Experimental Enhancement Factors Research Articles

Gold nanorings as substrates for surface-enhanced Raman scattering

Surface-enhanced Raman scattering using gold nanoring substrates is studied. The measured enhancement factors of arrays of single nanorings and nanoring dimers are compared with that of an array of nanodisk dimers. The measured average enhancement factor for the single nanorings is 4.2 x 10(6). The experimental enhancement factors are compared with the electromagnetic enhancement factors predicted by simulations.

Pushing the limit of liquid-state dynamic nuclear polarization at high field

Dynamic nuclear polarization in the liquid state was predicted more than 50 years ago by Overhauser. Its application for NMR sensitivity enhancement has been limited because of intrinsic and experimental problems to apply this method at high magnetic fields. Here we report on 95 GHz DNP experiments using the common TEMPO radical dissolved in water. In an efficient non-radiative microwave resonator, we observe average experimental enhancement factors up to -65. The local enhancement in the center of the resonator is calculated to reach a level of -94 at the highest microwave power. At high microwave power, the DNP enhancement shows a linear increase with no tendency to saturation. The results indicate that a substantial sensitivity enhancement is possible for liquid state NMR in nL sample volumes.

Vapour condensation of R22 retrofit substitutes R417A, R422A and R422D on CuNi turbo C tubes

Heat transfer coefficients (HTCs) for outer condensation of R22 and vapours of its retrofit substitutes R417A, R422A and R422D on 90/10 CuNi Turbo C tubes were experimentally measured. The tubes have 19.05 mm nominal outside diameter, 40 fins per inch (1575 fpm) on the outer surface and a smooth inner surface. The effective condensing length per tube was 1895 mm. Experimental data are reported at vapour saturation temperature of 40 °C and wall subcoolings from around 1.5 to 8 °C. A rapid increase of the HTCs for low wall subcoolings attributable to the presence of the hydrocarbon in the mixtures was found. For wall subcoolings greater than around 3 °C, the condensation HTCs slightly increase with raising the wall subcooling and they are for vapours of R417A, R422A and R422D lower by 65–76%, 24–31% and 60–67% than the HTCs for R22, respectively. Comparisons of the condensation performance amongst the different refrigerants and experimental enhancement factors for the condensation of R22 on 90/10 CuNi Turbo C tubes are reported in the paper.

Measurements of Coster–Kronig enhancement factors for Yb, Lu, Os and Pt elements

In this work X-ray production cross-sections’ measurements, L ι , L α , L β and L γ , of Yb, Lu, Os and Pt elements have been studied at energies in the range 9.572–14.384 keV and the effect of Coster–Kronig transitions on fluorescence cross-sections for L X-ray line has been obtained. From these studies absolute values of L X-ray cross-sections have been calculated with incorporation of the enhancement due to the Coster–Kronig effect. The experimental enhancement factors tend to be smaller than those predicted by theory.

Spectral Behavior of Linewidth Enhancement Factor of a Mid-Infrared Quantum Cascade Laser

We report the experimental linewidth enhancement factor (α-factor) results on mid-infrared InGaAs/InAlAs quantum cascade lasers (QCLs) obtained using the self-mixing method. The waveforms appearing under self-mixing conditions were different from those originally predicted, which assumed that the gain was symmetric around the gain peak and that α=0. The signs of the QCL α-factors were identified to be negative and asymmetric to the gain peak by using the nonsymmetrical mirror drive, and by comparing their wave patterns to those of conventional 1.55-µm laser diodes. The nonparabolicity of the subbands was a possible cause of the α-factor's asymmetry. The subbands are no longer parallel if the lasing energy is restricted by the nonparabolicity, which produces inhomogeneous broadening and an asymmetric optical gain spectrum with a long wavelength tail. Taking the nonparabolicity into account, we determined the QCL gain spectrum and the dependence of the α-factor on the spectral position relative to the gain peak. The dependence of the α-factor on detuning was in reasonable agreement with the calculation that accounts for the asymmetry in gain.

Transungual Iontophoretic Transport of Polar Neutral and Positively Charged Model Permeants: Effects of Electrophoresis and Electroosmosis

Transungual iontophoretic transport of model neutral permeants mannitol (MA), urea (UR), and positively charged permeant tetraethylammonium ion (TEA) across fully hydrated human nail plates at pH 7.4 were investigated in vitro. Four protocols were involved in the transport experiments with each protocol divided into stages including passive and iontophoresis transport of 0.1 and 0.3 mA. Water and permeant uptake experiments of nail clippings were also conducted to characterize the hydration and binding effects of the permeants to the nails. Iontophoresis enhanced the transport of MA and UR from anode to cathode, but this effect (electroosmosis) was marginal. The transport of TEA was significantly enhanced by anodal iontophoresis and the experimental enhancement factors were consistent with the Nernst-Planck theory predictions. Hindered transport was also observed and believed to be critical in transungual delivery. The barrier of the nail plates was stable over the time course of the study, and no significant electric field-induced alteration of the barrier was observed. The present results with hydrated nail plates are consistent with electrophoresis-dominant (the direct field effect) transungual iontophoretic transport of small ionic permeants with small contribution from electroosmosis.

Mathematical Modeling of Wet Magnesia Flue Gas Desulphurization Process

Desulphurization of flue gases from various chemical industries in a techno-econo-enviro manner is a demanding technology. The concentrations of sulphur dioxide in and around these plants overshoot the danger point. In recent years, the process analysis of chemical absorption in a slurry has become important in rational design and development of wet scrubbing processes for the removal ofSO2from flue gases. The elementary steps encountered in wet scrubbing by slurries are diffusion and reaction of gaseous species and solid dissolution in liquid film. In the present work, the process of the absorption of sulphur dioxide into wet magnesia slurry was theoretically analyzed according to the two-reaction plane model incorporating the solid dissolution promoted by the reactions with absorbed sulphur dioxide in the liquid film. A model based on Fick's second law has been developed to calculate enhancement factor for absorption of Sulphur dioxide intoMg(OH)2slurry. The concentration of accumulated species in the bulk of the liquid phase (sulphite ions for this case) which substantially control the absorption rates was included in the model for the prediction of theoretical enhancement factor. The values of theoretical enhancement factors obtained from model were compared with experimental enhancement factors available in literature. The model values of enhancement factors agreed well with the values of experimental enhancement factor available in literature.

An Extended Model Based on the Modified Nernst–Planck Equation for Describing Transdermal Iontophoresis of Weak Electrolytes

An extended model for iontophoretic enhancement of transdermal drug permeation under constant voltage is described based on the previously modified Nernst-Planck equation, which included the effect of convective solvent flow. This model resulted in an analytical expression for the enhancement factor as a function of applied voltage, convective flow velocity due to electroosmosis, ratio of lipid to aqueous pathway passive permeability, and weighted average net ionic valence of the permeant in the aqueous epidermis domain. The shift of pH in the epidermis compared to bulk caused by the electrical double layer at the lipid-aqueous domain interface was evaluated using the Poisson-Boltzmann equation. This was solved numerically for representative surface charge densities and yielded pH differences between bulk and epidermal aqueous domain between 0.05 and 0.4 pH units. The developed model was used to analyze the experimental enhancement of an amphoteric weak electrolyte measured in vitro using human cadaver epidermis and a voltage of 250 mV at different pH values. Parameter values characterizing the involved factors were determined that yielded the experimental enhancement factors and passive permeability coefficients at all pH values. The model provided a very good agreement between experimental and calculated enhancement and passive permeability. The deduced parameters showed (i) that the pH shift in the aqueous permeation pathway had a notable effect on the ionic valence and the partitioning of the drug in this domain for a high surface charge density and depending on the pK(a) and pI of the drug in relation to the bulk pH; (ii) the magnitude and the direction of convective transport due to electroosmosis typically reflected the density and sign, respectively, of surface charge of the tissue and its effect on enhancement was substantial for bulk pH values differing from the pI of epidermal tissue; (iii) the aqueous pathway predominantly determined passive permeability of the studied compound despite its measurable lipophilicity and therefore the lipid pathway did not notably affect enhancement. Hence, the proposed model can provide a good quantitative insight into the interplay between different phenomena and permeant properties influencing iontophoresis and can potentially be used as a predictive tool of the process.

Model To Describe Mass-Transfer Enhancement by Catalyst Particles Adhering to a Gas−Liquid Interface

A model is presented to describe mass-transfer enhancement in slurry reactors by catalyst particles adhering to the gas−liquid interface. This model is a combination of the particle−interface adhesion−dehesion (PIAD) model and the gas-to-liquid-to-solid (GLS)−gas-to-solid (GS) model. The PIAD model is a dynamic description of the equilibrium between the catalyst particle adhesion and dehesion rates at the gas−liquid interface. These rates determine the average residence time of the particles at the gas−liquid interface. The GLS−GS model is a combination of the classical, resistances-in-series, GLS mass-transfer model and a direct GS mass-transfer model. The average particle residence time at the gas−liquid interface, the solid−liquid partition coefficient, and the reaction rate determine the mass-transfer rate by shuttling of the particles between the gas−liquid interface and the bulk liquid. The model parameters are determined from mass-transfer and reactivity experiments, performed with two different slurry systems and two Pd-catalyzed reactions, i.e., oxidation of glucose (aqueous liquid) and hydrogenation of α-methylstyrene (organic liquid), with carbon and silica catalysts in a laboratory-scale surface-aeration stirred-slurry reactor with a known flat gas−liquid interfacial area. The mass-transfer coefficient under reactive absorption conditions is higher than that under nonreactive, physical absorption conditions. Experimental and theoretical mass-transfer enhancement factors under physical and reactive absorption conditions agree well. The GS mass-transfer coefficient increases with the mixing intensity, but the GLS mass-transfer coefficient increases more, finally leading to a decrease of the mass-transfer enhancement factor with the mixing intensity. The mass-transfer model is able to predict physical and reactive mass-transfer rates as a function of the mixing intensity and catalyst concentration.

Measurements of Coster–Kronig enhancement factors of some elements in the atomic number range 74⩽ Z⩽90

L ι, L α, L β and L γ X-ray production cross-sections for 4 elements, 74⩽ Z⩽90, at 10 different energies in the range 11–22 keV have been measured. The effect of Coster–Kronig transitions on fluorescence cross-sections for L X-ray line has been studied. Absolute values of L X-ray cross-sections have been calculated with incorporation of the enhancement due to the Coster–Kronig effect. The experimental enhancement factors tend to be smaller than those predicted by theory.

Mass transfer enhancement of gas absorption in oil-in-water systems: a review

A review is presented on the gas–liquid mass transfer enhancement due to the presence of a second dispersed liquid phase. An attempt has been made to describe the mass transfer characteristics in a gas–liquid–liquid system. The ability of an immiscible oil phase to influence the possible pathway for gas transfer from the gas phase to the aqueous phase and to affect the gas–liquid interface and the volumetric mass transfer coefficient k L a is considered. Though the mass transfer in series looks the most logical explanation, there are many gaps and contradictions in the reported results of k L a, preventing any definite conclusion being reached. An enhancement factor ( E), which quantifies the effect of the oil addition on the gas–liquid mass transfer, is defined. Experimental enhancement factors are reported and compared to the theoretical maximum attainable enhancement factor ( E max). Possible mechanisms (“bubble covering”, “shuttle effect” and “permeability effect”) involved in mass transfer enhancement are assessed in detail. The commonly used “shuttle effect” mechanism, whose model proposes a direct usable expression of the enhancement factor, underestimates the reported experimental enhancement factors by about 20%. However, to date, it is not possible to satisfactorily propose a unique theory explaining the influence of the presence of an immiscible oil on mass transfer enhancement. Moreover, the development of sophisticated models has not yet reached satisfactory levels. Recommendations have been made for future research.

Use of colloidal SERS for the trace detection of organic species: a survey based on pyridine as the probe molecule

AbstractIn view of the reported extreme sensitivity of surface enhanced Raman spectroscopy, the potential of colloidal silver and gold sols for the purpose of semi‐quantitative trace analysis of organic molecules was investigated. High irreproducibility in Raman intensities is reported regarding most of the variables that come into play when preparing the sols, e.g. stirring rate, addition time of chloride ions and ageing. Experimental enhancement factors differ by orders of magnitude even for sols prepared from the same recipe. The value of colloidal SERS for analytical purposes, in particular when employing silver sols, therefore seems to be limited to qualitative analysis.

Iontophoresis of Polypeptides: Effect of Ethanol Pretreatment of Human Skin

This paper explores the possibility of iontophoretically enhancing the in vitro transdermal flux of two polypeptides: leuprolide (a LHRH analogue; MW = 1209.4) and a cholecystokinin-8 analogue [CCK-8; MW = 1150.17). Control experiments at an applied voltage of 0.5V across full-thickness human skin did not yield measurable fluxes of either polypeptide, suggesting that despite the expected iontophoretic flux enhancements, the intrinsic permeability of these polypeptides through skin may be too low to allow significant amounts of the drug to permeate. Therefore, pretreatment with ethanol (to simulate the effect of a chemical permeation enhancer) followed by iontophoresis was investigated with the aim of evaluating the potential of the enhancer plus iontophoresis as a means for controlled transdermal delivery of these polypeptides. The ethanol pretreatment dramatically increased the passive fluxes of both polypeptides, and iontophoresis produced further enhancements in their fluxes. Also, the experimental enhancement factors for leuprolide as a function of the applied voltage appeared to be generally lower than the predictions of the constant field theory. A synergism of iontophoresis with a chemical permeation enhancer may be a potential route for controlled transdermal delivery of these and other high molecular weight polypeptides.

Temperature dependence of the enhancement factor of cidnp created by the photolysis of benzoyl peroxide

The enhancement factor of the nuclear polarization created by the photolysis of benzoyl peroxide in CDCl 3 is measured at various temperatures. The experimental enhancement factor agrees with the theoretical value calculated by the theory proposed by Pedersen and Freed. Further, the temperature dependence of the enhancement factor is well interpreted by the continuous diffusion model.

The3He(d,p) α reaction at astrophysical energies

We have performed a microscopic study of the3He(d,p) α reaction at astrophysical energies within the framework of the Resonating Group Method adopting three different effective nucleon-nucleon interactions. The calculations suggest that the low-energy3He(d,p) α cross section is in good approximation given by the contribution arising from the 3/2+ resonant state atE R =245 keV. In fact, the low-energy data can be better (and more physically) described by a single Breit-Wigner resonance parametrization than by a polynomial fit. Our fit to the3He(d,p) α cross section results in a noticeable reduction in the uncertainties of the resonance parameters of the 3/2+ resonant state as well as in a significantly improved extrapolation of the data to astrophysically important energies. On the basis of this extrapolation we were able to quantitatively deduce the enhancement of the low-energy cross section due to electron screening effects from the data of Krauss et al. and Engstler et al. These experimental enhancement factors were compared with various theoretical models which are all based on the Born-Oppenheimer approximation. As the models underestimate the observed enhancement we suggest that the theoretical study of electron screening effects requires a dynamical treatment.

Penetration model for gas absorption with reaction in a slurry containing fine insoluble particles

A pseudo-homogeneous penetration model describing the mass transfer of a gas to a slurry containing non-soluble reacting or adsorbing particles is presented. This numerical model takes into account the finite reaction/adsorption capacity of the particles. The consequences of this finite capacity on the enhanced absorption are demonstrated for the absorption of hydrogen in metal hydride slurries. Experimental enhancement factors for this system are evaluated and compared to the model predictions. A critical Hatta number has been derived above which saturation of the solid occurs resulting in decreased enhancement factors. The mass transfer of a gas into a slurry with adsorbing particles is a similar problem. For the regime of mass transfer limitation tot the particles with a linear adsorption isotherm the enhanced adsorption is discussed.

Enhancement of oxygen absorption by magnetite‐containing beads of immobilized glucose oxidase

AbstractRates of oxygen absorption into glucose solutions were measured using an immobilized‐enzyme reactor, in which magnetite‐containing beads of immobilized glucose oxidase were moved by a revolving magnetic field to reduce the mass transfer resistances at the gas–liquid interface and around the bead. Data were also obtained for oxygen absorption into glucose solutions containing soluble or immobilized glucose oxidase (without magnetite), as well as for physical absorption of oxygen. The rates of physical absorption for the runs with the magnetite‐containing beads increased because of mechanical stirring caused by spinning of the beads at the gas‐liquid interface. In this case the experimental enhancement factors were found to be larger than those predicted on the basis of the film theory for gas absorption with a pseudo‐first order reaction.

Kinetics of absorptions of lean sulfur dioxide into aqueous slurries of calcium carbonate and magnesium hydroxide

The process of the absorption of sulfur dioxide into an aqueous slurry of calcium carbonate or magnesium hydroxide was theoretically analyzed according to the two-reaction-plane model incorporating the solid dissolution promoted by the reactions with absorbed sulfur dioxide in the liquid film. Theoretical enhancement factors compared well with the experimental data using a stirred tank absorber with a plane gas—liquid interface at 25°C. The concentrations of the accumulated species in the bulk liquid phase (bicarbonate ion for the calcium carbonate slurry and sulfite ion for the magnesium hydroxide slurry) which substantially control the absorption rates, were assesed by comparing experimental enhancement factors with the theoretical predictions.

The mechanism of the Stevens rearrangement: a quantitative CIDNP study

Quantitative CIDNP measurements have been made on the Stevens rearrangements of the ylides (1a–e); the experimental enhancement factors (Vexp) are 25% or less than would be expected for a reaction proceeding only by a free radical pathway.

Upper Critical Field and the Density of States in Amorphous Strong-Coupling Superconductors

The upper critical field of the amorphous superconductors ${\mathrm{Bi}}_{0.85}$${\mathrm{Tl}}_{0.15}$, Ga, ${\mathrm{Sn}}_{0.86}$${\mathrm{Cu}}_{0.14}$, and ${\mathrm{Pb}}_{0.75}$${\mathrm{Bi}}_{0.25}$ is measured in the temperature range from 1.5 \ifmmode^\circ\else\textdegree\fi{}K to the zero-field transition temperature. Films of the amorphous metals about 1500 \AA{} thick are obtained by quenched condensation onto a substrate at He temperature. The initial slopes of the ${B}_{c2}(T)$ curves are used to determine the electronic density of states at the Fermi surface. For all the investigated materials these values were enhanced compared with the density of states which one obtains from the free electron model. For Ga, ${\mathrm{Sn}}_{0.86}$${\mathrm{Cu}}_{0.14}$, and ${\mathrm{Pb}}_{0.75}$${\mathrm{Bi}}_{0.25}$ the experimental enhancement factor agrees well with the electron-phonon enhancement factor $1+\ensuremath{\lambda}$, where $\ensuremath{\lambda}$ is taken from superconducting-tunneling experiments. The temperature dependence of ${B}_{c2}$ deviates from that predicted by Werthamer, Helfand, and Hohenberg, showing ${B}_{c2}$ values too large in the low-temperature region. It is suggested that the strong-coupling behavior of the amorphous superconductors is responsible for the deviation at low temperature.