Local Radial Research Articles

The Role of “Vortical” Hot Towers in the Formation of Tropical Cyclone Diana (1984)

A high-resolution (3-km horizontal grid spacing) near-cloud-resolving numerical simulation of the formation of Hurricane Diana (1984) is used to examine the contribution of deep convective processes to tropical cyclone formation. This study is focused on the 3-km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle. The numerical simulation reveals the presence of vortical hot towers, or cores of deep cumulonimbus convection possessing strong vertical vorticity, that arise from buoyancy-induced stretching of local absolute vertical vorticity in a vorticity-rich prehurricane environment. At near-cloud-resolving scales, these vortical hot towers are the preferred mode of convection. They are demonstrated to be the most important influence to the formation of the tropical storm via a two-stage evolutionary process: (i) preconditioning of the local environment via diabatic production of multiple small-scale lower-tropospheric cyclonic potential vorticity (PV) anomalies, and (ii) multiple mergers and axisymmetrization of these low-level PV anomalies. The local warm-core formation and tangential momentum spinup are shown to be dominated by the organizational process of the diabatically generated PV anomalies; the former process being accomplished by the strong vertical vorticity in the hot tower cores, which effectively traps the latent heat from moist convection. In addition to the organizational process of the PV anomalies, the cyclogenesis is enhanced by the aggregate diabatic heating associated with the vortical hot towers, which produces a net influx of low-level mean angular momentum throughout the genesis. Simpler models are examined to elucidate the underlying dynamics of tropical cyclogenesis in this case study. Using the Sawyer–Eliassen balanced vortex model to diagnose the macroscale evolution, the cyclogenesis of Diana is demonstrated to proceed in approximate gradient and hydrostatic balance at many instances, where local radial and vertical accelerations are small. Using a shallow water primitive equation model, a characteristic “moist” (diabatic) vortex merger in the cloud-resolving numerical simulation is captured in a large part by the barotropic model. Since a moist merger results in a stronger vortex and occurs twice as fast as a dry merger, it is inferred (consistent with related work) that a net low-level convergence can accelerate and intensify the merger process in the real atmosphere. Although the findings reported herein are based on a sole case study and thus cannot yet be generalized, it is believed the results are sufficiently interesting to warrant further idealized simulations of this nature.

Effects of Velocity Distribution of Dialysate on Mass Transfer in the Shell Side of a Hollow-Fiber Dialyzer

The relation between mass transfer and flow characteristics in the shell side of a hollow-fiber dialyzer has not been investigated sufficiently because of the tangled flow path. In this paper, the effects of velocity distribution of dialysate on mass transfer in the shell side were investigated experimentally. In order to measure the velocity at various radial and axial positions of a dialyzer, cut dialyzers of various lengths were used. The velocity distributions over the section of the cut dialyzers were measured by means of the electro-chemical method. In addition, the concentration distribution at the cross section of the outlet of lumens of the hollow-fibers was measured when the deionized water and aqueous solution of potassium chloride were fed into a dialyzer countercurrently. Potassium chloride was taken up as a model of low molecular weight species in blood. The velocity was not constant over cross sections of the shell side and the concentration was distributed over the cross section of the outlet of the lumens of the hollow-fibers. These results showed that the mass transfer coefficient in the shell side was varied over the dialyzer. It was considered that the mass transfer coefficient at the local radial position should be discussed in order to make the transport process in the shell side clear. The correlation between the Sherwood number and the Reynolds number based on the velocity and the mass transfer coefficient at local radial positions of the shell side was made. The result of the correlation suggested that the transport process in the center region of the shell side was similar to that in a laminar circular pipe flow.

Perioperative Hearing Impairment

Perioperative Hearing Impairment

Conceptual design of the real-time control system of MHD modes in RFX

Real-time control is a key issue in the upgrade of the magnetic boundary of the reverse field experiment (RFX) machine, a toroidal experiment in nuclear fusion research. The upgrade aims at providing RFX with effective instruments for the active plasma control. A new active system has been designed consisting of 48 (toroidal)/spl times/4 (poloidal) saddle coils arranged to cover the toroidal shell surface, a set of insulated gap bipolar transistors (IGBT)-based fast power supply units to feed the coils, an extensive number of magnetic probes to measure the local radial and toroidal field inside the vacuum vessel. By properly driving the currents in the saddle coils, the system can control the radial magnetic field outside the vacuum vessel (active shell), can generate magnetic rotating perturbations to drag the Magneto-hydro dynamic (MHD) modes, and can affect the plasma equilibrium and shape. The paper describes briefly the hardware arrangement of the new shell, focusing on the control operational scenarios. The requirements of the digital systems implementing the control are derived and presented, with particular reference to the required system reaction times and the envisaged data flow. Possible system architectures suitable for the implementation are discussed with emphasis on real-time communication and system distribution.

Nonlinear Identification and Adaptive Control of Combustion Engines

Advanced engine control systems require accurate models of the thermodynamic-mechanical process, which are substantially nonlinear and often time-variant. After briefly introducing the identification of nonlinear processes with grid-based look-up tables and a special local linear Radial Basis Function network (LOLIMOT), a comparison is made with regard to computation effort, storage requirements and convergence speed. A new training algorithm for online adaptation of look-up tables is introduced which reduces the convergence time considerably. Application examples and experimental results are shown for a multidimensional nonlinear model of NOx emissions of a Diesel engine, and for the adaptive feedforward control of the ignition angle of a SI engine.

ERS transform for the automated detection of bronchial abnormalities on CT of the lungs.

The identification of bronchi on Computed Tomography (CT) images of the lungs provides valuable clinical information in patients with suspected airways diseases including bronchiectasis, emphysema, or constrictive obliterative bronchiolitis. The automated recognition of the airways is, therefore, an important part of a diagnosis aid system for resolving potential ambiguities associated with intensity-based feature extractors. On CT images, near-perpendicular cross sections of bronchi normally appear as elliptical rings and this paper presents a novel technique for their recognition. The proposed method, the edge-radius-symmetry (ERS) transform, is based on the analysis of the distribution of edges in local polar coordinates. Pixels are ranked according to local edge (E) strength, radial (R), uniformity and local symmetry (S). A discrete implementation of the technique is provided which reduces the computational cost of the ERS transform by using a geometric approximation of the intensity patterns. The identification of the adjacent pulmonary vessels with template matching then allows for the automated measurement of bronchial dilatation and bronchial wall thickening. Computationally, the method compares favorably with other methods such as the Hough transform. Noise-sensitivity of the technique was evaluated on a set of synthetic images and nine patients under investigation for suspected airways disease. Agreement for the automated scoring of the presence and severity of bronchial abnormalities was demonstrated to be comparable to that of an experienced radiologist (kappa statistics kappa > 0.5 ).

Quantum Chemical Formulation of High-TC Superconductivity

A detailed understanding of superconductivity in the cuprates is formulated. A cluster model is defined and evaluated by means of the regularized complete active space self-consistent field method. Signatures of local pair-breaking excitations in a low-dispersive oxygen metal band, attenuated by the nearby buffer ions, and nonadiabatically spin-coupled to a disjoint antiferromagnetic band are quantified and proposed to be consistent with the spin−flip signature of high-TC superconductivity in YBa2Cu3O6+x. Critical properties of the scenario are (i) hole-clustering instabilities producing local angular (D-wave) and radial (S-wave) Cooper instabilities and (ii) nonadiabaticity between local hole cluster states and antiferromagnetism. The cuprates are said to belong to a class of superconductors for which the macroscopic ground state is accessed by means of phase coherent hole cluster resonances. This understanding is illustrated by a real-space BCS-like deduction of the superconducting gap. A microscopic understanding of the order parameter symmetry emerges.

Transition of Chaotic Flow in a Radially Heated Taylor-Couette System

Numerical simulations have been performed to study the stability of heated, incompressible Taylor-Couette flow for a radius ratio of 0.7 and a Prandtl number of 0.7. As Gr is increased, the Taylor cell that has the same direction of circulation as the natural convection current increases in size and the counterrotating cell becomes smaller. The flow remains axisymmetric and the average heat transfer decreases with the increase in Gr. When the cylinder is impulsively heated, the counterrotating cell vanishes and n = 1 spiral is formed for Gr = 1000. This transition marks an increase in the heat transfer due to an increase in the radial velocity component of the fluid. By slowly varying the Grashof number, the simulations demonstrate the existence of a hysteresis loop. Two different stable states with same heat transfer are found to exist at the same Grashof number. A time-delay analysis of the radial velocity and the local heat transfer coefficient time is performed to determine the dimension at two Grashof numbers. For a fixed Reynolds number of 100, the two-dimensional projection of the reconstructed attractor shows a limit cycle for Gr = −1700. The limit cycle behavior disappears at Gr = −2100, and the reconstructed attractor becomes irregular. The attractor dimension increases to about 3.2 from a value of 1 for the limit cycle case; similar values were determined for both the local heat transfer and the local radial velocity, indicating that the dynamics of the temperature variations can be inferred from that of the velocity variations.

A Modified Commercial Triaxial Testing System for Small Strain Measurements: Preliminary Results on Pisa Clay

Abstract A computer-controlled hydraulic triaxial cell was modified with the aim of obtaining (1) a better measuring accuracy of soil stiffness at small strains, (2) a reliable automatic procedure for K0 consolidation, and (3) a minimum disturbance during system saturation and specimen consolidation. To obtain the above objectives, many modifications were introduced. The cell structure and loading piston were modified and many transducers were introduced, including the LDTs for local radial and axial strain measurement. Finally, control software was developed to achieve the following testing procedures: (1) dry setting, (2) system saturation by flushing with stress control to avoid any swelling and back pressurization, and (3) K0 consolidation with control of nil radial strain by means of local measurement. The paper will benefit those interested in upgrading an existing hydraulic triaxial system in-house in an economical manner.

East-west inclination of large-scale photospheric magnetic fields

Sixteen years of WSO magnetogram data have been studied to determine the solar cycle variation and latitude dependence of the east-west inclination of photospheric magnetic field lines. East-west inclination is here defined as the angle between a field line and its local radial vector, as projected onto the plane of the latitude and line of sight. Inclination is determined by a least-squares fit of observed magnetic fields to a simple projection model, and is found to depend on polarity and to change with the solar cycle. Leading and following polarities are tipped towards each by about 9° and have an overall net tilt in the direction of rotation (to the west) of 0.6°. New cycles are seen to begin at high latitudes and to grow through the lower latitudes over approximately 5 years, providing evidence for an extended cycle length of 16–18 years.

Chaotic Behavior of Rotor/Stator Systems With Rubs

This paper outlines the dynamic behavior of externally excited rotor/stator systems with occasional, partial rubbing conditions. The observed phenomena have one major source of a strong nonlinearity: transition from no contact to contact state between mechanical elements, one of which is rotating, resulting in variable stiffness and damping, impacting, and intermittent involvement of friction. A new model for such a transition (impact) is developed. In case of the contact between rotating and stationary elements, it correlates the local radial and tangential (“super ball”) effects with global behavior of the system. The results of numerical simulations of a simple rotor/stator system based on that model are presented in the form of bifurcation diagrams, rotor lateral vibration time-base waves, and orbits. The vibrational behavior of the system considered is characterized by orderly harmonic and subharmonic responses, as well as by chaotic vibrations. A new result is obtained in case of heavy rub of an anisotropically supported rotor. The system exhibits an additional subharmonic regime of vibration due to the stiffness asymmetry. The correspondence between numerical simulation of that effect and previously obtained experimental data supports the adequacy of the new model of impact.

Particle velocity distributions and ionization processes in a gas-puff Z pinch.

We have measured the time-dependent radial velocity distributions of singly to five times ionized ions in an imploding plasma shell by observing the spectral shapes and intensities of emission lines in various directions. An ionization wave propagating much faster than the local radial ion velocities is observed. The ionization front velocity is found to be consistent with estimates of electron heat conduction into the plasma-neutral layer. The ionization and velocity histories of the particles are experimentally determined. The mechanisms of momentum transfer to the particles are also determined and compared with existing models.

The Use of Hall Effect Semiconductors in Geotechnical Instrumentation

Abstract For the past five years or so Hall effect semiconductors have been increasingly used in the geotechnical engineering laboratories at the University of Surrey. They have been incorporated as sensing elements in local radial and axial strain measuring devices, for the small-strain instrumentation of triaxial specimens, and in small diameter boundary normal and shear stress cells. Triaxial internal load cells are currently being built incorporating Hall effect semiconductors. This paper describes the Hall effect principle and the methods of configuring magnet/sensor systems to achieve suitable measuring systems. Some geotechnical instruments built at the University of Surrey are detailed, and their characteristics discussed. The calibrations of the instruments described in the paper show a performance generally at least as good as might be expected from some commercially available instruments. Hall effect semiconductors are shown to be of use in a range of situations where displacement can form the basis of measurement. The displacements measured can vary from as little as 5 µm to as much as 10 mm, and the best repeatability so far obtained has been of the order of 1/100 of a micrometre.

Theoretical Estimation of the Response of Helically Armored Cables to Tension, Torsion, and Bending

This paper concerns the mechanical behavior of ACSR (aluminum conductor steel-reinforced) conductors under static-loading conditions, which may comprise any combination of tension, torsion, and bending. The model described is quite general and can be applied to other types of helically armored cables. A stiffness matrix is developed and relations are given for axial, torsional, and flexural rigidities and for coupling parameters. For small curvatures, the flexural rigidity is comparable to the upper limit accepted in current practice by ACSR users. As the curvature increases, however, frictional forces develop between the outer layers and sliding of wires may occur, with the result that the flexural rigidity decreases. The tension level also influences the flexural rigidity of the conductor. Actually the model does not consider the flexural rigidity of the system as a fixed entity but as directly influenced by local compressive forces and internal radial and tensile forces. The analysis can also apply to situations where a given number of initial constituent wires have failed and the load is transferred to neighboring wires, leaving the conductor unbalanced; it will be seen how internal arrangements manage to accommodate the local perturbation.

Stress intensity factors for cracks at loaded holes-effect of load distribution

Stress intensity factors are evaluated for a radial crack at the edge of a circular hole subjected to a localized radial or tangential force on its perimeter. These factors can be used as Green's functions to determine the stress intensity factor when an arbitrary load distribution acts on the hole perimeter. Both the accuracy and ease-of-use of this Green's function technique are demonstrated by comparing some test cases with known results. The strong dependence of the stress intensity factor for short cracks upon the detailed load distribution on the perimeter of the hole is discussed, and the importance of fricitional forces is demonstrated in the determination of fatigue lifetimes in the presence of fretting

An axially symmetric explosion model in magnetogasdynamics: II

A method using Eulerian coordinate system is developed under a local radiality assumption to study a point explosion in a spheroid with axially symmetric exponential density distribution, including the effect of azimuthal magnetic field.

Radial and axial die pressures during solid phase compaction of polymeric powders

As part of a research programme to investigate the feasibility of producing components by the solid phase compaction of polymeric powders, measurements have been made of the local radial and axial pressures in a specially instrumented die. During single end die compaction, the highest axial pressures occur close to the die wall at the upper (moving punch) and on the centre line of the compact at the lower punch. The radial pressure distribution may be linear or non-linear depending on the compaction conditions and the maximum radial pressure occurs below the top surface of the compacts. The structural variations of the compacts, as determined by microhardness measurements, were found to be consistent with pressures recorded along the die wall and compaction punches.

Computer Controlled Beam Local Radial Perturbation and Rotation in CERN PS

Computer Controlled Beam Local Radial Perturbation and Rotation in CERN PS

A point explosion in a cold exponential atmosphere. Part 2. Radiating flow

The problem considered is that of a strong shock propagating from a point energy source into a cold exponential atmosphere with radiative heat transfer in the flow behind the shock. The radiation mean free path is taken to be small compared to the shock radius, so that the shock may be treated as discontinuous and the radiative heat flux represented by the Rosseland diffusion approximation. The solution obtained is an approximate one based upon the ‘local radiality’ assumption and integral method previously utilized by Laumbach & Probstein for the case of adiabatic flow. The ‘thin shock’ concepts, which underlie the integral method, are extended to the present case of a radiating flow enabling an approximate integral of the differential energy equation to be obtained. A radiation parameter is developed, which provides an index as to when the effects of radiation may be neglected and the flow taken to be adiabatic. The physical interpretation of this parameter is that of the ratio of a characteristic radiation energy flux to a characteristic kinetic energy flux. When the value of this parameter is less than about 0·1, radiation effects may be neglected. It is shown that, when the radiation mean free path varies as a power of the temperature (Tn), where , the infinity of solutions for various polar angles can be transformed into two distinct solutions thereby essentially eliminating the parametric dependence on the polar angle and the atmospheric scale height. For fixed values of the radiation parameter the dependence on the explosion energy and the atmospheric density at the point of explosion is also eliminated. The results presented are for the mean free path–temperature variation indicated, but the technique of solution does not have this restriction, though for other temperature dependences some of the scaling advantages are sacrificed. The solution demonstrates the existence of an independence principle in which the flow becomes isothermal and independent of the detailed radiation mechanism when the radiation parameter becomes large. The limiting results of the present analysis for a uniform density atmosphere correspond quite, well with the exact solutions of Elliott & Korobeinikov. The radiating far field behaviour of the descending shock is shown to approach that for adiabatic flow, and, consequently, the asymptotic adiabatic solution obtained by Raizer is an appropriate limit to the present solution. However, the asymptotic results for the ascending shock show that the radiating flow does not approach an adiabatic one but rather an isothermal one.

Theory of Non-Symmetrical Bending State for Cylindrical Shell : Stresses in a Cylindrical Shell with a Local Radial Load

In this paper the fundamental equations for bending states of cylindrical shells are derived in the terms of stress function and radial displacement component. These equations have the same accuracy as Flugge's equations. We can easily give the solutions of these equations especially for a stress boundary value problem. Stresses in a cylindrical vessel with a local radial load were calculated as a specific application. We obtained a good agreement with the results calculated by P.P. Bijlaard.