917 research outputs found
The alloy with a memory, 55-Nitinol: Its physical metallurgy, properties, and applications
A series of nickel titanium alloys (55-Nitinol), which are unique in that they possess a shape memory, are described. Components made of these materials that are altered in their shapes by deformation under proper conditions return to predetermined shapes when they are heated to the proper temperature range. The shape memory, together with the force exerted and the ability of the material to do mechanical work as it returns to its predetermined shape, suggest a wide variety of industrial applications for the alloy. Also included are discussions of the physical metallurgy and the mechanical, physical, and chemical properties of 55-Nitinol; procedures for melting and processing the material into useful shapes; and a summary of applications
Satellite and surface geophysical expression of anomalous crustal structure in Kentucky and Tennessee
An equivalent layer magnetization model is discussed. Inversion of long wavelength satellite magnetic anomaly data indicates a very magnetic source region centered in south central Kentucky. Refraction profiles suggest that the source of the gravity anomaly is a large mass of rock occupying much of the crustal thickness. The outline of the source delineated by gravity contours is also discernible in aeromagnetic anomaly patterns. The mafic plutonic complex, and several lines of evidence are consistent with a rift association. The body is, however, clearly related to the inferred position of the Grenville Front. It is bounded on the north by the fault zones of the 38th Parallel Lineament. It is suggested that such magnetization levels are achieved with magnetic mineralogies produced by normal oxidation and metamorphic processes and enhanced by viscous build-up, especially in mafic rocks of alkaline character
The Moho as a magnetic boundary
Magnetic data are presented for mantle derived rocks: peridtites from St. Pauls rocks, dunite xenoliths from the kaupulehu flow in Hawaii, as well as peridolite, dunite and eclogite xenoliths from Roberts Victor, Dutoitspan, Kilbourne Hole, and San Carlos diatremes. The rocks are paramagnetic or very weakly ferromagnetic at room temperature. Saturation magnetization values range from 0.013 emu/gm to less than 0.001 emu/gm. A review of pertinent literature dealing with analysis of the minerals in mantle xenoliths provides evidence that metals and primary Fe3O4 are absent, and that complex CR, Mg, Al, and Fe spinels dominate the oxide mineralogy. All of the available evidence supports the magnetic results, indicating that the seismic MOHO is a magnetic boundary
Quantum noise limited and entanglement-assisted magnetometry
We study experimentally the fundamental limits of sensitivity of an atomic
radio-frequency magnetometer. First we apply an optimal sequence of state
preparation, evolution, and the back-action evading measurement to achieve a
nearly projection noise limited sensitivity. We furthermore experimentally
demonstrate that Einstein-Podolsky-Rosen (EPR) entanglement of atoms generated
by a measurement enhances the sensitivity to pulsed magnetic fields. We
demonstrate this quantum limited sensing in a magnetometer utilizing a truly
macroscopic ensemble of 1.5*10^12 atoms which allows us to achieve
sub-femtoTesla/sqrt(Hz) sensitivity.Comment: To appear in Physical Review Letters, April 9 issue (provisionally
Quantum phase estimation with lossy interferometers
We give a detailed discussion of optimal quantum states for optical two-mode
interferometry in the presence of photon losses. We derive analytical formulae
for the precision of phase estimation obtainable using quantum states of light
with a definite photon number and prove that maximization of the precision is a
convex optimization problem. The corresponding optimal precision, i.e. the
lowest possible uncertainty, is shown to beat the standard quantum limit thus
outperforming classical interferometry. Furthermore, we discuss more general
inputs: states with indefinite photon number and states with photons
distributed between distinguishable time bins. We prove that neither of these
is helpful in improving phase estimation precision.Comment: 12 pages, 5 figure
Theory of quantum frequency translation of light in optical fiber: application to interference of two photons of different color
We study quantum frequency translation and two-color photon interference
enabled by the Bragg scattering four-wave mixing process in optical fiber.
Using realistic model parameters, we computationally and analytically determine
the Green function and Schmidt modes for cases with various pump-pulse lengths.
These cases can be categorized as either "non-discriminatory" or
"discriminatory" in regards to their propensity to exhibit high-efficiency
translation or high-visibility two-photon interference for many different
shapes of input wave packets or for only a few input wave packets,
respectively. Also, for a particular case, the Schmidt mode set was found to be
nearly equal to a Hermite-Gaussian function set. The methods and results also
apply with little modification to frequency conversion by sum-frequency
conversion in optical crystals
Experimental demonstration of entanglement-enhanced classical communication over a quantum channel with correlated noise
We present an experiment demonstrating entanglement-enhanced classical
communication capacity of a quantum channel with correlated noise. The channel
is modelled by a fiber optic link exhibiting random birefringence that
fluctuates on a time scale much longer than the temporal separation between
consecutive uses of the channel. In this setting, introducing entanglement
between two photons travelling down the fiber allows one to encode reliably up
to one bit of information into their joint polarization degree of freedom. When
no quantum correlations between two separate uses of the channel are allowed,
this capacity is reduced by a factor of more than three. We demonstrated this
effect using a fiber-coupled source of entagled photon pairs based on
spontaneous parametric down-conversion, and a linear-optics Bell state
measurement.Comment: 4 pages, 2 figures, REVTe
Entanglement generated by dissipation and steady state entanglement of two macroscopic objects
Entanglement is a striking feature of quantum mechanics and an essential
ingredient in most applications in quantum information. Typically, coupling of
a system to an environment inhibits entanglement, particularly in macroscopic
systems. Here we report on an experiment, where dissipation continuously
generates entanglement between two macroscopic objects. This is achieved by
engineering the dissipation using laser- and magnetic fields, and leads to
robust event-ready entanglement maintained for 0.04s at room temperature. Our
system consists of two ensembles containing about 10^{12} atoms and separated
by 0.5m coupled to the environment composed of the vacuum modes of the
electromagnetic field. By combining the dissipative mechanism with a continuous
measurement, steady state entanglement is continuously generated and observed
for up to an hour.Comment: This is an update of the preprint from June 2010. It includes new
results on the creation of steady state entanglement, which has been
maintained up to one hou
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