1,827 research outputs found
PMH58 TOOL: MULTI-ATTRIBUTE UTILITY FUNCTION REFLECTING PATIENT EXPERIENCE OF SIDE EFFECTS TO ANTIPSYCHOTIC THERAPY
A Variational Approach for Minimizing Lennard-Jones Energies
A variational method for computing conformational properties of molecules
with Lennard-Jones potentials for the monomer-monomer interactions is
presented. The approach is tailored to deal with angular degrees of freedom,
{\it rotors}, and consists in the iterative solution of a set of deterministic
equations with annealing in temperature. The singular short-distance behaviour
of the Lennard-Jones potential is adiabatically switched on in order to obtain
stable convergence. As testbeds for the approach two distinct ensembles of
molecules are used, characterized by a roughly dense-packed ore a more
elongated ground state. For the latter, problems are generated from natural
frequencies of occurrence of amino acids and phenomenologically determined
potential parameters; they seem to represent less disorder than was previously
assumed in synthetic protein studies. For the dense-packed problems in
particular, the variational algorithm clearly outperforms a gradient descent
method in terms of minimal energies. Although it cannot compete with a careful
simulating annealing algorithm, the variational approach requires only a tiny
fraction of the computer time. Issues and results when applying the method to
polyelectrolytes at a finite temperature are also briefly discussed.Comment: 14 pages, uuencoded compressed postscript fil
Interaction effects and transport properties of Pt capped Co nanoparticles
We studied the magnetic and transport properties of Co nanoparticles (NPs)
being capped with varying amounts of Pt. Beside field and temperature dependent
magnetization measurements we performed delta-M measurements to study the
magnetic interactions between the Co NPs. We observe a transition from
demagnetizing towards magnetizing interactions between the particles for an
increasing amount of Pt capping. Resistivity measurements show a crossover from
giant magnetoresistance towards anisotropic magnetoresistance
Existence of a phase transition under finite magnetic field in the long-range RKKY Ising spin glass DyYRuSi
A phase transition of a model compound of the long-range Ising spin glass
(SG) DyYRuSi, where spins interact via the RKKY
interaction, has been investigated. The static and the dynamic scaling analyses
reveal that the SG phase transition in the model magnet belongs to the
mean-field universality class. Moreover, the characteristic relaxation time in
finite magnetic fields exhibits a critical divergent behavior as well as in
zero field, indicating a stability of the SG phase in finite fields. The
presence of the SG phase transition in field in the model magnet strongly
syggests that the replica symmetry is broken in the long-range Ising SG.Comment: 4 pages, 4 figures, to be published in JPSJ (2010
Development and Application of Solid Phase Extraction Method for Polycyclic Aromatic Hydrocarbons in Water Samples in Johannesburg Area, South Africa
A solid phase extraction (SPE) technique has been developed for the quantitative determination of polyaromatic hydrocarbons (PAHs) in aqueous samples. The SPE technique involved extraction of PAHs froma 100 mL sample containing 10 % methanol as a modifier onto C18 cartridges. 40 % methanol in water was used as conditioning solvent, and 3 mL acetone:THF (1:1) as eluting solvent. After eluting, the extract was reduced to 1 mL under nitrogen and then analyzed by GC-MS. The extraction was optimized for the addition of organic modifier, sample load volume, conditioning solvent, washing solvent and eluting solvent. In order to evaluate the practical applicability of SPE technique, water samples were spiked with the PAHs to give final sample concentrationsbetween 3 and 7 μg L–1. Enrichment factors of 81–135 were achieved with relative standard deviations (RSDs) of less than 6 %. Recoveries obtained ranged from 81 to 135 %. Detection limits ranged from 20.0–52.0 ng L–1. The optimized method was validated by analyzing certified reference materials. The optimized method was then applied to spiked real river samples in and around the Johannesburg area, South Africa. The concentrations obtained varied from 22.0 to 1040.0 ng L–1. The RSDs were between 2.3 and 13 %. The overall order of PAHs levels was: phenanthrene > acenaphthene > naphthalene > fluoranthene > pyrene.Keywords: Solid phase extraction, polycyclic aromatic hydrocarbons, water samples, Johannesburg, South Afric
Spin Glasses: Model systems for non-equilibrium dynamics
Spin glasses are frustrated magnetic systems due to a random distribution of
ferro- and antiferromagnetic interactions. An experimental three dimensional
(3d) spin glass exhibits a second order phase transition to a low temperature
spin glass phase regardless of the spin dimensionality. In addition, the low
temperature phase of Ising and Heisenberg spin glasses exhibits similar
non-equilibrium dynamics and an infinitely slow approach towards a
thermodynamic equilibrium state. There are however significant differences in
the detailed character of the dynamics as to memory and rejuvenation phenomena
and the influence of critical dynamics on the behaviour. In this article, some
aspects of the non-equilibrium dynamics of an Ising and a Heisenberg spin glass
are briefly reviewed and some comparisons are made to other glassy systems that
exhibit magnetic non-equilibrium dynamics.Comment: To appear in J. Phys.: Condens. Matter, Proceedings from HFM2003,
Grenobl
Symmetrical Temperature-Chaos Effect with Positive and Negative Temperature Shifts in a Spin Glass
The aging in a Heisenberg-like spin glass Ag(11 at% Mn) is investigated by
measurements of the zero field cooled magnetic relaxation at a constant
temperature after small temperature shifts . A
crossover from fully accumulative to non-accumulative aging is observed, and by
converting time scales to length scales using the logarithmic growth law of the
droplet model, we find a quantitative evidence that positive and negative
temperature shifts cause an equivalent restart of aging (rejuvenation) in terms
of dynamical length scales. This result supports the existence of a unique
overlap length between a pair of equilibrium states in the spin glass system.Comment: 4 page
Aging and scaling laws in -hydroquinone-clathrate
The dielectric permittivity of the orientational glass
methanol(x=0.73)--hydroquinone-clathrate has been studied as function of
temperature and waiting time using different temperature-time-protocols. We
study aging, rejuvenation and memory effects in the glassy phase and discuss
similarities and differences to aging in spin-glasses. We argue that the
diluted methanol-clathrate, although conceptually close to its magnetic
pendants, takes an intermediate character between a true spin-glass and a pure
random field system
Toward Quantum Superposition of Living Organisms
The most striking feature of quantum mechanics is the existence of
superposition states, where an object appears to be in different situations at
the same time. The existence of such states has been tested with small objects,
like atoms, ions, electrons and photons, and even with molecules. More
recently, it has been possible to create superpositions of collections of
photons, atoms, or Cooper pairs. Current progress in optomechanical systems may
soon allow us to create superpositions of even larger objects, like micro-sized
mirrors or cantilevers, and thus to test quantum mechanical phenomena at larger
scales. Here we propose a method to cool down and create quantum superpositions
of the motion of sub-wavelength, arbitrarily shaped dielectric objects trapped
inside a high--finesse cavity at a very low pressure. Our method is ideally
suited for the smallest living organisms, such as viruses, which survive under
low vacuum pressures, and optically behave as dielectric objects. This opens up
the possibility of testing the quantum nature of living organisms by creating
quantum superposition states in very much the same spirit as the original
Schr\"odinger's cat "gedanken" paradigm. We anticipate our essay to be a
starting point to experimentally address fundamental questions, such as the
role of life and consciousness in quantum mechanics.Comment: 9 pages, 4 figures, published versio
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