474 research outputs found
Gap solitons in spatiotemporal photonic crystals
We generalize the concept of nonlinear periodic structures to systems that
show arbitrary spacetime variations of the refractive index. Nonlinear pulse
propagation through these spatiotemporal photonic crystals can be described,
for shallow nonstationary gratings, by coupled mode equations which are a
generalization of the traditional equations used for stationary photonic
crystals. Novel gap soliton solutions are found by solving a modified massive
Thirring model. They represent the missing link between the gap solitons in
static photonic crystals and resonance solitons found in dynamic gratings.Comment: 3 figures, submitte
Strong relative intensity squeezing by 4-wave mixing in Rb vapor
We have measured -3.5 dB (-8.1 dB corrected for losses) relative intensity
squeezing between the probe and conjugate beams generated by stimulated,
nondegenerate four-wave mixing in hot rubidium vapor. Unlike early observations
of squeezing in atomic vapors based on saturation of a two-level system, our
scheme uses a resonant nonlinearity based on ground-state coherences in a
three-level system. Since this scheme produces narrowband, squeezed light near
an atomic resonance it is of interest for experiments involving cold atoms or
atomic ensembles.Comment: Submitted to Optics Letter
Measurements of pernitric acid at the South Pole during ISCAT 2000
The first measurements of pernitric acid at the South Pole were performed during the second Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT 2000). Observed HO2NO2 concentrations averaged 25 pptv. Simple steady-state calculations constrained by measurements show that the lifetime of pernitric acid was largely controlled by dry deposition, with thermal decomposition becoming increasingly important at warmer temperatures. We determined that the pernitric acid equilibrium constant is less uncertain than indicated in the literature. One consequence of pernitric acid deposition to the snow surface is that it is an important sink for both NOx and HOx. Another is that the photochemistry of HO2NO2 in the Antarctic snowpack may be a NOx source in addition to nitrate photolysis. This might be one of the important differences in snow photochemistry between the South Pole and warmer polar sites
Economics of agroforestry (1996)
Agroforestry provides a landowner the opportunity to develop a portfolio of short- and long-term investments that allow for some spreading of financial risk through diversification. In general, diversification of investment provides financial advantages, although it also introduces the need for additional management expertise to deal with the added complexity of the farm operation. For farms with land particularly unsuitable for crops, agroforestry provides a way to remove the unsuitable land from crop production over an extended period as the trees mature. Agroforestry also provides social benefits by functioning as a protective system that ensures resource conservation, although some of these benefits are not directly measurable.New 5/96/5M
Conditional large Fock state preparation and field state reconstruction in Cavity QED
We propose a scheme for producing large Fock states in Cavity QED via the
implementation of a highly selective atom-field interaction. It is based on
Raman excitation of a three-level atom by a classical field and a quantized
field mode. Selectivity appears when one tunes to resonance a specific
transition inside a chosen atom-field subspace, while other transitions remain
dispersive, as a consequence of the field dependent electronic energy shifts.
We show that this scheme can be also employed for reconstructing, in a new and
efficient way, the Wigner function of the cavity field state.Comment: 4 Revtex pages with 3 postscript figures. Submitted for publicatio
Controlling trapping potentials and stray electric fields in a microfabricated ion trap through design and compensation
Recent advances in quantum information processing with trapped ions have
demonstrated the need for new ion trap architectures capable of holding and
manipulating chains of many (>10) ions. Here we present the design and detailed
characterization of a new linear trap, microfabricated with scalable
complementary metal-oxide-semiconductor (CMOS) techniques, that is well-suited
to this challenge. Forty-four individually controlled DC electrodes provide the
many degrees of freedom required to construct anharmonic potential wells,
shuttle ions, merge and split ion chains, precisely tune secular mode
frequencies, and adjust the orientation of trap axes. Microfabricated
capacitors on DC electrodes suppress radio-frequency pickup and excess
micromotion, while a top-level ground layer simplifies modeling of electric
fields and protects trap structures underneath. A localized aperture in the
substrate provides access to the trapping region from an oven below, permitting
deterministic loading of particular isotopic/elemental sequences via
species-selective photoionization. The shapes of the aperture and
radio-frequency electrodes are optimized to minimize perturbation of the
trapping pseudopotential. Laboratory experiments verify simulated potentials
and characterize trapping lifetimes, stray electric fields, and ion heating
rates, while measurement and cancellation of spatially-varying stray electric
fields permits the formation of nearly-equally spaced ion chains.Comment: 17 pages (including references), 7 figure
Quantum cryptography with a predetermined key, using continuous variable Einstein-Podolsky-Rosen correlations
Correlations of the type discussed by EPR in their original 1935 paradox for
continuous variables exist for the quadrature phase amplitudes of two spatially
separated fields. These correlations were experimentally reported in 1992. We
propose to use such EPR beams in quantum cryptography, to transmit with high
efficiency messages in such a way that the receiver and sender may later
determine whether eavesdropping has occurred. The merit of the new proposal is
in the possibility of transmitting a reasonably secure yet predetermined key.
This would allow relay of a cryptographic key over long distances in the
presence of lossy channels.Comment: 11 pages,3 figures, changes are important,presented at QELS(May,2000)
San Francisc
Extent and Distribution of Soils in Depressional Areas in the Clarion-Nicollet-Webster Soil Association in lowa
The extent and distribution of soils that occur in depressional areas in the Clarion-Nicollet-Webster soil association have been estimated for Iowa counties from a randomly selected sample. The sample consisted of detailed soil maps of approximately 1000 quarter-section (each about 160 acres), or about 2 percent of the total land area. The data from the soil maps of the samples were projected to give estimates of soil conditions by counties and for the area as a whole. The acreage of depressional soils is estimated to be 4.8 percent of the total soil association area with significant variation between counties. The following data are reported by counties for mineral and organic soils: (1) percentage of quarter-sections with depressional soil areas, (2) average number and acreage of depressional areas per quarter-section, and (3) size class distribution of depressional areas
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