bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of bis(1,4,7-triazacyclononane)nickel(II) by the peroxodisulphate anion in aqueous and binary aqueous media
Authors: Haines Robert I. , Butt Lori , Park Murray K. , Wheeler Debbie
Published: May 2006

The kinetics of oxidation of bis(1,4,7-triazacyclononane)nickel(II), [Ni(tacn)2]2+, by the peroxodisulphate anion has been studied in water as a function of S2O82− concentration and temperature. The reaction is first order in both the nickel(II) complex and S2O82−, with a second-order rate constant of 1.13 mol dm−3 s−1 at 298 K. The activation energy for the reaction is 38.3 ± 1.8 kJ mol−1. The reaction was also studied at 298 K in a series of mixed aqueous solvents. Rate retardation relative to water was observed in all solvent mixtures studied. Correlation of the solvent effects on the kinetics of reaction has been made with the free energy of transfer of the initial state and the transition state.
The acyloin reaction using tethered diesters
Authors: Daynard Tim S. , Eby Paul S. , Hutchinson John H.
Published: May 2006

A study of the intramolecular acyloin condensation using diesters tethered by their alkoxide groups was undertaken. The goal was to provide a method for optimizing the yield of mixed acyloin products from the reaction of two different esters by utilizing tethered dissimilar esters as substrates. The results of the study show that the yield of the acyloin condensation is dependant on the tether length. Tethers of 8 and 14 carbons in length give yields comparable to those obtained from an intermolecular control reaction while shorter tethers give reduced yields of product. However, the use of mixed tethered diesters and a crossover experiment between two different tethered substrates provides a statistical distribution of products. These observations have been interpreted as resulting from a fragmentation of the initially formed radical anion intermediate that destroys the tethered nature of the substrate(s).
Coordination chemistry of thioether–pyridazine macrocycles. III. Synthetic, structural, and spectroscopic studies of Cu(II), Cu(II)Cu(I), and Cu(I) complexes of a hexathiapyridazinophane macrocyclic ligand
Authors: Chen Liqin , Thompson Laurence K. , Bridson John N.
Published: May 2006

The preparation and properties of the thioether–pyridazine macrocycle (L4; C16H20S6N4) containing two pyridazine subunits, and its Cu(II), Cu(II)Cu(I), and Cu(I) complexes are described. The ligand is characterized by 1H nuclear magnetic resonance and mass spectrometry, and the complexes by infrared, eleetronic spectra, and magnetism, and in some cases by X-ray crystallography. The complex [Cu2(L4)Cl4]x, (1) crystallized in the triclinic system, space group [Formula: see text] with a = 8.6204(8) Å, b = 9.850(1) Å, c = 8.348(1) Å, α = 111.46(1)°, β = 102.50(1)°, γ = 71.818(9)°, V = 622.6(1) Å3, and Z = 1 (R = 0.043, Rw = 0.042 for 1312 reflections). Two monodentate pyridazine rings in the same ligand bind to one trans square-planar copper centre (CuN2Cl2) with two sulfurs from each ligand binding to another trans square-planar copper centre (CuS2Cl2) to form a polynuclear chain. The complex [Cu(L4)Cl2] (3) crystallized in the triclinic system, space group [Formula: see text] with a = 11.001(1) Å, b = 12.888(2) Å, c = 8.704(1) Å, α = 102.89(1)°, β = 103.36(1)°,γ = 75.84(1)°, V = 1145.8(3) Å3 and Z = 2 (R = 0.056, Rw = 0.044 for 2059 reflections). A trans square-planar structure (CuN2Cl2) exists for 3 with monodentate pyridazines. [Cu(L4)(NO3)2] (4) crystallized in the orthorhombic system, space group P212121, with a = 15.148(2) Å, b = 15.562(3) Å, c = 11.064(1) Å, V = 2608.2(7) Å3 and Z = 4 (R = 0.039, Rw = 0.034 for 1864 reflections). Two monodentate pyridazine rings and two bidentate nitrates bind to a pseudo-octahedral copper(II) centre.
Synthèse et propriétés de nouveaux triazaphospholes: les 5-méthylthio 1,2,4,3-triazaphospholes
Authors: Rodi Youssef Kandri , Lopez Lucien , Malavaud Christian , Boisdon Marie-Thérèse , Fayet Jean-Pierre
Published: May 2006

The synthesis of new 1,2,4,3-triazaphospholes is described: a number of 5-methylthio 1,2,4,3-triazaphospholes, substituted in the 1, 2, or 4 position. The 1,5-disubstituted compound 6 is stable, whereas 2,5-disubstituted compounds 14 and 16 undergo an equilibrium with their tetrameric form, the cyclotetraphosphazanes [14]4 and [16]4. 5-Methylthio 4-alkyl 1,2,4,3-triazaphospholes exist only in the tetrameric forms [12]4 and [13]4. [12]4 can be depolymerized by complexation with a Lewis acid, giving the complexed triazaphosphole 12•BF3. The 15N NMR spectrum of compound 16, the N-silylated derivative of 15, allows us to confirm the position of the trimethylsilyl group. MNDO calculations are in good agreement with experimental results, such as the reaction of 1,4-diazadienes with triazaphospholes providing new tetracoordinated phosphorus spirocompounds 21–25.
Synthesis and preliminary in vitro biological activity of non-steroidal cytotoxic estrogens designed for the treatment of breast cancer
Authors: Bérubé G. , Wheeler P. , Ford C.H.J. , Gallant M. , Tsaltas Z.
Published: May 2006

The development of resistance to endocrine therapy as well as chemotherapy is presently a major problem in the treatment of breast cancer. To minimize this obstacle, new, more selective and potent, chemotherapeutic agents should be designed. One way to improve selectivity is to link a cytotoxic moiety to a molecule possessing an affinity to the estrogen receptor (ER). The latter would be used to direct the cytotoxic portion of the molecule towards the target cells. Our initial approach led us to the synthesis of new triphenylethylene–platinum(II) complexes 1a–c. The commercially available desoxyanisoin (10) was efficiently transformed in seven steps into the platinum(II) complexes 1a–c with an overall yield exceeding 30%. The biological activity of compounds 1a–c was evaluated in vitro on ER+ and ER− human breast tumor cell lines: MCF-7 and MDA-MD-231.
Structures, binding energies, and thermodynamic functions of NH4+, NH3•+, and their H2O complexes
Authors: Armstrong David A. , Rauk Arvi , Yu Dake
Published: May 2006

Ab initio calculations are performed for [Formula: see text] and [Formula: see text] complexes for n = 0–5. For n = 0 and 1, the geometries of the complexes are optimized at the HF/6-31 + G* and MP2/6-31 + G* levels, and the energies are evaluated at the G2 level. For n = 2–5, the geometry optimizations and frequency calculations are carried out at the HF/6-31 + G* level, and the MP2/6-31 + G* energies are calculated at the HF optimized geometries. Basis set superposition errors are corrected by the Boys–Bernardi scheme at the HF/6-31 + G* level. The gas phase thermodynamic properties [Formula: see text] are evaluated as functions of temperature using standard statistical methods. Based on the calculated binding energies and the thermodynamic functions, the incremental changes in enthalpies and free energies, ΔHn and ΔGn, for the gas phase equilibria (H2O)n−1 M+ + H2O → (H2O)nM+ for M+ = NH4+ and NH3•+, are evaluated in comparison with the experimental data for [Formula: see text] the present results suggest conformations for the hydrated complexes observed in the experiments. The total free energy change for filling the first hydration shell is significantly more negative for NH3•+ than for NH4+.
Metal pyrazolate polymers. Part 4. Synthesis, characterization, and magnetic properties of [Co(pz*)2]x complexes (where pz* = pyrazolate, 3-methylpyrazolate, and 4-substituted 3,5-dimethylpyrazolate)
Authors: Ehlert Martin K. , Storr Alan , Thompson Robert C.
Published: May 2006

The title compounds were prepared and characterized by X-ray powder diffraction, scanning electron microscopy, vibrational and electronic spectroscopy, and magnetic susceptibility measurements. Indirect evidence supports polymeric one-dimensional chain structures involving double pyrazolate bridges linking pseudo-tetrahedrally coordinated metal centres in all six compounds. The spectroscopic studies indicate a greater degree of distortion of the CoN4 chromophore from regular stereochemistry in the 4-substituted 3,5-dimethylpyrazolate complexes. The magnetic studies reveal anisotropy in the susceptibilities and the presence of significant antiferromagnetic exchange. Magnetic modelling employing both Ising and Heisenberg models suggests the exchange behaviour is probably of the Heisenberg type with zero-field splitting effects producing Ising-like exchange at low temperatures. The derived J values (~ −2 to −6 cm−1) have been used to qualitatively rank the magnitude of exchange as follows: 4-Hpz ≈ 3-Mepz [Formula: see text] 4-Medmpz ≈ 4-Cldmpz ≈ 4-Brdmpz ≈ 4-Hdmpz.
Assignment and vibrational analysis of the 600 nm absorption band in the phenoxyl radical and some of its derivatives
Authors: Johnston Linda J. , Mathivanan N. , Negri Fabrizia , Siebrand Willem , Zerbetto Francesco
Published: May 2006

An experimental and theoretical study is reported of the 600 nm band system of phenoxyl and several methoxy substituted phenoxyls. These radicals, generated in freon, show a diffuse band in this region with a vibrational structure that is incompletely resolved but consistent with the 500 cm−1 "progression" observed earlier for phenoxyl in the vapour and in a rigid matrix. The low intensity of this band is considerably enhanced by ortho-methoxy substitution. To establish its assignment and analyze its structure, semi-empirical and ab initio quantum chemical calculations have been performed. It is found that, on the basis of the ordering of the states and the magnitude of their transition moments, all calculations favour a ππ* (2B2 → 2A2) rather than the earlier proposed nπ* assignment for this band. Of the methods used, only the (ab initio) CASSCF method is found to be able to simulate the observed vibrational structure adequately. This simulation is based on optimized structures and vibrational force fields calculated for the 1B2 and 1A2 states of phenoxyl. It identifies the dominant mode of about 500 cm−1 as ν6a the characteristic deformation mode of phenyl rings, but shows that higher members of the "progression" receive large intensity contributions from higher frequency modes. The chosen assignment and the assignments of higher-energy transitions reported in the literature are compared with those for the better known benzyl radical. It is shown that some of the phenoxyl assignments reported in the literature contain errors.
Diode laser spectrum and rovibrational analysis of the ν6 band of vinyl fluoride
Authors: Giorgianni S. , Stoppa P. , Pedrali M. , Ghersetti S.
Published: May 2006

The vibration–rotation spectrum of CH2=CHF has been investigated in the ν6 band region around 1305 cm−1 at Doppler limited resolution using a tunable diode laser spectrometer. The measurements have been performed at low temperature (240 K) to decrease hot band interferences. This fundamental of symmetry species A′ gives rise to an a/b hybrid band, which was mainly composed of a-type transitions. Both J and K structures have been resolved in the QQK(J) subbranches and the rovibrational analysis in the P, Q, and R branches has led to the identification of more than 1000 lines with J ≤ 43 and Ka ≤ 14. The ν6 band is affected by first-order b-type and second-order a-type Coriolis resonances with the ν9 + νn combination, and the perturbation effect has been found stronger for the [Formula: see text]level. About 870 transitions free of major resonance contributions were fitted using Watson's A-reduction Hamiltonian in the Ir representation, and a set of effective rotational and quartic centrifugal distortion constants was determined for the ν6 = 1 state of CH2=CHF.
Absorption and magnetic circular dichroism spectra of nitrogen homologues of magnesium and zinc phthalocyanine
Authors: Ough Edward A. , Stillman Martin J. , Creber Katherine A.M.
Published: May 2006

Absorption and magnetic circular dichroism (MCD) spectra are reported for the metallophthalocyanine-N-isologs: magnesium-3,4-pyridinoporphrazine (MgPcN4(−2)), zinc-3,4-pyridinoporphyrazine (ZnPcN4(−2)), and zinc-3,4-pyridazinoporphyrazine (ZnPcN8(−2)). Band deconvolution calculations, which couple both the absorption and the MCD spectra, are reported for each complex. The presence of the peripherally fused pyridine rings in MgPN4(−2) and ZnPcN4(−2) reduces the molecular symmetry and splits the degenerate Q band into its x and y components with zero field splitting parameters (ΔQxy) of 224 and 279 cm−1, respectively. Band fitting results for ZnPcN8(−2) show that with the fused pyridazine rings the degeneracy in the 1Eg excited state is retained and the MCD envelope in the region of the Q00 transition can be described by an MCD A term. Comparison of the fitted band energies with the results reported for ZnPc(−2) (T. Nyokong, Z. Gasyna, and M.J. Stillman. Inorg. Chem. 26, 1087 (1987)) and MgPc(−2) (E.A. Ough, T. Nyokong, K.A.M. Creber, and M.J. Stillman. Inorg. Chem. 27, 2725 (1988)) shows that as the number of nitrogens substituted increases from 0 to 8, the Q band blue shifts from 671 nm in ZnPc(−2) to 664 nm in ZnPcN4(−2) (midpoint between the x and y components) to 654 nm in ZnPcN8(−2) and from 672 nm in MgPc(−2) to 666 nm in MgPcN4(−2) (midpoint). These results demonstrate that chemical modification (symmetric and asymmetric) of the peripherally fused benzene rings influences both the energy and the symmetry of the states that form the inner 18-π-electron system.
Electrostriction volumes of α-amino acids from density measurements in water and in aqueous HCl and NaOH solutions at 25 °C
Authors: Abbate M. , Castronuovo G. , Elia V. , Puzziello S.
Published: May 2006

The values of the limiting partial molar volumes, [Formula: see text], for some α-amino acids bearing alkyl chains, in pure water and in aqueous solutions of hydrochloric acid and sodium hydroxide, have been obtained from density measurements. From these data it is possible to determine the volume change, ΔVZW, due to the formation of the amphionic molecule from the corresponding neutral molecule.
Studies of femtosecond relaxation dynamics and fast ion–molecule reactions with low-energy electrons
Authors: Sanche L. , Michaud M. , Parenteau L.
Published: May 2006

Electron localization in solids and liquids is caused by time-dependent perturbations of the media surrounding the charge. The perturbations active on the femtosecond time scale include electronic polarization, as well as intra and intermolecular vibrational excitations, which contribute to the formation of a potential well around the charge. It is shown that information on these perturbations as well as on femtosecond reactions can be obtained by studying the formation of transient anions in dielectric solids and at their surfaces using high-resolution electron beam techniques at low energies (0–20 eV). The results obtained with Ar, N2, O2, and organic thin solid films condensed on a Pt substrate are described.
A theoretical study on the interaction of dinitrogen with rhodium
Authors: Fang T.H. , McKee M.L. , Worley S. D.
Published: May 2006

Ab initio theoretical computations have been performed for RhN2, Rh+N2, Rh(N2)2, and Rh+(N2)2 species. The computed vibrational frequencies and binding-energy trends are in qualitative accord with prior FTIR studies of N2 interacting with supported Rh films. Computations of the type described herein should be useful in aiding the assignment of observed infrared bands to specific surface species in future work.
Transition state spectroscopy with electrons as studied by 3D-trajectory calculations of the reaction He+ + Br2− → He+Br− + Br
Authors: Morgner Harald , Seiberle Hubert
Published: May 2006

We investigate electron emission from the interaction of metastable helium (ls2s; 23S) with Br2 molecules. A small part of the electron energy spectrum is due to direct Penning ionization, giving rise to spectral features familiar from photoionization of Br2. However, the dominant contribution to electron emission originates from a collision complex that can be described as ion pair state He+–Br2−. In analogy to a collision between the alkali atom Li(2s) and Br2, which leads via Li+–Br2− to salt formation LiBr + Br, this system can be viewed as undergoing a chemical reaction to He+Br− Br. Of course, no stable products He+Br− can be produced in this way since the large recombination energy of He+ causes autoionization to He + Br+ + e−. On the other hand, this situation is ideal if one wishes to study spectroscopically the transition state of a chemical reaction, in our case the development of the system from He(1s2s) + Br2 to (He+Br−) + Br. Neither of the separate reaction partners is able to emit electrons. During the encounter the lifetime against autoionization is so short that decay into the ionized channel cannot occur long after the chemical reaction is complete. Thus, electron emission is confined to the lifetime of the reaction complex. Accordingly, the electron energy spectrum contains information exclusively on the transition state with no blending by emission from educts or products as could be the case in optical spectroscopy. As a case study we carry out 3D-trajectory calculations on the collision complex He+–Br2−, monitoring the energy distribution of emitted electrons throughout the lifetime of the complex. We find that the electron energy spectrum varies strongly from the initial to the final stages of the ongoing chemical reaction.
Synthesis of enantiomeric β-amino ketones via 1,3-dipolar cycloaddition and chromatographic resolution
Authors: Louis Chantal , Mill Sibel , Mancuso Vincent , Hootelé Claude
Published: May 2006

The cycloaddition reactions of 3,4,5,6-tetrahydropyridine 1-oxide 1 with the homochiral alkynyl sulfoxides 6a–e proceed in high yield to afford, with low asymmetric induction, mixtures of diastereomeric isoxazolines that are readily separated by column chromatography. The resolved isoxazolines can be subsequently converted, by hydrogenolysis, to enantiomeric β-amino ketones.
Sulfur bonding in cyclic P2S2N4 systems: a density functional comparison of 1,1,5,5-tetramethylbicyclo[3.3.0]-1,5-diphospha-3,7-dithia-2,4,6,8-tetrazocine with the 1,1,3,5,5-pentamethyl-1,5-diphospha-3,7-dithia-2,4,6,8-tetrazocine anion
Authors: Jacobsen Heiko , Ziegler Tom , Chivers Tristram , Vollmerhaus Rainer
Published: May 2006

The electronic structure and the bonding of the title compounds have been investigated using density functional theory within the local density approximation, adding nonlocal corrections to exchange and correlation energy. The çross-ring sulfur-sulfur bond energy in 1,1,5,5-tetramethylbicyclo[3.3.0]-1,5-diphospha-3,7-dithia-2,4,6,8-tetrazocine was estimated to be about 133 kJ/mol. The HOMO of the 1,1,3,5,5-pentamethyl-1,5-diphospha-3,7-dithia-2,4,6,8-tetrazocine anion is mainly localized at the site of the unmethylated sulfur atom and is antibonding with respect to the sulfur—carbon bond of the methylated sulfur atom, which has a relatively weak estimated bond strength of 218 kJ/mol.
Computational conformational analysis of neural membrane lipids:development of force field parameters for phospholipids using semi-empirical molecular orbital calculations
Authors: Jin Albert Y. , Benesch Lisbeth A. , Weaver Donald F.
Published: May 2006

MM2 force field parameters for phospholipids were developed. These parameters — MM2(Lipid) — were employed in energy-minimization calculations (using crystal structures as starting conformations) on four phospholipids: dimyristoylphosphatidylglycerol, dilauroylphosphatidyl-N,N-dimethylamine, 1,2-dilauroyl-dl-phosphatidylethanolamine, and deoxylysophosphatidylcholine. After minimization, slight conformational changes were seen in the hydrocarbon chains, while greater change was seen at the head group. The diacylglycerol backbone of the energy-minimized structures exhibited conformations corresponding to experimentally observed conformations. The energy minimization of a randomly and significantly altered geometry of 1,2-dilauroyl-dl-phosphatidylethanolamine resulted in a head group conformation that closely agreed with ab initio theoretical calculations. The utility of AM1 in molecular mechanics parameterization was demonstrated.
MESOSCOPIC SPECTRA IN TWO-DIMENSIONAL DECAYING TURBULENCE
Authors: HÁZI GÁBOR
Published: May 2006

Two-dimensional decaying turbulence is simulated using a lattice Boltzmann model with the Bhatnagar–Gross–Krook collision operator. Auto-power spectra of the one-velocity particle distribution functions are presented. The relation between the spectrum of the kinetic energy and the spectra of the distribution functions is given. An interpretation of the non-equilibrium spectra as a measure of the dissipation in different scales is given. A peak in the spectrum of the resting particle distribution functions is observed exactly at the ultraviolet cutoff. It is shown that the peak can be associated with enhanced acoustic activity, which might be a numerical artifact or a consequence of the compressibility of the lattice Boltzmann fluid.
THE THEORETICAL RESEARCH ON I-V CURVE IN MULTI-QUANTUM WELLS OF SEMICONDUCTORS
Authors: YANG BIN , ZHANG JIE , ZHAO YONG-FANG , JING XIAO-GONG
Published: May 2006

The I-V curves in multi-quantum wells of different semiconductors are studied theoretically using the formalism of the transmission coefficient directly derived from Schrödinger equation. Al0.5Ga0.5As/GaAs double-barrier quantum well, Al0.29Ga0.71As/GaAs multi-quantum well, and AlSb/InAs double-barrier structure are calculated. The influences of well width, barrier width, temperature, Fermi energy on I-V characteristic curves are discussed in detail. Calculated results show that obvious negative differential resistance effects presented by our simulated I-V curves has a good agreement with previous experiments. Therefore, it can be a theoretical expectation to design experimentally high-quality semiconductor devices.
STATISTICAL PROPERTIES OF THE INTERBEAT INTERVAL CASCADE IN HUMAN HEARTS
Authors: GHASEMI FATEMEH , PEINKE J. , REZA RAHIMI TABAR M. , SAHIMI MUHAMMAD
Published: May 2006

Statistical properties of interbeat intervals cascade in human hearts are evaluated by considering the joint probability distribution P (Δx2, τ2; Δx1, τ1) for two interbeat increments Δx1and Δx2of different time scales τ1and τ2. We present evidence that the conditional probability distribution P (Δx2, τ2| Δx1, τ1) may be described by a Chapman–Kolmogorov equation. The corresponding Kramers–Moyal (KM) coefficients are evaluated. The analysis indicates that while the first and second KM coefficients take on well-defined and significant values, the higher-order coefficients in the KM expansion are small. As a result, the joint probability distributions of the increments in the interbeat intervals are described by a Fokker–Planck equation, with the first two KM coefficients acting as the drift and diffusion coefficients. The method provides a novel technique for distinguishing two classes of subjects, namely, healthy ones and those with congestive heart failure, in terms of the drift and diffusion coefficients which behave differently for two classes of the subjects.
CRITICAL COARSENING DYNAMICS OF SPIN S =1/2, 3/2 ANTIFERROMAGNETIC ISING MODEL ON TRIANGULAR LATTICE
Authors: CHUNG KWANGHOON , CHEON MOOKYUNG , CHANG IKSOO
Published: May 2006

The critical coarsening dynamics of the spin S =1/2, 3/2 antiferromagnetic Ising model on a triangular lattice is studied by the dynamic Monte Carlo simulation using a heat bath algorithm. The triangular antiferromagnetic Ising (TAI) model possesses an intrinsic geometrical frustration and a large degeneracy of ground state which may affect the equilibrium and non-equilibrium critical behaviors. The S =1/2 TAI has no phase transition at a finite temperature, but it was suggested that the S =3/2 TAI has the Kosterlitz–Thouless (KT)-type phase transition at a finite temperature. We employ a finite size scaling approach for the correlation function from the short-time dynamics of the S =1/2, 3/2 TAI to calculate the values of the static critical exponent η and the dynamic exponent z. For the S =1/2 TAI, our dynamic scaling analysis provides η =0.498±0.006 and z =2.278±0.020 at T =0, agreeing with the previous results. For the S =3/2 TAI, after identifying a KT-transition temperature TKT =0.51±0.01, we find the temperature-dependent η ranging from 0.301±0.008 at T =0.51 to 0.224±0.016 at T =0 along the KT-line whereas the value of z =2.20±0.06 is constant for T≤TKT. It is shown that the spin S =3/2 TAI model and the two-dimensional XY model, sharing the KT-type phase transition, exhibit similar static critical and coarsening dynamics behavior. For both the S =1/2, 3/2 TAI, the value of z (η) is compatible with (larger than) that of the Ising model at Tc and the XY model for T≤TKT in two-dimension. Our results imply that although the quasi-long-range order disappears with ηXY =0 in the two-dimensional XY model at T =0, the S =3/2 TAI still maintains it with η TAI =0.224 due to the effect of a frustration and a high degeneracy of ground state.
Logic circuits in the plane
Authors: Dewdney A. K.
Published: May 2006

There are, essentially, just 17 subsets of the 16 binary logical operations which are both (a) complete in the sense that any n-variable logical function can be expressed with them and (b) minimal, subject to (a). For each of these bases, it is shown how to construct, for any logical function F, a planar logical circuit with gates from that base alone which realizes F. This is done by constructing a planar crossover circuit for each minimal base. Minimality of the crossover circuits is discussed.
Loops in esterel
Authors: Tardieu Olivier , Simone Robert de
Published: May 2006

ESTEREL is a synchronous design language for the specification of reactive systems. Thanks to its compact formal semantics, code generation for ESTEREL is essentially provably correct. In practice, due to the many intricacies of an optimizing compiler, an actual proof would be in order. To begin with, we need a
precise
description of an
efficient
translation scheme, into some lower-level formalism. We tackle this issue on a specific part of the compilation process: the translation of loop constructs. First, because of
instantaneous
loops, programs may generate runtime errors, which cannot be tolerated for embedded systems, and have to be predicted and prevented at compile time. Second, because of
schizophrenia
, loops must be partly unfolded, making C code generation, as well as logic synthesis, nonlinear in general. Clever expansion strategies are required to minimize the unfolding. We first characterize these two difficulties w.r.t. the formal semantics of ESTEREL. We then derive very efficient,
correct-by-construction
algorithms to verify and transform loops at compile time, using static analysis and program rewriting techniques. With this aim in view, we extend the language with a new gotopause construct, which we use to encode loops. It behaves as a noninstantaneous jump instruction compatible with concurrency.
Improving WCET by applying a WC code-positioning optimization
Authors: Zhao Wankang , Whalley David , Healy Christopher , Mueller Frank
Published: May 2006

Applications in embedded systems often need to meet specified timing constraints. It is advantageous to not only calculate the worst-case execution time (WCET) of an application, but to also perform transformation, which reduce the WCET, since an application with a lower WCET will be less likely to violate its timing constraints. Some processors incur a pipeline delay whenever an instruction transfers control to a target that is not the next sequential instruction. Code-positioning optimizations attempt to reduce these delays by positioning the basic blocks to minimize the number of unconditional jumps and taken conditional branches that occur. Traditional code-positioning algorithms use profile data to find the frequently executed edges between basic blocks, then minimize the transfers of control along these edges to reduce the average case execution time (ACET). This paper introduces a WCET code-positioning optimization, driven by the worst-case (WC) path information from a timing analyzer, to reduce the WCET instead of ACET. This WCET optimization changes the layout of the code in memory to reduce the branch penalties along the WC paths. Unlike the frequency of edges in traditional profile-driven code positioning, the WC path may change after code-positioning decisions are made. Thus, WCET code positioning is inherently more challenging than ACET code positioning. The experimental results show that this optimization typically finds the optimal layout of the basic blocks with the minimal WCET. The results show over a 7% reduction in WCET is achieved after code positioning is performed.
Antipodal shock
Authors: Gotterbarn Don
Published: May 2006

Recently I heard a consultant in the South Pacific discuss a product for developing better software. Later investigation, unfortunately, showed that he had not discussed some of this product's obvious and potentially harmful defects. As I thought about this incident, I was struck by how much harm a lack of candor about a product's failings can do to unsuspecting users, and how inconsistent this failure to warn of potential problems was with professional ethics. I was also reminded of how self-defeating this sort of behavior can be.
Recognizing outstanding achievement
Authors: Popyack Jeffrey
Published: May 2006

Greetings! There has been much good news this year for Upsilon Pi Epsilon, and I am only too eager to report it. We distributed $44,950 in student awards directly this year, plus an additional $2700 in contributions to IEEE-CS and CCSC awards. This was enabled through a high level of membership and growth in chapters. It's amazing that last year was the first year we reached the $30,000 mark.
The evolution of programming courses
Authors: Yusof Azwina M. , Abdullah Rukaini
Published: May 2006

This paper describes the programming courses curriculum implemented by the Faculty of Computer Science and Information Technology (FCSIT), University of Malaya (UM) from the year 1995 to the present time. It explains the idea and logic behind the various programming courses offered at the faculty, the changes that the programming courses went through throughout the years, and also the future plans that FCSIT shall take with regards to the programming courses offered. It also discusses the students' performance in the core programming courses throughout the years; taking into account the feedback from companies that offered placements to students during their industrial training, and also their examination results.
Teaching computer applications to pre-school teachers through problem based learning approach
Authors: Lai Yiu-chi
Published: May 2006

Traditional computer training heavily depends on lectures, systematic demonstrations, and intensive hands-on tasks. However, most tasks are not stimulating and the skills learnt are not transferable to other situations. Certainly, these artificial learning activities cannot cater for individual needs. On the contrary, we observe that problem-based learning activities are quite suitable for teaching computer applications and always help students develop problem solving skills. This paper will discuss how we use this approach in teaching computer applications to non-computing students such as in-service pre-school teachers
An honors course on Alan M. Turing
Authors: Sorenson Jonathan P.
Published: May 2006

In this paper, I share my experiences teaching a non-majors, upper-division honors course on Alan M. Turing during the fall semester of 2003.
Motivation for extensible languages
Authors: Cheatham Thomas E.
Published: May 2006

Our discussion of the motivation for extensible languages rests on a basic premise, namely that there exist diverse programming language requirements which are becoming continually more diverse, and that it is of critical importance that each user in the spectrum of users be supplied with a language facility appropriate to his problem area. That is, there are, in fact, "scientific" problems, "data processing" problems," information retrieval" problems, "symbol manipulation" problems, "system programming" problems, and so on and each problem area has its particular and peculiar units of data, unit transactions, and preferred ways of writing. For example, the kinds of unit data and unit transactions include integers which are to be added, floating point numbers to be multiplied, "infinite" precision rational numbers to be divided, strings to be concatenated, records into which a field is to be inserted, files to be sorted, matrices to be inverted, equations to be simplified, sets to be unioned, and so on. A part of our premise is that it is not enough to have a language which is formally sufficient to host the particular data and unit transactions some user has in mind. Rather, it is of critical importance that the kinds of data and unit transactions which he wants to think of as primitive be available, effectively as primitives, in his language facility.
Alternatives to extensible languages
Authors: McIlroy M. D.
Published: May 2006

One of the most important things, it seems to me, in extending a language, is somehow to have the extension smooth with respect to the base. Smoothness is an aesthetic requirement, and I can't be too precise about it; but it is also a very strong requirement, and one that is very hard to live up to when you actually come down to try to write an extension. For example, in extending a language by introducing a new data type, one should allow that new data type to appear in all contexts of the language or as many as possible. Not only in expressions, which we seem to know how to do, but also in places like input/output. If the language has parametric data types (for example, declarable precisions) and has corresponding polymorphic operators defined over all of them, then extension should likewise have comparable capabilities for parameterization and polymorphism. This is not possible in Algol 68, for instance. (I will make frequent reference to Algol 68 in this talk for the reason that Algol 68 is defined and available, has been thought about very carefully, and therefore, is much easier to shoot at since it is a reasonably stable target.)
Panel on the concept of extensibility
Authors: Wegner Peter
Published: May 2006

This panel was composed of Cheatham, Christensen, McIlroy, and Nicholls. It came at the end of the day, and the discussion sometimes became rather specialized. Remarks of general interest follow.
A data structure model of the B6700 computer system
Authors: Organick E. I. , Cleary J. G.
Published: May 2006

The coupling of the B6700 hardware and the data structures characteristic of the computations on which it (the B6700) must operate is described from two points of view. The body of the paper gives a conceptual (Contour) model view and introduces hardware concepts of the B6700 with a minimum of detail; the supporting appendix, on the other hand, offers a thorough exposure to the hardware details, which are brought into focus via a global view of the B6700 operating system. A somewhat different terminology is employed in the appendix.Procedure calls, interrupts and tasking are often considered unrelated topics. B6700 data structures, however, provide for regular treatment of such mechanisms, suggesting how these mechanisms are closely related to one another.
A generalized assembly language using regular expressions
Authors: Ferguson W. A. , Lipovski G. J.
Published: May 2006

A generalized assembly language with possible applications in the areas of computer networks and software support packages is developed and discussed. The development of the language was guided by the principle that those operations in different assembly languages that are similar should have the same operation codes in this language.The major areas of difference between assembly languages are discussed and their resolution is presented. The areas of difference included different standard word lengths, a wide variety of special operations and different methods for branching. These problems were resolved, respectively, by length specification statements, creation of a superset of assembly languages and by using regular expressions as a means of branching.The use of regular expressions for branching has interesting effects on the structure of programs. The most notable effect is that it requires programs to be segmented into subprograms which consist entirely of sequentially processed instructions. This lends to easier documentation of assembly languages and to simpler programming of lookahead machines.
Data and storage structures for interactive graphics
Authors: van Dam Andries
Published: May 2006

This is a tutorial paper that shows the relationship between the data structure and the rest of an interactive graphics system. The distinction between data structures and storage structures is emphasized, as is the problem of data structure segmentation. The implementation of typical graphical applications is described, along with analysis of various trade-off decisions. Finally, some high-level data structure specification languages are discussed.
Associative tabular data structures
Authors: Wilkes M. V.
Published: May 2006

A data structure may be defined as an organized set of words (comprising more than one word) in memory for which an accessing procedure is provided. According to this definition, an ALGOL array is a data structure, as are the list structures used in LISP and the more elaborate structures of the same type in which blocks of words are linked by pointers.
Management issues of internet/web systems
Authors: Walter Zhiping , Scott George
Published: May 2006

Both rapid development and the ways they are used make managing Internet/Web systems different from managing traditional computer systems. Understanding the differences is important for developing and managing these systems.
Creating an adaptive network of hubs using Schelling's model
Authors: Singh Atul , Haahr Mads
Published: May 2006

Adjusting the overlay network topology in a peer-to-peer network to satisfy performance criteria.
Using bulletin boards in an educational setting
Authors: Dos Santos Brian L. , Wright Andrew L.
Published: May 2006

Examining the benefits associated with the use of threaded message postings systems.
Industrial software engineering
Authors: Lanman Jeremy T.
Published: May 2006

Software Engineering is an incredibly complex interdisciplinary subject that requires intense problem solving and communication skills. It is an art and a science which requires an open mind and adaptation to various domains. . . in essence, a software engineer must think outside of the box! I started my path in software engineering with the undergraduate computer science program at Butler University. There I learned the common fundamentals of computer science through studying algorithms and data structures, theory of computing, databases, and of course discrete mathematics. In addition to a traditional computer science program, a software engineering curriculum was introduced. Although, nearing graduation, I decided to take a couple of these software classes, and afterwards it was clear to me that my passion was to develop software systems. I decided to learn more and enrolled into a graduate program in software engineering at Embry-Riddle Aeronautical University. At ERAU, I had specific courses in each area of the software engineering development lifecycle, and collaborative corporate internships to apply my knowledge. My most profound internship was with the aerospace defense contractor, Lockheed Martin Corporation. It was there where I truly learned how to be an "Industrial Software Engineer".
Lonesome hacker blues
Authors: Wing Michael
Published: May 2006

I'm sitting in my office, daydreaming. My friends are out skiing this weekend, but I promised to come in and fix this custom control, so it can be tested for shipment next week. The product managers told me about it at 5 last night.
Classboxes
Authors: Lumpe Markus , Schneider Jean-Guy
Published: May 2006

The development of flexible and reusable abstractions for software composition has suffered from the inherent problem that reusability and extensibility are hampered by the dependence on position and arity of parameters. In order to address this issue, we have defined λ
F
, a substitution-free variant of the λ-calculus where names are replaced with first-class namespaces and parameter passing is modeled using explicit contexts. We have used λ
F
to define a model for classboxes, a dynamically typed module system for object-oriented languages that provides support for controlling both the visibility and composition of class extensions. This model not only illustrates the expressive power and flexibility of λ
F
as a suitable formal foundation for compositional abstractions, but also assists us in validating and extending the concept of classboxes in a language-neutral way.
Non-null references by default in the Java modeling language
Authors: Chalin Patrice , Rioux Frédéric
Published: May 2006

Based on our experiences and those of our peers, we hypothesized that in Java code, the majority of declarations that are of reference types are meant to be non-null. Unfortunately, the Java Modeling Language (JML), like most interface specification and object-oriented programming languages, assumes that such declarations are possibly-null by default. As a consequence, developers need to write specifications that are more verbose than necessary in order to accurately document their module interfaces. In practice, this results in module interfaces being left incompletely and inaccurately specified. In this paper we present the results of a study that confirms our hypothesis. Hence, we propose an adaptation to JML that preserves its language design goals and that allows developers to specify that declarations of reference types are to be interpreted as non-null by default. We explain how this default is safer and results in less writing on the part of specifiers than null-by-default. The paper also reports on an implementation of the proposal in some of the JML tools.
Specification and design of component-based coordination systems by integrating coordination patterns
Authors: Pérez-Serrano Pedro L. , Sánchez-Alonso Marisol
Published: May 2006

Rewriting logic has been revealed as a powerful tool to represent concurrent and state-transitions aspects in a declarative way, providing an adequate environment to specify and execute system representations. Moreover, rewriting logic is reflective, allowing for the definition of operations that transform, combine and manipulate specification modules by making use of the logic itself. Taking advantage of these capabilities, this paper presents a set of tools based on the rewriting logic language Maude to express the specifications of component-based systems with important coordination constraints, where coordination aspects are treated as separate components from functional ones. This representation allows for the testing of the system behavior from the early stages in the development process by executing the specifications. In addition, the development of basic coordination patterns using UML is presented to describe the coordination relationships between components in any system, providing a standard notation that complements the tools of the proposal.
Exploring the digital universe
Authors: Korman Ken
Published: May 2006

Can an alliance of scientists, academics, and non-profit organizations reclaim the Web from disinterested hackers and commercial interests?
Phishing mongers and posers
Authors: Berghel Hal
Published: May 2006

Unmasking deceptive schemes that range from clever to clumsy.
Exploring the computing literature with visualization and stepping stones & pathways
Authors: Fox Edward A. , Neves Fernando Das , Yu Xiaoyan , Shen Rao , Kim Seonho , Fan Weiguo
Published: May 2006

An alternative interpretation of queries involves splitting a query into parts that cover different but connected aspects of the information needed.
Open questions in the theory of semifeasible computation
Authors: Faliszewski Piotr , Hemaspaandra Lane
Published: May 2006

The study of semifeasible algorithms was initiated by Selman's work a quarter of century ago [Sel79,Sel81,Sel82]. Informally put, this research stream studies the power of those sets
L
for which there is a deterministic (or in some cases, the function may belong to one of various nondeterministic function classes) polynomial-time function
f
such that when at least one of
x
and
y
belongs to
L
, then
f(x, y) ∈ L ∩ {x, y}
. The intuition here is that it is saying: "Regarding membership in
L
, if you put a gun to my head and forced me to bet on one of
x
or
y
as belonging to
L
, my money would be on
f(x, y)
."In this article, we present a number of open problems from the theory of semifeasible algorithms. For each we present its background and review what partial results, if any, are known.
News 2.0
Authors: Stanik John
Published: May 2006

Symantec’s Semantics
People and Process
Authors: Champy James
Published: May 2006

When Mike Hammer and I published
Reengineering the Corporation
in 1992, we understood the impact that real business process change would have on people. I say "real" process change, because managers have used the term
reengineering
to describe any and all corporate change programs. One misguided executive told me that his company did not know how to do real reengineering; so it just downsized large departments and business units, and expected that the people who were left would figure out how to get their work done. Sadly, this is how some companies still practice process redesign: leaving people overworked and demoralized, while customers experience bad service and poor quality. I am reminded of poorly managed mergers and consolidations in the retail banking industry and what employees and customers have suffered.
Fifteen compilers in fifteen days
Authors: Frens Jeremy D. , Meneely Andrew
Published: May 2006

Traditional approaches to semester-long projects in compiler courses force students to implement the early stages of a compiler in depth; since many students fall behind, they have little opportunity to implement the back end. Consequently, students have a deep knowledge of early material and no knowledge of latter material. We propose an approach based on incremental development and test-driven development; this approach solves the emphasis problem, provides experience with useful tools, and allows for such a course to be taught in a three or four weeks.
An interdisciplinary undergraduate science informatics degree in a liberal arts context
Authors: Deremer Dorothy , Herbert Katherine G.
Published: May 2006

In this paper, we describe a new interdisciplinary B.S. degree in Science Informatics at Montclair State University, a multipurpose public institution that includes a substantial General Education component. Beginning in the freshmen year, the Science Informatics curriculum contains 16 semester hours of interdisciplinary science informatics courses including a freshmen experience, internships, a research component, ethics, and a concentration currently in bioinformatics, cheminformatics, or computer science as well as core science and mathematics courses.
Adding concentrations to the CS major
Authors: Blahnik James , McVey Bonnie , Pankratz David
Published: May 2006

In response to recent studies on enrollment trends and our own assessment results, we have significantly modified our Computer Science major to include not only a traditional major in computer science but also to include concentrations in Business Information Systems and Graphic Design and Implementation. As we are a small liberal arts college with three faculty members and a small budget, we have partnered with other disciplines on campus to provide options for our majors to apply concepts and principles of computer science to other areas. We present here our plans of study for the three concentrations, our rationale for making these additions, and favorable responses from students, faculty, and administration.