Multiparameter regularization for Volterra kernel identification via multiscale collocation methods

Identification of the Volterra system is an ill-posed problem. We propose a regularization method for solving this ill-posed problem via a multiscale collocation method with multiple regularization parameters corresponding to the multiple scales. Many highly nonlinear problems such as flight data analysis demand identifying the system of a high order. This task requires huge computational costs due to processing a dense matrix of a large order. To overcome this difficulty a compression strategy is introduced to approximate the full matrix resulted in collocation of the Volterra kernel by an appropriate sparse matrix. A numerical quadrature strategy is designed to efficiently compute the entries of the compressed matrix. Finally, numerical results of three simulation experiments are presented to demonstrate the accuracy and efficiency of the proposed method.     

A PARACEST MRI contrast agent to detect enzyme activity

A "smart" PARACEST MRI contrast agent was synthesized to detect caspase-3, which is an important biomarker in apoptosis. The well-known caspase-3 substrate, DEVD (Asp-Glu-Val-Asp), was elongated using the amino group on one sidearm of lanthanide ligand anchored on the polymer support. The amide of DEVD-(Tm-DOTA) showed a PARACEST effect with MR saturation at -51 ppm. DEVD-(Tm-DOTA) amide was successfully cleaved by caspase-3, exposing the free amine group, which showed PARACEST with saturation at +8 ppm. The enzymatic activity of caspase-3 can be detected by the change in PARACEST effect caused by this biotransformation.     

Multiple-array passive acoustic source localization in urban environments

In many situations of interest, obstacles to acoustic wave propagation such as terrain or buildings exist that provide unique challenges to localization. These obstacles introduce multiple propagation paths, reflections, and diffraction into the propagation. In this paper, matched field processing is proposed as an effective method of acoustic localization in a two dimensional scattering environment. Numerical techniques can be used to model complex propagation in a space where analytical solutions are not feasible. Realistically, there is always some uncertainty in model parameters that in turn can adversely affect localization ability. In particular, uncertainty in array location, sound speed, and various parameters affecting inter-array coherence only are investigated. A spatially distributed, multiarray network is shown to mitigate the effects of uncertainty. Multiarray inverse filter processing techniques are evaluated through perturbation of uncertain model parameters. These techniques are more accurate and flexible to implement than other matched field processing methods such as time reversal.     

BOLD signal compartmentalization based on the apparent diffusion coefficient

Functional MRI (fMRI) can detect blood oxygenation level dependent (BOLD) hemodynamic responses secondary to neuronal activity. The most commonly used method for detecting fMRI signals is the gradient-echo echo-planar imaging (EPI) technique because of its sensitivity and speed. However, it is generally believed that a significant portion of these signals arises from large veins, with additional contribution from the capillaries and parenchyma. Early experiments using diffusion-weighted gradient-echo EPI have suggested that intra-voxel incoherent motion (IVIM) weighting inherent in the sequence can selectively attenuate contributions from different vessels based on the differences in the mobility of the blood within them. In the present study, we used similar approach to characterize the apparent diffusion coefficient (ADC) distribution within the activated areas of BOLD contrast. It is shown that the voxel values of the ADCs obtained from this technique can infer various vascular contributions to the BOLD signal.     

Development of a novel label-free amperometric immunosensor for the detection of okadaic acid

Okadaic acid (OA), a lipophilic phycotoxin is mainly produced by toxigenic dinoflagellates. The need to develop high performing methods for OA analysis able to improve the traditional ones is evident. In this work, a novel experimental methodology for label-free detection of OA was developed. Protein G magnetic beads (protein-G-MBs) modified gold electrode was used to immobilize anti-OA monoclonal antibody (anti-OA-MAb). Preliminary, colorimetric tests were performed in order to validate protein-G-MBs and anti-OA-MAb reaction. Electrochemical detection was carried out by differential pulse voltammetry in ferri/ferrocyanide solution. The limit of detection value obtained (0.5 μg L⁻¹) validated the developed electrochemical immunosensor as a promising tool for routine use. The matrix effect and the recovery rate were also assessed with real samples, showing a good percentage of recovery.     

A New Sol-Gel Derived Optical Fiber Sensor for High Acidity Measurements: Application in Nuclear Fuel Reprocessing

Nuclear fuel reprocessing requires high acidity levels that should be accurately and rapidly controlled in order to optimize extraction yields and process efficiency. A new optical fiber sensor based on a sol-gel film doped with an acid-sensitive indicator has been developed to improve remote and on-line monitoring.The organic molecule was physically incorporated in an acid-catalyzed sol-gel matrix and coated onto the core of a denuded optical fiber. The sensor response was evaluated in synthetic solutions of nitric acid, concentrations ranging from 1 to 10 mol · l^–1. Changes in absorption properties and response characteristics of the sensor, when compared to the indicator in solution, have been discussed. Analytical performances of the sensor, i.e. sensitivity, response time, reversibility and repeatability are very encouraging for the on-line analysis. Viability of the sensor for process measurements depends on the stability which might be improved by a strict control of the sensitive film porosity.     

Highly sensitive label-free in vitro detection of aflatoxin B1 in an aptamer assay using optical planar waveguide operating as a polarization interferometer

Analytical and Bioanalytical Chemistry - This work reports on further development of an optical biosensor for the in vitro detection of mycotoxins (in particular, aflatoxin B1) using a highly...     

First synthesis of segetalins B and G: two cyclopentapeptides with estrogen-like activity

The first synthesis of two segetalins B and G is described. The corresponding linear peptides were synthesized using standard automated continuous-flow SPPS methods. Ring closure positions were investigated for segetalin B. The best ring closure result was obtained between Val and Gly.     

Optimization of the isocratic non-aqueous reverse phase (NARP) HPLC separation of trans/cis-α-and β-carotenes

Non-aqueous reverse phase chromatography was used to optimize the separation of all-trans-α- and β-carotenes and their cis isomers extracted from dried carrots. The technique can easily be applied to routine assays. Optimization was carried out by modifying the concentrations of methylene chloride and acetonitrile, and by studying the influence of temperature on the capacity factors and selectivity. The effect of the type of C 18 stationary phase bonding (mono- and polyfunctional) on separation was also examined. The need for polymeric bonding on the stationary phase is stressed for the realization of the trans/cis isomer separation.