14,662 research outputs found
Vortex glass transition in a frustrated 3D XY model with disorder
The anisotropic frustrated three dimensional (3D) XY model with disorder in
the coupling constants is simulated as a model of a point disordered
superconductor in an applied magnetic field. From a finite size scaling
analysis of the helicity modulus it is concluded that the data is consistent
with a finite temperature transition with isotropic scaling and the correlation
length exponent is found to be \nu=1.50+/-0.12, consistent with 3D gauge glass
universality.Comment: For additional information, see
http://www.tp.umu.se/~olsson/VortexGlass.htm
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Simulating the Martian Chemical Enivronment
We report on new analogue materials to simulate Martian rocks and soils, especially under realistic redox conditions
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The Physio-Chemical Properties for the Interior of Enceladus
We have reviewed the current physical and chemical conditions of the Enceladus sub-surface environment, including the composition, temperature, pH and pressure. Here we have defined some of these parameters and, through the aid of modelling, will define and refine the remaining parameters needed for our experimental work. Simulations of the chemical reactions occurring within Enceladus can then be carried
out to advance our understanding of the internal environment of Enceladus and help evaluate its potential habitability. Once a better understanding of the chemical reactions occurring at the rock-water interface has been carried out, then potential analogues on Earth can be evaluated and known microbial life can be tested to see if it could survive the conditions of Enceladus
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Plastic Microbial Acclimation and Optimisation of Composting and Anaerobic Digestion Processes may Improve Degradation Times
Nonlinear Optics Studies on the MAX IV Storage Rings
The MAX IV Laboratory in Lund, Sweden, houses two electron storage rings operating at the energies 1.5, and 3 GeV. Both of these produce high-brilliance synchrotron radiation for beamline users. While the 1.5 GeV storage ring is a conventional third generation storage ring, employing a double-bend achromat structure, the MAX IV 3 GeV ring is the first realised fourth generation synchrotron. This ring employs a 7-bend achromat lattice structure to achieve a horizontal emittance of a few hundred pmrad. The multi-bend achromat design is the basis for many fourth generation synchrotron light sources. These lattice designs often require strong non-linear magnets in order to achieve their desired performance in terms of momentum acceptance and dynamic aperture, which in turn is needed to achieve the requirements in terms of beam lifetime and injection efficiency. The MAX IV 3 GeV storage ring itself is no exception, as it has a large number of chromatic sextupoles designed to minimize quadratic chromaticity. It also employs largely harmonic octupoles to minimise the amplitude-dependent tune shifts. Because of the high requirements of the fourth generation storage rings' non-linear magnets, it is of general interest to find schemes which allow for accurate tuning of these elements, as well as the characterisation of the non-linear optics of the accelerator. Schemes of these types are already well established when dealing with the linear optics of a storage ring, and need now be developed further for the non-linear case. This thesis presents schemes and results regarding the characterisation, correction, and optimisation of the non-linear optics of the MAX IV storage rings. These studies are mainly focussed on the MAX IV 3 GeV ring, but are aimed to be general enough that they can be applied on most fourth or third generation storage rings. This thesis also presents a specific case of the non-linear dynamics of a storage ring, where its properties are used to achieve pseudo single bunch through transverse resonance island buckets
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
New, efficient, and accurate high order derivative and dissipation operators satisfying summation by parts, and applications in three-dimensional multi-block evolutions
We construct new, efficient, and accurate high-order finite differencing
operators which satisfy summation by parts. Since these operators are not
uniquely defined, we consider several optimization criteria: minimizing the
bandwidth, the truncation error on the boundary points, the spectral radius, or
a combination of these. We examine in detail a set of operators that are up to
tenth order accurate in the interior, and we surprisingly find that a
combination of these optimizations can improve the operators' spectral radius
and accuracy by orders of magnitude in certain cases. We also construct
high-order dissipation operators that are compatible with these new finite
difference operators and which are semi-definite with respect to the
appropriate summation by parts scalar product. We test the stability and
accuracy of these new difference and dissipation operators by evolving a
three-dimensional scalar wave equation on a spherical domain consisting of
seven blocks, each discretized with a structured grid, and connected through
penalty boundary conditions.Comment: 16 pages, 9 figures. The files with the coefficients for the
derivative and dissipation operators can be accessed by downloading the
source code for the document. The files are located in the "coeffs"
subdirector
Polarization effects in tau production by neutrino
We studied polarization effects in tau production by neutrino-nucleon
scattering. Quasi-elastic scattering, resonance production and deep
inelastic scattering processes are taken into account for the CERN-to-Gran
Sasso projects. We show that the tau produced by neutrino has high degree of
polarization, and its spin direction depends non-trivially on the energy and
the scattering angle of tau in the laboratory frame.Comment: 6 pages, 5 eps figures, espcrc2.sty; Proceedings of the 3rd
International Workshop on Neutrino-Nucleus Interactions in the Few GeV Region
(NuInt04), March 17-21, 2004, Gran Sasso, Italy; minor changes, typos in Eq.
(6) correcte
In Search of the Vortex Loop Blowout Transition for a type-II Superconductor in a Finite Magnetic Field
The 3D uniformly frustrated XY model is simulated to search for a predicted
"vortex loop blowout" transition within the vortex line liquid phase of a
strongly type-II superconductor in an applied magnetic field. Results are shown
to strongly depend on the precise scheme used to trace out vortex line paths.
While we find evidence for a transverse vortex path percolation transition, no
signal of this transition is found in the specific heat.Comment: 11 pages, 17 figure
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Mars simulated exposure and the characteristic Raman biosignatures of amino acids and halophilic microbes
Though Raman bands of α-amino acids (AA) are well documented, often only the strongest intensity bands are quoted as identifiers (e.g. Jenkins et al., 2005; De Gelder et al., 2007; Zhu et al., 2011). Unknown regolith mixtures on Mars-sampling missions could obscure these bands. Here the case is made for determining, via a statistical method, sets of characteristic bands to be used as identifiers, independent of band intensity or number of bands (Rolfe et al., 2016). AA have upwards of 25 potentially identifying bands and this method defines sets of 10–19 bands per AA. Examination of AA-doped Mars-like basalt resulted in a maximum of eight bands being identified, as some characteristic bands were obscured by mineral bands, including the strongest intensity band in some cases. This proved the need for characteristic bands to be defined, enabling successful identification of AA. The ESA ExoMars Rover mission will crush and then pass the sample to the Raman Laser Spectrometer. We crushed a Mars-like basalt to a similar grain size expected to be created by the rover. Our samples were doped with 1 % (by weight) AA samples, resulting in no detection of AA, because of loss of original spatial context and spaces between the grains. We recommend that Raman spectroscopy on future missions should be conducted before the sample is crushed. Halite-entombed halophilic microbes, known to survive being entombed, were exposed to Mars-like surface (including temperature, pressure, atmospheric composition and UV) and freeze-thaw cycle (plus pressure and atmospheric composition) conditions. This test on the survival of the microbes showed that survival rates quickly deteriorated in surface conditions, but freeze-thaw cycle samples had well preserved Raman biosignatures, indicating that similar signatures could be detectable on Mars if similar life persists in evaporitic material or brines today
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