Poly(Dimethylsiloxane) Elastomers from Aqueous Emulsions: I. Preparations, and Characterization of the Curing and Aging Processes

1998 ◽  
Vol 71 (5) ◽  
pp. 906-927 ◽  
Author(s):  
D. W. McCarthy ◽  
J. E. Mark
Keyword(s):  
Crosslinking Agent ◽  
Inorganic Filler ◽  
Aging Effects ◽  
Soluble Polymer ◽  
Subsequent Aging ◽  
Barrier Effects ◽  
Effects Of Aging ◽  
Elastomeric Particles

Abstract Poly(dimethylsiloxane) (PDMS) elastomers were prepared from aqueous emulsions, in combination with one of several carefully chosen alkoxy silanes as a crosslinking agent, and either stannous-2-ethylhexanoate or dioctylitin dilaurate as catalyst. Conditions were generally chosen so as to generate silica/silicate phases within the elastomeric particles or at their surfaces, for improvements in mechanical properties of films to be cast from the emulsions. A series of such films was obtained from emulsions consisting of various combinations of these ingredients, and was then characterized, primarily by measurements of soluble fractions, and by extents of equilibrium swelling (as inverse measures of degrees of crosslinking). Of primary interest were experimental results clarifying the mechanisms for the PDMS crosslinking and for the subsequent “aging” of these materials. For all the systems, increase in concentration of crosslinking agent was found to decrease the fraction of soluble polymer present and to decrease the extent of swelling. The extent to which this occurred, however, varied significantly with the nature of the alkoxy silane crosslinking agent, its concentration, and the nature of the catalyst. The observed differences were used to propose mechanisms with regard to the role of the silanes in the formation of silica-like phases, as well as for the endlinking of the PDMS chains. The formation of this inorganic phase was found to have a large effect on the extraction and swelling results, particularly through its barrier effects on the surfaces of the emulsion particles. Aging effects were found to depend not only on the nature of the reactants and their concentrations in the preparation of the emulsions, but also on whether the aging had been carried out in the dry state or in the wet state. Two major effects were decreases in soluble polymer fraction and extent of swelling with time. These changes were associated with increases in degree of crosslinking, but opposing changes can arise from bond cleavages or reorganizations. It appeared that dry-state aging effects are greatest for systems with a low concentration of the precipitated inorganic phase, with the effects of aging being suppressed by the presence of the inorganic, filler-like phases.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

Effects of Aging on the Subcortical Encoding of Stop Consonants

2020 ◽  
Vol 29 (3) ◽  
pp. 391-403
Author(s):  
Dania Rishiq ◽  
Ashley Harkrider ◽  
Cary Springer ◽  
Mark Hedrick
Keyword(s):  
Older Adults ◽  
Repeated Measures ◽  
Mixed Model ◽  
Auditory Brainstem ◽  
Auditory Brainstem Responses ◽  
Aging Effects ◽  
Formant Frequency ◽  
Place Of Articulation ◽  
Second Formant ◽  
Effects Of Aging

Purpose The main purpose of this study was to evaluate aging effects on the predominantly subcortical (brainstem) encoding of the second-formant frequency transition, an essential acoustic cue for perceiving place of articulation. Method Synthetic consonant–vowel syllables varying in second-formant onset frequency (i.e., /ba/, /da/, and /ga/ stimuli) were used to elicit speech-evoked auditory brainstem responses (speech-ABRs) in 16 young adults ( M age = 21 years) and 11 older adults ( M age = 59 years). Repeated-measures mixed-model analyses of variance were performed on the latencies and amplitudes of the speech-ABR peaks. Fixed factors were phoneme (repeated measures on three levels: /b/ vs. /d/ vs. /g/) and age (two levels: young vs. older). Results Speech-ABR differences were observed between the two groups (young vs. older adults). Specifically, older listeners showed generalized amplitude reductions for onset and major peaks. Significant Phoneme × Group interactions were not observed. Conclusions Results showed aging effects in speech-ABR amplitudes that may reflect diminished subcortical encoding of consonants in older listeners. These aging effects were not phoneme dependent as observed using the statistical methods of this study.

Consideraciones en torno a la reducción solipsista

1970 ◽  
Vol 11 ◽  
Author(s):  
Natalia Carolina Petrillo

ResumenEn el presente trabajo se intentará mostrar que la fenomenología no conduce a una postura solipsista. Para ello, se caracterizará en qué consiste el solipsismo. Luego, se intentará refutar a lo que se ha de llamar “solipsismo metafísico” y “solipsismo gnoseológico”, con el objetivo principal de poner de manifiesto el fundamento de motivación para la salida de la ficción solipsista.Palabras claves:Phenomenology – solipsim – empatía - HusserlAbstractWith the aim of showing that phenomenology does not lead in solipsism, I will first attempt a characterization of it. Then, I will attempt a refutation of the so-called “metaphysical” and “epistemological” solipsisms. Finally, the nature and role of Husserl´s solipsistic fiction is examined, and the grounds that motivate the overcoming of this standpoint are disclosed.key wordsFenomenología – solipsismo - empathy – Husserl

ART STUDIOS – A WAY TO DEVELOPE CHILDREN’S IMAGINATION

2020 ◽  
Vol 11 (1) ◽  
pp. 144-148
Author(s):  
Liuba Zlatkova ◽  
Keyword(s):  
Fairy Tale ◽  
Psychological Effects ◽  
Complete Product ◽  
The Arts ◽  
The Creation ◽  
Role Of Parents

The report describes the steps for creating a musical tale by children in the art studios of „Art Workshop“, Shumen. These studios are led by students volunteers related to the arts from pedagogical department of Shumen University, and are realized in time for optional activities in the school where the child studies. The stages of creating a complete product with the help of different arts are traced – from the birth of the idea; the creation of a fairy tale plot by the children; the characterization of the fairy-tale characters; dressing them in movement, song and speech; creating sets and costumes and creating a finished product to present on stage. The role of parents as a link and a necessary helper for children and leaders is also considered, as well as the positive psychological effects that this cooperation creates.

Conceptual Analysis Rebooted

2017 ◽  
Author(s):  
Edouard Machery
Keyword(s):  
Experimental Method ◽  
Conceptual Analysis ◽  
Philosophical Tradition ◽  
Traditional Use ◽  
Philosophical Significance ◽  
Conceptual Engineering ◽  
Method Of Cases

Chapter 7 proposes a new, naturalistic characterization of conceptual analysis, defends its philosophical significance, and shows that usual concerns with conceptual analysis do not apply to this revamped version. So understood, conceptual analysis encompasses both a descriptive project and a normative project, similar to explication or to conceptual engineering. Chapter 7 also defends the philosophical significance of this novel form of conceptual analysis and its continuity with the role of conceptual analysis in the philosophical tradition. Furthermore, naturalized conceptual analysis often requires empirical tools to be pursued successfully, and an experimental method of cases 2.0 should often replace the traditional use of cases in philosophy.

Acid-Sensing Ion Channels

2020 ◽  
Author(s):  
Stefan Gründer
Keyword(s):  
Nervous System ◽  
Ion Channels ◽  
Excitatory Synapses ◽  
Detailed Characterization ◽  
High Affinity ◽  
Acid Sensing Ion Channels ◽  
Long Time ◽  
Pathological Pain

Acid-sensing ion channels (ASICs) are proton-gated Na+ channels. Being almost ubiquitously present in neurons of the vertebrate nervous system, their precise function remained obscure for a long time. Various animal toxins that bind to ASICs with high affinity and specificity have been tremendously helpful in uncovering the role of ASICs. We now know that they contribute to synaptic transmission at excitatory synapses as well as to sensing metabolic acidosis and nociception. Moreover, detailed characterization of mouse models uncovered an unanticipated role of ASICs in disorders of the nervous system like stroke, multiple sclerosis, and pathological pain. This review provides an overview on the expression, structure, and pharmacology of ASICs plus a summary of what is known and what is still unknown about their physiological functions and their roles in diseases.

Sign in / Sign up

Export Citation Format

Share Document