This paper addresses the problem of designing guidance, control and navigation systems for autonomous underwater vehicles (AUVs). Its contribution is twofold: i) it introduces a new methodology for integrated design o...
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This paper addresses the problem of designing guidance, control and navigation systems for autonomous underwater vehicles (AUVs). Its contribution is twofold: i) it introduces a new methodology for integrated design of guidance and control, and ii) it describes a novel approach to the analysis and design of multi-rate complementary filters for navigation. The methodologies proposed lead to an efficient procedure for the design of controllers for AUVs to accurately track reference trajectories defined in an inertial reference frame. The paper ilustrates the application of this procedure to the design of a tracking controller for the AUV MARIUS. The design phase is summarized, and the performance of the resulting controller is assessed in simulation using dynamic models of the vehicle and its sensor suite.
The capturability of a realistic generalized true proportional navigation (RGTPN) guidance law, against a nonmaneuvering target, is analyzed. The RGTPN law is obtained by relaxing the somewhat unrealistic assumption o...
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The capturability of a realistic generalized true proportional navigation (RGTPN) guidance law, against a nonmaneuvering target, is analyzed. The RGTPN law is obtained by relaxing the somewhat unrealistic assumption of constant closing velocity, made in all earlier studies on generalized true proportional navigation (GTPN), and incorporating the actual time-varying value in the guidance law. Closed-form solutions for the complete capture region of RGTPN is obtained in terms of both zero and acceptable non-zero miss distances. It is shown that the capture region of RGTPN in the initial relative velocity space is significantly smaller than that of GTPN, for reasonable values of navigation constant (N) and angular direction (eta) of the missile commanded latax. However, for certain values of N and eta, capturability of RGTPN is found to be better. It is also shown that if in one of the versions of GTPN, which uses constant values of both the closing velocity and the line-of-sight (LOS) angular velocity in the guidance law, the corresponding realistic time-varying quantities are used, the capture region actually expands to cover the whole of the initial relative velocity space. A number of examples are given to compare the capture performance of RGTPN with other versions of the GTPN guidance laws.
The rigorous numerical analysis of charge partitioning in a simple p-n junction structure is presented. Procedures for extracting the relevant terminal charges, based upon the concept of a ''pass-through'&...
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The rigorous numerical analysis of charge partitioning in a simple p-n junction structure is presented. Procedures for extracting the relevant terminal charges, based upon the concept of a ''pass-through'' current, are introduced. The calculation of the pass-through current, the electrostatic displacement current and the (distinct) current associated with the changes in internal charge distributions are described. Methods for dividing the various internal charges into ''quasineutral'' and ''space-charge'' components, are also presented. The results obtained by exact analysis are compared with the predictions of the conventional, analytic, charge partitioning models. Significant discrepancies are found to arise from the simplifications necessary for analytic modeling such as the dependence of the partitioning on the ramp speed and injection level and asymmetry between switch-on and switch-off transients. The numerical simulation results offer guidance for the future development of alternative, more accurate, nonquasi-static device models.
This paper presents a power limited low thrust guidance law for spacecraft transfer in a central gravitational field with drag effects considered. Drag forces act along and opposite the vehicle inertial velocity vecto...
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This paper presents a power limited low thrust guidance law for spacecraft transfer in a central gravitational field with drag effects considered. Drag forces act along and opposite the vehicle inertial velocity vector. For thrust control synthesis a two step approach is employed. First, assuming a stationary atmosphere with constant density, an extremal guidance law for the thrust acceleration is obtained analytically as a particular solution to the case of transfer with free final time. The extremal thrust acceleration is shown to be collinear with the spacecraft velocity vector multiplied by a time varying gain that depends on a single constant of integration. By adequately choosing the integration constant and the free final time, transfer to a final orbit with predesigned semimajor axis and eccentricity is performed. Next, based on the extremal thrust acceleration guidance analytically obtained for the constant density atmosphere, a suboptimal guidance for spacecraft orbit transfer in an atmosphere with variable density is developed. The suboptimal thrust acceleration is defined by the spacecraft drag acceleration multiplied by a time varying gain. Numerical results of representative cases are presented. Finally, a comparison is made with the true optimum obtained by numerical methods. It is shown that the suboptimal fuel cost is close to the true optimum.
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.
Frequency of a digital phaselock loop (DPLL) is necessarily quantized, Feedback around the quantizing nonlinearity leads to a steady-state limit cycle, Properties of the limit cycle were obtained by computer simulatio...
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Frequency of a digital phaselock loop (DPLL) is necessarily quantized, Feedback around the quantizing nonlinearity leads to a steady-state limit cycle, Properties of the limit cycle were obtained by computer simulation, and are reported here, Empirical formulas for guidance in DPLL design were developed.
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.
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
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.
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