76,514 research outputs found
An arbuscular mycorrhizal fungus accelerates decomposition and acquires nitrogen directly from organic material
Arbuscular mycorrhizal fungi (order Glomales), which form mycorrhizal symbioses with two out of three of all plant species, are believed to be obligate biotrophs that are wholly dependent on the plant partner for their carbon supply. It is thought that they possess no degradative capability and that they are unable to decompose complex organic molecules, the form in which most soil nutrients occur. Earlier suggestions that they could exist saprotrophically were based on observation of hyphal proliferation on organic materials. In contrast, other mycorrhizal types have been shown to acquire nitrogen directly from organic sources. Here we show that the arbuscular mycorrhizal symbiosis can both enhance decomposition of and increase nitrogen capture from complex organic material (grass leaves) in soil. Hyphal growth of the fungal partner was increased in the presence of the organic material, independently of the host plant
A modular radiative transfer program for gas filter correlation radiometry
The fundamentals of a computer program, simulated monochromatic atmospheric radiative transfer (SMART), which calculates atmospheric path transmission, solar radiation, and thermal radiation in the 4.6 micrometer spectral region, are described. A brief outline of atmospheric absorption properties and line by line transmission calculations is explained in conjunction with an outline of the SMART computational procedures. Program flexibility is demonstrated by simulating the response of a gas filter correlation radiometer as one example of an atmospheric infrared sensor. Program limitations, input data requirements, program listing, and comparison of SMART transmission calculations are presented
Direct frequency comb laser cooling and trapping
Continuous wave (CW) lasers are the enabling technology for producing
ultracold atoms and molecules through laser cooling and trapping. The resulting
pristine samples of slow moving particles are the de facto starting point for
both fundamental and applied science when a highly-controlled quantum system is
required. Laser cooled atoms have recently led to major advances in quantum
information, the search to understand dark energy, quantum chemistry, and
quantum sensors. However, CW laser technology currently limits laser cooling
and trapping to special types of elements that do not include highly abundant
and chemically relevant atoms such as hydrogen, carbon, oxygen, and nitrogen.
Here, we demonstrate that Doppler cooling and trapping by optical frequency
combs may provide a route to trapped, ultracold atoms whose spectra are not
amenable to CW lasers. We laser cool a gas of atoms by driving a two-photon
transition with an optical frequency comb, an efficient process to which every
comb tooth coherently contributes. We extend this technique to create a
magneto-optical trap (MOT), an electromagnetic beaker for accumulating the
laser-cooled atoms for further study. Our results suggest that the efficient
frequency conversion offered by optical frequency combs could provide a key
ingredient for producing trapped, ultracold samples of nature's most abundant
building blocks, as well as antihydrogen. As such, the techniques demonstrated
here may enable advances in fields as disparate as molecular biology and the
search for physics beyond the standard model.Comment: 10 pages, 5 figure
Data reduction analysis and application technique development for atmospheric trace gas constituents derived from remote sensors on satellite or airborne platforms
The applicability of the gas filter correlation radiometer (GFCR) to the measurement of tropospheric carbon monoxide gas was investigated. An assessment of the GFRC measurement system to a regional measurement program was conducted through extensive aircraft flight-testing of several versions of the GFRC. Investigative work in the following areas is described: flight test planning and coordination, acquisition of verifying CO measurements, determination and acquisition of supporting meteorological data requirements, and development of supporting computational software
Discrete local altitude sensing device Patent
Device for use in descending spacecraft as altitude sensor for actuating deceleration retrorocket
The Structure of 1-\u3cem\u3etert\u3c/em\u3e-butyl-2,2,3,4,4-pentamethylphosphetane 1-oxide, C\u3csub\u3e12\u3c/sub\u3eH\u3csub\u3e25\u3c/sub\u3eOP
Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System
Quantum simulators, in which well controlled quantum systems are used to
reproduce the dynamics of less understood ones, have the potential to explore
physics that is inaccessible to modeling with classical computers. However,
checking the results of such simulations will also become classically
intractable as system sizes increase. In this work, we introduce and implement
a coherent imaging spectroscopic technique to validate a quantum simulation,
much as magnetic resonance imaging exposes structure in condensed matter. We
use this method to determine the energy levels and interaction strengths of a
fully-connected quantum many-body system. Additionally, we directly measure the
size of the critical energy gap near a quantum phase transition. We expect this
general technique to become an important verification tool for quantum
simulators once experiments advance beyond proof-of-principle demonstrations
and exceed the resources of conventional computers
Alternative mathematical programming formulations for FSS synthesis
A variety of mathematical programming models and two solution strategies are suggested for the problem of allocating orbital positions to (synthesizing) satellites in the Fixed Satellite Service. Mixed integer programming and almost linear programming formulations are presented in detail for each of two objectives: (1) positioning satellites as closely as possible to specified desired locations, and (2) minimizing the total length of the geostationary arc allocated to the satellites whose positions are to be determined. Computational results for mixed integer and almost linear programming models, with the objective of positioning satellites as closely as possible to their desired locations, are reported for three six-administration test problems and a thirteen-administration test problem
Norman Julius Zabusky OBITUARY
Norman Julius Zabusky, who laid the foundations for several critical advancements in nonlinear science and experimental mathematics, died of idiopathic pulmonary fibrosis on 5 February 2018 in Beersheba, Israel. He also made fundamental contributions to computational fluid dynamics and advocated the importance of visualization in science.Published versio
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