4,240 research outputs found
Invariance of Structure in an Aging Colloidal Glass
We study concentrated colloidal suspensions, a model system which has a glass
transition. The non-equilibrium nature of the glassy state is most clearly
highlighted by aging -- the dependence of the system's properties on the time
elapsed since vitrification. Fast laser scanning confocal microscopy allows us
to image a colloidal glass and track the particles in three dimensions. We
analyze the static structure in terms of tetrahedral packing. We find that
while the aging of the suspension clearly affects its dynamics, none of the
geometrical quantities associated with tetrahedra change with age.Comment: Submitted to the proceedings of "The 3rd International Workshop on
Complex Systems" in Sendai, Japa
Properties of cage rearrangements observed near the colloidal glass transition
We use confocal microscopy to study the motions of particles in concentrated
colloidal systems. Near the glass transition, diffusive motion is inhibited, as
particles spend time trapped in transient ``cages'' formed by neighboring
particles. We measure the cage sizes and lifetimes, which respectively shrink
and grow as the glass transition approaches. Cage rearrangements are more
prevalent in regions with lower local concentrations and higher disorder.
Neighboring rearranging particles typically move in parallel directions,
although a nontrivial fraction move in anti-parallel directions, usually from
pairs of particles with initial separations corresponding to the local maxima
and minima of the pair correlation function , respectively.Comment: 5 pages, 4 figures; text & figures revised in v
Density fluctuations and the structure of a nonuniform hard sphere fluid
We derive an exact equation for density changes induced by a general external
field that corrects the hydrostatic approximation where the local value of the
field is adsorbed into a modified chemical potential. Using linear response
theory to relate density changes self-consistently in different regions of
space, we arrive at an integral equation for a hard sphere fluid that is exact
in the limit of a slowly varying field or at low density and reduces to the
accurate Percus-Yevick equation for a hard core field. This and related
equations give accurate results for a wide variety of fields
The equilibrium intrinsic crystal-liquid interface of colloids
We use confocal microscopy to study an equilibrated crystal-liquid interface
in a colloidal suspension. Capillary waves roughen the surface, but locally the
intrinsic interface is sharply defined. We use local measurements of the
structure and dynamics to characterize the intrinsic interface, and different
measurements find slightly different widths of this interface. In terms of the
particle diameter , this width is either (based on structural
information) or (based on dynamics), both not much larger than the
particle size. This work is the first direct experimental visualization of an
equilibrated crystal-liquid interface.Comment: 6 pages; revised version, submitted to PNA
The pair annihilation reaction D + D --> 0 in disordered media and conformal invariance
The raise and peel model describes the stochastic model of a fluctuating
interface separating a substrate covered with clusters of matter of different
sizes, and a rarefied gas of tiles. The stationary state is obtained when
adsorption compensates the desorption of tiles. This model is generalized to an
interface with defects (D). The defects are either adjacent or separated by a
cluster. If a tile hits the end of a cluster with a defect nearby, the defect
hops at the other end of the cluster changing its shape. If a tile hits two
adjacent defects, the defect annihilate and are replaced by a small cluster.
There are no defects in the stationary state.
This model can be seen as describing the reaction D + D -->0, in which the
particles (defects) D hop at long distances changing the medium and annihilate.
Between the hops the medium also changes (tiles hit clusters changing their
shapes). Several properties of this model are presented and some exact results
are obtained using the connection of our model with a conformal invariant
quantum chain.Comment: 8 pages, 12figure
Exact Polynomial Eigenmodes for Homogeneous Spherical 3-Manifolds
Observational data hints at a finite universe, with spherical manifolds such
as the Poincare dodecahedral space tentatively providing the best fit.
Simulating the physics of a model universe requires knowing the eigenmodes of
the Laplace operator on the space. The present article provides explicit
polynomial eigenmodes for all globally homogeneous 3-manifolds: the Poincare
dodecahedral space S3/I*, the binary octahedral space S3/O*, the binary
tetrahedral space S3/T*, the prism manifolds S3/D_m* and the lens spaces
L(p,1).Comment: v3. Final published version. 27 pages, 1 figur
Correlations of Structure and Dynamics in an Aging Colloidal Glass
We study concentrated colloidal suspensions, a model system which has a glass
transition. Samples in the glassy state show aging, in that the motion of the
colloidal particles slows as the sample ages from an initial state. We study
the relationship between the static structure and the slowing dynamics, using
confocal microscopy to follow the three-dimensional motion of the particles.
The structure is quantified by considering tetrahedra formed by quadruplets of
neighboring particles. We find that while the sample clearly slows down during
aging, the static properties as measured by tetrahedral quantities do not vary.
However, a weak correlation between tetrahedron shape and mobility is observed,
suggesting that the structure facilitates the motion responsible for the sample
aging.Comment: Submitted to Solid State Communication
The Responsiveness, Content Validity, and Convergent Validity of the Measure Yourself Concerns and Wellbeing (MYCaW) Patient-Reported Outcome Measure
Objective
Measure Yourself Concerns and Wellbeing (MYCaW) is a patient-centred questionnaire that allows cancer patients to identify and quantify the severity of their ‘Concerns’ and Wellbeing, as opposed to using a pre-determined list. MYCaW administration is brief and aids in prioritising treatment approaches. Our goal was to assess the convergent validity and responsiveness of MYCaW scores over time, the generalisability of the existing qualitative coding framework in different complementary and integrative healthcare settings and content validity.
Methods
Baseline and 6-week follow-up data (n=82) from MYCaW and FACIT-SpEx questionnaires were collected for a service evaluation of the ‘Living Well With The Impact of Cancer’ course at Penny Brohn Cancer Care. MYCaW construct validity was determined using Spearman's Rank Correlation test, and responsiveness indices assessed score changes over time. The existing qualitative coding framework was reviewed using a new dataset (n=158) and coverage of concern categories compared to items of existing outcome measures.
Results
Good correlation between MYCaW and FACIT-SpEx score changes were achieved (r= -0.57, p≥0.01). MYCaW Profile and Concern scores were highly responsive to change: SRM=1.02 and 1.08; effect size=1.26 and 1.22. MYCaW change scores showed the anticipated gradient of change according to clinically relevant degrees of change. Categories including ‘Spirituality’, ‘weight change’ and ‘practical concerns’ were added to the coding framework to improve generalisability.
Conclusions
MYCaW scores were highly responsive to change, allowing personalized patient outcomes to be quantified; the qualitative coding framework is generalisable across different oncology settings and has broader coverage of patient-identified concerns compared with existing cancer-related patient-reported outcome measures
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