User-defined Volume Research Articles

Image-guided focused ultrasound-mediated drug delivery andcomparison between 2-D and 3-D therapeutic strategies

The objective of this research was to test a new US image-guided FUS (USgFUS) system for stimulating microvascular permeabilization and enhancing intratumoral drug delivery in volume space. 3-D USgFUS therapy functionality was implemented on a programmable US system with a dual transducer for interleaved imaging and 3-D therapy. 3-D therapy consisted of focal zones distributed over a user-defined volume whereas 2-D treatment had the same focal zones but about a single plane. Using breast cancer-bearing mice (N = 4), US therapy was conducted with a mechanical index of 0.5, pulse repetition frequency of 10 Hz, and duty cycle of 10%. Therapy was performed immediately after a 100 μl bolus injection of microbubbles and IR-780 dye. In-vivo optical imaging was performed at 0, 24, and 48 h. Tumors were then excised for ex-vivo analysis. 3-D USgFUS treatment increased dye extravasation within the tumor space at 24 (245.5%) and 48 h (297.5%) when compared to 2-D US therapy (p = 0.01). Ex vivo optical images revealed a similar trend with 3-D US treatment producing a higher fluorescent signal than the 2-D approach. Preliminary results suggest that 3-D USgFUS-mediated drug delivery is an exciting prospect for treatment of the entire cancer burden.

Laguerre tessellations and polycrystalline microstructures: a fast algorithm for generating grains of given volumes

ABSTRACT We present a fast algorithm for generating Laguerre diagrams with cells of given volumes, which can be used for creating RVEs of polycrystalline materials for computational homogenisation, or for fitting Laguerre diagrams to EBSD or XRD measurements of metals. Given a list of desired cell volumes, we solve a convex optimisation problem to find a Laguerre diagram with cells of these volumes, up to any prescribed tolerance. The algorithm is built on tools from computational geometry and optimal transport theory which, as far as we are aware, have not been applied to microstructure modelling before. We illustrate the speed and accuracy of the algorithm by generating RVEs with user-defined volume distributions with up to 20,000 grains in 3D. We can achieve volume percentage errors of less than 1% in the order of minutes on a standard desktop PC. We also give examples of polydisperse microstructures with bands, clusters and size gradients, and of fitting a Laguerre diagram to 3D EBSD measurements of an IF steel.

Managing User Delay with a Focus on Pedestrian Operations

Across the United States, walking trips are increasing. However, pedestrians still face significantly higher delays than motor vehicles at signalized intersections because of the traditional signal timing practices of prioritizing vehicular movements. This study explored methods to reduce pedestrian delay through the development of a pedestrian priority algorithm that selects an operational plan favorable to pedestrian service, provided a user-defined volume threshold has been met for the major street. This algorithm—along with several operational scenarios—was analyzed with Vissim with the use of software-in-the-loop simulation to determine the impact these strategies have on user delays. One of the operational scenarios examined was that of actuating a portion of the coordinated phase, or actuated–coordinated operation. Following a discussion on platoon dispersion and the application of it in the design of actuated–coordinated signal timing parameters, a sensitivity analysis was performed on vehicle extension timers to explore the impact that this coordinated movement parameter has on user delay. In the scenario analysis, it was shown that employing fully actuated (also known as free) operation—either with the designed algorithm or without—was an effective method of reducing pedestrian delay on the minor street while decreasing average intersection vehicle delay for the volumes used in the simulation. The vehicle extension sensitivity analysis showed that shortening the extension timer of an actuated–coordinated phase can reduce pedestrian delay on the minor street without increasing overall vehicle delay. This tool could be used by agencies during coordinated operation to prioritize pedestrians.

Evaluation of a New 3‐Dimensional Color Doppler Flow Method to Quantify Flow Across the Mitral Valve and in the Left Ventricular Outflow Tract

The aim of this study was to assess the accuracy, feasibility, and reproducibility of determining stroke volume from a novel 3-dimensional (3D) color Doppler flow quantification method for mitral valve (MV) inflow and left ventricular outflow tract (LVOT) outflow at different stroke volumes when compared with the actual flow rate in a pumped porcine cardiac model. Thirteen freshly harvested pig hearts were studied in a water tank. We inserted a latex balloon into each left ventricle from the MV annulus to the LVOT, which were passively pumped at different stroke volumes (30-80 mL) using a calibrated piston pump at increments of 10 mL. Four-dimensional flow volumes were obtained without electrocardiographic gating. The digital imaging data were analyzed offline using prototype software. Two hemispheric flow-sampling planes for color Doppler velocity measurements were placed at the MV annulus and LVOT. The software computed the flow volumes at the MV annulus and LVOT within the user-defined volume and cardiac cycle. This novel 3D Doppler flow quantification method detected incremental increases in MV inflow and LVOT outflow in close agreement with pumped stroke volumes (MV inflow, r = 0.96; LVOT outflow, r = 0.96; P < .01). Bland-Altman analysis demonstrated overestimation of both (MV inflow, 5.42 mL; LVOT outflow, 4.46 mL) with 95% of points within 95% limits of agreement. Interobserver variability values showed good agreement for all stroke volumes at both the MV annulus and LVOT. This study has shown that the 3D color Doppler flow quantification method we used is able to compute stroke volumes accurately at the MV annulus and LVOT in the same cardiac cycle without electrocardiographic gating. This method may be valuable for assessment of cardiac output in clinical studies.

Estimation of the physical properties of nanocomposites by finite-element discretization and Monte Carlo simulation

This paper reviews and enhances numerical models for determining thermal, elastic and electrical properties of carbon nanotube-reinforced polymer composites. For the determination of the effective stress-strain curve and thermal conductivity of the composite material, finite-element analysis (FEA), in conjunction with the embedded fibre method (EFM), is used. Variable nanotube geometry, alignment and waviness are taken into account. First, a random morphology of a user-defined volume fraction of nanotubes is generated, and their properties are incorporated into the polymer matrix using the EFM. Next, incremental and iterative FEA approaches are used for the determination of the nonlinear properties of the nanocomposite. For the determination of the electrical properties, a spanning network identification algorithm is used. First, a realistic nanotube morphology is generated from input parameters defined by the user. The spanning network algorithm then determines the connectivity between nanotubes in a representative volume element. Then, interconnected nanotube networks are converted to equivalent resistor circuits. Finally, Kirchhoff's current law is used in conjunction with FEA to solve for the voltages and currents in the system and thus calculate the effective electrical conductivity of the nanocomposite. The model accounts for electrical transport mechanisms such as electron hopping and simultaneously calculates percolation probability, identifies the backbone and determines the effective conductivity. Monte Carlo analysis of 500 random microstructures is performed to capture the stochastic nature of the fibre generation and to derive statistically reliable results. The models are validated by comparison with various experimental datasets reported in the recent literature.

Fuel-Optimal Maneuvers for Constrained Relative Satellite Orbits

This research investigates strategies to enable a deputy satellite to hover within a defined volume fixed in the vicinity of a chief satellite in a circular orbit for an extended period of time. Previous research developed initial methodologies for maintaining restricted teardrop hover orbits that exist in a plane fixed within the chief's local reference frame. These methods use the natural drift of the deputy satellite in the relative frame and impulsive thrust to keep the deputy in a bounded volume relative to the chief, but do not address fuel optimality. This research extends and enhances that work by finding the optimal trajectories produced with discrete thrusts that minimize fuel spent per unit time and stay within the user-defined volume, thus providing a practical hover capability in the vicinity of the chief. The work assumes that the Clohessy―Wiltshire closeness assumption between the deputy and chief is valid. Using the new methodology developed in this work, feasible closed- and nonclosed-relative orbits are found and evaluated based on a fuel criterion and are compared with an easily calculated continuous-thrust baseline. It is shown that in certain scenarios (generally corresponding to a smaller total time of flight) a discrete-thrust solution provides a lower overall fuel cost than a continuous-thrust solution. A simple check is proposed that enables the mission planner to make the correct strategy choice.

Development of an approximate empirical-CFD model estimating coupled heat and water transfers of stacked food products placed in airflow

This paper reports on the development of an approximate empirical-CFD modelling procedure combining experimental correlations for the heat and mass transfer coefficient determination and specific user-defined functions (UDF) implemented in the commercial CFD code Fluent to simulate the interrelationships at play between airflow and transfers of unwrapped food products bathing in air. Transfer modelling required specific calculation to account for water evaporation from the product surface. Mean transfer coefficients at the air–product interface were determined empirically from validated experimental correlations, where the CFD mean air velocity that is calculated in a small user-defined volume surrounding the product was incorporated. Internal water diffusion was taken into account by considering the product as a motionless fluid composed of dry matter and water. The procedure developed allows, in a single CFD calculation using a single mesh, temperature and water concentration fields to be computed and the water loss kinetics of the products to be determined together with the temperature and relative humidity fields of the air flowing around them. Although the established procedure was set up with the aim of assessing heat and water exchanges occurring in large stacks of unwrapped food products subjected to airflow, this last was validated for modelling, first, one-dimensional drying of a meat cylinder and second, three-dimensional drying of five cylindrical plaster casts placed in a row. Its application to the ripening of a row of six cheeses is also discussed.

Database development and 3D modeling of textural variations in heterogeneous, unconsolidated aquifer media: Application to the Milan plain

The textural and hydrogeologic properties of loose deposits are closely connected to the sedimentary processes occurring in fluvial and glacio-fluvial systems. The proposed procedure combines geologic knowledge, coded well data logs stored in a hydrogeologic georeferenced database, geographic information system (GIS) and 3D calculation software to reconstruct the detailed distribution of the subsoil's hydrogeologic parameters. The calculations may apply to any subsoil part, bounded by one or more surfaces. This methodological approach may be applied to diverse investigation depths, vertical intervals detailed to varying extents, on a local or regional scale. Employing great quantities of well data logs, recorded in different ways and distributed across large areas, has enabled significant spatial sedimentologic reconstruction. Two groups of parameters were considered: textural (percentages of gravel, sand and clay) and hydrogeologic (hydraulic conductivity and porosity). In terms of sedimentology, the method reconstructs spatial heterogeneity both along cross-sections and for an entire user-defined volume to analyze the sediments’ energy functions and their distribution; deposition rates are proportional to process intensity and distribution with time. In terms of hydrogeology, detailed 3D hydrogeologic structural data provide detailed input for hydrogeologic models in groundwater resource management and planning, such as for transport models.