626 research outputs found
Exploring the relationship between tychoparthenogenesis and inbreeding depression in the Desert Locust, Schistocerca gregaria
Tychoparthenogenesis, a form of asexual reproduction in which a small proportion of unfertilized eggs can hatch spontaneously, could be an intermediate evolutionary link in the transition from sexual to parthenogenetic reproduction. The lower fitness of tychoparthenogenetic offspring could be due to either developmental constraints or to inbreeding depression in more homozygous individuals. We tested the hypothesis that in populations where inbreeding depression has been purged, tychoparthenogenesis may be less costly. To assess this hypothesis, we compared the impact of inbreeding and parthenogenetic treatments on eight life-history traits (five measuring inbreeding depression and three measuring inbreeding avoidance) in four laboratory populations of the desert locust, Schistocerca gregaria, with contrasted demographic histories. Overall, we found no clear relationship between the population history (illustrated by the levels of genetic diversity or inbreeding) and inbreeding depression, or between inbreeding depression and parthenogenetic capacity. First, there was a general lack of inbreeding depression in every population, except in two populations for two traits. This pattern could not be explained by the purging of inbreeding load in the studied populations. Second, we observed large differences between populations in their capacity to reproduce through tychoparthenogenesis. Only the oldest laboratory population successfully produced parthenogenetic offspring. However, the level of inbreeding depression did not explain the differences in parthenogenetic success between all studied populations. Differences in development constraints may arise driven by random and selective processes between populations. (Résumé d'auteur
Overcoming non-radiative losses with AlGaAs PIN junctions for near-field thermophotonic energy harvesting
In a thermophotonic device used in an energy-harvesting configuration, a hot
light-emitting diode (LED) is coupled to a photovoltaic (PV) cell by means of
electroluminescent radiation in order to produce electrical power. Using
fluctuational electrodynamics and the drift-diffusion equations, we optimise a
device made of an AlGaAs PIN LED and a GaAs PIN PV cell with matched bandgaps.
We find that the LED can work as an efficient heat pump only in the near field,
where radiative heat transfer is increased by wave tunnelling. A key reason is
that non-radiative recombination rates are reduced compared to radiative ones
in this regime. At 10 nm gap distance and for 100 cm.s --1 effective surface
recombination velocity, the power output can reach 2.2 W.cm --2 for a 600 K
LED, which highlights the potential for low-grade energy harvesting
Strong tip-sample coupling in thermal radiation scanning tunneling microscopy
We analyze how a probing particle modifies the infrared electromagnetic near
field of a sample. The particle, described by electric and magnetic
polarizabilities, represents the tip of an apertureless scanning optical
near-field microscope (SNOM). We show that the interaction with the sample can
be accounted for by ascribing to the particle dressed polarizabilities that
combine the effects of image dipoles with retardation. When calculated from
these polarizabilities, the SNOM signal depends only on the fields without the
perturbing tip. If the studied surface is not illuminated by an external source
but heated instead, the signal is closely related to the projected
electromagnetic local density of states (EM-LDOS). Our calculations provide the
link between the measured far-field spectra and the sample's optical
properties.We also analyze the case where the probing particle is hotter than
the sample and evaluate the impact of the dressed polarizabilities on
near-field radiative heat transfer. We show that such a heated probe above a
surface performs a surface spectroscopy, in the sense that the spectrum of the
heat current is closely related to the local electromagnetic density of states.
The calculations agree well with available experimental data.Comment: Soumis \`a JQSRT. arXiv admin note: substantial text overlap with
arXiv:1201.483
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