5,800 research outputs found
A Rule-Based Consultant for Accelerator Beam Scheduling Used in the CERN PS Complex
No full textThe CERN PS accelerator complex consists of nine interacting accelerators which work together to produce
particle beams for different end users, varying in particle type, energy, time structure, and geometry. The beam
production schedule is time sliced and depends on the current operational requirements and dynamically on the
accelerator status, so that production schedule changes occur in real time. Many potential schedules are not valid due
to various system constraints and these constraints vary over time as new operational modes are introduced. In order
to ensure that only valid schedules are given to the complex, an automated tool has been developed to indicate
whether a potential schedule is valid or not. This presentation describes the method by which the validity of a beam
schedule is determined and how this method was implemented using a rule-based approach based on SQL, avoiding
the use of an expert system shell. Both the data to instantiate the rules and the rules themselves are kept in an Oracle
data base. The SQL interpreter provides the inference engine for this knowledge-based system. A few examples are
presented and the running experience with the tool is discussed
Lewis Hairston
No full textPhotograph of Lewis "Big Sweet" Hairston playing his banjo in his home. He was born in McDowell County, West Virginia, and moved to Henry county, Virginia in 1955
Wavelength tunable 10-GHz 3-ps pulse source using a dispersion decreasing fiber-based nonlinear optical loop mirror
No full textWe experimentally demonstrate the use of a dispersion decreasing fiber (DDF)-based nonlinear optical loop mirror (NOLM) for the generation of wavelength tunable soliton-like pulses at a repetition rate of 10 GHz. We compress ~12 ps Gaussian pulses from an electro-absorption modulator (EAM) (followed by 125 m of DCF for preliminary linear dispersion compensation) into 3 ps pedestal-free pulses using both high-order soliton compression and nonlinear switching effects within an 8.5 km DDF-based loop mirror. The output pulses from the DDF-based NOLM show considerable pedestal reduction compared to those obtained by directly compressing the EAM seed pulses via a single passage through the DDF. Wavelength tuning of the compressed pulses over a ~15 nm bandwidth (from 1541 to 1556 nm) is demonstrated without a significant increase in pulse duration or degradation in pulse quality
Well-Defined Boron-Containing Polymeric Lewis Acids
No full textA general new route to well-defined polymeric Lewis acids via borylation of silylated polymers is reported. Trimethylsilylated polystyrene (PS-Si) of controlled molecular weight and low polydispersity (PDI PS-Si was quantitatively borylated using BBr3 to give poly(4-dibromoborylstyrene) (PS-B), a novel soluble boron-containing polymeric Lewis acid. PS-B readily reacted with nucleophiles serving as a precursor to a family of new polymers with boron centers of variable Lewis acidity. Reaction of PS-B with Cu(C6F5) gave the highly Lewis acidic polymer poly[4-bis(pentafluorophenyl)borylstyrene], the first polymeric analogue of tris(pentafluorophenyl)borane
Player agency in interactive narrative: audience, actor & author
No full textThe question motivating this review paper is, how can
computer-based interactive narrative be used as a constructivist learn-
ing activity? The paper proposes that player agency can be used to
link interactive narrative to learner agency in constructivist theory,
and to classify approaches to interactive narrative. The traditional
question driving research in interactive narrative is, ‘how can an in-
teractive narrative deal with a high degree of player agency, while
maintaining a coherent and well-formed narrative?’ This question
derives from an Aristotelian approach to interactive narrative that,
as the question shows, is inherently antagonistic to player agency.
Within this approach, player agency must be restricted and manip-
ulated to maintain the narrative. Two alternative approaches based
on Brecht’s Epic Theatre and Boal’s Theatre of the Oppressed are
reviewed. If a Boalian approach to interactive narrative is taken the
conflict between narrative and player agency dissolves. The question
that emerges from this approach is quite different from the traditional
question above, and presents a more useful approach to applying in-
teractive narrative as a constructivist learning activity
Trioxatriangulenium (TOTA+) as a Robust Carbon-based Lewis Acid in Frustrated Lewis Pair Chemistry
No full textWe report the reactivity between the Lewis acidic trioxatriangulenium ion (TOTA+) and a series of Lewis bases such as phosphines and N-heterocyclic carbene (NHC). The nature of the Lewis acid-base interaction was analyzed via variable temperature (VT) NMR spectroscopy, single-crystal X-ray diffraction, UV-visible spectroscopy, and DFT calculations. While small and strongly nucleophilic phosphines, such as PMe3, led to the formation of a stable Lewis acid-base adduct, frustrated Lewis pairs (FLPs) were observed for sterically hindered bases such as P(tBu)3. The TOTA+-P(tBu)3 FLP was characterized as an encounter complex, and was found to promote the heterolytic cleavage of disulfide bonds, formaldehyde fixation, dehydrogenation of 1,4-cyclohexadiene, heterolytic cleavage of C–Br bond, and interception of Staudinger reaction intermediate. Moreover, TOTA+ and NHC was found to first undergo single-electron transfer (SET) to form [TOTA]•[NHC] •+, which was confirmed via electron paramagnetic resonance (EPR) spectroscopy, and subsequently form a [TOTA-NHC]+ adduct or a mixture of products depending the reaction condition used
Polysiloxane/Polystyrene Thermo-Responsive and Self-Healing Polymer Network via Lewis Acid-Lewis Base Pair Formation
No full textThe use of thermo-reversible Lewis Pair (LP) interactions in the formation of transient polymer networks is still greatly underexplored. In this work, we describe the synthesis and characterization of polydimethylsiloxane/polystyrene (PDMS/PS) blends that form dynamic Lewis acid-Lewis base adducts resulting in reversible crosslinks. Linear PS containing 10 mol % of di-2-thienylboryl pendant groups randomly distributed was obtained in a two-step one-pot functionalization reaction from silyl-functionalized PS, while ditelechelic PDMS with pyridyl groups at the chain-termini was directly obtained via thiol-ene “click” chemistry from commercially available vinyl-terminated PDMS. The resulting soft gels, formed after mixing solutions containing the PDMS and PS polymers, behave at room temperature as elastomeric solid-like materials with very high viscosity (47,300 Pa·s). We applied rheological measurements to study the thermal and time dependence of the viscoelastic moduli, and also assessed the reprocessability and self-healing behavior of the dry gel
200W gain-switched-diode-seeded single-polarization narrow linewidth all-fiber picosecond MOPA
No full textWe report a fully fiberized, single-polarization, gain-switched, diode-seeded fiber MOPA delivering 28ps pulses at a repetition frequency of 214MHz with 200W of average output power and up to 0.93µJ pulse energy
Lewis Pairs as Highly Tunable Dynamic Cross-Links in Transient Polymer Networks
No full textClassical
Lewis pairs (LPs) between unhindered electron-poor Lewis
acids (LAs) and electron-rich Lewis bases (LBs) present an overlooked
motif with tremendous potential as dynamic cross-links in transient
polymer networks (TPNs) for self-healing and stimuli-responsive applications.
We demonstrate that simple and intuitive matching of weak/strong organoborane
LA and amine LB pairs offers access to a large set of binding equilibrium
constants, Keq, that span ∼6 orders
and dissociation rate constants, kdiss, that span ∼7 orders of magnitude. The implementation in
polystyrene (PS)/polydimethylsiloxane (PDMS) blends results in dynamically
cross-linked networks with bulk thermomechanical properties that are
directly correlated with the strength and kinetic parameters for the
LP interactions. The LP dynamic cross-link design is highly versatile
and broadly applicable to different polymer architectures as demonstrated
in the formation of reprocessable elastomers from Lewis base-decorated
high molecular weight PDMS in combination with Lewis acid-decorated
PS when reinforced with fumed silica as a filler
Lewis Pairs as Highly Tunable Dynamic Cross-Links in Transient Polymer Networks
No full textClassical
Lewis pairs (LPs) between unhindered electron-poor Lewis
acids (LAs) and electron-rich Lewis bases (LBs) present an overlooked
motif with tremendous potential as dynamic cross-links in transient
polymer networks (TPNs) for self-healing and stimuli-responsive applications.
We demonstrate that simple and intuitive matching of weak/strong organoborane
LA and amine LB pairs offers access to a large set of binding equilibrium
constants, Keq, that span ∼6 orders
and dissociation rate constants, kdiss, that span ∼7 orders of magnitude. The implementation in
polystyrene (PS)/polydimethylsiloxane (PDMS) blends results in dynamically
cross-linked networks with bulk thermomechanical properties that are
directly correlated with the strength and kinetic parameters for the
LP interactions. The LP dynamic cross-link design is highly versatile
and broadly applicable to different polymer architectures as demonstrated
in the formation of reprocessable elastomers from Lewis base-decorated
high molecular weight PDMS in combination with Lewis acid-decorated
PS when reinforced with fumed silica as a filler
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