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Interface control of bulk ferroelectric polarization.
Yu, P,Luo, W,Yi, D,Zhang, J X,Rossell, M D,Yang, C-H,You, L,Singh-Bhalla, G,Yang, S Y,He, Q,Ramasse, Q M,Erni, R,Martin, L W,Chu, Y H,Pantelides, S T,Pennycook, S J,Ramesh, R National Academy of Sciences 2012 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.109 No.25
<P>The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite underlayers extends the generality of this phenomenon.</P>
A CMOS Frequency divider for 2.4/5GHz WLAN Applications with a Simplified Structure
Q. Yu,Y. Liu,X.P. Yu,W. M. Lim,F. Yang,X. L. Zhang,Y. Peng 대한전자공학회 2011 Journal of semiconductor technology and science Vol.11 No.4
In this paper, a dual-band integer-N frequency divider is proposed for 2.4/5.2 GHz multistandard wireless local area networks. It consists of a multi-modulus imbalance phase switching prescaler and two all-stage programmable counters. It is able to provide dual-band operation with high resolution while maintaining a low power consumption. This frequency divider is integrated with a 5 GHz VCO for multi-standard applications. Measurement results show that the VCO with frequency divider can work at 5.2 GHz with a total power consumption of 22 mW.
A CMOS Frequency divider for 2.4/5GHz WLAN Applications with a Simplified Structure
Yu, Q.,Liu, Y.,Yu, X.P.,Lim, W.M.,Yang, F.,Zhang, X.L.,Peng, Y. The Institute of Electronics and Information Engin 2011 Journal of semiconductor technology and science Vol.11 No.4
In this paper, a dual-band integer-N frequency divider is proposed for 2.4/5.2 GHz multi-standard wireless local area networks. It consists of a multi-modulus imbalance phase switching prescaler and two all-stage programmable counters. It is able to provide dual-band operation with high resolution while maintaining a low power consumption. This frequency divider is integrated with a 5 GHz VCO for multi-standard applications. Measurement results show that the VCO with frequency divider can work at 5.2 GHz with a total power consumption of 22 mW.
Yu, A.Q.,Pratomo Juwono, N.K.,Foo, J.L.,Leong, S.S.J.,Chang, M.W. Academic Press 2016 Metabolic engineering Vol.34 No.-
Short branched-chain fatty acids (SBCFAs, C4-6) are versatile platform intermediates for the production of value-added products in the chemical industry. Currently, SBCFAs are mainly synthesized chemically, which can be costly and may cause environmental pollution. In order to develop an economical and environmentally friendly route for SBCFA production, we engineered Saccharomyces cerevisiae, a model eukaryotic microorganism of industrial significance, for the overproduction of SBCFAs. In particular, we employed a combinatorial metabolic engineering approach to optimize the native Ehrlich pathway in S. cerevisiae. First, chromosome-based combinatorial gene overexpression led to a 28.7-fold increase in the titer of SBCFAs. Second, deletion of key genes in competing pathways improved the production of SBCFAs to 387.4mg/L, a 31.2-fold increase compared to the wild-type. Third, overexpression of the ATP-binding cassette (ABC) transporter PDR12 increased the secretion of SBCFAs. Taken together, we demonstrated that the combinatorial metabolic engineering approach used in this study effectively improved SBCFA biosynthesis in S. cerevisiae through the incorporation of a chromosome-based combinatorial gene overexpression strategy, elimination of genes in competitive pathways and overexpression of a native transporter. We envision that this strategy could also be applied to the production of other chemicals in S. cerevisiae and may be extended to other microbes for strain improvement.
TRAVELING BEHAVIOR OF A WATER CLUSTER RELEASED FROM A CARBON NANOTUBE
H. Q. YU,Y. F. LI,H. LI,K. M. LIEW 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2011 NANO Vol.6 No.3
Molecular dynamics simulation is used to observe the traveling behavior of a water cluster released from the interior of single-walled carbon nanotube (SWCNT) to a graphite sheet. The simulation results reveal that there is a need for the water cluster overcoming the energy barrier of the binding energy between the water cluster and the SWCNT to escape from the tube. The water cluster undergoes a three-dimensional motion when released from the SWCNT, due to the effect of the thermal velocity. When encountering the graphite sheet in the forward direction, the x axis impact velocity has much effect on the delivery of the water cluster. The fact that the water cluster is bounced back reduces the possibility of being captured by the graphite sheet, resulting in a decrease in the delivery efficiency of the water cluster. The presence of the electric charges can help the graphite sheet to effectively trap the water cluster. These results have implications for the design and fabrication of novel drug delivery devices.
Xiang-Yu LI,J. Wu,W.Q. Chen,Hui-Ying Wang,Z.Q. Zhou 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.3
This paper examines the problem of a penny-shaped crack in a thermoporoelastic body. On the basis of the recently developed general solutions for thermoporoelasticity, appropriate potentials are suggested and the governing equations are solved in view of the similarity to those for pure elasticity. Exact and closed form fundamental solutions are expressed in terms of elementary functions. The singularity behavior is then discussed. The present solutions are compared with those in literature and an excellent agreement is achieved. Numerical calculations are performed to show the influence of the material parameters upon the distribution of the thermoporoelastic field. Due to its ideal property, the present solution is a natural benchmark to various numerical codes and simplified analyses.
AB INITIO STUDY OF NITROGEN-DOPED CARBON NANOTUBES
S. S. YU,Q. B. WEN,W. T. ZHENG,Q. JIANG 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2007 NANO Vol.2 No.3
Calculations have been made for carbon nanotubes containing substitutional nitrogen impurity atoms using ab initio density functional theory. It is found that the distribution of N atoms depends upon the chirality and diameter of the tube. When two nitrogen atoms are introduced into the (5, 5), (6, 6) and (7, 4) tubes, nitrogen atoms prefer to be adjacent to each other along the circumference, while they tend to be far from each other in other carbon nanotubes. As more nitrogen atoms are incorporated, they prefer to be localized, leading to the broken N–N bond and the interstice is formed in the thin tubes. However, for thick tubes, nitrogen atoms tend to distribute uniformly. It is the finding in this work that the high radial stress plays an important role in nitrogen atom distribution for the thin tubes. For thin N-doped tubes, the major contribution to the structural stabilization comes from the radial stress release after the N–N bond is broken.