Papers by John Abrahamson
Cold Regions Science and Technology, 1985
ABSTRACT New snow depth provides a valuable tool for forecasting avalanches. We have modified an ... more ABSTRACT New snow depth provides a valuable tool for forecasting avalanches. We have modified an ultrasonic rangefinder available from Polaroid, and have mounted the unit at the top of a tripod. By taking hourly measurements, the changes in distance between the transducer and the snowpack can be evaluated. Blowing snow during storms shows up as scattered data, and at the end of a storm the readings become stable. The data indicate the length of the storm as well as the new snow increment.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2002
A compilation of 17 observations of ball lightning showing the most energetic effects is presente... more A compilation of 17 observations of ball lightning showing the most energetic effects is presented along with estimates of their energy content. These observations were chosen from several thousand for the much stronger interaction of each ball lightning on its surroundings, and the method of energy estimation outlined. The case is put that some of the observations show a higher energy than self-contained chemical energy could provide. Comments have been added to the paper, arguing that the energy estimations themselves should be consistent with whatever model is used for ball lightning. For example, the presence of reacting nanoparticles releasing chemical energy may bring about the same observed effects with lower estimated energy.
World Journal of Surgery, 2001
Laparoscopic cholecystectomy is now also performed for acute cholecystitis. In the presence of in... more Laparoscopic cholecystectomy is now also performed for acute cholecystitis. In the presence of inflammatory conditions, technical difficulties leading to conversion to open cholecystectomy may occur and overshadow the advantages of the laparoscopic approach. Factors associated with these undue events combined with techniques capable of learning from them may help in determining when to completely avoid the laparoscopic procedure. In this study we determined predictors of conversion in acute cholecystitis and tested their predictive ability by means of statistical multivariate analysis and artificial neural networks. Between January 1994 and February 1997, 225 patients underwent laparoscopic cholecystectomy for acute cholecystitis. Preoperative and operative data were prospectively collected on standardized forms. The first 180 laparoscopically approached cases entered the training set, which was learned by both the statistical and the artificial neural networks methods. Conversion was first studied in relation to a set of preoperative data. Prediction models were then fitted by both of these methods. The last 45 operated cases, which remained unknown to the learning systems, served for testing the fitted models. The forward stepwise logistic regression technique, the forward stepwise linear discriminant analysis, and the artificial neural networks method enabled positive prediction of conversion in 0%, 27%, and 100% of the cases, and a negative prediction in 80%, 85.5%, and 97% respectively, in the training set. A positive prediction of conversion in 0%, 25%, and 67% of the cases, and a negative prediction in 82%, 88%, and 94%, respectively, in the untrained, validation set of patients. An artificial neural networks based model provides a practical tool for the prediction of successful laparoscopic cholecystectomies and their conversion. The high degree of certainty of prediction in untrained cases reveals its potential, and justifies, under appropriate conditions, the complete avoidance of laparoscopy and turning directly to open cholecystectomy.
Journal of Glaeiology, 1984
ABSTRACT. Measurements of snow properties across and down snow slopes have been used to calculate... more ABSTRACT. Measurements of snow properties across and down snow slopes have been used to calculate a safety margin- the difference between the basal shear strength and the applied static stress. Areas of basal deficit exist when the applied shear stress exceeds the basal shear strength (the safety margin is negative), and basal areas are pinned when the safety margin is positive. As the size of deficit increases, stresses within the overlying slab also increase, and these may be sufficient to cause an avalanche. Measurements made on five slopes (four of which had avalanched) were characterized by considerable spatial variability, and the safety margin has been treated as a random function which varies over the slope. Statistical models of Vanmarcke (1977[a], 1983) have been applied to determine the most likely size of deficit required for avalanching (95 % confidence). In one case, an avalanche occurred when the length of deficit was only 2.9 m, and in the other cases the length was ...
Abstract—Adsorption of proteins onto a solid surface is believed to be the initial and controllin... more Abstract—Adsorption of proteins onto a solid surface is believed to be the initial and controlling step in biofouling. A better knowledge of the fouling process can be obtained by controlling the formation of the first protein layer at a solid surface. A number of methods have been investigated to inhibit adsorption of proteins. In this study, the adsorption kinetics of �-casein onto bimodal PEG brushes on a stainless steel surface has been studied by means of a quartz crystal microbalance with dissipation (QCM-D). Bimodal brushes consist of long and short PEG chains were prepared in situ using a physisorption method. The adsorption kinetics of �-casein were monitored with different PEG combinations and concentrations. �-casein adsorptions onto monomodal PEG brushes were determined for comparison. �-casein adsorption was also studied on a bare stainless steel surface as a control. All adsorptions were conducted at 23�C and pH 7.2. The results obtained showed that depositing PEG from...
Journal of Glaciology
A simple field test of snow-slope stability is proposed, which allows decisions about a number of... more A simple field test of snow-slope stability is proposed, which allows decisions about a number of factors recently described by Conway and Abrahamson (1984). These include spatial variation of snow strength along a slope, and progression of failure from a localized initial failure. Strength within the snow slab is considered as well as that at its base. A snow saw is required for the test and, because a number of tests can be made in a few minutes, much information on the state of the slope can be obtained in a practical time.
Journal of Glaciology
Measurements of snow properties across and down snow slopes have been used to calculate a safety ... more Measurements of snow properties across and down snow slopes have been used to calculate a safety margin — the difference between the basal shear strength and the applied static stress. Areas of basal deficit exist when the applied shear stress exceeds the basal shear strength (the safety margin is negative), and basal areas are pinned when the safety margin is positive. As the size of deficit increases, stresses within the overlying slab also increase, and these may be sufficient to cause an avalanche. Measurements made on five slopes (four of which had avalanched) were characterized by considerable spatial variability, and the safety margin has been treated as a random function which varies over the slope. Statistical models of Vanmarcke (1977[a], 1983) have been applied to determine the most likely size of deficit required for avalanching (95% confidence). In one case, an avalanche occurred when the length of deficit was only 2.9 m, and in the other cases the length was always les...
Abstract—Adsorption of proteins onto a solid surface is believed to be the initial and controllin... more Abstract—Adsorption of proteins onto a solid surface is believed to be the initial and controlling step in biofouling. A better knowledge of the fouling process can be obtained by controlling the formation of the first protein layer at a solid surface. A number of methods have been investigated to inhibit adsorption of proteins. In this study, the adsorption kinetics of �-casein onto bimodal PEG brushes on a stainless steel surface has been studied by means of a quartz crystal microbalance with dissipation (QCM-D). Bimodal brushes consist of long and short PEG chains were prepared in situ using a physisorption method. The adsorption kinetics of �-casein were monitored with different PEG combinations and concentrations. �-casein adsorptions onto monomodal PEG brushes were determined for comparison. �-casein adsorption was also studied on a bare stainless steel surface as a control. All adsorptions were conducted at 23�C and pH 7.2. The results obtained showed that depositing PEG from solutions with increasing concentrations from 0.1 to 5.0 g / L decreased adsorption of �-casein by about 40 % on monomodal surfaces. Bimodal PEG surfaces appeared to be less effective than monomodal PEG brushes surfaces in preventing adsorption of �-casein. It is suggested that bimodal PEG surfaces behave like a ‘solid ’ which leads to �-casein adsorption at the surface via hydrophobic interaction for this observation. The difference between PEG combinations in suppressing the adsorption of �-casein was not very significant, indicating the existence of an optimal value of chain density to effectively suppress the adsorption of �-casein. Keywords—�-casein, QCM-D, stainless steel, bimodal brush,
A simple field test of snow-slope stability is proposed, which allows decisions about a number of... more A simple field test of snow-slope stability is proposed, which allows decisions about a number of factors recently described by Con way and Abrahamson (1984). These include spatial variation of snow strength along a slope, and progression of failure from a localized initial failure. Strength within the snow slab is considered as well as that at its base. A snow saw is required for the test and, because a number of tests can be made in a few minutes, much information on the state of the slope can be obtained in a practical time. RESUME. Un test de terrain pour eprouver la stabilite du mallteau neigeux. On propose un test simple de la stabilite du manteau neigeux qui permet une prise de decision a propos d'un certain nombre de facteurs recemment decrits par Conway et Abrahamson (1984). Cela inclu la variation spatiale de l'etat de tension le long du manteau neigeux et la propagation d'une fracture a partir de sa localisation ponctuelle initiale. L'etat de tension a l' interieur du manteau
Journal of Biotechnology, 2008
Food and Bioproducts Processing, 2007
Washable baghouses are increasingly used to filter the small size fractions of milk powder, known... more Washable baghouses are increasingly used to filter the small size fractions of milk powder, known as fines, which become entrained with spray dryer outlet air streams in milk powder plants. Surprisingly, very little is known about the quantity of powder that becomes fines, an important parameter for both the control of agglomeration rates and washable baghouse design. A convenient method is reported here that gives estimates of the fines fraction (the ratio of fines flow to total powder flow), using powder size distributions of samples from around the plant. This method was checked against isokinetic sampling using a thimble filter to independently determine powder flow rates. Results showed that that the fines fractions ranged from 49 + 8% to 86 + 2% depending on the powder type and plant operating conditions. These values are much greater than what was traditional thought (10-20%). Also, as part of this study results were compared with those from an online optical scintillation instrument. It was concluded that the newly developed particle size distribution method is a simple and reliable way to estimate spray dryer fines fractions, yet is sensitive enough to detect changes in operating conditions.
Journal of Biotechnology, 2008
Chemical Engineering Science, 1975
Chemical Engineering Research and Design, 2010
The air flow patterns in an industrial milk powder spray dryer were investigated. Isothermal thre... more The air flow patterns in an industrial milk powder spray dryer were investigated. Isothermal three-dimensional transient simulations were carried out using the commercial CFD code CFX10.0. The Shear Stress Transport (SST) turbulence model was implemented to model the effects of turbulence. These simulations differ from previously published studies of spray dryer air flows in that they include features found in industrial scale plant. First, they include a second inlet air stream through the internal fluid bed at the bottom of the drying chamber. Second, the two outlet ducts are located near the top rather than the bottom of the dryer, which has been the case in most previous studies. It was found that the main air jet oscillated and precessed about the central axis. In turn, the recirculation zones between the main jet and the chamber walls fluctuated in size relative to the movement of the jet. Validation was achieved by observing the oscillation of the main air jet of a large dryer visualised by tell-tail tufts attached to a central pole.
Carbon, 1973
A discussion is presented describing the possible influence of the internal surface energy of pol... more A discussion is presented describing the possible influence of the internal surface energy of polycrystalline and pyrolytic graphites on three phenomena: (a) the thermodynamic "standard" state of carbon, (b) the graphitization process, and (c) the structural stability of graphites at high temperatures. In order to do this, the surface enthalpies and free energies of the basal surface and edge faces have been calculated from a number of sources, and their temperature dependence up to .WOOK discussed. Suggestions have been made for methods to measure both basal surface and "edge" surface energies more directly.
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Papers by John Abrahamson