bluuebunny/crossref_metadata_2025 huggingface dataset:
1993 ALCAN Award Lecture Chemical binding within and between inorganic rings; the design and synthesis of molecular conductors
Authors: Oakley Richard T.
Published: May 2006

For a given number of skeletal atoms, the π-electron count of an unsaturated heterocycle can be modified by the incorporation of heteroatoms from different periodic groups. Sulfur and nitrogen are particularly effective in this regard, as their high electronegativity can stabilize electron-rich π-systems. A variety of aromatic, anti-aromatic, and radical systems can be prepared from admixtures of these elements. While the properties of these ring systems are interesting in their own right, the compounds are not without relevance in the design of new materials. The strong interannular interactions that are developed between these rings in the solid state makes them ideal candidates for the fabrication of molecular conductors. The origins and development of this area of research are the subjects of this presentation.
X-ray crystal structure of [Ni(III)(cyclam)(NO3)2](ClO4) and electron transfer reactions of the Ni(III)/Ni(II) couple
Authors: McAuley A. , Palmer T. , Whitcombe T.W.
Published: May 2006

The synthesis and crystal structure of [Ni(cyclam)(NO3)2](ClO4) are described (P1, a = 8.347(4) Å, b = 15.960(7) Å, c = 7.656(3) Å, α = 90.33(6)°, β = 110.97(4)°, γ = 104.45(5)°, V = 917.0(7) Å3, R = 0.0425, Rw = 0.0384). The crystal contains two unique Ni(III) cations within the unit cell, with a network of hydrogen bonding interactions linking one of the cations into a stacked configuration while the other cation contains a strong internal hydrogen bond. This provides an interesting inorganic example of multi-site cooperative binding involving a metal complex cation. By use of electron transfer data from known outer-sphere redox reagents, measurement of the cross-reactions with [Ni(cyclam)]3+/2+ in 3 M nitrate media yielded a self-exchange rate constant of 1.4 × 105 M−1 s−1. The structural data have been utilized to obtain a calculated estimate of the self-exchange rate constant (1.0 × 108 M−1 s−1) for this couple. The relationship between these two values is explored. The lack of adiabaticity is reflected in a value ≈0.01 for κeI not only for this couple but also for other related cyclam complexes.
Crystalline complexes of 18-crown-6 with methyl sulfonates.
Authors: Chênevert Robert , Gagnon René , Chamberland Daniel , Simard Michel
Published: May 2006

not available
Hammett pσ correlation for reactions of lactoperoxidase compound II with phenols
Authors: Zhang Hongchang , Dunford H. Brian
Published: May 2006

A stopped-flow kinetic study shows that the reaction rates of lactoperoxidase compound II with substituted phenols are greatly dependent upon the substituent on the benzene ring. Of the 15 phenols studied, it has been possible to relate the reaction rate constants with the ionization constants of 11 phenols by a linear Hammett free-energy relationship: (log (kX/kH) = ρσ) at pH 7.0 and 25.0 °C. The 11 m-and p-substituted phenols yield a ρ value of −2.7 ± 0.2. The data do not correlate with σ+ values using the Brown–Okamoto equation. These results can be explained by a mechanism in which the substrate simultaneously gives an electron and a proton to lactoperoxidase compound II, and they indicate that the active site is accessible to substrate. To explain the abnormal behavior of the four phenols that do not fit the Hammett plot we used Hansch hydrophobic factors π for all of the substituents. The resultant best-fit equation: log (kX/kH) = ρσ + rπ + c yielded the values ρ = −2.1 ± 0.5, r = 0.4 ± 0.1, and c = −0.2 ± 0.1. The rates of reduction of lactoperoxidase compound II by p-iodophenol have been studied from pH 6.5 to 11.2. The kinetics are influenced by an acid group of pKE 9.5 in the active site of lactoperoxidase compound II and by the ionization of the substrate (pKS 9.0). The acidic form of lactoperoxidase compound II and the electrically neutral, unionized form of phenol are the reactive species. A reanalysis of data on reactions of horseradish peroxidase compounds I and II with substituted phenols using more recent σ values yielded Hammett ρ values of −5.5 ± 0.3 and −4.5 ± 0.2.
Limiting quantum yield measurements for the disappearance of 1-propanol and propanal: an oxidative reaction study employing a TiO2 based photoreactor
Authors: Lepore Giuseppe P. , Pant Bhuvan C. , Langford Cooper H.
Published: May 2006

Relative initial quantum yields [Formula: see text] for the disappearance of 1-propanol and propanal were estimated based on total light intensity entering the reaction vessels. Two types of photocatalytic reactor geometries were compared, a commercial prototype flow reactor with immobilized TiO2 and a conventional reactor with TiO2 dispersion. A maximum relative quantum yield, [Formula: see text], was extrapolated for pure propanol and propanal in both geometries. The high quantum yields were attributed to efficient competition of substrate oxidation with electron–hole recombination, at high surface coverage. Propanal was identified as the primary intermediate generated from 1-propanol in both reactor systems, but yields of propanal were systematically 10 times lower than 1-propanol loss, indicating that there was an effective pathway for propanal oxidation on the surface prior to desorption. The inhibition of 1-propanol reaction caused by accumulation of product arises because both reactant and product compete for active sites on the photocatalyst surface. These propositions were confirmed by introducing propanal into the feed. The relative quantum yields converge to unity for pure substrates, suggesting that they are true yields. That is to say, absorption by TiO2 of light entering the reactor is efficient in these geometries.
Preparation and structure of oxo-rhenium(V) complexes with 7-azaindole
Authors: Lebuis Anne-Marie , Beauchamp André L.
Published: May 2006

Four Re(V) oxo compounds were obtained from 7-azaindole (Haza) and ReOCl3(PPh3)2: the oxo-bridged dimer Re2O3Cl4(Haza)4 (1), the oxo–ethoxo monomers ReO(OEt)Cl2(Haza)2 (2) and ReO(OEt)Cl2(Haza)(PPh3) (3), and the dioxo [ReO2(Haza)4]Cl salt (4a). [ReO2(Haza)4]I (4b) was also prepared from ReO2I(PPh3)2. The ReO(OEt)Cl2(Haza)2 complex was shown by X-ray diffraction (C2/c, a = 16.292, b = 9.395, c = 12.104 Å, β = 101.47°, R = 0.041) to consist of individual molecules of the trans-trans isomer in which azaindole is N7-bonded. Crystals of [Formula: see text] (C2/m a = 15.422, b = 13.055, c = 9.086 Å, β = 91.13°, R = 0.059) contain well separated Cl− anions and trans-dioxo cations. The N7-bonded azaindole ligands are held parallel to the O=Re=O direction by intramolecular [Formula: see text] hydrogen bonds, but the relative orientation of the four ligands cannot be determined because of disorder. Characteristic Re—oxygen vibrations are observed in infrared for each type of compounds. The 1H and 13C NMR spectra are discussed in relation with the azaindole binding mode.
Measurements and analysis of the excess enthalpies of some dichloroalkane + 2-ketone systems using UNIFAC group-contribution model
Authors: Menaut Consolación P. , Pico José M. , Fernández Josefa , Legido José L. , Andrade M. Inmaculada Paz
Published: May 2006

Experimental excess molar enthalpies hE at 298.15 K and normal atmospheric pressure were obtained for the binary mixtures 1,2-dichloropropane + (2-propanone, 2-butanone, or 2-pentanone), 1,3-dichloropropane + (2-butanone or 2-pentanone), 1,4-dichlorobutane + (2-butanone or 2-pentanone) using a Calvet microcalorimeter. The hE values for all the mixtures were negative. The experimental results used to test the capability of the interaction parameters of two versions of the UNIFAC group-contribution model to predict the proximity effect in these kind of mixtures.
Synthesis, reactions, and interconversions of some 2-(trimethylsilyl)ethyl substituted sulfur compounds
Authors: Schwan Adrian L. , Brillon Denis , Dufault Robert
Published: May 2006

In an effort to probe the compatibility of the 2-(trimethylsilyl)ethyl sulfur moiety with standard organosulfur transformations, several 2-(trimethylsilyl)ethanethiol derivatives have been prepared in excellent yield. Thus 2-(trimethylsilyl)ethanethiol (1) and 2-(trimethylsilyl)ethyl disulfide (4) and its corresponding thiosulfinate 9 and thiosulfonate 10 have been synthesized. One method of formation of 4 involves the breakdown of a 1-(trimethylsilyl)ethyl unit while the 2-(trimethylsilyl)ethyl fragment survives. Oxidation of 4 or 9 to 10 did not proceed efficiently with common reagents, but proceeded well with an iodine/water system. 2-(Trimethylsilyl)ethyl sulfide (11a) and its oxides (13, 14) were also prepared in good yield. Sulfoxide 13 and 2-(trimethylsilyl)ethyl tert-butyl sulfoxide 15 were shown to be good precursors to 2-(trimethylsilyl)ethanesulfinyl chloride (16). (Trimethylsilyl)methyl sulfine reacted with 16 in an inefficient manner to give thiosulfonates 10, 19, and 20. 2-(Trimethylsilyl)ethanesulfenyl chloride could be generated and captured by addition across cyclohexene. The reaction of thiosulfinate 9 with several thiosilanes is an excellent method for the synthesis of 2-(trimethylsilyl)ethyl containing mixed disulfides.
Synthesis and structure of 1,1,3,3,-tetramethyl-2-phenyl-2-(2′,6′-diphenyl-4′-pyrylio)-guanidinium diperchlorate
Authors: Galezowski Wlodzimierz , Bakshi Pradip K. , Leffek Kenneth T. , Cameron T. Stanley
Published: May 2006

The reaction of 2-N-phenyl-1,1,3,3-tetramethylguanidine with 2,6-diphenylpyran-4-one in the presence of phosphorus oxy-chloride, followed by treatment with perchloric acid, yields 1,1,3,3-tetramethyl-2-phenyl-2-(2′,6′-diphenyl-4′-pyrylio)guanidinium diperchlorate. Crystals of this material are monoclinic, space group P21/n, a = 14.535(3), b = 13.685(3), c = 23.579(7) Å, β = 140.38(2)°, R = 0.0633 based on 1691 observed reflections. The substitution of the positively charged pyrylio group on one of the three nitrogen atoms of the guanidinium cation disrupts the symmetry of the distribution of the positive charge on the nitrogen atoms. The two C—N bonds of the central carbon atom of the guanidinium ion to the two methylated nitrogen atoms show more double-bond character than that to the nitrogen carrying the pyrylio group.
Solvent and crown ether/cryptand effects on the oximate-promoted 1,2-elimination from β-phenylmercaptoethyl p-nitrophenolate. Formation and reactivity of a crown ether-complexed potassium oximate ion pair
Authors: Buncel Erwin , Kumar Anurag , Xie Hai-Qi , Moir Robert Y. , Purdon J. Garfield
Published: May 2006

The reactions of β-phenylmercaptoethyl p-nitrophenolate (1) with three potassium oximates, viz. potassium 2,3-butanedione monoximate (BDOK), acetophenone oximate (APOK), and acetone oximate (AOK) have been investigated in two nonhydroxylic dipolar aprotic solvents, tetraglyme and dimethyl sulfoxide (DMSO). The reaction products, as determined by 1H NMR spectroscopy, were p-nitrophenoxide ion and phenyl vinyl sulfide, in accord with an elimination process. A kinetic spectrophotometric study showed that in tetraglyme, the addition of oxime and water in small amounts drastically decreased the rate of reaction of 1 with APOK as a result of hydrogen-bonding interactions with the oximate anion. In tetraglyme as solvent the addition of 2.2.2 cryptand greatly enhanced the reactivity of the oximates but the macrocyclic crown ether DC-18-C6 had much smaller effect on rate. The results are consistent with formation of a crown ether-complexed potassium oximate ion pair, which is much less reactive than the free anion formed in the presence of 2.2.2 cryptand but more reactive than the potassium oximate ion pair. The kinetic data were analyzed to obtain specific rate coefficients for reaction of APOK as the dissociated anion, the ion-paired species, and as the crown ether-complexed oximate; equilibrium constants for potassium oximate ion pair formation and for the crown ether-complexed ion pair were obtained. In DMSO as solvent the rate of reaction remained unaffected on addition of the metal ion complexing agents, indicating that ion pairing is not important in this solvent. The reactivity of the free oximate anions in both solvents increased in the order BDOK < APOK < AOK, which parallels the pKa's of the corresponding oximes in DMSO. The unusually high reactivity of oximates in the low polarity tetraglyme compared to polar DMSO could be explained on the basis of stabilization of the transition state in tetraglyme. Trends in kTG/kDMSO for the oximates follow reactivity–selectivity considerations.
The lowest energy excited states of the binuclear silver(I) halide complexes, Ag2(dmb)2X2. Metal-centered or charge transfer states?
Authors: Piché Daniel , Harvey Pierre D.
Published: May 2006

The nature of the lowest energy excited states of the Ag2(dmb)2X2 complexes (X = Cl, Br, I; dmb = 1,8-diisocyano-ρ-menthane) have been addressed both experimentally and theoretically. It is shown that the lowest energy excited states of the complexes are charge transfer states from the silver-halide frame to the isocyanide ligands (M/XLCT) based upon UV-visible spectra and emission polarization ratio measurements, and extended Hückel molecular orbital calculations (EHMO). The metal-centered dσ* → pσ bands have been observed in the higher energy region of the spectra (232–242 nm). The complexes are luminescent (440 ≤ λe ≤ 480 nm) both in a glass and in the solid state at 77 K where the emission lifetimes, τe, range from 20 to 90 µs, which depend upon the nature of the halide (for the solid state data) and the media. No emission is observed at room temperature.
Optical–optical double resonance study of the and &([a-z]+);(3A2) states of thiophosgene
Authors: Simard Benoit , Mackenzie Valerie J. , Hackett Peter A. , Steer Ronald P.
Published: May 2006

The &([a-z]+);(3A2) and [Formula: see text] states of jet-cooled thiophosgene (Cl2CS) have been studied by optical–optical double resonance (OODR) spectroscopy. Two OODR schemes have been used to probe the [Formula: see text] state. One scheme uses selected vibronic levels of the &([a-z]+);(1A2) state as the intermediate state, while the other uses the vibrationless and 2131 levels of the &([a-z]+);(3A2) state. All of the vibronic levels in the 33 980−35 600 cm−1 region can be rationalized with the following origin band and fundamentals: 0° = 34 277 cm−1, v1 = 505 cm−1, v2 = 470 cm−1, v3 = 213 cm−1, v6 = 249 cm−1, 42 = 341 cm−1, 44 = 627 cm−1. The discrepancies among the various studies of the [Formula: see text] state will be discussed and reconciled. It is conjectured that the [Formula: see text] state potential along the C—S coordinate exhibits an asymmetric double-minimum potential resulting from the interaction of the 1A1 states arising from the [Formula: see text] configurations. The minimum corresponding to the [Formula: see text] configuration lies higher in energy and the principal decay mechanism for molecules pumped to its first few vibronic levels is fluorescence. On the other hand, molecules pumped to the minimum corresponding to the nominal [Formula: see text] configuration decay nonradiatively. The barrier height to inversion and the out-of-plane bending angle along the out-of-plane bending coordinate, v4, have been determined to be 945 cm−1 and 25°, respectively, by fitting quartic-quadratic and quadratic-Gaussian double-minimum potentials to the observed energy levels. The &([a-z]+);(3A2) state has been studied by a novel OODR scheme which uses the fluorescent vibrationless level of the [Formula: see text] state to monitor [Formula: see text]transitions. A vibronic analysis has been carried out and the following origin band and fundamentals derived for the &([a-z]+);(3A2) state: 0° = 17 499 cm−1, v1 = 923 cm−1, v2 = 474 cm−1, v3 = 247 cm−1, 42 = 297 cm−1, 44 = 560 cm−1, 46 = 741 cm−1. With the exception of a few corrections and additions, the results confirm the findings of previous studies, notably regarding the bent geometry and barrier height to inversion. An overall comparison of the data suggests that the wavenumber of v6 in theÃ(1A2) state is 279 cm−1 instead of 189 cm−1.
Proton transfer dynamics on highly attractive potential energy surfaces: Induced repulsive energy release in O− + HF at high collision energies
Authors: Carpenter M.A. , Zanni M.T. , Levandier D.J. , Varley D.F. , Farrar J.M.
Published: May 2006

We present the angular and kinetic energy distributions for the products of the proton transfer reaction O− + HF → OH + F− at center-of-mass collision energies of 45.0 and 55.8 kJ mol−l (0.47 and 0.58 eV, respectively). At both collision energies, the product angular distributions show forward–backward symmetry, characteristic of the decay of a transient complex living at least several rotational periods. The product kinetic energy distributions show structure that is clearly attributable to the formation of OH in v′ = 0,1, and 2. The kinetic energy distribution for a single vibrational state of OH is equivalent to the rotational state distribution for that state. At the higher collision energy, the product kinetic energy distribution shows a clear angular dependence, from which we infer a transition to more direct dynamics involving low impact parameter collisions that access the repulsive wall of the potential surface in bent geometries. The vibrational energy in the products decreases with increasing collision energy, with fV′, the fraction of available energy appearing in vibration, decreasing from 0.28 to 0.22 over the reported collision energy range. We attribute this behavior to a transition from mixed energy release of a Heavy + Light–Heavy collision system dominated by the strong attractive well to induced repulsive energy release as the system reaches the low energy repulsive wall of the potential energy surface.
Accidental conical intersections in H2Cl+(1A′)
Authors: Kuntz Philip J. , Whitton W. Neil , Paidarová Ivana , Polák Rudolf
Published: May 2006

Conical intersections in Cs, C2v, and linear configurations for the 1A′ states of the H2Cl+ molecule are investigated with the help of a 10 × 10 model Hamiltonian matrix in a valence-bond basis. The line of intersection (linea) between states 2 and 3 is traced from one end point, an intersection between two states of 1B2 symmetry in a C2V configuration, to the other end point, an intersection between two 1Σ+ states in a linear H—H—Cl configuration. The linea consists of 5 branches having symmetries Cs, Cs, C∞v, C2v, and Cs. A linea between states 3 and 4 starting at a crossing of 1Σ+ and 1Π states in a linear C∞v configuration consists of three branches (Cs, C2V, Cs) leading to the asymptotic region Cl + H2. The starting point of linea 3/4 is connected to the asymptotic region H + HCl via a linea in the linear configuration. Lineae of Cs symmetry could be found by examining the eigenvalues of the Hessian matrix of second derivatives along a line of intersection in a higher symmetry (C2v or linear), a useful method for locating accidental intersections that lends itself readily to ab initio calculations. The existence of the lineae could be related to physical properties of the molecule, such as the dipole moment, indicating that the model Hamiltonian does reflect the true physical behaviour.
On the mechanism of alkaline hydrogen peroxide oxidation of the lignin model p-hydroxyacetophenone
Authors: Hocking Martin B. , Crow John P.
Published: May 2006

The oxidation of p-hydroxyacetophenone by a small excess of alkaline hydrogen peroxide has been found to be an autocatalysed process in which hydroquinone monoacetate and the peracetate ion are generated and consumed at similar rates. The reaction proceeds at a maximum rate when the base concentration is about 0.3 M. A chain-type mechanism that involves peracetate as the oxidizing agent is proposed for the reaction that explains the observed dependence of rate on base concentration. At high pH o-hydroxyacetophenone reacts by the same mechanism, whereas m-hydroxyacetophenone does not react with hydrogen peroxide under these conditions.
1993 R.U. Lemieux Award Lecture Organometallic-type reactions in aqueous media—a new challenge in organic synthesis
Authors: Chan T.H. , Li C.J. , Lee M.C. , Wei Z.Y.
Published: May 2006

The development of organometallic-type reactions in aqueous media is reviewed. Coupling reactions of allyl halides with carbonyl compounds mediated by zinc, or tin, or indium in aqueous media to give homoallylic alcohols are discussed. The stereochemical outcome is compared with similar reactions in organic solvents. A concise synthesis of (+)-muscarine is used to illustrate the usefulness of aqueous organometallic-type reactions in organic synthesis. The procedure to protect–deprotect hydroxy functional groups may not be necessary in these reactions. An application in the carbohydrate area is demonstrated with the synthesis of (+)-3-deoxy-D-glycero-D-galacto-nonulosonic acid (KDN). The mechanistic possibilities of organometallic-type reactions in aqueous media are outlined.
Synthesis, spectroscopic, and structural studies of dimethyltellurium(IV) alkylene and diphenyl dithiophosphates. Crystal structures of and
Authors: Drake John E. , Khasrou Layla N. , Mislankar Anil G. , Ratnani Raju
Published: May 2006

Dimethyltellurium alkylene dithiophosphates of the type [Formula: see text] where G = —CMe2CMe2—, —CHMeCHMe—, —CH2CMe2CH2—, and —CH2CEt2CH2—, have been synthesized in 80–90% yields by reaction of the corresponding sodium or ammonium salts of the appropriate dithiophosphoric acids with dimethyltellurium dichloride in toluene. Me2Te[S2P(OPh)2]2 was also prepared in a similar fashion. The compounds have been characterised by elemental analyses and 1H, 13C, 31P, and 125Te NMR, infrared and Raman spectroscopy. The crystal structures of [Formula: see text] and [Formula: see text] were determined. [Formula: see text]1, crystallizes in space group P21/c (No. 14) with the cell parameters a = 12.707(3) Å, b = 11.482(2) Å, c = 16.782(2) Å, β = 98.00(1)°, V = 2424(1) Å3, Z = 4, R = 0.0399, Rw = 0.0343. [Formula: see text]4, crystallizes in space group [Formula: see text] (No. 2) with the cell parameters a = 12.580(3) Å, b = 13.313(3) Å, c = 8.206(1) Å, α = 91.28(2)°, β = 104.94(2)°, γ = 78.52(2)°, V = 1301(1) Å3, Z = 2, R = 0.0364, Rw = 0.0295. The immediate environment about tellurium in both molecules is that of the saw-horse structure typical of tellurium(IV) compounds with the two methyl groups equatorial and one sulfur atom from each dithiophosphate group occupying the axial positions. The consideration of the second sulfur atom as part of the coordinating sphere is discussed in terms of a modification of Pauling's approach to partial bond orders. The 1H NMR spectra suggest that these dithiophosphates may be fluxional in solution and/or that there is rapid exchange of the sulfur atoms.
Synthèses de diallylamines et triallylamines à partir des 3-acetoxy-3-aryl-2-méthylène propionitriles et des 3-acétoxy-3-aryl-2-méthylène propionates de méthyle
Authors: Akssira Mohamed , Guemmout Farid El , Bauchat Patrick , Foucaud André
Published: May 2006

The reactions of 3-acetoxy-3-aryl-2-methylene propionitriles 1 with ammonia yielded the corresponding diallylamines 3ZZ. The reaction of 1 with a primary allylamine or with ethylene diamine gave the diallylamine 11 or 13ZZ. The treatment of methyl 3-acetoxy-3-aryl-2-methylene propionates 2 with isopropylamine or ethylene diamine gave the allylamines 6EE or 14 and 15, but the reaction of 2 with ammonia gave only the triallylamines 4EEE in good yields.
Smith-degradative studies on the polysaccharide portion of A-band lipopolysaccharide from a mutant (AK1401) of Pseudomonas aeruginosa strain PAO1
Authors: Arsenault Todd L. , MacLean David B. , Zou Wei , Szarek Walter A.
Published: May 2006

Hepta-O-acetyl-O-α-D-Rhap-(1 → 3)-O-α-D-Rhap-(1 → 2)-glycerol (5) was the major component derived by way of Smith degradation of A-band polysaccharide (a D-rhamnan isolated from a mutant, AK1401, of Pseudomonas aeruginosa strain PAO1). The structure has been verified by an unambiguous synthesis of 5. Based on mass spectrometric evidence, hepta-O-acetyl-O-Ribp-(1 → 3)-O-α-D-Rhap-(1 → 2)-glycerol is considered to be one of the minor components. The Smith degradation of A-band polysaccharide and the synthesis of 5 are reported.
The volumetric and thermochemical properties of aqueous solutions of L-valine, L-leucine, and L-isoleucine at 288.15, 298.15, 313.15, and 328.15 K
Authors: Duke Michelle M. , Hakin Andrew W. , McKay Robert M. , Preuss Kathryn E.
Published: May 2006

Densities and volumetric heat capacities have been measured for aqueous solutions of L-valine, L-leucine, and L-isoleucine at 288.15, 298.15, 313.15, and 328.15 K. These data have been used to calculate apparent molar volumes, [Formula: see text] and apparent molar heat capacities, [Formula: see text] which in turn have been used to obtain standard state volumes, [Formula: see text] and standard state heat capacities, [Formula: see text] for each aqueous amino acid system. Helgeson, Kirkham, and Flowers equations, for neutral organics in water, have been used to model the calculated standard state volumes and heat capacities of the amino acids as a function of temperature at constant pressure. The results of our fitting procedures may be used to predict the behaviour of [Formula: see text] and [Formula: see text] for the selected amino acid systems outside of the temperature range utilised in this investigation.
The chemistry of thujone. XVII. The synthesis of ambergris fragrances and related analogues
Authors: Kutney James P. , Chen Yong-Huang
Published: May 2006

A strategy to utilize the thujone-derived enone 1 for the development of a synthetic route to ambergris fragrances is presented. Thujone (8) is transformed to the tricyclic enone 9, via the Robinson annulation reaction, and the latter is then elaborated to the cis-fused tricyclic intermediates 10, 11, and 12. Extrusion of the isopropyl side chain in 12 is achieved through an initial ozonation reaction and the resulting ketone 14 is then treated with m-CPBA to afford 16. Cyclopropyl ring opening in 16 is performed via initial saponification to the alcohol 17 and the latter is then reacted with FeCl3 and sodium acetate to enone 1. The necessary elaboration of a tetrahydrofuran ring attached to ring B of 1 is achieved through reaction of 1 with vinylmagnesium bromide, alkylation, hydroboration, and final acid-catalyzed ring closure of the 1,5-diol 4. The route affords the opportunity of synthesizing a variety of analogues within the Ambrox series.
A HYPERCHAOS GENERATED FROM CHEN'S SYSTEM
Authors: GAO TIEGANG , CHEN ZENGQIANG , YUAN ZHUZHI , CHEN GUANRONG
Published: May 2006

This paper presents a new hyperchaotic system, obtained by adding a controller to the second equation of the three-dimensional autonomous Chen's chaotic system. The hyper-chaos system undergoes a change from hyperchaos to limit cycle when the parameter varies. The system is not only demonstrated by computer simulations but also verified with bifurcation analysis.
NETWORK OF SOCIAL GROUPS OR LET'S HAVE A PARTY
Authors: BRANDAU MARIAN , TRIMPER STEFFEN
Published: May 2006

We present a simple model for growing up and depletion of parties due to the permanent communication between the participants of the events. Because of the rapid exchange of information, everybody is able to evaluate its own and all other parties by means of the list of its friends. Therefore, the number of participants at different parties can be changed incessantly. Depending on the depth of the social contacts, which will be characterized by a parameter α, a stable distribution of party members emerges. At a critical αc an abrupt depletion of almost all parties is observed and as the consequence all the people are assembled at a single party. The model is based on a hierarchical social network. The probability that a certain person is contacted by another one depends on the social distance introduced within the network and homophily parameter α.
Eliminating stack overflow by abstract interpretation
Authors: Regehr John , Reid Alastair , Webb Kirk
Published: May 2006

An important correctness criterion for software running on embedded microcontrollers is
stack safety
: a guarantee that the call stack does not overflow. Our first contribution is a method for statically guaranteeing stack safety of interrupt-driven embedded software using an approach based on context-sensitive dataflow analysis of object code. We have implemented a prototype stack analysis tool that targets software for Atmel AVR microcontrollers and tested it on embedded applications compiled from up to 30,000 lines of C. We experimentally validate the accuracy of the tool, which runs in under 10 sec on the largest programs that we tested. The second contribution of this paper is the development of two novel ways to reduce stack memory requirements of embedded software.
Analyzing data reuse for cache reconfiguration
Authors: Hu J. , Kandemir M. , Vijaykrishnan N. , Irwin M. J.
Published: May 2006

Classical compiler optimizations assume a fixed cache architecture and modify the program to take best advantage of it. In some cases, this may not be the best strategy because each nest might work best with a different cache configuration and transforming a nest for a given fixed cache configuration may not be possible due to data and control dependences. Working with a fixed cache configuration can also increase energy consumption in loops where the best required configuration is smaller than the default (fixed) one. In this paper, we take an alternate approach and modify the cache configuration for each nest, depending on the access pattern exhibited by the nest. We call this technique
compiler-directed cache polymorphism
(CDCP). More specifically, in this paper, we make the following contributions. First, we present an approach for analyzing data reuse properties of loop nests. Second, we give algorithms to simulate the footprints of array references in their reuse space. Third, based on our reuse analysis, we present an optimization algorithm to compute the cache configurations for each loop nest. Our experimental results show that CDCP is very effective in finding the near-optimal data cache configurations for different nests in array-intensive applications.
Shortest-path algorithms for real-time scheduling of FIFO tasks with minimal energy use
Authors: Gaujal Bruno , Navet Nicolas , Walsh Cormac
Published: May 2006

We present an algorithm for scheduling a set of nonrecurrent tasks (or jobs) with FIFO real-time constraints so as to minimize the total energy consumed when the tasks are performed on a dynamically variable voltage processor. Our algorithm runs in linear time and thus, in this case, is an improvement over the classical algorithm of Yao et al. It was inspired by considering the problem as a shortest-path problem. We also propose an algorithm to deal with the case where the processor has only a limited number of clock frequencies. This algorithm gives the optimum schedule with the minimum number of speed changes, which is important when the speed switching overhead cannot be neglected. All our algorithms are linear in the number of tasks if the arrivals and deadlines are sorted and otherwise need
O
(
N
log
N
) time. These complexities are shown to be the best possible. Finally, we extend our results to fluid tasks and to nonconvex cost functions.
Software-controlled fault tolerance
Authors: Reis George A. , Chang Jonathan , Vachharajani Neil , Rangan Ram , August David I. , Mukherjee Shubhendu S.
Published: May 2006

Traditional fault-tolerance techniques typically utilize resources ineffectively because they cannot adapt to the changing reliability and performance demands of a system. This paper proposes software-controlled fault tolerance, a concept allowing designers and users to tailor their performance and reliability for each situation. Several software-controllable fault-detection techniques are then presented: SWIFT, a software-only technique, and CRAFT, a suite of hybrid hardware/software techniques. Finally, the paper introduces PROFiT, a technique which adjusts the level of protection and performance at fine granularities through software control. When coupled with software-controllable techniques like SWIFT and CRAFT, PROFiT offers attractive and novel reliability options.
Disciplined design practices
Authors: Clear Tony
Published: May 2006

Reflecting upon the recent experience of teaching our undergraduate software engineering course has caused me to revisit several questions at the core of the discipline. What is the essence of software design, how should it be taught and how does it relate to software engineering?
Educational benefits of metadata creation by students
Authors: Or-Bach Rachel
Published: May 2006

Repositories of learning objects are developed and used by computer science educators especially for the teaching of programming, data types, and algorithms. Developing a learning object requires decisions about the granularity and the respective metadata for further retrieval. In this paper, we describe educational advantages of learning activities that deal with metadata creation by students. The learning objects relate to computer programming examples that the students use and reuse throughout a course.
A games-based approach for teaching the introductory programming course
Authors: Rajaravivarma Rathika
Published: May 2006

Introductory programming courses in computer science aim at building an effective foundation for the development of programming skills. A prudent way to develop these skills is by emphasizing problem solving and logical thinking. This paper proposes a games-based approach, as a way of engaging students and developing these skills. Common mistakes of novice programmers in traditional courses are summarized. Word and number games are used to illustrate the potential benefits of a games-based approach, which minimizes such mistakes.
Wavelet synopses for general error metrics
Authors: Garofalakis Minos , Kumar Amit
Published: May 2006

Several studies have demonstrated the effectiveness of the wavelet decomposition as a tool for reducing large amounts of data down to compact
wavelet synopses
that can be used to obtain fast, accurate approximate query answers. Conventional wavelet synopses that greedily minimize the overall root-mean-squared (i.e.,
L
2
-norm) error in the data approximation can suffer from important problems, including severe bias and wide variance in the quality of the data reconstruction, and lack of nontrivial guarantees for individual approximate answers. Thus,
probabilistic thresholding schemes
have been recently proposed as a means of building wavelet synopses that try to
probabilistically
control
maximum
approximation-error metrics (e.g., maximum relative error).A key open problem is whether it is possible to design efficient
deterministic
wavelet-thresholding algorithms for minimizing

general, non-L
2
error metrics

that are relevant to approximate query processing systems, such as maximum relative or maximum absolute error. Obviously, such algorithms can guarantee better maximum-error wavelet synopses and avoid the pitfalls of probabilistic techniques (e.g., “bad” coin-flip sequences) leading to poor solutions; in addition, they can be used to directly optimize the synopsis construction process for other useful error metrics, such as the
mean relative error
in data-value reconstruction. In this article, we propose novel, computationally efficient schemes for deterministic wavelet thresholding with the objective of optimizing
general approximation-error metrics
. We first consider the problem of constructing wavelet synopses optimized for
maximum error
, and introduce an
optimal
low polynomial-time algorithm for
one-dimensional
wavelet thresholding---our algorithm is based on a new Dynamic-Programming (DP) formulation, and can be employed to minimize the maximum relative or absolute error in the data reconstruction. Unfortunately, directly extending our one-dimensional DP algorithm to
multidimensional
wavelets results in a super-exponential increase in time complexity with the data dimensionality. Thus, we also introduce novel, polynomial-time
approximation schemes
(with tunable approximation guarantees) for deterministic wavelet thresholding in multiple dimensions. We then demonstrate how our optimal and approximate thresholding algorithms for maximum error can be extended to handle a broad, natural class of
distributive error metrics
, which includes several important error measures, such as mean weighted relative error and weighted
L

p

-norm error. Experimental results on real-world and synthetic data sets evaluate our novel optimization algorithms, and demonstrate their effectiveness against earlier wavelet-thresholding schemes.
Composing schema mappings
Authors: Fagin Ronald , Kolaitis Phokion G. , Popa Lucian , Tan Wang-Chiew
Published: May 2006

A schema mapping is a specification that describes how data structured under one schema (the source schema) is to be transformed into data structured under a different schema (the target schema). A fundamental problem is composing schema mappings: given two successive schema mappings, derive a schema mapping between the source schema of the first and the target schema of the second that has the same effect as applying successively the two schema mappings.In this article, we give a rigorous semantics to the composition of schema mappings and investigate the definability and computational complexity of the composition of two schema mappings. We first study the important case of schema mappings in which the specification is given by a finite set of source-to-target tuple-generating dependencies (source-to-target tgds). We show that the composition of a finite set of full source-to-target tgds with a finite set of tgds is always definable by a finite set of source-to-target tgds, but the composition of a finite set of source-to-target tgds with a finite set of full source-to-target tgds may not be definable by any set (finite or infinite) of source-to-target tgds; furthermore, it may not be definable by any formula of least fixed-point logic, and the associated composition query may be NP-complete. After this, we introduce a class of existential second-order formulas with function symbols and equalities, which we call
second-order tgds
, and make a case that they are the “right” language for composing schema mappings. Specifically, we show that second-order tgds form the smallest class (up to logical equivalence) that contains every source-to-target tgd and is closed under conjunction and composition. Allowing equalities in second-order tgds turns out to be of the essence, even though the “obvious” way to define second-order tgds does not require equalities. We show that second-order tgds without equalities are not sufficiently expressive to define the composition of finite sets of source-to-target tgds. Finally, we show that second-order tgds possess good properties for data exchange and query answering: the chase procedure can be extended to second-order tgds so that it produces polynomial-time computable universal solutions in data exchange settings specified by second-order tgds.
Optimization of query streams using semantic prefetching
Authors: Bowman Ivan T. , Salem Kenneth
Published: May 2006

Streams of relational queries submitted by client applications to database servers contain patterns that can be used to predict future requests. We present the Scalpel system, which detects these patterns and optimizes request streams using context-based predictions of future requests. Scalpel uses its predictions to provide a form of semantic prefetching, which involves combining a predicted series of requests into a single request that can be issued immediately. Scalpel's semantic prefetching reduces not only the latency experienced by the application but also the total cost of query evaluation. We describe how Scalpel learns to predict optimizable request patterns by observing the application's request stream during a training phase. We also describe the types of query pattern rewrites that Scalpels cost-based optimizer considers. Finally, we present empirical results that show the costs and benefits of Scalpel's optimizations.
FEMSTER
Authors: Castillo Paul , Rieben Robert , White Daniel
Published: May 2006

FEMSTER is a modular finite element class library for solving three-dimensional problems arising in electromagnetism. The library was designed using a modern geometrical approach based on differential forms (or
p
-forms) and can be used for high-order spatial discretizations of well-known H(
div
)- and H(
curl
)-conforming finite element methods. The software consists of a set of abstract interfaces and concrete classes, providing a framework in which the user is able to add new schemes by reusing the existing classes or by incorporating new user-defined data types.
Algorithm 846
Authors: Gao Tangan , Li T. Y. , Wu Mengnien
Published: May 2006

MixedVol is a C++ software package that computes the mixed volume of
n
finite subsets of ℤ

n

or the support of a system of
n
polynomials in
n
variables. The software produces the mixed volume as well as the mixed cells. The mixed cells are crucial for solving polynomial systems by the polyhedral homotopy continuation method. The software leads existing codes for mixed-volume computation in speed by a substantial margin and its memory requirement is very low.
Argumentation support
Authors: Moor Aldo de , Aakhus Mark
Published: May 2006

A plethora of technologies exist that are not necessarily tools. For technologies to become a tool, we contend, argumentation routines and design must coevolve.
Applications quest
Authors: Gilbert Juan E.
Published: May 2006

It helps admissions officers review college applicants holistically.
Computational thinking
Authors: Wing Jeannette M.
Published: May 2006

It represents a universally applicable attitude and skill set everyone, not just computer scientists, would be eager to learn and use.
Cognitive complexity metrics and its impact on software reliability based on cognitive software development model
Authors: Kushwaha Dharmender Singh , Misra A. K.
Published: May 2006

Software metrics provide a quantitative basis for the development and validation of models of software development process. Information gained from metrics is used in managing the development process in order to improve the reliability and quality of software product. The software metric is used to estimate various parameters of software development lifecycle such as cost, schedule productivity, quality and reliability. In this paper, an attempt has been made to frame the cognitive complexity metrics that will aid in increasing the reliability of software product being developed during the development lifecycle.
Component-interaction automata as a verification-oriented component-based system specification
Authors: Brim Luboš , Černá Ivana , Vařeková Pavlína , Zimmerova Barbora
Published: May 2006

In the paper, we present a new approach to component interaction specification and verification process which combines the advantages of both architecture description languages (ADLs) at the beginning of the process, and a general formal verification-oriented model connected to verification tools at the end. After examining current general formal models with respect to their suitability for description of component-based systems, we propose a new verification-oriented model,
Component-Interaction automata
, and discuss its features. The model is designed to preserve all the interaction properties to provide a rich base for further verification, and allows the system behaviour to be configurable according to the architecture description (bindings among components) and other specifics (type of communication used in the synchronization of components).
A categorical characterization for the compositional features of the # component model
Authors: de Carvalho Junior Francisco Heron , Lins Rafael Dueire
Published: May 2006

The # programming model attempts to address the needs of the high performance computing community for new paradigms that reconcile efficiency, portability, abstraction and generality issues on parallel programming for high-end distributed architectures. This paper provides a semantics for the compositional features of # programs, based on category theory.
When and how to develop domain-specific languages
Authors: Mernik Marjan , Heering Jan , Sloane Anthony M.
Published: May 2006

Domain-specific languages (DSLs) are languages tailored to a specific application domain. They offer substantial gains in expressiveness and ease of use compared with general-purpose programming languages in their domain of application. DSL development is hard, requiring both domain knowledge and language development expertise. Few people have both. Not surprisingly, the decision to develop a DSL is often postponed indefinitely, if considered at all, and most DSLs never get beyond the application library stage.Although many articles have been written on the development of particular DSLs, there is very limited literature on DSL development methodologies and many questions remain regarding when and how to develop a DSL. To aid the DSL developer, we identify patterns in the decision, analysis, design, and implementation phases of DSL development. Our patterns improve and extend earlier work on DSL design patterns. We also discuss domain analysis tools and language development systems that may help to speed up DSL development. Finally, we present a number of open problems.
Nontermination inference of logic programs
Authors: Payet Etienne , Mesnard Fred
Published: May 2006

We present a static analysis technique for nontermination inference of logic programs. Our framework relies on an extension of the subsumption test, where some specific argument positions can be instantiated while others are generalized. We give syntactic criteria to statically identify such argument positions from the text of a program. Atomic left looping queries are generated bottom-up from selected subsets of the binary unfoldings of the program of interest. We propose a set of correct algorithms for automating the approach. Then, nontermination inference is tailored to attempt proofs of optimality of left termination conditions computed by a termination inference tool. An experimental evaluation is reported and the analyzers can be tried online at http://www.univ-reunion.fr/~gcc. When termination and nontermination analysis produce complementary results for a logic procedure, then with respect to the leftmost selection rule and the language used to describe sets of atomic queries, each analysis is optimal and together, they induce acharacterizationof the operational behavior of the logic procedure.
The perceived roughness of resistive virtual textures
Authors: Lederman Susan J. , Klatzky Roberta L. , Tong Christine , Hamilton Cheryl
Published: May 2006

Klatzky and Lederman [2006] have shown that tangential resistive forces may be used to convey roughness in virtual textures using the WingMan force-feedback mouse. Modeling our experiment after this study, we directly examined the effect of viscous resistance on the perceived roughness magnitude of virtual gratings using a PHANTOM. For each virtual grating, the resistance level encountered at the ridges was varied by altering the viscosity coefficient. Perceived roughness systematically increased as the value of the viscosity coefficient was increased. The ridge-to-groove ratio contributed a small additional effect of microgeometry. These results suggest that simple models of viscous resistance may be used to simulate varying levels of surface roughness.