Search results for "Dispersion."

New model describing the total dispersion of dry powder agglomerates

2010

Micron and submicron particles tend to form agglomerates due to adhesive and cohesive forces. The disintegration of these dry powder agglomerates often represents a major task in powder technology. One model describing the mechanical stability of granulates is given by the planar fracture model of Rumpf. In the present work, a new model is introduced intended for applications where a complete disintegration of dry powder agglomerates is required (e.g. for pharmaceutical aerosol generation). Therefore, the breakup of every single connection inside an agglomerate is considered and the dispersion strength σdisp of model agglomerates is calculated and discussed. In order to balance the stabilit…

Efficient energy conversion for cubic third-harmonic generation that is phase matched in KTiOPO(4).

2000

We demonstrate, for the first time to our knowledge, that efficient third-harmonic generation can be achieved with a cubic contribution much larger than the quadratic processes. An energy-conversion efficiency of 2.4% is achieved for cubic third-harmonic generation that is phase matched along the x axis of a KTiOPO(4) crystal by use of a picosecond fundamental laser emitting at 1618 nm. The associated cascading processes are only 10% of the pure cubic interaction, which is very suitable for study of the specific quantum optical correlations. Calculations of the third-harmonic generation conversion efficiency with respect to group-velocity dispersion and to the longitudinal Gaussian beam pro…

Layered double hydroxide nanocomposites based on carbon nanoforms

2020

Abstract Carbon nanoform (CNF)/layered double hydroxide (LDH) nanocomposites have been widely studied in recent years thanks to the combination of properties of both LDH and carbon nanomaterials. They exhibit improved or unexpected properties as a consequence of their hierarchical structures. There are three main reported approaches to prepare the nanocomposites: reassembly of nanocarbons and LDHs, direct formation of LDHs on nanocarbon materials, and the direct synthesis of nanocarbons on the LDH phase. The resulting CNF/LDH nanocomposites exhibit improved conductivity, mechanical properties, and redox reactivity; moreover, the hybridization confers hierarchical porosities and better dispe…

Temperature dependence of the magnetic Casimir-Polder interaction

2009

We analyze the magnetic dipole contribution to atom-surface dispersion forces. Unlike its electrical counterpart, it involves small transition frequencies that are comparable to thermal energy scales. A significant temperature dependence is found near surfaces with a nonzero DC conductivity, leading to a strong suppression of the dispersion force at T > 0. We use thermal response theory for the surface material and discuss both normal metals and superconductors. The asymptotes of the free energy of interaction and of the entropy are calculated analytically over a large range of distances. Near a superconductor, the onset of dissipation at the phase transition strongly changes the interac…

Preparation of drug-polymer composites by polymerization in supercritical carbon dioxide: a new method to increase the dissolution rate of bioactive …

2008

Copolymerization of VDF and HFP in Supercritical Carbon Dioxide: A Robust Approach for Modeling Precipitation and Dispersion Kinetics

2011

A kinetic model is developed for the heterogeneous free-radical copolymerization of vinylidene fluoride and hexafluoropropylene in supercritical CO2. The model accounts for polymerization in both the dispersed (polymer-rich) phase and in the continuous (polymer-free) supercritical phase, for radical interphase transport, diffusion limitations, and chain-length-dependent termination in the polymer-rich phase. A parameter evaluation strategy is developed and detailed to estimate most of the kinetic parameters a priori while minimizing their evaluation by direct fitting. The resulting model predictions compare favorably with the experimental results of conversion and MWD at varying monomer fee…

Dispersion Copolymerization of Vinyl Monomers in Supercritical Carbon Dioxide.

2003

The thermally initiated free-radical dispersion copolymerization of methyl methacrylate (MMA) and N,N-dimethylacrylamide (DMA) in supercritical carbon dioxide has been studied in the presence of polysiloxane surfactants. The formation of a stable latex seems to be related to the presence of at least one reactive end group in the surfactant macromolecule, thus suggesting that anchoring of the stabilizer to the surface of the growing polymer particles occurs through chemical grafting. In the case of a molar ratio of DMA to MMA lower than 0.40, microspherical copolymer particles with yields ranging from 81 to 97% were collected from batch polymerizations carried out at 65 °C and 23-28 MPa usin…

Isotopic Effects and Surface Absorption in $^{35-37}$Cl+$^{24}$Mg Interactions

1992

Abstract The few-nucleon transfer is found to play an important role in the isotopic effects observed in absorption. This conclusion is obtained by measuring elastic scattering and quasielastic reactions and by analysing elastic data with both phenomenological and microscopic models. The sensitivity domain is found to be different for imaginary and real potentials. The implication for the validity of the dispersion relation for phenomenological potentials at the real sensitivity radius, when transfers are important, is discussed.

Review of wind tunnel modelling of flow and pollutant dispersion within and from naturally ventilated livestock buildings

2021

[EN] Ammonia emissions from naturally ventilated livestock buildings (NVLBs) pose a serious environmental problem. However, the mechanisms that control these emissions are still not fully understood. One promising method for understanding these mechanisms is physical modelling in wind tunnels. This paper reviews studies that have used this method to investigate flow or pollutant dispersion within or from NVLBs. The review indicates the importance of wind tunnels for understanding the flow and pollutant dispersion processes within and from NVLBs. However, most studies have investigated the flow, while only few studies have focused on pollutant dispersion. Furthermore, only few studies have s…

Improved time-resolved acousto-optic technique for optical fiber analysis of axial non-uniformities by using edge interrogation

2015

The time-resolved acousto-optic technique demonstrated recently to be a very useful method for the analysis of fiber axial non-uniformities, able to detect variations of fiber diameter in the nanometric scale with a spatial resolution of few cm. An edge interrogation approach is proposed to improve further the performance of this technique. The detection of subnanometer fiber diameter changes or sub-ppm changes of the core refractive index is demonstrated.