667 research outputs found
110 GHz rapid, continous tuning from an optical parametric oscillator pumped by a fiber-amplified DBR diode laser
A singly-resonant continuous-wave optical parametric oscillator (cw-OPO) pumped by a fiber-amplified diode laser is described. Tuning of the pump source allowed the OPO output to be tuned continuously, without mode-hops, over 110 GHz in 29 ms. Discontinuous pump tuning over 20 nm in the region of 3.4 µm was also obtained. The rapid and continuous idler tuning was demonstrated by the measurement of a methane absorption spectrum. We believe this to be the first example of a singly-resonant OPO pumped by a fiber-amplified diode laser and the mode-hop free tuning range to be the highest reported for a cw-OPO
Influence of nitrogen fertilization on winter wheat rooting patterns and soil water extraction
Non-Peer ReviewedA partial excavation technique, called the profile wall method, was utilized in 1985 and 1986 to investigate effects of ammonium nitrate additions on rooting patterns of Norstar winter wheat (Triticum aestivum
L.). Additional nitrogen was found to increase root growth, especially at tillering. Increases in soil water extraction were measured at the same time indicating a positive relationship between root density and soil
water utilization. Placement of the fertilizer in mid-row bands at seeding time did not change crop rooting patterns compared to spring broadcast nitrogen applications. Fall fertilization was actually less effective with respect to protein yield; broadcast applied treatments generally had higher grain yields and higher protein concentration. Roots of winter wheat grew to an average 120 cm depth. Nitrogen fertilization did not affect final root depth. Environmental factors appeared to be important in determining root depth. Soil moisture limitations were observed at several locations in 1986
A comparison of rooting patterns in spring and winter wheat
Non-Peer Reviewe
Electronic Structure of the Complex Hydride NaAlH4
Density functional calculations of the electronic structure of the complex
hydride NaAlH4 and the reference systems NaH and AlH3 are reported. We find a
substantially ionic electronic structure for NaAlH4, which emphasizes the
importance of solid state effects in this material. The relaxed hydrogen
positions in NaAlH4 are in good agreement with recent experiment. The
electronic structure of AlH3 is also ionic. Implications for the binding of
complex hydrides are discussed.Comment: 4 pages, 5 figure
Vortices and dynamics in trapped Bose-Einstein condensates
I review the basic physics of ultracold dilute trapped atomic gases, with
emphasis on Bose-Einstein condensation and quantized vortices. The hydrodynamic
form of the Gross-Pitaevskii equation (a nonlinear Schr{\"o}dinger equation)
illuminates the role of the density and the quantum-mechanical phase. One
unique feature of these experimental systems is the opportunity to study the
dynamics of vortices in real time, in contrast to typical experiments on
superfluid He. I discuss three specific examples (precession of single
vortices, motion of vortex dipoles, and Tkachenko oscillations of a vortex
array). Other unusual features include the study of quantum turbulence and the
behavior for rapid rotation, when the vortices form dense regular arrays.
Ultimately, the system is predicted to make a quantum phase transition to
various highly correlated many-body states (analogous to bosonic quantum Hall
states) that are not superfluid and do not have condensate wave functions. At
present, this transition remains elusive. Conceivably, laser-induced synthetic
vector potentials can serve to reach this intriguing phase transition.Comment: Accepted for publication in Journal of Low Temperature Physics,
conference proceedings: Symposia on Superfluids under Rotation (Lammi,
Finland, April 2010
Short-term fate of dietary dieldrin in the digestive tract of Juvenile Lake Trout ( Salvelinus namaycush )
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47979/1/128_2005_Article_BF01685015.pd
Ab initio atomistic thermodynamics and statistical mechanics of surface properties and functions
Previous and present "academic" research aiming at atomic scale understanding
is mainly concerned with the study of individual molecular processes possibly
underlying materials science applications. Appealing properties of an
individual process are then frequently discussed in terms of their direct
importance for the envisioned material function, or reciprocally, the function
of materials is somehow believed to be understandable by essentially one
prominent elementary process only. What is often overlooked in this approach is
that in macroscopic systems of technological relevance typically a large number
of distinct atomic scale processes take place. Which of them are decisive for
observable system properties and functions is then not only determined by the
detailed individual properties of each process alone, but in many, if not most
cases also the interplay of all processes, i.e. how they act together, plays a
crucial role. For a "predictive materials science modeling with microscopic
understanding", a description that treats the statistical interplay of a large
number of microscopically well-described elementary processes must therefore be
applied. Modern electronic structure theory methods such as DFT have become a
standard tool for the accurate description of individual molecular processes.
Here, we discuss the present status of emerging methodologies which attempt to
achieve a (hopefully seamless) match of DFT with concepts from statistical
mechanics or thermodynamics, in order to also address the interplay of the
various molecular processes. The new quality of, and the novel insights that
can be gained by, such techniques is illustrated by how they allow the
description of crystal surfaces in contact with realistic gas-phase
environments.Comment: 24 pages including 17 figures, related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
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