关于控制氯代烃的政策选择

本文分析了氯代烃的生产所引起的环境问题,并提出了减少氯代烃环境影响的政策选择的基本原则。     

Effect of polymerization initiator on early colour of poly(vinyl chloride)

The development of early colour and the dehydrochlorination rate were compared for poly(vinyl chloride) samples obtained by suspension polymerization using two different initiators, dicetylperoxydicarbonate and butylperoxyneodecanoate. The degree of discolouration was measured on pressed plates and expressed as yellowness index (YI), the polyene sequence distribution was monitored by UV/Vis-spectroscopy, and the degradation rate was determined by measuring evolved HCI conductometrically. The PVC sample initiated by dicetylperoxydicarbonate exhibited more extensive early colour and a higher dehydrochlorination rate as compared to the sample obtained with butylperoxyneodecanoate as initiator. The UV/Vis-spectra showed that the early colour originates from polyene sequences. After extraction of the PVC resins with heptane: acetone (85 : 15) the early colour turned out to be almost the same for the two samples. From ¹³C-NMR measurements it was found that the extract of the sample polymerized with dicetylperoxydicarbonate contains unreacted initiator. We suggest that the radicals formed when the remaining initiator decomposes initiate dehydrochlorination. Our results also indicate that radicals from dicetylperoxydicarbonate may cause long-chain branches during polymerization. The radicals formed from butylperoxyneodecanoate, on the other hand, do not seem to react with the polymer molecules. © 1993 John Wiley & Sons, Inc.     

Characterization of chemicals mediating ovipositional host-plant finding byAmyelois transitella females

Ovipositional host-finding in the navel orangeworm,Amyelois transitella (Walker), is brought about by an in-flight response to host odors. Wind-tunnel studies of the response of gravid females to almonds showed that this response is mediated primarily by long-chain fatty acids, particularly oleic acid and linoleic acid. Evidence for the behavioral activity of fatty acids is based on the fact that: (1) behavioral activity of almond oil was concentrated in a single liquid chromatographic fraction whose composition was predominantly long-chain fatty acids, (2) behavioral activity was lost when either almond oil or the active fraction of that oil was treated with diazomethane, (3) full activity was elicited by a selective extraction of free fatty acids from crude almond oil, and (4) upwind response by females was elicited by a blend of synthetic oleic and linoleic acids, albeit at a level less than that elicited by almond oil. Five fatty acids identified from the almond oil were: myristic acid (1%), palmitic acid (16%), stearic acid (3%), oleic acid (58%), and linoleic (22%). Attraction to various combinations of synthetic acids was observed only when oleic acid was present, and oleic acid elicited upwind flights to the source when presented alone; however, short-range responses were enhanced by the addition of linoleic acid, which elicited no long-range orientation by itself. Despite significant levels of attraction to synthetic blends, the percentage of females flying to the source was lower than that flying to acidulated almond oil, the best natural attractant tested. Thus, although longrange response may be mediated primarily by a blend of oleic and linoleic acids, additional and as yet unidentified components must also play an important role. Long-range chemically modulated host finding in this and other generalist plant feeders is discussed with respect to current models of the evolution of host finding, and it is argued that suggestions that long-range host finding should be correlated with narrowness of host utilization are logically flawed and are not supported by our current understanding of specific examples of host finding.     

Bark beetle olfaction. III. Antennal olfactory responsiveness ofDendroctonus frontalis Zimmerman andD. brevicomis Le Conte (Coleoptera: Scolytidae) to aggregation pheromones and host tree terpene hydrocarbons

Electroantennograms from males and females ofDendroctonus frontalis andD. brevicomis in response to serial dilutions of the pheromonesexo brevicomin and frontalin and the host terpene hydrocarbons 3-carene and α-pinene show no significant differences in the threshold concentration for response to the compounds for either sex or species. The intensity of response was greater to higher concentrations of the pheromones (10 to >10⁴ μg) than the terpene hydrocarbons, suggesting the presence of more receptors on the antennae for pheromones than terpene hydrocarbons. Antennal olfactory responses to the compounds did not correlate to published data on behavioral responses by the beetles to the compounds in both field and laboratory studies. Adaptation experiments indicated that forD. frontalis, both frontalin andexo brevicomin share the same receptors on the antennae. The results indicated that the terpene hydrocarbons share some, but not all, of the same receptors.     

Effect of lecithin on jejunal absorption of micellar lipids in man and on their monomer activity in vitro

The effect of lecithin on jejunal absorption of fatty acids and octadecenoylglycerol was studied in healthy volunteers with a jejunal perfusion system which excluded pancreatic and biliary secretions from the test segment. Lecithin significantly reduced the absorption of oleic acid (P<0.05) and octadecenoylglycerol (P<0.01), while it had no effect on the absorption of ricinoleic acid. In vitro, lecithin reduced monomer activities of all three lipids; the changes were greater for oleic acid and octadecenoylglycerol than for ricinoleic acid (P<0.02). From these data it is concluded that lecithin reduces monomer activity of fatty acids in mixed micellar solutions and that it can thereby reduce the absorption rates of micellar lipids. Intact lecithin is not absorbed under these conditions. Maldigestion of lecithin in pancreatic insufficiency may, therefore, aggravate the steatorrhea observed in this condition.     

Fast template tracking in video sequences

Tracking of poorly defined, rotating and/or distorted objects in a video sequence poses significant problems especially in medical diagnostics including ultrasound (sonographic) video used for examination and diagnosis of internal movement of tissue or muscle and nerve action. Cross-correlation techniques have been successful in retrieving dynamic information directly from ultrasound video data. We outline a fast implementation of tracking based on normalized cross-correlation using an adaptive template and present results from our application, developed in MATLAB?, which successfully tracks arbitrarily selected objects in deformed or severely compromised images. Common ultrasound image evaluation is qualitative but there is need to retrieve quantitative dynamic information such as the trajectory or velocity of selected areas. Our approach uses normalized two-dimensional cross-correlation to find the position of an initially selected template enclosing the feature of interest and map its trajectory frame-by-frame to produce displacement and velocity plots. We illustrate operation of the application using routine ultrasound data and demonstrate its performance using test video of objects rotating full circle and rolling down a ramp. We analyse errors associated with sampling to compare performance of our implementation with a more rigorous but tedious and computationally expensive correlation of a resampled, rotated, and shifted template.     

Building Trust and Cooperation through Technology Adaptation in Virtual Teams: Empirical Field Evidence

Abstract

This article reports findings of a study of how leaders of virtual information systems development teams improve team trust and cooperation by managing adaptation of information and communications tools. Results indicate how Theory X (command and control) and Theory Y (facilitate and support) styles of leadership enable and hinder effective outcomes.     

An interactive lung field segmentation scheme with automated capability

Feasible clinical application of any automated segmenting methodology demands more than just accuracy. Amendment to the automated delineation is necessary when the algorithm fails, however, integrated solution to such a scenario is largely absent in literature. Hence in this survey we devised an architecture that does both the automated and interactive lung field localizations using a single segmenting engine—random walker algorithm—so that intuitive amendment is only necessary when the automated generated delineation is unsatisfactory. The algorithm proceeds by first extracting 18 intensity profiles running horizontally, each of them equally spacing apart, and in each intensity profile three extreme points denoting the two lungs and the esophagus are determined through profile matching. This done, the algorithm removes profiles that do not intersect with the lung, and the rest of the extreme points are plugged into random walker algorithm to perform segmentation. The achieved accuracy in localization by the above was 0.8875 in terms of overlap measure (the maximum value for this parameter is 1) over 341 images. In the case where unsatisfactory delineation prompts amendment necessary, the user can interactively segment the lung by just a shift on some of the previous-determined points to the desired locations, and random walker algorithm is run again with the amended input. By such a fusion, the benefits of both the automated and interactive segmentation are shared in a single architecture.     

EVALUATING THE IMPACT OF THE INSTITUTIONAL REPOSITORY,OR POSITIONING INNOVATION BETWEEN A ROCK AND A HARD PLACE

Repositories remain an innovative but marginalised technology largely because there is no consensus about an agreed set of Performance Indicators (PIs) that demonstrate their overall impact on the research enterprise of our universities. A successful institutional repository (IR) should be evaluated in terms of the extent to which the open access repository builds a critical mass of scholarly content which is sustained and available through active university community engagement and ongoing scholarly contributions (faculty, researchers and students) that, when managed efficiently and effectively, ultimately strengthen, promote and give visibility to the research enterprise of the institution, and bring benefit to broader society. However, librarians are grappling with what and how best to demonstrate ‘institutional good’ but without clear evidence, assessment is fed by perception based on limited information which leads to diminished impact and value of the facility, a tyranny described as being caught between a rock and a hard place. Using Illuminative Evaluation to design a series of quantitative and qualitative metrics, it is proposed that a distinction be made between significant and secondary PIs where the former gather evidence to demonstrate the overall effect or impact of the IR on the individual and collective research community.