611 research outputs found
Incorporating collisions and resistance into the transition from field emission to the space charge regime
Advancements in microelectromechanical systems (MEMS) and microplasmas, particularly with respect to applications in combustion and biotechnology, motivate studies into microscale gas breakdown to enable safe system design and implementation. Breakdown at microscale deviates from that predicted by Paschenâs law due to field emissionâthe stripping of electrons from the cathode in the presence of strong surface fieldâand follows the Fowler-Nordheim (FN) law. As injected current increases at this length scale, electrons accumulate in the gap and FN electron emission becomes space charge limited, leading to the Child-Langmuir (CL) law at vacuum and the Mott-Gurney (MG) law at high pressure. While theoretical studies link CL to FN and CL to MG, none links all three to simultaneously assess the importance of pressure and external resistance (perturbation) on electron emission. This study extends existing theory to elucidate the transition between these regimes as a function of applied voltage, gap distance, electron mobility, and external resistance, and in particular, derives asymptotic equations illustrating the transitions between the three. It also demonstrates the presence of a triple point, where one theoretically encounters FN, CL, and MG at once, and characterizes the importance of gap pressure and distance on these regimes, especially when MG dominates at non-vacuum pressures. The sensitivity of the triple point to external resistance, representative of the effects of perturbations in system parameters on electron emission, receives special attention
In situ spectroscopic monitoring of CO2 reduction at copper oxide electrode
Copper oxide modified electrodes were investigated as a function of applied electrode potential using in situ infrared spectroscopy and ex situ Raman and X-ray photoelectron spectroscopy. In deoxygenated KHCO3 electrolyte bicarbonate and carbonate species were found to adsorb to the electrode during reduction and the CuO was reduced to Cu(I) or Cu(0) species. Carbonate was incorporated into the structure and the CuO starting material was not regenerated on cycling to positive potentials. In contrast, in CO2 saturated KHCO3 solution, surface adsorption of bicarbonate and carbonate was not observed and adsorption of a carbonato-species was observed with in situ infrared spectroscopy. This species is believed to be activated, bent CO2. On cycling to negative potentials, larger reduction currents were observed in the presence of CO2; however, less of the charge could be attributed to the reduction of CuO. In the presence of CO2 CuO underwent reduction to Cu2O and potentially Cu, with no incorporation of carbonate. Under these conditions the CuO starting material could be regenerated by cycling to positive potentials
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Re: Improvement of Siletz River Bar and Entrance and Drift Creek, Oregon
This report contains additional information on improvements of the Siletz River Bar. It includes information on nearby tributaries, as well as the growing annual yield of timber from the area and potential related commerce such as the Oregon Pulp and Paper Company
Family support and cardiac rehabilitation: A comparative study of the experiences of South Asian and White-European patients and their carer's living in the United Kingdom
Background: Effective lifestyle modification facilitated by cardiac rehabilitation is known to reduce the occurrence of adverse coronary events and mortality. South Asians have poorer outcomes after a myocardial infarction than the general UK population, but little is known about their experiences of family support, cardiac rehabilitation and lifestyle change. Aims: To explore the nature of family support available to a sample of South Asian and White-European cardiac patients and to highlight similarities and differences between these groups with regard to cardiac rehabilitation and lifestyle modification. Methods: Using a qualitative approach, semi-structured interviews (in 1 of 6 languages) were conducted by researchers with; 45 South Asian patients and 37 carers and 20 White-European patients and 17 carers. Interviews were conducted in a home setting, up to eighteen months after discharge from hospital following myocardial infarction, coronary artery bypass surgery or unstable angina. Results: The main themes that emerged related to the provision of advice and information, family support and burden, dietary change and exercise regimes. Conclusions: Several cultural and ethnic differences were identified between patients and their families alongside similarities, irrespective of ethnicity. These may represent generic characteristics of recovery after a cardiac event. Health professionals should develop a cultural repertoire to engage with diversity and difference. Not every difficulty a person encounters as they try to access appropriate service delivery can be attributed to ethnic background. By improving services generally, support for South Asian populations can be improved. The challenge is to know when ethnicity makes a difference and mediates a person's relationship with service support and when it does not. (C) 2007 European Society of Cardiology. Published by Elsevier B.V. All rights reserved
A prototype acid spray scrubber for absorbing ammonia emissions from exhaust fans of animal buildings
Mitigation of ammonia (NH3) emissions from animal production buildings has been a challenge because of the
large volume of low NH3 concentration laden air being released. Among emission mitigation technologies for concentrated
animal feeding operations, acid spray scrubbers have the greatest potential for adaptation to the existing large animal
facilities because of their lower fan airflow reduction, ability to simultaneously remove particulate and gaseous pollutants,
and viability for zero or less waste generation by recycling effluents as liquid fertilizer. A multi-stage wet scrubber prototype
that can be operated with a maximum of three stages was developed and optimized for reducing NH3 emissions using simulated
conditions typically encountered at an animal building exhaust. The parameters optimized for a single-stage wet scrubber
include nozzle type, nozzle operating pressure, sulfuric acid concentration, spray coverage, and air retention time. The
optimized single-stage wet scrubber settings can remove emissions from 60% ±1% at 5 ppmv inlet NH3 concentration (IAC)
to 27% ±2% at 100 ppmv IAC at a normal exhaust superficial air velocity (SAV) of 6.6 m s-1. A high concentration of droplets
inside the contact chamber increased the rate of inter-collision between droplets, which led to high droplet coagulation and
decreased surface area for gas-liquid contact. These phenomena were prevented by operating the nozzles in the higher stages
co-current to the airflow and by using fewer nozzles in higher stage. The two-stage and three-stage wet scrubbers were
therefore optimized by determining the least number of nozzles in each stage that provided the most effective NH3 removal.
The optimized two-stage scrubber could remove NH3 emissions from 60% ±0% at 5 ppmv IAC and 35% ±1% at 100 ppmv
IAC. The optimized three-stage scrubber could remove emissions from 63% ±3% at 5 ppmv IAC and 36% ±3% at 100 ppmv
IAC. Airflow retention time was found to significantly affect NH3 absorption. Reducing the superficial air velocity to 3.3 m
s-1 from 6.6 m s-1, which increased the air retention time from 0.2 s to 0.4 s, improved NH3 removal efficiencies to 98% ±3%
at 5 ppmv IAC and 46% ±2% at 100 ppmv IAC for the single-stage scrubber. Similarly, the performance of the two-stage
scrubber at a SAV of 3.3 m s-1 improved to 77% ±0% at 20 ppmv IAC and 57% ±1% at 100 ppm IAC. Lastly, the performance
of the three-stage scrubber at a SAV of 3.3 m s-1 improved to 70% ±1% at 30 ppmv IAC and 64% ±1% at 100 ppmv IAC.
It was observed that the three-stage wet scrubber did not increase the overall wet scrubber performance, as predicted
theoretically. Further studies are needed so that the application of these scrubber designs becomes feasible for treating air
emissions from animal buildings. The wet scrubber caused an additional backpressure of 27.5 Pa, resulting in about 8%
airflow reduction for a fan operating at 12.5 Pa
Space-charge-limited current density for nonplanar diodes with monoenergetic emission using Lie-point symmetries
Understanding space-charge limited current density (SCLCD) is fundamentally
and practically important for characterizing many high-power and high-current
vacuum devices. Despite this, no analytic equations for SCLCD with nonzero
monoenergetic initial velocity have been derived for nonplanar diodes from
first principles. Obtaining analytic equations for SCLCD for nonplanar
geometries is often complicated by the nonlinearity of the problem and over
constrained boundary conditions. In this letter, we use the canonical
coordinates obtained by identifying Lie-point symmetries to linearize the
governing differential equations to derive SCLCD for any orthogonal diode.
Using this method, we derive exact analytic equations for SCLCD with a
monoenergetic injection velocity for one-dimensional cylindrical, spherical,
tip-to-tip (t-t), and tip-to-plate (t-p) diodes. We specifically demonstrate
that the correction factor from zero initial velocity to monoenergetic emission
depends only on the initial kinetic and electric potential energies and not on
the diode geometry and that SCLCD is universal when plotted as a function of
the canonical gap size. We also show that SCLCD for a t-p diode is a factor of
four larger than a t-t diode independent of injection velocity. The results
reduce to previously derived results for zero initial velocity using
variational calculus and conformal mapping.Comment: 18 pages, 3 figure
Towards Defining, Assessing and Reporting Against National Standards for Literacy and Numeracy in New Zealand
The Education (National Standards) Amendment Act 2008 sets in place the
governmentâs ten-step Crusade for Literacy and Numeracy (Hon. John Key, 13
October, 2008). As part of that Crusade: (i) national standards will be set in literacy
and numeracy; (ii) every primary and intermediate student will be assessed regularly
against the national standards; and (iii) every primary and intermediate school will
report to parents in plain English about how their child is doing compared to national
standards and compared to other children their age. Where it is indicated, targeted
funding will be provided to enable schools to give assistance to the students who do
not meet national standards.
This paper discusses these elements of the Amendment Act, (referred to as ânational
standardsâ in this paper for simplicity), proposes a number of principles that should
underlie the design of an assessment, analysis and reporting system based on them;
and makes several suggestions for supporting their development and successful
implementation
An Interactive Spray Drift Simulator
The off target movement of pesticides, known as spray drift, results in a reduction in application rates, damage to non-target organisms, and environmental concerns. Much of this drift can be eliminated if its prevalence is understood and best management practices are implemented. Drift prediction software has been developed to serve as a management tool in determining the effects of applying pesticides under certain operating conditions. To further increase the usefulness and instructiveness of such programs, a program was developed which links spray drift prediction software (DRIFTSIM) with a GPS simulator to obtain a two dimensional representation of drift for simulated ground based spraying event. The program was evaluated using a variety of operating conditions to determine their respective effects on drift deposition levels. Results from the simulations show the importance of choosing the largest sufficient nozzle size, operating under low wind speeds, and spraying at the lowest possible boom height. Analysis of multi-swath simulations showed patterns of increased and reduced application rates due to spray drift
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