1,458 research outputs found
Theoretical analysis of reflected ray error from surface slope error and their application to the solar concentrated collector
Surface slope error of concentrator is one of the main factors to influence
the performance of the solar concentrated collectors which cause deviation of
reflected ray and reduce the intercepted radiation. This paper presents the
general equation to calculate the standard deviation of reflected ray error
from slope error through geometry optics, applying the equation to calculate
the standard deviation of reflected ray error for 5 kinds of solar concentrated
reflector, provide typical results. The results indicate that the slope error
is transferred to the reflected ray in more than 2 folds when the incidence
angle is more than 0. The equation for reflected ray error is generally fit for
all reflection surfaces, and can also be applied to control the error in
designing an abaxial optical system.Comment: 13 pages, 7 figure
Theoretical analysis of error transfer from surface slope to refractive ray and their application to the solar concentrated collector
This paper presents the general equation to calculate the standard deviation
of reflected ray error from optical error through geometry optics, applying the
equation to calculate the standard deviation of reflected ray error for 8 kinds
of solar concentrated reflector, provide typical results. The results indicate
that the slope errors in two direction is transferred to any one direction of
the focus ray when the incidence angle is more than 0 for solar trough and
heliostats reflector; for point focus Fresnel lens, point focus parabolic glass
mirror, line focus parabolic galss mirror, the error transferring coefficient
from optical to focus ray will increase when the rim angle increase; for TIR-R
concentrator, it will decrease; for glass heliostat, it relates to the
incidence angle and azimuth of the reflecting point. Keywords: optic error,
standard deviation, refractive ray error, concentrated solar collectorComment: 16 pages 10 figure
An Eye Tracking Study into the Effects of Graph Layout
Graphs are typically visualized as node-link diagrams. Although there is a
fair amount of research focusing on crossing minimization to improve
readability, little attention has been paid on how to handle crossings when
they are an essential part of the final visualizations. This requires us to
understand how people read graphs and how crossings affect reading performance.
As an initial step to this end, a preliminary eye tracking experiment was
conducted. The specific purpose of this experiment was to test the effects of
crossing angles and geometric-path tendency on eye movements and performance.
Sixteen subjects performed both path search and node locating tasks with six
drawings. The results showed that small angles can slow down and trigger extra
eye movements, causing delays for path search tasks, whereas crossings have
little impact on node locating tasks. Geometric-path tendency indicates that a
path between two nodes can become harder to follow when many branches of the
path go toward the target node. The insights obtained are discussed with a view
to further confirmation in future work
An Aggregation-Based Overall Quality Measurement for Visualization
Aesthetics are often used to evaluate the quality of graph drawings. However,
the existing aesthetic criteria are useful in judging the extents to which a
drawing conforms to particular drawing rules. They have limitations in
evaluating overall quality. Currently the overall quality of graph drawings is
mainly evaluated based on personal judgments and user studies. Personal
judgments are not reliable, while user studies can be costly to run. Therefore,
there is a need for a direct measure of overall quality. This measure can be
used by visualization designers to quickly compare the quality of drawings at
hand at the design stage and make decisions accordingly. In an attempt to meet
this need, we propose a measure that measures overall quality based on
aggregation of individual aesthetic criteria. We present a user study that
validates this measure and demonstrates its capacity in predicting the
performance of human graph comprehension. The implications of the proposed
measure for future research are discussed
Error Compensated Quantized SGD and its Applications to Large-scale Distributed Optimization
Large-scale distributed optimization is of great importance in various
applications. For data-parallel based distributed learning, the inter-node
gradient communication often becomes the performance bottleneck. In this paper,
we propose the error compensated quantized stochastic gradient descent
algorithm to improve the training efficiency. Local gradients are quantized to
reduce the communication overhead, and accumulated quantization error is
utilized to speed up the convergence. Furthermore, we present theoretical
analysis on the convergence behaviour, and demonstrate its advantage over
competitors. Extensive experiments indicate that our algorithm can compress
gradients by a factor of up to two magnitudes without performance degradation.Comment: Accepted by ICML 201
Prediction and optimization of the performance of parabolic solar dish concentrator with sphere receiver using analytical function
Parabolic solar dish concentrator with sphere receiver is less studied. We
present an analytic function to calculate the intercept factor of the system
with real sun bright distribution and Gaussian distribution, the results
indicate that the intercept factor is related to the rim angle of reflector and
the ratio of open angle of receiver at the top of reflector to optical error
when the optical error is larger than or equal to 5 mrad, but is related to the
rim angle, open angle and optical error in less than 5 mrad optical error.
Furthermore we propose a quick process to optimize the system to provide the
maximum solar energy to net heat efficiency for different optical error under
typical condition. The results indicate that the parabolic solar dish
concentrator with sphere receiver has rather high solar energy to net heat
efficiency which is 20% more than solar trough and tower system including
higher cosine factor and lower heat loss of the receiver.Comment: 15 pages, 10 figures; Corresponding author: Weidong Huang, email:
[email protected]
Metal-insulator transition in VO: a Peierls-Mott-Hubbard mechanism
The electronic structure of VO is studied in the frameworks of local
density approximation (LDA) and LDA+ to give a quantitative description of
the metal-insulator (MI) transition in this system. It is found that, both
structural distortion and the local Coulomb interaction, play important roles
in the transition. An optical gap, comparable to the experimental value has
been obtained in the monoclinic structure by using the LDA+ method. Based on
our results, we believe that both, the Peierls and the Mott-Hubbard mechanism,
are essential for a description of the MI transition in this system.Comment: 11 pages, 6 figure
Tuning electronic heat transport in graphene/metal heterostructures with ultralow thermal conductivity
Prior ultralow thermal conductivity materials are not suitable for
thermoelectric applications due to the limited electronic transport in the
materials. Here, we present a new class of ultralow thermal conductivity
materials with substantial electronic heat transport. Our samples are
graphene/metal heterostructures of transferred graphene and ultrathin metal
films (Pd, Au and Ni) deposited by either thermal evaporation or rf magnetron
sputtering. For the evaporated samples, we achieve an ultralow thermal
conductivity of 0.06 W m-1 K-1, with phonons as the dominant heat carriers. The
ultralow thermal conductivity is due to a huge disparity in phonon energy in
graphene and metals. Interestingly, for the sputtered samples, we find that
about 50 % of heat is carried by electrons, even when thermal conductivity is
about 0.1 W m-1 K-1. We attribute the electronic contribution to transmission
of electrons across atomic-scale pinholes in graphene. With the ultralow
thermal conductivity and substantial electronic transport, the new materials
could be explored for thermoelectric applications
A Force-Directed Method for Large Crossing Angle Graph Drawing
Recent empirical research has indicated that human graph reading performance
improves when crossing angles increase. However, crossing angle has not been
used as an aesthetic criterion for graph drawing algorithms so far. In this
paper, we introduce a force-directed method that aims to construct graph
drawings with large crossing angles. Experiments indicate that our method
significantly increases crossing angles. Surprisingly, the experimental results
further demonstrate that the resulting drawings produced by our method have
fewer edge crossings, a shorter total edge length and more uniform edge
lengths, compared to classical spring algorithms
A new method to calculate the Total Fertility Rate from the number of birth
The standard methods to calculate the Total Fertility Rate require the
reliable age-specific fertility rate including birth data and the related
age-specific women's population data. Historically, the number of births was
often not counted according to the age of the mother, so it is difficult to
estimate the historical total fertility rate with the standard methods. Many
empirical methods have been proposed, but their application is limited to
specific period and place. This paper deduces a new method for calculating the
total fertility rate from the number of birth and the population of women at
childbearing age, can be applied to most of cases. The relative error is
usually less than 5%. It is easier to calculate TFR, and may be applied to
obtain more TFRs for the history.Comment: 15 pages, 4 figure
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