60 research outputs found
Microcavity controlled coupling of excitonic qubits
Controlled non-local energy and coherence transfer enables light harvesting
in photosynthesis and non-local logical operations in quantum computing. The
most relevant mechanism of coherent coupling of distant qubits is coupling via
the electromagnetic field. Here, we demonstrate the controlled coherent
coupling of spatially separated excitonic qubits via the photon mode of a solid
state microresonator. This is revealed by two-dimensional spectroscopy of the
sample's coherent response, a sensitive and selective probe of the coherent
coupling. The experimental results are quantitatively described by a rigorous
theory of the cavity mediated coupling within a cluster of quantum dots
excitons. Having demonstrated this mechanism, it can be used in extended
coupling channels - sculptured, for instance, in photonic crystal cavities - to
enable a long-range, non-local wiring up of individual emitters in solids
Groupwise Multimodal Image Registration using Joint Total Variation
In medical imaging it is common practice to acquire a wide range of
modalities (MRI, CT, PET, etc.), to highlight different structures or
pathologies. As patient movement between scans or scanning session is
unavoidable, registration is often an essential step before any subsequent
image analysis. In this paper, we introduce a cost function based on joint
total variation for such multimodal image registration. This cost function has
the advantage of enabling principled, groupwise alignment of multiple images,
whilst being insensitive to strong intensity non-uniformities. We evaluate our
algorithm on rigidly aligning both simulated and real 3D brain scans. This
validation shows robustness to strong intensity non-uniformities and low
registration errors for CT/PET to MRI alignment. Our implementation is publicly
available at https://github.com/brudfors/coregistration-njtv
On Simulated Annealing and the Construction of Linear Spline Approximations for Scattered Data
Abstract. We describe a method to create optimal linear spline approximations to arbitrary functions of one or two variables, given as scattered data without known connectivity. We start with an initial approximation consisting of a fixed number of vertices and improve this approximation by choosing different ver-tices, governed by a simulated annealing algorithm. In the case of one variable, the approximation is defined by line segments; in the case of two variables, the vertices are connected to define a Delaunay triangulation of the selected subset of sites in the plane. In a second version of this algorithm, specifically designed for the bivariate case, we choose vertex sets and also change the triangulation to achieve both optimal vertex placement and optimal triangulation. We then cre-ate a hierarchy of linear spline approximations, each one being a superset of all lower-resolution ones.
Quasi-Normal Modes of Stars and Black Holes
Perturbations of stars and black holes have been one of the main topics of
relativistic astrophysics for the last few decades. They are of particular
importance today, because of their relevance to gravitational wave astronomy.
In this review we present the theory of quasi-normal modes of compact objects
from both the mathematical and astrophysical points of view. The discussion
includes perturbations of black holes (Schwarzschild, Reissner-Nordstr\"om,
Kerr and Kerr-Newman) and relativistic stars (non-rotating and
slowly-rotating). The properties of the various families of quasi-normal modes
are described, and numerical techniques for calculating quasi-normal modes
reviewed. The successes, as well as the limits, of perturbation theory are
presented, and its role in the emerging era of numerical relativity and
supercomputers is discussed.Comment: 74 pages, 7 figures, Review article for "Living Reviews in
Relativity
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
Acromioclavicular joint reconstruction with coracoacromial ligament transfer using the docking technique
<p>Abstract</p> <p>Background</p> <p>Symptomatic Acromioclavicular (AC) dislocations have historically been surgically treated with Coracoclavicular (CC) ligament reconstruction with transfer of the Coracoacromial (CA) ligament. Tensioning the CA ligament is the key to success.</p> <p>Methods</p> <p>Seventeen patients with chronic, symptomatic Type III AC joint or acute Type IV and V injuries were treated surgically. The distal clavicle was resected and stabilized with CC ligament reconstruction using the CA ligament. The CA ligament was passed into the medullary canal and tensioned, using a modified 'docking' technique. Average follow-up was 29 months (range 12–57).</p> <p>Results</p> <p>Postoperative ASES and pain significantly improved in all patients (p = 0.001). Radiographically, 16 (94%) maintained reduction, and only 1 (6%) had a recurrent dislocation when he returned to karate 3 months postoperatively. His ultimate clinical outcome was excellent.</p> <p>Conclusion</p> <p>The docking procedure allows for tensioning of the transferred CA ligament and healing of the ligament in an intramedullary bone tunnel. Excellent clinical results were achieved, decreasing the risk of recurrent distal clavicle instability.</p
Overexpression of c-erbB2 is an independent marker of resistance to endocrine therapy in advanced breast cancer
The present study investigated the interaction between c-erbB2 overexpression and the response to first-line endocrine therapy in patients with advanced breast cancer. The primary tumours of 241 patients who were treated at first relapse with endocrine therapy were assessed for overexpression of c-erbB2 by immunohistochemistry. c-erbB2 was overexpressed in 76 (32%) of primary breast cancers and did not correlate with any other prognostic factor. The overall response to treatment and time to progression were significantly lower in patients with c-erbB2-positive tumours compared to those that were c-erbB2-negative (38% vs 56%, P = 0.02; and 4.1 months vs 8.7 months, P < 0.001, respectively). In multivariate analysis, c-erbB2 status was the most significant predictive factor for a short time to progression (P = 0.0009). In patients with ER-positive primary tumours treated at relapse with tamoxifen (n = 170), overexpression of c-erbB2 was associated with a significantly shorter time to progression (5.5 months vs 11.2 months, P < 0.001). In conclusion, overexpression of c-erbB2 in the primary tumour is an independent marker of relative resistance to first-line endocrine therapy in patients with advanced breast cancer. In patients with ER-positive primary tumours, the overexpression of c-erbB2 defines a subgroup less likely to respond to endocrine therapy. © 1999 Cancer Research Campaig
Structure and evolution of the gorilla and orangutan growth hormone loci
In primates, the unigenic growth hormone (GH) locus of prosimians, expressed primarily in the anterior pituitary, evolved by gene duplications, independently in New World Monkeys (NWM) and Old World Monkeys (OWMs)/apes, to give complex clusters of genes expressed in the pituitary and placenta. In human and chimpanzee, the GH locus comprises five genes, GH-N being expressed as pituitary GH, whereas GH-V (placental GH) and CSHs (chorionic somatomammotropins) are expressed (in human and probably chimpanzee) in the placenta; the CSHs comprise CSH-A, CSH-B and the aberrant CSH-L (possibly a pseudogene) in human, and CSH-A1, CSH-A2 and CSH-B in chimpanzee. Here the GH locus in two additional great apes, gorilla (Gorilla gorilla gorilla) and orangutan (Pongo abelii), is shown to contain six and four GH-like genes respectively. The gorilla locus possesses six potentially expressed genes, gGH-N, gGH-V and four gCSHs, whereas the orangutan locus has just three functional genes, oGH-N, oGH-V and oCSH-B, plus a pseudogene, oCSH-L. Analysis of regulatory sequences, including promoter, enhancer and P-elements, shows significant variation; in particular the proximal Pit-1 element of GH-V genes differs markedly from that of other genes in the cluster. Phylogenetic analysis shows that the initial gene duplication led to distinct GH-like and CSH-like genes, and that a second duplication provided separate GH-N and GH-V. However, evolution of the CSH-like genes remains unclear. Rapid adaptive evolution gave rise to the distinct CSHs, after the first duplication, and to GH-V after the second duplication. Analysis of transcriptomic databases derived from gorilla tissues establishes that the gGH-N, gGH-V and several gCSH genes are expressed, but the significance of the many CSH genes in gorilla remains unclear
Coalition-structured governance improves cooperation to provide public goods
While the benefits of common and public goods are shared, they tend to be scarce when contributions are provided voluntarily. Failure to cooperate in the provision or preservation of these goods is fundamental to sustainability challenges, ranging from local fisheries to global climate change. In the real world, such cooperative dilemmas occur in multiple interactions with complex strategic interests and frequently without full information. We argue that voluntary cooperation enabled across overlapping coalitions (akin to polycentricity) not only facilitates a higher generation of non-excludable public goods, but it may also allow evolution toward a more cooperative, stable, and inclusive approach to governance. Contrary to any previous study, we show that these merits of multi-coalition governance are far more general than the singular examples occurring in the literature, and they are robust under diverse conditions of excludability, congestion of the non-excludable public good, and arbitrary shapes of the return-to-contribution function. We first confirm the intuition that a single coalition without enforcement and with players pursuing their self-interest without knowledge of returns to contribution is prone to cooperative failure. Next, we demonstrate that the same pessimistic model but with a multi-coalition structure of governance experiences relatively higher cooperation by enabling recognition of marginal gains of cooperation in the game at stake. In the absence of enforcement, public-goods regimes that evolve through a proliferation of voluntary cooperative forums can maintain and increase cooperation more successfully than singular, inclusive regimes.Supported by US Defense Advanced Research Projects Agency (D17AC00005), National Science Foundation grant GEO-1211972, and Fundacao para a Ciencia e Tecnologia (FCT) through grants PTDC/MAT/STA/3358/2014, PTDC/EEI-SII/5081/2014, and UID/BIA/04050/2013. P.M.H. was supported by the Walbridge Fund at the Princeton Environmental Institute
Exosome-Producing Follicle Associated Epithelium Is Not Involved in Uptake of PrPd from the Gut of Sheep (Ovis aries): An Ultrastructural Study
In natural or experimental oral scrapie infection of sheep, disease associated prion protein (PrPd) often first accumulates in Peyer's patch (PP) follicles. The route by which infectivity reaches the follicles is unknown, however, intestinal epithelial cells may participate in intestinal antigenic presentation by delivering exosomes as vehicles of luminal antigens. In a previous study using an intestinal loop model, following inoculation of scrapie brain homogenate, inoculum associated PrPd was detected by light microscopy shortly (15 minutes to 3.5 hours) after inoculation in the villous lacteals and sub-mucosal lymphatics. No PrPd was located within the follicle-associated epithelium (FAE), sub-FAE domes or the PP follicles. To evaluate this gut loop model and the transportation routes in more detail, we used electron microscopy (EM) to study intestinal tissues exposed to scrapie or control homogenates for 15 minutes to 10 days. In addition, immuno-EM was used to investigate whether exosomes produced in the FAE may possess small amounts of PrPd that were not detectable by light microscopy. This study showed that the integrity of the intestinal epithelium was sustained in the intestinal loop model. Despite prominent transcytotic activity and exosome release from the FAE of the ileal PP in sheep, these structures were not associated with transportation of PrPd across the mucosa. The study did not determine how infectivity reaches the follicles of PPs. The possibility that the infectious agent is transported across the FAE remains a possibility if it occurs in a form that is undetectable by the methods used in this study. Infectivity may also be transported via lymph to the blood and further to all other lymphoid tissues including the PP follicles, but the early presence of PrPd in the PP follicles during scrapie infection argues against such a mechanism
- …