| 480501. |
- Liu, LIu, et al.
(författare)
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Near-field optical storage system using a solid immersion lens with a left-handed material slab
- 2004
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Ingår i: Optical express. - 1094-4087. ; 12, s. 4835-4840
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Tidskriftsartikel (refereegranskat)abstract
- A new near-field optical storage system utilizing a left-handed material (LHM) is introduced by attaching an LHM slab to the lower surface of a conventional solid immersion lens (SIL). The performance of the present storage system is compared with a conventional SIL system through numerical simulation. The LHM slab in the present storage system can image very well the focused spot at the lower surface of the SIL to the surface of a disc. It allows a large air-gap for the mechanical convenience while keeping a large signal contrast and a high storage density. The tolerance of the air-gap is also improved.
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| 480502. |
- Liu, Linpeng, et al.
(författare)
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Ni and Fe catalyzed cascade radical reactions of oxime esters with diselenides
- 2022
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Ingår i: Organic Chemistry Frontiers. - : Royal Society of Chemistry (RSC). - 2052-4129. ; 9:13, s. 3480-3485
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Tidskriftsartikel (refereegranskat)abstract
- A radical cyclization and ring-opening of oxime esters with diselenides was developed. Both Ni(0) and Fe(II) catalysts could be employed for the selenylation of olefin-containing and cyclic oxime ester derivatives. With this method, a variety of functionalized pyrrolines and alkyl nitriles were synthesized in good yields. Moreover, a mechanism involving iminyl radical and carbon-centered radical intermediates was proposed.
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| 480503. |
- Liu, Liu, et al.
(författare)
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Novel surface plasmon waveguide for high integration
- 2005
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Ingår i: Optics Express. - 1094-4087. ; 13, s. 6645-6650
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Tidskriftsartikel (refereegranskat)abstract
- A novel surface plasmon waveguide structure is proposed for highly integrated planar lightwave circuits. By etching a small trench through a metallic thin film on a silica substrate, a guided mode with highly confined light fields is realized. The mode properties of the proposed structure are studied. The necessity of using a polymer upper-cladding is discussed. The coupling between two closely positioned waveguides and a 90° bending are also studied numerically. Sharp bending and high integration can be realized with the present surface plasmon waveguide. The proposed structure is easy to fabricate as compared with some other types of surface plasmon waveguides for high integration
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| 480504. |
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| 480505. |
- Liu, Lipeng, 1990-, et al.
(författare)
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On the critical charge required for positive leader inception in long air gaps
- 2018
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Ingår i: Journal of Physics D. - : Institute of Physics (IOP). - 0022-3727 .- 1361-6463. ; 51:3
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Tidskriftsartikel (refereegranskat)abstract
- The amount of the electric charge injected by the streamer corona bursts during the stage of leader inception determines the energy deposited to thermalize the corona stem into a leader segment. This paper is aimed at investigating the critical charge required for positive leader inception in air by using a thermo-hydrodynamic model with a detailed kinetic scheme. In order to simplify the analysis and to speed up the simulation, a reduced kinetic scheme for air is proposed. Numerical comparisons show that the reduced scheme can obtain almost the same results as the previous comprehensive kinetic scheme but with only half of the number of species and reactions. The thermo-hydrodynamic model with the reduced kinetics is then used to solve the radial dynamics of a single stem heated by current pulses typical of streamer corona bursts. The critical charge necessary for the direct transition of a first streamer corona into a leader under electrodes with large curvature radius is estimated between 0.08 and 0.5 uC per stem. Furthermore, the simulation shows that the gas heating of corona stem formed from electrodes with small curvature radius is mainly determined by the total accumulated charge injected by previous streamer corona bursts and the length of the dark periods in between the current pulses. The shape and the number of the corona current pulses in the discharge also play a role and their effects are discussed. It is suggested that the transition into a leader is triggered when a secondary streamer burst is initiated after the gas temperature is increased by the heating of previous streamers to about 1200 K. In addition, it is found that the heating produced by the charge injected by previous streamer corona bursts can be neglected if the dark period to the next burst is larger than few hundreds of for a corona stem with moderate initial stem radius. This indicates that the critical charge criterion obtained from laboratory experiments does not hold to evaluate the inception of positive leaders under conditions when long dark periods are present.
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| 480506. |
- Liu, Liguang, et al.
(författare)
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On the global Gaussian Lipschitz space
- 2017
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Ingår i: Proceedings of the Edinburgh Mathematical Society. - 1464-3839 .- 0013-0915. ; 60:3, s. 707-720
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Tidskriftsartikel (refereegranskat)abstract
- A Lipschitz space is defined in the Ornstein-Uhlenbeck setting, by means of abound for the gradient of the Ornstein-Uhlenbeck Poisson integral. This spaceis then characterized with a Lipschitz-type continuity condition. Thesefunctions turn out to have at most logarithmic growth at infinity. Theanalogous Lipschitz space containing only bounded functions was introducedby Gatto and Urbina and has been characterized by the authors.
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| 480507. |
- Liu, Lipeng, 1990-, et al.
(författare)
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On the transition from stable positive glow corona to streamers
- 2016
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Ingår i: Journal of Physics D. - : Institute of Physics (IOP). - 0022-3727 .- 1361-6463. ; 49:22, s. 225202-
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Tidskriftsartikel (refereegranskat)abstract
- A 2D numerical simulation of the transition from stable positive glow corona to streamers in coaxial cylindrical configuration is presented. The hydrodynamic model with several convection-dominated continuity equations together with Poisson equation are solved with consideration of the ionization layer. The transition from a stable positive glow corona produced under a DC voltage to streamers is investigated under a sudden change of the applied voltage. The critical rate of rise of voltage required for the transition from positive glow to streamer corona is evaluated with a voltage ramp. By introducing either physical or numerical instabilities into the model, streamers with filamentary structures are observed, which produce a sudden increase of the discharge current by more than two orders of magnitude. It is also found that the surface electric field of the corona-generating conductor deviates from the onset electric field, casting doubts about the validity of Kaptzov's approximation to evaluate the transition from stable glow to streamers.
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| 480508. |
- Liu, Longcheng, et al.
(författare)
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Permeability and expansibility of natural bentonite MX-80 in distilled water
- 2011
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Ingår i: Physics and Chemistry of the Earth. - : Elsevier. - 1474-7065 .- 1873-5193. ; 36:17-18, s. 1783-1791
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Tidskriftsartikel (refereegranskat)abstract
- Natural bentonite MX-80 differs from the purified and fully Na-exchanged bentonite in that it contains approximately 20.0% accessory minerals, in addition to the montmorillonite particles. Since the accessory minerals and montmorillonite particles have very different physical and chemical properties, natural bentonite MX-80 is found to expand much more slowly in distilled water, leading actually to a three-component system that has very different hydraulic properties from that of the fully Na-exchanged bentonite. To better understand and simulate the special features of expansion of natural bentonite MX-80 in distilled water, the focus is put primarily on the development of a Kozeny-Carman-like equation for its hydraulic permeability in the same way as it was done for Na-exchanged bentonite. With this permeability model, the dynamic force balance model that was originally developed for colloidal expansion of montmorillonite in a two-component system is applied to the natural MX-80 system. Without making any changes to the model, however, two strategies are used to account for both physical and chemical effects of the accessory minerals. The "lumped" strategy assumes that the accessory minerals are stuck onto the montmorillonite particles in such a way that they behave just like one solid component. The "stepwise" strategy changes the pore water chemistry gradually from initially distilled water to eventually achievement of the equilibrium condition. These strategies are simple but proved to function well. The agreement between the simulations and the experimental results indicates that the two-component dynamic force balance model works well in predicting the general features and the behavior of upward expansion of natural bentonite MX-80 in distilled water in a vertical test tube.
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| 480509. |
- Liu, Longcheng
(författare)
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Permeability and expansibility of sodium bentonite in dilute solutions
- 2010
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 358:1-3, s. 68-78
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Tidskriftsartikel (refereegranskat)abstract
- In developing the dynamic force balance model for colloidal expansion, it was acknowledged that accurate description of the viscous drag force, or equivalently the permeability, is very important to describe the swelling process of compacted bentonite as it expands and eventually turns from a gel into a sol in low ionic strength waters. We therefore developed a Kozeny-Carman-like equation to quantify the permeability of the purified and fully Na-exchanged bentonite in dilute homoionic solutions, based on a set of permeability measurements. The force balance model, together with a friction model derived from the permeability, is then validated against accurate observations of the expansion process of the Na-exchanged bentonite in a water filled vertical test tube. The expansion is followed in detail over a month, by use of the magnetic resonance imaging technique with a spatial resolution of 0.2 mm. as an initially compacted tablet of Na-bentonite expands in water. The model accurately predicts not only the expansion rate and the general features of the expansion but also the basic behaviour at the expanding gel/sol interface. In addition, the use of the developed Kozeny-Carman-like equation substantiates that the expansion rate depends strongly on the friction of the particles against the water.
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| 480510. |
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