作者：
Johnson, LDJohnson LD
US EPA NATL EXPOSURE RES LAB DIV AIR MEASUREMENTS RES METHODS BRANCH RES TRIANGLE PK NC 27711 USA
U.S. Environmental Protection Agency risk assessment guidance currently under development for evaluation of permitting information from hazardous waste combustors requires a quantity referred to as ''total org...
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U.S. Environmental Protection Agency risk assessment guidance currently under development for evaluation of permitting information from hazardous waste combustors requires a quantity referred to as ''total organic carbon'', The risk guidance does not define this term precisely, nor does it explain how it should be determined, This paper discusses basic principles of sampling and analysis of stack emissions for ''total organics'', best currently available technology, and the status of two ongoing projects designed to provide guidance and to improve analysis procedures, Determination of total organics from stack emissions is much more complicated than might be expected, and more published guidance is badly needed, The best scheme available for analysis of stack emissions for total organics to be used in material balance style ''bookkeeping'' includes determination of organics content in three boiling point ranges: <100 degrees C, 100 degrees C-300 degrees C, and >300 degrees C, Total organic carbon is not a useful quantity, since it includes soot, polymeric material, and other nonextractable organic materials, Total organics has been found to be an imperfect but less misleading term, Various calculations can be made and conclusions can be drawn on the basis of the contents of the individual boiling point ranges, as determined by the recommended methodology, The analysis strategy is complicated and difficult, and it contains limitations and compromises, It does not, however, require exotic analysis instrumentation,, nor is it very expensive, Each of these facets of the methodology is discussed in this paper, and a status report is provided on development of a guidance document and a research project intended to produce improved methods.
The neuronal network of the adult central nervous system (CNS) retains a limited capacity for growth and structural change. This structural plasticity has been best studied in the context of lesion-induced growth and ...
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The neuronal network of the adult central nervous system (CNS) retains a limited capacity for growth and structural change. This structural plasticity has been best studied in the context of lesion-induced growth and repair. More recently, structural changes underlying functional plasticity occurring under specific physiological conditions have also been documented, in particular in the cortex and the hippocampus. Areas known for their adult plastic potential retain high levels of the growth associated protein GAP-43, suggesting a persistence of important components of the intracellular growth machinery throughout life. Interestingly, a pronounced negative correlation exists between the levels of GAP-43 and myelination in the adult CNS. Because CNS myelin contains potent neurite growth inhibitory membrane proteins, neurite growth, sprouting and plasticity were investigated in the spinal cord and brain in areas where oligodendrocyte development and myelin formation was experimentally prevented, or in the presence of an inhibitor neutralizing antibody (mAB-IN-1). In all areas, lesion-induced or spontaneous sprouting was enhanced, in parallel with persistent high levels of GAP-43. Thus, spontaneous sprouting of side branches occurred from retinal axons in the optic nerve in the absence of myelin, and target-deprived retinal axons showed increased sprouting and innervation of the contralateral optic tectum in the presence of mAB IN-1. In experimentally myelin-free spinal cords collaterals from intact dorsal roots grew over long distances to innervate deafferented target regions following the section of three dorsal roots. Similarly, the corticospinal tract sprouted across the the midline and re-established a dense plexus of fibres on the contralateral side of the spinal cord following section of one corticospinal tract in juvenile rats. Following bilateral dorsal hemisection of the spinal cord including both corticospinal tracts in young and adult rats, long distance re
The semaphorins are a family of proteins thought to be involved in axonal guidance. Most of the known semaphorins have a similar primary structure characterized by the semaphorin domain and a carboxy-terminal Ig motif...
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The semaphorins are a family of proteins thought to be involved in axonal guidance. Most of the known semaphorins have a similar primary structure characterized by the semaphorin domain and a carboxy-terminal Ig motif. Here we report the cloning of two members (semF and G) of a novel class of membrane-bound semaphorins which contain seven carboxy-terminal thrombospondin repeats, a motif known to promote neurite outgrowth. SemF and G transcripts are expressed, together with semD and E, in specific regions of young mouse embryos, demarcating distinct compartments of the developing somites or the undifferentiated neuroepithelium. The identification of semF and G increases the number of vertebrate semaphorins to at least 20 and suggests that some semaphorins might act as positive axonal guidance cues.
Molecules and activities which repulse growing neurites or induce growth cone collapse and longlasting growth inhibition have been defined over the last 10 years. Recently, specific guidance roles for developing axons...
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Molecules and activities which repulse growing neurites or induce growth cone collapse and longlasting growth inhibition have been defined over the last 10 years. Recently, specific guidance roles for developing axons and pathways could be associated with such repulsive effects. A high molecular weight membrane protein located in CNS myelin acts as potent neurite growth inhibitor and may play a role as a negative control element for sprouting, neurite growth and regeneration, and for the plasticity of the adult CNS. Interestingly, some guidance molecules can have positive, growth-promoting as well as negative, repulsive effects for specific types of neurons. These results underline the complex mechanisms involved in neurite guidance which depends on the interpretation of combinations of incoming signals by particular growth cones.
The neural cell adhesion molecule N-CAM has been proposed to function in the guidance of outgrowing axons in the peripheral and central nervous system. Light microscopic observations have shown that the embryonic form...
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The neural cell adhesion molecule N-CAM has been proposed to function in the guidance of outgrowing axons in the peripheral and central nervous system. Light microscopic observations have shown that the embryonic form of N-CAM (200-230 kDa) is present in the ventralmost part of the dorsal funiculus during corticospinal tract (CST) ingrowth in the first postnatal week (Joosten, Dev. Brain Res., 78 (1994) 226-236). Here, the subcellular localization of the embryonic form of N-CAM (E-NCAM) is determined by pre-embedding staining on vibratome sections and by postembedding immunogold-labelling on Epon embedded spinal cord sections. The electron microscopical observations indicate that E-NCAM is present on the outer membrane of CST growth cones as well as other unmyelinated axons which are present in the ventralmost part of the dorsal funiculus. Furthermore, E-NCAM is localized in an irregular patchy way on the outer side of the axonal membrane of small unmyelinated, later arriving CST axons. From these results it may be deduced that E-NCAM is involved in CST tract formation through guidance of outgrowing pioneer CST growth cones along other unmyelinated axons and through mediation of axon fasciculation of later arriving CST axons.
Augmented proportional navigation requires the information of a target acceleration, which must be estimated by a filtering logic. The process necessary accompanies a time lag, which degrades the guidance performance....
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ISBN:
(纸本)0780337514
Augmented proportional navigation requires the information of a target acceleration, which must be estimated by a filtering logic. The process necessary accompanies a time lag, which degrades the guidance performance. A trade-off study between augmented and conventional proportional navigation is conducted with the time lag taken into consideration. The result shows that, the augmented proportional navigation has good performance even if a time lag exists in estimating the target acceleration, and is particularly useful against the target out-of-coplane maneuvers.
The modular integrated avionics group (MIAG) is a single unit approach to combining position, inertial and baro-altitude/air data sensors to provide optimized navigation, guidance and control performance. Lear Astroni...
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ISBN:
(纸本)0819421197
The modular integrated avionics group (MIAG) is a single unit approach to combining position, inertial and baro-altitude/air data sensors to provide optimized navigation, guidance and control performance. Lear Astronics Corporation is currently working within the navigation community to upgrade existing MIAG performance with precise GPS positioning mechanization tightly integrated with inertial, baro and other sensors. Among the immediate benefits are the following: (1) accurate target location in dynamic conditions; (2) autonomous launch and recovery using airborne avionics only; (3) precise flight path guidance; and (4) improved aircraft and payload stability information. This paper will focus on the impact of using the MIAG with its multimode navigation accuracies on the UAV targeting mission. Gimbaled electro-optical sensors mounted on a UAV can be used to determine ground coordinates of a target at the center of the field of view by a series of vector rotation and scaling computations. The accuracy of the computed target coordinates is dependent on knowing the UAV position and the UAV-to-target offset computation. Astronics performed a series of simulations to evaluate the effects that the improved angular and position data available from the MIAG have on target coordinate accuracy.
The growing interest in occupational stress is discussed, focusing on a recent successful claim againt an employer. Key legal issues, guidance for employers and the implications for health educators are covered.
The growing interest in occupational stress is discussed, focusing on a recent successful claim againt an employer. Key legal issues, guidance for employers and the implications for health educators are covered.
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