Application of a sensitivity analysis technique to high-order digital flight control systems

A sensitivity analysis technique for multiloop flight control systems is studied. This technique uses the scaled singular values of the return difference matrix as a measure of the relative stability of a control system. It then uses the gradients of these singular values with respect to system and controller parameters to judge sensitivity. The sensitivity analysis technique is first reviewed; then it is extended to include digital systems, through the derivation of singular-value gradient equations. Gradients with respect to parameters which do not appear explicitly as control-system matrix elements are also derived, so that high-order systems can be studied. A complete review of the integrated technique is given by way of a simple example: the inverted pendulum problem. The technique is then demonstrated on the X-29 control laws. Results show linear models of real systems can be analyzed by this sensitivity technique, if it is applied with care. A computer program called SVA was written to accomplish the singular-value sensitivity analysis techniques. Thus computational methods and considerations form an integral part of many of the discussions. A user's guide to the program is included. The SVA is a fully public domain program, running on the NASA/Dryden Elxsi computer

Super-resolution imaging using a camera array

The angular resolution of many commercial imaging systems is limited, not by diffraction or optical aberrations, but by pixilation effects. Multiaperture imaging has previously demonstrated the potential for super-resolution (SR) imaging using a lenslet array and single detector array. We describe the practical demonstration of SR imaging using an array of 25 independent commercial-off-the-shelf cameras. This technique demonstrates the potential for increasing the angular resolution toward the diffraction limit, but without the limit on angular resolution imposed by the use of a single detector array

Factors Influencing The Variability In Social Capital

This research provides insights into three aspects of social capital: the factors that influence its variability; its two-dimensional nature; and the relationship between social capital and membership in a YMCA. These insights have implications for social capital theory, for public policy, for organizational management and for individual well-being. Most social capital research treats the construct as a causal variable and analyzes the implications of different levels of social capital for certain aspects of individual and community well-being. This treatment implies that levels of social capital vary. Little research has been done to analyze the factors that cause social capital variability and therefore the understanding of social capital variability lacks insight. Before social capital variability can be explored, an intermediate issue must be addressed. Social capital is usually conceived of as a single-dimension construct. In fact social capital has two dimensions: the attitudes of social capital and the behaviors of social capital. Unidimensionality is sufficient when social capital is used exogenously but it is insufficiently nuanced when used for the purpose of recommending policies to increase it. This research analyzes the two-dimensional nature of social capital. Finally, a number of social capital behaviors have been studied but membership in the YMCA is not one of them. This research examines the relationship, ceteris paribus, between membership in the Central Florida YMCA and individual social capital. A survey questionnaire was mailed to 10,000 YMCA members in Central Florida and 21,000 residents who were demographically similar. There were 1,881 completed responses. The results were analyzed using structural equation modeling and were guided by social capital theory and the theory of reasoned action. iv The results of the study indicate that the two most influential factors of social capital variability are personal educational attainment and the average educational attainment of the community. The study also confirms that social capital is a two-dimensional construct and the two dimensions are iterative. The study results also revealed that members of the Central Florida YMCA had higher levels of social capital ceteris paribus. This study is significant in four areas: social capital theory, public policy, management of social capital-generating organizations and for individuals. At the theoretical level, insight has been gained into both the causes of social capital variability and the two-dimensional nature of social capital. Regarding public policy, this research provides clear evidence that education provides a greater role in building a community than simply creating human capital; it also creates social capital. Both educational institutions and those organizations that create social capital should be supported. Furthermore, social capital promulgation through public policy should target both dimensions of social capital to be most effective. For managers of social capital-generating organizations social capital can be used as a metric for measuring organizational effectiveness and community impact. For individuals, there is now an evidencebased approach for developing a life plan for creating personal social capital. This research is unique because it simultaneously brings insights into four distinct spheres of social capital

Multi-aperture foveated imaging

Foveated imaging, such as that evolved by biological systems to provide high angular resolution with a reduced space–bandwidth product, also offers advantages for man-made task-specific imaging. Foveated imaging systems using exclusively optical distortion are complex, bulky, and high cost, however. We demonstrate foveated imaging using a planar array of identical cameras combined with a prism array and superresolution reconstruction of a mosaicked image with a foveal variation in angular resolution of 5.9:1 and a quadrupling of the field of view. The combination of low-cost, mass-produced cameras and optics with computational image recovery offers enhanced capability of achieving large foveal ratios from compact, low-cost imaging systems

AML1, the Target of Multiple Chromosomal Translocations in Human Leukemia, Is Essential for Normal Fetal Liver Hematopoiesis

AbstractThe AML1–CBFβ transcription factor is the most frequent target of chromosomal rearrangements in human leukemia. To investigate its normal function, we generated mice lacking AML1. Embryos with homozygous mutations in AML1 showed normal morphogenesis and yolk sac–derived erythropoiesis, but lacked fetal liver hematopoiesis and died around E12.5. Sequentially targeted AML1−/− ES cells retained their capacity to differentiate into primitive erythroid cells in vitro; however, no myeloid or erythroid progenitors of definitive hematopoietic origin were detected in either the yolk sac or fetal livers of mutant embryos. Moreover, this hematopoietic defect was intrinsic to the stem cells in that AML1−/− ES cells failed to contribute to hematopoiesis in chimeric animals. These results suggest that AML1-regulated target genes are essential for definitive hematopoiesis of all lineages

“Bull's-eye” sign on gadolinium-enhanced magnetic resonance venography determines thrombus presence and age: A preliminary study

AbstractPurpose: Venous thrombosis is associated with a significant inflammatory response, which can be visualized by gadolinium magnetic resonance venography (MRV). Gadolinium extravasates into tissue during inflammation, producing perithrombus enhancement on magnetic resonance scanning. This study determines (1) whether gadolinium enhancement occurs during deep venous thrombosis (DVT); and (2) whether this enhancement changes with time and can therefore establish the age of thrombus.Methods: Patients with a diagnosis of iliofemoral DVT by duplex ultrasound who were referred for MRV to document central thrombus extent were studied. T1 weighted images were obtained before and after gadolinium injection (0.1 mmol/kg); repeat scans were obtained up to 3 months thereafter. At the level of maximum thrombus, measurements of signal intensity were made at the periphery (rim), and the center of the thrombosed vein, as well as the contralateral normal vein, on images after gadolinium enhancement. Rim-center vein signal intensity ratios were then calculated and followed.Results: A total of 39 scans were obtained in 14 patients (eight men, six women). The thrombosed veins were enlarged, with a peripheral rim of enhancement (“bull's-eye” sign). The rim-center ratio for thrombosed veins (2.16 ± 0.18) was different from that of normal veins (0.66 ± 0.10; n = 39; p < 0.001). For all acute studies (≤14 days) the rim-center ratio was 2.38 ± 0.17 (n = 31), whereas for all chronic studies (>14 days) the rim-center ratio was 1.29 ± 0.44 (n = 8; p = 0.001). Among patients who underwent both early and late studies, the rim-center ratio dropped significantly, from 2.33 ± 0.20 acutely to 1.29 ± 0.44 in chronic studies (n = 8; p = 0.03). One patient with active malignancy had a paradoxic increase in rim-center ratio over time and a clinical recurrence of symptoms, suggesting active thrombosis.Conclusions: We conclude that (1) a pattern of peripheral gadolinium enhancement (bull's-eye sign) is seen around acutely thrombosed veins on gadolinium-enhanced MRV, facilitating DVT diagnosis; and (2) the ratio of signal intensity at the rim versus the center of the thrombosed vein may be a good discriminator of acute compared with chronic DVT, which may help direct therapy. (J Vasc Surg 1997;26:809-16.

Discrete bands of petroleum hydrocarbons and molecular organic markers identified within massive coral skeletons

The tissues of corals deposit an aragonite exoskeleton beneath their outer living film at a rate dependent on growth and hence on environmental conditions. This typically results in annual (seasonal) bands being formed within colonies. By analysing molecular organic markers within these bands, our research suggests that coral skeletons record contamination from oil and potentially could be used to investigate other anthropogenic and biogenic organic inputs. Our analyses of sections from within corals (Porites lutea) sampled from the Gulf coasts of Kuwait and Saudi Arabia demonstrate discrete bands of oil contamination which, using selected terpenoid biomarkers, can be source-indexed to specific oil fields (i.e. Kuwait, Iranian or Arabian crude oils). Together with dating using microscopic and X-ray inspection, this offers the potential to investigate contamination during recent years. Further research is, however, necessary to elucidate degradation mechanisms during, and following, the occlusion process of organics within coral skeletons