199 research outputs found
Dynamics of semifluxons in Nb long Josephson 0-pi junctions
We propose, implement and test experimentally long Josephson 0-pi junctions
fabricated using conventional Nb-AlOx-Nb technology. We show that using a pair
of current injectors, one can create an arbitrary discontinuity of the
Josephson phase and in particular a pi-discontinuity, just like in
d-wave/s-wave or in d-wave/d-wave junctions, and study fractional Josephson
vortices which spontaneously appear. Moreover, using such junctions, we can
investigate the \emph{dynamics} of the fractional vortices -- a domain which is
not yet available for natural 0-pi-junctions due to their inherently high
damping. We observe half-integer zero-field steps which appear on the
current-voltage characteristics due to hopping of semifluxons.Comment: Fractional vortices in conventional superconductors ;-
Multigrid reduction-in-time convergence for advection problems: A Fourier analysis perspective
A long-standing issue in the parallel-in-time community is the poor
convergence of standard iterative parallel-in-time methods for hyperbolic
partial differential equations (PDEs), and for advection-dominated PDEs more
broadly. Here, a local Fourier analysis (LFA) convergence theory is derived for
the two-level variant of the iterative parallel-in-time method of multigrid
reduction-in-time (MGRIT). This closed-form theory allows for new insights into
the poor convergence of MGRIT for advection-dominated PDEs when using the
standard approach of rediscretizing the fine-grid problem on the coarse grid.
Specifically, we show that this poor convergence arises, at least in part, from
inadequate coarse-grid correction of certain smooth Fourier modes known as
characteristic components, which was previously identified as causing poor
convergence of classical spatial multigrid on steady-state advection-dominated
PDEs. We apply this convergence theory to show that, for certain
semi-Lagrangian discretizations of advection problems, MGRIT convergence using
rediscretized coarse-grid operators cannot be robust with respect to CFL number
or coarsening factor. A consequence of this analysis is that techniques
developed for improving convergence in the spatial multigrid context can be
re-purposed in the MGRIT context to develop more robust parallel-in-time
solvers. This strategy has been used in recent work to great effect; here, we
provide further theoretical evidence supporting the effectiveness of this
approach
Parallel Unsmoothed Aggregation Algebraic Multigrid Algorithms on GPUs
We design and implement a parallel algebraic multigrid method for isotropic
graph Laplacian problems on multicore Graphical Processing Units (GPUs). The
proposed AMG method is based on the aggregation framework. The setup phase of
the algorithm uses a parallel maximal independent set algorithm in forming
aggregates and the resulting coarse level hierarchy is then used in a K-cycle
iteration solve phase with a -Jacobi smoother. Numerical tests of a
parallel implementation of the method for graphics processors are presented to
demonstrate its effectiveness.Comment: 18 pages, 3 figure
The multiple gene duplication problem revisited
Motivation: Deciphering the location of gene duplications and multiple gene duplication episodes on the Tree of Life is fundamental to understanding the way gene families and genomes evolve. The multiple gene duplication problem provides a framework for placing gene duplication events onto nodes of a given species tree, and detecting episodes of multiple gene duplication. One version of the multiple gene duplication problem was defined by Guigó et al. in 1996. Several heuristic solutions have since been proposed for this problem, but no exact algorithms were known
Novi časopis zadarskog Odjela za povijest umjetnosti
Recenzija, prikaz časopisa Odjela za povijest umjetnosti Sveučilišta u Zadru "Ars Adriatica", 1(2011)
Reducing quantum control for spin-spin entanglement distribution
We present a protocol that sets maximum stationary entanglement between
remote spins through scattering of mobile mediators without initialization,
post-selection or feedback of the mediators' state. No time-resolved tuning is
needed and, counterintuitively, the protocol generates two-qubit singlet states
even when classical mediators are used. The mechanism responsible for such
effect is resilient against non-optimal coupling strengths and dephasing
affecting the spins. The scheme uses itinerant particles and scattering centres
and can be implemented in various settings. When quantum dots and photons are
used a striking result is found: injection of classical mediators, rather than
quantum ones, improves the scheme efficiency.Comment: 7 pages, 5 figures, replaced with published versio
A molecular insight into algal-oomycete warfare : cDNA analysis of Ectocarpus siliculosus infected with the basal oomycete Eurychasma dicksonii
Peer reviewedPublisher PD
The Dozen Things Experimental Economists Should Do (More of)
What was once broadly viewed as an impossibility—learning from experimental data in economics—has now become commonplace. Governmental bodies, think tanks, and corporations around the world employ teams of experimental researchers to answer their most pressing questions. For their part, in the past two decades academics have begun to more actively partner with organizations to generate data via field experimentation. Although this revolution in evidence‐based approaches has served to deepen the economic science, recently a credibility crisis has caused even the most ardent experimental proponents to pause. This study takes a step back from the burgeoning experimental literature and introduces 12 actions that might help to alleviate this credibility crisis and raise experimental economics to an even higher level. In this way, we view our “12 action wish list” as discussion points to enrich the field
Sex ratio biases in termites provide evidence for kin selection
Contains fulltext :
142755.pdf (publisher's version ) (Closed access)Molecular testing of tumor samples to guide treatment decisions is of increasing importance. Several drugs have been approved for treatment of molecularly defined subgroups of patients, and the number of agents requiring companion diagnostics for their prescription is expected to rapidly increase. The results of such testing directly influence the management of individual patients, with both false-negative and false-positive results being harmful for patients. In this respect, external quality assurance (EQA) programs are essential to guarantee optimal quality of testing. There are several EQA schemes available in Europe, but they vary in scope, size and execution. During a conference held in early 2012, medical oncologists, pathologists, geneticists, molecular biologists, EQA providers and representatives from pharmaceutical industries developed a guideline to harmonize the standards applied by EQA schemes in molecular pathology. The guideline comprises recommendations on the organization of an EQA scheme, defining the criteria for reference laboratories, requirements for EQA test samples and the number of samples that are needed for an EQA scheme. Furthermore, a scoring system is proposed and consequences of poor performance are formulated. Lastly, the contents of an EQA report, communication of the EQA results, EQA databases and participant manual are given
TRY plant trait database - enhanced coverage and open access
Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
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