A study of multiple-shaker modal survey testing

The principal objective was to examine and to assess the practical value of a method of multiple-shaker sinusoidal modal vibration testing known as Asher's method. Numerical studies which simulate the application of Asher's method and a unique experimental implementation of the method were completed. Another objective of the research was to develop and to demonstrate with numerical simulation a quantitative method for determining from transfer function data the number of dominant modes of vibration in sinusoidal structural response

A method for experimental modal separation

A method is described for the numerical simulation of multiple-shaker modal survey testing using simulated experimental data to optimize the shaker force-amplitude distribution for the purpose of isolating individual modes of vibration. Inertia, damping, stiffness, and model data are stored on magnetic disks, available by direct access to the interactive FORTRAN programs which perform all computations required by this relative force amplitude distribution method

Development and application of optimum sensitivity analysis of structures

The research focused on developing an algorithm applying optimum sensitivity analysis for multilevel optimization. The research efforts have been devoted to assisting NASA Langley's Interdisciplinary Research Office (IRO) in the development of a mature methodology for a multilevel approach to the design of complex (large and multidisciplinary) engineering systems. An effort was undertaken to identify promising multilevel optimization algorithms. In the current reporting period, the computer program generating baseline single level solutions was completed and tested out

Active damping of modal vibrations by force apportioning

Force apportioning, a method of active structural damping based on that used in modal vibration testing of isolating modes by multiple shaker excitation, was analyzed and numerically simulated. A distribution of as few forces as possible on the structure is chosen so as to maximally affect selected vibration modes while minimally exciting all other modes. The accuracy of numerical simulations of active damping, active damping of higher-frequency modes, and studies of imperfection sensitivity are discussed. The computer programs developed are described and possible refinements of the research are examined

Suspension systems for ground testing large space structures

A research program is documented for the development of improved suspension techniques for ground vibration testing of large, flexible space structures. The suspension system must support the weight of the structure and simultaneously allow simulation of the unconstrained rigid-body movement as in the space environment. Exploratory analytical and experimental studies were conducted for suspension systems designed to provide minimum vertical, horizontal, and rotational degrees of freedom. The effects of active feedback control added to the passive system were also investigated. An experimental suspension apparatus was designed, fabricated, and tested. This test apparatus included a zero spring rate mechanism (ZSRM) designed to support a range of weights from 50 to 300 lbs and provide vertical suspension mode frequencies less than 0.1 Hz. The lateral suspension consisted of a pendulum suspended from a moving cart (linear bearing) which served to increase the effective length of the pendulum. The torsion suspension concept involved dual pendulum cables attached from above to a pivoting support (bicycle wheel). A simple test structure having variable weight and stiffness characteristics was used to simulate the vibration characteristics of a large space structure. The suspension hardware for the individual degrees of freedom was analyzed and tested separately and then combined to achieve a 3 degree of freedom suspension system. Results from the exploratory studies should provide useful guidelines for the development of future suspension systems for ground vibration testing of large space structures

Registration of B99 and B100 Inbred Lines of Maize

Inbreds B99 (Reg. no. PL-174, P1 584528) and B100 (Reg. no. PL-175, P1 584529) are yellow dent maize (Zea mays L.) lines developed cooperatively by the Iowa Agriculture and Home Economics Experiment Station and the USDA-ARS. The lines were released 12 May 1993 for their potential value in the production of hybrid seed and as sources of germplasm in pedigree-selection breeding programs

Registration of B97 and B98, Two Parental Inbred Lines of Maize

Inbreds B97 (Reg. no. PL-169, P1 564682) and B98 (Reg. no. PL-170, P1 564683) are yellow dent maize (Lea mays L.) lines developed cooperatively by the Iowa Agriculture and Home Economics Experiment Station and the USDA-ARS. The lines were released (on 20 Mar. 1992) because of their potential value in the production of hybrid seed and as sources of germplasm in pedigree selection breeding programs of the hybrid seed industry

Cold Tolerance in Corn Hybrids as Affected by Tillage Systems and Planting Dates

Conservation tillage systems that leave greater crop residue on the soil surface to reduce wind and water erosion are becoming more popular with Iowa farmers. Conservation-tilled soils, however, tend to be wetter and cooler at planting time than conventional fall plowed soils. Our objective was to compare corn (Zea mays L.) hybrids classified as cold or not cold tolerant (based on laboratory germination tests) on soils that were either fall plowed (conventional tillage) or spring disked (conservation tillage). Our results did not show any clear advantage for using conventional instead of conservation tillage. Means for the hybrids classified as cold tolerant and not cold tolerant were similar for both tillage systems. No consistent differences in stand, yield, and grain moisture were found between the two tillage systems which suggested that comparable performance would be expected for the two methods of tillage

Quantitative analysis of Iowa stiff stalk synthetic

Stiff Stalk Synthetic is a synthetic variety that was deloped in the early 1930's by recombining 16 inbred lines that were considered to be above average for stalk quality. Because of the origin of the lines included in Stiff Stalk Synthetic, it is usually considered a Reid's Yellow Dent type. Stiff Stalk Synthetic (BSSS) has been used extensively in the cooperative federal-state corn breeding project at Ames, Iowa. BSSS has proved to be a good source of lines that have above average combining ability and stalk quality. BSSS was the source population for initiating half-sib recurrent selection in 1939 and one of the populations used for initiating reciprocal recurrent selection in 1949. Both selection programs have been continued to the present time. In addition, BSSS was included in basic research studies to determine the relative importance of different types of genetic effects and to estimate inbreeding depression for several quantitative traits. Results of these studies for BSSS were summarized and compared with data obtained from other corn populations. BSSS per se tended to yield below average, but it was above average for combining ability in crosses with other varieties. BSSS per formed as a Reid's Yellow Dent type because heterosis was greater in variety crosses with Lancaster Sure Crop types than in variety c rosses with Reid's Yellow Dent types. Regardless of the particular variety included in crosses, however, BSSS tended to make a positive contribution to the variety cross. Because nearly all variety cross trials were machine harvested with no gleaning, the above average stalk quality of BSSS may have been a contributing factor in the performance of BSSS in variety crosses. Quantitative genetic studies suggested BSSS has less genetic variability than many of the other corn varieties for yield. Whereas estimates of additive genetic variance in other corn populations were, on the average, 1.6 times greater than the variance due to dominance effects, the estimates of additive genetic variance for BSSS were similar to the variance for dominance effects. Estimates of inbreeding depression for yield, however, tended to be smaller for BSSS than for other varieties. Performance of BSSS per se, less additive genetic variance, and smaller inbreeding effects suggests that BSSS may have a higher frequency of favorable alleles than for other varieties. BSSS may be in the homozygous condition for some important loci. Gene frequencies of favorable alleles greater than 0.5 would reduce the relative proportion of the additive genetic variance to, the variance due to dominance effects and reduce the effects of inbreeding. Also, fixation of favorable alleles would affect variety performance per se and contribute to, improved combining ability. It seems the main features that distinguish BSSS from other corn varieties are better-than average stalk quality, source of lines with above average combining ability that have adaptation over wide areas, and frequencies of favorable alleles greater than 0.5. A wise choice of lines used to form BSSS and continued selection pressure for the past 40 years have developed improved strains of BSSS that have played an important role in continued genetic progress of hybrid corn.Arnel R. Hallauer, W. A. Russell, O. S. Smith, Department of Agronomy, Iowa State University, Ames, Iowa

Recurrent phenotypic selection and recurrent selection based on combining ability in tetraploid bahiagrass

Paspalum notatum Flüggé is an apomictic grass used for forage and turf. The recent generation of a sexual synthetic tetraploid population of the species provides the uniqueadvantagetoexploitheterosisbyaccumulatingfavorableallelesthroughrecurrent selection cycles. The objective was to evaluate recurrent phenotypic selection (RPS) and recurrent selection based on combining ability (RSCA) as breeding methods. The best sexual genotypes in terms of warm-season growth from a sexual synthetic tetraploid population were selected by RPS and RSCA. The selected genotypes were polycrossed and two new sexual populations were created, which were crossed with superior apomictic genotypes. Both methods allowed obtaining families that were evaluated for summer, fall, and spring growth. Breeding values and heterosis were also calculated. Summer growth for RPS families was greater than for RSCA families (33.1 and 29.08 g plant−1, respectively); however, fall, spring, and accumulated growth were similar. The breeding value for RPS sexual parents was greater than for RSCA sexual parents for summer growth, whereas those for fall and spring growth were similar. A greater level of families with heterosis (80%) was observed for RPS than for RSCA (30%) for summer growth, whereas the levels for fallandspringgrowthweresimilar.Theseresultsindicatethatbothbreedingmethods were successful in improving tetraploid P. notatum. They increased the mean value of the progenies and produced families superior for forage yield by accumulating favorable alleles.Fil: Marcón, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Martínez, Eric Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Zilli, Alex Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Rodríguez, Gustavo Rubén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Brugnoli, Elsa Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Acuña, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentin