546 research outputs found
On Approximately Symmetric Informationally Complete Positive Operator-Valued Measures and Related Systems of Quantum States
We address the problem of constructing positive operator-valued measures
(POVMs) in finite dimension consisting of operators of rank one which
have an inner product close to uniform. This is motivated by the related
question of constructing symmetric informationally complete POVMs (SIC-POVMs)
for which the inner products are perfectly uniform. However, SIC-POVMs are
notoriously hard to construct and despite some success of constructing them
numerically, there is no analytic construction known. We present two
constructions of approximate versions of SIC-POVMs, where a small deviation
from uniformity of the inner products is allowed. The first construction is
based on selecting vectors from a maximal collection of mutually unbiased bases
and works whenever the dimension of the system is a prime power. The second
construction is based on perturbing the matrix elements of a subset of mutually
unbiased bases.
Moreover, we construct vector systems in \C^n which are almost orthogonal
and which might turn out to be useful for quantum computation. Our
constructions are based on results of analytic number theory.Comment: 29 pages, LaTe
Ptychographic X-ray tomography reveals additive zoning in nanocomposite single crystals
Single crystals containing nanoparticles represent a unique class of nanocomposites whose properties are defined by both their compositions and the structural organization of the dispersed phase in the crystalline host. Yet, there is still a poor understanding of the relationship between the synthesis conditions and the structures of these materials. Here ptychographic X-ray computed tomography is used to visualize the three-dimensional structures of two nanocomposite crystals – single crystals of calcite occluding diblock copolymer worms and vesicles. This provides unique information about the distribution of the copolymer nano-objects within entire, micron-sized crystals with nanometer spatial resolution and reveals how occlusion is governed by factors including the supersaturation and calcium concentration. Both nanocomposite crystals are seen to exhibit zoning effects that are governed by the solution composition and interactions of the additives with specific steps on the crystal surface. Additionally, the size and shape of the occluded vesicles varies according to their location within the crystal, and therefore the solution composition at the time of occlusion. This work contributes to our understanding of the factors that govern nanoparticle occlusion within crystalline materials, where this will ultimately inform the design of next generation nanocomposite materials with specific structure/property relationships
Droplet Microfluidics XRD Identifies Effective Nucleating Agents for Calcium Carbonate
The ability to control crystallization reactions is required in a vast range of processes including the production of functional inorganic materials and pharmaceuticals and the prevention of scale. However, it is currently limited by a lack of understanding of the mechanisms underlying crystal nucleation and growth. To address this challenge, it is necessary to carry out crystallization reactions in well‐defined environments, and ideally to perform in situ measurements. Here, a versatile microfluidic synchrotron‐based technique is presented to meet these demands. Droplet microfluidic‐coupled X‐ray diffraction (DMC‐XRD) enables the collection of time‐resolved, serial diffraction patterns from a stream of flowing droplets containing growing crystals. The droplets offer reproducible reaction environments, and radiation damage is effectively eliminated by the short residence time of each droplet in the beam. DMC‐XRD is then used to identify effective particulate nucleating agents for calcium carbonate and to study their influence on the crystallization pathway. Bioactive glasses and a model material for mineral dust are shown to significantly lower the induction time, highlighting the importance of both surface chemistry and topography on the nucleating efficiency of a surface. This technology is also extremely versatile, and could be used to study dynamic reactions with a wide range of synchrotron‐based techniques
Collusion through Joint R&D: An Empirical Assessment
This paper tests whether upstream R&D cooperation leads to downstream collusion. We consider an oligopolistic setting where firms enter in research joint ventures (RJVs) to lower production costs or coordinate on collusion in the product market. We show that a sufficient condition for identifying collusive behavior is a decline in the market share of RJV-participating firms, which is also necessary and sufficient for a decrease in consumer welfare. Using information from the US National Cooperation Research Act, we estimate a market share equation correcting for the endogeneity of RJV participation and R&D expenditures. We find robust evidence that large networks between direct competitors – created through firms being members in several RJVs at the same time – are conducive to collusive outcomes in the product market which reduce consumer welfare. By contrast, RJVs among non-competitors are efficiency enhancing
Wake up, wake up! It's me! It's my life! patient narratives on person-centeredness in the integrated care context: a qualitative study
Person-centered care emphasizes a holistic, humanistic approach that puts patients first, at the center of medical care. Person-centeredness is also considered a core element of integrated care. Yet typologies of integrated care mainly describe how patients fit within integrated services, rather than how services fit into the patient's world. Patient-centeredness has been commonly defined through physician's behaviors aimed at delivering patient-centered care. Yet, it is unclear how 'person-centeredness' is realized in integrated care through the patient voice. We aimed to explore patient narratives of person-centeredness in the integrated care context
On the role of theory and modeling in neuroscience
In recent years, the field of neuroscience has gone through rapid
experimental advances and extensive use of quantitative and computational
methods. This accelerating growth has created a need for methodological
analysis of the role of theory and the modeling approaches currently used in
this field. Toward that end, we start from the general view that the primary
role of science is to solve empirical problems, and that it does so by
developing theories that can account for phenomena within their domain of
application. We propose a commonly-used set of terms - descriptive,
mechanistic, and normative - as methodological designations that refer to the
kind of problem a theory is intended to solve. Further, we find that models of
each kind play distinct roles in defining and bridging the multiple levels of
abstraction necessary to account for any neuroscientific phenomenon. We then
discuss how models play an important role to connect theory and experiment, and
note the importance of well-defined translation functions between them.
Furthermore, we describe how models themselves can be used as a form of
experiment to test and develop theories. This report is the summary of a
discussion initiated at the conference Present and Future Theoretical
Frameworks in Neuroscience, which we hope will contribute to a much-needed
discussion in the neuroscientific community
Environmental Factors in the Relapse and Recurrence of Inflammatory Bowel Disease:A Review of the Literature
The causes of relapse in patients with Crohn's disease (CD) and ulcerative colitis (UC) are largely unknown. This paper reviews the epidemiological and clinical data on how medications (non-steroidal anti-inflammatory drugs, estrogens and antibiotics), lifestyle factors (smoking, psychological stress, diet and air pollution) may precipitate clinical relapses and recurrence. Potential biological mechanisms include: increasing thrombotic tendency, imbalances in prostaglandin synthesis, alterations in the composition of gut microbiota, and mucosal damage causing increased permeability
Explicit vs. tacit collusion: the impact of communication in oligopoly experiments
publication-status: Acceptedtypes: ArticlePre-print draft published as working paper by Düsseldorf Institute for Competition Economics (DICE). NOTICE: this is the author’s version of a work that was accepted for publication in European Economic Review. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in European Economic Review, Elsevier, vol. 56(8), 2012, DOI: 10.1016/j.euroecorev.2012.09.002We explore the difference between explicit and tacit collusion by investigating the
impact communication has in experimental markets. For Bertrand oligopolies with
various numbers of firms, we compare pricing behavior with and without the possibility
to communicate among firms. We find strong evidence that talking helps to obtain
higher pro fits for any number of firms, however, the gain from communicating is nonmonotonic
in the number of firms, with medium-sized industries having the largest
additional profi t from talking. We also find that industries continue to collude successfully
after communication is disabled. Communication supports firms in coordinating
on collusive pricing schemes, and it is also used for conflict mediation.Financial support from Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledge
Determinants of self-reporting under the European corporate leniency program
We empirically investigate the determinants of self-reporting under the European corporate
leniency program. Applying a data set consisting of 442 firm groups that participated in 76
cartels decided by the European Commission between 2000 and 2011, we find that the
probability of a firm becoming the chief witness increases with its character as repeat
offender, the size of the expected basic fine, the number of countries active in one group as
well as the size of the firm’s share in the cartelized market. Our results have important
implications for an effective prosecution of anti-cartel law infringers
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