37 research outputs found
Electronic Structure of Calcium Hexaboride within the Weighted Density Approximation
We report calculations of the electronic structure of CaB using the
weighted density approximation (WDA) to density functional theory. We find a
semiconducting band structure with a sizable gap, in contrast to local density
approximation (LDA) results, but in accord with recent experimental data. In
particular, we find an -point band gap of 0.8 eV. The WDA correction of the
LDA error in describing the electronic structure of CaB is discussed in
terms of the orbital character of the bands and the better cancelation of
self-interactions within the WDA.Comment: 1 figur
Aspectos morfolĂłgicos, morfomĂ©tricos e histoquĂmicos dos tĂşbulos armazenadores de espermatozoides da fĂŞmea do peru Meleagris gallopavo
PerĂodo de permanĂŞncia de espermatozoides em glândulas hospedeiras de espermatozoides e glândulas infundibulares em codorna de corte
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Brookhaven air infiltration measurement system (BNL/AIMS) description and application
A unique capability to measure part-per-quadrillion concentrations of a family of perfluorocarbon tracers (PFTs) is presented. Together with our unique PFT source and passive sampler, measurement of average air exchange and infiltration rate can be determined for periods as short as 12 hours. A more expensive programmable sampler can provide information on a frequency of as little as once per minute for each of its 23 sampling tubes. The principal of AIMS is based on the applicable steady-state assumption that the average concentration (e.g., in pL/L) of a tracer vapor in a chamber (i.e., a building or room) is equal to the emission rate of the tracer source (e.g., in pL/min) divided by the air leakage or infiltration rate (e.g., in L/min). Knowing the source rate and measuring the average concentration then provides a means to calculate the air leakage rate. Extending this technique to a multichamber concept, in which a different type of PFT source is deployed in each chamber of a building, allows the calculation of not only the infiltration rates in each chamber but also the air exchange rates between chambers as well. Since both the PFT source and the passive sampler, a miniature Capillary Adsorption Tube Sampler (CATS), are about the size of a cigarette, inexpensive, and reusable, the BNL/AIMS is a very cost-effective means (if not the only means) for determining these air exchange rates
A Modular Approach for Remote Operation of Humanoid Robots in Search and Rescue Scenarios
In the present work we have designed and implemented a modular, robust and user-friendly Pilot Interface
meant to control humanoid robots in rescue scenarios during dangerous missions. We follow the common
approach where the robot is semi-autonomous and it is remotely controlled by a human operator. In our
implementation, YARP is used both as a communication channel for low-level hardware components and as an
interconnecting framework between control modules. The interface features the capability to receive the status
of these modules continuously and request actions when required. In addition, ROS is used to retrieve data
from different types of sensors and to display relevant information of the robot status such as joint positions,
velocities and torques, force/torque measurements and inertial data. Furthermore the operator is immersed into
a 3D reconstruction of the environment and is enabled to manipulate 3D virtual objects. The Pilot Interface
allows the operator to control the robot at three different levels. The high-level control deals with human-like
actions which involve the whole robot’s actuation and perception. For instance, we successfully teleoperated
IIT’s COmpliant huMANoid (COMAN) platform to execute complex navigation tasks through the composition
of elementary walking commands (e.g.[walk_forward, 1m]). The mid-level control generates tasks in cartesian
space, based on the position and orientation of objects of interest (i.e. valve, door handle) w.r.t. a reference
frame on the robot. The low level control operates in joint space and is meant as a last resort tool to perform fine
adjustments (e.g. release a trapped limb). Finally, our Pilot Interface is adaptable to different tasks, strategies
and pilot’s needs, thanks to a modular architecture of the system which enables to add/remove single front-end
components (e.g. GUI widgets) as well as back-end control modules on the fly
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Demonstration of rapid and sensitive module leak certification for space station freedom
A leak detection and quantification demonstration using perflurocarbon tracer (PFT) technology was successfully performed at the NASA Marshall Space Flight Center on January 25, 1991. The real-time Dual Trap Analyzer (DTA) at one-half hour after the start of the first run gave an estimated leak rate of 0.7 mL/min. This has since been refined to be 1.15 {plus minus} 0.09 mL/min. The leak rates in the next three runs were determined to be 9.8 {plus minus} 0.7, {minus}0.4 {plus minus} 0.3, and 76 {plus minus} 6 mL/min, respectively. The theory on leak quantification in the steady-state and time-dependent modes for a single zone test facility was developed and applied to the above determinations. The laboratory PFT analysis system gave a limit-of-detection (LOD) of 0.05 fL for ocPDCH. This is the tracer of choice and is about 100-fold better than that for the DTA. Applied to leak certification, the LOD is about 0.00002 mL/s (0.000075 L/h), a 5 order-of-magnitude improvement over the original leak certification specification. Furthermore, this limit can be attained in a measurement period of 3 to 4 hours instead of days, weeks, or months. A new Leak Certification Facility is also proposed to provide for zonal (three zones) determination of leak rates. The appropriate multizone equations, their solutions, and error analysis have already been derived. A new concept of seal-integrity certification has been demonstrated for a variety of controlled leaks in the range of module leak testing. High structural integrity leaks were shown to have a linear dependence of flow on {Delta}p. The rapid determination of leak rates at different pressures is proposed and is to be determined while subjecting the module to other external force-generating parameters such as vibration, torque, solar intensity, etc. 13 refs