42,519 research outputs found
Measurements and computational analysis of heat transfer and flow in a simulated turbine blade internal cooling passage
Visual and quantitative information was obtained on heat transfer and flow in a branched-duct test section that had several significant features of an internal cooling passage of a turbine blade. The objective of this study was to generate a set of experimental data that could be used to validate computer codes for internal cooling systems. Surface heat transfer coefficients and entrance flow conditions were measured at entrance Reynolds numbers of 45,000, 335,000, and 726,000. The heat transfer data were obtained using an Inconel heater sheet attached to the surface and coated with liquid crystals. Visual and quantitative flow field results using particle image velocimetry were also obtained for a plane at mid channel height for a Reynolds number of 45,000. The flow was seeded with polystyrene particles and illuminated by a laser light sheet. Computational results were determined for the same configurations and at matching Reynolds numbers; these surface heat transfer coefficients and flow velocities were computed with a commercially available code. The experimental and computational results were compared. Although some general trends did agree, there were inconsistencies in the temperature patterns as well as in the numerical results. These inconsistencies strongly suggest the need for further computational studies on complicated geometries such as the one studied
Seasonal and spatial dynamics of the primary vector of plasmodium knowlesi within a major transmission focus in Sabah, Malaysia
Background
The simian malaria parasite Plasmodium knowlesi is emerging as a public health problem in Southeast Asia, particularly in Malaysian Borneo where it now accounts for the greatest burden of malaria cases and deaths. Control is hindered by limited understanding of the ecology of potential vector species.
Methodology/Principal Findings
We conducted a one year longitudinal study of P. knowlesi vectors in three sites within an endemic area of Sabah, Malaysia. All mosquitoes were captured using human landing catch. Anopheles mosquitoes were dissected to determine, oocyst, sporozoites and parous rate. Anopheles balabacensis is confirmed as the primary vector of. P. knowlesi (using nested PCR) in Sabah for the first time. Vector densities were significantly higher and more seasonally variable in the village than forest or small scale farming site. However An. balabacensis survival and P. knowlesi infection rates were highest in forest and small scale farm sites. Anopheles balabacensis mostly bites humans outdoors in the early evening between 1800 to 2000hrs.
Conclusions/Significance
This study indicates transmission is unlikely to be prevented by bednets. This combined with its high vectorial capacity poses a threat to malaria elimination programmes within the region.
Author Summary
The first natural infection of Plasmodium knowlesi was reported 40 years ago. At that time it was perceived that the infection would not affect humans. However, now P. knowlesi is the predominant malaria species (38% of the cases) infecting people in Malaysia and is a notable obstacle to malaria elimination in the country. Plasmodium knowlesi has also been reported from all countries in Southeast Asia with the exception of Lao PDR and Timor Leste. In Sabah, Malaysian Borneo cases of human P. knowlesi are increasing. Thus, a comprehensive understanding of the bionomics of the vectors is required so as to enable proper control strategies. Here, we conducted a longitudinal study in Kudat district, Sabah, to determine and characterize the vectors of P. knowlesi within this transmission foci. Anopheles balabacensis was the predominant mosquito in all study sites and is confirmed as vector for P. knowlesi and other simian malaria parasites. The peak biting time was in the early part of the evening between1800 to 2000. Thus, breaking the chain of transmission is an extremely challenging task for the malaria elimination programme
Feature Generation by Convolutional Neural Network for Click-Through Rate Prediction
Click-Through Rate prediction is an important task in recommender systems,
which aims to estimate the probability of a user to click on a given item.
Recently, many deep models have been proposed to learn low-order and high-order
feature interactions from original features. However, since useful interactions
are always sparse, it is difficult for DNN to learn them effectively under a
large number of parameters. In real scenarios, artificial features are able to
improve the performance of deep models (such as Wide & Deep Learning), but
feature engineering is expensive and requires domain knowledge, making it
impractical in different scenarios. Therefore, it is necessary to augment
feature space automatically. In this paper, We propose a novel Feature
Generation by Convolutional Neural Network (FGCNN) model with two components:
Feature Generation and Deep Classifier. Feature Generation leverages the
strength of CNN to generate local patterns and recombine them to generate new
features. Deep Classifier adopts the structure of IPNN to learn interactions
from the augmented feature space. Experimental results on three large-scale
datasets show that FGCNN significantly outperforms nine state-of-the-art
models. Moreover, when applying some state-of-the-art models as Deep
Classifier, better performance is always achieved, showing the great
compatibility of our FGCNN model. This work explores a novel direction for CTR
predictions: it is quite useful to reduce the learning difficulties of DNN by
automatically identifying important features
Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64
The Epoch of Reionization (EoR) is an uncharted era in our Universe's history
during which the birth of the first stars and galaxies led to the ionization of
neutral hydrogen in the intergalactic medium. There are many experiments
investigating the EoR by tracing the 21cm line of neutral hydrogen. Because
this signal is very faint and difficult to isolate, it is crucial to develop
analysis techniques that maximize sensitivity and suppress contaminants in
data. It is also imperative to understand the trade-offs between different
analysis methods and their effects on power spectrum estimates. Specifically,
with a statistical power spectrum detection in HERA's foreseeable future, it
has become increasingly important to understand how certain analysis choices
can lead to the loss of the EoR signal. In this paper, we focus on signal loss
associated with power spectrum estimation. We describe the origin of this loss
using both toy models and data taken by the 64-element configuration of the
Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER).
In particular, we highlight how detailed investigations of signal loss have led
to a revised, higher 21cm power spectrum upper limit from PAPER-64.
Additionally, we summarize errors associated with power spectrum error
estimation that were previously unaccounted for. We focus on a subset of
PAPER-64 data in this paper; revised power spectrum limits from the PAPER
experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.)
and supersede results from previously published PAPER analyses.Comment: 25 pages, 18 figures, Accepted by Ap
A "poor man's" approach for high-resolution three-dimensional topology optimization of natural convection problems
This paper treats topology optimization of natural convection problems. A
simplified model is suggested to describe the flow of an incompressible fluid
in steady state conditions, similar to Darcy's law for fluid flow in porous
media. The equations for the fluid flow are coupled to the thermal
convection-diffusion equation through the Boussinesq approximation. The coupled
non-linear system of equations is discretized with stabilized finite elements
and solved in a parallel framework that allows for the optimization of high
resolution three-dimensional problems. A density-based topology optimization
approach is used, where a two-material interpolation scheme is applied to both
the permeability and conductivity of the distributed material. Due to the
simplified model, the proposed methodology allows for a significant reduction
of the computational effort required in the optimization. At the same time, it
is significantly more accurate than even simpler models that rely on convection
boundary conditions based on Newton's law of cooling. The methodology discussed
herein is applied to the optimization-based design of three-dimensional heat
sinks. The final designs are formally compared with results of previous work
obtained from solving the full set of Navier-Stokes equations. The results are
compared in terms of performance of the optimized designs and computational
cost. The computational time is shown to be decreased to around 5-20% in terms
of core-hours, allowing for the possibility of generating an optimized design
during the workday on a small computational cluster and overnight on a high-end
desktop
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