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Search Results: 1 - 10 of 127063 matches for " Yongzhi Li "
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An Improved Non-isolated LED Converter with Power Factor Correction and Average Current Mode Control  [PDF]
Renbo Xu, Hongjian Li, Yongzhi Li, Changqian Zhang
Circuits and Systems (CS) , 2011, DOI: 10.4236/cs.2011.23034
Abstract: A new type of high power LED drivers is proposed by adopting an improved two-stages non-isolated configuration. In order to improve power factor and achieve accurate average current control under universal input voltages ranging from 100 Vrms to 240 Vrms, the power factor correction and average current mode control methods operating in continuous current conduction mode are designed and implemented. With the LUMILEDS emitter type LEDs, a laboratory prototype is built and measured. And from the measured results, it could be concluded that the proposed driver has many better performances such as high power factor, low current harmonic, accurate average current control and switch protection.
Research on a High-Efficiency LED Driving Circuit Based on Buck Topology  [PDF]
Renbo Xu, Hongjian Li, Yongzhi Li, Xiaomao Hou
Circuits and Systems (CS) , 2011, DOI: 10.4236/cs.2011.24048
Abstract: A high efficiency LED(Light Emitting Diode) driver based on Buck converter, which could operate under a wide AC input voltage range(85V~265V) and drive a series of high power LEDs, is presented in this paper. The operation principles, power loss factors of the LED driver in this study are analyzed and discussed in detail and some effective ways to improve efficiency are proposed through system design considerations. To verify the feasibility, a laboratory prototype is also designed and tested for an LED lamp which consists of 16 LUMILEDS LEDs in series. Experimental results show that a high efficiency of 92% at I0=350mA can be achieved and the studied driver might be practical for driving high power LEDs. In the last, the overall efficiency over 90% is gained through some experiments under variable input and output voltages and verifies the validity of the designed driver.
Research of an Efficient LED Lighting Driver Based on Boost-Buck Converter  [PDF]
Renbo Xu, Yongzhi Li, Lixin Zhong, Jiaming Liu
Circuits and Systems (CS) , 2014, DOI: 10.4236/cs.2014.56017
Abstract:

Boost-Buck converter is widely used in LED lighting drivers. In this paper, Boost-Buck main circuit related characteristics are firstly discussed, and then a new Boost-Buck high power efficient double loop control strategy is built by adopting error amplifier and integrator control method. It is demonstrated that the new system has many advantages such as high efficiency, fast response, strong anti-interference, good stability after analyses and simulations of its working dynamic characteristics.

Multiple Positive Periodic Solutions for a Gilpin-Ayala Competition Predator-Prey System with Harvesting Terms
Yongzhi Liao,Yongkun Li,Xiaoyan Dou
Abstract and Applied Analysis , 2012, DOI: 10.1155/2012/427264
Abstract: By applying Mawhin’s continuation theorem of coincidence degree theory, we study the existence of multiple positive periodic solutions for a Gilpin-Ayala competition predator-prey system with harvesting terms and obtain some sufficient conditions for the existence of multiple positive periodic solutions for the system under consideration. The result of this paper is completely new. An example is employed to illustrate our result.
Property of alumina to adsorb long chain normal-paraffin hydrocarbons
Yongzhi Li,Xianliang Deng,Weile Yu
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02883924
Abstract: That alumina can strongly absorb long chain normal-paraffin hydrocarbon was found when alumina was used in the preparative group-type separation of heavy petroleum fractions. The reason for the above property of alumina may be that the normal-paraffin hydrocarbons can extend closely on the alumina surface.One molecule of long chain normal-paraffin hydrocarbon can be adsorbed by many active sites of alumina surface. The longer chain normal-paraffin hydrocarbon can be adsorbed by more active sites of alumina surface; this results in the longer chain normal-paraffin hydrocarbon has a stronger adsorption on alumina.
The cooling effect of crushed rock structures on permafrost under an embankment

QingBai Wu,MingYong Li,YongZhi Liu,

寒旱区科学 , 2009,
Abstract: Based on the analysis and comparison of soil temperature, thermal regime and permafrost table under the experimental embankment of crushed rock structures in Beiluhe, results show that crushed rock structures provide an extensive cooling effect, which produces a rising permafrost table and decreasing soil temperatures. The rise of the permafrost table under the embankment ranges from an increase of 1.08 m to 1.67 m, with an average of 1.27 m from 2004 to 2007. Mean annual soil temperatures under the crushed rock layer embankment decreased significantly from 2005 to 2007, with average decreases of ?1.03 °C at the depth of 0.5 m, ?1.14 °C at the depth of 1.5 m, and ?0.5 °C at the depth of 5 m. During this period, mean annual soil temperatures under the crushed rock cover embankment showed a slight decrease at shallow depths, with an average decrease of ?0.2 °C at the depth of 0.5 m and 1.5 m, but a slight rise at the depth of 5 m. After the crushed rock structures were closed or crammed with sand, the cooling effect of the crushed rock layer embankment was greatly reduced and that of the crushed rock cover embankment was just slightly reduced
Property of alumina to adsorb long chain normal-paraffinhydrocarbons

Yongzhi Li,Xianliang Deng,Weile Yu,

科学通报(英文版) , 1998,
Abstract: That alumina can strongly absorb long chain normal-paraffin hydrocarbon was found when alumina was used in the preparative group-type separation of heavy petroleum fractions. The reason for the above property of alumina may be that the normal-paraffin hydrocarbons can extend closely on the alumina surface.One molecule of long chain normal-paraffin hydrocarbon can be adsorbed by many active sites of alumina surface. The longer chain normal-paraffin hydrocarbon can be adsorbed by more active sites of alumina surface; this results in the longer chain normal-paraffin hydrocarbon has a stronger adsorption on alumina.
Existence and Multiplicity of Solutions to a Boundary Value Problem for Impulsive Differential Equations
Chunyan He,Yongzhi Liao,Yongkun Li
Journal of Applied Mathematics , 2013, DOI: 10.1155/2013/401740
Abstract:
Beneficial and Detrimental Effects of Plasmin(ogen) during Infection and Sepsis in Mice
Yongzhi Guo, Jinan Li, Elin Hagstr?m, Tor Ny
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0024774
Abstract: Plasmin has been proposed to be an important mediator during inflammation/infection. In this study, by using mice lacking genes for plasminogen, tissue-type plasminogen activator (tPA), and urokinase-type PA (uPA), we have investigated the functional roles of active plasmin in infection and sepsis. Two models were used: an infection model by intravenous injection of 1×107 CFU of S. aureus, and a sepsis model by intravenous injection of 1.6×108 CFU of S. aureus. We found that in the infection model, wild-type (WT) mice showed significantly higher survival rates than plasminogen-deficient (plg-/-) mice. However, in the sepsis model, plg-/- or tPA-/-/uPA-/- mice showed the highest survival rate whereas WT and tPA+/-/uPA+/- mice showed the lowest survival rate, and plg+/-, tPA-/-, and uPA-/- mice had an intermediate survival rate. These results indicate that the levels of active plasmin are critical in determining the survival rate in the sepsis, partly through high levels of inflammatory cytokines and enhanced STAT3 activation. We conclude that plasmin is beneficial in infection but promotes the production of inflammatory cytokines in sepsis that may cause tissue destruction, diminished neutrophil function, and an impaired capacity to kill bacteria which eventually causes death of these mice.
Optimization design for polymeric S-shaped ridge waveguide
RongGuo Lu,JinKun Liao,XiongGui Tang,HePing Li,YongZhi Liu
Chinese Science Bulletin , 2010, DOI: 10.1007/s11434-009-3352-8
Abstract: The dispersion characteristics and transverse field distribution of the fundamental and higher order modes are analyzed for polymeric ridge multimode waveguide by a new technique which is based on the combination of the effective index method and the variational method. An algorithm is implemented to study the effect of the structure parameters and dimensions on the dispersion curves. The optical field distribution of the fundamental and higher order modes for TM modes are computed. The single mode conditions of polymeric ridge waveguide are obtained. The relationship between the curvature radius and the bending loss of S-shaped ridge waveguide are studied with wide-angle finite-difference beam propagation method and effective index method. The conclusion is: when the curvature radius is larger than 5000 μm, the bending loss will not decrease distinctly even if the curvature radius increases, and the light can propagate stably in the S-shaped ridge waveguide.
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