238 research outputs found
Electromagnetic prompt response in an elastic wave cavity
A rapid, or prompt response, of an electromagnetic nature, is found in an
elastic wave scattering experiment. The experiment is performed with torsional
elastic waves in a quasi-one-dimensional cavity with one port, formed by a
notch grooved at a certain distance from the free end of a beam. The stationary
patterns are diminished using a passive vibration isolation system at the other
end of the beam. The measurement of the resonances is performed with
non-contact electromagnetic-acoustic transducers outside the cavity. In the
Argand plane, each resonance describes a circle over a base impedance curve
which comes from the electromagnetic components of the equipment. A model,
based on a variation of Poisson's kernel is developed. Excellent agreement
between theory and experiment is obtained.Comment: 4 pages, 5 figure
Scattering of Elastic Waves in a Quasi-one-dimensional Cavity: Theory and Experiment
We study the scattering of torsional waves through a quasi-one-dimensional
cavity both, from the experimental and theoretical points of view. The
experiment consists of an elastic rod with square cross section. In order to
form a cavity, a notch at a certain distance of one end of the rod was grooved.
To absorb the waves, at the other side of the rod, a wedge, covered by an
absorbing foam, was machined. In the theoretical description, the scattering
matrix S of the torsional waves was obtained. The distribution of S is given by
Poisson's kernel. The theoretical predictions show an excellent agreement with
the experimental results. This experiment corresponds, in quantum mechanics, to
the scattering by a delta potential, in one dimension, located at a certain
distance from an impenetrable wall
Assessing the Hierarchical Hamiltonian Splitting Integrator for Collisionless N-body Simulations
The N-body problem has become one of the hottest topics in the fields of
computational dynamics and cosmology. The large dynamical range in some
astrophysical problems led to the use of adaptive time steps to integrate
particle trajectories, however, the search of optimal strategies is still
challenging. We quantify the performance of the hierarchical time step
integrator Hamiltonian Splitting (HamSp) for collisionless multistep
simulations. We compare with the constant step Leap-Frog (LeapF) integrator and
the adaptive one (AKDK). Additionally, we explore the impact of different time
step assigning functions. There is a computational overhead in HamSp however
there are two interesting advantages: choosing a convenient time-step function
may compensate and even turn around the efficiency compared with AKDK. We test
both reversibility and time symmetry. The symmetrized nature of the HamSp
integration is able to provide time-reversible integration for medium time
scales and overall deliver better energy conservation for long integration
times, and the linear and angular momentum are preserved at machine precision.
We address the impact of using different integrators in astrophysical systems.
We found that in most situations both AKDK and HamSp are able to correctly
simulate the problems. We conclude that HamSp is an attractive and competitive
alternative to AKDK, with, in some cases, faster and with better energy and
momentum conservation. The use of recently discussed Bridge splitting
techniques with HamSp may allow to reach considerably high efficiency.Comment: 13 pages, 16 figure
The plant–mycorrhizal fungi collaboration gradient depends on plant functional group
1. Plant colonization by arbuscular mycorrhizal fungi (AMF) is widespread and can offer considerable benefits in terms of growth, nutrient uptake and plant yield. However, it is still unresolved how different plant species and plant functional groups respond to AMF and to different AMF taxa.
2. Here we established 336 grassland microcosms to determine the response of 14 plant species displaying contrasting functional groups (grasses, legumes and non-leguminous forbs) for the presence of three different AMF taxa. For each plant species, we calculated the degree to which plant growth depended on AMF colonization (i.e. mycorrhizal dependency [MD]). We also determined the degree to which each plant species relied on specific AMF taxa for optimal growth (i.e. mycorrhizal species sensitivity [MSS]). Additionally, we determined whether MD and MSS correlated to specific plant traits (i.e. specific root length [SRL], specific leaf area [SLA]).
3. The plant growth response to AMF ranged from −84.9% for a non-mycorrhizal plant (Luzula campestris) to +94.0% for a legume (Trifolium arvensis). The MD was systematically higher in legumes (91.9% ± 2.4%), followed by non-leguminous forbs (77.1% ± 11.06) and grasses (42.1% ± 15.73%). MSS was less variable (8.9%–37.7%); it was independent of plant functional group and did not correlate with MD. MD was linked to various mycorrhizal plant parameters, including AMF colonization (R2 = +0.80) and total dry biomass (R2 = +0.32). Moreover, among mycorrhizal plants (n = 12), MD negatively correlated with SRL (R2 = −0.24) and positively with SLA (R2 = +0.24).
4. Synthesis. This study shows that plants relying on AMF for biomass production also show higher root colonization, lower SRL, higher SLA and that different plant traits are interlinked with the way how plants respond to AMF. Overall, this study further demonstrates that different plant functional groups vary in their response to AMF
Influence of the use of milk replacers and pH on the texture profiles of raw and cooked meat of suckling kids
The aim of this work was to study the texture profile of fresh and cooked longissimus thoracis et lumborum muscle from suckling kids raised with natural milk or milk replacers. Suckling Male kids from eight goat breeds (Florida, FL; Cabra del Guadarrama, GU; Majorera, MA; Palmera, PL; Payoya, PY; Retinta, RE; Tinerfeña, TI; Verata, VE), all of single parturition, were raised with milk replacers (MR) or with natural milk from the dams (NM). The meat pH, Warner-Bratzler shear force, texture profile analysis and chemical composition were determined. Kids were clustered based on their pH by k-means clustering. The effect of the rearing system on the textural profile was strongly modulated by breed. The values of Warner-Bratzler shear force and hardness found in these breeds under both rearing systems were very low. Hence, the toughness of very light suckling kids should not be a determining factor in choosing a breed or rearing system. Nevertheless, the use of milk replacers increased the presence of meat with high pH, which modified the textural parameters, decreasing the shear force but increasing cohesiveness and adhesiveness. Consequently, depending on the commercial strategy of the farm, the election of the breed and rearing system must be considered together
Options of partners improve carbon for phosphorus trade in the arbuscular mycorrhizal mutualism
The mutualism between plants and arbuscular mycorrhizal fungi (AMF) is widespread and has persisted for over 400 million years. Although this mutualism depends on fair resource exchange between plants and fungi, inequality exists among partners despite mechanisms that regulate trade. Here, we use (33) P and (14) C isotopes and a split-root system to test for preferential allocation and reciprocal rewards in the plant-AMF symbiosis by presenting a plant with two AMF that differ in cooperativeness. We found that plants received more (33) P from less cooperative AMF in the presence of another AMF species. This increase in (33) P resulted in a reduced (14) C cost per unit of (33) P from less cooperative AMF when alternative options were available. Our results indicate that AMF diversity promotes cooperation between plants and AMF, which may be an important mechanism maintaining the evolutionary persistence of and diversity within the plant-AMF mutualism
Evaluación económica de los compromises de Colombia en el marco de COP21
The document presents the economic impacts from the fulfillment of Colombia’s commitment of the Paris Agreement on climate change. The traditional analysis is done with marginal curves of abatement costs. However, this technique has a set of limitations, which can be solved with a computable general equilibrium (CGE) model. Using the CGE for Colombia (MEG4C), the results show that growth rate of GDP would increase by 0.15% annually, for the period 2020-2040. On the other hand, the structural unemployment rate is reduced by the implementation of mitigation measures in the medium and long term. Due to the economic structure and the emissions matrix, the implementation of measures should be associated with energy efficiency in the transport, industrial and residential sectors, which will generate positive impacts on economic growth. © 2017, Universidad de los Andes, Facultad de Economia. All rights reserved
Nonlinear software sensor for monitoring genetic regulation processes with noise and modeling errors
Nonlinear control techniques by means of a software sensor that are commonly
used in chemical engineering could be also applied to genetic regulation
processes. We provide here a realistic formulation of this procedure by
introducing an additive white Gaussian noise, which is usually found in
experimental data. Besides, we include model errors, meaning that we assume we
do not know the nonlinear regulation function of the process. In order to
illustrate this procedure, we employ the Goodwin dynamics of the concentrations
[B.C. Goodwin, Temporal Oscillations in Cells, (Academic Press, New York,
1963)] in the simple form recently applied to single gene systems and some
operon cases [H. De Jong, J. Comp. Biol. 9, 67 (2002)], which involves the
dynamics of the mRNA, given protein, and metabolite concentrations. Further, we
present results for a three gene case in co-regulated sets of transcription
units as they occur in prokaryotes. However, instead of considering their full
dynamics, we use only the data of the metabolites and a designed software
sensor. We also show, more generally, that it is possible to rebuild the
complete set of nonmeasured concentrations despite the uncertainties in the
regulation function or, even more, in the case of not knowing the mRNA
dynamics. In addition, the rebuilding of concentrations is not affected by the
perturbation due to the additive white Gaussian noise and also we managed to
filter the noisy output of the biological systemComment: 21 pages, 7 figures; also selected in vjbio of August 2005; this
version corrects a misorder in the last three references of the published
versio
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