994 research outputs found
Airborne particle deposition in cleanrooms: deposition mechanisms
This article discusses the mechanisms
of particle deposition onto cleanroom
surfaces. The main mechanism
for particles above about 0.5μm is
gravitational settling. Turbulent
deposition and electrostatic attraction
can also occur at all particle sizes, and
for particles below 0.5μm Brownian
diffusion is important. Measurements
of particle deposition rates (PDRs) were
made of particles ≥ 0μm on witness
plates orientated in different directions
and exposed in different ventilation
conditions, and it was concluded that
over 80% of particles were deposited
by gravitational sedimentation, and
probably more than half of the
remainder by turbulent deposition
Slowing Down and Scattering of Ions in Solids
The interaction of particle beams with solids yields three parts, i.e. reflected particles, penetrating particles and trapped particles. At very low energies particle reflection is dominant, at very high energies penetration is the most important effect. Trapped particles are the result of energy loss processes, which on the other hand cause radiation damage in the solid. In the energy range discussed here, i.e. above energies where quantum effects, diffraction etc. are important and below energies where nuclear reactions, relativistic effects etc. may occur, the particle trajectories are classical. The energy loss process can be treated separately as nuclear and electronic stopping power. The collisions of the projectiles with target atoms are hence binary collisions involving a properly chosen screened Coulomb-potential. In single crystals the structural properties enable channeling, which is a very useful tool in sol id state analysis. The electronic stopping includes contributions from single collision processes and collective excitations. Both effects can be described by a dielectric response function. The range of applications covers analytical methods, means to modify solid state properties and also the production of thin films
Airborne particle deposition in cleanrooms: relationship between deposition rate and airborne concentration
This article is the second of a series that discusses the deposition of airborne particles onto cleanroom surfaces. It investigates the relationship between the airborne concentration of a range of cumulative sizes of particles and the particle deposition rate (PDR) onto cleanroom surfaces, through knowledge of the deposition velocity of particles in air. The deposition velocity of a range of cumulative particle sizes was obtained by means of experiments, theoretical calculations, and literature search and the influence of a number of variables found in cleanrooms on the deposition velocity was investigated. The use of the deposition velocity to calculate the amount of deposition on cleanroom surfaces, such as manufactured products, is discussed, along with its use in deciding the required ISO 14644-1 class of cleanroom; these subjects will be discussed in more depth in the final article of this series
Airborne particle deposition in cleanrooms: calculation of product contamination and required cleanroom class
This is the third and final article in a series that discusses the deposition of airborne particles onto critical surfaces in cleanrooms. This article explains a method for calculating the amount of particle or microbe-carrying particle deposition onto critical cleanroom surfaces, such as product, and a method for calculating the airborne particle cleanliness class, or airborne microbial concentration that is required to obtain a specified and acceptable amount of product contamination
Kinetics of absorption of carbon dioxide in aqueous ammonia solutions
AbstractIn the present work the absorption of carbon dioxide into aqueous ammonia solutions has been studied in a stirred cell reactor, at low temperatures and ammonia concentrations ranging from 0.1 to about 7 kmol m−3. The absorption experiments were carried out at conditions where the so-called pseudo first order mass transfer regime was obeyed–and hence the kinetics of the reaction between carbon dioxide and ammonia could be derived. The results were interpreted according to the well-established zwitterion mechanism
Integration through transients for Brownian particles under steady shear
Starting from the microscopic Smoluchowski equation for interacting Brownian
particles under stationary shearing, exact expressions for shear-dependent
steady-state averages, correlation and structure functions, and
susceptibilities are obtained, which take the form of generalized Green-Kubo
relations. They require integration of transient dynamics. Equations of motion
with memory effects for transient density fluctuation functions are derived
from the same microscopic starting point. We argue that the derived formal
expressions provide useful starting points for approximations in order to
describe the stationary non-equilibrium state of steadily sheared dense
colloidal dispersions.Comment: 17 pages, Submitted to J. Phys.: Condens. Matter; revised version
with minor correction
Stability transitions for axisymmetric relative equilibria of Euclidean symmetric Hamiltonian systems
In the presence of noncompact symmetry, the stability of relative equilibria
under momentum-preserving perturbations does not generally imply robust
stability under momentum-changing perturbations. For axisymmetric relative
equilibria of Hamiltonian systems with Euclidean symmetry, we investigate
different mechanisms of stability: stability by energy-momentum confinement,
KAM, and Nekhoroshev stability, and we explain the transitions between these.
We apply our results to the Kirchhoff model for the motion of an axisymmetric
underwater vehicle, and we numerically study dissipation induced instability of
KAM stable relative equilibria for this system.Comment: Minor revisions. Typographical errors correcte
- …