6,305 research outputs found
Extended x-ray absorption fine structure study of porous GaSb formed by ion implantation
Porous GaSb has been formed by Ga ion implantation into crystalline GaSb substrates at either room temperature or â180 °C. The morphology has been characterized using scanning electron microscopy and the atomic structure was determined using extended x-ray absorption fine structure spectroscopy. Room-temperature implantation at low fluences leads to the formation of âŒ20-nm voids though the material remains crystalline. Higher fluences cause the microstructure to evolve into a network of amorphous GaSb rods âŒ15 nm in diameter. In contrast, implantation at â180 °C generates large, elongated voids but no rods. Upon exposure to air, the surface of the porous material is readily oxidized yielding GaâOâ and metallic Sb precipitates, the latter resulting from the reduction of unstable SbâOâ. We consider and discuss the atomic-scale mechanisms potentially operative during the concurrent crystalline-to-amorphous and continuous-to-porous transformations
Development of a user experience enhanced teleoperation approach
In this paper, we have investigated various techniques that can be used to enhance user experience for robot teleoperation. In our teleoperation system design, the human operator are provided with both immersive visual feedback and intuitive skill transfer interface such that when controlling a telerobot arm, a user is able to feeÄŒ in a first person perspective in terms of both visual and haptic sense. A number of high-tech devices including Omni haptic joystick, MYO armband, Oculus Rift DK2 headset, and Kinect v2 camera are integrated. The surface electromyography (sEMG) signal allows operator to naturally and efficiently transfer his/her motion skill to the robot, based on the properly designed elastic force feedback. For visual feedback, operators can control the pose of a camera on the head of the robot via the wearable visual headset, such that the operator is able to perceive from the roboĆŁs perspective. Extensive tests have been performed with human subjects to evaluate the design, and the experimental results have shown that superior performance and better user experience have been achieved by the proposed method in comparison with the traditional methods
How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae
Metals from Population III (Pop III) supernovae led to the formation of less
massive Pop II stars in the early universe, altering the course of evolution of
primeval galaxies and cosmological reionization. There are a variety of
scenarios in which heavy elements from the first supernovae were taken up into
second-generation stars, but cosmological simulations only model them on the
largest scales. We present small-scale, high-resolution simulations of the
chemical enrichment of a primordial halo by a nearby supernova after partial
evaporation by the progenitor star. We find that ejecta from the explosion
crash into and mix violently with ablative flows driven off the halo by the
star, creating dense, enriched clumps capable of collapsing into Pop II stars.
Metals may mix less efficiently with the partially exposed core of the halo, so
it might form either Pop III or Pop II stars. Both Pop II and III stars may
thus form after the collision if the ejecta do not strip all the gas from the
halo. The partial evaporation of the halo prior to the explosion is crucial to
its later enrichment by the supernova.Comment: Accepted to Ap
The role of cosmic ray pressure in accelerating galactic outflows
We study the formation of galactic outflows from supernova explosions (SNe)
with the moving-mesh code AREPO in a stratified column of gas with a surface
density similar to the Milky Way disk at the solar circle. We compare different
simulation models for SNe placement and energy feedback, including cosmic rays
(CR), and find that models that place SNe in dense gas and account for CR
diffusion are able to drive outflows with similar mass loading as obtained from
a random placement of SNe with no CRs. Despite this similarity, CR-driven
outflows differ in several other key properties including their overall
clumpiness and velocity. Moreover, the forces driving these outflows originate
in different sources of pressure, with the CR diffusion model relying on
non-thermal pressure gradients to create an outflow driven by internal pressure
and the random-placement model depending on kinetic pressure gradients to
propel a ballistic outflow. CRs therefore appear to be non-negligible physics
in the formation of outflows from the interstellar medium.Comment: 8 pages, 4 figures, accepted for publication in ApJL; movie of
simulated gas densities can be found here:
http://www.h-its.org/tap-images/galactic-outflows
Leading Edge Boundary Layer Suction Device for the Cal Poly Rolling Road Wind Tunnel
Over the course of three quarters from Fall of 2016 to Spring of 2017, our team designed and built a boundary layer suction device. The boundary layer suction device has three main functions: a scoop that redirects most of the boundary layer air out of the wind tunnel, fans that suck the remaining boundary layer air through a porous plate and ducting and out of the wind tunnel, and a transition bridge that transitions the remaining air smoothly onto the rolling road. The wind tunnel is owned by Cal Poly and the rolling road is a new addition to it. By the end of our project, the rolling road was not yet functional. A variable-frequency drive (VFD) will be installed over the summer and belt suction fans will also be installed. Once these are in place, the rolling road can be used.
We were successful in building our device and installing it, but once the rolling road is functional, further iterations can be made on our device. The framing and ducting will likely stay in place without further iterations. However, which fans are used can be changed around. We designed our device with an American Fan model AF-10 in mind, but this fan cannot be used until the VFD is installed. There are other fans that can be repurposed and tested on this device as well, though. And, if necessary, a more powerful fan could be purchased.
The lid, consisting of the scoop, porous plate, and transition bridge, was also designed to be flexible enough for further iterations. All three of its components are separate pieces that fasten to each other and the lid itself is separate from the rest of the assembly and is only meant to attach to it during tests. Two issues could crop up with the scoop: less air than expected being redirected through the scoop, and the scoop creating flow separation. If the latter issue occurs, a new scoop could be made with the angle (currently 10 degrees) reduced. If the former issue occurs, a new scoop could be made with longer overhang, or ducting could be made from where the flow is redirected, to the end of the tunnel.
The following report details the process we went through to make this device. It provides details on the design process, final design analysis, manufacturing results, and test plans that show our progress from project ideation all the way to design acceptance and verification
Direct observation of substitutional Ga after ion implantation in Ge by means of extended x-ray absorption fine structure
We present an experimental lattice location study of Ga atoms in Ge after ion implantation at elevated temperature (250°C). Using extended x-rayabsorption fine structure (EXAFS) experiments and a dedicated sample preparation method, we have studied the lattice location of Ga atoms in Ge with a concentration ranging from 0.5 at. % down to 0.005 at. %. At Ga concentrations â€0.05âat.%, all Ga dopants are substitutional directly after ion implantation, without the need for post-implantation thermal annealing. At higher Ga concentrations, a reduction in the EXAFS amplitude is observed, indicating that a fraction of the Ga atoms is located in a defective environment. The local strain induced by the Ga atoms in the Ge matrix is independent of the Ga concentration and extends only to the first nearest neighbor Ge shell, where a 1% contraction in bond length has been measured, in agreement with density functional theory calculations.We acknowledge the support from the Research Foundation
Flanders, the epi-team from imec, the KU Leuven
GOA 09/06 project, the IUAP program P6/42 and the Australian
Research Council. S.C. acknowledges support from
OCAS NV by an OCAS-endowed chair at Ghent University
Fabrication of integrated planar gunn diode and micro-cooler on GaAs substrate
We demonstrate fabrication of an integrated
micro cooler with the planar Gunn diode and characterise
its performance. First experimental results have shown a
small cooling at the surface of the micro cooler. This is first
demonstration of an integrated micro-cooler with a planar
Gunn diode
Planar gunn diode characterisation and resonators elements to realise oscillator circuits
The paper describes the planar Gunn diode, which is well suited to providing milli-metric and tera hertz sources using microwave monolithic integrated circuit (MMIC) technologies. Different planar Gunn electrode geometries are described along with DC, RF and thermal characterisation. To realize the planar high frequency sources there is requirement for high frequency planar resonators, the paper will describe both the radial and new diamond shaped geometries
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