| 61. |
- Dong, Jingran, et al.
(författare)
-
Kinetics and mechanism of oxidation of the anti-tubercular prodrug isoniazid and its analog by iridium(IV) as models for biological redox systems
- 2017
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; 46:26, s. 8377-8386
-
Tidskriftsartikel (refereegranskat)abstract
- A complex reaction mechanism of oxidation of the anti-tubercular prodrug isoniazid (isonicotinic hydrazide, INH) by [IrCl6]2− as a model for redox processes of such drugs in biological systems has been studied in aqueous solution as a function of pH between 0 and 8.5. Similar experiments have been performed with its isomer nicotinic hydrazide (NH). All reactions are overall second-order, first-order in [IrCl6]2− and hydrazide, and the observed second-order rate constants k′ have been determined as a function of pH. Spectrophotometric titrations indicate a stoichiometry of [Ir(IV)]:[hydrazide] = 4:1. HPLC analysis shows that the oxidation product of INH is isonicotinic acid. The derived reaction mechanism, based on rate law, time-resolved spectra and stoichiometry, involves parallel attacks by [IrCl6]2− on all four protolytic species of INH and NH as rate-determining steps, depending on pH. These steps are proposed to generate two types of hydrazyl free radicals. These radicals react further in three rapid consecutive processes, leading to the final oxidation products. Rate constants for the rate-determining steps have been determined for all protolytic species I–IV of INH and NH. They are used to calculate reactivity–pH diagrams. These diagrams demonstrate that for both systems, species IV is ca. 105 times more reactive in the redox process than the predominant species III at the physiological pH of 7.4. Thus, species IV will be the main reactant, in spite of the fact that its concentration at this pH is extremely low, a fact that has not been considered in previous work. The results indicate that pH changes might be an important factor in the activation process of INH in biological systems also, and that in such systems this process most likely is more complicated than previously assumed
|
|
| 62. |
- Dong, Y. B., et al.
(författare)
-
High Light Extraction Efficiency AlGaInP LEDs With Proton Implanted Current Blocking Layer
- 2016
-
Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 37:10, s. 1303-1306
-
Tidskriftsartikel (refereegranskat)abstract
- Improving light extraction efficiency is the key issue for light-emitting diodes (LEDs). Nowadays, a vertical structure design dominates LEDs. However, the light from the active region just below the p-electrode is severely blocked by the metal contact. In this letter, we use proton implantation with a depth all the way to the active region to turn the part beneath the p-pad insulating, which constitutes the most-effective-ever current blocking method. Earlier particle implantation studies never reached the device active region. Our experimental results show that the H+-implanted LEDs improve the light output power by 75% compared with non-implanted counterparts and the light intensity increases by 64.48%. By virtue of indium tin oxide current spreading film, the increase in working voltage is negligible. Analyzing the reverse leakage current, the side effect associated with the implantation is limited to an acceptable range. Numerical simulation is performed to support the experiment. Our results represent a new and simple method for solving the light blocking problem in vertical LEDs, without introducing the seemingly existing severe implantation damage to the device structure.
|
|
| 63. |
- Dong, Y. B., et al.
(författare)
-
The growth of graphene on Ni–Cu alloy thin films at a low temperature and its carbon diffusion mechanism
- 2019
-
Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:11
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2 /Si substrate at a low temperature (~600◦ C).
|
|
| 64. |
- Dong, Y. B., et al.
(författare)
-
Transfer-free, lithography-free, and micrometer-precision patterning of CVD graphene on SiO 2 toward all-carbon electronics
- 2018
-
Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 6:2
-
Tidskriftsartikel (refereegranskat)abstract
- A method of producing large area continuous graphene directly on SiO 2 by chemical vapor deposition is systematically developed. Cu thin film catalysts are sputtered onto the SiO 2 and pre-patterned. During graphene deposition, high temperature induces evaporation and balling of the Cu, and the graphene "lands onto" SiO 2 . Due to the high heating and growth rate, continuous graphene is largely completed before the Cu evaporation and balling. 60 nm is identified as the optimal thickness of the Cu for a successful graphene growth and μm-large feature size in the graphene. An all-carbon device is demonstrated based on this technique.
|
|
| 65. |
- Dong, Yibo, et al.
(författare)
-
In Situ Growth of CVD Graphene Directly on Dielectric Surface toward Application
- 2020
-
Ingår i: ACS Applied Electronic Materials. - : American Chemical Society (ACS). - 2637-6113. ; 2:1, s. 238-246
-
Tidskriftsartikel (refereegranskat)abstract
- A technique for the in situ growth of patterned graphene by CVD has been achieved directly on insulating substrates at 800 degrees C. The graphene growth is catalyzed by a Ni-Cu alloy sacrificial layer, which integrates many advantages such as being lithography-free, and almost wrinkle-free, with a high repeatability and rapid growth. The etching method of the metal sacrificial layer is the core of this technique, and the mechanism is analyzed. Graphene has been found to play an important role in accelerating etching speeds. The Ni-Cu alloy exhibits a high catalytic activity, and thus, high-quality graphene can be obtained at a lower temperature. Moreover, the Ni-Cu layer accommodates a limited amount of carbon atoms, which ensures a high monolayer ratio of the graphene. The carbon solid solubility of the alloy is calculated theoretically and used to explain the experimental findings. The method is compatible with the current semiconductor process and is conducive to the industrialization of graphene devices.
|
|
| 66. |
- Dong, Yu, et al.
(författare)
-
Observation of a Ubiquitous (π, π)-Type Nematic Superconducting Order in the Whole Superconducting Dome of Ultra-Thin BaFe2–xNixAs2 Single Crystals
- 2021
-
Ingår i: Chinese Physics Letters. - : Institute of Physics Publishing (IOPP). - 0256-307X .- 1741-3540. ; 38:9
-
Tidskriftsartikel (refereegranskat)abstract
- In iron-based superconductors, the (0, pi) or (pi, 0) nematicity, which describes an electronic anisotropy with a four-fold symmetry breaking, is well established and believed to be important for understanding the superconducting mechanism. However, how exactly such a nematic order observed in the normal state can be related to the superconducting pairing is still elusive. Here, by performing angular-dependent in-plane magnetoresistivity using ultra-thin flakes in the steep superconducting transition region, we unveil a nematic superconducting order along the (pi, pi) direction in electron-doped BaFe2 - x Ni x As2 from under-doped to heavily overdoped regimes with x = 0.065-0.18. It shows superconducting gap maxima along the (pi, pi) direction rotated by 45 degrees from the nematicity along (0, pi) or (pi, 0) direction observed in the normal state. A similar (pi, pi)-type nematicity is also observed in the under-doped and optimally doped hole-type Ba1 - y K y Fe2As2, with y = 0.2-0.5. These results suggest that the (pi, pi) nematic superconducting order is a universal feature that needs to be taken into account in the superconducting pairing mechanism in iron-based superconductors.
|
|
| 67. |
- Dong, Yibo, et al.
(författare)
-
Transfer-free, lithography-free and fast growth of patterned CVD graphene directly on insulators by using sacrificial metal catalyst
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 29:36
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical vapor deposited graphene suffers from two problems: transfer from metal catalysts to insulators, and photoresist induced degradation during patterning. Both result in macroscopic and microscopic damages such as holes, tears, doping, and contamination, translated into property and yield dropping. We attempt to solve the problems simultaneously. A nickel thin film is evaporated on SiO2 as a sacrificial catalyst, on which surface graphene is grown. A polymer (PMMA) support is spin-coated on the graphene. During the Ni wet etching process, the etchant can permeate the polymer, making the etching efficient. The PMMA/graphene layer is fixed on the substrate by controlling the surface morphology of Ni film during the graphene growth. After etching, the graphene naturally adheres to the insulating substrate. By using this method, transfer-free, lithography-free and fast growth of graphene realized. The whole experiment has good repeatability and controllability. Compared with graphene transfer between substrates, here, no mechanical manipulation is required, leading to minimal damage. Due to the presence of Ni, the graphene quality is intrinsically better than catalyst-free growth. The Ni thickness and growth temperature are controlled to limit the number of layers of graphene. The technology can be extended to grow other two-dimensional materials with other catalysts.
|
|
| 68. |
- Dove, Abigail, et al.
(författare)
-
Association between social isolation and reduced mental well-being in Swedish older adults during the first wave of the COVID-19 pandemic : the role of cardiometabolic diseases
- 2022
-
Ingår i: Aging. - : Impact Journals, LLC. - 1945-4589. ; 14:6, s. 2462-2474
-
Tidskriftsartikel (refereegranskat)abstract
- Social isolation has been recommended as a strategy for reducing COVID-19 risk, but it may have unintended consequences for mental well-being. We explored the relationship between social isolation and symptoms of depression and anxiety in older adults during the first wave of the COVID-19 pandemic and assessed the role of cardiometabolic diseases (CMDs) in this association. Between May and September 2020, 1,190 older adults from the Swedish National Study on Aging and Care in Kungsholmen were surveyed about their behaviors and health consequences during the first wave of the COVID-19 pandemic. In total, 913 (76.7%) participants reported socially isolating at home to avoid infection during this period. Social isolation was associated with a greater likelihood of reduced mental well-being (i.e., feelings of depression or anxiety) (OR: 1.74, 95% CI: 1.15-2.65). In joint exposure analysis, there was a significant likelihood of reduced mental well-being only among people who were socially isolating and had CMDs (OR: 2.13, 95% CI: 1.22-3.71) (reference: not isolating, CMD-free). In conclusion, social isolation as a COVID-19 prevention strategy was related to reduced mental well-being in an urban sample of Swedish older adults, especially among individuals with CMDs.
|
|
| 69. |
- Dove, Abigail, et al.
(författare)
-
Cardiometabolic disease, cognitive decline, and brain structure in middle and older age
- 2024
-
Ingår i: Alzheimer's and Dementia. - 2352-8729. ; 16:2
-
Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: The presence of multiple cardiometabolic diseases (CMDs) has been linked to increased dementia risk, but the combined influence of CMDs on cognition and brain structure across the life course is unclear.METHODS: In the UK Biobank, 46,562 dementia-free participants completed a cognitive test battery at baseline and a follow-up visit 9 years later, at which point 39,306 also underwent brain magnetic resonance imaging. CMDs (diabetes, heart disease, and stroke) were ascertained from medical records. Data were analyzed using age-stratified (middle age [< 60] versus older [≥ 60]) mixed-effects models and linear regression.RESULTS: A higher number of CMDs was associated with significantly steeper global cognitive decline in older (β = –0.008; 95% confidence interval: −0.012, −0.005) but not middle age. Additionally, the presence of multiple CMDs was related to smaller total brain volume, gray matter volume, white matter volume, and hippocampal volume and larger white matter hyperintensity volume, even in middle age.DISCUSSION: CMDs are associated with cognitive decline in older age and poorer brain structural health beginning already in middle age.
|
|
| 70. |
- Du, Banghua, et al.
(författare)
-
Energy management and performance analysis of an off-grid integrated hydrogen energy utilization system
- 2024
-
Ingår i: Energy Conversion and Management. - 0196-8904. ; 299
-
Tidskriftsartikel (refereegranskat)abstract
- In integrated hydrogen energy utilization systems, due to the low efficiency of hydrogen/electricity conversion, coordination of energy management and efficient waste heat recovery is required to optimize performance. To address this challenge, this paper presents a comprehensive and sophisticated modeling and energy management strategy to enhance the off-grid energy utilization rate while prolonging the main components' lifetime. The developed model incorporates multiphase flow and heat transport balance for electricity and heat production, enabling a highly accurate representation of real-world behaviors of the system. The proposed off-grid operation strategy is complemented by a designed heat recovery scheme, ensuring the use of energy resources and waste heat. In addition, the proposed energy management strategy monitors the real-time status of each subsystem, actively reducing the number of harmful start-stop cycles of the hydrogen production system, thereby mitigating short-term power impacts and delaying its aging. Specifically, the voltage degradation of the reduction cell is reduced from 4.67 mV to 4.48 mV, the energy utilization rate is increased from 47.6 % to 53.9 %, and the energy efficiency of fuel cells significantly increases from 53.6 % to 78.1 %.
|
|
