The damping coefficient in welded bodies: Experimental results

Summary Validity of formulae obtained in the theoretical part of the present paper is checked by operating on soldered joints. The specimens were 5 steel rods of rectangular section, soldered in different positions; they were tested in compression and flexion vibrations. Satisfactory results were obtained in both vibrations separately; some discrepancy is shown when comparing the two types of tests.

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Sommario Si cerca una conferma sperimentale per le formule ottenute teoricamente. Le prove sono state effettuate su 5 provini di acciaio saldati a stagno in diverse posizioni; sono stati considerati i casi di vibrazione in compressione e flessione. I risultati ottenuti sono in soddisfacente accordo con le formule per i due tipi di vibrazione separatamente; nel confronto fra essi si nota invece qualche discrepanza.

     

Network Dynamics: Tools and Examples

Some mathematical tools and results are presented which may be used to study the dynamics of agents living on a network as well as the networks themselves as evolving dynamical systems. They include decomposition of differential dynamics, ergodic techniques, estimates of invariant measures, etc. Some examples are discussed as an application of the dynamical tools.     

PopGen: population-based recruitment of patients and controls for the analysis of complex genotype-phenotype relationships

OBJECTIVE: Patient samples used for mapping complex human disease genes are unlikely to be representative of the phenotype spectrum of the respective population as a whole. On the other hand, most ongoing prospective studies are probably too small for evaluating polygenic disease markers. DESIGN: Precise estimates of population-specific genotypic risks can be obtained efficiently through the complete ascertainment of patients in a geographically confined area. The PopGen project uses the most northern part of Germany as a target region for such a pursuit. RESULTS: PopGen currently pursues recruitment, sampling and processing activities in close collaboration with a multitude of clinical partners, covering cardiovascular, neuropsychiatric and environmental diseases. CONCLUSION: PopGen has successfully established itself as a large-scale genetic epidemiological project of international recognition.     

The rotating Bénard problem: new stability results for any Prandtl and Taylor numbers

By using the Lyapunov direct method, we study the nonlinear stability of the Bénard problem with rotation, in the stress-free boundary case. We prove the coincidence between the critical linear stability Rayleigh number and the nonlinear one for any Taylor number and for Prandtl numbers , under a computable restriction on the initial data. Therefore, in the linear case we obtain necessary and sufficient conditions for stab ility of the motionless state. Received April 7, 1997     

Genetics and congenital malformations: interpretations, attitudes and practices in suburban communities and the shamans of ecuador

OBJECTIVES: The purpose of the present article was to evaluate how shamans and the suburban communities of Quito interpret the terminology used in genetics. METHODS: One hundred people living in 5 suburban districts of Quito were surveyed as well as 19 shamans of the Salasaca community. RESULTS: The results show that members of both groups are little informed about genetics. As knowledge about genetics is correlated to educational level, which is very poor in both groups, knowledge and understanding of genetics are either very basic or nonexistent. As for the medical practices in treating genetic alterations, the surveys show that while in very severe cases scientific medicine is sought, in most cases explanations and a cure are given by shamanic medicine. CONCLUSION: There is limited knowledge of genetics and its terminology in the study population. Shamanic and marginal health practices seem to remain prevalent in these communities due to their low costs, the personal attention the individuals receive, and the holistic point of view employed. It is important that the community councils, the medical doctors and the shamans work together to set up community programs on medical education, particularly on genetics.     

Bubble dynamics: a review and some recent results

Several aspects of small-amplitude oscillations of bubbles containing gas, vapor, or a gas-vapor mixture are discussed. An application to pressure-wave propagation in a bubbly liquid is described. Nonlinear forced oscillations are considered in the light of recent research on forced oscillations of nonlinear systems. The growth of vapor bubbles, an extension of the Rayleigh-Plesset equation to non-Newtonian liquids and appreciable mass transfer at the interface, and a boundary integral numerical method for nonspherical cavitation bubble dynamics are also briefly discussed.     

Point vortex dynamics: recent results and open problems

he concept of point vortex motion, a classical model in the theory of two-dimensional, incompressible fluid mechanics, was introduced by Helmholtz in 1858. Exploration of the solutions to these equations has made fitful progress since that time as the point vortex model has been brought to bear on various physical situations: atomic structure, large scale weather patterns, “vortex street” wakes, vortex lattices in superfluids and superconductors, etc. The point vortex equations also provide an interesting example of transition to chaotic behavior. We give a brief historical introduction to these topics and develop two of them in particular to the point of current understanding: (i) Steadily moving configurations of point vortices; and (ii) Collision dynamics of vortex pairs.     

Non-Newtonian pseudoplastic fluids: Analytical results and exact solutions

A one layer model of laminar non-Newtonian fluids (Ostwald-de Waele model) past a semi-infinite flat plate is revisited. The stretching and the suction/injection velocities are assumed to be proportional to x^1/(1−2n) and x⁻¹, respectively, where n is the power-law index which is taken in the interval . It is shown that the boundary-layer equations display both similarity and pseudosimilarity reductions according to a parameter γ, which can be identified as suction/injection velocity. Interestingly, it is found that there is a unique similarity solution, which is given in a closed form, if and only if γ=0 (impermeable surface). For γ≠0 (permeable surface) we obtain a unique pseudosimilarity solution for any 0≠γ≥−((n+1)/3n(1−2n))^n/(n+1). Moreover, we explicitly show that any pseudosimilarity solution exhibits similarity behavior and it is, in fact, similarity solution to a modified boundary-layer problem for an impermeable surface. In addition, the exact similarity solution of the original boundary-layer problem is used, via suitable transverse translations, to construct new explicit solutions describing boundary-layer flows induced by permeable surfaces.     

The effect of aspect ratio in counter-current gas-liquid bubble columns: Experimental results and gas holdup correlations

It is generally admitted that the gas holdup is independent of the column dimensions and gas sparger design if three criteria are satisfied: the diameter of the bubble column is larger than 0.15 m, gas sparger openings are larger than 1–2 mm and the aspect ratio is larger than 5. This paper contributes to the existing discussion; in particular, the effect of the aspect ratio (within the range 1–15) in a counter-current gas-liquid bubble column has been experimentally studied and a new gas holdup correlation to estimate the influence of aspect ratio, operation mode and working fluid on the gas holdup has been proposed. The bubble column, equipped with a spider gas sparger, is 5.3 m in height, has an inner diameter of 0.24 m; gas superficial velocities in the range of 0.004–0.23 m/s have been considered, and, for the runs with water moving counter-currently to the gas phase, the liquid has been recirculated at a superficial velocity of −0.0846 m/s. Filtered air has been used as the gaseous phase in all the experiments, while the liquid phase has included tap water and different aqueous solutions of sodium chloride as electrolyte. Gas holdup measurements have been used to investigate the flow regime transitions and the global bubble column hydrodynamics. The counter-current mode has turned out to increase the gas holdup and destabilize the homogeneous flow regime; the presence of electrolytes has resulted in increasing the gas holdup and stabilizing the homogeneous flow regime; the aspect ratio, up to a critical value, has turned out to decrease the gas holdup and destabilize the homogeneous flow regime. The critical value of the aspect ratio ranged between 5 and 10, depending on the bubble column operation (i.e., batch or counter-current modes) and liquid phase properties. Since no correlation has been found in the literature that can correctly predict the gas holdup under the investigated conditions, a new scheme of gas holdup correlation has been proposed. Starting from considerations concerning the flow regime transition, corrective parameters are included in the gas holdup correlation to account for the effect of the changes introduced by the aspect ratio, operation mode and working fluid. The proposed correlation has been found to predict fairly well the present experimental data as well as previously published gas holdup data.     

Collagen Fiber Network Infiltration: Permeability and Capillary Infiltration

In dentin restoration, collagen fiber network infiltration is an issue. Using data from the literature, we have constructed a relevant numerical geometrical model of the network. The specificity of our model is that the fibers are taken into account implicitly using a regularized Heaviside function. This function is either used to set the viscosity or to localize the contact line where capillary forces are applied. A level set technique with respect to fluid infiltration front tracking in five fiber networks using the level set method and Navier–Stokes equations with capillary terms is used to point out efficient critical infiltration parameters. A variational formulation which can be implemented in a finite elements model is proposed both for the infiltration front and the contact line. Because of lack of knowledge on fiber orientation, different configurations were tested through permeability assessment of the whole network. Fiber orientation, interfibrillar space and contact angle influence were investigated.     

Archery simulation: Error estimation and comparison of numerical and experimental results

The method proposed by the author of this paper together with A.V. Zvyagin to solve the problem of bow shooting is verified. The method is briefly discussed. The effect of step sizes on the accuracy of computation is estimated. The numerical results are compared with experimental data.     

CFB cyclones at high temperature: Operational results and design assessment

Pressure drop and cut size measurements are reported for a full scale cyclone operating within a 58 MWth CFB-combustor unit at 775℃.The paper reviews the vast number of equations to calculate the pressure drop and separation efficiency of cyclones, generally for operation at ambient temperature and at low Cs[0.5]. None of the literature correlations predicts the pressure drop with a fair accuracy within the range of experimental operating conditions. The cut size d50 can be estimated using direct empirical methods or using the Stokes number, Stk50. Both methods were used to compare measured and predicted values of d50. With the exception of Muschelknautz and Krambrock, none of the equations made accurate predictions.Finally, an alternative method to determine the friction factor of the pressure drop equation (Euler number, Eu) and of the cut size is proposed. The Eu number is determined from the geometry of common cyclones, and the derived value of Stk50 defines more accurate cut sizes. The remaining discrepancy of less than 5%, when compared with the measured values, is tentatively explained in terms of a reduced cyclone diameter due to the solids layer formed near its wall. Further measurements, mostly using positron emission particle tracking, elucidate the particle motion in the cyclone and both tracking results and the influence of the particle movement on Eu and Stk50 will be discussed in a follow-up paper.     

Constant-temperature anemometry in hypersonic flow: critical issues and Sample results

The critical issues are examined in the application of constant-temperature hot-wire anemometry to hypersonic boundary layers. While continuous turbulence measurements are more challenging to make in hypersonic flows, it is shown here that the difficulties can be overcome for a wide range of flow conditions. An extensive review of the literature reveals that many of the heat transfer complexities associated with hypersonic anemometry have already been resolved. Frequency-response tests, calibration results and boundary-layer measurements in hypersonic flow are also presented. A hot-wire frequency response of about 500 kHz was obtained in a Mach 11 flow, and the resulting boundary-layer spectra are smooth and repeatable.The work of the first author was supported by NASA-Langley Grant NAG-1-1400, under the supervision of Dr. Stephen K. Robinson. The assistance of Mr. Mark Sheplak in acquiring some of the data presented in §3 is gratefully acknowledged.     

CFB cyclones at high temperature: Operational results and design assessment

Pressure drop and cut size measurements are reported for a full scale cyclone operating within a 58 MWth CFB-combustor unit at 775 ℃.
The paper reviews the vast number of equations to calculate the pressure drop and separation efficiency of cyclones, generally for operation at ambient temperature and at low Cs [〈0.5]. None of the literature correlations predicts the pressure drop with a fair accuracy within the range of experimental operating conditions. The cut size d50 can be estimated using direct empirical methods or using the Stokes number, Stk50. Both methods were used to compare measured and predicted values of d50. With the exception of Muschelknautz and Krambrock, none of the equations made accurate predictions.
Finally, an alternative method to determine the friction factor of the pressure drop equation （Euler number, Eu） and of the cut size is proposed. The Eu number is determined from the geometry of common cyclones, and the derived value of Stk50 defines more accurate cut sizes. The remaining discrepancy of less than 5%, when compared with the measured values, is tentatively explained in terms of a reduced cyclone diameter due to the solids layer formed near its wall. Further measurements, mostly using positron emission particle tracking, elucidate the particle motion in the cyclone and both tracking results and the influence of the particle movement on Eu and Stk50 will be discussed in a follow-up paper.     

Extreme wave solutions: Parametric studies and wavelet analysis

Wave fields for near homoclinic, single mode rogue-wave solutions of the periodic nonlinear Schrödinger equation are presented. Parameters of candidate solutions are estimated and refined through an eigenvalue solution procedure. An overview of the estimation and refining procedure used by the authors is provided. Solutions are scaled to facilitate experimental implementation. The continuous wavelet transform is used to carry out time–frequency analyses and the results obtained are demonstrative of the dispersion relation as well as the time varying side band energy transfer associated with the Benjamin–Feir instability. The analysis framework and approach used are validated with the Peregrine solution. Other extreme wave solutions are analyzed as well. The framework presented here could serve as a basis for experimental investigations into single mode rogue waves as well as other localizations in wave fields.