Numerical Study Of The Atmospheric Radiative Transfer Process With Application To The Arctic Energy Balance

Thesis (Ph.D.) University of Alaska Fairbanks, 1986A high-order discrete-ordinate approximation is utilized to solve the radiative transfer equation for both solar and terrestrial spectra. The solutions have been compared with other methods and found to be reliable and efficient. These solutions have been used to construct a complete and comprehensive radiation model for the arctic atmosphere. The bulk radiative properties (e.g. fluxes and heating/cooling rates) as well as the angular distribution of intensity can be computed as functions of wavelength at various levels in vertically inhomogeneous atmospheres. The radiation model treats Rayleigh scattering, gaseous absorption/emission, scattering and absorption/emission by cloud droplets and haze particles. Snow conditions of the arctic region are simulated by snow grains and soot contamination in the surface layers. A unified treatment of shortwave and longwave radiative transfer is achieved. Use has been made of the five McClatchey atmospheres and of data from the Arctic Stratus Clouds Experiment collected in 1980. Results are compared among broad-band, narrow-band and line-by-line (restricted to gases) computations. We find that at the expense of accuracy by a few watts.m('-2) for flux or a few tenth (DEGREES)C/day for heating/cooling rate computations, the broad-band models are very fast and suitable for certain types of climate modelling. During the arctic summer, stratus clouds are a persistent feature and decrease largely the downward flux at the surface. Arctic haze is important if it is above the cloud layer or in air with low relative humidity and also decreases the downward flux at the surface. The greenhouse effect of doubling the CO(,2) amount can be offset by the haze condition or by the increase in cloudiness of about 4%. In late June, we find that a clear sky condition results in more available downward flux for snow melt than does a cloudy sky condition. This is because the increase of infrared radiation diffused back to surface by the cloud can not compensate the reduction of solar radiation. If the snow starts to melt, the decreasing snow albedo further accelerates the melting process

Experiments in Nonlinear Adaptive Control of Multi-Manipulator, Free-Flying Space Robots

Sophisticated robots can greatly enhance the role of humans in space by relieving astronauts of low level, tedious assembly and maintenance chores and allowing them to concentrate on higher level tasks. Robots and astronauts can work together efficiently, as a team; but the robot must be capable of accomplishing complex operations and yet be easy to use. Multiple cooperating manipulators are essential to dexterity and can broaden greatly the types of activities the robot can achieve; adding adaptive control can ease greatly robot usage by allowing the robot to change its own controller actions, without human intervention, in response to changes in its environment. Previous work in the Aerospace Robotics Laboratory (ARL) have shown the usefulness of a space robot with cooperating manipulators. The research presented in this dissertation extends that work by adding adaptive control. To help achieve this high level of robot sophistication, this research made several advances to the field of nonlinear adaptive control of robotic systems. A nonlinear adaptive control algorithm developed originally for control of robots, but requiring joint positions as inputs, was extended here to handle the much more general case of manipulator endpoint-position commands. A new system modelling technique, called system concatenation was developed to simplify the generation of a system model for complicated systems, such as a free-flying multiple-manipulator robot system. Finally, the task-space concept was introduced wherein the operator's inputs specify only the robot's task. The robot's subsequent autonomous performance of each task still involves, of course, endpoint positions and joint configurations as subsets. The combination of these developments resulted in a new adaptive control framework that is capable of continuously providing full adaptation capability to the complex space-robot system in all modes of operation. The new adaptive control algorithm easily handles free-flying systems with multiple, interacting manipulators, and extends naturally to even larger systems. The new adaptive controller was experimentally demonstrated on an ideal testbed in the ARL-A first-ever experimental model of a multi-manipulator, free-flying space robot that is capable of capturing and manipulating free-floating objects without requiring human assistance. A graphical user interface enhanced the robot usability: it enabled an operator situated at a remote location to issue high-level task description commands to the robot, and to monitor robot activities as it then carried out each assignment autonomously

Commuting Analysis in a Small Metropolitan Area - A Case Study of Bowling Green/Warren County, Kentucky

In previous studies of urban commutes, little attention has been paid to commute patterns in smaller urban areas. In this study, the concept of excess commute (EC) is applied to the Bowling Green-Warren County Metropolitan Statistical Area (BGWCMSA) in Kentucky. EC quantifies the portion of commute distance explained by the overall spatial separation of jobs and households. Results in this thesis research show that approximately 65% of commute distance by persons driving alone in the study area can be explained by the physical locations of homes relative to job sites as well as the existing roadway network, leaving an EC of 35% attributable to other factors. This EC of 35% is less than those of larger metropolitan areas in previous studies, suggesting that EC does decline with the sizes of urban areas to a certain degree. I low ever, the analysis of used commute potential (UCP) reveals that workers in the study area on average use a higher percentage of its total potential in comparison to larger cities. A possible explanation is that BGWCMSA is the regional employment center for south central Kentucky. There is a relatively large percentage of commuters living in the rural areas and the surrounding counties, causing a significant number of commutes with long distances. In addition, the analysis of job distribution shows that BGWCMSA has developed a number of specialized employment subcenters. With some subcenters located in the outskirts of the urbanized area, cross-commuting between suburbs also accounts for a substantial portion of the overall commutes in the region, leading to trips with longer distances as well. Both EC and UCP are also applied to the data disaggregated by household income levels to determine if workers with lower household income are more likely to be spatially separated from their workplaces, necessitating longer commutes. In the disaggregate analysis, all workers in the study area are assigned to four household income groups; 1) those with less than $30,000 annually; 2) between$30,000 and $49,999 annually; 3) between$50,000 and $74,999; and 4)$75,000 or more. Results show that it is not the first income group but the second and third income groups of workers that, on average, travel the longest distances with the highest EC and UCP. Workers in the $75,000 or more income group are, on average, the most efficient commuters by both excess commute and commute potential measures. In summary, this work, by highlighting the presence of excess commuting methodology in the smallest metropolitan statistical area yet studied, provides an impetus for planning agencies in smaller urban areas to obviate the negative effects inherent in automobile use. As cities grow, there is a unique opportunity to develop policies and programs to reduce nonspatial factors that affect the amount of time and distance spent in the automobile in the journey to work (JTW). Nonspatial factors that may be impacted by policies include congestion, lack of transit, and parking availability, among many others. The prevailing trend of urban growth in recent decades is the emergence of employment subcenters on the urban fringe, with some being very specialized in employment type and others of a more mixed nature. Results from this stud} confirm the findings of previous work that smaller urban areas are more likely to use more of their commute capacity and are thus less efficient than larger ones, due to the lack of exurban centers with mixed land use types. Specifically, where there is already a regional jobshousing imbalance, the lack of such centers exacerbates the condition of longer commutes and higher UCP. This suggests that the placement and type of employment centers are critical to the commuting characteristics of a given area

Experimental and Computational Analysis of Chloroplast Transit Peptide Domain Architecture and Function

The Majority of chloroplast proteins are nuclear-encoded and utilize an N-terminal transit peptide (TP) to target into chloroplasts via the general import pathway. Bioinformatic and proteomic analyses provide thousands of predicted TPs, which show low sequence similarity. How the common chloroplast translocon components recognize these diverse TPs is not well understood. Previous results support either sequence- or physicochemical-specific recognitions. To further address this question, a reverse sequence approach was utilized such that the reverse TP contains the same amino acid composition as wild-type TP but lack similar sequence motifs. Using both native and reverse TPs of the two well-studied precursors, we explored these two modes of recognition. We found that reverse TPs behaved similar to wild-type TPs during binding but failed to support protein translocation. We further showed the importance of the N-terminal domain of TPs in governing protein translocation into plastids. When the TP N-termini were replaced with unrelated peptides with varying Hsp70 affinities, we showed that a subset of TP N-termini functions as Hsp70-interacting domains. We proposed that these domains interact with the stromal motor Hsp70. We further identified a conserved spacer distance between these N-terminal Hsp70 domains to the translocon receptor Toc34 binding sites called FGLK motifs. Using mutants with varying spacer lengths, we observed that the most efficient translocation occurred only at an optimal spacer length of around 28 to 31 aa. These results led us to propose the bimodal interaction model of TP architecture and function where a TP contains an N-terminal stromal interacting domain that is linked to a Toc interacting domain via an optimal spacer length. This configuration permits a temporal and/or spatial coupling between a capturing step by a TOC receptor and a trapping/pulling step by a stromal ATP-dependent molecular motor that is required for productive translocatio