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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

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

3

Enantio- and diastereoselective syntheses of cyclic Calpha-tetrasubstituted alpha-amino acids and their use to induce stable conformations in short peptides.  

PubMed

C(alpha)-tetrasubstituted alpha-amino acids are widely used to design and prepare peptides and peptide mimics with constrained conformations. Subcategories of these compounds are cyclic C(alpha)-tetrasubstituted alpha-amino acids, in which both alpha-substituents are covalently connected. This survey presents recent advances in the synthesis and application of cyclic C(alpha)-tetrasubstituted alpha-amino acids in a systematic order beginning with cyclopropane amino acids, continuing with four, five, six membered rings, and ring structures larger than six-membered. We discuss synthetic routes to the cyclic C(alpha)-tetrasubstituted alpha-amino acids and their use as conformation determining elements in peptides. PMID:18058895

Maity, Prantik; König, Burkhard

2008-01-01

4

Synthesis, structure and function of poly-alpha-amino acids--the simplest of protein models.  

PubMed

During the 1950s, linear and multichain poly-alpha-amino acids were synthesized by polymerization of the corresponding N-carboxyamino acid anhydrides in solution in the presence of suitable catalysts. The resulting homo- and heteropolymers have since been widely employed as simple protein models. Under appropriate conditions, poly-alpha-amino acids, in the solid state and in solution, were found to acquire conformations of an alpha-helix and of beta-parallel and antiparallel pleated sheets, or to exist as random coils. Their use in experimental and theoretical investigations of helix-coil transitions helped to shed new light on the mechanisms involved in protein denaturation. Conformational fluctuations of peptides in solution were analysed theoretically and studied experimentally by nonradiative energy-transfer techniques. Poly-alpha-amino acids played an important role in the deciphering of the genetic code. In addition, analysis of the antigenicity of poly-alpha-amino acids led to the elucidation of the factors determining the antigenicity of proteins and peptides. The synthetic procedures developed made possible the preparation of immobilized enzymes which were shown to be of considerable use as heterogeneous biocatalysts in the chemical and pharmaceutical industry. Interest in the biological and physicochemical characteristics of poly-alpha-amino acids was recently renewed because of the reported novel findings that some copolymers of amino acids are effective as drugs in multiple sclerosis, and that glutamine repeats and reiteration of other amino acids occur in inherited neurodegenerative diseases. PMID:9413549

Katchalski-Katzir, E

1997-10-01

5

Synthesis and evaluation of new omega-borono-alpha-amino acids as rat liver arginase inhibitors.  

PubMed

Recent studies have demonstrated that arginase plays important roles in pathologies such as asthma or erectile dysfunctions. We have synthesized new omega-borono-alpha-amino acids that are analogues of the previously known arginase inhibitors S-(2-boronoethyl)-l-cysteine (BEC) and 2-amino-6-boronohexanoic acid (ABH) and evaluated them as inhibitors of purified rat liver arginase (RLA). In addition to the distance between the B(OH)(2) and the alpha-amino acid functions, the position of the sulfur atom in the side chain also appears as a key determinant for the interaction with the active site of RLA. Furthermore, substitution of the alkyl side chain of BEC by methyl groups and conformational restriction of ABH by incorporation of its side chain in a phenyl ring led to inactive compounds. These results suggest that subtle interactions govern the affinity of inhibitors for the active site of RLA. PMID:15755639

Busnel, Olivier; Carreaux, François; Carboni, Bertrand; Pethe, Stephanie; Goff, Sandrine Vadon-Le; Mansuy, Daniel; Boucher, Jean-Luc

2005-04-01

6

Using enantioselective indicator displacement assays to determine the enantiomeric excess of alpha-amino acids.  

PubMed

Enantioselective indicator displacement assays (eIDAs) were used for the determination of enantiomeric excess (ee) of alpha-amino acids as an alternative to the labor-intensive technique of chromatography. In this study, eIDAs were implemented by the use of two chiral receptors [(Cu(II)(1)](2+), [Cu(II)(2)](2+)) in conjunction with the indicator chrome azurol S. The two receptors were able to enantioselectively discriminate 13 of the 17 analyzed alpha-amino acids. Enantiomeric excess calibration curves were made using both receptors and then used to analyze true test samples to check the system's ability to determine ee accurately. The proposed method uses a conventional UV-vis spectrophotometer to monitor the colorimetric signal, which allows for a potential high-throughput screening (HTS) method for determining ee. The techniques created consistently produced results accurate enough for rapid preliminary determination of ee. PMID:18714996

Leung, Diana; Folmer-Andersen, J Frantz; Lynch, Vincent M; Anslyn, Eric V

2008-09-17

7

Stereocontrolled routes to beta,beta'-disubstituted alpha-amino acids.  

PubMed

Owing to their significant abundance in natural products, chiral beta,beta'-disubstituted alpha-amino acids remain an important synthetic objective. Emphasis has been focused in this critical review on the great diversity of enantio- and diastereoselective methodologies to reach these highly functionalized compounds. The oldest and cutting edge synthetic methods are described in parallel with the synthesis of many relevant biologically active targets (224 references). PMID:19551183

Michaux, Julien; Niel, Gilles; Campagne, Jean-Marc

2009-07-01

8

Amino acids of the Murchison meteorite. I - Six carbon acyclic primary alpha-amino alkanoic acids  

NASA Technical Reports Server (NTRS)

Six of the seven chain isomers of six-carbon acyclic primary alpha-amino alkanoic acids (leucine isomers) have been either identified or confirmed in hot-water extracts of the Murchison meteorite using combined gas chromatography-mass spectrometry (GC-MS) and ion exchange chromatography. 2-Amino-2-ethylbutyric acid, 2-amino-2,3-dimethylbutyric acid, pseudoleucine, and 2-methylnorvaline were positively identified by GC-MS. These amino acids have not been previously reported to occur in natural materials and may be uniquely meteoritic in origin. The presence of leucine and isoleucine (including the diastereoisomer, alloisoleucine) was confirmed. Peaks corresponding to norleucine were seen by ion-exchange and gas chromatography but characteristic mass spectra were not obtained. The alpha-branched chain isomers in this series are quantitatively the most significant. These results are compared with literature data on amino acid synthesis by electrical discharge and Fischer-Tropsch-type catalysis. Neither model system produces an amino acid suite that is completely comparable to that found in the Murchison meteorite.

Cronin, J. R.; Gandy, W. E.; Pizzarello, S.

1981-01-01

9

Amino acids of the Murchison meteorite: I. Six carbon acyclic primary alpha-amino alkanoic acids.  

PubMed

Six of the seven chain isomers of six-carbon acyclic primary alpha-amino alkanoic acids (leucine isomers) have been either identified or confirmed in hot-water extracts of the Murchison meteorite using combined gas chromatography-mass spectrometry (GC-MS) and ion exchange chromatography. 2-Amino-2-ethylbutyric acid, 2-amino-2,3-dimethylbutyric acid, pseudoleucine, and 2-methylnorvaline were positively identified by GC-MS. These amino acids have not been previously reported to occur in natural materials and may be uniquely meteoritic in origin. The presence of leucine and isoleucine (including the diastereoisomer, alloisoleucine) was confirmed. Peaks corresponding to norleucine were seen by ion-exchange and gas chromatography but characteristic mass spectra were not obtained. The alpha-branched chain isomers in this series are quantitatively the most significant. These results are compared with literature data on amino acid synthesis by electrical discharge and Fischer-Tropsch-type catalysis. Neither model system produces an amino acids suite that is completely comparable to that found in the Murchison meteorite. PMID:7277509

Cronin, J R; Gandy, W E; Pizzarello, S

1981-01-01

10

Selective photodestruction of alpha-amino acids. [in carbonaceous chondrites and chemical evolution experiments  

NASA Technical Reports Server (NTRS)

A problem encountered in the analysis of amino acids in chemical evolution experiments and in extracts of meteorites is the large number present. A method for selectively destroying the alpha-amino acids, with only the beta- and gamma-amino acids remaining in the solution, is described. The amino acids used were racemic, with one milliliter of solution containing 0.0000025 mol of each acid irradiated in a 1-cm quartz cell having 254-nm monochromatic light in the presence of CuCl2. Excess H2S was added to precipitate the Cu (2+) as CuS. A gas chromatographic analysis was used to observe that irradiation with 254-nm light in the presence of Cu (2+) destroyed all the amino acids except the beta and the gamma types. It is concluded that with such a procedure, complex mixtures of amino acids can be simplified to make identification by GC mass spectrometry easier.

Levi, N.; Lawless, J. G.

1978-01-01

11

Synthesis, physicochemical and biological properties of poly-alpha-amino acids--the simplest of protein models.  

PubMed

During the 1950s, linear and multichain poly-alpha-amino acids were synthesized by polymerization of the corresponding N-carboxy-amino acid anhydrides in solution in the presence of suitable catalysts. The resulting homo- and heteropolymers have since been widely employed as simple protein models. Under appropriate conditions, poly-alpha-amino acids, in the solid state and in solution, were found to acquire conformations of an alpha-helix and of beta-parallel and antiparallel pleated sheets, or to exist as random coils. Their use in experimental and theoretical investigations of helix-coil transitions helped to shed new light on the mechanisms involved in protein denaturation. Poly-alpha-amino acids played an important role in the deciphering of the genetic code. In addition, analysis of the antigenicity of poly-alpha-amino acids led to the elucidation of the factors determining the antigenicity of proteins and peptides. Interest in the biological and physicochemical characteristics of poly-alpha-amino acids was recently renewed because of the reported novel findings that some copolymers of amino acids are effective as drugs in multiple sclerosis, and that glutamine repeats and reiteration of other amino acids occur in inherited neurodegenerative diseases. The presence of repeating sequences of amino acids in proteins, and of nucleotides in DNA, raises many interesting questions about their respective roles in determining protein structure and function, and gene performance and regulation. PMID:8790726

Katchalski-Katzir, E

1996-01-01

12

Practical synthesis of fluorous oxazolidinone chiral auxiliaries from alpha-amino acids.  

PubMed

[reaction: see text] A series of new fluorous-supported oxazolidinone chiral auxiliaries has been prepared using a versatile and general five-step pathway, starting from readily available chiral alpha-amino acids. The key feature of this synthesis is the efficient generation of a suitably active perfluoroalkyllithium species. By use of this protocol, the auxiliaries can be obtained in high enantiomeric purity and on multigram scales from L-phenylalanine and L-valine with overall yields as high as 55%. The new methodology also incorporates fluorous solid-phase extraction on the large scale, allowing bulk quantities (up to 25 g) of fluorous compounds to be purified from the crude reaction mixture. PMID:16292825

Hein, Jason E; Geary, Laina M; Jaworski, Ashley A; Hultin, Philip G

2005-11-25

13

An expedient and practical method for the synthesis of a diverse series of cyclopropane alpha-amino acids and amines.  

PubMed

A practical synthesis for the preparation of a diverse series of cyclopropane alpha-amino acids is described. Nitrocyclopropane carboxylates can be readily prepared through treatment of alpha-nitroesters and iodobenzene diacetate or alpha-nitro-alpha-diazoesters with a Rh(II) catalyst and an olefin. Reduction of the nitro group using zinc/HCl in i-PrOH affords substituted cyclopropane alpha-amino esters in modest to high yields (54-99%). A "one-pot" procedure involving sequential cyclopropanation and reduction is described. The method can also be applied to the preparation of arylcyclopropyl amines (three examples). PMID:14961679

Wurz, Ryan P; Charette, André B

2004-02-20

14

3D Structure Modeling of Alpha-Amino Acid Ester Hydrolase from Xanthomonas rubrilineans  

PubMed Central

Alpha-amino acid ester hydrolase (EC 3.1.1.43, AEH) is a promising biocatalyst for the production of semi-synthetic ?-lactam antibiotics, penicillins and cephalosporins. The AEH gene from Xanthomonas rubrilineans (XrAEH) was recently cloned in this laboratory. The three-dimensional structure of XrAEH was simulated using the homology modeling method for rational design experiments. The analysis of the active site was performed, and its structure was specified. The key amino acid residues in the active site - the catalytic triad (Ser175, His341 and Asp308), oxyanion hole (Tyr83 and Tyr176), and carboxylate cluster (carboxylate groups of Asp209, Glu310 and Asp311) - were identified. It was shown that the optimal configuration of residues in the active site occurs with a negative net charge -1 in the carboxylate cluster. Docking of different substrates in the AEH active site was carried out, which allowed us to obtain structures of XrAEH complexes with the ampicillin, amoxicillin, cephalexin, D-phenylglycine, and 4-hydroxy-D-phenylglycine methyl ester. Modeling of XrAEH enzyme complexes with various substrates was used to show the structures for whose synthesis this enzyme will show the highest efficiency.

Zarubina, S.A.; Uporov, I.V.; Fedorchuk, E.A.; Fedorchuk, V.V.; Sklyarenko, A.V.; Yarotsky, S.V.; Tishkov, V.I.

2013-01-01

15

Discrimination of enantiomers of alpha-amino acids by chiral derivatizing reagents from trans-1,2-diaminocyclohexane.  

PubMed

New chiral derivatizing reagents (CDAs) derived from trans-1,2-diaminocyclohexane, having an electron-deficient aromatic substituent (either an aromatic imide or 3,5-dinitrobenzamide) and rigid structure (either an amide or a urea linker), are reported. Significant shift differences of diastereotopic protons in the 1H NMR signals are observed for enantiomers of suitably protected alpha-amino acids, linked to CDA by a covalent bond. A simple, general model rationalizing the observed enantiomer discrimination and based on semiempirical conformational search is presented. PMID:17600850

Kaik, Magdalena; Gajewy, Jadwiga; Grajewski, Jakub; Gawronski, Jacek

2008-03-01

16

Diastereoselective functionalization of Baylis-Hillman adducts: a convenient approach to alpha-methyl-alpha-amino acids.  

PubMed

The N-tosyl carbamates 4a-e, easily prepared starting from the Baylis-Hillman adducts 3a-e, underwent cyclization carried out with I(2)/NIS in the presence of NaH, to give the corresponding 2-oxo-1,3-oxazolidines 5a-e in good yield and total stereoselection when the substituent at C-5 is Ar. After the removal of tosyl group, followed by the cleavage of the heterocyclic ring, the alpha-methyl-alpha-amino acids 8a,b and 10 were obtained in good yield as hydrochlorides. PMID:20213448

Martelli, Gianluca; Orena, Mario; Rinaldi, Samuele; Sabatino, Piera

2010-07-01

17

Dynamic kinetic resolution of amino acid amide catalyzed by D-aminopeptidase and alpha-amino-epsilon-caprolactam racemase.  

PubMed

Amino acid amide racemizing activity was discovered in alpha-amino-epsilon-caprolactam (ACL) racemase (EC 5. 1. 1. 15) from Achromobacter obae. The enzymatic synthesis of d-alanine from l-alanine amide has been demonstrated by use of d-aminopeptidase (DAP; EC 3. 4. 11. 19) from Ochrobactrum anthropi C1-38 and ACL racemase. The conversion of 45 mM l-alanine amide was carried out at 30 degrees C for 7 h; l-alanine amide was completely converted to d-alanine, and no l-alanine was detected. The result of successive enzymatic reaction shows that the combination of ACL racemase and DAP can be applied for dynamic kinetic resolution of dl-amino acid amides to yield d-amino acids. PMID:15913357

Asano, Yasuhisa; Yamaguchi, Shigenori

2005-06-01

18

Studies on the Asymmetric Synthesis of alpha-Amino Acids. Ii. New Systems for Highly Specific Asymmetric Synthesis with Conservation of the Chiral Reagent.  

National Technical Information Service (NTIS)

A new approach for the asymmetric synthesis of alpha-amino acids from alpha-keto acids has been extended with the development of a highly selective stereochemical system. The levorotatory chiral reagent 1-amino-1'-methyl indoline-2-methanol(I), has been p...

E. J. Corey H. S. Sachdev J. Z. Gougoutas W. Saenger

1969-01-01

19

Polymerization on the rocks: negatively-charged alpha-amino acids  

NASA Technical Reports Server (NTRS)

Oligomers of the negatively-charged amino acids, glutamic acid, aspartic acid, and O-phospho-L-serine are adsorbed by hydroxylapatite and illite with affinities that increase with oligomer length. In the case of oligo-glutamic acids adsorbed on hydroxylapatite, addition of an extra residue results in an approximately four-fold increase in the strength of adsorption. Oligomers much longer than the 7-mer are retained tenaciously by the mineral. Repeated incubation of short oligo-glutamic acids adsorbed on hydroxylapatite or illite with activated monomer leads to the accumulation of oligomers at least 45 units long. The corresponding reactions of aspartic acid and O-phospho-L-serine on hydroxylapatite are less effective in generating long oligomers, while illite fails to accumulate substantial amounts of long oligomers of aspartic acid or of O-phospho-L-serine.

Hill, A. R. Jr; Bohler, C.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

1998-01-01

20

Synthesis of gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids from fragmentation of gamma- and delta-lactones.  

PubMed

A noncoded amino acid of cyclomarin A (1) was synthesized in a racemic fashion. The method employs a six-membered ring template to control the relative stereochemistry and introduction of the functional groups. Ultimately, Pd-catalyzed fragmentation of the lactone provided gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids. A Pd-catalyzed ring opening of a gamma-lactone is also reported. PMID:14750809

Tarver, James E; Joullié, Madeleine M

2004-02-01

21

Alpha-amino acid phenolic ester derivatives: novel water-soluble general anesthetic agents which allosterically modulate GABA(A) receptors.  

PubMed

In the search for a novel water-soluble general anesthetic agent the activity of an alpha-amino acid phenolic ester lead, identified from patent literature, was markedly improved. In addition to improving in vivo activity in mice, good in vitro activity at GABA(A) receptors was also conferred. Within the series of compounds good enantioselectivity for both in vitro and in vivo activity was found, supporting a protein-mediated mechanism of action for anesthesia involving allosteric modulation of GABA(A) receptors. alpha-Amino acid phenolic ester 19, as the hydrobromide salt Org 25435, was selected for clinical evaluation since it retained the best overall anesthetic profile coupled with improved stability and water solubility. In the clinic it proved to be an effective intravenous anesthetic in man with rapid onset of and recovery from anesthesia at doses of 3 and 4 mg/kg. PMID:11606122

Anderson, A; Belelli, D; Bennett, D J; Buchanan, K I; Casula, A; Cooke, A; Feilden, H; Gemmell, D K; Hamilton, N M; Hutchinson, E J; Lambert, J J; Maidment, M S; McGuire, R; McPhail, P; Miller, S; Muntoni, A; Peters, J A; Sansbury, F H; Stevenson, D; Sundaram, H

2001-10-25

22

Growth Factor-Mediated Fyn Signaling Regulates alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Expression in Rodent Neocortical Neurons  

Microsoft Academic Search

Src-family protein tyrosine kinases (PTKs) transduce signals to regulate neuronal development and synaptic plasticity. However, the nature of their activators and molecular mechanisms underlying these neural processes are unknown. Here, we show that brain-derived neurotrophic factor (BDNF) and platelet-derived growth factor enhance expression of alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor 1 and 2\\/3 proteins in rodent neocortical neurons via the

Mako Narisawa-Saito; Alcino J. Silva; Tsuyoshi Yamaguchi; Takashi Hayashi; Tadashi Yamamoto; Hiroyuki Nawa

1999-01-01

23

New enzymatic method of chiral amino acid synthesis by dynamic kinetic resolution of amino acid amides: use of stereoselective amino acid amidases in the presence of alpha-amino-epsilon-caprolactam racemase.  

PubMed

D- and L-amino acids were produced from L- and D-amino acid amides by D-aminopeptidase from Ochrobactrum anthropi C1-38 and L-amino acid amidase from Pseudomonas azotoformans IAM 1603, respectively, in the presence of alpha-amino-epsilon-caprolactam racemase from Achromobacter obae as the catalyst by dynamic kinetic resolution of amino acid amides. PMID:17586677

Yamaguchi, Shigenori; Komeda, Hidenobu; Asano, Yasuhisa

2007-08-01

24

Thyroid receptor ligands. Part 8: Thyromimetics derived from N-acylated-alpha-amino acid derivatives displaying modulated pharmacological selectivity compared with KB-141.  

PubMed

Based on the scaffold of the pharmacologically selective thyromimetic 2b, structurally a close analog to KB-141 (2a), a number of novel N-acylated-alpha-amino acid derivatives were synthesized and tested in a TR radioligand binding assay as well as in a reporter cell assay. On the basis of TRbeta(1)-isoform selectivity and affinity, as well as affinity to the reporter cell assay, 3d was selected for further studies in the cholesterol-fed rat model. In this model 3d revealed an improved therapeutic window between cholesterol and TSH lowering but decreased margins versus tachycardia compared with 2a. PMID:17543524

Garg, Neeraj; Li, Yi-Lin; Garcia Collazo, Ana Maria; Litten, Chris; Ryono, Denis E; Zhang, Minsheng; Caringal, Yolanda; Brigance, Robert P; Meng, Wei; Washburn, William N; Agback, Peter; Mellström, Karin; Rehnmark, Stefan; Rahimi-Ghadim, Mahmoud; Norin, Thomas; Grynfarb, Marlena; Sandberg, Johnny; Grover, Gary; Malm, Johan

2007-08-01

25

Experimental evidence for the all-up reactive conformation of chiral rhodium(II) carboxylate catalysts: enantioselective synthesis of cis-cyclopropane alpha-amino acids.  

PubMed

Useful empirical insights onto the enantioinduction process of chiral Rh(II)-carboxylate catalysts are described in the first catalytic asymmetric cyclopropanation of alkenes with alpha-nitro diazoacetophenones. X-ray, solution NMR, and reactivity studies made on these complexes suggest that the level of asymmetric induction strongly depends on their active symmetry, which in turn relies on the nature of the chiral ligands' substituents. The catalyst's 'All Up' reactive conformation resulted in being necessary to obtain good stereoselectivity, and the resulting products are shown to be key intermediates in a concise synthesis of highly enantioenriched cis-cyclopropane alpha-amino acids. PMID:19860407

Lindsay, Vincent N G; Lin, Wei; Charette, André B

2009-11-18

26

Nootropic drugs positively modulate alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-sensitive glutamate receptors in neuronal cultures.  

PubMed

Micromolar concentrations of piracetam, aniracetam, and oxiracetam enhanced alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-stimulated 45Ca2+ influx in primary cultures of cerebellar granule cells. Nootropic drugs increased the efficacy but not the potency of AMPA and their action persisted in the presence of the voltage-sensitive calcium channel blocker nifedipine. Potentiation by oxiracetam was specific for AMPA receptor-mediated signal transduction, as the drug changed neither the stimulation of 45Ca2+ influx by kainate or N-methyl-D-aspartate nor the activation of inositol phospholipid hydrolysis elicited by quisqualate or (+-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid. Piracetam, aniracetam, and oxiracetam increased the maximal density of the specific binding sites for [3H]AMPA in synaptic membranes from rat cerebral cortex. Taken collectively, these results support the view that nootropic drugs act as positive modulators of AMPA-sensitive glutamate receptors in neurons. PMID:1372342

Copani, A; Genazzani, A A; Aleppo, G; Casabona, G; Canonico, P L; Scapagnini, U; Nicoletti, F

1992-04-01

27

Extended application of a chiral stationary phase based on (+)-(1 8-crown-6)-2,3,11,12-tetracarboxylic acid to the resolution of N-(substituted benzoyl)-alpha-amino acid amides.  

PubMed

A chiral stationary phase (CSP 1) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of N-(substituted benzoyl)-alpha-amino acid amides and esters. N-(Substituted benzoyl)-alpha-amino acid amides were well resolved using a mixture of acetic acid-triethylamine-acetonitrile (0.01:0.05:100, v/v/v) as an optimum mobile phase while N-(substituted benzoyl)-alpha-amino acid esters were not resolved at all. In contrast, both N-(substituted benzoyl)-alpha-amino acid amides and esters were not resolved at all or resolved very poorly on another CSP (CSP 2), which lacks the two N-H hydrogens of the amide tethers of CSP 1. Among the substituents on the benzoyl group of analytes, the nitro group was the best for good resolution of analytes on CSP 1. From these results, the two N-H hydrogens of the amide tethers of CSP 1, the carbonyl oxygen of the amide group of analytes, and the nitro group on the benzoyl group of analytes were concluded to play significant roles in chiral recognition. In addition, various N-(3,5-dinitrobenzoyl)leucine amides with different lengths of N-alkylamide chains were resolved on CSP 1 and N-(3,5-dinitrobenzoyl) leucine N-propylamide was found to show the best chiral recognition in terms of the separation (alpha = 1.30) and the resolution factor (Rs= 3.17). PMID:16894785

Tan, Guanghui; Xue, Jin Ying; Hyun, Myung Ho

2006-07-01

28

Glycine enolates: the effect of formation of iminium ions to simple ketones on alpha-amino carbon acidity and a comparison with pyridoxal iminium ions.  

PubMed

Equilibrium constants in D2O were determined by 1H NMR analyses for formation of imines/iminium ions from addition of glycine methyl ester to acetone and from addition of glycine to phenylglyoxylate. First-order rate constants, also determined by 1H NMR, are reported for deuterium exchange between solvent D2O and the alpha-amino carbon of glycine methyl ester and glycine in the presence of increasing concentrations of ketone and Brønsted bases. These rate and equilibrium data were used to calculate second-order rate constants for deprotonation by DO- and by Brønsted bases of the alpha-imino carbon of the ketone adducts. Formation of the iminium ion between acetone and glycine methyl ester and between phenylglyoxylate and glycine is estimated to cause 7 unit and 15 unit decreases, respectively, in the pKa's of 21 and 29 for deprotonation of the parent carbon acids. The effect of formation of iminium ions to phenylglyoxylate and to 5'-deoxypyridoxal (DPL) [Toth, K.; Richard, J. P. J. Am. Chem. Soc. 2007, 129, 3013-3021] on the carbon acidity of glycine is similar. However, DPL is a much better catalyst than phenylglyoxylate of deprotonation of glycine, because of the exceptionally large thermodynamic driving force for conversion of the amino acid and DPL to the reactive iminium ion. PMID:18198876

Crugeiras, Juan; Rios, Ana; Riveiros, Enrique; Amyes, Tina L; Richard, John P

2008-02-13

29

Synthesis of alpha-amino acids via asymmetric phase transfer-catalyzed alkylation of achiral nickel(II) complexes of glycine-derived Schiff bases.  

PubMed

Achiral, diamagnetic Ni(II) complexes 1 and 3 have been synthesized from Ni(II) salts and the Schiff bases, generated from glycine and PBP (7) and PBA (11), respectively, in MeONa/MeOH solutions. The requisite carbonyl-derivatizing agents pyridine-2-carboxylic acid(2-benzoyl-phenyl)-amide 7 (PBP) and pyridine-2-carboxylic acid(2-formyl-phenyl)-amide 11 (PBA) were readily prepared from picolinic acid and o-aminobenzophenone or picolinic acid and methyl o-anthranilate, respectively. The structure of 1 was established by X-ray crystallography. Complexes 1 and 3 were found to undergo C-alkylation with alkyl halides under PTC conditions in the presence of beta-naphthol or benzyltriethylammonium bromide as catalysts to give mono- and bis-alkylated products, respectively. Decomposition of the complexes with aqueous HCl under mild conditions gave the required amino acids, and PBP and PBA were recovered. Alkylation of 1 with highly reactive alkyl halides, carried out under the PTC conditions in the presence of 10% mol of (S)- or (R)-2-hydroxy-2'-amino-1,1'-binaphthyl 31a (NOBIN) and/or its N-acyl derivatives and by (S)- or (R)-2-hydroxy-8'-amino-1,1'-binaphthyl 32a (iso-NOBIN) and its N-acyl derivatives, respectively, gave rise to alpha-amino acids with high enantioselectivities (90-98.5% ee) in good-to-excellent chemical yields at room temperature within several minutes. An unusually large positive nonlinear effect was observed in these reactions. The Michael addition of acrylic derivatives 37 to 1 was conducted under similar conditions with up to 96% ee. The (1)H NMR and IR spectra of a mixture of the sodium salt of NOBIN and 1 indicated formation of a complex between the two components. Implications of the association and self-association of NOBIN for the observed sense of asymmetric induction and nonlinear effects are discussed. PMID:14558835

Belokon, Yuri N; Bespalova, Natalia B; Churkina, Tatiana D; Císarová, Ivana; Ezernitskaya, Marina G; Harutyunyan, Syuzanna R; Hrdina, Radim; Kagan, Henri B; Kocovský, Pavel; Kochetkov, Konstantin A; Larionov, Oleg V; Lyssenko, Konstantin A; North, Michael; Polásek, Miroslav; Peregudov, Alexander S; Prisyazhnyuk, Vladimir V; Vyskocil, Stepán

2003-10-22

30

Effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor blockade on increased cerebral O(2) consumption in Eker rats.  

PubMed

Previous work had demonstrated that there was elevated regional cerebral O2 consumption in the brains of a tuberous sclerosis model (Eker rat). We tested the hypothesis that the increased cerebral O2 consumption was related to an increased contribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors to the control of cerebral metabolism. Young (4weeks) male control Long Evans (N=14) and Eker (N=14) rats (70-100g) were divided into control and NBQX (50mg/kg, AMPA antagonist) treated animals. Cerebral regional blood flow (14C-iodoantipyrine) and O2 consumption (cryomicrospectrophotometry) were determined in isoflurane anesthetized rats. We found significantly increased basal O2 consumption (+85%) in the cortex, hippocampus, cerebellum and pons of the Eker rats. Regional cerebral blood flow was also elevated in Eker rats at baseline (+53%) as was cerebral O2 extraction (+22%). NBQX significantly lowered O2 consumption in all regions of the Long Evans rats (-41%). Cerebral O2 consumption was lowered in the cortex to a lesser extent (-24%) and there were no changes in other regions of the Eker rats after NBQX. Cerebral blood flow was reduced in the Long Evans, but not the Eker rats, after NBQX. In conclusion, Eker rats had significantly elevated cerebral O2 consumption, O2 extraction and blood flow, but this was not related to AMPA receptor activation. In fact, the importance of AMPA receptors in the control of basal cerebral O2 consumption was reduced. PMID:19686708

Weiss, Harvey R; Liu, Xia; Hunter, Christine; Z Chi, Oak

2009-10-19

31

Modulation of DL-. alpha. -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/quisqualate receptors by phospholipase A sub 2 : A necessary step in long-term potentiation  

SciTech Connect

The effects of kainate (KA)-induced epileptic seizures on the binding properites of hippocampal glutamate receptors, on the modulation of DL-{alpha}-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/quisqualate receptor by phospholipase A{sub 2} (PLA{sub 2}), and on the formation of long-term potentiation (LTP) were studied in hippocampal membranes and hippocampal slices. Systemic administration of KA produced specific changes in the binding properties of the AMPA/quisqualate receptors and its regulation. Whereas the binding of various ligands to the N-methyl-D-aspartate receptors was not modified by KA treatment, there was a singificant decrease in the maximal number of binding sites for ({sup 3}H)AMPA. The loss of LTP was not due to changes in postsynaptic responses elicited by the bursts that trigger the potentiation effect, thus suggesting that KA treatment disrupts processes that follow N-methyl-D-aspartate receptor activation. Systemic administration of KA was associated with calpain activation as the amount of spectrin breakdown products was increased severalfold in hippocampus but not in cerebellum. Pretreatment of telencephalic membranes with calpain greatly reduced the PLA{sub 2}-induced increase in ({sup 3}H)AMPA binding. The results provide evidence in favor of an essential role of PLA{sub 2} in the development of LTP and suggest that the order of activation of different calcium-dependent processes is critical for producing the final changes underlying LTP.

Massicotte, G.; Baudry, M. (Univ. of Southern California, Los Angeles (United States)); Vanderklish, P.; Lynch, G. (Univ. of California, Irvine (United States))

1991-03-01

32

DNA cleavage in red light promoted by copper(II) complexes of alpha-amino acids and photoactive phenanthroline bases.  

PubMed

Ternary copper(II) complexes [Cu(L-trp)(B)(H(2)O)](NO(3)) (1-3) and [Cu(L-phe)(B)(H(2)O)](NO(3)) (4-6) of L-tryptophan (L-trp) and L-phenylalanine (L-phe) having phenanthroline bases (B), viz. 1,10-phenanthroline (phen, 1 and 4), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2 and 5) and dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3 and 6), were prepared and characterized by physico-chemical techniques. Complexes 3 and 6 were structurally characterized by X-ray crystallography and show the presence of a square pyramidal (4 + 1) CuN(3)O(2) coordination geometry in which the N,O-donor amino acid (L-trp or L-phe) and N,N-donor phenanthroline base bind at the equatorial plane with an aqua ligand coordinated at the elongated axial site. Complex 3 shows significant distortion from the square pyramidal geometry and a strong intramolecular pi-pi stacking interaction between the pendant indole ring of L-trp and the planar dppz aromatic moiety. All the complexes display good binding propensity to the calf thymus DNA giving an order: 3,6 (dppz) > 2,5 (dpq) > 1,4 (phen). The binding constant (K(b)) values are in the range of 2.1 x 10(4)-1.1 x 10(6) mol(-1) with the binding site size (s) values of 0.17-0.63. The phen and dpq complexes are minor groove binders while the dppz analogues bind at the DNA major groove. Theoretical DNA docking studies on 2 and 3 show the close proximity of two photosensitizers, viz. the indole moiety of L-trp and the quinoxaline/phenazine of the dpq/dppz bases, to the complementary DNA strands. Complexes 2 and 3 show oxidative DNA double strand breaks (dsb) of supercoiled (SC) DNA forming a significant quantity of linear DNA along with the nicked circular (NC) form on photoexposure to UV-A light of 365 nm and red light of 647.1 nm (Ar-Kr laser). Complexes 1,5 and 6 show only single strand breaks (ssb) forming NC DNA. The red light induced DNA cleavage involves metal-assisted photosensitization of L-trp and dpq/dppz base resulting in the formation of a reactive singlet oxygen ((1)O(2)) species. PMID:19050783

Patra, Ashis K; Bhowmick, Tuhin; Ramakumar, Suryanarayanarao; Nethaji, Munirathinam; Chakravarty, Akhil R

2008-12-28

33

Hydrogen-mediated reductive coupling of conjugated alkynes with ethyl (N-Sulfinyl)iminoacetates: synthesis of unnatural alpha-amino acids via rhodium-catalyzed C-C bond forming hydrogenation.  

PubMed

Rhodium-catalyzed hydrogenation of 1,3-enynes 1a-8a and 1,3-diynes 9a-13a at ambient temperature and pressure in the presence of ethyl (N-tert-butanesulfinyl)iminoacetate and ethyl (N-2,4,6-triisopropylbenzenesulfinyl)iminoacetates, respectively, results in reductive coupling to afford unsaturated alpha-amino acid esters 1b-13b in good to excellent yields with exceptional levels of regio- and stereocontrol. Further hydrogenation of the diene containing alpha-amino acid esters 1b-8b using Wilkinson's catalyst at ambient temperature and pressure results in regioselective reduction to afford the beta,gamma-unsaturated alpha-amino acid esters 1c-8c in good to excellent yields. Exhaustive hydrogenation of the unsaturated side chains of the Boc- and Fmoc-protected derivatives of enyne and diyne coupling products 14b-16b occurs in excellent yield using Crabtree's catalyst at ambient temperature and pressure providing the alpha-amino acid esters 14d-16d, which possess saturated side chains. Finally, cross-metathesis of the Boc-protected reductive coupling product 14b with cis-1,4-diacetoxy-2-butene proceeds readily to afford the allylic acetate 14e. Isotopic labeling studies that involve reductive coupling of enyne 1a and diyne 9a under an atmosphere of elemental deuterium corroborate a catalytic mechanism in which oxidative coupling of the alkyne and imine residues is followed by hydrogenolytic cleavage of the resulting metallacycle. A stereochemical model accounting for the observed sense of asymmetric induction is provided. These studies represent the first use of imines as electrophilic partners in hydrogen-mediated reductive carbon-carbon bond formation. PMID:16089454

Kong, Jong-Rock; Cho, Chang-Woo; Krische, Michael J

2005-08-17

34

Hydrodynamic and pharmacological characterization of putative alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-sensitive L-glutamate receptors solubilized from pig brain.  

PubMed Central

L-[3H]Glutamate binding sites with characteristics resembling that of membrane-bound alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate-subtype L-glutamate receptors have been solubilized from pig brain synaptic junctions by Triton X-114. Binding of [3H]AMPA to these soluble sites in the presence of KSCN results in a curvilinear Scatchard plot that can be resolved into a high-affinity component and a low-affinity component. These Triton-X-114-solubilized sites can be further separated into two species of binding sites by gel-filtration chromatography or sucrose-density-gradient centrifugation. The pharmacological profiles of these two species of binding site are almost identical, and the rank orders of potency for glutamatergic drugs in displacing L-[3H]glutamate binding to these sites are quisqualate > 6,7-dinitroquinoxaline-2,3-dione > 6-cyano-7-nitroquinoxaline-2,3-dione > AMPA > L-glutamate > kainate >> N-methyl-D-aspartate = L-2-amino-4-phosphonobutyrate. Both sites are found to bind [3H]AMPA, and in the presence of KSCN the binding activities are significantly enhanced. Analysis of the hydrodynamic behaviour of these binding sites by sucrose-density-gradient centrifugation in H2O- and 2H2O-based solvents and gel-filtration chromatography has revealed that one of these sites (Stokes radius 8.3 nm, sedimentation coefficient 18.5 S) consists of 562 kDa protein and 281 kDa detergent, and the other site (Stokes radius 9.6 nm, sedimentation coefficient 13.4 S) consists of 352 kDa protein and 569 kDa detergent. Frictional coefficients of these sites indicate that these receptor-detergent complexes are asymmetrical in structure, consistent with large transmembrane proteins.

Wu, T Y; Chang, Y C

1994-01-01

35

Positive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor modulators have different impact on synaptic transmission in the thalamus and hippocampus.  

PubMed

Earlier studies showed that positive modulators of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors enhance synaptic responses and facilitate synaptic plasticity. Those studies focused mainly on hippocampal functions. However, AMPA receptors have regionally distinct subunit compositions and thus potencies and efficacies of modulators may vary across the brain. The present study compared the effects of CX546 [1-(1,4-benzodioxan-6-ylcarbonyl) piperidine], a benzamide-type modulator, on synaptic transmission in neurons of the reticular thalamic nucleus (RTN), which regulates the firing mode of relay cells in other thalamic nuclei, and on hippocampal CA1 pyramidal cells. CX546 greatly prolonged synaptic responses in CA1 pyramidal cells, but at the same concentration it had only weak modulatory effects in RTN neurons. Effects on miniature excitatory postsynaptic currents (EPSCs) were similar to those on EPSCs in both regions, suggesting that variations in neuronal morphology and transmitter release kinetics do not account for the differences. Relay cells in the ventrobasal thalamus also exhibited weak modulatory effects that were comparable with those in RTN neurons. Regionally different effects on response duration were also observed with CX516 [BDP-12, 1-(quinoxalin-6-ylcarbonyl)piperidine], a second benzamide drug. In contrast, 100 microM cyclothiazide produced comparable synaptic enhancements in hippocampus and RTN. The regional selectivity of benzamide drugs (ampakines) may be explained, at least in part, by a lower potency at thalamic AMPA receptors, perhaps due to the prevalence of the subunits GluR3 and 4. Although regional preferences of the ampakines were modest in their extent, they may be sufficient to be of relevance when considering future therapeutic applications of such compounds. PMID:15626725

Xia, Yan-Fang; Kessler, Markus; Arai, Amy C

2005-04-01

36

DNA cleavage by new oxovanadium(IV) complexes of N-salicylidene alpha-amino acids and phenanthroline bases in the photodynamic therapy window.  

PubMed

Oxovanadium(IV) complexes [VO(salmet)(B)] (1-3) and [VO(saltrp)(B)] (4-6), where salmet and saltrp are N-salicylidene-l-methionate and N-salicylidene-l-tryptophanate, respectively, and B is a N,N-donor heterocyclic base (viz. 1,10-phenanthroline (phen, 1, 4), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2, 5), and dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3, 6)) are prepared and characterized and their DNA binding and photoinduced DNA cleavage activity studied. Complexes 1, 2, and 4 are structurally characterized by single-crystal X-ray crystallography. The molecular structure shows the presence of a vanadyl group in the VO3N3 coordination geometry. The dianionic alpha-amino acid Schiff base acts as a tridentate O,N,O-donor ligand in a meridional binding mode. The N,N-donor heterocyclic base displays a chelating mode of bonding with a N-donor site trans to the oxo group. The complexes show a d-d band in the range of 680-710 nm in DMF with a shoulder near 840 nm. They exhibit an irreversible oxidative cyclic voltammetric response near 0.8 V assignable to the V(V)/V(IV) couple and a quasi-reversible V(IV)/V(III) redox couple near -1.1 V vs SCE in DMF-0.1 M TBAP. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range from 5.2 x 10(4) to 7.2 x 10(5) M(-1). The binding site size, thermal melting, and viscosity data suggest DNA surface and/or groove binding nature of the complexes. The complexes show poor "chemical nuclease" activity in the dark in the presence of 3-mercaptopropionic acid or hydrogen peroxide. The dpq and dppz complexes show efficient DNA cleavage activity on irradiation with UV-A light of 365 nm via a mechanistic pathway involving formation of singlet oxygen as the reactive species. They also show significant DNA cleavage activity on photoexcitation in red light (>750 nm) by (1)O2 species. Observation of red-light-induced cleavage of DNA is unprecedented in the vanadium chemistry. The DNA cleavage activity is metal promoted as the ligands or vanadyl sulfate alone are cleavage inactive on photoirradiation at these wavelengths. PMID:18020327

Sasmal, Pijus K; Patra, Ashis K; Nethaji, Munirathinam; Chakravarty, Akhil R

2007-12-24

37

Chiral high-performance liquid chromatography analysis of alpha-amino acid mixtures using a novel SH reagent--N-R-mandelyl-L-cysteine and traditional enantiomeric thiols for precolumn derivatization.  

PubMed

Several chiral thiols, i.e. traditionally used enantiomerically pure SH reagents and novel N-R-mandelyl-L-cysteine (R-NMC) containing additional chiral center, have been applied as co-reagents in precolumn derivatization with o-phthalaldehyde for enantiomeric HPLC analysis of individual alpha-amino acids and their mixtures. The R-NMC-derived isoindoles as well as adducts with other thiols have a characteristic absorption maximum at 340 nm, and are highly fluorescent allowing detection of 10 microg/l of an amino acid. Investigated 19 amino acids were analyzed separately and in a mixture by a gradient HPLC after precolumn derivatization. The chromatographic behavior of formed isoindoles substantially differs for each of the thiols used for modification. In contrast to traditional enantiomeric thiols application of diastereomeric R-NMC provides higher resolution for alpha-amino acid enantiomers, with L,D-elution order (except for Arg). Combined use of R-NMC and other thiol enlarges the possibilities of this method, allowing accurate chiral analysis of complex amino acid mixtures. PMID:17991478

Chernobrovkin, M G; Shapovalova, E N; Guranda, D T; Kudryavtsev, P A; Svedas, V K; Shpigun, O A

2007-12-14

38

Pb(II)-binding capability of aminohydroxamic acids: primary hydroxamic acid derivatives of alpha-amino acids as possible sequestering agents for Pb(II).  

PubMed

Complexes of aminohydroxamic acids, D,L-alpha-alaninehydroxamic acid (alpha-Alaha), sarcosinehydroxamic acid (Sarha), D,L-N-methyl-alpha-alaninehydroxamic acid (N-Me-alpha-Alaha), beta-alaninehydroxamic (beta-Alaha), L-aspartic acid-beta-hydroxamic acid (Asp-beta-ha), L-glutamic acid-gamma-hydroxamic acid (Glu-gamma-ha) and L-histidinehydroxamic acid (Hisha) with lead(II) in aqueous solution were studied by pH-potentiometric, 1H NMR and electrospray ionization mass spectrometric (ESI MS) methods. The results were compared to those of a simple monohydroxamic acid, acetohydroxamic acid and the effects of the amino group, hydroxamate-N, as well as, additional side chain donors on the co-ordination mode and on the stability of the complexes formed were evaluated. It was found that the amino nitrogen atom situating in beta- or in gamma-position (beta-Alaha, Asp-beta-ha, Glu-gamma-ha) does not co-ordinate to Pb(II), only hydroxamate type chelates are formed before the hydrolytic processes. However, the amino-N in alpha-position (alpha-Alaha, Sarha, Hisha) seems to form a stable 5-membered (N,N)-type chelate together with the deprotonated hydroxamate-N above pH 6. On the other hand, the hydroxamate (O,O)-type chelate also exists. Since steric reasons do not allow the coordination of these two chelates of a molecule to the same Pb(II) ion, polynuclear complexes with mixed co-ordination modes are formed with the alpha-derivatives above pH 6. Simple hydroxamate type complexes are formed with N-Me-alpha-Alaha, where the hydroxamate-N is not able to co-ordinate. The co-ordination of the side chain imidazole of Hisha is not measurable, while a weak interaction of the side chain carboxylates of Asp-beta-ha and especially of Glu-gamma-ha can be suggested. PMID:16274742

Bátka, Dávid; Farkas, Etelka

2006-01-01

39

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

40

Search for new anticonvulsant compounds. Part 1: Synthesis, physicochemical and anticonvulsant properties of new derivatives of alpha-amino-gamma-phthalimidobutyric acid.  

PubMed

Synthesis and physicochemical properties of new derivatives of alpha-substituted gamma-phthalimidobutyric acid are described. N-substituted amides of alpha-(4-phenylpiperazine)-gamma- phthalimidobutyric acid were prepared by condensation of the acid with the corresponding derivatives of benzylamine in the presence of BOP reagent. 2-(4-Phenylpiperazine)- or 2-(4-benzylpiperidine)-4-phthalimidobutyric acid were esterified with alkyl bromide in the presence of DBU or tetrabutylammonium bromide as catalyst. The obtained compounds were evaluated for anticonvulsant activity. 2-(4-Phenylpiperazine)-4-phthalimidobutyric acid and three N-substituted amides of this acid displaced protection against MES and scMet-induced seizures. PMID:8570669

Malawska, B; Zejc, A

1995-11-01

41

Petasis Borono-Mannich reaction and allylation of carbonyl compounds via transient allyl boronates generated by palladium-catalyzed substitution of allyl alcohols. an efficient one-pot route to stereodefined alpha-amino acids and homoallyl alcohols.  

PubMed

An efficient one-pot procedure was designed by integration of the pincer-complex-catalyzed borylation of allyl alcohols in the Petasis borono-Mannich reaction and in allylation of aldehydes and ketones. These procedures are suitable for one-pot synthesis of alpha-amino acids and homoallyl alcohols from easily available allyl alcohol, amine, aldehyde, or ketone substrates. In the presented transformations, the active allylating agents are in situ generated allyl boronic acid derivatives. These transient intermediates are proved to be reasonably acid-, base-, alcohol-, water-, and air-stable species, which allows a high level of compatibility with the reaction conditions of the allylation of various aldehyde/ketone and imine electrophiles. The boronate source of the reaction is diboronic acid or in situ hydrolyzed diboronate ester ensuring that the waste product of the reaction is nontoxic boric acid. The regio- and stereoselectivity of the reaction is excellent, as almost all products form as single regio- and stereoisomers. The described procedure is suitable to create quaternary carbon centers in branched allylic products without formation of the corresponding linear allylic isomers. Furthermore, products comprising three stereocenters were formed as single products without formation of other diastereomers. Because of the highly disciplined consecutive processes, up to four-step, four-component transformations could be performed selectively as a one-pot sequence. For example, stereodefined pyroglutamic acid could be prepared from a simple allyl alcohol, a commercially available amine, and glyoxylic acid in a one-step procedure. The presented method also grants an easy access to stereodefined 1,7-dienes that are useful substrates for Grubbs ring-closing metathesis. PMID:17929926

Selander, Nicklas; Kipke, Andreas; Sebelius, Sara; Szabó, Kalman J

2007-11-01

42

Chiral oxime ethers in asymmetric synthesis. O-(1-Phenylbutyl)benzyloxyacetaldoxime, a versatile reagent for the asymmetric synthesis of protected 1,2-aminoalcohols, alpha-amino acid derivatives, and 2-hydroxymethyl nitrogen heterocycles including iminosugars.  

PubMed

Addition of a range of organolithium and Grignard reagents to (E)-O-(1-phenylbutyl)benzyloxyacetaldoxime 1 in the presence of boron trifluoride diethyl etherate is highly diastereoselective. The resulting hydroxylamines undergo N-O bond cleavage upon treatment with zinc-acetic acid or molybdenum hexacarbonyl to give, after N-protection, protected 1,2-aminoalcohols 3 in high enantiomeric purity. Debenzylation of 3a and 3d gave N-Boc (R)-alaninol and (S)-phenylalaninol respectively. The hydroxylamines 2 also serve as alpha-amino acid precursors, 2i being converted into N-formyl-(R)-alaninyl-(S)-(4-bromo)phenylalanine ester 7, the N-terminal dipeptide of a natural depsipeptide. The versatility of the 1,2-aminoalcohol derivatives was further illustrated by their conversion into 5-, 6- and 7-membered 2-hydroxymethyl nitrogen heterocycles 15-19 in high enantiomeric excess by a ring-closing metathesis reaction. Further reaction of the dihydropyrrole 15 gave the iminosugar 1,4-dideoxy-1,4-imino-D-ribitol. PMID:15785815

Cooper, Tracey S; Larigo, Alexander S; Laurent, Pierre; Moody, Christopher J; Takle, Andrew K

2005-04-01

43

Chiral separation of phosphine-containing alpha-amino acid derivatives using two complementary cellulosic stationary phases in supercritical fluid chromatography.  

PubMed

Enantiomeric separations of six amino-acid derivatives have been studied using packed-column supercritical fluid chromatography with two polysaccharide-based enantioselective stationary phases: cellulose tris(3,5-dimethylphenylcarbamate) and cellulose tris(3-chloro-4-methylphenylcarbamate) (Lux Cellulose-1 and -2). The effect of analyte structure on retention and separation was studied. Varied mobile phase compositions were investigated: alcohol modifier percentage was increased from 3 to 40% but smaller amounts were most effective in separating these compounds. Besides, ethanol was preferred to methanol or isopropanol as it proved to be a good compromise to achieve sufficient resolution in a reasonable analysis time. Moreover, a carbon dioxide-ethanol mixture allows performing analyses in safe and green conditions. The effect of temperature at constant mobile phase composition was explored between 10 and 40 degrees C. In most cases, increasing the temperature improved the chiral separation, up to an optimum temperature. The results are discussed in line with the structure variation of the racemic derivatives analyzed and the two columns are compared. The two columns were shown to provide complementary selectivities for the investigated solutes: whereas Lux 1 provided separation for five of the six racemates, Lux 2 could resolve the last racemic mixture. Finally, optimized conditions of separation are defined. PMID:19551878

West, Caroline; Bouet, Alexis; Gillaizeau, Isabelle; Coudert, Gerard; Lafosse, Michel; Lesellier, Eric

2010-02-01

44

A role for alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid GluR1 phosphorylation in the modulatory effects of appetitive reward cues on goal-directed behavior.  

PubMed

Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor regulation has been shown to be critically involved in synaptic plasticity underlying learning and memory. This regulation occurs through trafficking of the receptor and modulation of the receptor's channel properties, both of which depend on protein phosphorylation. Using homologous recombination (knock-in) techniques we targeted two phosphorylation sites on the AMPA-GluR1 receptor: the Ser831 site, phosphorylated by calcium calmodulin-dependent protein kinase II/protein kinase C, and the Ser845 site, phosphorylated by protein kinase A. Mice with mutations that prevented phosphorylation at one or both of these sites were tested on a single-outcome Pavlovian-instrumental transfer task often used to assess the acquisition of incentive motivation by cues for food reinforcement. Mice were separately trained to associate a Pavlovian cue with food and to perform an instrumental lever-press response to earn that same reward. During a transfer test, the cue was presented while the mice were lever-pressing under extinction conditions. Whereas wild-type control mice showed substantial enhancement of lever-pressing when the cue was presented (i.e. showed Pavlovian-instrumental transfer), mice with mutations at both of these phosphorylation sites showed no evidence of such transfer. By contrast, mice with either serine site mutated alone showed normal transfer. These results suggest critical roles for GluR1 phosphorylation pathways in a form of incentive learning that can play an important part in regulating normal motivated behavior as well as maladaptive behaviors such as addiction and eating disorders. PMID:18598267

Crombag, Hans S; Sutton, Jeffrey M; Takamiya, Kogo; Holland, Peter C; Gallagher, Michela; Huganir, Richard L

2008-06-01

45

Activation of group I metabotropic glutamate receptors increases serine phosphorylation of GluR1 alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in the rat dorsal striatum.  

PubMed

Protein phosphorylation is an important mechanism for the post-translational modulation of ionotropic glutamate receptors. In this study, we investigated the regulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor GluR1 subunit phosphorylation by the stimulation of group I metabotropic glutamate receptors (mGluRs) in the rat dorsal striatum in vivo. Stimulation of group I mGluRs was found to increase GluR1 phosphorylation of Ser831 and Ser845 in phospholipase C (PLC)-coupled Ca(2+) cascades. Interactions of protein kinases activated by intracellular Ca(2+) release downstream to PLC modulate the phosphorylation state of GluR1 on Ser831 and Ser845: phosphorylation of GluR1 on Ser831 is up-regulated by the protein kinase C and calcium-calmodulin-dependent protein kinase (CaMK)/c-Jun N-terminal kinase (JNK) pathways, whereas phosphorylation of GluR1 on Ser845 is up-regulated by the protein kinase A (PKA), PKA/ERK1/2, and PKA/JNK pathways. The phosphorylation state of GluR1 on Ser831 and Ser845 and the activity of protein kinases are further regulated by protein phosphatases. These data suggest that GluR1 phosphorylation of Ser831 and Ser845 via stimulation of group I mGluRs is regulated by the interactions of PLC-coupled protein kinases and protein phosphatases in the dorsal striatum. PMID:19258522

Ahn, Sung Min; Choe, Eun Sang

2009-06-01

46

A role for alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid GluR1 phosphorylation in the modulatory effects of appetitive reward cues on goal-directed behavior  

PubMed Central

Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor regulation has been shown to be critically involved in synaptic plasticity underlying learning and memory. This regulation occurs through trafficking of the receptor and modulation of the receptor's channel properties, both of which depend on protein phosphorylation. Using homologous recombination (knock-in) techniques we targeted two phosphorylation sites on the AMPA-GluR1 receptor: the Ser831 site, phosphorylated by calcium calmodulin-dependent protein kinase II/protein kinase C, and the Ser845 site, phosphorylated by protein kinase A. Mice with mutations that prevented phosphorylation at one or both of these sites were tested on a single-outcome Pavlovian-instrumental transfer task often used to assess the acquisition of incentive motivation by cues for food reinforcement. Mice were separately trained to associate a Pavlovian cue with food and to perform an instrumental lever-press response to earn that same reward. During a transfer test, the cue was presented while the mice were lever-pressing under extinction conditions. Whereas wild-type control mice showed substantial enhancement of lever-pressing when the cue was presented (i.e. showed Pavlovian-instrumental transfer), mice with mutations at both of these phosphorylation sites showed no evidence of such transfer. By contrast, mice with either serine site mutated alone showed normal transfer. These results suggest critical roles for GluR1 phosphorylation pathways in a form of incentive learning that can play an important part in regulating normal motivated behavior as well as maladaptive behaviors such as addiction and eating disorders.

Crombag, Hans S.; Sutton, Jeffrey M.; Takamiya, Kogo; Holland, Peter C.; Gallagher, Michela; Huganir, Richard L.

2009-01-01

47

Developmental regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor subunit expression in forebrain and relationship to regional susceptibility to hypoxic/ischemic injury. I. Rodent cerebral white matter and cortex.  

PubMed

This is the first part of a two-part study to investigate the cellular distribution and temporal regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) subunits in the developing white matter and cortex in rat (part I) and human (part II). Western blot and immunocytochemistry were used to evaluate the differential expression of AMPAR subunits on glial and neuronal subtypes during the first 3 postnatal weeks in the Long Evans and Sprague Dawley rat strains. In Long Evans rats during the first postnatal week, GluR2-lacking AMPARs were expressed predominantly on white matter cells, including radial glia, premyelinating oligodendrocytes, and subplate neurons, whereas, during the second postnatal week, these AMPARs were highly expressed on cortical neurons, coincident with decreased expression on white matter cells. Immunocytochemical analysis revealed that cell-specific developmental changes in AMPAR expression occurred 2-3 days earlier by chronological age in Sprague Dawley rats compared with Long Evans rats, despite overall similar temporal sequencing. In both white and gray matter, the periods of high GluR2 deficiency correspond to those of regional susceptibility to hypoxic/ischemic injury in each of the two rat strains, supporting prior studies suggesting a critical role for Ca2+-permeable AMPARs in excitotoxic cellular injury and epileptogenesis. The developmental regulation of these receptor subunits strongly suggests that Ca2+ influx through GluR2-lacking AMPARs may play an important role in neuronal and glial development and injury in the immature brain. Moreover, as demonstrated in part II, there are striking similarities between rat and human in the regional and temporal maturational regulation of neuronal and glial AMPAR expression. PMID:16680782

Talos, Delia M; Fishman, Rachel E; Park, Hyunkyung; Folkerth, Rebecca D; Follett, Pamela L; Volpe, Joseph J; Jensen, Frances E

2006-07-01

48

Developmental regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor subunit expression in forebrain and relationship to regional susceptibility to hypoxic/ischemic injury. II. Human cerebral white matter and cortex.  

PubMed

This report is the second of a two-part evaluation of developmental differences in alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) subunit expression in cell populations within white matter and cortex. In part I, we reported that, in rat, developmental expression of Ca2+-permeable (GluR2-lacking) AMPARs correlated at the regional and cellular level with increased susceptibility to hypoxia/ischemia (H/I), suggesting an age-specific role of these receptors in the pathogenesis of brain injury. Part II examines the regional and cellular progression of AMPAR subunits in human white matter and cortex from midgestation through early childhood. Similarly to the case in the rodent, there is a direct correlation between selective vulnerability to H/I and expression of GluR2-lacking AMPARs in human brain. For midgestational cases aged 20-24 postconceptional weeks (PCW) and for premature infants (25-37 PCW), we found that radial glia, premyelinating oligodendrocytes, and subplate neurons transiently expressed GluR2-lacking AMPARs. Notably, prematurity represents a developmental window of selective vulnerability for white matter injury, such as periventricular leukomalacia (PVL). During term (38-42 PCW) and postterm neonatal (43-46 PCW) periods, age windows characterized by increased susceptibility to cortical injury and seizures, GluR2 expression was low in the neocortex, specifically on cortical pyramidal and nonpyramidal neurons. This study indicates that Ca2+-permeable AMPAR blockade may represent an age-specific therapeutic strategy for potential use in humans. Furthermore, these data help to validate specific rodent maturational stages as appropriate models for evaluation of H/I pathophysiology. PMID:16680761

Talos, Delia M; Follett, Pamela L; Folkerth, Rebecca D; Fishman, Rachel E; Trachtenberg, Felicia L; Volpe, Joseph J; Jensen, Frances E

2006-07-01

49

Enhancement of contextual fear-conditioning by putative (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor modulators and N-methyl-D-aspartate (NMDA) receptor antagonists in DBA/2J mice.  

PubMed

Previous studies demonstrated that DBA/2J (DBA) mice performed poorly while C57BL/6J (C57) mice performed normally on a number of complex learning and memory tasks. Chronic oxiracetam treatment dramatically improved the performance of DBA mice but not that of C57 mice on the Morris water task and in contextual fear conditioning. The present study demonstrates that acute treatment with nootropics, oxiracetam (10-1000 mg/kg) or aniracetam (10-100 mg/kg), and N-methyl-D-Aspartate (NMDA) antagonists, (+)-MK-801 (0.1-3 microg/kg), CPP (0.01-0.3 mg/kg), and (+)-HA-966 (0.1-3 mg/kg), administered prior to training and testing, reversed the contextual learning impairment in DBA mice in a dose-dependent manner without affecting auditory cue conditioning. These effects appeared to be independent of testing order (context vs. auditory cue tests) and were not due to state-dependent learning. The inactive stereoisomers, (-)-MK-801 and (-)-HA-966, were incapable of increasing contextual freezing in DBA mice. In DBA mice, the effects of 30 mg/kg oxiracetam and 100 mg/kg aniracetam were inhibited by the (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonists, NBQX, and GYKI-52466. The combined administration of 30 mg/kg oxiracetam and 1 microg/kg (+)-MK-801 produced an additive response. None of the pharmacological treatments altered performance in C57 mice at doses that were effective in DBA mice. These results suggest that DBA mice may be learning impaired due to altered glutamatergic receptor function. PMID:9369316

Lu, Y; Wehner, J M

1997-09-12

50

Prolonged positive modulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors induces calpain-mediated PSD-95/Dlg/ZO-1 protein degradation and AMPA receptor down-regulation in cultured hippocampal slices.  

PubMed

Prolonged exposure of cultured hippocampal slices to CX614 [2H,3H,6aH-pyrrolidino[2'',1''-3',2']1,3-oxazino[6',5'-5,4]-benzo[e]1,4-dioxan 10-one], a positive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAr) modulator, decreases receptor response to synaptic stimulation, an effect that could reflect reduced receptor expression. The present study investigates this down-regulation and its underlying mechanisms using cultured rat hippocampal slices. Chronic treatment with CX614 gradually reduced levels of glutamate receptor (GluR)1 and GluR2/3 AMPAr subunits and of their anchoring proteins synapse-associated protein 97 (SAP97) and glutamate receptor interacting protein 1 (GRIP1) through 48 h. Decline in SAP97 and GRIP1 levels was associated with increased abundance of lower molecular weight bands, suggesting degradation of these proteins. CX614 effects were partially reversible after drug removal. GluR1 and GluR2/3 down-regulation and their slow recovery were associated with similar changes in SAP97 and GRIP1 levels. Treatment with CX614 for 48 h significantly reduced AMPAr mRNA levels in hippocampus, whereas 8-h exposure did not. Blockade of ionotropic glutamate receptors prevented CX614-induced decrease in AMPAr subunits and mRNA, with regional selectivity, although an AMPAr blocker was more efficacious than an N-methyl-D-aspartate receptor blocker. Blockade of calpain activity reduced CX614-induced degradation of SAP97 and GRIP1 and prevented decreases in AMPAr subunit but not mRNA levels. Treatment with CX614 alone or in combination with glutamate receptor blockers or calpain inhibitor III did not modify lactate dehydrogenase release into culture medium, implying the absence of cell toxicity. We conclude that CX614-induced AMPAr protein loss is primarily mediated by AMPAr activation and involves calpain-dependent proteolysis of SAP97 and GRIP1. CX614-induced suppression of AMPAr gene expression is, however, calpain-independent, and all these effects are not associated with cell damage. PMID:15784649

Jourdi, Hussam; Lu, Xiaoying; Yanagihara, Ted; Lauterborn, Julie C; Bi, Xiaoning; Gall, Christine M; Baudry, Michel

2005-07-01

51

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

2002-11-01

52

Mechanism of alpha-amino-epsilon-caprolactam racemase reaction.  

PubMed

alpha-Amino-epsilon-caprolactam racemase catalyzes the exchange of the alpha-hydrogen of the substrate with deuterium during racemization in deuterium oxide. The rate of the hydrogen exchange measured by 1H NMR is lower than that of racemization in deuterium oxide for both the enantiomers. Both the enantiomers of alpha-amino-epsilon-caprolactam show an overshoot of the optical rotation during the enzymatic racemization in deuterium oxide (but not in water). This phenomenon may be attributable to a primary deuterium isotope effect at the alpha-position: alpha-deuterium isotope effects of 3.6 and 2.0 were observed for the racemization of the D and L enantiomers of alpha-amino-epsilon-caprolactam, respectively. Results of tritium-labeling experiments showed that the enzyme catalyzes both retention and inversion of configuration of the substrate with a similar probability in each turnover. Conversion of [alpha-2H]-D-alpha-amino-epsilon-caprolactam in water and unlabeled D-alpha-amino-epsilon-caprolactam in deuterium oxide into the L isomer under nearly single turnover conditions with the enzyme showed significant internal return of the alpha-hydrogen. These results support a single base mechanism for the racemization reaction catalyzed by the enzyme. PMID:3955003

Ahmed, S A; Esaki, N; Tanaka, H; Soda, K

1986-01-28

53

Incorporation of conformationally constrained beta-amino acids into peptides.  

PubMed

The use of norbornene units to induce the formation of beta-sheet and beta-turn type structures in peptides is discussed. The norbornene unit is readily prepared by a desymmetrization reaction and is easily incorporated into a peptide chain. Depending upon the exact nature of the norbornene unit, it is possible to form structures which resemble parallel beta-sheets, antiparallel beta-sheets or beta-turns. Similar peptide analogues incorporating a cis-2-amino-cyclopropane carboxylic acid unit can also be prepared. As an illustration of the application of this chemistry, a short, asymmetric synthesis of conformationally constrained metalloprotease inhibitors is presented. PMID:10946995

North, M

2000-07-01

54

Importance of the Terminal alpha -Amino Group of Bradykinin and Some Kynins on Capillary Permeability Increase.  

National Technical Information Service (NTIS)

A simple and reliable method is described for the quantitative evaluation of vascular permeability increase induced by vasoactive drugs with Evans blue labelled with iodine-125 or 131. By using this method the importance of alpha -amino group of bradykini...

S. Sugavara

1979-01-01

55

Four-component reaction for the preparation of alpha-amino phosphonates from methyleneaziridines.  

PubMed

Alpha-amino phosphonates can be rapidly assembled in moderate to good yields (42-65%) via a "one-pot" process that brings together four components through the construction of three new intermolecular bonds. PMID:19351179

Mumford, Peter M; Tarver, Gary J; Shipman, Michael

2009-05-01

56

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

57

Zinc mediated allylations of chlorosilanes promoted by ultrasound: Synthesis of novel constrained sila amino acids.  

PubMed

A simple, fast and efficient method for allylation and propargylation of chlorosilanes through zinc mediation and ultrasound promotion is reported. As a direct application of the resulting bis-allylsilanes, three novel, constrained sila amino acids are prepared for the first time. The design and synthesis of the constrained sila analogue of GABA (?-amino butyric acid) is a highlight of this work. PMID:24827151

Ramesh, Remya; Reddy, D Srinivasa

2014-05-28

58

Purification and properties of alpha-amino-epsilon-caprolactam racemase from Achromobacter obae.  

PubMed

We have purified a unique enzyme, alpha-amino-epsilon-caprolactam racemase 945-fold from an extract of Achromobacter obae by Octyl-Sepharose CL-4B and Thiopropyl-Sepharose 6B and some other chromatographies. The purified enzyme was found homogeneous by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and analytical ultracentrifugation. The enzyme has a monomeric structure with Mr approximately 50000 and a sedimentation coefficient (S20,w) of 4.28 S. The enzyme contains pyridoxal 5'-phosphate as a coenzyme. The pH optimum for the enzyme activity is approximately 9.0. D- and L-alpha-amino-epsilon-caprolactams are the only substrates. The Km values for the D- and L-isomers are, 8 and 6 mM, respectively. PMID:7160482

Ahmed, S A; Esaki, N; Soda, K

1982-12-27

59

Solid-state complexes of poly(alpha-amino acid)s and transition metal chlorides  

Microsoft Academic Search

Poly(4-vinyl pyridine) (P4VP) and dichlorotricarbonyl ruthenium(II) dimer are shown via fourier transform infrared (FTIR) analysis and group theory to form coordination crosslinks. The crosslinks occur by coordination of two pyridine groups to each Rusp{2+} metal center. As the percentage of dimer is increased, FTIR shows evidence of metal pendant groups in addition to the coordination crosslinks. Quantitative measurements from FTIR

Mary Pat McCurdie

1997-01-01

60

Solid-state complexes of poly(alpha-amino acid)s and transition metal chlorides  

NASA Astrophysics Data System (ADS)

Poly(4-vinyl pyridine) (P4VP) and dichlorotricarbonyl ruthenium(II) dimer are shown via fourier transform infrared (FTIR) analysis and group theory to form coordination crosslinks. The crosslinks occur by coordination of two pyridine groups to each Rusp{2+} metal center. As the percentage of dimer is increased, FTIR shows evidence of metal pendant groups in addition to the coordination crosslinks. Quantitative measurements from FTIR spectra are used to correlate the number of crosslinks with the amount of dimer present in the mixture. Poly(L-histidine) (PHIS) and poly(L-lysine) (PLYS) are shown to have glass transition temperatures when heated in the solid state. These transition temperatures at 169sp°C for PHIS and 178sp°C have never been reported in the literature. When combined with several first-row transition metal ions (Cosp{2+},\\ Nisp{2+},\\ Cusp{2+},\\ Znsp{2+}) PHIS forms coordination crosslinks. Differential scanning calorimetry (DSC) shows an increase in glass transition temperature for metal/PHIS complexes, with the greatest enhancement (6.9sp°C/mol% metal salt) from nickel chloride. FTIR shows evidence of coordination to both the histidine side chains and to the amide group in the backbone of PHIS. When combined with two second-row metal ions (Rusp{2+},\\ Pdsp{2+}) coordination crosslinks also form, with only histidine side chains involved in the crosslinking. Glass transition temperature is enhanced by 11.5sp°C/mol% metal salt with dichlorobisacetonitrile palladium(II). PLYS does not form coordination crosslinks in the presence of the same first-row metal ions. However, thermal and spectral data suggest a metal salts form pendant groups on the polymer chain via the carbonyl oxygen in the backbone. This metal-polymer coordination causes disruption of hydrogen bonding resulting in a decrease in the glass transition temperature with the addition of metal salts. Statistical models illustrate that ligand field stabilization is an important parameter for the prediction of a change in Tg when metal ions are added to the polymer. Statistical models also confirm that the mechanism, which changes Tg and the spectral data in PLYS/metal blends, is different than the mechanism suggested for PHIS and P4VP complexes.

McCurdie, Mary Pat

61

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

62

Does aspartic acid racemization constrain the depth limit of the subsurface biosphere?  

SciTech Connect

Previous studies of the subsurface biosphere have deduced average cellular doubling times of hundreds to thousands of years based upon geochemical models. We have directly constrained the in situ average cellular protein turnover or doubling times for metabolically active micro-organisms based on cellular amino acid abundances, D/L values of cellular aspartic acid, and the in vivo aspartic acid racemization rate. Application of this method to planktonic microbial communities collected from deep fractures in South Africa yielded maximum cellular amino acid turnover times of ~89 years for 1 km depth and 27 C and 1 2 years for 3 km depth and 54 C. The latter turnover times are much shorter than previously estimated cellular turnover times based upon geochemical arguments. The aspartic acid racemization rate at higher temperatures yields cellular protein doubling times that are consistent with the survival times of hyperthermophilic strains and predicts that at temperatures of 85 C, cells must replace proteins every couple of days to maintain enzymatic activity. Such a high maintenance requirement may be the principal limit on the abundance of living micro-organisms in the deep, hot subsurface biosphere, as well as a potential limit on their activity. The measurement of the D/L of aspartic acid in biological samples is a potentially powerful tool for deep, fractured continental and oceanic crustal settings where geochemical models of carbon turnover times are poorly constrained. Experimental observations on the racemization rates of aspartic acid in living thermophiles and hyperthermophiles could test this hypothesis. The development of corrections for cell wall peptides and spores will be required, however, to improve the accuracy of these estimates for environmental samples.

Onstott, T. C. [Princeton University] [Princeton University; Aubrey, A.D. [Jet Propulsion Laboratory, Pasadena, CA] [Jet Propulsion Laboratory, Pasadena, CA; Kieft, T L [New Mexico Institute of Mining and Technology] [New Mexico Institute of Mining and Technology; Silver, B J [Jet Propulsion Laboratory, Pasadena, CA] [Jet Propulsion Laboratory, Pasadena, CA; Phelps, Tommy Joe [ORNL] [ORNL; Van Heerden, E. [University of the Free State] [University of the Free State; Opperman, D. J. [University of the Free State] [University of the Free State; Bada, J L. [Geosciences Research Division, Scripps Instition of Oceanography, Univesity of California San Diego,] [Geosciences Research Division, Scripps Instition of Oceanography, Univesity of California San Diego,

2014-01-01

63

NMR studies of novel Schiff bases derived from L-alpha-amino methyl esters and 3-hydroxypyridin-4-carboxaldehyde.  

PubMed

Schiff bases of 3-hydroxypyridin-4-carboxaldehyde and L-alpha-amino esters as well as those derived from the structurally related amines lacking the ester function have been synthesised. In two cases a tetrahydro-1H-imidazo[4,5-c]pyridine was formed as a by-product. (1)H, (13)C, (15)N-NMR spectral data and density functional theory (DFT) calculations established the structure of all compounds. PMID:18618628

Perona, Almudena; Sanz, Dionisia; Claramunt, Rosa M; Elguero, José

2008-10-01

64

Enzymic synthesis of L-lysine from DL-alpha-amino-epsilon-caprolactam by new microbial strains.  

PubMed

The production of L-lysine from DL-alpha-amino-epsilon-caprolactam (DL-ACL) by new strains producing L-alpha-amino-epsilon-caprolactamase and aminocaprolactam racemase is described. Optimal conditions for hydrolysis of L-ACL by Cryptococcus sp. and for racemization of ACL by cells of a strain isolated in nature and identified as Pseudomonas sp. were determined. Synthesis of L-alpha-amino-epsilon-caprolactamase is induced by DL-ACL or L-lysine with the same effectivity. A positive effect of phosphates (potassium salts) on reduction of the induction lag was detected, the synthesis of this enzyme was found to be repressed by glucose and some possibilities of the reversion of this repressive effect were demonstrated. Under conditions optimal for the production of both enzymes a quantitative theoretical conversion of 10% aqueous DL-ACL to L-lysine by a mixture of native cells in a mass ratio of 1 : 2 (producer of ACL-hydrolase to producer of ACL-racemase) occurred in 8 h at 40 degrees C and pH 8.0. PMID:6816706

Plhácková, K; Vojtísek, V; Plachý, J

1982-01-01

65

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

66

The novel structure of a pyridoxal 5'-phosphate-dependent fold-type I racemase, alpha-amino-epsilon-caprolactam racemase from Achromobacter obae.  

PubMed

Alpha-amino-epsilon-caprolactam (ACL) racemase (ACLR) from Achromobacter obae catalyzes the interconversion of l- and d-ACL. ACLR belongs to the fold-type I group of pyridoxal 5'-phosphate (PLP) dependent enzymes. In this study, the first crystal structures of a fold-type I racemase are solved for the native form and epsilon-caprolactam-complexed form of ACLR at 2.21 and 2.40 A resolution, respectively. Based on the location of epsilon-caprolactam in the complex structure, the substrate-binding site is assigned between Trp49 and Tyr137. The carboxyl group of Asp210 is a reasonable candidate that recognizes the nitrogen atom of a lactam or amide in the substrate. Based on a structural comparison with fold-type III alanine racemase, Tyr137 is potentially the acid/base catalytic residue that is essential for the two-base racemization mechanism. The overall structure of ACLR is similar to that of fold-type I enzymes. A structural comparison with these enzymes explains the different reaction specificities. PMID:19146406

Okazaki, Seiji; Suzuki, Atsuo; Mizushima, Tsunehiro; Kawano, Takeshi; Komeda, Hidenobu; Asano, Yasuhisa; Yamane, Takashi

2009-02-10

67

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)] [Lawrence Berkeley National Lab., CA (United States)

1996-12-13

68

Mixed oligoureas based on constrained bicyclic and acyclic ?-amino acids derivatives: on the significance of the subunit configuration for folding.  

PubMed

The combination of a non-functionalized constrained bicyclo[2.2.2]octane motif along with urea linkages allowed the formation of a highly rigid 2.5(12/14) helical system both in solution and the solid state. In this work, we aimed at developing stable and functionalized systems as promising materials for biological applications in investigating the impact of this constrained motif and its configuration on homo and heterochiral mixed-oligourea helix formation. Di-, tetra-, hexa-, and octa-oligoureas alternating the highly constrained bicyclic motif of (R) or (S) configuration with acyclic (S)-?(3)-amino acid derivatives were constructed. Circular dichroism (CD), NMR experiments, and the X-ray crystal structure of the octamer unequivocally proved that the alternating heterochiral R/S sequences form a stable left-handed 2.5-helix in contrast to the mixed (S/S)-oligoureas, which did not adopt any defined secondary structure. We observed that the (-)-synclinal conformation around the C(?)-C(?) bond of the acyclic residues, although sterically less favorable than the (+)-synclinal conformation, was imposed by the (R)-bicyclic amino carbamoyl (BAC) residue. This highlighted the strong ability of the BAC residue to drive helical folding in heterochiral compounds. The role of the stereochemistry of the BAC unit was assessed and a model was proposed to explain the misfolding of the S/S sequences. PMID:24307359

André, Christophe; Legrand, Baptiste; Moulat, Laure; Wenger, Emmanuel; Didierjean, Claude; Aubert, Emmanuel; Averlant-Petit, Marie Christine; Martinez, Jean; Amblard, Muriel; Calmes, Monique

2013-12-01

69

The mycotoxin patulin induces intra- and intermolecular protein crosslinks in vitro involving cysteine, lysine, and histidine side chains, and alpha-amino groups.  

PubMed

As previous studies have indicated a multiple electrophilic reactivity of patulin (PAT) towards simple thiol nucleophiles, we have methodically investigated the ability of PAT to covalently crosslink proteins in vitro. By means of sodium dodecylsulphate polyacrylamide gel electrophoresis, the formation of PAT-induced intermolecular protein-protein crosslinks was clearly demonstrated for bovine serum albumin containing one thiol group per molecule, but also for the thiol-free hen egg lysozyme. Characterization of the crosslink sites was carried out by (1) modulation of the thiol groups with N-ethylimaleimide and 2-iminothiolane; (2) comparison with various known crosslinking agents, i.e. phenylenedimaleimide, glutardialdehyde, and dimethylsuberimidate, and (3) fluorescence incorporation studies using dansyl-labeled amino acids and a fluorescent glutathione derivative. The thiol group of cysteine was preferred for PAT-mediated crosslink reactions, but the side chains of lysine and histidine, and alpha-amino groups also exhibited reactivity. PAT can act both as a homobifunctional as well as a heterobifunctional crosslinking agent. The initial formation of a monoadduct with a thiol group appears to activate PAT for the subsequent reaction with an amino group, but also leads to rapid loss of further electrophilic properties when no second nucleophile for crosslink completion is available. Studies using microtubule proteins as a protein with experimentally controllable quarternary structure and a proposed cellular target for PAT toxicity emphasized the influence of specific sterical conditions on crosslink formation at low protein concentrations. Non-polymerized microtubule proteins, i.e. tubulin alpha,beta-dimers, formed a defined product with PAT consisting of an intramolecularly crosslinked beta-tubulin, whereas guanosine triphosphate- or paclitaxel-induced polymerization to microtubule-like quarternary structures prior to treatment with PAT gave rise to intermolecular crosslink formation between alpha- and beta-tubulin. In contrast, denaturated tubulin yielded none of those two new protein species, but only unspecific intramolecular crosslinks and highly crosslinked aggregates. Thus, in addition to the amino acid composition, the tertiary and quarternary superstructures of proteins appear to markedly influence their reactivity towards PAT. Under appropriate conditions, the generation of protein crosslinks could easily be observed at concentrations of PAT equal to or even below the concentration of the protein. The relevance of these novel reaction pathways of PAT demonstrated in vitro for its in vivo mechanisms of toxicity remains to be investigated. PMID:10597903

Fliege, R; Metzler, M

1999-11-30

70

Inhibition of human thymidine phosphorylase by conformationally constrained pyrimidine nucleoside phosphonic acids and their "open-structure" isosteres.  

PubMed

A series of conformationally constrained uridine-based nucleoside phosphonic acids containing annealed 1,3-dioxolane and 1,4-dioxane rings and their "open-structure" isosteres were synthesized and evaluated as potential multisubstrate-like inhibitors of the human recombinant thymidine phosphorylase (TP, EC 2.4.2.4) and TP obtained from peripheral blood mononuclear cells (PBMC). From a large set of tested nucleoside phosphonic acids, several potent compounds were identified that exhibited Ki values in the range of 0.048-1 ?M. The inhibition potency of the studied compounds strongly depended on the degree of conformational flexibility of the phosphonate moiety, the stereochemical arrangement of the sugar-phosphonate component, and the substituent at position 5 of the pyrimidine nucleobase. PMID:24462848

Košiová, Ivana; Šimák, Ond?ej; Panova, Natalya; Bud?šínský, Miloš; Petrová, Magdalena; Rejman, Dominik; Liboska, Radek; Páv, Ond?ej; Rosenberg, Ivan

2014-03-01

71

Organic reactions in water: a distinct novel approach for an efficient synthesis of alpha-amino phosphonates starting directly from nitro compounds.  

PubMed

A distinct approach for high-yielding synthesis of alpha-amino phosphonates has been discovered through three-component reaction of nitro compounds, aldehydes, or ketones and dialkyl or trialkyl phosphites using indium in dilute aqueous HCl at room temperature. This one-pot conversion consists of the following steps: (i) reduction of nitro compounds to amines, (ii) formation of imines from amines and carbonyl compounds, and (iii) hydrophosphonylation of imines. PMID:19775086

Das, Biswanath; Satyalakshmi, Gandham; Suneel, Kanaparthy; Damodar, Kongara

2009-11-01

72

Synthesis of conformationally constrained C-glycosyl alpha- and beta-amino acids and sugar-carbamino sugar hybrids via Diels-Alder reaction.  

PubMed

[structure: see text] Sugar-derived dienes undergo Diels-Alder reactions with methyl alpha-nitro acrylate and ethyl beta-nitro acrylate to form the corresponding cycloadducts which have been converted into conformationally constrained C-glycosyl alpha- and beta-amino acids. Further, these beta-amino acids are converted into sugar-carbamino sugar hybrid molecules. PMID:16288526

Jayakanthan, K; Vankar, Yashwant D

2005-11-24

73

Spontaneous generation and amplification of optical activity in alpha-amino acids by enantioselective occlusion into centrosymmetric crystals of glycine  

Microsoft Academic Search

Recent studies of crystal growth in the presence of specific additives have suggested a new approach to the generation and amplification of optical activity in initially racemic mixtures1-4. This approach is based on the observation that particular enantiomers can be selectively incorporated not only into chiral crystals5-7 but also into the opposite enantiotopic faces of centrosymmetric crystals3,4,8. If one such

I. Weissbuch; L. Addadi; Z. Berkovitch-Yellin; E. Gati; M. Lahav; L. Leiserowitz

1984-01-01

74

Impaired alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor trafficking and function by mutant huntingtin.  

PubMed

Emerging evidence from studies of Huntington disease (HD) pathophysiology suggests that huntingtin (htt) and its associated protein HAP1 participate in intracellular trafficking and synaptic function. However, it is largely unknown whether AMPA receptor trafficking, which is crucial for controlling the efficacy of synaptic excitation, is affected by the mutant huntingtin with polyglutamine expansion (polyQ-htt). In this study, we found that expressing polyQ-htt in neuronal cultures significantly decreased the amplitude and frequency of AMPAR-mediated miniature excitatory postsynaptic current (mEPSC), while expressing wild-type huntingtin (WT-htt) increased mEPSC. AMPAR-mediated synaptic transmission was also impaired in a transgenic mouse model of HD expressing polyQ-htt. The effect of polyQ-htt on mEPSC was mimicked by knockdown of HAP1 and occluded by the dominant negative HAP1. Moreover, we found that huntingtin affected mESPC via a mechanism depending on the kinesin motor protein, KIF5, which controls the transport of GluR2-containing AMPARs along microtubules in dendrites. The GluR2/KIF5/HAP1 complex was disrupted and dissociated from microtubules in the HD mouse model. Together, these data suggest that AMPAR trafficking and function is impaired by mutant huntingtin, presumably due to the interference of KIF5-mediated microtubule-based transport of AMPA receptors. The diminished strength of glutamatergic transmission could contribute to the deficits in movement control and cognitive processes in HD conditions. PMID:21832090

Mandal, Madhuchhanda; Wei, Jing; Zhong, Ping; Cheng, Jia; Duffney, Lara J; Liu, Wenhua; Yuen, Eunice Y; Twelvetrees, Alison E; Li, Shihua; Li, Xiao-Jiang; Kittler, Josef T; Yan, Zhen

2011-09-30

75

Formal nucleophilic substitution of bromocyclopropanes with amides en route to conformationally constrained ?-amino acid derivatives.  

PubMed

A chemo- and diastereoselective protocol for the formal nucleophilic substitution of 2-bromocyclopropylcarboxamides with secondary amides is described. This method allows for convergent and highly selective synthesis of trans-?-aminocyclopropane carboxylic acid derivatives. PMID:20726591

Prosser, Anthony R; Banning, Joseph E; Rubina, Marina; Rubin, Michael

2010-09-17

76

Simulated moving bed enantioseparation of amino acids employing memory effect-constrained chromatography columns.  

PubMed

Teicoplanin aglycone-based chromatography columns (Chirobiotic TAG) enable amino acid enantioseparation with aqueous mobile phases, which perfectly accommodates the distinct hydrophilicity of most amino acids. Therefore, this stationary phase constitutes a promising option in particular for preparative-scale separations that require high feed concentrations for economic operation. However, detailed studies revealed a solute-related memory effect when this column is subjected to high loadings of amino acids, conditions that prevail in SMB operation. High loadings yield an activation of the column as indicated by increased retention times when comparing finite injection chromatograms obtained before and after the column had been subjected to a concentrated amino acid feed. This effect can be slowly reversed by flushing the column with solvent devoid of amino acid. Obviously, the activation of the stationary phase needs to be accounted for in the determination of adsorption isotherms that are used for SMB design. In this work we introduce a perturbation method adapted specifically to capture the stationary phase behaviour at SMB-like conditions. The adsorption isotherms obtained from this method indeed allowed for accurate SMB design of a methionine enantioseparation as judged by the very good agreement of experimentally obtained and model-predicted purities. Furthermore, SMB operation over 3 days with constant purities (besides deviations originating from a dip in temperature) was accomplished indicating that the adsorption behaviour in the activated state is indeed time invariant and stable long-term SMB operation with these columns is principally feasible. PMID:22464004

Fuereder, Markus; Panke, Sven; Bechtold, Matthias

2012-05-01

77

Chance-constrained/stochastic linear programming model for acid rain abatement—II. Limited colinearity  

NASA Astrophysics Data System (ADS)

In Part I of this work, a deterministic model for development of acid rain abatement strategies was extended to a stochastic form through the incorporation of uncertainty in the transfer coefficients which describe long-range pollutant transport and transformation. The two extreme cases of: (i) complete dependence between transfer coefficients (i.e. colinearity); (ii) complete independence (noncolinearity) were developed. In this work, a more realistic 'middle ground' between these two extremes is investigated. This approach and its associated transfer coefficient covariance structure involve limited colinearity. A simplified linear version of the limited colinearity optimization model is employed. An application is presented which shows that a central three-state, one-receptor sub-system ('sub-airshed') in eastern North America plays a dominant role with respect to determining overall system performance characteristics. Nonlinear, nonlinearnonseparable and multiobjective extensions of the stochastic model are discussed.

Ellis, J. H.; McBean, E. A.; Farquhar, G. J.

78

Diastereoselection during 1,2-Addition of the Allylindium Reagent to alpha-Thia and alpha-Amino Aldehydes in Aqueous and Organic Solvents.  

PubMed

The stereochemistry of the indium-promoted reaction of allyl bromide with alpha-thia (PhS and MeS), disubstituted alpha-amino (Bn(2)N, Me(2)N, isoindolyl), and protected alpha-amino aldehydes (Ac and Boc) in water has been evaluated. The reactions involving the sulfur derivatives are minimally diastereoselective, indicating that the allylindium reagent is not thiophilic. Chelation is not observed and pi-facial discrimination is achieved via Felkin-Ahn transition states under the steric control of the substituents. The Garner aldehyde is also anti-diastereoselective. Interestingly, N-acetylmannosamine is appreciably responsive to chelation control and is capable of generating 90% of the syn beta-amino alcohol when reacted in a 0.5 M NH(4)Cl solution. While the alpha-dibenzylamino substituent is too bulky to enter into complexation, the alpha-dimethylamino group is not and can lead to high levels (99%) of syn diastereomer. The size of other neighboring substituents does have an impact on pi-facial discrimination in these systems and can erode the stereoselectivity accordingly. PMID:11671749

Paquette, Leo A.; Mitzel, Thomas M.; Isaac, Methvin B.; Crasto, Curtis F.; Schomer, William W.

1997-06-27

79

Aminocarbonylation of 4-iodo-1H-imidazoles with an amino acid amide nucleophile: synthesis of constrained H-Phe-Phe-NH2 analogues.  

PubMed

A simple and an expedient process to prepare 5-aryl-1-benzyl-1H-imidazole-4-carboxamides by the aminocarbonylation of 5-aryl-4-iodo-1H-imidazoles using ex situ generation of CO from Mo(CO)6 with an amino acid amide nucleophile is reported. Furthermore, a microwave-assisted protocol for the direct C-5 arylation of 1-benzyl-1H-imidazole and a regioselective C-4 iodination method to acquire starting material for our aminocarbonylation are presented. The method can be used to prepare imidazole based peptidomimetics, herein exemplified by the synthesis of constrained H-Phe-Phe-NH2 analogues. PMID:24171628

Skogh, Anna; Fransson, Rebecca; Sköld, Christian; Larhed, Mats; Sandström, Anja

2013-12-01

80

Diastereoselective synthesis of a conformationally restricted dinucleotide with predefined alpha and beta torsional angles for the construction of alpha,beta-constrained nucleic acids (alpha,beta-CNA).  

PubMed

[reaction: see text] The synthesis of a diastereopure 1,3,2-dioxaphosphorinane linkage in which two, alpha and beta, out of six torsion angles of the natural phosphodiester backbone are constrained with predefined values of ca. +60 degrees (g(+)) and 180 degrees (t), respectively, is described. The stable and unstrained six-membered cyclic phosphotriester structure represents the smallest possible ring allowing the conformational locking of the alpha torsion angle at a significant positive value that is typical of many bulged regions of nucleic acids. PMID:12529130

Le Clézio, Ingrid; Escudier, Jean-Marc; Vigroux, Alain

2003-01-23

81

Constrained poststratification.  

PubMed

Adjustment for covariates (or poststratification) is frequently used in the analysis of randomized clinical trials. The purpose of such analysis is mainly to eliminate some residual bias resulting from any imbalance between treatment groups for some important covariates. Usually, covariate effect is modeled with the data at hand. In this paper, we present a new method of poststratification ("constrained poststratification") which consists of estimating the prognostic significance of covariates in a large historical data base, transferring the model's coefficients into the (smaller) randomized trial data set, and estimating treatment effects conditional on this a priori information. In a simulated experiment, constrained poststratification allowed not only reduction of the bias but also enhancement of the efficiency of the estimation of treatment effect. PMID:3731761

Moise, A; Salamon, R; Raissis, M; Nanopoulos, P; Clement, B

1986-08-01

82

Sulfuric acid as an agent of carbonate weathering constrained by ?13C DIC: Examples from Southwest China  

NASA Astrophysics Data System (ADS)

Rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric CO 2. Current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important. Here, we use carbon isotopic evidence and water chemistry of springs and rivers from the Beipanjiang River basin (Guizhou Province, Southwest China) to demonstrate that sulfuric acid is also an important agent of rock weathering. The ?13C of dissolved inorganic carbon (DIC) in the water samples ranges from - 13.1‰ to - 2.4‰, and correlates negatively to [HCO 3-]/([Ca 2+] + [Mg 2+]) ratios and positively to [SO 42-]/([Ca 2+] + [Mg 2+]) ratios. These relationships are interpreted as mixing diagrams between two reactions of carbonate weathering, using carbonic acid and sulfuric acid as a proton donor, respectively. Mixing proportions show that around 42% of the divalent cations in the spring water from Guizhou are originated from the interaction between carbonate minerals and sulfuric acid. It is shown that 40% of this sulfuric acid is derived from the atmosphere and has an anthropogenic origin. The remaining 60% are derived from the oxidative weathering of sulfide minerals in sedimentary rocks. Our results show the positive action of sulfuric acid on the chemical weathering of carbonate. Particularly, we show that sulfuric acid generated by coal combustion has increased by almost 20% the weathering rates of carbonate in Southwest China. This is a clear evidence that human activities are changing the weathering rates of rocks and demonstrates a negative feedback on the acidification of the ocean by greenhouse gases. Because of the involvement of sulfuric acid in weathering reactions, 63% of the alkalinity exported by rivers is derived from carbonate, instead of 50% when atmospheric CO 2 is the only acid involved in chemical weathering of carbonate. In the Guizhou Province, the weathering of carbonate is thus, at least transiently, a net source of CO 2 to the atmosphere. When extrapolated at global scale, sulfuric acid-induced carbonate weathering could counterbalance a significant part of the CO 2 consumed by silicate weathering. This paper highlights the competition between silicate weathering by carbonic acid and carbonate weathering by sulfuric acid for the regulation of the atmospheric CO 2 level.

Li, Si-Liang; Calmels, Damien; Han, Guilin; Gaillardet, Jérôme; Liu, Cong-Qiang

2008-06-01

83

The Southern Ocean silicon trap: Data-constrained estimates of regenerated silicic acid, trapping efficiencies, and global transport paths  

NASA Astrophysics Data System (ADS)

We analyze an optimized model of the global silicon cycle embedded in a data-assimilated steady ocean circulation. Biological uptake is modeled by conditionally restoring silicic acid in the euphotic zone to observed concentrations where the modeled concentrations exceed the observational climatology. An equivalent linear model is formulated to which Green-function-based transport diagnostics are applied. We find that the models' opal export through 133 m depth is 166 ± 24 Tmol Si/yr, with the Southern Ocean (SO) providing ˜70% of this export, ˜50% of which dissolves above 2000 m depth. The global-scale gradients of the opal dissolution rate are primarily meridional, while the global-scale gradients of phosphate remineralization are primarily vertical. The mean depth of the temperature-dependent silicic-acid regeneration reaches 2300 m in the SO, compared to 600 m for phosphate remineralization. Silicic acid is stripped out of the euphotic zone far more efficiently than phosphate, with only (34 ± 5)% of the global silicic-acid inventory being preformed, compared to (61 ± 7)% for phosphate. Subantarctic and tropical waters contribute most of the ocean's regenerated silicic acid, while Antarctic waters provide most of the preformed silicic acid. About half of the global silicic-acid inventory is trapped in transport paths connecting successive SO utilizations, with silicic acid last utilized in the SO having only a (5 ± 2)% chance of being next utilized outside the SO. This trapping depletes subantarctic mode waters of silicic acid relative to phosphate, which has a (44 ± 2)% probability of escaping successive SO utilization.

Holzer, Mark; Primeau, François W.; DeVries, Timothy; Matear, Richard

2014-01-01

84

Prebiotic Synthesis of Hydrophobic and Protein Amino Acids  

Microsoft Academic Search

The formation of amino acids by the action of electric discharges on a mixture of methane, nitrogen, and water with traces of ammonia was studied in detail. The presence of glycine, alanine, alpha -amino-n-butyric acid, alpha -aminoisobutyric acid, valine, norvaline, isovaline, leucine, isoleucine, alloisoleucine, norleucine, proline, aspartic acid, glutamic acid, serine, threonine, allothreonine, alpha -hydroxy-gamma -aminobutyric acid, and alpha ,gamma

David Ring; Yecheskel Wolman; Nadav Friedmann; Stanley L. Miller

1972-01-01

85

Synthesis and calpain inhibitory activity of peptidomimetic compounds with constrained amino acids at the P2 position  

PubMed Central

The effect of incorporating ?,?’-diethylglycine and ?-aminocyclopentane carboxylic acid at the P2 position of inhibitors on ?-calpain inhibition was studied. Compound 3 with ?,?’-diethylglycine was over 20-fold more potent than 2 with ?-aminocyclopentane carboxylic acid. Additionally, 3 was over 35-fold selective for ?-calpain compared to cathepsin B, while 2 was 3-fold selective for cathepsin B compared to ?-calpain. Thus, the conformation induced by the P2 residue influenced the activities of the compounds versus the closely related cysteine proteases and suggests an approach to the discovery of selective ?-calpain inhibitors.

Korukonda, Rajani

2008-01-01

86

Preclinical Toxicologic Evaluation of 5-Isoxazoleacetic Acid, alpha-Amino-3-Chloro-4,5-Dihydro-(NSC 163501), in Dogs, Monkeys, and CDF1 Mice.  

National Technical Information Service (NTIS)

Dose-limiting gastrointestinal toxicosis was qualitatively similar in dogs, monkeys, and mice. In dogs and monkeys, anorexia and/or oligodipsia were cardinal signs. Severity of intoxication was indicated by progression to a diarrheal syndrome. Intoxicatio...

E. P. Denine L. D. Stout J. C. Peckham A. M. Guarino R. D. Davis

1978-01-01

87

Methyltrifluoropyruvate imines possessing N-oxalyl and N-phosphonoformyl groups--precursors to a variety of alpha-CF3-alpha-amino acid derivatives.  

PubMed

Convenient routes to methyl 2-oxalylimino- and 2-(phosphonoformimido)-3,3,3-trifluoropropanoates have been elaborated, based on the reaction of methyl trifluoropyruvate with ethyl oxamate or diethyl carbamoylphosphonate, respectively, followed by dehydration. The compounds obtained are useful synthetic intermediates toward a variety of novel 3,3,3-trifluoroalanine derivatives that are potential drug candidates. PMID:16990943

Skarpos, Hanna; Vorob'eva, Daria V; Osipov, Sergey N; Odinets, Irina L; Breuer, Eli; Röschenthaler, Gerd-Volker

2006-10-01

88

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

89

Wang-aldehyde resin as a recyclable support for the synthesis of alpha,alpha-disubstituted amino acid derivatives.  

PubMed

Merrifield resin was functionalised with hydroxybenzaldehyde under microwave irradiation. The resultant resin was used as a means for immobilisation and activation of alpha-amino acid esters for alkylation reactions. Alpha,alpha-disubstituted and cyclic amino acid esters were prepared in good yields. PMID:16106300

Guinó, Meritxell; Hii, King Kuok Mimi

2005-09-01

90

Reasons for the occurrence of the twenty coded protein amino acids  

NASA Technical Reports Server (NTRS)

Factors involved in the selection of the 20 protein L-alpha-amino acids during chemical evolution and the early stages of Darwinian evolution are discussed. The selection is considered on the basis of the availability in the primitive ocean, function in proteins, the stability of the amino acid and its peptides, stability to racemization, and stability on the transfer RNA. It is concluded that aspartic acid, glutamic acid, arginine, lysine, serine and possibly threonine are the best choices for acidic, basic and hydroxy amino acids. The hydrophobic amino acids are reasonable choices, except for the puzzling absences of alpha-amino-n-butyric acid, norvaline and norleucine. The choices of the sulfur and aromatic amino acids seem reasonable, but are not compelling. Asparagine and glutamine are apparently not primitive. If life were to arise on another planet, it would be expected that the catalysts would be poly-alpha-amino acids and that about 75% of the amino acids would be the same as on the earth.

Weber, A. L.; Miller, S. L.

1981-01-01

91

A constrained tricyclic nucleic acid analogue of ?-L-LNA: investigating the effects of dual conformational restriction on duplex thermal stability.  

PubMed

A constrained tricyclic analogue of ?-L-LNA (2), which contains dual modes of conformational restriction about the ribose sugar moiety, has been synthesized and characterized by X-ray crystallography. Thermal denaturation experiments of oligonucleotide sequences containing this tricyclic ?-L-LNA analogue (?-L-TriNA 2, 5) indicate that this modification is moderately stabilizing when paired with complementary DNA and RNA, but less stabilizing than both ?-L-LNA (2) and ?-L-TriNA 1 (4). PMID:23937256

Hanessian, Stephen; Wagger, Jernej; Merner, Bradley L; Giacometti, Robert D; Ostergaard, Michael E; Swayze, Eric E; Seth, Punit P

2013-09-20

92

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

93

Evolution from amino acids - Lunar occurrence of their precursors.  

NASA Technical Reports Server (NTRS)

Review of the present state of experimentally based concepts of organic evolution from amino acids. Earlier studies of the synthesis of amino acid precursors from meteoritic material, lunar dust, and terrestrial lava are briefly summarized, and laboratory experiments in which polymers of amino acids were obtained either by direct heating of dry amino acids or by heating aqueous solutions of mixtures of amino acids are described. In particular, a process is described by which alpha-amino acids were made to react to form linear chains of proteinoids. It is concluded that a proteinoid microsystem was a common ancestor of all life on earth.

Fox, S. W.

1972-01-01

94

Transient global ischemia enhances phosphorylation of the GluR1 subunit of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor in the hippocampal CA1 region in rats.  

PubMed

Phosphorylation of the GluR1 subunit of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor has been implicated in the regulation of the receptor channel. We investigated the effects of transient global ischemia in rats on phosphorylation of the GluR1 subunit in the hippocampal CA1 and CA3/dentate gyrus. Transient ischemia induced an increase in the phosphorylation of GluR1 at Ser831 in the CA1 at 1 h of reperfusion. In contrast, the phosphorylation of Ser845 in neither region was affected by the ischemia. The amounts of calcium/calmodulin-dependent kinase (CaMKII) and its activated form, but not cAMP-dependent protein kinase subunits, were increased in a crude membrane fraction after ischemia. The results suggest that an activated CaMKII may phosphorylate Ser831 of GluR1 and a consequent phosphorylation of GluR1 may be related to pathogenic events occurring in the vulnerable subfield of the hippocampus after transient global ischemia. PMID:12676337

Takagi, Yuko; Takagi, Norio; Besshoh, Shintaro; Miyake-Takagi, Keiko; Takeo, Satoshi

2003-04-24

95

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

96

Constrained nucleic acids (CNA). Part 2. Synthesis of conformationally restricted dinucleotide units featuring noncanonical alpha/beta/gamma or delta/epsilon/zeta torsion angle combinations.  

PubMed

Four dinucleotide building units of nucleic acids in which three out of six backbone torsion angles are included in a dioxaphosphorinane ring structure (D-CNA family) have been synthesized: two diastereoisomeric alpha,beta,gamma-D-CNA {cis and trans} and two diastereoisomeric delta,epsilon,zeta-D-CNA {(S(C4'),R(P)) and (S(C4'),S(P))}. The structural analysis of these conformationally restricted dinucleotides, using NMR spectroscopy and X-ray crystallography, shows that these D-CNA structural elements allow the stabilization of torsion angle combinations, alpha/beta/gamma and delta/epsilon/zeta, that are significantly different from those typically observed in canonical A- or B-form duplexes. PMID:15730280

Le Clézio, Ingrid; Gornitzka, Heinz; Escudier, Jean-Marc; Vigroux, Alain

2005-03-01

97

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

98

Locks with Constrained Sharing  

Microsoft Academic Search

In this paper, we propose a new mode for locks that permits sharing in a constrained manner. We develop a family of locking protocols, the strictest of which is the two phase locking protocol while the most permissive recognizes all conflict-preserving serializable histories. This is the first locking-based protocol that can recognize the entire class of conflict-preserving serializable histories.

Divyakant Agrawal; Amr El Abbadi

1990-01-01

99

Quantitative and qualitative changes in plasma amino nitrogen and amino acids during haemodialysis  

Microsoft Academic Search

Summary  Twenty-one patients undergoing haemodialysis on a coil dialyser were investigated for quantitative and qualitative changes\\u000a in plasma alpha amino nitrogen and amino acids. Blood samples obtained at the beginning and following the termination of dialysis\\u000a were analysed. There was an average fall of 29% in the level of circulating amino nitrogen during dialysis. In addition repeated\\u000a dialysis resulted in a

G. D. Doyle; W. F. O’Dwyer; M. Carmody; V. Gallagher

1924-01-01

100

Constraining primordial magnetism  

NASA Astrophysics Data System (ADS)

Primordial magnetic fields could provide an explanation for the galactic magnetic fields observed today; in which case, they may leave interesting signals in the CMB and the small-scale matter power spectrum. We discuss how to approximately calculate the important nonlinear magnetic effects within the guise of linear perturbation theory and calculate the matter and CMB power spectra including the Sunyaev-Zel’dovich contribution. We then use various cosmological data sets to constrain the form of the magnetic field power spectrum. Using solely large-scale CMB data (WMAP7, QUaD, and ACBAR) we find a 95% C.L. on the variance of the magnetic field at 1 Mpc of B?<6.4nG. When we include South Pole Telescope data to constrain the Sunyaev-Zel’dovich effect, we find a revised limit of B?<4.1nG. The addition of Sloan Digital Sky Survey Lyman-? data lowers this limit even further, roughly constraining the magnetic field to B?<1.3nG.

Shaw, J. Richard; Lewis, Antony

2012-08-01

101

Domino syntheses of bioactive tetronic and tetramic acids.  

PubMed

Natural products containing tetronic acid or tetramic acid moieties continue to attract the interest of chemists, biologists, and physicians due to their challenging structures and to the wide range of biological activities they display. This review portrays the structural varieties of tetronic and tetramic acids and the spectrum of possible therapeutically relevant effects in man for exemplary derivatives. Their biosynthetic origin from alpha-amino and alpha-hydroxy acids is briefly discussed as is the relationship between their structures and their modes of interaction with biochemical effectors such as metal cations or enzymes. A short overview of laboratory syntheses of the heterocyclic core structures of tetramic and tetronic acids is provided with an emphasis on those emulating the biosynthesis. A synthesis from the alpha-amino or alpha-hydroxy esters and the cumulated phosphorus ylide Ph(3)PCCO based upon a domino addition-intra-Wittig alkenation sequence is presented with applications to the preparation of the antibiotics reutericyclin and tenuazonic acid, the cytotoxic melophlin B, and the enzyme inhibitor RK-682. Procedural advantages of immobilizing either starting component by attaching it to a resin and its exploitation in the parallel synthesis of libraries of potential drug candidates are described. The basic domino reaction can even be extended by further C-C bond forming steps when starting from suitable alpha-hydroxy or alpha-amino allyl esters. Depending on the chosen reaction conditions, bioactive intermediates of formally three to seven step long cascades can be obtained. Among them, herbicidal 3-alkyltetronic acids and lactone endoperoxides with antiplasmodial activity exceeding that of the natural antimalarial lead artemisinin. Hence, this domino reaction gives access to diversely functionalized derivatives of tetronic and tetramic acids. As it can also be ported to solid phase, it is ideally suited for parallel and combinatorial processing. Future developments might include running such domino sequences in continuous mode in arrays of "labs on microchips". PMID:16944091

Schobert, Rainer

2007-01-01

102

Plasma amino acid quantitation using gas chromatography chemical ionization mass spectrometry and 13C amino acids as internal standards.  

PubMed

A specific and sensitive method for the quantitation of 16 alpha amino acids has been developed. The technique employed uses methane chemical ionization gas chromatography mass spectrometry of the carboxy-n-butyl, N-trifluoroacetyl amino acid derivatives. A commercial 13C amino acid mixture provided individual internal standards for 14 alpha amino acids. A computer controlled quadrupole mass spectrometer was used for selected ion monitoring of those ions characteristic of each N-trifluoroacetyl amino acid/13C amino acid pair. A BASIC computer program located peak maxima and background intensities in each selected ion recording. Standard curves for each amino acid/13C amino acid pair were utilized by the program to calculate the plasma concentration of each detected amino acid. The total instrumental analysis occupied 30 min with sample preparation and derivatization accounting for an additional 2 h. Based on the detection of known amounts of standard amino acids the method will quantitate at the 1-5 nanogram level of detection. PMID:749957

Kingston, E E; Duffield, A M

1978-11-01

103

Pyrolysis of amino acids - Mechanistic considerations  

NASA Technical Reports Server (NTRS)

Pyrolysis of several structurally different amino acids in a column at 500 C showed differences in the mechanisms and final products. The aliphatic protein amino acids decompose mainly by simple decarboxylation and condensation reactions, while the beta amino acids undergo deamination to unsaturated acids. Alpha amino acids with alpha alkyl substituents undergo an unusual intramolecular SN1 reaction with the formation of an intermediate alpha lactone which decomposes to yield a ketone. The alpha alkyl substituents appear to stabilize the developing negative charge formed by partial heterolytic cleavage of the alpha carbon - NH3 bond. The gamma and delta amino acids give 2-pyrrolidinone and 2-piperidone respectively, while the epsilon acids yield mixed products.

Ratcliff, M. A., Jr.; Medley, E. E.; Simmonds, P. G.

1974-01-01

104

Positive modulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors reverses sub-chronic PCP-induced deficits in the novel object recognition task in rats.  

PubMed

Cognitive deficits are a major clinical unmet need in schizophrenia. The psychotomimetic drug phencyclidine (PCP) is widely applied in rodents to mimic symptoms of schizophrenia, including cognitive deficits. Previous studies have shown that sub-chronic PCP induces an enduring episodic memory deficit in female Lister Hooded rats in the novel object recognition (NOR) task. Here we show that positive modulation of AMPA receptor (AMPAR) mediated glutamate transmission alleviates cognitive deficits induced by sub-chronic PCP treatment. Female Lister hooded rats were treated sub-chronically with either vehicle (0.9% saline) or PCP (2mg/kg two doses per day for 7 days), followed by a 7 days washout period. 30 min prior to the acquisition trial of the NOR task animals were dosed with either vehicle, CX546 (10, 40 or 80 mg/kg) or CX516 (0.5, 2.5, 10, 40 or 80 mg/kg). Our results show that sub-chronic PCP treatment induced a significant decrease in the discrimination index (DI) and both ampakines CX546 and CX516 were able to reverse this disruption of object memory in rats in the novel object recognition task. These data suggest that positive AMPAR modulation may represent a mechanism for treatment of cognitive deficits in schizophrenia. PMID:19822174

Damgaard, Trine; Larsen, Dorrit Bjerg; Hansen, Suzanne L; Grayson, Ben; Neill, Jo C; Plath, Niels

2010-02-11

105

Plastic changes in the cholinergic innervation of the rat cerebral cortex after unilateral lesion of the nucleus basalis with alpha-amino-3-OH-4-isoxozole propionic acid (AMPA): effects of basal forebrain transplants into neocortex.  

PubMed

Unilateral AMPA lesions of the nucleus basalis magnocellularis (nbm) produced a nearly complete loss of cholinergic markers in the ipsilateral frontal and parietal cortices with no recovery at 6 months. The loss was associated with compensatory increases in AChE-positive fibre density in the contralateral cortex, in ipsilateral cortical regions not receiving their cholinergic innervation from the nbm and in the size of cholinergic magnocellular neurones in the contralateral nbm. The hypertrophy and increase in AChE-positive fibre density were apparent at 4-6 weeks after lesion and increased with time. Cholinergic transplants to cholinergically deafferented cortex prevented development of the compensatory increases in AChE-positive fibre density and restored AChE-positive fibre density and ChAT activity to control levels in ipsilateral cholinergically deafferented regions, partially after 6-8 weeks and completely after 6 months. In contrast, when cholinergic grafts were placed into unlesioned cortex, axonal outgrowth was localized to the vicinity of the transplant and did not develop with time. These results support the concept that vacant synapses promote and direct axonal outgrowth from transplanted neurones and that grafted cholinergic neurones integrate into the lesioned forebrain cholinergic projections system and prevent the lesion-induced changes in AChE-positive fibre density and ChAT activity. PMID:8971411

Calaminici, M; Abdulla, F A; Sinden, J D; Stephenson, J D

1997-01-01

106

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

107

Release of Dissolved Amino Acids by Marine Zooplankton.  

PubMed

Marine net zooplankton release dissolved amino acids into the water. Release rates are positively correlated with temperature and can be estimated by the equation: Release rate, (milligrams of alpha-amino nitrogen per gram dry weight of zooplankton per day) = 1.0 x temperature ( degrees C) -5.9. Release rates appeared to be independent of the taxonomic composition of the test samples, which were variously dominated by copepods, salps, chaetognaths, coelenterates, or radiolarians. These amino acids constitute an important source of dissolved organic matter in the sea. PMID:17829748

Johannes, R E; Webb, K L

1965-10-01

108

Characteristics and formation of amino acids and hydroxy acids of the Murchison meteorite  

NASA Technical Reports Server (NTRS)

Eight characteristics of the unique suite of amino acids and hydroxy acids found in the Murchison meteorite can be recognized on the basis of detailed molecular and isotopic analyses. The marked structural correspondence between the alpha-amino acids and alpha-hydroxy acids and the high deuterium/hydrogen ratio argue persuasively for their formation by aqueous phase Strecker reactions in the meteorite parent body from presolar, i.e., interstellar, aldehydes, ketones, ammonia, and hydrogen cyanide. The characteristics of the meteoritic suite of amino acids and hydroxy acids are briefly enumerated and discussed with regard to their consonance with this interstellar-parent body formation hypothesis. The hypothesis has interesting implications for the organic composition of both the primitive parent body and the presolar nebula.

Cronin, J. R.; Cooper, G. W.; Pizzarello, S.

1995-01-01

109

Constrained Vapor Bubble  

NASA Technical Reports Server (NTRS)

The nonisothermal Constrained Vapor Bubble, CVB, is being studied to enhance the understanding of passive systems controlled by interfacial phenomena. The study is multifaceted: 1) it is a basic scientific study in interfacial phenomena, fluid physics and thermodynamics; 2) it is a basic study in thermal transport; and 3) it is a study of a heat exchanger. The research is synergistic in that CVB research requires a microgravity environment and the space program needs thermal control systems like the CVB. Ground based studies are being done as a precursor to flight experiment. The results demonstrate that experimental techniques for the direct measurement of the fundamental operating parameters (temperature, pressure, and interfacial curvature fields) have been developed. Fluid flow and change-of-phase heat transfer are a function of the temperature field and the vapor bubble shape, which can be measured using an Image Analyzing Interferometer. The CVB for a microgravity environment, has various thin film regions that are of both basic and applied interest. Generically, a CVB is formed by underfilling an evacuated enclosure with a liquid. Classification depends on shape and Bond number. The specific CVB discussed herein was formed in a fused silica cell with inside dimensions of 3x3x40 mm and, therefore, can be viewed as a large version of a micro heat pipe. Since the dimensions are relatively large for a passive system, most of the liquid flow occurs under a small capillary pressure difference. Therefore, we can classify the discussed system as a low capillary pressure system. The studies discussed herein were done in a 1-g environment (Bond Number = 3.6) to obtain experience to design a microgravity experiment for a future NASA flight where low capillary pressure systems should prove more useful. The flight experiment is tentatively scheduled for the year 2000. The SCR was passed on September 16, 1997. The RDR is tentatively scheduled for October, 1998.

Huang, J.; Karthikeyan, M.; Plawsky, J.; Wayner, P. C., Jr.

1999-01-01

110

Thermal copoly/amino acids/ as inhibitors of glyoxalase I  

NASA Technical Reports Server (NTRS)

A number of copoly(alpha-amino acids) have been prepared thermally; some have been found to function as inhibitors of glyoxalase I, an enzyme which occupies a central position in Szent-Gyorgyi's theory of tumour genesis. These polymers are also of interest in the search for synthetic peptides having carcinostatic activity, since many natural peptides are active. The way in which the inhibitory activity varies with composition of the synthetic polymers has been investigated. Various properties (hydrophobicity, molecular weight, UV absorption, kinetic type) have been examined in a search for correlates of inhibitory activity.

Fox, S. W.; Syren, R. M.; Windsor, C. R.

1979-01-01

111

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

112

Dynamics of constrained multibody systems  

NASA Astrophysics Data System (ADS)

A new automated procedure for obtaining and solving the governing equations of motion of constrained multibody systems is presented. The procedure is applicable when the constraints are either (a) geometrical (for example, 'closed-loops') or (b) kinematical (for example, specified motion). The procedure is based on a 'zero eigenvalues theorem', which provides an 'orthogonal complement' array which in turn is used to contract the dynamical equations. This contraction, together with the constraint equations, forms a consistent set of governing equations. An advantage of this formulation is that constraining forces are automatically eliminated from the analysis. The method is applied with Kane's equations - an especially convenient set of dynamical equations for multibody systems. Examples of a constrained hanging chain and a chain whose end has a prescribed motion are presented. Applications in robotics, cable dynamics, and biomechanics are suggested.

Kamman, J. W.; Huston, R. L.

1984-12-01

113

Optimization of retinotopy constrained source estimation constrained by prior.  

PubMed

Studying how the timing and amplitude of visual evoked responses (VERs) vary between visual areas is important for understanding visual processing but is complicated by difficulties in reliably estimating VERs in individual visual areas using noninvasive brain measurements. Retinotopy constrained source estimation (RCSE) addresses this challenge by using multiple, retinotopically mapped stimulus locations to simultaneously constrain estimates of VERs in visual areas V1, V2, and V3, taking advantage of the spatial precision of fMRI retinotopy and the temporal resolution of magnetoencephalography (MEG) or electroencephalography (EEG). Nonlinear optimization of dipole locations, guided by a group-constrained RCSE solution as a prior, improved the robustness of RCSE. This approach facilitated the analysis of differences in timing and amplitude of VERs between V1, V2, and V3, elicited by stimuli with varying luminance contrast in a sample of eight adult humans. The V1 peak response was 37% larger than that of V2 and 74% larger than that of V3, and also ?10-20 ms earlier. Normalized contrast response functions were nearly identical for the three areas. Results without dipole optimization, or with other nonlinear methods not constrained by prior estimates were similar but suffered from greater between-subject variability. The increased reliability of estimates offered by this approach may be particularly valuable when using a smaller number of stimulus locations, enabling a greater variety of stimulus and task manipulations. Hum Brain Mapp 35:1815-1833, 2014. © 2013 Wiley Periodicals, Inc. PMID:23868690

Hagler, Donald J

2014-05-01

114

Imino Acids in the Murchison Meteorite: Evidence of Strecker Reactions  

NASA Technical Reports Server (NTRS)

Both alpha-amino acids and alpha-hydroxy acids occur in aqueous extracts of the Murchison carbonaceous meteorite. The Strecker-cyanohydrin reaction, the reaction of carbonyl compounds, cyanide, and ammonia to produce amino and hydroxy acids, has been proposed as a source of such organic acids in meteorites. Such syntheses are consistent with the suggestion that interstellar precursors of meteoritic organic compounds accreted on the meteorite parent body together with other ices. Subsequent internal heating of the parent body melted these ices and led to the formation of larger compounds in synthetic reactions during aqueous alteration, which probably occurred at temperatures between 273K and 298K. In the laboratory, imino acids are observed as important by-products of the Strecker synthesis.

Lerner, N. R.; Cooper, G. W.

2003-01-01

115

Poisson Geometry in Constrained Systems  

Microsoft Academic Search

Associated to a constrained system with closed constraint algebra there are two Poisson manifolds P and Q forming a symplectic dual pair with respect to the original, unconstrained phase space: P is the image of the constraint map (equipped with the algebra of constraints) and Q the Poisson quotient with respect to the orbits generated by the constraints (the orbit

MARTIN BOJOWALD; THOMAS STROBL

2003-01-01

116

Structural and biological effects of a beta2- or beta3-amino acid insertion in a peptide.  

PubMed

Molecular mechanics calculations on conformers of Ac-HGly-NHMe, Ac-beta2-HAla-NHMe and Ac-beta3-HAla-NHMe indicate that low-energy conformations of the beta-amino acids backbone, corresponding to gauche rotamers around the Calpha-Cbeta bond, may overlap canonical backbone conformers observed for alpha-amino acids. Therefore, Substance P (SP) was used as a model peptide to analyse the structural and biological consequences of the substitution of Phe7 and Phe8 by (R)-beta2-HPhe and of Gly9 by HGly (R)-beta2-HAla or (S)-beta3-HAla. [(R)-beta2-HAla9]SP has pharmacological potency similar to that of SP while [HGly9]SP and [(S)-beta3-HAla9]SP show a 30- to 50-fold decrease in biological activities. The three analogues modified at position 9 are more resistant to degradation by angiotensin converting enzyme than SP and [Ala9]SP. NMR analysis of these SP analogues suggest that a beta-amino acid insertion in position 9 does not affect the overall backbone conformation. Altogether these data suggest that [HGly9]SP, [(S)-beta3-HAla9]SP and [(R)-beta2-HAla9]SP could adopt backbone conformations similar to that of SP, [Ala9]SP and [Pro9]SP. In contrast, incorporation of beta2-HPhe in position 7 and 8 of SP led to peptides that are almost devoid of biological activity. Thus, a beta-amino acid could replace an alpha-amino acid within the sequence of a bioactive peptide provided that the additional methylene group does not cause steric hindrance and does not confine orientations of the side chain to regions of space different from those permitted in the alpha-amino acid. PMID:12603327

Sagan, Sandrine; Milcent, Thierry; Ponsinet, Rachel; Convert, Odile; Tasseau, Olivier; Chassaing, Gérard; Lavielle, Solange; Lequin, Olivier

2003-03-01

117

Design and synthesis of a structurally constrained aminoglycoside.  

PubMed

The synthesis of a constrained tricyclic aminoglycoside derivative is described. This constrained compound fixes the spatial orientation of two critical rings for the minimal motif for binding to biological macromolecules such as RNA and proteins. Methanolysis of neomycin B under acidic conditions produced the bicyclic neamine. Transient protection by the Cu2+ ion and regioselective introduction of protective groups led to intermediate 7, which was used for a key annulation reaction that introduced the tricyclic nucleus into the structural framework. A final hydrogenolysis step to remove the protective groups produced the desired target molecule. The efficient eight-step synthesis was accomplished in 8% overall yield. PMID:17579461

Kling, Dale; Hesek, Dusan; Shi, Qicun; Mobashery, Shahriar

2007-07-01

118

Taste preferences for amino acids in the house musk shrew, Suncus murinus.  

PubMed

Taste preferences in house musk shrews for amino acids as well as NaCl, sucrose, quinine hydrochloride, HCl and saccharin Na were studied by employing the two-bottle preference technique. Shrews showed a preference for 0.2--05. M sucrose but a moderate rejection to NaCl and a strong rejection to quinine, HCl and saccharin. They exhibited a marked preference for many naturally occurring L-alpha-amino acids with aliphatic side chains at both 0.02 and 0.2 M. Increase in the aliphatic side chain length of DL-alpha-amino acids resulted in both lowering of the preference threshold and increase in the preference magnitude. Amino acids with side chains containing sulfur atoms, basic groups and Phe at 0.02 M were preferred to water, but Cys and Arg at 0.2 M was rejected. Shrews showed neither preference nor rejection to Trp, Asn, Gln and monosodium glutamate at 0.02 M, but rejected strongly Asp and Glu. D-Met from 0.001 to 0.1 M was preferred as well as L-Met, while D-Phe was more preferred than L-Phe. Such preferences for a wide variety of amino acids in shrews could be attributed to their food habit of predating on various kinds of insects and worms. PMID:7100283

Iwasaki, K; Sato, M A

1982-05-01

119

Isotopic analyses of amino acids from the Murchison meteorite  

NASA Technical Reports Server (NTRS)

An account is given of the results of H-2, C-13 isotopic analyses of the Murchison meteorite incorporating an ultrafiltration step to exclude the possibility of fine particulate contaminants. The meteorite's amino acids were chromatographically separated in order to preclude isotopic enrichment by basic compounds other than the amino acids. The results indicate that the Murchison amino acids are isotopically highly unusual; delta-C-13 is elevated by about 40 percent, and delta-D by fully 2500 percent. This high D content of the meteorite's alpha-amino acids may be due to the synthesis of their molecular precursors by low-temperature ion-molecule reactions in an interstellar cloud.

Pizzarello, S.; Cronin, J. R.; Krishnamurthy, R. V.; Epstein, S.

1991-01-01

120

Constraining spacetime torsion with LAGEOS  

NASA Astrophysics Data System (ADS)

We compute the corrections to the orbital Lense-Thirring effect (or frame-dragging) in the presence of spacetime torsion. We analyze the motion of a test body in the gravitational field of a rotating axisymmetric massive body, using the parametrized framework of Mao, Tegmark, Guth and Cabi. In the cases of autoparallel and extremal trajectories, we derive the specific approximate expression of the corresponding system of ordinary differential equations, which are then solved with methods of Celestial Mechanics. We calculate the secular variations of the longitudes of the node and of the pericenter. We also show how the LAser GEOdynamics Satellites (LAGEOS) can be used to constrain torsion parameters. We report the experimental constraints obtained using both the nodes and perigee measurements of the orbital Lense-Thirring effect. This makes LAGEOS and Gravity Probe B complementary frame-dragging and torsion experiments, since they constrain three different combinations of torsion parameters.

March, Riccardo; Bellettini, Giovanni; Tauraso, Roberto; Dell'Agnello, Simone

2011-11-01

121

Constrained Multiobjective Biogeography Optimization Algorithm  

PubMed Central

Multiobjective optimization involves minimizing or maximizing multiple objective functions subject to a set of constraints. In this study, a novel constrained multiobjective biogeography optimization algorithm (CMBOA) is proposed. It is the first biogeography optimization algorithm for constrained multiobjective optimization. In CMBOA, a disturbance migration operator is designed to generate diverse feasible individuals in order to promote the diversity of individuals on Pareto front. Infeasible individuals nearby feasible region are evolved to feasibility by recombining with their nearest nondominated feasible individuals. The convergence of CMBOA is proved by using probability theory. The performance of CMBOA is evaluated on a set of 6 benchmark problems and experimental results show that the CMBOA performs better than or similar to the classical NSGA-II and IS-MOEA.

Mo, Hongwei; Xu, Zhidan; Xu, Lifang; Wu, Zhou; Ma, Haiping

2014-01-01

122

Constraining walking and custodial technicolor  

Microsoft Academic Search

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

Roshan Foadi; Mads T. Frandsen; Francesco Sannino

2008-01-01

123

Extraterrestrial amino acids in Orgueil and Ivuna: tracing the parent body of CI type carbonaceous chondrites.  

PubMed

Amino acid analyses using HPLC of pristine interior pieces of the CI carbonaceous chondrites Orgueil and Ivuna have found that beta-alanine, glycine, and gamma-amino-n-butyric acid (ABA) are the most abundant amino acids in these two meteorites, with concentrations ranging from approximately 600 to 2,000 parts per billion (ppb). Other alpha-amino acids such as alanine, alpha-ABA, alpha-aminoisobutyric acid (AIB), and isovaline are present only in trace amounts (<200 ppb). Carbon isotopic measurements of beta-alanine and glycine and the presence of racemic (D/L approximately 1) alanine and beta-ABA in Orgueil suggest that these amino acids are extraterrestrial in origin. In comparison to the CM carbonaceous chondrites Murchison and Murray, the amino acid composition of the CIs is strikingly distinct, suggesting that these meteorites came from a different type of parent body, possibly an extinct comet, than did the CM carbonaceous chondrites. PMID:11226205

Ehrenfreund, P; Glavin, D P; Botta, O; Cooper, G; Bada, J L

2001-02-27

124

Insulin effect on amino acid uptake by unloaded rat hindlimb muscles  

NASA Technical Reports Server (NTRS)

The effect of insulin on the uptake of alpha-amino-isobutyric acid (AIB) by unloaded rat hindlimb muscles was investigated using soleus and extensor digitorum longus (EDL) muscles from intact and adrenalectomized (ADX) rats that were tail-casted for six days. It was found that, at insulin levels above 0.00001 units/ml, the in vitro rate of AIB uptake by muscles from intact animals was stimulated more in the weight bearing muscles than in unloaded ones. In ADX animals, this differential response to insulin was abolished.

Jaspers, S. R.; Tischler, M. E.

1988-01-01

125

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

126

Constraining Lorentz violation with cosmology.  

PubMed

The Einstein-aether theory provides a simple, dynamical mechanism for breaking Lorentz invariance. It does so within a generally covariant context and may emerge from quantum effects in more fundamental theories. The theory leads to a preferred frame and can have distinct experimental signatures. In this Letter, we perform a comprehensive study of the cosmological effects of the Einstein-aether theory and use observational data to constrain it. Allied to previously determined consistency and experimental constraints, we find that an Einstein-aether universe can fit experimental data over a wide range of its parameter space, but requires a specific rescaling of the other cosmological densities. PMID:19113765

Zuntz, J A; Ferreira, P G; Zlosnik, T G

2008-12-31

127

Constraining Lorentz Violation with Cosmology  

SciTech Connect

The Einstein-aether theory provides a simple, dynamical mechanism for breaking Lorentz invariance. It does so within a generally covariant context and may emerge from quantum effects in more fundamental theories. The theory leads to a preferred frame and can have distinct experimental signatures. In this Letter, we perform a comprehensive study of the cosmological effects of the Einstein-aether theory and use observational data to constrain it. Allied to previously determined consistency and experimental constraints, we find that an Einstein-aether universe can fit experimental data over a wide range of its parameter space, but requires a specific rescaling of the other cosmological densities.

Zuntz, J. A.; Ferreira, P. G.; Zlosnik, T. G [Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom)

2008-12-31

128

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

129

The Strecker synthesis from interstellar precursors as a source of amino acids in carbonaceous chondrites: Deuterium retention during synthesis. [Abstract only  

NASA Technical Reports Server (NTRS)

Amino acids in the Murchison carbonaceous chondrite are anomalously enriched in deuterium. Synthesis in Strecker reactions from D-enriched interstellar precursors during low temperature aqueous alteration of the parent body has been proposed by Cronin et al. (1988) to account for the isotopic observations. To test this hypothesis, we have measured the retention of deuterium in the glycine, alanine, and alpha-amino isobutyric acid produced, respectively, by reactions of formaldehyde-D2, acetaldehyde-D4, and acetone-D6 with HCN and NH3 in water.

Lerner, N. R.; Peterson, E.; Chang, S.

1994-01-01

130

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

131

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

132

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

133

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

134

BESO of Structures with Constrained Damping  

Microsoft Academic Search

Optimization of structures with constrained layer damping by bi-directional evolutionary structural optimization???BESO???was studied in this paper. The sensitivity equation of the objective function about deleted and added elements was built for maximization of modal loss factor of constrained layer damping structure. Firstly the FEA model of the metal structure without constrained layer damping are built, and the mode shapes are

Zhiying Mao; Guoping Chen

2010-01-01

135

Constrained controllability of discrete-time systems†  

Microsoft Academic Search

The constrained controllability of the discrete-time system xk+1=A(k)xk+B(k)u,k is considered where the control uk is termed admissible if it satisfies specified magnitude constraints. Constrained controllability is concerned with the existence of an admissible control which steers the state x to a given target set from a specified initial stateConditions for checking constrained controllability to a given target set from a

ROBERT P. VAN TIL; WILLIAM E. SCHMITENDORF

1986-01-01

136

Constrained photophysics of partially and fully encapsulated charge transfer probe (E)-3-(4-Methylaminophenyl) acrylic acid methyl ester inside cyclodextrin nano-cavities: Evidence of cyclodextrins cavity dependent complex stoichiometry  

NASA Astrophysics Data System (ADS)

The polarity sensitive intra-molecular charge transfer (ICT) emission from (E)-3-(4-Methylaminophenyl) acrylic acid methyl ester (MAPAME) is found to show distinct changes once introduced into the nano-cavities of cyclodextrins in aqueous environment. Movement of the molecule from the more polar aqueous environment to the less polar, hydrophobic cyclodextrin interior is marked by the blue shift of the CT emission band with simultaneous fluorescence intensity enhancement. The emission spectral changes on complexation with the ?- and ?-CD show different stoichiometries as observed from the Benesi-Hildebrand plots. Fluorescence anisotropy and lifetime measurements were performed to probe the different behaviors of MAPAME in aqueous ?- and ?-CD solutions.

Ghosh, Shalini; Jana, Sankar; Guchhait, Nikhil

2011-12-01

137

Conformationally constrained analogues of 2-arachidonoylglycerol.  

PubMed

Novel monocyclic analogues of 2-arachidonoylglycerol (2-AG) were designed in order to explore the pharmacophoric conformations of this endocannabinoid ligand at the key cannabinergic proteins. All 2-arachidonoyl esters of 1,2,3-cyclohexanetriol [meso-7 (AM5504), (+/-)-8 (AM5503), and meso-9 (AM5505)] were synthesized by regioselective acylation of 2,3-dihydroxycyclohexanone followed by selective reductions. The optically active isomers (+)-8 (AM4434) and (-)-8 (AM4435) were synthesized from (2S,3S)- and (2R,3R)-2,3-dihydroxycyclohexanone, respectively, via a chemoenzymatic route. These head group constrained and conformationally restricted analogues of 2-AG as well as the 1-keto precursors were evaluated as substrates for the endocannabinoid deactivating hydrolytic enzymes monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH), and also were tested for their affinities for CB1 and CB2 cannabinoid receptors. The observed biochemical differences between these ligands can help define the conformational requirements for 2-AG activity at each of the above endocannabinoid protein targets. PMID:17826996

Vadivel, Subramanian K; Vardarajan, Sundararaman; Duclos, Richard I; Wood, JodiAnne T; Guo, Jianxin; Makriyannis, Alexandros

2007-11-01

138

Hydrolysis of Al3+ from constrained molecular dynamics  

NASA Astrophysics Data System (ADS)

We investigated the hydrolysis reactions of Al3+ in AlCl3 aqueous solution using the constrained molecular dynamics based on the Car-Parrinello molecular-dynamics method. By employing the proton-aluminum coordination number as a reaction coordinate in the constrained molecular dynamics the deprotonation as well as dehydration processes are successfully realized. From our free-energy difference of ?G0~=8.0 kcal mol-1 the hydrolysis constant pKa1 is roughly estimated as 5.8, comparable to the literature value of 5.07. We show that the free-energy difference for the hydrolysis of Al3+ in acidic conditions is at least 4 kcal mol-1 higher than that in neutral condition, indicating that the hydrolysis reaction is inhibited by the presence of excess protons located around the hydrated ion, in agreement with the change of the predominant species by pH.

Ikeda, Takashi; Hirata, Masaru; Kimura, Takaumi

2006-02-01

139

Constrained exceptional supersymmetric standard model  

SciTech Connect

We propose and study a constrained version of the exceptional supersymmetric standard model (E{sub 6}SSM), which we call the cE{sub 6}SSM, based on a universal high energy scalar mass m{sub 0}, trilinear scalar coupling A{sub 0} and gaugino mass M{sub 1/2}. We derive the renormalization group (RG) Equations for the cE{sub 6}SSM, including the extra U(1){sub N} gauge factor and the low-energy matter content involving three 27 representations of E{sub 6}. We perform a numerical RG analysis for the cE{sub 6}SSM, imposing the usual low-energy experimental constraints and successful electroweak symmetry breaking. Our analysis reveals that the sparticle spectrum of the cE{sub 6}SSM involves a light gluino, two light neutralinos, and a light chargino. Furthermore, although the squarks, sleptons, and Z{sup '} boson are typically heavy, the exotic quarks and squarks can also be relatively light. We finally specify a set of benchmark points, which correspond to particle spectra, production modes, and decay patterns peculiar to the cE{sub 6}SSM, altogether leading to spectacular new physics signals at the Large Hadron Collider.

Athron, P. [Institut fuer Kern und Teilchenphysik, TU Dresden, Dresden, D-01062 (Germany); King, S. F. [School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ (United Kingdom); Miller, D. J.; Nevzorov, R. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Moretti, S. [School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ (United Kingdom); Dipartimento di Fisica Teorica, Universita degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino (Italy)

2009-08-01

140

White dwarfs constrain dark forces  

NASA Astrophysics Data System (ADS)

The white dwarf luminosity function, which provides information about the cooling of such stars, has been measured with high precision in the past few years. Simulations that include well known Standard Model physics give a good fit to the data. This leaves little room for new physics and makes these astrophysical objects a good laboratory for testing models beyond the Standard Model. It has already been suggested that white dwarfs might provide some evidence for the existence of axions. In this work we study the constraints that the white dwarf luminosity function puts on physics beyond the Standard Model involving new light particles (fermions or bosons) that can be pair-produced in a white dwarf and then escape to contribute to its cooling. We show, in particular, that we can severely constrain the parameter space of models with dark forces and light hidden sectors (lighter than a few tens of keV). The bounds we find are often more competitive than those from current lab searches and those expected from most future searches.

Dreiner, Herbert K.; Fortin, Jean-François; Isern, Jordi; Ubaldi, Lorenzo

2013-08-01

141

Pattern Search Methods for Linearly Constrained Minimization  

Microsoft Academic Search

We extend pattern search methods to linearly constrained minimization. We develop a general class of feasible point pattern search algorithms and prove global convergence to a Karush-Kuhn- Tucker point. As in the case of unconstrained minimization, pattern search methods for linearly constrained problems accomplish this without explicit recourse to the gradient or the directional derivative. Key to the analysis of

Robert Michael Lewis; Virginia Torczon

2000-01-01

142

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

143

Constrained layer damping with vitreous enamel  

Microsoft Academic Search

The concept of constrained layer damping with vitreous enamel has been experimentally evaluated. The constraining layer markedly broadens the free layer damping peak. The broadening has been explained on the basis of two simultaneous energy dissipation mechanisms and is related to the vitreous enamel's loss factor and viscosity.

B. Kumar; M. L. Drake

1984-01-01

144

Determination of optimal gains for constrained controllers  

SciTech Connect

In this report, we consider the determination of optimal gains, with respect to a certain performance index, for state feedback controllers where some elements in the gain matrix are constrained to be zero. Two iterative schemes for systematically finding the constrained gain matrix are presented. An example is included to demonstrate the procedures.

Kwan, C.M.; Mestha, L.K.

1993-08-01

145

A reexamination of amino acids in lunar soil  

NASA Technical Reports Server (NTRS)

Amino acids in lunar soils provide an important indicator of the level of prebiotic organic compounds on the moon. The results provide insight into the chemistry of amino acid precursors, and furthermore, given the flux of carbonaceous material to the moon, we can evaluate the survival of organics upon impact. The amino acid contents of both hydrolyzed and unhydrolyzed hot-water extracts of Apollo 17 lunar soil were determined using ophthaldialdehyde/N-acetyl cysteine (OPA/NAC) derivatization followed by HPLC analysis. Previous studies of lunar amino acids were inconclusive, as the technique used (derivatization with ninhydrin followed by HPLC analysis) was unable to discriminate between cosmogenic amino acids and terrestrial contaminants. Cosmogenic amino acids are racemic, and many of the amino acids found in carbonaceous meteorites such as Murchison, i.e., alpha-amino-i-butyric acid (aib), are extremely rare on Earth. The ninhydrin method does not distinguish amino acid enantiomers, nor does it detect alpha-alkyl amino acids such as aib, whereas the OPA/NAC technique does both.

Brinton, K. L. F.; Bada, J. L.; Arnold, J. R.

1993-01-01

146

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

147

Heterogeneous Distributions of Amino Acids Provide Evidence of Multiple Sources Within the Almahata Sitta Parent Body, Asteroid 2008 TC(sub 3)  

NASA Technical Reports Server (NTRS)

Two new fragments of the Almahata Sitta meteorite and a sample of sand from the related strewn field in the Nubian Desert, Sudan, were analyzed for two to six carbon aliphatic primary amino acids by ultrahigh performance liquid chromatography with UV-fluorescence detection and time-of-flight mass spectrometry (LC-FT/ToF-MS). The distribution of amino acids in fragment #25, an H5 ordinary chondrite, and fragment #27, a polymict ureilite, were compared with results from the previously analyzed fragment #4, also a polymict ureilite. All three meteorite fragments contain 180-270 parts-per-billion (ppb) of amino acids, roughly 1000-fold lower than the total amino acid abundance of the Murchison carbonaceous chondrite. All of the Almahata Sitta fragments analyzed have amino acid distributions that differ from the Nubian Desert sand, which primarily contains L-alpha-amino acids. In addition, the meteorites contain several amino acids that were not detected in the sand, indicating that many of the amino acids are extraterrestrial in origin. Despite their petrological differences, meteorite fragments #25 and #27 contain similar amino acid compositions; however, the distribution of amino acids in fragment #27 was distinct from those in fragment #4, even though both arc polymict ureilites from the same parent body. Unlike in CM2 and CR2/3 meteorites, there are low relative abundances of alpha-amino acids in the Almahata Sitta meteorite fragments, which suggest that Strecker-type chemistry was not a significant amino acid formation mechanism. Given the high temperatures that asteroid 2008 TC3 appears to have experienced and lack of evidence for aqueous alteration on the asteroid, it is possible that the extraterrestrial amino acids detected in Almahata Sitta were formed by Fischer-Tropsch/Haber-Bosch type gas-grain reactions at elevated temperatures.

Burton, Aaron S.; Glavin, Daniel P.; Callahan, Michael P.; Dworkin, Jason P.; Jenniskens, Peter; Shaddad, Muawia H.

2011-01-01

148

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

149

Active constrained clustering by examining spectral Eigenvectors  

NASA Technical Reports Server (NTRS)

This work focuses on the active selection of pairwise constraints for spectral clustering. We develop and analyze a technique for Active Constrained Clustering by Examining Spectral eigenvectorS (ACCESS) derived from a similarity matrix.

Wagstaff, Kiri L.; desJardins, Marie; Xu, Qianjun

2005-01-01

150

Maximum Likelihood Estimation for Constrained or Missing Data Models.  

National Technical Information Service (NTIS)

In statistical models involving constrained or missing data, likelihoods constrained integrals emerge. In the case of both constrained and missing data, the result is a ratio of integrals, which for multivariate data may defy exact or approximate analytic...

A. E. Gelfand B. P. Carlin

1993-01-01

151

21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 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...

2010-04-01

152

Compositionally Constraining Elysium Lava Fields  

NASA Astrophysics Data System (ADS)

Chemical provinces of Mars defined recently [1-3] became possible with the maps of elemental mass fractions generated with Mars Odyssey Gamma and Neutron Spectrometer (GS) data [4,5]. These provide a unique perspective by representing compositional signatures distinctive of the regolith vertically at decimeter depths and laterally at hundreds of kilometer scale. Some provinces overlap compellingly with regions highlighted by other remote sensing observations, such as the Mars Radar Stealth area [3]. The spatial convergence of mutually independent data with the consequent highlight of a region provides a unique opportunity of insight not possible with a single type of remote sensing observation. Among such provinces, previous work [3] highlighted Elysium lava flows as a promising candidate on the basis of convergence with mapped geologic units identifying Elysium's lava fields generally, and Amazonian-aged lava flows specifically. The South Eastern lava flows of Elysium Mons, dating to the recent Amazonian epoch, overlap compellingly with a chemical province of K and Th depletion relative to the Martian midlatitudes. We characterize the composition, geology, and geomorphology of the SE Elysium province to constrain the confluence of geologic and alteration processes that may have contributed to its evolution. We compare this with the North Western lava fields, extending the discussion on chemical products from the thermal evolution of Martian volcanism as discussed by Baratoux et al. [6]. The chemical province, by regional proximity to Cerberus Fossae, may also reflect the influence of recently identified buried flood channels [7] in the vicinity of Orcus Patera. Despite the compelling chemical signature from ? spectra, fine grained unconsolidated sediment hampers regional VNTIR (Visible, Near, and Thermal Infrared) spectral analysis. But some observations near scarps and fresh craters allow a view of small scale mineral content. The judicious synthesis of mineralogic and chemical information, along with geomorphology, may reveal how the chemical province represents compositional signatures of younger Elysium lava flows. Several broad constraints may apply for the Elysium chemical province. The more mountainous terrain abutted by the lava flows appears of an ancient provenance distinct from the lava flows themselves. Magmatic fractionation processes locally as well as planetary differentiation during potential magma ocean overturn [3,8] may have produced compositionally distinct lava. Conclusive evidence for magmatic volatiles, aqueous alteration of the lava flows, or recent fine debris deposits, as causative factors for the compositional trends of the province, may remain lacking. Future work advancing that by Baratoux et al. [6] would develop a magmatic evolution model for Elysium on a comparative basis between the NW and SE lava fields. References [1] Taylor, G. J. et al. Geology 38, 183-186 (2010) [2] Gasnault, O. et al. Icarus 207, 226-247 (2010) [3] Karunatillake, S. et al. JGR 114, E12001 (2009) [4] Boynton, W. V. et al. JGR 112, 1-15 (2007) [5] Feldman, W. C. JGR 109, E09006 (2004) [6] Baratoux, D. et al. Nature 472, 338-41 (2011) [7] Morgan, G. A. et al. Science 607, (2013) [8] Elkins-Tanton, L. T. et al. EPSL 236, 1-12 (2005)

Karunatillake, S.; Button, N. E.; Skok, J. R.

2013-12-01

153

Linearly constrained band selection for hyperspectral imagery  

NASA Astrophysics Data System (ADS)

Linearly constrained adaptive beamforming has been used to design hyperspectral target detection algorithms such as constrained energy minimization (CEM) and linearly constrained minimum variance (LCMV). It linearly constrains a desired target signature while minimizing interfering effects caused by other unknown signatures. This paper investigates this idea and further uses it to develop a new approach to band selection, referred to as linear constrained band selection (LCBS) for hyperspectral imagery. It interprets a band image as a desired target signature while considering other band images as unknown signatures. With this interpretation, the proposed LCBS linearly constrains a band image while also minimizing band correlation or dependence caused by other band images. As a result, two different methods referred to as Band Correlation Minimization (BCM) and Band Correlation Constraint (BCC) can be developed for band selection. Such LCBS allows one to select desired bands for data analysis. In order to determine the number of bands required to select, p, a recently developed concept, called virtual dimensionality (VD) is used to estimate the p. Once the p is determined, a set of p desired bands can be selected by LCBS. Finally, experiments are conducted to substantiate the proposed LCBS.

Wang, Su; Chang, Chein-I.

2006-06-01

154

Distribution of Active and Passive Constraining Sections for Hybrid Constrained Layer Damping Treatments  

Microsoft Academic Search

This paper investigates the effect of the distribution of the active and passive constraining materials on the damping performance of an active–passive hybrid constrained layer (HCL) treatment. Earlier studies have demonstrated that the HCL can provide higher open-loop and closed-loop damping than an active constrained layer (ACL) system when a stiffer passive material is integrated into the cover sheet and

Yanning Liu; Kon-Well Wang

2002-01-01

155

The dual-specific active site of 7,8-diaminopelargonic acid synthase and the effect of the R391A mutation.  

PubMed

7,8-diaminopelargonic acid (DAPA) synthase (EC 2.6.1.62) is a pyridoxal phosphate (PLP)-dependent transaminase that catalyzes the transfer of the alpha-amino group from S-adenosyl-L-methionine (SAM) to 7-keto-8-aminopelargonic acid (KAPA) to form DAPA in the antepenultimate step in the biosynthesis of biotin. The wild-type enzyme has a steady-state kcat value of 0.013 s(-1), and the K(m) values for SAM and KAPA are 150 and <2 microM, respectively. The k(max) and apparent K(m) values for the half-reaction of the PLP form of the enzyme with SAM are 0.016 s(-1) and 300 microM, respectively, while those for the reaction with DAPA are 0.79 s(-1) and 1 microM. The R391A mutant enzyme exhibits near wild-type kinetic parameters in the reaction with SAM, while the apparent K(m) for DAPA is increased 180-fold. The 2.1 A crystal structure of the R391A mutant enzyme shows that the mutation does not significantly alter the structure. These results indicate that the conserved arginine residue is not required for binding the alpha-amino acid SAM, but it is important for recognition of DAPA. PMID:12379100

Eliot, Andrew C; Sandmark, Jenny; Schneider, Gunter; Kirsch, Jack F

2002-10-22

156

Comparison between constrained and non-constrained Cobb techniques for the assessment of thoracic kyphosis and lumbar lordosis  

Microsoft Academic Search

Sagittal curvatures of the spine can be assessed using the constrained or non-constrained Cobb techniques. However, there\\u000a is no study that specifically compares these two techniques. The objective of this study is to assess the reproducibility\\u000a and clinical relevance of the non-constrained Cobb technique (non-constrained limit vertebrae) compared to the constrained\\u000a Cobb technique (constrained limit vertebrae). Standing sagittal radiographs of

Jean-Marc Mac-Thiong; Fanny-Maud Pinel-Giroux; Jacques A. de Guise; Hubert Labelle

2007-01-01

157

Determination of tranexamic acid in human serum by high-performance liquid chromatography using selective pre-column derivatization with phenyl isothiocyanate.  

PubMed

A high-performance liquid chromatographic method for determination of tranexamic acid in human serum using a selective derivatization has been developed. Tranexamic acid in the sample was allowed to react with phenyl isothiocyanate to form the phenylthiocarbamoyl derivative. Interfering alpha-amino acids in the sample were eliminated by selective derivatization to phenylthiohydantoin derivatives by acid treatment of the phenylthiocarbamoyl derivatives followed by solvent extraction. Then, the sample was analysed by conventional high-performance liquid chromatography with ultraviolet detection. The limit of detection of this method for serum sample was 0.2 micrograms/ml at a signal-to-noise ratio of 2. This method gave results comparable with those obtained by amino acid analysis (regression line: y = 0.4531x-0.02596, r = 0.9998, n = 21). PMID:3235550

Matsubayashi, K; Kojima, C; Tachizawa, H

1988-12-01

158

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

159

Vibration Control through Passive Constrained Layer Damping and Active Control  

Microsoft Academic Search

To add damping to systems, viscoelastic materials (VEM) are added to structures. In order to enhance the damping effects of the VEM, a constraining layer is attached, creating a passive constrained layer damping (PCLD) treatment. When this constraining layer is an active element, the treatment is called active constrained layer damping (ACLD). Recently, the investigation of ACLD treatments has shown

Margaretha J. Lam; Daniel J. Inman; William R. Saunders

1997-01-01

160

Synthesis and characterization of new chiral peptide nucleic acid (PNA) monomers.  

PubMed

PNAs are DNA analogues in which the nucleic acid's backbone is replaced by a chiral or achiral pseudopeptide backbone and nucleobases are attached to the backbone by methylene carbonyl linkers. The easy to modify PNA structure gives the possibility to obtain monomers, and subsequently oligomers, with improved properties. We have synthesised several new PNA monomers, starting from a series of 2'-substituted methyl N-(2-Boc-aminoethyl)glycinates. The pseudodipeptides were obtained using modified Kosynkina's method, based on the reductive amination of N-Boc-protected alpha-amino aldehydes [glycinal, isoleucinal, valinal, tryptophanal, serinal(Bzl), prolinal] with methyl glycinate. The compounds were then acylated with nucleic acid base derivatives by simplified procedure, and the purification was limited to the last step of the synthesis. The applied procedure is useful in synthesis of various chiral PNA monomers. PMID:10780363

Falkiewicz, B; Wisniowski, W; Kolodziejczyk, A S; Wisniewski, K; Lankiewicz, L

1999-01-01

161

Pattern Search Methods for Linearly Constrained Minimization  

NASA Technical Reports Server (NTRS)

We extend pattern search methods to linearly constrained minimization. We develop a general class of feasible point pattern search algorithms and prove global convergence to a Karush-Kuhn-Tucker point. As in the case of unconstrained minimization, pattern search methods for linearly constrained problems accomplish this without explicit recourse to the gradient or the directional derivative. Key to the analysis of the algorithms is the way in which the local search patterns conform to the geometry of the boundary of the feasible region.

Lewis, Robert Michael; Torczon, Virginia

1998-01-01

162

Spacecraft inertia estimation via constrained least squares  

NASA Technical Reports Server (NTRS)

This paper presents a new formulation for spacecraft inertia estimation from test data. Specifically, the inertia estimation problem is formulated as a constrained least squares minimization problem with explicit bounds on the inertia matrix incorporated as LMIs [linear matrix inequalities). The resulting minimization problem is a semidefinite optimization that can be solved efficiently with guaranteed convergence to the global optimum by readily available algorithms. This method is applied to data collected from a robotic testbed consisting of a freely rotating body. The results show that the constrained least squares approach produces more accurate estimates of the inertia matrix than standard unconstrained least squares estimation methods.

Keim, Jason A.; Acikmese, Behcet A.; Shields, Joel F.

2006-01-01

163

Pattern Search Algorithms for Bound Constrained Minimization  

NASA Technical Reports Server (NTRS)

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 pattern search methods for unconstrained problems. We prove global convergence despite the fact that pattern search methods do not have explicit information concerning the gradient and its projection onto the feasible region and consequently are unable to enforce explicitly a notion of sufficient feasible decrease.

Lewis, Robert Michael; Torczon, Virginia

1996-01-01

164

Isotopic analyses of amino acids from the Murchison meteorite  

SciTech Connect

Previous isotopic analyses of the total amino acids of the Murchison meteorite showed these compounds to be substantially enriched in {sup 2}H, {sup 13}C, and {sup 15}N relative to terrestrial organic matter. These analyses have been repeated ({sup 2}H, {sup 13}C) with inclusion of an ultrafiltration step to exclude the possibility that a fine particulate contaminant carried the isotopic excesses observed in the previous work. In addition, the meteorite amino acids were chromatographically separated to rule out the possibility that the isotopic enrichment of the meteorite extract could reside in basic compounds other than amino acids. The results indicate that the Murchison amino acids are truly isotopically unusual, that the isotopic excesses reside in at least several different amino acids, and that the isotopic contents of some of these amino acids reach values of about +40{per thousand} ({delta}{sup 13}C) and +2,500{per thousand} ({delta}D). If it is assumed that the high deuterium content of the meteroite {alpha}-amino acids is a result of the synthesis of their molecular precursors by low temperature ion-molecule reactions in an interstellar cloud, their formation by aqueous phase Strecker reactions in the parent body is consistent with their general characteristics and with known parent body processes.

Pizzarello, S.; Cronin, J.R. (Arizona State Univ., Tempe (United States)); Krishnamurthy, R.V.; Epstein, S. (California Inst. of Tech., Pasadena, CA (United States))

1991-03-01

165

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

166

A Model for Optimal Constrained Adaptive Testing.  

ERIC Educational Resources Information Center

Proposes a model for constrained computerized adaptive testing in which the information in the test at the trait level (theta) estimate is maximized subject to the number of possible constraints on the content of the test. Test assembly relies on a linear-programming approach. Illustrates the approach through simulation with items from the Law…

van der Linden, Wim J.; Reese, Lynda M.

1998-01-01

167

Nonlinear wave equations and constrained harmonic motion  

PubMed Central

The study of the Korteweg-deVries, nonlinear Schrödinger, Sine-Gordon, and Toda lattice equations is simply the study of constrained oscillators. This is likely to be true for any nonlinear wave equation associated with a second-order linear problem.

Deift, Percy; Lund, Fernando; Trubowitz, Eugene

1980-01-01

168

Constrained Hough Transforms for Curve Detection  

Microsoft Academic Search

This paper describes techniques to perform fast and accurate curve detection using constrained Hough transforms, in which localization error can be propagated efficiently into the parameter space. We first review a formal definition of Hough transform and modify it to allow the formal treatment localization error. We then analyze current Hough transform techniques with respect to this definition. It is

Clark F. Olson

1999-01-01

169

Stochastic Security-Constrained Unit Commitment  

Microsoft Academic Search

This paper presents a stochastic model for the long-term solution of security-constrained unit commitment (SCUC). The proposed approach could be used by vertically integrated utilities as well as the ISOs in electricity markets. In this model, random disturbances, such as outages of generation units and transmission lines as well as load forecasting inaccuracies, are modeled as scenario trees using the

Lei Wu; Mohammad Shahidehpour; Tao Li

2007-01-01

170

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

171

Constrained Layer Damping and Piezoceramic Active Control.  

National Technical Information Service (NTIS)

The work described in this paper is concerned with controlling the strain of the constraining layer of a composite structure in such a way as to enhance the shear generated in the viscoelastic material and hence improve the overall damping of the composit...

G. R. Tomlinson

1997-01-01

172

H   Control of Active Constrained Layer Damping  

Microsoft Academic Search

Conventional passive constrained layer damping treatments with visco-elastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. Two configurations of the resulting hybrid treatment are considered in this paper. In the first configuration the active control and passive operate separately; whereas in the second configuration, the two operate in unison in

JOHN L. CRASSIDIS; AMR BAZ; NORMAN WERELEY

2000-01-01

173

Plasma deposition of constrained layer damping coatings  

Microsoft Academic Search

Plasma techniques are used to generate constrained layer damping (CLD) coatings on metallic substrates. The process involves the deposition of relatively thick, hard ceramic layers on to soft polymeric damping materials while maintaining the integrity of both layers. Reactive plasma sputter-deposition from an aluminium alloy target is used to deposit alumina layers, with Young's modulus in the range 77-220 GPa

J A Rongong; A A Goruppa; V R Buravalla; G R Tomlinson; F R Jones

2004-01-01

174

Concrete-based constrained layer damping  

Microsoft Academic Search

This paper describes a novel structural damping method that allows a fabricated (welded) machine tool structure to be designed for minimum cost and maximum dynamic stiffness comparable to polymer concrete structures. The damping method is a constrained layer damping (CLD) design where the layers are replicated in place using expanding concrete inside of viscoelastic damping inserts. The novel design is

Eberhard Bamberg; Alexander Slocum

2002-01-01

175

Constraining Dark Halo Potentials with Tidal Tails  

Microsoft Academic Search

Massive and extended dark halos can inhibit the formation of long tidal tails in galaxy collisions. We examine this effect using an extensive survey of simulations with different dark halo potentials to constrain halo properties of interacting galaxies. These constraints are compared to other observational limits and theoretical predictions of halo structure. The dark halos predicted by $\\\\Omega=1$ cosmological models

J. Dubinski; L. Hernquist; J. C. Mihos

1998-01-01

176

Drug design, in vitro pharmacology, and structure-activity relationships of 3-acylamino-2-aminopropionic acid derivatives, a novel class of partial agonists at the glycine site on the N-methyl-D-aspartate (NMDA) receptor complex.  

PubMed

Retaining agonistic activity at the glycine coagonist site of the NMDA receptor in molecules derived from glycine or d-serine has proven to be difficult because in the vicinity of the alpha-amino acid group little substitution is tolerated. We have solved this problem by replacing the hydroxy group of d-serine with an amido group, thus keeping the hydrogen donor function and allowing for further substitution and exploration of the adjacent space. Heterocyclic substitutions resulted in a series of 3-acylamino-2-aminopropionic acid derivatives, with high affinities in a binding assay for the glycine site. In a functional assay assessing the activation of the glycine site, these compounds displayed a wide range of intrinsic efficacies, from antagonism to a high degree of partial agonism. Structure-activity relationships reveal that lipophilic substituents, presumably filling an additional hydrophobic pocket, are accepted by the glycine site, provided that they are separated from the alpha-amino acid group by a short linker. PMID:19642674

Urwyler, Stephan; Floersheim, Philipp; Roy, Bernard L; Koller, Manuel

2009-08-27

177

Calcium constrains plant control over forest ecosystem nitrogen cycling.  

PubMed

Forest ecosystem nitrogen (N) cycling is a critical controller of the ability of forests to prevent the movement of reactive N to receiving waters and the atmosphere and to sequester elevated levels of atmospheric carbon dioxide (CO2). Here we show that calcium (Ca) constrains the ability of northern hardwood forest trees to control the availability and loss of nitrogen. We evaluated soil N-cycling response to Ca additions in the presence and absence of plants and observed that when plants were present, Ca additions "tightened" the ecosystem N cycle, with decreases in inorganic N levels, potential net N mineralization rates, microbial biomass N content, and denitrification potential. In the absence of plants, Ca additions induced marked increases in nitrification (the key process controlling ecosystem N losses) and inorganic N levels. The observed "tightening" of the N cycle when Ca was added in the presence of plants suggests that the capacity of forests to absorb elevated levels of atmospheric N and CO2 is fundamentally constrained by base cations, which have been depleted in many areas of the globe by acid rain and forest harvesting. PMID:22164827

Groffman, Peter M; Fisk, Melany C

2011-11-01

178

DAMPING OPTIMIZATION BY INTEGRATING ENHANCED ACTIVE CONSTRAINED LAYER AND ACTIVE-PASSIVE HYBRID CONSTRAINED LAYER TREATMENTS  

Microsoft Academic Search

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

Y. Liu; K. W. WANG

2002-01-01

179

Enantiomeric interactions between nucleic acid bases and amino acids on solid surfaces.  

PubMed

Molecular interaction between nucleic acid bases and amino acids is a fundamental process in biology. The adsorption of the molecules on surfaces provides the opportunity to study such interactions in great detail by exploiting the high-resolution imaging capabilities of scanning tunnelling microscopy (STM). The chemisorption of prochiral molecules, such as adenine, on a metal surface causes the adsorbed species to become chiral. Subsequent interactions with inherently chiral molecules may then lead to the formation of diastereoisomers, if the enantiomeric interaction process is sufficiently strong. In the case of adenine adsorption on Cu[110], the chiral adsorbates form homochiral chains. Here, we show that the adenine chain direction is fully correlated with the chirality, and that the alpha-amino acid, phenylglycine, shows a strong chiral preference in its interaction with these chains. STM images clearly demonstrate that S-phenylglycine (R-phenylglycine) binds only to chains rotated 19.5 degrees (anti-) clockwise from the [001] direction. Closer examination reveals that the enantiomeric interaction involves double rows of phenylglycine molecules and the adenine chains. This is the first observation at the molecular level of diastereoisomeric interaction, and demonstrates that STM is a powerful method for studying the details of these interactions. PMID:12692537

Chen, Q; Richardson, N V

2003-05-01

180

Genome wide exploration of the origin and evolution of amino acids  

PubMed Central

Background Even after years of exploration, the terrestrial origin of bio-molecules remains unsolved and controversial. Today, observation of amino acid composition in proteins has become an alternative way for a global understanding of the mystery encoded in whole genomes and seeking clues for the origin of amino acids. Results In this study, we statistically monitored the frequencies of 20 alpha-amino acids in 549 taxa from three kingdoms of life: archaebacteria, eubacteria, and eukaryotes. We found that the amino acids evolved independently in these three kingdoms; but, conserved linkages were observed in two groups of amino acids, (A, G, H, L, P, Q, R, and W) and (F, I, K, N, S, and Y). Moreover, the amino acids encoded by GC-poor codons (F, Y, N, K, I, and M) were found to "lose" their usage in the development from single cell eukaryotic organisms like S. cerevisiae to H. sapiens, while the amino acids encoded by GC-rich codons (P, A, G, and W) were found to gain usage. These findings further support the co-evolution hypothesis of amino acids and genetic codes. Conclusion We proposed a new chronological order of the appearance of amino acids (L, A, V/E/G, S, I, K, T, R/D, P, N, F, Q, Y, M, H, W, C). Two conserved evolutionary paths of amino acids were also suggested: A?G?R?P and K?Y.

2010-01-01

181

The multi-objective constrained assignment problem  

NASA Astrophysics Data System (ADS)

Assignment problems are a common area of research in operational research and computer science. Military applications include military personnel assignment, combat radio frequency assignment, and weapon target assignment. In general, assignment problems can be found in a wide array of areas, from modular placement to resource scheduling. Many of these problems are very similar to one another. This paper models and compares some of the assignment problems in literature. These similar problems are then generalized into a generalized multi-objective problem, the constrained assignment problem. Using a multi-objective genetic algorithm, we solve an example of a constrained assignment problem called the airman assignment problem. Results show that good solutions along the interior portion of the Pareto front are found in earlier generations and later generations produce more exterior points.

Kleeman, Mark P.; Lamont, Gary B.

2007-05-01

182

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

2010-04-01

183

Constraining the Braneworld with Gravitational Wave Observations  

NASA Technical Reports Server (NTRS)

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 micron level for optimal cases, while the observation of a single galactic black hole binary with LISA results in an optimal constraint of L less than or equal to 5 microns.

McWilliams, Sean T.

2011-01-01

184

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

185

CONSTRAINED SPECTRAL CLUSTERING FOR IMAGE SEGMENTATION  

PubMed Central

Constrained spectral clustering with affinity propagation in its original form is not practical for large scale problems like image segmentation. In this paper we employ novelty selection sub-sampling strategy, besides using efficient numerical eigen-decomposition methods to make this algorithm work efficiently for images. In addition, entropy-based active learning is also employed to select the queries posed to the user more wisely in an interactive image segmentation framework. We evaluate the algorithm on general and medical images to show that the segmentation results will improve using constrained clustering even if one works with a subset of pixels. Furthermore, this happens more efficiently when pixels to be labeled are selected actively.

Sourati, Jamshid; Brooks, Dana H.; Dy, Jennifer G.; Erdogmus, Deniz

2013-01-01

186

Eigenvalue placement and stabilization by constrained optimization  

NASA Technical Reports Server (NTRS)

A pole placement algorithm is proposed which uses constrained nonlinear optimization techniques on a finite dimensional model of a linear n degree of freedom system. Low order feedback control is assumed where r poles may be assigned; r being the rank of the sensor coefficient matrix. It is shown that by combining feedback control theory methods with optimization techniques, one can ensure the stability characteristics of a system, and can alter its transient response.

Decaro, S. M.; Inman, D. J.

1985-01-01

187

Jamming by shape in kinetically constrained models  

NASA Astrophysics Data System (ADS)

We derive expressions for the critical density for jamming in a hyper-rhomboid system of arbitrary shape in any dimension for the Kob-Andersen and Fredrickson-Andersen kinetically constrained models. We find that changing the system's shape without altering its total volume or particle density may induce jamming. We also find a transition between shapes in which the correlation length between jammed particles is infinite and shapes that have a finite correlation length.

Teomy, Eial; Shokef, Yair

2014-03-01

188

Entropy-Constrained Successively Refinable Scaler Quantization  

Microsoft Academic Search

We study the design of entropy--constrained successively refinable scalar quantizers. Wepropose two algorithms to minimize the average distortion and design such a quantizer.We consider two sets of constraints on the entropy: (i) constraint on the average rate and(ii) constraint on aggregate rates. Both algorithms can be easily extended to design vectorquantizers.1 IntroductionSource coding systems that are successively refinable or scalable

Hamid Jafarkhani; Hugh Brunk; Nariman Farvardin

1997-01-01

189

Constraining Neutron Star Matter with Quantum Chromodynamics  

NASA Astrophysics Data System (ADS)

In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount—or even presence—of quark matter inside the stars.

Kurkela, Aleksi; Fraga, Eduardo S.; Schaffner-Bielich, Jürgen; Vuorinen, Aleksi

2014-07-01

190

Constrained layer damping system for box beams  

Microsoft Academic Search

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

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

1996-01-01

191

On the path integral of constrained systems  

SciTech Connect

Constrained Hamiltonian systems are investigated by using Gueler's method. Integration of a set of equations of motion and the action function is discussed. It is shown that the canonical path integral quantization is obtained directly as an integration over the canonical phase-space coordinates without any need to enlarge the initial phase-space by introducing extra- unphysical variables as in the Batalin-Fradkin-Tyutin (BFT) method. The abelian Proca model is analyzed by the two methods.

Muslih, Sami I. [Physics Department, Al-Azhar University, Gaza, Palestine (Country Unknown)

2004-10-04

192

Statistical mechanics of budget-constrained auctions  

Microsoft Academic Search

Finding the optimal assignment in budget-constrained auctions is a combinatorial optimization problem with many important applications, a notable example being in the sale of advertisement space by search engines (in this context the problem is often referred to as the off-line AdWords problem). On the basis of the cavity method of statistical mechanics, we introduce a message-passing algorithm that is

F. Altarelli; A. Braunstein; J. Realpe-Gomez; R. Zecchina

2009-01-01

193

Statistical mechanics of budget-constrained auctions  

Microsoft Academic Search

Finding the optimal assignment in budget-constrained auctions is a\\u000acombinatorial optimization problem with many important applications, a notable\\u000aexample being the sale of advertisement space by search engines (in this\\u000acontext the problem is often referred to as the off-line AdWords problem).\\u000aBased on the cavity method of statistical mechanics, we introduce a message\\u000apassing algorithm that is capable of

Fabrizio Altarelli; Alfredo Braunstein; J. Realpe-gomez; Riccardo Zecchina

2009-01-01

194

Constraining dark halos with tidal tails  

Microsoft Academic Search

Massive and extended dark halos can inhibit the formation of long tidal tails\\u000ain galaxy collisions. We examine this effect using an extensive survey of\\u000asimulations with different dark halo potentials to constrain halo properties of\\u000ainteracting galaxies. These constraints are compared to other observational\\u000alimits and theoretical predictions of halo structure. The dark halos predicted\\u000aby $\\\\Omega=1$ cosmological models

John Dubinski; Chris Mihos; Lars Hernquist

1997-01-01

195

Constrained Simulation of the Bullet Cluster  

NASA Astrophysics Data System (ADS)

In this work, we report on a detailed simulation of the Bullet Cluster (1E0657-56) merger, including magnetohydrodynamics, plasma cooling, and adaptive mesh refinement. We constrain the simulation with data from gravitational lensing reconstructions and the 0.5-2 keV Chandra X-ray flux map, then compare the resulting model to higher energy X-ray fluxes, the extracted plasma temperature map, Sunyaev-Zel'dovich effect measurements, and cluster halo radio emission. We constrain the initial conditions by minimizing the chi-squared figure of merit between the full two-dimensional (2D) observational data sets and the simulation, rather than comparing only a few features such as the location of subcluster centroids, as in previous studies. A simple initial configuration of two triaxial clusters with Navarro-Frenk-White dark matter profiles and physically reasonable plasma profiles gives a good fit to the current observational morphology and X-ray emissions of the merging clusters. There is no need for unconventional physics or extreme infall velocities. The study gives insight into the astrophysical processes at play during a galaxy cluster merger, and constrains the strength and coherence length of the magnetic fields. The techniques developed here to create realistic, stable, triaxial clusters, and to utilize the totality of the 2D image data, will be applicable to future simulation studies of other merging clusters. This approach of constrained simulation, when applied to well-measured systems, should be a powerful complement to present tools for understanding X-ray clusters and their magnetic fields, and the processes governing their formation.

Lage, Craig; Farrar, Glennys

2014-06-01

196

Constrained inversion of seismo-volcanic events  

NASA Astrophysics Data System (ADS)

The inversion of seismo-volcanic events is performed to retrieve the source geometry and to determine volumetric budgets of the source. Such observations have shown to be an important tool for the seismological monitoring of volcanoes. We developed a novel technique for the non-linear constrained inversion of low frequency seismo-volcanic events. Unconstrained linear inversion methods work well when a dense network of broadband seismometers is available. We propose a new constrained inversion technique, which has shown to be efficient also in a reduced network configuration and a low signal-noise ratio. The waveform inversion is performed in the frequency domain, constraining the source mechanism during the event to vary only in its magnitude. The eigenvectors orientation and the eigenvalue ratio are kept constant. This significantly reduces the number of parameters to invert, making the procedure more stable. The method has been tested over a synthetic dataset, reproducing realistic very-long-period (VLP) signals Stromboli volcano. We have applied the method to a VLP dataset recorded on Stromboli volcano and to low-frequency earthquakes recorded on Mt.Vesuvius.

Nocerino, Luciano; D'Auria, Luca; Giudicepietro, Flora; Martini, Marcello

2014-05-01

197

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

198

An English language interface for constrained domains  

NASA Technical Reports Server (NTRS)

The Multi-Satellite Operations Control Center (MSOCC) Jargon Interpreter (MJI) demonstrates an English language interface for a constrained domain. A constrained domain is defined as one with a small and well delineated set of actions and objects. The set of actions chosen for the MJI is from the domain of MSOCC Applications Executive (MAE) Systems Test and Operations Language (STOL) directives and contains directives for signing a cathode ray tube (CRT) on or off, calling up or clearing a display page, starting or stopping a procedure, and controlling history recording. The set of objects chosen consists of CRTs, display pages, STOL procedures, and history files. Translation from English sentences to STOL directives is done in two phases. In the first phase, an augmented transition net (ATN) parser and dictionary are used for determining grammatically correct parsings of input sentences. In the second phase, grammatically typed sentences are submitted to a forward-chaining rule-based system for interpretation and translation into equivalent MAE STOL directives. Tests of the MJI show that it is able to translate individual clearly stated sentences into the subset of directives selected for the prototype. This approach to an English language interface may be used for similarly constrained situations by modifying the MJI's dictionary and rules to reflect the change of domain.

Page, Brenda J.

1989-01-01

199

Mass-Additive Vibration Testing Of Constrained Structures  

NASA Technical Reports Server (NTRS)

Report describes study of mass-additive method of modal survey testing of flexible structures that, in normal use, constrained by other structures. Structure normally constrained by another structure is suspended freely and extra masses attached to boundary.

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

1995-01-01

200

Pattern Search Algorithms for Mixed Variable General Constrained Optimization Problems.  

National Technical Information Service (NTIS)

A new class of algorithms for solving nonlinearly constrained mixed variable optimization problems is presented The Audet-Dennis Generalized Pattern Search (GPS) algorithm for bound constrained mixed variable optimization problems is extended to problems ...

M. A. Abramson

2002-01-01

201

Position control and explicit force control of a constrained manipulator  

Microsoft Academic Search

The kinematically constrained dynamic system of a robotic manipulator is modeled by including constrained forces in the dynamic equations in this paper, and the constrained forces are expressed as an obvious function of the state and inputs of the system. A controller without involving any force sensor is therefore constructed by taking the advantage of the redundancy between the input

M. Minami; T. Asakura; L. X. Dong; Y. M. Huang

1997-01-01

202

Active constrained layer damping for micro-satellites  

Microsoft Academic Search

Active constrained layer damping for a lightweight precision pointing system is examined. The setup consists of a scale satellite whose dimensions are designed to have representative modal characteristics. The focus of the research is to assess active constrained layer damping integrated into this precision structure in terms of improved settling time. In particular we wish to compare active constrained layer

W. C. van Nostrand; G. J. Knowles; D. J. Inman

1993-01-01

203

Finite element model for active constrained layer damping  

Microsoft Academic Search

Constrained layer damping has been used for many years to increase the damping in engineering structures. Active damping using smart materials has been investigated a great deal recently. Several researchers have suggested the concept of using viscoelastic materials with piezoceramics as the constraining layer. Since the piezoceramics are active materials, this concept can be referred to as active constrained layer

William C. van Nostrand; Daniel J. Inman

1995-01-01

204

Vibration control through passive constrained layer damping and active control  

Microsoft Academic Search

To add damping to systems, viscoelastic materials (VEM) are added to structures. In order to enhance the damping effects of the VEM, a constraining layer is attached. When this constraining layer is an active element, the treatment is called active constrained layer damping (ACLD). Recently, the investigation of ACLD treatments has shown it to be an effective method of vibration

Margaretha J. Lam; Daniel J. Inman; William R. Saunders

1997-01-01

205

Feature and Pose Constrained Visual Aided Inertial Navigation for Computationally Constrained Aerial Vehicles  

NASA Technical Reports Server (NTRS)

A Feature and Pose Constrained Extended Kalman Filter (FPC-EKF) is developed for highly dynamic computationally constrained micro aerial vehicles. Vehicle localization is achieved using only a low performance inertial measurement unit and a single camera. The FPC-EKF framework augments the vehicle's state with both previous vehicle poses and critical environmental features, including vertical edges. This filter framework efficiently incorporates measurements from hundreds of opportunistic visual features to constrain the motion estimate, while allowing navigating and sustained tracking with respect to a few persistent features. In addition, vertical features in the environment are opportunistically used to provide global attitude references. Accurate pose estimation is demonstrated on a sequence including fast traversing, where visual features enter and exit the field-of-view quickly, as well as hover and ingress maneuvers where drift free navigation is achieved with respect to the environment.

Williams, Brian; Hudson, Nicolas; Tweddle, Brent; Brockers, Roland; Matthies, Larry

2011-01-01

206

The asymptotics of large constrained graphs  

NASA Astrophysics Data System (ADS)

We show, through local estimates and simulation, that if one constrains simple graphs by their densities ? of edges and ? of triangles, then asymptotically (in the number of vertices) for over 95% of the possible range of those densities there is a well-defined typical graph, and it has a very simple structure: the vertices are decomposed into two subsets V1 and V2 of fixed relative size c and 1 ? c, and there are well-defined probabilities of edges, gjk, between vj ? Vj, and vk ? Vk. Furthermore the four parameters c, g11, g22 and g12 are smooth functions of (?, ?) except at two smooth ‘phase transition’ curves.

Radin, Charles; Ren, Kui; Sadun, Lorenzo

2014-05-01

207

Resonant Normal Forms as Constrained Linear Systems  

NASA Astrophysics Data System (ADS)

We show that a nonlinear dynamical system in Poincaré-Dulac normal form (in Rn) can be seen as a constrained linear system; the constraints are given by the resonance conditions satisfied by the spectrum of (the linear part of) the system and identify a naturally invariant manifold for the flow of the ``parent'' linear system. The parent system is finite dimensional if the spectrum satisfies only a finite number of resonance conditions, as implied e.g. by the Poincaré condition. In this case our result can be used to integrate resonant normal forms, and sheds light on the geometry behind the classical integration method of Horn, Lyapounov and Dulac.

Gaeta, Giuseppe

208

Quantum annealing in a kinetically constrained system.  

PubMed

Classical and quantum annealing is discussed in the case of a generalized kinetically constrained model, where the relaxation dynamics of a system with trivial ground state is retarded by the appearance of energy barriers in the relaxation path, following a local kinetic rule. Effectiveness of thermal and quantum fluctuations in overcoming these kinetic barriers to reach the ground state are studied. It has been shown that for certain barrier characteristics, quantum annealing might by far surpass its thermal counter part in reaching the ground state faster. PMID:16196745

Das, Arnab; Chakrabarti, Bikas K; Stinchcombe, Robin B

2005-08-01

209

Security-constrained reactive power dispatch  

SciTech Connect

This paper presents a new method to solve the preventive security-constrained reactive power (var) dispatch problem. A decomposition-coordination scheme is conceived in order to take advantage of the special structure of the problem. Instead of tearing the network, the problem itself is decomposed into smaller sub-problems. Techniques are presented for contingency simulation and for the handling of these contingencies in the optimization process. The computing procedure is given for the step-by-step solution for on-line implementation. VAR-oriented load flow and optimal power flow methods are described. Numerical testing results are reported.

Terra, L.D.B.; Short, M.J. (Imperial Coll. of Science and Technology, London (UK))

1991-02-01

210

Constraining dynamical models with observational data  

NASA Astrophysics Data System (ADS)

The spatial distribution and kinematics of stars in the Milky Way are linked through the gravitational potential. Observations of the positions and velocities of stars can therefore be used to measure the mass distribution of the Milky Way. I review steady-state dynamical modeling approaches and illustrate their use in constraining the local matter distribution and the circular velocity curve from the kinematics of stellar tracers. In a few years, Gaia will increase the number of precise positions and velocities by multiple orders of magnitude. I describe some of the dynamical analyses that will be possible with the Gaia data and discuss some promising avenues for the optimal analysis of dynamical data.

Bovy, Jo

2014-01-01

211

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics.  

PubMed

In the recent past, the design and synthesis of peptide mimics (peptidomimetics) has received much attention. This because they have shown in many cases enhanced pharmacological properties over their natural peptide analogues. In particular, the incorporation of cyclic constructs into peptides is of high interest as they reduce the flexibility of the peptide enhancing often affinity for a certain receptor. Moreover, these cyclic mimics force the molecule into a well-defined secondary structure. Constraint structural and conformational features are often found in biological active peptides. For the synthesis of cyclic constrained peptidomimetics usually a sequence of multiple reactions has been applied, which makes it difficult to easily introduce structural diversity necessary for fine tuning the biological activity. A promising approach to tackle this problem is the use of multicomponent reactions (MCRs), because they can introduce both structural diversity and molecular complexity in only one step. Among the MCRs, the isocyanide-based multicomponent reactions (IMCRs) are most relevant for the synthesis of peptidomimetics because they provide peptide-like products. However, these IMCRs usually give linear products and in order to obtain cyclic constrained peptidomimetics, the acyclic products have to be cyclized via additional cyclization strategies. This is possible via incorporation of bifunctional substrates into the initial IMCR. Examples of such bifunctional groups are N-protected amino acids, convertible isocyanides or MCR-components that bear an additional alkene, alkyne or azide moiety and can be cyclized via either a deprotection-cyclization strategy, a ring-closing metathesis, a 1,3-dipolar cycloaddition or even via a sequence of multiple multicomponent reactions. The sequential IMCR-cyclization reactions can afford small cyclic peptide mimics (ranging from four- to seven-membered rings), medium-sized cyclic constructs or peptidic macrocycles (>12 membered rings). This review describes the developments since 2002 of IMCRs-cyclization strategies towards a wide variety of small cyclic mimics, medium sized cyclic constructs and macrocyclic peptidomimetics. PMID:24605172

Koopmanschap, Gijs; Ruijter, Eelco; Orru, Romano Va

2014-01-01

212

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

213

Regular Language Constrained Sequence Alignment Revisited  

NASA Astrophysics Data System (ADS)

Imposing constraints in the form of a finite automaton or a regular expression is an effective way to incorporate additional a priori knowledge into sequence alignment procedures. With this motivation, Arslan [1] introduced the Regular Language Constrained Sequence Alignment Problem and proposed an O(n 2 t 4) time and O(n 2 t 2) space algorithm for solving it, where n is the length of the input strings and t is the number of states in the non-deterministic automaton, which is given as input. Chung et al. [2] proposed a faster O(n 2 t 3) time algorithm for the same problem. In this paper, we further speed up the algorithms for Regular Language Constrained Sequence Alignment by reducing their worst case time complexity bound to O(n 2 t 3/logt). This is done by establishing an optimal bound on the size of Straight-Line Programs solving the maxima computation subproblem of the basic dynamic programming algorithm. We also study another solution based on a Steiner Tree computation. While it does not improve the run time complexity in the worst case, our simulations show that both approaches are efficient in practice, especially when the input automata are dense.

Kucherov, Gregory; Pinhas, Tamar; Ziv-Ukelson, Michal

214

Trajectory generation and constrained control of quadrotors  

NASA Astrophysics Data System (ADS)

Unmanned Aerial Systems, although still in early development, are expected to grow in both the military and civil sectors. As part of the UAV sector, the Quadrotor helicopter platform has been receiving a lot of interest from various academic and research institutions because of their simplistic design and low cost to manufacture, yet remaining a challenging platform to control. Four different controllers were derived for the trajectory generation and constrained control of a quadrotor platform. The first approach involves the linear version of the Model Predictive Control (MPC) algorithm to solve the state constrained optimization problem. The second approach uses the State Dependent Coefficient (SDC) form to capture the system non-linearities into a pseudo-linear system matrix, which is used to derive the State Dependent Riccati Equation (SDRE) based optimal control. For the third approach, the SDC form is exploited for obtaining a nonlinear equivalent of the model predictive control. Lastly, a combination of the nonlinear MPC and SDRE optimal control algorithms is used to explore the feasibility of a near real-time nonlinear optimization technique.

Tule, Carlos Alberto

215

Robust Control of Active Constrained Layer Damping  

NASA Astrophysics Data System (ADS)

ConventionalPassiveConstrainedLayerDamping (PCLD) treatments with visco-elastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The control gains of the resultingActiveConstrainedLayerDamping (ACLD) treatments are selected, in this paper, for fully treated beams using the theory of robust controls. In this regard, an optimal controller is designed to accommodate the uncertainties of the ACLD parameters, particularly those of the visco-elastic cores which arise from the variation of the operating temperature and frequency. The controller is also designed to reject the effects of the noise and external disturbances. The theoretical performance of beams treated with the optimally controlled ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with PCLD treatments. The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broadband attenuation capabilities over a wide range of operating temperatures as compared to PCLD treatments.

Baz, A.

1998-04-01

216

Robust control of active constrained layer damping  

NASA Astrophysics Data System (ADS)

Conventional passive constrained layer damping (PCLD) treatments with visco-elastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The control gains of the resulting active constrained layer damping (ACLD) treatments are selected, in this paper, for fully-treated beams using the theory of robust controls. In this regard, an optimal controller is designed to accommodate the uncertainties of the ACLD parameters particularly those of the visco-elastic cores which arise from the variation of the operating temperature and frequency. The controller is also designed to reject the effects of the noise and external disturbances. The theoretical performance of beams treated with the optimally controlled ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with PCLD treatments. The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broad-band attenuation capabilities over a wide range of operating temperatures as compared to PCLD treatments.

Baz, Amr M.

1996-05-01

217

Constrained concept factorization for image representation.  

PubMed

Matrix factorization based techniques, such as nonnegative matrix factorization and concept factorization, have attracted great attention in dimensionality reduction and data clustering. Previous studies show that both of them yield impressive results on image processing and document clustering. However, both of them are essentially unsupervised methods and cannot incorporate label information. In this paper, we propose a novel semisupervised matrix decomposition method for extracting the image concepts that are consistent with the known label information. With this constraint, we call the new approach constrained concept factorization. By requiring that the data points sharing the same label have the same coordinate in the new representation space, this approach has more discriminating power. The experimental results on several corpora show good performance of our novel algorithm in terms of clustering accuracy and mutual information. PMID:24196984

Liu, Haifeng; Yang, Genmao; Wu, Zhaohui; Cai, Deng

2014-07-01

218

Fluctuation theorem for constrained equilibrium systems.  

PubMed

We discuss the fluctuation properties of equilibrium chaotic systems with constraints such as isokinetic and Nosé-Hoover thermostats. Although the dynamics of these systems does not typically preserve phase-space volumes, the average phase-space contraction rate vanishes, so that the stationary states are smooth. Nevertheless, finite-time averages of the phase-space contraction rate have nontrivial fluctuations which we show satisfy a simple version of the Gallavotti-Cohen fluctuation theorem, complementary to the usual fluctuation theorem for nonequilibrium stationary states and appropriate to constrained equilibrium states. Moreover, we show that these fluctuations are distributed according to a Gaussian curve for long enough times. Three different systems are considered here: namely, (i) a fluid composed of particles interacting with Lennard-Jones potentials, (ii) a harmonic oscillator with Nosé-Hoover thermostatting, and (iii) a simple hyperbolic two-dimensional map. PMID:16605412

Gilbert, Thomas; Dorfman, J Robert

2006-02-01

219

Constrained multibody system dynamics: An automated approach  

NASA Technical Reports Server (NTRS)

The governing equations for constrained multibody systems are formulated in a manner suitable for their automated, numerical development and solution. The closed loop problem of multibody chain systems is addressed. The governing equations are developed by modifying dynamical equations obtained from Lagrange's form of d'Alembert's principle. The modifications is based upon a solution of the constraint equations obtained through a zero eigenvalues theorem, is a contraction of the dynamical equations. For a system with n-generalized coordinates and m-constraint equations, the coefficients in the constraint equations may be viewed as constraint vectors in n-dimensional space. In this setting the system itself is free to move in the n-m directions which are orthogonal to the constraint vectors.

Kamman, J. W.; Huston, R. L.

1982-01-01

220

Constraining The Hot Jupiter Kozai Mechanism Connection  

NASA Astrophysics Data System (ADS)

We have performed a systematic analysis to search for long-term trends in the radial velocity residuals of more than 120 exoplanetary hosts from the California-Carnegie Planet Search team to confirm or constrain the role that the Kozai mechanism plays in causing the hot Jupiter pile-up (an excess of exoplanets with 3-4 d periods). These long-term linear trends are likely indicative of stellar or substellar companions that could have induced the known exoplanet to migrate to its present position via the Kozai mechanism. Preliminary results suggest that the frequency of long-term linear trends are statistically similar in the hot Jupiter and the rest of the exoplanetary sample, thus suggesting that Kozai migration is not responsible for the majority of hot Jupiters.

Croll, Bryce; Murray, N.; Marcy, G. W.; Wright, J. T.; Cumming, A.

2007-12-01

221

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

222

Perceived visual speed constrained by image segmentation  

NASA Technical Reports Server (NTRS)

Little is known about how or where the visual system parses the visual scene into objects or surfaces. However, it is generally assumed that the segmentation and grouping of pieces of the image into discrete entities is due to 'later' processing stages, after the 'early' processing of the visual image by local mechanisms selective for attributes such as colour, orientation, depth, and motion. Speed perception is also thought to be mediated by early mechanisms tuned for speed. Here we show that manipulating the way in which an image is parsed changes the way in which local speed information is processed. Manipulations that cause multiple stimuli to appear as parts of a single patch degrade speed discrimination, whereas manipulations that perceptually divide a single large stimulus into parts improve discrimination. These results indicate that processes as early as speed perception may be constrained by the parsing of the visual image into discrete entities.

Verghese, P.; Stone, L. S.

1996-01-01

223

Statistical mechanics of budget-constrained auctions  

NASA Astrophysics Data System (ADS)

Finding the optimal assignment in budget-constrained auctions is a combinatorial optimization problem with many important applications, a notable example being in the sale of advertisement space by search engines (in this context the problem is often referred to as the off-line AdWords problem). On the basis of the cavity method of statistical mechanics, we introduce a message-passing algorithm that is capable of solving efficiently random instances of the problem extracted from a natural distribution, and we derive from its properties the phase diagram of the problem. As the control parameter (average value of the budgets) is varied, we find two phase transitions delimiting a region in which long-range correlations arise.

Altarelli, F.; Braunstein, A.; Realpe-Gomez, J.; Zecchina, R.

2009-07-01

224

Constrained Aerothermodynamic Design of Hypersonic Vehicles  

NASA Technical Reports Server (NTRS)

An investigation was conducted into possible methods of incorporating a hypersonic design capability with aerothermodynamic constraints into the CDISC aerodynamic design tool. The work was divided into two distinct phases: develop relations between surface curvature and hypersonic pressure coefficient which are compatible with CDISC's direct-iterative design method; and explore and implement possible methods of constraining the heat transfer rate over all or portions of the design surface. The main problem in implementing this method has been the weak relationship between surface shape and pressure coefficient at the stagnation point and the need to design around the surface blunt leading edge where there is a slope singularity. The final results show that some success has been achieved, but further improvements are needed.

Gally, Tom; Campbell, Dick

2002-01-01

225

Multiplier-continuation algorthms for constrained optimization  

NASA Technical Reports Server (NTRS)

Several path following algorithms based on the combination of three smooth penalty functions, the quadratic penalty for equality constraints and the quadratic loss and log barrier for inequality constraints, their modern counterparts, augmented Lagrangian or multiplier methods, sequential quadratic programming, and predictor-corrector continuation are described. In the first phase of this methodology, one minimizes the unconstrained or linearly constrained penalty function or augmented Lagrangian. A homotopy path generated from the functions is then followed to optimality using efficient predictor-corrector continuation methods. The continuation steps are asymptotic to those taken by sequential quadratic programming which can be used in the final steps. Numerical test results show the method to be efficient, robust, and a competitive alternative to sequential quadratic programming.

Lundberg, Bruce N.; Poore, Aubrey B.; Bing, Yang

1989-01-01

226

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

227

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

228

Computer-aided dynamic analysis of constrained multibody systems  

NASA Astrophysics Data System (ADS)

An efficient recursive algorithm for computer-aided dynamic analysis of constrained multibody systems is described. Dynamic differential equations can be constructed by computing indirect problems of dynamics rather than deriving analytic explicit expressions for these equations. The constrained equations can easily be obtained using neither derivation of explicit expressions nor any differentiation. A singular value decomposition reductive method is used to reduce and solve dynamic differential equations of constrained multibody systems so that the constrained forces and moments can be avoided. The use of results from the corresponding open-loop system avoids the use of much additional computation for a constrained system. A general-purpose FORTRAN program has been developed for computer-aided dynamic analysis of constrained multibody systems. Satisfactory results have been obtained for a five-link driven chain.

Chen, Jianping; Zhu, Mingming; Su, Yibo

1991-01-01

229

Asynchronous parallel generating set search for linearly-constrained optimization.  

SciTech Connect

Generating set search (GSS) is a family of direct search methods that encompasses generalized pattern search and related methods. We describe an algorithm for asynchronous linearly-constrained GSS, which has some complexities that make it different from both the asynchronous bound-constrained case as well as the synchronous linearly-constrained case. The algorithm has been implemented in the APPSPACK software framework and we present results from an extensive numerical study using CUTEr test problems. We discuss the results, both positive and negative, and conclude that GSS is a reliable method for solving small-to-medium sized linearly-constrained optimization problems without derivatives.

Lewis, Robert Michael (; ); Griffin, Joshua D.; Kolda, Tamara Gibson

2006-08-01

230

Second-order negative-curvature methods for box-constrained and general constrained optimization  

Microsoft Academic Search

A Nonlinear Programming algorithm that converges to second-order stationary points is introduced in this paper. The main tool\\u000a is a second-order negative-curvature method for box-constrained minimization of a certain class of functions that do not possess\\u000a continuous second derivatives. This method is used to define an Augmented Lagrangian algorithm of PHR (Powell-Hestenes-Rockafellar)\\u000a type. Convergence proofs under weak constraint qualifications are

R. Andreani; E. G. Birgin; J. M. Martínez; M. L. Schuverdt

2010-01-01

231

Synthesis, characterisation and biological evaluation of N-(ferrocenyl)naphthoyl amino acid esters as anticancer agents.  

PubMed

A series of N-(ferrocenyl)naphthoyl amino acid esters 5-18 has been prepared by coupling ferrocenyl naphthoic acids 3-4 to alpha-amino acids and linear amino acids in the presence of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and 1-hydroxybenzotriazole (HOBt). The compounds were fully characterised by a range of NMR spectroscopic techniques, UV-Vis spectroscopy, mass spectrometry and cyclic voltammetry. X-ray crystallographic studies of the intermediate compounds 1-2 were also performed. Biological evaluation of the intermediates 1-2 and N-(ferrocenyl)naphthoyl amino acid esters 5-18 was performed in the H1299 non-small cell lung cancer (NSCLC) cell line and the Sk-Mel-28 metastatic melanoma cell line. The intermediates 1-2 failed to produce an effect in either cell line. Compounds 5-18 exhibited a strong anti-proliferative effect in the H1299 cell line, whilst the Sk-Mel-28 cells were slightly more resistant to these compounds. N-(6-ferrocenyl-2-naphthoyl)-gamma-aminobutyric acid ethyl ester 17 shows a particularly high activity in both the H1299 cell line (IC(50) = 0.62 +/- 0.07 microM) and the Sk-Mel-28 cell line (IC(50) = 1.41 +/- 0.04 microM). PMID:20680224

Mooney, Aine; Corry, Alan J; Ní Ruairc, Cliodhna; Mahgoub, Thamir; O'Sullivan, Dermot; O'Donovan, Norma; Crown, John; Varughese, Sunil; Draper, Sylvia M; Rai, Dilip K; Kenny, Peter T M

2010-09-21

232

Performance characteristics of active constrained layer damping versus passive constrained layer damping with active control  

NASA Astrophysics Data System (ADS)

The shear strains in the visco-elastic cores of beams controlled by Active Constrained Layer Damping (ACLD) treatments are determined and compared with those of beams controlled by Active Control (AC) and conventional Passive Constrained Layer Damping (PCLD) treatments. Such comparison is essential in quantifying the individual contribution of the active and passive damping components, to the overall damping characteristics, when each operates separately and when both are combined to interact in unison as in the ACLD treatments. The comparisons are based on distributed-parameter and finite element models which describe the behavior of beams controlled by ACLD as well as beams treated by AC and PCLD treatments. The distributed-parameter models give closed-form expressions for the energy dissipation characteristics of the ACLD treatments in comparison with those of the AC/PCLD treatments. Also, the finite element models are validated experimentally using visco-elastic cores which are photo-elastic in order to study the distribution of the shear strains inside these cores. The results obtained indicate that the ACLD treatments are capable of developing shear deformations, in the visco-elastic cores, higher than those generated by the AC/PCLD treatments when the ratio of the longitudinal rigidity of the constraining layer to that of the base beam is less than 1. With such enhanced shear deformation capabilities, the ACLD treatments can develop high damping and effective attenuation of the vibration of critical systems as the blades of rotorcrafts.

Chen, T.; Baz, Amr M.

1996-05-01

233

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

234

Development and pharmacological characterization of conformationally constrained urotensin II-related peptide agonists.  

PubMed

Urotensin II (UII) and its paralog peptide, urotensin II-related peptide (URP), exert not only common but also divergent actions through the activation of UT, a specific membrane-bound receptor that belongs to the 1A G protein-coupled receptor subclass. In this study, we have designed and synthesized new URP analogues in which the intracyclic Trp residue was replaced with natural, unnatural, and constrained amino acids to determine important physicochemical features for receptor binding and activation. The biological data, highlighting the potent agonistic behavior of [Tiq(4)]URP and [Tpi(4)]URP, also suggest that the Trp residue, and more specifically the indole ring, is not critical for receptor interaction and could in fact be involved in the intramolecular stabilization of the bioactive conformation of URP. Finally, these analogues, which are intracyclic constrained URP-based agonists, could represent useful pharmacological tools for the study of the urotensinergic system. PMID:24251366

Chatenet, David; Folch, Benjamin; Feytens, Debby; Létourneau, Myriam; Tourwé, Dirk; Doucet, Nicolas; Fournier, Alain

2013-12-12

235

Should we still believe in constrained supersymmetry?  

NASA Astrophysics Data System (ADS)

We calculate partial 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 partial 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 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, Andy; Carter, Daniel; Farmer, Benjamin; White, Martin

2013-10-01

236

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

237

Constraining solar hidden photons using HPGe detector  

NASA Astrophysics Data System (ADS)

In this Letter we report on the results of our search for photons from a U(1) gauge factor in the hidden sector of the full theory. With our experimental setup we observe the single spectrum in a HPGe detector arising as a result of the photoelectric-like absorption of hidden photons emitted from the Sun on germanium atoms inside the detector. The main ingredient of the theory used in our analysis, a severely constrained kinetic mixing from the two U(1) gauge factors and massive hidden photons, entails both photon into hidden state oscillations and a minuscule coupling of hidden photons to visible matter, of which the latter our experimental setup has been designed to observe. On a theoretical side, full account was taken of the effects of refraction and damping of photons while propagating in Sun's interior as well as in the detector. We exclude hidden photons with kinetic couplings ?>(2.2×10-13-3×10-7) in the mass region 0.2 eV?m?30 keV. Our constraints on the mixing parameter ? in the mass region from 20 eV up to 15 keV prove even slightly better then those obtained recently by using data from the CAST experiment, albeit still somewhat weaker than those obtained from solar and HB stars lifetime arguments.

Horvat, R.; Kekez, D.; Kr?mar, M.; Kre?ak, Z.; Ljubi?i?, A.

2013-04-01

238

Scheduling Aircraft Landings under Constrained Position Shifting  

NASA Technical Reports Server (NTRS)

Optimal scheduling of airport runway operations can play an important role in improving the safety and efficiency of the National Airspace System (NAS). Methods that compute the optimal landing sequence and landing times of aircraft must accommodate practical issues that affect the implementation of the schedule. One such practical consideration, known as Constrained Position Shifting (CPS), is the restriction that each aircraft must land within a pre-specified number of positions of its place in the First-Come-First-Served (FCFS) sequence. We consider the problem of scheduling landings of aircraft in a CPS environment in order to maximize runway throughput (minimize the completion time of the landing sequence), subject to operational constraints such as FAA-specified minimum inter-arrival spacing restrictions, precedence relationships among aircraft that arise either from airline preferences or air traffic control procedures that prevent overtaking, and time windows (representing possible control actions) during which each aircraft landing can occur. We present a Dynamic Programming-based approach that scales linearly in the number of aircraft, and describe our computational experience with a prototype implementation on realistic data for Denver International Airport.

Balakrishnan, Hamsa; Chandran, Bala

2006-01-01

239

Founder niche constrains evolutionary adaptive radiation  

PubMed Central

Adaptive radiation of a lineage into a range of organisms with different niches underpins the evolution of life’s diversity. Although the role of the environment in shaping adaptive radiation is well established, theory predicts that the evolvability and niche of the founding ancestor are also of importance. Direct demonstration of a causal link requires resolving the independent effects of these additional factors. Here, we accomplish this using experimental bacterial populations and demonstrate how the dynamics of adaptive radiation are constrained by the niche of the founder. We manipulated the propensity of the founder to undergo adaptive radiation and resolved the underlying causal changes in both its evolvability and niche. Evolvability did not change, but the propensity for adaptive radiation was altered by changes in the position and breadth of the niche of the founder. These observations provide direct empirical evidence for a link between the niche of organisms and their propensity for adaptive radiation. This general mechanism may have rendered the evolutionary dynamics of extant adaptive radiations dependent on chance events that determined their founding ancestors.

Flohr, Regis C. E.; Blom, Carsten J.; Rainey, Paul. B.; Beaumont, Hubertus J. E.

2013-01-01

240

Constraining New Physics with D meson decays  

NASA Astrophysics Data System (ADS)

Latest Lattice results on D form factors evaluation from first principles show that the Standard Model (SM) branching ratios prediction for the leptonic Ds???? decays and the semileptonic SM branching ratios of the D0 and D+ meson decays are in good agreement with the world average experimental measurements. It is possible to disprove New Physics hypothesis or find bounds over several models beyond the SM. Using the observed leptonic and semileptonic branching ratios for the D meson decays, we performed a combined analysis to constrain non-standard interactions which mediate the csbar?l?bar transition. This is done either by a model-independent way through the corresponding Wilson coefficients or in a model-dependent way by finding the respective bounds over the relevant parameters for some models beyond the Standard Model. In particular, we obtain bounds for the Two Higgs Doublet Model Type-II and Type III, the Left-Right model, the Minimal Supersymmetric Standard Model with explicit R-parity violation and Leptoquarks. Finally, we estimate the transverse polarization of the lepton in the D0 decay and we found it can be as high as PT=0.23.

Barranco, J.; Delepine, D.; Gonzalez Macias, V.; Lopez-Lozano, L.

2014-04-01

241

Distributed Constrained Optimization with Semicoordinate Transformations  

NASA Technical Reports Server (NTRS)

Recent work has shown how information theory extends conventional full-rationality game theory to allow bounded rational agents. The associated mathematical framework can be used to solve constrained optimization problems. This is done by translating the problem into an iterated game, where each agent controls a different variable of the problem, so that the joint probability distribution across the agents moves gives an expected value of the objective function. The dynamics of the agents is designed to minimize a Lagrangian function of that joint distribution. Here we illustrate how the updating of the Lagrange parameters in the Lagrangian is a form of automated annealing, which focuses the joint distribution more and more tightly about the joint moves that optimize the objective function. We then investigate the use of "semicoordinate" variable transformations. These separate the joint state of the agents from the variables of the optimization problem, with the two connected by an onto mapping. We present experiments illustrating the ability of such transformations to facilitate optimization. We focus on the special kind of transformation in which the statistically independent states of the agents induces a mixture distribution over the optimization variables. Computer experiment illustrate this for &sat constraint satisfaction problems and for unconstrained minimization of NK functions.

Macready, William; Wolpert, David

2006-01-01

242

Constraining the Evolution of ZZ Ceti  

NASA Technical Reports Server (NTRS)

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt 5 (5.5 plus or minus 1.9) x 10(exp -15) ss(sup -1), after correcting for proper motion. Our results are consistent with previous P values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is |P||P(raised dot)|greater than or equal to 1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.13 s is only slightly less than the present measurement for another DAV, G117-B15A, for the period 215.2 s, establishing this mode in ZZ Ceti as the second most stable optical clock known, comparable to atomic clocks and more stable than most pulsars. Constraining the cooling rate of ZZ Ceti aids theoretical evolutionary models and white dwarf cosmochronology. The drift rate of this clock is small enough that we can set interesting limits on reflex motion due to planetary companions.

Mukadam, Anjum S.; Kepler, S. O.; Winget, D. E.; Nather, R. E.; Kilic, M.; Mullally, F.; vonHippel, T.; Kleinman, S. J.; Nitta, A.; Guzik, J. A.

2003-01-01

243

Constraining Simulated Photosynthesis with Fluorescence Observations  

NASA Astrophysics Data System (ADS)

The measurement of chlorophyll fluorescence from satellites is an emerging technology. To date, most applications have compared fluorescence to light use efficiency models of Gross Primary Productivity (GPP). A close correspondence between fluorescence and GPP has been found in these comparisons. Here, we 'go the other way' and calculate fluorescence using an enzyme kinetic photosynthesis model (the Simple Biosphere Model; SiB), and compare to spectral retrievals. We utilize multiple representations for model phenology as a sensitivity test, obtaining leaf area index (LAI) and fraction of photosynthetically active radiation absorbed (fPAR) from both MODIS-derived products as well as a prognostic model of LAI/fPAR based on growing season index (PGSI). We find that bidirectional reflectance distribution function (BRDF), canopy radiative transfer, and leaf-to-canopy scaling all contribute to variability in simulated fluorescence. We use our results to evaluate discrepancies between light use efficiency and enzyme kinetic models across latitudinal, vegetation and climatological gradients. Satellite retrievals of fluorescence will provide insight into photosynthetic process and constrain simulations of the carbon cycle across multiple spatiotemporal scales.

Baker, I. T.; Berry, J. A.; Lee, J.; Frankenberg, C.; Denning, S.

2012-12-01

244

Pressure compensated transducer system with constrained diaphragm  

NASA Astrophysics Data System (ADS)

An acoustic source apparatus has an acoustic transducer that is enclosed in a substantially rigid and watertight enclosure to resist the pressure of water on the transducer and to seal the transducer from the water. The enclosure has an opening through which acoustic signals pass and over which is placed a resilient, expandable and substantially water-impermeable diaphragm. A net stiffens and strengthens the diaphragm as well as constrains the diaphragm from overexpansion or from migrating due to buoyancy forces. Pressurized gas, regulated at slightly above ambient pressure, is supplied to the enclosure and the diaphragm to compensate for underwater ambient pressures. Gas pressure regulated at above ambient pressure is used to selectively tune the pressure levels within the enclosure and diaphragm so that diaphragm resonance can be achieved. Controls are used to selectively fill, as well as vent the enclosure and diaphragm during system descent and ascent, respectively. A signal link is used to activate these controls and to provide the driving force for the acoustic transducer.

Percy, Joseph L.

1992-08-01

245

Noise-constrained hyperspectral data compression techniques  

NASA Astrophysics Data System (ADS)

Storage and transmission requirements for hyperspectral data sets are significant. In order to reduce hardware costs, well-designed compression techniques are needed to preserve information content while maximizing compression ratios. Lossless compression techniques maintain data integrity, but yield small compression ratios. This paper presents three lossy compression algorithms that use the noise statistics of the data to preserve information content while maximizing compression ratios. The Spectral Compression and Noise Suppression (SCANS) algorithm adapts a noise estimation technique to exploit band-to-band correlation for optimizing linear prediction for data compression. The Adaptive Spectral Image Compression (ASIC) algorithm uses an iterative adaptive linear unmixing compression method, constrained by the noise statistics of the hypercube. By dynamically optimizing the end-members for each pixel this method minimizes the number of components required to represent the spectrum of any given pixel, yielding high compression ratios with minimal information content loss. The Adaptive Principal Components Analysis (APCA) algorithm uses noise statistics to determine the number of significant principal components and selects only those that are required to represent each pixel to within the noise level. We demonstrate the effectiveness of these methods with AVIRIS and HYMAP datasets.

Sharp, Mary H.; Rupert, Suzanne T.; Barkenhagen, J. L.

2001-12-01

246

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

247

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

248

Configuration-constrained Hartree-Fock method. An illustrative example.  

National Technical Information Service (NTIS)

The structure of solutions of the constrained Hartree-Fock method is studied within the time-dependent Hartree-Fock formalism. A new method for reaching various stationary Hartree-Fock points, not accessible by the usual adiabatic constrained Hartree-Fock...

K. Iwasawa F. Sakata W. Nazarewicz T. Marumori J. Terasaki

1994-01-01

249

Configuration-constrained Hartree-Fock method -an illustrative example  

Microsoft Academic Search

The structure of solutions of the constrained Hartree-Fock method is studied within the time-dependent Hartree-Fock formalism. A new method for reaching various stationary Hartree-Fock points, not accessible by the usual adiabatic constrained Hartree-Fock method, is proposed.

K. Iwasawa; F. Sakata; W. Nazarewicz; T. Marumori; J. Terasaki

1994-01-01

250

Size effects in the constrained deformation of metallic foams  

Microsoft Academic Search

The constrained deformation of an aluminium alloy foam sandwiched between steel substrates has been investigated. The sandwich plates are subjected to through-thickness shear and normal loading, and it is found that the face sheets constrain the foam against plastic deformation and result in a size e$ect: the yield strength increases with diminishing thickness of foam layer. The strain distribution across

C. Chen; N. A. Fleck

2002-01-01

251

A new smoothing Newton method for solving constrained nonlinear equations  

Microsoft Academic Search

In this paper, a new smoothing Newton method is proposed for solving constrained nonlinear equations. We first transform the constrained nonlinear equations to a system of semismooth equations by using the so-called absolute value function of the slack variables, and then present a new smoothing Newton method for solving the semismooth equations by constructing a new smoothing approximation function. This

Liu Yang; Yanping Chen; Xiaojiao Tong; Chunlin Deng

2011-01-01

252

Constrained spectral clustering under a local proximity structure assumption  

NASA Technical Reports Server (NTRS)

This work focuses on incorporating pairwise constraints into a spectral clustering algorithm. A new constrained spectral clustering method is proposed, as well as an active constraint acquisition technique and a heuristic for parameter selection. We demonstrate that our constrained spectral clustering method, CSC, works well when the data exhibits what we term local proximity structure.

Wagstaff, Kiri; Xu, Qianjun; des Jardins, Marie

2005-01-01

253

Experimental Evaluation of Segmented Active Constrained Layer Damping Treatments  

Microsoft Academic Search

The objective of this research is to demonstrate the effect of Active Constrained Layer segmentation on the enhancement of low frequency vibrations damping in flexible beams. The Active Constrained Layer Damping treatment, under consideration, consists of a viscoelastic layer sandwiched between two piezoelectric layers. The shear deformation of the viscoelastic layer causes loss of energy and thus the damping of

Rajiv K. Kapadia; Grzegorz Kawiecki

1997-01-01

254

Robust control of plate vibration via active constrained layer damping  

Microsoft Academic Search

In this paper, the theoretical modeling of a plate partially treated with active constrained layer damping (ACLD) treatments and its vibration control in an H? approach is discussed. Vibration of the flat plate is controlled with patches of ACLD treatments, each consisting of a viscoelastic damping layer which is sandwiched between the piezo-electric constrained layer and the host plate. The

TianXiong Liu; HongXing Hua; Zhiyi Zhang

2004-01-01

255

Optimal design of structures with active constrained-layer damping  

Microsoft Academic Search

A piezoelectric element and a constrained layer damping element are combined to allow for an active constrained layer damping treatment. The development of these elements is reviewed and results are compared with the literature to insure that the elements work together. A procedure for placing patches damping treatments or other material anomalies on structures is introduced. The patch placement process

Duane E. Veley; S. S. Rao

1995-01-01

256

Automated Analysis of Concurrent Systems With the Constrained Expression Toolset  

Microsoft Academic Search

The constrained expression approach to analysis of concurrent softwaresystems has several attractive features, including the facts that itcan be used with a variety of design and programming languages and thatit does not require a complete enumeration of the set of reachable statesof the concurrent system. This paper reports on the construction of atoolset automating the main constrained expression analysis techniquesand

George S. Avrunin; Ugo A. Buy; James C. Corbett; Laura K. Dillon; Jack C. Wileden

1991-01-01

257

Aircraft taxiway conformance monitoring with constrained stochastic linear hybrid systems  

Microsoft Academic Search

An algorithm, the modeled fault constrained innovation hybrid estimator (MF-CIHE), is proposed to quickly and correctly detect a nonconforming taxiing aircraft from a set of noisy measurements using estimation and fault detection techniques. Both spatial and temporal conformance monitoring are considered. The spatial conformance monitoring algorithm is based on formally modeling the aircraft and the assigned taxiway as a constrained

Garrett W Mann

2011-01-01

258

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

259

Zeroing polynomials using modified constrained neural network approach  

Microsoft Academic Search

This paper proposes new modified constrained learning neural root finders (NRFs) of polynomial constructed by backpropagation network (BPN). The technique is based on the relationships between the roots and the coefficients of polynomial as well as between the root moments and the coefficients of the polynomial. We investigated different resulting constrained learning algorithms (CLAs) based on the variants of the

De-Shuang Huang; Horace H. S. Ip; Ken Chee Keung Law; Zheru Chi

2005-01-01

260

Constructing large feasible suboptimal intervals for constrained nonlinear optimization  

Microsoft Academic Search

An algorithm for finding a large feasiblen-dimensional interval for constrained global optimization is presented. Then-dimensional interval is iteratively enlarged about a seed point while maintaining feasibility. An interval subdivision method may be used to check feasibility of the growing box. The resultant feasible interval is constrained to lie within a given level set, thus ensuring it is close to the

Tibor Csendes; Zelda B. Zabinsky; Birna P. Kristinsdottir

1995-01-01

261

Security-constrained optimal generation scheduling for GENCOs  

Microsoft Academic Search

This paper presents an approach for maximizing a GENCO's profit in a constrained power market. The proposed approach considers the Interior Point Method (IPM) and Benders decomposition for solving the security-constrained optimal generation scheduling (SC-GS) problem. The master problem represents the economic dispatch problem for a GENCO which intends to optimize its profit. The formulation of the master problem does

Hatim Yamin; Salem Al-Agtash; Mohammad Shahidehpour

2004-01-01

262

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

263

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

264

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 inter-model spread persists in the simulated summer sea ice losses over the 21st century for a given forcing scenario. The initial 1979-2010 sea ice properties (including the 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 SSIE anomalies (compared 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). In a new diagram (that does not consider the time as an independent variable) we show that the transition towards ice-free conditions is actually occuring in a very similar manner for all models. For these reasons, some quantities that do not explicitly depend on time, such as the year at which SSIE drops below a certain threshold, are likely to be constrained. 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 (between 2041 and 2060 for a high climate forcing scenario).

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

2012-07-01

265

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.

Fichefet, Thierry; Massonnet, François; Goosse, Hugues; Bitz, Cecilia; Philippon-Berthier, Gwenaëlle; Holland, Marika; Barriat, Pierre-Yves

2013-04-01

266

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

267

Optimal control strategies for constrained relative orbits  

NASA Astrophysics Data System (ADS)

The US Air Force's ability to protect space assets is enhanced by a proficiency in satellite proximity operations and Space Situational Awareness (SSA). In pursuit of that proficiency, this research develops a key capability of interest to mission planners; the ability of a deputy satellite to "hover" within a defined volume fixed in the vicinity of a chief satellite for an extended period of time. Previous research has developed initial methodologies for maintaining restricted teardrop hover orbits that exist in a plane fixed within the chief's local reference frame. These methods use the natural drift of the deputy satellite in the relative frame and impulsive thrust to keep the deputy in a bounded volume relative to the chief, but do not address fuel-optimality. This research extends and enhances that work by finding optimal trajectories, produced with discrete-thrusts, that minimize fuel spent per unit time and stay within the user-defined volume, thus providing a practical hover capability in the vicinity of the chief. The work assumes the Clohessy-Wiltshire closeness assumption between the deputy and chief is valid, however, elliptical chief orbits are allowed. Using the new methodology developed in this work, feasible closed and non-closed relative orbits are found and evaluated based on a fuel criterion and compared to an easily calculated continuous-thrust baseline. It is shown that in certain scenarios the discrete-thrust solution provides the lowest overall fuel cost. These scenarios are generally constrained to a smaller total time-of-flight. A simple check is proposed that enables the mission planner to make the correct strategy choice.

Irvin, David Jonathan, Jr.

268

Quantum dynamics by the constrained adiabatic trajectory method  

SciTech Connect

We develop the constrained adiabatic trajectory method (CATM), which allows one to solve the time-dependent Schroedinger equation constraining the dynamics to a single Floquet eigenstate, as if it were adiabatic. This constrained Floquet state (CFS) is determined from the Hamiltonian modified by an artificial time-dependent absorbing potential whose forms are derived according to the initial conditions. The main advantage of this technique for practical implementation is that the CFS is easy to determine even for large systems since its corresponding eigenvalue is well isolated from the others through its imaginary part. The properties and limitations of the CATM are explored through simple examples.

Leclerc, A.; Jolicard, G. [Institut UTINAM, CNRS UMR 6213, Universite de Franche-Comte, Observatoire de Besancon, 41 bis Avenue de l'Observatoire, Boite Postale 1615, F-25010 Besancon cedex (France); Guerin, S. [Laboratoire Interdisciplinaire Carnot de Bourgogne (CNRS UMR 5209, Universite de Bourgogne), Boite Postale 47870, F-21078 Dijon (France); Killingbeck, J. P. [Centre for Mathematics, University of Hull, Hull HU6 7RX (United Kingdom)

2011-03-15

269

Constrained-Optimization Based Data Transfer  

NASA Astrophysics Data System (ADS)

We formulate a new class of optimization-based methods for data transfer (remap) of a scalar conserved quantity between two close meshes with the same connectivity. We present the methods in the context of the remap of a mass density field, which preserves global mass (the integral of the density over the computational domain). The key idea is to formulate remap as a global inequality-constrained optimization problem for mass fluxes between neighboring cells. The objective is to minimize the discrepancy between these fluxes and the given high-order target mass fluxes, subject to constraints that enforce physically motivated bounds on the associated primitive variable. In so doing, we separate accuracy considerations, handled by the objective functional, from the enforcement of physical bounds, handled by the constraints. The resulting second-order, conservative, and bound-preserving optimization-based remap (OBR) formulation is applicable to general, unstructured, heterogeneous grids. Under some weak requirements on grid proximity we prove that the OBR algorithm preserves linear fields in one, two and three dimensions. The chapter also examines connections between the OBR and the flux-corrected remap (FCR), which can be interpreted as a modified version of OBR (M-OBR), with the same objective but a smaller feasible set. The feasible set for M-OBR (FCR) is given by simple box constraints derived by using a "worst-case" scenario approach, which may result in loss of linearity preservation and ultimately accuracy for some grid motions. The optimality of the OBR solution means that, given a set of target fluxes and a distance measure, OBR finds the best possible approximations of these fluxes with respect to this measure, which also satisfy the physically motivated bounds. In this sense, OBR can serve as a natural benchmark for evaluating the accuracy of existing and future numerical methods for data transfer with respect to a given class of flux reconstruction methods and flux distance measures. In this context, we perform numerical comparisons between OBR, FCR and iFCR (a version of FCR which utilizes an iterative procedure to enhance the accuracy of FCR numerical fluxes).

Bochev, Pavel; Ridzal, Denis; Scovazzi, Guglielmo; Shashkov, Mikhail

270

Vibrational pooling and constrained equilibration on surfaces  

NASA Astrophysics Data System (ADS)

In this thesis, we provide a statistical theory for the vibrational pooling and fluorescence time dependence observed in infrared laser excitation of CO on an NaCl surface. The pooling is seen in experiment and in computer simulations. In the theory, we assume a rapid equilibration of the quanta in the substrate and minimize the free energy subject to the constraint at any time t of a fixed number of vibrational quanta N(t). At low incident intensity, the distribution is limited to one-quantum exchanges with the solid and so the Debye frequency of the solid plays a key role in limiting the range of this one-quantum domain. The resulting inverted vibrational equilibrium population depends only on fundamental parameters of the oscillator (oe and oe?e) and the surface (oD and T). Possible applications and relation to the Treanor gas phase treatment are discussed. Unlike the solid phase system, the gas phase system has no Debye-constraining maximum. We discuss the possible distributions for arbitrary N-conserving diatom-surface pairs, and include application to H:Si(111) as an example. Computations are presented to describe and analyze the high levels of infrared laser induced vibrational excitation of a monolayer of absorbed 13CO on a NaCl(100) surface. The calculations confirm that, for situations where the Debye frequency limited n domain restriction approximately holds, the vibrational state population deviates from a Boltzmann population linearly in n, a result that we have derived earlier theoretically for a domain of n restricted to one-phonon transfers. This theoretically understood term, linear in n, dominates the Boltzmann term and is responsible for the inversion of the population of vibrational states, Pn We discuss the one-to-one relationship between N and gamma and the examine the state space of the new distribution function for varied gamma. We derive the Free Energy and effective chemical potential for the vibrational pool. We also find the anti correlation of neighbor vibrations leads to an emergent correlation that appears to extend further than nearest neighbor.

Boney, E. T. D.

271

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

272

CONDORR--CONstrained Dynamics of Rigid Residues: a molecular dynamics program for constrained molecules.  

PubMed

A computer program CONDORR (CONstrained Dynamics of Rigid Residues) was developed for molecular dynamics simulations of large and/or constrained molecular systems, particularly carbohydrates. CONDORR efficiently calculates molecular trajectories on the basis of 2D or 3D potential energy maps, and can generate such maps based on a simple force field. The simulations involve three translational and three rotational degrees of freedom for each rigid, asymmetrical residue in the model. Total energy and angular momentum are conserved when no stochastic or external forces are applied to the model, if the time step is kept sufficiently short. Application of Langevin dynamics allows longer time steps, providing efficient exploration of conformational space. The utility of CONDORR was demonstrated by application to a constrained polysaccharide model and to the calculation of residual dipolar couplings for a disaccharide. [Figure: see text]. Molecular models (bottom) are created by cloning rigid residue archetypes (top) and joining them together. As defined here, the archetypes AX, HM and BG respectively correspond to an alpha-D-Xyl p residue, a hydroxymethyl group, and a beta-D-Glc p residue lacking O6, H6a and H6b. Each archetype contains atoms (indicated by boxes) that can be shared with other archetypes to form a linked structure. For example, the glycosidic link between the two D-Glc p residues is established by specifying that O1 of the nonreducing beta-D-Glc p (BG) residue (2) is identical to O4 of the reducing Glc p (BG) residue (1). The coordinates of the two residues are adjusted so as to superimpose these two (nominally distinct) atoms. Flexible hydroxymethyl (HM) groups (3 and 4) are treated as separate residues, and the torsional angles (normally indicated by the symbol omega) that define their geometric relationships to the pyranosyl rings of the BG residues are specified as psi3 and psi4, respectively. The torsional angles phi3 and phi4, defined solely to maintain the orientation of the geminal H-atoms of the hydroxymethyl group, are not shown. (See text.). The illustrated trisaccharide is thus specified as a collection of 5 residues which are represented by 3 archetypes. Models of the disaccharide cellobiose (beta-D-Glc p-(1-->4)-D-Glc p) must include residues 1 and 2, but the hydroxymethyl groups (residues 3 and 4) can also be explicitly included in this model PMID:15322949

York, William S; Yi, Xiaobing

2004-08-01

273

Constrained Information Theoretic Characterizations in Consumer Purchase behavior.  

National Technical Information Service (NTIS)

The analysis called SAND DABS which has had a long history of use in consumer purchase behavior (including brand switching) at MRCA and elsewhere, is here given a constrained information theoretic characterization. This is made possible by recent developm...

A. Charnes W. W. Cooper D. B. Learner

1975-01-01

274

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

275

21 CFR 888.3720 - Toe joint polymer constrained prosthesis.  

Code of Federal Regulations, 2010 CFR

A toe joint polymer constrained prosthesis is a device made of silicone elastomer or polyester reinforced silicone elastomer intended to be implanted to replace the first metatarsophalangeal (big toe)...

2010-04-01

276

21 CFR 888.3720 - Toe joint polymer constrained prosthesis.  

Code of Federal Regulations, 2010 CFR

A toe joint polymer constrained prosthesis is a device made of silicone elastomer or polyester reinforced silicone elastomer intended to be implanted to replace the first metatarsophalangeal (big toe)...

2009-04-01

277

Experimental analysis and application of sparsity constrained deconvolution  

NASA Astrophysics Data System (ADS)

Sparsity constrained deconvolution can improve the resolution of band-limited seismic data compared to conventional deconvolution. However, such deconvolution methods result in nonunique solutions and suppress weak reflections. The Cauchy function, modified Cauchy function, and Huber function are commonly used constraint criteria in sparse deconvolution. We used numerical experiments to analyze the ability of sparsity constrained deconvolution to restore reflectivity sequences and protect weak reflections under different constraint criteria. The experimental results demonstrate that the performance of sparsity constrained deconvolution depends on the agreement between the constraint criteria and the probability distribution of the reflectivity sequences; furthermore, the modified Cauchyconstrained criterion protects the weak reflections better than the other criteria. Based on the model experiments, the probability distribution of the reflectivity sequences of carbonate and clastic formations is statistically analyzed by using well-logging data and then the modified Cauchy-constrained deconvolution is applied to real seismic data much improving the resolution.

Li, Guo-Fa; Qin, De-Hai; Peng, Geng-Xin; Yue, Ying; Zhai, Tong-Li

2013-06-01

278

Constrained Tracking of Ground Objects Using Regional Measurements.  

National Technical Information Service (NTIS)

A method for constrained tracking of objects using regional measurement. In one embodiment the system includes a plurality of sensors deployed in a region, wherein the sensors detect a mobile target. A first processing section receives target data from th...

P. J. Haney

2004-01-01

279

Asynchronous Parallel Generating Set Search for Linearly-Constrained Optimization.  

National Technical Information Service (NTIS)

Generating set search (GSS) is a family of direct search methods that encompasses generalized pattern search and related methods. We describe an algorithm for asynchronous linearly-constrained GSS, which has some complexities that make it different from b...

J. D. Griffin R. M. Lewis T. G. Kolda

2006-01-01

280

A Survey of Available Software for Nonlinearly Constrained Optimization.  

National Technical Information Service (NTIS)

The aim of this paper is to present a brief overview of current practice in solving nonlinearly constrained optimization problems. First, we consider selected theoretical and computational aspects of some of the widely used methods for such problems. Seco...

M. H. Wright

1978-01-01

281

Vibration control through passive constrained layer damping and active control  

NASA Astrophysics Data System (ADS)

To add damping to systems, viscoelastic materials (VEM) are added to structures. In order to enhance the damping effects of the VEM, a constraining layer is attached. When this constraining layer is an active element, the treatment is called active constrained layer damping (ACLD). Recently, the investigation of ACLD treatments has shown it to be an effective method of vibration suppression. In this paper, the treatment of a beam with a separate active element and passive constrained layer (PCLD) element is investigated. A Ritz- Galerkin approach is used to obtain discretized equations of motion. The damping is modeled using the GHM method and the system is analyzed in the time domain. By optimizing on the performance and control effort for both the active and passive case, it is shown that this treatment is capable of lower control effort with more inherent damping, and is therefore a better approach to damp vibration.

Lam, Margaretha J.; Inman, Daniel J.; Saunders, William R.

1997-05-01

282

Positive Invariance and Constrained Control of Linear Multivariable Systems.  

National Technical Information Service (NTIS)

Some contributions in the field of constrained linear multivariable systems are presented. The basic theoretical tool used is the positive invariance property of polyhedral domains for continuous time and discrete time linear systems. For such systems, th...

E. Debonacastelanneto

1992-01-01

283

Constrained Definite Hessians Tend to be Well Conditioned.  

National Technical Information Service (NTIS)

The testing of optimization algorithms requires the running of problems with ill-conditioned Hessians. For constrained problems, it is the projection of the Hessian onto the space determined by the active constraints that must be ill conditioned. In this ...

G. W. Stewart

1980-01-01

284

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

285

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

Code of Federal Regulations, 2010 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...

2010-04-01

286

21 CFR 888.3220 - Finger joint metal/polymer constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Finger joint metal/polymer constrained cemented prosthesis. 888... § 888.3220 Finger joint metal/polymer constrained cemented prosthesis. (a) Identification. A finger joint metal/polymer constrained cemented...

2010-04-01

287

21 CFR 888.3520 - Knee joint femorotibial metal/polymer non-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...false Knee joint femorotibial metal/polymer non-constrained cemented prosthesis...3520 Knee joint femorotibial metal/polymer non-constrained cemented prosthesis... A knee joint femorotibial metal/polymer non-constrained cemented...

2010-04-01

288

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

Code of Federal Regulations, 2010 CFR

...false Knee joint femorotibial metal/polymer semi-constrained cemented prosthesis...3530 Knee joint femorotibial metal/polymer semi-constrained cemented prosthesis... A knee joint femorotibial metal/polymer semi-constrained cemented...

2010-04-01

289

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

290

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

291

21 CFR 888.3800 - Wrist joint metal/polymer semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 false Wrist joint metal/polymer semi-constrained cemented prosthesis... § 888.3800 Wrist joint metal/polymer semi-constrained cemented prosthesis...Identification. A wrist joint metal/polymer semi-constrained...

2013-04-01

292

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 cemented prosthesis... § 888.3110 Ankle joint metal/polymer semi-constrained cemented prosthesis...Identification. An ankle joint metal/polymer semi-constrained...

2013-04-01

293

Penicillin acylase has a single-amino-acid catalytic centre.  

PubMed

Penicillin acylase (penicillin amidohydrolase, EC 3.5.1.11) is widely distributed among microorganisms, including bacteria, yeast and filamentous fungi. It is used on an industrial scale for the production of 6-aminopenicillanic acid, the starting material for the synthesis of semi-synthetic penicillins. Its in vivo role remains unclear, however, and the observation that expression of the Escherichia coli enzyme in vivo is regulated by both temperature and phenylacetic acid has prompted speculation that the enzyme could be involved in the assimilation of aromatic compounds as carbon sources in the organism's free-living mode. The mature E. coli enzyme is a periplasmic 80K heterodimer of A and B chains (209 and 566 amino acids, respectively) synthesized as a single cytoplasmic precursor containing a 26-amino-acid signal sequence to direct export to the cytoplasm and a 54-amino-acid spacer between the A and B chains which may influence the final folding of the chains. The N-terminal serine of the B chain reacts with phenylmethylsulphonyl fluoride, which is consistent with a catalytic role for the serine hydroxyl group. Modifying this serine to a cysteine inactivates the enzyme, whereas threonine, arginine or glycine substitution prevents in vivo processing of the enzyme, indicating that this must be an important recognition site for cleavage. Here we report the crystal structure of penicillin acylase at 1.9 A resolution. Our analysis shows that the environment of the catalytically active N-terminal serine of the B chain contains no adjacent histidine equivalent to that found in the serine proteases. The nearest base to the hydroxyl of this serine is its own alpha-amino group, which may act by a new mechanism to endow the enzyme with its catalytic properties. PMID:7816145

Duggleby, H J; Tolley, S P; Hill, C P; Dodson, E J; Dodson, G; Moody, P C

1995-01-19

294

Additive channel-constrained metallization of high-resolution features  

Microsoft Academic Search

The patterned, selective electroless deposition of submicron metal features has been achieved on Si by using a channel-constrained technique. Chemically-amplified negative tone photoresists, exposed with UV or e-beam sources, were developed to create patterned channels for constrained, additive, metal growth on an underlying ligating self-assembled monolayer film. The process is attractive for the production of plasma etch-resistant high resolution metal

Mu-San Chen; Susan L Brandow; Walter J Dressick

2000-01-01

295

Constraining the Initial Phase in Water-Fat Separation  

PubMed Central

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.

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

2010-01-01

296

Addressing capacity uncertainty in resource-constrained assignment problems  

Microsoft Academic Search

Resource-constrained assignment problems typically assume capacities are known. We focus on the situation when capacities are uncertain. In addition to the well-known generalized assignment problem (GAP) and the assignment problem with side-constraints (APSC), we discuss two other resource-constrained generalizations of the assignment problem. We identify two alternative approaches to utilize deterministic solution strategies while addressing capacity uncertainty, and illustrate how

Berkin Toktas; Joyce W. Yen; Zelda B. Zabinsky

2006-01-01

297

Review of methods for analyzing constrained-layer damped structures  

Microsoft Academic Search

This paper reviews and examines different numerical approaches for modeling and analyzing the behavior of structures having constrained-layer damping. Specific topics that are addressed included: modeling of the material behavior, implementation of structural damping and constrained-layer damping into two- and three-dimensional finite elements, and assessment of the different analysis methods for calculating the damped response and estimation of the damping

J. B. Kosmatka; S. L. Liguore

1993-01-01

298

Performance characteristics of active constrained-layer damping  

Microsoft Academic Search

Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) treatment are presented. The ACLD under consideration consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The three-layer composite ACLD when bonded to a vibrating structure acts as a SMART constraining layer damping treatment with built-in sensing and actuation capabilities.

Amr M. Baz; J. Ro

1994-01-01

299

Optimization of energy dissipation characteristics of active constrained layer damping  

Microsoft Academic Search

The energy dissipation characteristics of active constrained layer damping (ACLD) treatments, consisting of visco-elastic cores constrained by active piezo-electric layers, are optimized using rational design procedures. The optimal lengths and control gains of these ACLD treatments are determined when a globally stable boundary control strategy is utilized to control the longitudinal strain of the active piezo-electric layers in response to

A. Baz

1997-01-01

300

Minimally-Constrained Canonical Quantization of Geometrodynamics  

NASA Astrophysics Data System (ADS)

Finding a quantum theory of gravitation has been a long-standing problem. Einstein's theory of general relativity gives a classical description of gravity as the action of geometry on matter and matter on geometry. A theory of quantum gravity seeks to provide a quantum mechanical treatment of this process. In analogy with canonical quantization which, from classical mechanics and classical field theory, arrives at quantum mechanics and quantum field theory, canonical quantization of gravity is a family of different procedures following from the canonical (Hamiltonian) formulation of general relativity as pioneered by Dirac and Arnowitt, Deser, and Misner. Unfortunately, almost all of them exhibit pathologies, the most significant being "the problem of time evolution." Specifically, the problem arises with the use of a single operator equation both to describe quantization of the superhamiltonian constraint and as a means of enforcement of this constraint; this inhibits a meaningful notion of time-evolution. However, there is an approach that avoids this difficulty entirely: separation of the process of enforcement of constraints from the evolution of the quantum system. We investigate such an approach to gravity quantization known as minimally-constrained canonical (MC2) quantization. It is based on Wheeler's geometrodynamics and the identification of the correct dynamical degrees of freedom of the gravitational field as determined by York. Using MC2 quantization, we quantize only the dynamical degrees of freedom of gravitation. In this manuscript, we provide an exposition of this procedure as well as a presentation of other methods of canonical quantization of gravity with which to compare and contrast our approach. The first result is a justification of the way in which constraints are imposed. The problem of time evolution motivates imposing constraints as expectation values; the classical theory of general relativity---a theory with external gauge symmetry---requires, due to 3-diffeomorphism invariance, that the supermomentum constraints are automatically satisfied with the superhamiltonian constraint not automatically satisfied. In electromagnetism---a theory with internal gauge symmetry---the constraints can be applied at any point of the quantization. Practically, this manifests as selection of a particular field configuration which automatically satisfies the constraint(s). To investigate this result, we review MC2 quantization of anisotropic, homogeneous cosmologies and explore the procedure in at spacetime regarding electromagnetic plane waves, a charged particle in an electromagnetic field, and a scalar field to compare with prior approaches of quantization. The second result is an explicit demonstration that MC 2 quantization produces exactly the same results as previous quantization procedures applied to the plane wave electromagnetic field and to the scalar field. We discuss the charged particle in an electromagnetic field and how it differs, essentially by construction, from other approaches. Finally, we discuss future directions for gravity quantization including problems such as gravitational collapse, cosmology, and alternative theories of gravity.

Corne, Matthew Allan

301

Free and constrained symplectic integrators for numerical general relativity  

NASA Astrophysics Data System (ADS)

We consider symplectic time integrators in numerical general relativity and discuss both free and constrained evolution schemes. For free evolution of ADM-like equations we propose the use of the Störmer Verlet method, a standard symplectic integrator which here is explicit in the computationally expensive curvature terms. For the constrained evolution we give a formulation of the evolution equations that enforces the momentum constraints in a holonomically constrained Hamiltonian system and turns the Hamilton constraint function from a weak to a strong invariant of the system. This formulation permits the use of the constraint-preserving symplectic RATTLE integrator, a constrained version of the Störmer Verlet method. The behavior of the methods is illustrated on two effectively (1+1)-dimensional versions of Einstein's equations, which allow us to investigate a perturbed Minkowski problem and the Schwarzschild spacetime. We compare symplectic and non-symplectic integrators for free evolution, showing very different numerical behavior for nearly-conserved quantities in the perturbed Minkowski problem. Further we compare free and constrained evolution, demonstrating in our examples that enforcing the momentum constraints can turn an unstable free evolution into a stable constrained evolution. This is demonstrated in the stabilization of a perturbed Minkowski problem with Dirac gauge, and in the suppression of the propagation of boundary instabilities into the interior of the domain in Schwarzschild spacetime.

Richter, Ronny; Lubich, Christian

2008-11-01

302

How well constrained are well-constrained T, B, and P axes in moment tensor catalogs?  

NASA Astrophysics Data System (ADS)

The T, B and P axes of earthquake moment tensors (MT) are often used to evaluate regional stress directions and other tectonic parameters; we here undertake three comparisons to assess the uncertainty in the orientations of these axes. These are (1) a direct comparison of common MT in the Harvard, U.S. Geological Survey, or Earthquake Research Institute (ERI) catalogs; (2) a comparison of MT slip vectors and plate motion vectors in several tectonically straightforward regions; and (3) an analysis of the axial variability in the Harvard and ERI catalogs implied by the reported uncertainties in individual MT components. All three comparisons indicate that there is considerable variability within the catalog concerning the axial orientation of MT, but all suggest that axis orientations of the majority of Harvard MT have uncertainties of 15° or less. For compensated linear vector dipole (CLVD) components among the three catalogs, the correlation is very low. For the Harvard catalog, three statistics are especially useful for selecting better constrained MT; these are (1) the relative error Erel, which is the ratio of the scalar moments of the reported error tensor and of the MT itself; (2)ƒCLVD, a measure of the strength of the CLVD component; and (3) nfree, the number of MT elements not fixed at zero in the inversion. For selecting better constrained MT, the appropriate statistical cutoffs chosen depend on the problem of interest, the data available, arid personal preference. However, for analysis of shallow earthquakes we have used Erel ? 0.15, ƒCLVD ? 0.20, and nfree = 6. While this eliminates 53% of the catalog, our calculations suggest that nearly all the remaining events have T, B, and P axes with azimuth and inclination angle uncertainties of 5°-10° or less.

Frohlich, Cliff; Davis, Scott D.

1999-03-01

303

Amino acid conjugated sophorolipids: A new family of biologically active functionalized glycolipids.  

PubMed

Sophorolipids (SLs) are extra cellular glycolipids produced by Candida bombicola ATCC 22214 when grown in the presence of glucose and fatty acids. These compounds have a disaccharide head group connected to a long-chain hydroxyl-fatty acid by a glycosidic bond. To explore structure-activity of modified SLs, a new family of amino acid-SL derivatives was prepared. Synthesized analogs consist of amino acids linked by amide bonds formed between their alpha-amino moiety and the carboxyl group of ring-opened SL fatty acids. Their preparation involved the following: (i) hydrolysis of a natural SL mixture with aqueous alkali to give SL free acids, (ii) coupling of free acids to protected amino acids using dicarbodiimide, and (iii) removing amino acid carboxyl protecting groups. These conjugates were evaluated for their antibacterial, anti-HIV, and spermicidal activity. All tested analogs showed antibacterial activity against both gram +ve and gram -ve organisms. Leucine-conjugated SL was most efficient. For example, the minimum inhibitory concentrations (MIC) for Moraxella sp. and E. coli were 0.83 and 1.67 mg/mL, respectively. Among the alkyl esters of amino acid conjugated SLs, the ethyl ester of leucine-SLs was most active. Against Moraxella sp., S. sanguinis, and M. imperiale, MIC values are 7.62 x 10(-4), 2.28 x 10-(3) and 1.67 mg/mL, respectively. All compounds displayed virus-inactivating activity with 50% effective concentrations (EC50) below 200 microg/mL. The EC50 of leucine-SL ethyl ester was 24.1 microg/mL, showing that it is more potent than commercial spermicide nonoxynol-9 (EC50 approximately 65 microg/mL). PMID:17105232

Azim, Abul; Shah, Vishal; Doncel, Gustavo F; Peterson, Nicholas; Gao, Wei; Gross, Richard

2006-01-01

304

New procedure of the Mitsunobu reaction as the key step in peptide nucleic acid (PNA) monomers synthesis.  

PubMed

PNAs are relatively novel DNA analogues, intensively studied due to their potential as gene-targeted drugs with antigene and antisense properties. In 1996 we elaborated a new method of synthesis of PNA monomer backbones based on the Mitsunobu reaction with N-tosyl-protected (Tos) amino acid esters as acidic components of the reaction. Since the method used for the Tos group removal requires conditions incompatible with various functional groups, here we modified the procedure by replacing the tosyl group with o-nitrobenzenesulfonyl (o-NBS) group. Using the new procedure we obtained protected PNA monomer backbones with various amino acid side chains. The pseudodipeptide secondary amine groups were then deprotected by thiolysis, and after standard work-up acylated with thymin-1-ylacetic acid, to give the protected monomers. Since the deprotection of the secondary amine group occurs under mild conditions, the procedure is of general applicability and allows various modifications of PNA structure by using diverse beta-amino alcohols and alpha-amino acid esters. PMID:10780353

Falkiewicz, B; Kozyra, A; Kolodziejczyk, A S; Liberek, B; Wisniewski, K

1999-01-01

305

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

306

Novel carboranyl amino acids and peptides: reagents for antibody modification and subsequent neutron-capture studies.  

PubMed

A new alpha-amino acid derivative incorporating the 1,2-dicarba-closo- dodecarborane(12) cage, namely 5-(2-methyl-1,2-dicarba-closo-dodecarborane(12)-1-yl)- 2-aminopentanoic acid (2), was synthesized by the alkylation of the benzophenone Schiff's base of glycine methyl ester with 3-(2-methyl-1,2-dicarba-closo-dodecaborane(12)-1-yl)pr opyl iodide (8). This amino acid was employed in the synthesis of peptide derivatives such as 19-21 using solid-phase Merrifield methods. Dipeptide 19 was converted to a water-soluble ionic derivative by the pyrrolidine-mediated carborane cage degradation reaction followed by cation exchange to afford sodium salt 22. Dansylation of 22 with dansyl chloride yielded fluorescence-labeled dipeptide 23. Undecapeptide 21 was dansylated while still anchored to the Merrifield resin. Following its cleavage from the resin with hydrogen fluoride, product 25 was acetylated to block the free amino group on the lysine residue and then converted to water-soluble derivative 27. Trial conjugations of dipeptide 23 and undecapeptide 27 to T84.66, an anti-CEA antibody, were carried out by means of carboxyl activation with N-hydroxysulfosuccinimide and N,N-diisopropylcarbodiimide. Studies of the chemical syntheses of these and other peptide derivatives and the conjugation of 23 and 27 to the antibody are described. PMID:1772906

Varadarajan, A; Hawthorne, M F

1991-01-01

307

Constraining Effects of Brine Leakage from Carbon Sequestration Sites  

NASA Astrophysics Data System (ADS)

Research has shown that pressure build up associated with injection of CO2 into a deep saline aquifer has the potential to promote brine leakage into overlying formations. In order to understand and quantify chemical changes in an underground source of drinking water (USDW) invaded by deep saline brines, we analyzed over 90,000 brine geochemical data entries from the NETL NATCARB brine database to identify potential brine constituents of concern. Using a variety of statistical methods and EPA regulatory levels or standards (RLS) we narrowed the list of brine constituents of potential concern to USDWs to TDS, thallium, chloride, sulfate and arsenic. Somewhat surprisingly, the distribution of reported pH had a fairly narrow distribution around a median value of 7.4, with over 78% of values complying with EPA recommended secondary standard for drinking water acidity. The pH distribution implies that unlike pure CO2 leakage, far-field brine leakage (i.e., brine not in contact with CO2) is not expected to bear a low-pH signature, thus suggesting use of other means of geochemical monitoring for brine leakage, such as electrical conductivity. Geochemical mixing models of brine and dilute water were used to constrain mixing ratios where RLS values are exceeded for the TDS, thallium and chloride. TDS and chloride exceed the EPA secondary standards at a brine/USDW mixing ratio of 0.012 and 0.459, respectively. The thallium maximum contaminant level (MCL) is exceeded at a brine/USDW mixing ratio of 0.3753, smaller than the chloride mixing ratio. However, sorption and/or desorption processes may alter thallium concentrations along a leakage pathway resulting in lower concentrations in the aquifer than predicted by simple mixing models. While leakage into USDWs has received considerable attention, brine contamination of groundwater used for irrigation of agricultural crops is also an important area of research. Our calculations suggest that almost all crops grown in the United States will experience some decrease in yield at a brine/USDW ratio of <0.2, due to high salinity (expressed as TDS). As a stand-alone contaminant, boron that is present in brine may pose the most significant problem in irrigation waters due to low boron tolerance of many crops, particularly fruit.

Wunsch, A.; Navarre-Sitchler, A. K.; McCray, J. E.

2011-12-01

308

Time-dependent response of hydrogels under constrained swelling  

NASA Astrophysics Data System (ADS)

Constitutive equations are developed for the viscoplastic behavior of covalently cross-linked hydrogels subjected to swelling. The ability of the model to describe the time-dependent response is confirmed by comparison of results of simulation with observations on partially swollen poly(2-hydroxyethyl methacrylate) gel specimens in uniaxial tensile tests with a constant strain rate and tensile relaxation tests. The stress-strain relations are applied to study the kinetics of unconstrained and constrained swelling. The following conclusions are drawn from numerical analysis: (i) maximum water uptake under constrained swelling a viscoplastic hydrogel is lower than that for unconstrained swelling of its elastic counterpart and exceeds maximum water uptake under constrained swelling of the elastic gel, (ii) when the rate of water diffusion exceeds the rate of plastic flow in a polymer network, swelling curves (mass uptake versus time) for viscoplastic gels under constraints demonstrate characteristic features of non-Fickian diffusion.

Drozdov, A. D.; Sommer-Larsen, P.; Christiansen, J. deClaville; Sanporean, C.-G.

2014-06-01

309

Optimization of energy dissipation characteristics of active constrained layer damping  

NASA Astrophysics Data System (ADS)

The energy dissipation characteristics of active constrained layer damping (ACLD) treatments, consisting of visco-elastic cores constrained by active piezo-electric layers, are optimized using rational design procedures. The optimal lengths and control gains of these ACLD treatments are determined when a globally stable boundary control strategy is utilized to control the longitudinal strain of the active piezo-electric layers in response to the structural vibrations. The optimal parameters are obtained such that the sum of the passive and active loss coefficients of the ACLD treatments is maximized. The effect of the visco-elastic loss factor on the performance and the optimal parameters of the ACLD treatments is determined. Comparisons with optimal passive constrained layer damping (PCLD) indicate that the optimal ACLD is more effective in dissipating vibrational energy, particularly for visco-elastic cores with low-loss factors.

Baz, A.

1997-06-01

310

Optimization of segmented constrained layer damping with mathematical programming using strain energy analysis and modal data  

Microsoft Academic Search

A new method for enhancement of damping capabilities of segmented constrained layer damping material is proposed. Constrained layer damping has been extensively used since many years to damp flexural vibrations. The shear deformation occurring in the viscoelastic core is mainly responsible for the dissipation of energy. Cutting both the constraining and the constrained layer, which leads to segmentation, increases the

Grégoire Lepoittevin; Gerald Kress

2010-01-01

311

A constrained Ensemble Kalman Filter for improved streamflow forecasting  

NASA Astrophysics Data System (ADS)

Data assimilation techniques, such as the Kalman Filter and its variants, are often applied to physically or mathematically constrained hydrological models with little, if any, respect for physical laws. Model states can be adjusted beyond what is physically possible, compromising the integrity of model output. The challenge of constraining state updates, and the extent to which model predictions can be compromised without sensible constraints, has been largely ignored in the past. In this paper, a constrained Ensemble Kalman Filter (EnKF) is applied to a semi-distributed, physically-based conceptual model for the Tauranga-Taupo catchment, New Zealand. Streamflow observations are used to update the soil storage, baseflow, interflow and fastflow model states. Simple mass and flux constraints are placed on the data assimilation framework, encouraging state perturbations to have some physical meaning. The constrained EnKF is evaluated over 30 events between 2008 and 2011. This evaluation is based on model performance over a five day forecasting period, with EnKF state updating (both constrained and unconstrained) applied from 1998 up to the start each forecasting period. Constraining state updates shows significantly better overall performance compared to the unconstrained filter, according to the Kling Gupta Efficiency Index. Summary statistics for the 30 events are presented. For demonstration purposes, we focus on two events - 12 February 2009 and 21 January 2010. In these events, model performance was improved by 64% and 29%, respectively. More specifically, two of the three components of the KGE index, overall volume (bias) and the timing and shape of the hydrograph (correlation), show a better fit to the observations. The range of uncertainty between the five parameter sets applied was also reduced by 85% and 68%, respectively, resulting in more precise and reliable streamflow forecasts.

Maxwell, D. H.; Jackson, B. M.; McGregor, J.

2013-12-01

312

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

313

Value, Cost, and Sharing: Open Issues in Constrained Clustering  

NASA Technical Reports Server (NTRS)

Clustering is an important tool for data mining, since it can identify major patterns or trends without any supervision (labeled data). Over the past five years, semi-supervised (constrained) clustering methods have become very popular. These methods began with incorporating pairwise constraints and have developed into more general methods that can learn appropriate distance metrics. However, several important open questions have arisen about which constraints are most useful, how they can be actively acquired, and when and how they should be propagated to neighboring points. This position paper describes these open questions and suggests future directions for constrained clustering research.

Wagstaff, Kiri L.

2006-01-01

314

Thiazole constrained analogues of the thevinones: synthesis and structure.  

PubMed

A simple synthesis of ring-constrained endoethenomorphinans possessing 2'-substituted thiazole ring 4-6 has been achieved by regio- and stereoselective Diels-Alder reaction of thiazolomorphinandienes 1-3 and methyl vinyl ketone in high yield (72, 64 and 87%, respectively). The structure of cycloaddition products was determined by high resolution mass spectrometry (HRMS), IR, 1D and 2D NMR techniques. Double-pulsed field gradient spin-echo-nOe and HMBC were found to be particularly powerful and indispensable tools in the exact structural elucidation of the presented new class of spatially constrained thevinones. PMID:19431155

Sipos, Attila; Skaliczki, Tímea; Berényi, Sándor; Antus, Sándor

2009-09-01

315

Constrained optimization for image restoration using nonlinear programming  

NASA Technical Reports Server (NTRS)

The constrained optimization problem for image restoration, utilizing incomplete information and partial constraints, is formulated using nonlinear proramming techniques. This method restores a distorted image by optimizing a chosen object function subject to available constraints. The penalty function method of nonlinear programming is used. Both linear or nonlinear object function, and linear or nonlinear constraint functions can be incorporated in the formulation. This formulation provides a generalized approach to solve constrained optimization problems for image restoration. Experiments using this scheme have been performed. The results are compared with those obtained from other restoration methods and the comparative study is presented.

Yeh, C.-L.; Chin, R. T.

1985-01-01

316

Augmented Lagrangian method for constrained nuclear density functional theory  

NASA Astrophysics Data System (ADS)

The augmented Lagrangiam method (ALM), widely used in quantum chemistry constrained optimization problems, is applied in the context of the nuclear Density Functional Theory (DFT) in the self-consistent constrained Skyrme Hartree-Fock-Bogoliubov (CHFB) variant. The ALM allows precise calculations of multi-dimensional energy surfaces in the space of collective coordinates that are needed to, e.g., determine fission pathways and saddle points; it improves the accuracy of computed derivatives with respect to collective variables that are used to determine collective inertia; and is well adapted to supercomputer applications.

Staszczak, A.; Stoitsov, M.; Baran, A.; Nazarewicz, W.

2010-10-01

317

Constrained Coding for the Deep-Space Optical Channel  

NASA Astrophysics Data System (ADS)

We investigate methods of coding for a channel subject to a large dead-time constraint, i.e., a constraint on the minimum spacing between transmitted pulses, with the deep-space optical channel as the motivating example. Several constrained codes designed to satisfy the dead-time constraint are considered and compared on the basis of throughput, complexity, and decoded error rate. The performance of an iteratively decoded serial concatenation of a constrained code with an outer code is evaluated and shown to provide significant gains over a Reed-Solomon code concatenated with pulse-position modulation.

Moision, B.; Hamkins, J.

2002-01-01

318

Composite scalars at CERN LEP: Constraining technicolor theories  

NASA Astrophysics Data System (ADS)

CERN LEP I and LEP II data can be used to constrain technicolor models with light, neutral pseudo- Nambu-Goldstone bosons Pa. We use published limits on branching ratios and cross sections for final states with photons, large missing energy, jet pairs, or bb¯ pairs to constrain the anomalous PaZ0Z0, PaZ0?, and Pa?? couplings. From these results, we derive bounds on the size of the technicolor gauge group and the number of technifermion doublets in models such as low-scale technicolor.

Lynch, Kevin R.; Simmons, Elizabeth H.

2001-08-01

319

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

320

A Geometric Approach to Constrained Molecular Dynamics and Free Energy  

Microsoft Academic Search

We consider a molecule constrained to a hypersurface S\\u000ain the conguration space Rm<\\/sup>.\\u000aIn order to derive an expression for the mean force\\u000aacting along the constrained coordinate\\u000awe decompose the molecular vector field,\\u000aand single out the direction of the respective coordinate\\u000autilising the structure of affine connections.\\u000aBy these means we reconsider the well-known results derived by

Carsten Hartmann; Christof Schutte

2005-01-01

321

The treatment of osteoarthritis with unconstrained and constrained knee prostheses.  

PubMed

The first cases of knee prosthesis implantation at the orthopaedic department of the Freiburg university hospital are discussed. Surgery was indicated by advanced osteoarthritis which showed no improvement under conservative treatment. Indications concerning the choice of knee joint replacement with unconstrained or constrained prostheses are also discussed. Considerations of these indications as well as operative technique and consequent functional treatment usually produced good results. Follow up studies show equally good results for the GSB-total knee endoprosthesis (constrained) as for the surface type prosthesis (unconstrained). PMID:547962

Stock, D; Diezemann, E D; Gottstein, J; Mathias, M

1979-01-01

322

Therapeutic Agents in Acne Vulgaris: Part II. D-Alpha Amino Benzyl Penicillin, Erythromycin and Sulfadimethoxine.  

PubMed

A total of 379 patients with pustular and cystic acne vulgaris were selected for study in three groups. Each group was assigned one of the following medications: benzyl penicillin, erythromycin, sulfadimethoxine, or placebo; these were to be compared with tetracycline, a medication whose effectiveness was previously demonstrated in this type of acne. The study revealed a larger number of favourable responses to tetracycline and erythromycin than to sulfadimethoxine. Sulfadimethoxine, however, produced a greater number of favourable responses than did the benzyl penicillin or the placebo; the last-named had equivalent results. PMID:20328262

Stewart, W D; Maddin, S; Nelson, A J; Danto, J L

1965-06-26

323

Anti-inflammatory activity of some novel alpha-amino naphthalene derivatives.  

PubMed

alpha-Acetylamino naphthalene (1) was reacted with different aromatic aldehydes and with primary or secondary amines to give alpha-aminonaphthylsubstitutedaryl chalkones (2-5) and alpha-(substituted aminoethyl)-amidonaphthalenes (14-25), respectively. These substituted chalkones were treated with hydrazinehydrate and hydroxylamine hydrochloride to give 1-acetyl-5-substitutedaryl-3-(alpha-aminonaphthyl)-2-pyrazolines (6-9) and alpha-(2-substitutedaryl-isoxazolin-4-yl)-aminonaphthalenes (10-13), respectively. Their chemical structures were confirmed by IR and 1H-NMR spectral data and elemental analysis. Studies of the anti-inflammatory and ulcerogenic activities and acute toxicity of these newly synthesized compounds were performed in vivo and compared with the standard drug, phenylbutazone (CAS 50-33-9). Some of these compounds showed potent anti-inflammatory activity and less ulcerogenic effects than phenylbutazone. PMID:12608014

Sharma, Shalabh; Srivastava, Virendra Kishore; Kumar, Ashok

2003-01-01

324

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

325

A genetic learning strategy in constrained search spaces  

Microsoft Academic Search

The performance of an adaptive learning algorithm based on evolution (the genetic algorithm) is investigated in constrained boolean search spaces where some solutions may be infeasible. This paper describes a randomized validation procedure to limit the genetic search to feasible regions of the search space. Analysis of the effect of the validation procedure on genetic optimization is presented. The performance

Venkataramana Kommu; I. Pomeranz; T. Abdelrahman

1992-01-01

326

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

327

Pseudospectral Chebyshev Optimal Control of Constrained Nonlinear Dynamical Systems  

Microsoft Academic Search

A pseudospectral method for generating optimal trajectories of linear and nonlinear constrained dynamic systems is proposed. The method consists of representing the solution of the optimal control problem by an mth degree interpolating polynomial, using Chebyshev nodes, and then discretizing the problem using a cell-averaging technique. The optimal control problem is thereby transformed into an algebraic nonlinear programming problem. Due

Gamal N. Elnagar; Mohammad A. Kazemi

1998-01-01

328

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

329

An efficient constrained learning algorithm with momentum acceleration  

Microsoft Academic Search

An algorithm for efficient learning in feedforward networks is presented. Momentum acceleration is achieved by solving a constrained optimization problem using nonlinear programming techniques. In particular, minimization of the usual mean square error cost function is attempted under an additional condition for which the purpose is to optimize the alignment of the weight update vectors in successive epochs. The algorithm

Stavros J. Perantonis; Dimitris A. Karras

1995-01-01

330

Metal artifact reduction in computed tomography by constrained optimization  

NASA Astrophysics Data System (ADS)

Computed tomography (CT) streak artifacts caused by metal implants have long been recognized as a problem that limits various applications of CT imaging. An effective and robust algorithm is highly desirable to minimize metal artifacts and achieve clinically acceptable CT images. In this work, the raw projection data is viewed as "incomplete" in the presence of metal shadows. Shape and location of metal objects are automatically identified and used as prior knowledge for accurate segmentation of metal shadows in projection domain. An iterative algorithm based on constrained optimization is then used for the image reconstruction. This algorithm minimizes a quadratic penalized smoothness measure function of the image, subject to the constraint that the estimated projection data is within a specified tolerance of the available metal-shadow-excluded projection data, with image non-negativity enforced. The constrained minimization problem is optimized through the combination of projection onto convex sets (POCS) and steepest gradient descent of the smoothness measure objective. Digital phantom study shows that the proposed constrained optimization algorithm has superior performance in reducing metal artifacts, suppressing noise and improving soft-tissue visibility. Some comparisons are performed with the filtered-back-projection (FBP), FDK, POCS and constrained optimization with total-variation (TV) objective. Although the algorithm is presented in the context of metal artifacts, it can be generated to image reconstruction from incomplete projections caused by limited angular range or low angular sampling rate in both 2D and 3D cases.

Zhang, Xiaomeng; Wang, Jing; Xing, Lei

2010-03-01

331

Constrained surface controllers for three-dimensional image data reformatting.  

PubMed

This study did not require ethical approval in the United Kingdom. The aim of this work was to create two controllers for navigating a two-dimensional image plane through a volumetric data set, providing two important features of the ultrasonographic paradigm: orientation matching of the navigation device and the desired image plane in the three-dimensional (3D) data and a constraining surface to provide a nonvisual reference for the image plane location in the 3D data. The first constrained surface controller (CSC) uses a planar constraining surface, while the second CSC uses a hemispheric constraining surface. Ten radiologists were asked to obtain specific image reformations by using both controllers and a commercially available medical imaging workstation. The time taken to perform each reformatting task was recorded. The users were also asked structured questions comparing the utility of both methods. There was a significant reduction in the time taken to perform the specified reformatting tasks by using the simpler planar controller as compared with a standard workstation, whereas there was no significant difference for the more complex hemispheric controller. The majority of users reported that both controllers allowed them to concentrate entirely on the reformatting task and the related image rather than being distracted by the need for interaction with the workstation interface. In conclusion, the CSCs provide an intuitive paradigm for interactive reformatting of volumetric data. PMID:19420319

Graves, Martin J; Black, Richard T; Lomas, David J

2009-07-01

332

Constrained optimisation and robust function optimisation with EIWO  

Microsoft Academic Search

A robust variant of invasive weed optimisation (IWO) algorithm, called enhanced invasive weed optimisation (EIWO) algorithm, is proposed in this paper for the optimisation of constrained benchmark problems. Enjoying the ecological behaviour of colonising weeds, IWO has demonstrated its ability in solving different optimisation problems. Since making a proper balance between these two components is essential, especially to cope with

Milad Ahangaran; Xin-She Yang

2013-01-01

333

Explicit constrained model predictive control. The influence of constraints redundancy  

Microsoft Academic Search

The paper deals with the constrained model predictive control and tries to identify the influences of the redundancy in the constraints when developing explicit laws. Methods exist to eliminate the redundant constraints, the solution is given in terms of a cutting in the parameters space, the question is whether such a redundancy-free formulation decreases the computational load and further, which

Sorin Olaru; D. Dumur

2005-01-01

334

On Maximizing Delay-Constrained Coverage of Urban Vehicular Networks  

Microsoft Academic Search

The success of a real-time sensing application with a vehicular network highly depends on the spatiotemporal coverage of sensing data that can be collected from the vehicular network. Deploying broadband wireless base stations is an effective way to collect vehicular sensing data and the deployment of base stations has a great impact on delay-constrained coverage. This paper considers the critical

Yanmin Zhu; Youchen Bao; Bo Li

2012-01-01

335

Methods for Preparing Internally Constrained Peptides and Peptidomimetics.  

National Technical Information Service (NTIS)

The present invention relates to a method for preparing a peptide having a stable, internally constrained alpha-helical, beta-sheet/beta-turn, 3(sub 10)-helical, or pi-helical region and a method of stabilizing an alpha-helical, beta-sheet/beta-turn, 3(su...

P. Arora R. Chapman

2005-01-01

336

Design of regularity constrained linear phase modulated lapped transforms  

Microsoft Academic Search

The regularity constrained linear phase filter banks reported recently are based on generalized bi-orthogonal lapped transforms. They do not have a modulated structure and hence all the basis functions are to be optimized separately. Design and implementation complexity increases with the size of the block transform. In this paper, a cosine-modulated approach for the design of orthogonal modulated lapped transforms

K. M. Abdul Hameed; Elizabeth Elias

2006-01-01

337

An algorithm for linearly constrained adaptive array processing  

Microsoft Academic Search

A constrained least mean-squares algorithm has been derived which is capable of adjusting an array of sensors in real time to respond to a signal coming from a desired direction while discriminating against noises coming from other directions. Analysis and computer simulations confirm that the algorithm is able to iteratively adapt variable weights on the taps of the sensor array

OTIS LAMONT FROST

1972-01-01

338

Algorithm 872: Parallel 2D constrained Delaunay mesh generation  

Microsoft Academic Search

Delaunay refinement is a widely used method for the construction of guaranteed quality triangular and tetrahedral meshes. We present an algorithm and a software for the parallel constrained Delaunay mesh generation in two dimensions. Our approach is based on the decomposition of the original mesh generation problem into N smaller subproblems which are meshed in parallel. The parallel algorithm is

Andrey N. Chernikov; Nikos P. Chrisochoides

2008-01-01

339

A Distributed Context-Free Language Constrained Shortest Path Algorithm  

Microsoft Academic Search

Formal language constrained shortest path problems are concerned with finding shortest paths in labeled graphs. These labeled paths have the constraint that the concatenation of labels along a path constitute a valid string in some formal language Lambda over alphabet Sigma. These problems are well studied where the formal language is regular or context-free, and have been used in a

Charles B. Ward; Nathan M. Wiegand; Phillip G. Bradford

2008-01-01

340

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

341

Constraining gravitational and cosmological parameters with astrophysical data  

Microsoft Academic Search

We use astrophysical data to shed light on fundamental physics by constraining parametrized theoretical cosmological and gravitational models. Gravitational parameters are those constants that parametrize possible departures from Einstein's general theory of relativity (GR). We develop a general framework to describe torsion in the spacetime around the Earth, and show that certain observables of the Gravity Probe B (GPB) experiment

Yi Mao

2008-01-01

342

Head shape evolution in Tropidurinae lizards: does locomotion constrain diet?  

Microsoft Academic Search

Different components of complex integrated systems may be specialized for different functions, and thus the selective pressures acting on the system as a whole may be conflicting and can ultimately constrain organismal perfor- mance and evolution. The vertebrate cranial system is one of the most striking examples of a complex system with several possible functions, being associated to activities as

T. KOHLSDORF; M. B. GRIZANTE; C. A. NAVAS; A. HERREL

2008-01-01

343

Fixed cost allocation and the constrained product mix decision  

Microsoft Academic Search

This paper focuses on the benefits of fixed cost allocation in product mix decisions. We show that in a constrained production environment where at least one factor of production is fixed and in short supply, oligopoly firms can earn higher profits by allocating the costs of these fixed factors The higher profits occur because the use of full absorption product

Susan Haka; Fred Jacobs; Ronald Marshall

2002-01-01

344

A reference monitor for workflow systems with constrained task execution  

Microsoft Academic Search

We describe a model, independent of any underlying access control paradigm, for specifying authorization constraints such as separation of duty and cardinality constraints in workflow systems. We present a number of results enabling us to simplify the set of authorization constraints. These results form the theoretical foundation for an algorithm that can be used to determine whether a given constrained

Jason Crampton

2005-01-01

345

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

346

Using Diagnostic Text Information to Constrain Situation Models  

ERIC Educational Resources Information Center

During reading, the model of the situation described by the text is continuously accommodated to new text input. The hypothesis was tested that readers are particularly sensitive to diagnostic text information that can be used to constrain their existing situation model. In 3 experiments, adult participants read narratives about social situations…

Dutke, Stephan; Baadte, Christiane; Hahnel, Andrea; von Hecker, Ulrich; Rinck, Mike

2010-01-01

347

Extension of Karmarkar's algorithm onto convex quadratically constrained quadratic problems  

Microsoft Academic Search

Convex quadratically constrained quadratic problems are considered. It is shown that such problems can be transformed to aconic form. The feasible set of the conic form is the intersection of a direct product of standard quadratic cones intersected with\\u000a a hyperplane (the analogue of a simplex), and a linear subspace. For a problem of such form, the analogue of Karmarkar's

Arkadii Nemirovskii; Katya Scheinberg

1996-01-01

348

Security-Constrained Unit Commitment with Stochastic Constraints  

Microsoft Academic Search

This paper presents a stochastic model for the long-term solution of security-constrained unit commitment (SCUC). The proposed approach could be used by vertically integrated utilities as well as the ISOs in electricity markets. In this model, random disturbances, such as outages of generation units and transmission lines as well as load forecasting inaccuracies, are modeled as scenario trees using the

Mohammad Shahidehpour

2007-01-01

349

A constrained optimal data association for multiple target tracking  

Microsoft Academic Search

One of the major problems in multiple target tracking is to obtain an accurate association between targets and noisy measurements. We introduce a new scheme, called constrained optimal data association (CODA), that finds the optimal data association by a MAP estimation method and uses a new energy function. In this scheme, the natural constraints between targets and measurements are defined

Hong Jeong; Jeong-Ho Park

1999-01-01

350

Constrained Least Squares Estimators of Oblique Common Factors.  

ERIC Educational Resources Information Center

An expression is given for weighted least squares estimators of oblique common factors of factor analyses, constrained to have the same covariance matrix as the factors they estimate. A proof of the uniqueness of the solution is given. (Author/JKS)

McDonald, Roderick P.

1981-01-01

351

VIBRATION ANALYSIS OF BEAMS WITH MULTIPLE CONSTRAINED LAYER DAMPING PATCHES  

Microsoft Academic Search

A new analytical, energy based approach is described that predicts the harmonic vibration response of a damped beam with multiple viscoelastic patches. Each damping patch consists of a metallic constraining layer and an adhesive viscoelastic layer with spectrally-varying material properties. Since this approach relates all deformation variables in various layers, only flexural shape functions need to be incorporated in the

S.-W. Kung; R. Singh

1998-01-01

352

An experimental comparison of piezoelectric and constrained layer damping  

Microsoft Academic Search

A qualitative comparison between a piezoelectric vibration absorber and a constrained layer damping treatment is presented. Piezoelectric materials convert mechanical strains into electrical charge. Dissipation of the charge results in attenuation of vibration. The damping is concentrated to a single mode by constructing a piezoelectric absorber. The damped vibration absorber is comprised of the piezoelectric material and a passive electronic

Joseph J. Hollkamp; Robert W. Gordon

1996-01-01

353

DYNAMIC BOUNDARY CONTROL OF BEAMS USING ACTIVE CONSTRAINED LAYER DAMPING  

Microsoft Academic Search

A globally stable boundary control strategy is developed to damp the vibration of beams fully treated with active constrained layer damping (ACLD) treatments. The devised boundary controller is compatible with the operating nature of the ACLD treatments where the strain induced generates a control force and moment acting at the boundary of the treated beam. The development of the boundary

A. Baz

1997-01-01

354

Active Vibration Control of Beam Using Electromagnetic Constrained Layer Damping  

Microsoft Academic Search

This paper investigates vibration control of beam through electro-magnetic constrained layer damping (EMCLD) which consists of electromagnet layer, permanent magnet layer and viscoelastic damping layer. When the coil of the electromagnet is electrified with proper control strategy, the electromagnet can exert magnetic force opposite to the direction of structural deformation so that the structural vibration is attenuated. A mathematical model

Niu Hongpan; Zhang Yahong; Zhang Xinong; Xie Shilin

2008-01-01

355

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

356

FINITE ELEMENT MODELLING OF MAGNETIC CONSTRAINED LAYER DAMPING  

Microsoft Academic Search

The performance of a new treatment consisting of integrated arrays of constrained visco elastic damping layers passively controlled by a specially arranged network of permanent magnets is evaluated. The interaction between the magnets and the viscoelastic layers aims at enhancing the energy dissipation characteristics of the damping treatments. In this manner, it would be possible to manufacture structures that are

M. Ruzzene; J. Oh; A. Baz

2000-01-01

357

Vibration control of beams with active constrained layer damping  

Microsoft Academic Search

An analytical methodology is presented to study the active vibration control of beams treated with active constrained layer damping (ACLD). This analytical method is based on the conventional theory of structural dynamics. The process of deriving equations is precise and easy to understand. Hamilton's principle with the Rayleigh-Ritz method is used to derive the equation of motion of the beam\\/ACLD

Feng-Ming Li; Kikuo Kishimoto; Yue-Sheng Wang; Zhao-Bo Chen; Wen-Hu Huang

2008-01-01

358

ACTIVE CONSTRAINED LAYER DAMPING OF THIN CYLINDRICAL SHELLS  

Microsoft Academic Search

The effectiveness of the active constrained layer damping (ACLD) treatments in enhancing the damping characteristics of thin cylindrical shells is presented. A finite element model (FEM) is developed to describe the dynamic interaction between the shells and the ACLD treatments. Experiments are performed to verify the numerical predictions. The obtained results suggest the potential of the ACLD treatments in controlling

M. C. RAY; J. Oh; A. Baz

2001-01-01

359

Evolution of constrained layer damping using a cellular automaton algorithm  

Microsoft Academic Search

Constrained layer damping (CLD) is a highly effective passive vibration control strat- egy if optimized adequately. Factors controlling CLD performance are well documented for the flexural modes of beams but not for more complicated mode shapes or structures. The current paper introduces an approach that is suitable for locating CLD on any type of structure. It fol- lows the cellular

C M Chia; J A Rongong; K Worden

2008-01-01

360

Vibration control of plates with active constrained layer damping  

Microsoft Academic Search

Bending vibration of flat plates is controlled using patches of active constrained layer damping (ACLD) treatments. Each ACLD patch consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The first layer is directly bonded to the plate to sense its vibration and the second layer acts as an actuator to actively control the shear deformation of

A. Baz; J. Ro

1996-01-01

361

Vibration control of plates using magnetic constrained layer damping  

Microsoft Academic Search

A new class of surface treatment is proposed to provide effective means for attenuating undesirable structural vibrations. The proposed treatment relies in its operation on the use of smart damping treatments which consists of integrated arrays of constrained visco-elastic damping layers that are controlled passively by a specially arranged network of permanent magnets. The interaction between the magnets and the

A. K. Ebrahim; Amr M. Baz

1998-01-01

362

LMIs for constrained polynomial interpolation with application in trajectory planning  

Microsoft Academic Search

We consider an open-loop trajectory planning problem for linear systems with bound constraints originating from saturations or physical limitations. Using an algebraic approach and results on positive polynomials, we show that this control problem can be cast into a constrained polynomial interpolation problem admitting a convex linear matrix inequality (LMI) formulation.

Didier Henrion; Jean-Bernard Lasserre

2006-01-01

363

Constraining Mid Pliocene North Atlantic Warming Using a Multiproxy Approach  

Microsoft Academic Search

Relatively high sea surface temperature during the mid Pliocene (~3.0 Ma) has been documented in many oceanic regions. Constraining the magnitude, variability, and regional extent of warming is critical for modeling experiments being undertaken based upon reconstruction of mid Pliocene conditions. A comprehensive re-evaluation of the mid Pliocene of the North Atlantic region using a multiproxy approach that includes quantitative

H. Dowsett; M. Robinson; G. Dwyer; T. Cronin; M. Chandler

2005-01-01

364

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

365

Seriation by constrained correspondence analysis: A simulation study  

Microsoft Academic Search

One of the many areas in which correspondence analysis (CA) is an effective method, concerns seriation problems. For example, CA is a well-known technique for the seriation of archaeological assemblages. A problem with the CA seriation solution, however, is that only a relative ordering of the assemblages is obtained. To improve the usual CA solution, a constrained CA approach that incorporates

Michel van de Velden; Patrick J. F. Groenen; Jeroen Poblome

2009-01-01

366

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

367

Active control of plates using compressional constrained layer damping  

Microsoft Academic Search

Sound radiation from a plate into an acoustic cavity is actively controlled using patches of Active Compressional Constrained Layer Damping (ACCLD). The ACCLD, under consideration, consists of piezoelectric fibers embedded across the thickness of a visco-elastic matrix in order to control the compressional damping characteristics of the composite. The effectiveness of the ACCLD treatments in attenuating the sound radiation from

Wilfred Henry Shields

1997-01-01

368

Constraining the MOdified Newtonian Dynamics from spherically symmetrical hydrodynamic accretion  

Microsoft Academic Search

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

Nirupam Roy

2011-01-01

369

Reflections on How Color Term Acquisition Is Constrained  

ERIC Educational Resources Information Center

Compared with object word learning, young children typically find learning color terms to be a difficult linguistic task. In this reflections article, I consider two questions that are fundamental to investigations into the developmental acquisition of color terms. First, I consider what constrains color term acquisition and how stable these…

Pitchford, Nicola J.

2006-01-01

370

Active Semi-Supervision for Pairwise Constrained Clustering  

Microsoft Academic Search

Semi-supervised clustering uses a small amount of super- vised data to aid unsupervised learning. One typical ap- proach specifies a limited number of must-link and cannot- link constraints between pairs of examples. This paper presents a pairwise constrained clustering framework and a new method for actively selecting informative pairwise con- straints to get improved clustering performance. The clus- tering and

Sugato Basu; Arindam Banerjee; Raymond J. Mooney

2004-01-01

371

Hop Constrained Network Design Problem with Partial Survivability  

Microsoft Academic Search

This paper studies the hop constrained network design problem with partial survivability, namely, given an undirected network, a set of point-to-point demands (commodities), and transmission link costs, identify two node disjoint paths for each demand (commodity) to minimize the total costs subject to the constraints that each demand is routed and traverses at most a specified number of links (or

Samit Soni

2001-01-01

372

Constrained Longest Common Subsequence Computing Algorithms in Practice  

Microsoft Academic Search

The problem of finding a constrained longest common subsequence (CLCS) for the sequences A and B with respect to the sequence P was introduced recently. Its goal is to find a longest subsequence C of A and B such that P is a subsequence of C. There are several algorithms solving the CLCS problem, but there is no real experimental

Sebastian Deorowicz; Joanna Obstoj

2010-01-01

373

Complexity of self-similar hierarchically constrained ensembles  

NASA Astrophysics Data System (ADS)

The complexity measure of the infinite set of self-similar hierarchically constrained ensembles is determined in the framework of the generalized combinatory approach. It is shown that, as the hierarchical coupling increases, the complexity increases to a value that decreases with increasing the dispersion of this coupling and with decreasing the branching degree of the hierarchical tree.

Olemsko?, A. I.

2007-03-01

374

Thermally constrained motor operation for a climbing robot  

Microsoft Academic Search

Climbing robots are especially susceptible to ther- mal overload during normal operation, due to the need to op- pose gravity and to frequently apply internal forces for clinging. As an alternative to setting conservative limits on the motor peak and average current, we investigate methods for measuring motor temperatures, predicting motor thermal conditions and generating thermally constrained behavior. A thermal

Salomon Trujillo; Mark R. Cutkosky

2009-01-01

375

The 1.9 A Structure of the Branched-Chain Amino-Acid Transaminase (IlvE) from Mycobacterium tuberculosis  

SciTech Connect

Unlike mammals, bacteria encode enzymes that synthesize branched-chain amino acids. The pyridoxal 5'-phosphate-dependent transaminase performs the final biosynthetic step in these pathways, converting keto acid precursors into {alpha}-amino acids. The branched-chain amino-acid transaminase from Mycobacterium tuberculosis (MtIlvE) has been crystallized and its structure has been solved at 1.9 {angstrom} resolution. The MtIlvE monomer is composed of two domains that interact to form the active site. The biologically active form of IlvE is a homodimer in which each monomer contributes a substrate-specificity loop to the partner molecule. Additional substrate selectivity may be imparted by a conserved N-terminal Phe30 residue, which has previously been observed to shield the active site in the type IV fold homodimer. The active site of MtIlvE contains density corresponding to bound PMP, which is likely to be a consequence of the presence of tryptone in the crystallization medium. Additionally, two cysteine residues are positioned at the dimer interface for disulfide-bond formation under oxidative conditions. It is unknown whether they are involved in any regulatory activities analogous to those of the human mitochondrial branched-chain amino-acid transaminase.

Tremblay, L.; Blanchard, J

2009-01-01

376

Synthesis and biological evaluation of flexible and conformationally constrained LpxC inhibitors.  

PubMed

Inhibitors of the UDP-3-O-[(R)-3-hydroxymyristoyl]-N-acetylglucosamine deacetylase (LpxC) represent promising candidates for the development of antibiotics possessing a so far unexploited mechanism of action. In a chiral pool synthesis, starting from the D-mannose derived mannonolactone 4, conformationally constrained C-glycosidic as well as open chained hydroxamic acids with a defined stereochemistry were prepared. Diversity was introduced by performing C–C coupling reactions like the Sonogashira and Suzuki cross-coupling reactions. The biological evaluation of the synthesized compounds revealed that in the case of the C-glycosides a long, linear and rigid hydrophobic side chain is required for antibiotic activity against E. coli. The open chain derivatives show higher biological activity than the conformationally constrained C-glycosides. The morpholinomethyl substituted open chain derivative 43, being the most potent compound presented in this paper, inhibits LpxC with a Ki value of 0.35 ?M and represents a promising lead structure. PMID:23917427

Löppenberg, Marius; Müller, Hannes; Pulina, Carla; Oddo, Alberto; Teese, Mark; Jose, Joachim; Holl, Ralph

2013-09-28

377

CONMIN: A FORTRAN program for constrained function minimization: User's manual  

NASA Technical Reports Server (NTRS)

CONMIN is a FORTRAN program, in subroutine form, for the solution of linear or nonlinear constrained optimization problems. The basic optimization algorithm is the Method of Feasible Directions. The user must provide a main calling program and an external routine to evaluate the objective and constraint functions and to provide gradient information. If analytic gradients of the objective or constraint functions are not available, this information is calculated by finite difference. While the program is intended primarily for efficient solution of constrained problems, unconstrained function minimization problems may also be solved, and the conjugate direction method of Fletcher and Reeves is used for this purpose. This manual describes the use of CONMIN and defines all necessary parameters. Sufficient information is provided so that the program can be used without special knowledge of optimization techniques. Sample problems are included to help the user become familiar with CONMIN and to make the program operational.

Vanderplaats, G. N.

1973-01-01

378

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

379

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

380

Spectral finite-element methods for parametric constrained optimization problems.  

SciTech Connect

We present a method to approximate the solution mapping of parametric constrained optimization problems. The approximation, which is of the spectral finite element type, is represented as a linear combination of orthogonal polynomials. Its coefficients are determined by solving an appropriate finite-dimensional constrained optimization problem. We show that, under certain conditions, the latter problem is solvable because it is feasible for a sufficiently large degree of the polynomial approximation and has an objective function with bounded level sets. In addition, the solutions of the finite-dimensional problems converge for an increasing degree of the polynomials considered, provided that the solutions exhibit a sufficiently large and uniform degree of smoothness. Our approach solves, in the case of optimization problems with uncertain parameters, the most computationally intensive part of stochastic finite-element approaches. We demonstrate that our framework is applicable to parametric eigenvalue problems.

Anitescu, M.; Mathematics and Computer Science

2009-01-01

381

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

382

A Constrained Multibody System Dynamics Avoiding Kinematic Singularities  

NASA Astrophysics Data System (ADS)

In the analysis of constrained multibody systems, the constraint reaction forces are normally expressed in terms of the constraint equations and a vector of Lagrange multipliers. Because it fails to incorporate conservation of momentum, the Lagrange multiplier method is deficient when the constraint Jacobian matrix is singular. This paper presents an improved dynamic formulation for the constrained multibody system. In our formulation, the kinematic constraints are still formulated in terms of the joint constraint reaction forces and moments; however, the formulations are based on a second-order Taylor expansion so as to incorporate the rigid body velocities. Conservation of momentum is included explicitly in this method; hence the problems caused by kinematic singularities can be avoided. In addition, the dynamic formulation is general and applicable to most dynamic analyses. Finally the 3-leg Stewart platform is used for the example of analysis.

Huang, Chih-Fang; Yan, Chang-Dau; Jeng, Shyr-Long; Cheing, Wei-Hua

383

Evolutionary pattern search algorithms for unconstrained and linearly constrained optimization  

SciTech Connect

The authors describe a convergence theory for evolutionary pattern search algorithms (EPSAs) on a broad class of unconstrained and linearly constrained problems. EPSAs adaptively modify the step size of the mutation operator in response to the success of previous optimization steps. The design of EPSAs is inspired by recent analyses of pattern search methods. The analysis significantly extends the previous convergence theory for EPSAs. The analysis applies to a broader class of EPSAs,and it applies to problems that are nonsmooth, have unbounded objective functions, and which are linearly constrained. Further, they describe a modest change to the algorithmic framework of EPSAs for which a non-probabilistic convergence theory applies. These analyses are also noteworthy because they are considerably simpler than previous analyses of EPSAs.

HART,WILLIAM E.

2000-06-01

384

Multiply-constrained semantic search in the Remote Associates Test.  

PubMed

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 by using Latent Semantic Analysis to measure the similarity between the guesses, cues, and answers. We found that people use two systematic strategies to solve multiply-constrained problems: (a) people produce guesses primarily on the basis of just one of the three cues at a time; and (b) people adopt a local search strategy--they make new guesses based in part on their previous guesses. These results inform how people combine constraints to search through and retrieve semantic information from memory. PMID:23587845

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

2013-07-01

385

Topoisomerase V relaxes supercoiled DNA by a constrained swiveling mechanism.  

PubMed

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. PMID:17804808

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

2007-09-11

386

Composite scalars at CERN LEP: Constraining technicolor theories  

SciTech Connect

CERN LEP I and LEP II data can be used to constrain technicolor models with light, neutral pseudo--Nambu-Goldstone bosons P{sup a}. We use published limits on branching ratios and cross sections for final states with photons, large missing energy, jet pairs, or b{bar b} pairs to constrain the anomalous P{sup a}Z{sup 0}Z{sup 0}, P{sup a}Z{sup 0}{gamma}, and P{sup a}{gamma}{gamma} couplings. From these results, we derive bounds on the size of the technicolor gauge group and the number of technifermion doublets in models such as low-scale technicolor.

Lynch, Kevin R.; Simmons, Elizabeth H.

2001-08-01

387

A second-generation constrained reaction volume shock tube  

NASA Astrophysics Data System (ADS)

We have developed a shock tube that features a sliding gate valve in order to mechanically constrain the reactive test gas mixture to an area close to the shock tube endwall, separating it from a specially formulated non-reactive buffer gas mixture. This second-generation Constrained Reaction Volume (CRV) strategy enables near-constant-pressure shock tube test conditions for reactive experiments behind reflected shocks, thereby enabling improved modeling of the reactive flow field. Here we provide details of the design and operation of the new shock tube. In addition, we detail special buffer gas tailoring procedures, analyze the buffer/test gas interactions that occur on gate valve opening, and outline the size range of fuels that can be studied using the CRV technique in this facility. Finally, we present example low-temperature ignition delay time data to illustrate the CRV shock tube's performance.

Campbell, M. F.; Tulgestke, A. M.; Davidson, D. F.; Hanson, R. K.

2014-05-01

388

The CLUES project: Constrained Local UniversE Simulations  

NASA Astrophysics Data System (ADS)

Constrained simulations of the Local Universe are an invaluable tool to investigate many aspects of dark halo and galaxy formation in environments that look pretty much like the the one our Milky Way resides. In this way, we can minimize the effect of cosmic variance when comparing the results of numerical simulations with observations of the Local Volume (LV, a sphere of 7-8 Mpc around us). In this paper we present the CLUES Project, an international collaboration whose main goal is to produce realistic cosmological simulations of the Local Universe, by imposing observational constrains on the mass and velocity fields of the initial random gaussian fluctuation realizations. The advantage of this technique is that we reproduce the large scale structures regardless whether we change the cosmological model, or the nature of dark matter candidates. In this regard, we can then make reliable comparisons between simulation outputs and draw conclusions that are less affected by cosmic variance.

Yepes, G.; Martínez-Vaquero, L. A.; Gottlöber, S.; Hoffman, Y.

2009-10-01

389

A second-generation constrained reaction volume shock tube.  

PubMed

We have developed a shock tube that features a sliding gate valve in order to mechanically constrain the reactive test gas mixture to an area close to the shock tube endwall, separating it from a specially formulated non-reactive buffer gas mixture. This second-generation Constrained Reaction Volume (CRV) strategy enables near-constant-pressure shock tube test conditions for reactive experiments behind reflected shocks, thereby enabling improved modeling of the reactive flow field. Here we provide details of the design and operation of the new shock tube. In addition, we detail special buffer gas tailoring procedures, analyze the buffer/test gas interactions that occur on gate valve opening, and outline the size range of fuels that can be studied using the CRV technique in this facility. Finally, we present example low-temperature ignition delay time data to illustrate the CRV shock tube's performance. PMID:24880416

Campbell, M F; Tulgestke, A M; Davidson, D F; Hanson, R K

2014-05-01

390

An Automated Translator for Model Checking Time Constrained Workflow Systems  

NASA Astrophysics Data System (ADS)

Workflows have proven to be a useful conceptualization for the automation of business processes. While formal verification methods (e.g., model checking) can help ensure the reliability of workflow systems, the industrial uptake of such methods has been slow largely due to the effort involved in modeling and the memory required to verify complex systems. Incorporation of time constraints in such systems exacerbates the latter problem. We present an automated translator, YAWL2DVE-t, which takes as input a time constrained workflow model built with the graphical modeling tool YAWL, and outputs the model in DVE, the system specification language for the distributed LTL model checker DiVinE. The automated translator, together with the graphical editor and the distributed model checker, provides a method for rapid design, verification and refactoring of time constrained workflow systems. We present a realistic case study developed through collaboration with the local health authority.

Mashiyat, Ahmed Shah; Rabbi, Fazle; Wang, Hao; Maccaull, Wendy

391

Controlling spin contamination using constrained density functional theory  

NASA Astrophysics Data System (ADS)

We have extended the constrained density functional theory (DFT) approach to explicitly control the magnitude of spin contamination. Unlike a restricted or restricted open-shell approach, the present method allows finer granularity, not only constraining the magnitude of the spin contamination but also allowing for the possibility of applying the constraint to a subsystem of a much larger system. This allows for the description of spin polarization where physically meaningful, while simultaneously enabling the reduction of spurious overpolarization that is present in many DFT functionals. We utilize this constraint in two particular model applications: The calculation of isotropic and anisotropic hyperfine couplings of a transition metal complex, [Mn(CN)5NO]2-, and the calculation of the diabatic dissociation curves of OF radical. In both cases, the spin contamination constraint is essential for obtaining physically meaningful, qualitatively correct, results.

Schmidt, J. R.; Shenvi, Neil; Tully, John C.

2008-09-01

392

Fine tuning in the constrained exceptional supersymmetric standard model  

NASA Astrophysics Data System (ADS)

Supersymmetric unified models in which the Z' couples to the Higgs doublets, as in the E6 class of models, have large fine tuning dominated by the experimental mass limit on the Z'. To illustrate this, we investigate the degree of fine tuning throughout the parameter space of the constrained exceptional supersymmetric standard model (cE6SSM) that is consistent with a Higgs mass mh˜125GeV. Fixing tan??=10, and taking specific values of the mass of the Z' boson, with MZ'˜2-4TeV, we find that the minimum fine tuning is set predominantly from the mass of Z' and varies from ˜200 to 400 as we vary MZ' from ˜2 to 4 TeV. However, this is significantly lower than the fine tuning in the constrained minimal supersymmetric standard model, of O(1000), arising from the large stop masses required to achieve the Higgs mass.

Athron, P.; Binjonaid, Maien; King, S. F.

2013-06-01

393

On constrained and regularized high-dimensional regression *  

PubMed Central

High-dimensional feature selection has become increasingly crucial for seeking parsimonious models in estimation. For selection consistency, we derive one necessary and sufficient condition formulated on the notion of degree-of-separation. The minimal degree of separation is necessary for any method to be selection consistent. At a level slightly higher than the minimal degree of separation, selection consistency is achieved by a constrained L0-method and its computational surrogate–the constrained truncated L1-method. This permits up to exponentially many features in the sample size. In other words, these methods are optimal in feature selection against any selection method. In contrast, their regularization counterparts–the L0-regularization and truncated L1-regularization methods enable so under slightly stronger assumptions. More importantly, sharper parameter estimation/prediction is realized through such selection, leading to minimax parameter estimation. This, otherwise, is impossible in absence of a good selection method for high-dimensional analysis.

Shen, Xiaotong; Pan, Wei; Zhu, Yunzhang; Zhou, Hui

2013-01-01

394

The Pendulum: From Constrained Fall to the Concept of Potential  

NASA Astrophysics Data System (ADS)

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 pendulums and assuming the impossibility of perpetual motion Huygens obtained a law of conservation of vis viva at specific positions, beautifully commented by Mach. Daniel Bernoulli generalised Huygens results introducing the concept of potential and the related independence of the ‘work’ done from the trajectories (paths) followed: vis viva conservation at specific positions is now linked with the potential. Feynman’s modern way of teaching the subject shows striking similarities with Bernoulli’s approach. A number of animations and simulations can help to visualise and teach some of the pendulum’s interpretations related to what we now see as instances of energy conservation.

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

2006-08-01

395

Asynchronous parallel generating set search for linearly-constrained optimization.  

SciTech Connect

We describe an asynchronous parallel derivative-free algorithm for linearly-constrained optimization. Generating set search (GSS) is the basis of ourmethod. At each iteration, a GSS algorithm computes a set of search directionsand corresponding trial points and then evaluates the objective function valueat each trial point. Asynchronous versions of the algorithm have been developedin the unconstrained and bound-constrained cases which allow the iterations tocontinue (and new trial points to be generated and evaluated) as soon as anyother trial point completes. This enables better utilization of parallel resourcesand a reduction in overall runtime, especially for problems where the objec-tive function takes minutes or hours to compute. For linearly-constrained GSS,the convergence theory requires that the set of search directions conform to the3 nearby boundary. The complexity of developing the asynchronous algorithm forthe linearly-constrained case has to do with maintaining a suitable set of searchdirections as the search progresses and is the focus of this research. We describeour implementation in detail, including how to avoid function evaluations bycaching function values and using approximate look-ups. We test our imple-mentation on every CUTEr test problem with general linear constraints and upto 1000 variables. Without tuning to individual problems, our implementationwas able to solve 95% of the test problems with 10 or fewer variables, 75%of the problems with 11-100 variables, and nearly half of the problems with100-1000 variables. To the best of our knowledge, these are the best resultsthat have ever been achieved with a derivative-free method. Our asynchronousparallel implementation is freely available as part of the APPSPACK software.4

Kolda, Tamara G.; Griffin, Joshua; Lewis, Robert Michael

2007-04-01

396

Social Emotional Optimization Algorithm for Nonlinear Constrained Optimization Problems  

NASA Astrophysics Data System (ADS)

Nonlinear programming problem is one important branch in operational research, and has been successfully applied to various real-life problems. In this paper, a new approach called Social emotional optimization algorithm (SEOA) is used to solve this problem which is a new swarm intelligent technique by simulating the human behavior guided by emotion. Simulation results show that the social emotional optimization algorithm proposed in this paper is effective and efficiency for the nonlinear constrained programming problems.

Xu, Yuechun; Cui, Zhihua; Zeng, Jianchao

397

Jamming Transition in Kinetically Constrained Models with Reflection Symmetry  

NASA Astrophysics Data System (ADS)

A class of kinetically constrained models with reflection symmetry is proposed as an extension of the Fredrickson-Andersen model. It is proved that the proposed model on the square lattice exhibits a freezing transition at a non-trivial density. It is conjectured by numerical experiments that the known mechanism of the singular behaviors near the freezing transition in a previously studied model (spiral model) is not responsible for that in the proposed model.

Ohta, Hiroki; Sasa, Shin-ichi

2014-04-01

398

A Simple SQP Algorithm for Constrained Finite Minimax Problems  

PubMed Central

A simple sequential quadratic programming method is proposed to solve the constrained minimax problem. At each iteration, through introducing an auxiliary variable, the descent direction is given by solving only one quadratic programming. By solving a corresponding quadratic programming, a high-order revised direction is obtained, which can avoid the Maratos effect. Furthermore, under some mild conditions, the global and superlinear convergence of the algorithm is achieved. Finally, some numerical results reported show that the algorithm in this paper is successful.

2014-01-01

399

Template-constrained cyclic sulfopeptide HIV-1 entry inhibitors†  

PubMed Central

Template-constrained cyclic sulfopeptides that inhibit HIV-1 entry were rationally designed based on a loop from monoclonal antibody (mAb) 412d. A focused set of sulfopeptides was synthesized using Fmoc-Tyr(SO3DCV)-OH (DCV = 2,2-dichlorovinyl). Three cyclic sulfopeptides that inhibit entry of HIV-1 and complement the activity of known CCR5 antagonists were identified.

Rudick, Jonathan G.; Laakso, Meg M.; Schloss, Ashley C.; DeGrado, William F.

2013-01-01

400

Engineering Label-Constrained Shortest-Path Algorithms  

Microsoft Academic Search

We consider a generalization of the shortest-path problem: given an alphabet ?, a graph G whose edges are weighted and ?-labeled, and a regular language L ? ??, the L-constrained shortest-path problem consists of finding a shortest path p in G such that the concatenated labels along p form a word of L. This definition allows to model, e.g., many

Christopher L. Barrett; Keith Bisset; Martin Holzer; Goran Konjevod; Madhav V. Marathe; Dorothea Wagner

2008-01-01

401

Multi-disciplinary constrained optimization of wind turbines  

Microsoft Academic Search

We describe procedures for the multi-disciplinary design optimization of wind turbines, where design parameters are optimized\\u000a by maximizing a merit function, subjected to constraints that translate all relevant design requirements. Evaluation of merit\\u000a function and constraints is performed by running simulations with a parametric high-fidelity aero-servo-elastic model; a detailed\\u000a cross-sectional structural model is used for the minimum weight constrained sizing

C. L. Bottasso; F. Campagnolo; A. Croce

402

Boundary Search for Constrained Numerical Optimization Problems in ACO Algorithms  

Microsoft Academic Search

This paper presents a novel boundary approach which is included as a constraint-handling technique in an ant colony algorithm.\\u000a The necessity of approaching the boundary between the feasible and infeasible search space for many constrained optimization\\u000a problems is a paramount challenge for every constraint-handling technique. Our proposed technique precisely focuses the search\\u000a on the boundary region and can be either

Guillermo Leguizamón; Carlos A. Coello Coello

2006-01-01

403

Jamming Transition in Kinetically Constrained Models with Reflection Symmetry  

NASA Astrophysics Data System (ADS)

A class of kinetically constrained models with reflection symmetry is proposed as an extension of the Fredrickson-Andersen model. It is proved that the proposed model on the square lattice exhibits a freezing transition at a non-trivial density. It is conjectured by numerical experiments that the known mechanism of the singular behaviors near the freezing transition in a previously studied model (spiral model) is not responsible for that in the proposed model.

Ohta, Hiroki; Sasa, Shin-ichi

2014-06-01

404

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

405

On the chemical equilibrium concept: Constrained word associations and conception  

Microsoft Academic Search

The use of the method of constrained word associations to gain knowledge on the conception of the chemical equilibrium concept is reported. The analysis provides information on:(a)A general indication of change in the cognitive structure of students associated with chemical comprehension.(b)The comparison of clusters of concepts at pre- and postinstruction indicating the associated concepts.(c)A graphical representation of the links among

Esther Gussarsky; Malka Gorodetsky

1988-01-01

406

Video personalization in heterogeneous and resource-constrained environments  

Microsoft Academic Search

Access to multimedia data and multimedia services is becoming increasingly common in networked mobile environments. In such\\u000a environments, both the mobile client devices and multimedia servers are typically resource constrained. Moreover, the mobile\\u000a client population is often heterogeneous in terms of the clients’ preferences with regard to multimedia content, the clients’\\u000a quality of service requirements and system-level resource constraints. In

Yong WeiSuchendra; Suchendra M. Bhandarkar; Kang Li; Lakshmish Ramaswamy

407

Time-Constrained Query Processing in CASE-DB  

Microsoft Academic Search

CASE-DB is a real-time, single-user, relational prototype DBMS that permits the specificationof strict time constraints for relational algebra queries. Given a time constrained non-aggregaterelational algebra query and a "fragment chain" for each relation involved in the query, CASEDBinitially obtains a response to a modified version of the query and then uses an "iterative queryevaluation" technique to successively improve and evaluate

Gultekin Özsoyoglu; Sujatha Guru Swamy; Kaizheng Du; Wen-chi Hou

1995-01-01

408

Unscented filtering for equality-constrained nonlinear systems  

Microsoft Academic Search

This paper addresses the state-estimation problem for nonlinear systems in a context where prior knowledge, in addition to the model and the measurement data, is available in the form of an equality constraint. Three novel suboptimal algorithms based on the unscented Kalman filter are developed, namely, the equality-constrained unscented Kalman filter, the projected unscented Kalman filter, and the measurement-augmented unscented

Bruno O. Soares Teixeira; Jaganath Chandrasekar; L. A. B. Torres; Luis A. Aguirre; Dennis S. Bernstein

2008-01-01

409

Constrained Test Problems for Multi-objective Evolutionary Optimization  

Microsoft Academic Search

Over the past few years, researchers have developed a number of multi-objective evolutionary algorithms (MOEAs). Although\\u000a most studies concentrated on solving unconstrained optimization problems, there exists a few studies where MOEAs have been\\u000a extended to solve constrained optimization problems. As the constraint handling MOEAs gets popular, there is a need for developing\\u000a test problems which can evaluate the algorithms well.

Kalyanmoy Deb; Amrit Pratap; T. Meyarivan

410

Security-Constrained Generation and Transmission Outage Scheduling With Uncertainties  

Microsoft Academic Search

This study presents a stochastic model for the independent system operator's (ISO's) optimal coordinated long-term maintenance scheduling of generation units and transmission lines with short-term security-constrained unit commitment (SCUC). Random disturbances of power systems including forced outages of generation units and transmission lines, load forecast errors, and fuel price fluctuations are modeled as scenario trees using the Monte Carlo simulation.

Lei Wu; Mohammad Shahidehpour; Yong Fu

2010-01-01

411

Sandwich beam theory and the analysis of constrained layer damping  

Microsoft Academic Search

This paper deals with the analysis of sandwich beams and constrained layer damping in beams. A three-layered beam theory has been given in which the continuity of displacements and the transverse shear stresses has been satisfied at the interfaces. Axial displacement field in each layer has been assumed to be non-linear with respect to the thickness co-ordinate. This resulted in

A. Bhimaraddi

1995-01-01

412

Damped response of shells by a constrained viscoelastic layer  

NASA Technical Reports Server (NTRS)

Vibration absorbers are introduced into an asymmetric configuration of thin cylinders and tori enclosing an acoustic medium. The absorbers consist of thin axial strips bonded to the cylinder with a thin viscoelastic layer. The constrained layer dissipates the energy of relative motions between strip and cylinder. The absorber is most effective on response modes with two or more circumferential waves. The use of transfer matrices is extended to the coupled cylinder-absorber system.

El-Raheb, M.; Wagner, P.

1986-01-01

413

Singular divergence instability thresholds of kinematically constrained circulatory systems  

NASA Astrophysics Data System (ADS)

Static instability or divergence threshold of both potential and circulatory systems with kinematic constraints depends singularly on the constraints' coefficients. Particularly, the critical buckling load of the kinematically constrained Ziegler's pendulum as a function of two coefficients of the constraint is given by the Plücker conoid of degree n=2. This simple mechanical model exhibits a structural instability similar to that responsible for the Velikhov-Chandrasekhar paradox in the theory of magnetorotational instability.

Kirillov, O. N.; Challamel, N.; Darve, F.; Lerbet, J.; Nicot, F.

2014-01-01

414

Fundamentals of energy-constrained sensor network systems  

Microsoft Academic Search

This article is an overview of energy-constrained sensor networks, focusing on energy-conserving communications and signal processing strategies. We assume battery-driven nodes, employing robust communications, with little or no fixed infrastructure. Our discussion includes architectures, communications connectivity, capacity and scalability, mobility, network localization and synchronization, distributed signal processing, and cross-layer issues. Because energy is a precious system resource, all aspects of

BRIAN M. SADLER

2005-01-01

415

Constraining dark energy through the stability of cosmic structures  

NASA Astrophysics Data System (ADS)

For a general dark-energy equation of state, we estimate the maximum possible radius of massive structures that are not destabilized by the acceleration of the cosmological expansion. A comparison with known stable structures constrains the equation of state. The robustness of the constraint can be enhanced through the accumulation of additional astrophysical data and a better understanding of the dynamics of bound cosmic structures.

Pavlidou, V.; Tetradis, N.; Tomaras, T. N.

2014-05-01

416

Filtering Numerical CSPs Using Well-Constrained Subsystems  

Microsoft Academic Search

When interval methods handle systems of equations over the reals, two main types of filtering\\/contraction algorithms are used to re- duce the search space. When the system is well-constrained, interval Newton algorithms behave like a global constraint over the whole n? n system. Also, filtering algorithms issued from constraint programming perform an AC3-like propagation loop, where the constraints are iter-

Ignacio Araya; Gilles Trombettoni; Bertrand Neveu

2009-01-01

417

Groundwater availability as constrained by hydrogeology and environmental flows.  

PubMed

Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes-St. Lawrence River Basin Water Resources?Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications. PMID:23582026

Watson, Katelyn A; Mayer, Alex S; Reeves, Howard W

2014-01-01

418

Constraining Solar Flare Differential Emission Measures with EVE and RHESSI  

NASA Astrophysics Data System (ADS)

Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from lsim2 to gsim50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly observed solar flares. EVE is sensitive to ~2-25 MK thermal plasma emission, and RHESSI to gsim10 MK together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from the EVE data also constrain the low energy cutoff of the non-thermal electrons, a crucial parameter for flare energetics. The DEM analysis can also be used to predict the soft X-ray flux in the poorly observed ~0.4-5 nm range, with important applications for geospace science.

Caspi, Amir; McTiernan, James M.; Warren, Harry P.

2014-06-01

419

Pattern search algorithms for mixed variable general constrained optimization problems  

NASA Astrophysics Data System (ADS)

A new class of algorithms for solving nonlinearly constrained mixed variable optimization problems is presented. The Audet-Dennis Generalized Pattern Search (GPS) algorithm for bound constrained mixed variable optimization problems is extended to problems with general nonlinear constraints by incorporating a filter, in which new iterates are accepted whenever they decrease the incumbent objective function value or constraint violation function value. Additionally, the algorithm can exploit any available derivative information (or rough approximation thereof) to speed convergence without sacrificing the flexibility often employed by GPS methods to find better local optima. In generalizing existing GPS algorithms, the new theoretical convergence results presented here reduce seamlessly to existing results for more specific classes of problems. While no local continuity or smoothness assumptions are made, a hierarchy of theoretical convergence results is given, in which the assumptions dictate what can be proved about certain limit points of the algorithm. A new Matlab(c) software package was developed to implement these algorithms. Numerical results are provided for several nonlinear optimization problems from the CUTE test set, as well as a difficult nonlinearly constrained mixed variable optimization problem in the design of a load-bearing thermal insulation system used in cryogenic applications.

Abramson, Mark Aaron

420

Vibration control of plates using magnetic constrained layer damping  

NASA Astrophysics Data System (ADS)

A new class of surface treatment is proposed to provide effective means for attenuating undesirable structural vibrations. The proposed treatment relies in its operation on the use of smart damping treatments which consists of integrated arrays of constrained visco-elastic damping layers that are controlled passively by a specially arranged network of permanent magnets. The interaction between the magnets and the visco-elastic layers aims at enhancing the energy dissipation characteristics of the damping treatment. In this manner, it would be possible to manufacture structures that are light in weight which are capable of meeting strict constraints on structural vibration when subjected to unavoidable disturbances. This new treatment will be called Magnetic Constrained Layer Damping (MCLD) treatment. A finite element modeling of a plate treated with MCLD treatments is developed. This model describes the dynamics and the damping characteristics of this structure. The numerical results are verified experimentally using a cantilever plate fully treated with MCLD with the magnets placed at the root of the plate. Close agreement is obtained between theory and experiments. Also the performance characteristics of the MCLD is compared with the corresponding performance of the conventional Passive Constrained Layer Damping (PCLD). The effectiveness of the MCLD in attenuating structural vibration of the plate has been clearly demonstrated in the frequency domain. The developed theoretical and experimental techniques present invaluable tools for designing and predicting the performance of plates treated with MCLD.

Ebrahim, A. K.; Baz, Amr M.

1998-06-01

421

Finite Element Modelling of Magnetic Constrained Layer Damping  

NASA Astrophysics Data System (ADS)

The performance of a new treatment consisting of integrated arrays of constrained visco elastic damping layers passively controlled by a specially arranged network of permanent magnets is evaluated. The interaction between the magnets and the viscoelastic layers aims at enhancing the energy dissipation characteristics of the damping treatments. In this manner, it would be possible to manufacture structures that are light in weight and are capable of meeting strict constraints on structural vibration when subjected to unavoidable disturbances. In this paper, a finite element model is developed to study the interactions between the permanent magnets and their influence on the dynamic behavior of treated beams. The model is used to develop a thorough understanding of the basic phenomena governing the operation of this new class of smart magnetic constrained layer damping (MCLD) treatments. The performance characteristics of the MCLD are determined for fully treated beams and compared with the corresponding performance of conventional passive constrained layer damping (PCLD). Such a comparison is used to determine the merits and limitations of the proposed MCLD treatments.

RUZZENE, M.; OH, J.; BAZ, A.

2000-09-01

422

Vibration control of beams with magnetic constrained layer damping  

NASA Astrophysics Data System (ADS)

A new class of surface treatment is proposed to provide effective means for attenuating undesirable structural vibrations. The proposed treatment relies in its operation on the use of smart damping treatments which consist of integrated arrays of constrained viscoelastic damping layers that are controlled passively by a specially arranged network of permanent magnets. The interaction between the magnets and the viscoelastic layers aims at enhancing the energy dissipation characteristics of the damping treatments. In this manner, it would be possible to manufacture structures that are light in weight which are also capable of meeting strict constraints on structural vibration when subjected to unavoidable disturbances. Emphasis is placed here on using the Bond-Graph technique to develop a thorough understanding of the basic phenomena governing the operation of this new class of smart Magnetic Constrained Layer Damping (MCLD) treatments. Also, the performance characteristics of the MCLD are determined for full and segmented treatments of beams. These characteristics are compared with the corresponding performance of conventional Passive Constrained Layer Damping (PCLD). Such a comparison is used to determine the merits and limitation of the MCLD treatments.

Abdou, Shehta El-Sayed

423

Constrained TV-minimization image reconstruction for industrial CT system  

NASA Astrophysics Data System (ADS)

In this work, we investigate the applicability of the constrained total-variation (TV)-minimization reconstruction method to industrial CT system. In general, industrial CT systems have the same principles of imaging process with clinical CT systems, but different imaging objectives and evaluation metrics. Optimization-based image reconstruction methods have been actively developed to meet practical challenges and extensively tested for clinical CT systems. However, the utility of optimization-based reconstruction methods is task-specific and not necessarily transferrable among different tasks. In this work, we adopt constrained TV-minimization programs together with adaptive-steepest-descent-projection-ontoconvex-sets (ASD-POCS) algorithm for reconstructing images from data of a concrete sample collected using a laboratory industrial CT system developed for non-destructive evaluation. Our results, compared to those reconstructed from FBPbased algorithm, suggest that the constrained TV-minimization program combined with ASD-POCS algorithm can yield images with comparable or improved visual quality and achieve equivalent or better imaging objectives over the currently used FBP-based algorithm under dense sampling data condition.

Chen, Buxin; Yang, Min; Zhang, Zheng; Bian, Junguo; Han, Xiao; Sidky, Emil; Pan, Xiaochuan

2014-02-01

424

Constrained droplets for high resolution microscopy of protein fibrillization  

NASA Astrophysics Data System (ADS)

The use of constrained droplets (droplets with pinned contact lines on solid surfaces) is proposed here as a method for sample support in optical microscopy studies. Capillarity acts to contain the liquid sample, allowing access for observations in the bulk and at the gas/liquid interface. At the capillary length scale, surface tension forms stable interfaces, virtually immune to gravity and with curvatures that can be adjusted. This is particularly useful when studying the gas/liquid interface and its vicinity under high resolution optical microscopy. Such observations are normally performed using oil immersion objectives which must be positioned within distances only tens of microns from the region of interest. Constrained droplets can also be used at small scales, requiring minute volumes of analyte. The use of the constrained droplet method is demonstrated by studying the aggregation of insulin into amyloid fibrils in the solution and at the gas/liquid interface, where proteins are prone to denaturation and subsequent fibrillization. Such an aggregation process is associated with many neurodegenerative diseases, including Alzhemier's.

Posada, David; Tessier, Peter; Hirsa, Amir

2011-11-01

425

Constrained Stochastic Differential Equations Driven by Fractional Brownian Motions: Stationarity and Parameter Estimation Problems.  

National Technical Information Service (NTIS)

We study stationary solutions of constrained stochastic differential equations driven by fractional Brownian motions. Key motivations for this study originate from the fact that such constrained processes serve as approximation models for a large class of...

C. Lee

2013-01-01

426

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...joint femorotibial metal/composite non-constrained cemented...polyethylene with carbon fibers composite and are intended for use with bone cement (§...

2009-04-01

427

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...joint femorotibial metal/composite non-constrained cemented...polyethylene with carbon fibers composite and are intended for use with bone cement (§...

2010-04-01

428

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

429

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

430

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

431

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

432

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

433

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

434

Prior image constrained image reconstruction in emerging computed tomography applications  

NASA Astrophysics Data System (ADS)

Advances have been made in computed tomography (CT), especially in the past five years, by incorporating prior images into the image reconstruction process. In this dissertation, we investigate prior image constrained image reconstruction in three emerging CT applications: dual-energy CT, multi-energy photon-counting CT, and cone-beam CT in image-guided radiation therapy. First, we investigate the application of Prior Image Constrained Compressed Sensing (PICCS) in dual-energy CT, which has been called "one of the hottest research areas in CT." Phantom and animal studies are conducted using a state-of-the-art 64-slice GE Discovery 750 HD CT scanner to investigate the extent to which PICCS can enable radiation dose reduction in material density and virtual monochromatic imaging. Second, we extend the application of PICCS from dual-energy CT to multi-energy photon-counting CT, which has been called "one of the 12 topics in CT to be critical in the next decade." Numerical simulations are conducted to generate multiple energy bin images for a photon-counting CT acquisition and to investigate the extent to which PICCS can enable radiation dose efficiency improvement. Third, we investigate the performance of a newly proposed prior image constrained scatter correction technique to correct scatter-induced shading artifacts in cone-beam CT, which, when used in image-guided radiation therapy procedures, can assist in patient localization, and potentially, dose verification and adaptive radiation therapy. Phantom studies are conducted using a Varian 2100 EX system with an on-board imager to investigate the extent to which the prior image constrained scatter correction technique can mitigate scatter-induced shading artifacts in cone-beam CT. Results show that these prior image constrained image reconstruction techniques can reduce radiation dose in dual-energy CT by 50% in phantom and animal studies in material density and virtual monochromatic imaging, can lead to radiation dose efficiency improvement in multi-energy photon-counting CT, and can mitigate scatter-induced shading artifacts in cone-beam CT in full-fan and half-fan modes.

Brunner, Stephen T.

435

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

436

Are consumers Ricardian when some are liquidity constrained? Evidence for the United States  

Microsoft Academic Search

This paper formulates and estimates a revised specification of Evans' (1988) test for Ricardian equivalence which incorporates the possible presence of liquidity constrained consumers. If liquidity constrained consumers are significant in number, tests using aggregate consumption data may tend to reject the Ricardian equivalence hypothesis when the model allows for liquidity constraints. A test which incorporated liquidity constrained consumers could

Duane W. Rockerbie

1997-01-01

437

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

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Ankle joint metal/polymer semi-constrained cemented prosthesis...Devices § 888.3110 Ankle joint metal/polymer semi-constrained cemented prosthesis...Identification. An ankle joint metal/polymer semi-constrained cemented...

2010-04-01

438

21 CFR 888.3160 - Elbow joint metal/polymer semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Elbow joint metal/polymer semi-constrained cemented prosthesis...Devices § 888.3160 Elbow joint metal/polymer semi-constrained cemented prosthesis...Identification. An elbow joint metal/polymer semi-constrained cemented...

2010-04-01

439

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

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Hip joint metal/polymer semi-constrained cemented prosthesis...Devices § 888.3350 Hip joint metal/polymer semi-constrained cemented prosthesis...Identification. A hip joint metal/polymer semi-constrained cemented...

2010-04-01

440

21 CFR 888.3800 - Wrist joint metal/polymer semi-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Wrist joint metal/polymer semi-constrained cemented prosthesis...Devices § 888.3800 Wrist joint metal/polymer semi-constrained cemented prosthesis...Identification. A wrist joint metal/polymer semi-constrained...

2010-04-01

441

21 CFR 888.3310 - Hip joint metal/polymer constrained cemented or uncemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Hip joint metal/polymer constrained cemented or uncemented prosthesis...Devices § 888.3310 Hip joint metal/polymer constrained cemented or uncemented prosthesis...Identification. A hip joint metal/polymer constrained cemented or...

2010-04-01

442

21 CFR 888.3120 - Ankle joint metal/polymer non-constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Ankle joint metal/polymer non-constrained cemented prosthesis...Devices § 888.3120 Ankle joint metal/polymer non-constrained cemented prosthesis...Identification. An ankle joint metal/polymer non-constrained cemented...

2010-04-01

443

A finite element formulation for composite laminates with smart constrained layer damping  

Microsoft Academic Search

A composite laminate with active constrained-layer damping treatment is studied. The interface element for viscoelastic damping layers has been developed based on the relative displacements between composite plates and piezoelectric constraining layers. As an example, the problem of forced oscillations of the laminated composite structure with a smart constrained damping treatment is solved and the vibration response of the composite

Sung Yi; Kam Yim Sze

2000-01-01

444

Applications of Electro-Rheological Fluids for Constrained Layer Damping Treatment of Structures  

Microsoft Academic Search

Constrained layer damping (CLD) technique employs solid viscoelastic materials for controlling the vibration characteristics of structures. The effectiveness of the CLD treatment depends on the dynamic mechanical properties and geometrical dimensions of the viscoelastic and constraining layers. It also depends on the percentage coverage of the structure by the viscoelastic and constraining layers. Since the complex dynamic properties of electro-rheological

S. O. Oyadiji

1996-01-01

445

Some design considerations for active and passive constrained layer damping treatments  

Microsoft Academic Search

Active constrained layer damping treatments promise to be an effective means of vibration suppression in structures. Basically, the concept consists in either replacing or augmenting the constraining layer of a constrained viscoelastic material with piezoceramic actuators in an attempt to improve vibration suppression properties by capitalizing on both passive and active damping techniques. An important issue in such configurations is

S. C. Huang; D. J. Inman; E. M. Austin

1996-01-01

446

A self-sensing active constrained layer damping treatment for a Euler - Bernoulli beam  

Microsoft Academic Search

In a self-sensing active constrained layer (SACL) damping treatment, the piezoelectric constraining layer is used simultaneously as both a sensor and an actuator. A variational formulation of ACL damping treatments has shown that an ACL damping treatment using a self-sensing and actuating piezoelectric element as the constraining layer in combination with rate of strain feedback as the control law will

Jessica M. Yellin; I. Y. Shen

1996-01-01

447

A compressional-shear model for vibration control of beams with active constrained layer damping  

Microsoft Academic Search

In the modeling of the active constrained layer damping (ACLD) structures, the transverse displacements of the constraining layer and the host structures are usually assumed to be compatible. However, when performing active control, even a small difference between the transverse displacement of the constraining layer attached with actuator and that of the host structures bonded with sensor may destabilize the

Dongchang Sun; Liyong Tong

2004-01-01

448

Dynamic responses of flexible linkage mechanisms with viscoelastic constrained layer damping treatment  

Microsoft Academic Search

Dynamic transient responses of high-speed flexible linkage mechanisms with viscoelastic constrained damping layer are studied in order to evaluate constrained layer damping treatment performances. A new type of shape function for three layer frame element containing a heavily damped viscoelastic layer, a base layer and a constraining layer is developed. The generalized equations of motion of flexible linkage mechanism systems

Xianmin Zhang; Arthur G. Erdman

2001-01-01

449

N-Acetylated alpha-linked acidic dipeptidase converts N-acetylaspartylglutamate from a neuroprotectant to a neurotoxin.  

PubMed

We previously reported that inhibition of the brain enzyme N-acetylated alpha-linked acidic dipeptidase (NAALADase; glutamate carboxypeptidase II) robustly protects cortical neurons from ischemic injury. Since NAALADase hydrolyzes N-acetylaspartylglutamate (NAAG) to glutamate we hypothesized that inhibiting NAALADase would both decrease glutamate and increase NAAG. Increasing NAAG is potentially important because NAAG is a metabotropic glutamate receptor agonist and an N-methyl-D-aspartate (NMDA) partial antagonist, both of which have previously been shown to be neuroprotective. To understand the likely effects of endogenous NAAG in the central nervous system, we have now investigated the activity of NAAG in primary cortical cultures while manipulating NAALADase activity. Under hydrolyzing conditions, when NAALADase was active, NAAG had toxic effects that were blocked by NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonists and by NAALADase inhibition. NAAG's toxic effects were presumably due to the liberation of glutamate. Under nonhydrolyzing conditions, when NAALADase was inhibited, NAAG demonstrated neuroprotective effects against both NMDA toxicity and metabolic inhibition. In the case of NMDA-induced toxicity, NAAG provided neuroprotection through its partial antagonist activity at the NMDA receptor. In the case of metabolic inhibition, NAAG had an additional neuroprotective effect mediated through its agonist properties at the type II metabotropic glutamate receptor. These results indicate that NAAG might play an important role in the central nervous system, under certain pathological conditions, as a neurotoxin or as a neuroprotectant, depending on the activity of NAALADase. PMID:10991955

Thomas, A G; Vornov, J J; Olkowski, J L; Merion, A T; Slusher, B S

2000-10-01

450

Biochemical characterization of an autoradiographic method for studying excitatory amino acid receptors using L-(/sup 3/H)glutamate  

SciTech Connect

A method was developed for radiolabeling excitatory amino acid receptors of rat brain with L-(/sup 3/H)glutamate. Effective labeling of glutamate receptors in slide-mounted 10-microns sections was obtained using a low incubation volume (0.15 ml) and rapid washing: a procedure where high ligand concentrations were achieved with minimal waste. Saturation experiments using (/sup 3/H)glutamate revealed a single binding site of micromolar affinity. The Bmax was trebled in the presence of Ca2+ (2.5 mM) and Cl- (20 mM) with no change in the Kd. Binding was rapid, saturable, stereospecific, and sensitive to glutamate receptor agonists. The proportions of (/sup 3/H)glutamate binding sensitive to N-methyl-D-aspartate (NMDA), kainate, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were 34, 54, and 51%, respectively. NMDA inhibited binding at a distinct subset of L-(/sup 3/H)glutamate sites, whereas AMPA and kainate competed for some common sites. Labeling of sections with L-(/sup 3/H)glutamate in the presence of the selective agonists allowed autoradiographic visualization of glutamate receptor subtypes in brain tissue.

Cincotta, M.; Summers, R.J.; Beart, P.M.

1989-02-15

451

Quantitative differences in the effects of de novo produced and exogenous kynurenic acid in rat brain slices.  

PubMed

Kynurenic acid (KYNA) is an antagonist of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors and it blocks the glycine site of the NMDA receptor preferentially (IC50 = 7.9 microM). KYNA is produced endogenously by transamination of its precursor L-kynurenine (L-KYN). We tested the hypothesis that effects of endogenous, de novo produced KYNA, following bath-application of L-KYN to slices, would be different than effects of commercially-synthesized (exogenous) KYNA. The ability to block spontaneous epileptiform activity, induced by lowering extracellular magnesium, was examined in area CA3 of hippocampus and the entorhinal cortex. At a concentration of 200 microM L-KYN, which produced 0.89 +/- 0.20 microM KYNA, there were fewer slices with spontaneous epileptiform activity than slices exposed to 2 microM exogenous KYNA. The results indicate a more potent neuromodulatory action of endogenous KYNA than has been previously realized. PMID:10553950

Scharfman, H E; Hodgkins, P S; Lee, S C; Schwarcz, R

1999-10-22

452

Ethynylglycine synthon from Garner's aldehyde: a useful precursor for the synthesis of non-natural amino acids.  

PubMed

The ethynylglycine synthon, namely (R)-2,2-dimethyl-3-(tert-butoxycarbonyl)-4-ethynyl-oxazolidine, can be obtained through the synthetic elaboration of naturally occurring serine. This compound has been exploited as a helpful and versatile non-racemic building block to be used for the design and synthesis of biologically important compounds, mainly non-natural alpha-amino acids. Taking advantage of the terminal acetylene moiety several synthetic applications can be designed. Metalation followed by trapping with electrophiles or Cu/Pd catalysed coupling with aromatic halogenides are shown to deliver useful precursors of ethynylglycine derivatives. Additions of bimetallic reagents like stannyl- or silylcuprates are useful entries for the regio- and stereoselective functionalization of the lateral chain, aimed at the synthesis of modified vinylglycine precursors. An overview of our recent work in the field will be given, and the use of ethynylglycine synthon in the synthesis of non-racemic saturated and unsaturated non-natural amino acids will be briefly reviewed. PMID:15812682

Reginato, G; Meffre, P; Gaggini, F

2005-08-01

453

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

Code of Federal Regulations, 2010 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...

2010-04-01

454

21 CFR 888.3330 - Hip joint metal/metal semi-constrained, with an uncemented acetabular component, prosthesis.  

Code of Federal Regulations, 2010 CFR

...semi-constrained, with an uncemented acetabular component, prosthesis. 888.3330...semi-constrained, with an uncemented acetabular component, prosthesis. (a) Identification...semi-constrained, with an uncemented a