Aromatic hydrocarbon and methyl tert-butyl ether measurements in ambient air of Helsinki (Finland) using diffusive samplers

The diffusive sampling method was evaluated for measuring benzene, toluene, ethylbenzene, xylenes, styrene, propylbenzene, ethyltoluenes, trimethylbenzenes and methyl tert-butyl ether (MTBE) in the urban air of Helsinki, Finland. Concentrations were measured in 2-week periods at four different sites during the year 2000. Tube type adsorbent tubes were pre-packed with Carbopack-B (60/80). Analysis was conducted using thermal desorption and gas chromatograph coupled to a mass spectrometer. In different seasons, during five diffusive sampling periods, parallel measurements were conducted using pumped and online sampling. The compared techniques agreed reasonably well for other compounds than trimethylbenzenes. Based on comparisons, diffusive uptake rates for ethyltoluenes, styrene, propylbenzene and MTBE were determined, and for trimethylbenzenes, uptake rates were revised. The concentrations of aromatic compounds in Helsinki metropolitan area were also compared to the concentrations of a rural, forested site in Central Finland.     

Aircraft control for take-off in windshear

Aircraft take-off control under conditions of windshear has recently received considerable attention in the control-theory literature. Severe windshear may cause difficulties during aircraft take-off, it has been a major cause of at least 30 aircraft accidents during the two last decades. We study the controlled take-off of an aircraft flying through an unavoidable windshear. The purpose of the guidance is to guarantee aircraft take-off without crash; no other performance criteria are applied. The proposed aircraft take-off control scheme consists of a memoryless state feedback control strategy for a class of continuous-time aircraft models including unpredictable but bounded windshear. The design of the take-off control scheme is carried out by applying a theory of deterministic control of uncertain systems. The time or the place of encountering a windshear is not known but, according to the basic assumption, the upper bound of the uncertainty—here the maximum rate of the change of the wind velocity—is assumed to be known. Such knowledge allows one to design a deterministic controller to stabilize the relative path inclination of the aircraft.     

Stabilizing management of fishery resources in a fluctuating environment

We consider the problem of stabilizing the management of uncertain fishery resources. Stabilizing management policies are designed on the basis of memoryless state feedback-control strategies for a class of discrete-time resource models, which contain unknown but bounded fluctuations. The theory is based on conditions developed for a Lyapunov-type stability of sets. The theory is illustrated by simulation examples from fisheries econimics. Parent stock is stabilized by a feedback harvesting strategy, when the catchability of the resource or the stock-recruitment relationship fluctuates. Entry and exit of fishermen are stabilized in an open-access common-property fishery, where the entry and exit dynamics are determined by fluctuating revenues obtained from the fishery.     

Pulsed time-of-flight radar for fiber-optic strain sensing

This article describes a fiber-optic interrogation device based on the pulsed time-of-flight technique. The apparatus is capable of measuring time delays between wideband reflectors, such as connectors, along a fiber path with a precision of about 280 fs (rms value) and a spatial resolution of about 3 ns (0.30 m) in a measurement time of 25 ms. Potential application areas include measuring integral strain and its derivatives such as cracks, deflections, and displacements, particularly in large civil engineering and composite structures. The operation and basic blocks of the measurement system are presented in detail together with measurement results obtained in laboratory and field conditions. It is shown that by using a fiber loop sensor with a reference fiber, it is possible to achieve a strain precision below 1 microstrain and a measurement frequency of 4 Hz. System performance proved adequate for the study of both static and dynamic phenomena in a bridge deck.     

W/SiC x-ray multilayers optimized for use above 100 keV

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard x-ray reflective coatings operating in the energy range 100-200 keV. Grazing-incidence x-ray reflectance at E = 8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W/SiC structures, whereas synchrotron radiation was used to measure the hard x-ray reflectance of a depth-graded multilayer designed specifically for use in the range E approximately 150-170 keV. We have modeled the hard x-ray reflectance using newly derived optical constants, which we determined from reflectance versus incidence angle measurements also made using synchrotron radiation, in the range E = 120-180 keV. We describe our experimental investigation in detail compare the new W/SiC multilayers with both W/Si and W/B4C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard x-ray nuclear line telescope.     

太阳纸业^#20机完成部投入运行

山东太阳纸业有限公司^＃20机的整套完成部生产线，于8月10日在兖州纸厂提前投入运行。