Snore signal enhancement and activity detection via translation-invariant wavelet transform

Acoustical properties of snores have been widely studied as a potentially cost-effective and reliable alternative to diagnosing obstructive sleep apnea (OSA), with a common recognition that the diagnostic accuracy depends heavily on the snore signal quality and intelligibility. This paper proposes a novel preprocessing system that performs two critical tasks concurrently in a translation-invariant wavelet transform domain. These tasks include enhancement of snore signals via a level-correlation-dependent (LCD) threshold, and identification of snore presence through a snore activity (SA) detector. Various experiments were conducted to warrant the robustness of the system in terms of theoretical statistics quality, signal-to-noise ratio, mean opinion score, and clinical usefulness in detecting OSA. Results indicate that the proposed LCD threshold and SA detector are highly comparable to the existing denoising methodologies using level-dependent threshold and segmentation approaches using short-time energy and zero-crossing rate, yielding the best results in all the experiments. Given the strong initial performance of the proposed preprocessing system for snore signals, continued exploration in this direction could potentially lead to additional improvement in signal integrity, thereby increasing the diagnostic accuracy for OSA.     

Multiparticulate drug delivery system of aceclofenac: development and in vitro studies

The aim of this study was to develop an enteric-coated multiunit dosage form containing aceclofenac, a nonsteroidal anti-inflammatory drug. The pellets were prepared by using extrusion/spheronization method, and the core pellets were coated with a pH-sensitive poly(meth) acrylate copolymer (Eudragit L100-55) to achieve site-specific drug release. The formulated pellets were characterized for percentage yield, size distribution, surface morphology studies, drug content, and flow properties. In vitro dissolution test was used for comparison of drug release profiles of various coated pellets. The practical yield was found to be 90-95%. The particle size of enteric-coated pellets was found to be in the range of 0.59-0.71 mm. The pellets were spherical in shape and surfaces of pellets were found to be rough and showing micropores. Enteric-coated pellets showed good flow properties and in vitro dissolution profile. Dissolution tests were carried out in a USP type II dissolution apparatus in media-simulating pH conditions of the gastrointestinal tract. The release of the aceclofenac from formulated pellets was established to be minimum in the pH 1.2 (<5%) for a period of 2 h, and at pH 6.8, it shows the maximum release (85 +/- 5% release within 1 h) which indicates gastric resistance of the formulated pellets. The 20% wt/wt enteric-coated pellets were compared to that of marketed product (tablets), it was observed that pellets showed better release profile. The study concluded that the formulated multiparticulate dosage forms can be used as an ideal drug delivery system for the aceclofenac.     

Developing Biodegradable Mulch Films from Starch‐Based Polymers

This paper examines the development of starch‐based plastics for use as biodegradable mulch film. A variety of starch‐based polymers are blended with high performance biodegradable polyester polymers in order to determine the applicability of films to be processed on a film blowing line and to perform well in mulch film field trials. The process of material formulation, film blowing processing and scale‐up and performance properties are highlighted for a successful material. Insights into future developments of starch‐derived biodegradable polymers are given.     

Robust Adaptive Gain Higher Order Sliding Mode Observer Based Control-constrained Nonlinear Model Predictive Control for Spacecraft Formation Flying

This work deals with the development of a decentralized optimal control algorithm, along with a robust observer, for the relative motion control of spacecraft in leader-follower based formation. An adaptive gain higher order sliding mode observer has been proposed to estimate the velocity as well as unmeasured disturbances from the noisy position measurements. A differentiator structure containing the Lipschitz constant and Lebesgue measurable control input, is utilized for obtaining the estimates. Adaptive tuning algorithms are derived based on Lyapunov stability theory, for updating the observer gains, which will give enough flexibility in the choice of initial estimates. Moreover, it may help to cope with unexpected state jerks. The trajectory tracking problem is formulated as a finite horizon optimal control problem, which is solved online. The control constraints are incorporated by using a nonquadratic performance functional. An adaptive update law has been derived for tuning the step size in the optimization algorithm, which may help to improve the convergence speed. Moreover, it is an attractive alternative to the heuristic choice of step size for diverse operating conditions. The disturbance as well as state estimates from the higher order sliding mode observer are utilized by the plant output prediction model, which will improve the overall performance of the controller. The nonlinear dynamics defined in leader fixed Euler-Hill frame has been considered for the present work and the reference trajectories are generated using Hill-Clohessy-Wiltshire equations of unperturbed motion. The simulation results based on rigorous perturbation analysis are presented to confirm the robustness of the proposed approach.      

Embedded proteins and sacrificial bonds provide the strong adhesive properties of gastroliths

The adhesive properties of gastroliths from a freshwater crayfish (Cherax quadricarinatus) were quantified by colloidal probe atomic force microscopy (AFM) between heavily demineralized gastrolith microparticles and gastrolith substrates of different composition. Combined AFM and transmission electron microscopy studies demonstrated that the sequential detachment and large adhesion energies that characterise the adhesive behaviour of a native gastrolith substrate are dominated by sacrificial bonds between chitin fibres and between chitin fibres and CaCO(3). The sacrificial bonds were shown to be strongly related to the gastrolith proteins and when the majority of these proteins were removed by ethylenediaminetetraacetic acid (EDTA), the sequential detachment disappeared and the adhesive energy was reduced by more than two orders of magnitude.     

The effects of HNE on ovine oxymyoglobin redox stability in a microsome model

The effect of 4-hydroxy-2-nonenal (HNE), a secondary lipid oxidation product, on ovine myoglobin (Mb) redox stability was investigated. HNE increased oxymyoglobin (OxyMb) oxidation under all pH/temperature conditions studied. Mono-, di- and tri-HNE adducts were detected by ESI-Q-TOF MS analysis. Sites of adduction, His 120, His 25 and His 65, were determined by ESI–CID–MS/MS analysis. The relationship between ovine Mb (with/without HNE) and lipid oxidation was also studied in a microsome model in the presence of α-tocopherol. Surprisingly, preincubation of Mb with HNE did not affect subsequent Mb redox stability in the microsome model (P < 0.05). Microsomes with elevated concentrations of α-tocopherol delayed lipid and Mb oxidations relative to controls. HNE-treated ovine Mb caused greater lipid oxidation compared to control ovine Mb in control microsomes (P < 0.05). This study demonstrated an interaction between ovine Mb oxidation and lipid oxidation.     

Engineering Nanoparticle Cluster Arrays for Bacterial Biosensing: The Role of the Building Block in Multiscale SERS Substrates

Noble metal nanoparticle cluster arrays (NCAs) are a novel class of engineered substrates for surface enhanced Raman spectroscopy (SERS), in which the noble metal nanoparticles interact on multiple length scales to create a multiscale E‐field cascade enhancement. In this work the role of the building block for the NCA performance is quantified. Periodic NCAs with constant cluster diameter (D = 200 nm) but variable nanoparticle diameter (d) and intercluster separation (Λ) were assembled on glass and their optical response and SERS enhancement were systematically characterized as a function of D, Λ, and d. An increase of d from 40 to 80 nm and simultaneous decrease of Λ from 200 to 50 nm led to an improvement of the ensemble averaged SERS enhancement factor by a factor of up to ～8. The coefficient of variation (c_v) of the enhancement factors (G) is significantly lower for the d = 80 nm NCAs than for the d = 40 nm and d = 60 nm NCAs. Optimized (D = 200 nm, Λ = 50 nm, d = 80 nm) NCAs show the overall highest signal reproducibility of all investigated NCAs and random nanoparticle substrates and achieve effective single cell detection sensitivity.     

On the difference between surface-enhanced raman scattering (SERS) spectra of cell growth media and whole bacterial cells

It has been recently suggested [N. E. Marotta and L. A. Bottomley, Appl. Spectrosc. 64, 601-606 (2010)] that previously reported surface-enhanced Raman scattering (SERS) spectra of vegetative bacterial cells are due to residual cell growth media that were not properly removed from samples of the lab-cultured microorganism suspensions. SERS spectra of several commonly used cell growth media are similar to those of bacterial cells, as shown here and reported elsewhere. However, a multivariate data analysis approach shows that SERS spectra of different bacterial species grown in the same growth media exhibit different characteristic vibrational spectra, SERS spectra of the same organism grown in different media display the same SERS spectrum, and SERS spectra of growth media do not cluster near the SERS spectra of washed bacteria. Furthermore, a bacterial SERS spectrum grown in a minimal medium, which uses inorganics for a nitrogen source and displays virtually no SERS features, exhibits a characteristic bacterial SERS spectrum. We use multivariate analysis to show how successive water washing and centrifugation cycles remove cell growth media and result in a robust bacterial SERS spectrum in contrast to the previous study attributing bacterial SERS signals to growth media.