Modelling ripples in Orion with coupled dust dynamics and radiative transfer

In light of the recent detection of direct evidence for the formation of Kelvin-Helmholtz instabilities in the Orion nebula, we expand upon previous modelling efforts by numerically simulating the shear-flow driven gas and dust dynamics in locations where the H$_{II}$ region and the molecular cloud interact. We aim to directly confront the simulation results with the infrared observations. Methods: To numerically model the onset and full nonlinear development of the Kelvin-Helmholtz instability we take the setup proposed to interpret the observations, and adjust it to a full 3D hydrodynamical simulation that includes the dynamics of gas as well as dust. A dust grain distribution with sizes between 5-250 nm is used, exploiting the gas+dust module of the MPI-AMRVAC code, in which the dust species are represented by several pressureless dust fluids. The evolution of the model is followed well into the nonlinear phase. The output of these simulations is then used as input for the SKIRT dust radiative transfer code to obtain infrared images at several stages of the evolution, which can be compared to the observations. Results: We confirm that a 3D Kelvin-Helmholtz instability is able to develop in the proposed setup, and that the formation of the instability is not inhibited by the addition of dust. Kelvin-Helmholtz billows form at the end of the linear phase, and synthetic observations of the billows show striking similarities to the infrared observations. It is pointed out that the high density dust regions preferentially collect on the flanks of the billows. To get agreement with the observed Kelvin-Helmholtz ripples, the assumed geometry between the background radiation, the billows and the observer is seen to be of critical importance.Comment: 8 pages, 10 figure

Apollo experience report: Command and service module electrical power distribution on subsystem

A review of the design philosophy and development of the Apollo command and service modules electrical power distribution subsystem, a brief history of the evolution of the total system, and some of the more significant components within the system are discussed. The electrical power distribution primarily consisted of individual control units, interconnecting units, and associated protective devices. Because each unit within the system operated more or less independently of other units, the discussion of the subsystem proceeds generally in descending order of complexity; the discussion begins with the total system, progresses to the individual units of the system, and concludes with the components within the units

Robotically assisted eye surgery : a haptic master console

Vitreo-retinal surgery encompasses the surgical procedures performed on the vitreous humor and the retina. A procedure typically consists of the removal of the vitreous humor, the peeling of a membrane and/or the repair of a retinal detachment. Operations are performed with needle shaped instruments which enter the eye through surgeon made scleral openings. An instrument is moved by hand in four degrees of freedom (three rotations and one translation) through this opening. Two rotations (? and ? ) are for a lateral instrument tip movement. The other two DoFs (z and ?) are the translation and rotation along the instrument axis. Actuation of for example a forceps can be considered as a fifth DoF. Characteristically, the manipulation of delicate, micrometer range thick intraocular tissue is required. Today, eye surgery is performed with a maximum of two instruments simultaneously. The surgeon relies on visual feedback only, since instrument forces are below the human detection limit. A microscope provides the visual feedback. It forces the surgeon to work in a static and non ergonomic body posture. Although the surgeon’s proficiency improves throughout his career, hand tremor may become a problem around his mid-fifties. Robotically assisted surgery with a master-slave system enhances dexterity. The slave with instrument manipulators is placed over the eye. The surgeon controls the instrument manipulators via haptic interfaces at the master. The master and slave are connected by electronic hardware and control software. Implementation of tremor filtering in the control software and downscaling of the hand motion allow prolongation of the surgeon’s career. Furthermore, it becomes possible to do tasks like intraocular cannulation which can not be done by manually performed surgery. This thesis focusses on the master console. Eye surgery procedures are observed in the operating room of different hospitals to gain insight in the requirements for the master. The master console as designed has an adjustable frame, a 3D display and two haptic interfaces with a coarse adjustment arm each. The console is mounted at the head of the operating table and is combined with the slave. It is compact, easy to place and allows the surgeon to have a direct view on and a physical contact with the patient. Furthermore, it fits in today’s manual surgery arrangement. Each haptic interface has the same five degrees of freedom as the instrument inside the eye. Through these interfaces, the surgeon can feel the augmented instrument forces. Downscaling of the hand motion results in a more accurate instrument movement compared to manually performed surgery. Together with the visual feedback, it is like the surgeon grasps the instrument near the tip inside the eye. The similarity between hand motion and motion of the instrument tip as seen on the display results in an intuitive manipulation. Pre-adjustment of the interface is done via the coarse adjustment arm. Mode switching enables to control three or more instruments manipulators with only two interfaces. Two one degree of freedom master-slave systems with force feedback are built to derive the requirements for the haptic interface. Hardware in the loop testing provides valuable insights and shows the possibility of force feedback without the use of force sensors. Two five DoF haptic interfaces are realized for bimanual operation. Each DoF has a position encoder and a force feedback motor. A correct representation of the upscaled instrument forces is only possible if the disturbance forces are low. Actuators are therefore mounted to the fixed world or in the neighborhood of the pivoting point for a low contribution to the inertia. The use of direct drive for ' and and low geared, backdriveable transmissions for the other three DoFs gives a minimum of friction. Disturbance forces are further minimized by a proper cable layout and actuator-amplifier combinations without torque ripple. The similarity in DoFs between vitreo-retinal eye surgery and minimally invasive surgery (MIS) enables the system to be used for MIS as well. Experiments in combination with a slave robot for laparoscopic and thoracoscopic surgery show that an instrument can be manipulated in a comfortable and intuitive way. User experience of surgeons and others is utilized to improve the haptic interface further. A parallel instead of a serial actuation concept for the ' and DoFs reduces the inertia, eliminates the flexible cable connection between frame and motor and allows that the heat of the motor is transferred directly to the frame. A newly designed z-?? module combines the actuation and suspension of the hand held part of the interface and has a three times larger z range than in the first design of the haptic interface

Black-tailed Prairie Dog (Cynomys ludovicianus) State-and-Transition Model for Loamy Ecological Sites in MLRA 62 in Custer State Park, South Dakota

Black-tailed prairie dogs (Cynomys ludovicianus) are native burrowing rodents that occupy large areas in the shortgrass and mixed-grass prairies of the Northern Great Plains. They are an important component of these prairie systems due to their impacts on plant communities. Currently State-and-Transition models (STMs) for grassland Ecological Site Descriptions (ESDs) address grazing by livestock as a major factor affecting states and phases within states. Impacts from other grazers, such as prairie dogs, are either not addressed directly, or are included only in a transition to a generalized early seral state. There are, however, dramatic differences in plant communities within prairie dog towns associated with time of prairie dog occupancy as well as other biotic and abiotic factors. These differences are not captured by current STMs. For managers who are tasked with managing prairies occupied by prairie dogs, current STMs do not provide the needed conceptual framework for understanding spatial variation and temporal changes to grassland vegetation affected by prairie dogs, nor do they provide information on management practices and strategies needed to manage these lands effectively. This study was conducted in Custer State Park in southwestern South Dakota. The goal was to develop a state-and-transition model for prairie dog towns on the Loamy Ecological Site (ES) in Major Land Use Area (MLRA 62). Cover data of plant species was collected on and off of prairie dog towns in 2014 and 2015. These data were used to identify 5 distinct vegetation states associated with prairie dog colonies using a combination of Nonmetric Multidimensional Scaling (NMS) Ordination and Cluster analysis. The 5 states are: State 2, Native Invaded; State 3, Kentucky Bluegrass Dominated; State 4, Shortgrass Sod; State 5, Early Seral; and State 6, Fringed Sage Dominated. These 5 states are influenced by the interactions of fire, grazing by prairie dogs and large ungulates, presence of invasive plant species, and climatic factors (e.g. wet/dry cycles and temperature), all of which were used to describe transition pathways between states and community pathways within states. The resulting prairie dog stateand- transition model allows managers to determine the status and health of plant communities on prairie dog towns on the Loamy ES in MLRA 62. It will also help land managers understand vegetation variations across colonies, identify early warning signs that an undesirable transition is likely to occur, and provide potential restoration options that might be able to return a site to a more desirable plant community for management purposes

Energy Options for Future Humans on Titan

We review the possibilities for in situ energy resources on Titan for use by future humans, including chemical, nuclear, wind, solar, geothermal and hydropower. All of these options, with the possible exception of geothermal, represent effective sources of power. Combustion of methane (after electrolysis of the native water), in combination with another source of power such as nuclear, is a viable option; another chemical source of energy is the hydrogenation of acetylene. The large seas Kraken and Ligeia potentially represent effective sources of hydropower. Wind power, particularly at altitudes ~40 km, is expected to be productive. Despite the distance from the sun and the absorbing atmosphere, solar power is (as on Earth) an extremely efficient source of power on Titan