12,830 research outputs found
Nuclear fusion induced by X-rays in a crystal
The nuclei that constitute a crystalline lattice, oscillate relative to each
other with a very low energy that is not sufficient to penetrate through the
Coulomb barriers separating them. An additional energy, which is needed to
tunnel through the barrier and fuse, can be supplied by external
electromagnetic waves (X-rays or the synchrotron radiation). Exposing to the
X-rays the solid compound LiD (lithium-deuteride) for the duration of 111
hours, we have detected 88 events of the nuclear fusion d+Li6 ---> Be8*. Our
theoretical estimate agrees with what we observed. One of possible applications
of the phenomenon we found, could be the measurements of the rates of various
nuclear reactions (not necessarily fusion) at extremely low energies
inaccessible in accelerator experiments.Comment: 27 pages, 12 figures; submitted to Phys. Rev. C on 28 October 201
Electrical observation of a tunable band gap in bilayer graphene nanoribbons at room temperature
We investigate the transport properties of double-gated bilayer graphene
nanoribbons at room temperature. The devices were fabricated using conventional
CMOS-compatible processes. By analyzing the dependence of the resistance at the
charge neutrality point as a function of the electric field applied
perpendicular to the graphene surface, we show that a band gap in the density
of states opens, reaching an effective value of ~sim50 meV. This demonstrates
the potential of bilayer graphene as FET channel material in a conventional
CMOS environment.Comment: 3 pages, 3 figure
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Do we (need to) care about canopy radiation schemes in DGVMs? Caveats and potential impacts
Dynamic global vegetation models (DGVMs) are an essential part of current state-of-the-art Earth system models. In recent years, the complexity of DGVMs has increased by incorporating new important processes like, e.g., nutrient cycling and land cover dynamics, while biogeophysical processes like surface radiation have not been developed much further. Canopy radiation models are however very important for the estimation of absorption and reflected fluxes and are essential for a proper estimation of surface carbon, energy and water fluxes.
The present study provides an overview of current implementations of canopy radiation schemes in a couple of state-of-the-art DGVMs and assesses their accuracy in simulating canopy absorption and reflection for a variety of different surface conditions. Systematic deviations in surface albedo and fractions of absorbed photosynthetic active radiation (faPAR) are identified and potential impacts are assessed.
The results show clear deviations for both, absorbed and reflected, surface solar radiation fluxes. FaPAR is typically underestimated, which results in an underestimation of gross primary productivity (GPP) for the investigated cases. The deviation can be as large as 25% in extreme cases. Deviations in surface albedo range between −0.15 ≤ Δα ≤ 0.36, with a slight positive bias on the order of Δα ≈ 0.04. Potential radiative forcing caused by albedo deviations is estimated at −1.25 ≤ RF ≤ −0.8 (W m−2), caused by neglect of the diurnal cycle of surface albedo.
The present study is the first one that provides an assessment of canopy RT schemes in different currently used DGVMs together with an assessment of the potential impact of the identified deviations. The paper illustrates that there is a general need to improve the canopy radiation schemes in DGVMs and provides different perspectives for their improvement
Transparency and Pre-meetings
Some committees are made up of experts, persons interested in both the (subject) matter at hand and in coming across as able decision-makers. Such committees would like to concea
How committees of experts interact with the outside world: some theory, and evidence from the FOMC
Some committees are made up of experts, persons who care both
about the matter at hand and about coming across as able decision-
makers. We derive two propositions about the way members of such
committees interact with the outside world. First, they would like
to conceal disagreement from the public. That is, once the decision
has been reached, they show a united front to the outside world.
Second, if such committees are required to become transparent, e.g.,
by publishing verbatim transcripts of their meetings, members will
organize pre-meetings away from the public eye. Large part of the
paper is dedicated to a case study of the U.S. Federal Open Market
Committee in the United States. It provides suggestive evidence
supporting the two propositions
Recombination dramatically speeds up evolution of finite populations
We study the role of recombination, as practiced by genetically-competent
bacteria, in speeding up Darwinian evolution. This is done by adding a new
process to a previously-studied Markov model of evolution on a smooth fitness
landscape; this new process allows alleles to be exchanged with those in the
surrounding medium. Our results, both numerical and analytic, indicate that for
a wide range of intermediate population sizes, recombination dramatically
speeds up the evolutionary advance
Microscopic dynamics of thin hard rods
Based on the collision rules for hard needles we derive a hydrodynamic
equation that determines the coupled translational and rotational dynamics of a
tagged thin rod in an ensemble of identical rods. Specifically, based on a
Pseudo-Liouville operator for binary collisions between rods, the Mori-Zwanzig
projection formalism is used to derive a continued fraction representation for
the correlation function of the tagged particle's density, specifying its
position and orientation. Truncation of the continued fraction gives rise to a
generalised Enskog equation, which can be compared to the phenomenological
Perrin equation for anisotropic diffusion. Only for sufficiently large density
do we observe anisotropic diffusion, as indicated by an anisotropic mean square
displacement, growing linearly with time. For lower densities, the Perrin
equation is shown to be an insufficient hydrodynamic description for hard
needles interacting via binary collisions. We compare our results to
simulations and find excellent quantitative agreement for low densities and
qualtitative agreement for higher densities.Comment: 21 pages, 6 figures, v2: clarifications and improved readabilit
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