Hybrid Former

Twin wire hybrid former where a rotating second wire is mounted on top of the fourdrinier wire, dewatering part of the suspension through the top wire. 

The majority of paper machines worldwide produce graphic paper grades on fourdrinier wire sections or on hybrid formers. These kinds of conventional forming section usually satisfy the quaHty requirements. Their disadvantages are the limitation in machine speed of about 1200 m min and for some paper grades the nonsymmetry in the web z-direction. 

The base sheet forming concept for specialty papers is the fourdrinier. It can be used for the whole basis weight range and up to a machine speed of about 1200 m mimf In order to achieve best results concerning formation and dimensional stability Dandy rolls or hybrid formers and effective vidre shaking units are frequently used. New machines however can exceed the speed limit of fourdri-niers, so gap former concepts are used in this case. 

The general understanding of the electronic structure and the bonding properties of transition-metal silicides is in terms of low-lying Si(3.s) and metal-d silicon-p hybridization. There are two dominant contributions to the bonding in transition-metal compounds, the decrease of the d band width and the covalent hybridization of atomic states. The former is caused by the increase in the distance between the transition-metal atoms due to the insertion of the silicon atoms, which decreases the d band broadening contribution to the stability of the lattice. 

In the interaction of the local 2pv orbitals, two more bonding molecular orbitals are formed against one less bonding. In all previous cases the opposite occurred. This is due to the negative overlap between adjacent 2py orbitals—whether, by convention, all positive lobes point in the clockwise direction, or whether all positive lobes point in the anticlockwise direction. The two bonding 2pv combinations in fact fall below the two antibonding (hybrid 2s, 2px) combinations. The former each have two electrons while the latter are empty. The six electrons of the three C—C bonds are nicely accounted for. The method creates simultaneously the acc and or c molecular orbitals of cyclopropane (note that the latter three lie relatively close in energy). 

Now this resonance hybrid may react by the addition of another monomer at either carbon 4 or 2. The former alternative leads to the 1,4 structure... 

In the case of an unsymmetrical diene such as isoprene, different orientations of the structural units are possible depending on which end of the diene unites with the chain radical. Of the two competing reactions (6) and (7) shown on page 241, the former would appear to be the more probable one on account of the influence of the methyl substituent in stabilizing to some extent one of the resonance hybrid structures which are shown. 

A substantial improvement in the theoretical modeling of this substrate, able to overcome the drawbacks of both former approaches (standard GGA and localized atomic basis set B3LYP) is the implementation of the HSE03 [36] hybrid functionals in a plane-wave formalism. 

To create a chiral center at an sp3-hybridized carbon requires a chiral environment to stereodirect the reaction. This chiral environment may exist as a chirally substituted sp3-hybridized carbon, on which appropriate substitution creates a new molecule with the same or inverted chirality at the former chiral center or as a chiral arrangement near a prochiral (prechiral) sp2 carbon. 

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