5,079 research outputs found
Stream Sampling for Frequency Cap Statistics
Unaggregated data, in streamed or distributed form, is prevalent and come
from diverse application domains which include interactions of users with web
services and IP traffic. Data elements have {\em keys} (cookies, users,
queries) and elements with different keys interleave. Analytics on such data
typically utilizes statistics stated in terms of the frequencies of keys. The
two most common statistics are {\em distinct}, which is the number of active
keys in a specified segment, and {\em sum}, which is the sum of the frequencies
of keys in the segment. Both are special cases of {\em cap} statistics, defined
as the sum of frequencies {\em capped} by a parameter , which are popular in
online advertising platforms. Aggregation by key, however, is costly, requiring
state proportional to the number of distinct keys, and therefore we are
interested in estimating these statistics or more generally, sampling the data,
without aggregation. We present a sampling framework for unaggregated data that
uses a single pass (for streams) or two passes (for distributed data) and state
proportional to the desired sample size. Our design provides the first
effective solution for general frequency cap statistics. Our -capped
samples provide estimates with tight statistical guarantees for cap statistics
with and nonnegative unbiased estimates of {\em any} monotone
non-decreasing frequency statistics. An added benefit of our unified design is
facilitating {\em multi-objective samples}, which provide estimates with
statistical guarantees for a specified set of different statistics, using a
single, smaller sample.Comment: 21 pages, 4 figures, preliminary version will appear in KDD 201
Spatiotemporal chaos and the dynamics of coupled Langmuir and ion-acoustic waves in plasmas
A simulation study is performed to investigate the dynamics of coupled
Langmuir waves (LWs) and ion-acoustic waves (IAWs) in an unmagnetized plasma.
The effects of dispersion due to charge separation and the density nonlinearity
associated with the IAWs, are considered to modify the properties of Langmuir
solitons, as well as to model the dynamics of relatively large amplitude wave
envelopes. It is found that the Langmuir wave electric field, indeed, increases
by the effect of ion-wave nonlinearity (IWN). Use of a low-dimensional model,
based on three Fourier modes shows that a transition to temporal chaos is
possible, when the length scale of the linearly excited modes is larger than
that of the most unstable ones. The chaotic behaviors of the unstable modes are
identified by the analysis of Lyapunov exponent spectra. The space-time
evolution of the coupled LWs and IAWs shows that the IWN can cause the
excitation of many unstable harmonic modes, and can lead to strong IAW
emission. This occurs when the initial wave field is relatively large or the
length scale of IAWs is larger than the soliton characteristic size. Numerical
simulation also reveals that many solitary patterns can be excited and
generated through the modulational instability (MI) of unstable harmonic modes.
As time goes on, these solitons are seen to appear in the spatially partial
coherence (SPC) state due to the free ion-acoustic radiation as well as in the
state of spatiotemporal chaos (STC) due to collision and fusion in the
stochastic motion. The latter results the redistribution of initial wave energy
into a few modes with small length scales, which may lead to the onset of
Langmuir turbulence in laboratory as well as space plasmas.Comment: 10 Pages, 14 Figures; to appear in Physical Review
Observation of Quantum Hall Valley Skyrmions
We report measurements of the interaction-induced quantum Hall effect in a
spin-polarized AlAs two-dimensional electron system where the electrons occupy
two in-plane conduction band valleys. Via the application of in-plane strain,
we tune the energies of these valleys and measure the energy gap of the quantum
Hall state at filling factor = 1. The gap has a finite value even at zero
strain and, with strain, rises much faster than expected from a single-particle
picture, suggesting that the lowest energy charged excitations at are
"valley Skyrmions".Comment: 4 pages, 3 figure
Ion-acoustic solitary waves and shocks in a collisional dusty negative ion plasma
We study the effects of ion-dust collisions and ion kinematic viscosities on
the linear ion-acoustic instability as well as the nonlinear propagation of
small amplitude solitary waves and shocks (SWS) in a negative ion plasma with
immobile charged dusts. {The existence of two linear ion modes, namely the
`fast' and `slow' waves is shown, and their properties are analyzed in the
collisional negative ion plasma.} {Using the standard reductive perturbation
technique, we derive a modified Korteweg-de Vries-Burger (KdVB) equation which
describes the evolution of small amplitude SWS.} {The profiles of the latter
are numerically examined with parameters relevant for laboratory and space
plasmas where charged dusts may be positively or negatively charged.} It is
found that negative ion plasmas containing positively charged dusts support the
propagation of SWS with negative potential. However, the perturbations with
both positive and negative potentials may exist when dusts are negatively
charged. The results may be useful for the excitation of SWS in laboratory
negative ion plasmas as well as for observation in space plasmas where charged
dusts may be positively or negatively charged.Comment: 13 pages, 9 figures; To appear in Physical Review
INTRINSIC MECHANISM FOR ENTROPY CHANGE IN CLASSICAL AND QUANTUM EVOLUTION
It is shown that the existence of a time operator in the Liouville space
representation of both classical and quantum evolution provides a mechanism for
effective entropy change of physical states. In particular, an initially
effectively pure state can evolve under the usual unitary evolution to an
effectively mixed state.Comment: 20 pages. For more information or comments contact E. Eisenberg at
[email protected] (internet)
"Big" Divisor D3/D7 Swiss Cheese Phenomenology
We review progress made over the past couple of years in the field of Swiss
Cheese Phenomenology involving a mobile space-time filling D3-brane and
stack(s) of fluxed D7-branes wrapping the "big" (as opposed to the "small")
divisor in (the orientifold of a) Swiss-Cheese Calabi-Yau. The topics reviewed
include reconciliation of large volume cosmology and phenomenology, evaluation
of soft supersymmetry breaking parameters, one-loop RG-flow equations'
solutions for scalar masses, obtaining fermionic (possibly first two
generations' quarks/leptons) mass scales in the O(MeV-GeV)-regime as well as
(first two generations') neutrino masses (and their one-loop RG flow) of around
an eV. The heavy sparticles and the light fermions indicate the possibility of
"split SUSY" large volume scenario.Comment: Invited review for MPLA, 14 pages, LaTe
Computing the multifractal spectrum from time series: An algorithmic approach
We show that the existing methods for computing the f(\alpha) spectrum from a
time series can be improved by using a new algorithmic scheme. The scheme
relies on the basic idea that the smooth convex profile of a typical f(\alpha)
spectrum can be fitted with an analytic function involving a set of four
independent parameters. While the standard existing schemes [16, 18] generally
compute only an incomplete f(\alpha) spectrum (usually the top portion), we
show that this can be overcome by an algorithmic approach which is automated to
compute the Dq and f(\alpha) spectrum from a time series for any embedding
dimension. The scheme is first tested with the logistic attractor with known
f(\alpha) curve and subsequently applied to higher dimensional cases. We also
show that the scheme can be effectively adapted for analysing practcal time
series involving noise, with examples from two widely different real world
systems. Moreover, some preliminary results indicating that the set of four
independant parameters may be used as diagnostic measures is also included.Comment: 10 pages, 16 figures, submitted to CHAO
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