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.     

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.     

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.     

Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

Elastic wave thermal fluctuations,ultrasonic waveforms by correlation of thermal phonons

It is widely recognized that acoustic degrees of freedom coupled to a thermal bath have amplitudes which fluctuate with a mean square proportional to temperature; this is the basis for the Debye theory of the heat capacity of insulating solids. It is shown here that these elastic wave thermal phonons have correlation functions identical to the system's ultrasonic Green's function, and furthermore that thermal noise in ultrasonic detectors should have correlation functions equivalent to conventional waveforms obtained by active transmission and reception. This suggests the possibility of doing ultrasonics without a source. Theory for the identity is presented, and several room temperature laboratory confirmations are conducted in the frequency range 0.1-1.0 MHz. The thermal nature of the origin of these correlations is established by comparing their strength with theoretical expectations. Applications are discussed.