Energy trapping and shock disintegration in a composite granular medium

We report the first experimental observation of impulse confinement and the disintegration of shock and solitary waves in one-dimensional strongly nonlinear composite granular materials. The chains consist of alternating ensembles of beads with high and low elastic moduli (more than 2 orders of magnitude difference) of different masses. The trapped energy is contained within the "softer" sections of the composite chain and is slowly released in the form of weak, separated pulses over an extended period of time. This effect is enhanced by using a specific group assembly and precompression.     

Fluorescent Dimers of Merocyanine 540 (MC540) in the Gel Phase of Phosphatidylcholine Liposomes

Abstract— Fluorescence emission from merocyanine 540 (MC540) dimers was observed in dipalmitoylphosphatidylcholine (DPPC) vesicles. This unusual behavior was observed only for vesicles in the gel-phase state. No dimer fluorescence was observed either in monopalmitoylphosphati-dylcholine (C₁₆PC) micelles or in liquid-crystalline DPPC vesicles, indicating that dimer fluorescence efficiency increases in highly packed interfaces. The excitonic theory of Kasha was used to interpret the spectral features. The overall fluorescence quantum yield (φ_r) decreases with decreasing lipid: probe ratio, not only because of the presence of a weakly fluorescent dimer that absorbs a high fraction of the total absorbed light but also due to quenching of monomer emission. This suggests the existence of probe domains. The dimer fluorescence quantum yields (φ_m) were estimated in DPPC large unilamellar vesicles (LUV) and DPPC multilamellar vesicles. The dependence of φ_r with probe concentration is compatible with values of φ_m lower than 0.05. The dimerization equilibrium of MC540 in C₁₆PC micelles and DPPC-LUV was also studied. Apparent dimerization equilibrium constants, K_dapp and dimer absorption spectrum were calculated in C₁₆PC micelles for the first time. The dimerization equilibrium constant in DPPC-LUV was calculated and discussed in terms of the fraction of volume occupied by the lipid phase.     

Exogenous crimes and the assessment of public safety efficiency and effectiveness

Annals of Operations Research - This work discusses the issue on how to include data about property and violent crimes in the production technology for the assessment of police technical...     

Carboxylated zinc-phthalocyanines--II. Dimerization and singlet molecular oxygen sensitization in hexadecyltrimethylammonium bromide micelles.

The dimerization of the diamide of zinc-tetracarboxyphthalocyanine was studied spectroscopically in hexadecyltrimethylammonium bromide (CTAB) micelles at surfactant concentrations from 0.026 to 0.1 M and dye concentrations between 0.1 and 10 microM. The apparent dimerization constant in CTAB 0.1 M is 8.6 x 10(5) M-1, while the intramicellar dimerization constant is 1.8 x 10(3). The dimer absorption spectrum was also obtained. Singlet molecular oxygen sensitization was studied by steady state photolysis using 1,3-diphenylisobenzofurane as scavenger in 0.1 M CTAB. The usual sensitization mechanism is extended to include dimer reactions. Singlet molecular oxygen sensitization yields for monomer and dimer in the micelles are 0.7 and 0.1, respectively. With the reported values it is possible to calculate the average yield of singlet molecular oxygen production at any surfactant and dye concentrations.     

Thin and Thermally Stable Periodic Metastructures

We design, fabricate, and test thin thermally stable metastructures consisting of bi-metallic unit cells and show how the coefficient of thermal expansion (CTE) of these metastructures can be finely and coarsely tuned by varying the CTE of the constituent materials and the unit cell geometry. Planar and three-dimensional finite element method modeling (FEM) is used to drive our design and inform experiments, and predict the response of these metastructures. We develop a robust experimental fabrication procedure in order to fabricate thermally stable samples with high aspect ratios. We use digital image correlation (DIC) and an infrared camera to experimentally measure displacement and temperature during testing and compute the CTE of our samples. The samples, composed of an aluminum core and an external titanium frame, exhibit a CTE of 2.6 ppm/°C, which is significantly lower than either constituent. These unit cells can be assembled over a large area to create thin low-CTE foils. Finally, we demonstrate how the approach developed in this work can be used to fabricate metastructures with CTE’s ranging from ?3.6 ppm/°C to 8.4 ppm/°C.     

Copper adsorption on magnetite-loaded chitosan microspheres: A kinetic and equilibrium study

A composite of Fe₃O₄ nanoparticles and the biopolymer chitosan, chemically crosslinked, was prepared as microspheres and used to adsorb copper ions, which were chosen as a model of contaminant metal in water.     

Explaining inefficiency in nonparametric production models: the state of the art

The performance of economic producers is often affected by external or environmental factors that, unlike the inputs and the outputs, are not under the control of the Decision Making Units (DMUs). These factors can be included in the model as exogenous variables and can help to explain the efficiency differentials, as well as improve the managerial policy of the evaluated units. A fully nonparametric methodology, which includes external variables in the frontier model and defines conditional DEA and FDH efficiency scores, is now available for investigating the impact of external-environmental factors on the performance. In this paper, we offer a state-of-the-art review of the literature, which has been proposed to include environmental variables in nonparametric and robust (to outliers) frontier models and to analyse and interpret the conditional efficiency scores, capturing their impact on the attainable set and/or on the distribution of the inefficiency scores. This paper develops and complements the approach of B?din et al. (2012) by suggesting a procedure that allows us to make local inference and provide confidence intervals for the impact of the external factors on the process. We advocate for the nonparametric conditional methodology, which avoids the restrictive “separability” assumption required by the two-stage approaches in order to provide meaningful results. An illustration with real data on mutual funds shows the usefulness of the proposed approach.     

An Experimental Technique for the Dynamic Characterization of Soft Complex Materials

We describe an experimental technique to study the dynamic behavior of complex soft materials, based on high-speed microscopic imaging and direct measurements of dynamic forces and deformations. The setup includes high sensitivity dynamic displacement measurements based on geometric moiré interferometry and high-speed imaging for in-situ, full-field visualization of the complex micro-scale dynamic deformations. The method allows extracting dynamic stress-strain profiles both from the moiré interferometry and from the high-speed microscopic imaging. We discuss the advantages of using these two complementing components concurrently. We use this technique to study the dynamic response of vertically aligned carbon nanotube foams subjected to impact loadings at variable deformation rates. The same technique can be used to study other micro-structured materials and complex hierarchical structures.     

Iron silicide root formation in carbon nanotubes grown by microwave PECVD

Aligned carbon nanotubes have been grown using microwave plasma enhanced chemical vapor deposition (PECVD). The carbon nanotubes are nucleated from iron catalyst particles which, during growth, remain adherent to the silicon substrates. By analysis with high-resolution electron microscopy, we observe iron silicide roots penetrating into the silicon substrate at the interface of the catalyst particles and the substrate, thus providing strong adhesion of the carbon nanotubes onto the substrate. The iron silicide roots assist in the attachment of the catalyst particles to the substrate and play a role in the evolution of the catalyst particle morphology and resulting base growth mode. Carbon nanotubes grown by microwave PECVD could exhibit superior electrical and thermal transport properties over other PECVD processes, so an understanding of the growth mechanism is important for utilization in device applications.