[en] Energy-related applications with aggressive environments at high temperatures require the development of advanced structural materials. Alumina forming alloys (e.g. Ni-based, Fe-based) have received a great attention for high temperature applications because of their excellent oxidation resistance and adequate mechanical properties. By adding appropriate amounts of Al and Cr, these alloys are able to form protective alumina-rich oxide scales when exposed to the oxygen-containing extreme conditions (e.g. high temperature, corrosivity). Ferritic FeCrAl alloys have been successfully developed for use in liquid Pb environment. However, ferritic steels as well as ferritic FeCrAl alloys suffer from liquid metal embrittlement in liquid Pb. Alumina-forming austenitic alloys (AFA) have the potential to mitigate the corrosion issues in molten Pb and to avoid liquid metal embrittlement at the same time, due to the austenitic structure. Another promising material type is high entropy alloys (HEA). Typically, they have five or more principle elements with the atomic fraction of each element in the range of 5-35 at.%. By alloying passive layer forming elements like Al and Cr, the alloys are able to withstand oxidizing conditions at temperatures above 1000 °C by the formation of a protective alumina-rich scale. In this dissertation, AFA and HEA model alloys, based on the backbone composition of Fe-Ni-Cr-Al are designed in order to search for the composition map of target materials that are compatible with the selected aggressive environments (molten Pb and steam). AFA model alloys based on Fe-(20-29)Ni-(12-16)Cr-(2-4)Al (in wt.%) have been designed based on equilibrium phase calculations (Thermo-Calc) and the Schaeffler diagram. All the annealed alloys are single FCC phase with specific heat capacity, thermal conductivity and thermal expansion comparable with SS316. Nine alumina-forming HEA alloys have been designed based on the empirical parameters, including enthalpy of mixing (ΔHmix), atomic size difference (δr), parameter $\mathrm{\Omega <!--\; ??\; -->}$ ((Ʃc${}_i$T${}_{m,i}$)ΔSmix/|ΔHmix|) and valance electron concentration (VEC). The designed alloys include four quaternary alloys with dual phase (Al${}_{8.91-<!--\; ???\; -->11.7}$Cr${}_{22.40-<!--\; ???\; -->30.28}$Fe${}_{32.62-<!--\; ???\; -->34.50}$Ni${}_{26.91-<!--\; ???\; -->34.28}$, FCC+B2 or BCC), two quaternary alloys with single FCC phase (Al${}_{6.02-<!--\; ???\; -->7.96}$Cr${}_{23.23-<!--\; ???\; -->25.01}$Fe${}_{33.99-<!--\; ???\; -->34.06}$Ni${}_{34.75-<!--\; ???\; -->34.98}$), and three quinary alloys alloyed with Nb/Ti/Cu (Al${}_{7.90-<!--\; ???\; -->8.24}$Cr${}_{21.37-<!--\; ???\; -->22.04}$Fe${}_{30.29-<!--\; ???\; -->31.96}$Ni${}_{33.01-<!--\; ???\; -->35.02}$Nb${}_{5.08}$/Ti${}_{5.01}$/Cu${}_{5.00}$, FCC+Laves or γ' phase and single FCC). The thermo-physical properties of as-cast HEA alloys have comparable thermal physical properties like SS 316 at temperatures below 800 °C. Compatibility tests have been performed in 10${}^{-<!--\; ???\; -->6}$ wt.% oxygen containing molten Pb at 550 °C and 600 °C for 1000 h and 2000 h. The excellent corrosion resistance of the AFA alloys observed in these tests is due to the formation of a protective oxide scale (<200 nm) based on an outer layer of II Cr${}_2$O${}_3$ and an inner layer of Cr${}_2$O${}_3$-Al${}_2$O${}_3$ solid solutions. The passivated alloys also preserve their austenitic matrix. By adding yttrium, the uniformity in scale thickness and in Al and Cr distribution has been improved. In case of Nb containing samples, TEM evaluation of the alloy matrix indicates the formation of B2-NiAl and Laves (Fe${}_2$Nb) phases in addition to the austenite phase. The mechanism of the oxide layer passivation on HEA alloys is almost identical to that of the AFA alloys. A continuous oxide scale is formed based on Cr${}_2$O${}_3$ or (Fe,Cr)${}_3$O${}_4$ (in case of BCC phase) or TiO${}_2$ (HEA alloyed with Ti), which acts as a first corrosion barrier. Then, alloys with sufficient Al addition form a protective oxide scale underneath the first corrosion barrier, based on Cr${}_2$O${}_3$-Al${}_2$O${}_3$ solid solution or α-Al${}_2$O${}_3$. Four HEA model alloys have shown their microstructure stabilities during exposure in low-oxygen containing molten Pb at 550-600 °C. Three HEA alloys show precipitations of B2-NiAl phases at the grain boundaries. Sample with Ti addition exhibits phase transformations, namely FCC $\to <!--\; ???\; -->$ sigma and γ' $\to <!--\; ???\; -->$$\mathrm{\eta <!--\; ??\; -->}$ phase. For the tests in steam at 1200 °C three AFA alloys based on the compositions with Y or Nb addition and four HEA alloys, two with Nb and Ti have been selected. The AFA alloys containing Y (Fe-15Cr-2.5Al-20Ni-0.5Y, Fe-16Cr-2.5Al-22Ni-0.5Y) and the three HEA alloys not containing Ti have formed protective α-Al2O3 scales on the alloy surface. Considering both test environments, a general formula of AFA alloys that are compatible with oxygen containing Pb at 550-600 °C and steam at 1200 °C is derived: Fe-(20-29)Ni-(15.2-16.5)Cr-(2.3- 4.3)Al (wt.%). A formula of HEA alloys based on the backbone composition of Fe-Ni-Cr-Al that are compatible with oxygen containing molten Pb at 550-600 °C and steam at 1200 °C, and maintaining the FCC structure in the matrix, is defined as: (30.29-34.50)Fe-(33.15-35.02)Ni-(21.37-25.01)Cr-(6.02- 11.69)Al (at.%). In addition, elements like Nb or Y used either as principle element (Nb in HEA) or as minor additions (AFA) have an additional positive effect on the alumina scale formation in aggressive environments. The addition of Nb foster in addition the mechanical strength at high temperatures.

[en] Tuning the optical adsorption edge of TiO_2 is attracting increasing attention as a potential solution to the worldwide energy shortage. A possible strategy to achieve high efficiency photocatalysis with TiO_2 is through dopants to modulate chemical composition. Based on first-principles calculations, we propose a hole-strain-mediated coupling mechanism between co-doped acceptors in anatase TiO_2. When the dopant complex on neighboring oxygen sites contains a large radius atom, and the doped system has at least one net hole, the dopants will strongly couple to form a pair through the local lattice strain induced by the large dopant. The coupling results in bandgap narrowing due to the appearance of the fully occupied mid-gap states, leading to a much more effective band gap reduction than that induced by mono-doping or conventional donor–acceptor codoping. The calculated absorption spectra show that acceptor–acceptor codopings could shift the absorption edge to the visible light region. - Highlights: • We model two acceptors codoping in anatase TiO_2. • We propose a hole-strain-mediated coupling mechanism between acceptors. • The coupling results in significant bandgap narrowing. • Acceptor–acceptor codopings shift the absorption edge to the visible light region

[en] The morbidity of hypoxic-ischemic encephalopathy (HIE) is high in the neonates, and its disability rate and fatality rate also stay at a high level. MRI has become the main examination to diagnose and evaluate the prognosis. In recent years, some new MRI techniques, such as diffusion weighted imaging, diffusion tensor imaging, diffusion kurtosis imaging, arterial spin labeling, and intravoxel incoherent motion, have achieved significant developments in the diffusion and perfusion imaging. These techniques can better reflect the pathological changes of HIE. In this paper, the characteristics and applications of the diffusion and perfusion MRI in HIE were summarized. (authors)

[en] Highlights: • The fluid flow nonuniformity in microchannel ceramic heat exchanger is optimized. • A new method for the control of flow distribution in multichannel is employed. • Surrogate model, genetic algorithm and numerical method are coupled to complete the optimization. • Modified method for prediction of flow nonuniformity is employed and compared with previous method. • The nonuniformity of fluid flow is reduced by 68.2% and pressure drop is increased by 6.6%. - Abstract: High temperature resistance and corrosion resistance make ceramic materials available for heat exchangers operating under high temperature or harsh chemical conditions. And the importance of the effect of flow maldistribution on thermal-hydraulic performance of heat exchangers has been demonstrated by a lot of researches. In this work, the nonuniformity of fluid flow is focused on to improve the performance of a microchannel ceramic heat exchanger. The inlet part of a microchannel ceramic heat exchanger is optimized using surrogate model coupled with genetic algorithm. Specifically, 30 sample points are designed by Latin hypercube sampling method and calculated by computational fluid dynamics. Radial basis neural network is established with the sample data and employed to predict the specific fluid flow distribution within design space as a surrogate model. Specifically, the surrogate model predicts the specific flow distribution instead of a single target value of nonuniformity in previous surrogate model. The results indicate that such a method has a significant advantage over the previous surrogate model. The genetic algorithm is implemented to search for the optimal point. The nonuniformity of fluid flow is reduced by 68.2% and pressure drop is increased by 6.6% by the optimization, which means the uniformity of fluid flow in the heat exchanger is improved significantly with just a little cost of pressure drop.

[en] Objective: To evaluate the diagnostic and differential value of triphasic, especially the arterial phase, contrast enhanced CT scans for the hepatocellular adenoma, and to improve CT diagnostic accuracy. Methods: Spiral CT scanning of pre- and post-contrast arterial phase, portal venous phase and delayed phase was performed in 5 patients with hepatocellular adenomas proved surgically and pathologically. The enhancement was administrated with venous injection of 3 ml/sec, totally 100 ml angiografin. Arterial phase of contrast-enhanced scanning started 20-30 sec, portal venous phase 60-70 sec and delay scanning 3 min after the injection of contrast medium. The degrees of the enhancement of adenoma and normal tissues of liver in the three contrast enhanced phases were calculated and compared statistically. Results: In plain CT, the lesions were iso-density in 4 cases and slight hypo density in 1 case, which was hardly distinguished from the normal tissue. In all 5 cases, the lesions showed marked enhancement in the arterial phase compared with normal tissue of liver (38 HU high), and there were markedly statistical difference (t = 18.94, P < 0.01). In the portal venous and delay phase, the lesions showed iso-density in 4 caes and slight hypo density in 1 case, the differences of average CT values were (3.7 +- 7.1) HU and (-4.3 +- 3.6) HU compared with normal tissue of liver, there were no statistic differences (t = 1.10, t = 0.75; P > 0.05). The mean CT value of hepatocellular adenoma in the arterial phase was much higher than that in portal venous and delay phase, there were statistical differences between them (F = 18.39, P < 0.01). Conclusion: Triphasic contrast enhanced spiral CT scan, especially the arterial phase scan, is valuable in detecting and differentiating hepatocellular adenoma

[en] Objective: To study the visualization capability and scanning technique of SCTA in celiac artery, superior mesenteric artery (SMA) and other branches. Methods: Thirty patients, with normal abdominal SCTA results, were given small injection test dose after plain scan. The abdominal aorta parallel to the body of pancreas was chosen as target vessel, the peak-time plus 2 seconds as the best delay scan time. Iodine contrast medium 90∼110 ml was injected into antecubital vein at the speed of 3.5 ml/s, then scan from cranial to caudal was performed. Pitch 1.0 and slice thickness 3.2 mm were selected as the scan parameters. Maximum intensity projection (MaxIP) was employed in all patients and shaded surface display (SSD) in 23 cases. Results: The display rate using MaxIP and SSD of celiac artery, splenic artery, common hepatic artery, proper hepatic artery and SMA were all 100%, the gastroduodenal artery 100% and 91%, the left gastric artery 83% and 87%, respectively. Conclusions: SCTA as a minimally invasive examination is a valuable method to detect and diagnose disease or variations of celiac artery, its branches and SMA. Spiral scanning technique and image processing have a decisive effect on the image quality

[en] Objective: To investigate the imaging diagnosis of acetabular dysplastic coxarthrosis. Method: The imaging of the acetabular dysplasia was analyzed in 51 patients (87 hips). All but four patients were women. The age ranged from 22 to 78 years, and the mean age was 42.6 years. Pelvis radiographs were studied in all cases, and CT scan was performed in 18 cases and MRI in 10 cases. Results: The fundamental signs on the plain film included shallow acetabulum, increased obliquity and insufficient coverage of the femoral head by the acetabulum. The CE angles were determined in all the cases, ranging from -10 degree to 30 degree, mean 12.9 degree. The sharp angles ranged from 35 degree to 67 degree, mean 45.3 degree. The secondary osteoarthritis were revealed in 75 hips (84.2%). 54 hips (62.1%) had cyst-like lesions in weight-bear area of the acetabulum or femoral head. 19 hips had subluxation of femoral head. CT and MRI displayed small cyst-like lesions and forward shift of the femoral head, which could not be shown on plain film, respectively in 13 and 10 hips. Conclusion: The cyst-like lesion of subarticular region is a common sign in acetabular dysplastic coxarthrosis. CT or MRI can show the early osteolytic lesion and forward subluxations

[en] Considering the advantages and disadvantages of CuW alloys with different single particle size of tungsten powder, CuW alloys with three kinds of tungsten powders: ultramicron (50 μm), micron(6–8 μm), submicron(0.4 μm) were prepared by the infiltration method. Microstructure of the CuW alloy with different grading ration of tungsten powder were characterized via field-emission scanning electron microscope (SEM). The Vacuum electrical breakdown properties were studied by electrical breakdown test. The results shows that the grading tungsten powders can form a variety of W-W sintered necks, strengthen the tungsten skeleton. SEM results show that a suitable ratio of grading tungsten powders can make the infiltrated copper phase more dispersed and uniform. Compared with the tradition CuW alloy, the conductivity is greater than 53.5%IACS, with the lowest hardness of 203HB, the lowest CuW/CrCu bonding strength of 417 MPa and the highest of 495 MPa, the hardness and electrical conductivity increased by 20%–30%, the bonding strength of new CuW/CrCu monolithic materials increased by 20%, vacuum electrical breakdown properties performed good. (paper)

[en] An effective structural codoping approach is proposed to modify the photoelectrochemical (PEC) properties of anatase TiO₂ by being doped with nonmetal (N or/and C) and transition metal (Re) elements. The electronic structures and formation energies of different doped systems are investigated using spin-polarized density functional theory. We find that (C, Re) doped TiO₂, with a low formation energy and a large binding energy, reduces the band gap to a large extent, thus it could contribute to the significant enhancement of the photocatalytic activity in the visible-light region. It should be pointed out that, to be successful, the proper proportion of the dopants C and Re should be controlled, so that reasonable PEC properties can be achieved. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

[en] Latin hypercube sampling (LHS) method with better space-filling property is often used for computer simulation, to solve the problem of huge computation cost for complex systems, simulation and establish more accurate substitution models. LHS method's advantages in passive system reliability analysis are introduced in this paper. Improved Latin hypercube sampling, optimized Latin hypercube sampling and extension method of samples are summarized. LHS method's applications and deficiencies in nuclear field are proposed. Lastly, LHS method's future application and development direction in passive system reliability analysis are suggested. (authors)