3,461 research outputs found
Experimental study of radiatively cooled magnetically driven plasma jets
This thesis presents the results of experiments to study the formation and dynamics of plasma jets in the laboratory, in particular their scaling to astrophysical jets. The experiments were performed on the MAGPIE generator, which delivered a peak current of 1 MA in 250 ns. A variety of plasma diagnostics allowed the dynamics of the jets to be studied and the conditions of the plasma to be determined. Radial wire array experiments were performed in which the mass of the wires and the magnitude of the toroidal magnetic field was varied. These results show that it is possible to control the time of formation and the expansion velocity of the magnetically driven jet that characterizes this configuration. In addition, the experiments allowed the introduction of a poloidal magnetic field into the radial wire array with the aim of studying its effect on the dynamics and stability of the plasma jet. The radial foil is introduced as a novel configuration to produce episodic magnetic-tower jets. Magnetic cavities were observed to emerge in timescales of ~ 30 ns, with increasing expansion velocities reaching ~ 300 km/s. The formation of episodic magnetically driven jets occurs due to reconnection of current at the base of the cavity, allowing 3-4 episodes to be produced per experiment. Results allowed the energy balance, the magnitude of the trapped toroidal magnetic field, and the characteristic temperatures in these outflows to be determined, as well as other plasma parameters. This experimental setup allowed the study of the interaction of episodic jets with an ambient medium by introducing a neutral gas above the foil. The dynamics of the formation of several shock structures at early times was studied, opening new possibilities for laboratory astrophysics experiments in the future
Mixed-state dynamics in one-dimensional quantum lattice systems: a time-dependent superoperator renormalization algorithm
We present an algorithm to study mixed-state dynamics in one-dimensional
quantum lattice systems. The algorithm can be used, e.g., to construct thermal
states or to simulate real time evolutions given by a generic master equation.
Its two main ingredients are (i) a superoperator renormalization scheme to
efficiently describe the state of the system and (ii) the time evolving block
decimation (TEBD) technique to efficiently update the state during a time
evolution. The computational cost of a simulation increases significantly with
the amount of correlations between subsystems but it otherwise depends only
linearly in the system size. We present simulations involving quantum spins and
fermions in one spatial dimension.Comment: See also F. Verstraete et al. cond-mat/040642
An explicit substructuring method for overlapping domain decomposition based on stochastic calculus
In a recent paper [{\em F. Bernal, J. Mor\'on-Vidal and J.A. Acebr\'on,
Comp. Math. App. 146:294-308 (2023)}] an hybrid supercomputing algorithm
for elliptic equations has been put forward. The idea is that the interfacial
nodal solutions solve a linear system, whose coefficients are expectations of
functionals of stochastic differential equations confined within patches of
about subdomain size. Compared to standard substructuring techniques such as
the Schur complement method for the skeleton, the hybrid approach renders an
explicit and sparse shrunken matrix -- hence suitable for being substructured
again. The ultimate goal is to push strong scalability beyond the state of the
art, by leveraging the scope for parallelisation of stochastic calculus. Here,
we present a major revamping of that framework, based on the insight of
embedding the domain in a cover of overlapping circles (in two dimensions).
This allows for efficient Fourier interpolation along the interfaces (now
circumferences) and -- crucially -- for the evaluation of most of the
interfacial system entries as the solution of small boundary value problems on
a circle. This is both extremely efficient (as they can be solved in parallel
and by the pseudospectral method) and free of Monte Carlo error. Stochastic
numerics are only needed on the relatively few circles intersecting the domain
boundary. In sum, the new formulation is significantly faster, simpler and more
accurate, while retaining all of the advantageous properties of PDDSparse.
Numerical experiments are included for the purpose of illustration
Occurrence of ferredoxin-dependent glutamate synthase in plant cell fraction of soybean root nodules (Glycine max)
AbstractFerredoxin-dependent glutamate synthase (EC 1.4.7.1) and NADH-dependent glutamate synthase (EC 1.4.1.14) have been identified in the plant cells of soybean nodules. Ferredoxin-dependent glutamate synthase is 2-fold more active than NADH-dependent enzyme in vitro. Ferredoxin-dependent glutamate synthase cross-reacts with IgG against ferredoxin-dependent glutamate synthase of rice green leaves, whereas NADH-dependent glutamate synthase does not recognize the IgG, indicating that there are two distinct enzyme proteins. Ferredoxin-dependent glutamate synthase is composed of polypeptide chain(s) of 165 kDa and has a high affinity to spinach leaf ferredoxin as an electron carrier
X-ray scattering from surfaces: discrete and continuous components of roughness
Incoherent surface scattering yields a statistical description of the
surface, due to the ensemble averaging over many independently sampled volumes.
Depending on the state of the surface and direction of the scattering vector
relative to the surface normal, the height distribution is discrete,
continuous, or a combination of the two. We present a treatment for the
influence of multimodal surface height distributions on Crystal Truncation Rod
scattering. The effects of a multimodal height distribution are especially
evident during in situ monitoring of layer-by-layer thin-film growth via Pulsed
Laser Deposition. We model the total height distribution as a convolution of
discrete and continuous components, resulting in a broadly applicable
parameterization of surface roughness which can be applied to other scattering
probes, such as electrons and neutrons. Convolution of such distributions could
potentially be applied to interface or chemical scattering. Here we find that
this analysis describes accurately our experimental studies of SrTiO3
annealing and homoepitaxial growth.Comment: 15 pages, 7 figure
Efficient simulation of one-dimensional quantum many-body systems
We present a numerical method to simulate the time evolution, according to a
Hamiltonian made of local interactions, of quantum spin chains and systems
alike. The efficiency of the scheme depends on the amount of the entanglement
involved in the simulated evolution. Numerical analysis indicate that this
method can be used, for instance, to efficiently compute time-dependent
properties of low-energy dynamics of sufficiently regular but otherwise
arbitrary one-dimensional quantum many-body systems.Comment: 4 pages, 1 figur
Detection of the Messenger RNA Encoding for the Ferredoxin-Dependent Glutamate Synthase in Maize Leaf
Target Design for XUV Probing of Radiative Shock Experiments
Radiative shocks are strong shocks characterized by plasma at a high
temperature emitting an important fraction of its energy as radiation.
Radiative shocks are commonly found in many astrophysical systems and are
templates of radiative hydrodynamic flows, which can be studied experimentally
using high-power lasers. This is not only important in the context of
laboratory astrophysics but also to benchmark numerical studies. We present
details on the design of experiments on radiative shocks in xenon gas performed
at the kJ scale PALS laser facility. It includes technical specifications for
the tube targets design and numerical studies with the 1-D radiative
hydrodynamics code MULTI. Emphasis is given to the technical feasibility of an
XUV imaging diagnostic with a 21 nm (~58 eV) probing beam, which allows to
probe simultaneously the post-shock and the precursor region ahead of the
shock. The novel design of the target together with the improved X-ray optics
and XUV source allow to show both the dense post-shock structure and the
precursor of the radiative shock.Comment: 12 pages, 4 figure
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