Understanding conditions for which biological effects of nonionizing electromagnetic fields can be expected

Scientific interest in the interaction of nonionizing electromagnetic fields with biological systems is longstanding, but often still controversial. Theories, models and computer simulations have usually emphasized physical interactions with subsystems (e.g. cell membranes) of a biological system. By extending this first necessary physical step to a second step of explicitly and quantitatively considering chemical changes, increased understanding appears possible. In the case of "strong fields", the role of field-altered chemistry is important to electrochemotherapy [Biochem. Pharmacol. 42, Suppl. (1991) 567] and creation of transdermal microconduits [Bioelectrochem. Bioenerg. 49 (1999) 11; J. Controlled Release 61 (1999) 185; J. Invest. Dermatol. 116 (2001) 40] For "weak fields" (a topic with much more controversy) consideration of chemical change shows that organized multicellular systems can be understood to respond to extremely small electric [Chaos 8 (1998) 576] or magnetic fields [Nature 405 (2000) 707]. In contrast, isolated individual cells interacting via voltage-gated channels [Proc. Natl. Acad. Sci. 92 (1995) 3740; Biophys. J. 75 (1998) 2251; Bioelectromagnetics 20 (1999) 102], or processes without "temperature compensation" [Biophys. J. 76 (1999) 3026], appear implausible. Satisfactory understanding is likely only if experimental and theoretical work is reconciled, which should therefore be emphasized. The interaction of electromagnetic fields with biological systems is of interest because of fundamental scientific curiosity, potential medical benefits and possible human health hazards.     

Surface modification without desorption: recycling of Cl on Si(100)-(2 x 1)

We demonstrate chlorine-induced modification of Si(100)-(2 x 1) under conditions where Cl is recycled rather than desorbed as SiCl2. A dimer with 2 Cl atoms, 2SiCl, converts to SiCl2+Si, allowing the bare Si atom to escape onto the terrace. At temperatures below the desorption threshold, the SiCl2 unit decays through Cl diffusion, allowing the second Si atom to escape. The result is a dimer vacancy, terrace regrowth structures, and Cl that is able to participate in another pitting event. Access to this unexpected roughening pathway is controlled by the Cl concentration and temperature. This previously overlooked process represents an important component of Si(100) surface processing.     

Analysis of 13C-mixed triacylglycerol in stool by bulk (EA-IRMS) and compound specific (GC/MS) methods

This paper was presented in poster form at the 17th International Congress of Nutrition, August 27-31, Vienna, Austria (Annals of Nutrition & Metabolism 2001; 45(Suppl.1):349). Some of the data were also presented in poster form at the British Society of Gastroenterology Meeting, March 18-21, Glasgow, UK (Gut 2001; 48(Suppl.1):A91). The 13C-mixed triacylglycerol (MTG) breath test is used to measure intraluminal fat digestion. In normal digestion, 20-40% of the ingested 13C label is recovered in breath CO2. We aimed to identify the proportions of ingested label excreted in stool, as well as breath following ingestion of 13C-MTG by children with impaired exocrine pancreatic function and healthy controls. 13C enrichment of breath samples was measured by continuous flow isotope ratio mass spectrometry (IRMS) and cumulative percent dose recovered (cPDR) in 10 h was calculated. Total 13C of a faecal fat extract from each stool was measured by elemental analyser-IRMS, and 13C enrichment and concentration of the TBDMS derivative of octanoic acid was measured by GC/MS after hydrolysis of the fat extract. Stool 5-day cPDR was calculated. Mean breath cPDR was 35%. Mean cPDR in stool by combustion-IRMS and GC/ MS, respectively, was 0.8% and 1.0%. Therefore, the remaining 64% of the 13C label must remain in the body and variability in breath cPDR is due to postabsorptive rather than predigestive factors.     

Production of 13C labelled pea flour for use in human digestion and fermentation studies

Stable isotope breath tests offer a new approach to the study of digestion and fermentation of carbohydrates in man. In this study, 13C labelled peas were grown by pulsing 250 ml 13CO2 into a sealed growth chamber. A second pulse was added to a portion of the peas to increase the 13C enrichment. This generated pea flour with an enrichment of 2.36 at.% excess (range 2.09-2.71 n = 3) and 8.64 atom % excess (range 7.37-9.78 n = 3) respectively. This represented incorporation of an absolute yield of 3.8% of the 13CO2 into peas in the 'once-labelled' treatment and 7.5% in the 'twice-labelled' treatment. Ingestion of a mixture of the labelled pea flour (300 mg) by two volunteers generated measurable 13CO2 excretion for breath test analysis. The profile of breath 13CO2 enrichment increased to a maximum within three hours after consuming the pea flour followed by a decrease almost back to baseline by 13 hours. Breath 13CO2 appeared to rise again after this apparent nadir at 13 hours until the end of the sampling period. Mathematical analysis of the data suggested that two peaks best described the profile of breath 13CO2 up to 13 hours. A third peak was necessary to describe the late rise in breath 13CO2 enrichment. This use of 13C enriched pea flour may provide a useful non invasive method for measurement of digestion and fermentation in vivo.     

Measures of distance for atomic charge and momentum densities and their relationship to physical properties

Atomic charge and momentum densities of 91 atoms (He? U) are classified in terms of their L₁, L₂, and entropic measures of distance from the densities of the preceding atoms. The relationship between these distances and the first ionization energies is also considered. © 1995 John Wiley & Sons, Inc.     

Determination of gas/surface interaction potentials: Extraction of the Lennard-Jones,Devonshire strength parameter

A simple relationship is established which allows the extraction of the strength of the periodic part of the Lennard-Jones, Devonshire gas/surface potential. Applications are made illustrating the usage of the method.     

Toward a theory of wave energy transport in large irregular structures

An ansatz is proposed by which the energy transport behavior observed at early times in a direct numerical simulation (DNS) of a large irregular structure may be extrapolated to arbitrary times. In the slow-transport limit, this ansatz leads to a diffusion-like equation, similar to that of time-domain statistical energy analysis (SEA), but it does not require substructuring. The model is successfully used to extract diffusion parameters from simulated data of unambiguously diffusive character. The model is then successfully used to extract diffusion parameters from data obtained in a DNS of a simple undamped two-room structure of a kind typically analyzed by SEA or room acoustics.