3,901 research outputs found
Landscape phage, phage display, stripped phage, biosensors, detection, affinity reagent, nanotechnology, Salmonella typhimurium, Bacillus anthracis
Filamentous phage, such as fd used in this study, are thread-shaped bacterial
viruses. Their outer coat is a tube formed by thousands equal copies of the
major coat protein pVIII. We constructed libraries of random peptides fused to
all pVIII domains and selected phages that act as probes specific for a panel
of test antigens and biological threat agents. Because the viral carrier is
infective, phage borne bio-selective probes can be cloned individually and
propagated indefinitely without needs of their chemical synthesis or
reconstructing. We demonstrated the feasibility of using landscape phages and
their stripped fusion proteins as new bioselective materials that combine
unique characteristics of affinity reagents and self assembling membrane
proteins. Biorecognition layers fabricated from phage-derived probes bind
biological agents and generate detectable signals. The performance of
phage-derived materials as biorecognition films was illustrated by detection of
streptavidin-coated beads, Bacillus anthracis spores and Salmonella typhimurium
cells. With further refinement, the phage-derived analytical platforms for
detecting and monitoring of numerous threat agents may be developed, since the
biodetector films may be obtained from landscape phages selected against any
bacteria, virus or toxin. As elements of field-use detectors, they are superior
to antibodies, since they are inexpensive, highly specific and strong binders,
resistant to high temperatures and environmental stresses.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Linear response within the projection-based renormalization method: Many-body corrections beyond the random phase approximation
The explicit evaluation of linear response coefficients for interacting
many-particle systems still poses a considerable challenge to theoreticians. In
this work we use a novel many-particle renormalization technique, the so-called
projector-based renormalization method, to show how such coefficients can
systematically be evaluated. To demonstrate the prospects and power of our
approach we consider the dynamical wave-vector dependent spin susceptibility of
the two-dimensional Hubbard model and also determine the subsequent magnetic
phase diagram close to half-filling. We show that the superior treatment of
(Coulomb) correlation and fluctuation effects within the projector-based
renormalization method significantly improves the standard random phase
approximation results.Comment: 17 pages, 7 figures, revised versio
The stellar atmosphere simulation code Bifrost
Context: Numerical simulations of stellar convection and photospheres have
been developed to the point where detailed shapes of observed spectral lines
can be explained. Stellar atmospheres are very complex, and very different
physical regimes are present in the convection zone, photosphere, chromosphere,
transition region and corona. To understand the details of the atmosphere it is
necessary to simulate the whole atmosphere since the different layers interact
strongly. These physical regimes are very diverse and it takes a highly
efficient massively parallel numerical code to solve the associated equations.
Aims: The design, implementation and validation of the massively parallel
numerical code Bifrost for simulating stellar atmospheres from the convection
zone to the corona.
Methods: The code is subjected to a number of validation tests, among them
the Sod shock tube test, the Orzag-Tang colliding shock test, boundary
condition tests and tests of how the code treats magnetic field advection,
chromospheric radiation, radiative transfer in an isothermal scattering
atmosphere, hydrogen ionization and thermal conduction.
Results: Bifrost completes the tests with good results and shows near linear
efficiency scaling to thousands of computing cores
Two-dimensional Radiative Magnetohydrodynamic Simulations of Partial Ionization in the Chromosphere. II. Dynamics and Energetics of the Low Solar Atmosphere
We investigate the effects of interactions between ions and neutrals on the
chromosphere and overlying corona using 2.5D radiative MHD simulations with the
Bifrost code. We have extended the code capabilities implementing ion-neutral
interaction effects using the Generalized Ohm's Law, i.e., we include the Hall
term and the ambipolar diffusion (Pedersen dissipation) in the induction
equation. Our models span from the upper convection zone to the corona, with
the photosphere, chromosphere and transition region partially ionized. Our
simulations reveal that the interactions between ionized particles and neutral
particles have important consequences for the magneto-thermodynamics of these
modeled layers: 1) ambipolar diffusion increases the temperature in the
chromosphere; 2) sporadically the horizontal magnetic field in the photosphere
is diffused into the chromosphere due to the large ambipolar diffusion; 3)
ambipolar diffusion concentrates electrical currents leading to more violent
jets and reconnection processes, resulting in 3a) the formation of longer and
faster spicules, 3b) heating of plasma during the spicule evolution, and 3c)
decoupling of the plasma and magnetic field in spicules. Our results indicate
that ambipolar diffusion is a critical ingredient for understanding the
magneto-thermo-dynamic properties in the chromosphere and transition region.
The numerical simulations have been made publicly available, similar to
previous Bifrost simulations. This will allow the community to study realistic
numerical simulations with a wider range of magnetic field configurations and
physics modules than previously possible.Comment: 13 figures. Accepted to be published in Ap
On red shifs in the transition region and corona
We present evidence that transition region red-shifts are naturally produced
in episodically heated models where the average volumetric heating scale height
lies between that of the chromospheric pressure scale height of 200 km and the
coronal scale height of 50 Mm. In order to do so we present results from 3d MHD
models spanning the upper convection zone up to the corona, 15 Mm above the
photosphere. Transition region and coronal heating in these models is due both
the stressing of the magnetic field by photospheric and convection `zone
dynamics, but also in some models by the injection of emerging magnetic flux.Comment: 8 pages, 9 figures, NSO Workshop #25 Chromospheric Structure and
Dynamic
Bond strength of plasma sprayed ceramic coatings on the phosphated steels
In the presented work, results of adhesion measurements for different systems of steel sheet-phosphate interlayer-ceramiccoating are described. The interlayers were produced by zinc phosphating; alumina, olivine and zirconiasilica-alumina (e.g. eucor) coatings were deposited by water stabilized plasma torch WSP®. However, successful application of the WSP technique depends on the choice of correct deposition parameters preserving the hydrated phosphates from thermal destruction by the molten ceramic particles. For the adhesion measurement ISO 4624standardized test was used. Corrosion resistivity was measured by polarisation resistance and free corrosion potential in 3 % NaCl solution.
Key words
Incommensurate magnetic fluctuations and Fermi surface topology in LiFeAs
Using the angle-resolved photoemission spectroscopy (ARPES) data accumulated
over the whole Brillouin zone (BZ) in LiFeAs we analyze the itinerant component
of the dynamic spin susceptibility in this system in the normal and
superconducting state. We identify the origin of the incommensurate magnetic
inelastic neutron scattering (INS) intensity as scattering between the electron
pockets, centered around the point of the BZ and the large
two-dimensional hole pocket, centered around the -point of the BZ. As
the magnitude of the superconducting gap within the large hole pocket is
relatively small and angle dependent, we interpret the INS data in the
superconducting state as a renormalization of the particle-hole continuum
rather than a true spin exciton. Our comparison indicates that the INS data can
be reasonably well described by both the sign changing symmetry of the
superconducting gap between electron and hole pockets as well as sign
preserving gap, depending on the assumptions made for the fermionic damping.Comment: 7 pages, 5 figure
Modelling magnetic flux emergence in the solar convection zone
[Abridged] Bipolar magnetic regions are formed when loops of magnetic flux
emerge at the solar photosphere. Our aim is to investigate the flux emergence
process in a simulation of granular convection. In particular we aim to
determine the circumstances under which magnetic buoyancy enhances the flux
emergence rate (which is otherwise driven solely by the convective upflows). We
use three-dimensional numerical simulations, solving the equations of
compressible magnetohydrodynamics in a horizontally-periodic Cartesian domain.
A horizontal magnetic flux tube is inserted into fully developed hydrodynamic
convection. We systematically vary the initial field strength, the tube
thickness, the initial entropy distribution along the tube axis and the
magnetic Reynolds number. Focusing upon the low magnetic Prandtl number regime
(Pm<1) at moderate magnetic Reynolds number, we find that the flux tube is
always susceptible to convective disruption to some extent. However, stronger
flux tubes tend to maintain their structure more effectively than weaker ones.
Magnetic buoyancy does enhance the flux emergence rates in the strongest
initial field cases, and this enhancement becomes more pronounced when we
increase the width of the flux tube. This is also the case at higher magnetic
Reynolds numbers, although the flux emergence rates are generally lower in
these less dissipative simulations because the convective disruption of the
flux tube is much more effective in these cases. These simulations seem to be
relatively insensitive to the precise choice of initial conditions: for a given
flow, the evolution of the flux tube is determined primarily by the initial
magnetic field distribution and the magnetic Reynolds number.Comment: 12 pages, 15 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
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