6,632 research outputs found
All-optical diode action with Thue-Morse quasiperiodic photonic crystals
We theoretically investigate the possibility of realizing a nonlinear
all-optical diode by using the unique features of quasiperiodic 1D photonic
crystals. The interplay between the intrinsic spatial asymmetry in odd-order
Thue-Morse lattices and Kerr nonlinearity, combined with the unconventional
field localization properties of this class of quasiperiodic sequences, gives
rise to sharp resonances that can be used to give a polarization-insensitive,
nonreciprocal propagation with a contrast close to unity for low optical
intensities.Comment: submitted to JAP. Scale of Fig. 4 correcte
Thermal and mechanical properties of a DNA model with solvation barrier
We study the thermal and mechanical behavior of DNA denaturation in the frame
of the mesoscopic Peyrard- Bishop-Dauxois model with the inclusion of solvent
interaction. By analyzing the melting transition of a homogeneous A-T sequence,
we are able to set suitable values of the parameters of the model and study the
formation and stability of bubbles in the system. Then, we focus on the case of
the P5 promoter sequence and use the Principal Component Analysis of the
trajectories to extract the main information on the dynamical behavior of the
system. We find that this analysis method gives an excellent agreement with
previous biological results.Comment: Physical Review E (in press
Bounds for the discrete correlation of infinite sequences on k symbols and generalized Rudin-Shapiro sequences
Motivated by the known autocorrelation properties of the Rudin-Shapiro
sequence, we study the discrete correlation among infinite sequences over a
finite alphabet, where we just take into account whether two symbols are
identical. We show by combinatorial means that sequences cannot be "too"
different, and by an explicit construction generalizing the Rudin-Shapiro
sequence, we show that we can achieve the maximum possible difference.Comment: Improved Introduction and new Section 6 (Lovasz local lemma
Deficiency and abelianized deficiency of some virtually free groups
Let be the HNN extension of where the stable letter
conjugates the first factor to the second. We explore small presentations of
the groups . We show that for certain choices of
(m,n), for example (2,3), the group has a relation gap unless it
admits a presentation with at most 3 defining relations, and we establish
restrictions on the possible form of such a presentation. We then associate to
each (m,n) a 3-complex with 16 cells. This 3-complex is a counterexample to the
D(2) conjecture if has a relation gap.Comment: 7 pages; no figures. Minor changes; now to appear in Math. Proc.
Camb. Phil. So
Language extraction from ZnS
Perhaps the most fundamental questions we can ask about a solid are What is it made of? and How are the constituent parts assembled? This is so elementary, and yet so basic to any detailed understanding of the thermal, electrical, magnetic, optical, and elastic properties of materials. At the beginning of the twenty-first century, concern over the placement of the atoms in a solid seems quaint and anachronistic, more suited to the dawn of the twentieth century. X-ray diffraction, electron diffraction, optical microscopy, x-ray diffraction tomography, to name a few, are powerful techniques to uncover structure in solids. With this arsenal of tools, and the efforts of many researchers, surely we can have nothing novel to say about the discovery and description of structure in solids, save perhaps the refinement of well-worn techniques or the analysis of particularly obstinate cases. But careful examination of present technology reveals that while we are quite good at finding and describing periodic order in nature, cases that lack such order are much more difficult. Certainly in the complete absence of structural order, as in a gas, statistical methods exist that permit a satisfying understanding of the properties of the system without knowing ( or even wanting to know) the details of the microscopic placement of the constituents. But it is the in-between cases, where order and disorder coexist, that has proven so elusive to both analyze and describe. In this thesis, we will tackle these in-between cases for a special type of layered material, called polytypes. They exhibit disorder in one dimension only, making the analysis more tractable. We will give a method for determining the structure of these solids from experimental data and demonstrate how this structure, both the random and the non-random part, can be compactly expressed. From our solution, we will be able to calculate the effective range of the inter-layer interactions, as well as the configurational energies of the disordered stacking sequences
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