1,159 research outputs found
A logic for reasoning about time and reliability
We present a logic for stating properties such as, "after a request
for service there is at least a 98\045 probability that the service will
be carried out within 2 seconds". The logic extends the temporal
logic CTL by Emerson, Clarke and Sistla with time and probabilities. Formulas are interpreted over discrete time Markov chains.
We give algorithms for checking that a given Markov chain satis-
fies a formula in the logic. The algorithms require a polynomial
number of arithmetic operations, in size of both the formula and\003This research report
is a revised and extended version of a paper that has appeared under the title "A
Framework for Reasoning about Time and Reliability" in the
Proceeding of the 10thIEEE Real-time Systems Symposium, Santa Monica CA,
December 1989. This work was partially supported by the Swedish Board for Technical
Development (STU) as part of Esprit BRA Project SPEC, and by the Swedish
Telecommunication Administration.1the Markov chain. A simple example is included to
illustrate the
algorithms
The Danish royal flagship gribshunden : Dendrochronology on a late medieval carvel sunk in the Baltic Sea
The Royal flagship Gribshunden carried the Danish King Hans on its way to the city of Kalmar in Sweden when the ship sank in the summer of 1495. The ship caught fire while anchored north of the Stora Ek o Island and sank to the seafloor, where it lies to this day. The wreck was rediscovered in the 1970s and is remarkably well preserved.Since 2001, scientific investigations have been performed on the wreck by various organizations. In total, 13 dendrochronological samples from different parts of the ship construction have been collected and analyzed with standard dendrochronological methods with respect to age and provenance. The results show that all dated samples could have been felled during the winter season of 1482/83, although only one sample contains sapwood and waney edge. The highest correlations are obtained from reference chronologies that originate from the River Meuse drainage area, with correlations peaking around the city of Namur in Belgium. Most likely, theship was constructed in a shipyard close to the mouth of the River Meuse in the southern Netherlands. It seems King Hans realized the potential of the new ship type represented by Gribshunden, but his shipwrights did not have the knowledge to build such a ship in Denmark. Instead, he purchased the ship from abroad. This studyhighlights late medieval economic and political connections throughout northern Europe
Gauge independent description of Aharonov-Bohm Effect
The Aharonov-Bohm (AB) effect is a pure quantum effect that implies a
measurable phase shift in the wave function for a charged particle that
encircles a magnetic flux located in a region \textit{inaccessible} to the
particle. Classically, such a non-local effect appears to be impossible since
the Lorentz force depends on only the magnetic field at the location of the
particle. In quantum mechanics, the Hamiltonian, and thus the Schr\"odinger
equation, has a local coupling between the current due to the particle, and the
electromagnetic vector potential , which extends to the entire
space beyond the region with finite magnetic field. This has sometimes been
interpreted as meaning that in quantum mechanics is in some sense
more "fundamental" than in spite of the former being gauge
dependent, and thus unobservable. Here we shall, with a general proof followed
by a few examples, demonstrate that the AB-effect can be fully accounted for by
considering only the gauge invariant field, as long as it is
included as part of the quantum action of the entire isolated system. The price
for the gauge invariant formulation is that we must give up locality -- the
AB-phase for the particle will arise from the change in the action for the
field in the region inaccessible to the particle
Charge Fractionalization on Quantum Hall Edges
We discuss the propagation and fractionalization of localized charges on the
edges of quantum Hall bars of variable widths, where interactions between the
edges give rise to Luttinger liquid behavior with a non-trivial interaction
parameter g. We focus in particular on the separation of an initial charge
pulse into a sharply defined front charge and a broader tail. The front pulse
describes an adiabatically dressed electron which carries a non-integer charge,
which is \sqrt{g} times the electron charge. We discuss how the presence of
this fractional charge can, in principle, be detected through measurements of
the noise in the current created by tunneling of electrons into the system. The
results are illustrated by numerical simulations of a simplified model of the
Hall bar.Comment: 15 page
PREPARATION OF PLASMA MEMBRANE FROM ISOLATED NEURONS
A bulk fraction enriched with respect to neuronal cell bodies was used as starting material for the isolation of neuronal plasma membrane The cells were gently homogenized in isotonic sucrose and a crude membrane containing fraction sedimented at 3000 g. Subsequently, the membrane fraction was purified on a discontinuous sucrose density gradient between 35% and 25 5% sucrose (w/w). Enzymatic analyses showed a 4–5-fold enrichment in plasma membrane markers, and a 10–15% contamination of mitochondrial and microsomal material. Electron micrographs of the membrane fraction confirmed the enzymatic data Fragmented membranes were found, mainly in vesicular form No ribosomes, but a few mitochondria and some multilamellar membranes were see
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