Inertial-space disturbance rejection for space-based manipulators

The implementation of a disturbance rejection controller for a 6-DOF PUMA manipulator mounted on a 3-DOF platform was described. A control algorithm is designed to track the desired position and attitude of the end-effector in inertial space, subject to unknown disturbances in the platform axes. Experimental results are presented for step, sinusoidal, and random disturbances in the platform rotational axis and in the neighborhood of kinematic singularities. Robotic manipulators were proposed as a means of reducing the amount of extra vehicular activity time required for space station assembly and maintenance. The proposed scenario involves a robotic manipulator attached to some mobile platform, such as a spacecraft, satellite, or the space station itself. Disturbances in the platform position and attitude may prevent the manipulator from successfully completing the task. The possibility of using the manipulator to compensate for platform disturbances was explored. The problem of controlling a robotic manipulator on a mobile platform has received considerable attention in the past few years. Joshi and Desrochers designed a nonlinear feedback control law to carry out tasks (with respect to the robot base frame) in the presence of roll, pitch and yaw disturbances in the platform axes. Dubowsky, Vance, and Torres proposed a time-optimal planning algorithm for a robotic manipulator mounted on a spacecraft, subject to saturation limits in the attitude control reaction jets. Papadopoulos and Dubowsky developed a general framework for analyzing the control of free-floating space manipulator systems. Most recently, Torres and Dubowsky have presented a technique called the enhanced disturbance map to find manipulator trajectories that reduce the effect of disturbances in the spacecraft position and attitude. One common assumption in the literature is that the disturbance signal is exactly known. If this is the case, then the end-effector location can be calculated without relying on direct end-point sensing. However, this assumption is invalid if there is a significant delay in the platform position and attitude measurements, or if the kinematics of the platform are not well known, or if the platform is a non-rigid structure. In the more likely case that only the nominal platform location and upper bound on the disturbance signal are known, direct end-point sensing is needed to measure the end-effector location

A Cenozoic-style scenario for the end-Ordovician glaciation

The end-Ordovician was an enigmatic interval in the Phanerozoic, known for massive glaciation potentially at elevated CO2 levels, biogeochemical cycle disruptions recorded as large isotope anomalies and a devastating extinction event. Ice-sheet volumes claimed to be twice those of the Last Glacial Maximum paradoxically coincided with oceans as warm as today. Here we argue that some of these remarkable claims arise from undersampling of incomplete geological sections that led to apparent temporal correlations within the relatively coarse resolution capability of Palaeozoic biochronostratigraphy. We examine exceptionally complete sedimentary records from two, low and high, palaeolatitude settings. Their correlation framework reveals a Cenozoic-style scenario including three main glacial cycles and higher-order phenomena. This necessitates revision of mechanisms for the end-Ordovician events, as the first extinction is tied to an early phase of melting, not to initial cooling, and the largest δ13C excursion occurs during final deglaciation, not at the glacial apex

Aerodynamic study of a tricycle wheel subsystem for drag reduction

This paper deals with a computational fluid dynamics (CFD) and experimental drag analysis on an isolated rotating wheel subsystem (including its accessories: tire, suspension, A-arms, and fender) of a motor tricycle vehicle with two wheels in front. The main goal of the present work is to study the effect of the fender on the wheel subsystem drag and its optimization. The Star CCM+ commercial code was used for the numerical simulations. Different flow conditions were simulated and some results were validated by comparison to wind tunnel experimental results. To perform drag optimization, several aerodynamic fender shapes were designed and simulated as part of the subsystem. A drastic drag reduction up to 30.6% compared to the original wheel subsystem was achieved through numerical simulations

Single-step production of autologous bovine platelet concentrate for clinical applications in cattle.

Platelet concentrate (PC) is an alternative therapy to treat mastitis in dairy cattle and is an alternative treatment for reproduction problems such as endometritis. Unfortunately, double-centrifugation processing methods described are time-consuming, require specialized laboratory equipment, and are usually done in a heterologous way, which risks herd health. To overcome this limitation, we evaluated single-step bovine PC processing methods readily applicable to a farm setting using an autologous conditioned plasma (ACP) production system. We investigated the hematologic findings, cytokines, and growth factors of the obtained PC samples. Autologous conditioned plasma was prepared using whole blood (WB) from 4 cows (group 1) using single-step centrifugation and 16 different processing methods. The 2 protocols that yielded the highest ratio of platelet to white blood cell (WBC) concentration were ACP-1 [720 × g (2,200 rpm), 5 min] and ACP-2 [929 × g (2,500 rpm), 3 min]. They were subsequently reproduced and compared using WB from 8 cows (group 2). Hematologic findings were quantified, IL-1β (cytokine) and growth factors [platelet-derived growth factor (PDGF), transforming growth factor (TGF)-β, bovine fibroblast growth factor (b-FGF)] were measured, and enrichment factors were compared between samples and processing methods. Hematological characteristics and platelet enrichment varied markedly among tested protocols and all were statistically different from WB. Protocol ACP-2 resulted in significantly greater platelet enrichment (mean 169% of WB) than ACP-1 (125% of WB). We found no significant difference between the 2 ACP preparation protocols with regard to leukocyte reduction (7.53-9.75% WBC compared with WB) or growth factor enrichment (124-125% PDGF, 95-100% TGF-β, 102-104% b-FGF, and 56-74% IL-1β compared with WB). In conclusion, both ACP protocols yielded a platelet concentration shown to promote healing for clinical applications in cattle, and the ACP-2 protocol resulted in a greater degree of platelet enrichment. Therefore, this protocol could be used for ACP production for clinical applications in cattle

Sapling age structure and growth series reveal a shift in recruitment dynamics of sugar maple and American beech over the last 40 years

Northern hardwoods have undergone a marked change in their dynamics, with American beech (Fagus grandifolia Ehrh.) increasing in abundance relative to sugar maple (Acer saccharum Marsh.). This study aims to better understand this sudden shift in recruitment dynamics. We performed an extensive analysis of the age structure, radial growth pattern, and release history on >700 saplings from 34 mature maple–beech stands of southern Quebec. We found (i) that the sapling age structures showed a progressive decrease in the establishment of maple relative to beech starting about 40 years ago, (ii) a change in the species growth hierarchy that started in the 1980s due to increasing radial growth of beech, (iii) that this growth trend is negligible for both maple and beech when we account for size and suppression status, and finally (iv) that the growth trend appears to be independent of present soil conditions. These results contrast with previous studies conducted at the adult stage that reported a growth decline for maple. We conclude that this change in recruitment dynamics is not related to growth, and consequently, further studies investigating this phenomenon should concentrate on establishment and survival

10 Years of Environmental Change on the Slopes of Mount Kilimanjaro and Its Associated Shift in Malaria Vector Distributions.

INTRODUCTION: Malaria prevalence has declined in the Kilimanjaro region of Tanzania over the past 10 years, particularly at lower altitudes. While this decline has been related to the scale-up of long-lasting insecticidal nets to achieve universal coverage targets, it has also been attributed to changes in environmental factors that are important for enabling and sustaining malaria transmission. OBJECTIVES: Herein, we apply spatial analytical approaches to investigate the impact of environmental and demographic changes, including changes in temperature, precipitation, land cover, and population density, on the range of the major malaria vector species Anopheles arabiensis in two districts of Tanzania, situated on the southern slope of Mount Kilimanjaro. These models are used to identify environmental changes that have occurred over a 10-year period and highlight the implications for malaria transmission in this highland region. METHODS: Entomological data were collected from the Hai and Lower Moshi districts of Tanzania in 2001-2004 and 2014-2015. Vector occurrence data were applied alongside satellite remote sensing indices of climate and land cover, and gridded population data, to develop species distribution models for An. arabiensis for the 2004 and 2014 periods using maximum entropy. Models were compared to assess the relative contribution of different environmental and demographic factors to observed trends in vector species distribution in lowland and highland areas. RESULTS: Changes in land cover were observed in addition to increased population densities, increased warm season temperature, and decreased wetness at low altitudes. The predicted area and extent of suitable habitat for An. arabiensis declined across the study area over the 10-year period, with notable contraction at lower altitudes, while species range in higher altitude zones expanded. Importantly, deforestation and warmer temperatures at higher altitudes may have created stable areas of suitable vector habitat in the highlands capable of sustaining malaria transmission. CONCLUSION: We show that environmental changes have had an important influence on the distribution of malaria vector species in a highland area of northern Tanzania. Highland areas may be at continued risk for sporadic malaria outbreaks despite the overall range contraction of principal vector species at lower altitudes, where malaria transmission remains at low intensity