bluuebunny/crossref_metadata_2025 huggingface dataset:
A variational method for the calculation of dynamic polarizabilities and two-photon transition moments. The dressed molecule approach
Authors: Huo Winifred M.
Published: February 2003

The solution of the time-dependent Schrödinger equation of the molecule+radiation field system is analyzed. A quantized radiation field is used. The relationship between the oscillatory wave function and the dressed state wave function is established. The oscillatory wave function being the solution if the radiation field is turned on at t=0 and the dressed state being the stationary solution satisfying the boundary condition only if the field is present at t=−∞. In general, the oscillatory wave function can be expressed using a complete set of dressed states. However, in the presence of a nonresonant radiation field, the system is well represented by a single dressed state. Molecular properties such as dynamic polarizabilities and two-photon transition moments can be deduced from the dressed state wave function instead of the oscillatory wave function as in previous methods. Because of its stationary character, the dressed state is more amenable to approximate calculations. A CI method is developed for this purpose. The CI matrix is simple in form and can be readily constructed using existing computer codes. The present method can also be adapted to calculate other optical properties.
A proposed antiferroelectric structure for proton ordered ice Ih
Authors: Davidson Ernest R. , Morokuma Keiji
Published: February 2003

A new antiferroelectric structure for proton ordered ice Ih is proposed which has lower energy than the currently popular ferroelectric model. This new structure has eight molecules per unit cell and Pna21 space group symmetry. The nearest neighbor interactions are optimum consistent with the oxygen P63/mmc lattice.
Calculation of semiclassical eigenvalues with one arbitrary trajectory
Authors: Miller William H.
Published: February 2003

A method is described for determining semiclassical eigenvalues for systems with many degrees of freedom that requires the calculation of only one trajectory per eigenvalue. Furthermore, this trajectory is ‘‘arbitrary’’, i.e., one must not carry out an iterative root-search procedure to find it. The method is a derivative of earlier approaches developed by Sorbie and Handy and by De Leon and Heller. It is also shown that within the local linearization approximation used by De Leon and Heller, the Sorbie–Handy method is exact (semiclassically).
A study of the CH2NO2 radical using a multiconfiguration self-consistent field approach
Authors: McKee Michael L.
Published: February 2003

The CH2NO2 radical is used as a model for the first likely reactive species in the decomposition of high energy materials such as TNT (1,3,5-trinitrotoluene) or HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine). Semiempirical, single configurational, and eventually multiconfigurational ab initio calculations were carried out to determine the ground electronic state and the electronic distribution. At the highest level, the MCSCF results indicate that the ground state is a planar 2A″ state which results from a second-order Jahn–Teller interaction of the planar 2B1 and 2A2 states that cross at a common C2v geometry and lead to a favorable asymmetric distortion from C2v symmetry to a lower Cs symmetry. A similar distortion was observed by Davidson and co-workers for the 2B1 and 2A2 excited states of NO2. The planar 2A″ state is 14.6 kcal/mol more stable than the planar 2B1 state and 19.9 kcal/mol more stable than the planar 2A2 state. The staggered 2B2 state which is the C2v ground state is 6.8 kcal/mol higher than 2A″ state.
The asymptotic dispersion of particles in N-layer systems
Authors: Van den Broeck C. , Mazo R. M.
Published: February 2003

A fluid flows parallel to the strata of an N-layer stratified system. Particles suspended in the flow are carried along, and additionally make random jumps to neighboring strata where the flow velocity is different. The distribution of particles in the flow direction is shown to be asymptotically (for long times) Gaussian. The dispersion is calculated exactly in the long time limit for arbitrary N, jump rates, and velocity field. The results are applied to a variety of phenomena, e.g., chromatography, Taylor diffusion, random walk residence times, adsorbing boundaries, and porous stratified media.
Nonergodicity in path integral molecular dynamics
Authors: Hall Randall W. , Berne B. J.
Published: February 2003

Molecular dynamics can be used to evaluate the path integral representation of the density matrix. Implicit in this method is the assumption that the dynamical system is ergodic. It is shown here that this is not the case in many systems that are of interest. For example water or liquid neon can not be simulated by this method. Monte Carlo methods do not suffer from this weakness.
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o description of large amplitude motions in solid N2. II. Librons in the β-phase and the α–β phase transition
Authors: van der Avoird Ad , Briels W. J. , Jansen A. P. J.
Published: February 2003

Using an ab initio pair potential, we have performed mean field and time-dependent Hartree calculations for the reorientational motions in disordered β nitrogen, in a basis of tesseral harmonics. The results show that orientationally localized librational solutions with neighboring molecules rotated over 180° around the crystal c axis are energetically more favorable than (nearly) free precession of the molecules. The experimental symmetry can be obtained by allowing rapid jumps between six equivalent localized states; such a jump model predicts the α–β phase transition at the correct temperature.
Classical trajectory study of adsorption and surface diffusion of Si on Si(100)
Authors: NoorBatcha I. , Raff L. M. , Thompson Donald L.
Published: February 2003

Adsorption and surface diffusion of silicon on the Si(100) plane have been investigated by classical trajectory methods using a realistic potential-energy surface. The calculated sticking probability for adsorption is 0.965 at 1500 K and is independent of temperature. The diffusion coefficient for Si on Si(100) is evaluated by modeling the diffusion process as the jumping of the adatom from one adsorption site to another. The diffusion coefficient calculated by this approach is given by D=(6.35±1.44)×10−4 exp(−3.63±0.47 kcal mol−1/RT) cm2 s−1. This value is found to be in good agreement with the diffusion coefficients calculated from the long-time behavior of the mean square displacement and from the integrated velocity autocorrelation function. The activation energy for diffusion is found to be less than the reported experimental value of 4.6 kcal mol−1 for the diffusion of Si on Si(111). The diffusion of Si on Si(100) is found to be directional, occurring only along channels described by the intersection of the (022̄) planes with the (110) plane. Transverse diffusion in directions described by the intersection of the (022) planes with the (100) plane is a much higher-energy process.
Conformational substates and barrier height distributions in ligand binding to heme proteins
Authors: Young R. D. , Bowne S. F.
Published: February 2003

A model of the enthalpy barrier between the heme pocket and heme iron is proposed for the recombination of small ligands to heme proteins after flash photolysis. The model is based on the concept of conformational substates as developed by Frauenfelder and co-workers. The model assumes a temperature-independent energy surface which depends on a reaction coordinate (ligand–iron distance) and a protein coordinate x. The protein coordinate parameterizes the conformational substates of the protein. The conformational energy of the substates is given by an anharmonic power law Vν(x)∝x1/ν, x≥0 for the liganded (A) , unliganded (B), and transition states. The barrier height for the B→A transition depends on the protein coordinate because the conformational energy has different proportionality coefficients in state B and the transition state. The distribution of barrier heights at low temperature follows because the protein coordinate satisfies a Boltzmann distribution which depends on the appropriate conformational energy. The Boltzmann distribution at low temperature is determined by the temperature at which the conformational substates are frozen. The resulting temperature-independent barrier-height distribution is a gamma distribution which yields good fits to the low temperature rebinding kinetics. Above the freezing temperature, the gamma distribution is temperature-dependent owingto protein fluctuations among the conformational substates. If the conformational energies of states A and B are the same, the temperature-dependent distribution is determined by the low-temperature kinetics. The average rate coefficient for B→A transition at physiological temperature agrees with the same rate coefficient used by Frauenfelder and co-workers to within a factor of 3.
Direct measurements of formation rates of allylic radicals from vibrationally excited ethylene derivatives
Authors: Nakashima Nobuaki , Shimo Nobuo , Ikeda Noriaki , Yoshihara Keitaro
Published: February 2003

Formation rates of allylic radicals have been observed directly for the first time to be 4×107 s−1 by photodissociation of 2,3,3-trimethyl-1-butene and to be 2×107 s−1 from 2,3-dimethyl-2-pentene at low pressure by excitation with an ArF laser.
Bifurcating families of periodic solutions for the generalized Henon–Heiles potential
Authors: Thiele Everett , Stone J.
Published: February 2003

Generalizations of the Floquet method are developed for investigating periodic solutions in classical systems of coupled oscillators. A new iterative procedure which converges on exact initial conditions for periodic solutions is applied to the generalized Henon–Heiles potential. A stability map for the symmetric mode is generated and families of periodic solutions bifurcating from the symmetric mode at stability/instability boundaries are investigated using the iterative procedure.
Monte Carlo simulation of electron thermalization in gases. IV. Subexcitation electrons in hard-sphere and Maxwell model rare gases
Authors: Koura Katsuhisa
Published: February 2003

The Monte Carlo simulation (MCS) of the thermalization of subexcitation electrons in rare gases is performed for both the hard-sphere and Maxwell model gases. The MCS result for the mass ratio m/M≲0.01 is found to be in agreement within the statistical error with the rigorous solution of the Fokker–Planck equation; therefore the upper limit value of m/M=0.01 is sufficient for the MCS to be performed within a reasonable computation time.
Chirality and hydrogen bonding in molecular crystals for phase-matched second-harmonic generation: N-(4-nitrophenyl)-(L)-prolinol (NPP)
Authors: Zyss J. , Nicoud J. F. , Coquillay M.
Published: February 2003

The higher second-harmonic efficiency, in powder, of a new organic molecular crystal N-(4-nitrophenyl)-(L)-prolinol (NPP) is reported. Electronic polarizability of NPP molecules relates to that of other para-nitroaniline-like structures such as that of previously reported N-(2,4-dinitrophenyl) methyl alaninate (MAP), and the increase in crystalline nonlinear efficiency by one order of magnitude above the latter is ascribed to an ‘‘optimized’’ crystalline structure rather than to minor changes of the molecular hyperpolarizability. The simultaneous chiral and hydrogen-bonding character of the prolinol electron-donating group leads to a quasioptimal angle, with respect to quadratic phase-matched nonlinear interactions, between the molecular transition dipole moments and the twofold axis of the monoclinic P21 crystal structure. Based on a simple oriented gas description of the quasiplanar structure of the crystal, two possible mutually exclusive second-harmonic phase-matched configurations are evidenced and shown to promote the optimized nonlinear tensor coefficient.
MS-Xα calculations on the ligand-field spectrum and the 3p x-ray photoelectron spectrum of the NiCl−24 ion
Authors: Hayes Robert G.
Published: February 2003

We have performed a number of MS-Xα calculations on various spin orbital configurations of NiCl−24. We have used the results to calculate the ligand field spectrum of the ion and also its 3p XPS spectrum. The calculated ligand field spectrum is in fair agreement with observations. The observed spectrum extends over a greater energy range than do the calculations but the ordering of levels is essentially correct. The calculations on the XPS spectrum suggest strongly that part of the observed spectrum comes from satellite features and that multiplet splitting of ligand-field states cannot represent the spectrum.
Vibrational frequencies for the classical and nonclassical forms of protonated acetylene–C2H+3
Authors: Raine Gwendolyn P. , Schaefer Henry F.
Published: February 2003

The equilibrium geometries and harmonic vibrational frequencies of the classical and nonclassical structures of H3C+2 have been predicted using ab initio molecular electronic structure theory. Self-consistent-field (SCF) methods were used with a double zeta plus polarization (DZ+P) basis set. For the complete set of normal modes of vibration for both structures, the infrared intensities have been predicted. In addition, for a subset of these harmonic frequencies, actual vibrational fundamentals have been estimated using scaling techniques.
Nitroxide radical induced solvent proton relaxation: Measurement of localized translational diffusion
Authors: Polnaszek C. F. , Bryant R. G.
Published: February 2003

The field dependence of solvent proton nuclear magnetic relaxation is shown to provide a test of whether the relaxation is dominated by translational or rotational motions. When a paramagnetic center is present with a sufficiently long electron relaxation time, the dominance of translational contributions to the correlation time for the electron–nucleus interaction permits characterization of the translational diffusion of the solvent in local environment of the paramagnetic center. For bovine serum albumin covalently labeled with nitroxide radicals the approach yields a value of (3±1)×10−6 cm2 s−1 for water within the first 10 Å of the protein surface. The method is general for the measurement of localized solvent diffusion coefficients.
Computer experiments on aqueous solutions. VI. Potential energy function for tert-butyl alcohol dimer and molecular dynamics calculation of 3 mol % aqueous solution of tert-butyl alcohol
Authors: Tanaka Hideki , Nakanishi Koichiro , Touhara Hidekazu
Published: February 2003

Molecular dynamics (MD) calculation has been carried out for a dilute aqueous solution of tert-butyl alcohol (TBA) at 298.15 K and with experimental density value by the use of constant temperature technique developed previously. The total number of molecule is 216, seven of which are TBA. The mole fraction of TBA is thus 0.032. For water–water and TBA–water interactions, the MCY (Matsuoka–Clementi–Yoshimine) potential and previously reported potential determined by MO calculation are used. A new potential for TBA–TBA is determined by ab initio LCAO SCF calculations for more than 500 different configurations with an STO-3G basis set and subsequent multiparameter fitting of the MO data to a 12-6-3-1 type potential energy function. The MD calculation is extended up to 84 000 time steps (26 ps) and final 60 000 time steps are used to calculate both static and dynamic properties of the system. Both hydrophobic hydration and interaction due to TBA molecules are proved to be stronger than those of methanol studied previously. Structural promotion of water is clearly observed in radial distribution functions and trajectories of each molecule. The configuration and trajectory of all the molecules in solution indicate clearly the association of TBA molecules. It is also found from pair interaction distribution functions that no hydrogen bonding interaction occurs between two TBA molecules. The self-diffusion coefficient of water in the solution is appreciably smaller than that in pure water.
Pair correlations at an electrified interface
Authors: Giaquinta P. V. , Parrinello M.
Published: February 2003

A study is made of a spherical average of the pair correlation functions in a fluid of charged hard spheres in the presence of a uniformly charged flat wall. Exact expressions for the asymptotic behavior of these functions are obtained. Approximate integral equations are derived and analytically solved by assuming a mean spherical model type of closure. The resulting expressions are explicit functionals of the local density profile. The Coulomb energy density is also explicitly evaluated.
Hydroxyl impurity effects in YAG (Y3Al5O12)
Authors: Devor D. P. , Pastor R. C. , DeShazer L. G.
Published: February 2003

Evidence is reported of 1020 cm−3 hydroxyl impurity density affecting crystal fields and color center formations in YAG and Nd:YAG. Also reported is a high-temperature reactive atmosphere process to control H bonding and to bleach coloration. Absorption by O–H⋅⋅⋅O and O–D⋅⋅⋅O transitions in the 3–4 μm spectral region was observed in different crystals. Two independent O–H⋅⋅⋅O lines, both with weak satellites, were detected at 3340 and 3374 cm−1. H-bonding sites were assigned by (i) frequency dependence on O2−–O2− distance and (ii) Nd:YAG nonequivalent crystal field effects seen in Nd3+ fluorescence. H+ concentrations 1020 cm−3 were derived from these results. Bonding site relative densities also varied with the different crystals observed. Reactive atmosphere processing (RAP) could cause H+ or D+ to be coordinated into or out of crystals, concomitant with color center bleaching. Color center formations were dissociated by surface reaction with I2 + H2O or I2 + O2 reactive atmosphere at temperatures in the range of 1350–1880 °C. The RAP effect was to produce bulk crystal electronic transfers related to hydrogen in the crystal metal–oxide system. However, photoinduced coloration was again possible. Intense coloration also resulted from vacuum heating, causing an H2O effluent. The evidence indicated YAG and Nd:YAG contained a high concentration of largely mobile H+ affecting O− -center coloration and influencing crystal fields by bound-small polaron formations.
Second harmonic generation at thin film silver electrodes via surface polaritons
Authors: Corn Robert M. , Romagnoli Marco , Levenson Marc D. , Philpott Michael R.
Published: February 2003

The generation of second harmonic light from a silver–mica capacitor and from thin film silver electrodes provides information on the charge and composition of the metal–dielectric interface. The second harmonic light is created by the injection of surface polaritons onto the electrode surface via prism coupling techniques. A theory relating the second harmonic intensity to the square of the charge on the electrode successfully predicts the dependence of the SHG on applied voltage or potential and the time dependence of the SHG in response to a potential step. The time dependent second harmonic signal is also used to monitor the growth of a lead monolayer onto the silver electrode in the region of underpotential deposition.
Optical study of poly-β, β′-dimethylpyrrole perchlorate: Evidence for bipolarons
Authors: Yakushi K. , Lauchlan L. J. , Street G. B. , Brédas J. L.
Published: February 2003

The optical conductivity spectra of the conducting and insulating forms of the poly-β, β′-dimethylpyrrole perchlorate (PβDMP–ClO4) films have been determined by the Kramers–Kronig transformation of the transmittance spectra from 0.074 to 6.25 eV. The optical spectrum of the conducting form is not consistent with Drude-like free carriers. Absorption spectra have been measured on PβDMP-ClO4 films with various concentrations of perchlorate anions obtained using an electrochemical technique. Compared to those of polypyrrole perchlorate, the absorption spectra of PβDMP–ClO4 show some significant differences, especially in the low energy region of the almost neutral forms. Evolution of the PβDMP–ClO4 absorption spectra as a function of doping level is inconsistent with a rigid band model and is interpreted in terms of bipolaron formation on the chains.
The interpretation of very low frequency Raman scattering from roughened silver electrodes: Clusters, cavities, or complexes?
Authors: Corn Robert M. , Philpott Michael R.
Published: February 2003

The potential dependence of the broad low frequency (5–8 cm−1) Raman scattering features from roughened silver electrodes and their sensitivity to the chemical composition of the supporting electrolyte are presented. We find that the electromagnetic enhancement theories which relate these Raman bands to the vibrations of the silver surface structures are unable to account for all of the data; electronic coupling to the stabilizing adsorbates requires that some of the charge transfer concepts of the adatom complex theories be included in the model.
C2N2 photodissociation at 1576 Å. I. CN(A 2Π) radiative lifetimes, nascent vibrational distribution, and C2N2 quenching
Authors: Taherian M. R. , Slanger T. G.
Published: February 2003

Photodissociation of C2N2 at the 1576 Å F2 laser line generates CN(A 2Π) up to the thermodynamic limit of v=5, with a bimodal vibrational distribution peaking at v=0 and v=2. Radiative lifetimes for the six observed levels have been obtained by extrapolating time decays to zero pressure, and the data show rapidly decreasing lifetimes with increasing v, in accord with recent theoretical predictions, and contrary to previous experimental determinations. The range of lifetimes observed is 4.3–8.5 μs. Quenching of these levels by the parent molecule shows a factor of 12 increase in rate coefficient in going from v=0 to v=5, correlated to the energy gap between the A 2Π state and the closest lower X 2Σ+ level, suggesting that the quenching mechanism is one involving cross relaxation between CN(A) and CN(X).
Semiclassical treatment of rotational excitation of NH3 colliding with 4He
Authors: Billing Gert Due , Poulsen Lise Lotte
Published: February 2003

The semiclassical (classical path) theory is formulated for an atom colliding with a symmetric top molecule. Cross sections for rotational excitation of NH3 colliding with 4He are calculated and compared with numbers obtained from exact quantum, coupled states, and other semiclassical calculations. The validity of the semiclassical coupled states approximation is investigated.
The use of exponential perturbation theory in the determination of scattering wave functions
Authors: Eno Larry
Published: February 2003

Exponential perturbation theory (EPT) is used as the basis for generating multichannel scattering wave functions. The wave functions are constructed so that at each order of perturbation theory, the corresponding order of EPT scattering matrix is generated asymptotically. The relationship between this analysis and earlier work is examined. The usefulness of the present approach is illustrated by application to collinear single channel scattering. Perturbative solutions are generated for the test problem by separating a zeroth order interaction potential from the complete interactions. Finally, these developments are briefly reviewed and further applications discussed.
Detection of the NH2O radical by far infrared LMR
Authors: Davies P. B. , Dransfeld P. , Temps F. , Wagner H. Gg.
Published: February 2003

New far infrared laser magnetic resonance spectra have been detected at 11 laser wavelengths using the reaction of fluorine atoms with NH2OH as source. Weaker but identical spectra were found in the reaction NH2+O3. On the basis of their chemical behavior and hyperfine structure they are assigned to the NH2O radical. Rotational transitions calculated using a planar symmetric structure from ab initio calculations are in good agreement with the frequencies of the observed LMR spectra.
Photoexcitation of NO at 1576 Å
Authors: Taherian M. R. , Slanger T. G.
Published: February 2003

An accidental resonance between the 1576.299 Å line of the F2 laser and the Q11 (7.5) line in the B′ 2Δ−X2 Π 3–0 band of NO provides a means of generating intense emission in three NO transitions—B′ 2Δ–X 2Π, and B′ 2Δ–B 2Π, and B 2Π–X 2Π. By accessing a particular B′ 2Δ level in this manner, state-to-state kinetics involving a variety of high electronic states of NO can be easily studied. These include the H′ E, D, C, B, and A states. The specific nature of the process makes it possible to use the emission as an unambiguous measure of laser power and also as a technique for detecting small amounts of NO. Observations can be made at wavelengths from the vacuum UV to the visible, and intercalibration between UV and visible bands result in a branching ratio of 155 for emission from NO(B′ 2Δ) to the X 2Π and B 2Π states.
3motif: visualizing conserved protein sequence
motifs in the protein structure database
Authors: Bennett Steven P. , Nevill-Manning Craig G. , Brutlag Douglas L.
Published: February 2003

Summary: 3motif is a web application that visually maps conserved sequence motifs onto three-dimensional protein structures in the Protein Data Bank (PDB; Berman et al., Nucleic Acids Res., 28, 235–242, 2000). Important properties of motifs such as conservation strength and solvent accessible surface area at each position are visually represented on the structure using a variety of color shading schemes. Users can manipulate the displayed motifs using the freely available Chime plugin.

Availability: http://motif.stanford.edu/3motif/

Contact: brutlag@stanford.edu

Supplementary information: http://motif.stanford.edu/3motif/supplementary/

* To whom correspondence should be addressed.

† Present adress: Google, Inc., 2400 Bayshore Parkway, Mountain View, CA~94043, USA
IS: a web-site for intron statistics
Authors: Barta Endre , Kaján László , Pongor Sándor
Published: February 2003

Summary: A web server has been established for the statistical evaluation of introns in various taxonomic groups and the comparison of taxonomic groups in terms of intron type, length, base composition, etc. The options include the graphic analysis of splice sites and a probability test for exon-shuffling within the selected group.

Availability: introns.abc.hu, http://www.icgeb.trieste.it/introns

Contact: barta@abc.hukajan@icgeb.trieste.itpongor@icgeb.trieste.it

* To whom correspondence should be addressed.
The European Bioinformatics Institute web site: a new view
Authors: Lopez Rodrigo , Robinson Stephen , Kibria Asif , Harte Nicola , Patel Gulam , Harper Rob , Quevillon Emmanuel , Silventoinen Ville , Kallio Kimmo , Jokinen Petteri
Published: February 2003

Summary: The European Bioinformatics Institute (EBI), and outstation of the European Molecular Biology laboratory, has revamped its web site for the second time since 1997 in order to address increased user demand as well as establishing better uniformity and easier accessibility for the ever growing number of users and services it offers to the community. A GRID-like hardware infrastructure has been put in place to provide round the clock services in a redundant and reliable fashion.

Availability: http://www.ebi.ac.uk/

Contact: rls@ebi.ac.uk

* To whom correspondence should be addressed.

† EBI’s Systems group.
Subnetwork hierarchies of biochemical pathways
Authors: Holme Petter , Huss Mikael , Jeong Hawoong
Published: February 2003

Motivation: The vastness and complexity of the biochemical networks that have been mapped out by modern genomics calls for decomposition into subnetworks. Such networks can have inherent non-local features that require the global structure to be taken into account in the decomposition procedure. Furthermore, basic questions such as to what extent the network (graph theoretically) can be said to be built by distinct subnetworks are little studied.

Results: We present a method to decompose biochemical networks into subnetworks based on the global geometry of the network. This method enables us to analyze the full hierarchical organization of biochemical networks and is applied to 43 organisms from the WIT database. Two types of biochemical networks are considered: metabolic networks and whole-cellular networks (also including for example information processes). Conceptual and quantitative ways of describing the hierarchical ordering are discussed. The general picture of the metabolic networks arising from our study is that of a few core-clusters centred around the most highly connected substances enclosed by other substances in outer shells, and a few other well-defined subnetworks.

Availability: An implementation of our algorithm and other programs for analyzing the data is available from http://www.tp.umu.se/forskning/networks/meta/

Supplementary information: Supplementary material is available at http://www.tp.umu.se/forskning/networks/meta/

Contact: holme@tp.umu.sehussm@kth.sehjeong@nd.edu

* To whom correspondence should be addressed.
Ultrathin SiO2 on Si.  I. Quantifying and removing carbonaceous contamination
Authors: Seah M. P. , Spencer S. J.
Published: February 2003

An analysis is made of the amount of carbonaceous contamination remaining on silicon wafers with a thin oxide overlayer. Wafers are either left “as-received” or deliberately contaminated with a thumbprint and then subjected to one of 42 different cleaning procedures with the remaining carbon level monitored by x-ray photoelectron spectroscopy (XPS). The XPS measurement of the carbon level in terms of a thickness in nm, using the traditional equation, depends sensitively on the assumed form of the carbon; the thickness for an average polymerlike contamination being computed as 1.67 times the thickness for a glassy carbon layer for a given spectrum. However, if the measurement is defined in terms of carbon atoms/m2, this sensitivity is removed. Alternatively, if absolute measurements are used, the sensitivity in terms of the thickness in nm is also reduced and the data are consistent with the results for the average polymer. Of the cleaning methods, ultraviolet radiation with ozone is best but this affects the substrate by increasing the oxide thickness by approximately 0.2 nm and so is not recommended for work where the oxide thickness should remain unaltered. The best group of methods that leave the oxide unaltered are those involving an overnight soak in a high purity solvent such as isopropyl alcohol (IPA), chloroform, or heptane, followed by an ultrasonic agitation for 1 min in fresh solvent, a rinse in further fresh solvent, and drying in an argon jet. This reduces the final carbon level to thicknesses, in terms of an average polymer, of around 0.16 nm, with IPA giving the best result for the selected solvents. This level may be further reduced, by heating on a hot plate in air to 325 °C for 15 min, to a final thickness of 0.12 nm. Cleaned samples that are then stored in glass or Fluoroware polypropylene containers retain much of their cleanness and the carbonaceous contamination does not exceed 0.26 nm during the 100 days of the study.
Initial deposition of calcium phosphate ceramic on polystyrene and polytetrafluoroethylene by rf magnetron sputtering deposition
Authors: Feddes B. , Wolke J. G. C. , Jansen J. A. , Vredenberg A. M.
Published: February 2003

Calcium phosphate (CaP) coatings can be applied to improve the biological performance of polymeric medical implants. A strong interfacial bond between ceramic and polymer is required for clinical applications. Because the chemical structure of an interface plays an important role in the adhesion of a coating, we studied the formation of the interface between CaP and polystyrene (PS) and polytetrafluoroethylene (PTFE). The coating was deposited in a radio frequency (rf) magnetron sputtering deposition system. Prior to the deposition, some samples received an oxygen plasma pretreatment. We found that the two substrates show a strongly different reactivity towards CaP. On PS a phosphorus and oxygen enrichment is present at the interface. This is understood from POx complexes that are able to bind to the PS. The effects of the plasma pretreatment are overruled by the deposition process itself. On PTFE, a calcium enrichment and an absence of phosphorus is found at the interface. The former is the result of CaF2-like material being formed at the interface. The latter may be the result of phosphorus reacting with escaping fluorine to a PF3 molecule, which than escapes from the material as a gas molecule. We found that the final structure of the interface is mostly controlled by the bombardment of energetic particles escaping either from the plasma or from the sputtering target. The work described here can be used to understand and improve the adhesion of CaP coatings deposited on medical substrates.
Plasma-enhanced chemical vapor deposition of low-kdielectric films using methylsilane, dimethylsilane, and trimethylsilane precursors
Authors: Wu Qingguo , Gleason Karen K.
Published: February 2003

Pulsed plasma-enhanced chemical vapor deposition from mixtures containing methylsilane (1MS), dimethylsilane (2MS), or trimethylsilane (3MS), systematically varied the methyl content in the resulting low dielectric constant films. The refractive index was found to depend strongly on methyl content but was relatively independent of the precursor used. However, the precursor used strongly impacted the local bonding structure of these organosilicate glass materials as revealed by Si29 nuclear magnetic resonance. The variations in local bonding structure did impact film hardness. No significant changes were found for the concentrations of CH3 and Si–CH3 after annealing and relative humidity treatment for all Si:O:C:H films grown from 1MS, 2MS and 3MS, which suggests that Si:O:C:H films have high thermal stability and very low moisture uptake. The dielectric constants of 2.4–2.6 were observed after annealing.
Structure and mechanical properties of tungsten carbide films deposited by off-plane double bend filtered cathodic vacuum arc
Authors: Cheng Y. H. , Tay B. K.
Published: February 2003

High quality nanocrystalline tungsten carbide films were deposited by a filtered cathodic vacuum arc technique at room temperatures. X-ray diffraction and atomic force microscopy were used to characterize the crystalline structure and surface morphology of the films. Substrate bending methods and nanoindenter were used to measure internal stress, hardness, and Young’s modulus of the films. The film structure evolves from a single hexagonal α-W2C phase to a mixture phase, which is composed of a hexagonal α-W2C, a cubic WC1−x, and a cubic W phase, as the substrate bias, which is always negative, is increased to 200 V. As the substrate bias is further increased, the film structure changes gradually to a single α-W2C phase again. The variation trends of internal stress, hardness, and Young’s modulus with the substrate bias are similar. They increase with substrate bias, reaching a maximum of 7.2, 26, and 270 GPa, respectively, at a substrate bias of 200 V, then decrease with further increase of substrate bias.
Effect of thin-film stress on the formation of Cr texture and on the coercivity of CoCrX/Cr magnetic thin film
Authors: Kim J. H. , Park J. K.
Published: February 2003

The effect of thin-film stress on the formation of Cr texture and on the coercivity of CoCrX(X=Pt, Ta)/Cr magnetic thin films was investigated. The stress was controlled by varying the applied bias and deposition temperature during the film formation. The coercivity of CoCrX/Cr magnetic thin films was dependent on the grain size of the Cr underlayer and increased with the grain size for a grain size smaller than about 20 nm. This was closely related to the change of Cr texture from the (110) to the (200) orientations. The (200) Cr texture is preponderant over the (110) Cr texture in a deposition condition in which the adatoms are highly energetic and mobile. The (200) texture of Cr thin films tended to suddenly appear at average film stresses smaller than a critical stress. This sudden change of Cr texture is, however, not directly determined by this change of average film stress. The stress that is critical is, instead, the surface stress. It attains a sufficiently large compressive stress at this critical film stress to energetically favor the (200) over the (110) Cr orientation. The coherency between the film and substrate is not a necessary condition for the formation of the (200) Cr texture. The only requirement is to achieve a dynamic surface structure containing a high density of compressive ledge. This can be achieved not only by controlling the energy of adatoms but also by controlling the average film stress.
Dependence of the seal property of ConFlat-type flanges on the fine dimensions of the knife edge
Authors: Kurokouchi Satoshi , Shinoda Satsuo , Morita Shinsaku
Published: February 2003

The shape of the sealing face on ConFlat-type flanges has not been addressed at all in the International Standards Organization standards, yet it is the distinct shape of the sealing face on the flange, generally referred to as the “knife edge” that primarily distinguishes the ConFlat sealing system. Results of profiling on the sealing face of 70 mm diameter ConFlat-type flanges, provided by ten individual manufacturers, reveal that while all the sealing faces share a common 20° angle on the taper face, there are variations in the tip radius of the knife edge, and in the angle of the counterslope against the 20° taper face. In flange tightening tests using the ConFlat flanges, the tip radius was observed to influence flange penetration into the gasket. It was also determined that the knife edges of all the test flanges were plastically deformed to some extent in the process of tightening twice at a torque of 120 kgf cm. The knife-edge shape was neither found to be dependent on the magnitude of deformation, nor did the deformation have an observable influence on the seal property. In order to closely investigate the dependence of the ConFlat-type flange seal property on the fine shape of its sealing face, four types of 152 mm diameter flanges, each with a different knife-edge shape, were subjected to flange tightening tests. The results indicated that flanges with a small tip radius and a small counterslope angle maintained a satisfactory seal ability, even when applied tightening torque was lower, but had difficulty retaining sealing stability under an elevated temperature. On the other hand, flanges with a large tip radius or large counterslope angle on the knife edge had an advantage in terms of seal stability in baking conditions, but required relatively higher tightening torque to attain secure sealing. To evaluate the tip radius and the counterslope angle at which the flange seal capability and the sealing stability at an elevated temperature are in good balance, the stress condition in the tightened gasket and the flange penetration into the gasket was computer simulated at various tip radii and counterslope angles, using the finite-element method. Based on the results of the computer simulation, a reasonable range for the tip radius and the counterslope angle was estimated to be 0.1 mm to 0.2 mm, and 20° to 40°, respectively.
Silicon nitride etching in high- and low-density plasmas using SF6/O2/N2 mixtures
Authors: Reyes-Betanzo C. , Moshkalyov S. A. , Swart J. W. , Ramos A. C. S.
Published: February 2003

Results of a comparative study of SiNx, SiO2 and Si etching in high- and low-density O2–N2 based plasmas with small additions of SF6 are presented. Higher selectivities of SiNx etching over both SiO2 (up to 50–70) and Si (up to 20) are obtained in a high-density reactor as compared with low-density reactive ion etching. Plasma and surface processes responsible for etching are analyzed. Kinetics of NO molecules responsible for enhanced nitride etching is shown to be distinctly different for low- and high-density plasma conditions. Possible ways of further optimization of the process are discussed.
The security of urban women: practice, research, and partnerships
Authors: Michaud A , Paquin S
Published: February 2003

All public bodies whose mandate includes responsibility for the quality of urban life cannot ignore the question of security. On a global level, it is agreed that action needs to be taken locally, with the input of everyone involved. Since women have more at stake where safety issues are concerned, it is logical that security plans be drawn up that prioritize them. The interaction of public bodies, community organizations, and individual women is in itself innovative, enriching everyone involved, despite the inherent drawbacks and demands. International information networks on women’s security are expanding and can help the new partnerships refine their working methods, to the benefit of all, regardless of gender. Still, the transfer of knowledge between partners and among the population is fundamental and demanding. The same applies to the need to develop methods and criteria of evaluation that are adapted to the specific realities of the partnership for prevention of crime and violence towards women.
Media coverage as a risk factor in suicide
Authors: Stack S
Published: February 2003

A total of 293 findings from 42 studies on the impact of publicized suicide stories in the media on the incidence of suicide in the real world were analyzed by logistic regression analysis. Studies measuring the effect of either an entertainment or political celebrity suicide story were 14.3 times more likely to find a copycat effect than studies that did not. Studies based on a real as opposed to fictional story were 4.03 times more likely to uncover a copycat effect. Research based on televised stories was 82% less likely to report a copycat effect than research based on newspapers. A review of recent events in Austria and Switzerland indicates that suicide prevention organizations can successfully convince the media to change the frequency and content of their suicide coverage in an effort to reduce copycat effects.
Glamour puff
Authors: Lawson V
Published: February 2003

Australia has a total ban on tobacco advertising and promotion . . .but tobacco marketing goes on. This article is reprinted with the kind permission of the Sydney Morning Herald, 5 October 2002
First, tell the truth: a dialogue on human rights, deception, and the use of smokeless tobacco as a substitute for cigarettes
Authors: Kozlowski L T
Published: February 2003

The use of smokeless tobacco as a substitute for cigarettes raises many scientific and ethical issues, as the fictitious discussion below reveals
Economic burden of smoking in Korea
Authors: Kang H Y , Kim H J , Park T K , Jee S H , Nam C M , Park H W
Published: February 2003

Objective:To support tobacco control policies in Korea by providing the estimated annual economic burden attributed to cigarette smoking.

Methods:The following two different approaches were used to estimate the cost: “disease specific” and “all causes”. In the disease specific approach, we focused on estimating direct and indirect costs involved in treatments of cardiovascular, respiratory, and gastrointestinal diseases, and cancer as a result of smoking, by using an epidemiologic approach—the population attributable risk (PAR). To compute PAR, the relative risks of smoking in terms of physician visits, hospital admission, and death were estimated using the Cox proportional hazard model. In the all causes approach, we examined the differences in direct and indirect costs between smokers and non-smokers for all conditions and types of disease. The major data source was the Korea Medical Insurance Corporation cohort study, which had complete records of smoking status as of 1992 for 115 682 male and 67 932 female insured workers.

Results:By the disease specific approach, the estimated costs attributable to smoking in 1998 in Korea ranged from US$2269.42 million ($4.89 million per 100 000 population; 0.59% of gross domestic product (GDP)) to $2956.75 million ($6.37 million; 0.78% of GDP). The all causes approach yielded a minimum cost of $3154.75 million ($6.79 million; 0.82% GDP) and a maximum of $4580.25 million ($9.86 million; 1.19% GDP).

Conclusion:The study confirms that smoking places a substantial economic burden on Korean society. In light of this, our study provides evidence for a strong need to develop a national policy to effectively control tobacco consumption in Korea.
The importance of social sources of cigarettes to school students
Authors: Croghan E , Aveyard P , Griffin C , Cheng K K
Published: February 2003

Objective:To discover the importance of social sources of tobacco to young people as opposed to commercial sources; to describe the peer market for cigarettes in schools and the consequences for young people of their involvement in it.

Study design:Cross sectional questionnaire survey, one-to-one interviews, and focus groups.

Setting:Seven schools in Birmingham, UK.

Subjects:All students in two randomly selected classes from each school completed the questionnaire, and never smokers, occasional smokers, and regular smokers were interviewed.

Results:Two thirds of occasional smokers and one quarter of regular smokers obtained cigarettes socially, mostly for free. A few smokers regularly bought their cigarettes from others. Among friendship groups, both smokers and non-smokers were involved in the exchange of cigarettes, often for money, which is a common activity. A few young people use the selling of cigarettes to fund their own smoking. Some young people, smokers and non-smokers, are involved in semi-commercial selling of cigarettes. All school students are aware of where to purchase cigarettes from non-friends, which is only used “in emergency” because of the high price. One school had a strong punishment policy for students caught with cigarettes. In this school, more people bought singles from the peer market and the price was higher.

Conclusions:The passing and selling of cigarettes in school is a common activity, which from the young persons perspective, ensures that all share cross counter purchases. A few people are prepared to use the peer market for monetary gain and it appears to be responsive to external conditions. The peer market might mean that efforts to control illegal sales of cigarettes are not as effective as hoped.
Cigarette use among male and female grade 8–10 students of different ethnicity in South African schools
Authors: Swart D , Reddy P , Ruiter R A C , de Vries H
Published: February 2003

Objectives:To provide data on the prevalence of cigarette use by male and female South African students of different ethnic backgrounds in grades 8–10 (ages ⩽ 11 to ⩾ 17 years), their age of initiation of cigarette use, as well as their access to cigarettes through underage sales.

Design:A nationally representative survey was conducted using self administered questionnaires translated into seven languages.

Setting:School based.

Participants:Students in grades 8–10 in all of South Africa’s nine provinces.

Outcome measures:The prevalence data for current users of cigarettes (smoked on one or more days in 30 days preceding the survey), and for the age of initiation (first smoking cigarettes before the age of 10) were analysed.

Results:Of the 160 selected schools, 123 schools participated in the survey. The completed survey comprised 6045 of 7074 selected students; 23% of the sample reported being current users of cigarettes. Significantly more males (28.8%) than females (17.5%), and significantly more “Coloured” students than “Black/African” students were classified as current smokers. Sex was the strongest contributor to the prediction of current smoking status. On the issue of age of initiation, 18.5% of students reported having first smoked cigarettes before the age of 10 years with more “Black/African” students than “Coloured” having done so.

Conclusions:In order to tailor tobacco control programmes to the needs of students, historical “racial”/ethnic and sex differences have to be taken into account. Specific determinant studies are needed to understand these differences and to develop appropriate responses.