scholarly journals Waves and Oscillations in the Non-Magnetic Photosphere

1990 ◽  
Vol 138 ◽  
pp. 217-228 ◽  
Author(s):  
Franz - Ludwig Deubner
Keyword(s):  
Direct Observation ◽  
Outer Boundary ◽  
Dynamical Behaviour ◽  
Solar Photosphere ◽  
Complex Patterns

The solar photosphere is the outer boundary of the cavity which defines the spectrum of the global p-modes. It is also the lowest layer that permits direct observation of the boiling mixture of motions which eventually create the complex patterns apparent in the chromosphere and corona. Studies of the dynamical behaviour of this layer are therefore of paramount importance for an overall understanding of the dynamic sun.

scholarly journals Swimming in shear

2014 ◽  
Vol 744 ◽  
pp. 1-4 ◽  
Author(s):  
David Saintillan
Keyword(s):  
Pattern Formation ◽  
Shear Flow ◽  
Thermal Convection ◽  
Degrees Of Freedom ◽  
Theoretical Models ◽  
Dynamical Behaviour ◽  
Strong Similarity ◽  
Complex Patterns ◽  
Rayleigh Benard

AbstractThe complex patterns observed in experiments on suspensions of swimming cells undergoing bioconvection have fascinated biologists, physicists and mathematicians alike for over a century. Theoretical models developed over the last few decades have shown a strong similarity with Rayleigh–Bénard thermal convection, albeit with a richer dynamical behaviour due to the orientational degrees of freedom of the cells. In a recent paper, Hwang & Pedley (J. Fluid Mech., vol. 738, 2014, pp. 522–562) revisit previous models for bioconvection to investigate the effects of an external shear flow on pattern formation. In addition to casting light on new mechanisms for instability, their study demonstrates a subtle interplay between shear, swimming motions and bioconvection patterns.

scholarly journals Stability in the most external region of the Oort Cloud: evolution of the ejected comets

2019 ◽  
Vol 490 (2) ◽  
pp. 2495-2506
Author(s):  
J A Correa-Otto ◽  
M F Calandra
Keyword(s):  
Binary Stars ◽  
Outer Boundary ◽  
Oort Cloud ◽  
Dynamical Behaviour ◽  
Dynamical Structure ◽  
Wide Binary ◽  
External Region ◽  
Test Particles ◽  
The Galaxy ◽  
Galactic Tide

ABSTRACTIn this paper, we present a study of the dynamical effects of the Galaxy on the external region of the Oort Cloud. The aims of this paper are: (i) to determine an outer limit for the Oort Cloud; and (ii) to analyse the dynamical behaviour of the most external objects of the Oort Cloud and how they are ejected from the Solar system. To achieve these aims, we follow the temporal evolution of massless test particles in the Galactic environment of the solar neighbourhood. We show that the effect of the perturbations from the Galactic tide in the particles is similar to that found for the evolution of the population of wide binary stars. Moreover, in the Oort Cloud, we find a dynamical structure around 105 au conformed by objects unbound from the Sun. This structure allows us to define a transition region of stability and an outer boundary for the Oort Cloud, and it is also in agreement with previous results about the disruption of wide binary stars.

Direct Observation of Heat Exchanger Deposits by Cross Sectioning

1967 ◽  
Vol 25 ◽  
pp. 364-365
Author(s):  
R. W. Anderson ◽  
D. L. Senecal
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Heat Exchanger ◽  
Direct Observation ◽  
Cross Sections ◽  
Preparation Method ◽  
Specimen Preparation ◽  
Flowing Water ◽  
Transmission Electron ◽  
Deposit Layer

A problem was presented to observe the packing densities of deposits of sub-micron corrosion product particles. The deposits were 5-100 mils thick and had formed on the inside surfaces of 3/8 inch diameter Zircaloy-2 heat exchanger tubes. The particles were iron oxides deposited from flowing water and consequently were only weakly bonded. Particular care was required during handling to preserve the original formations of the deposits. The specimen preparation method described below allowed direct observation of cross sections of the deposit layers by transmission electron microscopy.The specimens were short sections of the tubes (about 3 inches long) that were carefully cut from the systems. The insides of the tube sections were first coated with a thin layer of a fluid epoxy resin by dipping. This coating served to impregnate the deposit layer as well as to protect the layer if subsequent handling were required.

Application of a Simple Cold Stub to the Direct Observation of Frozen Hydrated Sand

1973 ◽  
Vol 31 ◽  
pp. 212-213
Author(s):  
John M. Wehrung ◽  
Richard J. Harniman
Keyword(s):  
United States ◽  
Surface Water ◽  
Direct Observation ◽  
Controlled Study ◽  
Clay Particles ◽  
Organic Debris ◽  
Rock Formations ◽  
Water Tables ◽  
Permeable Rock ◽  
Natural Means

Water tables in aquifer regions of the southwest United States are dropping off at a rate which is greater than can be replaced by natural means. It is estimated that by 1985 wells will run dry in this region unless adequate artificial recharging can be accomplished. Recharging with surface water is limited by the plugging of permeable rock formations underground by clay particles and organic debris.A controlled study was initiated in which sand grains were used as the rock formation and water with known clay concentrations as the recharge media. The plugging mechanism was investigated by direct observation in the SEM of frozen hydrated sand samples from selected depths.

Direct Observation of the Diffusionless β → β + ω Transformation in Titanium Alloys

1971 ◽  
Vol 29 ◽  
pp. 122-123
Author(s):  
N. E. Paton ◽  
D. de Fontaine ◽  
J. C. Williams
Keyword(s):  
Electron Microscope ◽  
Titanium Alloys ◽  
Direct Observation ◽  
Dark Field ◽  
X Ray Diffraction ◽  
Resistivity Measurements ◽  
Selected Area Electron Diffraction ◽  
Ti Alloys ◽  
Thin Foils ◽  
Field Device

The electron microscope has been used to study the diffusionless β → β + ω transformation occurring in certain titanium alloys at low temperatures. Evidence for such a transformation was obtained by Cometto et al by means of x-ray diffraction and resistivity measurements on a Ti-Nb alloy. The present work shows that this type of transformation can occur in several Ti alloys of suitable composition, and some of the details of the transformation are elucidated by means of direct observation in the electron microscope.Thin foils were examined in a Philips EM-300 electron microscope equipped with a uniaxial tilt, liquid nitrogen cooled, cold stage and a high resolution dark field device. Selected area electron diffraction was used to identify the phases present and the ω-phase was imaged in dark field by using a (101)ω reflection. Alloys were water quenched from 950°C, thinned, and mounted between copper grids to minimize temperature gradients in the foil.

A New 1000kv Electron Microscope

1969 ◽  
Vol 27 ◽  
pp. 100-101
Author(s):  
J.L. Williams ◽  
K. Heathcote ◽  
E.J. Greer
Keyword(s):  
Electron Microscope ◽  
Direct Observation ◽  
High Voltage ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Specimen Thickness ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Dynamic Experiments ◽  
Conventional Instrument

High Voltage Electron Microscope already offers exciting experimental possibilities to Biologists and Materials Scientists because the increased specimen thickness allows direct observation of three dimensional structure and dynamic experiments on effectively bulk specimens. This microscope is designed to give maximum accessibility and space in the specimen region for the special stages which are required. At the same time it provides an ease of operation similar to a conventional instrument.

Direct Observation of Monolayer Zones in Al-wt 4% Cu

1990 ◽  
Vol 48 (1) ◽  
pp. 14-15
Author(s):  
B. Jouffrey ◽  
D. Dorignac ◽  
A. Bourret
Keyword(s):  
Solid Solution ◽  
Synchrotron Radiation ◽  
Direct Observation ◽  
Supersaturated Solid Solution ◽  
Original Model ◽  
X Ray ◽  
Image Position

Since the early works on GP zones and the model independently proposed by Preston and Guinier on the first steps of precipitation in supersaturated solid solution of aluminium containing a few percent of copper, many works have been performed to understand the structure of different stages in the sequence of precipitation.The scheme which is generally admitted can be drawn from a work by Phillips.In their original model Guinier and Preston analysed a GP zone as composed of a single (100) copperrich plane surrounded by aluminum atomic planes with a slightly shorter distance from the original plane than in the solid solution.From X-ray measurements it has also been shown that GP1 zones were not only copper monolayer zones. They could be up to a few atomic planes thick. Different models were proposed by Guinier, Gerold, Toman. Using synchrotron radiation, proposals have been recently made.

Clinical Update: Functional Capacity Evaluations and Disability

1998 ◽  
Vol 3 (2) ◽  
pp. 4-5
Author(s):  
Glenn Pransky
Keyword(s):  
Direct Observation ◽  
Functional Capacity ◽  
Work Capacity ◽  
Functional Capacity Evaluation ◽  
Whole Body ◽  
Validity Of Results ◽  
Job Tasks ◽  
Capacity Evaluation ◽  
Physical Abilities ◽  
The Relationship

Abstract According to the AMA Guides to the Evaluation of Permanent Impairment, a functional capacity evaluation (FCE) measures an individual's physical abilities via a set of activities in a structured setting and provides objective data about the relationship between an impairment and maximal ability to perform work activities. A key distinction between FCEs and self-reported activities of daily living is that the former involve direct observation by professional evaluators. Numerous devices can quantify the physical function of a specific part of the musculoskeletal system but do not address the performance of whole body tasks in the workplace, and these devices have not been shown to predict accurately the ability to perform all but the simplest job tasks. Information about reliability has been proposed as a way to identify magnification and malingering, but variability due to pain and poor comprehension of instructions may cause variations in assessments. Structured work capacity evaluations involve a set of activities but likely underestimate the individual's ability to do jobs that involve complex or varying activities. Job simulations involve direct observation of an individual performing actual job tasks, require a skilled and experienced evaluator, and raise questions about expense, time, objectivity and validity of results, and interpretation of results in terms of the ability to perform specific jobs. To understand the barriers to return to work, examiners must supplement FCEs with information regarding workplace environment, accommodations, and demotivators.

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