DNA-protein interactions as the source of large-length-scale chirality evident in the liquid crystal behavior of filamentous bacteriophages

Although all filamentous phages are constructed of chiral components, this study of eight of these phages (fd, IKe, I(2)2, X-2, Pf1, Pf3, tf-1, and X) shows that some form nematic liquid crystals, which are apparently oblivious to the chirality of the components, while others form cholesteric liquid crystals revealing a type of structural chirality not normally encountered. Additions of dopants that interact with the DNA or protein components of the viruses change the liquid crystal properties of seven of the phages. In these seven, DNA-capsid symmetry differences do not allow strict structural equivalency among the protein subunits. The polymorphism arising from this nonequivalency is proposed here to give rise to coiling of the filaments, a large-length-scale chirality that is responsible for forming cholesteric liquid crystal phases. Only one phage of those studied here, Pf1, which is distinguished from the others in its DNA-capsid interactions, forms nematic phases under all conditions tried. The formation of liquid crystals has been developed as a method to detect subtle overall shape effects arising from DNA-subunit-derived polymorphism, an unusual role for the mesogenic state and a new tool for the study of filamentous phage structure.     

An alternative approach to determine the spot-size of a multi-mode laser beam and its application to diode laser beams

An alternative approach is suggested to determine the spot-size of a multi-mode laser beam. It has been shown by simulations that the suggested approach can give the beam quality factor and characteristic radius with less than 5% error. Unlike the power content method, the proposed method is applicable to the beams even with diameter one tenth of the CCD size. The new approach has been applied to a multi-mode diode laser output and it is shown that the ABCD matrix analysis can be used for beam propagation, with the measured parameters of the laser.     

Energy spectra and angular distribution of projectile-like fragments in 84 MeV <Superscript>12</Superscript>C + <Superscript>169</Superscript>Tm

Kinetic-energy spectra and angular distribution of projectile-like fragments have been measured in the reaction of 84 MeV ¹²C on ¹⁶⁹Tm, using the surface barrier silicon-based ΔE-E telescopes. The fragments close to the projectile show typical spectra of quasi-elastic transfer reactions, which were found to be in agreement with the calculations based on the direct surface transfer reaction model. A significant cross-section of fast alpha-particles was found at forward angles, reminiscent of incomplete fusion reactions, which could be explained in terms of the direct surface transfer reaction model after taking into account the level density of continuum states in the heavy reaction product. The results have been explained in terms of the continuous evolution of the reaction mechanism as a function of the mass transfer. Received: 13 March 2002 / Accepted: 3 May 2002     

Angular momentum transfer in incomplete fusion

Isomeric cross-section ratios of evaporation residues formed in¹²C+⁹³Nb and¹⁶O+⁸⁹Y reactions were measured by recoil catcher technique followed by off-line γ-ray spectrometry in the beam energy range of 55.7–77.5 MeV for¹²C and 68–81 MeV for¹⁶O. The isomeric cross-section ratios were resolved into that for complete and incomplete fusion reactions. The angular momentum of the intermediate nucleus formed in incomplete fusion was deduced from the isomeric cross-section ratio by considering the statistical deexcitation of the incompletely fused composite nucleus. The data show that incomplete fusion is associated with angular momenta slightly smaller than critical angular momentum for complete fusion, indicating the deeper interpenetration of projectile and target nuclei than that in peripheral collisions.     

Wave propagation in thermo-chiral elastic medium

The propagation of time harmonic waves through an infinite thermo-chiral elastic material has been investigated. The elastic field of thermo-chiral medium has been described by extending the governing equations and constitutive relations of hemitropic micropolar material to include temperature field. Seven basic waves consisting of three coupled dilatational waves and four coupled shear waves traveling with distinct speeds may exist in the medium. All the waves are found to be dispersive, however the coupled dilatational waves are attenuating and temperature dependent, while the coupled shear waves are independent of temperature field. The phase speeds and corresponding attenuation quality factors of all the coupled dilatational waves have been computed numerically for a specific model. The effect of chirality and temperature field have been shown graphically.