Organically modified silicate coatings for optical fibers

ABSTRACT Three kinds of UV-curable organically modified silicates have been prepared to be used as protective coatings for optical fibers. The synthesis involves the reaction of the thiol group of 3-mercaptopropyltrimethoxysilane with a C =C bond in one of the acrylic groups of three commercially available aliphatic triacrylates. The methoxysilyl groups of the synthesized diacrylate methoxysilanes were subjected to hydrolysis and condensation to form Si-O-Si units. Transparent, viscous, solvent-free resins were obtained that hardened in seconds when exposed to UV radiation. The coating derived from the reaction with glycerol propoxy triacrylate (GPTA) proved to adhere the best of the three to both plastic and glass substrates. It was then tested as a protective coating for silica fibers. Reliability tests were carried out including bending strength and fatigue tests at pH 7 and 10. The results show improved water resistance of the coated fiber in neutral conditions. INTRODUCTION Present formulations for UV-curable coatings applied to protect optical fibers consist of several components. Generally, the formulations include (1) a high viscosity reactive oligomer (epoxy acrylate, urethane acrylate, polysiloxane acrylate), (2) a reactive diluent (mono or multiacrylate monomers), (3) a photoinitiator, and (4) an adhesion promoting agent. The final properties of the cured coating such as hardness, flexibility, toughness, abrasion, optical transparency, adhesion and glass transition (Ta) are determined directly by the chemistry and composition of the liquid formulation. There are several commercially available UV-curable materials to satisfy a variety of applications. All of these materials are highly toxic in the liquid state. We are therefore investigating formulations which contain no volatile components in order to reduce the hazards related to their removal. Ideally, a coating formulation would be one component, nonvolatile, highly reactive, sufficiently viscous, with good wetting to the substrate. In addition, the resulting coating should have the desired mechanical, optical and physical properties after curing under dynamic conditions (in a high speed fiber drawing operation). We would like to be able to tailor these properties simply by controlling the synthesis parameters of this one component system. A promising class of materials for this kind of "ideal" coating is inorganic-organic hybrid materials with organics chemically linked to inorganics. In particular, organically modified silicates were investigated. In the search for new UV curable materials combining both good optical and protective properties, we synthesized three different types of diacryloalkoxysilanes. Upon hydrolysis and partial condensation of alkoxysilyl groups, they formed viscous, one component UV-curable liquids containing photoinitiator. The acrylosilicate coatings were synthesized by the method used previously by Wolter et al.1 in which 3-mercaptopropyltrimethoxysilane was coupled via its S-H group to the C =C bond of the acrylic group of aliphatic triacrylate. Three commercially available triacrylates commonly used as reactive diluents in UV curing technology were O-8194-1339-9/94/$6.OO SPIE Vol. 2074 / 13

Oxygen isotope and sapropel stratigraphy in the Eastern Mediterranean during the last 3.2 million years

Stable oxygen isotope data from four holes drilled at the Ocean Drilling Program Site 967, which is located on the lower northern slope of the Eratosthenes Seamount, provide a continuous record of Eastern Mediterranean surface-water conditions during the last 3.2 Ma. A high-resolution stratigraphy for the Pliocene-Pleistocene sequence was established by using a combination of astronomical calibration of sedimentary cycles, nannofossil stratigraphy, and stable oxygen isotope fluctuations. Sapropels and color cycles are present throughout the last 3.2 Ma at Site 967, and their ages, as determined by calibration against the precessional component of the astronomical record, are consistent with those estimated for the sapropels of the classical land-based marine sequences of the Punta Piccola, San Nicola, Singa, and Vrica sections (southern Italy). The Site 967 oxygen isotope record shows large amplitude fluctuations mainly caused by variations in surface water salinity throughout the entire period. Spectral analysis shows that fluctuations in the d18O record were predominantly influenced by orbital obliquity and precessional forcing from 3.2 to 1 Ma, and all main orbital frequencies characterize the d18O record for the last million years. The start of sapropel formation at 3.2 Ma indicates a possible link between sapropel formation and the build up of northern hemisphere ice sheets. The dominance of the obliquity cycle in the interval from 3.2-1 Ma further points to the sensitivity of Eastern Mediterranean climate to the fluctuations in the volume of Arctic ice sheets. An intensification of negative isotope anomalies at Site 967, relative to the open ocean, supports a link between high run-off (during warm periods) and sapropel formation. freshwater input would have inhibited deep-water formation, which led to stagnation of deeper waters. Comparison with the land sections also confirms that differential preservation and diagenesis play a key role in sapropel occurrence

Multi-level selection and the issue of environmental homogeneity

In this paper, I identify two general positions with respect to the relationship between environment and natural selection. These positions consist in claiming that selective claims need and, respectively, need not be relativized to homogenous environments. I then show that adopting one or the other position makes a difference with respect to the way in which the effects of selection are to be measured in certain cases in which the focal population is distributed over heterogeneous environments. Moreover, I show that these two positions lead to two different interpretations – the Pricean and contextualist ones – of a type of selection scenarios in which multiple groups varying in properties affect the change in the metapopulation mean of individual-level traits. Showing that these two interpretations stem from different attitudes towards environmental homogeneity allows me to argue: a) that, unlike the Pricean interpretation, the contextualist interpretation can only claim that drift or selection is responsible for the change in frequency of the focal trait in a given metapopulation if details about whether or not group formation is random are specified; b) that the traditional main objection against the Pricean interpretation – consisting in arguing that the latter takes certain side-effects of individual selection to be effects of group selection – is unconvincing. This leads me to suggest that the ongoing debate about which of the two interpretations is preferable should concentrate on different issues than previously thought

Cumulative readings of every do not provide evidence for events and thematic roles

An argument by Kratzer (2000) based on Schein (1986, 1993) does not conclusively show that events and thematic roles are necessary ingredients of the logical representation of natural language sentences. The argument claims that cumulative readings of every can be represented only with these ingredients. But scope-splitting accounts make it possible to represent cumulative readings of every in an eventless framework. Such accounts are motivated by obligatory reconstruction effects of every and by crosslinguistic considerations. Kratzer proposes that agent but not theme occurs in the logical representation of sentences because this allows her to model subject-object asymmetries in the distribution of cumulative every. But the reason for these asymmetries seems to be that every must be c-commanded by another quantifier in order to cumulate with it, no matter what its thematic role is. So the distribution of cumulative every does not provide support for Kratzer’s proposal

Mass Mortality of Adult Male Subantarctic Fur Seals: Are Alien Mice the Culprits?

Background: Mass mortalities of marine mammals due to infectious agents are increasingly reported. However, in contrast to previous die-offs, which were indiscriminate with respect to sex and age, here we report a land-based mass mortality of Subantarctic fur seals with apparent exclusivity to adult males. An infectious agent with a male-predilection is the most plausible explanation for this die-off. Although pathogens with gender-biased transmission and pathologies are unusual, rodents are known sources of male-biased infectious agents and the invasive Mus musculus house mouse, occurs in seal rookeries. Methodology / Principal Findings: Molecular screening for male-biased pathogens in this potential rodent reservoir host revealed the absence of Cardiovirus and Leptospirosis genomes in heart and kidney samples, respectively, but identified a novel Streptococcus species with 30 % prevalence in mouse kidneys. Conclusions / Significance: Inter-species transmission through environmental contamination with this novel bacterium, whose congenerics display male-bias and have links to infirmity in seals and terrestrial mammals (including humans)

External representations and scientific understanding

This paper provides an inferentialist account of model-based understanding by combining a counterfactual account of explanation and an inferentialist account of representation with a view of modeling as extended cognition. This account makes it understandable how the manipulation of surrogate systems like models can provide genuinely new empirical understanding about the world. Similarly, the account pro- vides an answer to the question how models, that always incorporate assumptions that are literally untrue of the model target, can still provide factive explanations. Finally, the paper shows how the contrastive counterfactual theory of explanation can provide tools for assessing the explanatory power of models.Peer reviewe