Improving Pure-Tone Audiometry Using Probabilistic Machine Learning Classification

Hearing loss is a critical public health concern, affecting hundreds millions of people worldwide and dramatically impacting quality of life for affected individuals. While treatment techniques have evolved in recent years, methods for assessing hearing ability have remained relatively unchanged for decades. The standard clinical procedure is the modified Hughson-Westlake procedure, an adaptive pure-tone detection task that is typically performed manually by audiologists, costing millions of collective hours annually among healthcare professionals. In addition to the high burden of labor, the technique provides limited detail about an individual’s hearing ability, estimating only detection thresholds at a handful of pre-defined pure-tone frequencies (a threshold audiogram). An efficient technique that produces a detailed estimate of the audiometric function, including threshold and spread, could allow for better characterization of particular hearing pathologies and provide more diagnostic value. Parametric techniques exist to efficiently estimate multidimensional psychometric functions, but are ill-suited for estimation of audiometric functions because these functions cannot be easily parameterized. The Gaussian process is a compelling machine learning technique for inference of nonparametric multidimensional functions using binary data. The work described in this thesis utilizes Gaussian process classification to build an automated framework for efficient, high-resolution estimation of the full audiometric function, which we call the machine learning audiogram (MLAG). This Bayesian technique iteratively computes a posterior distribution describing its current belief about detection probability given the current set of observed pure tones and detection responses. The posterior distribution can be used to provide a current point estimate of the psychometric function as well as to select an informative query point for the next stimulus to be provided to the listener. The Gaussian process covariance function encodes correlations between variables, reflecting prior beliefs on the system; MLAG uses a composite linear/squared exponential covariance function that enforces monotonicity with respect to intensity but only smoothness with respect to frequency for the audiometric function. This framework was initially evaluated in human subjects for threshold audiogram estimation. 2 repetitions of MLAG and 1 repetition of manual clinical audiometry were conducted in each of 21 participants. Results indicated that MLAG both agreed with clinical estimates and exhibited test-retest reliability to within accepted clinical standards, but with significantly fewer tone deliveries required compared to clinical methods while also providing an effectively continuous threshold estimate along frequency. This framework’s ability to evaluate full psychometric functions was then evaluated using simulated experiments. As a feasibility check, performance for estimating unidimensional psychometric functions was assessed and directly compared to inference using standard maximum-likelihood probit regression; results indicated that the two methods exhibited near identical performance for estimating threshold and spread. MLAG was then used to estimate 2-dimensional audiometric functions constructed using existing audiogram phenotypes. Results showed that this framework could estimate both threshold and spread of the full audiometric function with high accuracy and reliability given a sufficient sample count; non-active sampling using the Halton set required between 50-100 queries to reach clinical reliability, while active sampling strategies reduced the required number to around 20-30, with Bayesian active leaning by disagreement exhibiting the best performance of the tested methods. Overall, MLAG’s accuracy, reliability, and high degree of detail make it a promising method for estimation of threshold audiograms and audiometric functions, and the framework’s flexibility enables it to be easily extended to other psychophysical domains

Isospin Symmetry Breaking in the Chiral Quark Model

We discuss the isospin symmetry breaking (ISB) of the valence- and sea-quark distributions between the proton and the neutron in the framework of the chiral quark model. We assume that isospin symmetry breaking is the result of mass differences between isospin multiplets and then analyze the effects of isospin symmetry breaking on the Gottfried sum rule and the NuTeV anomaly. We show that, although both flavor asymmetry in the nucleon sea and the ISB between the proton and the neutron can lead to the violation of the Gottfried sum rule, the main contribution is from the flavor asymmetry in the framework of the chiral quark model. We also find that the correction to the NuTeV anomaly is in an opposite direction, so the NuTeV anomaly cannot be removed by isospin symmetry breaking in the chiral quark model. It is remarkable that our results of ISB for both valence- and sea-quark distributions are consistent with the Martin-Roberts-Stirling-Thorne parametrization of quark distributions.Comment: 14 latex pages, 3 figures, final version for journal publicatio

Harmless delays and global attractivity for nonautonomous predator-prey system with dispersion

AbstractIn this paper, we consider a nonautonomous predator-prey model with dispersion and a finite number of discrete delays. The system consists of two Lotka-Volterra patches and has two species: one can disperse between two patches, but the other is confined to one patch and cannot disperse. Our purpose is to demonstrate that the time delays are harmless for uniform persistence of the solutions of the system. Furthermore, we establish conditions under which the system admits a positive periodic solution which attracts all solutions

Periodic Solutions and Homoclinic Bifurcations of Two Predator-Prey Systems with Nonmonotonic Functional Response and Impulsive Harvesting

Two predator-prey models with nonmonotonic functional response and state-dependent impulsive harvesting are formulated and analyzed. By using the geometry theory of semicontinuous dynamic system, we obtain the existence, uniqueness, and stability of the periodic solution and analyse the dynamic phenomenon of homoclinic bifurcation of the first system by choosing the harvesting rate β as control parameter. Besides, we also study the homoclinic bifurcation of the second system about parameter δ on the basis of the theory of rotated vector field. Finally, numerical simulations are presented to illustrate the results

Structure properties change of ready-to-use nonwoven wiping materials over storage time

Healthcare-associated infections (HAIs) caused by the transfer of nosocomial pathogens from high-touch environmental surfaces and medical devices are responsible for significant patient morbidity, mortality and economic cost.[1] An effective cleaning and disinfection practice plays a key role in preventing cross-contaminations and spread of HAIs.[2] Traditionally, healthcare staff has used the “bucket method”, which consists of towels saturated with diluted disinfectant contained in a bucket. This method exhibits several limitations such as improper disinfectant dilution, inadequate saturation, uneven moisture distribution, unknown material compatibility and possible contamination from reusing.[3-4] Among the most effective surface disinfection methods, the nonwoven ready-to-use disinfectant wipes are increasingly accepted for decontamination of high-touch surfaces because of its convenience and reliable performance.[5] Though some research has been done on the effectiveness of commercial available disinfecting wipes in practical use.[6] Whereas their behaviour during storage remains unknown. In addition, a lower or even abolished disinfectant efficacy of the active ingredients due to their interaction with the textile materials has been also reported.[7] This project studied the ageing of the disinfecting wipes over storage time. Chloramine as a surface disinfectant and 3 commercial wiping materials of polyester, viscose, and their combination have been selected. The wipes before and after the contact with disinfectant solution were analysed by FTIR (Fourier-transform infrared spectroscopy) and DMA (Dynamic mechanical analysis).Xinyu Song acknowledges Fundação para a Ciência e Tecnologia (FCT), Portugal, for its PhD grant financial support (SFRH/BD/130028/2017). Andrea Zille also acknowledges FCT through the iFCT Research contract (IF/00071/2015) and the project POCI-01-0145-FEDER-007136 under the COMPETE and FCT/MCTES (PIDDAC) co-financed by European funds (FEDER) through the PT2020 program.info:eu-repo/semantics/publishedVersio

Stability analysis of a ratio-dependent predator-prey system with diffusion and stage structure

A two-species predator-prey system with diffusion term and stage structure is discussed, local stability of the system is studied using linearization method, and global stability of the system is investigated by strong upper and lower solutions. The asymptotic behavior of solutions and the negative effect of stage structure on the permanence of populations are given