Characteristics of Velocity and Excess Density Profiles of Saline Underflows and Turbidity Currents Flowing over a Mobile Bed

Turbidity currents in the ocean and lakes are driven by suspended sediment. The vertical profiles of velocity and excess density are shaped by the interaction between the current and the bed as well as between the current and the ambient water above. We present results of a set of 74 experiments that focus on the characteristics of velocity and fractional excess density profiles of saline density and turbidity currents flowing over a mobile bed. The gravity flows include saline density flows, hybrid saline/turbidity currents and a pure turbidity current. The use of dissolved salt is a surrogate for suspended mud that is so fine that it does not settle out readily. Thus, all the currents can be considered to be model turbidity currents. The data cover both Froude-subcritical and Froude-supercritical regimes. Depending on flow conditions, the bed remains flat or bed forms develop over time, which in turn affect vertical profiles. For plane bed experiments, subcritical flow profiles have velocity peaks located higher up in the flow, and display a sharper interface at the top of the current, than their supercritical counterparts. The latter have excess density profiles that decline exponentially upward from the bed, whereas subcritical flows show profiles with a region near the bed where excess density varies little. Wherever bed forms are present, they have a significant effect on the profiles. Especially for Froude-supercritical flow, bed forms push the location of peak velocity upward, and render the near-bed fractional excess density more uniform. In the case of subcritical flow, bed forms do not significantly affect fractional excess density profiles; velocity profiles are pushed farther upward from the bed than in the case of a plane bed, but to a lesser extent than for supercritical bed forms. Overall, the relative position of the velocity peak above the bed shows a dependence upon flow regime, being lowered for increasing Froude number Fd. Gradient Richardson numbers Rig in the near-bed region increase with increasing Fd, but are lower than the critical value of 0.25, indicating that near-bed turbulent structures are not notably suppressed. At the top interface, values of Rig are above the critical value for subcritical and mildly supercritical Fd, effectively damping turbulence. However as Fd increases, Rig goes below the critical value. Shape factors calculated from the profiles for use in the depth-averaged equation of motion are evaluated for different flow and bed conditions. Normalized experimental profiles for supercritical currents scale up well with observations of field-scale turbidity currents in the Monterey Canyon, and the range of average bed slopes and Froude numbers also compare favorably with estimated field-scale flow conditions for the Amazon canyon and fan. This suggests that the experimental results can be used to interpret the kinds of flows that are responsible for the shaping of major submarine canyon-fan systems.     

Vascular compression of the duodenum related to a plaster cast (the cast syndrome)

During the last ten years 218 dacryocystorhinostomies were done, 8 of them on under 10-years-old children (3.7%). Dacryocystorhinostomy remains the only curative intervention which may be done on children even when the lacrimal ways sounding is inefficient. The surgical technique was the same as the one used for the adults, with some characteristic features imposed by the age of the patient. The intervention was some especially on children with congenital imperforations of the lacrimo-nasal channel, when the repermeability of the lacrimal ways could not be obtained by repeated soundings, but also in traumatic and congenital malformed dacryocystitis. The operation was made with good results even after the extirpation of the lacrimal sac, followed by the formation of a neosac. In the observations we presented the underlimit of the intervention has been 2 years and 4 months.     

Clear lens extraction to correct high myopia

PURPOSE: To assess the refractive outcome and postoperative complications in a single surgeon series of clear lens extraction for high myopia. SETTING: Ophthalmology Department, Cornea and Refractive Surgery Unit, Vall d'Hebrón Hospital, Autónoma University of Barcelona, Spain. METHODS: Forty-six clear lens extraction procedures performed in 37 patients from November 1992 to January 1994 by one surgeon were retrospectively analyzed. Capsule tear and vitreous loss, endothelial cell loss, preoperative and postoperative best corrected visual acuity and cycloplegic refraction, and retinal detachment occurrence were looked at. RESULTS: Capsule tear with vitreous loss occurred in one eye (2.17%). Mean endothelial cell loss was 2.6% during the first postoperative year. Best corrected visual acuity was 6/12 or better in 69.4% of eyes preoperatively and in 88.5% postoperatively. Mean cycloplegic refraction was -16.05 diopters (D) preoperatively; the residual cycloplegic refraction was within 1.00 D in 48.4% of eyes and within 2.00 D in 92.5% postoperatively. CONCLUSION: Because of its high predictability, stability, and low morbidity, we believe clear lens extraction is a reasonable refractive surgery option for middle-aged patients with myopia.     

Kinetic study of austenite formation during continuous heating of unalloyed ductile iron

The austenite formation kinetics in unalloyed cast ductile iron was studied on the basis of dilatometry measurements, and Avrami’s equation was used to estimate the material’s kinetic parameters. A con...     

Toward Aerial Grasping and Manipulation with Multiple UAVs

In this paper, a multiple UAVs control scheme is developed considering the full nonlinear position/orientation model of a j-Quadrotor system. A novel second order sliding mode controller is presented which guarantees exponential and robust tracking of admissible time-varying pose. The harmful chattering is not involved and no dynamic model is required to implement the controller to yield fast and precise tracking. Additionally, well-posed terminal and controlled time convergence allows an enforced contact at given pre-defined stable contact points at the same time. A stiffness control is proposed for grasping objects considering virtual linkages approach. Our approach yields high performance from the control system, in contrast to other simple controllers proposed for load carrying. In this sense, our advanced nonlinear control solves the apparent limitations imposed by the available technology from the viewpoint of the precise tracking control, and control of the inherent unstable underactuated dynamics, for frictionless contact points (neither rolling nor sliding are considered). A numerical simulation study, under various conditions, shows the numerical feasibility of the proposed approach.     

Air-coupled linear and sparse cMUT array manufactured using MUMPs process

An assessment of the standard fabrication Micro-Electro-Mechanical Systems (MEMS) process Multi-User MEMS Processes (MUMPs) for complex air-coupled capacitive Micromachined Ultrasonic Transducer array aperture manufacture is reported. A 1-D linear array and a 2-D sparse symmetric binned-array have been designed and manufactured, and then characterised experimentally using electrical impedance measurements, laser vibrometry and air-coupled field measurement; the experimental data are supported by simulated data using Finite Element technique and field simulation based on Huygens’ principle. A methodology for the manufacture of the array structures using the MUMPs process is described. Electrical characterisation shows the devices operation at 770 kHz and the existence of large parasitic capacitances and electrical losses. Mechanical crosstalk of array substrate has been measured at −40 dB using laser vibrometry. Moreover, the laser vibrometry measurement and the field characteristics of one element reveal that each element operates as a piston radiator.

     

Mechanism of fracture of NiTi superelastic endodontic rotary instruments

The aim is to investigate the premature catastrophic fracture produced for different periods during clinical endodontic treatment of two brands of NiTi endodontic rotary instruments. 3 samples as-received, 6 samples used with patients for 2 and 7?h and 5 samples fractured were studied for each brand of endodontic NiTi rotary instruments. Transformation temperatures (M_s, M_f, A_s and A_f) and enthalpies of transformation were determined by calorimetry. Critical stresses until fracture (σ^β→SIM, σ^SIM→β) were obtained using an electromechanical testing machine. The samples were also visualized by Scanning Electron Microscopy. Calorimetric studies have shown an increase of the M_s and A_s transformation temperatures with time of use as well as a decrease of their stress transformations. Moreover, reverse transformation enthalpies decreased along the time. The enthalpies of transformation decreased because martensitic plates were anchored, which prevented their transformation to austenite; thus losing its superelastic effect. The stabilisation of the martensitic plates induced the collapse of the structure and so the main cause for the fracture. The heat treatment proposed has been increased the life in service of NiTi superelastic endodontic instruments recovering theirs superelastic effect.     

Control Algorithm for Taking off and Landing Manoeuvres of Quadrotors in Open Navigation Environments

International Journal of Control, Automation and Systems - This paper presents a control algorithm for the taking off and landing manoeuvres of a quadrotor aircraft in open navigation environments....     

Stabilization of the inverted spherical pendulum via Lyapunov approach

In this paper a nonlinear controller is presented for the stabilization of the spherical inverted pendulum system. The control strategy is based on the Lyapunov approach in conjunction with LaSalle's invariance principle. The proposed controller is able to bring the pendulum to the unstable upright equilibrium point with the position of the movable base at the origin. The obtained closed‐loop system has a very large domain of attraction, that can be as large as desired, for any initial position of the pendulum which lies above the horizontal plane. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society