Large Active Volume Research Articles

Large positive activation volume (+38 cm3mol-1) for the intramolecular electron-transfer reaction from iron (II) to cobalt (III) in (.mu.-pyrazine-N,N') pentaamminecobalt(III) pentacyanoferrate(II) in aqueous solution

Il semblerait que les interactions de liaison H entre les coordinats et les molecules d'eau (solvant) jouent un role significatif dans la determination du volume d'activation

High-power XeCl discharge laser with a large active volume

An x-ray preionized discharge-pumped XeCl laser with a 10-cm laser-electrode separation has been developed. The laser has a pulse-transmission line in the excitation circuit to realize a high pulse-forming line voltage and a low output impedance. The maximum laser energy obtained is 44 J in an 85-ns pulse (FWHM), corresponding to the peak power of 520 MW. The highest electrical efficiency of 2.9% has been achieved with a laser energy of 16.4 J.

ChemInform Abstract: Laser Probing of Molecules Desorbing and Scattering from Solid Surfaces

In recent years the availability of intense, narrow-linewidth tunable dye lasers has greatly improved our ability to detect species in the gaseous or the liquid phase at very low concentration levels by means of laser-induced fluorescence (UF) ( 1-3). For the detection of gas phase species, which is dealt with exclusively in this review, LIF can provide a routine measure­ ment of molecules at a specific state with density as low as � 1 07 par­ ticles/cm3. With the use of resonance-enhanced multiphoton ionization (REMPI) a significant improvement in detectivity can be achieved. This is because ions can be more efficiently collected and detected than photons. In fact, the single atom detection of Cs by REMPI was demonstrated many years ago (4). Both LIF and REMPI have a much better sensitivity and spatial resolution than another commonly used technique, resonance absorption, which requires a long absorption path and thus a com­ paratively larger active volume. The improved detectivity with LIF and REM PI allows us to measure

Kinetics of imidazole addition to the axial site of the iron(II) complex of 2, 3, 9,10-tetraphenyl-1,4, 8,11-tetraaza-1,3, 8,10-cyclotetradecatetraene in dimethyl sulfoxide. Evidence for a dissociative-interchange mechanism

The axial adduct formation of the iron(II) complex of 2,3,9,10-tetraphenyl-l,4,8,11-tetraaza-1,3,8,10-cyclotetradecatetraene (L) with imidazole in dimethyl sulfoxide has been investigated spectrophotometrically at various temperatures and pressures. In the presence of a large excess of imidazole the reaction with the two phases has been observed. The first faster reaction is the formation of the monoimidazole complex of FeL 2+, and the second slower reaction corresponds to the formation of the bisimidazole complex. Activation parameters are as follows: for the first step with k 1 (25.0°C) = (6.8 ±0.2)×10 5 mol −1 kg s −1, ΔH ‡ 1 = 47.5 ± 4.9 kJ mol −1, Δ S ‡ 1 = 26±16 J K −1 mol −1, and Δ V ‡ 1 (30.0°C) = 27.2±1.5 cm 3 mol −1; for the second step with k 2 (25.0°C) = 26.8±0.8 mol −1 kg s −1, Δ H ‡ 2 = 91.6± 0.8 kJ mol −1, Δ S ‡ 2 = 90±3 J K −1 mol −1, and Δ V ‡ 2 (35.0°C) = 21.8±0.9 cm 3 mol −1. The large positive activation volumes strongly indicate a dissociative character of the activation process.

Output and discharge characteristics of an X-ray preionized XeCl laser with a large active volume.

The output and discharge characteristics of an x-ray preionized Xe Cl laser with a pulse forming line (PFL), a rail-gap switch (RGS) and a pulse transmission line (PTL) in the excitation circuit are described in detail. It is found that the relatively large inductance of the RGS leads to the efficient energy deposition into the discharge plasmas when the RGS is placed between the PFL and the PTL. The laser system with a low output impedance of 0.26Ω has produced the maximum laser energy of 50 J in an 85-ns pulse (FWHM). The highest electrical efficiency obtained is 3.1%. The discharge stability is also discussed, based on the measurements of laser pulse-shape, laser energy and voltage on the laser electrode.

Ultrasonic studies of rotational isomerism in 2,3-dimethyl-butane and 2,2,4-trimethylpentane at elevated pressures

Ultrasonic velocity and attenuation have been measured in 2,3-dimethyl-butane and 2,2,4-trimethylpentane from 213 to 243 K and pressures up to 100 MPa. The temperature- and pressure-dependences of the relaxation frequency permit the calculation of the activation enthalpy and the activation volume, respectively. Furthermore, equilibrium parameters are derived from the maximum of absorption per wavelength. Large and positive activation volumes of the order of 10 cm3 mol–1 are observed, whereas the volume change associated with the rotational isomerism is negative, indicating a preference for the gauche states at elevated pressures.

Development of a X-Ray Preionized XeCl Laser with a Large Active Volume

A x-ray preionized XeCl laser with a large active volume has been developed. Use of a transformer between the rail-gap switch and the laser electrode could realize high charging voltage of pulse forming line and a low output impedance. This laser system produced output energy of more than 20 J in a laser-pulse of-90 nsec (FWHM). The maximum output energy of 33 J was extracted from an active volume of 7.7 1 with an electric efficiency of 1.3%.

Apparent activation volumes of hydrophobic ions and carriers in planar lipid bilayers.

A gas-free high-pressure cell has been developed to measure planar bilayer conductances induced by hydrophobic ions and ionophores as a function of hydrostatic pressure. Plots of log conductance versus pressure for valinomycin and nonactin-mediated potassium transport in egg phosphatidyl cholinedecane membranes are essentially linear over a pressure range of 1 to 818 atm. Calculated activation volumes give similar results for both nonactin and valinomycin yielding values of + 48 and + 42 cc/mole, respectively. The valinomycin activation volume agrees reasonably well with the results obtained by Johnson and Miller (Biochim. Biophys. Acta 375:286-291, 1975) for K+-valinomycin transport in liposomes. In contrast to the activation volumes for nonactin and valinomycin, relaxation measurements of tetraphenyl boron (TPB) and dipicrylamine (DPA) give very small values of less than 5 cc/mole for the translocation rate constant, ki. Similarly, steady-state conductance measurements on tetraphenyl arsonium (TPA) and carbonylcyanide m-chlorophenylhydrazone (CCCP), give small values of 6 and 7 cc/mole, respectively. These low figures do not support transport theories based on the formation of bilayer holes or kinks (H. Träuble, J. Membrane Biol. 4:193-208, 1971). The low values for TPB and TPA are especially interesting because their cross-sectional areas are not much different than those of valinomycin and nonactin. Pressure-induced changes in membrane dielectric constant and thickness which lower the bilayer electrostatic barrier could explain the low values for the hydrophobic ions. Additionally, larger activation volumes might be expected for carriers such as nonactin and valinomycin that undergo significant rearrangement and change in hydration during surface complexation of cations.

Grinding Mill Operation and Scale-up: Theory and Equations

Current scale-up equations are discussed critically. The ratio: rotational mass flow of media to axial mass flow of ore—a concept recently introduced—has been refined and extended. It can account for similar breakage in scaled mills by the trade-off between ore/media encounter frequency and average impact energy with specific energy constant. Further consequences are that in scaled mills the average number of revolutions during the residence of an element of ore in the mill, and ore flow path tortuosity, both decrease strongly while axial flow increases very strongly as mill diameter increases. These factors can result in capacity limitations when mill diameters reach a critical range, especially for coarser feed sizes of certain ores. Autogenous mills can operate satisfactorily at relatively large diameters because their large active volumes are occupied either completely or mostly by ore, resulting in higher values of nominal residence time and flow path tortuosity.

Anion exchange in human erythrocytes has a large activation volume

Sulfate equilibrium exchange in human red cells has an activation volume of +150±20 cm 3/mol over the pressure range 0.1 to 83 MPa (15 to 12000 lb/in 2) at 30°C. This value greatly exceeds the expected contribution from sulfate binding to the anion exchanger. We suggest that the activation volume reflects conformational changes during the transport cycle.

Pressure dependence of sodium gating currents in the squid giant axon

Asymmetric displacement currents, Ig, were measured in squid axons at different hydrostatic pressures, P, up to 60 MPa. Potassium and sodium currents were abolished by intracellular Cs+ and TEA+, by extracellular Tetrodotoxin (TTX), and by Na+ substitution with Tris+. The time course of Ig became progressively slower with increasing pressure, and the amplitude decreased. With appropriate scaling in time and amplitude, Ig records at any given P could be made to superimpose very well with those obtained at atmospheric pressure. The same scaling factors yielded a good superposition of all records obtained for voltage steps to membrane potentials in the range -30 to +42 mV. The ratio between the amplitude and time factors was larger than unity and increased with P, indicating a progressive decrease (up to 35% at 60 MPa) of the total charge displaced, Q, with no significant change in its voltage dependence. The time-scaling factor increased exponentially with P, as expected if all the steps involved in the opening of a sodium channel, and producing a major charge redistribution, have the same activation volume, delta V not equal to g approximately 17 cm3/mol. This value is roughly one-half of that characterizing the pressure dependence of sodium current activation, suggesting that some late, rate-limiting step in the opening of sodium channels has a large activation volume without being accompanied by an easily detected charge movement. Part of the decrease of Q with pressure could be attributed to an increase in sodium inactivation. However, we cannot exclude the possibility that there is a reversible reduction in the number of fast activating sodium channels, similar to the phenomenon that has been reported to occur at low temperatures (Matteson and Armstrong 1982).

Activation volumes of the calcium dependent para-nitrophenyl phosphate hydrolysis of the sarcoplasmic reticulum calcium transport enzyme.

The effect of pressure on the calcium dependent hydrolysis of para-nitrophenyl phosphate by the calcium transport enzyme of the sarcoplasmic reticulum was studied under different conditions: temperature, solutes, substrate and ion concentrations. The calcium transport enzyme exhibits a large positive activation volume which does neither depend on the enzyme's inhibition by high salt concentrations nor its activation by ethylene glycol. The activation volume further proves to be pressure-independent but exhibits a pronounced negative temperature coefficient. The volume changes connected with the entrance of para-nitrophenyl phosphate, calcium or magnesium ions into the substrate ion complex are quite small, indicating that the transfer of water connected with the binding of these ligands is compensated by volume changes of the protein, accompanying the transition of the enzyme from its activated into its ground state.

Pressure effect on photo-induced electron-transfer reactions between tris-(2,2′-bipyridine)ruthenium(II) and various metal complex ions

The electron-transfer quenching of photo-excited [Ru(bpy)32+](bpy = 2,2′-bipyridine) by [Mo(CN)8]4– and Euaq2+ gives large positive and negative activation volumes (ΔV‡+ 24.7 and –11.0 cm3 mol–1), respectively, whereas quenching by other quenchers having quenching rate constants of > 109 mol–1 dm3 s–1 has a negligibly small pressure effect regardless of the charge of quencher.

A magnetically stabilized radial discharge for a high-powered laser

Details of a new ’’magnetically stabilized’’ coaxial electrode system supporting a radial discharge geometry is presented. Performance was found to be largely independent of gas mixture and pressure such that high-power cw discharges were easily obtained in all the gases tested, including SF6. The technique is exceedingly simple and appears scalable to provide a very large active volume in an unusually small physical package. A cw power loading in excess of 40 kW/l has already been attained without experiencing any glow-to-arc transitions.

Pressure effect on the rate of outer-sphere electron-transfer within the ion-pair between µ-ethylenediaminetetra-acetato-di-µ-oxo-bis[oxomolybdate(V)] and µ-hyperoxo-bis[penta-amminecobalt(III)] ions

The title reaction gave large positive activation volumes for both the precursor (ion-pair) formation constant and the first-order electron-transfer rate constant within the ion-pair; this result was interpreted mainly in terms of the change in solvation state in each process.

The mechanism of growth of quartz crystals into fused silica

It is proposed that the growth of quartz crystals into fused silica is effected by a mechanism involving the breaking of an Si-O bond and its association with an OH group, followed by cooperative motion of the nonbridging oxygen and the hydroxyl group which results in the crystallization of a row of several molecules along a crystalline-amorphous interfacial ledge. This mechanism explains, at least qualitatively, all the results of our earlier experimental study of the dependence of quartz crystal growth upon applied pressure: large negative activation volume; single activation enthalpy below Si-O bond energy; growth velocity constant in time, proportional to the hydroxyl and chlorine content, decreasing with increasing degree of reduction, and enhanced by nonhydrostatic stresses; lower preexponential for the synthetic than for the natural silica.

A transversely excited copper halide laser with large active volume

Operation of a pulsed copper halide laser excited by transverse discharge and with an active volume of 250 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> is reported. Total laser output pulse energies (at λ5106 and 5782 Å combined) of 2.5 mJ per pulse and peak powers exceeding 100 kW have been achieved in the double-pulse mode with CuBr as the lasant.

Pulse radiolysis of liquids at high pressures. V. Absorption spectrum and yield of the solvated electron in liquid ammonia at 23 °C and pressures up to 6.7 kbar

The absorption spectrum and primary yield of the solvated electron in liquid ammonia (eam−) have been determined by nanosecond pulse radiolysis of liquid ammonia at 23°C and pressures up to 6.7 kbar. With increase in pressure from 0.009 kbar (vapor pressure at 23°C) to 6.7 kbar, the following changes occur in the absorption spectrum: The transition energy at the absorption maximum (Emax) increases from 0.67 to 0.91 eV; the observable portion W of the bandwidth at half-maximum, from Emax to the high-energy side of the spectrum, increases by 35%; and optical density at the absorption maximum (ODmax) decreases by 32%. The pressure and temperature dependences of Emax are attributed to changes in (1) size of the electron cavity and (2) the local dielectric constant associated with the solvation shell of the electron. At 23°C and 0 kbar, (∂lnEmax/∂P)T for eam− exceeds that for solvated electrons in water, methanol, and ethanol by a factor of ∼4. Such a result indicates that the cavity of eam−(V̄=98 ml mol−1) is more compressible than that of the electron in water (V̄ = 7 ml mol−1 for eaq−) and the alcohols. From the changes in W and ODmax with increase in pressure from 0.009 to 6.7 kbar, the extinction coefficient at the absorption maximum is estimated to decrease by 19% (similar to the result for eaq−) and the primary yield is estimated to decrease from 3.2 to 2.0 solvated electrons per 100 eV (in contrast with invariance of the eaq− yield). The decrease in primary yield is attributed to an increase in the probability of neutralization relative to separation of geminate NH4+−eam− pairs owing to the large negative activation volume of the neutralization reaction as a consequence of the large volume of eam−.

Anomalous Viscoelastic Behavior of Metallic Glasses of Pd–Si-Based Alloys

The temperature and the stress dependence of viscoelastic properties of metallic glasses of three compositions: Pd0.795Au0.04Si0.165, Pd0.795Ag0.04Si0.165 and Pd0.775Cu0.06Si0.165 have been studied near the glass temperature. The total retarded tensile compliance of these alloy glasses, J̃d0 is small at low temperature (of the order of glass compliance J̃g) but increases rapidly in a narrow temperature range when the temperature approaches Ta, at which the viscosity of the glass attains 1012 P, and attains a value as high as 200 times the glass compliance J̃g for the Pd0.775Cu0.06Si0.165 glassy alloy, at T &amp;gt; Ta + 15°K. Concurrent with an increase in J̃d0 near Ta, the alloy liquids become non-Newtonian in the stress range employed (σ varies from 6×106 to 3×108 dyn/cm2). The apparent shear activation volume for the viscous flow deduced from the non-Newtonian behavior increases with temperature and attains a value as high as 100 times the atomic volume. These results have been compared with viscoelastic behavior of other types of liquids. It is suggested that the strong temperature dependence of the shear compliance of metallic liquids near Tg may be attributed to some sort of macroscopic structural rearrangements taking place as temperature is changed. The large activation volume of viscous flow seems to imply that the flow mechanism involves a large number of simultaneous atomic displacements in the flow direction.

9A5 - Wide field active imaging

In this paper we report the results of some experiments in active imaging-image processing in which the pictorial information is placed within the laser cavity. By the use of an active medium which provides high gain over a wide aperture, in conjunction with a highly degenerate conjugate resonator, we have been able to obtain diffraction limited resolution with an information content orders of magnitude greater than previously reported. The resonator used is the Flat-Field Conjugate Resonator (FFCR), which can support as many as 107modes of nearly equal Q when properly designed lenses are used. As active medium we used the pulsed hollow cathode Hg+laser. In the present FFCR, two plane mirrors are imaged one upon the other by means of two achromatic doublets (focal lengths about 200 mm) located between the ends of the discharge tube and the mirrors. Active imaging is accomplished by masking one of the mirrors and observing the pattern resulting on the other mirror. Masks used include pinholes, wire meshes, and photographic transparencies as well as patterns etched in thin metallic films that were used directly as mirrors. With the doublets working near f/10 , the resolution over a 15mm diameter field was greater than 100 lines/mm, which corresponds quite well to the observed resolution of the passive system. The resonator was thus capable of actively imaging photographic transparencies having more than 106bits. One characteristic of active imaging in this type of resonator is that all the modes have a large common active volume, and the suppression of some of the modes enhances the intensity of the others. Furthermore, the nonlinear behavior of a laser as an oscillator allows sharp discrimination between differing loss levels in the cavity. These effects have been observed, and their possible application to contrast enhancement and image dissection is discussed.