Effect of curing under pressure on compressive strength development of cemented paste backfill

The mechanical performance of cemented paste backfill (CPB) placed in underground openings (e.g., mine stopes) often differs from laboratory-predicted performance, even under the same atmospheric curing conditions (ambient temperature and relative humidity). This is probably due to the specific self-weight consolidation, different drainage conditions and confinement pressures encountered in the paste backfilled stopes. A new test system named CUAPS (Curing Under Applied Pressure System) was designed at the Université du Québec en Abitibi-Témiscamingue (UQAT) to assess the hydro-mechanical performance of in situ CPB samples at laboratory scale. The CUAPS apparatus allows the effective curing of CPB samples subjected to an assortment of vertical pressure applications (curing under stresses) that can mimic in situ placement and consolidation conditions. The compressive strength development of CPB samples prepared from sulphide-rich mine tailings from Garpenberg polymetallic mine (Sweden) was investigated using CUAPS apparatus and conventional plastic moulds (unconsolidated undrained samples) in parallel. The effect of curing stress (i.e. simulating different consolidation conditions) on resultant geotechnical index parameters and hydromechanical properties of CPB samples was analyzed. The primary observation is the confirmation that the compressive strength development of the consolidated CPB samples is higher than that of unconsolidated undrained ones. It could be attributed to the removal of excess pore water mainly due to the applied pressure during the effective curing process, which seems to improve consolidation process of the CPB material. The results also account for the differences in the CPB strength observed between laboratory samples and in situ samples. Thus, CUAPS would be more suitable than conventional plastic moulds to collect data for preliminary and final design of CPB systems.     

Chemical factors that influence the performance of mine sulphidic paste backfill

Sulphide-rich tailings from four Canadian mines were sampled (Mines A1, A2, B and C) to prepare several different paste backfill mixtures. The sulphur grade within these tailings samples range from 5 to 32 wt.%. The binders used were Portland-cement-based binders, fly-ash-based binders and slag-based binders with proportions ranging from 3 to 6 wt.%. The study was carried out in two stages. Stage I allowed us to understand the effects of binder type, binder proportion and tailings properties on compressive strength development of paste backfill during the course of curing time. It was pointed out that for high sulphide tailings, neither the slag-based binders nor the fly-ash-based binders were effective, whereas the sulphate-resistant-based binder (mix of Type I [TI] and Type V [TV] Portland cements) gave good long-term strength. However, the slag-based binders gave the best strength for low and medium sulphide-bearing tailings for which the Portland- and the fly-ash-based mixtures have a relatively low strength. Stage II allowed us to study the early stage strength acquisition of the various mixtures. It was found that the chemical composition of the mixing water plays a role on the mechanical behavior of certain cemented backfills.     

Seasonal pattern of inhibition of Ostertagia ostertagi in calves in northeast Mississippi

The composition of, and seasonal changes in, populations of gastrointestinal parasites of calves in northeast Mississippi were determined for 10 months post-weaning. After weaning on 15 October, 20 mixed breed beef steers were grazed together on a 4 ha fescue/bermudagrass pasture. From November through August of the following year, two of the calves were removed each month for necropsy and counting of gastrointestinal nematodes. Eight species of worms were found: Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, Bunostomum phlebotomum, Cooperia spp., Trichostrongylus colubriformis, Oesophagostomum spp., and Trichuris ovis. During all months, Ostertagia ostertagi and Cooperia spp. combined comprised at least 89% of gastrointestinal nematode burdens. Cooperia spp. represented 92.6% of the total worm burden of calves in November but declined to about 56% in January and February. From March through August, Ostertagia ostertagi comprised at least 79% of the worms from calves. Numbers of inhibited Ostertagia ostertagi increased markedly from February to March and remained at high levels prior to resumption of development in August. The proportion of Trichostrongylus axei remained about 4% throughout the year, but the highest numbers were recorded in the summer months. Other species were minor components of the worm population. These data indicate that with respect to Ostertagia ostertagi, northeast Mississippi can be considered a summer inhibition zone.     

Production of Bioingredients from Kluyveromyces marxianus Grown on Whey: An Alternative

Whey waste is a major problem for the dairy industry. Finding alternative means to reduce its pollution potential and produce high value-added bioingredients has been attempted by many researchers. Kluyveromyces marxianus var. marxianus is a dairy yeast that produces β-galactosidase, allowing for whey fermentation. Also, K. marxianus has been proposed as a source of: (1) oligonucleotides, used as flavor enhancers in food products; (2) oligosaccharides, used as prebiotics to stimulate the growth of Bifidobacterium sp. in the animal and human intestines; and (3) oligopeptides, immunostimulators added to dairy products that are released in the wort after whey protein proteolysis. Fed-batch fermentation can be used as an alternative process to avoid increases in lactose concentration and prevent the catabolite repression of the respiratory enzyme synthesis during aerobic fermentation, thus allowing for high biomass yields. The relevance of these factors on yeast fermentation of whey is summarized in this critical review.     

Experimental characterization of the stress–strain behaviour of cemented paste backfill in compression

It is of great interest for economical and security reasons to understand the compressive properties of underground cemented paste backfill. In this paper, the stress–strain behaviours of cemented paste backfill (CPB) subjected to uniaxial compression and conventional triaxial tests are presented and discussed. The effect of CPB basic components, strength, ageing and confining pressure on the deformation behaviour of CPB are evaluated and discussed. The results show that the stress–strain behaviour of CPB is strongly influenced by the confinement, the age and strength of CPB, and its components. The increase in confining pressure leads to a change in the mode of failure, in the stiffness, and an increase in the strength.     

Proposing sequences for peptides derived from whey fermentation with potential bioactive sites

In fed-batch fermentation by Kluyveromyces marxianus var. marxianus, whey-soluble proteins were converted into oligopeptides. To assess whether bioactive peptides could be produced during whey fermentation, K. marxianus was cultured in batch in deproteinized media containing 5 or 15% (wt/vol) dehydrated whey for 20 h and then was in fed-batch mode for 50 h. After harvesting the biomass (25,000 x g, 15 min), at 6-h intervals, the wort was analyzed to determine protein consumption and oligopeptide production by HPLC. The proteins in the wort showed an oscillatory degradation with a constant increase in the production of oligopeptides. Four major peaks were collected and were analyzed by API mass spectroscopy. Sequences of fermented peptides were compared with sequences of known bioactive peptides. On the basis of their molecular weights, two amino acid sequences were proposed. The presence of sites containing the peptide sequence of beta-lactorphin (YLLF) suggests that these oligopeptides may have antihypertensive properties.     

Hydrolyzed collagen on PVA-based electrospun membranes: Synthesis and characterization

Physicochemical, structural, and thermal properties of electrospun membranes depend on process conditions and the type and concentration of the raw materials used to produce them. In this work, the electrospinning technique (ES) is used to synthesize membranes with hydrolyzed collagen (HC) and polyvinyl alcohol (PVA) at two different distances. The characterization of these membranes is then carried out by X-Ray diffraction, Raman spectroscopy, differential scanning calorimetry, water vapor permeability (WVP), microscopy techniques, and porosity measurements. Results show that the morphology of the ES membranes depends mainly on the polymer/solvent system's physicochemical properties and the distance to the collector. Thicker samples (68–86 μm) are formed when using the furthest distance (10 cm), having fiber diameters smaller than 1 μm, porosity percentages up to 90%, and WVP values close to or in the recommended range for wound dressing commercial products. Moreover, the presence of HC results in samples with a less crystalline structure. To the best of our knowledge, this is the first report in which PVA and HC membranes are successfully synthesized by electrospinning and physicochemically characterized.     

Sliding Mode Control for the Regulation Problem of an Aerodynamic Angular System: Experimental Platform and Validation

Based on a previous theoretical work, this paper focuses on the experimental validation of a sliding mode control (SMC) technique applied to an aerodynamic angular system (AAS). To do so, an aerodynamic experimental platform is presented together with its electronic interface and its closed-loop behavior generated by the aforementioned SMC strategy. The control performance is widely reviewed under different regulation tasks and gain variations. Experimental results prove that the control strategy guarantees a stable behavior. Moreover, the robustness of the control strategy is proved when the system is subject to the influence of external disturbances.

     

Production of bioingredients from Kluyveromyces marxianus grown on whey: an alternative

Whey waste is a major problem for the dairy industry. Finding alternative means to reduce its pollution potential and produce high value-added bioingredients has been attempted by many researchers. Kluyveromyces marxianus var. marxianus is a dairy yeast that produces beta-galactosidase, allowing for whey fermentation. Also, K. marxianus has been proposed as a source of: (1) oligonucleotides, used as flavor enhancers in food products; (2) oligosaccharides, used as prebiotics to stimulate the growth of Bifidobacterium sp. in the animal and human intestines; and (3) oligopeptides, immunostimulators added to dairy products that are released in the wort after whey protein proteolysis. Fed-batch fermentation can be used as an alternative process to avoid increases in lactose concentration and prevent the catabolite repression of the respiratory enzyme synthesis during aerobic fermentation, thus allowing for high biomass yields. The relevance of these factors on yeast fermentation of whey is summarized in this critical review.     

Practical stability and stabilization of a class of nonlinear neutral type time delay systems with multiple delays: BMI’s approaches

In this paper, the practical stability and stabilization of a class of nonlinear neutral type time delay systems with multiple delays and bounded perturbations is discussed. Sufficient conditions based on Lyapunov-Krasovskii functionals are derived. They are formulated in terms of the feasibility of a set of Bilinear Matrix Inequalities (BMI’s). A practical exponential estimate of the system response is also obtained. This approach is shown to be useful in the solution of an engineering problem: the elimination of the stick-slip phenomenon in the drilling process.