Quantum Spheres for OSp_q(1/2)

Using the corepresentation of the quantum supergroup OSp_q(1/2) a general method for constructing noncommutative spaces covariant under its coaction is developed. In particular, a one-parameter family of covariant algebras, which may be interpreted as noncommutative superspheres, is constructed. It is observed that embedding of the supersphere in the OSp_q(1/2) algebra is possible. This realization admits infinitesimal characterization a la Koornwinder. A covariant oscillator realization of the supersphere is also presented.Comment: 30pages, no figure. to be published in J. Math. Phy

Semi-dynamic connectivity in the plane

Motivated by a path planning problem we consider the following procedure. Assume that we have two points $s$ and $t$ in the plane and take $\mathcal{K}=\emptyset$. At each step we add to $\mathcal{K}$ a compact convex set that does not contain $s$ nor $t$. The procedure terminates when the sets in $\mathcal{K}$ separate $s$ and $t$. We show how to add one set to $\mathcal{K}$ in $O(1+k\alpha(n))$ amortized time plus the time needed to find all sets of $\mathcal{K}$ intersecting the newly added set, where $n$ is the cardinality of $\mathcal{K}$, $k$ is the number of sets in $\mathcal{K}$ intersecting the newly added set, and $\alpha(\cdot)$ is the inverse of the Ackermann function

Tunneling splitting of magnetic levels in Fe8 detected by 1H NMR cross relaxation

Measurements of proton NMR and the spin lattice relaxation rate 1/T1 in the octanuclear iron (III) cluster [Fe8(N3C6H15)6O2(OH)12][Br8 9H2O], in short Fe8, have been performed at 1.5 K in a powder sample aligned along the main anisotropy z axis, as a function of a transverse magnetic field (i.e., perpendicular to the main easy axis z). A big enhancement of 1/T1 is observed over a wide range of fields (2.5-5 T), which can be attributed to the tunneling dynamics; in fact, when the tunneling splitting of the pairwise degenerate m=+-10 states of the Fe8 molecule becomes equal to the proton Larmor frequency a very effective spin lattice relaxation channel for the nuclei is opened. The experimental results are explained satisfactorily by considering the distribution of tunneling splitting resulting from the distribution of the angles in the hard xy plane for the aligned powder, and the results of the direct diagonalization of the model Hamiltonian.Comment: J. Appl. Phys., in pres

Coupled Oscillators with Chemotaxis

A simple coupled oscillator system with chemotaxis is introduced to study morphogenesis of cellular slime molds. The model successfuly explains the migration of pseudoplasmodium which has been experimentally predicted to be lead by cells with higher intrinsic frequencies. Results obtained predict that its velocity attains its maximum value in the interface region between total locking and partial locking and also suggest possible roles played by partial synchrony during multicellular development.Comment: 4 pages, 5 figures, latex using jpsj.sty and epsf.sty, to appear in J. Phys. Soc. Jpn. 67 (1998

New aspects of the Z2_{\textrm 2} ×\times Z2_{\textrm 2}-graded 1D superspace: induced strings and 2D relativistic models

A novel feature of the ${\mathbb Z}_2\times {\mathbb Z}_2$-graded supersymmetry which finds no counterpart in ordinary supersymmetry is the presence of $11$-graded exotic bosons (implied by the existence of two classes of parafermions). Their interpretation, both physical and mathematical, presents a challenge. The role of the "exotic bosonic coordinate" was not considered by previous works on the one-dimensional ${\mathbb Z}_2\times {\mathbb Z}_2$-graded superspace (which was restricted to produce point-particle models). By treating this coordinate at par with the other graded superspace coordinates new consequences are obtained. The graded superspace calculus of the ${\mathbb Z}_2\times {\mathbb Z}_2$-graded worldline super-Poincar\'e algebra induces two-dimensional ${\mathbb Z}_2\times {\mathbb Z}_2$-graded relativistic models; they are invariant under a new ${\mathbb Z}_2\times {\mathbb Z}_2$-graded $2D$ super-Poincar\'e algebra which differs from the previous two ${\mathbb Z}_2\times {\mathbb Z}_2$-graded $2D$ versions of super-Poincar\'e introduced in the literature. In this new superalgebra the second translation generator and the Lorentz boost are $11$-graded. Furthermore, if the exotic coordinate is compactified on a circle ${\bf S}^1$, a ${\mathbb Z}_2\times {\mathbb Z}_2$-graded closed string with periodic boundary conditions is derived. The analysis of the irreducibility conditions of the $2D$ supermultiplet implies that a larger $(\beta$-deformed, where $\beta\geq 0$ is a real parameter) class of point-particle models than the ones discussed so far in the literature (recovered at $\beta=0$) is obtained. While the spectrum of the $\beta=0$ point-particle models is degenerate (due to its relation with an ${\cal N}=2$ supersymmetry), this is no longer the case for the $\beta> 0$ models.Comment: 28 page

Chiral symmetry analysis and rigid rotational invariance for the lattice dynamics of single-wall carbon nanotubes

In this paper, we provide a detailed expression of the vibrational potential for the lattice dynamics of the single-wall carbon nanotubes (SWCNT) satisfying the requirements of the exact rigid translational as well as rotational symmetries, which is a nontrivial generalization of the valence force model for the planar graphene sheet. With the model, the low frequency behavior of the dispersion of the acoustic modes as well as the flexure mode can be precisely calculated. Based upon a comprehensive chiral symmetry analysis, the calculated mode frequencies (including all the Raman and infrared active modes), velocities of acoustic modes and the polarization vectors are systematically fitted in terms of the chiral angle and radius, where the restrictions of various symmetry operations of the SWCNT are fulfilled