Experimental visualization of bubble formation from an orifice in microgravity in the presence of electric fields

 The formation of air bubbles injected into a stagnant, isothermal liquid in microgravity through an orifice was studied. The bubbles grew very large in microgravity. They attained a nearly spherical shape and showed pronounced affinity towards coalescence in the absence of electric fields and other perturbations. Under the influence of electric fields, periodic detachment was observed, with bubble sizes larger than in terrestrial conditions. The bubble shape was elongated. After detachment, the bubbles moved away from the electrode at which they formed without coalescing with other bubbles. Experimental data on bubble shape and size at detachment showed good agreement with models. Received: 26 March 2001 / Accepted: 16 August 2001     

Application of Uniform Asymptotics to the Second Painlevé Transcendent

In this work we propose a new method for investigating connection problems for the class of nonlinear second‐order differential equations known as the Painlevé equations. Such problems can be characterized by the question as to how the asymptotic behaviours of solutions are related as the independent variable is allowed to pass towards infinity along different directions in the complex plane. Connection problems have been previously tackled by a variety of methods. Frequently these are based on the ideas of isomonodromic deformation and the matching of WKB solutions. However, the implementation of these methods often tends to be heuristic in nature and so the task of rigorising the process is complicated. The method we propose here develops uniform approximations to solutions. This removes the need to match solutions, is rigorous, and can lead to the solution of connection problems with minimal computational effort. Our method relies on finding uniform approximations of differ ential equations of the generic form as the complex‐valued parameter . The details of the treatment rely heavily on the locations of the zeros of the function F in this limit. If they are isolated, then a uniform approximation to solutions can be derived in terms of Airy functions of suitable argument. On the other hand, if two of the zeros of F coalesce as , then an approximation can be derived in terms of parabolic cylinder functions. In this paper we discuss both cases, but illustrate our technique in action by applying the parabolic cylinder case to the “classical” connection problem associated with the second Painlevé transcendent. Future papers will show how the technique can be applied with very little change to the other Painlevé equations, and to the wider problem of the asymptotic behavio ur of the general solution to any of these equations. (Accepted May 15, 1997)     

Use of caged fluorescent dyes for the study of turbulent passive scalar mixing

The non-intrusive initialization of a flow field with distinct and spatially segregated scalar components represents a significant experimental difficulty. Here a new technique is described which makes possible the non-intrusive initialization of a spatially binary passive scalar field in a laminar or turbulent flow field. This technique uses photoactivatable (caged) fluorescent dyes dissolved in the flow medium. The scalar field within the flow field is tagged or initialized by uncaging the appropriate regions with an ultraviolet excimer laser. Mixing between the tagged and untagged regions is quantified using standard laser induced fluorescence techniques. The method is currently being used to study mixing in a turbulent pipe flow.     

Evaluation of creep damage behavior of nickel-base directionally solidified superalloys with different crystallographic orientations

A crystallographic creep damage constitutive model is developed for nickel-base directionally solidified superalloys. The rates of material degradation and grain boundary void growth are considered. The governing parameters are determined from the creep test data of single crystals and directionally solidified superalloys with a crystallographic orientation. A finite element program is used to analyze the creep damage behavior of nickel-base directionally solidified superalloys for different crystallographic orientations. The results depend on the number of grains modelled and compare well with the experimental data.     

Characteristics of singular entities of simple cell mappings

The method of cell-to-cell mapping has the potential to be a very effective and general method of global analysis for strongly non-linear systems. However, simple cell mappings being integer mappings, most of the classical methods of analysis based upon continuity and differentiability of the mapping are no longer applicable and, therefore, new notions need be introduced. In [6] the concept of singular multiplets is introduced for the cell functions associated with the cell mappings. In this paper we study the characteristics of these singular entities by examining the mapping properties of the cells in the singular entities and in their neighborhoods. The key tool used in classifying the mapping properties is the limit set of the mapping process of a cell. The work represents a continuing effort to develop the method of cell-to-cell mapping as a tool of global analysis and to provide the method with a sound and appropriate structure.     

Application of a microprocessor for acquisition of load,strain and acoustic-emission data

This paper describes an automatic system for acquisition, logging and analysis of stress, strain and acoustic-emission data. The complete system is a combination of several standard items of equipment and a newly developed intelligent data logger which has the capability to send data directly to a large-scale computer for reduction and plotting. The data logging and all interfacing with peripheral equipment are accomplished using digital electronics. The heart of the system is a four-bit microprocessor and digital cassette-tape unit. The system, which is controlled by instructions from a cathode-ray-tube terminal, has the capability to transmit data from the cassette unit to a large computer via a time-sharing aption. Typical results are presented for acoustic-emission count rate and total-count curves superimposed on stress-strain diagrams for boron/epoxy advanced composites.     

Surface-strain measurements on a hemispherical shell using holographic interferometry

A method is presented for using real-time fringe counting and double-exposure single-hologram interferometry to measure surface strain on pressurized hemispherical shells. An aluminum shell is employed for experimental verification of these techniques. Surface-strain variations caused by a defect in the aluminum wall are detected and measured. Strain-gage arrays are used for comparison of experimental results. Bendix Kansas City Division is a prime contractor to the Atomic Energy Commission.     

Similitude in exploding wires

Conditions for similarity have been derived for phenomena involving an exploding wire, propagation of the resulting shock through a fluid, and inelastic deformation or fracture of a structure. This analysis considers the capacitance, voltage and material properties of the exploding wire, as well as the geometry and material properties of the fluid and structure. Model experiments involving large inelastic deformation of aluminum diaphragms agree well with the theoretical predictions. Comparison of deformations due to chemical explosives and exploding wires has been made in an effort to establish an ‘equivalence’ between chemical and electrical explosions. The purpose of this is to provide a basis for using small-scale experiments with exploding wires to predict the performance of larger systems using chemical explosives. The exploding wire appears to provide a precise loading for small-scale structural-model experiments and explosion-forming experiments.     

Thermohydrodynamic conditions at the peak flux of horizontal heaters in superfluid liquid helium II at zero net mass flow

Measurements of the peak flux (at the onset of film boiling) in He II are used as a diagnostic tool to investigate the non-classical thermohydrodynamics of superfluid liquid helium for horizontal heaters at zero net mass flow. Data for the single horizontal cylinder in a large pool of He II are approximately accounted for by a power law describing the dimensionless nonclassical superfluid transport number as a function of the fourth root of the dimensionless thermo-mechanical driving potential. Results for transport in narrow vertical cylinders (with insulated walls and lower end closed) are approximately described on the basis of the Gorter-Mellink transport equations. The saturation hypothesis is used which postulates local onset of boiling when vapor-liquid equilibrium is reached at the heater.     

Human subjects, third parties, and informed consent: a brief historical perspective of developments in the United States

The protection of human subjects in biomedical research has become a source of increasing concern over the past century. During the early days of human experimentation, the human subject was rarely if ever consulted about his or her participation in research because scientists and physicians acted in the traditional paternalistic role with respect to their subjects and patients. However, as options for both researchers and their subjects increased, more attention was focused on the rights and obligations of participants on both sides of the research relationship. Investigators became more aware of the costs and benefits associated with their research programs, and subjects became more curious about the nature of research and what could be reasonably expected from their participation. This paper reviews the evolution of the doctrine of informed consent in biomedical research and the development of rules and guidelines for the conduct of research in the United States, for the benefit of both researchers and their human subjects.