44,767 research outputs found
Bayesian analysis of the linear reaction norm model with unknown covariate
The reaction norm model is becoming a popular approach for the analysis of G x E interactions. In a classical reaction norm model, the expression of a genotype in different environments is described as a linear function (a reaction norm) of an environmental gradient or value. A common environmental value is defined as the mean performance of all genotypes in the environment, which is typically unknown. One approximation is to estimate the mean phenotypic performance in each environment, and then treat these estimates as known covariates in the model. However, a more satisfactory alternative is to infer environmental values simultaneously with the other parameters of the model. This study describes a method and its Bayesian MCMC implementation that makes this possible. Frequentist properties of the proposed method are tested in a simulation study. Estimates of parameters of interest agree well with the true values. Further, inferences about genetic parameters from the proposed method are similar to those derived from a reaction norm model using true environmental values. On the other hand, using phenotypic means as proxies for environmental values results in poor inferences
Cantilever-based Resonant Gas Sensors with Integrated Recesses for Localized Sensing Layer Deposition
This work presents mass-sensitive hammerhead resonators with integrated recesses as a gas-phase chemical microsensor platform. Recesses are etched into the head region of the resonator to locally deposit chemically sensitive polymers by ink-jet printing. This permits the sensing films to be confined to areas that (a) are most effective in detecting mass loading and (b) are not strained during the in-plane vibrations of the resonator. As a result of the second point, even 5-μm thick polymer coatings on resonators with a 9-12 μm silicon thickness barely affect the Q-factor in air. This translates into higher frequency stability and ultimately higher sensor resolution compared to uniformly coated devices
Compensation of compliance errors in parallel manipulators composed of non-perfect kinematic chains
The paper is devoted to the compliance errors compensation for parallel
manipulators under external loading. Proposed approach is based on the
non-linear stiffness modeling and reduces to a proper adjusting of a target
trajectory. In contrast to previous works, in addition to compliance errors
caused by machining forces, the problem of assembling errors caused by
inaccuracy in the kinematic chains is considered. The advantages and practical
significance of the proposed approach are illustrated by examples that deal
with groove milling with Orthoglide manipulator.Comment: Advances in Robot Kinematics, France (2012
Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare
We analyzed high-cadence sit-and-stare observations acquired with the
Hinode/EIS spectrometer and HXR measurements acquired with RHESSI during an
M-class flare. During the flare impulsive phase, we observe no significant
flows in the cooler Fe XIII line but strong upflows, up to 80-150 km/s, in the
hotter Fe XVI line. The largest Doppler shifts observed in the Fe XVI line were
co-temporal with the sharp intensity peak. The electron density obtained from a
Fe XIII line pair ratio exhibited fast increase (within two minutes) from the
pre-flare level of 5.01x10^(9) cm^(-3) to 3.16x10^(10) cm^(-3) during the flare
peak. The nonthermal energy flux density deposited from the coronal
acceleration site to the lower atmospheric layers during the flare peak was
found to be 1.34x10^(10) erg/s/cm^(2) for a low-energy cut-off that was
estimated to be 16 keV. During the decline flare phase, we found a secondary
intensity and density peak of lower amplitude that was preceded by upflows of
15 km/s that were detected in both lines. The flare was also accompanied by a
filament eruption that was partly captured by the EIS observations. We derived
Doppler velocities of 250-300 km/s for the upflowing filament material.The
spectroscopic results for the flare peak are consistent with the scenario of
explosive chromospheric evaporation, although a comparatively low value of the
nonthermal energy flux density was determined for this phase of the flare. This
outcome is discussed in the context of recent hydrodynamic simulations. It
provides observational evidence that the response of the atmospheric plasma
strongly depends on the properties of the electron beams responsible for the
heating, in particular the steepness of the energy distribution.Comment: 13 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Aharonov-Casher phase and persistent current in a polyacetylene ring
We investigate a polyacetylene ring in an axially symmetric, static electric
field with a modified SSH Hamiltonian of a polyacetylene chain. An effective
gauge potential of the single electron Hamiltonian due to spin-field
interaction is obtained and it results in a Fr\"{o}hlich's type of
superconductivity equivalent to the effect of travelling lattice wave. The
total energy as well as the persistent current density are shown to be a
periodic function of the flux of the gauge field embraced by the polyacetylene
ring.Comment: 12 pages, 5 figure
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