The structure of montmorillonite intercalated with [Al13O4(OH)24+x(H2O)12−x](7−x)+ cations ( for short), where x = 0, 2 and 4, has been studied using the Cerius2 modeling environment. The Crystal Packer module used in the present study takes into account only the nonbonded interactions between the silicate layer and the Keggin cations. Minimization of the total sublimation energy led to the following conclusions: the structure of the interlayer (that is, the orientation of Keggin cations and the basal spacing) depends on the charge of cations (that is, on the degree of hydrolysis, x). The values of basal spacings in the range 19.38–20.27 Å have been obtained, depending on the charge and arrangement of cations in the interlayer. The dominating contribution to the total sublimation energy comes from the electrostatic interactions. Translations of cations along the 2:1 layers give only small fluctuations of the total sublimation energy and basal spacings. No preference for the position of cations in the interlayer of montmorillonite was found during translation along the 2:1 layers. This result confirmed the inhomogeneous distribution of cations in the interlayer and turbostratic stacking of layers.

The Crystal Packer module in the Cerius2 modeling environment has been used to study the structure of montmorillonite intercalated with Al(OH)3-fragment (gibbsite-like) polymers. Basal spacings in gibbsite-like polymers arranged in 2 layers in the interlayer of montmorillonite varied in the range 19.54–20.13 Å, depending on the type and arrangement of Al(OH)3 fragments. The inhomogeneous distribution of intercalating species in the interlayer and, consequently, the turbostratic stacking of layers has been found for gibbsite-like polymers as well as in the case of Keggin cations (Čapková et al. 1998). The dominating contribution to the total sublimation energy comes from electrostatic interactions for both intercalating species, gibbsite-like polymers and Keggin cations.

Molecular simulations using the Cerius2 modelling environment have been used to investigate the structure of montmorillonite (MMT) intercalated with Zn cations. Basal spacing and bonding of Zn2+ cations in the interlayer have been investigated with regard to their dependence on the water content. In the first part of the work, Zn cations in the interlayer are coordined by six water molecules and the energy of the system is discussed. The energy discussion is focused on the influence of the different starting orientations of the Zn octahedron, and different positions of Mg atoms in the octahedral sheet. An energy scan at fixed d-spacing was carried out. Later the hydration simulation giving the hydration curve (i.e. the dependence of d-spacing on the number of water molecules in the interlayer) was also carried out. Two different hydration states were found — for certain humidity ranges there is almost constant d-spacing and between these intervals there is a sharp edge. Finally the structure of totally dehydrated Zn-MMT was simulated.

This article examines the large interstate variation in levels of unconventional gas development in the U.S. states. The following hypotheses are advanced to predict whether a state will be predisposed toward development: (H1) the availability of unconventional gas reserves; (H2) the availability of infrastructure to support development; (H3) a recent history of conventional oil and gas development; (H4) Republican party control of the Governor's office and state legislature; (H5) relatively low sensitivity to environmental issues; (H6) regulatory systems that treat UGD as a variant of conventional gas development; (H7) a pressing need for economic benefits as indicated by state and local measures of household income, unemployment and poverty; (H8) and public opinion supportive of development. To various degrees, each of the hypotheses is supported but important exceptions and surprises are uncovered in the qualitative and semi-quantitative analyses. Future research should continue the effort to explain the variation of development by expanding the geographical scope of inquiry and enlarging the sample of jurisdictions.

In the framework of the study of the relationship between crystal packing of solid dyes and their visible reflectance spectra, the crystal structure of 3-methoxy-7H-benz[de]anthracen-7-one (Disperse Yellow 13, C18H12O2) has been determined using a combined set of Bragg–Brentano diffractometer and Guinier–Johannson photographic data with the grid search procedure. Parameters of the orthorhombic cell (P212121, No.19, Z=4) at 295 K are a=15.265(9) Å, b=20.524(9) Å, c=3.990(2) Å. Rietveld refinement gave Rp=0.085, Rb=0.135. The molecules form stacks along [001] with an interplanar spacing of 3.46 Å.

The powder diffraction data for 1-aminoanthraquinone at 295 K (P1¯, No. 2, Z=1) are given. The cell parameters found are a=8.205(1), b=8.396(1), c=3.7882(3) Å, α=93.46(1), β=92.57(1), γ=105.13(1)°. The crystal packing model is proposed giving Rb=0.095. The disordered molecule of 1-aminoanthraquinone occupies a special position on the inversion center.

The crystal structure of 1-amino-4-methoxycarbonyl-3-methyl-8-oxopyrazolo[1,5-a]pyrimidine monohydrate, C9H10N4O3·H2O, from the family of pyrazolo[1,5-a]pyrimidines which demonstrate an activity against the influenzavirus A and coxsackievirus B3, has been determined from laboratory (Guinier-Johannson photograph) powder diffraction data using a grid search procedure. Parameters of the monoclinic cell (P21/a, No. 14, Z=4) at 295 K are a=11.599(7) Å, b=11.550(7) Å, c=8.575(5) Å, β=110.76(4)°. Rietveld refinement (full-pattern-decomposition) gave χ2=4.8(4.5), Rp=0.048(0.043), Rwp=0.065(0.062). The observed microstrain-induced anisotropy of diffraction line broadening was approximated by a quartic form in h,k,l. The obtained results allowed to distinguish between several isomers which were indistinguishable by others methods.

Powder diffraction data for 2-aminophenalenone at 295 K (P21/n, Z=4) are given, strong lines: 7.54/X, 7.26/9, 3.34/3. The cell parameters found are a=3.7213(3), b=16.550(2), c=15.095(2) Å, β=92.61(2)°. The crystal structure was determined using powder data and refined giving Rb=0.089. Disordered molecules form stacks along [100] with interplanar spacing of 3.48 Å.

This paper reports on first results obtained on GaN epitaxial layer grown on a single wafer with a lateral variation in defect density. The chemically homogeneous GaN epitaxial layer was deposited by metalorganic chemical vapour deposition onto a specially prepared buffer layer. A chemical gradient in the nitrogen contents of the precursor flux was induced during the growth of the GaN buffer layer. This condition leads a corresponding gradient of the dislocation density within the epilayer. The electrical and optical properties of the GaN epilayer have been analysed by means of electron beam induced current, photoluminescence and photocurrent techniques. All our measurements reveal lateral gradients in the epilayer properties as concern (i) the density of recombining centres in the GaN film and (ii) their recombination activity, both radiative and nonradiative. This paper shows that a proper combination of beam based techniques can contribute to the detailed analysis of the well know yellow luminescence band which in the GaN epilayer here investigated consist of four well distinct peaks.

Background and objective Efficacy and side–effects of piritramide (pirinitramide) and morphine, given intravenously for postoperative analgesia after hysterectomy, were compared in a randomized controlled double-blind trial in 92 ASA class I–III patients.

Methods Administration was investigator–controlled during the first 90 min and subsequently via a patientcontrolled device. Visual analogue scales for pain intensity and verbal rating scales for side-effects were taken repeatedly.

Results Median visual analogue scores for pain intensity on a 100-mm scale 4, 8 and 24 h after surgery were 10, 8.5 and 5mm in the piritramide group and 18, 10 and 8.5mm in the morphine group. These differences are neither statistically nor clinically significant. Median values for nausea on a verbal rating scale from 0 to 3 were zero for both groups at all times with similar ranges. There was no difference in number of episodes of vomiting and retching and usage of antiemetics. The mean amount of piritramide used for initial titration was 15.2 mg; the respective amount of morphine was 15.4 mg.

Conclusions In this setting the two agents are equally effective and show a similar profile of sideeffects.

The effects of substrate cleaning, nitridation time, and substrate temperature in the range 800–1000 °C on the microstructure of AlN/Si(111) films grown by simultaneous plasma-assisted molecular beam epitaxy have been investigated. It has been demonstrated, using a combination of conventional and high-resolution transmission electron microscopy, that the interface structure, the film defect structure, and the film surface roughness are strongly related. The formation of single crystal 2H–AlN films with atomically flat surfaces occurs at 800 °C for conditions of 2.5 nm/min growth rate on very pure, atomically flat Si substrates.

Poly(p-phenylene vinylene)s (PPVs) are very promising materials for optoelectronic applications, especially for displays based on polymer light emitting diodes (PLEDs). We report here our findings concerning defect structures in this materials and the influence of the discovered irregularities on an important property of the materials, i.e. the operational life in a PLED. Recent improvements, which were deviated from this findings are presented: optimized PPVs with a lower amount of defects result in a strong increase of operational lifetime.

Poly(ρ-phenylene vinylene)s (PPVs) are very promising materials for optoelectronic applications, especially for displays based on polymer light emitting diodes (PLEDs). We report here our findings concerning defect structures in this materials and the influence of the discovered irregularities on an important property of the materials, i.e. the operational life in a PLED. Recent improvements, which were deviated from this findings are presented: optimized PPVs with a lower amount of defects result in a strong increase of operational lifetime.

Epitaxial wurtzite aluminum nitride (AIN) films have been grown on (111) oriented silicon substrates by plasma-assisted solid source molecular beam epitaxy (MBE). The growth has been performed in the two-dimensional (2D) growth mode. Occuring surface reconstructions have been monitored by reflection of high-energy electron diffraction (RHEED). The films have been characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). 2D grown films exhibit atomically smooth surfaces, are singlecrystalline and void of oriented domains. High-resolution (HR) TEM micrographs of the heterointerface show the presence of an interfacial atomic arrangement where (5:4) unit cells coincide along the AIN[2110]/Si[110] direction.

Surface acoustic wave (SAW) properties of MBE-grown AIN(0001)/Si(ll1) have been studied for the first time. The AIN film exhibits very good piezoelectricity. The SAW time response indicates low scattering of the waves during their propagation. An electromechanical coupling coefficient (EMC) of 0.07% has been measured for the present interdigital transducer (IDT) geometry.

The effects of long-term carbon dioxide enrichment on competition for nutrients and light in a ryegrass/clover association were determined for simulated swards of perennial ryegrass (Lolium perenne L. cv. Parcour) and white clover (Trifolium repens L. cv. Karina), which were grown as monocultures and in three mixtures (25/75, 50/50, 75/25), according to the replacement design, at two levels of nitrogen (N) supply (no additional N and 200 kg N ha−1) and at season-long ambient (380 ppm) and elevated (670 ppm) CO2 concentrations, in open-top chambers. Stands were cut four times, at about monthly intervals, to a height of 5 cm. Plant material was separated into different species, fresh and dry weights were determined and the content of macroelements (N, P, K, S, Mg) in both species was measured. In addition, plant height of both species at harvest dates and during several regrowth periods was monitored.

Results indicate that both species made demand on different resources and profited from growth in a mixed sward. CO2-related yield increase amounted to 16–42% for white clover whereas the effect of high CO2 on ryegrass yield ranged between −33% and +9% depending on N supply, mixture and year. As a result the contribution of white clover to total yield in mixed swards was significantly enhanced by CO2 enrichment at many harvests in both N supply treatments. Without additional N supply, shoot competition for light was intensified by CO2 enrichment to the disadvantage of ryegrass, since clover petioles grew longer and ryegrass was shorter at elevated CO2. With N fertilization, no marked effect of CO2 enrichment on interspecific competition could be observed. Since clover and total yield were increased by CO2 enrichment, nutrient requirements were also increased and potassium deficiency and increased intraspecific competition of clover for K was observed in the mixtures under elevated CO2 which had the highest nutrient withdrawal. Although white clover profited much more from CO2 enrichment in both N fertilization treatments, the suppression of ryegrass in mixed swards could only be observed under low N conditions.

Generally, the effect of N fertilization on competitive interference between both species was much greater than the effect of CO2 enrichment and it is suggested that the effect of elevated CO2 on the balance of species and the outcome of competition in a grass/clover sward is mainly dependent on the N status.