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Molecular dynamics simulations were performed to characterize the ablation process induced by a picosecond infrared laser (PIRL) operating in the regime of desorption by impulsive vibrational excitation (DIVE) of a model peptide (lysozyme)/counter-ion system in aqueous solution. The simulations were performed for ablation under typical experimental conditions found within a time-of-flight mass spectrometer (TOF-MS), that is in vacuum with an applied electric field (E = ± 107 V/m), for up to 2 ns post-ablation and compared to the standard PIRL-DIVE ablation condition (E = 0 V/m). Further, a simulation of ablation under an extreme field condition (E = 1010 V/m) was performed for comparison to extend the effective dynamic range of the effect of the field on charge separation. The results show that the plume dynamics were retained under a typical TOF-MS condition within the first 1 ns of ablation. Efficient desorption was observed with more than 90% of water molecules interacting with lysozyme stripped off within 1 ns post-ablation. The processes of ablation and desolvation of analytes were shown to be independent of the applied electric field and thus decoupled from the ion separation process. Unlike under the extreme field conditions, the electric field inside a typical TOF-MS was shown to modify the ions' motion over a longer time and in a soft manner with no enhancement to fragmentation observed as compared to the standard PIRL-DIVE. The study indicates that the PIRL-DIVE ablation mechanism could be used as a new, intrinsically versatile, and highly sensitive ion source for quantitative mass spectrometry. [ABSTRACT FROM AUTHOR]

The formation of negative ions in molecular beams of ethylene sulfite (ES, alternately called glycol sulfite or ethylene glycol, C2H4SO3) molecules has been studied using both Rydberg electron transfer (RET) and free electron attachment methods. RET experiments with jet-cooled ES show an unexpected broad profile of anion formation as a function of the effective quantum number (n*) of the excited rubidium atoms, with peaks at nmax*∼13.5 and 16.8. The peak at nmax*∼16.8 corresponds to an expected dipole-bound anion with an electron binding energy of 8.5 meV. It is speculated that the peak at nmax*∼13.5 derives from the formation of a distorted C2H4SO3- ion. We suggest that quasifree electron attachment promotes the breaking of one ring bond giving a long-lived acyclic anion and term this process incomplete dissociative electron attachment. Theoretical calculations of plausible ionic structures are presented and discussed. Electron beam studies of ES reveal the presence of multiple dissociative attachment channels, with the dominant fragment, SO2-, peaking at 1.3 eV and much weaker signals due to SO3-, SO-, and (ES-H)- peaking at 1.5, 1.7, and 0.9 eV, respectively. All of these products appear to originate from a broad temporary negative ion resonance centered at ∼1.4 eV. [ABSTRACT FROM AUTHOR]

Electron impact ionization of the chlorodifluoromethane molecule is studied using crossed beams of high-resolution electrons and an effusive molecular beam of CHF[sub 2]Cl. Ionization energies (IEs) for many positive ions from CHF[sub 2]Cl (CHF[sub 2]Cl[sup +],CF[sub 2]Cl[sup +],CHFCl[sup +],CFCl[sup +],CHF[sub 2][sup +],CF[sub 2][sup +],HCl[sup +],Cl[sup +],CF[sup +],CH[sup +],F[sup +] C[sup +]) are determined from a careful examination of the threshold behavior of the ionization cross sections. Reaction pathways for the dissociative ionization products are suggested using known thermodynamic quantities. Surprisingly, it is observed that the ionization threshold for the parent positive ion IE(CHF[sub 2]Cl[sup +]/CHF[sub 2]Cl)=12.50(±0.05) eV lies above that for the fragment ions CHF[sub 2][sup +], CHFCl[sup +], and CF[sup +] [IE(CHF[sub 2][sup +]/CHF[sub 2]Cl)=12.24(±0.03) eV, IE(CHFCl[sup +]/CHF[sub 2]Cl)=12.3(±0.05) eV, and IE(CF[sup +]/CHF[sub 2]Cl)=11.5(±0.1) eV]. Experiments using a three sector field BEE mass spectrometer provide evidence for the existence of two states of the parent CHF[sub 2]Cl[sup +] ion, one exhibiting a short lifetime of about 2 μs and another parent ion state which appears to be stable on the time scale of the experiment (>20 μs) with an IE of 12.50 eV. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

W. D. Robertson [a] D. W. Blowes [a] C. J. Ptacek [a] J. A. Cherry [a] Abstract Nitrate is now recognized as a widespread ground water contaminant, which has led [...]

Background: Providing medical assistance in dying ceased to be illegal in Canada on 17 June 2016. In the months before the Criminal Code was amended with the passage of Bill C-14, a BC-wide committee was established to standardize the provision of medical assistance in dying. A Vancouver Island Health Authority (Island Health) working group was also established to coordinate all aspects of medically assisted death. After medical assistance in dying became legal, a case review was proposed to consider the assisted deaths that took place on Vancouver Island in 2016. Methods: Data were collected on assisted death cases for 6 months beginning 17 June 2016. The Island Health working group on medical assistance in dying analyzed the data to determine patient age and place of death, geographic distribution of cases, the availability of prescribers and assessors, discernible trends in assisted deaths, and gaps in data collection. Results: In the 6-month study period, 72 assisted deaths (37 male, 35 female) occurred in patients ranging in age from 49 to 96 (74.75) years. Assisted deaths made up approximately 2% of the total deaths in that time and took place at home (64%), in acute care (21%), in hospice (12%), and in residential care (3%). The geographic distribution of cases varied, with more assisted deaths occurring in South Island (62%) than in Centre Island (21%) and North Island (16%). Underlying conditions in patients seeking assisted death included neoplasm (57%) and organ failure (25%). In 69 cases (96%) death occurred with intravenous administration of medication. In three cases (4%) oral administration was used, with intravenous administration being adopted in one case after death did not occur by a previously agreedupon time. Deaths were expedited in 25% of cases and took place within the 10-day "period of reflection" required by federal law. Conclusions: On Vancouver Island, access to medical assistance in dying is restricted by the geographic distribution of prescribers, and the high percentage of South Island cases probably reflects ease of access in this more densely populated region. The large number of cases relative to population size on Vancouver Island is likely the result of demographic factors and greater awareness resulting from a history of assisted dying advocates in BC such as Sue Rodriguez and Kay Carter. With the data we have it is not possible to reliably report on the number of patients who made initial inquiries, the number who made formal requests and did not meet criteria, and the number who died without medical assistance or who decided not to go ahead with medical assistance in dying. Prescriber experience suggests that access to medical assistance in dying is inadequate relative to demand and that coordination is needed in all aspects of provision, data-gathering, and governance. [ABSTRACT FROM AUTHOR]

A 5-year-old wood particle reactor treating agricultural tile drainage in southern Ontario was monitored for its ongoing ability to treat both nitrate (NO3–) and perchlorate (ClO4–). Prior to sampling undertaken in the fifth year of operation, a highway safety flare containing ClO4– was immersed in the inlet pipe elevating influent ClO4– concentrations to up to 33.7 μg/L. ClO4– removal rates were inhibited in the presence of more than 1 to 2 mg/L NO3–-N, but increased rapidly to about 60 μg/L/d upon NO3– depletion. Nitrate removal rates, measured subsequently in the sixth and seventh years of operation, varied with temperature in the range of 2 to 16 mg N/L/d, but remained similar to rates measured in the second year. Additionally, no deterioration in the hydraulic conductivity (K) of the coarse core layer (0.5 3– removal rates and can remain highly permeable over a number of years. The media can also provide high removal rates for other redox sensitive contaminants such as ClO4–. The ability to directly measure the reactor flow rate, in this case via an outlet pipe, greatly simplified the task of estimating hydraulic properties and reaction rates. [ABSTRACT FROM AUTHOR]

Permeable reactive barriers (PRBs) have gained popularity in recent years as a low-cost method for ground water remediation. However, their cost advantage usually requires that these barriers remain maintenance free for a number of years after installation. In this study, sediment cores were retrieved from a pilot-scale PRB consisting of a sand and wood particle (sawdust) mixture that has been in continuous operation for 15 years treating nitrate from a septic system plume in southern Ontario (Long Point site). Reaction rates for the 15-year-old media were measured in dynamic flow column tests and were compared to rates measured in year 1 using the same reactive mixture. Nitrate removal rates in the 15-year-old media varied, as expected, with temperature in the range of 0.22 to 1.1 mg N/L/d at 6 °C to 10 °C to 3.5 to 6.0 mg N/L/d at 20 °C to 22 °C. The latter rates remained within about 50% of the year 1 rates (10.2 ± 2.7 mg N/L/d at 22 °C). Near the end of the year 15 column test, media particles >0.5 mm in diameter, containing most of the wood particles, were removed from the reactive media by sieving. Nitrate removal subsequently declined by about 80%, indicating that the wood particles were the principal energy source for denitrification. This example shows that some denitrifying PRBs can remain maintenance free and be adequately reactive for decades. [ABSTRACT FROM AUTHOR]

A stock assessment was undertaken for the tropical sparid Acanthopagrus berda harvested in the Kosi Bay estuarine system, northern KwaZulu-Natal, South Africa, by a multi-sectoral fishery using traditional traps and gillnets, and recreational angling using rod-and-line. Input parameters used in a catch curve analysis included age and growth parameters, and an estimate of natural mortality derived from life-history parameters. The values of spawner biomass-per-recruit estimated from this model, using different selectivity curves for the gear types used in the different fishing sectors, indicate that A. berda is likely to be reduced to around 24% of its unfished level of spawner biomassper- recruit by current levels of fishing mortality. These results indicate that A. berda in Kosi Bay is heavily overexploited. The longevity of the species, coupled with its late maturation, sex change and estuarine dependency, and the increasing catches of A. berda give cause for concern for the continued sustainable use of this species in northern KwaZulu-Natal. [ABSTRACT FROM AUTHOR]

The mobility of phosphorus (P) in septic system plumes remains a topic of debate because of the considerable reactivity of this constituent. In this study, a septic system plume in Ontario was monitored over a 16-year period with detail that clearly shows the advancing frontal portion of the P plume. This monitoring record provides insight into the extent of secondary P attenuation in the ground water zone beyond that available from previous studies. A P plume 16 m in length developed over the monitoring period with PO4-P concentrations (3 to 6 mg/L) that approached the concentrations present under the tile bed. Simulations using an analytical model showed that when first-order solute decay was considered to account for the possibility of secondary P attenuation in the ground water zone, field values could only be matched when decay was absent or occurred at an exceedingly slow rate (half-life greater than 30 years). Thus, hypothesized secondary P attenuation mechanisms such as slow recystallization of sorbed P into insoluble metal phosphate minerals, diffusion into microsites, or kinetically slow direct precipitation of P minerals such as hydroxyapatite were inactive in the ground water zone at this site or occurred at rates that were too slow to be observed in the context of the current 16-year study. Desorption tests on sediment samples from below the tile bed indicated a PO4 distribution coefficient ( Kd) of 4.8, which implies a P retardation factor of 25, similar to the field apparent value of 37 determined from model calibrations. This example of inactive secondary P attenuation in the ground water zone shows that phosphorus in some ground water plumes can remain mobile and conservative for decades. This has important implications for septic systems located in lakeshore environments when long-term usage scenarios are considered. [ABSTRACT FROM AUTHOR]

Detailed distribution of nitrate (NO3) adjacent to a permeable reactive layer comprising coarse wood particles with high hydraulic conductivity ( K∼ 1 cm/s) showed that ground water converged into the layer, allowing treatment of aquifer zones located up to 1.1 m below the bottom of the layer. NO3-N of 6 to 99 mg/L was highly attenuated (generally <0.1 mg/L) within the first third of the 4-m-wide reactive layer. Hydraulic retention time estimates based on borehole dilution velocity values indicated a nitrate reaction rate of approximately 10 mg N/L/d at the ground water temperature of 10°C. In addition to denitrification, sulfate reduction, reductive dissolution of ferric and manganic oxyhydroxide minerals, and calcite dissolution likely occurred within the layer. The plume water continued to evolve in the downgradient area, where geochemical modeling suggested that CO2 degassing likely occurred, resulting in pH increase and possibly the precipitation of calcite, siderite, and rhodochrosite. At a distance of 4 to 6 m downgradient, the plume water had returned to a composition similar to the upgradient ground water, but with lower NO3, SO4, and Ca concentrations. The reactive layer was also successful in treating trace quantities (∼1 μg/L) of perchlorate (ClO4) present in the aquifer. The wood particle layer used in this study was of low cost and was simple to install and maintain; thus larger scale aquifer remediation could be feasible, particularly at sites where nitrate contamination occurs at shallow depths. [ABSTRACT FROM AUTHOR]

Two denitrification reactor designs, utilizing alternate layers of fine and coarse wood particles, were monitored for their ability to achieve passive, maintenance-free nitrate removal in agricultural tile drainage. A lateral flow design was tested over a 26-month period on drainage from a cornfield in southern Ontario, and an upflow design was tested over a 20-month period on drainage from a golf course, also in southern Ontario. At the cornfield site, flow through the reactor averaged 7.7 L/min at an average influent NO3 concentration of 11.8 mg N/L, and removal averaged 3.9 mg N/L. At the golf course site, flow through the reactor averaged 7.8 L/min at an average influent NO3 concentration of 3.2 mg N/L, and removal averaged 1.7 mg N/L. A real removal rates averaged 2.5 g N/m²/d in the cornfield reactor and 0.95 g N/m²/d in the golf course reactor, and are about an order of magnitude higher than rates reported for other passive treatment systems such as constructed wetlands even though average operating temperatures were relatively low (7°C to 9°C). Mass balance calculations indicate that carbon consumption from denitrification was <2% per year; thus, these reactors have the potential m operate for a number of years without the need for media replenishment. Both reactors were successful in achieving maintenance-free operation during all seasonal conditions, including unassisted startup after drought and freeze periods. Reactors such as these have the potential for a range of applications in agricultural settings because of their low cost and low maintenance characteristics. They are most usefully applied in the treatment of base flows rather titan peak flows and can be readily used in combination with other treatment systems such as constructed wetlands. [ABSTRACT FROM AUTHOR]

A nitrate-reactive porous media layer comprising wood particles with very high hydraulic conductivity (K ∼ 1 cm/s) was used to successfully treat nitrate in a shallow sand-and-gravel aquifer in southern Ontario. Nitrate concentrations of 1.3 to 14 mg/L as N in the aquifer were attenuated to <0.5 mg/L as N in the reactive layer. Borehole dilution testing indicated that ground water velocities in the reactive layer, although variable, averaged five times higher than in the surrounding aquifer, suggesting that the layer was capturing ground water flow from deeper in the aquifer. The use of high-K reactive media opens up the possibility of installing permeable reactive barriers as horizontal layers in the shallow water table zone that do not necessarily have to penetrate the full depth of a contaminant plume to be effective. Model simulations show that the depth of capture of a high-K layer increases as the layer width in the direction of flow increases. Shallower emplacement could decrease barrier costs at some sites. [ABSTRACT FROM AUTHOR]

Measures the population size and capture rates of mature Acanthopagrus berda fishes in the Kosi lake system in South Africa. Background on the Kosi lake system; Formula for the estimation of population size; Recovery rate of tagged fishes.