Development of solid-phase extraction method and its application for determination of hydrochlorothiazide in human plasma using HPLC

A high-performance liquid chromatographic method was developed, validated and applied for the determination of hydrochlorothiazide in human plasma. The effects of mobile phase composition, buffer concentration, mobile phase pH and concentration of organic modifiers on retention of hydrochlorothiazide and internal standard were investigated. The method involves solid-phase extraction on RP-select B cartridges followed by isocratic reversed-phase chromatography on a Hibar Lichrospher 100 RP-8 column with UV detection at 230 nm. The recovery, selectivity, linearity, precision and accuracy of the method were evaluated from spiked human plasma samples. Limit of quantification was 10 ng mL(-1). The method has been implemented to monitor hydrochlorothiazide levels in patient samples.     

Benchmarking Attention-Based Interpretability of Deep Learning in Multivariate Time Series Predictions

The adaptation of deep learning models within safety-critical systems cannot rely only on good prediction performance but needs to provide interpretable and robust explanations for their decisions. When modeling complex sequences, attention mechanisms are regarded as the established approach to support deep neural networks with intrinsic interpretability. This paper focuses on the emerging trend of specifically designing diagnostic datasets for understanding the inner workings of attention mechanism based deep learning models for multivariate forecasting tasks. We design a novel benchmark of synthetically designed datasets with the transparent underlying generating process of multiple time series interactions with increasing complexity. The benchmark enables empirical evaluation of the performance of attention based deep neural networks in three different aspects: (i) prediction performance score, (ii) interpretability correctness, (iii) sensitivity analysis. Our analysis shows that although most models have satisfying and stable prediction performance results, they often fail to give correct interpretability. The only model with both a satisfying performance score and correct interpretability is IMV-LSTM, capturing both autocorrelations and crosscorrelations between multiple time series. Interestingly, while evaluating IMV-LSTM on simulated data from statistical and mechanistic models, the correctness of interpretability increases with more complex datasets.     

A comparative study of amphiphilic PAMAM dendrimers at the air-water interface with different hydrophobe attachment groups

Generation 0 through 5 polyamidoamine (PAMAM) dendrimers with three different types of groups connecting to hydrophobic C12 tails and one type of group connecting to C18 tails were synthesized and studied as monolayers at the air-water interface with a Langmuir trough. The molecular areas were significantly influenced by the size and the type of connecting group. Higher-generation (e.g., G4 and G5) amphiphilic PAMAMs with amide connecting groups were more responsive to changes in compression rate and subphase temperature and less stable than the corresponding opened epoxide- or ester-connected counterparts. Intramolecular (and possibly also intermolecular) attractive hydrogen-bond interactions between the amide connectors are proposed as the reason for this behavior.     

Functionalization of Multi‐Walled Carbon Nanotubes by Electrografting of Polyacrylonitrile

Summary: Multi‐walled carbon nanotubes (MWNTs) have been successfully modified with polyacrylonitrile (PAN) by a cathodic electrochemical process. The surface‐modified MWNTs afforded are then dispersible in good solvents for PAN, such as N,N‐dimethylformamide (DMF). Collected from a dilute dispersion, these MWNTs are essentially disentangled, as confirmed by transmission electron microscopy (TEM) analysis. From the differential scanning calorimetry (DSC) traces for polyacrylonitrile and polyacrylonitrile‐grafted MWNTs, the maximum grafting ratio is estimated at 0.28.

Electrochemical grafting of polyacrylonitriles onto the surface of multi‐walled carbon nanotubes.     

Characterization and Optimization of a Resonant Cavity Enhanced P-i-N Photodiode Response

This paper presents linear pulse response of a Resonant Cavity Enhanced (RCE) P-i-N fotodiode. The RCE P-i-N photodiode designed for high-speed aplication is analysed for various submicron thicknesses of absorption layer, bias voltages, active areas and incident pulse optical excitations. The results are obtained by numerical simulation of the complete phenomenological model for two valley semiconductor. Great enhancement of the quantum efficiency and the product bandwidth-quantum efficiency, is obvious from obtained results for this photodiode type.     

Dinuclear vs. Mononuclear Copper(II) Coordination Species of Tylosin and Tilmicosin in Non-Aqueous Solutions

The veterinary 16-membered macrolide antibiotics tylosin (HTyl, 1a) and tilmicosin (HTilm, 1b) react with copper(II) ions in acetone at metal-to-ligand molar ratio of 1:2 to form blue (2) or green (3) metal(II) coordination species, containing nitrate or chloride anions, respectively. The complexation processes and the properties of 2–3 were studied by an assortment of physicochemical techniques (UV-Vis, EPR, NMR, FTIR, elemental analysis). The experimental data revealed that the main portion of copper(II) ions are bound as neutral EPR-silent dinuclear complexes of composition [Cu₂(µ-NO₃)₂L₂] (2a–b) and [Cu₂(µ-Cl)₂Cl₂(HL)₂] (3a–b), containing impurities of EPR-active mono-species [Cu(NO₃)L] (2a’–b’) and [CuCl₂(HL)] (3a’–b’). The possible structural variants of the dinuclear- and mono-complexes were modeled by the DFT method, and the computed spectroscopic parameters of the optimized constructs were compared to those measured experimentally. Using such a combined approach, the main coordination unit of the macrolides, involved in the complex formation, was defined to be their mycaminosyl substituent, which acts as a terminal ligand in a bidentate mode through the tertiary nitrogen atom and the oxygen from a deprotonated (2) or non-dissociated (3) hydroxyl group, respectively.     

A reduced basis approach to large‐scale pseudospectra computation

For studying spectral properties of a nonnormal matrix $A\in {\mathbb{C}}^{n\times n}$, information about its spectrum σ(A) alone is usually not enough. Effects of perturbations on σ(A) can be studied by computing ε‐pseudospectra, i.e. the level sets of the resolvent norm function $\mathsf{g}(z)=\Vert {(zI?A)}^{?1}{\Vert }_2$. The computation of ε‐pseudospectra requires determining the smallest singular values ${\sigma }_{\min }(zI?A)$ for all z on a portion of the complex plane. In this work, we propose a reduced basis approach to pseudospectra computation, which provides highly accurate estimates of pseudospectra in the region of interest, in particular, for pseudospectra estimates in isolated parts of the spectrum containing few eigenvalues of A. It incorporates the sampled singular vectors of zI ? A for different values of z, and implicitly exploits their smoothness properties. It provides rigorous upper and lower bounds for the pseudospectra in the region of interest. In addition, we propose a domain splitting technique for tackling numerically more challenging examples. We present a comparison of our algorithms to several existing approaches on a number of numerical examples, showing that our approach provides significant improvement in terms of computational time.     

On Trigonometric Blending Interpolation and Cubature Formulae

We discuss error representations for Hermite-Lagrange trigonometric interpolation introduced in Dryanov and Petrov (Interpolation and L ₁-approximation by trigonometric polynomials and blending functions, J. Approx. Theory 164, 1049–1064 (2012)) and obtain one-sided trigonometric quadratures for approximate integration of one-dimensional integrals. Next, we study error representations of multivariate Hermite-Lagrange transfinite trigonometric interpolation and derive one-sided trigonometric blending interpolants to multivariate functions, under some restrictions. Then, we construct one-sided transfinite cubature formulae for approximate integration of multivariate integrals. We construct also cubature formulae with positive coefficients, based on line integrals and exact in a vector space of trigonometric blending functions with prescribed order.