Simulation of crack coalescence mechanism underneath single and double disc cutters by higher order displacement discontinuity method

The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method.The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs.The effects of specific disc parameters(except speed) on the thrust force Ft, the rolling force Fr, and the specific energy ES are investigated. It has been shown that the specific energy(energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth Pd(i.e. S/Pd ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.

Design and experiment of the pneumatic double disc precision seed metering device for Chinese flowering cabbage

Single seed metering devices for Chinese flowering cabbage planting machines have suffered such deficiencies as low efficiency,poor accuracy,and instability.To overcome these limitations,a pneumatic double disc precision seed metering device was designed.This innovative device can simultaneously plant four rows,considering the specific agricultural requirements and the geometric characteristics for Chinese flowering cabbage seeds.The precise parameters of the key component seed disc were derived through theoretical calculation.In addition,a detailed account was given for the working principle and workflow of the seed metering device.The discrete element method and EDEM software were employed to optimize the seed disc by exploring the effects of seed disc rotational speed and interleaving seed slots on seed viability.Orthogonal rotation experiments were conducted to evaluate the impact of seed disc rotational speed and negative pressure.While rates of qualified seeding,double seeding and missing seeding were adopted as test indicators.Testing results show that,at a seed disc rotational speed of 41.5 r/min and a negative pressure of 3.80 kPa,the average qualified seeding rate is 90.13%,the average missing seeding rate is 3.30%,and the average double seeding rate is 6.02%.These values satisfy the agricultural requirements for planting Chinese flowering cabbage.The findings can also provide valuable insights for the structural optimization and design of precision seed metering devices for Chinese flowering cabbage.

Double tractors swing microendoscopic discectomy technique for multi-segmental lumbar disc herniation

Objective To evaluate the effect of double tractors swing microendoscopic discectomy technique in multisegmental lumbar disc herniation.Methods From December 2006 to November 2009,153 patients with multisegmental lumbar disc herniation

Determination of the prevalence of extended spectrum β-lactamase in clinical samples collected from Dehradun City Hospital

Objective:To detect extended spectrumβ-lactamase(ESBL)and determine its prevalence in various clinical samples collected from Dehradun City Hospital.Methods:The samples were first cultured in MacConkey’s agar plates by streak plate method,then identified by Gram staining and biochemical tests.The isolated bacterial strains were then tested for antibiotic susceptibility by Kirby-Bauer method.The ESBL detection is then carried out by double disc diffusion method.Results:Off the 56 samples cultured,21 strains were identified which were six Escherichia coli(E.coli),six Klebsiella,four Proteus,four Pseudomonas aeruginosa(P.aeruginosa)and only one Acinetobacter.Eight out of 21(38.1%)strains including three of E.coli,three of Klebsiella and two of P.aeruginosa,were found to be resistance to all five antibiotics(piperacillin,amikacin,ampicillin,gentamicin,and ciprofloxacin).Initial screening using four antibiotics(cefotaxime,ceftazidime,aztreonam and ceftriaxone)and the final confirmatory test using ceftazidime/clavulanic acid and ceftazidime alone showed that 19.05%of all strains isolated were ESBL producers.Individually,16.67%E.coli,16.67%Klebsiella pneumoniae,25%P.aeruginosa and 100%Acinetobacter were found to be ESBL producers.Conclusions:Antibiotic resistance by ESBL has become a major risk factor worldwide,therefore routine checkup and accordingly prescription are suggested.