Breakage Efficiency Research Articles

Modeling Agglomeration Behavior in High Temperature Gas–Solid Fluidized Beds via Monte Carlo Method

Particles and bubbles are important discrete elements in gas–solid fluidized beds. The interactions between them affect the evolution of agglomerates. Based on the analyses of microscopic physical processes, mathematical models of particle coalescence and agglomerate breakage caused by bubble expansion were developed. Coupling with the constant-number Monte Carlo method, the evolution of particle size distribution was simulated. Modeling results matched well with cold-mode experiment results, which demonstrated that the approach is a promising way to predict agglomeration behavior in the fluidized beds. Also, the coalescence efficiency β0 and breakage efficiency βb extracted from Monte Carlo results can provide rate constants for the kernels in population balance modeling. Further investigations of the effects of process parameters show that decreasing bed temperature or increasing superficial gas velocity reduces the coalescence efficiency and increases the breakage efficiency, which are beneficial to pr...

Study on the influence of joint spacing on rock fragmentation under TBM cutter by linear cutting test

Joint spacing is one of the most important geological factors influencing rock fragmentation by TBM cutters and TBM performance. In order to study the influence of joint spacing, full-scale linear cutting tests have been conducted for the Beishan granite samples with different joint spacing (i.e. one intact sample, two jointed samples with joint spacing of 100mm and 400mm). For different joint spacing, the influence of penetration depth on rock fragmentation was also explored by varying the penetration depth with an interval of 0.5mm. During the test process, the three directional forces acting on the TBM cutter were recorded, and the rock chips formed by each cutting pass were weighed, respectively. By analysing the cutting force, crack initiation/propagation and rock chips, the influences of joint spacing on rock fragmentation process by TBM cutter were investigated. The test results showed that the increase of penetration depth cannot improve the TBM breakage efficiency after reaching a certain value for the intact rock sample, and the normal force for intruding the intact rock is larger than that for intruding the rock jointed samples. It is also found that the sample part below the joint plane is intact, thus joint can restrain the crack propagating cross the joint plane and facilitates the chips formation on the cutting surface. For the rock sample with joint spacing of 100mm, two rock fragmentation modes were found during the cutting process. One mode is that the cracks initiate from the crushed zone under TBM cutter, and the cracks propagate to the joint plane, consequently form large rock chips. The other one is that the cracks initiate from the joint plane and then propagate to the rock cutting surface, and the cracks initiate before the formation of the crushed zone under the cutter. For the rock sample with joint spacing of 400mm, there are two rock fragmentation stages, i.e., the normal rock fragmentation stage and the joint-controlled rock fragmentation stage. There is a transitional process between these two stages, and also the median crack can be promoted to propagate vertically to joint plane due to the joint existence. This study can provide useful guidance for operation optimization and performance prediction for TBM operating in jointed rock masses.

Comparison and discussion on fragmentation behavior of soft rock in multi-indentation tests by a single TBM disc cutter

This paper is to investigate the mechanical responses and failure characteristics of soft rock in multi-indentation tests by a single TBM constant cross section (CCS) disc cutter. Different pre-set penetration depths and totally three cycles of indentation processes were employed in the repeated indentation tests conducted on the cubic cement mortar specimens. The load-penetration depth curve, penetration load, peak-load penetration depth, rock breakage work and compacted zone depth for the three indentation processes were analyzed. The strength and deformation properties and failure behavior of soft rock under different indentation conditions were revealed. The rock breakage behavior after several indentation processes still presents brittle failure characteristic with small pre-set penetration depths, but the specimens with large pre-set penetration depths appear obvious plastic failure mode. Approximately equal leap loads are obtained from both the intact specimen in direct indentation failure test and the weakened specimens after several indentation processes with different pre-set penetration depths, but the peak-load penetration depths for specimens with different pre-set penetration depths are varying. Curves of the cumulative penetration depth and cumulative rock breakage work both reach the corresponding peak values for one certain pre-set penetration depth. Along with this most unfavourable pre-set penetration depth, rock breakage efficiency is the lowest and energy consumption is the highest.

Optimization of Tunnel Boring Machine (TBM) Disc Cutter Spacing in Jointed Hard Rock Using a Distinct Element Numerical Simulation

The Tunnel Boring Machine (TBM) tunneling process in hard rock is actually breakage of a rock mass that is not necessarily intact. Thus, undoubtedly, joints and discontinuities play a role in TBM performance. In addition, this performance depends on the rock breakage efficiency induced by the TBM cutterhead. Both the rock mass and the TBM specifications affect the rock breakage and chipping process and thus in the machine efficiency. In this paper, the chipping process in a type of jointed hard rock under indentation by two TBM disc cutters has been numerically simulated using the Discrete Element Method (DEM) in two dimensions. The spacing of the cutters has been optimized regarding optimization of some defined criteria such as chip thickness, chipping area and also significantly the penetration rate. The optimum cutter spacings on the selected hard and jointed rock were identified to be in the range about 110 to 140 mm for different joints frequencies. According to the simulation results, it is believed that the numerical simulation will contribute to an improved knowledge of rock fragmentation, which will in turn help to enhance mining, drilling and tunneling efficiency through the improved design of mining tools and equipment.

The DSIF Subunits Spt4 and Spt5 Have Distinct Roles at Various Phases of Immunoglobulin Class Switch Recombination

Class-switch recombination (CSR), induced by activation-induced cytidine deaminase (AID), can be divided into two phases: DNA cleavage of the switch (S) regions and the joining of the cleaved ends of the different S regions. Here, we show that the DSIF complex (Spt4 and Spt5), a transcription elongation factor, is required for CSR in a switch-proficient B cell line CH12F3-2A cells, and Spt4 and Spt5 carry out independent functions in CSR. While neither Spt4 nor Spt5 is required for transcription of S regions and AID, expression array analysis suggests that Spt4 and Spt5 regulate a distinct subset of transcripts in CH12F3-2A cells. Curiously, Spt4 is critically important in suppressing cryptic transcription initiating from the intronic Sμ region. Depletion of Spt5 reduced the H3K4me3 level and DNA cleavage at the Sα region, whereas Spt4 knockdown did not perturb the H3K4me3 status and S region cleavage. H3K4me3 modification level thus correlated well with the DNA breakage efficiency. Therefore we conclude that Spt5 plays a role similar to the histone chaperone FACT complex that regulates H3K4me3 modification and DNA cleavage in CSR. Since Spt4 is not involved in the DNA cleavage step, we suspected that Spt4 might be required for DNA repair in CSR. We examined whether Spt4 or Spt5 is essential in non-homologous end joining (NHEJ) and homologous recombination (HR) as CSR utilizes general repair pathways. Both Spt4 and Spt5 are required for NHEJ and HR as determined by assay systems using synthetic repair substrates that are actively transcribed even in the absence of Spt4 and Spt5. Taken together, Spt4 and Spt5 can function independently in multiple transcription-coupled steps of CSR.

A Numerical Model for Bubble Size Distribution in Turbulent Gas-Liquid Dispersion

In present study a numerical model for bubble size distribution is developed that considers bothbreakage and coalescence in turbulent gas liquid dispersion. Two-step mechanisms are considered forboth breakage and coalescence of bubbles. The bubble breakage is structured as the product of thebubble-eddy collision frequency and breakage efficiency in gas-liquid dispersions. The coalescencefunction considers the product of bubble-bubble collision frequency and coalescence efficiency. Themodel overcomes several limitations observed in previous efforts such as empirical parameters,narrow range of operating conditions, and narrow range of geometries. Favorable agreement is foundbetween the predicted bubble size distribution and the experimental data reported in the literature. Thepercentage of error obtained for the average bubble size was found within ± 17%.Journal of Chemical Engineering Vol.ChE 24 2006 25-34

Break‐Up of Nanoparticle Agglomerates by Hydrodynamically Limited Processes

When dry nanoparticulate powders are first added into a liquid, clusters as large as hundreds of microns can be formed. In this study, high shear impellers, such as the sawtooth Ekatomizer and rotor‐stator impellers were used to suspend and break‐up these agglomerates in a stirred vessel. The high local energy dissipation rates generated by these impeller could slowly break up clusters to submicron sizes by an erosional mechanism. In comparison, single and multiple passes through a valve homogenizer could quickly break the nanoparticle clusters to submicron sizes; single pass operation had the highest breakage efficiency for a given specific energy input. For both equipment types, the rate of fines generation was found to be controlled by the maximum energy dissipation rate. However, the size of the fine aggregates produced was a constant and was not a function of the energy dissipation rate.

Plasmid breakage by 125I-labelled DNA ligands: Effect of DNA-iodine atom distance on breakage efficiency

Purpose: The aim of the study is to establish the relationship between the efficiency of DNA double-stranded breakage by 125I-labelled DNA ligands and the distance from the decaying atom to the helical axis.Materials and methods: Two new iodinated minor groove binding ligands were synthesized which, on the basis of molecular modelling studies, place the iodine atom at different distances from the DNA helical axis (namely 7.4 and 11.2 A°). Plasmid DNA breakage experiments, in both buffer-only and buffer + 2M dimethylsulfoxide (DMSO), were used to determine the efficiency of induction of internal double-stranded breaks (DSB) of the two new ligands, as well as that for 125I-Hoechst 33258, which is characterized by a helical axis-iodine atom distance of 9.1 A°.Results: The results showed a progressive decrease in the efficiency of DNA DSB induction with the axis-iodine atom distance, for both incubation conditions. The distance-damage relationship was somewhat steeper than previously predicted from the theoretical studies by Humm and Charlton, based on radical-mediated damage. Another distinctive trend was revealed by comparison of breakage efficiency with and without DMSO. The extent of DMSO protection increased significantly with DNA-iodine distance.Conclusions: The steeper than predicted decrease in DSB induction with DNA-iodine distance is consistent with a substantial contribution to DNA breakage of the charge neutralization effect (arising from the transient positive charge left on the daughter Te atom), and the expectation that this contribution would be very dependent on the distance of the site of hole injection from the base-pair π-stack. An important caveat to the results and conclusions is the need to confirm the estimated helical axis-iodine distances with X-ray crystallography studies, and for further exemplification with a more extensive collection of DNA ligands.

Experimental investigations on ultrasound mediated particle breakage

This paper investigates the effect of high-intensity ultrasound on the breakage characteristics of particles suspended in water. A continuous sonicated flow experimental apparatus is used involving a 24 kHz horn type transducer and continuous in-line particle chord length measurement. The effects of sonication power (150–350 W) and temperature (10–50 °C) on the breakage characteristics are investigated. Higher breakage is favored at higher sonication power. An optimum temperature in the range tested is observed to exist between 25 °C and 37 °C. The acoustic cavitation field is influenced by temperature through a complex interplay of vapor pressure, surface tension and viscosity leading to the optimum observed in particle breakage. The efficiency of ultrasound energy conversion to particle breakage is calculated using calorimetry and found along with the net breakage efficiency to initially increase with temperature followed by a decrease after the optimum. It is found to be independent of input ultrasonic power. The effects of contact time is also investigated.

In situ TBM penetration tests and rock mass boreability analysis in hard rock tunnels

Boreability is popularly adopted to express the ease or difficulty with which a rock mass can be penetrated by a tunnel boring machine. Because the boreability is related to the rock mass properties, TBM specifications and TBM operation parameters, an accurately definable quantity has not been obtained so far. In order to analyze and compare rock mass boreability, a series of TBM shield friction tests were conducted in a TBM tunneling site. Two sets of TBM penetration tests were performed in different rock mass conditions during tunneling in rock. In each step of the penetration test, the rock muck was collected to perform the muck sieve analyses and the shape of large chips was surveyed in order to analyze the TBM chipping efficiency under different cutter thrusts. The results showed that a critical point exists in the penetration curves. The penetration per revolution increases rapidly with increasing thrust per cutter when it is higher than the critical value. The muck sieve analysis results verified that with increasing thrust force, the muck size increases and the rock breakage efficiency also increases. When the thrust is greater than the critical value, the muck becomes well-graded. The muck shape analysis results also showed with the increase of the thrust, the chip shape changes from flat to elongated and flat. The boreability index at the critical point of penetration of 1 mm/rev. defined as the specific rock mass boreability index is proposed to evaluate rock mass boreability.

Numerical simulation of rock fragmentation process induced by two TBM cutters and cutter spacing optimization

TBM performance depends on the rock breakage efficiency induced by TBM cutterhead. The rock breakage process is the interaction process between TBM and rock mass, which is affected by the TBM specifications, such as cutter thrust force, cutter tip width and profile, cutter spacing, revolution per minute, and torque, and rock mass properties mainly including rock material strength, rock brittleness index, joint spacing and orientation. In this study, rock chipping process induced by two TBM cutters was performed using the discrete element method (DEM). The chipping process is composed of formation of crushed zone, cracks initiation and propagation, side cracks coalescence and chip formation. The influence of the difference cutter spacing on the penetration process was also simulated by setting up a series of two dimensional UDEC models. The optimum cutter spacing on the Bukit Timah granite found in Singapore was identified to be about 100 mm provided the critical cutter thrust force can be reached. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Establishment of subcellular fractionation techniques to monitor the intracellular fate of polymer therapeutics I. Differential centrifugation fractionation B16F10 cells and use to study the intracellular fate of HPMA copolymer–doxorubicin

Polymer therapeutics are being designed for lysosomotropic, endosomotropic and transcellular drug delivery. Their appropriate intracellular routing is thus crucial for successful use. For example, polymer–anticancer drug conjugates susceptible to lysosomal enzyme degradation will never deliver their drug payload unless they encounter the appropriate activating enzymes. Many studies use confocal microscopy to monitor intracellular fate, but there is a pressing need for more quantitative methods able to define intracellular compartmentation over time. Only then will it be possible to optimise the next generation of polymer therapeutics for specific applications. The aim of this study was to establish a subcellular fractionation method for B16F10 murine melanoma cells and subsequently to use it to define the intracellular trafficking of N-(2-hydroxyproplylmethacrylamide) (HPMA) copolymer-bound doxorubicin (PK1). Free doxorubicin was used as a reference. The cell cracker method was used to achieve cell breakage and optimised to reproducibly achieve ∼90% breakage efficiency. This ensured that subsequent subcellular fractionation experiments were representative for the whole cell population. To characterise the subcellular fractions obtained by differential centrifugation, DNA (nuclei), succinate dehydrogenase (mitochondria), N-acetyl-β-glucosaminidase (lysosomes), alkaline phosphatase (plasma membrane) and lactate dehydrogenase (cytosol) were selected as markers and their assay was carefully validated. The relative specific activity (RSA) of the fractions obtained from B16F10 cells were: nuclei (2.2), mitochondria (4.1), lysosomes (3.7) and cytosol (2.5). When used to study the intracellular distribution at non-toxic concentrations of PK1 and doxorubicin, time-dependent accumulation of PK1 in lysosomes was evident and the expected nuclear localisation of free doxorubicin was seen. Live cell fluorescence microscopy and confocal co-localisation studies gave qualitative corroboration of these results, but by using this method, we were unable to accurately define organelle localisation. In conclusion, the B16F10 subcellular fractionation method developed here provides a useful tool to allow comparison of the intracellular trafficking of other polymer conjugates.

Development of a novel compact sonicator for cell disruption

Ultrasound microbial cell disrupters operating at around 20 kHz are often physically large and, due to significant heating, can be unsuitable for small sample volumes where biochemical integrity of the extracted product is required. Development of a compact device based on a 63.5-mm diameter, 6.5-mm thick tubular transducer for rapid cell disruption in small-volume samples in a high-intensity acoustic cavitation field with minimal temperature rises is described here. Suspensions of Saccharomyces cerevisiae were exposed to cavitation for various times in the compact device and a 20-kHz probe sonicator. Cell disruption was assessed by protein release and by staining. Yeast cell disruption was greater in the novel 267-kHz sonicator than in the 20-kHz probe sonicator for the same exposure time. A 1-dimensional (1-D) transfer matrix model analysis for piezoelectric resonators was applied to an axial cross-section of the tubular sonicator to predict frequencies of mechanical resonance in the sample volume associated with maximum acoustic pressure. Admittance measurements identified frequencies of electrical resonance. Ultrasonic cavitation noise peaks were detected by a hydrophone at both the mechanical and electrical resonances. Cell breakage efficiency was twice as great in terms of protein released per dissipated watt at the mechanical resonance predicted by the model, compared to those at the electrical resonance frequencies. The results form a basis for rational design of an ultrasound cell disruption technique for small-volume samples.

Initial Damage in Human Interphase Chromosomes from Alpha Particles with Linear Energy Transfers Relevant to Radon Exposure

To determine the efficiency at which alpha particles at LETs chosen to simulate exposure to radon progeny break chromosomes, the premature chromosome condensation technique was used to measure breaks soon after irradiation. Noncycling human fibroblasts were irradiated with graded doses of monoenergetic alpha particles accelerated to produce LETs of 90, 120, 150, 180 and 200 keV/microns at the midpoint of the cell nuclei. Premature chromosome condensation was initiated immediately after irradiation and cells were scored for the total number of prematurely condensed chromosomes and fragments per cell. Similar experiments were conducted with 250 kVp X rays for comparison. Irradiation with alpha particles produced 8.6 to 13.1 excess fragments per gray, while X rays produced 5.8 excess fragments, resulting in RBEs around 2. Calculations of the number of breaks produced on average by a single particle traversal of a cell nucleus indicated that at the LETs tested more than one break (1.5-2.8) was produced by each traversal, the maximum being that produced by 180 keV/microns alpha particles. When chromosome aberrations are scored at metaphase after high-LET irradiation, RBEs considerably greater than those recorded here (approximately 2) have been reported. These results showing relatively small differences in initial break levels for alpha particles in the LET range of the radon progeny relative to X rays indicate that the greater aberration frequencies are not due principally to an increase in breakage efficiency, but interactions between breaks along the same particle track are important.

Breakage and coalescence models for drops in turbulent dispersions

AbstractA substantial effort has been made by numerous investigators to describe droplet breakage and coalescence in turbulent dispersions. An attempt is made here to improve these models based on existing frameworks and recent advances described in the literature. Two‐step mechanisms are considered for both the breakage and coalescence models. The drop breakage function is structured as the product of the drop‐eddy collision frequency and breakage efficiency which reflect the energetics of turbulent liquid‐liquid dispersions. The coalescence function retains the former structure of the product of drop‐drop collision frequency and coalescence efficiency. The coalescence efficiency model has been modified to account for the effects of film drainage for drops with partially mobile interfaces. These models overcome several inconsistencies observed in previous efforts and are applicable for dense dispersions (about ϕ[0.10–0.30]). For the daughter drops produced by breakage, a probability density is proposed based on the energy requirements for the formation of daughter drops.

Electrostatic Coalescence: Reactor, Process Control, and Important Parameters

Abstract An optimal breakage of liquid membrane emulsions is desirable for the industrial application of liquid membrane extraction. The electrostatic emulsion breakage process was investigated with regard to its parameters. The results show that the breakage efficiency increases with the applied field strength, frequency, and the achievable polarization of the membrane phase molecules. An on-line measurement of the applied field strength allows control of the process efficiency.

Analogy between indentation and blasting tests on brittle rocks

Analogy Between Indentation and Blasting Tests on Brittle Rocks This paper presents a common mechanism of breaking quasi-brittle rocks either by drilling and blasting or by indentation. Only minor modifications, to account for the prevailing boundary conditions pertaining to either one of these cutting processes, are required. Rock breakage by drilling and blasting or by indentation is based on the formation of a heterogeneous stress field due to the application of concentrated loads either by the indentor or by the detonation of the explosives. Rock behavior varies according to the stress level generated into the material. In the high stress zone it is plastic or pseudoplastic. In low stress region, failure is of the brittle extension type. In indentation the formation of a confined plastic zone is essential before chipping. However, for blasting plasticity is not necessary to occur prior to chipping because the high pressure gases that are generated from the explosion are usually quite sufficient — under suitable conditions — to create failure by extension cracking. Energy consumed in these rock cutting processes is a function of the relative amount of fines produced and their size distribution (or degree of fineness). Further improvements in rock breakage efficiency can be achieved by the proper choice of the important parameters for the specific techniques. The above analogy can be extended to other well known rock testing and breakage techniques.

A semi-empirical relationship between selection function and particle load in batch ball milling

On assuming a Maxwell-Boltzman distribution of ball energies in tumbling mills, a relationship is obtained to predict the influence of particle load on the selection parameters of the discretized batch grinding equation. The model is derived in terms of two partial probabilities of impact and of breakage efficiency per impact, with the latter accounting for the energy distribution of tumbling balls. The relationship is in extremely good agreement with recent experimental data found in the literature.

The production and repair of double strand breaks in cells from normal humans and from patients with ataxia telangiectasia

The production and repair of double strand breaks induced by γ-rays in the DNA of human fibroblasts have been measured by sedimentation in sucrose gradients under non-denaturing conditions. Unirradiated DNA formed a rapidly sedimenting gel. Low doses of radiation released freely sedimenting DNA molecules from this gel. Higher doses reduced the rate of sedimentation of the free DNA due to the introduction of double strand breaks. The breakage efficiency was 1 break 1.3 × 10 10 daltons of DNA/krad. Postirradiation incubation after a high dose of radiation resulted in an increase in molecular weight of the free DNA molecules, and after a low dose the rapidly-sedimenting gel was reformed. These data suggest that double strand breaks are repaired in human fibroblasts. No significant differences were found between fibroblasts from two normal donors and four patients with the radiosensitive disorder, ataxia telangiectasia, in either the production or repair of double strand breaks.

Lethality and double-strand scissions from 14C decay in the DNA of micro-organisms.

14C-2-thymidine was incorporated into the DNA of E. coli B/r and of coliphage T4. The labelled organisms were stored for several years at -196 degrees C. Both were periodically assayed for loss of viability, and the coliphage also for the appearance of double-strand breaks (DSBs) in DNA. E. coli B/r exhibited a survival curve with a substantial initial shoulder, extrapolation number 5-2 +/- 2-3, and a final exponential portion corresponding to a lethal efficiency per 14C decay per 2-5 X 10(9) daltons of DNA, of 0-009 +/- 0-002. For coliphage T4, our best estimate for the lethal efficiency per 14C decay is 0-03 +/- 0-04, and that for the DNA breakage efficiency is -0-002 +/- 0-004. The large standard errors result from the very small number of 14C decays occurring in each phage. These results suggest that 14C decay in the DNA of micro-organisms does not cause DSBs but does cause potentially lethal damage to the thymine bases in which decay occurs, and that wild-type E. coli can repair a large number of such DNA lesions.