Unsolved problem

An actual calculation of the maximal force of repulsion between two symmetrically charged parallel cylinders in an electrolyte solution (see 2.2). 

Proof of boundedness of the force of interaction between two charged particles of an arbitrary shape in H3, held at a given distance from each other in an electrolyte solution, upon an infinite increase of the particle s charge. (It was shown in 2.2 that the repulsion force between parallel symmetrically charged cylinders saturates upon an infinite increase of the particle s charge. This is also true for infinite parallel charged plane interaction [9]. The appropriate result is expected to be true for particles of an arbitrary shape.) 

Study of counterion condensation as a limiting property of the solutions of the Poisson-Boltzmann equation for arbitrary, charged cylindrical manifolds in H3 (see 2.3). 

Counterion condensation on a point charge in three dimensions for the excluded volume equation (1.68). It is expected that in contrast to the previous case (Problem 4) the limiting equilibrium solution will exist for the appropriate version of (1.68) and the corresponding limiting singularity in the electric potential should be studied. 

A number of polyfalkyi methacrylates) are available. Explain how the glass transition temperature will change with increasing alliyl chain length  

Polyetherketone (PEK) and polyfether etherketonc) (PEEK) are two engineering polymers which are highly chemical resistant. 

Which of the two has a higher glass transition temperature Tg, PEK or PEEK WTiy do you think that these materials are highly chemical resistant  

The chemical structure of the polymer main chain is very important for the properties of a polymer. Set the following polymers in a sequence with increasing T.  

Give qualitatively the difference in various physical properties of high density polyethylene fHDPE) versus low density polyethylene (LDPE) glass transition temperantre, melt temperature, E-modulus at 25 C, helium penneabUity, water vapour p ermeability. 

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The two possible initiations for the free-radical reaction are step lb or the combination of steps la and 2a from Table 1. The role of the initiation step lb in the reaction scheme is an important consideration in minimising the concentration of atomic fluorine (27). As indicated in Table 1, this process is spontaneous at room temperature [AG25 = —24.4 kJ/mol (—5.84 kcal/mol) ] although the enthalpy is slightly positive. The validity of this step has not yet been conclusively estabUshed by spectroscopic methods which makes it an unsolved problem of prime importance. Furthermore, the fact that fluorine reacts at a significant rate with some hydrocarbons in the dark at temperatures below —78° C indicates that step lb is important and may have Httie or no activation energy at RT. At extremely low temperatures (ca 10 K) there is no reaction between gaseous fluorine and CH or 2 6... 

Prediction of protein structure from sequence is an unsolved problem... 

It should now be clear that there are a number of unsolved problems with regard... 

HarF60 Harary, F. Unsolved problems in the enumeration of graphs. Proc. Math. Inst. Hung. Acad. Sci. Ser A 5 (1960) 63-95. 

HarF70a Harary, F. Enumeration under group action Unsolved problems in graphical enumeration IV. J. Combinatorial Theory 8 (1970) 1-11 9 (1970) 221. 

This is a method which is very attractive in principle and which has been applied to yield approximate barriers for a number of molecules. There are, however, difficulties in its use. In the first place, it is not easy to measure the intensities of microwave lines with accuracy. There are unsolved problems of saturation, reflections in the wave guide, and variation of detector efficiency with frequency which are presumably reponsible for the fact that measurements made with ordinary wave guide spectrometers are not very reproducible. In addition, both the spectral lines may be split into components by tunnelling from one potential minimum to another and this splitting, even though it is not resolved, can alter the apparent intensity. Furthermore, it is often difficult to find pairs of lines such that neither is obscured by Stark lobes from the other. 

Kunitake, T. Ionic polymerization - Unsolved problems. Furukawa, J., and Vogl, O. (Ed.) Marcel Dekker, Inc. 1976... 

The B atoms fill the center points (site 24e) of an antiprism formed by four metal atoms of site 32f and four metal atoms of site 48h. Usually no boron defects occur, but a still unsolved problem is where xs B would be accommodated in the structure... 

In the later 1990s, some other advancements have been made in experiments made by Gao and Spikes [36] and Haiti et al. [37] and in theory by Thompson et al. [38] and Hu et al. [39]. However, there are many unsolved problems in the area of nano-lubrication [40]. 

Crowe, J.H. (1971). Anhydrobiosis an unsolved problem. American Naturalist, 105, 563-73. 

A so far unsolved problem is the development of asymmetric procedures for the above described Fe(0)-catalyzed cycloisomerizations and cycloadditions. The option to use the element of planar chirality might allow to successfully address this issue in future applications. 

Arthur E. Humphrey, Some Unsolved Problems of Biotechnology... 

There are also other unsolved problems. For instance, we have sufficient knowledge neither about the structures of chromium(V) and chromium(IV) species nor about the mechanism of striping of the covalently-bonded oxygen atoms from the chromate ion. 

If one wishes to predict the future of additive analysis in polymers, it is relevant to consider the prospects of further evolution of polymeric and additive materials the influence of legislation and environment instrumental developments and currently unsolved problems. It then becomes clear that additive analysis stands a fair chance remaining in use for some time, certainly in a strongly competitive environment, which will require improved product design specifications, quality assurance and research for new applications. As ideal production environments are rare, customer complaints will also require continuous attention. Government regulations are another reason for continuous analytical efforts. 

The major problem remains control of regioselectivity in favor of the branched regioisomer. While aryl alkenes as well as heteroatom-substituted alkenes favor the chiral branched isomer, for aliphatic alkenes such an intrinsic element of regiocontrol is not available. As a matter of fact branched-selective and asymmetric hydroformylation of aliphatic alkenes stands as an unsolved problem. In this respect regio- and enantioselective hydroformy-... 

Mahdihassan, S. Alchemy as a branch of medicine, its unsolved problems and unrecognized terms. HamdardMed 18, no. 7 (1975) 3-39. 

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