845 research outputs found
Waveguide-based single-pixel up-conversion infrared spectrometer
A periodically poled lithium niobate (PPLN) waveguide-based single-pixel
up-conversion infrared spectrometer was demonstrated. Sum-frequency generation
between a 1.5 micrometer band scanning pump laser and a 1.3 micrometer band
signal generated visible radiation which was detected by a silicon
single-photon detector. The noise equivalent power of the upconversion
spectrometer was two-orders-of-magnitude lower than that of a commercial
optical spectrum analyzer.Comment: 5 pages, 3 figure
Risk Preferences, Perceptions and Systematic Biases
Replaced with revised version of paper 07/21/06.Risk and Uncertainty,
Markov-switching generalized additive models
We consider Markov-switching regression models, i.e. models for time series
regression analyses where the functional relationship between covariates and
response is subject to regime switching controlled by an unobservable Markov
chain. Building on the powerful hidden Markov model machinery and the methods
for penalized B-splines routinely used in regression analyses, we develop a
framework for nonparametrically estimating the functional form of the effect of
the covariates in such a regression model, assuming an additive structure of
the predictor. The resulting class of Markov-switching generalized additive
models is immensely flexible, and contains as special cases the common
parametric Markov-switching regression models and also generalized additive and
generalized linear models. The feasibility of the suggested maximum penalized
likelihood approach is demonstrated by simulation and further illustrated by
modelling how energy price in Spain depends on the Euro/Dollar exchange rate
Estimating the Benefits of Bt Corn and Cost of Insect Resistance Management Ex Ante
This paper estimates farmer benefits for corn rootworm (CRW) active Bt corn and costs of complying with Environmental Protection Agency insect resistance management requirements. The estimates are obtained from farmer survey data that were collected in Minnesota in 2002, just prior to the commercial releases of CRW Bt corn. Benefit estimates range from 33.4 million, while compliance cost estimated range from 8.7 million depending on whether or not CRW Bt corn also controlled the European corn borer and whether of not it was approved for sale in major export markets.Bt corn, compliance costs, corn rootworm, insect resistance management, willingness to pay, Crop Production/Industries,
Nonparametric inference in hidden Markov models using P-splines
Hidden Markov models (HMMs) are flexible time series models in which the
distributions of the observations depend on unobserved serially correlated
states. The state-dependent distributions in HMMs are usually taken from some
class of parametrically specified distributions. The choice of this class can
be difficult, and an unfortunate choice can have serious consequences for
example on state estimates, on forecasts and generally on the resulting model
complexity and interpretation, in particular with respect to the number of
states. We develop a novel approach for estimating the state-dependent
distributions of an HMM in a nonparametric way, which is based on the idea of
representing the corresponding densities as linear combinations of a large
number of standardized B-spline basis functions, imposing a penalty term on
non-smoothness in order to maintain a good balance between goodness-of-fit and
smoothness. We illustrate the nonparametric modeling approach in a real data
application concerned with vertical speeds of a diving beaked whale,
demonstrating that compared to parametric counterparts it can lead to models
that are more parsimonious in terms of the number of states yet fit the data
equally well
100 km secure differential phase shift quantum key distribution with low jitter up-conversion detectors
We present a quantum key distribution experiment in which keys that were
secure against all individual eavesdropping attacks allowed by quantum
mechanics were distributed over 100 km of optical fiber. We implemented the
differential phase shift quantum key distribution protocol and used low timing
jitter 1.55 um single-photon detectors based on frequency up-conversion in
periodically poled lithium niobate waveguides and silicon avalanche
photodiodes. Based on the security analysis of the protocol against general
individual attacks, we generated secure keys at a practical rate of 166 bit/s
over 100 km of fiber. The use of the low jitter detectors also increased the
sifted key generation rate to 2 Mbit/s over 10 km of fiber.Comment: 10 pages, 5 figure
Flexible and practical modeling of animal telemetry data: hidden Markov models and extensions
We discuss hidden Markov-type models for fitting a variety of multistate random walks to wildlife movement data. Discrete-time hidden Markov models (HMMs) achieve considerable computational gains by focusing on observations that are regularly spaced in time, and for which the measurement error is negligible. These conditions are often met, in particular for data related to terrestrial animals, so that a likelihood-based HMM approach is feasible. We describe a number of extensions of HMMs for animal movement modeling, including more flexible state transition models and individual random effects (fitted in a non-Bayesian framework). In particular we consider so-called hidden semi-Markov models, which may substantially improve the goodness of fit and provide important insights into the behavioral state switching dynamics. To showcase the expediency of these methods, we consider an application of a hierarchical hidden semi-Markov model to multiple bison movement paths
Correlated photon-pair generation in reverse-proton-exchange PPLN waveguides with integrated mode demultiplexer at 10 GHz clock
We report 10-ps correlated photon pair generation in periodically-poled
reverse-proton-exchange lithium niobate waveguides with integrated mode
demultiplexer at a wavelength of 1.5-um and a clock of 10 GHz. Using
superconducting single photon detectors, we observed a coincidence to
accidental count ratio (CAR) as high as 4000. The developed photon-pair source
may find broad application in quantum information systems as well as quantum
entanglement experiments.Comment: 6 pages, 4 figures, presented at 2007 CLEO conferenc
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