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Chemical Analysis

Posted by on 19/ 11/ 15

7.6.2.1 Introduction

Chemical analysis allows determination of the chemical composition of collected samples and, therefore, to identify specific compounds in the chosen environment. Each chemical compound has one or more analytical methods, from the many dif­ferent methods available, that are more suitable for obtaining an accurate determi­nation of concentration. This section of this chapter presents a brief summary of the analytical methods most used at present for chemical composition identification. It includes coverage of toxicity tests that properly supplement chemical analyses when used to assess the possible impact on living organisms.

7.6.2.2 Selective Ion Measurement

Ion selective electrodes (ISE) are membrane electrodes that respond selectively to specified ions in the presen...

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Window and Door Screens

Posted by on 19/ 11/ 15

Windows and sliding glass doors generally come with removable screens. Screens for french doors or glass swinging doors usually are not provided by the manufacturer and must be custom made. Aluminum screening was standard in the past but has been almost
completely replaced with fiberglass or nylon mesh. These materials are more flexible, more transparent, do not dent, and are easy to re­place. Unfortunately, they also can be odor­ous, especially if they have been treated with insect repellents, pesticides, or other chemi­cals. When windows arrive onsite the screens should be unwrapped and stacked in a pro­tected environment so they have an oppor­tunity to air out prior to installation in the completed home...

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Materials ESTIMATES FOR A ROOF

Posted by on 19/ 11/ 15

DETERMINING THE QUANTITY of materials needed to cover and shingle a roof is rather easy. First, measure the roof to determine its square footage. Add the width of both sides of the roof and multi­ply that number by the length of the roof. Let’s look at an example: A roof with an overall width of 28 ft. and a length of 46 ft. has a total area of 1,288 sq. ft., which I’d round up to 1,300 sq. ft.

Figure felt paper first. The first material you will need is felt paper. The coverage you can obtain from a roll of felt paper varies, but it’s often 300 sq. ft. (to make sure, ask your building – materials supplier). Divide 1,300 sq. ft. by 300 sq. ft. for a total of 4.33 or 4Уз rolls...

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Roadside Geometry

Posted by on 19/ 11/ 15

Except for flat roadsides, a motorist leaving the roadway may encounter a foreslope (negative grade such as on an embankment), a backslope (positive grade such as in a cut section), a transverse slope (such as caused by an intersecting side road), or a drainage channel (change from negative to positive grade).

Foreslopes parallel to the traffic flow may be categorized as recoverable, nonrecov­erable, or critical. Recoverable slopes are 1:4 (vertical to horizontal) or flatter, and the

Подпись: CLEAR ZONE WIDTH = 6m
Подпись: ANSWER:
Подпись: CD P

Подпись: THROUGH TRAVEL'

Roadside Geometry Подпись: лоокщЪ- Oesi9n Spe
Roadside Geometry
Подпись: 750- 1500 DESIGN A.D
Подпись: UNDER 750 DES GN A

Roadside GeometryCLEAR-ZONE DISTANCE (m)

FIGURE 6.2 Clear zone distance curves. (a) SI units; (b) U. S. Customary units. (From Roadside Design Guide, AASHTO, Washington, D. C., 2002 and 2006, with permission) clear zone distance from Fig. 6.2 applies directly...

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APPLICATION OF CLEAR ZONE CONCEPT TO SLOPE AND DRAINAGE DESIGN

Posted by on 19/ 11/ 15

The clear roadside concept has a direct and obvious application to the selection of slopes and design of drainage features such as ditches, curbs, culverts, and drop inlets. A traversable, unobstructed roadside zone should extend beyond the edge of the driving lane for an appropriate distance so that the motorist can generally stop or slow the vehicle and return to the roadway safely.

The width of the zone depends on the traffic volume, the design speed, and the road­side slope. Vehicles on high-volume, high-speed routes obviously require more room to recover than those on less congested routes. A suggested guide for determining the width of the clear zone is presented in Fig. 6.2...

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Vibratory Rollers

Posted by on 19/ 11/ 15

Vibratory rollers should be carefully or, more precisely, consciously used. An addi­tional condition for using vibration is maintaining the appropriate temperature behind the paver to enable the movement of particles during rolling. Applying vibra­tion to a cool SMA mixture is a mistake that leads to the crushing of particles. Vibration is not an option when SMA is being placed in a thin layer (i. e., 20-30 mm), on a stiff base (e. g., concrete slabs or a brick or block pavement), or at too cold of a mixture. Compacting SMA with vibratory steel rollers is generally permitted, but high frequency and low amplitude vibrations are a must (Asphalt Review, December 2004).

Determining the correct type of vibratory roller to use from among the following is important when considering the use of v...

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Types of Rollers

Posted by on 19/ 11/ 15

The following types of rollers can be used for compacting SMA mixtures:

• Static—used as basic equipment for SMA compaction. The heavy (fin­isher) and medium ones operate chiefly in the set. When compacting is executed on thin layers or layers on a stiff underlying, heavy rollers are excluded.

• Vibratory— used for compacting SMA, but only according to some rules mentioned later.

Pneumatic rollers are not typically used due to the risks of mastic sticking to the tires and dragging particles out of the rolled layer and of squeezing mastic out on the surface.

The following rules should be observed when planning for a combination of roll­ers for a work site: [63]

• An extra roller with a side-roll for layer edges should be provided, espe­cially with an increased number of constructi...

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Building Techniques: Timber Framing for the Rest of Us

Posted by on 19/ 11/ 15

T

O THIS POINT, WE HAVE SPOKEN OF CONSIDERATIONS APPROPRIATE for all timber framing projects. But now we have reached a juncture where traditional timber framers go one way and the rest of us take another path. As Yogi Berra said at a college commencement speech, “When you get to that fork in the road take it.” I say, “Let’s start at the bottom and work up.”

Foundation Options

Timber framing can be married quite happily to a variety of foundation methods, which, in general, can be characterized under four separate categories: piers, footings, masonry walls, and slab-on-grade.

I. Piers. Piers can also be called pillars, columns or posts, and can be made of wood (such as 75-year ground contact six-by-six timbers or railway ties) or of poured concrete...

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Films Create Super Windows

Posted by on 19/ 11/ 15

Another way to control the flow of heat through a window is with suspended films. These films come in two varieties: high solar gain and low solar gain.

Because these films (similar to mylar) are so lightweight and thin, as many as three films can be suspended between two glass panes. The additional insulating spaces in­crease the insulating ability of the window, replicating the performance of three-, four-, or five-pane windows without the weight. Serious Windows® uses this approach to cre­ate high-performance windows with both high and low solar-gain properties. The com­pany’s premium fixed window has an insu­lating value of R-11.1 (U-factor 0.09), nearly rivaling many wall insulations. The operable version of the window is R-7.1 (U-factor 0.14)...

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Relationships among failure density function, failure rate, and reliability

Posted by on 19/ 11/ 15

According to Eq. (5.3), given the failure density function ft(t) it is a straight­forward task to derive the failure rate h(t). Furthermore, based on Eq. (5.3), the reliability can be computed directly from the failure rate as

Ps(t) = exp

 

I h(x) dr

0

 

(5.10)

 
Подпись: ft (t) = h(t) exp Подпись: I h(x)dr 0 Подпись: (5.11)

Substituting Eq. (5.10) into Eq. (5.3), the failure density function ft(t) can be expressed in terms of the failure rate as

Example 5.3 (after Mays and Tung, 1992) Empirical equations have been developed for the break rates of water mains using data from a specific water distribution system. As an example, Walski and Pelliccia (1982) developed break-rate equations for the water distribution system in Binghamton, New York. These equations are

Pit cast iron: N(t) = 0.02577e00207t

Sandspun...

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