Dominant rock properties affecting the performance of conical picks and the comparison of some experimental and theoretical results

Conical picks are the essential cutting tools used especially on roadheaders, continuous miners and shearers and their cutting performance affects directly the efficiency and the cost of rock/mineral excavation. In this study, in order to better understand the effects of dominant rock properties on cutter performance, 22 different rock specimens having compressive strength values varying from 10 to 170 MPa are first subjected to a wide range of mechanical tests. Then, laboratory full-scale linear cutting tests with different depth of cut and cutter spacing values are realized on large blocks of rock specimens using one type of conical pick. Specific energy, cutting and normal force values for relieved and unrelieved cutting modes are recorded using a triaxial force dynamometer with capacity of 50 tonnes and a data acquisition system. Cutter force and specific energy values are correlated with rock properties and theoretical force and specific energy values obtained from widely used theoretical approaches.The results indicate that uniaxial compressive strength among the rock properties investigated is best correlated with the measured cutter performance values, which is in good agreement with previous studies. However, it is also emphasized in this study that Brazilian tensile strength, Schmidt hammer rebound values, static and dynamic elasticity modulus are also dominant rock properties affecting cutter performance.Theoretical specific energy defined by different researchers has a meaningful relationship with the experimental specific energy, which is an essential parameter for predicting the instantaneous cutting rates of mechanical excavation systems. It is also demonstrated that the experimental cutter forces obtained for 5 mm depth of cut are in good agreement with theoretical force values, if the friction angle between rock and cutting tool is included in the theoretical formulation. It is emphasized that, to some extend, laboratory tests can help to minimize high cost of a trial–error approach in the field.     

Effect of replacing disc cutters with chisel tools on performance of a TBM in difficult ground conditions

A summary of a research program covering a period of two years on the performance of a TBM in a very complex and difficult geology is presented in this study. The formations in the study area varied from alluvium, sludge, mudstone, shale and limestone to quartzite with strengths from soft to very hard. The dykes frequently intruded the sedimentary rocks resulting in different degrees of weathering and fracturing in the country rock causing tremendous delays in progress rate of the TBM. The disc cutters started cutting inefficiently in clayey medium strength ground with extreme water income, at where also excessive disc consumptions started due to insufficient friction between the disc cutters and very soft (sludgy) formation, and it was decided to replace all disc cutters with chisel tools (ripper, scraper). Before making this important decision that could affect totally the excavation efficiency and production rate, some theoretical estimations were performed using the Evans’ cutting theory after some modifications based on the previous experimental studies for relieved cutting mode and wear flat, front ridge and vee-bottom angles found in complex shapes of chisel tools to estimate deterministically the torque and thrust requirements of the TBM.Field measurements of the torque and thrust requirements of the TBM equipped with the chisel tools validated the theoretical considerations and the deterministic model used for predicting the performance. Statistical analysis indicated that the model could be used reliably for performance prediction. This study also gave a unique opportunity to compare the performance of disc cutters and chisel tools used on the same TBM at variety of grounds and to analyze the effect of replacing disc cutters with chisel tools on the performance of the TBM. The field measurements indicated that the chisel tools were superior to the disc cutters in especially soft to medium strength rocks.     

Disrupted temporal control in the R6/2 mouse model of Huntington’s disease.

Huntington’s disease is characterized by corticostriatal dysfunction and degeneration of the striatum with progressive loss of the medium spiny neurons. These circuits are important for instrumental responding, interval timing, and temporal control over motor output. We investigated the acquisition of timed operant responding in two R6/2 Huntington’s Disease models, differing in CAG repeat length and genetic background (115 and 250 CAG repeats, and a mixed CBAxC57 or pure C57 background) and their corresponding wild type controls using the peak procedure. Both mouse lines exhibited similar response control deficits. In unreinforced peak trials, mice either did not learn to terminate an ongoing response past reinforcement time or required more trials to acquisition compared to the wild type mice. While transgenic and wild type mice did not exhibit differences in temporal accuracy, response curves were flatter in transgenic mice, suggesting decreased temporal control over operant responding. The results are discussed in terms of the neurobiology of interval timing, instrumental responding, and the neuropathology of HD and R6/2 mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Catalytic coating of virus particles with zinc oxide

We show that the rod-shaped Tobacco mosaic virus (TMV) can be coated with the wide band gap semiconductor zinc oxide by electroless deposition under mild reaction conditions. The process involves pretreatment with aqueous Pd(II), followed by nucleation of ZnO, directed to palladium centers formed on the surface of TMV. The mechanism is based on the local pH change due to the reduction of nitrate by dimethylamine borane at the palladium. Morphology and chemical composition have been analyzed by transmission electron microscopy (TEM) and by energy filtering TEM, respectively. The optical properties were elucidated by cathodoluminescence, which showed the desired near-band edge emission.     

Oxidation Behavior of Bi(Pb,Ga) SrCaCuO System

A nominal compositions of BiSrCaCuO (3:2:2:3), (2:2:2:3), (4:3:3:4), and BiPbGaSrCaCuO (3:0.5:2:2:3), (3:0.3:0.3:2:2:3) have been prepared by conventional melt-quenching method. The oxidation behaviors of samples prepared were analyzed using a thermogravimetric analyser, TGA. Total mass gains of samples, average oxidation rates and maximum oxidation rates were calculated separately. TGA measurements of all samples were carried out under the normal atmosphere pressure.     

Sibs diagnosed prenatally with situs inversus totalis, renal and pancreatic dysplasia, and cysts: a new syndrome?

We describe two sib fetuses with situs inversus, cystic dysplastic kidney and pancreas, bowing of the lower limbs and clavicles, severe intrauterine growth retardation (IUGR), and oligohydramnios. Early prenatal diagnosis of pancreatic and dysplastic renal cysts and situs inversus totalis were made in the 18-week-old fetus. This syndrome differs from that of Ivemark and related syndromes because of the presence of situs inversus totalis and absence of hepatic fibrosis and cysts. The parents were first cousins, and did not have any cysts of kidney, liver, or pancreas detected by ultrasonography.     

Synthesis and characterization of V,Mo and Nb incorporated micro–mesoporous MCM-41 materials

Highly microporous metal-MCM-41 ordered mesoporous structure catalysts having different metal/Si (V, Mo, Nb) atomic ratios and combinations of metal sources were hydrothermally synthesized. The structural properties estimated using different techniques were found to be in agreement with each other. Metals were successfully incorporated into MCM-41 without deteriorating the ordered hexagonal structure. The metal ions in the synthesis solutions probably settled on the hydrophilic end of the template hence the metal incorporation resulted improvements in the micropore structure. Low loading of metals caused an increase in the surface area and pore volume values of the catalysts. The highest total (1310 m² g^?1) and micropore surface area values (1083 m² g^?1) were obtained by Nb incorporation. The micro- and mesopore dimensions of MCM-41 increased from 0.5 to 1.1 nm and from 2.5 to 2.8 nm, respectively, with metal incorporation. Low V/Si ratios and presence of Nb in the starting solution enhanced narrow mesopore size distribution. The pore dimension and wall thickness values estimated from nitrogen adsorption and X-ray diffraction methods were consistent with the corresponding values obtained using transmission electron microscopy.     

Down syndrome associated with systemic lupus erythematosus: a mere coincidence or a significant association?

An 8-year-old male, who had Down syndrome associated with systemic lupus erythematosus (SLE), is described. He also had a partial complement 4 deficiency. This case is a reminder that the physician should be aware of the possibility of an immune defect in a male presenting with SLE at a young age. The question of whether the association of Down syndrome with SLE is coincidental or whether there is a predilection for autoimmune disorders in Down syndrome is discussed.