Time for a Time Window Extension: Insights from Late Presenters in the ESCAPE Trial.

BACKGROUND AND PURPOSE: The safety and efficacy of endovascular therapy for large-artery stroke in the extended time window is not yet well-established. We performed a subgroup analysis on subjects enrolled within an extended time window in the Endovascular Treatment for Small Core and Proximal Occlusion Ischemic Stroke (ESCAPE) trial. MATERIALS AND METHODS: Fifty-nine of 315 subjects (33 in the intervention group and 26 in the control group) were randomized in the ESCAPE trial between 5.5 and 12 hours after last seen healthy (likely to have groin puncture administered 6 hours after that). Treatment effect sizes for all relevant outcomes (90-day mRS shift, mRS 0-2, mRS 0-1, and 24-hour NIHSS scores and intracerebral hemorrhage) were reported using unadjusted and adjusted analyses. RESULTS: There was no evidence of treatment heterogeneity between subjects in the early and late windows. Treatment effect favoring intervention was seen across all clinical outcomes in the extended time window (absolute risk difference of 19.3% for mRS 0-2 at 90 days). There were more asymptomatic intracerebral hemorrhage events within the intervention arm (48.5% versus 11.5%, P = .004) but no difference in symptomatic intracerebral hemorrhage. CONCLUSIONS: Patients with an extended time window could potentially benefit from endovascular treatment. Ongoing randomized controlled trials using imaging to identify late presenters with favorable brain physiology will help cement the paradigm of using time windows to select the population for acute imaging and imaging to select individual patients for therapy.

Self-organization of S adatoms on Au(111): √3R30° rows at low coverage.

Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30° from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √3 times the surface lattice constant, a. Monte Carlo simulations are performed on lattice-gas models, derived using a limited cluster expansion based on density functional theory energetics. Models which include long-range pairwise interactions (extending to 5a), plus selected trio interactions, successfully reproduce the linear rows of S atoms at reasonable temperatures.

Reconstruction of steps on the Cu(111) surface induced by sulfur.

A rich menagerie of structures is identified at 5 K following adsorption of low coverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their original sites and form a base for S adsorption at (mostly) 4fh sites. We propose a mechanism by which these triangles could generate Cu-S complexes and short chains like those observed on the terraces.

Communication: Structure, formation, and equilibration of ensembles of Ag-S complexes on an Ag surface.

We have utilized conditions of very low temperature (4.7 K) and very low sulfur coverage to isolate and identify Ag-S complexes that exist on the Ag(111) surface. The experimental conditions are such that the complexes form at temperatures above the temperature of observation. These complexes can be regarded as polymeric chains of varying length, with an Ag4S pyramid at the core of each monomeric unit. Steps may catalyze the formation of the chains and this mechanism may be reflected in the chain length distribution.

Formation of a novel ordered Ni3Al surface structure by codeposition on NiAl(110).

The formation of a new type of ordered 2D Ni3Al overlayer by low-temperature codeposition on NiAl(110) is demonstrated by kinetic Monte Carlo simulation of a multisite atomistic lattice-gas model with a precise treatment of surface diffusion kinetics. Simultaneous codeposition with 3:1 Ni:Al yields poor ordering at 300 K but well-ordered structures by ~500 K. Sequential codeposition of Ni then Al yields unmixed core-ring nanostructures at 300 K but strong intermixing and ordering by ~500 K.

Schloegl's second model for autocatalysis on hypercubic lattices: Dimension dependence of generic two-phase coexistence.

Schloegl's second model on a (d ≥ 2)-dimensional hypercubic lattice involves: (i) spontaneous annihilation of particles with rate p and (ii) autocatalytic creation of particles at vacant sites at a rate proportional to the number of suitable pairs of neighboring particles. This model provides a prototype for nonequilibrium discontinuous phase transitions. However, it also exhibits nontrivial generic two-phase coexistence: Stable populated and vacuum states coexist for a finite range, pf(d)

Temperature-dependent growth shapes of Ni nanoclusters on NiAl(110).

Scanning tunneling microscopy studies reveal that two-dimensional nanoscale Ni islands formed by deposition of Ni on NiAl(110) between 200-400 K exhibit far-from-equilibrium growth shapes which change systematically with temperature. Island structure reflects the two types of adsorption sites available for Ni adatoms, and island shapes are controlled by the details of adatom diffusion along island edges accounting for numerous local configurations. The temperature dependence of the island shapes is captured and elucidated by kinetic Monte Carlo simulation of a realistic atomistic-level multisite lattice-gas model incorporating precise diffusion barriers. These barriers are obtained by utilizing density functional theory to probe energetics not just at adsorption sites but also at transition states for diffusion. This success demonstrates a capability for predictive atomistic-level modeling of nanocluster formation and shape selection in systems that have a high level of energetic and kinetic complexity.

Nucleation and growth of Ag islands on the (√3 × âˆš3)R30° phase of Ag on Si(111).

We use scanning tunneling microscopy to measure densities and characteristics of Ag islands that form on the (√3 × âˆš3)R30°-Ag phase on Si(111), as a function of deposition temperature. Nucleation theory predicts that the logarithm of island density varies linearly with inverse deposition temperature. The data show two linear regimes. At 50-125 K, islands are relatively small, and island density decreases only slightly with increasing temperature. At 180-250 K, islands are larger and polycrystalline, and island density decreases strongly with increasing temperature. At 300 K, Ag atoms can travel for distances of the order of 1 µm. Assuming that Ag diffusion occurs via thermally activated motion of single atoms between adjacent sites, the data can be explained as follows. At 50-125 K, the island density does not follow conventional Arrhenius scaling due to limited mobility and a consequent breakdown of the steady-state condition for the adatom density. At ∼ 115-125 K, a transition to conventional Arrhenius scaling with critical nucleus size (i = 1) begins, and at 180-250 K, i > 1 prevails. The transition points indicate a diffusion barrier of 0.20-0.23 eV and a pairwise Ag-Ag bond strength of 0.14 eV. These energy values lead to an estimate of i≈3-4 in the regime 180-250 K, where island density varies strongly with temperature.

Self-assembly of metal nanostructures on binary alloy surfaces.

Deposition of metals on binary alloy surfaces offers new possibilities for guiding the formation of functional metal nanostructures. This idea is explored with scanning tunneling microscopy studies and atomistic-level analysis and modeling of nonequilibrium island formation. For Au/NiAl(110), complex monolayer structures are found and compared with the simple fcc(110) bilayer structure recently observed for Ag/NiAl(110). We also consider a more complex codeposition system, (Ni + Al)/NiAl(110), which offers the opportunity for fundamental studies of self-growth of alloys including deviations for equilibrium ordering. A general multisite lattice-gas model framework enables analysis of structure selection and morphological evolution in these systems.

Metastability in Schloegl's second model for autocatalysis: Lattice-gas realization with particle diffusion.

We analyze metastability associated with a discontinuous nonequilibrium phase transition in a stochastic lattice-gas realization of Schloegl's second model for autocatalysis. This model realization involves spontaneous annihilation, autocatalytic creation, and diffusion of particles on a square lattice, where creation at empty sites requires an adjacent diagonal pair of particles. This model, also known as the quadratic contact process, exhibits discontinuous transition between a populated active state and a particle-free vacuum or "poisoned" state, as well as generic two-phase coexistence. The poisoned state exists for all particle annihilation rates p>0 and hop rates h≥0 and is an absorbing state in the sense of Markovian processes. The active or reactive steady state exists only for p below a critical value, p{e}=p{e}(h) , but a metastable extension appears for a range of higher p up to an effective upper spinodal point, p{s+}=p{s+}(h) (i.e., p{s+}>p{e} ). For selected h , we assess the location of p{s+}(h) by characterizing both the poisoning kinetics and the propagation of interfaces separating vacuum and active states as a function of p .

Polymer length distributions for catalytic polymerization within mesoporous materials: non-Markovian behavior associated with partial extrusion.

We analyze a model for polymerization at catalytic sites distributed within parallel linear pores of a mesoporous material. Polymerization occurs primarily by reaction of monomers diffusing into the pores with the ends of polymers near the pore openings. Monomers and polymers undergo single-file diffusion within the pores. Model behavior, including the polymer length distribution, is determined by kinetic Monte Carlo simulation of a suitable atomistic-level lattice model. While the polymers remain within the pore, their length distribution during growth can be described qualitatively by a Markovian rate equation treatment. However, once they become partially extruded, the distribution is shown to exhibit non-Markovian scaling behavior. This feature is attributed to the long-tail in the "return-time distribution" for the protruding end of the partially extruded polymer to return to the pore, such return being necessary for further reaction and growth. The detailed form of the scaled length distribution is elucidated by application of continuous-time random walk theory.

Rapid decay of vacancy islands at step edges on Ag(111): step orientation dependence.

Previous work has established that vacancy islands or pits fill much more quickly when they are in contact with a step edge, such that the common boundary is a double step. The present work focuses on the effect of the orientation of that step, with two possibilities existing for a face centered cubic (111) surface: A- and B-type steps. We find that the following features can depend on the orientation: (1) the shapes of islands while they shrink; (2) whether the island remains attached to the step edge; and (3) the rate of filling. The first two effects can be explained by the different rates of adatom diffusion along the A- and B-steps that define the pit, enhanced by the different filling rates. The third observation--the difference in the filling rate itself--is explained within the context of the concerted exchange mechanism at the double step. This process is facile at all regular sites along B-steps, but only at kink sites along A-steps, which explains the different rates. We also observe that oxygen can greatly accelerate the decay process, although it has no apparent effect on an isolated vacancy island (i.e. an island that is not in contact with a step).

Group specific optimisation of fMRI processing steps for child and adult data.

Motion is a major issue in functional magnetic resonance imaging (fMRI) dataseries and causes artifacts or increased overall noise obscuring signals of interest. It is particularly important to be able to control for and correct these artifacts when dealing with child data. We analysed the data from 35 children (4-8 years old) and 13 adults (18-30 years old) during an emotional face paradigm. The children were split into low and high motion groups on the basis of having less or more than an estimated maximal movement of one voxel (3.75 mm) and one degree of rotation in any motion direction between any pair of scans in the run. Several different preprocessing steps were evaluated for their ability to correct for the excess motion using agnostic canonical variates analysis (aCVA) in the NPAIRS (Nonparametric, Prediction, Activation, Influence, Reproducibility, re-Sampling) framework. The adult dataset was reasonably stable whereas the motion-prone child datasets benefited greatly from motion parameter regression (MPR). Motion parameter regression had a strong beneficial impact on all datasets, a result that was largely unaffected by other preprocessing choices; however, motion correction on its own did not have as much impact. The low motion child group subjected to MPR had reproducibility values at par with those of the adult group, but needed almost twice as many subjects to achieve this result, indicating weaker responses in young children. The aCVA showed greater sensitivity to the task response pattern than the mixed effects general linear model (mGLM) in the expected face processing regions, although the mGLM showed more responses in some other areas. This work illustrates that preprocessing choices must be made in a group-specific fashion to optimise fMRI results.

Statistical mechanical modeling of catalytic polymerization within surface-functionalized mesoporous materials.

A discrete lattice model is developed to describe diffusion-mediated polymerization occurring within mesopores, where reaction is enhanced at catalytic sites distributed within the interior of the pores. Diffusive transport of monomers and polymers is one-dimensional, diffusion coefficients for the latter decreasing with polymer length. Kinetic Monte Carlo simulation is utilized to analyze model behavior focusing on a "clogging" regime, where the amount of polymer within the pores grows. We characterize the evolution of the overall and mean length of polymers, the mean number of polymers, as well as the polymer spatial and length distributions.

Structure and growth of height-selected Ag islands on fivefold i-AlPdMn quasicrystalline surfaces: STM analysis and step dynamics modeling.

The development and local structure of height-selected 3-layer Ag islands on fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals is characterized by STM for Ag deposition at 365 K. Heterogeneous nucleation of pseudomorphic single layer high islands is followed by rapid formation of 2nd and 3rd layers and subsequent lateral spreading, where each of these 3 layers consists of a family of nonfcc structures. The behavior is elucidated by step dynamics modeling incorporating strain buildup for larger islands, enhanced binding in higher layers, and height selection due to quantum size effects.

Accelerated coarsening of Ag adatom islands on Ag(111) due to trace amounts of S: mass-transport mediated by Ag-S complexes.

Scanning tunneling microscopy studies reveal that trace amounts of adsorbed S below a critical coverage on the order of 10 mML have little effect on the coarsening and decay of monolayer Ag adatom islands on Ag(111) at 300 K. In contrast, above this critical coverage, decay is greatly accelerated. This critical value appears to be determined by whether all S can be accommodated at step edges. Accelerated coarsening derives from the feature that the excess S (above that incorporated at steps) produces significant populations on the terraces of metal-sulfur complexes, which are stabilized by strong Ag-S bonding. These include AgS(2), Ag(2)S(2), Ag(2)S(3), and Ag(3)S(3). Such complexes are sufficiently populous and mobile that they can potentially lead to greatly enhanced metal mass transport across the surface. This picture is supported by density functional theory analysis of the relevant energetics, as well as by reaction-diffusion equation modeling to assess the mechanism and degree of enhanced coarsening.

Schloegl's second model for autocatalysis with particle diffusion: Lattice-gas realization exhibiting generic two-phase coexistence.

We analyze a discontinuous nonequilibrium phase transition between an active (or reactive) state and a poisoned (or extinguished) state occurring in a stochastic lattice-gas realization of Schloegl's second model for autocatalysis. This realization, also known as the quadratic contact process, involves spontaneous annihilation, autocatalytic creation, and diffusion of particles on a square lattice, where creation at empty sites requires a suitable nearby pair of particles. The poisoned state exists for all annihilation rates p>0 and is an absorbing particle-free "vacuum" state. The populated active steady state exists only for p below a critical value, p(e). If p(f) denotes the critical value below which a finite population can survive, then we show that p(f)

Formation of complex wedding-cake morphologies during homoepitaxial film growth of Ag on Ag(111): atomistic, step-dynamics, and continuum modeling.

An atomistic lattice-gas model is developed which successfully describes all key features of the complex mounded morphologies which develop during deposition of Ag films on Ag(111) surfaces. We focus on this homoepitaxial thin film growth process below 200 K. The unstable multilayer growth mode derives from the presence of a large Ehrlich-Schwoebel step-edge barrier, for which we characterize both the step-orientation dependence and the magnitude. Step-dynamics modeling is applied to further characterize and elucidate the evolution of the vertical profiles of these wedding-cake-like mounds. Suitable coarse-graining of these step-dynamics equations leads to instructive continuum formulations for mound evolution.

A kinetic Monte Carlo study on the role of defects and detachment in the formation and growth of In chains on Si(100).

Deposition on a Si(100) surface and subsequent self-assembly of In atoms into one-dimensional (1D) atomic chains at room temperature is investigated via kinetic Monte Carlo simulation of a suitable atomistic model. Model development is guided by recent experimental observations in which 1D In chains nucleate effectively exclusively at C-type defects, although In atoms can detach from chains. We find that a monotonically decreasing form of the scaled island size distribution (ISD) is consistent with a high defect density which facilitates persistent chain nucleation even at relatively high coverages. The predominance of heterogeneous nucleation may be attributed to several factors including low surface diffusion barriers, a high defect density, and relatively weak In-In binding.