Response to the comments of D. R. Blackman and Y. Peleg (JRA 14, 411-14)

2002 ◽  
Vol 15 ◽  
pp. 349-351 ◽  
Author(s):  
Paul Kessener
Keyword(s):  
Free Water ◽  
Ground Level ◽  
Pressure Source ◽  
Elevated Pressures ◽  
Inverted Siphon ◽  
Gravity Driven ◽  
Air Pockets ◽  
Engineering Practices ◽  
Closed Conduit ◽  
Gradient Line

The comments on my article (JRA 13,104-32) by Blackman and Peleg, which are much appreciated, reflect prevailing discussions on Roman hydraulic engineering practices as well as on the relevant paragraphs of Vitruvius (8.6). Blackman focuses mainly on technical aspects, while Peleg aims at archaeological arguments.Blackman starts with a discussion of the term ‘siphon’, which he regrets being used as it could lead to misunderstanding: ‘siphon’ would represent a “real” siphon, not an “inverted” siphon, suggesting that I must have meant that there was a real siphon at Aspendos. However, in archaeology “siphon” is generally accepted to represent an inverted siphon. There is no misunderstanding: at Aspendos we have an inverted siphon, and since real siphons are not known in classical aqueduct systems, there is no objection to using ‘siphon’ and ‘inverted siphon’ for one and the same notion. Subsequently he states: “The presence of air pockets and so on is almost irrelevant to operations [of siphons] if no point in the system lies above the Hydraulic Gradient Line; were it not so, no garden hose would work reliably” This is a misconception. It is only due to the fact that our garden hoses are connected to supplies with elevated pressures that we get water from them. If we would connect the hose to a low-pressure source (e.g., to a rainwater container standing at ground level), we have to straighten out the coils before water will emerge. If the hose is coiled up, for example, on a wall support but positioned below the free water surface in the container to which it is connected, while we are holding the free end somewhere near the ground, we have nothing but an inverted siphon with high points. If air pockets are irrelevant, water should come out, but it does not if air is in the hose. For problems associated with air pockets in gravity-driven closed conduit systems (which classical siphons must be considered to be), see G. Corcos, Air in water pipes (1989) and H. T. Falvey, Air-water flow in hydraulic structures (1980).

Two sets of technical comments on P. Kessener, “The aqueduct at Aspendos,” JRA 13

2001 ◽  
Vol 14 ◽  
pp. 411-414
Author(s):  
Deane R. Blackman ◽  
Yehuda Peleg
Keyword(s):  
Hydrostatic Pressure ◽  
Atmospheric Pressure ◽  
Internal Flow ◽  
Technical Term ◽  
Pipe System ◽  
The World ◽  
To Come ◽  
Scholarly Contribution ◽  
Air Pockets ◽  
Closed Conduit

Kessener's comprehensive and scholarly contribution, which bravely tackles the basic science in some detail and which will surely be an enduring reference, nevertheless perpetuates some technical misunderstandings that recur in the literature. I begin with the term “siphon”. It is unfortunate that this term continues to be used. The term applies to the situation when, at some point in a closed conduit, the hydrostatic pressure is less than atmospheric. It is not just that the overwhelming proportion of the innumerable pipe systems in the world never know sub-atmospheric pressure and should not be confused with this unusual arrangement, which warrants a technical term of its own (indeed, many modern textbooks do not mention siphons); but to introduce the term inappropriately also leads to misleading reporting and misconceptions. When we reach the discussion of the hydraulics of this system, real siphons find their way into the argument (p. 125), though the evidence shows that there was no siphon at Aspendos. The presence of air pockets and so on is almost irrelevant to operations if no point in the system lies above the Hydraulic Grade Line; were it not so, no garden hose would work reliably.It is quite true that the problems of getting a siphon to start and to keep it running are significant: even without leaks, air tends to come out of solution and will eventually destroy the liquid column. But in a pipe system which does not go sub-atmospheric, the inverse (if we might dare to use the word) applies: air trapped at a high point will tend to be taken into solution, and the confused internal flow at such a point will be very efficient at entraining and so removing air. Just as a garden hose may splutter when first turned on, very rapidly all air is expelled from the system and there is no question that flow will eventually be established without further intervention.

scholarly journals Application of horizontal flow constructed wetland and solar driven disinfection technologies for wastewater treatment in India

2018 ◽  
Vol 13 (3) ◽  
pp. 469-480 ◽  
Author(s):  
Virendra Kumar Mishra ◽  
Philipp Otter ◽  
Reetika Shukla ◽  
Alexander Goldmaier ◽  
J. A. Alvarez ◽  
...  
Keyword(s):  
Constructed Wetland ◽  
Oxygen Demand ◽  
Free Water ◽  
Treated Wastewater ◽  
Electrolytic Production ◽  
Soil Enrichment ◽  
Physico Chemical ◽  
Treated Sewage ◽  
Gravity Driven ◽  
Filter Bed

Abstract The present study was conducted to treat primary and secondary treated sewage for its reuse in irrigation, soil enrichment and aquaculture activities. The study involves treatment of this sewage through a subsurface horizontal gravity-fed gravel filter bed with an area of 35 m2. The effluent was then subjected to filtration by zeolite medium and disinfection by inline electrolytic production of chlorine. In order to provide pathogen-free water, an anodic oxidation (AO) disinfection system was implemented, treating a flow of up to 10 m3/d. The gravity-driven constructed wetland and solar-driven disinfection systems were evaluated for their treatment capacity for various physico-chemical and biological parameters. The wetland removed almost 84% of the nitrate (NO3−) and 77% of the phosphate (PO43−). Five-day biological oxygen demand was reduced from 48 mg/l to 10 mg/l from the secondary treated wastewater. The wetland was able to remove 65–70% of bacteria in the wastewater, whereas the AO disinfection system removed the bacterial content to below the detection limit. The implementation of the systems will provide a suitable option for the treatment of wastewater in a very economical and sustainable way.

scholarly journals Buoyancy-driven dispersion in a layered porous rock

2015 ◽  
Vol 767 ◽  
pp. 226-239 ◽  
Author(s):  
Adrian Farcas ◽  
Andrew W. Woods
Keyword(s):  
Constant Pressure ◽  
Single Layer ◽  
Flow Speed ◽  
Longitudinal Dispersion ◽  
Longitudinal Distribution ◽  
Porous Rock ◽  
Pressure Source ◽  
Number Of Layers ◽  
Gravity Driven ◽  
Gravity Driven Flow

AbstractWe investigate the longitudinal dispersion of a passive tracer by a gravity-driven flow in a porous medium consisting of a series of independent horizontal layers connected to a constant pressure source. We show that in a formation of given vertical extent, the total flux is only weakly dependent on the number of layers, and is very similar to that in a single layer of the same total depth. However, although the flow speed in each layer is approximately uniform, the speed gradually increases with layer depth. As a result, if a pulse of tracer is released in the flow it will migrate more rapidly through the lower layers, leading to longitudinal dispersion of the tracer. Eventually, the location of the tracer in the different layers may become separated in space so that a sufficiently distant observation well would detect a series of discrete pulses of tracer rather than the original coherent input, as would occur in a single permeable layer. For a constant pressure source, at long times, the standard deviation of the longitudinal distribution of tracer asymptotes to a fraction of order 0.1 of the position of the centre of mass, depending on the number of layers and the overpressure of the source.

Effects of Vibration on the Preparation of Ultrathin Sections

1973 ◽  
Vol 31 ◽  
pp. 358-359
Author(s):  
Joseph M. Blum ◽  
Edward P. Gargiulo ◽  
J. R. Sawers
Keyword(s):  
Cutting Speed ◽  
Ground Level ◽  
Environmental Vibration ◽  
Block Face ◽  
Ultrathin Sections ◽  
Embedding Medium ◽  
Thickness Variations ◽  
Building Walls ◽  
Cutting Direction ◽  
Diamond Knife

It is now well-known that chatter (Figure 1) is caused by vibration between the microtome arm and the diamond knife. It is usually observed as a cyclical variation in “optical” density of an electron micrograph due to sample thickness variations perpendicular to the cutting direction. This vibration might be induced by using too large a block face, too large a clearance angle, excessive cutting speed, non-uniform embedding medium or microtome vibration. Another prominent cause is environmental vibration caused by inadequate building construction. Microtomes should be installed on firm, solid floors. The best floors are thick, ground-level concrete pads poured over a sand bed and isolated from the building walls. Even when these precautions are followed, we recommend an additional isolation pad placed on the top of a sturdy table.

The internal structure of medullated wool

1984 ◽  
Vol 42 ◽  
pp. 388-389
Author(s):  
Leo Barish
Keyword(s):  
Light Microscopy ◽  
Internal Structure ◽  
Wool Fiber ◽  
Guard Hair ◽  
Bright Field ◽  
Wool Fibers ◽  
Thin Skin ◽  
Air Pockets

Although most of the wool used today consists of fine, unmedullated down-type fibers, a great deal of coarse wool is used for carpets, tweeds, industrial fabrics, etc. Besides the obvious diameter difference, coarse wool fibers are often medullated.Medullation may be easily observed using bright field light microscopy. Fig. 1A shows a typical fine diameter nonmedullated wool fiber, Fig. IB illustrates a coarse fiber with a large medulla. The opacity of the medulla is due to the inability of the mounting media to penetrate to the center of the fiber leaving air pockets. Fig. 1C shows an even thicker fiber with a very large medulla and with very thin skin. This type of wool is called “Kemp”, is shed annually or more often, and corresponds to guard hair in fur-bearing animals.

A global perspective of ground level, 'ambient' carbon dioxide for assessing the response of plants to atmospheric CO2

2001 ◽  
Vol 7 (7) ◽  
pp. 789-796 ◽  
Author(s):  
L. H. Ziska ◽  
O. Ghannoum ◽  
J. T. Baker ◽  
J. Conroy ◽  
J. A. Bunce ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Ground Level ◽  
Global Perspective ◽  
Atmospheric Co2

Analysis of athletes’ stadium stress source based on improved layered K-means algorithm

2020 ◽  
Vol 39 (4) ◽  
pp. 5905-5914
Author(s):  
Chen Gong
Keyword(s):  
Experimental Data ◽  
Machine Learning Algorithms ◽  
User Preference ◽  
Experimental Comparison ◽  
Actual Situation ◽  
Medical Field ◽  
Pressure Source ◽  
Preference Model ◽  
Related Research ◽  
Analysis System

Most of the research on stressors is in the medical field, and there are few analysis of athletes’ stressors, so it can not provide reference for the analysis of athletes’ stressors. Based on this, this study combines machine learning algorithms to analyze the pressure source of athletes’ stadium. In terms of data collection, it is mainly obtained through questionnaire survey and interview form, and it is used as experimental data after passing the test. In order to improve the performance of the algorithm, this paper combines the known K-Means algorithm with the layering algorithm to form a new improved layered K-Means algorithm. At the same time, this paper analyzes the performance of the improved hierarchical K-Means algorithm through experimental comparison and compares the clustering results. In addition, the analysis system corresponding to the algorithm is constructed based on the actual situation, the algorithm is applied to practice, and the user preference model is constructed. Finally, this article helps athletes find stressors and find ways to reduce stressors through personalized recommendations. The research shows that the algorithm of this study is reliable and has certain practical effects and can provide theoretical reference for subsequent related research.

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