Singular Position Research Articles

Optical singularities in plasmonic fields near single subwavelength holes

We identify phase and polarization singularities in near-field measurements and theoretical modeling of the electric near-field distributions that result from the scattering of surface plasmon polaritons from single subwavelength holes in optically thick gold films. We discuss properties of the singularities, such as their topological charge or the field amplitudes at their locations. We show that it is possible to tune the in-plane field amplitude at the positions of the polarization singularities by three orders of magnitude simply by varying the hole or incident plasmon beam size.

From the Taylor series of analytic functions to their global analysis

We analyze the conditions on the Taylor coefficients of an analytic function to admit global analytic continuation, complementing a recent paper of Breuer and Simon on general conditions for natural boundaries to form. A new summation method is introduced to convert a relatively wide family of infinite sums and local expansions into integrals. The integral representations yield global information such as analytic continuability, position of singularities, asymptotics for large values of the variable and asymptotic location of zeros.

Terahertz–infrared electrodynamics of overdoped manganites La1–xCaxMnO3

We have measured low-temperature terahertz and infrared spectra of La1–xCa xMnO3 with x = 0.5; 0.6; 2/3, 0.7; 3/4, 0.85; 0.9; 0.95; 0.98 and x = 1 in the form of ceramics and epitaxial films. In the charge-ordered state for commensurate dopings (x = 2/3 and 3/4), we observed an absorption band at frequencies corresponding to the position of the lowest energy van Hove singularity in the folded Brillouin zone. The band is assigned to the boson peak. We observed qualitatively the same boson peak in Raman spectra of La1/3Ca2/3MnO3 ceramics. In antiferromagnetic phase, for the 0.5 ≤ x < 0.85 range of doping, the conductivity mechanism gradually changes from a hopping-like transport at low temperatures to the Drude behavior at elevated temperatures in the paramagnetic phase. For 0.85 ≤ x < 1 (canted antiferromagnetic phase), the electrons behave as Drude-like carriers in the whole temperature interval 5–300 K.

Sports and Violence Reflected in the Mirror of Modern Societies: Sport Ambiguities

The theory of Norbert Elias, with regard to the ‘civilising process’, widely taken up and nourished by his epigons such as Eric Dunning, does not fully explain the reasons why sport, far from systematically pacifying, tends equally to reproduce or amplify certain violent tendencies in societal groups, when it does not in itself constitute the germ of the violence in the heart of contemporary societies. In fact, Elias considers the ‘new’ social configuration as a tool used to control violence, forgetting that the institutionalisation of budding practices also bears witness to social and societal transformations, including free time, access to education, growth of cities, the economic development of states, circulation of goods, merchandise and people, the forming of the media and communication cultures, and the dissemination of information and cultural models. The purpose of this study is to show how his singular posture prevents Elias from understanding all the facets of sport as being prey to its own tensions and contradictions, particularly when it is a case of examining the ‘educational’ positions of the activity reflected in the mirror of the socio-historical conditions of the production of culture and the ways in which the practice of sport has been instrumentalised.

Multi-furcation in a derivative queer-square mechanism

This paper investigates the phenomena of multi-furcation through the derivative mechanism from the “queer square” paper fold by allowing a full rotation of the joints and reveals the four categories and fourteen states of multi-furcation based on two phenomena that result in change of mobility and motion type. Specifically, phenomenon one occurs when the mechanism moves past the constraint singularity and subsequently changes the mobility though directions of the joint axes remain the same. Phenomenon two occurs by passing the constraint singularity when the direction of joint axes changes, leading to different mobility. Both phenomena are demonstrated by the derivative queer-square mechanism, on account of its first six states belonging to phenomenon one and its last eight states belonging to phenomenon two. More precisely, for the derivative queer-square mechanism, the change of angle relations for the links, which may form one or two parallel combinations, realises phenomena one and two. Changing from phenomenon one to two is achieved by changing the corresponding angles which makes one of the two parallel combinations to change to antiparallel combination. In each phenomenon, two categories are presented as two different motions, specifically, single translation and double translations belong to phenomenon one and one screw motion about x-axis and one screw motion about y-axis belong to phenomenon two. Different angle ranges make each category split into two states and one state changes to the other state by passing though the singular posture. The analysis of the state configurations is achieved by the platform motion–screw system of the derivative queer-square mechanism via screw theory and the platform motion–screw system presents its ability in mobility change.

Merkel cell polyomavirus: molecular insights into the most recently discovered human tumour virus.

A fifth of worldwide cancer cases have an infectious origin, with viral infection being the foremost. One such cancer is Merkel cell carcinoma (MCC), a rare but aggressive skin malignancy. In 2008, Merkel cell polyomavirus (MCPyV) was discovered as the causative agent of MCC. It is found clonally integrated into the majority of MCC tumours, which require MCPyV oncoproteins to survive. Since its discovery, research has begun to reveal the molecular virology of MCPyV, as well as how it induces tumourigenesis. It is thought to be a common skin commensal, found at low levels in healthy individuals. Upon loss of immunosurveillance, MCPyV reactivates, and a heavy viral load is associated with MCC pathogenesis. Although MCPyV is in many ways similar to classical oncogenic polyomaviruses, such as SV40, subtle differences are beginning to emerge. These unique features highlight the singular position MCPyV has as the only human oncogenic polyomavirus, and open up new avenues for therapies against MCC.

How to Write a Killer Op‐Ed: Sharpening the Persuasive Writing Blade

How to Write a Killer Op‐Ed: Sharpening the Persuasive Writing Blade

Sliding–crawling parallelogram mechanism

This paper introduces two mobile devices based on variations of a single parallelogram mechanism with one degree of freedom. The mechanisms can execute sliding and crawling motions along the ground. Each design has two opposite links in contact with the ground (called left foot and right foot in this paper) and two other links (called the cranks) that move in the air. With the cranks installed on a horizontal plane, and rotating in the same direction, the mechanism can slide along the ground. With the cranks installed on different heights and rotating in opposite sense relative to each other, the mechanism can slide and crawl along the ground. The former design is referred to as the sliding mechanism, and the latter one as the sliding–crawling mechanism. The sliding–crawling mechanism can switch its locomotion modes between sliding and crawling at its singular position. A detailed kinematic and dynamic analysis is presented for both designs. The results of testing the designs via experiments conducted on physical prototypes are presented.

Boson peak in manganites

After the phase transition occurs in manganites La1-xCaxMnO3 (x ≥ 0.5) into a dielectric phase with charge order, right below the corresponding temperature of TCO = 240 K a series of absorption lines appear in the terahertz spectral range, only in case of commensurate x values. We show that the lines originate from acoustic phonons that become optically active by folding of the Brillouin zone. At even lower temperatures, a strongly asymmetric extra absorption band develops at frequencies around 20 cm−1 – 30 cm−1 corresponding to the position of the lowest-energy van Hove singularity in the reduced Brillouin zone. The band is assigned to the Boson Peak, i.e. to the excess of lattice vibrational states over the standard Debye contribution. The folded phonons and the boson peak do not show up for incommensurate calcium.

Some aspects of topology and kinematics of a 3DOF translational parallel mechanism

The paper presents elements of the topology, geometry and the kinematic analysis of a translational parallel mechanism with three degrees of freedom. In such mechanisms the selection of a proper structure and geometry ensures that the driven link maintains a fixed orientation relative to the base. The method of determination of the configuration of mechanisms using contour vector notation was elaborated in the paper. The equations for the analysis of the direct and inverse kinematics task are determined. An analytical procedure for determining the system’s singular positions is presented and illustrated with examples

Population Dynamics with Nonlinear Delayed Carrying Capacity

We consider a class of evolution equations describing the population dynamics in the presence of a carrying capacity depending on the population with delay. In an earlier work, we presented an exhaustive classification of the logistic equation where the carrying capacity is linearly dependent on the population with a time delay, which we refer to as the "linear delayed carrying capacity" model. Here, we generalize it to the case of a nonlinear delayed carrying capacity. The nonlinear functional form of the carrying capacity characterizes the delayed feedback of the evolving population on the capacity of their surrounding by either creating additional means for survival or destroying the available resources. The previously studied linear approximation for the capacity assumed weak feedback, while the nonlinear form is applicable to arbitrarily strong feedback. The nonlinearity essentially changes the behavior of solutions to the evolution equation, as compared to the linear case. All admissible dynamical regimes are analyzed, which can be of the following types: punctuated unbounded growth, punctuated increase or punctuated degradation to a stationary state, convergence to a stationary state with sharp reversals of plateaus, oscillatory attenuation, everlasting fluctuations, everlasting up–down plateau reversals, and divergence in finite time. The theorem is proved that, for the case characterizing the evolution under gain and competition, solutions are always bounded, if the feedback is destructive. We find that even a small noise level profoundly affects the position of the finite-time singularities. Finally, we demonstrate the feasibility of predicting the critical time of solutions having finite-time singularities from the knowledge of a simple quadratic approximation of the early time dynamics.

Topology of arrangements and position of singularities

Topology of arrangements and position of singularities

振幅比对矢量光束相干和非相干叠加合成Stokes奇点的影响

Based on the Stokes parameters,the complex Stokes scalar fields and the Fresnel diffraction integral method,the expressions for the composite Stokes singularities versus amplitude ratioηin two coherently and incoherently superimposed paraxial monochromatic vector optical beams were derived.The properties of composite Stokes singularities in coherently and incoherently superimposed vector optical beams with amplitude ratio propagating in free space were investigated,and the degree of polarization versus the amplitude ratio is analyzed.It is found that,during propagating in free space,the number,position and singularity index of composite Stokes singularities are affected by the amplitude ratio of two vector beams.In the coherent superposition the degree of polarization P=1.At the z=0plane,when the amplitude ratioη≠1,singularity indices of C-points,S23and S31singularities may be reversed.The creation of S23singularity with double singularity index may take place at the z0plane.In the incoherent superposition,the degree of polarization Pis less than 1and is variable withη,by varying the amplitude ratioηV-points may appear,which are unstable and split up into S23singularities and C-points with handedness reversal.With a further increase ofηS23singularities may annihilate.In addition,the sum of singularity indices of composite Stokes singularities is conserved in the process.

振幅比对矢量光束相干和非相干叠加合成Stokes奇点的影响

Based on the Stokes parameters,the complex Stokes scalar fields and the Fresnel diffraction integral method,the expressions for the composite Stokes singularities versus amplitude ratioηin two coherently and incoherently superimposed paraxial monochromatic vector optical beams were derived.The properties of composite Stokes singularities in coherently and incoherently superimposed vector optical beams with amplitude ratio propagating in free space were investigated,and the degree of polarization versus the amplitude ratio is analyzed.It is found that,during propagating in free space,the number,position and singularity index of composite Stokes singularities are affected by the amplitude ratio of two vector beams.In the coherent superposition the degree of polarization P=1.At the z=0plane,when the amplitude ratioη≠1,singularity indices of C-points,S23and S31singularities may be reversed.The creation of S23singularity with double singularity index may take place at the z0plane.In the incoherent superposition,the degree of polarization Pis less than 1and is variable withη,by varying the amplitude ratioηV-points may appear,which are unstable and split up into S23singularities and C-points with handedness reversal.With a further increase ofηS23singularities may annihilate.In addition,the sum of singularity indices of composite Stokes singularities is conserved in the process.

EVD Dualdating Based Online Subspace Learning

Conventional incremental PCA methods usually only discuss the situation of adding samples. In this paper, we consider two different cases: deleting samples and simultaneously adding and deleting samples. To avoid the NP-hard problem of downdating SVD without right singular vectors and specific position information, we choose to use EVD instead of SVD, which is used by most IPCA methods. First, we propose an EVD updating and downdating algorithm, called EVD dualdating, which permits simultaneous arbitrary adding and deleting operation, via transforming the EVD of the covariance matrix into a SVD updating problem plus an EVD of a small autocorrelation matrix. A comprehensive analysis is delivered to express the essence, expansibility, and computation complexity of EVD dualdating. A mathematical theorem proves that if the whole data matrix satisfies the low-rank-plus-shift structure, EVD dualdating is an optimal rank-kestimator under the sequential environment. A selection method based on eigenvalues is presented to determine the optimal rank k of the subspace. Then, we propose three incremental/decremental PCA methods: EVDD-IPCA, EVDD-DPCA, and EVDD-IDPCA, which are adaptive to the varying mean. Finally, plenty of comparative experiments demonstrate that EVDD-based methods outperform conventional incremental/decremental PCA methods in both efficiency and accuracy.

Design and Singularity Analysis for Nine-Bar Mechanism of Three Crank Hybrid Driven

With two degrees of freedom five-bar linkage as the foundation, carry on the multiple loop coupling, built three crank controllable nine bar mechanism similar to that of the crank slider pressing, which can meet the controlled flexible output, and conform to the mechanical properties of crank slider pressing mechanism. We use the loop analysis method to analyze the singularity of the mechanism. Analysis through two steps, first of all analysis on three crank existence conditions and the entire organization singularity, it is concluded that the condition of mechanism dont have singularity, and according to the singular condition carrying on research of singularity position, the long rod assembly condition is obtained.

Eliminating singularity of a parallel driving mechanism of axisymmetric vectoring exhaust nozzle

The singularity is the inherent characteristics of parallel manipulators. At near-singular configurations, the parallel manipulator cannot resist externally applied force/torque along certain directions. The axisymmetric vectoring exhaust nozzle is driven by the 3-SPS + 3-PRS parallel manipulator to change its exit area A9 and make the universal vector of its divergent section. Preventing the 3-SPS + 3-PRS parallel manipulator from falling into the singular configuration is very important for the maneuverability and safety of the jet-thrust aircraft equipping with the axisymmetric vectoring exhaust nozzle. In this paper, a methodology to eliminate the singularity of the 3-SPS + 3-PRS parallel manipulator is presented. At first, with the aid of the configuration homotopy-tracing algorithm, the configuration curves relative to the input parameters are figured out. It is found that the singularity-free zone corresponding to the input parameter exists between the left and the right extreme singular positions. Based on the extended equation algorithm, the curves of singular points going with the input parameters are drawn. By selecting the suitable initial working point and letting the input parameters locate within the singularity-free zones of input parameters determined by these curves, the singularity can be eliminated in the design stage. The method to eliminate the singularity presented in this paper is simple, efficient, and easy to be implemented directly through inspecting the lengths of the input parameters.

Numerical Comparison of Damping Amplification Effects Obtained in Neighbourhood of a Mechanism's Singular Position - Viscous and Electromagnetic Cases

In the paper, effects of numerical investigations are presented. Vibrations of mechanical and electromechanical systems are considered and compared. In the system, a continuous beam is considered as the main vibrating element. Two energy dissipations methods are compared: viscous dampers and DC generators. To increase the damping effectiveness, velocity amplification is proposed, i.e., a mechanism is introduced between the beam and the damping element, and the mechanism configuration is set as closed to the singular position of it. According to some observed fundamental differences in the guiding physical properties of some blocks present in the considered system, two structurally different sub-models are introduced in the numerical model of the complete system. The first sub-model corresponds to the amplification mechanism (considered as composed of rigid elements). The mechanism is modelled as a multibody system. The second sub-model corresponds to the continuous beam. The beam is modelled with used of the finite elements technique. To joint the sub-models, constraint equations are proposed. They express a revolute joint that is present between the mechanisms second rod and the beam enforced to vibrate.

Braking BRAF: AMPK Leaves ERK Stranded in the Desert

In this issue, Shen etal. (2013) show that BRAF phosphorylation by AMPK attenuates BRAF signaling and inhibits cell proliferation. This identifies BRAF as a novel AMPK substrate and further reveals how these pathways interact.

Real time estimation of slant path tropospheric delay at very low elevation based on singular ground‐based global positioning system station

Real time slant path tropospheric delay (STD) is of benefit in near real-time weather forecasting, climatologic applications, and reconstructing refractivity profile. For low elevation ( < 5°), the traditional method precision of calculating STD is poor. A new method of estimating real-time STD at very low elevation (0° − 5°), which is based on singular ground-based Global Positioning System (GPS) with International GPS Service ultra-rapid product, is presented in this study. An experiment was carried out to validate the feasibility on an island in Shantou, south China during July 2009. Results from radiosondes, GPS and models are compared and show that GPS-derived results have agreement with those from radiosonde for low elevation ( < 5°). Consequently, the method can potentially offset some drawbacks of traditional method, and even may be used for monitoring the troposphere without radiosondes in some aspects in the future.