Quantum dots as versatile probes in medical sciences: Synthesis,modification and properties

Quantum dots (QDs) are semiconductor inorganic fluorescent nanocrystals in the size range between 1 and 20 nm. Due to their very small size, they possess unique properties and behave in different way than crystals in macro scale. The specificity of QDs makes them widespread in many branches of human life. The disciplines that took recently huge advantage from the development of nanotechnology are medicine and pharmacy. The creation of particles of very tiny sizes allowed these two sciences to develop or revolutionize the techniques of diagnosis or drug delivery. The most important feature for application of fluorescent nanocrystals in medical and pharmaceutical sciences is their high surface to volume ratio enabling QDs' conjugation to multiple ligands. Other properties of great importance are dispersibility and water stability, high and not easy quenched fluorescence, biocompatibility, and small and uniform sizes. In this review with ca. 200 references the recent developments in QD synthesis, surface modification, QD-based bioimaging, biotracking of drug molecules, biosensing and photodynamic therapy are summarized.     

Enzymatic and molecular characteristics of Geotrichum candidum strains as a starter culture for malting

Geotrichum candidum yeasts are proposed as a starter culture during malting. They have a double positive effect on the process. They eliminate the fungal pathogenic microflora and improve the technological properties of the finished product, malt. Among published research little or no information can be found considering the biosynthesis of hydrolytic enzymes. Most of the data is related to the production of lipases, proteases and cellulases. This paper examines the enzymology of a number of G. candidum strains. The main focus within the evaluation process was placed on whole cell barley grain cultivation. Hydrolase, which is present in cell wall degradation, was found at a satisfactory level. All tested strains produced both β‐1,3‐glucanases and β‐1,4‐glucanases capable of hydrolysing barley β‐glucan and reducing the amount of this polysaccharide in the wort. Molecular analysis of the tested strains with the use of restriction fragment length polymorphism–polymerase chain reaction and randomly amplified polymorphic DNA confirmed not only the species affiliation, but also the genetic similarity between the tested strains. Copyright © 2014 The Institute of Brewing & Distilling     

Non-minimum-phase property of N-trailer kinematics resulting from off-axle interconnections

Off-axle interconnections between segments of N-trailer vehicles may imply specific oscillatory behaviour of trailers during vehicle manoeuvres. The paper reveals that this kind of oscillations is a direct consequence of the non-minimum-phase property of vehicle kinematics resulting from application of off-axle interconnections between vehicle segments. First we show the non-minimum-phase property for dynamics of a single pair of interconnected segments, and then how it propagates along the N-trailers equipped with arbitrary number of off-axle interconnections. By referring to available results for linear systems, we locally analyse linearly approximated vehicle kinematics around selected steady-motion conditions. We focus on the time-response effects like undershooting, zero-crossing, and overshooting caused by off-axle interconnections. We show how the number and type of interconnections influence the non-minimum-phase effects. Numerical results obtained for three-trailer kinematics validate theoretical considerations providing some quantitative view of the problem. Short discussion has been provided on the possible control-level consequences resulting from the non-minimum-phase property of N-trailers.     

Determination of Thermal-Diffusivity Dependence on Temperature of Transparent Samples by Thermal Wave Method

The use of a typical measuring cryostat with a standard temperature controller was proposed for investigation of the temperature dependence of the thermal diffusivity of transparent samples. The basic idea is to use the cryostat heater to control the mean sample temperature and to generate the thermal wave in it, simultaneously. Because of the relatively high thermal inertia of the system, the measurements are carried out at frequencies not exceeding 50 mHz. The periodic temperature disturbance in the sample was detected optically by the use of the mirage effect. The proposed method was used for determination of the thermal diffusivity of yttrium aluminum garnet single crystals in a temperature range from 20 °C to 200 °C.     

Discrimination of Korean beef from beef of other origin by stable isotope measurements

Beef samples from Korea and from some of the main beef exporting countries (USA, Mexico, Australia, New Zealand) were analysed for carbon, nitrogen and hydrogen isotope ratios of the defatted dried matter. Results showed that the samples from each country investigated could be assigned to a typical isotope signature and can be separated from each other. The main discriminating factors were δ¹³C and δ²H, which mainly reflect feeding of C₃ and C₄-plants and the isotopic composition of the water, respectively, consumed by the cattle. Australian beef showed the largest variation in its isotopic signature, suggesting heterogeneous rearing conditions. By contrast, for beef from New Zealand, Mexico, USA and Korea, each batch had typical signatures with a smaller variability.     

Effect of metal purity and testing procedure on surface tension measurements of liquid tin

The surface tension of liquid tin of three different grades of purity (99.85, 99.96, and 99.999%) was measured by the classical sessile drop method over the temperature range 523–1023 K, in heating and cooling regimes. The results obtained show that the metal purity affects the values of surface tension and its temperature dependence. The highest values of surface tension and smooth linear temperature dependence were obtained in cooling regime for tin of the highest purity. With increasing content of impurities, both surface tension and its temperature coefficient decrease while the scatter of the data increases. The surface tension values measured on heating regime show higher scatter, compared to those obtained in cooling regime, and the temperature dependence of the surface tension is curvilinear rather than linear.     

On the modelling of heat conduction problem in laminated bodies

Summary The paper deals with the heat conduction modelling problem for micro-periodic composites. The models proposed there take into account certain micromorphic effects resulting from the fine periodic structure of the body. The governing equations describing heatfluxes and temperature distributions in these composites in the nonlinear as well as linear cases have been derived. Two examples of the application of the presented models are detailed.With 4 Figures     

Testing of explosive welding and welded joints: joint mechanism and properties of explosive welded joints

In this study physical mechanism of explosive welding joint was analysed. The mechanism refers to wavy joint with interpass and without one. Plastic strain, viscosity and acoustic waves were applied to explain the problem. The own model of the mechanism of oxide removal for the direct joint and test results confirming the bonding mechanism were showed.     

Tribological Properties of the Oxide Coatings Produced onto 6061-T6 Aluminum Alloy in the Hard Anodizing Process

The aim of this work was to establish the influence of the thickness of the anodic coatings on their mechanical properties and to understand the relation between their hardness and the abrasion resistance. The coatings were produced in the hard anodizing process onto the 6061-T6 aluminum alloy. Their thickness was in the range between 19 and 43 µm. The abrasion resistance was determined by using Taber abrasion test. The weight losses of the coatings obtained were in the range between 15 and 11 mg and decreased with their increasing thickness. It has been shown that the hardness measured on the cross sections of the coatings did not correspond to their abrasion resistance. Thus, the new approach has been proposed. The hardness of the coatings was estimated on the basis of the results of the scratch test performed at the constant load. The results obtained correspond to the abrasion resistance of the coatings.