Optimal consumption of the finite time horizon Ramsey problem

AbstractIn this paper, we study the stochastic Ramsey problem related to an economic growth model with the CES production function in a finite time horizon. By changing variables, the Hamilton–Jacobi–Bellman equation associated with this optimization problem is transformed. By the viscosity solution technique, we show the existence of a classical solution of the transformed Hamilton–Jacobi–Bellman equation, and then give an optimal consumption policy of the original problem

Quantitative and cell type-specific transcriptional regulation of A-type cyclin-dependent kinase in Arabidopsis thaliana

AbstractA-type cyclin-dependent kinase (CDKA) is an ortholog of yeast Cdc2/Cdc28p, and is assumed to have an essential function in plant growth and organogenesis. Previous studies revealed that its kinase activity is controlled by post-translational modifications, such as binding to cyclins and phosphorylations, but its transcriptional regulation is poorly understood. Here, we generated a promoter dissection series of Arabidopsis (Arabidopsis thaliana) CDKA;1, and used β-glucuronidase (GUS) gene-fused reporter constructs for expression analyses in planta. The results revealed two types of transcriptional control in shoots: general quantitative regulation and cell type-specific regulation. We identified a promoter region that promotes CDKA;1 expression in the leaf epidermis, but not in the L1 layer of the shoot apical meristem. This region also directed abaxial side-biased expression, which may be linked to the adaxial/abaxial side specification. Another reporter construct showed that CDKA;1 expression in the inner layers of leaves is controlled by a distinct regulatory region in the promoter. These results suggest that the transcriptional regulation of CDKA;1 may play a key role in proper development of leaves by coordinating cell division and differentiation of different cell types

Purely excitonic lasing in ZnO microcrystals: Temperature-induced transition between exciton-exciton and exciton-electron scattering

Since the seminal observation of room-temperature laser emission from ZnO thin films and nanowires, numerous attempts have been carried out for detailed understanding of the lasing mechanism in ZnO. In spite of the extensive efforts performed over the last decades, the origin of optical gain at room temperature is still a matter of considerable discussion. In this work, we show that a ZnO film consisting of well-packed micrometer-sized ZnO crystals exhibits purely excitonic lasing at room temperature without showing any symptoms of electron-hole plasma emission, even under optical excitation more than 25 times above the excitonic lasing threshold. The lasing mechanism is shifted from the exciton-exciton scattering to the exciton-electron scattering with increasing temperature from 3 to 150 K. The exciton-electron scattering process continues to exist with further increasing temperature from 150 to 300 K. Thus, we present distinct experimental evidence that the room-temperature excitonic lasing is achieved not by exciton-exciton scattering, as has been generally believed, but by exciton-electron scattering. We also argue that the long carrier diffusion length and the low optical loss nature of the micrometer-sized ZnO crystals, as compared to those of ZnO nanostructures, plays a key role in showing room-temperature excitonic lasing