bluuebunny/crossref_metadata_2025 huggingface dataset:
Sex Trafficking in Women from Central and East European Countries: Promoting a ‘Victim-Centred’ and ‘Woman-Centred’ Approach to Criminal Justice Intervention
Authors: Goodey Jo
Published: March 2004

Since the collapse of the Berlin wall, women and girls have been trafficked from central and eastern Europe to work as prostitutes in the European Union. This paper looks at the response of the international community to the problem of sex trafficking as it impacts on the EU. The focus is on criminal justice intervention with respect to protection of and assistance to ‘victims’, and a specially witness protection, in the light of the following: the tensions and promises between treatment of trafficked women as ‘victims’ of crime and criminal justice informants; and the need to re-focus on a ‘woman-centred’ approach to criminal justice intervention for trafficked women. Given the diverse nature of law and criminal justice practice between EU Member States, the paper necessarily presents a generic critique of current EU and international ‘best practice’ recommendations, with some commentary on practice based on the author's research, with respect to what ‘gold standards’ of practice offer in theory and what is delivered in reality. The question of ‘victim-centred’ justice and/or ‘woman-centred’ justice is raised in an effort to promote effective policy recommendations.
Turbidity determination of the critical exponent η in the liquid–liquid mixture methanol and cyclohexane
Authors: Lytle Amy , Jacobs D. T.
Published: March 2004

The turbidity of the liquid–liquid mixture methanol–cyclohexane has been measured very near its critical point and used to test competing theoretical predictions and to determine the critical correlation-correction exponent η. By measuring the ratio of the transmitted to incident light intensities over five decades in reduced temperature, we are able to determine that Ferrell’s theoretical prediction for the turbidity explains the data with the correlation length amplitude ξ0=0.330±0.003 nm and critical exponents η=0.041±0.005 and ν=0.632±0.002. These values are consistent with the values measured before for ξ0 in this system and with the exponents predicted by theory. The data allow five different theoretical expressions to be tested and to select two as being equivalent when very close to the critical point.
Thermodynamic perturbation theory for fused sphere hard chain fluids using nonadditive interactions
Authors: Abu-Sharkh Basel F. , Sunaidi Abdallah , Hamad Esam Z.
Published: March 2004

A model is developed for the equation of state of fused chains based on Wertheim thermodynamic perturbation theory and nonadditive size interactions. The model also assumes that the structure (represented by the radial distribution function) of the fused chain fluid is the same as that of the touching hard sphere chain fluid. The model is completely based on spherical additive and nonadditive size interactions. The model has the advantage of offering good agreement with simulation data while at the same time being independent of fitted parameters. The model is most accurate for short chains, small values of Δ (slightly fused spheres) and at intermediate (liquidlike) densities.
The influence of bond flexibility and molecular size on the chemically selective bonding of In2O and Ga2O on GaAs(001)-c(2×8)/(2×4)
Authors: Hale M. J. , Sexton J. Z. , Winn D. L. , Kummel A. C. , Erbudak M. , Passlack M.
Published: March 2004

The surface structures formed upon deposition of In2O and Ga2O by molecular beam epitaxy onto the arsenic-rich GaAs(001)-c(2×8)/(2×4) surface have been studied using scanning tunneling microscopy and density functional theory. In2O initially bonds, with indium atoms bonding to second layer gallium atoms within the trough, and proceeds to insert into or between first layer arsenic dimer pairs. In contrast, Ga2O only inserts into or between arsenic dimer pairs due to chemical site constraints. The calculated energy needed to bend a Ga2O molecule approximately 70°, so that it can fit into an arsenic dimer pair, is 0.6 eV less than that required for In2O. The greater flexibility of the Ga2O molecule causes its insertion site to be 0.77 eV more exothermic than the In2O insertion site. This result shows that although trends in the periodic table can be used to predict some surface reactions, small changes in atomic size can play a significant role in the chemistry of gas/surface reactions through the indirect effects of bond angle flexibility and bond length stiffness.
Vibrational dynamics of 9-fluorenemethanol using infrared–ultraviolet double-resonance spectroscopy
Authors: Basu Swarna , Knee J. L.
Published: March 2004

Vibrational spectroscopy of jet-cooled 9-fluorenemethanol and its clusters 9-fluorenemethanol–H2O, 9-fluorenemethanol–CH3OH, 9-fluorenemethanol–C2H5OH, and 9-fluorenemethanol–C3H7OH has been carried out using an IR–UV double-resonance method. The spectrum of the OH stretching vibration, vOH, has been measured for the 9-fluorenemethanol monomer and for each of the clusters. Two conformers of 9-fluorenemethanol, symmetric (sym) and unsymmetric (unsym), have been identified using a combination of spectroscopy and quantum chemical calculations with B3LYP and HF methods using the 6-31G(d) basis set. Vibrational dynamics resulting from IR excitation has also been studied using the S0–S1 transition probed by a nanosecond-time-delayed UV laser. The data suggest that isomerization occurs as a result of the IR excitation, but the breadth of the probe spectra makes an unequivocal conclusion difficult. The effect of hydrogen bonding on the vOH of 9-fluorenemethanol has also been studied in clusters with water, methanol, ethanol, and propanol by measuring the IR spectra. Cluster dissociation dynamics have also been studied following IR excitation. It is observed that upon excitation of the cluster of a particular conformation the monomer product is generally produced in both conformer forms. Energetic considerations indicate that isomerization occurs before dissociation.
Solution of the linearized Poisson–Boltzmann equation
Authors: Chipman Daniel M.
Published: March 2004

Improved methods are formulated for solution of the linearized Poisson–Boltzmann equation, to be used in conjunction with electronic structure calculation on a solute together with dielectric continuum representation of the salt-containing solvent. Volume polarization effects due to quantum mechanical penetration of solute charge density outside the cavity that excludes solvent are treated by exact and by approximate methods analogous to those previously developed for the salt-free case. With boundary element approaches, exact solutions lead to coupled equations for a pair of cavity surface distributions that mimic the polarization of the solvent dielectric and the ionic atmosphere. A novel means is found to effectively decouple these equations, yielding more efficient practical methods for their numerical solution. Detailed comparisons are given to related boundary element formulations previously reported in the literature, which neglect volume polarization, and analogous decoupling is also found for the pair of surface distributions invoked there. Illustrative results are provided for a simple spherical example.
Molecular dynamic simulation methods for anisotropic liquids
Authors: Aoki Keiko M. , Yoneya Makoto , Yokoyama Hiroshi
Published: March 2004

Methods of molecular dynamics simulations for anisotropic molecules are presented. The new methods, with an anisotropic factor in the cell dynamics, dramatically reduce the artifacts related to cell shapes and overcome the difficulties of simulating anisotropic molecules under constant hydrostatic pressure or constant volume. The methods are especially effective for anisotropic liquids, such as smectic liquid crystals and membranes, of which the stacks of layers are compressible (elastic in direction perpendicular to the layers) while the layer itself is liquid and only elastic under uniform compressive force. The methods can also be used for crystals and isotropic liquids as well.
Isomers of HSCO: IR absorption spectra of t-HSCO in solid Ar
Authors: Lo Wen-Jui , Chen Hui-Fen , Wu Yu-Jong , Lee Yuan-Pern
Published: March 2004

Irradiation of an Ar matrix sample containing H2S and CO (or OCS) with an ArF excimer laser at 193 nm yields trans-HSCO (denoted t-HSCO). New lines at 1823.3, 931.6, and 553.3 cm−1 appear after photolysis and their intensity enhances after annealing; secondary photolysis at 248 nm diminishes these lines and produces OCS and CO. These lines are assigned to C–O stretching, HSC-bending, and C–S stretching modes of t-HSCO, respectively, based on results of C13-isotopic experiments and theoretical calculations. Theoretical calculations using density-functional theories (B3LYP and PW91PW91) predict four stable isomers of HSCO: t-HSCO, c-HSCO, HC(O)S, and c-HOCS, listed in increasing order of energy. According to calculations with B3LYP/aug-cc-pVTZ, t-HSCO is planar, with bond lengths of 1.34 Å (H–S), 1.81 Å (S–C), and 1.17 Å (C–O), and angles ∠HSC≅93.4° and ∠SCO≅128.3°; it is more stable than c-HSCO and HC(O)S by ∼9 kJ mol−1 and more stable than c-HOCS by ∼65 kJ mol−1. Calculated vibrational wave numbers, IR intensities, and C13-isotopic shifts for t-HSCO fit satisfactorily with experimental results. This new spectral identification of t-HSCO provides information for future investigations of its roles in atmospheric chemistry.
A study on the anisole–water complex by molecular beam–electronic spectroscopy and molecular mechanics calculations
Authors: Becucci M. , Pietraperzia G. , Pasquini M. , Piani G. , Zoppi A. , Chelli R. , Castellucci E. , Demtroeder W.
Published: March 2004

An experimental and theoretical study is made on the anisole–water complex. It is the first van der Waals complex studied by high resolution electronic spectroscopy in which the water is seen acting as an acid. Vibronically and rotationally resolved electronic spectroscopy experiments and molecular mechanics calculations are used to elucidate the structure of the complex in the ground and first electronic excited state. Some internal dynamics in the system is revealed by high resolution spectroscopy.
Relativistic double group spinor representations of nonrigid molecules
Authors: Balasubramanian K.
Published: March 2004

The character theory of relativistic double group spinor representations is developed in order to represent the total rovibronic states of nonrigid molecules. It is shown that the double groups can be represented in terms of wreath products and powerful matrix cycle type generators that are used to construct their character tables. It is shown that these tables are of use when spin–orbit coupling is included in the Hamiltonian even for molecules containing lighter atoms. Applications to nonrigid molecules such as Tl2H4/Tl2H4+ are considered. It is shown that the tunneling splittings and the nuclear spin statistical weights can be obtained for such species using the character tables thus constructed. The spinor double groups of several other molecules such as hexamethyl dilead and heavy weakly bound clusters such as (PoH2)4 are also considered.
Comparison of spectroscopic potentials and an a priori analytical function. The potential energy curve of the ground state of the sodium dimer, X 1Σg+ Na2
Authors: Matsunaga Nikita , Zavitsas Andreas A.
Published: March 2004

The results of a “universal” potential energy function, one that incorporates electronegativity and Slater’s effective nuclear charge into a Morse-type function, are compared to spectroscopically derived potential energy curves of the X 1Σg+ state of Na2. The function is a priori in that it does not require prior knowledge of the actual potential and has no adjustable parameters. Criteria used to evaluate the performance of the function are comparisons of predicted versus spectroscopic energies at Rydberg–Klein–Rees (RKR) procedure turning points, predicted distances at measured energies versus RKR distances, and eigenvalues derived from the a priori potential versus spectroscopically deduced energy levels. The a priori function describes the Na2 potential with deviations approaching the magnitude of those found among some spectroscopic potentials from different sources. By examining the behavior of the “spectroscopic” parameter of the Morse function, irregularities are found in five of the seven spectroscopic potentials examined. A new procedure is demonstrated for correcting irregularities on the inner branch of spectroscopic potentials at high extents of dissociation and for extending reliably the potential in this region beyond the domain of the measurements.
Three-dimensional Ewald method with correction term for a system periodic in one direction
Authors: Bródka A. , Śliwiński P.
Published: March 2004

A three-dimensional Ewald summation formula with a shape-dependent correction term for Coulomb interactions in systems with one-dimensional periodicity is derived. Test molecular dynamics simulations of acetone molecules in cylindrical silica pores show that the formula is efficient only when size of the system in a plane perpendicular to the periodicity direction is small in comparison with the periodicity length.
Molecular simulation of the reversible mechanical unfolding of proteins
Authors: Rathore Nitin , Yan Qiliang , de Pablo Juan J.
Published: March 2004

In this work we have combined a Wang–Landau sampling scheme [F. Wang and D. Landau, Phys. Rev. Lett. 86, 2050 (2001)] with an expanded ensemble formalism to yield a simple and powerful method for computing potentials of mean force. The new method is implemented to investigate the mechanical deformation of proteins. Comparisons are made with analytical results for simple model systems such as harmonic springs and Rouse chains. The method is then illustrated on a model 15-residue alanine molecule in an implicit solvent. Results for mechanical unfolding of this oligopeptide are compared to those of steered molecular dynamics calculations.
Dissociative ionization of methane by chirped pulses of intense laser light
Authors: Mathur D. , Rajgara F. A.
Published: March 2004

Measurements have been made of optical field-induced ionization and fragmentation of methane molecules at laser intensities in the 1016 W cm−2 range using near transform limited pulses of 100 fs duration as well as with chirped pulses whose temporal profiles extend up to 1500 fs. Data is taken both in constant-intensity and constant-energy modes. The temporal profile of the chirped laser pulse is found to affect the morphology of the fragmentation pattern that is measured. Besides, the sign of the chirp also affects the yield of fragments like C2+, H+, and H2+ that originate from methane dications that are formed by optical field-induced double ionization.
Relaxation of H2O from its |04〉− vibrational state in collisions with H2O, Ar, H2, N2, and O2
Authors: Barnes Peter W. , Sims Ian R. , Smith Ian W. M.
Published: March 2004

We report rate coefficients at 293 K for the collisional relaxation of H2O molecules from the highly excited |04〉± vibrational states in collisions with H2O, Ar, H2, N2, and O2. In our experiments, the |04〉− state is populated by direct absorption of radiation from a pulsed dye laser tuned to ∼719 nm. Evolution of the population in the (|04〉±) levels is observed using the combination of a frequency-quadrupled Nd:YAG laser, which selectively photolyses H2O(|04〉±), and a frequency-doubled dye laser, which observes the OH(v=0) produced by photodissociation via laser-induced fluorescence. The delay between the pulse from the pump laser and those from the photolysis and probe lasers was systematically varied to generate kinetic decays. The rate coefficients for relaxation of H2O(|04〉±) obtained from these experiments, in units of cm3 molecule−1 s−1, are: k(H2O)=(4.1±1.2)×10−10, k(Ar)=(4.9±1.1)×10−12, k(H2)=(6.8±1.1)×10−12, k(N2)=(7.7±1.5)×10−12, k(O2)=(6.7±1.4)×10−12. The implications of these results for our previous reports of rate constants for the removal of H2O molecules in selected vibrational states by collisions with H atoms (P. W. Barnes et al., Faraday Discuss. Chem. Soc. 113, 167 (1999) and P. W. Barnes et al., J. Chem. Phys. 115, 4586 (2001).) are fully discussed.
Multicanonical basin hopping: A new global optimization method for complex systems
Authors: Zhan Lixin , Piwowar Bart , Liu Wing-Ki , Hsu P. J. , Lai S. K. , Chen Jeff Z. Y.
Published: March 2004

We introduce a new optimization algorithm that combines the basin-hopping method, which can be used to efficiently map out an energy landscape associated with minima, with the multicanonical Monte Carlo method, which encourages the system to move out of energy traps during the computation. As an example of implementing the algorithm for the global minimization of a multivariable system, we consider the Lennard-Jones systems containing 150–185 particles, and find that the new algorithm is more efficient than the original basin-hopping method.
Self-assembly of rod–coil block copolymers
Authors: Pryamitsyn Victor , Ganesan Venkat
Published: March 2004

We present a self-consistent field theory model for the self-assembly behavior of rod–coil block copolymers. The orientational interactions between the rods were modeled through a Maier–Saupe interaction, while the enthalpic interactions between rods and coils were modeled through a standard Flory–Huggins approach. We outline a “real-space” numerical approach to solve the self-consistent field equations for such rod–coil block copolymers. A major focus of our work is upon the nonlamellar phases observed in the experiments on such polymers. To develop a physical understanding of these phases and their regimes of occurrence, we compute the two-dimensional phase diagram for our model. The latter shows significant departures from the one-dimensional phase diagram, but matches qualitatively with the existing experimental results. We also present scaling arguments that rationalize the numerical results for the self-assembly behavior.
Insulator to metal transition in fluid deuterium
Authors: Hood Randolph Q. , Galli Giulia
Published: March 2004

We have investigated the insulator to metal transition in fluid deuterium using first principles simulations. Both density functional and quantum Monte Carlo calculations indicate that the electronic energy gap of the liquid vanishes at about ninefold compression and 3000 K. At these conditions the computed conductivity values are characteristic of a poor metal. These findings are consistent with those of recent shock wave experiments but the computed conductivity is larger than the measured value. From our ab initio results we conclude that the transition is driven by molecular dissociation rather than disorder and that both temperature and pressure play a key role in determining structural changes in the fluid.
Basis set study of classical rotor lattice dynamics
Authors: Witkoskie James B. , Wu Jianlan , Cao Jianshu
Published: March 2004

The reorientational relaxation of molecular systems is important in many phenomenon and applications. In this paper, we explore the reorientational relaxation of a model Brownian rotor lattice system with short range interactions in both the high and low temperature regimes. In this study, we use a basis set expansion to capture collective motions of the system. The single particle basis set is used in the high temperature regime, while the spin wave basis is used in the low temperature regime. The equations of motion derived in this approach are analogous to the generalized Langevin equation, but the equations render flexibility by allowing nonequilibrium initial conditions. This calculation shows that the choice of projection operators in the generalized Langevin equation (GLE) approach corresponds to defining a specific inner-product space, and this inner-product space should be chosen to reveal the important physics of the problem. The basis set approach corresponds to an inner-product and projection operator that maintain the orthogonality of the spherical harmonics and provide a convenient platform for analyzing GLE expansions. The results compare favorably with numerical simulations, and the formalism is easily extended to more complex systems.
Stress relaxation of deformed gel in a good solvent
Authors: Sasaki Shigeo
Published: March 2004

A method for obtaining elastic moduli and frictional properties of gel chains, diagonal and off-diagonal elements of a friction tensor, from a tensile force relaxation of cylindrical gel that is stretched in a good solvent is presented. The theory to describe the relaxation is developed on the assumption that an off-diagonal element of the friction tensor is nonzero and compared with experimental results obtained for the poly(acrylamide) gel in water. The experiments revealed that the tensile force relaxation, F(t) at a long t, was described by a function: F(t)=A(Fi−FS)exp(−t/τ)+FS, where Fi, FS, and A, respectively, were tensile forces at the initiation and the steady state, and a constant. The τ was found to be proportional to a square of radius of the gel. The experiments also revealed that the elastic force relaxation was synchronized with a change of the gel diameter. The theory well elucidates the experimental results to reveal the bulk and shear moduli, and the diagonal and off-diagonal elements of friction tensor.
Self-assembly of peptides into a β-barrel motif
Authors: Friedel Miriam , Shea Joan-Emma
Published: March 2004

We report the results of a study of the self-assembly of four minimalist peptide strands with a native β-barrel structure. Using a soft-well potential to mimic cellular crowding, molecular dynamics simulations were performed in confining spheres of varying radii. By utilizing a previously introduced scaling factor λ for the non-native hydrophobic interactions (0<λ<1), we were able to study models with varying degrees of frustration. Both the thermodynamics and kinetics of a Gō-like model (λ=0) and a highly frustrated model (λ=0.9) were studied. Additionally, we used an extrapolation technique to investigate the thermodynamics of assembly at intermediate values of λ. As in our earlier work [J. Chem. Phys. 118, 8106 (2003)] on a connected Gō-like model β-barrel protein, we find that the stability of the assembled protein increases with decreasing sphere size, and that larger confining spheres result in increased assembly times. Additionally, the λ=0 model seems to undergo distinct phase transitions during the assembly process. In contrast, the more frustrated model (λ=0.9) appears to undergo a glasslike transition at temperatures comparable to the assembly temperature of the Gō model, and that this transition is relatively nonspecific. Our results suggest the assembly process is dependent on both sequence and environment, with implications for the formation of misassembled aggregates.
The shape of transmission spectra of thin films deposited on a substrate
Authors: Bortchagovsky E. G. , Fischer U. C. , Fuchs H.
Published: March 2004

On the basis of the previous considerations [E. G. Bortchagovsky and U. C. Fischer, J. Chem. Phys. 117, 5384 (2002)] we analyze here the shape of the spectral lines created in transmission spectra by thin films deposited on a substrate. We demonstrate that such lines have as a rule the shape of an asymmetrical Fano line with the minimum shifted from the resonance position. Thus we present the additional argument that the popular visual estimation of the parameters of resonances from the shape of those lines should be made with care.
Adsorption and reaction of methanol on clean and oxygen modified rhodium/vanadium surface alloys
Authors: Krenn G. , Schennach R.
Published: March 2004

The dehydrogenation of methanol on Rh(111), on a Rh(111)/V subsurface alloy and on Rh(111) with V islands has been studied with and without preadsorbed oxygen using a supersonic molecular beam and temperature programmed desorption. The reactivity is highest for the V islands surface without oxygen. But this surface is deactivated due to CO dissociation. The subsurface alloy is less reactive than the islands, but still more active than the Rh(111) surface. The reaction products are carbon monoxide and hydrogen only. With preadsorbed oxygen Rh(111) is the most active surface, but a strong dependence of the activity on the amount of preadsorbed oxygen is found for all three surfaces. The reaction products with preadsorbed oxygen are water, hydrogen, carbon dioxide and carbon monoxide. The reactions follow the same mechanism on all surfaces, but the activation energy of the individual reaction steps is different leading to significant changes in the thermal desorption spectra and in King and Wells-type experiments.
Molecular binding at gold transport interfaces. IV. Thiol chemisorption
Authors: Basch Harold , Ratner Mark A.
Published: March 2004

Alkene thiol/coinage metal molecular interfaces are relatively easy to make, and can result in well-ordered self-assembled monolayer films. The energetics of such formation is complex-differing experimental and theoretical accounts have focused on the nature of the binding, the energetics via different pathways (thiol radical, thiol or thiolate) and the geometry of binding. We report density functional theory calculations on a four atom gold cluster interacting with different (alkane, alkene, alkyne) thiolates. We find thiolate addition to be strongly exoergic, thiol radical to be roughly half as favorable, and thiol to be slightly favorable. We also find that the S–H bond can remain when the thiol attaches to the gold cluster, formally resulting in increased coordination on the sulfur atom.
Generalized monotonically convergent algorithms for solving quantum optimal control problems
Authors: Ohtsuki Yukiyoshi , Turinici Gabriel , Rabitz Herschel
Published: March 2004

A wide range of cost functionals that describe the criteria for designing optimal pulses can be reduced to two basic functionals by the introduction of product spaces. We extend previous monotonically convergent algorithms to solve the generalized pulse design equations derived from those basic functionals. The new algorithms are proved to exhibit monotonic convergence. Numerical tests are implemented in four-level model systems employing stationary and/or nonstationary targets in the absence and/or presence of relaxation. Trajectory plots that conveniently present the global nature of the convergence behavior show that slow convergence may often be attributed to “trapping” and that relaxation processes may remove such unfavorable behavior.
The elementary steps of the photodissociation and recombination reactions of iodine molecules enclosed in cages and channels of zeolite crystals: A femtosecond time-resolved study of the geometry effect
Authors: Flachenecker G. , Materny A.
Published: March 2004

We present femtosecond time-resolved pump–probe experiments on iodine molecules enclosed into well-defined cages and channels of different crystalline SiO2 modifications of zeolites. The new experimental results obtained from iodine in TON (Silica-ZSM-22), FER (Silica-Ferrierit), and MFI (Silicalit-1) porosils are compared with data published earlier on the iodine/DDR (Decadodecasil 3R) porosil system [Flachenecker et al., Phys. Chem. Chem. Phys. 5, 865 (2003)]. A summary of all findings is given. The processes analyzed by means of the ultrafast spectroscopy are the vibrational relaxation as well as the dissociation and recombination reactions, which are caused by the interaction of the photo-excited iodine molecules with the cavity walls of the porosils. A clear dependence of the observed dynamics on the geometry of the surrounding lattice structure can be seen. These measurements are supported by temperature-dependent experiments. Making use of a theoretical model which is based on the classical Langevin equation, an analysis of the geometry-reaction relation is performed. The Brownian dynamics simulations show that in contrast to the vibrational relaxation the predissociation dynamics are independent of the frequency of collisions with the surroundings. From the results obtained in the different surroundings, we conclude that mainly local fields are responsible for the crossing from the bound B state to the repulsive a/a′ states of the iodine molecules.
Quantum initial value representation simulation of water trimer far infrared absorption spectrum
Authors: Shalashilin D. V. , Child M. S. , Clary D. C.
Published: March 2004

We extend the technique of quantum propagation on a grid of trajectory guided coupled coherent states to simulate experimental absorption spectra. The approach involves calculating the thermally averaged dipole moment autocorrelation function by means of quantum propagation in imaginary time. The method is tested on simulation of the far infrared spectrum of water trimer based on a three-dimensional model potential. Results are in good agreement with experiment and with other calculations.
Gas-Phase Ignition of a Solid Fuel in a Shock Tube
Authors: Chang Ching Ming
Published: March 2004

A new gas-phase ignition theory of solid propellants is presented in which the surface temperature is allowed to change and the fuel vapor consumption during the ignition period is taken into account. Use is made of the heat balance condition as well as the relation connecting fuel concentration and temperature at the propellant surface. Analytical approximate solutions are derived for the temperature and fuel concentration in the gas phase. Ignition delays are calculated for an organic solid fuel in the oxygen atmosphere as an example. In the temperature region investigated T = 1250-2500°K, these theoretical results agree fairly well with the corresponding experimental data obtained in a shock tube. It is concluded that by using the achieved analytical solutions, the gas-phase ignition behavior of solid propellants can be properly described.
Single-Pulse Shock-Tube Studies of the Pyrolysis of Fluorocarbons and of the Oxidation of Perfluoroethylene
Authors: Bauer S. H. , Hou K. C. , Resler E. L.
Published: March 2004

The gas phase pyrolysis and oxidation of several low molecular weight fluorocarbons were investigated in single-pulse shock tubes, using vapor phase chromatography and mass spectral analyses to establish the nature and the relative amounts of all the products generated as a function of the reflected shock temperature and the initial composition. Dwell times were approximately 1 msec and quenched rates were about 1°/μsec. Shocks were run in mixtures ranging from 0.5-3% of fluorocarbons in argon. Plots of product distributions as a function of reflected shock temperatures have been prepared for perfluorocyclobutane, butadiene, cyclopropane, propene, and ethylene. Several equilibrium constants for the interconversions of fluorocarbons were evaluated at a function of temperature, a mechanism of the pyrolysis reactions δ developed, and the corresponding rate constants estimated. Mixtures of perfluoro-ethylene in oxygen, highly diluted in argon, were shock-heated for periods of about 1.3 msec to temperatures in the range 1200-2000°K. The major products were F2CO, CO, CF4, C2F6 and very small amounts of C3F6 and CO2. On the basis of the product distribution analyses a plausible mechanism for the oxidation reaction has been developed.
Study of the Thermal Decomposition of n-Butane
Authors: Wittig Sigmar L. K.
Published: March 2004

The use of a new opening mechanism for diaphragms simplifies the investigation of the thermal decomposition of hydrocarbons with the single-pulse shock tube. In addition to achievement of good reproducibility, the pressure range is extended so that the conditions of the tailored interface can be varied over a wide range. The pyrolysis of n-butane was investigated up to 1400°K and the reaction was found to be of first order. The activation energy, frequency factor, and product distribution are given.
Interaction of an Advancing Shock Front with a Concentrated Heat (Entropy) Source
Authors: Dosanjh Darshan S. , Hamernik Roger P.
Published: March 2004

The results of an experimental investigation conducted in a shock tube on the interaction of a reflected normal shock front with a two-dimensional highly heated thin gaseous filament are reported. The heated gaseous filament was created at a predetermined time either by exploding a fine gauge copper wire or by an arc discharge between two thin needle electrodes in the drift flow of the incident shock wave. The transient interaction phenomena were recorded systematically by spark interferometric and schlieren techniques. These data revealed that; (a) A cylindrical band of acoustic waves centered on the transmitted (interacted) heated filament is generated behind the reflected shock front. On the basis of the analysis of the interferometric data, the leading acoustic wave front was found to have an alternate compression-rarefaction type of density distribution along its circumference. (b) Owing to its passage through the heated filament, the reflected normal shock becomes distorted. (c) The interacted heated gaseous filament split into two vortexlike flow regions.
Improvements in Design of Thin-Film Heat Transfer Gages for a Low-Pressure Shock Tube
Authors: Bowman Robert M.
Published: March 2004

The theoretical optimum ballast resistance for maximum response of a film gage circuit is derived. This resistance leads to a much higher gage voltage than is ordinarily used. Provided platinum leads are used, so that bimetallic mismatch and the consequent burnout is eliminated, the response of the gage is limited only by the increase of its resistance with temperature. Such a gage is capable of producing shock arrival time, thickness, and structure data over the entire operating range of a low-pressure shock tube without amplification external to the oscilloscope. Adequate unamplified response has been demonstrated down to 3 × 10−4 Torr (a factor of 100 better than was obtainable by the piezoceramic gages previously in use). Order of magnitude improvements in spatial and temporal resolution over previous gages have also been made.
Diagnostic Experiments on Converging Detonations
Authors: Knystautas R. , Lee B. H. K. , Lee J. H. S.
Published: March 2004

Photographic observations of the formation of a cylindrical detonation wave from the “patching up” of a number of planar detonation wavelets are reported. It is shown that “Mach type” reflections are responsible for the smoothing out of the curvature of the original polygonal wave front. There is evidence that stable cylindrical convergence is achieved on the basis that large-scale vorticity in the flow field behind the reflected shock wave after collapse is absent, and an extremely high temperature lasting for a few microseconds is detected. Spectroscopic studies show that a temperature of 1.89 × 105 °K is obtained when the imploding wave reflects from the center of symmetry.
Measurements with Powdered Solids in Shock Tubes
Authors: Hooker W. J. , Watson R. , Morsell A. L.
Published: March 2004

An application of the two-phase powder shock tube to the study of solid particle vaporization and hypervelocity impact is described. The measured vaporization rate of Teflon powder in a shock-heated argon bath is shown to be consistent with analytical predictions based on free molecular heat transfer with unit thermal accommodation coefficient. Measurements of hypervelocity impact of micron-size Alundum particles on flat and conical lead models showed that crater mass loss becomes independent of impact angle of incidence once the target roughness dimensions become comparable to impacting particle size.
Atomic Spectroscopy with the Shock Tube
Authors: Wilkerson T. D. , Koopman D. W. , Miller M. , Bengtson R. , Charatis G.
Published: March 2004

The application of the shock tube to transition probability measurements is discussed, with particular attention to determination of the thermodynamic state of the radiating gas. Specific examples from earlier work on the spectrum of neutral chromium and from current measurements for light atoms clarify the need for redundant temperature determinations and illustrate the value of a new technique of data analysis which circumvents the sensitive dependence of level populations on temperature.
Radiation Gas Dynamics in the Shock Tube
Authors: Griffith Wayland C. , Wood Allen D.
Published: March 2004

An assessment of the shock tube as an instrument for research in radiation gas dynamics is presented. Principal results obtained since Kantrowitz and Laporte first observed luminous fronts are described and the roles of impurity and nonequilibrium radiation, spectral intensities, rate processes, and continuum radiation are discussed. Spectroscopy was originally used as an aid to understanding problems in gas dynamics at moderate temperatures. More recently the shock tube has been used as a tool for spectroscopic research. The present trend is toward a fusion of these two interests in studying radiation-coupled flows where radiant energy transport affects the flow field. Present day shock tubes with arc-heated drivers attain thermodynamic conditions typical of superorbital speeds—the regime where radiant energy transfer becomes important. The current interest is in determining the radiative properties of gases at these high temperatures (10 000-20 000°K). Here the presence of significant amounts of vacuum ultraviolet radiation causes instrumentation problems which hamper investigations at present. However, solutions have been devised. Shock-tube results are compared to current theoretical predictions for the spectrally integrated total radiant intensity of high-temperature air. These reveal differences on the order of a factor of 2 and also clarify certain important areas of future endeavor. These include thermodynamic state measurements of gases shocked to temperatures above 10 000°K, additional measurements of the total intensity, and measurements of the spectral radiant intensity of high-temperature gases. An extensive bibliography is included.
Influence of Reflected Shock and Boundary-Layer Interaction on Shock-Tube Flows
Authors: Davies L. , Wilson J. L.
Published: March 2004

During the last decade the study of the interaction between normal shocks and boundary layers in the shock tube has been carried out by many research workers. This interest has been fostered by the requirement to understand the effects that this phenomenon may have on the flow properties in the region between the reflected shock and the end of the tube. This so-called reflected shock region is important in chemical kinetics studies and as a reservoir of gas for hypersonic shock tunnels. In this paper a review is given of the various analyses of the problem together with the results of experimental studies. Reflected and transmitted shock bifurcation, the rate of growth of the bifurcated foot, and the effects of transition to turbulence are discussed. The influence of bifurcation on the flow in the shock tube is assessed, especially as a mechanism for transporting cold driver gas to the end plate, causing early cooling of the gas on the reflected shock region.
Shock-Tube Measurements of van der Waals Broadened Silicon Lines
Authors: Day Richard A.
Published: March 2004

The widths of van der Waals broadened Si I spectral lines were measured by using a conventional shock tube and a scanning Fabry-Perot interferometer. The experiments have been performed by using argon as the perturbing gas in the reflected region of the shock wave at a temperature of about 5500°K and over a pressure range of 2-10 atm. The temperature was determined by a line reversal technique; the pressure was measured using a quartz transducer. The scanning Fabry-Perot was driven by a piezoelectric crystal operating at its resonant frequency (10.5 kc/sec); the line profiles were detected photoelectrically and displayed on an oscilloscope for photographing and analyzing. A set of calculated curves was used to obtain the contribution of the pressure broadening to the widths of the spectral lines. The experimental widths thus determined are within a factor of two of the results obtained from theory.
Radiation Cooling behind a Strong Shock in Krypton
Authors: Rehder L. , Bötticher W. , Carls H. , Graap V.
Published: March 2004

Strong shocks at Mach numbers from 10 to 15 and at initial pressures between 1 and 10 Torr are produced in a conventional diaphragm shock tube. The effect of radiative energy loss from the plasma behind the shock is studied by quantitative measurement of the decay of continuous emission at λ = 4000 Å. It is shown that for high electron densities the maximum emissivity deviates remarkably from Unsöld's theory. The variation of flow parameters with increasing distance from the shock front is calculated using an iterative method developed by Pomerantz. The results indicate that the observed luminosity decay cannot be explained by losses of continuous radiation alone. The influence of resonance radiation and line emission on the plasma cooling rate is briefly discussed.
Measurement of Ionization Relaxation Times in Shock Tubes
Authors: Frohn A. , de Boer P. C. T.
Published: March 2004

Ion density profiles for low Mach numbers (7-9) have been obtained in a pressure-driven shock tube. In this Mach number range the ionization process is strongly influenced by small amounts of impurities. Various techniques for minimizing the impurity level due to outgassing from the shock tube walls and back diffusion of pump oil are discussed. Preliminary results for argon are described. For air new results for the ionization relaxation time are obtained.
Experimental Determination of the Gladstone-Dale Constants for Dissociating Oxygen
Authors: Anderson J. H. B.
Published: March 2004

Details are presented of an experimental determination of the Gladstone-Dale constants for dissociating high-temperature oxygen. The hot dissociating gas was obtained by shock heating (M = 8.8-16.6, p1 = 4-54 Torr), and the index of refraction of the hot gas relative to room temperature gas was determined by photographing the shock wave with an interferometer. The change in density across the shock was obtained from normal shock calculations and, thus, the Gladstone-Dale constants could be determined. The results were: 1.93 cm3/g ± 1% for the oxygen molecule, and 2.04 cm3/g ± 2% for the oxygen atom, which were in agreement with the results obtained by Alpher and White. Details are presented of the high-speed photographic techniques employed, of the method used to reduce the data, and of the problems encountered during the investigation.
Normal and Transverse Ionizing Shock Studies
Authors: Gross R. A. , Levine L. S. , Meehan R. J. , Miller B.
Published: March 2004

Recent experimental and theoretical studies of normal and transverse ionizing shocks are summarized. Results of normal ionizing shock studies are reviewed briefly. Transverse ionizing shocks have been observed traveling with speeds and drive currents that are in excellent agreement with a snowplow-type theory. It is noted that small bias fields cause significant shunting of the total discharge current at the launch end of the shock tube while large bias fields inhibit shunting and thereby enhance shock-tube performance. Evidence is presented supporting the hypothesis that this effect is caused by sputtering of heavy-metal vapors from the launch area of the shock tube.
Generation of a Fissioning Plasma in a Shock Tube
Authors: Podney Walter N. , Smith Harold P. , Oppenheim A. K.
Published: March 2004

A method of producing a fissioning plasma in a shock tube is proposed. For this purpose a tube is filled with UF6235 gas and one end is imbedded in a suitable neutron-reflecting material such as graphite, deuterium, or beryllium. Tube diameter, reflector depth, and initial gas density are chosen so that neutron multiplication within the reflector zone is somewhat less than unity. A shock wave is then introduced into the reflector zone. The additional amount of fissionable material compiled by the wave produces a supercritical mass within the reflector zone; consequently, the fission rate increases rapidly. The subsequent flow field generated by fission-fragment energy deposited in the medium is determined by assuming that the state of the fissioning medium is variable in time but uniform in space. On this basis it is demonstrated that a substantial induction time (∼200 msec) is required before the power density is large enough to start expansion of the fissioning substance. For a tube of 10-cm radius with a deuterium reflector extending over a length of 3 m, the estimated energy density produced by a shock of Mach 2 is of the order of 30 kW-sec cm−3. The maximum pressure and temperature attained are of the order of 100 atm and 10 000°K.
Side-Pinch Effect of a Magnetically Driven Shock Tube with Parallel Plate Electrodes
Authors: Chang C. T. , Korsbech U. , Mondrup K.
Published: March 2004

To study the possible effect of the side pinch on the steady-state current and the steady-state shock speed of a magnetically driven shock tube, a semiempirical model is formulated. The time history of the current, the radial and the translational motion of the current-carrying region are expressed by three interacting nonlinear equations with five adjustable parameters describing the variation of the electric circuit elements, the geometry of the shock tube, and the initial running conditions. Within the range of practical interest for values of the parameters investigated, computational results show that the current-carrying region oscillates radially, but the current and the translational velocity of the current-carrying region approach the quasi-steady state rapidly. The deviation of the current from its “steady-state” value (when the pinch effect is absent) in no case amounts to more than 5%.
Evaluation of the Driver Chamber Efficiency for an Arc Driven Shock Tube
Authors: Kelley Joseph G. , Levine Morton A. , Besse Arthur L. , Tatarian Albert
Published: March 2004

A prestressed ceramic driver chamber, which is capable of withstanding 30 000 psi internal pressure, has been designed, built and operated. Energy input to the chamber was determined by the voltage on the capacitor bank used to arc heat the gas. Temperature in the head was derived from the velocity of expansion into a vacuum. The results indicated an 0.49 efficiency for transfer of energy from the capacitor bank to the gas. This was confirmed within the experimental accuracy of 10% by pressure measurements with a piezoelectric probe mounted in the driver chamber. Driver chamber temperatures up to 28 000°K were observed. No significant radiation or ablation effects were noted. Energy transfer is achieved in 35 msec after which equilibrium conditions are observed until the diaphragm opens at 70 msec. Driver pressures of up to 18 000 psi were recorded.
Shock-Tube Spectroscopy of Ablative Species
Authors: Wurster Walter H.
Published: March 2004

A technique has been developed which permits shock-tube spectrometric measurements of radiation to be made from molecules normally occurring as solids prior to decomposition. Use is made of a metallic-aerosol generator, in which a wire of suitable material is exploded in a controlled gaseous environment. The resultant aerosol serves as the test gas upon expansion into the shock tube. The particles are vaporized by shock waves, and spectra are recorded behind the reflected shock. Several advantages accrue from this technique. Most important for spectroscopic purposes is the fact that the metals are introduced in pure form. The metallic-aerosol technique and its experimental validation are discussed.