Interactions with 3D isotropic and homogeneous radiation fields: a Monte Carlo simulation algorithm

Monte Carlo techniques have become important tools for many biomedical applications. Many of these involve simulations of radiation fields that rely on the isotropy and homogeneity of the radiation source. The current study proposes a general algorithm to simulate such a radiation field around a fixed object. The idea is to surround the object with a sphere and to limit the source of radiation to the surface of that sphere. To insure the isotropy of the radiation source, each point on the sphere surface as seen from the object defines a direction at which a unidirectional field of particles is created. The combination of all unidirectional fields approaching from all points on the source sphere creates the effect of an isotropic and homogeneous radiation source. The algorithm is first presented without mathematical detail. Next, the expressions for the position and direction of the particles that compose the field are derived using analytical geometry. The radius of the source sphere is the only parameter needed for this algorithm. The randomness of each particle is simulated by the choice of four random numbers. Two algorithms using these analytical results are proposed, and an example of a C program is given for each. Both algorithms can be easily adapted to any situation that involves the Monte Carlo simulation of radiation interactions of a fixed object immersed within an isotropic and homogeneous radiation field.     

Degradation of perchloroethylene in cosolvent solutions by zero-valent iron

Remediation of sites contaminated by chlorinated organic compounds is a significant priority in the environmental field. Subsequently, the addition of cosolvent solutions for in situ flushing of contaminated source zones has been successfully field tested. However, the treatment of effluent fluids in such cleanup efforts is an often overlooked component of this technology implementation. The purpose of this research was to evaluate the effectiveness of zero-valent iron (Fe(0)) in treating perchloroethylene (PCE) in an aqueous solution, and how the presence of a cosolvent (ethanol) and modification of the iron surface altered dechlorination. The modified iron surfaces included in this study were nickel-plated iron, acid-treated iron, and untreated iron surfaces. PCE dechlorination in the presence of each of the iron surfaces displayed pseudo first-order kinetics. The highest degradation rate of PCE occurred on the nickel-plated iron surface, 5.83 x 10(-3)h(-1), followed by the acid-treated iron, 4.92 x 10(-3)h(-1), and the untreated iron, 3.34 x 10(-3)h(-1). Dechlorination on each of the surfaces decreased with increasing cosolvent fractions. It was shown that as cosolvent fractions increased, PCE adsorption decreased and resulted in a concomitant decrease in PCE degradation rates.     

Angstrom-range optical path-length measurement with a high-speed scanning heterodyne optical interferometer

A highly accurate method of optical path-length measurement is introduced by use of a scanning heterodyne optical interferometer with no moving parts. The instrument has demonstrated the potential to measure optical path length at angstrom resolution over continuous thickness in the micrometer range. This optical path length can be used to calculate the thickness of any material if the refractive index is known or to measure the refractive index of the material if the thickness is known. The instrument uses a single acousto-optic device in an in-line ultra-stable reflective geometry to implement rapid scanning in the microsecond domain for thickness measurements of the test medium.     

Laser-enhanced ionization with avalanche amplification: detection of cesium at fg/mL levels

The avalanche amplification of the laser-enhanced ionization signal of Cs atoms in a flame has been studied. Ionization of Cs atoms, enhanced by two-step excitation, was detected in hydrogen and propane flames. By employing the effect of avalanche amplification of electrons, high signal-to-noise ratio (approximately 10(4)) was obtained for a 100 ppt Cs solution. The extrapolated limit of detection was 30 fg/mL (ppq).     

Automatic correction of continuum background in laser-induced breakdown and Raman spectrometry

The goal of this work was the development and evaluation of an algorithm for the approximation and automatic subtraction of continuum backgrounds in laser-induced breakdown and Raman spectra. The background correction algorithm was applied to simple and complex spectra and its effect on identification accuracy was studied. Linear correlation was used for the identification of plastic samples using both laser-induced breakdown and Raman spectra. For both techniques, the algorithm successfully eliminated continuum background without compromising spectral integrity. A significant improvement in the percentage of correct plastic identifications was observed for Raman spectra. The approach should be applicable to a wide range of background correction problems in atomic and molecular spectroscopy.     

Two-dimensional imaging biosensor for the monitoring of lactate released from brain slices

Real-time monitoring of lactate release from brain slices has been studied with an optical two-dimensional (2D) imaging biosensor. The 2D biosensor is prepared by direct immobilization of lactate dehydrogenase (LDH) molecules onto a flat silica glass surface through a covalent binding mechanism. The biosensor is able to spatially differentiate lactate concentration variations with conventional optical microscopic spatial resolution. This biosensor has the capability to effectively detect lactate down to a concentration of 100 nM. The 2D biosensor responds uniformly with 2.5% RSD from pixel to pixel. With a 100 ms response time, this 2D biosensor has the capability of monitoring simultaneously many cells in one image. We have studied the impact of KCI on lactate release from brain slices. Clear differences have been observed in lactate release for different regions of the tissue. The real-time determination of the newly released lactate from the mouse brain slices clearly demonstrates the feasibility of monitoring lactate release from living specimens. The 2D biosensor will enable us to study cellular communications and possibly other biological processes that require simultaneous temporal and spatial resolution.     

High-resolution field desorption/ionization fourier transform ion cyclotron resonance mass analysis of nonpolar molecules

We report the first field desorption ionization broadband high-resolution (m/Deltam(50%) approximately 65 000) mass spectra. We have interfaced a field ionization/field desorption source to a home-built 9.4-T FT-ICR mass spectrometer. The instrumental configuration employs convenient sample introduction (in-source liquid injection) and external ion accumulation. We demonstrate the utility of this configuration by generating high-resolution positive-ion mass spectra of C(60) and a midboiling crude oil distillate. The latter contains species not accessible by common soft-ionization methods, for example, low-voltage electron ionization, electrospray ionization, and matrix-assisted laser desorption/ionization. The present work demonstrates significant advantages of FI/FD FT-ICR MS for analysis of nonpolar molecules in complex mixtures.     

Propagation of partially coherent beams through particulate media

When propagating through particulate media, optical beams are degraded owing to scattering. We found that the ratio between the width of the distorted beam and the width of the initial beam decreases when the spatial coherence of the incident beam is reduced. These experimental observations are well described within the paraxial approximation of the transport theory.     

An Assessment of the Singerian Inquiring Organizational Model: Cases from Academia and the Utility Industry

The Singerian model of inquiring organizations is reviewed (Proceedings of the Americas Conference on Information Systems, Phoenix, Arizona Aug. 16–18,1996:443–445; Australian Journal of Information Systems, 1998;6(1):3–15, reprinted in Foundations of Information Systems: Towards a Philosophy of Informative Technology, http://www.cba.uh.edu/~parks/fis/fisart.htm.) and two cases of organizations representing the Singerian approach are analyzed. The Singerian organization, based on Churchman's (The Design of Inquiring Systems: Basic Concepts of Systems and Organizations, New York, NY: Basic Books Inc., 1971.) Singerian inquiring system, has ethical purposes, treats employees, customers and other stakeholders with trust and respect, and pursues socially responsible goals, including a respect for the environment. Decision making in Singerian organizations is holistic and systemic, and includes diverse stakeholders, thus requiring an open, cooperative culture, wherein debate is encouraged. Authority is diffuse. Measurement is fundamental. A system of measures is continuously monitored, refined, compared and revised to assess progress. Cooperation and communication are supported with various types of groupware, including e-mail, electronic meeting systems, group support systems, negotiation support systems, discussion forums, knowledge bases, knowledge management systems and the like. The Internet and World Wide Web may serve as resource and dissemination agents for exoteric knowledge created by the organization. Two organizations, an Energy Service Company and an academic Center for the Management of Information Systems, are analyzed for their conformance to and success with the Singerian approach. The organizations tended to prosper when the model was followed, but ran into difficulties when it was not.     

A Web-Based Knowledge Network for Supporting Emerging Internet Applications

Although the Internet and the World Wide Web technologies have gained a tremendous amount of popularity among people and organizations, the network that these technologies created is not much more than a multimedia data network. It provides tools and services for people to browse and search for data but does not provide the facilities for automatically delivering the relevant information for supporting decision–making to the right people or applications at the right time. Nor does it provide the means for users to enter and share their knowledge that would be useful for making the right decisions. In this work, we introduce the concept of a Web–based knowledge network, which allows users and organizations to publish, not only their multimedia data, but also their knowledge in terms of events, parameterized event filters, customizable rules and triggers that are associated with their data and application systems. Operations on the data and application systems may post events over the Internet to trigger the processing of rules defined by both information providers and consumers. The knowledge network is constructed by a number of replicable software components, which can be installed at various network sites. They, together with the existing Web servers, form a network of knowledge Web servers.