935 research outputs found
Solar Potential Analysis of Rooftops Using Satellite Imagery
Solar energy is one of the most important sources of renewable energy and the
cleanest form of energy. In India, where solar energy could produce power
around trillion kilowatt-hours in a year, our country is only able to produce
power of around in gigawatts only. Many people are not aware of the solar
potential of their rooftop, and hence they always think that installing solar
panels is very much expensive. In this work, we introduce an approach through
which we can generate a report remotely that provides the amount of solar
potential of a building using only its latitude and longitude. We further
evaluated various types of rooftops to make our solution more robust. We also
provide an approximate area of rooftop that can be used for solar panels
placement and a visual analysis of how solar panels can be placed to maximize
the output of solar power at a location
Manin's b-constant in families
We show that the -constant (appearing in Manin's conjecture) is constant
on very general fibers of a family of algebraic varieties. If the fibers of the
family are uniruled, then we show that the -constant is constant on general
fibers.Comment: 16 page
Counterexamples to Mercat's Conjecture
For any n>3, we provide examples of curves lying on K3 surfaces and vector
bundles on those curves which invalidate Mercat's conjecture for rank n
bundles.Comment: 6 pages, Proof of a lemma added in Section 2, Slight change in the
proof of the main theorem, added reference
Manin's Conjecture and the Fujita invariant of finite covers
We prove a conjecture of Lehmann-Tanimoto about the behaviour of the Fujita
invariant (or -constant appearing in Manin's conjecture) under pull-back to
generically finite covers. As a consequence we obtain results about geometric
consistency of Manin's conjecture.Comment: Typos correcte
A Fourier extension based numerical integration scheme for fast and high-order approximation of convolutions with weakly singular kernels
Computationally efficient numerical methods for high-order approximations of
convolution integrals involving weakly singular kernels find many practical
applications including those in the development of fast quadrature methods for
numerical solution of integral equations. Most fast techniques in this
direction utilize uniform grid discretizations of the integral that facilitate
the use of FFT for computations on a grid of size . In general,
however, the resulting error converges slowly with increasing when the
integrand does not have a smooth periodic extension. Such extensions, in fact,
are often discontinuous and, therefore, their approximations by truncated
Fourier series suffer from Gibb's oscillations. In this paper, we present and
analyze an scheme, based on a Fourier extension approach for
removing such unwanted oscillations, that not only converges with high-order
but is also relatively simple to implement. We include a theoretical error
analysis as well as a wide variety of numerical experiments to demonstrate its
efficacy
Bird Species Classification using Transfer Learning with Multistage Training
Bird species classification has received more and more attention in the field
of computer vision, for its promising applications in biology and environmental
studies. Recognizing bird species is difficult due to the challenges of
discriminative region localization and fine-grained feature learning. In this
paper, we have introduced a Transfer learning based method with multistage
training. We have used both Pre-Trained Mask-RCNN and an ensemble model
consisting of Inception Nets (InceptionV3 & InceptionResNetV2 ) to get
localization and species of the bird from the images respectively. Our final
model achieves an F1 score of 0.5567 or 55.67 % on the dataset provided in CVIP
2018 Challenge
Detecting 21 cm EoR Signal using Drift Scans: Correlation of Time-ordered Visibilities
We present a formalism to extract the EoR HI power spectrum for drift scans
using radio interferometers. Our main aim is to determine the coherence time
scale of time-ordered visibilities. We compute the two-point correlation
function of the HI visibilities measured at different times to address this
question. We determine, for a given baseline, the decorrelation of the
amplitude and the phase of this complex function. Our analysis uses primary
beams of four ongoing and future interferometers---PAPER, MWA, HERA, and
SKA1-Low. We identify physical processes responsible for the decorrelation of
the HI signal and isolate their impact by making suitable analytic
approximations. The decorrelation time scale of the amplitude of the
correlation function lies in the range of 2--20~minutes for baselines of
interest for the extraction of the HI signal. The phase of the correlation
function can be made small after scaling out an appropriate term, which also
causes the coherence time scale of the phase to be longer than the amplitude of
the correlation function. We find that our results are insensitive to the input
HI power spectrum and therefore they are directly applicable to the analysis of
the drift scan data. We also apply our formalism to a set of point sources and
statistically homogeneous diffuse correlated foregrounds. We find that point
sources decorrelate on a time scale much shorter than the HI signal. This
provides a novel mechanism to partially mitigate the foregrounds in a drift
scan.Comment: 22 pages and 5 figures. Accepted for publication in Ap
Random walks and forbidden minors II: A -query tester for minor-closed properties of bounded-degree graphs
Let be a graph with vertices and maximum degree . Fix some
minor-closed property (such as planarity). We say that is
-far from if one has to remove
edges to make it have . The problem of property testing
was introduced in the seminal work of Benjamini-Schramm-Shapira
(STOC 2008) that gave a tester with query complexity triply exponential in
. Levi-Ron (TALG 2015) have given the best tester to date,
with a quasipolynomial (in ) query complexity. It is an open
problem to get property testers whose query complexity is
, even for planarity.
In this paper, we resolve this open question. For any minor-closed property,
we give a tester with query complexity .
The previous line of work on (independent of , two-sided) testers is
primarily combinatorial. Our work, on the other hand, employs techniques from
spectral graph theory. This paper is a continuation of recent work of the
authors (FOCS 2018) analyzing random walk algorithms that find forbidden
minors
Finding forbidden minors in sublinear time: a -query one-sided tester for minor closed properties on bounded degree graphs
Let be an undirected, bounded degree graph with vertices. Fix a
finite graph , and suppose one must remove edges from to
make it -minor free (for some small constant ). We give an
-time randomized procedure that, with high probability, finds an
-minor in such a graph. As an application, suppose one must remove
edges from a bounded degree graph to make it planar. This
result implies an algorithm, with the same running time, that produces a
or minor in . No prior sublinear time bound was known for
this problem.
By the graph minor theorem, we get an analogous result for any minor-closed
property. Up to factors, this resolves a conjecture of
Benjamini-Schramm-Shapira (STOC 2008) on the existence of one-sided property
testers for minor-closed properties. Furthermore, our algorithm is nearly
optimal, by an lower bound of Czumaj et al (RSA 2014).
Prior to this work, the only graphs for which non-trivial one-sided
property testers were known for -minor freeness are the following: being
a forest or a cycle (Czumaj et al, RSA 2014), , -grid,
and the -circus (Fichtenberger et al, Arxiv 2017).Comment: 31 page
Approximation Algorithms for Digraph Width Parameters
Several problems that are NP-hard on general graphs are efficiently solvable
on graphs with bounded treewidth. Efforts have been made to generalize
treewidth and the related notion of pathwidth to digraphs. Directed treewidth,
DAG-width and Kelly-width are some such notions which generalize treewidth,
whereas directed pathwidth generalizes pathwidth. Each of these digraph width
measures have an associated decomposition structure.
In this paper, we present approximation algorithms for all these digraph
width parameters. In particular, we give an O(sqrt{logn})-approximation
algorithm for directed treewidth, and an O({\log}^{3/2}{n})-approximation
algorithm for directed pathwidth, DAG-width and Kelly-width. Our algorithms
construct the corresponding decompositions whose widths are within the above
mentioned approximation factors
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