Characterization of Nanoparticles and Colloids in Aquatic Systems 1. Small Angle Neutron Scattering Investigations of Suwannee River Fulvic Acid Aggregates in Aqueous Solutions

Fulvic acids (FA) and humic acids (HA) constitute 30–50% of dissolved organic matter in natural aquatic systems. In aqueous solutions, a commonly accepted view is that FA and HA exist as soluble macroligands at low concentration and as supramolecular aggregates at higher concentration. The size, shape and structure of these aggregates are still the subject of ongoing debate in the environmental chemistry literature. In this article, we use small angle neutron scattering (SANS) to assess the effects of solute concentration, solution pH and background electrolyte (NaCl) concentration on the structures of Suwannee River FA (SRFA) aggregates in D₂O. The qualitative features of the SANS curves and data analysis are not consistent with the view point that SRFA forms micelle-like aggregates as its concentration in aqueous solution increases. We find that SRFA forms fractal aggregates in D₂0 with size greater than 242 nm. The SRFA aggregates undergo a significant degree of restructuring in compactness as solution pH, solute concentration and NaCl concentration increase.     

The neuroblast and angioblast chemotaxic factor SDF-1 (CXCL12) expression is briefly up regulated by reactive astrocytes in brain following neonatal hypoxic-ischemic injury

Background  

Stromal cell-derived factor 1 (SDF-1 or CXCL12) is chemotaxic for CXCR4 expressing bone marrow-derived cells. It functions in brain embryonic development and in response to ischemic injury in helping guide neuroblast migration and vasculogenesis. In experimental adult stroke models SDF-1 is expressed perivascularly in the injured region up to 30 days after the injury, suggesting it could be a therapeutic target for tissue repair strategies. We hypothesized that SDF-1 would be expressed in similar temporal and spatial patterns following hypoxic-ischemic (HI) injury in neonatal brain.     

Synthesis and evaluation of a series of novel 2-substituted poly(allylalcohol) side chain liquid crystalline oligomers exhibiting ferroelectricity

The recently published Baylis-Hillman methodology has been used to prepare a number of side chain liquid crystalline poly(allylalcohols) incorporating a ferroelectric mesogenic side chain. These poly(allylalcohols) exhibited wide range S*_C phases and, in the case of two of these materials, low glass transition temperatures. The transition temperatures and phase behaviour of the SCLC poly(allylalcohols) were compared to acrylate and methacrylate SCLC oligomers containing a similar mesogenic side chain. The response times for two poly(allylalcohols) exhibiting low glass transition temperatures were also measured over a wide temperature range. Although the poly(allylalcohols) had comparable response times to the analogous acrylate and methacrylate SCLCP, they showed the greater temperature dependence of the response time. However, at 39°C one of the SCLC poly(allylalcohols) showed a response time of 65 ms.     

A zwitterionic cyclopentadienyl annulated imidazolium salt

The first directly annulated cyclopentadienyl-imidazolium salt has been synthesized and fully characterized. In the solid-state, this zwitterion arranges itself in a hydrogen-bridged head to tail trimer which optimizes ionic interactions. Substantial π-π interactions are absent. The UV spectrum of the imidazolium innersalt reflects the intimate electronic interaction arising from direct fusion of cationic and anionic fragments of the molecule.     

The gravitational searchlight effect from synchrotron radiation in the Schwarzschild geometry

Gravitational synchrotron radiation is studied using the techniques of geometrical optics. It is found that the geometry of the Schwarzschild black hole creates a rotating searchlight effect, even for a source particle which radiates only during an infinitesimally brief interval of coordinate time. The period of rotation of the searchlight is shown to provide a measurement of the mass of the blackhole, since the period T is related to the mass M by T = 2π27^1/2 M for the Schwarzschild geometry and by T = 4πM for the extreme (a = M) Kerr geometry.     

Bestimmung von Alkali- und Erdalkaliionen in Regenwasserproben mit der Ionen-Chromatographie

Summary Alkali and alkaline earth ions in rain water can be determined by ion chromatography (IC) without preconcentration. The detection limits for alkali ions are between about 0.05 and 0.15 mol/l and those for alkaline earth ions between about 0.2 and 0.6 mol/l. The main advantages of IC are: very small sample volumes are sufficient; the simultaneous determination of the alkali ions or the alkaline earth ions requires less than 30 min; NH ₄ ⁺ ions can also be determined. The results are compared with those obtained by flame AAS and AES-ICP.     

General density gradients in general domains: the “two-tank” method revisited

 An experimental technique for the creation of any statically stable density profile is presented. This technique is essentially a generalized, unsteady version of the “two-tank” method that is well known to the stratified flow community. It involves specifying the desired density profile and then solving an inverse problem in order to determine the necessary flow rates of light and dense fluid into the test-section tank. In addition to creating nonlinear density profiles, this technique is also useful for creating linear profiles in tanks whose planform areas vary with the vertical coordinate. The execution of this technique is carried out with computer-controlled peristaltic pumps. Several tests of the method are presented. The first consists of creating a hyperbolic tangent density profile in a rectangular tank. The second consists of creating, again in a rectangular tank, a density profile that is representative of those found in oceans and lakes. Finally, the third test involves creating a linear profile in a tank whose planform area is not constant. In all cases, the measured density profile shows excellent agreement with the requested profile. Received: 12 June 2001 / Accepted: 12 October 2001