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A new type of step-index optical fiber, the helically cladded fiber (HCF), in which a conducting sheath helix is introduced at the core–cladding interface boundary, is proposed. By application of the appropriate sheathhelix boundary condition at the core–cladding interface, the modal characteristic equation is determined. The dispersion curves are also obtained. Analysis of the modal characteristic equation and dispersion curves reveals that only hybrid modes are supported, and the lowest-order mode is HE_01. The pitch angle of the helix has no effect on the cutoff condition. Its effect is more pronounced in the case of the first odd modes. One retrieves the modal characteristics of the step-index fiber by setting the pitch angle equal to zero. Further, a fact of technical importance emerges: that the HCF behaves as a monomode guide for a comparatively large core radius.

For improved DIAL measurements of water vapor in the upper troposphere or lower stratosphere, we have generated narrowband (~0.03-cm^−1) laser radiation at 720- and 940-nm wavelengths by stimulated Raman scattering (SRS) using the narrow linewidth (~0.02-cm^−1) output of a Nd:YAG-pumped dye laser. For a hydrogen pressure of 350 psi, the first Stokes conversion efficiencies to 940 nm were 20% and 35% when using a conventional and waveguide Raman cell, respectively. We measured the linewidth of the first Stokes line at high cell pressures and inferred collisional broadening coefficients that agree well with those previously measured in spontaneous Raman scattering.

Assembly of polyribosomes is the ubiquitous manifestation of the activation of translational machinery in cells. This is accompanied by a concomitant appearance of mRNAs either from an activation of pre-existing ribo-nucleoprotein particles (RNP) or from newly synthesized transcripts. The size-distributions of polyribosomes as inferred from their sedimentation profiles are essentially defined by various kinetic parameters responsible for continuous flux of ribosomes due to their recycling between the “free” and the “bound” states. In the theoretical analysis presented here the time-evolution of polyribosomes and their sustenance in the steady state is considered as a Markovian process with the states of mRNAs defined as the number of ribosomes attached. Expressions for the elements of one-step transition matrix as a function of kinetic parameters related to the initiation, translocation and the release of ribosomes and the size of mRNA are derived. The latter is shown to be relevant only in so far as it sets an upper limit to the size of polyribosomes. Implications of transient arrest of ribosomes at the initiation site as envisaged in the signal hypothesis for the synthesis of secretory proteins and the putative role of receptor-mediated post-translational transport of proteins have been examined. Results of computer simulations on model systems have focused attention on the diverse types of profiles that may appear under varying physiological conditions.

The radial distribution function (RDF) and thermodynamic properties of a two-dimensional hard-disc mixture are calculated by using the perturbation theory. Numerical results are given for theRDF, pressure and excess-free energy of the binary mixture of both additive and non-additive hard discs. It is found that the thermodynamic properties of the binary mixture of non-additive hard discs increase with Δ, the non-additive parameter.

Thermodynamic properties of molecular fluid mixtures of hard ellipsoids are calculated. Numerical results are given for equation of state and excess-free energy of the binary mixture of both additive and non-additive hard ellipsoids. It is found that the equation of state and free energy of mixtures increase with increase of anisotropy parameterx0.

If $ T$ $ {S^{ - 1}}{T^{ - 1}}S = {T^ \ast }$ $ 0 \notin {\text{Cl}}(W(S))$, where $ {\text{Cl}}(W(S))$ and $ {T^ \ast }$, then it is shown that is similar to a unitary operator. In fact, this has been proved as a corollary to a more general result, which also includes the corresponding result of J. P. Williams for selfadjoint operators.