Synthesis and characterization of a novel nano-scale magnetic solid base catalyst involving a layered double hydroxide supported on a ferrite core

A nano-scale magnetic solid base catalyst MgAl-OH-LDH/MgFe₂O₄ (where LDH denotes layered double hydroxide) composed of MgAl-OH-LDH Brønsted base catalytic layers coated on MgFe₂O₄ spinel cores has been prepared. A magnetic precursor MgAl-CO₃-LDH/MgFe₂O₄ was prepared by a method involving separate nucleation and aging steps, and subsequently calcined to give a mixed metal oxide composite MgAl(O)/MgFe₂O₄ which was rehydrated to give MgAl-OH-LDH/MgFe₂O₄. The structure and magnetic properties of the nano-scale magnetic solid base MgAl-OH-LDH/MgFe₂O₄, together with those of the magnetic precursor MgAl-CO₃-LDH/MgFe₂O₄ and MgFe₂O₄ were characterized by XRD, XPS, low temperature N₂ adsorption and vibrating sample magnetometry (VSM). The MgAl-OH-LDH/MgFe₂O₄ composite possesses a mesoporous structure with pore size ranging from 2 to 20 nm with particle size mainly in the range 35-130 nm. The catalytic properties of MgAl-OH-LDH/MgFe₂O₄ were evaluated using the self-condensation of acetone at 273 K as a probe reaction. The results showed that the conversion of acetone to diacetone alcohol reached the thermodynamic equilibrium value of 23% at 273 K. The catalyst was easily recovered through application of an external magnetic field, and when the reclaimed catalyst was used in a second run for the same reaction, the reactivity remained unchanged.     

The spectrum of cyclic BSA(ν, 3, λ; α) with α = 2, 3

Balanced sampling plans excluding contiguous units (or BSEC) were first introduced by Hedayat, Rao, and Stufken in 1988. In this paper, we generalize the concept of a cyclic BSEC to a cyclic balanced sampling plan to avoid the selection of adjacent units (or CBSA for short) and use Langford and extended Langford sequences to construct a cyclic BSA(ν, 3, λ; α) with α = 2, 3. We finally establish the necessary and sufficient conditions for the existence of a cyclic BSA(ν, 3, λ; α) where α = 2, 3. © 2005 Wiley Periodicals, Inc. J Combin Designs.     

Synthesis of MgAl2O4 Spinel Nanometer Powder via Biology Polysaccharide Assisted Sol-Gel Process

A novel and cost-effective sol-gel process for preparation of MgAl₂O₄ spinel nanometer powders has been developed in this study. A solution of magnesium and aluminum nitrates in stoichiometric proportion was successfully embraced in the biology polysaccharide gel network, formed by the synergistic interaction between xanthan gum (XG) and locust bean gum (LBG) utilizing their broad-spectrum stability of salt tolerance and character of transformation from sol to gel on the condition of proper temperature and relative proportion of polymeric components. Dry gel could be obtained by vacuum dehydration of aqueous gel at low temperatures. Monolithic MgAl₂O₄ spinel nanometer powders were produced by calcining the dry gel above 800°C, with average crystallite size of 20 nanometers.     

CO（ a）+ NO（X）传能体系中的新传能通道

在相对碰撞平动能为 0 .0 5eV的分子束实验条件下 ,研究了亚稳态CO(a) +NO(X)的E E传能通道 .通过测量和分析交碰区的传能发射光谱 ,在 780和 860nm处观测到了NO(b -a)跃迁Ogawa带的△v =+ 4和△v =+ 3序的发射光谱 .从而首次在实验上直接证实了传能过程中第四通道的存在 (CO (a) +NO(X)→CO (X) +NO(b) ) .这一通道的发现解释了前人测量到的在CO(a)与NO(X)碰撞传能过程中CO(a)的猝灭速率远大于NO(A ,B)生成速率的实验结果 ,并进一步证实了这一“经典”E E传能体系为电子交换机理的传能观点     

Stationary Distributions of GI/M/c Queue with PH Type Vacations

We study a GI/M/c type queueing system with vacations in which all servers take vacations together when the system becomes empty. These servers keep taking synchronous vacations until they find waiting customers in the system at a vacation completion instant.The vacation time is a phase-type (PH) distributed random variable. Using embedded Markov chain modeling and the matrix geometric solution methods, we obtain explicit expressions for the stationary probability distributions of the queue length at arrivals and the waiting time. To compare the vacation model with the classical GI/M/c queue without vacations, we prove conditional stochastic decomposition properties for the queue length and the waiting time when all servers are busy. Our model is a generalization of several previous studies.     

Operating Parameters Optimization of Buffer Gas in Optically Pumped Submillimeter Wave Laser

Based on the basic theory of molecular vibration relaxation and semi-classical density matrix theory, operating parameters optimization of buffer gas in the process of miniature pulsed optically pumped submillimeter wave laser was systemically studied and the theoretical calculated result was tested by experiments. The result would do favor to develop and study high-power and wide-range tunable miniature and high-efficient pulsed optically pumped submillimeter wave laser and also had some instruction to its application.     

Synthesis of side‐chain liquid‐crystalline homopolymers and triblock copolymers with p‐methoxyazobenzene moieties and poly(ethylene glycol) as coil segments by atom transfer radical polymerization and their thermotropic phase behavior

A series of side‐chain liquid‐crystalline (LC) homopolymers of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with different degrees of polymerization were synthesized by atom transfer radical polymerization (ATRP), which were prepared with a wide range of number‐average molecular weights from 5.1 × 10³ to 20.6 × 10³ with narrow polydispersities of around 1.17. Thermal investigation showed that the homopolymers exhibit two mesophases, a smectic phase, and a nematic phase, and the phase‐transition temperatures of the homopolymers increase clearly with increasing molecular weights. A series of novel LC coil triblock copolymers with narrow polydispersities was synthesized by ATRP, and their thermotropic phase behavior was investigated with differential scanning calorimetry and polarized optical microscopy. The LC coil triblocks were designed to have an LC conformation of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with a wide range of molecular weights from 3.5 × 10³ to 1.7 × 10⁴ and the coil conformation of poly(ethylene glycol) (PEG) (number‐average molecular weight: 6000 or 12,000) segment. Their characterization was investigated with ¹H NMR, Fourier transform infrared spectra, and gel permeation chromatography. Triblock copolymers exhibited a crystalline phase, a smectic phase, and a nematic phase. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased, and the crystallization of PEG depressed with increasing molecular weight of the LC block. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2854–2864, 2003     

Tunneling injection quantum-dot lasers with polarization-dependent photon-mediated carrier redistribution and gain narrowing

A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation.     

The Characteristic of Threading Dislocation in Different Structures GaN Films Grown by MOCVD

Three mechanisms to reduce threading dislocations(TDs) in GaN films as the epitaxial films grow thicker are suggested by SEM and TEM     

Analysis of a Duopoly Supply Chain and its Application in Electricity Spot Markets

This paper studies a supply chain consisting of two suppliers and one retailer in a spot market, where the retailer uses the newsvendor solution as its purchase policy, and suppliers compete for the retailer’s purchase. Since each supplier’s bidding strategy affects the other’s profit, a game theory approach is used to identify optimal bidding strategies. We prove the existence and uniqueness of a Nash solution. It is also shown that the competition between the supplier leads to a lower market clearing price, and as a result, the retailer benefits from it. Finally, we demonstrate the applicability of the obtained results by deriving optimal bidding strategies for power generator plants in the deregulated California energy market. Supported in part by RGC (Hong Kong) Competitive Earmarked Research Grants (CUHK4167/04E and CUHK4239/03E), a Distinguished Young Investigator Grant from the National Natural Sciences Foundation of China, and a grant from Hundred Talents Program of the Chinese Academy of Sciences.