5,342 research outputs found
Noncontact true temperature measurement, 2
A laser pyrometer was developed for acquiring the true temperature of a levitated sample. The reflectivity is measured by first expanding the laser beam to cover the entire cross-sectional surface of the diffuse target. The reflectivity calibration of this system is determined from the surface emissivity of a target with a blackbody cavity. The emissivity of the real target can then be calculated. The overall system constant is obtained by passively measuring the radiance of the blackbody cavity (emissivity = 1.0) at a known, arbitrary temperature. Since the photosensor used is highly linear over the entire operating temperature range, the true temperature of the target can then be computed. The latest results available from this on-going research indicate that true temperatures thus obtained are in very good quantitative agreement with thermocouple measured temperatures
Noncontact temperature pattern measuring device
Laser pyrometer techniques are utilized to accurately image a true temperature distribution on a given target without touching the target and without knowing the localized emissivity of the target. The pyrometer utilizes a very high definition laser beam and photodetector, both having a very narrow focus. The pyrometer is mounted in a mechanism designed to permit the pyrometer to be aimed and focused at precise localized points on the target surface. The pyrometer is swept over the surface area to be imaged, temperature measurements being taken at each point of focus
Geometric phases in dressed state quantum computation
Geometric phases arise naturally in a variety of quantum systems with
observable consequences. They also arise in quantum computations when dressed
states are used in gating operations. Here we show how they arise in these
gating operations and how one may take advantage of the dressed states
producing them. Specifically, we show that that for a given, but arbitrary
Hamiltonian, and at an arbitrary time {\tau}, there always exists a set of
dressed states such that a given gate operation can be performed by the
Hamiltonian up to a phase {\phi}. The phase is a sum of a dynamical phase and a
geometric phase. We illustrate the new phase for several systems.Comment: 4 pages, 2 figure
The Transition between Nonorthogonal Polarization Modes in PSR B2016+28 at 1404 MHz
Polarization observations of the radio emission from PSR B2016+28 at 1404 MHz
reveal properties that are consistent with two, very different, interpretations
of the pulsar's viewing geometry. The pulsar's average polarization properties
show a rapid change in position angle (PA) near the pulse center, suggesting
that the observer's sightline nearly intersects the star's magnetic pole. But
single pulse, polarization observations of the pulsar show nearly orthogonal
modes of polarization following relatively flat and parallel PA trajectories
across the pulse, suggesting that the sightline is far from the pole.
Additionally, PA histograms reveal a "modal connecting bridge", of unknown
origin, joining the modal PA trajectories over much of the pulse and following
the rapid PA change shown in the average data. The nonorthogonality of
polarization modes is incorporated in a statistical model of radio polarization
to account for the deviations from mode orthogonality that are observed in the
pulsar. The model is used to interpret the rapid PA change and modal connecting
bridge as a longitudinally-resolved transition between modes of nonorthogonal
polarization. Thus, the modal PA trajectories are argued to reflect the
pulsar's true viewing geometry. This interpretation is consistent with the
pulsar's morphological classification, preserves the Radhakrishnan & Cooke
model of pulsar radio emission, and avoids the complication that the modal
connecting bridge might be produced by some other emission mechanism. The
statistical model's ability to simulate the rich variety of polarization
properties observed in the emission lends additional support to the model's
applicability and its underlying assumption that the polarization modes occur
simultaneously.Comment: Accepted for publication in Ap
High Fidelity State Transfer Over an Unmodulated Linear XY Spin Chain
We provide a class of initial encodings that can be sent with a high fidelity
over an unmodulated, linear, XY spin chain. As an example, an average fidelity
of ninety-six percent can be obtained using an eleven-spin encoding to transmit
a state over a chain containing ten-thousand spins. An analysis of the magnetic
field dependence is given, and conditions for field optimization are provided.Comment: Replaced with published version. 8 pages, 5 figure
Frequency precision of two-dimensional lattices of coupled oscillators with spiral patterns
Two-dimensional lattices of N synchronized oscillators with reactive coupling are considered as high-precision frequency sources in the case where a spiral pattern is formed. The improvement of the frequency precision is shown to be independent of N for large N, unlike the case of purely dissipative coupling where the improvement is proportional to N, but instead depends on just those oscillators in the core of the spiral that acts as the source region of the waves. Our conclusions are based on numerical simulations of up to N = 29 929 oscillators and analytic results for a continuum approximation to the lattice in an infinite system. We derive an expression for the dependence of the frequency precision on the reactive component of the coupling constant, depending on a single parameter given by fitting the frequency of the spiral waves to the numerical simulations
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