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1

Synthesis of conformationally constrained hydroxy-alpha-amino acids by intramolecular conjugate addition.  

PubMed

An efficient and easily applicable method for the synthesis of a variety of hydroxy-alpha-amino acids analogues of serine and phenylalanine has been established. The method involves the stereoselective intramolecular conjugate addition of the benzamide group to cyclohexenone promoted by Lewis acid. Subsequent transformations of functional groups provide the conformationally constrained 2-hydroxy- and 2,4-dihydroxy-6-phenylcyclohexane-alpha-amino acids. PMID:10817404

Avenoza, A; Busto, J H; Cativiela, C; Peregrina, J M

2000-01-01

2

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

3

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

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

Synthesis of alpha-amino acids  

DOEpatents

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

Davis, J.W. Jr.

1983-01-25

6

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

7

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

8

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

PubMed Central

Alpha-amino acid ester hydrolase (EC 3.1.1.43, AEH) is a promising biocatalyst for the production of semi-synthetic ?-lactam antibiotics, penicillins and cephalosporins. The AEH gene from Xanthomonas rubrilineans (XrAEH) was recently cloned in this laboratory. The three-dimensional structure of XrAEH was simulated using the homology modeling method for rational design experiments. The analysis of the active site was performed, and its structure was specified. The key amino acid residues in the active site - the catalytic triad (Ser175, His341 and Asp308), oxyanion hole (Tyr83 and Tyr176), and carboxylate cluster (carboxylate groups of Asp209, Glu310 and Asp311) - were identified. It was shown that the optimal configuration of residues in the active site occurs with a negative net charge -1 in the carboxylate cluster. Docking of different substrates in the AEH active site was carried out, which allowed us to obtain structures of XrAEH complexes with the ampicillin, amoxicillin, cephalexin, D-phenylglycine, and 4-hydroxy-D-phenylglycine methyl ester. Modeling of XrAEH enzyme complexes with various substrates was used to show the structures for whose synthesis this enzyme will show the highest efficiency. PMID:24455184

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

2013-01-01

9

alpha-Hydroxy and alpha-Amino Acids Under Possible Hadean, Volcanic Origin-of-Life Conditions  

Microsoft Academic Search

To test the theory of a chemoautotrophic origin of life in a volcanic, hydrothermal setting, we explored mechanisms for the buildup of bio-organic compounds by carbon fixation on catalytic transition metal precipitates. We report the carbon monoxide-dependent formation of carbon-fixation products, including an ordered series of alpha-hydroxy and alpha-amino acids of the general formula R-CHA-COOH (where R is H, CH3,

Claudia Huber; Günter Wächtershäuser

2006-01-01

10

Synthesis of P,N-heterocycles from omega-amino-H-phosphinates: conformationally restricted alpha-amino acid analogs.  

PubMed

P,N-heterocycles (3-hydroxy-1,3-azaphospholane and 3-hydroxy-1,3-azaphosphorinane-3-oxide) are synthesized in moderate yield from readily available omega-amino-H-phosphinates and aldehydes or ketones via an intramolecular Kabachnik-Fields reaction. The products are conformationally restricted phosphinic analogs of alpha-amino acids. The multigram-scale syntheses of the H2N(CH2)(n)PO2H2 phosphinic precursors (n = 1, 2, 3) and some derivatives are also described. PMID:18855477

Queffelec, Clémence; Ribière, Patrice; Montchamp, Jean-Luc

2008-11-21

11

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

PubMed

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

Huber, Claudia; Wächtershäuser, Günter

2006-10-27

12

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

PubMed

Oligomers of the negatively-charged amino acids, glutamic acid, aspartic acid, and O-phospho-L-serine are adsorbed by hydroxylapatite and illite with affinities that increase with oligomer length. In the case of oligo-glutamic acids adsorbed on hydroxylapatite, addition of an extra residue results in an approximately four-fold increase in the strength of adsorption. Oligomers much longer than the 7-mer are retained tenaciously by the mineral. Repeated incubation of short oligo-glutamic acids adsorbed on hydroxylapatite or illite with activated monomer leads to the accumulation of oligomers at least 45 units long. The corresponding reactions of aspartic acid and O-phospho-L-serine on hydroxylapatite are less effective in generating long oligomers, while illite fails to accumulate substantial amounts of long oligomers of aspartic acid or of O-phospho-L-serine. PMID:9611764

Hill, A R; Böhler, C; Orgel, L E

1998-06-01

13

One pot, rapid and efficient synthesis of water dispersible gold nanoparticles using alpha-amino acids  

NASA Astrophysics Data System (ADS)

A detailed study on the synthesis of spherical and monodispersed gold nanoparticles (AuNPs) using all of the 20 naturally occurring ?-amino acids has been reported. The synthesized nanoparticles have been further characterized using various techniques such as absorbance spectroscopy, transmission electron microscopy, dynamic light scattering and nuclear magnetic resonance. Size control of the nanoparticles has been achieved by varying the ratio of the gold ion to the amino acid. These monodispersed water soluble AuNPs synthesized using non-toxic, naturally occurring ?-amino acids as reducing and capping/stabilizing agents serve as a remarkable example of green chemistry.

Wangoo, Nishima; Kaur, Sarabjit; Bajaj, Manish; Jain, D. V. S.; Sharma, Rohit K.

2014-10-01

14

One pot, rapid and efficient synthesis of water dispersible gold nanoparticles using alpha-amino acids.  

PubMed

A detailed study on the synthesis of spherical and monodispersed gold nanoparticles (AuNPs) using all of the 20 naturally occurring ?-amino acids has been reported. The synthesized nanoparticles have been further characterized using various techniques such as absorbance spectroscopy, transmission electron microscopy, dynamic light scattering and nuclear magnetic resonance. Size control of the nanoparticles has been achieved by varying the ratio of the gold ion to the amino acid. These monodispersed water soluble AuNPs synthesized using non-toxic, naturally occurring ?-amino acids as reducing and capping/stabilizing agents serve as a remarkable example of green chemistry. PMID:25300279

Wangoo, Nishima; Kaur, Sarabjit; Bajaj, Manish; Jain, D V S; Sharma, Rohit K

2014-10-31

15

Simulation of organismic morphology and behavior by synthetic poly-alpha-amino acids.  

PubMed

Experiments imitating spontaneous geothermal occurrences have yielded most of the amino acids found in protein. All of the amino acids found in protein are simultaneously condensed, by heating in a range of appropriate conditions, to polymers which have many of the properties of proteins. These properties include molecular weights of many thousand, digestibility by proteolytic enzymes, and catalytic activities. One of the other properties is the tendency to form structured units; these units have many of the attributes of biocells. The processes indicated, and others, comprise a conceptual continuum which, according to accumulated information, must have occurred under the conditions existing in regions of the primitive Earth. PMID:11915883

Fox, S W; McCauley, R; Joseph, D; Windsor, C R; Yuyama, S

1966-01-01

16

Catalytic enantioselective aza-Diels-alder reactions of imines--an approach to optically active nonproteinogenic alpha-amino acids  

PubMed

A catalytic enantioselective aza-Diels-Alder reaction of imines has been developed. The reaction of N-tosyl alpha-imino ester with different dienes including activated, non-activated, cyclic, and acyclic dienes has been investigated in the presence of various chiral Lewis acids. A series of phosphino-oxazoline ligands have been synthesized and evaluated for the reaction. It was found that the combination of phosphino-oxazoline ligands with copper(I) salts gives the best results for the activated dienes, while BINAP-copper(I) complexes are good catalysts for all the dienes studied. In the case of activated acyclic dienes the aza-Diels-Alder products can be obtained in higher than 80% isolated yield and 96% ee, while for the unactivated cyclic dienes the exo diastereomer is formed as the major product in up to 95 % ee. For an activated cyclic conjugated diene, 2-trimethylsilyloxy-1,3-cyclohexadiene, the reaction proceeds as a Mannich-type addition reaction giving optically active gamma-oxo alpha-amino acid derivatives in good yields and up to 96% ee. The reaction of an unactivated acyclic diene, 2,3-dimethyl-1,3-butadiene, with the N-tosyl alpha-imino ester gives both the aza-Diels-Alder and aza-ene products, in a ratio of 9:1 favoring the aza-Diels-Alder product. Furthermore, a series of different imines have been synthesized and investigated as possible substrates for the present catalytic enantioselective aza-Diels-Alder reaction in order to obtain mechanistic insight. All imines studied gave moderate to high ee. Particularly, the reaction of the N-phenyl and N-p-methoxyphenyl substituted glyoxylate imines with Danishefsky's diene proceeded well affording the corresponding aza-Diels-Alder product in high yield with up to 91% ee at room temperature. The present catalytic enantioselective reaction of imines provided an effective route to optically active nonproteinogenic alpha-amino acids. The products of the catalytic enantioselective aza-Diels-Alder reaction of the cyclic dienes can be used for the preparation of key compounds such as natural products and compounds of pharmaceutical interest. The absolute configurations of five products have been solved by X-ray structural analysis, and it is found that the absolute configuration of the aza-Diels-Alder adduct is dependent on the substituent on the imine nitrogen atom. It turned out that the N-tosyl glyoxylate imine and N-p-methoxyphenyl glyoxylate imine give the aza-Diels-Alder adduct with opposite absolute configuration using the same enantiomer of the catalyst. On the basis of the results the mechanistic aspects for the reactions are discussed. PMID:10939745

Yao; Saaby; Hazell; Jorgensen

2000-07-01

17

A method for solid-phase synthesis of oligonucleotide 5'-peptide-conjugates using acid-labile alpha-amino protections.  

PubMed

We describe the development of a solid-phase technique for the synthesis of 5'-peptide-oligonucleotide conjugates (POCs) with a uniform protection strategy for the nucleic acid and the peptide fragments. On the alpha-amino function, the amino acid building blocks were protected with the 2-(biphenyl-4-yl)propan-2-yloxycarbonyl (Bpoc) group. This protection is removed during the stepwise peptide elongation by the same acidic conditions used for removal of the dimethoxytrityl (DMT) group used in the oligonucleotide assembly (3% trichloroacetic acid, 2 min). The 2-(3,5-dimethoxyphenyl)propan-2-yloxycarbonyl (Ddz) group was also tested. With this somewhat more stable group, a prolonged contact with the acid (at least 16 min) was required for accomplishing complete alpha-amino deprotection, which resulted in some degree of depurination of the acid-sensitive DNA chain. Base-labile acyl protections were adopted for the side-chains of histidine, lysine, and the nucleobase amino functions. These were all removed in the final deblocking step by ammonolysis. This uniform protection scheme for the peptide and the oligonucleotide enabled the total stepwise synthesis of model conjugates in the 3' --> N direction with high efficiency and purity. PMID:15506766

Zaramella, Simone; Yeheskiely, Esther; Strömberg, Roger

2004-11-01

18

New entry for synthesis of N-acylhydrazones, pyridazinones, and 1,3,4-oxadiazin-6-ones from alpha-amino acid esters.  

PubMed

Versatile electrophiles N-acylhydrazones are synthesized via diazotization, reduction, and acylation of alpha-amino acid esters. Reduction of diazo esters with L-selectride or tributylphosphine affords the corresponding hydrazones in good yields. Both reducing agents give anti-hydrazones as the major product although the reactivity of each reductant is slightly different. The resulting hydrazones are acylated to give N-acylhydrazones, which are subjected to further reactions to give 1,3,4-oxadiazin-6-ones that serve as useful synthetic intermediates for the Diels-Alder reaction. PMID:17978531

Yasui, Eiko; Wada, Masao; Takamura, Norio

2007-11-01

19

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

SciTech Connect

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

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

1991-03-01

20

Synthesis of alpha-trifluoromethyl alpha-amino acids with aromatic, heteroaromatic and ferrocenyl subunits in the side chain.  

PubMed

5-Benzyloxy-4-trifluoromethyl-1,3-oxazoles, obtained from 5-fluoro-4-trifluoromethyloxazoles and benzyl alcohols, are capable for rearrangements. A 1,3 shift of a benzyl group is the key step of a new general route toward alpha-trifluoromethyl substituted aromatic and heteroaromatic amino acids, demonstrating that 5-fluoro-4-trifluoromethyl-1,3-oxazole is a synthetic Tfm-Gly equivalent. On reaction with benzpinacol partially fluorinated oxazoles are transformed into bis(trifluoromethyl) substituted 2,5-diamino adipic acid and N-benzoyl-2-benzhydryl-3,3,3-trifluoroalanine. PMID:16715413

Burger, K; Hennig, L; Tsouker, P; Spengler, J; Albericio, F; Koksch, B

2006-07-01

21

Effects of streptozotocin-induced diabetes in pregnant rats on placental transport and tissue uptake of alpha-amino-isobutyric acid.  

PubMed

Placental transport and tissue uptake of amino acids were studied in streptozotocin (STZ)-induced diabetic rats by using the non-metabolizable amino acid [U-14C]-alpha-amino-isobutyric acid (AIB). Fifteen minutes prior to autopsy, animals of each group, control (C), diabetic (D), diabetic-insulin treated (DI) and diabetic-T4 followed by 3-5-Dimethyl-3'-isopropyl-L-thyronine (DIMIT) treated (DTD), received an injection of the [U-14C]-AIB SC. Disintegrations per minute (DPM) were measured in serum and tissues subsequent to autopsy. There were no differences in maternal serum DPM/ml among groups. Fetal serum DPM, however, were lower in D and DTD groups than in the C group. The whole fetal tissue homogenate radioactivity was lower in the D, DTD, and DI groups than in the C group. In general, more AIB was taken up by fetal tissues of C than D animals. Maternal liver AIB uptake was reduced in D, DI, and DTD from C animals and net placental transport of AIB was less in D and DTD than C animals. Fetal liver protein concentrations were depressed in D and DTD animals from C and DI, but fetal brain protein concentrations showed no significant differences. Furthermore, the lower organ and fetal body weights of the D and DTD groups compared with the C and DI groups support the proposal that fetal anabolism is impaired. Maternal and fetal serum T4 concentrations were lower in D and DTD than in C and DI animals. Insulin therapy improved serum T4 levels in both mother and fetuses. It did not, however, correct all other measured parameters.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3557285

Copeland, A D; Porterfield, S P

1987-02-01

22

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

PubMed

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

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

2005-04-01

23

Studies on the effects of L(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125) on 4-aminophenol-induced nephrotoxicity in the Fischer 344 rat.  

PubMed

4-Aminophenol (para-aminophenol; PAP) causes selective necrosis to the S3 segment of the proximal tubule in experimental animals. The mechanism of PAP nephrotoxicity has not been fully elucidated, although it has been suggested to involve glutathione (GSH)-dependent S-conjugation followed by processing by the enzyme gamma-glutamyl transpeptidase (gamma GT) to the corresponding cysteine S-conjugate. This proposed toxicity mechanism was probed further by administering L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125), a potent gamma GT inhibitor, to Fischer 344 (F344) rats before treatment with PAP (100 mg/kg). AT-125 pretreatment did not appear to protect against PAP-induced nephrotoxicity as assessed by renal histopathology, clinical chemistry and proton nuclear magnetic resonance (1H NMR) spectroscopy of urine. These data suggest that renal gamma GT activity is not a prerequisite for PAP nephrotoxicity and that the generation of a cysteine S-conjugate is not a unique requirement for the induction of PAP nephrotoxicity. PMID:7907856

Anthony, M L; Beddell, C R; Lindon, J C; Nicholson, J K

1993-01-01

24

Effect of DNA interaction involving antioxidative 4-aminoantipyrine incorporating mixed ligand complexes having alpha-amino acid as co-ligand  

NASA Astrophysics Data System (ADS)

Few new mixed ligand transition metal complexes of the stoichiometry [ML(A)2], where M = Co(II), Ni(II), Cu(II) and Zn(II), L = FFAP (furfurylidene-4-aminoantipyrine) and A = amino acid (glycine/alanine/valine), have been designed, synthesized and characterized. The molar conductivity of the complexes in DMF at 10-3 M concentration shows that they are non-electrolytes. The interaction of these complexes with CT-DNA indicates that the valine mixed ligand complexes are having higher binding constant than alanine and glycine mixed ligand complexes. This analysis reveals that binding constant depends on the size of the alkyl group present in the amino acid. The binding constants of valine mixed ligand complexes are in the order of 104 to 105 M-1 revealing that the complexes interact with DNA through moderate intercalation mode. The metal complexes exhibit effective cleavage of pUC19 DNA but it is not preceded via radical cleavage and superoxide anion radical. They are good antimicrobial agents than the free ligand. On comparing the IC50 values, [Ni(L)(Gly)2] is considered as a potential drug to eliminate the hydroxyl radical.

Raman, Natarajan; Sakthivel, Arunagiri; Selvaganapathy, Muthusamy; Mitu, Liviu

2014-02-01

25

Role of spinal cord alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in complete Freund's adjuvant-induced inflammatory pain  

PubMed Central

Spinal cord ?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) mediate acute spinal processing of nociceptive and non-nociceptive information, but whether and how their activation contributes to the central sensitization that underlies persistent inflammatory pain are still unclear. Here, we examined the role of spinal AMPARs in the development and maintenance of complete Freund's adjuvant (CFA)-induced persistent inflammatory pain. Intrathecal application of two selective non-competitive AMPAR antagonists, CFM-2 (25 and 50 ?g) and GYKI 52466 (50 ?g), significantly attenuated mechanical and thermal hypersensitivities on the ipsilateral hind paw at 2 and 24 h post-CFA injection. Neither CFM-2 nor GYKI 52466 affected the contralateral basal responses to thermal and mechanical stimuli. Locomotor activity was not altered in any of the drug-treated animals. CFA-induced inflammation did not change total expression or distribution of AMPAR subunits GluR1 and GluR2 in dorsal horn but did alter their subcellular distribution. The amount of GluR2 was markedly increased in the crude cytosolic fraction and decreased in the crude membrane fraction from the ipsilateral L4–5 dorsal horn at 24 h (but not at 2 h) post-CFA injection. Conversely, the level of GluR1 was significantly decreased in the crude cytosolic fraction and increased in the crude membrane fraction from the ipsilateral L4–5 dorsal horn at 24 h (but not at 2 h) post-CFA injection. These findings suggest that spinal AMPARs might participate in the central spinal mechanism of persistent inflammatory pain. PMID:19116032

Park, Jang-Su; Yaster, Myron; Guan, Xiaowei; Xu, Ji-Tian; Shih, Ming-Hung; Guan, Yun; Raja, Srinivasa N; Tao, Yuan-Xiang

2008-01-01

26

Benzodiazepine withdrawal-induced glutamatergic plasticity involves up-regulation of GluR1-containing alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in Hippocampal CA1 neurons.  

PubMed

Modification of glutamatergic synaptic function, a mechanism central to neuronal plasticity, may also mediate long-term drug effects, including dependence and addiction. Benzodiazepine withdrawal results in increased glutamatergic strength, but whether alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors (AMPARs) are functionally and structurally remodeled during benzodiazepine withdrawal is uncertain. Whole-cell recordings of rat hippocampal CA1 neurons, either acutely dissociated or in hippocampal slices, revealed that AMPAR function was enhanced up to 50% during flurazepam (FZP) withdrawal, without changes in whole-cell channel kinetic properties. Agonist-elicited AMPA currents showed a negative shift in rectification in the presence of spermine, suggesting augmented membrane incorporation of glutamate receptor (GluR) 2-lacking AMPARs. As GluR1-containing AMPARs are critical for activity-dependent alterations in excitatory strength, we sought to determine whether changes in GluR1 subunit distribution in CA1 neurons occurred during benzodiazepine withdrawal. Confocal image analysis revealed that FZP withdrawal promoted GluR1 subunit incorporation into somatic and proximal dendritic membranes of CA1 neurons without GluR2 subunit alterations. Findings of immunoblot studies were consistent with immunofluorescent studies indicating increased GluR1, but not GluR2, subunit protein levels in cytosolic, crude membrane and postsynaptic density-enriched fractions from CA1 minislices. As with long-term potentiation (LTP), the FZP-withdrawal-induced GluR1 incorporation into CA1 neuron membranes may require the GluR1-trafficking protein, synapse-associated protein 97, which was also elevated in membrane-associated fractions. Together, our findings provide evidence that during FZP withdrawal, increased membrane incorporation of GluR1-containing AMPARs and associated up-regulation of AMPAR functions in hippocampal CA1 pyramidal neurons share fundamental similarities with the mechanisms underlying LTP. This implies that glutamatergic neuronal remodeling observed in LTP also subserves physiological adaptations to drug withdrawal. PMID:17510319

Song, Jun; Shen, Guofu; Greenfield, L John; Tietz, Elizabeth I

2007-08-01

27

Benzodiazepine-induced hippocampal CA1 neuron alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA) receptor plasticity linked to severity of withdrawal anxiety: differential role of voltage-gated calcium channels and N-methyl-D-aspartic acid receptors.  

PubMed

Withdrawal from 1-week oral administration of the benzodiazepine, flurazepam (FZP) is associated with increased alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA) receptor (AMPAR) miniature excitatory postsynaptic currents (mEPSCs) but reduction of N-methyl-D-aspartic acid (NMDA) receptor (NMDAR)-evoked (e)EPSCs in hippocampal CA1 neurons. A positive correlation was observed between increased AMPAR-mediated mEPSC amplitude and anxiety-like behavior in 1-day FZP-withdrawn rats. These effects were disrupted by systemic AMPAR antagonist administration (GYKI-52466, 0.5 mg/kg, intraperitoneal) at withdrawal onset, strengthening the hypothesis that CA1 neuron AMPAR-mediated hyperexcitability is a central component of a functional anatomic circuit associated with the expression of withdrawal anxiety. Abolition of AMPAR current upregulation in 2-day FZP withdrawn rats by GYKI-52466 injection also reversed the reduction in NMDAR-mediated eEPSC amplitude in CA1 neurons from the same rats, suggesting that downregulation of NMDAR function may serve a protective, negative-feedback role to prevent AMPAR-mediated neuronal overexcitation. NMDAR antagonist administration (MK-801, 0.25 mg/kg intraperitoneally) had no effect on modifying increased glutamatergic strength or on withdrawal anxiety, whereas injection of an L-type voltage-gated calcium channel antagonist, nimodipine (10 mg/kg, intraperitoneally) averted AMPAR current enhancement and anxiety-like behavior, suggesting that these manifestations may be initiated by a voltage-gated calcium channel-dependent signal transduction pathway. An evidence-based model of likely cellular mechanisms in the hippocampus contributing to benzodiazepine withdrawal anxiety was proposed implicating regulation of multiple CA1 neuron ion channels. PMID:17762513

Xiang, Kun; Tietz, Elizabeth I

2007-09-01

28

Synthesis of a new conformationally constrained glycoamino acid building block  

Microsoft Academic Search

The synthesis of a suitably protected ?-d-glucopyranosyl-(S)-?-methylserine derivative—a new conformationally constrained glycosylated quaternary amino acid analogue of ?-d-glucopyranosyl-l-serine—is described. This compound can be used as an attractive building block for the synthesis of new, constrained glycopeptides.

Alberto Avenoza; Jesús M. Peregrina; Emilio San Mart??n

2003-01-01

29

Catalytic asymmetric hydrogenation of alpha-amino-beta-keto ester hydrochlorides using homogeneous chiral nickel-bisphosphine complexes through DKR.  

PubMed

Homogeneous chiral nickel-bisphosphine complexes catalyze the asymmetric hydrogenation of alpha-amino-beta-keto ester hydrochlorides through dynamic kinetic resolution to efficiently afford anti-beta-hydroxy-alpha-amino esters with high diastereo- and enantioselectivities. PMID:19082121

Hamada, Yasumasa; Koseki, Yu; Fujii, Takefumi; Maeda, Tsukuru; Hibino, Takuya; Makino, Kazuishi

2008-12-14

30

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

31

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

NASA Astrophysics Data System (ADS)

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

McCurdie, Mary Pat

32

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. Claudia; Nusantoro, Suluh; Kaushik, Sadasivam; Verreth, Johan; Schrama, Johan W.

2013-01-01

33

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

34

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

SciTech Connect

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

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

2014-01-01

35

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.

36

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-Loic; Maturano, Marie; Payrastre, Corinne; Tarrat, Nathalie; Escudier, Jean-Marc

2012-01-01

37

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'Inge´nierie, Toulouse, France, 3 Laboratoire de Synthe`se et Physico-Chimie de Mole´cules d'Inte´re^t Biologique, Unite in a single stranded DNA so as to preorganize it into a loop-like structure, and they have been shown

Paris-Sud XI, Université de

38

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

PubMed

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

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

2009-11-01

39

In-vitro characterization of YM872, a selective, potent and highly water-soluble alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor antagonist.  

PubMed

The in-vitro pharmacological properties of (2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydro-1-quinoxal inyl)-acetic acid monohydrate, YM872, a novel and highly water-soluble alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-receptor antagonist were investigated. YM872 is highly water soluble (83 mg mL(-1) in Britton-Robinson buffer) compared with 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX), 6-(1H-imidazol-1-yl)-7-nitro-2,3(1H,4H)-quinoxalinedione hydrochloride (YM90K) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). YM872 potently inhibits [3H]AMPA binding with a Ki (apparent equilibrium dissociation constant) value of 0.096 +/- 0.0024 microM. However, YM872 had very low affinity for other ionotropic glutamate receptors, as measured by competition with [3H]kainate (high-affinity kainate binding site, concentration resulting in half the maximum inhibition (IC50) = 4.6 +/- 0.14 microM), [3H]glutamate (N-methyl-D-aspartate (NMDA) receptor glutamate binding site, IC50 > 100 microM) and [3H]glycine (NMDA receptor glycine-binding site, IC50 > 100 microM). YM872 competitively antagonized kainate-induced currents in Xenopus laevis oocytes which express rat AMPA receptors, with a pA2 value of 6.97 +/- 0.01. In rat hippocampal primary cultures, YM872 blocked a 20-microM AMPA-induced increase of intracellular Ca2+ concentration with an IC50 value of 0.82 +/- 0.031 microM, and blocked 300-microM kainate-induced neurotoxicity with an IC50 value of 1.02 microM. These results show that YM872 is a potent and highly water-soluble AMPA antagonist with great potential for treatment of neurodegenerative disorders such as stroke. PMID:9720630

Kohara, A; Okada, M; Tsutsumi, R; Ohno, K; Takahashi, M; Shimizu-Sasamata, M; Shishikura, J; Inami, H; Sakamoto, S; Yamaguchi, T

1998-07-01

40

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

41

N-Methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors involved in the induction of sedative effects under an acute stress in neonatal chicks.  

PubMed

Glutamate, an excitatory amino acid, acts at several glutamate receptor subtypes. Recently, we reported that central administration of glutathione induced hypnosis under stressful conditions in neonatal chicks. Glutathione appears to bind to the N-methyl-D-aspartate (NMDA) receptor. To clarify the involvement of each glutamate receptor subtype during stressful conditions, intracerebroventricular (i.c.v.) injection of several glutamate receptor agonists was given to chicks under social separation stress. Glutamate dose-dependently induced a hypnotic effect. NMDA, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and kainate are characterized as ionotropic glutamate receptors (iGluRs). Although NMDA also induced a sedative effect, [corrected] the potency of NMDA for sleep-like behavior [corrected] was less than that of glutamate. AMPA tended to decrease distress vocalizations induced by acute stress and brought about a sedative effect. Kainate and (S)-3, 5-dehydroxyphenylglycine, which is a metabotropic glutamate receptor agonist, had no influence on chick behavior. Thus, it is suggested that the iGluRs, NMDA and AMPA, are important in inducing hypnosis and sedation under acute stress in chicks. PMID:19018608

Yamane, H; Tsuneyoshi, Y; Denbow, D M; Furuse, M

2009-10-01

42

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

E-print Network

. Interestingly, polyalanine and polyglutamine repeats associated with disease show very distinctive features Inc. All rights reserved. Keywords: Amino acid repeat; Slippage; Triplet expansion; Protein codon repeat tracts in repeat- coding sequences [7,8]. In humans, coding triplet repeat instability

Mularoni, Loris

43

Behavioural effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-receptor antagonists and their relevance to substance abuse.  

PubMed

This review presents some of the work that has been carried out to investigate the behavioural effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-receptor antagonists in animal models of substance abuse. Many of the studies have been conducted in light of current ideas that emphasise the analogous role of glutamatergic mechanisms in synaptic plasticity and long-term behavioural adaptation to drugs. Experiments on behavioural sensitisation indicate that whereas N-methyl-D-aspartate receptors are involved in induction, AMPA-receptors may mediate expression of the established response. In this regard, an important factor may be the degree of drug-environment conditioning. Thus, studies of the effects of AMPA-receptor antagonists on conditioned behaviours are reviewed here. Relatively few studies on the effects of AMPA-receptor antagonists on primary reinforcement from self-administered drugs and the subjective effects of drugs have been carried out, but a profile that contrasts with that of the N-methyl-D-aspartate antagonists appears to be emerging. Studies of withdrawal from opioids suggest that whilst AMPA-receptor antagonists may not be able to prevent tolerance or dependence from developing, they may ameliorate both the physical and emotional consequences of withdrawal. Overall, the AMPA-receptor antagonists may represent a promising new approach for treating the consequences of drug abuse. However, as results are often complicated by the use of the less-selective compounds, it will be important to use better tools in future studies. PMID:11033384

Jackson, A; Mead, A N; Stephens, D N

2000-10-01

44

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

45

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

Microsoft Academic Search

Rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric CO2. Current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important. Here, we use carbon isotopic evidence and water chemistry of springs and rivers

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

2008-01-01

46

A role for alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid GluR1 phosphorylation in the modulatory  

E-print Network

in the control of aspects of motivated behavior relevant to issues of public health, such as substance abuse, animals are separately trained to associate a Pavlovian CS with a reinforcer, such as food, and to perform for the first time while the animal is performing the instrumental response. Enhanced performance

Holland, Peter

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

48

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

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

49

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

PubMed

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

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

2011-04-14

50

Carboxylic Acids as Indicators of Parent Body Conditions  

NASA Astrophysics Data System (ADS)

Alpha-hydroxy and alpha-amino carboxylic acids found on the Murchison meteorite are deuterium enriched [1]. It is postulated that they arose from a common interstellar source: the reaction of carbonyl compounds in an aqueous mixture containing HCN and NH3. Carbonyl compounds react with HCN to form alph-hydroxy nitriles, RR'CO + HCN <--> RR'C(OH)CN. If ammonia is also present, the alpha-hydroxy nitriles will exist in equilibirum with the alpha-amino nitriles, RR'C(OH)CN +NH3 .<--> RRCNH2CN + H2O. Both nitriles are hydrolyzed by water to form carboxylic acids: RR'C(OH)CN + H2O --> RR'C(OH)CO2H and RR'C(NH2)CN + H2O --> RR'C(NH2)CO2H. Carbonyl compounds observed in the interstellar medium have been shown to be deuterium enriched [2]. The combined alpha-amino acids found on Murchison have deltaD = +1751 o/oo while the combined alpha-hydroxy acids have deltaD = +573. o/oo [1]. This large discrepancy in deltaD values does not preclude common precursors for the alpha-amino acids and the alpha-hydroxy acids. Different relative amounts of specific alpha-amino and alpha-hydroxy acids could lead to quite different combined D/H ratios. If the alpha-hydroxy acids lose significantly more deuterium during synthesis than the alpha-amino acids or if they have a higher rate of H/D exchange with liquid water than alpha-amino acids, the alpha-hydroxy acids would be isotopically lighter than the alpha-amino acids, because the water responsible for the aqueous alteration of the Murchison parent body was deuterium depleted with deltaD = -100. o/oo [3]. To determine between these alternative mechanisms we measured the rates of hydrogen-deuterium exchange of glycolic acid (the alpha-hydroxy analog of glycine), lactic acid (the alpha-hydroxy analog of alanine), and alpha-hydroxy isobutyric acid have been measured in D2O as a function of pH, temperature and the presence of Allende or Murchison minerals. No detectable H/D exchange was observed. Glycine subjected to similar conditons exchanged as much as 80% of its carbon-bonded deuterium, and alanine 43% [4]. Evidently, the relative deuterium content of the alpha-amino acids and alpha-hydroxy acids found on the Murchison meteorite was not determined by H/D exchange with water. In order to determine if deuterium retention is less for alpha-hydroxy acids than it is for alpha-amino carboxylic acids during synthesis a solution was prepared containing: KCN, 0.005M; NH4Cl, 0.002 M; CD2O, 0.0007M; CD3CDO, 0.0008 M; and (CD3)2CO 0.0006 M, and divided into aliquots which were maintained at 263 K and at 295 K. At the end of one month the carbonyls, alpha-amino acids and alpha-hydroxy acids were separated from the mixture and their deuterium content determined from their mass spectra (see Table 1). The retention of deuterium during synthesis varies significantly between the alpha-hydroxy acids and the alpha-amino acids with common precursors. Only comparisons of D/H ratios of specific acids with a postulated common precursor are meaningful. References: [1] Cronin J. R. et al. (1993) GCA, 57, 4745-4752. [2] Zinner E. (1988) in Meteorites and the Early Solar System (J. R. Kerridge and M. S. Matthews, eds.), 956-983, Univ. of Arizona. [3] Robert F. and Epstein S. (1982) GCA, 46, 81-95. [4] Lerner N. R. (1995) GCA, 59, 1623-1631. Table 1 shows D/(D+H) of carbon-bonded hydrogen in compounds separated after one month from a simulated meteorite solution.

Lerner, N. R.

1995-09-01

51

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

52

Switchable reactivity of acylated alpha, beta-dehydroamino ester in the Friedel-Crafts alkylation of indoles by changing the Lewis acid.  

PubMed

Highly regioselective electrophilic substitution of indoles with N-acetylated alpha,beta-dehydroalanine methyl ester, promoted by different transition metal salts was achieved. The orthogonal regioselectivity provides an efficient protocol toward highly functionalized 3-indolyl-alpha-amino acids. The mechanism of the reactions was explored by NMR studies. PMID:18558761

Angelini, Elena; Balsamini, Cesarino; Bartoccini, Francesca; Lucarini, Simone; Piersanti, Giovanni

2008-07-18

53

Evolution from amino acids - Lunar occurrence of their precursors.  

NASA Technical Reports Server (NTRS)

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

Fox, S. W.

1972-01-01

54

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.

55

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

56

Design, Synthesis, and Biological Evaluation of Novel Constrained meta-Substituted Phenyl Propanoic Acids as Peroxisome Proliferator-Activated Receptor r and Dual Agonists  

E-print Network

Acids as Peroxisome Proliferator-Activated Receptor r and Dual Agonists Young-Ger Suh,*, Nam-Jung Kim. Introduction Peroxisome proliferator-activated receptors (PPARsa ) regulate the lipid and glucose metabolism

Suh, Young-Ger

57

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

58

Choosing health, constrained choices.  

PubMed

In parallel with the neo-liberal retrenchment of the welfarist state, an increasing emphasis on the responsibility of individuals in managing their own affairs and their well-being has been evident. In the health arena for instance, this was a major theme permeating the UK government's White Paper Choosing Health: Making Healthy Choices Easier (2004), which appealed to an ethos of autonomy and self-actualization through activity and consumption which merited esteem. As a counterpoint to this growing trend of informed responsibilization, constrained choices (constrained agency) provides a useful framework for a judicious balance and sense of proportion between an individual behavioural focus and a focus on societal, systemic, and structural determinants of health and well-being. Constrained choices is also a conceptual bridge between responsibilization and population health which could be further developed within an integrative biosocial perspective one might refer to as the social ecology of health and disease. PMID:20028669

Chee Khoon Chan

2009-12-01

59

Single-step, quantitative derivatization of amino, carboxyl, and hydroxyl groups in iodothyronine amino acids with ethanolic pivalic anhydride containing 4-dimethylaminopyridine.  

PubMed

Reaction of thyroxine with ethanol and pivalic anhydride in the presence of 4-dimethylaminopyridine quantitatively forms N,O-dipivalyl thyroxine ethyl ester. Other iodothyronines react similarly and the procedure is moisture insensitive. Apparently this reaction is successful, in contrast to similar procedures reported for the derivatization of alpha-amino acids, because it overcomes the problem in other procedures of irreversible side reactions arising from an oxazolone intermediate. PMID:3963377

Joppich, M; Joppich-Kuhn, R; Sentissi, A; Giese, R W

1986-02-15

60

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

61

Distributed constrained heuristic search  

Microsoft Academic Search

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

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

1991-01-01

62

Thermal copoly/amino acids/ as inhibitors of glyoxalase I  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

63

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

PubMed

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

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

2009-01-01

64

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

65

Deamination of the amino acid fragment in imine metallacycles: unexpected synthesis of an NH-aldimine organometallic compound.  

PubMed

We report that the action of Lewis bases, such as triphenylphosphine, pyridine, or trimethylamine, on imine metallacycles derived from amino acids leads to the formation of the first organometallic compound of an NH aldimine, a highly reactive organic species, and the corresponding alpha-ketoester, in a deamination reaction that mimics the metabolism of alpha-amino acids. The synthesis of different cyclopalladated compounds by a reaction between palladium acetate and the Schiff bases 2,4,6-Me(3)C(6)H(2)CH=NCH(R(1))COOR(2) (R(1) = CH(2)Ph, R(2) = Et and R(1) = Ph, R(2) = Me) is also reported. PMID:16224753

Albert, Joan; Cadena, J Magali; González, Asensio; Granell, Jaume; Solans, Xavier; Font-Bardia, Mercè

2006-01-11

66

Optimal Anytime Constrained Simulated Annealing for Constrained Global Optimization?  

E-print Network

Optimal Anytime Constrained Simulated Annealing for Constrained Global Optimization? Benjamin W cooling schedule in generating a solution of sim- ilar quality. Here, an optimal cooling schedule is one global minimum (CGM). In our study, we have observed a monotonically non-decreasing function relating

Neumaier, Arnold

67

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

68

Constraining neutrinoless double beta decay  

E-print Network

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

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

2011-11-23

69

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 is disclosed. 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. 17 figs.

Heckendorn, F.M.; Anderson, E.K.; Robinson, C.W.; Haynes, H.B.

1999-05-11

70

Constrained Vapor Bubble  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

71

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

2008-03-05

72

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

73

Line constrained between two curves  

NASA Astrophysics Data System (ADS)

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

Ahmad, Afida; Ali, Jamaludin Md.

2013-04-01

74

Wavelet library for constrained devices  

Microsoft Academic Search

The wavelet transform is a powerful tool for image and video processing, useful in a range of applications. This paper is concerned with the efficiency of a certain fast-wavelet-transform (FWT) implementation and several wavelet filters, more suitable for constrained devices. Such constraints are typically found on mobile (cell) phones or personal digital assistants (PDA). These constraints can be a combination

Johan Hendrik Ehlers; Sabah A. Jassim

2007-01-01

75

Generalized Constrained Multiple Correspondence Analysis.  

ERIC Educational Resources Information Center

Proposes a comprehensive approach, generalized constrained multiple correspondence analysis, for imposing both row and column constraints on multivariate discrete data. Each set of discrete data is decomposed into several submatrices and then multiple correspondence analysis is applied to explore relationships among the decomposed submatrices.…

Hwang, Heungsun; Takane, Yoshio

2002-01-01

76

Constrained Sums of Information Systems  

Microsoft Academic Search

\\u000a We study properties of infomorphisms between information systems. In particular, we interpret infomorphisms between information\\u000a systems in terms of sums with constraints (constrained sums, for short) that are some operations on information systems. Applications\\u000a of approximation spaces, used in rough set theory, to study properties of infomorphisms are included.

Andrzej Skowron; Jaroslaw Stepaniuk

2004-01-01

77

A reexamination of amino acids in lunar soil  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

78

Constrained multiobjective biogeography optimization algorithm.  

PubMed

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

79

Diameter-Constrained Steiner Tree  

NASA Astrophysics Data System (ADS)

Given an edge-weighted undirected graph G = (V,E,c,w), where each edge e ? E has a cost c(e) and a weight w(e), a set S ? V of terminals and a positive constant D 0, we seek a minimum cost Steiner tree where all terminals appear as leaves and its diameter is bounded by D 0. Note that the diameter of a tree represents the maximum weight of path connecting two different leaves in the tree. Such problem is called the minimum cost diameter-constrained Steiner tree problem. This problem is NP-hard even when the topology of Steiner tree is fixed. In present paper we focus on this restricted version and present a fully polynomial time approximation scheme (FPTAS) for computing a minimum cost diameter-constrained Steiner tree under a fixed topology.

Ding, Wei; Lin, Guohui; Xue, Guoliang

80

Constrained ballistics and geometrical optics  

E-print Network

The problem of constant-speed ballistics is studied under the umbrella of non-linear non-holonomic constrained systems. The Newtonian approach is shown to be equivalent to the use of Chetaev's rule to incorporate the constraint within the initially unconstrained formulation. Although the resulting equations are not, in principle, obtained from a variational statement, it is shown that the trajectories coincide with those of geometrical optics in a medium with a suitably chosen refractive index, as prescribed by Fermat's principle of least time. This fact gives rise to an intriguing mechano-optical analogy. The trajectories are further studied and discussed.

Epstein, Marcelo

2014-01-01

81

Constraining Disformally Coupled Scalar Fields  

E-print Network

Light scalar fields can naturally couple disformally to matter fields. Static, non-relativistic sources do not generate a classical field profile for a disformally coupled scalar, and so such scalars are free from the constraints on the existence of fifth forces that are so restrictive for conformally coupled scalars. In this work we show that disformally coupled scalars can still be studied and constrained through their microscopic interactions with fermions and photons, both in terrestrial laboratories and from observations of stars. The strongest constraint on the coupling scale comes from mono-photon searches at the LHC and requires $M \\gtrsim 10^2 \\mbox{ GeV}$.

Philippe Brax; Clare Burrage

2014-07-07

82

Constraining Disformally Coupled Scalar Fields  

E-print Network

Light scalar fields can naturally couple disformally to matter fields. Static, non-relativistic sources do not generate a classical field profile for a disformally coupled scalar, and so such scalars are free from the constraints on the existence of fifth forces that are so restrictive for conformally coupled scalars. In this work we show that disformally coupled scalars can still be studied and constrained through their microscopic interactions with fermions and photons, both in terrestrial laboratories and from observations of stars. The strongest constraint on the coupling scale comes from mono-lepton searches at the LHC and requires $M \\gtrsim 10^2 \\mbox{ GeV}$.

Brax, Philippe

2014-01-01

83

Bacillus subtilis SSE4 produces subtulene A, a new lipopeptide antibiotic possessing an unusual C15 unsaturated beta-amino acid.  

PubMed

Subtulene A, a new cyclic lipopeptide, was isolated from the culture broth of Bacillus subtilis SSE4. This antibiotic compound contained the seven common alpha-amino acids, L-Asn-1, D-Tyr-2, D-Asn-3, L-Gln-4, L-Pro-5, D-Asn-6, L-Ser-7 and the unique beta-amino acid-8 present in the iturin family. 1D and 2D NMR, as well as MS analyses, identified the beta-amino acid as 3-amino-13-methyltetradec-8-enoic acid, an Iso C15 long chain beta-amino acid. B. subtilis SSE4 was also found to produce iturin A. B. subtilis SSE4 culture filtrate exhibited both antifungal and antibacterial activities. PMID:20541548

Thasana, Nopporn; Prapagdee, Benjaphorn; Rangkadilok, Nuchanart; Sallabhan, Ratiboot; Aye, Seaim Lwin; Ruchirawat, Somsak; Loprasert, Suvit

2010-07-16

84

Polyamine spider toxins are potent un-competitive antagonists of rat cortex excitatory amino acid receptors.  

PubMed

We examined the effect of argiopine and argiopinine 3, low molecular weight polyamine venom components of the spider Argiope lobata, on rat cortical excitatory amino acid (EAA) receptors expressed in Xenopus oocytes. Responses to 100 microM N-methyl-D-aspartate (NMDA) with 10 microM glycine were blocked by both of the polyamine toxins in a dose-dependent manner. Both compounds had similar potencies against 100 microM kainate or 50 microM (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (L-AMPA). Oscillatory responses to 2 microM quisqualate were unaffected by either polyamine toxin. Increasing concentrations of either NMDA, kainate or AMPA were unable to overcome the antagonism by either spider toxin. We were able to demonstrate a use-dependent phenomenon similar to that of phencyclidine; neither polyamine toxin affected the NMDA, kainate or AMPA response without the presence of the respective agonist. PMID:1385187

Davies, M S; Baganoff, M P; Grishin, E V; Lanthorn, T H; Volkova, T M; Watson, G B; Wiegand, R C

1992-09-01

85

Covalent protein crosslinks: general detection, quantitation, and characterization via modification with diphenylborinic acid.  

PubMed

Progressive crosslinking of proteins appears to be a general phenomenon in aging cells and tissues. Crosslinked proteins can form insoluble aggregates which become increasingly resistant to proteolysis as more crosslinks form. However, most evidence for progressive crosslinking with age is indirect, and little is known about the chemical mechanisms involved. We have therefore developed a method for detection and isolation of any type of stable covalent crosslink from protein hydrolysates which requires no prior knowledge of the molecular structure of whatever crosslink(s) may be present. It utilizes the specificity of the diphenylborinic acid reagent for alpha-amino acid groups and the chromatographic properties and uv absorbance of the crosslink derivatives. The method is demonstrated using eight different crosslinks from collagen and fibrin, and a general procedure is given for detection of any type of crosslink in a protein hydrolysate. PMID:8203759

Graham, L; Gallop, P M

1994-03-01

86

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

87

Exploring constrained quantum control landscapes  

NASA Astrophysics Data System (ADS)

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.

Moore, Katharine W.; Rabitz, Herschel

2012-10-01

88

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

89

Continuous Dynamic Constrained Optimisation – The Challenges  

E-print Network

May 24, 2012 ... Continuous Dynamic Constrained Optimisation – The Challenges ... benchmark problems with these characteristics and test several representative ... special characteristics that can significantly affect algorithm performance.

Nguyen Trung Thanh

2012-05-24

90

Hydrolysis of Al3+ from constrained molecular dynamics  

NASA Astrophysics Data System (ADS)

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

Ikeda, Takashi; Hirata, Masaru; Kimura, Takaumi

2006-02-01

91

Constrained subpixel target detection for hyperspectral imagery  

NASA Astrophysics Data System (ADS)

Target detection in remotely sensed images can be conducted spatially, spectrally or both. The difficulty of detecting targets in remotely sensed images with spatial image analysis arises from the fact that the ground sampling distance is generally larger than the size of the targets of interest in which case targets are embedded in a single pixel and cannot be detected spatially. Under this circumstance target detection must be carried out at subpixel level and spectral analysis offers a valuable alternative. This paper compares two constrained approaches for subpixel detection of targets in remote sensing images. One is a target abundance-constrained approach, referred to as the nonnegatively constrained least squares (NCLS) method. It is a constrained least squares linear spectral mixture analysis method which implements a nonnegatively constraint on the abundance fractions of targets of interest. A common drawback of linear spectral mixture analysis based methods is the requirement for prior knowledge of the endmembers present in an image scene. In order to mitigate this drawback, the NCLS method is extended to create an unsupervised approach, referred to as the unsupervised nonnegatively constrained least present in the image scene. The second approach is a target signature-constrained method, called the constrained energy minimization (CEM) method. It constrains the desired target signature with a specific gain while minimizing effects caused by other unknown signatures. Data from the HYperspectral Digital Imagery Collection Experiment (HYDICE) sensor are used to compare the performance of these methods.

Chang, Chein-I.; Heinz, Daniel C.

2000-07-01

92

Variational integrators for constrained dynamical systems  

Microsoft Academic Search

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

Sigrid Leyendecker; Jerrold E. Marsden; Michael Ortiz

2008-01-01

93

Determination of optimal gains for constrained controllers  

SciTech Connect

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

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

1993-08-01

94

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

95

Wavelet library for constrained devices  

NASA Astrophysics Data System (ADS)

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

Ehlers, Johan Hendrik; Jassim, Sabah A.

2007-04-01

96

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

97

BICEP2 constrains composite inflation  

NASA Astrophysics Data System (ADS)

In light of BICEP2, we re-examine single field inflationary models in which the inflation is a composite state stemming from various four-dimensional strongly coupled theories. We study in the Einstein frame a set of cosmological parameters, the primordial spectral index ns and tensor-to-scalar ratio r, predicted by such models. We confront the predicted results with the joint Planck data, and with the recent BICEP2 data. We constrain the number of e-foldings for composite models of inflation in order to obtain a successful inflation. We find that the minimal composite inflationary model is fully consistent with the Planck data. However it is in tension with the recent BICEP2 data. The observables predicted by the glueball inflationary model can be consistent with both Planck and BICEP2 contours if a suitable number of e-foldings are chosen. Surprisingly, the super Yang-Mills inflationary prediction is significantly consistent with the Planck and BICEP2 observations.

Channuie, Phongpichit

2014-07-01

98

Gyrification from constrained cortical expansion.  

PubMed

The exterior of the mammalian brain--the cerebral cortex--has a conserved layered structure whose thickness varies little across species. However, selection pressures over evolutionary time scales have led to cortices that have a large surface area to volume ratio in some organisms, with the result that the brain is strongly convoluted into sulci and gyri. Here we show that the gyrification can arise as a nonlinear consequence of a simple mechanical instability driven by tangential expansion of the gray matter constrained by the white matter. A physical mimic of the process using a layered swelling gel captures the essence of the mechanism, and numerical simulations of the brain treated as a soft solid lead to the formation of cusped sulci and smooth gyri similar to those in the brain. The resulting gyrification patterns are a function of relative cortical expansion and relative thickness (compared with brain size), and are consistent with observations of a wide range of brains, ranging from smooth to highly convoluted. Furthermore, this dependence on two simple geometric parameters that characterize the brain also allows us to qualitatively explain how variations in these parameters lead to anatomical anomalies in such situations as polymicrogyria, pachygyria, and lissencephalia. PMID:25136099

Tallinen, Tuomas; Chung, Jun Young; Biggins, John S; Mahadevan, L

2014-09-01

99

Towards spatially constrained gust models  

NASA Astrophysics Data System (ADS)

With the trend of moving towards 10-20 MW turbines, rotor diameters are growing beyond the size of the largest turbulent structures in the atmospheric boundary layer. As a consequence, the fully uniform transients that are commonly used to predict extreme gust loads are losing their connection to reality and may lead to gross overdimensioning. More suiting would be to represent gusts by advecting air parcels and posing certain physical constraints on size and position. However, this would introduce several new degrees of freedom that significantly increase the computational burden of extreme load prediction. In an attempt to elaborate on the costs and benefits of such an approach, load calculations were done on the DTU 10 MW reference turbine where a single uniform gust shape was given various spatial dimensions with the transverse wavelength ranging up to twice the rotor diameter (357 m). The resulting loads displayed a very high spread, but remained well under the level of a uniform gust. Moving towards spatially constrained gust models would therefore yield far less conservative, though more realistic predictions at the cost of higher computation time.

Bos, René; Bierbooms, Wim; van Bussel, Gerard

2014-06-01

100

21 CFR 888.3720 - Toe joint polymer constrained prosthesis.  

Code of Federal Regulations, 2010 CFR

... 2010-04-01 false Toe joint polymer constrained prosthesis. 888.3720...Prosthetic Devices § 888.3720 Toe joint polymer constrained prosthesis. (a) Identification. A toe joint polymer constrained prosthesis is a...

2010-04-01

101

21 CFR 888.3720 - Toe joint polymer constrained prosthesis.  

Code of Federal Regulations, 2011 CFR

... 2011-04-01 false Toe joint polymer constrained prosthesis. 888.3720...Prosthetic Devices § 888.3720 Toe joint polymer constrained prosthesis. (a) Identification. A toe joint polymer constrained prosthesis is a...

2011-04-01

102

21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Wrist joint polymer constrained prosthesis. 888.3780...Devices § 888.3780 Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a...

2010-04-01

103

21 CFR 888.3230 - Finger joint polymer constrained prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Finger joint polymer constrained prosthesis... Prosthetic Devices § 888.3230 Finger joint polymer constrained prosthesis. (a) Identification. A finger joint polymer constrained...

2010-04-01

104

21 CFR 888.3230 - Finger joint polymer constrained prosthesis.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Finger joint polymer constrained prosthesis... Prosthetic Devices § 888.3230 Finger joint polymer constrained prosthesis. (a) Identification. A finger joint polymer constrained...

2011-04-01

105

Convex Approximations of Chance Constrained Programs  

E-print Network

Key words: stochastic programming, chance constraints, convex programming, ... Chance constrained optimization problems were introduced in Charnes et al ... Typically, the only way to estimate the probability for a chance constraint to be ...

2005-12-20

106

Nonlinear contraction tools for constrained optimization  

E-print Network

This thesis derives new results linking nonlinear contraction analysis, a recent stability theory for nonlinear systems, and constrained optimization theory. Although dynamic systems and optimization are both areas that ...

Soto, Jonathan

2010-01-01

107

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

108

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

Microsoft Academic Search

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

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

2007-01-01

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

Unique antitumour effects of L-2,4 diaminobutyric acid on cultured hepatoma cells.  

PubMed

A single hepatoma cell line was grown in vitro and incubated with L-2,4 diaminobutyric acid (DAB), a non-metabolizable amino acid, under various conditions. The tumour cells were irreversibly damaged by incubation for 8 hours with 8 mmol/L of DAB. The tumour cell-destroying effect of DAB was dose- and time-dependent with no effect at a DAB concentration of 1.6 mmol/L. The presence of N-methyl alpha-aminoisobutyric acid (a specific substrate of amino acid transport system A) in the incubation medium abrogated the tumour cell destructive effect of DAB in a dose-dependent fashion. The presence of non-physiological amino acids in the incubation medium per se was not the cause of tumour cell destruction, since inclusion of alpha-amino-isobutyric acid and N-methyl alpha-aminoisobutyric acid in the incubation medium did not influence the viability of hepatoma cells. We conclude that the tumour cell destructive effect of DAB was the result of a huge and unlimited uptake of DAB energized by the Na(+)-gradient and that this uptake was not subjected to the law of saturation kinetics. This was combined with a tumour cell energy crisis in attempts to restore the Na(+)-gradient. PMID:12820378

Blind, Per-Jonas; Waldenström, Anders; Hafström, Larsolof; Berggren, Diana; Ronquist, Gunnar

2003-01-01

111

Vibration Control through Passive Constrained Layer Damping and Active Control  

Microsoft Academic Search

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

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

1997-01-01

112

Iterative Clustering with Constrained Graph Cut  

NASA Astrophysics Data System (ADS)

This paper proposes a constrained clustering method based on an iterative data division by a constrained graph cutting approach. Since our proposed constrained graph cut problem is formalized by semidefinite programming, must-link constraints can be naturally imported to the problem. Though the solution matrix obtained by solving the problem does not directly reflect cluster members, we introduce an efficient heuristic algorithm to produce clusters without any complex procedures such as matrix decomposition. In the experiments, we compared our method with other state-of-the art and well-known clustering techniques on the UCI repository and CLUTO datasets. Our method showed outperformed or comparable results compared with other traditional ones on more than half of the datasets. We also compared the calculation cost. Though our method tends to consume more time to calculate, the total cost is at most double compared with other SDP based method.

Okabe, Masayuki; Yamada, Seiji

113

Constraining Ceres' interior from its Rotational Motion  

E-print Network

Context. Ceres is the most massive body of the asteroid belt and contains about 25 wt.% (weight percent) of water. Understanding its thermal evolution and assessing its current state are major goals of the Dawn Mission. Constraints on internal structure can be inferred from various observations. Especially, detailed knowledge of the rotational motion can help constrain the mass distribution inside the body, which in turn can lead to information on its geophysical history. Aims. We investigate the signature of the interior on the rotational motion of Ceres and discuss possible future measurements performed by the spacecraft Dawn that will help to constrain Ceres' internal structure. Methods. We compute the polar motion, precession-nutation, and length-of-day variations. We estimate the amplitudes of the rigid and non-rigid response for these various motions for models of Ceres interior constrained by recent shape data and surface properties. Results. As a general result, the amplitudes of oscillations in the r...

Rambaux, Nicolas; Dehant, Véronique; Kuchynka, Petr

2011-01-01

114

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

115

Protein biosynthesis with conformationally restricted amino acids  

SciTech Connect

The incorporation of conformationally constrained amino acids into peptides is a powerful approach for generating structurally defined peptides as conformational probes and bioactive agents. The ability to site-specifically introduce constrained amino acids into large polypeptide chains would provide a similar opportunity to probe the flexibility, conformation, folding and stability of proteins. To this end, we have examined the competence of the Escherichia coli protein biosynthetic machinery to incorporate a number of these unnatural amino acids into the 164 residue protein T4 lysozyme (T4L). Results clearly demonstrate that the protein biosynthetic machinery can accommodate a wide variety of conformationally constrained amino acids. The expansion of structural motifs that can be biosynthetically incorporated into proteins to include a large number of conformationally constrained amino acids significantly increases the power of mutagenesis methods as probes of protein structure and function and provides additional insights into the steric requirements of the translational machinery. 13 refs., 2 figs.

Mendel, D. (Univ. of California, Berkeley (United States) Lawrence Berkeley Lab., CA (United States)); Ellman, J.; Schultz, P.G. (Univ. of California, Berkeley (United States))

1993-05-19

116

Spacecraft inertia estimation via constrained least squares  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

117

CONSTRAINED CENTROIDAL VORONOI TESSELLATIONS FOR SURFACES  

E-print Network

CONSTRAINED CENTROIDAL VORONOI TESSELLATIONS FOR SURFACES QIANG DU, MAX D. GUNZBURGER, AND LILI JU­1506 Abstract. Centroidal Voronoi tessellations are useful for subdividing a region in Euclidean space into Voronoi regions whose generators are also the centers of mass, with respect to a prescribed density

Du, Qiang

118

Remote gaming on resource-constrained devices  

Microsoft Academic Search

Games have become important applications on mobile devices. A mobile gaming approach known as remote gaming is being developed to support games on low cost mobile devices. In the remote gaming approach, the responsibility of rendering a game and advancing the game play is put on remote servers instead of the resource constrained mobile devices. The games rendered on the

Waazim Reza; Hari Kalva; Richard Kaufman

2010-01-01

119

Magnetic permeability of constrained scalar QED vacuum  

Microsoft Academic Search

We compute the influence of boundary conditions on the effective Lagrangian of scalar QED for the case of a pure magnetic field. The boundary conditions assumed here constrain the quantum scalar field but not the radiation field, so that the effect to be considered already appears at the one-loop level. The boundary conditions generate new contributions to the effective Lagrangian

M. V. Cougo-Pinto; C. Farina; M. R. Negrao; A. C. Tort

2000-01-01

120

Magnetic permeability of constrained scalar QED vacuum  

Microsoft Academic Search

We compute the influence of boundary conditions on the Euler-Heisenberg effective Lagrangian scalar QED scalar for the case of a pure magnetic field. The boundary conditions constrain the quantum scalar field to vanish on two parallel planes separeted by a distance $a$ and the magnetic field is assumed to be constant, uniform and perpendicular to the planes. The effective Lagrangian

M. V. Cougo-Pinto; C. Farina; M. R. Negrao; A. C. Tort

1998-01-01

121

TECHNICAL REPORT 9413 Directmapped Constrained Migration Problem  

E-print Network

TECHNICAL REPORT 94­13 Direct­mapped Constrained Migration Problem Susanne Albers and Hisashi Koga AUTHORS Susanne Albers and Hisashi Koga KEY WORDS AND PHRASES competitive analysis, distributed shared­Planck­Institut f¨ur Informatik Saarbr¨ucken, Germany albers@mpi­sb.mpg.de Hisashi Koga The University of Tokyo

Imai, Hiroshi

122

Efficient Dynamic Mining of Constrained Frequent Sets  

E-print Network

, Canada and RAYMOND T. NG The University of British Columbia, Vancouver, BC, Canada Data miningEfficient Dynamic Mining of Constrained Frequent Sets LAKS V. S. LAKSHMANAN The University of British Columbia, Vancouver, BC, Canada CARSON KAI-SANG LEUNG The University of Manitoba, Winnipeg, MB

Lakshmanan, Laks V.S.

123

On Tree-Constrained Matchings and Generalizations  

E-print Network

-Constrained Bipartite Matching problem: Given two rooted trees T1 = (V1, E1), T2 = (V2, E2) and a weight function w : V1, rooted trees, approximation algorithms, local ratio technique, inapproximability, computational biology 1 important biological processes, such as tis- sue repair, the analysis of drug performance, and immune system

Elbassioni, Khaled

124

Coordination as Constrained Interaction (Extended Abstract)  

E-print Network

Coordination as Constrained Interaction (Extended Abstract) Peter Wegner Brown University 1 Introduction Protocols that coordinate interactive communication among software compo- nents have qualitatively be expressed algorithmically [We2]. For example, driving home from work can be viewed as a coordination problem

Wegner, Peter

125

Hierarchical model of slow constrained dynamics  

Microsoft Academic Search

We introduce a simple hierarchically constrained model of slow relaxation. The configurational energy has a simple form as there is no coupling among the spins defining the system; the associated stationary distribution is an equilibrium, Gibbsian one. However, due to the presence of hierarchical constraints in the dynamics the system is found to relax to its equilibrium distribution in an

M. A. Muñoz; A. Gabrielli; H. Inaoka; L. Pietronero

1998-01-01

126

Variable-Metric Algorithm For Constrained Optimization  

NASA Technical Reports Server (NTRS)

Variable Metric Algorithm for Constrained Optimization (VMACO) is nonlinear computer program developed to calculate least value of function of n variables subject to general constraints, both equality and inequality. First set of constraints equality and remaining constraints inequalities. Program utilizes iterative method in seeking optimal solution. Written in ANSI Standard FORTRAN 77.

Frick, James D.

1989-01-01

127

Optimisation algorithms for spatially constrained forest planning  

Microsoft Academic Search

We compared genetic algorithms, simulated annealing and hill climbing algorithms on spatially constrained, integrated forest planning problems. There has been growing interest in algorithms that mimic natural processes, such as genetic algorithms and simulated annealing. These algorithms use random moves to generate new solutions, and employ a probabilistic acceptance\\/rejection criterion that allows inferior moves within the search space. Algorithms for

Guoliang Liu; Shijie Han; Xiuhai Zhao; John D. Nelson; Hongshu Wang; Weiying Wang

2006-01-01

128

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

129

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

130

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

131

Automation of constrained-value business forms  

SciTech Connect

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

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

1993-05-01

132

Automated Induction with Constrained Tree Automata  

E-print Network

Automated Induction with Constrained Tree Automata Adel Bouhoula1 and Florent Jacquemard2 1 Higher a procedure for automated implicit inductive theorem proving for equational specifications made of rewrite in the inductive proofs first as an induction scheme for the generation of sub- goals at induction steps, second

Paris-Sud XI, Université de

133

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

134

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

135

Geochemical Processes Constraining Iron Uptake in Strategy II Fe Acquisition.  

PubMed

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

Schenkeveld, W D C; Schindlegger, Y; Oburger, E; Puschenreiter, M; Hann, S; Kraemer, S M

2014-11-01

136

Constrained Optimization Path Following of Wheeled Robots  

E-print Network

Abstract. A smooth-primitive constrained-optimization-based path-tracking algorithm for mobile robots that compensates for rough terrain, predictable vehicle dynamics, and vehicle mobility constraints has been developed, implemented, and tested on the DARPA LAGR platform. Traditional methods for the geometric path following control problem involve trying to meet position constraints at fixed or velocity dependent look-ahead distances using arcs. We have reformulated the problem as an optimal control problem, using a trajectory generator that can meet arbitrary boundary state constraints. The goal state along the target path is determined dynamically by minimizing a utility function based on corrective trajectory feasibility and cross-track error. A set of field tests compared the proposed method to an implementation of the pure pursuit algorithm and showed that the smooth corrective trajectory constrained optimization approach exhibited higher performance than pure pursuit by achieving rough four times lower average cross-track error and two times lower heading error. 1

Thomas M. Howard; Alonzo Kelly

2006-01-01

137

The totally constrained model: three quantization approaches  

NASA Astrophysics Data System (ADS)

We provide a detailed comparison of the different approaches available for the quantization of a totally constrained system with a constraint algebra generating the non-compact group. In particular, we consider three schemes: the Refined Algebraic Quantization, the Master Constraint Programme and the Uniform Discretizations approach. For the latter, we provide a quantum description where we identify semiclassical sectors of the kinematical Hilbert space. We study the quantum dynamics of the system in order to show that it is compatible with the classical continuum evolution. Among these quantization approaches, the Uniform Discretizations provides the simpler description in agreement with the classical theory of this particular model, and it is expected to give new insights about the quantum dynamics of more realistic totally constrained models such as canonical general relativity.

Gambini, Rodolfo; Olmedo, Javier

2014-08-01

138

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

139

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

140

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

141

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

142

Supergravity as a constrained BF theory  

SciTech Connect

In this paper we formulate N=1 supergravity as a constrained BF theory with OSp(4|1) gauge superalgebra. We derive the modified supergravity Lagrangian that, apart from standard supergravity with a negative cosmological constant, contains terms proportional to the (inverse of the) Immirzi parameter. Although these terms do not change classical field equations, they might be relevant in quantum theory. We briefly discuss the perturbation theory around the supersymmetric topological vacuum.

Durka, R.; Kowalski-Glikman, J.; Szczachor, M. [Institute for Theoretical Physics, University of Wroclaw, Maxa Borna 9, Pl-50-204 Wroclaw (Poland)

2010-02-15

143

Constrained Simulation of the Bullet Cluster  

NASA Astrophysics Data System (ADS)

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

Lage, Craig; Farrar, Glennys

2014-06-01

144

Firefly Algorithm for Continuous Constrained Optimization Tasks  

Microsoft Academic Search

The paper provides an insight into the improved novel metaheuristics of the Firefly Algorithm for constrained continuous optimization\\u000a tasks. The presented technique is inspired by social behavior of fireflies and the phenomenon of bioluminescent communication.\\u000a The first part of the paper is devoted to the detailed description of the existing algorithm. Then some suggestions for extending\\u000a the simple scheme of

Szymon ?ukasik; S?awomir ?ak

145

Constraining Neutron Star Matter with Quantum Chromodynamics  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

146

Fast features for time constrained object detection  

Microsoft Academic Search

This paper concerns itself with the development and design of fast features suitable for time constrained object detection. Primarily we consider three aspects of feature design; the form of the precomputed datatype (e.g. the integral image), the form of the features themselves (i.e. the measurements made of an image), and the models\\/weak- learners used to construct weak classifiers (class, non-class

Gary Overett; Lars Petersson

2009-01-01

147

Constraining bubbling of methane from thermokarst lakes  

NASA Astrophysics Data System (ADS)

In northern thermokarst lakes, which form in depressions left as permafrost thaws, methane, a greenhouse gas, can be released from lake sediments to the atmosphere through bubbling, or ebullition. Constraining the amount of methane released through bubbling would help scientists understand the role of thawing permafrost in the carbon cycle and global climate change. However, bubbling is highly variable in both space and time and thus difficult to measure accurately, so there are large uncertainties in estimates of methane emissions from northern ecosystems.

Balcerak, Ernie

2013-08-01

148

Morphological alterations accompanying the effect of peptaibiotics, alpha-aminoisobutyric acid-rich secondary metabolites of filamentous fungi, on Culex pipiens larvae.  

PubMed

The effect of different representatives of the group of peptaibiotics, alpha-amino-isobutyric acid rich secondary metabolites of filamentous fungi, on Culex pipiens larvae was studied. Light and transmission electron microscopy techniques were used to localize the intracellular damage and to determine the target organells for the mode of action of peptaibols in mosquito larvae. Though different in insecticidal activity, all tested compounds induced the same type of tissue damage, which was characterized by heavy challenge of mitochondria followed by partial swelling, crystaeolysis and destruction of mitochondrial walls. It is concluded that the mode of action of peptaibols in mosquito larvae is mediated through the damage of mitochondria. The structure-mosquitocidal effect of these compounds, their potential mode of action and role in the natural fungal entomopathogenic process are briefly discussed. PMID:1359675

Matha, V; Jegorov, A; Kiess, M; Brückner, H

1992-01-01

149

CONSTRAINING SOURCE REDSHIFT DISTRIBUTIONS WITH GRAVITATIONAL LENSING  

SciTech Connect

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

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

2012-09-10

150

Constrained effective potential in hot QCD  

NASA Astrophysics Data System (ADS)

Constrained effective potentials in hot gauge theory give the probability that a configuration p of the order parameter (Polyakov loop) occurs. They are important in the analysis of surface effects and bubble formation in the plasma. The vector potential appears non-linearly in the loop; in weak coupling the linear term gives rise to the traditional free-energy graphs. But the non-linear terms generate insertions of the constrained modes into the free-energy graphs, through renormalisations of the Polyakov loop. These insertions are gauge dependent and are necessary to cancel the gauge dependence of the free-energy graphs. The latter is shown, through the BRST identities, to have again the form of constrained mode insertions. We stress that the effective action, without this insertion, is gauge variant and gives quite deceptive information. Amongst more it follows, that absolute minima of the potential are at the center group values of the loop, once the insertion is done. We evaluate the two-loop contributions for SU( N) gauge theories, with and without quarks, for the full domain of the N - 1 variables.

Altes, C. P. Korthals

1994-06-01

151

An Alternating Direction Method for Chance-Constrained ...  

E-print Network

School of Economics and Management, Tongji University, Shanghai 200092, ... Chance-constrained or probabilistically constrained optimization problems were first in- ...... Chair Grant at School of Business, National University of Singapore.

2013-11-22

152

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.

153

The canonical equilibrium of constrained molecular models  

NASA Astrophysics Data System (ADS)

In order to increase the efficiency of the computer simulation of biological molecules, it is very common to impose holonomic constraints on the fastest degrees of freedom; normally bond lengths, but also possibly bond angles. Since the maximum time step required for the stability of the dynamics is proportional to the shortest period associated with the motions of the system, constraining the fastest vibrations allows to increase it and, assuming that the added numerical cost is not too high, also increase the overall efficiency of the simulation. However, as any other element that affects the physical model, the imposition of constraints must be assessed from the point of view of accuracy: both the dynamics and the equilibrium statistical mechanics are model-dependent, and they will be changed if constraints are used. In this review, we investigate the accuracy of constrained models at the level of the equilibrium statistical mechanics distributions produced by the different dynamics. We carefully derive the canonical equilibrium distributions of both the constrained and unconstrained dynamics, comparing the two of them by means of a "stiff" approximation to the latter. We do so both in the case of flexible and hard constraints, i.e., when the value of the constrained coordinates depends on the conformation and when it is a constant number. We obtain the different correcting terms associated with the kinetic energy mass-metric tensor determinants, but also with the details of the potential energy in the vicinity of the constrained subspace (encoded in its first and second derivatives). This allows us to directly compare, at the conformational level, how the imposition of constraints changes the thermal equilibrium of molecular systems with respect to the unconstrained case. We also provide an extensive review of the relevant literature, and we show that all models previously reported can be considered special cases of the most general treatments presented in this work. Finally, we numerically analyze a simple methanol molecule in order to illustrate the theoretical concepts in a practical case.

Echenique, P.; Cavasotto, C. N.; García-Risueño, P.

2011-11-01

154

Position control and explicit force control of a constrained manipulator  

Microsoft Academic Search

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

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

1997-01-01

155

Quantum dynamics by the constrained adiabatic trajectory method  

Microsoft Academic Search

We develop the constrained adiabatic trajectory method (CATM), which allows one to solve the time-dependent Schroedinger equation constraining the dynamics to a single Floquet eigenstate, as if it were adiabatic. This constrained Floquet state (CFS) is determined from the Hamiltonian modified by an artificial time-dependent absorbing potential whose forms are derived according to the initial conditions. The main advantage of

A. Leclerc; G. Jolicard; S. Guerin; J. P. Killingbeck

2011-01-01

156

Quantum dynamics by the constrained adiabatic trajectory method  

Microsoft Academic Search

We develop the constrained adiabatic trajectory method (CATM), which allows one to solve the time-dependent Schrödinger equation constraining the dynamics to a single Floquet eigenstate, as if it were adiabatic. This constrained Floquet state (CFS) is determined from the Hamiltonian modified by an artificial time-dependent absorbing potential whose forms are derived according to the initial conditions. The main advantage of

A. Leclerc; S. Guérin; G. Jolicard; J. P. Killingbeck

2011-01-01

157

Vibration control through passive constrained layer damping and active control  

Microsoft Academic Search

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

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

1997-01-01

158

21 CFR 888.3790 - Wrist joint metal constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...joint metal constrained cemented prosthesis. 888.3790 Section 888...joint metal constrained cemented prosthesis. (a) Identification. A wrist joint metal constrained cemented prosthesis is a device intended...

2010-04-01

159

DeltapH-Dependent Amino Acid Transport into Plasma Membrane Vesicles Isolated from Sugar Beet (Beta vulgaris L.) Leaves: II. Evidence for Multiple Aliphatic, Neutral Amino Acid Symports.  

PubMed

Proton-coupled aliphatic, neutral amino acid transport was investigated in plasma membrane vesicles isolated from sugar beet (Beta vulgaris L., cv Great Western) leaves. Two neutral amino acid symport systems were resolved based on inter-amino acid transport competition and on large variations in the specific activity of each porter in different species. Competitive inhibition was observed for transport competition between alanine, methionine, glutamine, and leucine (the alanine group) and between isoleucine, valine, and threonine (the isoleucine group). The apparent K(m) and K(i) values were similar for transport competition among amino acids within the alanine group. In contrast, the kinetics of transport competition between these two groups of amino acids did not fit a simple competitive model. Furthermore, members of the isoleucine group were weak transport antagonists of the alanine group. These results are consistent with two independent neutral amino acid porters. In support of that conclusion, the ratio of the specific activity of alanine transport versus isoleucine transport varied from two- to 13-fold in plasma membrane vesicles isolated from different plant species. This ratio would be expected to remain relatively stable if these amino acids were moving through a single transport system and, indeed, the ratio of alanine to glutamine transport varied less than twofold. Analysis of the predicted structure of the aliphatic, neutral amino acids in solution shows that isoleucine, valine, and threonine contain a branched methyl or hydroxyl group at the beta-carbon position that places a dense electron cloud close to the alpha-amino group. This does not occur for the unbranched amino acids or those that branch further away, e.g. leucine. We hypothesize that this structural feature of isoleucine, valine, and threonine results in unfavorable steric interactions with the alanine transport system that limits their flux through this porter. Hydrophobicity and hydrated volumes did not account for the observed differences in transport specificity. PMID:16668339

Li, Z C; Bush, D R

1991-08-01

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

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics  

PubMed Central

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

Koopmanschap, Gijs; Ruijter, Eelco

2014-01-01

162

Quantization of soluble classical constrained systems  

NASA Astrophysics Data System (ADS)

The derivation of the brackets among coordinates and momenta for classical constrained systems is a necessary step toward their quantization. Here we present a new approach for the determination of the classical brackets which does neither require Dirac's formalism nor the symplectic method of Faddeev and Jackiw. This approach is based on the computation of the brackets between the constants of integration of the exact solutions of the equations of motion. From them all brackets of the dynamical variables of the system can be deduced in a straightforward way.

Belhadi, Z.; Menas, F.; Bérard, A.; Mohrbach, H.

2014-12-01

163

Constraining dark halos with tidal tails  

E-print Network

Massive and extended dark halos can inhibit the formation of long tidal tails in galaxy collisions. We examine this effect using an extensive survey of simulations with different dark halo potentials to constrain halo properties of interacting galaxies. These constraints are compared to other observational limits and theoretical predictions of halo structure. The dark halos predicted by $\\Omega=1$ cosmological models like CDM are too massive and extended to produce the long tidal tails seen in nearby galaxy collisions. There is also a conflict with the halo potentials inferred from satellite kinematics; such halos would likewise inhibit tail formation in galaxy collisions.

John Dubinski; Chris Mihos; Lars Hernquist

1997-12-08

164

Quantization of soluble classical constrained systems  

E-print Network

The derivation of the brackets among coordinates and momenta for classical constrained systems is a necessary step toward their quantization. Here we present a new approach for the determination of the classical brackets which does neither require Dirac's formalism nor the symplectic method of Faddeev and Jackiw. This approach is based on the computation of the brackets between the constants of integration of the exact solutions of the equations of motion. From them all brackets of the dynamical variables of the system can be deduced in a straightforward way.

Belhadi, Zahir; Bérard, Alain; Mohrbach, Herve

2014-01-01

165

Quantization of soluble classical constrained systems  

E-print Network

The derivation of the brackets among coordinates and momenta for classical constrained systems is a necessary step toward their quantization. Here we present a new approach for the determination of the classical brackets which does neither require Dirac's formalism nor the symplectic method of Faddeev and Jackiw. This approach is based on the computation of the brackets between the constants of integration of the exact solutions of the equations of motion. From them all brackets of the dynamical variables of the system can be deduced in a straightforward way.

Zahir Belhadi; Ferhat Ménas; Alain Bérard; Herve Mohrbach

2014-06-15

166

Force induced melting of the constrained DNA  

E-print Network

We develop a simple model to study the effects of an applied force on the melting of a double stranded DNA (dsDNA). Using this model, we could study the stretching, unzipping, rupture and slippage like transition in a dsDNA. We show that in absence of an applied force, the melting temperature and the melting profile of dsDNA strongly depend on the constrained imposed on the ends of dsDNA. The nature of the phase boundary which separates the zipped and the open state for the shearing like transition is remarkably different than the DNA unzipping

Amit Raj Singh; D. Giri; S. Kumar

2009-12-12

167

Plasma free amino acid concentrations of breast-fed infants.  

PubMed

Photometric determination of alpha-amino nitrogen in peripheral venous plasma and urine from 20 healthy, full-term infants, 1--5 months of age, showing normal growth and development during an uncomplicated lactation, revealed lower plasma levels than what has been found in adults, or 3.7 +/- 1.1 mg/100 ml, and a urinary excretion of 41 +/- 14 mg/24 hours. Ion-exchange chromatography of deproteinized peripheral venous plasma showed low valine concentrations, an increased glycine/valine ratio and high cystine and very high taurine levels when compared to the levels of healthy American infants of comparable ages fed 3--3.5 g/kg of cow-milk protein. The findings indicate that a formula based on cow-milk protein should optimally contain only 1.0--1.2 g protein/100 ml provided that it is "humanized" not only with regard to the lactalbumin/casein ratio, but also to the cystine and taurine content. The pattern of the plasma concentrations of free amino acids reported in the present investigation may be used as a normal reference for breast-fed infants. PMID:567930

Lindblad, B S; Alfvén, G; Zetterström, R

1978-09-01

168

Extraterrestrial Amino Acids Identified in Metal-Rich CH and CB Carbonaceous Chondrites from Antarctica  

NASA Technical Reports Server (NTRS)

Carbonaceous chondrites contain numerous indigenous organic compounds and could have been an important source of prebiotic compounds required for the origin of life on Earth or elsewhere. Extraterrestrial amino acids have been reported in five of the eight groups of carbonaceous chondrites and are most abundant in CI, CM, and CR chondritesbut are also present in the more thermally altered CV and CO chondrites. We report the abundance, distribution, and enantiomeric and isotopic compositions of simple primary amino acids in six metal-rich CH and CB carbonaceous chondrites that have not previously been investigated for amino acids: Allan Hills (ALH) 85085 (CH3), Pecora Escarpment(PCA) 91467 (CH3), Patuxent Range (PAT) 91546 (CH3), MacAlpine Hills (MAC) 02675(CBb), Miller Range (MIL) 05082 (CB), and Miller Range (MIL) 07411 (CB). Amino acid abundances and carbon isotopic values were obtained by using both liquid chromatography time-of-flight mass spectrometry and fluorescence, and gas chromatography isotope ratiomass spectrometry. The (delta D, delta C-13, delta N-15) ratios of multiple amino acids fall outside of the terrestrial range and support their extraterrestrial origin. Extracts of CH chondrites were found to be particularly rich in amino acids (1316 parts per million, ppm) while CB chondrite extracts had much lower abundances (0.22 ppm). The amino acid distributions of the CH and CB chondrites were distinct from the distributions observed in type 2 and 3 CM and CR chondrites and contained elevated levels of beta-, gamma-, and delta-amino acids compared to the corresponding alpha-amino acids, providing evidence that multiple amino acid formation mechanisms were important in CH and CB chondrites.

Burton, Aaron S.; Elsila, Jamie E.; Hein, Jason E.; Glavin, Daniel P.; Dworkin, Jason P.

2013-01-01

169

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

170

Distribution of free amino acids in streptozotocin-induced diabetic pregnant rats, their placentae and fetuses.  

PubMed

Amino acid levels in the non-pregnant streptozotocin (STZ)-induced diabetic rat have been shown to be abnormal. Our preliminary studies showed that placental transport, fetal serum levels and tissue uptake of the non-metabolizable amino acid alpha-amino isobutyric acid (AIB) were decreased in STZ-diabetic pregnant rats. In the present experiments, amino acid concentrations were measured in maternal (MS) and fetal (FS) sera and placentae (PL) by high performance liquid chromatography (HPLC) after triple extraction in 80% ethanol. Control (C), STZ-diabetic (D) and insulin-treated diabetic (DI) animals were studied at 22 days gestation. Pregnant diabetic rats had low serum levels of Gln, Lys, and Ser and insulin treatment corrected Gln and Ser but not Lys levels. Branched-chain amino acids did not show the large elevation characteristic of the non-pregnant diabetic rat. Placental levels of Tau, Gln, HPr, Thr and Lys were depressed in the diabetic animals and insulin treatment only partially improved these amino acid profiles. Placental amino acid levels did not always reflect maternal serum levels. Serum levels of most amino acids were lower in the fetus of the diabetic rat than in the fetus of the control rat. The notable exception was Ala which was higher in the fetuses of the diabetic animals. Insulin treatment of the mother did not correct many of the fetal amino acid levels even though maternal and fetal serum glucose levels at the time of autopsy were normal. The ability to maintain normal serum levels of many amino acids is impaired in the fetus of the diabetic rat.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2182503

Copeland, A D; Hendrich, C E; Porterfield, S P

1990-02-01

171

Ocean acidification-induced food quality deterioration constrains trophic transfer.  

PubMed

Our present understanding of ocean acidification (OA) impacts on marine organisms caused by rapidly rising atmospheric carbon dioxide (CO(2)) concentration is almost entirely limited to single species responses. OA consequences for food web interactions are, however, still unknown. Indirect OA effects can be expected for consumers by changing the nutritional quality of their prey. We used a laboratory experiment to test potential OA effects on algal fatty acid (FA) composition and resulting copepod growth. We show that elevated CO(2) significantly changed the FA concentration and composition of the diatom Thalassiosira pseudonana, which constrained growth and reproduction of the copepod Acartia tonsa. A significant decline in both total FAs (28.1 to 17.4 fg cell(-1)) and the ratio of long-chain polyunsaturated to saturated fatty acids (PUFA:SFA) of food algae cultured under elevated (750 µatm) compared to present day (380 µatm) pCO(2) was directly translated to copepods. The proportion of total essential FAs declined almost tenfold in copepods and the contribution of saturated fatty acids (SFAs) tripled at high CO(2). This rapid and reversible CO(2)-dependent shift in FA concentration and composition caused a decrease in both copepod somatic growth and egg production from 34 to 5 eggs female(-1) day(-1). Because the diatom-copepod link supports some of the most productive ecosystems in the world, our study demonstrates that OA can have far-reaching consequences for ocean food webs by changing the nutritional quality of essential macromolecules in primary producers that cascade up the food web. PMID:22509351

Rossoll, Dennis; Bermúdez, Rafael; Hauss, Helena; Schulz, Kai G; Riebesell, Ulf; Sommer, Ulrich; Winder, Monika

2012-01-01

172

Ocean Acidification-Induced Food Quality Deterioration Constrains Trophic Transfer  

PubMed Central

Our present understanding of ocean acidification (OA) impacts on marine organisms caused by rapidly rising atmospheric carbon dioxide (CO2) concentration is almost entirely limited to single species responses. OA consequences for food web interactions are, however, still unknown. Indirect OA effects can be expected for consumers by changing the nutritional quality of their prey. We used a laboratory experiment to test potential OA effects on algal fatty acid (FA) composition and resulting copepod growth. We show that elevated CO2 significantly changed the FA concentration and composition of the diatom Thalassiosira pseudonana, which constrained growth and reproduction of the copepod Acartia tonsa. A significant decline in both total FAs (28.1 to 17.4 fg cell?1) and the ratio of long-chain polyunsaturated to saturated fatty acids (PUFA:SFA) of food algae cultured under elevated (750 µatm) compared to present day (380 µatm) pCO2 was directly translated to copepods. The proportion of total essential FAs declined almost tenfold in copepods and the contribution of saturated fatty acids (SFAs) tripled at high CO2. This rapid and reversible CO2-dependent shift in FA concentration and composition caused a decrease in both copepod somatic growth and egg production from 34 to 5 eggs female?1 day?1. Because the diatom-copepod link supports some of the most productive ecosystems in the world, our study demonstrates that OA can have far-reaching consequences for ocean food webs by changing the nutritional quality of essential macromolecules in primary producers that cascade up the food web. PMID:22509351

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

2012-01-01

173

Group Sparsity Constrained Automatic Brain Label Propagation  

PubMed Central

In this paper, we present a group sparsity constrained patch based label propagation method for multi-atlas automatic brain labeling. The proposed method formulates the label propagation process as a graph-based theoretical framework, where each voxel in the input image is linked to each candidate voxel in each atlas image by an edge in the graph. The weight of the edge is estimated based on a sparse representation framework to identify a limited number of candidate voxles whose local image patches can best represent the local image patch of each voxel in the input image. The group sparsity constraint to capture the dependency among candidate voxels with the same anatomical label is also enforced. It is shown that based on the edge weight estimated by the proposed method, the anatomical label for each voxel in the input image can be estimated more accurately by the label propagation process. Moreover, we extend our group sparsity constrained patch based label propagation framework to the reproducing kernel Hilbert space (RKHS) to capture the nonlinear similarity of patches among different voxels and construct the sparse representation in high dimensional feature space. The proposed method was evaluated on the NA0-NIREP database for automatic human brain anatomical labeling. It was also compared with several state-of-the-art multi-atlas based brain labeling algorithms. Experimental results demonstrate that our method consistently achieves the highest segmentation accuracy among all methods used for comparison.

Liao, Shu; Zhang, Daoqiang; Yap, Pew-Thian; Wu, Guorong; Shen, Dinggang

2013-01-01

174

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

175

A stochastic framework for inequality constrained estimation  

NASA Astrophysics Data System (ADS)

Quality description is one of the key features of geodetic inference. This is even more true if additional information about the parameters is available that could improve the accuracy of the estimate. However, if such additional information is provided in the form of inequality constraints, most of the standard tools of quality description (variance propagation, confidence ellipses, etc.) cannot be applied, as there is no analytical relationship between parameters and observations. Some analytical methods have been developed for describing the quality of inequality constrained estimates. However, these methods either ignore the probability mass in the infeasible region or the influence of inactive constraints and therefore yield only approximate results. In this article, a frequentist framework for quality description of inequality constrained least-squares estimates is developed, based on the Monte Carlo method. The quality is described in terms of highest probability density regions. Beyond this accuracy estimate, the proposed method allows to determine the influence and contribution of each constraint on each parameter using Lagrange multipliers. Plausibility of the constraints is checked by hypothesis testing and estimating the probability mass in the infeasible region. As more probability mass concentrates in less space, applying the proposed method results in smaller confidence regions compared to the unconstrained ordinary least-squares solution. The method is applied to describe the quality of estimates in the problem of approximating a time series with positive definite functions.

Roese-Koerner, Lutz; Devaraju, Balaji; Sneeuw, Nico; Schuh, Wolf-Dieter

2012-11-01

176

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

177

Regular Language Constrained Sequence Alignment Revisited  

NASA Astrophysics Data System (ADS)

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

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

178

Regular language constrained sequence alignment revisited.  

PubMed

Imposing constraints in the form of a finite automaton or a regular expression is an effective way to incorporate additional a priori knowledge into sequence alignment procedures. With this motivation, the Regular Expression Constrained Sequence Alignment Problem was introduced, which proposed an O(n²t?) time and O(n²t²) space algorithm for solving it, where n is the length of the input strings and t is the number of states in the input non-deterministic automaton. A faster O(n²t³) time algorithm for the same problem was subsequently proposed. In this article, we further speed up the algorithms for Regular Language Constrained Sequence Alignment by reducing their worst case time complexity bound to O(n²t³)/log t). This is done by establishing an optimal bound on the size of Straight-Line Programs solving the maxima computation subproblem of the basic dynamic programming algorithm. We also study another solution based on a Steiner Tree computation. While it does not improve the worst case, our simulations show that both approaches are efficient in practice, especially when the input automata are dense. PMID:21554020

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

2011-05-01

179

Constraining double parton correlations and interferences  

E-print Network

Double parton scattering (DPS) has become very relevant as a background to interesting analyses performed by the experiments at the LHC. It encodes knowledge of correlations between the proton constituents not accessible in single parton scattering. Within perturbative QCD DPS is described in terms of partonic subprocesses and double parton distributions (DPDs). There exists a large number of different DPDs describing the different possible states of two partons inside a proton. They include correlations between the two partons and interferences between the two hard subprocesses. Taking the probability interpretation of the DPDs as starting point, we derive limits on the interference DPDs and thereby constrain the size of correlations between two partons inside an unpolarized proton.

Tomas Kasemets; Piet J. Mulders

2014-11-03

180

Remote gaming on resource-constrained devices  

NASA Astrophysics Data System (ADS)

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

Reza, Waazim; Kalva, Hari; Kaufman, Richard

2010-08-01

181

Magnetic permeability of constrained scalar QED vacuum  

E-print Network

We compute the influence of boundary conditions on the Euler-Heisenberg effective Lagrangian scalar QED scalar for the case of a pure magnetic field. The boundary conditions constrain the quantum scalar field to vanish on two parallel planes separeted by a distance $a$ and the magnetic field is assumed to be constant, uniform and perpendicular to the planes. The effective Lagrangian is obtained using Schwinger's proper-time representation and exhibits new contributions generated by the boundary condition much in the same way as a material pressed between two plates exhibits new magnetic properties. The confined bosonic vacuum presents the expected diamagnetic properties and besides the new non-linear $a$-dependent contributions to the susceptibility we show that there exists also a new $a$-dependent contribution for the vacuum permeability in the linear approximation.

M. V. Cougo-Pinto; C. Farina; M. R. Negrao; A. C. Tort

1998-09-30

182

Fluctuation theorem for constrained equilibrium systems.  

PubMed

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

Gilbert, Thomas; Dorfman, J Robert

2006-02-01

183

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.

Broedel, Johannes; Plefka, Jan; Rosso, Matteo

2014-01-01

184

Constraining the cratering chronology of Vesta  

NASA Astrophysics Data System (ADS)

Vesta has a complex cratering history, with ancient terrains as well as recent large impacts that have led to regional resurfacing. Crater counts can help constrain the relative ages of different units on Vesta's surface, but converting those crater counts to absolute ages requires a chronology function. We present a cratering chronology based on the best current models for the dynamical evolution of asteroid belt, and calibrate it to Vesta using the record of large craters on its surface. While uncertainties remain, our chronology function is broadly consistent with an ancient surface of Vesta as well as other constraints such as the bombardment history of the rest of the inner Solar System and the Ar-Ar age distribution of howardite, eucrite and diogenite (HED) meteorites from Vesta.

O‘Brien, David P.; Marchi, Simone; Morbidelli, Alessandro; Bottke, William F.; Schenk, Paul M.; Russell, Christopher T.; Raymond, Carol A.

2014-11-01

185

Constrained analytical interrelations in neutrino mixing  

E-print Network

Hermitian squared mass matrices of charged leptons and light neutrinos in the flavor basis are studied under general additive lowest order perturbations away from the tribimaximal (TBM) limit in which a weak basis with mass diagonal charged leptons is chosen. Simple analytical expressions are found for the three measurable TBM-deviants in terms of perturbation parameters appearing in the neutrino and charged lepton eigenstates in the flavor basis. Taking unnatural cancellations to be absent and charged lepton perturbation parameters to be small, constrained analytical and testable interrelations are derived among neutrino masses, mixing angles and the amount of CP-violation, posing the challenge of verification to forthcoming experiments at the intensity frontier.

Biswajoy Brahmachari; Probir Roy

2014-03-09

186

Cosmic-Flows-1: First Constrained Simulations  

NASA Astrophysics Data System (ADS)

Local galaxies have deviant motions from the Hubble expansion but with origins not yet totally understood. Mapping the Local Universe very precisely to understand Large Scale Structures is part of the international project Cosmic Flows. The project first catalog of accurate galaxy peculiar velocities Cosmic-Flows-1 samples the Local Universe up to 40 Mpc. The reconstructed velocity field obtained using the Wiener-Filter technique on this first catalog provides Initial Conditions for the second generation of CLUES constrained simulations of the Local Universe. The combination and comparison between the observed and the simulated Universe gives a possibility and a specificity that should lead to understand the fundamental cosmology observation of our motion at 630 km/s with respect to the CMB.

Sorce, Jenny; Courtois, H.

2013-01-01

187

Constraining Lorentz violations with Gamma Ray Bursts  

E-print Network

Gamma ray bursts are excellent candidates to constrain physical models which break Lorentz symmetry. We consider deformed dispersion relations which break the boost invariance and lead to an energy-dependent speed of light. In these models, simultaneously emitted photons from cosmological sources reach Earth with a spectral time delay that depends on the symmetry breaking scale. We estimate the possible bounds which can be obtained by comparing the spectral time delays with the time resolution of available telescopes. We discuss the best strategy to reach the strongest bounds. We compute the probability of detecting bursts that improve the current bounds. The results are encouraging. Depending on the model, it is possible to build a detector that within several years will improve the present limits of 0.015 m_pl.

Maria Rodriguez Martinez; Tsvi Piran

2006-01-10

188

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 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

189

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

190

Constraining the Cratering Chronology of Vesta  

E-print Network

Vesta has a complex cratering history, with ancient terrains as well as recent large impacts that have led to regional resurfacing. Crater counts can help constrain the relative ages of different units on Vesta's surface, but converting those crater counts to absolute ages requires a chronology function. We present a cratering chronology based on the best current models for the dynamical evolution of asteroid belt, and calibrate it to Vesta using the record of large craters on its surface. While uncertainties remain, our chronology function is broadly consistent with an ancient surface of Vesta as well as other constraints such as the bombardment history of the rest of the inner Solar System and the Ar-Ar age distribution of howardite, eucrite and diogenite (HED) meteorites from Vesta.

O'Brien, David P; Morbidelli, Alessandro; Bottke, William F; Schenk, Paul M; Russell, Christopher T; Raymond, Carol A

2014-01-01

191

Disappearance and Creation of Constrained Amorphous Phase  

NASA Astrophysics Data System (ADS)

We report observation of the disappearance and recreation of rigid, or constrained, amorphous phase by sequential thermal annealing. Tempera- ture modulated differential scanning calorimetry (MDSC) is used to study the glass transition and lower melting endotherm after annealing. Cold crystallization of poly(phenylene sulfide), PPS, at a temperature just above Tg creates an initial large fraction of rigid amorphous phase (RAP). Brief, rapid annealing to a higher temperature causes RAP almost to disappear completely. Subsequent reannealing at the original lower temperature restores RAP to its original value. At the same time that RAP is being removed, Tg decreases; when RAP is restored, Tg also returns to its initial value. The crystal fraction remains unaffected by the annealing sequence.

Cebe, Peggy; Lu, Sharon X.

1997-03-01

192

Explaining evolution via constrained persistent perfect phylogeny  

PubMed Central

Background The perfect phylogeny is an often used model in phylogenetics since it provides an efficient basic procedure for representing the evolution of genomic binary characters in several frameworks, such as for example in haplotype inference. The model, which is conceptually the simplest, is based on the infinite sites assumption, that is no character can mutate more than once in the whole tree. A main open problem regarding the model is finding generalizations that retain the computational tractability of the original model but are more flexible in modeling biological data when the infinite site assumption is violated because of e.g. back mutations. A special case of back mutations that has been considered in the study of the evolution of protein domains (where a domain is acquired and then lost) is persistency, that is the fact that a character is allowed to return back to the ancestral state. In this model characters can be gained and lost at most once. In this paper we consider the computational problem of explaining binary data by the Persistent Perfect Phylogeny model (referred as PPP) and for this purpose we investigate the problem of reconstructing an evolution where some constraints are imposed on the paths of the tree. Results We define a natural generalization of the PPP problem obtained by requiring that for some pairs (character, species), neither the species nor any of its ancestors can have the character. In other words, some characters cannot be persistent for some species. This new problem is called Constrained PPP (CPPP). Based on a graph formulation of the CPPP problem, we are able to provide a polynomial time solution for the CPPP problem for matrices whose conflict graph has no edges. Using this result, we develop a parameterized algorithm for solving the CPPP problem where the parameter is the number of characters. Conclusions A preliminary experimental analysis shows that the constrained persistent perfect phylogeny model allows to explain efficiently data that do not conform with the classical perfect phylogeny model.

2014-01-01

193

A Path Algorithm for Constrained Estimation  

PubMed Central

Many least-square problems involve affine equality and inequality constraints. Although there are a variety of methods for solving such problems, most statisticians find constrained estimation challenging. The current article proposes a new path-following algorithm for quadratic programming that replaces hard constraints by what are called exact penalties. Similar penalties arise in l1 regularization in model selection. In the regularization setting, penalties encapsulate prior knowledge, and penalized parameter estimates represent a trade-off between the observed data and the prior knowledge. Classical penalty methods of optimization, such as the quadratic penalty method, solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ?, one recovers the constrained solution. In the exact penalty method, squared penalties!are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. The exact path-following method starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. Path following in Lasso penalized regression, in contrast, starts with a large value of the penalty constant and works its way downward. In both settings, inspection of the entire solution path is revealing. Just as with the Lasso and generalized Lasso, it is possible to plot the effective degrees of freedom along the solution path. For a strictly convex quadratic program, the exact penalty algorithm can be framed entirely in terms of the sweep operator of regression analysis. A few well-chosen examples illustrate the mechanics and potential of path following. This article has supplementary materials available online. PMID:24039382

Zhou, Hua; Lange, Kenneth

2013-01-01

194

Simulated Annealing with Asymptotic Convergence for Nonlinear Constrained Global Optimization  

Microsoft Academic Search

In this paper, we present constrained simulated annealing (CSA), an algo- rithm that extends conventional simulated annealing to look for constrained local minima of nonlinear constrained optimization problems. The algorithm is based on the theory of extended saddle points (ESPs) that shows the one-to-one correspon- dencebetweenaconstrainedlocalminimumandanESPofthecorrespondingpenalty function. CSA finds ESPs by systematically controlling probabilistic descents in the problem-variable subspace of

Benjamin W. Wah; Tao Wang

1999-01-01

195

Constraining gravitational and cosmological parameters with astrophysical data  

E-print Network

We use astrophysical data to shed light on fundamental physics by constraining parametrized theoretical cosmological and gravitational models. Gravitational parameters are those constants that parametrize possible departures ...

Mao, Yi, Ph. D. Massachusetts Institute of Technology

2008-01-01

196

Effect of the mobile phase on antibody-based enantiomer separations of amino acids in high-performance liquid chromatography.  

PubMed

The effect of the mobile phase parameters flow rate, temperature, pH and ionic strength, as well as the addition of various organic modifiers on the enantiomer separation of various aromatic alpha-amino acids was investigated using two antibody-based chiral stationary phases that have opposing stereoselectivity. On both columns, a decrease in flow rate or temperature resulted in increased interaction with the retained enantiomer. It was found that the retention factor k2 depends on the affinity between the analyte and the immobilized antibody and is not independent of the flow rate. Optimum separations of all amino acids investigated were obtained at pH 7.4 on both columns. While increased k2 values were obtained at low ionic strength on the anti-D-amino acid antibody column, no such effect was observed on the anti-L-amino acid antibody column. The addition of organic modifiers did not improve separations. In all studies, the unretained enantiomer eluted with the void volume. PMID:15499920

Hofstetter, Oliver; Lindstrom, Heather; Hofstetter, Heike

2004-09-17

197

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

PubMed

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

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

2013-12-12

198

Observability-constrained Vision-aided Inertial Navigation  

E-print Network

Observability-constrained Vision-aided Inertial Navigation Joel A. Hesch, Dimitrios G. Kottas, Sean-0572 URL: http://www.cs.umn.edu/joel #12;#12;Observability-constrained Vision-aided Inertial Navigation in Vision-aided Inertial Navigation Systems (VINS) from a standpoint of system observability. We postulate

Plotkin, Joshua B.

199

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

200

The Pendulum: From Constrained Fall to the Concept of Potential  

ERIC Educational Resources Information Center

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

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

2006-01-01

201

Transcriptional regulation constrains the organization of genes on eukaryotic chromosomes  

E-print Network

Transcriptional regulation constrains the organization of genes on eukaryotic chromosomes Sarath in eukaryotes is tightly packaged in a hierarchical manner into multiple linear chromosomes within the nucleus-order organization of genes across and within chromosomes that is constrained by transcriptional regulation

Babu, M. Madan

202

Network Formation Among Selfish Energy-Constrained Wireless Devices  

E-print Network

Network Formation Among Selfish Energy-Constrained Wireless Devices Hithesh Nama, Narayan Mandayam energy-constrained wireless devices that are primarily interested in being connected with other devices. We use a non-cooperative bilateral connection game (BCG) framework to study network formation

Mandayam, Narayan

203

Invariant approximations of robustly positively invariant sets for constrained  

E-print Network

Invariant approximations of robustly positively invariant sets for constrained linear discrete/F-INFENG/TR.473 8 January 2004 #12;Invariant approximations of robustly positively invariant sets for constrained of Cambridge, UK 8 January 2004 Abstract This paper provides results on invariant approximations of robustly

Cambridge, University of

204

ADAPTIVE CONTROL OF CONSTRAINED MARKOV CHAINS: CRITERIA AND POLICIES*  

E-print Network

ADAPTIVE CONTROL OF CONSTRAINED MARKOV CHAINS: CRITERIA AND POLICIES* Eitan Altman and Adam Shwartz Electrical Engineering Technion --- Israel Institute of Technology Haifa, 32000 Israel ABSTRACT We consider the constrained optimization of a finite­state, finite action Markov chain. In the adaptive problem

205

Trust Region Method of Conic Model for Linearly Constrained Optimization  

E-print Network

Trust Region Method of Conic Model for Linearly Constrained Optimization by Wenyu Sun, Jinyun Yuan and Ya-xiang Yuan Report No.ICM-96-003 January 1996 #12;Trust Region Method of Conic Model for Linearly present a trust region method of conic model for linearly constrained optimization problems. We discuss

Yuan, Ya-xiang

206

Efficient Traffic Management Based on Deterministically Constrained Traffic Flows  

E-print Network

Efficient Traffic Management Based on Deterministically Constrained Traffic Flows by Ching-fong Su of Texas at Austin May 1998 #12;Efficient Traffic Management Based on Deterministically Constrained Traffic- tiservice networks, traffic management is critical to the success of network operations. In general, traffic

de Veciana, Gustavo

207

Constrained Biogeography-Based Optimization for Invariant Set Computation  

E-print Network

and Hanz Richter Abstract-- We discuss the application of biogeography-based optimization (BBO) to invariant set approximation. BBO is a recently developed evolutionary algorithm (EA) that is moti- vated problem as a constrained optimization problem, and we use a constrained BBO algorithm to solve it. We

Simon, Dan

208

End effector constrained path planning for 7DOF manipulator  

Microsoft Academic Search

This paper presents more reliable and fast path planning method for end effector constrained 7DOF redundant manipulators. Conventional path planning for redundant manipulators used jacobian based planning method for convenience. But it is not easy to apply in case of constrained tasks and redundant manipulators. On the contrary in this paper we uses position based path planning by inverse kinematics.

Kyongmo Koo; Xin Jiang; Atsushi Konno; Masaru Uchiyama

2010-01-01

209

Blind CDMA detection and equalization using linearly constrained CMA  

Microsoft Academic Search

A linearly constrained constant modulus algorithm (CMA) for CDMA detection and equalization is proposed in this paper. Multipath propagation is assumed and only the code sequence of a particular desired user is known. The new algorithm overcomes the shortcoming that the unconstrained CMA cannot lock to the desired user, and yields better performance compared to the existing constrained minimum output

Li Li; H. Howard Fan

2000-01-01

210

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.

211

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

212

Functional Integration on Constrained Function Spaces II: Applications  

E-print Network

Some well-known examples of constrained quantum systems commonly quantized via Feynman path integrals are re-examined using the notion of conditional integrators introduced in [1]. The examples yield some new perspectives on old results. As an interesting new application, the formalism is used to construct a physical model of average prime counting functions modeled as a constrained gamma process.

J. LaChapelle

2014-05-02

213

Generating constrained randomized sequences: item frequency matters.  

PubMed

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

French, Robert M; Perruchet, Pierre

2009-11-01

214

Constraining Galactic Dynamo Models with NIR Polarimetry  

NASA Astrophysics Data System (ADS)

Polarization of background starlight is used to probe interstellar magnetic fields. While it has been widely used at optical wavelengths, the near-infrared polarimetric sky remains largely unexplored. In addition to probing longer sightlines, NIR polarimetry is less affected by foreground magnetic structures which allows us to study the large-scale, quiescent Galactic magnetic field. We combine observed NIR polarimetry with simulated observations to constrain dynamo models of the Galactic magnetic field. Polarimetric data were obtained with the Mimir instrument on the Perkins Telescope along a line of constant Galactic longitude (l=150) with pointings spaced between -75

Pavel, Michael D.; Clemens, D. P.; Pinnick, A. F.

2011-01-01

215

Constraining New Physics with D meson decays  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

216

Constrained blackbox optimization: The SEARCH perspective  

SciTech Connect

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

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

1996-02-02

217

Optimal performance of constrained control systems  

NASA Astrophysics Data System (ADS)

This paper presents a method to compute optimal open-loop trajectories for systems subject to state and control inequality constraints in which the cost function is quadratic and the state dynamics are linear. For the case in which inequality constraints are decentralized with respect to the controls, optimal Lagrange multipliers enforcing the inequality constraints may be found at any time through Pontryagin’s minimum principle. In so doing, the set of differential algebraic Euler-Lagrange equations is transformed into a nonlinear two-point boundary-value problem for states and costates whose solution meets the necessary conditions for optimality. The optimal performance of inequality constrained control systems is calculable, allowing for comparison to previous, sub-optimal solutions. The method is applied to the control of damping forces in a vibration isolation system subjected to constraints imposed by the physical implementation of a particular controllable damper. An outcome of this study is the best performance achievable given a particular objective, isolation system, and semi-active damper constraints.

Harvey, P. Scott, Jr.; Gavin, Henri P.; Scruggs, Jeffrey T.

2012-08-01

218

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.

Zhu, Wei; Huang, Chelsea X.; Zhou, George; Lin, D. N. C.

2014-11-01

219

Constraining sterile neutrinos using reactor neutrino experiments  

NASA Astrophysics Data System (ADS)

Models of neutrino mixing involving one or more sterile neutrinos have resurrected their importance in the light of recent cosmological data. In this case, reactor antineutrino experiments offer an ideal place to look for signatures of sterile neutrinos due to their impact on neutrino flavor transitions. In this work, we show that the high-precision data of the Daya Bay experiment constrain the 3+1 neutrino scenario imposing upper bounds on the relevant active-sterile mixing angle sin2 2 ? 14 ? 0.06 at 3 ? confidence level for the mass-squared difference ?m {41/2} in the range (10-3, 10-1) eV2. The latter bound can be improved by six years of running of the JUNO experiment, sin2 2 ? 14 ? 0.016, although in the smaller mass range ?m {41/2} ? (10-4, 10-3) eV2. We have also investigated the impact of sterile neutrinos on precision measurements of the standard neutrino oscillation parameters ? 13 and ?m {31/2} (at Daya Bay and JUNO), ? 12 and ?m {21/2} (at JUNO), and most importantly, the neutrino mass hierarchy (at JUNO). We find that, except for the obvious situation where ?m {41/2} ? ?m {31/2}, sterile states do not affect these measurements substantially.

Girardi, Ivan; Melon, Davide; Ohlsson, Tommy; Zhang, He; Zhou, Shun

2014-08-01

220

Multiply constrained cardiac electrical imaging methods  

NASA Astrophysics Data System (ADS)

Accurate characterization of the electrical activity of the heart is of great physiological and medical import. The only truly non-invasive sites to measure this activity are on the body surface, as in an ECG, but the signals are attenuated and distorted by the thorax volume conductor. Thus even an array of body surface electrodes records a remote observation of cardiac electrical activity. The goal of cardiac electrical imaging is to accurately and reliably reconstruct the source image sequence from this observed image sequence using a model of the volume conductor. Since the problem is ill-posed, we need to constrain solutions using prior knowledge of source characteristics. Because the source is quite complex and distributed in time and space, and reconstructions are sensitive to the choice and weighting of constraints, several groups, including ours, have recently introduced methods to impose multiple constraints. We will review the problem and some of these methods and describe recent work which uses a convex optimization framework to impose multiple constraints, combining traditional smoothing with preservation of sharp gradients in the reconstructed image sequences. We pay particular attention to efficient distributed computational implementations of these solution methods.

Brooks, Dana H.; Srinidhi, Kadagattur G.; MacLeod, Robert S.; Kaeli, David R.

1999-10-01

221

4D active time constrained resistivity inversion  

NASA Astrophysics Data System (ADS)

Techniques that incorporate regularization in space and time have been proposed to reduce inversion artifacts that may lead a misinterpretation of geophysical monitoring data. Applying this time regularization, however, may result in a model too smoothly carrying in the time domain. To alleviate this problem, we propose an algorithm for inverting time-lapse resistivity monitoring data. Here the time regularization is not considered to be constant between different time steps but is now allowed to vary depending on the degree of spatial resistivity changes occurring between different monitoring stages. Two methods are proposed to assign different time Lagrangian values, one based on a pre-estimation during execution time, and one using a-priori information. Both methods require a threshold to characterize the significance of the observed resistivity changes with time. We performed numerous numerical experiments using synthetic data to provide reasonable threshold values. Synthetic data tests illustrate that the new algorithm, named 4D Active Time Constrained (4D-ATC), produces in most cases improved time-lapse images when compared with existing techniques. Further the applicability of the new scheme is demonstrated with real data. Overall, the new algorithm is shown to be a useful tool for processing time-lapse resistivity data, which can be used with minor modifications to other types of time-lapse geophysical data.

Karaoulis, M. C.; Kim, J.-H.; Tsourlos, P. I.

2011-01-01

222

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

223

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

SciTech Connect

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

Tremblay, L.; Blanchard, J

2009-01-01

224

Constraining Cosmic Evolution of Type Ia Supernovae  

E-print Network

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 UV 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 the same slit width, 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 ~0.02 mag. The variance in the composite spectra give an estimate of the intrinsic variance in low-redshift maximum-light SN spectra of ~3% in the optical and growing toward the UV. 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.

Ryan J. Foley; A. V. Filippenko; C. Aguilera; A. C. Becker; S. Blondin; P. Challis; A. Clocchiatti; R. Covarrubias; T. M. Davis; P. M. Garnavich; S. Jha; R. P. Kirshner; K. Krisciunas; B. Leibundgut; W. Li; T. Matheson; A. Miceli; G. Miknaitis; G. Pignata; A. Rest; A. G. Riess; B. P. Schmidt; R. C. Smith; J. Sollerman; J. Spyromilio; C. W. Stubbs; J. L. Tonry; N. B. Suntzeff; W. M. Wood-Vasey; A. Zenteno

2007-10-11

225

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

226

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

227

Onomatopoeia characters extraction from comic images using constrained Delaunay triangulation  

NASA Astrophysics Data System (ADS)

A method for extracting onomatopoeia characters from comic images was developed based on stroke width feature of characters, since they nearly have a constant stroke width in a number of cases. An image was segmented with a constrained Delaunay triangulation. Connected component grouping was performed based on the triangles generated by the constrained Delaunay triangulation. Stroke width calculation of the connected components was conducted based on the altitude of the triangles generated with the constrained Delaunay triangulation. The experimental results proved the effectiveness of the proposed method.

Liu, Xiangping; Shoji, Kenji; Mori, Hiroshi; Toyama, Fubito

2014-02-01

228

Residual flexibility test method for verification of constrained structural models  

NASA Technical Reports Server (NTRS)

A method is presented for deriving constrained modes and frequencies from a model correlated to a set of free-free test modes and a set of measured residual flexibilities. The method involves a simple modification of the MacNeal and Rubin component mode representation to allow verification of a constrained structural model. Results for two spaceflight structures show quick convergence of constrained modes using an easily measurable set of free-free modes plus the residual flexibility matrix or its boundary partition. This paper further validates the residual flexibility approach as an alternative test/analysis method when fixed-base testing proves impractical.

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

1992-01-01

229

Vibrational pooling and constrained equilibration on surfaces  

NASA Astrophysics Data System (ADS)

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

Boney, E. T. D.

230

1-13C amino acid selective labeling in a 2H15N background for NMR studies of large proteins.  

PubMed

Isotope labeling by residue type (LBRT) has long been an important tool for resonance assignments at the limit where other approaches, such as triple-resonance experiments or NOESY methods do not succeed in yielding complete assignments. While LBRT has become less important for small proteins it can be the method of last resort for completing assignments of the most challenging protein systems. Here we present an approach where LBRT is achieved by adding protonated (14)N amino acids that are (13)C labeled at the carbonyl position to a medium for uniform deuteration and (15)N labeling. This has three important benefits over conventional (15)N LBRT in a deuterated back ground: (1) selective TROSY-HNCO cross peaks can be observed with high sensitivity for amino-acid pairs connected by the labeling, and the amide proton of the residue following the (13)C labeled amino acid is very sharp since its alpha position is deuterated, (2) the (13)C label at the carbonyl position is less prone to scrambling than the (15)N at the alpha-amino position, and (3) the peaks for the 1-(13)C labeled amino acids can be identified easily from the large intensity reduction in the (1)H-(15)N TROSY-HSQC spectrum for some residues that do not significantly scramble nitrogens, such as alanine and tyrosine. This approach is cost effective and has been successfully applied to proteins larger than 40 kDa. PMID:17390105

Takeuchi, Koh; Ng, Elise; Malia, Thomas J; Wagner, Gerhard

2007-05-01

231

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

Code of Federal Regulations, 2011 CFR

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

2011-04-01

232

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

Code of Federal Regulations, 2011 CFR

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

2011-04-01

233

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

Code of Federal Regulations, 2011 CFR

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

2011-04-01

234

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

Code of Federal Regulations, 2010 CFR

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

2010-04-01

235

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

Code of Federal Regulations, 2010 CFR

...femorotibial metallic constrained cemented prosthesis. 888.3480 Section 888.3480...femorotibial metallic constrained cemented prosthesis. (a) Identification. A knee...femorotibial metallic constrained cemented prosthesis is a device intended to be...

2010-04-01

236

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

Code of Federal Regulations, 2010 CFR

...metal constrained cemented or uncemented prosthesis. 888.3300 Section 888.3300...metal constrained cemented or uncemented prosthesis. (a) Identification. A hip...metal constrained cemented or uncemented prosthesis is a device intended to be...

2010-04-01

237

21 CFR 888.3210 - Finger joint metal/metal constrained cemented prosthesis.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Finger joint metal/metal constrained cemented... Prosthetic Devices § 888.3210 Finger joint metal/metal constrained cemented prosthesis. (a) Identification. A finger joint metal/metal constrained...

2011-04-01

238

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

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Finger joint metal/polymer constrained cemented... Prosthetic Devices § 888.3220 Finger joint metal/polymer constrained cemented prosthesis. (a) Identification. A finger joint metal/polymer constrained...

2011-04-01

239

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

Code of Federal Regulations, 2010 CFR

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

2010-04-01

240

21 CFR 888.3200 - Finger joint metal/metal constrained uncemented prosthesis.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Finger joint metal/metal constrained uncemented... Prosthetic Devices § 888.3200 Finger joint metal/metal constrained uncemented prosthesis. (a) Identification. A finger joint metal/metal constrained...

2011-04-01

241

21 CFR 888.3210 - Finger joint metal/metal constrained cemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Finger joint metal/metal constrained cemented... Prosthetic Devices § 888.3210 Finger joint metal/metal constrained cemented prosthesis. (a) Identification. A finger joint metal/metal constrained...

2010-04-01

242

21 CFR 888.3200 - Finger joint metal/metal constrained uncemented prosthesis.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Finger joint metal/metal constrained uncemented... Prosthetic Devices § 888.3200 Finger joint metal/metal constrained uncemented prosthesis. (a) Identification. A finger joint metal/metal constrained...

2010-04-01

243

Conical Intersections using Constrained DFT-Configuration Interaction  

E-print Network

The constrained density functional theory–configuration interaction (CDFT-CI) method has previously been used to calculate ground-state energies and barrier heights. In this work, it is examined for use in computing ...

Kaduk, Benjamin J.

244

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

245

LEVENBERG-MARQUARDT METHODS FOR CONSTRAINED NONLINEAR EQUATIONS WITH  

E-print Network

Levenberg-Marquardt-type algorithms that differ in the way they compute their search di- rections. The first are often constrained. For example, in chemical equilibrium systems (see, e.g., [16, 17]), the variables

Kanzow, Christian

246

Maturationally-Constrained Competence-Based Intrinsically Motivated Learning  

E-print Network

Maturationally-Constrained Competence-Based Intrinsically Motivated Learning Adrien Baranes conceptualized as active learning heuristics [8], these two kinds of approaches to intrinsic motivation typically the self-adaptive goal generation algorithm (SAGG), instantiating an intrinsically motivated goal

Paris-Sud XI, Université de

247

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.

248

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

249

Triplet Excitation Energy Transfer with Constrained Density Functional Theory  

E-print Network

We study the electronic coupling matrix element for triplet excitation energy-transfer processes with a number of different computational methods. For the first time, constrained density functional theory (CDFT) is applied ...

Yeganeh, Sina

250

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

251

Computational study of a chance constrained portfolio selection ...  

E-print Network

Key words: Chance Constraints, Sample Average Approximation, Portfo- lio Selection ... where an extensive list of references can be found. Applications of chance constrained programming include, e.g., soil management [29], water man

2008-02-01

252

Peter Bergmann and the invention of constrained Hamiltonian dynamics  

E-print Network

Peter Bergmann was a co-inventor of the algorithm for converting singular Lagrangian models into a constrained Hamiltonian dynamical formalism. This talk focuses on the work of Bergmann and his collaborators in the period from 1949 to 1951.

Salisbury, D C

2006-01-01

253

Peter Bergmann and the invention of constrained Hamiltonian dynamics  

E-print Network

Peter Bergmann was a co-inventor of the algorithm for converting singular Lagrangian models into a constrained Hamiltonian dynamical formalism. This talk focuses on the work of Bergmann and his collaborators in the period from 1949 to 1951.

D. C. Salisbury

2006-08-07

254

COCONUT Deliverable D1 Algorithms for Solving Nonlinear Constrained  

E-print Network

COCONUT Deliverable D1 Algorithms for Solving Nonlinear Constrained and Optimization Problems: The State of The Art June 8, 2001 The Coconut Project Christian Bliek ILOG Peter Spellucci TU Darmstadt Lu

Neumaier, Arnold

255

Amino acid adduct formation by the nevirapine metabolite, 12-hydroxynevirapine--a possible factor in nevirapine toxicity.  

PubMed

Nevirapine (NVP) is a non-nucleoside reverse transcriptase inhibitor used against the human immunodeficiency virus type-1 (HIV-1), mostly to prevent mother-to-child transmission of the virus in developing countries. However, reports of severe NVP-induced hepatotoxicity and serious adverse cutaneous effects have raised concerns about its use. NVP metabolism involves oxidation of the 4-methyl substituent to 4-hydroxymethyl-NVP (12-hydroxy-NVP) and the formation of phenolic derivatives. Further metabolism, through either oxidation to quinoid derivatives or phase II esterification, may produce electrophilic derivatives capable of reacting with bionucleophiles to yield covalent adducts. These adducts could potentially be involved in the initiation of toxic responses. To gain insight into potentially reactive sites in proteins and prepare reliable and fully characterized NVP-amino acid adduct standards for subsequent assessment as biomarkers of NVP toxicity, we have used the model electrophile, 12-mesyloxy-NVP, as a synthetic surrogate for the NVP metabolite, 12-sulfoxy-NVP. Reactions of this model ester were conducted with glutathione and the nucleophilic amino acids arginine, cysteine, histidine, and tryptophan. Moreover, because adducts through the N-terminal valine of hemoglobin are convenient biomarkers of exposure to electrophilic toxicants, we also investigated the reaction with valine. We obtained very efficient (>80%) binding through the sulfur of both glutathione and N-acetylcysteine and moderate yields (10-14%) for binding through C2 of the indole ring of tryptophan and N1 of the imidazole ring of histidine. Reaction with arginine occurred through the alpha-amino group, possibly due to the high basicity of the guanidino group in the side chain. Reaction at the alpha-amino group of valine occurred to a significant extent (33%); the resulting adduct was converted to a thiohydantoin derivative, to obtain a standard useful for prospective biomonitoring studies. All adducts were characterized by a combination of (1)H and (13)C NMR spectroscopy and mass spectrometry techniques. The NVP conjugates with glutathione and N-acetylcysteine identified in this work were previously reported to be formed in vivo, although the corresponding structures were not fully characterized. Our results support the validity of 12-mesyloxy-NVP as a surrogate for 12-sulfoxy-NVP and suggest that NVP metabolism to 12-hydroxy-NVP, and subsequent esterification, could potentially be a factor in NVP toxicity. They further imply that multiple sites in proteins may be targets for modification by 12-hydroxy-NVP-derived electrophiles in vivo. Additionally, we obtained reliable, fully characterized standards for the assessment of protein modification by NVP in vivo, which should help clarify the potential role of metabolism in NVP-induced toxicity. PMID:20392079

Antunes, Alexandra M M; Godinho, Ana L A; Martins, Inês L; Justino, Gonçalo C; Beland, Frederick A; Marques, M Matilde

2010-05-17

256

Branch and Bound Algorithms for Highly Constrained Integer Programs  

Microsoft Academic Search

In this paper we describe a new branch and bound algorithm for solving 0-1 integer linear programs (ILP). Thealgorithm is specifically targeted at ILP instances that are highly constrained, i.e. instances for which the constraintsare hard to satisfy. Our approach is based on recent algorithms for solving instances of Propositional Satisfiability(SAT) which are also highly constrained. In particular we illustrate

Vasco M. Manquinho; João P. Marques Silva; Arlindo L. Oliveira; Karem A. Sakallah; R. Alves Redol

257

Husain-Kuchar model as a constrained BF theory  

E-print Network

We write the Husain-Kuchar model as a constrained BF theory by giving an action principle for it. The action principle turns out to be very close to Plebanski action for general relativity; the difference with respect to gravity lies in the fact that the condition on the Lagrange multipliers of Plebanski's formulation is not present anymore in the constrained BF action for the Husain-Kuchar model reported in this paper.

Montesinos, Merced

2008-01-01

258

Unsupervised constrained linear Fisher's discriminant analysis for hyperspectral image classification  

Microsoft Academic Search

Fisher's linear discriminant analysis (FLDA) has been widely used in pattern classification due to its criterion, called Fisher's ratio, based on the ratio of between-class variance to within-class variance. Recently, a linear constrained discriminant analysis (LCDA) was developed for huperspectral image classification where Fisher's ratio was replaced with the ratio of inter-distance to intra-distance and the target signatures were constrained

Bahong Ji; Chein-I. Chang; Janet L. Jensen; James O. Jensen

2004-01-01

259

Free and constrained symplectic integrators for numerical general relativity  

E-print Network

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

Ronny Richter; Christian Lubich

2008-07-07

260

Mechanisms of 5-aminolevulinic acid uptake at the choroid plexus.  

PubMed

5-Aminolevulinic acid (5-ALA) is a precursor of porphyrins and heme that has been implicated in the neuropsychiatric symptoms associated with porphyrias. It is also being used clinically to delineate malignant gliomas. The blood-CSF barrier may be an important interface for 5-ALA transport between blood and brain as in vivo studies have indicated 5-ALA is taken up by the choroid plexuses whereas the normal blood-brain barrier appears to be relatively impermeable. This study examines the mechanisms of 5-[(3)H]ALA uptake into isolated rat lateral ventricle choroid plexuses. Results suggest that there are two uptake mechanisms. The first was a Na(+)-independent uptake system that was pH dependent (being stimulated at low pH). Uptake was inhibited by the dipeptide Gly-Gly and by cefadroxil, an alpha-amino-containing cephalosporin. These properties are the same as the proton-dependent peptide transporters PEPT1 and PEPT2, which have recently been shown to transport 5-ALA in frog oocyte expression experiments. Choroid plexus uptake was not inhibited by captopril, a PEPT1 inhibitor, suggesting PEPT2-mediated uptake. The presence of PEPT2 and absence of PEPT1 in the choroid plexus were confirmed by western blotting. The second potential mechanism was both Na(+) and HCO(3)(-) dependent and appears to be an organic anion transporter, although it is possible that removal of Na(+) and HCO(3)(-) may indirectly affect PEPT2 by affecting intracellular pH. The presence of PEPT2 and a putative Na(+)/HCO(3)(-)-dependent organic anion transporter is important not only for an understanding of 5-ALA movement between blood and brain but also because these transporters may affect the distribution of a number of drugs between blood and CSF. PMID:10854277

Novotny, A; Xiang, J; Stummer, W; Teuscher, N S; Smith, D E; Keep, R F

2000-07-01

261

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

262

Constraining Effects of Brine Leakage from Carbon Sequestration Sites  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

263

SENSE Phase-Constrained Magnitude Reconstruction With Iterative Phase Refinement  

PubMed Central

Conventional sensitivity encoding (SENSE) reconstruction is based on equations in the complex domain. However, for many MRI applications only the magnitude is relevant. If there exists an estimate of the underlying phase information, a magnitude-only phase-constrained reconstruction can help to improve the conditioning of the SENSE reconstruction problem. Consequently, this reduces g-factor-related noise enhancement. In previous attempts at phase-constrained SENSE reconstruction, image quality was hampered by strong aliasing artifacts resulting from inadequate phase estimates and high sensitivity to phase errors. If a full-resolution phase image is used, a significant reduction in aliasing errors and better noise properties compared to SENSE can be obtained. An iterative scheme that improves the phase estimate to better approximate the phase is presented. The mathematical framework of the new approach is provided together with comparisons of conventional SENSE, phase-constrained SENSE, and the new phase-refinement method. Both theory and experimental verification demonstrate significantly better noise performance at high reduction factors, i.e., close to the theoretical limit. For applications that need only magnitude data, an iterative phase-constrained SENSE reconstruction can provide substantial SNR improvement over SENSE reconstruction and less artifacts than phase-constrained SENSE. PMID:17969127

Lew, Calvin; Pineda, Angel R.; Clayton, David; Spielman, Dan; Chan, Frandics; Bammer, Roland

2012-01-01

264

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

265

A Constrained Random Demodulator for Sub-Nyquist Sampling  

NASA Astrophysics Data System (ADS)

This paper presents a significant modification to the Random Demodulator (RD) of Tropp et al. for sub-Nyquist sampling of frequency-sparse signals. The modification, termed constrained random demodulator, involves replacing the random waveform, essential to the operation of the RD, with a constrained random waveform that has limits on its switching rate because fast switching waveforms may be hard to generate cleanly. The result is a relaxation on the hardware requirements with a slight, but manageable, decrease in the recovery guarantees. The paper also establishes the importance of properly choosing the statistics of the constrained random waveform. If the power spectrum of the random waveform matches the distribution on the tones of the input signal (i.e., the distribution is proportional to the power spectrum), then recovery of the input signal tones is improved. The theoretical guarantees provided in the paper are validated through extensive numerical simulations and phase transition plots.

Harms, Andrew; Bajwa, Waheed U.; Calderbank, Robert

2013-02-01

266

Residual flexibility test method for verification of constrained structural models  

NASA Technical Reports Server (NTRS)

A method is described for deriving constrained modes and frequencies from a reduced model based on a subset of the free-free modes plus the residual effects of neglected modes. The method involves a simple modification of the MacNeal and Rubin component mode representation to allow development of a verified constrained (fixed-base) structural model. Results for two spaceflight structures having translational boundary degrees of freedom show quick convergence of constrained modes using a measureable number of free-free modes plus the boundary partition of the residual flexibility matrix. This paper presents the free-free residual flexibility approach as an alternative test/analysis method when fixed-base testing proves impractical.

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

1994-01-01

267

Degree-constrained multicast routing for multimedia communications  

NASA Astrophysics Data System (ADS)

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

Wang, Yanlin; Sun, Yugeng; Li, Guidan

2005-02-01

268

Effective constrained polymeric theories and their continuum limit  

NASA Astrophysics Data System (ADS)

The classical limit of polymer quantum theories yields a one-parameter family of “effective” theories labeled by ?. Here we consider such families for constrained theories and pose the problem of taking the “continuum limit,” ??0. We put forward criteria for such a question to be well-posed, and propose a concrete strategy based on the definition of appropriately constructed Dirac observables. We analyze two models in detail, namely a constrained oscillator and a cosmological model arising from loop quantum cosmology. For both of these models we show that the program can indeed be completed, provided one makes a particular choice of ?-dependent internal time with respect to which the dynamics is described and compared. We show that the limiting theories exist and discuss the corresponding limit. These results might shed some light on the problem of defining the corresponding continuum limit for quantum constrained systems.

Corichi, Alejandro; Vukašinac, Tatjana

2012-09-01

269

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

270

Plasticity in excitatory amino acid receptor-mediated descending pain modulation after inflammation.  

PubMed

The role for excitatory amino acids (EAAs) in the rostral ventromedial medulla (RVM) in descending pain modulation after persistent noxious input is unclear. In an animal model of inflammatory hyperalgesia, we examined the effects of intra-RVM microinjection of EAA receptor agonists and antagonists on paw withdrawal and tail-flick responses in lightly anesthetized rats. N-Methyl-D-aspartate (NMDA) produced effects that depended upon the postinflammatory time period. At 3 h postinflammation, NMDA induced facilitation at a lower dose (10 pmol) and inhibition at a higher dose (1000 pmol). At 24 h postinflammation, NMDA (0.1-1000 pmol) produced a dose-dependent inhibition. The facilitation and inhibition, respectively, were attenuated significantly by the preadministration of an NMDA receptor antagonist, DL-2-amino-5-phosphonovaleric acid (APV) (10 pmol, P < 0.05), to the same site. Intra-RVM microinjection of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (0.1-100 pmol) produced dose-dependent inhibition at both 3 and 24 h postinflammation that was blocked by the preadministration of an AMPA/kainate receptor antagonist, 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline (100 pmol, P < 0.05). Unexpectedly, AMPA-produced inhibition was also significantly attenuated by preadministration of APV (10 pmol, P < 0.05). Compared with 3 h postinflammation, both NMDA and AMPA showed a leftward shift in their dose-response curves at 24 h postinflammation. These results demonstrate that NMDA and AMPA receptors in the RVM are involved in the descending modulation after inflammatory hyperalgesia. There is a time-dependent increase in EAA neurotransmission in the RVM after inflammation and NMDA receptors play an important role in AMPA-produced inhibition. PMID:11805211

Guan, Yun; Terayama, Ryuji; Dubner, Ronald; Ren, Ke

2002-02-01

271

Dynamic Resource Management in Energy Constrained Heterogeneous Computing  

E-print Network

Dynamic Resource Management in Energy Constrained Heterogeneous Computing Systems Using Voltage management becomes a critical issue. As devices are heterogeneous, battery capacity may also be heterogeneous management system (RMS) takes care of allocating resources of a certain system. The power management aspect

Maciejewski, Anthony A.

272

Effective Constrained Dynamic Simulation Using Implicit Constraint Enforcement  

E-print Network

simulation in a stable and effective manner, both in intuitively defining and accurately enforcingEffective Constrained Dynamic Simulation Using Implicit Constraint Enforcement Min Hong, Min, *Mechanical Engineering University of Colorado at Denver and Health Sciences Center 4200 E. 9th Avenue Campus

Choi, Min-Hyung

273

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

274

On the Convex Parameterization of Constrained Spacecraft Reorientation  

Microsoft Academic Search

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

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

2010-01-01

275

Treating 'thooft-Polyakov Monopole as Constrained System  

E-print Network

The 'tHooft-Polyakov monopole is treated as constrained system using the Hamilton-Jacobi method. The set of the Hamilton-Jacobi partial differential equations and the equations of motion are obtained. The quantization of the system is also discussed.

Hatem Widyan

2008-12-29

276

Transient analysis with the linearly constrained TLS Prony method  

Microsoft Academic Search

The authors present an LCTLS (linearly constrained total least squares) based Prony method for use in scattering analysis problems where additive white noise and known signal components hamper the exponential parameter estimation process. The LCTLS-Prony and TLS-TSD (time series deflation) methods were derived in a common framework for comparison. It was shown that the LCTLS constraint transformations could be expressed

Eric M. Dowling; R. D. DeGroat; D. A. Linebarger

1993-01-01

277

Constrained metabolic network analysis: discovering pathways using CP(Graph)  

E-print Network

Constrained metabolic network analysis: discovering pathways using CP(Graph) Gregoire Dooms, Yves of the working of the cell. Such networks can be modeled as graphs. Metabolic networks are typical examples network analysis consists in finding simple paths in the metabolic graph[2­6]. Here we focus

Deville, Yves

278

MPC for tracking piecewise constant references for constrained linear systems  

Microsoft Academic Search

In this paper, a novel model predictive control (MPC) for constrained (non-square) linear systems to track piecewise constant references is presented. This controller ensures constraint satisfaction and asymptotic evolution of the system to any target which is an admissible steady-state. Therefore, any sequence of piecewise admissible setpoints can be tracked without error. If the target steady state is not admissible,

D. Limón; I. Alvarado; T. Alamo; Eduardo F. Camacho

2008-01-01

279

INFOCOM 2000 100 Constrained Multicast Routing in WDM  

E-print Network

, these algorithms can be used to con- struct a source-based multicast light-forest (consisting one or more trees- ting, Light Forest I. INTRODUCTION S the Internet traffic continues to increase expo- nentiallyINFOCOM 2000 100 Constrained Multicast Routing in WDM Networks with Sparse Light Splitting Xijun

Qiao, Chunming

280

Efficient Particle Filtering for Road-Constrained Target Tracking  

E-print Network

estimation falls into the category of non- linear filtering even if every single model is a linear systemEfficient Particle Filtering for Road-Constrained Target Tracking Yang Cheng Department at Buffalo, State University of New York Amherst, NY 14260 Email: tsingh@buffalo.edu Abstract-- The variable

Singh, Tarunraj

281

Energy-Efficient Communication in Battery-Constrained Portable Devices  

E-print Network

1 Energy-Efficient Communication in Battery-Constrained Portable Devices Athina Markopoulou, Yan Li high-performance operation and long battery lifetime. This optimization com- plements improvements on limited batteries. In order to maximize the battery lifetime, it is necessary to optimize the use

Markopoulou, Athina

282

Integrated Multidisciplinary Constrained Optimization of Offshore Support Structures  

E-print Network

Integrated Multidisciplinary Constrained Optimization of Offshore Support Structures Rad Haghi1 structure more positively. Previous studies show the advantages of the integrated design with either limited.haghi@siemens.com Abstract. In the current offshore wind turbine support structure design method, the tower and foundation

Papalambros, Panos

283

Stability-constrained model predictive control with state estimation  

Microsoft Academic Search

This article presents an extension to stability-constrained model predictive control (SCMPC) incorporating state estimation. It is proved that asymptotic stability of the closed loop system is guaranteed for SCMPC when a stable state estimator is used rather than direct measurement of the full state variables. The results are illustrated with experimental results from a real-time implementation of SCMPC with state

Xu Cheng; Bruce H. Krogh

1997-01-01

284

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.

Keser, R; Oberacker, V E; Maruhn, J A; Reinhard, P -G

2014-01-01

285

Heuristics for Scheduling Resource-Constrained Projects: An Experimental Investigation  

Microsoft Academic Search

This paper considers the project scheduling problem with multiple constrained resources. Two classes of heuristic procedure, both making use of priority rules, are discussed: the parallel method, which generates just one schedule; and the sampling method, which generates a set of schedules using probabilistic techniques and selects the best schedule from this sample. An experimental investigation is described in which

Dale F. Cooper

1976-01-01

286

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

287

Tumor localization using diffuse optical tomography and linearly constrained  

E-print Network

Tumor localization using diffuse optical tomography and linearly constrained minimum variance. nehorai@ese.wustl.edu Abstract: We present a tumor localization method for diffuse optical tomography as a possible position of abnormality (e.g., tumor). We then design a spatial filter based on the linearly

Nehorai, Arye

288

CSR: Constrained Selfish Routing in Ad-hoc Networks  

E-print Network

CSR: Constrained Selfish Routing in Ad-hoc Networks Christine Bassem and Azer Bestavros Computer protocols for ad-hoc networks assume that the nodes forming the network are either under a single authority of a return. These assumptions are unrealistic since in ad-hoc networks, nodes are likely to be autonomous

289

Accurate Face Alignment using Shape Constrained Markov Network  

Microsoft Academic Search

In this paper, we present a shape constrained Markov network for accurate face alignment. The global face shape is defined as a set of weighted shape samples which are integrated into the Markov network optimization. These weighted samples provide structural constraints to make the Markov network more robust to local image noise. We pro- pose a hierarchical Condensation algorithm to

Lin Liang; Fang Wen; Ying-qing Xu; Xiaoou Tang; Heung-yeung Shum

2006-01-01

290

Will COROT constrain the turbulent spectrum of solarlike oscillating stars ?  

E-print Network

Will COROT constrain the turbulent spectrum of solar­like oscillating stars ? Râ??eza Samadi­to­star comparison. We conclude that COROT's performances will be able to discriminate between several turbulent experiment COROT (Baglin & The Corot Team, 1998) will provide highly accurate photometric measurements

Demoulin, Pascal

291

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

292

MATH 478/878 Introduction to Coding for Constrained Systems  

E-print Network

://www.mast.queensu.ca/math478 All assignments and important announcements will be posted here. Pre/Corequisites: Linear algebra of finite-state encoders & sliding-block decoders. · Constrained systems: Labeled graphs and definition. The Perron-Frobenius theorem. · Finite-State Encoders: Definitions and various decodability properties

Linder, Tamás

293

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

294

Reliability-Constrained Latent Structure Peter Westfall and Kevin Henning  

E-print Network

allow you to estimate reliability of your measure of the fuzzy concept · LSMs allow you to estimate cannot identify reliability. · LSMs cannot identify relationships between fuzzy concepts. · LSMs cannotReliability-Constrained Latent Structure Models Peter Westfall and Kevin Henning Texas Tech

Westfall, Peter H.

295

Reliability-Constrained Latent Structure Peter Westfall and Kevin Henning  

E-print Network

Reliability-Constrained Latent Structure Models Peter Westfall and Kevin Henning Texas Tech science, often for survey data analysis Goal: Model fuzzy concepts, "Love of humanity," "Adventurousness," etc. The Social Science Paradigm: (fuzzy concept is to observed measure) as (genotype is to phenotype

Westfall, Peter H.

296

Fast Algorithms For Slew Constrained Minimum Cost Buffering  

E-print Network

Fast Algorithms For Slew Constrained Minimum Cost Buffering Shiyan Hu, Charles J. Alpert , Jiang demand for buffer- ing resources. This problem requires ultra-fast buffering techniques to handle large volume of nets, while also min- imizing buffering cost. This problem is intensively studied in this paper

Hu, Jiang

297

DISTRIBUTED COGNITIVE MAC FOR ENERGY-CONSTRAINED OPPORTUNISTIC SPECTRUM ACCESS  

E-print Network

existence of spectrum opportunities. Real measurements show that, at any given time and location, a large opportunities among secondary users so that the network-level spectrum efficiency is maximized subject to someDISTRIBUTED COGNITIVE MAC FOR ENERGY-CONSTRAINED OPPORTUNISTIC SPECTRUM ACCESS Yunxia Chen, Qing

Islam, M. Saif

298

Bursty Traffic in Energy-Constrained Opportunistic Spectrum Access  

E-print Network

]. Measurements obtained from spectrum monitoring test- beds demonstrate the Makovian transition between busy channels even if its buffer is empty. II. SYSTEM MODEL A. Primary Network Model We consider a spectrumBursty Traffic in Energy-Constrained Opportunistic Spectrum Access Yunxia Chen, Qing Zhao

Islam, M. Saif

299

Bursty Traffic in Energy-Constrained Opportunistic Spectrum Access  

E-print Network

. Modeling of spectrum occupancy has been addressed in [7]. Measurements obtained from spectrum monitoring independently and selfishly seek spectrum opportunities in a slotted primary network. We formulateBursty Traffic in Energy-Constrained Opportunistic Spectrum Access Yunxia Chen, Qing Zhao

Islam, M. Saif

300

A New Active Set Algorithm for Box Constrained Optimization  

Microsoft Academic Search

An active set algorithm (ASA) for box constrained optimization is developed. The algorithm consists ofa nonmonotone gradient projection step, an unconstrained optimization step, and a set ofrules f or branching between the two steps. Global convergence to a stationary point is established. For a nondegenerate stationary point, the algorithm eventually reduces to uncon- strained optimization without restarts. Similarly, for a

William W. Hager; Hongchao Zhang

2006-01-01

301

Dark Matter, Constrained Minimal Supersymmetric Standard Model, and Lattice QCD  

SciTech Connect

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

Giedt, Joel [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180-3590 (United States); Thomas, Anthony W. [Jefferson Lab, 12000 Jefferson Avenue, Newport News, Virginia 23606 (United States); Special Research Centre for the Subatomic Structure of Matter, School of Chemistry and Physics, University of Adelaide, Adelaide SA 5005 (Australia); Young, Ross D. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2009-11-13

302

PRICE-DIRECTIVE TRAFFIC MANAGEMENT: APPLICATIONS OF SIDE CONSTRAINED  

E-print Network

6 PRICE-DIRECTIVE TRAFFIC MANAGEMENT: APPLICATIONS OF SIDE CONSTRAINED TRAFFIC"oteborg, Sweden ABSTRACT We propose a systematic means for achieving a set of overall traffic management a Stackelberg game invol* *ving the traffic manager and the users of the network. The model is shown to yield

Patriksson, Michael

303

Constrained Nonlinear Predictive Control for Maximizing Production in Polymerization Processes  

Microsoft Academic Search

In this brief, a new constrained nonlinear predictive control scheme is proposed for maximizing the production in polymerization processes. The key features of the proposed feedback strategy are its ability to rigorously handle the process constraints (input saturation, maximum allowed heat production, maximal temperature values, and rate of change) as well as its real time implementability due to the low

Mazen Alamir; Nida Sheibat-Othman; Sami Othman

2007-01-01

304

Positive Scattering Cross Sections using Constrained Least Squares  

Microsoft Academic Search

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

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

1999-01-01

305

CONSTRAINED ICA FOR SEIZURE ONSET ANALYSIS IN THE EEG  

Microsoft Academic Search

The extraction of epileptic seizure waveform from the electroencephalogram (EEG) using Independent Component Analysis (ICA) was demonstrated by James and Lowe. A recent variation, Constrained ICA, allows a supplied reference signal to select a single component to be extracted. We show how this algorithm can be applied to the problem of seizure waveform extraction from EEG signals prior to the

Oliver Gibson; Christopher James

306

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

307

The explicit linear quadratic regulator for constrained systems  

Microsoft Academic Search

We present a technique to compute the explicit state-feedback solution to both the xnite and inxnite horizon linear quadratic optimal control problem subject to state and input constraints. We show that this closed form solution is piecewise linear and continuous. As a practical consequence of the result, constrained linear quadratic regulation becomes attractive also for systems with high sampling rates,

Alberto Bemporad; Manfred Morari; Vivek Dua; Efstratios N. Pistikopoulos

2002-01-01

308

Constrained nonlinear multivariable control of a fluid catalytic cracking process  

Microsoft Academic Search

In this paper, a nonlinear constrained optimization strategy is proposed and applied to the reactor-regenerator section of a fluid catalytic cracking (FCC) unit. A nonlinear dynamic model of the fluid catalytic cracking process was used for the dynamic analysis of the plant and nonlinear multivariable control system. The model realistically simulates the riser-reactor and the one stage regenerator by assembling

R. M. Ansari; M. O. Tadé

2000-01-01

309

Budget constrained location problem with opening and closing of facilities  

Microsoft Academic Search

In this paper, we study a budget constrained location problem in which we simultaneously consider opening some new facilities and closing some existing facilities. Motivations for this problem stem from applications where, due to a change in the distribution of customer demand, the existing facility system no longer provides adequate service. The objective is to minimize the total weighted travel

Qian Wang; Rajan Batta; Joyendu Bhadury; Christopher M. Rump

2003-01-01

310

Weight Selection for Gap Robustness with Degree-Constrained Controllers  

E-print Network

Weight Selection for Gap Robustness with Degree-Constrained Controllers Johan Karlsson, Tryphon the correspondence between weighted entropy functionals and minimizing interpolants in order to find appropriate ways of shaping minimizers via suitable choices of weights. These results are used in order

Lindquist, Anders

311

Applications of a constrained mechanics methodology in economics  

Microsoft Academic Search

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

Jitka Janová

2011-01-01

312

Applications of a constrained mechanics methodology in economics  

Microsoft Academic Search

The paper presents instructive interdisciplinary applications of constrained mechanics calculus in economics on a level appropriate for the undergraduate physics education. The aim of the paper is: 1. to meet the demand for illustrative examples suitable for presenting the background of the highly expanding research field of econophysics even on the undergraduate level and 2. to enable the students to

Jitka Janova

2011-01-01

313

ECM and MM algorithms for mixtures with constrained parameters  

E-print Network

ECM and MM algorithms for mixtures with constrained parameters Didier Chauveau1 David R. Hunter2 1 to an EM generalization known as an ECM algorithm. With certain types of variance constraints, yet another software that implements these algorithms. Keywords: generalized EM algorithms, ECM algorithms, MM

Paris-Sud XI, Université de

314

ECM and MM algorithms for normal mixtures with constrained parameters  

E-print Network

ECM and MM algorithms for normal mixtures with constrained parameters Didier Chauveau1 David R as an ECM algorithm. For certain types of variance constraints, yet another generalization of EM, known of these algorithms in the mixtools package for the R statistical software. Keywords: generalized EM algorithms, ECM

Paris-Sud XI, Université de

315

Application of genetic algorithms in resource constrained network optimization  

Microsoft Academic Search

There are limited solution techniques available for resource constrained project scheduling problems with stochastic task durations. Due to computational complexity, scheduling heuristics have been found useful for large deterministic problems. In this paper, the authors demonstrate the use of a genetic algorithm to optimize over a linear combination of scheduling heuristics. A simulation model is used to evaluate the performance

J. Pet-Edwards; M. Mollaghasemi

1995-01-01

316

A Filter-Based Evolutionary Algorithm for Constrained Optimization  

Microsoft Academic Search

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

Lauren M. Clevenger; Lauren Ferguson; William E. Hart

2005-01-01

317

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.

318

Inferring Meaningful Communities from Topology-Constrained Correlation Networks  

PubMed Central

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 . 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 -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

319

Joint Power Allocation and Scheduling for Deadline Constrained Wireless Traffic  

Microsoft Academic Search

We study the problem of joint power allocation and scheduling for deadline constrained traffic on the downl ink of a cellular wireless communication system, where multiple users can be scheduled simultaneously on orthogonal spreading codes (HSDPA), or sub-carriers (OFDMA), subject to a sum power constraint. We formulate the problem for a canonical two-user model within a dynamic programming (DP) frame-

Aditya Dua; Nicholas Bambos

2006-01-01

320

A Hybrid Approach for Simulating Human Motion in Constrained Environments  

E-print Network

A Hybrid Approach for Simulating Human Motion in Constrained Environments Jia Pan , Liangjun Zhang to simulating human-like motion in robotics, biomechanics, animation and related areas. This includes motion present a new algorithm to generate plausible motions for high-DOF human-like articulated figures

North Carolina at Chapel Hill, University of

321

Constrained Molecular Dynamics as a Search and Optimization Tool  

E-print Network

partly inspired by) particle swarm optimization (PSO) [5]. Like our system, PSOs use groups of interacting par- ticles. In PSOs such particles fly over the fitness landscape, recording the best places seen by PSOs. Our system differs from a PSO in many ways. Firstly, the motion of our particles is constrained

Poli, Riccardo

322

Real-time constrained linear discriminant analysis for hyperspectral imagery  

Microsoft Academic Search

A constrained linear discriminant analysis (CLDA) approach is presented for hyperspectral image detection and classification. Its basic idea is to design an optimal transformation matrix which can maximize the ratio of inter- class distance to intra-class distance while imposing the constraint that different class centers after transformation are along different directions such that different classes can be better separated. The

Qian Du; Hsuan Ren

2001-01-01

323

Balance of Payments Constrained Growth Model: The Case of India  

Microsoft Academic Search

This study applies the Balance of Payments Constrained Growth (BPCG) model to India, a large developing country with a relatively low trade to GDP ratio. Rather than assuming similar elasticities of substitution between goods produced in different regions, the study extends the model to relax these assumptions. Johansen's cointegration technique is employed to estimate trade parameters. Short-run adjustments are explored

Arslan Razmi

2004-01-01

324

Balance of Payments Constrained Growth Model: The Case of India  

Microsoft Academic Search

This study applies the Balance of Payments Constrained Growth (BPCG) model to India, a large developing country with a relatively low trade to GDP ratio. Rather than assuming similar elasticities of substitution between goods produced in different regions, the study extends the model to relax these assumptions. Johansen’s cointegration technique is employed to estimate trade parameters. Short-run adjustments are explored

Arslan Razmi

2005-01-01

325

Constrained Automated Mechanism Design for Infinite Games of Incomplete Information  

E-print Network

successful within a wide range of academic disciplines, much of its progress came as a series of arduous theConstrained Automated Mechanism Design for Infinite Games of Incomplete Information Yevgeniy wellman@umich.edu Abstract We present a functional framework for au- tomated mechanism design based

Wellman, Michael P.

326

Metal artifact reduction in computed tomography by constrained optimization  

NASA Astrophysics Data System (ADS)

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

Zhang, Xiaomeng; Wang, Jing; Xing, Lei

2010-04-01

327

Simulation study of magnetic resonance imagingguided cortically constrained diffuse  

E-print Network

optical imaging and MRI has the potential to provide more quantitative estimates of the total oxygenation, as provided by optical absorption spectroscopy, than can be provided by fMRI.20 This potentialSimulation study of magnetic resonance imaging­guided cortically constrained diffuse optical

Boas, David

328

REGULARIZING FLOWS FOR CONSTRAINED MATRIX-VALUED IMAGES  

E-print Network

, such as image restoration, segmen- tation, stereo-based 3D reconstruction, or optical flow estimation (seeREGULARIZING FLOWS FOR CONSTRAINED MATRIX-VALUED IMAGES C. CHEFD'HOTEL, D. TSCHUMPERL´E, R. DERICHE, AND O. FAUGERAS Abstract. Nonlinear diffusion equations are now widely used to restore and enhance

Faugeras, Olivier

329

MATLAB package for solving Box-Constrained Integer Least  

E-print Network

to keep to code simple and clean. Errors, comments, and descriptions of interesting applications shouldBILS: 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

Toronto, University of

330

Subspace identification with guaranteed stability using constrained optimization  

Microsoft Academic Search

In system identification, the true system is often known to be stable. However, due to finite sample constraints, modeling errors, plant disturbances and measurement noise, the identified model may be unstable. We present a constrained optimization method to ensure asymptotic stability of the identified model in the context of subspace identification methods. In subspace identification, we first obtain an estimate

Seth L. Lacy; Dennis S. Bernstein

2003-01-01

331

A quasi-Newton projection method for nonnegatively constrained ...  

E-print Network

a sum of the Kullback-Leibler divergence, used to minimize the error in the presence ..... have been executed on a Pentium IV PC using Matlab 7.0 (Release 14). The stopping ... convolved with an Adaptive Optic PSF (AOPSF) from the CAOS (Code for. Adaptive ... Constrained Optimization and Lagrange Multiplier Methods.

2010-11-21

332

Constrained Spectral Clustering through Affinity Propagation Zhengdong Lu  

E-print Network

Constrained Spectral Clustering through Affinity Propagation Zhengdong Lu CSEE, OGI, Oregon Health combination of the scarce pairwise constraints with the original affinity matrix. We propose to combine the two sources of affinity by propagating the pairwise con- straints information over the original

Carreira-Perpiñán, Miguel Á.

333

Fully Constrained Least Squares Spectral Unmixing by Simplex Projection  

Microsoft Academic Search

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

Rob Heylen; Dževdet Burazerovic; Paul Scheunders

2011-01-01

334

Improved Genetic Algorithms to Solving Constrained Optimization Problems  

Microsoft Academic Search

The slow convergence speed and the lack of effective constraint handling strategies are the major concerns when applying genetic algorithms (Gas) to constrained optimization problem. An improved genetic algorithm was proposed by dividing population into three parts: optimal subpopulation, elitists subpopulation and spare subpopulation. We applied genetic algorithm on three subpopulations with different evolutionary strategies. Isolation of optimal subpopulation was

Zhu Can; Liang Xi-Ming; Zhou Shu-renhu

2009-01-01

335

Optimal Bu er Constrained Independent Bit Allocation 1  

E-print Network

27 Chapter 2 Optimal Bu er Constrained Independent Bit Allocation 1 Contents 2.1 Introduction applications makes it necessary to bu er the source as excessive delay would produce loss of information that the probability of eventual bu er over ow is 1 for any bu er size, even when the average rate of the source

Ortega, Antonio

336

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

337

Restoration of Digital Multiplane Tomosynthesis by a Constrained Iteration Method  

Microsoft Academic Search

Tomosynthetic reconstructions suffer from the disadvantage that blurred images of object detail lying outside the plane of interest are superimposed over the desired image of structures in the tomosynthetic plane. It is proposed to selectively reduce these undesired superimpositions by a constrained iterative restoration method, suitably generalized to permit simultaneous deconvolution of multiple planes. Sufficient conditions are derived ensuring the

Urs E. Ruttimann; Roelf A. J. Groenhuis; Richard L. Webber

1984-01-01

338

STATIONARITY RESULTS FOR GENERATING SET SEARCH FOR LINEARLY CONSTRAINED OPTIMIZATION  

E-print Network

STATIONARITY RESULTS FOR GENERATING SET SEARCH FOR LINEARLY CONSTRAINED OPTIMIZATION TAMARA G. KOLDA, ROBERT MICHAEL LEWIS, AND VIRGINIA TORCZON Abstract. We present a new generating set search (GSS) approach for minimizing functions subject to linear constraints. GSS is a class of direct search

Torczon, Virginia

339

Constrained Reconstruction Applied to 2-D Chemical Shift Imaging  

Microsoft Academic Search

The method of constrained reconstruction, previously applied to magnetic resonance imaging (MRI), is extended to magnetic resonance spectroscopy. This method assumes a model for the MR signal. The model parameters are estimated directly from the phase encoded data. This process obviates the need for the fast Fourier transform (FFT) (which often exhibits limited resolution and ringing artifact). The technique is

Keith A. Wear; Kyle J. Myers; Sunder S. Rajan; Laurence W. Grossman

1997-01-01

340

Constrained Delaunay Tetrahedralizations and Provably Good Boundary Recovery  

E-print Network

Constrained Delaunay Tetrahedralizations and Provably Good Boundary Recovery Jonathan Richard recovery: it usually requires fewer additional vertices to be inserted, it yields provably good bounds on edge lengths (i.e. edges are not made unnecessarily short), and it interacts well with provably good

California at Berkeley, University of

341

A new filled function algorithm for constrained global optimization problems  

Microsoft Academic Search

A new filled function with one parameter is proposed for solving constrained global optimization problems without the coercive condition, in which the filled function contains neither exponential term nor fractional term and is easy to be calculated. A corresponding filled function algorithm is established based on analysis of the properties of the filled function. At last, we perform numerical experiments

Suxiang He; Weilai Chen; Hui Wang

2011-01-01

342

Optimal dispatch in dynamic security constrained open power market  

Microsoft Academic Search

Power system security is a new concern in the competitive power market operation, because the integration of the system controller and the generation owner has been broken. This paper presents an approach for dynamic security constrained optimal dispatch in restructured power market environment. The transient energy margin using transient energy function (TEF) approach has been used to calculate the stability

S. N. Singh; A. K. David

2002-01-01

343

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

344

Controlling the motion of robot manipulators on constrained surfaces  

Microsoft Academic Search

We present a methodology to steer the end effector of a robotic manipulator, which is constrained in terms of joint rates, on the surface within the workspace, to perform surface tasks. We develop smooth controllers for stabilizing the end effector to a point, and for tracking a trajectory on this surface, while respecting the input constraints, and the same time

Xanthi Papageorgiou; Kostas J. Kyriakopoulos

2009-01-01

345

Conduit flow experiments help constraining the regime of explosive eruptions  

Microsoft Academic Search

It is currently impractical to measure what happens in a volcano during an explosive eruption, and up to now much of our knowledge depends on theoretical models. Here we show, by means of large-scale experiments, that the regime of explosive events can be constrained on the basis of the characteristics of magma at the point of fragmentation and conduit geometry.

P. Dellino; F. Dioguardi; B. Zimanowski; R. Büttner; D. Mele; L. La Volpe; R. Sulpizio; D. M. Doronzo; I. Sonder; R. Bonasia; S. Calvari; E. Marotta

2010-01-01

346

Rosenfeld, Bergmann, and the Invention of Constrained Hamiltonian Dynamics  

NASA Astrophysics Data System (ADS)

Significant progress in the invention of constrained Hamiltonian dynamics was made by Leon Rosenfeld in a paper he published in the Annalen der Physik in 1930. He applied his general formalism to general relativity with electrodynamical field and Dirac electron sources. His proposed Hamiltonian will be compared and contrasted with an independently developed precursor investigated by Peter Bergmann and collaborators in 1949-50.

Salisbury, Donald

2006-04-01

347

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

348

Workforce-Constrained Preventive Maintenance Scheduling using Evolution Strategies  

E-print Network

capital investments. An excellent case in point is the maintenance of aircraft in the airline #12 Administration threatened to shut down major aircraft overhaul maintenance at Alaska Airlines in the wakeWorkforce-Constrained Preventive Maintenance Scheduling using Evolution Strategies ABSTRACT Heavy

Terwilliger, Mark

349

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

350

A Constrained Semi-supervised Learning Approach to Data Association  

Microsoft Academic Search

Data association (obtaining correspondences) is a ubiquitous problem in computer vision. It appears when matching image features across multiple images, matching image features to object recognition models and matching image features to semantic concepts. In this pa- per, we show how a wide class of data association tasks arising in com- puter vision can be interpreted as a constrained semi-supervised

Hendrik Kück; Peter Carbonetto; Nando De Freitas

2004-01-01

351

Hierarchical Iterative Algorithm for a Coupled Constrained OSNR Nash Game  

E-print Network

Hierarchical Iterative Algorithm for a Coupled Constrained OSNR Nash Game Lacra Pavel Department@control.toronto.edu Abstract-- This paper develops a hierarchical iterative OSNR algorithm based on a game theory framework. A Nash game is formulated between channels with channel utility related to maximizing channel optical

Pavel, Lacra

352

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

353

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

354

Optimisation of derivatisation procedures for the determination of delta13C values of amino acids by gas chromatography/combustion/isotope ratio mass spectrometry.  

PubMed

Compound-specific stable carbon isotope analysis of amino acids by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) is a highly selective and sensitive method for probing the biosynthetic/diagenetic pathways, pool size and turnover rates of proteins, previously intractable to bulk isotope analyses. However, amino acids are polyfunctional, non-volatile compounds which require derivatisation prior to GC analysis. While a wide range of derivatives exist for the GC analysis of amino acids only a handful have been utilised for their GC/C/IRMS analysis. Significantly, none of those derivatives currently employed appear completely satisfactory and a thorough assessment of their relative utility is lacking. Seven derivatives (three previously reported and four novel) for obtaining delta(13)C values of amino acids via GC/C/IRMS analysis were compared. More specifically, standard mixtures of 15 protein amino acids were converted into N-acetylmethyl (NACME) esters, N-acetyl n-propyl (NANP) esters, N-acetyl i-propyl (NAIP) esters, N-trifluoroacetyl-i-propyl (TFA-IP) esters, N-pivaloyl methyl (NPME) esters, N-pivaloyl n-propyl (NPNP) esters and N-pivaloyl i-propyl (NPIP) esters. Each derivative was assessed with respect to its applicability to carbon isotope determinations of all the common alpha-amino acids, reaction yield, chromatographic resolution, stability, analyte-to-derivative carbon ratio, kinetic isotope effects and errors associated with their carbon isotope determinations. The NACME derivative was concluded to be the preferred derivative mainly due to the highest analyte-to-derivative carbon ratio being achieved, resulting in the lowest analytical errors for amino acid delta(13)C value determinations, ranging from +/-0.6 per thousand for phenylalanine, leucine and isoleucine to +/-1.1 per thousand for serine and glycine. PMID:17990247

Corr, Lorna T; Berstan, Robert; Evershed, Richard P

2007-01-01

355

Beyond Sulphuric Acid — What else is in the Clouds of Venus?  

NASA Astrophysics Data System (ADS)

Venus clouds are apparently composed primarily of sulphuric acid mixed with water - but what else is there? From the UV absorber, to meteoritic dust and volcanic ash, we review evidence constraining particle composition and discuss measurement needs.

Wilson, C. F.

2014-05-01

356

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

357

A surface-associated retinol- and fatty acid-binding protein (Gp-FAR-1) from the potato cyst nematode Globodera pallida: lipid binding activities, structural analysis and expression pattern.  

PubMed Central

Parasitic nematodes produce at least two structurally novel classes of small helix-rich retinol- and fatty-acid-binding proteins that have no counterparts in their plant or animal hosts and thus represent potential targets for new nematicides. Here we describe a protein (Gp-FAR-1) from the plant-parasitic nematode Globodera pallida, which is a member of the nematode-specific fatty-acid- and retinol-binding (FAR) family of proteins but localizes to the surface of this species, placing it in a strategic position for interaction with the host. Recombinant Gp-FAR-1 was found to bind retinol, cis-parinaric acid and the fluorophore-tagged lipids 11-(dansylamino)undecanoic acid and dansyl-D,L-alpha-amino-octanoic acid. The fluorescence emission characteristics of the dansylated analogues indicated that the entire ligand enters the binding cavity. Fluorescence competition experiments showed that Gp-FAR-1 binds fatty acids in the range C(11) to C(24), with optimal binding at C(15). Intrinsic fluorescence analysis of a mutant protein into which a tryptophan residue had been inserted supported computer-based predictions of the position of this residue at the protein's interior and possibly also at the binding site. Of direct relevance to plant defence systems was the observation that Gp-FAR-1 binds two lipids (linolenic and linoleic acids) that are precursors of plant defence compounds and the jasmonic acid signalling pathway. Moreover, Gp-FAR-1 was found to inhibit the lipoxygenase-mediated modification of these substrates in vitro. Thus not only does Gp-FAR-1 function as a broad-spectrum retinol- and fatty-acid-binding protein, the results are consistent with the idea that Gp-FAR-1 is involved in the evasion of primary host plant defence systems. PMID:11368765

Prior, A; Jones, J T; Blok, V C; Beauchamp, J; McDermott, L; Cooper, A; Kennedy, M W

2001-01-01

358

Novel alpha- and beta-amino acid inhibitors of influenza virus neuraminidase.  

PubMed

In an effort to discover novel, noncarbohydrate inhibitors of influenza virus neuraminidase we hypothesized that compounds which contain positively charged amino groups in an appropriate position to interact with the Asp 152 or Tyr 406 side chains might be bound tightly by the enzyme. Testing of 300 alpha- and beta-amino acids led to the discovery of two novel neuraminidase inhibitors, a phenylglycine and a pyrrolidine, which exhibited K(i) values in the 50 microM range versus influenza virus A/N2/Tokyo/3/67 neuraminidase but which exhibited weaker activity against influenza virus B/Memphis/3/89 neuraminidase. Limited optimization of the pyrrolidine series resulted in a compound which was about 24-fold more potent than 2-deoxy-2,3-dehydro-N-acetylneuraminic acid in an anti-influenza cell culture assay using A/N2/Victoria/3/75 virus. X-ray structural studies of A/N9 neuraminidase-inhibitor complexes revealed that both classes of inhibitors induced the Glu 278 side chain to undergo a small conformational change, but these compounds did not show time-dependent inhibition. Crystallography also established that the alpha-amino group of the phenylglycine formed hydrogen bonds to the Asp 152 carboxylate as expected. Likewise, the beta-amino group of the pyrrolidine forms an interaction with the Tyr 406 hydroxyl group and represents the first compound known to make an interaction with this absolutely conserved residue. Phenylglycine and pyrrolidine analogs in which the alpha- or beta-amino groups were replaced with hydroxyl groups were 365- and 2,600-fold weaker inhibitors, respectively. These results underscore the importance of the amino group interactions with the Asp 152 and Tyr 406 side chains and have implications for anti-influenza drug design. PMID:11502530

Kati, W M; Montgomery, D; Maring, C; Stoll, V S; Giranda, V; Chen, X; Laver, W G; Kohlbrenner, W; Norbeck, D W

2001-09-01

359

Vibratory response of frictionally constrained gas turbine engine blades  

SciTech Connect

This thesis investigates the forced response of frictionally constrained gas turbine engine blades. The main objective is to determine the optimal normal load to be applied at the friction interface for maximum reduction in resonant vibratory stresses in blades. A systematic approach is developed for performing dynamic analyses of frictionally constrained structures, in which linear structures are represented by receptances and friction joints are characterized by nonlinear impedances. The method of harmonic balance, which is widely used in the design of nonlinear dynamic systems, is augmented to solve this particular class of problems. Using this method the structural and the friction interface calculations are carried out independently and then the results are use to perform the nonlinear part of the dynamic analysis. With this particular feature of the approach, complex structural and friction interface models can be quite easily incorporated in design of friction dampers which control the vibratory motion of blades.

Menq, C.H.

1985-01-01

360

Constraining the noncommutative spectral action via astrophysical observations.  

PubMed

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

Nelson, William; Ochoa, Joseph; Sakellariadou, Mairi

2010-09-01

361

Effect of Fir Fluxes on Constraining Properties of YSOs  

NASA Astrophysics Data System (ADS)

YSOs in the early evolutionary stages are very embedded, and thus, they emit most of their energy at long wavelengths such as FIR and Submm. Therefore, the FIR observational data are very important to classify the accurate evolutionary stages of these embedded YSOs, and to constrain better their physical parameters in the dust continuum modeling. We selected 28 YSOs, which were detected in the AKARI FIS, from the Spitzer c2d legacy YSO catalogs to test the effect of the FIR fluxes in the classification of their evolutionary stages and in the constraining of the envelope properties, the internal luminosity, and the UV strength of the ISRF. According to our test, one can mis-classify the evolutionary stages of YSOs,especially the very embedded ones if the FIR fluxes are not included. In addition, the total amount of heating of YSOs can be underestimated without the FIR observational data.

Ha, Ji-Sung Ha; Lee, Jeong-Eun; Jeong, Woong-Seob

2010-12-01

362

Image coding using entropy-constrained residual vector quantization  

NASA Technical Reports Server (NTRS)

The residual vector quantization (RVQ) structure is exploited to produce a variable length codeword RVQ. Necessary conditions for the optimality of this RVQ are presented, and a new entropy-constrained RVQ (ECRVQ) design algorithm is shown to be very effective in designing RVQ codebooks over a wide range of bit rates and vector sizes. The new EC-RVQ has several important advantages. It can outperform entropy-constrained VQ (ECVQ) in terms of peak signal-to-noise ratio (PSNR), memory, and computation requirements. It can also be used to design high rate codebooks and codebooks with relatively large vector sizes. Experimental results indicate that when the new EC-RVQ is applied to image coding, very high quality is achieved at relatively low bit rates.

Kossentini, Faouzi; Smith, Mark J. T.; Barnes, Christopher F.

1993-01-01

363

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

364

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

365

Planck results - Non Gaussianity constrained with Minkowski Functionals  

NASA Astrophysics Data System (ADS)

We use a morphological tool, the Minkowski Functionals, to constrain non Gaussianity in the Cosmic Microwave Background (CMB) temperature anisotropies measured by the Planck satellite. Two types of non Gaussianities are studied, primordial non Gaussianity with the estimate of the `local' bispectrum parameter fnllocal, and non Gaussianity induced by cosmic strings, related to the string tension Gmu. We use a Bayesian method to constrain these specific models, on Wiener filtered maps and we account for secondaries and foregrounds using the linear properties of the functionals. We find fnllocal=4.2 ± 20.5 (1?) consistent with primordial Gaussianity and with bi-spectrum based estimator results. We show no evidence for cosmic strings, with Gmu < 6.0 × 10^{-7} (95% C.L.). Minkowski Functionals prove to be a nice complementary tool to bispectrum estimators in the case of primordial non Gaussianity and an efficient estimator for cosmic strings induced non Gaussianity.

Ducout, A.

2013-11-01

366

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

367

Assessing working memory capacity through time-constrained elementary activities.  

PubMed

Working memory (WM) capacity measured through complex span tasks is among the best predictors of fluid intelligence (Gf). These tasks usually involve maintaining memoranda while performing complex cognitive activities that require a rather high level of education (e.g., reading comprehension, arithmetic), restricting their range of applicability. Because individual differences in such complex activities are nothing more than the concatenation of small differences in their elementary constituents, complex span tasks involving elementary processes should be as good of predictors of Gf as traditional tasks. The present study showed that two latent variables issued from either traditional or new span tasks involving time-constrained elementary activities were similarly correlated with Gf. Moreover, a model with a single unitary WM factor had a similar fit as a model with two distinct WM factors. Thus, time-constrained elementary activities can be integrated in WM tasks, permitting the assessment of WM in a wider range of populations. PMID:24846786

Lucidi, Annalisa; Loaiza, Vanessa; Camos, Valérie; Barrouillet, Pierre

2014-01-01

368

Constraining effective rheology through parallel joint geodynamic inversion  

NASA Astrophysics Data System (ADS)

The dynamics of crust and lithosphere is to a large extent controlled by its effective viscosity. Unfortunately, extrapolation of laboratory experiments indicates that viscosity is likely to vary over many orders of magnitude. Additional methods are thus required to constrain the effective viscosity of the present-day lithosphere using more direct geophysical observations. Here we discuss a method, which couples 3D geodynamic models with observations (surface velocities and gravity anomalies) and with a Bayesian inversion scheme on massively parallel high performance computers. We illustrate that the basic principle of a joint geodynamic and gravity inversion works well with a simple analytical example. In a next step, we test our approach using a synthetic 3D model of salt tectonics with erosion and sedimentation, and check how much noise conditions, model resolution, and sparse data coverage affect the resolving power of the method. Results show that it is possible to constrain the effective viscosity and density of layers that contribute to the large-scale dynamics, provided that those layers are numerically well resolved. The properties of thin layers that do not contribute much to the overall dynamics cannot be constrained, but noise or sparse data sampling does not significantly affect the inversion results. This thus illustrates that a joint geodynamic and gravity inversion is a potentially powerful method to constrain the dynamics of the crust and lithosphere. Having better constraints on the structure of the present-day crust and lithosphere will help to narrow the parameter space for models that aim to unravel lithosphere dynamics on a geological time scale.

Baumann, Tobias S.; Kaus, Boris J. P.; Popov, Anton A.

2014-09-01

369

Particle Swarm Topologies for Resource Constrained Project Scheduling  

Microsoft Academic Search

We analyze static and dynamic population topologies for a robust evolutionary computation algorithm, which is based on particle\\u000a swarm optimization (PSO), for the resource constrained project scheduling problem (RCPSP). The algorithm incorporates well-known\\u000a procedures such as the serial schedule generation scheme and forward-backward improvement. We investigate the application\\u000a of PSO in combination with different population topologies in comparison to state-of-the-art

Jens Czogalla; Andreas Fink

2008-01-01

370

Trusted Routing for Resource-Constrained Wireless Sensor Networks  

Microsoft Academic Search

Designing a reliable and trusted routing scheme for resource-constrained Wireless Sensor Networks (WSNs) is a challenging task due to the lack of infrastructure and the highly dynamic network topology. To ensure trustworthy end-to-end communications between wirelessly connected sensor nodes, a considerable amount of bidirectional traffic must be relayed either between neighboring sensor nodes or between source sensor nodes and the

Khaled Daabaj; Mike Dixon; Terry Koziniec; Kevin Lee

2010-01-01

371

An Upwind-Biased Constrained Transport Scheme for Magnetohydrodynamics  

NASA Astrophysics Data System (ADS)

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

Lee, D.

2013-04-01

372

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

373

A constrained line search approach to general discriminative HMM training  

Microsoft Academic Search

Recently, we proposed a novel optimization algorithm called constrained line search (CLS) to train Gaussian mean vectors of HMMs in the MMI sense. In this paper, we extend and re-formulate it in a more general framework. The new CLS can optimize any discriminative objective functions including MMI, MCE, MPE\\/MWE etc. Also, closed-form solutions to update all Gaussian mixture parameters, including

Peng Liu; Cong Liu; Hui Jiang; Frank K. Soong; Ren-Hua Wang

2007-01-01

374

Estimation Strategies for Constrained and Hybrid Dynamical Systems  

E-print Network

with differential algebraic equations (DAEs), and hybrid dynamical equations, which are governed by integro- partial differential equations (IPDEs). Many aerospace systems are modeled with these types of equations. For space applications, tethered satellite... systems and flex- ible satellites are examples of systems that can be modeled with DAEs and IPDEs, respectively [6, 7]. The journal model is IEEE Transactions on Automatic Control. 2 Regarding constrained systems, three specific types are considered...

Parish, Julie Marie Jones

2012-10-19

375

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

376

Jamming Transition in Kinetically Constrained Models with Reflection Symmetry  

NASA Astrophysics Data System (ADS)

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

Ohta, Hiroki; Sasa, Shin-ichi

2014-06-01

377

Explicit dynamics equations of the constrained robotic systems  

Microsoft Academic Search

Recursive matrix relations concerning the kinematics and the dynamics of a constrained robotic system, schematized by several\\u000a kinematical chains, are established in this paper. Introducing frames and bases, we first analyze the geometrical properties\\u000a of the mechanism and derive a general set of relations. Kinematics of the vector system of velocities and accelerations for\\u000a each element of robot are then

Stefan Staicu; Xin-Jun Liu; Jianfeng Li

2009-01-01

378

Extremal Fields and Neighboring Optimal Control of Constrained Systems  

E-print Network

OF SCIENCE December 2010 Major Subject: Aerospace Engineering EXTREMAL FIELDS AND NEIGHBORING OPTIMAL CONTROL OF CONSTRAINED SYSTEMS A Thesis by MATTHEW WADE HARRIS Submitted to the O ce of Graduate Studies of Texas A&M University in partial ful... llment of the requirements for the degree of MASTER OF SCIENCE Approved by: Chair of Committee, John Valasek Committee Members, Swaroop Darbha John Junkins Srinivas Vadali Head of Department, Dimitris Lagoudas December 2010 Major Subject...

Harris, Matthew Wade

2012-02-14

379

Local study of newton type algorithms for constrained problems  

Microsoft Academic Search

Newton type algorithms have been widely studied for nonlinearly constrained problems in connection with exact penalty functions,\\u000a but essentially with the hypothesis that the approximation of the Hessian of the Lagrangian is positive definite. This excludes\\u000a Newton's method for nonconvex problems. Assuming the linear independence of the gradients of active constraints, under a weak\\u000a second-order sufficiency condition, we prove the

J. F. BONNANS

380

Simulations of the Local Universe constrained by observational peculiar velocities  

NASA Astrophysics Data System (ADS)

Peculiar velocities, obtained from direct distance measurements, are data of choice to achieve constrained simulations of the Local Universe reliable down to a scale of a few megaparsec. Unlike redshift surveys, peculiar velocities are direct tracers of the underlying gravitational field as they trace both baryonic and dark matter. This paper presents the first attempt to use solely observational peculiar velocities to constrain cosmological simulations of the nearby Universe. In order to set up initial conditions, a Reverse Zel'dovich Approximation (RZA) is used to displace constraints from their positions at z = 0 to their precursors' locations at higher redshifts. An additional new feature replaces original observed radial peculiar velocity vectors by their full 3D reconstructions provided by the Wiener-Filter (WF) estimator. Subsequently, the constrained realization (CR) of Gaussian fields technique is applied to build various realizations of the initial conditions. The WF/RZA/CR method is first tested on realistic mock catalogues built from a reference simulation similar to the Local Universe. These mocks include errors on peculiar velocities, on data point positions and a large continuous zone devoid of data in order to mimic galactic extinction. Large-scale structures are recovered with a typical accuracy of 5 h-1 Mpc in position, the best realizations reaching a 2-3 h-1 Mpc precision, the limit imposed by the RZA linear theory. Then, the method is applied to the first observational radial peculiar velocity catalogue of the project Cosmicflows. This paper is a proof of concept that the WF/RZA/CR method can be applied to observational peculiar velocities to successfully build constrained initial conditions.

Sorce, Jenny G.; Courtois, Hélène M.; Gottlöber, Stefan; Hoffman, Yehuda; Tully, R. Brent

2014-02-01

381

Dynamical spacetimes and gravitational radiation in a Fully Constrained Formulation  

NASA Astrophysics Data System (ADS)

This contribution summarizes the recent work carried out to analyze the behavior of the hyperbolic sector of the Fully Constrained Formulation (FCF) derived in Bonazzola et al. 2004. The numerical experiments presented here allows one to be confident in the performances of the upgraded version of CoCoNuT's code by replacing the Conformally Flat Condition (CFC) approximation of the Einstein equations by the FCF.

Cordero-Carrión, Isabel; Cerdá-Durán, Pablo; María Ibáñez, José

2010-05-01

382

Constrained geometric simulation of the nicotinic acetylcholine receptor.  

PubMed

Constrained geometric simulations have been performed for the recently published closed-channel state of the nicotinic acetylcholine receptor. These simulations support the theory that correlated motion in the flexible ?-sheet structure of the extracellular domain helps to communicate a "conformational wave", spreading from the acetylcholine binding pocket. Furthermore, we have identified key residues that act at the interface between subunits and between domains that could potentially facilitate rapid communication between the binding site and the transmembrane gate. PMID:24955489

Belfield, William J; Cole, Daniel J; Martin, Ian L; Payne, Mike C; Chau, P-L

2014-07-01

383

Unsupervised constrained linear Fisher's discriminant analysis for hyperspectral image classification  

NASA Astrophysics Data System (ADS)

Fisher's linear discriminant analysis (FLDA) has been widely used in pattern classification due to its criterion, called Fisher's ratio, based on the ratio of between-class variance to within-class variance. Recently, a linear constrained discriminant analysis (LCDA) was developed for huperspectral image classification where Fisher's ratio was replaced with the ratio of inter-distance to intra-distance and the target signatures were constrained to orthogonal directions. This paper directly extends the FLDA to constrained Fisher's linear discriminant analysiss (CFLDA), which uses Fisher's ratio as a classification criterion. Since CFLDA is supervised which requires a set of training samples, this paper further extends the CFLDA to an unsupervised CFLDA (UCFLDA) by including a new unsupervised training sample generation algorithm to automatically produce a sample pool of training data to be used for CFLDA. In order to determine the number of classes, p, to be classified, a newly developed concept, called virtual dimensionality (VD) is used to estimate the p where a Neyman-Pearson-based eigen-analysis approach developed by Harsanyi, Farrand and Chang, called noise-whitened HFC (NWHFC)'s method, is implemented to find the VD. The experimental results have shown that the proposed UCFLDA perform effectively for HYDICE data and provides a promising unsupervised classification technique for hyperspectral imagery.

Ji, Bahong; Chang, Chein-I.; Jensen, Janet L.; Jensen, James O.

2004-10-01

384

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

385

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

386

Physics constrained nonlinear regression models for time series  

NASA Astrophysics Data System (ADS)

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

Majda, Andrew J.; Harlim, John

2013-01-01

387

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

388

Interpreting single turnover catalysis measurements with constrained mean dwell times.  

PubMed

Observation of a chemical transformation at the single-molecule level yields a detailed view of kinetic pathways contributing to the averaged results obtained in a bulk measurement. Studies of a fluorogenic reaction catalyzed by gold nanoparticles have revealed heterogeneous reaction dynamics for these catalysts. Measurements on single nanoparticles yield binary trajectories with stochastic transitions between a dark state in which no product molecules are adsorbed and a fluorescent state in which one product molecule is present. The mean dwell time in either state gives information corresponding to a bulk measurement. Quantifying fluctuations from mean kinetics requires identifying properties of the fluorescence trajectory that are selective in emphasizing certain dynamic processes according to their time scales. We propose the use of constrained mean dwell times, defined as the mean dwell time in a state with the constraint that the immediately preceding dwell time in the other state is, for example, less than a variable time. Calculations of constrained mean dwell times for a kinetic model with dynamic disorder demonstrate that these quantities reveal correlations among dynamic fluctuations at different active sites on a multisite catalyst. Constrained mean dwell times are determined from measurements of single nanoparticle catalysis. The results indicate that dynamical fluctuations at different active sites are correlated, and that especially rapid reaction events produce particularly slowly desorbing product molecules. PMID:22070308

Ochoa, Maicol A; Zhou, Xiaochun; Chen, Peng; Loring, Roger F

2011-11-01

389

Interpreting single turnover catalysis measurements with constrained mean dwell times  

NASA Astrophysics Data System (ADS)

Observation of a chemical transformation at the single-molecule level yields a detailed view of kinetic pathways contributing to the averaged results obtained in a bulk measurement. Studies of a fluorogenic reaction catalyzed by gold nanoparticles have revealed heterogeneous reaction dynamics for these catalysts. Measurements on single nanoparticles yield binary trajectories with stochastic transitions between a dark state in which no product molecules are adsorbed and a fluorescent state in which one product molecule is present. The mean dwell time in either state gives information corresponding to a bulk measurement. Quantifying fluctuations from mean kinetics requires identifying properties of the fluorescence trajectory that are selective in emphasizing certain dynamic processes according to their time scales. We propose the use of constrained mean dwell times, defined as the mean dwell time in a state with the constraint that the immediately preceding dwell time in the other state is, for example, less than a variable time. Calculations of constrained mean dwell times for a kinetic model with dynamic disorder demonstrate that these quantities reveal correlations among dynamic fluctuations at different active sites on a multisite catalyst. Constrained mean dwell times are determined from measurements of single nanoparticle catalysis. The results indicate that dynamical fluctuations at different active sites are correlated, and that especially rapid reaction events produce particularly slowly desorbing product molecules.

Ochoa, Maicol A.; Zhou, Xiaochun; Chen, Peng; Loring, Roger F.

2011-11-01

390

A degree-constrained multicast routing algorithm for multimedia communications  

NASA Astrophysics Data System (ADS)

Multicast services have been increasingly used by many multimedia applications. As one of the key techniques to support multimedia applications, the rational and effective multicast routing algorithms are very important to networks performance. When switch nodes in networks have different multicast capability, multicast routing problem is modeled as the degree-constrained Steiner problem. We presented a genetic algorithm, named DCGA, for the degree-constrained case in multimedia communications. The algorithm is used to generate degree-constrained multicast trees with bandwidth and end to end delay bound. Simulations over random networks were carried out to compare the performance of the proposed algorithm. Experimental results show that DCGA has better ability in balance load among the nodes in networks, and has capability of finding unsaturated links and (or) unsaturated nodes to generate multicast trees than BMSTA. Moreover, the proposed algorithm can generate multicast tree with lower cost in any networks and can also achieve optimal multicast tree rapidly with the smaller group size.

Wang, Yanlin; Lu, Ying; Sun, Yugeng

2005-11-01

391

Road-constrained target tracking and identification a particle filter  

NASA Astrophysics Data System (ADS)

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

Agate, Craig S.; Sullivan, Kevin J.

2003-12-01

392

Road-constrained target tracking and identification a particle filter  

NASA Astrophysics Data System (ADS)

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

Agate, Craig S.; Sullivan, Kevin J.

2004-01-01

393

Effect of surface induced nucleation of ferroelastic domains on polarization switching in constrained ferroelectrics  

E-print Network

Effect of surface induced nucleation of ferroelastic domains on polarization switching polarization switching in constrained ferroelectrics is investigated using the time-dependent Ginzburg. A square-shaped finite sized constrained ferroelectric system with vanishing surface polarization

Cao, Wenwu

394

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

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Knee joint femorotibial metallic constrained...DEVICES Prosthetic Devices § 888.3480 Knee joint femorotibial metallic constrained...prosthesis. (a) Identification. A knee joint femorotibial metallic...

2011-04-01

395

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

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Knee joint femorotibial metallic constrained...DEVICES Prosthetic Devices § 888.3480 Knee joint femorotibial metallic constrained...prosthesis. (a) Identification. A knee joint femorotibial metallic...

2013-04-01

396

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

Code of Federal Regulations, 2012 CFR

...2012-04-01 2012-04-01 false Knee joint femorotibial metallic constrained...DEVICES Prosthetic Devices § 888.3480 Knee joint femorotibial metallic constrained...prosthesis. (a) Identification. A knee joint femorotibial metallic...

2012-04-01

397

4-Amino-2,6-dichlorophenol nephrotoxicity in the Fischer 344 rat: protection by ascorbic acid, AT-125, and aminooxyacetic acid.  

PubMed

A halogenated derivative of 4-aminophenol, 4-amino-2, 6-dichlorophenol (ADCP), is a potent nephrotoxicant and a weak hepatotoxicant in Fischer 344 rats. Although the mechanism of ADCP nephrotoxicity is unknown, ADCP could undergo oxidation to a reactive intermediate, such as a 4-amino-2,6-dichlorophenoxy radical or 2,6-dichloro-1,4-benzoquinoneimine, which can generate additional free radicals and/or covalently bind to cellular proteins. The toxic process might also be mediated by glutathione (GSH) conjugates of ADCP, as suggested for the mechanism of 4-aminophenol nephrotoxicity. In this study, the effects of modulators of oxidation and GSH conjugation-related metabolism or transport on ADCP-induced nephrotoxicity were examined. In one set of experiments, male Fischer 344 rats (four/group) were intraperitoneally (ip) administered ADCP (0.38 mmol/kg) only or coadministered an antioxidant, ascorbic acid (1.14 mmol/kg, ip) with ADCP. Administration of ascorbic acid markedly reduced both functional nephrotoxicity and morphological changes induced by ADCP. Administration of a gamma-glutamyltransferase (GGT) inhibitor, l-(alphaS, 5S)-alpha-amino-3-chloro-4,5-dihydroxy-5-isoxazoleacetic acid (10 mg/kg, ip), or a cysteine conjugate beta-lyase inhibitor, aminooxyacetic acid (0.5 mmol/kg, ip), 1 hr before ADCP (0.38 mmol/kg) challenge partially protected rats against ADCP nephrotoxicity. In contrast, administration of an organic anion transport inhibitor, probenecid (140 mg/kg, ip), 30 min before ADCP had little effect on ADCP nephrotoxicity. The GSH depletor, buthionine sulfoximine (890 mg/kg, ip), was given 2 hr prior to ADCP and only minimal protection was noted. In addition, the nonprotein sulfhydryl (NPSH) contents in renal cortex and liver were determined at 2 hr following the administration of ADCP only or ascorbic acid/ADCP. Ascorbic acid afforded complete prevention of the depletion of NPSH in the kidney and liver caused by ADCP administration and also prevented the elevation of renal glutathione disulfide content induced by ADCP. The results indicate that oxidation of ADCP appears to be essential to ADCP nephrotoxicity and that GSH or GSH-derived conjugates of ADCP may be partly responsible for the nephrotoxic effects of ADCP via a GGT-mediated mechanism. PMID:9356314

Hong, S K; Anestis, D K; Ball, J G; Valentovic, M A; Brown, P I; Rankin, G O

1997-11-01

398

Free vibrations of a spherical drop constrained at an azimuth  

NASA Astrophysics Data System (ADS)

Two droplets coupled through a liquid filled (a) hole in a plate or (b) tube is referred to as a double droplet system (DDS) or a capillary switch. Such capillary systems are gaining increasing attention due to their utility in applications. A particularly exciting application is one where a DDS is employed as a liquid lens, one flavor of which entails using a DDS as a variable focus lens by keeping it under sustained oscillations at its natural frequencies. The natural modes of oscillation of a DDS are determined analytically here in the limit in which the plate thickness (or tube length) is vanishingly small and when the effect of gravity is negligible compared to that of surface tension. In this limit, a DDS at rest reduces to two spherical caps that are pinned to and coupled along a common circular ring of contact of negligible thickness. Here, the caps are taken to be complementary pieces of a sphere so that the equilibrium state of the system is a sphere that is constrained by a ring of negligible thickness at an azimuthal angle with respect to the center of the sphere. Both the constrained drop and the fluid exterior to it are taken to be inviscid fluids undergoing irrotational flow. Similar to the linear oscillations of a free drop first studied by Rayleigh, the analytical formulation of the linear oscillations of the constrained drop results in a linear operator eigenvalue problem but with one additional boundary condition, i.e., that which accounts for zero shape perturbation along the circle of contact. Exploiting properties of linear operators, an implicit expression is obtained for the frequency of each mode of oscillation, a feat that appears not to have been accomplished to date in any problem involving oscillations of constrained drops. An extension of a method based on Green's functions that was developed to analyze the linear oscillations of a drop in contact with a spherical bowl [M. Strani and F. Sabetta, "Free-vibrations of a drop in partial contact with a solid support," J. Fluid Mech. 141, 233-247 (1984)], 10.1017/S0022112084000811 is also employed to verify the aforementioned results. Results obtained from these two approaches are then compared to those reported by Bostwick and Steen ["Capillary oscillations of a constrained liquid drop," Phys. Fluids 21, 032108 (2009)], 10.1063/1.3103344. Careful examination of flow fields within drops reveals that by pinning a drop, it should be possible to selectively excite just a portion of a drop's surface.

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

2012-08-01

399

Acid rain  

Microsoft Academic Search

Acid precipitation is a global problem. The effects were first seen in Europe; it affects the Great Lakes and the Midwest because higher-than-normal levels of acidity in rain are found in these areas. Several bays of the Great Lakes are now known to receive substantial runoff from freshwater streams that have been made acidic by acid rains. These areas may

1979-01-01

400

CFlood: A Constrained Flooding Protocol for Real-Time Data Delivery in Wireless Sensor Networks  

E-print Network

CFlood: A Constrained Flooding Protocol for Real-Time Data Delivery in Wireless Sensor Networks Bo networks. We present a constrained flooding protocol, called CFlood that enhances the deadline satisfaction-time perfor- mance by flooding, but effectively constrains energy consumption by controlling the scale

Ravindran, Binoy

401

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

Code of Federal Regulations, 2011 CFR

...2011-04-01 false Ankle joint metal/polymer semi-constrained cemented prosthesis...Devices § 888.3110 Ankle joint metal/polymer semi-constrained cemented prosthesis...Identification. An ankle joint metal/polymer semi-constrained cemented...

2011-04-01

402

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

Code of Federal Regulations, 2011 CFR

...2011-04-01 false Elbow joint metal/polymer semi-constrained cemented prosthesis...Devices § 888.3160 Elbow joint metal/polymer semi-constrained cemented prosthesis...Identification. An elbow joint metal/polymer semi-constrained cemented...

2011-04-01

403

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

Code of Federal Regulations, 2010 CFR

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

2010-04-01

404

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

Code of Federal Regulations, 2010 CFR

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

2010-04-01

405

A Constrained Cauchy-Born Elasticity Accelerated Multi-grid Method for Nanoindentation  

E-print Network

A Constrained Cauchy-Born Elasticity Accelerated Multi- grid Method for Nanoindentation Jingrun to study the lattice statics model aris- ing from nanoindentation. A constrained Cauchy-Born elasticity15, 74G65, 74S05 Key words: Multigrid method, Constrained Cauchy-Born elasticity, Nanoindentation

Ming, Ping-bing

406

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

407

Ion and pH effect on the lower critical solution temperature phase behavior in neutral and acidic poly(organophosphazene) counterparts.  

PubMed

Ion and pH effects on the phase transition behaviors are studied with a series of thermosensitive neutral and acidic poly(organophosphazene) counterparts. Poly(organophosphazenes) are substituted by hydrophobic L-isoleucine ethyl ester (IleOEt) and hydrophilic alpha-amino-omega-methoxy-poly(ethylene glycol) 550 Da (PEG550) together with a relatively small amount of glycylglycine ally ester (GlyGlyOALL). After deprotection, GlyGlyOALL changes into glycylglycine (GlyGlyOH), and neutral GlyGlyOALL and acidic GlyGlyOH polymers with same substituent ratios are compared as counterparts. All the synthesized poly(organophosphazenes) in this work exhibit lower critical solution temperature (LCST) for which sequential phase transitions are suggested: (i) homogeneous solution, (ii) homogeneous gel, (iii) heterogeneous gel, to (iv) heterogeneous solution as hydrophobicity increases either driven by temperature or substituent composition. Ions act on the hydrophobicity modification of the polymers where the polymers with lower hydrophobic/hydrophilic ratios are more sensitively salted-out by NaCl, while those with higher ratios are more effectively salted-in by NaI. At higher concentration of the added ions, the acid group effect on the cloud point becomes deactivated. Meanwhile, because of the conflicting role of amine and carboxylic acid in pH-responsiveness, neutral and acidic polymer counterparts exhibit opposite tendencies in the cloud points. Systematically controlled responsiveness to temperature, ion, and pH changes are created in random amphiphilic graft copolymers, poly(organophosphazenes). The results highlight the importance of the cooperative function of the dominant components in the poly(organophosphazenes) and also expand the general understanding in designing stimuli-responsive smart materials especially useful for various biomedical applications. PMID:19140714

Ahn, Sungsook; Monge, Estela C; Song, Soo-Chang

2009-02-17

408

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

Code of Federal Regulations, 2010 CFR

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

2010-04-01

409

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

410

Constrained Cluster Parameters from Sunyaev-Zel'dovich Observations  

E-print Network

Near-future SZ surveys such as ACT, SPT, APEX, and Planck will find thousands of galaxy clusters. Multi-frequency arcminute-resolution SZ observations can, in principle, determine each cluster's gas temperature (T_e), bulk velocity (v_pec), and optical depth (tau). However, the frequency bands and detector sensitivity employed by upcoming surveys will generally not be sufficient to disentangle the degeneracy between these three cluster parameters, even in the absence of SZ signal contamination from point sources and imperfect primary microwave background subtraction. Assuming contaminants can be removed, we find that near-future SZ surveys will be able to constrain well two cluster gas parameters that are linear combinations of tau*T_e, tau*v_z, and tau*T_e^2. Because the SZ intensity shift is nearly a linear function of tau*T_e, tau*v_z, and tau*T_e^2, a correspondence exists between the two effective gas parameters that SZ surveys can constrain and simple line-of-sight integrals through the three dimensional cluster. We illustrate the parameter constraints and correspondence to line-of-sight integrals using 3D Nbody + hydro cluster simulations and a Markov chain Monte Carlo method. We show that adding an independent T_e measurement to upcoming SZ data breaks the parameter degeneracy. The cluster effective velocity thus constrained is approximately the optical-depth-weighted velocity integrated along the cluster line of sight. A temperature prior with an error as large as 2 keV still gives bulk velocity errors < 100 km/sec, even for a more typical cluster with an electron temperature of 3 keV, for ACT-like SZ observations in the absence of signal contamination. The Markov chain constraints on v_pec and tau are more encouraging and likely more accurate than those obtained from Fisher matrices.

Neelima Sehgal; Arthur Kosowsky; Gilbert Holder

2005-04-12

411

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

412

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

413

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

414

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

415

Constraining the MSSM with Dark Matter indirect detection data  

E-print Network

ar X iv :0 91 1. 19 86 v1 [ he p- ph ] 10 N ov 20 09 CAVENDISH-HEP-2009-23 Constraining the MSSM with Dark Matter indirect detection data Are R. Raklev1 and Martin J. White2 1The Oskar Klein Centre for Cosmoparticle Physics, Department... of Physics, Stockholm University, SE-10691 Stockholm, Sweden 2Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, UK Recently, a claim of possible evidence for Dark Matter in data from the Fermi LAT experiment was made...

Raklev, Are R; White, Martin J

416

Constraining axion dark matter with Big Bang Nucleosynthesis  

NASA Astrophysics Data System (ADS)

We show that Big Bang Nucleosynthesis (BBN) significantly constrains axion-like dark matter. The axion acts like an oscillating QCD ? angle that redshifts in the early Universe, increasing the neutron-proton mass difference at neutron freeze-out. An axion-like particle that couples too strongly to QCD results in the underproduction of He4 during BBN and is thus excluded. The BBN bound overlaps with much of the parameter space that would be covered by proposed searches for a time-varying neutron EDM. The QCD axion does not couple strongly enough to affect BBN.

Blum, Kfir; D'Agnolo, Raffaele Tito; Lisanti, Mariangela; Safdi, Benjamin R.

2014-10-01

417

The unreasonable effectiveness of experiments in constraining nova nucleosynthesis  

NASA Astrophysics Data System (ADS)

Classical nova explosions arise from thermonuclear ignition in the envelopes of accreting white dwarfs in close binary star systems. Detailed observations of novae have stimulated numerous studies in theoretical astrophysics and experimental nuclear physics. These phenomena are unusual in nuclear astrophysics because most of the thermonuclear reaction rates thought to be involved are constrained by experimental measurements. This situation allows for rather precise statements to be made about which measurements are still necessary to improve the nuclear physics input to astrophysical models. We briefly discuss desired measurements in these environments with an emphasis on recent experimental progress made to better determine key rates.

Parikh, Anuj

2014-09-01

418

A simple SQP algorithm for constrained finite minimax problems.  

PubMed

A simple sequential quadratic programming method is proposed to solve the constrained minimax problem. At each iteration, through introducing an auxiliary variable, the descent direction is given by solving only one quadratic programming. By solving a corresponding quadratic programming, a high-order revised direction is obtained, which can avoid the Maratos effect. Furthermore, under some mild conditions, the global and superlinear convergence of the algorithm is achieved. Finally, some numerical results reported show that the algorithm in this paper is successful. PMID:24683318

Wang, Lirong; Luo, Zhijun

2014-01-01

419

Rosmarinic acid  

Microsoft Academic Search

Rosmarinic acid is an ester of caffeic acid and 3,4-dihydroxyphenyllactic acid. It is commonly found in species of the Boraginaceae and the subfamily Nepetoideae of the Lamiaceae. However, it is also found in species of other higher plant families and in some fern and hornwort species. Rosmarinic acid has a number of interesting biological activities, e.g. antiviral, antibacterial, antiinflammatory and

Maike Petersen; Monique S. J Simmonds

2003-01-01

420

Real-time constrained linear discriminant analysis for hyperspectral imagery  

NASA Astrophysics Data System (ADS)

A constrained linear discriminant analysis (CLDA) approach is presented for hyperspectral image detection and classification. Its basic idea is to design an optimal transformation matrix which can maximize the ratio of inter- class distance to intra-class distance while imposing the constraint that different class centers after transformation are along different directions such that different classes can be better separated. The solution turns out to be a constrained version of orthogonal subspace projection (OSP) implemented with a data whitening process. The CLDA approach can be applied to solve both detection and classification problems. In particular, by introducing color for display the classification is achieved with a single classified image where a predetermined color is used to display a specified class. The real-time implementation is also developed to meet the requirement of on-line image analysis when immediate data assessment is critical. The experiments using HYDICE data demonstrate the strength of CLDA approach in discriminating the small targets with subtle spectral difference.

Du, Qian; Ren, Hsuan

2001-09-01

421

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

422

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

2014-05-01

423

Particle filtering algorithm for tracking multiple road-constrained targets  

NASA Astrophysics Data System (ADS)

We propose a particle filtering algorithm for tracking multiple ground targets in a road-constrained environment through the use of GMTI radar measurements. Particle filters approximate the probability density function (PDF) of a target's state by a set of discrete points in the state space. The particle filter implements the step of propagating the target dynamics by simulating them. Thus, the dynamic model is not limited to that of a linear model with Gaussian noise, and the state space is not limited to linear vector spaces. Indeed, the road network is a subset (not even a vector space) of R2. Constraining the target to lie on the road leads to adhoc approaches for the standard Kalman filter. However, since the particle filter simulates the dynamics, it is able to simply sample points in the road network. Furthermore, while the target dynamics are modeled with a parasitic acceleration, a non-Gaussian discrete random variable noise process is used to simulate the target going through an intersection and choosing the next segment in the road network on which to travel. The algorithm is implemented in the SLAMEM simulation (an extensive simulation which models roads, terrain, sensors and vehicles using GVS). Tracking results from the simulation are presented.

Agate, Craig S.; Sullivan, Kevin J.

2003-08-01

424

Constraining Modern and Historic Mercury Emissions From Gold Mining  

NASA Astrophysics Data System (ADS)

Mercury emissions from both historic gold and silver mining and modern small-scale gold mining are highly uncertain. Historic mercury emissions can affect the modern atmosphere through reemission from land and ocean, and quantifying mercury emissions from historic gold and silver mining can help constrain modern mining sources. While estimates of mercury emissions during historic gold rushes exceed modern anthropogenic mercury emissions in North America, sediment records in many regions do not show a strong gold rush signal. We use the GEOS-Chem chemical transport model to determine the spatial footprint of mercury emissions from mining and compare model runs from gold rush periods to sediment and ice core records of historic mercury deposition. Based on records of gold and silver production, we include mercury emissions from North and South American mining of 1900 Mg/year in 1880, compared to modern global anthropogenic emissions of 3400 Mg/year. Including this large mining source in GEOS-Chem leads to an overestimate of the modeled 1880 to preindustrial enhancement ratio compared to the sediment core record. We conduct sensitivity studies to constrain the level of mercury emissions from modern and historic mining that is consistent with the deposition records for different regions.

Strode, S. A.; Jaeglé, L.; Selin, N. E.; Sunderland, E.

2007-12-01

425

Constraining thawing dark energy using galaxy cluster number counts  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

426

Characteristics of constrained optimum trajectories with specified range  

NASA Technical Reports Server (NTRS)

Necessary conditions of optimality are derived for trajectories whose structure is limited to climb, steady cruise, and descent segments. The performance function consists of the sum of fuel and time costs, referred to as direct operating cost (DOC). The state variable is range to go and the independent variable is energy. In this formulation a cruise segment always occurs at the optimum cruise energy for sufficiently large range. At short ranges (500 n. mi. and less) a cruise segment may also occur below the optimum cruise energy. The existence of such a cruise segment depends primarily on the fuel flow vs thrust characteristics and on thrust constraints. If thrust is a free control variable along with airspeed, it is shown that such cruise segments will not generally occur. If thrust is constrained to some maximum value in climb and to some minimum in descent, such cruise segments generally will occur. Computer calculations of typical short-range trajectories obtained about a 1% cost penalty for constraining the thrust.

Erzberger, H.; Lee, H.

1978-01-01

427

Constraining a possible variation of G with Type Ia supernovae  

E-print Network

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 dataset 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 |G dot / 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 delta w < 0.02. We also examine the parameterization G ~ 1 + z. Its short expansion age conflicts with the measured values of the expansion rate and the density in a flat Universe. In conclu...

Mould, Jeremy

2014-01-01

428

Constraining dark sector perturbations I: cosmic shear and CMB lensing  

E-print Network

We present current and future constraints on equations of state for dark sector perturbations. The equations of state considered are those corresponding to a generalized scalar field model and time-diffeomorphism invariant $L(g)$ theories that are equivalent to models of a relativistic elastic medium and also Lorentz violating massive gravity. We develop a theoretical understanding of the observable impact of these models. In order to constrain these models we use CMB temperature data from Planck, BAO measurements, CMB lensing data from Planck and the South Pole Telescope, and weak galaxy lensing data from CFHTLenS. We find non-trivial exclusions on the range of parameters, although the data remains compatible with $w=-1$. We gauge how future experiments will help to constrain the parameters. This is done via a likelihood analysis for CMB experiments such as CoRE and PRISM, and tomographic galaxy weak lensing surveys, focussing in on the potential discriminatory power of Euclid on mildly non-linear scales.

Battye, Richard A; Pearson, Jonathan A

2014-01-01

429

Conformationally constrained peptides as protein tyrosine kinase inhibitors.  

PubMed

Protein kinases are enzymes that catalyze the transfer of the ?-phosphate group from ATP to the hydroxyl groups in side chains of tyrosine, serine, or threonine. Protein kinases are divided in two classes: tyrosine kinases (TKs) and serine/threonine kinases (STKs). Overexpression or activation of protein tyrosine kinases (PTKs) has been found to be responsible for the development of many diseases, including cancer, inflammation, and many cardiovascular and neurodegenerative disorders. Thus, the design of PTK inhibitors (PTKIs) has become a subject of a major interest for the pharmaceutical industry. A number of marketed PTKIs that target conserved ATP binding site of PTKs were found to demonstrate toxicity (e.g., imitanib and sorafenib) or to generate resistance (e.g., imitanib and vemurafenib in chronic myeloid leukemia and metastatic melanoma, respectively). Thus, alternative strategies are urgently required for designing novel PTKIs. Linear peptides designed based on the natural protein substrates of PTKs have been introduced to target unique and non conserved PTK regions, such as substrate binding site. These compounds are more specific than the small molecules that usually target conserved ATP binding site. On the other hand, linear peptides are susceptible to hydrolysis by endogenous peptidases. Cyclization of linear peptides has led to generation of diverse conformationally constrained structures as PTKIs. Introduction of the conformational constraints enhances the stability towards proteases, the free energy upon binding, and binding affinity, but reduces the conformational entropy penalty upon receptor binding. Herein, design strategies for conformationally constrained peptides and their application as PTKIs are discussed. PMID:22571654

Tiwari, Rakesh K; Parang, Keykavous

2012-01-01

430

Constraining Solar Flare Differential Emission Measures with EVE and RHESSI  

E-print Network

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 $\\lesssim$2 to $\\gtrsim$50 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 $\\gtrsim$10 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 ...

Caspi, Amir; Warren, Harry P

2014-01-01

431

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

2013-10-07

432

How Well do the Mentawai Corals Constrain the 1797 Tsunami?  

NASA Astrophysics Data System (ADS)

Vertical coseismic displacements recorded in corals on the Sumatran forearc offer a unique opportunity to reconstruct past earthquakes on the Sunda megathrust. These observations not only constrain the time and magnitude of the 1797 event but also place some bounds on possible slip distributions for this great earthquake. Here we explore the range of slip distributions which are consistent with the coral data. We choose a brute-force technique in which the displacements at the corals are computed for many possible, stochastic slip distributions. The technique makes no assumptions about the earthquake other than the geometry of the fault and the autocorrelation function of the slip distribution which limits the post-seismic strain on the megathrust. We expose several internal inconsistencies in the data with respect to a double couple event on a single inclined plane. We also show that while the along strike length of the rupture is reasonably well constrained, the down-dip distribution of slip, a first order control on the tsunamigenic potential of the earthquake, is only poorly resolved. Numerical simulations of tsunamis that would have resulted from possible 1797 earthquakes may help to advise on possible hazard from a near future Mentawai earthquake.

McCloskey, J.; Nalbant, S.; Kelly, C.; Piatanesi, A.; Lorito, S.; Romano, F.; Antonioli, A.; Cocco, M.; Main, I.; Bell, A.; Naylor, M.; Greenhough, J.

2008-12-01

433

How well do the Mentawai corals constrain great historical earthquakes?  

NASA Astrophysics Data System (ADS)

Vertical coseismic displacements recorded in corals on the Sumatran forearc offer a unique opportunity to reconstruct past earthquakes on the Sunda megathrust. These observations not only constrain the time and magnitude of historical earthquakes but also place some bounds on possible slip distributions for them. Here we explore the range of slip distributions which are consistent with the coral data. We choose a brute-force technique in which the displacements at the corals are computed for many possible slip distributions. The technique makes no assumptions about the earthquake other than the geometry of the fault and the autocorrelation function of the slip distribution which limits the post-seismic strain. We expose several internal inconsistencies in the data which may indicate that the displacements suggested by the corals may not have resulted from pure double couple displacement on the megathrust. Movement on splay faults, for example, may be required to reconcile the discrepancies. We also show that while the along-strike length of the rupture is reasonably well constrained, the location of high slip down dip is only poorly resolved. Numerical simulations of tsunamis that would have resulted from possible historical earthquakes may help to advise on possible hazard from a near future Mentawai earthquake.

McCloskey, J.; Nalbant, S. S.; Bell, A.; Main, I. G.; Naylor, M.; Greenhough, J.; Antonioli, A.

2009-04-01

434

Tropospheric Precursors of Sudden Stratospheric Warmings: Data-Constrained Simulations  

NASA Astrophysics Data System (ADS)

The external factors that cause sudden stratospheric warmings to occur in the Northern Hemisphere are not yet entirely understood. For example, recent studies have found that the Madden Julian Oscillation in tropical weather influences the occurence of sudden warmings, but the number of observed warmings is so small that it is difficult to establish statistical significance. Studies that focus on single sudden warming events generally rely on reanalysis data and are therefore unable to separate the different factors influencing sudden warmings. On the other hand, studies that composite over many warming events in a climate model simulation can be difficult to interpret because individual events vary greatly from one another in their precursors, magnitude, downward-propagation, and lifecycle. We present a modeling framework that makes it possible to study individual winters by constraining the model's dynamical variables to observations using an Ensemble Kalman Filter. The ensemble filter is advantageous because it gives not just an estimate of the atmospheric state, but also of the probability distribution of the state variables, conditioned upon the available meteorological observations. We show that the tropical precursors of sudden warmings can be observed in variations in the rotation rate of the Earth, while extratropical precursors can be observed in variations in polar motion. This makes it possible to evaluate the degree to which observations are able to truly constrain the winter precurors of sudden warmings, by comparing the model's atmospheric angular momentum to observations of Earth rotation parameters.

Neef, Lisa; Matthes, Katja

2014-05-01

435

Galactic disk abundance ratios: constraining SNIa stellar yields  

SciTech Connect

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

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

2005-10-21

436

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.

437

Acid rain  

Microsoft Academic Search

For the past five years, scientists at the Univ. of Colorado have been measuring acid precipitation in a subalpine watershed of the Colorado Rockies. Their measurements of snow and rain and creek water show a strong trend of increasing acidity that is traceable to the chemical reactions of burning fossil fuels. Possible effects of acid precipitation on the watershed's aquatic

Caile

2009-01-01

438

Antagonism of responses to excitatory amino acids on rat cortical neurones by the spider toxin, argiotoxin636.  

PubMed Central

1. Several low molecular weight spider toxins have recently been shown to block potently glutamatergic neuromuscular transmission at the invertebrate neuromuscular junction. The aim of the present investigation was to evaluate the effects of one such toxin, argiotoxin636, on excitatory amino acid receptor-mediated responses in mammalian neurones. 2. Membrane currents were recorded from rat cortical neurones after 2-6 weeks in cell culture, by the whole-cell variant of the patch-clamp technique. N-methyl-D-aspartate (NMDA) and kainate were used as selective agonists for their respective receptor subtypes. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) was used as a selective agonist for the quisqualate receptor subtype. 3. Responses to these agonists were characterised with respect to their concentration and voltage-dependence. Argiotoxin636 (3-30 microM) was found to attenuate markedly responses to NMDA in an agonist- and voltage-dependent manner. Thus, argiotoxin636 progressively reduced successive responses to NMDA when membrane potentials were voltage clamped between -40mV to -100 mV. The more negative the membrane potential the more rapid the development of the block of inward current. 4. The antagonism of NMDA-induced currents by argiotoxin636 could be reversed by clamping the membrane at positive potentials (+20 to +60 mV) and reapplying NMDA. 5. Responses to AMPA and kainate were less affected by argiotoxin636, with an antagonist action only becoming evident at a concentration of 100 microM. 6. These results suggest that argiotoxin636 is an open-channel blocker of the NMDA activated ion-channel in mammalian neurones. Furthermore, our results indicate at least a 30 fold selectivity for NMDA over the quisqualate- and kainate-activated ion-channels. PMID:2790385

Priestley, T.; Woodruff, G. N.; Kemp, J. A.

1989-01-01

439

Theoretical calculation of reorganization energy for electron self-exchange reaction by constrained density functional theory and constrained equilibrium thermodynamics.  

PubMed

Within the framework of constrained density functional theory (CDFT), the diabatic or charge localized states of electron transfer (ET) have been constructed. Based on the diabatic states, inner reorganization energy ?in has been directly calculated. For solvent reorganization energy ?s, a novel and reasonable nonequilibrium solvation model is established by introducing a constrained equilibrium manipulation, and a new expression of ?s has been formulated. It is found that ?s is actually the cost of maintaining the residual polarization, which equilibrates with the extra electric field. On the basis of diabatic states constructed by CDFT, a numerical algorithm using the new formulations with the dielectric polarizable continuum model (D-PCM) has been implemented. As typical test cases, self-exchange ET reactions between tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) and their corresponding ionic radicals in acetonitrile are investigated. The calculated reorganization energies ? are 7293 cm(-1) for TCNE/TCNE(-) and 5939 cm(-1) for TTF/TTF(+) reactions, agreeing well with available experimental results of 7250 cm(-1) and 5810 cm(-1), respectively. PMID:23895675

Ren, Hai-Sheng; Ming, Mei-Jun; Ma, Jian-Yi; Li, Xiang-Yuan

2013-08-22

440

Magma chamber dynamics constrained by crystal isotope stratigraphy  

NASA Astrophysics Data System (ADS)

The architecture of subvolcanic magma plumbing systems controls the thermal regime transited by magmas in the lithosphere, and consequently influences the rates and processes by which magmas evolve. The resolution of current geophysical methods is unable to accurately define the shapes, sizes and crystallinity of small magma bodies. Exhumed fossil magma chambers may provide terminal or cumulative plumbing system assemblies but cannot provide snapshots of the system at a given time, and fail to identify ephemeral components such as dikes, which may open and close to transport magma. Petrographically-constrained in situ analysis of the components of volcanic rocks, including crystal isotope stratigraphy, has recently proved an important new approach to constraining the dynamics of magma storage systems. Core-to-rim decreases in 87Sr/86Sr accompanied by increases in Sr concentration for single plagioclase crystals seen at volcanoes such as El Chichon, Mexico, are explained by frequent recharge of a storage reservoir(s). The fact that high 87Sr/86Sr values are restricted to cores suggests that contamination occurs at the initial stages of injection and contact between magma and the crust. This in turn suggests that crystallization occurs at the margins of the magma body where the thermal gradient is strongest, volatiles are concentrated and epitaxial crystallization is promoted. The crystallized boundary zone then isolates the magma and prevents subsequent recharge magma from interacting directly with the crust. In cases such as Ngauruhoe volcano, New Zealand, 87Sr/86Sr increases from core-to-rim of plagioclase crystals suggest that the magma was not completely isolated from a crustal contaminant. In either case, changes in Sr isotope ratio are correlated with punctuated textural evidence for disequilibrium events, underscoring the importance of recharge. Recharge disaggregates and remobilizes much of the material crystallized from earlier events. Petrographic and geochemical observations from many volcanic systems suggest that the crystalline components are mechanical aggregates of crystals grown in different places and times in the magma storage and delivery system. Indeed the occurrence of true phenocrysts in volcanic rocks is arguably rare. Repeated remobilization of crystalline material by recharge magma indicates that the solids exist in a sufficiently weak state (as a crystal mush or framework) such that an injection of magma can cause disaggregation. This in turn limits the cooling time available for solidification between recharge episodes. The potential now exists for diffusional treatment of trace element and isotopic profiles from mineral phases to constrain effective residence times, and thereby determine crystallization and differentiation rates.

Davidson, J. P.; Tepley, F. J., III; Hora, J. M.

2003-04-01

441

Rosmarinic acid.  

PubMed

Rosmarinic acid is an ester of caffeic acid and 3,4-dihydroxyphenyllactic acid. It is commonly found in species of the Boraginaceae and the subfamily Nepetoideae of the Lamiaceae. However, it is also found in species of other higher plant families and in some fern and hornwort species. Rosmarinic acid has a number of interesting biological activities, e.g. antiviral, antibacterial, antiinflammatory and antioxidant. The presence of rosmarinic acid in medicinal plants, herbs and spices has beneficial and health promoting effects. In plants, rosmarinic acid is supposed to act as a preformed constitutively accumulated defence compound. The biosynthesis of rosmarinic acid starts with the amino acids L-phenylalanine and L-tyrosine. All eight enzymes involved in the biosynthesis are known and characterised and cDNAs of several of the involved genes have been isolated. Plant cell cultures, e.g. from Coleus blumei or Salvia officinalis, accumulate rosmarinic acid in amounts much higher than in the plant itself (up to 36% of the cell dry weight). For this reason a biotechnological production of rosmarinic acid with plant cell cultures has been proposed. PMID:12482446

Petersen, Maike; Simmonds, Monique S J

2003-01-01

442

Constraining X-ray Absorption in Emergent BAL Quasars  

NASA Astrophysics Data System (ADS)

Quasar outflows are important for their feedback on galaxy evolution and black hole growth. These outflows are observed as broad UV absorption lines (BALs) in quasars, reaching velocities >0.1c. In radiative acceleration models, UV-absorbing gas must be shielded by X-ray absorbing gas to reach such velocities and, typically, BAL quasars are indeed X-ray-weaker than non-BAL quasars. However, recent observations are shaking our understanding on how the X-ray and UV absorbers are connected. We propose to re-observe with XMM-Newton three z~2 quasars that did not display UV absorption at the time of the first XMM-Newton observations, but that have recently developed new BAL troughs. These observations will allow us to constrain, for the first time, the X-ray/UV connection on newly emerged BALs.

Rodriguez Hidalgo, Paola

2013-10-01

443

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

444

Constraining Neutron Star Properties with Chandra Observations of Millisecond Pulsars  

NASA Astrophysics Data System (ADS)

Neutron star observables influenced by r-mode physics, such as their spin and thermal evolution, can provide a unique window on their exotic interiors. We propose ACIS-S observations of four non-accreting millisecond pulsars (PSRs J1640+2224, J2019_2425, J1709+2313 and J1923+2515) with low inferred magnetic fields in order to constrain their neutron star surface temperatures, obtain limits on the amplitude of unstable r-modes in them, and make comparisons with similar limits obtained for a sample of accreting LMXB neutron stars. Perhaps surprisingly, none of our proposed targets is yet detected in the X-ray band. Our observations will provide the first X-ray detections of these objects, and will enable further exploration of the r-mode instability in neutron stars.

Strohmayer, Tod

2014-09-01

445

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

446

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

447

Bootstrap percolation and kinetically constrained models on hyperbolic lattices  

E-print Network

We study bootstrap percolation (BP) on hyperbolic lattices obtained by regular tilings of the hyperbolic plane. Our work is motivated by the connection between the BP transition and the dynamical transition of kinetically constrained models, which are in turn relevant for the study of glass and jamming transitions. We show that for generic tilings there exists a BP transition at a nontrivial critical density, $0<\\rho_c<1$. Thus, despite the presence of loops on all length scales in hyperbolic lattices, the behavior is very different from that on Euclidean lattices where the critical density is either zero or one. Furthermore, we show that the transition has a mixed character since it is discontinuous but characterized by a diverging correlation length, similarly to what happens on Bethe lattices and random graphs of constant connectivity.

François Sausset; Cristina Toninelli; Giulio Biroli; Gilles Tarjus

2009-07-06

448

Constrained hidden Markov models for population-based haplotyping  

PubMed Central

Background Haplotype Reconstruction is the problem of resolving the hidden phase information in genotype data obtained from laboratory measurements. Solving this problem is an important intermediate step in gene association studies, which seek to uncover the genetic basis of complex diseases. We propose a novel approach for haplotype reconstruction based on constrained hidden Markov models. Models are constructed by incrementally refining and regularizing the structure of a simple generative model for genotype data under Hardy-Weinberg equilibrium. Results The proposed method is evaluated on real-world and simulated population data. Results show that it is competitive with other recently proposed methods in terms of reconstruction accuracy, while offering a particularly good trade-off between computational costs and quality of results for large datasets. Conclusion Relatively simple probabilistic approaches for haplotype reconstruction based on structured hidden Markov models are competitive with more complex, well-established techniques in this field. PMID:17493258

Landwehr, Niels; Mielikainen, Taneli; Eronen, Lauri; Toivonen, Hannu; Mannila, Heikki

2007-01-01

449

Constrained quantum particles and geometric phases in noninertial frames  

NASA Astrophysics Data System (ADS)

We consider particles constrained to move in the close vicinity of a space curve through a steep quadratic potential in the plane normal to the curve. As is known, the effective 1D Hamiltonian that governs the motion along the curve involves both its curvature and torsion. Thus, the adiabatic cyclic deformations of the curve might give rise to geometric phases being accumulated by the particle. We report that this is indeed, in general, the case, and analyze in detail the origin of the phases, as described in both an inertial Cartesian frame and a noninertial one, adapted to the curve. We extend previous work to include non-locally arclength preserving deformations, and derive general formulas for Berry’s curvature in this case.

Aguilar, P.; Chryssomalakos, C.; Hernandez-Coronado, H.; Okon, E.

2013-08-01

450

SAR image segmentation using MPM and constrained stochastic relaxation  

NASA Astrophysics Data System (ADS)

A segmentation method using maximization of the Posterior marginals (MPM) and constrained stochastic relaxation (CSR) for SAR images is proposed. This method improves the regularity of MPM based segmentation result by introducing CSR. Multi-Level Logistic (MLL) model is used for the underlying label image to introduce regularity prior of segmentation. Gamma distribution is used for SAR intensity data. The hyper parameters of MLL model are supposed to be known a priori. This method is an iterative scheme consists of two alternating steps: to approximate the MPM estimation of the pixel class labels and to estimate gamma distribution parameters. The weight of the prior energy in goal energy function is increased slowly versus the increasing iteration times until certain number of iteration has finished. The segmentation results for synthetic and real SAR images show that the proposed method has a good performance.

Zhao, Huiyan; Cao, Yongfeng; Yang, Wen

2005-10-01

451

A Sequential Quadratically Constrained Quadratic Programming Method of Feasible Directions  

SciTech Connect

In this paper, a sequential quadratically constrained quadratic programming method of feasible directions is proposed for the optimization problems with nonlinear inequality constraints. At each iteration of the proposed algorithm, a feasible direction of descent is obtained by solving only one subproblem which consist of a convex quadratic objective function and simple quadratic inequality constraints without the second derivatives of the functions of the discussed problems, and such a subproblem can be formulated as a second-order cone programming which can be solved by interior point methods. To overcome the Maratos effect, an efficient higher-order correction direction is obtained by only one explicit computation formula. The algorithm is proved to be globally convergent and superlinearly convergent under some mild conditions without the strict complementarity. Finally, some preliminary numerical results are reported.

Jian Jinbao [Guangxi University, College of Mathematics and Informatics Science (China)], E-mail: jianjb@gxu.edu.cn; Hu Qingjie [Hunan Business College, Department of Information (China); Tang Chunming; Zheng Haiyan [Guangxi University, College of Mathematics and Informatics Science (China)

2007-12-15

452

Constraining the MSSM sfermion mass matrices with light fermion masses  

SciTech Connect

We study the finite supersymmetric loop corrections to fermion masses and mixing matrices in the generic MSSM. In this context the effects of non-decoupling chirally-enhanced self-energies are studied beyond leading order in perturbation theory. These NLO corrections are not only necessary for the renormalization of the CKM matrix to be unitary, they are also numerically important for the light fermion masses. Focusing on the trilinear A-terms with generic flavor-structure we derive very strong bounds on the chirality-changing mass insertions {delta}{sub IJ}{sup fLR,RL} by applying 't Hooft's naturalness criterion. In particular, the NLO corrections to the up quark mass allow us to constrain the unbounded element {delta}{sub 13}{sup uRL} if at the same time {delta}{sub 13}{sup uLR} is unequal to zero. Our result is important for single-top production at the LHC.

Crivellin, Andreas; Girrbach, Jennifer [Institut fuer Theoretische Teilchenphysik, Karlsruhe Institute of Technology, Universitaet Karlsruhe, D-76128 Karlsruhe (Germany)

2010-04-01

453

Constrained independent component analysis approach to nonobtrusive pulse rate measurements.  

PubMed

Nonobtrusive pulse rate measurement using a webcam is considered. We demonstrate how state-of-the-art algorithms based on independent component analysis suffer from a sorting problem which hinders their performance, and propose a novel algorithm based on constrained independent component analysis to improve performance. We present how the proposed algorithm extracts a photoplethysmography signal and resolves the sorting problem. In addition, we perform a comparative study between the proposed algorithm and state-of-the-art algorithms over 45 video streams using a finger probe oxymeter for reference measurements. The proposed algorithm provides improved accuracy: the root mean square error is decreased from 20.6 and 9.5 beats per minute (bpm) for existing algorithms to 3.5 bpm for the proposed algorithm. An error of 3.5 bpm is within the inaccuracy expected from the reference measurements. This implies that the proposed algorithm provided performance of equal accuracy to the finger probe oximeter. PMID:22894523

Tsouri, Gill R; Kyal, Survi; Dianat, Sohail; Mestha, Lalit K

2012-07-01

454

Constraining the Variation of G by Cosmic Microwave Background Anisotropies  

E-print Network

We use the Cosmic Microwave Background Anisotropies (CMBA) power spectra to constrain the cosmological variation of gravitational constant G. It is found that the sensitivity of CMBA to the variation of G is enhanced when G is required to converge to its present value. The variations of G from the CMB decoupling epoch z ~ 1000 to the present time are modelled by a step function and a linear function of scale factor $a$ respectively, and the corresponding 95% confidence intervals for G/G_0 are [0.95, 1.05] and [0.89, 1.13], G_0 being the present value. The CMBA constraint is unique in the sense that it entails the range of redshift from z \\approx 1000 to 0.

K. C. Chan; M. -C. Chu

2006-11-28

455

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

456

Stabilizing model predictive control for constrained nonlinear distributed delay systems.  

PubMed

In this paper, a model predictive control scheme with guaranteed closed-loop asymptotic stability is proposed for a class of constrained nonlinear time-delay systems with discrete and distributed delays. A suitable terminal cost functional and also an appropriate terminal region are utilized to achieve asymptotic stability. To determine the terminal cost, a locally asymptotically stabilizing controller is designed and an appropriate Lyapunov-Krasoskii functional of the locally stabilized system is employed as the terminal cost. Furthermore, an invariant set for locally stabilized system which is established by using the Razumikhin Theorem is used as the terminal region. Simple conditions are derived to obtain terminal cost and terminal region in terms of Bilinear Matrix Inequalities. The method is illustrated by a numerical example. PMID:21232739

Mahboobi Esfanjani, R; Nikravesh, S K Y

2011-04-01

457

Geometric momentum for a particle constrained on a curved hypersurface  

E-print Network

A strengthened canonical quantization scheme for the constrained motion on a curved hypersurface is proposed with introduction of the second category of fundamental commutation relations between Hamiltonian and positions/momenta, whereas those between positions and moments are categorized into the first. As an $N-1$ ($N\\geq2$) dimensional hypersurface is embedded in an N dimensional Euclidean space, we obtain the proper momentum that depends on the mean curvature. For the surface is the spherical one, a long-standing problem on the form of the geometric potential is resolved in a lucid and unambiguous manner, which turns out to be identical to that given by the so-called confining potential technique. In addition, a new dynamical group SO(N,1) symmetry for the motion on the sphere is demonstrated.

Q. H. Liu

2013-05-04

458

Use of energy loss mechanisms to constrain Lorentz invariance violations  

NASA Astrophysics Data System (ADS)

In light of recent and probably incoming observations of very high energy astroparticles, such as those reported by the IceCube collaboration, we readdress the energy loss mechanism by Lorentz violating particles. We analytically show that Cohen-Glashow's formula for energy loss is connected with a Poisson distribution for the number of decays, for which the large fluctuations prevent placing bounds on Lorentz invariance violations. However, this model ignores the sharp change in the decay width after each process. We propose replacing Poisson statistics with a new distribution that takes this into account. We study the average final energy and its fluctuations according to the new statistics, contrasting it with Cohen-Glashow's result, and discussing the reliability of energy loss mechanisms to constrain violations of Lorentz invariance.

Mazón, Diego

2014-03-01

459

Conflict processing in the anterior cingulate cortex constrains response priming.  

PubMed

A prominent function of the anterior cingulate cortex (ACC) is to process conflict between competing response options. In this study, we investigated the role of conflict processing in a response-priming task in which manual responses were either validly or invalidly cued. Examining electrophysiological measurements of oscillatory brain activity on the source level, we found response priming to be related to a beta power decrease in the premotor cortex and conflict processing to be linked to a theta power increase in the ACC. In particular, correlation of oscillatory brain activities in the ACC and the premotor cortex showed that conflict processing reduces response priming by slowing response time in valid trials and lowering response errors in invalid trials. This relationship emerged on a between subjects level as well as within subjects, on a single trial level. These findings suggest that conflict processing in the ACC constrains the automatic priming process. PMID:20123025

Pastötter, Bernhard; Hanslmayr, Simon; Bäuml, Karl-Heinz T

2010-05-01

460

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

461

Variational Principles for Constrained Electromagnetic Field and Papapetrou Equation  

E-print Network

In our previous article [4] an approach to derive Papapetrou equations for constrained electromagnetic field was demonstrated by use of field variational principles. The aim of current work is to present more universal technique of deduction of the equations which could be applied to another types of non-scalar fields. It is based on Noether theorem formulated in terms of Cartan' formalism of orthonormal frames. Under infinitesimal coordinate transformation the one leads to equation which includes volume force of spin-gravitational interaction. Papapetrou equation for vector of propagation of the wave is derived on base of the equation. Such manner of deduction allows to formulate more accurately the constraints and clarify equations for the potential and for spin.

A. T. Muminov

2007-06-28

462

Dynamic propensity in a kinetically constrained lattice gas  

NASA Astrophysics Data System (ADS)

We apply the concept of dynamic propensity to a simple kinetically constrained model of glass formers, the two-vacancy assisted triangular lattice gas, or (2)-TLG. We find that the propensity field, defined in our case as the local root-mean-square displacement averaged over the ensemble of trajectories with identical initial configurations, is a good measure of dynamical heterogeneity. This suggests a configurational origin for spatial fluctuations of the dynamics, but just as in the case of atomistic systems, we find that propensity is not correlated to any simple structural property. We show instead that certain extended clusters of particles connected to vacancies correlate well with propensity, indicating that these are the fundamental excitations of the (2)-TLG. We also discuss time correlations and the correlation between configurations within the propensity ensemble.

Hedges, Lester O.; Garrahan, Juan P.

2007-05-01

463

Advanced Techniques for Constrained Internal Coordinate Molecular Dynamics  

PubMed Central

Internal coordinate molecular dynamics (ICMD) methods provide a more natural description of a protein by using bond, angle and torsional coordinates instead of a Cartesian coordinate representation. Freezing high frequency bonds and angles in the ICMD model gives rise to constrained ICMD (CICMD) models. There are several theoretical aspects that need to be developed in order to make the CICMD method robust and widely usable. In this paper we have designed a new framework for 1) initializing velocities for non-independent CICMD coordinates, 2) efficient computation of center of mass velocity during CICMD simulations, 3) using advanced integrators such as Runge-Kutta, Lobatto and adaptive CVODE for CICMD simulations, and 4) cancelling out the “flying ice cube effect” that sometimes arises in Nosé-Hoover dynamics. The Generalized Newton-Euler Inverse Mass Operator (GNEIMO) method is an implementation of a CICMD method that we have developed to study protein dynamics. GNEIMO allows for a hierarchy of coarse-grained simulation models based on the ability to rigidly constrain any group of atoms. In this paper, we perform tests on the Lobatto and Runge-Kutta integrators to determine optimal simulation parameters. We also implement an adaptive coarse graining tool using the GNEIMO Python interface. This tool enables the secondary structure-guided “freezing and thawing” of degrees of freedom in the molecule on the fly during MD simulations, and is shown to fold four proteins to their native topologies. With these advancements we envision the use of the GNEIMO method in protein structure prediction, structure refinement, and in studying domain motion. PMID:23345138

Wagner, Jeffrey R.; Balaraman, Gouthaman S.; Niesen, Michiel J. M.; Larsen, Adrien B.; Jain, Abhinandan; Vaidehi, Nagarajan

2013-01-01

464

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

465

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

466

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