899 research outputs found
Livre des délibérations de l'Église réformée de l'Albenc (1606-1682). Édition du manuscrit conservé à la Bibliothèque d'étude et d'information, Fonds dauphinois, Grenoble, cote R 9723, établie par François Francillon, Paris, Honoré Champion éditeur, 1998 (coll. Champion Varia, série « Vie des huguenots » II)
No full textCarbonnier-Burkard Marianne. Livre des délibérations de l'Église réformée de l'Albenc (1606-1682). Édition du manuscrit conservé à la Bibliothèque d'étude et d'information, Fonds dauphinois, Grenoble, cote R 9723, établie par François Francillon, Paris, Honoré Champion éditeur, 1998 (coll. Champion Varia, série « Vie des huguenots » II). In: Revue d'histoire et de philosophie religieuses, 79e année n°3, Juillet-septembre 1999. pp. 417-418
Assignment Problems
No full textThis volume presents a comprehensive view of the huge area of the assignment problem, starting from the conceptual foundations laid down since the Twenties by the studies on matching problems, and examining in detail theoretical, algorithmic and practical developments of the various assignment problems. Although the covered area is wide, each of the ten chapters is essentially self contained, and the readers can easily follow a single chapter they are interested in, by encountering few pointers to the essential background given in previous parts
Assignment Problems - Revised Reprint
No full textThis book provides a comprehensive treatment of assignment problems from their conceptual beginnings in the 1920s through present-day theoretical, algorithmic, and practical developments. The revised reprint provides details on a recent discovery related to one of Jacobi’s results, new material on inverse assignment problems and quadratic assignment problems, and an updated bibliography.The authors have organized the book into 10 self-contained chapters to make it easy for readers to use the specific chapters of interest to them without having to read the book linearly. The topics covered include bipartite matching algorithms, linear assignment problems, quadratic assignment problems, multi-index assignment problems, and many variations of these problems. Exercises in the form of numerical examples provide readers with a method of self-study or students with homework problems, and an associated webpage offers applets that readers can use to execute some of the basic algorithms as well as links to computer codes that are available online. (http://www.ec-securehost.com/SIAM/OTR106.htmll
The shoelace book: a mathematical guide to the best (and worst) ways to lace your shoes
No full textCrisscross, zigzag, bowtie, devil, angel, or star: which are the longest, the shortest, the strongest, and the weakest lacings? Pondering the mathematics of shoelaces, the author paints a vivid picture of the simple, beautiful, and surprising characterizations of the most common shoelace patterns. The mathematics involved is an attractive mix of combinatorics and elementary calculus. This book will be enjoyed by mathematically minded people for as long as there are shoes to lace. Burkard Polster is a well-known mathematical juggler, magician, origami expert, bubble-master, shoelace charmer, a
Relative Efficiencies of the Burkard 7-Day, Rotorod and Burkard Personal Samplers for Poaceae and Urticaceae Pollen under Field Conditions
No full textIntroduction: In aerobiological studies it is often necessary to compare concentration data recorded with different models of sampling instrument. Sampler efficiency typically varies from device to device, and depends on the target aerosol and local atmospheric conditions. To account for these differences inter-sampler correction factors may be applied, however for many pollen samplers and pollen taxa such correction factors do not exist and cannot be derived from existing published work. Materials and methods: In this study the relative efficiencies of the Burkard 7-Day Recording Volumetric Spore Trap, the Sampling Technologies Rotorod Model 20 and the Burkard Personal Volumetric Air Sampler were evaluated for Urticaceae and Poaceae pollen under field conditions, and the influence of wind speed and relative humidity on these efficiency relationships was assessed. Data for the two pollen taxa were collected during 2010 and 2011-12 respectively. Results: The three devices were found to record significantly different concentrations for both pollen taxa, with the exception of the 7-Day and Rotorod samplers for Poaceae pollen. Under the range of conditions present during the study wind speed was found to only have a significant impact on inter-sampler relationships involving the vertically orientated Burkard Personal sampler, whilst no interaction between relative efficiency and relative humidity was observed. Conclusions: Data collected with the three models of sampler should only be compared once the appropriate correction has been made, with wind speed taken into account where appropriate
Law and science: risk assessment and risk management in the WTO agreement on the application of sanitary and phytosanitary measures
No full textAssessing and managing risks relating to the consumption of food stuffs for humans and to the environment has been one of the most complex legal issues in WTO law, ever since the Agreement on Sanitary and Phytosanitary Measures was adopted at the end of the Uruguay Round and entered into force in 1995. The problem was expounded in a number of cases. Panels and the Appellate Body adopted different philosophies in interpreting the agreement and the basic concept of risk assessment as defined in Annex A para. 4 of the Agreement. Risk assessment entails fundamental question on law and science. Different interpretations reflect different underlying perceptions of science and its relationship to the law.
The present thesis supported by the Swiss National Research Foundation undertakes an in-depth analysis of these underlying perceptions. The author expounds the essence and differences of positivism and relativism in philosophy and natural sciences. He clarifies the relationship of fundamental concepts such as risk, hazards and probability. This investigation is a remarkable effort on the part of lawyer keen to learn more about the fundamentals based upon which the law – often unconsciously – is operated by the legal profession and the trade community. Based upon these insights, he turns to a critical assessment of jurisprudence both of panels and the Appellate Body. Extensively referring and discussing the literature, he deconstructs findings and decisions in light of implied and assumed underlying philosophies and perceptions as to the relationship of law and science, in particular in the field of food standards. Finding that both positivism and relativism does not provide adequate answers, the author turns critical rationalism and applies the methodologies of falsification developed by Karl R. Popper. Critical rationalism allows combining discourse in science and law and helps preparing the ground for a new approach to risk assessment and risk management.
Linking the problem to the doctrine of multilevel governance the author develops a theory allocating risk assessment to international for a while leaving the matter of risk management to national and democratically accountable government. While the author throughout the thesis questions the possibility of separating risk assessment and risk management, the thesis offers new avenues which may assist in structuring a complex and difficult proble
Quantum computation and communication using electron spins in quantum dots and wires
No full textThe recent discovery of efficient quantum algorithms for factoring and database search has shown that quantum computing would allow to solve important problems which are intractable with conventional computers. In contrast to the very demanding task of building a large-scale quantum computer, there are quantum communication protocols, e.g. quantum key distribution for cryptography, which—though still difficult—require much less effort and can be implemented with current technology. Apart from the technological motivation, the study of quantum information offers (at least) two additional benefits. First, new insight into fundamental questions on quantum mechanics, e.g. concerning non-locality and entanglement, are gained from an information-theoretical approach. And second, investigating a particular physical implementation of quantum information can give rise to independent physical results. Spintronics, the use of spin as opposed to charge in (classical) electronics is a new field for which some results presented here could be relevant. In this dissertation we investigate several theoretical aspects of the physical implementation of quantum computation and communication in which the fundamental unit of quantum information, the qubit, is represented by the spin of electrons in semiconductor quantum dots. The required coupling between the spins can be obtained by allowing for tunneling of electrons between adjacent dots, leading to a Heisenberg exchange coupling J S1 · S2 between the spins, a scenario which we study for laterally coupled quantum dots in a two-dimensional electron system, and for a three-dimensional setup with vertically coupled quantum dots. Furthermore, an alternative scheme to couple the spins via the interaction with an optical cavity mode is presented. Quantum error correction represents one of the important ingredients for the physical implementation of a quantum computer by protecting
it from the e�ects of a noisy environment. As a �rst test for errorcorrection
in a solid-state device using spins, we propose an optimized
implementation of the most primitive error correction scheme (the threebit
code). In this context, we introduce parallel switching, allowing
to operate a quantum computer more e�ciently than the usual serial
switching.
Coupling spins with the exchange interaction J S1 �S2 is not su�cient
for quantum computation; the spins also have to be addressed individually
using controllable local magnetic �elds or g-factors giBi �Si in order
to allow for single-qubit operations. On the one hand, we discuss several
schemes for overcoming the di�culty of applying local magnetic �elds
(requiring large gradients), e.g. g-factor engineering, which allows for
all-electric operation of the device. On the other hand, we show that
at the expense of additional devices (spins) and switching operations,
single-spin rotations can be dispensed with completely.
Addressing the feasibility of quantum communication with entangled
electrons in mesoscopic wires, i.e. interacting many-body environments,
we propose an interference experiment using a scattering set-up with an
entangler and a beam splitter. The current noise for electronic singlet
states turns out to be enhanced (bunching), while it is reduced for triplets
(antibunching). Due to interactions, the �delity of the entangled singlet
and triplet states is reduced by z4F
in a conductor described by Fermi
liquid theory, zF being the quasiparticle weight factor.
Finally, we study the related but more general problem of the noise of
the cotunneling current through one or several tunnel-coupled quantum
dots in the Coulomb blockade regime. The various regimes of weak and
strong, elastic and inelastic cotunneling are analyzed for quantum-dot
systems (QDS) with few-level, nearly-degenerate, and continuous electronic
spectra. In contrast to sequential tunneling, the noise in inelastic
cotunneling can be super-Poissonian. In order to investigate strong cotunneling
we develop a microscopic theory of cotunneling based on the
density-operator formalism and using the projection operator technique.
We have derived the master equation for the QDS and the current and
noise in cotunneling in terms of the stationary state of the QDS. These
results are then applied to QDS with a nearly degenerate and continuous
spectrum
Exploiting Group Symmetry in Semidefinite Programming Relaxations of the Quadratic Assignment Problem
No full textWe consider semidefinite programming relaxations of the quadratic assignment problem, and show how to exploit group symmetry in the problem data. Thus we are able to compute the best known lower bounds for several instances of quadratic assignment problems from the problem library: [R.E. Burkard, S.E. Karisch, F. Rendl. QAPLIB — a quadratic assignment problem library. Journal on Global Optimization, 10: 291–403, 1997]. AMS classification: 90C22, 20Cxx, 70-08.quadratic assignment problem;semidefinite programming;group sym- metry
Strong spin-orbit interaction, helical hole states, and spin qubits in nanowires and quantum dots
No full textSemiconducting nanowires (NWs) and quantum dots (QDs) are promising platforms for spintronics and quantum computation. Great experimental and theoretical efforts have been made to continuously improve their performances, which is evident from the large variety of setups, material combinations, and operation schemes under investigation. With the work summarized in this PhD thesis, we want to contribute to a better understanding of some of these systems.
The main result of our work is the discovery of a novel spin-orbit interaction (SOI) of Rashba type that arises for holes in NWs in the presence of an electric field. In contrast to conventional Rashba and Dresselhaus SOI, this mechanism is not suppressed by the fundamental band gap and therefore unusually strong. As a consequence, we find that Ge/Si core/shell NWs can host helical hole states with remarkably large spin-orbit energies on the order of millielectronvolts. Furthermore, we propose a setup for universal and electrically controlled quantum information processing with hole-spin qubits in Ge/Si NW QDs. Single-qubit gates can be performed on a subnanosecond timescale; two-qubit gates can be controlled independently and over long distances; idle qubits are well protected against electrical noise and lattice vibrations (phonons).
Another key result follows from our analysis of the phonon-mediated decay of singlet-triplet qubits in lateral GaAs double quantum dots (DQDs). We find that two-phonon processes lead to strong dephasing when the DQDs are biased, and the predicted temperature dependence provides a possible explanation for recent experimental data. When the DQDs are unbiased, the dephasing is highly suppressed and the decoherence times of the qubits are by orders of magnitude longer than those for biased DQDs.
In the last part of the thesis, we present a technique for manipulating the emission polarization and the nuclear spins of a single self-assembled QD. Our scheme exploits a natural cycle in which an electron spin is repeatedly created with resonant optical excitation when the QD is tunnel coupled to a Fermi sea. Among other things, we find that the nuclear spin polarization and the effective electron g factor can be changed continuously from negative to positive via the laser wavelength, with a region of bistability near a particular detuning. An analogous behavior is observed for the average polarization of the spontaneously emitted photons. Our experimental results, some of which are counterintuitive, are very well reproduced with a quantitative model.
The thesis is organized as follows. In Chapter 1, we review experimental and theoretical progress toward quantum computation with spins in QDs, with particular focus on NW QDs, lateral QDs, and self-assembled QDs. In Chapter 2, we study the low-energy hole states of Ge/Si NWs in the presence of electric and magnetic fields. We also consider the shell-induced strain, which strongly affects the NW and QD spectra. In Chapter 3, hole-spin qubits in Ge/Si NW QDs are investigated. We find a highly anisotropic and electrically tunable g factor and analyze the qubit lifetimes due to phonon-mediated decay. A setup for quantum information processing with these qubits is proposed in Chapter 4, where we also present surprisingly simple formulas for the effective Hamiltonian of the qubits. A detailed analysis of the static strain and the low-energy phonons in core/shell NWs is provided in Chapter 5, completing the part on NWs and NW QDs. In Chapter 6, we investigate the phonon-mediated decay of singlet-triplet qubits in lateral DQDs. The developed technique for controlling the emission polarization and the nuclear spins of optically active QDs is discussed in Chapter 7. Supplementary information to Chapters 2-7 is appended
Electronic implementations of interaction-free measurements
No full textThree different implementations of interaction-free measurements (IFMs) in solid-state nanodevices are discussed. The first one is based on a series of concatenated Mach-Zehnder interferometers, in analogy to optical-IFM setups. The second one consists of a single interferometer and concatenation is achieved in the time domain making use of a quantized electron emitter. The third implementation consists of an asymmetric Aharonov-Bohm ring. For all three cases we show that the presence of a dephasing source acting on one arm of the interferometer can be detected without degrading the coherence of the measured current. Electronic implementations of IFMs in nanoelectronics may play a fundamental role as very accurate and noninvasive measuring schemes for quantum devices
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