Life Cycle Greenhouse Gas Emissions from Uranium Mining and Milling in Canada.

Life cycle greenhouse gas (GHG) emissions from the production of nuclear power (in g CO2e/kWh) are uncertain due partly to a paucity of data on emissions from individual phases of the nuclear fuel cycle. Here, we present the first comprehensive life cycle assessment of GHG emissions produced from the mining and milling of uranium in Canada. The study includes data from 2006-2013 for two uranium mine-mill operations in northern Saskatchewan (SK) and data from 1995-2010 for a third SK mine-mill operation. The mine-mill operations were determined to have GHG emissions intensities of 81, 64, and 34 kg CO2e/kg U3O8 at average ore grades of 0.74%, 1.54%, and 4.53% U3O8, respectively. The production-weighted average GHG emission intensity is 42 kg CO2e/kg U3O8 at an average ore grade of 3.81% U3O8. The production-weighted average GHG emission intensity drops to 24 kg CO2e/kg U3O8 when the local hydroelectric GHG emission factor (7.2 g CO2e/kWh) is substituted for the SK grid-average electricity GHG emission factor (768 g CO2e/kWh). This results in Canadian uranium mining-milling contributing only 1.1 g CO2e/kWh to total life cycle GHG emissions from the nuclear fuel cycle (0.7 g CO2e/kWh using the local hydroelectric emission factor).

Overcoming catastrophic interference in connectionist networks using Gram-Schmidt orthogonalization.

Connectionist models of memory storage have been studied for many years, and aim to provide insight into potential mechanisms of memory storage by the brain. A problem faced by these systems is that as the number of items to be stored increases across a finite set of neurons/synapses, the cumulative changes in synaptic weight eventually lead to a sudden and dramatic loss of the stored information (catastrophic interference, CI) as the previous changes in synaptic weight are effectively lost. This effect does not occur in the brain, where information loss is gradual. Various attempts have been made to overcome the effects of CI, but these generally use schemes that impose restrictions on the system or its inputs rather than allowing the system to intrinsically cope with increasing storage demands. We show here that catastrophic interference occurs as a result of interference among patterns that lead to catastrophic effects when the number of patterns stored exceeds a critical limit. However, when Gram-Schmidt orthogonalization is combined with the Hebb-Hopfield model, the model attains the ability to eliminate CI. This approach differs from previous orthogonalisation schemes used in connectionist networks which essentially reflect sparse coding of the input. Here CI is avoided in a network of a fixed size without setting limits on the rate or number of patterns encoded, and without separating encoding and retrieval, thus offering the advantage of allowing associations between incoming and stored patterns. PACS Nos.: 87.10.+e, 87.18.Bb, 87.18.Sn, 87.19.La.

Use of the harmonic scalpel in thyroidectomy.

Thyroidectomy is a surgical procedure that requires meticulous dissection, safe anatomical exposure and effective haemostasis. Use of the harmonic scalpel in thyroidectomy may assist in achieving these goals, particularly in respect to enabling efficient haemostatic coagulation and division of small vessels. This report demonstrates the results of utilizing the harmonic scalpel in a series of 88 prospective thyroidectomies in patients under the care of two surgeons over a 2-year period recording a number of parameters, including operative times and post-operative complications. These data were compared with a retrospective cohort of 57 patients who underwent thyroidectomies by the same two surgeons prior to the introduction of the harmonic scalpel. The results of this study show that the use of the harmonic scalpel decreased surgical operating time by 20 min (22.5%) for a hemithyroidectomy and 13.5 min (12%) for a total thyroidectomy. Harmonic scalpel use was not associated with an increased complication rate and has been demonstrated to be a very efficient and safe tool in assisting with the conduct of a thyroidectomy.

Transient motion of a circular plate after an impact.

The transient response of a flat circular plate to a sudden impact has been studied experimentally and theoretically. High-speed electronic speckle pattern interferometry reveals the presence of pulses that travel around the edge of the plate ahead of the bending motion initiated by the strike. It is found that the transient motion of the plate is well described by Kirchhoff thin-plate theory over a time approximately equal to the time required for the initial impulse to circumvent the plate; however, a more sophisticated model is required to describe the motion after this time has elapsed.

Modification of ilmenite surface chemistry for enhancing surfactants adsorption and bubble attachment.

In this study, microwave irradiation is used to modify ilmenite surface chemistry to enhance the adsorption of surfactants and the air bubble attachment. The results indicate that microwave irradiation can increase ilmenite flotation recovery by 20%. A positron emission particle tracking technique is used to study the dynamic behaviour of ilmenite particles in a Denver cell. The data shows that the poor flotation recovery of ilmenite is not only due to the reduce probability of ilmenite being captured by air bubbles, but also the short residence time of the particles remaining in the froth phase. The ilmenite particles can be frequently captured by air bubbles, but dropped to the bulk liquid from the froth phase, normally over 15 s. Microwave irradiation changes the ilmenite flow pattern in the Denver cell. The average time of ilmenite remaining in froth phase is increased from 11.5 to 29.1 s.

An investigation of the reaction kinetics of luciferase and the effect of ionizing radiation on the reaction rate.

The bioluminescence produced by luciferase, a firefly enzyme, requires three substrates: luciferin, ATP and oxygen. We find that ionizing radiation, in the form of a proton beam from a cyclotron, will eliminate dissolved oxygen prior to any damage to other substrates or to the protein. The dose constant for removal of oxygen is 70 +/- 20 Gy, a much smaller dose than required to cause damage to protein. Removal of oxygen, which is initially in excess, leads to a sigmoidal response of bioluminescence to radiation dose, consistent with a Michaelis-Menten relationship to substrate concentration. When excess oxygen is exhausted, the response becomes exponential. Following the irradiation, bioluminescence recovers due to a slow leak of oxygen into the solution. This may also explain previous observations on the response of bioluminescent bacteria to radiation. We have studied the dependence of the reaction rate on enzyme and substrate concentration and propose a model for the reaction pathway consistent with this data. The light output from unirradiated samples decreases significantly with time due to product inhibition. We observe that this inhibition rate changes dramatically immediately after a sample is exposed to the beam. This sudden change of the inhibition rate is unexplained but shows that enzyme regulatory function responds to ionizing radiation at a dose level less than 0.6 Gy.

Asymmetry in the auditory brainstem response following experience of monaural amplification.

Hearing aids can induce perceptual changes in some elderly listeners and there is recent evidence that this might be associated with reorganization within the auditory system. We compared the click-evoked auditory brainstem response in adults with and without monaural hearing aid experience. In listeners with monaural hearing aid experience, the mean peak-to-peak amplitude between wave V and SN10 was approximately 100 nV larger in the ear with hearing aid experience and this difference was statistically significant (P<0.01). The response was symmetrical in adults with no hearing aid experience. This suggests that hearing aids can induce physiological changes at the level of the auditory brainstem in elderly monaural hearing aid users.

Insights into the nature of the hydrogen bonding of *Tyr272 in apo-galactose oxidase.

The synthesis and structure of an o-methylthio-phenol-imidazole, 2-(2'-(4'-tert-butyl-6'-methylsulfanyl)-hydroxyphenyl))-4,5-diphenyl-imidazole ((MeS)LH), is reported; X-ray crystallographic studies have shown that (MeS)LH involves an O-H...N(+) hydrogen bond between the phenol and an imidazole nitrogen. (MeS)LH undergoes a reversible, one-electron, oxidation to form the radical cation [(MeS)LH](*)(+) the EPR spectrum of which is remarkably similar to that of (*)Tyr(272) in Cu-free, oxidized, apo-GO. Density Functional Theory calculations, have shown that the proton-transferred (R-O(*)...H-N(+)) form of [(MeS)LH](*)(+) has a spin density distribution--with a substantial delocalization of the unpaired electron spin density onto the ortho sulfur atom--and EPR properties that are in good agreement with those of (*)Tyr(272) in Cu-free, oxidized, apo-GO whereas the non-proton-transferred (R-O(*)(+)-H...N) form does not. The results reported herein are a further demonstration of the influence of hydrogen bonding on the nature and properties of phenoxyl radicals and strongly suggest that the phenoxyl oxygen of (*)Tyr(272) in Cu-free, oxidized, apo-GO is involved in a O(*)...H-O/N hydrogen bond.

A simple and selective method for the separation of Cu radioisotopes from nickel.

Separation of copper radioisotopes from a nickel target is normally performed using solvent extraction or anion exchange rather than using cationic exchange. A commonly held opinion is that cationic exchangers have very similar thermodynamic complexation constants for metallic ions with identical charges, therefore making the separation very difficult or impossible. The results presented in this article indicate that the selectivity of Chelex-100 (a cationic ion exchanger) for Cu radioisotope and Ni ions not only depends on the thermodynamic complexation constant in the resin but also markedly varies with the concentration of mobile H+. In our developed method, separation of copper radioisotopes from a nickel target was fulfilled in a column filled with Chelex-100 via controlling the HNO3 concentration of the eluent, and the separation is much more effective, simple and economical in comparison with the common method of anion exchange. For an irradiated nickel target with 650 mg Ni, after separation, the loss of Cu radioisotopes in the nickel portion was reduced from 30% to 0.33% of the total initial radioactivity and the nickel mixed into the radioactive products was reduced from 9.5 to 0.5 mg. This significant improvement will make subsequent labeling much easier and reduce consumption of chelating agents and other chemicals during labeling. If the labeled agent is used in human medical applications, the developed method will significantly decrease the uptake of Ni and chelating agents by patients, therefore reducing both the stress on human body associated with clearing the chemicals from blood and tissue and the risk of various types of acute and chronic disorder due to exposure to Ni.

Preliminary investigation of proton and helium ion radiation effects on fluorescent dyes for use in astrobiology applications.

The Specific Molecular Identification of Life Experiment (SMILE) instrument (Sims et al. Planet. Space Science 2005, 53, 781-791) proposes to use specific molecular receptors for the detection of organic biomarkers on future astrobiology missions (e.g., to Mars). Such receptors will be used in assays with fluorescently labeled assay reagents. A key uncertainty of this approach is whether the fluorescent labels used in the system will survive exposure to levels of solar and galactic particle radiation encountered during a flight to Mars. Therefore, two fluorescent dyes (fluorescein and Alexa Fluor 633) have been exposed to low-energy proton and alpha radiation with total fluences comparable or exceeding that expected during an unshielded cruise to Mars. The results of these initial experiments are presented, which show that both dyes retain their fluorescent properties after irradiation. No significant alteration in the absorption and emission wavelengths or the quantum yields of the dyes with either radiation exposure was found. These results suggest other structurally similar fluorophores will likely retain their fluorescent properties after exposure to similar levels of proton and alpha radiation. However, more extensive radiation fluorophore testing is needed before their suitability for astrobiology missions to Mars can be fully confirmed.

A soft solid surface on Titan as revealed by the Huygens Surface Science Package.

The surface of Saturn's largest satellite--Titan--is largely obscured by an optically thick atmospheric haze, and so its nature has been the subject of considerable speculation and discussion. The Huygens probe entered Titan's atmosphere on 14 January 2005 and descended to the surface using a parachute system. Here we report measurements made just above and on the surface of Titan by the Huygens Surface Science Package. Acoustic sounding over the last 90 m above the surface reveals a relatively smooth, but not completely flat, surface surrounding the landing site. Penetrometry and accelerometry measurements during the probe impact event reveal that the surface was neither hard (like solid ice) nor very compressible (like a blanket of fluffy aerosol); rather, the Huygens probe landed on a relatively soft solid surface whose properties are analogous to wet clay, lightly packed snow and wet or dry sand. The probe settled gradually by a few millimetres after landing.

Contemporary issues in audiology: a hearing scientist's perspective.

Audiology has developed significantly over the last 30 years leading to better identification and assessment of hearing loss and better habilitation services for both children and adults with congenital or acquired deafness. Advancement in the profession and its services has been largely dependent on the technological development of key methodologies such as the auditory brainstem response and otoacoustic emissions. These methodologies have been used for the identification and assessment of the severity of hearing loss. As a result, these methodologies have underpinned the emergence of service development initiatives such as hearing screening and provision of hearing aids, particularly for newborn babies and young children. This review identifies, describes and evaluates the key methodologies and services involved and presents a hearing scientist's perspective on the developments to date. The aim is to provide state-of-the-art information to those working with children and adults with communication disorders, particularly speech and language therapists.