57 research outputs found
Attitude Determination from Single-Antenna Carrier-Phase Measurements
A model of carrier phase measurement (as carried out by a satellite
navigation receiver) is formulated based on electromagnetic theory. The model
shows that the phase of the open-circuit voltage induced in the receiver
antenna with respect to a local oscillator (in the receiver) depends on the
relative orientation of the receiving and transmitting antennas. The model
shows that using a {\it single} receiving antenna, and making carrier phase
measurements to seven satellites, the 3-axis attitude of a user platform (in
addition to its position and time) can be computed relative to an initial
point. This measurement model can also be used to create high-fidelity
satellite signal simulators that take into account the effect of platform
rotation as well as translation.Comment: 12 pages, and one figure. Published in J. Appl. Phys. vol. 91, No. 7,
April 1, 200
Absence of correlation between built-in electric dipole moment and quantum Stark effect in InAs/GaAs self-assembled quantum dots
We report significant deviations from the usual quadratic dependence of the
ground state interband transition energy on applied electric fields in
InAs/GaAs self-assembled quantum dots. In particular, we show that conventional
second-order perturbation theory fails to correctly describe the Stark shift
for electric field below kV/cm in high dots. Eight-band calculations demonstrate this effect is predominantly due to
the three-dimensional strain field distribution which for various dot shapes
and stoichiometric compositions drastically affects the hole ground state. Our
conclusions are supported by two independent experiments.Comment: 4 pages, 4 figure
Navigation in Curved Space-Time
A covariant and invariant theory of navigation in curved space-time with
respect to electromagnetic beacons is written in terms of J. L. Synge's
two-point invariant world function. Explicit equations are given for navigation
in space-time in the vicinity of the Earth in Schwarzschild coordinates and in
rotating coordinates. The restricted problem of determining an observer's
coordinate time when their spatial position is known is also considered
The effectiveness of quantum operations for eavesdropping on sealed messages
A quantum protocol is described which enables a user to send sealed messages
and that allows for the detection of active eavesdroppers. We examine a class
of eavesdropping strategies, those that make use of quantum operations, and we
determine the information gain versus disturbance caused by these strategies.
We demonstrate this tradeoff with an example and we compare this protocol to
quantum key distribution, quantum direct communication, and quantum seal
protocols.Comment: 10 pages, 2 figures. Third Feynman Festival, 25 -- 29 August 2006,
University of Maryland, College Park, Maryland, U.S.
On the Doppler effect for light from orbiting sources in Kerr-type metrics
A formula is derived for the combined motional and gravitational Doppler
effect in general stationary axisymmetric metrics for a photon emitted parallel
or antiparallel to the assumed circular orbital motion of its source. The same
formula is derived from eikonal approximation and Killing vector approaches to
elucidate connections between observational astronomy and modern Relativity.
The formula yields expected results in the limits of a moving or stationary
source in the exterior Kerr and Schwarzschild metrics and a moving source in
flat space.Comment: Accepted for publication in in Monthly Notices of the Royal
Astronomical Society Main Journal 1.23.15. This version has substantially
shortened and clarified derivations and added content regarding applicability
of the derivation
Confinement of Interchain Hopping by Umklapp Scattering in Two-Coupled Chains
The effect of umklapp scattering on interchain hopping has been investigated
for two-coupled chains of interacting electrons with half-filled band. By
analyzing in terms of renormalization group method, we have found that
interchain hopping is renormalized to zero and is confined when a gap induced
by umklapp scattering becomes larger than a critical value. From a phase
diagram calculated on a plane of the interchain hopping and the gap, we discuss
a role of the correlation gap which has been studied in metallic state at
temperatures above spin density wave state in organic conductors.Comment: 5 pages, 3 figure
Linear Momentum Density in Quasistatic Electromagnetic Systems
We discuss a couple of simple quasistatic electromagnetic systems in which
the density of electromagnetic linear momentum can be easily computed. The
examples are also used to illustrate how the total electromagnetic linear
momentum, which may also be calculated by using the vector potential, can be
understood as a consequence of the violation of the action-reaction principle,
because a non-null external force is required to maintain constant the
mechanical linear momentum. We show how one can avoid the divergence in the
interaction linear electromagnetic momentum of a system composed by an
idealization often used in textbooks (an infinite straight current) and a point
charge.Comment: 22 pages, 5 figures, to appear in Eur. J. Phy
Confinement-deconfinement transition in two-coupled chains with umklapp scattering
A role of umklapp scattering has been examined for two-coupled chains with
both forward and backward scatterings by applying renormalization group method
to bosonized Hamiltonian. It has been found that a state with relevant
interchain hopping changes into a state with irrelevant (confined) one when the
magnitude of umklapp scattering becomes larger than that of interchain hopping.
Critical value of umklapp scattering for such a confinement-deconfinement
transition is calculated as the function of interchain hopping and intrachain
interactions. A crossover from one-dimensional regime into that of coupled
chains is also shown with decreasing temperature.Comment: 13 pages, 7 figures, to be published in Phys. Rev.
Derbid Planthoppers (Hemiptera: Fulgoroidea: Derbidae) Associated with Coconut and Oil Palm in Brazil.
We present surveys of derbid planthoppers associated with coconut (Cocos nucifera L.) and oil palm (Elaeis guineensis Jacq.) collected in Northeastern (Sergipe) and North (Pará and Roraima) Brazil. The surveys were intended to contribute to our knowledge of possible vectors of phytoplasmas or other phloem-restricted plant pathogens. Eight derbid taxa were found, two in the subfamily Cedusinae, tribe Cedusini (Cedusa yipara Kramer and C. yowza Kramer) and six in the subfamily Derbinae, tribe Cenchreini: Herpis sp., Persis pugnax Stål, Omolicna anastomosa (Caldwell), O. nigripennis (Caldwell), and two new species in the genus Agoo Bahder & Bartlett are described here. Genus-level features between Omolicna and Agoo are discussed and a key to the species of Agoo is provided
Investigation of carrier confinement in direct bandgap GeSn/SiGeSn 2D and 0D heterostructures
Since the first demonstration of lasing in direct bandgap GeSn semiconductors, the research efforts for the realization of electrically pumped group IV lasers monolithically integrated on Si have significantly intensified. This led to epitaxial studies of GeSn/SiGeSn hetero- and nanostructures, where charge carrier confinement strongly improves the radiative emission properties. Based on recent experimental literature data, in this report we discuss the advantages of GeSn/SiGeSn multi quantum well and quantum dot structures, aiming to propose a roadmap for group IV epitaxy. Calculations based on 8-band k∙p and effective mass method have been performed to determine band discontinuities, the energy difference between Γ- and L-valley conduction band edges, and optical properties such as material gain and optical cross section. The effects of these parameters are systematically analyzed for an experimentally achievable range of Sn (10 to 20 at.%) and Si (1 to 10 at.%) contents, as well as strain values (−1 to 1%). We show that charge carriers can be efficiently confined in the active region of optical devices for experimentally acceptable Sn contents in both multi quantum well and quantum dot configurations
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