Confinement dynamics of a semiflexible chain inside nano-spheres.

We study the conformations of a semiflexible chain, confined in nano-scaled spherical cavities, under two distinct processes of confinement. Radial contraction and packaging are employed as two confining procedures. The former method is performed by gradually decreasing the diameter of a spherical shell which envelopes a confined chain. The latter procedure is carried out by injecting the chain inside a spherical shell through a hole on the shell surface. The chain is modeled with a rigid body molecular dynamics simulation and its parameters are adjusted to DNA base-pair elasticity. Directional order parameter is employed to analyze and compare the confined chain and the conformations of the chain for two different sizes of the spheres are studied in both procedures. It is shown that for the confined chains in the sphere sizes of our study, they appear in spiral or tennis-ball structures, and the tennis-ball structure is more likely to be observed in more compact confinements. Our results also show that the dynamical procedure of confinement and the rate of the confinement are influential parameters of the structure of the chain inside spherical cavities.

Definition of the persistence length in the coarse-grained models of DNA elasticity.

By considering the detailed structure of DNA in the base pair level, two possible definitions of the persistence length are compared. One definition is related to the orientation of the terminal base pairs, and the other is based on the vectors which connect two adjacent base pairs at each end of the molecule. It is shown that although these definitions approach each other for long DNA molecules, they are dramatically different on short length scales. We show analytically that the difference mostly comes from the shear flexibility of the molecule and can be used to measure the shear modulus of DNA.

Accessory tragi and associated syndromes involving the first branchial arch.

Although most deformities in front of the tragi are limited abnormalities, they may be signs of certain associated congenital syndromes that result from maldevelopment of the mandibular arch.

Pigmentary changes in Seckel's syndrome.

Seckel's syndrome consists of multiple congenital anomalies, including bird-headed dwarfism, mental deficiency, and skeletal and ophthalmic defects. We report a patient with this syndrome who demonstrated pigmentary changes, including streaks of brown pigmentation on the neck, groin, and axillae. Histologic examination revealed pigment incontinence.