Measurements of Argon-39 at the U20az underground nuclear explosion site.

Pacific Northwest National Laboratory reports on the detection of 39Ar at the location of an underground nuclear explosion on the Nevada Nuclear Security Site. The presence of 39Ar was not anticipated at the outset of the experimental campaign but results from this work demonstrated that it is present, along with 37Ar and 85Kr in the subsurface at the site of an underground nuclear explosion. Our analysis showed that by using state-of-the-art technology optimized for radioargon measurements, it was difficult to distinguish 39Ar from the fission product 85Kr. Proportional counters are currently used for high-sensitivity measurement of 37Ar and 39Ar. Physical and chemical separation processes are used to separate argon from air or soil gas, yielding pure argon with contaminant gases reduced to the parts-per-million level or below. However, even with purification at these levels, the beta decay signature of 85Kr can be mistaken for that of 39Ar, and the presence of either isotope increases the measurement background level for the measurement of 37Ar. Measured values for the 39Ar measured at the site ranged from 36,000 milli- Becquerel/standard-cubic-meter-of-air (mBq/SCM) for shallow bore holes to 997,000 mBq/SCM from the rubble chimney from the underground nuclear explosion.

Thermophysical properties and oxygen transport in (Thx,Pu1-x)O2.

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Thx,Pu1-x)O2 (0 ≤ x ≤ 1) between 300-3500 K. In particular, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Thx,Pu1-x)O2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and the increase in oxygen diffusivity. The increase in oxygen diffusivity for (Thx,Pu1-x)O2 is explained in terms of lower oxygen defect formation enthalpies for (Thx,Pu1-x)O2 than PuO2 and ThO2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.

Pipe and grain boundary diffusion of He in UO2.

Molecular dynamics simulations have been conducted to study the effects of dislocations and grain boundaries on He diffusion in [Formula: see text]. Calculations were carried out for the {1 0 0}, {1 1 0} and {1 1 1} [Formula: see text] edge dislocations, the screw [Formula: see text] dislocation and Σ5, Σ13, Σ19 and Σ25 tilt grain boundaries. He diffusivity as a function of distance from the dislocation core and grain boundaries was investigated for the temperature range 2300-3000 K. An enhancement in diffusivity was predicted within 20 Å of the dislocations or grain boundaries. Further investigation showed that He diffusion in the edge dislocations follows anisotropic behaviour along the dislocation core, suggesting that pipe diffusion occurs. An Arrhenius plot of He diffusivity against the inverse of temperature was also presented and the activation energy calculated for each structure, as a function of distance from the dislocation or grain boundary.

Development of Xe and Kr empirical potentials for CeO2, ThO2, UO2 and PuO2, combining DFT with high temperature MD.

The development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO2, ThO2, UO2 and PuO2. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matching to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO2, ThO2, UO2 and PuO2, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO2 as well as advanced MOX fuels.

Atomic scale mobility of the volatile fission products Xe, Kr and I in cubic SiC.

The migration barriers for the vacancy-assisted migration of fission products in 3C-SiC are reported and analysed in the context of the five frequency model, which enables one to calculate an effective diffusion coefficient from elementary mechanisms. Calculations were carried out using the nudged elastic band method (NEB) with interatomic forces determined from density functional theory (DFT). Justification for treating vacancy-assisted fission product migration as limited to the FCC carbon sublattice is based on the stability of carbon vacancies, unfavourable silicon vacancy formation and the accommodation of fission products on the carbon sublattice. Results show that for most Fermi levels within the band gap the activation energy for I exceeds that of Xe which exceeds that of Kr. Results also indicate that activation energies are higher near the conduction edge, thus, implying that enhanced fission product retention can be achieved through n-type doping of 3C-SiC, which limits the availability of the migration mediating carbon vacancies.

Thermal conductivity and energetic recoils in UO2 using a many-body potential model.

Classical molecular dynamics simulations have been performed on uranium dioxide (UO2) employing a recently developed many-body potential model. Thermal conductivities are computed for a defect free UO2 lattice and a radiation-damaged, defect containing lattice at 300 K, 1000 K and 1500 K. Defects significantly degrade the thermal conductivity of UO2 as does the presence of amorphous UO2, which has a largely temperature independent thermal conductivity of ∼1.4 Wm(-1) K(-1). The model yields a pre-melting superionic transition temperature at 2600 K, very close to the experimental value and the mechanical melting temperature of 3600 K, slightly lower than those generated with other empirical potentials. The average threshold displacement energy was calculated to be 37 eV. Although the spatial extent of a 1 keV U cascade is very similar to those generated with other empirical potentials and the number of Frenkel pairs generated is close to that from the Basak potential, the vacancy and interstitial cluster distribution is different.

A many-body potential approach to modelling the thermomechanical properties of actinide oxides.

A many-body potential model for the description of actinide oxide systems, which is robust at high temperatures, is reported for the first time. The embedded atom method is used to describe many-body interactions ensuring good reproduction of a range of thermophysical properties (lattice parameter, bulk modulus, enthalpy and specific heat) between 300 and 3000 K for AmO2, CeO2, CmO2, NpO2, ThO2, PuO2 and UO2. Additionally, the model predicts a melting point for UO2 between 3000 and 3100 K, in close agreement with experiment. Oxygen-oxygen interactions are fixed across the actinide oxide series because it facilitates the modelling of oxide solid solutions. The new potential is also used to predict the energies of Schottky and Frenkel pair disorder processes.

Source term estimation of radioxenon released from the Fukushima Dai-ichi nuclear reactors using measured air concentrations and atmospheric transport modeling.

Systems designed to monitor airborne radionuclides released from underground nuclear explosions detected radioactive fallout across the northern hemisphere resulting from the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. Sampling data from multiple International Modeling System locations are combined with atmospheric transport modeling to estimate the magnitude and time sequence of releases of (133)Xe. Modeled dilution factors at five different detection locations were combined with 57 atmospheric concentration measurements of (133)Xe taken from March 18 to March 23 to estimate the source term. This analysis suggests that 92% of the 1.24 × 10(19) Bq of (133)Xe present in the three operating reactors at the time of the earthquake was released to the atmosphere over a 3 d period. An uncertainty analysis bounds the release estimates to 54-129% of available (133)Xe inventory.

New approach for measuring properties of rp-process nuclei.

A new experimental approach was developed that can reduce the uncertainties in astrophysical rapid proton capture (rp) process calculations due to nuclear data. This approach utilizes neutron removal from a radioactive ion beam to populate the nuclear states of interest. Excited states were deduced by the gamma-decay spectra measured in a semiconductor Ge-detector array. In the first case studied, 33Ar, excited states were measured with uncertainties of several keV. The 2 orders of magnitude improvement in the uncertainty of the level energies resulted in a 3 orders of magnitude improvement in the uncertainty of the calculated 32Cl(p,gamma)33Ar rate that is critical to the modeling of the rp process. This approach has the potential to measure key properties of almost all interesting nuclei on the rp-process path.

Use of ultrasonography to characterize ovarian status in chicken.

Much research has been conducted to investigate the effects of environmental and nutritional treatments on ovarian development in poultry. However, to investigate the ovary, the hen must be killed, and thus, lifelong egg production can only be inferred. To date, the ability to noninvasively determine ovarian status has not been available. Improvements in ultrasound technology now make it possible to observe ovarian condition in vivo, thereby allowing for repeated sampling of the same bird over an entire egg production cycle. In the current study, large yellow follicles (LYF; diameter greater than 10 mm) were characterized in broiler breeder hens using Aloka ultrasound diagnostic equipment. Ultrasound images were used to determine the number and diameter of the LYF as well as the presence of an egg in the oviduct. Immediately following ultrasonography, hens were killed and dissected to determine the number and diameter of LYF. From the ultrasound images, the number of LYF +/- 1 was predicted with 96.3% accuracy in Experiment 1 and 93.3% accuracy in Experiment 2. Diameter measurements were used to classify follicles hierarchically. Of the birds determined via dissection to have multiple hierarchies, 77.8% were identified with ultrasound. All regressing or regressed ovaries were correctly identified with ultrasound.

The gastroenterologist and his endoscope: the embodiment of technology and the necessity for a medical ethics.

The purpose of this essay is to argue for the necessity of an ethics of the practice of the specialist-technologist in medicine. In the first part I sketch three stages of medical ethics, each with a particular viewpoint regarding the technology of medicine. I focus on Brody's consideration of the "physician's power" as a example of contemporary medical ethics which explicitly excludes the specialist-technologist as a locus of development of medical ethics. Next, the philosophy of Heidegger is examined to suggest an approach to the problem, and, finally, some of Levinas' contributions regarding the "other" are introduced to suggest a preliminary approach to a medical ethics of the specialist-technologist.

Transient entrainment: the evolution of a medical concept from description to prescription.

Entrainment is a phenomenon that has come to have considerable utility in cardiac electro-physiology diagnosis and treatment; specifically, to identify a zone of slow conduction in a reentrant circuit, a zone hypothetically vulnerable to intervention from the application of RF energy. The observation of entrainment has gone through an evolutionary sequence in the literature, from the initial simple observations of the phenomenon to the present stage of relatively fixed criteria of identification. This article follows the evolution of the specific features of the criteria of entrainment to their current crystallization into features that are suggested to prescribe sites for attempted ablation. This examination of the evolutionary course of the development of the conception of entrainment is of interest not only to cardiac electrophysiology, but also to philosophers of science, by illustrating how scientists emphasize and develop certain observations with the ultimate aim of applying the observations for successful intervention in pathological entities.

Arterial oxygen saturation during upper gastrointestinal endoscopy in elderly patients: the role of endoscope diameter.

The effect of endoscope diameter upon arterial oxygen saturation was investigated in 52 elderly patients by comparing two groups of 26 patients examined with different diameter endoscopes (PQ20 and Q10). In the group of 26 patients examined with the larger endoscope (Q10), the baseline oxygen saturation values and those during intubation were significantly higher than in the group examined with the smaller instrument (PQ20). There was no significant difference in oxygen saturation between the two groups after sedation or during the procedure as a whole. Our findings suggest that the examination of elderly patients using a standard diameter endoscope does not pose any greater risk.

Clinical and electrophysiologic features and role of catheter ablation techniques in adult patients with automatic atrioventricular junctional tachycardia.

A total of 8 patients with junctional tachycardia (JT) were included for study. Patients with JT had a supraventricular arrhythmia that was initiated by a junctional complex without PR prolongation and episodes of atrioventricular (AV) dissociation. JT could not be initiated by pacing and occurred either spontaneously (3 patients) or with isoproterenol (5 patients). Tachycardia could be consistently terminated by either carotid sinus massage (1 patient), intravenous adenosine (2 patients), or critically timed ventricular premature complexes (3 patients). In 6 of the 8 other patients, tachycardia foci (atrial or ventricular) or mechanisms (AV node reentry) were found. Two patients underwent complete AV junctional ablation and 2 had termination of tachycardia without change in the AV conduction by perinodal application of radiofrequency lesions. AVJT appears to be due to abnormal automaticity and may be successfully ablated by application of radiofrequency energy to perinodal areas.

Is medicine hermeneutics all the way down?

Several recent publications have suggested that hermeneutics, the method of literary criticism, might prove to be useful in medicine. In this essay I consider this thesis with particular attention to the claim that medicine "is hermeneutics all the way down". After examining an anti-positivist critique of positivist medicine and arguing that hermeneutic interpretation involves a more radical critique of modern medicine, I examine the supposed consequences of hermeneutical universalism: relativism, skepticism and antirealism which further evaluation reveals to be only potential consequences of hermeneutics. A brief discussion of phronesis and of the possible "texts" of medicine concludes the article.

Postextrasystolic potentiation. Do we really know what it means and how to use it?

Postextrasystolic potentiation (PESP), the increase in contractility that follows an extrasystole, is an interesting phenomenon that has been known for almost 100 years. The literature on this effect is reviewed. It is found that there is significant evidence that the phenomenon is independent of muscle loading and represents a distinct property of the myocardium. Examination of the literature pertaining to the cause of the effect suggests that calcium shifts within the sarcoplasmic reticulum are responsible, although there are some conflicts with this conclusion. Regarding the utility of PESP as a diagnostic test of latent viability of ischemic myocardium, the literature review reveals contradictions and conflicts with several methodological problems of the experiments. Finally, concerning the utility of continuous PESP (paired-pacing) to augment ventricular function in the failing ventricle, the studies again are inconclusive and methodologically suspect. Conditions for the proper analysis of the PESP response are reported, and suggestions for future studies are introduced.

Should physicians be bayesian agents?

Because physicians use scientific inference for the generalizations of individual observations and the application of general knowledge to particular situations, the Bayesian probability solution to the problem of induction has been proposed and frequently utilized. Several problems with the Bayesian approach are introduced and discussed. These include: subjectivity, the favoring of a weak hypothesis, the problem of the false hypothesis, the old evidence/new theory problem and the observation that physicians are not currently Bayesians. To the complaint that the prior probability is subjective, Bayesians reply that there will be ultimate convergence, but the rebuttal to this is that there will not be uniform convergence. Secondly, since the Bayesian scheme favors a weak hypothesis, theories turn out to be a gratuitous risk. The problem with the false hypothesis comes out in the denominator of the theorem, revealing that a factor which is not a theory at all is being considered in the reasoning. On the old evidence/new theory problem old evidence cannot confirm a new theory so that the posterior probability will equal the prior probability. Finally, empiric studies have shown that current physicians are not Bayesians. But on consideration of Bayesian inference as a system of inference, it can be reasoned that physicians should be Bayesians. However, the problem of physicians' and patients' own subjectivity continue to plague this system of medical decision making.

A real-time analysis of growth cone-target cell interactions during the formation of stable contacts between hippocampal neurons in culture.

Mechanisms of cell-cell recognition and structural changes of growth cones (g.c.) and target membranes during contact formation are poorly understood. To examine these issues, we obtained a high magnification, real-time record of stable contact formation in cultured cells from the hippocampal CA1 area in the newborn rat. We used differential interference contrast (DIC) optics coupled to a video microscope for periods of over 24 h of continuous time-lapse recording. Our goal was to observe the sequential changes exhibited by afferent and target cells as they form a stable contact. Understanding the process of how stable contacts are made is important because such contacts are the first step in synapse formation. Four principal observations emerged from our study: (1) The target cell was receptive to a contact on a specific patch on its surface defined by the presence of lamellae and filopodia. This specific patch (named target site) was invariably present on the target cell surface before the time the growth cone arrived. (2) Stable adhesion between filopodia on the two cells initiated events leading to cell-cell contact formation. Specifically, the remaining filopodia on the growth cone and target cell were redirected toward the adhering filopodia, and the growth cone size decreased dramatically. (3) The axonal process then grew at a significantly accelerated rate (up to 50 times its baseline growth rate). (4) In addition, a number of observations were obtained on axonal turns towards the target cell, induction of target sites, and architectural remodelling of cells after the formation of a new contact. Our findings indicate that in this neuronal system, filopodia are the means used by cells to interact at stages prior to and during contact formation. We speculate that the molecules involved in cell recognition and the machinery that initiates contact formation are embedded in the fine structure of filopodia. Finally, our results provide possible clues as to some of the stages that may be involved in synapse formation in the mammalian central nervous system.

Comparison of ionic and non-ionic contrast agents in cardiac catheterization: the effects of ventriculography and coronary arteriography on hemodynamics, electrocardiography, and serum creatinine.

We compared two nonionic contrast agents (ioxaglate and iohexol) with an ionic agent (Renografin-76) on the effects of ventriculography and coronary arteriography on the hemodynamics, electrocardiography, and serum creatinine in one hundred consecutive patients. Patients were randomized to nonionic or ionic groups and were further evaluated regarding the effect of fluid loading prior to catheterization. The ionic agent more often produced subjective reactions (rash, nausea/vomiting). Following ventriculography, both ionic and non-ionic agents produced an increase in left ventricular end diastolic pressure and this effect was undetermined by fluid loading. Nonionic agents decreased aortic diastolic pressure following ventriculography and this effect was unaltered by fluid loading. In contrast, the ionic agent produced profound hemodynamic changes (drop in both systolic and diastolic pressures) following coronary arteriography and these effects were blunted by prior fluid loading. The ionic agent produced significantly greater heart rate slowing and prolongation of the QT interval than the nonionic agents, suggesting that the latter are potentially less arrhythmogenic. Comparing the two non-ionic agents, we found that both decreased aortic diastolic pressure and increased left ventricular end diastolic pressure following ventriculography. Iohexol produced greater heart rate slowing than did ioxaglate, though the increase was minor compared to the ionic agent. Neither nonionic agent appeared to significantly affect serum creatinine. In conclusion, the two nonionic agents appeared to offer significant advantages over the ionic agent in ventriculography and coronary arteriography.