Characterization of a second-generation focal-plane camera coupled to an inductively coupled plasma Mattauch-Herzog geometry mass spectrograph

A second-generation Faraday-strip array detector has been coupled to an inductively coupled plasma Mattauch-Herzog geometry mass spectrograph, thereby offering simultaneous acquisition of a range of mass-to-charge ratios. The second-generation device incorporates narrower, more closely spaced collectors than the earlier system. Furthermore, the new camera can acquire signal on all collectors at a frequency greater than 2 kHz and has the ability to independently adjust the gain level of each collector. Each collector can also be reset independently. With these improvements, limits of detection in the hundreds of picograms per liter for metals in solution have been obtained. Some additional features, such as a broader linear dynamic range (over 7 orders of magnitude), greater resolving power (up to 600), and improved isotope ratio accuracy were attained. In addition, isotope ratio precision as low as 0.018% RSD was achieved.     

Volatile organic compound detection using nanostructured copolymers

Regioregular polythiophene-based conductive copolymers with highly crystalline nanostructures are shown to hold considerable promise as the active layer in volatile organic compound (VOC) chemresistor sensors. While the regioregular polythiophene polymer chain provides a charge conduction path, its chemical sensing selectivity and sensitivity can be altered either by incorporating a second polymer to form a block copolymer or by making a random copolymer of polythiophene with different alkyl side chains. The copolymers were exposed to a variety of VOC vapors, and the electrical conductivity of these copolymers increased or decreased depending upon the polymer composition and the specific analytes. Measurements were made at room temperature, and the responses were found to be fast and appeared to be completely reversible. Using various copolymers of polythiophene in a sensor array can provide much better discrimination to various analytes than existing solid state sensors. Our data strongly indicate that several sensing mechanisms are at play simultaneously, and we briefly discuss some of them.     

Remote sensing of ammonia and sulfur dioxide from on-road light duty vehicles

This study reports the largest data set of on-road, fuel-based mass emissions of ammonia and sulfur dioxide from vehicles of known make, model year, and fuel type. Ammonia is the first pollutant observed for which the emissions decrease with increasing fleet age from 10 to 20 years. The fixed nitrogen emission ratio is 15.0% by mass and 24.7% by mole, larger than current models predict. Diesel fueled vehicles emit more SO2 than gasoline, and unexpectedly, gasoline SO2 emissions decrease continuously with newer model year vehicles.     

Curve-fitting-based method for modeling voltage–current characteristic of an ac electric arc furnace

Field measurements of voltage and current are the most effective way for characterizing the electric response of an ac electric arc furnace that describes its nonlinear behavior. Sufficient measured information can be adopted to determine the background harmonic level in a power system, to characterize specific sources of harmonics, and to develop an appropriate nonlinear voltage–current characteristic. In this paper, a curve-fitting-based method called cubic spline interpolation is proposed to model the voltage–current characteristic of an ac electric arc furnace in the steady state. Meanwhile, the actual measured data are collected for modeling use. Two classic methods, harmonic current injections and equivalent harmonic voltage sources, for modeling the electric arc furnace load are reviewed and used to evaluate the performance of proposed model. Results obtained from the measured data and computer simulations of the three electric arc furnace models are then compared according to the voltage and current waveforms, as well as the voltage–current characteristic. It is shown that the proposed model is more accurate than the two classic approaches for harmonic assessment of electric arc furnaces and can be used for modeling similar types of nonlinear loads in the harmonic penetration study.     

In-plane effects on segmented-mirror control

Extremely large optical telescopes are being designed with primary mirrors composed of hundreds of segments. The "out-of-plane" piston, tip, and tilt degrees of freedom of each segment are actively controlled using feedback from relative height measurements between neighboring segments. The "in-plane" segment translations and clocking (rotation) are not actively controlled; however, in-plane motions affect the active control problem in several important ways, and thus need to be considered. We extend earlier analyses by constructing the "full" interaction matrix that relates the height, gap, and shear motion at sensor locations to all six degrees of freedom of segment motion, and use this to consider three effects. First, in-plane segment clocking results in height discontinuities between neighboring segments that can lead to a global control system response. Second, knowledge of the in-plane motion is required both to compensate for this effect and to compensate for sensor installation errors, and thus, we next consider the estimation of in-plane motion and the associated noise propagation characteristics. In-plane motion can be accurately estimated using measurements of the gap between segments, but with one unobservable mode in which every segment clocks by an equal amount. Finally, we examine whether in-plane measurements (gap and/or shear) can be used to estimate out-of-plane segment motion; these measurements can improve the noise multiplier for the "focus-mode" of the segmented-mirror array, which involves pure dihedral angle changes between segments and is not observable with only height measurements.     

Thermal performance of a novel rooftop solar micro-concentrating collector

Concentrating solar thermal systems offer a promising method for large scale solar energy collection. Although concentrating collectors are generally thought of as large-scale stand-alone systems, there is a huge opportunity to use novel concentrating solar thermal systems for rooftop applications such as domestic hot water, industrial process heat and solar air conditioning for commercial, industrial and institutional buildings. This paper describes the thermal performance of a new low-cost solar thermal micro-concentrating collector (MCT), which uses linear Fresnel reflectors, and is designed to operate at temperatures up to 220 °C. The modules of this collector system are approximately 3 m long by 1 m wide and 0.3 m high. The objective of the study is to optimise the design to maximise the overall thermal efficiency. The absorber is contained in a sealed enclosure to minimise convective losses. The main heat losses are due to natural convection inside the enclosure and radiation heat transfer from the absorber tube. In this paper we present the results of a computational and experimental investigation of radiation and convection heat transfer in order to understand the heat loss mechanisms. A computational model for the prototype collector has been developed using ANSYS–CFX, a commercial computational fluid dynamics software package. The numerical results are compared to experimental measurements of the heat loss from the absorber, and flow visualisation within the cavity. This paper also presents new correlations for the Nusselt number as a function of Rayleigh number.     

Excretion of volatile ¹³¹I from rats following administration of Na¹³¹I or MIBG-¹³¹I

Current practice for radiation protection associated with (131)I therapy mainly focuses on external and internal exposure caused by physical contamination of the hospital staff, other patients and family members. However, if volatile (131)I is excreted by the treated patients, these individuals could also be exposed through inhalation of (131)I. This study quantifies the amount of volatile (131)I excreted by rats after intravenous administration of metaiodobenzylguanidine (MIBG)-(131)I or Na(131)I, the two most common forms of (131)I therapy. The results indicate that in 4 d following administration, the total excretion of volatile (131)I was 0.036 and 0.17 % of the administered activities of MIBG-(131)I and Na(131)I, respectively. As administered activities for (131)I therapy are typically of the order of 1-10 GBq, the overall excretion of volatile (131)I from a patient can be as high as 20 MBq. As a result, a family member can receive up to 0.07 mSv committed effective dose from inhaling the volatile (131)I excreted by the patient.