Fragmentation of a Circular Disc by Impact on a Frictionless Plate

The break-up of a two-dimensional circular disc by normal and oblique impact on a hard frictionless plate is investigated by molecular dynamics simulations. The disc is composed of numerous unbreakable randomly shaped convex polygons connected together by simple elastic beams that break when bent or stretched beyond a certain limit. It is found that for both normal and oblique impacts the crack patterns are the same and depend solely on the normal component of the impact velocity. Analysing the pattern of breakage, amount of damage, fragment masses and velocities, we show the existence of a critical velocity which separates two regimes of the impact process: below the critical point only a damage cone is formed at the impact site (damage), cleaving of the particle occurs at the critical point, while above the critical velocity the disc breaks into several pieces (fragmentation). In the limit of very high impact velocities the disc suffers complete disintegration (shattering) into many small fragments. In agreement with experimental results, fragment masses are found to follow the Gates-Gaudin-Schuhmann distribution (power law) with an exponent independent of the velocity and angle of impact. The velocity distribution of fragments exhibit an interesting anomalous scaling behavior when changing the impact velocity and the size of the disc.Comment: submitted to J. Phys: Condensed Matter special issue on Granular Medi

A quadtree-polygon-based scaled boundary finite element method for image-based mesoscale fracture modelling in concrete

A quadtree-polygon scaled boundary finite element-based approach for image-based modelling of concrete fracture at the mesoscale is developed. Digital images representing the two-phase mesostructure of concrete, which comprises of coarse aggregates and mortar are either generated using a take-and-place algorithm with a user-defined aggregate volume ratio or obtained from X-ray computed tomography as an input. The digital images are automatically discretised for analysis by applying a balanced quadtree decomposition in combination with a smoothing operation. The scaled boundary finite element method is applied to model the constituents in the concrete mesostructure. A quadtree formulation within the framework of the scaled boundary finite element method is advantageous in that the displacement compatibility between the cells are automatically preserved even in the presence of hanging nodes. Moreover, the geometric flexibility of the scaled boundary finite element method facilitates the use of arbitrary sided polygons, allowing better representation of the aggregate boundaries. The computational burden is significantly reduced as there are only finite number of cell types in a balanced quadtree mesh. The cells in the mesh are connected to each other using cohesive interface elements with appropriate softening laws to model the fracture of the mesostructure. Parametric studies are carried out on concrete specimens subjected to uniaxial tension to investigate the effects of various parameters e.g. aggregate size distribution, porosity and aggregate volume ratio on the fracture of concrete at the meso-scale. Mesoscale fracture of concrete specimens obtained from X-ray computed tomography scans are carried out to demonstrate its feasibility

Fragmentation processes in impact of spheres

We study the brittle fragmentation of spheres by using a three-dimensional Discrete Element Model. Large scale computer simulations are performed with a model that consists of agglomerates of many particles, interconnected by beam-truss elements. We focus on the detailed development of the fragmentation process and study several fragmentation mechanisms. The evolution of meridional cracks is studied in detail. These cracks are found to initiate in the inside of the specimen with quasi-periodic angular distribution. The fragments that are formed when these cracks penetrate the specimen surface give a broad peak in the fragment mass distribution for large fragments that can be fitted by a two-parameter Weibull distribution. This mechanism can only be observed in 3D models or experiments. The results prove to be independent of the degree of disorder in the model. Our results significantly improve the understanding of the fragmentation process for impact fracture since besides reproducing the experimental observations of fragment shapes, impact energy dependence and mass distribution, we also have full access to the failure conditions and evolution

The E3-Ubiquitin Ligase TRIM50 Interacts with HDAC6 and p62, and Promotes the Sequestration and Clearance of Ubiquitinated Proteins into the Aggresome.

In this study we report that, in response to proteasome inhibition, the E3-Ubiquitin ligase TRIM50 localizes to and promotes the recruitment and aggregation of polyubiquitinated proteins to the aggresome. Using Hdac6-deficient mouse embryo fibroblasts (MEF) we show that this localization is mediated by the histone deacetylase 6, HDAC6. Whereas Trim50-deficient MEFs allow pinpointing that the TRIM50 ubiquitin-ligase regulates the clearance of polyubiquitinated proteins localized to the aggresome. Finally we demonstrate that TRIM50 colocalizes, interacts with and increases the level of p62, a multifunctional adaptor protein implicated in various cellular processes including the autophagy clearance of polyubiquitinated protein aggregates. We speculate that when the proteasome activity is impaired, TRIM50 fails to drive its substrates to the proteasome-mediated degradation, and promotes their storage in the aggresome for successive clearance

Gastrointestinal stromal tumors (GISTs): Our experience in the management of 26 patients

19506 Background: GISTs represents 0.1–3% of gastrointestinal neoplasms; most cases occur in people 40 to 80 years old, and are more common in men than in women. More than half of all GISTs patients present with locally advanced, recurrent, or metastatic disease (mainly to liver or peritoneum). Methods: From January 2001 to December 2005 we observed in our Institution 26 pts with GISTs; all were CD117+.The main characteristics of these pts were as follows: median age: 61 yr; sex (F/M): 14/12; primary tumor site: stomach 13 (50 %), small intestine 7 (27 %), rectum 1 (4 %), retroperitoneum 4 (15 %), liver 1 (4 %); first symptoms: epigastric pain 10 (38 %); abdominal pain 4 (15 %); hematemesis 1 (3 %); anemia 5 (18,5 %), palpable abdominal mass 1 (3 %), defecation disorders 2 (7 %); melena 3 (11 %); rectal bleeding 1 (3 %); ascites 1 (3 %). Results: Radical surgical resection was performed in 21 patients (81 %), 2 patients received a debulking surgery, and no postoperative mortality or major complications were observed; 3 pts showed an advanced disease. Seven pts (33%) developed recurrence, local or at distance, and the median time to relapse was 7,5 months (range 2–11). One pt with advanced disease dead before any treatment and 11 pts received Imatinib (I), at the standard dose (400 mg/d), starting from the date of diagnosis of advanced disease or metastatic relapse and given until development of intolerance or progressive disease. Main toxicities of I included: neutropenia G3 (4%), skin rash (4%), periorbital oedema (4%). We achieved 3 PR (lasting 12+, 21+ and 40 mos), 6 SD and 2 PD. With a median follow-up of 30 months, all but three pts (dead for progressive diseases) are alive. The overall survival rate was 88.5 % and the median overall survival was 16 mos (range 1–49). Conclusions: Surgical resection remains the only effective treatment for GISTs. However, in pts with advanced or relapsed disease treatment with I is effective with an high disease control rate. No significant financial relationships to disclose. </jats:p

Male breast cancer: Our experience

10733 Background: Male breast is an uncommon disease, accounting for &lt;1% of all malingnancies in the man. In contrast to women with breast cancer, men with breast cancer are older and have more advanced disease. Methods: Data regarding 25 male patients who underwent surgery for breast cancer in the our Istitution between January 1994 and December 2005 were analyzed. The main characteristics of these patients included: median age 64 years (range 32–87); positivity family cancer history: specific 4 pts, non-specific 3, no circumstance 18; risk factors: obesity 6 pts, gynaecomastia 4, diabetes 5, liver transplant 1. Five cases of second neoplasia were observed: 2 patient with prostate cancer, 1 synchronous colon carcinoma, 1 head and neck cancer, 1 pancreatic cancer. Results: All but one pts (with syncrhronous metastases at presentation) underwent mastectomy. Pathological characteristics included: pT1 tumors 3 pts (12%); pT2 7 pts (28%), pT3 2 (8%), pT4 13 (52 %); infiltrating ductal carcinomas in 88% of cases; axillary lymph node involvement in 12 (50%); 22 patients had estrogen- and progesterone-receptor positive tumors, 2 pts negative, 1 pts unknown. After surgery 14 pts received RT, 13 pts hormonotherapy and 16 patients adjuvant chemotherapy (7 CMF, 9 anthracyclin-based therapy). Median disease free survival was 41.5 months (range 5–116).With a median follow-up of 66 months, we observed 12 deaths (10 pts for progressive disease) and the overall survival rate was 52% (13 pts; 11 disease-free). According to the family cancer history we observed 5/7 (71%) and 7/18 (39%) deaths in positive and negative cases, respectively. Conclusions: The approach to male breast cancer patients is similar to that for female patients. Our data confirm the suspected epidemiologic risk factors such as prostate cancer, gynecomastia and dietary factors; furthermore, cases with family cancer history seems to have a worse prognosis. No significant financial relationships to disclose. </jats:p

Experience of 170 cases of ductal carcinoma in ‘ (DCIS)

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