Comment on "Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition"

In the Letter [PRL 102, 085703 (2009)] Brambilla, et al. claimed to observe activated dynamics in colloidal hard spheres above the critical packing fraction of mode coupling theory (MCT). By performing microscopic MCT calculations, we show that polydispersity in their system shifts the critical packing fraction above the value determined by van Megen et al. for less polydisperse samples, and that the data agree with theory except for, possibly, the highest packing fraction.Comment: Comment in print in Phys. Rev. Lett.; for accompanying reply see arXiv Brambilla et al. (Monday 18.10.2010

On the coarse-grained density and compressibility of non-ideal crystals: general theory and an application to cluster crystals

The isothermal compressibility of a general crystal is analyzed within classical density functional theory. Our approach can be used for homogeneous and unstrained crystals containing an arbitrarily high density of local defects. We start by coarse-graining the microscopic particle density and then obtain the long wavelength limits of the correlation functions of elasticity theory and the thermodynamic derivatives. We explicitly show that the long wavelength limit of the microscopic density correlation function differs from the isothermal compressibility. It also cannot be obtained from the static structure factor measured in a scattering experiment. We apply our theory to crystals consisting of soft particles which can multiply occupy lattice sites ('cluster crystals'). The multiple occupancy results in a strong local disorder over an extended range of temperatures. We determine the cluster crystals' isothermal compressibility, the fluctuations of the lattice occupation numbers and their correlation functions, and the dispersion relations. We also discuss their low-temperature phase diagram.Comment: 20 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1206.618

Visual Integration of Data and Model Space in Ensemble Learning

Ensembles of classifier models typically deliver superior performance and can outperform single classifier models given a dataset and classification task at hand. However, the gain in performance comes together with the lack in comprehensibility, posing a challenge to understand how each model affects the classification outputs and where the errors come from. We propose a tight visual integration of the data and the model space for exploring and combining classifier models. We introduce a workflow that builds upon the visual integration and enables the effective exploration of classification outputs and models. We then present a use case in which we start with an ensemble automatically selected by a standard ensemble selection algorithm, and show how we can manipulate models and alternative combinations.Comment: 8 pages, 7 picture

New maverick coset theories

We present new examples of maverick coset conformal field theories. They are closely related to conformal embeddings and exceptional modular invariants.Comment: 6 pages, LaTeX2

Projections in string theory and boundary states for Gepner models

In string theory various projections have to be imposed to ensure supersymmetry. We study the consequences of these projections in the presence of world sheet boundaries. A-type boundary conditions come in several classes; only boundary fields that do not change the class preserve supersymmetry. Our analysis takes in particular properly into account the resolution of fixed points under the projections. Thus e.g. the compositeness of some previously considered boundary states of Gepner models follows from chiral properties of the projections. Our arguments are model independent; in particular, integrality of all annulus coefficients is ensured by model independent arguments.Comment: 37 pages, LaTeX2

Heat transfer challenge and design evaluation for a multi-stage temperature swing adsorption (TSA) process

Functionalized solid amine-based temperature swing adsorption (TSA) processes have recently been proposed as a potential way to reduce the energy-penalty of post-combustion carbon capture processes (1). If TSA is to be carried out at large scale and with high energy-efficiency, continuously operated counter-current contactors are required for thermodynamic reasons. This could, generally, be achieved by using moving bed contactors. However, the heat exchange requirement of TSA is significant and heat transfer is poor in fixed and moving beds. Therefore, multi-stage fluidized bed contactors with counter-current flow of solids and gas phase and immersed heat exchange surfaces may solve the heat transfer challenge while maintaining the thermodynamic process requirements. Experiments have shown that adsorption and desorption kinetics of suitable functionalized amine sorbents are fast and equilibrium loadings are practically reached in the stages (1). Thus, heat exchange is the dominant limiting factor for a practical stage design in multi-stage fluidized bed TSA. The present work rationally develops design requirements for TSA stages based on the necessary heat exchange rates. The considered particles are Geldart Type B (diameter 200-300 µm, particle density 1000-1500 kg/m3). Scalability of the design proposal is considered and vertically orientated heat exchanger tubes are compared to horizontal tube bundles. The net movement and mixing of particles within the bubbling bed stage must be maintained in spite of the emulsified heat exchangers (possible dead zones in the area of the tube bundles). It is shown that the pressure drop of multi-stage fluidized bed TSA units for flue gas CO2 capture is practically determined by the heat exchange requirement and not by the space-time of the solids for the adsorption. Future work will employ a bubbling fluidized bed heat exchange testing device for optimization of the heat exchanger geometry with respect to heat transfer rates and particle residence time distribution in the stage. Heat exchange measurement devices have been presented recently in literature for horizontal tube bundles and Geldart Type A particles (2), but the importance of the heat exchanger issue in continuous fluidized bed TSA requires the detailed investigation for the Geldart B range, potentially considering the macroscopic particle movement relative to the heat exchangers within each individual TSA stage. Please click Additional Files below to see the full abstract

Methacholine challenge in young children as evaluated by spirometry and impulse oscillometry

SummaryBackgroundIn young children, it is difficult to obtain a reproducible flow-volume curve throughout all stages of bronchial challenge. The forced oscillation technique (FOT) is especially established in paediatrics because this method does not require forced or maximal manoeuvres and is less cooperation-dependent than conventional spirometry.ObjectivesTo evaluate the association of spirometric and impulse oscillometric (IOS) indices in a short protocol for methacholine provocation.MethodsThe primary endpoint was the methacholine dose that caused a 20% decrease in FEV1 (PD−20FEV1) compared to baseline. Changes in respiratory resistance (Rrs5) and reactance (Xrs5) acquired by IOS were compared with FEV1.ResultsForty-eight children (5.3 ± 0.9 years) were challenged. The mean maximal reduction in FEV1 was 29.8% ± 14.7 (p < 0.0001), the mean increase in Rsr5 was 55.3% ± 31.7, and the mean decrease in Xrs5 was 0.37 kPa s L−1 ± 0.23 (p < 0.001). An increase in Rrs5 of 45.2% and a decrease in Xrs5 of 0.69 kPa s L−1 showed the optimal combination of sensitivity and specificity to detect a 20% reduction in FEV1 (0.72 and 0.73; 0.80 and 0.76, respectively), and the area under the ROC curve was 0.76 and 0.81, respectively (p < 0.005). In 28 patients with significant changes in FEV1 and Rsr5, the PD−20FEV1 was 0.48 mg methacholine ±0.59 and the PD+40Rrs5 was 0.28 mg methacholine ±0.45 (p = 0.03).ConclusionsA short protocol for methacholine challenge testing is feasible in young children. IOS detected 70–80% of patients who responded in spirometry. During the challenge, the Rrs5 response preceded the FEV1 response