2,512 research outputs found
Linear programming of a slate quarry
[Abstract] A new exploitation of roofing slate has several possibilities of marketing
depending on the sizes of the pieces that it makes. Three sizes has been chosen
among aH the possibilities in base of the conditions and the production of the
rock in the quarry, the marketing limitation and the final price of the producto
We've procces aH these data to obtain the optimun output, with the simplex
algorithm. The objective function (week invoicing) and the restrictions of the
problem are created in canonical and standard formo Optimun solution has been
obtained among aH the basic and practical ones, using the graphic and the
analytic method. Sorne conclusions come from the algorithm matrix about the
outputs for each marketing option
Compositional analysis of InAs-GaAs-GaSb heterostructures by low-loss electron energy loss spectroscopy
As an alternative to Core-Loss Electron Energy Loss Spectroscopy, Low-Loss EELS is suitable for compositional analysis of complex heterostructures, such as the InAs-GaAs-GaSb system, since in this energy range the edges corresponding to these elements are better defined than in Core-Loss. Furthermore, the analysis of the bulk plasmon peak, which is present in this energy range, also provides information about the composition. In this work, compositional information in an InAs-GaAs-GaSb heterostructure has been obtained from Low-Loss EEL spectra
Effect of deforestation and subsequent land use management on soil carbon stocks in the South American Chaco
The subhumid Chaco region of Argentina, originally covered by dry
sclerophyll forest, has been subjected to clearing since the end of the 1970s
and replacement of the forest by no-till farming. Land use changes produced a
decrease in aboveground carbon (C) stored in forests, but little is known
about the impact on soil organic C stocks. The aim of this study was to
evaluate soil C stocks and C fractions up to 1 m depth in soils under
different land use: < 10-year continuous cropping, > 20-year continuous
cropping, warm-season grass pasture and native forest in 32 sites distributed
over the Chaco region. The organic C stock content up to 1 m depth expressed
as equivalent mass varied as follows: forest
(119.3 Mg ha−1)  >  pasture (87.9 Mg ha−1)  >  continuous
cropping (71.9 and 77.3 Mg ha−1), with no impact of the number of
years under cropping. The coarse particle fraction (2000–212 µm) at
0–5 and 5–20 cm depth layers was the most sensitive organic carbon
fraction to land use change. Resistant carbon ( < 53 µm) was the
main organic matter fraction in all sample categories except in the forest.
Organic C stock, its quality and its distribution in the profile were responsive
to land use change. The conversion of the Chaco forest to crops was
associated with a decrease of organic C stock up to 1 m depth and with the
decrease of the labile fraction. The permanent pastures of warm-season
grasses allowed higher C stocks to be sustained than cropping systems and so could
be considered a sustainable land use system in terms of soil C preservation.
As soil organic C losses were not restricted to the first few centimetres of the soil,
the development of models that would allow the estimation of soil organic C
changes in depth would be useful to evaluate the
impact of land use change on C stocks with greater precision.</p
Estimation of the mechanical properties of the eye through the study of its vibrational modes
Measuring the eye's mechanical properties in vivo and with minimally invasive
techniques can be the key for individualized solutions to a number of eye
pathologies. The development of such techniques largely relies on a
computational modelling of the eyeball and, it optimally requires the synergic
interplay between experimentation and numerical simulation. In Astrophysics and
Geophysics the remote measurement of structural properties of the systems of
their realm is performed on the basis of (helio-)seismic techniques. As a
biomechanical system, the eyeball possesses normal vibrational modes
encompassing rich information about its structure and mechanical properties.
However, the integral analysis of the eyeball vibrational modes has not been
performed yet. Here we develop a new finite difference method to compute both
the spheroidal and, specially, the toroidal eigenfrequencies of the human eye.
Using this numerical model, we show that the vibrational eigenfrequencies of
the human eye fall in the interval 100 Hz - 10 MHz. We find that compressible
vibrational modes may release a trace on high frequency changes of the
intraocular pressure, while incompressible normal modes could be registered
analyzing the scattering pattern that the motions of the vitreous humour leave
on the retina. Existing contact lenses with embebed devices operating at high
sampling frequency could be used to register the microfluctuations of the
eyeball shape we obtain. We advance that an inverse problem to obtain the
mechanical properties of a given eye (e.g., Young's modulus, Poisson ratio)
measuring its normal frequencies is doable. These measurements can be done
using non-invasive techniques, opening very interesting perspectives to
estimate the mechanical properties of eyes in vivo. Future research might
relate various ocular pathologies with anomalies in measured vibrational
frequencies of the eye.Comment: Published in PLoS ONE as Open Access Research Article. 17 pages, 5
color figure
FooPar: A Functional Object Oriented Parallel Framework in Scala
We present FooPar, an extension for highly efficient Parallel Computing in
the multi-paradigm programming language Scala. Scala offers concise and clean
syntax and integrates functional programming features. Our framework FooPar
combines these features with parallel computing techniques. FooPar is designed
modular and supports easy access to different communication backends for
distributed memory architectures as well as high performance math libraries. In
this article we use it to parallelize matrix matrix multiplication and show its
scalability by a isoefficiency analysis. In addition, results based on a
empirical analysis on two supercomputers are given. We achieve close-to-optimal
performance wrt. theoretical peak performance. Based on this result we conclude
that FooPar allows to fully access Scala's design features without suffering
from performance drops when compared to implementations purely based on C and
MPI
Strain balanced quantum posts
Quantum posts are assembled by epitaxial growth of closely spaced quantum dot
layers, modulating the composition of a semiconductor alloy, typically InGaAs.
In contrast with most self-assembled nanostructures, the height of quantum
posts can be controlled with nanometer precision, up to a maximum value limited
by the accumulated stress due to the lattice mismatch. Here we present a strain
compensation technique based on the controlled incorporation of phosphorous,
which substantially increases the maximum attainable quantum post height. The
luminescence from the resulting nanostructures presents giant linear
polarization anisotropy.Comment: Submitted to Applied Physics Letters (7th March 2011). 4 pages, 4
figure
Rational exploitation of a granite outcrop
[Abstract] This piece analizes the possibilities of mining exploitation in a little outcrop of rOSfl granite. The zone has been researched, recognizing the main structural discontinuities, and characterizing the rock mass by the geomechanic classificationofBARTON. Two core drilling have been made to study the evolution ofthe deeper bed. The volume ofthe bed has been calculated by geometric calculation in the researched area. The theories ofCASTAING and RABU have been developed to estimate the useful volume of the bed for a minimum block size of 1 m3. We have implerríented a computer program in base ofEXCEL 4.0. The result is a useful volume of 51.67 %. By the application of the reduction coefficients ofsterility and irregularity, the maximum estimated efficiency of the exploitation is 33 %
Emissões de N2o de um chernossolo cultivado : o tempo ideal do dia para amostragem e papel da temperatura do solo
1814-1819The correct use of closed field chambers to determine N2O emissions requires defining the time of day that best represents the daily mean N2O flux. A short-term field experiment was carried out on a Mollisol soil, on which annual crops were grown under no-till management in the Pampa Ondulada of Argentina. The N2O emission rates were measured every 3 h for three consecutive days. Fluxes ranged from 62.58 to 145.99 ug N-N2O m-2 h-1 (average of five field chambers) and were negatively related (R2 equal 0.34, p less than 0.01) to topsoil temperature (14 - 20 oC). N2O emission rates measured between 9:00 and 12:00 am presented a high relationship to daily mean N2O flux (R2 equal 0.87, p less than 0.01), showing that, in the study region, sampling in the mornings is preferable for GHG
Propagation Failure in Excitable Media
We study a mechanism of pulse propagation failure in excitable media where
stable traveling pulse solutions appear via a subcritical pitchfork
bifurcation. The bifurcation plays a key role in that mechanism. Small
perturbations, externally applied or from internal instabilities, may cause
pulse propagation failure (wave breakup) provided the system is close enough to
the bifurcation point. We derive relations showing how the pitchfork
bifurcation is unfolded by weak curvature or advective field perturbations and
use them to demonstrate wave breakup. We suggest that the recent observations
of wave breakup in the Belousov-Zhabotinsky reaction induced either by an
electric field or a transverse instability are manifestations of this
mechanism.Comment: 8 pages. Aric Hagberg: http://cnls.lanl.gov/~aric; Ehud
Meron:http://www.bgu.ac.il/BIDR/research/staff/meron.htm
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