scholarly journals TIME-LAG OF DUNES FOR UNSTEADY FLOW CONDITIONS

1978 ◽  
Vol 1 (16) ◽  
pp. 109
Author(s):  
Horst Nasner
Keyword(s):  
Unsteady Flow ◽  
Time Lag ◽  
Flow Conditions ◽  
The Past ◽  
Bed Forms ◽  
Hydraulic Conditions ◽  
Bed Form ◽  
Theoretical Considerations ◽  
Reconstruction Time ◽  
Made In

Many publications based on theoretical considerations or model tests, give utterance to the demand that there should be unequivocal relations between hydraulic conditions and bed form characteristics which should be generally applicable. These relationships determined for steady conditions and limited water depths should be handled with care when being applied to natural rivers. The bed configurations do not immediately fit themselves to the varying flow conditions. The bed forms need a certain reconstruction time in case of a changing discharge. The time-lag of dunes was observed on numerous rivers, in the past. A general review of investigations made in this field is given by ALLEN (1976 b). In the following contribution, an attempt is made to describe the magnitude of the time lag of bed forms for unsteady flow conditions.

scholarly journals Effect of unsteady flows on the development and magnitude of bed forms

2021 ◽  
Author(s):  
Le Wang ◽  
Alan Cuthbertson ◽  
Gareth Pender ◽  
Zhixian Cao
Keyword(s):  
Unsteady Flow ◽  
Morphological Changes ◽  
Unsteady Flows ◽  
Coarse Sand ◽  
Total Water ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Bed Forms ◽  
Bed Form ◽  
Water Work

<p>Sediment transport and associated morphological changes in alluvial rivers occur primarily under unsteady flow conditions that are manifested as well-defined flood hydrograph events. At present, typical bed forms generated by such unsteady flows is far less studied and, thus, more poorly understood, than equivalent bed forms generated under steady flow conditions. In view of this, the objective of this work is to investigate the development of morphological bed features, and specifically variability in the length, height and steepness of bed forms that develop in a mobile coarse-sand bed layer under unsteady flow hydrographs under zero sediment feed conditions. A series of laboratory flume experiments is conducted within which different flow hydrograph events are simulated physically by controlling their shape, unsteadiness and magnitude. Experimental results indicate that different categories of bed forms such as dunes, alternate bars or transitional dune-bar structures develop within the erodible bed layer when subject to varying hydrograph flow conditions. Examination of relative importance of three parameters used to describe the hydrograph characteristics (i.e. asymmetry, unsteadiness and total water work) on bed form dimensional descriptors (i.e. wavelength, height and steepness) reveals that hydrograph unsteadiness and total water work are the primary and second-order controls on bed deformations or corresponding bed form dimensions. By contrast, hydrograph asymmetry appears to have minimal or negligible influence on bed form development in terms of their type and magnitude. Based on these findings, a physical model was developed and tested to describe the effect of unsteady flow hydrographs with varying unsteadiness and total water work on the nature and size of resulting bed forms that are generated in sand-bed layers. </p>

A Method for Predicting Compressor Cascade Total Pressure Losses When the Inlet Relative Mach Number Is Greater Than Unity

1971 ◽  
Vol 93 (1) ◽  
pp. 119-124 ◽  
Author(s):  
R. L. Balzer
Keyword(s):  
Total Pressure ◽  
Axial Flow ◽  
Shock Formation ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Viscous Effects ◽  
Pressure Losses ◽  
The Past ◽  
Flow Compressor ◽  
Made In

During the last few years, considerable progress has been made in predicting the total pressure losses from viscous effects for axial-flow compressor cascades. With the advent of the transonic and the supersonic stage, another pressure loss generating mechanism was introduced—the shock wave. Various methods have been published over the past few years accounting for the pressure losses associated with the shock formation, but of those reviewed by this author, none of them has been consistently successful for predicting the losses at other than design conditions. This paper develops a method which has given consistent success at all flow conditions for compressors with subsonic axial and supersonic relative velocities.

The Restraining of Vulcanization in Rubber Manufacture

1935 ◽  
Vol 8 (2) ◽  
pp. 230-238
Author(s):  
D. F. Twiss ◽  
F. A. Jones
Keyword(s):  
Hydrogen Atom ◽  
Time Lag ◽  
Rubber Mixture ◽  
The Past ◽  
Chemical Derivatives ◽  
Other Substances ◽  
Delayed Action ◽  
Derivatives Of ◽  
Vulcanization Accelerator ◽  
Made In

Abstract Delayed-Action Accelerators During the past few years, considerable advance has been made in the ordinary method of compounding technic with respect to scorching. The advances fall essentially into two well-marked divisions, viz., the development of “delayed-action accelerators” and the addition of “vulcanization restrainers,” “inhibitors of prevulcanization,” or “antiscorch agents.” With a true delayed-action accelerator vulcanization should not occur until a certain period of time has elapsed, after which rapid vulcanization takes place. The existence of this “time lag” can be explained on the basis that the reputed accelerators are inactive, but on heating are decomposed into other substances which constitute the real accelerators. Some organic accelerators give a temperature lag, and though comparatively safe from prevulcanization in processing, they vulcanize only above a certain critical temperature. Hence, when the rubber mixture is heated, vulcanization does not take place until this temperature is attained. Such accelerators are not delayed-action accelerators in the narrower sense. In all organic accelerators the activity can be associated with a particular grouping, and in the simplest form of accelerator generally with a particular hydrogen atom. Most if not all delayed-action accelerators can be regarded as chemical derivatives of known powerful accelerators in which the place of the active hydrogen atom is occupied by a more or less easily displaceable organic grouping; the delayed-action accelerator is consequently often a compound, e. g., of the thio-ester or thio-ether (or even “thio-anhydride”) type, which itself strictly is not a vulcanization accelerator, but is capable of undergoing decomposition (e. g., “hydrolysis” or fission) with formation of one.

scholarly journals The thermal expansion of quartz by x-ray measurements

1933 ◽  
Vol 142 (846) ◽  
pp. 237-247 ◽  
Keyword(s):  
Thermal Expansion ◽  
Coefficient Of Thermal Expansion ◽  
Optical Measurements ◽  
Optical Methods ◽  
X Rays ◽  
Atomic Lattice ◽  
X Ray ◽  
The Past ◽  
Theoretical Considerations ◽  
Made In

The study of the coefficients of thermal expansion of substances has in the past, for the most part, been confined to direct measurement by optical methods. At the present time X-rays are being used for determining the expansion of the atomic lattice as distinct from the specimen block. A question has arisen as to tire relation between the coefficient of expansion as measured visually and that measured by X-rays. From theoretical considerations Zwicky* has predicted that the two are not identical. X -ray measurements on the thermal expansion of single crystals of bismuth by Goetz and Hergenrothers have shown that there is a difference between the values obtained by the two methods of measurement. On the other hand Y. Tu finds no evidence in his experiments on rock salt of the secondary structure described by Zwicky. The question to be answered is thus one of great importance. the present paper gives evidence to shown that for silver and quarts there is no difference between the coefficients of expansion as measured by X-rays and those from optical measurements. The work described in this paper was carried out to measure the thermal expansion of quartz by X-rays and by comparing the results with those from optical measurements to test the validity of the assumption, made in previous papers, that the coefficient of thermal expansion of silver is the same whether measured by X-rays or optical methods.

Imprecision of Laboratory Determinations and Diagnostic Accuracy: Theoretical Considerations

1974 ◽  
Vol 13 (03) ◽  
pp. 151-158 ◽  
Author(s):  
D. A. B. Lindbebo ◽  
Fr. R. Watson
Keyword(s):  
Mathematical Model ◽  
Diagnostic Accuracy ◽  
Diagnostic Process ◽  
Clinical Laboratories ◽  
Non Linear ◽  
Theoretical Considerations ◽  
Made In

Recent studies suggest the determinations of clinical laboratories must be made more precise than at present. This paper presents a means of examining benefits of improvement in precision. To do this we use a mathematical model of the effect upon the diagnostic process of imprecision in measurements and the influence upon these two of Importance of Diagnosis and Prevalence of Disease. The interaction of these effects is grossly non-linear. There is therefore no proper intuitive answer to questions involving these matters. The effects can always, however, be calculated.Including a great many assumptions the modeling suggests that improvements in precision of any determination ought probably to be made in hospital rather than screening laboratories, unless Importance of Diagnosis is extremely high.

South Asian Developmental Crisis (Review Article)

1973 ◽  
Vol 12 (2) ◽  
pp. 181-188
Author(s):  
Rafiq Ahmad
Keyword(s):  
Second World War ◽  
World War ◽  
The Past ◽  
The Great Depression ◽  
Political Independence ◽  
Integrated Theory ◽  
Pass Through ◽  
Developed World ◽  
Second World ◽  
Made In

Like nations and civilizations, sciences also pass through period of crises when established theories are overthrown by the unpredictable behaviour of events. Economics is passing through such a crisis. The challenge thrown by the Great Depression of early 1930s took a decade before Keynes re-established the supremacy of economics. But this supremacy has again been upset by the crisis of poverty in the vast under-developed world which attained political independence after the Second World War. Poverty had always existed but never before had it been of such concern to economists as during the past twenty five years or so. Economic literature dealing with this problem has piled up but so have the agonies of poverty. No plausible and well-integrated theory of economic development or under-development has emerged so far, though brilliant advances have been made in isolated directions.

Mass Spectrometry Techniques: Principles and Practices for Quantitative Proteomics

2020 ◽  
Vol 21 ◽  
Author(s):  
Rocco J. Rotello ◽  
Timothy D. Veenstra
Keyword(s):  
Mass Spectrometry ◽  
Quantitative Proteomics ◽  
Protein Identification ◽  
Dynamic Nature ◽  
Complete Coverage ◽  
The Past ◽  
Proteome Level ◽  
A Cell ◽  
Quantitative Changes ◽  
Made In

: In the current omics-age of research, major developments have been made in technologies that attempt to survey the entire repertoire of genes, transcripts, proteins, and metabolites present within a cell. While genomics has led to a dramatic increase in our understanding of such things as disease morphology and how organisms respond to medications, it is critical to obtain information at the proteome level since proteins carry out most of the functions within the cell. The primary tool for obtaining proteome-wide information on proteins within the cell is mass spectrometry (MS). While it has historically been associated with the protein identification, developments over the past couple of decades have made MS a robust technology for protein quantitation as well. Identifying quantitative changes in proteomes is complicated by its dynamic nature and the inability of any technique to guarantee complete coverage of every protein within a proteome sample. Fortunately, the combined development of sample preparation and MS methods have made it capable to quantitatively compare many thousands of proteins obtained from cells and organisms.

Evidence-based Assessment

2010 ◽  
pp. 76-98
Author(s):  
John Hunsley ◽  
Eric J. Mash
Keyword(s):  
Decision Making ◽  
Clinical Assessment ◽  
Assessment Process ◽  
Evidence Based ◽  
The Past ◽  
Specific Assessment ◽  
The Many ◽  
Selection Of ◽  
Made In

Evidence-based assessment relies on research and theory to inform the selection of constructs to be assessed for a specific assessment purpose, the methods and measures to be used in the assessment, and the manner in which the assessment process unfolds. An evidence-based approach to clinical assessment necessitates the recognition that, even when evidence-based instruments are used, the assessment process is a decision-making task in which hypotheses must be iteratively formulated and tested. In this chapter, we review (a) the progress that has been made in developing an evidence-based approach to clinical assessment in the past decade and (b) the many challenges that lie ahead if clinical assessment is to be truly evidence-based.

The Role of Histones and Heparin in Sepsis: A Review

2021 ◽  
pp. 088506662199232
Author(s):  
Xiaojuan Zhang ◽  
Xin Li
Keyword(s):  
Septic Shock ◽  
Multiple Organ ◽  
Clinical Settings ◽  
The Past ◽  
Life Saving ◽  
Extracellular Histones ◽  
Sepsis And Septic Shock ◽  
Development And Management ◽  
Made In

Septic shock with multiple organ failure is a devastating situation in clinical settings. Through the past decades, much progress has been made in the management of sepsis and its underlying pathogenesis, but a highly effective therapeutic has not been developed. Recently, macromolecules such as histones have been targeted in the treatment of sepsis. Histones primarily function as chromosomal organizers to pack DNA and regulate its transcription through epigenetic mechanisms. However, a growing body of research has shown that histone family members can also exert cellular toxicity once they relocate from the nucleus into the extracellular space. Heparin, a commonly used anti-coagulant, has been shown to possess life-saving capabilities for septic patients, but the potential interplay between heparin and extracellular histones has not been investigated. In this review, we summarize the pathogenic roles of extracellular histones and the therapeutic roles of heparin in the development and management of sepsis and septic shock.

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