3,621 research outputs found
Decision Trees, Protocols, and the Fourier Entropy-Influence Conjecture
Given , define the \emph{spectral
distribution} of to be the distribution on subsets of in which the
set is sampled with probability . Then the Fourier
Entropy-Influence (FEI) conjecture of Friedgut and Kalai (1996) states that
there is some absolute constant such that . Here,
denotes the Shannon entropy of 's spectral distribution, and
is the total influence of . This conjecture is one
of the major open problems in the analysis of Boolean functions, and settling
it would have several interesting consequences.
Previous results on the FEI conjecture have been largely through direct
calculation. In this paper we study a natural interpretation of the conjecture,
which states that there exists a communication protocol which, given subset
of distributed as , can communicate the value of using
at most bits in expectation.
Using this interpretation, we are able show the following results:
1. First, if is computable by a read- decision tree, then
.
2. Next, if has and is computable by a
decision tree with expected depth , then .
3. Finally, we give a new proof of the main theorem of O'Donnell and Tan
(ICALP 2013), i.e. that their FEI conjecture composes.
In addition, we show that natural improvements to our decision tree results
would be sufficient to prove the FEI conjecture in its entirety. We believe
that our methods give more illuminating proofs than previous results about the
FEI conjecture
Mining Measured Information from Text
We present an approach to extract measured information from text (e.g., a
1370 degrees C melting point, a BMI greater than 29.9 kg/m^2 ). Such
extractions are critically important across a wide range of domains -
especially those involving search and exploration of scientific and technical
documents. We first propose a rule-based entity extractor to mine measured
quantities (i.e., a numeric value paired with a measurement unit), which
supports a vast and comprehensive set of both common and obscure measurement
units. Our method is highly robust and can correctly recover valid measured
quantities even when significant errors are introduced through the process of
converting document formats like PDF to plain text. Next, we describe an
approach to extracting the properties being measured (e.g., the property "pixel
pitch" in the phrase "a pixel pitch as high as 352 {\mu}m"). Finally, we
present MQSearch: the realization of a search engine with full support for
measured information.Comment: 4 pages; 38th International ACM SIGIR Conference on Research and
Development in Information Retrieval (SIGIR '15
Characterisation and optimisation of PECVD SiNx as an antireflection coating and passivation layer for silicon solar cells
In this work, we investigate how the film properties of silicon nitride (SiNx) depend on its deposition conditions when formed by plasma enhanced chemical vapour deposition (PECVD). The examination is conducted with a Roth & Rau AK400 PECVD reactor, where the varied parameters are deposition temperature, pressure, gas flow ratio, total gas flow, microwave plasma power and radio-frequency bias voltage. The films are evaluated by Fourier transform infrared spectroscopy to determine structural properties, by spectrophotometry to determine optical properties, and by capacitance–voltage and photoconductance measurements to determine electronic properties. After reporting on the dependence of SiNx properties on deposition parameters, we determine the optimized deposition conditions that attain low absorption and low recombination. On the basis of SiNx growth models proposed in the literature and of our experimental results, we discuss how each process parameter affects the deposition rate and chemical bond density. We then focus on the effective surface recombination velocity S eff, which is of primary importance to solar cells. We find that for the SiNx prepared in this work, 1) S eff does not correlate universally with the bulk structural and optical properties such as chemical bond densities and refractive index, and 2) S eff depends primarily on the defect density at the SiNx-Si interface rather than the insulator charge. Finally, employing the optimized deposition condition, we achieve a relatively constant and low S eff,UL on low-resistivity (≤1.1 Ωcm) p- and n-type c-Si substrates over a broad range of n = 1.85–4.07. The results of this study demonstrate that the trade-off between optical transmission and surface passivation can be circumvented. Although we focus on photovoltaic applications, this study may be useful for any device for which it is desirable to maximize light transmission and surface passivation.This work was supported by an Australian Research Council Linkage between The
Australian National University and Braggone Oy under Grant LP0989593
Satisfiability and Evolution
We show that, if truth assignments on variables reproduce through
recombination so that satisfaction of a particular Boolean function confers a
small evolutionary advantage, then a polynomially large population over
polynomially many generations (polynomial in and the inverse of the initial
satisfaction probability) will end up almost certainly consisting exclusively
of satisfying truth assignments. We argue that this theorem sheds light on the
problem of novelty in Evolution
On the Distribution of the Fourier Spectrum of Halfspaces
Bourgain showed that any noise stable Boolean function can be
well-approximated by a junta. In this note we give an exponential sharpening of
the parameters of Bourgain's result under the additional assumption that is
a halfspace
Approximate resilience, monotonicity, and the complexity of agnostic learning
A function is -resilient if all its Fourier coefficients of degree at
most are zero, i.e., is uncorrelated with all low-degree parities. We
study the notion of of Boolean
functions, where we say that is -approximately -resilient if
is -close to a -valued -resilient function in
distance. We show that approximate resilience essentially characterizes the
complexity of agnostic learning of a concept class over the uniform
distribution. Roughly speaking, if all functions in a class are far from
being -resilient then can be learned agnostically in time and
conversely, if contains a function close to being -resilient then
agnostic learning of in the statistical query (SQ) framework of Kearns has
complexity of at least . This characterization is based on the
duality between approximation by degree- polynomials and
approximate -resilience that we establish. In particular, it implies that
approximation by low-degree polynomials, known to be sufficient for
agnostic learning over product distributions, is in fact necessary.
Focusing on monotone Boolean functions, we exhibit the existence of
near-optimal -approximately
-resilient monotone functions for all
. Prior to our work, it was conceivable even that every monotone
function is -far from any -resilient function. Furthermore, we
construct simple, explicit monotone functions based on and that are close to highly resilient functions. Our constructions are
based on a fairly general resilience analysis and amplification. These
structural results, together with the characterization, imply nearly optimal
lower bounds for agnostic learning of monotone juntas
- …