255 research outputs found
Considering Fluctuation Energy as a Measure of Gyrokinetic Turbulence
In gyrokinetic theory there are two quadratic measures of fluctuation energy,
left invariant under nonlinear interactions, that constrain the turbulence. The
recent work of Plunk and Tatsuno [Phys. Rev. Lett. 106, 165003 (2011)] reported
on the novel consequences that this constraint has on the direction and
locality of spectral energy transfer. This paper builds on that work. We
provide detailed analysis in support of the results of Plunk and Tatsuno but
also significantly broaden the scope and use additional methods to address the
problem of energy transfer. The perspective taken here is that the fluctuation
energies are not merely formal invariants of an idealized model
(two-dimensional gyrokinetics) but are general measures of gyrokinetic
turbulence, i.e. quantities that can be used to predict the behavior of the
turbulence. Though many open questions remain, this paper collects evidence in
favor of this perspective by demonstrating in several contexts that constrained
spectral energy transfer governs the dynamics.Comment: Final version as published. Some cosmetic changes and update of
reference
Angular momenta creation in relativistic electron-positron plasma
Creation of angular momentum in a relativistic electron-positron plasma is
explored. It is shown that a chain of angular momentum carrying vortices is a
robust asymptotic state sustained by the generalized nonlinear Schrodinger
equation characteristic to the system. The results may suggest a possible
electromagnetic origin of angular momenta when it is applied to the MeV epoch
of the early Universe.Comment: 20 pages, 6 figure
Linearized model Fokker-Planck collision operators for gyrokinetic simulations. II. Numerical implementation and tests
A set of key properties for an ideal dissipation scheme in gyrokinetic
simulations is proposed, and implementation of a model collision operator
satisfying these properties is described. This operator is based on the exact
linearized test-particle collision operator, with approximations to the
field-particle terms that preserve conservation laws and an H-Theorem. It
includes energy diffusion, pitch-angle scattering, and finite Larmor radius
effects corresponding to classical (real-space) diffusion. The numerical
implementation in the continuum gyrokinetic code GS2 is fully implicit and
guarantees exact satisfaction of conservation properties. Numerical results are
presented showing that the correct physics is captured over the entire range of
collisionalities, from the collisionless to the strongly collisional regimes,
without recourse to artificial dissipation.Comment: 13 pages, 8 figures, submitted to Physics of Plasmas; typos fixe
Effects of thermal fluctuation and the receptor-receptor interaction in bacterial chemotactic signalling and adaptation
Bacterial chemotaxis is controlled by the conformational changes of the
receptors, in response to the change of the ambient chemical concentration. In
a statistical mechanical approach, the signalling due to the conformational
changes is a thermodynamic average quantity, dependent on the temperature and
the total energy of the system, including both ligand-receptor interaction and
receptor-receptor interaction. This physical theory suggests to biology a new
understanding of cooperation in ligand binding and receptor signalling
problems. How much experimental support of this approach can be obtained from
the currently available data? What are the parameter values? What is the
practical information for experiments? Here we make comparisons between the
theory and recent experimental results. Although currently comparisons can only
be semi-quantitative or qualitative, consistency is clearly shown. The theory
also helps to sort a variety of data.Comment: 26 pages, revtex. Journal version. Analysis on another set of data on
adaptation time is adde
Gyrokinetic turbulence: a nonlinear route to dissipation through phase space
This paper describes a conceptual framework for understanding kinetic plasma
turbulence as a generalized form of energy cascade in phase space. It is
emphasized that conversion of turbulent energy into thermodynamic heat is only
achievable in the presence of some (however small) degree of collisionality.
The smallness of the collision rate is compensated by the emergence of
small-scale structure in the velocity space. For gyrokinetic turbulence, a
nonlinear perpendicular phase mixing mechanism is identified and described as a
turbulent cascade of entropy fluctuations simultaneously occurring at spatial
scales smaller than the ion gyroscale and in velocity space. Scaling relations
for the resulting fluctuation spectra are derived. An estimate for the
collisional cutoff is provided. The importance of adequately modeling and
resolving collisions in gyrokinetic simulations is biefly discussed, as well as
the relevance of these results to understanding the dissipation-range
turbulence in the solar wind and the electrostatic microturbulence in fusion
plasmas.Comment: iop revtex style, 14 pages, 1 figure; submitted to PPCF; invited talk
for EPS Conference on Plasma Physics, Crete, June 2008; Replaced to match
published versio
The host metabolite D-serine contributes to bacterial niche specificity through gene selection
Escherichia coli comprise a diverse array of both commensals and niche-specific pathotypes. The ability to cause disease results from both carriage of specific virulence factors and regulatory control of these via environmental stimuli. Moreover, host metabolites further refine the response of bacteria to their environment and can dramatically affect the outcome of the host–pathogen interaction. Here, we demonstrate that the host metabolite, D-serine, selectively affects gene expression in E. coli O157:H7. Transcriptomic profiling showed exposure to D-serine results in activation of the SOS response and suppresses expression of the Type 3 Secretion System (T3SS) used to attach to host cells. We also show that concurrent carriage of both the D-serine tolerance locus (dsdCXA) and the locus of enterocyte effacement pathogenicity island encoding a T3SS is extremely rare, a genotype that we attribute to an ‘evolutionary incompatibility’ between the two loci. This study demonstrates the importance of co-operation between both core and pathogenic genetic elements in defining niche specificity
Vortex solitons - Mass, Energy and Angular momentum bunching in relativistic electron-positron plasmas
It is shown that the interaction of large amplitude electromagnetic waves
with a hot electron-positron (e-p) plasma (a principal constituent of the
universe in the MeV epoch) leads to a bunching of mass, energy, and angular
momentum in stable, long-lived structures. Electromagnetism in the MeV epoch,
then, could provide a possible route for seeding the observed large-scale
structure of the universe.Comment: 17 pages with 2 figure
Measurement of the strong interaction induced shift and width of the 1s state of kaonic deuterium at J-PARC
The antikaon-nucleon interaction close to threshold provides crucial
information on the interplay between spontaneous and explicit chiral symmetry
breaking in low-energy QCD. In this context the importance of kaonic deuterium
X-ray spectroscopy has been well recognized, but no experimental results have
yet been obtained due to the difficulty of the measurement. We propose to
measure the shift and width of the kaonic deuterium 1s state with an accuracy
of 60 eV and 140 eV respectively at J-PARC. These results together with the
kaonic hydrogen data (KpX at KEK, DEAR and SIDDHARTA at DAFNE) will then permit
the determination of values of both the isospin I=0 and I=1 antikaon-nucleon
scattering lengths and will provide the most stringent constraints on the
antikaon-nucleon interaction, promising a breakthrough. Refined Monte Carlo
studies were performed, including the investigation of background suppression
factors for the described setup. These studies have demonstrated the
feasibility of determining the shift and width of the kaonic deuterium atom 1s
state with the desired accuracy of 60 eV and 140 eV.Comment: 12 pages, 9 figure
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