Blog Archives

On the steppes of central Asia: Irrigation in Bactria and Margiana before the arrival of Alexander the Great

Posted by on 13/ 11/ 15

Bactria, to the east of the Zagros mountains and the Iranian plateau, is connected to the Syro-Mesopotamian world through a continuous thread of ancient exchanges, and thus it also must be mentioned in this chapter. Bactria was a land of plenty and fertile val­leys as noted by Strabo:

“Man has only to take the trouble to irrigate, and all crops grown abundantly with the excep – 53

tion of the olive tree”.

In Chapter 1 we mentioned the appearance of the Bactria-Margiana civilization, or the Oxus civilization, for which the mastery of irrigation is a fundamental pillar. It is doubtful that Bactria ever really fell under the Assyrian yoke, as is suggested in certain ancient sources...

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Covariance and correlation coefficient

Posted by on 13/ 11/ 15

When a problem involves two dependent random variables, the degree of linear dependence between the two can be measured by the correlation coefficient pXyy, which is defined as

Corr(X, Y) = px, y = Cov(X, Y )laTay (2.47)

where Cov(X, Y) is the covariance between random variables X and Y, defined as

Cov(X, Y) = E[(X – ,ix)(Y – iiy)] = E(XY) – pPy (2.48)

Various types of correlation coefficients have been developed in statistics for measuring the degree of association between random variables. The one defined by Eq. (2.47) is called the Pearson product-moment correlation coefficient, or correlation coefficient for short in this and general use.

It can be shown easily that Cov(X^, X’2) = Corr(Xь X2), with X^ and X’2 being the standardized random variables...

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Compression

Posted by on 13/ 11/ 15

Compression — in wood, not my father’s car engine — can be thought of as the tendency to crush or compress under a load. The actual crushing or compressing does not have to be measurable to be real. If 1 stand on a stout — say, 12-inch diameter by 12-inch high — oak chopping block, my weight puts that chopping block in compression, even though I am having no measurable impact upon it. My entire family could balance atop the block to no effect, yet the block is definitely in compression. It might seem that such a stout block would never fail under compression, and yet it can under extreme circumstances. In October of 2003, Jaki and 1 rotated a 20-foot long 20-ton stone on a 12-inch-wide pivot made of a dense hardwood, an incredible concentrated load...

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FOUNDATION & STORM DRAINAGE

Posted by on 13/ 11/ 15

FOUNDATION & STORM DRAINAGE

Drainage is essential in protecting a basement from groundwater, but waterproofing the basement wall from the outside is also vital. In selecting a water­proofing material, consider the method of application, the elasticity, and the cost. Below are common water­proofing and drainage materials.

Bituminous coatings—Tar or asphalt can be rolled, sprayed, troweled, or brushed on a dry surface. Often applied over a troweled-on coating of cement plaster that is called parging, some bituminous coatings may be fiberglass reinforced. They have minimal elasticity, and thin coats may not be impervious to standing water.

Modified portland-cement plaster—Plaster with water-repellent admixtures can look exactly like stucco. It is usually applied with a brush or a trowel to a moist­ened surface...

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POWER TOOLS

Posted by on 13/ 11/ 15

POWER TOOLS

Power tools have revolutionized the way houses are built. Some of the tools common on the job site include (clockwise from bottom) 3/s-in. drills, miter saws, belt sanders, cordless drills, reciprocating saws, У2-ІП. drills, trim saws, and circular saws (worm drive left, sidewinder right).

Tools aren’t like stretch socks where one size fits all. A saw that has the right combination of power, weight, and feel for one carpenter may be the wrong choice for another. But here are a few tips that should help you make an educated choice when it comes time to invest in a power tool.

• The tool should be comfortable to use, so (if pos­sible) try before you buy. Do some homework, and try out a few to see how each one feels.

POWER TOOLS

An 18-volt cordless circular saw can make short work of...

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Techniques ADJUSTING THE MUDSILL TO FIX FOUNDATION WALLS

Posted by on 13/ 11/ 15

Techniques ADJUSTING THE MUDSILL TO FIX FOUNDATION WALLS

But here’s some good news: If von know how far off it is, yon can usually make the appro­priate corrections when installing the sills (see the sidebar on the facing page). It’s worth it to make the sills as straight, parallel, square, and level as possible. Otherwise, the mistakes made at this preliminary stage tend to become even more troublesome further down the line. Here’s how to check the foundation:

Подпись: USING A WATER LEVEL
Подпись: Clear plastic
Подпись: This side of the foundation is Уг in, lower than the other side.
Подпись: A simple v/ater level can be used to check the foundation for level. These are available at home improvement centers.
Techniques ADJUSTING THE MUDSILL TO FIX FOUNDATION WALLS

Подпись:

STRAIGHT. Check the walls for straightness bv stretching a dry line (string) from comer to corner. At this point, you just need to know­how straight the top outside edge of the foun­dation is, because you’ll be measuring in from this edge to locate the sill.

PARALLEL. Measure across the walls at both ends and in the middle...

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Designing a Gradation Curve

Posted by on 13/ 11/ 15

Some hold the opinion that the best gradation curve is the one passing exactly in the middle of the space between the upper and lower gradation limits. To a certain extent in some cases this may be true; however, in the majority of cases it is not. The shape of a design gradation curve exerts a significant impact on mix properties. For example, by looking at its shape, one may determine if the mix is more or less coarse or has the probability of being overfilled with mastic. Therefore the shape of a design gradation curve is not an unimportant question.

The subsequent phases of design will be discussed later, starting with the coarse aggregate fraction, going through the sand fraction, and ending with the filler content...

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The qanats: a new technique for obtaining water

Posted by on 13/ 11/ 15

When surface water cannot meet the needs of irrigation, one must tap groundwater. It was probably at the beginning of the Ist millennium BC, in Persia or in neighbouring lands, that a remarkable device for obtaining high quality water was invented: the qanat.[80]

This word means “reed” in Akkadian. The device comprises a gallery, or shaft, dug nearly horizontally from the flank of a natural slope back into the aquifer, but with a small slope (of the order of one or two per thousand) so that the water can flow out by gravity (Figure 2.19). In general, the construction of a qanat begins with the drilling of what will become its terminal well, called the “mother well”, through which the nature and level of the water table can be determined...

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DESIGNING AN AGGREGATE MIX BY. APPLYING GRADATION LIMITS

Posted by on 13/ 11/ 15

The application of gradation limits has become the most commonly used method for designing SMA mix composition. This method involves gradation analyses of all the constituent aggregates, including the filler, followed by balancing the proportions of all the aggregates in such a way that the ultimate gradation curve is situated between the adopted gradation limits. Used alone, it is a very simple method. Unfortunately it is characterized by some drawbacks that may result in a poor SMA mix design.

The advantages of the method of gradation limits include the following:

• The method is simple to use and quick to produce results...

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