Heterogeneity Research Papers - Academia.edu (original) (raw)

Simple arguments show that ascending thermal plumes will entrain their surroundings as the result of coupling between conduction of heat and laminar stirring driven by the plume motion. In the initial stages of ascent of a plume fed by a... more

Simple arguments show that ascending thermal plumes will entrain their surroundings as the result of coupling between conduction of heat and laminar stirring driven by the plume motion. In the initial stages of ascent of a plume fed by a continuous buoyancy flux (a starting plume) the plume consists of a large buoyant head followed by a narrow vertical conduit.

Montmorillonite is the most often studied swelling clay mineral. The layers have permanent negative charges due to isomorphic substitutions, and pH-dependent charges develop on the surface hydroxyls at the edges. Wyoming montmorillonite... more

Montmorillonite is the most often studied swelling clay mineral. The layers have permanent negative charges due to isomorphic substitutions, and pH-dependent charges develop on the surface hydroxyls at the edges. Wyoming montmorillonite samples with different extents of isomorphic substitutions (Swy-1 and Swy-2) were studied. The acid–base titration of Na-montmorillonite suspensions between pH 4 and 9 at 0.01, 0.1 and 1 M NaCl was used to characterize pH-dependent charge development on amphoteric edge sites and to determine the point of zero charge (PZC) of edges. The evaluation of reversible net proton surface excess vs. pH functions revealed that the OH groups at edges having PZC at pH ∼6.5 are less basic than the –OH and less acidic than the –OH groups. Positive charges can develop in a protonation reaction of –OH sites at edges only at pHs below ∼6.5, and deprotonation of –OH then that of the –OH sites takes place with increasing pH of solution resulting in negative charges at edges. Therefore, patch-wise charge heterogeneity of montmorillonite, i.e. oppositely charged surface parts of layers, exists only under acidic conditions. Coagulation kinetics measurements resulted in reliable stability ratio data for fine montmorillonite sols at different pHs, and provided undisputable characterization of hetero- and homocoagulation. Edge-to-face heterocoagulation occurs above NaCl concentration 25–26 mmol l−1 at pH ∼4, where the hidden electric double layer (edl) of positively charged edge region has emerged. Edge-to-face attraction between the poorly charged edges and negatively charged faces of platelets around the pH of PZC of edges (pHPZC, edge∼6.5) in relatively low concentration of the indifferent electrolytes (typically around 50 mmol l−1 NaCl) is probable. The homocoagulation of uniformly charged lamellae at pH 8–8.5, formation of face-to-face aggregates requires much higher salt concentration (typically around 100 mmol l−1 NaCl) to compress the dominant edl on the highly charged faces of particles. XRD patterns of montmorillonite films prepared from slightly acidic suspensions proved that formation of well-ordered layer packages is hindered by the attraction between edges and faces. Characteristic changes in gel formation and in rheological properties induced by decreasing pH in dense suspensions containing 0.01 M NaCl provided experimental evidence for the structure of particle network. A significant increase in thixotropy and yield values, and also the formation of viscoelastic gels only below pH ∼6.5 verify that attractive interaction exists between oppositely charged parts of lamellar particles.

Single-cell RNA-seq technologies enable high throughput gene expression measurement of individual cells, and allow the discovery of heterogeneity within cell populations. Measurement of cell-to-cell gene expression similarity is critical... more

Single-cell RNA-seq technologies enable high throughput gene expression measurement of individual cells, and allow the discovery of heterogeneity within cell populations. Measurement of cell-to-cell gene expression similarity is critical to identification, visualization and analysis of cell populations. However, single-cell data introduce challenges to conventional measures of gene expression similarity because of the high level of noise, outliers and dropouts. Here, we propose a novel similarity-learning framework, SIMLR (single-cell interpretation via multi-kernel learning), which learns an appropriate distance metric from the data for dimension reduction, clustering and visualization applications. Benchmarking against state-of-the-art methods for these applications, we used SIMLR to re-analyse seven representative single-cell data sets, including high-throughput droplet-based data sets with tens of thousands of cells. We show that SIMLR greatly improves clustering sensitivity and accuracy, as well as the visualization and interpretability of the data.

In this paper we derive a model of aggregate investment that builds from the lumpy microeconomic behavior of firms facing stochastic fixed adjustment costs. Instead of the standard sharp (S,s) bands, firms' adjustment policies take the... more

In this paper we derive a model of aggregate investment that builds from the lumpy microeconomic behavior of firms facing stochastic fixed adjustment costs. Instead of the standard sharp (S,s) bands, firms' adjustment policies take the form of a probability of adjustment (adjustment hazard) that responds smoothly to changes in firms' capacity gap. The model has appealing aggregation properties, and yields nonlinear aggregate time series processes. The passivity of normal times is, occasionally, more than offset by the brisk response to large accumulated shocks. Using within and out-of-sample criteria, we find that the model performs substantially better than the standard linear models of investment for postwar sectoral U.S. manufacturing equipment and structures investment data.

Understanding disturbance and recovery of forest landscapes is a challenge because of complex interactions over a range of temporal and spatial scales. Landscape _ O _, simulation models offer an approach to studying such systems at broad... more

Understanding disturbance and recovery of forest landscapes is a challenge because of complex interactions over a range of temporal and spatial scales. Landscape _ O _, simulation models offer an approach to studying such systems at broad scales. Fire can be _ _ _ I:_ simulated spatially using mechanistic or stochastic approaches. We describe the fire module f0 to ;-,-