Brendan Nichols

Control-Relevant Erythropoiesis Modeling in End-Stage Renal Disease

Anemia is prevalent in end-stage renal disease (ESRD). The discovery of recombinant human erythropoietin (rHuEPO) over 30 years ago has shifted the treatment of anemia for patients on dialysis from blood transfusions to rHuEPO therapy. Many anemia management protocols (AMPs) used by clinicians comprise a set of experience-based rules for weekly-to-monthly titration of rHuEPO doses based on hemoglobin (Hb) measurements. In order to facilitate the design of an AMP using model-based feedback control theory, we present a physiologically relevant erythropoiesis model and demonstrate its applicability using clinical data.

Simplification of an erythropoiesis model for design of anemia management protocols in end stage renal disease

Many end stage renal disease (ESRD) patients suffer from anemia due to insufficient endogenous production of erythropoietin (EPO). The discovery of recombinant human EPO (rHuEPO) over 30 years ago has shifted the treatment of anemia for patients on dialysis from blood transfusions to rHuEPO therapy. Many anemia management protocols (AMPs) used by clinicians comprise a set of experience-based rules for weekly-to-monthly titration of rHuEPO doses based on hemoglobin (Hgb) measurements. In order to facilitate the design of an AMP based on formal control design methods, we present a physiologically-relevant erythropoiesis model, and show that its nonlinear dynamics can be approximated using a static nonlinearity, a step that greatly simplifies AMP design. We demonstrate applicability of our results using clinical data.

Cross-coherent vector sensor processing for spatially distributed glider networks

Autonomous underwater gliders fitted with vector sensors can be used as a spatially distributed sensor array to passively locate underwater sources. However, to date, the positional accuracy required for robust array processing (especially coherent processing) is not achievable using dead-reckoning while the gliders remain submerged. To obtain such accuracy, the gliders can be temporarily surfaced to allow for global positioning system contact, but the acoustically active sea surface introduces locally additional sensor noise. This letter demonstrates that cross-coherent array processing, which inherently mitigates the effects of local noise, outperforms traditional incoherent processing source localization methods for this spatially distributed vector sensor network.

Information content of ship noise on a drifting volumetric array for passive environmental sensing

This study investigates the information content of ship noise received on a drifting volumetric array of hydrophones in shallow water marine environments for the purposes of conducting acoustic thermometry or other environmental inversions. Passive inversions for physical oceanographic parameters are conducted using travel time differences, determined by cross-correlating ship noise received on hydrophones suspended beneath drifting buoys. Ships are tracked using the Automatic Identification System (AIS). Information content gained from the inversion is assessed using traditional a-posteriori error analysis. Numerical simulations using a standard normal mode propagation model are used to test limitations of the proposed approach with respect to frequency band, drifting receiver configuration, precision and accuracy of the inversion results, along with sensitivity to environmental and position mismatch. Performance predictions using this model are compared with results from a field experiment using at-sea data collected off the coast of New London, CT in Long Island Sound. Information gathered using passive acoustic inversion methods on drifting arrays can be used to constrain general circulation models (GCMs), in coastal environments, where ship noise is ubiquitous, environmental data are sparse, and the oceanography is dynamic and important for understanding large-scale ocean processes.This study investigates the information content of ship noise received on a drifting volumetric array of hydrophones in shallow water marine environments for the purposes of conducting acoustic thermometry or other environmental inversions. Passive inversions for physical oceanographic parameters are conducted using travel time differences, determined by cross-correlating ship noise received on hydrophones suspended beneath drifting buoys. Ships are tracked using the Automatic Identification System (AIS). Information content gained from the inversion is assessed using traditional a-posteriori error analysis. Numerical simulations using a standard normal mode propagation model are used to test limitations of the proposed approach with respect to frequency band, drifting receiver configuration, precision and accuracy of the inversion results, along with sensitivity to environmental and position mismatch. Performance predictions using this model are compared with results from a field experiment using at-sea ...

Passive underwater acoustic markers for navigation and information encoding for high frequency sound navigation and ranging (SONAR) devices

AUV navigation requires accurate positioning information from the surrounding environment. Currently, several underwater navigation and surveying paradigms employ active transponders that assist in triangulation. These systems are expensive, require maintenance, and additional power sources. This paper presents a novel system that may be implemented to guide AUVs equipped with high frequency SONAR, using passive acoustic tags that are cost effective, and simple to deploy. The acoustic tags are constructed by layering multiple sheets of different acoustically reflective materials. When a deployed tag is ensonified by an encoded signal sent from a collocated source/receiver pair, the backscattered waveform by the tag yields a time-domain signature unique to the properties of the materials and geometry of the tag. The signature can be used to locate and identify any given tag within a known library of various tag designs. Numerical simulations and experimental results will demonstrate the feasibility of the ...

Weighted coherent processing on sparse volumetric vector sensor arrays

A network of drifting sensors, such as vector sensors mounted to freely drifting buoys, can be used as an array for locating acoustic sources underwater. Localizing a source using traditional coherent processing methods has been improved through arbitrary selection of element-wise weights of the covariance matrix [Nichols and Sabra, JASA 2015, Vol. 138]. However, the selection of weights offers an opportunity to optimize localization performance measures such as accuracy or precision. Here, the performance of source localization is compared between optimal weightings and traditional weightings for both simulated and at-sea data collected from a freely-drifting vector sensor array deployed in the Long Island Sound.

Relocating drifting sensor networks with ambient noise correlations

A network of drifting sensors, such as hydrophones mounted to freely drifting buoys, can be used as an array for locating acoustic sources underwater. However, for accurate localization of such a source using coherent processing, the positions of the sensors need to be known to a high degree of accuracy, typically more accurately than provided by dead reckoning or GPS alone. Past work has demonstrated the inter-sensor distances can be obtained from long-term ambient noise correlations on fixed arrays [Sabra et al., IEEE J. Ocean Engineering, 2005, 30]. Here, the approach was extended for tracking drifting sensor motion by combining a stochastic search algorithm with ambient noise correlation processing. Optimization of the stochastic search method was explored and performance compared to acoustic data collected from a volumetric hydrophone vs. vector sensor array deployed in the Long Island Sound.

Passive ocean acoustic tomography using ships as sources of opportunity recorded on an irregularly spaced free-floating array: A feasibility study

This presentation investigates the practical feasibility of using an adaptive volumetric array, such as a series of free-floating buoys with suspended hydrophones, which record ships as acoustic sources of opportunity in coastal waters for performing acoustic thermometry or other environmental inversions in near-shore environments in a totally passive manner. Ships are tracked using the Automatic Identification System (AIS). Numerical simulations using a standard normal mode propagation model were first used to test limitations of the proposed approach with respect to frequency band, drifting receiver configuration, signal to noise ratio, precision, and accuracy of the inversion results, along with sensitivity to environmental and position mismatch. Performance predictions using this model are compared with experimental results using at-sea data collected off the coast of New London, CT, in Long Island Sound during August of 2015.

Using ambient noise correlations for relocating drifting sensor networks

A drifting sensor network, such as hydrophones mounted on autonomous underwater vehicles or drifting buoys, can be used as a random volumetric array for locating underwater acoustic sources. However, navigational uncertainties of mobile platforms underwater limit the positioning accuracy of their acoustic sensors. Precise positioning is required to perform coherent processing for sound source localization using this random volumetric array. It has been shown that ambient ocean noise correlations between fixed receivers can provide additional inter-element distance information to perform array element self-localization [Sabra et al., IEEE J.Ocean Eng., 30 (2005)]. An extension of this approach for an array of drifting sensors will be proposed by optimizing the required averaging duration to account for sensor drift motion. Performance of this proposed approach will be demonstrated using at-sea data collected in the Long Island Sound.

Coherent vector sensor processing for autonomous underwater glider networks

A distributed array of autonomous underwater gliders, each fitted with a vector sensor measuring acoustic pressure and velocity, form an autonomous sensor network theoretically capable of detecting and tracking objects in an ocean environment. However, uncertainties in sensor positions impede the ability of this glider network to perform optimally. Our work aims to compare the performance of coherent and incoherent processing for acoustic source localization using an array of underwater gliders. Data used in the study were obtained from numerical simulations as well as experimental data collected using the research vessel as a source for localization purposes. By estimating the vessel position with a single glider’s data (incoherent) and comparing to the location estimated with both gliders’ data (coherent), it was determined that location estimation accuracy could be improved using coherent processing, provided the gliders’ positions could be measured with sufficient precision. The results of this study ...