5,288 research outputs found
Metagenetic analysis of patterns of distribution and diversity of marine meiobenthic eukaryotes
AimMeiofaunal communities that inhabit the marine benthos offer unique opportunities to simultaneously study the macroecology of numerous phyla that exhibit different life-history strategies. Here, we ask: (1) if the macroecology of meiobenthic communities is explained mainly by dispersal constraints or by environmental conditions; and (2) if levels of meiofaunal diversity surpass existing estimates based on morphological taxonomy. LocationUK and mainland European coast. MethodsNext-generation sequencing techniques (NGS; Roche 454 FLX platform) using 18S nuclear small subunit ribosomal DNA (rDNA) gene. Pyrosequences were analysed using AmpliconNoise followed by chimera removal using Perseus. ResultsRarefaction curves revealed that sampling saturation was only reached at 15% of sites, highlighting that the bulk of meiofaunal diversity is yet to be discovered. Overall, 1353 OTUs were recovered and assigned to 23 different phyla. The majority of sampled sites had c. 60-70 unique operational taxonomic units (OTUs) per site, indicating high levels of beta diversity. The environmental parameters that best explained community structure were seawater temperature, geographical distance and sediment size, but most of the variability (R-2=70%-80%) remains unexplained. Main conclusionsHigh percentages of endemic OTUs suggest that meiobenthic community composition is partly niche-driven, as observed in larger organisms, but also shares macroecological features of microorganisms by showing high levels of cosmopolitanism (albeit on a much smaller scale). Meiobenthic communities exhibited patterns of isolation by distance as well as associations between niche, latitude and temperature, indicating that meiobenthic communities result from a combination of niche assembly and dispersal processes. Conversely, isolation-by-distance patterns were not identified in the featured protists, suggesting that animals and protists adhere to radically different macroecological processes, linked to life-history strategies.Natural Environment Research Council (NERC) [NE/E001505/1, NE/F001266/1, MGF-167]; Portuguese Foundation for Science and Technology (FCT) [SFRH/BD/27413/2006, SFRH/BPD/80447/2014]; EPSRC [EP/H003851/1]; BBSRC CASE studentship; Unilever; Biotechnology and Biological Sciences Research Council [987347]; Engineering and Physical Sciences Research Council [EP/H003851/1]; Natural Environment Research Council [NE/F001290/1, NE/F001266/1, NE/E001505/1, NBAF010002]info:eu-repo/semantics/publishedVersio
Study of fuel cells using storable rocket propellants Final report, 28 Jan. 1964 - 29 Jan. 1965
Fuel cells using storable rocket propellants for reactant
Gravitational Geons Revisited
A careful analysis of the gravitational geon solution found by Brill and
Hartle is made. The gravitational wave expansion they used is shown to be
consistent and to result in a gauge invariant wave equation. It also results in
a gauge invariant effective stress-energy tensor for the gravitational waves
provided that a generalized definition of a gauge transformation is used. To
leading order this gauge transformation is the same as the usual one for
gravitational waves. It is shown that the geon solution is a self-consistent
solution to Einstein's equations and that, to leading order, the equations
describing the geometry of the gravitational geon are identical to those
derived by Wheeler for the electromagnetic geon. An appendix provides an
existence proof for geon solutions to these equations.Comment: 18 pages, ReVTeX. To appear in Physical Review D. Significant changes
include more details in the derivations of certain key equations and the
addition of an appendix containing a proof of the existence of a geon
solution to the equations derived by Wheeler. Also a reference has been added
and various minor changes have been mad
Experimental Observation of Energy Modulation in Electron Beams Passing Through Terahertz Dielectric Wakefield Structures
We report observation of a strong wakefield induced energy modulation in an
energy-chirped electron bunch passing through a dielectric-lined waveguide.
This modulation can be effectively converted into a spatial modulation forming
micro-bunches with a periodicity of 0.5 - 1 picosecond, hence capable of
driving coherent THz radiation. The experimental results agree well with
theoretical predictions.Comment: v3. Reviewers' suggestions incorporated. Accepted by PR
The Dipole Coupling of Atoms and Light in Gravitational Fields
The dipole coupling term between a system of N particles with total charge
zero and the electromagnetic field is derived in the presence of a weak
gravitational field. It is shown that the form of the coupling remains the same
as in flat space-time if it is written with respect to the proper time of the
observer and to the measurable field components. Some remarks concerning the
connection between the minimal and the dipole coupling are given.Comment: 10 pages, LaTe
Temperature dependence of the magnetic Casimir-Polder interaction
We analyze the magnetic dipole contribution to atom-surface dispersion
forces. Unlike its electrical counterpart, it involves small transition
frequencies that are comparable to thermal energy scales. A significant
temperature dependence is found near surfaces with a nonzero DC conductivity,
leading to a strong suppression of the dispersion force at T > 0. We use
thermal response theory for the surface material and discuss both normal metals
and superconductors. The asymptotes of the free energy of interaction and of
the entropy are calculated analytically over a large range of distances. Near a
superconductor, the onset of dissipation at the phase transition strongly
changes the interaction, including a discontinuous entropy. We discuss the
similarities with the Casimir interaction beween two surfaces and suggest that
precision measurements of the atom-surface interaction may shed new light upon
open questions around the temperature dependence of dispersion forces between
lossy media.Comment: 11 figure
Derivation of the Planck Spectrum for Relativistic Classical Scalar Radiation from Thermal Equilibrium in an Accelerating Frame
The Planck spectrum of thermal scalar radiation is derived suggestively
within classical physics by the use of an accelerating coordinate frame. The
derivation has an analogue in Boltzmann's derivation of the Maxwell velocity
distribution for thermal particle velocities by considering the thermal
equilibrium of noninteracting particles in a uniform gravitational field. For
the case of radiation, the gravitational field is provided by the acceleration
of a Rindler frame through Minkowski spacetime. Classical zero-point radiation
and relativistic physics enter in an essential way in the derivation which is
based upon the behavior of free radiation fields and the assumption that the
field correlation functions contain but a single correlation time in thermal
equilibrium. The work has connections with the thermal effects of acceleration
found in relativistic quantum field theory.Comment: 23 page
Program on Earth Observation Data Management Systems (EODMS), appendixes
The needs of state, regional, and local agencies involved in natural resources management in Illinois, Iowa, Minnesota, Missouri, and Wisconsin are investigated to determine the design of satellite remotely sensed derivable information products. It is concluded that an operational Earth Observation Data Management System (EODMS) will be most beneficial if it provides a full range of services - from raw data acquisition to interpretation and dissemination of final information products. Included is a cost and performance analysis of alternative processing centers, and an assessment of the impacts of policy, regulation, and government structure on implementing large scale use of remote sensing technology in this community of users
Using fiberless, wearable fNIRS to monitor brain activity in real-world cognitive tasks
Functional Near Infrared Spectroscopy (fNIRS) is a neuroimaging technique that uses near-infrared light to monitor brain activity. Based on neurovascular coupling, fNIRS is able to measure the haemoglobin concentration changes secondary to neuronal activity. Compared to other neuroimaging techniques, fNIRS represents a good compromise in terms of spatial and temporal resolution. Moreover, it is portable, lightweight, less sensitive to motion artifacts and does not impose significant physical restraints. It is therefore appropriate to monitor a wide range of cognitive tasks (e.g., auditory, gait analysis, social interaction) and different age populations (e.g., new-borns, adults, elderly people). The recent development of fiberless fNIRS devices has opened the way to new applications in neuroscience research. This represents a unique opportunity to study functional activity during real-world tests, which can be more sensitive and accurate in assessing cognitive function and dysfunction than lab-based tests. This study explored the use of fiberless fNIRS to monitor brain activity during a real-world prospective memory task. This protocol is performed outside the lab and brain haemoglobin concentration changes are continuously measured over the prefrontal cortex while the subject walks around in order to accomplish several different tasks
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