Probabilistic structural analysis methods for select space propulsion system components

The Probabilistic Structural Analysis Methods (PSAM) project developed at the Southwest Research Institute integrates state-of-the-art structural analysis techniques with probability theory for the design and analysis of complex large-scale engineering structures. An advanced efficient software system (NESSUS) capable of performing complex probabilistic analysis has been developed. NESSUS contains a number of software components to perform probabilistic analysis of structures. These components include: an expert system, a probabilistic finite element code, a probabilistic boundary element code and a fast probability integrator. The NESSUS software system is shown. An expert system is included to capture and utilize PSAM knowledge and experience. NESSUS/EXPERT is an interactive menu-driven expert system that provides information to assist in the use of the probabilistic finite element code NESSUS/FEM and the fast probability integrator (FPI). The expert system menu structure is summarized. The NESSUS system contains a state-of-the-art nonlinear probabilistic finite element code, NESSUS/FEM, to determine the structural response and sensitivities. A broad range of analysis capabilities and an extensive element library is present

A new displacement-based approach to calculate stress intensity factors with the boundary element method

The analysis of cracked brittle mechanical components considering linear elastic fracture mechanics is usually reduced to the evaluation of stress intensity factors (SIFs). The SIF calculation can be carried out experimentally, theoretically or numerically. Each methodology has its own advantages but the use of numerical methods has be-come very popular. Several schemes for numerical SIF calculations have been developed, the J-integral method being one of the most widely used because of its energy-like formulation. Additionally, some variations of the J-integral method, such as displacement-based methods, are also becoming popular due to their simplicity. In this work, a simple displacement-based scheme is proposed to calculate SIFs, and its performance is compared with contour integrals. These schemes are all implemented with the Boundary Element Method (BEM) in order to exploit its advantages in crack growth modelling. Some simple examples are solved with the BEM and the calculated SIF values are compared against available solutions, showing good agreement between the different schemes

Higher Population and Twin Row Configuration Does Not Benefit Strip Intercropped Corn

Increased corn (Zea mays L.) grain yield with strip intercropping, made possible because of increased edge effects, makes this soil-conserving crop production system appealing to farmers. The objective of this study was to determine the population and row configuration needed to optimize the additional yield potential in each outside corn row. Treatments \u27included: 74, 99, and 124 thousand plants ha-1 were grown in twin rows and 74 thousand plants ha-1 grown in single rows. Single rows or twin row centers were spaced 0.76 m. The experiment was conducted at four central Iowa sites during 1996 and 1997. Grain yield was not increased by increasing population, nor did it respond consistently to the twin row configuration. There was little interaction between row position in the strip and treatment response. Higher plant population decreased the number of ears per plant, kernels per row, and kernel weight. The twin row configuration increased the number of ears per plant, but this was offset by a decrease in the number of kernels per row and kernel weight. Farmers should follow current cropping recommendations until this optimum is determined. Given the inconsistent grain yield response to twin rows, there is no current rationale for investing in twin row planting equipment

Profitability of Crop Rotations in Iowa in a Stress Environment

Small grains crops have traditionally been included in Midwestern cropping systems, but their use is restricted by uncertain yields, poor prices, and lack of on-farm uses in operations without livestock. We compared the corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) crop rotation to actual or simulated three-yr rotations at two sites in Iowa between 1986 and 1989. Water was generally more limiting than was nitrogen, which produced minimal response in the corn to which it was applied. April-November precipitation at Nashua, Iowa ranged from 59 to 111 % of average, while at Des Moines, Iowa it was 77% of normal in 1988 and 102% in 1989. Each rotation was subjected to economic analysis using Iowa State University figures for costs of operations and inputs. Commodity prices were set assuming nonparticipation in the government programs of the time. The rotations that depended on hay cuttings to recoup seeding costs never achieved that goal. Oat (Avena sativa L.) and wheat (Triticum aestivum L.) harvests did largely recover the cropping expenses of the systems that included them. Thus, in certain environments no sacrifice in short-term profitability is required in trade-off for the long-term conservation and economic benefits of diversified rotations

Corn (Zea mays L.) Yield Response to Nitrogen Fertilizer in Conventional and Alternative Rotations

Nitrogen (N) fertilization recommendations are not available for corn in rotation with small grains or forages despite the possibility that the N response may differ from that of more conventional corn-soybean rotations. Rotations of corn with soybean (CS), corn with soybean and oat (CSO) and corn with soybean and an oat/berseem clover intercrop (CSOB) were established in 1991 and studied from 1993 through 1998 to determine the optimal N fertilization level for corn produced in each rotation. Corn in each rotation received NH4N03 applied at the rates of 0, 56, 112, or 168 kg N ha-1. Significant differences in corn grain yield occurred between rotations in three years, but no rotation was consistently superior. Corn grain yield increased with N fertilizer in each year, but in 3 of 6 years there was no advantage to applying Nat a rate greater than 112 kg ha-1. No difference in N response between rotations was observed

The contributions of diverse sense organs in the control of leg movement by a walking insect

Cruse H, Dean J, Suilmann M. The contributions of diverse sense organs in the control of leg movement by a walking insect. Journal of Comparative Physiology, A. 1984;154(5):695-705

Tillage Index Based on Created Soil Conditions

The ambiguity of current tillage nomenclature has led to much confusion. This report explains a uniform, comprehensive tillage index that was developed to avoid that ambiguity. It is based on row topography, residue cover, roughness, and tillage depth that result from passage of the tillage tool rather than on the tillage tool used. Examples of the use of this tillage index are presented. This index, because of its percentage crop residue cover and potential surface water storage components, will be useful when the Universal Soil Loss Equation is to be used for estimating erosion potential on a given field

The influence of auditory attention on rhythmic speech tracking: Implications for studies of unresponsive patients

Language comprehension relies on integrating words into progressively more complex structures, like phrases and sentences. This hierarchical structure-building is reflected in rhythmic neural activity across multiple timescales in E/MEG in healthy, awake participants. However, recent studies have shown evidence for this “cortical tracking” of higher-level linguistic structures also in a proportion of unresponsive patients. What does this tell us about these patients’ residual levels of cognition and consciousness? Must the listener direct their attention toward higher level speech structures to exhibit cortical tracking, and would selective attention across levels of the hierarchy influence the expression of these rhythms? We investigated these questions in an EEG study of 72 healthy human volunteers listening to streams of monosyllabic isochronous English words that were either unrelated (scrambled condition) or composed of four-word-sequences building meaningful sentences (sentential condition). Importantly, there were no physical cues between four-word-sentences. Rather, boundaries were marked by syntactic structure and thematic role assignment. Participants were divided into three attention groups: from passive listening (passive group) to attending to individual words (word group) or sentences (sentence group). The passive and word groups were initially naïve to the sentential stimulus structure, while the sentence group was not. We found significant tracking at word- and sentence rate across all three groups, with sentence tracking linked to left middle temporal gyrus and right superior temporal gyrus. Goal-directed attention to words did not enhance word-rate-tracking, suggesting that word tracking here reflects largely automatic mechanisms, as was shown for tracking at the syllable-rate before. Importantly, goal-directed attention to sentences relative to words significantly increased sentence-rate-tracking over left inferior frontal gyrus. This attentional modulation of rhythmic EEG activity at the sentential rate highlights the role of attention in integrating individual words into complex linguistic structures. Nevertheless, given the presence of high-level cortical tracking under conditions of lower attentional effort, our findings underline the suitability of the paradigm in its clinical application in patients after brain injury. The neural dissociation between passive tracking of sentences and directed attention to sentences provides a potential means to further characterise the cognitive state of each unresponsive patient

A personal vision for quality leadership: A reflective essay

Educational administration of today presents many challenges for both new and veteran administrators. Many of these challenges have evolved in response to federal, state, and local pressures. Today\u27s administrators can no longer be blind to these influential agencies, but must be visional strategic planners in order to effectively handle the problems they are faced with today