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Unit square visibility graphs (USV) are described by axis-parallel visibility between unit squares placed in the plane. If the squares are required to be placed on integer grid coordinates, then USV become unit square grid visibility graphs (USGV), an alternative characterisation of the well-known rectilinear graphs. We extend known combinatorial results for USGV and we show that, in the weak case (i.e., visibilities do not necessarily translate into edges of the represented combinatorial graph), the area minimisation variant of their recognition problem is N P -hard. We also provide combinatorial insights with respect to USV, and as our main result, we prove their recognition problem to be N P -hard, which settles an open question. [ABSTRACT FROM AUTHOR]

In many applied problems, the individual components of the unknown vector are interconnected and therefore splitting schemes are applied in order to get a simple problem for evaluating unknowns at a new time level. On the basis of additive schemes (splitting schemes), there are constructed efficient computational algorithms for numerical solving the initial value problems for systems of time-dependent PDEs. The present paper deals with computational algorithms that are based on using explicit-implicit approximations in time. Typically, additive operator-difference schemes for systems of evolutionary equations are constructed for operators that are coupled in space. Here we investigate more general problems, where we have coupling of derivatives in time for components of the solution vector. [ABSTRACT FROM AUTHOR]

In this article, we consider k-way vertex cut: the problem of finding a graph separator of a given size that decomposes the graph into the maximum number of components. Our main contribution is the derivation of an efficient polynomial-time approximation scheme for the problem on planar graphs. Also, we show that k-way vertex cut is polynomially solvable on graphs of bounded treewidth and fixed-parameter tractable on planar graphs with the size of the separator as the parameter. © 2013 Wiley Periodicals, Inc. NETWORKS, Vol. 63(2), 170-178 2014 [ABSTRACT FROM AUTHOR]

A reliable and high throughput high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed and validated for determining levels of the antitubercular drug- d -cycloserine in human plasma. Plasma samples analyte with an internal standard (IS) (niacin) were prepared by solid-phase extraction using Waters Oasis MCX cartridges. The chromatographic separation was performed using the HILIC mode on a YMC-Pack SIL-06 column (150 × 4.6 mm; 3 μm) under isocratic conditions. The run time of analysis was 5 min. The mobile phase consisted of methanol, propanol-2 and 0.075 % trifluoroacetic acid (66.5:28.5:5, v/ v/ v). Protonated ions formed by turbo ion spray in positive mode were used to detect the analyte and the IS. MS/MS detection was used to monitor the fragmentation of 103-75 m/ z for cycloserine and 124 to 80 m/ z for niacin (IS) on an API 4000 (AB Sciex) triple quadrupole mass spectrometer. A linear dynamic range of 0.3-30 μg/mL was established for cycloserine using 0.2 mL human plasma and a 1 μL injection volume. The mean relative recovery of cycloserine and niacin were 77.2 and 82.4 %, respectively. The procedure of sample preparation was consistent and reproducible (precision, 0.8-3.4 %; accuracy, 93.8-104.9 %). The method was validated in accordance with requirements of the European Medicines Agency and successfully applied to a bioequivalence study of 250 mg tablet formulations in 23 healthy human subjects. [ABSTRACT FROM AUTHOR]

• Home-made HILIC column with surface quaternary ammonium groups and terminal diols. • Chromatographic behaviour of eremomycin and vancomycin on different HILIC columns. • Good eremomycin peak shape and its separation from admixtures on self-made column. • Dissolution test for preclinical study of novel antibiotic drug using home-made column. • HILIC-MS/MS determination of eremomycin in rabbit plasma for pharmacokinetic study. A complex of hydrophilic interaction liquid chromatography (HILIC) methods for simple and efficient determination of eremomycin (ERM) as an active pharmaceutical ingredient (API) of a novel drug is proposed for preclinical study, which includes the dissolution test and pharmacokinetic study on the animals. A home-made HILIC silica-based stationary phase (SP) containing diol functionalities and positively charged nitrogen atoms in its structure was synthesized for this research and applied for the first time for performing the first step of preclinical study (dissolution test) of the novel ERM-containing drug. HILIC method developed using novel home-made SP allowed us to avoid any interferences from polyethylene glycol (PEG) contained in the drug matrix thus providing a unique advantage of the proposed approach over RP HPLC. The home-made SP demonstrated better chromatographic performance as compared to the tested commercially available columns with various functionalities. Different retention behaviour and mechanisms with various electrostatic impact were demonstrated for two glycopeptide antibiotics, namely, ERM and its analogue vancomycin (VAN), on the home-made SP. For the second step of the preclinical study HILIC-MS/MS method for ERM determination in rabbit plasma was developed and validated in accordance with the EMA requirements and successfully applied to the preclinical study on rabbits after intravenous and intraperitoneal drug administration. The results of dissolution test and pharmacokinetic study revealed similar in vitro solubility of ERM and VAN and low ERM bioavailability, which proved the potential safety and efficiency of the novel drug. [ABSTRACT FROM AUTHOR]

Investigations of the in-plane positioning capabilities of microscopes using machine-readable encoded patterned scales are presented. The scales have patterns that contain absolute position information, and adequate software accurately determines the in-plane position from the scale images captured by the microscope camera. This makes in-plane positioning experiments simple and fast. The scales and software used in this study are commercially available. We investigated different microscopy systems and found that positioning performance is a system issue that is not determined solely by stage performance. In some cases, our experiments revealed software or hardware glitches that limited the positioning performance, which we easily fixed. We have also shown that it is possible to investigate vibrations using this approach and quantify their impact on image blurring. This is, for example, useful for experimentally determining the settling time after a stage movement., (© 2023. The Author(s).)

For the first time, an HPLC-MS/MS method for the determination pmol/l levels of troventol (TRV) and clenbuterol as an internal standard (IS) in human plasma was developed, validated and tested on biological samples. The method included solid phase extraction by Waters Oasis WCX cartridges and chromatographic separation on a YMC-Pack SIL (100mm×2.1mm, 5μm, 12nm) analytical column with acetonitrile-water-formic acid (50:50:0.1, v/v/v) as the mobile phase; the selected ion transitions were m/z 332.2→138.2 and m/z 277.0→203.1 for TRV and IS, respectively, in positive ionization mode. The calibration curve for TRV showed good linearity in the concentration range of 35-500pg/ml. The method was applied to real samples taken from healthy subjects after inhalation of an aerosol containing 640μg of TRV., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The method for simultaneous determination of nifedipine (NIF) and lidocaine (LID) in human plasma by one-step sample preparation has been developed for the first time. Due to the photosensitivity of nifedipine and its low plasma concentrations a precise and reliable method was required. The method involved liquid-liquid extraction (methyl tert-butyl ether, MTBE), and 10μL of the resulting sample was analyzed by HPLC-MS/MS. Chromatographic separation was achieved on an YMC-Triart C18 HPLC column (100×2.0mm; S-5μm 12nm). The mobile phase was methanol:water, 60:40 (v/v) and contained 0.15% acetic acid. The linearity of the method was established in the concentration ranges of 0.5-50ng/mL for NIF and 1.0-500ng/mL for LID. Photodestruction of NIF under ambient light was evaluated. The validated method was successfully applied to analyze human plasma samples after rectal application of the drug (1g) containing 2.0% LID and 0.3% NIF., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A simple, precise, and rapid method to simultaneously determine the levels of oseltamivir (OS) and oseltamivir carboxylate (OSC) in human plasma was developed. Additionally, the stability of both substances in plasma was investigated under different conditions. The method involved protein precipitation (0.01 % HCl in acetonitrile), and then the supernatant was injected into the high-performance liquid chromatography (HPLC)-MS/MS. The chromatographic separation was achieved on a YMC-Triart C18 (100 × 2.0 mm, 5 μm) column using acetonitrile/water (30:70, v/v) containing 0.1 % formic acid as the mobile phase. Sample volume was 5 μl. The linearity of the method was established in the concentration range of 0.5-100 ng/mL for OS and 1.0-1000 ng/mL for OSC. The intra-day precision and accuracy for oseltamivir were 1.5-8.9 and 94.4-101.0 %, respectively. For oseltamivir carboxylate, the intra-day precision and accuracy were 3.2-12.7 and 92.8-108.8 %, respectively, whereas the inter-day precision and accuracy were 5.5-11.5 and 94.6-104.0 % for oseltamivir and 4.7-11.5 and 99.9-103.9 % for oseltamivir carboxylate, respectively. The application of this method was demonstrated by a bioequivalence study in 28 healthy humans with 75 mg oseltamivir phosphate capsules (Tamiflu®). Sodium fluoride (2.4 mg/mL) with potassium oxalate (3 mg/mL) was used as anticoagulant within sampling of trial. The assay reproducibility was established by reanalysis of 80 incurred samples.