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Search Results: 1 - 10 of 134027 matches for " Wei-Min Chen "
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Synthetic Studies on Erythromycin Derivatives: Reactivity of the C12-21 Alkene
Wei-Min Chen
Molecules , 2006, DOI: 10.3390/11010121
Abstract: The reactivity of the C12-21 alkene of some erythromycin A derivatives was studied. This double bond was easily oxidized to the corresponding epoxide with excellent stereoselectivity. A single crystal X-ray structure showed that the epoxide moiety was on the same side as the acetonide. When an erythromycin derivative containing a C12-21 alkene was treated with diazomethane a [3+2] cycloaddition affording a pyrazoline occurred. In the case of 6-O-allylated erythromycin derivatives the C12-21 alkene was selectively epoxidized in the presence of the 6-O-allyl moiety. These results show that the C12-21 alkene is an active reaction site, which can be used for useful further modification of erythromycin derivatives.
Examining the Types of Mathematical Tasks Used to Explore the Mathematics Instruction by Elementary School Teachers  [PDF]
Wei-Min Hsu
Creative Education (CE) , 2013, DOI: 10.4236/ce.2013.46056

This study examined the different types of mathematical tasks used in the classroom to explore the nature of mathematics instruction of three sixth grade teachers in an elementary school. Case studies, instructional observations, and classroom artifacts were used to collect data. The results showed that the three teachers used different types of mathematical tasks and implementation methods. One teacher focused on high cognitive demand tasks, most of which involved substantial group discussion and students working cooperatively. Even though the other two also used many high cognitive demand tasks, these were mainly presented via teacher-student dialogue. By examining the types of mathematical tasks and their implementation, it was found that the group discussion tasks were generally all high cognitive demand tasks, in which the students fully explained the solution process. As for the tasks administered through teacher-student dialogue, due to the usage of large amounts of closed-ended dialogue, the students used low cognition to solve the mathematical tasks and did not have the opportunity to completely explain their thinking about the solutions. Thus, in order to fully understand the nature of mathematics instruction by teachers, there should be simultaneous consideration of the types of mathematical tasks used as well as how the tasks were implemented.

Wei-Min Chen,Long-Mei Zeng
Molecules , 1998, DOI: 10.3390/m90
Abstract: No abstract available
Wei-Min Chen,Long-Mei Zeng
Molecules , 1998, DOI: 10.3390/m74
Abstract: No abstract available
On the progenitors of millisecond pulsars by the recycling evolutionary channel
Wei-Min Liu,Wen-Cong Chen
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19202.x
Abstract: The recycling model suggested that low-mass X-ray binaries (LMXBs) could evolve into binary millisecond pulsars (BMSPs). In this work, we attempt to investigate the progenitor properties of BMSPs formed by the recycling evolutionary channel, and if sub-millisecond pulsars can be produced by this channel. Using Eggleton's stellar evolution code, considering that the dead pulsars can be spun up to a short spin period by the accreting material and angular momentum from the donor star, we have calculated the evolution of close binaries consisting of a neutron star and a low-mass main-sequence donor star, and the spin evolution of NSs. In calculation, some physical process such as the thermal and viscous instability of a accretion disk, propeller effect, and magnetic braking are included. Our calculated results indicate that, all LMXBs with a low-mass donor star of 1.0 - 2.0 $M_\odot$ and a short orbital period ($\la 3-4 \rm d$) can form millisecond pulsars with a spin period less than 10 ms. However, it is difficult to produce sub-millisecond pulsars by this evolutionary channel. In addition, our evolutionary scenario cannot account for the existence of BMSPs with a long orbital period ($P_{\rm orb}\ga 70-80\rm d$).
Some Problems in Defining Functional Integration over the Gauge Group
Wei-Min Sun,Xiang-Song Chen,Fan Wang
Physics , 2000,
Abstract: We find that sometimes the usual definition of functional integration over the gauge group through limiting process may have internal difficulties.
A Note on Functional Integral over the Local Gauge Group
Wei-Min Sun,Xiang-Song Chen,Fan Wang
Physics , 2001,
Abstract: We evaluated some particular type of functional integral over the local gauge group C^{\infty}({\bf R}^n, U(1)) by going to a discretized lattice. The results explicitly violates the property of the Haar measure. We also analysed the Faddeev-Popov method through a toy example. The results also violates the property of the Haar measure.
A simple proof that $C^{\infty}({\bf R}^n,U(1))$ does not have a Haar measure
Wei-Min Sun,Xiang-Song Chen,Fan Wang
Physics , 2001,
Abstract: We give a simple proof that there does not exist a Haar measure on the group $C^{\infty}({\bf R}^n,U(1))$.
Difficulties in a Kind of Averaging Procedure for Constructing Gauge-invariant Operators out of Gauge-variant Ones
Wei-Min Sun,Xiang-Song Chen,Fan Wang
Physics , 2000, DOI: 10.1016/S0370-2693(00)00562-1
Abstract: We prove that a kind of averaging procedure for constructing gauge-invariant operators(or functionals) out of gauge-variant ones is erroneous and inapplicable for a large class of operators(or functionals).
Magnetic braking of Ap/Bp stars: an alternative formation mechanism of compact intermediate-mass binary pulsars
Wei-Min Liu,Wen-Cong Chen
Physics , 2014, DOI: 10.1093/mnras/stu823
Abstract: It is difficult for the intermediate-mass X-ray binaries (IMXBs) evolutionary channel to form intermediate-mass binary pulsars (IMBPs) with a short orbital period (less than 3 d) via stable mass transfer. The main reason is that the magnetic braking mechanisms are generally thought not to work for donor stars with a mass of greater than 1.5 $\rm M_{\odot}$ in the canonical model. However, some intermediate-mass stars have anomalously strong magnetic fields (about 100 -- 10000 G), i. e. so-called Ap or Bp stars. With the coupling between the magnetic field and the irradiation-driven wind from the surface of Ap/Bp stars, a plausible magnetic braking mechanism should be expected. In this work, we attempt to investigate if IMXBs with Ap/Bp stars can produce IMBPs with a short orbital period (less than 3 d) by such an anomalous magnetic braking mechanism. Using a stellar evolution code, we have simulated the evolution of a large number of IMXBs consisting of a NS and an Ap/Bp star. For the spin evolution of the NS, we consider the accretion torque, the propeller torque, and the spin-down torque caused by the interaction between the magnetic field and the accretion disc. The calculated results show that, employing anomalous magnetic braking of Ap/Bp stars, IMXBs can evolve into compact IMBPs with short orbital periods of less than 3 d. However, there exists significant discrepancy between the spin periods of IMBPs in our simulated results and those observed.
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