Verification of the model for calculating conjugated heat and moisture transfer when moistening porous material

This paper presents a mathematical model used to calculate conjugated heat and moisture transfer in porous building materials. The initial region of the sorption isotherm for a given material was reconstructed based on the experimental data on moisture transfer in aerated concrete. The calculation results are compared with the experimental data on porous material moistening under different heat and moisture conditions. The calculations performed confirmed that model works well for sorption moistening, and not quite well with capillary impregnation. This does not exclude the possibility of engineering calculations using this model; however, at over-hygroscopic region their accuracy is not quite high.

Detection of the initial region of the current transformer core saturation

In the first part of the paper the detailed analysis of the existing current transformer (CT) saturation detection methods with their classification is presented. A new saturation detection method has been proposed in second part of the paper. Mathematical description of the method is given. In the next section of the paper a CT model with test scheme is presented. To identify the reliability of proposed method against nose and remanent flux density experiments have been produced in the fourth section. Comparative analysis between proposed and existing methods is also given. Finally, in conclusion a detailed description of the method is given regarding its behavior with respect to remanent flux and noise

Site-Specific Ventricular Tachycardia Inducibility

Introduction Programmed electrical stimulation is an essential part of VT ablation procedures but VT is not always inducible, usually for reasons that are not clear. We sought to review pacing site-specific failure of programmed electrical stimulation (PES) to induce scar-related ventricular tachycardia (VT). Methods A series of patients in whom aggressive programmed stimulation from traditional RV pacing sites failed to induce VT, but VT was easily inducible from a non-traditional site are reviewed. Computer simulations in a simple 2-dimensional model of reentry were performed. Results Six patients who had no inducible sustained VT from the RV apex/outflow tract with at least 3 extrastimuli, but relatively easily induced VT from the LV, basal RV, epicardium, or atrium are described. In 5 of these patients, the site that induced VT was closer to the likely reentry circuit region based on mapping and ablation. Computer simulations illustrated that the spatial relation between the pacing site and the entrance and exits of a reentry isthmus can determine the ease of initiation of reentry by determining the time available for recovery of excitability at the initial region of block. Conclusions The site of PES has a marked effect on inducibility of VT in some patients such that PES from the RV apex and outflow regions will fail to expose clinically relevant VTs. The frequency with which this occurs is not certain. Stimulation from alternative sites is a reasonable consideration in selected patients.

A proposed wavy shield for suppression of supersonic jet noise utilizing reflections

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

On Computing Losses in Blading Sections of Liquid Rocket Engine Pressurisation Stations

Designing more sophisticated contemporary liquid rocket engines requires a precise understanding of the hydrodynamics in the blading sections of the pressurisation station, which is most often a turbopump. Friction loss in blade passages and outlets forms a significant proportion of all losses. The paper shows that it is necessary to account for the initial region of hydrodynamically unbalanced flow in the boundary layer, which is most characteristic of relatively short passages in blading sections of liquid rocket engine turbopumps. We performed the analysis required to select friction drag laws for components of pressurisation station blading sections. We considered and proposed a method for numerically integrating a system of equations to determine the variation in characteristic thickness of a spatial boundary layer and friction loss, accounting for the inertial component of the flow core velocity, depending on which flow modes occur in the components of pressurisation station blading sections in a liquid rocket engine. We show that it is necessary to correctly select the friction laws and to take the initial region into account so as to precisely determine the power parameters

Bacterial quorum sensing applied to the coordination of autonomous robot swarms

This paper proposes a strategy for the coordination of a swarm of robots in an unknown environment. The basic idea is to achieve the autonomous movement of the group from an initial region to a target region avoiding obstacles. We use a behavior model similar to bacterial Quorum Sensing (QS) as a technique for the coordination of robots. This behavior has been described as a key element in the interaction between bacteria, and we use it as a basic tool for local interaction, both between the robot and between the robot and the environment. The movement of the swarm of robots, or multi-agent robotic system, is shown as an emerging behavior resulting from the interaction of agents (in the context of artificial intelligence) from basic rules of behavior. The proposed strategy was successfully evaluated by simulation on a set of robots.

Multiphase Scouting Control of an Agricultural Field Robot With Reachability Analyses

Accurate path scouting control of an autonomous agricultural robot is substantially influenced by terrain variability, field patterns, and uncertainties in sensed information. Based on conventional farming techniques, the targeted test crop of strawberries grows in semi-structured environments. Thus in this study, the proposed scouting control architecture comprises of three distinct portions and in each portion different sensors are used. Based on range finder (RF) information, the first region uses a proportional-integral-derivative (PID) controller with logic steps to account for undesirable pop-up events. In the other two portions, vision-based robust controllers are developed, in which a new bound is derived for the focal length uncertainty in vision. Stabilities of the controllers are proven and the reachabilities are analyzed to guarantee that the final state of each portion is within a desired initial region of the next portion controller. The proposed multiphase scouting control is successfully validated for our custom-designed robot in a commercial strawberry farm.