Showing papers by "Chao Zhang published in 2002"

The Saccharomyces cerevisiae Mob2p–Cbk1p kinase complex promotes polarized growth and acts with the mitotic exit network to facilitate daughter cell–specific localization of Ace2p transcription factor

Abstract: The Saccharomyces cerevisiae mitotic exit network (MEN) is a conserved signaling network that coordinates events associated with the M to G1 transition. We investigated the function of two S. cerevisiae proteins related to the MEN proteins Mob1p and Dbf2p kinase. Previous work indicates that cells lacking the Dbf2p-related protein Cbk1p fail to sustain polarized growth during early bud morphogenesis and mating projection formation (Bidlingmaier, S., E.L. Weiss, C. Seidel, D.G. Drubin, and M. Snyder. 2001. Mol. Cell. Biol. 21:2449-2462). Cbk1p is also required for Ace2p-dependent transcription of genes involved in mother/daughter separation after cytokinesis. Here we show that the Mob1p-related protein Mob2p physically associates with Cbk1p kinase throughout the cell cycle and is required for full Cbk1p kinase activity, which is periodically activated during polarized growth and mitosis. Both Mob2p and Cbk1p localize interdependently to the bud cortex during polarized growth and to the bud neck and daughter cell nucleus during late mitosis. We found that Ace2p is restricted to daughter cell nuclei via a novel mechanism requiring Mob2p, Cbk1p, and a functional nuclear export pathway. Furthermore, nuclear localization of Mob2p and Ace2p does not occur in mob1-77 or cdc14-1 mutants, which are defective in MEN signaling, even when cell cycle arrest is bypassed. Collectively, these data indicate that Mob2p-Cbk1p functions to (a) maintain polarized cell growth, (b) prevent the nuclear export of Ace2p from the daughter cell nucleus after mitotic exit, and (c) coordinate Ace2p-dependent transcription with MEN activation. These findings may implicate related proteins in linking the regulation of cell morphology and cell cycle transitions with cell fate determination and development.

Microwave-assisted ring-opening polymerization of ∈-caprolactone

Abstract: Ring-opening polymerization of ϵ-caprolactone was carried out smoothly and effectively with constant microwave powers of 170, 340, 510, and 680 W, respectively, with a microwave oven at a frequency of 2.45 GHz. The temperature of the polymerization ranged from 80 to 210 °C. Poly(ϵ-caprolactone) (PCL) with a weight-average molar mass (Mw) of 124,000 g/mol and yield of 90% was obtained at 680 W for 30 min using 0.1% (mol/mol) stannous octanoate as a catalyst. When the polymerization was catalyzed by 1% (w/w) zinc powder, the Mw of PCL was 92,300 g/mol after the reaction mixture was irradiated at 680 W for 270 min. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1749–1755, 2002

Synthesis of a Highly Fluorescent β-Diketone−Europium Chelate and Its Utility in Time-Resolved Fluoroimmunoassay of Serum Total Thyroxine

Abstract: A new highly fluorescent beta-diketone-europium chelate was synthesized and employed as a tracer to develop a time-resolved fluoroimmunoassay (TRFIA) for detection of serum total thyroxine (T4). The tetradentate beta-diketone chelator, 1,10-bis(thiophene-2'-yl)-4,4,5,5,6,6,7,7-octafluorodecane-1,3,8,10-tetraone (BTOT), was structurally composed of two units of thenoyltrifluoroacetone (TTA) derivatives but expressed fluorescence that was greatly enhanced, as compared to the original TTA molecules, in the presence of excess amount of Eu3+. The luminescence properties of the europium chelate of BTOT werestudied in aqueous solution. Chlorosulfonylation of BTOT afforded 1, 10-bis(5'-chlorosulfo-thiophene-2'-yl)-4,4,5,5,6,6,7,7-octafluorodecane-1,3,8,10-tetraone (BCTOT), which could be coupled to proteins (i.e., streptavidin or the BSA-T4 conjugate) and used as a tracer for TRFIA. Although the BCTOT-Eu complex could be detected at a very low level (approximately 1.07 x 10(-12) mol/L) in buffered aqueous solution (50 mmoVLTris-HCl; pH, 8.0), the application of the chelate label in direct serum T4 TRFIA experienced a problem of matrix interference, which was probably caused by some unknown chelating components in the samples as a result of the fact that the fluorescence of the BCTOT-Eu chelate was prone to quenching or enhancement by some chelating reagents. To remove this problem, an indirect serum T4 TRFIA was proposed with the use of BCTOT-Eu-labeled streptavidin (SA) as signal generation reagent. The concentrations of T4 in 27 human serums were determined by indirect T4 TRFIA, and the assay results correlated well with those obtained by commercial Coming-CLIA (r = 0.955) and Wallac-DELFIA (r 0.965).

Engineering of a dual-periodic optical superlattice used in a coupled optical parametric interaction

Abstract: Quasi-phase matching facilitates the phase matching of any parametric interaction by setting an appropriately modulated period. We propose a dual-periodic structure that is used in the construction of a frequency-conversion device. For example, we have designed and fabricated such a dual-periodic structure in a LiTaO3 crystal. Using a fundamental source at 1.064 µm, we obtained ultraviolet radiation at 355 nm and green radiation at 532 nm simultaneously by frequency tripling and frequency doubling the fundamental source. Theoretically, this idea can be further extended to the design of a multiperiodic structure for achievement of more quasi-phase-matched processes in a single optical superlattice.

Frequency-dependent electrical transport under intense terahertz radiation

Abstract: By using a formalism based on quantum transport equation, we study the current response of an electron gas strongly coupled to an intense terahertz laser. The effect of laser is treated exactly, which gives rise to the electron-photon sidebands. Our formalism includes up to the second order in electron-impurity scattering and to any order in optical transitions between the sidebands. Resonant scattering can occur when the frequency of the probing field equals a multiple of the terahertz laser frequency. The usual linear response theory is the zero-photon term in our formalism. This result can be applied to study the electrical transport in strongly coupled electron-photon systems. One such system is a two-dimensional semiconductor structure under an intense terahertz radiation.

Design of optical superlattice to realize third-harmonic generation and multi-wavelength laser output and its application in the all-solid state laser

Abstract: The design of a special type of optical superlattice and its application in the all-solid state laser is involved in this invention. Nd ions doped laser crystal in common use can radiate three relatively intense spectral lines when excited: the first wavelength is around 900 nm; the second wavelength is around 1064 nm; the third wavelength is around 1300 nm, whose accurate wavelength are depended on their host crystal (for example, to Nd:YAG, they are 946 nm, 1064 nm and 1319 nm, respectively). On the other hand, for LiNbO3 (LN), LiTaO3 (LT), KTP and other ferroelectric crystals, the positive and negative 180° ferroelectric domains in these crystals can be arranged orderly according to certain sequence via crystal growth, electric field poling, and other state-of-the-art domain reversion technique, forming superlattice that is applicable to quasi-phase-matching (QPM) laser frequency conversion. This invention aims at the design of optical superlattice that can realize third-harmonic generation and coupled parametric process for such three emitting lines of Nd doped crystals and its application in the all-solid state laser. Such a superlattice, which can provide two or more effective reciprocal vectors, can participate in two or more QPM optical parametric processes. Different optical parametric processes in this kind of superlattice can couple each other via cascade effect. Therefore this type of superlattice can be used as an especial frequency-conversion crystal to acquire high-order harmonic generation of laser; in addition, it can realize the simultaneous output of multicolor laser or make the output of laser tunable by quasi-phase-matched frequency down-conversion. For instance, it is applicable to the frequency-conversion devices of all-solid state blue or ultraviolet laser, red-blue or green-ultraviolet dual color laser, and red-green-blue three fundamental colors laser, and can also be used as the source of entangled photon pair in the quantum telecommunication. The scheme can be extended to other active ions (such as Er, Yb, Tm, Sm etc.) doped laser crystal comprised in an all solid-state laser system.

Experimental Characterization of Interlaminar Shear Strengths of Graphite/Epoxy Laminated Composites

Abstract: An investigation is conducted to study the effects of fiber orientations on the interlaminar shear (ILS) strengths of CYTEC® G40-800/5276-1 graphite/epoxy laminated composites The results of this investigation are going to be reported in two separate parts; experimental characterization and stochastic simulation The present paper demonstrates the experimental program and the experimental resultsThe ILS strengths at the θ-interfaces (θ=0, 10, 20, 30, 40, 50, 60, 70, 80 and 90°), around which the two neighboring plies have a fiber orientation difference angle, are experimentally measured using the modified double notch shear specimens with an elaborately designed lay-up Because of the potentially considerable scatter in the matrix-dominated ILS strengths, each data set at a specified interface is obtained through a larger sample with 35 specimens A 3D finite element analysis is also performed to aid in the design of the multi-directional laminated composite specimens, so as to minimize the edge effects

Dynamic screening and collective excitation of an electron gas under intense terahertz radiation

Abstract: By using time-dependent wave functions for electrons under an intense laser, we calculated the charge-density fluctuation of an electronic system under a weak probing potential. The dielectric function of the system as a function of the laser frequency and intensity is derived. The spectrum of the collective excitation is calculated. The spectrum exhibits the contribution of various multiphoton processes.

Analytical Expression for the Fourier Spectrum of a Quasiperiodic Fibonacci Superlattice with k Components (k ≤ 3)

Abstract: The two-component quasiperiodic optical superlattice has been proved useful to some coupled parametric processes such as the direct third-harmonic generation. In this paper a three-component quasiperiodic superlattice has been studied theoretically. Using the projection method, the analytical expression of its Fourier spectrum has been deduced. The results might be conducive to the design of nonlinear optical devices related to the coupled parametric processes, such as the fifth-harmonic generation.

Terahertz-driven nonlinear electrical transport in semiconductor nanostructures

Abstract: In this work, we used the quantum transport equation and density matrix formalism to calculate the frequency dependent electrical current of a two-dimensional electron gas directly driven by an intense terahertz laser. It is found that due to increased electron-photon coupling, the electron-impurity scattering decreases rapidly with the electric field.

Wireless power transmission via ad hoc network

Abstract: Wireless power transmission (WPT) has been proposed for many years and is expected to be one of the most promising power transmission style in the near future, especially in space power supply and emergency power recovery. The long distance WPT often enrolls the relay procedures and forms a power transmission network. In this paper, we talk about the wireless power transmission based on Ad Hoc networks. Meanwhile, the adaptive architecture and flexible deployment of WPT Ad Hoc networks have been given a special further discussion. We also bring along a novel multi-trace power routing concept and analyze the major challenges of WPT Ad Hoc networks.

Thermal and electrical characteristics of a multilayer thermionic device

Abstract: We report our recent experimental and numerical investigation into the thermal and electrical transport in GaAs-AlGaAs semiconductor multilayer structures. Electrical and thermal conduction measurements were performed on multilayer structures to determine the temperature gradient across the sample. AuGe was used for top contact metallisation, and an InGa eutectic for bottom substrate contact. Metallisation contacts were also grown directly onto the substrate in order to compare results with and without the device included. By using a variable load resistor connected in series with the device, we can accurately determine the current-voltage characteristics of the device. Thus the power input can be obtained. The temperature distribution on the top and bottom substrate was measured with micro thermocouples. Since the cooling device is grown on an n-type semiconductor substrate the effects of joule heating in the substrate had to be considered. Treating the substrate as bulk material and calculating joule heating showed that this effect is negligible. Comparing experimental measurements of the device and of the substrate alone support this. The experimental I-V characteristics of the device differ significantly in shape from theoretical I-V characteristics. This may be due to that fact that space-charge effects are not included in the currently accepted model (Richardson's equation). Due to the small size of the devices and therefore very large electric fields, this effect may be important. Work is currently being carried out to modify the model. The devices studied so far have been made from undoped GaAs-AI/sub 0.07/Ga/sub 0.03/As heterostructures. For large cooling power it is a requirement that the conduction band of the layers be close to the Fermi level.