Blood-flow models of the circle of Willis from magnetic resonance data

Detailed knowledge of the cerebral hemodynamics is important for a variety of clinical applications. Cerebral perfusion depends not only on the status of the diseased vessels but also on the patency of collateral pathways provided by the circle of Willis. Due to the large anatomical and physiologic variability among individuals, realistic patient-specific models can provide new insights into the cerebral hemodynamics. This paper presents an image-based methodology for constructing patient-specific models of the cerebral circulation. This methodology combines anatomical and physiologic imaging techniques with computer simulation technology. The methodology is illustrated with a finite element model constructed from magnetic resonance image data of a normal volunteer. Several of the remaining challenging problems are identified. This work represents a starting point in the development of realistic models that can be applied to the study of cerebrovascular diseases and their treatment.     

Zinc use efficiency of maize-wheat cropping after inoculation with Azospirillum brasilense

Nutrient Cycling in Agroecosystems - Sustainable zinc (Zn) management strategies are needed to improve cereal yield production, particularly under tropical savannah conditions. Inoculation with...     

A Statistical Sampler for a New On-Line Analog Test Method

This work shows a new strategy to the on-line test of analog circuits. The technique presents a very low analog overhead and it is completely digital. In the System-on-Chip (SoC) environment the on-line test can be developed by using processing power already available in the system. As all the signal processing is done in the digital domain, it allows use of a purely digital tester or a digital BIST technique. The main principle of operation is based on the observation of statistical properties of the circuit under test. Since it has low analog power and performance overhead, the proposed technique can be used to analyze the output of several stages of complex analog systems without the use of switches or analog multiplexors for reconfiguration, and no additional AD converter is needed. This paper presents the fundamentals of the proposed test method and some experimental results illustrating the operation of the Statistical Sampler concerning linear analog systems.     

k–ε Turbulence Modeling of Density Currents Developing Two Dimensionally on a Slope

Dense underflows developing two dimensionally on a slope are simulated numerically. The k–ε model is used for the turbulence closure. The boundary-layer approximation renders the governing equations in the form of parabolic partial differential equations, which are easier to solve numerically than elliptic equations. Evolution of vertical structures of dense underflows is computed along the streamwise direction. Excellent similarity collapses of the computed vertical structures are obtained. The computed profiles of velocity and concentration are compared with measured data, resulting in good agreement. The impact of a parameter representing the stratification level in the k–ε model is investigated. Appropriate values of this parameter, yielding results that are nearly identical to the integral model, are proposed. Water entrainment coefficients are estimated from computed solutions, and are observed to fall within the range of previous measurements. Finally, by using the collapsed vertical structures, profile constants defined in the integral model are calculated, which assures that the top-hat assumption necessary for deriving the integral model is valid.     

Technical potential for developing natural gas use in the Brazilian red ceramic industry

The red ceramic industry in Brazil, consisting of over 7000 companies, requires large amounts of thermal energy, currently being met mainly by native fuelwood, which causes serious deforestation and soil erosion problems. The use of firewood does not allow achieving good energy performance in industrial ceramic kilns, causing high energy losses, low productivity and low quality products (bricks and roof tiles). Thus, to implement higher added value products, besides mitigate environmental problems caused by deforestation, the use of natural gas by the sector seems to be a promising alternative. Brazil’s natural gas market has grown at a fast pace in recent years. Its share in the country’s primary energy consumption increased from 3.7% to 9.3% between 1998 and 2007, compared to almost 21% in the world. The development of the Brazilian natural gas industry was grounded on stepping up supplies through integration with Bolivia from where natural gas is imported, together with fiscal incentives for promoting the demand. This paper estimates that the natural gas market that could be developed in the Brazilian red ceramic industry corresponds to less than 5% of the total industrial natural gas consumption, meaning that a major technological transformation of the country’s red ceramic industry will not severely affect the natural gas market equilibrium, contributing to reduce the country’s high rates of deforestation.     

Control of Unsteady Solidification Via Optimized Magnetic Fields

This article presents a numerical procedure for automatically controlling desired features of a melt undergoing solidification by applying an external magnetic field whose time-varying intensity and spatial distribution are obtained by the use of a hybrid optimization algorithm. The intensities of the magnets along the boundaries of the container were discretized by using B-splines. The inverse problem is then formulated to find the magnetic boundary conditions (the coefficients of the B-splines) in such a way that the gradients of temperature along the gravity direction are minimized at each instant as the solidification front advances through a moving melt. For this task, a hybrid optimization code was used that automatically switches among the following six optimization modules; the Davidon-Fletcher-Powell (DFP) gradient method, a genetic algorithm (GA), the Nelder-Mead (NM) simplex method, quasi-Newton algorithm of Pshenichny-Danilin (LM), differential evolution (DE), and sequential quadratic programming (SQP). Transient Navier-Stokes and Maxwell's equations were discretized by using a finite volume method in a generalized curvilinear nonorthogonal coordinate system. For the phase change problems, an enthalpy formulation was used. The computer code was validated against analytical and numerical benchmark results with very good agreements in both cases.     

SnO2 nanoparticles functionalized in amorphous silica and glass

Two different routes to obtain SnO₂ nanoparticles, undoped and doped with rare earth metals (Eu or Pr), are described herein. The first route was based on the polymeric precursor method that led to the obtainment of SnO₂ nanoparticles dispersed in amorphous silica. The second route was simply the impregnation with SnCl₄ aqueous solution of SiO₂–CaO glass microparticles functionalized with hydroxyl (^?OH) groups. The materials were characterized by N₂ physisorption, XRD, EDS and TEM analyses. We also present the results of catalytic experiments involving the nanocrystalline composites in ethanol steam reforming. The catalytic properties of the undoped composites with SnO₂ supported on SiO₂–CaO glass differ from their doped analogues, however, they were both selective towards ethylene formation, in contrast to the doped composite obtained by the polymeric precursor method.     

A compliant end-effector coupling for vertical assembly: design and evaluation

Many manipulation tasks require compliance, i.e. the robot's ability to comply with the environment and accomplish force as well as position control. Examples are constrained motion tasks and tasks associated with touch or feel in fine assembly. Few compliance-related tasks have been automated, and usually by active means of active compliance control: the need for passive compliance offered by the manipulator itself has been recognized and has led to the development of compliant end-effectors and/or wrists. In this paper we present a novel passively compliant coupling, the compliant end-effector coupling (CEEC), which aids automated precision assembly. It serves as a mechanical interface between the end of the robot arm and the end-effector. The coupling has 6 degrees of freedom. The design of the coupling is based on a “lock and free” assembly idea. The coupling is locked and behaves like a stiff member during robot motion, and is free (compliant) during constrained motion. It features an air bearing, a variable stiffness air spring and a center-locking mechanism. The end-effector assembly, being centrally unlocked, will float within the designed compliance limits assisted by the air bearing. These frictionless and constraint-free conditions facilitate a fast correction of any initial lateral and angular misalignments. In a peg insertion assembly, such accommodation is possible provided that the tip of the peg is contained within the chamfer of the hole. A variable stiffness air spring was incorporated in the design to allow variable and passive vertical compliance. This vertical compliance allows the accommodation of angular and vertical errors. The center-locking mechanism will return the end-effector assembly to its initial position upon an error correction. In a robot application program, the CEEC can be locked during rapid motion to securely transport a part or be set free during assembly or disassembly processes when the motions are constrained.