35,076 research outputs found
Extensions of a result of Elekes and R\'onyai
Many problems in combinatorial geometry can be formulated in terms of curves
or surfaces containing many points of a cartesian product. In 2000, Elekes and
R\'onyai proved that if the graph of a polynomial contains points of an
cartesian product in , then the polynomial
has the form or . They used this to
prove a conjecture of Purdy which states that given two lines in
and points on each line, if the number of distinct distances between pairs
of points, one on each line, is at most , then the lines are parallel or
orthogonal. We extend the Elekes-R\'onyai Theorem to a less symmetric cartesian
product. We also extend the Elekes-R\'onyai Theorem to one dimension higher on
an cartesian product and an asymmetric cartesian
product. We give a proof of a variation of Purdy's conjecture with fewer points
on one of the lines. We finish with a lower bound for our main result in one
dimension higher with asymmetric cartesian product, showing that it is
near-optimal.Comment: 23 page
Simultaneous Arithmetic Progressions on Algebraic Curves
A simultaneous arithmetic progression (s.a.p.) of length k consists of k
points (x_i, y_\sigma(i)), where x_i and y_i are arithmetic progressions and
\sigma is a permutation. Garcia-Selfa and Tornero asked whether there is a
bound on the length of an s.a.p. on an elliptic curve in Weierstrass form over
Q. We show that 4319 is such a bound for curves over R. This is done by
considering translates of the curve in a grid as a graph. A simple upper bound
is found for the number of crossings and the 'crossing inequality' gives a
lower bound. Together these bound the length of an s.a.p. on the curve. We then
use a similar method to extend the result to arbitrary real algebraic curves.
Instead of considering s.a.p.'s we consider k^2/3 points in a grid. The number
of crossings is bounded by Bezout's Theorem. We then give another proof using a
result of Jarnik bounding the number of grid points on a convex curve. This
result applies as any real algebraic curve can be broken up into convex and
concave parts, the number of which depend on the degree. Lastly, these results
are extended to complex algebraic curves.Comment: 11 pages, 6 figures, order of email addresses corrected 12 pages,
closing remarks, a reference and an acknowledgment adde
Activity Recognition based on a Magnitude-Orientation Stream Network
The temporal component of videos provides an important clue for activity
recognition, as a number of activities can be reliably recognized based on the
motion information. In view of that, this work proposes a novel temporal stream
for two-stream convolutional networks based on images computed from the optical
flow magnitude and orientation, named Magnitude-Orientation Stream (MOS), to
learn the motion in a better and richer manner. Our method applies simple
nonlinear transformations on the vertical and horizontal components of the
optical flow to generate input images for the temporal stream. Experimental
results, carried on two well-known datasets (HMDB51 and UCF101), demonstrate
that using our proposed temporal stream as input to existing neural network
architectures can improve their performance for activity recognition. Results
demonstrate that our temporal stream provides complementary information able to
improve the classical two-stream methods, indicating the suitability of our
approach to be used as a temporal video representation.Comment: 8 pages, SIBGRAPI 201
TE Wave Measurement and Modeling
In the TE wave method, microwaves are coupled into the beam-pipe and the
effect of the electron cloud on these microwaves is measured. An electron cloud
(EC) density can then be calculated from this measurement. There are two
analysis methods currently in use. The first treats the microwaves as being
transmitted from one point to another in the accelerator. The second more
recent method, treats the beam-pipe as a resonant cavity. This paper will
summarize the reasons for adopting the resonant TE wave analysis as well as
give examples from CESRTA and DA{\Phi}NE of resonant beam-pipe. The results of
bead-pull bench measurements will show some possible standing wave patterns,
including a cutoff mode (evanescent) where the field decreases exponentially
with distance from the drive point. We will outline other recent developments
in the TE wave method including VORPAL simulations of microwave resonances, as
well as the simulation of transmission in the presence of both an electron
cloud and magnetic fields.Comment: Presented at ECLOUD'12: Joint INFN-CERN-EuCARD-AccNet Workshop on
Electron-Cloud Effects, La Biodola, Isola d'Elba, Italy, 5-9 June 2012;
CERN-2013-002, pp. 193-20
Are all Credit Default Swap databases equal?
The presence of different prices in different databases for the same securities can impair the comparability of research efforts and seriously damage the management decisions based upon such research. In this study we compare the six major sources of corporate Credit Default Swap prices: GFI, Fenics, Reuters EOD, CMA, Markit and JP Morgan, using the most liquid single name 5-year CDS of the components of the leading market indexes, iTraxx (European firms) and CDX (US firms) for the period from 2004 to 2010. We find systematic differences between the data sets implying that deviations from the common trend among prices in the different databases are not purely random but are explained by idiosyncratic factors as well as liquidity, global risk and other trading factors. The lower is the amount of transaction prices available the higher is the deviation among databases. Our results suggest that the CMA database quotes lead the price discovery process in comparison with the quotes provided by other databases. Several robustness tests confirm these results.Credit Default Swap prices, Databases, Liquidity
Lexicographic choice functions without archimedeanicity
We investigate the connection between choice functions and lexicographic probabilities, by means of the convexity axiom considered by Seidenfeld, Schervisch and Kadane (2010) but without imposing any Archimedean condition. We show that lexicographic probabilities are related to a particular type of sets of desirable gambles, and investigate the properties of the coherent choice function this induces via maximality. Finally, we show that the convexity axiom is necessary but not sufficient for a coherent choice function to be the infimum of a class of lexicographic ones
Experimental demonstration of a dual-frequency laser free from anti-phase noise
A reduction of more than 20 dB of the intensity noise at the anti-phase
relaxation oscillation frequency is experimentally demonstrated in a
two-polarization dual-frequency solid-state laser without any optical or
electronic feedback loop. Such a behavior is inherently obtained by aligning
the two orthogonally polarized oscillating modes with the crystallographic axes
of a (100)-cut neodymium-doped yttrium aluminum garnet active medium. The
anti-phase noise level is shown to increase as soon as one departs from this
peculiar configuration, evidencing the predominant role of the nonlinear
coupling constant. This experimental demonstration opens new perspectives on
the design and realization of extremely low noise dual-frequency solid-state
lasers
Loss of brain inter-frequency hubs in Alzheimer's disease
Alzheimer's disease (AD) causes alterations of brain network structure and
function. The latter consists of connectivity changes between oscillatory
processes at different frequency channels. We proposed a multi-layer network
approach to analyze multiple-frequency brain networks inferred from
magnetoencephalographic recordings during resting-states in AD subjects and
age-matched controls. Main results showed that brain networks tend to
facilitate information propagation across different frequencies, as measured by
the multi-participation coefficient (MPC). However, regional connectivity in AD
subjects was abnormally distributed across frequency bands as compared to
controls, causing significant decreases of MPC. This effect was mainly
localized in association areas and in the cingulate cortex, which acted, in the
healthy group, as a true inter-frequency hub. MPC values significantly
correlated with memory impairment of AD subjects, as measured by the total
recall score. Most predictive regions belonged to components of the
default-mode network that are typically affected by atrophy, metabolism
disruption and amyloid-beta deposition. We evaluated the diagnostic power of
the MPC and we showed that it led to increased classification accuracy (78.39%)
and sensitivity (91.11%). These findings shed new light on the brain functional
alterations underlying AD and provide analytical tools for identifying
multi-frequency neural mechanisms of brain diseases.Comment: 27 pages, 6 figures, 3 tables, 3 supplementary figure
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