Effect of wire eccentricity on the performance of cylindrical proportional counters

A theoretical and experimental investigation of the influence of eccentricity of the multiplication wire on the performance of cylindrical proportional counters is presented. The electric field in the counter is calculated by the method of images, and the Townsend formalism is used to derive the gas gain. The experimental determination of detector performance is carried out with³⁷Ar. The dependence of the gas gain and of the counter resolution on eccentricity is discussed, and it is shown that eccentricities up to 0.2 are of no concern in microdosimetric measurements with cylindrical proportional counters.     

Interaction of near-IR laser radiation with plasma of a continuous optical discharge

The interaction of 1.07-μm laser radiation with plasma of a continuous optical discharge (COD) in xenon and argon at a pressure of p = 3–25 bar and temperature of T = 15 kK has been studied. The threshold power required to sustain COD is found to decrease with increasing gas pressure to P _t < 30 W in xenon at p > 20 bar and to P _t < 350 W in argon at p > 15 bar. This effect is explained by an increase in the coefficient of laser radiation absorption to 20?25 cm^–1 in Xe and 1?2 cm^–1 in Ar due to electronic transitions between the broadened excited atomic levels. The COD characteristics also depend on the laser beam refraction in plasma. This effect can be partially compensated by a tighter focusing of the laser beam. COD is applied as a broadband light source with a high spectral brightness.     

Hydrogen-dependent control of the continuous anaerobic digestion process

Summary Membrane inlet mass spectrometry was used to directly measure the concentrations of CH₄ and H₂ in a mesophilic (37°C) completely mixed, laboratory scale, anaerobic digester, continuously fed at a retention time of 7 days with a glucose (50 mM) mineral salts medium. When the digester was overloaded by an increase in the influent substrate concentration, equivalent to 15.5 kg (COD) m^-3 (digester) day^-1 the concentrations of H₂ and short chain fatty acids increased with a concomitant decline in the pH: following an initial stimulation methanogenesis was inhibited. Regulation of the H₂ signal from the mass spectrometer in a closed feedback loop by controlled addition of carbon source under a potential overload condition, enabled the H₂ concentration to the controlled around 1M and a high steady state rate of methanogenesis of 42 M min^-1 to be maintained; this is equivalent to 1.4 volumes of CH₄ per culture volume per day. The hydrogen-dependent control system was also used to prevent inhibition of methanogenesis when the digester was subject to volumetric overloading potentially equivalent to a retention time of 1 day.     

Primary Human Bronchial Epithelial Cells Grown from Explants

Human bronchial epithelial cells are needed for cell models of disease and to investigate the effect of excipients and pharmacologic agents on the function and structure of human epithelial cells. Here we describe in detail the method of growing bronchial epithelial cells from bronchial airway tissue that is harvested by the surgeon at the times of lung surgery (e.g. lung cancer or lung volume reduction surgery). With ethics approval and informed consent, the surgeon takes what is needed for pathology and provides us with a bronchial portion that is remote from the diseased areas. The tissue is then used as a source of explants that can be used for growing primary bronchial epithelial cells in culture. Bronchial segments about 0.5-1cm long and ≤1cm in diameter are rinsed with cold EBSS and excess parenchymal tissue is removed. Segments are cut open and minced into 2-3mm³ pieces of tissue. The pieces are used as a source of primary cells. After coating 100mm culture plates for 1-2 hr with a combination of collagen (30 μg/ml), fibronectin (10 μg/ml), and BSA (10 μg/ml), the plates are scratched in 4-5 areas and tissue pieces are placed in the scratched areas, then culture medium (DMEM/Ham F-12 with additives) suitable for epithelial cell growth is added and plates are placed in an incubator at 37°C in 5% CO₂ humidified air. The culture medium is changed every 3-4 days. The epithelial cells grow from the pieces forming about 1.5 cm diameter rings in 3-4 weeks. Explants can be re-used up to 6 times by moving them into new pre-coated plates. Cells are lifted using trypsin/EDTA, pooled, counted, and re-plated in T75 Cell Bind flasks to increase their numbers. T75 flasks seeded with 2-3 million cells grow to 80% confluence in 4 weeks. Expanded primary human epithelial cells can be cultured and allowed to differentiate on air-liquid interface. Methods described here provide an abundant source of human bronchial epithelial cells from freshly isolated tissues and allow for studying these cells as models of disease and for pharmacology and toxicology screening.Download video file.^{(144M, mp4)}     

Influence of a Nitrogen Admixture on the Anomalous Memory Effect in the Breakdown of Low-Pressure Argon in a Long Discharge Tube

The memory effect (the dependence of the dynamic breakdown voltage U _b on the time interval τ between voltage pulses) in pulse-periodic discharges in pure argon and the Ar + 1%N₂ mixture was studied experimentally. The discharge was ignited in a 2.8-cm-diameter tube with an interelectrode distance of 75 cm. The measurements were performed at gas pressures of P = 1, 2, and 5 Torr and discharge currents in a steady stage of the discharge of I = 20 and 56 mA. Breakdown was produced by applying positive-polarity voltage pulses, the time interval between pulses being in the range of τ = 0.5–40 ms. In this range of τ values, a local maximum (the anomalous memory effect) was observed in the dependence U _b (τ). It is shown that addition of nitrogen to argon substantially narrows the range of τ values at which this effect takes place. To analyze the measurement results, the plasma parameters in a steady-state discharge (in both pure argon and the Ar + 1%N₂ mixture) and its afterglow were calculated for the given experimental conditions. Analysis of the experimental data shows that the influence of the nitrogen admixture on the shape of the dependence U _b (τ) is, to a large extent, caused by the change in the decay rate of the argon afterglow plasma in the presence of a nitrogen admixture.     

Mapping of antibody specificities to V H gene families

V _H gene segments represent the products of the repeated duplication and subsequent diversification of a primordial V gene element. It is widely assumed that natural selection, operating via pathogens, has played the dominant role in this process. Here, we screen some 3.7 × 10⁴ C ⁺ colonies of mitogen-activated B cells for the production of antibodies specific for phosphorylcholine or hen egg lysozyme and expression of the V _H X-24, S107, Q52, or J558 gene families. These gene families were expressed at frequencies proportional to their genomic complexity among both unselected and antigen-specific C ⁺ colonies. Thus, the capacity to encode equivalent antibody-combining sites is dispersed uniformly among V _Hfamilies. This result suggests that individual V _H genes have not evolved to address specific antigens.     

First Nations status and emergency department triage scores in Alberta: a retrospective cohort study

Background:Previous studies have found that race is associated with emergency department triage scores, raising concerns about potential health care inequity. As part of a project on quality of care for First Nations people in Alberta, we sought to understand the relation between First Nations status and triage scores.Methods:We conducted a population-based retrospective cohort study of health administrative data from April 2012 to March 2017 to evaluate acuity of triage scores, categorized as a binary outcome of higher or lower acuity score. We developed multivariable multilevel logistic mixed-effects regression models using the levels of emergency department visit, patient (for patients with multiple visits) and facility. We further evaluated the triage of visits related to 5 disease categories and 5 specific diagnoses to better compare triage outcomes of First Nations and non–First Nations patients.Results:First Nations status was associated with lower odds of receiving higher acuity triage scores (odds ratio [OR] 0.93, 95% confidence interval [CI] 0.92–0.94) compared with non–First Nations patients in adjusted models. First Nations patients had lower odds of acute triage for all 5 disease categories and for 3 of 5 diagnoses, including long bone fractures (OR 0.82, 95% CI 0.76–0.88), acute upper respiratory infection (OR 0.90, 95% CI 0.84–0.98) and anxiety disorder (OR 0.67, 95% CI 0.60–0.74).Interpretation:First Nations status was associated with lower odds of higher acuity triage scores across a number of conditions and diagnoses. This may reflect systemic racism, stereotyping and potentially other factors that affected triage assessments.

Health outcomes are markedly worse for First Nations than non–First Nations people. Although this is largely because of inequities in the social determinants of health,^1–4 inequities in the provision of health care also exist.^5,6 Emergency departments serve as a point of accessible health care. Status First Nations patients make up 4.8% of unique patients and 9.4% of emergency visits in Alberta,⁷ and Canadian studies describe First Nations patients’ experiences with racism when seeking emergency care.^8,9Evaluating triage contributes empirically to understanding the health care of First Nations patients insofar as triage is a quantifiable, intermediate process by which systemic racism¹⁰ may influence patient outcomes. The Canadian Triage Acuity Scale¹¹ is a 5-level scale used to classify the severity of patient symptoms. Triage nurses use a brief assessment, medical history, and presenting signs and symptoms to assign each patient a triage score that determines the priority in which the patient should be seen by a provider. Therefore, accurate triage is important for patient health outcomes.¹² In practice, triage is a social interaction where local practice, biases, stereotypes and communication barriers come into play. Studies have found that women receive less acute triage scores than men,^13,14 and that racial minority^13,15–17 and Indigenous^18–20 patients receive less acute triage scores than white or non-Indigenous patients. Indeed, Indigenous patients in Canada have described a perception “of social triaging in the [emergency department], whereby decisions about who is seen first seemed to them [to be] based less on triaged clinical priorities but on the social positioning of the patient.”²¹ Differential triage scores for minority populations raise health equity concerns.As part of a larger mixed-methods project evaluating the quality of emergency care for First Nations people in Alberta, we sought to evaluate quantitative differences in emergency visit characteristics and outcomes of First Nations and non–First Nations people in Alberta. Specifically, we aimed to estimate the relation between First Nations status and acuity of triage, and to evaluate whether predictors of acuity differ by First Nations status.     

The response of tissue-equivalent proportional counters to heavy ions

The paper presents a theoretical model for the response of a tissue-equivalent proportional counter (TEPC) irradiated with charged particles. Heavy ions and iron ions in particular constitute a significant part of radiation in space. TEPCs are used for all space shuttle and International Space Station (ISS) missions to estimate the dose and radiation quality (in terms of lineal energy) inside spacecraft. The response of the tissue-equivalent proportional counters shows distortions at the wall/cavity interface. In this paper, we present microdosimetric investigation using Monte Carlo track structure calculations to simulate the response of a TEPC to charged particles of various LET (1 MeV protons, 2.4 MeV alpha particles, 46 MeV/nucleon 20Ne, 55 MeV/nucleon 20Ne, 45 MeV/nucleon 40Ar, and 1.05 GeV/nucleon 56Fe). Data are presented for energy lost and energy absorbed in the counter cavity and wall. The model calculations are in good agreement with the results of Rademacher et al. (Radiat. Res. 149, 387-389, 1998), including the study of the interface between the wall and the sensitive region of the counter. It is shown that the anomalous response observed at large event sizes in the experiment is due to an enhanced entry of secondary electrons from the wall into the gas cavity.     

Microiontophoresis and Micromanipulation for Intravital Fluorescence Imaging of the Microcirculation

Microiontophoresis entails passage of current through a micropipette tip to deliver a solute at a designated site within an experimental preparation. Microiontophoresis can simulate synaptic transmission¹ by delivering neurotransmitters and neuropeptides onto neurons reproducibly². Negligible volume (fluid) displacement avoids mechanical disturbance to the experimental preparation. Adapting these techniques to the microcirculation³ has enabled mechanisms of vasodilation and vasoconstriction to be studied at the microscopic level in vivo^4,5. A key advantage of such localized delivery is enabling vasomotor responses to be studied at defined sites within a microvascular network without evoking systemic or reflexive changes in blood pressure and tissue blood flow, thereby revealing intrinsic properties of microvessels.A limitation of microiontophoresis is that the precise concentration of agent delivered to the site of interest is difficult to ascertain⁶. Nevertheless, its release from the micropipette tip is proportional to the intensity and duration of the ejection current^2,7, such that reproducible stimulus-response relationships can be readily determined under defined experimental conditions (described below). Additional factors affecting microiontophoretic delivery include solute concentration and its ionization in solution. The internal diameter of the micropipette tip should be ˜ 1 μm or less to minimize diffusional ''leak'', which can be counteracted with a retaining current. Thus an outward (positive) current is used to eject a cation and a negative current used to retain it within the micropipette.Fabrication of micropipettes is facilitated with sophisticated electronic pullers⁸. Micropipettes are pulled from glass capillary tubes containing a filament that ''wicks'' solution into the tip of the micropipette when filled from the back end ("backfilled"). This is done by inserting a microcapillary tube connected to a syringe containing the solution of interest and ejecting the solution into the lumen of the micropipette. Micromanipulators enable desired placement of micropipettes within the experimental preparation. Micromanipulators mounted on a movable base can be positioned around the preparation according to the topography of microvascular networks (developed below). The present protocol demonstrates microiontophoresis of acetylcholine (ACh⁺ Cl^-) onto an arteriole of the mouse cremaster muscle preparation (See associated protocol: JoVE ID#2874) to produce endothelium-dependent vasodilation. Stimulus delivery is synchronized with digitized image acquisition using an electronic trigger. The use of Cx40^BAC-GCaMP2 transgenic mice⁹ enables visualization of intracellular calcium responses underlying vasodilation in arteriolar endothelial cells in the living microcirculation.Download video file.^{(37M, mov)}     

Use of a simple gamma flow cell to monitor chromatography column effluents containing 75Se.

Scintillation flow cells provide a convenient means of monitoring column effluents for radioactively labeled compounds. The use of flow cells to monitor effluents containing ³H, ¹⁴C, and other β-emitting isotopes is well established (1) and such cells are readily available as accessories for use with liquid scintillation counters. β-Flow cells have occasionally been used to monitor γ emitters [e.g., Martin et al. (2)] but the counting efficiency is extremely low even for weak γ emitters such as ⁷⁵Se, due to the limited mass of scintillant available to absorb the radiation.Spencer et al. (3) described a simple γ flow cell consisting of a coiled polyethylene tube inserted in to the well crystal of a γ counter, but no information on counting efficiency was given. Although spiral plastic γ cells have been manufactured commercially (e.g., Nuclear Enterprises Ltd., NE702¹) they are not offered as a standard accessory for most common makes of γ counter and do not appear to be readily available from commercial sources.This communication describes a simple, low cost γ flow cell constructed for use in a study on selenium transport in higher plants, which involved the separation of ⁷⁵Se-labeled constituents in a large number of samples of xylem sap.     

Study of microdosimetric energy deposition patterns in tissue-equivalent medium due to low-energy neutron fields using a graphite-walled proportional counter

To improve radiation protection dosimetry for low-energy neutron fields encountered in nuclear power reactor environments, there is increasing interest in modeling neutron energy deposition in metrological instruments such as tissue-equivalent proportional counters (TEPCs). Along with these computational developments, there is also a need for experimental data with which to benchmark and test the results obtained from the modeling methods developed. The experimental work described in this paper is a study of the energy deposition in tissue-equivalent (TE) medium using an in-house built graphite-walled proportional counter (GPC) filled with TE gas. The GPC is a simple model of a standard TEPC because the response of the counter at these energies is almost entirely due to the neutron interactions in the sensitive volume of the counter. Energy deposition in tissue spheres of diameter 1, 2, 4 and 8 μm was measured in low-energy neutron fields below 500 keV. We have observed a continuously increasing trend in microdosimetric averages with an increase in neutron energy. The values of these averages decrease as we increase the simulated diameter at a given neutron energy. A similar trend for these microdosimetric averages has been observed for standard TEPCs and the Rossi-type, TE, spherical wall-less counter filled with propane-based TE gas in the same energy range. This implies that at the microdosimetric level, in the neutron energy range we employed in this study, the pattern of average energy deposited by starter and insider proton recoil events in the gas is similar to those generated cumulatively by crosser and stopper events originating from the counter wall plus starter and insider recoil events originating in the sensitive volume of a TEPC.     

Drug formulations that require less than 0.1 mL of stock solution to prepare doses for infants and children

Intravenous doses of medications require formulations that permit accurate preparation and administration. Current equipment does not permit accurate measurement of volumes less than 0.1 mL. In a study of four hypothetical standard pediatric patients, we found that 28 common medications required less than 0.1 mL of available formulation to prepare the dose. In a clinical study of actual use in a pediatric intensive care unit (ICU), 5245 (7.4%) of 71 218 intravenous doses required preparation from less than 0.1 mL of stock solution. For 28.5% of the 1531 ICU admissions, at least one dose was prepared from a volume of less than 0.1 mL. Our findings identify a substantial source of dosing error. Correction will require revision of preparation methods, regulatory requirements and manufacturing practices.Preparation of parenteral doses of medications from small volumes using commercially available syringes is imprecise and may result in serious dosing errors.^1–3 Previously, we showed that 60% of 116 doses prepared from 0.06 mL of stock solution had a dosing error of more than 10%, and 27% had a two-fold dosing error.² We hypothesized that small volumes of commercially available formulations are often required to prepare intravenous doses for infants and children.     

Ammonia volatilization in a Mexican bat cave ecosystem

Direct measurements of gaseous ammonia in the atmosphere of a dry bat cave containing several million insectivorous bats revealed a peak concentration of 1779 ppm (0.96 mg/dm³). Observations indicate that the origin of the gaseous ammonia is rapid microbial decomposition of bat urea, not chitinous guano. Modelling of ammonia distribution and diffusion indicates that ammonia production at the Cueva del Tigre is 257 g NH₃/day, equivalent to the decomposition of 454 g urea/day. Ammonia production is also characterized by significant isotopic fractionation favoring isotopically light (¹⁵N depleted) ammonia.     

Assaying the Ability of Diffusible Signaling Molecules to Reorient Embryonic Spinal Commissural Axons

Dorsal commissural axons in the vertebrate spinal cord¹ have been an invaluable model system in which to identify axon guidance signals. Here, we describe an in vitro assay, "the reorientation assay", that has been used extensively to study the effect of extrinsic and intrinsic signals on the orientation of commissural axons². This assay was developed by numerous people in the laboratories of Jane Dodd, Thomas Jessell and Andrew Lumsden (see acknowledgements for more details) and versions of this assay were used to demonstrate the reorientation activities of key axon guidance molecules, including the BMP chemorepellent in the roof plate^3,4 and the chemoattractive activities of Netrin1⁵ and Sonic Hedgehog (Shh)⁶ in the floor plate in the spinal cord.Explants comprising 2-3 segments of the dorsal two-thirds of spinal cord are dissected from embryonic day (E) 11 rats and cultured in three dimensional collagen gels⁷. E11 dorsal spinal explants contain newly born commissural neurons, which can be identified by their axonal expression of the glycoprotein, Tag1⁸. Over the course of 30-40 hours in culture, the commissural axon trajectory is recapitulated in these dorsal explants with a time course similar to that seen in vivo. This axonal trajectory can be challenged by placing either test tissues or a COS cell aggregate expressing a candidate signaling molecule in contact with one of the lateral edges of the dorsal explant. Commissural axons extending in the vicinity of the appended tissue will grow under the influence of both the endogenous roof plate and signals from the ectopic lateral tissue. The degree to which commissural axons are reoriented under these circumstances can be quantified. Using this assay, it is possible both to examine the sufficiency of a particular signal to reorient commissural axons^3,4 as well the necessity for this signal to direct the commissural trajectory⁹.Download video file.^{(108M, mp4)}     

Improved synchronized accumulating radioisotope detector for gas chromatography

A synchronized accumulating radioisotope detector for radio gas chromatography was developed. It comprised seven gas-flow proportional counters each with an inner volume of 10 ml. Every counter tube was connected by a mutual anti-coincidence circuit to reduce the background. The transit time of gas particles in one counter tube could be set to an optimal value between 1 and 4 s by regulating the flow-rate of the counting gas, according to analytical requirements. The improved detector maintained high chromatographic resolution, which suggested the applicability of the apparatus to capillary gas chromatography.     

Requirement for calcium ions in mycobacteriophage I3 DNA injection and propagation

Ca²⁺ ions are absolutely necessary for the propagation of mycobacteriophage I3 in synthetic medium. These ions are required for successful infection of the host and during the entire span of the intracellular development of the phage. A direct assay of the phage DNA injection using ³²[P] labelled phage, showns that Ca²⁺ ions are necessary for the injection process. The injection itself is a slow process and takes 15 min to complete at 37°C. The bacteria infected in presence of Ca²⁺ tend to abort if the ions are subsequently withdrawn from the growth medium. The effect of calcium withdrawal is maximally felt during the early part of the latent period; however, later supplementation of Ca²⁺ ions salvage phage production and the mature phage progeny appear after a delayed interval, proportional to the time of addition of Ca²⁺.Abbreviations moi multiplicity of infection - PFU plaque forming units - EGTA ethylene-glycol-bis (-aminoethyl ether) N,N-tetraacetic acid     

Mutants in yeast affecting ethidium bromide induced rho- formation and their effects on transmission and recombination of mitochondrial genes.

Summary A series of mutants called ebi, less inducible by ethidium bromide than the parental strain for the ^+– mutation have been isolated after E.M.S. mutagenesis. Some of the ebi mutants also show an important accumulation of ^– cells, in the absence of ethidium bromide. Ebi mutations are nuclearly inherited as shown by meiotic segregation. The effects of these mutants on the transmission and recombination of mitochondrial genes among the diploid progeny of crosses have been studied. Some of the ebi mutants show a non coordinated transmission of the oli1 mitochondrial marker with respect to other mitochondrial markers unexpected for homosexual crosses. This bias which is independent from will be discussed in relation to the segregation and recombination. No significant decrease of the frequency of recombinants has been detected.Abbreviations E.B. Ethidium bromide - E.M.S. Ethyl méthane sulfonate - C^S/C^R Allelic forms of the rib 1 locus conferring chloramphenicol sensitivity/resistance - E^S/E^R Allelic forms of the rib 3 locus conferring erythromycine sensitivity/resistance - O^R/O^R Allelic forms of the oli 1 locus conferring oligomycin sensitivity/resistance - P^S/P^R Allelic forms of the par 1 locus conferring paromomycine sensitivity/resistance - D^S/D^R Allelic forms of the diu 1 or diu 2 loci conferring diuron sensitivity/resistance - C^S/C^R Allelic forms of the mitochondrial locus - ⁺ grande or respiratory competent cells - ^– petite or cytoplasmic respiratory deficient cells     

Thermodynamics of Mn2+-binding to goat α-lactalbumin

By means of reaction calorimetry we measured the apparent enthalpy change, H^app, of the binding of Mn²⁺-ions to goat -lactalbumin as a function of temperature. The observed H^app can be written as the sum of contributions resulting from a conformational and a binding process. In combination with the thermal unfolding curve of goat -lactalbumin, we succeeded in separating the complete set of thermodynamic parameters (H, G, S, C_p) into the binding and conformational contributions. By circular dichroism we showed that NH ₄ ⁺ -ions, upon binding to bovine a-lactalbumin, induce the same conformational change as do Na⁺ and K⁺: the binding constant equals 98 ± 9 M^–1.Abbreviations BLA bovine -lactalbumin - GLA goat -lactalbumin - HLA human -lactalbumin - CD circular dichroism Offprint requests to: H. Van DaelDeceased