131 research outputs found
A history & future of implantable antennas
pre-printImplantable antennas have been used for communication with medical implants for decades. This paper traces their roots from early transcutaneous inductively coupled devices to the microstrip and wire antennas in use today. A suggestion for where this technology may go in the future as medical devices shrink is also given
Driving Performance in a Simulator as a Function of Pavement and Shoulder Width, Edge Line Presence, and Oncoming Traffic
Driving simulation has primarily been used to study issues of driver distraction and to evaluate in-vehicle devices. The visualization and driver performance capabilities of simulators can be applied to more traditional traffic engineering problems as well. This project aims to demonstrate the usefulness of a driving simulator in evaluating geometric designs for two-lane roads. Paved surface width has been shown to be correlated with crash rates and travel speeds on two-lane rural roads throughout Texas. The current project examines how travel lane width, edge line striping, and shoulder width affect driver errors on these roadway types. Issues of simulator validity, scenario development, and simulator sickness are discussed
Positronium formation in graphene and graphite
Positronium (Ps) formation on the surface of clean polycrystalline copper
(Cu), highly oriented pyrolytic graphite (HOPG) and multi layer graphene (MLG)
grown on a polycrystalline copper substrate has been investigated as a function
of incident positron kinetic energy (1.5eV to 1keV). Measurments on Cu indicate
that as the kinetic energy of the incident positrons increases from 1.5eV to
900eV, the fraction of positrons that form Ps () decreases from ~0.5 to
~0.3. However, in HOPG and MLG, instead of a monotonic decrease of
with positron kinetic energy, a sharp peak is observed at ~ 5eV and above
~200eV,remains nearly constant in HOPG and MLG. We propose that in HOPG and
MLG, at low incident positron energies the Ps formation is dominated either by
a surface Plasmon assisted electron pick up process or by an energy dependent
back scattering process. Both these processes can explain the peak observed and
the present data can help to augment the understanding of Ps formation from
layered materials.Comment: Presented at 18th International Conference on Positron Annihilation,
August 19-24, 2018 | Orlando, USA. The following article has been accepted by
AIP Conference Proceedings. After it is published, it will be found at
https://aip.scitation.org/journal/ap
Application of Doppler Broadened Gamma Spectroscopy to Study the Surface of Graphene
We present Doppler broadened gamma spectra, obtained using the newly
developed advanced positron beam at the University of Texas at Arlington, from
a sample consisting of 6 to 8 layers of graphene (MLG) on polycrystalline Cu.
The kinetic energy of the positron beam was varied form 2 eV to 20 keV allowing
for a depth resolved measurement. The ratio curves formed by dividing the
measured Doppler broadened gamma spectra obtained at low positron kinetic
energies (~2eV) to the gamma spectra obtained at 20 keV were compared to ratio
curves found by dividing the calculated spectra of bulk graphite to bulk Cu.
The ratio curves obtained from the measured results show qualitative agreement
with those obtained from the calculated spectra. In particular, both sets of
curves indicate a much reduced intensity at high momentum. The agreement
between the measured and calculated curves is consistent with the hypothesis
that the 2eV spectra correspond to the Doppler broadened spectra from the thin
overlayer of Graphene (which we anticipate should be similar to the spectra
obtained from bulk graphite) and that the spectra taken at 20 keV corresponds
to bulk Cu due to the fact that most of the positrons implanted at this energy
annihilate in the Cu substrate. The results taken at 2 eV provide evidence that
it is possible to obtain chemically sensitive information from the top atomic
layers of surfaces (both internal and external) from an analysis of the high
momentum tail of the Doppler broadened gamma spectra obtained from the
annihilation of positrons at the surface.Comment: Presented at 18th International Conference on Positron Annihilation,
August 19-24, 2018 | Orlando, USA. The following article has been accepted by
AIP Conference Proceedings. After it is published, it will be found at
https://aip.scitation.org/journal/ap
Measurement and analysis of the Doppler broadened energy spectra of annihilation gamma radiation originating from clean and adsorbate-covered surfaces
We present measurements and theoretical modeling demonstrating the capability
of Doppler Broadened annihilation gamma Spectroscopy (DBS) to provide
element-specific information from the topmost atomic layer of surfaces that are
either clean or covered with adsorbates or thin films. Our measurements show
that the energy spectra of Doppler-shifted annihilation gamma photons emitted
following the annihilation of positrons from the topmost atomic layers of clean
gold (Au) and copper (Cu) differ significantly. With the aid of the positron
annihilation-induced Auger electron spectroscopy (PAES) performed
simultaneously with DBS, we show that measurable differences between the
Doppler broadened gamma spectra from Au and Cu surfaces in the high energy
region of the gamma spectra can be used for the quantification of surface
chemical composition. Modeling the measured Doppler spectra from clean Au and
Cu surfaces using gamma spectra obtained from ab initio calculations after
considering the detector energy resolution and surface positronium formation
pointed to an increase in the relative contribution of gamma from positron
annihilation with valence shell electrons. The fit result also suggests that
the surface-trapped positrons predominantly annihilated with the delocalized
valence shell (s and p) electrons that extended into the vacuum as compared to
the highly localized d electrons. Simultaneous DBS and PAES measurements from
adsorbate (sulfur, oxygen, carbon) or thin film (selenium (Se), graphene)
covered Cu surface showed that it is possible to distinguish and quantify the
surface adsorbate and thin-film composition just based on DBS. DBS of elemental
surfaces presents a promising avenue for developing a characterization tool
that can be used to probe external and internal surfaces that are inaccessible
by conventional surface science techniques
Objection to Motion /First Supplemental Objection of the Chrysler Non-TARP Lenders to the Debtors Motion for an Order (Docket 286 of Chrysler Bankruptcy)
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