1,288 research outputs found
Fluctuations from dissipation in a hot non-Abelian plasma
We consider a transport equation of the Boltzmann-Langevin type for
non-Abelian plasmas close to equilibrium to derive the spectral functions of
the underlying microscopic fluctuations from the entropy. The correlator of the
stochastic source is obtained from the dissipative processes in the plasma.
This approach, based on classical transport theory, exploits the well-known
link between a linearized collision integral, the entropy and the spectral
functions. Applied to the ultra-soft modes of a hot non-Abelian (classical or
quantum) plasma, the resulting spectral functions agree with earlier findings
obtained from the microscopic theory. As a by-product, it follows that
B\"odeker's effective theory is consistent with the fluctuation-dissipation
theorem.Comment: 9 pages, revtex, no figures, identical to published versio
Mean Field Dynamics in Non-Abelian Plasmas from Classical Transport Theory
Based on classical transport theory, we present a general set of covariant
equations describing the dynamics of mean fields and their statistical
fluctuations in a non-Abelian plasma in or out-of-equilibrium. A procedure to
obtain the collision integrals for the Boltzmann equation from the microscopic
theory is described. As an application, we study a hot non-Abelian plasma close
to equilibrium, where the fluctuations are integrated out explicitly. For soft
fields, and at logarithmic accuracy, we obtain B\"odeker's effective theory.Comment: 4 pages, revtex, no figures. Typo removed, a reference updated,
version as to appear in Phys. Rev. Let
Duration and nature of the end-Cryogenian (Marinoan) glaciation
The end-Cryogenian glaciation (Marinoan) is portrayed commonly as the archetype of snowball Earth, yet its duration and character remain uncertain. Here we report U-Pb zircon ages for two ash beds from widely separated localities of the Marinoan-equivalent Ghaub Formation in Namibia: 639.29 ± 0.26 Ma and 635.21 ± 0.59 Ma. These findings verify, for the first time, the key prediction of the snowball Earth hypothesis for the Marinoan glaciation, i.e., longevity, with a duration of â„4 m.y. They also show that the nonglacial interlude of Cryogenian time spanned 20 m.y. or less and that glacigenic erosion and sedimentation, and at least intermittent open-water conditions, occurred 4 m.y. prior to termination of the Marinoan glaciation
Chiminey: Reliable Computing and Data Management Platform in the Cloud
The enabling of scientific experiments that are embarrassingly parallel, long
running and data-intensive into a cloud-based execution environment is a
desirable, though complex undertaking for many researchers. The management of
such virtual environments is cumbersome and not necessarily within the core
skill set for scientists and engineers. We present here Chiminey, a software
platform that enables researchers to (i) run applications on both traditional
high-performance computing and cloud-based computing infrastructures, (ii)
handle failure during execution, (iii) curate and visualise execution outputs,
(iv) share such data with collaborators or the public, and (v) search for
publicly available data.Comment: Preprint, ICSE 201
Spin-Selective Electron Transport Through Single Chiral Molecules
The interplay between chirality and magnetism has been a source of
fascination among scientists for over a century. In recent years,
chirality-induced spin selectivity (CISS) has attracted renewed interest. It
has been observed that electron transport through layers of homochiral
molecules leads to a significant spin polarization of several tens of percent.
Despite the abundant experimental evidence gathered through mesoscopic
transport measurements, the exact mechanism behind CISS remains elusive. In
this study, we report spin-selective electron transport through single helical
aromatic hydrocarbons that were sublimed in vacuo onto ferromagnetic cobalt
surfaces and examined with spin-polarized scanning tunneling microscopy
(SP-STM) at a temperature of 5 K. Direct comparison of two enantiomers under
otherwise identical conditions revealed magnetochiral conductance asymmetries
of up to 50% when either the molecular handedness was exchanged or the
magnetization direction of the STM tip or Co substrate was reversed.
Importantly, our results rule out electron-phonon coupling and ensemble effects
as primary mechanisms responsible for CISS.Comment: 15 pages, 4 figures, plus Supporting Informatio
Atmospheric observation-based global SF6 emissions - comparison of top-down and bottom-up estimates
Emissions of sulphur hexafluoride (SF6), one of the strongest greenhouse gases on a per molecule basis, are targeted to be collectively reduced under the Kyoto Protocol. Because of its long atmospheric lifetime (â3000 years), the accumulation of SF6 in the atmosphere is a direct measure of its global emissions. Examination of our extended data set of globally distributed high-precision SF6 observations shows an increase in SF6 abundance from near zero in the 1970s to a global mean of 6.7 ppt by the end of 2008. In-depth evaluation of our long-term data records shows that the global source of SF6 decreased after 1995, most likely due to SF6 emission reductions in industrialised countries, but increased again after 1998. By subtracting those emissions reported by Annex I countries to the United Nations Framework Convention of Climatic Change (UNFCCC) from our observation-inferred SF6 source leaves a surprisingly large gap of more than 70â80% of non-reported SF6 emissions in the last decade
Enantioselective adsorption on magnetic surfaces
From the beginning of molecular theory, the interplay of chirality and
magnetism has intrigued scientists. There is still the question if
enantiospecific adsorption of chiral molecules occurs on magnetic surfaces.
Enantiomer discrimination was conjectured to arise from chirality-induced spin
separation within the molecules and exchange interaction with the substrate's
magnetization. Here we show that single helical aromatic hydrocarbons undergo
enantioselective adsorption on ferromagnetic cobalt surfaces. Spin and
chirality sensitive scanning tunneling microscopy reveals that molecules of
opposite handedness prefer adsorption onto cobalt islands with opposite
out-of-plane magnetization. As mobility ceases in the final chemisorbed state,
it is concluded that enantioselection must occur in a physisorbed transient
precursor state. State-of-the-art spin-resolved ab initio simulations support
this scenario by refuting enantio-dependent chemisorption energies. These
findings demonstrate that van der Waals interaction should also include
spin-fluctuations which are crucial for molecular magnetochiral processes
Live imaging molecular changes in junctional tension upon VE-cadherin in zebrafish
Forces play diverse roles in vascular development, homeostasis and disease. VE-cadherin at endothelial cell-cell junctions links the contractile acto-myosin cytoskeletons of adjacent cells, serving as a tension-transducer. To explore tensile changes across VE-cadherin in live zebrafish, we tailored an optical biosensor approach, originally established in vitro. We validate localization and function of a VE-cadherin tension sensor (TS) in vivo. Changes in tension across VE-cadherin observed using ratio-metric or lifetime FRET measurements reflect acto-myosin contractility within endothelial cells. Furthermore, we apply the TS to reveal biologically relevant changes in VE-cadherin tension that occur as the dorsal aorta matures and upon genetic and chemical perturbations during embryonic development
Manufacturing, high heat flux testing and post mortem analyses of a W-PIM mock-up
In the framework of the European material development programme for fusion power plants beyond the international thermonuclear experimental reactor (ITER), tungsten (W) is an attractive candidate as plasma facing material for future fusion reactors. The selection of tungsten is owing to its physical properties such as the high melting point of 3420âŻÂ°C, the high strength and thermal conductivity, the low thermal expansion and low erosion rate. Disadvantages are the low ductility and fracture toughness at room temperature, low oxidation resistance, and the manufacturing by mechanical machining such as milling and turning, because it is extremely cost and time intensive.
Powder Injection Molding (PIM) as near-net-shape technology allows the mass production of complex parts, the direct joining of different materials and the development and manufacturing of composite and prototype materials presenting an interesting alternative process route to conventional manufacturing technologies. With its high precision, the PIM process offers the advantage of reduced costs compared to conventional machining. Isotropic materials, good thermal shock resistance, and high shape complexity are typical properties of PIM tungsten.
This contribution describes the fabrication of tungsten monoblocks, in particular for applications in divertor components, via PIM. The assembly to a component (mock-up) was done by Hot Radial Pressing (HRP). Furthermore, this component was characterized by High Heat Flux (HHF) tests at GLADIS and at JUDITH 2, and achieved 1300 cycles @ 20 MW/mÂČ.
Post mortem analyses were performed quantifying and qualifying the occurring damage by metallographic and microscopical means. The crystallographic texture was analysed by EBSD measurements. No change in microstructure during testing was observed
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