A sea ice terrain model and its application to surface vehicle trafficability

Pressure ridges are the primary obstacle to the movement of amphibious surface vehicles travelling over the Arctic ice pack. Ridge height and spacing data can now be obtained with remote sensing methods and used to construct a realistic three-dimensional ridge model for sea ice terrain. This model can be used to perform trafficability analyses. The results, when combined with vehicle characteristics, can be used to predict vehicle operational performance. There is good agreement between predictions from the model and from simulated routes through sea ice areas selected from aerial photographs.

The terrain model is also useful for mapping regional variations in ridge characteristics throughout the Arctic Basin. The paper also discusses the nature of the rugged shear zone in the offshore region, and the presence of leads caused by dilation of the ice pack in strong weather systems.     

Spatially aggregated multiclass pattern classification in functional MRI using optimally selected functional brain areas

In previous works, boosting aggregation of classifier outputs from discrete brain areas has been demonstrated to reduce dimensionality and improve the robustness and accuracy of functional magnetic resonance imaging (fMRI) classification. However, dimensionality reduction and classification of mixed activation patterns of multiple classes remain challenging. In the present study, the goals were (a) to reduce dimensionality by combining feature reduction at the voxel level and backward elimination of optimally aggregated classifiers at the region level, (b) to compare region selection for spatially aggregated classification using boosting and partial least squares regression methods and (c) to resolve mixed activation patterns using probabilistic prediction of individual tasks. Brain activation maps from interleaved visual, motor, auditory and cognitive tasks were segmented into 144 functional regions. Feature selection reduced the number of feature voxels by more than 50%, leaving 95 regions. The two aggregation approaches further reduced the number of regions to 30, resulting in more than 75% reduction of classification time and misclassification rates of less than 3%. Boosting and partial least squares (PLS) were compared to select the most discriminative and the most task correlated regions, respectively. Successful task prediction in mixed activation patterns was feasible within the first block of task activation in real-time fMRI experiments. This methodology is suitable for sparsifying activation patterns in real-time fMRI and for neurofeedback from distributed networks of brain activation.     

Dimensional stability of adsorbents subjected to thermal cycling

The dimensional stability of adsorbent beads subjected to varying temperature conditions must be understood to assess the effect of thermal cycling on both the adsorbent and the structure that contains it. Most of the literature on the coefficient of thermal expansion (CTE) of adsorbents relates to zeolite crystals or clusters of crystals with application to membranes. Such crystals or powder materials have been shown to exhibit both positive and negative volume expansion coefficients depending upon the temperature range. This duality in the CTE with increasing temperature and the large variation in the CTE magnitude for a given zeolite structure suggest that the dimensional stability of zeolite crystals under varying thermal conditions is not likely a good indicator of the thermal stability of agglomerated zeolites. In this study, a method has been developed and applied to measure the CTE of activated alumina and 13X molecular sieve adsorbent beads. A McBain gravimetric microbalance was modified in a simple manner to be used as a dilatometer. The method was validated by measuring the CTE of a 316 stainless steel rod and showing that the measured CTE of this study agreed with the published CTE within 3.3 %. Average CTEs for alumina and 13X adsorbents were determined as 4.88 × 10^?6 and 2.96 × 10^?6 mm/mm/ °C, respectively for the range of temperature 20–400 °C.     

Height variation along sea ice pressure ridges and the probability of finding “holes” for vehicle crossings

Sea ice pressure ridges are major obstacles to vehicle mobility in the Arctic Basin. An estimate of the expectation of holes of various heights and widths in the ridges is desirable for optimum vehicle design. This study uses probability theory and ridge shadow measurements from aerial photographs of sea ice to determine the distribution of holes of various heights and widths in pressure ridges. General conclusions are drawn regarding trafficability of this terrain for vehicles of various sizes.     

Separation of metalloporphyrins by capillary electrophoresis with UV detection and inductively coupled plasma mass spectrometric detection

Vitamin B12, cobalt protoporphyrin, manganese protoporphyrin, and zinc protoporphyrin were separated using capillary electrophoresis, and a comparison was made between detection with inductively coupled plasma mass spectrometry (ICP-MS) and UV detection. Absolute limits of detection were slightly better with ICP-MS detection than with UV detection, but for both methods absolute detection limits were in the picogram range. The migration times of the analytes decreased by several minutes when ICP MS detection was employed, and this phenomenon was believed to be a result of a "suction effect" that developed when the CE capillary was interfaced to the ICP-MS nebulizer. However, the resolution between species containing the same metal atom was not altered significantly, and the separation was completed in much less time relative to separations performed with UV detection.     

Discrete element simulation of the dynamics of adsorbents in a radial flow reactor used for gas prepurification

Radial flow reactors (RFR) are used in thermal swing adsorption (TSA) processes for gas prepurification. The aim of this work is to show the validity of the discrete element method (DEM) to simulate the effect of thermal expansion and contraction cycles occurring in such processes on the packed bed of RFR reactors. Both mono-layered and bi-layered packed beds of adsorbents are investigated. A DEM-based model of a full-scale size unit was developed, the parameters of which were calibrated by means of particle-scale experimental measurements and simple auxiliary DEM simulations. The DEM-based model used is isothermal and the thermal expansion and contraction phenomena are modelled through the displacement of the inner and outer walls of the computational domain. First, the accuracy of this model is assessed using analytical values of the static wall pressure (i.e. with no wall motion) as well as experimental measurements of the dynamic wall pressure (i.e. with wall motion) of a bi-layered bed. Next, simulation results for a few process cycles in the case of a bi-layered packed bed indicates that little mixing occurs at the interface between the two types of adsorbents. To our knowledge, this is the first time that simulation is used to investigate the behavior of the packed bed of a RFR in a TSA process. The results obtained with the proposed model show that the DEM is a valuable tool for the investigation of such slow dynamical processes, provided a careful calibration is done.     

Development of chiral HPLC for selenoamino acids with ICP-MS detection:application to selenium nutritional supplements

The enantiomeric separation of three underivatized seleno-amino acids, D,L-selenocystine, and D,L-selenomethionine, and D,L-selenomethionine, with UV and ICP-MS detection is described. An HPLC column with a chiral crown ether stationary phase and a mobile phase of 0.10 M HCIO4 was used. Absolute detection limits obtained with UV detection ranged from 34.5 to 47.1 ng whereas those obtained with the plasma detector were ca. 40-400 times better. The separations with either detector were good, with the little detector effect on the resolution. Ten commercially available dietary selenium supplements were analyzed using the chiral column to identify and quantify the selenium species present with both detection modes. Selenium species were easily identified using ICP-MS detection, whereas UV detection was not viable because of interferences from the sample matrix and inadequate sensitivity. Selenium species that were unretained using the chiral column were identified using anion exchange chromatography. Total amounts in the samples were also measured using a conventional digestion and enzymatic digestion with ICP-MS detection.     

A mechanistic study of ciprofloxacin removal by kaolinite

As one of the most important soil components, kaolinite plays a vital role in transport and retention of ionizable contaminants in soils of warm and wet climate. Ciprofloxacin (Cip) is a second generation fluoroquinolone (FQ) antibiotic of high use. It has high aqueous solubility under high and low pH conditions and higher stability in soil system. In this study, the interactions between Cip and kaolinite in aqueous solution were investigated by batch experiments, XRD and FTIR analyses. Quantitative correlation between the exchangeable cations desorbed and Cip adsorbed confirmed experimentally that cation exchange was the dominant mechanism of Cip adsorption on kaolinite. Fitting of experimental data to the cation exchange model resulted in a selectivity coefficient of 27, suggesting a strong affinity of Cip on negatively charged kaolinite surfaces. At the adsorption maximum 190-200 ?(2) was available per Cip molecule, much larger than the Cip molecule area, confirming charge-limited instead of surface-limited Cip adsorption. The invariable d-spacing after uptake of different amounts of Cip suggested that the adsorption of Cip was on the external surfaces of kaolinite. As solution pH increased beyond 8, the amount of Cip adsorption decreased significantly and reached close to zero at pH 11. The high adsorption rate constant due to surface adsorption instead of intercalation and the wide distribution of kaolinite in different soils suggest that the fate and transport of Cip may be governed by the transport of colloidal sized clays.