Fragment Size Distribution Research Articles

Dynamic fragmentation of microwave irradiated rock

Abstract The microwave-assisted rock fragmentation has been proven to be a promising approach in reducing cutting tools wear and improving efficiency in rock crushing and excavation. Thus, understanding the influence of damage induced by microwave irradiation on rock fragmentation is necessary. In this context, cylindrical Fangshan granite (FG) specimens were exposed to microwave irradiation at a power of 6 kW for different durations up to 4.5 min. The damages of the specimens induced by irradiation were quantified by using both X-ray micro-CT scanning and ultrasonic wave measurement. The CT value and P-wave velocity decreased with increase of irradiation duration. The irradiated specimens were then tested using a split Hopkinson pressure bar (SHPB) system to simulate rock fragmentation. A momentum-trap technique was utilized to ensure single-pulse loading on the specimen in SHPB tests, enabling valid fragment size distribution (FSD) analysis. The dependence of dynamic uniaxial compressive strength (UCS) on the irradiation duration and loading rate was revealed. The dynamic UCS increased with increase of loading rate while decreased with increase of irradiation duration. Using the sieve analysis, three fragmentation types were proposed based on FSD, which were dictated by both loading rate and irradiation duration. In addition, an average fragment size was proposed to quantify FSD. The results showed that the average fragment size decreased with increase of loading rate. A loading rate range was identified, where a dramatic reduction of the average fragment size occurred. The dependence of fragmentation on the irradiation duration and loading rate was also discussed.

Mechanism of the in-hole detonation wave interactions in dual initiation with electronic detonators in bench blasting operation

With the development of electronic detonators, the precise initiation timing has been controlled at the microsecond level, which are accurate enough to guarantee waveform collision at precise locations in hole. The accumulated energy effect by collision of two oppositely traveling in-hole detonation waves was proved theoretically based on impact dynamics theory. And the fragment size distributions and blasting vibration under different initiation modes with electronic detonators were also investigated by comparing the field test and numerical simulations results of bench blasting. The results show that the detonation products density near the collision point is increased, the particle velocity is reduced, and the kinetic energy is converted into pressure energy, the pressure near the collision point is greater than the sum of the strength of the two detonation waves, demonstrating the potential for an increase in fragmentation and throw. At the same time, the angle of the shock wave formed in the rock mass is deflected, changing from tilt to horizontal direction, direct the pressure toward to the bench face. The field test also indicated that the in-hole dual initiation method could cause both higher peak particle velocity and higher vibration frequency.

Development of a new empirical fragmentation model using rock mass properties, blasthole parameters, and powder factor

Rock fragmentation as one of the most important blasting results plays an indispensable role in subsequent stages such as secondary breakage, loading, hauling, crushing and grinding, and relevant energy consumption. Since several rock mass properties, blasthole parameters, and powder factor can affect the fragmentation results, development of an accurate model to predict fragment size has long been a complicated subject. In this study, rock mass properties, blasthole parameters, powder factor (q), and fragment size distribution of blasted rock using image analysis technique were determined for several blasting operations in different zones of Sungun open pit copper mine, Rashakan limestone mine, Soufian limestone mine, and Golgohar open pit iron mine. The median fragment size (X50) varied from 10.4 to 32.1 cm, and the predicted X50 by the modified Kuz–Ram models was significantly different from the X50 of the results. Because only a coefficient has been changed from one model to another and the impact of the combination of the parameters on X50 has not yet been well investigated, the impact of individual essential parameters such as blasthole diameter (ϕh), charge per blasthole (Q), rock mass properties, and q on the X50, X80, and uniformity index (n) was originally analyzed to clarify how their combination affects the fragment size of blasted rocks. ϕh and Q had a similar or a parallel effect on the fragmentation results. Two types of relations between X50 with the new combination of Q, q, SANFO, and blastability index (BI) and X50 with the combination of ϕh, q, SANFO, and BI with acceptable correlations were obtained and the correlations also increased when the parameter of joint plane spacing (JPS) was adjusted in the BI system. At the end, a new empirical model was achieved to predict X50 as a function of combination of Q, q, SANFO and adjusted BI with higher correlation (R2 = 0.865), less root mean square error (RMSE = 3.3 cm), and less coefficient of variation (CV = 19.9%) with actual field results.

Characterization of high-temperature nuclear fuel-coolant interactions through X-ray visualization and image processing

High-resolution X-ray imaging was employed at the JAEA MELT facility to visualize a kilogram-scale interaction between a jet of high temperature molten stainless steel and sodium, mimicking a sodium-cooled fast-neutron reactor in the aftermath of a core-disruptive accident. A novel software, SPECTRA, has been developed for the quantitative characterization of jet quenching and fragmentation. Tracking and 3D reconstruction of the melt phase traversing the imaging window enabled the detection of 72% of the debris mass recovered post-experiment. The rebounding of melt fragments confirmed a solid outer crust at the melt-coolant interface, while a thermal fragmentation event induced rapid vapor expansion. Jet fragmentation is best explained by the vaporization of coolant entrained within the melt jet generating an internal over-pressure sufficient for fragmentation of the crust. Thermal fragmentation produced missiles with velocities exceeding that of the jet, and a bimodal debris size distribution of coarse jet shells and finer fragments.

Breakage Characterization of Magnetite under Impact Loads and Cyclic Impact Loading

A series of impact compression tests were conducted to study the breakage characteristics of magnetite, as well as the impact pressure on its strain rate and dynamic compressive strength. The dynamic mechanical properties and fragmentation size distribution of magnetite under diverse impact loads and cyclic impact were investigated, with fractal theory as a basis and split Hopkinson pressure bar (SHPB). Breakage methods were also employed to analyze the fracture morphology of magnetite. According to the result, the fractal dimension can reflect the distribution of fragments in various sizes. If the strain rate increases, the fractal dimension will be larger, the fragment size will be finer, and the fragmentation degree will be more influential. A micro-analysis of SEM images demonstrates that the fracture morphology is determined by mineral properties. Under low load cyclic impact, intergranular fracture is the main fractography. Besides, the intergranular fracture will be changed to a transgranular one as the impact load increases.

Long-term effects of wildfire on rock weathering and soil stoniness in the Mediterranean landscapes

The severe wildfire at Mt. Carmel, Israel, in 2010, caused massive destruction of carbonate rocks. The thermal shock caused extreme exfoliation, producing large and flat clasts, affecting rocks to a depth of up to 20 cm. A decade after the fire, most flakes and spalls disappeared from the rock outcrops and adjacent soils. From these observations, this study pursued two objectives: (a) to monitor and analyze the spatio-temporal distribution of the disintegrated flakes 10 years after the fire and (b) to test the hypothesis that fires contribute to increased soil stoniness via physical and chemical flake erosion.The studied area included five lithostratigraphic units composed of chalk, limestone, and dolomite. The Schmidt Hammer test showed that after a decade, most of the spalled surface on the burned outcrops was lost, exposing new rock surfaces to atmospheric and weathering processes. The spalls and flakes were broken down and pulverized.The most prominent effects were changes in surface stoniness on the rendzina soils over the chalks, while there was less impact on the dolomite and limestone samples. The stoniness of the non-burned chalk was 23–39% and increased significantly to 69–86% in the burned area. Chalk erosion produced large (>16 mm, median 8–16 mm) and abundant gravel, suggesting fragmentation of large spalls, and particles that lost their bladed shapes becoming oblate and equant.While earlier works suggested that increasing rock fragment cover is often associated with the removal of fine particles, our results showed a substantial increase in rock fragments due to fire-induced exfoliation of rock surfaces, leading to long-term changes in soil properties. We therefore propose that the size, shape, and spatial distribution of rock fragments should be considered when examining the effects of rock fragments on hydrological and geomorphological processes or on post-fire soil rehabilitation.

Analysis of wood pellet degradation characteristics based on single particle impact tests

The knowledge of size reduction of wood pellets during pneumatic conveying is important to achieve failure-free system operation and to set-up adequate quality assurance processes. In the present study, experiments are performed with a single particle impact test facility. A stereoscopic high-speed camera set allows 3D-particle tracking and visual analysis of the particles' degradation properties. Based on the data obtained, empirical correlations for the statistical description of the pellets' breakage behaviour are presented depending on particle length, impact velocity and collision angle. These relationships are expressed mathematically by two key functions: the so-called selection function (breakage probability) and the breakage function (fragment size distribution). As expected, higher impact velocities lead to more damage, especially at normal collisions (90°) due to the maximum change of momentum. Furthermore, smaller particles tend to be more breakage resistant as they contain less impurities and cracks. Finally, an outlook on the influence of pellet quality and target material on the particles' degradation behaviour is given. Here, pellets with higher durability tend to break at higher impact loads and into larger fragments. In addition, a softer target material (e.g. HDPE) causes less particle breakage than e.g. steel.

Numerical investigation of blast-induced rock fragmentation

Optimum fragmentation of rocks during blasting is pivotal for the productivity of mining and civil engineering systems. Extensive studies on the ubiquitous fragmentation phenomena in nature and artificial processes have attested to the dominant control of the effective dimensionality and material brittleness on the size distribution of fragments. In this study, by further demonstrating that the impact of brittleness on fragmentation is physically inherent in the material dimension, we present new mechanistic insights into the blast-induced rock fragmentation via integrated analytical modelling, finite element simulation and image processing. A continuous-surface viscoplastic cap model was first calibrated step-by-step against rock behavior in different pressure and strain-rate regimes on various scales. Then, rock blasting was simulated under various bench dimensions and the fracture patterns were image-processed to provide quantitative insights into blast fragmentation. Our findings suggest that the fragments become smaller and rounder while their size distribution becomes more uniform as the rock dimensions decrease. We demonstrated that at smaller rock dimensions, the equivalent increase in energy density and suppression of pressure-induced ductility can conspire to assist crack bifurcation and thus create successively finer fragments towards the unbreakable limit. We also identified significant correlations between the fragment aspect ratio and its size and uniformity of distribution, highlighting the potential use of fragment shape as an indicator for evaluating blasting performance alongside conventional grading analysis.

Investigating the impact of the estimation error of fracture intensity (P32) on the evaluation of in-situ rock fragmentation and potential of blocks forming around tunnels

The purpose of this work is to highlight the impact of input parameters uncertainty in discrete fracture network (DFN) models and their engineering applications. We show how the error of an input parameter, here the volumetric discontinuity intensity P32, impacts the DFN model and two important rock mechanics engineering applications: the in-situ fragmentation size distribution and the potential of formation of removable blocks around tunnels, as two key parameters at block cave mining designs. The volumetric discontinuity intensity (P32) is estimated by two different approaches: the first one estimates P32 directly from 1D data and it is straightforward to implement, while the second one is based on the simulation of DFN models and needs both 1D and 2D data sets, which makes it less flexible and time consuming. The estimated values of P32 obtained from the direct approach are found to be more accurate than those by the simulation approach, with significant impacts observed in the constructed discrete fracture network models and in the estimation of the in-situ fragmentation size distribution and potential of formation of removable blocks around tunnels.

Experimental Study of the Influence of Drawbell Geometry on Hang-Ups in Cave Mine Applications

Coarse arches are a common issue in caving mines where large fragments are expected. These arches interrupt ore flow in drawpoints, decreasing available draw area, and also increasing the possibility of non-uniform draw, which can increase fine migration, mud-rush risk, and induced stress in the caved column. Moreover, hang-up removal is operationally complex and dangerous. The literature on gravity flow indicates that coarse arches are mainly influenced by the ratio between the rock fragments and the size of the opening and stresses, but some key variables have not been quantified. Here, the influence of fragment-size distribution and drawbell geometry on hang-up formation is analyzed through controlled laboratory experiments in a physical model. Results show that drawbell parameters, such as length, width and angle are relevant parameters in hang-up events. In particular, the ratios DL/d80 and DW/d80 as well as VDB/Vp are key to hang-up events, the probability of which will decrease when these ratios increase.

A simple method for high molecular-weight genomic DNA extraction suitable for long-read sequencing from spores of an obligate biotroph oomycete

Long-read sequencing technologies are having a major impact on our approaches to studying non-model organisms and microbial communities. By significantly reducing the cost and facilitating the genome assembly pipelines, any laboratory can now develop its own genomics program regardless of the complexity of the genome studied. The most crucial current challenge is to develop efficient protocols for extracting genomic DNA (gDNA) with high quality and integrity adapted to the organism of interest. This can be particularly complex for obligate pathogens that must maintain intimate interactions inside infected host tissues. Here we propose a simple and cost-effective method for high molecular weight gDNA extraction from spores of Plasmopara halstedii, an obligate biotroph oomycete pathogen responsible for downy mildew in sunflower. We optimized the yield, the quality and the integrity of the extracted gDNA by fine-tuning three critical parameters, the grinding, the lysis temperature and the lysis duration. We obtained gDNA with a fragment size distribution reaching a peak ranging from 79 to 145 kb. More than half of the extracted gDNA consisted of DNA fragments larger than 42 kb, with 23% of fragments larger than 100 kb. We then demonstrated the relevance of this protocol for long-read sequencing using PacBio RSII technology. With this protocol, we were able to obtain a mean read length of 9.3 kb, a max read length of 71 kb and an N50 of 13.3 kb. The development of such DNA extraction protocols is an essential prerequisite for fully exploiting technologies requiring high molecular weight gDNA (e.g. long-read sequencing or optical mapping). These technological advances will help generate data to answer questions such as the role of newly duplicated gene clusters, repeated regions, genomic structural variations or to define number of chromosomes that still remains undefined in many species of pathogenic fungi and oomycetes.

Shatter Thresholds and Fragment Size Distributions of Deuterium–Neon Mixture Cryogenic Pellets for Tokamak Thermal Mitigation

Reliable mitigation is necessary to eliminate the detrimental effects of a disruption event in large high-current tokamaks such as ITER. To avoid serious damage to plasma-facing components during the thermal quench phase of a disruption, material is injected to radiate the plasma energy over the inner surface of the machine. The most promising method of material injection is a process known as shattered pellet injection (SPI). SPI utilizes cryogenic cooling to desublimate gas into the barrel of a pipe gun to form a solid pellet. High-pressure gas or a mechanical punch is used to dislodge the pellet and accelerate it into a bent tube to intentionally fracture it. Pellets made of a mixture of deuterium and neon are likely candidates for thermal mitigation. The survivability of these pellets throughout their flight path, before striking the shatter tube, is essential for reliable SPI operation. Experiments were conducted to determine intact speed limits for various mixtures. This paper outlines the details of brittle fracture theory and compares a theory-based model to experimental results from various mixtures of deuterium and neon pellets.

A stochastic particle replacement strategy for simulating breakage in DEM

Description of particle breakage embedded in a simulation using the discrete element method (DEM) qualifies it to describe processes in which breakage is either desired or undesired. DEM codes evolved significantly in recent years, many of which describing breakage. In spite of their limitations representing real particles, spheres have several important advantages from the standpoint of computation efficiency, being the basis for several particle replacement schemes. However, one of its biggest disadvantages lies in the fact that size distributions that are generated are very jagged and unnatural. The work describes a stochastic approach to generate realistic size distributions from breakage of spheres. Families of fragment size distributions were obtained from testing various materials in a drop weight tester. The model also incorporates the description of the unresolved fines. Its application to individual particles demonstrates that the method captures properly the effect of stressing energy described in the analytical model.

Microstructure based simulation of the disintegration and dissolution of immediate release pharmaceutical tablets

The design of pharmaceutical tablets involves the determination of formulation parameters that define the tablet composition and internal microstructure. These parameters must be chosen so that the release of an active pharmaceutical ingredient (API) from the tablet follows a prescribed dissolution curve. In the case of immediate release formulations, the dissolution process typically consists of tablet disintegration, followed by the dissolution of the disintegration fragments. In order to find the appropriate values of formulation parameters, numerous experiments are typically required. In the present work, we propose a computational methodology for in silico design of tablet formulations with the aim of reducing the amount experimental work required during tablet design. The methodology is based on the coupling of two modelling approaches: (i) tablet fragmentation triggered by the swelling of the disintegrant is simulated by the discrete element method (DEM), and (ii) the dissolution of the resulting population of disintegration fragments is simulated using a finite volume grid-based model. The final API release curve is then obtained by the superposition of dissolution curves originating from the individual disintegration fragments. Using directly compressed tablets containing ibuprofen as the API and croscarmellose sodium as the disintegrant, the model was validated against experimental data. The fragment size distribution was evaluated by static light scattering and the dissolution profiles were obtained by a standard dissolution apparatus with UV/Vis spectroscopic detection. We demonstrate that the computational methodology is able to quantitatively predict the effect of disintegrant content and API primary particle size on the fragment size distribution and the final dissolution profiles, and is therefore useful as a tool for computer-assisted tablet formulation design.

Dynamic disintegration processes accompanying transport of an earthquake-induced landslide

Aiming to understand the dynamic disintegration and transport behavior of an earthquake-induced landslide, a dynamic discrete element method has been employed to analyze the Wangjiayan landslide triggered by the 2008 Ms 8.0 Wenchuan earthquake. Absorbing boundary condition is used for the seismic wave transmission and reflection at the slope base. The numerical results show that under seismic loading, internal rock damage initiates, propagates, and coalesces progressively along the weak solid structure and subsequently leads to fragmentation and pulverization of the slope mass. This can be quantitatively interpreted with the continuously rapid increase of the damage ratio and sudden decline of growth ratio of the number of fragments after the peak seismic shaking. During emplacement evolution, fragmented deformation patterns within the translating joint-defined granular assemblies are affected by the locally high dilatancy with a simultaneous occurrence of highly energetic collisions related to the action of shearing, and this can be quantified by the enhancement of particle kinematic activities (high vibrational and rotational granular temperatures) and intense fluctuations of location-dependent global dispersive stress. In this process, slope destabilized and transports downward in a rapid pulsing motion as friction bonds are locally and continually overcome by the seismic- and gravity-induced shear forces. The joint-determined fragment network before movement initiation and the final fragmented depositions after the rapidly sheared transport have been systematically investigated by fragment statistics (fragment size distribution, fragment mass distribution, and fractal dimension) and morphometric characters (fragment shape isotropy) to offer new insights into the disintegration characteristics of the earthquake-induced catastrophic mass movements.

Fragmentation Processes During Strombolian Explosions Revealed Using Particle Size Distribution Mapping

Fragmentation dynamics can be described by the size distribution of the fragments generated during an explosion. We approach the problem of magma fragmentation during a Strombolian explosion using the grain size distribution (GSD) of a ballistically-emplaced lapilli-and-bomb deposit. We present a novel method of collecting juvenile fragments landing in a well-defined near-vent zone (around 50 m from the source). The method uses four plastic sheets (tarpaulins or tarps) deployed below the SW crater rim of Stromboli volcano (Aeolian Islands, Italy). Due to the vicinity of the collection site to the vent, the fragments were still hot when they landed and created a map of melt holes on the sheets. This map was processed to calculate cumulative fragment size distributions (FSD) and grain size distributions (GSD). The cumulative FSD (number based) and GSD (mass-based) are best described by unique power laws with fractal dimensions of 1.40 and 2.03, respectively, testifying to the fractal nature of fragmentation. The fractal dimension is consistent with low energy fragmentation of a brittle material. This method represents a new way of measuring fragmentation dynamics and classifying volcanic eruptions according to their fragmentation energy.

Magma fragmentation and particle size distributions in low intensity mafic explosions: the July/August 2015 Piton de la Fournaise eruption

Understanding magma fragmentation mechanisms in explosive eruptions is a key requirement for volcanic hazard assessment, eruption management and risk mitigation. This paper focuses on a type case small explosivity eruption (July–August 2015 eruption of Piton de la Fournaise). These eruptions, despite being often overlooked, are exceedingly frequent on local-to-global scales and constitute a significant hazard in vent-proximal areas, which are often populated by guides, tourists and, indeed, volcanologists due to their accessibility. The explosions presented here are ideal cases for the study of the dynamics of magma fragmentation and how it relates to the size distribution of scoria generated at the vent. We documented these events visually and thermally, and characterised the products through sample-return. This allowed us to describe small-scale gas bursts sending ejecta up to 30 m during intermittent lava fountains. Surface tension instabilities and inertial forces played a major role in fragmentation processes and generated particles with coarse-skewed distributions and median diameters ranging from − 8 to − 10 ϕ. However, with time distributions of particles in the most energetic fountains shifted towards more symmetrical shapes as median grains sizes became finer. Analyses of sequences of images demonstrate that the evolution of particle size distributions with time is due to instability of magma droplets and (in-flight) fragmentation.

Abstract 781: Methylation-based liquid biopsy of meningioma primary and recurrent samples

Abstract Meningiomas are mostly benign CNS tumors however, a subset of these tumors may become atypical or malignant. The standard of care to monitor patients after diagnosis requires serial MRI assessments, which have limited value in distinguishing malignant tumors from benign disease. Therefore the discovery of non-invasive methodologies that reflect meningioma tumor burden and its dynamic evolution in real-time is highly desirable. Liquid biopsy (LB) could be used to fine-tune surveillance and treatment with minimal risk to patients. Evidence of circulating tumor cells and cell-free (cf) tumor DNA in the blood has been shown in several tumor types however, limited progress has been made for brain tumors with known biomarkers; possibly due to the unlikelihood of capturing point mutations in circulating DNA fragments. On the other hand, DNA methylation signatures are maintained even in small DNA fragments, which suggests that DNA methylation is an attractive biomarker to be studied in liquid biopsy of brain cancers. In order to identify DNA methylation-based biomarkers using archival serum and tissue specimens, we generated and analyzed the epigenome (Illumina Human EPIC array) of patients with meningioma (including primary (n=6); recurrent (n=8)) and non-meningioma (including non-tumor patients (n=5), pituitary tumor (n=13), colorectal cancer (n=2) and other CNS diseases (n=6), such as inflammatory tissue and radiation necrosis). cfDNA fragment size distribution revealed peaks with 150~200bp on average. By randomly selecting 70% of our cohort as a discovery set, we identified 500 CpGs (FDR<0.05) differentially methylated between meningiomas and non-meningiomas, which show a DNA methylation profile similar to the matched meningioma tissue. Then, we trained a random-forest machine learning using the same signature and applied the model to the remaining 30% samples (validation set) from our cohort. The model was able to correctly classify samples into meningioma and non-meningiomas with a sensitivity of 100% and specificity of 100%. From this pilot data, we were able to investigate the LB methylome of meningioma patients and identify potential markers to detect tumor cells in the serum of these patients, which could eventually allow clinicians to monitor impending disease progression and recurrence. Citation Format: Thais S. Sabedot, Tathiane M. Malta, Ruicong She, James Snyder, Tobias Walbert, Ian Lee, Steven Kalkanis, James Ewing, AnaValeria Castro, Houtan Noushmehr. Methylation-based liquid biopsy of meningioma primary and recurrent samples [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 781.

Abstract 3670: Development of cfDNA-based methylation assay for early cancer detections

Abstract Introduction: DNA methylation is the essential epigenetic mechanism of cell regulation, and one of the earliest signatures in cancer development. Blood-based DNA methylation has been tested for cancer early detection. Several methods have been used for DNA methylation sequencing, which include whole genome bisulfite sequencing (WGBS) and antibody-dependent DNA immunoprecipitation (MeDIP). However, WGBS has known issues of DNA loss and fragmentations, and MeDIP only captures the methylated DNA regions and are biased. Therefore, methods that can accurately quantify DNA methylation status while keeping DNA less damaged and loss are highly needed, especially for liquid biopsy at early cancer stages (due to its low cfDNA amount). Methods: We developed a probe capture-based cfDNA methylation assay using proprietary in-house developed liquid biopsy NGS platform and DeepSEA software algorithm. Analytic assay validation has been conducted using reference materials with known methylation profiles. Both cell line gDNA with known methylation profiles and plasma cfDNA from patients were used for this methylation study. Methylation profiles, DNA damages, and losses were evaluated and compared. Fragment distribution and copy number variations (CNV) were compared between untreated and treated samples. Results: In this study, we developed a cfDNA-based methylation assay that measures DNA methylation status and genomic profiling simultaneously. Using both cell line gDNA and plasma cfDNA, the assay detects both methylation change and genomic alterations, including fragment size distribution and CNV in a single test. Discussion: The successful development of cfDNA methylation assay could help identify cancer at its early stage. It also enables the detection and monitoring of minimal residual disease (MRD) and in obtaining information on therapeutic targets and resistance mechanisms relevant to the management of personalized cancer care. Citation Format: Binggang Xiang, Zhixin Zhao, Maya Stevens, Chao Dai, Feng Xie, Xiaohong Wang, Kemin Zhou, Shidong Jia, Pan Du, Jianjun Yu. Development of cfDNA-based methylation assay for early cancer detections [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3670.

Analysis of Fragmentation of Rock Blocks from Real-Scale Tests

Real-scale fragmentation tests provide high quality data in order to study the fragmentation pattern of rock blocks. In the tests carried out, the initial rock mass, in terms of both volume and shape, was reconstructed by means of 3D photogrammetry. The fragments size distribution of the bocks tested was measured by hand using a tape. The drop tests were performed in four different sites, releasing a total of 124 blocks and measuring 2907 fragments. The obtained fragment size distributions may be well fitted using power laws. The survival rate (Sr), which is the proportion of remaining block shows a wide range of values. Observing the fragment distribution, two parameters are needed to characterize the fragmentation: the number of fragments produced and Sr. The intensity of the fragmentation is expressed by the exponent of the fitted power laws. Although the results are highly variable and show a stochastic behavior of the fragmentation, we have identified different patterns that reflect some local test conditions.