Chemical Engineering @ChemengFiles.Com

Silicon nanoparticle-based floating gate metal-oxide-semiconductor (MOS) field effect devices have potential for terabit [...] density nonvolatile memory applications. Aerosol synthesis of silicon nanoparticles is an important route toward the formation of discontinuous silicon nanoparticle floating gate structures that affords excellent control over particle size and size distribution, particle density, and oxide passivation. We have fabricated nanoparticle memory devices in a conventional MOS ultra-large scale integration (ULSI) process with channel lengths from 0.2 - 10 [...] with a silicon nanoparticle floating gate fabricated by aerosol deposition.

Atmospheric particles, or particulate matter, can be solid or liquid with diameters varying from around 0.002[micrometers] to roughly 100[micrometers]. Atmospheric aerosol sources can be classified as primary or secondary, with the primary aerosol being directly emitted from the corresponding sources and the secondary particles being formed in the atmosphere, for example, from gas-phase chemical reactions that produce condensable vapors. At the same time aerosol particles are ultimately connected with the formation of water droplets and equivalently with the formation of clouds and fogs in the atmosphere.

Part I: Rate studies of the air oxidation and thermal decomposition of aqueous sodium dithionite, Na2S2O4, were conducted. These experiments were supplemented by studies of the electron-paramagnetic-resonance properties and the electrolytic formation of dithionite.

In the air-oxidation experiments, the overall rate was observed to have half-order dependence on the dithionite concentration and a first-order dependence on molecular oxygen concentration. This could be explained mechanistically on the basis of an instantaneous equilibrium reaction between dithionite and the [...] radical ion.

Predicting how the future climate of Earth will change as a result of increasing human emissions is one of the greatest problems facing science today. The earth’s climate is the result of a delicate balance between incoming and outgoing radiation. Anthropogenic emissions of aerosol particles into the atmosphere have the potential to affect the earth’s climate in significant ways through both direct and indirect effects on the earth’s radiative balance. One of the largest uncertainties in aerosol radiative forcing is associated with the relationship between atmospheric aerosols and cloud formation, properties, and lifetime. Clouds form by water condensing on small particles (aerosols) in the air (referred to as cloud condensation nuclei, or CCN), and how the increasing levels of atmospheric particles will affect Earth’s clouds and its hydrologic cycle represents one of the key problems in the science of climate. Through theoretical, field, and laboratory investigations, the results presented here reinforce the importance of atmospheric aerosol chemical composition in determining the ability of an aerosol particle to act as a CCN. A study that incorporates surface tension and limited solubility effects, especially of organic compounds, in parameterizations of cloud droplet activation indicate that these chemical effects can rival those of the meteorological environment. An inverse CCN/aerosol closure study of field measurements indicates that assumptions of simple chemistry and mixing state in the interpretation and analysis of field cloud condensation nuclei (CCN) measurements may not necessarily be sufficient and/or realistic, depending heavily on the location of the field study. Properties of organic compounds, such as functional groups, extent of dissociation, and solubility were found to influence the CCN activity of the compounds in laboratory experiments with pure organic aerosols. However, the importance of careful planning of laboratory experiments, in consideration of the properties of the organic compounds, was reinforced and results were carefully interpreted to avoid experimental bias in the conclusions.

This thesis describes a novel "microplasma" source that is suitable for microreactor applications. The high-pressure "microplasma" is a direct current microdischarge, formed between two metal electrodes: a cathode with a pin-hole (diameter~100 �m) and an anode of unspecified shape. Strong radial electric fields are produced in the microhollow cathode geometry, causing electrons to oscillate (Pendel effect). As a result of enhanced ionization processes, it is possible to produce a stable high-intensity discharge at pressures of 1 atmosphere or higher. We have utilized these microdischarges for several applications including pattern transfer, diamond deposition, excimer emission, and nanoparticle synthesis.

Plasmid-host cell interactions have been characterized experimentally for recombinant Escherichia coli populations. The plasrnids used contain pMB1 replication origins and propagate in E coli at different copy number levels ranging from 12 to 408. Host E. coli HB101 strains transformed with those plasmids were used throughout this research.

The specific growth rate and amount of cloned-gene product ([...]lactamase) were determined in batch cultivations as a function of plasmid copy number. Maximum specific growth rates in LB and M9 media were reduced monotonically for increasing plasmid content per cell. The maximum specific growth rate for a recombinant strain with copy number 408 was reduced by 25% relative to the plasmid-free strain. The ratio of [...]- lactamase specific activity to plasmid content, as a measure of the overall efficiency of plasmid-gene expression, declines by a factor of 7 as the copy number increases from 12 to 408. The relationship between copy number and cloned-gene product activity can be reasonably approximated by a parabolic equation, with approximately linear proportionality for copy numbers up to 60 but subsequently with reduction in the product/copy number ratio.

The internal energy and the entropy components of the elastic restoring force in rubbers were determined for natural rubber up to an extension ratio of about 3.0. Four different experimental measurements were necessary to determine these components: (1) the force-temperature coefficient at constant temperature and length; (2) the force-pressure coefficient at constant temperature and length; (3) the thermal expansion coefficient at constant length; and (4) the isothermal compressibility at constant length. The force-temperature and the force-pressure coefficients were functions of strain whereas the expansion coefficients and the isothermal compressibilities were independent of strain. These measurements gave an internal energy contribution of 23% for natural rubber independent of the strain over the range of extensions studied.

Interest in accurate measurements of the time-dependent Poisson's ratio of polymers arises because it is a component commonly needed in stress analysis and it appears in most theories predicting the behavior of filled materials and composites. Because of the paucity of data and the difficulties in determining [...](t) experimentally, it has been customary in the past to treat [...](t) as a constant. This is unsatisfactory theoretically and inadequate for accurate work.

Much is understood about the behavior of perfectly flexible and perfectly rigid polymer chains; however, many polymers, for example DNA, are somewhere in between these two limiting cases. Such polymers are termed semiflexible, and their molecular elasticity can play a significant role in single-chain behavior as well as contribute to collective effects. Using analytical theory and numerical methods, we address several problems that focus on the equilibrium and dynamic behavior of semiflexible polymers to gain a deeper understanding of their fundamental physics.

Perchloric Acid is a substance resembling sulfuric acid in many respects. It is a strong acid, very stable in solution, and has a high boiling point. It possesses some advantages over sulfuric acid, such as being monobasic, and having relatively few insoluble salts. (K, Rb, Cs, and Tl perchlorates are only slightly soluble.) Hence a cheap way of making perchloric acid would be highly advantageous to the chemical industry. The present methods of its production are rather expensive, employing the electrolytic production of sodium perchlorate and the distillation of the latter with sulfuric acid under reduced pressure. The product, a 60% perchloric acid is now sold for $7 to $8 per pound. Ammonium perchlorate is obtainable at a fairly low cost, (about 2O [cents] per pound) and might be used as a basis for the cheaper preparation of perchloric acid.