Sub-micron

In the dense interstellar medium characteristic of sites of star fonuation, for example, scattering of visible/UV light by sub-micron-sized dust grains makes molecular clouds optically opaque and lowers their internal temperature to only a few tens of Kelvin. The thenual radiation from such objects therefore peaks in the FIR and only becomes optically thin at even longer wavelengths. Rotational motions of small molecules and rovibrational transitions of larger species and clusters thus provide, in many cases, the only or the most powerfiil probes of the dense, cold gas and dust of the interstellar medium. 

One interesting new field in the area of optical spectroscopy is near-field scaiming optical microscopy, a teclmique that allows for the imaging of surfaces down to sub-micron resolution and for the detection and characterization of single molecules [, M]- Wlien applied to the study of surfaces, this approach is capable of identifying individual adsorbates, as in the case of oxazine molecules dispersed on a polymer film, illustrated in figure Bl.22,11 [82], Absorption and emission spectra of individual molecules can be obtamed with this teclmique as well, and time-dependent measurements can be used to follow the dynamics of surface processes. 

Mineral matter derived from ash constituents of liquid and solid fuels can vaporize and condense as sub-micron-size aerosols. Larger mineral matter fragments are formed from mineral inclusions which melt and resolidify downstream. 

A particularly interesting feature of industrial crystallization systems is the relatively wide range of particle sizes encountered. Particle sizes range over several orders of magnitude from the sub micron (nanometers) to several millimetres or more, i.e. from colloidal to coarse . Such particles comprise a large part of the world on a human scale and a great source of industrially generated wealth. 

Anonymous, Particle Charging Aids Wet Scrubber s Sub-Micron Efficiency, Chem. Engineering,]u y 21, 1975, p. 74. 

This type of collector has found wide application in general engineering and very high collection efficiencies are possible, but at the expense of considerable power requirements. General-purpose collectors at pressure drops across the collector of 150 mm will have collection efficiencies of 98 per cent at 10 pm and above. Units with pressure drops of 800 mm and efficiencies of more than 99 per cent on sub-micron particles are available. 

Spray-type collectors In this system water is sprayed or cascaded onto the contaminated air directly or through packed towers, and the fumes or dust are washed away by absorption. These collectors are used extensively on the treatment of fumes of all types and have low pressure drops and hence low power requirements compared to induced spray. A development of this collector is the venturi scrubber, which injects high-pressure water into a venturi through which the fume-laden air is passing. The intimate contact of the two ensures absorption and removal from the air stream. These collectors are used in fume removal and have efficiencies of more than 99 per cent on sub-micron particles. 

Other more exotic types of calamitic liquid crystal molecules include those having chiral components. This molecular modification leads to the formation of chiral nematic phases in which the director adopts a natural helical twist which may range from sub-micron to macroscopic length scales. Chirality coupled with smectic ordering may also lead to the formation of ferroelectric phases [20]. 

Luo, J. and Dorfeld, D. A., Material Removal Regions in Chemical Mechanical Planarization for Sub-micron Integrated Circuit Fabrication Coupling Effects of Slurry Chemicals, Abrasive Size Distribution and Wafer-Pad Contact Area, IEEE Trans. Semicond. Manuf, Vol. 16, No. 1, 2003, pp. 45-56. 

Morphology of the enzymatically synthesized phenolic polymers was controlled under the selected reaction conditions. Monodisperse polymer particles in the sub-micron range were produced by HRP-catalyzed dispersion polymerization of phenol in 1,4-dioxane-phosphate buffer (3 2 v/v) using poly(vinyl methyl ether) as stabihzer. °° ° The particle size could be controlled by the stabilizer concentration and solvent composition. Thermal treatment of these particles afforded uniform carbon particles. The particles could be obtained from various phenol monomers such as m-cresol and p-phenylphenol. 

The importance of particle size is directly proportional to the sub-sample size recommended by the analytical method. The larger the sub-sample size the larger the acceptable particle size. For sub-sample sizes of ig or greater a soil sieved through a imm screen is generally acceptable. Therefore if the sample is relatively coarse, e.g up to 2mm particles and the matrix CRM is an uniform sub-micron powder, it may be necessary to use a much larger sample from the material under test than for the CRM. 

Venkatakrishnan K, Tan B, Sivakumar NR. 2002. Sub-micron ablation of metallic thin film by femtosecond pulse laser. Opt Laser Tech 34 575-578. 

James AC. 1878. Lung deposition of sub-micron aerosols calculated as a function of age and breathing rate. In National Radiological Protection Board annual Research and Development Report. National Radiological Protection Board. Harwell, United Kingdom,71-75. 

The first nuclear microbeam with a spatial resolution of 1 pm was built by Watt et al. (1981), and the first sub-micron instrument was built by Grime et al. (1987). Khodja et al. (2001) have published a description of the nuclear microprobe at the Pierre Sue Laboratory in France, which is a national facility dedicated to microbeam analysis. Its unique facility is that it is capable of analysing radioactive samples by means of a dedicated beamline. Figure 4.1 shows a schematic diagram of the apparatus. 

The deposition of sub-micron aerosols in a hollow cast of human bronchi has recently been measured under realistic conditions (Cohen et al., in press). Typical data are shown in Figure 4. These are inconsistent with convective enhancement of deposition but support the classical treatment of deposition by diffusion (Chamberlain and Dyson, 1956). 

Because additives are normally present in low concentration, this parameter is much larger for additives than for the metal ion. Hence, while ionic transport does not place an important limit on deposition rate inside sub-micron trenches, additive diffusion does. Both scale with L2/b so that as L is reduced at constant L/D, D becomes smaller, and additive diffusion becomes less controlling. 

Kapany, N. S., High resolution fibre optics using sub micron multiple fibres, Nature 1959, 184, 881 883... 

Cyclone filters are effective at removing larger particles and can operate over a wide range of temperatures, limited primarily by the material of construction. Cyclone filters are often designed as multiple units in series (multi-clones). They can remove >90% of particulates above about 5 microns in diameter at minimal pressure drops of 0.01 atm. Partial removal of material in the 1.5 micron range is also possible, but cyclonic filters become ineffective with sub-micron particles. 

Barrier filters include a range of porous materials that allow gases to penetrate but prevent the passage of particulates. These filters effectively remove small-diameter particulates in the range of 0.5 to 100 pm in diameter from gas streams. Barrier filters can be designed to remove almost any size of particulate, including those in the sub-micron range, but the pressure differential across the filter will increase as the pore size decreases. 

Bag filters are composed of woven material that intercepts small particles on the filter surface by impingement and electrostatic attraction. The efficiency of collection increases as the depth of the filter cake increases, making these filters highly efficient for small diameter, even sub-micron, particle size. Filters are periodically shaken or back-flushed to remove particulate accumulation. These filters are usually constructed of woven materials suitable for operation at low temperatures up to about 350°C. 

M. Granstrom and O. Inganas, Flexible arrays of sub-micron sized polymeric light-emitting diodes, Adv. Mater., 7 1012-1015, 1995. 

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