, Debby; Buysse, Koen; Chung, Nga N.; Lemieux, Carole; Tumati, Suneeta; Keresztes, Attila; Van Duppen, Joost; Lai, Josephine; Varga, Eva; Porreca, Frank; Schiller, Peter W.; Broeck, Jozef Vanden; Tourwe, Dirk

2011-01-01

65

Ultrastructural characterization of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-induced cell death in embryonic dopaminergic neurons  

Microsoft Academic Search

Developing neuronal populations undergo significant attrition by natural cell death. Dopaminergic neurons in the substantia\\u000a nigra pars compacta undergo apoptosis during synaptogenesis. Following this time window, destruction of the anatomic target\\u000a of dopaminergic neurons results in dopaminergic cell death but the morphology is no longer apoptotic. We describe ultrastructural\\u000a changes that appear unique to dying embryonic dopaminergic neurons. In primary

D. A. Dorsey; D. H. Mascó; K. Dikranian; K. Hyrc; L. Masciotra; B. Faddis; M. Soriano; A. A. Gru; M. P. Goldberg; G. A. de Erausquin

2006-01-01

66

Shock Synthesis of Amino Acids in Simulated Primitive Environments  

Microsoft Academic Search

A mixture of gases roughly simulating the primitive terrestrial atmosphere has been subjected to shock heating followed by a rapid thermal quench. Under strictly homogeneous conditions there is a very high efficiency of 5 × 1010 molecules per erg of shock-injected energy for production of alpha-amino acids. Calculations suggest that rapid quenching bypasses the usual thermochemical barrier. The product of

A. Bar-Nun; N. Bar-Nun; S. H. Bauer; Carl Sagan

1970-01-01

67

Constrained egalitarian allocations  

Microsoft Academic Search

This paper proposes a constrained egalitarian solution concept for TU games which combines commitment for egalitarianism and promotion of individual inter- ests in a consistent manner. The paper shows that the set of constrained egalitar- ian allocations is nonempty for weakly superadditive games. The solution is \\

Bhaskar Dutta; Debraj Ray

1991-01-01

68

Constrained Vapor Bubble Experiment  

Microsoft Academic Search

Microgravity experiments on the Constrained Vapor Bubble Heat Exchanger, CVB, are being developed for the International Space Station. In particular, we present results of a precursory experimental and theoretical study of the vertical Constrained Vapor Bubble in the Earth's environment. A novel non-isothermal experimental setup was designed and built to study the transport processes in an ethanol\\/quartz vertical CVB system.

Shripad Gokhale; Joel Plawsky; Peter C. Wayner Jr.; Ling Zheng; Ying-Xi Wang

2002-01-01

69

Constrained Nearest Neighbor Queries  

Microsoft Academic Search

In this paper we introduce the notion of constrained nearest neighbor queries (CNN) and propose a series of methods to answer them. This class of queries can be thought of as nearest neighbor queries with range constraints. Although both nearest neighbor and range queries have been analyzed extensively in previous literature, the implications of constrained nearest neighbor queries have not

Hakan Ferhatosmanoglu; Ioanna Stanoi; Divyakant Agrawal; Amr El Abbadi

2001-01-01

70

Constraining the dark fluid  

SciTech Connect

Cosmological observations are normally fit under the assumption that the dark sector can be decomposed into dark matter and dark energy components. However, as long as the probes remain purely gravitational, there is no unique decomposition and observations can only constrain a single dark fluid; this is known as the dark degeneracy. We use observations to directly constrain this dark fluid in a model-independent way, demonstrating, in particular, that the data cannot be fit by a dark fluid with a single constant equation of state. Parametrizing the dark fluid equation of state by a variety of polynomials in the scale factor a, we use current kinematical data to constrain the parameters. While the simplest interpretation of the dark fluid remains that it is comprised of separate dark matter and cosmological constant contributions, our results cover other model types including unified dark energy/matter scenarios.

Kunz, Martin; Liddle, Andrew R.; Parkinson, David [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom); Gao Changjun [National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 (China)

2009-10-15

71

cap alpha. -1,4-thiazine alkanephosphonic acids as corrosion inhibitors  

Microsoft Academic Search

cap alpha..-1,4-thiazine alkanephosphonic acids are described as corrosion inhibitors. An ..cap alpha..-aminoalkanephosphonic acid is reacted with an equal molar amount of a divinyl sulfur compound to produce the thiazine alkanephosphonic acids. It is preferred to carry out the reaction in a solvent or a mixture of solvents in which the ..cap alpha..-amino phosphonic acid is soluble. To the solution of

1982-01-01

72

Asymmetric synthesis of L-azetidine-2-carboxylic acid and 3-substituted congeners—conformationally constrained analogs of phenylalanine, naphthylalanine, and leucine  

Microsoft Academic Search

Enantiopure L-azetidine-2-carboxylic acid, the (3R)-phenyl, (3R)-naphthyl and (3S)-isopropyl analogs were prepared based on a zinc-mediated asymmetric addition of allylic halides to the camphor sultam derivative of glyoxylic acid O-benzyl oxime.

Stephen Hanessian; Naomy Bernstein; Rui-Yang Yang; Robert Maguire

1999-01-01

73

Distributed constrained heuristic search  

Microsoft Academic Search

A model of decentralized problem solving, called distributed constrained heuristic search (DCHS), that provides both structure and focus in individual agent search spaces to optimize decisions in the global space, is presented. The model achieves this by integrating decentralized constraint satisfaction and heuristic search. It is a formalism suitable for describing a large set of distributed artificial intelligence problems. The

K. Sycara; S. F. Roth; N. Sadeh; M. S. Fox

1991-01-01

74

On Constrained Randomized Quantization  

NASA Astrophysics Data System (ADS)

Randomized (dithered) quantization is a method capable of achieving white reconstruction error independent of the source. Dithered quantizers have traditionally been considered within their natural setting of uniform quantization. In this paper we extend conventional dithered quantization to nonuniform quantization, via a subterfage: dithering is performed in the companded domain. Closed form necessary conditions for optimality of the compressor and expander mappings are derived for both fixed and variable rate randomized quantization. Numerically, mappings are optimized by iteratively imposing these necessary conditions. The framework is extended to include an explicit constraint that deterministic or randomized quantizers yield reconstruction error that is uncorrelated with the source. Surprising theoretical results show direct and simple connection between the optimal constrained quantizers and their unconstrained counterparts. Numerical results for the Gaussian source provide strong evidence that the proposed constrained randomized quantizer outperforms the conventional dithered quantizer, as well as the constrained deterministic quantizer. Moreover, the proposed constrained quantizer renders the reconstruction error nearly white. In the second part of the paper, we investigate whether uncorrelated reconstruction error requires random coding to achieve asymptotic optimality. We show that for a Gaussian source, the optimal vector quantizer of asymptotically high dimension whose quantization error is uncorrelated with the source, is indeed random. Thus, random encoding in this setting of rate-distortion theory, is not merely a tool to characterize performance bounds, but a required property of quantizers that approach such bounds.

Akyol, Emrah; Rose, Kenneth

2013-07-01

75

Constrained Graph Layout  

Microsoft Academic Search

Most current graph layout technology does not lend itself to interactive applications such as animation or advanced user interfaces. We introduce the constrained graph layout model which is better suited for interactive applications. In this model, input to the layout module includes suggested positions for nodes and constraints over the node positions in the graph to be laid out. We

Weiqing He; Kim Marriott

1996-01-01

76

Isolation of dealanylalahopcin, a new amino acid, and its biological activity.  

PubMed

A new amino acid, dealanylalahopcin, was isolated from a culture filtrate of Streptomyces albulus subsp. ochragerus; it was also formed by the enzymatic hydrolysis of alahopcin using microbial alpha-amino acid ester hydrolase. The amino acid was obtained as colorless needles and its molecular formula is C6H10N2O5. It showed very weak antibacterial activity against Gram-positive and Gram-negative bacteria, and weak inhibitory activity against the collagen prolylhydroxylase. PMID:4008327

Higashide, E; Kanamaru, T; Fukase, H; Horii, S

1985-03-01

77

Upgrading bottleneck constrained forests  

Microsoft Academic Search

We study bottleneck constrained network upgrading problems. We are given an edge weighted graph G=(V,E) where node v?V can be upgraded at a cost of c(v). This upgrade reduces the delay of each link emanating from v. The goal is to find a minimum cost set of nodes to be upgraded so that the resulting network has a good performance.

Sven Oliver Krumke; Madhav V. Marathe; Hartmut Noltemeier; S. S. Ravi; Hans-christoph Wirth

2001-01-01

78

Constrained noninformative priors  

SciTech Connect

The Jeffreys noninformative prior distribution for a single unknown parameter is the distribution corresponding to a uniform distribution in the transformed model where the unknown parameter is approximately a location parameter. To obtain a prior distribution with a specified mean but with diffusion reflecting great uncertainty, a natural generalization of the noninformative prior is the distribution corresponding to the constrained maximum entropy distribution in the transformed model. Examples are given.

Atwood, C.L.

1994-10-01

79

Synthesis of Stereodefined Piperidines from Aziridines and Their Transformation into Conformationally Constrained Amino Acids, Amino Alcohols and 2,7-Diazabicyclo[3.3.1]nonanes.  

PubMed

2-(2-Cyano-2-phenylethyl)aziridines were converted into novel cis- and trans-2-chloromethyl-4-phenylpiperidine-4-carbonitriles via alkylation with 1-bromo-2-chloroethane followed by microwave-assisted 6-exo-tet cyclization and regiospecific ring opening. The latter piperidines were used as eligible substrates for the synthesis of stereodefined 2-chloromethyl-, 2-hydroxymethyl-, and 2-carboxymethyl-4-phenylpiperidine-4-carboxylic acids, 2-hydroxymethyl-4-phenylpiperidine-4-carbonitriles, 3-hydroxy-5-phenylazepane-5-carbonitriles, and 5-phenyl-2,7-diazabicyclo[3.3.1]nonanes. PMID:20977252

Vervisch, Karel; D'hooghe, Matthias; To?rnroos, Karl W; De Kimpe, Norbert

2010-10-26

80

Constraining entropic cosmology  

NASA Astrophysics Data System (ADS)

It has been recently proposed that the interpretation of gravity as an emergent, entropic phenomenon might have nontrivial implications to cosmology. Here several such approaches are investigated and the underlying assumptions that must be made in order to constrain them by the BBN, SneIa, BAO and CMB data are clarified. Present models of inflation or dark energy are ruled out by the data. Constraints are derived on phenomenological parameterizations of modified Friedmann equations and some features of entropic scenarios regarding the growth of perturbations, the no-go theorem for entropic inflation and the possible violation of the Bekenstein bound for the entropy of the Universe are discussed and clarified.

Koivisto, Tomi S.; Mota, David F.; Zumalacárregui, Miguel

2011-02-01

81

Studies on the Borchelate Formation and Acylation of Variously N-Oxidized Aminoalcohol and Aminocarboxylic acid Derivatives (Untersuchungen zur Borchelatbildung und Acylierung Unterschiedlich N-Oxidierter Aminoalkohol und Aminocarbonsaeure-Derivate).  

National Technical Information Service (NTIS)

Comparative studies were carried out on isomeric O-(2-hydroxyalkyl)-N,N-dialkylhydroxylamines and N-(2-hydroxyalkyl)-N,N-dialkylamine-N-oxides; the reactions of isomeric N-hydroxy-alpha-amino- and alpha-aminooxycarboxylic acids with diphenylboric anhydrid...

J. Graumann

1980-01-01

82

Constrained space camera assembly  

DOEpatents

A constrained space camera assembly which is intended to be lowered through a hole into a tank, a borehole or another cavity. The assembly includes a generally cylindrical chamber comprising a head and a body and a wiring-carrying conduit extending from the chamber. Means are included in the chamber for rotating the body about the head without breaking an airtight seal formed therebetween. The assembly may be pressurized and accompanied with a pressure sensing means for sensing if a breach has occurred in the assembly. In one embodiment, two cameras, separated from their respective lenses, are installed on a mounting apparatus disposed in the chamber. The mounting apparatus includes means allowing both longitudinal and lateral movement of the cameras. Moving the cameras longitudinally focuses the cameras, and moving the cameras laterally away from one another effectively converges the cameras so that close objects can be viewed. The assembly further includes means for moving lenses of different magnification forward of the cameras.

Heckendorn, Frank M. (Aiken, SC); Anderson, Erin K. (Augusta, GA); Robinson, Casandra W. (Trenton, SC); Haynes, Harriet B. (Aiken, SC)

1999-01-01

83

Amino Acid Chemistry as a Link Between Small Solar System Bodies and Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

Establishing chemical links between meteorites and small solar system bodies, such as comets and asteroids, provides a tool for investigating the processes that occurred during the formation of the solar system. Carbonaceous meteorites are of particular interest, since they may have seeded the early Earth with a variety of prebiotic organic compounds including amino acids, purines and pyrimidines, which are thought to be necessary for the origin of life. Here we report the results of high-performance liquid chromatography (HPLC) based amino acid analyses of the acid-hydrolyzed hot water extracts from pristine interior pieces of the CI carbonaceous chondrites Orgueil and Ivuna and the CM meteorites Murchison and Murray. We found that the CI meteorites Orgueil and Ivuna contained high abundances of beta-alanine and glycine, while only traces of other amino acids like alanine, alpha-amino-n-butryic acid (ABA) and alpha-aminoisobutyric acid (AIB) were detected in these meteorites. Carbon isotopic measurements of beta-alanine and glycine in Orgueil by gas chromatography combustion-isotope ratio mass spectrometry clearly indicate an extraterrestrial origin of these amino acids. The amino acid composition of Orgueil and Ivuna was strikingly different from the CM chondrites Murchison and Murray. The most notable difference was the high relative abundance of B-alanine in Orgueil and Ivuna compared to Murchison and Murray. Furthermore, AIB, which is one of the most abundant amino acids found in Murchison and Murray, was present in only trace amounts in Orgueil and Ivuna. Our amino acid data strongly suggest that the CI meteorites Orgueil and Ivuna came from a different type of parent body than the CM meteorites Murchison and Murray, possibly from an extinct comet. It is generally thought that carbonaceous meteorites are fragments of larger asteroidal bodies delivered via near Earth objects (NEO). Orbital and dynamic studies suggest that both fragments of main belt asteroids and comets replenish the NEO population, therefore extinct comets may contribute up to half of all NEO's. A comparison of an amino acid analysis of a returned NEO sample to CI and CM carbonaceous chondrites would help establish a link between small solar system bodies and meteorites. Based on our amino acid measurements of CI and CM chondrites, amino acid chemistry can be included as an additional set of criteria to constrain the nature of meteorite parent bodies.

Glavin, Daniel P.; Ehrenfreund, Pascale; Botta, Oliver; Cooper, George; Bada, Jeffrey L.

2000-01-01

84

Robust convex quadratically constrained programs  

Microsoft Academic Search

In this paper we study robust convex quadratically constrained programs, a subset of the class of robust convex programs introduced by Ben-Tal and Nemirovski (4). Unlike (4), our focus in this paper is to identify uncertainty structures that allow the corresponding robust quadratically constrained programs to be reformulated as second-order cone programs. We propose three classes of uncertainty sets that

Donald Goldfarb; Garud Iyengar

2003-01-01

85

Greedy Sparsity-Constrained Optimization  

Microsoft Academic Search

Sparsity-constrained optimization has wide applicability in machine learning, statistics, and signal processing problems such as feature selection and Compressive Sensing. A vast body of work has studied the sparsity-constrained optimization from theoretical, algorithmic, and application aspects in the context of sparse estimation in linear models where the fidelity of the estimate is measured by the squared error. In contrast, relatively

Sohail Bahmani; Bhiksha Raj; Petros Boufounos

2013-01-01

86

Constraining neutrinoless double beta decay  

NASA Astrophysics Data System (ADS)

A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude.

Dorame, L.; Meloni, D.; Morisi, S.; Peinado, E.; Valle, J. W. F.

2012-08-01

87

Constraining Dark Energy  

NASA Astrophysics Data System (ADS)

Future advances in cosmology will depend on the next generation of cosmological observations and how they shape our theoretical understanding of the universe. Current theoretical ideas, however, have an important role to play in guiding the design of such observational programs. The work presented in this thesis concerns the intersection of observation and theory, particularly as it relates to advancing our understanding of the accelerated expansion of the universe (or the dark energy). Chapters 2 - 4 make use of the simulated data sets developed by the Dark Energy Task Force (DETF) for a number of cosmological observations currently in the experimental pipeline. We use these forecast data in the analysis of four quintessence models of dark energy: the PNGB, Exponential, Albrecht-Skordis and Inverse Power Law (IPL) models. Using Markov Chain Monte Carlo sampling techniques we examine the ability of each simulated data set to constrain the parameter space of these models. We examine the potential of the data for differentiating time-varying models from a pure cosmological constant. Additionally, we introduce an abstract parameter space to facilitate comparison between models and investigate the ability of future data to distinguish between these quintessence models. In Chapter 5 we present work towards understanding the effects of systematic errors associated with photometric redshift estimates. Due to the need to sample a vast number of deep and faint galaxies, photometric redshifts will be used in a wide range of future cosmological observations including gravitational weak lensing, baryon accoustic oscillations and type 1A supernovae observations. The uncertainty in the redshift distributions of galaxies has a significant potential impact on the cosmological parameter values inferred from such observations. We introduce a method for parameterizing uncertainties in modeling assumptions affecting photometric redshift calculations and for propagating these uncertainties through to uncertainties in the cosmological parameters.

Abrahamse, Augusta

2010-12-01

88

Characterization of a broad-scope amino acid transport system in sand dollars.  

PubMed

Both echinoderm embryos and adults take up alpha-amino acids by an apparent broad-scope transport system. This transporter can be characterized as follows: alanine transport is not blocked by alpha-(methylamino)isobutyric acid. Leucine and other lipophilic neutral amino acids are preferentially transported. Transport is sodium dependent and blocked by 2-aminobicyclo-[2,2,1]heptane-2-carboxycylic acid. Lysine and aspartate transport is inhibited by lipophilic neutral amino acids. Taurine, a beta-neutral amino acid, is translocated via a second and independent carrier. PMID:3126672

Davis, J P; Bellis, S; Stephens, G C

1988-03-01

89

Line constrained between two curves  

NASA Astrophysics Data System (ADS)

In this paper, the method of finding the line constrained between two quadratic Bezier curves and also finding the line constrained between a quadratic Bezier curve and a circle is presented. The application of the line constrained can be used in the construction of railway tracks between any obstacle or rolling a ball to the other side of a wall in a way that it just touches the wall. The method used is by using equal root properties of a quadratic equation in order to find one point where the line touches the curve. The work examples involved different curve orientations and different circle positions. Mathematica software is used to compute the solutions for the line constrained and present the solutions graphically. By using the method proposed, the number of intersection points obtained is used to determine the number of lines constrained between two curves and between a curve and a circle. The conclusion on whether all lines are acceptable to be considered as the line constrained are depending on the application of the line.

Ahmad, Afida; Ali, Jamaludin Md.

2013-04-01

90

Metabolism of Indole-3-acetic Acid: IV. Biological Properties of Amino Acid Conjugates.  

PubMed

The biological activity of 20 l-alpha-amino acid conjugates of indole-3-acetic acid (IAA) to stimulate cell elongation of Avena sativa coleoptile sections and to stimulate growth of soybean cotyledon tissue cultures has been examined at concentrations of 10(-4) to 10(-7)m. In the Avena coleoptile test, most of the amino acid conjugates stimulated elongation. Several of the conjugates stimulated as much elongation as IAA but their half-maximum concentrations tended to be higher. Some of the more active conjugates were alanine, glycine, lysine, serine, aspartic acid, cystine, cysteine, methionine, and glutamic acid.In the soybean cotyledon tissue culture test, all of the l-alpha-amino acid conjugates of IAA stimulated growth except for the phenylalanine, histidine, and arginine conjugates. Most of the conjugates produced responses at least as great as that caused by IAA. Conjugates with half-maximum concentrations lower than IAA included cysteine, cystine, methionine, and alanine. These conjugates exceed the IAA-induced callus growth at all tested concentrations. Other conjugates significantly better than IAA at 10(-6)m were serine, glycine, leucine, proline, and threonine. PMID:16659795

Feung, C S; Hamilton, R H; Mumma, R O

1977-01-01

91

Somatostatin prevents the postoperative increases in plasma amino acid clearance and urea synthesis after elective cholecystectomy.  

PubMed Central

The importance of glucagon on postoperative changes in hepatic amino-nitrogen conversion were investigated in six patients undergoing elective cholecystectomy for uncomplicated gall stones. Patients were given infusions of somatostatin (bolus of 6 micrograms/kg followed by continuous infusion of 6 micrograms/kg/h) from induction of anaesthesia to the end of investigation, the first postoperative day (30 hours). Controls were 16 patients undergoing the same procedures omitting the somatostatin infusion. In all patients blood concentration and plasma clearance of total alpha-amino-nitrogen, and amino acid stimulated rate of urea synthesis were measured. Elective cholecystectomy decreased blood alpha-amino-nitrogen concentration from mean (SEM) 2.9 (0.2) to 2.4 (0.1) mmol/l (p < 0.05), increased the clearance of total alpha-amino-nitrogen from 5.2 (0.3) to 6.6 (0.3) ml/s (p < 0.05), and increased the rate of amino acid stimulated urea synthesis from 27 (1) to 37 (2) mumol/s (p < 0.05) pointing to increased hepatic removal of amino-nitrogen at expense of plasma amino-nitrogen. Infusion of somatostatin prevented increase of glucagon for 24 hours after surgery, and prevented the negative changes in postoperative nitrogen homeostasis resulting from the postoperative changes in hepatic nitrogen conversion, suggesting glucagon as mediator. The exact mechanism remains in doubt, however, because of the multiple effects of somatostatin.

Heindorff, H; Billesb?lle, P; Pedersen, S L; Hansen, R; Vilstrup, H

1995-01-01

92

A 3(10)-helical pentapeptide in water: interplay of alpha,alpha-disubstituted amino acids and the central residue on structure formation.  

PubMed

C(alpha,alpha)-disubstituted amino acids (alphaalphaAAs) are widely used to conformationally constrain peptides. A series of pentapeptides containing dipropylglycine (Dpg) at alternating positions and their alpha-amino acid counterpart L-norvaline (Nva) analogues were synthesized to fully investigate the impact of Dpg on peptide backbone structure in aqueous solution. CD, VCD, and NMR spectral analysis suggest that Dpg containing peptides adopt more ordered structures relative to their Nva containing analogues. The central residues (Ala, Thr, Tyr, Val) and the charged side-chains of Glu and Lys play important roles in the degree of peptide folding. Hydrophobic and branched residues (Val, Tyr) at the central position of the peptide produce greater folding as judged by CD and NMR. Variation of the chemical shift with temperature (Deltadelta/DeltaT NH) of Ac-Glu-Dpg-Tyr-Dpg-Lys-NH(2) suggests a series of i --> i + 3 hydrogen bonds between the N-terminal acetyl carbonyl and the Tyr(3) NH, and the Glu(1) carbonyl and the Dpg(4) NH. The solution conformation of Ac-Glu-Dpg-Tyr-Dpg-Lys-NH(2) calculated from NMR-derived constraints shows a 3(10)-helical structure (two repetitive type-III beta-turns) at residues 1-4, which is supported by 2D NMR, CD, and VCD spectra. Analysis of NMR-derived models of these peptides suggest that there is a strong hydrophobic interaction of the pro-S propyl side chain of Dpg(2) and the Tyr(3) side-chain that may be a strong stabilizing force of the peptide folding in water. PMID:19489061

Wang, Jia; McElheny, Dan; Fu, Yanwen; Li, Guangyu; Kim, Joohyun; Zhou, Zhe; Wu, Ling; Keiderling, Timothy A; Hammer, Robert P

2009-01-01

93

Entropy-constrained vector quantization  

Microsoft Academic Search

An iterative descent algorithm based on a Lagrangian formulation for designing vector quantizers having minimum distortion subject to an entropy constraint is discussed. These entropy-constrained vector quantizers (ECVQs) can be used in tandem with variable-rate noiseless coding systems to provide locally optimal variable-rate block source coding with respect to a fidelity criterion. Experiments on sampled speech and on synthetic sources

PHILIP A. CHOU; TOM LOOKABAUGH; ROBERT M. GRAY

1989-01-01

94

Constrained minimization for monotonic reconstruction  

SciTech Connect

The authors present several innovations in a method for monotonic reconstructions. It is based on the application of constrained minimization techniques for the imposition of monotonicity on a reconstruction. In addition, they present extensions of several classical TVD limiters to a genuinely multidimensional setting. In this case the linear least squares reconstruction method is expanded upon. They also clarify data dependent weighting techniques used with the minimization process.

Rider, W.J.; Kothe, D.B.

1996-08-20

95

Formal Language Constrained Path Problems  

Microsoft Academic Search

Given an alphabet ?, a (directed) graph G whose edges are weighted and ?-labeled, and a formal language L ? ??, the formal-language-constrained shortest\\/simple path problem con- sists of finding a shortest (simple) path p in G complying with the additional constraint that l(p) ? L. Here l(p) denotes the unique word obtained by concatenating the ?-labels of the edges

Christopher L. Barrett; Riko Jacob; Madhav V. Marathe

1998-01-01

96

Fiber Segmentation Using Constrained Clustering  

Microsoft Academic Search

\\u000a In this work we introduce the novel concept of applying constraints into the fiber segmentation problem within a clustering\\u000a based framework. The segmentation process is guided in an interactive manner. It allows the definition of relationships between\\u000a individual and sets of fibers. These relationships are realized as pairwise linkage constraints to perform a constrained clustering.\\u000a Furthermore, they can be refined

Daniel Duarte Abdala; Xiaoyi Jiang

2010-01-01

97

Amino acid balance across tissues of the forearm in postabsorptive man. Effects of insulin at two dose levels  

PubMed Central

Amino acid balance across skeletal muscle and across subcutaneous adipose tissue plus skin of the forearm has been quantified in postabsorptive man before and after insulin infusion into the brachial artery. Skeletal muscle released significant amounts of alpha amino nitrogen after an overnight fast. Most individual amino acids were released. Alanine output was by far the greatest. The pattern of release probably reflects both the composition of muscle protein undergoing degradation and de novo synthesis of alanine by transamination. A significant correlation was observed between the extent of release of each amino acid and its ambient arterial concentration. Elevation of forearm insulin in eight subjects from postabsorptive (12 ?U/ml) to high physiologic levels (157 ?U/ml) in addition to stimulating muscle glucose uptake blocked muscle alpha amino nitrogen release by 74%. Consistent declines in output were seen for leucine, isoleucine, tyrosine, phenylalanine, threonine, glycine, and ?-aminobutyric acid. Alanine output was insignificantly affected. Doubling forearm insulin levels (from 10 to 20 ?U/ml) in eight subjects increased muscle glucose uptake in three and blocked alpha amino nitrogen output in two although both effects were seen concurrently in only one subject. Changes in net amino acid balance after insulin could be accounted for by increased transport of amino acids into muscle cells or retardation of their exit. It is likely that ambient arterial amino acid concentrations are established and maintained primarily by the extent of muscle amino acid release. The individual amino acids whose outputs from forearm muscle decline after forearm insulinization correspond well with those whose levels fall systematically after systemic insulinization. This suggests that declines in amino acid levels after systemic insulinization are due to inhibition of muscle release. Doubling basal insulin approaches the threshold both for blockade of muscle amino acid output and stimulation of glucose uptake, effects which appear to occur independently.

Pozefsky, Thomas; Felig, Philip; Tobin, Jordan D.; Soeldner, J. Stuart; Cahill, George F.

1969-01-01

98

Incorporation of side-chain groups of basic amino acids into oligonucleotides via the 2'-position of uridine.  

PubMed

Certain amino acids and short peptides are known to act as enhancers of ribozyme-mediated RNA cleavage at low concentration of magnesium ion. Thus, covalent conjugates of oligonucleotides and some amino acids may have a potential for development as sequence-specific artificial ribonucleases. Here we would like to report an incorporation of basic amino acids, lysine and histidine, into oligonucleotides at the 2'-position of a uridine residue. The approach involves the 2'-O-alkylation and attachment of the corresponding amino acid by the alpha-amino group through a urethane-type linker. PMID:17150776

Zubin, Eugeny M; Stetsenko, Dmitry A; Kachalova, Anna V; Gait, Michael J; Oretskaya, Tatiana S

2005-01-01

99

Constraining relativistic viscous hydrodynamical evolution  

SciTech Connect

We show that by requiring positivity of the longitudinal pressure it is possible to constrain the initial conditions one can use in second-order viscous hydrodynamical simulations of ultrarelativistic heavy-ion collisions. We demonstrate this explicitly for (0+1)-dimensional viscous hydrodynamics and discuss how the constraint extends to higher dimensions. Additionally, we present an analytic approximation to the solution of (0+1)-dimensional second-order viscous hydrodynamical evolution equations appropriate to describe the evolution of matter in an ultrarelativistic heavy-ion collision.

Martinez, Mauricio [Helmholtz Research School and Otto Stern School, Goethe-Universitaet Frankfurt am Main Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany); Strickland, Michael [Physics Department, Gettysburg College Gettysburg, Pennsylvania 17325 (United States)

2009-04-15

100

Constraining walking and custodial technicolor  

SciTech Connect

We show how to constrain the physical spectrum of walking technicolor models via precision measurements and modified Weinberg sum rules. We also study models possessing a custodial symmetry for the S parameter at the effective Lagrangian level - custodial technicolor - and argue that these models cannot emerge from walking-type dynamics. We suggest that it is possible to have a very light spin-one axial (vector) boson. However, in the walking dynamics the associated vector boson is heavy while it is degenerate with the axial in custodial technicolor.

Foadi, Roshan; Frandsen, Mads T.; Sannino, Francesco [University of Southern Denmark, Campusvej 55, DK-5230 Odense M (Denmark); Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark)

2008-05-01

101

Fuzzy coding in constrained ordinations.  

PubMed

Canonical correspondence analysis and redundancy analysis are two methods of constrained ordination regularly used in the analysis of ecological data when ordinations based on several response variables (for example, species abundances) are related linearly to several explanatory variables (for example, environmental variables, spatial positions of samples). In this report I demonstrate the advantages of the fuzzy coding of explanatory variables: first, nonlinear relationships can be diagnosed; second, more variance in the responses can be explained; and third, in the presence of categorical explanatory variables (for example, years, regions) the interpretation of the resulting triplot ordination is unified because all explanatory variables are measured at a categorical level. PMID:23691646

Greenacre, Michael

2013-02-01

102

Symmetry, constrained bosons and collectivity  

NASA Astrophysics Data System (ADS)

Collective states in a given nucleus can be associated with a subset of states of the oscillator shell model (OSM). This subset is characterized by a definite irreducible representation (irrep) of the orthogonal subgroup O(n) of the U(3n) symmetry group of the OSM, where n is the number of nucleons. We show that these collective states can be described with the help of s and d bosons also constrained by the same irrep of O(n) and indicate a procedure by which these bosons can be determined as functions of the coordinates a and momenta of the many nucleon problem. An analogy with the Zeeman effect for a one particle problem in an oscillator potential, illustrates the elementary nature of the concepts involved.

Moshinsky, Marcos

1984-06-01

103

Constrained search of conformational hyperspace.  

PubMed

We introduce a new method for determining pharmacophore or active site geometries by analysis of the structures of a series of active compounds. The method, constrained search, and the key concepts on which it is based, is described and illustrated by its application to 28 potent inhibitors of angiotensin-converting enzyme (ACE). The data set is one utilized by Mayer et al. [J. Comput.-Aided Mol. Design, 1 (1987) 3-16] to determine a unique geometry for the active site. Our experiment validated the previously reported results, obtained by a systematic search, while reducing the computer time requirement by more than two orders of magnitude. The experiment also identified a previously unrecognized alternative active site geometry for the ACE series. PMID:2715794

Dammkoehler, R A; Karasek, S F; Shands, E F; Marshall, G R

1989-03-01

104

Formal language constrained path problems  

SciTech Connect

In many path finding problems arising in practice, certain patterns of edge/vertex labels in the labeled graph being traversed are allowed/preferred, while others are disallowed. Motivated by such applications as intermodal transportation planning, the authors investigate the complexity of finding feasible paths in a labeled network, where the mode choice for each traveler is specified by a formal language. The main contributions of this paper include the following: (1) the authors show that the problem of finding a shortest path between a source and destination for a traveler whose mode choice is specified as a context free language is solvable efficiently in polynomial time, when the mode choice is specified as a regular language they provide algorithms with improved space and time bounds; (2) in contrast, they show that the problem of finding simple paths between a source and a given destination is NP-hard, even when restricted to very simple regular expressions and/or very simple graphs; (3) for the class of treewidth bounded graphs, they show that (i) the problem of finding a regular language constrained simple path between source and a destination is solvable in polynomial time and (ii) the extension to finding context free language constrained simple paths is NP-complete. Several extensions of these results are presented in the context of finding shortest paths with additional constraints. These results significantly extend the results in [MW95]. As a corollary of the results, they obtain a polynomial time algorithm for the BEST k-SIMILAR PATH problem studied in [SJB97]. The previous best algorithm was given by [SJB97] and takes exponential time in the worst case.

Barrett, C.; Jacob, R.; Marathe, M.

1997-07-08

105

Constrained ordination analysis with flexible response functions  

Microsoft Academic Search

Canonical correspondence analysis (CCA) is perhaps the most popular multivariate technique used by environmental ecologists for constrained ordination; it is an approximation to the maximum likelihood solution of the Gaussian response model. In this article, we look at the constrained ordination problem from a slightly different point of view and argue that it is this particular point of view that

Mu Zhu; Trevor J. Hastie; Guenther Walther

2005-01-01

106

PATTERN SEARCH ALGORITHMS FOR BOUND CONSTRAINED MINIMIZATION  

Microsoft Academic Search

We present a convergence theory for pattern search methods for solving bound constrained nonlinear programs. The analysis relies on the abstract structure of pattern search methods and an understanding of how the pattern interacts with the bound constraints. This analysis makes it possible to develop pattern search methods for bound constrained problems while only slightly restricting the flexibility present in

ROBERT MICHAEL LEWIS; VIRGINIA TORCZON

107

Constrained Tucker3 model for blind beamforming  

Microsoft Academic Search

This paper presents a constrained Tucker-3 model for blind beamforming. The constrained structure of this model is parameterized by two constraint matrices that capture the spatial and temporal structure of the channel. We first present a generalized Tucker-3 model that considers a multipath propagation scenario with large delay spread and different number of paths per source. This tensor model generalizes

André L. F. De Almeida; Gérard Favier; João Cesar M. Mota

2009-01-01

108

Theory and geometry of constrained cutting  

Microsoft Academic Search

The geometric parameters of tools in constrained cutting are determined. A new dynamic coordinate system is proposed, and\\u000a conversion formulas to other coordinate systems are presented. The cross section of the cut layer in constrained cutting is\\u000a described.

S. I. Petrushin; A. V. Proskokov

2009-01-01

109

Variational integrators for constrained dynamical systems  

Microsoft Academic Search

A variational formulation of constrained dynamics is presented in the continuous and in the discrete setting. The existing theory on variational integration of constrained problems is extended by aspects on the initialization of simulations, the discrete Legendre transform and certain postprocessing steps. Furthermore, the discrete null space method which has been introduced in the framework of energy-momentum conserving integration of

Sigrid Leyendecker; Jerrold E. Marsden; Michael Ortiz

2008-01-01

110

Separation of variables for the constrained flows  

SciTech Connect

The separation of variables for some constrained flows of soliton hierarchies are shown. The Lax matrix and r-matrix (either constant or dynamical type) are used to construct the separation variables and separation equation for the constrained flows. {copyright} {ital 1997 American Institute of Physics.}

Zeng, Y. [Department of Applied Mathematics, Tsinghua University, Beijing 100084, Peoples Republic of (China)

1997-01-01

111

The genetic code constrains yet facilitates Darwinian evolution.  

PubMed

An important goal of evolutionary biology is to understand the constraints that shape the dynamics and outcomes of evolution. Here, we address the extent to which the structure of the standard genetic code constrains evolution by analyzing adaptive mutations of the antibiotic resistance gene TEM-1 ?-lactamase and the fitness distribution of codon substitutions in two influenza hemagglutinin inhibitor genes. We find that the architecture of the genetic code significantly constrains the adaptive exploration of sequence space. However, the constraints endow the code with two advantages: the ability to restrict access to amino acid mutations with a strong negative effect and, most remarkably, the ability to enrich for adaptive mutations. Our findings support the hypothesis that the standard genetic code was shaped by selective pressure to minimize the deleterious effects of mutation yet facilitate the evolution of proteins through imposing an adaptive mutation bias. PMID:23754851

Firnberg, Elad; Ostermeier, Marc

2013-06-10

112

Wavelet library for constrained devices  

NASA Astrophysics Data System (ADS)

The wavelet transform is a powerful tool for image and video processing, useful in a range of applications. This paper is concerned with the efficiency of a certain fast-wavelet-transform (FWT) implementation and several wavelet filters, more suitable for constrained devices. Such constraints are typically found on mobile (cell) phones or personal digital assistants (PDA). These constraints can be a combination of; limited memory, slow floating point operations (compared to integer operations, most often as a result of no hardware support) and limited local storage. Yet these devices are burdened with demanding tasks such as processing a live video or audio signal through on-board capturing sensors. In this paper we present a new wavelet software library, HeatWave, that can be used efficiently for image/video processing/analysis tasks on mobile phones and PDA's. We will demonstrate that HeatWave is suitable for realtime applications with fine control and range to suit transform demands. We shall present experimental results to substantiate these claims. Finally this library is intended to be of real use and applied, hence we considered several well known and common embedded operating system platform differences; such as a lack of common routines or functions, stack limitations, etc. This makes HeatWave suitable for a range of applications and research projects.

Ehlers, Johan Hendrik; Jassim, Sabah A.

2007-05-01

113

Design, synthesis and evaluation of constrained methoxyethyl (cMOE) and constrained ethyl (cEt) nucleoside analogs.  

PubMed

Antisense drug discovery technology is a powerful method to modulate gene expression in animals and represents a novel therapeutic platform.(1) We have previously demonstrated that replacing 2'O-methoxyethyl (MOE, 2) residues in second generation antisense oligonucleotides (ASOs) with LNA (3) nucleosides improves the potency of some ASOs in animals. However, this was accompanied with a significant increase in the risk for hepatotoxicity.(2) We hypothesized that replacing LNA with novel nucleoside monomers that combine the structural elements of MOE and LNA might mitigate the toxicity of LNA while maintaining potency. To this end we designed and prepared novel nucleoside analogs 4 (S-constrained MOE, S-cMOE) and 5 (R-constrained MOE, R-cMOE) where the ethyl chain of the 2'O-MOE moiety is constrained back to the 4' position of the furanose ring. As part of the SAR series, we also prepared nucleoside analogs 7 (S-constrained ethyl, S-cEt) and 8 (R-constrained Ethyl, R-cEt) where the methoxymethyl group in the cMOE nucleosides was replaced with a methyl substituent. A highly efficient synthesis of the nucleoside phosphoramidites with minimal chromatography purifications was developed starting from cheap commercially available starting materials. Biophysical evaluation revealed that the cMOE and cEt modifications hybridize complementary nucleic acids with the same affinity as LNA while greatly increasing nuclease stability. Biological evaluation of oligonucleotides containing the cMOE and cEt modification in animals indicated that all of them possessed superior potency as compared to second generation MOE ASOs and a greatly improved toxicity profile as compared to LNA. PMID:18776499

Seth, Punit P; Siwkowski, Andrew; Allerson, Charles R; Vasquez, Guillermo; Lee, Sam; Prakash, Thazha P; Kinberger, Garth; Migawa, Michael T; Gaus, Hans; Bhat, Balkrishen; Swayze, Eric E

2008-01-01

114

constrainedKriging: An R-package for customary, constrained and covariance-matching constrained point or block kriging  

NASA Astrophysics Data System (ADS)

The article describes the R-package constrainedKriging, a tool for spatial prediction problems that involve change of support. The package provides software for spatial interpolation by constrained (CK), covariance-matching constrained (CMCK), and customary universal (UK) kriging. CK and CMCK yield approximately unbiased predictions of nonlinear functionals of target quantities under change of support and are therefore an attractive alternative to conditional Gaussian simulations. The constrainedKriging package computes CK, CMCK, and UK predictions for points or blocks of arbitrary shape from data observed at points in a two-dimensional survey domain. Predictions are computed for a random process model that involves a nonstationary mean function (modeled by a linear regression) and a weakly stationary, isotropic covariance function (or variogram). CK, CMCK, and UK require the point-block and block-block averages of the covariance function if the prediction targets are blocks. The constrainedKriging package uses numerically efficient approximations to compute these averages. The article contains, apart from a brief summary of CK and CMCK, a detailed description of the algorithm used to compute the point-block and block-block covariances, and it describes the functionality of the software in detail. The practical use of the package is illustrated by a comparison of universal and constrained lognormal block kriging for the Meuse Bank heavy metal data set.

Hofer, Christoph; Papritz, Andreas

2011-10-01

115

21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 false Wrist joint polymer constrained prosthesis. 888.3780...Devices § 888.3780 Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a...

2013-04-01

116

Automation of constrained-value business forms.  

National Technical Information Service (NTIS)

Expert systems can improve many business tasks. However, the nature of a constrained-value business form can result in a rule base that contains circular reasoning, unsuitable for expert system implementation. A methodology is presented for restructuring ...

M. L. Carson T. G. Beaumariage F. L. Greitzer

1993-01-01

117

Bandwidth Management in Resource Constrained Networks.  

National Technical Information Service (NTIS)

Hastily Formed Networks (HFNs) are typically deployed in resource constrained environments. Clients operating within HFNs have inadvertently utilized excessive bandwidth without user interaction. Our research focuses on managing bandwidth usage in resourc...

C. T. Schrock

2012-01-01

118

Study of the Constrained Vapor Bubble Thermosyphon.  

National Technical Information Service (NTIS)

The objective of this effort is to better understand the physics of evaporation, condensation, and fluid flow as they affect the heat transfer processes in a constrained vapor bubble heat exchanger (CVBHX). This CVBHX consists of a small enclosed containe...

P. C. Wayner J. L. Plawsky

2000-01-01

119

Characterization of the cereulide NRPS alpha-hydroxy acid specifying modules: activation of alpha-keto acids and chiral reduction on the assembly line.  

PubMed

Several nonribosomal peptide natural products are composites of alpha-hydroxy acid and alpha-amino acid monomers. Cereulide, the emetic toxin from the human pathogen Bacillus cereus, and valinomycin, from Streptomyces spp., are closely related macrocyclic K+ ionophores. The macrocyclic core of each natural product contains alternating peptide (six) and ester (six) bonds, and their cyclododecadepsipeptide structures consist of a tetradepsipeptide unit repeated three times. Here we overexpress the cereulide NRPS alpha-hydroxy acid specifying modules from CesA and CesB and demonstrate that each contains an alpha-keto acid activating adenylation domain and a chiral alpha-ketoacyl-S-carrier protein reductase (alpha-KR). The logic used by the cereulide NRPS is likely at work in the valinomycin NRPS and may be the general strategy used in bacterial NRPSs to form alpha-hydroxy acid containing natural products. PMID:16910662

Magarvey, Nathan A; Ehling-Schulz, Monika; Walsh, Christopher T

2006-08-23

120

Constraining weak annihilation using semileptonic D decays  

SciTech Connect

The recently measured semileptonic D{sub s} decay rate can be used to constrain weak annihilation (WA) effects in semileptonic D and B decays. We revisit the theoretical predictions for inclusive semileptonic D{sub (s)} decays using a variety of quark mass schemes. The most reliable results are obtained if the fits to B decay distributions are used to eliminate the charm quark mass dependence, without using any specific charm mass scheme. Our fit to the available data shows that WA is smaller than commonly assumed. There is no indication that the WA octet contribution (which is better constrained than the singlet contribution) dominates. The results constrain an important source of uncertainty in the extraction of |V{sub ub}| from inclusive semileptonic B decays.

Ligeti, Zoltan [Ernest Orlando Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States); Luke, Michael [Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada M5S 1A7 (Canada); Manohar, Aneesh V. [Department of Physics, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093 (United States)

2010-08-01

121

Amino acid analogs for tumor imaging  

DOEpatents

The invention provides novel amino acid compounds of use in detecting and evaluating brain and body tumors. These compounds combine the advantageous properties of 1-amino-cycloalkyl-1-carboxylic acids, namely, their rapid uptake and prolonged retention in tumors with the properties of halogen substituents, including certain useful halogen isotopes including fluorine-18, iodine-123, iodine-125, iodine-131, bromine-75, bromine-76, bromine-77 and bromine-82. In one aspect, the invention features amino acid compounds that have a high specificity for target sites when administered to a subject in vivo. Preferred amino acid compounds show a target to non-target ratio of at least 5:1, are stable in vivo and substantially localized to target within 1 hour after administration. An especially preferred amino acid compound is [{sup 18}F]-1-amino-3-fluorocyclobutane-1-carboxylic acid (FACBC). In another aspect, the invention features pharmaceutical compositions comprised of an {alpha}-amino acid moiety attached to either a four, five, or a six member carbon-chain ring. In addition, the invention features analogs of {alpha}-aminoisobutyric acid.

Goodman, M.M.; Shoup, T.

1998-09-15

122

Amino acid analogs for tumor imaging  

DOEpatents

The invention provides novel amino acid compounds of use in detecting and evaluating brain and body tumors. These compounds combine the advantageous properties of 1-amino-cycloalkyl-1-carboxylic acids, namely, their rapid uptake and prolonged retention in tumors with the properties of halogen substituents, including certain useful halogen isotopes including fluorine-18, iodine-123, iodine-125, iodine-131, bromine-75, bromine-76, bromine-77 and bromine-82. In one aspect, the invention features amino acid compounds that have a high specificity for target sites when administered to a subject in vivo. Preferred amino acid compounds show a target to non-target ratio of at least 5:1, are stable in vivo and substantially localized to target within 1 hour after administration. An especially preferred amino acid compound is ›.sup.18 F!-1-amino-3-fluorocyclobutane-1-carboxylic acid (FACBC). In another aspect, the invention features pharmaceutical compositions comprised of an .alpha.-amino acid moiety attached to either a four, five, or a six member carbon-chain ring. In addition, the invention features analogs of .alpha.-aminoisobutyric acid.

Goodman, Mark M. (Atlanta, GA); Shoup, Timothy (Decatur, GA)

1998-09-15

123

Amino acid analogs for tumor imaging  

DOEpatents

The invention provides novel amino acid compounds of use in detecting and evaluating brain and body tumors. These compounds combine the advantageous properties of 1-amino-cycloalkyl-1-carboxylic acids, namely, their rapid uptake and prolonged retention in tumors with the properties of halogen substituents, including certain useful halogen isotopes including fluorine-18, iodine-123, iodine-125, iodine-131, bromine-75, bromine-76, bromine-77 and bromine-82. In one aspect, the invention features amino acid compounds that have a high specificity for target sites when administered to a subject in vivo. Preferred amino acid compounds show a target to non-target ratio of at least 5:1, are stable in vivo and substantially localized to target within 1 hour after administration. An especially preferred amino acid compound is ›.sup.18 F!-1-amino-3-fluorocyclobutane-1-carboxylic acid (FACBC). In another aspect, the invention features pharmaceutical compositions comprised of an .alpha.-amino acid moiety attached to either a four, five, or a six member carbon-chain ring. In addition, the invention features analogs of .alpha.-aminoisobutyric acid.

Goodman, Mark M. (Atlanta, GA); Shoup, Timothy (Decatur, GA)

1998-10-06

124

Amino acid analogs for tumor imaging  

DOEpatents

The invention provides novel amino acid compounds of use in detecting and evaluating brain and body tumors. These compounds combine the advantageous properties of 1-amino-cycloalkyl-1-carboxylic acids, namely, their rapid uptake and prolonged retention in tumors with the properties of halogen substituents, including certain useful halogen isotopes including fluorine-18, iodine-123, iodine-125, iodine-131, bromine-75, bromine-76, bromine-77 and bromine-82. In one aspect, the invention features amino acid compounds that have a high specificity for target sites when administered to a subject in vivo. Preferred amino acid compounds show a target to non-target ratio of at least 5:1, are stable in vivo and substantially localized to target within 1 hour after administration. An especially preferred amino acid compound is [{sup 18}F]-1-amino-3-fluorocyclobutane-1-carboxylic acid (FACBC). In another aspect, the invention features pharmaceutical compositions comprised of an {alpha}-amino acid moiety attached to either a four, five, or a six member carbon-chain ring. In addition, the invention features analogs of {alpha}-aminoisobutyric acid.

Goodman, M.M.; Shoup, T.

1998-10-06

125

Constrained caloric curves for hot nuclei  

NASA Astrophysics Data System (ADS)

Simulations based on experimental data obtained from multifragmenting quasi-fused nuclei produced in central 129Xe + natSn collisions have been used to deduce event by event freeze-out properties on the thermal excitation energy range 4-12 AMeV. From such properties, information on constrained caloric curves has been derived. At constant average volumes caloric curves exhibit a monotonous behavior whereas for constrained pressures backbending is observed. Such results support the existence of a first order phase transition for hot nuclei.

Borderie, B.; Piantelli, S.; Rivet, M.-F.; Raduta, Ad. R.

2012-07-01

126

Evolutionary Techniques for Constrained Optimization Problems  

Microsoft Academic Search

: An Evolutionary Algorithm to solve general constrained optimization problems is proposed inthis paper. Mathematical programming problems such as linear, nonlinear, integer, boolean and mixed programmingproblems can be solved by using this technique. Some important characteristics of the EvolutionaryAlgorithm are a natural representation of solutions, a problem-independent technique for constraint satisfaction,tournament selection, complete generational replacement, and elitism strategy....

Fernando Jiménez; José L. Verdegay

1999-01-01

127

Constrained tri-sphere kinematic positioning system  

DOEpatents

A scalable and adaptable, six-degree-of-freedom, kinematic positioning system is described. The system can position objects supported on top of, or suspended from, jacks comprising constrained joints. The system is compatible with extreme low temperature or high vacuum environments. When constant adjustment is not required a removable motor unit is available.

Viola, Robert J (Jackson, WY)

2010-12-14

128

On Model Formulation in Constrained Ordination Analysis  

Microsoft Academic Search

Canonical correspondence analysis (CCA) is perhaps the most popular multivariate method used by envi- ronmental ecologists for constrained ordination analysis. It provides an approximate maximum likelihood estimate for the Gaussian response model. In this article, we argue that, for compelling reasons, the response model should be re-formulated so that the response function is regarded as a probability density function on

Mu Zhu; Trevor J. Hastie

129

Rhythmic Grouping Biases Constrain Infant Statistical Learning  

ERIC Educational Resources Information Center

|Linguistic stress and sequential statistical cues to word boundaries interact during speech segmentation in infancy. However, little is known about how the different acoustic components of stress constrain statistical learning. The current studies were designed to investigate whether intensity and duration each function independently as cues to…

Hay, Jessica F.; Saffran, Jenny R.

2012-01-01

130

Constrained Clustering for the Evolving Data Stream  

Microsoft Academic Search

In order to import the domain knowledge or application dependent parameters into the data min- ing systems, constraint-based mining has attracted a lot of research attention recently. However, most of the constraint-based mining algorithms are designed for static data sets, and are not investigated in the data stream environment. In this paper, we devise a framework of Constrained Clustering for

Bi-Ru Dai; Ming-Syan Chen

2007-01-01

131

Constrained Subjective Assessment of Student Learning  

ERIC Educational Resources Information Center

|Student learning is a complex incremental cognitive process; assessment needs to parallel this, reporting the results in similar terms. Application of fuzzy sets and logic to the criterion-referenced assessment of student learning is considered here. The constrained qualitative assessment (CQA) system was designed, and then applied in assessing a…

Saliu, Sokol

2005-01-01

132

Passive and active closures by constraining mechanisms  

Microsoft Academic Search

This paper provides a unified theoretical framework for grasping and manipulation by robotic grippers and hands as well as for fixing works by fixtures and vises. The concept of passive closure and active closure for general constraining mechanisms is introduced. Passive closure is further classified into passive form closure and passive force closure. Conditions for these closures to hold are

Tsuneo Yoshikawa

1996-01-01

133

Dynamic Response of Geometrically Constrained Vapor Bubbles  

Microsoft Academic Search

Geometrically constrained vapor bubbles are important in many microelectromechanical systems (MEMS), such as actuators and micro-pumps. We consider a two-dimensional model of a vapor bubble between two horizontal parallel boundaries held at different temperatures. When the temperatures are constant, a steady state can be achieved such that evaporation near the contact lines at the hot bottom plate is balanced by

Vladimir S. Ajaev; G. M. Homsy

2001-01-01

134

Constrained Control for Surgical Assistant Robots  

Microsoft Academic Search

This paper presents an approach to implement virtual fixtures for surgical robot assistants. Our approach uses a weighted, multi-objective (both linear and nonlinear) constrained optimization framework to formalize a library of virtual fixtures for task primitives. By our formulation, we provide a library of virtual fixtures on task primitives and a way to assemble multiple virtual fixture objects. We implement

Ankur Kapoor; Ming Li; Russell H. Taylor

2006-01-01

135

Stability-constrained operation for UPFC devices  

Microsoft Academic Search

Improper operations of UPFC can make power system lose its synchronism. This paper explores the principle of this stability problem, and a simple system with single UPFC is set up to demonstrate the existence of such stability problems. An algorithm is proposed to determine whether a UPFC operation is stability constrained or not. An additional UPFC operational constraint is also

Xiaohe Wu; Zhihua Qu; R. N. Mohapatra

2001-01-01

136

Constrained Pricing for Cloud Resource Allocation  

Microsoft Academic Search

Constrained pricing in a cloud computing envi- ronment is addressed using game theory. The objective of the model and the game is to enable cloud providers to maximize their revenue while satisfying users by maximizing their utilities. The users net utility is modeled as a function of resource demand with a corresponding price. The game consists in the cloud provider

Makhlouf Hadji; Wajdi Louati; Djamal Zeghlache

2011-01-01

137

Hard Constrained Semi-Markov Decision Processes  

Microsoft Academic Search

In multiple criteria Markov Decision Processes (MDP) where multiple costs are incurred at every decision point, current methods solve them by minimising the expected primary cost criterion while constraining the expectations of other cost criteria to some critical values. However, systems are of- ten faced with hard constraints where the cost criteria should never exceed some criticalvalues at any time,

Wai-leong Yeow; Chen-khong Tham; Wai-choong Wong

2006-01-01

138

Convexity and Bayesian constrained local models  

Microsoft Academic Search

The accurate localization of facial features plays a fundamental role in any face recognition pipeline. Constrained local models (CLM) provide an effective approach to localization by coupling ensembles of local patch detectors for non-rigid object alignment. A recent improvement has been made by using generic convex quadratic fitting (CQF), which elegantly addresses the CLM warp update by enforcing convexity of

Ulrich Paquet

2009-01-01

139

Convexity and Bayesian constrained local models  

Microsoft Academic Search

The accurate localization of facial features plays a fun- damental role in any face recognition pipeline. Constraine d local models (CLM) provide an effective approach to lo- calization by coupling ensembles of local patch detectors for non-rigid object alignment. A recent improvement has been made by using generic convex quadratic fitting (CQF), which elegantly addresses the CLM warp update by

Ulrich Paquet

2009-01-01

140

Automation of constrained-value business forms  

SciTech Connect

Expert systems can improve many business tasks. However, the nature of a constrained-value business form can result in a rule base that contains circular reasoning, unsuitable for expert system implementation. A methodology is presented for restructuring such a rule base for compatibility with a backward-chaining expert system.

Carson, M.L.; Beaumariage, T.G.; Greitzer, F.L.

1993-05-01

141

The Timetable Constrained Distance Minimization Problem  

Microsoft Academic Search

We define the timetable constrained distance minimization problem (TCDMP) which is a sports scheduling problem applicable for tournaments where the total travel distance must be min- imized. The problem consists of finding an optimal home-away assignment when the opponents of each team in each time slot are given. We present an integer programming, a constraint programming formulation and describe two

Rasmus V. Rasmussen; Michael A. Trick

2006-01-01

142

Peak-constrained least-squares optimization  

Microsoft Academic Search

We presented the basic concepts for peak-constrained least-squares (PCLS) optimization in previous papers. We present advanced PCLS optimization concepts in this paper. This paper discusses only a few of the many ways that PCLS design problems can be formulated. We believe that the PCLS optimality criterion can be customized to fit virtually any practical application. For example, PCLS optimization can

John W. Adams; James L. Sullivan

1998-01-01

143

Numerical methods for nonlinearly constrained optimization  

Microsoft Academic Search

A detailed description of a new feasible-point algorithm for nonlinearly constrained optimization is presented. The new method is based on the properties of the trajectory of minima obtained by varying the barrier parameter of the logarithmic barrier function. A nonfeasible-point method based on the trajectory of the quadratic penalty function is also described in detail. The search direction in the

M. H. Wright

1976-01-01

144

On Budget-Constrained Flow Improvement  

Microsoft Academic Search

This paper investigates the complexity of budget-constrained flow improvement problems. We are given a directed graph with capacities on the edges which can be increased at linear costs up to some upper bounds. The problem is to increase the capacities within budget restrictions such that the flow from the source to the sink vertex is maximized.We show that the problem

S. Schwarz; Sven Oliver Krumke

1998-01-01

145

A Transient Stability Constrained Optimal Power Flow  

Microsoft Academic Search

Stability is an important constraint in power system operation. Often trial and error heuristics are used that can be costly and imprecise. A new methodology that eliminates the need for repeated simulation to determine a transiently secure operating point is presented. The methodology involves a stability constrained Optimal Power Flow (OPF). The theoretical development is straightforwa rd: swing equations are

Deqiang Gan; Robert J. Thomas; Ray D. Zimmerman

146

Constrained Load Flow Using Recursive Quadratic Programming  

Microsoft Academic Search

The present paper will discuss the efficient, practical and definitive algorithm for dealing with constrained load flow problems. Algorithms based on mathematical programming and algorithms based on the load flow calculation methods have been studied since earlier days. However, on account of numerous control variables to be determined and of inadequate calculating efficiency, the guarantee of unfailing solution is yet

K. Aoki; A. Nishikori; R. Yokoyama

1987-01-01

147

Gröbner basis solutions of constrained interpolation problems  

Microsoft Academic Search

This paper extends the previous work of the authors on recursive Gröbner basis techniques in coding theory, Padé approximation, partial realization, interpolation, and modelling discrete-time behaviours. We present a general algorithm, applicable to a wide range of constrained interpolation problems in coding theory and systems theory, including list decoding and M-Padé approximation.

Henry O'Keeffe; Patrick Fitzpatrick

2002-01-01

148

Gustatory responses of eel palatine receptors to amino acids and carboxylic acids  

PubMed Central

The gustatory receptors of the eel palate were found to be extremely sensitive to amino acids and carboxylic acids. The results obtained are as follows: (a) 11 amino acids which are among naturally occurring amino acids elicited responses in the palatine nerve, but 9 amino acids did not elicit a response even at a high concentration. The effect of D- amino acids was always much less than that of their corresponding L- isomers. There was no appreciable difference in the effectiveness of an alpha-amino acid (alpha-alanine) and beta-amino acid (beta-alanine). (b) The threshold concentrations of the most potent amino acids (arginine, glycine) were between 10(-8) and 10(-9) M. A linear relation between the magnitude of the response and log stimulus concentration held for a wide concentration range for all the amino acids examined. (c) The palatine receptors responded sensitively to various carboxylic acid solutions whose pH was adjusted to neutral. The threshold concentrations varied between 10(-4) and 10(-7) M. The magnitude of the response at 10(-2) M increased with an increase of carbon chain length. (d) The extent of cross-adaptation was examined with various combinations of amino acids. A variety of the response patterns showing complete cross-adaptation, no cross-adaptation, or synergetic interaction was observed. The synergetic interaction was also observed when one amino acid below its threshold concentration was added to the other amino acid below its threshold concentration was added to the other amino acid. No cross-adaptation was observed between amino acids and fatty acids. (e) The treatment of the palate with papain led to loss of the responses to arginine, glycine, and histidine without affecting those to proline and acetic acid. The treatment with pronase E eliminated selectively the response to proline. The possibility that the eel gustatory receptors are responsible for sensing food at a distance was discussed.

1979-01-01

149

Constraining the braneworld with gravitational wave observations.  

PubMed

Some braneworld models may have observable consequences that, if detected, would validate a requisite element of string theory. In the infinite Randall-Sundrum model (RS2), the AdS radius of curvature, l, of the extra dimension supports a single bound state of the massless graviton on the brane, thereby reproducing Newtonian gravity in the weak-field limit. However, using the AdS/CFT correspondence, it has been suggested that one possible consequence of RS2 is an enormous increase in Hawking radiation emitted by black holes. We utilize this possibility to derive two novel methods for constraining l via gravitational wave measurements. We show that the EMRI event rate detected by LISA can constrain l at the approximately 1 microm level for optimal cases, while the observation of a single galactic black hole binary with LISA results in an optimal constraint of l < or = 5 microm. PMID:20481929

McWilliams, Sean T

2010-04-08

150

Constraining the Braneworld with Gravitational Wave Observations  

SciTech Connect

Some braneworld models may have observable consequences that, if detected, would validate a requisite element of string theory. In the infinite Randall-Sundrum model (RS2), the AdS radius of curvature, l, of the extra dimension supports a single bound state of the massless graviton on the brane, thereby reproducing Newtonian gravity in the weak-field limit. However, using the AdS/CFT correspondence, it has been suggested that one possible consequence of RS2 is an enormous increase in Hawking radiation emitted by black holes. We utilize this possibility to derive two novel methods for constraining l via gravitational wave measurements. We show that the EMRI event rate detected by LISA can constrain l at the {approx}1 {mu}m level for optimal cases, while the observation of a single galactic black hole binary with LISA results in an optimal constraint of l{<=}5 {mu}m.

McWilliams, Sean T. [Gravitational Astrophysics Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt Maryland 20771 (United States)

2010-04-09

151

Constraining interactions in cosmology's dark sector  

SciTech Connect

We consider the cosmological constraints on theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the universe, in light of the most recent supernovae, large scale structure and cosmic microwave background data. For a variety of models, we show that the strength of the coupling of dark matter to a quintessence field is constrained to be less than 7% of the coupling to gravity. We also show that long-range interactions between fermionic dark matter particles mediated by a light scalar with a Yukawa coupling are constrained to be less than 5% of the strength of gravity at a distance scale of 10 Mpc. We show that all of the models we consider are quantum mechanically weakly coupled, and argue that some other models in the literature are ruled out by quantum mechanical strong coupling.

Bean, Rachel; Laszlo, Istvan [Department of Astronomy, Cornell University, Ithaca, New York 14853 (United States); Flanagan, Eanna E. [Department of Astronomy, Cornell University, Ithaca, New York 14853 (United States); Laboratory for Elementary Particle Physics, Cornell University, Ithaca, New York 14853 (United States); Trodden, Mark [Department of Physics, Syracuse University, Syracuse, New York 13244 (United States)

2008-12-15

152

Self-constrained inversion of potential fields  

NASA Astrophysics Data System (ADS)

We present a potential-field-constrained inversion procedure based on a priori information derived exclusively from the analysis of the gravity and magnetic data (self-constrained inversion). The procedure is designed to be applied to underdetermined problems and involves scenarios where the source distribution can be assumed to be of simple character. To set up effective constraints, we first estimate through the analysis of the gravity or magnetic field some or all of the following source parameters: the source depth-to-the-top, the structural index, the horizontal position of the source body edges and their dip. The second step is incorporating the information related to these constraints in the objective function as depth and spatial weighting functions. We show, through 2-D and 3-D synthetic and real data examples, that potential field-based constraints, for example, structural index, source boundaries and others, are usually enough to obtain substantial improvement in the density and magnetization models.

Paoletti, V.; Ialongo, S.; Florio, G.; Fedi, M.; Cella, F.

2013-11-01

153

?-convergence of Variational Integrators for Constrained Systems  

NASA Astrophysics Data System (ADS)

For a physical system described by a motion in an energy landscape under holonomic constraints, we study the ?-convergence of variational integrators to the corresponding continuum action functional and the convergence properties of solutions of the discrete Euler-Lagrange equations to stationary points of the continuum problem. This extends the results in Müller and Ortiz (J. Nonlinear Sci. 14:279-296, 2004) to constrained systems. The convergence result is illustrated with examples of mass point systems and flexible multibody dynamics.

Schmidt, Bernd; Leyendecker, Sigrid; Ortiz, Michael

2009-04-01

154

Regularized constrained total least squares image restoration  

Microsoft Academic Search

In this paper the problem of restoring an image distorted by a linear space-invariant(LSI) point-spread function (psf) which is not exactly known is formulated as the solution ofa perturbed set of linear equations. The regularized constrained total least-squares (RCTLS)method is used to solve this set of equations. Using the diagonalization properties of thediscrete Fourier transform (DFT) for circulant matrices, the

Vladimir Z. Mesarovic; Nikolas P. Galatsanos; Aggelos K. Katsaggelos

1995-01-01

155

Reference governor for constrained piecewise affine systems  

Microsoft Academic Search

We present a methodology for designing reference tracking controllers for constrained, discrete-time piecewise affine systems. The approach follows the idea of reference governor techniques where the desired set-point is filtered by a system called the “reference governor”. Based on the system current state, set-point, and prescribed constraints, the reference governor computes a new set-point for a low-level controller so that

Francesco Borrelli; Paolo Falcone; Jaroslav Pekar; Greg Stewart

2009-01-01

156

Constraining Source Redshift Distributions with Gravitational Lensing  

NASA Astrophysics Data System (ADS)

We introduce a new method for constraining the redshift distribution of a set of galaxies, using weak gravitational lensing shear. Instead of using observed shears and redshifts to constrain cosmological parameters, we ask how well the shears around clusters can constrain the redshifts, assuming fixed cosmological parameters. This provides a check on photometric redshifts, independent of source spectral energy distribution properties and therefore free of confounding factors such as misidentification of spectral breaks. We find that ~40 massive (? v = 1200 km s-1) cluster lenses are sufficient to determine the fraction of sources in each of six coarse redshift bins to ~11%, given weak (20%) priors on the masses of the highest-redshift lenses, tight (5%) priors on the masses of the lowest-redshift lenses, and only modest (20%-50%) priors on calibration and evolution effects. Additional massive lenses drive down uncertainties as N_lens^{-{1\\over 2}}, but the improvement slows as one is forced to use lenses further down the mass function. Future large surveys contain enough clusters to reach 1% precision in the bin fractions if the tight lens-mass priors can be maintained for large samples of lenses. In practice this will be difficult to achieve, but the method may be valuable as a complement to other more precise methods because it is based on different physics and therefore has different systematic errors.

Wittman, D.; Dawson, W. A.

2012-09-01

157

Constrained layer damping system for box beams  

NASA Astrophysics Data System (ADS)

This paper discusses the results of a project aimed at developing an effective constrained layer damping system for a large steel box beam. The primary box beam evaluated was a 4.0-inch by 8.0-inch by 0.375-inch section box which was 96.0 inches long. The goal of the project was to obtain the most damping possible in the bending, twisting, and axial modes while meeting cost, weight, and installation requirements. The project started with the evaluation of the box beam as an appropriate solid beam with a continuous constrained layer damping system applied using a 6th order theory analysis program. The next analysis step was to advance to finite elements. During the FEA, bending modes in both planes, twisting modes, and axial modes were examined. The design iterations considered damping on the 8.0-inch surfaces only, damping on all surfaces, the effects of a standoff, and multiple segmentation in the constraining layer. After the analysis had developed the best damping configuration which met all the nondamping requirements, the damping system was fabricated and installed on the box beam for testing. This paper presents the results of the project from concept development through the test results.

Drake, Michael L.; Hopkins, David M.; Stack, Christopher

1996-05-01

158

CONSTRAINING SOURCE REDSHIFT DISTRIBUTIONS WITH GRAVITATIONAL LENSING  

SciTech Connect

We introduce a new method for constraining the redshift distribution of a set of galaxies, using weak gravitational lensing shear. Instead of using observed shears and redshifts to constrain cosmological parameters, we ask how well the shears around clusters can constrain the redshifts, assuming fixed cosmological parameters. This provides a check on photometric redshifts, independent of source spectral energy distribution properties and therefore free of confounding factors such as misidentification of spectral breaks. We find that {approx}40 massive ({sigma}{sub v} = 1200 km s{sup -1}) cluster lenses are sufficient to determine the fraction of sources in each of six coarse redshift bins to {approx}11%, given weak (20%) priors on the masses of the highest-redshift lenses, tight (5%) priors on the masses of the lowest-redshift lenses, and only modest (20%-50%) priors on calibration and evolution effects. Additional massive lenses drive down uncertainties as N{sub lens}{sup -1/2}, but the improvement slows as one is forced to use lenses further down the mass function. Future large surveys contain enough clusters to reach 1% precision in the bin fractions if the tight lens-mass priors can be maintained for large samples of lenses. In practice this will be difficult to achieve, but the method may be valuable as a complement to other more precise methods because it is based on different physics and therefore has different systematic errors.

Wittman, D.; Dawson, W. A., E-mail: dwittman@physics.ucdavis.edu [Physics Department, University of California, Davis, CA 95616 (United States)

2012-09-10

159

On Tree-Constrained Matchings and Generalizations  

Microsoft Academic Search

\\u000a We consider the following Tree-Constrained Bipartite Matching problem: Given two rooted trees T\\u000a 1?=?(V\\u000a 1,E\\u000a 1), T\\u000a 2?=?(V\\u000a 2,E\\u000a 2) and a weight function w: V\\u000a 1×V\\u000a 2 ???+?, find a maximum weight matching M\\\\mathcal{M} between nodes of the two trees, such that none of the matched nodes is an ancestor of another matched node in either of the\\u000a trees.

Stefan Canzar; Khaled Elbassioni; Gunnar W. Klau; Julián Mestre

2011-01-01

160

Modular implementations of linearly constrained beamformers  

NASA Astrophysics Data System (ADS)

This paper describes a cascade decomposition of the generalized sidelobe canceller (GSC) implementation for linearly constrained minimum variance beamformers. The GSC is initially separated into an adaptive interference cancellation module followed by a non-adaptive beamformer. We prove that the adaptive interference cancellation module can be decomposed into a cascade of first (or higher) order adaptive interference cancellation modules, where the order corresponds to the number of adaptive degrees of freedom represented in the module. This distributes the computational burden associated with determining the adaptive weights over several lower order problems and facilitates simultaneous implementation of beamformers with differing numbers of adaptive degrees of freedom.

Liu, Tsung-Ching; van Veen, Barry D.

1991-12-01

161

Constrained extremal problems for the difference product  

Microsoft Academic Search

Let ?n(x) be the difference product of n variables: ?n(x)=?(x1,…,xn)=?1?ij?n(xi?xj) and x1?xn=An,?i=1n(1+xi)=Bn,x1+?+xn=nSn. In this paper, constrained extremal problems of the difference product ?n(x) in which An,Bn or An,Sn are assigned, and the extremal problem of Bn where An and ?n(x)2 are assigned are studied. In particular limiting behaviour of the extremal values is found when the number of the variables

Jyoichi Kaneko

2010-01-01

162

Charged particles constrained to a curved surface  

NASA Astrophysics Data System (ADS)

We study the motion of charged particles constrained to arbitrary two-dimensional curved surfaces but interacting in three-dimensional space via the Coulomb potential. To speed up the interaction calculations, we use the parallel compute capability of the Compute Unified Device Architecture of today's graphics boards. The particles and the curved surfaces are shown using the Open Graphics Library. This paper is intended to give graduate students, who have basic experiences with electrostatics and the Lagrangian formalism, a deeper understanding of charged particle interactions and a short introduction of how to handle a many particle system using parallel computing on a single home computer.

Müller, Thomas; Frauendiener, Jörg

2013-01-01

163

Constrained statistical thermodynamic treatment of friction  

NASA Astrophysics Data System (ADS)

The molecular description of friction at a single, ideal microscopic contact of the sort realizable in scanning surface probe devices is greatly complicated by wide variations in the temporal regime t*[identical with]texpt/tr of the measurement, where texpt is the time taken to measure the frictional force Fs and tr is the time required for the system to attain a state of thermodynamic equilibrium. At one extreme (t*)>1 the system remains in equilibrium for the duration of the measurement and one can employ statistical thermodynamics (in practice, Monte Carlo simulation) to compute Fs, which depends only on the thermodynamic state. At the other extreme (t*)<1 the system remains out of equilibrium. One must then account for the dynamic history of the system, typically by means of nonequilibrium molecular dynamics. The range of t* between these extremes can be handled within a single theoretical framework based on the concept of "equivalent equilibrated states." Through addition of auxiliary potential fields to the Hamiltonian specific degrees of freedom of the system can be constrained. The properties of the constrained system are computed from the free energy of the system trapped in the equivalent equilibrated state by the constraints. The constraints are chosen to correspond to t*. The results of the theory applied to a one-dimensional model demonstrate dramatically the impact of history on Fs.

Diestler, D. J.

2002-08-01

164

Stability constrained optimal rescheduling of generation  

SciTech Connect

In this paper, an effective approach, based on the transient energy function (TEF) method of transient stability analysis, is proposed for stability constrained rescheduling of the generation and critical line flows for a given initial operating condition and designated contingency. In the proposed approach, the sensitivities of the energy margin with respect to changes in generation are used in the transient stability constraints, and distribution factors are used to monitor and constrain the critical line flows. The problem is formulated as a multiobjective optimization problem. A goal programming algorithm that incorporates an explicit knowledge base is used to solve the optimization problem. There are three objectives when the generation is rescheduled. (1) Energy margin is changed to the specific value which indicates the desired stability index of the system. (2) Critical line flows achieve the desired values as closely as possible. (3) Changes in generation are minimal. The proposed approach has been successfully tested on two power systems: a 17-generator and a 50-generator test networks.

Fouad, A.A.; Jianzhong, Tong (Iowa State Univ., Ames, IA (United States))

1993-02-01

165

Lnk constrains myeloproliferative diseases in mice  

PubMed Central

Hematopoietic stem and progenitor cell (HSPC) expansion is regulated by intrinsic signaling pathways activated by cytokines. The intracellular kinase JAK2 plays an essential role in cytokine signaling, and activating mutations in JAK2 are found in a number of hematologic malignancies. We previously demonstrated that lymphocyte adaptor protein (Lnk, also known as Sh2b3) binds JAK2 and attenuates its activity, thereby limiting HSPC expansion. Here we show that loss of Lnk accelerates and exacerbates oncogenic JAK2-induced myeloproliferative diseases (MPDs) in mice. Specifically, Lnk deficiency enhanced cytokine-independent JAK/STAT signaling and augmented the ability of oncogenic JAK2 to expand myeloid progenitors in vitro and in vivo. An activated form of JAK2, unable to bind Lnk, caused greater myeloid expansion than activated JAK2 alone and accelerated myelofibrosis, indicating that Lnk directly inhibits oncogenic JAK2 in constraining MPD development. In addition, Lnk deficiency cooperated with the BCR/ABL oncogene, the product of which does not directly interact with or depend on JAK2 or Lnk, in chronic myeloid leukemia (CML) development, suggesting that Lnk also acts through endogenous pathways to constrain HSPCs. Consistent with this idea, aged Lnk–/– mice spontaneously developed a CML-like MPD. Taken together, our data establish Lnk as a bona fide suppressor of MPD in mice and raise the possibility that Lnk dysfunction contributes to the development of hematologic malignancies in humans.

Bersenev, Alexey; Wu, Chao; Balcerek, Joanna; Jing, Jiang; Kundu, Mondira; Blobel, Gerd A.; Chikwava, Kudakwashe R.; Tong, Wei

2010-01-01

166

Constraining the divertor heat width in ITER  

NASA Astrophysics Data System (ADS)

A model is developed which constrains heat width, ?r based on global power balance, momentum conservation, pedestal stability and sheath heat transmission. The model relies on measurements of the ratio of separatrix to pedestal pressure; a ratio ˜5% is found to be expected for ITER. Applying this model indicates a constraint that the allowed ?r ˜ 10-30 mm for ITER if the divertor is in the high-recycling regime as expected (T < 20 eV) while a ?r ˜ 1-3 mm requires a separatrix pressure approximately equal to the top pedestal pressure in violation of physical reasoning and the concept of a pedestal. A weaker constraint is applied in the model that upstream separatrix temperature simultaneously satisfies power balance. The constrained model cannot satisfy power balance with ?r < 3 mm, and in order to obtain ?r ˜ 5 mm requires divertor plasma temperature >100 eV, a condition which would have very negative consequences for the divertor, but has never been observed experimentally.

Whyte, D. G.; LaBombard, B.; Hughes, J. W.; Lipschultz, B.; Terry, J.; Brunner, D.; Stangeby, P. C.; Elder, D.; Leonard, A. W.; Watkins, J.

2013-07-01

167

Geometrically Constrained Walls in Two Dimensions  

NASA Astrophysics Data System (ADS)

We address the effect of extreme geometry on a non-convex variational problem, motivated by studies on magnetic domain walls trapped by thin necks. The recent analytical results of Kohn and Slastikov (Calc. Var. Partial Differ. Equ. 28:33-57, 2007) revealed a variety of magnetic structures in three-dimensional ferromagnets depending on the size of the constriction. The main purpose of this paper is to study geometrically constrained walls in two dimensions. The analysis turns out to be significantly more challenging and requires the use of different techniques. In particular, the purely variational point of view of Kohn and Slastikov (loc. cit.) cannot be adopted in the present setting and is here replaced by a PDE approach. The existence of local minimizers representing geometrically constrained walls is proven under suitable symmetry assumptions on the domains and an asymptotic characterization of the wall profile is given. The limiting behavior, which depends critically on the scaling of length and height of the neck, turns out to be more complex than in the higher-dimensional case and a richer variety of regimes is shown to exist.

Morini, M.; Slastikov, V.

2012-02-01

168

Constraining torsion with Gravity Probe B  

SciTech Connect

It is well-entrenched folklore that all torsion gravity theories predict observationally negligible torsion in the solar system, since torsion (if it exists) couples only to the intrinsic spin of elementary particles, not to rotational angular momentum. We argue that this assumption has a logical loophole which can and should be tested experimentally, and consider nonstandard torsion theories in which torsion can be generated by macroscopic rotating objects. In the spirit of action=reaction, if a rotating mass like a planet can generate torsion, then a gyroscope would be expected to feel torsion. An experiment with a gyroscope (without nuclear spin) such as Gravity Probe B (GPB) can test theories where this is the case. Using symmetry arguments, we show that to lowest order, any torsion field around a uniformly rotating spherical mass is determined by seven dimensionless parameters. These parameters effectively generalize the parametrized post-Newtonian formalism and provide a concrete framework for further testing Einstein's general theory of relativity (GR). We construct a parametrized Lagrangian that includes both standard torsion-free GR and Hayashi-Shirafuji maximal torsion gravity as special cases. We demonstrate that classic solar system tests rule out the latter and constrain two observable parameters. We show that Gravity Probe B is an ideal experiment for further constraining nonstandard torsion theories, and work out the most general torsion-induced precession of its gyroscope in terms of our torsion parameters.

Mao Yi; Guth, Alan H.; Cabi, Serkan [Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Tegmark, Max [Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); MIT Kavli Institute for Astrophysics and Space Research, Cambridge, Massachusetts 02139 (United States)

2007-11-15

169

Substrate specificity of the amino acid transporter PAT1.  

PubMed

The proton coupled amino acid transporter PAT1 expressed in intestine, brain, and other organs accepts L- and D-proline, glycine, and L-alanine but also pharmaceutically active amino acid derivatives such as 3-amino-1-propanesulfonic acid, L-azetidine-2-carboxylic acid, and cis-4-hydroxy-D-proline as substrates. We systematically analyzed the structural requirements for PAT1 substrates by testing 87 amino acids, proline homologs, indoles, and derivatives. Affinity data and effects on membrane potential were determined using Caco-2 cells. For aliphatic amino acids, a blocked carboxyl group, the distance between amino and carboxyl group, and the position of the hydroxyl group are affinity limiting factors. Methylation of the amino group enhances substrate affinity. Hetero atoms in the proline template are well tolerated. Aromatic alpha-amino acids display low affinity. PAT1 interacts strongly with heterocyclic aromatic acids containing an indole scaffold. The structural requirements of PAT1 substrates elucidated in this study will be useful for the development of prodrugs. PMID:16699824

Metzner, L; Neubert, K; Brandsch, M

2006-05-15

170

Formaldehyde in the Far Outer Galaxy: Constraining the Outer Boundary of the Galactic Habitable Zone  

Microsoft Academic Search

We present results from an initial survey of the 212111 transition of formaldehyde (H2CO) at 140.8 GHz in giant molecular clouds in the far outer Galaxy (RG 16 kpc). Formaldehyde is a key prebiotic molecule that likely plays an important role in the development of amino acids. Determining the outermost extent of the H2CO distribution can constrain the outer limit

Samantha K. Blair; Loris Magnani; Jan Brand; Jan G. A. Wouterloot

2008-01-01

171

Damping Optimization by Integrating Enhanced Active Constrained Layer and Active-Passive Hybrid Constrained Layer Treatments  

NASA Astrophysics Data System (ADS)

The feasibility of integrating the enhanced active constrained layer (EACL) and active-passive hybrid constrained layer (HCL) treatments to achieve a better combination of the system's closed-loop damping and open-loop (fail-safe) damping (without active action) is investigated in this research. Given a uniform strain field in the host structure, the EACL with stiff and equal edge elements (symmetric EACL) has been shown to provide high closed-loop damping by significantly increasing the direct active control authority of the cover sheet. The open-loop damping of the system, however, could be low. On the other hand, the HCL has been demonstrated to offer more balanced open-loop and closed-loop damping actions, although the HCL closed-loop damping is not as high as that of the EACL. The idea here is therefore to combine the two approaches and develop an integrated HCL-EACL treatment. The focus is to maximize the system closed-loop damping while maintaining an open-loop damping margin for fail-safe reasons. For a given strain field in the host structure, optimization routines are used to search for the best design parameters: the optimal control gain, the stiffness of the edge elements and the active material coverage ratio in the constraining layer. It is found that integrating the EACL and the HCL will introduce more flexibility in the design of constrained layer damping treatments with actively enhanced actions. Higher open-loop damping can be achieved for the same closed-loop damping requirement and vice versa. The hybrid cover sheet is found to create significant shear in the viscoelastic layer while the edge elements are used to provide strong direct active control authority for the constraining layer. A better mixture of the open-loop and closed-loop damping can generally be obtained with the integrated system.

Liu, Y.; Wang, K. W.

2002-08-01

172

Gauge fields and extrapotentials in constrained quantum systems  

NASA Astrophysics Data System (ADS)

We derive an effective Hamiltonian for a quantum system constrained to a submanifold (the constraint manifold) of configuration space (the ambient space) by an infinite restoring force. We pay special attention to how this Hamiltonian depends on quantities which are external to the constraint manifold, such as the extrinsic curvature of the constraint manifold, the curvature of the ambient space, and the constraining potential. In particular, we find the remarkable fact that the twisting of the constraining potential appears as a gauge potential in the constrained Hamiltonian. This gauge potential is closely related to the geometric phase originally discussed by Berry. The constrained Hamiltonian also contains an effective potential depending on the extrinsic curvature of the constraint manifold, the curvature of the ambient space, and the twisting of the constraining potential. The general nature of our analysis allows applications to a wide variety of problems, such as rigid molecules, the evolution of molecular systems along reaction paths, and quantum strip waveguides.

Mitchell, Kevin A.

2001-04-01

173

Remote gaming on resource-constrained devices  

NASA Astrophysics Data System (ADS)

Games have become important applications on mobile devices. A mobile gaming approach known as remote gaming is being developed to support games on low cost mobile devices. In the remote gaming approach, the responsibility of rendering a game and advancing the game play is put on remote servers instead of the resource constrained mobile devices. The games rendered on the servers are encoded as video and streamed to mobile devices. Mobile devices gather user input and stream the commands back to the servers to advance game play. With this solution, mobile devices with video playback and network connectivity can become game consoles. In this paper we present the design and development of such a system and evaluate the performance and design considerations to maximize the end user gaming experience.

Reza, Waazim; Kalva, Hari; Kaufman, Richard

2010-08-01

174

Constraining Dark Energy with Neutrino Physics  

SciTech Connect

We show that the particle properties of the Standard Model fields can determine the nature of Dark Energy. In particular, the mass of the neutrinos plays an important role in the determination of the equation of state w of Dark Energy. Using the Heidelberg-Moscow double beta decay experiment, which detects a large neutrino mass, we show that the impact of this measurement with the other cosmological data sets constrains the equation of state to -1.67

Macorra, A. de la [Instituto de Fisica, Universidad Nacional Autonoma de Mexico Apdo. Postal 20-364, 01000 Mxico D.F. (Mexico)

2009-04-20

175

Constraining metasomatism in the oceanic lithosphere  

NASA Astrophysics Data System (ADS)

Serpentinization is the most prominent fluid-mediated alteration process in the oceanic lithosphere, but the physical and chemical conditions of this process are difficult to constrain. It is crucial to establish a framework of mineralogical markers that constrain (a) whether the reaction proceeded without substantial addition of elements from the fluid (isochemical), (b) the reaction is isovolumetric generating no internal stresses and (c) if the overall system was closed with respect to certain elements. We have examined ophiolitic metaperidotites from Norway, combining microtextural and microchemical observations to gain further insight into the complex fluid-mediated phase transformations occurring during the alteration of the oceanic lithosphere. Serpentinization can be isovolumetric, resulting in pseudomorphic mineral replacement reactions (e.g. Viti et al., 2005), or produce an observable volume increase (e.g. Shervais et al., 2005). In the case of olivine, the ideal reaction is commonly written as forsteritic olivine reacting to lizardite and brucite, i.e. 2 Mg2SiO4 + 3 H2O - Mg3[Si2O5](OH)4 + Mg(OH)2, implying a total volume increase of approximately 20%. However, if Mg was lost from the system, the reaction can also be written as 2 Mg2SiO4 + 2 H+ + H2O - Mg3[Si2O5](OH)4 + Mg2+. This suggests that the solid volume is preserved and no internal stresses are generated. Therefore, the presence of brucite could be used to constrain volumetric changes during serpentinization. However, the small size and sparse distribution of brucite makes it difficult to find in serpentinized metaperidotites. Here we show that micro-Raman spectroscopy is a reliable tool to identify even nanometer-sized brucite in serpentine. In addition, we also used the electron backscatter diffraction (EBSD) technique to identify volume increase illustrated by the progressive change of olivine orientation at the tip of a crack induced by serpentinization. Furthermore, it is important to constrain the degree of system openness and the transport of elements through the fluid phase. Observations from fractures in metapyroxenite layers from the Røragen-Feragen ultramafic complex provide closer insight into the late stage alteration of the oceanic lithosphere. Detailed electron microscopy reveals that these fractures are filled with polyhedral serpentine, indicating late stage open system conditions (Andreani et al., 2007). However, microtextures and reactive transport modeling suggest that Ca from clinopyroxene dissolution in the metapyroxenite layers was instantaneously precipitated as andradite within the fracture, without major Ca transport. Hence, although the overall system can be regarded as open for water, Ca exhibits closed system behavior on the decimeter scale within the metapyroxenite layers. Our observations show that mineralogical and microtextural markers, such as characteristic phases, their spatial relationship and stress generation associated with replacement, provide an insight into the metasomatic conditions of oceanic lithosphere alteration. References: Andreani et al. (2007), Geochem. Geophys. Geosyst., 8 (2). Shervais et al. (2005), Int. Geol. Rev., 47, 1-23. Viti et al. (2005) Min. Mag., 69 (2), 491-507.

Plümper, Oliver; Beinlich, Andreas; Austrheim, Hâkon

2010-05-01

176

Constraining the anisotropic expansion of the Universe  

NASA Astrophysics Data System (ADS)

We study the possibly existing anisotropy in the accelerating expansion Universe with the Union2 type Ia supernovae data and gamma-ray burst data. We construct a direction-dependent dark energy model and constrain the anisotropy direction and strength of modulation. We find that the maximum anisotropic deviation direction is (l,b)=(126°,13°) [or, equivalently, (l,b)=(306°,-13°)], and the current anisotropy level is g0=0.030+0.010-0.030 (1? confidence level with Union2 data). Our results do not show strong evidence for the anisotropic dark energy model. We also discuss potential methods that may distinguish the peculiar velocity field from the anisotropic dark energy model.

Cai, Rong-Gen; Ma, Yin-Zhe; Tang, Bo; Tuo, Zhong-Liang

2013-06-01

177

Constraining CO emission estimates using atmospheric observations  

NASA Astrophysics Data System (ADS)

We apply a four-dimensional variational (4D-Var) data assimilation system to optimize carbon monoxide (CO) emissions and to reduce the uncertainty of emission estimates from individual sources using the chemistry transport model TM5. In the first study only a limited amount of surface network observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) is used to test the 4D-Var system. Uncertainty reduction up to 60% in yearly emissions is observed over well-constrained regions and the inferred emissions compare well with recent studies for 2004. However, since the observations only constrain total CO emissions, the 4D-Var system has difficulties separating anthropogenic and biogenic sources in particular. The inferred emissions are validated with NOAA aircraft data over North America and the agreement is significantly improved from the prior to posterior simulation. Validation with the Measurements Of Pollution In The Troposphere (MOPITT) instrument shows a slight improved agreement over the well-constrained Northern Hemisphere and in the tropics (except for the African continent). However, the model simulation with posterior emissions underestimates MOPITT CO total columns on the remote Southern Hemisphere (SH) by about 10%. This is caused by a reduction in SH CO sources mainly due to surface stations on the high southern latitudes. In the second study, we compare two global inversions to estimate carbon monoxide (CO) emissions for 2004. Either surface flask observations from NOAA or CO total columns from the MOPITT instrument are assimilated in a 4D-Var framework. In the Southern Hemisphere (SH) three important findings are reported. First, due to their different vertical sensitivity, the stations-only inversion increases SH biomass burning emissions by 108 Tg CO/yr more than the MOPITT-only inversion. Conversely, the MOPITT-only inversion results in SH natural emissions (mainly CO from oxidation of NMVOCs) that are 185 Tg CO/yr higher compared to the stations-only inversion. Second, MOPITT-only derived biomass burning emissions are reduced with respect to the prior which is in contrast to previous (inverse) modeling studies. Finally, MOPITT derived total emissions are significantly higher for South America and Africa compared to the stations-only inversion. This is likely due to a positive bias in the MOPITT V4 product. This bias is also apparent from validation with surface stations and ground-truth FTIR columns. In the final study we present the first inverse modeling study to estimate CO emissions constrained by both surface (NOAA) and satellite (MOPITT) observations using a bias correction scheme. This approach leads to the identification of a positive bias of maximum 5 ppb in MOPITT column-averaged CO mixing ratios in the remote Southern Hemisphere (SH). The 4D-Var system is used to estimate CO emissions over South America in the period 2006-2010 and to analyze the interannual variability (IAV) of these emissions. We infer robust, high spatial resolution CO emission estimates that show slightly smaller IAV due to fires compared to the Global Fire Emissions Database (GFED3) prior emissions. Moreover, CO emissions probably associated with pre-harvest burning of sugar cane plantations are underestimated in current inventories by 50-100%.

Hooghiemstra, P. B.

2012-06-01

178

Maximizing power to constrain simple conceptual models  

NASA Astrophysics Data System (ADS)

Traditionally, hydrological models are calibrated to observables such as discharge or groundwater levels. However, in recent years more and more researchers recognize that catchments organize themselves, and there have been strong arguments for behavioral models (i.e. models that constrain their parameters by an organizing principle). The principle of Maximum Entropy Production (MEP) is an often mentioned candidate. But until now, only limited studies explore the use of this principle. In this study we explore the principle of maximum power (which is equivalent to MEP) to constrain the water partitioning in the unsaturated zone and link that to widely applied bucket models such as HBV. Maximum power (or MEP) only applies to systems that are in steady state. By only considering the yearly water balance, the system can be assumed to be in steady state. Therefore we limit ourselves to the unsaturated zone in which the partitioning between transpiration and runoff takes place. For each time step the matrix potential in the unsaturated zone has been determined. The matrix potential influences the driving gradients of both evapotranspiration and runoff to the stream. Power was then determined by multiplying the water flux with the gradient driving that flux. By varying the unsaturated hydraulic conductivity, soil depth and a shape factor accounting for the spatial variability in soil depth, power has been maximized. Since a catchment is never in steady state due to e.g. tectonic movement, only those parameter sets were considered that mimic the yearly water balance correctly. This study is one of the first studies that explore the principle of maximum Power (or MEP) to model real world catchments. It sheds light on its usefulness in hydrology and its limitation and it may bring the hydrological sciences a step further in understanding catchment behavior.

Westhoff, M.; Zehe, E.

2012-04-01

179

A Path Algorithm for Constrained Estimation  

PubMed Central

Many least-square problems involve affine equality and inequality constraints. Although there are a variety of methods for solving such problems, most statisticians find constrained estimation challenging. The current article proposes a new path-following algorithm for quadratic programming that replaces hard constraints by what are called exact penalties. Similar penalties arise in l1 regularization in model selection. In the regularization setting, penalties encapsulate prior knowledge, and penalized parameter estimates represent a trade-off between the observed data and the prior knowledge. Classical penalty methods of optimization, such as the quadratic penalty method, solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ?, one recovers the constrained solution. In the exact penalty method, squared penalties!are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. The exact path-following method starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. Path following in Lasso penalized regression, in contrast, starts with a large value of the penalty constant and works its way downward. In both settings, inspection of the entire solution path is revealing. Just as with the Lasso and generalized Lasso, it is possible to plot the effective degrees of freedom along the solution path. For a strictly convex quadratic program, the exact penalty algorithm can be framed entirely in terms of the sweep operator of regression analysis. A few well-chosen examples illustrate the mechanics and potential of path following. This article has supplementary materials available online.

Zhou, Hua; Lange, Kenneth

2013-01-01

180

A phenomenological model of active constrained layers  

NASA Astrophysics Data System (ADS)

Active constrained layer (ACL) treatments consist of a layer of viscoelastic material bonded to the host structure and constrained by an actuator. These treatments control vibrations by means of several mechanisms: the actuator increases the dissipation of energy by increasing the shearing in the viscoelastic layer, and simultaneously it controls the vibrations by applying forces to the host structure through the viscoelastic layer. To optimise ACL treatments, it is necessary to understand their physics. While several models in the literature successfully predict the response of structures treated with ACL, the complexity of these models is not well suited for investigating the mechanisms underlying the behaviour of ACL treatments. This paper describes a simple model of beams treated with ACL, which allows analytical investigations of the damping and control mechanisms of ACL treatment. The model is based on a modal approach in which each mode of the structure is represented by a mass spring system. The two layers of the ACL patch are represented by two springs in series, the control voltage in effect driving one of these springs. A numerical validation indicates that the model accuracy is good for ACL patches whose length is smaller than the wavelength of the beam and located at appropriate positions on the host structure. In order to demonstrate the usefulness of the lumped parameter model to get insight into the behaviour of ACL treatments, the various ACL damping mechanisms are briefly discussed. Results indicate that proportional feedback control is associated with an increase of shearing in the viscoelastic layer, while the action of active forces dominates when derivative feedback is used.

Illaire, Hélène; Kropp, Wolfgang; Mace, Brian

2005-07-01

181

Ocean Acidification-Induced Food Quality Deterioration Constrains Trophic Transfer  

PubMed Central

Our present understanding of ocean acidification (OA) impacts on marine organisms caused by rapidly rising atmospheric carbon dioxide (CO2) concentration is almost entirely limited to single species responses. OA consequences for food web interactions are, however, still unknown. Indirect OA effects can be expected for consumers by changing the nutritional quality of their prey. We used a laboratory experiment to test potential OA effects on algal fatty acid (FA) composition and resulting copepod growth. We show that elevated CO2 significantly changed the FA concentration and composition of the diatom Thalassiosira pseudonana, which constrained growth and reproduction of the copepod Acartia tonsa. A significant decline in both total FAs (28.1 to 17.4 fg cell?1) and the ratio of long-chain polyunsaturated to saturated fatty acids (PUFA:SFA) of food algae cultured under elevated (750 µatm) compared to present day (380 µatm) pCO2 was directly translated to copepods. The proportion of total essential FAs declined almost tenfold in copepods and the contribution of saturated fatty acids (SFAs) tripled at high CO2. This rapid and reversible CO2-dependent shift in FA concentration and composition caused a decrease in both copepod somatic growth and egg production from 34 to 5 eggs female?1 day?1. Because the diatom-copepod link supports some of the most productive ecosystems in the world, our study demonstrates that OA can have far-reaching consequences for ocean food webs by changing the nutritional quality of essential macromolecules in primary producers that cascade up the food web.

Hauss, Helena; Schulz, Kai G.; Riebesell, Ulf; Sommer, Ulrich; Winder, Monika

2012-01-01

182

Divergent routes to chiral cyclobutane synthons from (-)-alpha-pinene and their use in the stereoselective synthesis of dehydro amino acids.  

PubMed

Several polyfunctionalized cyclobutane derivatives have been synthesized using commercial (-)-alpha-pinene and (-)-verbenone as chiral precursors. Thus, oxidative cleavage of these compounds by using ruthenium trichloride afforded quantitatively (-)-cis-pinonic and (-)-cis-pinononic acids, respectively, without epimerization. These products were converted into several types of aldehydes, which are the key intermediates in the synthesis of cyclobutane dehydro amino acids via Wittig-Horner condensations with suitable phosphonates. These reactions are highly stereoselective, affording exclusively (Z) isomers, stereochemistry being assessed by NMR experiments. The obtained dehydro amino acids are polyfunctionalized molecules useful for the synthesis of other alpha-amino acids, with additional chiral centers, whose configuration must be induced by the chirality of the terpene employed as a precursor. PMID:10866610

Moglioni, A G; García-Expósito, E; Aguado, G P; Parella, T; Branchadell, V; Moltrasio, G Y; Ortuño, R M

2000-06-30

183

Sequential unconstrained minimization algorithms for constrained optimization  

NASA Astrophysics Data System (ADS)

The problem of minimizing a function f(x):RJ ? R, subject to constraints on the vector variable x, occurs frequently in inverse problems. Even without constraints, finding a minimizer of f(x) may require iterative methods. We consider here a general class of iterative algorithms that find a solution to the constrained minimization problem as the limit of a sequence of vectors, each solving an unconstrained minimization problem. Our sequential unconstrained minimization algorithm (SUMMA) is an iterative procedure for constrained minimization. At the kth step we minimize the function G_k(x)=f(x)+g_k(x), to obtain xk. The auxiliary functions gk(x):D ? RJ ? R+ are nonnegative on the set D, each xk is assumed to lie within D, and the objective is to minimize the continuous function f:RJ ? R over x in the set C=\\overline D , the closure of D. We assume that such minimizers exist, and denote one such by \\hat x . We assume that the functions gk(x) satisfy the inequalities 0\\leq g_k(x)\\leq G_{k-1}(x)-G_{k-1}(x^{k-1}), for k = 2, 3, .... Using this assumption, we show that the sequence {f(xk)} is decreasing and converges to f({\\hat x}) . If the restriction of f(x) to D has bounded level sets, which happens if \\hat x is unique and f(x) is closed, proper and convex, then the sequence {xk} is bounded, and f(x^*)=f({\\hat x}) , for any cluster point x*. Therefore, if \\hat x is unique, x^*={\\hat x} and \\{x^k\\}\\rightarrow {\\hat x} . When \\hat x is not unique, convergence can still be obtained, in particular cases. The SUMMA includes, as particular cases, the well-known barrier- and penalty-function methods, the simultaneous multiplicative algebraic reconstruction technique (SMART), the proximal minimization algorithm of Censor and Zenios, the entropic proximal methods of Teboulle, as well as certain cases of gradient descent and the Newton-Raphson method. The proof techniques used for SUMMA can be extended to obtain related results for the induced proximal distance method of Auslander and Teboulle.

Byrne, Charles

2008-02-01

184

CONSTRAINING DARK ENERGY WITH GAMMA-RAY BURSTS  

SciTech Connect

We use the measurement of gamma-ray burst (GRB) distances to constrain dark energy cosmological model parameters. We employ two methods for analyzing GRB data-fitting luminosity relation of GRBs in each cosmology and using distance measures computed from binned GRB data. Current GRB data alone cannot tightly constrain cosmological parameters and allow for a wide range of dark energy models.

Samushia, Lado; Ratra, Bharat, E-mail: lado@phys.ksu.ed, E-mail: ratra@phys.ksu.ed [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, KS 66506 (United States)

2010-05-10

185

Positioning mobile manipulators to perform constrained linear trajectories  

Microsoft Academic Search

For mobile manipulators envisioned in home en- vironments a kitchen scenario provides a challenging testbed for numerous skills. Diverse manipulation actions are required, e.g. simple pick and place for moving objects and constrained motions for opening doors and drawers. The robot kinematics and link limits however are restrictive. Therefore especially a constrained trajectory will not be executable from arbitrary placements

Franziska Zacharias; Christoph Borst; Michael Beetz; Gerd Hirzinger

2008-01-01

186

Regularized Partial and/or Constrained Redundancy Analysis  

ERIC Educational Resources Information Center

Methods of incorporating a ridge type of regularization into partial redundancy analysis (PRA), constrained redundancy analysis (CRA), and partial and constrained redundancy analysis (PCRA) were discussed. The usefulness of ridge estimation in reducing mean square error (MSE) has been recognized in multiple regression analysis for some time,…

Takane, Yoshio; Jung, Sunho

2008-01-01

187

A GLOBAL OPTIMIZATION APPROACH TO RATIONALLY CONSTRAINED RATIONAL PROGRAMMING  

Microsoft Academic Search

The rationally constrained rational programming (RCR) problem is shown, for the first time, to be equivalent to the quadratically constrained quadratic programming problem with convex objective function and constraints that are all convex except for one that is concave and separable. This equivalence is then used in developing a novel implementation of the Generalized Benders Decomposition (GBDA) which, unlike all

VASILIOS MANOUSIOUTHAKIS; DENNIS SOURLAS

1992-01-01

188

Asymptotic and Lyapunov stability of constrained and Poisson equilibria  

Microsoft Academic Search

This paper includes results centered around three topics, all of them related with the nonlinear stability of equilibria in constrained dynamical systems. First, we prove an energy-Casimir type sufficient condition for stability that uses functions that are not necessarily conserved by the flow and that takes into account the asymptotically stable behavior that may occur in certain constrained systems, such

Juan-Pablo Ortega; Víctor Planas-Bielsa; Tudor S. Ratiu

2005-01-01

189

The Pendulum: From Constrained Fall to the Concept of Potential  

ERIC Educational Resources Information Center

Kuhn underlined the relevance of Galileo's gestalt switch in the interpretation of a swinging body from constrained fall to time metre. But the new interpretation did not eliminate the older one. The constrained fall, both in the motion of pendulums and along inclined planes, led Galileo to the law of free fall. Experimenting with physical…

Bevilacqua, Fabio; Falomo, Lidia; Fregonese, Lucio; Giannetto, Enrico; Giudice, Franco; Mascheretti, Paolo

2006-01-01

190

The Pendulum: From Constrained Fall to the Concept of Potential  

ERIC Educational Resources Information Center

|Kuhn underlined the relevance of Galileo's gestalt switch in the interpretation of a swinging body from constrained fall to time metre. But the new interpretation did not eliminate the older one. The constrained fall, both in the motion of pendulums and along inclined planes, led Galileo to the law of free fall. Experimenting with physical…

Bevilacqua, Fabio; Falomo, Lidia; Fregonese, Lucio; Giannetto, Enrico; Giudice, Franco; Mascheretti, Paolo

2006-01-01

191

Dynamic security constrained optimal power flow\\/VAr planning  

Microsoft Academic Search

Traditionally security constrained optimal power flow and VAr planning methods consider static security observing voltage profile and flow constraints under normal and post contingency conditions. Ideally, these formulations should be extended to consider dynamic security. This paper reports on a BC Hydro\\/CEPEL joint effort establishing a dynamic security constrained OPF\\/VAr planning tool which considers simultaneously static constraints as well as

Ebrahim Vaahedi; Yakout Mansour; Chris Fuchs; Sergio Granville; Maria de Lujan Latore; Hamid Hamadanizadeh

2001-01-01

192

Point Constrained Optical Flow For LV Motion Detection  

Microsoft Academic Search

In this paper, we propose a new method for left ventricle (LV) motion estimation. The method is based on a point- constrained optical flow algorithm for heart motion estimation. The constrained points are the corresponding point pairs in subsequent images. The motion estimation of these characteristic points can be obtained using techniques such as shape- based tracking of perceptually salient

Tvrtko Macan

193

Point-constrained optical flow for LV motion detection  

Microsoft Academic Search

In this paper, we propose a new method for left ventricle (LV) motion estimation. The method is based on a point-constrained optical flow algorithm for heart motion estimation. The constrained points are the corresponding point pairs in subsequent images. The motion estimation of these characteristic points can be obtained using techniques such as shape-based tracking of perceptually salient points on

Sven Loncaric; Tvrtko Macan

2000-01-01

194

Probabilistic constrained load flow based on sensitivity analysis  

Microsoft Academic Search

This paper presents a method for network constrained setting of power system control variables based on probabilistic load flow analysis. The method determines operating constraint violations for a whole planning period together with the probability of each violation. An iterative algorithm is subsequently employed providing adjustments of the control variables based on sensitivity analysis of the constrained variables with respect

T. S. Karzikatsanis; N. D. Hatziargyriou

1994-01-01

195

Constraining groundwater modeling with magnetic resonance soundings.  

PubMed

Magnetic resonance sounding (MRS) is a noninvasive geophysical method that allows estimating the free water content and transmissivity of aquifers. In this article, the ability of MRS to improve the reliability of a numerical groundwater model is assessed. Thirty-five sites were investigated by MRS over a ?5000 km(2) domain of the sedimentary Continental Terminal aquifer in SW Niger. Time domain electromagnetic soundings were jointly carried out to estimate the aquifer thickness. A groundwater model was previously built for this section of the aquifer and forced by the outputs from a distributed surface hydrology model, to simulate the observed long-term (1992 to 2003) rise in the water table. Uncertainty analysis had shown that independent estimates of the free water content and transmissivity values of the aquifer would facilitate cross-evaluation of the surface-water and groundwater models. MRS results indicate ranges for permeability (K = 1 × 10(-5) to 3 × 10(-4) m/s) and for free water content (w = 5% to 23% m(3) /m(3) ) narrowed by two orders of magnitude (K) and by ?50% (w), respectively, compared to the ranges of permeability and specific yield values previously considered. These shorter parameter ranges result in a reduction in the model's equifinality (whereby multiple combinations of model's parameters are able to represent the same observed piezometric levels), allowing a better constrained estimate to be derived for net aquifer recharge (?22 mm/year). PMID:22150349

Boucher, Marie; Favreau, Guillaume; Nazoumou, Yahaya; Cappelaere, Bernard; Massuel, Sylvain; Legchenko, Anatoly

2011-12-07

196

Security constrained optimization - A case study  

SciTech Connect

This paper describes the solution to a voltage study problem which determines the amount, location, and type of high voltage capacitors to be placed in the bulk transmission system to provide voltage support during severe system contingencies. A new solution method is compared with a more conventional approach to reactive power planning by applying the new method to a scaled down version of a recently completed study conducted by the New York Power Pool. A new optimization approach is introduced to solve the contingency constrained Optimal Power Flow problem, which is to minimize an objective function such as capacitor additions, while satisfying all steady-state power flow and voltage constraints for both the pre- and all post-contingency states. The results of a conventional study using a power flow program and an Optimal Power Flow program are compared with those of the new software tool presented here. The comparison shows that the optimization approach produces similar var allocations with considerably less effort than the conventional approach, with all of the added benefits of an Optimal Power Flow solution.

Merritt, W.C.; Saylor, C.H.; Burchett, R.C.

1988-08-01

197

Prior Image Constrained Compressed Sensing (PICCS).  

PubMed

It has been known for a long time that, in order to reconstruct a streak-free image in tomography, the sampling of view angles should satisfy the Shannon/Nyquist criterion. When the number of view angles is less than the Shannon/Nyquist limit, view aliasing artifacts appear in the reconstructed images. Most recently, it was demonstrated that it is possible to accurately reconstruct a sparse image using highly undersampled projections provided that the samples are distributed at random. The image reconstruction is carried out via an ?(1) norm minimization procedure. This new method is generally referred to as compressed sensing (CS) in literature. Specifically, for an N × N image with S significant image pixels, the number of samples for an accurate reconstruction of the image is O(S ln N). In medical imaging, some prior images may be reconstructed from a different scan or from the same acquired time-resolved data set. In this case, a new image reconstruction method, Prior Image Constrained Compressed Sensing (PICCS), has been recently developed to reconstruct images using a vastly undersampled data set. In this paper, we introduce the PICCS algorithm and demonstrate how to use this new algorithm to solve problems in medical imaging. PMID:19724658

Chen, Guang-Hong; Tang, Jie; Leng, Shuai

2008-03-01

198

Dynamic characteristic analysis of the constrained beams  

NASA Astrophysics Data System (ADS)

A procedure is developed in this investigation to study the propagation of impact-induced axial waves in the constrained beams that undergo large rigid body displacements. The solution of the wave equations is obtained using the Fourier method. Kinematic conditions which describe mechanical joints in the system are formulated using a set of nonlinear algebraic constraint equations that are introduced to the dynamic formulation using the vector of Lagrange multipliers. The initial conditions which represent the jump discontinuity in the elastic coordinates as the result of impact are predicted using the generalized impulse momentum equations that involve the coefficient of restitution as well as the Jacobian matrix of the kinematic constraints. The convergence of the series solutions presented in this paper is examined and the analytical and numerical results are found to be consistent with the solutions obtained by the use of the classical theory of elasticity in the case of plastic impact. The cases in which without and with the gravity are also examined and it is shown that the generalized impulse momentum equations can be used with confidence to study the propagation of elastic waves in applications related to multibody dynamic systems.

Hwang, Yunn-Lin; Gau, Wei-Hsin

2011-08-01

199

Constrained Sypersymmetric Flipped SU (5) GUT Phenomenology  

SciTech Connect

We explore the phenomenology of the minimal supersymmetric flipped SU(5) GUT model (CFSU(5)), whose soft supersymmetry-breaking (SSB) mass parameters are constrained to be universal at some input scale, Min, above the GUT scale, M{sub GUT}. We analyze the parameter space of CFSU(5) assuming that the lightest supersymmetric particle (LSP) provides the cosmological cold dark matter, paying careful attention to the matching of parameters at the GUT scale. We first display some specific examples of the evolutions of the SSB parameters that exhibit some generic features. Specifically, we note that the relationship between the masses of the lightest neutralino {chi} and the lighter stau {tilde {tau}}{sub 1} is sensitive to M{sub in}, as is the relationship between m{sub {chi}} and the masses of the heavier Higgs bosons A,H. For these reasons, prominent features in generic (m{sub 1/2}, m{sub 0}) planes such as coannihilation strips and rapid-annihilation funnels are also sensitive to Min, as we illustrate for several cases with tan {beta} = 10 and 55. However, these features do not necessarily disappear at large Min, unlike the case in the minimal conventional SU(5) GUT. Our results are relatively insensitive to neutrino masses.

Ellis, John; /CERN /King's Coll. London; Mustafayev, Azar; /Minnesota U., Theor. Phys. Inst.; Olive, Keith A.; /Minnesota U., Theor. Phys. Inst. /Minnesota U. /Stanford U., Phys. Dept. /SLAC

2011-08-12

200

Constrained inversion for basal and englacial properties  

NASA Astrophysics Data System (ADS)

When inverting for basal slipperiness and (C retrieval) the rate factor in Glen's flow law (A retrieval) using surface data, the inversion needs to be constrained for the retrieved values to be positive. Some other constraints may also have to be imposed on the retrieved fields. There are various ways of enforcing such constraints. Using an adjoint model of the shallow-ice stream equations, several different algorithms are tested and compared with respect to rate of convergence and cost per iteration. These methods included the projected gradient method, the limited-memory projected BFGS method, the interior-point method, and an incomplete Newton iteration using a barrier function. All these methods perform favourably for small problem sizes (O(1000) unknowns). It is shown that for large-scale optimisation problems the convergence rate for A retrieval is generally lower than for C retrieval. Both projection methods suffer from slow convergence for large problem sizes (O(100 000) unknowns.) Interior-point methods, especially when coupled with an incomplete inner iteration of the Newton system appear to give the best large-scale performance.

Gudmundsson, G. H.

2012-04-01

201

Should we still believe in constrained supersymmetry?  

NASA Astrophysics Data System (ADS)

We calculate Bayes factors to quantify how the feasibility of the constrained minimal supersymmetric standard model (CMSSM) has changed in the light of a series of observations. This is done in the Bayesian spirit where probability reflects a degree of belief in a proposition and Bayes' theorem tells us how to update it after acquiring new information. Our experimental baseline is the approximate knowledge that was available before LEP, and our comparison model is the Standard Model with a simple dark matter candidate. To quantify the amount by which experiments have altered our relative belief in the CMSSM since the baseline data we compute the Bayes factors that arise from learning in sequence the LEP Higgs constraints, the XENON100 dark matter constraints, the 2011 LHC supersymmetry search results, and the early 2012 LHC Higgs search results. We find that LEP and the LHC strongly shatter our trust in the CMSSM (with $M_0$ and $M_{1/2}$ below 2 TeV), reducing its posterior odds by a factor of approximately two orders of magnitude. This reduction is largely due to substantial Occam factors induced by the LEP and LHC Higgs searches.

Balázs, Csaba; Buckley, A.; Carter, D.; Farmer, B.; White, M.

202

Constraining neutrino masses by CMB experiments alone  

SciTech Connect

It is shown that a subelectronvolt upper limit can be derived on the neutrino mass from the cosmic microwave background (CMB) data alone in the {lambda}CDM model with the power-law adiabatic perturbations, without the aid of any other cosmological data. Assuming the flatness of the Universe, the constraint we can derive from the current Wilkinson Microwave Anisotropy Probe observations is at the 95% confidence level for the sum over three species of neutrinos (m{sub {nu}}<0.66 eV for the degenerate neutrinos) by maximizing the likelihood over six other cosmological parameters. This constraint modifies little even if we abandon the flatness assumption for the spatial curvature. We argue that it would be difficult to improve the limit much beyond using only the CMB data, even if their statistics are substantially improved. However, a significant improvement of the limit is possible if an external input is introduced that constrains the Hubble constant from below. The parameter correlation and the mechanism of CMB perturbations that give rise to the limit on the neutrino mass are also elucidated.

Ichikawa, Kazuhide; Fukugita, Masataka; Kawasaki, Masahiro [Institute for Cosmic Ray Research, University of Tokyo, Kashiwa 277 8582 (Japan)

2005-02-15

203

Constrained bounds on measures of entanglement  

SciTech Connect

Entanglement measures constructed from two positive, but not completely positive, maps on density operators are used as constraints in placing bounds on the entanglement of formation, the tangle, and the concurrence of 4N mixed states. The maps are the partial transpose map and the phi map introduced by Breuer [H.-P. Breuer, Phys. Rev. Lett. 97, 080501 (2006)]. The norm-based entanglement measures constructed from these two maps, called negativity and phi negativity, respectively, lead to two sets of bounds on the entanglement of formation, the tangle, and the concurrence. We compare these bounds and identify the sets of 4N density operators for which the bounds from one constraint are better than the bounds from the other. In the process, we present a derivation of the already known bound on the concurrence based on the negativity. We compute bounds on the three measures of entanglement using both the constraints simultaneously. We demonstrate how such doubly constrained bounds can be constructed. We discuss extensions of our results to bipartite states of higher dimensions and with more than two constraints.

Datta, Animesh; Flammia, Steven T.; Shaji, Anil; Caves, Carlton M. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131-1156 (United States)

2007-06-15

204

Constrained Graph Optimization: Interdiction and Preservation Problems  

SciTech Connect

The maximum flow, shortest path, and maximum matching problems are a set of basic graph problems that are critical in theoretical computer science and applications. Constrained graph optimization, a variation of these basic graph problems involving modification of the underlying graph, is equally important but sometimes significantly harder. In particular, one can explore these optimization problems with additional cost constraints. In the preservation case, the optimizer has a budget to preserve vertices or edges of a graph, preventing them from being deleted. The optimizer wants to find the best set of preserved edges/vertices in which the cost constraints are satisfied and the basic graph problems are optimized. For example, in shortest path preservation, the optimizer wants to find a set of edges/vertices within which the shortest path between two predetermined points is smallest. In interdiction problems, one deletes vertices or edges from the graph with a particular cost in order to impede the basic graph problems as much as possible (for example, delete edges/vertices to maximize the shortest path between two predetermined vertices). Applications of preservation problems include optimal road maintenance, power grid maintenance, and job scheduling, while interdiction problems are related to drug trafficking prevention, network stability assessment, and counterterrorism. Computational hardness results are presented, along with heuristic methods for approximating solutions to the matching interdiction problem. Also, efficient algorithms are presented for special cases of graphs, including on planar graphs. The graphs in many of the listed applications are planar, so these algorithms have important practical implications.

Schild, Aaron V [Los Alamos National Laboratory

2012-07-30

205

FPGA design for constrained energy minimization  

NASA Astrophysics Data System (ADS)

The Constrained Energy Minimization (CEM) has been widely used for hyperspectral detection and classification. The feasibility of implementing the CEM as a real-time processing algorithm in systolic arrays has been also demonstrated. The main challenge of realizing the CEM in hardware architecture in the computation of the inverse of the data correlation matrix performed in the CEM, which requires a complete set of data samples. In order to cope with this problem, the data correlation matrix must be calculated in a causal manner which only needs data samples up to the sample at the time it is processed. This paper presents a Field Programmable Gate Arrays (FPGA) design of such a causal CEM. The main feature of the proposed FPGA design is to use the Coordinate Rotation DIgital Computer (CORDIC) algorithm that can convert a Givens rotation of a vector to a set of shift-add operations. As a result, the CORDIC algorithm can be easily implemented in hardware architecture, therefore in FPGA. Since the computation of the inverse of the data correlction involves a series of Givens rotations, the utility of the CORDIC algorithm allows the causal CEM to perform real-time processing in FPGA. In this paper, an FPGA implementation of the causal CEM will be studied and its detailed architecture will be also described.

Wang, Jianwei; Chang, Chein-I.; Cao, Mang

206

Acoustic characteristics of listener-constrained speech  

NASA Astrophysics Data System (ADS)

Relatively little is known about the acoustical modifications speakers employ to meet the various constraints-auditory, linguistic and otherwise-of their listeners. Similarly, the manner by which perceived listener constraints interact with speakers' adoption of specialized speech registers is poorly Hypo (H&H) theory offers a framework for examining the relationship between speech production and output-oriented goals for communication, suggesting that under certain circumstances speakers may attempt to minimize phonetic ambiguity by employing a ``hyperarticulated'' speaking style (Lindblom, 1990). It remains unclear, however, what the acoustic correlates of hyperarticulated speech are, and how, if at all, we might expect phonetic properties to change respective to different listener-constrained conditions. This paper is part of a preliminary investigation concerned with comparing the prosodic characteristics of speech produced across a range of listener constraints. Analyses are drawn from a corpus of read hyperarticulated speech data comprising eight adult, female speakers of English. Specialized registers include speech to foreigners, infant-directed speech, speech produced under noisy conditions, and human-machine interaction. The authors gratefully acknowledge financial support of the Irish Higher Education Authority, allocated to Fred Cummins for collaborative work with Media Lab Europe.

Ashby, Simone; Cummins, Fred

2003-04-01

207

Constrained blackbox optimization: The SEARCH perspective  

SciTech Connect

Search and optimization in the context of blackbox objective function evaluation subject to blackbox constraints satisfaction is the thesis of this work. The SEARCH (Search Envisioned As Relation and Class Hierarchizing) framework introduced by Kargupta (1995) offered an alternate perspective of blackbox optimization in terms of relations, classes, and partial ordering. The primary motivation comes from the observation that sampling in blackbox optimization is essentially an inductive process and in the absence of any relation among the members of the search space, induction is no better than enumeration. SEARCH also offers conditions for polynomial complexity search and bounds on sample complexity using its ordinal, probabilistic, and approximate framework. In this work the authors extend the SEARCH framework to tackle constrained blackbox optimization problems. The methodology aims at characterizing the search domain into feasible and infeasible relations among which the feasible relations can be explored further to optimize an objective function. Both -- objective function and constraints -- can be in the form of blackboxes. The authors derive results for bounds on sample complexity. They demonstrate their methodology on several benchmark problems.

Hanagandi, V.; Kargupta, H.; Buescher, K. [Los Alamos National Lab., NM (United States). Computational Science Methods Div.

1996-02-02

208

Generating constrained randomized sequences: item frequency matters.  

PubMed

All experimental psychologists understand the importance of randomizing lists of items. However, randomization is generally constrained, and these constraints-in particular, not allowing immediately repeated items-which are designed to eliminate particular biases, frequently engender others. We describe a simple Monte Carlo randomization technique that solves a number of these problems. However, in many experimental settings, we are concerned not only with the number and distribution of items but also with the number and distribution of transitions between items. The algorithm mentioned above provides no control over this. We therefore introduce a simple technique that uses transition tables for generating correctly randomized sequences. We present an analytic method of producing item-pair frequency tables and item-pair transitional probability tables when immediate repetitions are not allowed. We illustrate these difficulties and how to overcome them, with reference to a classic article on word segmentation in infants. Finally, we provide free access to an Excel file that allows users to generate transition tables with up to 10 different item types, as well as to generate appropriately distributed randomized sequences of any length without immediately repeated elements. This file is freely available from http://leadserv.u-bourgogne.fr/IMG/xls/TransitionMatrix.xls. PMID:19897832

French, Robert M; Perruchet, Pierre

2009-11-01

209

Constraining asteroid dynamical models using GAIA data  

NASA Astrophysics Data System (ADS)

GAIA is expected to greatly enhance our knowledge on the orbital, spin-state, spectral and size distribution of individual asteroids and asteroid families. Dynamical models, incorporating resonant phenomena and thermal (Yarkovsky/YORP) effects, can be used to understand the observations, in particular the orbital, size-frequency and spin-axis distributions in families and groups. Conversely, the GAIA data can be used to appropriately modify/constrain our models. Such work will necessarily involve an optimization procedure, for which a large number of dynamical experiments will typically be needed; this is clearly a limiting factor. We present here a preliminary version of a statistical model that describes asteroid transport due to gravitational perturbations in the 3-D space of proper elements, coupled with Yarkovsky drift effects. Computationally, the model is very efficient for studying the long-term evolution of large ensembles of asteroids (e.g. families). Thus, given a "final" distribution of orbits, spins and sizes, our model could be used in an iterative fashion, to derive e.g. an optimal guess of the initial ejection velocity field in a family-forming event.

Tsiganis, K.; Varvoglis, H.; Tsirvoulis, G.; Voyatzis, G.

2012-12-01

210

Constrained flow around a magnetic obstacle  

NASA Astrophysics Data System (ADS)

Many practical applications exploit an external local magnetic field as an essential part of their operation. It has been demonstrated that the flow of an electrically conducting fluid influenced by an external field can show several kinds of recirculation. The present paper reports a three-dimensional numerical study, some results of which are compared with an experiment on such a flow in a rectangular duct. First, we derive equations to compute analytically the external magnetic field and verify these equations by comparing with experimentally measured field intensity. Then, we study flow characteristics for different magnetic field configurations. The flow inside the magnetic gap is dependent mainly on the interaction parameter N, which represents the ratio of the Lorentz force to the inertial force. Depending on the constrainment factor , a six-vortex ensemble at moderate . Recirculation appears when N is higher than a critical value Nc,m. The driving force for the recirculation is the reverse electromotive force that arises to balance the reverse electrostatic field. The reversal of the electrostatic field is caused by the concurrence of internal and external vorticity respectively related to the internal and external slopes in the M-shaped velocity profile. The critical value of Nc,m grows quickly as rmán vortex street forms, when one suddenly applies a retarding local magnetic field to a constant flow.

Votyakov, Evgeny V.; Zienicke, Egbert; Kolesnikov, Yuri B.

211

Constraining Particle Sizes of Saturn's F Ring  

NASA Astrophysics Data System (ADS)

Saturn's beauty is often attributed to the magnificent rings that encircle the planet. Although admired for hundreds of years, we are now just beginning to understand the complexity of the rings as a result of new data from the Cassini orbiter. Studying occultations of the rings provides information about the distribution and sizes of the particles that define the rings. During one solar occultation, the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini was slightly misaligned with the Sun, decreasing the amount of direct solar signal to ~1% of the normal value. As a result, UVIS detected a peak in photon counts above the non-occulted signal due to forward-scattered light diffracted by the small particles in the F Ring. There is a direct relationship between the size of the particles and the intensity of the light scattered. We utilize this relationship in a model that replicates the misalignment and calculates the amount of light that would be detected as a function of the particle sizes in the ring. We present new results from the model that constrain the size distribution of the dynamically active F Ring, contributing to the study of the origin and evolution of Saturn's ring system.

Becker, T. M.; Colwell, J.; Esposito, L. W.

2011-12-01

212

Constrained de novo sequencing of conotoxins.  

PubMed

De novo peptide sequencing by mass spectrometry (MS) can determine the amino acid sequence of an unknown peptide without reference to a protein database. MS-based de novo sequencing assumes special importance in focused studies of families of biologically active peptides and proteins, such as hormones, toxins, and antibodies, for which amino acid sequences may be difficult to obtain through genomic methods. These protein families often exhibit sequence homology or characteristic amino acid content; yet, current de novo sequencing approaches do not take advantage of this prior knowledge and, hence, search an unnecessarily large space of possible sequences. Here, we describe an algorithm for de novo sequencing that incorporates sequence constraints into the core graph algorithm and thereby reduces the search space by many orders of magnitude. We demonstrate our algorithm in a study of cysteine-rich toxins from two cone snail species (Conus textile and Conus stercusmuscarum) and report 13 de novo and about 60 total toxins. PMID:22709442

Bhatia, Swapnil; Kil, Yong J; Ueberheide, Beatrix; Chait, Brian T; Tayo, Lemmuel; Cruz, Lourdes; Lu, Bingwen; Yates, John R; Bern, Marshall

2012-07-02

213

Two ultimate tests of constrained supersymmetry  

NASA Astrophysics Data System (ADS)

We examine the prospects of using two alternative and complementary ways to explore the regions that are favored by global constraints in two simple unified supersymmetric models: the CMSSM and the NUHM. First, we consider BR ( B s ? ? + ? -), which has recently been for the first time measured by LHCb. In the CMSSM we show that ultimate, but realistic, improvement in the determination of the observable to about 5-10% around the Standard Model value would strongly disfavor the A-funnel region, while not affecting much the other favored regions. Second, we show that all the favored regions of the CMSSM will be, for the most part, sensitive to direct dark matter searches in future one-tonne detectors. A signal at low WIMP mass (? 450 GeV) and low spin-independent cross section would then strongly favor the stau coannihilation region while a signal at higher WIMP mass (~ 800 GeV to ~ 1 .2 TeV) would clearly point to the region where the neutralino is higgsino-like with mass ~ 1 TeV. A nearly complete experimental testing of the CMSSM over multi-TeV ranges of superpartner masses, far beyond the reach of direct SUSY searches at the LHC, can therefore be achievable. In the NUHM, in contrast, similar favored regions exist but a sample study reveals that even a precise determination of BR ( B s ? ? + ? -) would have a much less constraining power on the model, including the A-funnel region. On the other hand, this could allow one to, by detecting in one-tonne detectors a signal for 500 GeV ? m? ? 800 GeV, strongly disfavor the CMSSM.

Kowalska, Kamila; Roszkowski, Leszek; Sessolo, Enrico Maria

2013-06-01

214

Carbon-constrained health care enterprise.  

PubMed

RATIONALE: The health economy is a significant part of a national economy accounting typically for about 8% of GDP spent. As national economies respond to the dual challenges of severe economic turbulence on the global scale and climate change mitigation, the health economy is coming under increasing pressure to respond. Indications for sharp reductions in budgets and reductions in greenhouse gas emissions, such as carbon dioxide, are widespread. AIMS: In this paper an analysis is undertaken of the diverse forces acting on a typical health care enterprise. The forces, both economic and carbon related, are investigated in terms of their effects through the enterprise and across its boundaries on the supply, demand and waste sides. The overall aim is to show how the enterprise and whole supply chains may flip synchronously into a low-carbon evolutionary pathway. OBJECTIVES: By illustrating how different elements of the health care enterprise may respond to these developments, diverse opportunities for cost reduction, carbon reduction and product (goods and services) development are identified. These opportunities involve a variety of waste reduction and energy and materials conservation measures as well as new ways of collaborating with other enterprises going through similar transformations. The overall objective is to show that the carbon-constrained health care enterprise and the low-carbon health economy in which it sits may broaden its role in the coming decades to include a degree of responsibility for the health of the environment. This broader role is likely to supplement and entangle with the traditional role of the health economy, currently focused narrowly on human health, and lead to extensive organisational transformation, and infrastructure and product developments. PMID:20367839

Gell, Michael

2010-02-01

215

Constraining Cosmic Evolution of Type Ia Supernovae  

SciTech Connect

We present the first large-scale effort of creating composite spectra of high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88 high-redshift SNe Ia with excellent light-curve information. In addition, we have obtained 397 spectra of low-redshift SNe through a multiple-decade effort at Lick and Keck Observatories, and we have used 45 ultraviolet spectra obtained by HST/IUE. The low-redshift spectra act as a control sample when comparing to the ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra appear very similar. The addition of galaxy light to the Lick composite spectra allows a nearly perfect match of the overall spectral-energy distribution with the ESSENCE composite spectra, indicating that the high-redshift SNe are more contaminated with host-galaxy light than their low-redshift counterparts. This is caused by observing objects at all redshifts with similar slit widths, which corresponds to different projected distances. After correcting for the galaxy-light contamination, subtle differences in the spectra remain. We have estimated the systematic errors when using current spectral templates for K-corrections to be {approx}0.02 mag. The variance in the composite spectra give an estimate of the intrinsic variance in low-redshift maximum-light SN spectra of {approx}3% in the optical and growing toward the ultraviolet. The difference between the maximum-light low and high-redshift spectra constrain SN evolution between our samples to be < 10% in the rest-frame optical.

Foley, Ryan J.; Filippenko, Alexei V.; Aguilera, C.; Becker, A.C.; Blondin, S.; Challis, P.; Clocchiatti, A.; Covarrubias, R.; Davis, T.M.; Garnavich, P.M.; Jha, S.; Kirshner, R.P.; Krisciunas, K.; Leibundgut, B.; Li, W.; Matheson, T.; Miceli, A.; Miknaitis, G.; Pignata, G.; Rest, A.; Riess, A.G.; /UC, Berkeley, Astron. Dept. /Cerro-Tololo InterAmerican Obs. /Washington U., Seattle, Astron. Dept. /Harvard-Smithsonian Ctr. Astrophys. /Chile U., Catolica /Bohr Inst. /Notre Dame U. /KIPAC, Menlo Park /Texas A-M /European Southern Observ. /NOAO, Tucson /Fermilab /Chile U., Santiago /Harvard U., Phys. Dept. /Baltimore, Space Telescope Sci. /Johns Hopkins U. /Res. Sch. Astron. Astrophys., Weston Creek /Stockholm U. /Hawaii U. /Illinois U., Urbana, Astron. Dept.

2008-02-13

216

Constraining projections of summer Arctic sea ice  

NASA Astrophysics Data System (ADS)

We examine the recent (1979-2010) and future (2011-2100) characteristics of the summer Arctic sea ice cover as simulated by 29 Earth system and general circulation models from the Coupled Model Intercomparison Project, phase 5 (CMIP5). As was the case with CMIP3, a large intermodel spread persists in the simulated summer sea ice losses over the 21st century for a given forcing scenario. The 1979-2010 sea ice extent, thickness distribution and volume characteristics of each CMIP5 model are discussed as potential constraints on the September sea ice extent (SSIE) projections. Our results suggest first that the future changes in SSIE with respect to the 1979-2010 model SSIE are related in a complicated manner to the initial 1979-2010 sea ice model characteristics, due to the large diversity of the CMIP5 population: at a given time, some models are in an ice-free state while others are still on the track of ice loss. However, in phase plane plots (that do not consider the time as an independent variable), we show that the transition towards ice-free conditions is actually occurring in a very similar manner for all models. We also find that the year at which SSIE drops below a certain threshold is likely to be constrained by the present-day sea ice properties. In a second step, using several adequate 1979-2010 sea ice metrics, we effectively reduce the uncertainty as to when the Arctic could become nearly ice-free in summertime, the interval [2041, 2060] being our best estimate for a high climate forcing scenario.

Massonnet, F.; Fichefet, T.; Goosse, H.; Bitz, C. M.; Philippon-Berthier, G.; Holland, M. M.; Barriat, P.-Y.

2012-11-01

217

Constraining the Evolution of Poor Clusters  

NASA Astrophysics Data System (ADS)

There currently exists no method by which to quantify the evolutionary state of poor clusters (PCs). Research by Broming & Fuse (2010) demonstrated that the evolution of Hickson compact groups (HCGs) are constrained by the correlation between the X-ray luminosities of point sources and diffuse gas. The current investigation adopts an analogous approach to understanding PCs. Plionis et al. (2009) proposed a theory to define the evolution of poor clusters. The theory asserts that cannibalism of galaxies causes a cluster to become more spherical, develop increased velocity dispersion and increased X-ray temperature and gas luminosity. Data used to quantify the evolution of the poor clusters were compiled across multiple wavelengths. The sample includes 162 objects from the WBL catalogue (White et al. 1999), 30 poor clusters in the Chandra X-ray Observatory archive, and 15 Abell poor clusters observed with BAX (Sadat et al. 2004). Preliminary results indicate that the cluster velocity dispersion and X-ray gas and point source luminosities can be used to highlight a weak correlation. An evolutionary trend was observed for multiple correlations detailed herein. The current study is a continuation of the work by Broming & Fuse examining point sources and their properties to determine the evolutionary stage of compact groups, poor clusters, and their proposed remnants, isolated ellipticals and fossil groups. Preliminary data suggests that compact groups and their high-mass counterpart, poor clusters, evolve along tracks identified in the X-ray gas - X-ray point source relation. While compact groups likely evolve into isolated elliptical galaxies, fossil groups display properties that suggest they are the remains of fully coalesced poor clusters.

Broming, Emma J.; Fuse, C. R.

2012-01-01

218

Preparation of alpha-(2,2-diphenylhydrazino)lactones and related compounds by radical cyclization: use of glyoxylic acid hydrazone derivatives.  

PubMed

Glyoxylic acid diphenylhydrazone (2a) and the corresponding O-benzyloxime (2b) are easily esterified in high yield by beta-bromo alcohols. The resulting esters undergo radical cyclization to alpha-(2,2-diphenylhydrazino)- or alpha-[(phenylmethoxy)amino]lactones on treatment with tributyltin hydride. Esters for radical cyclization were also made using a beta-(phenylseleno) alcohol and an enol ether. Several derivatives of glyoxylic acid were evaluated, but none was as effective as 2a or 2b. The imine 28 was prepared by an indirect route; it undergoes radical cyclization with displacement of the nitrogen substituent (28 --> 30) so that an alpha-amino lactone can be generated by acid hydrolysis of the cyclization product. PMID:11312953

Clive, D L; Zhang, J; Subedi, R; Bouétard, V; Hiebert, S; Ewanuk, R

2001-02-23

219

Inhibited muscle amino acid uptake in sepsis.  

PubMed Central

Amino acid uptake in vivo was determined in soleus (SOL) muscle, diaphragm, heart, and liver following intravenous injection of [3H]-alpha-amino-isobutyric acid ([3H]-AIB) in rats made septic by cecal ligation and puncture (CLP) and in sham-operated controls. Muscle amino acid transport was also measured in vitro by determining uptake of [3H]-AIB in incubated extensor digitorum longus (EDL) and SOL muscles. Results were expressed as distribution ratio between [3H]-AIB in intracellular and extracellular fluid. AIB uptake in vivo was reduced by 90% in SOL and cardiac muscle and by 45% in diaphragm 16 hours after CLP. In contrast, AIB uptake by liver was almost four times higher in septic than in control animals. AIB uptake in vitro was reduced by 18% in EDL 8 hours after CLP but was not significantly altered in SOL at the same time point. Sixteen hours after CLP, AIB uptake was significantly reduced in both muscles, i.e., by 17% in EDL and by 65% in SOL. When muscles from untreated rats were incubated in the presence of plasma from septic animals (16 hours CLP) or from animals injected with endotoxin (2 mg/kg body weight), AIB uptake was reduced. Addition of endotoxin in vitro (2-200 micrograms/ml) to incubated muscles did not affect AIB uptake. The results suggest that sepsis leads to marked impairment of amino acid transport system A in muscle and that this impairment is mediated by a circulating factor that is not endotoxin. Reduced uptake of amino acids by skeletal muscle during sepsis may divert amino acids to the liver for increased gluconeogenesis and protein synthesis.

Hasselgren, P O; James, J H; Fischer, J E

1986-01-01

220

Multiple constrained folding of programmable logic arrays Theory and applications  

NASA Astrophysics Data System (ADS)

Programmable logic arrays are important building blocks of VLSI circuits and systems. The problem of optimizing the silicon area and the performances of large logic arrays is addressed. In particular, a general method for compacting a logic array defined as multiple row and column folding is described and the problem of interconnecting a PLA to the outside circuitry is addressed, and a constrained optimization problem to achieve minimal silicon area occupation with constrained positions of electrical inputs and outputs is defined. Also, presented is a new computer program, PLEASURE, which implements several algorithms for multiple and/or constrained PLA folding.

de Micheli, G.; Sangiovanni-Vincentelli, A.

1983-07-01

221

Constraining volcano eruption dynamics with infrasound  

NASA Astrophysics Data System (ADS)

Infrasonic airwaves produced by exploding volcanoes provide an indispensable tool for understanding dynamics of diverse eruptions. Unlike the seismicity generated during eruption, which is a complex superposition of internal and surface source and wave propagation processes, the infrasonic pressure field can be unequivocally associated with the flux rate of gas released at the volcanic vent. Because the atmosphere does not support shear waves, and internal scattering, topographic echoes, site, and weather effects are substantially predictable, it is possible to objectively compare the infrasound, and assess degassing from diverse volcanic systems. With its utility for continuously tracking eruptive activity, even when line-of-sight view to the vent is obscured, infrasound greatly enhances the efficacy of volcano monitoring and interpretation of conduit processes / eruption dynamics. We showcase new results from Erebus, Fuego, Villarrica, and Santiaguito volcanoes to demonstrate the utility of infrasound for recovering quantitative parameters, such as eruption duration, source dimensions and mechanism, and explosive gas release. At Erebus, infrasound can constrain the physical dimension of enormous bubbles, with diameters up to 10 m and containing more than 1000 kg gas, that burst individually and infrequently from the lava lake surface. At Villarrica, longer-duration infrasonic transients reveal the eruptive mechanism to be a succession of gas slugs bursting from the free surface, occurring at 60-90 s intervals and representing a stable long-term mode of degassing. At Fuego, the infrasound associated with vigorous explosions is inferred to result from the fragmentation of a bubble foam layer, which continues for tens of seconds until the gas foam is depleted. And at Santiaguito, large eruptions, which generate low intensity infrasound, suggest a diffuse source region with dimensions comparable to the radiated infrasonic wavelength (vent radii > 100 m). The recorded infrasound from these 4 volcanoes complements our infrasound archives for an additional 6 volcanoes, which encompasses a wide range of eruptive behaviors. Infrasound recorded within a few km of a volcanic vent thus provides an ideal tool for objective comparison of associated degassing.

Johnson, J. B.; Aster, R. C.

2003-12-01

222

21 CFR 888.3550 - Knee joint patellofemorotibial polymer/metal/metal constrained cemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...false Knee joint patellofemorotibial polymer/metal/metal constrained cemented prosthesis...3550 Knee joint patellofemorotibial polymer/metal/metal constrained cemented prosthesis...Identification. A knee joint patellofemorotibial polymer/metal/metal constrained...

2013-04-01

223

21 CFR 888.3510 - Knee joint femorotibial metal/polymer constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...Knee joint femorotibial metal/polymer constrained cemented prosthesis...Knee joint femorotibial metal/polymer constrained cemented prosthesis...knee joint femorotibial metal/polymer constrained cemented...solid bolt passing through a journal bearing of greater...

2010-04-01

224

21 CFR 888.3510 - Knee joint femorotibial metal/polymer constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...Knee joint femorotibial metal/polymer constrained cemented prosthesis...Knee joint femorotibial metal/polymer constrained cemented prosthesis...knee joint femorotibial metal/polymer constrained cemented...solid bolt passing through a journal bearing of greater...

2009-04-01

225

21 CFR 888.3790 - Wrist joint metal constrained cemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 false Wrist joint metal constrained cemented prosthesis. ...Devices § 888.3790 Wrist joint metal constrained cemented prosthesis. (a) Identification. A wrist joint metal constrained cemented...

2013-04-01

226

21 CFR 888.3530 - Knee joint femorotibial metal/polymer semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...false Knee joint femorotibial metal/polymer semi-constrained...3530 Knee joint femorotibial metal/polymer semi-constrained... A knee joint femorotibial metal/polymer semi-constrained...across-the-joint. This generic type of device includes...

2013-04-01

227

Generation of Granulites Constrained by Thermal Modeling  

NASA Astrophysics Data System (ADS)

The heat source needed to generate granulites facies metamorphism is still an unsolved problem in geology. There is a close spatial relationship between granulite terrains and extensive silicic plutonism, suggesting heat advection by melts is critical to their formation. To investigate the role of heat advection by melt in the generation of granulites we use numerical 1-D models which include the movement of melt from the base of the crust to the middle crust. The model is in part constrained by petrological observations from the Coast Plutonic Complex (CPC) in British Columbia, Canada at ~ 54° N where migmatite and granulite are widespread. The model takes into account time dependent heat conduction and advection of melts generated at the base of the crust. The model starts with a crust of 55 km, consistent with petrologic and geochemical data from the CPC. The lower crust is assumed to be amphibolite in composition, consistent with seismologic and geochemical constraints for the CPC. An initial geothermal gradient estimated from metamorphic P-T-t paths in this region is ~37°C/km, hotter than normal geothermal gradients. The parameters used for the model are a coefficient of thermal conductivity of 2.5 W/m°C, a density for the crust of 2700 kg/m3 and a heat capacity of 1170 J/Kg°C. Using the above starting conditions, a temperature of 1250°C is assumed for the mantle below 55 km, equivalent to placing asthenosphere in contact with the base of the crust to simulate delamination, basaltic underplating and/or asthenospheric exposure by a sudden steepening of slab. This condition at 55 km results in melting the amphibolite in the lower crust. Once a melt fraction of 10% is reached the melt is allowed to migrate to a depth of 13 km, while material at 13 km is displaced downwards to replace the ascending melts. The steady-state profile has a very steep geothermal gradient of more than 50°C/km from the surface to 13 km, consistent with the generation of andalusite grade rocks. In order to match the observations of the granulite terrane within the CPC two extreme cases were found. The first case is when the mantle heat flux achieved a minimum persistent value of 95 mW/ m2 after decaying from initially having the asthenosphere at the base of the crust. This is equivalent to intruding 0.72 km/Ma of basalt at a depth of 68 km. Within the first 5 Ma, a pluton is formed at 13 km depth diffusing heat downwards into the colder lower crust for 30 Ma. After 35 Ma the model arrives to a steady-state profile where a pluton is at 13 km and the middle and lower crust are at temperatures above 700°C with partial melting within the bottom 12 km of the crust. Melting of the lowermost crust is constrained by the solidus curve of amphibolite. With greater mantle heat fluxes (asthenosphere even closer to the moho) the quasi-steady state is arrived at sooner. In the second case, when the mantle heat flux is 50 mW/m2, equivalent to intruding 0.38 km/Ma of basalts at constant rate at a depth of 80 km, the steady-state profile does not generate granulites in the middle crust. In this case, in order to produce granulites in the middle crust focusing of the melt is needed. Focusing implies that there is more melt being accumulated in the pluton than that being generated in the rock column directly below it, implying that melt migrates laterally from other areas and are accumulated in the profile. This increases the thickness of the crust. By focusing the melt by a factor of two, the steady state is arrived after 16 Ma. Our simulation shows that melt focusing is required for all mantle heat fluxes below 75 mW/m2.

Depine, G. V.; Andronicos, C. L.; Phipps-Morgan, J.

2006-12-01

228

Supply-Constrained Equilibria in Economies with Indexed Prices.  

National Technical Information Service (NTIS)

The paper gives an existence theorem for existence of equilibrium, particularly supply-constrained equilibrium, with price rigiditels, when prices are restricted by index functions, of a general type but excluding circularity of indexes. It uses the conce...

C. Weddepohl

1985-01-01

229

Constraining the Pressure Threshold of Impact Induced Calcite Twinning  

NASA Astrophysics Data System (ADS)

To better constrain the pressure threshold of impact-induced calcite twinning, calcite targets have been experimentally impacted. This study has implications for the deformation history of carbonaceous chondrite parent bodies.

Lindgren, P.; Price, M. C.; Lee, M. R.; Burchell, M.

2012-03-01

230

FXR agonist activity of conformationally constrained analogs of GW 4064  

SciTech Connect

Two series of conformationally constrained analogs of the FXR agonist GW 4064 1 were prepared. Replacement of the metabolically labile stilbene with either benzothiophene or naphthalene rings led to the identification of potent full agonists 2a and 2g.

Akwabi-Ameyaw, Adwoa; Bass, Jonathan Y.; Caldwell, Richard D.; Caravella, Justin A.; Chen, Lihong; Creech, Katrina L.; Deaton, David N.; Madauss, Kevin P.; Marr, Harry B.; McFadyen, Robert B.; Miller, Aaron B.; Navas, III, Frank; Parks, Derek J.; Spearing, Paul K.; Todd, Dan; Williams, Shawn P.; Wisely, G. Bruce; (GSKNC)

2010-09-27

231

Mandatory Spending: Using Budget Triggers to Constrain Growth.  

National Technical Information Service (NTIS)

Prepared as part of GAO's basic statutory responsibility for monitoring the condition of the nation's finances, the objectives of this report were to (1) determine the feasibility of designing and using trigger mechanisms to constrain growth in mandatory ...

2006-01-01

232

Slow logarithmic relaxation in models with hierarchically constrained dynamics  

NASA Astrophysics Data System (ADS)

A general kind of model with hierarchically constrained dynamics is shown to exhibit logarithmic anomalous relaxation similar to a variety of complex strongly interacting materials. The logarithmic behavior describes most of the decay of the response function.

Brey, J. J.; Prados, A.

2001-02-01

233

Constrained KP Hierarchy and Bi-Hamiltonian Structures.  

National Technical Information Service (NTIS)

The Kadomtsev-Petviashvili (KP) hierarchy is considered together with the evolutions of eigenfunctions and adjoint eigenfunctions. By constraining the KP flows in terms of squared eigenfunctions, 1 + 1 dimensional integrable equations with scattering prob...

W. Oevel W. Strampp

1992-01-01

234

Curvature-constrained directional-cost paths in the plane  

Microsoft Academic Search

This paper looks at the problem of finding the minimum cost curvature-constrained path between two directed points where the\\u000a cost at every point along the path depends on the instantaneous direction. This generalises the results obtained by Dubins\\u000a for curvature-constrained paths of minimum length, commonly referred to as Dubins paths. We conclude that if the reciprocal\\u000a of the directional-cost function

Alan J. Chang; Marcus Brazil; J. Hyam Rubinstein; Doreen A. Thomas

2012-01-01

235

Stability Constrained Optimal Power Flow in Deregulated Power Systems  

Microsoft Academic Search

The dynamic security-constrained dispatch of an electric power network is a difficult task facing an independent system operator mandated to provide equitable and fair transmission services in an open-market environment. In this article, a novel technique based on iterative stability-constrained optimum power flow is proposed. The particle swarm optimization methodology is employed to maximize the social welfare with consideration of

E. Nasr Azadani; S. H. Hosseinian; P. Hasanpor Divshali; B. Vahidi

2011-01-01

236

Residual flexibility test method for verification of constrained structural models  

Microsoft Academic Search

A method is described for deriving constrained modes and frequencies from a reduced model based on a subset of the free-free modes plus the residual effects of neglected modes. The method involves a simple modification of the MacNeal and Rubin component mode representation to allow development of a verified constrained (fixed-base) structural model. Results for two spaceflight structures having translational

John R. Admire; Michael L. Tinker; Edward W. Ivey

1994-01-01

237

Finite Element Analysis of Periodic Structures Without Constrained Meshes  

Microsoft Academic Search

A finite element analysis is detailed of periodic structures without constrained meshes. The infinite periodic analysis domain is reduced to the unit cell analysis by means of the Floquet-Bloch decomposition, where an admittance-type matrix approach is carried out. Special emphasis is placed on the admittance-type matrix generation in such a way that the constrained meshing problem is no longer required.

ValentÍn de la Rubia; Juan Zapata; Miguel A. Gonzalez

2008-01-01

238

Constraining the initial phase in water-fat separation.  

PubMed

An algorithm is described for use in chemical shift-based water-fat separation to constrain the phase of both species to be equal at an echo time of zero. This constraint is physically reasonable since the initial phase should be a property of the excitation pulse and receiver coil only. The advantages of phase constrained water-fat separation, namely, improved noise performance and/or reduced data requirements (fewer echos), are demonstrated in simulations and experiments. PMID:21159457

Bydder, Mark; Yokoo, Takeshi; Yu, Huanzhou; Carl, Michael; Reeder, Scott B; Sirlin, Claude B

2010-12-14

239

Evolutionary programming based security constrained optimal power flow  

Microsoft Academic Search

This paper presents an algorithm for solving security constrained optimal power flow problem through the application of evolutionary programming (EP). The controllable system quantities in the base-case state are optimised to minimize some defined objective function subject to the base-case operating constraints as well as the contingency-case security constraints. An IEEE 30-bus system is taken for investigation. The security constrained

P. Somasundaram; K. Kuppusamy; R. P. Kumudini Devi

2004-01-01

240

Diffusion Barriers Constrain Receptors at Synapses  

PubMed Central

The flux of neurotransmitter receptors in and out of synapses depends on receptor interaction with scaffolding molecules. However, the crowd of transmembrane proteins and the rich cytoskeletal environment may constitute obstacles to the diffusion of receptors within the synapse. To address this question, we studied the membrane diffusion of the ?-aminobutyric acid type A receptor (GABAAR) subunits clustered (?2) or not (?5) at inhibitory synapses in rat hippocampal dissociated neurons. Relative to the extrasynaptic region, ?2 and ?5 showed reduced diffusion and increased confinement at both inhibitory and excitatory synapses but they dwelled for a short time at excitatory synapses. In contrast, ?2 was ?3-fold more confined and dwelled ?3-fold longer in inhibitory synapses than ?5, indicating faster synaptic escape of ?5. Furthermore, using a gephyrin dominant-negative approach, we showed that the increased residency time of ?2 at inhibitory synapses was due to receptor-scaffold interactions. As shown for GABAAR, the excitatory glutamate receptor 2 subunit (GluA2) of the ?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) had lower mobility in both excitatory and inhibitory synapses but a higher residency time at excitatory synapses. Therefore barriers impose significant diffusion constraints onto receptors at synapses where they accumulate or not. Our data further reveal that the confinement and the dwell time but not the diffusion coefficient report on the synapse specific sorting, trapping and accumulation of receptors.

Renner, Marianne; Schweizer, Claude; Bannai, Hiroko; Triller, Antoine; Levi, Sabine

2012-01-01

241

Constrained layer damping treatments with actively enhanced actions  

NASA Astrophysics Data System (ADS)

This thesis studies self-contained constrained layer treatments with active-passive hybrid damping. In particular, two shortcomings of traditional active constrained layer (ACL) configurations, the low active control authority and weak constraining action of the active cover sheet, are addressed. The objective is to design a treatment with the best combination of open-loop (for fail-safe property) and closed-loop (for performance) damping. A comprehensive study of enhanced active constrained layer (EACL) treatments is first performed to understand the effects of using edge elements to increase the control authority for different host structure strain distributions. It is found that to select the best stiffness distribution of the edge elements for damping performance, various system parameters including the host structure strain field need to be considered. When multiple strain fields exist at the same time, the EACL is still possible to provide higher open-loop and closed-loop damping by selecting proper edge element stiffness compared to ACL. A new configuration, active-passive hybrid constrained layer (HCL), is proposed to improve the constraining action of the ACL cover sheet while maintaining its active action. Instead of using a purely active constraining layer, active and passive materials are connected together to form a hybrid cover sheet. It is shown analytically and experimentally that by selecting a stiffer passive constraining material and assigning appropriate active material coverage ratio, the HCL can outperform the ACL, both in terms of its open-loop and closed-loop damping performance. The effects of the active and passive materials distribution in the constraining layer and the strain distribution in the host structure are also investigated. A better open-loop and closed-loop damping combination can be obtained by integrating the EACL and HCL. The hybrid constraining layer will create significant shear deformation in the viscoelastic layer even when stiff edge elements are used for a uniform strain field. This configuration offers considerable open-loop damping while maintaining strong closed-loop damping. Compared to the individual EACL or HCL design, the integrated EACL-HCL system provides more flexibility to meet different open-loop and closed-loop damping requirements.

Liu, Yanning

2001-11-01

242

Induction of Arabidopsis tryptophan pathway enzymes and camalexin by amino acid starvation, oxidative stress, and an abiotic elicitor.  

PubMed Central

The tryptophan (Trp) biosynthetic pathway leads to the production of many secondary metabolites with diverse functions, and its regulation is predicted to respond to the needs for both protein synthesis and secondary metabolism. We have tested the response of the Trp pathway enzymes and three other amino acid biosynthetic enzymes to starvation for aromatic amino acids, branched-chain amino acids, or methionine. The Trp pathway enzymes and cytosolic glutamine synthetase were induced under all of the amino acid starvation test conditions, whereas methionine synthase and acetolactate synthase were not. The mRNAs for two stress-inducible enzymes unrelated to amino acid biosynthesis and accumulation of the indolic phytoalexin camalexin were also induced by amino acid starvation. These results suggest that regulation of the Trp pathway enzymes under amino acid deprivation conditions is largely a stress response to allow for increased biosynthesis of secondary metabolites. Consistent with this hypothesis, treatments with the oxidative stress-inducing herbicide acifluorfen and the abiotic elicitor alpha-amino butyric acid induced responses similar to those induced by the amino acid starvation treatments. The role of salicylic acid in herbicide-mediated Trp and camalexin induction was investigated.

Zhao, J; Williams, C C; Last, R L

1998-01-01

243

Constrained block-iterative Landweber scheme for image reconstruction  

NASA Astrophysics Data System (ADS)

The Landweber method provides a framework to formulate iterative algorithms for image reconstruction problems with large, sparse and unstructured system matrices. In a previous study, the authors established the convergence conditions for a general Landweber scheme in both simultaneous and block-iterative [or ordered-subset (OS)] formats with either consistent or inconsistent data, without constraints. Constrained iterative algorithms provide a mechanism for incorporating prior knowledge such nonnegativity, bounds, finite spatial or spectral supports, etc. Hence, they have been widely used in practice. Although the simultaneous constrained (or projected) Landweber scheme was well studied, the convergence of the constrained block-iterative Landweber scheme is unknown. Block-iterative schemes are recently intensively studied theoretically and applied widely. In this paper, we report convergence conditions of a constrained block-iterative Landweber scheme. Prior knowledge is represented as convex sets in which an image of interest must stay. The constrained block-iterative Landweber scheme is constructed by alternatively performing a projection onto convex sets (POCS) and a conventional block-iterative Landweber iteration. The POCS method has been used before for constrained image reconstruction to satisfy both imaging equations and convex constraints. Our approach is different from the conventional application of the POCS method in that we use Landweber iteration for the imaging equations and perform POCS only for the convex constraints. While the conventionally applied POCS method requires Moore-Penrose inverses of matrix blocks, our constrained block-iterative method only takes transposes of such matrix blocks, and improves the computational complexity greatly.

Jiang, Ming; Wang, Ge

2004-10-01

244

Use of a peptide rather than free amino acid nitrogen source in chemically defined "elemental" diets.  

PubMed

Previous studies have shown that amino acid (AA) residues are absorbed more rapidly from di- tripeptides than from free AA. In the present study, an intestinal perfusion technique has been used in normal human subjects to compare absorption of AA residues and total alpha-amino nitrogen (N) from 4 partial enzymic hydrolysates of protein (50--80% of the N contents present as small peptides) and their respective equimolar free AA mixtures. alpha-Amino N absorption was greater from 2 casein hydrolytes and a lactalbumin hydrolysate than from the respective free AA mixtures but similar to that from a fish protein hydrolysate and its AA mixture. The considerable variation in absorption of individual AA residues from the AA mixtures was much reduced when the protein hydrolysates were perfused, as a number of AA which were poorly absorbed from the AA mixtures were absorbed to a greater extent from the protein hydrolysates. The casein and lactalbumin hydrolysates had a stimulatory effect on jejunal absorption of water and electrolytes. In contrast, the fish protein hydrolysate appeared to cause a mean net secretion of fluid and electrolytes. The findings indicate that when absorption is limited by diminished luminal hydrolysis or absorptive capacity, serious consideration might be given to using partial enzymic hydrolysates of whole protein rather than free AA mixtures as the N source in "elemental" diets. Care should be taken, however, in ensuring that the preparation of choice does not promote a net secretion of fluid and electrolytes for such a property could have a deleterious effect in the clinical setting. PMID:6780707

Silk, D B; Fairclough, P D; Clark, M L; Hegarty, J E; Marrs, T C; Addison, J M; Burston, D; Clegg, K M; Matthews, D M

245

Conformationally Constrained Histidines in the Design of Peptidomimetics: Strategies for the ?-Space Control  

PubMed Central

A successful design of peptidomimetics must come to terms with ?-space control. The incorporation of ?-space constrained amino acids into bioactive peptides renders the ?1 and ?2 torsional angles of pharmacophore amino acids critical for activity and selectivity as with other relevant structural features of the template. This review describes histidine analogues characterized by replacement of native ? and/or ?-hydrogen atoms with alkyl substituents as well as analogues with ?, ?-didehydro unsaturation or C?-C? cyclopropane insertion (ACC derivatives). Attention is also dedicated to the relevant field of ?-aminoacid chemistry by describing the synthesis of ?2- and ?3-models (?-hHis). Structural modifications leading to cyclic imino derivatives such as spinacine, aza-histidine and analogues with shortening or elongation of the native side chain (nor-histidine and homo-histidine, respectively) are also described. Examples of the use of the described analogues to replace native histidine in bioactive peptides are also given.

Stefanucci, Azzurra; Pinnen, Francesco; Feliciani, Federica; Cacciatore, Ivana; Lucente, Gino; Mollica, Adriano

2011-01-01

246

Degree-constrained multicast routing for multimedia communications  

NASA Astrophysics Data System (ADS)

Multicast services have been increasingly used by many multimedia applications. As one of the key techniques to support multimedia applications, the rational and effective multicast routing algorithms are very important to networks performance. When switch nodes in networks have different multicast capability, multicast routing problem is modeled as the degree-constrained Steiner problem. We presented two heuristic algorithms, named BMSTA and BSPTA, for the degree-constrained case in multimedia communications. Both algorithms are used to generate degree-constrained multicast trees with bandwidth and end to end delay bound. Simulations over random networks were carried out to compare the performance of the two proposed algorithms. Experimental results show that the proposed algorithms have advantages in traffic load balancing, which can avoid link blocking and enhance networks performance efficiently. BMSTA has better ability in finding unsaturated links and (or) unsaturated nodes to generate multicast trees than BSPTA. The performance of BMSTA is affected by the variation of degree constraints.

Wang, Yanlin; Sun, Yugeng; Li, Guidan

2005-02-01

247

Fast Energy Minimization of large Polymers Using Constrained Optimization  

SciTech Connect

A new computational technique is described that uses distance constraints to calculate empirical potential energy minima of partially rigid molecules. A constrained minimuzation algorithm that works entirely in Cartesian coordinates is used. The algorithm does not obey the constraints until convergence, a feature that reduces ill-conditioning and allows constrained local minima to be computed more quickly than unconstrained minima. Computational speedup exceeds the 3-fold factor commonly obtained in constained molecular dynamics simulations, where the constraints must be strictly obeyed at all times.

Todd D. Plantenga

1998-10-01

248

A filter-based evolutionary algorithm for constrained optimization.  

SciTech Connect

We introduce a filter-based evolutionary algorithm (FEA) for constrained optimization. The filter used by an FEA explicitly imposes the concept of dominance on a partially ordered solution set. We show that the algorithm is provably robust for both linear and nonlinear problems and constraints. FEAs use a finite pattern of mutation offsets, and our analysis is closely related to recent convergence results for pattern search methods. We discuss how properties of this pattern impact the ability of an FEA to converge to a constrained local optimum.

Clevenger, Lauren M. (University of New Mexico); Hart, William Eugene; Ferguson, Lauren Ann (Texas Tech University)

2004-02-01

249

Constrained caloric curves and phase transition for hot nuclei  

NASA Astrophysics Data System (ADS)

Simulations based on experimental data obtained from multifragmenting quasi-fused nuclei produced in central Xe129+natSn collisions have been used to deduce event by event freeze-out properties in the thermal excitation energy range 4–12 AMeV [S. Piantelli, et al., INDRA Collaboration, Nucl. Phys. A 809 (2008) 111]. From these properties and the temperatures deduced from proton transverse momentum fluctuations, constrained caloric curves have been built. At constant average volumes caloric curves exhibit a monotonic behaviour whereas for constrained pressures a backbending is observed. Such results support the existence of a first order phase transition for hot nuclei.

Borderie, B.; Piantelli, S.; Rivet, M. F.; Raduta, Ad. R.; Ademard, G.; Bonnet, E.; Bougault, R.; Chbihi, A.; Frankland, J. D.; Galichet, E.; Gruyer, D.; Guinet, D.; Lautesse, P.; Le Neindre, N.; Lopez, O.; Marini, P.; Pârlog, M.; Pawlowski, P.; Rosato, E.; Roy, R.; Vigilante, M.

2013-06-01

250

Translational diffusion of class II major histocompatibility complex molecules is constrained by their cytoplasmic domains  

PubMed Central

Site-directed mutagenesis in vitro was used to introduce stop codons in the genomic DNA of the alpha and beta chains of the murine class II major histocompatibility complex antigen, I-Ak. Mutated DNA was transfected into B lymphoma cells that were then selected by neomycin resistance and for their ability to express I-Ak molecules on their plasma membrane. The translational diffusion coefficient (Dlat) of I-Ak molecules composed of a wild-type beta chain paired with an alpha chain missing either 6 or 12 amino acids from the cytoplasmic domain is on the average threefold higher than the Dlat of wild-type I-Ak molecules as measured by fluorescence photobleaching and recovery. The removal of 12 amino acids from the cytoplasmic domain of the beta chain did not change the Dlat value from that of wild-type I-Ak if the truncated beta chain was paired with a wild-type alpha chain. Removing all amino acids of the cytoplasmic domains of both the alpha and beta chains resulted in a 10-fold increase in the Dlat, the highest value for any of the truncated I-Ak molecules tested. These data indicate that the carboxy- terminal six amino acids of the cytoplasmic domain of the alpha chain and the six plasma membrane-proximal amino acids of the beta chain are important in constraining the translational diffusion of I-Ak molecules in the plasma membrane.

1989-01-01

251

Electrophysiological evidence for acidic, basic, and neutral amino acid olfactory receptor sites in the catfish  

PubMed Central

Electrophysiological experiments indicate that olfactory receptors of the channel catfish, Ictalurus punctatus, contain different receptor sites for the acidic (A), basic (B), and neutral amino acids; further, at least two partially interacting neutral sites exist, one for the hydrophilic neutral amino acids containing short side chains (SCN), and the second for the hydrophobic amino acids containing long side chains (LCN). The extent of cross-adaptation was determined by comparing the electro-olfactogram (EOG) responses to 20 "test" amino acids during continuous bathing of the olfactory mucosa with water only (control) to those during each of the eight "adapting" amino acid regimes. Both the adapting and test amino acids were adjusted in concentrations to provide approximately equal response magnitudes in the unadapted state. Under all eight adapting regimes, the test EOG responses were reduced from those obtained in the unadapted state, but substantial quantitative differences resulted, depending upon the molecular structure of the adapting stimulus. Analyses of the patterns of EOG responses to the test stimuli identified and characterized the respective "transduction processes," a term used to describe membrane events initiated by a particular subset of amino acid stimuli that are intricately linked to the origin of the olfactory receptor potential. Only when the stimulus compounds interact with different transduction processes are the stimuli assumed to bind to different membrane "sites." Four relatively independent L-alpha-amino acid transduction processes (and thus at least four binding sites) identified in this report include: (a) the A process for aspartic and glutamic acids; (b) the B process for arginine and lysine; (c) the SCN process for glycine, alanine, serine, glutamine, and possibly cysteine; (d) the LCN process for methionine, ethionine, valine, norvaline, leucine, norleucine, glutamic acid-gamma-methyl ester, histidine, phenylalanine, and also possibly cysteine. The specificities of these olfactory transduction processes in the catfish are similar to those for the biochemically determined receptor sites for amino acids in other species of fishes and to amino acid transport specificities in tissues of a variety of organisms.

1984-01-01

252

Kynurenic acid has a dual action on AMPA receptor responses.  

PubMed

Glutamate is the predominant excitatory neurotransmitter in the central nervous system. The receptors that bind glutamate, including N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subtypes, are strongly implicated in higher cognitive processes, especially learning and memory. Loss of glutamate receptor function impairs the ability to acquire and retain information in some patients subsequent to stroke or brain injury, and positive allosteric modulators of glutamate receptors can restore learning and memory in some of these patients. Here we demonstrate that kynurenic acid (KYNA), an endogenous tryptophan metabolite, acts upon heterologous AMPA receptors via two distinct mechanisms. Low (nanomolar to micromolar) concentrations of KYNA facilitate AMPA receptor responses, whereas high (millimolar) concentrations of KYNA competitively antagonize glutamate receptors. Low concentrations of KYNA appear to increase current responses through allosteric modulation of desensitization of AMPA receptors. These findings suggest the possibility that low concentrations of endogenous KYNA acting at AMPA receptors may be a positive modulator of excitatory synaptic transmission. PMID:16644124

Prescott, Christina; Weeks, Autumn M; Staley, Kevin J; Partin, Kathryn M

2006-04-27

253

CHANCE CONSTRAINED PROGRAMMING FOR SECURITY ANALYSIS AND PORTFOLIO MANAGEMENT  

Microsoft Academic Search

The focus of this research paper is to develop a model for security analysis and investment decisions using multiobjective chance constrained programming (CCP). Using relevant variables and constraints a deterministic nonlinear programming model is derived using CCP technique. The model's efficiency and effectiveness is also evaluated as applied to a sample of stocks selected from the Dow Jones Industrial Average

Hari P. Sharma; Dinesh K. Sharma; Princess Anne; R. K. Jan

254

A Bidirectional Ant colony algorithm for resource constrained project scheduling  

Microsoft Academic Search

The resource-constrained project scheduling problem is a typical combinatorial optimization problem. An ant algorithm with dual ant colonies is proposed to improve the effective allocation of project resources. The algorithm adaptively adjusts resource allocation according to the pheromone updated by artificial ants employed to search for feasible schedules. Two separate ant colonies are employed. The forward scheduling technique is applied

Yongyi Shou

2007-01-01

255

Greedy Optimization for Contiguity-Constrained Hierarchical Clustering  

Microsoft Academic Search

The discovery and construction of inherent regions in large spatial datasets is an important task for many research domains such as climate zoning, eco-region analysis, public health mapping, and political redistricting. From the perspective of cluster analysis, it requires that each cluster is geographically contiguous. This paper presents a contiguity constrained hierarchical clustering and optimization method that can partition a

Diansheng Guo

2009-01-01

256

Output feedback constrained H? control of active vehicle suspensions  

Microsoft Academic Search

This paper develops an LMI-based solution for output-feedback constrained H? control design, and considers it for active vehicle suspension system. A quarter car model, which captures many features of real structures, is used in this study. To take more general road disturbances than white noise into account in the design procedure, H? performance measure is used to judge ride comfort,

Ahmad Akbari; Milad Geravand; Boris Lohmann

2010-01-01

257

Improving Temporal Flexibility of Position Constrained Metric Temporal Plans  

Microsoft Academic Search

In this paper w ea ddress the problem of post-processing posi- tio nc onstrained plans, output by many of the recent efficient metric temporal planners, to improve their execution flexibil- ity. Specifically, given a position constrained plan, we con- sider theproblem of generating apartiallyordered (aka \\

Minh Binh Do; Subbarao Kambhampati

2003-01-01

258

Multiply-Constrained Semantic Search in the Remote Associates Test  

ERIC Educational Resources Information Center

Many important problems require consideration of multiple constraints, such as choosing a job based on salary, location, and responsibilities. We used the Remote Associates Test to study how people solve such multiply-constrained problems by asking participants to make guesses as they came to mind. We evaluated how people generated these guesses…

Smith, Kevin A.; Huber, David E.; Vul, Edward

2013-01-01

259

Information Retrieval by Constrained Spreading Activation in Semantic Networks.  

ERIC Educational Resources Information Center

|Describes GRANT, an expert system for finding sources of funding given research proposals. The architecture of GRANT and the implementation of constrained spreading activation (a modified search algorithm based on semantic memory) are described, and recall and precision rates are analyzed. (Author/LRW)|

Cohen, Paul R.; Kjeldsen, Rick

1987-01-01

260

Dynamic optimization of constrained chemical engineering problems using dynamic programming  

Microsoft Academic Search

In many chemical engineering process control applications, one frequently encounters differential-algebraic optimization problems. Such optimal control problems are difficult to solve, in general, because of the presence of singular arcs for systems whose Hamiltonian is linear with respect to the control variable. We propose the use of absolute error penalty functions (AEPF) in handling constrained optimal control problems in chemical

S. A. Dadebo; K. B. Mcauley

1995-01-01

261

Constraining the Distribution of L & T Dwarfs in the Galaxy  

Microsoft Academic Search

We address the distribution of L- & T-dwarfs as a function of Galactic coordinates to study their contamination in high redshift galaxy surveys which employ the dropout method. A Monte Carlo simulation was used to exponentially distribute 1010}-10{11 points in both vertical scale height and radius, while constraining the local number density to a published value. Then, by assuming a

R. E. Ryan Jr.; N. P. Hathi; S. H. Cohen; R. A. Windhorst

2004-01-01

262

Optimal Website Design with the Constrained Subtree Selection Problem  

Microsoft Academic Search

We introduce the Constrained Subtree Selection (CSS) prob- lem as a model for the optimal design of websites. Given a hierarchy of topics represented as a DAG G and a probability distribution over the topics, we select a subtree of the transitive closure of G which minimizes the expected path cost. We define path cost as the sum of the

Brent Heeringa; Micah Adler

2004-01-01

263

Justice-constrained libertarian claims and Pareto efficient collective decisions  

Microsoft Academic Search

This paper discusses justice-constrained libertarian claims that were proposed as a way to circumvent the impossibility of the Paretian liberal. Since most of the results are negative in character, we suggest an alternative route: A requirement on the structure of individual orderings should be combined with the idea that under particular circumstances individual decisiveness should be controlled by higher-order principles.

Wulf Gaertner

1985-01-01

264

Holocene geocentric dipole tilt model constrained by sedimentary paleomagnetic data  

Microsoft Academic Search

Paleomagnetic data, although undeniably limited, have been used to constrain complex time-varying geomagnetic field models. Here we present four different versions of a time varying geocentric dipole model for the past approximately 9000 years based on a limited selection of sedimentary paleomagnetic data with good spatial coverage. The robustness of the modeling approach is evaluated using modern magnetic observation station

Andreas Nilsson; Ian Snowball; Raimund Muscheler; Cintia Bertacchi Uvo

2010-01-01

265

Constrained optimization of aerodynamic shapes via minimization of total drag  

Microsoft Academic Search

In this study, a robust and efficient approach to the multipoint constrained design is developed and applied to the optimization of aerodynamic wings. The objective is to minimize the total drag at fixed lift subject to various geometrical and aerodynamical constraints. The approach employs Genetic Algorithms (GAs) as an optimization tool in combination with a Reduced Order Models (ROM) method

S. Peigin; B. Epstein

2005-01-01

266

Degree-constrained multicast routing for multimedia communications  

Microsoft Academic Search

Multicast services have been increasingly used by many multimedia applications. As one of the key techniques to support multimedia applications, the rational and effective multicast routing algorithms are very important to networks performance. When switch nodes in networks have different multicast capability, multicast routing problem is modeled as the degree-constrained Steiner problem. We presented two heuristic algorithms, named BMSTA and

Yanlin Wang; Yugeng Sun; Guidan Li

2005-01-01

267

Force and Motion Control of a Constrained Flexible Robot Arm  

Microsoft Academic Search

The results of a study on the combined joint motion control, vibration control, and force control of a constrained rigid-flexible robot arm for both regulation and tracking are presented. A nonlinear modified Corless-Leitmann controller is proposeed for control of the flexible motion using only joint actuators. Experimental studies, which demonstrate the effectiveness of the proposed method, are described.

F. L. Hu; A. G. Ulsoy

1993-01-01

268

Constrained-Layer Model Investigation Based on Exact Elasticity Theory.  

National Technical Information Service (NTIS)

The model for constrained-layer damping proposed by Kerwin provides a direct insight into the effect of the various physical and geometric parameters on the attenuation. It does not account for extensional-wave damping and is limited to lower frequencies ...

P. S. Dubbelday

1986-01-01

269

Time Management for virtual worlds based on constrained communication model  

Microsoft Academic Search

Time Management (TM) is an integral part of the parallel and distributed systems that maintains the temporal order of events in a system. In this paper, we present a decentralised TM approach using a constrained communication model based on the inherent properties of virtual worlds. The proposed method uses a flat communication model and a region synchronises itself with a

Umar Farooq; John Glauert

2010-01-01

270

Scatter correction for gamma cameras using constrained deconvolution  

Microsoft Academic Search

Several groups have proposed the use of multiwindow (usually dual window) techniques for scatter correction in SPECT (single photon emission computed tomography) and conventional gamma camera imaging. The authors have developed a technique for constrained deconvolution of the primary photopeak from the observed spectrum using multiple (5-30) windows. They have tested it both with simulations and with a modified gamma

D. R. Haynor; R. L. Harrison; T. K. Lewellen

1992-01-01

271

A practical anti-cycling procedure for linearly constrained optimization  

Microsoft Academic Search

A procedure is described for preventing cycling in active-set methods for linearly constrained optimization, including the simplex method. The key ideas are a limited acceptance of infeasibilities in all variables, and maintenance of a “working” feasibility tolerance that increases over a long sequence of iterations. The additional work per iteration is nominal, and “stalling” cannot occur with exact arithmetic. The

Philip E. Gill; Walter Murray; Michael A. Saunders; Margaret H. Wright

1989-01-01

272

Estimation and optimal control for constrained Markov chains  

Microsoft Academic Search

The (optimal) design of many engineering systems can be adequately recast as a Markov decision process, where requirements on system performance are captured in the form of constraints. In this paper, various optimality results for constrained Markov decision processes are briefly reviewed; the corresponding implementation issues are discussed and shown to lead to several problems of parameter estimation. Simple situations

D.-J. Ma; A. M. Makowski; A. Shwartz

1986-01-01

273

Constraining-unification and the programming language unicorn  

Microsoft Academic Search

Up to this point direct implementations of axiomatic or equational specifications have been limited because the implementation mechanisms used are incapable of capturing the full semantics of the specifications. The programming language Unicorn was designed and implemented with the intention of exploring the full potential of programming with equations. Unicorn introduces a new language mechanism, called constraining-unification. When coupled with

Robert G. Bandes

1984-01-01

274

Constrained Cartesian motion control for teleoperated surgical robots  

Microsoft Academic Search

This paper addresses the problem of optimal motion control for teleoperated surgical robots, which must maneuver in constrained workspaces, often through a narrow entry portal into the patient's body. The control problem is determining how best to use the available degrees of freedom of a surgical robot to accomplish a particular task, while respecting geometric constraints on the work volume,

Janez Funda; Russell H. Taylor; Benjamin Eldridge; Stephen Gomory; Kreg G. Gruben

1996-01-01

275

Design of entropy-constrained multiple-description scalar quantizers  

Microsoft Academic Search

The problem of entropy-constrained multiple-description scalar quantizer design is posed as an optimization problem, necessary conditions for optimality are derived, and an iterative design algorithm is presented. Performance results are presented for a Gaussian source, along with comparisons to the multiple-description rate distortion bound and a reference system

Vinay Anant Vaishampayan; Jaroslaw Domaszewicz

1994-01-01

276

Constrained nonlinear multivariable control of a catalytic reforming process  

Microsoft Academic Search

A constrained nonlinear multivariable control and optimization strategy for handling constraints has been proposed and applied in real time to a catalytic reforming reactor-section. A dynamic model of the catalytic reforming process was developed and used in a nonlinear multivariable control application on the reactor section to provide target values for the reactor inlet temperature. The model results were tested

R. M. Ansari; M. O. Tade

1998-01-01

277

On constrained manipulation in robotics-assisted minimally invasive surgery  

Microsoft Academic Search

Results of a study on the restricted motion of manipulators in robotics-assisted minimally invasive surgery are presented in this paper. The governing equations of trocar kinematics are derived and the constrained manipulation is generically formulated in terms of the trocar geometry as well as the kinematics of the manipulator. The results are validated through a numerical simulation with a Mitsubishi

Hamidreza Azimian; Rajni V. Patel; Michael D. Naish

2010-01-01

278

Applications of a Constrained Mechanics Methodology in Economics  

ERIC Educational Resources Information Center

|This paper presents instructive interdisciplinary applications of constrained mechanics calculus in economics on a level appropriate for undergraduate physics education. The aim of the paper is (i) to meet the demand for illustrative examples suitable for presenting the background of the highly expanding research field of econophysics even at the…

Janova, Jitka

2011-01-01

279

On the Convex Parameterization of Constrained Spacecraft Reorientation  

Microsoft Academic Search

Guiding the rotational motion of a spacecraft subject to constraints on its permissible orientation often leads to nonconvex optimal control problems. In this paper, we consider convex parameterizations of sets associated with the constrained rigid body orientations. We then elaborate on ramifications of such a parameterization in the development of steering laws for autonomous spacecraft reorientation that are based on

Yoonsoo Kim; Mehran Mesbahi; Gurkirpal Singh; Fred Y. Hadaegh

2010-01-01

280

Constrained Quantum Mechanics: Chaos in Non-Planar Billiards  

ERIC Educational Resources Information Center

|We illustrate some of the techniques to identify chaos signatures at the quantum level using as guiding examples some systems where a particle is constrained to move on a radial symmetric, but non-planar, surface. In particular, two systems are studied: the case of a cone with an arbitrary contour or "dunce hat billiard" and the rectangular…

Salazar, R.; Tellez, G.

2012-01-01

281

Dark matter, constrained minimal supersymmetric standard model, and lattice QCD.  

SciTech Connect

Recent lattice measurements have given accurate estimates of the quark condensates in the proton. We use these results to significantly improve the dark matter predictions in benchmark models within the constrained minimal supersymmetric standard model. The predicted spin-independent cross sections are at least an order of magnitude smaller than previously suggested and our results have significant consequences for dark matter searches.

Giedt, J.; Thomas, A. W.; Young, R. D.; Physics; Rensselaer Polytechnic Inst.; Jefferson Lab.; Coll. of William & Mary

2009-11-13

282

Robust output feedback model predictive control of constrained linear systems  

Microsoft Academic Search

This paper provides a solution to the problem of robust output feedback model predictive control of constrained, linear, discrete-time systems in the presence of bounded state and output disturbances. The proposed output feedback controller consists of a simple, stable Luenberger state estimator and a recently developed, robustly stabilizing, tube-based, model predictive controller. The state estimation error is bounded by an

D. Q. Mayne; Sasa V. Rakovic; R. Findeisen; Frank Allgöwer

2006-01-01

283

Constrained Subspace ICA Based on Mutual Information Optimization Directly  

Microsoft Academic Search

We introduce a new approach to constrained Independent Compo- nent Analysis (ICA) by formulating the original, unconstrained ICA problem as well as the constraints in mutual information terms di- rectly. As an estimate of mutual information, a robust version of the Edgeworth expansion is used, and on which gradient descent is performed. As an application, we consider the extraction of

Marc M. Van Hulle

2008-01-01

284

Azimuthal seismic anisotropy constrains net rotation of the lithosphere  

Microsoft Academic Search

Net rotation (NR) of the lithosphere is found in hot spot reference frames, important for tectonics and plume models, but difficult to constrain. Using mantle flow and crystallographic texture modeling, I show that NRs lead to mantle shearing which is recorded in azimuthal seismic anisotropy. The NR amplitude in some hot spot models is so large that it degrades the

T. W. Becker

2008-01-01

285

Robust Positively Invariant Cylinders in Constrained Variable Structure Control  

Microsoft Academic Search

This paper proposes the use of cylinders as primary invariant sets to be used in certain state-constrained control designs. Following the idea originally introduced by O'Dell, the primary invariant set is intersected with the state constraints to yield sets which retain the invariance under some conditions. Although several results presented here apply to fairly general nonlinear systems and primary invariant

Hanz Richter; Brian D. O'Dell; Eduardo A. Misawa

2007-01-01

286

Fully Constrained Least Squares Spectral Unmixing by Simplex Projection  

Microsoft Academic Search

We present a new algorithm for linear spectral mixture analysis, which is capable of supervised unmixing of hyperspectral data while respecting the constraints on the abun- dance coefficients. This simplex-projection unmixing algorithm is based upon the equivalence of the fully constrained least squares problem and the problem of projecting a point onto a simplex. We introduce several geometrical properties of

Rob Heylen; Dževdet Burazerovic; Paul Scheunders

2011-01-01

287

CPOP: Cryptography Process Offloading Proxy for Resource Constrained Devices  

Microsoft Academic Search

Feasibility study on implementing a strong cryptographic function for resource constrained devices such as embedded devices has been carry out over the past. These studies found that it is not efficient to run an extensive security solution to those devices. For that reason, we tense to provide a security offloading approach to minimize the computing resources involved but maximizing the

Yu-Shu They; Seong-Yee Phang; Sanggon Lee; HoorJae Lee; Hyotaek Lim

2008-01-01

288

New approaches to constrained optimization of digital filters  

Microsoft Academic Search

Two algorithms are presented for the design of constrained least-squares digital filters. They can bound the error according to user specifications while also minimizing the total weighted squared error (TWSE). Although the two algorithms are very different internally, they produce very similar results. One algorithm produces nearly optimal solutions, and the other algorithm produces solutions that are guaranteed to be

J. W. Adams; J. L. Sullivan; R. Hashemi; C. Ghadimi; J. Franklin; B. Tucker

1993-01-01

289

Testing a Constrained MPC Controller in a Process Control Laboratory  

ERIC Educational Resources Information Center

This paper describes an experiment performed by the fourth year chemical engineering students in the process control laboratory at the University of Waterloo. The objective of this experiment is to test the capabilities of a constrained Model Predictive Controller (MPC) to control the operation of a Double Pipe Heat Exchanger (DPHE) in real time.…

Ricardez-Sandoval, Luis A.; Blankespoor, Wesley; Budman, Hector M.

2010-01-01

290

Constraining Galaxy Evolution With Hubble's Next Generation Spectral Library  

NASA Astrophysics Data System (ADS)

We present Hubble's Next Generation Spectral Library, a library of UV-optical spectra (0.2-1.0 ?) of 378 stars. We show that the mid-UV spectrum can be used to constrain the ages and metallicities of high-redshift galaxies presently being observed with large, ground-based telescopes.

Heap, S.; Lindler, D. J.

2009-03-01

291

Hummingbird: Ultra-Lightweight Cryptography for Resource-Constrained Devices  

Microsoft Academic Search

Due to the tight cost and constrained resources of high- volume consumer devices such as RFID tags, smart cards and wireless sensor nodes, it is desirable to employ lightweight and specialized cryp- tographic primitives for many security applications. Motivated by the design of the well-known Enigma machine, we present a novel ultra- lightweight cryptographic algorithm, referred to as Hummingbird, for

Daniel Engels; Xinxin Fan; Guang Gong; Honggang Hu; Eric M. Smith

2010-01-01

292

Improving the performance of time-constrained workflow processing  

Microsoft Academic Search

Many workflow applications often have timing constraints such that each processing of a workflow needs to be finished within its deadline. There have been some works to improve the performance of time-constrained workflow processing such as predictive workflow scheduling. They, however, have not much considered appropriate analyses to determine the processing capacities for certain activities so that most workflow instances

Jin Hyun Son; Myoung-ho Kim

2001-01-01

293

On Efficient Semidefinite Relaxations for Quadratically Constrained Quadratic Programming  

Microsoft Academic Search

Abstract Two important topics in the study of Quadratically Constrained Quadratic Programming (QCQP) are how to exactly solve a QCQP with few constraints in polynomial time and how to find an inexpensive and strong relaxation bound for a QCQP with many constraints. In this thesis, we first review some important results on QCQP, like the S-Procedure, and the strength of

Yichuan Ding

2007-01-01

294

Testing a Constrained MPC Controller in a Process Control Laboratory  

ERIC Educational Resources Information Center

|This paper describes an experiment performed by the fourth year chemical engineering students in the process control laboratory at the University of Waterloo. The objective of this experiment is to test the capabilities of a constrained Model Predictive Controller (MPC) to control the operation of a Double Pipe Heat Exchanger (DPHE) in real time.…

Ricardez-Sandoval, Luis A.; Blankespoor, Wesley; Budman, Hector M.

2010-01-01

295

Constraining Forces and the Work Performance of Finance Company Cashiers  

Microsoft Academic Search

A field study was performed examining the influence of situational constraints on the job performance of 368 finance company cashiers. Increasing levels of contextual constraint (as rated by a cashier's immediate supervisor) were negatively related to supervisory performance ratings, self-appraisals, and objective performance criteria. No differences were in evidence in the degree ofperformance variation found in high and low constraining

Robert P. Steel; Anthony J. Mento; William H. Hendrix

1987-01-01

296

An Inexact Fuzzy-Chance-Constrained Air Quality Management Model  

Microsoft Academic Search

Regional air pollution is a major concern for almost every country because it not only directly relates to economic development, but also poses significant threats to environment and public health. In this study, an inexact fuzzy-chance-constrained air quality management model (IFAMM) was developed for regional air quality management under uncertainty. IFAMM was formulated through integrating interval linear programming (ILP) within

Ye Xu; Guohe Huang; Xiaosheng Qin; Krzysztof Pikon´; Krzysztof Gaska; Lingjuan Wang; Edgar Oviedo-Rondon; John Small; Zifei Liu; Brian Sheldon; Gerald Havenstein; C. Williams; Di Tian; Daniel Cohan; Sergey Napelenok; Michelle Bergin; Yongtao Hu; Michael Chang; Armistead Russell; Kuo-Pin Yu; Grace Lee; Guo-Hao Huang; Prabhakar Sharma; Tjalfe Poulsen; William Vizuete; Leiran Biton; Harvey Jeffries; Evan Couzo; Yi-Chi Chien; Chenju Liang; Shou-Heng Liu; Shu-Hua Yang; Maciej Kryza; Malgorzata Werner; Marek Blas; Anthony Dore; Mieczyslaw Sobik; Daniel Olsen; Morgan Kohls; Gregg Arney; Kaushlendra Singh; L. Risse; K. C. Das; John Worley; Sidney Thompson; Bryan Comer; James Corbett; J. Hawker; Karl Korfmacher; Earl Lee; Chris Prokop; James Winebrake

2010-01-01

297

Applying Family Competition to Evolution Strategies for Constrained Optimization  

Microsoft Academic Search

This paper applies family competition to evolution strategies to solve constrained optimization problems. The family competition of Family Competition Evolution Strategy (FCES) can be viewed as a local competition involving the children generated from the same parent, while the selection is a global competition among all of the members in the population. According to our experimental results, the self-adaptation of

Jinn-moon Yang; Ying-ping Chen; Jorng-tzong Horng; Cheng-yan Kao

1997-01-01

298

Constrained Transport vs. Divergence Cleanser Options in Astrophysical MHD Simulations  

NASA Astrophysics Data System (ADS)

In previous work, we presented results from global numerical simulations of the evolution of black hole accretion disks using the Cosmos++ GRMHD code. In those simulations we solved the magnetic induction equation using an advection-split form, which is known not to satisfy the divergence-free constraint. To minimize the build-up of divergence error, we used a hyperbolic cleanser function that simultaneously damped the error and propagated it off the grid. We have since found that this method produces qualitatively and quantitatively different behavior in high magnetic field regions than results published by other research groups, particularly in the evacuated funnels of black-hole accretion disks where Poynting-flux jets are reported to form. The main difference between our earlier work and that of our competitors is their use of constrained-transport schemes to preserve a divergence-free magnetic field. Therefore, to study these differences directly, we have implemented a constrained transport scheme into Cosmos++. Because Cosmos++ uses a zone-centered, finite-volume method, we can not use the traditional staggered-mesh constrained transport scheme of Evans & Hawley. Instead we must implement a more general scheme; we chose the Flux-CT scheme as described by Toth. Here we present comparisons of results using the divergence-cleanser and constrained transport options in Cosmos++.

Lindner, Christopher C.; Fragile, P.

2009-01-01

299

Density-Constrained TDHF Calculation of Fusion and Fission Barriers  

SciTech Connect

The density-constrained time-dependent Hartree-Fock (DC-TDHF) theory is a fully microscopic approach for calculating heavy-ion interaction potentials and fusion cross sections below and above the fusion barrier. We discuss applications of DC-TDHF method to fusion, the effects of neutron transfer, and potential application to fission barrier calculations.

Umar, A. S.; Oberacker, V. E. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Maruhn, J. A. [Institut fuer Theoretische Physik, Goethe-Universitaet, 60438 Frankfurt am Main (Germany); Reinhard, P.-G. [Institut fur Theoretische Physik, Universitat Erlangen, D-91054 Erlangen (Germany)

2009-08-26

300

Abnormal equality-constrained optimization problems: sensitivity theory  

Microsoft Academic Search

For the equality-constrained optimization problem, we consider the case when the customary regularity of constraints can be violated. Under the assumptions substantially weaker than those previously used in the literature, we develop a reasonably complete local sensitivity theory for this class of problems, including upper and lower bounds for the rate of change of the optimal value function subject to

A. V. Arutyunov; A. F. Izmailov

2004-01-01

301

Using Intensive Variables to Constrain Magma Source Regions  

Microsoft Academic Search

In the modern world of petrology, magma source region characterization is commonly the realm of trace element and isotopic geochemistry. However, major element analyses of rocks representing magmatic compositions can also be used to constrain source region charactertistics, which enhance the results of isotopic and trace element studies. We show examples from the northern Cordilleran volcanic province (NCVP), in the

B. R. Edwards; J. K. Russell

2006-01-01

302

Constrained quantum mechanics: chaos in non-planar billiards  

NASA Astrophysics Data System (ADS)

We illustrate some of the techniques to identify chaos signatures at the quantum level using as guiding examples some systems where a particle is constrained to move on a radial symmetric, but non-planar, surface. In particular, two systems are studied: the case of a cone with an arbitrary contour or dunce hat billiard and the rectangular billiard with an inner Gaussian surface.

Salazar, R.; Téllez, G.

2012-07-01

303

Arch parameter estimation via constrained two stage least squares method  

Microsoft Academic Search

This paper discusses the constrained two stage least squares (CLS2) estimator of the parameters of ARCH models under known order. This estimator is a modified version of the two stage least squares (TSLS) estimation. The estimator is easy to obtain and fast since it involves only quadratic optimization. At the same time, the estimator has the same asymptotic efficiency as

S. Mousazadeh; M. Karimi; M. Farrokhrooz

2007-01-01

304

Flexible composite propeller design using constrained optimization techniques  

Microsoft Academic Search

An investigation of a conventional propeller, made from composite materials, was conducted in which its characteristics were studied under quasi-static aerodynamic loading. Also, optimized designing of a composite propeller was performed for various constrained and unconstrained design objectives. Only symmetric ply stacking sequences were considered to eliminate the effect of centrifugal force on the propeller. Results show that the ply

Abdul Monuem Khan

1997-01-01

305

Performance of algorithms for large-scale bound constrained problems.  

National Technical Information Service (NTIS)

We discuss issues that affect the performance of algorithms for the solution of large-scale bound constrained problems on parallel computers. The discussion centers on the solution of the elastic-plastic torsion problem and the journal bearing problem. Th...

J. J. More

1990-01-01

306

Contractive model predictive control for constrained nonlinear systems  

Microsoft Academic Search

This paper addresses the development of stabilizing state and output feedback model predictive control (MPC) algorithms for constrained continuous-time nonlinear systems with discrete observations. Moreover, we propose a nonlinear observer structure for this class of systems and derive sufficient conditions under which this observer provides asymptotically convergent estimates. The MPC scheme proposed consists of a basic finite horizon nonlinear MPC

S. L. de Oliveira Kothare; Manfred Morari

2000-01-01

307

Artificial Immune System for Solving Constrained Optimization Problems  

Microsoft Academic Search

In this paper, we present an artificial immune system (AIS) based on the CLONALG algorithm for solving constrained (numerical) optimization problems. We develop a new mutation operator which produces large and small step sizes and which aims to provide better exploration capabilities. We validate our proposed approach with 13 test functions taken from the specialized literature and we compare our

Susana C. Esquivel; Carlos Artemio Coello Coello; Victoria S. Aragón

2007-01-01

308

Confinor and anti-confinor in constrained “Lorenz” system  

Microsoft Academic Search

The bifurcation of possibly chaotic oscillatory patterns of a family of differential equations constrained on the cusp surface\\u000a is studied. Notions of “confinor” and “anti-confinor” are introduced to get a rough diagram of bifurcations of this family.\\u000a “Anti-bifurcation” and “rainbow-bifurcation” are found as bifurcations of confinors.

Shigehiro Ushiki; René Lozi

1987-01-01

309

Dynamic constrained optimal power flow using semi-infinite programming  

Microsoft Academic Search

Dynamic constrained optimal power flow can be modeled as a semi-infinite programming problem. In this letter, a local reduction based on infinite norm is proposed to replace the infinite constraints with finite constraints. The equivalent problem is then solved by the standard finite programming method. A case study on the WSCC nine-bus system showed that the proposed model and approach

Yan Xia; Ka Wing Chan

2006-01-01

310

Umbrella Contingencies in Security-Constrained Optimal Power Flow  

Microsoft Academic Search

The notion of umbrella contingencies is rigor- ously defined in the context of the security-constrained opti- mal power flow (SCOPF) problem in both its deterministic and probabilistic forms. The set of umbrella contingencies is a subset of the set of credible contingencies that is suffi- cient to attain levels of security and economic performance identical or nearly identical to those

Francois Bouffard; Francisco D. Galiana; M. Arroyo

2005-01-01

311

Expressional face image analysis with constrained optical flow  

Microsoft Academic Search

Face recognition is one of the most intensively studied topics in computer vision and pattern recognition. A constrained optical flow algorithm, which combines the advantages of the unambiguous correspondence of feature point labeling and the flexible representation of optical flow computation has been proposed in our pervious work. Facial expression normalization, from expressive to neutral facial images, based on optical

Chao-kuei Hsieh; Shang-hong Lai; Yung-chang Chen

2008-01-01

312

Stabilization of Constrained Mechanical Systems with DAEs and Invariant Manifolds  

Microsoft Academic Search

Many methods have been proposed for the simulation of constrained mechanical systems. The most obvious of these have mild instabilities and drift problems. Consequently, stabilization techniques have been proposed A popular stabilization method is Baumgarte's technique, but the choice of parameters to make it robust has been unclear in practice.Some of the simulation methods that have been proposed and used

Uri M. Ascher; Hongsheng Chin; Linda R. Petzold; Sebastian Reich

1995-01-01

313

Tight bounds for online class-constrained packing  

Microsoft Academic Search

We consider class-constrained packing problems, in which we are given a set of bins, each having a capacity v and c compartments, and n items of M different classes and the same (unit) size. We need to fill the bins with items, subject to capacity constraints, such that items of different classes are placed in separate compartments; thus, each bin

Hadas Shachnai; Tami Tamir

2004-01-01

314

Tight Bounds for Online Class-Constrained Packing  

Microsoft Academic Search

We consider class constrained packing problems, in which we are given a set of bins, each having a capacity v and c compartments, and n items of M different classes and the same (unit) size. We need to fill the bins with items, subject to capacity constraints, such that\\u000a items of different classes are placed in separate compartments; thus, each

Hadas Shachnai; Tami Tamir

2002-01-01

315

Self-adaptive fitness formulation for constrained optimization  

Microsoft Academic Search

A self-adaptive fitness formulation is presented for solving constrained optimization problems. In this method, the dimensionality of the problem is reduced by representing the constraint violations by a single infeasibility measure. The infeasibility measure is used to form a two-stage penalty that is applied to the infeasible solutions. The performance of the method has been examined by its application to

Raziyeh Farmani; Jonathan A. Wright

2003-01-01

316

Power Constrained Electric Propulsion Missions to the Outer Planets  

Microsoft Academic Search

The presented study has analyzed the transfer characteristics of missions based on small, power constrained spacecraft that employ Electric Propulsion in combination with a power- ful launcher, to the outer planets. Power requirements at these solar distances are fulfilled by a radioisotope thermoelectric generator and the required high launch energy is based on an existing launcher, avoiding the reliance on

K. Geurts; C. Casaregola; P. Pergolaand; M. Andrenucci

317

Force and position control of manipulators during constrained motion tasks  

Microsoft Academic Search

Trajectory control of a manipulator constrained by the contact of the end-effector with the environment represents an important class of control problems. A method is proposed whereby both contact force exerted by the manipulator, and the position of the end-effector while in contact with the surface are controlled. The controller parameters are derived based on a linearized dynamic model of

J. K. Mills; A. A. Goldenberg

1989-01-01

318

Realtime Obstacle Detection and Tracking Based on Constrained Delaunay Triangulation  

Microsoft Academic Search

We introduce a realtime vehicle detection and tracking algorithm for in-vehicle video images. Although various vehicle detection approaches have been proposed, it is difficult to find a fast and reliable algorithm for realtime applications, such as for vehicle collision warning. We introduce a realtime appearance-based vehicle detection approach. It uses constrained Delaunay triangulation to make image evidence collection for multiple

Zu Kim

2006-01-01

319

Maximizing minimum Euclidean distance of spectrally constrained partial response CPM  

Microsoft Academic Search

Optimized phase pulses, which maximizes the minimum Euclidean distance of spectrally constrained partial response CPM with different pulse lengths and different alphabet sizes, are numerically found. The channel is specified by a narrow spectrum mask, which puts hard requirements on both the width of the spectral main lobe and the size of the spectral side lobes, and AWGN. The phase

Tommy Svensson; Arne Svensson

2001-01-01

320

Structure and Nuclease Resistance of 2?,4?-Constrained 2?-O-Methoxyethyl (cMOE) and 2?-O-Ethyl (cEt) Modified DNAs†  

PubMed Central

Combining the structural elements of the second generation 2?-O-methoxyethyl (MOE) and locked nucleic acid (LNA) antisense oligonucleotide (AON) modifications yielded the highly nuclease resistant 2?,4?-constrained MOE and ethyl bicyclic nucleic acids (cMOE and cEt BNA, respectively). Crystal structures of DNAs with cMOE or cEt BNA residues reveal their conformational preferences. Comparisons with MOE and LNA structures allow insights into their favourable properties for AON applications.

Pallan, Pradeep S.; Allerson, Charles R.; Berdeja, Andres; Seth, Punit P.; Swayze, Eric E.; Prakash, Thazha P.; Egli, Martin

2012-01-01

321

Structure and nuclease resistance of 2',4'-constrained 2'-O-methoxyethyl (cMOE) and 2'-O-ethyl (cEt) modified DNAs.  

PubMed

Combining the structural elements of the second generation 2'-O-methoxyethyl (MOE) and locked nucleic acid (LNA) antisense oligonucleotide (AON) modifications yielded the highly nuclease resistant 2',4'-constrained MOE and ethyl bicyclic nucleic acids (cMOE and cEt BNA, respectively). Crystal structures of DNAs with cMOE or cEt BNA residues reveal their conformational preferences. Comparisons with MOE and LNA structures allow insights into their favourable properties for AON applications. PMID:22614180

Pallan, Pradeep S; Allerson, Charles R; Berdeja, Andres; Seth, Punit P; Swayze, Eric E; Prakash, Thazha P; Egli, Martin

2012-05-22

322

How well do different tracers constrain the firn diffusivity profile?  

NASA Astrophysics Data System (ADS)

Firn air transport models are used to interpret measurements of the composition of air in firn and bubbles trapped in ice in order to reconstruct past atmospheric composition. The diffusivity profile in the firn is usually calibrated by comparing modelled and measured concentrations for tracers with known atmospheric history. However, in some cases this is an under-determined inverse problem, often with multiple solutions giving an adequate fit to the data (this is known as equifinality). Here we describe a method to estimate the firn diffusivity profile that allows multiple solutions to be identified, in order to quantify the uncertainty in diffusivity due to equifinality. We then look at how well different combinations of tracers constrain the firn diffusivity profile. Tracers with rapid atmospheric variations like CH3CCl3, HFCs and 14CO2 are most useful for constraining molecular diffusivity, while ?15N2 is useful for constraining parameters related to convective mixing near the surface. When errors in the observations are small and Gaussian, three carefully selected tracers are able to constrain the molecular diffusivity profile well with minimal equifinality. However, with realistic data errors or additional processes to constrain, there is benefit to including as many tracers as possible to reduce the uncertainties. We calculate CO2 age distributions and their spectral widths with uncertainties for five firn sites (NEEM, DE08-2, DSSW20K, South Pole 1995 and South Pole 2001) with quite different characteristics and tracers available for calibration. We recommend moving away from the use of a single firn model with one calibrated parameter set to infer atmospheric histories, and instead suggest using multiple parameter sets, preferably with multiple representations of uncertain processes, to allow quantification of the uncertainties.

Trudinger, C. M.; Enting, I. G.; Rayner, P. J.; Etheridge, D. M.; Buizert, C.; Rubino, M.; Krummel, P. B.; Blunier, T.

2012-07-01

323

How well do different tracers constrain the firn diffusivity profile?  

NASA Astrophysics Data System (ADS)

Firn air transport models are used to interpret measurements of the composition of air in firn and bubbles trapped in ice in order to reconstruct past atmospheric composition. The diffusivity profile in the firn is usually calibrated by comparing modelled and measured concentrations for tracers with known atmospheric history. However, in most cases this is an under-determined inverse problem, often with multiple solutions giving an adequate fit to the data (this is known as equifinality). Here we describe a method to estimate the firn diffusivity profile that allows multiple solutions to be identified, in order to quantify the uncertainty in diffusivity due to equifinality. We then look at how well different combinations of tracers constrain the firn diffusivity profile. Tracers with rapid atmospheric variations like CH3CCl3, HFCs and 14CO2 are most useful for constraining molecular diffusivity, while &delta:15N2 is useful for constraining parameters related to convective mixing near the surface. When errors in the observations are small and Gaussian, three carefully selected tracers are able to constrain the molecular diffusivity profile well with minimal equifinality. However, with realistic data errors or additional processes to constrain, there is benefit to including as many tracers as possible to reduce the uncertainties. We calculate CO2 age distributions and their spectral widths with uncertainties for five firn sites (NEEM, DE08-2, DSSW20K, South Pole 1995 and South Pole 2001) with quite different characteristics and tracers available for calibration. We recommend moving away from the use of a firn model with one calibrated parameter set to infer atmospheric histories, and instead suggest using multiple parameter sets, preferably with multiple representations of uncertain processes, to assist in quantification of the uncertainties.

Trudinger, C. M.; Enting, I. G.; Rayner, P. J.; Etheridge, D. M.; Buizert, C.; Rubino, M.; Krummel, P. B.; Blunier, T.

2013-02-01

324

Aromatic amino acid transport in Yersinia pestis.  

PubMed Central

The uptake and concentration of aromatic amino acids by Yersinia pestis TJW was investigated using endogenously metabolizing cells. Transport activity did not depend on either protein synthesis or exogenously added energy sources such as glucose. Aromatic amino acids remained as the free, unaltered amino acid in the pool fraction. Phenylalanine and tryptophan transport obeyed Michaelis-Menten-like kinetics with apparent Km values of 6 x 10(-7) to 7.5 x 10(-7) and 2 x 10(-6) M, respectively. Tyrosine transport showed biphasic concentration-dependent kinetics that indicated a diffusion-like process above external tyrosine concentrations of 2 x 10(-6) M. Transport of each aromatic amino acid showed different pH and temperature optima. The pH (7.5 TO8) and temperature (27 C) optima for phenylalanine transport were similar to those for growth. Transport of each aromatic amino acid was characterized by Q10 values of approximately 2. Cross inhibition and exchange experiments between the aromatic amino acids and selected aromatic amino acid analogues revealed the existence of three transport systems: (i) tryptophan specific, (ii) phenylalanine specific with limited transport activity for tyrosine and tryptophan, and (iii) general aromatic system with some specificity for tyrosine. Analogue studies also showed that the minimal stereo and structural features for phenylalanine recognition were: (i) the L isomer, (ii) intact alpha amino and carboxy group, and (iii) unsubstituted aromatic ring. Aromatic amino acid transport was differentially inhibited by various sulfhydryl blocking reagents and energy inhibitors. Phenylalanine and tyrosine transport was inhibited by 2,4-dinitrophenol, potassium cyanide, and sodium azide. Phenylalanine transport showed greater sensitivity to inhibition by sulfhydryl blocking reagents, particularly N-ethylmaleimide, than did tyrosine transport. Tryptophan transport was not inhibited by either sulfhydryl reagents or sodium azide. The results on the selective inhibition of aromatic amino acid transport provide additional evidence for multiple transport systems . These results further suggest both specific mechanisms for carrier-mediated active transport and coupling to metabolic energy.

Smith, P B; Montie, T C

1975-01-01

325

Characterization of neutral amino acid transport in a marine pseudomonad.  

PubMed Central

The transport of neutral amino acids in marine pseudomonad B-16 (ATCC 19855) has been investigated. From patterns of competitive inhibition, mutant analysis, and kinetic data, two active transport systems with overlapping substrate specificities were distinguished and characterized. One system (DAG) served glycine, D-alanine, D-serine, and alpha-aminoisobutyric acid (AIB) and, to a lesser extent, L-alanine and possibly other related neutral D- and L-amino acids. The other system (LIV) showed high stereospecificity for neutral amino acids with the L configuration and served primarily to transport L-leucine, L-isoleucine, L-valine, and L-alanine. This system exhibited low affinity for alpha-aminoisobutyric acid. Neither system was able to recognize structural analogues with modified alpha-amino or alpha-carboxyl groups. The kinetic parameters for L-alanine transport by the DAG and LIV systems were determined with appropriate mutants defective in either system. For L-alanine, Kt values of 4.6 X 10(-5) and 1.9 X 10(-4) M and Vmax values of 6.9 and 20.8 nmol/min per mg of cell dry weight were obtained for transport via the DAG and LIV systems respectively. alpha-Aminoisobutyric acid transport heterogeneity was also resolved with the mutants, and Kt values of 2.8 X 10(-5) and 1.4 X 10(-3) M AIB were obtained for transport via the DAG and LIV systems, respectively. Both systems required Na+ for activity (0.3 M Na+ optimal) and in this regard are distinguished from systems of similar substrate specificity reported in nonmarine bacteria.

Fein, J E; MacLeod, R A

1975-01-01

326

Brain amino acid requirements and toxicity: the example of leucine.  

PubMed

Glutamic acid is an important excitatory neurotransmitter of the brain. Two key goals of brain amino acid handling are to maintain a very low intrasynaptic concentration of glutamic acid and also to provide the system with precursors from which to synthesize glutamate. The intrasynaptic glutamate level must be kept low to maximize the signal-to-noise ratio upon the release of glutamate from nerve terminals and to minimize the risk of excitotoxicity consequent to excessive glutamatergic stimulation of susceptible neurons. The brain must also provide neurons with a constant supply of glutamate, which both neurons and glia robustly oxidize. The branched-chain amino acids (BCAAs), particularly leucine, play an important role in this regard. Leucine enters the brain from the blood more rapidly than any other amino acid. Astrocytes, which are in close approximation to brain capillaries, probably are the initial site of metabolism of leucine. A mitochondrial branched-chain aminotransferase is very active in these cells. Indeed, from 30 to 50% of all alpha-amino groups of brain glutamate and glutamine are derived from leucine alone. Astrocytes release the cognate ketoacid [alpha-ketoisocaproate (KIC)] to neurons, which have a cytosolic branched-chain aminotransferase that reaminates the KIC to leucine, in the process consuming glutamate and providing a mechanism for the "buffering" of glutamate if concentrations become excessive. In maple syrup urine disease, or a congenital deficiency of branched-chain ketoacid dehydrogenase, the brain concentration of KIC and other branched-chain ketoacids can increase 10- to 20-fold. This leads to a depletion of glutamate and a consequent reduction in the concentration of brain glutamine, aspartate, alanine, and other amino acids. The result is a compromise of energy metabolism because of a failure of the malate-aspartate shuttle and a diminished rate of protein synthesis. PMID:15930465

Yudkoff, Marc; Daikhin, Yevgeny; Nissim, Ilana; Horyn, Oksana; Luhovyy, Bohdan; Luhovyy, Bogdan; Lazarow, Adam; Nissim, Itzhak

2005-06-01

327

Modulation of the pharmacokinetic properties of PNA: preparation of galactosyl, mannosyl, fucosyl, N-acetylgalactosaminyl, and N-acetylglucosaminyl derivatives of aminoethylglycine peptide nucleic acid monomers and their incorporation into PNA oligomers.  

PubMed

A series of N-(2-aminoethyl)-alpha-amino acid thymine peptide nucleic acid (PNA) monomers bearing glycosylated side chains in the alpha-amino acid position have been synthesized. These include PNA monomers where glycine has been replaced by serine and threonine (O-glycosylated), derivatives of lysine and nor-alanine (C-glycosylated), and amide derivatives of aspartic acid (N-glycosylated). The Boc and Fmoc derivatives of these monomers were used for incorporation in PNA oligomers. Twelve PNA decamers containing the glycosylated units in one, two, or three positions were prepared, and the thermal stability (T(m)) of their complexes with a complementary RNA was determined. Incorporation of the glycosyl monomers reduced the duplex stability by 0-6 degrees C per substitution. A cysteine was attached to the amino terminus of eight of the PNA decamers (Cys-CTCATACTCT-NH(2)) for easy conjugation to a [(18)F]radiolabeled N-(4-fluorobenzyl)-2-bromoacetamide. The in vivo biodistribution of these PNA oligomers was determined in rat 2 h after intravenous administration. Most of the radioactivity was recovered in the kidneys and in the urine. However, N-acetylgalactosamine (and to a lesser extent galactose and mannose)-modified PNAs were effectively targeting the liver (40-fold over unmodified PNA). Thus, the pharmacodistribution in rats of PNA oligomers can be profoundly changed by glycosylation. These results could be of great significance for PNA drug development, as they should allow modulation and fine-tuning of the pharmacokinetic profile of a drug lead. PMID:13129397

Hamzavi, Ramin; Dolle, Frédéric; Tavitian, Bertrand; Dahl, Otto; Nielsen, Peter E

328

Topoisomerase V relaxes supercoiled DNA by a constrained swiveling mechanism  

PubMed Central

Topoisomerase V is a type I topoisomerase without structural or sequence similarities to other topoisomerases. Although it belongs to the type I subfamily of topoisomerases, it is unrelated to either type IA or IB enzymes. We used real-time single-molecule micromechanical experiments to show that topoisomerase V relaxes DNA via events that release multiple DNA turns, employing a constrained swiveling mechanism similar to that for type IB enzymes. Relaxation is powered by the torque in the supercoiled DNA and is constrained by friction between the protein and the DNA. Although all type IB enzymes share a common structure and mechanism and type IA and type II enzymes show marked structural and functional similarities, topoisomerase V represents a different type of topoisomerase that relaxes DNA in a similar overall manner as type IB molecules but by using a completely different structural and mechanistic framework.

Taneja, Bhupesh; Schnurr, Bernhard; Slesarev, Alexei; Marko, John F.; Mondragon, Alfonso

2007-01-01

329

Mutualism meltdown in insects: Bacteria constrain thermal adaptation  

PubMed Central

Predicting whether and how organisms will successfully cope with climate change presents critical questions for biologists and environmental scientists. Models require knowing how organisms interact with their abiotic environment, as well understanding biotic interactions that include a network of symbioses in which all species are embedded. Bacterial symbionts of insects offer valuable models to examine how microbes can facilitate and constrain adaptation to a changing environment. While some symbionts confer plasticity that accelerates adaptation, long-term bacterial mutualists of insects are characterized by tight lifestyle constraints, genome deterioration, and vulnerability to thermal stress. These essential bacterial partners are eliminated at high temperatures, analogous to the loss of zooanthellae during coral bleaching. Recent field-based studies suggest that thermal sensitivity of bacterial mutualists constrains insect responses. In this sense, highly dependent mutualisms may be the Achilles’ heel of thermal responses in insects.

Wernegreen, Jennifer J.

2013-01-01

330

Toward a theory for design of kinematically constrained mechanical assemblies  

SciTech Connect

This paper summarizes a theory to support the design of assemblies. It describes a top-down process for designing kinematically constrained assemblies that deliver geometric key characteristics (KCs) that achieve top-level customer requirements. The theory applies to assemblies that take the form of mechanisms (e.g., engines) or structures (e.g., aircraft fuselages). The process begins by creating a kinematic constraint structure and a systematic scheme by which parts are located in space relative to each other, followed by declaration of assembly features that join parts in such a way as to create the desired constraint relationships. This process creates a connective data model containing information to support relevant analyses such as variation buildup, constraint analysis, and establishment of constraining-consistent assembly sequences. Adjustable assemblies, assemblies built using fixtures, and selective assemblies can also be described by this theory.

Whitney, D.E.; Mantripragada, R.; Adams, J.D.; Rhee, S.J.

1999-12-01

331

Constrained Next-to-Minimal Supersymmetric Standard Model  

SciTech Connect

We consider the fully constrained version of the next-to-minimal supersymmetric extension of the standard model (cNMSSM) in which a singlet Higgs superfield is added to the two doublets that are present in the minimal extension (MSSM). Assuming universal boundary conditions at a high scale for the soft supersymmetry-breaking mass parameters as well as for the trilinear interactions, we find that the model is more constrained than the celebrated minimal supergravity model. The phenomenologically viable region in the parameter space of the cNMSSM corresponds to a small value for the universal scalar mass m{sub 0}: in this case, one single input parameter is sufficient to describe the model's phenomenology once constraints from collider data and cosmology are imposed.

Djouadi, A.; Ellwanger, U.; Teixeira, A. M. [Laboratoire de Physique Theorique, Universite Paris-Sud and CNRS, F-91405 Orsay (France)

2008-09-05

332

Constraint-Based Local Search for Constrained Optimum Paths Problems  

NASA Astrophysics Data System (ADS)

Constrained Optimum Path (COP) problems arise in many real-life applications and are ubiquitous in communication networks. They have been traditionally approached by dedicated algorithms, which are often hard to extend with side constraints and to apply widely. This paper proposes a constraint-based local search (CBLS) framework for COP applications, bringing the compositionality, reuse, and extensibility at the core of CBLS and CP systems. The modeling contribution is the ability to express compositional models for various COP applications at a high level of abstraction, while cleanly separating the model and the search procedure. The main technical contribution is a connected neighborhood based on rooted spanning trees to find high-quality solutions to COP problems. The framework, implemented in COMET, is applied to Resource Constrained Shortest Path (RCSP) problems (with and without side constraints) and to the edge-disjoint paths problem (EDP). Computational results show the potential significance of the approach.

Pham, Quang Dung; Deville, Yves; van Hentenryck, Pascal

333

Constrained next-to-minimal supersymmetric standard model.  

PubMed

We consider the fully constrained version of the next-to-minimal supersymmetric extension of the standard model (cNMSSM) in which a singlet Higgs superfield is added to the two doublets that are present in the minimal extension (MSSM). Assuming universal boundary conditions at a high scale for the soft supersymmetry-breaking mass parameters as well as for the trilinear interactions, we find that the model is more constrained than the celebrated minimal supergravity model. The phenomenologically viable region in the parameter space of the cNMSSM corresponds to a small value for the universal scalar mass m_{0}: in this case, one single input parameter is sufficient to describe the model's phenomenology once constraints from collider data and cosmology are imposed. PMID:18851204

Djouadi, A; Ellwanger, U; Teixeira, A M

2008-09-02

334

Wavelet-constrained stereo matching under photometric variations  

NASA Astrophysics Data System (ADS)

We propose a new method to address the problem of stereo matching under varying illumination conditions. First, a spatially varying multiplicative model is developed to account for photometric changes induced between both images in the stereo pair. The stereo matching problem based on this model is then formulated as a constrained optimization problem in which an appropriate convex objective function is minimized under convex constraints. These constraints arise from prior knowledge and rely on various properties of both disparity and illumination fields. In order to obtain a smooth disparity field while preserving discontinuities around object edges, we consider an appropriate wavelet-based regularization constraint. The resulting multi-constrained optimization problem is solved via an efficient block iterative algorithm which offers great flexibility in the incorporation of several constraints. Experimental results demonstrate the efficiency of the proposed method to recover illumination changes and disparity map simultaneously, making stereo matching very robust w.r.t. such changes.

Miled, Wided; Pesquet, Jean-Christophe; Parent, Michel

2008-05-01

335

Causes of illness-constraining and facilitating beliefs.  

PubMed

The aim of this study was to enhance knowledge about patients' beliefs related to different kinds of illnesses and to describe and understand their beliefs as they relate to their outlook on their illnesses. Fifty-two patients with various illness symptoms receiving integrative anthroposophic care answered an item in a questionnaire about their own thinking of the causes of their illness. The method used for analysis was qualitative content analysis. The result showed that from a patient's perspective a complex combination of causes led to illness. The most prominent causes were psychosocial factors, but personal attitudes, biological factors and chance were also mentioned. Beliefs act as either facilitating or constraining. The informants displayed more constraining than facilitating beliefs, which might prevent them from improving their health. Furthermore, the informants might improve their ability to deal with their illness by identifying their own personal internal resources. PMID:21781216

Järemo, Pirjo; Arman, Maria

2011-08-01

336

Constraining the noncommutative spectral action via astrophysical observations.  

PubMed

The noncommutative spectral action extends our familiar notion of commutative spaces, using the data encoded in a spectral triple on an almost commutative space. Varying a rather simple action, one can derive all of the standard model of particle physics in this setting, in addition to a modified version of Einstein-Hilbert gravity. In this Letter we use observations of pulsar timings, assuming that no deviation from general relativity has been observed, to constrain the gravitational sector of this theory. While the bounds on the coupling constants remain rather weak, they are comparable to existing bounds on deviations from general relativity in other settings and are likely to be further constrained by future observations. PMID:20867510

Nelson, William; Ochoa, Joseph; Sakellariadou, Mairi

2010-09-02

337

Constraining the Noncommutative Spectral Action via Astrophysical Observations  

SciTech Connect

The noncommutative spectral action extends our familiar notion of commutative spaces, using the data encoded in a spectral triple on an almost commutative space. Varying a rather simple action, one can derive all of the standard model of particle physics in this setting, in addition to a modified version of Einstein-Hilbert gravity. In this Letter we use observations of pulsar timings, assuming that no deviation from general relativity has been observed, to constrain the gravitational sector of this theory. While the bounds on the coupling constants remain rather weak, they are comparable to existing bounds on deviations from general relativity in other settings and are likely to be further constrained by future observations.

Nelson, William; Ochoa, Joseph; Sakellariadou, Mairi [Institute of Gravitation and the Cosmos, Penn State University, State College, Pennsylvania 16801 (United States); Department of Physics, King's College, University of London, Strand WC2R 2LS, London (United Kingdom)

2010-09-03

338

T Cell Determinants Incorporating [beta]-Amino Acid Residues Are Protease Resistant and Remain Immunogenic In Vivo  

SciTech Connect

A major hurdle in designing successful epitope-based vaccines resides in the delivery, stability, and immunogenicity of the peptide immunogen. The short-lived nature of unmodified peptide-based vaccines in vivo limits their therapeutic application in the immunotherapy of cancers and chronic viral infections as well as their use in generating prophylactic immunity. The incorporation of {beta}-amino acids into peptides decreases proteolysis, yet its potential application in the rational design of T cell mimotopes is poorly understood. To address this, we have replaced each residue of the SIINFEKL epitope individually with the corresponding {beta}-amino acid and examined the resultant efficacy of these mimotopes. Some analogs displayed similar MHC binding and superior protease stability compared with the native epitope. Importantly, these analogs were able to generate cross-reactive CTLs in vivo that were capable of lysing tumor cells that expressed the unmodified epitope as a surrogate tumor Ag. Structural analysis of peptides in which anchor residues were substituted with {beta}-amino acids revealed the basis for enhanced MHC binding and retention of immunogenicity observed for these analogs and paves the way for future vaccine design using {beta}-amino acids. We conclude that the rational incorporation of {beta}-amino acids into T cell determinants is a powerful alternative to the traditional homologous substitution of randomly chosen naturally occurring {alpha}-amino acids, and these mimotopes may prove particularly useful for inclusion in epitope-based vaccines.

Webb, Andrew I.; Dunstone, Michelle A.; Williamson, Nicholas A.; Price, Jason D.; Kauwe, Andreade; Chen, Weisan; Oakley, Aaron; Perlmutter, Patrick; McCluskey, James; Aguilar, Marie-Isabel; Rossjohn, Jamie; Purcell, Anthony W. (Monash); (Melbourne); (ANU)

2010-07-20

339

Steroselective synthesis and application of L-( sup 15 N) amino acids  

SciTech Connect

We have developed two general approaches to the stereoselective synthesis of {sup 15}N- and {sup 13}C-labeled amino acids. First, labeled serine, biosynthesized using the methylotrophic bacterium M. extorquens AM1, serves as a chiral precursor for the synthesis of other amino acids. For example, pyridoxal phosphate enzymes can be used for the conversion of L-({alpha}-{sup 15}N)serine to L-({alpha}-{sup 15}N)tyrosine, L-({alpha}-{sup 15}N)tryptophan, and L-({alpha}-{sup 15}N)cysteine. In the second approach, developed by Oppolzer and Tamura, an electrophilic amination'' reagent, 1-chloro-1-nitrosocyclohexane, was used to convert chiral enolates into L-{alpha}-amino acids. We prepared 1-chloro-1-({sup 15}N) nitrosocyclohexane and used it to aminate chiral enolates to produce L-({alpha}-{sup 15}N)amino acids. The stereoselectivity of this scheme using the Oppolzer sultam chiral auxiliary is remarkable, producing enantiomer ratios of 200 to 1. 22 refs., 4 figs.

Unkefer, C.J. (Los Alamos National Lab., NM (United States)); Lodwig, S.N. (Centralia Coll., WA (United States). Div. of Science)

1991-01-01

340

Molecular basis for amino acid sensing by family C G-protein-coupled receptors.  

PubMed

Family C of human G-protein-coupled receptors (GPCRs) is constituted by eight metabotropic glutamate receptors, two gamma-aminobutyric acid type B (GABA(B1-2)) subunits forming the heterodimeric GABA(B) receptor, the calcium-sensing receptor, three taste1 receptors (T1R1-3), a promiscuous L-alpha;-amino acid receptor G-protein-coupled receptor family C, group 6, subtype A (GPRC6A) and seven orphan receptors. Aside from the orphan receptors, the family C GPCRs are dimeric receptors characterized by a large extracellular Venus flytrap domain which bind the endogenous agonists. Except from the GABA(B1-2) and T1R2-3 receptor, all receptors are either activated or positively modulated by amino acids. In this review, we outline mutational, biophysical and structural studies which have elucidated the interaction of the amino acids with the Venus flytrap domains, molecular mechanisms of receptor selectivity and the initial steps in receptor activation. PMID:19298394

Wellendorph, P; Bräuner-Osborne, H

2009-03-01

341

Anti-B-B Mixing Constrains Topcolor-Assisted Technicolor  

SciTech Connect

We argue that extended technicolor augmented with topcolor requires that all mixing between the third and the first two quark generations resides in the mixing matrix of left-handed down quarks. Then, the anti-B_d--B_d mixing that occurs in topcolor models constrains the coloron and Z' boson masses to be greater than about 5 TeV. This implies fine tuning of the topcolor couplings to better than 1percent.

Burdman, Gustavo; Lane, Kenneth; Rador, Tonguc

2000-12-06

342

Ultraconservation identifies a small subset of extremely constrained developmental enhancers  

PubMed Central

Extended perfect human-rodent sequence identity of at least 200 base pairs (ultraconservation) is potentially indicative of evolutionary or functional uniqueness. We used a transgenic mouse assay to compare the embryonic enhancer activity of 231 noncoding ultraconserved human genome regions with that of 206 extremely conserved regions lacking ultraconservation. Developmental enhancers were equally prevalent in both populations, suggesting instead that ultraconservation identifies a small, functionally indistinct subset of similarly constrained cis-regulatory elements.

Visel, Axel; Prabhakar, Shyam; Akiyama, Jennifer A; Shoukry, Malak; Lewis, Keith D; Holt, Amy; Plajzer-Frick, Ingrid; Afzal, Veena; Rubin, Edward M; Pennacchio, Len A

2009-01-01

343

Constrained Non-Monotone Submodular Maximization: Offline and Secretary Algorithms  

Microsoft Academic Search

Constrained submodular maximization problems have long been studied, with\\u000anear-optimal results known under a variety of constraints when the submodular\\u000afunction is monotone. The case of non-monotone submodular maximization is less\\u000aunderstood: the first approximation algorithms even for the unconstrainted\\u000asetting were given by Feige et al. (FOCS '07). More recently, Lee et al. (STOC\\u000a'09, APPROX '09) show how

Anupam Gupta; Aaron Roth; Grant Schoenebeck; Kunal Talwar

2010-01-01

344

Constraining Models of Postglacial Rebound Using Space Geodesy  

NASA Astrophysics Data System (ADS)

We are using observations from five space techniques (VLBI, SLR, GPS, DORIS, and GRACE) to (1) determine the character of Earth's viscous response to unloading of the ice sheets 5 to 20 thousand years ago, and (2) constrain models of postglacial rebound determined primarily from Holocene estimates of relative sea level and geophysical observations of Earth's spin and shape. The horizontal estimates of site velocity are constraining the postglacial rebound model. Places along the margins of the former Laurentide and Fennoscandia ice sheets are moving horizontally away from the centers at about 1 millimeter per year, at the speed predicted by the model of Peltier [1994], but significantly slower than the speeds predicted by the models of Peltier [1996] and Peltier [2004]. The parts of Antarctic, Eurasian, and North American plate interiors neither beneath nor along the margins of the former ice sheets are hardly deforming at all, allowing the angular velocity of the plates to be estimated meaningfully. The vertical estimates of site velocity are also constraining the postglacial rebound model. Algonquin Park (Ontario) is rising at 2.5 millimeters per year and Yellowknife (Northwest Territories) at 6 millimeters per year, constraining the thickness of the Laurentia ice sheet 20 thousand years ago. The eastern and central United States is subsiding at 1 to 2 millimeter per year, at about the speeds predicted by the models of Peltier [1994], Peltier [1996], and Peltier [2004]. We are attempting to modify the ice sheet thickness, mantle viscosity, and elastic lithospheric thickness in the model to fit all geodetic and geologic observations. We are furthermore quantifying the uncertainty in estimates of vertical velocity due to uncertainty in the velocity of Earth's center.

Argus, D. F.; Peltier, W.

2008-12-01

345

Compression of raw SAR data using entropy-constrained quantization  

Microsoft Academic Search

For the compression of raw SAR (synthetic aperture radar) data on-board spacecraft, the block adaptive quantization (BAQ) algorithm is often used due to its effectiveness and low implementation complexity. However, the entropy-constrained block adaptive quantization (ECBAQ) algorithm outperforms BAQ with respect to signal-to-quantization-noise-ratio and equals the performance of more complicated methods such as vector quantization and trellis coding variants. ECBAQ

T. Algra

2000-01-01

346

Constraining dark energy from the abundance of weak gravitational lenses  

Microsoft Academic Search

We examine the prospect of using the observed abundance of weak gravitational lenses to constrain the equation-of-state parameter w=p\\/rho of dark energy. Dark energy modifies the distance-redshift relation, the amplitude of the matter power spectrum, and the rate of structure growth. As a result, it affects the efficiency with which dark-matter concentrations produce detectable weak-lensing signals. Here we solve the

Nevin N. Weinberg; Marc Kamionkowski

2002-01-01

347

An Upwind-Biased Constrained Transport Scheme for Magnetohydrodynamics  

NASA Astrophysics Data System (ADS)

We introduce a new constrained transport (CT) scheme that advects magnetic field in a stable manner using proper upwind information in taking averages of electric fields. Alternatively, the conventional CT approaches that are based on 1D Riemann solvers would easily show instabilities in the problems we present in this paper. The proposed method is available in the USM-MHD solver (Lee & Deane 2009; Lee 2012) in the FLASH code of the University of Chicago.

Lee, D.

2013-04-01

348

From Eager to Lazy Constrained Data Acquisition: A General Framework  

Microsoft Academic Search

*1 Constraint Satisfaction Problems (CSPs)17) are an effective framework for modeling a variety of real life applications and many techniques have been proposed for solving\\u000a them efficiently. CSPs are based on the assumption that all constrained data (values in variable domains) are available at\\u000a the beginning of the computation. However, many non-toy problems derive their parameters from an external environment.

Paola Mello; Michela Milano; Marco Gavanelli; Evelina Lamma; Massimo Piccardi; Rita Cucchiara

2001-01-01

349

Evolutionary Constrained Design of Seismically Excited Buildings: Sensor Placement  

Microsoft Academic Search

\\u000a Appropriate sensor placement can strongly influence the control performance of structures. However, there is not yet a systematic\\u000a method for sensor placement. In this paper, a general method based on a proposed constrained GA is suggested to optimally\\u000a place sensors in structures. The optimal placement scheme is general for passive, active and semi-active controls and it does\\u000a not depend on

Alireza Rowhanimanesh; Abbas Khajekaramodin

350

Digital filter bank design quadratic-constrained formulation  

Microsoft Academic Search

Formulate the filter bank design problem as an quadratic-constrained least-squares minimization problem. The solution of the minimization problem converges very quickly since the cost function as well as the constraints are quadratic functions with respect to the unknown parameters. The formulations of the perfect-reconstruction cosine-modulated filter bank, of the near-perfect-reconstruction pseudo-QMF bank, and of the two-channel biorthogonal linear-phase filter bank

Truong Q. Nguyen

1995-01-01

351

Constraining heavy colored resonances from top-antitop quark events  

SciTech Connect

Recent measurements of the top quark charge asymmetry at Tevatron disfavor the existence of flavor universal axigluons and colorons at 2{sigma}. In this letter, we explore the possibility of reconciling the data with these models and use the charge asymmetry and the invariant mass distribution of top-antitop quark pair events to constrain the mass and couplings of massive color-octet gauge bosons decaying to top quarks.

Ferrario, Paola; Rodrigo, German [Instituto de Fisica Corpuscular, Consejo Superior de Investigaciones Cientificas - UVEG, Apartado de Correos 22085, E-46071 Valencia (Spain)

2009-09-01

352

A note on optimal care by wealth-constrained injurers  

Microsoft Academic Search

This paper clarifies the relationship between an injurer’s wealth level and his care choice by highlighting the distinction between monetary and non-monetary care. When care is non-monetary, wealth-constrained injurers generally take less than optimal care, and care is increasing in their wealth level under both strict liability and negligence. In contrast, when care is monetary, injurers may take too much

Thomas J. Miceli; Kathleen Segerson

2003-01-01

353

Some preliminary thoughts on the invention of constrained Hamiltonian dynamics  

NASA Astrophysics Data System (ADS)

I will present some tentative remarks on the origins of constrained Hamiltonian dynamics, based in part on interviews recently conducted by myself and Dean Rickles with several key contributers. These interviews with James Anderson, Stanley Deser, Charles Misner, and Josh Goldberg were partially supported by the Center for the History of Physics of the American Institute of Physics, and will eventually be made available on the Center web page.

Salisbury, Donald

2011-10-01

354

Strategic bidding in network constrained electricity markets using FAPSO  

Microsoft Academic Search

Purpose – The purpose of this paper is to develop an optimal bidding strategy for a generation company (GenCo) in the network constrained electricity markets and to analyze the impact of network constraints and opponents bidding behavior on it. Design\\/methodology\\/approach – A bi-level programming (BLP) technique is formulated in which upper level problem represents an individual GenCo payoff maximization and

Prabodh Bajpai; Sri Niwas Singh

2008-01-01

355

Nitrogen limitation constrains sustainability of ecosystem response to CO2  

Microsoft Academic Search

Enhanced plant biomass accumulation in response to elevated atmospheric CO2 concentration could dampen the future rate of increase in CO2 levels and associated climate warming. However, it is unknown whether CO2-induced stimulation of plant growth and biomass accumulation will be sustained or whether limited nitrogen (N) availability constrains greater plant growth in a CO2-enriched world. Here we show, after a

Peter B. Reich; Sarah E. Hobbie; Tali Lee; David S. Ellsworth; Jason B. West; David Tilman; Johannes M. H. Knops; Shahid Naeem; Jared Trost

2006-01-01

356

Gauge transformations of constrained KP flows: New integrable hierarchies  

Microsoft Academic Search

Integrable systems in 1+1 dimensions arise from the KP hierarchy as symmetryreductions involving square eigenfunctions. Exploiting the residual gauge freedom inthese constraints new integrable systems are derived. They include generalizationsof the hierarchy of the Kundu-Eckhaus equation and higher order extensions of theYajima-Oikawa and Melnikov hierarchies. Constrained modified KP flows yield furtherintegrable equations such as the hierarchies of the derivative NLS

Anjan Kundu; Walter Strampp; Walter Oevel

1995-01-01

357

Binary constrained flows and separation of variables for soliton equations  

Microsoft Academic Search

In contrast to mono-constrained flows with N degrees of freedom, binary\\u000aconstrained flows of soliton equations, admitting 2x2 Lax matrices, have 2N\\u000adegrees of freedom. By means of the existing method, Lax matrices only yield\\u000athe first N pairs of canonical separated variables. An approach for\\u000aconstructing the second N pairs of canonical separated variables with\\u000aadditional N separated equations

Wen-Xiu Ma; Yunbo Zeng

2002-01-01

358

Approximate Subgradient Methods for Nonlinearly Constrained Network Flow Problems  

Microsoft Academic Search

The minimization of nonlinearly constrained network flow problems can be performed by using approximate subgradient methods.\\u000a The idea is to solve this kind of problem by means of primal-dual methods, given that the minimization of nonlinear network\\u000a flow problems can be done efficiently exploiting the network structure. In this work, it is proposed to solve the dual problem\\u000a by using

E. Mijangos

2006-01-01

359

Stability of computational methods for constrained dynamics systems  

Microsoft Academic Search

Many methods have been proposed for numerically integrating the differential-algebraic systems arising from the Euler-Lagrange equations for constrained motion. These are based on various problem formulations and discretizations. The authors offer a critical evaluation of these methods from the standpoint of stability. Considering a linear model, the authors first give conditions under which the differential-algebraic problem is well conditioned. This

Uri M. Ascher; Linda R. Petzold

1993-01-01

360

Constrained Least-Squares Optimization in Conformal Array Antenna Synthesis  

Microsoft Academic Search

The least mean square error of the constrained least-squares optimization method is studied. The phases of non-zero goal values and the phases of non-zero constraint values can be selected by a fast iteration for optimum fit to the goal function amplitude. This kind of modified least-squares optimization method opens up a fast and robust synthesis method for large conformal antenna

Leo I. Vaskelainen

2007-01-01

361

Constrained molecular dynamics simulations of atomic ground states  

SciTech Connect

The constrained molecular dynamics model, previously introduced for nuclear dynamics, has been extended to the atomic structure and collision calculations. Quantum effects, corresponding to the Pauli and Heisenberg principles, are enforced by constraints, following the idea of the Lagrange multiplier method. Our calculations for a small atomic system, H, He, Li, Be, and F reproduce the ground-state binding energies reasonably, compared with the experimental data. We discuss also the shell splitting due to e-e correlation.

Kimura, Sachie; Bonasera, Aldo [Laboratorio Nazionale del Sud, INFN, via Santa Sofia, 62, 95123 Catania (Italy)

2005-07-15

362

21 CFR 888.3480 - Knee joint femorotibial metallic constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Knee joint femorotibial metallic constrained...DEVICES Prosthetic Devices § 888.3480 Knee joint femorotibial metallic constrained...prosthesis. (a) Identification. A knee joint femorotibial metallic...

2010-04-01

363

21 CFR 888.3490 - Knee joint femorotibial metal/composite non-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...Knee joint femorotibial metal/composite non-constrained cemented prosthesis...knee joint femorotibial metal/composite non-constrained cemented...molecular weight polyethylene with carbon fibers composite and are intended for use...

2009-04-01

364

21 CFR 888.3100 - Ankle joint metal/composite semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...3100 Ankle joint metal/composite semi-constrained cemented...Identification. An ankle joint metal/composite semi-constrained cemented...molecular weight polyethylene with carbon fibers composite, and is limited to those...

2009-04-01

365

21 CFR 888.3490 - Knee joint femorotibial metal/composite non-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...Knee joint femorotibial metal/composite non-constrained cemented prosthesis...knee joint femorotibial metal/composite non-constrained cemented...molecular weight polyethylene with carbon fibers composite and are intended for use...

2010-04-01

366

21 CFR 888.3100 - Ankle joint metal/composite semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...3100 Ankle joint metal/composite semi-constrained cemented...Identification. An ankle joint metal/composite semi-constrained cemented...molecular weight polyethylene with carbon fibers composite, and is limited to those...

2010-04-01

367

21 CFR 888.3500 - Knee joint femorotibial metal/composite semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...Knee joint femorotibial metal/composite semi-constrained cemented...knee joint femorotibial metal/composite semi-constrained cemented...molecular weight polyethylene with carbon-fibers composite and is limited to those...

2010-04-01

368

21 CFR 888.3500 - Knee joint femorotibial metal/composite semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...Knee joint femorotibial metal/composite semi-constrained cemented...knee joint femorotibial metal/composite semi-constrained cemented...molecular weight polyethylene with carbon-fibers composite and is limited to those...

2009-04-01

369

21 CFR 888.3340 - Hip joint metal/composite semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...888.3340 Hip joint metal/composite semi-constrained cemented...Identification. A hip joint metal/composite semi-constrained cemented...molecular weight polyethylene with carbon fibers composite. Both components are...

2009-04-01

370

21 CFR 888.3340 - Hip joint metal/composite semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...888.3340 Hip joint metal/composite semi-constrained cemented...Identification. A hip joint metal/composite semi-constrained cemented...molecular weight polyethylene with carbon fibers composite. Both components are...

2010-04-01

371

Constrained-Clustering Approach to the Analysis of Remote Sensing Data.  

National Technical Information Service (NTIS)

One old and two new clustering methods were applied to the constrained-clustering problem of separating different agricultural fields based on multispectral remote sensing satellite data. (Constrained-clustering involves double clustering in multispectral...

C. J. Ryan

1983-01-01

372

LETTER TO THE EDITOR: Deriving N-soliton solutions via constrained flows  

Microsoft Academic Search

The soliton equations can be factorized by two commuting x - and t -constrained flows. We propose a method to derive N -soliton solutions of soliton equations directly from the x - and t -constrained flows.

Yunbo Zeng

2000-01-01

373

Constraining ecosystem processes from tower fluxes and atmospheric profiles.  

PubMed

The planetary boundary layer (PBL) provides an important link between the scales and processes resolved by global atmospheric sampling/modeling and site-based flux measurements. The PBL is in direct contact with the land surface, both driving and responding to ecosystem processes. Measurements within the PBL (e.g., by radiosondes, aircraft profiles, and flask measurements) have a footprint, and thus an integrating scale, on the order of 1-100 km. We use the coupled atmosphere-biosphere model (CAB) and a Bayesian data assimilation framework to investigate the amount of biosphere process information that can be inferred from PBL measurements. We investigate the information content of PBL measurements in a two-stage study. First, we demonstrate consistency between the coupled model (CAB) and measurements, by comparing the model to eddy covariance flux tower measurements (i.e., water and carbon fluxes) and also PBL scalar profile measurements (i.e., water, carbon dioxide, and temperature) from Canadian boreal forest. Second, we use the CAB model in a set of Bayesian inversions experiments using synthetic data for a single day. In the synthetic experiment, leaf area and respiration were relatively well constrained, whereas surface albedo and plant hydraulic conductance were only moderately constrained. Finally, the abilities of the PBL profiles and the eddy covariance data to constrain the parameters were largely similar and only slightly lower than the combination of both observations. PMID:21830696

Hill, T C; Williams, M; Woodward, F I; Moncrieff, J B

2011-07-01

374

CONSTRAINING INTRACLUSTER GAS MODELS WITH AMiBA13  

SciTech Connect

Clusters of galaxies have been extensively used to determine cosmological parameters. A major difficulty in making the best use of Sunyaev-Zel'dovich (SZ) and X-ray observations of clusters for cosmology is that using X-ray observations it is difficult to measure the temperature distribution and therefore determine the density distribution in individual clusters of galaxies out to the virial radius. Observations with the new generation of SZ instruments are a promising alternative approach. We use clusters of galaxies drawn from high-resolution adaptive mesh refinement cosmological simulations to study how well we should be able to constrain the large-scale distribution of the intracluster gas (ICG) in individual massive relaxed clusters using AMiBA in its configuration with 13 1.2 m diameter dishes (AMiBA13) along with X-ray observations. We show that non-isothermal {beta} models provide a good description of the ICG in our simulated relaxed clusters. We use simulated X-ray observations to estimate the quality of constraints on the distribution of gas density, and simulated SZ visibilities (AMiBA13 observations) for constraints on the large-scale temperature distribution of the ICG. We find that AMiBA13 visibilities should constrain the scale radius of the temperature distribution to about 50% accuracy. We conclude that the upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the large-scale distribution of the ICG.

Molnar, Sandor M.; Umetsu, Keiichi; Ho, Paul T. P.; Koch, Patrick M.; Victor Liao, Yu-Wei; Lin, Kai-Yang; Liu, Guo-Chin; Nishioka, Hiroaki [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China); Birkinshaw, Mark [H. H. Wills Physics Laboratory, University of Bristol, Tyndall Ave, Bristol BS8 1TL (United Kingdom); Bryan, Greg; Haiman, Zoltan; Shang, Cien [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Hearn, Nathan [ASC/Alliances Center for Astrophysical Thermonuclear Flashes, University of Chicago, Chicago, IL 60637 (United States); Huang, Chih-Wei Locutus; Wang, Fu-Cheng; Wu, Jiun-Huei Proty, E-mail: sandor@asiaa.sinica.edu.t [Department of Physics, Institute of Astrophysics, and Center for Theoretical Sciences, National Taiwan University, Taipei 10617, Taiwan (China)

2010-11-10

375

Road-constrained target tracking and identification a particle filter  

NASA Astrophysics Data System (ADS)

Sequential Monte Carlo methods have attracted the attention of the tracking community as a solution to Bayesian estimation particularly for nonlinear problems. Several attributes of particle filters support their use in jointly tracking and identifying ground targets in a road-constrained network. First, since the target dynamics are simulated, propagating a target within a constrained state space is handled quite naturally since the particle filter is not restricted to propagating Gaussian PDFs. Furthermore, a particle filter can approximate a PDF which is a mixture of continuous random variables (the target kinematic state) and discrete random variables (the target ID) which is necessary for the joint tracking and identification problem. Given HRRGMTI measurements of a target, we propose to jointly estimate a target's kinematic state and identification by propagating the joint PDF of the target kinematic state (position and velocity) and target ID. In this way, we capitalize on the inherent coupling between the target's feature measurement (the HRR profile) and the target's kinematic state. In addition to the coupling between a target's feature measurement and the target's kinematic state, there exists a coupling between a target's dynamics and the target's ID which can also be exploited through particle filtering methods. We develop the particle filtering algorithm for tracking and identifying ground targets in a road-constrained environment and present simulation results for a two-class problem.

Agate, Craig S.; Sullivan, Kevin J.

2003-12-01

376

Road-constrained target tracking and identification a particle filter  

NASA Astrophysics Data System (ADS)

Sequential Monte Carlo methods have attracted the attention of the tracking community as a solution to Bayesian estimation particularly for nonlinear problems. Several attributes of particle filters support their use in jointly tracking and identifying ground targets in a road-constrained network. First, since the target dynamics are simulated, propagating a target within a constrained state space is handled quite naturally since the particle filter is not restricted to propagating Gaussian PDFs. Furthermore, a particle filter can approximate a PDF which is a mixture of continuous random variables (the target kinematic state) and discrete random variables (the target ID) which is necessary for the joint tracking and identification problem. Given HRRGMTI measurements of a target, we propose to jointly estimate a target's kinematic state and identification by propagating the joint PDF of the target kinematic state (position and velocity) and target ID. In this way, we capitalize on the inherent coupling between the target's feature measurement (the HRR profile) and the target's kinematic state. In addition to the coupling between a target's feature measurement and the target's kinematic state, there exists a coupling between a target's dynamics and the target's ID which can also be exploited through particle filtering methods. We develop the particle filtering algorithm for tracking and identifying ground targets in a road-constrained environment and present simulation results for a two-class problem.

Agate, Craig S.; Sullivan, Kevin J.

2004-01-01

377

Physics constrained nonlinear regression models for time series  

NASA Astrophysics Data System (ADS)

A central issue in contemporary science is the development of data driven statistical nonlinear dynamical models for time series of partial observations of nature or a complex physical model. It has been established recently that ad hoc quadratic multi-level regression (MLR) models can have finite-time blow up of statistical solutions and/or pathological behaviour of their invariant measure. Here a new class of physics constrained multi-level quadratic regression models are introduced, analysed and applied to build reduced stochastic models from data of nonlinear systems. These models have the advantages of incorporating memory effects in time as well as the nonlinear noise from energy conserving nonlinear interactions. The mathematical guidelines for the performance and behaviour of these physics constrained MLR models as well as filtering algorithms for their implementation are developed here. Data driven applications of these new multi-level nonlinear regression models are developed for test models involving a nonlinear oscillator with memory effects and the difficult test case of the truncated Burgers-Hopf model. These new physics constrained quadratic MLR models are proposed here as process models for Bayesian estimation through Markov chain Monte Carlo algorithms of low frequency behaviour in complex physical data.

Majda, Andrew J.; Harlim, John

2013-01-01

378

Physical basis for constrained lattice density functional theory  

NASA Astrophysics Data System (ADS)

To study nucleation phenomena in an open system, a constrained lattice density functional theory (LDFT) method has been developed before to identify the unstable directions of grand potential functional and to stabilize nuclei by imposing a suitable constraint. In this work, we answer several questions about the method on a fundamental level, and give a firmer basis for the constrained LDFT method. First, we demonstrate that the nucleus structure and free energy barrier from a volume constraint method are equivalent to those from a surface constraint method. Then, we show that for the critical nucleus, the constrained LDFT method in fact produces a bias-free solution for both the nucleus structure and nucleation barrier. Finally, we give a physical interpretation of the Lagrange multiplier in the constraint method, which provides the generalized force to stabilize a nucleus in an open system. The Lagrange multiplier is found to consist of two parts: part I of the constraint produces an effective pressure, and part II imposes a constraint to counteract the supersaturation.

Men, Yumei; Zhang, Xianren

2012-03-01

379

Free vibrations of a spherical drop constrained at an azimuth  

NASA Astrophysics Data System (ADS)

Two droplets coupled through a liquid filled (a) hole in a plate or (b) tube is referred to as a double droplet system (DDS) or a capillary switch. Such capillary systems are gaining increasing attention due to their utility in applications. A particularly exciting application is one where a DDS is employed as a liquid lens, one flavor of which entails using a DDS as a variable focus lens by keeping it under sustained oscillations at its natural frequencies. The natural modes of oscillation of a DDS are determined analytically here in the limit in which the plate thickness (or tube length) is vanishingly small and when the effect of gravity is negligible compared to that of surface tension. In this limit, a DDS at rest reduces to two spherical caps that are pinned to and coupled along a common circular ring of contact of negligible thickness. Here, the caps are taken to be complementary pieces of a sphere so that the equilibrium state of the system is a sphere that is constrained by a ring of negligible thickness at an azimuthal angle with respect to the center of the sphere. Both the constrained drop and the fluid exterior to it are taken to be inviscid fluids undergoing irrotational flow. Similar to the linear oscillations of a free drop first studied by Rayleigh, the analytical formulation of the linear oscillations of the constrained drop results in a linear operator eigenvalue problem but with one additional boundary condition, i.e., that which accounts for zero shape perturbation along the circle of contact. Exploiting properties of linear operators, an implicit expression is obtained for the frequency of each mode of oscillation, a feat that appears not to have been accomplished to date in any problem involving oscillations of constrained drops. An extension of a method based on Green's functions that was developed to analyze the linear oscillations of a drop in contact with a spherical bowl [M. Strani and F. Sabetta, ``Free-vibrations of a drop in partial contact with a solid support,'' J. Fluid Mech. 141, 233-247 (1984)] is also employed to verify the aforementioned results. Results obtained from these two approaches are then compared to those reported by Bostwick and Steen [``Capillary oscillations of a constrained liquid drop,'' Phys. Fluids 21, 032108 (2009)]. Careful examination of flow fields within drops reveals that by pinning a drop, it should be possible to selectively excite just a portion of a drop's surface.

Ramalingam, Santhosh; Ramkrishna, Doraiswami; Basaran, Osman A.

2012-08-01

380

The constrained natural element method (C-NEM) for treating thermal models involving moving interfaces  

Microsoft Academic Search

In this paper, the features of the natural neighbor (Sibson) interpolant are used within the context of a constrained Voronoi diagram, dual to the constrained Delaunay triangulation, for treating moving interface (Stefan) problems. The constrained natural element method (C-NEM) uses the Voronoi cells instead of the Delaunay triangles for both interpolation and integration, and thus permits the use of very

J. Yvonnet; F. Chinesta; Ph. Lorong; D. Ryckelynck

2005-01-01

381

21 CFR 888.3300 - Hip joint metal constrained cemented or uncemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Hip joint metal constrained cemented or uncemented prosthesis...Prosthetic Devices § 888.3300 Hip joint metal constrained cemented or uncemented prosthesis. (a) Identification. A hip joint metal constrained cemented or...

2013-04-01

382

21 CFR 888.3350 - Hip joint metal/polymer semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Hip joint metal/polymer semi-constrained cemented prosthesis...Prosthetic Devices § 888.3350 Hip joint metal/polymer semi-constrained cemented prosthesis... (a) Identification. A hip joint metal/polymer semi-constrained...

2013-04-01

383

21 CFR 888.3110 - Ankle joint metal/polymer semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 false Ankle joint metal/polymer semi-constrained... § 888.3110 Ankle joint metal/polymer semi-constrained...Identification. An ankle joint metal/polymer semi-constrained...across-the-joint. This generic type of device includes...

2013-04-01

384

21 CFR 888.3640 - Shoulder joint metal/metal or metal/polymer constrained cemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...Shoulder joint metal/metal or metal/polymer constrained cemented prosthesis. 888...Shoulder joint metal/metal or metal/polymer constrained cemented prosthesis. ...shoulder joint metal/metal or metal/polymer constrained cemented...

2013-04-01

385

Neuromodulatory actions of dopamine in the neostriatum are dependent upon the excitatory amino acid receptor subtypes activated.  

PubMed Central

In the mammalian neostriatum, dopamine modulates neuronal responses mediated by activation of excitatory amino acid receptors. The direction of this modulation varies with the specific subtype of excitatory amino acid receptor activated. Responses evoked by iontophoretic application of glutamate (Glu) and the non-N-methyl-D-aspartate (NMDA) agonists quisqualate and alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid were significantly attenuated when dopamine was applied. In contrast, responses evoked by NMDA were markedly potentiated. The enhancement of NMDA-evoked excitations was mimicked by bath application of SKF 38393, a D1 receptor agonist. The D1 receptor antagonist SCH 23390 blocked the dopamine enhancement of NMDA-induced excitations. Quinpirole, a D2 receptor agonist, attenuated responses evoked by both NMDA and non-NMDA receptor agonists. These results indicate that the complex modulatory actions of dopamine in the neostriatum are a function of the excitatory amino acid receptor as well as the specific dopamine receptor subtype activated. These findings are of clinical relevance since the actions of dopamine and excitatory amino acids have been implicated in neurological and affective disorders.

Cepeda, C; Buchwald, N A; Levine, M S

1993-01-01

386

Conformationally constrained opioid ligands: The Dmt-Aba and Dmt-Aia versus Dmt-Tic scaffold  

Microsoft Academic Search

Replacement of the constrained phenylalanine analogue 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) in the opioid Dmt-Tic-Gly-NH-Bn scaffold by the 4-amino-1,2,4,5-tetrahydro-indolo[2,3-c]azepin-3-one (Aia) and 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one (Aba) scaffolds has led to the discovery of novel potent ?-selective agonists (Structures 5 and 12) as well as potent and selective ?-opioid receptor antagonists (Structures 9 and 15). Both stereochemistry and N-terminal N,N-dimethylation proved to be crucial factors for

Steven Ballet; Debby Feytens; Rien De Wachter; Magali De Vlaeminck; Ewa D. Marczak; Severo Salvadori; Chris de Graaf; Didier Rognan; Lucia Negri; Roberta Lattanzi; Lawrence H. Lazarus; Dirk Tourwé; Gianfranco Balboni

2009-01-01

387

Successful Closed Reduction of a Dislocated Constrained Total Hip Arthroplasty: A Case Report and Literature Review  

PubMed Central

Many surgeons use acetabular components with constrained polyethylene liners to improve stability after total hip arthroplasty in patients with a history of hip dislocation. Surgical treatment is generally thought to be the only available option for the dislocated constrained liner. The success rate and clinical results of closed reduction for such patients is unclear. This report presents a case of a successful closed reduction of a dislocated constrained liner. Few papers have so far addressed closed reduction of a dislocated constrained liner. Furthermore, previous studies reported a variety of components. Publication of additional successful and unsuccessful case reports is therefore needed to help establish the optimal treatment protocol for a dislocated constrained liner.

Sonohata, Motoki; Waewsawangwong, Warit; Goodman, Stuart B

2012-01-01

388

Detection and characterization of carrier-mediated cationic amino acid transport in lysosomes of normal and cystinotic human fibroblasts. Role in therapeutic cystine removal  

SciTech Connect

The discovery of a trans-stimulation property associated with lysine exodus from lysosomes of human fibroblasts has enabled us to characterize a system mediating the transport of cationic amino acids across the lysosomal membrane of human fibroblasts. The cationic amino acids arginine, lysine, ornithine, diaminobutyrate, histidine, 2-aminoethylcysteine, and the mixed disulfide of cysteine and cysteamine all caused trans-stimulation of the exodus of radiolabeled lysine from the lysosomal fraction of human fibroblasts at pH 6.5. In contrast, neutral and acidic amino acids did not affect the rate of lysine exodus. Trans-stimulation of lysine exodus was observed over the pH range from 5.5 to 7.6, was specific for the L-isomer of the cationic amino acid, and was intolerant to methylation of the alpha-amino group of the amino acid. The lysosomotropic amine, chloroquine, greatly retarded lysine exodus, whereas the presence of sodium ion was without effect. The specificity and lack of Na+ dependence of this lysosomal transport system is similar to that of System y+ present on the plasma membrane of human fibroblasts. An important mechanism by which cysteamine treatment of cystinosis allows cystine escape from lysosomes may be the ability of the mixed disulfide of cysteine and cysteamine formed by sulfhydryl-disulfide exchange to migrate by this newly discovered system mediating cationic amino acid transport.

Pisoni, R.L.; Thoene, J.G.; Christensen, H.N.

1985-04-25

389

CONSTRAINING PERTURBATIVE EARLY DARK ENERGY WITH CURRENT OBSERVATIONS  

SciTech Connect

In this work, we study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and constrain these models using current observations. We consider EDE models in which the dark energy equation of state is at least w{sub m} {approx_gt} -0.1 at early times, which could lead to an EDE density of up to {Omega}{sub DE}(z{sub CMB})= 0.03{Omega}{sub m}(z{sub CMB}). Our analysis shows that marginalizing over the non-DE parameters such as {Omega}{sub m}, H{sub 0}, andn{sub s} , current CMB observations alone can constrain the scale factor of transition from EDE to late-time dark energy to a{sub t} {approx_gt} 0.44 and width of transition to {Delta}{sub t} {approx_lt} 0.37. The equation of state at present is somewhat weakly constrained to w{sub 0} {approx_lt} -0.6, if we allow H{sub 0} < 60 km s{sup -1} Mpc{sup -1}. Taken together with other observations, such as SNe, Hubble Space Telescope, and Sloan Digital Sky Survey luminous red galaxies, w{sub 0} is constrained much more tightly to w{sub 0} {approx_lt} -0.9, while redshift of transition and width of transition are also tightly constrained to a{sub t} {approx_lt} 0.19 and{Delta}{sub t} {approx_lt} 0.21. The evolution of the equation of state for EDE models is thus tightly constrained to {Lambda}CDM-like behavior at low redshifts. Incorrectly assuming dark energy perturbations to be negligible leads to different constraints on the equation of state parameters-w{sub 0} {approx_lt} -0.8, a{sub t} {approx_lt} 0.33, and{Delta}{sub t} {approx_lt} 0.31, thus highlighting the necessity of self-consistently including dark energy perturbations in the analysis. If we allow the spatial curvature to be a free parameter, then the constraints are relaxed to w{sub 0} {approx_lt} -0.77, a{sub t} {approx_lt} 0.35, and{Delta}{sub t} {approx_lt} 0.35 with -0.014 < {Omega}{sub {kappa}} < 0.031 for CMB + other observations. For perturbed EDE models, the 2{sigma} lower limit on {sigma}{sub 8} ({sigma}{sub 8} {>=} 0.59) is much lower than that in {Lambda}CDM ({sigma}{sub 8} {>=} 0.72), thus raising the interesting possibility of discriminating EDE from {Lambda}CDM using future observations such as halo mass functions or the Sunyaev-Zeldovich power spectrum.

Alam, Ujjaini [ISR-1, ISR Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2010-05-10

390

Damping characteristics of active-passive hybrid constrained-layer treated beam structures  

NASA Astrophysics Data System (ADS)

A new configuration of surface damping treatments, Active- Passive Hybrid Constrained Layer (HCL) damping, is analyzed and experimentally investigated. The purpose is to improve the performance of the current active constrained layer (ACL) and passive constrained layer (PCL) treatments by mixing passive and active materials in the constraining layer. In HCL, the viscoelastic material is constrained by an active-passive hybrid constraining layer -- the active part is made of PZT ceramics, and the passive part can be selected by the designer to meet different requirements, such as higher damping performance or lighter weight. The active and passive constraining parts are mechanically connected such that the displacement and force are continuous at the connecting surface, but are isolated electrically so the passive constraining part will not affect the function of its active counterpart. Following a generic study of the HCL concept by the authors earlier, the purpose of this paper is to illustrate and validate the HCL performance through both numerical and experimental investigations on a beam structure. The governing equations and boundary conditions of an HCL treated beam are derived and a finite element model is formulated. Tabletop tests with cantilever beam specimens are used for the experimental study. The new hybrid constrained layer is found to have the advantages of both ACL and PCL. By selecting a stiffer passive constraining material and an optimal active-to-passive length ratio, the HCL can achieve better closed-loop and open-loop performances than the treatment with a pure active constraining layer.

Liu, Yanning; Wang, Kon-Well

2000-04-01

391

Constraining clumpy dusty torus models using optimized filter sets  

NASA Astrophysics Data System (ADS)

Recent success in explaining several properties of the dusty torus around the central engine of active galactic nuclei has been gathered with the assumption of clumpiness. The properties of such clumpy dusty tori can be inferred by analysing spectral energy distributions (SEDs), sometimes with scarce sampling given that large aperture telescopes and long integration times are needed to get good spatial resolution and signal. We aim at using the information already present in the data and the assumption of clumpy dusty torus, in particular, the CLUMPY models of Nenkova et al., to evaluate the optimum next observation such that we maximize the constraining power of the new observed photometric point. To this end, we use the existing and barely applied idea of Bayesian adaptive exploration, a mixture of Bayesian inference, prediction and decision theories. The result is that the new photometric filter we use is the one that maximizes the expected utility, which we approximate with the entropy of the predictive distribution. In other words, we have to sample where there is larger variability in the SEDs compatible with the data with what we know of the model parameters. We show that Bayesian adaptive exploration can be used to suggest new observations, and ultimately optimal filter sets, to better constrain the parameters of the clumpy dusty torus models. In general, we find that the region between 10 and 200 ?m produces the largest increase in the expected utility, although sub-mm data from Atacama Large Millimeter Array also prove to be useful. It is important to note that here we are not considering the angular resolution of the data, which is key when constraining torus parameters. Therefore, the expected utilities derived from this methodology must be weighted with the spatial resolution of the data.

Asensio Ramos, A.; Ramos Almeida, C.

2013-01-01

392

Constraining the Endogenic Power of Enceladus' Tiger Stripe Region  

NASA Astrophysics Data System (ADS)

On 12th March 2008, and again on 11th August 2008, the Cassini spacecraft flew past the South Pole of Enceladus at a distance of a few hundred kilometers. During both encounters the long-wavelength detector (FP1) on Cassini's Composite Infrared Spectrometer (CIRS) took over one hundred 10 to 600 cm-1 (1000 - 17 micron) spectra of the thermal emission from the active tiger stripes. The wavelength region covered by FP1 contains most of the power radiated by the tiger stripes and thus is very valuable for constraining total heat flow. Previous estimates of endogenic heat flow were derived by extrapolation from shorter-wavelength CIRS data. During the August encounter FP1 achieved a maximum resolution of 3 km, over the tiger stripe Arabia Sulcus. Whilst the best spatial resolution during the March encounter was significantly lower (50 km to 200 km) a larger number of spectra were taken, covering single or multiple tiger stripes. Using these measurements and previously determined surface thermal properties of Enceladus the total magnitude of the endogenic power from this region is constrained. An important part of this process is the subtraction of the background emission from re-radiated sunlight, using a passive thermal model, which is constrained by CIRS FP1 observations that do not include the tiger stripes. The good spatial coverage of the tiger stripes has enabled the endogenic heat released by individual tiger stripes to also be determined. It is shown that the release of this heat by the tiger stripes is not uniform, but rather varies between stripes and along the stripes. The magnitude and scale of this variation will be fully explored.

Howett, C. J.; Spencer, J. R.; Pearl, P. C.; Segura, M.; Cirs Cassini Team

2008-12-01

393

Constraining the dark energy and smoothness parameter with supernovae  

SciTech Connect

The presence of inhomogeneities modifies the cosmic distances through the gravitational lensing effect, and, indirectly, must affect the main cosmological tests. Assuming that the dark energy is a smooth component, the simplest way to account for the influence of clustering is to suppose that the average evolution of the expanding Universe is governed by the total matter-energy density whereas the focusing of light is only affected by a fraction of the total matter density quantified by the {alpha} Dyer-Roeder parameter. By using two different samples of SNe type Ia data, the {omega}{sub m} and {alpha} parameters are constrained by applying the Zeldovich-Kantowski-Dyer-Roeder luminosity distance-redshift relation for a flat ({lambda}CDM) model. A {chi}{sup 2}-analysis using the 115 SNe Ia data of the Astier et al. sample (2006) constrains the density parameter to be {omega}{sub m}=0.26{sub -0.07}{sup +0.17} (2{sigma}) while the {alpha} parameter is weakly limited (all the values set-membership sign [0,1] are allowed even at 1{sigma}). However, a similar analysis based the 182 SNe Ia data of Riess et al. (2007) constrains the pair of parameters to be {omega}{sub m}=0.33{sub -0.07}{sup +0.09} and {alpha}{>=}0.42 (2{sigma}). Basically, this occurs because the Riess et al. sample extends to appreciably higher redshifts. As a general result, even considering the existence of inhomogeneities as described by the smoothness {alpha} parameter, the Einstein-de Sitter model is ruled out by the two samples with a high degree of statistical confidence (11.5{sigma} and 9.9{sigma}, respectively). The inhomogeneous Hubble-Sandage diagram discussed here highlights the necessity of the dark energy, and a transition deceleration/accelerating phase at z{approx}0.5 is also required.

Santos, R. C.; Cunha, J. V.; Lima, J. A. S. [Departamento de Astronomia, Universidade de Sao Paulo, 05508-900 Sao Paulo, SP (Brazil)

2008-01-15

394

Constraining predictions of the carbon cycle using data.  

PubMed

We use a carbon-cycle data assimilation system to estimate the terrestrial biospheric CO(2) flux until 2090. The terrestrial sink increases rapidly and the increase is stronger in the presence of climate change. Using a linearized model, we calculate the uncertainty in the flux owing to uncertainty in model parameters. The uncertainty is large and is dominated by the impact of soil moisture on heterotrophic respiration. We show that this uncertainty can be greatly reduced by constraining the model parameters with two decades of atmospheric measurements. PMID:21502169

Rayner, P J; Koffi, E; Scholze, M; Kaminski, T; Dufresne, J-L

2011-05-28

395

Energy constrained transport maximization across a fluid interface.  

PubMed

With enhancing mixing in micro- or nanofluidic applications in mind, the problem of maximizing fluid transport across a fluid interface subject to an available energy budget is examined. The optimum cross-interface perturbing velocity is obtained explicitly in the time-periodic instance using an Euler-Lagrange constrained optimization approach. Numerical investigations which calculate transferred lobe areas and cross-interface flux are used to verify that the predicted strategy achieves optimum transport. Explicit active protocols for achieving this optimal transport are suggested. PMID:23004278

Balasuriya, Sanjeeva; Finn, Matthew D

2012-06-15

396

Current-Induced Exchange Length and Geometrically Constrained Magnetic Wall  

NASA Astrophysics Data System (ADS)

We analyzed stable magnetic structures of a geometrically constrained magnetic wall under direct current (dc) and found that there exists a characteristic length induced by the competition between the spin transfer torque and the torque due to exchange interaction. This current-induced exchange length is inversely proportional to the applied dc, and the magnetic ripple structure appears when the current-induced exchange length is smaller than the nanoscale constriction. We also found that the amplitude of the magnetic ripple structure oscillates as a function of the applied dc, which can be observed as an oscillation of the resistance against the applied dc.

Matsushita, Katsuyoshi; Sato, Jun; Imamura, Hiroshi

2010-03-01

397

Adaptively Learning an Importance Function Using Transport Constrained Monte Carlo  

SciTech Connect

It is well known that a Monte Carlo estimate can be obtained with zero-variance if an exact importance function for the estimate is known. There are many ways that one might iteratively seek to obtain an ever more exact importance function. This paper describes a method that has obtained ever more exact importance functions that empirically produce an error that is dropping exponentially with computer time. The method described herein constrains the importance function to satisfy the (adjoint) Boltzmann transport equation. This constraint is provided by using the known form of the solution, usually referred to as the Case eigenfunction solution.

Booth, T.E.

1998-06-22

398

Positive Scattering Cross Sections using Constrained Least Squares  

SciTech Connect

A method which creates a positive Legendre expansion from truncated Legendre cross section libraries is presented. The cross section moments of order two and greater are modified by a constrained least squares algorithm, subject to the constraints that the zeroth and first moments remain constant, and that the standard discrete ordinate scattering matrix is positive. A method using the maximum entropy representation of the cross section which reduces the error of these modified moments is also presented. These methods are implemented in PARTISN, and numerical results from a transport calculation using highly anisotropic scattering cross sections with the exponential discontinuous spatial scheme is presented.

Dahl, J.A.; Ganapol, B.D.; Morel, J.E.

1999-09-27

399

Constraining the Physical Parameters of the Circumstellar Disk of ? Ophiuchi  

NASA Astrophysics Data System (ADS)

We present a numerical model describing a circularly symmetric gaseous disk around the Be star ? Ophiuchi. The model is constrained by long-baseline interferometric observations that are sensitive to the H? Balmer line emission from the disk. For the first time, our interferometric observations spatially resolve the inner region of the circumstellar disk around ? Oph, and we use these results to place a constraint on the physical extent of the H?-emitting region. We demonstrate how this in turn results in very specific constraints on the parameters that describe the variation of the gas density as a function of radial distance from the central star.

Tycner, C.; Jones, C. E.; Sigut, T. A. A.; Schmitt, H. R.; Benson, J. A.; Hutter, D. J.; Zavala, R. T.

2008-12-01

400

Constraining ocean diffusivity from the 8.2 ka event  

Microsoft Academic Search

Greenland ice-core data containing the 8.2 ka event are utilized by a model-data intercomparison within the Earth system model\\u000a of intermediate complexity, CLIMBER-2.3 to investigate their potential for constraining the range of uncertain ocean diffusivity\\u000a properties. Within a stochastic version of the model (Bauer et al. in Paleoceanography 19:PA3014, 2004) it has been possible to mimic the pronounced cooling of the 8.2 ka

Alexander Lorenz; Hermann Held; Eva Bauer; Thomas Schneider von Deimling

2010-01-01

401

Structure-based design of potent, conformationally constrained Smac mimetics.  

PubMed

A successful structure-based design and synthesis of a class of highly potent conformationally constrained Smac mimetics is described. The most potent compound has a Ki value of 25 nM binding to the XIAP BIR3 protein and is 23 times more potent than natural Smac peptides. These potent Smac mimetics can serve as powerful chemical and pharmacological tools to further elucidate the role of Smac and its cellular binding partners in apoptosis regulation and may be developed as a new class of anti-cancer drugs. PMID:15612682

Sun, Haiying; Nikolovska-Coleska, Zaneta; Yang, Chao-Yie; Xu, Liang; Liu, Meilan; Tomita, York; Pan, Hongguang; Yoshioka, Yoshiko; Krajewski, Krzysztof; Roller, Peter P; Wang, Shaomeng

2004-12-29

402

QoS-constrained Energy Minimization in Multiuser Multicarrier Systems  

NASA Astrophysics Data System (ADS)

In this paper the QoS-constrained resource allocation problem in multicarrier systems is considered. Within the established cross-layer framework, parameters for subchannel assignment, adaptive modulation and coding, and ARQ/HARQ protocols are jointly optimized. Instead of the conventional transmit power minimization, the total energy consumption for the successful transmissions of all information bits is set as the optimization goal. The nonconvex primal problem is solved by using Lagrange dual decomposition and the ellipsoid method. Numerical results indicate that the recovered primal solution is well acceptable in performance, and efficient in terms of computational effort.

Bai, Qing; Ivrla?, Michel T.; Nossek, Josef A.

403

Semismooth Newton method for gradient constrained minimization problem  

NASA Astrophysics Data System (ADS)

In this paper we treat a gradient constrained minimization problem, particular case of which is the elasto-plastic torsion problem. In order to get the numerical approximation to the solution we have developed an algorithm in an infinite dimensional space framework using the concept of the generalized (Newton) differentiation. Regularization was done in order to approximate the problem with the unconstrained minimization problem and to make the pointwise maximum function Newton differentiable. Using semismooth Newton method, continuation method was developed in function space. For the numerical implementation the variational equations at Newton steps are discretized using finite elements method.

Anyyeva, Serbiniyaz; Kunisch, Karl

2012-08-01

404

Effect of structurally constrained oxime-ether linker on PPAR subtype selectivity: Discovery of a novel and potent series of PPAR-pan agonists.  

PubMed

A novel series of thaizole and oxazole containing phenoxy acetic acid derivatives is reported as PPAR-pan agonists. Incorporation of structurally constrained oxime-ether based linker in the chemotype of a potent PPAR? selective agonist GW-501516 was adapted as designing strategy. In vitro, selected test compounds 12a, 12c, 17a and 18a showed PPAR-pan agonists activities and among these four compounds tested, 12a emerged as highly potent and efficacious compound, while 17a exhibited moderate and balanced PPAR-pan agonistic activity. In vivo, selected test compounds 12a and 17a exhibited significant anti-hyperglycemic and anti-hyperlipidemic activities in relevant animal models. These results support our hypothesis that the introduction of structurally constrained oxime-ether linker between lipophilic tail and acidic head plays an important role in modulating subtype selectivity and subsequently led to the discovery of potent PPAR-pan agonists. PMID:21215640

Makadia, Pankaj; Shah, Shailesh R; Pingali, Harikishore; Zaware, Pandurang; Patel, Darshit; Pola, Suresh; Thube, Baban; Priyadarshini, Priyanka; Suthar, Dinesh; Shah, Maanan; Giri, Suresh; Trivedi, Chitrang; Jain, Mukul; Patel, Pankaj; Bahekar, Rajesh

2010-12-13

405

Galactic disk abundance ratios: constraining SNIa stellar yields  

SciTech Connect

Stellar abundance ratios of very good quality are now available for a large number of stars in the solar vicinity. Moreover, for an increasing number of stars informations on kinematics is also available. The combined information on abundance and kinematics enables one to select objects belonging to the different components of our Galaxy (thin disk, thick disk and halo). In this work we show that a careful comparison of our chemical evolution model for the Milky Way with the available abundance ratio measurements for stars in the solar neighborhood can be used to constrain the stellar yields. In particular, yields of Type Ia SNe are constrained by the abundance pattern of thin disk stars. Our results suggest that the 3-D models for SNIa explosion studied here lead to discrepancies once their predicted stellar yields are used as input in our chemical evolution model. These models produce flat Si/O and Mg/O ratios in disagreement with what is observed in thin disk stars. Moreover, our results indicate that larger quantities of Mg (at least a factor of 10 more than current theoretical predictions of either 1-D or multi-D models) need to be produced in SNIa.

Chiappini, Cristina [Osservatorio Astronomico di Trieste - OAT/INAF - Via G. B. Tiepolo 11, Trieste 34131 (Italy)

2005-10-21

406

Constraining ozone-precursor responsiveness using ambient measurements  

NASA Astrophysics Data System (ADS)

This study develops probabilistic estimates of ozone (O3) sensitivities to precursor emissions by incorporating uncertainties in photochemical modeling and evaluating model performance based on ground-level observations of O3 and oxides of nitrogen (NOx). Uncertainties in model formulations and input parameters are jointly considered to identify factors that strongly influence O3 concentrations and sensitivities in the Dallas-Fort Worth region in Texas. Weightings based on a Bayesian inference technique and screenings based on model performance and statistical tests of significance are used to generate probabilistic representation of O3 response to emissions and model input parameters. Adjusted (observation-constrained) results favor simulations using the sixth version of the carbon bond chemical mechanism (CB6) and scaled-up emissions of NOx, dampening the overall sensitivity of O3 to NOx and increasing the sensitivity of O3 to volatile organic compounds in the study region. This approach of using observations to adjust and constrain model simulations can provide probabilistic representations of pollutant responsiveness to emission controls that complement the results obtained from deterministic air-quality modeling.

Digar, Antara; Cohan, Daniel S.; Xiao, Xue; Foley, Kristen M.; Koo, Bonyoung; Yarwood, Greg

2013-01-01

407

Can ozone assimilation constrain inorganic chlorine in the stratosphere?  

NASA Astrophysics Data System (ADS)

During the PROMOTE project (www.gse-promote.org), BIRA-IASB has assimilated UARS MLS chemical observations of O3, HNO3, H2O and ClO between 1992 and 1997 using the BASCOE 4D-Var system (Viscardy et al., accepted for publication in JSTARS). This system is based on a stratospheric chemistry transport model (CTM) where chemical reactions are calculated explicitly. Thus, the chemical module of the adjoint of the CTM allows the system to constrain not only the observed constituents but also those that are chemically coupled to the observed constituents. In this contribution, we study how O3 MLS observations are able to constrain stratospheric inorganic chlorines. In the Upper Stratosphere-Lower Mesosphere, it is shown that O3 observations could correct modeled HCl and improve the comparison against independent HALOE observations. For example, BASCOE is able to reproduce the trend of HCl volume mixing ratio observed by HALOE between 1992 and 1995 at 0.5 hPa. From 1996, the HCl trend from BASCOE becomes negative, which is not observed by HALOE. The possible causes for this disagreement will be discussed as well as the potential use of chemical 4D-Var to derive trends of non-assimilated species.

Errera, Quentin; Chabrillat, Simon; Viscardy, Sébastien

2010-05-01

408

Constraining thawing dark energy using galaxy cluster number counts  

NASA Astrophysics Data System (ADS)

We study the formation of galaxy clusters in the presence of thawing class of scalar field dark energy (DE). We consider cases where the scalar field has canonical as well as non-canonical kinetic terms in its action. We also consider various forms for the potential of the scalar field, e.g. linear, quadratic, inverse quadratic, exponential as well as Pseudo-Nambu Goldstone Boson (PNGB) type. Moreover, we investigate a situation where DE is homogeneous along with a situation where DE takes part in virialization process. We use the Sheth-Tormen formalism while calculating the number density of galaxy clusters. Our results show that cluster number density for different DE models has a significant deviation from the corresponding value for the ?cold dark matter (?CDM) case. The deviation is more for higher redshifts. Moreover, the tachyon-type scalar field with linear potential has the highest deviation from the ?CDM case. For the total cluster number counts, different DE models can have substantial deviation from ?CDM and this deviation is most significant around z ˜ 0.5 for all the models we considered. We also constrain thawing class of models using the presently available data for number counts of massive X-ray clusters. The results show that current cluster data are not suitable enough for constraining potentials for the thawing scalar fields as well as for other cosmological parameters like ns. But one can get significant constraint for the parameter ?8 and a lower bound on ?m0.

Devi, N. Chandrachani; Choudhury, T. Roy; Sen, Anjan A.

2013-06-01

409

Constraining the North Pacific carbon sink: biological and physical processes  

NASA Astrophysics Data System (ADS)

The transition zone region of the North Pacific is a notably large sink for atmospheric carbon dioxide on a mean annual basis, though seasonally the region varies between strong wintertime uptake and weak summertime outgassing. Because the direction of air-sea carbon flux is effectively set by the sea surface pCO2, we seek to identify and quantify those processes most responsible for its variability in this region. While changes in temperature, salinity, dissolved inorganic carbon, and alkalinity are all factors that impact sea surface pCO2 on a seasonal basis, on a mean annual basis the region must be maintained as a sink by processes that remove carbon from surface waters: biological drawdown as well as the result of advection/mixing. In this work we constrain the quantitative contribution of each of these processes throughout an annual cycle. The least constrained of these processes is the biological pump, which we estimate in two independent ways: bottom-up, using satellite data-based primary productivity models coupled with export estimates from literature; and top-down, by determining what the biological pump would need to be to maintain the observed sea surface pCO2 values in the region, given our estimates of all the other regulatory processes.

Ayers, J.; Lozier, M.

2010-12-01

410

Data-constrained reionization and its effects on cosmological parameters  

NASA Astrophysics Data System (ADS)

We perform an analysis of the recent WMAP7 data considering physically motivated and viable reionization scenarios with the aim of assessing their effects on cosmological parameter determinations. The main novelties are: (i) the combination of cosmic microwave background data with astrophysical results from quasar absorption line experiments; (ii) the joint variation of both the cosmological and astrophysical [governing the evolution of the free electron fraction xe(z)] parameters. Including a realistic, data-constrained reionization history in the analysis induces appreciable changes in the cosmological parameter values deduced through a standard WMAP7 analysis. Particularly noteworthy are the variations in ?bh2=0.02258-0.00056+0.00057 [WMAP7 (Sudden)] vs ?bh2=0.02183±0.00054 [WMAP7+ASTRO (CF)] and the new constraints for the scalar spectral index, for which WMAP7+ASTRO (CF) excludes the Harrison-Zel’dovich value ns=1 at >3?. Finally, the electron-scattering optical depth value is considerably decreased with respect to the standard WMAP7, i.e. ?e=0.080±0.012. We conclude that the inclusion of astrophysical data sets, allowing to robustly constrain the reionization history, in the extraction procedure of cosmological parameters leads to relatively important differences in the final determination of their values.

Pandolfi, S.; Ferrara, A.; Choudhury, T. Roy; Melchiorri, A.; Mitra, S.

2011-12-01

411

Orientational ordering in fluids with partially constrained molecule orientations  

PubMed

Molecular orientations in anisotropic fluids can be partially constrained as a result of electric or magnetic fields or interface influences. A statistical approach for the investigation of the orientational ordering in such systems is proposed. The long-range correlations are taken into account consistently. The method is illustrated for the well-known thermotropic nematic model in an infinite disorienting field W, when the molecules are constrained to orient perpendicularly to the field direction. For this problem the analytical solution of the anisotropic Ornstein-Zernike equation is obtained, and the asymptotic expression for the long-range correlations on large distances is given. The phase diagram and elastic constants are calculated for W-->infinity and are compared with the usual case of a uniaxial nematic ordering at W=0. In the case W-->infinity when the temperature decreases the orientational phase transition of the second order becomes the one of the first order at a tricritical point. The disorienting field W increases much the region of an ordered fluid. It is shown that at a given pressure the orientational ordering temperature for W-->infinity is higher about 1.2-1.5 times than the one at W=0. The orientational ordering pressure is less about 4-5 times than the pressure of the uniaxial nematic ordering (W=0) at the same temperature. The disorienting field increases elastic properties of the model under consideration. PMID:11102029

Sokolovska; Sokolovskii; Holovko

2000-11-01

412

Constrained optimization framework for joint inversion of geophysical data sets  

NASA Astrophysics Data System (ADS)

Many experimental techniques in geophysics advance the understanding of Earth processes by estimating and interpreting Earth structure (e.g. velocity and/or density structure). Different types of geophysical data can be collected and analysed separately, sometimes resulting in inconsistent models of the Earth depending on the data used. We present a constrained optimization approach for a joint inversion least-squares (LSQ) algorithm to characterize 1-D Earth's structure. We use two geophysical data sets sensitive to shear velocities: receiver function and surface wave dispersion velocity observations. We study the use of bound constraints on the regularized inverse problem, which are more physical than the regularization parameters required by conventional unconstrained formulations. Specifically, we develop a constrained optimization formulation that is solved with a primal-dual interior-point (PDIP) method, and validate our results with a traditional, unconstrained formulation that is solved with a truncated singular value decomposition (TSVD) for a set of numerical experiments with synthetic crustal velocity models. We conclude that the PDIP results are as accurate as those from the regularized TSVD approach, are less affected by noise, and honour the geophysical constraints.

Sosa, A.; Velasco, A. A.; Velazquez, L.; Argaez, M.; Romero, R.

2013-09-01

413

Constrained Large Eddy Simulation of Separated Turbulent Flows  

NASA Astrophysics Data System (ADS)

Constrained Large-eddy Simulation (CLES) has been recently proposed to simulate turbulent flows with massive separation. Different from traditional large eddy simulation (LES) and hybrid RANS/LES approaches, the CLES simulates the whole flow domain by large eddy simulation while enforcing a RANS Reynolds stress constraint on the subgrid-scale (SGS) stress models in the near-wall region. Algebraic eddy-viscosity models and one-equation Spalart-Allmaras (S-A) model have been used to constrain the Reynolds stress. The CLES approach is validated a posteriori through simulation of flow past a circular cylinder and periodic hill flow at high Reynolds numbers. The simulation results are compared with those from RANS, DES, DDES and other available hybrid RANS/LES methods. It is shown that the capability of the CLES method in predicting separated flows is comparable to that of DES. Detailed discussions are also presented about the effects of the RANS models as constraint in the near-wall layers. Our results demonstrate that the CLES method is a promising alternative towards engineering applications.

Xia, Zhenhua; Shi, Yipeng; Wang, Jianchun; Xiao, Zuoli; Yang, Yantao; Chen, Shiyi

2011-11-01

414

Multiple Sclerosis Lesion Detection Using Constrained GMM and Curve Evolution  

PubMed Central

This paper focuses on the detection and segmentation of Multiple Sclerosis (MS) lesions in magnetic resonance (MRI) brain images. To capture the complex tissue spatial layout, a probabilistic model termed Constrained Gaussian Mixture Model (CGMM) is proposed based on a mixture of multiple spatially oriented Gaussians per tissue. The intensity of a tissue is considered a global parameter and is constrained, by a parameter-tying scheme, to be the same value for the entire set of Gaussians that are related to the same tissue. MS lesions are identified as outlier Gaussian components and are grouped to form a new class in addition to the healthy tissue classes. A probability-based curve evolution technique is used to refine the delineation of lesion boundaries. The proposed CGMM-CE algorithm is used to segment 3D MRI brain images with an arbitrary number of channels. The CGMM-CE algorithm is automated and does not require an atlas for initialization or parameter learning. Experimental results on both standard brain MRI simulation data and real data indicate that the proposed method outperforms previously suggested approaches, especially for highly noisy data.

Freifeld, Oren; Greenspan, Hayit; Goldberger, Jacob

2009-01-01

415

Wavelet-based face verification for constrained platforms  

NASA Astrophysics Data System (ADS)

Human Identification based on facial images is one of the most challenging tasks in comparison to identification based on other biometric features such as fingerprints, palm prints or iris. Facial recognition is the most natural and suitable method of identification for security related applications. This paper is concerned with wavelet-based schemes for efficient face verification suitable for implementation on devices that are constrained in memory size and computational power such as PDA"s and smartcards. Beside minimal storage requirements we should apply as few as possible pre-processing procedures that are often needed to deal with variation in recoding conditions. We propose the LL-coefficients wavelet-transformed face images as the feature vectors for face verification, and compare its performance of PCA applied in the LL-subband at levels 3,4 and 5. We shall also compare the performance of various versions of our scheme, with those of well-established PCA face verification schemes on the BANCA database as well as the ORL database. In many cases, the wavelet-only feature vector scheme has the best performance while maintaining efficacy and requiring minimal pre-processing steps. The significance of these results is their efficiency and suitability for platforms of constrained computational power and storage capacity (e.g. smartcards). Moreover, working at or beyond level 3 LL-subband results in robustness against high rate compression and noise interference.

Sellahewa, Harin; Jassim, Sabah A.

2005-03-01

416

Observational constrains on the EoS of neutron stars.  

NASA Astrophysics Data System (ADS)

In observations of neutron star Soft X-ray Transients (SXTs) in quiescence which allow for a spectral study, the spectrum was found to be well-fit by a neutron star atmosphere model (NSA) sometimes supplemented with a power-law component. Theories about the time averaged mass accretion rates in neutron star SXTs, the pycnonuclear reactions taking place in the neutron star crust combined with neutron star cooling theory predictions, yield a neutron star core temperature. This hot neutron star core, moderated by the neutron star atmosphere, is thought to be observed during the quiescent phase of neutron star SXTs. In theory, a NSA-fit provides means to measure the mass and radius of the neutron star and hence constrain the equation of state (EoS) of matter at supranuclear densities. In addition several neutron star SXTs so far remain undetected, constraining their cooling rate. I'll discuss the current state of the observations and indicate possible future observations that could help contrain the equation of state further.

Jonker, Peter

417

Vibration control of cylindrical shells using active constrained layer damping  

NASA Astrophysics Data System (ADS)

The fundamentals of controlling the structural vibration of cylindrical shells treated with active constrained layer damping (ACLD) treatments are presented. The effectiveness of the ACLD treatments in enhancing the damping characteristics of thin cylindrical shells is demonstrated theoretically and experimentally. A finite element model (FEM) is developed to describe the dynamic interaction between the shells and the ACLD treatments. The FEM is used to predict the natural frequencies and the modal loss factors of shells which are partially treated with patches of the ACLD treatments. The predictions of the FEM are validated experimentally using stainless steel cylinders which are 20.32 cm in diameter, 30.4 cm in length and 0.05 cm in thickness. The cylinders are treated with ACLD patches of different configurations in order to target single or multi-modes of lobar vibrations. The ACLD patches used are made of DYAD 606 visco-elastic layer which is sandwiched between two layers of PVDF piezo-electric films. Vibration attenuations of 85% are obtained with maximum control voltage of 40 volts. Such attenuations are attributed to the effectiveness of the ACLD treatment in increasing the modal damping ratios by about a factor of four over those of conventional passive constrained layer damping (PCLD) treatments. The obtained results suggest the potential of the ACLD treatments in controlling the vibration of cylindrical shells which constitute the major building block of many critical structures such as cabins of aircrafts, hulls of submarines and bodies of rockets and missiles.

Ray, M.; Chen, T.; Baz, Amr M.

1997-05-01

418

Constrained traffic regulation in variable-length packet networks  

NASA Astrophysics Data System (ADS)

The availability of high bandwidth in optical networks coupled with the evolution of applications such as video on demand and telemedicine create a clear need for providing quality-of-service (QoS) guarantees in optical networks. Proliferation of the IP-over-WDM model in these networks requires the network to provide QoS guarantees for variable-length packets. In this context, we address the problem of constrained traffic regulation--traffic regulation with buffer and delay constraints--in variable-length packet networks. We use the filtering theory under max-plus (max, +) algebra to address this problem. For a constrained traffic-regulation problem with maximum tolerable delay and maximum buffer size, the traffic regulator that generates g-regular output traffic minimizing the number of discarded packets is a concatenation of the f clipper and the minimal g regulator. f is a function of g, maximum delay, and maximum buffer size. The f clipper is a bufferless device, which drops the packets as necessary so that its output is f regular. The minimal g regulator is a buffered device that delays packets as necessary so that its output is g regular. The g regulator is a linear shift-invariant filter with impulse response g, under the (max, +) algebra.

Karumanchi, Ashok; Varadarajan, Sridhar; Rao, Kalyan; Talabattula, Srinivas

2004-02-01

419

Conformationally Constrained Peptidomimetic Inhibitors of Signal Transducer and Activator of Transcription 3: Evaluation and Molecular Modeling  

PubMed Central

Signal transducer and activator of transcription 3 (Stat3) is involved in aberrant growth and survival signals in malignant tumor cells and is a validated target for anti-cancer drug design. We are targeting its SH2 domain to prevent docking to cytokine and growth factor receptors and subsequent signaling. The amino acids of our lead phosphopeptide, Ac-pTyr-Leu-Pro-Gln-Thr-Val-NH2, were replaced with conformationally constrained mimics. Structure-affinity studies led to the peptidomimetic, pCinn-Haic-Gln-NHBn (21) which had an IC50 of 162 nM (fluorescence polarization), as compared to 290 nM for the lead phosphopeptide (pCinn = 4-phosphoryloxycinnamate, Haic = (2S,5S)-5-amino-1,2,4,5,6,7-hexahydro-4-oxo-azepino[3,2,1-hi]indole-2-carboxylic acid). pCinn-Haic-Gln-OH was docked to the SH2 domain (AUTODOCK) and the two highest populated clusters were subjected to molecular dynamics simulations. Both converged to a common peptide conformation. The complex exhibits unique hydrogen bonding between Haic and Gln and Stat3 as well as hydrophobic interactions between the protein and pCinn and Haic.

Mandal, Pijus K.; Limbrick, Donald; Coleman, David R.; Dyer, Garrett A.; Ren, Zhiyong; Birtwistle, J. Sanderson; Xiong, Chiyi; Chen, Xiaomin; Briggs, James M.; McMurray, John S.

2009-01-01

420

Studies towards the synthesis of alpha-amino-epoxyquinol natural products  

Microsoft Academic Search

Biocatalytically-derived enantiopure compounds originating from p-benzoquinone (1) have been used in methodological studies towards the synthesis of members of the ?-amino-epoxyquinol family of natural products. The target compounds LL-C10037? and manumycin A are of interest as potential antitumor and antibiotic agents Several highlights of the methodology are: lipase-resolution to seems a key enantiopure alcohol, nitrogen incorporation by addition to allylic

Josef Roland Bencsik

1999-01-01

421

Effect of structurally constrained oxime–ether linker on PPAR subtype selectivity: Discovery of a novel and potent series of PPAR-pan agonists  

Microsoft Academic Search

A novel series of thaizole and oxazole containing phenoxy acetic acid derivatives is reported as PPAR-pan agonists. Incorporation of structurally constrained oxime–ether based linker in the chemotype of a potent PPAR? selective agonist GW-501516 was adapted as designing strategy. In vitro, selected test compounds 12a, 12c, 17a and 18a showed PPAR-pan agonists activities and among these four compounds tested, 12a

Pankaj Makadia; Shailesh R. Shah; Harikishore Pingali; Pandurang Zaware; Darshit Patel; Suresh Pola; Baban Thube; Priyanka Priyadarshini; Dinesh Suthar; Maanan Shah; Suresh Giri; Chitrang Trivedi; Mukul Jain; Pankaj Patel; Rajesh Bahekar

2011-01-01

422

Constrained WZWN models on G/{S?U(1} and exchange algebra of G-primaries  

NASA Astrophysics Data System (ADS)

Consistently constrained WZWN models on G/{S?U(1} is given by constraining currents of the WZWN models with G. Poisson brackets are set up on the light-like plane. Using them we show the Virasoro algebra for the energy-momentum tensor of constrained WZWN models. We find a G-primary which satisfies a classical exchange algebra in an arbitrary representation of G. The G-primary and the constrained currents are also shown to obey the conformal transformation with respect to the energy-momentum tensor. It is checked that conformal weight of the constrained currents is 0. This is necessary for the consistency for our formulation of constrained WZWN models.

Aoyama, Shogo; Ishii, Katsuyuki

2013-11-01

423

Characterization of a dual specificity aryl acid adenylation enzyme with dual function in nikkomycin biosynthesis.  

PubMed

Nikkomycin Z is a dipeptide antifungal antibiotic characterized by two nonproteinogenic amino acids, nikkomycin C(Z) and 4-(4'-hydroxy-2'-pyridinyl)-homothreonine (HPHT). The HPHT scaffold is assembled by an aldol reaction between 2-oxobutyrate and picolinaldehyde, the latter of which is derived from picolinic acid that is activated and loaded to coenzyme A by the aryl-activating adenylation enzyme, NikE. We now provide evidence that NikE is also involved in the activation and loading of the alpha-keto acid precursor, 4-(2'-pyridinyl)-2-oxo-4-hydroxyisovalerate (POHIV), to a phosphopantetheinyl group of an acyl carrier protein domain of NikT. POHIV was synthesized using Escherichia coli 2-dehydro-3-deoxy-phosphogluconate aldolase, and phenylalanine dehydrogenase from Bacillus sp. NRRL B-14911 was used to prepare the alpha-amino acid, 4-(2'-pyridinyl)-homothreonine (PHT). Using the carboxylic acid-dependent, ATP-[(32)P]PP(i) exchange assay, NikE is shown to activate both picolinic acid and POHIV but not PHT. Furthermore, NikE loads POHIV to holo-NikT to generate a new thioester-linked intermediate, which was not observed using a NikT(S33A) mutant. Thus, NikE activates two distinct carboxylic acids to form two new thioester intermediates, one of which is subsequently reduced to the aldehyde and the other that likely serves as a substrate for the aminotransferase domain of NikT prior to condensation with nikkomycin C(Z) to yield the dipeptide. PMID:20577996

Moon, Mary; Van Lanen, Steven G

2010-09-01

424

Influence of a Gamma Amino Acid on the Structures and Reactivity of Peptide a3 Ions  

PubMed Central

Collision-induced dissociation of protonated AGabaAIG (where Gaba is gamma-amino butyric acid, NH2-(CH2)3-COOH) leads to an unusually stable a3 ion. Tandem mass spectrometry and theory are used here to probe the enhanced stability of this fragment, whose counterpart is not usually observed in CID of protonated peptides containing only alpha amino acids. Experiments are carried out on the unlabelled and 15N-Ala labeled AGabaAIG (labeled separately at residue one or three) probing the b3, a3, a3-NH3 (a3*), and b2 fragments while theory is used to characterize the most stable b3, a3, and b2 structures and the formation and dissociation of the a3 ion. Our results indicate the AGabaA oxazolone b3 isomer undergoes head-to-tail macrocyclization and subsequent ring opening to form the GabaAA sequence isomer while this chemistry is energetically disfavored for the AAA sequence. The AGabaA a3 fragment also undergoes macrocyclization and rearrangement to form the rearranged imine-amide isomer while this reaction is energetically disfavored for the AAA sequence. The barriers to dissociation of the AGabaA a3 ion via the a3?b2 and a3?a3* channels are higher than the literature values reported for the AAA sequence. These two effects provide a clear explanation for the enhanced stability of the AGabaA a3 ion.

Bernier, Matthew C.; Paizs, Bela; Wysocki, Vicki H.

2012-01-01

425

Cyclothiazide potently inhibits gamma-aminobutyric acid type A receptors in addition to enhancing glutamate responses.  

PubMed

Ionotropic glutamate and gamma-aminobutyric acid type A (GABAA) receptors mediate critical excitatory and inhibitory actions in the brain. Cyclothiazide (CTZ) is well known for its effect of enhancing glutamatergic transmission and is widely used as a blocker for alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor desensitization. Here, we report that in addition to its action on AMPA receptors, CTZ also exerts a powerful but opposite effect on GABAA receptors. We found that CTZ reversibly inhibited both evoked and spontaneous inhibitory postsynaptic currents, as well as GABA application-induced membrane currents, in a dose-dependent manner. Single-channel analyses revealed further that CTZ greatly reduced the open probability of GABAA receptor channels. These results demonstrate that CTZ interacts with both glutamate and GABAA receptors and shifts the excitation-inhibition balance in the brain by two independent mechanisms. Understanding the molecular mechanism of this double-faceted drug-receptor interaction may help in designing new therapies for neurological diseases. PMID:14534329

Deng, Lunbin; Chen, Gong

2003-10-08

426

Capacity-constrained traffic assignment in networks with residual queues  

SciTech Connect

This paper proposes a capacity-constrained traffic assignment model for strategic transport planning in which the steady-state user equilibrium principle is extended for road networks with residual queues. Therefore, the road-exit capacity and the queuing effects can be incorporated into the strategic transport model for traffic forecasting. The proposed model is applicable to the congested network particularly when the traffic demands exceeds the capacity of the network during the peak period. An efficient solution method is proposed for solving the steady-state traffic assignment problem with residual queues. Then a simple numerical example is employed to demonstrate the application of the proposed model and solution method, while an example of a medium-sized arterial highway network in Sioux Falls, South Dakota, is used to test the applicability of the proposed solution to real problems.

Lam, W.H.K.; Zhang, Y.

2000-04-01

427

How examples may (and may not) constrain creativity.  

PubMed

Three experiments were performed to test Smith, Ward, and Schumacher's (1993) conformity hypothesis-that people's ideas will conform to examples they are shown in a creative generation task. Conformity was observed in all three experiments; participants tended to incorporate critical features of experimenter-provided examples. However, examination of total output, elaborateness of design, and the noncritical features did not confirm that the conformity effect constrained creative output in any of the three experiments. Increasing the number of examples increased the conformity effect (Experiment 1). Examples that covaried features that are naturally uncorrelated in the real world led to a greater subjective rating of creativity (Experiment 2). A delay between presentation and test increased conformity (Experiment 3), just as models of inadvertent plagiarism would predict. The explanatory power of theoretical accounts such as activation, retrieval blocking, structured imagination, and category abstraction are evaluated. PMID:8870535

Marsh, R L; Landau, J D; Hicks, J L

1996-09-01

428

CONSTRAINING GALACTIC MAGNETIC FIELD MODELS WITH STARLIGHT POLARIMETRY  

SciTech Connect

This paper provides testable predictions about starlight polarizations to constrain the geometry of the Galactic magnetic field, in particular the nature of the poloidal component. Galactic dynamo simulations and Galactic dust distributions from the literature are combined with a Stokes radiative transfer model to predict the observed polarizations and position angles of near-infrared starlight, assuming that the light is polarized by aligned anisotropic dust grains. S0 and A0 magnetic field models and the role of magnetic pitch angle are all examined. All-sky predictions are made, and particular directions are identified as providing diagnostic power for discriminating among the models. Cumulative distribution functions of the normalized degree of polarization and plots of polarization position angle versus Galactic latitude are proposed as tools for testing models against observations.

Pavel, Michael D., E-mail: pavelmi@bu.edu [Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)

2011-10-10

429

Solving constrained optimization problems with hybrid particle swarm optimization  

NASA Astrophysics Data System (ADS)

Constrained optimization problems (COPs) are very important in that they frequently appear in the real world. A COP, in which both the function and constraints may be nonlinear, consists of the optimization of a function subject to constraints. Constraint handling is one of the major concerns when solving COPs with particle swarm optimization (PSO) combined with the Nelder-Mead simplex search method (NM-PSO). This article proposes embedded constraint handling methods, which include the gradient repair method and constraint fitness priority-based ranking method, as a special operator in NM-PSO for dealing with constraints. Experiments using 13 benchmark problems are explained and the NM-PSO results are compared with the best known solutions reported in the literature. Comparison with three different meta-heuristics demonstrates that NM-PSO with the embedded constraint operator is extremely effective and efficient at locating optimal solutions.

Zahara, Erwie; Hu, Chia-Hsin

2008-11-01

430

Constrained recycling: a framework to reduce landfilling in developing countries.  

PubMed

This article presents a model that integrates three branches of research: (i) economics of solid waste that assesses consumer's willingness to recycle and to pay for disposal; (ii) economics of solid waste that compares private and social costs of final disposal and recycling; and (iii) theories on personal attitudes and social influence. The model identifies two arenas where decisions are made: upstream arena, where residents are decision-makers, and downstream arena, where municipal authorities are decision-makers, and graphically proposes interactions between disposal and recycling, as well as the concept of 'constrained recycling' (an alternative to optimal recycling) to guide policy design. It finally concludes that formative instruments, such as environmental education and benchmarks, should be combined with economic instruments, such as subsidies, to move constraints on source separation and recycling in the context of developing countries. PMID:23129605

Diaz, Ricardo; Otoma, Suehiro

2012-11-04

431

Constrained dynamics of an inertial particle in a turbulent flow  

NASA Astrophysics Data System (ADS)

Most of theoretical and numerical works for free advected particles in a turbulent flow, which only consider the drag force acting on the particles, fails to predict recent experimental results for the transport of finite size particles. These questions have motivated a series of experiments trying to emphasize the actual role of the drag force by imposing this one as an unambiguous leading forcing term acting on a particle in a turbulent background. This is achieved by considering the constrained dynamics of towed particles in a turbulent environment. In the present work, we focus on the influence of particles inertia on its velocity and acceleration Lagrangian statistics and energy spectral density. Our results are consistent with a filtering scenario resulting from the viscous response time of an inertial particle whose dynamics is coupled to the surrounding fluid via strong contribution of drag.

Obligado, M.; Baudet, C.; Gagne, Y.; Bourgoin, M.

2011-12-01

432

Fast algorithm and architecture for constrained adaptive sidelobe cancellation  

NASA Astrophysics Data System (ADS)

This paper describes an efficient implementation of auxiliary constraints for a concurrent block least squares adaptive sidelobe canceller when a single array of sensors is used to form one or more main beams. The approach is to compute QR decomposition of the auxiliary data matrix and then send this information to main beam processors, where the constraints are applied using a blocking matrix and the individual residuals are computed. The blocking matrix can be chosen with special structure which is used to derive a new fast algorithm and architecture for constrained main beam processing that reduces the operation count from order n3 to order n2, where n is the number of auxiliary sensors.

Games, Richard A.; Eastman, Willard L.; Sousa, Michael J.

1991-12-01

433

A dynamic hybrid framework for constrained evolutionary optimization.  

PubMed

Based on our previous work, this paper presents a dynamic hybrid framework, called DyHF, for solving constrained optimization problems. This framework consists of two major steps: global search model and local search model. In the global and local search models, differential evolution serves as the search engine, and Pareto dominance used in multiobjective optimization is employed to compare the individuals in the population. Unlike other existing methods, the above two steps are executed dynamically according to the feasibility proportion of the current population in this paper, with the purpose of reasonably distributing the computational resource for the global and local search during the evolution. The performance of DyHF is tested on 22 benchmark test functions. The experimental results clearly show that the overall performance of DyHF is highly competitive with that of a number of state-of-the-art approaches from the literature. PMID:21824851

Wang, Yong; Cai, Zixing

2011-08-04

434

Computational strategies in the dynamic simulation of constrained flexible MBS  

NASA Astrophysics Data System (ADS)

This research focuses on the computational dynamics of flexible constrained multibody systems. At first a recursive mapping formulation of the kinematical expressions in a minimum dimension as well as the matrix representation of the equations of motion are presented. The method employs Kane's equation, FEM, and concepts of continuum mechanics. The generalized active forces are extended to include the effects of high temperature conditions, such as creep, thermal stress, and elastic-plastic deformation. The time variant constraint relations for rolling/contact conditions between two flexible bodies are also studied. The constraints for validation of MBS simulation of gear meshing contact using a modified Timoshenko beam theory are also presented. The last part deals with minimization of vibration/deformation of the elastic beam in multibody systems making use of time variant boundary conditions. The above methodologies and computational procedures developed are being implemented in a program called DYAMUS.

Amirouche, F. M. L.; Xie, M.

1993-02-01

435

Evolution of Equilibrium Microstructures in Constrained Heterophase Solids  

NASA Astrophysics Data System (ADS)

Evolution of Equilibrium Microstructures in Constrained Heterophase Solids.A.ROYTBURD and J.SLUTSKER, University of Maryland, College Park, MD 20742, USA. Equilibrium microstructures during a phase transformation are calculated at displacement and load controlled deformation. The evolution of the microstuctures under deformation due to the displacement of the interfaces is modeled. The stress-strain curves which reflect the evolution of microstructure are calculated. For deformation under a strain controlled the calculated equilibrium stress-strain curves have a section with negative slope that corresponds to a negative Young's modulus. If deformation proceeds under stress control, hysteretic stress-strain curves on loading and unloading will result from a section with negative slope.

Slutsker, Julia

1996-03-01

436

Esophagus Segmentation by Spatially-Constrained Shape Interpolation  

NASA Astrophysics Data System (ADS)

The segmentation and visualization of the esophagus is helpful during planing and performing atrial ablation therapy to avoid esophageal injury. Only very few studies have addressed this segmentation problem which is challenging because the esophagus has a low contrast in medical images. In this work we present a technique to segment the esophagus based on the interpolation of Fourier descriptors of manually drawn contours. The interpolation is spatially-constrained using a dedicated correction term to avoid intersections with the convex shaped left atrial posterior wall. Our technique is fast, modality independent and achieves optimal results if at least three input contours are used. We validated our technique successfully with patient data and discuss the use of our technique in the clinical workflow.

Fieselmann, Andreas; Lautenschläger, Stefan; Deinzer, Frank; John, Matthias; Poppe, Björn

437

Limited view CT reconstruction and segmentation via constrained metric labeling  

PubMed Central

This paper proposes a new discrete optimization framework for tomographic reconstruction and segmentation of CT volumes when only a few projection views are available. The problem has important clinical applications in coronary angiographic imaging. We first show that the limited view reconstruction and segmentation problem can be formulated as a “constrained” version of the metric labeling problem. This lays the groundwork for a linear programming framework that brings metric labeling classification and classical algebraic tomographic reconstruction (ART) together in a unified model. If the imaged volume is known to be comprised of a finite set of attenuation coefficients (a realistic assumption), given a regular limited view reconstruction, we view it as a task of voxels reassignment subject to maximally maintaining consistency with the input reconstruction and the objective of ART simultaneously. The approach can reliably reconstruct (or segment) volumes with several multiple contrast objects. We present evaluations using experiments on cone beam computed tomography.

Singh, Vikas; Mukherjee, Lopamudra; Dinu, Petru M.; Xu, Jinhui; Hoffmann, Kenneth R.

2008-01-01

438

Constraining omega and bias from the Stromlo-APM survey  

SciTech Connect

Galaxy redshift surveys provide a distorted picture of the universe due to the non-Hubble component of galaxy motions. By measuring such distortions in the linear regime one can constrain the quantity {beta} = {Omega}{sup 0.6} where {Omega} is the cosmological density parameter and b is the (linear) bias factor for optically-selected galaxies. In this paper we estimate {beta} from the Stromlo-APM redshift survey by comparing the amplitude of the direction-averaged redshift space correlation function to the real space correlation function. We find a 95% confidence upper limit of {beta} = 0.75, with a `best estimate` of {beta} {approx} 0.48. A bias parameter b {approx} 2 is thus required if {Omega} {equivalent_to} 1. However, higher-order correlations measured from the APM galaxy survey indicate a low value for the bias parameter b {approx} 1, requiring that Q {approx_lt} 0.6.

Loveday, J.

1995-05-01

439

Bipartite entanglement induced by classically-constrained quantum dissipative dynamics  

NASA Astrophysics Data System (ADS)

The properties of some complex many body systems can be modeled by introducing in the dissipative dynamics of each single component a set of kinetic constraints that depend on the state of the neighbor systems. Here, we characterize this kind of dynamics for two quantum systems whose independent dissipative evolutions are defined by a Lindblad equation. The constraints are introduced through a set of projectors that restrict the action of each single dissipative Lindblad channel to the state of the other system. Conditions that guarantee a classical interpretation of the kinetic constraints are found. The generation and evolution of entanglement is studied for two optical qubits systems. Classically constrained dissipation leads to a stationary state whose degree of entanglement depends on the initial state. Nevertheless, independently of the initial conditions, a maximal entangled state is generated when both systems are subjected to the action of local Hamiltonian fields that do not commutate with the constraints. The underlying physical mechanism is analyzed in detail.

Budini, Adrián A.

2013-10-01

440

Constrained multiple indicator kriging using sequential quadratic programming  

NASA Astrophysics Data System (ADS)

Multiple indicator kriging (MIK) is a nonparametric method used to estimate conditional cumulative distribution functions (CCDF). Indicator estimates produced by MIK may not satisfy the order relations of a valid CCDF which is ordered and bounded between 0 and 1. In this paper a new method has been presented that guarantees the order relations of the cumulative distribution functions estimated by multiple indicator kriging. The method is based on minimizing the sum of kriging variances for each cutoff under unbiasedness and order relations constraints and solving constrained indicator kriging system by sequential quadratic programming. A computer code is written in the Matlab environment to implement the developed algorithm and the method is applied to the thickness data.

Soltani-Mohammadi, Saeed; Erhan Tercan, A.

2012-11-01

441

The Constrained Interpolation Profile Method for Multiphase Analysis  

NASA Astrophysics Data System (ADS)

We present a review of the constrained interpolation profile (CIP) method that is known as a general numerical solver for solid, liquid, gas, and plasmas. This method is a kind of semi-Lagrangian scheme and has been extended to treat incompressible flow in the framework of compressible fluid. Since it uses primitive Euler representation, it is suitable for multiphase analysis. The recent version of this method guarantees the exact mass conservation even in the framework of a semi-Lagrangian scheme. We provide a comprehensive review of the strategy of the CIP method, which has a compact support and subcell resolution, including a front-capturing algorithm with functional transformation, a pressure-based algorithm, and other miscellaneous physics such as the elastic-plastic effect and surface tension. Some practical applications are also reviewed, such as milk crown or coronet, laser-induced melting, and turbulent mixing layer of liquid-gas interface.

Yabe, Takashi; Xiao, Feng; Utsumi, Takayuki

2001-05-01

442

Entropy-constrained quantization for existing video decoders  

NASA Astrophysics Data System (ADS)

Once video coding standards are finalized, decoders are completely specified so that encoders from different providers can maintain the inter-operability. However, some of the encoding parameters such as the decision thresholds of the embedded quantizers and the buffer-control schemes still remain at designer's freedom. Taking advantage of this freedom, this paper concentrates on the design of encoders for existing decoders. More specifically, an entropy- constrained design approach is described only for the quantizer decision thresholds within encoders while the reconstruction levels and the variable-length code (VLC) table remain unchanged. The efficiency of the new method is demonstrated through an example of the well- known Lloyd-Max quantizers operating on broad-tailed generalized Gaussian distributed memoryless sources.

Kim, Yong H.; Sawada, Katsutoshi

1992-11-01

443

A new active constrained layer configuration with enhanced boundary actions  

NASA Astrophysics Data System (ADS)

In this paper, a new active constrained layer (ACL) configuration is proposed to improve the active action transmissibility of the current ACL treatment. Introducing edge elements, the active action from the piezoelectric cover sheet can be transmitted to the host structure more directly. Results from this study illustrate that, compared to the current ACL, the proposed new configuration can significantly improve the active action transmissibility while retaining a similar level of passive damping ability. In other words, it could be a more effective active - passive hybrid system. It is also shown that the new arrangement is more robust: it can outperform both the purely active and passive systems throughout a much broader design space than the current ACL.

Liao, W. H.; Wang, K. W.

1996-10-01

444

An algorithm for fully constrained abundance estimation in hyperspectral unmixing  

NASA Astrophysics Data System (ADS)

This paper presents an algorithm for abundance estimation in hyperspectral imagery. The fully constrained abundance estimation problem where the positivity and the sum to less than or equal to one (or sum equal to one) constraints are enforced is solved by reformulating the problem as a least distance (LSD) least squares (LS) problem. The advantage of reformulating the problem as a least distance problem is that the resulting LSD problem can be solved using a duality theory using a nonnegative LS problem (NNLS). The NNLS problem can then be solved using Hanson and Lawson algorithm or one of several multiplicative iterative algorithms presented in the literature. The paper presents the derivation of the algorithm and a comparison to other approaches described in the literature. Application to HYPERION image taken over La Parguera, Puerto Rico is presented.

Rosario-Torres, Samuel; Velez-Reyes, Miguel

2005-06-01

445

Constraining the MOdified Newtonian Dynamics from spherically symmetrical hydrodynamic accretion  

NASA Astrophysics Data System (ADS)

The MOdified Newtonian Dynamics (MOND) is an alternative to the dark matter assumption that can explain the observed flat rotation curve of galaxies. Here hydrodynamic accretion is considered to critically check the consistency and to constrain the physical interpretation of this theory. It is found that, in case of spherically symmetrical hydrodynamic accretion, the modified Euler's equation has real solution if the interpretation is assumed to be a modification of the law of dynamics. There is no real solution if it is assumed to be an acceleration-scale-dependent modification of the gravitational law. With the modified Euler's equation, the steady-state mass accretion rate is found to change up to ˜15 per cent. The astrophysical and cosmological implications of these results are also discussed.

Roy, Nirupam

2011-06-01

446

Do Subtle Cues About Belongingness Constrain Women's Career Choices?  

PubMed Central

Nilanjana Dasgupta’s (this issue) stereotype inoculation model (SIM) helps explain why what feels like a free choice to pursue one life path over another “is often constrained by subtle cues in achievement environments that signal who naturally belongs there and is most likely to succeed and who else is a dubious fit” (p. 231). She posits that seeing others like themselves in successful roles inoculates women against negative stereotypes that impede their success and persistence in specific achievement contexts. As is true of classic theoretical positions (see Nagel, 1961), Dasgupta presents postulates from which she deduces a specific set of hypotheses, and she reviews the relevant empirical/observational data in support of them. It is precisely what this area of research has long needed—moving beyond demonstrations of identity threats to a theory about their underlying causes, conditions, and interventions. This proposal leads her to four broad predictions, the first of which is the primary focus of our comment.

Ceci, Stephen J.; Williams, Wendy M.; Sumner, Rachel A.; DeFraine, William C.

2012-01-01

447

Adaptive matching pursuit with constrained total least squares  

NASA Astrophysics Data System (ADS)

Compressive sensing (CS) can effectively recover a signal when it is sparse in some discrete atoms. However, in some applications, signals are sparse in a continuous parameter space, e.g., frequency space, rather than discrete atoms. Usually, we divide the continuous parameter into finite discrete grid points and build a dictionary from these grid points. However, the actual targets may not exactly lie on the grid points no matter how densely the parameter is grided, which introduces mismatch between the predefined dictionary and the actual one. In this article, a novel method, namely adaptive matching pursuit with constrained total least squares (AMP-CTLS), is proposed to find actual atoms even if they are not included in the initial dictionary. In AMP-CTLS, the grid and the dictionary are adaptively updated to better agree with measurements. The convergence of the algorithm is discussed, and numerical experiments demonstrate the advantages of AMP-CTLS.

Huang, Tianyao; Liu, Yimin; Meng, Huadong; Wang, Xiqin

2012-12-01

448

Phenolate constrained geometry polymerization catalyst and method for preparing  

DOEpatents

The subject invention involves a method of preparing and the constrained geometry catalyst thereby prepared of the general formula Ar'R4(O)Ar"R'.sub.4 M(CH.sub.2 Ph).sub.2 where Ar' is a phenyl or naphthyl group; Ar" is a cyclopentadienyl or indenyl group, R and R' are H or alkyl substituents (C.ltoreq.10) and M is Ti, Zr or Hf. The synthetic method involves a simple alkane elimination approach which permits a "one-pot" procedure. The catalyst, when combined with a cocatalyst such as Pb.sub.3 C.sup.+ B(Ar.sub.3.sup.F).sub.4 BAr.sub.3.sup.F or methyl alumoxane where Ar.sup.F is a fluoroaryl group, is an effective catalyst for the polymerization of .alpha.-olefins such as ethylene, propylene and styrene.

Marks, Tobin J. (Evanston, IL); Chen, You-Xian (Chicago, IL)

1999-01-01

449

Constraining grand unification using first and second generation sfermions  

NASA Astrophysics Data System (ADS)

We investigate the spectrum of supersymmetric grand unification models based on the gauge groups SU(5), SO(10) and E6, paying particular attention to the first and second generation. We demonstrate how the measurement of the first or second generation sfermion spectrum may be used to constrain the underlying grand unification structure. The smallness of first and second generation Yukawa interactions allows us to perform an analytic analysis, deriving expressions for the high scale parameters in terms of the low scale sfermion masses. We also describe a sum rule that provides an SO(10) mass prediction, distinct from SU(5), and discuss E6 models, both with and without extra exotic matter at low energies. The derived relations are compared with numerical results including two-loop running and the full Yukawa dependence.

Miller, D. J.; Morais, A. P.; Pandita, P. N.

2013-01-01

450

A Sequential Quadratically Constrained Quadratic Programming Method of Feasible Directions  

SciTech Connect

In this paper, a sequential quadratically constrained quadratic programming method of feasible directions is proposed for the optimization problems with nonlinear inequality constraints. At each iteration of the proposed algorithm, a feasible direction of descent is obtained by solving only one subproblem which consist of a convex quadratic objective function and simple quadratic inequality constraints without the second derivatives of the functions of the discussed problems, and such a subproblem can be formulated as a second-order cone programming which can be solved by interior point methods. To overcome the Maratos effect, an efficient higher-order correction direction is obtained by only one explicit computation formula. The algorithm is proved to be globally convergent and superlinearly convergent under some mild conditions without the strict complementarity. Finally, some preliminary numerical results are reported.

Jian Jinbao [Guangxi University, College of Mathematics and Informatics Science (China)], E-mail: jianjb@gxu.edu.cn; Hu Qingjie [Hunan Business College, Department of Information (China); Tang Chunming; Zheng Haiyan [Guangxi University, College of Mathematics and Informatics Science (China)

2007-12-15

451

Recursive estimation based on the equality-constrained optimization for intersection origin–destination matrices  

Microsoft Academic Search

A fast constrained recursive identification (CRI) algorithm is proposed to estimate intersection origin–destination (O–D) matrices dynamically. The basic idea of the CRI algorithm is to estimate intersection O–D matrices based on equality-constrained optimization and then to adjust them by Bell’s correction (Bell, 1991a. The estimation of origin–destination matrices by constrained generalized least squares. Transporation Research 25B, 13–22; Bell, 1991b. The

Baibing Li; Bart De Moor

1999-01-01

452

Constraining the shallow subtropical overturning circulation with archived radiocarbon records  

NASA Astrophysics Data System (ADS)

Archived radiocarbon records in accretionary skeletons can be used to constrain the shallow overturning subtropical cells (STC's) that transport significant amounts of tropical heat poleward in the world's oceans. Radiocarbon values of DIC in the world's oceans reflect a continuum between waters residing on the surface over long periods (high ?14C due to equilibration with "modern" atmosphere) and waters decoupled from the atmosphere in the abyss (low ?14C due to radioisotope decay), as well as mixtures between water masses of different ages. Thus, measurements of radiocarbon have demonstrated utility in assessing convective heat tranport such as the Meridional Overturning Circulation that is central to global climate. A prominent radiocarbon gradient is also present between the subsiding subtropical surface waters and the upwelling equatorial surface waters in the world's oceans due to the presence of STC's. These convection cells transport a major proportion of tropical heat in the Pacific and a significant proportion of tropical heat in the Atlantic towards the poles. Archived radiocarbon records in surface corals and subsurface sclerosponges constrain the N. Atlantic STC's on a centennial time scale. Published short records from Cape Verde corals indicate significant changes in radiocarbon content; this is potentially related to migration of the front between upwelled tropical waters and downwelled subtropical waters. An approach is outlined to estimate the proportion of tropical to subtropical waters at Cape Verde using as endmembers high-resolution sclerosponge radiocarbon records from Bahamas subsurface waters and coral radiocarbon records from São Tome and Principe in the Gulf of Guinea. Preliminary data from Bahamas sclerosponges indicate the need for high-resolution subsampling of the skeletons. Initial novel AMS measurements from fine scale laser-decomposition of the skeletons are presented.

Rosenheim, B. E.; Swart, P. K.; Thorrold, S. R.; Roberts, M. L.

2007-12-01

453

Advanced techniques for constrained internal coordinate molecular dynamics.  

PubMed

Internal coordinate molecular dynamics (ICMD) methods provide a more natural description of a protein by using bond, angle, and torsional coordinates instead of a Cartesian coordinate representation. Freezing high-frequency bonds and angles in the ICMD model gives rise to constrained ICMD (CICMD) models. There are several th