Short-distance network

Single mode glass fiber is widely used in the trunk area of the telecommunication system and the optical fiber system is expected to extend to the subscriber area and the network in building, offices, and homes. However, use of the single mode glass fiber system in short distance network is not necessarily suitable because it requires the precise handling and connection due to the small core size (5-10 [im) and thus it would be expensive in broadband residential area network, ATM-LAN, interconnection, etc. In contrast, polymer optical fiber (POP) which has more than 500 jim of core is promising candidate to solve such problems. 

With various improvements in the fabrication process enabling the avoidance of contaminants and the formation of Gl profiles, low-loss and high-bandwidth POFs have become leading candidates for short-distance networks (e.g.. 

The third case city, Helsinki (http ptp.hel.fi/wlan/) exemplifies a business driven fragmented competition model of Internet service provision. The mayor of Helsinki has stated that the city will not start to compete with Internet operators by providing no cost or low cost Internet access services. Therefore, Internet use in the center of Helsinki is more expensive and is based on numerous private actors. Helsinki misses the collaboration link that smaller cities have been able to produce. From the end-user point of view the collective and wide coverage network in Helsinki would be easier and cheaper to use than fragmented private sector short-distance networks. Table 9.1 summarizes case study locations of Helsinki, Turku and Oulu. 

For the experiments referred to in Fig. 4.25(a), McEnaney was able to show, on reasonable assumptions, that the stress induced by adsorption swelling should be sufficient to fracture the carbon over short distances. A memory effect in the carbon network would lead to trapping of some adsorbed carbon tetrachloride molecules during the desorption run. 

Figure 9.12 Three-dimensional map of the calculated electrostatic potential at 0.25 nm above the symmetry plane in a hexagonally ordered network of dipoles with a dipole-dipole distance of 1.61 nm and a dipole moment of 10 D. The dipoles are positioned at the minima. Note that the potential is lowered at every position on the surface. Equipotential lines for -1.05, -0.84, -0.63 and -0.42 V are indicated in the bottom plane. The contours are circular at short distances from a potassium atom, indicating that at these sites the nearest potassium atom largely dominates the potential. The equipotential tine for -0.42 V, however, has hexagonal symmetry due to the influence of the dipoles further away (from Janssens et al. [40]).

A similar C, symmetric arrangement can be found for Cu[pz(iV-Me2)8] C60 (Fig. 32) (38). The distance from the centroid of the C60 molecule to the N4 coordination planes is found to be the same as 1121 p (/V-Mc2)>,I C60 (6.32 A). Interesting is the short distance of one of the carbons of C60, which is only 2.36 A above the copper coordination plane. The structure of Cu[pz(iV-Me2)8] C60 includes solvent molecules but it crystallizes in a 2D rather than a 3D network. The pattern of -pz-C60-pz-pz-C60-pz- and -C60l-sol vcn t-C60,-sol vcn I- sandwiches are retained, but in the third direction adjacent sheets are laterally displaced so that there is no linear -C60-Cgo-Cgo- sequence present. 

Aromatic polycarboxylates easily form 2D or 3D networks, for instance [Nd2(122)3(dmf)4]-H2O which present a 2D structure in which the 1,4-naphthalenedicarboxylate anions link Ndm ions of two adjacent double chains keeping them at a short distance of about 4.1 A (J. Yang et al., 2006). This allows up-conversion to take place, albeit with very low efficiency a blue emission is seen at 449.5 nm upon excitation at 580 nm (corresponding to the 4Gs/2 magnetic properties an energy-transfer up-conversion mechanism involving no excited state absorption is more likely. 

For densely crosslinked networks such as epoxies, n could conceivably be less than 5, and the validity of Eq. (8) is therefore questionable. King and Andrews were apparently the first investigators to address this point. The lack of q values for epoxy polymers motivated them to derive an alternate expression for 2J o that did not incorporate q. The main assumption of their theory was that the distance between nearest crosslinks, L, in short-chain networks was equivalent to the mean displacement length, L, of the network chains. They then showed that the number of chains crossing a unit area of crack plane was given by (1/2) and therefore expressed 2 /q as... 

Many polymer materials contain polymer-polymer interfaces. These include polymer blends, interpenetrating networks, core-shell polymer colloids, and polymer micelles. The properties of these materials depend, one believes, on the nature of the interface and on factors which operate within very short distances (50A - lOOA) of the interface. These are the dimensions of polymer molecules, which means that a proper understanding of the performance of these materials requires understanding of the interface at the molecular level. 

The application of the proposed polymeric ophcal integrated devices will be used for local area network (LAN) for home use or for short-distance interconnections. For the use of the polymeric waveguide and the organic devices, i.e., OLED and OPD, the transmission speed will be in the range of several hundreds megahertz. In Figure 15.3, schemahc of OLEDs fabricated by vacuum [9] and solution processes [10] are shown. A typical vacuum... 

The coordination numbers of all cations which occupy sites in the vitreous network, i.e., the building blocks which constitute the network, provide the most basic element of any model for glass structures. Since these building blocks are usually well defined structures such as tetrahe-dra or triangles, they exhibit order at the level of several associated atoms or ions. Since this order only extends over a very short distance, it is termed short range order. 

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