270 research outputs found
Auditory discrimination and reading readiness
The purpose of this paper was to explore the following specific areas: 1. the relationship between auditory discrimination (psycholinguistic process) and reading. Is auditory discrimination a necessary reading readiness skill? 2. The relevance of auditory discrimination training to developing reading readiness skills; that is, should auditory discrimination training be accomplished solely in relation to the product of reading? 3. The practicality of psycholinguistic teaching for learning disabled children
Impact of teaching summarizing to improve comprehension and retention of a religion textbook
This study analyzed the impact of summarizing on studentsâ comprehension and retention of a religion textbook. The study consisted of an eight-week intervention during which the participants engaged in a variety of summarizing activities three days each week in religion class. Fifteen eighth grade girls from an urban, all-girls, Catholic school in a Midwestern city participated in the study. The researcher used oral and written summaries as well as objective quizzes and exams for pre- and posttests. In addition, the researcher monitored the studentsâ progress by collecting the studentsâ notes and written summary paragraphs. Results indicated that the study had a positive impact on the studentsâ ability to comprehend and retain information from the religion textbook. The study did not impact studentsâ ability to recognize main ideas and write summaries
Results of a partial cycloplegic on the visual system
Results of a partial cycloplegic on the visual syste
Foulingverhalten einer kommunalen MBR-Anlage
Angesichts steigender Anforderungen an die AblaufqualitĂ€t, der Notwendigkeit der Ab-wasserwiederverwendung und des eingeschrĂ€nkten Platzangebotes im urbanen Raum, gilt das MBR-Verfahren als SchlĂŒsseltechnologie fĂŒr die zukĂŒnftige Abwasser-behandlung. Die Vorteile des MBR-Verfahrens gehen allerdings einher mit höheren Investitions- und Betriebskosten und einer höheren Herausforderung an den Betrieb durch sogenanntes Membranfouling und chemische Reinigungen. FĂŒr einen wirtschaft-lichen und prozessstabilen Betrieb von MBR-Anlagen ist es unerlĂ€sslich, die chemische Membranreinigung zu optimieren, die Energieeffizienz von Membrananlagen zu steigern und Ursachen und Vermeidungsstrategien von Membranfouling aufzuzeigen.
Bei der gröĂten MBR-Anlage Bayerns (21.000 EW) traten ganzjĂ€hrig â besonders aus-geprĂ€gt aber in den Wintermonaten â hydraulische LeistungseinbrĂŒche auf, die eine erhöhte ReinigungshĂ€ufigkeit verursachten. Dieses ungewöhnliche Foulingverhalten gab viele RĂ€tsel auf und fĂŒhrte zu einer umfangreichen wissenschaftlichen Begleitung des Anlagenbetriebs ĂŒber einen Zeitraum von gut 10 Jahren.
ZunĂ€chst wurden die Bemessungs-, Betriebs- und Leistungsdaten der Anlage sowie die Langzeiterfahrungen der chemischen Reinigungen grundlegend ausgewertet. Die chemischen Reinigungen fĂŒhrten zu einer anlagenspezifisch optimierten Reinigungs-strategie und zu neuen Erkenntnissen ĂŒber die Auswirkung der Chemikalienexposition auf die Membranalterung. In 7,5 Betriebsjahren waren die Membranen einer unge-wöhnlich hohen Cl/H2O2-Exposition von bis zu 1,22 Mio ppmh ausgesetzt. Die Alterung der Membran Ă€uĂerte sich durch eine offenere Struktur, was sich an einem höheren Reinwasserfluss als auch an einer geringeren RĂŒckhalteleistung deutlich machte. In der Praxis war ein PermeabilitĂ€tsrĂŒckgang von 30 % zu verzeichnen.
BezĂŒglich Fouling konnten Membran- bzw. Moduleigenschaften, die gĂ€ngigen Pro-zessparameter der biologischen Stufe und konkrete Verdachtssubstanzen als Ursache ausgeschlossen werden. Ein negativer Einfluss von Industrieeinleitern erwies sich ebenfalls als unwahrscheinlich. Belagsanalysen identifizierten den typischen, gelartigen Membranbelag als Biofouling, so dass die Ursachen hauptsĂ€chlich in einer Beein-trĂ€chtigung des biologischen Prozesses zu suchen waren. Einen signifikanten Einfluss auf die PermeabilitĂ€t wiesen vor allem Mischwasserereignisse auf, insbesondere Schneeschmelze, und stark wechselnde Schlammbelastungen. Die PermeabilitĂ€tsent-wicklung zeigte einen deutlichen Zusammenhang mit der Schlammfiltrierbarkeit (SFI) und dem Auftreten von organischen Substanzen (SMP) in der Klarwasserphase der Belebung. Die Temperatur war nicht direkt ursĂ€chlich fĂŒr die Entwicklung von SFI, SMP und PermeabilitĂ€t, ihr ist aber eine stark beeintrĂ€chtigende Wirkung auf den belebten Schlamm und dessen RegenerationsfĂ€higkeit zuzuschreiben. Mehrere Indizien legten ein ungĂŒnstiges KationenverhĂ€ltnis des Belebtschlamms und Streusalz als Ursache fĂŒr die LeistungseinbrĂŒche nahe. Laboruntersuchungen belegten die grundlegende BeeintrĂ€chtigung der Belebtschlammbeschaffenheit und -aktivitĂ€t durch Salz in AbhĂ€ngigkeit von deren M/D-VerhĂ€ltnisses. Als GegenmaĂnahme zeigte eine Ca-Konditionierung der Belebung der groĂtechnischen Anlage einen stabilisierenden Effekt und erwies sich als empfehlenswerte Strategie, um die Salztoleranz des Belebtschlamms zu steigern. Durch die KomplexitĂ€t der Foulingproblematik lieĂen sich weitere PermeabilitĂ€tseinbrĂŒche aber nicht vermeiden.
Die Erweiterung der AnlagenkapazitĂ€t um ein zusĂ€tzliches Membranmodul stabilisierte schlieĂlich den Anlagenbetrieb und reduzierte die Auswirkungen des Membranfoulings und die ReinigungshĂ€ufigkeit. Bei dem neuen Modul handelte es sich um ein rotieren-des Membransystem in Kombination mit einem rĂŒckspĂŒlbaren Flachmembranlaminat, das eine innovative Weiterentwicklung gĂ€ngiger Plattenmodule darstellte. Untersu-chungen zu dessen Reinigungsstrategie und Energieeffizienz belegten einen SAD von weniger als 0,1 NmÂł/(mÂČ*h), was 50 % unterhalb gĂ€ngiger Literaturwerte anderer MBR-Module liegt. Diese neue Modulgeneration lĂ€sst einen Mehr-Energieverbrauch eines MBRs gegenĂŒber einer konventionellen KlĂ€ranlage von nur noch 0,13 kWh/mÂł erwar-ten.
Bislang erfolgte die Bemessung der erforderlichen MembranflĂ€che von kommunalen MBR-Anlagen unter BerĂŒcksichtigung der minimalen Abwassertemperatur in Kombina-tion mit der hydraulischen Zulaufsituation. Die zu erwartende Belebtschlammbeschaf-fenheit bzw. das Foulingpotenzial des Belebtschlamms wird bei der Planung bisher nicht beachtet. Die Erkenntnisse dieser Arbeit zeigen, dass neben der Höhe auch die HĂ€ufigkeit, Dauer und Schwankungsbreite der hydraulischen Zulaufsituation, kritische Zulauf- und Betriebsbedingungen fĂŒr die Biologie und das Foulingpotenzial von Be-lebtschlamm in Form einer schlechten Schlammfiltrierbarkeit und organischer Substan-zen im KlarwasserĂŒberstand mit einem entsprechenden Sicherheitsfaktor fĂŒr die Be-messungsfluxrate zu berĂŒcksichtigen sind
Hydrate-phobic surfaces: fundamental studies in clathrate hydrate adhesion reduction
Clathrate hydrate formation and subsequent plugging of deep-sea oil and gas pipelines represent a significant bottleneck for deep-sea oil and gas operations. Current methods for hydrate mitigation are expensive and energy intensive, comprising chemical, thermal, or flow management techniques. In this paper, we present an alternate approach of using functionalized coatings to reduce hydrate adhesion to surfaces, ideally to a low enough level that hydrodynamic shear stresses can detach deposits and prevent plug formation. Systematic and quantitative studies of hydrate adhesion on smooth substrates with varying solid surface energies reveal a linear trend between hydrate adhesion strength and the practical work of adhesion (γ[superscript total][1 + cos Ξ[subscript rec]]) of a suitable probe liquid, that is, one with similar surface energy properties to those of the hydrate. A reduction in hydrate adhesion strength by more than a factor of four when compared to bare steel is achieved on surfaces characterized by low Lewis acid, Lewis base, and van der Waals contributions to surface free energy such that the practical work of adhesion is minimized. These fundamental studies provide a framework for the development of hydrate-phobic surfaces, and could lead to passive enhancement of flow assurance and prevention of blockages in deep-sea oil and gas operations.Massachusetts Institute of Technology. Energy Initiative (Chevron Corporation)Massachusetts Institute of Technology. Dept. of Mechanical EngineeringNational Research Council (U.S.) (Postdoctoral Fellowship
Designing Durable Vapor-Deposited Surfaces for Reduced Hydrate Adhesion
The formation and accumulation of clathrate hydrates inside oil and gas pipelines cause severe problems in deep-sea oil/gas operations. In the present work, durable and mechanically robust bilayer poly-divinyl benzene/poly(perfluorodecylacrylate) coatings are developed using initiated chemical vapor deposition (iCVD) to reduce the adhesion strength of hydrates to underlying substrates (silicon and steel). Tetrahydrofuran (THF) dissolved in water with a wt% concentration of 0â70 is used to study the formation of hydrates and their adhesion strength. Goniometric measurements of the THFâwater droplets on the substrates exhibit a reduction in advancing and receding contact angles with an increase in the THF concentration. The strength of hydrate adhesion experiences a tenfold reduction when substrates are coated with these iCVD polymers: from 1050 ± 250 kPa on bare silicon to 128 ± 100 kPa on coated silicon and from 1130 ± 185 kPa on bare steel to 153 ± 86 kPa on coated steel. The impact of subcooling temperature and time on the adhesion strength of hydrate on substrates is also studied. The results of this work suggest that the THFâwater mixture repellency of a given substrate can be utilized to assess its hydrate-phobic behavior; hence, it opens a pathway for studying hydrate-phobicity.Chevron Corporation (MIT-Chevron University Partnership Program
The solution of the puzzle of smectic-Q: The phase structure and the origin of spontaneous chirality
The so-called smectic-Q (SmQ) liquid crystal phase was discovered in 1983 in rod-like molecules, but its structure remain unclear in spite of numerous attempts to solve it. Herein, we report what we believe to be the solution: A unique bicontinuous phase that is non-cubic and is made up of orthogonal twisted columns with planar 4-way junctions. While SmQ had only been observed in chiral compounds, we show that this chiral phase forms also in achiral materials through spontaneous symmetry breaking. The results strongly support the idea of a helical substructure of bicontinuous phases and long-range homochirality being sustained by helicity-matching at network junctions. The model also explains the triangular shape of double-gyroid domains growing within a SmQ environment. SmQ-forming materials hold potential for applications such as circularly polarized light emitters that require no alignment or asymmetric synthesis
Wettability-independent bouncing on flat surfaces mediated by thin air films
The impingement of drops onto solid surfaces1, 2 plays a crucial role in a variety of processes, including inkjet printing, fog harvesting, anti-icing, dropwise condensation and spray coating3, 4, 5, 6. Recent efforts in understanding and controlling drop impact behaviour focused on superhydrophobic surfaces with specific surface structures enabling drop bouncing with reduced contact time7, 8. Here, we report a different universal bouncing mechanism that occurs on both wetting and non-wetting flat surfaces for both high and low surface tension liquids. Using high-speed multiple-wavelength interferometry9, we show that this bouncing mechanism is based on the continuous presence of an air film for moderate drop impact velocities. This submicrometre âair cushionâ slows down the incoming drop and reverses its momentum. Viscous forces in the air film play a key role in this process: they provide transient stability of the air cushion against squeeze-out, mediate momentum transfer, and contribute a substantial part of the energy dissipation during bouncing
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Polydispersity effects in poly(isoprene-b-styrene-b-ethylene oxide) triblock terpolymers
At time of publication all authors were at the University of Minnesota. Christopher Ellison is currently Asst. Professor at the University of Texas at Austin.Four hydroxyl-terminated poly (isoprene-b-styrene) diblock copolymers with comparable molecular
weights and compositions (equivalent volume fractions of polyisoprene and polystyrene) but
different polystyrene block polydispersity indices (Mw/Mn=1.06, 1.16, 1.31, 1.44) were synthesized
by anionic polymerization using either sec-butyllithium or the functional organolithium
3-triisopropylsilyloxy-1-propyllithium. Poly (ethylene oxide) (PEO) blocks were grown from the
end of each of these parent diblocks to yield four series of poly(isoprene-b-styrene-b-ethylene
oxide) (ISO) triblock terpolymers that were used to interrogate the effects of varying the
polydispersity of the middle bridged polystyrene block. In addition to the neat triblock samples, 13
multicomponent blends were prepared at four different compositions from the ISO materials
containing a polystyrene segment with Mw/Mn=1.06; these blends were used to probe the effects of
increasing the polydispersity of the terminal PEO block. The melt-phase behavior of all samples was
characterized using small-angle X-ray scattering and dynamic mechanical spectroscopy. Numerous
polydispersity-driven morphological transitions are reported, including transitions from lamellae to
core-shell gyroid, from core-shell gyroid to hexagonally packed cylinders, and from network
morphologies [either O70 (the orthorhombic Fddd network) or core-shell gyroid] to lamellae.
Domain periodicities and order-disorder transition temperatures also vary with block
polydispersities. Self-consistent field theory calculations were performed to supplement the
experimental investigations and help elucidate the molecular factors underlying the polydispersity
effects. The consequences of varying the polydispersity of the terminal PEO block are comparable
to the polydispersity effects previously reported in AB diblock copolymers. Namely, domain
periodicities increase with increasing polydispersity and domain interfaces tend to curve toward
polydisperse blocks. The changes in phase behavior that are associated with variations in the
polydispersity of the middle bridged polystyrene block, however, are not analogous to those
reported in AB diblock copolymers, as increases in this middle block polydispersity are not always
accompanied by (i) increased domain periodicities and (ii) a tendency for domain interfaces to curve
toward the polydisperse domain. These results highlight the utility of polydispersity as a tool to tune
the phase behavior of ABC block terpolymers.Chemical Engineerin
Investigations Into Accumulator 4-8 GHz Pickup Loop / Combiner Board Performance
A set of pickup measurements performed in August of 1999 (see Pbar note 618) indicated problems with the pickup sensitivity for frequencies above {approx}4.8 GHz. This note describes the effort made to determine if the problems with system performance were due to the design of the 4-8 GHz circuit board
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