Symmetry Of Double Helix Research Articles

Spontaneous Emission of a Two-Level Atom in Chiral Photonic Structures

The spontaneous emission spectrum of a two-level atom in a one-dimensional (1D) anisotropic photonic crystal with symmetry of double helix is investigated using Laplace transform. Properties of spectrum of the radiation modes are discussed in detail under different values of detuning of atomic resonant frequency from a band-edge. Since spontaneous emission is proportional to the density of states (DOS), it is suppressed within the reflection band, corresponding to vanishing of the DOS. However, it is enhanced at the band edge. Therefore, spontaneous emission spectrum of the system is influenced at the edge of the stop band rather than at its centre.

Coupled-Mode Analysis for Chiral Fiber Long-Period Gratings Using Local Mode Approach

Starting from the conventional coupled-mode theory and using the mode transformation method, a unified local mode approach is presented to analyze the chiral fiber long-period gratings (CLPGs) formed by twisting a high-birefringence fiber as an example of a chiral fiber with double-helix symmetry. Similarly, a helical-core fiber, as an example of single-helix CLPGs, is analyzed by using the ideal mode approach. The coupled-mode equations for both the cases are transformed and reduced to two-mode equations. The derivation is simple, and the results are explicit in concept. These results reveal the scheme of polarization selectivity of mode coupling, and for the first time, the necessary condition for achieving the polarization selection is given. The analysis indicates that conventional coupled-mode theory is efficient for studying chiral fiber grating, and more importantly, it is better to be understood. A numerical simulation has been done on a twisted conventional Panda fiber with a beat length of 2.5 mm. It has been shown that in a right-handed twisted structure, a total power transfer of a right-handed circular polarization light is obtained with a grating pitch of 0.382 mm and a grating length of 64.9 mm at the wavelength of 1.55 μm . On the other hand, through the simulation on single-helix CLPG with an eccentric core, it has been shown that a total power transfer of the core mode to LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode is obtained with a grating pitch of 0.723 mm and a grating length of 10.46 mm at the wavelength of 1.55 μm.

Optimized Design of 1GYF-200 Sugarcane Leaf Shattering and Returning Machine’s Cutter Roller

After studying and analyzing the types of cutter roller’s movable blades, various arrangements and layouts of movable blades and structures of such cutter roller of current sugarcane leaf shattering and returning machine in China, a totally new cutter roller design is proposed for 1GYF-200 sugarcane leaf shattering and returning machine: blades are arranged in unequally-spaced double-helix symmetry, the movable blades arranged on both sides of the cutter roller are increased appropriately, and combination of two straight blades and one improved L-blade are adopted as movable blades. Comparing with the original prototype, the improved machine’s pick-up rate has increased by 0.8% and shattering rate has improved by 2.5%. This study provides theoretical basis and reference in designing an effective and reliable machine for shattering sugarcane leaves and incorporating it into soil.

Single- and double-helix chiral fiber sensors

Copropagating core and cladding modes in optical fibers can be coupled by a grating with a period greatly exceeding the wavelength, since their propagation constants are similar. In contrast to conventional long-period gratings, in which the modulation is imposed by exposing a photosensitive core to ultraviolet light, we have created chiral long-period gratings with single- or double-helix symmetry by twisting optical fibers with nonconcentric or noncircular cores, respectively, as they pass through a short heat zone. The difference in symmetry between single- and double-helix gratings is manifested in their polarization properties. The use of these gratings as sensors of liquid level and temperature is demonstrated.

Chiral fiber gratings.

Chiral gratings with double helix symmetry were produced by twisting glass optical fiber with a noncircular core cross section as it passed through a miniature oven. We observed polarization-selective transmission in chiral fibers with pitches of tens of micrometers. Two modes of optical interaction were differentiated. In chirallong-period gratings, dips in transmission were observed at wavelengths associated with scattering into distinct cladding modes mediated by the chiral grating. In chiral intermediateperiod gratings, a broad scattering band was observed. These gratings can be used to produce sharp or broad polarization-selective filters.

Double-helix chiral fibers.

A polarization-selective photonic stop band is demonstrated in a new chiral fiber structure with double-helix symmetry. The stop band exists for only circularly polarized radiation with the same handedness as the structure and is centered at a wavelength in the fiber equal to the fiber pitch. When one part of the chiral fiber is twisted about its axis, a localized mode is produced, which can be tuned across the gap by changing the twist angle. Observations in single-mode fibers are in good agreement with one-dimensional simulations of a dispersive cholesteric material. At higher frequencies, however, we find a sharp onset of a broad polarization-selective scattering band, which is not present in one-dimensional simulations.

Concerted motion of protons in hydrogen bonds of DNA-type molecules

We study the dynamical behaviour of the proton transfer in the hydrogen bonds in the base-pairs of the double helices of the DNA type. Under the assumption that the elastic and the tunnelling degrees of freedom may be coupled, we derive a non-linear and non-local Schrodinger equation (SNLNL) that describes the concerted motion of the proton tunnelling. Rough estimates of the solutions to the SNLNL show an intimate interplay between the concerted tunnelling of protons and the symmetry of double helix.