剩余格与FI代数的可嵌入性

给出剩余格可嵌入于全序剩余格的乘积的充要条件。还给出定义在格上的FI代数可嵌入于全序FI代数的乘积的充要条件。     

Ionic conductivity of epitactic MBE-grown BaF2 films

We studied parallel conductivities of pure BaF₂ films with thicknesses ranging from 35 to 300 nm, epitaxially grown on Al₂O₃(0 1 2) substrates by molecular beam epitaxy technique. The overall conductivities of the films are found to increase with decreasing thickness. The detailed investigation of the overall conductance as a function of the thickness permits the deconvolution of bulk and boundary effects, the latter being attributed to distinct space charge effects in the interface between BaF₂ film and Al₂O₃ substrate. The (extrinsic) Debye length (λ) is estimated to be about 8 nm at T=593 K, which corresponds to an impurity content of 10¹⁸/cm³ (singly ionized dopant assumed). This is consistent with the fact that we observed a constant boundary contribution for all investigated films (film thickness >4λ). It is also consistent with the Debye length observed in a previous report on CaF₂/BaF₂ heterolayers fabricated by the same technique, in which the low temperature enhancement was also attributed to space charges in BaF₂ [Nature 408 (2000) 946]. Only at low temperatures (below 370 °C), the conductance seems to be influenced by strain effect.     

Roughness reduction in submicron waveguides by low-molecular weight development

Roughness reduction of a submicron waveguide profile in chemically amplified negative resist is here performed by proper selection of an alkali-based developer, taking into account that its smaller molecules lead to smoother resist surface by altering the developing mechanism of aggregate extraction performed with standard quaternary ammonium hydroxide. Roughness is then analyzed by means of classical Atomic Force Microscope inspection; furthermore, a non-invasive line edge roughness analysis approach based on top-down scanning electron microscope acquisition gives comparable results, in terms of standard deviation and molecular aggregate periodicity.     

Making equation of state models predictive: Part 2: An improved PCP-SAFT equation of state

We use the PCP-SAFT equation of state, which is of the Van der Waals type and has a sound physical basis, to predict mixture properties, such as vapor–liquid and liquid–liquid equilibria, as well as excess enthalpies. We use molecular properties, such as dipole moment, quadrupole moment, polarizability and dispersion interaction coefficients, that have been determined quantum mechanically in Part I of this publication and adjust the remaining three pure compound parameters to pure compound data. We finally present a new combination rule for the dispersion energy parameter ? that is based on the quantum mechanically determined data. The predictions based on quantum mechanically determined pure compound properties along with the new combination rule show an improved performance compared to the original PCP-SAFT combination rule.     

Surface reconstructions of InGaAs alloys

The surface reconstructions of In_xGa_1−xAs alloys grown by molecular beam epitaxy on the (0 0 1) surfaces of GaAs and InAs have been studied by reflection high-energy electron diffraction and scanning tunnelling microscopy. A surface phase diagram is presented for the nominally strain-free alloy as a function of substrate temperature and alloy composition, and structural models for the commonly observed 3× reconstructions are discussed. Two new, electronically stable structural models are described that account for the transition of the In_xGa_1−xAs surface alloy from a c(4 × 4) to an asymmetric 3× reconstruction and that are fully consistent with all current experimental evidence.     

A one-pot synthesis of 1,2,4,5-tetraarylimidazoles using molecular iodine as an efficient catalyst

Molecular iodine is a cheap, nontoxic catalyst, which acts as an efficient catalyst for the synthesis of 1,2,4,5-tetraarylimidazoles using benzoin, an aromatic aldehyde and an amine in the presence of ammonium acetate. The advantage of this method is the direct use of benzoin, which is transformed into benzil in situ and condenses further to generate the imidazole in a one-pot sequence.     

Ab initio modelling of crosslinking in polymers. A case of chains with furan rings

A quantum chemical model (Abinitio HF-MO and DFT-B3LYP) of polyfurfuryl alcohol crosslinking is shown. Two pathways were considered: (a) a Diels–Alder (D–A) reaction between a dihydrofuran moiety and a furan ring; (b) the addition reaction of electrophilic specimens on conjugated double bonds. The ability for the formation of D–A adducts (dienes and dienophiles) was investigated by the frontier molecular orbital (FMO) theory. Energy gaps between the FMO's of diene and dienophile structures suggest that the occurrence of the D–A reaction is possible. The results suggest that the carbons of the exo double bonds attached to dihydrofuran rings are the sites most likely to be attacked by electrophilic species, while the C₃ and C₄ atoms display the opposite tendency due to their low HOMO electron densities. Results of a thermochemical approach to these reactions at the MP2 level was in agreement with reactivity modelled by MO predictions.     

Epitaxy: the motion picture

The engineering of many modern electronic devices demands control over a crystal down to the thickness of a single layer of atoms—and future demands will be even more challenging. Such control is achieved by the method of crystal growth known as epitaxy, and that makes this method the subject of intense study. More than that, recent advances are revolutionizing our knowledge of how surfaces grow. In fact, growing surfaces show a beautifully rich variety of phenomena, many of which are only now beginning to be uncovered. In the past few years many surface imaging techniques have been used to give us a close look at how crystals grow—while they are growing. The purpose of this article will be to illustrate some of the ways real surfaces grow and change as revealed by some of the latest in situ microscopic imaging technologies.

It is often said that crystal growth is more of an art than a science. Here we will show that it is emphatically both.     

Structural transition of the human lymphocyte plasma membrane: an ESR approach

Summary The electron spin resonance spectroscopy and the spin label technique have been used to study the thermotropic structural transition of the plasma membrane ofin toto human peripheral blood lymphocytes in the temperature range (25÷41)°C. A discontinuity in the plot probe order parametervs. temperature, at a temperature of about 31°C, is observed. This discontinuity is upward shifted to a temperature of 35°C in the presence of staphylococcal enterotoxinB and is no longer observed when using isolated plasma membrane. These results are interpreted as being due to a change in the structural properties of the lipid phase of plasma membrane during the activation of the lymphocyte cells.     

Towards a fully optimised organic LED device: Analysis of surface synthesis using coupling reactions by ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and polarisation-modulation reflection-absorption infrared spectroscopy (PM-RAIRS) have been used to monitor the surface synthesis of self-assembled aromatic π-conjugated molecular wires on gold substrates as a step towards a novel structure for organic electroluminescent devices (OLEDs). The wires have been synthesised using a series of Schiff's base coupling reactions in solution on a self-assembled monolayer of an aromatic thiolate anchor. ToF-SIMS and PM-RAIRS measurements have demonstrated that: (i) the anchor molecules self-assemble at the gold surface, (ii) the anchor molecules selectively react through imino coupling reactions with additional wire units with high efficiency and (iii) the wire-like structure is predominantly orientated normal to the surface.