468 research outputs found
Satellite and ground radiotracking of elk
Radiotracking and monitoring of free-living animals in natural environments is providing an effective new technique for acquiring information on biological processes, including animal orientation and navigation. To test the practicability of extending the technique by using satellite systems for tracking animals, a female elk was instrumented with an electronic collar. It contained both the Interrogation Recording Location System (IRLS) transponder and a Craighead-Varney ground-tracking transmitter. The elk was successfully tracked and monitored by satellite during month of April 1970. This was the first time an animal had been tracked by satellite on the surface of the earth
Assessment of needs for satellite tracking of birds and suggestions for expediting a program
Equipment development and testing, animal-instrument interphase or attachment methods, and the evaluation of various feasibility-tracking experiments with raptors are described as well as suggestions for expediting a future program. Results of animal-instrument interphases work indicate that large free-flying birds can be successfully instrumented with radio packages comparable in weight to satellite-transmitter packages. The 401 MHz frequency proved satisfactory for a combination of satellite and ground tracking of migrating birds. Tests run for nearly a year with the Nimbus 6 satellite and a miniaturized, one-watt prototype RAMS transmitter produced encouraging results in regard to location accuracy, frequency of contact with satellite and use of whip antennas. A future program is recommended with priority given to development of six operational transmitters for feasibility experiments
Surface dissipation in nanoelectromechanical systems: Unified description with the standard tunneling model and effects of metallic electrodes
By modifying and extending recent ideas [C. Seoanez et al., Europhys. Lett.
78, 60002 (2007)], a theoretical framework to describe dissipation processes in
the surfaces of vibrating micro- and nanoelectromechanical devices, thought to
be the main source of friction at low temperatures, is presented. Quality
factors as well as frequency shifts of flexural and torsional modes in doubly
clamped beams and cantilevers are given, showing the scaling with dimensions,
temperature, and other relevant parameters of these systems. Full agreement
with experimental observations is not obtained, leading to a discussion of
limitations and possible modifications of the scheme to reach a quantitative
fitting to experiments. For nanoelectromechanical systems covered with metallic
electrodes, the friction due to electrostatic interaction between the flowing
electrons and static charges in the device and substrate is also studied.Comment: 17 pages, 7 figure
Quantum manipulation via atomic-scale magnetoelectric effects
Magnetoelectric effects at the atomic scale are demonstrated to afford unique
functionality. This is shown explicitly for a quantum corral defined by a wall
of magnetic atoms deposited on a metal surface where spin-orbit coupling is
observable. We show these magnetoelectric effects allow one to control the
properties of systems placed inside the corral as well as their electronic
signatures; they provide alternative tools for probing electronic properties at
the atomic scale
Stamp transferred suspended graphene mechanical resonators for radio-frequency electrical readout
We present a simple micromanipulation technique to transfer suspended
graphene flakes onto any substrate and to assemble them with small localized
gates into mechanical resonators. The mechanical motion of the graphene is
detected using an electrical, radio-frequency (RF) reflection readout scheme
where the time-varying graphene capacitor reflects a RF carrier at f=5-6 GHz
producing modulation sidebands at f +/- fm. A mechanical resonance frequency up
to fm=178 MHz is demonstrated. We find both hardening/softening Duffing effects
on different samples, and obtain a critical amplitude of ~40 pm for the onset
of nonlinearity in graphene mechanical resonators. Measurements of the quality
factor of the mechanical resonance as a function of DC bias voltage Vdc
indicate that dissipation due to motion-induced displacement currents in
graphene electrode is important at high frequencies and large Vdc
Dirac electrons in graphene-based quantum wires and quantum dots
In this paper we analyse the electronic properties of Dirac electrons in
finite-size ribbons and in circular and hexagonal quantum dots made of
graphene.Comment: Contribution for J. Phys.: Cond. Mat. special issue on graphene
physic
Graphene Photonics and Optoelectronics
The richness of optical and electronic properties of graphene attracts
enormous interest. Graphene has high mobility and optical transparency, in
addition to flexibility, robustness and environmental stability. So far, the
main focus has been on fundamental physics and electronic devices. However, we
believe its true potential to be in photonics and optoelectronics, where the
combination of its unique optical and electronic properties can be fully
exploited, even in the absence of a bandgap, and the linear dispersion of the
Dirac electrons enables ultra-wide-band tunability. The rise of graphene in
photonics and optoelectronics is shown by several recent results, ranging from
solar cells and light emitting devices, to touch screens, photodetectors and
ultrafast lasers. Here we review the state of the art in this emerging field.Comment: Review Nature Photonics, in pres
A Geochemical Record of Late- Holocene Hurricane Events From the Florida Everglades
A 5.25- m sediment core SRM- 1 and 45 surface samples from mangrove forests at the Shark River Estuary in the Everglades National Park, Florida, were examined by using X- ray fluorescence and carbon isotopic analyses to study the history of intense hurricane landfall during the Late- Holocene. Significance testing of the surface samples in relation to storm deposits from Hurricane Wilma suggests that elemental concentration of Sr and Cl and the ratio of Cl/Br are the most sensitive indicators for major hurricane events in our study area. The geochemical data sets of core SRM- 1 identified five active periods of intense hurricane activities during the last 3,500 years at ~3,400- 3,000, ~2,200- 1,500, ~1,000- 800, ~600- 300, and ~150 calibrated years before present to present. This is the longest paleohurricane record to date from South Florida. Our results are consistent with the view that intense hurricane activities in South Florida were modulated by Intertropical Convergence Zone (ITCZ) movements, El Niño/Southern Oscillation (ENSO) activities, and North Atlantic Oscillation (NAO) strength. This study contributes to the methodological advancement in paleotempestological studies by demonstrating that geochemical signals, particularly signals of saltwater intrusions, can be preserved in the sediment profiles on millennial time- scale and measured by X- ray fluorescence techniques, thereby enabling more storm records to be produced from otherwise suboptimal sand- limited coastal systems such as the Florida Everglades. More work needs to be done to explore the use of geochemical and stable isotopic analyses in detecting storm signals from sand- limited coastal environments.Plain Language SummaryThis study uses geochemical analyses to detect intense hurricanes that made landfall near the southwest coast of the Florida Everglades from sediment profiles. The geochemical data sets identified five active periods of intense hurricane activities during the last 3,500 years at ~3,400- 3,000, ~2,200- 1,500, ~1,000- 800, ~600- 300, and ~150 years ago. Results from this study agree with previous studies that intense hurricane activities in the western Atlantic Basin were controlled by the position of ITCZ, ENSO activities, and NAO strength.Key PointsThis study demonstrates the use of XRF analysis in detecting major hurricane events in sand- limited coastal systemsFive active hurricane periods were identified at ~3,400- 3,000, ~2,200- 1,500, ~1,000- 800, ~600- 300, and ~150 cal yr BP to presentThis study suggests that intense hurricane activities in the western Atlantic Basin were modulated by ITCZ, ENSO, and NAO activitiesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156482/2/wrcr24787_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156482/1/wrcr24787.pd
Quantum Vacuum Experiments Using High Intensity Lasers
The quantum vacuum constitutes a fascinating medium of study, in particular
since near-future laser facilities will be able to probe the nonlinear nature
of this vacuum. There has been a large number of proposed tests of the
low-energy, high intensity regime of quantum electrodynamics (QED) where the
nonlinear aspects of the electromagnetic vacuum comes into play, and we will
here give a short description of some of these. Such studies can shed light,
not only on the validity of QED, but also on certain aspects of nonperturbative
effects, and thus also give insights for quantum field theories in general.Comment: 9 pages, 8 figur
Moving liquids with light: Photoelectrowetting on semiconductors
Liquid transport in microchip-based systems is important in many areas such
as Laboratory-on-a-chip, Microfluidics and Optofluidics. Actuation of liquids
in such systems is usually achieved using either mechanical displacement11 or
via energy conversion e.g. electrowetting which modifies wetting. However, at
the moment there is no clear way of actuating a liquid using light. Here, by
linking semiconductor physics and wetting phenomenon a brand new effect
"photoelectrowetting" is demonstrated for a droplet of conducting liquid
resting on an insulator-semiconductor stack. Optical generation of carriers in
the space-charge region of the underlying semiconductor alters the capacitance
of the insulator-semiconductor stack; the result of this is a modification of
the wetting contact angle of the droplet upon illumination. The effect is
demonstrated using commercial silicon wafers, both n- and p-type having a
doping range spanning four orders of magnitude (6\times1014-8\times1018 cm-3),
coated with a commercial fluoropolymer insulating film (Teflon\textregistered).
Impedance measurements confirm that the observations are semiconductor
space-charge related effects. The impact of the work could lead to new
silicon-based technologies in the above mentioned areas
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