Increase In Effective Volume Research Articles

Light absorption by weakly rough metal surfaces

We study light absorption by weakly rough metal surfaces with the roughness amplitude and correlation length smaller than the skin depth in metal. We develop a systematic perturbative approach for calculation of the absorptance in such systems and find that roughness-related absorptance variations are determined by an interplay between several system parameters which can result, in particular, in a greater absorption for smaller roughness amplitudes. We show that, for small-scale roughness, the absorptance variations are mainly caused by roughness-induced increase in effective volume of the surface layer, in which the incident light is predominantly absorbed. We argue that such absorptance fluctuations between different samples, even though not related to any electron scattering processes, can appear as sample-to-sample variations of the Drude scattering rate reported in recent measurements of the metal dielectric function.

Controlled Diffusion of Photoswitchable Receptors by Binding Anti-electrostatic Hydrogen-Bonded Phosphate Oligomers.

Dihydrogen phosphate anions are found to spontaneously associate into anti-electrostatic oligomers via hydrogen bonding interactions at millimolar concentrations in DMSO. Diffusion NMR measurements supported formation of these oligomers, which can be bound by photoswitchable anion receptors to form large bridged assemblies of approximately three times the volume of the unbound receptor. Photoisomerization of the oligomer-bound receptor causes a decrease in diffusion coefficient of up to 16%, corresponding to a 70% increase in effective volume. This new approach to external control of diffusion opens prospects in controlling molecular transport using light.

Specimen size effect of explosive sensitivity under low velocity impact

Low velocity impact may ignite the solid high explosives and cause undesired explosion incidents. The safety of high explosives under low velocity impact is one of the most important issues in handling, manufacture, storage, and transportation procedures. Various evaluation tests have been developed for low velocity impact scenarios, including, but not limited to the drop hammer test, the Susan test, the Spigot test, and the Steven test, with a charge mass varying from tens of milligrams to several kilograms. The effects of specimen size on explosive sensitivity were found in some impact tests such as drop hammer test and Steven tests, including the threshold velocity/height and reaction violence. To analyse the specimen size effects on explosive sensitivity under low velocity impacts, we collected the impact sensitivity data of several PBX explosives in the drop hammer test, the Steven test, the Susan test and the Spigot test. The effective volume of explosive charge and the critical specific mechanical energy were introduced to investigate the size-effect on the explosive reaction thresholds. The effective volumes of explosive charge in Steven test and Spigot test were obtained by numerical simulation, due to the deformation localization of the impact loading. The critical specific mechanical energy is closely related to the effective volume of explosive charge. The results show that, with the increase of effective volume, the critical mechanical energy needed for explosive ignition decreases and tends to reach a constant value. The mechanisms of size effects on explosive sensitivity are also discussed.

The influence of the size and surface modification of TiO2 nanoparticles on the rheological properties of alkyd resin

Spherical TiO2 particles of different size were dispersed in alkyd resin based on soybean oil. Four samples of TiO2 particles were used, three commercial and one obtained by acid catalyzed hydrolysis of titanium tetraisopropoxide. The size of the synthesized nanoparticles was determined by transmission electron microscopy. Surface modification of TiO2 nanoparticles was performed with propyl gallate and lauryl gallate. The influence of the size of TiO2 nanoparticles, their concentration and type of the surface modification on the rheological properties of alkyd resin was investigated. The obtained results have shown that the viscosity of the prepared dispersions was higher than viscosity of the pure resin, it increases with decreasing particle diameter and decreases with frequency increase. Surface modified particles showed higher influence on the viscosity of alkyd resin than unmodified, because their hydrodynamic volume is higher due to the presence of the adsorbed gallates, leading to the increase of effective volume fraction of particles in dispersion. For the lowest TiO2 concentration, the viscosity was higher for sample modified with lauryl gallate, due to the higher thickness of the adsorbed layer. The increase of concentration, because of less dispersion stability of the particles modified with propyl gallate, leads to particles agglomeration. The presence of agglomerates, which was confirmed by a change in the slope of the functional dependence of storage modulus on loss modulus, leads to a rapid increase in viscosity.

Anomalous Size Dependent Rheological Behavior of Alumina Based Nanofluids

Rheological characteristics of alumina (Al 2 O 3 ) nanofluids (NFs) were found to exhibit an unexpected behavior. Two base-fluids viz, water and ethylene glycols (EG) with particles of average diameter of 11, 45 and 150 nm were examined. An anomalous reduction in viscosity compared to that of the base fluid was seen for EG based NFs. However, viscosity reduction was absent in water based NFs. The inter-related effects of particle size, concentration and mode of dispersion (mono or poly-dispersed) were investigated. Particle migration under shear is attributed to the reduction of viscosity. The increase in bulk viscosity with particle size reduction is attributed to the surface forces acting between the particles and the medium in a suspension and the increase of effective volume with size.

BOVINE SERUM ALBUMIN IN LITHIUM CHLORIDE SOLUTIONS. III. A Comparative Study of Li+ and H3O+ Effects

The effects of li+ and H3O+ on the conformation of bovine serum albumin in azqueous solutions at room temperature are compared. At low pH (high concentration of H3O+) the change in conformation of the protein is demonstrated by an increase in effective volume, a decrease in helical content and a blue shift of tyrosyl residue. A similar change is observed for the protein in highly concentrated LiC1 solution (6.0-7.0M) at neutral pH. However, the H3O+ is 12,000 times more powerful than the Li+ in destabilizing the protein molecule. This is consistent with their thermodynamic and kinetic properties, since the H3O+ is often different from the Li+ in several orders of magnitude. While the changes in structural properties of the protein are almost identical in both the acidic solution and the highly concentrated LiC1 solution, further study using dioxane as a probe suggests different mechanisms under which the changes occur. The effect of H3O+ is related to electrostatic force, whereas the effect of Li+ is related to both the electrostatic hydrophobic forces. These two major forces are believed to be responsible for the conformation of protein molecules.

Fold surface of polyethylene single crystals as assessed by selective degradation. I. Ozone degradation method

AbstractOzone has been used as a selective oxidizing agent for degrading polyethylene single crystals at room temperature in order to confirm and extend results on surface structure obtained by use of fuming nitric acid at temperatures above 60°C. The surfaces of the crystals were rendered highly accessible to the ozone gas by preparing the crystalline material in a highly expanded form; the solvent in which the crystals were suspended was removed by sublimation from the solid state. The extent and nature of the reaction were studied by measuring the increase in weight and in density, by direct chemical analyses, and by making use of infrared spectroscopy and gel‐permeation chromatography. It was found that the surfaces of the crystals are attacked at room temperature by ozone, with resulting chain scission, and the broad features of the chemical reaction were established. Some folded chains are found to be as long as the original thickness of the crystal, and once folds have been cut, continuing reaction shortens the chains. In the early stages of the degradation, during which most of the weight increase takes place, the density of the crystals increases, and the magnitude of the increase is that expected from the increase in weight alone, i.e., assuming no increase in effective volume.