Neutral Community Theory: How Stochasticity and Dispersal-Limitation Can Explain Species Coexistence

Neutral community theory explains biodiversity, i.e. the coexistence of several species, as the result of a stochastic balance between immigration and extinction on a local level, and between speciation and extinction on a regional level. The most popular model, presented by Hubbell in 2001, has seen many analytical developments in recent years, which can be used in model analysis, model testing and model comparison. We review these developments here, and present alternative derivations and shine previously unnoticed lights on them.     

Etude structurale des sulfotellurures de terres rares (LS)2Te1+x (L = Tb,Dy, Ho,Er, Tm et Y). I. Sous-structure de la phase ordonnée de (HoS)2Te1,34. Structure de la phase desordonnée de (TbS)2Te

The lanthanide sulfotellurides (LS)₂Te_1+x (0 ≤ x < 0.50) show order-disorder phenomena. Above 450°C, they crystallize in a partially disordered structure, orthorhombic with cell parameters a, b, and c close to 4.1, 5.2, and 13.6 Å, respectively. This structure is determined from diffractometer data on a (HoS)₂Te_1.34 crystal (R = 0.061). It is built up along the c axis from (L₄S) tetrahedra layers, separated by Te planes. Disorder and nonstoichiometry are related to the two vacant Te sites.     

On the uniqueness of minimizing harmonic maps to a closed hemisphere

We study the uniqueness of minimizing harmonic maps to a closed hemisphere. We are able to describe the boundary data for which there are more than one minimizer, and to describe in these cases the corresponding set of minimizers. This is a limiting case for a former result of W.Jäger and H.Kaul.This article was processed by the author using the Springer-Verlag T_EX PJourlg macro package 1991.     

111In–L–LDL and 153Gd–L–LDL as radiotracers for detection of AR4‐2J rat pancreatic tumors

Pancreatic cancer has an extremely poor prognosis, due, in part, to lack of methods for early diagnosis. The present study was designed to evaluate the potential of labeling low‐density lipoprotein (LDL) with a radionuclide using a lipid chelating agent, bis(stearylamide) of diethylenetriaminepentaacetic acid (L), to detect pancreatic tumors by gamma‐scintigraphy. Previous studies indicated that the difficulty of visualization of pancreatic tumors was due to their poor vascularization. This study compares the ability of two radiotracers, ¹¹¹In–L–LDL and ¹⁵³Gd–L–LDL to target highly vascularized rat pancreatic tumors (AR4‐2J) implanted in nude mice. Biodistribution studies showed that the tumor uptake of ¹¹¹In–L–LDL and ¹⁵³Gd–L–LDL tracers was twofold and fivefold higher respectively than with the controls (¹¹¹In citrate and ¹⁵³Gd citrate respectively). These tracers would thus be suitable for scintigraphic imaging. We show here that LDL could be employed as a delivery system for tracers such as ¹¹¹In or ¹⁵³Gd when these two radionuclides are complexed by a lipid‐chelating anchor, and that ¹¹¹In–L–LDL and ¹⁵³Gd–L–LDL enabled better visualization of the pancreatic tumor tissues, with a better result with ¹⁵³Gd–L–LDL. Copyright © 2004 John Wiley & Sons, Ltd.     

Rate of Convergence of a Stochastic Particle System for the Smoluchowski Coagulation Equation

By continuing the probabilistic approach of Deaconu et al. (2001), we derive a stochastic particle approximation for the Smoluchowski coagulation equations. A convergence result for this model is obtained. Under quite stringent hypothesis we obtain a central limit theorem associated with our convergence. In spite of these restrictive technical assumptions, the rate of convergence result is interesting because it is the first obtained in this direction and seems to hold numerically under weaker hypothesis. This result answers a question closely connected to the Open Problem 16 formulated by Aldous (1999).     

Tribological properties of ormosil coatings

Transparent plastics are not scratch resistant. The damage leads to a loss of optical properties. Coatings prepared using either tetraethoxysilane or colloidal silica particles embedded in glymo is a way to avoid these disadvantages. Tribological experiments are carried out to better understand the surface modification due to a sliding friction. It is shown that the wear track is not directly related to usual mechanical properties such as Young's modulus and the hardness of the coating. The different stages leading to material loss are discussed in term of particle removal and debris circulation (accumulation or elimination) through the friction track. The mechanical properties of the film combined with the film to substrate adhesion are expected to play an important role as it can be deduced from results obtained as a function of the coating composition.     

Structural characterisation of a sol-gel copolymer synthesised from aliphatic and aromatic alkoxysilanes using 29Si-NMR spectroscopy

A hybrid organic-inorganic material was prepared from the hydrolytic co-condensation of 3-trimethoxysilylpropylmethacrylate (MAPTMS) and diphenyldiethoxysilane (DPHDES). The synthesis was performed in three steps: (1) MAPTMS pre-hydrolysis, (2) addition of DPHDES, and (3) further hydrolysis of the obtained mixture. ²⁹Si nuclear magnetic resonance spectroscopy was used to characterise the structural evolution of the mineral network during the synthesis. It revealed the catalytic effect of DPHDES on the condensation reaction of silanol groups, initially observed for pre-hydrolysed MAPTMS. In addition, it was clearly demonstrated that the formation of the highest condensed species of the aromatic oligomers (D₂ species) occurred only in the presence of aliphatic oligomers, which decrease the sterical hindrance about the silicon nuclei.     

Stamp collapse in soft lithography

We have studied the so-called roof collapse in soft lithography. Roof collapse is due to the adhesion between the PDMS stamp and substrate, and it may affect the quality of soft lithography. Our analysis accounts for the interactions of multiple punches and the effect of elastic mismatch between the PDMS stamp and substrate. A scaling law among the stamp modulus, punch height and spacing, and work of adhesion between the stamp and substrate is established. Such a scaling law leads to a simple criterion against the unwanted roof collapse. The present study agrees well with the experimental data.     

Synthesis of Gels in the System Na2O-ZrO2-SiO2

Gels have been synthesized in the SiO₂-Na₂O-ZrO₂ system and calcined at various temperatures up to 700°C. They have been studied by infrared absorption spectroscopy. The position of the asymmetric stretching frequency of the SiO₄ unit is used as a tracer of the homogeneity. It is shown that sodium increases the solubility of zirconium in the silica matrix as already observed in fused glasses.