Non-zero Index Research Articles

Modal birefringence in weakly guiding fibers

We examine wave propagation in few-mode and multimode fibers with a small index difference between core and cladding, where linearly polarized (LP) “modes” serve as a highly useful simplified solution. However, for a nonzero index difference, each LP “mode” decomposes into two true fiber waveguide modes, typically an HE and an EH mode. These two constituent modes have different group delays, which results in an effect termed modal birefringence. This effect needs to be understood in the design of mode-multiplexed transmission systems. We report an analysis of modal birefringence including scaling rules for fiber design, and provide numerical results for about 50 of the lower order modes.

Topological crystalline insulators in the SnTe material class

Topological crystalline insulators are new states of matter in which the topological nature of electronic structures arises from crystal symmetries. Here we predict the first material realization of topological crystalline insulator in the semiconductor SnTe by identifying its non-zero topological index. We predict that as a manifestation of this non-trivial topology, SnTe has metallic surface states with an even number of Dirac cones on high-symmetry crystal surfaces such as {001}, {110} and {111}. These surface states form a new type of high-mobility chiral electron gas, which is robust against disorder and topologically protected by reflection symmetry of the crystal with respect to {110} mirror plane. Breaking this mirror symmetry via elastic strain engineering or applying an in-plane magnetic field can open up a continuously tunable band gap on the surface, which may lead to wide-ranging applications in thermoelectrics, infra-red detection and tunable electronics. Closely related semiconductors PbTe and PbSe also become topological crystalline insulators after band inversion by pressure, strain and alloying.

A practical design of digital video watermarking in H.264/AVC for content authentication

In this research, we propose a practical digital video watermarking scheme mainly used for authenticating the H.264/AVC compressed videos to ensure their correct content order. The watermark signals, which represent the serial numbers of video segments, are embedded into nonzero quantization indices of frames to achieve both the effectiveness of watermarking and the compact data size. The human visual characteristics are taken into account to guarantee the imperceptibility of watermark signals and to attain an efficient implementation in H.264/AVC. The issues of synchronized watermark detections are settled by selecting the shot-change frames for calculating the distortion-resilient hash, which helps to determine the watermark sequence. The experimental results demonstrate the feasibility of the proposed scheme as the embedded watermarks can survive the allowed transcoding processes while the edited segments in the tampered video can be located.

Redistribution Mechanisms for Assignment of Heterogeneous Objects

There are p heterogeneous objects to be assigned to n competing agents (n > p) each with unit demand. It is required to design a Groves mechanism for this assignment problem satisfying weak budget balance, individual rationality, and minimizing the budget imbalance. This calls for designing an appropriate rebate function. When the objects are identical, this problem has been solved which we refer as WCO mechanism. We measure the performance of such mechanisms by the redistribution index. We first prove an impossibility theorem which rules out linear rebate functions with non-zero redistribution index in heterogeneous object assignment. Motivated by this theorem, we explore two approaches to get around this impossibility. In the first approach, we show that linear rebate functions with non-zero redistribution index are possible when the valuations for the objects have a certain type of relationship and we design a mechanism with linear rebate function that is worst case optimal. In the second approach, we show that rebate functions with non-zero efficiency are possible if linearity is relaxed. We extend the rebate functions of the WCO mechanism to heterogeneous objects assignment and conjecture them to be worst case optimal.

A novel image denoising algorithm in wavelet domain using total variation and grey theory

Purpose – The traditional total variation (TV) models in wavelet domain use thresholding directly in coefficients selection and show that Gibbs' phenomenon exists. However, the nonzero coefficient index set selected by hard thresholding techniques may not be the best choice to obtain the least oscillatory reconstructions near edges. This paper aims to propose an image denoising method based on TV and grey theory in the wavelet domain to solve the defect of traditional methods.Design/methodology/approach – In this paper, the authors divide wavelet into two parts: low frequency area and high frequency area; in different areas different methods are used. They apply grey theory in wavelet coefficient selection. The new algorithm gives a new method of wavelet coefficient selection, solves the nonzero coefficients sort, and achieves a good image denoising result while reducing the phenomenon of “Gibbs.”Findings – The results show that the method proposed in this paper can distinguish between the information of ...

Social structure of bottlenose dolphins,Tursiops truncatus, in Panama City, Florida

Social organization is an important attribute of the animal society. We describe the social structure of a bottlenose dolphins population living in Panama City, a seaside resort located on the north-west coast of Florida. Study was conducted with 46 individuals. Dolphins are associated on average half weight index of 0.11. Preferred long-term associations are observed. The proportion of the non-zero association indices suggests that some dolphins seem to avoid others. Associations between and within sex-classes were investigated using only dolphins of known sex and observed at least 4 times. Highly significant differences are found in associations between and within sex-classes (Mantel test,t = 3.7987;P = 1); indeed, male associations are stronger than between inter-sexual associations or between females only. Sociogram of males reveals a complex network with strong associations between pairs or trios that reach up to 0.97, whereas female associations are lower than males. The cluster analysis shows no clear division in the social organization of bottlenose dolphins in Panama City, except for dyads, triads and their multiple networks. The population structure seems to be temporally stable over the study and constant companionships are observed in the dolphin population in Panama City.

Spectral Triples and the Super-Virasoro Algebra

We construct infinite dimensional spectral triples associated with representations of the super-Virasoro algebra. In particular the irreducible, unitary positive energy representation of the Ramond algebra with central charge c and minimal lowest weight h = c/24 is graded and gives rise to a net of even θ-summable spectral triples with non-zero Fredholm index. The irreducible unitary positive energy representations of the Neveu-Schwarz algebra give rise to nets of even θ-summable generalised spectral triples where there is no Dirac operator but only a superderivation.

Dynamical toroidal Hopfions in a ferromagnet with easy-axis anisotropy

Three-dimensional toroidal precession solitons with a nonzero Hopf index, which uniformly move along the anisotropy axis in a uniaxial ferromagnet, have been found. The structure and existence region of the solitons have been numerically determined by solving the Landau-Lifshitz equation.

THE EXISTENCE AND CLASSIFICATION OF SYNCHRONY-BREAKING BIFURCATIONS IN REGULAR HOMOGENEOUS NETWORKS USING LATTICE STRUCTURES

For regular homogeneous networks with simple eigenvalues (real or complex), all possible explicit forms of lattices of balanced equivalence relations can be constructed by introducing lattice generators and lattice indices [Kamei, 2009]. Balanced equivalence relations in the lattice correspond to clusters of partially synchronized cells in a network. In this paper, we restrict attention to regular homogeneous networks with simple real eigenvalues, and one-dimensional internal dynamics for each cell. We first show that lattice elements with nonzero indices indicate the existence of codimension-one synchrony-breaking steady-state bifurcations, and furthermore, the positions of such lattice elements give the number of partially synchronized clusters. Using four-cell regular homogeneous networks as an example, we then classify a large number of regular homogeneous networks into a small number of lattice structures, in which networks share an equivalent clustering type. Indeed, some of these networks even share the same generic bifurcation structure. This classification leads us to explore how regular homogeneous networks that share synchrony-breaking bifurcation structure are topologically related.

Fractional Quantum Hall Effects in Graphene and Its Bilayer

Single-layer and Bilayer of graphene are new classes of two-dimensional electron systems with unconventional band structures and valley degrees of freedom. The ground states and excitations in the integer and fractional quantum Hall regimes are investigated on torus and spherical geometries with the use of the density matrix renormalization group (DMRG) method. At nonzero Landau level indices, the ground states at effective filling factors 1, 1/3, 2/3 and 2/5 are valley polarized both in single-layer and bilayer graphenes. We examine the elementary charge excitations which could couple with the valley degrees of freedom (so called valley skyrmions). The excitation gaps are calculated and extrapolated to the thermodynamic limit. The largest excitation gap at effective filling 1/3 is obtained in bilayer graphene, which is a good candidate for experimental observation of fractional quantum Hall effect.

Existence of regularly varying solutions with nonzero indices of half-linear differential equations with retarded arguments

Sharp conditions are established for the existence of a pair of regularly varying solutions with nonzero indices of half-linear functional differential equations of the type ( | x ′ ( t ) | α sgn x ′ ( t ) ) ′ = q ( t ) | x ( g ( t ) ) | α sgn x ( g ( t ) ) , α > 0 , q ( t ) > 0 , g ( t ) < t .

Effects of osteoarthritis on radiographic measures of laxity and congruence in hip joints of Labrador Retrievers

OBJECTIVE- To determine effects of hip joint osteoarthritis on radiographic measures of hip joint laxity and congruence. DESIGN- Longitudinal study. ANIMALS- 40 Labrador Retrievers. PROCEDURES- Dogs were assigned to 2 groups based on radiographic evidence of osteoarthritis. Dogs in the osteoarthritis group were free of osteoarthritis at initial radiographic evaluation (t(1)) and developed osteoarthritis by a subsequent radiographic evaluation (t(2)). Dogs in the nonosteoarthritis group had no radiographic osteoarthritis at either evaluation. Hip joint laxity was quantified by use of the distraction index (DI) from a distraction radiographic view and use of the Norberg angle (NA) from a ventrodorsal hip-extended radiographic view. The compression index (CI) from a compression radiographic view was used as a measure of joint congruence (concentricity). RESULTS- Hip joint laxity (NA or DI) did not change over time in the nonosteoarthritis group. Mean hip joint laxity (NA and DI) for the osteoarthritis group was greater at t(1) than for the nonosteoarthritis group. With the onset of osteoarthritis, mean NA decreased significantly and mean CI increased significantly, but mean DI remained unchanged. CONCLUSIONS AND CLINICAL RELEVANCE- No radiographic evidence for compensatory hip joint tightening associated with osteoarthritis was detected. Hip-extended radiography revealed that hip joints got looser with osteoarthritis and NA decreased. Hip joint laxity (DI) on distraction radiographs was unchanged by the onset of osteoarthritis and remained constant in the osteoarthritis and nonosteoarthritis groups at both evaluations. However, the CI increased with osteoarthritis, as reflected in nonzero indices (incongruence). The CI may be a valid marker for early hip joint osteoarthritis.

Polarization-maintaining photonic bandgap Bragg fiber

The possibility of fabricating a polarization-maintaining Bragg fiber has been studied. It is shown that violation of the cylindrical symmetry of a Bragg mirror in most cases results in a sharp increase in optical loss, which is caused by resonance transmission through the Bragg mirror at wavelengths near the cutoffs of the modes of the high-index rings with a nonzero azimuthal index. It is shown that placing stress-applied parts or air holes inside the Bragg fiber core allows one to avoid this effect. A polarization-maintaining Bragg fiber with perfect light confinement in the core is demonstrated for the first time to our knowledge.

Asymmetry and non-zero mean of neuronal oscillations: What is essential for the generation of evoked responses?

Evoked responses (ERs) from magneto- and electroencephalographic recordings (MEG/EEG) are the primary real-time objective measures of cognitive and perceptual processes in the human brain. For the past fifty years, only two mechanisms for the generation of ERs have been discussed in the literature: „additive“ responses and „phase resetting“ of ongoing oscillations. Recently we introduced a novel mechanism for the generation of ERs (Nikulin et al., 2007), which can be deduced entirely from the properties of the ongoing neuronal oscillations, e.g., alpha oscillations. We have shown analytically and experimentally that neuronal oscillations with a non-zero mean (i.e., the integrated field of one oscillatory cycle is not zero) is a sufficient prerequisite for oscillations to contribute to evoked responses through a mechanism of amplitude modulation. Recently in another study (Mazaheri and Jensen, 2008) it was proposed that an „amplitude fluctuation asymmetry index“ (AFA, the amplitude asymmetry of peaks and troughs around zero) might reveal whether or not an amplitude modulation of oscillations contributes to ERs. Necessarily, oscillations with a non-zero mean will have a non-zero AFA index. Critically, however, the reverse is not true in general, because – as we show here – the AFA index is sensitive also to the non-sinusoidal (e.g., comb-like) shape of neuronal oscillations. We prove analytically and experimentally that the amplitude modulation of non-sinusoidal oscillations with zero mean cannot give rise to evoked responses. Consequently, it is not possible to infer from the AFA index of an oscillation whether its amplitude modulation will contribute to an evoked response. It is therefore crucial to choose methodological approach that is specifically sensitive to the non-zero-mean properties of neuronal oscillations in order to be able to make conclusions about the contribution of the novel ER mechanism to the measured data.

Discovering subword associations in strings in time linear in the output size

Given a text string x of n symbols and an integer constant d, we consider the problem of finding, for any pair ( y , z ) of subwords of x, the tandem index associated with the pair, which is defined as the number of times that y and z occur in tandem (i.e., with no intermediate occurrence of either one of them) within a distance of d symbols of x. Although in principle there might be O ( n 4 ) distinct subword pairs in x, it is seen that it suffices to consider a family of only O ( n 2 ) such pairs, with the property that for any neglected pair ( y ′ , z ′ ) there exists a corresponding pair ( y , z ) contained in our family such that: (i) y ′ is a prefix of y and z ′ is a prefix of z; and (ii) the tandem index of ( y ′ , z ′ ) equals that of ( y , z ) . The main contribution of the paper consists of an algorithm showing that the computation of all non-zero tandem indices for a string can be carried out optimally in time and space linear in the size of the output.

Stationary precession topological solitons with nonzero Hopf invariant in a uniaxial ferromagnet

Three-dimensional stationary precession solitons with nonzero Hopf indices are found numerically by solving the Landau-Lifshitz equation. The structure and existence domain of the solitons are found.

Characterization of enantiospecific chemisorption on chiral Cu surfaces vicinal to Cu(111) and Cu(100) using density functional theory

Surfaces of simple fcc metals such as Cu with nonzero and unequal Miller indices are intrinsically chiral. Density functional theory (DFT) calculations are a useful way to study the enantiospecific adsorption of small chiral molecules on these chiral metal surfaces. We report DFT calculations of seven chiral molecules on several structurally distinct chiral Cu surfaces. These surfaces include two surfaces with (111)-oriented terraces and one with (100)-oriented terraces. Calculations are also described on a surface that was modified to mimic the surface structures that typically appear on real metal surfaces following thermally driven fluctuations in step edges. Our results provide initial information on how variation in the surface structure of intrinsically chiral metal surfaces can affect the enantiospecific adsorption of small molecules on these surfaces.

Propagation and diffraction of optical vortices

We explore the propagation and diffraction of optical vortices (Laguerre–Gaussian beams) of varying azimuthal index past a circular obstacle and Young’s double slits. When the beam and obstacle centers are aligned the famous spot of Arago, which arises for zero azimuthal index, is replaced for non-zero azimuthal indices by a dark spot of Arago, a simple consequence of the conserved phase singularity at the beam center. We explore how for larger azimuthal indices, as the beam and obstacle centers are progressively misaligned, the central dark spot breaks up into several dark spots of Arago. Using Young’s double slits we can easily measure the azimuthal index of the vortex beam, even for polychromatic vortices generated by broadband supercontinuum radiation.

The dark spots of Arago

We explore the diffraction and propagation of Laguerre- Gaussian beams of varying azimuthal index past a circular obstacle both experimentally and numerically. When the beam and obstacle centers are aligned the famous spot of Arago, which arises for zero azimuthal index, is replaced for non-zero azimuthal indices by a dark spot of Arago, a simple consequence of the conserved phase singularity at the beam center. We explore how the dark spot of Arago behaves as the beam and obstacle centers are progressively misaligned, and find that the central dark spot may break into several dark spots of Arago for higher incident azimuthal index beams.

Interfacial electronic structure of magnesium deposited on Ag-covered tris(8-hydroxyquinolato) aluminum film: A synchrotron radiation photoemission study

The deposition of magnesium on tris(8-hydroxyquinolato) aluminum (Alq3) precovered with thin silver was investigated with high resolution synchrotron radiation photoemission. The noble-metal deposit first occupies the vicinity of the pyridyl ring. The appearance of a Fermi level suggests that the incorporated Ag behaves as a metallic cluster, consistent with the results of the Ag 3d cores, which show a nonzero Doniach-Sunjic singularity index of 0.061. Upon Mg adsorption on the Ag∕Alq3 surface, a MgAg mixture begins to develop such that the Ag 4d valence band becomes narrowed and its centroid shifts towards higher binding energy. A phase transformation is thus observed at the interface, from a Ag-rich phase to a Mg-rich phase. The product of the MgAg mixture prevents subsequent Mg atoms from penetrating into the Alq3 film, which grows as a metal on top of the MgAg∕Alq3 interface.