The Long Periods

The sixth and the seventh periods are the long periods. The sixth period includes 32 elements, and only 28 elements of the seventh period elements are known. 

The sixth period starts by filling of 6s orbital with cesium (Cs) and barium (Ba).The 4f orbitals start to be occupied after one electron goes to the 5d orbitals. 

The 14 elements starting with 57La, are called lanthanides. In this period, there are a total of 32 elements. 

Currently, 28 elements filling the 7s, 6d and 5f orbitals have been discovered. In the seventh period, the 14 elements coming after 8gAc are called actinides. All the elements in the 6d block have been discovered, but not all of the elements in the 7p block. 

Lanthanides and actinides are known as rare earth metals or inner transition metals. 

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Copolymers of vinyUdene chloride and methyl acrylate have been studied by x-ray techniques (75). For example, the long period (lamellar thickness) for an 8.5 wt % methyl acrylate copolymer was found to be 9.2 nm by smaH-angle x-ray scattering. The unit cell is monoclinic, with a = 0.686 and c = 1.247 nm by wide-angle x-ray scattering. 

Another technique for organics measurement that overcomes the long period required for the BOD test is the use of continuous respirometry. Here the waste (full-strength rather than diluted as in the standard BOD test) is contacted with biomass in an apparatus that continuously measures the dissolved oxygen consumption. This test determines the ultimate BOD in a few hours if a high level of biomass is used. The test can also yield information on toxicity, the need to... 

The discovery of ozone holes over Antarctica in the mid-1980s was strong observational evidence to support the Rowland and Molina hypothesis. The atmosphere over the south pole is complex because of the long periods of total darkness and sunlight and the presence of a polar vortex and polar stratospheric clouds. However, researchers have found evidence to support the role of CIO in the rapid depletion of stratospheric ozone over the south pole. Figure 11-3 shows the profile of ozone and CIO measured at an altitude of 18 km on an aircraft flight from southern Chile toward the south pole on September 21, 1987. One month earlier the ozone levels were fairly uniform around 2 ppm (vol). 

Table 1 Values of the Long Period of Differently Drawn PET Fibers...

If we knew that the long periods are varying from stack to stack, but not within one and the same stack, the quantities... 

Peaks in SAXS patterns rest on a rapidly decaying background. Figure 8.7 shows an example for a typical isotropic bulk semicrystalline polymeric material. The long period of such data should never be determined from the peak maximum found in the... 

Figure 8.9. The scattering curve of an isotropic ideal two-phase system after multiplication by i 4 (cf. Eq. (8.43)). The Porod region in which the oscillations are almost faded away is generally beginning after the 2nd order of the long period reflection... 

Figure 8.36. SAXS pattern of a thermoplastic elastomer during straining. The thin horizontal line in the center is called an equatorial streak. In this case it is well-separated from the long-period peaks above and below... 

Figure 8.46. Construction of observable distances (dal, Lf) in a paracrystal from its fundamental distances, L (not observable pseudo long-periods), and dcl (observable crystallite thicknesses). Advancing to the bottom the relations to the observable thicknesses of amorphous layers, dm, and the long periods, L , are sketched...

Figure 10.4. MGZ analysis of an undrawn polyamide 6 fiber, (a) Plot of the peak maximum position as a function of the detector coordinates (x,y). Relations to the parameters of the ellipse and the structure (long periods Lm, Lq) are indicated, (b) Separation of meridional long period, Lm, from the long period L . (courtesy S. MURTHY)...

It is well known that the stacked lamellae of semi-crystalline polymers result in the long period which usually gives two (or three) diffuse Bragg reflections. We will focus on the first reflection (named LI) and the secondary reflection (named L2) at two (/-ranges, denoted as qu and qu, respectively [30,31]. 

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