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1.
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 相似文献
2.
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. 相似文献
3.
C.L. Li T.Y. Yan G.O. Barasa Y.H. Li R. Zhang Q.S. Fu X.H. Chen S.L. Yuan 《Ceramics International》2018,44(13):15446-15452
Polycrystalline ceramics of Co(Cr1-xFex)2O4 (0?≤?x?≤?0.12) were experimentally studied based on a series of temperature and time-dependent dc magnetic measurements using different magnetic field histories. Magnetization in field cooling process was continuously decreased for doping content x in the range of 0?≤?x?≤?0.04. Remarkable negative magnetization is observed when x reaches to 0.06 and persists up to x?=?0.1. Two-sublattice model is established and competition of the two magnetic sublattices is responsible for the phenomenon. The magnetic switching effect is realized just by changing the magnitude of the applied magnetic field and double magnetocaloric effects are obtained. These unique features under low magnetic fields show attractive for application in spintronic devices due to that the magnetic state can effectively be tuned through magnetic field or temperature. Besides, the system exhibits both positive and negative exchange bias fields which are considered to be originating from the unidirectional anisotropy of exchange coupling of antiferromagnetic/ferromagnetic phases and spin reorientation of the two sublattices magnetic moments, respectively. 相似文献
4.
Yilin Han Marianne King Evgenii Tikhomirov Povilas Barasa Cleide Dos Santos Souza Jonas Lindh Daiva Baltriukiene Laura Ferraiuolo Mimoun Azzouz Maurizio R. Gullo Elena N. Kozlova 《International journal of molecular sciences》2022,23(10)
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. 相似文献
5.
Povilas Bertasius Jan Macutkevic Juras Banys Sergejs Gaidukovs Anda Barkane Romans Vaivodiss 《应用聚合物科学杂志》2020,137(24):48814
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. 相似文献
6.
Meilutė Samulevičienė Povilas MiečinskasKonstantinas Leinartas Asta GrigucevičienėPutinas Kalinauskas Vitalija JasulaitienėRemigijus Juškėnas Eimutis Juzeliūnas 《Materials Chemistry and Physics》2011
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. 相似文献
7.
Eimutis Juzeliūnas Konstantinas LeinartasMeilut? Samulevi?ien? Povilas Mie?inskasRemigijus Jušk?nas Aloyzas Sudavi?ius 《Corrosion Science》2002,44(7):1541-1554
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. 相似文献
8.
Povilas Lukinskas Stefan Kuba Bernd Spliethoff Robert K. Grasselli Bernd Tesche Helmut Knözinger 《Topics in Catalysis》2003,23(1-4):163-173
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. 相似文献
9.
Mykolas Daunys Romualdas Dundulis Albertas Grybenas Povilas Krasauskas 《Nuclear Engineering and Design》2008,238(10):2536-2545
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 KQ, , JIC—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 KQ, more depends on temperature than on hydrogen concentration. Critical JIC 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 JIC dependence due to the mechanical characteristics of zirconium alloy has showed that the modified plasticity Zmod = (Rp0.2/Rm)Z satisfactorily approximates the influence of temperature and hydrogen concentration on variation of these characteristics. 相似文献
10.
Cain Sean W.; Verwey Michael; Hood Suzanne; Leknickas Povilas; Karatsoreos Ilia; Yeomans John S.; Ralph Martin R. 《Canadian Metallurgical Quarterly》2004,118(1):131
Circadian rhythms in rodents respond to arousing, nonphotic stimuli that contribute to daily patterns of entrainment. To examine whether the motivational significance of a stimulus is important for eliciting nonphotic circadian phase shirts in Syrian hamsters (Mesocricetus auratus), the authors compared responses to a highly rewarding stimulus (lateral hypothalamic brain stimulation reward [BSR]) and a highly aversive stimulus (footshock). Animals were housed on a 14:10-hr light-dark cycle until test day, when they were given a 1-hr BSR session (trained animals) or a 1-mA electric footshock at 1 of 8 circadian times, and were maintained in constant dark thereafter. Both BSR pulses and footshock produced nonphotic phase response curves. These results support the hypothesis that arousal resulting from the motivational significance of a stimulus is a major factor in nonphotic phase shifts. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献