Kinematic rate control of simulated robot hand at or near wrist singularity

A robot hand should obey movement commands from an operator on a computer program as closely as possible. However, when two of the three rotational axes of the robot wrist are colinear, the wrist loses a degree of freedom, and the usual resolved rate equations (used to move the hand in response to an operator's inputs) are indeterminant. Furthermore, rate limiting occurs in close vicinity to this singularity. An analysis shows that rate limiting occurs not only in the vicinity of this singularity but also substantially away from it, even when the operator commands rotational rates of the robot hand that are only a small percentage of the operational joint rate limits. Therefore, joint angle rates are scaled when they exceed operational limits in a real time simulation of a robot arm. Simulation results show that a small dead band avoids the wrist singularity in the resolved rate equations but can introduce a high frequency oscillation close to the singularity. However, when a coordinated wrist movement is used in conjunction with the resolved rate equations, the high frequency oscillation disappears

A design study of hydrazine and biowaste resistojets

A generalized modeling program was adapted in BASIC on a personal computer to compare the performance of four types of biowaste resistojets and two types of hydrazine augmenters. Analyzed biowaste design types were: (1) an electrically conductive ceramic heater-exchanger of zirconia; (2) a truss heater of platinum in cross flow; (3) an immersed bicoiled tubular heater-exchanger; and (4) a nonexposed, refractory metal, radiant heater in a central cavity within a heat exchanger case. Concepts 2 and 3 are designed to have an efficient, stainless steel outer pressure case. The hydrazine design types are: (5) an immersed bicoil heater exchanger and (6) a nonexposed radiant heater now with a refractory metal case. The ceramic biowaste resistojet has the highest specific impulse growth potential at 2000 K of 192.5 (CO2) and 269 s (H2O). The bicoil produces the highest augmenter temperature of 1994 K for a 2073 K heater giving 317 s at .73 overall efficiency. Detailed temperature profiles of each of the designs are shown. The scaled layout drawings of each are presented with recommended materials and fabrication methods

Studies in matter antimatter separation and in the origin of lunar magnetism

Antimatter experiments of the University of Santa Clara are investigated. Topics reported include: (1) planetary geology, (2) lunar Apollo magnetometer experiments, and (3) Roche limit of a solid body

Roles of Fiscal Policy in New Zealand

Economic growth is one of the objectives of the current government. Fiscal policy, encompassing government expenditure and taxation decisions, can significantly impact on economic growth. This paper proposes a framework which views fiscal policy through three lenses and applies this approach to consider how fiscal policy affects economic growth. The three lenses are: fiscal sustainability, fiscal structure and fiscal stabilisation. The paper reviews international literature pertaining to these three lenses and discusses the extent to which these lenses are incorporated into New Zealand’s current fiscal framework. Contemporary New Zealand fiscal challenges are discussed and, in light of these challenges, the paper concludes with consideration of areas to investigate which may yield improvements to the New Zealand fiscal framework.Fiscal policy, sustainability, stability, structure, taxation, government spending, economic growth

The 8^8B Neutrino Spectrum

Knowledge of the energy spectrum of $^8$B neutrinos is an important ingredient for interpreting experiments that detect energetic neutrinos from the Sun. The neutrino spectrum deviates from the allowed approximation because of the broad alpha-unstable $^8$Be final state and recoil order corrections to the beta decay. We have measured the total energy of the alpha particles emitted following the beta decay of $^8$B. The measured spectrum is inconsistent with some previous measurements, in particular with a recent experiment of comparable precision. The beta decay strength function for the transition from $^8$B to the accessible excitation energies in $^8$Be is fit to the alpha energy spectrum using the R-matrix approach. Both the positron and neutrino energy spectra, corrected for recoil order effects, are constructed from the strength function. The positron spectrum is in good agreement with a previous direct measurement. The neutrino spectrum disagrees with previous experiments, particularly for neutrino energies above 12 MeV.Comment: 15 pages, 13 figures, 4 tables, submitted to Phys. Rev. C, typos correcte

Studies in matter antimatter separation and in the origin of lunar magnetism

A progress report, covering lunar and planetary research is introduced. Data cover lunar ionospheric models, lunar and planetary geology, and lunar magnetism. Wind tunnel simulations of Mars aeolian problems and a comparative study of basaltic analogs of Lunar and Martial volcanic features was discussed

Modelos jerárquicos de marcaje–recaptura: un marco para la inferencia de procesos demográficos

The development of sophisticated mark–recapture models over the last four decades has provided fundamental tools for the study of wildlife populations, allowing reliable inference about population sizes and demographic rates based on clearly formulated models for the sampling processes. Mark–recapture models are now routinely described by large numbers of parameters. These large models provide the next challenge to wildlife modelers: the extraction of signal from noise in large collections of parameters. Pattern among parameters can be described by strong, deterministic relations (as in ultrastructural models) but is more flexibly and credibly modeled using weaker, stochastic relations. Trend in survival rates is not likely to be manifest by a sequence of values falling precisely on a given parametric curve; rather, if we could somehow know the true values, we might anticipate a regression relation between parameters and explanatory variables, in which true value equals signal plus noise. Hierarchical models provide a useful framework for inference about collections of related parameters. Instead of regarding parameters as fixed but unknown quantities, we regard them as realizations of stochastic processes governed by hyperparameters. Inference about demographic processes is based on investigation of these hyperparameters. We advocate the Bayesian paradigm as a natural, mathematically and scientifically sound basis for inference about hierarchical models. We describe analysis of capture–recapture data from an open population based on hierarchical extensions of the Cormack–Jolly–Seber model. In addition to recaptures of marked animals, we model first captures of animals and losses on capture, and are thus able to estimate survival probabilities (i.e., the complement of death or permanent emigration) and per capita growth rates f (i.e., the sum of recruitment and immigration rates). Covariation in these rates, a feature of demographic interest, is explicitly described in the model.El desarrollo de sofisticados modelos de marcaje–recaptura a lo largo de las últimas cuatro décadas ha proporcionado herramientas fundamentales para el estudio de poblaciones de fauna silvestre, lo que ha permitido inferir con fiabilidad los tamaños poblacionales y las tasas demográficas a partir de modelos claramente formulados para procesos estocásticos. En la actualidad, los modelos de marcaje–recaptura se describen de forma rutinaria mediante una extensa serie de parámetros. Dichos modelos representan el siguiente reto al que deberán enfrentarse los modeladores de fauna silvestre: discriminar las señales del ruido en amplias series de parámetros. La pauta que encontramos en los parámetros puede describirse mediante sólidas relaciones deterministas (como en los modelos ultraestructurales), pero resulta más flexible y creíble si se modela utilizando relaciones estocásticas más débiles. No es probable que la tendencia en las tasas de supervivencia se manifieste por una secuencia de valores hallados concretamente en una curva paramétrica dada; por ello, si pudiéramos llegar a conocer los valores reales, podríamos prever una relación de regresión entre parámetros y variables explicativas, de forma que el valor verdadero equivaldría a la señal más el ruido. Los modelos jerárquicos proporcionan un marco útil para la inferencia acerca de series de parámetros relacionados. Así, en lugar de interpretar los parámetros como cantidades fijas, pero desconocidas, los interpretamos como realizaciones de procesos estocásticos regidos por hiperparámetros. La inferencia acerca de los procesos demográficos se basa en la investigación de dichos hiperparámetros. Por este motivo, defendemos el paradigma bayesiano como una base natural, matemática y científicamente sólida para la inferencia acerca de modelos jerárquicos. En el presente estudio describimos el análisis de datos de captura–recaptura obtenidos a partir de una población abierta basada en ampliaciones jerárquicas del modelo de Cormack–Jolly–Seber. Además de las recapturas de animales marcados, también modelamos las primeras capturas de animales y de pérdidas durante la captura, lo que nos permitió estimar las probabilidades de supervivencia de (es decir, el complemento de la muerte o la emigración permanente) y las tasas de crecimiento per cápita f (es decir, la suma de las tasas de reclutamiento y de migración). En el modelo se describe explícitamente la covariación en estas tasas, que constituye una característica de interés demográfico

Entrapment: an important mechanism to explain the shortwave 3D radiative effect of clouds

Several mechanisms have previously been proposed to explain differences between the shortwave reflectance of realistic cloud scenes computed using the 1D independent column approximation (ICA) and 3D solutions of the radiative transfer equation. When the sun is low in the sky, interception of sunlight by cloud sides tends to increase reflectance relative to ICA estimates that neglect this effect. When the sun is high, 3D radiative transfer tends to make clouds less reflective, which we argue is explained by the mechanism of “entrapment” whereby horizontal transport of radiation beneath a cloud layer increases the chances, relative to the ICA, of light being absorbed by cloud or the surface. It is especially important for multilayered cloud scenes. We describe modifications to the previously described Speedy Algorithm for Radiative Transfer through Cloud Sides (SPARTACUS) to represent different entrapment assumptions, and test their impact on 65 contrasting scenes from a cloud-resolving model. When entrapment is represented explicitly via a calculation of the mean horizontal distance traveled by reflected light, SPARTACUS predicts a mean “3D radiative effect” (the difference in top-of-atmosphere irradiances between 3D and ICA calculations) of 8.1 W m−2 for overhead sun. This is within 2% of broadband Monte Carlo calculations on the same scenes. The importance of entrapment is highlighted by the finding that the extreme assumptions in SPARTACUS of “zero entrapment” and “maximum entrapment” lead to corresponding mean 3D radiative effects of 1.7 and 19.6 W m−2, respectively

The Lennard-Jones-Devonshire cell model revisited

We reanalyse the cell theory of Lennard-Jones and Devonshire and find that in addition to the critical point originally reported for the 12-6 potential (and widely quoted in standard textbooks), the model exhibits a further critical point. We show that the latter is actually a more appropriate candidate for liquid-gas criticality than the original critical point.Comment: 5 pages, 3 figures, submitted to Mol. Phy