We use dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres. Our study covers an ...unprecedented density range and spans seven decades in structural relaxation time, tau(alpha0, including equilibrium measurements above phi(c), the location of the glass transition deduced from fitting our data to mode-coupling theory. Instead of falling out of equilibrium, the system remains ergodic above phi(c) and enters a new dynamical regime where tau(alpha) increases with a functional form that was not anticipated by previous experiments, while the amplitude of dynamic heterogeneity grows slower than a power law with tau(alpha), as found in molecular glass formers close to the glass transition.
We use a standard Monte Carlo algorithm to study the slow dynamics of a binary Lennard-Jones glass-forming mixture at low temperature. We find that the Monte Carlo approach is by far the most ...efficient way to simulate a stochastic dynamics since the relaxation is about 10 times faster than in Brownian dynamics and about 30 times faster than in stochastic dynamics. Moreover, the average dynamical behaviour of the system is in quantitative agreement with that obtained using Newtonian dynamics, apart from at very short times where thermal vibrations are suppressed. We show, however, that dynamic fluctuations quantified by four-point dynamic susceptibilities do retain a dependence on the microscopic dynamics, as recently predicted theoretically.
Amorphous solids lack long-range order. Therefore identifying structural defects -- akin to dislocations in crystalline solids -- that carry plastic flow in these systems remains a daunting ...challenge. By comparing many different structural indicators in computational models of glasses, under a variety of conditions we carefully assess which of these indicators are able to robustly identify the structural defects responsible for plastic flow in amorphous solids. We further demonstrate that the density of defects changes as a function of material preparation and strain in a manner that is highly correlated with the macroscopic material response. Our work represents an important step towards predicting how and when an amorphous solid will fail from its microscopic structure.
Aphasia, the loss or impairment of language caused by brain damage, is one of the most devastating cognitive impairments of stroke. Aphasia is present in 21-38% of acute stroke patients and is ...associated with high short- and long-term morbidity, mortality and expenditure. Recovery from aphasia is possible even in severe cases. While speech-language therapy remains the mainstay treatment of aphasia, the effectiveness of conventional therapies has not been conclusively proved. This has motivated attempts to integrate knowledge from several domains in an effort to plan more rational therapies and to introduce other therapeutic strategies, including the use of intensive language therapy and pharmacological agents. Several placebo-controlled trials suggest that piracetam is effective in recovery from aphasia when started soon after the stroke, but its efficacy vanishes in patients with chronic aphasia. Drugs acting on catecholamine systems (bromocriptine, dexamfetamine) have shown varying degrees of efficacy in case series, open-label studies and placebo-controlled trials. Bromocriptine is useful in acute and chronic aphasias, but its beneficial action appears restricted to nonfluent aphasias with reduced initiation of spontaneous verbal messages. Dexamfetamine improves language function in subacute aphasia and the beneficial effect is maintained in the long term, but its use is restricted to highly selected samples. Pharmacological agents operating on the cholinergic system (e.g. donepezil) have shown promise. Data from single-case studies, case series and an open-label study suggest that donepezil may have beneficial effects on chronic poststroke aphasia. Preliminary evidence suggests that donepezil is well tolerated and its efficacy is maintained in the long term. Randomised controlled trials of donepezil and other cholinergic agents in poststroke aphasia are warranted.
Understanding glass formation is a challenge, because the existence of a true glass state, distinct from liquid and solid, remains elusive: Glasses are liquids that have become too viscous to flow. ...An old idea, as yet unproven experimentally, is that the dynamics becomes sluggish as the glass transition approaches, because increasingly larger regions of the material have to move simultaneously to allow flow. We introduce new multipoint dynamical susceptibilities to estimate quantitatively the size of these regions and provide direct experimental evidence that the glass formation of molecular liquids and colloidal suspensions is accompanied by growing dynamic correlation length scales.
The encapsulation of photolabile 2‐oxoacetates in core–shell microcapsules allows the light‐induced, controlled release of bioactive compounds. On irradiation with UVA light these compounds degrade ...to generate an overpressure of gas inside the capsules, which expands or breaks the capsule wall. Headspace measurements confirmed the light‐induced formation of CO and CO2 and the successful release of the bioactive compound, while optical microscopy demonstrated the formation of gas bubbles, the cleavage of the capsule wall, and the leakage of the oil phase out of the capsule. The efficiency of the delivery system depends on the structure of the 2‐oxoacetate, the quantity used with respect to the thickness of the capsule wall, and the intensity of the irradiating UVA light.
A burst of aroma: Bioactive compounds, such as fragrances, can be efficiently released from core–shell microcapsules by the light‐induced decomposition of encapsulated 2‐oxoacetates, generating an overpressure of gas that expands or even breaks the capsule wall.
We assess the validity of “microscopic” approaches of glass-forming liquids based on the sole knowledge of the static pair density correlations. To do so, we apply them to a benchmark provided by two ...liquid models that share very similar static pair density correlation functions while displaying distinct temperature evolutions of their relaxation times. We find that the approaches are unsuccessful in describing the difference in the dynamical behavior of the two models. Our study is not exhaustive, and we have not tested the effect of adding corrections by including, for instance, three-body density correlations. Yet, our results appear strong enough to challenge the claim that the slowdown of relaxation in glass-forming liquids, for which it is well established that the changes of the static structure factor with temperature are small, can be explained by “microscopic” approaches only requiring the static pair density correlations as nontrivial input.
Objective
We conducted a randomized, double‐blind, placebo‐controlled, parallel‐group study of both memantine and constraint‐induced aphasia therapy (CIAT) on chronic poststroke aphasia followed by ...an open‐label extension phase.
Methods
Patients were randomized to memantine (20mg/day) or placebo alone during 16 weeks, followed by combined drug treatment with CIAT (weeks 16–18), drug treatment alone (weeks 18–20), and washout (weeks 20–24), and finally, an open‐label extension phase of memantine (weeks 24–48). After baseline evaluations, clinical assessments were done at two end points (weeks 16 and 18), and at weeks 20, 24, and 48. Outcome measures were changes in the Western Aphasia Battery‐Aphasia Quotient and the Communicative Activity Log.
Results
Twenty‐eight patients were included, and 27 completed both treatment phases. The memantine group showed significantly better improvement on Western Aphasia Battery‐Aphasia Quotient compared with the placebo group while the drug was taken (week 16, p = 0.002; week 18, p = 0.0001; week 20, p = 0.005) and at the washout assessment (p = 0.041). A significant increase in Communicative Activity Log was found in favor of memantine‐CIAT relative to placebo‐CIAT (week 18, p = 0.040). CIAT treatment led to significant improvement in both groups (p = 0.001), which was even greater under additional memantine treatment (p = 0.038). Beneficial effects of memantine were maintained in the long‐term follow‐up evaluation, and patients who switched to memantine from placebo experienced a benefit (p = 0.02).
Interpretation
Both memantine and CIAT alone improved aphasia severity, but best outcomes were achieved combining memantine with CIAT. Beneficial effects of memantine and CIAT persisted on long‐term follow‐up. Ann Neurol 2009;65:577–585
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