Scattering of electrons in beta-spectroscopy sources

Experimental spectra of the¹⁶⁹Yb conversion lines having kinetic energies of 3.7–18.4 keV and the beta spectrum from the decay of²⁴¹Pu are compared with calculations by the Monte Carlo method which take into account the individual elastic and inelastic scattering processes of the electrons in the source, in the substrate, and in a carbon layer contaminating the source. Good agreement is obtained between the theoretical and experimental results. It is also shown that the scattering of the electrons depends on their emission angle. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 63–65, August. 1997.     

Sphinganine‐Like Biogenesis of (E)‐1‐Nitropentadec‐1‐ene in Termite Soldiers of the Genus Prorhinotermes

In 1974, (E)‐1‐nitropentadec‐1‐ene, a strong lipophilic contact poison of soldiers of the termite genus Prorhinotermes, was the first‐described insect‐produced nitro compound. However, its biosynthesis remained unknown. In the present study, we tested the hypothesis that (E)‐1‐nitropentadec‐1‐ene biosynthesis originates with condensation of amino acids with tetradecanoic acid. By using in vivo experiments with radiolabeled and deuterium‐labeled putative precursors, we show that (E)‐1‐nitropentadec‐1‐ene is synthesized by the soldiers from glycine or L ‐serine and tetradecanoic acid. We propose and discuss three possible biosynthetic pathways.     

Determination of corrosion rate of orthodontic wires based on nickel‐titanium alloy in artificial saliva

The goal of this study was to determine corrosion behavior of three orthodontic wires based on nickel‐titanium alloy (NiTi) in artificial saliva at temperature of 37 °C as function of immersion time. Following orthodontic wires were used: uncoated (NiTi), rhodium coated (Rh NiTi) and nitrified (N NiTi) orthodontic wires. Corrosion of investigated orthodontic wires were monitored by measuring of Ni²⁺ and Ti⁴⁺ ions released in artificial saliva by inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) after 3, 7, 14, 21 and 28 days of immersion. Obtained results indicate that corrosion reaction of the NiTi wires in artificial saliva follows the parabolic rate law. According to the obtained values of parabolic corrosion rate constants, corrosion susceptibility of orthodontic wires decreases in the following order: Rh NiTi wire (K_p = 2.48 μg²/cm⁴ h) > NiTi wire (K_p = 1.6 × 10^–3 μg²/cm⁴ h) > N NiTi wire (K_p = 6.0 × 10^–4 μg²/cm⁴ h). These results indicate that in comparison with uncoated NiTi wire, rhodium coating significantly increases corrosion susceptibility, while nitrification effectively suppresses the release of Ni²⁺ and Ti⁴⁺ ions.     

Asphalt concrete modification with waste PMMA/ATH

This paper presents recycling of waste PMMA/ATH powder in asphalt concrete mixture. Waste PMMA/ATH is generated in large amounts during shaping process of acrylic sheets. Recycling waste polymers rationally and efficiently has become one of the priorities of road pavement industry in recent years. Therefore, in this study waste PMMA/ATH powder was incorporated in an asphalt mixture. In one case waste PMMA/ATH was used as an asphalt binder modifier and in other case as a partial replacement for fine aggregate fraction. Basic performance characteristics of asphalt mixtures were evaluated by measuring material properties such as rutting potential and stripping resistance. Binder characteristics were determined also on artificially aged samples. With both modification methods, improved performance characteristics of asphalt mixture were achieved which can increase road pavement durability. Finally, waste PMMA/ATH allowed us to prepare an asphalt mixture that had strongly enhanced mechanical properties regarding to the wheel tracking test and could also have less negative effects on the environment as indicated by moisture susceptibility test results.     

Force‐Driven Single‐Atom Manipulation on a Low‐Reactive Si Surface for Tip Sharpening

A single atomic manipulation on the delta‐doped B:Si(111)‐()R30° surface using a low temperature dynamic atomic force microscopy based on the Kolibri sensor is investigated. Through a controlled vertical displacement of the probe, a single Si adatom in order to open a vacancy is removed. It is shown that this process is completely reversible, by accurately placing a Si atom back into the vacancy site. In addition, density functional theory simulations are carried out to understand the underlying mechanism of the atomic manipulation in detail. This process also rearranges the atoms at the tip apex, which can be effectively sharpened in this way. Such sharper tips allow for a deeper look into the Si adatom vacancy site. Namely, high‐resolution images of the vacancy showing subsurface Si dangling bond triplets, which surround the substitutional B dopant atom in the first bilayer, are achieved.     

Shear strength and wettability of active Sn3.5Ag4Ti(Ce,Ga) solder on Al2O3 ceramics

The work deals with the study of wettability of Sn3.5Ag4Ti(Ce,Ga) solder on ceramic material of Al₂O₃. The Sn3.5Ag4Ti(Ce,Ga) solder is used for ultrasonic soldering of metallic and ceramic materials. The microstructure of Sn3.5Ag4Ti(Ce,Ga) solder consists of a tin matrix, where non-uniformly distributed constituents of partially dissolved Ti and uniformly distributed fine needles of Ag–Sn phase were observed. The solder was of heterogeneous composition. X-ray diffraction analysis has revealed the presence of following phases: Ag₃Sn, Ti₆Sn₅, Ti₃Sn. For determination of melting point, the Differential scanning calorimetry analysis (DSC) was performed. Wettability of Sn3.5Ag4Ti(Ce,Ga) solder was determined at temperatures 800, 850 and 900 °C in dependence on wetting time. The best wettability of solder Θ = 46° was achieved at 850 °C/43 min. The experiments with high-temperature activation were performed in vacuum of 10^?4 Pa. On the basis of experience attained by measurement of contact angle, the soldered joints of Al₂O₃/Al₂O₃ and Al₂O₃/metal were fabricated in conditions of high-temperature activation in vacuum at temperature 850 °C/10 min. For comparison, also the joints fabricated in the conditions of ultrasonic activation in the air at temperature 280 °C/1 min were applied. The shear strength of joints of Al₂O₃/Al₂O₃ and Al₂O₃/metal fabricated with Sn3.5Ag4Ti(Ce,Ga) solder varied from 17 to 35 MPa. The shear strength of joints fabricated in vacuum is slightly higher than in the case of joints fabricated by use of power ultrasound.     

Characterizing the structure of pharmaceutical granules obtained by wet granulation with varying amounts of water via Raman chemical imaging

A pharmaceutical formulation containing metformin hydrochloride (MET), hydroxypropyl cellulose (HPC), and microcrystalline cellulose (MCC) was wet granulated with varying amounts of water and the structure of the obtained granules was characterized by Raman chemical mapping. Univariate Raman mapping was found to be satisfactory for producing the images of the two components of interest (HPC and MCC). In addition to the images, the average Raman spectra from the maps as well as the micro-Raman spectra from the hot pixels were analyzed. HPC is found to strongly respond to the addition of water, with its domain dissipating and Raman bands becoming weaker as the water addition increases. MCC is also responsive to water, reacting similarly to HPC but to a much smaller extent and only for the largest amounts of water. Granules made with increasing water content also have improved tabletting properties and flow.     

Oxygen‐Free Highly Conductive Graphene Papers

Graphene papers have a potential to overcome the gap from nanoscale graphene to real macroscale applications of graphene. A unique process for preparation of highly conductive graphene thin paper by means of Ar⁺ ion irradiation of graphene oxide (GO) papers, with carbon/oxygen ratio reduced to 100:1, is presented. The composition of graphene paper in terms of carbon/oxygen ratio and in terms of types of individual oxygen‐containing groups is monitored throughout the process. Angle‐resolved high resolution X‐ray photoelectron spectroscopy helps to investigate the depth profile of carbon and oxygen within reduced GO paper. C/O ratios over 100 on the surface and 40 in bulk material are observed. In order to bring insight to the processes of oxygen removal from GO paper by low energy Ar⁺ ion bombardment, the gases released during the irradiation are analyzed by mass spectroscopy. It is proven that Ar⁺ ion beam can be applied as a technique for fabrication of highly reduced graphene papers with high conductivities. Such highly conductive graphene papers have great potential to be used in application for construction of microelectronic and sensor devices.     

Decentralized PI/PD position control for active magnetic bearings

This paper discusses a closed-loop decentralized control for active magnetic bearings. A cascade connection of PI and PD position controllers is proposed. The control design is based on a simplified linearized model for one axis using a root locus. An excellent agreement is noticeable between simulation and experimental results. It has been shown, that the presented PI/PD control guarantees satisfactory high damping and stiffness of the overall system.