Turbulence characteristics of the B\"{o}dewadt layer in a large enclosed rotor-stator system

A three-dimensional (3D) direct numerical simulation is combined with a laboratory study to describe the turbulent flow in an enclosed annular rotor-stator cavity characterized by a large aspect ratio G=(b-a)/h=18.32 and a small radius ratio a/b=0.152, where a and b are the inner and outer radii of the rotating disk and h is the interdisk spacing. The rotation rate Omega under consideration is equivalent to the rotational Reynolds number Re=Omegab2/nu=9.5 x 104, where nu is the kinematic viscosity of the fluid. This corresponds to a value at which an experiment carried out at the laboratory has shown that the stator boundary layer is turbulent, whereas the rotor boundary layer is still laminar. Comparisons of the 3D computed solution with velocity measurements have given good agreement for the mean and turbulent fields. The results enhance evidence of weak turbulence at this Reynolds number, by comparing the turbulence properties with available data in the literature. An approximately self-similar boundary layer behavior is observed along the stator side. The reduction of the structural parameter a1 under the typical value 0.15 and the variation in the wall-normal direction of the different characteristic angles show that this boundary layer is three-dimensional. A quadrant analysis of conditionally averaged velocities is performed to identify the contributions of different events (ejections and sweeps) on the Reynolds shear stress producing vortical structures. The asymmetries observed in the conditionally averaged quadrant analysis are dominated by Reynolds stress-producing events in this B\"{o}dewadt layer. Moreover, case 1 vortices (with a positive wall induced velocity) are found to be the major source of generation of special strong events, in agreement with the conclusions of Lygren and Andersson.Comment: 16 page

Imaging the stick-slip peeling of an adhesive tape under a constant load

Using a high speed camera, we study the peeling dynamics of an adhesive tape under a constant load with a special focus on the so-called stick-slip regime of the peeling. It is the first time that the very fast motion of the peeling point is imaged. The speed of the camera, up to 16000 fps, allows us to observe and quantify the details of the peeling point motion during the stick and slip phases: stick and slip velocities, durations and amplitudes. First, in contrast with previous observations, the stick-slip regime appears to be only transient in the force controlled peeling. Additionally, we discover that the stick and slip phases have similar durations and that at high mean peeling velocity, the slip phase actually lasts longer than the stick phase. Depending on the mean peeling velocity, we also observe that the velocity change between stick and slip phase ranges from a rather sudden to a smooth transition. These new observations can help to discriminate between the various assumptions used in theoretical models for describing the complex peeling of an adhesive tape. The present imaging technique opens the door for an extensive study of the velocity controlled stick-slip peeling of an adhesive tape that will allow to understand the statistical complexity of the stick-slip in a stationary case

Green's function probe of a static granular piling

We present an experiment which aim is to investigate the mechanical properties of a static granular assembly. The piling is an horizontal 3D granular layer confined in a box, we apply a localized extra force at the surface and the spatial distribution of stresses at the bottom is obtained (the mechanical Green's function). For different types of granular media, we observe a linear pressure response which profile shows one peak centered at the vertical of the point of application. The peak's width increases linearly when increasing the depth. This green function seems to be in -at least- qualitative agreement with predictions of elastic theory.Comment: 9 pages, 3 .eps figures, submitted to PR

Imaging features of extraskeletal mesenchymal chondrosarcoma of the hand

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Multiple or metastatic clear cell chondrosarcoma: a case report

We report multiple synchronous clear-cell chondrosarcomas in a 43-year-old patient. The patient had a lesion in the right proximal humerus and in the left femoral condyle. Bone scintigraphy revealed increased uptake in both foci. Pathological analysis confirmed the diagnosis in both locations. In the proximal humerus, wide resection of the tumour was performed with allograft reconstruction of the joint with osteosynthesis. The femoral condyle was treated with curettage, phenolization, and cementation. Over a follow-up of 10 years no recurrence or metastasis was observed

Stresses in silos: Comparison between theoretical models and new experiments

We present precise and reproducible mean pressure measurements at the bottom of a cylindrical granular column. If a constant overload is added, the pressure is linear in overload and nonmonotonic in the column height. The results are {\em quantitatively} consistent with a local, linear relation between stress components, as was recently proposed by some of us. They contradict the simplest classical (Janssen) approximation, and may pose a rather severe test of competing models.Comment: 4 pages, 2 figures, final version to appear in Phys. Rev. Let

Sound and light from fractures in scintillators

Prompted by intriguing events observed in certain particle-physics searches for rare events, we study light and acoustic emission simultaneously in some inorganic scintillators subject to mechanical stress. We observe mechanoluminescence in ${Bi}_4{Ge}_{3}{O}_{12}$, ${CdWO}_{4}$ and ${ZnWO}_{4}$, in various mechanical configurations at room temperature and ambient pressure. We analyze how the light emission is correlated to acoustic emission during fracture. For ${Bi}_4{Ge}_{3}{O}_{12}$, we set a lower bound on the energy of the emitted light, and deduce that the fraction of elastic energy converted to light is at least $3 \times 10^{-5}$

Imprinting the memory into paste and its visualization as crack patterns in drying process

In the drying process of paste, we can imprint into the paste the order how it should be broken in the future. That is, if we vibrate the paste before it is dried, it remembers the direction of the initial external vibration, and the morphology of resultant crack patterns is determined solely by the memory of the direction. The morphological phase diagram of crack patterns and the rheological measurement of the paste show that this memory effect is induced by the plasticity of paste.Comment: 4 pages, 3 figures, submitted to JPS

Inflammation and infiltration: can the radiologist draw a line? MRI versus CT to accurately assess medullary involvement in parosteal osteosarcoma

Cancer causes inflammation as it progresses through healthy tissue. The differentiation of tumoral growth from the surrounding inflammatory change is paramount in planning surgeries seeking to preserve function. This retrospective study aims at illustrating how a careful use of imaging (computed tomography (CT)/magnetic resonance imaging (MRI)) can help to draw the line between infiltration and inflammation. Out of 72 cases of parosteal osteosarcoma in our institution we selected 22 which had pretreatment imaging, and out of those, 14 that had both MRI and CT. Using Fisher’s exact test, we evaluated the performance of each technique on accurately diagnosing medullary tumor infiltration, using histological analysis as a gold standard. All cases (14/14) demonstrated medullary abnormality on MRI, but only 6/14 (42.9%) demonstrated abnormality on CT. The 8/14 cases with MRI abnormality but no CT abnormality (57.1%) showed inflammation with no tumoral cells present on histological analysis. In the cases where the two examinations showed medullary abnormality (6/14) histology demonstrated tumoral infiltration. MRI demonstrated high sensitivity and negative predictive value, but low specificity and low positive predictive value and accuracy (P=1). CT demonstrated high sensitivity, specificity, high positive and negative predictive values and accuracy (P = 0.000333). MRI is highly sensitive for the detection of medullary abnormality but lacks specificity for tumor invasion. Correlation with CT is recommended in all cases of positive MR to add specificity for tumors. The adequate use of the two imaging methods allows to differentiate between inflammatory change and tumoral infiltration in POS, relevant for surgical planning

Random close packing of granular matter

We propose an interpretation of the random close packing of granular materials as a phase transition, and discuss the possibility of experimental verification.Comment: 6 page