Amperometric ATP microbiosensors for the analysis of chemosensitivity at rat carotid bodies

The physiological application of amperometric adenosine triphosphate (ATP) microbiosensors for characterizing the stimulus-response at rat carotid bodies superfused with high potassium concentrations, during normoxic hypercapnia, and during hypoxia is demonstrated using the peripheral arterial chemoreceptors in the carotid body of rats as a model system. Amperometric microbiosensors based on glucose oxidase (GOD) and hexokinase (HEX) immobilized within a polymer matrix at the surface of Pt disk microelectrodes (diameter: 25 microm) are positioned at a distance of approximately 100 microm above the carotid body surface for detecting extracellular ATP. A linear calibration function of ATP microbiosensors in the physiologically relevant concentration range of 0-40 microM ATP enables quantitative detection of ATP released at the carotid body surface in response to physiological stimuli. It is shown that these stimuli induce extracellular ATP release from the carotid body at levels of 4-10 microM. Other electroactive neurotransmitters such as, e.g., catecholamines are coreleased by the carotid body at hypercapnic, hypoxic and high-potassium stimulus, are simultaneously detected utilizing a dual-electrode assembly with an ATP microbiosensor and a second bare channel providing a colocalized reference measurement for ATP quantification.     

Quantitative measurement of cardiac markers in undiluted serum

Two mycocardial infarction biomarkers, myoglobin (MG) and cardiac troponin I (cTnI), were quantified at biological levels and in undiluted serum without sample pretreatment using surface plasmon resonance (SPR) sensors. To achieve detection of biomarkers in undiluted serum (72 mg/mL total protein concentration), minimization of the nonspecific signal from the serum protein was achieved by immobilizing the antibody for the biomarkers on an N-hydroxysuccinimide activated 16-mercaptohexadecanoic acid self-assembled monolayer. This monolayer reduces the nonspecific signal from serum proteins in such a manner that short exposure of the sensor to serum prior to analysis prevents any further nonspecific adsorption during analysis. Thus, sensing of MG and cTnI was achieved on the basis of the difference between signals from the active sensor and a reference sensor that captured background interference. This resulted in direct measurement of these biomarkers in undiluted serum. Detection limits for both markers were below 1 ng/mL, which is below the threshold needed to detect myocardial infarction. Detecting biomarkers in the low ng/mL range without signal amplification in such a complex matrix as serum corresponds to a selectivity of 108. The root-mean-square-error (RMSE) of calibration was below 2 ng/mL.     

Very fast blind source separation by signal to noise ratio based stopping threshold for the SHIBBS/SJAD algorithm

This paper works on joint approximate diagonalization of simplified fourth order cumulant matrices for very fast and large scale blind separation of instantaneous mixing model sources. The JADE algorithm is widely accepted but only limited to small scale separation tasks. The SHIBBS algorithm calculates a fraction of the fourth order cumulant set and avoids eigenmatrix decomposition to reduce calculation cost. However, it was seen to be slower than JADE at the time of its first publication and is hence less known. On the other hand, the SJAD algorithm using the same approach is shown to be very fast. This paper studies the iteration convergence criterion and proposes to use a signal to noise ratio based iteration stopping threshold approach. The improved SHIBBS/SJAD algorithm is very fast, and capable of large scale separation. Experimental separation comparisons between the SHIBBS/SJAD and FastICA are presented.     

Satellite and satellite subsystems reliability: Statistical data analysis and modeling

Reliability has long been recognized as a critical attribute for space systems. Unfortunately, limited on-orbit failure data and statistical analyses of satellite reliability exist in the literature. To fill this gap, we recently conducted a nonparametric analysis of satellite reliability for 1584 Earth-orbiting satellites launched between January 1990 and October 2008. In this paper, we extend our statistical analysis of satellite reliability and investigate satellite subsystems reliability. Because our dataset is censored, we make extensive use of the Kaplan–Meier estimator for calculating the reliability functions. We derive confidence intervals for the nonparametric reliability results for each subsystem and conduct parametric fits with Weibull distributions using the maximum likelihood estimation (MLE) approach. We finally conduct a comparative analysis of subsystems failure, identifying the “culprit subsystems” that drive satellite unreliability. The results here presented should prove particularly useful to the space industry for example in redesigning subsystem test and screening programs, or providing an empirical basis for redundancy allocation.     

鞋履奇才Michel Perry的梦想庄园

Voudenay庄园位于著名的葡萄酒故乡——法国勃艮第(Bourgogne),建造于十八世纪,周围风景如画,一派诗情画意。这座美丽的庄园曾经破败不堪,仿如废墟,但被鞋履设计师Michel Perry购买、翻修后又重现生机。Michel Perry夫妇是在无意间发现Vaudenay庄园的,故事开始说     

Laser Surface Nitriding of Ti-6A1-4V Titanium Alloy

Titanium and its alloys are known for their high specific strength as well as fatigue and corrosion resistance. However, they suffer from poor wear and friction resistance, limiting their use in tribological applications. Nitriding of these materials may be carried out favourably to harden them and thus to improve both wear and friction resistance. The laser nitriding process involves using the intense energy of the laser to melt the surface in a nitrogen comprising atmosphere. This results in creation of a very hard layer consisting of dendritic structures of nitride. But the non-uniformity of the melt pool and cracks in the nitrided layers have been generally observed. Our study deals with the results of Ti-6Al-4V laser surface nitriding and with the effects of a sample preheating on the cracks generation.     

Crosslinked polyethers as media for ionic conduction

A broad outline is given of a comprehensive investigation dealing with solid polymeric electrolytes containing ionic species. These materials are based on various types of polyethers (homopolymers, block and graft copolymers) crosslinked via urethane chemistry and either filled with a salt or transformed into ionomers with the anions attached to the chains. The properties studied were specific volume, swelling, glass transition temperature, viscoelasticity, ionic conductivity, transport numbers, magnetic relaxation of nuclei from both the polymer chains and the ions, and redox stability. Mechanisms and models are proposed to explain chain partitioning by cations and the mode of ionic transport. An all-solid-state battery was prepared with one of these materials to prove its good performance.     

Evolutionary design of discrete controllers for hybrid mechatronic systems

This paper investigates the issue of evolutionary design of controllers for hybrid mechatronic systems. Finite State Automaton (FSA) is selected as the representation for a discrete controller due to its interpretability, fast execution speed and natural extension to a statechart, which is very popular in industrial applications. A case study of a two-tank system is used to demonstrate that the proposed evolutionary approach can lead to a successful design of an FSA controller for the hybrid mechatronic system, represented by a hybrid bond graph. Generalisation of the evolved FSA controller to unknown control targets is also tested. Further, a comparison with another type of controller, a lookahead controller, is conducted, with advantages and disadvantages of each discussed. The comparison sheds light on which type of controller representation is a better choice to use in various stages of the evolutionary design of controllers for hybrid mechatronic systems. Finally, some important future research directions are pointed out, leading to the major work of the succeeding part of the research.     

Applying SVMs and weight-based factor analysis to unsupervised adaptation for speaker verification

This paper presents an extended study on the implementation of support vector machine (SVM) based speaker verification in systems that employ continuous progressive model adaptation using the weight-based factor analysis model. The weight-based factor analysis model compensates for session variations in unsupervised scenarios by incorporating trial confidence measures in the general statistics used in the inter-session variability modelling process. Employing weight-based factor analysis in Gaussian mixture models (GMMs) was recently found to provide significant performance gains to unsupervised classification. Further improvements in performance were found through the integration of SVM-based classification in the system by means of GMM supervectors.This study focuses particularly on the way in which a client is represented in the SVM kernel space using single and multiple target supervectors. Experimental results indicate that training client SVMs using a single target supervector maximises performance while exhibiting a certain robustness to the inclusion of impostor training data in the model. Furthermore, the inclusion of low-scoring target trials in the adaptation process is investigated where they were found to significantly aid performance.     

Comments on: Deville and Särndal’s calibration: revisiting a 25 years old successful optimization problem

TEST - We provide a brief discussion on the development of model calibration techniques and optimal calibration estimation in survey sampling and its relation to Deville and Särndal’s...