bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of D-gluconic acid by chromium(VI) in perchloric acid
Authors: Signorella Sandra R. , Santoro Mabel I. , Mulero Mirta N. , Sala Luis F.
Published: May 2006

The oxidation of gluconic acid by chromium(VI) in perchloric acid has been found to follow the rate law: −d[CrVI]/dt = (k′1 + k′2[GA])[H+]2[CrVI], where k′1 = (7.1 ± 0.2) × 10−4 M−2 s−1 and k′2 = (9.4 ± 0.2) × 10−2 M−3 s−1. This rate law corresponds to the reaction leading to the formation of 2-ketogluconic acid by C—H cleavage when a 20-fold or higher excess of acid over chromium(VI) is employed. Buildup and decay of chromium(V) intermediates accompany the decay of chromium(VI). Chromium(V) rates of decay are similar or slower than those of chromium(VI), as observed by electron paramagnetic resonance (epr) and visible spectrophotometry.
Transition state dynamics of F + Br2 reactive scattering
Authors: Zhu Zhen Zheng , White Richard W.P. , Smith David J. , Grice Roger
Published: May 2006

Reactive scattering of F atoms with Br2 molecules has been studied at an initial translational energy E ∼ 16 kJ mol−1 using a supersonic beam of F atoms seeded in Ne buffer gas. Laboratory angular and velocity distributions of BrF product have been measured. They show sharp peaking in the forward direction with almost isotropic wide angle scattering of relative intensity ∼ 0.2. Approximately half the total available energy is disposed into product translation for scattering in the forward and backward directions with slightly lower translational energy for the sideways scattering. The combination of sharp forward scattering and high product translational energy is attributed to early migratory trajectories in large impact parameter collisions whereby the F atom reacts with the more distant Br atom of the Br2 molecule lying in the forward hemisphere. The isotropic wide angle scattering arises from direct trajectories in which the F atom reacts with the nearer Br atom of the Br2 molecule. Migratory dynamics are promoted by charge transfer interaction of the form Br2+F− which stabilises the potential energy surface in elongated isosceles triangular FBr2 configurations as well as in slightly bent FBrBr configurations. Comparison is made with the dynamics of the F + Cl2, I2, and CCl3Br reactions.
Gas-phase association reactions of fullerene cations: modelling the influence of charge state and other molecular parameters on association efficiency
Authors: Petrie Simon , Bohme Diethard K.
Published: May 2006

The efficiency of association reactions of fullerene cations observed in helium at pressures of 0.35–0.4 Torr sustained in a Selected-Ion Flow Tube (SIFT) at room temperature has been examined with a view to the influence of the charge state and the size of the fullerene ion and the size, structure, and degree of unsaturation of the neutral. The association efficiency is found to be strongly dependent on these molecular parameters. The calculated lifetime of the intermediate collision complex provides insight into the well depth associated with the formation of this complex and the effectiveness of vibrational and (or) rotational degrees of freedom of the reactants in the dispersal of the energy of complex formation. The results are considered in terms of single-well and double-well models for the potential energy surface leading to association and are best accommodated by the double-well model involving the formation of an initial electrostatic collision complex that must overcome a barrier to proceed to the formation of a chemically bonded adduct. The observed competition between association and charge transfer can also be accommodated with a double-well model, which provides a lower limit for the depth of the electrostatic well for those systems that exhibit such competition.
Experimental and theoretical study of monoligand complexes of nickel atoms with simple alkynes
Authors: Mitchell S.A. , Blitz M.A. , Fournier R.
Published: May 2006

Monoligand complexes of nickel atoms with simple alkynes have been investigated by kinetic studies of association reactions of nickel atoms with ethyne, propyne, and 2-butyne in the gas phase near room temperature, and by quantum chemical calculations on the Ni[C2H2] complex using a Linear Combination of Gaussian-Type Orbitals – Density Functional (LCGTO–DF) method. Experimental estimates of binding energies of the monoligand complexes have been made by using RRKM unimolecular reaction theory to model the pressure dependence of second-order rate coefficients for the association reactions: [Formula: see text] and 29 ± 5 kcal mol−1, for Ni[C2H2], Ni[propyne], and Ni[2-butyne], respectively. The trend in binding energy with methyl substitution on ethyne is discussed and compared with similar data for monoligand complexes of alkynes with copper atoms. The harmonic vibrational frequencies and binding energy for the 1A1 ground state of Ni[C2H2] have been calculated using the LCGTO–DF method, and the results are compared with experimental data on the infrared spectrum of matrix-isolated Ni[C2H2] and with the estimate of the binding energy of Ni[C2H2] from the present experimental study. There is excellent agreement between the experimental and theoretical results. The calculations indicate that at least one triplet state of Ni[C2H2] is bound relative to ground state Ni + C2H2 reactants. This is consistent with indications from the kinetic results that the association reaction occurs on more than one potential energy surface.
Internal, translational, and angular momentum product state distributions of CuF molecules desorbing associatively from copper surfaces
Authors: Bracker A. , Jakob P. , Näher U. , Rüdiger M. , Sugawara K. , Wanner J.
Published: May 2006

The dry etching reaction of solid copper surfaces with fluorine atoms or molecules has been studied with laser-induced fluorescence spectroscopy. The reaction product, copper monofluoride, CuF, is produced in the X1Σ+ electronic ground state and desorbs into the gas phase at surface temperatures above approximately 750 K. Rotationally resolved LIF excitation spectra of the C1П ← X1Σ+ band system of CuF molecules desorbing from an isotopically purified 63Cu polycrystalline sample are obtained under conditions of coherent saturation. From the product state analysis it is deduced that the rovibrational product populations are in thermal equilibrium with the surface. The same holds for the translational velocity distribution obtained by Doppler-shift measurements. A pronounced polarization effect, particularly strong for Q branch transitions, can be traced back to photoselection of single-parity levels in the Λ doublets of the C1П state. A theoretical analysis for the distribution of J vectors, based on the formalism of Greene and Zare, shows that the measured degree of polarization is quantitatively in agreement with an isotropic distribution of rotational angular momentum vectors. The vibrational and translational product equilibration is not affected by changing the reactants from F2 molecules to F atoms, which increases the exoergicity of the overall reaction. The results are interpreted in terms of the absence of a barrier for desorption and a long residence time of the chemisorbed CuF molecules at the copper surface. The lack of any translational and rotational cooling is discussed within the framework of a model.
Molecular dynamics study of the surface diffusion of large adsorbates: III. Role of adsorbate shape
Authors: Zeiri Yehuda
Published: May 2006

The present study is dedicated to the investigation of the relationship between the surface diffusion mechanism of large adsorbates and the adsorbate shape. Three different shapes of model adsorbates were examined: linear chains, branched chains, and cyclic molecules. It was found that the surface diffusion mechanism of linear and branched chain adsorbates is quite similar, while a markedly different diffusion mechanism is observed for cyclic adsorbates. For all types of adsorbates the temperature dependence of the diffusion coefficient was found to obey an Arrhenius expression. The results of the simulations have shown good qualitative agreement with the available experimental data.
Bound–free B2Σ+ –X2Π, A2Σ+ emission in the BAr van der Waals complex
Authors: Hwang Eunsook , Dagdigian Paul J. , Alexander Millard H.
Published: May 2006

Spectrally resolved bound–free fluorescence emission spectra for the excitation of several vibrational levels in the excited B2Σ+ electronic state of the van der Waals molecule 11BAr are presented. This excited state emits to the ground X2Π and low-lying A2Σ+ states, both of which correlate with the ground state atomic asymptote B(2p2P) + Ar. Because of the large differences in equilibrium internuclear separations, the emission occurs mainly to the repulsive walls. In order to gain more information on this portion of the potential energy curves, the experimental emission spectra were compared with simulated spectra derived from ab initio calculated B–Ar interaction potentials. The simulated spectra reproduce the experimental spectra well if the lower-state potential energy curves are shifted slightly inward. This discrepancy is consistent with our previous observation that the ab initio calculations slightly overestimate the vibrationally averaged internuclear separation, which we determined experimentally. This reflects the difficulty of accurately calculating weak van der Waals interaction energies.
Dynamics of I*(2P1/2) production in the ultraviolet photodissociation of alkyl iodides
Authors: Uma S. , Das Puspendu Kumar
Published: May 2006

The relative quantum yields, [Formula: see text] for the production of I*(2Pl/2) at 266, 280, and ∼305 nm are reported for a series of primary alkyl iodides using the technique of two-photon laser-induced fluorescence for the detection of I(2P3/2) and I*(2P1/2) atoms. Results are analyzed by invoking the impulsive energy disposal model, which summarizes the dynamics of dissociation as a single parameter. Comparison of our data with those calculated by a more sophisticated time-dependent quantum mechanical model is also made. Near the red edge of the alkyl iodide A band, absorption contribution from the 3Q1 state is important and the dynamics near the 3Q0−1Q1 curve-crossing region seem to be influenced by the kinematics of the dissociation process.
Electron impact studies of autoionizing states in CO2 using a multi-angle parallel detection electron spectrometer
Authors: Wen A.T. , Tremblay D. , Tremblay B. , Roy D.
Published: May 2006

The MAPDESS, a multi-angle-detector electron scattering spectrometer, has been adapted to electron ejection measurements. A study of autoionization from Rydberg states has been carried out for the neutral linear molecule CO2 in the continuum region 15–19 eV by low-energy electron impact. Observations have been made of structure due to excitation of these states by slow electron scattering and their decay by ejection of electrons. A multi-angle parallel detection technique has been used and this has enabled some CO2 autoionizing states resulting from non-dipole transitions to be observed clearly. The major features appearing in the ejected electron spectra of CO2 have tentatively been classified and (or) assigned in terms of autoionization to the ground ionic state X, from highly excited electronic states corresponding to the "Tanaka progression I" and "Tanaka–Ogawa" Rydberg series converging to the ionic A state, as well as from the Henning "sharp" and "diffuse" series, along with the forbidden npσu series, converging to the B state. In addition to the features already known, new features have been observed, and they seem to be rather sensitive to electron impact energies employed. Strong relative intensity variations are observed at the different impact energies, and marked angular effects are also found in the ejected electron spectra.
Quantum chemical shape: new density domain relations for the topology of molecular bodies, functional groups, and chemical bonding
Authors: Mezey Paul G.
Published: May 2006

A density domain (DD) is the formal body enclosed by a molecular isodensity contour (MIDCO) surface. Individual nuclear neighborhoods and various formal molecular fragments can be regarded as fuzzy moieties of electron densities, dominated by one or several nuclei. Such a fuzzy fragment involves a whole range of density values, hence it cannot be described by a single MIDCO, but it can be represented by a sequence of density domains. Within the chemically important range of density values, there are only a finite number of topologically different bodies of density domains. In the Density Domain Approach, chemical bonding is described by the interfacing and mutual interpenetration of local fuzzy charge density clouds. The bonding between fragments of a molecule is characterized by a finite sequence of density domains within a wide range of density values and by the correponding sequence of topological patterns of the mutual interpenetration of these fragments. In earlier works, the DD approach was advocated as an alternative to the conventional "skeletal model" of chemical bonding. The classically motivated line diagrams as representatives of bonding are replaced by the pattern of interpenetration of fuzzy fragment bodies at various density thresholds. In this study, novel DD relations are described, suitable for a quantum chemical characterization of functional groups, the local shape properties of such groups, and their contributions to global molecular shape.
1992 Lemieux Award Lecture Studies related to the penicillin receptor
Authors: Wolfe Saul
Published: May 2006

The relative antibacterial activities of penicillins and cephalosporins are discussed in terms of their differing abilities to complex to and react with penicillin-binding proteins. The insights gained from such an analysis are being used to attempt the design of new kinds of structures targeted to the penicillin receptor. Details of such design, and examples of several new classes of compounds suggested by this work, are described. Some of these compounds exhibit interesting antibacterial activity.
Solvent effects on the reactivity of solvated electrons with ions in isobutanol/water mixed solvents
Authors: Chen Ruzhong , Avotinsh Yuris , Freeman Gordon R.
Published: May 2006

The effective reaction radii KRr, where Rr is the reactive encounter radius and K is the probability of reaction per encounter, for [Formula: see text] with [Formula: see text], are all 0.7 ± 0.1 nm in isobutanol containing 10–20 mol% water. The value remains at 0.7 ± 0.1 nm for [Formula: see text] in pure isobutanol, and for the two transition metal ions in pure water solvent. The value for [Formula: see text] reduces to 0.35 nm in pure isobutanol and pure water solvents, whereas for [Formula: see text] in pure water solvent it is only 0.14 nm and 2.6 × 10−5 nm, respectively. The low reactivity of [Formula: see text] with [Formula: see text] in water is attributed to the symmetry of the hydrogen-bonded solvation structure of [Formula: see text] in water, and the higher reactivity of [Formula: see text] is attributed to the lower symmetry of its hydrogen-bonded solvation structure. The [Formula: see text] ions have no low-lying orbital for an electron to occupy, so either reaction occurs by proton transfer to the electron site or the neutral species must decompose. We suggest that the proton transfer or the decomposition of the neutral species is facilitated by an unsymmetrical solvation structure.Reaction of [Formula: see text] in Al(ClO4)3 solutions in water is due mainly to [Formula: see text] from hydrolysis of [Formula: see text] and partly to partially hydroxylated aluminum(III) species. Reaction of [Formula: see text] with [Formula: see text] itself appears to be negligible in water. The reactivity of the solutions of Al(ClO4)3 in isobutanol-rich solvents is 3–5 times greater than that in water.In pure C1 to C4 1-alcanol solvents the value of [Formula: see text] increases linearly with the dielectric relaxation time τ1 of the solvent. In these solvents the probability of permanent capture per encounter increases approximately as the square of the encounter duration.
Unusual Weiss–Cook condensation of dimethyl 2,3-dioxobutanedioate and dimethyl 3-oxoglutarate
Authors: Deslongchamps Ghislain , Mink Daniel , Boyle Paul D. , Singh Nina
Published: May 2006

The Weiss–Cook condensation of dimethyl 2,3-dioxobutanedioate with two equivalents of dimethyl 3-oxoglutarate in aqueous bicarbonate produces an "abnormal" product, pentamethyl cis-3-(carbomethoxymethyl)-3,7-dihydroxy-2-oxabicyclo-[3.3.0]oct-7-ene-1,4,5,6,8-pentacarboxylate 7, whose structure has been determined by X-ray crystallography. Rrapcho decarbomethoxylation (sodium chloride, aqueous dimethyl sulfoxide, 140 °C) of this compound produces dimethyl cis-3,7-dioxobi-cyclo[3.3.0]octane-1,5-dicarboxylate 4 in quantitative yield. These results suggest that compound 7 may be the product of a kinetically controlled reaction pathway involving 4-hydroxypent-2-en-1-one intermediate 5. Heating of 7 in dimethyl sulfoxide may have promoted thermodynamic equilibration to a Weiss–Cook product, which then decarbomethoxylated to produce 4.
Alkene adducts of cyclic thiazenes. Identification of exo and endo addition of 1,3,2,4,6-dithiatriazines to 1,5-norbornadiene by 2-D NMR methods and the crystal structure of a single molecule in which both modes of addition are displayed
Authors: Boeré Renè T. , Eng John A. , Preuss Kathryn , Parvez Masood , Bryan C.D. , Cordes A.W.
Published: May 2006

4-CF3—C6H4—CN3S2, 1, forms symmetrical sulfur-bound adducts with norbornene (NBE), norbornadiene (NBD), and 1-heptene (C7H14), which were studied by 1H, 13C, COSY-45, and HETCORR NMR. 1•NBE exists in solution in a single isomeric form which corresponds to that found in the solid state for 4-CH3O—C6H4—CN3S2•NBE by single-crystal X-ray diffraction: orthorhombic, P212121 with Z = 4, a = 10.224(3), b = 10.369(5), c = 14.075(5). R = 0.0475 and Rw = 0.0492 for 634 data. 1•NBD exists in solution in two isomeric forms which are not interchangeable. One of these corresponds to that found in the NBE adduct, i.e. exo addition; the other is the first example of endo addition. Two bis adducts of stoichiometry NBD•21 have been prepared and separated. They are isomers exhibiting exo-exo and exo-endo addition. The structure of the latter was confirmed by X-ray diffraction: orthorhombic, Pcab with Z = 8, a = 7.816(2), b = 17.264(3), c = 36.842(5). R = 0.068 and Rw = 0.106 for 1506 data. 1•C7H14 exists as a mixture of syn and anti isomers. NMR structure parameters derived here have been applied to published data on over 15 thiazene NBE and NBD adducts.
The photochemistry of 1-naphthylmethyl carbonates and carbamates
Authors: Parman T. , Pincock J.A. , Wedge P.J.
Published: May 2006

The photochemistry in methanol of 1-naphthylmethyl phenyl carbonate (3) and 1-naphthylmethyl benzyl carbonate (4) has been studied. Products resulting from both the 1-naphthylmethyl cation and the 1-naphthylmethyl radical are obtained for 3, but only from the cation for 4. Similar results were obtained for the corresponding 1-naphthylmethyl derivatives 5 and 6 of N-phenyl and N-benzyl carbamic acids. The product yields for all four compounds can be explained by a mechanism of initial homolytic cleavage of the 1-naphthylmethyl carbon–oxygen bond from the excited singlet state. The radical pair generated then partitions between the two pathways: electron transfer to form the ion pair or decarboxylation. For PhO-CO-O• and PhNH-CO-O•, decarboxylation is rapid and competitive with electron transfer. For PhCH2O-CO-O• and PhCH2NH-CO-O•, decarboxylation is slower, electron transfer dominates, and only products from the ion pair are obtained.
Total asymmetric syntheses of (1S,2S)-norcoronamic acid, and of (1R,2R)- and (1S,2S)-coronamic acids from the diastereoselective cyclization of 2-(N-benzylideneamino)-4-chlorobutyronitriles
Authors: Gaucher Anne , Ollivier Jean , Marguerite Jacqueline , Paugam Renée , Salaün Jacques
Published: May 2006

(3R)-2-(N-Benzylideneamino)-4-chloro-3-methylbutyronitrile 3, prepared from the commercially available methyl (2S)-3-hydroxy-2-methyl propionate 5 (96% ee), readily underwent potassium carbonate induced cyclization to provide, after acid hydrolysis (6 N HCl) and chromatography, the (1S,2S)-norcoronamic acid 1a with 88% diastereoselectivity and > 95% enantiomeric excess. From (2R)-2-(hydroxymethyl)butyl acetate 23 (> 88% ee) obtained by enzymatic enantioselective hydrolysis with lipase PS, was prepared the (3S)-2-(N-benzylideneamino)-3-(chloromethyl)valeronitrile 29, which after base-induced cyclization (K2CO3) and acid (6 N HCl) or basic (0.8 N NaOH) hydrolysis led to the non-natural (1R,2R)-coronamic acid 18 (> 88% ee). Also from this same acetate (2R)-23 was prepared the (3R)-3-(chloromethyl)-2-[(diphenylmethylene)amino]pentanenitrile 37, which provided the (1S,2S)-coronamic acid 17 (> 88% ee) after base-induced cyclization (K2CO3 or LDA) and acid hydrolysis (6 N HCl). It is noteworthy that these short synthetic sequences, which do not require any expensive chiral auxiliary or optically active precursors, do not alter the enantiomeric purity of the stereogenic centers of these 2,3-methanoamino acids. However, the E diastereoselectivity of these cyclizations was not improved by using bulky N-(diphenylmethylene)amino substituent, contrary to results of some molecular mechanic calculations (MAD).
The oxidation of ortho-anisidine in alkaline medium. A product characterization and an EPR study
Authors: Bolognese Adele , Buonanno Marina , Cantilena Antonio , Musci Giovanni , Alberti Angelo
Published: May 2006

Alkaline oxidation of ortho-anisidine by potassium ferricyanide in alkaline aqueous solution was examined. Azo compounds, a diamine, and para-iminoquinones were isolated from the highly coloured reaction mixture. The reaction was also carried out within the cavity of an EPR spectrometer and two radical species have been detected. Following these product results and EPR studies, a radical mechanism is proposed for the process.
Structural elucidation of the backbone oligosaccharide from the lipopolysaccharide of Moraxella catarrhalis serotype A
Authors: Masoud Hussein , Perry Malcolm B. , Brisson Jean-Robert , Uhrin Dušan , Richards James C.
Published: May 2006

The cell-surface lipopolysaccharide produced by Moraxella catarrhalis serotype A is composed of a hydrophobic lipid A moiety and an oligosaccharide, but lacks high-molecular-weight O-polysaccharide chains. The oligosaccharide component is composed of D-glucose, D-galactose, D-glucosamine, and 3-deoxy-D-manno-octulosonic acid. The carbohydrate backbone was obtained from the lipopolysaccharide by employing a reaction sequence involving deacylation, dephosphorylation, and reduction of the reducing D-glucosamine terminus of the lipid A moiety. Structural analysis of the backbone oligosaccharide employed a combination of microanalytical methods and nuclear magnetic resonance spectroscopy. Homo- and hetero-nuclear chemical shift correlation techniques and nuclear Overhauser enhancement (NOE) experiments led to the unambiguous assignment of the 1H and l3C resonances associated with each of the component glycosyl residues and established their sequence within the backbone oligosaccharide as shown,[Formula: see text]This lipopolysaccharide was found to consist of a highly branched, D-glucose-containing inner-core region which possesses a unique and unusual solution conformation. This was established by measurement of transglycosidic NOEs and three-bond 1H−13C coupling constants, in conjunction with molecular modeling. A D-galactose-containing disaccharide identified as a terminal group of the lipopolysaccharide was structurally identical to antigenic epitopes expressed by certain mammalian epithelial cells and may be related to the virulence potential of this human pathogen.
Binding and transport of calcium ions by synthetic analogues of ionomycin
Authors: Hu Thomas Q. , Weiler Larry
Published: May 2006

The transport of calcium ions across an organic barrier by a series of synthetic analogues of ionomycin was measured in a cylindrical glass cell using chloroform as the artificial membrane. The presence of a β-diketone and carboxyl group in the same molecule and a sufficient lipid solubility of the compounds were shown to be necessary and sufficient conditions for Ca2+ transport. Small and no transport of Ca2+ were found for analogues 5 and 6, respectively, due to the low lipid solubility of these compounds. The Ca2+ transport rate for analogues 8 and 13−15 followed the order of 8 > 13 > 14 > 15, which demonstrated that optimal Ca2+ transport was achieved when the β-diketone was separated from the carboxyl group by seven methylene units, identical to that found in ionomycin. Analogues 8−10 were comparable to ionomycin and calcimycin in terms of Ca2+ transport. Ca2+ transport by the analogues was found to be a saturable process that obeyed Michaelis–Menten kinetics. It was dependent on the pH in the aqueous source phase and independent of the pH in the receiving phase. Both the carboxyl and the β-diketo groups were ionized in the transport of Ca2+, indicating that the stoichiometry of Ca2+ complex in transport was 1:1. The pKa of the β-diketone of the analogues was determined to be in the range of 10.90−11.16 in 80% MeOH–H2O. The pKa values were related to the lipid solubility of the compounds and the hydrocarbon chain length between the β-diketone and the carboxyl group. The binding constants of the analogues with Ca2+ and Mg2+ in 80% MeOH–H2O were determined to be in the order of 102 M−1 and 103 M−1, respectively, using the pKa method. The stoichiometry of Mg2+ binding was found to be 1:1 by the mole ratio method. The selectivity in binding and in transport followed the same order, being Mg2+ > Ca2+ >> Na+, K+.[Formula: see text]
The photochemistry of 8-methyl 1-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene
Authors: Bender Christopher Owen , Bengtson Donald Laverne , Dolman Douglas , McKay Ryan Todd
Published: May 2006

8-Methyl-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene (20) was prepared by Shapiro reaction from 8-methyl-2,3-benzobicyclo[4.2.0]octa-2,7-dien-4-one (19). Triene 20 was found to be thermally and photochemically reactive. 6-Methylbenzocyclooctatetraene (i.e., 6-methyl COT 21) was the unique product formed when solutions of 20 were heated at 150 °C for 10 h. The direct irradiation of triene 20 gave 6-methylbenzosemibullvalene (i.e., SB 22, 46%, Φ = 0.073), 5-methyl-7,8-benzotetra-cyclo[3.3.02,4.03,6]oct-7-ene (23, 35%, Φ = 0.062), 6-methyl COT 21 (4%, Φ = 0.008), 7-methyl COT 24 (1%, Φ = 0.002), and naphthalene (3%, Φ = 0.006). Sensitized irradiations of 20 gave SB 22 (45%, Φ = 0.022), 6-methyl COT 21 (2%, Φ = 0.001), and naphthalene (4%, Φ = 0.002). Studies with deuterium-labelled triene (20a) indicated that the semibullvalene 22 was produced from both S1 and T1 excited states of 20 by Zimmerman di-π-methane rearrangement.
Photophysical behavior of oligoethylene glycols labeled with naphthalene carboxylate and phosphate esters
Authors: Lee Sam , Winnik Mitchell A.
Published: May 2006

The fluorescence spectra of tri- and tetraethylene glycol esterified with 2-(1-naphthyl)ethyl ethyl phosphate and 2-(1-naphthyl)ethyl 2-(ethoxy)ethyl phosphate were studied in dilute solutions of tetrahydrofuran (THF) and diethyl ether. They were compared with the fluorescence from tri- and tetraethylene glycol esterified with 1-naphthyl acetic acid. These compounds form intramolecular excimers. The extent of excimer formation is not extensive, but the relative amount of excimer emission from these compounds varies with the choice of solvent. Three synthetic intermediates to the phosphates, the 2-(1-naphthyl)ethyl N, N-diisopropylphosphoramidites of tri- and tetraethylene glycol and of 2-ethoxyethanol, were also examined. These compounds form intramolecular exciplexes. In THF, the relative amount of exciplex emission from the phosphoramidites follows the same trend as the carboxylate esters. In diethyl ether, the trend is different. Rates of fluorescence decay have been measured for these compounds. The results are discussed in terms of how information about the conformational and dynamic behavior of these molecules in solution can be obtained, and how the solvent can influence the relative amounts of excimer or exciplex fluorescence
A HIGHLY ACCURATE AND EFFICIENT TRIGONOMETRICALLY-FITTED P-STABLE THREE-STEP METHOD FOR PERIODIC INITIAL-VALUE PROBLEMS
Authors: WANG ZHONGCHENG , DAI YONGMING , WU DONGMEI
Published: May 2006

In this paper we present a new three-step method, which is a trigonometrically-fitted P-stable Obrechkoff method with phase-lag (frequency distortion) infinity. In this new method, we make use of higher-even-order derivatives including the eighth-order to increase the accuracy. On the other hand, we adopt a special structure to reduce the computational complexity of high-derivatives. The numerical illustration demonstrate that the new method has advantage in accuracy, periodic stability and efficiency.
Minesweeper as an NP-complete problem
Authors: Ben-Ari Mordechai (Moti)
Published: May 2006

Richard Kaye's demonstration that a puzzle based on the Minesweeper game is NP-complete makes this important computer science topic accessible to high school students. The resource described here is a set of slides showing the detailed solution of two introductory puzzles, following by the step-by-step simulation of digital circuit elements required for proving NP-completeness.
Constructivism as guiding philosophy for software engineering education
Authors: Hadjerrouit Said
Published: May 2006

Within the last few years constructivism has attracted both computer science and software engineer educators, because of its potential for improving academic learning. Currently, however, the application of constructivism is limited to examples in specific contexts so that it is difficult to transfer them to other institutions or even other courses. To apply effectively constructivism to software engineering and computer science education, instructors need a generic pedagogical model for translating constructivist principles into practice. This paper reports on the application of a pedagogical model for translating constructivism into a Web-based course in object-oriented software engineering.
Content and emphasis in CS1
Authors: Dale Nell
Published: May 2006

In the spring of 2004, 351 faculty members responded to a survey concerning the content and topic emphasis in the first course in computing. The survey targeted two different groups of faculty, one SIGCSE members and the other faculty who had contacted a medium-sized publisher of Computer Science textbooks. The questions fell into five categories: design methodology, general programming issues, object-oriented issues, software engineering issues, and other topics. The results are analyzed and, where possible, some conclusions are drawn.
Song debugging
Authors: Lapidot Tami , Hazzan Orit
Published: May 2006

This article suggests a song debugging activity that brings together two key ideas - the
analogy
between learning and debugging and the
pedagogical potential
of music in Computer Science Education (CSE). The paper can be viewed as the fourth in a series of papers published in
inroads
about the course Methods of Teaching Computer Science in the High School, but it can also stand on its own merit, since it discusses issues that are relevant to CSE in general.
Building a sense of history
Authors: Almstrum Vicki L. , Barker Lecia J. , Owens Barbara Boucher , Adams Elizabeth , Aspray William , Dale Nell B. , Dann Wanda , Lawrence Andrea , Schwartzman Leslie
Published: May 2006

This working group laid the groundwork for the collection and analysis of oral histories of women computing educators. This endeavor will eventually create a body of narratives to serve as role models to attract students, in particular women, to computing; it will also serve to preserve the history of the female pioneers in computing education. Pre-conference work included administration of a survey to assess topical interest. The working group produced aids for conducting interviews, including an opening script, an outline of topics to be covered, guidelines for conducting interviews, and a set of probing questions to ensure consistency in the interviews. The group explored issues such as copyright and archival that confront the large-scale implementation of the project and suggested extensions to this research. This report includes an annotated bibliography of resources. The next steps will include training colleagues in how to conduct interviews and establishing guidelines for archival and use of the interviews.
Graph indexing based on discriminative frequent structure analysis
Authors: Yan Xifeng , Yu Philip S. , Han Jiawei
Published: May 2006

Graphs have become increasingly important in modelling complicated structures and schemaless data such as chemical compounds, proteins, and XML documents. Given a
graph query
, it is desirable to retrieve graphs quickly from a large database via indices. In this article, we investigate the issues of indexing graphs and propose a novel indexing model based on
discriminative frequent structures
that are identified through a graph mining process. We show that the compact index built under this model can achieve better performance in processing graph queries. Since discriminative frequent structures capture the intrinsic characteristics of the data, they are relatively stable to database updates, thus facilitating sampling-based feature extraction and incremental index maintenance. Our approach not only provides an elegant solution to the graph indexing problem, but also demonstrates how database indexing and query processing can benefit from data mining, especially frequent pattern mining. Furthermore, the concepts developed here can be generalized and applied to indexing sequences, trees, and other complicated structures as well.
Algorithm 848
Authors: Shellman Spencer , Sikorski K.
Published: May 2006

We present the PFix algorithm for approximating a fixed point of a function f that has arbitrary dimensionality, is defined on a rectangular domain, and is Lipschitz continuous with respect to the infinity norm with constant 1. PFix has applications in economics, game theory, and the solution of partial differential equations. PFix computes an approximation that satisfies the residual error criterion, and can also compute an approximation satisfying the absolute error criterion when the Lipschitz constant is less than 1. For functions defined on all rectangular domains, the worst-case complexity of PFix has order equal to the logarithm of the reciprocal of the tolerance, raised to the power of the dimension. Dividing this order expression by the factorial of the dimension yields the order of the worst-case bound for the case of the unit hypercube. PFix is a recursive algorithm, in that it uses solutions to a
d
-dimensional problem to compute a solution to a (
d
+ 1)-dimensional problem. A full analysis of PFix may be found in Shellman and Sikorski [2003b], and a C implementation is available through ACM ToMS.
GPL, a general purpose language
Authors: Garwick Jan V.
Published: May 2006

When studying a programming language, three questions must be answered: (1) Which entities does the language operate upon and which operations can it perform upon them? This is the questions of semantics. (2) How do we express what we want to say? This is the question of syntax. (3) How is the language realized? This is the question of implementation.
The extension facilities of IMP
Authors: Irons Edgar T.
Published: May 2006

The objective for the extension feature of the programming language Imp is to provide an extension capability powerful enough to describe in detail the construction of a useful compiler for common programming languages, yet simple enough to allow unsophisticated programmers to make useful modifications to the language. Particular emphasis is given to keeping the concepts and constructions concise and few in number.
Panel of language authors
Authors: Shaw Christopher J.
Published: May 2006

This was the panel of the language designers who had described their work in the previous sessions of the Symposium, namely: Garwick, Mailloux, Peck, Irons, Standish, Bell, and MacLaren. Early portions of the panel discussion were lost through malfunction of the tape recorder. The remaining discussion, in edited form, follows.
Introduction to Oregano
Authors: Berry Daniel M.
Published: May 2006

This paper introduces Oregano, a practical generalization of ALGOL 60. The semantic definition of the language is in terms of an information structure model for its implementation, the contour model. Some of the major features are emphasized, including that of retention (non-deallocation of still accessible cells). The contour model is briefly described as a cell-based, fixed program component model with a retentive deallocation scheme. Modes (data types) are described as cell templates. Then, blocks, declarations, assignments, and pointer handling are illustrated in terms of sequences of pictorial snapshots in the model. A wide variety of heterogeneous and homogeneous multiple values are described using the data structure models of their implementation. Labels and procedures, which can be called recursively, are generalized to the full status of values. Coroutines and tasks are introduced as simple extensions of procedure calls, and various synchronization devices such as locking and events are illustrated. Finally, the practicality and ease of use of the language are demonstrated.
A Conversation with Jarod Jenson
Authors: O'Hanlon Charlene
Published: May 2006

One of the industry’s go-to guys in performance improvement for business systems is Jarod Jenson, the chief systems architect for a consulting company he founded called Aeysis. He received a B.S. degree in computer science from Texas A&M University in 1995, then went to work for Baylor College of Medicine as a system administrator. From there he moved to Enron, where he played a major role in developing EnronOnline. After the collapse of Enron, Jenson worked briefly for UBS Warburg Energy before setting up his own consulting company. His focus since then has been on performance and scalability with applications at numerous companies where he has earned a reputation for quickly delivering substantial performance gains. Recently, Jarod made a splash at JavaOne: he ran a booth to which attendees could bring their Java applications, and he guaranteed application performance improvements in under an hour.
Biologically inspired self-adaptive multi-path routing in overlay networks
Authors: Leibnitz Kenji , Wakamiya Naoki , Murata Masayuki
Published: May 2006

Using randomness to find optimal solutions in selecting network paths.
π-AAL
Authors: Mateescu Radu , Oquendo Flavio
Published: May 2006

A key aspect of the design of any software system is its architecture. An architecture description, from a runtime perspective, provides a formal representation of the architecture in terms of its components and connectors, their ports and behaviours, and how they are composed together. In the past decade, several Architecture Description Languages (ADLs) have been defined for representing the structure and behaviour of software architectures. However, describing the structure and behaviour of an architecture in terms of a configuration of components and connectors is needed, but it is not enough. Indeed, in addition to representing software architectures, we need to rigorously specify their required and desired architectural properties, in particular related to completeness, consistency and correctness. This article presents π-AAL, a novel Architecture Analysis Language (AAL) that has been designed in the ArchWare European Project to address formal analysis of software architectures. It is a formal, well-founded theoretically language based on the modal μ-calculus designed to enable the specification of structural and behavioural properties and their verification using an analytical toolset based on theorem proving and model checking techniques.
Surfing the net for software engineering notes
Authors: Doernhoefer Mark
Published: May 2006

I've titled this article "Requirements Management", but I actually want to discuss several topics related to the collection, modeling, management, implementation, testing, and tracing of requirements in a software system. That's quite a list of topics associated with software requirements, but the requirement set is typically the starting point for building any software-based system. Sure, if you're prototyping or a hobbyist just messing around, you may be able to dive in and just start coding. But a professional software engineer, building a product for a customer, will use some form of requirements specification to describe what is to be built and to set the customer expectations on what the finished product will do.
Assume-guarantee testing
Authors: Blundell Colin , Giannakopoulou Dimitra , Pǎsǎreanu Corina S.
Published: May 2006

Verification techniques for component-based systems should ideally be able to predict properties of the assembled system through analysis of individual components before assembly. This work introduces such a modular technique in the context of testing. Assume-guarantee testing relies on the (automated) decomposition of key system-level requirements into local component requirements at design time. Developers can verify the local requirements by checking components in isolation; failed checks may indicate violations of system requirements, while valid traces from different components compose via the assume-guarantee proof rule to potentially provide system coverage. These local requirements also form the foundation of a technique for efficient predictive testing of assembled systems: given a correct system run, this technique can predict violations by alternative system runs without constructing those runs. We discuss the application of our approach to testing a multi-threaded NASA application, where we treat threads as components.
Dream types
Authors: Bidinger Philippe , Leclercq Matthieu , Quéma Vivien , Schmitt Alan , Stefani Jean-Bernard
Published: May 2006

We present a type system for the Dream component-based message-oriented middleware. This type system aims at preventing the erroneous use of messages, such as the access of missing content. To this end, we adapt to our setting a type system developed for extensible records.
A specification-based approach to reasoning about pointers
Authors: Kulczycki Gregory , Sitaraman Murali , Weide Bruce W. , Rountev Atanas
Published: May 2006

This paper explains how a uniform, specification-based approach to reasoning about component-based programs can be used to reason about programs that manipulate pointers. No special axioms, language semantics, global heap model, or proof rules for pointers are necessary. We show how this is possible by capturing pointers and operations that manipulate them in the specification of a software component. The proposed approach is mechanizable as long as programmers are able to understand mathematical specifications and write assertions, such as loop invariants. While some of the previous efforts in reasoning do not require such mathematical sophistication on the part of programmers, they are limited in the kinds of properties they can prove about programs that use pointers. We illustrate the idea using a "Splice" operation for linked lists, which has been used previously to explain other analysis techniques. Not only can the proposed approach be used to establish shape properties given lightweight specifications, but also it can be used to establish total correctness given more complete specifications.
The perceived roughness of resistive virtual textures
Authors: Klatzky Roberta L. , Lederman Susan J.
Published: May 2006

In previous work, we demonstrated that people reliably perceive variations in surface roughness when textured surfaces are explored with a rigid link between the surface and the skin [e.g., Klatzky and Lederman 1999; Klatzky et al. 2003]. Parallel experiments here investigated the potential of a force-feedback mouse to render surfaces varying in roughness. The stimuli were surfaces with alternating regions of high and low resistance to movement in the x (frontal) dimension (called ridges and grooves, respectively). Experiment 1 showed that magnitude ratings of roughness varied systematically with the spatial period of the resistance variation. Experiments 2 and 3 used a factorial design to disentangle the contributions of ridge and groove width. The stimuli constituted eight values of groove width at each of five levels of ridge width (Experiment 2) or the reverse (Experiment 3). Roughness magnitude increased with ridge width while remaining essentially invariant over groove width. Kinematic variations in exploration were observed across the surfaces. The data point to the promise of using inexpensive devices to create virtual textural variations under conditions of unconstrained exploration.
Lights, camera, inaction
Authors: Schindler Esther
Published: May 2006

All the ingredients for webcam-based personal videoconferencing are in place. So why hasn't the technology taken off?
Does color in email make a difference?
Authors: Zviran Moshe , Te'eni Dov , Gross Yuval
Published: May 2006

Yes, if used correctly, it can excite and please, prompting recipients to respond as the sender intended---clicking a designated link or even buying something.
IT managers' requisite skills
Authors: Lee Sang M. , Lee Choong Kwon
Published: May 2006

Matching job seekers' qualifications with employers' skill requirements.
Research issues in data stream association rule mining
Authors: Jiang Nan , Gruenwald Le
Published: May 2006

There exist emerging applications of data streams that require association rule mining, such as network traffic monitoring and web click streams analysis. Different from data in traditional static databases, data streams typically arrive continuously in high speed with huge amount and changing data distribution. This raises new issues that need to be considered when developing association rule mining techniques for stream data. This paper discusses those issues and how they are addressed in the existing literature.
Towards a dynamic multi-policy dissemination control model
Authors: Li Zude , Ye Xiaojun
Published: May 2006

Dissemination control (
DCON
) is a security policy of controlling digital resource access before and after distribution. It is an extension of traditional access control within client-side domain, digital rights management by payment-free applications, and originator control on recipients' re-dissemination rights allowance. Different application domains may adopt dynamically different resource dissemination policies, but current
DCON
models cannot solve the multi-policy coexistence and compatibility problems. A dynamic multi-policy dissemination control model (
DMDCON
) is proposed to express the dynamic and multi-policy nature existing in reality, which are indispensable for well formed resource dissemination control application. The goal of this paper is to define and extend formally some basic concepts related with resource dissemination (such as dissemination policy, chain, tree, etc.) and further, propose a comprehensive
DMDCON
model to describe universal resource dissemination applications through specifying temporal dissemination features, restrictions, and policy revocation (cascade or non-cascade). Finally, we briefly discuss the importance of
DCON
within the usage control domain.