900 research outputs found
Approximation Techniques for Planar Periodic Structures
The rigorous calculation of electromagnetic properties of periodic meshes using moment methods requires considerable algebraic work and computer resources. In this paper, a number of easy to use approximation techniques for analyzing thin structures with square, rectangular, and circular holes are presented. Formulas for the effective impedante of these meshes are described which can easily take into account oblique incidence and the presence of a dielectric substrate. In addition, techniques for analyzing more complex-shaped apertures such as a cross are discussed. These methods are more accurate than existing approximation techniques and can be applied to a wide range of situations that could not be handled before
Elf: computer automation and error correction for a microwave network analyzer
A microwave measurement system has been developed that combines a personal computer (PC) and an conventional vector network analyzer to yield a full complex-error-corrected automatic network analyzer. The system consists of a Hewlett-Packard HP 8410C network analyzer, an HP 8350B sweep oscillator, and an IBM PC. A program called Elf runs on the PC, performing calibration and measurement algorithms and providing a flexible, menu-oriented user interface. The system, when calibrated, achieves a worst-case measurement error vector of magnitude ≤ 0.02 for transmission and reflection coefficient measurements over the 2-12.4-GHz frequency range and has a measurement speed of three frequency points/s. Elf provides an inexpensive method for upgrading the HP 8410 to achieve the high accuracy of an automatic network analyzer
Puff, an Interactive Microwave Computer Aided Design Program for Personal Computers
We will demonstrate a CAD program designed for the lay out
and analysis of microstrip circuits. The program runs on the
IBM PC or AT. Circuit elements are selected from a parts list
and drawn on the screen using the cursor keys. The analysis
may then be performed, directly from the screen drawing. Puff
has been used by microwave students in classes at the California
Institute of Technology and the University of California at Los
Angeles
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)
Electrochemistry needs electrochemists: “goodbye to rotating discs”
The essential need for expert, fully trained electrochemists in the successful application of the subject is illustrated with several examples including the use of rotating electrodes and impedance spectroscopy where the use of the techniques in “black box” mode non-experts is likely to lead to disappointment or embarrassment
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
Ecological Benefits of Creating Stormwater Wetlands and Woodlands in Philadelphia, PA
Urban development and wetland loss have negatively impacted water quality. Natural areas and systems can help mitigate those impacts. With over two centuries of utilizing the Schuylkill River as a source of drinking water, Philadelphia has adapted from land preservation to wetland creation to achieve sediment Total Maximum Daily Load (TMDL) standards. This case study highlights how the innovation of constructed stormwater wetlands coupled with the restoration of forested natural areas provides water quality and ecological benefits
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