Synthesis,Characterization, and Spectroscopic Analysis of NdxY1−xTiNbO6 Microwave Ceramics

Solid solutions of Nd_xY_1−xTiNbO₆ ceramics were prepared through the solid-state ceramic route. The materials were calcined at 1250°C and sintered in the range 1400–1550°C. The structure of the system was analyzed using the X-ray diffraction and vibrational spectroscopic analysis. The morphology and the sintering behavior of the samples were analyzed using scanning electron microscopy. The dielectric constant (ɛ_r), temperature coefficient of resonant frequency (τ_f), and the unloaded quality factor (Q_u) were measured in the microwave frequency region using the cavity resonator method. The ɛ_r and τ_f increased with an increase in the concentration of Nd in the solid solutions. Nearly zero temperature coefficient of resonant frequency was obtained for the Nd_0.6Y_0.4TiNbO₆ ceramic. Samples are of high quality factor and are useful for microwave applications.     

On the Issue of Incomplete and Missing Water-Quality Data in Mine Site Databases: Comparing Three Imputation Methods

Large water-quality databases are valuable for predicting mine drainage chemistry, identifying optimal measures for mitigation and remediation, and refuting/refining models and theories. However, such databases often have missing values due to periodic lack of sampling and analysis or input errors. These missing values lead to problems in machine learning and statistical analysis of water-quality data from mine sites. Using water-quality data collected from 1971 to 1994 from many locations at a copper-molybdenum-gold-silver-rhenium mine site, we compared three imputation methods to estimate missing water-quality data: iterative robust model-based imputation (IRMI), multiple imputations of incomplete multivariate data (AMELIA), and sequential imputation for missing values (IMPSEQ). These methods were evaluated based on mean absolute error, relative absolute error, and percent bias techniques. The results showed that IMPSEQ and IRMI are suitable to impute missing values in water-quality databases at mine sites, whereas AMELIA is not.     

Field tests of a radon progeny sampler for the determination of effective dose

A two-screen sampler (an effective dosimeter), with a collection efficiency matched to the particle size response of the radon progeny dose conversion factors (DCF), obtained from the ICRP respiratory tract model as implemented in the computer code RADEP, has been developed to assess the inhalation dose from exposure to radon progeny. In order to evaluate the performance of this sampler, the second stage of a six-stage wire screen diffusion battery was designed to operate as an Effective Dosimeter. This hybrid system allowed two methods for the determination of the radon progeny DCF. For the first method, the activity size distributions, measured using the diffusion battery, were used to obtain a size-weighted DCF. A second determination of DCF was obtained directly from the fraction collected by the Effective Dosimeter. The hybrid diffusion battery was used to measure radon progeny in the Fairy Cave, Buchan, Victoria at 20-min intervals over a 30-h period. This cave had radon concentrations exceeding 2000 Bq m(-3), with low aerosol concentration and low ventilation rates. The measurements were analysed for the radon progeny PAEC, the activity size distribution, the size-weighted DCF and the effective dosimeter collected fraction. The Effective Dosimeter DCFs were determined from the collected fraction using firstly a simple linear function and then using a more complex polynomial function to correct for residual errors. For the linear factor alone, the calculated Effective Dosimeter DCFs were on average 11% lower than the equivalent size-weighted DCF values. The agreement using the polynomial function was improved markedly, with a linear regression of the DCF yielding a fitted ratio of 0.965, with an R value of 0.99. For this study, the use of the ICRP conversion convention to estimate the occupational exposure to the tour guides working in the Fairy Cave would under estimate the effective dose by up to a factor of 2.     

An ELISA for brown trout (Salmo trutta) vitellogenin and its use in bioassays for environmental estrogens

An enzyme linked immunosorbent assay (ELISA) was developed for the detection of the egg yolk precursor vitellogenin (Vg) in plasma of brown trout (Salmo trutta). Purified Vg from a 17 beta-estradiol-induced trout was used as the competing antigen in the ELISA which is based on polyclonal antibodies. The ELISA's performance was optimized and characterized. The assay's working range was (25-500 ng ml-1), its sensitivity was (10.5 ng ml-1), and it had an intra-assay coefficient of variation of less than 10% between 30 and 1000 ng ml-1. The ELISA was used in bioassays for the detection of environmental estrogens, including estrogen mimics, in whole and fractionated industrial waste waters. Those bioassays were based on intraperitoneal (i.p.) injection-, static renewal-, and flow through exposure systems. The response threshold of both bioassays is limited to 1-2 micrograms ml-1 Vg by a low level plasma interference that was regularly detected in plasma from non-induced male fish. The responsiveness of the bioassays was characterized using progressive doses of 17 beta-estradiol. The i.p.-based assay, which was responsive to at least 100 micrograms kg-1 of 17 beta-estradiol, was used to screen extracts of pulp mill effluent and black liquor for estrogenic effects. Neither extract induced Vg in our assay. The i.p. assay was also used to test 4-tert-octylphenol (OP) and the PAH derivative, retene, for estrogenic activity. OP induced Vg in the i.p.-exposed fish; no Vg induction was detected in the retene-exposed fish. The static renewal bioassay, which was responsive to at least 0.1 microgram ml-1 of 17 beta-estradiol over a 15-day exposure period, was used to screen whole pulp mill effluents for estrogenic effects. No Vg induction was detected in the effluent-treated fish.     

Dielectric and optical properties of ZnO and Eu2O3 doped Pr0.22Y0.78TiTaO6 ceramic

Pr_0.22Y_0.78TiTaO₆ ceramic prepared using the conventional solid state synthesis route is calcined at 1,175 °C and is doped with ZnO and Eu₂O₃. The doping has reduced the sintering temperature by 160 and 100 °C, respectively. The structure is studied using the X-ray diffraction technique, the surface morphology by scanning electron microscopy and the elemental composition by energy dispersive spectrum. Dielectric properties in the microwave frequency range are measured using the cavity resonator method. The dielectric constant, the conductance and the loss factor are measured in the radio frequency region. The UV–Visible spectrum is recorded and the band gap is calculated. Photoluminescence spectrum of the doped composites is recorded and analyzed. The compositions have good dielectric and optical properties and hence are suitable for microwave and optoelectronic applications.     

Cumulative carbon as a policy framework for achieving climate stabilization

The primary objective of the United Nations Framework Convention on Climate Change is to stabilize greenhouse gas concentrations at a level that will avoid dangerous climate impacts. However, greenhouse gas concentration stabilization is an awkward framework within which to assess dangerous climate change on account of the significant lag between a given concentration level and the eventual equilibrium temperature change. By contrast, recent research has shown that global temperature change can be well described by a given cumulative carbon emissions budget. Here, we propose that cumulative carbon emissions represent an alternative framework that is applicable both as a tool for climate mitigation as well as for the assessment of potential climate impacts. We show first that both atmospheric CO(2) concentration at a given year and the associated temperature change are generally associated with a unique cumulative carbon emissions budget that is largely independent of the emissions scenario. The rate of global temperature change can therefore be related to first order to the rate of increase of cumulative carbon emissions. However, transient warming over the next century will also be strongly affected by emissions of shorter lived forcing agents such as aerosols and methane. Non-CO(2) emissions therefore contribute to uncertainty in the cumulative carbon budget associated with near-term temperature targets, and may suggest the need for a mitigation approach that considers separately short- and long-lived gas emissions. By contrast, long-term temperature change remains primarily associated with total cumulative carbon emissions owing to the much longer atmospheric residence time of CO(2) relative to other major climate forcing agents.     

Inspection and maintenance of oil & gas pipelines: a review of policies

Oil and gas (O&G) pipelines are expensive assets that cross through both the ecologically sensitive and densely populated urban areas. The pipeline failure may have potentially significant consequences for both the natural and human environments. In order to maintain the integrity of O&G pipelines, inspection and maintenance processes should be governed by efficient policies. The objective of this paper is to conduct a state-of-the-art review of maintenance policies of O&G pipelines to investigate their advantages, limitations, and associated implementation issues. Maintenance policies can be categorised into corrective, preventive, predictive and proactive. Corrective maintenance policies (1940s) were based on the ‘repair when broke’ philosophy. Economic considerations shifted practice towards preventive maintenance (1970s to 1990s); later with improved inspection techniques and environmental regulations, predictive and proactive or risk-based maintenance (RBM) policies were developed. This review explicates different methodologies for RBM and related issues, e.g. uncertainties and variability, conservative assumptions, etc. Uncertainties associated with investigation and prediction of defects have been more frequently reported in the literature so far. Moreover, existing studies primarily focused on reducing the likelihood and cost of failure, whereas consideration of environmental factors in overall risk has been a relatively less addressed issue.     

“Modeling the impact of natural resource-based poverty traps on food security in Kenya: The Crops, Livestock and Soils in Smallholder Economic Systems (CLASSES) model”

We investigate the interactions between natural resource-based poverty traps and food security for smallholder farms in highland Kenya using a recently developed system dynamics bio-economic model. This approach permits examination of the complex interactions and feedback between farm household economic decision-making and long-term soil fertility dynamics that characterize persistent poverty and food insecurity among smallholders in rural highland Kenya. We examine the effects of changing initial endowments of land and stocks of soil organic matter on smallholders?? well being, as reflected in several different indicators. We show that larger and higher quality land endowments permit accumulation of cash and livestock resources and conservation of soil organic matter relative to smaller or more degraded farms. This suggests the existence of asset thresholds that divide food secure households from food insecure ones.