2,472 research outputs found
Blue flag with yellow tiger? Flags, authenticity and identity
The Flag of the Formosa Republic in the collection of the National Taiwan Museum is a national icon. It is a copy of one made in 1895 to mark the formation of a new Taiwanese republic; this replica, described in a contemporary newspaper account as an exact copy, was made in Japan in 1909. The painted flag was an intriguing puzzle. Instrumental analysis and a close study of the flag itself and of surviving historic photographs and records were used to try to establish whether what looked like later additions and repairs were actually part of the original construction. An international team of conservators and scientists from Taiwan, the UK, the USA and Germany carried out the investigation and the conservation treatment. Although dye analysis was inconclusive and it has not yet been possible to ascertain the original colour, it was felt that an addition in the upper right corner and some of the repairs could well be part of the original construction and these were left in situ though other repairs were removed. The paper lining was removed, revealing that the flag was painted on both sides. The fabric was cleaned using a vacuum suction table, while the paint surface was cleaned with swabs. The flag was supported using an adhesive treatment with Lascaux acrylic resin
Uniform approximation of barrier penetration in phase space
A method to approximate transmission probabilities for a nonseparable
multidimensional barrier is applied to a waveguide model. The method uses
complex barrier-crossing orbits to represent reaction probabilities in phase
space and is uniform in the sense that it applies at and above a threshold
energy at which classical reaction switches on. Above this threshold the
geometry of the classically reacting region of phase space is clearly reflected
in the quantum representation. Two versions of the approximation are applied. A
harmonic version which uses dynamics linearised around an instanton orbit is
valid only near threshold but is easy to use. A more accurate and more widely
applicable version using nonlinear dynamics is also described
Determination and emulation of motor-like flux conditions for loss characterization by means of a single tooth geometry
High quantities and a demand on low costs in automotive drives result in new production methods of electrical machines. Besides, the electric drive train efficiency is improved to offer long ranges. Referring to this relationship the loss models of electrical machines are improved more and more. Focusing on iron losses, remarkable influences on the loss characteristics are attributed to the manufacturing processes. In this publication, a new approach of measuring the losses of a single stator tooth of an electrical machine considering motor-like flux conditions is introduced. Derivation of motor-like flux conditions is described, transfer to the test bench is defined and measurements are shown - concluding with a comparison of simulation and measurement as well as the identified tooth losses of the investigated machine. This gives the possibility to improve iron loss models in case of additional losses due to manufacturing influences
Cross-link governed dynamics of biopolymer networks
Cytoskeletal networks of biopolymers are cross-linked by a variety of
proteins. Experiments have shown that dynamic cross-linking with physiological
linker proteins leads to complex stress relaxation and enables network flow at
long times. We present a model for the mechanical properties of transient
networks. By a combination of simulations and analytical techniques we show
that a single microscopic timescale for cross-linker unbinding leads to a broad
spectrum of macroscopic relaxation times, resulting in a weak power-law
dependence of the shear modulus on frequency. By performing rheological
experiments, we demonstrate that our model quantitatively describes the
frequency behavior of actin network cross-linked with -Actinin- over
four decades in frequency.Comment: 4 page
Geometrical Models of the Phase Space Structures Governing Reaction Dynamics
Hamiltonian dynamical systems possessing equilibria of stability type display \emph{reaction-type
dynamics} for energies close to the energy of such equilibria; entrance and
exit from certain regions of the phase space is only possible via narrow
\emph{bottlenecks} created by the influence of the equilibrium points. In this
paper we provide a thorough pedagogical description of the phase space
structures that are responsible for controlling transport in these problems. Of
central importance is the existence of a \emph{Normally Hyperbolic Invariant
Manifold (NHIM)}, whose \emph{stable and unstable manifolds} have sufficient
dimensionality to act as separatrices, partitioning energy surfaces into
regions of qualitatively distinct behavior. This NHIM forms the natural
(dynamical) equator of a (spherical) \emph{dividing surface} which locally
divides an energy surface into two components (`reactants' and `products'), one
on either side of the bottleneck. This dividing surface has all the desired
properties sought for in \emph{transition state theory} where reaction rates
are computed from the flux through a dividing surface. In fact, the dividing
surface that we construct is crossed exactly once by reactive trajectories, and
not crossed by nonreactive trajectories, and related to these properties,
minimizes the flux upon variation of the dividing surface.
We discuss three presentations of the energy surface and the phase space
structures contained in it for 2-degree-of-freedom (DoF) systems in the
threedimensional space , and two schematic models which capture many of
the essential features of the dynamics for -DoF systems. In addition, we
elucidate the structure of the NHIM.Comment: 44 pages, 38 figures, PDFLaTe
Catalog of selected heavy duty transport energy management models
A catalog of energy management models for heavy duty transport systems powered by diesel engines is presented. The catalog results from a literature survey, supplemented by telephone interviews and mailed questionnaires to discover the major computer models currently used in the transportation industry in the following categories: heavy duty transport systems, which consist of highway (vehicle simulation), marine (ship simulation), rail (locomotive simulation), and pipeline (pumping station simulation); and heavy duty diesel engines, which involve models that match the intake/exhaust system to the engine, fuel efficiency, emissions, combustion chamber shape, fuel injection system, heat transfer, intake/exhaust system, operating performance, and waste heat utilization devices, i.e., turbocharger, bottoming cycle
Five-year follow-up of bilateral stimulation of the subthalamic nucleus in advanced Parkinson's disease
Background: Although the short-term benefits of bilateral stimulation of the subthalamic nucleus in patients with advanced Parkinson's disease have been well documented, the long-term outcomes of the procedure are unknown.
Methods: We conducted a five-year prospective study of the first 49 consecutive patients whom we treated with bilateral stimulation of the subthalamic nucleus. Patients were assessed at one, three, and five years with levodopa (on medication) and without levodopa (off medication), with use of the Unified Parkinson's Disease Rating Scale. Seven patients did not complete the study: three died, and four were lost to follow-up.
Results: As compared with base line, the patients' scores at five years for motor function while off medication improved by 54 percent (P<0.001) and those for activities of daily living improved by 49 percent (P<0.001). Speech was the only motor function for which off-medication scores did not improve. The scores for motor function on medication did not improve one year after surgery, except for the dyskinesia scores. On-medication akinesia, speech, postural stability, and freezing of gait worsened between year 1 and year 5 (P<0.001 for all comparisons). At five years, the dose of dopaminergic treatment and the duration and severity of levodopa-induced dyskinesia were reduced, as compared with base line (P<0.001 for each comparison). The average scores for cognitive performance remained unchanged, but dementia developed in three patients after three years. Mean depression scores remained unchanged. Severe adverse events included a large intracerebral hemorrhage in one patient. One patient committed suicide.
Conclusions: Patients with advanced Parkinson's disease who were treated with bilateral stimulation of the subthalamic nucleus had marked improvements over five years in motor function while off medication and in dyskinesia while on medication. There was no control group, but worsening of akinesia, speech, postural stability, freezing of gait, and cognitive function between the first and the fifth year is consistent with the natural history of Parkinson's disease
Monte-Carlo Simulations of the Dynamical Behavior of the Coulomb Glass
We study the dynamical behavior of disordered many-particle systems with
long-range Coulomb interactions by means of damage-spreading simulations. In
this type of Monte-Carlo simulations one investigates the time evolution of the
damage, i.e. the difference of the occupation numbers of two systems, subjected
to the same thermal noise. We analyze the dependence of the damage on
temperature and disorder strength. For zero disorder the spreading transition
coincides with the equilibrium phase transition, whereas for finite disorder,
we find evidence for a dynamical phase transition well below the transition
temperature of the pure system.Comment: 10 pages RevTeX, 8 Postscript figure
Dissipative Quantum Systems with Potential Barrier. General Theory and Parabolic Barrier
We study the real time dynamics of a quantum system with potential barrier
coupled to a heat-bath environment. Employing the path integral approach an
evolution equation for the time dependent density matrix is derived. The time
evolution is evaluated explicitly near the barrier top in the temperature
region where quantum effects become important. It is shown that there exists a
quasi-stationary state with a constant flux across the potential barrier. This
state generalizes the Kramers flux solution of the classical Fokker-Planck
equation to the quantum regime. In the temperature range explored the quantum
flux state depends only on the parabolic approximation of the anharmonic
barrier potential near the top. The parameter range within which the solution
is valid is investigated in detail. In particular, by matching the flux state
onto the equilibrium state on one side of the barrier we gain a condition on
the minimal damping strength. For very high temperatures this condition reduces
to a known result from classical rate theory. Within the specified parameter
range the decay rate out of a metastable state is calculated from the flux
solution. The rate is shown to coincide with the result of purely thermodynamic
methods. The real time approach presented can be extended to lower temperatures
and smaller damping.Comment: 29 pages + 1 figure as compressed ps-file (uufiles) to appear in
Phys. Rev.
Semiclassical time evolution of the density matrix and tunneling
The time dependent density matrix of a system with potential barrier is
studied using path integrals. The characterization of the initial state, which
is assumed to be restricted to one side of the barrier, and the time evolution
of the density matrix lead to a three-fold path integral which is evaluated in
the semiclassical limit. The semiclassical trajectories are found to move in
the complex coordinate plane and barrier penetration only arises due to
fluctuations. Both the form of the semiclassical paths and the relevant
fluctuations change significantly as a function of temperature. The
semiclassical analysis leads to a detailed picture of barrier penetration in
the real time domain and the changeover from thermal activation to quantum
tunneling. Deep tunneling is associated with quasi-zero modes in the
fluctuation spectrum about the semiclassical orbits in the long time limit. The
connection between this real time description of tunneling and the standard
imaginary time instanton approach is established. Specific results are given
for a double well potential and an Eckart barrier.Comment: 27 pages, 8 figures, to be published in Phys. Rev.
- …