4,544 research outputs found
Global Change: A Biogeochemical Perspective
A research program that is designed to enhance our understanding of the Earth as the support system for life is described. The program change, both natural and anthropogenic, that might affect the habitability of the planet on a time scale roughly equal to that of a human life is studied. On this time scale the atmosphere, biosphere, and upper ocean are treated as a single coupled system. The need for understanding the processes affecting the distribution of essential nutrients--carbon, nitrogen, phosphorous, sulfur, and water--within this coupled system is examined. The importance of subtle interactions among chemical, biological, and physical effects is emphasized. The specific objectives are to define the present state of the planetary life-support system; to ellucidate the underlying physical, chemical, and biological controls; and to provide the body of knowledge required to assess changes that might impact the future habitability of the Earth
Lightweight composite reflector panels
The Hexel Corp. has produced additional composite panels, based on JPL designs, that: (1) have increased the panel size from 0.15 to 0.40 meters, (2) have improved the as-manufactured surface precision 3.0 to approx. 1.0 micron RMS, (3) have utilized different numbers of face sheet plys, (4) have improved face sheet fiber orientation, (5) have variations of aluminum honeycomb core cell size, (6) have combined graphite/epoxy (Gr/Ep) face sheets with E-glass honeycomb cores, and (7) have used standard aluminum core with face sheets composed of combinations of glass, Kevlar, and carbon fibers. Additionally, JPL has identified candidate alternate materials for the facesheets and core, modified the baseline polymer panel matrix material, and developed new concepts for panel composite cores. Dornier designed and fabricated three 0.6 meter Gr/Ep panels, that were evaluated by JPL. Results of both the Hexel and Dornier panel work were used to characterize the state-of-the-art for Gr/Ep mirrors
The earth's trapped radiation belts
The near-earth charged particle environment is discussed in terms of spacecraft design criteria. Models are presented of the trapped radiation belts and based on in-situ data obtained from spacecraft
Understory Species Increase Project: Evaluating Establishment From Seed
Urban forest fragments are frequently managed with an aim to reduce invasive species and promote native species diversity. However, natural regeneration of native forest species, including herbaceous understory species that are especially sensitive to site conditions, is often lacking in these environments. Herbaceous understory species are important for nutrient dynamics in forests and they contain higher biodiversity than other forest strata. Many restoration projects implemented throughout the Willamette Valley in Oregon focus primarily on the establishment of the dominant woody species typical of a Pacific Northwest riparian forest. The lack of focus on the herbaceous understory species can be attributed to the relatively high costs and scarcity of plant material as well as limitations in technical information. The Understory Species Increase Project (USIP) is a collaborative effort started by City of Portland’s Reveg Program, Clean Water Services, and Metro that aims to fill these knowledge and resource gaps by researching, developing, and amplifying diverse herbaceous understory species. The current project stage examines which species readily establish from seed, using in-situ trial plots throughout the Portland Metro Area, half of which were seeded with a mix of native herbaceous understory species. Data from year 1-4 post-seeding have revealed significantly greater richness and abundance of herbaceous understory species in seeded plots compared to controls, but results vary greatly by site and species. Here, we investigate which herbaceous understory species have the greatest overall success and which environmental conditions have the strongest effect on the germination, establishment, and growth of target species
The chemistry of Antarctic ozone 1960-1987
The factors that influence Antarctic ozone are examined with a view to understanding the observed historical trend. Researchers show that reduced ambient temperatures can dramatically enhance the efficiency of chemical removal processes. Attention is focused on positive feedback between levels of ozone, temperature, and rates of heterogeneous chemical reactions. ClO and its dimer, and high levels of these gases are maintained until the clouds evaporate, on 15 September for the simulation shown here
The temperature dependence of the local tunnelling conductance in cuprate superconductors with competing AF order
Based on the model with proper chosen parameters for describing
the cuprate superconductors, it is found that near the optimal doping at low
temperature (), only the pure d-wave superconductivity (SC) prevails and
the antiferromagnetic (AF) order is completely suppressed. At higher , the
AF order with stripe modulation and the accompanying charge order may emerge,
and they could exist above the SC transition temperature. We calculate the
local differential tunnelling conductance (LDTC) from the local density of
states (LDOS) and show that their energy variations are rather different from
each other as increases. Although the calculated modulation periodicity in
the LDTC/LDOS and bias energy dependence of the Fourier amplitude of LDTC in
the "pseudogap" region are in good agreement with the recent STM experiment
[Vershinin , Science {\bf 303}, 1995 (2004)], we point out that some of
the energy dependent features in the LDTC do not represent the intrinsic
characteristics of the sample
Acute Patella Subluxation in Crossfit Athlete
Please refer to the pdf version of the abstract located adjacent to the title
IFU observations of luminous type II AGN - I. Evidence for ubiquitous winds
We present observations of 17 luminous (log(L[O III]/L_Sun) > 8.7) local (z <
0.11) type II AGN. Our aim is to investigate the prevalence and nature of AGN
driven outflows in these galaxies by combining kinematic and ionization
diagnostic information. We use non-parametric methods (e.g. W80, the width
containing 80% of the line flux) to assess the line widths in the central
regions of our targets. The maximum values of W80 in each galaxy are in the
range 400 - 1600 km/s, with a mean of 790 +- 90 km/s. Such high velocities are
strongly suggestive that these AGN are driving ionized outflows. Multi-Gaussian
fitting is used to decompose the velocity structure in our galaxies. 14/17 of
our targets require 3 separate kinematic components in the ionized gas in their
central regions. The broadest components of these fits have FWHM = 530 - 2520
km/s, with a mean value of 920 +- 50 km/s. By simultaneously fitting both the
H{\beta}/[O III] and H{\alpha}/[N II] complexes we construct ionization
diagnostic diagrams for each component. 13/17 of our galaxies show a
significant (> 95 %) correlation between the [N II]/H{\alpha} ratio and the
velocity dispersion of the gas. Such a correlation is the natural consequence
of a contribution to the ionization from shock excitation and we argue that
this demonstrates that the outflows from these AGN are directly impacting the
surrounding ISM within the galaxies.Comment: 37 pages, 30 figures. Accepted for publication in MNRA
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