396 research outputs found
Thermodynamic Limit Of The Ginzburg-Landau Equations
We investigate the existence of a global semiflow for the complex
Ginzburg-Landau equation on the space of bounded functions in unbounded domain.
This semiflow is proven to exist in dimension 1 and 2 for any parameter values
of the standard cubic Ginzburg-Landau equation. In dimension 3 we need some
restrictions on the parameters but cover nevertheless some part of the
Benjamin-Feijer unstable domain.Comment: uuencoded dvi file (email: [email protected]
Role of bulk and surface phonons in the decay of metal surface states
We present a comprehensive theoretical investigation of the electron-phonon
contribution to the lifetime broadening of the surface states on Cu(111) and
Ag(111), in comparison with high-resolution photoemission results. The
calculations, including electron and phonon states of the bulk and the surface,
resolve the relative importance of the Rayleigh mode, being dominant for the
lifetime at small hole binding energies. Including the electron-electron
interaction, the theoretical results are in excellent agreement with the
measured binding energy and temperature dependent lifetime broadening.Comment: 4 pages, 3 figure
Dynamics of Gaseous Disks in a Non-axisymmetric Dark Halo
The dynamics of a galactic disk in a non-axisymmetric (triaxial) dark halo is
studied in detail using high-resolution, numerical, hydrodynamical models. A
long-lived, two-armed spiral pattern is generated for a wide range of
parameters. The spiral structure is global, and the number of turns can be two
or three, depending on the model parameters. The morphology and kinematics of
the spiral pattern are studied as functions of the halo and disk parameters.
The spiral structure rotates slowly, and its angular velocity varies
quasi-periodically. Models with differing relative halo masses, halo semi-axis
ratios, distributions of matter in the disk, Mach numbers in the gaseous
component, and angular rotational velocities of their halos are considered.Comment: 22 pages, 11 figure
Finite-Size Scaling in Two-Dimensional Superfluids
Using the model and a non-local updating scheme called cluster Monte
Carlo, we calculate the superfluid density of a two dimensional superfluid on
large-size square lattices up to . This technique
allows us to approach temperatures close to the critical point, and by studying
a wide range of values and applying finite-size scaling theory we are able
to extract the critical properties of the system. We calculate the superfluid
density and from that we extract the renormalization group beta function. We
derive finite-size scaling expressions using the Kosterlitz-Thouless-Nelson
Renormalization Group equations and show that they are in very good agreement
with our numerical results. This allows us to extrapolate our results to the
infinite-size limit. We also find that the universal discontinuity of the
superfluid density at the critical temperature is in very good agreement with
the Kosterlitz-Thouless-Nelson calculation and experiments.Comment: 13 pages, postscript fil
On the validity of mean-field amplitude equations for counterpropagating wavetrains
We rigorously establish the validity of the equations describing the
evolution of one-dimensional long wavelength modulations of counterpropagating
wavetrains for a hyperbolic model equation, namely the sine-Gordon equation. We
consider both periodic amplitude functions and localized wavepackets. For the
localized case, the wavetrains are completely decoupled at leading order, while
in the periodic case the amplitude equations take the form of mean-field
(nonlocal) Schr\"odinger equations rather than locally coupled partial
differential equations. The origin of this weakened coupling is traced to a
hidden translation symmetry in the linear problem, which is related to the
existence of a characteristic frame traveling at the group velocity of each
wavetrain. It is proved that solutions to the amplitude equations dominate the
dynamics of the governing equations on asymptotically long time scales. While
the details of the discussion are restricted to the class of model equations
having a leading cubic nonlinearity, the results strongly indicate that
mean-field evolution equations are generic for bimodal disturbances in
dispersive systems with \O(1) group velocity.Comment: 16 pages, uuencoded, tar-compressed Postscript fil
Evaluating different adoption scenarios for TIL-therapy and the influence on its (early) cost-effectiveness
Background: Treatment with tumor-Infiltrating Lymphocytes (TIL) is an innovative therapy for advanced melanoma with promising clinical phase I/II study results and likely beneficial cost-effectiveness. As a randomized controlled trial on the effectiveness of TIL therapy in advanced melanoma compared to ipilimumab is still ongoing, adoption of TIL therapy by the field is confronted with uncertainty. To deal with this, scenario drafting can be used to identify potential barriers and enables the subsequent anticipation on these barriers. This study aims to inform adoption decisions of TIL by evaluating various scenarios and evaluate their effect on the cost-effectiveness.Methods: First, 14 adoption scenarios for TIL-therapy were drafted using a Delphi approach with a group of involved experts. Second, the likelihood of the scenarios taking place within 5 years was surveyed among international experts using a web-based questionnaire. Third, based on the questionnaire results and recent literature, scenarios were labeled as being either "likely" or "-unlikely". Finally, the cost-effectiveness of TIL treatment involving the "likely" scored scenarios was calculated.Results: Twenty-nine experts from 12 countries completed the questionnaire. The scenarios showed an average likelihood ranging from 29 to 58%, indicating that future developments of TIL-therapy were surrounded with quite some uncertainty. Eight of the 14 scenarios were labeled as "likely". The net monetary benefit per patient is presented as a measure of cost-effectiveness, where a positive value means that a scenario is cost-effective. For six of these scenarios the cost-effectiveness was calculated: "Commercialization of TIL production" (the price was assumed to be 3 times the manufacturing costs in the academic setting) (-€51,550), "Pharmaceutical companies lowering the prices of ipilimumab" (€11,420), "Using TIL-therapy combined with ipilimumab" (-€10,840), "Automatic TIL production" (€22,670), "TIL more effective" (€23,270), "Less Interleukin-2" (€20,370).Conclusions: Incorporating possible future developments, TIL-therapy was calculated to be cost-effective compared to ipilimumab in the majority of "likely" scenarios. These scenarios could function as facilitators for adoption. Contrary, TIL therapy was expected to not be cost-effective when sold at commercial prices, or when combined with ipilimumab. These scenarios should be considered in the adoption decision as these may act as crucial barriers.</p
The lower mass function of the young open cluster Blanco 1: from 30 Mjup to 3 Mo
We performed a deep wide field optical survey of the young (~100-150 Myr)
open cluster Blanco1 to study its low mass population well down into the brown
dwarf regime and estimate its mass function over the whole cluster mass
range.The survey covers 2.3 square degrees in the I and z-bands down to I ~ z ~
24 with the CFH12K camera. Considering two different cluster ages (100 and 150
Myr), we selected cluster member candidates on the basis of their location in
the (I,I-z) CMD relative to the isochrones, and estimated the contamination by
foreground late-type field dwarfs using statistical arguments, infrared
photometry and low-resolution optical spectroscopy. We find that our survey
should contain about 57% of the cluster members in the 0.03-0.6 Mo mass range,
including 30-40 brown dwarfs. The candidate's radial distribution presents
evidence that mass segregation has already occured in the cluster. We took it
into account to estimate the cluster mass function across the
stellar/substellar boundary. We find that, between 0.03Mo and 0.6Mo, the
cluster mass distribution does not depend much on its exact age, and is well
represented by a single power-law, with an index alpha=0.69 +/- 0.15. Over the
whole mass domain, from 0.03Mo to 3Mo, the mass function is better fitted by a
log-normal function with m0=0.36 +/- 0.07Mo and sigma=0.58 +/- 0.06. Comparison
between the Blanco1 mass function, other young open clusters' MF, and the
galactic disc MF suggests that the IMF, from the substellar domain to the
higher mass part, does not depend much on initial conditions. We discuss the
implications of this result on theories developed to date to explain the origin
of the mass distribution.Comment: 18 pages, 15 figures and 5 tables accepted in A&
Scalar field induced oscillations of neutron stars and gravitational collapse
We study the interaction of massless scalar fields with self-gravitating
neutron stars by means of fully dynamic numerical simulations of the
Einstein-Klein-Gordon perfect fluid system. Our investigation is restricted to
spherical symmetry and the neutron stars are approximated by relativistic
polytropes. Studying the nonlinear dynamics of isolated neutron stars is very
effectively performed within the characteristic formulation of general
relativity, in which the spacetime is foliated by a family of outgoing light
cones. We are able to compactify the entire spacetime on a computational grid
and simultaneously impose natural radiative boundary conditions and extract
accurate radiative signals. We study the transfer of energy from the scalar
field to the fluid star. We find, in particular, that depending on the
compactness of the neutron star model, the scalar wave forces the neutron star
either to oscillate in its radial modes of pulsation or to undergo
gravitational collapse to a black hole on a dynamical timescale. The radiative
signal, read off at future null infinity, shows quasi-normal oscillations
before the setting of a late time power-law tail.Comment: 12 pages, 13 figures, submitted to Phys. Rev.
Simulation techniques for cosmological simulations
Modern cosmological observations allow us to study in great detail the
evolution and history of the large scale structure hierarchy. The fundamental
problem of accurate constraints on the cosmological parameters, within a given
cosmological model, requires precise modelling of the observed structure. In
this paper we briefly review the current most effective techniques of large
scale structure simulations, emphasising both their advantages and
shortcomings. Starting with basics of the direct N-body simulations appropriate
to modelling cold dark matter evolution, we then discuss the direct-sum
technique GRAPE, particle-mesh (PM) and hybrid methods, combining the PM and
the tree algorithms. Simulations of baryonic matter in the Universe often use
hydrodynamic codes based on both particle methods that discretise mass, and
grid-based methods. We briefly describe Eulerian grid methods, and also some
variants of Lagrangian smoothed particle hydrodynamics (SPH) methods.Comment: 42 pages, 16 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 12; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Relaxation and reconstruction on (111) surfaces of Au, Pt, and Cu
We have theoretically studied the stability and reconstruction of (111)
surfaces of Au, Pt, and Cu. We have calculated the surface energy, surface
stress, interatomic force constants, and other relevant quantities by ab initio
electronic structure calculations using the density functional theory (DFT), in
a slab geometry with periodic boundary conditions. We have estimated the
stability towards a quasi-one-dimensional reconstruction by using the
calculated quantities as parameters in a one-dimensional Frenkel-Kontorova
model. On all surfaces we have found an intrinsic tensile stress. This stress
is large enough on Au and Pt surfaces to lead to a reconstruction in which a
denser surface layer is formed, in agreement with experiment. The
experimentally observed differences between the dense reconstruction pattern on
Au(111) and a sparse structure of stripes on Pt(111) are attributed to the
details of the interaction potential between the first layer of atoms and the
substrate.Comment: 8 pages, 3 figures, submitted to Physical Review
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