Scale-dependent maximum reinforcement percentage in reinforced concrete beams

The Cohesive/Overlapping Crack Model is able to describe the transition between cracking and crushing failures occurring in reinforced concrete beams by increasing beam depth and/or steel percentage. Within this Nonlinear Fracture Mechanics model, the tensile and compressive ultimate behaviors of the concrete matrix are modeled through two different process zones that advance independently one of another. Moreover, this model is able to investigate local mechanical instabilities occurring in the structural behavior of reinforced concrete structures: tensile snap-back and snap-through, which are due to concrete cracking or steel fracture, and the compressive snap-back occurring at the end of the plastic plateau, which is generated by the unstable growth of the crushing zone. In this context, the application of the Cohesive/Overlapping Crack Model highlights that the ductility, which is represented by the plastic rotation capacity of a reinforced concrete element subjected to bending, decreases as reinforcement percentage and/or beam depth increase. Thus, a scale-dependent maximum reinforcement percentage beyond which concrete crushing occurs prior to steel yielding is demonstrated to exist. In particular, the maximum steel percentage results to be inversely proportional to h0.25, h being the beam depth. In this way, a rational and quantitative definition of over-reinforcement is provided as a steel percentage depending on the beam depth

Body composition in clinical practice

Nutritional status is the results of nutrients intake, absorption and utilization, able to influence physiological and pathological conditions. Nutritional status can be measured for individuals with different techniques, such as CT Body Composition, quantitative Magnetic Resonance Imaging, Ultrasound, Dual-Energy X-Ray Absorptiometry and Bioimpendance. Because obesity is becoming a worldwide epidemic, there is an increasing interest in the study of body composition to monitor conditions and delay in development of obesity-related diseases. The emergence of these evidence demonstrates the need of standard assessment of nutritional status based on body weight changes, playing an important role in several clinical setting, such as in quantitative measurement of tissues and their fluctuations in body composition, in survival rate, in pathologic condition and illnesses. Since body mass index has been shown to be an imprecise measurement of fat-free and fat mass, body cell mass and fluids, providing no information if weight changes, consequently there is the need to find a better way to evaluate body composition, in order to assess fat-free and fat mass with weight gain and loss, and during ageing. Monitoring body composition can be very useful for nutritional and medical interventional. This review is focused on the use of Body Composition in Clinical Practice

Fast interceptor of a dynamic object

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 99-100).This thesis presents a path planning and control strategy that enables an unmanned non-holonomic vehicle to intercept a fast moving object. The path planning is performed under model uncertainty, with respect to the vehicle's maneuverability, as well as uncertainty in the estimation of the object's future trajectory and position. This problem involves the tracking of the dynamic object in a cluttered environment and the accurate estimation of its future position in the presence of noisy measurements. The ground vehicle (interceptor) is required to intercept the dynamic object at a predicted (catch) location in a finite amount of time. This time restriction presents quite a challenge given the inherent limitation in the vehicle's steering and maneuverability. The solution strategy is divided into three sub-problems: 1) prediction, 2) path planning and 3) control. The prediction of the parameters that describe the dynamic's object in space is accomplished via Kalman Filtering which, in conjunction with an impact predictor, provide the waypoints needed to construct a reference path that will place the interceptor on a collision course with the dynamic object (target.) A pure pursuit algorithm was used to steer the interceptor along a reference trajectory, which was designed to make the vehicle engage the dynamic object on a near tail-on aspect. In the endgame, the pure pursuit algorithm was modified to ensure arrival to the catch point while a position controller was added to ensure timely arrival to the predicted catch location. The problem statement was then augmented to include obstacle avoidance.(cont.) The dynamic object was required to navigate around fixed obstacles in order to catch the dynamic object. Results will show that the proposed strategy performed very well in the absence of obstacles and was well suited to handle the maneuverability constraints of the non-holonomic vehicle. Results also will show that, with minor modifications to the path planner, the interceptor successfully managed to avoid obstacles and catch the dynamic object although at a slightly lower success rate. The proposed solution was first demonstrated in simulation and then tested using MIT's RAVEN testbed.by Sergio A. Cafarelli.S.M

Community rotorcraft air transportation benefits and opportunities

Information about rotorcraft that will assist community planners in assessing and planning for the use of rotorcraft transportation in their communities is provided. Information useful to helicopter researchers, manufacturers, and operators concerning helicopter opportunities and benefits is also given. Three primary topics are discussed: the current status and future projections of rotorcraft technology, and the comparison of that technology with other transportation vehicles; the community benefits of promising rotorcraft transportation opportunities; and the integration and interfacing considerations between rotorcraft and other transportation vehicles. Helicopter applications in a number of business and public service fields are examined in various geographical settings

Incompressible flow in porous media with fractional diffusion

In this paper we study the heat transfer with a general fractional diffusion term of an incompressible fluid in a porous medium governed by Darcy's law. We show formation of singularities with infinite energy and for finite energy we obtain existence and uniqueness results of strong solutions for the sub-critical and critical cases. We prove global existence of weak solutions for different cases. Moreover, we obtain the decay of the solution in $L^p$, for any $p\geq2$, and the asymptotic behavior is shown. Finally, we prove the existence of an attractor in a weak sense and, for the sub-critical dissipative case with $\alpha\in (1,2]$, we obtain the existence of the global attractor for the solutions in the space $H^s$ for any $s > (N/2)+1-\alpha$

Ex-vivo quantitative ultrasound assessment of cartilage degeneration

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Development and validation of low-intensity pulsed ultrasound systems for highly controlled in vitro cell stimulation

This work aims to describe the development and validation of two low-intensity pulsed ultrasound stimulation systems able to control the dose delivered to the biological target. Transducer characterization was performed in terms of pressure field shape and intensity, for a high-frequency range (500 kHz to 5 MHz) and for a low- frequency value (38 kHz). This allowed defining the distance, on the beam axis, at which biological samples should be placed during stimulation and to exactly know the intensity at the target. Carefully designed retaining systems were developed, for hosting biological samples. Sealing tests proved their impermeability to external contaminants. The assembly/de-assembly time of the systems resulted ~3 min. Time-domain acoustic simula- tions allowed to precisely estimate the ultrasound beam within the biological sample chamber, thus enabling the possibility to precisely control the pressure to be transmitted to the biological target, by modulating the trans- ducer’s input voltage. Biological in vitro tests were also carried out, demonstrating the sterility of the system and the absence of toxic and inflammatory effects on growing cells after multiple immersions in water, over seven day

Development and validation of low-intensity pulsed ultrasound systems for highly controlled in vitro cell stimulation

This work aims to describe the development and validation of two low-intensity pulsed ultrasound stimulation systems able to control the dose delivered to the biological target. Transducer characterization was performed in terms of pressure field shape and intensity, for a high-frequency range (500 kHz to 5 MHz) and for a low-frequency value (38 kHz). This allowed defining the distance, on the beam axis, at which biological samples should be placed during stimulation and to exactly know the intensity at the target. Carefully designed retaining systems were developed, for hosting biological samples. Sealing tests proved their impermeability to external contaminants. The assembly/de-assembly time of the systems resulted ~3 min. Time-domain acoustic simulations allowed to precisely estimate the ultrasound beam within the biological sample chamber, thus enabling the possibility to precisely control the pressure to be transmitted to the biological target, by modulating the transducer's input voltage. Biological in vitro tests were also carried out, demonstrating the sterility of the system and the absence of toxic and inflammatory effects on growing cells after multiple immersions in water, over seven days