1,531 research outputs found
Voltammetry at porous electrodes: A theoretical study
Theory is presented to simulate both chronoamperometry and cyclic voltammetry
at porous electrodes fabricated by means of electro-deposition around spherical
templates. A theoretical method to extract heterogeneous rate constants for
quasireversible and irreversible systems is proposed by the approximation of
decoupling of the diffusion within the porous electrode and of bulk diffusion
to the electrode surface
Double potential step chronoamperometry at a microband electrode: Theory and experiment
Numerical simulation is used to characterise double potential step
chronoamperometry at a microband electrode for a simple redox process A + e-
goes to B, under conditions of full support such that diffusion is the only
active form of mass transport. The method is shown to be highly sensitive for
the measurement of the diffusion coefficient of both A and B, and is applied to
the one electron reduction of decamethylferrocene (DMFc), DMFc - e- goes to
DMFc+, in the room temperature ionic liquid 1-propyl-3-methylimidazolium
bistrifluoromethylsulfonylimide. Theory and experiment are seen to be in
excellent agreement and the following values of the diffusion coefficients were
measured at 298 K: D_(DMFc) = 2.50 x 10^(-7) cm^(2) s^(-1) and D_(DMFc+) = 9.50
x 10^(-8) cm^(2) s^(-1)
Monolithic circuit test standards
Monolithic circuit test standards and methods for line certificatio
Dual Band Electrodes in Generator-Collector Mode: Simultaneous Measurement of Two Species
A computational model for the simulation of a double band collector-generator
experiment is applied to the situation where two electrochemical reactions
occur concurrently. It is shown that chronoamperometric measurements can be
used to take advantage of differences in diffusion coefficients to measure the
concentrations of both electroactive species simultaneously, by measuring the
time at which the collection efficiency reaches a specific value. The
separation of the electrodes is shown to not affect the sensitivity of the
method (in terms of percentage changes in the measured time to reach the
specified collection efficiency), but wider gaps can provide a greater range of
(larger) absolute values of this characteristic time. It is also shown that
measuring the time taken to reach smaller collection efficiencies can allow for
the detection of smaller amounts of whichever species diffuses faster. The case
of a system containing both ascorbic acid and opamine in water is used to
exemplify the method, and it is shown that mole fractions of ascorbic acid
between 0.055 and 0.96 can, in principle, be accurately measured.Comment: 34 pages, 8 figure
Quantitative localized proton-promoted dissolution kinetics of calcite using scanning electrochemical microscopy (SECM)
Scanning electrochemical microscopy (SECM) has been used to determine quantitatively the kinetics of proton-promoted dissolution of the calcite (101̅4) cleavage surface (from natural “Iceland Spar”) at the microscopic scale. By working under conditions where the probe size is much less than the characteristic dislocation spacing (as revealed from etching), it has been possible to measure kinetics mainly in regions of the surface which are free from dislocations, for the first time. To clearly reveal the locations of measurements, studies focused on cleaved “mirror” surfaces, where one of the two faces produced by cleavage was etched freely to reveal defects intersecting the surface, while the other (mirror) face was etched locally (and quantitatively) using SECM to generate high proton fluxes with a 25 μm diameter Pt disk ultramicroelectrode (UME) positioned at a defined (known) distance from a crystal surface. The etch pits formed at various etch times were measured using white light interferometry to ascertain pit dimensions. To determine quantitative dissolution kinetics, a moving boundary finite element model was formulated in which experimental time-dependent pit expansion data formed the input for simulations, from which solution and interfacial concentrations of key chemical species, and interfacial fluxes, could then be determined and visualized. This novel analysis allowed the rate constant for proton attack on calcite, and the order of the reaction with respect to the interfacial proton concentration, to be determined unambiguously. The process was found to be first order in terms of interfacial proton concentration with a rate constant k = 6.3 (± 1.3) × 10–4 m s–1. Significantly, this value is similar to previous macroscopic rate measurements of calcite dissolution which averaged over large areas and many dislocation sites, and where such sites provided a continuous source of steps for dissolution. Since the local measurements reported herein are mainly made in regions without dislocations, this study demonstrates that dislocations and steps that arise from such sites are not needed for fast proton-promoted calcite dissolution. Other sites, such as point defects, which are naturally abundant in calcite, are likely to be key reaction sites
Kinematics and hydrodynamics of spinning particles
In the first part (Sections 1 and 2) of this paper --starting from the Pauli
current, in the ordinary tensorial language-- we obtain the decomposition of
the non-relativistic field velocity into two orthogonal parts: (i) the
"classical part, that is, the 3-velocity w = p/m OF the center-of-mass (CM),
and (ii) the so-called "quantum" part, that is, the 3-velocity V of the motion
IN the CM frame (namely, the internal "spin motion" or zitterbewegung). By
inserting such a complete, composite expression of the velocity into the
kinetic energy term of the non-relativistic classical (i.e., newtonian)
lagrangian, we straightforwardly get the appearance of the so-called "quantum
potential" associated, as it is known, with the Madelung fluid. This result
carries further evidence that the quantum behaviour of micro-systems can be
adirect consequence of the fundamental existence of spin. In the second part
(Sections 3 and 4), we fix our attention on the total 3-velocity v = w + V, it
being now necessary to pass to relativistic (classical) physics; and we show
that the proper time entering the definition of the four-velocity v^mu for
spinning particles has to be the proper time tau of the CM frame. Inserting the
correct Lorentz factor into the definition of v^mu leads to completely new
kinematical properties for v_mu v^mu. The important constraint p_mu v^mu = m,
identically true for scalar particles, but just assumed a priori in all
previous spinning particle theories, is herein derived in a self-consistent
way.Comment: LaTeX file; needs kapproc.st
Radio tomographic imaging of sporadic-E layers during SEEK-2
During the SEEK-2 Rocket Campaign in August 2002, a Dual Band Beacon (DBB) transmitting to Ground Receivers provided unique data on E-Region electron densities. Information from two rocket beacons and four ground receivers yielded multiple samples of E-region horizontal and vertical variations. The radio beacon measurements were made at four sites (Uchinoura, Tarumizu, Tanegashima, Takazaki) in Japan for two rockets (S310-31 and S310-32) launched by the Institute of Space and Aeronautical Science (ISAS). Analysis was completed for four sets of beacon data to provide electron density images of sporadic-E layers. Signals from the two-frequency beacons on the SEEK-2 rockets were processed to yield total electron content (TEC) data that was converted into electron density measurements. Wide variations in layer structures were detected. These included horizontal sporadic-E variations, vertical profiles of double, single, and weak layers. The radio beacon measurements were shown to be in agreement with the in-situ SEEK-2 sensors. The first tomographic image of a sporadic-E layer was produced from the data. The rocket beacon technique was shown to be an excellent tool to study sporadic-E layers because absolute TEC accuracy of 0.01 TEC Units can be easily obtained and, with proper receiver placement, electron density images can be produced using computerized ionospheric tomography with better than 1km horizontal and vertical resolution
Samakalina, Vol. 7 (Agrahayana, 1366)
Samakalina is a Bengali journal of literary criticism published from Calcutta between 1953 and 1993. Publishers and Printers changed several times
Interdigitated ring electrodes: Theory and experiment
The oxidation of potassium ferrocyanide, K_4Fe(CN)_6, in aqueous solution
under fully supported conditions is carried out at interdigitated band and ring
electrode arrays, and compared to theoretical models developed to simulate the
processes. Simulated data is found to fit well with experimental results using
literature values of diffusion coefficients for Fe(CN)_6^(4-) and
Fe(CN)_6^(3-). The theoretical models are used to compare responses from
interdigitated band and ring arrays, and the size of ring array required to
approximate the response to a linear band array is investigated. An equation is
developed for the radius of ring required for a pair of electrodes in a ring
array to give a result with 5% of a pair of electrodes in a band array. This
equation is found to be independent of the scan rate used over six orders of
magnitude
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