We consider the annihilation process of an electron-positron pair into a pair of heavier fermions when the initial electron and positron beams are polarized. By calculating the polarization of the final-state particles, we discuss in detail the effect due to the produced particle masses in the T-charm energy region at BEPC/BES, and also compare the effect with that at the B-factory. Such a study is useful for the design of possible polarization investigation at the BEPC/BES facility and the B-factory.
Most studies of the time-reversibility are limited to a linear or an affine involution.In this paper,the authors consider the case of a quadratic involution.For a polynomial differential system with a linear part in the standard form(-y,x)in R~2,by using the method of regular chains in a computer algebraic system,the computational procedure for finding the necessary and sufficient conditions of the system to be time-reversible with respect to a quadratic involution is given.When the system is quadratic,the necessary and sufficient conditions can be completely obtained by this procedure.For some cubic systems,the necessary and sufficient conditions for these systems to be time-reversible with respect to a quadratic involution are also obtained.These conditions can guarantee the corresponding systems to have a center.Meanwhile,a property of a center-focus system is discovered that if the system is time-reversible with respect to a quadratic involution,then its phase diagram is symmetric about a parabola.
A series of nanosized Co/Zn/Mn/K composite catalysts for Fischer-Tropsch synthesis （FTS） were prepared by supercritical fluid drying （SCFD） method and common drying （CD） method. The nanosized cobalt-based catalysts were characterized by XRD, TEM and BET techniques. Their catalytic performances were tested in a slurry-bed reactor under FTS reaction conditions. The drying and crystallization were carried out simultaneously during SCFD, therefore, the catalysts prepared by SCFD method have ideal structure and show the FTS performance superior to the others prepared by CD method. The FTS activity and selectivity were improved via adding Zn, Mn and K promoters, and less CH4 and CO2 as well as higher yield of C5＋ products were achieved. The optimal performance of a 92% CO conversion and a 65% C5＋ product yield was obtained over a catalyst with the component of Co/Zn/Mn/K = 100/50/10/7. Furthermore, the catalytic performance was studied under the conditions of liquid-phase and supercritical phase slurry-bed, and C5＋ product yield were 57.4% and 65.4%, respectively. In summary, better catalytic performance was obtained using the nanosized catalyst prepared by SCFD method under supercritical reaction conditions, resulting in higher conversion of CO, less CO2 byproduct, and higher yield of C5＋ products.
Jingmiao Li Jingchang Zhang Runduo Zhang Weiliang Cao
