772 research outputs found
Calculation of air supply rates and concentrations of airborne contamination in non-UDAF cleanrooms
This article reviews a series of scientific articles written by the authors, where the following topics
were investigated in relation to non-unidirectional airflow cleanrooms.
(1) The air supply rate required to obtain a specified concentration of airborne contamination.
(2) The calculation of concentrations of airborne contaminants in different ventilation and dispersion
of contamination situations.
(3) The decay of airborne contamination
(a) during the ‘clean up’ test described in Annex 1 of the EU Guidelines to Good Manufacturing
Practice (2008);
(b) during the recovery rate test described in Annex B12 of ISO 14644-3 (2005);
(c) associated with clean areas, such as airlocks, to reduce airborne contamination before a door
into a cleanroom is opened.
Worked examples are provided to demonstrate the calculation methods to provide solutions to the
above topics
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
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: 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
Development of explosive forming techniques for Saturn V components Final report, 24 Jun. 1964 - 28 Jan. 1966
Explosive forming techniques development for aluminum alloy, carbon steel, and titanium components for Saturn V launch vehicl
Killing spinors in supergravity with 4-fluxes
We study the spinorial Killing equation of supergravity involving a torsion
3-form \T as well as a flux 4-form \F. In dimension seven, we construct
explicit families of compact solutions out of 3-Sasakian geometries, nearly
parallel \G_2-geometries and on the homogeneous Aloff-Wallach space. The
constraint \F \cdot \Psi = 0 defines a non empty subfamily of solutions. We
investigate the constraint \T \cdot \Psi = 0, too, and show that it singles
out a very special choice of numerical parameters in the Killing equation,
which can also be justified geometrically
Ventilation effectiveness in cleanrooms and its relation to decay rate, recovery rate, and air change rate
Non-unidirectional airflow cleanrooms are supplied with filtered air to minimise the contamination
of a product or process by airborne contamination. The effectiveness of the ventilation system in
providing the required type of airflow in the cleanroom that will minimise airborne contamination
can be assessed by measuring ventilation effectiveness indexes. This article provides information on
what ventilation effectiveness indexes are suitable for cleanrooms, and how they can be obtained by
test methods in common use in cleanrooms. Three methods of measuring ventilation effectiveness are
discussed, namely, the Contamination Removal Effectiveness (CRE) index, the Air Change
Effectiveness (ACE) index and the Performance Index (PI), and it was considered that the ACE index
and PI were the most suitable for use in cleanrooms.
The decay rate and recovery rate of airborne contamination in relation to the air change rate in
non-unidirectional cleanrooms is also considered, and it is demonstrated that when measured at the
same location, the three rates are identical. Also considered is the measurement of these rates in
cleanrooms and how they can be used to obtain the ACE index
Risk factors of gastrointestinal nematode parasite infections in small ruminants kept in smallholder mixed farms in Kenya
<p>Abstract</p> <p>Background</p> <p>Helminth infections in small ruminants are serious problems in the developing world, particularly where nutrition and sanitation are poor. This study investigated the burden and risk factors of gastrointestinal nematode parasite infections in sheep and goats kept in smallholder mixed farms in the Kenyan Central Highlands. Three hundred and seven small ruminants were sampled from 66 smallholder mixed farms in agro-ecological zones 1 (humid) and 3 (semi-humid) in the Kenyan Central highlands. The farms were visited once a month for eight months during which a health and production survey questionnaire was administered. Fecal samples were collected at each visit from each animal. Fecal egg counts (FEC) were performed using the modified McMaster technique. Associations between potential risk factors and FEC were assessed using 3-level Poisson models fit in SAS using GLIMMIX macro. Correlations among repeated observations were adjusted for using three different correlation structures.</p> <p>Results</p> <p>A rise in FEC was observed two months after the onset of rains. Farmer education, age category, de-worming during the preceding month and grazing system were significant predictors of FEC. Additionally, there were significant interactions between grazing system and both de-worming and age category implying that the effect of grazing system is dependent on both de-worming status and age category; and that the effect of de-worming depends on the grazing system. The most important predictors of FEC in the study area were grazing system, de-worming status and education of the farmers.</p> <p>Conclusion</p> <p>Since several factors were important predictors of FEC, controlling gastrointestinal helminths of small ruminants in these resource-poor smallholder mixed farms requires a sustainable integrated helminth control strategy that includes adoption of zero-grazing and more farmer education probably through extension services. Achieving improved helminth controls in these resource-poor farming systems offers an opportunity to increase small ruminant productivity and hence has a potential of improving the livelihood of the resource-poor farmers.</p
Shrouded CMC Rotor Blades for High Pressure Turbine Applications
The density of Ceramic Matrix Compos-ite(CMC) materials is approximately 1/3 the density of metals currently used for High Pressure Turbine(HPT) blades. A lower density, and consequently lower centrifugal stresses, increases the feasibility of shrouding HPT blades. Shrouding HPT blades improves aerodynamic eciency, especially for low aspect ratio turbine blades. This paper explores aerodynamic and structural issues associated with shrouding HPT rotor blades. Detailed Navier-Stokes analysis of a rotor blade showed that shrouding improved blade row aerodynamic eciency by 1.3%, when the clearance was 2% of the blade span. Recessed casings were used. Without a shroud the depth of the recess equaled the clearance. With a shroud the recess depth increased by the shroud thickness, which included a knife seal. There was good agreement between the predicted stage eciency for the unshrouded blades and the experimentally measured efficiency. Structural analysis showed a strong interaction between stresses in the shroud and peak stresses at the hub of the blade. A thin shroud of uniform thickness only moderately increased maximum blade stress, but there were very high stresses in the shroud itself. Increasing shroud thickness reduced stresses in the shroud, but increased blade stresses near the hub. A single knife seal added to the thin shroud noticeably decreased maximum shroud stress, without increasing maximum blade stress. Maximum stresses due to pressure loads and combined pressure and centrifugal loads were nearly the same as the maximum stresses for individual pressure or cen-trifugal loads. Stresses due to a 100K temperatur
Explosive forming of 2219 aluminum final report
Variables affecting metal springback of aluminum during explosive deformation and influence of high energy forming on metallurgical behavio
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