Experimental Investigation of Local Heat Transfer and Skin Friction in Tube Coils

Local heat transfer and skin friction around the tube perimeter of coils were studied in airflow. The heat transfer experiments were performed with two different coils D/d = 23 and 15.6, and skin friction experiments were performed with three different coils D/d = 25, 13.3 and 6.67 In the wide range of Re number from 4×103 till 105 . Variation of the local heat transfer around the perimeter and along the tube was defined. The behavior of the shear stresses at the wall and of the flow modes were studied. Investigations of the heat transfer indicated that with the increase of D/d the difference between heat transfer in the initial thermal section and the stabilized heat transfer increases. Investigations of the shear stress and its fluctuations indicated that, in large-curvature coils, the transition from laminar-vortex flow to turbulent flow around the tube perimeter takes place at different values of Re. In the region of the external generatrix of the bend, the transition occurs at smaller Re, whereas a     

Modelling of the shielding capabilities of the existing solid radioactive waste storages at Ignalina NPP

There is only one nuclear power plant in Lithuania--Ignalina NPP (INPP). The INPP operates two similar units with design electrical power of 1500 MW. The units were commissioned in 1983 and 1987 respectively. From the beginning of the INPP operation all generated solid radioactive waste was collected and stored at the Soviet type solid radwaste facility located at INPP site. The INPP solid radwaste storage facility consists of four buildings, namely building No. 155, No. 155/1, No. 157 and No. 157/1. The buildings of the INPP solid radwaste storage facility are reinforced concrete structures above ground. State Nuclear Safety Inspectorate (VATESI) has specified that particular safety analysis must be performed for existing radioactive waste storage facilities of the INPP. As part of the safety analysis, shielding capabilities of the walls and roofs of these buildings were analysed. This paper presents radiation shielding analysis of the buildings No. 157 and No. 157/1 that are still in operation. The buildings No. 155 and No. 155/1 are already filled up with the waste and no additional waste loading is expected.     

Towards 3D Bioprinted Spinal Cord Organoids

Three-dimensional (3D) cultures, so-called organoids, have emerged as an attractive tool for disease modeling and therapeutic innovations. Here, we aim to determine if boundary cap neural crest stem cells (BC) can survive and differentiate in gelatin-based 3D bioprinted bioink scaffolds in order to establish an enabling technology for the fabrication of spinal cord organoids on a chip. BC previously demonstrated the ability to support survival and differentiation of co-implanted or co-cultured cells and supported motor neuron survival in excitotoxically challenged spinal cord slice cultures. We tested different combinations of bioink and cross-linked material, analyzed the survival of BC on the surface and inside the scaffolds, and then tested if human iPSC-derived neural cells (motor neuron precursors and astrocytes) can be printed with the same protocol, which was developed for BC. We showed that this protocol is applicable for human cells. Neural differentiation was more prominent in the peripheral compared to central parts of the printed construct, presumably because of easier access to differentiation-promoting factors in the medium. These findings show that the gelatin-based and enzymatically cross-linked hydrogel is a suitable bioink for building a multicellular, bioprinted spinal cord organoid, but that further measures are still required to achieve uniform neural differentiation.     

C18 Dienes as attractants for eighteen clearwing (Sesiidae), tineid (Tineidae), and choreutid (Choreutidae) moth species

By screening singly and binary mixed 2,13- and 3,13-octadecadien-yl acetates and alcohols (2,13- and 3,13-18: Ac/OH)in Lithuania, Armenia, Azerbaijan, Turkmenistan, Ukraine, and the far east of Russia, sex attractants were discovered for 12 Sesiidae, four Tineidae, and one Choreutidae moth species. Males ofSesia yezoensis andBembecia puella as well asNemapogon flavifrons were attracted by mixture ofZ3,Z13-18:Ac/OH in a ratio of 91,Pyropteron sp. n. by the same mixture (ratio 19),Bembecia romanovi andB. zuwandica byZ3,Z13-18:Ac andE3,Z13-18:Ac (91),Synanthedon caucasicum by the same mixture in the opposite ratio (19),B. scopigera by 23,213-18:Ac andE2,Z13-18:OH in a ratio 91,Synasphecia triannuliformis byZ3,Z13-18:OH andE3,Z13-18:OH (91),Similipepsis takizawai andArchimeessia sp. n. by E3,Z13-18:OH andE2,Z13-18:Ac (11),Prochoreutis sechestediana by a mixture ofE3,Z13-18:Ac plusE2,Z13-18:OH (1),Microsphecia brosiformis by E3,Z13-18:Ac,Synanthedon conopiformis by the analogous alcohol,Synanthedon scoliaeformis andNemaxera betulinella byE2,Z13-18:Ac,Triaxomera fulvimitrella byZ3,Z13-18:Ac. An analogous alcohol component is essential for the attraction ofB. ichneumoniformis males. Inhibitors forB. romanovi, B. scopigera andB. zuwandica attraction were discovered. Preliminary data on attractants for six other species as well as on the diurnal rhythm of sexual activity of three species are presented. A new method for the stereoselective synthesis of 3,13–18:Ac/OH andE2,Z13-18:Ac/OH is described.     

Synergy effects in dielectric and thermal properties of layered ethylene vinyl acetate composites with carbon and Fe3O4 nanoparticles

Properties of layered composites with carbon nanotube (CNT), GnP, Fe₃O₄ nanoinclusions, and hybrid composites with these nanoinclusions were investigated in the wide frequency range (from 20 Hz to 2 THz). All investigated composites (except with single Fe₃O₄ inclusions) are above percolation threshold. The strong enhancement of microwave and terahertz radiation absorption is observed in hybrid composites in comparison with composites with single inclusions. The synergy effect is discussed in terms of the complex impedance and the distribution of relaxation times. At low temperatures (below 200 K), the electrical conductivity of all hybrid composites follows the tunneling law model and the lowest potential barrier was estimated for composites with CNT inclusions. The best thermal properties are observed for composites with CNT inclusions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48814.     

Corrosion resistance of nanocrystalline Mg–Cr alloys deposited by magnetron sputtering

Nanocrystalline Mg–Cr alloys were formed by dc magnetron sputtering in a wide range of concentrations. Structure, composition and grain sizes of the deposits were studied by XRD and XPS. EIS and dc-voltammetry showed that small chromium concentrations (2–8 at.%) had detrimental effect, while high corrosion resistance was observed when chromium content reached one third or so. Chromium refinement effect on alloy crystalline structure was found by XRD. The values of grain sizes were determined as follows: Mg–3Al (chromium-free) – over 100 nm, Mg–2Cr – 60.5 nm, Mg–8Cr – 44.6 nm, Mg–20Cr – 31.0 nm, Mg–45Cr, Mg–53Cr – ∼11.0 nm and ∼15 nm for sputtered Cr. Mott–Schottky plots showed that the spontaneous oxide layers formed on the alloys with high Cr content (Mg–36Cr, Mg–53Cr) were highly doped semiconductors of n-type. A conductivity change n–p was observed at E = 0.0 V (Ag/AgCl) in a buffer solution (pH 9.9). The conductivity change was also confirmed by photo-electrochemical measurements. Surface enrichment by chromium during initial stages of corrosion was determined, which promote corrosion resistance and provides an opportunity of surface auto-protection (self-healing) in damaged locations.     

Magnetron sputtered Au-Pd-In alloys: microgravimetric and electrochemical characterisation in simulated physiological solutions

An electrochemical quartz crystal microbalance (EQCM) has been applied in corrosion sensing of magnetron sputtered Au-Pd-In alloy in simulated physiological solutions. The piezoelectric resonators were prepared by alloy deposition on quartz substrates by a DC magnetron-sputtering (MS) technique. X-ray photoelectron spectroscopy (XPS) analysis showed that the deposit composition was similar to that of the MS target, which was a commercially available casting alloy. X-ray diffraction indicated that the sputtered alloy has a crystalline structure. Measurements by using impedance spectroscopy and DC voltammetry showed some differences in electrochemical behaviour of both sputtered and cast alloy; however, these data did not indicate superior corrosion resistance of the sputtered specimen. Alloy corrosion has been studied by EQCM in three simulated physiological solutions: 0.9 N NaCl, 0.1 N NaCl+0.1 N lactic acid and artificial saliva. The EQCM indicated corrosion as increase in electrode mass, which was due to accumulation of corrosion products on the surface. The mass gain curves were similar in both neutral (pH 6) and acidic (pH 2.2) solutions, what implies dissolution of corrosion products in both media to be insignificant. XPS analysis showed that In₂O₃ was the main corrosion product on the surface. Corrosion current calculations from the mass curves were undertaken, which yielded the same corrosion rate assuming different oxides on the surface. The average corrosion rates in oxygenated 0.9 N NaCl and 0.1 N NaCl+0.1 N lactic acid solutions were similar and about twice as high as that in saliva.     

Role of Promoters on Tungstated Zirconia Catalysts

The isomerization of straight-chain alkanes is effectively catalyzed by tungstated zirconia promoted by Pt or Pt and Fe. In the present paper, it is attempted to better understand the role of these promoters. The materials were characterized by CO chemisorption and by transmission electron microscopy (TEM) in combination with EDX, and their catalytic performance was tested by the isomerization of n-pentane to isopentane in the presence of H₂. At low calcination temperature, very high Pt dispersion is observed with Pt atoms/clusters being embedded in or decorated by oxide material. The highly dispersed Pt moieties appear to catalyze the hydrogenolysis reaction, thus leading to low isoalkane selectivities. Higher calcination temperatures yield larger Pt particles (lower dispersion), which results in high catalytic activity and selectivity toward the isoalkane target product. It is inferred that the dissociative H₂ chemisorption occurs on the Pt particles and facilitates the reduction of the surface tungstate, which is responsible for the dehydrogenation and isomerization of n-alkane. The role of the additional promoter iron oxide still remains unresolved.     

Hydrogen influence on mechanical and fracture mechanics characteristics of zirconium Zr–2.5Nb alloy at ambient and elevated temperatures

This article deals with the investigation of the hydrogen concentration and temperature influence onto mechanical and fracture mechanics characteristics of RBMK-1500 Ignalina NPP unit 2 reactor fuel channel material—Zr–2.5Nb zirconium alloy (TMT-2) at temperatures from ambient up to 300 °C. The investigation of mechanical characteristics was performed on tensile specimens, fracture mechanics characteristics K_Q, , J_IC—on compact specimens (B = 4 mm) of hydrogen-free and saturated by hydrogen (52, 100 and 140 ppm) at 20, 170, 200 and 300 °C. The investigation showed that temperature increasing calls mechanical strength decreasing, whereas the reductions of area increase. Stronger influence of hydrogen concentration onto mechanical characteristics is noticed only at 20–170 °C temperature, however this influence diminishes as the temperature increases and weakest hydrogen influence is given at 300 °C. Fracture toughness characteristics K_Q, more depends on temperature than on hydrogen concentration. Critical J_IC integral values for the specimens containing hydrogen were given lowest at 20 °C, increases when temperature were raised up to 140 °C and were given highest when it reaches 300 °C.The analysis of and J_IC dependence due to the mechanical characteristics of zirconium alloy has showed that the modified plasticity Z_mod = (R_p0.2/R_m)Z satisfactorily approximates the influence of temperature and hydrogen concentration on variation of these characteristics.     

Cardiac and visual responses to moving stimuli presented either successively or simultaneously to the central and peripheral visual fields in 4-month-old infants.

Measured cardiac and visual orienting responses as indices of attention in 41 4-mo-old infants. Two stimulus situations were used. In the 1st situation, the presentation of a peripheral stimulus followed the offset of a central fixation stimulus. In the 2nd situation, the peripheral stimulus came on while the central fixation stimulus was on. Each stimulus comprised a horizontal black and white bar pattern. Corneal reflection was used to monitor infant gaze. The visual-response measure confirmed that with simultaneous presentation the probability of orienting to the peripheral stimulus decreased. The extent of this reduction was determined by the speed difference between the central and peripheral stimuli. The cardiac data indicate that on the trials in which the peripheral stimulus did not elicit lateral eye/head movements the stimulus was still being detected. Thus, cardiac change can reflect attentional processes without evidence of somatic orienting. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)