Experimental investigations of the effects of cutting angle on chattering of a flexible manipulator

When a machine tool is mounted at the tip of a robotic manipulator, the manipulator becomes more flexible (the natural frequencies are lowered). Moreover, for a given flexible manipulator, its compliance will be different depending on feedback gains, configurations, and direction of interest. Here, the compliance of a manipulator is derived analytically, and its magnitude is represented as a compliance ellipsoid. Then, using a two-link flexible manipulator with an abrasive cut off saw, the experimental investigation shows that the chattering varies with the saw cutting angle due to different compliance. The main work is devoted to finding a desirable cutting angle which reduces the chattering

A search for CO+ in planetary nebulae

We have carried out a systematic search for the molecular ion CO+ in a sample of 8 protoplanetary and planetary nebulae in order to determine the origin of the unexpectedly strong HCO+ emission previously detected in these sources. An understanding of the HCO+ chemistry may provide direct clues to the physical and chemical evolution of planetary nebulae. We find that the integrated intensity of the CO+ line may be correlated with that of HCO+, suggesting that the reaction of CO+ with molecular hydrogen may be an important formation route for HCO+ in these planetary nebulae.Comment: 6 pages, 4 figures, accepted for publication in MNRA

Summary of the Status of Harvest Mice, Cricetidae: Reithrodontomys, in Arkansas

Although four species of harvest mice, Reithrodoniomyx, are known to occur in Arkansas, the distributional status of the genus in the state is poorly understood. Recent museum specimens significantly extend the range of R. megalotix and R. fulvescens in the state. R. megalotis is shown to range south through Phillips Co. in eastern Arkansas, and R. fulvescens is shown to range throughout most of the state, now including most of the Mississippi Alluvial Plain. A new specimen of R. humulis from Delaware Co., Oklahoma, suggests that this species probably ranges throughout northwestern Arkansas. R montanus remains known only from Washington Co. in northwestern Arkansas

A principled approach to the measurement of situation awareness in commercial aviation

The issue of how to support situation awareness among crews of modern commercial aircraft is becoming especially important with the introduction of automation in the form of sophisticated flight management computers and expert systems designed to assist the crew. In this paper, cognitive theories are discussed that have relevance for the definition and measurement of situation awareness. These theories suggest that comprehension of the flow of events is an active process that is limited by the modularity of attention and memory constraints, but can be enhanced by expert knowledge and strategies. Three implications of this perspective for assessing and improving situation awareness are considered: (1) Scenario variations are proposed that tax awareness by placing demands on attention; (2) Experimental tasks and probes are described for assessing the cognitive processes that underlie situation awareness; and (3) The use of computer-based human performance models to augment the measures of situation awareness derived from performance data is explored. Finally, two potential example applications of the proposed assessment techniques are described, one concerning spatial awareness using wide field of view displays and the other emphasizing fault management in aircraft systems

Statistical Phylogenetic Tree Analysis Using Differences of Means

We propose a statistical method to test whether two phylogenetic trees with given alignments are significantly incongruent. Our method compares the two distributions of phylogenetic trees given by the input alignments, instead of comparing point estimations of trees. This statistical approach can be applied to gene tree analysis for example, detecting unusual events in genome evolution such as horizontal gene transfer and reshuffling. Our method uses difference of means to compare two distributions of trees, after embedding trees in a vector space. Bootstrapping alignment columns can then be applied to obtain p-values. To compute distances between means, we employ a "kernel trick" which speeds up distance calculations when trees are embedded in a high-dimensional feature space, e.g. splits or quartets feature space. In this pilot study, first we test our statistical method's ability to distinguish between sets of gene trees generated under coalescence models with species trees of varying dissimilarity. We follow our simulation results with applications to various data sets of gophers and lice, grasses and their endophytes, and different fungal genes from the same genome. A companion toolkit, {\tt Phylotree}, is provided to facilitate computational experiments.Comment: 17 pages, 6 figure

Redox reactions with empirical potentials: Atomistic battery discharge simulations

Batteries are pivotal components in overcoming some of today's greatest technological challenges. Yet to date there is no self-consistent atomistic description of a complete battery. We take first steps toward modeling of a battery as a whole microscopically. Our focus lies on phenomena occurring at the electrode-electrolyte interface which are not easily studied with other methods. We use the redox split-charge equilibration (redoxSQE) method that assigns a discrete ionization state to each atom. Along with exchanging partial charges across bonds, atoms can swap integer charges. With redoxSQE we study the discharge behavior of a nano-battery, and demonstrate that this reproduces the generic properties of a macroscopic battery qualitatively. Examples are the dependence of the battery's capacity on temperature and discharge rate, as well as performance degradation upon recharge.Comment: 14 pages, 10 figure

Speech Communication

Contains three reports on research facilities and systems.U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research, under Contract F19628-69-C-0044National Institutes of Health (Grant 2 ROl NB-04332-06

Solid state television camera system Patent

Solid state television camera system consisting of monolithic semiconductor mosaic sensor and molecular digital readout system

Evaluation of EPIC for Three Minnesota Cropping Systems

The Erosion Productivity Impact Calculator (EPIC) model was tested using four years of field data collected at a site near Lamberton, Minnesota, under three different crop rotations: continuous corn (Zea mays L.) or CC, soybean (Glycine max L.)-corn (SC), continuous alfalfa (Medicago sativa L.) or CA. The model was evaluated by comparing measured versus predicted subsurface drainage flow (tile flow), nitratenitrogen (NO3-N) loss in tile flow, residual NO3-N in the soil profile, crop N uptake, and yield. Initially, EPIC was run using standard Soil Conservation Service (SCS) runoff curve numbers (CN2) suggested for the soil type at the site. Two different SC runs were performed with a nitrogen fixation parameter denoted as parm(7) set at either 1.0 or 0.3, reflecting uncertainty for this parameter. Under this scenario, EPIC accurately tracked monthly CC and SC variations of tile flow (r2 = 0.86 and 0.90) and NO3- N loss (r2 = 0.69 and 0.52 or 0.62). However, average annual CC and SC tile flows were under-predicted by 32 and 34 percent, and corresponding annual NO3-N losses were under-predicted by 11 and 41 or 52 percent. Predicted average annual tile flows and NO3-N losses improved following calibration of the CN2; CC and SC tile flow under-predictions were -9 and -12 percent while NO3-N losses were 0.6 and -54 or -24 percent. In general, EPIC reliably replicated the impacts of different crop management systems on nitrogen fate; e.g., greater N loss under CC and SC than CA, and less residual soil N under CA as compared to the other cropping systems. The simulated CA monthly tile flows and NO3-N losses also compared poorly with observed values (r2 values of 0.27 and 0.19). However, the predicted CA annual drainage volumes and N losses were of similar magnitude to those measured, which is of primary interest when applying models such as EPIC on a regional scale