具有销售成本的小额信贷模型

首先剖析了我国小额贷款实践的现状和存在的问题,通过理论和数学模型分析,指出信贷约束本身并不是贫困产生和持续的充分条件.由于农户存在产品销售成本带来的销售规模效应给农户的贫困的影响及其对农村小额信贷项目的影响,过低的贷款额度可能会使得小额贷款项目对农户失去吸引力,造成小额贷款需求萎缩.因此,适当扩大小额贷款的额度限制,有利于农户更加积极地参与到小额贷款项目中,通过正当经营,增加收入,从而提高生活水平.     

Responsive mechanism and molecular design of di-2-picolylamine-based two-photon fluorescent probes for zinc ions

The properties of one-photon absorption(OPA), emission and two-photon absorption(TPA) of a di-2-picolylaminebased zinc ion sensor are investigated by employing the density functional theory in combination with response functions.The responsive mechanism is explored. It is found that the calculated OPA and TPA properties are quite consistent with experimental data. Because the intra-molecular charge transfer(ICT) increases upon zinc ion binding, the TPA intensity is enhanced dramatically. According to the model sensor, we design a series of zinc ion probes which differ by conjugation center, acceptor and donor moieties. The properties of OPA, emission and TPA of the designed molecules are calculated at the same computational level. Our results demonstrate that the OPA and emission wavelengths of the designed probes have large red-shifts after zinc ions have been bound. Comparing with the model sensor, the TPA intensities of the designed probes are enhanced significantly and the absorption positions are red-shifted to longer wavelength range. Furthermore, the TPA intensity can be improved greatly upon zinc ion binding due to the increased ICT mechanism. These compounds are potential excellent candidates for two-photon fluorescent zinc ion probes.     

Isomerism and coordination mode effects on two-photon absorption of tris(picolyl)amine-based fluorescent probes for zinc ions

One-photon absorption and two-photon absorption(TPA) properties of three tris(picolyl)amine-based zinc ion sensors are investigated by employing the density functional response theory in combination with the polarizable continuum model.The different isomer and coordination geometry of each probe are taken into account. Special emphasis is placed on the effects of isomerism and the coordination mode on the optical properties. The intra-molecular charge transfer(ICT)properties are specified by natural bond orbital charge analysis. It is shown that the isomerism has non-negligible effects on TPA properties of free ligands. It is found that both the TPA wavelength and the cross section are highly dependent on the coordination mode. When the zinc ion connects with the picolyl unit in the middle of a ligand, the zinc complex has a large TPA intensity in a long wavelength range due to the increased ICT mechanism.     

社会保障税的经济归宿分析

社会保障税的税负应由雇主与雇员共同分担,采用数理方法可以理论上推理出:在其他条件不变的情况下,雇主与雇员所分担的社会保障税税负比例为劳动供给弹性与未征税时劳动需求弹性.在政府设计社会保障税制度时,要减少征税成本与税负转嫁成本,以减少社会保障税对经济效率所产生的扭曲及其他负面影响;要结合现时劳动供求状况制定雇主与雇员的法定分担比例;社会保障税税率在短期内应是相对稳定的,但在长期内应是动态变化的.