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1

Efficient synthesis of serically constrained smmetrically alpha,alpha-disubstituted alpha-amino acids under operationally convenient conditions.  

PubMed

Homologation of the nucleophilic glycine equivalent Ni-Gly-PABP [Ni(II) complex of glycine Schiff base with 2-[N-(alpha-picolyl)amino]benzophenone (PABP)] 2 via alkyl halide alkylations and Michael addition reactions was systematically studied as a general method for preparing symmetrically alpha,alpha-disubstituted alpha-amino acids (sym-alpha,alpha-AA). The dialkylation reactions are conducted under operationally convenient conditions without recourse to inert atmosphere, dried solvents, and low temperatures, thus enjoying key advantages of the experimental simplicity and attractive cost structure. The method has been shown to be particularly successful for the dialkylation of complex 2 with activated and nonactivated alkyl halides, including propargyl derivatives, affording a generalized and practical access to the corresponding sym-alpha,alpha-AA. This study has also shown some limitation of the method, as it cannot be extended to alpha- or beta-branched alkyl halides or Michael acceptors to be used for the dialkylation of glycine equivalent 2. High chemical yields of the dialkylated products, combined with the simplicity of the experimental procedure, render this method worth immediate use for multigram scale preparation of the sym-alpha,alpha-AA. PMID:12895052

Ellis, Trevor K; Martin, Collin H; Tsai, Gary M; Ueki, Hisanori; Soloshonok, Vadim A

2003-08-01

2

Synthesis of alpha-amino acids  

DOEpatents

A method for synthesizing alpha amino acids proceding 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 snythesis methods of the prior art.

Davis, Jr., Jefferson W. (San Francisco, CA)

1983-01-01

3

Synthesis of alpha-amino acids  

DOEpatents

A method 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 12 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.

Davis, Jr., Jefferson W. (San Francisco, CA)

1983-01-01

4

Synthesis of alpha-amino acids  

DOEpatents

A method for synthesizing alpha amino acids proceding 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 12 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.

Davis, Jr., Jefferson W. (San Francisco, CA)

1983-01-01

5

Scaleable catalytic asymmetric Strecker syntheses of unnatural alpha-amino acids  

Microsoft Academic Search

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

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

2009-01-01

6

Scaleable catalytic asymmetric Strecker syntheses of unnatural alpha-amino acids.  

PubMed

Alpha-amino acids are the building blocks of proteins and are widely used as components of medicinally active molecules and chiral catalysts. Efficient chemo-enzymatic methods for the synthesis of enantioenriched alpha-amino acids have been developed, but it is still a challenge to obtain non-natural amino acids. Alkene hydrogenation is broadly useful for the enantioselective catalytic synthesis of many classes of amino acids, but it is not possible to obtain alpha-amino acids bearing aryl or quaternary alkyl alpha-substituents using this method. The Strecker synthesis-the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis-is an especially versatile chemical method for the synthesis of racemic alpha-amino acids. Asymmetric Strecker syntheses using stoichiometric amounts of a chiral reagent have been applied successfully on gram-to-kilogram scales, yielding enantiomerically enriched alpha-amino acids. In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent could provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen limited use on preparative scales (more than a gram). The limited utility of existing catalytic methods may be due to several important factors, including the relatively complex and precious nature of the catalysts and the requisite use of hazardous cyanide sources. Here we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-natural amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. This catalyst is robust, without sensitive functional groups, so it is compatible with aqueous cyanide salts, which are safer and easier to handle than other cyanide sources; this makes the method adaptable to large-scale synthesis. We have used this new method to obtain enantiopure amino acids that are not readily prepared by enzymatic methods or by chemical hydrogenation. PMID:19829379

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

2009-10-15

7

A new method proposed for the determination of absolute configurations of alpha-amino acids.  

PubMed

Enantiopure alpha-amino acids were converted to 4-substituted 2-aryl- and 2-alkyl-5(4H)-oxazolones under partial racemization. These nonracemic mixtures were dissolved in CDCl(3), an equimolar amount of the chiral dirhodium complex Rh(II)(2)[(R)-(+)-MTPA](4) (MTPA-H = Mosher's acid) was added, and the (1)H NMR spectra of the resulting samples were recorded (dirhodium method). The relative intensities of (1)H signals dispersed by the formation of diastereomeric adducts allow to determine the absolute configuration (AC) of the starting alpha-amino acids. Binding atoms in the adducts were identified by comparing the (1)H and (13)C chemical shifts of the oxazolones in the absence and presence of Rh(II)(2)[(R)-(+)-MTPA](4). Thereby, information about the scope and limits of this method can be extracted. A protocol how to use this method is presented. PMID:19072975

Gómez, Edison Díaz; Duddeck, Helmut

2009-03-01

8

Optically pure alpha-amino acids production by the "Hydantoinase Process".  

PubMed

Optically pure D- or L-amino acids are used as intermediates in several industries. D-amino acids are involved in the synthesis of antibiotics, pesticides, sweeteners and other biologically active peptides. L-amino acids are used as feed and food additives, as intermediates for pharmaceuticals, cosmetics, pesticides and as chiral synthons in organic synthesis. The specific activity of these optically pure amino acids depends on their structure, chirality and purity. There are two main approaches to obtain optically pure amino acids, namely chemical and enzymatic synthesis. Chemical synthesis gives racemic mixtures of amino acids of low yield and is not environment friendly. One of the most widely-used enzymatic method is the "Hydantoinase Process". In this cascade of reactions, the chemically synthesized D,L-5-monosubstituted hydantoin ring is first hydrolyzed by a stereoselective hydantoinase enzyme to give the corresponding N-carbamoyl alpha-amino acid that is hydrolyzed by highly enantiospecific N-carbamoyl alpha-amino acid amidohydrolase (N-carbamoylase) to yield the free amino acid. At the same time, the remaining non-hydrolyzed 5-monosubstituted hydantoin is racemized by the hydantion racemase enzyme. This process has evolved over the years from the isolation of microorganisms with one or several of these enzymes to the construction of recombinant systems for industrial application. PMID:19075851

Clemente-Jiménez, Josefa M; Martínez-Rodríguez, Sergio; Rodríguez-Vico, Felipe; Heras-Vázquez, Francisco J L

2008-01-01

9

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

SciTech Connect

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

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

2008-07-08

10

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

KINETICS AND MECHANISMS OF THE DECOMPOSITION OF N-CHLORO-ALPHA-AMINO ACIDS AND DICHLORAMINE IN AQUEOUS SOLUTIONS  

Microsoft Academic Search

The decomposition of N-chloro-(alpha)-amino acids in neutral solutions gives Cl('-); imines, which hydrolyze rapidly to amine and carbonyl products; and CO(,2). The reactions are first order in {N-Cl-amino acid} and independent of pH. At 25.0(DEGREES)C the rate constants (s('-1)) are: N-Cl-glycine, 4.2 x 10('-6); N-Cl-sarcosine, 5.1 x 10('-5); N-Cl-threonine, 2 x 10('-4); N-Cl-alanine, 2.7 x 10('-4); N-Cl-proline, 8.8 x 10('-3);

VINCENT CYRIL HAND

1982-01-01

12

Synthesis of boronic acid analogues of alpha-amino acids by introducing side chains as electrophiles.  

PubMed

A synthetic route has been developed which has allowed us to prepare novel alpha-aminoboronic acids as inhibitors of serine proteases. These compounds were prepared to study the roles of proteases in biological systems. This methodology affords alpha-aminoboronic acids with the general formula R'-NHCH(R)BO(2)-pinanediol, where R = -CH(2)CHF(2), -CH(2)CO(2)tBu, and -(CH(2))(2)CO(2)Me and R' = either H or C(O)R". The latter two compounds are the boronic acid analogues of the natural amino acids aspartic acid and glutamic acid with the side chain carboxylate protected as a tert-butyl or a methyl ester, respectively. Following acylation of the amino group, the side chain tert-butyl ester of boroaspartic acid was removed by treatment with TFA. Boroglutamic acid was obtained as the free boronic acid by hydrolysis with HCl. Prior syntheses of alpha-aminoboronic acids involve the initial addition of an organometallic reagent to a trialkyl borate ester. These conditions do not allow the preparation of compounds with functionalities that are not stable to the strongly basic reaction conditions. The methodology described here allows the preparation of alpha-aminoboronic acids by introducing side chains as electrophiles. This is particularly advantageous for side chains which are prone to elimination or unwanted enolate formation. Specifically, BrCH(2)CHF(2), BrCH(2)COO(t)Bu, and CH(2)=CHCOOMe were allowed to react with the stabilized anion of (phenylthio)methane boronate, PhSCH(2)BO(2)C(6)H(12), to give the substituted boronate. The substituted (phenylthio)methane boronate was converted to the corresponding sulfonium ion by treatment with methyl iodide and subsequently displaced with iodide. The alpha-iodo derivative was converted to the amine by conventional methods. PMID:11559189

Jagannathan, S; Forsyth, T P; Kettner, C A

2001-09-21

13

Age-related resistance to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid-induced hippocampal lesion.  

PubMed

This study compares the effects of acute alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) administration in the hippocampus in adult (3 months) and middle-aged (15 months) rats at 15 days postinjection. Injection of 1 and 2.7 mM AMPA produced dose-dependent neurodegeneration, assessed by Nissl staining; a glial reaction shown by glial fibrillary acidic protein immunocytochemistry; and calcification, revealed by alizarin red staining. Furthermore, at both doses, these alterations were significantly greater in 3-month-old rats. Finally, at AMPA 2.7 mM, no significant changes in the density of hippocampal parvalbumin- or calbindin-immunoreactive neurons or in choline acetyltransferase, glutamate uptake, or GABA uptake activities were found in 15-month-old animals, whereas significant reductions in parvalbumin (-76%) and calbindin (-32%) immunostaining and in GABA uptake (-27%) were observed in 3-month-old animals compared to the respective sham-operated or control animals. In conclusion, this study clearly demonstrates that in rats the vulnerability of hippocampal neurons and the glial and calcification reactions to AMPA-induced injury decreased with age between 3 and 15 months. Our results also indicate that hippocampal cholinergic, glutamatergic, and GABAergic systems show an adaptive response to excitotoxic damage in both adult and middle-aged animals. PMID:10902899

Bernal, F; Andrés, N; Samuel, D; Kerkerian-LeGoff, L; Mahy, N

2000-01-01

14

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

PubMed

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

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

2002-12-20

15

Modulation of DL-alpha-Amino-3Hydroxy5Methyl4- Isoxazolepropionic Acid\\/Quisqualate Receptors by Phospholipase A_2: A Necessary Step in Long-Term Potentiation?  

Microsoft Academic Search

The effects of kainate (KA)-induced epileptic seizures on the binding properties of hippocampal glutamate receptors, on the modulation of DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)\\/quisqualate receptor by phospholipase A_2 (PLA_2), and on the formation of long-term potentiation (LTP) were studied in hippocampal membranes and hippocampal slices. Systemic administration of KA (10 mg\\/kg; 15 hr survival) produced specific changes in the binding properties of

Guy Massicotte; Pete Vanderklish; Gary Lynch; Michel Baudry

1991-01-01

16

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

17

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

18

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

19

Oligomerization and ligand-binding properties of the ectodomain of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor subunit GluRD.  

PubMed

The extracellular part of ionotropic glutamate receptor (iGluR) subunits can be divided into a conserved two-lobed ligand-binding domain ("S1S2") and an N-terminal approximately 400-residue segment of unknown function ("X domain") which shows high sequence variation among subunits. To investigate the structure and properties of the N-terminal domain, we have now produced affinity-tagged recombinant fragments which represent the X domain of the GluRD subunit of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-selective glutamate receptors either alone or covalently linked to the ligand-binding domain ("XS1S2"). These fragments were expressed in insect cells as secreted soluble proteins and were recognized by a conformation-specific anti-GluRD monoclonal antibody. A hydrodynamic analysis of the purified fragments revealed them to be dimers, in contrast to the S1S2 ligand-binding domain which is monomeric. The X domain did not bind radiolabeled AMPA or glutamate nor did its presence affect the ligand binding properties of the S1S2 domain. Our findings demonstrate that the N-terminal domain of AMPA receptor can be expressed as a soluble polypeptide and suggest that subunit interactions in iGluR may involve the extracellular domains. PMID:10506139

Kuusinen, A; Abele, R; Madden, D R; Keinänen, K

1999-10-01

20

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

PubMed

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

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

2004-10-01

21

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  

Microsoft Academic Search

The effects of kainate (KA)-induced epileptic seizures on the binding properites of hippocampal glutamate receptors, on the modulation of DL-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)\\/quisqualate receptor by phospholipase Aâ (PLAâ), 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

G. Massicotte; M. Baudry; P. Vanderklish; G. Lynch

1991-01-01

22

Molybdenum(VI) Peroxo alpha-Amino Acid Complexes: Synthesis, Spectra, and Properties of MoO(O(2))(2)(alpha-aa)(H(2)O) for alpha-aa = Glycine, Alanine, Proline, Valine, Leucine, Serine, Asparagine, Glutamine, and Glutamic Acid. X-ray Crystal Structures of the Glycine, Alanine, and Proline Compounds.  

PubMed

The compounds MoO(O(2))(2)(alpha-aa)(H(2)O), alpha-aa = glycine (1), alanine (2), proline (3), valine (4), leucine (5), serine (6), asparagine (7), glutamine (8), and glutamic acid (9), were prepared from the acidic aqueous solutions and characterized by examination of their IR, (1)H and (13)C NMR, and UV-visible spectra. They represent the first complexes containing a peroxo-alpha-amino acid combination in a metal ion ligand sphere. The synthesis and crystallization of these complexes was pH and concentration dependent, and their stability varied for different alpha-amino acids. X-ray structural studies of 1-3 have shown that the alpha-amino acids are coordinated as a zwitterion via one oxygen. This oxygen of the monodentate carboxylato group occupies an equatorial position in a distorted pentagonal bipyramid and encloses the pentagonal ring with the two bidentate peroxo groups. The apical positions are occupied by an oxo group and a water molecule, respectively. The Mo-O(O(2)) bonds are nonsymmetrical, differing in length by 0.009-0.045 Å. The longer bonds are located next to the coordinated carboxylato oxygen. A correlation between O-O and Mo-O bond lengths with the IR and UV-visible spectra of complexes 1-3 is discussed. Crystal structure of MoO(O(2))(2)(alanine)(H(2)O): monoclinic, space group P2(1)/c; Z = 4; a = 10.727(3) Å; b = 8.026(2) Å; c = 10.794(4) Å; beta = 110.81(2) degrees; V = 869 (Å)(3); R = 0.041. (1)H and (13)C NMR spectra in D(2)O solutions showed the presence of one complex species, which decomposed by standing in solution. Analogies and differences between Mo(VI) and V(V) peroxo complexes are outlined. PMID:11669783

Djordjevic, Cirila; Vuletic, Nikola; Jacobs, Bradley A.; Lee-Renslo, Myunghi; Sinn, Ekk

1997-04-23

23

A study of the oligomeric state of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-preferring glutamate receptors in the synaptic junctions of porcine brain.  

PubMed

The number of the subunits in an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-preferring L-glutamate receptor in the synaptic junctions of porcine brain was investigated in this study. Upon incubation of the synaptic junctions with three cross-linking regents, dimethyl adipimidate (DMA), dimethyl suberimidate (DMS) and N-succinimidyl-(4-azidophenyl)-1,3'-dithiopropionate (SADP), AMPA receptor subunits in higher-molecular-mass aggregates were detected by immunoblotting. These aggregates migrated as proteins of approx. 200, 300 and 400 kDa. The number and identity of the subunits in a solubilized AMPA receptor were also investigated here. Two samples, W1 and W2, enriched in AMPA receptors were prepared from synaptic junctions by a combination of detergent-solubilization, anion-exchange chromatography and wheatgerm agglutinin affinity chromatography. Hydrodynamic behaviour analyses revealed that the majority of the AMPA receptors in either one of these samples were asymmetrical detergent-surrounded particles with a protein mass around 350 kDa. SDS/PAGE analysis revealed that the majority of AMPA receptors in the W1 sample were comprised of dimers of 106 kDa subunits which were covalently linked by disulphide bonds. Cross-linking these receptors with SADP yielded a new band of approx. 400 kDa. The results obtained here, either from the studies of AMPA receptors embedding in synaptic junctions or from those of detergent-solubilized and partially purified receptors, suggest that AMPA receptors contain a basic core structure comprising of four 106 kDa subunits. PMID:8920974

Wu, T Y; Liu, C I; Chang, Y C

1996-11-01

24

A study of the oligomeric state of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-preferring glutamate receptors in the synaptic junctions of porcine brain.  

PubMed Central

The number of the subunits in an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-preferring L-glutamate receptor in the synaptic junctions of porcine brain was investigated in this study. Upon incubation of the synaptic junctions with three cross-linking regents, dimethyl adipimidate (DMA), dimethyl suberimidate (DMS) and N-succinimidyl-(4-azidophenyl)-1,3'-dithiopropionate (SADP), AMPA receptor subunits in higher-molecular-mass aggregates were detected by immunoblotting. These aggregates migrated as proteins of approx. 200, 300 and 400 kDa. The number and identity of the subunits in a solubilized AMPA receptor were also investigated here. Two samples, W1 and W2, enriched in AMPA receptors were prepared from synaptic junctions by a combination of detergent-solubilization, anion-exchange chromatography and wheatgerm agglutinin affinity chromatography. Hydrodynamic behaviour analyses revealed that the majority of the AMPA receptors in either one of these samples were asymmetrical detergent-surrounded particles with a protein mass around 350 kDa. SDS/PAGE analysis revealed that the majority of AMPA receptors in the W1 sample were comprised of dimers of 106 kDa subunits which were covalently linked by disulphide bonds. Cross-linking these receptors with SADP yielded a new band of approx. 400 kDa. The results obtained here, either from the studies of AMPA receptors embedding in synaptic junctions or from those of detergent-solubilized and partially purified receptors, suggest that AMPA receptors contain a basic core structure comprising of four 106 kDa subunits. PMID:8920974

Wu, T Y; Liu, C I; Chang, Y C

1996-01-01

25

CCAAT/enhancer binding protein-alpha amino acid motifs with dual TBP and TFIIB binding ability co-operate to activate transcription in both yeast and mammalian cells.  

PubMed Central

We have analysed the molecular basis for the function of the C/EBP alpha transactivation domain. We have previously found that the three C/EBP alpha transactivation elements (TEs) synergistically activate transcription in mammalian cells. We now report that two of these elements, TE-I and -II, co-operatively mediate in vitro binding of C/EBP alpha to TBP and TFIIB, two essential components of the RNA polymerase II basal transcriptional apparatus. The TBP and TFIIB binding elements of C/EBP alpha coincide, and require amino acid motifs conserved between the activating members of the C/EBP family. These same motifs are necessary for the transcription activation function of TE-I and -II in both yeast and mammalian cells. Our data demonstrate a biochemical basis for the modular buildup of transactivation domains, and indicate that this modularity is conserved in eukaryote evolution. We also show that the same amino acid motifs in a cellular activator can co-operate to mediate contacts between the activator and two distinct basal transcription factors. These results suggest that domains of TBP and TFIIB that interact with activating surfaces are functionally similar and may be structurally related, and support the idea that the same amino acid motifs in an activator carry out multiple functions during the initiation process. Images PMID:7556073

Nerlov, C; Ziff, E B

1995-01-01

26

Solid-phase synthesis of chiral stationary phases based on 2,4,5,6-tetrachloro-1,3-dicyanobenzene derivatives spaced from N-3,5-dinitrobenzoyl alpha-amino acids: comparative study of their resolution efficacy.  

PubMed

Two new chiral stationary phases, 3-[5-chloro-1,3-dicyano-2,4-[2'-(N'-1,3-dinitrobenzoyl-D-phenylglycinyl) aminoethyl]aminophen-1-yl] aminopropyl silica (CSP-1) and 3-[5-chloro-1,3-dicyano-2,4-[2'-(N'-1,3-dinitrobenzoyl-L-leucinyl) aminoethyl] aminophen-1-yl] aminopropyl silica (CSP-2), were prepared by solid-phase synthesis. They comprise chiral unit, 3,5-dinitrobenzoyl derivative of the amino acid, D-PhGly or L-Leu, bound via spacer 1,2-diaminoethane to 2,4-positions of the persubstituted benzene ring, derived from compound 1, and possess pseudo-C2 symmetry. Preparation of model compounds 6 and 7 confirmed the structure of chiral selectors, which comprise pi-donor persubsituted aromatic ring and two strong pi-acceptor 3,5-dinitrobenzoyl amido units. CD spectra of model selectors 6 and 7, run in DMSO above 250 nm, exhibit negative exciton coupling (EC) between pi-acceptor and pi-donor chromophores, C(1) symmetric model compound 8 exhibited much weaker EC and 9, devoid of pi-donor unit, does not exhibit any significant CD. Combined pi-donor and pi-acceptor properties enable the new CSPs to separate a broad range of racemates. The columns with CSP-1 and CSP-2 were tested for the separation of 22 racemates by HPLC with two different mobile phase systems and the results are compared with those obtained by using a structurally related commercial column. PMID:11370018

Kontrec, D; Abatangelo, A; Vinkovic, V; Sunjic, V

2001-06-01

27

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

PubMed

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

Balaram, Padmanabhan

2010-01-01

28

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

PubMed

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

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

1999-07-01

29

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. PMID:23873957

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

2013-01-01

30

Highly constrained proteins contain an unexpectedly large number of amino acid tandem repeats  

E-print Network

Highly constrained proteins contain an unexpectedly large number of amino acid tandem repeats Loris Single-amino-acid tandem repeats are very common in mammalian proteins but their function and evolution are still poorly understood. Here we investigate how the variability and prevalence of amino acid repeats

Mularoni, Loris

31

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

E-print Network

a,b-D-Constrained Nucleic Acids Are Strong Terminators of Thermostable DNA Polymerases, RP) a,b-D- Constrained Nucleic Acids (CNA) are dinucleotide building blocks that can feature either B. Citation: Marti´nez O, Ecochard V, Mahe´o S, Gross G, Bodin P, et al. (2011) a,b-D-Constrained Nucleic

Paris-Sud XI, Université de

32

Toward phenanthridin-2-ylidene: electrophilicity versus acidity in planar-constrained C-aryl iminium salts  

PubMed Central

Abstract—A phenanthridinium salt was prepared in four steps, including an intramolecular CH-arylation and a hydride abstraction reaction. Treatment with sterically demanding bases does not lead to the corresponding carbene, but rather to addition products: the planar-constrained geometry significantly enhances the electrophilicity over the acidity of C-aryl iminium salts. PMID:18776944

Cattoën, Xavier; Bourissou, Didier; Bertrand, Guy

2008-01-01

33

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. PMID:23991148

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

2013-01-01

34

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

PubMed

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. PMID:24289240

Onstott, T C; Magnabosco, C; Aubrey, A D; Burton, A S; Dworkin, J P; Elsila, J E; Grunsfeld, S; Cao, B H; Hein, J E; Glavin, D P; Kieft, T L; Silver, B J; Phelps, T J; van Heerden, E; Opperman, D J; Bada, J L

2014-01-01

35

The mechanism of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor desensitization after removal of glutamate.  

PubMed Central

We have examined responses of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors in the chick nucleus magnocellularis to pairs of pulses of glutamate and determined the extent of desensitization and the rate of recovery. Receptors recovered from desensitization with a time constant of 16 ms, regardless of the concentration or duration of the conditioning pulse. Even with very brief conditioning pulses, evoking submaximal currents, desensitization occurred at a consistent rate after the removal of free ligand. A quantitative kinetic model based on these data shows that receptors must desensitize from a closed state. The results provide evidence that very brief exposure to glutamate, on the time scale of uniquantal synaptic transmission, will result in a significant reduction in sensitivity of postsynaptic receptors. Images FIGURE 4 PMID:7711235

Raman, I M; Trussell, L O

1995-01-01

36

Mathematical models of diffusion-constrained polymerase chain reactions: basis of high-throughput nucleic acid assays and simple self-organizing systems  

E-print Network

Mathematical models of diffusion-constrained polymerase chain reactions: basis of high- throughput "Mathematical models of diffusion-constrained polymerase chain reactions: basis of high-throughput nucleic acid

Church, George M.

37

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. PMID:23150809

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

2012-01-01

38

Conformational studies of ?-turn in pseudopeptides containing ?-amino acid and conformationally constrained meta amino benzoic acid/meta nitro aniline  

NASA Astrophysics Data System (ADS)

Reverse turns (commonly ?-turns and ?-turns), a common motif in proteins and peptides, have attracted attention due to their relevance in a wide variety of biological processes. In an attempt to artificially imitate and stabilize these turns in short acyclic peptides, a series of N-terminally protected pseudopeptides comprising of an ?-amino acid and conformationally constrained meta amino benzoic acid (mABA)/meta nitro aniline (mNA) (peptides I-VI) have been synthesized. The molecules were well characterized by various spectroscopic techniques and subjected to a systematic conformational analysis. Our experimental results reveal that only pseudopeptides I and II with methyl as the sidechain, tertiary butyloxy carbonyl as the N-terminal protecting group and (mABA)/(mNA) at the C-terminus adopt ?-turn conformations in solid state as well as in solution. Even slight modification of any of the stated conditions donot support the formation of this ?-turn architecture in the solid state. Interestingly, the peptides III-V which displays extended conformation in solid state forms ?-turn structure in solution. Thus this result reflects the importance of co-operative steric interactions amongst various amino acid residues in stabilizing a particular conformation in peptides in different phases (solid and solution). This report may open a new avenue in introducing ?-turn motifs within the bioactive conformation of selected peptides.

Dutt Konar, Anita

2013-03-01

39

Differential effects on allele selective silencing of mutant huntingtin by two stereoisomers of ?,?-constrained nucleic acid.  

PubMed

We describe the effects of introducing two epimers of neutral backbone ?,?-constrained nucleic acid (CNA) on the activity and allele selectivity profile of RNase H active antisense oligonucleotides (ASOs) targeting a single nucleotide polymorphism (SNP) for the treatment of Huntington's disease (HD). ASOs modified with both isomers of ?,?-CNA in the gap region showed good activity versus the mutant allele, but one isomer showed improved selectivity versus the wild-type allele. Analysis of the human RNase H cleavage patterns of ?,?-CNA modified ASOs versus matched and mismatched RNA revealed that both isomers support RNase H cleavage on the RNA strand across from the site of incorporation in the ASO--an unusual observation for a neutral linkage oligonucleotide modification. Interestingly, ASOs modified with (R)- and (S)-5'-hydroxyethyl DNA (RHE and SHE respectively) formed by partial hydrolysis of the dioxaphosphorinane ring system in ?,?-CNA also showed good activity versus the mutant allele but an improved selectivity profile was observed for the RHE modified ASO. Our observations further support the profiling of neutral and 5'-modified nucleic acid analogs as tools for gene silencing applications. PMID:25050989

Østergaard, Michael E; Gerland, Béatrice; Escudier, Jean-Marc; Swayze, Eric E; Seth, Punit P

2014-09-19

40

Conformationally constrained aliphatic-aromatic amino-acid-conjugated hybrid foldamers with periodic beta-turn motifs.  

PubMed

In this note, we describe the design, synthesis, and structural studies of novel hybrid foldamers derived from Aib-Pro-Adb building blocks that display repeat beta-turn structure motif. The foldamer having a conformationally constrained aliphatic-aromatic amino acid conjugate adopts a well-defined, compact, three-dimensional structure, governed by a combined conformational restriction imposed by the individual amino acids with which it is made of. Conformational investigations by single-crystal X-ray and solution-state NMR studies were undertaken to investigate the conformational preference of these foldamers with a hetero-backbone. Our findings suggest that constrained aliphatic-aromatic amino acid conjugates would offer new avenues for the de novo design of hybrid foldamers with distinctive structural architectures. PMID:17691737

Srinivas, Deekonda; Gonnade, Rajesh; Ravindranathan, Sapna; Sanjayan, Gangadhar J

2007-08-31

41

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

SciTech Connect

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

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

2012-10-09

42

Direct chromatographic enantioresolution of fully constrained ?-amino acids: exploring the use of high-molecular weight chiral selectors.  

PubMed

To the best of our knowledge enantioselective chromatographic protocols on ?-amino acids with polysaccharide-based chiral stationary phases (CSPs) have not yet appeared in the literature. Therefore, the primary objective of this work was the development of chromatographic methods based on the use of an amylose derivative CSP (Lux Amylose-2), enabling the direct normal-phase (NP) enantioresolution of four fully constrained ?-amino acids. Also, the results obtained with the glycopeptide-type Chirobiotic T column employed in the usual polar-ionic (PI) mode of elution are compared with those achieved with the polysaccharide-based phase. The Lux Amylose-2 column, in combination with alkyl sulfonic acid containing NP eluent systems, prevailed over the Chirobiotic T one, when used under the PI mode of elution, and hence can be considered as the elective choice for the enantioseparation of this class of rigid ?-amino acids. Moreover, the extraordinarily high ? (up to 4.60) and R S (up to 10.60) values provided by the polysaccharidic polymer, especially when used with camphor sulfonic acid containing eluent systems, make it also suitable for preparative-scale enantioisolations. PMID:24500113

Sardella, Roccaldo; Ianni, Federica; Lisanti, Antonella; Scorzoni, Stefania; Marini, Francesca; Sternativo, Silvia; Natalini, Benedetto

2014-05-01

43

Synthesis, characterization and antiinflammatory-analgesic properties of 6-(alpha-amino-4-chlorobenzyl)thiazolo [3,2-b]-1,2,4-triazol-5-ols.  

PubMed

A series of 6-(alpha-amino-4-chlorobenzyl)-thiazolo[3,2-b]-1,2,4-triazol-5-ols (2a-j) were synthesized from 6-(4-chlorobenzylidene) thiazolo[3,2-b]-1,2,4-triazolo-5(6H)-one (2) by applying Michael addition reaction. All the compounds were characterized by their melting points, elementary analysis, IR and 1H-NMR spectra and screened for their anti-inflammatory and analgesic activities. Among the derivatives compound 2i bearing 4-(4-acetylphenyl)piperazine showed the highest and dose-dependent analgesic and anti-inflammatory activity without inducing any gastric lesion. PMID:14979607

Tozkoparan, Birsen; Gökhan, Nesrin; Küpeli, Esra; Ye?ilada, Erdem; Ertan, Mevlüt

2004-01-01

44

OCEANOGRAPHY Stratigraphic Distribution of Amino Acids in Peats from Cedar Creek  

E-print Network

LIMNOLOGY AND OCEANOGRAPHY April 1959 VOLUME IV NUMBER 2 Stratigraphic Distribution of Amino Acids. MILLERS University of Minnesota, Minneapolis ABSTRACT The concentration of several alpha-amino acids. Seven amino acids are consistently present in the natural accumulations: glycine, aspartic acid

Minnesota, University of

45

Design and synthesis of conformationally constrained analogues of cis-cinnamic acid and evaluation of their plant growth inhibitory activity.  

PubMed

1-O-cis-Cinnamoyl-?-D-glucopyranose is known to be one of the most potent allelochemical candidates and was isolated from Spiraea thunbergii Sieb by Hiradate et al. (2004), who suggested that it derived its strong inhibitory activity from cis-cinnamic acid, which is crucial for phytotoxicity. In this study, key structural features and substituent effects of cis-cinnamic acid (cis-CA) on lettuce root growth inhibition was investigated. These structure-activity relationship studies indicated the importance of the spatial relationship of the aromatic ring and carboxylic acid moieties. In this context, conformationally constrained cis-CA analogues, in which the aromatic ring and cis-olefin were connected by a carbon bridge, were designed, synthesized, and evaluated as plant growth inhibitors. The results of the present study demonstrated that the inhibitory activities of the five-membered and six-membered bridged compounds were enhanced, up to 0.27 ?M, and were ten times higher than cis-CA, while the potency of the other compounds was reduced. PMID:24176527

Nishikawa, Keisuke; Fukuda, Hiroshi; Abe, Masato; Nakanishi, Kazunari; Tazawa, Yuta; Yamaguchi, Chihiro; Hiradate, Syuntaro; Fujii, Yoshiharu; Okuda, Katsuhiro; Shindo, Mitsuru

2013-12-01

46

Constrained beta-proline analogues in organocatalytic aldol reactions: the influence of acid geometry.  

PubMed

7-Azabicyclo[2.2.1]heptane-2-carboxylic acid 11 was prepared in enantiopure form, and its catalytic potential in the direct aldol reaction between acetone and 4-nitrobenzaldehyde was assessed. The bicyclic system was found to be more selective than its monocyclic analogue beta-proline 5b. A comparative density functional theory study of proline 1, beta-proline 5b, and 11 in the latter reaction revealed the origin of the improved enantioselectivity of 11 over 5b. The geometry of the carboxylic acid group in the transition states, which depended critically on pyrrolidine ring conformation, was found to play a key role. PMID:19485343

Armstrong, Alan; Bhonoah, Yunas; White, Andrew J P

2009-07-17

47

Hydrogen-bond motifs in the crystals of hydrophobic amino acids.  

PubMed

A computer program has been developed to survey a set of crystal structures for hydrogen-bond motifs. Possible ring and chain motifs are generated automatically from a user-defined list of interacting molecular fragments and intermolecular interactions. The new program was used to analyse the hydrogen-bond networks in the crystals of 52 zwitterionic alpha-amino acids. All the possible chain motifs (repeating 1-4 molecules) are frequent, while the frequency of ring motifs (2-6 molecules) ranges from 0 to 85% of the structures. The list of motifs displayed by each structure reveals structural similarities and it can be used to compare polymorphs. The motifs formed in cocrystals of alpha-amino acids and in crystals of beta- and gamma-amino acids are similar to those of alpha-amino acids. PMID:18641453

Fábián, László; Chisholm, James A; Galek, Peter T A; Motherwell, W D Samuel; Feeder, Neil

2008-08-01

48

Design and synthesis of conformationally constrained 3-(N-alkylamino)propylphosphonic acids as potent agonists of sphingosine-1-phosphate (S1P) receptors.  

PubMed

A series of conformationally constrained 3-(N-alkylamino)propylphosphonic acids were systematically synthesized and their activities as S1P receptor agonists were evaluated. Several pyrrolidine and cyclohexane analogs had S1P receptor profiles comparable to the acyclic lead compound, 3-(N-tetradecylamino)propylphosphonic acid (3), lowered circulating lymphocytes in mice after iv administration and were thus identified as being suitable for further investigations. PMID:15341940

Yan, Lin; Hale, Jeffrey J; Lynch, Christopher L; Budhu, Richard; Gentry, Amy; Mills, Sander G; Hajdu, Richard; Keohane, Carol Ann; Rosenbach, Mark J; Milligan, James A; Shei, Gan-Ju; Chrebet, Gary; Bergstrom, James; Card, Deborah; Rosen, Hugh; Mandala, Suzanne M

2004-10-01

49

Enantiomeric excesses in meteoritic amino acids  

NASA Technical Reports Server (NTRS)

Gas chromatographic-mass spectral analyses of the four stereoisomers of 2-amino-2,3-dimethylpentanoic acid (dl-alpha-methylisoleucine and dl-alpha-methylalloisoleucine) obtained from the Murchison meteorite show that the L enantiomer occurs in excess (7.0 and 9.1%, respectively) in both of the enantiomeric pairs. Similar results were obtained for two other alpha-methyl amino acids, isovaline and alpha-methylnorvaline, although the alpha hydrogen analogs of these amino acids, alpha-amino-n-butyric acid and norvaline, were found to be racemates. With the exception of alpha-amino-n-butyric acid, these amino acids are either unknown or of limited occurrence in the biosphere. Because carbonaceous chondrites formed 4.5 billion years ago, the results are indicative of an asymmetric influence on organic chemical evolution before the origin of life.

Cronin, J. R.; Pizzarello, S.

1997-01-01

50

Shock Synthesis of Amino Acids in Simulated Primitive Environments  

Microsoft Academic Search

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

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

1970-01-01

51

5-Benzoylamino-3-bromo-4-(4-methoxyphenyl)-4,5-dihydroisoxazole-5-carboxylic acid.  

PubMed

The title compound, C18H15BrN2O5, a promising N-protected alpha-amino acid, was synthesized directly from an unusual bromo dipole and a 4-(arylmethylene)oxazolone. The crystal packing of the title compound is a racemic mixture. Peculiar graph-set motifs driven by the most important hydrogen bonds are described. PMID:15237175

Bruno, Giuseppe; Rotondo, Archimede; Grassi, Giovanni; Foti, Francesco; Risitano, Francesco; Nicoló, Francesco

2004-07-01

52

Constraining credences  

E-print Network

This dissertation is about ways in which our rational credences are constrained: by norms governing our opinions about counterfactuals, by the opinions of other agents, and by our own previous opinions. In Chapter 1, I ...

Moss, Sarah (Sarah E.)

2009-01-01

53

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

54

Exogenous amino acids as fuel in shock.  

PubMed

It has been suggested that in shock branched-chain amino acids are preferentially oxidized resulting in continued proteolysis and stimulated gluconeogenesis. To determine if exogenous amino acids could be used as fuel in shock, dogs rendered hypotensive by controlled cardiac tamponade and normotensive controls were infused with amino acid mixtures and individual amino acids. When Nephramine, a mixture rich in branched-chain amino acids, was infused, plasma alpha-amino nitrogen levels rose but urea output did not increase in either the control state or in shock, suggesting that these amino acids were not rapidly deaminated to serve as fuels. Travasol, which in addition contained large amounts of alanine and glycine, tripled urea output in the controls and doubled it in shock. The limit of urea production was reached in both groups at 35 mumoles urea/minute/kg. In the Travasol-infused animals plasma alpha-amino nitrogen levels were maintained in normotension but rose sharply in shock. When glycine alone was infused into five dogs in shock urea production rate was 30.6 + 2.1 mumoles/minute/kg; with alanine the same value was 22.5 + 2.2 mumoles/minute/kg. In both cases plasma alpha-amino nitrogen levels were high, suggesting that transport of these amino acids into the cell was slow in shock. In four dogs in shock glycine-14C was added to the glycine infusate as a tracer. At radioactive equilibrium 28% of the label infused appeared in CO2; another 22% appeared in glucose. It is concluded that of all the amino acids tested only glycine and alanine are deaminated rapidly enough to serve as exogenous fuels in shock. PMID:6814205

Daniel, A M; Kapadia, B; MacLean, L D

1982-01-01

55

Exact and efficient calculation of Lagrange multipliers in constrained biological polymers: Proteins and nucleic acids as example cases  

E-print Network

In order to accelerate molecular dynamics simulations, it is very common to impose holonomic constraints on their hardest degrees of freedom. In this way, the time step used to integrate the equations of motion can be increased, thus allowing, in principle, to reach longer total simulation times. The imposition of such constraints results in an aditional set of Nc equations (the equations of constraint) and unknowns (their associated Lagrange multipliers), that must be solved in one way or another at each time step of the dynamics. In this work it is shown that, due to the essentially linear structure of typical biological polymers, such as nucleic acids or proteins, the algebraic equations that need to be solved involve a matrix which is banded if the constraints are indexed in a clever way. This allows to obtain the Lagrange multipliers through a non-iterative procedure, which can be considered exact up to machine precision, and which takes O(Nc) operations, instead of the usual O(Nc3) for generic molecular...

García-Risueño, Pablo; Alonso, José Luis

2011-01-01

56

Polymerization of beta-amino acids in aqueous solution  

NASA Technical Reports Server (NTRS)

We have compared carbonyl diimidazole (CDI) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC) as activating agents for the oligomerization of negatively-charged alpha- and beta-amino acids in homogeneous aqueous solution. alpha-Amino acids can be oligomerized efficiently using CDI, but not by EDAC. beta-Amino acids can be oligomerized efficiently using EDAC, but not by CDI. Aspartic acid, an alpha- and beta-dicarboxylic acid is oligomerized efficiently by both reagents. These results are explained in terms of the mechanisms of the reactions, and their relevance to prebiotic chemistry is discussed.

Liu, R.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

1998-01-01

57

A loss of taurine and other amino acids from ventricles of patients undergoing bypass surgery.  

PubMed Central

OBJECTIVE--To study the changes in amino acid content of left ventricles of patients during cardiac surgery that involves cardiopulmonary bypass and cold cardioplegia. DESIGN--Biopsy specimens (up to 10 mg wet weight) from the left ventricle of 30 patients undergoing coronary artery bypass graft and valve replacement surgery on cardiopulmonary bypass (protected by cold cardioplegia with St Thomas' solution) were taken immediately before the infusion of the cardioplegic solution and just before the removal of the cross clamp, and were analysed for their amino acid content. RESULTS--Of the most abundant cellular amino acids in the left ventricle taurine, glutamine, glutamate, and aspartate, but not alanine, showed a significant fall during the period of cross clamping. A rise in intracellular sodium (Na) is known to occur during cold cardioplegic arrest so that an activation of an amino acid/Na efflux, similar to that seen in animal experiments, seems a likely mechanism. The anomalous behaviour of alanine suggests some recovery of metabolism. CONCLUSIONS--The loss of alpha amino acids (by contrast with the loss of taurine) will depress protein synthesis and reduce energy reserves after cardiac surgery. Attempts to preserve the concentrations of intracellular alpha amino acids must be balanced against the need to regulate intracellular Na concentration and hence intracellular pH and calcium ions. The presence of alpha amino acids in the cardioplegic solution (or in a resuscitation solution) should maintain the intracellular concentrations and favour activation of the taurine/Na symport to oppose the rise in intracellular Na concentration. Because the reservoir of tissue taurine is limited, the potential benefits of increasing the concentration of taurine in the heart by diet before surgery and addition of alpha amino acids to the cardioplegic solution merits further assessment. PMID:8461223

Suleiman, M S; Fernando, H C; Dihmis, W C; Hutter, J A; Chapman, R A

1993-01-01

58

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. PMID:21413804

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

2011-01-01

59

Deuterium Enrichment of Amino and Hydroxy Acids Found in the Murchison Meteorite: Constraints on Parent Body Conditions  

NASA Technical Reports Server (NTRS)

The alpha-amino and alpha-hydroxy acids found in the Murchison carbonaceous chondrite are deuterium enriched. These compounds are thought to have originated from common deuterium enriched carbonyl precursors, by way of a Strecker synthesis which took place in a solution of HCN, NH3, and carbonyl compounds during the period of aqueous alteration of the meteorite parent body. However, the hydroxy acids found on Murchison are less deuterium enriched than the amino acids. With the objective of determining if the discrepancy in deuterium enrichment between the amino acids and the hydroxy acids found on Murchison is consistent with their formation in a Strecker synthesis, we have measured the deuterium content of alpha-amino and alpha-hydroxy acids produced in solutions of deuterated carbonyl compounds, KCN and NH4Cl, and also in mixtures of such solutions and Allende dust at 263 K and 295 K. Retention of the isotopic signature of the starting carbonyl by both alpha amino acids and alpha hydroxy acids is more dependent upon temperature, concentration and pH than upon the presence of meteorite dust in the solution. The constraints these observations place on Murchison parent body conditions will be discussed.

Lerner, Narcinda R.; Chang, Sherwood (Technical Monitor)

1997-01-01

60

Mathematical models of diffusion-constrained polymerase chain reactions: basis of high-throughput nucleic acid assays and simple self-organizing systems  

E-print Network

Mathematical models of diffusion-constrained polymerase chain reactions: basis of high- throughput DNA templates amplified by polymerase chain reaction in thin polyacrylamide gels form diffusion://arep.med.harvard.edu/polony_models/. KEYWORDS polymerase chain reaction, diffusion, polony, self-organizing system 2 #12;1. INTRODUCTION High

Church, George M.

61

The spark discharge synthesis of amino acids from various hydrocarbons  

NASA Technical Reports Server (NTRS)

The spark discharge synthesis of amino acids using an atmosphere of CH4+N2+H2O+NH3 has been investigated with variable pNH3. The amino acids produced using higher hydrocarbons (ethane, ethylene, acetylene, propane, butane, and isobutane) instead of CH4 were also investigated. There was considerable range in the absolute yields of amino acids, but the yields relative to glycine (or alpha-amino-n-butyric acid) were more uniform. The relative yields of the C3 to C6 aliphatic alpha-amino acids are nearly the same (with a few exceptions) with all the hydrocarbons. The glycine yields are more variable. The precursors to the C3-C6 aliphatic amino acids seem to be produced in the same process, which is separate from the synthesis of glycine precursors. It may be possible to use these relative yields as a signature for a spark discharge synthesis provided corrections can be made for subsequent decomposition events (e.g. in the Murchison meteorite).

Ring, D.; Miller, S. L.

1984-01-01

62

Introduction Constrained distribution  

E-print Network

Introduction Constrained distribution Observed pattern distribution Counting patterns-9 September 2009 G. Nuel Counting patterns in degenerated sequences #12;Introduction Constrained distribution Observed pattern distribution Outline 1 Introduction Special letters in biological sequences Counting

Nuel, Gregory

63

14N NMR relaxation times of several protein amino acids in aqueous solution-comparison with 17O NMR data and estimation of the relative hydration numbers in the cationic and zwitterionic forms  

Microsoft Academic Search

The 14N nuclear magnetic resonance (NMR) linewidths of the alpha-amino groups of several protein amino acids were measured in aqueous solution, with and without composite proton decoupling, to estimate the effect of proton exchange and molecular weight on the linewidths. It is shown that, contrary to earlier claims, the increase in the linewidth at low pH is not exclusively due

Anastassios N. Troganis; Constantinos Tsanaktsidis; Ioannis P. Gerothanassis

2003-01-01

64

Constraining Galileon inflation  

NASA Astrophysics Data System (ADS)

In this short paper, we present constraints on the Galileon inflationary model from the CMB bispectrum. We employ a principal-component analysis of the independent degrees of freedom constrained by data and apply this to the WMAP 9-year data to constrain the free parameters of the model. A simple Bayesian comparison establishes that support for the Galileon model from bispectrum data is at best weak.

Regan, Donough; Anderson, Gemma J.; Hull, Matthew; Seery, David

2015-02-01

65

Prompt transgression and gradual salinisation of the Black Sea during the early Holocene constrained by amino acid racemization and radiocarbon dating  

NASA Astrophysics Data System (ADS)

The restricted environment of the Black Sea is particularly sensitive to climatic and oceanographic fluctuations, owing to its connection with the Mediterranean Sea via the narrow Bosphorus Strait. The exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post-glacial history of the Black Sea being dependent on radiocarbon dating for numerical ages. Here we present new 23 accelerator mass spectrometer (AMS) radiocarbon ages on peat and bivalve molluscs, supported by the first amino acid racemization (AAR) dating of bivalve molluscs ( n = 66) in the Black Sea. These data indicate infilling of the Black Sea during the early Holocene from an initial depth 107 m below sea-level, and 72 m below that of the Bosphorus Sill. These data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post-glacial Black Sea. A sea-level curve based on conventional and AMS radiocarbon ages on peat and AMS-based ages on Dreissena sp. shells indicate the water-level in the earlier lake phase continued, until the early Holocene, to be lower than the Bosphorus Sill after the Younger Dryas ended. However, the absence of AMS-dated mollusc ages from the shelves of this basin older than the Younger Dryas is suggestive of sub-aerial exposure of the shelves, and comparatively lower water-levels when the Younger Dryas began. Thus post-glacial outflow from the Black Sea occurred through a lowered or open Bosphorus seaway. Basin-wide radiocarbon ages on peat indicate a prompt increase in water-level from that of the pre-existing and unconnected palaeo-lake during the earliest Holocene (9600-9200 cal a BP). Mass colonisation of the Black Sea by Mediterranean taxa did not occur until salinity had risen sufficiently, a process which took 1000 a or more from the initial transgressive event. This gradual change in salinity contrasts with the prompt transgression which would have taken ˜400 a to occur.

Nicholas, William Anthony; Chivas, Allan R.; Murray-Wallace, Colin V.; Fink, David

2011-12-01

66

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

67

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

68

Indigenous amino acids in primitive CR meteorites  

E-print Network

CR meteorites are among the most primitive meteorites. In this paper, we report the first measurements of amino acids in Antarctic CR meteorites, two of which show the highest amino acid concentrations ever found in a chondrite. EET92042, GRA95229 and GRO95577 were analyzed for their amino acid content using high performance liquid chromatography with UV fluorescence detection (HPLC-FD) and gas chromatographymass spectrometry (GC-MS). Our data show that EET92042 and GRA95229 are the most amino acid-rich chondrites ever analyzed, with total amino acid concentrations ranging from 180 parts-per-million (ppm) to 249 ppm. GRO95577, however, is depleted in amino acids. The most abundant amino acids present in the EET92042 and GRA95229 meteorites are the alpha-amino acids glycine, isovaline, alpha-aminoisobutyric acid (alpha-AIB), and alanine, with delta13C values ranging from +31.6per mil to +50.5per mil. The carbon isotope results together with racemic enantiomeric ratios determined for most amino acids strongly indicate an extraterrestrial origin of these compounds. In addition, the relative abundances of alpha-AIB and beta-alanine in the Antarctic CR meteorites analyzed appear to correspond to the degree of aqueous alteration on their respective parent body.

Z. Martins; C. M. O'D. Alexander; G. E. Orzechowska; M. L. Fogel; P. Ehrenfreund

2008-03-10

69

Indigenous amino acids in primitive CR meteorites  

E-print Network

CR meteorites are among the most primitive meteorites. In this paper, we report the first measurements of amino acids in Antarctic CR meteorites, two of which show the highest amino acid concentrations ever found in a chondrite. EET92042, GRA95229 and GRO95577 were analyzed for their amino acid content using high performance liquid chromatography with UV fluorescence detection (HPLC-FD) and gas chromatographymass spectrometry (GC-MS). Our data show that EET92042 and GRA95229 are the most amino acid-rich chondrites ever analyzed, with total amino acid concentrations ranging from 180 parts-per-million (ppm) to 249 ppm. GRO95577, however, is depleted in amino acids. The most abundant amino acids present in the EET92042 and GRA95229 meteorites are the alpha-amino acids glycine, isovaline, alpha-aminoisobutyric acid (alpha-AIB), and alanine, with delta13C values ranging from +31.6per mil to +50.5per mil. The carbon isotope results together with racemic enantiomeric ratios determined for most amino acids strongly i...

Martins, Z; Orzechowska, G E; Fogel, M L; Ehrenfreund, P

2008-01-01

70

Constraining the dark fluid  

SciTech Connect

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

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

2009-10-15

71

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

72

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

73

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

74

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

75

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

76

Time-Constrained Machine Translation  

Microsoft Academic Search

This paper defines the class of time-constrained applications: applications in which the user has limited time to process the system output. This class is differentiated\\u000a from real-time systems, where it is production time rather than comprehension time that is constrained. Examples of time-constrained MT\\u000a applications include the translation of multi-party dialogue and the translation of closed-captions. The constraints on comprehension

Janine Toole; Davide Turcato; Fred Popowich; Dan Fass; Paul Mcfetridge

1998-01-01

77

Constrained space camera assembly  

DOEpatents

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

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

1999-01-01

78

Emission constrained economic dispatch  

SciTech Connect

This paper presents a methodology to include emission constraints in classical Economic Dispatch (ED), which contains an efficient weights estimation technique. Also, a partial closed form technique is presented to implement the Emission Constrained Economic Dispatch (ECED). A simple technique is proposed to identify the binding constraints. The methods proposed do not need any user-supplied tuning or conversion factors. Dispatch quality is not compromised, and any practical sized problem can be solved efficiently. The proposed methods have rapid and consistent convergence to the Kuhn-Tucker optimality conditions. Different methods of including emissions as well as their advantages and disadvantages are discussed. Sample test results are presented. The proposed two methodologies have potential for on-line implementation.

Ramanathan, R. (ESCA Corp., Bellevue, WA (United States))

1994-11-01

79

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

80

Interaction of metal ions and amino acids - Possible mechanisms for the adsorption of amino acids on homoionic smectite clays  

NASA Technical Reports Server (NTRS)

A semiempirical molecular orbital method is used to characterize the binding of amino acids to hexahydrated Cu(2+) and Ni(2+), a process presumed to occur when they are adsorbed in the interlamellar space of homoionic smectite clays. Five alpha-amino acids, beta-alanine, and gamma-aminobutyric acid were used to investigate the metal ion and amino acid specificity in binding. It was assumed that the alpha, beta, and gamma-amino acids would bind as bidentate anionic ligands, forming either 1:1 or 1:2 six-coordinated five, six, and seven-membered-ring chelate complexes, respectively. Energies of complex formation, optimized geometries, and electron and spin distribution were determined; and steric constraints of binding of the amino acids to the ion-exchanged cations in the interlamellar spacing of a clay were examined. Results indicate that hexahydrated Cu(2+) forms more stable complexes than hexahydrated Ni(2+) with all the amino acids studied. However, among these amino acids, complex formation does not favor the adsorption of the biological subset. Calculated energetics of complex formation and steric constraints are shown to predict that 1:1 rather than 1:2 metal-amino acid complexes are generally favored in the clay.

Gupta, A.; Loew, G. H.; Lawless, J.

1983-01-01

81

Noisy Constrained Capacity Philippe Jacquet  

E-print Network

Noisy Constrained Capacity Philippe Jacquet INRIA Rocquencourt 78153 Le Chesnay Cedex France Email: philippe.jacquet@inria.fr Gadiel Seroussi Hewlett-Packard Laboratories Palo Alto, CA 94304 U.S.A. Email

Szpankowski, Wojciech

82

Global Estimation in Constrained Environments  

E-print Network

vehicle operating in a planar polygonal obstacle environment; a simulated helicopter searching are constrained due to their natural kinematics and dynamics and due to obstacles in the environment. The task

Del Moral , Pierre

83

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

84

The 3-amino-derivative of gamma-cyclodextrin as chiral selector of Dns-amino acids in electrokinetic chromatography.  

PubMed

The enantioseparation of the enantiomeric pairs of 10 Dns derivatives of alpha-amino acids was successfully carried out by using for the first time the 3-amino derivative of the gamma-cyclodextrin. The effects of pH and selector concentration on the migration times and the resolutions of analytes were studied in detail. 3-Deoxy-3-amino-2(S),3(R)-gamma-cyclodextrin (GCD3AM) shows very good chiral recognition ability even at very low concentrations at all the three investigated values of pH, as shown by the very large values of selectivity and resolution towards several pairs of amino acids. The role played by the cavity, the substitution site and the protonation equilibria on the observed properties of chiral selectivity, on varying the specific amino acid involved, is discussed. PMID:19124131

Giuffrida, A; Contino, A; Maccarrone, G; Messina, M; Cucinotta, V

2009-04-24

85

Cyclobutane amino acid analogues of furanomycin obtained by a formal [2 + 2] cycloaddition strategy promoted by methylaluminoxane.  

PubMed

The synthesis and conformational analysis of a new type of conformationally restricted alpha-amino acid analogue of the amino acid antibiotic furanomycin is presented. The restriction involves the cis-fused cyclobutane and tetrahydrofuran units, generating the unusual 2-oxabicyclo[3.2.0]heptane core, which is found in a great number of biologically active natural products. The synthetic strategy is based on a formal [2 + 2] cycloaddition between 2-(acylamino)acrylates as acceptor alkenes and 2,3-dihydrofuran as a donor alkene, promoted by bulky aluminum-derived Lewis acids, particularly by methylaluminoxane (MAO). Additionally, following the same strategy, the synthesis of furanomycin analogues incorporating the 2-oxabicyclo[4.2.0]octane is reported. PMID:20038109

Avenoza, Alberto; Busto, Jesús H; Canal, Noelia; Corzana, Francisco; Peregrina, Jesús M; Pérez-Fernández, Marta; Rodríguez, Fernando

2010-02-01

86

Rapid Communication Constraining Holocene 10  

E-print Network

to link 10 Be exposure dating chronologies of ice-margin change to independent records of rapid climate of climate change. Users of 10 Be dating currently have several 10 Be production rate calibration data setsRapid Communication Constraining Holocene 10 Be production rates in Greenland JASON P. BRINER,1

Briner, Jason P.

87

Vibrational analysis of amino acids and short peptides in hydrated media. I. L-glycine and L-leucine.  

PubMed

Raman scattering and Fourier-transform infrared (FT-IR) attenuated transmission reflectance (ATR) spectra of two alpha-amino acids (alpha-AAs), i.e., glycine and leucine, were measured in H2O and D2O (at neutral pH and pD). This series of observed vibrational data gave us the opportunity to analyze vibrational features of both AAs in hydrated media by density functional theory (DFT) calculations at the B3LYP/6-31++G* level. Harmonic vibrational modes calculated after geometry optimization on the clusters containing each AA and 12 surrounding water molecules, which represent primary models for hydration scheme of amino acids, allowed us to assign the main observed peaks. PMID:17243664

Derbel, Najoua; Hernández, Belén; Pflüger, Fernando; Liquier, Jean; Geinguenaud, Frédéric; Jaïdane, Nejmeddine; Lakhdar, Zohra Ben; Ghomi, Mahmoud

2007-02-15

88

A spirocyclohexyl nitroxide amino acid spin label for pulsed EPR spectroscopy distance measurements.  

PubMed

Site-directed spin labeling and EPR spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide alpha-amino acid and its N-(9-fluorenylmethoxycarbonyl) derivative, have been synthesized, which exhibit slow enough spin-echo dephasing to permit accurate distance measurements by pulsed EPR spectroscopy at temperatures up to 125 K in 1:1 water/glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR spectroscopy to the study of structure and conformation of peptides and proteins. PMID:20391558

Rajca, Andrzej; Kathirvelu, Velavan; Roy, Sandip K; Pink, Maren; Rajca, Suchada; Sarkar, Santanu; Eaton, Sandra S; Eaton, Gareth R

2010-05-17

89

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

90

Explicit construction of constrained instantons  

E-print Network

Instantons in massless theories do not carry over to massive theories due to Derrick's theorem. This theorem can, however, be circumvented, if a constraint that restricts the scale of the instanton is imposed on the theory. Constrained instantons are considered in four dimensions in phi^4 theory and SU(2) Yang-Mills-Higgs theory. In each of these theories a calculational sceme is set up and solved in the lowest few orders in the mass parameter in such a way that the need for a constraint is exhibited clearly. Constrained instantons are shown to exist as finite action solutions of the field equations with exponential fall off only for specific constraints that are unique in lowest order in the mass parameter in question.

Morten Nielsen; N. K. Nielsen

1999-12-01

91

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. PMID:25006591

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

2014-01-01

92

Constraining Modified Gravity with Euclid  

E-print Network

Future proposed satellite missions as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios as those predicted by scalar-tensor and $f(R)$ theories. We found that Euclid will improve constraints expected from the PLANCK satellite on these modified gravity models by two orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modified gravity.

Matteo Martinelli; Erminia Calabrese; Francesco De Bernardis; Alessandro Melchiorri; Luca Pagano; Roberto Scaramella

2010-10-27

93

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

94

Amino acid-containing membrane lipids in bacteria.  

PubMed

In the bacterial model organism Escherichia coli only the three major membrane lipids phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin occur, all of which belong to the glycerophospholipids. The amino acid-containing phosphatidylserine is a major lipid in eukaryotic membranes but in most bacteria it occurs only as a minor biosynthetic intermediate. In some bacteria, the anionic glycerophospholipids phosphatidylglycerol and cardiolipin can be decorated with aminoacyl residues. For example, phosphatidylglycerol can be decorated with lysine, alanine, or arginine whereas in the case of cardiolipin, lysine or d-alanine modifications are known. In few bacteria, diacylglycerol-derived lipids can be substituted with lysine or homoserine. Acyl-oxyacyl lipids in which the lipidic part is amide-linked to the alpha-amino group of an amino acid are widely distributed among bacteria and ornithine-containing lipids are the most common version of this lipid type. Only few bacterial groups form glycine-containing lipids, serineglycine-containing lipids, sphingolipids, or sulfonolipids. Although many of these amino acid-containing bacterial membrane lipids are produced in response to certain stress conditions, little is known about the specific molecular functions of these lipids. PMID:19703488

Geiger, Otto; González-Silva, Napoleón; López-Lara, Isabel M; Sohlenkamp, Christian

2010-01-01

95

Constraining fundamental physics with cosmology  

NASA Astrophysics Data System (ADS)

It is shown in three examples that future cosmological data may allow us to constrain fundamental physics in interesting ways. The first example illustrates that correlations in the polarization of the cosmic microwave background may allow us to put the strongest limit yet on the mass of a particle, the graviton, at a level of m [Special characters omitted.] 10 -30 eV. In the second example, it is shown that observations of the correlations of temperature anisotropies and polarization of the cosmic microwave background may reveal hints for the realization of a class of string theoretic inflationary models that go by the name of axion monodromy inflation, or, rule them out. If the evidence for inflation strengthens substantially, just the requirement that inflation occurred may be used to constrain models of fundamental physics. The third example shows that a class of string compactifications that are commonly used in the context of string phenomenology cannot support inflation and might thus be ruled out by cosmology. For completeness, a review of the physics underlying the cosmic microwave background radiation is included and some analytical results for the signatures of primordial gravitational waves in the cosmic microwave background are given.

Flauger, Raphael Manfred

96

Label Image Constrained Multiatlas Selection.  

PubMed

Multiatlas based method is commonly used in medical image segmentation. In multiatlas based image segmentation, atlas selection and combination are considered as two key factors affecting the performance. Recently, manifold learning based atlas selection methods have emerged as very promising methods. However, due to the complexity of prostate structures in raw images, it is difficult to get accurate atlas selection results by only measuring the distance between raw images on the manifolds. Although the distance between the regions to be segmented across images can be readily obtained by the label images, it is infeasible to directly compute the distance between the test image (gray) and the label images (binary). This paper tries to address this problem by proposing a label image constrained atlas selection method, which exploits the label images to constrain the manifold projection of raw images. Analyzing the data point distribution of the selected atlases in the manifold subspace, a novel weight computation method for atlas combination is proposed. Compared with other related existing methods, the experimental results on prostate segmentation from T2w MRI showed that the selected atlases are closer to the target structure and more accurate segmentation were obtained by using our proposed method. PMID:25415994

Yan, Pingkun; Cao, Yihui; Yuan, Yuan; Turkbey, Baris; Choyke, Peter L

2014-11-14

97

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

Microsoft Academic Search

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

Christoph Hofer; Andreas Papritz

2011-01-01

98

The genetic code constrains yet facilitates Darwinian evolution  

PubMed Central

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

Firnberg, Elad; Ostermeier, Marc

2013-01-01

99

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. PMID:6481334

1984-01-01

100

Exploring constrained quantum control landscapes.  

PubMed

The broad success of optimally controlling quantum systems with external fields has been attributed to the favorable topology of the underlying control landscape, where the landscape is the physical observable as a function of the controls. The control landscape can be shown to contain no suboptimal trapping extrema upon satisfaction of reasonable physical assumptions, but this topological analysis does not hold when significant constraints are placed on the control resources. This work employs simulations to explore the topology and features of the control landscape for pure-state population transfer with a constrained class of control fields. The fields are parameterized in terms of a set of uniformly spaced spectral frequencies, with the associated phases acting as the controls. This restricted family of fields provides a simple illustration for assessing the impact of constraints upon seeking optimal control. Optimization results reveal that the minimum number of phase controls necessary to assure a high yield in the target state has a special dependence on the number of accessible energy levels in the quantum system, revealed from an analysis of the first- and second-order variation of the yield with respect to the controls. When an insufficient number of controls and/or a weak control fluence are employed, trapping extrema and saddle points are observed on the landscape. When the control resources are sufficiently flexible, solutions producing the globally maximal yield are found to form connected "level sets" of continuously variable control fields that preserve the yield. These optimal yield level sets are found to shrink to isolated points on the top of the landscape as the control field fluence is decreased, and further reduction of the fluence turns these points into suboptimal trapping extrema on the landscape. Although constrained control fields can come in many forms beyond the cases explored here, the behavior found in this paper is illustrative of the impacts that constraints can introduce. PMID:23039591

Moore, Katharine W; Rabitz, Herschel

2012-10-01

101

Formal language constrained path problems  

SciTech Connect

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

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

1997-07-08

102

Constrained Wiki: an Oxymoron? Angelo Di Iorio  

E-print Network

Constrained Wiki: an Oxymoron? Angelo Di Iorio Department of Computer Science University of Bologna@cs.unibo.it ABSTRACT In this paper we propose a new wiki concept -- light con- straints -- designed to encode community of constraining user editing of wiki con- tent seems to inherently contradict "The Wiki Way", it is well

Zacchiroli, Stefano - Laboratoire Preuves, Programmes et Systèmes, Université Paris 7

103

Using ecological restoration to constrain biological invasion  

Microsoft Academic Search

Summary 1. Biological invasion can permanently alter ecosystem structure and function. In- vasive species are difficult to eradicate, so methods for constraining invasions would be ecologically valuable. We examined the potential of ecological restoration to constrain invasion of an old field by Agropyron cristatum , an introduced C 3 grass. 2. A field experiment was conducted in the northern Great

JONATHAN D. BAKKER; SCOTT D. WILSON

104

Optimization-Based Constrained Iterative Learning Control  

Microsoft Academic Search

We consider the problem of synthesis of iterative learning control (ILC) schemes for constrained linear systems executing a repetitive task. The ILC problem with affine constraints and quadratic objective functions is formulated as a convex quadratic program, for which there exist computationally efficient solvers. The key difference between standard convex optimization and the corresponding constrained ILC problem is that each

Sandipan Mishra; Ufuk Topcu; Masayoshi Tomizuka

2011-01-01

105

A phenomenological model of active constrained layers  

Microsoft Academic Search

Active constrained layer (ACL) treatments consist of a layer of viscoelastic material bonded to the host structure and constrained by an actuator. These treatments control vibrations by means of several mechanisms: the actuator increases the dissipation of energy by increasing the shearing in the viscoelastic layer, and simultaneously it controls the vibrations by applying forces to the host structure through

Hélène Illaire; Wolfgang Kropp; Brian Mace

2005-01-01

106

Constrained orbital intercept-evasion  

NASA Astrophysics Data System (ADS)

An effective characterization of intercept-evasion confrontations in various space environments and a derivation of corresponding solutions considering a variety of real-world constraints are daunting theoretical and practical challenges. Current and future space-based platforms have to simultaneously operate as components of satellite formations and/or systems and at the same time, have a capability to evade potential collisions with other maneuver constrained space objects. In this article, we formulate and numerically approximate solutions of a Low Earth Orbit (LEO) intercept-maneuver problem in terms of game-theoretic capture-evasion guaranteed strategies. The space intercept-evasion approach is based on Liapunov methodology that has been successfully implemented in a number of air and ground based multi-player multi-goal game/control applications. The corresponding numerical algorithms are derived using computationally efficient and orbital propagator independent methods that are previously developed for Space Situational Awareness (SSA). This game theoretical but at the same time robust and practical approach is demonstrated on a realistic LEO scenario using existing Two Line Element (TLE) sets and Simplified General Perturbation-4 (SGP-4) propagator.

Zatezalo, Aleksandar; Stipanovic, Dusan M.; Mehra, Raman K.; Pham, Khanh

2014-06-01

107

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

108

Conformationally constrained farnesoid X receptor (FXR) agonists: alternative replacements of the stilbene.  

PubMed

To further explore the optimum placement of the acid moiety in conformationally constrained analogs of GW 4064 1a, a series of stilbene replacements were prepared. The benzothiophene 1f and the indole 1g display the optimal orientation of the carboxylate for enhanced FXR agonist potency. PMID:21890356

Akwabi-Ameyaw, Adwoa; Caravella, Justin A; Chen, Lihong; Creech, Katrina L; Deaton, David N; Madauss, Kevin P; Marr, Harry B; Miller, Aaron B; Navas, Frank; Parks, Derek J; Spearing, Paul K; Todd, Dan; Williams, Shawn P; Wisely, G Bruce

2011-10-15

109

Journal of Theoretical Biology 228 (2004) 3146 Mathematical models of diffusion-constrained polymerase chain  

E-print Network

-constrained polymerase chain reactions: basis of high-throughput nucleic acid assays and simple self-organizing systems reserved. Keywords: Polymerase chain reaction; Diffusion; Polony; Self-organizing system 1. Introduction out methods for using the polymerase chain reaction (PCR) to amplify dilute populations of linear NA

Church, George M.

110

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

PubMed

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

Wellendorph, P; Bräuner-Osborne, H

2009-03-01

111

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

SciTech Connect

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

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

1991-01-01

112

21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.  

Code of Federal Regulations, 2011 CFR

... Wrist joint polymer constrained prosthesis. 888.3780 Section 888.3780... Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a device made of...

2011-04-01

113

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

114

Ecological and Biogeochemical Interactions Constrain Planktonic  

E-print Network

Ecological and Biogeochemical Interactions Constrain Planktonic Nitrogen Fixation in Estuaries Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA; 2 Ecosystems nitrogen (N) is strongly limiting to primary production. Estuaries generally fit this pat- tern

Pace, Michael L.

115

Efficient Incremental Constrained Clustering Ian Davidson  

E-print Network

Efficient Incremental Constrained Clustering Ian Davidson SUNY - Albany Computer Science Albany, NY 12222 davidson@cs.albany.edu Martin Ester Simon Fraser University Computing Science Burnaby, BC V5A 1S6

Davidson, Ian

116

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

SciTech Connect

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

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

1985-04-25

117

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

118

The Sun's Interior Metallicity Constrained by Neutrinos  

E-print Network

Observed solar neutrino fluxes are employed to constrain the interior composition of the Sun. Including the effects of neutrino flavor mixing, the results from Homestake, Sudbury, and Gallium experiments constrain the Mg, Si, and Fe abundances in the solar interior to be within a factor 0.89 to 1.34 of the surface values with 68% confidence. If the O and/or Ne abundances are increased in the interior to resolve helioseismic discrepancies with recent standard solar models, then the nominal interior Mg, Si, and Fe abundances are constrained to a range of 0.83 to 1.24 relative to the surface. Additional research is needed to determine whether the Sun's interior is metal poor relative to its surface.

Guillermo Gonzalez

2006-05-25

119

Bayesian evaluation of inequality constrained hypotheses.  

PubMed

Bayesian evaluation of inequality constrained hypotheses enables researchers to investigate their expectations with respect to the structure among model parameters. This article proposes an approximate Bayes procedure that can be used for the selection of the best of a set of inequality constrained hypotheses based on the Bayes factor in a very general class of statistical models. The software package BIG is provided such that psychologists can use the approach proposed for the analysis of their own data. To illustrate the approximate Bayes procedure and the use of BIG, we evaluate inequality constrained hypotheses in a path model and a logistic regression model. Two simulation studies on the performance of our approximate Bayes procedure show that it results in accurate Bayes factors. (PsycINFO Database Record (c) 2014 APA, all rights reserved). PMID:25046447

Gu, Xin; Mulder, Joris; Dekovi?, Maja; Hoijtink, Herbert

2014-12-01

120

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

121

Geochemical Processes Constraining Iron Uptake in Strategy II Fe Acquisition  

PubMed Central

Phytosiderophores (PS) are natural chelating agents, exuded by graminaceous plants (grasses) for the purpose of Fe acquisition (Strategy II). They can form soluble Fe complexes with soil-Fe that can be readily taken up. PS are exuded in a diurnal pulse release, and with the start of PS release a “window of iron uptake” opens. In the present study we examined how this window is constrained in time and concentration by biogeochemical processes. For this purpose, a series of interaction experiments was done with a calcareous clay soil and the phytosiderophore 2?-deoxymugineic acid (DMA), in which metal and DMA speciation were examined as a function of time and DMA concentration. Various kinetically and thermodynamically controlled processes affected the size of the window of Fe uptake. Adsorption lowered, but did not prevent Fe mobilization by DMA. Microbial activity depleted DMA from solution, but not on time scales jeopardizing Strategy II Fe acquisition. Complexation of competing metals played an important role in constraining the window of Fe uptake, particularly at environmentally relevant PS concentrations. Our study provides a conceptual model that takes into account the chemical kinetics involved with PS-mediated Fe acquisition. The model can help to explain how success or failure of PS-mediated Fe acquisition depends on environmental conditions. PMID:25275965

2014-01-01

122

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

123

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

124

Nonlinear constrained tracking of targets on roads  

Microsoft Academic Search

Ground targets are constrained to move on the Earth's surface and are most likely to travel along a road network. For targets on road, their interaction with the environment and with each other particularly at intersections is more structured, thus useful to tracking algorithms. Indeed, the knowledge of terrain database and road maps can be used as constraints and incorporated

C. Yang; M. Bakich; E. Blasch

2005-01-01

125

Database Transposition for Constrained (Closed) Pattern Mining  

E-print Network

Database Transposition for Constrained (Closed) Pattern Mining Baptiste Jeudy1 and Fran¸cois Rioult pat- terns in databases with pathological size. For example, experiments in genome biology usually provide databases with thousands of attributes (genes) but only tens of objects (experiments

Paris-Sud XI, Université de

126

Constrained Analysis of Topologically Massive Gravity  

E-print Network

We quantize the Einstein gravity in the formalism of weak gravitational fields by using the constrained Hamiltonian method. Special emphasis is given to the 2+1 spacetime dimensional case where a (topological) Chern-Simons term is added to the Lagrangian.

J. Barcelos-Neto; T. G. Dargam

1994-08-08

127

Commodity tax competition with Constrained Taxes  

E-print Network

Commodity tax competition with Constrained Taxes Pascal Belan St´ephane Gauthier 6th August 2008 that there can be only two rates of tax on the different commodities, a positive rate and the zero-rate. The main by countries, i.e., the level of the positive rate and the set of taxed commodities. Under the origin principle

Paris-Sud XI, Université de

128

Constraining fossil calibrations for molecular clocks  

E-print Network

Constraining fossil calibrations for molecular clocks Sir, In a recent paper, Mu¨ller and Reisz(1) proposed how fossil calibrations should be selected for application in molecular clock studies. The topic molecules. Nonetheless, we believe that these authors have erred both in their proposal of fossil

Kumar, Sudhir

129

Rhythmic Grouping Biases Constrain Infant Statistical Learning  

ERIC Educational Resources Information Center

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

Hay, Jessica F.; Saffran, Jenny R.

2012-01-01

130

Analytical solutions to constrained hypersonic flight trajectories  

NASA Technical Reports Server (NTRS)

The flight trajectory of aerospace vehicles subject to a class of path constraints is considered. The constrained dynamics is shown to be a natural two-time-scale system. Asymptotic analytical solutions are obtained. Problems of trajectory optimization and guidance can be dramatically simplified with these solutions. Applications in trajectory design for an aerospace plane strongly support the theoretical development.

Lu, Ping

1993-01-01

131

Analytical solutions to constrained hypersonic flight trajectories  

NASA Technical Reports Server (NTRS)

The flight trajectory of aerospace vehicles subject to a class of path constraints is considered. The constrained dynamics is shown to be a natural two-time-scale system. Asymptotic analytical solutions are obtained. Problems of trajectory optimization and guidance can be dramatically simplified with these solutions. Applications in trajectory design for an aerospace plane strongly support the theoretical development.

Lu, Ping

1992-01-01

132

SYSTEMS BIOLOGY Metabolically constrained regulatory networks  

E-print Network

have developed an approach -- Gene Expression and Metabolism Integrated for Network Interference occluded genes Cell fusion can be used to define a class of genes termed occluded genes, the expression (GEMINI) -- that is able to constrain predicted gene regulatory networks on the basis of metabolic data

Pilpel, Yitzhak

133

Constrained TSP and Low-Power Computing  

Microsoft Academic Search

In the precedence-constrained traveling salesman problem (PTSP ) we are given a partial order on nodes, each of which is labeled by one of points in a metric space. We are to find a visit order consistent with the precedence constraints that minimizes the total cost of the corresponding path in th e metric space. We give negative results on

Moses Charikar; Rajeev Motwani; Prabhakar Raghavan; Craig Silverstein

1997-01-01

134

Searching the Web by Constrained Spreading Activation.  

ERIC Educational Resources Information Center

Discussion of intelligent information retrieval focuses on the use of Constrained Spreading Activation (CSA) techniques to search on the World Wide Web. Highlights include associative and ostensive information retrieval; hypertext links; query formulation; a prototype system that used CSA to search the Web; and results of an evaluation. (LRW)

Crestani, Fabio; Lee, Puay Leng

2000-01-01

135

Constraining Mercury Oxidation Using Wet Deposition  

E-print Network

Constraining Mercury Oxidation Using Wet Deposition Noelle E. Selin and Christopher D. Holmes mercury oxidation [Selin & Jacob, Atmos. Env. 2008] 30 60 90 120 150 30 60 90 120 150 30 60 90 120 150 30 Influences on Mercury Wet Deposition · Hg wet dep = f(precipitation, [Hg(II)+Hg(P)]) Correlation (r2) between

Selin, Noelle Eckley

136

Globally Convergent Evolution Strategies for Constrained Optimization  

E-print Network

Jul 10, 2014 ... In this paper we propose, analyze, and test algorithms for linearly constrained optimiza- ... Support for this research was provided by FCT under grants ..... Definition 2.1 A vector d ? Rn is said to be a hypertangent vector to the set ? ? Rn at ..... the models are computed by least squares regression, up to a ...

2014-07-10

137

Robust constrained shortest path problems under budgeted ...  

E-print Network

2Department of Mechanical, Energy and Management Engineering, University of ... We study the robust constrained shortest path problem under resource uncertainty. ... can readily extend the algorithms presented in this paper to problems that ... such properties are related to the computational complexity and probabilistic ...

2014-09-12

138

Constraining dark matter through 21-cm observations  

Microsoft Academic Search

Beyond reionization epoch cosmic hydrogen is neutral and can be directly observed through its 21-cm line signal. If dark matter (DM) decays or annihilates, the corresponding energy input affects the hydrogen kinetic temperature and ionized fraction, and contributes to the Lyalpha background. The changes induced by these processes on the 21-cm signal can then be used to constrain the proposed

M. Valdés; A. Ferrara; M. Mapelli; E. Ripamonti

2007-01-01

139

Constrained CP-nets Steve Prestwich1  

E-print Network

Constrained CP-nets Steve Prestwich1 , Francesca Rossi2 , Kristen Brent Venable2 , Toby Walsh1 1, soft constraints, and CP nets. We construct a set of hard constraints whose solutions are the optimal. Among the many existing approaches to represent preferencess, we will consider CP nets [5,3], which

Rossi, Francesca

140

Constrained CP-nets Steve Prestwich  

E-print Network

Constrained CP-nets Steve Prestwich , Francesca Rossi ¡ , Kristen Brent Venable ¡, Toby Walsh 1, soft constraints, and CP-nets. We construct a set of hard constraints whose solutions are the optimal to represent preferences, we will consider CP-nets [6, 3], which is a quali- tative approach where preferences

Walsh, Toby

141

Accelerated Gradient Methods for Constrained Image Deblurring  

E-print Network

, Italy 2 Dipartimento di Matematica Pura e Applicata, Universit`a di Modena e Reggio Emilia, Via G. Campi of the maximum likelihood approach. We present the method in a very general form and we give convergence results investigated in literature. This approach leads to model the deblurring problem as a constrained large scale

Bertero, Mario

142

Constrained Principal Component Analysis: Various Applications.  

ERIC Educational Resources Information Center

Provides example applications of constrained principal component analysis (CPCA) that illustrate the method on a variety of contexts common to psychological research. Two new analyses, decompositions into finer components and fitting higher order structures, are presented, followed by an illustration of CPCA on contingency tables and the CPCA of…

Hunter, Michael; Takane, Yoshio

2002-01-01

143

Stochastic Multiscale Segmentation Constrained by Image Content  

E-print Network

Stochastic Multiscale Segmentation Constrained by Image Content Luc Gillibert and Dominique Jeulin- eter k needs to be proportional to the number of desired regions in the segmented image. Therefore be automatically computed from the image and is used as a constraint during iterations of segmentation steps. 2

Paris-Sud XI, Université de

144

Constrained Pricing for Cloud Resource Allocation  

Microsoft Academic Search

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

Makhlouf Hadji; Wajdi Louati; Djamal Zeghlache

2011-01-01

145

DEPARTAMENTO DE COMPUTACION Constrained Clustering Algorithms  

E-print Network

DEPARTAMENTO DE COMPUTACI´ON Constrained Clustering Algorithms: Practical Issues and Applications PHD THESIS TESE DE DOUTORAMENTO Manuel Eduardo Ares Brea 2013 #12;#12;DEPARTAMENTO DE COMPUTACI´ON Computaci´on e Intelixencia Artificial da Universidade da Coru~na CERTIFICA Que a presente memoria

Barreiro, Alvaro

146

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

PubMed Central

Collision-induced dissociation of protonated AGabaAIG (where Gaba is gamma-amino butyric acid, NH2-(CH2)3-COOH) leads to an unusually stable a3 ion. Tandem mass spectrometry and theory are used here to probe the enhanced stability of this fragment, whose counterpart is not usually observed in CID of protonated peptides containing only alpha amino acids. Experiments are carried out on the unlabelled and 15N-Ala labeled AGabaAIG (labeled separately at residue one or three) probing the b3, a3, a3-NH3 (a3*), and b2 fragments while theory is used to characterize the most stable b3, a3, and b2 structures and the formation and dissociation of the a3 ion. Our results indicate the AGabaA oxazolone b3 isomer undergoes head-to-tail macrocyclization and subsequent ring opening to form the GabaAA sequence isomer while this chemistry is energetically disfavored for the AAA sequence. The AGabaA a3 fragment also undergoes macrocyclization and rearrangement to form the rearranged imine-amide isomer while this reaction is energetically disfavored for the AAA sequence. The barriers to dissociation of the AGabaA a3 ion via the a3?b2 and a3?a3* channels are higher than the literature values reported for the AAA sequence. These two effects provide a clear explanation for the enhanced stability of the AGabaA a3 ion. PMID:23258959

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

2012-01-01

147

Hypochlorous acid-mediated protein oxidation: how important are chloramine transfer reactions and protein tertiary structure?  

PubMed

Hypochlorous acid (HOCl) is a powerful oxidant generated from H2O2 and Cl- by the heme enzyme myeloperoxidase, which is released from activated leukocytes. HOCl possesses potent antibacterial properties, but excessive production can lead to host tissue damage that occurs in numerous human pathologies. As proteins and amino acids are highly abundant in vivo and react rapidly with HOCl, they are likely to be major targets for HOCl. In this study, two small globular proteins, lysozyme and insulin, have been oxidized with increasing excesses of HOCl to determine whether the pattern of HOCl-mediated amino acid consumption is consistent with reported kinetic data for isolated amino acids and model compounds. Identical experiments have been carried out with mixtures of N-acetyl amino acids (to prevent reaction at the alpha-amino groups) that mimic the protein composition to examine the role of protein structure on reactivity. The results indicate that tertiary structure facilitates secondary chlorine transfer reactions of chloramines formed on His and Lys side chains. In light of these data, second-order rate constants for reactions of Lys side chain and Gly chloramines with Trp side chains and disulfide bonds have been determined, together with those for further oxidation of Met sulfoxide by HOCl and His side chain chloramines. Computational kinetic models incorporating these additional rate constants closely predict the experimentally observed amino acid consumption. These studies provide insight into the roles of chloramine formation and three-dimensional structure on the reactions of HOCl with isolated proteins and demonstrate that kinetic models can predict the outcome of HOCl-mediated protein oxidation. PMID:17676767

Pattison, David I; Hawkins, Clare L; Davies, Michael J

2007-08-28

148

Video Personalization and Caching for Resource Constrained Environments  

E-print Network

Video Personalization and Caching for Resource Constrained Environments Siddhartha Chattopadhyay Dept. of Computer Science, The University of Georgia, Athens, Georgia 30602-7404, USA Abstract: Video constrained, various video personalization strategies are used to provide personalized video content

Bhandarkar, Suchendra "Suchi" M.

149

Risk allocation strategies for distributed chance-constrained task allocation  

E-print Network

This paper addresses the issue of allocating risk amongst agents in distributed chance-constrained planning algorithms. Building on previous research that extended chance-constrained planning to stochastic multi-agent ...

Ponda, Sameera S.

150

Constraining the Braneworld with Gravitational Wave Observations  

SciTech Connect

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

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

2010-04-09

151

Constraining 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

152

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

153

Compilation for critically constrained knowledge bases  

SciTech Connect

We show that many {open_quotes}critically constrained{close_quotes} Random 3SAT knowledge bases (KBs) can be compiled into disjunctive normal form easily by using a variant of the {open_quotes}Davis-Putnam{close_quotes} proof procedure. From these compiled KBs we can answer all queries about entailment of conjunctive normal formulas, also easily - compared to a {open_quotes}brute-force{close_quotes} approach to approximate knowledge compilation into unit clauses for the same KBs. We exploit this fact to develop an aggressive hybrid approach which attempts to compile a KB exactly until a given resource limit is reached, then falls back to approximate compilation into unit clauses. The resulting approach handles all of the critically constrained Random 3SAT KBs with average savings of an order of magnitude over the brute-force approach.

Schrag, R. [Univ. of Texas, Austin, TX (United States)

1996-12-31

154

Many-electron systems with constrained current  

NASA Astrophysics Data System (ADS)

A many-body theory is formulated for an inhomogeneous, interacting electron gas with electronic current. Electronic current is induced by a constraint condition imposed as a vector Lagrange multiplier. Constrained minimization of the total energy on the manifold of an arbitrary constant current leads to a many-electron Schrödinger equation with a complex, momentum-dependent potential. Constant current Hartree-Fock and Kohn-Sham approximations are formulated within the method and application to transport for quantum wires is developed.

Kosov, D. S.; Greer, J. C.

2001-11-01

155

Haplotype inference constrained by plausible haplotype data.  

PubMed

The haplotype inference problem (HIP) asks to find a set of haplotypes which resolve a given set of genotypes. This problem is important in practical fields such as the investigation of diseases or other types of genetic mutations. In order to find the haplotypes which are as close as possible to the real set of haplotypes that comprise the genotypes, two models have been suggested which are by now well-studied: The perfect phylogeny model and the pure parsimony model. All known algorithms up till now for haplotype inference may find haplotypes that are not necessarily plausible, i.e., very rare haplotypes or haplotypes that were never observed in the population. In order to overcome this disadvantage, we study in this paper, a new constrained version of HIP under the above-mentioned models. In this new version, a pool of plausible haplotypes H is given together with the set of genotypes G, and the goal is to find a subset H ? H that resolves G. For constrained perfect phlogeny haplotyping (CPPH), we provide initial insights and polynomial-time algorithms for some restricted cases of the problem. For constrained parsimony haplotyping (CPH), we show that the problem is fixed parameter tractable when parameterized by the size of the solution set of haplotypes. PMID:20733241

Fellows, Michael R; Hartman, Tzvika; Hermelin, Danny; Landau, Gad M; Rosamond, Frances; Rozenberg, Liat

2011-01-01

156

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

157

Energy and Deadline Constrained Robust Stochastic Static Resource Allocation  

E-print Network

Energy and Deadline Constrained Robust Stochastic Static Resource Allocation Mark A. Oxley1 of energy and deadline constrained static resource allocation where a collection of independent tasks ("bag of tasks stochastically. This research focuses on the design of energy-constrained resource allocation

Maciejewski, Anthony A.

158

Rate-Constrained Multi-Hypothesis Motion-Compensated Prediction  

E-print Network

Rate-Constrained Multi-Hypothesis Motion-Compensated Prediction for Video Coding Markus Flierl-hypothesis motion-compensated prediction with multiple reference frames 2. Rate-constrained multi-hypothesis motion on multiple reference frames Markus Flierl: Rate-Constrained Multi-Hypothesis Motion-Compensated Prediction 1

Flierl, Markus

159

Profitable and dynamically feasible operating point selection for constrained processes  

E-print Network

Profitable and dynamically feasible operating point selection for constrained processes M. Nabila are active, i.e, the solution is constrained. Though it is profitable to operate at the constrained optimal: Feasibility, dynamic back-off, linear matrix inequality, profit control 1. Background Profitability

Skogestad, Sigurd

160

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

161

Tryptophan metabolism in Klebsiella aerogenes: regulation of the utilization of aromatic amino acids as sources of nitrogen.  

PubMed Central

Klebsiella aerogenes utilized aromatic amino acids as sole sources of nitrogen but not as sole sources of carbon. K. aerogenes abstracted the alpha-amino group of these compounds by transamination and excreted the arylpyruvate portions into the medium. When tryptophan was utilized as the sole source of nitrogen by K. aerogenes, indolepyruvate was excreted into the medium, where it polymerized non-enzymatically to form a brick red pigment. At least four separate aromatic aminotransferase activities were found in K. aerogenes. One activity (aromatic aminotransferase I) appeared to be solely responsible for the aminotransferase reaction necessary for the growth of K. aerogenes when tryptophan was the source of nitrogen; the loss of this activity by mutation (tut) prevented the growth of cells on media containing this and other aromatic amino acids. None of the other aminotransferase activities in the cells could substitute for aromatic aminotransferase in this regard. Tryptophan-dependent pigment formation in K. aerogenes was positively controlled by the intracellular level of glutamine synthetase. Nevertheless, the aromatic aminotransferase activity in cells varied less than 2-fold in response to 10-fold or greater changes in the levels of glutamine synthetase. Glutamine synthetase affected the ability of the cells to take up tryptophan from the medium. Images PMID:6109705

Paris, C G; Magasanik, B

1981-01-01

162

Nonstationary sparsity-constrained seismic deconvolution  

NASA Astrophysics Data System (ADS)

The Robinson convolution model is mainly restricted by three inappropriate assumptions, i.e., statistically white reflectivity, minimum-phase wavelet, and stationarity. Modern reflectivity inversion methods (e.g., sparsity-constrained deconvolution) generally attempt to suppress the problems associated with the first two assumptions but often ignore that seismic traces are nonstationary signals, which undermines the basic assumption of unchanging wavelet in reflectivity inversion. Through tests on reflectivity series, we confirm the effects of nonstationarity on reflectivity estimation and the loss of significant information, especially in deep layers. To overcome the problems caused by nonstationarity, we propose a nonstationary convolutional model, and then use the attenuation curve in log spectra to detect and correct the influences of nonstationarity. We use Gabor deconvolution to handle nonstationarity and sparsity-constrained deconvolution to separating reflectivity and wavelet. The combination of the two deconvolution methods effectively handles nonstationarity and greatly reduces the problems associated with the unreasonable assumptions regarding reflectivity and wavelet. Using marine seismic data, we show that correcting nonstationarity helps recover subtle reflectivity information and enhances the characterization of details with respect to the geological record.

Sun, Xue-Kai; Sam, Zandong Sun; Xie, Hui-Wen

2014-12-01

163

Constraining dark matter through 21-cm observations  

NASA Astrophysics Data System (ADS)

Beyond reionization epoch cosmic hydrogen is neutral and can be directly observed through its 21-cm line signal. If dark matter (DM) decays or annihilates, the corresponding energy input affects the hydrogen kinetic temperature and ionized fraction, and contributes to the Ly? background. The changes induced by these processes on the 21-cm signal can then be used to constrain the proposed DM candidates, among which we select the three most popular ones: (i) 25-keV decaying sterile neutrinos, (ii) 10-MeV decaying light dark matter (LDM) and (iii) 10-MeV annihilating LDM. Although we find that the DM effects are considerably smaller than found by previous studies (due to a more physical description of the energy transfer from DM to the gas), we conclude that combined observations of the 21-cm background and of its gradient should be able to put constrains at least on LDM candidates. In fact, LDM decays (annihilations) induce differential brightness temperature variations with respect to the non-decaying/annihilating DM case up to ??Tb = 8 (22) mK at about 50 (15) MHz. In principle, this signal could be detected both by current single-dish radio telescopes and future facilities as Low Frequency Array; however, this assumes that ionospheric, interference and foreground issues can be properly taken care of.

Valdés, M.; Ferrara, A.; Mapelli, M.; Ripamonti, E.

2007-05-01

164

Constrained Simulation of the Bullet Cluster  

E-print Network

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 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 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 NFW 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 velocitie...

Lage, Craig

2013-01-01

165

Constraining torsion with Gravity Probe B  

SciTech Connect

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

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

2007-11-15

166

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

167

Amino acids  

MedlinePLUS

Amino acids are organic compounds that combine to form proteins . Amino acids and proteins are the building blocks of life. When proteins are digested or broken down, amino acids are left. The human body uses amino acids ...

168

Constrained layer damping treatments with actively enhanced actions  

Microsoft Academic Search

This thesis studies self-contained constrained layer treatments with active-passive hybrid damping. In particular, two shortcomings of traditional active constrained layer (ACL) configurations, the low active control authority and weak constraining action of the active cover sheet, are addressed. The objective is to design a treatment with the best combination of open-loop (for fail-safe property) and closed-loop (for performance) damping. A

Yanning Liu

2001-01-01

169

Constraining subleading soft gluon and graviton theorems  

E-print Network

We show that the form of the recently proposed subleading soft graviton and gluon theorems in any dimension are severely constrained by elementary arguments based on Poincar\\'e and gauge invariance as well as a self-consistency condition arising from the distributional nature of scattering amplitudes. Combined with the assumption of a local form as it would arise from a Ward identity the orbital part of the subleading operators is completely fixed by the leading universal Weinberg soft pole behavior. The polarization part of the differential subleading soft operators in turn is determined up to a single numerical factor for each hard leg at every order in the soft momentum expansion. In four dimensions, factorization of the Lorentz group allows to fix the subleading operators completely.

Johannes Broedel; Marius de Leeuw; Jan Plefka; Matteo Rosso

2014-07-04

170

Traveltime tomography and nonlinear constrained optimization  

SciTech Connect

Fermat's principle of least traveltime states that the first arrivals follow ray paths with the smallest overall traveltime from the point of transmission to the point of reception. This principle determines a definite convex set of feasible slowness models - depending only on the traveltime data - for the fully nonlinear traveltime inversion problem. The existence of such a convex set allows us to transform the inversion problem into a nonlinear constrained optimization problem. Fermat's principle also shows that the standard undamped least-squares solution to the inversion problem always produces a slowness model with many ray paths having traveltime shorter than the measured traveltime (an impossibility even if the trial ray paths are not the true ray paths). In a damped least-squares inversion, the damping parameter may be varied to allow efficient location of a slowness model on the feasibility boundary. 13 refs., 1 fig., 1 tab.

Berryman, J.G.

1988-10-01

171

Constraining Van der Waals quintessence by observations  

E-print Network

We discuss an alternative approach to quintessence modifying the usual equation of state of the cosmological fluid in order to see if going further than the approximation of perfect fluid allows to better reproduce the available data. We consider a cosmological model comprising only two fluids, namely baryons (modelled as dust) and dark matter with a Van der Waals equation of state. First, the general features of the model are presented and then the evolution of the energy density, the Hubble parameter and the scale factor are determined showing that it is possible to obtain accelerated expansion choosing suitably the model parameters. We use the estimated age of the universe and the data on the dimensionless coordinate distances to Type Ia supernovae and distant radio galaxies to see whether Van der Waals quintessence is viable to explain dark energy and to constrain its parameters.

S. Capozziello; V. F. Cardone; S. Carloni; S. De Martino; M. Falanga; A. Troisi; M. Bruni

2005-03-18

172

Constraining the inflationary equation of state  

SciTech Connect

We explore possible constraints on the inflationary equation state: p = w?. While w must be close to -1 for those modes that contribute to the observed power spectrum, for those modes currently out of experimental reach, the constraints on w are much weaker, with only w < ?1/3 as an a priori requirement. We find, however, that limits on the reheat temperature and the inflationary energy scale constrain w further, though there is still ample parameter space for a vastly different (accelerating) equation of state between the end of quasi-de Sitter inflation and the beginning of the radiation-dominated era. In the event that such an epoch of acceleration could be observed, we review the consequences for the primordial power spectrum.

Ackerman, Lotty; Fischler, Willy; Kundu, Sandipan; Sivanandam, Navin, E-mail: lotty@astro.as.utexas.edu, E-mail: fischler@physics.utexas.edu, E-mail: sandyk@physics.utexas.edu, E-mail: navin.sivanandam@gmail.com [Texas Cosmology Center, University of Texas, Austin, TX 78712 (United States)

2011-05-01

173

Constraining subleading soft gluon and graviton theorems  

NASA Astrophysics Data System (ADS)

We show that the form of the recently proposed subleading soft graviton and gluon theorems in any dimension are severely constrained by elementary arguments based on Poincaré and gauge invariance as well as a self-consistency condition arising from the distributional nature of scattering amplitudes. Combined with the assumption of a local form as it would arise from a Ward identity the orbital part of the subleading operators is completely fixed by the leading universal Weinberg soft pole behavior. The polarization part of the differential subleading soft operators in turn is determined up to a single numerical factor for each hard leg at every order in the soft momentum expansion. In four dimensions, factorization of the Lorentz group allows us to fix the subleading operators completely.

Broedel, Johannes; de Leeuw, Marius; Plefka, Jan; Rosso, Matteo

2014-09-01

174

Structure-constrained low-rank representation.  

PubMed

Benefiting from its effectiveness in subspace segmentation, low-rank representation (LRR) and its variations have many applications in computer vision and pattern recognition, such as motion segmentation, image segmentation, saliency detection, and semisupervised learning. It is known that the standard LRR can only work well under the assumption that all the subspaces are independent. However, this assumption cannot be guaranteed in real-world problems. This paper addresses this problem and provides an extension of LRR, named structure-constrained LRR (SC-LRR), to analyze the structure of multiple disjoint subspaces, which is more general for real vision data. We prove that the relationship of multiple linear disjoint subspaces can be exactly revealed by SC-LRR, with a predefined weight matrix. As a nontrivial byproduct, we also illustrate that SC-LRR can be applied for semisupervised learning. The experimental results on different types of vision problems demonstrate the effectiveness of our proposed method. PMID:25420240

Tang, Kewei; Liu, Risheng; Su, Zhixun; Zhang, Jie

2014-12-01

175

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

176

Constraining nonstandard neutrino-electron interactions  

SciTech Connect

We present a detailed analysis on nonstandard neutrino interactions (NSI) with electrons including all muon and electron (anti)-neutrino data from existing accelerators and reactors, in conjunction with the 'neutrino counting' data (e{sup +}e{sup -}{yields}{nu}{nu}{gamma}) from the four LEP collaborations. First we perform a one-parameter-at-a-time analysis, showing how most constraints improve with respect to previous results reported in the literature. We also present more robust results where the NSI parameters are allowed to vary freely in the analysis. We show the importance of combining LEP data with the other experiments in removing degeneracies in the global analysis constraining flavor-conserving NSI parameters which, at 90% and 95% C.L., must lie within unique allowed regions. Despite such improved constraints, there is still substantial room for improvement, posing a big challenge for upcoming experiments.

Barranco, J.; Miranda, O. G.; Moura, C. A.; Valle, J. W. F. [Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del IPN, Apdo. Postal 14-740 07000 Mexico, D.F. (Mexico); AHEP Group, Instituto de Fisica Corpuscular-C.S.I.C./Universitat de Valencia Edificio Institutos de Paterna, Apt 22085, E-46071 Valencia (Spain)

2008-05-01

177

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

178

Constraining MOND with Solar System dynamics  

E-print Network

In this letter we investigate the deep Newtonian regime of the MOND paradigm from a purely phenomenological point of view by exploiting the least-square estimated corrections to the secular rates of the perihelia of the inner and of some of the outer planets of the Solar System by E.V. Pitjeva with the EPM2004 ephemerides. By using $\\mu(x)\\approx 1-k_0(1/x)^n$ for the interpolating MONDian function, and by assuming that $k_0$, considered body-independent so to avoid violations of the equivalence principle, experiences no spatial variations throughout the Solar System we tightly constrain $n$ with the ratios of the perihelion precessions for different pairs of planets. We find that the range $1\\leq n\\leq 2$ is neatly excluded at much more than $3-\\sigma$ level. Such a test would greatly benefit from the use of extra-precessions of perihelia independently estimated by other groups as well.

Lorenzo Iorio

2007-11-18

179

Noisy Constrained Capacity for BSC Channels Philippe Jacquet  

E-print Network

Noisy Constrained Capacity for BSC Channels Philippe Jacquet INRIA Rocquencourt 78153 Le Chesnay Cedex France Email: philippe.jacquet@inria.fr Wojciech Szpankowski Department of Computer Science Purdue

Szpankowski, Wojciech

180

Synthesis and coordination chemistry of topologically constrained azamacrocycles  

E-print Network

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.1 Choosing metal ions and topologically constrained ligands for biomimicry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.2 Cross-bridged tetraazamacrocycle complexes for biomimicry

Hubin, Tim

181

Isotropic submanifolds and the inverse problem for mechanical constrained systems  

NASA Astrophysics Data System (ADS)

We give a new characterization of the inverse problem of the calculus of variations that is easily extended to constrained systems, both in the autonomous and non-autonomous cases. The transition from unconstrained to constrained systems is given by passing from Lagrangian submanifolds to isotropic ones. If the constrained system is variational we use symplectic techniques to extend these isotropic submanifolds to Lagrangian ones and describe the solutions of the constrained system as solutions of a variational problem without constraints. Mechanical examples such as the rolling disk are provided to illustrate the main results.

Barbero-Liñán, María; Farré Puiggalí, Marta; Martín de Diego, David

2015-01-01

182

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

183

Very constrained minimal supersymmetric standard models  

SciTech Connect

We consider very constrained versions of the minimal supersymmetric extension of the standard model (VCMSSMs) which, in addition to constraining the scalar masses m{sub 0} and gaugino masses m{sub 1/2} to be universal at some input scale, impose relations between the trilinear and bilinear soft supersymmetry-breaking parameters A{sub 0} and B{sub 0}. These relations may be linear, as in simple minimal supergravity models, or nonlinear, as in the Giudice-Masiero mechanism for generating the Higgs-mixing {mu} term. We discuss the application of the electroweak vacuum conditions in VCMSSMs, which may be used to make a prediction for tan{beta} as a function of m{sub 0} and m{sub 1/2} that is usually unique. We baseline the discussion of the parameter spaces allowed in VCMSSMs by updating the parameter space allowed in the CMSSM for fixed values of tan{beta} with no relation between A{sub 0} and B{sub 0} assumed a priori, displaying contours of B{sub 0} for a fixed input value of A{sub 0}, incorporating the latest CDF/D0 measurement of m{sub t} and the latest BNL measurement of g{sub {mu}}-2. We emphasize that phenomenological studies of the CMSSM are frequently not applicable to specific VCMSSMs, notably those based on minimal supergravity, which require m{sub 0}=m{sub 3/2} as well as A{sub 0}=B{sub 0}+m{sub 0}. We then display (m{sub 1/2},m{sub 0}) planes for selected VCMSSMs, treating in a unified way the parameter regions where either a neutralino or the gravitino is the lightest supersymmetric particle. In particular, we examine in detail the allowed parameter space for the Giudice-Masiero model.

Ellis, John [TH Division, CERN, Geneva (Switzerland); Olive, Keith A.; Santoso, Yudi; Spanos, Vassilis C. [William I. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

2004-09-01

184

A phenomenological model of active constrained layers  

NASA Astrophysics Data System (ADS)

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

Illaire, Hélène; Kropp, Wolfgang; Mace, Brian

2005-07-01

185

Dynamic changes of excitatory amino acid receptors in the rat hippocampus following transient cerebral ischemia  

SciTech Connect

The changes in excitatory amino acid receptor ligand binding induced by transient cerebral ischemia were studied in the rat hippocampal subfields. Ten minutes of ischemia was induced by common carotid artery occlusion combined with hypotension, and the animals were allowed variable periods of recovery ranging from 1 day to 4 weeks. The binding of 3H-AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) to quisqualate receptors, 3H-kainic acid (KA) to kainate receptors, and 3H-glutamate to N-methyl-D-aspartate (NMDA) receptors as determined by quantitative autoradiography. One week following ischemia the CA1 region of the hippocampus displayed a severe (90%) dendrosomatic lesion with preservation of presynaptic terminals. This was associated with a 60% decrease in AMPA binding and a 25% decrease in glutamate binding to NMDA receptors. At 4 weeks postischemia, both AMPA and NMDA sites were greatly reduced. Although the dentate gyrus granule cells are resistant to an ischemic insult of this magnitude, this region showed marked changes in receptor binding. One week following ischemia, the AMPA and NMDA binding decreased by approximately 40 and 20%, respectively. Following 2 weeks of recovery, the NMDA binding was not significantly different from control level, while the AMPA binding remained depressed up to 4 weeks postischemia. The high density of KA binding sites in the inner molecular layer of the dentate gyrus was unaffected by the ischemic insult, despite an extensive degeneration of cells in the hilus of dentate gyrus which projects glutamatergic afferents to this area.

Westerberg, E.; Monaghan, D.T.; Kalimo, H.; Cotman, C.W.; Wieloch, T.W.

1989-03-01

186

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, Tung-Huei; Baz, Amr M.

1996-05-01

187

Effect of tryptophan analogs on derepression of the Escherichia coli tryptophan operon by indole-3-propionic acid.  

PubMed

The abilities of 14 tryptophan analogs to repress the tryptophan (trp) operon have been studied in Escherichia coli cells derepressed by incubation with 0.25 mM indole-3-propionic acid (IPA). trp operon expression was monitored by measuring the specific activities of anthranilate synthase (EC 4.1.3.27) and the tryptophan synthase (EC 4.2.1.20) beta subunit. Analogs characterized by modification or removal of the alpha-amino group or the alpha-carboxyl group did not repress the trp operon. The only analogs among this group that appeared to interact with the trp aporepressor were IPA, which derepressed the trp operon, and d-tryptophan. Analogs with modifications of the indole ring repressed the trp operon to various degrees. 7-Methyl-tryptophan inhibited anthranilate synthase activity and consequently derepressed the trp operon. Additionally, 7-methyltryptophan prevented IPA-mediated derepression but, unlike tryptophan, did so in a non-coordinate manner, with the later enzymes of the operon being relatively more repressed than the early enzymes. The effect of 7-methyltryptophan on IPA-mediated derepression was likely not due to the interaction of IPA with the allosteric site of anthranilate synthase, even though feedback-resistant mutants of anthranilate synthase were partially resistant to derepression by IPA. The effect of 7-methyltryptophan on derepression by IPA was probably due to the effect of the analog-aporepressor complex on trp operon expression. PMID:361689

Pauley, R J; Fredricks, W W; Smith, O H

1978-10-01

188

A cost function for neutralizing acidic Adirondack surface waters  

Microsoft Academic Search

A cost function for neutralizing acidic surface waters by base addition (liming) is derived based upon constrained cost minimization. The model is estimated using a sample of 547 acidic Adirondack lakes with total costs projected for neutralizing each lake to one of six possible target alkalinity levels. Empirical findings indicate that relatively accurate forecasts of lake neutralization costs can be

Donald Dutkowsky; Fredrick C. Menz

1985-01-01

189

Security-Constrained Adequacy Evaluation of Bulk Power System Reliability  

E-print Network

Security-Constrained Adequacy Evaluation of Bulk Power System Reliability Fang Yang, Student Member. Stefopoulos, Student Member, IEEE Abstract -- A framework of security-constrained adequacy evaluation (SCAE electric load while satisfying security constraints. It encompasses three main steps: (a) critical

190

CONSTRAINING QUESTIONS ABOUT THE ORGANISATION AND REPRESENTATION OF  

E-print Network

CONSTRAINING QUESTIONS ABOUT THE ORGANISATION AND REPRESENTATION OF CONCEPTUAL KNOWLEDGE Bradford Z-specific organisation of conceptual knowledge and consider two questions: How does this architecture constrain further assumptions that might be made regarding (1) the organisation of conceptual knowledge in the brain, and (2

Caramazza, Alfonso

191

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

192

Constraining fault constitutive behavior with slip and stress heterogeneity  

E-print Network

Constraining fault constitutive behavior with slip and stress heterogeneity B. T. Aagaard1 and T. H and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required on a vertical, planar strike-slip fault show that the conditions that lead to slip heterogeneity remain in place

Greer, Julia R.

193

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

194

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

195

Motion Planning of Human-Like Robots using Constrained Coordination  

E-print Network

Motion Planning of Human-Like Robots using Constrained Coordination Liangjun Zhang Jia Pan Dinesh to generate realistic motions. Recent research in robotics has focused on motion planning of humanoids due and ergonomic analysis of the CAD models [6, 21]. 1 #12;2 Motion Planning of Human-Like Robots using Constrained

North Carolina at Chapel Hill, University of

196

Two-Dimensional Weight-Constrained Codes through Enumeration Bounds  

E-print Network

Two-Dimensional Weight-Constrained Codes through Enumeration Bounds Erik Ordentlich i into An m at a rate H( );( m =m);( n =n). Keywords: Two-dimensional coding Weight-constrained codes Balanced is motivated primarily by the coding problem of two-dimensional balanced binary n m arrays, in which each row

Roth, Ronny

197

SelfScaling Fast Rotations for Stiff and Equality Constrained  

E-print Network

Self­Scaling Fast Rotations for Stiff and Equality Constrained Linear Least Squares Problems Andrew rotations to the QR decomposition for stiff least squares problems. We show that both fast and standard with extremely large weights when equality constrained least squares problems are solved by the weighting method

Park, Haesun

198

Automated Design of Pin-Constrained Digital Microfluidic Biochips Under  

E-print Network

14 Automated Design of Pin-Constrained Digital Microfluidic Biochips Under Droplet Corporation and KRISHNENDU CHAKRABARTY Duke University Microfluidics-based biochips, also referred to as lab automation method for pin-constrained biochips that manipulate nanoliter volumes of discrete droplets

Chakrabarty, Krishnendu

199

FREE AND CONSTRAINED MOTION TELEOPERATION VIA NATURALLY-TRANSITIONING  

E-print Network

FREE AND CONSTRAINED MOTION TELEOPERATION VIA NATURALLY-TRANSITIONING RATE-TO-FORCE CONTROL Robert:http://www.ent.ohiou.edu/~bobw #12;FREE AND CONSTRAINED MOTION TELEOPERATION VIA NATURALLY-TRANSITIONING RATE-TO-FORCE CONTROL Robert 45701 Daniel W. Repperger AFRL / HECP Wright-Patterson AFB, OH 45433 ABSTRACT The Naturally

Williams II, Robert L.

200

MATLAB package for solving Ellipsoid-Constrained Integer  

E-print Network

EILS: MATLAB package for solving Ellipsoid-Constrained Integer Least Squares Problems User's Guide) as the ellipsoid-constrained integer least squares (EILS) prob- lem. This MATLAB package provides the solution to the EILS problem. The purpose of this document is to show how to use this package. For the theory

Toronto, University of

201

Solving constrained matrix equations and Cramer rule q  

E-print Network

Solving constrained matrix equations and Cramer rule q Guorong Wang a,*, Sanzheng Qiao b an explicit expression for the elements of the solution matrix using Cramer rule. Ã? 2003 Elsevier Inc. All rights reserved. Keywords: Constrained matrix equations; Generalized inverses; Cramer rule 1

Qiao, Sanzheng

202

A PENALTY FUNCTION METHOD FOR CONSTRAINED MOLECULAR DYNAMICS SIMULATION  

E-print Network

A PENALTY FUNCTION METHOD FOR CONSTRAINED MOLECULAR DYNAMICS SIMULATION By Ajith Gunaratne­000 A PENALTY FUNCTION METHOD FOR CONSTRAINED MOLECULAR DYNAMICS SIMULATION AJITH GUNARATNE AND ZHIJUN WU FOR MOLECULAR DYNAMICS SIMULATION 1 that the new iterate can satisfy the constraints [3]. Depending

203

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

204

Constraining inflation with future galaxy redshift surveys  

SciTech Connect

With future galaxy surveys, a huge number of Fourier modes of the distribution of the large scale structures in the Universe will become available. These modes are complementary to those of the CMB and can be used to set constraints on models of the early universe, such as inflation. Using a MCMC analysis, we compare the power of the CMB with that of the combination of CMB and galaxy survey data, to constrain the power spectrum of primordial fluctuations generated during inflation. We base our analysis on the Planck satellite and a spectroscopic redshift survey with configuration parameters close to those of the Euclid mission as examples. We first consider models of slow-roll inflation, and show that the inclusion of large scale structure data improves the constraints by nearly halving the error bars on the scalar spectral index and its running. If we attempt to reconstruct the inflationary single-field potential, a similar conclusion can be reached on the parameters characterizing the potential. We then study models with features in the power spectrum. In particular, we consider ringing features produced by a break in the potential and oscillations such as in axion monodromy. Adding large scale structures improves the constraints on features by more than a factor of two. In axion monodromy we show that there are oscillations with small amplitude and frequency in momentum space that are undetected by CMB alone but can be measured by including galaxy surveys in the analysis.

Huang, Zhiqi; Vernizzi, Filippo [CEA, Institut de Physique Théorique, 91191 Gif-sur-Yvette cédex (France); Verde, Licia, E-mail: zhiqi.huang@cea.fr, E-mail: liciaverde@icc.ub.edu, E-mail: filippo.vernizzi@cea.fr [Institute of Sciences of the Cosmos (ICCUB), University of Barcelona, Marti i Franques 1, Barcelona 08024 (Spain)

2012-04-01

205

Constraining uncertainties in terrestrial carbon cycle modeling  

NASA Astrophysics Data System (ADS)

Global climate models differ in their representation of uptake of CO2 in the biosphere. Our study focuses on constraining the uncertainty in terrestrial carbon cycle modeling by comparing climate model results to observed atmospheric CO2 concentrations. The goal is to improve the representations of the seasonal cycle of terrestrial carbon uptake in the land model. We use the NCAR Community Earth System Model (CESM) climate components CLM4CN and CAM4 to run a prognostic version of the coupled land-atmosphere model where the atmospheric CO2 concentration in CAM4 is interactively calculated. Atmospheric CO2 concentrations from the model are compared to observations provided by flux towers in the AMERIFLUX network through the FLUXNET database and from the WDCGG for year 2000. We compare model results from sensitivity studies using different Q10 and Vcmax parameterizations, which are important functions in calculating plant growth. The carbon uptake in the biosphere is also under anthropogenic influence through emission of nitrogen and ozone from air pollution. Whereas nitrogen limitations in the soil reduce land ecosystem response to increasing CO2 concentrations, nitrogen from anthropogenic emissions increases the nitrogen availability and hence stimulates plant growth. These two nitrogen effects as well as the damaging impact on plants due to tropospheric ozone fertilization have been included in this study.

Kvalevåg, M.; Myhre, G.

2011-12-01

206

Acoustic characteristics of listener-constrained speech  

NASA Astrophysics Data System (ADS)

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

Ashby, Simone; Cummins, Fred

2003-04-01

207

Constrained Sypersymmetric Flipped SU (5) GUT Phenomenology  

SciTech Connect

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

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

2011-08-12

208

Constraining the Oblateness of Kepler Planets  

NASA Astrophysics Data System (ADS)

We use Kepler short-cadence light curves to constrain the oblateness of planet candidates in the Kepler sample. The transits of rapidly rotating planets that are deformed in shape will lead to distortions in the ingress and egress of their light curves. We report the first tentative detection of an oblate planet outside the solar system, measuring an oblateness of 0.22-0.11+0.11 for the 18 MJ mass brown dwarf Kepler 39b (KOI 423.01). We also provide constraints on the oblateness of the planets (candidates) HAT-P-7b, KOI 686.01, and KOI 197.01 to be <0.067, <0.251, and <0.186, respectively. Using the Q' values from Jupiter and Saturn, we expect tidal synchronization for the spins of HAT-P-7b, KOI 686.01, and KOI 197.01, and for their rotational oblateness signatures to be undetectable in the current data. The potentially large oblateness of KOI 423.01 (Kepler 39b) suggests that the Q' value of the brown dwarf needs to be two orders of magnitude larger than that of the solar system gas giants to avoid being tidally spun down.

orcid="0000-0003-4027-4711" affil="1" non latin="??">Wei Zhu,

2014-11-01

209

Constrained Graph Optimization: Interdiction and Preservation Problems  

SciTech Connect

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

Schild, Aaron V [Los Alamos National Laboratory

2012-07-30

210

Conformationally Constrained and Nanoparticle Targeted Paclitaxels*  

PubMed Central

Paclitaxel (Taxol®) is one of the most important anticancer agents developed over the last 30 years. Its primary mechanism of action is by interaction with the cellular protein tubulin, causing irreversible polymerization to microtubules. A detailed knowledge of this crucial interaction is thus of paramount importance in the design and development of highly potent analogs and also for the potential development of “non-taxane” tubulin polymerization agents. This review briefly describes the discovery and development of taxol, and then describes our work on delineating the tubulin-binding conformation of paclitaxel by a combination of REDOR NMR and molecular modeling. The resulting “T-taxol” conformation was validated by the synthesis of conformationally constrained paclitaxel analogs, which had bioactivities up to twenty-fold higher than those of paclitaxel. The review concludes with recent work on the development of a gold nanoparticle derivative of paclitaxel. This delivery method has the potential to lower the dosage of paclitaxel needed while maintaining or increasing its effectiveness, thus significantly improving the benefits of this important chemotherapeutic agent.

Tamarkin, Lawrence; Paciotti, Giulio F.

2014-01-01

211

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

212

Constraining asteroid dynamical models using GAIA data  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

213

Progressive constrained energy minimization for subpixel detection  

NASA Astrophysics Data System (ADS)

Constrained energy minimization (CEM) has been widely used for subpixel detection. It makes use of the sample correlation matrix R by suppressing the background thus enhancing detection of targets of interest. In many real world problems, implementing target detection on a timely basis is crucial, specifically moving targets. However, since the calculation of the sample correlation matrix R needs the complete data set prior to its use in detection, CEM is prevented from being implemented as a real time processing algorithm. In order to resolve this dilemma, the sample correlation matrix R must be replaced with a causal sample correlation matrix formed by only those data samples that have been visited and the currently being processed data sample. This causality is a pre-requisite to real time processing. By virtue of such causality, designing and developing a real time processing version of CEM becomes feasible. This paper presents a progressive CEM (PCEM) where the causal sample correlation matrix can be updated sample by sample. Accordingly, PCEM allows the CEM to be implemented as a causal CEM (C-CEM) as well as real time (RT) CEM via a recursive update equation in real time.

Wang, Yulei; Schultz, Robert; Chen, Shih-Yu; Liu, Chunhong; Chang, Chein-I.

2013-05-01

214

Equilibrium and transport properties of constrained systems  

NASA Astrophysics Data System (ADS)

Systems under external confinement and constraints often show interesting properties. In this thesis, we study some systems under external confinement. We begin by finding out the probability distribution of end-to-end separation of a Worm Like Chain (WLC) polymer whose ends are positionally (and orientationally) constrained. We use Monte-Carlo simulations (MC) and a theoretical mapping of the WLC to a quantum particle moving on the surface of an unit sphere to find multimodality in Helmholtz ensemble as a generic signature of semi-flexibility. Secondly, we study Laser Induced Freezing using a Kosterlitz-Thouless type renormalization group calculation and a restricted MC simulation to obtain phase diagrams for Hard Disk, Soft Disk and DLVO potentials. They show very good agreement with phase diagrams simulated by other groups. Lastly, we study the strain response and failure mechanism of a two-dimensional solid confined within a hard wall channel using MC and molecular dynamics simulations. We find a reversible plastic failure through solid-smectic coexistence and observe layering transitions. Mean field calculations can capture some of these features. We study the heat transport in this system thorugh nonequilibrium molecular dynamics simulations and find strong signatures of the transitions. We propose a simple free volume calculation that reproduces some qualitative features of the strain response of heat current for small strains.

Chaudhuri, Debasish

2006-10-01

215

Constrained Cosmological Simulations of Dark Matter Halos  

E-print Network

The formation and structure of dark matter (DM) halos is studied by means of constrained realizations of Gaussian fields using N-body simulations. A series of experiments of the formation of a 10^{12} Msun halo is designed to study the dependence of the density profile on its merging history. We confirm that the halo growth consists of violent and quiescent phases, with the density well approximated by the Navarro-Frenk-White (NFW) profile during the latter phases. We find that (1) the NFW scale radius R_s stays constant during the quiescent phase and grows abruptly during the violent one. In contrast, the virial radius grows linearly during the quiescent and abruptly during the violent phases. (2) The central density stays unchanged during the quiescent phase while dropping abruptly during the violent phase. (3) The value of \\rs reflects the violent merging history of the halo, and depends on the number of violent events and their fractional magnitudes, independent of the time and order of these events. It does not reflect the formation time of the halo. (4) The fractional change in R_s is a nonlinear function of the fractional absorbed kinetic energy within R_s in a violent event.

Emilio Romano-Diaz; Andreas Faltenbacher; Daniel Jones; Clayton Heller; Yehuda Hoffman; Isaac Shlosman

2005-08-11

216

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

217

Constraining the Oblateness of Kepler Planets  

E-print Network

We use Kepler short cadence light curves to constrain the oblateness of planet candidates in the Kepler sample. The transits of rapidly rotating planets that are deformed in shape will lead to distortions in the ingress and egress of their light curves. We report the first tentative detection of an oblate planet outside of the solar system, measuring an oblateness of $0.22 \\pm 0.11$ for the 18 $M_J$ mass brown dwarf Kepler 39b (KOI-423.01). We also provide constraints on the oblateness of the planets (candidates) HAT-P-7b, KOI-686.01, and KOI-197.01 to be 186, respectively. Using the Q'-values from Jupiter and Saturn, we expect tidal synchronization for the spins of HAT-P-7b, KOI-686.01 and KOI-197.01, and for their rotational oblateness signatures to be undetectable in the current data. The potentially large oblateness of KOI-423.01 (Kepler 39b) suggests that the Q'-value of the brown dwarf needs to be two orders of magnitude larger than that of the solar system gas giants ...

Zhu, Wei; Zhou, George; Lin, D N C

2014-01-01

218

Prior image constrained compressed sensing (PICCS)  

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

219

Constrained resistivity inversion using seismic data  

NASA Astrophysics Data System (ADS)

In this paper we describe and apply a method for constraining structure in anisotropic electrical resistivity inversion. Structural constraints are routinely used to achieve improved model inversion. Here, a second-order (curvature-based) regularization tensor (model covariance) is used to build structure in the model. This structure could be obtained from other imaging methods such as seismic tomography, core samples or otherwise known structure in the model. Our method allows the incorporation of existing geophysical data into the inversion, in a general form that does not rely on any one-to-one correlation between data sets or material properties. Ambiguities in the resistivity distribution from electrical inversion, and in particular anisotropic inversion, may be reduced with this approach. To demonstrate the approach we invert a synthetic data set, showing the regularization tensor explicitly in different locations. We then apply the method to field data where we have some knowledge of the subsurface from seismic imaging. Our results show that it is possible to achieve a high level of convergence while using spatially varying structural constraints. Common problems associated with resistivity inversion such as source/receiver effects and false imaging of strongly resistive or conductive zones may also be reduced. As part of the inversion method we show how the magnitude of the constraints in the form of penalty parameters appropriate to an inversion may be estimated, reducing the computational expense of resistivity inversion.

Saunders, J. H.; Herwanger, J. V.; Pain, C. C.; Worthington, M. H.; de Oliveira, C. R. E.

2005-03-01

220

Blockade of Lysosomal Acid Ceramidase Induces GluN2B-Dependent Tau Phosphorylation in Rat Hippocampal Slices  

PubMed Central

The lysosomal acid ceramidase, an enzyme known to limit intracellular ceramide accumulation, has been reported to be defective in neurodegenerative disorders. We show here that rat hippocampal slices, preincubated with the acid ceramidase inhibitor (ACI) d-NMAPPD, exhibit increased N-methyl-D-aspartate (NMDA) receptor-mediated field excitatory postsynaptic potentials (fEPSPs) in CA1 synapses. The ACI by itself did not interfere with either paired pulse facilitation or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-mediated fEPSPs, indicating that its influence on synaptic transmission is postsynaptic in origin and specific to the NMDA subtype of glutamate receptors. From a biochemical perspective, we observed that Tau phosphorylation at the Ser262 epitope was highly increased in hippocampal slices preincubated with the ACI, an effect totally prevented by the global NMDA receptor antagonist D/L(?)-2-amino-5-phosphonovaleric acid (AP-5), the calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N?,N?-tetraacetic acid (BAPTA), and the GluN2B (but not the GluN2A) receptor antagonist RO25-6981. On the other hand, preincubation of hippocampal slices with the compound KN-62, an inhibitor known to interfere with calcium/calmodulin-dependent protein kinase II (CaMKII), totally abolished the effect of ACI on Tau phosphorylation at Ser262 epitopes. Collectively, these results provide experimental evidence that ceramides play an important role in regulating Tau phosphorylation in the hippocampus via a mechanism dependent on GluN2B receptor subunits and CaMKII activation. PMID:25276436

Laurier-Laurin, Marie-Elaine; Attiori Essis, Suzanne; Cyr, Michel

2014-01-01

221

Folic Acid  

MedlinePLUS

Folic acid is used to treat or prevent folic acid deficiency. It is a B-complex vitamin needed by ... Folic acid comes in tablets. It usually is taken once a day. Follow the directions on your prescription label ...

222

Folic Acid  

MedlinePLUS

Folic acid is a B vitamin. It helps the body make healthy new cells. Everyone needs folic acid. For women who may get pregnant, it is really important. Getting enough folic acid before and during pregnancy can prevent major birth ...

223

Folic Acid  

MedlinePLUS

... acid Description Folic acid, or folate, is a B vitamin found in many beans, grains, fortified breakfast cereals, ... for use? Folic acid, or folate, is a B vitamin. It is promoted mainly as part of a ...

224

Stereochemically constrained complex organic molecules extracted from olivine crystal matrix  

NASA Astrophysics Data System (ADS)

Paradoxically, the dense solid state of magmatic minerals is a medium, in which organic synthesis can take place. The reason is that gas-fluid components such as H2O, CO/CO2/N2 and H2S are omnipresent in terrestrial magmatic environments. Any silicate mineral that crystallizes from such magmas will incorporate small quantities of the fluid-phase components in the form of structurally incompatible low-z impurities. During cooling the solute species undergo a redox conversion, resulting in chemically reduced low-z elements. To the extent that these low-z impurities are diffusively mobile, they will exsolve to the surface and/or to major structural defects inside the crystal matrix such as dislocations. Dislocations provide a 3-D structured environment, where the low-z impurities will tend to form stereochemically constrained polyatomic Cn-H-O-N-S entities, which we call organic protomolecules. In Nature, during weathering, such protomolecules will be released into the environment in the form of complex organic molecules. In our study we crush samples under clean conditions as a way to expose Cn-H-O-N-S entities at the fracture surfaces. We conduct identical experiments with selected large olivine single crystals, mm-sized olivine from peridiotite nodules from the San Carlos Volcanic Field, Arizona, and the vesiculated basalt that had carried the nodules upward in the volcanic conduit. We Soxhlet-extract the crushed powders with water, THF and ethyl acetate. The extracts are analyzed at the FTICR-MS facility at Florida State University using ultrahigh resolution Mass Spectrometry techniques capable of determining the chemical composition of the organic molecules up to 600 amu and more. So far we have found several analog sequences of oxygen-rich aliphatic hydrocarbons, families with up to 34 carbon atoms, probably poly-carboxylic acids, and some families containing sulfur.

Gerasimenko, I.; Freund, F. T.; Imanaka, H.; Rodgers, R.

2011-12-01

225

Coexpression of striatal dopamine receptor subtypes and excitatory amino acid subunits.  

PubMed

The striatal cellular coexpression patterns for the D(1A) and D2 dopamine (DA) receptor subtypes and the ionotropic excitatory amino acid (EAA) subunits of the N-methyl-D-aspartate (NMDA-R1) and the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) (GluR1 and GluR2/3) receptor subunits were examined morphologically. Their coincidence was assessed by visualization of mRNA transcripts, localization of encoded receptor proteins, and binding analysis using concurrently paired methods of fluorescence detection. The findings indicated that 1) mRNA transcripts for both receptor systems were detected in the medium-sized neuron population, and the distribution of receptor message closely reflected protein and binding patterns, with the exception of the GluR1 subunit; 2) both DA receptor mRNA transcripts were coexpressed with each ionotropic EAA receptor subunit examined and with each other, and NMDA and AMPA receptor subunits also showed coincident expression; 3) D(1A) DA receptor protein was detected in neurons which coexpressed EAA subunit proteins; and 4) GluR2/3 and NMDA-R1 subunit proteins were coexpressed in medium-sized neurons which also demonstrated D2 DA receptor binding sites. These findings suggest morphological receptor "promiscuity" since the coexpression patterns between DA and EAA receptors were found in all permutations. The results provide a spatial framework for physiological findings describing functional interactions between the two DA receptor types and between specific DA and EAA receptors in the striatum. PMID:9215599

Ariano, M A; Larson, E R; Noblett, K L; Sibley, D R; Levine, M S

1997-08-01

226

Constraining the Evolution of Poor Clusters  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

227

Constrained layer damping of a tennis racket  

NASA Astrophysics Data System (ADS)

When a tennis ball strikes a racket the impact causes vibrations which are distracting and undesirable to the player. In this work a passive damping system used to reduce vibration is described. The damping system uses a viscoelastic material along with a stiff composite constraining layer which is molded on the inner surface of the tennis racket frame. When a ball strikes a racket with this damping system the vibration causes shearing strain in the viscoelastic material. This strain energy is partially dissipated by the viscoelastic material, thereby increasing the racket damping. An analysis of the design was performed by creating a solid CAD model of the racket using Pro/Engineer. A finite element mesh was created and the mesh was then exported to ANSYS for the finite element modal analysis. The technique used to determine the damping ratio is the modal strain energy method. Experimental testing using accelerometers was conducted to determine the natural frequency and the damping ratio of rackets with and without the damping system. The natural frequency of the finite element model was benchmarked to the experimental data and damping ratios were compared. The modal strain energy method was found to be a very effective means of determining the damping ratio, and the frequencies and damping ratios correlated well with the experimental data. Using this analysis method, the effectiveness of the damping ratio to the change in key variables can be studied, minimizing the need for prototypes. This method can be used to determine an optimum design by maximizing the damping ratio with minimal weight addition.

Harms, Michael R.; Gopal, H. S.; Lai, Ming-Lai; Cheng, Po-Jen

1996-05-01

228

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

229

The cost-constrained traveling salesman problem  

SciTech Connect

The Cost-Constrained Traveling Salesman Problem (CCTSP) is a variant of the well-known Traveling Salesman Problem (TSP). In the TSP, the goal is to find a tour of a given set of cities such that the total cost of the tour is minimized. In the CCTSP, each city is given a value, and a fixed cost-constraint is specified. The objective is to find a subtour of the cities that achieves maximum value without exceeding the cost-constraint. Thus, unlike the TSP, the CCTSP requires both selection and sequencing. As a consequence, most results for the TSP cannot be extended to the CCTSP. We show that the CCTSP is NP-hard and that no K-approximation algorithm or fully polynomial approximation scheme exists, unless P = NP. We also show that several special cases are polynomially solvable. Algorithms for the CCTSP, which outperform previous methods, are developed in three areas: upper bounding methods, exact algorithms, and heuristics. We found that a bounding strategy based on the knapsack problem performs better, both in speed and in the quality of the bounds, than methods based on the assignment problem. Likewise, we found that a branch-and-bound approach using the knapsack bound was superior to a method based on a common branch-and-bound method for the TSP. In our study of heuristic algorithms, we found that, when selecting modes for inclusion in the subtour, it is important to consider the neighborhood'' of the nodes. A node with low value that brings the subtour near many other nodes may be more desirable than an isolated node of high value. We found two types of repetition to be desirable: repetitions based on randomization in the subtour buildings process, and repetitions encouraging the inclusion of different subsets of the nodes. By varying the number and type of repetitions, we can adjust the computation time required by our method to obtain algorithms that outperform previous methods.

Sokkappa, P.R.

1990-10-01

230

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

231

Folding of Small Proteins Using Constrained Molecular Dynamics  

PubMed Central

The focus of this paper is to examine whether conformational search using constrained molecular dynamics (MD) method is more enhanced and enriched towards “native-like” structures compared to all-atom MD for the protein folding as a model problem. Constrained MD methods provide an alternate MD tool for protein structure prediction and structure refinement. It is computationally expensive to perform all-atom simulations of protein folding because the processes occur on a timescale of microseconds. Compared to the all-atom MD simulation, constrained MD methods have the advantage that stable dynamics can be achieved for larger time steps and the number of degrees of freedom is an order of magnitude smaller, leading to a decrease in computational cost. We have developed a generalized constrained MD method that allows the user to “freeze and thaw” torsional degrees of freedom as fit for the problem studied. We have used this method to perform all-torsion constrained MD in implicit solvent coupled with the replica exchange method to study folding of small proteins with various secondary structural motifs such as, ?-helix (polyalanine, WALP16), ?-turn (1E0Q), and a mixed motif protein (Trp-cage). We demonstrate that constrained MD replica exchange method exhibits a wider conformational search than all-atom MD with increased enrichment of near native structures. “Hierarchical” constrained MD simulations, where the partially formed helical regions in the initial stretch of the all-torsion folding simulation trajectory of Trp-cage were frozen, showed a better sampling of near native structures than all-torsion constrained MD simulations. This is in agreement with the zipping-and-assembly folding model put forth by Dill and coworkers for folding proteins. The use of hierarchical “freeze and thaw” clustering schemes in constrained MD simulation can be used to sample conformations that contribute significantly to folding of proteins. PMID:21591767

Balaraman, Gouthaman S.; Park, In-Hee; Jain, Abhinandan; Vaidehi, Nagarajan

2011-01-01

232

Acid Rain.  

ERIC Educational Resources Information Center

Provides some background information on acid deposition. Includes a historical perspective, describes some effects of acid precipitation, and discusses acid rain in the United Kingdom. Contains several experiments that deal with the effects of acid rain on water quality and soil. (TW)

Openshaw, Peter

1987-01-01

233

Acid rain  

Microsoft Academic Search

Acid precipitation includes not only rain but also acidified snow, hail and frost, as well as sulfur and nitrogen dust. The principal source of acid precipitation is pollution emitted by power plants and smelters. Sulfur and nitrogen compounds contained in the emissions combine with moisture to form droplets with a high acid content - sometimes as acidic as vinegar. When

1980-01-01

234

Constraining duty cycles through a Bayesian technique  

NASA Astrophysics Data System (ADS)

The duty cycle (DC) of astrophysical sources is generally defined as the fraction of time during which the sources are active. It is used to both characterize their central engine and to plan further observing campaigns to study them. However, DCs are generally not provided with statistical uncertainties, since the standard approach is to perform Monte Carlo bootstrap simulations to evaluate them, which can be quite time consuming for a large sample of sources. As an alternative, considerably less time-consuming approach, we derived the theoretical expectation value for the DC and its error for sources whose state is one of two possible, mutually exclusive states, inactive (off) or flaring (on), as based on a finite set of independent observational data points. Following a Bayesian approach, we derived the analytical expression for the posterior, the conjugated distribution adopted as prior, and the expectation value and variance. We applied our method to the specific case of the inactivity duty cycle (IDC) for supergiant fast X-ray transients, a subclass of flaring high mass X-ray binaries characterized by large dynamical ranges. We also studied IDC as a function of the number of observations in the sample. Finally, we compare the results with the theoretical expectations. We found excellent agreement with our findings based on the standard bootstrap method. Our Bayesian treatment can be applied to all sets of independent observations of two-state sources, such as active galactic nuclei, X-ray binaries, etc. In addition to being far less time consuming than bootstrap methods, the additional strength of this approach becomes obvious when considering a well-populated class of sources (Nsrc ? 50) for which the prior can be fully characterized by fitting the distribution of the observed DCs for all sources in the class, so that, through the prior, one can further constrain the DC of a new source by exploiting the information acquired on the DC distribution derived from the other sources. R-Language, IDL, and C-language programs are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A97

Romano, P.; Guidorzi, C.; Segreto, A.; Ducci, L.; Vercellone, S.

2014-12-01

235

Resource constrained scheduling problem at U.S. Naval Shipyards  

E-print Network

Submarine repair schedules are some of the most complex schedules seen in project management. Repairs of a nuclear U.S. submarine are resource constrained since resources are divided among approximately thirty shops (e.g. ...

Nawara, Terrence M. (Terrence Michael)

2013-01-01

236

Constrained Density-Functional Theory--Configuration Interaction  

E-print Network

In this thesis, I implemented a method for performing electronic structure calculations, "Constrained Density Functional Theory-- Configuration Interaction" (CDFT-CI), which builds upon the computational strengths of Density ...

Kaduk, Benjamin James

2012-01-01

237

On the modified constrained Kadomtsev-Petviashvili equations  

NASA Astrophysics Data System (ADS)

Three reduction sub-hierarchies in constrained KP hierarchies are studied. The corresponding matrix integrable systems are presented. Furthermore, Bäcklund transformations, bi-Hamiltonian structures, and ?-functions are formulated.

Wu, Zhiwei

2012-10-01

238

Decomposition Algorithms for Two-Stage Chance-Constrained ...  

E-print Network

Mar 1, 2014 ... Computational results on a chance-constrained resource planing problem indicate ...... Tables 3 and 4 highlight the benefits of obtaining strong opti- ..... 5th IEEE/ACM International Conference on Utility and Cloud Computing.

2014-08-11

239

Local Search for Hop-constrained Directed Steiner Tree Problem ...  

E-print Network

For the hop-constrained DSTP, we propose local search strategies aimed at ...... relatively inexpensive miniature vehicles with limited communication range. Fur- ... arbitrary measures for evaluating the suitability of positions for UAV placement.

2014-08-20

240

Constraining climate model properties using optimal fingerprint detection methods  

E-print Network

We present a method for constraining key properties of the climate system that are important for climate prediction (climate sensitivity and rate of heat penetration into the deep ocean) by comparing a model's response to ...

Forest, Chris Eliot.; Allen, Myles R.; Sokolov, Andrei P.; Stone, Peter H.

241

Constraining North Atlantic circulation with transient tracer observations  

E-print Network

The capability of transient tracers to constrain the ocean circulation in the North Atlantic is explored. Study of an idealized tracer shows that inferences of circulation properties from transient state distributions are ...

Li, Xingwen, 1968-

2003-01-01

242

Constrained minimization of smooth functions using a genetic algorithm  

NASA Technical Reports Server (NTRS)

The use of genetic algorithms for minimization of differentiable functions that are subject to differentiable constraints is considered. A technique is demonstrated for converting the solution of the necessary conditions for a constrained minimum into an unconstrained function minimization. This technique is extended as a global constrained optimization algorithm. The theory is applied to calculating minimum-fuel ascent control settings for an energy state model of an aerospace plane.

Moerder, Daniel D.; Pamadi, Bandu N.

1994-01-01

243

The use of a constrained acetabular component for recurrent dislocation  

Microsoft Academic Search

The poor results of surgical treatment of chronic instability after total hip arthroplasty (THA) led to the development of a constrained acetabular component. In this study, 87 constrained THAs implanted for recurrent instability were reviewed retrospectively. Eighty-five hips were available for follow-up evaluation, with an average follow-up period of 58 months. These 85 hips were evaluated at a minimum of

Gary S. Shapiro; Daniel E. Weiland; David C. Markel; Douglas E. Padgett; Thomas P. Sculco; Paul M. Pellicci

2003-01-01

244

Synthesis of conformationally constrained benzoylureas as BH3-mimetics.  

PubMed

The design of small molecules that mimic the BH3 domain and bind to Bcl-2 proteins has emerged as a promising approach to discovering novel anti-cancer therapeutics. We reveal the design and synthesis of conformationally constrained benzoylurea scaffolds as conformational probes. Central to helix mimicry, the intramolecular hydrogen bond in the benzoylurea plays a key role in the pre-organisation of the acyclic substrates for cyclisation via ring closing metathesis, providing efficient access to the constrained mimetics. PMID:22648632

Brady, Ryan M; Hatzis, Effie; Connor, Theresa; Street, Ian P; Baell, Jonathan B; Lessene, Guillaume

2012-07-21

245

Mantle Convection Models Constrained by Seismic Tomography  

NASA Astrophysics Data System (ADS)

Although available three dimensional models of the lateral heterogeneity of the mantle, based upon the latest advances in seismic tomographic imaging (e.g. Ritsema et al., 2004, JGR) have provided profound insights into aspects of the mantle general circulation that drives continental drift, the compatibility of the tomography with explicit models of mantle mixing has remained illusive. For example, it remains a significant issue as to whether hydrodynamic models of the mixing process alone are able to reconcile the observed detailed pattern of surface plate velocities or whether explicit account must be taken of elastic fracture processes to account for the observed equipartition of kinetic energy between the poloidal and toroidal components of the surface velocity pattern (e.g. Forte and Peltier, 1987, JGR). It is also an issue as to the significance of the role of mantle chemical heterogeneity in determining the buoyancy distribution that drives mantle flow, especially given the expected importance of the spin transition of iron that onsets in the mid-lower mantle, at least in the ferropericlase component of the mineralogy. In this paper we focus upon the application of data assimilation techniques to the development of a model of mantle mixing that is consistent with a modern three dimensional tomography based model of seismic body wave heterogeneity. Beginning with the simplest possible scenario, that chemical heterogeneity is irrelevant to first order, we employ a three dimensional version of the recently published control volume based convection model of Shahnas and Peltier (2010, JGR) as the basis for the assimilation of a three dimensional density field inferred from our preferred tomography model (Ritsema et al., 2004, JGR). The convection model fully incorporates the dynamical influence of the Olivine-Spinel and Spinel-Perovskite+Magnesiowustite solid-solid phase transformations that bracket the mantle transition zone as well as the recently discovered Perovskite-post-Perovskite transition (Murakami et al., 2004, Science) that appears to define the D" layer at the base of the mantle. In this initial phase of what will be a longer term project we are assuming that the internal mantle viscosity structure is spherically symmetric and compatible with the recent inferences of Peltier and Drummond (2010, Geophys. Res. Lett.) based upon glacial isostatic adjustment and Earth rotation constraints. The internal density structure inferred from the tomography model is assimilated into the convection model by continuously "nudging" the modification to the input density structure predicted by the convection model back towards the tomographic constraint at the long wavelengths that the tomography specifically resolves, leaving the shorter wavelength structure free to evolve, essentially "slaved" to the large scale structure. We focus upon the ability of the nudged model to explain observed plate velocities, including both their poloidal (divergence related) and toroidal (strike slip fault related) components. The true plate velocity field is then used as an additional field towards which the tomographically constrained solution is nudged.

Durbin, C. J.; Shahnas, M.; Peltier, W. R.; Woodhouse, J. H.

2011-12-01

246

Constrained layer damping treatments with actively enhanced actions  

NASA Astrophysics Data System (ADS)

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

Liu, Yanning

2001-11-01

247

Aminocaproic Acid  

MedlinePLUS

Aminocaproic acid is used to control bleeding that occurs when blood clots are broken down too quickly. This type ... the baby is ready to be born). Aminocaproic acid is also used to control bleeding in the ...

248

Ethacrynic Acid  

MedlinePLUS

Ethacrynic acid, a 'water pill,' is used to treat swelling and fluid retention caused by various medical problems. It ... Ethacrynic acid comes as a tablet to take by mouth. It is usually taken once or twice a day ...

249

Mefenamic Acid  

MedlinePLUS

Mefenamic acid is used to relieve mild to moderate pain, including menstrual pain (pain that happens before or during a menstrual period). Mefenamic acid is in a class of medications called NSAIDs. ...

250

Soil phosphorus constrains biodiversity across European grasslands.  

PubMed

Nutrient pollution presents a serious threat to biodiversity conservation. In terrestrial ecosystems, the deleterious effects of nitrogen pollution are increasingly understood and several mitigating environmental policies have been developed. Compared to nitrogen, the effects of increased phosphorus have received far less attention, although some studies have indicated that phosphorus pollution may be detrimental for biodiversity as well. On the basis of a dataset covering 501 grassland plots throughout Europe, we demonstrate that, independent of the level of atmospheric nitrogen deposition and soil acidity, plant species richness was consistently negatively related to soil phosphorus. We also identified thresholds in soil phosphorus above which biodiversity appears to remain at a constant low level. Our results indicate that nutrient management policies biased toward reducing nitrogen pollution will fail to preserve biodiversity. As soil phosphorus is known to be extremely persistent and we found no evidence for a critical threshold below which no environmental harm is expected, we suggest that agro-environmental schemes should include grasslands that are permanently free from phosphorus fertilization. PMID:24895112

Ceulemans, Tobias; Stevens, Carly J; Duchateau, Luc; Jacquemyn, Hans; Gowing, David J G; Merckx, Roel; Wallace, Hilary; van Rooijen, Nils; Goethem, Thomas; Bobbink, Roland; Dorland, Edu; Gaudnik, Cassandre; Alard, Didier; Corcket, Emmanuel; Muller, Serge; Dise, Nancy B; Dupré, Cecilia; Diekmann, Martin; Honnay, Olivier

2014-12-01

251

Shikimic Acid  

NSDL National Science Digital Library

The molecule for this month comes from the article Isolation of Shikimic Acid from Star Aniseed by Richard Payne and Michael Edmonds. Shikimic acid plays a key role in the biosynthesis of many important natural products including aromatic amino acids, alkaloids, phenolics, and phenylpropanoids. It plays such an important role that one of the key biosynthetic pathways is referred to as the shikimate pathway.

252

Acid rain  

Microsoft Academic Search

The acid rain problem in the northeastern U.S. has been growing in severity and geographical areas affected. Acid rain has damaged, or will result in damage to visibility, physical structures and materials, aquatic life, timber, crops, and soils. The principal causes of acid rain in the northeastern U.S. are sulfur oxide and nitrogen oxide emissions from large power plants and

1980-01-01

253

Ultrastructural and biochemical studies on the neuroprotective effects of excitatory amino acid antagonists in the ischemic rat retina.  

PubMed

The effects of glutamate receptor agonists were evaluated, by utilizing the electron microscope, in a photothrombotic occlusion model of rat retinal vessels in order to study the ischemic damage and its antagonism in each morphologically identified population of retinal neurons. Rats were systemically injected with rose bengal fluorescein dye and one of their eyes was then exposed to bright light. This treatment caused neuronal damage and reduced the activities of the neuronal marker enzymes, choline acetyltransferase and glutamate decarboxylase, by approximately 75%. A single intravitreal injection of 2,3-dihydroxy-6-nitro-7-sulfamoylbenzoquinoxaline (NBQX, 10-50 nmol), an antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors, or of thiokynurenate (100-400 nmol), which also antagonizes N-methyl-D-aspartate (NMDA) receptors, performed immediately after the lesion, significantly reduced this loss. The electron microscope examination showed major damage in each type of retinal neuron, the pigment epithelium, and the microvessels. NBQX or thiokynurenic acid reduced, in a comparable manner, the effects of ischemia on the pigment epithelium, the photoreceptors, and the bipolar and the horizontal cells. NBQX was particularly efficient in reducing the damage to the amacrine cells located in the inner nuclear layer. The displaced amacrine and ganglion cells were not protected by NBQX but were almost completely spared in animals treated with thiokynurenate. These results show that antagonism of AMPA receptors is sufficient to reduce ischemic damage in a large number of retinal neurons, but that neuroprotection in the ganglion cell layer may be obtained only with agents which also antagonize NMDA receptors. PMID:9270053

Matini, P; Moroni, F; Lombardi, G; Faussone-Pellegrini, M S; Moroni, F

1997-08-01

254

Trilogy-Constrained Acetabular Component for Recurrent Dislocation  

PubMed Central

32 patients received a Trilogy- or Trilogy-Longevity-constrained acetabular liner for recurrent dislocations after total hip replacement. The constrained liner was inserted into a well-fixed Trilogy acetabular shell with snap fit. At 1.8-year followup (range 3–63 months), 4 patients had suffered further dislocation(s) (12%), and one patient had revision surgery for a loosened acetabular shell. Radiologic evaluation detected no definitively loose components, but one patient with progressing radiolucent lines around the femoral component and one patient with an acetabular cyst were found, as well as a patient with a loose locking ring (but otherwise no failure). The nineteen patients who were available for the present followup had a mean Harris Hip Score of 81. The constrained liner is an effective method of dealing with recurrent dislocations in well-fixed components. PMID:24967111

Andersen, Annette Vest; Kjersgaard, Anne Grete; Solgaard, Søren

2013-01-01

255

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

256

PDE-constrained optimization with error estimation and control  

NASA Astrophysics Data System (ADS)

The paper describes an algorithm for PDE-constrained optimization that controls numerical errors using error estimates and grid adaptation during the optimization process. A key aspect of the algorithm is the use of adjoint variables to estimate errors in the first-order optimality conditions. Multilevel optimization is used to drive the optimality conditions and their estimated errors below a specified tolerance. The error estimate requires two additional adjoint solutions, but only at the beginning and end of each optimization cycle. Moreover, the adjoint systems can be formed and solved with limited additional infrastructure beyond that found in typical PDE-constrained optimization algorithms. The approach is general and can accommodate both reduced-space and full-space formulations of the optimization problem. The algorithm is illustrated using the inverse design of a nozzle constrained by the quasi-one-dimensional Euler equations.

Hicken, J. E.; Alonso, J. J.

2014-04-01

257

Constrained modes in control theory - Transmission zeros of uniform beams  

NASA Technical Reports Server (NTRS)

Mathematical arguments are presented demonstrating that the well-established control system concept of the transmission zero is very closely related to the structural concept of the constrained mode. It is shown that the transmission zeros of a flexible structure form a set of constrained natural frequencies for it, with the constraints depending explicitly on the locations and the types of sensors and actuators used for control. Based on this formulation, an algorithm is derived and used to produce dimensionless plots of the zero of a uniform beam with a compatible sensor/actuator pair.

Williams, T.

1992-01-01

258

Pseudo-updated constrained solution algorithm for nonlinear heat conduction  

NASA Technical Reports Server (NTRS)

This paper develops efficiency and stability improvements in the incremental successive substitution (ISS) procedure commonly used to generate the solution to nonlinear heat conduction problems. This is achieved by employing the pseudo-update scheme of Broyden, Fletcher, Goldfarb and Shanno in conjunction with the constrained version of the ISS. The resulting algorithm retains the formulational simplicity associated with ISS schemes while incorporating the enhanced convergence properties of slope driven procedures as well as the stability of constrained approaches. To illustrate the enhanced operating characteristics of the new scheme, the results of several benchmark comparisons are presented.

Tovichakchaikul, S.; Padovan, J.

1983-01-01

259

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

260

Hybrid functions approach for nonlinear constrained optimal control problems  

NASA Astrophysics Data System (ADS)

In this paper, a new numerical method for solving the nonlinear constrained optimal control with quadratic performance index is presented. The method is based upon hybrid functions approximation. The properties of hybrid functions consisting of block-pulse functions and Bernoulli polynomials are presented. The operational matrix of integration is introduced. This matrix is then utilized to reduce the solution of the nonlinear constrained optimal control to a nonlinear programming one to which existing well-developed algorithms may be applied. Illustrative examples are included to demonstrate the validity and applicability of the technique.

Mashayekhi, S.; Ordokhani, Y.; Razzaghi, M.

2012-04-01

261

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

262

Failure of a constrained acetabular liner without reinforcement ring disruption.  

PubMed

Several risk factors for dislocation after total hip arthroplasty (THA) have been identified including operative-, patient-, and implant-related factors. The following case report describes the dislocation of a revision THA without disruption of the constrained liner or containment ring. The possible mechanisms leading to this type of failure include lever-out impingement and poor abductor function, or tension secondary to prior surgery. Dislocation without disruption of containment ring has not been described for the Pinnacle Acetabular Cup with the Enhanced Stability Constrained Liner (DePuy Orthopaedics, Warsaw, Indiana). PMID:24471147

Arthur, Jeffrey A; Amanatullah, Derek F; Kennedy, Gannon D; Di Cesare, Paul E

2013-12-01

263

Distribution on contingency of alignment of two literal sequences under constrains.  

PubMed

The case of ungapped alignment of two literal sequences under constrains is considered. The analysis lead to general formulas for probability mass function and cumulative distribution function for the general case of using an alphabet with a chosen number of letters (e.g. 4 for deoxyribonucleic acid sequences) in the expression of the literal sequences. Formulas for three statistics including mean, mode, and standard deviation were obtained. Distributions are depicted for three important particular cases: alignment on binary sequences, alignment of trinomial series (such as coming from generalized Kronecker delta), and alignment of genetic sequences (with four literals in the alphabet). A particular case when sequences contain each letter of the alphabet at least once in both sequences has also been analyzed and some statistics for this restricted case are given. PMID:25524134

Jäntschi, Lorentz; Bolboac?, Sorana D

2015-03-01

264

Basically Acids  

NSDL National Science Digital Library

Students learn the basics of acid/base chemistry in a fun, interactive way by studying instances of acid/base chemistry found in popular films such as Harry Potter and the Prisoner of Azkaban and National Treasure. Students learn what acids, bases and indicators are and how they can be used, including invisible ink. They also learn how engineers use acids and bases every day to better our quality of life. Students' interest is piqued by the use of popular culture in the classroom.

University of Houston,

265

Excitatory amino acid-receptor-mediated EPSPs in rat dorsolateral septal nucleus neurones in vitro.  

PubMed Central

1. Intracellular recordings were made from rat dorsolateral septal nucleus (DLSN) neurones in vitro. We investigated depolarizations resulting from pressure application of excitatory amino acids and compared these to synaptically evoked excitatory postsynaptic potentials (EPSPs). 2. EPSPs evoked by focal fimbrial afferent stimulation in saline with 30-50 microM-bicuculline and 1.2 mM-Mg2+ yielded a linear amplitude-voltage relationship: their reversal potential was -3 mV. These EPSPs exhibited little sensitivity to 2-amino-5-phosphonopentanoate (APV), an N-methyl-D-aspartate(NMDA)-receptor-specific antagonist, but were markedly depressed by kynurenic acid, a broad-spectrum excitatory amino acid antagonist. 3. In Mg2(+)-free solution, the amplitude and the duration of EPSPs were increased markedly masking the following inhibitory postsynaptic potential (IPSP) and the late hyperpolarizing potential (LHP). These facilitated and broadened EPSPs were sensitive to APV or Mg2+. The APV or Mg2(+)-sensitive component of the EPSP obtained by digital subtraction suggests a slower time course for the NMDA-receptor-mediated EPSP compared to the non-NMDA-receptor-mediated EPSP. On the other hand, in normal Mg2+ solution an EPSP evoked by either a single strong stimulus or by repetitive stimuli had APV-sensitive components. 4. The depolarizing potentials induced by pressure application of glutamate, kainate, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), quisqualate or NMDA were compared. The amplitude-voltage relationship of depolarizations induced by NMDA obtained in a normal Mg2+ solution was non-linear, but approached linearity when the same responses were recorded in a Mg2(+)-free solution. Depolarizations induced by kainate, AMPA and quisqualate were linear in their amplitude-voltage relationship in the presence or absence of Mg2+. APV blocked NMDA-induced depolarizations specifically, while kynurenic acid blocked all the depolarizations induced by NMDA, quisqualate, or kainate. 5. Our data demonstrate the existence of NMDA-receptor-mediated synaptic potentials in the rat DLSN, the characteristics of which are similar to those in other central nervous system regions. PMID:2576066

Gallagher, J P; Hasuo, H

1989-01-01

266

The role of amino acid neurotransmitters in the regulation of pituitary gonadotropin release in fish.  

PubMed

Both glutamate and gamma-aminobutyric acid (GABA) are involved in pituitary hormone release in fish. Glutamate serves 2 purposes, both as a neurotransmitter and as a precursor for GABA synthesis. Glutamate can be catabolized to GABA by the actions of 2 distinct but related enzymes, glutamate decarboxylase 65 (GAD65) and GAD67. They derive from 2 different genes that likely arose from an early gene duplication prior to the emergence of teleosts more than 400 million years ago. There is good evidence for the involvement of GABA in luteinizing hormone (LH) release in fish. The mechanism of GABA action to stimulate LH release appears to be a combination of effects on GnRH release, potentiation of gonadotropin hormone-releasing hormone (GnRH) action, and in some cases directly at the LH cell. These actions appear to be dependent on such factors as sex or sex steroid levels, and there may also be species differences. Nevertheless, the stimulatory effects of GABA on LH are present in at least 4 fish species. In contrast, convincing data for the inhibitory effects of GABA on LH release have only been observed in 1 fish species. The sites and mechanisms of action of amino acid neurotransmitters on LH release have yet to be fully characterized. Both 130N-methyl-D-aspartic acid (NMDA) and S-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamate receptors are likely to have important roles. We suggest that it is a receptor similar to the GABA(A) type which mediates the effects of GABA on LH release in fish, at least partially acting on the GnRH neuron, but likely directly acting at the gonadotroph as well. GABA may also be involved in regulating the release of other pituitary hormones in fish, namely follicle stimulating hormone (FSH = GTH-I), prolactin, and growth hormone. Based on the findings described in this review, a working model for the involvement of glutamate and GABA in the regulation of LH release in teleost fish is proposed. PMID:10949077

Trudeau, V L; Spanswick, D; Fraser, E J; Larivière, K; Crump, D; Chiu, S; MacMillan, M; Schulz, R W

2000-01-01

267

Glutamate release evoked by glutamate receptor agonists in cultured chick retina cells: modulation by arachidonic acid.  

PubMed

We studied the effect of ionotropic glutamate receptor agonists on the release of endogenous glutamate or of [3H]D-aspartate from reaggregate cultures (retinospheroids) or from monolayer cultures of chick retinal cells, respectively. Kainate increased the fluorescence ratio of the Na+ indicator SBFI and stimulated a dose-dependent release of glutamate in low (0.1 mM) Ca2+ medium, as measured using a fluorometric assay. Under the same experimental conditions, the release evoked by N-methyl-D-aspartate (NMDA; 400 microM) was about half of that evoked by the same kainate concentration; alpha-amino-3-hydroxy-5-methyl-4-isoxasolepropionic acid (AMPA; 400 microM) did not trigger a significant response. In the presence of 1 mM CaCl2, all of the agonists increased the [Ca2+]i, as determined with the fluorescence dye Indo-1, but the glutamate release evoked by NMDA and kainate was significantly lower than that measured in 0.1 mM CaCl2 medium. Inhibition by Ca2+ of the kainate-stimulated release of glutamate was partially reversed by the phospholipase A2 inhibitor oleiloxyethyl phosphorylcholine (OPC), suggesting that the effect was mediated by the release of arachidonic acid, which inhibits the glutamate carrier. Accordingly, kainate, NMDA, and AMPA stimulated a Ca(2+)-dependent release of [3H]arachidonic acid, and the direct addition of the exogenous fatty acid to the medium decreased the release of glutamate evoked by kainate in low (0.1 mM) CaCl2 medium. In monolayer cultures, we showed that NMDA, kainate, and AMPA also stimulated the release of [3H]D-aspartate, but in this case release in the presence of 1 mM CaCl2 was significantly higher than that evoked in media with no added Ca2+. The ranking order of efficacy for stimulation of Ca(2+)-dependent release of [3H]D-aspartate was NMDA > > kainate > AMPA. PMID:8739156

Duarte, C B; Santos, P F; Sánchez-Prieto, J; Carvalho, A P

1996-05-15

268

How well can future CMB missions constrain cosmic inflation?  

NASA Astrophysics Data System (ADS)

We study how the next generation of Cosmic Microwave Background (CMB) measurement missions (such as EPIC, LiteBIRD, PRISM and COrE) will be able to constrain the inflationary landscape in the hardest to disambiguate situation in which inflation is simply described by single-field slow-roll scenarios. Considering the proposed PRISM and LiteBIRD satellite designs, we simulate mock data corresponding to five different fiducial models having values of the tensor-to-scalar ratio ranging from 10-1 down to 10-7. We then compute the Bayesian evidences and complexities of all Encyclopædia Inflationaris models in order to assess the constraining power of PRISM alone and LiteBIRD complemented with the Planck 2013 data. Within slow-roll inflation, both designs have comparable constraining power and can rule out about three quarters of the inflationary scenarios, compared to one third for Planck 2013 data alone. However, we also show that PRISM can constrain the scalar running and has the capability to detect a violation of slow roll at second order. Finally, our results suggest that describing an inflationary model by its potential shape only, without specifying a reheating temperature, will no longer be possible given the accuracy level reached by the future CMB missions.

Martin, Jérôme; Ringeval, Christophe; Vennin, Vincent

2014-10-01

269

Ant colony optimization for resource-constrained project scheduling  

Microsoft Academic Search

An ant colony optimization approach (ACO) for the resource-constrained project schedul- ing problem (RCPSP) is presented. Combi- nations of two pheromone evaluation meth- ods are used by the ants to find new solutions. We tested our ACO algorithm on a set of large benchmark problems from the PSPLIB. Compared to several other heuristics for the RCPSP including genetic algorithms, simu-

Daniel Merkle; Martin Middendorf; Hartmut Schmeck

2002-01-01

270

Experimental comparison of piezoelectric and constrained-layer damping  

NASA Astrophysics Data System (ADS)

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 shunt. Previous research has applied the piezoelectric absorber to one-dimensional structures. This paper applies the absorber to a two-dimensional planar problem. The simple mathematical description of the absorber is modified for the two-dimensional problem. An analytical means of estimating the effectiveness of the piezoelectric absorber is derived. The effectiveness is estimated for an electronics chassis box subjected to random excitation. A typical constrained layer damping treatment is also analytically designed for the problem. The piezoelectric absorber and the constrained layer damping treatment are experimentally applied to identical boxes. Results show that the piezoelectric absorber can provide vibration suppression comparable to that obtained by the constrained layer damping treatment.

Hollkamp, Joseph J.; Gordon, Robert W.

1995-05-01

271

Inferring meaningful communities from topology-constrained correlation networks.  

PubMed

Community structure detection is an important tool in graph analysis. This can be done, among other ways, by solving for the partition set which optimizes the modularity scores [Formula: see text]. Here it is shown that topological constraints in correlation graphs induce over-fragmentation of community structures. A refinement step to this optimization based on Linear Discriminant Analysis (LDA) and a statistical test for significance is proposed. In structured simulation constrained by topology, this novel approach performs better than the optimization of modularity alone. This method was also tested with two empirical datasets: the Roll-Call voting in the 110th US Senate constrained by geographic adjacency, and a biological dataset of 135 protein structures constrained by inter-residue contacts. The former dataset showed sub-structures in the communities that revealed a regional bias in the votes which transcend party affiliations. This is an interesting pattern given that the 110th Legislature was assumed to be a highly polarized government. The [Formula: see text]-amylase catalytic domain dataset (biological dataset) was analyzed with and without topological constraints (inter-residue contacts). The results without topological constraints showed differences with the topology constrained one, but the LDA filtering did not change the outcome of the latter. This suggests that the LDA filtering is a robust way to solve the possible over-fragmentation when present, and that this method will not affect the results where there is no evidence of over-fragmentation. PMID:25409022

Hleap, Jose Sergio; Blouin, Christian

2014-01-01

272

SNOPT: An SQP Algorithm For Large-Scale Constrained Optimization  

Microsoft Academic Search

. Sequential quadratic programming (SQP) methods have proved highly effective forsolving constrained optimization problems with smooth nonlinear functions in the objective andconstraints. Here we consider problems with general inequality constraints (linear and nonlinear).We assume that first derivatives are available, and that the constraint gradients are sparse.We discuss an SQP algorithm that uses a smooth augmented Lagrangian merit function andmakes explicit

Philip E. Gill; Walter Murray; Michael A. Saunders

1997-01-01

273

Vestibuloocular reflex arc analysis using an experimentally constrained neural network  

Microsoft Academic Search

The primary function of the vestibuloocular reflex (VOR) is to maintain the stability of retinal images during head movements. This function is expressed through a complex array of dynamic and adaptive characteristics whose essential physiological basis is a disynaptic arc. We present a model of normal VOR function using a simple neural network architecture constrained by the physiological and anatomical

K. J. Quinn; Nestor A. Schmajuk; A. Jain; J. F. Baker; B. W. Peterson

1992-01-01

274

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

275

Control of Constrained Discrete-Time Systems With Bounded Gain  

Microsoft Academic Search

We consider the problem of designing a control law for a constrained linear system with bounded disturbances that ensures constraint satisfaction over an infinite horizon, while also guaranteeing that the closed-loop system has bounded lscr2 gain. To this end, we propose a receding horizon control strategy based on the repeated calculation of optimal finite horizon feedback policies. We parameterize these

Paul J. Goulart; Eric C. Kerrigan; Teodoro Alamo

2009-01-01

276

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

277

Mechanized Safety Proofs for Disc-Constrained Aircraft  

E-print Network

Mechanized Safety Proofs for Disc-Constrained Aircraft David Renshaw Sarah M. Loos Andr´e Platzer, formal verification. #12;1 Introduction Safety-critical systems such as aircraft controllers must between aircraft to increase throughput, and on-board collision avoidance systems become ever more

278

A new constrained edit distance between quotiented ordered trees  

Microsoft Academic Search

In this paper we propose a dynamic programming algorithm to compare two quo- tiented ordered trees using a constrained edit distance. An ordered tree is a tree in which the left-to-right order among siblings is significant. A quotiented ordered tree is an ordered tree T with an equivalence relation on vertices and such that, when the equivalence classes are collapsed

Aïda Ouangraoua; Pascal Ferraro

2009-01-01

279

An experimental comparison of piezoelectric and constrained layer damping  

NASA Astrophysics Data System (ADS)

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 shunt. Previous research has applied the piezoelectric absorber to one-dimensional structures. This paper applies the absorber to a two-dimensional planar problem. The simple mathematical description of the absorber is modified for the two-dimensional problem. An analytical means of estimating the effectiveness of the piezoelectric absorber is derived. The effectiveness is estimated for an electronics chassis box subjected to random excitation. A typical constrained layer damping treatment is also analytically designed for the problem. The piezoelectric absorber and the constrained layer damping treatment are experimentally applied to identical boxes. Results show that the piezoelectric absorber can provide vibration suppression comparable to that obtained by the constrained layer damping treatment.

Hollkamp, Joseph J.; Gordon, Robert W.

1996-10-01

280

EUROPEAN LARGE LAKES III Identification of factors constraining nitrate assimilation  

E-print Network

EUROPEAN LARGE LAKES III Identification of factors constraining nitrate assimilation in Lake Science+Business Media Dordrecht 2013 Abstract Despite a well-documented rise in nitrate concentration to assess the influence of light and nutrients (P, Fe) on nitrate assimilation by a Lake Superior

Berges, John A.

281

On rho-Constrained Upward Topological Book Embeddings  

Microsoft Academic Search

\\u000a Giordano, Liotta and Whitesides [1] developed an algorithm that, given an embedded planar st-digraph and a topological numbering ? of its vertices, computes in O(n2) time a ?-constrained upward topological book embedding with at most 2n–4 spine crossings per edge. The number of spine crossings per edge is asymptotically worst case optimal.

Tamara Mchedlidze; Antonios Symvonis

2009-01-01

282

Construction of Quasi Interval Wavelet Based on Constrained Variational Principle  

Microsoft Academic Search

A construction method of the interval wavelet is proposed based on constrained variational principle, and a quasi-Shannon interval wavelet is constructed by this method. The linear, the conic, the quartic and the sine function are approximated using quasi interval wavelet, the affection of width parameter r and the number of external collocation points L on the computation precision is discussed,

Qin Ma; Shu-Li Mei; De-Hai Zhu

2009-01-01

283

Constrained connectivity for hierarchical image partitioning and simplification  

Microsoft Academic Search

This paper introduces an image partitioning and simplification method based on the constrained connectivity paradigm. According to this paradigm, two pixels are said to be connected if they satisfy a series of constraints defined in terms of simple measures such as the maximum gray-level differences over well-defined pixel paths and regions. The resulting connectivity relation generates a unique partition of

Pierre Soille

2008-01-01

284

Constrained Data Decomposition and Regression for Analyzing Healthy Aging from  

E-print Network

Constrained Data Decomposition and Regression for Analyzing Healthy Aging from Fiber Tract@sci.utah.edu Abstract. It has been shown that brain structures in normal aging un- dergo significant changes attributed aging will be necessary to explain differences to neurodegenera- tive patterns observed in mental

Prastawa, Marcel

285

Mercury's thermo-chemical evolution from numerical models constrained  

E-print Network

Mercury's thermo-chemical evolution from numerical models constrained by MESSENGER observations Globe de Paris, France #12;Basics facts about Mercury · Semi-major axis: 0.39 AU · 3:2 spin Earth!) · Black body temperature: 440 K #12;Exploration of Mercury Mariner10 ·First spacecraft to use

Cerveny, Vlastislav

286

CONSTRAINED-HAMILTONIAN SHALLOW-WATER DYNAMICS ON THE SPHERE  

E-print Network

CONSTRAINED-HAMILTONIAN SHALLOW-WATER DYNAMICS ON THE SPHERE F. J. BERON-VERA RSMAS, University of Miami, Florida, USA Abstract. Salmon's nearly geostrophic model for rotating shallow-water flow to the height field in Hamilton's principle for rotating shallow-water dynamics, constitutes an important

Beron-Vera, Francisco Javier

287

Constraining the gluon in the proton via photoproduction reactions  

E-print Network

Two reactions, the photoproduction of a direct photon plus a jet and the photoproduction of a charged hadron plus a jet, are studied in view of their potential to constrain the gluon distribution in the proton. The results are based on a program of partonic event generator type which includes the full set of NLO corrections.

G. Heinrich

2003-04-16

288

A Stepwise uncertainty reduction approach to constrained global optimization  

E-print Network

a measure of the uncertainty on the minimizer location, in the spirit of Villemonteix et al. (2009A Stepwise uncertainty reduction approach to constrained global optimization Victor Picheny INRA to guide sequen- tial evaluations of complex computer exper- iments is now a well-established practice

Kaski, Samuel

289

Finite volume schemes for locally constrained conservation laws  

E-print Network

Finite volume schemes for locally constrained conservation laws Boris Andreianov Paola Goatin model proposed by Colombo and Goatin in [CG07]. The model involves a standard conservation law a "green wave" are presented. Key words: Hyperbolic Scalar Conservation Law, Finite Volume Scheme, Entropy

Boyer, Edmond

290

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

291

Power Allocations in Minimum-Energy SER Constrained Cooperative Networks  

E-print Network

1 Power Allocations in Minimum-Energy SER Constrained Cooperative Networks Behrouz Maham for repetition-based amplify- and-forward (AF) relaying, given a required symbol error rate (SER the total relay power subject to the SER requirement at the destination. Two outstanding features

Paris-Sud XI, Université de

292

CONSTRAINED SPECTRUM NORMALIZATION FOR ROBUST SPEECH RECOGNITION IN NOISE  

Microsoft Academic Search

This paper presents a new approach to robust speech recogni- tion in noise based on spectral subtraction. A conventional spectral subtraction technique leads to nonlinear distortions of the normal- ized speech signals and resulting degradation of speech recognition accuracy. A new method is proposed to constrain spectral subtrac- tion by imposing upper bounds on the estimates of the noise spectra.

Filipp Korkmazskiy; Frank K. Soong; Olivier Siohan

293

KRYLOV SUBSPACE METHODS FOR LARGE SCALE CONSTRAINED SYLVESTER EQUATIONS  

E-print Network

KRYLOV SUBSPACE METHODS FOR LARGE SCALE CONSTRAINED SYLVESTER EQUATIONS STEPHEN SHANK AND VALERIA@temple.edu) Dipartimento di Matematica, Universit`a di Bologna, Piazza di Porta S. Donato, 5,40127 Bologna, Italy (valeria and Valeria Simoncini for solving (1.1)-(1.2) in the large scale setting, at a computational cost and memory

Simoncini, Valeria

294

Constrained Inverse Volume Rendering for Planetary Nebulae Marcus Magnor  

E-print Network

Constrained Inverse Volume Rendering for Planetary Nebulae Marcus Magnor MPI Informatik, Germany, USA Neb Duric Dept. Physics and Astronomy University of New Mexico, USA Figure 1: The planetary nebula Mz-3. Left to right: the nebula's color-composited original image, the same view rendered from

Utah, University of

295

An Adaptive Penalty Approach for Constrained GeneticAlgorithm Optimization  

E-print Network

). These include: 1. Rejection of infeasible solutions (the death penalty). 2. Using a mapping function so that allAn Adaptive Penalty Approach for Constrained Genetic­Algorithm Optimization Khaled Rasheed shehata@cs.rutgers.edu ABSTRACT In this paper we describe a new adaptive penalty approach for handling

Rasheed, Khaled

296

Applications of a Constrained Mechanics Methodology in Economics  

ERIC Educational Resources Information Center

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

Janova, Jitka

2011-01-01

297

Hydrology-Aware Constrained Triangulation of Terrain Data  

E-print Network

Hydrology-Aware Constrained Triangulation of Terrain Data Jonathan Muckella , Marcus Andradeb , W present a new data structure for simplifing terrain that captures hydrology significant features using. This allows better compression ratios the standard Triangu- lated Irregular Networks with highier hydrology

Franklin, W. Randolph

298

Constrained Quantum Mechanics: Chaos in Non-Planar Billiards  

ERIC Educational Resources Information Center

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

Salazar, R.; Tellez, G.

2012-01-01

299

Improving option pricing with the product constrained hybrid neural network  

Microsoft Academic Search

In the past decade, many studies across various financial markets have shown conventional option pricing models to be inaccurate. To improve their accuracy, various researchers have turned to artificial neural networks (ANNs). In this work a neural network is constrained in such a way that pricing must be rational at the option-pricing boundaries. The constraints serve to change the regression

Paul Lajbcygier

2004-01-01

300

Fusion using time-dependent density-constrained DFT  

E-print Network

We present results for calculating fusion cross-sections using a new microscopic approach based on a time-dependent density-constrained DFT calculations. The theory is implemented by using densities and other information obtained from TDDFT time-evolution of the nuclear system as constraint on the density for DFT calculations.

R. Keser; A. S. Umar; V. E. Oberacker; J. A. Maruhn; P. -G. Reinhard

2014-02-06

301

Frequency Constrained ShiftCP Modeling of Neuroimaging Data  

E-print Network

@drcmr.dk Abstract--The shift invariant multi-linear model based on the CandeComp/PARAFAC (CP) model denoted Shift]. Consequently, modeling repeated trials by CP in theory re- solves the ambiguities encountered when modelingFrequency Constrained ShiftCP Modeling of Neuroimaging Data Morten Mørup and Lars K. Hansen Section

302

MATLAB package for solving Box-Constrained Integer Least  

E-print Network

BILS: MATLAB package for solving Box-Constrained Integer Least Squares Problems User's Guide Xiao. This MATLAB package provides the solution to the BILS problem. The purpose of this document is to show how to use this package. For the theory and al- gorithms implemented in this package, see the paper "Solving

Toronto, University of

303

A constrained adaptive beamformer for medical ultrasound: initial results  

Microsoft Academic Search

Adaptive beamforming has been widely used as a way to improve image quality in medical ultrasound applications by correcting phase and amplitude aberration errors resulting from tissue inhomogeneity. A less-studied concern in ultrasound beamforming is the deleterious contribution of bright off-axis targets. This paper describes a new approach, the constrained adaptive beamformer (CAB), which builds on classic array processing methods

J. A. Mann; W. F. Walker

2002-01-01

304

Profitable and dynamically feasible operating point selection for constrained processes  

E-print Network

Profitable and dynamically feasible operating point selection for constrained processes Nabil to operate the plant close to the optimal point to achieve economic benefits. Though it is profitable the proposed approach. 2 Background Profitability is the major concern of a chemical plant and one approach

Skogestad, Sigurd

305

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

306

Variationally Constrained Numerical Solution of Electrical Impedance Tomography  

E-print Network

Variationally Constrained Numerical Solution of Electrical Impedance Tomography Liliana Borcea the electric field and the electric current at location x # # Electrical Impedance Tomography (EIT or voids, in metals [5, 6, 24, 37, 45, 83]. Electrical impedance tomography has been studied extensively

Zhang, Yin

307

Broadcast Scheduling for Time-Constrained Information Delivery  

E-print Network

Broadcast Scheduling for Time-Constrained Information Delivery Majid Raissi-Dehkordi OPNET. INTRODUCTION The increasing demand for content delivery applications in recent years have resulted into numerous research works on more efficient methods for the delivery of information. In a typical data

Baras, John S.

308

Secure AES Hardware Module for Resource Constrained Devices  

Microsoft Academic Search

Low power consumption, low gate count, and high through- put are standard design criteria for cryptographic coprocessors desig- nated for resource constrained devices such as smart cards. With the advent of side channel attacks, devices' resistance to such attacks be- came another major requirement. This paper describes a cryptographic hardware module for an AES algorithm that provides complete protec- tion

Elena Trichina; Tymur Korkishko

2004-01-01

309

Design of PID controllers based on constrained optimization  

Microsoft Academic Search

This paper presents a new design method for PID controllers based on optimization of load disturbance rejection with constraints on robustness to model uncertainties. The design also delivers parameters to deal with measurement noise and set point response. Thus, the formulation of the design problem captures four essential aspects of industrial control problems, leading to a constrained optimization problem which

H. Panagopoulos; K. J. Astrom; T. Hagglund

1999-01-01

310

Blue Moon sampling, vectorial reaction coordinates, and unbiased constrained dynamics  

E-print Network

Blue Moon sampling, vectorial reaction coordinates, and unbiased constrained dynamics Giovanni force in terms of a conditional expectation which can be computed by Blue Moon sampling Introduction Fifteen years ago the Blue Moon ensemble method was introduced to sample rare events that occur

Van Den Eijnden, Eric

311

Analysis of the Constrained Runs Algorithm(s)  

E-print Network

for Mathematics Modelling, Analysis & Simulation Amsterdam, The Netherlands Jointly with C. W. Gear , T. J. Kaper of Model Reduction, Leicester 2007 | August 29, 2007 ­ p. #12;Outline setting of the problem the zero-derivative principle the constrained runs scheme summary Mathematics of Model Reduction, Leicester 2007 | August 29

Gorban, Alexander N.

312

Constraining magnesium cycling in marine sediments using magnesium isotopes  

E-print Network

Constraining magnesium cycling in marine sediments using magnesium isotopes J.A. Higgins *, D Abstract Magnesium concentrations in deep-sea sediment pore-fluids typically decrease down core due to net and differentiate these processes, we have measured magnesium isotopes in pore-fluids and sediment samples from

Paytan, Adina

313

STATE-CONSTRAINED OPTIMAL CONTROL PROBLEMS OF IMPULSIVE DIFFERENTIAL EQUATIONS  

E-print Network

STATE-CONSTRAINED OPTIMAL CONTROL PROBLEMS OF IMPULSIVE DIFFERENTIAL EQUATIONS NICOLAS FORCADEL by measure driven differential systems and in presence of state constraints. The first result shows a reparametrized control problem of absolutely continuous trajectories but with time-dependent state

Paris-Sud XI, Université de

314

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

315

Thinning and Flow of Tibetan Crust Constrained by  

E-print Network

Thinning and Flow of Tibetan Crust Constrained by Seismic Anisotropy Nikolai M. Shapiro,1 * Michael with a thinning of the middle crust by about 30%. The anisotropy is largest in the western part of the plateau, where moment tensors of earthquakes indicate active crustal thinning. The preferred orientation of mica

Shapiro, Nikolai

316

Constrained optimization schemes for geophysical inversion of seismic data  

NASA Astrophysics Data System (ADS)

Many experimental techniques in geophysics advance the understanding of Earth processes by estimating and interpreting Earth structure (e.g., velocity and/or density structure). These techniques use different types of geophysical data which can be collected and analyzed separately, sometimes resulting in inconsistent models of the Earth depending on data quality, methods and assumptions made. This dissertation presents two approaches for geophysical inversion of seismic data based on constrained optimization. In one approach we expand a one dimensional (1-D) joint inversion least-squares (LSQ) algorithm by introducing a constrained optimization methodology. Then we use the 1-D inversion results to produce 3-D Earth velocity structure models. In the second approach, we provide a unified constrained optimization framework for solving a 1-D inverse wave propagation problem. In Chapter 2 we present a constrained optimization framework for joint inversion. This framework characterizes 1-D Earth's structure by using seismic shear wave velocities as a model parameter. We create two geophysical synthetic data sets sensitive to shear velocities, namely receiver function and surface wave dispersion. We validate our approach by comparing our numerical results with a traditional unconstrained method, and also we test our approach robustness in the presence of noise. Chapter 3 extends this framework to include an interpolation technique for creating 3-D Earth velocity structure models of the Rio Grande Rift region. Chapter 5 introduces the joint inversion of multiple data sets by adding delay travel times information in a synthetic setup, and leave the posibility to include more data sets. Finally, in Chapter 4 we pose a 1-D inverse full-waveform propagation problem as a PDE-constrained optimization program, where we invert for the material properties in terms of shear wave velocities throughout the physical domain. We facilitate the implementation and comparison of different constrained optimization methods, through a unified affine invariant approach that incorporates inequality constraints for solving the inverse problem. We expect to contribute in broadening the use of constrained optimization algorithms to solve geophysical inverse problems.

Sosa Aguirre, Uram Anibal

317

How well do different tracers constrain the firn diffusivity profile?  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

318

Acids (GCMP)  

NSDL National Science Digital Library

Acids: this is a resource in the collection "General Chemistry Multimedia Problems". We will observe the reaction of sodium bicarbonate with three acid solutions. General Chemistry Multimedia Problems ask students questions about experiments they see presented using videos and images. The questions asked apply concepts from different parts of an introductory course, encouraging students to decompartmentalize the material.

319

Acid rain  

SciTech Connect

This book presents the proceedings of the third annual conference sponsored by the Acid Rain Information Clearinghouse (ARIC). Topics covered include: Legal aspects of the source-receptor relationship: an energy perspective; Scientific uncertainty, agency inaction, and the courts; and Acid rain: the emerging legal framework.

White, J.C. (Cornell University, Ithaca, NY (US))

1988-01-01

320

Acid Rain  

Microsoft Academic Search

Measurements of the acidity of rain and snow reveal that in parts of the eastern U.S. and of western Europe precipitation has changed from a nearly neutral solution 200 years ago to a dilute solution of sulfuric and nitric acids today. The trend is a result of the emission of sulfur and nitrogen oxides to the atmosphere accompanying the rise

Gene E. Likens; Richard F. Wright; James N. Galloway; Thomas J. Butler

1979-01-01

321

Acid rain  

SciTech Connect

This book was written in a concise and readable style for the lay public. It's purpose was to make the public aware of the damage caused by acid rain and to mobilize public opinion to favor the elimination of the causes of acid rain.

Elsworth, S.

1985-01-01

322

Acid test  

NSDL National Science Digital Library

Baking soda can be used as an indicator of how much acid a substance contains. Lemons and limes have more acid in them than grapefruits and oranges. Indophenol can be used as an indicator of how much vitamin C is in a substance.

Olivia Worland (Purdue University;Biological Sciences)

2008-06-06

323

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

PubMed

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

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

2011-01-15

324

ErrorCorrecting Constrained Coding In this chapter, we consider codes that have combined errorcorrection and constrained  

E-print Network

of 0's on either side of a 1. The edit distance, or Levenshtein metric, and the Lee metric arise designed with other criteria in mind beyond optimization of minimum Hamming distance. Among these models Euclidean distance. In practice, constrained codes must limit error propagation. Sliding­block decoders

Siegel, Paul H.

325

Error-Correcting Constrained Coding In this chapter, we consider codes that have combined error-correction and constrained  

E-print Network

of 0's on either side of a 1. The edit distance, or Levenshtein metric, and the Lee metric arise designed with other criteria in mind beyond optimization of minimum Hamming distance. Among these models Euclidean distance. In practice, constrained codes must limit error propagation. Sliding-block decoders

Siegel, Paul H.

326

Acid rain  

SciTech Connect

The acid rain problem in the northeastern U.S. has been growing in severity and geographical areas affected. Acid rain has damaged, or will result in damage to visibility, physical structures and materials, aquatic life, timber, crops, and soils. The principal causes of acid rain in the northeastern U.S. are sulfur oxide and nitrogen oxide emissions from large power plants and smelters in the Ohio River Valley. Immediate corrective action and appropriate research are needed to reduce acid precipitation. Short-term programs that will define the rate of environmental deterioration, remaining environmental capacity to resist sudden deterioration, mechanisms of acid rain formation, and costs of various control options must be developed. (3 maps, 13 references, 1 table)

Bess, F.D.

1980-01-01

327

Constraining Perturbative Early Dark Energy with Current Observations  

NASA Astrophysics Data System (ADS)

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

Alam, Ujjaini

2010-05-01

328

Acid Rain  

NSDL National Science Digital Library

Due to the presence of dissolved gases such as carbon dioxide, rainfall is naturally acidic. The release of other gases and chemicals such as sulfur dioxide during the combustion of coal and oil can cause rainfall to become even more acidic, sometimes to the point of toxicity. In this activity, students will measure the pH of local rainfall to see what effect these gases have in their region. They will also check an online resource to see how the releases of acid rain-causing chemicals have varied over the past 20 years, and answer questions about the information they uncover.

Fox, Chris

329

Coordinated Vehicle Platoon Control: Weighted and Constrained Consensus and Communication Network Topologies  

E-print Network

Coordinated Vehicle Platoon Control: Weighted and Constrained Consensus and Communication Network a new method for enhancing highway safety and efficiency by coordinated control of vehicle platoons. One performance. Vehicle deployment is formulated as a weighted and constrained consensus control problem

Zhang, Hongwei

330

Edinburgh Research Explorer Space-based formaldehyde measurements as constrains on  

E-print Network

Edinburgh Research Explorer Space-based formaldehyde measurements as constrains on volatile organic, 'Space-based formaldehyde measurements as constrains on volatile organic compound emissions in east record in Edinburgh Research Explorer Published In: Journal of Geophysical Research Publisher Rights

Millar, Andrew J.

331

Shared developmental programme strongly constrains beak shape diversity in songbirds.  

PubMed

The striking diversity of bird beak shapes is an outcome of natural selection, yet the relative importance of the limitations imposed by the process of beak development on generating such variation is unclear. Untangling these factors requires mapping developmental mechanisms over a phylogeny far exceeding model systems studied thus far. We address this issue with a comparative morphometric analysis of beak shape in a diverse group of songbirds. Here we show that the dynamics of the proliferative growth zone must follow restrictive rules to explain the observed variation, with beak diversity constrained to a three parameter family of shapes, parameterized by length, depth and the degree of shear. We experimentally verify these predictions by analysing cell proliferation in the developing embryonic beaks of the zebra finch. Our findings indicate that beak shape variability in many songbirds is strongly constrained by shared properties of the developmental programme controlling the growth zone. PMID:24739280

Fritz, Joerg A; Brancale, Joseph; Tokita, Masayoshi; Burns, Kevin J; Hawkins, M Brent; Abzhanov, Arhat; Brenner, Michael P

2014-01-01

332

Constrained output feedback control of flexible rotor-bearing systems  

NASA Astrophysics Data System (ADS)

The design of an optimal constrained output feedback controller for a rotor-bearing system is described, based on a reduced order model. The aims are to stabilize the unstable or marginally stable motion and to control the large build-up of periodic disturbances occurring during operation. The reduced order model is constructed on the basis of a modal model and singular perturbation, retaining the advantages of the two methods. The onset of instability due to spillover is prevented by the constrained optimization, and the robustness and pole assignability are improved by designing not merely a static output feedback but a dynamic compensator. The periodic disturbances, usually caused by rotation, are reduced by using the disturbance observer and feed-forward compensation. The efficiency of the proposed method is demonstrated through two simulation models, a rigid shaft supported by soft bearings at its ends and an overhung rotor system with a tip disk, under both transient vibration and sudden imbalance situations.

Kim, Jong-Sun; Lee, Chong-Won

1990-04-01

333

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

334

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. PMID:22381679

Wernegreen, Jennifer J.

2013-01-01

335

Fractal Dimension of Geologically Constrained Crater Populations of Mercury  

NASA Astrophysics Data System (ADS)

Data gathered during the Mariner10 and MESSENGER missions are collated in this paper to classify craters into four geo-chronological units constrained to the geological map produced after MESSENGER's flybys. From the global catalogue, we classify craters, constraining them to the geological information derived from the map. We produce a size frequency distribution (SFD) finding that all crater classes show fractal behaviour: with the number of craters inversely proportional to their diameter, the exponent of the SFD (i.e., the fractal dimension of each class) shows a variation among classes. We discuss this observation as possibly being caused by endogenic and/or exogenic phenomena. Finally, we produce an interpretative scenario where, assuming a constant flux of impactors, the slope variation could be representative of rheological changes in the target materials.

Mancinelli, Paolo; Pauselli, Cristina; Perugini, Diego; Lupattelli, Andrea; Federico, Costanzo

2014-08-01

336

Constraining the Noncommutative Spectral Action via Astrophysical Observations  

SciTech Connect

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

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

2010-09-03

337

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

338

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

339

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

340

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

341

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

342

Conformationally constrained peptidomimetic inhibitors of signal transducer and activator of transcription. 3: Evaluation and molecular modeling.  

PubMed

Signal transducer and activator of transcription 3 (Stat3) is involved in aberrant growth and survival signals in malignant tumor cells and is a validated target for anticancer drug design. We are targeting its SH2 domain to prevent docking to cytokine and growth factor receptors and subsequent signaling. The amino acids of our lead phosphopeptide, Ac-pTyr-Leu-Pro-Gln-Thr-Val-NH(2), were replaced with conformationally constrained mimics. Structure-affinity studies led to the peptidomimetic, pCinn-Haic-Gln-NHBn (21), which had an IC(50) of 162 nM (fluorescence polarization), compared to 290 nM for the lead phosphopeptide (pCinn = 4-phosphoryloxycinnamate, Haic = (2S,5S)-5-amino-1,2,4,5,6,7-hexahydro-4-oxo-azepino[3,2,1-hi]indole-2-carboxylic acid). pCinn-Haic-Gln-OH was docked to the SH2 domain (AUTODOCK), and the two highest populated clusters were subjected to molecular dynamics simulations. Both converged to a common peptide conformation. The complex exhibits unique hydrogen bonding between Haic and Gln and Stat3 as well as hydrophobic interactions between the protein and pCinn and Haic. PMID:19334714

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

2009-04-23

343

ACID RAIN  

EPA Science Inventory

Acid precipitation has become one of the major environmental problems of this decade. It is a challenge to scientists throughout the world. Researchers from such diverse disciplines as plant pathology, soil science, bacteriology, meteorology and engineering are investigating diff...

344

Tranexamic Acid  

MedlinePLUS

... used to treat heavy bleeding during the menstrual cycle (monthly periods) in women. Tranexamic acid is in ... as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this ...

345

Quantum cosmology of a classically constrained nonsingular Universe  

E-print Network

The quantum cosmological version of a nonsingular Universe presented by Mukhanov and Brandenberger in the early nineties has been developed and the Hamilton Jacobi equation has been found under semiclassical (WKB) approximation. It has been pointed out that, parameterization of classical trajectories with semiclassical time parameter, for such a classically constrained system, is a nontrivial task and requires Lagrangian formulation rather than the Hamiltonian formalism.

Sanyal, Abhik Kumar

2009-01-01

346

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

347

Control of the constrained planar simple inverted pendulum  

NASA Technical Reports Server (NTRS)

Control of a constrained planar inverted pendulum by eigenstructure assignment is considered. Linear feedback is used to stabilize and decouple the system in such a way that specified subspaces of the state space are invariant for the closed-loop system. The effectiveness of the feedback law is tested by digital computer simulation. Pre-compensation by an inverse plant is used to improve performance.

Bavarian, B.; Wyman, B. F.; Hemami, H.

1983-01-01

348

Bounds on the capacity of constrained two-dimensional codes  

Microsoft Academic Search

Bounds on the capacity of constrained two-dimensional (2-D) codes are presented. The bounds of Calkin and Wilf (see SIAM J. Discr. Math., vol.11, no.1, p.54-60, 1998) apply to first-order symmetric constraints. The bounds are generalized in a weaker form to higher order and nonsymmetric constraints. Results are given for constraints specified by run-length limits or a minimum distance between pixels

Søren Forchhammer; Jørn Justesen

2000-01-01

349

Constrained semi-analytical models of galactic outflows  

Microsoft Academic Search

We present semi-analytic models of galactic outflows that are constrained by available observations on high-redshift star formation and reionization. Galactic outflows are modelled in a manner akin to models of stellar wind-blown bubbles. Large-scale outflows can generically escape from low-mass haloes (M <~ 109Msolar) for a wide range of model parameters while this is not the case in high-mass haloes

Saumyadip Samui; Kandaswamy Subramanian; Raghunathan Srianand

2008-01-01

350

Constrained molecular dynamics simulations of atomic ground states  

SciTech Connect

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

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

2005-07-15

351

Cumulative Decision Feedback Technique for Energy Constrained Wireless Sensor Networks  

NASA Astrophysics Data System (ADS)

The application of Cumulative Decision Feedback (DF) technique for energy/complexity constrained Wireless Sensor Networks (WSN) is considered. Theoretical bit error probability and average rate of a BPSK modulated DF are derived together with PHY-MAC layers' energy efficiency model for DF and Forward Error Correction (FEC) techniques. Moreover, an empirical optimization, which in turn relies upon a low complexity SNR estimation method also derived in this letter, is applied to the DF technique in order to obtain maximum energy efficiency.

Porto Villardi, Gabriel; Thadeu Freitas de Abreu, Giuseppe; Kohno, Ryuji

352

Some preliminary thoughts on the invention of constrained Hamiltonian dynamics  

NASA Astrophysics Data System (ADS)

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

Salisbury, Donald

2011-10-01

353

Constrained Semi-Markov decision processes with average rewards  

Microsoft Academic Search

This paper deals with constrained average reward Semi-Markov Decision Processes (SMDPs) with finite state and action sets. We consider two average reward criteria. The first criterion is time-average rewards, which equal the lower limits of the expected average rewards per unit time, as the horizon tends to infinity. The second criterion is ratio-average rewards, which equal the lower limits of

Eugene A. Feinberg; W. A. Harriman

1994-01-01

354

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. PMID:24065278

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

2013-01-01

355

Acidic precipitation  

SciTech Connect

The authors present an overview of the environmental chemistry and transport phenomena of air pollutants, biological and ecological effects of acidic precipitation, mitigation of acidified aquatic ecosystems, and modelling approaches. This book reviews what is known about the impact of acidic deposition in the biota and processes in complex ecosystems such as lakes, streams, and forests. The specific effects on crops, trees, fish, and microorganisms are also discussed.

Adriano, D.C. (Georgia Univ., Aiken, SC (USA)); Johnson, A.H. (Pennsylvania Univ., Philadelphia, PA (USA))

1989-01-01

356

Benzotetramisole-catalyzed dynamic kinetic resolution of azlactones.  

PubMed

Enantioselective acyl transfer catalyst benzotetramisole (BTM) has been found to promote dynamic kinetic resolution of azlactones providing di(1-naphthyl)methyl esters of alpha-amino acids with up to 96% ee. PMID:20099896

Yang, Xing; Lu, Guojian; Birman, Vladimir B

2010-02-19

357

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

358

Applications of a constrained mechanics methodology in economics  

NASA Astrophysics Data System (ADS)

This paper presents instructive interdisciplinary applications of constrained mechanics calculus in economics on a level appropriate for undergraduate physics education. The aim of the paper is (i) to meet the demand for illustrative examples suitable for presenting the background of the highly expanding research field of econophysics even at the undergraduate level and (ii) to enable the students to gain a deeper understanding of the principles and methods routinely used in mechanics by looking at the well-known methodology from the different perspective of economics. Two constrained dynamic economic problems are presented using the economic terminology in an intuitive way. First, the Phillips model of the business cycle is presented as a system of forced oscillations and the general problem of two interacting economies is solved by the nonholonomic dynamics approach. Second, the Cass-Koopmans-Ramsey model of economical growth is solved as a variational problem with a velocity-dependent constraint using the vakonomic approach. The specifics of the solution interpretation in economics compared to mechanics is discussed in detail, a discussion of the nonholonomic and vakonomic approaches to constrained problems in mechanics and economics is provided and an economic interpretation of the Lagrange multipliers (possibly surprising for the students of physics) is carefully explained. This paper can be used by the undergraduate students of physics interested in interdisciplinary physics applications to gain an understanding of the current scientific approach to economics based on a physical background, or by university teachers as an attractive supplement to classical mechanics lessons.

Janová, Jitka

2011-11-01

359

Constraining the growth of perturbations with lensing of supernovae  

E-print Network

A recently proposed technique allows one to constrain both the background and perturbation cosmological parameters through the distribution function of supernova Ia apparent magnitudes. Here we extend this technique to alternative cosmological scenarios, in which the growth of structure does not follow the $\\Lambda$CDM prescription. We apply the method first to the supernova data provided by the JLA catalog combined with redshift distortion data and with low-redshift cluster data and show that although the supernovae alone are not very constraining, they help in reducing the confidence regions. Then we apply our method to future data from LSST and from a survey that approximates the Euclid satellite mission. In this case we show that the combined data are nicely complementary and can constrain the normalization $\\sigma_8$ and the growth rate index $\\gamma$ to within $0.6\\%$ and $7\\%$, respectively. In particular, the LSST supernova catalog is forecast to give the constraint $\\gamma (\\sigma_8/0.83)^{6.7} = 0.55 \\pm 0.1$. We also report on constraints relative to a step-wise parametrization of the growth rate of structures. These results show that supernova lensing serves as a good cross-check on the measurement of perturbation parameters from more standard techniques.

Luca Amendola; Tiago Castro; Valerio Marra; Miguel Quartin

2014-12-11

360

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

361

Real-time optimal trajectory generation for constrained dynamical systems  

NASA Astrophysics Data System (ADS)

With the advent of powerful computing and efficient computational algorithms, real-time solutions to constrained optimal control problems are nearing a reality. In this thesis, we develop a computationally efficient Nonlinear Trajectory Generation (NTG) algorithm and describe its software implementation to solve, in real-time, nonlinear optimal trajectory generation problems for constrained systems. NTG is a nonlinear trajectory generation software package that combines nonlinear control theory, B-spline basis functions, and nonlinear programming. We compare NTG with other numerical optimal control problem solution techniques, such as direct collocation, shooting, adjoints, and differential inclusions. We demonstrate the performance of NTG on the Caltech Ducted Fan testbed. Aggressive, constrained optimal control problems are solved in real-time for hover-to-hover, forward flight, and terrain avoidance test cases. Real-time trajectory generation results are shown for both the two-degree of freedom and receding horizon control designs. Further experimental demonstration is provided with the station-keeping, reconfiguration, and deconfiguration of micro-satellite formation with complex nonlinear constraints. Successful application of NTG in these cases demonstrates reliable real-time trajectory generation, even for highly nonlinear and non-convex systems. The results are among the first to apply receding horizon control techniques for agile flight in an experimental setting, using representative dynamics and computation.

Milam, Mark Bradley

362

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

363

Constraining ecosystem processes from tower fluxes and atmospheric profiles.  

PubMed

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

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

2011-07-01

364

A Lightweight Secure Cyber Foraging Infrastructure for Resource-Constrained Sachin Goyal and John Carter  

E-print Network

A Lightweight Secure Cyber Foraging Infrastructure for Resource-Constrained Devices Sachin Goyal-constrained embedded and mobile devices are becoming increasingly common. Cyber foraging, which al- lows such devices the resources of less resource-constrained computers, a concept called surrogate computing or cyber foraging [15

Carter, John B.

365

High Failure Rate of a Constrained Acetabular Liner in Revision Total Hip Arthroplasty  

Microsoft Academic Search

Fifty-five consecutive revision total hip arthroplasties (THAs) in 51 patients in which a constrained acetabular liner was used (Duraloc Constrained Liner, DePuy, Warsaw, Ind) were reviewed. In these revisions, 41 constrained liners were placed for recurrent instability and 14 for inadequate stability at the time of revision THA. The mean age of the cohort was 62 years, and 38 of

Craig J. Della Valle; Dennis Chang; Scott Sporer; Richard A. Berger; Aaron G. Rosenberg; Wayne G. Paprosky

2005-01-01

366

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

367

The Equivalence of Constrained and Weighted Designs in Multiple Objective Design Problems  

E-print Network

The Equivalence of Constrained and Weighted Designs in Multiple Objective Design Problems Merlise of Cook and Wong on the equivalence of the weighted and constrained problems also apply much more criteria, Cook and Wong (1994) showed that the constrained and weighted optimal designs are equivalent

West, Mike

368

Towards better constrained models of the solar magnetic cycle  

NASA Astrophysics Data System (ADS)

The best tools we have for understanding the origin of solar magnetic variability are kinematic dynamo models. During the last decade, this type of models has seen a continuous evolution and has become increasingly successful at reproducing solar cycle characteristics. The basic ingredients of these models are: the solar differential rotation -- which acts as the main source of energy for the system by shearing the magnetic field; the meridional circulation -- which plays a crucial role in magnetic field transport; the turbulent diffusivity -- which attempts to capture the effect of convective turbulence on the large scale magnetic field; and the poloidal field source -- which closes the cycle by regenerating the poloidal magnetic field. However, most of these ingredients remain poorly constrained which allows one to obtain solar-like solutions by "tuning" the input parameters, leading to controversy regarding which parameter set is more appropriate. In this thesis we revisit each of those ingredients in an attempt to constrain them better by using observational data and theoretical considerations, reducing the amount of free parameters in the model. For the meridional flow and differential rotation we use helioseismic data to constrain free parameters and find that the differential rotation is well determined, but the available data can only constrain the latitudinal dependence of the meridional flow. For the turbulent magnetic diffusivity we show that combining mixing-length theory estimates with magnetic quenching allows us to obtain viable magnetic cycles and that the commonly used diffusivity profiles can be understood as a spatiotemporal average of this process. For the poloidal source we introduce a more realistic way of modeling active region emergence and decay and find that this resolves existing discrepancies between kinematic dynamo models and surface flux transport simulations. We also study the physical mechanisms behind the unusually long minimum of cycle 23 and find it to be tied to changes in the meridional flow. Finally, by carefully constraining the system through surface magnetic field observations, we find that what is believed to be the primary source of poloidal field (also known as Babckock-Leigthon mechanism) may not be enough to sustain the solar magnetic cycle.

Munoz-Jaramillo, Andres

2010-12-01

369

Uric acid - urine  

MedlinePLUS

The urine uric acid test measures the level of uric acid in urine. Uric acid level can also be checked using a blood ... to choose the best medicine to lower uric acid level in the blood. Uric acid is a ...

370

Amino Acid Metabolism Conflicts with Protein Diversity  

PubMed Central

The 20 protein-coding amino acids are found in proteomes with different relative abundances. The most abundant amino acid, leucine, is nearly an order of magnitude more prevalent than the least abundant amino acid, cysteine. Amino acid metabolic costs differ similarly, constraining their incorporation into proteins. On the other hand, a diverse set of protein sequences is necessary to build functional proteomes. Here, we present a simple model for a cost-diversity trade-off postulating that natural proteomes minimize amino acid metabolic flux while maximizing sequence entropy. The model explains the relative abundances of amino acids across a diverse set of proteomes. We found that the data are remarkably well explained when the cost function accounts for amino acid chemical decay. More than 100 organisms reach comparable solutions to the trade-off by different combinations of proteome cost and sequence diversity. Quantifying the interplay between proteome size and entropy shows that proteomes can get optimally large and diverse. PMID:25086000

Krick, Teresa; Verstraete, Nina; Alonso, Leonardo G.; Shub, David A.; Ferreiro, Diego U.; Shub, Michael; Sánchez, Ignacio E.

2014-01-01

371

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

NASA Astrophysics Data System (ADS)

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

Liu, Yanning; Wang, Kon-Well

2000-04-01

372

Salicylic acids  

PubMed Central

Salicylic acid is well known phytohormone, emerging recently as a new paradigm of an array of manifestations of growth regulators. The area unleashed yet encompassed the applied agriculture sector to find the roles to strengthen the crops against plethora of abiotic and biotic stresses. The skipped part of integrated picture, however, was the evolutionary insight of salicylic acid to either allow or discard the microbial invasion depending upon various internal factors of two interactants under the prevailing external conditions. The metabolic status that allows the host invasion either as pathogenesis or symbiosis with possible intermediary stages in close systems has been tried to underpin here. PMID:22301975

Hayat, Shamsul; Irfan, Mohd; Wani, Arif; Nasser, Alyemeni; Ahmad, Aqil

2012-01-01

373

Acid Stomach  

NSDL National Science Digital Library

This Science NetLinks lesson is intended for a high-school, introductory chemistry class or health class. The lesson begins with an article on the history of the development of aspirin. Students will then complete a lab that compares the reaction of regular aspirin, buffered aspirin, and enteric aspirin in neutral, acidic, and basic solutions. They will then analyze the results of the experiment to gain insight into how this information was used by researchers to solve some of the problems associated with aspirin. To complete the lesson, students must understand acids and bases.

Science Netlinks

2003-08-07

374

CONSTRAINING PERTURBATIVE EARLY DARK ENERGY WITH CURRENT OBSERVATIONS  

SciTech Connect

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

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

2010-05-10

375

Constrained dynamics approach for motion synchronization and consensus  

NASA Astrophysics Data System (ADS)

In this research we propose to develop constrained dynamical systems based stable attitude synchronization, consensus and tracking (SCT) control laws for the formation of rigid bodies. The generalized constrained dynamics Equations of Motion (EOM) are developed utilizing constraint potential energy functions that enforce communication constraints. Euler-Lagrange equations are employed to develop the non-linear constrained dynamics of multiple vehicle systems. The constraint potential energy is synthesized based on a graph theoretic formulation of the vehicle-vehicle communication. Constraint stabilization is achieved via Baumgarte's method. The performance of these constrained dynamics based formations is evaluated for bounded control authority. The above method has been applied to various cases and the results have been obtained using MATLAB simulations showing stability, synchronization, consensus and tracking of formations. The first case corresponds to an N-pendulum formation without external disturbances, in which the springs and the dampers connected between the pendulums act as the communication constraints. The damper helps in stabilizing the system by damping the motion whereas the spring acts as a communication link relaying relative position information between two connected pendulums. Lyapunov stabilization (energy based stabilization) technique is employed to depict the attitude stabilization and boundedness. Various scenarios involving different values of springs and dampers are simulated and studied. Motivated by the first case study, we study the formation of N 2-link robotic manipulators. The governing EOM for this system is derived using Euler-Lagrange equations. A generalized set of communication constraints are developed for this system using graph theory. The constraints are stabilized using Baumgarte's techniques. The attitude SCT is established for this system and the results are shown for the special case of three 2-link robotic manipulators. These methods are then applied to the formation of N-spacecraft. Modified Rodrigues Parameters (MRP) are used for attitude representation of the spacecraft because of their advantage of being a minimum parameter representation. Constrained non-linear equations of motion for this system are developed and stabilized using a Proportional-Derivative (PD) controller derived based on Baumgarte's method. A system of 3 spacecraft is simulated and the results for SCT are shown and analyzed. Another problem studied in this research is that of maintaining SCT under unknown external disturbances. We use an adaptive control algorithm to derive control laws for the actuator torques and develop an estimation law for the unknown disturbance parameters to achieve SCT. The estimate of the disturbance is added as a feed forward term in the actual control law to obtain the stabilization of a 3-spacecraft formation. The disturbance estimates are generated via a Lyapunov analysis of the closed loop system. In summary, the constrained dynamics method shows a lot of potential in formation control, achieving stabilization, synchronization, consensus and tracking of a set of dynamical systems.

Bhatia, Divya

376

Constrained model predictive control, state estimation and coordination  

NASA Astrophysics Data System (ADS)

In this dissertation, we study the interaction between the control performance and the quality of the state estimation in a constrained Model Predictive Control (MPC) framework for systems with stochastic disturbances. This consists of three parts: (i) the development of a constrained MPC formulation that adapts to the quality of the state estimation via constraints; (ii) the application of such a control law in a multi-vehicle formation coordinated control problem in which each vehicle operates subject to a no-collision constraint posed by others' imperfect prediction computed from finite bit-rate, communicated data; (iii) the design of the predictors and the communication resource assignment problem that satisfy the performance requirement from Part (ii). Model Predictive Control (MPC) is of interest because it is one of the few control design methods which preserves standard design variables and yet handles constraints. MPC is normally posed as a full-state feedback control and is implemented in a certainty-equivalence fashion with best estimates of the states being used in place of the exact state. However, if the state constraints were handled in the same certainty-equivalence fashion, the resulting control law could drive the real state to violate the constraints frequently. Part (i) focuses on exploring the inclusion of state estimates into the constraints. It does this by applying constrained MPC to a system with stochastic disturbances. The stochastic nature of the problem requires re-posing the constraints in a probabilistic form. In Part (ii), we consider applying constrained MPC as a local control law in a coordinated control problem of a group of distributed autonomous systems. Interactions between the systems are captured via constraints. First, we inspect the application of constrained MPC to a completely deterministic case. Formation stability theorems are derived for the subsystems and conditions on the local constraint set are derived in order to guarantee local stability or convergence to a target state. If these conditions are met for all subsystems, then this stability is inherited by the overall system. For the case when each subsystem suffers from disturbances in the dynamics, own self-measurement noises, and quantization errors on neighbors' information due to the finite-bit-rate channels, the constrained MPC strategy developed in Part (i) is appropriate to apply. In Part (iii), we discuss the local predictor design and bandwidth assignment problem in a coordinated vehicle formation context. The MPC controller used in Part (ii) relates the formation control performance and the information quality in the way that large standoff implies conservative performance. We first develop an LMI (Linear Matrix Inequality) formulation for cross-estimator design in a simple two-vehicle scenario with non-standard information: one vehicle does not have access to the other's exact control value applied at each sampling time, but to its known, pre-computed, coupling linear feedback control law. Then a similar LMI problem is formulated for the bandwidth assignment problem that minimizes the total number of bits by adjusting the prediction gain matrices and the number of bits assigned to each variable. (Abstract shortened by UMI.)

Yan, Jun

377

Constraining a Possible Variation of G with Type Ia Supernovae  

NASA Astrophysics Data System (ADS)

Astrophysical cosmology constrains the variation of Newton's Constant in a manner complementary to laboratory experiments, such as the celebrated lunar laser ranging campaign. Supernova cosmology is an example of the former and has attained campaign status, following planning by a Dark Energy Task Force in 2005. In this paper, we employ the full SNIa data set to the end of 2013 to set a limit on G variation. In our approach, we adopt the standard candle delineation of the redshift distance relation. We set an upper limit on its rate of change |dot{G}/G| of 0.1 parts per billion per year over 9 Gyrs. By contrast, lunar laser ranging tests variation of G over the last few decades. Conversely, one may adopt the laboratory result as a prior and constrain the effect of variable G in dark energy equation of state experiments to ?w < 0.02. We also examine the parameterisation G 1 + z. Its short expansion age conflicts with the measured values of the expansion rate and the density in a flat Universe. In conclusion, supernova cosmology complements other experiments in limiting G variation. An important caveat is that it rests on the assumption that the same mass of 56Ni is burned to create the standard candle regardless of redshift. These two quantities, f and G, where f is the Chandrasekhar mass fraction burned, are degenerate. Constraining f variation alone requires more understanding of the SNIa mechanism.

Mould, Jeremy; Uddin, Syed A.

2014-03-01

378

Constraining modified gravitational theories by weak lensing with Euclid  

SciTech Connect

Future proposed satellite missions such as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak-lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios such as those predicted by scalar-tensor and f(R) theories. We find that Euclid will improve constraints expected from the Planck satellite on these modified theories of gravity by 2 orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modifications to gravity.

Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco; Melchiorri, Alessandro; Pagano, Luca [Physics Department and INFN, Universita di Roma 'La Sapienza', Ple Aldo Moro 2, 00185, Rome (Italy); Scaramella, Roberto [INAF, Osservatorio Astronomico di Roma, via Frascati 33, 0040 Monte Porzio Catone (Italy)

2011-01-15

379

Semismooth Newton method for gradient constrained minimization problem  

NASA Astrophysics Data System (ADS)

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

Anyyeva, Serbiniyaz; Kunisch, Karl

2012-08-01

380

Polar stimulation and constrained cell migration in microfluidic channels.  

PubMed

Asymmetrical delivery of stimuli to moving cells for perturbing spatially-heterogeneous intracellular signaling is an experimental challenge not adequately met by existing technologies. Here, we report a robust microfluidic platform allowing localized treatment of the front and/or back of moving cells which crawl through narrow channels that they completely occlude. The enabling technical element for this study is a novel design for precise, passive balancing of flow inside the microfluidic device by contacting two fluid streams before splitting them again. The microchannels constrain cell morphology and induce qualitative and quantitative changes in neutrophil chemotaxis that mimic cells crawling through tissues. PMID:18030401

Irimia, Daniel; Charras, Guillaume; Agrawal, Nitin; Mitchison, Timothy; Toner, Mehmet

2007-12-01

381

Rate-Controlled Constrained-Equilibrium Theory of Chemical Reactions  

NASA Astrophysics Data System (ADS)

The Rate-Controlled Constrained-Equilibrium (RCCE) method for simplifying the treatment of reactions in complex systems is summarized and the selection of constraints for both close-to and far-from equilibrium systems is discussed. Illustrative examples of RCCE calculations of carbon monoxide concentrations in the exhaust products of an internal combustion engine and ignition delays for methane-oxygen mixtures in a constant volume adiabatic chamber are given and compared with "detailed" calculations. The advantages of RCCE calculations over "detailed" calculations are discussed.

Keck, James C.

2008-08-01

382

Hierarchically Parallelized Constrained Nonlinear Solvers with Automated Substructuring  

NASA Technical Reports Server (NTRS)

This paper develops a parallelizable multilevel multiple constrained nonlinear equation solver. The substructuring process is automated to yield appropriately balanced partitioning of each succeeding level. Due to the generality of the procedure,_sequential, as well as partially and fully parallel environments can be handled. This includes both single and multiprocessor assignment per individual partition. Several benchmark examples are presented. These illustrate the robustness of the procedure as well as its capability to yield significant reductions in memory utilization and calculational effort due both to updating and inversion.

Padovan, Joe; Kwang, Abel

1994-01-01

383

Novel technique for Constraining r-Process (n, ?) Reaction Rates.  

PubMed

A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the ? spectra from the ? decay of ^{76}Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and ?-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the ^{75}Ge(n,?)^{76}Ge cross section and reaction rate. PMID:25526121

Spyrou, A; Liddick, S N; Larsen, A C; Guttormsen, M; Cooper, K; Dombos, A C; Morrissey, D J; Naqvi, F; Perdikakis, G; Quinn, S J; Renstrøm, T; Rodriguez, J A; Simon, A; Sumithrarachchi, C S; Zegers, R G T

2014-12-01

384

Novel technique for constraining r-process (n,$?$) reaction rates  

E-print Network

A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r-process. As a proof-of-principle, the $\\gamma$-spectra from the $\\beta$-decay of $^{76}$Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and $\\gamma$-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the $^{75}$Ge($n,\\gamma$)$^{76}$Ge cross section and reaction rate.

A. Spyrou; S. N. Liddick; A. C. Larsen; M. Guttormsen; K. Cooper; A. C. Dombos; D. J. Morrissey; F. Naqvi; G. Perdikakis; S. J. Quinn; T. Renstrøm; J. A. Rodriguez; A. Simon; C. S. Sumithrarachchi; R. G. T. Zegers

2014-08-27

385

Dynamic probe of dust wakefield interactions using constrained collisions.  

PubMed

The magnitude and the structure of the ion-wakefield potential below a negatively charged dust particle levitated in the plasma-sheath region have been determined. Attractive and repulsive components of the interaction force were extracted from a trajectory analysis of low-energy dust collisions in a well-defined electrostatic potential, which constrained the dynamics of the collisions to be one dimensional. The peak attraction was on the order of 100 fN. The structure of the ion-wakefield-induced attractive potential was significantly different from a screened-Coulomb repulsive potential. PMID:12935254

Hebner, G A; Riley, M E; Marder, B M

2003-07-01

386

Positive Scattering Cross Sections using Constrained Least Squares  

SciTech Connect

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

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

1999-09-27

387

Amino Acids  

NSDL National Science Digital Library

The Featured Molecules this month are the 20 standard ?-amino acids found in proteins and serve as background to the paper by Barone and Schmidt on the Nonfood Applications of Proteinaceous Renewable Materials. The molecules are presented in two formats, the neutral form and the ionized form found in solution at physiologic pH.

388

Acid Rain  

NSDL National Science Digital Library

This activity is part of Planet Diary and is an online examination into acid rain and sulfur dioxide emissions. Students research which states have succeeded in reducing sulfur dioxide emissions between 1980 and 1999, and which states emissions have increased. This activity is accompanied by a page of websites for further information.

389

Acid Attack  

NSDL National Science Digital Library

In this activity, students explore the effect of chemical erosion on statues and monuments. They use chalk to see what happens when limestone is placed in liquids with different pH values. They also learn several things that engineers are doing to reduce the effects of acid rain.

Integrated Teaching And Learning Program

390

Pharmacology of oleanolic acid and ursolic acid  

Microsoft Academic Search

Oleanolic acid and ursolic acid are triterpenoid compounds that exist widely in food, medicinal herbs and other plants. This review summarizes the pharmacological studies on these two triterpenoids. Both oleanolic acid and ursolic acid are effective in protecting against chemically induced liver injury in laboratory animals. Oleanolic acid has been marketed in China as an oral drug for human liver

Jie Liu

1995-01-01

391

Constrained hyperbolic divergence cleaning for smoothed particle magnetohydrodynamics  

NASA Astrophysics Data System (ADS)

We present a constrained formulation of Dedner et al.'s hyperbolic/parabolic divergence cleaning scheme for enforcing the ?·B=0 constraint in smoothed particle magnetohydrodynamics (SPMHD) simulations. The constraint we impose is that energy removed must either be conserved or dissipated, such that the scheme is guaranteed to decrease the overall magnetic energy. This is shown to require use of conjugate numerical operators for evaluating ?·B and ?? in the SPMHD cleaning equations. The resulting scheme is shown to be stable at density jumps and free boundaries, in contrast to an earlier implementation by Price and Monaghan (2005). Optimal values of the damping parameter are found to be ?=0.2-0.3 in 2D and ?=0.8-1.2 in 3D. With these parameters, our constrained Hamiltonian formulation is found to provide an effective means of enforcing the divergence constraint in SPMHD, typically maintaining average values of h??·B?/?B? to 0.1-1%, up to an order of magnitude better than artificial resistivity without the associated dissipation in the physical field. Furthermore, when applied to realistic, 3D simulations we find an improvement of up to two orders of magnitude in momentum conservation with a corresponding improvement in numerical stability at essentially zero additional computational expense.

Tricco, Terrence S.; Price, Daniel J.

2012-08-01

392

Non-linear Constrained Realizations of the Large Scale Structure  

E-print Network

The linear algorithm of the Wiener filter and constrained realizations (CRs) of Gaussian random fields is extended here to perform non-linear CRs. The procedure consists of: (1) Using low resolution data to constrain a high resolution realization of the underlying field, as if the linear theory is valid; (2) Taking the linear CR backwards in time, by the linear theory, to set initial conditions for N-body simulations; (3) Forwarding the field in time by an N-body code. An intermediate step is introduced to `linearize' the low resolution data. The non-linear CR can be applied to any observational data set that is quasi-linearly related to the underlying field. Here it is applied to the IRAS 1.2Jy catalog using 846 data points within a sphere of 6000 km/s, to reconstruct the full non-linear large scale structure of our `local' universe. The method is tested against mock IRAS surveys, taken from random non-linear realizations. A detaile analysis of the reconstructed non-linear structure is presented.

V. Bistolas; Y. Hoffman

1997-07-22

393

A Method to Constrain the Size of the Protosolar Nebula  

NASA Astrophysics Data System (ADS)

Observations indicate that the gaseous circumstellar disks around young stars vary significantly in size, ranging from tens to thousands of AU. Models of planet formation depend critically upon the properties of these primordial disks, yet in general it is impossible to connect an existing planetary system with an observed disk. We present a method by which we can constrain the size of our own protosolar nebula using the properties of the small body reservoirs in the solar system. In standard planet formation theory, after Jupiter and Saturn formed they scattered a significant number of remnant planetesimals into highly eccentric orbits. In this paper, we show that if there had been a massive, extended protoplanetary disk at that time, then the disk would have excited Kozai oscillations in some of the scattered objects, driving them into high-inclination (i >~ 50°), low-eccentricity orbits (q >~ 30 AU). The dissipation of the gaseous disk would strand a subset of objects in these high-inclination orbits; orbits that are stable on Gyr timescales. To date, surveys have not detected any Kuiper-belt objects with orbits consistent with this dynamical mechanism. Using these non-detections by the Deep Ecliptic Survey and the Palomar Distant Solar System Survey we are able to rule out an extended gaseous protoplanetary disk (RD >~ 80 AU) in our solar system at the time of Jupiter's formation. Future deep all sky surveys such as the Large Synoptic Survey Telescope will allow us to further constrain the size of the protoplanetary disk.

Kretke, K. A.; Levison, H. F.; Buie, M. W.; Morbidelli, A.

2012-04-01

394

Grand unified theory constrained supersymmetry and neutrinoless double ? decay  

NASA Astrophysics Data System (ADS)

We analyze the contributions to the neutrinoless double ? decay (0??? decay) coming from the grand unified theory (GUT) constrained minimal supersymmetric standard model (MSSM) with trilinear R-parity breaking. We discuss the importance of two-nucleon and pion-exchange realizations of the quark-level 0???-decay transitions. In this context, the questions of reliability of the calculated relevant nuclear matrix elements within the renormalized quasiparticle random phase approximation for several medium and heavy open-shell nuclei are addressed. The importance of gluino and neutralino contributions to 0??? decay is also analyzed. We review the present experiments and deduce limits on the trilinear R-parity breaking parameter ?'111 from the nonobservability of 0??? decay for different GUT constrained supersymmetry scenarios. In addition, a detailed study of limits on the MSSM parameter space coming from the B-->Xs? processes by using the recent CLEO and OPAL results is performed. Some studies in respect to the future 0???-decay project GENIUS are also presented.

Wodecki, Andrzej; Kami?ski, Wies?aw A.; Šimkovic, Fedor

1999-12-01

395

An inexact fuzzy-chance-constrained air quality management model.  

PubMed

Regional air pollution is a major concern for almost every country because it not only directly relates to economic development, but also poses significant threats to environment and public health. In this study, an inexact fuzzy-chance-constrained air quality management model (IFAMM) was developed for regional air quality management under uncertainty. IFAMM was formulated through integrating interval linear programming (ILP) within a fuzzy-chance-constrained programming (FCCP) framework and could deal with uncertainties expressed as not only possibilistic distributions but also discrete intervals in air quality management systems. Moreover, the constraints with fuzzy variables could be satisfied at different confidence levels such that various solutions with different risk and cost considerations could be obtained. The developed model was applied to a hypothetical case of regional air quality management. Six abatement technologies and sulfur dioxide (SO2) emission trading under uncertainty were taken into consideration. The results demonstrated that IFAMM could help decision-makers generate cost-effective air quality management patterns, gain in-depth insights into effects of the uncertainties, and analyze tradeoffs between system economy and reliability. The results also implied that the trading scheme could achieve lower total abatement cost than a nontrading one. PMID:20681428

Xu, Ye; Huang, Guohe; Qin, Xiaosheng

2010-07-01

396

Adaptive Ranking Mutation Operator Based Differential Evolution for Constrained Optimization.  

PubMed

Differential evolution (DE) is a powerful evolutionary algorithm (EA) for numerical optimization. Combining with the constraint-handling techniques, recently, DE has been successfully used for the constrained optimization problems (COPs). In this paper, we propose the adaptive ranking mutation operator (ARMOR) for DE when solving the COPs. The ARMOR is expected to make DE converge faster and achieve feasible solutions faster. In ARMOR, the solutions are adaptively ranked according to the situation of the current population. More specifically, the population is classified into three situations, i.e., infeasible situation, semi-feasible situation, and feasible situation. In the infeasible situation, the solutions are ranked only based on their constraint violations; in the semi-feasible situation, they are ranked according to the transformed fitness; while in the feasible situation, the objective function value is used to assign ranks to different solutions. In addition, the selection probability of each solution is calculated differently in different situations. The ARMOR is simple, and it can be easily combined with most of constrained DE (CDE) variants. As illustrations, we integrate our approach into three representative CDE variants to evaluate its performance. The 24 benchmark functions presented in CEC 2006 and 18 benchmark functions presented in CEC 2010 are chosen as the test suite. Experimental results verify our expectation that the ARMOR is able to accelerate the original CDE variants in the majority of test cases. Additionally, ARMOR-based CDE is able to provide highly competitive results compared with other state-of-the-art EAs. PMID:25055390

Gong, Wenyin; Cai, Zhihua; Liang, Dingwen

2014-07-18

397

Feature selection with redundancy-constrained class separability.  

PubMed

Scatter-matrix-based class separability is a simple and efficient feature selection criterion in the literature. However, the conventional trace-based formulation does not take feature redundancy into account and is prone to selecting a set of discriminative but mutually redundant features. In this brief, we first theoretically prove that in the context of this trace-based criterion the existence of sufficiently correlated features can always prevent selecting the optimal feature set. Then, on top of this criterion, we propose the redundancy-constrained feature selection (RCFS). To ensure the algorithm's efficiency and scalability, we study the characteristic of the constraints with which the resulted constrained 0-1 optimization can be efficiently and globally solved. By using the totally unimodular (TUM) concept in integer programming, a necessary condition for such constraints is derived. This condition reveals an interesting special case in which qualified redundancy constraints can be conveniently generated via a clustering of features. We study this special case and develop an efficient feature selection approach based on Dinkelbach's algorithm. Experiments on benchmark data sets demonstrate the superior performance of our approach to those without redundancy constraints. PMID:20227975

Zhou, Luping; Wang, Lei; Shen, Chunhua

2010-05-01

398

Quadratic constrained mixed discrete optimization with an adiabatic quantum optimizer  

E-print Network

We extend the family of problems that may be implemented on an adiabatic quantum optimizer (AQO). When a quadratic optimization problem has at least one set of discrete controls and the constraints are linear, we call this a quadratic constrained mixed discrete optimization (QCMDO) problem. QCMDO problems are NP-hard, and no efficient classical algorithm for their solution is known. Included in the class of QCMDO problems are combinatorial optimization problems constrained by a linear partial differential equation (PDE) or system of linear PDEs. An essential complication commonly encountered in solving this type of problem is that the linear constraint may introduce many intermediate continuous variables into the optimization while the computational cost grows exponentially with problem size. We resolve this difficulty by developing a constructive mapping from QCMDO to quadratic unconstrained binary optimization (QUBO) such that the size of the QUBO problem depends only on the number of discrete control variables. With a suitable embedding, taking into account the physical constraints of the realizable coupling graph, the resulting QUBO problem can be implemented on an existing AQO. The mapping itself is efficient, scaling cubically with the number of continuous variables in the general case and linearly in the PDE case if an efficient preconditioner is available.

Rishabh Chandra; N. Tobias Jacobson; Jonathan E. Moussa; Steven H. Frankel; Sabre Kais

2014-03-20

399

Constraining fast radio burst progenitors with gravitational lensing  

NASA Astrophysics Data System (ADS)

Fast Radio Bursts (FRBs) are new transient radio sources discovered recently. Because of the angular resolution restriction in radio surveys, no optical counter part has been identified yet so it is hard to determine the progenitor of FRBs. In this paper we propose to use radio lensing survey to constrain FRB progenitors. We show that, different types of progenitors lead to different probabilities for a FRB to be gravitationally lensed by dark matter halos in foreground galaxies, since different type progenitors result in different redshift distributions of FRBs. For example, the redshift distribution of FRBs arising from double stars shifts toward lower redshift than of the FRBs arising from single stars, because double stars and single stars have different evolution timescales. With detailed calculations, we predict that the FRB sample size for producing one lensing event varies significantly for different FRB progenitor models. We argue that this fact can be used to distinguish different FRB models and also discuss the practical possibility of using lensing observation in radio surveys to constrain FRB progenitors.

Li, ChunYu; Li, LiXin

2014-07-01

400

Performance of redirected walking algorithms in a constrained virtual world.  

PubMed

Redirected walking algorithms imperceptibly rotate a virtual scene about users of immersive virtual environment systems in order to guide them away from tracking area boundaries. Ideally, these distortions permit users to explore large unbounded virtual worlds while walking naturally within a physically limited space. Many potential virtual worlds are composed of corridors, passageways, or aisles. Assuming users are not expected to walk through walls or other objects within the virtual world, these constrained worlds limit the directions of travel and as well as the number of opportunities to change direction. The resulting differences in user movement characteristics within the physical world have an impact on redirected walking algorithm performance. This work presents a comparison of generalized RDW algorithm performance within a constrained virtual world. In contrast to previous studies involving unconstrained virtual worlds, experimental results indicate that the steer-to-orbit keeps users in a smaller area than the steer-to-center algorithm. Moreover, in comparison to steer-to-center, steer-to-orbit is shown to reduce potential wall contacts by over 29%. PMID:24650985

Hodgson, Eric; Bachmann, Eric; Thrash, Tyler

2014-04-01

401

Observational constrains on the EoS of neutron stars.  

NASA Astrophysics Data System (ADS)

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

Jonker, Peter

402

Understanding (sessile/constrained) bubble and drop oscillations.  

PubMed

The diffuse literature on drop oscillation is reviewed, with an emphasis on capillary wave oscillations of constrained drops. Based on the review, a unifying conceptual framework is presented for drop and bubble oscillations, which considers free and constrained drops/bubbles, oscillation of the surface or the bulk (i.e. center of mass) of the drop/bubble, as well as different types of restoring forces (surface tension, gravity, electromagnetic, etc). Experimental results (both from literature and from a new set of experiments studying sessile drops in cross flowing air) are used to test mathematical models from literature, using a novel whole profile analysis technique for the new experiments. The cause of oscillation (cross flowing air, vibrated surface, etc.) is seen not to affect oscillation frequency. In terms of models, simplified models are seen to poorly predict oscillation frequencies. The most advanced literature models are found to be relatively accurate at predicting frequency. However it is seen that no existing models are reliably accurate across a wide range of contact angles, indicating the need for advanced models/empirical relations especially for drops undergoing the lowest frequency mode of oscillation (the order 1 degree 1 non-axisymmetric 'bending' mode that corresponds to a lateral 'rocking' motion of the drop). PMID:24359696

Milne, A J B; Defez, B; Cabrerizo-Vílchez, M; Amirfazli, A

2014-01-01

403

Constrained optimization framework for joint inversion of geophysical data sets  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

404

Constraining neutron star tidal Love numbers with gravitational wave detectors  

E-print Network

Ground-based gravitational wave detectors may be able to constrain the nuclear equation of state using the early, low frequency portion of the signal of detected neutron star - neutron star inspirals. In this early adiabatic regime, the influence of a neutron star's internal structure on the phase of the waveform depends only on a single parameter lambda of the star related to its tidal Love number, namely the ratio of the induced quadrupole moment to the perturbing tidal gravitational field. We analyze the information obtainable from gravitational wave frequencies smaller than a cutoff frequency of 400 Hz, where corrections to the internal-structure signal are less than 10 percent. For an inspiral of two non-spinning 1.4 solar mass neutron stars at a distance of 50 Mpc, LIGO II detectors will be able to constrain lambda to lambda < 2.0 10^{37} g cm^2 s^2 with 90% confidence. Fully relativistic stellar models show that the corresponding constraint on radius R for 1.4 solar mass neutron stars would be R < 13.6 km (15.3 km) for a n=0.5 (n=1.0) polytrope.

Eanna E. Flanagan; Tanja Hinderer

2007-12-07

405

HYDROFLUORIC ACID Safety Office  

E-print Network

acids like Sulfuric and Hydrochloric. Hydrofluoric Acid is an acid like no other. It is so potentHYDROFLUORIC ACID SAFETY Safety Office University ofTennessee Space Institute Tullahoma, TN #12;What is Hydrofluoric Acid ? Hydrofluoric acid is a "weak" inorganic acid. Primarily used

Davis, Lloyd M.

406

Hypergraph model of multi-residue interactions in proteins: sequentially-constrained partitioning algorithms for optimization of site-directed protein recombination.  

PubMed

Relationships among amino acids determine stability and function and are also constrained by evolutionary history. We develop a probabilistic hypergraph model of residue relationships that generalizes traditional pairwise contact potentials to account for the statistics of multi-residue interactions. Using this model, we detected non-random associations in protein families and in the protein database. We also use this model in optimizing site-directed recombination experiments to preserve significant interactions and thereby increase the frequency of generating useful recombinants. We formulate the optimization as a sequentially-constrained hypergraph partitioning problem; the quality of recombinant libraries with respect to a set of breakpoints is characterized by the total perturbation to edge weights. We prove this problem to be NP-hard in general, but develop exact and heuristic polynomial-time algorithms for a number of important cases. Application to the beta-lactamase family demonstrates the utility of our algorithms in planning site-directed recombination. PMID:17691894

Ye, Xiaoduan; Friedman, Alan M; Bailey-Kellogg, Chris

2007-01-01

407

Domoic Acid  

NSDL National Science Digital Library

This highly detailed chemical information page features domoic acid, a toxin associated with Amnesic shellfish poisoning and naturally produced by the red algae Chondria armata and diatoms of the genus Pseudo-nitzschia. Created by the International Programme on Chemical Safety, this web page organizes information under the following sections: Name, Summary, Physio-Chemical Properties, Uses, Routes of Entry, Kinetics, Toxicology, Toxicological and Biomedical Investigations, Clinical Effects, Management, Illustrative Cases, Additional Information, References, and Authors.

INCHEM

408

Nicotinuric Acid  

PubMed Central

OBJECTIVE Metabolic syndrome is a multiplex disorder and puts patients on the road to type 2 diabetes and atherosclerotic cardiovascular diseases. However, a surrogate biomarker in plasma or urine in fully reflecting features of metabolic syndrome has not been explored. RESEARCH DESIGN AND METHODS Urine metabolomics has potential utility in metabolic profiling because urine metabolites analysis reflects global outflux of metabolic change. Accordingly, we collected data on subjects (n = 99) with overweight, dyslipidemia, hypertension or impaired glucose tolerance and took a metabolomics approach to analyze the metabolites of urine revealed in metabolic syndrome by high-performance liquid chromatography–time-of-flight mass spectrometry and elicit potential biomarkers to picture metabolic syndrome. RESULTS Our results revealed that the urine nicotinuric acid value of subjects with diabetes (HbA1c ?6.5% or those receiving diabetes medications) (n = 25) was higher than subjects without diabetes (n = 37) (221 ± 31 vs. 152 ± 13 × 103 mAU, P = 0.0268). Moreover, urinary nicotinuric acid level was positively correlated with body mass index, blood pressure, total cholesterol, low-density lipoprotein cholesterol, triacylglycerol and high sensitivity C-reactive protein, but negatively correlated with high-density lipoprotein cholesterol. CONCLUSIONS This is the first study, to our knowledge, to propose that nicotinuric acid represents an important pathogenic mechanism in process from metabolic syndrome to diabetes and atherosclerotic cardiovascular disease. PMID:23275373

Huang, Chun-Feng; Cheng, Mei-Ling; Fan, Chun-Ming; Hong, Chuang-Ye; Shiao, Ming-Shi

2013-01-01

409

Absence of sterols constrains carbon transfer between cyanobacteria and a freshwater herbivore (Daphnia galeata).  

PubMed Central

A key process in freshwater plankton food webs is the regulation of the efficiency of energy and material transfer. Cyanobacterial carbon (C) in particular is transferred very inefficiently to herbivorous zooplankton, which leads to a decoupling of primary and secondary production and the accumulation of cyanobacterial biomass, which is associated with reduced recreational quality of water bodies and hazards to human health. A recent correlative field study suggested that the low transfer efficiency of cyanobacterial C is the result of the absence of long-chain polyunsaturated fatty acids (PUFA) in the diet of the zooplankton. By supplementation of single-lipid compounds in controlled growth experiments, we show here that the low C transfer efficiency of coccal and filamentous cyanobacteria to the keystone herbivore Daphnia is caused by the low sterol content in cyanobacteria, which constrains cholesterol synthesis and thereby growth and reproduction of the herbivore. Estimations of sterol requirement in Daphnia suggest that, when cyanobacteria comprise more than 80% of the grazed phytoplankton, growth of the herbivore may be limited by sterols and Daphnia may subsequently fail to control phytoplankton biomass. Dietary sterols therefore may play a key role in freshwater food webs and in the control of water quality in lakes dominated by cyanobacteria. PMID:12816661

von Elert, Eric; Martin-Creuzburg, Dominik; Le Coz, Jean R

2003-01-01

410

Clinical and radiographic results of the total condylar III and constrained condylar total knee arthroplasty  

Microsoft Academic Search

The Total Condylar III (Johnson and Johnson, Braintree, MA) and Constrained Condylar (Zimmer, Warsaw, IN) knee prostheses are nonlinked, semi-constrained prosthetic alternatives to rigid or rotating hinge prostheses for use in complex knee reconstructions. Forty-six Total Condylar III or Constrained Condylar prostheses were implanted with cement in 36 patients and followed for a mean of 5 years (range, 2–9 years).

Paul F. Lachiewicz; Stephen P. Falatyn

1996-01-01

411

Constrained denumerable state non-stationary MDPs with expected total reward criterion  

Microsoft Academic Search

In this paper, we consider constrained denumerable state non-stationary Markov decision processes (MDPs, for short) with expected\\u000a total reward criterion. By the mechanics of introducing Lagrange multiplier and using the methods of probability and analytics,\\u000a we prove the existence of constrained optimal policies. Moreover, we prove that a constrained optimal policy may be a Markov\\u000a policy, or be a randomized

Guo Xianping

2000-01-01

412

Constraining U.S. ammonia emissions using TES remote sensing observations and the GEOS-Chem adjoint model  

NASA Astrophysics Data System (ADS)

Ammonia (NH3) has significant impacts on biodiversity, eutrophication, and acidification. Widespread uncertainty in the magnitude and seasonality of NH3 emissions hinders efforts to address these issues. In this work, we constrain U.S. NH3 sources using observations from the TES satellite instrument with the GEOS-Chem model and its adjoint. The inversion framework is first validated using simulated observations. We then assimilate TES observations for April, July, and October of 2006 through 2009. The adjoint-based inversion allows emissions to be adjusted heterogeneously; they are found to increase in California throughout the year, increase in different regions of the West depending upon season, and exhibit smaller increases and occasional decreases in the Eastern U.S. Evaluations of the inversion using independent surface measurements show reduced model underestimates of surface NH3 and wet deposited NHx in April and October; however, the constrained simulation in July leads to overestimates of these quantities, while TES observations are still under predicted. Modeled sulfate and nitrate aerosols concentrations do not change significantly, and persistent nitrate overestimation is noted, consistent with previous studies. Overall, while satellite-based constraints on NH3 emissions improve model simulations in several aspects, additional assessment at higher horizontal resolution of spatial sampling bias, nitric acid formation, and diurnal variability and bi-directionality of NH3 sources may be necessary to enhance year-round model performance across the full range of gas and aerosol evaluations.

Zhu, L.; Henze, D. K.; Cady-Pereira, K. E.; Shephard, M. W.; Luo, M.; Pinder, R. W.; Bash, J. O.; Jeong, G.-R.

2013-04-01

413

Folic acid - test  

MedlinePLUS

Folic acid is a type of B vitamin. This article discusses the test to measure the amount of folic acid in the blood. ... that may interfere with test results, including folic acid supplements. Drugs that can decrease folic acid measurements ...

414

Methylmalonic acid blood test  

MedlinePLUS

... acid is a substance produced when proteins (called amino acids) in the body break down. A test can ... Cederbaum S, Berry GT. Inborn errors of carbohydrate, ammonia, amino acid, and organic acid metabolism. In: Gleason CA, Devaskar ...

415

Solving constrained optimization problems with hybrid particle swarm optimization  

NASA Astrophysics Data System (ADS)

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

Zahara, Erwie; Hu, Chia-Hsin

2008-11-01

416

Computational strategies in the dynamic simulation of constrained flexible MBS  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

417

Blind and Fully Constrained Unmixing of Hyperspectral Images  

NASA Astrophysics Data System (ADS)

This paper addresses the problem of blind and fully constrained unmixing of hyperspectral images. Unmixing is performed without the use of any dictionary, and assumes that the number of constituent materials in the scene and their spectral signatures are unknown. The estimated abundances satisfy the desired sum-to-one and nonnegativity constraints. Two models with increasing complexity are developed to achieve this challenging task, depending on how noise interacts with hyperspectral data. The first one leads to a convex optimization problem, and is solved with the Alternating Direction Method of Multipliers. The second one accounts for signal-dependent noise, and is addressed with a Reweighted Least Squares algorithm. Experiments on synthetic and real data demonstrate the effectiveness of our approach.

Ammanouil, Rita; Ferrari, Andre; Richard, Cedric; Mary, David

2014-12-01

418

Hippocampal shape classification using redundancy constrained feature selection.  

PubMed

Landmark-based 3D hippocampal shape classification involves high-dimensional descriptor space, many noisy and redundant features, and a very small number of training samples. Feature selection becomes critical in this situation, because it not only improves classification performance, but also identifies the regions that contribute more to shape discrimination. This work identifies the drawbacks of SVM-RFE, and proposes a novel class-separability-based feature selection approach to overcome them. We formulate feature selection as a constrained integer optimization and develop a new algorithm to efficiently and optimally solve this problem. Theoretical analysis and experimental study on both synthetic data and real hippocampus data demonstrate its superior performance over the prevailing SVM-RFE. Our work provides a new efficient feature selection tool for hippocampal shape classification. PMID:20879324

Zhou, Luping; Wang, Lei; Shen, Chunhua; Barnes, Nick

2010-01-01

419

Truncated and constrained helical analogs of antimicrobial esculentin-2EM.  

PubMed

Esculentin-2EM is a 37-residue, cationic, amphipathic, ?-helical antimicrobial peptide isolated from a Korean frog, Glandirama emeljanovi. Many studies revealed that truncation of this peptide results in substantial decreases in its antimicrobial activity. Lee and his colleagues have recently reported that a 23-residue esculentin-2EM analog containing a tryptophanyl substitution at position 16 showed a significant recovery of the antimicrobial activity of the parent peptide. Here we report a new series of 15-residue esculentin-2EM analogs which are constrained into an ?-helical conformation via an oct-4-enyl cross-link. The resulting 'stapled' derivatives displayed remarkable increases not only in antimicrobial activity but also in helical content and protease resistance compared to Lee's original 23-residue esculentin-2EM analog. The preliminary data obtained in this work strongly supports the potential of our strategy for the development of a new class of peptide antibiotics. PMID:24211019

Pham, Thanh Kim; Kim, Do-Hee; Lee, Bong-Jin; Kim, Young-Woo

2013-12-15

420

Phenolate constrained geometry polymerization catalyst and method for preparing  

DOEpatents

The subject invention involves a method of preparing and the constrained geometry catalyst thereby prepared of the general formula Ar'R4(O)Ar"R'.sub.4 M(CH.sub.2 Ph).sub.2 where Ar' is a phenyl or naphthyl group; Ar" is a cyclopentadienyl or indenyl group, R and R' are H or alkyl substituents (C.ltoreq.10) and M is Ti, Zr or Hf. The synthetic method involves a simple alkane elimination approach which permits a "one-pot" procedure. The catalyst, when combined with a cocatalyst such as Pb.sub.3 C.sup.+ B(Ar.sub.3.sup.F).sub.4 BAr.sub.3.sup.F or methyl alumoxane where Ar.sup.F is a fluoroaryl group, is an effective catalyst for the polymerization of .alpha.-olefins such as ethylene, propylene and styrene.

Marks, Tobin J. (Evanston, IL); Chen, You-Xian (Chicago, IL)

1999-01-01

421

Phenolate constrained geometry polymerization catalyst and method for preparing  

DOEpatents

The subject invention involves a method of preparing and the constrained geometry catalyst thereby prepared of the general formula Ar{prime}R4(O)Ar{double_prime}R{prime}{sub 4}M(CH{sub 2}Ph){sub 2} where Ar{prime} is a phenyl or naphthyl group; Ar{double_prime} is a cyclopentadienyl or indenyl group, R and R{prime} are H or alkyl substituents (C{<=}10) and M is Ti, Zr or Hf. The synthetic method involves a simple alkane elimination approach which permits a ``one-pot`` procedure. The catalyst, when combined with a cocatalyst such as Pb{sub 3}C{sup +}B(Ar{sub 3}{sup F}){sub 4}BAr{sub 3}{sup F} or methyl alumoxane where Ar{sup F} is a fluoroaryl group, is an effective catalyst for the polymerization of {alpha}-olefins such as ethylene, propylene and styrene. 1 fig.

Marks, T.J.; Chen, Y.X.

1999-01-05

422

Forced to be free? Increasing patient autonomy by constraining it.  

PubMed

It is universally accepted in bioethics that doctors and other medical professionals have an obligation to procure the informed consent of their patients. Informed consent is required because patients have the moral right to autonomy in furthering the pursuit of their most important goals. In the present work, it is argued that evidence from psychology shows that human beings are subject to a number of biases and limitations as reasoners, which can be expected to lower the quality of their decisions and which therefore make it more difficult for them to pursue their most important goals by giving informed consent. It is further argued that patient autonomy is best promoted by constraining the informed consent procedure. By limiting the degree of freedom patients have to choose, the good that informed consent is supposed to protect can be promoted. PMID:22318413

Levy, Neil

2014-05-01

423

Dynamical Heterogeneity in Higher Dimensions: Kinetically Constrained Models  

NASA Astrophysics Data System (ADS)

We use kinetically constrained models to investigate the dimensional dependence of dynamic heterogeneity in supercooled liquid systems. Higher dimensional generalizations of one dimensional East model and its variation with an embedded probe particle are used as a representative fragile liquid system. We first investigate how the breakdown of the Stokes-Einstein relation changes with the system dimensionality from d=1 up to d=10. The fractional scaling behavior D?^-? are observed, where D and ? are the diffusion constant of the probe and the relaxation time of the liquid, respectively. The scaling exponent, ?, decreases as the dimensionality increases. The decoupling between persistence and exchange times are also characterized as the dimensionality changes. Time and length scales of the dynamic heterogeneity are analyzed by calculating persistence functions and the dynamic susceptibility. Comparisons are made with respect to recent atomistic MD simulation results.

Jung, Younjoon; Kim, Soree

2013-03-01

424

Constraining the MOdified Newtonian Dynamics from spherically symmetrical hydrodynamic accretion  

NASA Astrophysics Data System (ADS)

The MOdified Newtonian Dynamics (MOND) is an alternative to the dark matter assumption that can explain the observed flat rotation curve of galaxies. Here hydrodynamic accretion is considered to critically check the consistency and to constrain the physical interpretation of this theory. It is found that, in case of spherically symmetrical hydrodynamic accretion, the modified Euler's equation has real solution if the interpretation is assumed to be a modification of the law of dynamics. There is no real solution if it is assumed to be an acceleration-scale-dependent modification of the gravitational law. With the modified Euler's equation, the steady-state mass accretion rate is found to change up to ˜15 per cent. The astrophysical and cosmological implications of these results are also discussed.

Roy, Nirupam

2011-06-01

425

Total energy control system autopilot design with constrained parameter optimization  

NASA Technical Reports Server (NTRS)

A description is given of the application of a multivariable control design method (SANDY) based on constrained parameter optimization to the design of a multiloop aircraft flight control system. Specifically, the design method is applied to the direct synthesis of a multiloop AFCS inner-loop feedback control system based on total energy control system (TECS) principles. The design procedure offers a structured approach for the determination of a set of stabilizing controller design gains that meet design specifications in closed-loop stability, command tracking performance, disturbance rejection, and limits on control activities. The approach can be extended to a broader class of multiloop flight control systems. Direct tradeoffs between many real design goals are rendered systematic by proper formulation of the design objectives and constraints. Satisfactory designs are usually obtained in few iterations. Performance characteristics of the optimized TECS design have been improved, particularly in the areas of closed-loop damping and control activity in the presence of turbulence.

Ly, Uy-Loi; Voth, Christopher

1990-01-01

426

Landmark Constrained Non-parametric Image Registration with Isotropic Tolerances  

NASA Astrophysics Data System (ADS)

The incorporation of additional user knowledge into a nonrigid registration process is a promising topic in modern registration schemes. The combination of intensity based registration and some interactively chosen landmark pairs is a major approach in this direction. There exist different possibilities to incorporate landmark pairs into a variational non-parametric registration framework. As the interactive localization of point landmarks is always prone to errors, a demand for precise landmark matching is bound to fail. Here, the treatment of the distances of corresponding landmarks as penalties within a constrained optimization problem offers the possibility to control the quality of the matching of each landmark pair individually. More precisely, we introduce inequality constraints, which allow for a sphere-like tolerance around each landmark. We illustrate the performance of this new approach for artificial 2D images as well as for the challenging registration of preoperative CT data to intra-operative 3D ultrasound data of the liver.

Papenberg, Nils; Olesch, Janine; Lange, Thomas; Schlag, Peter M.; Fischer, Bernd

427

Constraining top partner and naturalness at the LHC and TLEP  

NASA Astrophysics Data System (ADS)

We investigate indirect constraints on the top partner within the minimal fermionic top partner model. By performing a global fit of the latest Higgs data, Bs ??+?- measurements and the electroweak precision observables we find that the top partner with the mass up to 830 GeV is excluded at 2? level. Our bound on the top partner mass is much stronger than the bounds obtained from the direct searches at the LHC. Under the current constraints the fine-tuning measure is less than 9% and the branching ratio of T ? tZ is bounded between 14% and 25%. We also find that precise measurements of Higgs couplings at 240 GeV TLEP will constrain the top partner mass in multi-TeV region.

Han, Chengcheng; Kobakhidze, Archil; Liu, Ning; Wu, Lei; Yang, Bingfang

2015-01-01

428

Constraining fast radio burst progenitors with gravitational lensing  

E-print Network

Fast Radio Bursts (FRBs) are new transient radio sources discovered recently. Because of the angular resolution restriction in radio surveys, no optical counter part has been identified yet so it is hard to determine the progenitor of FRBs. In this paper we propose to use radio lensing survey to constrain FRB progenitors. We show that, different types of progenitors lead to different probabilities for a FRB to be gravitationally lensed by dark matter halos in foreground galaxies, since different type progenitors result in different redshift distributions of FRBs. For example, the redshift distribution of FRBs arising from double stars shifts toward lower redshift than of the FRBs arising from single stars, because double stars and single stars have different evolution timescales. With detailed calculations, we predict that the FRB sample size for producing one lensing event varies significantly for different FRB progenitor models. We argue that this fact can be used to distinguish different FRB models and als...

Li, Chun-Yu

2014-01-01

429

A Study of the Constrained Vapor Bubble Thermosyphon  

NASA Technical Reports Server (NTRS)

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 container with a square cross section (inside dimensions. 3 x 3 x 40 mm) partially filled with a liquid. The major portion of the liquid is in the corners, which act as arteries. When a temperature difference is applied to the ends of the CVBHX, evaporation occurs at the hot end and condensation at the cold end resulting in a very effective heat transfer device with great potential in space applications. Liquid is returned by capillary flow in the corners. A complete description of the system and the results obtained to date are given in the papers listed.

Wayner, Peter C., Jr.; Plawsky, J. L.

2000-01-01

430

Constraining Nonstandard Interactions in Neutrino-Electron Processes  

SciTech Connect

We present a detailed analysis on nonstandard neutrino interactions with electrons including muon and electron (anti)-neutrino data from existing accelerators and reactors in conjunction with data from the four LEP collaborations. First we perform a one-parameter-at-a-time analysis, showing how most constraints improve with respect to previous results reported in the literature. We show the importance of combining LEP data with the other experiments in removing degeneracies in the global analysis constraining flavor-conserving nonstandard neutrino interactions parameters which, at 90% and 95% C.L., lie within unique allowed regions. Despite such improved constraints, there is still substantial room for improvement, posing a big challenge for upcoming experiments.

Moura, C. A. [Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del IPN, Apdo. Postal 14-740 07000 Mexico, D.F. (Mexico); Instituto de Fisica Gleb Wataghin-UNICAMP Cx.P. 6165, 13083-970 Campinas, SP (Brazil)

2008-07-02

431

Mechanical transition in a highly stretched and torsionally constrained DNA  

NASA Astrophysics Data System (ADS)

We show results of our high force (up to 1.8 nN) atomic force microscopy force spectroscopy measurements of a double stranded DNA. We have found that the force spectra of torsionally constrained molecules display a small plateau occurring at a force of approximately 1 nN. This transition is absent in molecules with rotational freedom. Based on all-atom molecular dynamics simulations, we suggest that this plateau is a result of reducing the diameter of a double helix through extreme stretching. The simulation suggests that the molecule is forced into a form resembling an underwound P-DNA, with bases protruding outside of the backbones. These results broaden our understanding of the fundamental aspects of DNA nanomechanics.

Strzelecki, Janusz; Peplowski, Lukasz; Lenartowski, Robert; Nowak, Wieslaw; Balter, Aleksander

2014-02-01

432

Constraining grand unification using first and second generation sfermions  

NASA Astrophysics Data System (ADS)

We investigate the spectrum of supersymmetric grand unification models based on the gauge groups SU(5), SO(10) and E6, paying particular attention to the first and second generation. We demonstrate how the measurement of the first or second generation sfermion spectrum may be used to constrain the underlying grand unification structure. The smallness of first and second generation Yukawa interactions allows us to perform an analytic analysis, deriving expressions for the high scale parameters in terms of the low scale sfermion masses. We also describe a sum rule that provides an SO(10) mass prediction, distinct from SU(5), and discuss E6 models, both with and without extra exotic matter at low energies. The derived relations are compared with numerical results including two-loop running and the full Yukawa dependence.

Miller, D. J.; Morais, A. P.; Pandita, P. N.

2013-01-01

433

Limited view CT reconstruction and segmentation via constrained metric labeling  

PubMed Central

This paper proposes a new discrete optimization framework for tomographic reconstruction and segmentation of CT volumes when only a few projection views are available. The problem has important clinical applications in coronary angiographic imaging. We first show that the limited view reconstruction and segmentation problem can be formulated as a “constrained” version of the metric labeling problem. This lays the groundwork for a linear programming framework that brings metric labeling classification and classical algebraic tomographic reconstruction (ART) together in a unified model. If the imaged volume is known to be comprised of a finite set of attenuation coefficients (a realistic assumption), given a regular limited view reconstruction, we view it as a task of voxels reassignment subject to maximally maintaining consistency with the input reconstruction and the objective of ART simultaneously. The approach can reliably reconstruct (or segment) volumes with several multiple contrast objects. We present evaluations using experiments on cone beam computed tomography. PMID:19802346

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

2008-01-01

434

Drying-induced cavitation in a constrained hydrogel.  

PubMed

Cavitation can be often observed in soft materials. Most previous studies were focused on cavitation in an elastomer, which is under different mechanical loadings. In this paper, we investigate cavitation in a constrained hydrogel induced by drying. Taking account of surface tension and chemo-mechanics of gels, we calculate the free energy of the system as a function of cavity size. The free energy landscape shows a double-well structure, analogous to first-order phase transition. Above the critical humidity, a cavity inside the gel is tiny. Below the critical humidity, the size of the cavity is large. At the critical humidity, the cavity size grows suddenly and discontinuously. We further show that local large stretches can be induced in the gel during the drying process, which may result in fractures. PMID:25592184

Wang, Huiming; Cai, Shengqiang

2015-01-28

435

Constrained incremental predictive controller design for a flexible joint robot.  

PubMed

In this paper, an improved predictive control algorithm for controlling a typical nonlinear flexible-joint robot (FJR) with input constraint is proposed. The receding horizon algorithm, called generalized incremental predictive control (GIPC), utilizes both present and previous states rather than present states only. The GIPC algorithm includes the weighted difference of the current and the previous states and the summation of the control action increments. In order to illustrate the effectiveness of the proposed control strategy, it is implemented to the FJR and the results are compared with those of generalized predictive control (GPC). It is demonstrated that the proposed GIPC algorithm is more robust than the standard GPC method. Furthermore, the constrained GIPC algorithm using the quadratic programming removes instabilities caused by actuator saturation. PMID:19278677

Ghahramani, Nemat Ollah; Towhidkhah, Farzad

2009-07-01

436

Prior image constrained compressed sensing: a quantitative performance evaluation  

NASA Astrophysics Data System (ADS)

The appeal of compressed sensing (CS) in the context of medical imaging is undeniable. In MRI, it could enable shorter acquisition times while in CT, it has the potential to reduce the ionizing radiation dose imparted to patients. However, images reconstructed using a CS-based approach often show an unusual texture and a potential loss in spatial resolution. The prior image constrained compressed sensing (PICCS) algorithm has been shown to enable accurate image reconstruction at lower levels of sampling. This study systematically evaluates an implementation of PICCS applied to myocardial perfusion imaging with respect to two parameters of its objective function. The prior image parameter ? was shown here to yield an optimal image quality in the range 0.4 to 0.5. A quantitative evaluation in terms of temporal resolution, spatial resolution, noise level, noise texture, and reconstruction accuracy was performed.

Thériault Lauzier, Pascal; Tang, Jie; Chen, Guang-Hong

2012-03-01

437

Constraining Extended Theories of Gravity using Solar System Tests  

E-print Network

Solar System tests give nowadays constraints on the estimated value of the cosmological constant, which can be accurately derived from different experiments regarding gravitational redshift, light deflection, gravitational time-delay and geodesic precession. Assuming that each reasonable theory of gravitation should satisfy Solar System tests, we use these limits on the estimated value of the cosmological constant to constrain extended theories of Gravity, which are nowadays studied as possible theories for cosmological models and provide viable solutions to the cosmological constant problem and the explanation of the present acceleration of the Universe. We obtain that the estimated values, from Solar System tests, for the parameters appearing in the extended theories of Gravity are orders of magnitude bigger than the values obtained in the framework of cosmologically relevant theories.

Gianluca Allemandi; Matteo Luca Ruggiero

2006-10-21

438

Optimal Constrained Resource Allocation Strategies under Low Risk Circumstances  

E-print Network

In this paper we consider multiple constrained resource allocation problems, where the constraints can be specified by formulating activity dependency restrictions or by using game-theoretic models. All the problems are focused on generic resources, with a few exceptions which consider financial resources in particular. The problems consider low-risk circumstances and the values of the uncertain variables which are used by the algorithms are the expected values of the variables. For each of the considered problems we propose novel algorithmic solutions for computing optimal resource allocation strategies. The presented solutions are optimal or near-optimal from the perspective of their time complexity. The considered problems have applications in a broad range of domains, like workflow scheduling in industry (e.g. in the mining and metallurgical industry) or the financial sector, motion planning, facility location and data transfer or job scheduling and resource management in Grids, clouds or other distribute...

Andreica, Mugurel Ionut; Visan, Costel

2009-01-01

439

An approach to constrained aerodynamic design with application to airfoils  

NASA Technical Reports Server (NTRS)

An approach was developed for incorporating flow and geometric constraints into the Direct Iterative Surface Curvature (DISC) design method. In this approach, an initial target pressure distribution is developed using a set of control points. The chordwise locations and pressure levels of these points are initially estimated either from empirical relationships and observed characteristics of pressure distributions for a given class of airfoils or by fitting the points to an existing pressure distribution. These values are then automatically adjusted during the design process to satisfy the flow and geometric constraints. The flow constraints currently available are lift, wave drag, pitching moment, pressure gradient, and local pressure levels. The geometric constraint options include maximum thickness, local thickness, leading-edge radius, and a 'glove' constraint involving inner and outer bounding surfaces. This design method was also extended to include the successive constraint release (SCR) approach to constrained minimization.

Campbell, Richard L.

1992-01-01

440

Constraining Late Pleistocene Pluvial Lake Chronologies in Northeastern Nevada  

NASA Astrophysics Data System (ADS)

The presence of lakes in closed basins of the northern Great Basin during pluvial episodes of the Pleistocene has been recognized for over a century. Some of these lakes, such as Bonneville in western Utah and Lahontan in western Nevada, were large, and their histories are well constrained by field mapping, stratigraphic investigations, and geochronology. Dozens of other lakes with smaller dimensions are known to have existed, however with few exceptions their histories are virtually unknown. This situation is unfortunate because smaller, hydrologically closed lakes should be particularly sensitive to climatic changes that shifted the balance of precipitation and evaporation. Records of their fluctuations, therefore, could provide important information about atmospheric reorganization during the last glacial-interglacial transition. Ongoing work in northeastern Nevada is aimed at developing these records through detailed mapping, investigation of natural exposures and artificial excavations, and radiocarbon dating. Gastropod shells recovered from two sites along a beach ridge in the northeast Independence Valley indicate that Lake Clover reached its late Pleistocene highstand between 14,400 and 14,200 14C years BP (~17.5 cal. ka BP). Similarly, radiocarbon dating of gastropod shells from a beach ridge in the Ruby Valley indicates that Lake Franklin was near its late Pleistocene highstand at 13,400 14C years BP (~16.4 cal. ka BP). These ages are essentially synchronous with the highstands of Lakes Newark and Jakes ~150 km to the south, overlap with the hydrologic maximum of Lake Bonneville, and appear to predate the highstand of Lake Lahontan. Additional radiocarbon dating will refine these age relationships and attempt to constrain the timing of stillstands during the overall regression of these lakes in the latest Pleistocene.

Munroe, J. S.; Laabs, B. J.

2011-12-01

441

Nonlinearly-constrained optimization using asynchronous parallel generating set search.  

SciTech Connect

Many optimization problems in computational science and engineering (CS&E) are characterized by expensive objective and/or constraint function evaluations paired with a lack of derivative information. Direct search methods such as generating set search (GSS) are well understood and efficient for derivative-free optimization of unconstrained and linearly-constrained problems. This paper addresses the more difficult problem of general nonlinear programming where derivatives for objective or constraint functions are unavailable, which is the case for many CS&E applications. We focus on penalty methods that use GSS to solve the linearly-constrained problems, comparing different penalty functions. A classical choice for penalizing constraint violations is {ell}{sub 2}{sup 2}, the squared {ell}{sub 2} norm, which has advantages for derivative-based optimization methods. In our numerical tests, however, we show that exact penalty functions based on the {ell}{sub 1}, {ell}{sub 2}, and {ell}{sub {infinity}} norms converge to good approximate solutions more quickly and thus are attractive alternatives. Unfortunately, exact penalty functions are discontinuous and consequently introduce theoretical problems that degrade the final solution accuracy, so we also consider smoothed variants. Smoothed-exact penalty functions are theoretically attractive because they retain the differentiability of the original problem. Numerically, they are a compromise between exact and {ell}{sub 2}{sup 2}, i.e., they converge to a good solution somewhat quickly without sacrificing much solution accuracy. Moreover, the smoothing is parameterized and can potentially be adjusted to balance the two considerations. Since many CS&E optimization problems are characterized by expensive function evaluations, reducing the number of function evaluations is paramount, and the results of this paper show that exact and smoothed-exact penalty functions are well-suited to this task.

Griffin, Joshua D.; Kolda, Tamara Gibson

2007-05-01

442

Dynamics of large constrained nonlinear systems -- A taxonomy theory  

SciTech Connect

This paper provides an overview of the taxonomy theory which has been proposed as a fundamental platform for solving practical stability related problems in large constrained nonlinear systems such as the electric power system. The theory reveals a two-level intertwined cellular nature of the constrained system dynamics which serves as a unifying structure, a taxonomy, for analyzing nonlinear phenomena in large system models. These broadly divide into the state space aspects (related to dynamic stability issues among others) and the parameter space aspects (connected with bifurcation phenomena among others). In the state-space formulation, the boundary of the region of attraction for the operating point is shown (under certain Morse-Smale like assumptions) to be composed of stable manifolds of certain anchors and portions of the singularity surface. Such boundary characterization provides the foundation for rigorous Lyapunov theoretic transient stability methods. In the parameter space analysis, the feasibility region which is bounded by the feasibility boundary provides a safe operating region for guaranteeing local stability at the equilibrium under slow parametric variations. The feasibility boundary where the operating point undergoes loss of local stability is characterized in the form of three principal bifurcations including a new bifurcation called the singularity induced bifurcation. An overview of the recent results which prove that the two-level structure exists even in nonsmooth models that incorporate the effects of system hard limits is also included. Specifically hard limits induce a number of new bifurcations. This natural taxonomy of the system dynamics stands as the backbone for developing practical and rigorous computational techniques in detecting diverse instability mechanisms.

Venkatasubramanian, V. [Washington State Univ., Pullman, WA (United States). School of Electrical Engineering and Computer Science] [Washington State Univ., Pullman, WA (United States). School of Electrical Engineering and Computer Science; Schaettler, H.; Zaborszky, J. [Washington Univ., St. Louis, MO (United States). Dept. of Systems Science and Mathematics] [Washington Univ., St. Louis, MO (United States). Dept. of Systems Science and Mathematics

1995-11-01

443

CONSTRAINING INTERMEDIATE-MASS BLACK HOLES IN GLOBULAR CLUSTERS  

SciTech Connect

Decades after the first predictions of intermediate-mass black holes (IMBHs) in globular clusters (GCs) there is still no unambiguous observational evidence for their existence. The most promising signatures for IMBHs are found in the cores of GCs, where the evidence now comes from the stellar velocity distribution, the surface density profile, and, for very deep observations, the mass-segregation profile near the cluster center. However, interpretation of the data, and, in particular, constraints on central IMBH masses, require the use of detailed cluster dynamical models. Here we present results from Monte Carlo cluster simulations of GCs that harbor IMBHs. As an example of application, we compare velocity dispersion, surface brightness and mass-segregation profiles with observations of the GC M10, and constrain the mass of a possible central IMBH in this cluster. We find that, although M10 does not seem to possess a cuspy surface density profile, the presence of an IMBH with a mass up to 0.75% of the total cluster mass, corresponding to about 600 M{sub Sun }, cannot be excluded. This is also in agreement with the surface brightness profile, although we find it to be less constraining, as it is dominated by the light of giants, causing it to fluctuate significantly. We also find that the mass-segregation profile cannot be used to discriminate between models with and without IMBH. The reason is that M10 is not yet dynamically evolved enough for the quenching of mass segregation to take effect. Finally, detecting a velocity dispersion cusp in clusters with central densities as low as in M10 is extremely challenging, and has to rely on only 20-40 bright stars. It is only when stars with masses down to 0.3 M{sub Sun} are included that the velocity cusp is sampled close enough to the IMBH for a significant increase above the core velocity dispersion to become detectable.

Umbreit, Stefan; Rasio, Frederic A., E-mail: s-umbreit@northwestern.edu, E-mail: rasio@northwestern.edu [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208 (United States)

2013-05-01

444

A METHOD TO CONSTRAIN THE SIZE OF THE PROTOSOLAR NEBULA  

SciTech Connect

Observations indicate that the gaseous circumstellar disks around young stars vary significantly in size, ranging from tens to thousands of AU. Models of planet formation depend critically upon the properties of these primordial disks, yet in general it is impossible to connect an existing planetary system with an observed disk. We present a method by which we can constrain the size of our own protosolar nebula using the properties of the small body reservoirs in the solar system. In standard planet formation theory, after Jupiter and Saturn formed they scattered a significant number of remnant planetesimals into highly eccentric orbits. In this paper, we show that if there had been a massive, extended protoplanetary disk at that time, then the disk would have excited Kozai oscillations in some of the scattered objects, driving them into high-inclination (i {approx}> 50 Degree-Sign ), low-eccentricity orbits (q {approx}> 30 AU). The dissipation of the gaseous disk would strand a subset of objects in these high-inclination orbits; orbits that are stable on Gyr timescales. To date, surveys have not detected any Kuiper-belt objects with orbits consistent with this dynamical mechanism. Using these non-detections by the Deep Ecliptic Survey and the Palomar Distant Solar System Survey we are able to rule out an extended gaseous protoplanetary disk (R{sub D} {approx}> 80 AU) in our solar system at the time of Jupiter's formation. Future deep all sky surveys such as the Large Synoptic Survey Telescope will allow us to further constrain the size of the protoplanetary disk.

Kretke, K. A.; Levison, H. F.; Buie, M. W. [Southwest Research Institute, Department of Space Studies, 1050 Walnut Street, Suite 400, Boulder, CO 80302 (United States); Morbidelli, A., E-mail: kretke@boulder.swri.edu [Observatoire de la Cote d'Azur, BP 4229, 06304 Nice Cedex 4 (France)

2012-04-15

445

Polynomial normal forms of constrained differential equations with three parameters  

NASA Astrophysics Data System (ADS)

We study generic constrained differential equations (CDEs) with three parameters, thereby extending Takens's classification of singularities of such equations. In this approach, the singularities analyzed are the Swallowtail, the Hyperbolic, and the Elliptic Umbilics. We provide polynomial local normal forms of CDEs under topological equivalence. Generic CDEs are important in the study of slow-fast (SF) systems. Many properties and the characteristic behavior of the solutions of SF systems can be inferred from the corresponding CDE. Therefore, the results of this paper show a first approximation of the flow of generic SF systems with three slow variables. There are some important features, such as canards, of slow-fast systems that cannot be studied in the limit ?=0[3,9,22]. However, having a generic model of the constrained equation is important in order to study the complicated phenomena that related SF systems exhibit. We are interested in the case where the layer equation (or fast dynamics) is given as a gradient system. More specifically, we assume that there exists a smooth m-parameter family V:Rn×Rm?R such that f(x,?,0)=?V/?x(x,?). Although not every slow-fast system satisfies (1.5), there is a motivation behind this. From the mathematical point of view, it is interesting to see how the classification of singularities of smooth maps can be used to find normal forms. It is precisely the purpose of this document to exploit such an idea. Applications are also an important motivation. Two remarkable features of SF systems, canards and relaxation oscillations are found in models where f(x,?,0) is locally a fold singularity [16,17]. Furthermore, there are interesting real life phenomena which can indeed be modeled by systems satisfying (1.5). Two examples are shown in Section 3 and some more can be consulted in [13,15,18,19].

Jardón-Kojakhmetov, H.; Broer, Henk W.

2014-08-01

446

Is Statistical Learning Constrained by Lower Level Perceptual Organization?  

PubMed Central

In order for statistical information to aid in complex developmental processes such as language acquisition, learning from higher-order statistics (e.g. across successive syllables in a speech stream to support segmentation) must be possible while perceptual abilities (e.g. speech categorization) are still developing. The current study examines how perceptual organization interacts with statistical learning. Adult participants were presented with multiple exemplars from novel, complex sound categories designed to reflect some of the spectral complexity and variability of speech. These categories were organized into sequential pairs and presented such that higher-order statistics, defined based on sound categories, could support stream segmentation. Perceptual similarity judgments and multi-dimensional scaling revealed that participants only perceived three perceptual clusters of sounds and thus did not distinguish the four experimenter-defined categories, creating a tension between lower level perceptual organization and higher-order statistical information. We examined whether the resulting pattern of learning is more consistent with statistical learning being “bottom-up,” constrained by the lower levels of organization, or “top-down,” such that higher-order statistical information of the stimulus stream takes priority over the perceptual organization, and perhaps influences perceptual organization. We consistently find evidence that learning is constrained by perceptual organization. Moreover, participants generalize their learning to novel sounds that occupy a similar perceptual space, suggesting that statistical learning occurs based on regions of or clusters in perceptual space. Overall, these results reveal a constraint on learning of sound sequences, such that statistical information is determined based on lower level organization. These findings have important implications for the role of statistical learning in language acquisition. PMID:23618755

Emberson, Lauren L.; Liu, Ran; Zevin, Jason D.

2013-01-01

447

Acid Ocean  

NSDL National Science Digital Library

The I2I-Acid Ocean virtual lab is an e-learning activity where students become virtual scientists studying the impact of ocean acidification on sea urchin larval growth. Students recreate a real, up-to-date climate change experiment. They also learn important general scientific principles, such as the importance of sample size and numbers of replicates, and discuss what this research into a specific impact of climate change may mean for the future of our oceans. There is a French translation available.

448

Amino-group-specific natural abundance nitrogen isotope ratio analysis in amino acids.  

PubMed

Amino acid (AA) nitrogen (N) stable isotope ratio analysis has found a wide variety of important applications including indication of the trophic level of an organism, tracing N transfer within food webs, and monitoring of AA resynthesis during heterotrophic microbial reworking of organic matter. Despite its utility, the current methodology is difficult to employ consistently for natural abundance level precision. Here, we report a new and robust method for high-precision N-compound-specific isotope analysis (N-PCIA) for single-N-containing AAs and N-position-specific isotope analysis (N-PSIA) for poly-N AAs. First the amino-N in AAs was liberated and oxidized to NO2(-) by hypochlorite at high pH. The NO2(-) produced was then quantified colorimetrically with excess hypochlorite quenched using arsenite. Subsequently, buffered azide was used to reduce NO2(-) to N2O for isotope ratio analysis using a purge-and-trap isotope ratio mass spectrometer. In the case of glycine delta15N, the average precision was SD = 0.3 per thousand. Reaction yields and labeling experiments show that this oxidation reaction is highly specific, targeting the alpha-amino group (peptide-N) of most poly-N AAs. This permits specific determination of the delta15N of peptide-N in arginine, tryptophan, and histidine. In the case of lysine, however, the side-chain amino group was found to be partially labile to hypochlorite oxidation. Using isotope fractionation factors estimated from single-N analogues of lysine, the intramolecular delta15N of lysine was calculated by mass balance, and this generally agreed with results for the same sample material analyzed by a previously published enzymatic method. Our method has the advantages of being relatively rapid, robust, and applicable to all poly-N AAs. We have also found it to work well for determining total delta15N of amino-N in complex sample matrices that have not been susceptible to previous approaches. PMID:18231965

Zhang, Lin; Altabet, Mark A

2008-01-01

449

New bioactive fatty acids  

Technology Transfer Automated Retrieval System (TEKTRAN)

Many oxygenated fatty acids are bioactive compounds. Nocardia cholesterolicum and Flavobacterium DS5 convert oleic acid to 10 hydroxy stearic acid and linoleic acid to 10-hydroxy-12(Z)-octadecanoic acid. Pseudomonas aeruginosa PR3 converts oleic acid to the new compounds, 7,10-dihydroxy-8(E)-octad...

450

New Bioactive Fatty Acids  

Technology Transfer Automated Retrieval System (TEKTRAN)

Many oxygenated fatty acids are bioactive compounds. Nocardia cholesterolicum and Flavobacterium DS5 convert oleic acid to 10 hydroxy stearic acid and linoleic acid to 10-hydroxy-12(Z)-octadecanoic acid. Pseudomonas aeruginosa PR3 converts oleic acid to new compounds, 7,10-dihydroxy-8(E)-octadecen...

451

Understanding Acid Rain  

ERIC Educational Resources Information Center

The term acid rain describes rain, snow, or fog that is more acidic than normal precipitation. To understand what acid rain is, it is first necessary to know what an acid is. Acids can be defined as substances that produce hydrogen ions (H+), when dissolved in water. Scientists indicate how acidic a substance is by a set of numbers called the pH…

Damonte, Kathleen

2004-01-01

452

Brnsted Acids The Strongest Isolable Acid**  

E-print Network

Brønsted Acids The Strongest Isolable Acid** Mark Juhasz, Stephan Hoffmann, Evgenii Stoyanov, Kee-Chan Kim, and Christopher A. Reed* Acids based on carborane anions as conjugate bases (Figure 1) are a new class of Brønsted (protic) acids, notable for their "strong yet gentle" qualities.[1] For example

Reed, Christopher A.

453

Multiple Observation Types Jointly Constrain Terrestrial Carbon and Water Cycles  

NASA Astrophysics Data System (ADS)

Information about the carbon cycle potentially constrains the water cycle, and vice versa. This paper explores the utility of multiple observation sets to constrain carbon and water fluxes and stores in a land surface model, and a resulting determination of the Australian terrestrial carbon budget. Observations include streamflow from 416 gauged catchments, measurements of evapotranspiration (ET) and net ecosystem production (NEP) from 12 eddy-flux sites, litterfall data, and data on carbon pools. The model is a version of CABLE (the Community Atmosphere-Biosphere-Land Exchange model), coupled with CASAcnp (a biogeochemical model) and SLI (Soil-Litter-Iso, a soil hydrology model including liquid and vapour water fluxes and the effects of litter). By projecting observation-prediction residuals onto model uncertainty, we find that eddy flux measurements provide a significantly tighter constraint on Australian continental net primary production (NPP) than the other data types. However, simultaneous constraint by multiple data types is important for mitigating bias from any single type. Results emerging from the multiply-constrained model are as follows (with all values applying over 1990-2011 and all ranges denoting ±1 standard error): (1) on the Australian continent, a predominantly semi-arid region, over half (0.64±0.05) of the water loss through ET occurs through soil evaporation and bypasses plants entirely; (2) mean Australian NPP is 2200±400 TgC/y, making the NPP/precipitation ratio about the same for Australia as the global land average; (3) annually cyclic ("grassy") vegetation and persistent ("woody") vegetation respectively account for 0.56±0.14 and 0.43±0.14 of NPP across Australia; (4) the average interannual variability of Australia's NEP (±180 TgC/y) is larger than Australia's total anthropogenic greenhouse gas emissions in 2011 (149 TgCeq/y), and is dominated by variability in desert and savannah regions. The mean carbon budget over 1990-2011 reveals that climate variability and rising CO2 respectively contributed 12±29 and 68±35 TgC/y to Net Biosphere Productivity (NBP, positive to land). However these terrestrial carbon gains were partially offset by fire and land use change (mainly clearing of woody savannah), which caused net losses of 31±5 TgC/y and 18±7 TgC/y respectively. The resultant overall NBP of 31±35 TgC/y offset fossil fuel emissions (95±6 TgC/y) by 32±36%. However, territorial fossil fuel emissions are increasingly being dwarfed by fossil fuel exports: in 2009-2010, Australia exported 2.5 times more carbon in fossil fuels than it emitted by burning fossil fuels for domestic use.

Raupach, M. R.; Haverd, V.; Briggs, P. R.; Canadell, J.; Davis, S. J.; Isaac, P. R.; Law, R.; Meyer, M.; Peters, G. P.; Pickett Heaps, C.; Roxburgh, S. H.; Sherman, B.; van Gorsel, E.; Viscarra Rossel, R.; Wang, Z.

2012-12-01

454

Acid rain  

SciTech Connect

Acid rain, says Boyle is a chemical leprosy eating into the face of North America and Europe, perhaps the major ecological problem of our time. Boyle describes the causes and scope of the phenomenon; the effects on man, wildlife, water, and our cultural heritage. He probes the delays of politicians and the frequent self-serving arguments advanced by industry in the face of what scientists have proved. The solutions he offers are to strengthen the Clean Air Act and require emission reductions that can be accomplished by establishing emission standards on a regional or bubble basis, burn low-sulfur coal, install scrubbers at critical plants, and invest in alternative energy sources. 73 references, 1 figure.

Boyle, R.H.; Boyle, R.A.

1983-01-01

455

New method of acidizing or acid fracturing: crosslinked acid gels  

SciTech Connect

Acid polymer gels having pH less than one have been crosslinked for retarding the chemical and physical activity of hydrochloric acid on calcareous formations. Hydrochloric acid concentrations from .0025 to 28% have been successfully crosslinked. This stimulation fluid offers high viscosity with adequate shear stability, perfect support for proppants, and clay stabilization. Additionally, the fluid provides effective fluid loss control and retardation of acid reaction enabling live acid to penetrate deeper into the formation for better formation conductivity and practically a residue-free break for rapid clean-up of the well after the job. Results of lab and field tests show the acid crosslinked system to be an effective stimulation fluid for acidizing and acid fracturing in calcareous and sandstone formations having low formation permeability.

Pabley, A.S.; Holcomb, D.L.

1980-01-01

456

Real-Time System Design Based on Logic OR Constrained Optimization  

Microsoft Academic Search

The logic relationship among the equality and inequality constraints in a standard constrained optimization problem (SCOP) is the logical AND. Various efficient, convergent and robust algorithms have been developed for such a SCOP. However, a more general constrained optimization problem (GCOP) with not only logic AND but also OR relationships exists in many practical applications. In order to solve such

Jun-Xiang LIU; WANG Yong-Ji; WANG Yuan; XING Jian-Sheng; ZENG Hai-Tao

2006-01-01

457

Robust Constrained Fuzzy Affine Model Predictive Control With Application to a Fluidized Bed Combustion Plant  

Microsoft Academic Search

In this paper, robust constrained model predictive control of uncertain fuzzy affine systems is considered. Based on piecewise quadratic Lyapunov functions, highly efficient robust constrained predictive control approaches are developed so that the closed-loop stability is guaranteed, and the transient control performance is improved even under input or state constraints. Moreover, by using approximate ellipsoid and S -procedure, the solution

Tiejun Zhang; Gang Feng; Jianhong Lu; Wenguo Xiang

2008-01-01

458

Counterion-only electrical double layer: A constrained entropy approach Wuge H. Briscoea)  

E-print Network

Counterion-only electrical double layer: A constrained entropy approach Wuge H. Briscoea) Physical Received 4 March 2002; accepted 21 June 2002 A counterion-only double-layer theory is developed taking a constrained entropy maximization approach based on an isothermal thermodynamic system. The double-layer

Attard, Phil

459

Optimal water resource planning under fixed budget by interval-parameter credibility constrained programming  

Microsoft Academic Search

In this study, an interval credibility constrained programming (ICCP) was developed through introducing the concept of intervals into credibility constrained programming framework. Interval credibility levels can help decision makers to reflect uncertainties of preferences. By ICCP, a water resource planning model with fixed fuzzy budget was developed for supporting the planning of agriculture development and environmental protection. Surface and ground

Y. M. Zhang; G. H. Huang

2011-01-01

460

Data Assimilation for Estimating the Terrestrial Water Budget Using a Constrained Ensemble Kalman Filter  

E-print Network

Data Assimilation for Estimating the Terrestrial Water Budget Using a Constrained Ensemble Kalman A procedure is developed to incorporate equality constraints in Kalman filters, including the Ensemble Kalman filter (EnKF) and is referred to as the Constrained Ensemble Kalman Filter (CEnKF). The constraint

Pan, Ming

461

A Harmonic Approach for Calculating Daily Temperature Normals Constrained by2 Homogenized Monthly Temperature Normals3  

E-print Network

1 1 A Harmonic Approach for Calculating Daily Temperature Normals Constrained by2 Homogenized a constrained harmonic technique that forces the daily30 temperature normals to be consistent with the monthly, or harmonic even though the annual march of temperatures for some locations can be highly asymmetric. Here, we

462

Network resilience against intelligent attacks constrained by the degree-dependent node removal cost  

E-print Network

Network resilience against intelligent attacks constrained by the degree-dependent node removal.1088/1751-8113/43/39/395001 Network resilience against intelligent attacks constrained by the degree-dependent node removal cost 23 August 2010 Online at stacks.iop.org/JPhysA/43/395001 Abstract We study the resilience of complex

Coolen, ACC "Ton"

463

Using Lidar and Radar measurements to constrain predictions of forest2 ecosystem structure and function3  

E-print Network

#12;1 1 Using Lidar and Radar measurements to constrain predictions of forest2 ecosystem structure in their spatial extent. Lidar and Synthetic Aperture Radar are promising remote47 sensing-based techniques investigate how Lidar-derived forest heights and49 Radar-derived above-ground biomass can be used to constrain

Moorcroft, Paul R.

464

Techno-economic Optimization of Integrating Wind Power into Constrained Electric Networks  

E-print Network

Techno-economic Optimization of Integrating Wind Power into Constrained Electric Networks by Jesse-economic Optimization of Integrating Wind Power into Constrained Electric Networks by Jesse David Maddaloni B-carbon energy sources such as wind and small-scale hydroelectric power. Models generally employ only a simple

Victoria, University of

465

Offset-free control of constrained linear discrete-time systems subject to persistent  

E-print Network

Offset-free control of constrained linear discrete-time systems subject to persistent unmeasured disturbances Gabriele Pannocchia and Eric C. Kerrigan CUED/F-INFENG/TR.466 September 10, 2003 #12;#12;Offset-free Technical report CUED/F-INFENG/TR.466 September 10, 2003 #12;#12;Offset-free control of constrained linear

Cambridge, University of

466

Offset-free Receding Horizon Control of Constrained Linear Gabriele Pannocchia1 Eric C. Kerrigan2  

E-print Network

Offset-free Receding Horizon Control of Constrained Linear Systems Gabriele Pannocchia1 Eric C stability and offset-free control of constrained linear systems in the presence of time-varying setpoints and unmeasured disturbances. This objective is obtained by first designing a dynamic linear offset-free

Cambridge, University of

467

Offset-free Receding Horizon Control of Constrained Linear Systems subject to  

E-print Network

Offset-free Receding Horizon Control of Constrained Linear Systems subject to Time/F-INFENG/TR.468 November 4, 2003 #12;Offset-free Receding Horizon Control of Constrained Linear Systems subject and offset-free control of con- strained, linear time-invariant systems in the presence of time

Cambridge, University of

468

Stability-Constrained Optimal Power Flow and Its Application to Pricing Power System Stabilizers  

E-print Network

1 Stability-Constrained Optimal Power Flow and Its Application to Pricing Power System Stabilizers stability constrained optimal power flow technique is proposed in this paper. The proposed methodology accounts for system dynamics through the use of a recently proposed stability index as an additional

Cañizares, Claudio A.

469

Synchronization of Concurrently-Implemented Fluidic Operations in Pin-Constrained Digital Microfluidic Biochips  

E-print Network

Microfluidic Biochips Yang Zhao1, Ryan Sturmer2, Krishnendu Chakrabarty1 and Vamsee K. Pamula2 1Duke University-- The implementation of bioassays in pin-constrained biochips may involve pin-actuation conflicts if the concurrently is demonstrated for a representative 3-plex assay performed on a fabricated pin- constrained biochip. I

Chakrabarty, Krishnendu

470

Optimized regional and interannual variability of lightning in a global chemical transport model constrained  

E-print Network

constrained by LIS/OTD satellite data Lee T. Murray,1 Daniel J. Jacob,1 Jennifer A. Logan,1 Rynda C. Hudman,1 Imaging Sensor (LIS) and the Optical Transient Detector (OTD) satellite instruments. We present an optimal of lightning in a global chemical transport model constrained by LIS/OTD satellite data, J. Geophys. Res., 117

Jacob, Daniel J.

471

LINE-CONSTRAINED GEOMETRIC SERVER PLACEMENT Mugurel Ionu ANDREICA, Eliana-Dina TRA  

E-print Network

LINE-CONSTRAINED GEOMETRIC SERVER PLACEMENT Mugurel Ionu ANDREICA, Eliana-Dina TÃ?RA Computer.andreica, eliana.tirsa}@cs.pub.ro Key words: server placement; geometric problems; K-center Abstract: In this paper we present new algorithmic solutions for several constrained geometric server placement problems. We

Paris-Sud XI, Université de

472

A Comparison of Four Item-Selection Methods for Severely Constrained CATs  

ERIC Educational Resources Information Center

This study compares the four existing procedures handling the item selection in severely constrained computerized adaptive tests (CAT). These procedures include weighted deviation model (WDM), weighted penalty model (WPM), maximum priority index (MPI), and shadow test approach (STA). Severely constrained CAT refer to those adaptive tests seeking…

He, Wei; Diao, Qi; Hauser, Carl

2013-01-01

473

The Application of Constrained Least Squares Estimation to Image Restoration by Digital Computer  

Microsoft Academic Search

Constrained least squares estimation is a technique for solution of integral equations of the first kind. The problem of image restoration requires the solution of an integral equation of the first kind. However, application of constrained least squares estimation to image restoration requires the solution of extremely large linear systems of equations. In this paper we demonstrate that, for convolution-type

B. R. Hunt

1973-01-01

474

The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic observations  

E-print Network

The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic. [1] After the January 12, 2010, Haiti earthquake, we deployed a mainly offshore temporary network), The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic observations

Brest, Université de

475

NATURALLY-TRANSITIONING RATE-TO-FORCE CONTROL IN FREE AND CONSTRAINED MOTION  

E-print Network

1 NATURALLY-TRANSITIONING RATE-TO-FORCE CONTROL IN FREE AND CONSTRAINED MOTION Robert L. Williams;2 NATURALLY-TRANSITIONING RATE-TO-FORCE CONTROL IN FREE AND CONSTRAINED MOTION Robert L. Williams II 1 , Jason. Repperger3 Human Sensory Feedback Laboratory, Wright-Patterson AFB ABSTRACT The Naturally-Transitioning Rate

Williams II, Robert L.

476

Bayesian Evaluation of Inequality and Equality Constrained Hypotheses for Contingency Tables  

ERIC Educational Resources Information Center

In this article, a Bayesian model selection approach is introduced that can select the best of a set of inequality and equality constrained hypotheses for contingency tables. The hypotheses are presented in terms of cell probabilities allowing researchers to test (in)equality constrained hypotheses in a format that is directly related to the data.…

Klugkist, Irene; Laudy, Olav; Hoijtink, Herbert

2010-01-01

477

Inflation model of Uzon caldera, Kamchatka, constrained by satellite radar interferometry observations  

E-print Network

Inflation model of Uzon caldera, Kamchatka, constrained by satellite radar interferometry 2000 to 2003 approximately 0.15 m of inflation occurred at Uzon caldera, extending beneath adjacent: Lundgren, P., and Z. Lu (2006), Inflation model of Uzon caldera, Kamchatka, constrained by satellite radar

478

GEOMETRY-CONSTRAINED CORONARY ARTERIES MOTION ESTIMATION FROM 2D ANGIOGRAMS -APPLICATION TO INJECTION SIDE RECOGNITION  

E-print Network

GEOMETRY-CONSTRAINED CORONARY ARTERIES MOTION ESTIMATION FROM 2D ANGIOGRAMS - APPLICATION of coronary arteries. It exploits the geometry of acquisition to strongly constrain the problem, thereby of an angiographic exam into right or left artery tree. Index Terms-- Coronary arteries, motion estimation. 1

Paris-Sud XI, Université de

479

Constraining supersymmetry with heavy scalars: Using the CMB  

NASA Astrophysics Data System (ADS)

If low-energy supersymmetry (SUSY) exists, LHC data favors a high mass scale for scalar superpartners (above a TeV), while sfermions and the dark matter can be parametrically lighter—leading to a so-called split spectrum. When combining this fact with the motivation from fundamental theory for shift-symmetric scalars (moduli) prior to SUSY breaking, this leads to a nonthermal history for the early universe. Such a history implies different expectations for the microscopic properties of dark matter, as well as the possibility of dark radiation and a cosmic axion background. In this paper we examine how correlated and mixed isocurvature perturbations are generated in such models, as well as the connection to dark radiation. WMAP constraints on multiple correlated isocurvature modes allow up to half of the primordial perturbations to be isocurvature, contrary to the case of a single isocurvature mode where perturbations must be dominantly adiabatic. However, such bounds are strongly prior dependent, and have not been investigated with the latest Planck data. In this paper we use the example of a SUSY nonthermal history to establish theoretical priors on cosmological parameters. Of particular interest, we find that priors on dark radiation are degenerate with those on the total amount of isocurvature—they are inversely correlated. Dark radiation is tightly constrained in the early universe and has been used recently to place stringent constraints on string-based approaches to beyond the standard model. Our results suggest such constraints can require more input from theory. Specifically, we find that in many cases constraints on dark radiation are avoidable because the density can be reduced at the expense of predicting an amount of multicomponent isocurvature. The latter are poorly constrained by existing probes, and lead to the interesting possibility that such models could have new predictions for the next generation of observations. Our results are not only important for establishing the postinflationary universe in the presence of SUSY, but also suggest that data from cosmological probes—such as Planck—can help guide model building in models of the minimal SUSY standard model, split SUSY, and beyond. Our model also demonstrates the utility of UV models in constructing cosmological priors.

Iliesiu, Luca; Marsh, David J. E.; Moodley, Kavilan; Watson, Scott

2014-05-01

480

Patterning and structural engineering of dimensionally constrained functional oxide nanostructures  

NASA Astrophysics Data System (ADS)

The current trend of ceramic nanotechnology has motivated an ever-increasing need to achieve exquisite control over size, shape, and spatial confinement for functional oxide architectures, in an equivalent manner demonstrated for semiconductors. However, the unique nature of ceramics has posed major challenges for most traditional nanofabrication technologies, putting the development of innovative oxide nanopatterning schemes under the spotlight. Dimensional and spatial confinement of functional oxides has also raised extensive intellectual interests since it carries a profound bearing upon their microstructure variation and leads to often superior performances. This further underlines the need for exploring the "materials science and engineering" of nano-constrained oxides, i.e., to fabricate nanopatterns with precise geometrical control at various dimensionalities, and to tailor their microstructural and functional characteristics. This dissertation presents one strategy to achieve such objectives. We have developed a versatile nanofabrication approach, termed variable pressure-soft-electron beam lithography (VP-soft-eBL) that successfully resolves the generic challenges in patterning oxides and enables high resolution fabrication of diverse materials on a multitude of substrates. A strategy based on VP-soft-eBL was derived for microstructural and morphological control on the nanostructures, particularly that of ferroelectrics and ferrimagnets. The effect of pattern aspect ratio on the microstructure evolution has been investigated for CoFe 2O4 and BaTiO3 nanodiscs on single crystal substrates with appropriate lattice matching. Following this strategy, high quality epitaxial patterns can be readily achieved from amorphous form during annealing. VP-soft-eBL portfolio was then expand