Spinodal decomposition in a model colloid-polymer mixture in microgravity

We study phase separation in a deeply quenched colloid-polymer mixture in microgravity on the International Space Station using small-angle light scattering and direct imaging. We observe a clear crossover from early-stage spinodal decomposition to late-stage, interfacial-tension-driven coarsening. Data acquired over 5 orders of magnitude in time show more than 3 orders of magnitude increase in domain size, following nearly the same evolution as that in binary liquid mixtures. The late-stage growth approaches the expected linear growth rate quite slowly.     

A modified evidential methodology of identifying influential nodes in weighted networks

How to identify influential nodes in complex networks is still an open hot issue. In the existing evidential centrality (EVC), node degree distribution in complex networks is not taken into consideration. In addition, the global structure information has also been neglected. In this paper, a new Evidential Semi-local Centrality (ESC) is proposed by modifying EVC in two aspects. Firstly, the Basic Probability Assignment (BPA) of degree generated by EVC is modified according to the actual degree distribution, rather than just following uniform distribution. BPA is the generation of probability in order to model uncertainty. Secondly, semi-local centrality combined with modified EVC is extended to be applied in weighted networks. Numerical examples are used to illustrate the efficiency of the proposed method.     

On Growth Types of Quotients of Coxeter Groups by Parabolic Subgroups

The principal objects studied in this note are infinite, non-affine Coxeter groups W. A well-known result of de la Harpe asserts that such groups have exponential growth. We study the growth type of quotients of W by parabolic subgroups and by a certain class of reflection subgroups. Our main result is that these quotients have exponential growth as well.     

Additive hazards models for gap time data with multiple causes

Recurrent event data with multiple causes are often observed in biomedical studies. The additive hazards model describes a different aspect of the association between covariates and the failure time than does the proportional hazards model. In this paper, we introduce additive hazards models for the analysis of gap time data of recurrent events with multiple causes. We estimate the regression parameter vector and cumulative baseline cause specific hazard rate function using counting process approach. Asymptotic properties of the estimators are studied. The proposed model is applied to the kidney dialysis data given in Lawless (2003). A simulation study is carried out to assess the performance of the estimates.     

Methodology for studying particle–particle triboelectrification in granular materials

A critical challenge for experimental studies of triboelectric charging is to generate reproducible and unambiguous data that can be linked to theoretical concepts. We have developed a methodology to investigate the triboelectric charging of granular materials due solely to particle–particle interactions (i.e. no particle–wall interactions). The methodology is based on a particle flow apparatus that generates a fountain-like flow in which the particles contact only other particles, but no equipment surfaces. Non-contact methods of measuring charge and separating particles by charge are employed so that probe-particle charging does not occur.     

A method for stochastic constrained optimization using derivative-free surrogate pattern search and collocation

Recent advances in coupling novel optimization methods to large-scale computing problems have opened the door to tackling a diverse set of physically realistic engineering design problems. A large computational overhead is associated with computing the cost function for most practical problems involving complex physical phenomena. Such problems are also plagued with uncertainties in a diverse set of parameters. We present a novel stochastic derivative-free optimization approach for tackling such problems. Our method extends the previously developed surrogate management framework (SMF) to allow for uncertainties in both simulation parameters and design variables. The stochastic collocation scheme is employed for stochastic variables whereas Kriging based surrogate functions are employed for the cost function. This approach is tested on four numerical optimization problems and is shown to have significant improvement in efficiency over traditional Monte-Carlo schemes. Problems with multiple probabilistic constraints are also discussed.     

Unsteady deflagration speed of an auto-ignitive dimethyl-ether (DME)/air mixture at stratified conditions

The propagation speed of an auto-ignitive dimethyl-ether (DME)/air mixture at elevated pressures and subjected to monochromatic temperature oscillations is numerically evaluated in a one-dimensional statistically stationary configuration using fully resolved numerical simulations with reduced kinetics and transport. Two sets of conditions with temperatures within and slightly above the negative temperature coefficient (NTC) regime are simulated to investigate the fundamental aspects of auto-ignition and flame propagation along with the transition from auto-ignitive deflagration to spontaneous propagation regimes under thermal stratification. Contrary to the standard laminar flame speed, the steady propagation speed of an auto-ignitive front is observed to scale proportionally to its level of upstream reactivity. It is shown that this interdependence is primarily influenced by the characteristic residence time and the homogeneous auto-ignition delay. Furthermore, the unsteady reaction front in either of the two cases responds distinctly to the imposed stratification. Specifically, the results in both cases show that the dynamic flame response depends on the mean temperature at the flame base T_b and the time-scale of thermal stratification. It is also found that, based on T_b and the propensity of the mixture to two-stage chemistry, the instantaneous peak propagation speed and the overall time taken to achieve that speed differs considerably. A displacement speed analysis is carried out to elucidate the underlying combustion modes that are responsible for such a variation in flame response.     

Monitoring redox-sensitive paramagnetic contrast agent by EPRI, OMRI and MRI

A comparative study of tissue redox-status imaging using commonly used redox sensitive nitroxides has been carried out using electron paramagnetic resonance imaging (EPRI), Overhauser magnetic resonance imaging (OMRI) and conventional T(1)-weighted magnetic resonance imaging, MRI. Imaging studies using phantoms of different nitroxides at different concentration levels showed that EPRI and OMRI sensitivities were found to be linearly dependent on line width of nitroxides up to 2 mM, and the enhancement in MRI intensity was linear up to 5 mM. The sensitivity and resolution of EPRI and OMRI images depended significantly on the line width of the nitroxides whereas the MRI images were almost independent of EPR line width. Reduction of the paramagnetic 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (3CP) by ascorbic acid (AsA) to the diamagnetic by hydroxylamine was monitored from a sequence of temporal images, acquired using the three imaging modalities. The decay rates determined by all the three modalities were found to be similar. However the results suggest that T(1)-weighted MRI can monitor the redox status, in addition to providing detailed anatomical structure in a short time. Therefore, a combination of MRI with nitroxides as metabolically responsive contrast agents can be a useful technique for the in vivo imaging probing tissue redox status.     

Interaction of plane turbulent jets in a confined space: mean flow characteristics

The present study deals with the experimental investigations of static pressure and mean velocity fields obtained as a result of the interaction of two plane turbulent jets at impingement angles of α equal to 30° and 45°, with an additional central jet in a confined space. The investigation is carried out for the velocity ratios of U _c/U _o=1.0, 2.0 and 3.0, where U _c and U _o are the velocities in the central plane at the exit of the central jet and the outer jets, respectively. The introduction of the central jet alters the various recirculation zones present in the flow field for all the cases considered above. Also, the change in the velocity ratio U _c/U _o has a significant effect on the pressure and mean velocity flow fields. Flow visualisation results are presented which give a better physical insight into the flow field considered. Received: 26 July 1999/Accepted: 14 February 2000     

Colloidal Flower‐Shaped Iron Oxide Nanoparticles: Synthesis Strategies and Coatings

The assembly of magnetic cores into regular structures may notably influence the properties displayed by a magnetic colloid. Here, key synthesis parameters driving the self‐assembly process capable of organizing colloidal magnetic cores into highly regular and reproducible multi‐core nanoparticles are determined. In addition, a self‐consistent picture that explains the collective magnetic properties exhibited by these complex assemblies is achieved through structural, colloidal, and magnetic means. For this purpose, different strategies to obtain flower‐shaped iron oxide assemblies in the size range 25–100 nm are examined. The routes are based on the partial oxidation of Fe(OH)₂, polyol‐mediated synthesis or the reduction of iron acetylacetonate. The nanoparticles are functionalized either with dextran, citric acid, or alternatively embedded in polystyrene and their long‐term stability is assessed. The core size is measured, calculated, and modeled using both structural and magnetic means, while the Debye model and multi‐core extended model are used to study interparticle interactions. This is the first step toward standardized protocols of synthesis and characterization of flower‐shaped nanoparticles.