6,632 research outputs found
Hydrodynamic model for expansion and collisional relaxation of x-ray laser-excited multi-component nanoplasma
The irradiation of an atomic cluster with a femtosecond x-ray free-electron
laser pulse results in a nanoplasma formation. This typically occurs within a
few hundreds femtoseconds. By this time the x-ray pulse is over, and the direct
photoinduced processes no longer contributing. All created electrons within the
nanoplasma are thermalized. The nanoplasma thus formed is a mixture of atoms,
electrons and ions of various charges. While expanding, it is undergoing
electron impact ionization and three-body recombination. Below we present a
hydrodynamic model to describe the dynamics of such multi-component nanoplasma.
The model equations are derived by taking the moments of the corresponding
Boltzmann kinetic equations. We include the equations obtained, together with
the source terms due to electron impact ionization and three-body
recombination, in our hydrodynamic solver. Model predictions for a test case:
expanding spherical Ar nanoplasma are obtained. With this model we complete the
two-step approach to simulate x-ray created nanoplasmas, enabling
computationally efficient simulations of their picosecond dynamics. Moreover,
the hydrodynamic framework including collisional processes can be easily
extended for other source terms and then applied to follow relaxation of any
finite non-isothermal multi-component nanoplasma with its components relaxed
into local thermodynamic equilibrium.Comment: 12 pages, 4 figures. This article has been accepted by Physics of
Plasmas. After it is published, it will be found at
http://scitation.aip.org/content/aip/journal/po
CARETS: A prototype regional environmental information system. Volume 5: Interpretation, compilation and field verification procedures in the CARETS project
The author has identified the following significant results. Level 2 land use mapping from high altitude aircraft photography at a scale of 1:100,000 required production of a photomosaic mapping base for each of the 48, 50 x 50 km sheets, and the interpretation and coding of land use polygons on drafting film overlays. To enhance the value of the land use sheets, a series of overlays was compiled, showing cultural features, county boundaries and census tracts, surface geology, and drainage basins. In producing level 1 land use maps from LANDSAT imagery, at a scale of 1:250,000 drafting film was directly overlaid on LANDSAT color composite transparencies. Numerous areas of change were identified, but extensive areas of false changes were also noted
Orbital electron capture by the nucleus
The theory of nuclear electron capture is reviewed in the light of current understanding of weak interactions. Experimental methods and results regarding capture probabilities, capture ratios, and EC/Beta(+) ratios are summarized. Radiative electron capture is discussed, including both theory and experiment. Atomic wave function overlap and electron exchange effects are covered, as are atomic transitions that accompany nuclear electron capture. Tables are provided to assist the reader in determining quantities of interest for specific cases
Effects of CO2 Concentration on Leaf Photosynthesis and Stomatal Conductance of Potatoes Grown Under Different Irradiance Levels and Photoperiods
Potato (Solanum tuberosum L.) cvs. Russet Burbank, Denali, and Norland, were grown in environmental rooms controlled at approx 350 micro mol/mol (ambient during years 1987/1988) and 1000 micro mol/mol (enriched) CO2 concentrations. Plants and electric lamps were arranged to provide two irradiance zones, 400 and 800 micro mol/mol/square m/S PPF and studies were repeated using two photoperiods (12-h light / 12-h dark and continuous light). Leaf photosynthetic rates and leaf stomatal conductance were measured using fully expanded, upper canopy leaves at weekly intervals throughout growth (21 through 84 days after transplanting). Increasing the CO2 from approx 350 to 1000 micro mol/mol under the 12-h photoperiod increased leaf photosynthetic rates by 39% at 400 micro mol/mol/square m/S PPF and 27% at 800 micro mol/mol/square m/S PPF. Increasing the CO2 from approx 350 to 1000 micro mol/mol under continuous light decreased leaf photosynthetic rates by 7% at 400 micro mol/mol/square m/S PPF and 13% at 800 micro mol/mol/square m/S PPF. Increasing the CO2 from approx 350 to 1000 micro mol/mol under the 12-h photoperiod plants decreased stomatal conductance by an average of 26% at 400 micro mol/mol/square m/S PPF and 42% at 800 micro mol/mol/square m/S PPF. Under continuous light, CO2 enrichment resulted in a small increase (2%) of stomatal conductance at 400 micro mol/mol/square m/S PPF, and a small decrease (3%) at 800 micro mol/mol/square m/S PPF. Results indicate that CO2 enrichment under the 12-h photoperiod showed the expected increase in photosynthesis and decrease in stomatal conductance for a C3 species like potato, but the decreases in leaf photosynthetic rates and minimal effect on conductance from CO2 enrichment under continuous light were not expected. The plant leaves under continuous light showed more chlorosis and some rusty flecking versus plants under the 12-h photoperiod, suggesting the continuous light was more stressful on the plants. The increased rates of leaf photosynthesis with increased CO2 concentration paralleled trends in biomass production (published previously) but were not proportional to the biomass yields
Antilocalization of Coulomb Blockade in a Ge-Si Nanowire
The distribution of Coulomb blockade peak heights as a function of magnetic
field is investigated experimentally in a Ge-Si nanowire quantum dot. Strong
spin-orbit coupling in this hole-gas system leads to antilocalization of
Coulomb blockade peaks, consistent with theory. In particular, the peak height
distribution has its maximum away from zero at zero magnetic field, with an
average that decreases with increasing field. Magnetoconductance in the
open-wire regime places a bound on the spin-orbit length ( < 20 nm),
consistent with values extracted in the Coulomb blockade regime ( < 25
nm).Comment: Supplementary Information available at http://bit.ly/19pMpd
Exceptional rigidity and biomechanics of amyloid revealed by 4D electron microscopy
Amyloid is an important class of proteinaceous material because of its close association with protein misfolding disorders such as Alzheimer’s disease and type II diabetes. Although the degree of stiffness of amyloid is critical to the understanding of its pathological and biological functions, current estimates of the rigidity of these β-sheet–rich protein aggregates range from soft (10^8 Pa) to hard (10^(10) Pa) depending on the method used. Here, we use time-resolved 4D EM to directly and noninvasively measure the oscillatory dynamics of freestanding, self-supporting amyloid beams and their rigidity. The dynamics of a single structure, not an ensemble, were visualized in space and time by imaging in the microscope an amyloid–dye cocrystal that, upon excitation, converts light into mechanical work. From the oscillatory motion, together with tomographic reconstructions of three studied amyloid beams, we determined the Young modulus of these highly ordered, hydrogen-bonded β-sheet structures. We find that amyloid materials are very stiff (10^9 Pa). The potential biological relevance of the deposition of such a highly rigid biomaterial in vivo are discussed
Nanomechanics and intermolecular forces of amyloid revealed by four-dimensional electron microscopy
The amyloid state of polypeptides is a stable, highly organized
structural form consisting of laterally associated β-sheet protofilaments
that may be adopted as an alternative to the functional,
native state. Identifying the balance of forces stabilizing amyloid is
fundamental to understanding the wide accessibility of this state
to peptides and proteins with unrelated primary sequences, various
chain lengths, and widely differing native structures. Here, we
use four-dimensional electron microscopy to demonstrate that the
forces acting to stabilize amyloid at the atomic level are highly
anisotropic, that an optimized interbackbone hydrogen-bonding
network within β-sheets confers 20 times more rigidity on the
structure than sequence-specific sidechain interactions between
sheets, and that electrostatic attraction of protofilaments is only
slightly stronger than these weak amphiphilic interactions. The
potential biological relevance of the deposition of such a highly
anisotropic biomaterial in vivo is discussed
The fundamental problem of command : plan and compliance in a partially centralised economy
When a principal gives an order to an agent and advances resources for its implementation, the temptations for the agent to shirk or steal from the principal rather than comply constitute the fundamental problem of command. Historically, partially centralised command economies enforced compliance in various ways, assisted by nesting the fundamental problem of exchange within that of command. The Soviet economy provides some relevant data. The Soviet command system combined several enforcement mechanisms in an equilibrium that shifted as agents learned and each mechanism's comparative costs and benefits changed. When the conditions for an equilibrium disappeared, the system collapsed.Comparative Economic Studies (2005) 47, 296–314. doi:10.1057/palgrave.ces.810011
Hydrodynamic model for expansion and collisional relaxation of x-ray laser-excited multi-component nanoplasma
Ernst equation and spheroidal coordinates with a cosmological constant term
We discuss solution generating techniques treating stationary and axially
symmetric metrics in the presence of a cosmological constant. Using the
recently found extended form of Ernst's complex equation, which takes into
account the cosmological constant term, we propose an extension of spheroidal
coordinates adapted to asymptotically de-Sitter and anti de-Sitter static
spacetimes. In the absence of a cosmological constant we show in addition that
any higher dimensional metric parametrised by a single angular momentum can be
given by a 4 dimensional solution and Weyl potentials parametrising the extra
Killing directions. We explicitly show how a stationary, and a static axially
symmetric spacetime solution in 4 dimensions, can be {\it added} together to
give a 5 dimensional stationary and axisymmetric solution.Comment: 9 pages, no figures, some additional results to gr-qc/0610091.
Prepared for 12th Conference on Recent Developments in Gravity (NEB XII),
Nafplio, Greece, 29 Jun - 2 Jul 200
- …