Preparation of TiO2-carbon surface composites with high photoactivity by supercritical pretreatment and sol-gel processing

TiO₂-carbon surface (TCS) composites were prepared by pretreatment of a sealing substrate in supercritical carbon dioxide using paraffin as a plugging agent, and sol-gel processing using tetrabutyl orthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), optical absorption spectroscopy and nitrogen absorption. The photoactivity of TCS was checked by monitoring the decomposition of methylene blue (MB) in aqueous solution under UV irradiation. The results indicated that compared with TC prepared only by the sol-gel method, the small nanosize TiO₂ particles are well dispersed on carbon surface with large amount of micropores and high Eg values, meanwhile TCS have high Ti³⁺ concentration due to supercritical pretreatment providing a amount of carbon on the composite surface with interfacial energy effects, which controls the growth of TiO₂ nanoparticles, baffles the agglomeration of TiO₂ nanoparticles and easily produces Ti³⁺ ions. These are reasons why TCS has a higher efficiency of decomposing MB than TiO₂-carbon (TC) composites and pure TiO₂. Additional, it is also attributed to the fact that TCS produce a high concentration of organic compounds near TiO₂ in comparison with TC and pure TiO₂, because their surface area are greater than that of TC and pure TiO₂.     

Preparation and surface modification of silicon nanowires under normal conditions

Preparation and surface modification of silicon nanowires (SiNWs) grown by the metal catalyzed solution method under normal conditions (room temperature, 1 atm) had been studied in this paper. Firstly, SiNWs using a simple solution method via electroless metal deposition (EMD) of silver under room temperature, standard pressure had been prepared. The influence of the growth parameters such as solution concentration, etching time on the SiNWs formation had been studied. Secondly, the surface modification of SiNWs with platinum and copper had been investigated. The results indicated that the SiNWs modified with Pt and Cu showed different surface morphologies. Pt modification on SiNWs presented in the form of nanoparticles, whereas Cu modification in the form of membrane. Therefore, the Pt modified SiNWs have more vast surface-to-bulk ratio than the unmodified ones, and SiNWs modified with copper nanoparticles will lead to the smaller surface-to-bulk ratio. So the platinum-modified SiNWs have a promising application in sensors’ field.     

Rapid sea-level change in the Late Guadalupian (Permian) on the Tethyan side of South China: litho- and biostratigraphy of the Chaotian section in Sichuan

The Capitanian (Late Guadalupian) Maokou Formation at Chaotian in northern Sichuan, South China, is composed mainly of shallow marine shelf carbonates deposited on the Tethyan side of South China. By detailed field mapping and scientific drilling, we newly found out unique fossil assemblages and a sharp lithologic change in the upper part of the Maokou Formation. The main part of the Maokou Formation (over 130 m thick) is composed of algal packstone with Wordian-Capitanian large-tested fusulines, rugose corals and other sessile benthos, whereas the Uppermost Member (13 m thick) is composed of black limy mudstone/chert with Capitanian offshore biota (ammonoids, radiolarians, and conodonts). The topmost Capitanian conodont zones are missing; however, the Maokou Formation is disconformably overlain by 260+/-4 Ma volcanic ash (Wangpo bed) and the Early Lopingian Wujiaping Formation with plant-bearing coaly mudstone and shallow marine carbonates (packstone). The newly identified facies change indicates that northern Sichuan has experienced rapid sea-level changes in the late Guadalupian, i.e., first a transgression in the mid-Capitanian and then a regression across the Guadalupian-Lopingian boundary. As the end-Guadalupian is characterized by a global regression, such a volatile sea-level fluctuation, in particular the sea-level rise, is unique to the Tethyan side of South China. The newly recognized relatively deep-water late Guadalupian sequence adds new paleo-environmental information and further provides a paleotectonic interpretation of the low-latitude eastern Tethyan margin immediately before the end-Guadalupian mass extinction.     

Computing the Abel map

We present the next step in an ongoing research program to allow for the black-box computation of the so-called finite-genus solutions of integrable differential equations. This next step consists of the black-box computation of the Abel map from a Riemann surface to its Jacobian. Using a plane algebraic curve representation of the Riemann surface, we provide an algorithm for the numerical computation of this Abel map. Since our plane algebraic curves are of arbitrary degree and may have arbitrary singularities, the Abel map of any connected compact Riemann surface may be obtained in this way. This generality is necessary in order for these algorithms to be relevant for the computation of the finite-genus solutions of any integrable equation.     

Polymer adsorption on the surface of highly dispersed silica

Attempts at modification of silica surface with a polymer (natural latex) directly in the course of the precipitation process have been made. The effects of temperature, non-ionic surfactants and silane coupling agent in preparation of poly[cis-isoprene]-coated silica on the precipitation of polymer/silica composites initiated by ammonium salts (NH₄Cl, (NH₄)₂SO₄, NH₄HCO₃), have been studied. The influence of the process parameters on the quality of the silicas obtained and the character of the polymer adsorption on the silica surface has been determined along with the effect of the surface impregnation with natural latex on physicochemical parameters of the silicas (bulk density, capacities to absorb water, dibutyl phthalate and paraffin oil) and their surface structure.     

Measurement of στ product of solid state laser materials by an alternative method: Application to Nd3+ doped YVO4 crystal for 4 F 3/2→4 I 11/2 transition

In this paper an alternative approach for measurement of στ product for ⁴ F _3/2→⁴ I _11/2 transition of Nd³⁺ doped YVO₄ crystal is reported. In this method a microchip laser is formed by keeping a small piece of the sample in plane-plane resonator and a diode laser (808 nm) is used for pumping. The pump power induced thermal lensing effect is used to make the cavity stable. The cavity mode area is estimated by measuring the thermal lens focal length at the threshold and the average pump area is measured by Gaussian fit to the intensity profiles of the pump beam. The value of στ product of Nd:YVO₄ crystal obtained by this method is within 10% of the reported values. The advantage of this method is that it is a simple method for direct measurement of στ product of laser crystals.     

Determination of the Gamow–Teller strength function for the neutron-deficient isotopes In

The Gamow–Teller β decays of the neutron-deficient indium isotopes ^104–107In have been investigated by using total absorption γ-ray spectrometry on mass-separated sources. The experimental Gamow–Teller strength, deduced as a function of the excitation energy in the daughter nuclei ^104–107Cd, is compared to shell-model predictions.     

Macroscopic Determinism in Noninteracting Systems Using Large Deviation Theory

We consider a general system of n noninteracting identical particles which evolve under a given dynamical law and whose initial microstates are a priori independent. The time evolution of the n-particle average of a bounded function on the particle microstates is then examined in the large-n limit. Using the theory of large deviations, we show that if the initial macroscopic average is constrained to be near a given value, y, then the macroscopic average at time t converges in probability as n to a value _t(y) given explicitly in terms of a canonical expectation. Some general features of the graph of _t(y) versus t are examined, particularly in regard to continuity, symmetry, and convergence.     

饱和吸附H原子的Si（100）表面的光学二次谐波研究

测量了Ｓｉ（１００）（２×１）－Ｈ表面和Ｓｉ（１００）（３×１）－Ｈ表面的反射二次谐波强度随温度的变化关系，并与清洁的Ｓｉ（１００）（２×１）表面进行了比较。Ｓｉ（１００）（２×１）表面和Ｓｉ（１００）（３×１）－Ｈ表面的二次谐波强度随温度的上升而单调地减小，Ｓｉ（１００）（２×１）－Ｈ表面二次谐波强度随温度的变化不是单调的，约在４７０Ｋ时信号最大。可以根据二次谐波信号的强度及其随温度的变化关系来确定样品温度和表面结构。     

Observations on the role of MgCl2 in the Weissler reaction

Aqueous solutions of Nal containing CCl₄ and MgCl₂ at various concentrations were irradiated under air with 1 MHz ultrasound and the yield of I₃⁻ was determined. The yield was not affected by MgCl₂ at concentrations up to 0.1 M. This contrasts with the finding of Lepoint and co-workers, who reported a sharp minimum in the yield at a MgCl₂ concentration of 2.5 × 10⁻³M, the yield decreased to 60% at 1 M MgCl₂, the reason being the lower solubility of CCl₄ at high MgCl₂ concentrations. In the absence of CCl₄, another dependence on the MgCl₂ concentration was observed: the yield was not affected up to 1 M, and at higher MgCl₂ concentrations the yield rapidly decreased owing to the increased viscosity of the solution. On the basis of these observations, there is no strong reason to postulate an electrical mechanism for the initiation of chemical reactions in the cavitation bubbles.