2,172 research outputs found
Quantum Computers and Dissipation
We analyse dissipation in quantum computation and its destructive impact on
efficiency of quantum algorithms. Using a general model of decoherence, we
study the time evolution of a quantum register of arbitrary length coupled with
an environment of arbitrary coherence length. We discuss relations between
decoherence and computational complexity and show that the quantum
factorization algorithm must be modified in order to be regarded as efficient
and realistic.Comment: 20 pages, Latex, 7 Postscript figure
Pressure of the Standard Model Near the Electroweak Phase Transition
We extend our previous determination of the thermodynamic pressure of the
Standard Model so that the result can be applied down to temperatures
corresponding to the electroweak crossover. This requires a further resummation
which can be cleanly organised within the effective theory framework. The
result allows for a precise determination of the expansion rate of the Universe
for temperatures around the electroweak crossover.Comment: 16 pages, 6 figures. v2: published versio
The idea of robots as independent machines is science fiction
The world is unpredictable, and robots function in pre-defined narrow contexts, writes Antti Lyyr
Advances in robotics will only get you so far: context is crucial
Robots and intelligent systems have gained a significant amount of attention recently. Various authors and reports detail advances in robotics and artificial intelligence and speculate on the role of humans in the robotic future. In such commentaries, robots are often presented as independent and tireless machines that are rational and efficient; they are removed from their creators and contexts of use. Unfortunately, as appealing as this image might be, it resembles more of a science fiction hero than the contextual nitty-gritty that revolves around the development and deployment of robotic applications. To obtain a more holistic picture, let us have a look at some contextual factors that surround robotics innovation today
DFT study of graphene antidot lattices: The roles of geometry relaxation and spin
Graphene sheets with regular perforations, dubbed as antidot lattices, have
theoretically been predicted to have a number of interesting properties. Their
recent experimental realization with lattice constants below 100 nanometers
stresses the urgency of a thorough understanding of their electronic
properties. In this work we perform calculations of the band structure for
various hydrogen-passivated hole geometries using both spin-polarized density
functional theory (DFT) and DFT based tight-binding (DFTB) and address the
importance of relaxation of the structures using either method or a combination
thereof. We find from DFT that all structures investigated have band gaps
ranging from 0.2 eV to 1.5 eV. Band gap sizes and general trends are well
captured by DFTB with band gaps agreeing within about 0.2 eV even for very
small structures. A combination of the two methods is found to offer a good
trade-off between computational cost and accuracy. Both methods predict
non-degenerate midgap states for certain antidot hole symmetries. The inclusion
of spin results in a spin-splitting of these states as well as magnetic moments
obeying the Lieb theorem. The local spin texture of both magnetic and
non-magnetic symmetries is addressed
Pressure of the Standard Model at High Temperatures
We compute the pressure of the standard model at high temperatures in the
symmetric phase to three loops, or to O(g^5) in all coupling constants. We find
that the terms of the perturbative expansion in the SU(2) + Higgs sector
decrease monotonically with increasing order, but the large values of the
strong coupling constant g_s and the Yukawa coupling of the top quark g_Y make
the expansion in the full theory converge more slowly. The final result is
observed to be about 10% smaller than the ideal gas pressure commonly used in
cosmological calculations.Comment: 30 pages, 4 figures. v2: one reference added, minor revisions,
accepted for publication in JHE
Rule-based Test Generation with Mind Maps
This paper introduces basic concepts of rule based test generation with mind
maps, and reports experiences learned from industrial application of this
technique in the domain of smart card testing by Giesecke & Devrient GmbH over
the last years. It describes the formalization of test selection criteria used
by our test generator, our test generation architecture and test generation
framework.Comment: In Proceedings MBT 2012, arXiv:1202.582
With software updates, Tesla upends product life cycle in the car industry
With this system, any product can be open-ended and continuously in the making, argue Antti Lyyra and Kari Koskine
Topological Solitons and Folded Proteins
We propose that protein loops can be interpreted as topological domain-wall
solitons. They interpolate between ground states that are the secondary
structures like alpha-helices and beta-strands. Entire proteins can then be
folded simply by assembling the solitons together, one after another. We
present a simple theoretical model that realizes our proposal and apply it to a
number of biologically active proteins including 1VII, 2RB8, 3EBX (Protein Data
Bank codes). In all the examples that we have considered we are able to
construct solitons that reproduce secondary structural motifs such as
alpha-helix-loop-alpha-helix and beta-sheet-loop-beta-sheet with an overall
root-mean-square-distance accuracy of around 0.7 Angstrom or less for the
central alpha-carbons, i.e. within the limits of current experimental accuracy.Comment: 4 pages, 4 figure
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