Assessing the quality of a network of vector-field sensors

An experiment consisting of a network of sensors can endow several advantages over an experiment with a single sensor: improved sensitivity, error corrections, spatial resolution, etc. However, there is often a question of how to optimally set up the network to yield the best results. Here, we consider a network of devices that measure a vector field along a given axis; namely for magnetometers in the Global Network of Optical Magnetometers for Exotic physics searches (GNOME). We quantify how well the network is arranged, explore characteristics and examples of ideal networks, and characterize the optimal configuration for GNOME. We find that by re-orienting the sensitive axes of existing magnetometers, the sensitivity of the network can be improved relative to the past science runs.

Reverse-correlation reveals internal error-corrections during information-seeking

In the area of metacognition research, different methods have been used to study participants’ subjective sense of confidence in their choices. Among the most often used methods are explicit reports of subjective confidence, post-decision wagering and measuring additional info-seeking behavior. While all three methods are thought to measure confidence, they differ greatly in terms of practical execution and theoretical foundation. The method of reverse correlation has previously been used to determine which aspects of the stimulus influence decisions and confidence judgments. Here we compare the three methods of confidence assessment using reverse correlation analysis. Explicit reports and post-decision wagering revealed a positive association of stimulus information with choices and reduced decision weights for low-confidence trials. When confidence was assessed using the info-seeking method, low-confidence trials showed an inverted association with primary stimulus information. Using modelling of the behavioral data, we show how the reverse correlation results of all three methods can be explained by a simple model of confidence when internal error-corrections are allowed during seeking of additional information.

Self-correcting Sun Compass, Spherical Geometry and Cue-transfers Predict Naïve Migratory Performance

Migratory orientation of many animals is inheritable, enabling naïve migrants to reach remote destinations independently following stepwise (often, nightly) geomagnetic or celestial cues. Which if any such “compass courses” can explain narrow-front trans-continental routes remains unresolved, and evident error-corrections by naïve migrants remain unexplained. We assessed robustness to errors among airborne compass courses and quantified inaugural migration performance globally, accounting for cue transfers (e.g., sun to star compass), in-flight cue maintenance, and previously-overlooked spherical-geometry (longitude) effects. We found (i) sun-compass courses partially self-correct, making them most robust between flight-steps, (ii) within nocturnal flight-steps, geomagnetic or star-compass headings outperform cue-transferred sun-compass steps, (iii) across diverse airborne migration routes, the relative favourability of sun-compass over other courses increases with increasing goal-area, required flight steps and a spherical-geometry factor. Our results can explain enhanced naïve migrant performance, observed diversity in compass-cue hierarchies, and sun-compass orientation being key to many long-distance inaugural migrations.

Insights from an Evaluation of Nitrate Load Estimation Methods in the Midwestern United States

This study investigated the accuracy and suitability of several methods commonly used to estimate riverine nitrate loads at eight watersheds located southwest of Lake Erie in the Midwestern United States. This study applied various regression methods, including a regression estimator with five, six, and seven parameters, an estimator enhanced by composite, triangular, and rectangular error corrections with residual and proportional adjustment methods, the weighted regressions on time, discharge, and season (WRTDS) method, and a simple linear interpolation (SLI) method. Daily discharge and nitrate concentration data were collected by the National Center for Water Quality Research. The methods were compared with subsampling frequencies of 6, 12, and 24 times per year for daily concentrations, daily loads, and annual loads. The results indicate that combinations of the seven-parameter regression method with composite residual and rectangular residual adjustments provided the best estimates under most of the watershed and sampling frequency conditions. On average, WRTDS was more accurate than the regression models alone, but less accurate than those models enhanced by residual adjustments, except for the most urbanized watershed, Cuyahoga. SLI was the most accurate in the Vermilion and Maumee watersheds. The results also provide some information about the effects of rating curve shape and slope, land use, and record length on model performance.

Majority Voting-Based MAC Protocol for Exploiting Link-Layer Diversity in Wireless Networks

In wireless local area networks (WLANs), the effect of interference signals between neighboring nodes increases as the number of wireless nodes using limited radio frequency resources in a limited space increases, which can significantly degrade the reliability of data transmission. In high-density WLANs, there can be several neighboring access points (APs) that can receive uplink transmission from a station. In conventional medium access control (MAC) protocols, uplink data frames containing errors or transmitted from a non-associated station are discarded at APs. Alternatively, we propose a MAC protocol using redundant wireless links between neighboring APs and the non-associated stations. In the proposed MAC protocol, we consider a centralized WLAN with a control node that performs error corrections of erroneous uplink data frames via a majority voting algorithm-based link-layer diversity scheme using uplink data received from multiple APs to increase the reliability of data transmission. In addition, we propose an adaptive carrier sensing ranging mechanism to improve the uplink network throughput in the proposed centralized WLAN system. Further, we conduct simulation studies and software-defined radio-based experiments to evaluate the performance of the proposed MAC protocol in various WLAN scenarios.