bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequential analysis by cooperative reactions on copolymers. II. Binary copolymers with one protecting monomer type
Authors: González J. J. , Hemmer P. C.
Published: February 2003

We develop an exact theory for the kinetics of reactions on linear binary copolymers. One of the two types of monomer units is assumed to exhibit a cooperative effect in the sense that after such a unit has reacted, the reactivities of the adjacent two monomer units are changed. Hence the reaction pattern depends upon the sequential structure of the copolymer. Both periodic and aperiodic copolymers are considered: in particular, random, Markovian, and second-order Markovian sequential structures.
Vibrational excitation in H2 and D2 electric discharges
Authors: Shirley J. A. , Hall R. J.
Published: February 2003

Spontaneous Raman scattering has been used to measure the effective vibrational temperature of the v=1 level as a function of input power in a self-sustaining low pressure dc glow discharge in pure H2 and D2 gases. A nonmonotonic dependence of vibrational temperature on input specific power, yielding Tv=1440–1960 °K in H2, has been measured downstream of the discharge. Results of numerical calculations modeling the discharge/afterglow are presented. The agreement between theory and experiment is good and suggest that the behavior observed is caused by the effect of the temperature dependent vibrational–translation energy transfer rate.
Optically pumped Hg2 studies
Authors: Komine H. , Byer R. L.
Published: February 2003

The continuous emission bands of molecular mercury at 0.335 and 0.485 μm are excited in a pure mercury vapor by direct optical pumping of the weakly bound ground state molecules with a 5 nsec pulse of intense 0.266 μm radiation in order to study the radiative and collisional properties of the excited molecules at densities between 1014 and 1015 cm−3. Fluorescence time history of both bands are empirically analyzed in terms of dynamics governing the excited molecules. The analysis includes a density-dependent nonexponential decay caused by bimolecular excimer quenching with a measured rate constant of k?2±1×10−10 cm3 sec−1 molecule−1. Because of interest in the mercury system as a potential laser medium, estimates of gain coefficients are derived from fluorescent power measurements. However, transmission measurements of the excited medium at 0.325 and 0.4416 μm show significant net loss due to excited state absorption with an estimated absorption cross section on the order of 10−17 cm2 at 0.325 μm. Energy storage limitations implied by the bimolecular excimer quenching are also examined.
Generalized Langevin equation approach for atom–solid surface scattering: Techniques for construction of time domain kernels
Authors: Doll J. D. , Dion D. R.
Published: February 2003

The time domain Langevin kernels necessary for the treatment of inelastic gas–solid surface collisions are examined for several model systems. General techniques are presented for construction of these time domain kernels. A preliminary examination of results for disordered lattices is made.
Temperature dependent Raman spectra of the ordered and disordered phases of Ag2HgI4 and Cu2HgI4
Authors: Greig D. R. , Joy G. C. , Shriver D. F.
Published: February 2003

Raman spectra of Ag2HgI4 were collected over the temperature range 8–470 °K. The ordered phase of Ag2HgI4 exhibits strong temperature dependent damping of the 85 cm−1 mode. The reduced Raman spectra of the disordered phases of both Ag2HgI4 and Cu2HgI4 are found to be temperature dependent. This unusual temperature dependence is attributed to the combined influence of anharmonicity, multiphonon processes, and the correlation time for ion hopping. An estimate of the latter was obtained from the line broadening data. Based on polarized scattering data obtained on very small crystals, symmetry assignments are made for some of the Raman bands of Ag2HgI4.
The water monomer on the basal plane of ice Ih: an effective pair, central force potential model of the static interaction
Authors: Kiefer Jerry , Hale Barbara N.
Published: February 2003

The H2O–H2O intermolecular central force potential of Lemberg and Stillinger is used to obtain optimal binding energy surfaces, vibrational frequencies, and bonding configurations of an adsorbed water monomer on a model basal plane of ice Ih. The monomer interacts (pairwise) with 50 molecules arranged in two layers of the unrelaxed bulk ice lattice. The results of calculations for three model surface sites of differing proton arrangement indicate the existence of diffusion barriers of the order of 2.5 kcal/mole and optimal monomer bonding sites at about 9 kcal/mole with nonepitaxial characteristics. Perspective computer-drawn plots of the optimal monomer binding energy surfaces and the center of mass height of the monomer over each of the three sites are shown. Similar diagrams showing the variations in the monomer dipole orientation along ’’walks’’ across the sites are also presented. Mean residence times and mean path lengths of the monomer diffusing over the model ice surface are estimated from the monomer vibrational modes and the estimated average diffusion barriers and binding energies. A sample diffusion path is discussed.
High pressure studies of interimpurity (donor–acceptor) luminescence in ZnS and ZnSe phosphors
Authors: House G. L. , Drickamer H. G.
Published: February 2003

The effect of pressure has been measured on the emission peak location, half-width, integrated intensity, and lifetime for a series of ZnS phosphors doped with Cu+ or Ag+ with Cl−, Al+3, In+3, or Ga+3 as coactivator, as well as on self-activated (SA) ZnS and on ZnSe:Cu:Cl. The emission peaks shift to higher energy with increasing pressure, but less strongly than does the absorption edge of the host. The peak intensities decrease rapidly with increasing pressure. The intensity changes could be accounted for quantitatively in terms of the donor–acceptor pair model. The shift of the luminescence peak with respect to the absorption edge is attributed to the pressure coefficient of the donor binding energy ED. The observed intensity changes with pressure could be related directly to changes in ED.
Configurational partition functions and entropies for polyoxide chains having the repeat unit [(CH2)y–O–]
Authors: Mark J. E.
Published: February 2003

Rotational isomeric state theory is used to calculate values of the configurational partition function z and entropy S for polyoxide chains having the repeat unit [(CH2)y–O–]. The values of z are at least qualitatively useful in interpreting the effect of the number y of methylene groups in the repeat unit on the characteristic ratio 〈r2〉0/nl2 of the unperturbed dimensions relative to the number of skeletal bonds and the average square of their lengths. For example, z has a maximum (corresponding to maximum ’’equilibrium flexibility’’ of the chain) at y=3, where 〈r2〉0/nl2 is at a minimum. The configurational entropy S, however, shows a very poor correlation with either z or 〈r2〉0/nl2; similar difficulties have been noted in comparisons between some polypeptide chains, and between some polysaccharide chains.
Molecular photoionization. II. Photoelectron angular distributions
Authors: Chapman Frank M. , Hayes Edward F.
Published: February 2003

Photoelectron angular distributions of atomic and molecular systems are discussed. The theory is developed in terms of the single center expansion model, and the photoionization differential cross section is separated into terms corresponding to the various partial wave components of the photoelectron wavefunction. The differential cross section is decomposed into a series of (1) direct (incoherent) terms for each final state partial wave, plus (2) a series of interference (coherent) terms between the various partial waves. The resulting description is particularly useful for emphasizing the contribution of individual partial wave components to the differential cross section. Illustrative results are presented for the photoionization of the hydrogen molecule–ion. These results provide further evidence of the reliability of the noniterative integral equation method for studying photoionization processes.
Vibrational relaxation in seeded supersonic alkali halide beams
Authors: Mariella R. P. , Neoh S. K. , Herschbach D. R. , Klemperer W.
Published: February 2003

A seeded supersonic beam source for alkali halides is described which can provide high intensity, a narrow velocity distribution, enhanced or reduced translational energy (by choice of diluent mass), low rotational temperature, and partially relaxed vibrational populations. Alkali halide vapor at ∼1200–1400 °K and ∼0.1 Torr is mixed with a diluent gas at ∼30–100 Torr and expanded through a pinhole nozzle 0.1 mm in diameter. Velocity analysis of a seeded CsF beam with Ar as the diluent indicates the beam properties conform approximately to the theory of isentropic expansions, with deviations attributable to the relatively low source pressure used. The vibrational populations of the v=0, 1, 2, 3 states in seeded beams of LiF with Ar, NH3, ND3, and SF6 as diluents were determined by electric resonance spectroscopy. For Ar as diluent, the LiF vibrational energy has a Boltzmann distribution with a temperature only ∼10% lower than the beam source. For the polyatomic diluents, the LiF vibrational distribution is markedly non-Boltzmann. The nominal vibrational temperature Tv, defined by comparing the population of state v to that of the ground state, drops substantially for the higher v states. The vibrational relaxation becomes more pronounced as the source pressure of alkali halide or diluent gas is increased. For the experimental conditions used here, Tv for the v=3 state drops to ∼2/3 of the source temperature; much stronger relaxation can be expected at higher source pressures.
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o molecular orbital calculations on the reaction path of the ketocarbene–ketene rearrangement
Authors: Strausz O. P. , Gosavi R. K. , Gunning H. E.
Published: February 2003

An ab initio type SCF MO study using a double zeta quality basis set has been carried out on the formylmethylene–ketene rearrangement reaction which is the last step of the Wolff rearrangement–decomposition sequence of α-diazoketones and α-diazoesters. The ketene structure is computed to be 74.3 kcal/mole more stable than the isomeric formylmethylene and the reaction features a computed activation energy of 5.7 kcal/mole, corresponding to a bridged activated complex. The computed geometry of the ketene molecule is in good agreement with the experimental geometry.
High resolution Raman spectroscopy of gases with laser sources. XI. The spectrum of cyanogen
Authors: Wang I-Yan , Weber Alfons
Published: February 2003

The pure rotational and rotation–vibrational Raman spectra of cyanogen, C2N2, were photographed under high resolution. The spectra were excited with a single mode argon laser operating at λ=4880 Å. The pure rotation spectrum shows a partially resolved hot band structure that is assigned to the ν51 and 2ν5 vibrationally excited states. The l-type doubling in the pure rotational spectrum of molecules in the ν15 state is sufficiently well resolved at high J values to allow a determination of the l-type doubling constant. The ν1(Σ+g) and ν14(Πg) fundamental rotation–vibration bands were also photographed. Both fundamentals are overlapped by vibrational hot bands originating in low-lying vibrational levels. Molecular constants obtained in the present work are, in units of cm−1, The constants for the ν15 and 2ν50,2 states were obtained from the pure rotation spectrum. The vibrational constants were found to be The ground state constants B0 and D0 and their uncertainties were determined by an extrapolation procedure. For all other constants the quoted errors are one standard deviation and only represent the internal errors generated in the least squares analysis of the data. Vibrational constants determined from Q-branch measurements only are indicated by (Q).
Potential energy curves and predicted fluorescence for neon fluoride
Authors: Winter N. W. , Bender C. F. , Rescigno T. N.
Published: February 2003

Potential energy curves for the lowest four states of NeF have been computed and used to determine the bound-free Franck–Condon factors. Combining these with the calculated transition moments, the fluorescence spectra of NeF has been predicted. The dominant feature is the charge transfer band 2 2Σ→1 2Σ at 108 nm. Several other weaker transitions are shown to overlap this band.
Quantum corrections to the equilibrium properties of dense fluids: Application to hard-sphere fluids
Authors: Singh B. P. , Sinha S. K.
Published: February 2003

A simple theory for the equation of state of dense fluids in the semiclassical limit, where the quantum effects are small, is developed, based on an interpretation of the reciprocal of the activity. The theory has been applied to calculate the quantum effect on the equation of state of a dense hard-sphere fluid.
Photodissociation of positive and negative ions formed in O2
Authors: Vestal M. L. , Mauclaire G. H.
Published: February 2003

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of O2+, O3+, O4+, O2−, and O3− formed in O2 at pressures between 0.01–1 torr. At low pressures O2+ photodissociation was observed using 600 nm radiation, and pressure studies indicate that an excited state of O2+ is involved, which is collisionally relaxed with a rate constant of approximately 2×10−11 cm3/sec. Photodissociation of O3+ was found to occur at ∼600 nm primarily by the reaction O3+→O++O2 with a large cross section (10−17 cm2).
Matrix reactions of chlorine atoms with NO2 molecules
Authors: Tevault D. E. , Smardzewski R. R.
Published: February 2003

Matrix reactions of chlorine atoms with NO2 molecules diluted in argon yielded Cl–N bonded nitryl chloride ClNO2 as well as the Cl–O bonded isomer nitrosyl hypochlorite ClONO. Infrared absorptions at 1714.1, 855.6, 398.0, and 390.4 cm−1 were assigned to the ClONO species, which was shown from nitrogen-15 and oxygen-18 isotopic studies to be comprised of two weakly coupled diatomic radicals ClO and NO. Infrared spectroscopic evidence also suggested the presence of a third isomer OClNO which is produced by the insertion of a chlorine atom into an N–O bond of NO2 as well as by the direct maxtrix combination of ClO and NO radicals. The photolytic behavior of the ClONO species indicates that it undergoes intramolecular rearrangement, in the argon matrix cage, to produce the more stable ClNO2 form via a two-step process which involves the OClNO molecule as an intermediate.
Ionization of ammonia and deuterated ammonia by electron impact from threshold up to 180 eV
Authors: Märk T. D. , Egger F. , Cheret M.
Published: February 2003

Electron impact ionization has been studied in NH3 and in a mixture of NH3 and ND3 as a function of electron energy up to 180 eV with a double focusing mass spectrometer. Absolute partial ionization cross section functions have been obtained in NH3 for the production of NH+3, NH+2, NH+, N+, H+2, H+, and NH++3 by normalization against the Ar ionization cross section. The ions NH++2 and N++, produced by the process NH3+e, have been found for the first time, and an estimate of the ionization cross section is given. From the measured partial ionization cross section functions the total ionization cross section function of NH3 has been deduced. In addition, it has been possible to measure the ratio of the partial cross section for double and single ionization of the parent ions ND2H and ND3 as a function of electron energy. The ionization cross section results obtained are compared with previous determinations where available and with a recent semiempirical total ionization cross section calculation by Jain and Khare. Using nth root extrapolation the following ionization and appearance potentials have been derived fom the low energy cross section function: I.P. (NH+3/NH3) =10.4±0.1 eV; A.P. (NH+2/NH3) =16.5±0.2 eV; A.P. (NH+/NH3) =22.9±0.5 and 27.2±0.5 eV; A.P. (N+/NH3) =29.5±0.5 eV; A.P. (H+2/NH3) =14.8±0.2 eV; A.P. (H+/NH3) =23.0±0.2, 27.7±0.5, and 30.6±0.5 eV; I.P. (ND2H+/ND2H) =10.5±0.1 eV; I.P. (ND+3/ND3) =10.7±0.1 eV; I.P. (NH++3/NH3) =34.4±0.2 eV; I.P. (NDH++2/NDH2) = 34.6±1.0 eV; I.P. (ND2H++/ND2H) =34.6±0.5 eV; and I.P. (ND++3/ND3) =34.6±0.5 eV. For the doubly ionized parent molecules a square law has been found from threshold up to some 20 eV above onset. The ionization and appearance potentials obtained are also compared with such earlier results as are available.
The proton chemical shift tensor in trichloroacetic acid
Authors: Dybowski C. R. , Gerstein B. C. , Vaughan R. W.
Published: February 2003

The proton chemical shift tensor for the hydrogen-bonded hydroxyl proton in trichloroacetic acid is reported as determined by multiple pulse NMR measurements. The deviation of the principal axis corresponding to the most positive principal value from the hydroxyl bond direction is characterized, and this twisting is discussed in terms of the locations of nearby concentrations of electron density.
A thermodynamic study of dilute solutions of hydrogen and deuterium in Pd0.9Ag0.1 at 555 and 700 K
Authors: Boureau G. , Kleppa O. J. , Hong K. C.
Published: February 2003

Precise determinations of the partial molar thermodynamic properties of hydrogen and deuterium in the alloy Pd0.9Ag0.1 have been carried out at 555 and 700 K, using a combined calorimetric-equilibrium method. These quantities are compared with the corresponding values for hydrogen and deuterium in pure palladium. Our measurements confirm the significant increase in Δ?H with increasing temperature, which was observed already for solutions in pure palladium. It is found that the enthalpy of solution of hydrogen is about 900 cal mol−1 more exothermic in the alloy than in pure palladium. This difference depends somewhat on temperature. The partial entropies of solution of hydrogen are about 0.4 cal mol−1 K−1 smaller in Pd0.9Ag0.1 than in pure palladium. Because of the large number of different physical measurements that have been carried out previously on palladium and on palladium–silver alloys, it is possible to give a detailed analysis and interpretation of these entropy differences, which may be understood in terms of vibrational, electronic, and configurational entropy contributions. The major effect is configurational, arising from a preference of the hydrogen atoms for interstitial sites surrounded by only palladium atoms. It also is shown that very simple models are not capable of explaining the magnitude of the H–H interaction energies and our thermodynamic measurements of the isotope effects.
Flow-drift tube investigation of some Ar++ reactions
Authors: Lindinger W. , Alge E. , Störi H. , Pahl M. , Varney R. N.
Published: February 2003

A new flow–drift technique for the investigation of ion–molecule reactions in the near thermal range, somewhat similar to the NOAA flow drift technique, is presented. Data on Ar+ reactions with H2, O2 and CO2 obtained to check the system agree well with recent NOAA results. The investigations of the first reactions of Ar++ with O2, CO2, and C2H2 show single charge transfers to be the only existing reaction channels, capture of two electrons by the Ar++ not being observed to occur. By contrast H2 showed no sign of reacting at all with Ar++ at rates within the range of these measurements.
Empirical potential energy surface for the Hg+I2 reaction
Authors: Mayer T. M. , Muckerman J. T. , Wilcomb B. E. , Bernstein R. B.
Published: February 2003

The general features of the ground state adiabatic potential energy hypersurface for the Hg+I2 system have been deduced using results of recent molecular beam scattering experiments, spectroscopic and structural data, and electronic state correlation diagrams. The key element of the potential energy surface (p.e.s.) is a deep attractive ’’basin,’’ implied from the reactive scattering data which provided evidence for the existence of a long-lived intermediate complex, believed to be IHgI. This empirical p.e.s. is characterized by the following features: (a) a shallow well in the entrance valley corresponding to the weakly bound (by ∼0.06 eV) van der Waals adduct Hg⋅I2; (b) a subsequent barrier of ∼0.7 eV in the entrance valley due to avoided crossings of diabatic potential curves, followed by a ’’falloff’’ leading to insertion of the Hg(1S0) into the I2(1Σg+) molecule; (c) a deep potential well (−1.45 eV) corresponding to the stable IHgI complex, taken to be gaseous mercuric iodide in its ground electronic state, 1A1(1Σg+); (d) an exit valley with a minimum energy path rising essentially monotonically, with a negligible intrinsic barrier (≲0.03 eV) from −1.45 to +1.15 eV to yield HgI(X 2Σ+)+I(2P3/2); (e) an essentially monotonic exit path rising to the threshold (+1.54 eV) for collision-induced dissociation; (f) a barrier to reaction in the collinear configuration (Hg–I–I) in which IHgI complex formation is sterically precluded.
Removal of phosgene impurity from boron trichloride by laser radiation
Authors: Merritt J. A. , Robertson L. C.
Published: February 2003

The removal of the COCl2 impurity in BCl3 can be accomplished by using CO2 laser radiation. Mixtures of BCl3 and COCl2, and C2H4 and COCl2, were irradiated by a cw CO2 laser. The COCl2 was dissociated with no detectable BCl3 dissociation. The BCl3 acts as an infrared sensitizer.
Generalized van der Waals theory of nematic liquid crystals: Requirements for self-consistency
Authors: Cotter Martha A.
Published: February 2003

In the generalized van der Waals (GVDW) theory of nematic liquid crystals, nematogenic molecules are assumed to interact via hard core repulsions and longer ranged attractive forces, and the latter are treated in the mean field approximation. The resulting expression for the configurational Helmholtz free energy Ac as a functional of the orientational distribution function f (Ω) is N−1Ac[ρ,T;f (Ω)]=N−1Ac[ρ,T;f (Ω)] + N−1V(a)N(ρ) =N−1Ac[ρ,T;f (Ω)] + 1/2ℱf (Ω) ? (ρ,Ω) dΩ, where ρ is the number density, Ac[f (Ω)] is the free energy functional for a system of molecules with only hard core repulsions, ?(a)N is the GVDW average of the total potential energy of attraction V(a)N, and ? (ρ,Ω) is the pseudopotential describing the interaction between a molecule with orientation Ω and the mean field produced by intermolecular attractions. In this paper, it is shown that the theory exhibits statistical mechanical self-consistency if and only if both N−1?(A)Nand?(Ω)are directly proportional to the first power of the density ρ. This result is independent of the shape of the molecular hard cores and of the assumed orientation dependence of the pseudopotential ?.
Effect of the selective adsorption on the reactive scattering process of molecular beams from stepped surfaces
Authors: García N.
Published: February 2003

An indicative proposal which may explain the diffusion of incident atomic beams scattered by a crystal surface is made in terms of the selective adsorption mechanism. In this sense, the stepped metallic surfaces present characteristics which enhance the displacements and the lifetimes of the beams on the surface. This may be important for increasing the exchange reactive scattering of molecules from crystal surfaces.
High field CIDNP. general analytic results
Authors: Pedersen J. Boiden
Published: February 2003

The radical pair theory of chemically induced dynamic nuclear polarization (CIDNP) in high magnetic field has been reexamined using an analytic approach. General expressions can be given for the spin dependent probability of reaction. These expressions are independent of the diffusive behavior of the radicals and can thus be applied to any diffusion model. We have applied these results to the three-dimensional continuous diffusion model and derived analytic expressions that permit a simple and accurate calculation of CIDNP polarization for all diffusional rates and all magnitudes of the magnetic interactions. The results are exact for a short range exchange interaction and the results for the combination of a long-range exchange interaction and slow diffusion are within 10% of the published numerical solutions. Exact analytic expressions are also given for the case where a scavenging reaction is present.
Raman spectra of SiF4 and GeF4 crystals
Authors: Bernstein E. R. , Meredith G. R.
Published: February 2003

The Raman scattering spectra of large single crystals of SiF4 and GeF4 at 77 K are reported. These data have been reinterpreted based on the absence of any observable changes in the spectra for scattering angles between 0° and 90°. The previous assignment of the dipole allowed ν3 and ν4 modes based on a TO/LO splitting model is thereby shown to be incorrect. In the absence of an apparently correct crystal structure, an exact interpretation of the data in terms of a factor group-exciton analysis is not possible; nonetheless all observations appear to be consistent with a centrosymmetric space group having a multimolecular primitive unit cell. Mixed SiF4/GeF4 crystal spectra have also been obtained which demonstrate that GeF4 does not substitute into the SiF4 lattice but that SiF4 does enter the GeF4 crystal substitutionally.
Representations of molecular force fields. IV. Vibrational stress, isotope effects, and structure of ethane
Authors: Bartell L. S. , Fitzwater Susan
Published: February 2003

The transformation of molecular force fields from natural curvilinear coordinates S̃ to rectilinear coordinates S (yielding simpler equations of motion) is discussed. Rectilinear cubic constants include mass dependent terms arising from the nonlinear coordinate transformation as well as contributions from the cubic constants for the S̃ displacements. These contributors to anharmonicity lead to intramolecular ’’vibrational stresses’’ resolvable into components ℱC, ℱT, and ℱF which induce rectilinear molecular strain components 〈S〉C, 〈S〉T, and 〈S〉F, each of which has its own physical interpretation. More significant than the rectilinear quantities are the curvilinear stresses and strains which, it is shown, are readily expressed in terms of the above components. Each of the foregoing quantities is easily decomposed into contributions from the various types of vibration. Magnitudes are illustrated by computations of cubic force constants and selected stress and strain components in C2H6 and C2D6.
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o computation of force constants. IV. The theoretical anharmonic force fields and vibrational frequencies of methylamine, methanol, and methanethiol
Authors: Schlegel H. Bernhard , Wolfe Saul , Bernardi Fernando
Published: February 2003

The anharmonic force fields of methylamine, methanol, and methanethiol have been computed ab initio. The harmonic force constants agree fairly well with experiment. Better agreement is found between the experimental frequencies and the theoretical anharmonic frequencies. The stretching modes are predicted especially well. The calculated ν13 and ν14 for CH3NH2 agree with the solid phase but not the gas phase experimental results. Methylamine, methanol, and methanethiol exhibit Bohlmann bands, i.e., a lowering of the stretching frequency of a C–H bond antiperiplanar to a lone pair. The computations reveal that these bands are linked to a smaller force constant for the anti CH bond and to Fermi resonance between the symmetric C–H stretch and CH bending overtones.
Energy and angular distributions of electrons ejected in the ionization of SF6 and TeF6 by fast protons
Authors: Toburen L. H. , Wilson W. E. , Porter L. E.
Published: February 2003

Absolute cross sections, differential in ejected electron energy and emission angle, have been measured for ionization of SF6 and TeF6 molecules by protons in the energy range from 0.3 to 1.8 MeV. Evidence of potential barrier effects is observed in the structure of the low-energy portion of the ejected electron energy spectra. This structure, as well as cross sections for direct ionization processes, is discussed with respect to dependence on emission angle and incident particle energy. Emission cross sections are compared to similar measurements for molecules with constituents of only low atomic number.
Temperature dependence of the total reaction rates for Cl+HI and Cl+HBr
Authors: Mei Chang-Chi , Moore C. Bradley
Published: February 2003

Thermal reaction rate constants have been determined for the reactions Cl+HI and Cl+HBr in the temperature range 220–400 °K. The rates vary slowly with temperature. For Cl+HI the effective reaction cross section reaches a maximum of 31 Å2 near 300 °K. A tentative reaction model is proposed in which the attacking halogen atom is attracted to the halogen end of the hydrogen halide and then rotation of the hydrogen, with little or no activation energy, completes the reaction.
Density functional theory and molecular bonding. I. First-row diatomic molecules
Authors: Gunnarsson O. , Harris J. , Jones R. O.
Published: February 2003

The density functional equations of Hohenberg, Kohn, and Sham (HKS) are solved self-consistently for simple molecules using a method described originally by Andersen and Woolley. Spectroscopic constants, calculated for B2, N2, O2, F2, CO, and BF and for the four lowest lying states of C2, are in good agreement with experiment. Results are consistently better than Hartree–Fock and comparable with those of configuration interaction calculations.
Mass dependence of the ionic dynamics in molten salts
Authors: Lantelme Frederic , Turq Pierre , Schofield Peter
Published: February 2003

The dynamical properties of condensed media are studied on the basis of molecular dynamics in a two component system of charged particles. The short-time behavior of the particle motion is described in terms of velocity autocorrelation functions. In order to get a better understanding of the mechanism of the transport process the effect of isotope substitution is examined. It is shown that the collision theory does not provide a suitable model; the results are interpreted within the framework of perturbation theory. Expressions are derived which give a correct representation of the influence of a mass change on the self-diffusion coefficients; this approach is used to calculate the isotope effects in naturally occurring systems. Comparisons with experimental results are interpreted by introducing strongly correlated motions.
Effect of initial excitation in the photofragmentation of model HCN and DCN. Comparison between approximate and exact calculations
Authors: Beswick J. A. , Shapiro M. , Sharon R.
Published: February 2003

In this paper we present calculations for direct photodissociation and predissociation for model linear HCN and DCN. We compare the detailed product-vibrational state distributions and absorption spectra as obtained by a ’’half-collision’’ approximate scheme and an exact numerical integration of the coupled equations. It is predicted that large isotope effects can be encountered in certain regions of the spectrum for direct photodissociation of vibrationally excited molecules.
A study of supply chain management practice in UK industrial SMEs
Authors: Quayle Michael
Published: February 2003

This paper provides the outcomes of a supply chain management (SCM) practice survey designed to identify current trends in UK industrial small‐ to medium‐sized enterprises. The analysis identifies the adaptation of SCM techniques and relationships between customers and smaller suppliers. The outcomes, based on a survey of 288 firms, indicates a lack of effective adaptation from traditional adversarial relationships to the modern collaborative “e” – supply chain; identifies issues businesses need to address to improve the performance of their supply chains, and so improve their competitive position by grasping the benefits of effective SCM.
Detection of Coronary Artery Stenoses With Thin-Slice Multi-Detector Row Spiral Computed Tomography and Multiplanar Reconstruction
Authors: Ropers Dieter , Baum Ulrich , Pohle Karsten , Anders Katharina , Ulzheimer Stefan , Ohnesorge Bernd , Schlundt Christian , Bautz Werner , Daniel Werner G. , Achenbach Stephan
Published: February 2003

Background—

We analyzed the accuracy of multi-detector row spiral computed tomography (MDCT) using a 16-slice CT scanner with improved spatial and temporal resolution, as well as routine premedication with β-blockers for detection of coronary stenoses.

Methods and Results—

Seventy-seven patients with suspected coronary disease were studied by MDCT (12×0.75-mm cross-sections, 420 ms rotation, 100 mL contrast agent IV at 5 mL/s). Patients with a heart rate above 60/min received 50 mg atenolol before the scan. In axial MDCT images and multiplanar reconstructions, all coronary arteries and side branches with a diameter of 1.5 mm or more were assessed for the presence of stenoses exceeding 50% diameter reduction. In comparison to invasive coronary angiography, MDCT correctly classified 35 of 41 patients (85%) as having at least 1 coronary stenosis and correctly detected 57 of 78 coronary lesions (73%). After excluding 38 of 308 coronary arteries (left main, left anterior descending, left circumflex, and right coronary artery in 77 patients) classified as unevaluable by MDCT (12%), 57 of 62 lesions were detected, and absence of stenosis was correctly identified in 194 of 208 arteries (sensitivity: 92%; specificity: 93%; accuracy: 93%; positive and negative predictive values: 79% and 97%).

Conclusions—

MDCT coronary angiography with improved spatial resolution and premedication with oral β-blockade permits detection of coronary artery stenoses with high accuracy and a low rate of unevaluable arteries.
Non-IgE–dependent activation of human lung– and cord blood–derived mast cells is induced by eosinophil major basic protein and modulated by the membrane form of stem cell factor
Authors: Piliponsky Adrian M. , Gleich Gerald J. , Nagler Arnon , Bar Ilan , Levi-Schaffer Francesca
Published: February 2003

The allergic reaction begins with the antigen-induced aggregation of occupied high-affinity IgE receptors expressed on mast cell surface, their activation, and the release of proinflammatory mediators that cause the “early phase” of this process. In addition, mast cell activation induces the onset of a “late phase” reaction characterized by the tissue infiltration of inflammatory cells, mainly eosinophils. We have hypothesized that during the late phase mast cells interact with and are activated by eosinophils. Here we report that highly purified human lung mast cells became responsive to eosinophil major basic protein (MBP) when in coculture with human lung fibroblasts. In addition, cord blood–derived mast cells maintained in coculture with 3T3 fibroblasts released more histamine and prostaglandin D2 (PGD2) compared with cells maintained in suspension. The fibroblast-derived membrane form of stem cell factor (SCF) was found to be involved in the mast cell increased responsiveness to MBP. In fact, cord blood–derived mast cells cocultured with 3T3 in the presence of antisense for SCF or cocultured with fibroblasts that do not express the membrane form of SCF were inhibited in their histamine-releasing activity toward MBP. In addition, this form of SCF induced the expression of a pertussis toxin–sensitive Gi protein, Gi3 that interacts with MBP to trigger mast cell non-IgE–dependent activation in a manner similar to other cationic compounds such as compound 48/80. Mast cell responsiveness to eosinophil mediators is a potentially novel evidence for an alternative pathway of allergen-independent activation able to contribute to the perpetuation of allergy.
BVL-1–like VL30 promoter sustains long-term expression in erythroid progenitor cells
Authors: Staplin William R. , Knezetic Joseph A.
Published: February 2003

Congenital blood disorders are common and yet clinically challenging globin disorders. Gene therapy continues to serve as a potential therapeutic method to treat these disorders. While tremendous advances have been made in vivo, gene delivery protocols and vector prototypes still require optimization. Alternativecis-acting promoter elements derived from VL30 retroelements have been effective in expressing tissue-specific transgene expression in vivo in nonerythroid cells. VL30 promoter elements were isolated from ELM-I-1 erythroid progenitor cells upon erythropoietin (epo) treatment. These promoters were inserted into a VL30-derived expression vector and reintroduced into the ELM-I-1 cells. β-Galactosidase reporter gene activity from the ELM 5 clone, a BVL-1–like VL30 promoter, was capable of expressing sustained levels of the transgene expression over a 16-week assay period. These findings delineate the potential utility of these retroelement promoters as transcriptionally active, erythroid-specific, long terminal repeat (LTR) components for current globin vector constructs.
Stochastic analysis in life office management: applications to large annuity portfolios
Authors: Coppola Mariarosaria , Di Lorenzo Emilia , Sibillo Marilena
Published: February 2003

The paper deals with the riskiness analysis for a large portfolio of life annuities. By means of the limiting distribution of the present value of the portfolio, in the first part of the paper a model for evaluating the investment and the projection risks is presented. In the second part, with regard to the investment risk's effects, the insolvency risk is measured considering the cumulative probability distribution function of the discounted average cost per policy. Copyright © 2003 John Wiley & Sons, Ltd.
SPE/RIA vs LC/MS for measurement of low levels of budesonide in plasma
Authors: Dimova H. , Wang Y. , Pommery S. , Moellmann H. , Hochhaus G.
Published: February 2003

A radioimmunoassay is described that measures budesonide in plasma after solid‐phase extraction (SPE/RIA) of the analyte. The performance of the assay was compared with that of a selective LC/MS method. The limit of quantitation of budesonide determined for the LC/MS and SPE/RIA assay was 50 pg/mL and 120 pg/mL, respectively. Based on quality control samples, a higher variability was observed for the SPE/RIA (CV between 4.5 and 23.0%) than for the LC/MS method (CV between 7.5 and 12.5%). Plasma samples obtained from healthy volunteers after administration of budesonide rectal foam were assayed by both methods. In a subset of samples, these results were compared with those measured by direct RIA to evaluate the selectivity of two assays. About two times higher budesonide levels were measured with the direct RIA (lacking the extraction step), presumably because of cross‐reactivity with budesonide metabolites, indicating that the extraction step in SPE/RIA is necessary for selectivity. Both SPE/RIA and LC/MS methods were found to be selective, sensitive and suitable for pharmacokinetic studies. Results obtained from the two methods were compared with a number of statistical methods. Ratios of results obtained for the clinical samples were close to 1 (ratio LC‐MS/ SPE/RIA = 0.98 ± 0.27). Linear regression indicated a slope of 1.17 ± 0.0378. The concordance correlation (r = 0.91) indicated that the agreement between both methods was fair while the Bland–Altman plot indicated that the agreement was less pronounced at higher concentrations (1–3 ng/mL). In summary, the results confirm that the SPE/RIA is an alternative to HPLC/MS and that among the statistical methods tested the concordance correlation analysis was judged to be the most informative test to assess the comparability of two methods. Copyright © 2002 John Wiley & Sons, Ltd.
Quantitative determination of saquinavir from Caco‐2 cell monolayers by HPLC‐UV
Authors: Ucpinar Sibel Demirbas , Stavchansky Salomon
Published: February 2003

The validation and quantitative determination of the protease inhibitor, saquinavir, from confluent Caco‐2 monolayers and from aqueous solution is reported. The high performance liquid chromatographic method consisted of an Ultramex™ 5 C8 reverse‐phase column (250 × 4.6 mm i.d.) and a mobile phase of acetonitrile:water:triethylamine (55:44:1, v/v/v, pH 6.5). Samples were analyzed using an ultraviolet detector at 238 nm, and diltiazem hydrochloride (66 µg/mL) was used as an internal standard. A linear response over a broad concentration range (0.4–8.0 µg/mL, r2 = 0.997) was obtained. The limit of detection and quantitation was set at 0.14 and 0.4 µg/mL, respectively. Over a 4 day period, the intra‐day and inter‐day precision ranged from 1 to 7% with a mean of 4%, and from 1 to 2% with a mean of 1.5%, respectively. Bench–top and storage stability of saquinavir was found to be satisfactory. The permeability of saquinavir through Caco‐2 monolayers was estimated using this assay. Copyright © 2002 John Wiley & Sons, Ltd.
Capillary electrophoresis and enzyme solid phase assay for examining the purity of a synthetic heparin proteoglycan‐like conjugate and identifying binding to basic fibroblast growth factor
Authors: Dimitrellos V. , Lamari F. N. , Militsopoulou M. , Kanakis I. , Karamanos N. K.
Published: February 2003

Interaction of basic fibroblast growth factor (bFGF) with heparin/heparan sulfate proteoglycans protects the growth factor against proteolytic degradation and is essential for its cellular activity. Although the structural requirements of heparin and heparan sulfate for the high‐affinity binding to bFGF have been extensively examined, studies on intact heparin proteoglycans are limited. In this report, the purity and the binding ability of a heparin proteoglycan‐like molecule—the heparin–bovine serum albumin (heparin–BSA) conjugate—was examined using capillary zone electrophoresis (CZE). Furthermore, the affinity of bFGF binding to the heparin‐BSA conjugate was studied using an enzyme solid‐phase assay. Chondroitin sulfate, dermatan sulfate, hyaluronan, heparan sulfate and variously sulfated disaccharides derived from heparin and heparan sulfate were also studied for their ability to compete with the binding of bFGF to heparin. Heparin–BSA conjugate was synthesized by reductive amination and, following precipitation with 1.5 vols of ethanol–sodium acetate, it was obtained free of contaminating heparin. Heparin–BSA–bFGF conjugate was obtained following incubation of heparin–BSA with bFGF for 2 h at 37°C. Intact heparin, heparin–BSA and heparin–BSA–bFGF conjugates were completely resolved by CZE using 50 mM phosphate, pH 3.5, as operating buffer, reversed polarity (30 kV) and detection at 232 nm. Competitive solid phase assay showed that, among the glycosaminoglycans tested, heparin exhibits the highest affinity binding to bFGF (IC50 = 6.4 nM). Heparan sulfate showed a lower affinity as compared with that of heparin, whereas all other glycosaminoglycans and heparin/heparan sulfate‐derived disaccharides tested showed minute effects. The developed CZE method is rapid and accurate and can be easily used to identify bFGF‐interacting heparin preparations of biopharmaceutical importance. Copyright © 2003 John Wiley & Sons, Ltd.
Fragmentation of Transition Metal Carbonyl Cluster Anions: Structural Insights from Mass Spectrometry
Authors: Butcher Colin P. G. , Dyson Paul J. , Johnson Brian F. G. , Khimyak Tetyana , McIndoe J. Scott
Published: February 2003

The anionic clusters [HOs5(CO)15]−, [PtRu5C(CO)15]2−, [Os10C(CO)24]2−, [Os17(CO)36]2−, [Os20(CO)40]3−, [Co6C(CO)15]2−, [Pt3Ru10C2(CO)32]2− and [Pd6Ru6(CO)24]2− have been analysed by energy‐dependent electrospray ionisation mass spectrometry (EDESI‐MS). Three main features have emerged. Firstly, carbonyl ligands are fragmented from clusters with compact metal cores in an orderly fashion, with each of the ions generated by CO loss having approximately equal intensity. Secondly, electron autodetachment takes place in multiply charged anionic clusters, but only after elimination of a large proportion of their carbonyl ligands. Thirdly, clusters with open metal cores do not undergo CO loss in an orderly fashion, but certain peaks are considerably less intense. The appearance of these low‐intensity peaks is believed to signify polyhedral core rearrangements, with open clusters folding to form more compact geometries. In some cases, the gas‐phase transformations observed by EDESI‐MS mirror those that are known to take place in solution.
Preorganization and Reorganization as Related Factors in Enzyme Catalysis: The Chorismate Mutase Case
Authors: Martí Sergio , Andrés Juan , Moliner Vicent , Silla Estanislao , Tuñón Iñaki , Bertrán Juan
Published: February 2003

In this paper a deeper insight into the chorismate‐to prephenate‐rearrangement, catalyzed by Bacillus subtilis chorismate mutase, is provided by means of a combination of statistical quantum mechanics/molecular mechanics simulation methods and hybrid potential energy surface exploration techniques. The main aim of this work is to present an estimation of the preorganization and reorganization terms of the enzyme catalytic rate enhancement. To analyze the first of these, we have studied different conformational equilibria of chorismate in aqueous solution and in the enzyme active site. Our conclusion is that chorismate mutase preferentially binds the reactive conformer of the substrate—that presenting a structure similar to the transition state of the reaction to be catalyzed—with shorter distances between the carbon atoms to be bonded and more diaxial character. With respect to the reorganization effect, an energy decomposition analysis of the potential energies of the reactive reactant and of the reaction transition state in aqueous solution and in the enzyme shows that the enzyme structure is better adapted to the transition structure. This means not only a more negative electrostatic interaction energy with the transition state but also a low enzyme deformation contribution to the energy barrier. Our calculations reveal that the structure of the enzyme is responsible for stabilizing the transition state structure of the reaction, with concomitant selection of the reactive form of the reactants. This is, the same enzymatic pattern that stabilizes the transition structure also promotes those reactant structures closer to the transition structure (i.e., the reactive reactants). In fact, both reorganization and preorganization effects have to be considered as the two faces of the same coin, having a common origin in the effect of the enzyme structure on the energy surface of the substrate.
Feste Zähne durch Kupfer
Authors: Jacoby Petra
Published: February 2003

Die meisten Tiere härten ihre Zähne mit Calciumverbindungen. Anders jedoch der Meereswurm Glycera dibranchiata — er bildet ein kupferhaltiges Mineral und liefert mit dieser Strategie einen interessanten Ansatzpunkt zur Entwicklung neuer Werkstoffe.
Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: I. Growth habit and surface morphology
Authors: Sangwal K. , Mielniczek‐Brzóska E. , Borc J.
Published: February 2003

The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as‐grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30 °C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH4)2C2O4 · H2O molecules are in excellent agreement with the low‐index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph.