经济增长模型中的内生劳动力迁移与经济波动

建立了两部门经济增长模型，说明工资差异导致的劳动力部门间的迁移过程．通过引入迁移函数，得到一个三维的离散动力系统．证明模型存在惟一的非零平衡点，经济增长方式由非零平衡点的性态确定．在CobbDouglas生产函数下，通过数值计算表明，当劳动力迁移的反应系数增大时，系统的平衡点由稳定的平衡点转变为不稳定的平衡点，系统出现分歧，模型所描述的经济由平稳的增长转变为波动增长，最终经济体系出现崩溃．     

Why concave rather than convex inflaton potential?

The Planck data on cosmic microwave background indicates that the Starobinsky-type model with concave inflation potential is favored over the convex-type chaotic inflation. Is there any reason for that? Here we argue that if our universe began with a Euclidean wormhole, then the Starobinsky-type inflation is probabilistically favored. It is known that for a more generic choice of parameters than that originally assumed by Hartle and Hawking, the Hartle–Hawking wave function is dominated by Euclidean wormholes, which can be interpreted as the creation of two classical universes from nothing. We show that only one end of the wormhole can be classicalized for a convex potential, while both ends can be classicalized for a concave potential. The latter is therefore more probable.     

关于扇和完全等二部图联图的边染色

得到了扇和完全等二部图联图的边色数.     

A dynamic gait stabilization algorithm for quadrupedal locomotion through contact time modulation

In this paper, we propose a stabilization method for dynamic gaits of quadrupedal walking robots covering a wide range of speeds and various types of gait. Our stabilization method is based on adjusting the contact time between the four legs and ground. By modulating the contact time, the impact applied to the body can be controlled and stabilized. The stability provided by the proposed algorithm was proved in the sense of Lyapunov. The proposed algorithm also demonstrated robust performance under large external disturbances, and the performance was compared with other algorithms through simulations. Simulation results of bounding gaits under different ground conditions were compared, and the various types of stable gait implemented by the proposed algorithm are also presented.

     

Efficient RFID authentication protocols based on pseudorandom sequence generators

In this paper, we introduce a new class of PRSGs, called partitioned pseudorandom sequence generators(PPRSGs), and propose an RFID authentication protocol using a PPRSG, called S-protocol. Since most existing stream ciphers can be regarded as secure PPRSGs, and stream ciphers outperform other types of symmetric key primitives such as block ciphers and hash functions in terms of power, performance and gate size, S-protocol is expected to be suitable for use in highly constrained environments such as RFID systems. We present a formal proof that guarantees resistance of S-protocol to desynchronization and tag-impersonation attacks. Specifically, we reduce the availability of S-protocol to pseudorandomness of the underlying PPRSG, and the security of the protocol to the availability. Finally, we give a modification of S-protocol, called S*-protocol, that provides mutual authentication of tag and reader.      

Metal-insulator transition in Au atomic chains on Si with two proximal bands

One-dimensional atomic chains on Au/Si(557) feature two proximal 1D bands near the Fermi level, which were controversially attributed as a spinon-holon pair of a Luttinger liquid. Angle-resolved photoemission shows that only one band is metallic with the neighboring one gapped at room temperature. Furthermore, even the metallic branch is found to undergo a metal-insulator transition upon cooling, which follows a mean-field-type behavior. Scanning tunneling microscopy observes two apparently unequivocal chains on the surface, one of which exhibits periodicity doubling accompanying the metal-insulator transition. The surface 1D structure is thus concluded to be insulating at low temperature with a Peierls-type instability.     

Liquid chromatographic assay of carbovir, a carbocyclic nucleoside active against human immunodeficiency virus

Carbovir is a novel carbocyclic guanosine derivative that has potent in vitro activity against human immunodeficiency virus, the causative agent of acquired immunodeficiency syndrome (AIDS). Two methods of sample preparation were developed for the analysis of carbovir in rat blood. Solid-phase extraction on C18 extraction columns proved to be the most effective. Whole rat blood (200 microliters) was diluted with 0.8 ml of distilled water containing the internal standard. After two freeze-thaw cycles to lyse the red blood cells and subsequent centrifugation at 13,000 g, the supernatant was loaded on the C18 extraction columns. Carbovir and the internal standard were eluted with methanol-water (60:40). The extract was evaporated and reconstituted in mobile phase and the samples were injected onto a high-capacity reversed-phase column. The compounds were detected at 252 nm. Other nucleosides that could be used in the treatment of AIDS such as zidovudine and acyclovir did not interfere. Standard curves were linear over the concentration range 0.156-28.0 micrograms/ml (r2 greater than 0.99). The within-day coefficient of variation was less than 7.6% at all concentrations (n = 4). The between-day coefficient of variation ranged from 16.7 to 2.0% (n = 14). The limit of sensitivity was 0.05 micrograms/ml with a 200-microliters blood sample and the average extraction recovery was 74%. Carbovir was stable in rat blood for at least 4 h at 37 degrees C. The assay was used to determine the blood levels of carbovir in a rat after a 20 mg/kg intravenous dose.     

Au(I)-catalyzed tandem [3,3]-sigmatropic rearrangement-cycloisomerization cascade as a route to spirocyclic furans

Gold-catalyzed reaction of 1-(3-hydroxypropynyl)cycloalkanol derivatives was studied. The reaction profile was highly dependent on the ring size, migrating group, as well as reaction conditions. An efficient route to spirocyclic furans via tandem [3,3]-sigmatropic rearrangement-cycloisomerization is reported.