1,224 research outputs found
Assembly, Elasticity, And Structure Of Lyotropic Chromonic Liquid Crystals And Disordered Colloids
This dissertation describes experiments which explore the structure and dynamics in two classes of soft materials: lyotropic chromonic liquid crystals and colloidal glasses and super-cooled liquids.
The first experiments found that the achiral LCLCs, sunset yellow FCF (SSY) and disodium cromoglycate (DSCG) both exhibit spontaneous mirror symmetry breaking in the nematic phase driven by a giant elastic anisotropy of their twist modulus compared to their splay and bend moduli. Resulting structures of the confined LCLCs display interesting director configurations due to interplay of topologically required defects and twisted director fields. At higher concentrations, the LCLC compounds form columnar phases. We studied the columnar phase confined within spherical drops and discovered and understood configurations of the LC that sometimes led to non-spherical droplet shapes. The second experiments with SSY LCLCs confined in hollow cylinders uncovered director configurations which were driven in large measure by an exotic elastic modulus known as saddle-splay. We measured this saddle-splay modulus in a LCLC for the first time and found it to be more than 50 times greater than the twist elastic modulus. This large relative value of the saddle-splay modulus violates a theoretical result/assumption known as the Ericksen inequality.
A third group of experiments on LCLCs explored the drying process of sessile drops containing SSY solutions, including evaporation dynamics, morphology, and deposition patterns. These drops differ from typical, well-studied evaporating colloidal drops primarily due to the LCLC\u27s concentration-dependent isotropic, nematic, and columnar phases. Phase separation occurs during evaporation, creating surface tension gradients and significant density and viscosity variation within the droplet. Thus, the drying multiphase drops exhibit new convective currents, drop morphologies, deposition patterns, as well as a novel ordered crystalline phase.
Finally, experiments in colloidal glasses and super-cooled liquids were initiated to probe the relationship between structure and dynamics in their constituent particles. The displacements of individual particles in the colloids can be decomposed into small cage fluctuations and large rearrangements into new cages. We found a correlation between the rate of rearrangement and the local cage structure associated with each particle. Particle trajectories of a two-dimensional binary mixture of soft colloids are captured by video microscopy. We use a machine learning method to calculate particle ``softness\u27\u27, which indicates the likelihood of rearrangement based on many radial structural features for each particle. We measured the residence time between consecutive rearrangements and related probability distribution functions (PDFs). The softness-dependent conditional PDF is well fit by an exponential with decay time decreasing monotonically with increasing softness. Using these data and a simple thermal activation model, we determined activation energies for rearrangements
Tungsten diboride for high energy nuclear applications
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On some fundamental results about higher-rank graphs and their C*-algebras
Results of Fowler and Sims show that every k-graph is completely determined
by its k-coloured skeleton and collection of commuting squares. Here we give an
explicit description of the k-graph associated to a given skeleton and
collection of squares and show that two k-graphs are isomorphic if and only if
there is an isomorphism of their skeletons which preserves commuting squares.
We use this to prove directly that each k-graph {\Lambda} is isomorphic to the
quotient of the path category of its skeleton by the equivalence relation
determined by the commuting squares, and show that this extends to a
homeomorphism of infinite-path spaces when the k-graph is row finite with no
sources. We conclude with a short direct proof of the characterisation,
originally due to Robertson and Sims, of simplicity of the C*-algebra of a
row-finite k-graph with no sources.Comment: 21 pages, two pictures prepared using TiK
Between the crowd and the band: Performance experience, creative practice, and wellbeing for professional touring musicians
In some musical genres, professional performers play live shows many times a week. Arduous touring schedules bring encounters with wildly diverse audiences across many different performance ecologies. We investigate the kinds of creativity involved in such repeated live performance, kinds of creativity that are quite unlike songwriting and recording, and examine the central factors that influence musiciansâ wellbeing over the course of a tour. The perspective of the professional musician has been underrepresented in research on relations between music and wellbeing, with little attention given to the experience of touring. In this case study, we investigate influences on positive and negative performance experiences for the four professional musicians of Australian pop/rock band Cloud Control. Geeves conducted intensive cognitive ethnographic fieldwork with Cloud Control members over a two-week national Australian tour for their second album, Dream Cave (2013). Adapting a Grounded Theory approach to data analysis, we found the level of wellbeing musicians reported and displayed on tour to be intimately linked to their creative performance experiences through the two emergent, overarching and interdependent themes of Performance Headspace (PH) and Connection with Audience (CA). We explore these themes in detail and provide examples to demonstrate how PH and CA can feed off each other in virtuous ways that positively shape musiciansâ wellbeing, or loop in vicious ways that negatively shape musiciansâ wellbeing. We argue that their creative practice, in thus re-enacting musical performance afresh in each venueâs distinctive setting, emerges within unique constraints each night, and is in a sense a co-creation of the crowd and the band
Overlapping jurisdiction between admiralty and insolvency law: an evaluation and comparison of the South African and English legal approaches?
Includes bibliographical references
Filling Conversation Ellipsis for Better Social Dialog Understanding
The phenomenon of ellipsis is prevalent in social conversations. Ellipsis
increases the difficulty of a series of downstream language understanding
tasks, such as dialog act prediction and semantic role labeling. We propose to
resolve ellipsis through automatic sentence completion to improve language
understanding. However, automatic ellipsis completion can result in output
which does not accurately reflect user intent. To address this issue, we
propose a method which considers both the original utterance that has ellipsis
and the automatically completed utterance in dialog act and semantic role
labeling tasks. Specifically, we first complete user utterances to resolve
ellipsis using an end-to-end pointer network model. We then train a prediction
model using both utterances containing ellipsis and our automatically completed
utterances. Finally, we combine the prediction results from these two
utterances using a selection model that is guided by expert knowledge. Our
approach improves dialog act prediction and semantic role labeling by 1.3% and
2.5% in F1 score respectively in social conversations. We also present an
open-domain human-machine conversation dataset with manually completed user
utterances and annotated semantic role labeling after manual completion.Comment: Accepted to AAAI 202
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