16,751 research outputs found
Minimizing Vessel Strikes to Endangered Whales: A Crash Course in Conservation Science and Policy
The North Atlantic right whale is one of the most endangered of all large whales: about 350-400 individuals remain. Species recovery is, in part, contingent on reducing vessel-strike mortality. Our science-based conservation program resulted in three efforts specifically designed to minimize the risk of lethal vessel-strikes of endangered baleen whales without compromising vessel navigation and safety. In Atlantic Canada, the Bay of Fundy Traffic Separation Scheme (TSS) was relocated to reduce the risk of lethal vessel strikes by 90% where the original outbound lane of the TSS intersected the Right Whale Conservation Area, and an Area To Be Avoided (ATBA) adopted for Roseway Basin has demonstrated an 82% reduction in the risk of lethal vessel-strikes. In the Gulf of Maine, the Boston TSS through the Stellwagen Bank National Marine Sanctuary was relocated to reduce the overlap between vessels and endangered baleen whales by ~81% and by ~58% for right whales alone. This rerouting of vessels for whale conservation, as sanctioned by the International Maritime Organization, sets a precedent for national and international marine conservation policy by providing vessels with direct actions they can take to protect endangered whales – both regulated (TSS) and voluntary (ATBA). This demonstrate that despite contentious conditions, effective science-driven policy tools for conservation can be identified, made available, and implemented. The science also provides the quantitative means to measure policy efficacy through monitoring of vessel compliance and, in some cases, can increase compliance through improved real-time communications regarding whale locations in high-risk areas
On the Energy Efficiency of LT Codes in Proactive Wireless Sensor Networks
This paper presents an in-depth analysis on the energy efficiency of Luby
Transform (LT) codes with Frequency Shift Keying (FSK) modulation in a Wireless
Sensor Network (WSN) over Rayleigh fading channels with pathloss. We describe a
proactive system model according to a flexible duty-cycling mechanism utilized
in practical sensor apparatus. The present analysis is based on realistic
parameters including the effect of channel bandwidth used in the IEEE 802.15.4
standard, active mode duration and computation energy. A comprehensive
analysis, supported by some simulation studies on the probability mass function
of the LT code rate and coding gain, shows that among uncoded FSK and various
classical channel coding schemes, the optimized LT coded FSK is the most
energy-efficient scheme for distance d greater than the pre-determined
threshold level d_T , where the optimization is performed over coding and
modulation parameters. In addition, although the optimized uncoded FSK
outperforms coded schemes for d < d_T , the energy gap between LT coded and
uncoded FSK is negligible for d < d_T compared to the other coded schemes.
These results come from the flexibility of the LT code to adjust its rate to
suit instantaneous channel conditions, and suggest that LT codes are beneficial
in practical low-power WSNs with dynamic position sensor nodes.Comment: accepted for publication in IEEE Transactions on Signal Processin
Adaptive Demodulation in Differentially Coherent Phase Systems: Design and Performance Analysis
Adaptive Demodulation (ADM) is a newly proposed rate-adaptive system which
operates without requiring Channel State Information (CSI) at the transmitter
(unlike adaptive modulation) by using adaptive decision region boundaries at
the receiver and encoding the data with a rateless code. This paper addresses
the design and performance of an ADM scheme for two common differentially
coherent schemes: M-DPSK (M-ary Differential Phase Shift Keying) and M-DAPSK
(M-ary Differential Amplitude and Phase Shift Keying) operating over AWGN and
Rayleigh fading channels. The optimal method for determining the most reliable
bits for a given differential detection scheme is presented. In addition,
simple (near-optimal) implementations are provided for recovering the most
reliable bits from a received pair of differentially encoded symbols for
systems using 16-DPSK and 16- DAPSK. The new receivers offer the advantages of
a rate-adaptive system, without requiring CSI at the transmitter and a coherent
phase reference at the receiver. Bit error analysis for the ADM system in both
cases is presented along with numerical results of the spectral efficiency for
the rate-adaptive systems operating over a Rayleigh fading channel.Comment: 25 pages, 11 Figures, submitted to IEEE Transactions on
Communications, June 1, 201
Another fine mess? Which theory for which English?
Language learning theory is in a state of disarray. This has always been the case. Progress in approaches and techniques has been made on a step by step basis and teachers have found themselves struggling – doing their best to do their best. But lack of a general theory is not necessarily a negative situation for from it has come a diversity of methodologies which guarantee variety and cater for the majority of teaching/learning environments. Furthermore, one might wonder if a general theory ..
The shock process and light element production in supernovae envelopes
Detailed hydrodynamic modeling of the passage of supernova shocks through the hydrogen envelopes of blue and red progenitor stars was carried out to explore the sensitivity to model conditions of light element production (specifically Li-7 and B-11) which was noted by Dearborn, Schramm, Steigman and Truran (1989) (DSST). It is found that, for stellar models with M is less than or approximately 100 M solar mass, current state of the art supernova shocks do not produce significant light element yields by hydrodynamic processes alone. The dependence of this conclusion on stellar models and on shock strengths is explored. Preliminary implications for Galactic evolution of lithium are discussed, and it is suspected that intermediate mass red giant stars may be the most consistent production site for lithium
A Granger Causality Measure for Point Process Models of Ensemble Neural Spiking Activity
The ability to identify directional interactions that occur among multiple neurons in the brain is crucial to an understanding
of how groups of neurons cooperate in order to generate specific brain functions. However, an optimal method of assessing
these interactions has not been established. Granger causality has proven to be an effective method for the analysis of the
directional interactions between multiple sets of continuous-valued data, but cannot be applied to neural spike train
recordings due to their discrete nature. This paper proposes a point process framework that enables Granger causality to be
applied to point process data such as neural spike trains. The proposed framework uses the point process likelihood
function to relate a neuron’s spiking probability to possible covariates, such as its own spiking history and the concurrent
activity of simultaneously recorded neurons. Granger causality is assessed based on the relative reduction of the point
process likelihood of one neuron obtained excluding one of its covariates compared to the likelihood obtained using all of
its covariates. The method was tested on simulated data, and then applied to neural activity recorded from the primary
motor cortex (MI) of a Felis catus subject. The interactions present in the simulated data were predicted with a high degree
of accuracy, and when applied to the real neural data, the proposed method identified causal relationships between many
of the recorded neurons. This paper proposes a novel method that successfully applies Granger causality to point process
data, and has the potential to provide unique physiological insights when applied to neural spike trains.National Institutes of Health (U.S.) (Grant DP1-OD003646)National Institutes of Health (U.S.) (Grant R01-EB006385
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