Showing papers by "Quaid-i-Azam University published in 1980"
TL;DR: In this paper, a detailed development of Kilb's model for gelation is given and the expression αc (f − 1)(1 − λab)2 = 1 is derived as the condition for gelations.
Abstract: The assumptions involved in approximate theories of gelation forRA2 +RBf type random polymerisations are examined in detail. When the assumptioncint ≪cext is removed it is apparent that, contrary to previous findings, theFrisch theory is unable to explain existing gel-point data. A detailed development ofKilb's model for gelation is given and the expression αc (f – 1)(1 – λab)2 = 1 is derived as the condition for gelation. αc is the product of extents of reaction ofA andB groups at the gel point,f is the branchunit functionality, and λab is a ring-forming parameter. λab depends on the dilution of a reaction system, the molecular weights of the reactants and chain structures. It is shown how the derived expression can be used for reasonable predictions of αc for a given polymerisation system.
46 citations
13 citations
TL;DR: The first stage in the thermal decomposition of tetraalkylammonium haloborates involves the loss of one mole of an alkyl halide with the formation of a 1∶1 complex as discussed by the authors.
Abstract: Thermal decompositions of tetraalkylammonium haloborates, R4N+BX4− (whereR=Et orn-Bu, andX=Cl, Br or PhBCl2), have been studied by both bench pyrolysis and thermoanalytical techniques. The first stage in the thermal decomposition of the haloborates involves the loss of one mole of an alkyl halide with the formation of a 1∶1 complex. Thermal decomposition of the haloborates beyond the stage of formation of haloboranes leads to the evolution of further quantities of alkyl halides together with the corresponding boron trihalide. In many instances the final products were polymeric materials of the general type:
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10 citations
6 citations
TL;DR: In the immature spiny-tailed lizard, androgenesis resulting in detectable levels of testosterone in peripheral plasma and testicular tissue precedes gamatogenic activity and the steroidogenic tissue in this species has been shown to be responsive to exogenous gonadotropins even in the earliest phase of posthatching development.
6 citations
TL;DR: In this article, the authors consider the problem of verifying the existence of gravitons in the early universe by observing the decay of a proton, and show that the life of the proton must be greater than the age of the universe.
Abstract: One of the fundamental ly new predictions of re la t iv i ty theory was the existence of gravi ta t ional waves (~). Despite many efforts to detect them (~-4) there is no general ly accepted evidence of their existence (5). Nevertheless there is an almost universal belief tha t they do exist. Recently CARR considered various possible scenarios for the production of gravi ta t ional waves in the early universe (~). BV.RTOTTI and C ~ R also considered a possible experimental method for detecting a random background gravi tat ional radia t ion (7). A major problem of re la t iv i ty theory is the a t t empt to combine i t with the quantum theory. More specifically, there are fundamental problems in t rying to develop a satisfactory theory of quantum grav i ty (s). All in all i t might seem tha t there could be no hope of experimental ly verifying the existence of gravi tons (quantized grav i ty waves). However, any a t tempt to unify all the forces of nature along the lines of the Salam (~)Weinberg (~o) scheme of the unification of weak and electromagnetic forces, must assume the existence of gravitons. Is the entire unification programme, then, to be discarded as being untestable? We should not be too has ty in doing so. After all, even though we may not be able to test the grand unified theories of Georgi and Glashow or Pa t i and Salam, an indirect tes t of some unification of strong and electro-weak forces by observing proton decay is in progress at present. According to any emTent theory, the life of the proton must be greater than the age of the universe. The a t t empt to observe proton decay may have been considered impossible on account of the accuracy required, and yet i t can be performed at present. In the same way an immensely high
3 citations
TL;DR: The left-right symmetric gauge group U L (2) ⊗U R (2), which is considered as the unifying electroweak gauge group, has been shown to have the merit of fixing the mixing parameter sin 2 θ W of the standard model at 0.25 as mentioned in this paper.
2 citations
TL;DR: In this paper, it was shown that it is possible to get a small mass for Dirac neutrino in a left-right symmetric gauge model in a natural manner, which is related to the smallness of the right-handed weak interactions.
2 citations
01 Jan 1980
TL;DR: For example, the experimental upper limit on the life time of the proton is τp ≥ 2(1030) years as mentioned in this paper, which is the longest known life time for any particle.
Abstract: Until about 1932, only three particles were regarded as elementary, namely, electron (e), proton (p) and neutrino (v). Still there is something special about these three particles in that they are the only stable particles, electron and neutrino are regarded as absolutely stable while the experimental upper limit on the life time of the proton is τp ≥ 2(1030) years.
1 citations
01 Jan 1980
TL;DR: In this paper, the authors investigated the routes of the formation of linear polymers, both involving the 1:1 adduct and trialkyl-amine trihaloboranes, and the products isolated include, Bisaminohaloborane (R2N)2BX), dialkylaminodihalobore(R2NBX2)
Abstract: Thermal decomposition of Quaternaryammonium tetrahaloborates has been investigated in the routes of the formation of linear Polymers, both involving the 1:1 adduct and trialkyl-amine trihaloboranes The products isolated include, Bisaminohaloboranes (R2N)2BX), dialkylaminodihaloborane (R2NBX2) and linear polymers A possible reaction pathway to the formation of linear polymers involving these intermediates is discussed