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We have observed ultrasmall unilamellar vesicles, with diameters of less than 20 nm, in mixtures of the tricyclic antidepressant drug amitriptyline hydrochloride (AMT) and the unsaturated zwitterionic phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) in physiological saline solution. The size and shape of spontaneously formed self-assembled aggregates have been characterized using complementary techniques, i.e., small-angle neutron and X-ray scattering (SANS and SAXS) and cryo-transmission electron microscopy (cryo-TEM). We observe rodlike mixed micelles in more concentrated samples that grow considerably in length upon dilution, and a transition from micelles to vesicles is observed as the concentration approaches the critical micelle concentration of AMT. Unlike the micelles, the spontaneously formed vesicles decrease in size with each step of dilution, and ultrasmall unilamellar vesicles, with diameters as small as about 15 nm, were observed at the lowest concentrations. The spontaneously formed ultrasmall unilamellar vesicles maintain their size for as long we have investigated them (i.e., several months). To the best of our knowledge, such small vesicles have never before been reported to form spontaneously in a biocompatible phospholipid-based system. Most interestingly, the size of the vesicles was observed to be strongly dependent on the chemical structure of the phospholipid, and in mixtures of AMT and the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), the vesicles were observed to be considerably larger in size. The self-assembly behavior in the phospholipid–drug surfactant system in many ways resembles the formation of equilibrium micelles and vesicles in mixed anionic/cationic surfactant systems.

We present a Monte-Carlo package for simulation of high-redshift supernova data, SNOC. Optical and near-infrared photons from supernovae are ray-traced over cosmological distances from the simulated host galaxy to the observer at Earth. The distances to the sources are calculated from user provided cosmological parameters in a Friedmann-Lemaître universe, allowing for arbitrary forms of “dark energy”. The code takes into account gravitational interactions (lensing) and extinction by dust, both in the host galaxy and in the line-of-sight. The user can also choose to include exotic effects like a hypothetical attenuation due to photon-axion oscillations. SNOC is primarily useful for estimations of cosmological parameter uncertainties from studies of apparent brightness of type Ia supernovae vs redshift, with special emphasis on potential systematic effects. It can also be used to compute standard cosmological quantities like luminosity distance, lookback time and age of the universe in any Friedmann-Lemaître model with or without quintessence.

Scattering and absorption of light by a homogeneous distribution of intergalactic large dust grains has been proposed as an alternative, non-cosmological explanation for the faintness of type Ia supernovae at $z\sim 0.5$. We investigate the differential extinction for high-redshift sources caused by extragalactic dust along the line of sight. Future observations of type Ia supernovae up to $z\sim 2$, e.g. by the proposed SNAP satellite, will allow the measurement of the properties of dust over cosmological distances. We show that 1% relativespectrophotometric accuracy (or broadband photometry) in the wavelength interval 0.7–1.5 μm is required to measure the extinction caused by “grey” dust down to $\delta m=0.02$mag. We also argue that the presence of grey dust is not necessarily inconsistent with the recent measurement of the brightness of a supernova at $z=1.7$(SN 1997ff), in the absence of accurate spectrophotometric information of the supernova.

Expressions have been derived from which the spontaneous curvature (H0), bending rigidity (kc), and saddle-splay constant (c) of mixed monolayers and bilayers may be calculated from molecular and solution properties as well as experimentally available quantities such as the macroscopic hydrophobic−hydrophilic interfacial tension. Three different cases of binary surfactant mixtures have been treated in detail:  (i) mixtures of an ionic and a nonionic surfactant, (ii) mixtures of two oppositely charged surfactants, and (iii) mixtures of two ionic surfactants with identical headgroups but different tail volumes. It is demonstrated that kcH0, kc, and cfor mixtures of surfactants with flexible tails may be subdivided into one contribution that is due to bending properties of an infinitely thin surface as calculated from the Poisson−Boltzmann mean field theory and one contribution appearing as a result of the surfactant film having a finite thickness with the surface of charge located somewhat outside the hydrophobic−hydrophilic interface. As a matter of fact, the picture becomes completely different as finite layer thickness effects are taken into account, and as a result, the spontaneous curvature is extensively lowered whereas the bending rigidity is raised. Furthermore, an additional contribution to kcis present for surfactant mixtures but is absent for kcH0and c. This contribution appears as a consequence of the minimization of the free energy with respect to the composition of a surfactant layer that is open in the thermodynamic sense and must always be negative (i.e., kcis generally found to be brought down by the process of mixing two or more surfactants). The magnitude of the reduction of kcincreases with increasing asymmetry between two surfactants with respect to headgroup charge number and tail volume. As a consequence, the bending rigidity assumes the lowest values for layers formed in mixtures of two oppositely charged surfactants, and kcis further reduced in anionic/cationic surfactant mixtures where the surfactant in excess has the smaller tail volume. Likewise, the reduction of kcis enhanced in mixtures of an ionic and a nonionic surfactant where the ionic surfactant has the smaller tail. The effective bilayer bending constant (kbi) is also found to be reduced by mixing, and as a result, kbiis seen to go through a minimum at some intermediate composition. The reduction of kbiis expected to be most pronounced in mixtures of two oppositely charged surfactants where the surfactant in excess has the smaller tail in agreement with experimental observations.

The bending properties of charged one-component surfactant films of finite thickness have been theoretically investigated. It is demonstrated that finite thickness effects are of crucial importance for layers formed by an ionic surfactant with a flexible hydrophobic tail, whereas the influence on layers formed by a surfactant with a rigid tail is less pronounced. As a matter of fact, in the former case, the spontaneous curvature and mean and Gaussian bending constants all become significantly modified as compared to an infinitely thin surface and assume identical values as if the surfactant layer were bent at constant layer thickness. As a result, the spontaneous curvature is found to decrease, whereas the magnitudes of the mean and Gaussian bending constants both increase with increasing layer thickness as well as with increasing hydrophobic−hydrophilic interfacial tension. All of these trends are consistent with experimental observations. In addition, it is demonstrated that separating the hydrophilic−hydrophobic interface and the surface of charge a certain distance from each other tends to increase the spontaneous curvature and the mean bending constant, whereas the Gaussian bending constant becomes increasingly negative. It is also found that the work of bending a bilayer into a geometrically closed vesicle is substantially raised to large positive values for surfactants with flexible aliphatic chains, whereas the corresponding quantity is negative for surfactants with rigid tails, indicating that stable bilayer structures may only be formed by the former surfactant. Furthermore, each of the bending elasticity constants for monolayers formed by a double-chain ionic surfactant are found to assume lower values as compared with layers formed by the corresponding single-chain surfactant.

Maize (Zea maysL.) production in the smallholder farming areas of Zimbabwe is based on both organic and mineral nutrient sources. A study was conducted to determine the effect of composted cattle manure, mineral N fertilizer, and their combinations on NO3concentrations in leachate leaving the root zone and to establish N fertilization rates that minimize leaching. Maize was grown for three seasons (1996–1997, 1997–1998, and 1998–1999) in field lysimeters repacked with a coarse‐grained sandy soil (Typic Kandiustalf). Leachate volumes ranged from 480 to 509 mm yr−1(1395 mm rainfall) in 1996–1997, 296 to 335 mm yr−1(840 mm rainfall) in 1997–1998, and 606 to 635 mm yr−1(1387 mm rainfall) in 1998–1999. Mineral N fertilizer, especially the high rate (120 kg N ha−1), and manure plus mineral N fertilizer combinations resulted in high NO3leachate concentrations (up to 34 mg N L−1) and NO3losses (up to 56 kg N ha−1yr−1) in 1996–1997, which represent both environmental and economic concerns. Although the leaching losses were relatively small in the other seasons, they are still of great significance in African smallholder farming where fertilizer is unaffordable for most farmers. Nitrate leaching from sole manure treatments was relatively low (average of less than 20 kg N ha−1yr−1), whereas the crop uptake efficiency of mineral N fertilizer was enhanced by up to 26% when manure and mineral N fertilizer were applied in combination. The low manure (12.5 Mg ha−1) plus 60 kg N ha−1fertilizer treatment was best in terms of maintaining dry matter yield and minimizing N leaching losses.

Abstract: Shear induced aggregation of a Pectin stabilised emulsion trapped at the air-liquid interface was studied in a Couette system by video enhanced microscopy. From dimension analysis, Brownian motion was identified to enhance the probability of bond formation. The characteristic time scale of aggregation was found to scale as tc ∼ η/φ rather than tc ∼ 1/γ˙φ as expected for orthokinetic aggregation. The structure of very large clusters showed strongly rearranged strands and fractal scaling for low γ˙ and φ, analysed by density auto-correlation. At high γ˙ and φ, the cluster was dominated by larger drops and no fractal scaling could be determined for the accessible length scales.

The interactions between adsorbed polyelectrolyte layers have been studied using direct force measurements with an atomic force microscope. The results were correlated to adsorption studies using ellipsometry and we found that interactions can be described as electrosteric where the relative importance of the electrostatic and steric contribution varies with the adsorption and solution conditions. For adsorption at high pH (same charge on polyelectrolyte and surface), the adsorbed amount is relatively low but the adsorbed chains attain a relatively extended conformation. Reducing the pH results in a collapse of the adsorbed layer with a larger change in layer thickness at low ionic strength. For polyelectrolyte adsorbed at low pH (opposite charge on a weakly dissociated polyelectrolyte and surface), the adsorbed amount is higher and little chain expansion was observed when increasing pH.

The effects of neonatal handling on the opioid dynorphin peptides in the brain and pituitary gland of Sprague-Dawley rats were investigated. Ten weeks after the neonatal handling, handled rats had higher tissue levels of dynorphin A and B in the hypothalamus, pituitary gland and striatum and slightly higher dynorphin B levels in the hippocampus, medulla oblongata and midbrain as compared with non-handled controls. The results indicate a persistent upregulation of the dynorphin system in certain brain areas after neonatal handling, which could contribute to the behavioural changes in these rats observed later in life. Observation in the open field and the elevated plus-maze tests confirmed behavioural effects of neonatal handling, i.e. showing that handled rats exhibit attenuated fearfulness in novel environments as compared with non-handled rats. Copyright 1999 Harcourt Publishers Ltd

The decay rates of scalar and tensor mesons into two photons are calculated in the Bethe-Salpeter bound state formalism. The suppression of the non-relativistic estimates due to relativistic kinematics is found to be substantial. Production crosssections in colliding beam experiments are estimated to be in the picobarn range. Also in the relativistic case the helicity 0 production cross-section of tensor mesons is found to be negligible.

The problem of the radiative non-leptonic weak baryon decays is reviewed in light of the new experimental findings. With the aim of exploring the structure of the weak non-leptonic Hamiltonian, we present a detailed phenomenological analysis of Σ+→pℓ+ℓ− transitions. Lower and upper limits for rates derivable with standard physics are determined as Γ(Σ+→pe+e−)/Σ+→pγ)≧7.2×10−3 and 1/1210≲ Γ(Σ+→pe+e+)/Γ(Σ+→pe+e−)≲1/120. From existing data on Σ+→pe+e− we obtain limits on the values of the charge radius form factors |c1/b1|≲5;|c2/b1|≲ 10, where the magnetic form factor is given by the Σ+→dγ, decay asb1(0)= 6.9±0.9 MeV. The short distance contribution of the QCD corrected single quarks→dλ transition is shown not to play a dominant role in these decays.

Nitrate leaching was measured in field lysimeters containing undisturbed soils of different texture and organic matter content. Spring barley (Hordeum distichumL.) was sown on each lysimeter and fertilized with 100 kg N ha–1. Each soil type received supplementary watering to simulate either “average” or “worst‐case” precipitation. The largest leaching losses of NO–3, ca. 65 kg N ha–1yr–1, occurred in a sandy soil that contained little organic matter and in a peat soil. Two loamy soils lost between 25 and 40 kg N ha–1yr–1. Smallest leaching losses, ca. 20 kg N ha–1yr–1or less, occurred in a clay soil and another sandy soil rich in organic matter. With the exception of the clay and peat soils, the watering treatment did not significantly affect the amounts of NO–3leached, although the temporal distribution of leaching was clearly influenced by weather conditions. The difference in leaching between the two sandy soils was explained by differences in crop growth, whereas leaching differences between soil types were mainly considered to be due to different textural and structural properties. The results show that to make a thorough comparison of NO–3leaching between different soil types they have to be tested simultaneously at the same site.

A model dealing with transport and transformations of nitrogen in soil is briefly described. The model has a one-dimensional layered structure and considers processes such as plant uptake, mineralization/immobilization, leaching and denitrification. A soil water and heat model provides daily values for abiotic conditions, which are used as driving variables in the nitrogen simulation. In this study, the model was run with data from a polder-soil area in the Netherlands, with winter wheat as the crop. The simulation results showed that if a measured time course of crop nitrogen uptake throughout the growing season is available, mineral-N dynamics in soil can be satisfactorily described with this model. The main problems identified in the simulations were related to the partitioning between above- and below-ground plant-N, and supplying the crop with sufficient N, as given by the measurements.

The activities of two groups of cyclic agonists of substance P (SP) have been studied. The disulfide bridge constraints have been designed on the basis of conformational studies on SP and physalaemin indicating an alpha-helical structure for the core of these two tachykinins (group I) and a folding of the C-terminal carboxamide towards the side chains of the glutamines 5 and 6 (group II). Only peptides simulating the alpha-helix present substantial potencies. [Cys3,6]SP is as active as SP in inhibiting 125I-labeled Bolton and Hunter SP-specific binding on rat brain synaptosomes and on dog carotid bioassay, two assays specific for the neurokinin 1 receptor. Moreover, [Cys3,6]SP is as potent as neurokinin B in inhibiting 125I-labeled Bolton and Hunter eledoisin-specific binding on rat cortical synaptosomes as well as in stimulating rat portal vein, two tests specific for the neurokinin 3 receptor. Interestingly, in contrast to neurokinin B, [Cys3,6]SP is a weak agonist of the neurokinin 2 receptor subtype, as evidenced by its binding potency in inhibiting 3H-labeled neurokinin A-specific binding on rat duodenum and in inducing the contractions of the rabbit pulmonary artery, a neurokinin 2-type bioassay. To increase the specificity of the cyclic analogue [Cys3,6]SP positions 8 and 9 were modified. [Cys3,6, Tyr8, Ala9]SP is slightly less selective than SP for the neurokinin 1 receptor subtype. [Cys2,5]neurokinin B constitutes a selective cyclic agonist for the neurokinin 3 receptor. The very weak potencies of the peptides from group II indicate that a certain degree of flexibility in the C-terminal moiety is required. Collectively, these results suggest that the neurokinin 1 and neurokinin 3 tachykinin receptors may recognize a similar three-dimensional structure of the core of the tachykinins. Different orientations of the common C-terminal tripeptide may be related to the selectivity for the different receptor subtypes.

3H-Neurokinin A (3H-NKA) with high specific activity (75 Ci/mmol) was synthesized to study NKA (NK-2)-binding sites on membrane preparations of various tissues in the rat, including brain, spinal cord, duodenum, vas deferens, and ileum. The binding capacity of 3H-NKA (0.9 nM) was very low in membrane preparations of different central nervous system regions and the ileum smooth muscle (0.2-2 fmol/mg of protein). In contrast, relatively high specific binding was found in membrane suspensions of the rat duodenal smooth muscle (18 fmol/mg of protein) and the vas deferens (8 fmol/mg of protein). 3H-NKA-binding sites were further characterized on the rat duodenal smooth muscle. The specific binding of 3H-NKA was shown to be temperature dependent, saturable, reversible, and increased in parallel with the protein concentration. Scatchard analyses and Hill plots of equilibrium binding studies in the concentration range of 0.40-30 nM revealed that 3H-NKA bound to a single class of noninteracting binding sites (Bmax = 270 fmol/mg of protein, KD = 13.3 nM). Displacement of 3H-NKA with different tachykinin-related peptides gave the following rank order of potencies: NKA greater than NKA (4-10) greater than kassinin greater than eledoisin greater than NKB much greater than substance P greater than physalaemin, which suggests that the binding site labeled by 3H-NKA is different from substance P (NK-1)-and NKB (NK-3)-binding sites. The biological activities of tachykinins and related peptides were tested by measuring their contractile effects on the rat duodenum and rabbit pulmonary artery, two tissues known to be sensitive for NKA. Ki values were correlated with the EC50 obtained in biological assays. The results revealed a significant correlation (r = 0.86, p less than 0.01) between Ki and EC50 values obtained in the isolated rabbit pulmonary artery, whereas there was no significant correlation between binding affinities and biological responses on the rat duodenum (r = 0.62, p greater than 0.05).

The rare electromagnetic decay of a neutral pseudoscalar meson into a lepton pair is calculated in a bound state quark model. For heavy mesons, the leading QCD diagram is argued to be dominant allowing higher order QCD corrections to be neglected for the branching ratio of this decay to the two-photon decay. The experimentally interesting case of pion decay is treated separately, and the rates for competing processes (weak neutral currents, axions, technicolour ...) are estimated. We conclude that existing data may well allow for such contributions.

QED radiative corrections to the decay of a pseudoscalar meson into a lepton pair have been estimated. The results are applied to the decay of the neutral pion into electron and positron. Formulas are also given for a pseudoscalar Higgs-like particle decaying to a lepton or quark pair. The results are also of relevance for QCD sum rules for the pseudoscalar current, where conflicting calculations exist in the literature.

AbstractThe deep minimum in the absorption spectrum of ice and a number of other highly transparent solids is often truncated by a segment proportional to (wavelength)−4. We interpret such a feature as due to Rayleigh scattering which was not discriminated from true absorption by the measurement technique. The magnitude of the scattering is enhanced above the intrinsic Rayleigh scattering by the presence of nanoscale defects and can be used to diagnose the presence of such defects.

A new application of atomic force microscopy (AFM) for evaluation of surface ionization parameters on the basis of a charge-regulation model is demonstrated. Interactions between symmetrical silicon nitride and silica surfaces have been measured in aqueous electrolytic solutions at different pHs and separations from a few Debye lengths down to zero. The obtained experimental data are reported and interpreted on a quantitative level in the framework of Derjaguin's approximation; the computational procedure used for this purpose is outlined. Surface charge density, surface potential, and species concentrations are calculated as functions of pH and separation, unveiling the limits of applicability of classical constant-charge and constant-potential approximations. The integrity of the results on the charge properties of interacting surfaces is discussed in reference to electrokinetic and titration data, potential problems caused by the existence of non-DLVO forces and surface irregularities being highlighted.

The rheological properties of both aqueous and non-aqueous composite suspensions were investigated together with a characterization of the colloidal stability of the separate components. The colloidally stable, concentrated aqueous SiCwand Al2O3-SiCwcomposite suspensions displayed strong shear thinning followed by a severe, sometimes discontinuous, shear thickening at a critical shear rate. The non-aqueous composite suspensions, containing weakly flocculated SiCw, only showed a continuous shear thinning behaviour. The variations in the steady shear behaviour were related to the differences in the colloidal stability and possible shear induced effects on the suspension structure. It was possible to fit the volume fraction dependence of both the SiCwand the Al2O3suspensions to a modified Krieger-Dougherty model which yields values of the maximum volume fraction; φm(Al2O3)=0.61, φm(SiCw)=0.28. The viscosity of the composite suspensions were successfully predicted from the Farris theory using the rheological data for the separate components.

Binding sites for substance P were labeled on intact cortical glial cells from newborn mice in primary culture using 125I-labeled Bolton-Hunter-labeled substance P. Maximal specific binding (95% of total binding) was reached after 2-3 weeks in culture. The binding was saturable, reversible, and temperature dependent. Scatchard and Hill analysis revealed a single population of noninteracting high-affinity binding sites (Kd, 0.33 nM; Bmax, 14.4 fmol per dish). Competition studies made with tachykinins and substance P analogues indicated that the characteristics of the 125I-labeled Bolton-Hunter labeled substance P binding sites on glial cells were identical to those on rat brain synaptosomes. 125I-labeled Bolton-Hunter labeled substance P binding sites were visualized by autoradiography, and differences in the intensity of labeling were seen among astrocytes. Substance P was found to stimulate phosphatidylinositol turnover; the EC50 value (0.36 nM) was identical to the IC50 value (0.38 nM) determined in binding studies. 125I-labeled Bolton-Hunter labeled substance P binding sites were also found on astrocytes derived from other brain structures and from the spinal cord of mice.

A general system of equations describing the dissolution of polydisperse solids having a porous particulate structure is set up and applied to study the hydrolysis and subsequent dissolution of silicon nitride powder in aqueous suspensions. The latter process has been found to follow a simple kinetic equation, c(t)= cs[1 − exp(−kt)], with the dissolution rate constant k= 2.3 × 10−6s−1(or 2.5 × 10−11mol m−2s−1) and the saturation concentration cs= 3.2 mmol dm−3at room temperature and pH 9. The role of diffusion is unimportant, so the concentration of soluble species in pore water changes almost simultaneously with their concentration in the surrounding solution.

In studies of water and solute movement in soils, use of undisturbed monoliths is usually preferred. A drilling technique to collect such monoliths (0.295 m i.d.; 1.0, 0.5, or 0.3 m in length) with minimal soil disturbance was developed. The drill consists of a steel cylinder with four mounted cutting teeth at the bottom, into which a plastic casing is inserted. The drill‐cylinder rotates around the casing and carves out a soil core that is gently pushed into the casing using only a minimum of hydraulic pressure. The technique has been used in a wide variety of research applications within soil science, including the measurement of hydraulic properties, soil evaporation, and soil aeration studies. Here, one application is described in which the monoliths were used as field lysimeters planted with either barley (Hordeum vulgareL.) or meadow fescue (Festuca pratensisHudson). During a 6‐mo period, the grass lysimeters had a much lower total drainage (106 compared with 213 mm for barley) and also lower mean NO3concentrations in the drainage water (<0.1 compared with 9.3 mg N L−1). The uniformity of response among the replicates and large differences between the two treatments was taken as indirect evidence that sidewall flows were of little significance when using this technique.