| 301. |
- Li, Rong, et al.
(författare)
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Three-dimensional trueness and margin quality of monolithic zirconia restorations fabricated by additive 3D gel deposition
- 2020
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Ingår i: Journal of Prosthodontic Research. - : Japan Prosthodontic Society. - 1883-1958 .- 2212-4632. ; 64:4, s. 478-484
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The aim of this in vitro study was to evaluate the three-dimensional trueness and margin quality of monolithic zirconia restorations fabricated by additive 3D gel deposition, compared with those by subtractive milling.Methods: Ten single crowns and ten 4-unit FPDs of different occlusal geometries and margin thickness were fabricated by additive 3D gel deposition (additive group) and subtractive milling (subtractive group). An intraoral scanner was used to digitalize the restorations. 3D deviation analysis was applied and root mean square (RMS) was used to assess the trueness. Margin quality was characterized using optical stereomicroscopy and 3D laser scanning microscopy.Results: For single crowns with shallow fossae and grooves and normal margin, RMS value of additive group and subtractive group showed no significant difference in external surface, while additive group showed higher RMS value in intaglio surface. As for 4-unit FPDs with deep fossae and grooves and thin margin, RMS value of additive group in external surface was significantly lower than that of subtractive group and in intaglio surface there was no significant difference between two groups. With a 0.5 mm chamfer design, single crowns in additive group showed flawless margin with a smooth contour line, whereas minor flaws could be observed in 4-unit FPDs with thin margin. In subtractive group, restorations showed minor flaws or defects of various number and severity.Conclusions: Monolithic zirconia restorations fabricated by additive 3D gel deposition have comparable trueness and better margin quality than those fabricated by subtractive milling. Besides it is more capable of enabling complex geometry.
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| 302. |
- Li, Xiaoqing, et al.
(författare)
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Antihyperuricemic Effect of Green Alga Ulva lactuca Ulvan through Regulating Urate Transporters
- 2021
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 69:38, s. 11225-11235
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Tidskriftsartikel (refereegranskat)abstract
- A novel polysaccharide from Ulva lactuca (ULP) was purified using a Sepharose CL-4B column. Fourier transform infrared spectroscopy, high-performance liquid chromatography, and nuclear magnetic resonance spectroscopy were employed to analyze the structure of ULP. It consisted of rhamnose (Rha), glucuronic acid (GluA), galactose (Gal), and xylose (Xyl) at a molar ratio of 32.75:22.83:1.07:6.46 with the molecular weight of 2.24 x 10(5) Da. The four major glycosidic residues found in ULP were -> 2,3)-alpha-L-Rhap-(1 ->, -> 4)-beta-D-GlcpA-(1 ->, -> 2,6)-beta-D-Galp-(1 ->, and -> 4)-beta-D-Xylp-(1 ->. The antihyperuricemic activity of ULP was exhibited by detecting related biochemical indexes, urate transporter gene expressions, renal histopathology, and intestinal microbiota shifts. ULP obviously decreased the levels of serum uric acid (UA), blood urea nitrogen, and creatinine, while inhibited serum and hepatic xanthine oxidase activities as well as improved renal injury in hyperuricemic mice. Furthermore, the upregulation of UA excretion genes ABCG2/OAT1 and downregulation of UA resorption genes URAT1 and GLUT9 were detected. In addition, ULP exerted its antihyperuricemic effect through regulating the intestinal microbiome, characterized by elevating the helpful microbial abundance, meanwhile declining the harmful bacterial abundance and restoring the gut microbiome homeostasis. This study demonstrates the antihyperuricemic activity of ULP and its potential effect for the treatment of hyperuricemia-related diseases.
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| 303. |
- Li, Xueqiang, et al.
(författare)
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Noncovalent assembly of a metalloporphyrin and an iron hydrogenase active-site model : Photo-induced electron transfer and hydrogen generation
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207 .- 1089-5647. ; 112:27, s. 8198-8202
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Tidskriftsartikel (refereegranskat)abstract
- A noncovalent assembly of a pyridyl-functionalized hydrogenase active-site model complex and zinc tetraphenylporphyrin has been obtained and characterized. Upon light irradiation, fluorescence quenching by electron transfer was observed from the singlet excited state of the porphyrin to the diiron center, and the mechanism was verified by fluorescence lifetime and transient absorption spectroscopic measurements. In contrast to molecular dyads linked by covalent bonds, the assembled system was designed to avoid charge recombination via complex dissociation after photo-induced electron transfer. Visible light-driven hydrogen generation was observed from this self-assembled system. The assembling strategy employed in this study has the potential to be used for any other hydrogenase models in the future.
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| 304. |
- Li, Yong
(författare)
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Atom and Group Transfer Reactions Involving High-valent Iron Complexes
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron enzymes play critical roles in biological oxidation reactions by utilizing highly reactive high-valent iron intermediates, such as FeIV=O, FeV(O)(OH), and FeIV=NR species, for catalytic reactions. These intermediates exhibit remarkable catalytic behavior with high reactivities and high regio- and stereospecificity in various biochemical reactions. Understanding these metal intermediates is crucial not only for replicating their activity but also for discovering new synthetic possibilities in chemical synthesis.To address the challenge of comprehending high-valent iron intermediates in biology, chemists have developed a number of bio-inspired functional models that exhibit a diverse range of catalytic properties. The main objective of this thesis is to examine the functional mimicry of mononuclear non-heme active sites in iron enzymes, specifically targeting FeIV=O, FeV(O)(OH) and FeIV=NR intermediates. Chapter 1 provides an introduction to active sites of iron enzymes in biological systems and related bio-inspired models utilizing iron complexes. Chapter 2 relates to Papers I and IV. Paper I describes the syntheses and characterizations of four new FeIV=O complexes based on new ligands with minor steric restriction. The reactivity of these complexes in C-H activation and O-atom transfer reactions has been investigated in detail. As the ligands include negligible steric restrictions, the reactivity differences between these FeIV=O complexes are attributed to the electronic properties of the ligands. On the other hand, Paper IV provides an example of a ligand framework where the steric restrictions of the specific ligand dictate the substrate accessibility. Chapter 3 relates to Paper II and gives a comparative study on the structure and reactivity patterns of a new FeIV=NR complex versus its FeIV=O congener. Chapter 4 relates to Paper III and studies the epoxidation of alkenes by two mononuclear non-heme FeIV=O complexes based on ligands with different electron-donating properties. The catalysis and kinetics studies shed light on the influence of electron-donating properties on the reactivity and mechanism of alkene epoxidation.This research provides insights into the influence exerted by ligand environments on the reactivities of FeIV=O, FeV(O)(OH) and FeIV=NR complexes. The study may contribute to the development of new, highly active catalysts for important oxidation reactions.
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| 305. |
- Li, Yong, et al.
(författare)
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Buoyancy and Thermal Acceleration of Supercritical n-Decane in a Rectangular Channel
- 2022
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Ingår i: Journal of Thermophysics and Heat Transfer. - 0887-8722. ; 36:2, s. 419-430
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Tidskriftsartikel (refereegranskat)abstract
- In this work, supercritical n-decane flowing in ducts with different orientations is thoroughly investigated in terms of secondary flow, wall shear stress, and thermal acceleration. It is known that the secondary flow strength hardly plays a role in cases of flowing upward, flowing downward, or flowing horizontally at a small heat flux/mass flux. Still, an attachment point can be found at the center for cases of flowing upward and flowing downward, and this enhances the heat transfer. For a large heat flux/mass flux, thermal transport depends not only on the secondary flow strength but also on the secondary flow structure. Besides, a separation point is found at the center for flowing up/downward cases, and the more adjacent the attachment point is to the heated wall, the more serious is the thermal transport. The wall shear stress is beneficial to heat transfer but also relies on the distribution profile. Thermal acceleration can really diminish or even restrain the HTD phenomenon, but it is not the reason to cause the difference of heat transfer behavior for channels with different orientations.
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| 306. |
- Li, Yong, et al.
(författare)
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Effect of thermal pyrolysis on heat transfer and upward flow characteristics in a rectangular channel using endothermic hydrocarbon fuel
- 2021
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 244
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Tidskriftsartikel (refereegranskat)abstract
- Supercritical heat transfer deterioration can be found in active regenerative cooling processes. Thermal pyrolysis occurs once the temperature of the hydrocarbon fuel exceeds a certain value. To investigate the influence of thermal pyrolysis on the heat transfer behavior and flow-upward characteristics in a rectangular channel, the wall temperature distribution, thermal acceleration, mass fraction of n-decane, streamline characteristics and vortex structure are analyzed based on a 26-step chemical reaction including 16 species. It is found that the wall temperature increases when the velocity in the viscous sublayer is similar to that in the buffer layer under the influence of thermal pyrolysis. This is because the shear stress and turbulence kinetic energy are diminished. Still affected by thermal pyrolysis, the velocities in the boundary layer become large so that the wall temperature is greatly decreased. This is because the n-decane near the wall is highly cracked and the density of the product is greatly decreased compared to cases without thermal pyrolysis. This indicates that thermal acceleration is beneficial to heat transfer. Besides, many vortices are created under the influence of thermal pyrolysis and this fact can be observed in terms of the distribution of the vortex structures. Vortices are also beneficial to heat transfer. This work is meaningful and significant to the practical design of active regenerative cooling systems.
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| 307. |
- Li, Yong, et al.
(författare)
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Effects of horizontal self-rotation on flow and heat transfer of supercritical n-decane in regenerative circular/rectangular cooling channels
- 2024
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Ingår i: International Journal of Heat and Fluid Flow. - 0142-727X. ; 105
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Tidskriftsartikel (refereegranskat)abstract
- Concerning the rotation flight of a hypersonic vehicle centered on its geometric axis, the rotational flow and heat transfer characteristics of supercritical n-decane in horizontal circular and rectangular tubes were comprehensively analyzed based on numerical simulation. The computational domain was established and the corresponding governing equations of mass conservation, momentum conservation, and energy conservation were mathematically formulated as well were the thermophysical properties and boundary conditions. A procedure for setting up the numerical simulation was finally implemented. A mesh independence study in the case of a rotating speed of 300 rpm and a turbulence model study based on a stationary/swinging tube were comprehensively conducted and the RANS model was well validated. For the circular tube, the wall temperature distribution trend along the flow direction is similar but the magnitude is not uniform. Also, the fluid temperature near the upper wall is larger than that in the vicinity of the lower wall, i.e., the relaminarization plays an essential role in this phenomenon. The velocity difference near the wall can be weakened by the centrifugal force. For the rectangular tube, the velocity magnitude and temperature distribution are found to be greatly affected by the rotation (i.e., centrifugal force). The relative temperature magnitude near the upper and lower walls will be reversed at a rotation speed of n = 100–500 rpm. Subsequently, a symmetrical temperature distribution can be observed once the speed increases to a certain value (e.g., n = 700–900 rpm). In summary, the centrifugal force plays a more important role in a rectangular tube than in a circular tube.
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| 308. |
- Li, Yong, et al.
(författare)
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Flow and thermal performance of supercritical n-decane in double-layer channels for regenerative cooling of a scramjet combustor
- 2020
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 180
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Tidskriftsartikel (refereegranskat)abstract
- In order to improve the active regenerative cooling performance of a scramjet using supercritical n-decane, a new type of cooling channel, the double-layer channel, is proposed. Based on reliable numerical simulations, temperature profiles, fluid flow track, vortex structure and buoyancy force distribution of three cases are presented, respectively. It is found that the heat transfer performance of the double-layer channel with the same flow direction is better than the other cases and the heat transfer deterioration (HTD) phenomenon is effectively weakened and the wall temperature is greatly reduced. A cross-flow and a large vortex structure induced by the buoyancy forces are helpful to the occurrence of the HTD phenomenon. An “M” type temperature profile and an “M” type buoyancy force distribution are important characteristics of the HTD phenomenon.
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| 309. |
- Li, Yong, et al.
(författare)
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Flow Characteristics and Heat Transfer of Supercritical n-decane in Novel Nested Channels for Scramjet Regenerative Cooling
- 2021
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 167
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Tidskriftsartikel (refereegranskat)abstract
- A novel kind of regenerative cooling channel, a so-called nested channel, is proposed to further reduce the combustion chamber wall temperature of a scramjet. The supercritical n-decane heat transfer in the horizontal up-channel and horizontal down-channel with different flow directions are numerically investigated. The temperature distribution, flow field, and vortex structure are presented to discuss the thermal performance and flow characteristics. It is found that the nested channel with the same flow direction performs well particularly for the up-channel with the gravity direction points at the heated wall, and the vortices induced by the gravity are beneficial to the heat transfer performance. This feature is also confirmed by the Case B1 (up-channel, parallel-flow) with the n-decane flowing into the heated wall assisted by the nesting inner channel taking more heat away.
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| 310. |
- Li, Yong, et al.
(författare)
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Heat Transfer and Secondary Flow Characteristics in a Horizontally Round Pipe for Cooling a Scramjet Combustor by Supercritical n-Decane
- 2021
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Ingår i: Journal of Energy Resources Technology. - : ASME International. - 0195-0738 .- 1528-8994. ; 143:2
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Tidskriftsartikel (refereegranskat)abstract
- To figure out the abnormal flow characteristics and thermal performance of supercritical fluids, some detailed information of supercritical pressure n-decane flowing in a horizontally round pipe is studied in terms of secondary flow induced by the huge density change or buoyancy force. According to an evaluation of turbulence models, the shear stress transport k-ω is suitable to execute the case of horizontal flow. It is observed that the temperature distributions between the upper wall region and the lower wall region are asymmetric and the location of the maximum buoyancy force coincided with the position of Tpc (pseudo-critical temperature). The generation of a rotating flow arising from the heated wall determines the occurrence of heat transfer deterioration (HTD). In the boom stage of the HTD phenomenon, a dead zone that is close to the upper wall was formed due to the influence of vortices. In contrast, the maximum buoyancy force is located in the core flow zone and it forces the fluid in the mainstream to participate in the cooling process of the heated wall. In addition, the dead zone in the vicinity of the upper wall is broken. This is the main reason why heat transfer deterioration could be inhibited effectively.
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