Spectroscopic properties of Yb and Er ions in heavy metal glasses

Selected heavy metal glasses containing Yb³⁺ and Er³⁺ ions have been studied. Near-infrared luminescence spectra at 1.53 μm and up-conversion spectra of Er³⁺ ions were registered under excitation of Yb³⁺ ions by 975 nm diode laser line. The luminescence bands correspond to ⁴I_13/2-⁴I_15/2 (NIR), ⁴S_3/2-⁴I_15/2 (green) and ⁴F_9/2-⁴I_15/2 (red) transitions of Er³⁺, respectively. The optical transitions of rare earth ions have been examined as a function of glass host. The unusual large spectral linewidth nearly close to 110 nm for ⁴I_13/2-⁴I_15/2 transition of Er³⁺ ions in Yb-Er co-doped lead borate glass was obtained, whereas long-lived NIR luminescence at 1.53 μm was detected in lead germanate glass. The NIR luminescence and up-conversion phenomena strongly depend on stretching vibrations of glass host, which was confirmed by FT-IR spectroscopy.     

Microstructure,chemical composition,wear, and corrosion resistance of FeB–Fe<Subscript>2</Subscript>B–Fe<Subscript>3</Subscript>B surface layers produced on Vanadis-6 steel using CO<Subscript>2</Subscript> laser

The paper presents the study results of laser modification of FeB–Fe₂B surface layers produced on Vanadis-6 steel using pack cementation method. Microstructure, x-ray phase analysis, chemical composition study using wave dispersive spectrometry method, microhardness, corrosion resistance as well as surface condition, roughness, and wear resistance were investigated. The diffusion boronizing processes were performed at 900 °C for 5 h in the EKabor® powder mixture. The boronized layers had a dual-phase microstructure composed of two types of iron borides, FeB and Fe₂B, and their microhardness ranged from 1800 to 1400 HV. The laser surface modification was carried out on specimens after diffusion boronizing process using CO₂ laser with a nominal power of 2600 W. Laser beam power used in this experiment was equal to 1040 W and was constant. While the three values of scanning speed were used: 19, 48, and 75 mm/s. During laser modification, the multiple tracks were made where distance between of axis tracks was equal to 0.5 mm. As a result of this process, microstructure consisted of remelted zone, heat-affected zone, and substrate was obtained. In remelted zone, the boron-martensite eutectic was observed. Boronized layers after laser modification were characterized by the mild gradient of microhardness from surface to the substrate and their value was dependent on the scanning speed used and was between 1700 and 1100 HV. Corrosion resistance tests revealed reducing the current of corrosion in case of laser modification process. Wear resistance of laser modified specimens was improved in comparison to diffusion boronized layers.     

The solution algorithms for the multiprocessor scheduling with workspan criterion

In this paper, we consider multiprocessor scheduling problems, where each job (task) must be executed simultaneously by the specified number of processors, but the indices of the processors allotted to each job do not have to be contiguous (i.e., jobs can be fragmentable). Unlike other research in this domain, we analyse the problem under the workspan criterion, which is defined as the product of the maximum job completion time (makespan) and the number of used processors. Moreover, the job processing times can be described by non-increasing or non-decreasing functions dependent on the start times of jobs that model improvement (learning) or degradation (deteriorating), respectively. To solve the problems, we construct some polynomial time algorithms and analyse numerically their efficiency.     

Dyes based on the 6,7‐dichloro‐5,8‐quinolinedione skeleton as new type II photoinitiators for radical polymerisation

Several dyes based on the 6,7‐dichloro‐5,8‐quinolinedione skeleton have been synthesised and characterised by proton nuclear magnetic resonance spectroscopy and electron ionisation mass spectrometry. The spectroscopic and electrochemical properties of these dyes were investigated. Photoredox pairs consisting of the synthesised dyes and commercially available hydrogen donors (2‐mercaptobenzoxazole, 2‐mercaptobenzothiazole, 2‐mercaptobenzimidazole, and 2,5‐dimercapto‐1,3,4‐thiadiazole) were tested for use as effective initiator systems for radical polymerisation of trimethylolpropane triacrylate with visible light. The efficiencies of these initiator systems are discussed in terms of the free energy change for the electron transfer process from the dye to the hydrogen donor.     

Reaction sintering of dense gadolinium-iron garnet (GdIG) material

Two synthesis methods of gadolinium-iron garnet (GdIG) materials were described. The first one was a typical co-precipitation-calcination method (CP method). In the second one gadolinium-iron perovskite (GdIP, GdFeO3) and iron oxide (α-Fe2O3) were mixed in proper amounts for GdIG stoichiometry (RS method). DSC data for precursor powder mixtures obtained from both synthesis routes allowed to examine heat effects. In the case of the CP method, two crucial reactions were observed. The first one at ab. 767 °C was associated with the formation of GdIP phase, whereas the second one at ab. 1080 °C was attributed to GdIG formation. For the RS method, only formation of GdIG at 1122 °C was observed. Both powder mixtures were sintered at 1200, 1300, and 1400 °C for 2 h. For the CP method, the highest density was below 90 % even at 1400 °C whereas for the RS method the density of materials sintered at the same temperature exceeded 97 %.     

Dyes derived from benzo[a]phenoxazine – synthesis,spectroscopic properties,and potential application as sensors for l-cysteine

Several benzo[a]phenoxazine dyes containing a maleimide moiety have been synthesised and characterised by proton nuclear magnetic resonance spectroscopy and mass spectrometry. The spectroscopic properties, such as absorption and emission spectra, of these dyes – 9-maleimido-5H-benzo[a]phenoxazin-5-one ( 7a ), 6-chloro-9-maleimido-5H-benzo[a]phenoxazin-5-one ( 7b ), and 6-bromo-9-maleimido-5H-benzo[a]phenoxazin-5-one ( 7c ) – were examined. These compounds were evaluated as potential fluorescent and colorimetric probes for the detection of biothiols. Results show that the studied compounds exhibit colorimetric and fluorescent responses to l -cysteine at pH 7.4. In the presence of l -cysteine, the fluorescence intensity of synthesised dyes is greatly enhanced. The addition of l -cysteine to solutions of dyes 7a to 7c also results in red shifts of their absorption bands. The cytotoxic effect of tested dyes 7a to 7c against human neuroblastoma cells (SH-SY5Y) was determined by MTT assay. The fluorescent response of these compounds to thiols SH-SY5Y was examined. The results show that the tested compounds exhibit fluorescent response in this cell line, and the benzo[a]phenoxazine dyes substituted in the 6-position with a halogen ( 7b and 7c ) are less toxic against cells under experimental conditions than their unsubstituted analogue ( 7a ).     

From Trajectory Tracking Control to Leader–Follower Formation Control

Abstract

This work investigates the leader–follower formation control of multiple nonholonomic mobile robots. First, the formation control problem is converted into a trajectory tracking problem and a tracking controller based on the dynamic feedback linearization technique drives each follower robot toward its corresponding reference trajectory in order to achieve the formation. The desired orientation for each follower is selected such that the nonholonomic constraint of the robot is respected, and thus the tracking of the reference trajectory for each follower is feasible. An adaptive dynamic controller that considers the actuators dynamics in the design procedure is proposed. The dynamic model of the robots includes the actuators dynamics in order to obtain the velocities as control inputs instead of torques or voltages. Using Lyapunov control theory, the tracking errors are proven to be asymptotically stable and the formation is achieved despite the uncertainty of the dynamic model parameters. In order to assess the proposed control laws, a ROS-framework is developed to conduct real experiments using four ROS-enabled mobile robots TURTLEBOTs. Moreover, the leader fault problem, which is considered as the main drawback of the leader–follower approach, is solved under ROS. An experiment is conducted where in order to overcome this problem, the desired formation and the leader role are modified dynamically during the experiment.     

Behavioral economics in software quality engineering

This article describes empirical research results regarding the “history effect” in software quality evaluation processes. Most software quality models and evaluation processes models assume that software quality may be deterministically evaluated, especially when it is evaluated by experts. Consequently, software developers focus on the technical characteristics of the software product. A similar assumption is common in most engineering disciplines. However, in regard to other kinds of goods, direct violations of the assumption about objective evaluation were shown to be affected by the consequences of cognitive processes limitations. Ongoing discussion in the area of behavioral economics raises the question: are the experts prone to observation biases? If they are, then software quality models overlook an important aspect of software quality evaluation. This article proposes an experiment that aims to trace the influence of users’ knowledge on software quality assessment. Measuring the influence of single variables for the software quality perception process is a complex task. There is no valid quality model for the precise measurement of product quality, and consequently software engineering does not have tools to freely manipulate the quality level for a product. This article proposes a simplified method to manipulate the observed quality level, thereby making it possible to conduct research. The proposed experiment has been conducted among professional software evaluators. The results show the significant negative influence (large effect size) of negative experience of users on final opinion about software quality regardless of its actual level.     

Silphium L. extracts – composition and protective effect on fatty acids content in sunflower oil subjected to heating and storage

The influence of ethanol and hexane extracts from leaves, inflorescences, and rhizomes of Silphium perfoliatum, Silphium trifoliatum, Silphium integrifolium on fatty acid content changes in sunflower oil subjected to heating and storage was studied in comparison to the synthetic antioxidant – butylated hydroxyanisole (BHA). A positive effect of extracts made of above-ground and underground organs of Silphium on the durable quantitative composition of fatty acids was proven. Tested extracts elevated the value of change inhibition with reference to linoleic acid to a level comparable with BHA, and sometimes, in appropriate systems, they were characterized by better values (for oil stored for 180 days at room temperature, the inhibition coefficient for linoleic acid changes reached 4.6% for 0.04% BHA, and 7.09% for hexane extract made of S. trifoliatum inflorescences, 400 μl/2 g; for oil heated for 120 h, the inhibition coefficient of linoleic acid changes amounted to 11.32% for 0.06% BHA, and 15.69% for hexane extract made of S. perfoliatum rhizomes, 600 μl/2 g). It was found that active substances groups such as phenolic acids, flavonoids and terpenes were present in tested extracts.