765 research outputs found
Simulations and cosmological inference: A statistical model for power spectra means and covariances
We describe an approximate statistical model for the sample variance
distribution of the non-linear matter power spectrum that can be calibrated
from limited numbers of simulations. Our model retains the common assumption of
a multivariate Normal distribution for the power spectrum band powers, but
takes full account of the (parameter dependent) power spectrum covariance. The
model is calibrated using an extension of the framework in Habib et al. (2007)
to train Gaussian processes for the power spectrum mean and covariance given a
set of simulation runs over a hypercube in parameter space. We demonstrate the
performance of this machinery by estimating the parameters of a power-law model
for the power spectrum. Within this framework, our calibrated sample variance
distribution is robust to errors in the estimated covariance and shows rapid
convergence of the posterior parameter constraints with the number of training
simulations.Comment: 14 pages, 3 figures, matches final version published in PR
Robustness of Cosmological Simulations I: Large Scale Structure
The gravitationally-driven evolution of cold dark matter dominates the
formation of structure in the Universe over a wide range of length scales.
While the longest scales can be treated by perturbation theory, a fully
quantitative understanding of nonlinear effects requires the application of
large-scale particle simulation methods. Additionally, precision predictions
for next-generation observations, such as weak gravitational lensing, can only
be obtained from numerical simulations. In this paper, we compare results from
several N-body codes using test problems and a diverse set of diagnostics,
focusing on a medium resolution regime appropriate for studying many
observationally relevant aspects of structure formation. Our conclusions are
that -- despite the use of different algorithms and error-control methodologies
-- overall, the codes yield consistent results. The agreement over a wide range
of scales for the cosmological tests is test-dependent. In the best cases, it
is at the 5% level or better, however, for other cases it can be significantly
larger than 10%. These include the halo mass function at low masses and the
mass power spectrum at small scales. While there exist explanations for most of
the discrepancies, our results point to the need for significant improvement in
N-body errors and their understanding to match the precision of near-future
observations. The simulation results, including halo catalogs, and initial
conditions used, are publicly available.Comment: 32 pages, 53 figures, data from the simulations is available at
http://t8web.lanl.gov/people/heitmann/arxiv, accepted for publication in
ApJS, several minor revisions, reference added, main conclusions unchange
Improving quality of life in patients with end-stage age-related macular degeneration: focus on miniature ocular implants
Low vision devices in the past have been mainly extraocular. There are now four new devices in different stages of development and implementation that are currently available. Three of them, the Implantable Miniature Telescope (IMT, VisionCare Ophthalmic Technologies, Saratoga, CA), Intraocular Lens for Visually Impaired People (IOL-VIP, IOL-VIP System, Soleko, Pontecorvo, Italy), and Lipschitz Mirror Implant (LMI, Optolight Vision Technology, Herzlia, Israel) are implanted into the anterior segment while the Argus II (Second Sight Medical Products, Sylmar, CA) is implanted into the posterior segment. The goal of these devices is to increase the patient quality of life which has been measured by Visual Functioning Questionnaire (VFQ) scales. The IMT is the only device that has been shown to increase the VFQ score by seven points at 6 months compared to baseline. It is the only FDA-approved device in the US while the Argus has been approved in Europe. Each of these prosthetics has potential benefits for patients
Deep learning classification of chest x-ray images
We propose a deep learning based method for classification of commonly
occurring pathologies in chest X-ray images. The vast number of publicly
available chest X-ray images provides the data necessary for successfully
employing deep learning methodologies to reduce the misdiagnosis of thoracic
diseases. We applied our method to the classification of two example
pathologies, pulmonary nodules and cardiomegaly, and we compared the
performance of our method to three existing methods. The results show an
improvement in AUC for detection of nodules and cardiomegaly compared to the
existing methods.Comment: 4 pages, 4 figures, 2 tables, conference , SSIAI 202
Novel hepatocyte growth factor (HGF) binding domains on fibronectin and vitronectin coordinate a distinct and amplified Met-integrin induced signalling pathway in endothelial cells
BACKGROUND: The growth of new blood vessels in adult life requires the initiation of endothelial cell migration and proliferation from pre-existing vessels in addition to the recruitment and differentiation of circulating endothelial progenitor cells. Signals emanating from growth factors and the extracellular matrix are important in regulating these processes. RESULTS: Here we report that fibronectin (FN) and vitronectin (VN) modulate the responses of endothelial cells to HGF (Scatter Factor), an important pro-angiogenic mediator. Novel binding sites for HGF were identified on both FN and VN that generate molecular complexes with enhanced biological activity and these were identified in the supernatants of degranulated platelet suspensions implicating their release and formation in vivo. In the absence of co-stimulation with an ECM glycoprotein, HGF could not promote endothelial cell migration but retained the capacity to induce a proliferative response utilising the Map kinase pathway. Through promoting Met-Integrin association, HGF-FN and HGF-VN complexes coordinated and enhanced endothelial cell migration through activation of the PI-3 kinase pathway involving a Ras-dependent mechanism whereas a Ras-independent and attenuated migratory response was promoted by co-stimulation of cells with HGF and a non-binding partner ECM glycoprotein such as collagen-1. CONCLUSIONS: These studies identify a novel mechanism and pathway of HGF signalling in endothelial cells involving cooperation between Met and integrins in a Ras dependent manner. These findings have implications for the regulation of neovascularization in both health and disease
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NetServ: Reviving Active Networks
In 1996, Tennenhouse and Wetherall proposed active networks, where users can inject code modules into network nodes. The proposal sparked intense debate and follow-on research, but ultimately failed to win over the networking community. Fifteen years later, the problems that motivated the active networks proposal persist. We call for a revival of active networks. We present NetServ, a fully integrated active network system that provides all the necessary functionality to be deployable, addressing the core problems that prevented the practical success of earlier approaches. We make the following contributions. We present a hybrid approach to active networking, which combines the best qualities from the two extreme approaches — integrated and discrete. We built a working system that strikes the right balance between security and performance by leveraging current technologies. We suggest an economic model based on NetServ between content providers and ISPs. We built four applications to illustrate the model
Identifying the origin of delayed electroluminescence in a polariton organic light-emitting diode
Modifying the energy landscape of existing molecular emitters is an
attractive challenge with favourable outcomes in chemistry and organic
optoelectronic research. It has recently been explored through strong
light-matter coupling studies where the organic emitters were placed in an
optical cavity. Nonetheless, a debate revolves around whether the observed
change in the material properties represents novel coupled system dynamics or
the unmasking of pre-existing material properties induced by light-matter
interactions. Here, for the first time, we examined the effect of strong
coupling in polariton organic light-emitting diodes via time-resolved
electroluminescence studies. We accompanied our experimental analysis with
theoretical fits using a model of coupled rate equations accounting for all
major mechanisms that can result in delayed electroluminescence in organic
emitters. We found that in our devices the delayed electroluminescence was
dominated by emission from trapped charges and this mechanism remained
unmodified in the presence of strong coupling.Comment: 11 pages + 8 supp pages, 4 figures + 8 supp figure
NetServ Framework Design and Implementation 1.0
Eyeball ISPs today are under-utilizing an important asset: edge routers. We present NetServ, a programmable node architecture aimed at turning edge routers into distributed service hosting platforms. This allows ISPs to allocate router resources to content publishers and application service pro\-vi\-ders motivated to deploy content and services at the network edge. This model provides important benefits over currently available solutions like CDN. Content and services can be brought closer to end users by dynamically installing and removing custom modules as needed throughout the network. Unlike previous programmable router proposals which focused on customizing features of a router, NetServ focuses on deploying content and services. All our design decisions reflect this change in focus. We set three main design goals: a wide-area deployment, a multi-user execution environment, and a clear economic benefit. We built a prototype using Linux, NSIS signaling, and the Java OSGi framework. We also implemented four prototype applications: ActiveCDN provides publisher-specific content distribution and processing; KeepAlive Responder and Media Relay reduce the infrastructure needs of telephony providers; and Overload Control makes it possible to deploy more flexible algorithms to handle excessive traffic
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