604 research outputs found
Solving Large-Scale Optimization Problems Related to Bell's Theorem
Impossibility of finding local realistic models for quantum correlations due
to entanglement is an important fact in foundations of quantum physics, gaining
now new applications in quantum information theory. We present an in-depth
description of a method of testing the existence of such models, which involves
two levels of optimization: a higher-level non-linear task and a lower-level
linear programming (LP) task. The article compares the performances of the
existing implementation of the method, where the LPs are solved with the
simplex method, and our new implementation, where the LPs are solved with a
matrix-free interior point method. We describe in detail how the latter can be
applied to our problem, discuss the basic scenario and possible improvements
and how they impact on overall performance. Significant performance advantage
of the matrix-free interior point method over the simplex method is confirmed
by extensive computational results. The new method is able to solve problems
which are orders of magnitude larger. Consequently, the noise resistance of the
non-classicality of correlations of several types of quantum states, which has
never been computed before, can now be efficiently determined. An extensive set
of data in the form of tables and graphics is presented and discussed. The
article is intended for all audiences, no quantum-mechanical background is
necessary.Comment: 19 pages, 7 tables, 1 figur
A tRNA world
Knowledge about the kinetics of chemical reactions in cells is important for an understanding
of signaling pathways and regulation. Even though there are many kinetic measurements
of in vitro reactions in literature, methods for in vivo measurements are sparse. With help
of Temperature Oscillation Optical Lock-in (TOOL) microscopy we measure the kinetics of
DNA hybridization inside cells and detect signicant acceleration or deceleration compared to
in vitro measurements, dependent on the DNA sample. The dierences can not be explained
by molecular crowding eects. Only models that take the background interactions with genomic
DNA and RNA as well as the activity of single stranded and double stranded binding
proteins into account, can be tted to data. The results imply that the biological relevance
of kinetic rates measured in vitro has to be rejudged carefully.
The RNA world hypothesis predicts catalytic molecules based on RNA, as for example
early replicators, as precursor of modern biology. But how can a pool of appropriate RNA
molecules arise under early earth conditions? In a Gillespie-model, we observe the length distribution,
secondary structure and sequences of a pool of RNA molecules in porous rocks like
they appear near sites of volcanic activity. We assume a monomer in
ux, a length dependent
out
ux, a random, non-templated polymerisation and a degradation that is much stronger
for single stranded than for double stranded RNA. After equilibrium is reached, the pool
is populated with many hairpin-like structures due to the selection pressure for hybridized
strands that can be bricks for RNA machines.
Once sequence motifs and their complements appear in the reactor, they protect each other
and are present longer than statistically expected. This "protection by hybridization" has
the same ngerprint as a weak replication. As a consequence, the pool does not cover the
full sequence space but includes more similar sequences, which is an important condition for
chemical reactions.
Replication of genetic information by RNA molecules is considered to be a key process in the
beginning of evolution. It is so crucial that traces of this early replication are expected to be
present in key processes of modern biology. We present a replication scheme based on hairpins
derived from the sequence of tRNA that replicates the genetic information about a succession
of sequence snippets. The replication is driven by temperature oscillations as they occur
naturally inside of porous rocks in presence of temperature gradients, and independent on
external chemical energy sources. It is selective for correct information and shows exponential
growth rates with doubling times in the range of seconds to minutes and is thereby the fastest
early replicator in the literature.
The replication scheme can naturally be expanded to longer successions by using double
hairpins derived from full tRNA sequences by only few mutations. By charging double hairpins
with amino acids or peptides, the proposed replication bridges the gap from the RNA world
to modern biology by oering a rudimentary translation mechanism, that sorts amino acids
to chains according to genetic information
High temperature supercapacitors
The scientific objective of this research program was to determine the feasibility of
manufacturing an ionic liquid-based supercapacitor that could operate at temperatures up to
220 °C. A secondary objective was to determine the compatibility of ionic liquids with other
cell components (e.g. current collectors) at high temperature and, if required, consider means
of mitigating any problems.
The industrial motivation for the present work was to develop a supercapacitor capable of
working in the harsh environment of deep offshore boreholes. If successful, this technology
would allow down-hole telemetry under conditions of mechanical vibration and high
temperature. The obstacles, however, were many. All supercapacitor components had to be
stable against thermal decomposition up to T ≥ 220 °C. Volatile components had to be
eliminated. If possible, the finished device should be able to withstand voltages greater than 4
V, in order to maximise the amount of stored energy. The internal resistance should be as low
as possible. Side reactions, particularly faradaic reactions, should be eliminated or
suppressed. All liquid components should be gelled to minimise leakage in the event of cell
damage. Finally, any emergent problems should be identified. [Continues.
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