bluuebunny/crossref_metadata_2025 huggingface dataset:
MNDO calculations of the molecular and electronic structure of thionitroso, dithionitro and related compounds
Authors: Mehlhorn Achim
Published: June 2010

Compounds with the formulae RNS and RNS2 (thionitroso I and dithionitro compounds II, dithionitrites III, N-thiosulfinylamines IV, dithia-aziridines V and thiazylthiols VI, R = H, CH3, C6H5)and the corresponding radical cations HNS2+ and anions HNS2- have been investigated by MNDO calculations with respect to their molecular geometries, relative stabilities, ionization and electron capture properties and dipole moments. For the simplest representatives (R = H) the infrared spectra have been calculated. The lengths of NS triple (in VI), double (in I, III, IV) and partial double (in II, III) bonds are predicted to be in the region of 147-150, 152-155 and 158-162 pm, respectively. Within these regions systematic shifts result from different substituents R. Contraction of NS bonds (1-6 pm) is observed in the case of ionization whereas electron capture causes bond elongation (2-6 pm). The MNDO sequence of stability deviates from that of ab initio calculations for compounds with tetravalent sulfur the stabilization effect of which is obviously underestimated by the MNDO approach. All compounds studied are characterized by negative non-vertical electron affinities suggesting vigorous reactivity with nucleophilic reactants. The patterns of infrared spectra enable recognition, discrimination and characterization of these mostly unknown compounds which might be accessible as short-living transients.
On macroscopic spatial averaging of contact and long-range microscopic forces
Authors: Blaive Bruno , Metzger Jacques
Published: June 2010

Even though ensemble averages are sometimes equivalent, or even preferable, to spatial averages, the latter have incontestable significance. Spatial averaging, which has been restricted until now to basic electromagnetic equations, is applied here to the Cauchy equation of movement. Spatial filtration of microscopic properties is especially useful in the case of continuous media subjected to long-range forces, for which no intuitive macroscopic reasoning is possible.
Ab initio study of the anharmonic properties of dipole moment functions of ammonia and the oxonium ion
Authors: Pracna Petr , Havlas Zdeněk
Published: June 2010

Ab initio SCF electric dipole moment functions of the electronic ground states of ammonia and the oxonium ion are determined over a wide range of vibrational coordinates. The dipole moment functions are used within the framework of the nonrigid invertor Hamiltonian to evaluate transition moments for various types of vibrational bands. Reasonable agreement with experimental data for ammonia is achieved by scaling the dipole moment function. Several new transition moments for combination and hot bands are predicted.
Accurate gaussian expansion of STO's. Test of many-center slater integrals
Authors: Fernández Rico Jaime , Ramírez Guillermo , López Rafael , Fernández-Alonso José I.
Published: June 2010

The use of large STO-NG expansions for testing algorithms and procedures designed for the calculation of many-center molecular integrals with Slater basis functions was previously proposed. Expansions up to the STO-12G for the 1s and 2s cases and a method for calculating integrals involving higher quantum numbers were there reported. Here, we present the corresponding expansions from STO-13G to STO-27G. Further tests on the convergence in the integral calculations with the new expansions are also included and the results are compared with those obtained previously. These new expansions are necessary when highly accurate comparisons are required.
Generalized exchange local-spin-density-functional theory: One-electron energies and eigenvalues
Authors: Manoli Soheil D. , Whitehead Michael A.
Published: June 2010

Within the Generalized Exchange (GX) LSD scheme, a method to calculate the ionization potential (IP) of an atom has been developed involving correction terms to the negative of the eigenvalue of the highest occupied atomic orbital (HOAO). These correction terms are evaluated non-iteratively using the fully occupied orbitals of the ground state of the neutral atom. Within the unrelaxed orbital approximation, this corrected eigenvalue IP, IPcorr, is completely equivalent to the Transition State IP, calculated from an SCF calculation at half-occupancy of the HOAO, when used with density-functional (DF) schemes that do not include self-interaction. The present scheme can also be used with self-interaction corrected DF schemes. In both cases, the corrected eigenvalue method of calculating IP's gives good results. The techniques used to derive IPcorr are applied to derive an expression for the electronegativity of the free atom which can be used with both self-interaction and non-self-interaction corrected DF schemes. The results of IP and electronegativity calculations for the helium to krypton atoms are reported using a variety of DF schemes. These are compared to each other and to the experimental values whenever possible.
A preliminary report on a quantum-mechanical model for the energetics of a solute at the surface separating two immiscible liquid phases
Authors: Bonaccorsi Rosanna , Ojalvo Evaristo , Tomasi Jacopo
Published: June 2010

The model considered here is directed to the problem of evaluation of free energy changes in the course of the passage of a solute M from solvent A to the second solvent B. It is applied to detailed description of the energetics of the solute passage (M in contact with the A/B separating surface) for n-alkanes, n-alcohols and n-primary amines. The difference in the behaviour due to the different composition of M is evident (engulfing versus buoyancy processes). The further text regards the transfer free energy change (A = water, B = p-xylene) for amines. A discussion of possible improvements of the model is presented also.
The influence of fluoro substituents on cyclopropa-benzene, -naphthalene, and -anthracene
Authors: Lecoultre Jacques , Heilbronner Edgar , Müller Paul , Rodriguez Domingo
Published: June 2010

The He(Iα) PE spectra of cyclopropabenzene, cyclopropa[b]naphthalene, cyclopropa[b]anthracene, their 1,1-difluoro derivatives and of some of their substituted derivatives have been recorded, analyzed and assigned by correlation with the PE spectra of the parent molecules benzene, naphthalene and anthracene. It is shown that the PE spectroscopic data yield no information about the presence or absence of a Mills-Nixon effect in the molecules investigated. The inductive effect of the bridging CH2 group of the cyclopropeno ring is close to zero, whereas that of the CF2 group leads to positive ionization energy shifts in good agreement with previous experience. The hyperconjugative interaction of the local pseudo-π orbital of the CH2 group yields a significant destabilization of the π-orbitals of B1 symmetry.
Noninvasive continuous monitoring of solid-phase peptide synthesis by acid-base indicator
Authors: Krchňák Viktor , Vágner Josef , Šafář Pavel , Lebl Michal
Published: June 2010

The course and the end point of the acylation of resin-bound amino groups in solid-phase peptide synthesis was monitored by a novel noninvasive qualitative and quantitative test based on the use of the acid-base indicator bromophenol blue.
Configurational requirements of aromatic amino acid residues for the activity of PRP-hexapeptide
Authors: Kubik Aleksandra , Szewczuk Zbigniew , Siemion Ignacy Z. , Wieczorek Zbigniew , Spiegel Krystyna , Zimecki Michal , Janusz Maria , Lisowski Józef
Published: June 2010

The three analogues with D-amino acid substituents at position 1 and 5 of PRP-hexapeptide were synthesized and tested for its biological activity to check the influence of the spacial orientation of aromatic rings on the immune response. One of the analogs (Tyr-Val-Pro-Leu-D-Phe-Pro) was found to have the immunoregulatory activity.
The influence of certain substitutions on 1 and 2 positions of angiotensin II on biological responses
Authors: Cordopatis Paul , Belté Urania , Theodoropoulos Dimitrios , Bossé Roger , Escher Emanuel
Published: June 2010

Position 1 modified analogues of angiotensin II, as well as two analogues with additional elimination of Arg in position 2, were prepared by means of solid phase peptide synthesis. These compounds, namely [Ser1]AT, [DOPA1]AT, [Cys1]AT, [Cys(Acm)1]AT, [N-MeAib1]AT, [Aib1, Aib2]AT and [GABA1, GABA2]AT, were tested in the classical smooth-muscle assay (rabbit aorta strip) and, for binding potency, on bovine adrenal membranes and possessed a pD2 value of 7·23, 6·79, 6·43, 5·80, 6·43, and IC50(10-10 mol l-1) value of 31·6, 23·2, nd, nd, 170·0, respectively. The last two analogues were found to be totally inactive.
Synthesis and properties of analogues of vasopressin with 1-aminocyclopropane-1-carboxylic acid in position 9
Authors: Procházka Zdenko , Ancans Juris E. , Slaninová Jiřina , Machová Alena , Barth Tomislav , Škopková Jana , Buděšínský Miloš , Pavlíková Františka , Lebl Michal
Published: June 2010

Solid phase methodology on benzhydrylamine resin was used for the synthesis of three analogues of vasopressin with non-coded amino acid, 1-aminocyclopropane 1-carboxylic acid, in position 9. Two analogues of lysine-vasopressin ([Lys8, Acc9]vasopressin (I) and Gly3-[Lys8, Acc9]vasopressin (II)) and one analogue of arginine-vasopressin ([Arg8, Acc9]vasopressin (III)) have been synthesized. The dubious value of the biological activity of [Lys8, D-Ala9]vasopressin was reevaluated and [Lys8, L-Ala9]vasopressin was also synthesized and tested for the comparison. Differences in solution conformation of these two analogues were studied by 1H and 13C NMR spectroscopy. Biological activities of all analogues were either significantly lowered or almost completely eliminated. Analogues I-III were found to be completely inactive in analgesia and the CNS activities tested (active and passive avoidance).
Screening the recognition properties of peptide hormone sequence mutants by analytical high performance liquid affinity chromatography on immobilized neurophysin
Authors: Fassina Giorgio , Lebl Michal , Chaiken Irwin M.
Published: June 2010

Analytical high performance liquid affinity chromatography with immobilized neurophysin was used as a molecular screen to evaluate the effects of peptide hormone structure modification on protein recognition. Immobilization of neurophysin on silica and highly cross-linked agarose occurred with retention of oxytocin and vasopressin binding properties. The effects of one-residue-at-a-time mutation, multi-site sequence simplification, and sequence randomization of critical contact residues were evaluated by extent of binding of the peptides on the affinity matrix. The analytical chromatography method also was used as a stereoselective detector to identify racemic contaminants in peptide hormone preparations.
Synthesis of modified human C-peptide and its fragments
Authors: Bendlová Běla , Lebl Michal , Štolba Pavel , Stárka Luboslav
Published: June 2010

Syntheses of the modified human C-peptide containing residues suitable for the introduction of the radioactive label (tyrosine) and internal marker for monitoring binding to carrier (norvaline) and five of its fragments are described. The syntheses were performed by solid phase method using either 9-fluorenylmethoxycarbonyl or tert-butyloxycarbonyl protecting groups. The products were purified by gel filtration, ion exchange chromatography and reversed phase HPLC. The reactivity of prepared peptides with antisera was determined and the modified C-peptide was found fully reactive.
Isomerism and topicity in three- and four-dimensional space: A review
Authors: Jonas Jaroslav
Published: June 2010

Isomerism is a notion of a considerably broad meaning. Not only chemists but also physicists, biologists and philosophers come across it. In the sequel, some basic problems of the contemporary understanding of the phenomenon of isomerism of molecular structures and related problems of topic relationships between homomorphic ligands and faces are dealt with. Illustrating factual material is selected within the domain of organic chemistry. With the rapid development of nomenclature in this area in mind, the issues are presented from a point of view stressing the unity of historical and logical moments. Problems arising when moving from the analysis of molecular structure models towards the analysis of real sets of molecules are highlighted. Differences between the analysis of static molecular structures in three-dimensional space and the analysis of real dynamic molecular structures in four-dimensional space are dealt with in greater detail. The method of NMR spectroscopy is discussed from this standpoint as an example of the most widespread research tool for investigating intramolecular dynamism at present. Stereo-differentiating reactions are also treated briefly and a suggestion is made to introduce into the teaching of isomerism and topicity a classification of differentiating interactions. The relationships discussed are demonstrated comprehensively using the chemical behaviour of an optically active trisubstituted cycloheptatriene-norcaradiene system as an example and, are also discussed in connection with some new findings concerning actual chiral geometries in some conventionally achiral systems. Attention is paid to didactic presentation of the topic and an attempt is made to show probable trends in future development in this domain.
Influence of the solvent on the transmission of polar effects in free radical reactions. A theoretical study
Authors: Ponec Robert , Hájek Milan
Published: June 2010

The influence of the solvents on the transmission of polar effects in free radical reactions has been analysed theoretically by using the combined approach based on the incorporation of delocalizabilities as static indices of chemical reactivity into the framework of virtual charge model. The possibility of using this theoretical description as a general methodology of characterizing solvent effects is discussed.
Noncataleptic neuroleptic agents: 2-(4-(2-(2-Chloro-10,11-dihydrodibenzo[b,f]thiepin-10-yloxy)ethyl)piperazine-1-yl)ethanol and some related compounds
Authors: Jílek Jiří , Valchář Martin , Holubek Jiří , Dlohožková Nataša , Pomykáček Josef , Matoušová Oluše , Metyšová Jiřina , Protiva Miroslav
Published: June 2010

10-(2-Bromoethoxy)-2-chloro-10,11-dihydrodibenzo[b,f]thiepin (X), prepared by two methods, was subjected to substitution reactions with 2-(1-piperazinyl)ethanol, 3-(1-piperazinyl)propanol, 1-methylpiperazine, 3-(1-piperazinyl)propionamide, piperazine, and 1-(ethoxycarbonyl)piperazine and gave the title compounds II-VII. The alcohol II was esterified by treatment with acid chlorides to compounds VIII and IX. Compounds II, V, and VIII proved to be noncataleptic neuroleptic agents and II (clopithepin, VÚFB-17 076) was selected for preclinical studies.
New approach to the use of 2-bromoethyl esters in peptide synthesis
Authors: Amaral Trigo M. Joaquina S. A. , Oliveira Santos M. Isabel A.
Published: June 2010

The synthesis of six new fully protected dipeptides 2-bromoethyl esters and a new method for the removal of the C-protection by the action of the sulphide anion, at room temperature, are described.
Analysis of short interproton distances in proline peptides as a guide in the interpretation of nuclear Overhauser effects
Authors: Ramakrishnan Chandrashekharan , Sowdhamini Ramanathan , Balaram Padmanabhan
Published: June 2010

The conformational dependence of interproton distances in model proline peptides has been investigated in order to facilitate interpretation of the results of Nuclear Overhauser Effect (NOE) studies on such peptides. For this purpose two model systems, namely, Ac-Pro-NHMe and Ac-Pro-X-NHMe have been chosen and used. In the former, short interproton distances detectable in NOE experiments permit a clear distinction between conformations with Pro ψ = -300 (helical region) and those in which ψ is around 1200 (polyproline region). For the latter, the variation of distances between the protons of methyl amide and the Pro ring have been studied by superimposing on the Ramachandran map in the (φ3, ψ3) plane. The results show that β-turns and non-β-turn conformations can be readily distinguished from NOE data and such long range NOEs should be detectable for specific non-β-turn conformations. NOEs involving Cβ and Cγ protons are particularly sensitive to the state of pyrrolidine ring puckering.
Alpha and beta conformations of water soluble sequential iso polypeptides
Authors: Barbier Bernard , Perello Margarita , Brack André
Published: June 2010

Alternating poly(Leu-Lys) and its isopolypeptide poly(Leu-Lys-Lys-Leu) were synthesized via polycondensation of p-nitrophenyl esters of the corresponding protected peptides. Addition of one equivalent of 1-hydroxybenzotriazole and varying amounts of a tertiary base allowed to control the molecular weights of the samples. The conformation of the water soluble polypeptides was investigated by circular dichroism. Poly(Leu-Lys) adopts a β-sheet conformation in the presence of salt while poly(Leu-Lys-Lys-Leu) adopts an α-helical conformation. For polypeptides based on a 1 : 1 composition of hydrophobic (A) and hydrophilic (B) residues, the shortest repeat for the formation of a β-sheet is -AB- whereas -AABB- represents the shortest repeat for an α-helix formation.
Efficient routes to the Arnstein's tripeptide δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (LLD ACV) from the oxidation products of L-lysine derivatives
Authors: Liberek Bogdan , Kasprzykowska Regina , Wiśniewski Kazimierz
Published: June 2010

Two efficient syntheses of the linear tripeptide precursor of penam and cephem antibiotics are presented. The routes are characterised by the use of L-lysine derivatives, Z-L-Lys(Z)-OH and H-L-Lys(Z)-OH as starting materials. By the permanganate oxidation the protected side chain amino grouping in L-lysine derivatives is transformed into the benzyloxycarbonylcarbamoyl substituent with formation of Z-L-Aad(NHZ)-OH and H-L-Aad(NHZ)-OH compounds. Both oxidation products are easily transformed into [N, Cα]-diprotected derivatives. Subsequent condensation at the δ-carboxy group afforded protected LLD ACV tripeptide.
Synthesis and X-ray diffraction analysis of the tetrazole peptide analogue Pro-LeuΨ[CN4]Gly-NH2
Authors: Valle Giovanni , Crisma Marco , Yu Kuo-Long , Toniolo Claudio , Mishra Ram K. , Johnson Rodney L.
Published: June 2010

The synthesis of an analogue of the neuropharmacologically active peptide Pro-Leu-Gly-NH2 in which the Leu-Gly peptide bond has been replaced with a tetrazole moiety was carried out. The molecular and crystal structure of the tetrazole analogue Pro-Leuψ[CN4]Gly-NH2 was determined by X-ray diffraction and a comparison was made with the published X-ray structure of Pro-Leu-Gly-NH2. The tetrazole annular system turns out to be a good conformationally-restricted replacement for the cis-peptide bond in terms of bond lengths, bond angles and the ω torsion angle. The molecule was found to be folded at the -Leuψ[CN4]Gly- sequence, but it did not form the intramolecular N-H···O=C hydrogen bond characteristic of the type Vla β-bend conformation. In contrast to Pro-Leu-Gly-NH2, Pro-Leuψ[CN4]Gly-NH2 was found to be unable to enhance the binding of dopamine receptor agonists to the dopamine receptor.
Synthesis and biological activity of new metallocenic angiotensin II analogs
Authors: Maes Pierrette , Ricouart Annie , Escher Emmanuel , Tartar André , Sergheraert Christian
Published: June 2010

Analogs of angiotensin II in which phenylalanine in position 8 was replaced with cymantrenylalanine or with its triphenylphosphine photosubstitution product were synthesized by the solid-phase method. On rabbit aorta strips, these peptides were found to be pure antagonists of angiotensin II. Their relative affinities are higher than most other analogs substituted in position 8 with bulky amino-acids.
Synthesis of an insulin-like compound consisting of the B chain of insulin and an A chain corresponding to the A and D domains of human insulin-like growth factor I
Authors: Schwartz Gerald P. , Burke G. Thompson , Sheikh Maqsood , Zong Lin , Katsoyannis Panayotis G.
Published: June 2010

We report the synthesis and biological evaluation of a two-chain, disulfide-linked, insulin-like compound in which the A chain amino acid sequence corresponds to that of the A- and D-domains of human insulin-like growth factor I (IGF-I), and the B chain is that of bovine insulin. The compound displays reduced insulin-like activity, but considerably increased growth-promoting activity relative to insulin, and is not recognized by IGF carrier proteins. These data confirm some of our earlier conclusions regarding the role of the A-, B- and D-domains in the expression of the biological profile of IGF-I: The A-domain, but not the B- or D-domain is associated with the growth-promoting activity of IGF-I; the B-domain, but not the A- or D-domain, contains determinants for the recognition of IGF carrier proteins; and the D-domain acts to supress insulin-like activity in IGF-I.
Retard-insulins formed by complexing with polyamino acids
Authors: Losse Günter , Naumann Wolfgang , Raddatz Heike , Koszowicz Joachim
Published: June 2010

Polyglycine, polyalanine, polyleucine, poly-α-glutamic acid, poly-γ-glutamic acid and poly-α-lysine were complexed with insulin under non-denaturating conditions. The liberation behaviour of the hormone was investigated in vivo and in vitro in dependence on the insulin content, molecular weight, ionic interactions and hydrophobicity of the polyamino acid. The in vitro results were confirmed by the in vivo experiments with animals. They clearly pointed out the influence of physicochemical parameters on the bioavailability of insulin. Complexes of poly-α-lysine and polyglycine were shown to be the most suitable retard forms, producing significant blood glucose lowering effects over 12 hours.
A polycentric growth model of gallium arsenide epitaxial layers from the gas phase with simultaneous diffusion, adsorption and chemical reaction
Authors: Erdös Emerich , Leitner Jindřich , Voňka Petr , Stejskal Josef , Klíma Přemysl
Published: June 2010

For a quantitative description of the epitaxial growth rate of gallium arsenide, two models are proposed including two rate controlling steps, namely the diffusion of components in the gas phase and the surface reaction. In the models considered, the surface reaction involves a reaction triple - or quadruple centre. In both models three mechanisms are considered which differ one from the other by different adsorption - and impact interaction of reacting particles. In every of the six cases, the pertinent rate equations were derived, and the models have been confronted with the experimentally found dependences of the growth rate on partial pressures of components in the feed. The results are discussed with regard to the plausibility of individual mechanisms and of both models, and also with respect to their applicability and the direction of further investigations.
Dependence of transversely scattered light flux on concentration in coarse polydisperse suspensions
Authors: Tockstein Antonín , Skopal František
Published: June 2010

The flux of light scattered by a polydisperse system at 90°, integrated along the optical path of the incident beam, exhibits an extremum in dependence on the suspension concentration, and is formally described by the same equation as holds for monodisperse systems. The coefficients in this equation are the mean values of the individual coefficients of the monodisperse components.
Isotachophoretic determination of soluble nitrates, nitriles, sulfates and phosphates in plant material
Authors: Matejovič Igor , Bieliková Magdaléna
Published: June 2010

Testing and statistical evaluation of six operating systems suitable for the isotachophoretic determination of NO3-, SO42-, NO2- and H2PO4-, with the aim of the determination of the mentioned anions in plant material, are described. The proposed sample pretreatment reflecting the effort to minimize the number of unavoidable steps consisted only of extraction and filtration. The attention was paid to quantitative aspects of the extraction and to the possibility of extracts contamination during filtration. Influence of the sample amount on the anion zone lengths and the reproducibility of the determination were investigated too.
An ESR study of irradiated mixtures of hydrogen peroxide and Cu(II) complexes at 77 K
Authors: Stopka Pavel
Published: June 2010

When aqueous solutions containing hydrogen peroxide and CuSO4 are irradiated by a high-pressure mercury lamp at room temperature and at 77 K, hydrogen peroxide decomposes and hydroxyl radicals generated in high concentrations coordinate to CuSO4. The catalytic activity of Cu(II), which depends on the choice of the ligand (triene, diene, ethylenediamine, ammonia, EDTA, oxalic acid and glycerine) and the proportion between the monomeric and dimeric forms of the Cu(II) complex, shows a maximum at a concentration of 10-4 mol dm-3. The catalytically active species is the monomeric Cu(II) complex, the dimer being inactive.
Structure and permeability of composition carboxyl membranes on the basis of polyacrylonitrile
Authors: Hruška Zdeněk , Tyráčková Věra , Tischenko Galina A. , Shatayeva Larisa K.
Published: June 2010

Article in Russian
Reactions of primary aliphatic and cycloaliphatic amines with 1-butyl acrylate
Authors: Horálek Jiří , Švestka Štefan , Krejcar Emil , Novák Jiří
Published: June 2010

The addition reactions of primary aliphatic and cycloaliphatic amines with 1-butyl acrylate have been investigated by means of near IR spectroscopy. The additions proceed contrary to the Markownikoff rule and are consecutive competitive reactions which can be treated as isolated reactions with respect to the considerable difference between rate constants of the individual steps. The value of rate constants determined from the spectral data have been compared and discussed in terms of the steric hindrance of alkyl groups which co-determines the reactivity of amines in the reactions investigated.
Synthesis of some new 3-substituted-4-hydroxy-1-methyl-quinolin-2-one derivatives as potential antibacterial and antifungal agents
Authors: Girges Margret Mansour , Hanna Mokhtar Ayad , Hassan Hussien Mohamed , Moawad Evelin Boshra
Published: June 2010

3-Acetyl-4-hydroxy-1-methylquinolin-2-one (I) and its bromo derivative II were allowed to react with different reagents to get new quinoline derivatives that have different heterocyclic moieties at position 3. The antibacterial and antifungal activities of the products were also evaluated.
Flavonoids from Ephedra sinica STAPF
Authors: Purev Ondgenij , Pospíšil František , Motl Otakar
Published: June 2010

From the above-ground part of Ephedra sinica STAPF seven flavonoids were isolated - apigenin, tricin, kaempferol, apigenin-5-rhamnoside, herbacetin, and 3-methoxyherbacetin; one flavonoid glycoside was characterized as kaempferol rhamnoside.
Chromogenic substrates for papain with a C-terminal S-benzylcysteine residue
Authors: Kasafírek Evžen , Fukal Ladislav , Káš Jan
Published: June 2010

Two types of chromogenic substrates for papain were prepared, namely p-nitroanilides of N-acetyltripeptides of general formula Ac-Leu-Leu-A-NAn, where A = Gly, Ala, Leu, and p-nitroanilides of 3-carboxypropionyldi- and tripeptides of general formula Suc-B-Cys(Bzl)-NAn, where B = Gly, Gly-Gly, Ala, Ala-Ala, Leu, Leu-Leu, Gly-Leu, Leu-Ala and Ala-Met. The values of Km, kcat and C (kcat/Km) for these substrates were determined. Suc-Leu-Leu-Cys(Bzl)-NAn is the best substrate for papain its C being 60 000 mol-1 l s-1.
Immobilization of mold beta-galactosidase
Authors: Kmínková Milena , Prošková Alexandra , Kučera Jiří
Published: June 2010

We immobilized beta-galactosidase (EC 3.2.1.23) from the mold Aspergillus oryzae by various methods on the derivatives of bead cellulose manufactured by Czechoslovak industry. The activity, specific activity and operational stability of the immobilized enzyme were determined. The best results were obtained with the mold enzyme which had been immobilized by ionic adsorption to DEAHP bead cellulose (Ostsorb DEAHP); its activity was 275 U/g and its operational stability at 40 °C was 30·6 days. The pH-optimum of this enzyme is 4·3 and the optimum temperature determined from the linearized Arrhenius plot is 65 °C. Beta-galactosidase of Kluyveromyces fragilis was also immobilized on the same supports and its properties determined for comparison. The immobilized enzyme from the yeast Kluyveromyces fragilis showed a higher activity in all experiments yet its operational stability was 5 to 14 times lower in the individual cases.
Surveillance of Barrett's oesophagus: do we yet know whether it is worthwhile?
Authors: Somerville Margaret , Pitt Martin
Published: June 2010

In 2004, the Peninsula Technology Assessment Group developed an economic model to assess the effectiveness and cost effectiveness of surveillance of Barrett's oesophagus in preventing morbidity and mortality from oesophageal adenocarcinoma. The conclusion then was that surveillance was dominated (ie, cost more and conferred less health benefit) by non-surveillance in most scenarios and that surveillance was unlikely to be cost effective at usual levels of willingness to pay. The model outputs were highly sensitive, however, to several parameters for which the data were very uncertain. While there are now better estimates of some of the model inputs, such as cancer risk and quality of life, the revised values make it less likely that surveillance could prove cost effective. There remains considerable uncertainty around other key inputs. At present, there seems little reason to change our original conclusion that surveillance of Barrett's oesophagus is unlikely to be cost effective and a definitive answer may only be possible from clinical trials now in progress. As newer endoscopic techniques for treating Barrett's oesophagus and adenocarcinoma become more widely used, however, conventional surveillance programmes may no longer be undertaken, and revised economic models will be needed to assess the cost effectiveness of the new clinical pathways.
Sessile serrated adenomas: prevalence of dysplasia and carcinoma in 2139 patients
Authors: Lash Richard H , Genta Robert M , Schuler Christopher M
Published: June 2010

Background and aims

Sessile serrated adenomas (SSAs) are recognised as precursors to microsatellite unstable adenocarcinomas. This study attempts to estimate the progression rate of SSAs based upon the epidemiology of a large cohort as well as identify relationships to other colorectal polyps.

Methods

Pathological reports generated at Caris Diagnostics from 290 810 colonoscopic specimens on 179 111 patients were analysed using computerised algorithms.

Results

SSAs with or without dysplasia/carcinoma (SSA+/–) were identified in 2416 specimens from 2139 patients (54% women). The distribution of SSA+/– was: right-sided (81.2%); left-sided (11.2%); both right- and left-sided (3.2%); not specified (4.3%). There were 1816 (85%) patients without dysplasia (SSA–), 257 (12%) with low-grade dysplasia (SSA-LD), 45 (2%) with high-grade dysplasia (SSA-HD) and 21 (1%) with adenocarcinoma (SSA-CA). The difference in median age between almost all groups was significant (SSA–=61 years versus SSA-LD=66 years (p<0.001) vs SSA-HD=72 years (p=0.002) vs SSA-CA=76 years (p=0.07, NS)). Women comprised 53% of the SSA– group (968/1816), 57% of the SSA-LD group (147/257), 69% of the SSA-HD group (31/45) and 76% of the SSA-CA group (16/21), being more likely to have high-grade dysplasia (OR 1.94, 95% CI 1.03 to 3.67) and adenocarcinoma (OR 2.80, 95% CI 1.02 to 7.68).

Conclusions

1.7% of patients with mucosal polyps had SSAs (with and without dysplasia), more commonly in women and primarily in the right colon. Dysplasia or carcinoma was identified in 15% of patients and significantly disproportionately among women. Based on significant age differences between groups, there appears to be a stepwise progression of dysplasia and carcinoma in SSAs over 10 to 15 years, a period two to three times longer than that for conventional adenomas.
Associations between adolescent socioeducational status and use of snus and smoking
Authors: Øverland Simon , Tjora Tore , Hetland Jørn , Aarø Leif Edvard
Published: June 2010

Background

Findings from studies on the association between smoking and socioeconomic status are mixed. While adolescent smoking is reduced in many countries, use of smokeless tobacco seems to increase. Associations between socioeducational status and smoking as well as use of snus (smokeless tobacco), and to what extent these associations had changed significantly from 2004 to 2007 (a period of relatively abrupt changes in tobacco use in Norway), were examined.

Methods

Data from two national representative cross-sectional studies of Norwegian 16–20 year olds, where participants were asked questions allowing us to construct indicators of socioeducational status, was used. Information was also collected about the adolescents' smoking and use of snus, as well as their intentions with regard to future use of these products.

Results

Adolescents with a lower socioeducational status had much higher odds for smoking compared to those with higher socioeducational status (ORs ranged from 2.9 to 3.8). There was no similar association between socioeducational status and snus use (ORs ranged from 0.6 to 1.2). No support was found for a change in the socioeducational status–smoking/snus use association from 2004 to 2007.

Conclusions

Adolescents' socioeducational status was associated with smoking for boys and girls, while there was no similar association with snus use. This may indicate that snus truly deviates from how smoking is distributed across social strata or that snus is at a much earlier stage in the social diffusion process.
Self-synchronizing properties of CSMA wireless multi-hop networks
Authors: Xu Kuang , Dousse Olivier , Thiran Patrick
Published: June 2010

We show that CSMA is able to spontaneously synchronize transmissions in a wireless network with constant-size packets, and that this property can be used to devise efficient synchronized CSMA scheduling mechanisms without message passing. Using tools from queuing theory, we prove that for any connected wireless networks with arbitrary interference constraints, it is possible to implement self-synchronizing TDMA schedules without any explicit message passing or clock synchronization besides transmitting the original data packets, and the interaction can be fully local in that each node decides when to transmit next only by overhearing its neighbors' transmissions. We also provide a necessary and sufficient condition on the emergence of self-synchronization for a given TDMA schedule, and prove that such conditions for self-synchronization can be checked in a finite number of steps for a finite network topology.
Incentive compatibility and dynamics of congestion control
Authors: Godfrey P. Brighten , Schapira Michael , Zohar Aviv , Shenker Scott
Published: June 2010

his paper studies under what conditions congestion control schemes can be both efficient, so that capacity is not wasted, and incentive compatible, so that each participant can maximize its utility by following the prescribed protocol. We show that both conditions can be achieved if routers run strict priority queueing (SPQ) or weighted fair queueing (WFQ) and end-hosts run any of a family of protocols which we call Probing Increase Educated Decrease (PIED). A natural question is whether incentive compatibility and efficiency are possible while avoiding the per-flow processing of WFQ. We partially address that question in the negative by showing that any policy satisfying a certain "locality" condition cannot guarantee both properties.

Our results also have implication for convergence to some steady-state throughput for the flows. Even when senders transmit at a fixed rate (as in a UDP flow which does not react to congestion), feedback effects among the routers can result in complex dynamics which do not appear in the simple topologies studied in past work.
Dynamics in congestion games
Authors: Shah Devavrat , Shin Jinwoo
Published: June 2010

Game theoretic modeling and equilibrium analysis of congestion games have provided insights in the performance of Internet congestion control, road transportation networks, etc. Despite the long history, very little is known about their transient (non equilibrium) performance. In this paper, we are motivated to seek answers to questions such as how long does it take to reach equilibrium, when the system does operate near equilibrium in the presence of dynamics, e.g. nodes join or leave. , or the tradeoff between performance and the rate of dynamics. In this pursuit, we provide three contributions in this paper. First, a novel probabilistic model to capture realistic behaviors of agents allowing for the possibility of arbitrariness in conjunction with rationality. Second, evaluation of (a) time to converge to equilibrium under this behavior model and (b) distance to Nash equilibrium. Finally, determination of tradeoff between the rate of dynamics and quality of performance (distance to equilibrium) which leads to an interesting uncertainty principle. The novel technical ingredients involve analysis of logarithmic Sobolov constant of Markov process with time varying state space and methodically this should be of broader interest in the context of dynamical systems.
A query language and runtime tool for evaluating behavior of multi-tier servers
Authors: Ghanbari Saeed , Soundararajan Gokul , Amza Cristiana
Published: June 2010

As modern multi-tier systems are becoming increasingly large and complex, it becomes more difficult for system analysts to understand the overall behavior of the system, and diagnose performance problems. To assist analysts inspect performance behavior, we introduce SelfTalk, a novel declarative language that allows analysts to query and understand the status of a large scale system. SelfTalk is sufficiently expressive to encode an analyst's high-level hypotheses about system invariants, normal correlations between system metrics, or other a priori derived performance models, such as, "I expect that the throughputs of interconnected system components are linearly correlated". Given a hypothesis, Dena, our runtime support system, instantiates and validates it using actual monitoring data within specific system configurations. We evaluate SelfTalk/Dena by posing several hypotheses about system behavior and querying Dena to validate system behavior in a multi-tier dynamic content server. We find that Dena automatically validates the system performance based on the pre-existing hypotheses and helps to diagnose system misbehavior.
Optimal tradeoff between exposed and hidden nodes in large wireless networks
Authors: van de Ven Peter M. , Janssen Augustus J.E.M. , van Leeuwaarden Johan S.H.
Published: June 2010

Wireless networks equipped with the CSMA protocol are subject to collisions due to interference. For a given interference range we investigate the tradeoff between collisions (hidden nodes) and unused capacity (exposed nodes). We show that the sensing range that maximizes throughput critically depends on the activation rate of nodes. For infinite line networks, we prove the existence of a threshold: When the activation rate is below this threshold the optimal sensing range is small (to maximize spatial reuse). When the activation rate is above the threshold the optimal sensing range is just large enough to preclude all collisions. Simulations suggest that this threshold policy extends to more complex linear and non-linear topologies.
Qualitative properties of α-weighted scheduling policies
Authors: Shah Devavrat , Tsitsiklis John N. , Zhong Yuan
Published: June 2010

We consider a switched network, a fairly general constrained queueing network model that has been used successfully to model the detailed packet-level dynamics in communication networks, such as input-queued switches and wireless networks. The main operational issue in this model is that of deciding which queues to serve, subject to certain constraints.

In this paper, we study qualitative performance properties of the well known α-weighted scheduling policies. The stability, in the sense of positive recurrence, of these policies has been well understood. We establish exponential upper bounds on the tail of the steady-state distribution of the backlog.

Along the way, we prove finiteness of the expected steady-state backlog when α<1, a property that was known only for α ≥ 1.

Finally, we analyze the excursions of the maximum backlog over a finite time horizon for α ≥ 1. As a consequence, for α ≥ 1, we establish the full state space collapse property.
Randomized load balancing with general service time distributions
Authors: Bramson Maury , Lu Yi , Prabhakar Balaji
Published: June 2010

Randomized load balancing greatly improves the sharing of resources in a number of applications while being simple to implement. One model that has been extensively used to study randomized load balancing schemes is the supermarket model. In this model, jobs arrive according to a rate-nλ Poisson process at a bank of n rate-1 exponential server queues. A notable result, due to Vvedenskaya
et.al.
(1996), showed that when each arriving job is assigned to the shortest of d ≥ 2 randomly chosen queues, the equilibrium queue sizes decay doubly exponentially in the limit as n to ∞. This is a substantial improvement over the case d=1, where queue sizes decay exponentially.

The method of analysis used in the above paper and in the subsequent literature applies to jobs with exponential service time distributions and does not easily generalize. It is desirable to study load balancing models with more general, especially heavy-tailed, service time distributions since such service times occur widely in practice.

This paper describes a modularized program for treating randomized load balancing problems with general service time distributions and service disciplines. The program relies on an
ansatz
which asserts that any finite set of queues in a randomized load balancing scheme becomes independent as n to ∞. This allows one to derive queue size distributions and other performance measures of interest. We establish the
ansatz
when the service discipline is FIFO and the service time distribution has a decreasing hazard rate (this includes heavy-tailed service times). Assuming the
ansatz
, we also obtain the following results: (i) as n to ∞, the process of job arrivals at any fixed queue tends to a Poisson process whose rate depends on the size of the queue, (ii) when the service discipline at each server is processor sharing or LIFO with preemptive resume, the distribution of the number of jobs is insensitive to the service distribution, and (iii) the tail behavior of the queue-size distribution in terms of the service distribution for the FIFO service discipline.
A unified modeling framework for distributed resource allocation of general fork and join processing networks
Authors: Zhao Haiquan (Chuck) , Xia Cathy H. , Liu Zhen , Towsley Don
Published: June 2010

This paper addresses the problem of distributed resource allocation in general fork and join processing networks. The problem is motivated by the complicated processing requirements arising from distributed data intensive computing. In such applications, the underlying data processing software consists of a rich set of semantics that include synchronous and asynchronous data fork and data join. The different types of semantics and processing requirements introduce complex interdependence between various data flows within the network.

We study the distributed resource allocation problem in such systems with the goal of achieving the maximum total utility of output streams. Past research has dealt with networks with specific types of fork/join semantics, but none of them included all four types. We propose a novel modeling framework that can represent all combinations of fork and join semantics, and formulate the resource allocation problem as a convex optimization problem on this model. We propose a shadow-queue based decentralized iterative algorithm to solve the resource allocation problem. We show that the algorithm guarantees optimality and demonstrate through simulation that it can adapt quickly to dynamically changing environments.
Distributed caching over heterogeneous mobile networks
Authors: Ioannidis Stratis , Massoulie Laurent , Chaintreau Augustin
Published: June 2010

Sharing content over a mobile network through opportunistic contacts has recently received considerable attention.

In proposed scenarios, users store content they download in a local cache and share it with other users they meet, e.g., via Bluetooth or WiFi. The storage capacity of mobile devices is typically limited; therefore, identifying which content a user should store in her cache is a fundamental problem in the operation of any such content distribution system.

In this work, we propose Psephos, a novel mechanism for determining the caching policy of each mobile user. Psephos is fully distributed: users compute their own policies individually, in the absence of a central authority. Moreover, it is designed for a heterogeneous environment, in which demand for content, access to resources, and mobility characteristics may vary across different users. Most importantly, the caching policies computed by our mechanism are optimal: we rigorously show that Psephos maximizes the system's social welfare. Our results are derived formally using techniques from stochastic approximation and convex optimization; to the best of our knowledge, our work is the first to address caching with heterogeneity in a fully distributed manner.
The price of anarchy in parallel queues revisited
Authors: Anselmi Jonatha , Gaujal Bruno
Published: June 2010

We consider a network of parallel, non-observable queues and analyze the Price of Anarchy (PoA) from the new point of view where the router has the memory of previous dispatching choices. In the regime where the demands grow with the network size, we provide an upper bound on the PoA by means of convex programming. To study the impact of non-Bernoulli routers, we introduce the Price of Forgetting (PoF) and prove that it is bounded from above by two.

Numerical experiments show that the benefit of having memory in the router is independent of the network size and heterogeneity, and monotonically depends on the network load only.
Coordinated power management of voltage islands in CMPs
Authors: Mishra Asit K. , Srikantaiah Shekhar , Kandemir Mahmut , Das Chita R.
Published: June 2010

Multiple clock domain architectures have recently been proposed to alleviate the power problem in CMPs by having different frequency/voltage values assigned to each domain based on workload requirements. However, accurate allocation of power to these voltage/frequency islands based on time varying workload characteristics as well as controlling the power consumption at the provisioned power level is non-trivial. Toward this end, we propose a two-tier feedback-based control theoretic solution. Our first-tier consists of a global power manager that allocates power targets to individual islands based on the workload dynamics. The power consumptions of these islands are in turn controlled by a second-tier, consisting of local controllers that regulate island power using dynamic voltage and frequency scaling in response to workload requirements.
Rigorous statistical analysis of internet loss measurements
Authors: Nguyen Hung X. , Roughan Matthew
Published: June 2010

In this paper we present a rigorous technique for estimating confidence intervals of packet loss measurements. Our approach is motivated by simple observations that the loss process can be modelled as an alternating renewal process. We use this structure to build a Hidden Semi-Markov Model (HSMM) for the measurement process, and from this estimate both loss rates, and their confidence intervals. We use both simulations and a set of more than 18000 hours of real Internet measurements (between dedicated measurement hosts, PlanetLab hosts, web and DNS servers) to cross-validate our estimates, and show that they are significantly more accurate than any current alternative.