1,587 research outputs found
Holographic optical elements: Fabrication and testing
The basic properties and use of holographic optical elements were investigated to design and construct wide-angle, Fourier-transform holographic optical systems for use in a Bragg-effect optical memory. The performance characteristics are described along with the construction of the holographic system
Josephson junction between anisotropic superconductors
The sin-Gordon equation for Josephson junctions with arbitrary misaligned
anisotropic banks is derived. As an application, the problem of Josephson
vortices at twin planes of a YBCO-like material is considered. It is shown that
for an arbitrary orientation of these vortices relative to the crystal axes of
the banks, the junctions should experience a mechanical torque which is
evaluated. This torque and its angular dependence may, in principle, be
measured in small fields, since the flux penetration into twinned crystals
begins with nucleation of Josephson vortices at twin planes.Comment: 6 page
Impact of geomagnetic excursions on atmospheric chemistry and dynamics
Geomagnetic excursions, i.e. short periods in time with much weaker
geomagnetic fields and substantial changes in the position of the geomagnetic
pole, occurred repeatedly in the Earth's history, e.g. the Laschamp event
about 41 kyr ago. Although the next such excursion is certain to come,
little is known about the timing and possible consequences for the state of
the atmosphere and the ecosystems. Here we use the global chemistry climate
model SOCOL-MPIOM to simulate the effects of geomagnetic excursions on
atmospheric ionization, chemistry and dynamics. Our simulations show
significantly increased concentrations of nitrogen oxides (NO<sub>x</sub>)
in the entire stratosphere, especially over Antarctica (+15%), due to
enhanced ionization by galactic cosmic rays. Hydrogen oxides
(HO<sub>x</sub>) are also produced in greater amounts (up to +40%) in
the tropical and subtropical lower stratosphere, while their destruction by
reactions with enhanced NO<sub>x</sub> prevails over the poles and in high
altitudes (by −5%). Stratospheric ozone concentrations decrease globally
above 20 km by 1–2% and at the northern hemispheric tropopause by up to
5% owing to the accelerated NO<sub>x</sub>-induced destruction. A 5%
increase is found in the southern lower stratosphere and troposphere. In
response to these changes in ozone and the concomitant changes in atmospheric
heating rates, the Arctic vortex intensifies in boreal winter, while the
Antarctic vortex weakens in austral winter and spring. Surface wind anomalies
show significant intensification of the southern westerlies at their poleward
edge during austral winter and a pronounced northward shift in spring. Major
impacts on the global climate seem unlikely
Digital optical recorder-reproducer system
A mass archival optical recording and reproduction system includes a recording light source such as a laser beam focussed and directed upon an acousto-optic linear modulator array (or page composer) that receives parallel blocks of data converted from a serial stream of digital data to be stored. The page composer imparts to the laser beam modulation representative of a plurality of parallel channels of data and through focussing optics downstream of the page composer parallel arrays of optical spots are recorded upon a suitable recording medium such as a photographic film floppy disc. The recording medium may be substantially frictionlessly and stably positioned for recording at a record/read station by an air-bearing platen arrangement which is preferably thermodynamically non-throttling so that the recording film may be positioned in the path of the information-carrying light beam in a static or dynamic mode. During readout, the page composer is bypassed and a readout light beam is focussed directly upon the recording medium containing an array of previously recorded digital spots, a sync bit, data positioning bits, and a tracking band. The readout beam which has been directed through the recording medium is then imaged upon a photodetector array, the output of which may be coupled to suitable electronic processing circuitry, such as a digital multiplexer, whereby the parallel spot array is converted back into the original serial data stream
Significant subsoil accumulation of mineral nitrogen under perennial crops in a ferralitic Amazonian upland soil: effects of land use systems and single-tree patterns.
bitstream/item/180979/1/ID-3848-38-57.pd
Oxygen-isotope effect on the in-plane penetration depth in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} as revealed by muon-spin rotation
The oxygen-isotope (^16O/^18O) effect (OIE) on the in-plane penetration depth
in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} was studied by
muon-spin rotation. A pronounced OIE on was observed
with a relative isotope shift of
=-5(2)% for x =0.3 and -9(2)% for
x=0.4. It arises mainly from the oxygen-mass dependence of the in-plane
effective mass . The OIE exponents of T_{c} and of
exhibit a relation that appears to be generic for
cuprate superconductors.Comment: 4 pages, 4 eps figures, RevTex
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