Onset of runaway nucleation in aerosol reactors

The onset of homogeneous nucleation of new particles from the products of gas phase chemical reactions was explored using an aerosol reactor in which seed particles of silicon were grown by silane pyrolysis. The transition from seed growth by cluster deposition to catastrophic nucleation was extremely abrupt, with as little as a 17% change in the reactant concentration leading to an increase in the concentration of measurable particles of four orders of magnitude. From the structure of the particles grown near this transition, it is apparent that much of the growth occurs by the accumulation of clusters on the growing seed particles. The time scale for cluster diffusion indicates, however, that the clusters responsible for growth must be much smaller than the apparent fine structure of the product particles

Submicron silicon powder production in an aerosol reactor

Powder synthesis by thermally induced vapor phase reactions is described. The powder generated by this technique consists of spherical, nonagglomerated particles of high purity. The particles are uniform in size, in the 0.1–0.2 µm size range. Most of the particles are crystalline spheres. A small fraction of the spheres are amorphous. Chain agglomerates account for less than 1% of the spherules

Optimizing the Design of Oligonucleotides for Homology Directed Gene Targeting

BACKGROUND: Gene targeting depends on the ability of cells to use homologous recombination to integrate exogenous DNA into their own genome. A robust mechanistic model of homologous recombination is necessary to fully exploit gene targeting for therapeutic benefit. METHODOLOGY/PRINCIPAL FINDINGS: In this work, our recently developed numerical simulation model for homology search is employed to develop rules for the design of oligonucleotides used in gene targeting. A Metropolis Monte-Carlo algorithm is used to predict the pairing dynamics of an oligonucleotide with the target double-stranded DNA. The model calculates the base-alignment between a long, target double-stranded DNA and a probe nucleoprotein filament comprised of homologous recombination proteins (Rad51 or RecA) polymerized on a single strand DNA. In this study, we considered different sizes of oligonucleotides containing 1 or 3 base heterologies with the target; different positions on the probe were tested to investigate the effect of the mismatch position on the pairing dynamics and stability. We show that the optimal design is a compromise between the mean time to reach a perfect alignment between the two molecules and the stability of the complex. CONCLUSION AND SIGNIFICANCE: A single heterology can be placed anywhere without significantly affecting the stability of the triplex. In the case of three consecutive heterologies, our modeling recommends using long oligonucleotides (at least 35 bases) in which the heterologous sequences are positioned at an intermediate position. Oligonucleotides should not contain more than 10% consecutive heterologies to guarantee a stable pairing with the target dsDNA. Theoretical modeling cannot replace experiments, but we believe that our model can considerably accelerate optimization of oligonucleotides for gene therapy by predicting their pairing dynamics with the target dsDNA

Powder Synthesis in Aerosol Reactors

The onset of homogeneous nucleation of new particles from the products of gas phase chemical reactions has been explored using an aerosol flow reactor. Silicon seed particles were used as a probe to study the transition from seed growth by cluster deposition to runaway nucleation. This transition was found to be very abrupt. The mechanism of formation of solid particles from large excesses of low vapor pressure condensible species has been investigated by studying the microstructure of the product aerosol. A discrete - sectional solution of the aerosol general dynamic equation was derived in order to examine the aerosol evolution associated with fast chemical reactions. This kinetic model quantitatively predicts the aforementioned transition. Application of the understanding of aerosol generation and growth has led to the production of a high quality silicon powder suitable for ceramic applications. This powder was synthesized by the pyrolysis of silane in an aerosol reactor and has nearly ideal characteristics, i.e., controlled size distribution, spherically shaped, nonagglomerated submicron particles. A simple reaction coagulation model was developed to facilitate mapping of the nucleation and growth domains. This, in conjuction with the discrete-sectional model, was used to evaluate the various aerosol processes for powder synthesis. The influence of the initial reactant concentration, reaction rate, temperature profile, seed particle conditions, and residence time on the final powder characteristics were examined. The structure of the particles also depends on the way particles fuse together. Particle fusing was therefore, modeled along with the formation and growth processes to study the effects of coalescence on the extent of agglomeration of the product powder. A recipe for the synthesis of ideal powders was proposed.</p

[[alternative]]Automatic Traffic Monitoring System

[[abstract]]The importance of the transportation system to a country can be just like that of the blood circulation system to the human body. Many countries have spent a great amount of annual budget for maintaining, improving, and enhancing their transportation systems. It was common in the past that hardware resources (e.g., roads and vehicles) were introduced in order to meet the rapidly increasing requests on transportation. However, the former almost always hardly catches up with the latter. Moreover, introducing hardware equipments could be inadequate for the areas with limited sizes and crowded people. Therefore, under present conditions how to increase the efficacy, safety, and comfortability of transportation systems with the help of currently available high technologies, such as computers, networks, communication, controls, and advance managements may become more practicable. Traffic monitoring systems collect such data as traffic flows, headways, road occupancies, average car speeds, driving directions and trajectories from main arteries and critical hinges. The collected data would be useful for traffic control centers to manage either manually or automatically traffic signals. Vehicle drivers will be able to plan in advance their routes before leaving for destinations based on the information delivered from traffic control centers. Long-term observed traffic data will provide valuable references for the personnels who maintain and construct roads as well as the researchers who would like to investigate the relationships among transportation equipments, driving behaviors, and accidents at important transit spots. Furthermore, some traffic surveillance systems can detect unusual events (e.g., collisions, breakdowns, and traffic law violations) and afterwards put on record the processes of the events. In the above, we only name a few applications regarding traffic monitoring systems. There are actually more to say with the systems. In this project, a prototype of traffic surveillance system is proposed. The details of implementing the system are described in depth. We mention the difficulties probably encountered during the development of the system and provide possible solutions to the difficulties as well.

Energy coherence and charge diffusion in dissipative reaction

In the framework of the transport theory, the distribution of coherent In the framework of the transport theory, the distribution of coheren