OPTIMUM-AIV: A planning and scheduling system for spacecraft AIV

This paper presents a project undertaken for the European Space Agency (ESA). The project is developing a knowledge based system for planning and scheduling of activities for spacecraft assembly, integration and verification (AIV). The system extends to the monitoring of plan execution and the plan repair phases.

The objectives of the contract are to develop an operational kernel of a planning, scheduling and plan repair tool, called OPTIMUM-AIV, and to provide facilities which will allow individual projects to customize the kernel to suit its specific needs. The kernel shall consist of a set of software functionalities for assistance in the initial specification of the AIV plan, in the verification and generation of valid plans and schedules for the AIV activities, and in interactive monitoring and execution problem recovery for the detailed AIV plans. Embedded in OPTIMUM-AIV are external interfaces which allow integration with alternative scheduling systems and project databases.

The current status of the OPTIMUM-AIV project, as of May 1991, is that the architectural design of the system has been agreed on by ESTEC/ESA and detailed design and implementation is now underway, expecting a final delivery in October of 1991.     

Genetic control of differential baseline breathing pattern

The purpose of the present study was to determine the genetic control of baseline breathing pattern by examining the mode of inheritance between two inbred murine strains with differential breathing characteristics. Specifically, the rapid, shallow phenotype of the C57BL/6J (B6) strain is consistently distinct from the slow, deep phenotype of the C3H/HeJ (C3) strain. The response distributions of segregant and nonsegregant progeny were compared with the two progenitor strains to determine the mode of inheritance for each ventilatory characteristic. The BXH recombinant inbred (RI) strains derived from the B6 and C3 progenitors were examined to establish strain distribution patterns for each ventilatory trait. To establish the mode of inheritance, baseline breathing frequency (f), tidal volume, and inspiratory time (TI) were measured five times in each of 178 mature male animals from the two progenitor strains and their progeny by using whole body plethysmography. With respect to f and TI, the two progenitor strains were consistently distinct, and segregation analyses of the inheritance pattern suggest that the most parsimonious genetic model for response distributions of f and TI is a two-loci model. In similar experiments conducted on 82 mature male animals from 12 BXH RI strains, each parental phenotype was represented by one or more of the RI strains. Intermediate phenotypes emerged to confirm the likelihood that parental strain differences in f and TI were determined by more than one locus. Taken together, these studies suggest that the phenotypic difference in baseline respiratory timing between male B6 and C3 mice is best explained by a genetic model that considers at least two loci as major determinants.     

Mode of vascularization of control and basic fibroblast growth factor-stimulated prefabricated skin flaps

This study, using 62 rabbits, examines the rate and pattern of vascular outgrowth from a subcutaneously implanted vascular pedicle, how the newly formed vessels connect to preexisting skin vessels, and whether local application of basic fibroblast growth factor can accelerate the angiogenic process. When the femoral artery and vein of rabbits are implanted beneath the skin, angiogenesis from both the pedicle and small blood vessels within the adjacent skin begins within 3 days. Perfusion with India ink reveals connections between the pedicle and dermal vessels as early as 5 days after implantation of the pedicle. Provided the pedicle does not thrombose, skin flaps based on it may survive completely when elevated as early as 2 weeks after implantation. Flap survival depends on the development of a small number of vascular connections between vessels arising from the pedicle and preexisting dermal vessels. If elevation is delayed until 4 weeks after implantation a flap may survive even if its pedicle has thrombosed. Prolonged release of basic fibroblast growth factor adjacent to the pedicle significantly increases the survival of flaps elevated 1 week after implantation but does not alter the survival of flaps elevated at 2 and 4 weeks.     

Macrophage activation results in bone resorption

Monocytes or macrophages from important accessory cells in the regulation of bone metabolism and destruction. Cells of the mononuclear phagocyte lineage form the precursor cells of the osteoclasts. Soluble products produced by activated macrophages regulate progenitor cell proliferation, recruitment, differentiation, and activity of osteoblasts and osteoclasts. After osteoclasts are removed from the resorption site, macrophages process bone surfaces and create a cement line before osteoblasts enter to form new bone. Although osteolysis associated with normal bone remodeling is seen as an osteoclast driven process, it may be that in chronic inflammation macrophage activation and vascular derangements lead to low pH, local bone demineralization (acid attack), and H+ mediated stimulation of the primary afferent nociceptive nerve fibers (bone pain). Osteoclasts are not able to attach to demineralized bone or to osteoid surfaces. However, if macrophages degrade the demineralized organic bone matrix, chemotactic factors and attachment sites for osteoclasts are produced. In such a scenario, the osteoclast-osteoblast mediated activation, resorption, and formation cycle would be secondarily activated. Such events may play a role in the most common orthopaedic problem related to macrophage activation, aseptic loosening of orthopaedic joint implants, which is secondary to a chronic foreign body reaction and to micromovement.     

Shape estimation of distorted flexible structures

The present work discusses the optimal placement of sensors in truss structures in order to obtain best possible information regarding the distortions of the structure. The estimation goal is to reconstruct the deformed shape of the structure, at the controlled degrees of freedom, from the sensor readings. A basic assumption is that the structure is subjected to a parametric disturbance field. We distinguish between disturbances which cause uniform or arbitrary distortions of the structure, and disturbances which cause structured distortions. Uniform distortions can be construed as white noise, that is, distortions which have no characteristics. Structured distortions are chromatic, they have some characteristics which can be helpful in estimating the shape. Although the disturbance in either case is random it is assumed that its magnitude is confined to a hyper sphere. The estimator is based on the least squares method, hence the estimated shape is the one with least RMS displacement for the given sensor readings. To evaluate the performance of each set of sensors a measure is derived based on the concept of the worst case distortion. The measure is the largest possible error between the estimated and the actual displacements, at the CDOF. For small number of sensors all possible arrangements can be generated and compared. Larger trusses with a moderate number of sensors generate prohibitively large number of possible configurations, hence heuristic search techniques are employed. The theory has been applied to 2D and 3D flexible trusses. Results show that for reasonable shape estimation a relatively large number of sensors is needed. It is also shown that when using sensors which measure mainly the distortions of the controlled degrees of freedom, significant improvements in the shape estimation can be obtained.