Souza Dutra, A. de; Santos, V. G. C. S. dos; Amaro de Faria, A. C. Jr.
2007-06-15
Some kinks for non-Hermitian quantum field theories in 1+1 dimensions are constructed. A class of models where the soliton energies are stable and real are found. Although these kinks are not Hermitian, they are symmetric under PT transformations.
NASA Astrophysics Data System (ADS)
West, Carl T.; Kottos, Tsampikos; Prosen, Tomaz
2010-03-01
We study a new class of chaotic systems with dynamical localization, where gain/loss processes break the hermiticity, while allowing for parity-time PT symmetry. For a value γPT of the gain/loss parameter the spectrum undergoes a spontaneous phase transition from real (exact phase) to complex values (broken phase). We develop a one parameter scaling theory for γPT, and show that chaos assists the exact PT-phase. Our results will have applications to the design of optical elements with PT-symmetry.
NASA Astrophysics Data System (ADS)
Christodoulides, Demetrios
2015-03-01
Interest in complex Hamiltonians has been rekindled after the realization that a wide class of non-Hermitian Hamiltonians can have entirely real spectra as long as they simultaneously respect parity and time reversal operators. In non-relativistic quantum mechanics, governed by the Schrödinger equation, a necessary but not sufficient condition for PT symmetry to hold is that the complex potential should involve real and imaginary parts which are even and odd functions of position respectively. As recently indicated, optics provides a fertile ground to observe and utilize notions of PT symmetry. In optics, the refractive index and gain/loss profiles play the role of the real and imaginary parts of the aforementioned complex potentials. As it has been demonstrated in several studies, PT-symmetric optical structures can exhibit peculiar properties that are otherwise unattainable in traditional Hermitian (conservative) optical settings. Among them, is the possibility for breaking this symmetry through an abrupt phase transition, band merging effects and unidirectional invisibility. Here we review recent developments in the field of -symmetric optics.
Step- vs. kink-formation energies on Pt(111)
FEIBELMAN,PETER J.
2000-05-01
Ab-initio kink-formation energies are about 0.25 and 0.18 eV on the (100)- and (111)-microfacet steps of Pt(111), while the sum of the step-formation energies is 0.75 eV/atom. These results imply a specific ratio of formation energies for the two step types, namely 1.14, in excellent agreement with experiment. If kink-formation costs the same energy on the two step types, an inference recently drawn from scanning probe observations of step wandering, this ratio ought to be 1.
Q kink of the nonlinear O(3) {sigma} model involving an explicitly broken symmetry
Loginov, A. Yu.
2011-05-15
The (1 + 1)-dimensional nonlinear O(3) {sigma} model involving an explicitly broken symmetry is considered. Sphalerons are known to exist in this model. These sphalerons are of a topological origin and are embedded kinks of the sine-Gordon model. In the case of a compact spatial manifold S{sup 1}, sine-Gordon multikinks exist in the model. It is shown that the model admits a nonstatic generalization of the sine-Gordon kink/multikink, Q kink/multikink. Explicit expressions are obtained for the dependence of the Q kink energy and charge on the phase frequency of rotation. The Q kink is studied for stability, and expressions are obtained for the eigenfunctions and eigenfrequencies of the operator of quadratic fluctuations. It is shown that the Q kink is unstable over the entire admissible frequency range {omega} Element-Of [-1, 1]. The one-loop quantum correction to the static-kink mass is calculated, and the Q-kink zero mode is quantized. It is shown that, in a general static case, the field equations of the model are integrable in quadratures.
\\cal{PT} -symmetry in Rydberg atoms
NASA Astrophysics Data System (ADS)
Ziauddin; Chuang, You-Lin; Lee, Ray-Kuang
2016-07-01
We propose a scheme to realize parity-time ( {PT} )-symmetry in an ensemble of strongly interacting Rydberg atoms, which act as superatoms due to the dipole blockade mechanism. We show that Rydberg-dressed 87Rb atoms in a four-level inverted Y-type configuration is highly efficient to generate the refractive index for a probe field, with a symmetric (antisymmetric) profile spatially in the corresponding real (imaginary) part. Comparing with earlier investigations, the present scheme provides a versatile platform to control the system from {PT} -symmetry to non-PT -symmetry via different external parameters, i.e., coupling field detuning, probe field intensity and control field intensity.
Yang, Fan; Lei Mei, Zhong
2015-01-01
The concept of parity-time (PT) symmetry in SPPs is proposed and confirmed for the first time in this work. By introducing periodic modulation of the effective refractive index in SPP system, the asymmetric propagation is theoretically predicted and numerically demonstrated. After validation of this concept, we apply it in two applications: PT-waveguide and PT-cloak. Both two applications further illustrate the wide applicability of this concept in SPP system. PMID:26446520
PT Symmetry, Conformal Symmetry, and the Metrication of Electromagnetism
NASA Astrophysics Data System (ADS)
Mannheim, Philip D.
2016-05-01
We present some interesting connections between PT symmetry and conformal symmetry. We use them to develop a metricated theory of electromagnetism in which the electromagnetic field is present in the geometric connection. However, unlike Weyl who first advanced this possibility, we do not take the connection to be real but to instead be PT symmetric, with it being iA_{μ } rather than A_{μ } itself that then appears in the connection. With this modification the standard minimal coupling of electromagnetism to fermions is obtained. Through the use of torsion we obtain a metricated theory of electromagnetism that treats its electric and magnetic sectors symmetrically, with a conformal invariant theory of gravity being found to emerge. An extension to the non-Abelian case is provided.
Point interactions, metamaterials, and PT-symmetry
NASA Astrophysics Data System (ADS)
Mostafazadeh, Ali
2016-05-01
We express the boundary conditions for TE and TM waves at the interfaces of an infinite planar slab of homogeneous metamaterial as certain point interactions and use them to compute the transfer matrix of the system. This allows us to demonstrate the omnidirectional reflectionlessness of Veselago's slab for waves of arbitrary wavelength, reveal the translational and reflection symmetry of this slab, explore the laser threshold condition and coherent perfect absorption for active negative-index metamaterials, introduce a point interaction modeling phase-conjugation, determine the corresponding antilinear transfer matrix, and offer a simple proof of the equivalence of Veselago's slab with a pair of parallel phase-conjugating plates. We also study the connection between certain optical setups involving metamaterials and a class of PT-symmetric quantum systems defined on wedge-shape contours in the complex plane. This provides a physical interpretation for the latter.
PT-symmetry breaking in resonant tunneling heterostructures
NASA Astrophysics Data System (ADS)
Gorbatsevich, A. A.; Shubin, N. M.
2016-06-01
We present fermionic model based on symmetric resonant tunneling heterostructure, which demonstrates spontaneous symmetry breaking in respect to combined operations of space inversion (P) and time reversal (T). PT-symmetry breaking manifests itself in resonance coalescence (collapse of resonances). We show that resonant energies are determined by eigenvalues of auxiliary pseudo-Hermitian PT-invariant Hamiltonian.
Giant Goos-Hänchen shift using PT symmetry
NASA Astrophysics Data System (ADS)
Ziauddin; Chuang, You-Lin; Lee, Ray-Kuang
2015-07-01
Influence of PT symmetry on the Goos-Hänchen (GH) shift in the reflected light is presented for an ensemble of atomic medium in a cavity, in the configuration of four-level N -type (87Rb atoms) systems driving by two copropagating strong laser fields and a weak probe field. The atom-field interaction follows the realization of PT symmetry by adjusting the coupling field detunings [J. Shenget al., Phys. Rev. A 88, 041803(R) (2013), 10.1103/PhysRevA.88.041803]. A giant enhancement for the GH shift in the reflected light is revealed when the PT -symmetry condition is satisfied.
Local PT symmetry violates the no-signaling principle.
Lee, Yi-Chan; Hsieh, Min-Hsiu; Flammia, Steven T; Lee, Ray-Kuang
2014-04-01
Bender et al. [Phys. Rev. Lett. 80, 5243 (1998)] have developed PT-symmetric quantum theory as an extension of quantum theory to non-Hermitian Hamiltonians. We show that when this model has a local PT symmetry acting on composite systems, it violates the nonsignaling principle of relativity. Since the case of global PT symmetry is known to reduce to standard quantum mechanics A. Mostafazadeh [J. Math. Phys. 43, 205 (2001)], this shows that the PT-symmetric theory is either a trivial extension or likely false as a fundamental theory. PMID:24745396
Twofold PT symmetry in doubly exponential optical lattices
NASA Astrophysics Data System (ADS)
Cole, J. T.; Makris, K. G.; Musslimani, Z. H.; Christodoulides, D. N.; Rotter, S.
2016-01-01
We introduce a family of non-Hermitian optical potentials that are given in terms of double-exponential periodic functions. The center of PT symmetry is not around zero and the potential satisfies a shifted PT -symmetry relation at two distinct locations. Motivated by wave transmission through thin phase screens and gratings, we examine these refractive index modulations from the perspective of optical lattices that are homogeneous along the propagation direction. The diffraction dynamics, abrupt phase transitions in the eigenvalue spectrum, and exceptional points in the band structure are examined in detail. In addition, the nonlinear properties of wave propagation in Kerr nonlinearity media are studied. In particular, coherent structures such as lattice solitons are numerically identified by applying the spectral renormalization method. The spatial symmetries of such lattice solitons follow the shifted PT -symmetric relations. Furthermore, such lattice solitons have a power threshold and their linear and nonlinear stabilities are critically dependent on their spatial symmetry point.
Unbreakable PT symmetry of solitons supported by inhomogeneous defocusing nonlinearity.
Kartashov, Yaroslav V; Malomed, Boris A; Torner, Lluis
2014-10-01
We consider bright solitons supported by a symmetric inhomogeneous defocusing nonlinearity growing rapidly enough toward the periphery of the medium, combined with an antisymmetric gain-loss profile. Despite the absence of any symmetric modulation of the linear refractive index, which is usually required to establish a parity-time (PT) symmetry in the form of a purely real spectrum of modes, we show that the PT symmetry is never broken in the present system, and that the system always supports stable bright solitons, i.e., fundamental and multi-pole ones. This fact is connected to the nonlinearizability of the underlying evolution equation. The increase of the gain-loss strength results, in lieu of the PT symmetry breaking, in merger of pairs of different soliton branches, such as fundamental and dipole, or tripole and quadrupole ones. The fundamental and dipole solitons remain stable at arbitrarily large values of the gain-loss coefficient. PMID:25360948
Non-Hermitian quantum Hamiltonians with PT symmetry
Jones-Smith, Katherine; Mathur, Harsh
2010-10-15
We formulate quantum mechanics for non-Hermitian Hamiltonians that are invariant under PT, where P is the parity and T denotes time reversal, for the case that time-reversal symmetry is odd (T{sup 2}=-1), generalizing prior work for the even case (T{sup 2}=1). We discover an analog of Kramer's theorem for PT quantum mechanics, present a prototypical example of a PT quantum system with odd time reversal, and discuss potential applications of the formalism.
Nonlinearity-induced PT-symmetry without material gain
NASA Astrophysics Data System (ADS)
Miri, Mohammad-Ali; Alù, Andrea
2016-06-01
Parity-time symmetry has raised a great deal of attention in optics in recent years, yet its application has been so far hindered by the stringent requirements on coherent gain balanced with loss. In this paper, we show that the conditions to enable parity and time symmetry can be simultaneously satisfied for a pair of modes with mixed frequencies interacting in a nonlinear medium, without requiring the presence of material gain. First, we consider a guided wave structure with second order nonlinearity and we derive the PT-symmetric Hamiltonian that governs the interaction of two waves of mixed frequencies when accompanied by a high intensity pump beam at the sum frequency. We also extend the results to an array of coupled nonlinear waveguide channels. It is shown that the evolution dynamics of the low-frequency waves is associated with a periodic PT-symmetric lattice while the phase of the pump beams can be utilized as a control parameter to modify the gain and loss distribution, thus realizing different PT lattices by design. Our results suggest that nonlinear wave mixing processes can form a rich platform to realize PT-symmetric Hamiltonians of arbitrary dimensions in optical systems, without requiring material gain.
Explicit definition of PT symmetry for nonunitary quantum walks with gain and loss
NASA Astrophysics Data System (ADS)
Mochizuki, Ken; Kim, Dakyeong; Obuse, Hideaki
2016-06-01
PT symmetry, that is, a combined parity and time-reversal symmetry, is a key milestone for non-Hermitian systems exhibiting entirely real eigenenergy. In the present work, motivated by a recent experiment, we study PT symmetry of the time-evolution operator of nonunitary quantum walks. We present the explicit definition of PT symmetry by employing a concept of symmetry time frames. We provide a necessary and sufficient condition so that the time-evolution operator of the nonunitary quantum walk retains PT symmetry even when parameters of the model depend on position. It is also shown that there exist extra symmetries embedded in the time-evolution operator. Applying these results, we clarify that the nonunitary quantum walk in the experiment does have PT symmetry.
Floquet modulation of {{PT}}𝒫𝒯 symmetry in an atomic Bose-Josephson junction
NASA Astrophysics Data System (ADS)
Zhong, Honghua; Zhu, Bo; Qin, Xizhou; Huang, Jiahao; Ke, Yongguan; Zhou, Zheng; Lee, Chaohong
2016-07-01
We study a periodically driven {{PT}}𝒫𝒯-symmetric Bose-Josephson junction and explore how the driving field affects the {{PT}}𝒫𝒯 symmetry in such a non-Hermitian many-body quantum system. In the absence of interaction, by employing the high-frequency Floquet method, the condition of spontaneous {{PT}}𝒫𝒯-symmetry-breaking transition is analytically given. In the presence of interaction, it is found that even weak atom-atom interaction can shift the critical point of the {{PT}}𝒫𝒯-symmetry-breaking transition. Furthermore, we numerically obtain the {{PT}}𝒫𝒯-symmetric phase diagram, where the region of unbroken {{PT}}𝒫𝒯 symmetry sensitively depends on the interaction strength and the driving parameter. Our results provide a promising way for manipulating {{PT}}𝒫𝒯-symmetric many-body quantum system by utilizing periodic driving fields.
Quantum criticality, kink confinement, and emergent symmetries in coupled Ising chains and ladders
NASA Astrophysics Data System (ADS)
Tennant, Alan
2011-03-01
In this talk I cover the physics in three of the central quantum phase transitions in 1D. First, the transverse Ising model which is realized in CoNb2O6. While this is perhaps the simplest textbook case of a quantum phase transition, a remarkable emergence of E8 symmetry arises close to the quantum critical point. This manifests itself in an octave of bound states. We observe these experimentally and in particular the interval of the first two resonances on this octave which are found to match the golden ratio 1.618... - just as predicted for the emergence of this extraordinary symmetry. I then plan to show with the example of the Heisenberg chain how we can probe the quantum critical volume experimentally and show the characteristic scaling behaviour in space and time. The third example is of a spin ladder CaCu2O3 which is near the long sought after Wess-Zumino-Novikov-Witten quantum critical point.
Effects of parity-time symmetry in nonlinear Klein-Gordon models and their stationary kinks.
Demirkaya, A; Frantzeskakis, D J; Kevrekidis, P G; Saxena, A; Stefanov, A
2013-08-01
In this work, we introduce some basic principles of PT-symmetric Klein-Gordon nonlinear field theories. By formulating a particular antisymmetric gain and loss profile, we illustrate that the stationary states of the model do not change. However, the stability critically depends on the gain and loss profile. For a symmetrically placed solitary wave (in either the continuum model or a discrete analog of the nonlinear Klein-Gordon type), there is no effect on the steady state spectrum. However, for asymmetrically placed solutions, there exists a measurable effect of which a perturbative mathematical characterization is offered. It is generally found that asymmetry towards the lossy side leads towards stability, while towards the gain side produces instability. Furthermore, a host of finite size effects, which disappear in the infinite domain limit, are illustrated in connection to the continuous spectrum of the problem. PMID:24032958
Phase-space representation of a non-Hermitian system with PT symmetry
NASA Astrophysics Data System (ADS)
Praxmeyer, Ludmila; Yang, Popo; Lee, Ray-Kuang
2016-04-01
We present a phase-space study of a non-Hermitian Hamiltonian with PT symmetry based on the Wigner distribution function. For an arbitrary complex potential, we derive a generalized continuity equation for the Wigner function flow and calculate the related circulation values. Studying the vicinity of an exceptional point, we show that a PT -symmetric phase transition from an unbroken PT -symmetry phase to a broken one is a second-order phase transition.
Observation and elimination of broken symmetry in L1{sub 0} FePt nanostructures
Quarterman, P.; Wang, Hao; Qiu, Jiao-Ming; Ma, Bin; Liu, Xiaoqi; Wang, Jian-Ping; Guo, Honghua
2015-12-07
An unexplained surface anisotropy effect was observed and confirmed in the magnetization reversal process of both L1{sub 0} phase FePt nanoparticles with octahedral shape and (001) textured L1{sub 0} FePt thin films with island nanostructures. We suggest that the nature of the observed surface effect is caused by broken symmetry on the FePt surface, which results in weakened exchange coupling for surface atoms. Furthermore, we propose, and experimentally demonstrate, a method to repair the broken symmetry by capping the FePt islands with a Pt layer, which could prove invaluable in understanding fundamental limitations of magnetic nanostructures.
PT symmetry in quantum physics: From a mathematical curiosity to optical experiments
NASA Astrophysics Data System (ADS)
Bender, Carl M.
2016-04-01
Space-time reflection symmetry, or PT symmetry, first proposed in quantum mechanics by Bender and Boettcher in 1998 [1], has become an active research area in fundamental physics. More than two thousand papers have been published on the subject and papers have appeared in two dozen categories of the arXiv. Over two dozen international conferences and symposia specifically devoted to PT symmetry have been held and many PhD theses have been written.
Universal routes to spontaneous PT-symmetry breaking in non-Hermitian quantum systems
NASA Astrophysics Data System (ADS)
Schomerus, Henning
2011-03-01
PT-symmetric systems can have a real spectrum even when their Hamiltonian is non-Hermitian, but develop a complex spectrum when the degree of non-Hermiticity increases. Here we utilize random-matrix theory to show that this spontaneous PT-symmetry breaking can occur via two distinct mechanisms, whose predominance is associated to different universality classes. Present optical experiments fall into the orthogonal class, where symmetry-induced level crossings render the characteristic absorption rate independent of the coupling strength between the symmetry-related parts of the system.
Universal routes to spontaneous PT-symmetry breaking in non-Hermitian quantum systems
Schomerus, Henning
2011-03-15
PT-symmetric systems can have a real spectrum even when their Hamiltonian is non-Hermitian, but develop a complex spectrum when the degree of non-Hermiticity increases. Here we utilize random-matrix theory to show that this spontaneous PT-symmetry breaking can occur via two distinct mechanisms, whose predominance is associated to different universality classes. Present optical experiments fall into the orthogonal class, where symmetry-induced level crossings render the characteristic absorption rate independent of the coupling strength between the symmetry-related parts of the system.
Tunneling decay of false kinks
NASA Astrophysics Data System (ADS)
Dupuis, Éric; Gobeil, Yan; MacKenzie, Richard; Marleau, Luc; Paranjape, M. B.; Ung, Yvan
2015-07-01
We consider the decay of "false kinks," that is, kinks formed in a scalar field theory with a pair of degenerate symmetry-breaking false vacua in 1 +1 dimensions. The true vacuum is symmetric. A second scalar field and a peculiar potential are added in order for the kink to be classically stable. We find an expression for the decay rate of a false kink. As with any tunneling event, the rate is proportional to exp (-SE) where SE is the Euclidean action of the bounce describing the tunneling event. This factor varies wildly depending on the parameters of the model. Of interest is the fact that for certain parameters SE can get arbitrarily small, implying that the kink is only barely stable. Thus, while the false vacuum itself may be very long-lived, the presence of kinks can give rise to rapid vacuum decay.
Spontaneous PT -symmetry breaking in non-Hermitian Kitaev and extended Kitaev models
NASA Astrophysics Data System (ADS)
Wang, Xiaohui; Liu, Tingting; Xiong, Ye; Tong, Peiqing
2015-07-01
The spontaneous parity-time (PT ) symmetry breaking is discussed in non-Hermitian PT -symmetric Kitaev and extended Kitaev models whose Hermiticity is broken by the presence of two conjugated imaginary potentials ±i γ at two end sites. In the case of the non-Hermitian Kitaev model, a spontaneous PT -symmetry breaking transition (S PT B T ) occurs at a certain γc in the topologically trivial phase (TTP) region, similar to that of the Su-Schrieffer-Heeger (SSH) model. However, unlike the SSH model, the system also undergoes such a transition in the topologically nontrivial phase (TNP) region. We study an extended Kitaev model by combining the superconducting pairing in the Kitaev model and the staggered hopping in the SSH model. This model contains three different topological phases: the TTP, the Kitaev-like TNP, and the SSH-like TNP. For the non-Hermitian extended Kitaev model, a S PT B T occurs in the Kitaev-like TNP region, as well as in part of the TTP and SSH-like TNP regions, whereas the PT symmetry is broken for an arbitrary nonzero γ in the rest of the TTP and SSH-like TNP regions. Therefore, we can conclude that there is no universal correlation between topological properties and the S PT B T .
PT symmetry breaking and nonlinear optical isolation in coupled microcavities
NASA Astrophysics Data System (ADS)
Zhou, Xin; Chong, Y. D.
2016-04-01
We perform a theoretical study of nonlinear optical isolator devices based on coupled microcavities with gain and loss. Using coupled-mode theory, we derive a correspondence between the boundary of asymptotic stability in the nonlinear regime, where gain saturation is present, and the PT-breaking transition in the underlying linear system. For zero detuning and weak input intensity, the onset of optical isolation can be rigorously derived, and corresponds precisely to the PT transition point. When the couplings to the external ports are unequal, the isolation ratio exhibits an abrupt jump at the transition point, determined by the ratio of the couplings. This could be exploited to realize an actively controlled nonlinear optical isolator, in which strong optical isolation can be switched on or off using tiny variations in the inter-resonator separation.
Spontaneous PT symmetry breaking of a ferromagnetic superfluid in a gradient field
NASA Astrophysics Data System (ADS)
Vanderbruggen, T.; Palacios Álvarez, Silvana; Coop, S.; Martinez de Escobar, N.; Mitchell, M. W.
2015-09-01
We consider the interaction of a ferromagnetic spinor Bose-Einstein condensate with a magnetic-field gradient. The magnetic-field gradient realizes a spin-position coupling that explicitly breaks time-reversal symmetry T and space parity P , but preserves the combined PT symmetry. We observe, using numerical simulations, a phase transition spontaneously breaking this remaining symmetry. The transition to a low-gradient phase, in which gradient effects are frozen out by the ferromagnetic interaction, suggests the possibility of high-coherence magnetic sensors unaffected by gradient dephasing.
PT -symmetry breaking for the scattering problem in a one-dimensional non-Hermitian lattice model
NASA Astrophysics Data System (ADS)
Zhu, Baogang; Lü, Rong; Chen, Shu
2016-03-01
We study the PT -symmetry breaking for the scattering problem in a one-dimensional non-Hermitian tight-binding lattice model with balanced gain and loss distributed on two adjacent sites. In the scattering process the system undergoes a transition from the exact PT -symmetric phase to the phase with spontaneously breaking PT symmetry as the amplitude of complex potentials increases. Using the S-matrix method, we derive an exact discriminant, which can be used to distinguish different symmetry phases, and determine the exceptional point for the symmetry breaking analytically. In the PT -symmetry-breaking region, we also confirm the appearance of the unique feature, i.e., the coherent perfect absorption laser, in this simple non-Hermitian lattice model. The study of the scattering problem of such a simple model provides an additional way to unveil the physical effect of non-Hermitian PT -symmetric potentials.
Armchair graphene nanoribbons: PT-symmetry breaking and exceptional points without dissipation
Fagotti, Maurizio; Bonati, Claudio; Logoteta, Demetrio; Marconcini, Paolo; Macucci, Massimo
2011-06-15
We consider a single-layer graphene nanoribbon with armchair edges and with a longitudinally constant external potential, pointing out that it can be described by means of an effective non-Hermitian Hamiltonian. We show that this system has some features typical of dissipative systems, namely, the presence of exceptional points and of PT-symmetry breaking, although it is not dissipative.
PT -symmetry breaking in waveguides with competing loss-gain pairs
NASA Astrophysics Data System (ADS)
Kalozoumis, P. A.; Morfonios, C. V.; Diakonos, F. K.; Schmelcher, P.
2016-06-01
We consider a periodic waveguide array whose unit cell consists of a PT -symmetric quadrimer with two competing loss-gain parameter pairs which lead to qualitatively different symmetry-broken phases. It is shown that the transitions between the phases are described by a symmetry-adapted nonlocal current which maps the spectral properties to the spatially resolved field, for the lattice as well as for the isolated quadrimer. Its site average acts like a natural order parameter for the general class of one-dimensional PT -symmetric Hamiltonians, vanishing in the unbroken phase and being nonzero in the broken phase. We investigate how the beam dynamics in the array is affected by the presence of competing loss-gain rates in the unit cell, showing that the enriched band structure yields the possibility to control the propagation length before divergence when the system resides in the broken PT phase.
Parametric symmetries in exactly solvable real and PT symmetric complex potentials
NASA Astrophysics Data System (ADS)
Yadav, Rajesh Kumar; Khare, Avinash; Bagchi, Bijan; Kumari, Nisha; Mandal, Bhabani Prasad
2016-06-01
In this paper, we discuss the parametric symmetries in different exactly solvable systems characterized by real or complex PT symmetric potentials. We focus our attention on the conventional potentials such as the generalized Pöschl Teller (GPT), Scarf-I, and PT symmetric Scarf-II which are invariant under certain parametric transformations. The resulting set of potentials is shown to yield a completely different behavior of the bound state solutions. Further, the supersymmetric partner potentials acquire different forms under such parametric transformations leading to new sets of exactly solvable real and PT symmetric complex potentials. These potentials are also observed to be shape invariant (SI) in nature. We subsequently take up a study of the newly discovered rationally extended SI potentials, corresponding to the above mentioned conventional potentials, whose bound state solutions are associated with the exceptional orthogonal polynomials (EOPs). We discuss the transformations of the corresponding Casimir operator employing the properties of the so(2, 1) algebra.
2 × 2 random matrix ensembles with reduced symmetry: from Hermitian to {PT} -symmetric matrices
NASA Astrophysics Data System (ADS)
Gong, Jiangbin; Wang, Qing-hai
2012-11-01
A possibly fruitful extension of conventional random matrix ensembles is proposed by imposing symmetry constraints on conventional Hermitian matrices or parity-time ( {PT})-symmetric matrices. To illustrate the main idea, we first study 2 × 2 complex Hermitian matrix ensembles with O(2)-invariant constraints, yielding novel level-spacing statistics such as singular distributions, the half-Gaussian distribution, distributions interpolating between the GOE (Gaussian orthogonal ensemble) distribution and half-Gaussian distributions, as well as the gapped-GOE distribution. Such a symmetry-reduction strategy is then used to explore 2 × 2 {PT}-symmetric matrix ensembles with real eigenvalues. In particular, {PT}-symmetric random matrix ensembles with U(2) invariance can be constructed, with the conventional complex Hermitian random matrix ensemble being a special case. In two examples of {PT}-symmetric random matrix ensembles, the level-spacing distributions are found to be the standard GUE (Gaussian unitary ensemble) statistics or the ‘truncated-GUE’ statistics. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.
Low-energy excitations, symmetry breaking and specific heat in YbBiPt
Robinson, R.A.; Christianson, A.; Nakotte, H. |; Beyermann, W.P.; Canfield, P.C.
1998-12-31
The heavy fermion compound YbBiPt has a very large linear coefficient of specific heat {gamma} = 8 Jmol{sup {minus}1} K{sup {minus}2} and this is understood, to first order, in terms of the observed low-energy neutron scattering response. However, at low temperatures, symmetry forbidden splittings at 1 and 2 meV respectively are observed. These levels give good qualitative agreement with the measured specific heat, but poor quantitative agreement. Indeed, the specific heat drops more rapidly with temperature that can be accounted for assuming a temperature-independent density of states. The authors also present new low-temperature crystallographic data, which rule out any significant structural distortions.
Random-matrix theory of amplifying and absorbing resonators with {PT} or {PTT}^{\\prime } symmetry
NASA Astrophysics Data System (ADS)
Birchall, Christopher; Schomerus, Henning
2012-11-01
We formulate Gaussian and circular random-matrix models representing a coupled system consisting of an absorbing and an amplifying resonator, which are mutually related by a generalized time-reversal symmetry. Motivated by optical realizations of such systems we consider a {PT} or a {PTT}^{\\prime } time-reversal symmetry, which impose different constraints on magneto-optical effects, and then focus on five common settings. For each of these, we determine the eigenvalue distribution in the complex plane in the short-wavelength limit, which reveals that the fraction of real eigenvalues among all eigenvalues in the spectrum vanishes if all classical scales are kept fixed. Numerically, we find that the transition from real to complex eigenvalues in the various ensembles display a different dependence on the coupling strength between the two resonators. These differences can be linked to the level spacing statistics in the Hermitian limit of the considered models. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.
NASA Astrophysics Data System (ADS)
Harter, Andrew K.; Lee, Tony E.; Joglekar, Yogesh N.
2016-06-01
Aubry-André-Harper lattice models, characterized by a reflection-asymmetric sinusoidally varying nearest-neighbor tunneling profile, are well known for their topological properties. We consider the fate of such models in the presence of balanced gain and loss potentials ±i γ located at reflection-symmetric sites. We predict that these models have a finite PT -breaking threshold only for specific locations of the gain-loss potential and uncover a hidden symmetry that is instrumental to the finite threshold strength. We also show that the topological edge states remain robust in the PT -symmetry-broken phase. Our predictions substantially broaden the possible experimental realizations of a PT -symmetric system.
NASA Astrophysics Data System (ADS)
Ge, Li; Makris, Konstantinos G.; Christodoulides, Demetrios N.; Feng, Liang
2015-12-01
We extend the generalized conservation law of light propagating in a one-dimensional PT -symmetric system, i.e., |T -1 | =√{RLRR } for the transmittance T and the reflectance RL ,R from the left and right, to a multimode waveguide with either PT or RT symmetry, in which higher dimensional investigations are necessary. These conservation laws exist not only in a matrix form for the transmission and reflection matrices; they also exist in a scalar form for real-valued quantities by defining generalized transmittance and reflectance. We then discuss how a multimode PT -symmetric waveguide can be used to observe spontaneous symmetry breaking of the scattering matrix, which typically requires tuning the non-Hermiticity of the system (i.e., the strength of gain and loss). Here the advantage of using a multimode waveguide is the elimination of tuning any system parameters: the transverse mode order m plays the role of the symmetry-breaking parameter, and one observes the symmetry breaking by simply performing a scattering experiment in each waveguide channel at a single frequency and fixed strength of gain and loss.
Symmetry approach to the (P,T) diagram of TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane)
Megtert, S.; Bjeli, A.; Przystawa, J.; Bariic, S.
1985-11-15
Following structural neutron scattering experiments on TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) and the resulting pressure-temperature phase diagram, a detailed symmetry analysis of all possible displacive modes coupled to the conduction electrons is performed. This analysis leads to the determination of the modes participating in the onset of the lines T/sub H/(P), T/sub M//sub 1/(P), and T/sub M//sub 2/(P) (T/sub H/ = 54 K, T/sub M//sub 1/roughly-equalT2 = 49 K at ambient pressure) in the P-T diagram. These are, respectively, the transverse acoustic mode on TCNQ chains, the longitudinal optic mode on TCNQ chains, and the longitudinal optic mode on TTF chains. Furthermore, the Landau expansion for the first two phase lines T/sub H/(P) and T/sub M//sub 1/(P) is developed and analyzed. The resulting pressure behavior of these two lines is in good agreement with experimental observations.
Hexagonal pnictide SrPtAs; the role of spin-orbit interaction and locally broken inversion symmetry
NASA Astrophysics Data System (ADS)
Rhim, S. H.; Youn, S. J.; Fischer, M. H.; Agterberg, D. F.; Sigrist, M.; Weinert, M.; Freeman, A. J.
2012-02-01
The first hexagonal pnictide superconductor SrPtAs which consists of stacked PtAs layers has been studied using the FLAPW methodootnotetextWimmer, Krakauer, Weinert, and Freeman, Phys.Rev.B. 24, 864 (1981) and tight-binding methods. The single PtAs layer forms a honeycomb structure that exhibits: (1) locally broken inversion symmetry despite the presence of the global inversion center, and (2) strong spin-orbit interaction, for which physical consequences are nontrivial. Based on these findings, we predict significant enhancement of both the spin susceptibility and the paramagnetic limiting field with respect to the usual s wave superconductors. Further, we suggest an increase of TC by electron doping of a van Hove singularity.
NASA Astrophysics Data System (ADS)
Heitzer, Joerg
1992-05-01
Two methods for the numerical solution of the integral equation describing the kinked interface crack, one proposed by Erdogan et al. (1973) and the other by Theokaris and Iokimidis (1979), are examined. The method of Erdogan et al. is then used to solve the equation in order to determine the kinking angle of the interface crack. Results are presented for two material combinations, aluminum/epoxy and glass/ceramic, under uniaxial tension in the direction normal to the interface.
NASA Astrophysics Data System (ADS)
Li, Jiahua; Yu, Rong; Ding, Chunling; Wu, Ying
2016-02-01
It is important to control and tune the Fano-resonance spectra to achieve a large slope with, in addition, a relatively high extinction ratio for low-power optical switching and high-sensitivity sensing. Here, we explore the evolution of sharp asymmetric Fano-like line shapes in a three-cavity array with local parity-time (PT ) symmetry. In this three-cavity configuration, a single cavity is coupled to a PT -symmetric combination of two cavities via a common waveguide. The influences of local PT symmetry on the asymmetric Fano-like line shapes are investigated by monitoring the output transmission spectra at various system parameters. It is found that both the slope and the extinction ratio within the sharp asymmetric line shapes can be significantly enhanced by introducing the PT -symmetric unit, compared with the configuration of two indirectly coupled cavities. Subsequently we discuss the application of such a PT -assisted configuration as a family of high-sensitivity refractive index sensors by numerical analysis. For practical parameters based on microring resonators, the best sensitivity of refractive index sensors is more than five orders of magnitude larger than two indirectly coupled lossy cavities. The proposed scheme can be implemented in current state-of-the-art experiments. This investigation can help us to understand the interplay between the Fano resonance and PT symmetry.
Spontaneous PT-Symmetry Breaking for Systems of Noncommutative Euclidean Lie Algebraic Type
NASA Astrophysics Data System (ADS)
Dey, Sanjib; Fring, Andreas; Mathanaranjan, Thilagarajah
2015-11-01
We propose a noncommutative version of the Euclidean Lie algebra E 2. Several types of non-Hermitian Hamiltonian systems expressed in terms of generic combinations of the generators of this algebra are investigated. Using the breakdown of the explicitly constructed Dyson maps as a criterium, we identify the domains in the parameter space in which the Hamiltonians have real energy spectra and determine the exceptional points signifying the crossover into the different types of spontaneously broken PT-symmetric regions with pairs of complex conjugate eigenvalues. We find exceptional points which remain invariant under the deformation as well as exceptional points becoming dependent on the deformation parameter of the algebra.
Non-Hermitian trimers: PT-symmetry versus pseudo-Hermiticity
NASA Astrophysics Data System (ADS)
Suchkov, Sergey V.; Fotsa-Ngaffo, Fernande; Kenfack-Jiotsa, Aurelien; Tikeng, Arnaud D.; Kofane, Timoleon C.; Kivshar, Yuri S.; Sukhorukov, Andrey A.
2016-06-01
We study a structure composed of three coupled waveguides with gain and loss, a non-Hermitian trimer. We demonstrate that the mode spectrum can be entirely real if the waveguides are placed in a special order and at certain distances between each other. Such structures generally lack a spatial symmetry, in contrast to parity-time symmetric trimers which are known to feature a real spectrum. We also determine a threshold for wave amplification and analyse the scattering properties of such non-conservative systems embedded into a chain of conservative waveguides.
Semirelativity and Kink Solitons
ERIC Educational Resources Information Center
Nowak, Mariusz Karol
2014-01-01
It is hard to observe relativistic effects in everyday life. However, table experiments using a mechanical transmission line for solitons may be an efficient and simple way to show effects such as Lorentz contraction in a classroom. A kink soliton is a deformation of a lattice of several dozen or more pendulums placed on a wire and connected by a…
Permanent Rabi oscillations in coupled exciton-photon systems with PT -symmetry
Chestnov, Igor Yu.; Demirchyan, Sevak S.; Alodjants, Alexander P.; Rubo, Yuri G.; Kavokin, Alexey V.
2016-01-01
We propose a physical mechanism which enables permanent Rabi oscillations in driven-dissipative condensates of exciton-polaritons in semiconductor microcavities subjected to external magnetic fields. The method is based on stimulated scattering of excitons from the incoherent reservoir. We demonstrate that permanent non-decaying oscillations may appear due to the parity-time symmetry of the coupled exciton-photon system realized in a specific regime of pumping to the exciton state and depletion of the reservoir. At non-zero exciton-photon detuning, robust permanent Rabi oscillations occur with unequal amplitudes of exciton and photon components. Our predictions pave way to realization of integrated circuits based on exciton-polariton Rabi oscillators. PMID:26790534
Permanent Rabi oscillations in coupled exciton-photon systems with PT-symmetry.
Chestnov, Igor Yu; Demirchyan, Sevak S; Alodjants, Alexander P; Rubo, Yuri G; Kavokin, Alexey V
2016-01-01
We propose a physical mechanism which enables permanent Rabi oscillations in driven-dissipative condensates of exciton-polaritons in semiconductor microcavities subjected to external magnetic fields. The method is based on stimulated scattering of excitons from the incoherent reservoir. We demonstrate that permanent non-decaying oscillations may appear due to the parity-time symmetry of the coupled exciton-photon system realized in a specific regime of pumping to the exciton state and depletion of the reservoir. At non-zero exciton-photon detuning, robust permanent Rabi oscillations occur with unequal amplitudes of exciton and photon components. Our predictions pave way to realization of integrated circuits based on exciton-polariton Rabi oscillators. PMID:26790534
Inverse dispersion method for calculation of complex photonic band diagram and PT symmetry
NASA Astrophysics Data System (ADS)
Rybin, Mikhail V.; Limonov, Mikhail F.
2016-04-01
We suggest an inverse dispersion method for calculating a photonic band diagram for materials with arbitrary frequency-dependent dielectric functions. The method is able to calculate the complex wave vector for a given frequency by solving the eigenvalue problem with a non-Hermitian operator. The analogy with PT -symmetric Hamiltonians reveals that the operator corresponds to the momentum as a physical quantity, and the singularities at the band edges are related to the branch points and responses for the features on the band edges. The method is realized using a plane wave expansion technique for a two-dimensional periodic structure in the case of TE and TM polarizations. We illustrate the applicability of the method by the calculation of the photonic band diagrams of an infinite two-dimensional square lattice composed of dielectric cylinders using the measured frequency-dependent dielectric functions of different materials (amorphous hydrogenated carbon, silicon, and chalcogenide glass). We show that the method allows one to distinguish unambiguously between Bragg and Mie gaps in the spectra.
The role of symmetry-breaking-induced interface anisotropy in [Fe/Pt]{sub n} multilayer films
Li Zhenghua; Xie Hailong; Liu Xi; Bai Jianmin; Wei Fulin; Wei Dan; Yoshimura, S.; Saito, H.; Liu Xiaoxi
2011-04-01
The FePt films were deposited with [Fe/Pt]{sub n} multilayer structure on preheated Corning 1737F glass substrate using pure Fe and Pt target in a CMS-18 sputtering system. The dependence of FePt's texture and magnetic properties on the multilayer structure was investigated. The XRD patterns indicate that (111) texture is dominant for all [Fe/Pt]{sub n} (n = 8, 16, 20, 32) multilayer films. However, the measured M-H loops show that the perpendicular anisotropy is greatly enhanced in samples with n = 16, 20, and 32. The origin of the increased perpendicular anisotropy of [Fe/Pt]{sub n} multilayer films is related to the contributions of the interfaces, which will be analyzed using the micromagnetic models, with careful discussions of the crystalline and interface anisotropies. Finally, it is confirmed that the Fe/Pt interfaces favor the perpendicular orientation in the multilayer structure.
Xe adsorption site distributions on Pt(111), Pt(221) and Pt(531)
NASA Astrophysics Data System (ADS)
Gellman, Andrew J.; Baker, L.; Holsclaw, B. S.
2016-04-01
The ideal structures of the Pt(111), Pt(221) and Pt(531) surfaces expose adsorption sites that can be qualitatively described as terrace sites on Pt(111), both step and terrace sites on Pt(221), and kink sites on Pt(531). The real surface structures of these surfaces can be complicated by imperfections such as misorientation, reconstruction and thermal roughening, all of which will influence their distributions of adsorption sites. Xe adsorption sites on the Pt(111), Pt(221) and Pt(531) surfaces have been probed using both photoemission of adsorbed Xe (PAX) and temperature programmed desorption (TPD) of Xe. Both PAX and Xe TPD are sensitive to the adsorption sites of the Xe and serve as complementary means of assessing the distributions of adsorption sites on these three Pt surfaces. The adsorption of Xe is sufficiently sensitive to detect the presence of residual steps on the Pt(111) surface at a density of ~ 1.5% step atoms per Pt atom. On the Pt(221) surface, PAX and Xe TPD reveal adsorption at both terrace and step sites simultaneously. Although the ideal structure of the Pt(531) surface has no well-defined steps or terraces, Xe adsorption indicates that its adsorption sites are best described as a distribution of both step and kink sites with roughly twice as many steps sites as kinks.
Defects on semiflexible filaments: Kinks and twist kinks
NASA Astrophysics Data System (ADS)
Lee, Nam-Kyung; Johner, Albert
2016-04-01
Due to local interactions with ligands or to global constraints, semiflexible filaments can exhibit localized defects. We focus on filaments laying flat on a surface. The two lowest order singularities are addressed: discontinuities of the orientation, which are called kink, and discontinuities of the curvature. The latter are called twist kinks in flattened helical filaments where they can form spontaneously. We calculate the partition functions for a given defect fugacity and discuss some often measured quantities like the correlation of the orientation along the filament.
Gap solitons in PT -symmetric lattices with a lower refractive-index core
NASA Astrophysics Data System (ADS)
Dong, Liangwei; Gu, Linlin; Guo, Dengchu
2015-05-01
We address the existence and stability properties of families of gap solitons in a lower refractive-index core, sandwiched between two optical lattices with a parity-time (PT ) symmetry imprinted in a defocusing medium. The scale of flat-topped complex solitons can be controlled arbitrarily by varying the embedded index core. Multipeaked solitons are found to exhibit equal peak values in the region of the index core, and they have no analog in other lattice-modulated or bulk media. We demonstrate that, in sharp contrast to solitons in regular PT lattices, flat-topped and multipeaked solitons are either stable or suffer a negligibly weak instability, even when the gain-loss coefficient approaches the PT -symmetry-breaking point. Our results, thus, build a bridge between the PT defect solitons in a narrow index core and the PT kink pairs in a broad index core. We also suggest an effective way for the observation of "surface solitons" in PT -symmetric lattices.
Non-Abelian twisted kinks in chiral Gross-Neveu model with isospin
NASA Astrophysics Data System (ADS)
Thies, Michael
2016-04-01
The two-dimensional, massless Gross-Neveu model with Nc colors and SU(2) isospin is studied analytically in the large Nc limit. The chiral SU (2 )L×SU (2 )R symmetry is broken spontaneously in the vacuum. Twisted kinks connecting two arbitrary points on the vacuum manifold S3 are constructed, and their properties are explored. The phase diagram as a function of temperature and baryon and isospin chemical potential is discussed, with special emphasis on inhomogeneous phases. The preferred form of the condensate is a product of the real kink crystal and the chiral spiral. Kink-kink scattering is solved, using the general solution of the multicomponent Bogoliubov-de Gennes equation recently presented by Takahashi.
The external kink mode in diverted tokamaks
NASA Astrophysics Data System (ADS)
Turnbull, A. D.; Hanson, J. M.; Turco, F.; Ferraro, N. M.; Lanctot, M. J.; Lao, L. L.; Strait, E. J.; Piovesan, P.; Martin, P.
2016-06-01
> . The resistive kink behaves much like the ideal kink with predominantly kink or interchange parity and no real sign of a tearing component. However, the growth rates scale with a fractional power of the resistivity near the surface. The results have a direct bearing on the conventional edge cutoff procedures used in most ideal MHD codes, as well as implications for ITER and for future reactor options.
Kinks, extra dimensions, and gravitational waves
O'Callaghan, Eimear; Gregory, Ruth
2011-03-01
We investigate in detail the gravitational wave signal from kinks on cosmic (super)strings, including the kinematical effects from the internal extra dimensions. We find that the signal is suppressed, however, the effect is less significant that that for cusps. Combined with the greater incidence of kinks on (super)strings, it is likely that the kink signal offers the better chance for detection of cosmic (super)strings.
Asymmetric Kinks: Stabilization by Entropic Forces
Costantini, G.; Marchesoni, F.
2001-09-10
Asymmetric kinks bridging two adjacent potential valleys of equal depth but different curvature are unstable against phonon modes. When coupled to a heat bath, a kink-bearing string tends to cross over into the shallower valley; kinks are thus predicted to drift in the appropriate direction with velocity proportional to the temperature, in close agreement with numerical simulation. When contrasted by a mechanical bias, these entropic forces give rise to a rich phenomenology that includes configurational phase transitions, double-kink dissociation, and noise-directed signal transmission.
Kink ratchet induced by a time-dependent symmetric field potential
NASA Astrophysics Data System (ADS)
Sánchez-Rey, Bernardo; Casado-Pascual, Jesús; Quintero, Niurka R.
2016-07-01
The ratchet effect of a sine-Gordon kink is investigated in the absence of any external force while the symmetry of the field potential at every time instant is maintained. The directed motion appears by a time shift of the sine-Gordon potential through a time-dependent additional phase. A symmetry analysis provides the necessary conditions for the existence of net motion. It is also shown analytically, by using a collective coordinate theory, that the novel physical mechanism responsible for the appearance of the ratchet effect is the coupled dynamics of the kink width with the background field. Biharmonic and dichotomic periodic variations of the additional phase of the sine-Gordon potential are considered. The predictions established by the symmetry analysis and the collective coordinate theory are verified by means of numerical simulations. Inversion and maximization of the resulting current as a function of the system parameters are investigated.
Kink ratchet induced by a time-dependent symmetric field potential.
Sánchez-Rey, Bernardo; Casado-Pascual, Jesús; Quintero, Niurka R
2016-07-01
The ratchet effect of a sine-Gordon kink is investigated in the absence of any external force while the symmetry of the field potential at every time instant is maintained. The directed motion appears by a time shift of the sine-Gordon potential through a time-dependent additional phase. A symmetry analysis provides the necessary conditions for the existence of net motion. It is also shown analytically, by using a collective coordinate theory, that the novel physical mechanism responsible for the appearance of the ratchet effect is the coupled dynamics of the kink width with the background field. Biharmonic and dichotomic periodic variations of the additional phase of the sine-Gordon potential are considered. The predictions established by the symmetry analysis and the collective coordinate theory are verified by means of numerical simulations. Inversion and maximization of the resulting current as a function of the system parameters are investigated. PMID:27575137
Analysis of kink band formation under compression
NASA Technical Reports Server (NTRS)
Hahn, H. Thomas
1987-01-01
The kink band formation in unidirectional composites under compression is analyzed in the present paper. The kinematics of kink band formation is described in terms of a deformation tensor. Equilibrium conditions are then applied to relate the compression load to the deformation of fibers. Since the in situ shear behavior of the matrix resin is not known, an analysis-experiment correlation is used to find the shear failure strain in the kink band. The present analysis thus elucidates the mechanisms and identifies the controlling parameters, of compression failure.
NASA Astrophysics Data System (ADS)
West, Carl T.; Kottos, Tsampikos; Prosen, Tomaž
2010-02-01
We study a new class of chaotic systems with dynamical localization, where gain or loss mechanisms break the Hermiticity, while allowing for parity-time (PT) symmetry. For a value γPT of the gain or loss parameter the spectrum undergoes a spontaneous phase transition from real (exact phase) to complex values (broken phase). We develop a one parameter scaling theory for γPT, and show that chaos assists the exact PT phase. Our results have applications to the design of optical elements with PT symmetry.
The Kinked Demand Curve When Demand Shifts.
ERIC Educational Resources Information Center
Frasco, Gregg P.
1993-01-01
Reviews recent research into the theory of the kinked demand curve in economics. Applies this theory to economic concepts such as marginal cost and price flexibility. Discusses the implications for corporations and government policymakers. (CFR)
Compactlike kinks and vortices in generalized models
Bazeia, D.; Hora, E. da; Menezes, R.; Oliveira, H. P. de; Santos, C. dos
2010-06-15
This work deals with the presence of topological defects in k-field models, where the dynamics is generalized to include higher order power in the kinetic term. We investigate kinks in (1, 1) dimensions and vortices in (2, 1) dimensions, focusing on some specific features of the solutions. In particular, we show how the kinks and vortices change to compactlike solutions, controlled by the parameter used to introduce the generalized models.
Kinks in topological soft matter
NASA Astrophysics Data System (ADS)
Chen, Bryan; Upadhyaya, Nitin; Vitelli, Vincenzo
2014-03-01
Weakly connected mechanical systems near the isostatic threshold are fragile in the sense that they exhibit large deformations in response to tiny perturbations. Kane and Lubensky have recently defined a new topological invariant of isostatic mechanical lattices which leads within linear elasticity to zero energy modes at the boundary akin to the edge modes studied in topological quantum matter. What happens when such prototype topological soft materials are subject to an external mechanical perturbation? In our work, we demonstrate that the linear soft modes can often integrate to non-linear deformations described by topological solitons. These solitons that are moving kinks between distinct topological phases are the basic excitations of fragile mechanical systems. We illustrate the general soliton construction in the context of a 1D chain of rotors connected by springs that can be considered the archetype of a topological mechanical structure. In the continuum limit, this chain is described by a Lorentz invariant ϕ4 theory and the corresponding solitons exhibit a Lorentz contraction of the width, as their speed is raised.
Development of kink jams in traffic flow
NASA Astrophysics Data System (ADS)
Kurtze, Douglas
Near the threshold of absolute stability of uniform, steady traffic flow, car-following models can often be reduced to a modified Korteweg-deVries (mKdV) equation plus small corrections. The mKdV equation has a continuous family of hyperbolic-kink solutions describing boundaries between regions of different traffic densities, i.e. the edges of traffic jams. A solvability calculation picks out the one member of this family which is consistent with the correction terms; this is usually labelled the ``selected'' kink. This identification is problematic, however, since it must be the downstream boundary condition that determines which kink solution is realized. We display a two-parameter family of mKdV solutions which has the kink solutions as one limit and uniform flow as another, and show how the correction terms can lead to kinks developing from initially near-uniform traffic. We then clarify the meaning of the usual solvability calcuation and of the ``selected'' kink.
Self-similarity and optical kinks in resonant nonlinear media
Ponomarenko, Sergey A.; Haghgoo, Soodeh
2010-11-15
We show that self-similar optical waves with a kink structure exist in a wide class of resonant nonlinear media, adequately treated in the two-level approximation. The self-similar structure of the present kinks is reflected in the time evolution of the field profile, atomic dipole moment, and one-atom inversion. We develop an analytical theory of such kinks. We show that the discovered kinks are accelerating nonlinear waves, asymptotically attaining their shape and the speed of light. We also numerically explore the formation and eventual disintegration of our kinks due to energy relaxation processes. Thus, the present kinks can be viewed as intermediate asymptotics of the system.
On Buckling, Kink Boundaries and Kinking Nonlinear Elastic Solids
NASA Astrophysics Data System (ADS)
Shamma, Mohamed
The mechanical behavior of materials has been under investigation for decades. However, there is always unknown information to be researched and characterized. Extensive research has been performed on materials deforming by slip and twin mechanisms due to their presence in a lot of materials used in practical applications. Conversely, much less attention was directed to investigating the dislocation mechanism responsible for the fully reversible energy dissipating mechanical response of Kinking Nonlinear Elastic (KNE) solids. Herein, the buckling dislocation mechanism responsible for the KNE mechanical behavior of MAX phases is investigated. The main features of the buckling dislocation mechanism are identified that are globally applicable for layered structured materials as well. This was done by analyzing the deformation of a single crystal layered structure. The single crystal layered structure is a setup consisting of a pile of paper supported by sponge and ply wood in which paper buckles during compression. The displacement of the paper layers is studied in relation to dislocation nucleation across the layers called dislocation walls (DW). Schmid factor maps where developed that recognize the shape and progress of traction applied on the layers during deformation. Hence, the evolution of buckling dislocation mechanism that occurs in layered structures has been discovered distinguishing between two possible buckling modes (extrusion and indentation) that depend on the layered structure surrounding support and constraints. In situ neutron diffraction and ultrasonic bias stress techniques were used to perform in situ experiments on selected MAX phases to obtain information about the dislocation mechanism during its activity. Linear elastic Ti 2SC was investigated as well for comparison with Ti3SiC 2 and Ti2AlC MAX phases which demonstrate KNE mechanical response in bulk. The in situ ND results of textured Ti2AlC showed typical results except for the (0004) grains
Fermions on one or fewer kinks
Chu Yizen; Vachaspati, Tanmay
2008-01-15
We find the full spectrum of fermion bound states on a Z{sub 2} kink. In addition to the zero mode, there are int[2m{sub f}/m{sub s}] bound states, where m{sub f} is the fermion and m{sub s} the scalar mass. We also study fermion modes on the background of a well-separated kink-antikink pair. Using a variational argument, we prove that there is at least one bound state in this background, and that the energy of this bound state goes to zero with increasing kink-antikink separation, 2L, and faster than e{sup -a2L} where a=min(m{sub s},2m{sub f}). By numerical evaluation, we find some of the low lying bound states explicitly.
Exotic supersymmetry of the kink-antikink crystal, and the infinite period limit
Plyushchay, Mikhail S.; Arancibia, Adrian; Nieto, Luis-Miguel
2011-03-15
Some time ago, Thies et al. showed that the Gross-Neveu model with a bare mass term possesses a kink-antikink crystalline phase. Corresponding self-consistent solutions, known earlier in polymer physics, are described by a self-isospectral pair of one-gap periodic Lame potentials with a Darboux displacement depending on the bare mass. We study an unusual supersymmetry of such a second-order Lame system, and show that the associated first-order Bogoliubov-de Gennes Hamiltonian possesses its own nonlinear supersymmetry. The Witten index is ascertained to be zero for both of the related exotic supersymmetric structures, each of which admits several alternatives for the choice of a grading operator. A restoration of the discrete chiral symmetry at zero value of the bare mass, when the kink-antikink crystalline condensate transforms into the kink crystal, is shown to be accompanied by structural changes in both of the supersymmetries. We find that the infinite period limit may or may not change the index. We also explain the origin of the Darboux-dressing phenomenon recently observed in a nonperiodic self-isospectral one-gap Poeschl-Teller system, which describes the Dashen, Hasslacher, and Neveu kink-antikink baryons.
Kink Wave Propagation in Thin Isothermal Magnetic Flux Tubes
NASA Astrophysics Data System (ADS)
Lopin, I. P.; Nagorny, I. G.; Nippolainen, E.
2014-08-01
We investigated the propagation of kink waves in thin and isothermal expanding flux tubes in cylindrical geometry. By using the method of radial expansion for fluctuating variables we obtained a new kink wave equation. We show that including the radial component of the tube magnetic field leads to cutoff-free propagation of kink waves along thin flux tubes.
Kink-antikink collisions for twin models
NASA Astrophysics Data System (ADS)
Gomes, A. R.; Menezes, R.; Nobrega, K. Z.; Simas, F. C.
2014-09-01
In this work we consider kink-antikink collisions for some classes of (1,1)-dimensional nonlinear models. We are particularly interested to investigate in which aspect the presence of a general kinetic content in the Lagrangian could be revealed in a collision process. We consider a particular class of models known as twin theories, where different models lead to the same solutions for the equations of motion and the same energy density profile. The theories can be distinguished in the level of the linear stability of a defect structure We study a class of k-defect theories depending on a parameter M, which is the twin theory of the usual ϕ4 theory with standard dynamics. For M→∞, both models are characterized by the same potential. In the regime 1/M2≪1, we obtain analytically the spectrum of excitations around the kink solution. It is shown that with increasing the parameter 1/M2 (i) the gap between the zero mode and the first-excited mode increases, and (ii) the tendency of a one-bounce collision between the kink antikink increases. We numerically investigate kink-antikink scattering, looking for the influence of the parameter changing for the thickness and number of two-bounce windows and confronting the results with our analytical findings.
Driven kink in the Frenkel-Kontorova model
NASA Astrophysics Data System (ADS)
Braun, O. M.; Hu, Bambi; Zeltser, A.
2000-09-01
The dynamics of dc driven chain of harmonically interacting atoms in the external sinusoidal potential (the Frenkel-Kontorova model) is studied. It is shown that in the underdamped case the motion of the topological soliton (kink) becomes unstable at a high velocity due to excitation of the localized intrinsic kink mode (the discrete shape mode, or discrete breather) in the kink tail. When the amplitude of the breather's oscillation becomes large enough, it decays into a kink-antikink pair. The subsequent collision of newly created kink and antikink leads to a sharp transition to the running state, where all atoms of the chain slide over the external potential almost freely.
Parity-time symmetry under magnetic flux
NASA Astrophysics Data System (ADS)
Jin, L.; Song, Z.
2016-06-01
We study a parity-time-(PT -) symmetric ring lattice, with one pair of balanced gain and loss located at opposite positions. The system remains PT -symmetric when threaded by a magnetic flux; however, the PT symmetry is sensitive to the magnetic flux in the presence of a large balanced gain and loss, or in a large system. We find a threshold gain or loss above which any nontrivial magnetic flux breaks the PT symmetry. We obtain the maximally tolerable magnetic flux for the exact PT -symmetric phase, which is approximately linearly dependent on a weak gain or loss.
Examining the Conservation of Kinks in Alpha Helices
Wilman, Henry R.; Kelm, Sebastian; Shi, Jiye; Deane, Charlotte M.
2016-01-01
Kinks are a structural feature of alpha-helices and many are known to have functional roles. Kinks have previously tended to be defined in a binary fashion. In this paper we have deliberately moved towards defining them on a continuum, which given the unimodal distribution of kink angles is a better description. From this perspective, we examine the conservation of kinks in proteins. We find that kink angles are not generally a conserved property of homologs, pointing either to their not being functionally critical or to their function being related to conformational flexibility. In the latter case, the different structures of homologs are providing snapshots of different conformations. Sequence identity between homologous helices is informative in terms of kink conservation, but almost equally so is the sequence identity of residues in spatial proximity to the kink. In the specific case of proline, which is known to be prevalent in kinked helices, loss of a proline from a kinked helix often also results in the loss of a kink or reduction in its kink angle. We carried out a study of the seven transmembrane helices in the GPCR family and found that changes in kinks could be related both to subfamilies of GPCRs and also, in a particular subfamily, to the binding of agonists or antagonists. These results suggest conformational change upon receptor activation within the GPCR family. We also found correlation between kink angles in different helices, and the possibility of concerted motion could be investigated further by applying our method to molecular dynamics simulations. These observations reinforce the belief that helix kinks are key, functional, flexible points in structures. PMID:27314675
The collision of two-kinks defects
NASA Astrophysics Data System (ADS)
Mendonça, T. S.; de Oliveira, H. P.
2015-09-01
We have investigated the head-on collision of a two-kink and a two-antikink pair that arises as a generalization of the ϕ 4 model. We have evolved numerically the Klein-Gordon equation with a new spectral algorithm whose accuracy and convergence were attested by the numerical tests. As a general result, the two-kink pair is annihilated radiating away most of the scalar field. It is possible the production of oscillons-like configurations after the collision that bounce and coalesce to form a small amplitude oscillon at the origin. The new feature is the formation of a sequence of quasi-stationary structures that we have identified as lump-like solutions of non-topological nature. The amount of time these structures survives depends on the fine-tuning of the impact velocity.
Exact kink solitons in Skyrme crystals
NASA Astrophysics Data System (ADS)
Chen, Shouxin; Li, Yijun; Yang, Yisong
2014-01-01
We present an explicit integration of the kink soliton equation obtained in a recent interesting study of the classical Skyrme model where the field configurations are of a generalized hedgehog form which is of a domain-wall type. We also show that in such a reduced one-dimensional setting the first-order and second-order equations are equivalent. Consequently, in such a context, all finite-energy solitons are Bogomolnyi-Prasad-Sommerfield type and precisely known.
1st-Principles Step- and Kink-Formation Energies on Cu(111)
Feibelman, Peter J.
1999-05-26
In rough agreement with experimental values derived from Cu island shapes vs. temperature, ab-initio calculations yield formation energies of 0.27 and 0.26 eV/ step-edge-atom for (100)- and (111)-micro facet steps on Cu(lll), and 0.09 and 0.12 eV per kink in those steps. Comparison to ab-initio results for Al and Pt shows that as a rule, the average formation energy of straight steps on a close-packed metal surface equals -7% of the metal's cohesive energy.
Amore, Paolo; Fernández, Francisco M.; Garcia, Javier; Gutierrez, German
2014-04-15
We study both analytically and numerically the spectrum of inhomogeneous strings with PT-symmetric density. We discuss an exactly solvable model of PT-symmetric string which is isospectral to the uniform string; for more general strings, we calculate exactly the sum rules Z(p)≡∑{sub n=1}{sup ∞}1/E{sub n}{sup p}, with p=1,2,… and find explicit expressions which can be used to obtain bounds on the lowest eigenvalue. A detailed numerical calculation is carried out for two non-solvable models depending on a parameter, obtaining precise estimates of the critical values where pair of real eigenvalues become complex. -- Highlights: •PT-symmetric Hamiltonians exhibit real eigenvalues when PT symmetry is unbroken. •We study PT-symmetric strings with complex density. •They exhibit regions of unbroken PT symmetry. •We calculate the critical parameters at the boundaries of those regions. •There are exact real sum rules for some particular complex densities.
Nudged Elastic Band Simulations of Kink Pairs in Tungsten
Cereceda, D.; Marian, J.
2015-01-16
Atomistic techniques have been used to calculate energy barriers for dislocation motion that control the strength (yield stress and flow stress) of the material. In particular, the calculations focus on the change in enthalpy as a straight dislocation moves through the crystal lattice (the Peierls barrier) and kink pair formation enthalpy that controls the thermally activated double-kink mechanism important at low to moderate stresses. A novel means of assessing kink widths within atomistic simulations is introduced.
Stochastic Dynamics of DC and AC Driven Dislocation Kinks
NASA Astrophysics Data System (ADS)
Vardanyan, A.; Kteyan, A.
2013-02-01
Dynamics of a pinned dislocation kink controlled by the acting DC and AC forces is studied analytically. The motion of the kink, described by sine-Gordon (sG) equation, is explored within the framework of McLaughlin-Scott perturbation theory. Assuming weakness of the acting AC force, the equation of motion of the dislocation kink in the pinning potential is linearized. Based on the equations derived, we study stochastic behavior of the kink, and determine the probability of its depinning. The dependencies of the depinning probability on DC and AC forces are analyzed in detail.
Predicting cusps or kinks in Nambu-Goto dynamics
NASA Astrophysics Data System (ADS)
Cervantes, Aldrin; García-Aspeitia, Miguel A.
2015-11-01
It is known that Nambu-Goto extended objects present some pathological structures, such as cusps and kinks, during their evolution. In this paper, we propose a model through the generalized Raychaudhuri (Rh) equation for membranes to determine if there are cusps and kinks in the worldsheet. We extend the generalized Rh equation for membranes to allow the study of the effect of higher order curvature terms in the action on the issue of cusps and kinks, using it as a tool for determining when a Nambu-Goto string generates cusps or kinks in its evolution. Furthermore, we present three examples where we test graphically this approach.
Mass gap in the critical gravitational collapse of a kink
NASA Astrophysics Data System (ADS)
Barreto, W.; Crespo, J. A.; de Oliveira, H. P.; Rodrigues, E. L.; Rodriguez-Mueller, B.
2016-03-01
We study the gravitational collapse of a kink within spherical symmetry and the characteristic formulation of general relativity. We explore some expected but elusive gravitational collapse issues which have not been studied before in detail, finding new features. The numerical one-parametric solution and the structure of the spacetime are calculated using finite differences, Galerkin collocation techniques, and some scripting for automated grid coverage. We study the threshold of black hole formation and confirm a mass gap in the phase transition. In the supercritical case we find a mass scaling power law MBH=MBH*+K [λ -λ*]2γ+f (K [λ -λ*]2γ), with γ ≈0.37 independent of the initial data for the cases considered, and MBH*, K and λ* each depending on the initial datum. The spacetime has a self-similar structure with a period of Δ ≈3.4 . In the subcritical case the Bondi mass at null infinity decays in cascade with Δ /2 interval as expected.
Non-Hermitian Hamiltonians with unitary and antiunitary symmetries
Fernández, Francisco M. Garcia, Javier
2014-03-15
We analyse several non-Hermitian Hamiltonians with antiunitary symmetry from the point of view of their point-group symmetry. It enables us to predict the degeneracy of the energy levels and to reduce the dimension of the matrices necessary for the diagonalization of the Hamiltonian in a given basis set. We can also classify the solutions according to the irreducible representations of the point group and thus analyse their properties separately. One of the main results of this paper is that some PT-symmetric Hamiltonians with point-group symmetry C{sub 2v} exhibit complex eigenvalues for all values of a potential parameter. In such cases the PT phase transition takes place at the trivial Hermitian limit which suggests that the phenomenon is not robust. Point-group symmetry enables us to explain such anomalous behaviour and to choose a suitable antiunitary operator for the PT symmetry. -- Highlights: •PT-symmetric Hamiltonians exhibit real eigenvalues when PT symmetry is unbroken. •PT-symmetric multidimensional oscillators appear to show PT phase transitions. •This transition was conjectured to be a high-energy phenomenon. •We show that point group symmetry is useful for predicting broken PT symmetry in multidimensional oscillators. •PT-symmetric oscillators with C{sub 2v} symmetry exhibit phase transitions at the trivial Hermitian limit.
Parity-time symmetry broken by point-group symmetry
Fernández, Francisco M. Garcia, Javier
2014-04-15
We discuss a parity-time (PT) symmetric Hamiltonian with complex eigenvalues. It is based on the dimensionless Schrödinger equation for a particle in a square box with the PT-symmetric potential V(x, y) = iaxy. Perturbation theory clearly shows that some of the eigenvalues are complex for sufficiently small values of |a|. Point-group symmetry proves useful to guess if some of the eigenvalues may already be complex for all values of the coupling constant. We confirm those conclusions by means of an accurate numerical calculation based on the diagonalization method. On the other hand, the Schrödinger equation with the potential V(x, y) = iaxy{sup 2} exhibits real eigenvalues for sufficiently small values of |a|. Point group symmetry suggests that PT-symmetry may be broken in the former case and unbroken in the latter one.
Damped kink oscillations of flowing prominence threads
NASA Astrophysics Data System (ADS)
Soler, R.; Ruderman, M. S.; Goossens, M.
2012-10-01
Transverse oscillations of thin threads in solar prominences are frequently reported in high-resolution observations. Two typical features of the observations are that the oscillations are damped in time and that simultaneous mass flows along the threads are detected. Flows cause the dense threads to move along the prominence magnetic structure while the threads are oscillating. The oscillations have been interpreted in terms of standing magnetohydrodynamic (MHD) kink waves of the magnetic flux tubes, which support the threads. The damping is most likely due to resonant absorption caused by plasma inhomogeneity. The technique of seismology uses the observations combined with MHD wave theory to estimate prominence physical parameters. This paper presents a theoretical study of the joint effect of flow and resonant absorption on the amplitude of standing kink waves in prominence threads. We find that flow and resonant absorption can either be competing effects on the amplitude or both can contribute to damp the oscillations depending on the instantaneous position of the thread within the prominence magnetic structure. The amplitude profile deviates from the classic exponential profile of resonantly damped kink waves in static flux tubes. Flow also introduces a progressive shift of the oscillation period compared to the static case, although this effect is in general of minor importance. We test the robustness of seismological estimates by using synthetic data aiming to mimic real observations. The effect of the thread flow can significantly affect the estimation of the transverse inhomogeneity length scale. The presence of random background noise adds uncertainty to this estimation. Caution needs to be paid to the seismological estimates that do not take the influence of flow into account.
Kink and kink-like waves in pre-stretched Mooney-Rivlin viscoelastic rods
NASA Astrophysics Data System (ADS)
Wang, Y. Z.; Dai, H.-H.; Chen, W. Q.
2015-08-01
The present paper theoretically investigates kink and kink-like waves propagating in pre-stretched Mooney-Rivlin viscoelastic rods. In the constitutive modeling, the Cauchy stress tensor is assumed to consist of an elastic part and a dissipative part. The asymptotic method is adopted to simplify the nonlinear dynamic equations in the limit of finite-small amplitude and long wavelength. Using the reductive perturbation method, we further derive the well-known far-field equation (i.e. the KdV-Burgers equation), to which two kinds of explicit traveling wave solutions are presented. Examples are given to show the influences of pre-stretch and viscosity on the wave shape and wave velocity. It is shown that pre-stretch could be an effective method for modulating the two types of waves. In addition, such waves may be utilized to measure the viscosity coefficient of the material. The competition between the effects of pre-stretch and viscosity on the kink and kink-like waves is also revealed.
Self-Diffusion Along Step-Bottoms on Pt(111)
Feibelman, P.J.
1999-04-05
First-principles total energies of periodic vicinals are used to estimate barriers for Pt-adatom diffusion along straight and kinked steps on Pt(111), and around a corner where straight steps intersect. In all cases studied, hopping diffusion has a lower barrier than concerted substitution. In conflict with simulations of dendritic Pt island formation on Pt(111), hopping from a corner site to a step whose riser is a (111)-micro facet is predicted to be more facile than to one whose riser is a (100).
Current-Driven Kink Instability in Relativistic Jets
NASA Astrophysics Data System (ADS)
Mizuno, Yosuke; Hardee, Philip E.; Lyubarsky, Yuri; Nishikawa, Ken-Ichi
We have investigated the development of current-driven (CD) kink instability in relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depend moderately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.
Current-Driven Kink Instability in Relativistic Jets
NASA Astrophysics Data System (ADS)
Mizuno, Yosuke; Hardee, Philip E.; Lyubarsky, Yuri; Nishikawa, Ken-Ici
2011-06-01
We have investigated the development of current-driven (CD) kink instability in relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic field configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends moderately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.
Intersecting kink bands quantified by laser scanning and differential geometry
NASA Astrophysics Data System (ADS)
Dunham, R. E.; Crider, J. G.
2010-12-01
Microtopography derived from laser scanning is expressed by DEMs that can be analyzed using differential geometry. We apply this technique to rock hand samples containing intersecting kink bands in order to quantitatively describe the shape of a folded surface and understand the localization of strain in deformed rocks. This study is the first to apply laser scanning and geometric curvature analysis to intersecting kink bands in order to better describe the variation of kink band geometries and intersections in plan view and to evaluate relationships between different kink band parameters. A complex set of monoclinal contractional kink bands is well exposed in outcrops of the Darrington Phyllite on Samish Island, northwestern Washington, which provide a three-dimensional view of kink band geometries. Kink bands in cross section have straight, parallel boundaries that deform a well-defined foliation; in plan view, however, kink band hinges curve and anastomose across the foliation surface, and adjacent bands commonly intersect. Three types of intersections are common: crossing (X), bifurcating (Y), and obliquely truncating (λ); many kink bands also taper out along strike. Geometric curvature analyses were performed on millimeter-resolution DEMs of hand samples containing intersecting kink bands. Maps of different curvature parameters (e.g. mean curvature, geologic curvature) clearly outline kink bands in the samples and illuminate the behavior of kink band hinges in each type of intersection. In X-type intersections, curvature increases where two hinges of similar kink sense cross (i.e. anticlinal/anticlinal hinges), increasing strain; where two hinges of opposing sense cross (anticlinal/synclinal), curvature decreases and the surface is effectively unfolded. In Y-type intersections, a single parent band widens and splits into two equally narrow daughter bands, and new inner hinges are nucleated below the bifurcation point. The two daughter bands accommodate
Nonlinear waves in PT -symmetric systems
NASA Astrophysics Data System (ADS)
Konotop, Vladimir V.; Yang, Jianke; Zezyulin, Dmitry A.
2016-07-01
Recent progress on nonlinear properties of parity-time (PT )-symmetric systems is comprehensively reviewed in this article. PT symmetry started out in non-Hermitian quantum mechanics, where complex potentials obeying PT symmetry could exhibit all-real spectra. This concept later spread out to optics, Bose-Einstein condensates, electronic circuits, and many other physical fields, where a judicious balancing of gain and loss constitutes a PT -symmetric system. The natural inclusion of nonlinearity into these PT systems then gave rise to a wide array of new phenomena which have no counterparts in traditional dissipative systems. Examples include the existence of continuous families of nonlinear modes and integrals of motion, stabilization of nonlinear modes above PT -symmetry phase transition, symmetry breaking of nonlinear modes, distinctive soliton dynamics, and many others. In this article, nonlinear PT -symmetric systems arising from various physical disciplines are presented, nonlinear properties of these systems are thoroughly elucidated, and relevant experimental results are described. In addition, emerging applications of PT symmetry are pointed out.
Dependence of kink oscillation damping on the amplitude
NASA Astrophysics Data System (ADS)
Goddard, C. R.; Nakariakov, V. M.
2016-05-01
Context. Kink oscillations of coronal loops are one of the most intensively studied oscillatory phenomena in the solar corona. In the large-amplitude rapidly damped regime, these oscillations are observed to have a low quality factor with only a few cycles of oscillation detected before they are damped. The specific mechanism responsible for rapid damping is commonly accepted to be associated with the linear coupling between collective kink oscillations and localised torsional oscillations, the phenomenon of resonant absorption of the kink mode. The role of finite amplitude effects, however, is still not clear. Aims: We investigated the empirical dependence of the kink oscillation damping time and its quality factor, which is defined as the ratio of damping time to oscillation period, on the oscillation amplitude. Methods: We analysed decaying kink oscillation events detected previously with TRACE, SDO/AIA and and STEREO/EUVI in the extreme ultraviolet (EUV) 171 Å band. Results: We found that the ratio of the kink oscillation damping time to the oscillation period systematically decreases with the oscillation amplitude. We approximated the quality factor dependence on the oscillation displacement amplitude via the power-law dependence with the exponent of -1/2, however we stress that this is a by-eye estimate, and a more rigorous estimation of the scaling law requires more accurate measurements and increased statistics. We conclude that damping of kink oscillations of coronal loops depends on the oscillation amplitude, indicating the possible role of non-linear mechanisms for damping.
Edge plasma boundary layer generated by kink modes in tokamaks
Zakharov, Leonid E.
2011-06-15
This paper describes the structure of the electric current generated by external wall touching and free boundary kink modes at the plasma edge using the ideally conducting plasma model. Both kinds of modes generate {delta}-functional surface current at the plasma edge. Free boundary kink modes also perturb the core plasma current, which in the plasma edge compensates the difference between the {delta}-functional surface currents of free boundary and wall touching kink modes. In addition, the resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.
Edge plasma boundary layer generated by kink modes in tokamaks
NASA Astrophysics Data System (ADS)
Zakharov, Leonid E.
2011-06-01
This paper describes the structure of the electric current generated by external wall touching and free boundary kink modes at the plasma edge using the ideally conducting plasma model. Both kinds of modes generate δ-functional surface current at the plasma edge. Free boundary kink modes also perturb the core plasma current, which in the plasma edge compensates the difference between the δ-functional surface currents of free boundary and wall touching kink modes. In addition, the resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.
Gravitational waves from kinks on infinite cosmic strings
Kawasaki, Masahiro; Miyamoto, Koichi; Nakayama, Kazunori
2010-05-15
Gravitational waves emitted by kinks on infinite strings are investigated using detailed estimations of the kink distribution on infinite strings. We find that gravitational waves from kinks can be detected by future pulsar timing experiments such as SKA for an appropriate value of the string tension, if the typical size of string loops is much smaller than the horizon at their formation. Moreover, the gravitational wave spectrum depends on the thermal history of the Universe and hence it can be used as a probe into the early evolution of the Universe.
Seol, J; Lee, S G; Park, B H; Lee, H H; Terzolo, L; Shaing, K C; You, K I; Yun, G S; Kim, C C; Lee, K D; Ko, W H; Kwak, J G; Kim, W C; Oh, Y K; Kim, J Y; Kim, S S; Ida, K
2012-11-01
It is observed that the magnitude of the toroidal rotation speed is reduced by the central electron cyclotron resonance heating (ECRH) regardless of the direction of the toroidal rotation. The magnetohydrodynamics activities generally appear with the rotation change due to ECRH. It is shown that the internal kink mode is induced by the central ECRH and breaks the toroidal symmetry. When the magnetohydrodynamics activities are present, the toroidal plasma viscosity is not negligible. The observed effects of ECRH on the toroidal plasma rotation are explained by the neoclassical toroidal viscosity in this Letter. It is found that the neoclassical toroidal viscosity torque caused by the internal kink mode damps the toroidal rotation. PMID:23215391
Spatiospectral separation of exceptional points in PT-symmetric optical potentials
NASA Astrophysics Data System (ADS)
Yu, Sunkyu; Piao, Xianji; Mason, Daniel R.; In, Sungjun; Park, Namkyoo
2012-09-01
Non-Hermitian Hamiltonians satisfying parity-time (PT) symmetry reveal unusual physical phenomena related to exceptional points, where the onset of PT symmetry breaking occurs. Here, by permitting dispersive variations in the PT-symmetric potential along the propagation axis of a wave, we show that it is possible to obtain PT-induced exceptional points of spatiospectral separation. As an example, we demonstrate “rainbow nonreciprocity” using a PT-symmetric chirped optical potential.
The kink-pair nucleation in edge dislocation motion
NASA Astrophysics Data System (ADS)
Yu, Song; Wang, Chong-Yu; Yu, Tao
2009-03-01
The motion of edge dislocations (EDs) and kinked EDs in body-centered cubic Fe are studied at atom level. We find the kink-pair nucleation mechanism directly from the atom configuration evolution of dislocation, the EDs move primarily by the kink-pair nucleation, and the pre-existing kink does not affect this motion mode. The result is in agreement with the energy calculation. Furthermore, the Peierls stress, dislocation velocity, and phonon-drag coefficient are discussed. There are obviously two motion regions with different stresses. In the low-stress region, the stress exercises a great influence on the dislocation motion, the dislocation velocity increase significantly with the increase of stress. In the high-stress region, however, phonon drag practice a dominant factor on the dislocation motion, the dislocation move with approximately constant speed close to the transverse speed of sound.
Quantum simulation of magnetic kinks with dipolar lattice gases
NASA Astrophysics Data System (ADS)
Cao, Lushuai; Yin, Xiangguo; Schmelcher, Peter
2015-05-01
We propose an effective Ising spin chain constructed with dipolar quantum gases confined in a one-dimensional optical superlattice. Mapping the motional degrees of freedom of a single particle in the lattice onto a pseudo-spin results in effective transverse and longitudinal magnetic fields. This effective Ising spin chain exhibits a quantum phase transition from a paramagnetic to a single-kink phase as the dipolar interaction increases. Particularly in the single-kink phase, a magnetic kink arises in the effective spin chain and behaves as a quasi-particle in a pinning potential exerted by the longitudinal magnetic field. Being realizable with current experimental techniques, this effective Ising chain presents a unique platform for emulating the quantum phase transition as well as the magnetic kink effects in the Ising-spin chain and enriches the toolbox for quantum emulation of spin models by ultracold quantum gases.
Step and Kink Dynamics in Inorganic and Protein Crystallization
NASA Technical Reports Server (NTRS)
Chernov, A. A.; Rashkovich, L. N.; Vekilov, P. G.; DeYoreo, J. J.
2004-01-01
Behavior of low-kink-density steps in solution growth and consequences for general understanding of spiral crystal growth processes will be overviewed. Also, influence of turbulence on step bunching and possibility to diminish this bunching will be presented.
Ideal internal kink modes in a differentially rotating cylindrical plasma
Mikhailovskii, A. B.; Lominadze, J. G.; Galvao, R. M. O.; Churikov, A. P.; Erokhin, N. N.; Pustovitov, V. D.; Konovalov, S. V.; Smolyakov, A. I.; Tsypin, V. S.
2008-07-15
The Velikhov effect leading to magnetorotational instability (MRI) is incorporated into the theory of ideal internal kink modes in a differentially rotating cylindrical plasma column. It is shown that this effect can play a stabilizing role for suitably organized plasma rotation profiles, leading to suppression of MHD (magnetohydrodynamic) instabilities in magnetic confinement systems. The role of this effect in the problem of the Suydam and the m = 1 internal kink modes is elucidated, where m is the poloidal mode number.
Alpha particle effects on the internal kink modes
Wu, Yanlin; Cheng, C.Z.
1994-08-01
The {alpha}-particle effects on the internal kink mode stability are studied. Finite Grad-Shafranov Shift, plasma {beta}, and plasma shape can significantly enhance the trapped particle drift reversal domain in pitch angle space and reduce average magnetic drift frequency. The drift reversal effect on the ideal kink mode is small, but the {beta}{sub {alpha}} threshold for the fishbone mode can be much lower than previously predicted. In addition, the ion diamagnetic drift has a stronger destabilizing effect.
Stability of neuronal pulses composed of concatenated unstable kinks
NASA Astrophysics Data System (ADS)
Romeo, Mónica M.; Jones, Christopher K.
2001-01-01
We demonstrate that a traveling pulse solution, emerging from the concatenation of two unstable kinks, can be stable. By means of stability analysis and numerical simulations, we show the stability of neuronal pulses (action potentials) with increasing refractory periods, which decompose into two (radiationally) unstable kinks in the limit. These action potentials are solutions of an ultrarefractory version of the FitzHugh-Nagumo system.
ABC of kink kinetics and density in a complex solution
Chernov, A. A.; DeYoreo, J. J.; Rashkovich, L. N.
2007-06-14
This tutorial lecture explains the ways supersaturation in complex solutions may be introduced to be most relevant to describe experimental data on kink and step kinetics. To do so, we express the kink rate via the frequencies of attachment and detachment of the building units and then link these frequencies to the measurable activities of these units in solution. Furthermore, possible reasons for violation of the Gibbs–Thomson law are also briefly discussed with reference to our earlier work.
Canonical quantization of the kink model beyond the static solution
Kapustnikov, A.A.; Pashnev, A.; Pichugin, A.
1997-02-01
A new approach to the quantization of the relativistic kink model around the solitonic solution is developed on the grounds of the collective coordinates method. The corresponding effective action is proved to be the action of the nonminimal d=1+1 point particle with curvature. It is shown that upon canonical quantization this action yields the spectrum of the kink solution obtained first with the help of WKB quantization. {copyright} {ital 1997} {ital The American Physical Society}
Jarzynski equality in PT-symmetric quantum mechanics
Deffner, Sebastian; Saxena, Avadh
2015-04-13
We show that the quantum Jarzynski equality generalizes to PT -symmetric quantum mechanics with unbroken PT -symmetry. In the regime of broken PT -symmetry the Jarzynski equality does not hold as also the CPT -norm is not preserved during the dynamics. These findings are illustrated for an experimentally relevant system – two coupled optical waveguides. It turns out that for these systems the phase transition between the regimes of unbroken and broken PT -symmetry is thermodynamically inhibited as the irreversible work diverges at the critical point.
External Kink Mode in Diverted Tokamaks
NASA Astrophysics Data System (ADS)
Turnbull, A. D.; Ferraro, N. M.; Lao, L. L.; Hanson, J. M.; Turco, F.; Piovesan, P.
2014-10-01
In a straight tokamak model, the external kink mode with toroidal mode number n and poloidal mode number m is predicted to be unstable when the edge safety factor, qedge , lies just below a rational value. In a torus, the picture is essentially unchanged and the 2/1 instability in particular is always encountered when qedge = 2 . For a diverted plasma, the edge q is infinite, but, the experimental limit is then q95 = 2 , where q95 is at the 95% flux surface. However, no theoretical basis has been established for the importance of q95 and ideal predictions indicate stability with qedge > 2 and q95 < 2 instability is found only when the actual q at the edge is below 2. Two possible solutions present themselves. The observed mode may be destabilized as a result of small 3D error fields. Alternatively, the observed mode may be destabilized by the rapidly increased resistivity at the plasma edge. Both possibilities are examined using ideal and resistive MHD tools in two and three dimensions. Work supported in part by the US DOE under DE-FG02-95ER54309, DE-FG02-04ER54761, and DE-FG02-07ER54917.
Gyrokinetic simulation of internal kink modes
Naitou, Hiroshi; Tsuda, Kenji; Lee, W.W.; Sydora, R.D.
1995-05-01
Internal disruption in a tokamak has been simulated using a three-dimensional magneto-inductive gyrokinetic particle code. The code operates in both the standard gyrokinetic mode (total-f code) and the fully nonlinear characteristic mode ({delta}f code). The latter, a recent addition, is a quiet low noise algorithm. The computational model represents a straight tokamak with periodic boundary conditions in the toroidal direction. The plasma is initially uniformly distributed in a square cross section with perfectly conducting walls. The linear mode structure of an unstable m = 1 (poloidal) and n = 1 (toroidal) kinetic internal kink mode is clearly observed, especially in the {delta}f code. The width of the current layer around the x-point, where magnetic reconnection occurs, is found to be close to the collisionless electron skin depth. This is consistent with the theory in which electron inertia has a dominant role. The nonlinear behavior of the mode is found to be quite similar for both codes. Full reconnection in the Alfven time scale is observed along with the electrostatic potential structures created during the full reconnection phase. The E x B drift due to this electrostatic potential dominates the nonlinear phase of the development after the full reconnection.
Simulations of Edge Current Driven Kink Modes with BOUT + + code
NASA Astrophysics Data System (ADS)
Li, G. Q.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Xia, T. Y.; Ma, C. H.; Xi, P. W.
2013-10-01
Edge kink modes (or peeling modes) play a key role in the ELMs. The edge kink modes are driven by peak edge current, which comes from the bootstrap current. We calculated sequences of equilibria with different edge current using CORSICA by keeping total current and pressure profile fixed. Based on these equilibria, with the 3-field BOUT + + code, we calculated the MHD instabilities driven by edge current. For linear low-n ideal MHD modes, BOUT + + results agree with GATO results. With the edge current increasing, the dominant modes are changed from high-n ballooning modes to low-n kink modes. The edge current provides also stabilizing effects on high-n ballooning modes. Furthermore, for edge current scan without keeping total current fixed, the increasing edge current can stabilize the high-n ballooning modes and cannot drive kink modes. The diamagnetic effect can stabilize the high-n ballooning modes, but has no effect on the low-n kink modes. Also, the nonlinear behavior of kink modes is analyzed. Work supported by China MOST grant 2013GB111000 and by China NSF grant 10975161. Also performed for USDOE by LLNL under DE-AC52-07NA27344.
The CD Kink Instability in Magnetically Dominated Relativistic Jets
NASA Astrophysics Data System (ADS)
Hardee, Philip E.; Mizuno, Y.; Lyubarsky, Y.; Nishikawa, K.
2010-03-01
The relativistic jets associated with blazar emission from radio through TeV gamma-rays are thought to be accelerated and collimated by strong helically twisted magnetic fields with footpoints threading the black hole ergosphere and the surrounding accretion disk. The resulting magnetically dominated jet is current-driven (CD) unstable. In a resistive system instability may lead to magnetic reconnection, particle acceleration to the high energies required by the observed emission, and also to the observed kinetically dominated jets far from the central engine. We have investigated the temporal development of current-driven kink instability in magnetically dominated relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We find that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends moderately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch. We also present preliminary results showing the effect of velocity shear on the spatial and temporal development of the CD kink instability.
The CD Kink Instability in Magnetically Dominated Relativistic Jets
NASA Astrophysics Data System (ADS)
Nishikawa, Ken-Ichi; Mizuno, Yosuke; Lyubarsky, Yuri; Hardee, Phil
The relativistic jets associated with blazar emission from radio through TeV gamma-rays are thought to be accelerated and collimated by strong helically twisted magnetic fields with foot-points threading the black hole ergosphere and/or the surrounding accretion disk. The resulting magnetically dominated jet is current-driven (CD) unstable. In a resistive system instability may lead to magnetic reconnection, particle acceleration to the high energies required by the observed emission, and also to the observed kinetically dominated jets far from the central engine. We have investigated the temporal development of current-driven kink instability in magnetically dominated relativistic jets via 3D RMHD simulations. In this investigation a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We find that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends mod-erately on the radial density profile and strongly on the magnetic pitch profile. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch. We also present preliminary results showing the effect of velocity shear on the spatial and temporal development of the CD kink instability.
Moubayidin, Laila; Østergaard, Lars
2015-09-01
985 I. 985 II. 986 III. 987 IV. 988 V. 989 989 References 989 SUMMARY: The development of multicellular organisms depends on correct establishment of symmetry both at the whole-body scale and within individual tissues and organs. Setting up planes of symmetry must rely on communication between cells that are located at a distance from each other within the organism, presumably via mobile morphogenic signals. Although symmetry in nature has fascinated scientists for centuries, it is only now that molecular data to unravel mechanisms of symmetry establishment are beginning to emerge. As an example we describe the genetic and hormonal interactions leading to an unusual bilateral-to-radial symmetry transition of an organ in order to promote reproduction. PMID:26086581
Singular Elasto-Static Field Near a Fault Kink
NASA Astrophysics Data System (ADS)
Arias, Rodrigo; Madariaga, Raúl; Adda-Bedia, Mokhtar
2011-12-01
We study singular elastic solutions at an angular corner left by a crack that has kinked. We have in mind a geophysical context where the faults on either side of the kink are under compression and are ready to slip, or have already slipped, under the control of Coulomb friction. We find separable static singular solutions that are matched across the sides of the corner by applying appropriate boundary conditions. In our more general solution we assume that one of the sides of the corner is about to slide, i.e. it is just contained by friction, and the other may be less pressured. Our solutions display power law behaviour with real exponents that depend continuously on the angle of the corner, the coefficient of static friction and the difference of shear load on both sides of the corner. When friction is the same on both sides of the kink, the solutions split into a symmetric and an antisymmetric solution. The antisymmetric solution corresponds to the simple shear case; while the symmetric solution appears when the kink is loaded by uniaxial stress along the bisector of the kink. The antisymmetric solution is ruled out under this model with contact since the faults cannot sustain tension. When one side of the corner is less pressured one can also distinguish modes with contact overall from others that must open up on one side. These solutions provide an insight into the stress distributions near fault kinks, they can also be used as tools for improving the numerical calculation of kinks under static or dynamic loads.
Doppler displacements in kink MHD waves in solar flux tubes
NASA Astrophysics Data System (ADS)
Goossens, Marcel; Van Doorsselaere, Tom; Terradas, Jaume; Verth, Gary; Soler, Roberto
Doppler displacements in kink MHD waves in solar flux tubes Presenting author: M. Goossens Co-authors: R. Soler, J. Terradas, T. Van Doorsselaere, G. Verth The standard interpretation of the transverse MHD waves observed in the solar atmosphere is that they are non-axisymmetric kink m=1) waves on magnetic flux tubes. This interpretation is based on the fact that axisymmetric and non-axisymmetric fluting waves do not displace the axis of the loop and the loop as a whole while kink waves indeed do so. A uniform transverse motion produces a Doppler displacement that is constant across the magnetic flux tube. A recent development is the observation of Doppler displacements that vary across the loop. The aim of the present contribution is to show that spatial variations of the Doppler displacements across the loop can be caused by kink waves. The motion associated with a kink wave is purely transverse only when the flux tube is uniform and sufficiently thin. Only in that case do the radial and azimuthal components of displacement have the same amplitude and is the azimuthal component a quarter of a period ahead of the radial component. This results in a unidirectional or transverse displacement. When the flux tube is non-uniform and has a non-zero radius the conditions for the generation of a purely transverse motion are not any longer met. In that case the motion in a kink wave is the sum of a transverse motion and a non-axisymmetric rotational motion that depends on the azimuthal angle. It can produce complicated variations of the Doppler displacement across the loop. I shall discuss the various cases of possible Doppler displacenents that can occur depending on the relative sizes of the amplitudes of the radial and azimuthal components of the displacement in the kink wave and on the orientation of the line of sight.
Sustained spheromaks with ideal n = 1 kink stability and pressure confinement
Victor, B. S. Jarboe, T. R.; Hansen, C. J.; Akcay, C.; Morgan, K. D.; Hossack, A. C.; Nelson, B. A.
2014-08-15
Increasing the helicity injector drive frequency up to 68.5 kHz on the Helicity Injected Torus-Steady Inductive (HIT-SI) experiment has produced spheromaks with current amplifications of 3.8, ideal n = 1 kink stability, improved toroidal symmetry and pressure confinement. Current centroid calculations from surface magnetic probes show an outward shift in the magnetic field at frequencies above 50 kHz. Grad-Shafranov equilibria indicate pressure confinement at higher injector operating frequencies. The minimum characteristic frequency needed to achieve this confining effect on HIT-SI plasmas is found to be approximately 30 kHz by analysis of the density fluctuations.
Arnadottir, Liney; Stuve, Eric M.; Jonsson, Hannes
2012-02-01
Surface diffusion of water monomer, dimer, and trimer on the (111) terrace, (221) and (322) stepped, and (763) and (854) kinked surfaces of platinum was studied by density functional theory using the PW91 approximation to the energy functional. Monomer diffusion on the terrace is facile, with an activation barrier of 0.20 eV, while dimer and trimer diffusions are restricted due to their high activation barriers of 0.43 and 0.48 eV, respectively. During monomer diffusion on the terrace the O–Pt distance increases by 0.54 Å, about 23% of the initial distance of 2.34 Å. The calculated rate of monomer diffusion hops is in good agreement with the onset temperature of diffusion measurements of Daschbach et al., J. Chem. Phys., 120 (2004) 1516. Alternative monomer diffusion pathways, in which the molecule rolls or flips, were also found. These pathways have diffusion barriers of 0.22 eV. During dimer diffusion on the terrace, the donor molecule rises 0.4 Å at the saddle point, while the acceptor rises by only 0.03 Å. Monomer diffusion up to steps and kinks, with activation barriers of 0.11–0.13 eV, facilitate chain formation on top of step edges. The energy landscape of monomer diffusion from terrace to step to kink sites is downhill with a maximum activation barrier of 0.26 eV. A model for water adsorption is presented inwhichmonomer diffusion leads to concurrent formation of terrace clusters and population of steps/kinks, the latter consistent with the STMmeasurements ofMorgenstern et al., Phys. Rev. Lett., 77 (1996) 703.
COUPLED ALFVEN AND KINK OSCILLATIONS IN CORONAL LOOPS
Pascoe, D. J.; Wright, A. N.; De Moortel, I.
2010-03-10
Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. However, there is ongoing discussion regarding their interpretation as kink or Alfven waves. To investigate the nature of transverse waves propagating in the solar corona and their potential for use as a coronal diagnostic in MHD seismology, we perform three-dimensional numerical simulations of footpoint-driven transverse waves propagating in a low beta plasma. We consider the cases of both a uniform medium and one with loop-like density structure and perform a parametric study for our structuring parameters. When density structuring is present, resonant absorption in inhomogeneous layers leads to the coupling of the kink mode to the Alfven mode. The decay of the propagating kink wave as energy is transferred to the local Alfven mode is in good agreement with a modified interpretation of the analysis of Ruderman and Roberts for standing kink modes. Numerical simulations support the most general interpretation of the observed loop oscillations as a coupling of the kink and Alfven modes. This coupling may account for the observed predominance of outward wave power in longer coronal loops since the observed damping length is comparable to our estimate based on an assumption of resonant absorption as the damping mechanism.
Twisted kinks, Dirac transparent systems, and Darboux transformations
NASA Astrophysics Data System (ADS)
Correa, F.; Jakubský, V.
2014-12-01
Darboux transformations are employed in construction and analysis of Dirac Hamiltonians with pseudoscalar potentials. By this method, we build a four-parameter class of reflectionless systems. Their potentials correspond to the composition of complex kinks, also known as twisted kinks, that play an important role in the 1 +1 Gross-Neveu and Nambu-Jona-Lasinio field theories. The twisted kinks turn out to be multisolitonic solutions of the integrable Ablowitz-Kaup-Newell-Segur hierarchy. Consequently, all the spectral properties of the Dirac reflectionless systems are reflected in a nontrivial conserved quantity, which can be expressed in a simple way in terms of Darboux transformations. We show that the four-parameter pseudoscalar systems reduce to well-known models for specific choices of the parameters. An associated class of transparent nonrelativistic models described by a matrix Schrödinger Hamiltonian is studied and the rich algebraic structure of their integrals of motion is discussed.
Trapped particle destabilization of the internal kink mode
White, R.B.; Chen, L.; Romanelli, F.; Hay, R.
1984-06-01
The internal kink mode is destabilized by trapped high energy particles, leading to a new branch of the internal kink dispersion relation with a real frequency near the average trapped particle precession frequency and a growth rate of the same magnitude. This trapped particle branch of the dispersion relation is investigated numerically for a variety of particle distributions. Mode growth rate and frequency are found as a function of plasma ..beta.., density, and trapped particle energy and distribution. The high energy trapped particle sources considered are neutral beam injection, ion cyclotron heating, and fusion alpha particles. Relevance for various plasma heating schemes is discussed.
Edge Plasma Boundary Layer Generated By Kink Modes in Tokamaks
L.E. Zakharov
2010-11-22
This paper describes the structure of the electric current generated by external kink modes at the plasma edge using the ideally conducting plasma model. It is found that the edge current layer is created by both wall touching and free boundary kink modes. Near marginal stability, the total edge current has a universal expression as a result of partial compensation of the δ-functional surface current by the bulk current at the edge. The resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.
Parity-time-symmetry breaking in two-dimensional photonic crystals: Square lattice
NASA Astrophysics Data System (ADS)
Mock, Adam
2016-06-01
We consider theoretically materials whose electromagnetic properties possess parity-time (PT ) symmetry and are periodic in two dimensions. When designed for optical frequencies such structures are commonly known as two-dimensional (2D) photonic crystals. With the addition of PT symmetry the optical modes of 2D photonic crystals exhibit thresholdless spontaneous PT -symmetry breaking near the Brillouin zone boundary, which is analogous to what has previously been studied in PT -symmetric structures with one-dimensional periodicity. Consistent with previous work, we find that spontaneous PT -symmetry breaking occurs at band crossings in the photonic dispersion diagram. Due to the extra spatial degree of freedom in 2D periodic systems, their band structures contain more band crossings and higher-order degeneracies than their one-dimensional counterparts. This work provides a comprehensive theoretical analysis of spontaneous PT -symmetry breaking at these points in the band structure. We find that, as in the case of one-dimensional structures, photonic band gaps exist at k =0 . We also find that at points of degeneracy with order higher than 2, bands merge pairwise to form broken-PT -symmetry supermodes. If the degeneracy order is even, this means multiple pairs of bands can form distinct (nondegenerate) broken-symmetry supermodes. If the order of degeneracy is odd, at least one of the bands will have protected PT symmetry. At other points of degeneracy, we find that the PT symmetry of the modes may be protected and we provide a spatial mode symmetry argument to explain this behavior. Finally, we identify a point at which two broken-PT -symmetry supermodes become degenerate, creating a point of fourfold degeneracy in the broken-PT -symmetry regime.
Numerical Illustration of pi-Kinks as Fundamental Nonlinear Modes in Sine-Lattice Equation
NASA Astrophysics Data System (ADS)
Homma, S.
1987-05-01
We study the dynamics of the sine-lattice equation by ddot{u}_{n}-sin (u_{n+1}-u_{n})+sin (u_{n}-u_{n-1})=0, in which there exist pi-kinks as well as 2pi-kinks. Numerical simulations show that a static 2pi-kink (antikink), initially put on a system, splits into two pi-kinks (antikinks), moving opposite directions with each other. It is also observed that with an appropriate initial impulse a pair of pi-kink and anti pi-kink is created from the ground state. These facts suggest that pi-kink [pi-K] and anti pi-kink [pi-bar{K}] are fundamental nonlinear modes in the system described by the equation given above.
Erickson, Jeremiah D; Mednikov, Evgueni G; Ivanov, Sergei A; Dahl, Lawrence F
2016-02-10
We present the first successful isolation and crystallographic characterization of a Mackay 55-metal-atom two-shell icosahedron, Pd55L12(μ3-CO)20 (L = PPr(i)3) (1). Its two-shell icosahedron of pseudo-Ih symmetry (without isopropyl substituents) enables a structural/bonding comparison with interior 55-metal-atom two-shell icosahedral geometries observed within the multi-shell capped 145-metal-atom three-shell Pd145(CO)72(PEt3)30 and 165-metal-atom four-shell Pt-centered (μ12-Pt)Pd164-xPtx(CO)72(PPh3)20 (x ≈ 7) nanoclusters, and within the recently reported four-shell Au133(SC6H4-p-Bu(t))52 nanocluster. DFT calculations carried out on a Pd55(CO)20(PH3)12 model analogue, with triisopropyl phosphine substituents replaced by H atoms, revealed a positive +0.84 e charge for the entire Pd55 core, with a highly positive second-shell Pd42 surface of +1.93 e. PMID:26790717
Global gyrokinetic particle-in-cell simulations of internal kink instabilities
Mishchenko, Alexey; Zocco, Alessandro
2012-12-15
Internal kink instabilities have been studied in straight tokamak geometry employing an electromagnetic gyrokinetic particle-in-cell (PIC) code. The ideal-MHD internal kink mode and the collisionless m=1 tearing mode have been successfully simulated with the PIC code. Diamagnetic effects on the internal kink modes have also been investigated.
Morphology and Growth Kinetics of Straight and Kinked Tin Whiskers
NASA Astrophysics Data System (ADS)
Susan, Donald; Michael, Joseph; Grant, Richard P.; McKenzie, Bonnie; Yelton, W. Graham
2013-03-01
Time-lapse SEM studies of Sn whiskers were conducted to estimate growth kinetics and document whisker morphologies. For straight whiskers, growth rates of 3 to 4 microns per day were measured at room temperature. Two types of kinked whiskers were observed. For Type A kinks, the original growth segment spatial orientation remains unchanged, there are no other changes in morphology or diameter, and growth continues. For Type B kinks, the spatial orientation of the original segment changes and it appears that the whisker bends over. Whiskers with Type B kinks show changes in morphology and diameter at the base, indicating grain boundary motion in the film, which eliminates the conditions suitable for long-term whisker growth. To estimate the errors in the whisker growth measurements, a technique is presented to correct for SEM projection effects. With this technique, the actual growth angles and lengths of a large number of whiskers were collected. It was found that most whiskers grow at moderate or shallow angles with respect to the surface; few straight whiskers grow nearly normal to the surface. In addition, there is no simple correlation between growth angles and lengths for whiskers observed over an approximate 2-year period.
Euler buckling and nonlinear kinking of double-stranded DNA.
Fields, Alexander P; Meyer, Elisabeth A; Cohen, Adam E
2013-11-01
The bending stiffness of double-stranded DNA (dsDNA) at high curvatures is fundamental to its biological activity, yet this regime has been difficult to probe experimentally, and literature results have not been consistent. We created a 'molecular vise' in which base-pairing interactions generated a compressive force on sub-persistence length segments of dsDNA. Short dsDNA strands (<41 base pairs) resisted this force and remained straight; longer strands became bent, a phenomenon called 'Euler buckling'. We monitored the buckling transition via Förster Resonance Energy Transfer (FRET) between appended fluorophores. For low-to-moderate concentrations of monovalent salt (up to ∼150 mM), our results are in quantitative agreement with the worm-like chain (WLC) model of DNA elasticity, without the need to invoke any 'kinked' states. Greater concentrations of monovalent salts or 1 mM Mg(2+) induced an apparent softening of the dsDNA, which was best accounted for by a kink in the region of highest curvature. We tested the effects of all single-nucleotide mismatches on the DNA bending. Remarkably, the propensity to kink correlated with the thermodynamic destabilization of the mismatched DNA relative the perfectly complementary strand, suggesting that the kinked state is locally melted. The molecular vise is exquisitely sensitive to the sequence-dependent linear and nonlinear elastic properties of dsDNA. PMID:23956222
One-loop kink mass shifts: A computational approach
NASA Astrophysics Data System (ADS)
Alonso Izquierdo, A.; Guilarte, J. Mateos
2011-11-01
In this paper we develop a procedure to compute the one-loop quantum correction to the kink masses in generic (1+1)-dimensional one-component scalar field theoretical models. The procedure uses the generalized zeta function regularization method helped by the Gilkey-de Witt asymptotic expansion of the heat function via Mellin's transform. We find a formula for the one-loop kink mass shift that depends only on the part of the energy density with no field derivatives, evaluated by means of a symbolic software algorithm that automates the computation. The improved algorithm with respect to earlier work in this subject has been tested in the sine-Gordon and λ(ϕ)24 models. The quantum corrections of the sG-soliton and λ(-kink masses have been estimated with a relative error of 0.00006% and 0.00007% respectively. Thereafter, the algorithm is applied to other models. In particular, an interesting one-parametric family of double sine-Gordon models interpolating between the ordinary sine-Gordon and a re-scaled sine-Gordon model is addressed. Another one-parametric family, in this case of ϕ models, is analyzed. The main virtue of our procedure is its versatility: it can be applied to practically any type of relativistic scalar field models supporting kinks.
Standing Kink modes in three-dimensional coronal loops
Pascoe, D. J.; De Moortel, I.
2014-04-01
So far, the straight flux tube model proposed by Edwin and Roberts is the most commonly used tool in practical coronal seismology, in particular, to infer values of the (coronal) magnetic field from observed, standing kink mode oscillations. In this paper, we compare the period predicted by this basic model with three-dimensional (3D) numerical simulations of standing kink mode oscillations, as the period is a crucial parameter in the seismological inversion to determine the magnetic field. We perform numerical simulations of standing kink modes in both straight and curved 3D coronal loops and consider excitation by internal and external drivers. The period of oscillation for the displacement of dense coronal loops is determined by the loop length and the kink speed, in agreement with the estimate based on analytical theory for straight flux tubes. For curved coronal loops embedded in a magnetic arcade and excited by an external driver, a secondary mode with a period determined by the loop length and external Alfvén speed is also present. When a low number of oscillations is considered, these two periods can result in a single, non-resolved (broad) peak in the power spectrum, particularly for low values of the density contrast for which the two periods will be relatively similar. In that case (and for this particular geometry), the presence of this additional mode would lead to ambiguous seismological estimates of the magnetic field strength.
Anti-parity-time symmetry via flying atoms
NASA Astrophysics Data System (ADS)
Wen, Jianming; Jiang, Liang; Xiao, Yanhong; Peng, Peng; Cao, Wanxia; Shen, Ce; Qu, Weizhi
We report the first experimental demonstration of optical anti-parity-time (anti-PT) symmetry, a counterpart of conventional PT symmetry, in a warm atomic-vapor cell. By exploiting rapid coherence transport via flying atoms, our scheme illustrates essential features of anti-PT symmetry with an unprecedented precision on phase-transition threshold, and substantially reduces experimental complexity and cost, in contrast to most previous experimental studies relying highly on the advances of nanotechnologies and sophisticated fabrication techniques to synthesize solid-state materials. Of importance, our results represent a significant advance in non-Hermitian physics by bridging a firm connection with the field of atomic, molecular and optical physics, where novel phenomena and applications in quantum and nonlinear optics aided by (anti-)PT symmetry can be anticipated
ERIC Educational Resources Information Center
Attanucci, Frank J.; Losse, John
2008-01-01
In a first calculus course, it is not unusual for students to encounter the theorems which state: If f is an even (odd) differentiable function, then its derivative is odd (even). In our paper, we prove some theorems which show how the symmetry of a continuous function f with respect to (i) the vertical line: x = a or (ii) with respect to the…
Consistency of PT-symmetric quantum mechanics
NASA Astrophysics Data System (ADS)
Brody, Dorje C.
2016-03-01
In recent reports, suggestions have been put forward to the effect that parity and time-reversal (PT) symmetry in quantum mechanics is incompatible with causality. It is shown here, in contrast, that PT-symmetric quantum mechanics is fully consistent with standard quantum mechanics. This follows from the surprising fact that the much-discussed metric operator on Hilbert space is not physically observable. In particular, for closed quantum systems in finite dimensions there is no statistical test that one can perform on the outcomes of measurements to determine whether the Hamiltonian is Hermitian in the conventional sense, or PT-symmetric—the two theories are indistinguishable. Nontrivial physical effects arising as a consequence of PT symmetry are expected to be observed, nevertheless, for open quantum systems with balanced gain and loss.
Clash of symmetries in a Randall-Sundrum-like spacetime
Dando, Gareth; George, Damien P.; Volkas, Raymond R.; Davidson, Aharon; Wali, K.C.
2005-08-15
We present a toy model that exhibits clash-of-symmetries style Higgs field kink configurations in a Randall-Sundrum-like spacetime. The model has two complex scalar fields {phi}{sub 1,2}, with a sextic potential obeying global U(1)xU(1) and discrete {phi}{sub 1}{r_reversible}{phi}{sub 2} interchange symmetries. The scalar fields are coupled to 4+1 dimensional gravity endowed with a bulk cosmological constant. We show that the coupled Einstein-Higgs field equations have an interesting analytic solution provided the sextic potential adopts a particular form. The 4+1 metric is shown to be that of a smoothed-out Randall-Sundrum type of spacetime. The thin-brane Randall-Sundrum limit, whereby the Higgs field kinks become step functions, is carefully defined in terms of the fundamental parameters in the action. The 'clash-of-symmetries' feature, defined in previous papers, is manifested here through the fact that both of the U(1) symmetries are spontaneously broken at all nonasymptotic points in the extra dimension w. One of the U(1)'s is asymptotically restored as w{yields}-{infinity}, with the other U(1) restored as w{yields}+{infinity}. The spontaneously broken discrete symmetry ensures topological stability. In the gauged version of this model we find new flat-space solutions, but in the warped metric case we have been unable to find any solutions with nonzero gauge fields.
Chiral selectivity of amino acid adsorption on chiral surfaces—The case of alanine on Pt
Franke, J.-H.; Kosov, D. S.
2015-02-07
We study the binding pattern of the amino acid alanine on the naturally chiral Pt surfaces Pt(531), Pt(321), and Pt(643). These surfaces are all vicinal to the (111) direction but have different local environments of their kink sites and are thus a model for realistic roughened Pt surfaces. Alanine has only a single methyl group attached to its chiral center, which makes the number of possible binding conformations computationally tractable. Additionally, only the amine and carboxyl group are expected to interact strongly with the Pt substrate. On Pt(531), we study the molecule in its pristine as well as its deprotonated form and find that the deprotonated one is more stable by 0.47 eV. Therefore, we study the molecule in its deprotonated form on Pt(321) and Pt(643). As expected, the oxygen and nitrogen atoms of the deprotonated molecule provide a local binding “tripod” and the most stable adsorption configurations optimize the interaction of this “tripod” with undercoordinated surface atoms. However, the interaction of the methyl group plays an important role: it induces significant chiral selectivity of about 60 meV on all surfaces. Hereby, the L-enantiomer adsorbs preferentially to the Pt(321){sup S} and Pt(643){sup S} surfaces, while the D-enantiomer is more stable on Pt(531){sup S}. The binding energies increase with increasing surface density of kink sites, i.e., they are largest for Pt(531){sup S} and smallest for Pt(643){sup S}.
Strained DNA is kinked by low concentrations of Zn2+
Han, Wenhai; Dlakic, Mensur; Zhu, Yinwen Judy; Lindsay, S. M.; Harrington, Rodney E.
1997-01-01
A novel atomic force microscope with a magnetically oscillated tip has provided unprecedented resolution of small DNA fragments spontaneously adsorbed to mica and imaged in situ in the presence of divalent ions. Kinks (localized bends of average angle 78°) were observed in axially strained minicircles consisting of tandemly repeated d(A)5 and d(GGGCC[C]) sequences. The frequency of kinks in identical minicircles increased 4-fold in the presence of 1 mM Zn2+ compared with 1 mM Mg2+. Kinking persisted in mixed Mg2+/Zn2+ electrolytes until the Zn2+ concentration dropped below 100 μM, indicating that this type of kinking may occur under physiological conditions. Kinking appears to replace intrinsic bending, and statistical analysis shows that kinks are not localized within any single sequence element. A surprisingly small free energy is associated with kink formation. PMID:9380675
Kink instability suppression with stochastic cooling pickup and kicker
Hao Y.; Blaskiewicz, M.; Litvinenko, V.N.; Ptitsyn, V.
2012-05-20
The kink instability is one of the major beam dynamics issues of the linac-ring based electron ion collider. This head-tail type instability arises from the oscillation of the electron beam inside the opposing ion beam. It must be suppressed to achieve the desired luminosity. There are various ways to suppress the instability, such as tuning the chromaticity in the ion ring or by a dedicated feedback system of the electron beam position at IP, etc. However, each method has its own limitation. In this paper, we will discuss an alternative opportunity of suppressing the kink instability of the proposed eRHIC at BNL using the existing pickup-kicker system of the stochastic cooling system in RHIC.
Exactly solvable PT -symmetric models in two dimensions
NASA Astrophysics Data System (ADS)
Agarwal, Kaustubh S.; Pathak, Rajeev K.; Joglekar, Yogesh N.
2015-11-01
Non-Hermitian, PT -symmetric Hamiltonians, experimentally realized in optical systems, accurately model the properties of open, bosonic systems with balanced, spatially separated gain and loss. We present a family of exactly solvable, two-dimensional, PT potentials for a non-relativistic particle confined in a circular geometry. We show that the PT -symmetry threshold can be tuned by introducing a second gain-loss potential or its Hermitian counterpart. Our results explicitly demonstrate that PT breaking in two dimensions has a rich phase diagram, with multiple re-entrant PT -symmetric phases.
Kinks and bell-type solitons in microtubules
NASA Astrophysics Data System (ADS)
Zdravković, Slobodan; Gligorić, Goran
2016-06-01
In the present paper, we study the nonlinear dynamics of microtubules relying on the known u-model. As a mathematical procedure, we use the simplest equation method. We recover some solutions obtained earlier using less general methods. These are kink solitons. In addition, we show that the solution of the crucial differential equation, describing nonlinear dynamics of microtubules, can be a bell-type soliton. The discovery of this new solution is supported by numerical analysis.
Hexagons, kinks, and disorder in oscillated granular layers
Melo, F.; Umbanhowar, P.B.; Swinney, H.L.
1995-11-20
Experiments on vertically oscillated granular layers in an evacuated container reveal a sequence of well-defined pattern bifurcations as the container acceleration is increased. Period doublings of the layer center of mass motion and a standing wave instability interact to produce hexagons and more complicated patterns composed of distinct spatial domains of different relative phase separated by kinks (phase discontinuities). A simple model displays quantitative agreement with the observed transition sequence. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.
Kinks and bell-type solitons in microtubules.
Zdravković, Slobodan; Gligorić, Goran
2016-06-01
In the present paper, we study the nonlinear dynamics of microtubules relying on the known u-model. As a mathematical procedure, we use the simplest equation method. We recover some solutions obtained earlier using less general methods. These are kink solitons. In addition, we show that the solution of the crucial differential equation, describing nonlinear dynamics of microtubules, can be a bell-type soliton. The discovery of this new solution is supported by numerical analysis. PMID:27368766
Kink folding in an extended terrane: Tortilla Mountains, southeastern Arizona
NASA Astrophysics Data System (ADS)
Naruk, Stephen J.; Bykerk-Kauffman, Ann; Currier-Lewis, Debra; Davis, George H.; Faulds, James E.; Lewis, Scott W.
1986-12-01
Structural analysis of early Miocene metre-scale kink folds in southeastern Arizona shows that they formed in an extensional stress field and that they record horizontal extension. The folds represent a previously unrecognized style of extensional fold. *Present addresses: Faulds—Department of Geology, University of New Mexico, Albuquerque, New Mexico 87131; Currier-Lewis and Lewis—Calpine Energy Corporation, San Jose, California 95110
Kink modes and surface currents associated with vertical displacement events
NASA Astrophysics Data System (ADS)
Manickam, Janardhan; Boozer, Allen; Gerhardt, Stefan
2012-08-01
The fast termination phase of a vertical displacement event (VDE) in a tokamak is modeled as a sequence of shrinking equilibria, where the core current profile remains constant so that the safety-factor at the axis, qaxis, remains fixed and the qedge systematically decreases. At some point, the n = 1 kink mode is destabilized. Kink modes distort the magnetic field lines outside the plasma, and surface currents are required to nullify the normal component of the B-field at the plasma boundary and maintain equilibrium at finite pressure. If the plasma touches a conductor, the current can be transferred to the conductor, and may be measurable by the halo current monitors. This report describes a practical method to model the plasma as it evolves during a VDE, and determine the surface currents, needed to maintain equilibrium. The main results are that the onset conditions for the disruption are that the growth-rate of the n = 1 kink exceeds half the Alfven time and the associated surface current needed to maintain equilibrium exceeds one half of the core plasma current. This occurs when qedge drops below a low integer, usually 2. Application to NSTX provides favorable comparison with non-axisymmetric halo-current measurements. The model is also applied to ITER and shows that the 2/1 mode is projected to be the most likely cause of the final disruption.
Low-temperature dynamics of kinks on Ising interfaces.
Karma, Alain; Lobkovsky, Alexander E
2005-03-01
The anisotropic motion of an interface driven by its intrinsic curvature or by an external field is investigated in the context of the kinetic Ising model in both two and three dimensions. We derive in two dimensions (2D) a continuum evolution equation for the density of kinks by a time-dependent and nonlocal mapping to the asymmetric exclusion process. Whereas kinks execute random walks biased by the external field and pile up vertically on the physical 2D lattice, they execute hard-core biased random walks on a transformed 1D lattice. Their density obeys a nonlinear diffusion equation which can be transformed into the standard expression for the interface velocity, v=M [ (gamma+gamma'') kappa+H] , where M , gamma+gamma", and kappa are the interface mobility, stiffness, and curvature, respectively. In 3D, we obtain the velocity of a curved interface near the 100 orientation from an analysis of the self-similar evolution of 2D shrinking terraces. We show that this velocity is consistent with the one predicted from the 3D tensorial generalization of the law for anisotropic curvature-driven motion. In this generalization, both the interface stiffness tensor and the curvature tensor are singular at the 100 orientation. However, their product, which determines the interface velocity, is smooth. In addition, we illustrate how this kink-based kinetic description provides a useful framework for studying more complex situations by modeling the effect of immobile dilute impurities. PMID:15903500
Spectral Element Simulations of Rupture Dynamics along kinked faults
NASA Astrophysics Data System (ADS)
Vilotte, J.; Festa, G.; Madariaga, R.
2005-12-01
Numerical simulation of earthquake source dynamics provides key elements for ground-motion prediction and insights into the physics of dynamic rupture propagation. Faulting is controlled by non-linear frictional interactions and damage within the fault zone. Important features of the earthquakes dynamics, such as rupture velocity, arrest phase and high-frequency radiation are believed to be strongly influenced by the geometry of the faults (kinks, jogs and forks). Data analysis as well as kinematic inversions have pointed out potential links between super-shear and geometry, as in the case of the Denali and Izmit earthquakes. Finally, recent laboratory experiments of sub- and super-shear rupture propagation along kink interfaces have shed new lights on these phenomena. We present here spectral element simulations of the dynamic rupture propagation along kinked and curved fault interfaces, a problem that has been experimentally investigated by Rousseau and Rosakis (2003). Depending on the state of the initial stress, we numerically analyze the mechanics of the dynamical fault branching for sub- and super-shear rupture propagation. Special interest is devoted to source directivity effects and high frequency generation related to the branching process. Implications for strong motion analysis will be discussed. This work was supported by the SPICE - Research and Training project
Wang, Lijun; Zhao, Feng; Wang, Daming; Hu, Shen; Liu, Jiachun; Zhou, Zhilun; Lu, Jun; Qi, Peng; Song, Shiying
2016-01-01
Background. Whether carotid tortuosity/kinking of the internal carotid artery leads to cerebral ischemia remains unclear. There is very little research about the hemodynamic variation induced by carotid tortuosity/kinking in the literature. The objective of this study was to research the blood pressure changes induced by carotid tortuosity/kinking. Methods. We first created a geometric model of carotid tortuosity/kinking. Based on hemodynamic boundary conditions, the hemodynamics of carotid tortuosity and kinking were studied via a finite element simulation. Then, an in vitro system was built to validate the numerical simulation results. The mean arterial pressure changes before and after carotid kinking were measured using pressure sensors in 12 patients with carotid kinking. Results. Numerical simulation revealed that the pressure drops increased with increases in the kinking angles. Clinical tests and in vitro experiments confirmed the numerical simulation results. Conclusions. Carotid kinking leads to blood pressure reduction. In certain conditions, kinking may affect the cerebral blood supply and be associated with cerebral ischemia. PMID:27195283
None
2011-10-06
- Physics, as we know it, attempts to interpret the diverse natural phenomena as particular manifestations of general laws. This vision of a world ruled by general testable laws is relatively recent in the history of mankind. Basically it was initiated by the Galilean inertial principle. The subsequent rapid development of large-scale physics is certainly tributary to the fact that gravitational and electromagnetic forces are long-range and hence can be perceived directly without the mediation of highly sophisticated technical devices. - The discovery of subatomic structures and of the concomitant weak and strong short-range forces raised the question of how to cope with short-range forces in relativistic quantum field theory. The Fermi theory of weak interactions, formulated in terms of point-like current-current interaction, was well-defined in lowest order perturbation theory and accounted for existing experimental data.However, it was inconsistent in higher orders because of uncontrollable divergent quantum fluctuations. In technical terms, in contradistinction to quantum electrodynamics, the Fermi theorywas not ?renormalizable?. This difficulty could not be solved by smoothing the point-like interaction by a massive, and therefore short-range, charged ?vector? particle exchange: theories with massive charged vector bosons were not renormalizable either. In the early nineteen sixties, there seemed to be insuperable obstacles to formulating a consistent theory with short-range forces mediated by massive vectors. - The breakthrough came from the notion of spontaneous symmetry breaking which arose in the study of phase transitions and was introduced in field theory by Nambu in 1960. - Ferromagnets illustrate the notion in phase transitions. Although no direction is dynamically preferred, the magnetization selects a global orientation. This is a spontaneous broken symmetry(SBS)of rotational invariance. Such continuous SBS imply the existence of ?massless? modes
NASA Astrophysics Data System (ADS)
Ikonomov, Julian; Starbova, Kirilka; Giesen, Margret
2007-03-01
Using temperature-variable scanning tunneling microscopy, we studied the coalescence of vacancy islands on Cu(0 0 1) in ultra-high vacuum. From the temperature dependence of the relaxation of merged vacancy islands to the equilibrium shape we obtain an activation energy of the island coalescence process of 0.76 eV. From that value we deduce an activation energy for the atomic hopping coefficient of E=0.89 eV. Comparing our result with previous STM data on step fluctuations with dominant diffusion along straight step segments ( E=0.68 eV; [M. Giesen, S. Dieluweit, J. Mol. Catal. A: Chem. 216 (2004) 263]) and step fluctuations with kink crossing ( E=0.9 eV; [M. Giesen-Seibert, F. Schmitz, R. Jentjens, H. Ibach, Surf. Sci. 329 (1995) 47]), we conclude that there is a large extra barrier for diffusion of atoms across kinks on Cu(0 0 1) of the order of 0.23 eV. This is the first direct experimental evidence for the existence of a large kink Ehrlich-Schwoebel barrier on Cu(0 0 1).
NASA Astrophysics Data System (ADS)
John, T.; Klemd, R.; Scherer, E. E.; Rondenay, S.; Gao, J.
2012-12-01
Sudden changes in the dip of subducted oceanic plates have been resolved by seismic imaging [1, 2]. Such kinking often coincides with the seismic disappearance of the low-velocity subducted oceanic crust, i.e., at a depth where eclogitization (dehydration) of the upper oceanic crust is nearly complete and the oceanic crust becomes almost seismically indistinguishable from mantle peridotite. We present petrological evidence for this phenomenon derived from oceanic blueschist- and eclogite-facies rocks from the Chinese Tianshan. The peak-metamorphic conditions of the samples range between 330 and 580°C at 1.5 to 2.3 GPa. Such a wide range of peak conditions for intercalated high- and ultrahigh-pressure rocks has also been reported from other Tianshan localities. These observations suggest that the rocks were derived from different depths within the subduction zone and later juxtaposed during exhumation within the subduction channel. Multi-point Lu-Hf isochrons from four high-pressure rocks yield consistent garnet-growth ages of around ~315 Ma, confirming that the eclogite-facies metamorphism of the Tianshan high-pressure rocks resulted from a single subduction event in the Late Carboniferous. These ages, in conjunction with the ~311 Ma cluster of 40Ar-39Ar and Rb-Sr white mica ages from the same localities imply rapid exhumation. Previously reported peak P-T estimates from UHP metasediments and eclogites all lie on a lower geothermal gradient—and thus on a colder P-T path at the slab-wedge interface—than that defined by the HP eclogites and meta-volcaniclastic rocks studied here. This suggests that the slab-subduction angle steepened sharply at approximately 90 km depth, just between the depths at which the HP and UHP rocks equilibrated. The increase in subduction angle may result from a greater slab pull resulting from eclogitization densification. An additional factor may be an ephemeral weakening of the slab as it undergoes eclogitization reactions [3, 4]. We
Sublattice Interference as the Origin of σ Band Kinks in Graphene.
Jung, Sung Won; Shin, Woo Jong; Kim, Jimin; Moreschini, Luca; Yeom, Han Woong; Rotenberg, Eli; Bostwick, Aaron; Kim, Keun Su
2016-05-01
Kinks near the Fermi level observed in angle-resolved photoemission spectroscopy (ARPES) have been widely accepted to represent electronic coupling to collective excitations, but kinks at higher energies have eluded a unified description. We identify the mechanism leading to such kink features by means of ARPES and tight-binding band calculations on σ bands of graphene, where anomalous kinks at energies as high as ∼4 eV were reported recently [Phys. Rev. Lett. 111, 216806 (2013)]. We found that two σ bands show a strong intensity modulation with abruptly vanishing intensity near the kink features, which is due to sublattice interference. The interference induced local singularity in the matrix element is a critical factor that gives rise to apparent kink features, as confirmed by our spectral simulations without involving any coupling to collective excitations. PMID:27203340
Sublattice Interference as the Origin of σ Band Kinks in Graphene
NASA Astrophysics Data System (ADS)
Jung, Sung Won; Shin, Woo Jong; Kim, Jimin; Moreschini, Luca; Yeom, Han Woong; Rotenberg, Eli; Bostwick, Aaron; Kim, Keun Su
2016-05-01
Kinks near the Fermi level observed in angle-resolved photoemission spectroscopy (ARPES) have been widely accepted to represent electronic coupling to collective excitations, but kinks at higher energies have eluded a unified description. We identify the mechanism leading to such kink features by means of ARPES and tight-binding band calculations on σ bands of graphene, where anomalous kinks at energies as high as ˜4 eV were reported recently [Phys. Rev. Lett. 111, 216806 (2013)]. We found that two σ bands show a strong intensity modulation with abruptly vanishing intensity near the kink features, which is due to sublattice interference. The interference induced local singularity in the matrix element is a critical factor that gives rise to apparent kink features, as confirmed by our spectral simulations without involving any coupling to collective excitations.
A quasi-cyclic RNA nano-scale molecular object constructed using kink turns.
Huang, Lin; Lilley, David M J
2016-08-18
k-Turns are widespread RNA architectural elements that mediate tertiary interactions. We describe a double-kink-turn motif comprising two inverted k-turns that forms a tight horse-shoe structure that can assemble into a variety of shapes by coaxial association of helical ends. Using X-ray crystallography we show that these assemble with two (dumbell), three (triangle) and four units (square), with or without bound protein, within the crystal lattice. In addition, exchange of a single basepair can almost double the pore radius or shape of a molecular assembly. On the basis of this analysis we synthesized a 114 nt self-complementary RNA containing six k-turns. The crystal structure of this species shows that it forms a quasi-cyclic triangular object. These are randomly disposed about the three-fold axis in the crystal lattice, generating a circular RNA of quasi D3 symmetry with a shape reminiscent of that of a cyclohexane molecule in its chair conformation. This work demonstrates that the k-turn is a powerful building block in the construction of nano-scale molecular objects, and illustrates why k-turns are widely used in natural RNA molecules to organize long-range architecture and mediate tertiary contacts. PMID:27506301
Internal Kink Mode Dynamics in High-beta NSTX Plasmas
J.E. Menard; R.E. Bell; E.D. Fredrickson; D.A. Gates; S.M. Kaye; B.P. LeBlanc; S.S. Medley; W. Park; S.A. Sabbagh; A. Sontag; D. Stutman; K. Tritz; W. Zhu; the NSTX Research Team
2004-12-22
Saturated internal kink modes have been observed in many of the highest toroidal {beta} discharges of the National Spherical Torus Experiment (NSTX). These modes often cause rotation flattening in the plasma core, can degrade energy confinement, and in some cases contribute to the complete loss of plasma angular momentum and stored energy. Characteristics of the modes are measured using soft X-ray, kinetic profile, and magnetic diagnostics. Toroidal flows approaching Alfvenic speeds, island pressure peaking, and enhanced viscous and diamagnetic effects associated with high-{beta} may contribute to mode nonlinear stabilization. These saturation mechanisms are investigated for NSTX parameters and compared to experimental data.
Kinks and small-scale structure on cosmic strings
Copeland, E. J.; Kibble, T. W. B.
2009-12-15
We discuss some hitherto puzzling features of the small-scale structure of cosmic strings. We argue that kinks play a key role, and that an important quantity to study is their sharpness distribution. In particular we suggest that for very small scales the two-point correlation function of the string tangent vector varies linearly with the separation and not as a fractional power, as proposed by Polchinski and Rocha [Phys. Rev. D 74, 083504 (2006)]. However, our results are consistent with theirs, because the range of scales to which this linearity applies shrinks as evolution proceeds.
Henley, E.M.
1981-09-01
Internal and space-time symmetries are discussed in this group of lectures. The first of the lectures deals with an internal symmetry, or rather two related symmetries called charge independence and charge symmetry. The next two discuss space-time symmetries which also hold approximately, but are broken only by the weak forces; that is, these symmetries hold for both the hadronic and electromagnetic forces. (GHT)
NASA Astrophysics Data System (ADS)
Bender, Carl M.
2015-07-01
The average quantum physicist on the street would say that a quantum-mechanical Hamiltonian must be Dirac Hermitian (invariant under combined matrix transposition and complex conjugation) in order to guarantee that the energy eigenvalues are real and that time evolution is unitary. However, the Hamiltonian H = p2 + ix3, which is obviously not Dirac Hermitian, has a positive real discrete spectrum and generates unitary time evolution, and thus it defines a fully consistent and physical quantum theory. Evidently, the axiom of Dirac Hermiticity is too restrictive. While H = p2 + ix3 is not Dirac Hermitian, it is PT symmetric; that is, invariant under combined parity P (space reflection) and time reversal T. The quantum mechanics defined by a PT-symmetric Hamiltonian is a complex generalization of ordinary quantum mechanics. When quantum mechanics is extended into the complex domain, new kinds of theories having strange and remarkable properties emerge. In the past few years, some of these properties have been verified in laboratory experiments. A particularly interesting PT-symmetric Hamiltonian is H = p2 - x4, which contains an upside-down potential. This potential is discussed in detail, and it is explained in intuitive as well as in rigorous terms why the energy levels of this potential are real, positive, and discrete. Applications of PT-symmetry in quantum field theory are also discussed.
Atomistic simulations reveal bubbles, kinks and wrinkles in supercoiled DNA
Mitchell, J. S.; Laughton, C. A.; Harris, Sarah A.
2011-01-01
Although DNA is frequently bent and supercoiled in the cell, much of the available information on DNA structure at the atomistic level is restricted to short linear sequences. We report atomistic molecular dynamics (MD) simulations of a series of DNA minicircles containing between 65 and 110 bp which we compare with a recent biochemical study of structural distortions in these tight DNA loops. We have observed a wealth of non-canonical DNA structures such as kinks, denaturation bubbles and wrinkled conformations that form in response to bending and torsional stress. The simulations show that bending alone is sufficient to induce the formation of kinks in circles containing only 65 bp, but we did not observe any defects in simulations of larger torsionally relaxed circles containing 110 bp over the same MD timescales. We also observed that under-winding in minicircles ranging in size from 65 to 110 bp leads to the formation of single stranded bubbles and wrinkles. These calculations are used to assess the ability of atomistic MD simulations to determine the structure of bent and supercoiled DNA. PMID:21247872
Plasticity of the RNA Kink Turn Structural Motif
Antonioli, A.; Cochrane, J; Lipchock, S; Strobel, S
2010-01-01
The kink turn (K-turn) is an RNA structural motif found in many biologically significant RNAs. While most examples of the K-turn have a similar fold, the crystal structure of the Azoarcus group I intron revealed a novel RNA conformation, a reverse kink turn bent in the direction opposite that of a consensus K-turn. The reverse K-turn is bent toward the major grooves rather than the minor grooves of the flanking helices, yet the sequence differs from the K-turn consensus by only a single nucleotide. Here we demonstrate that the reverse bend direction is not solely defined by internal sequence elements, but is instead affected by structural elements external to the K-turn. It bends toward the major groove under the direction of a tetraloop-tetraloop receptor. The ability of one sequence to form two distinct structures demonstrates the inherent plasticity of the K-turn sequence. Such plasticity suggests that the K-turn is not a primary element in RNA folding, but instead is shaped by other structural elements within the RNA or ribonucleoprotein assembly.
Observation of parity-time symmetry in optics
NASA Astrophysics Data System (ADS)
Rüter, Christian E.; Makris, Konstantinos G.; El-Ganainy, Ramy; Christodoulides, Demetrios N.; Segev, Mordechai; Kip, Detlef
2010-03-01
One of the fundamental axioms of quantum mechanics is associated with the Hermiticity of physical observables. In the case of the Hamiltonian operator, this requirement not only implies real eigenenergies but also guarantees probability conservation. Interestingly, a wide class of non-Hermitian Hamiltonians can still show entirely real spectra. Among these are Hamiltonians respecting parity-time (PT) symmetry. Even though the Hermiticity of quantum observables was never in doubt, such concepts have motivated discussions on several fronts in physics, including quantum field theories, non-Hermitian Anderson models and open quantum systems, to mention a few. Although the impact of PT symmetry in these fields is still debated, it has been recently realized that optics can provide a fertile ground where PT-related notions can be implemented and experimentally investigated. In this letter we report the first observation of the behaviour of a PT optical coupled system that judiciously involves a complex index potential. We observe both spontaneous PT symmetry breaking and power oscillations violating left-right symmetry. Our results may pave the way towards a new class of PT-synthetic materials with intriguing and unexpected properties that rely on non-reciprocal light propagation and tailored transverse energy flow.
Nonlinear hybrid simulation of internal kink with beam ion effects in DIII-D
Shen, Wei; Sheng, Zheng-Mao; Fu, G. Y.; Tobias, Benjamin; Zeeland, Michael Van; Wang, Feng
2015-04-15
In DIII-D sawteething plasmas, long-lived (1,1) kink modes are often observed between sawtooth crashes. The saturated kink modes have two distinct frequencies. The mode with higher frequency transits to a fishbone-like mode with sufficient on-axis neutral beam power. In this work, hybrid simulations with the global kinetic-magnetohydrodynamic (MHD) hybrid code M3D-K have been carried out to investigate the linear stability and nonlinear dynamics of the n = 1 mode with effects of energetic beam ions for a typical DIII-D discharge where both saturated kink mode and fishbone were observed. Linear simulation results show that the n = 1 internal kink mode is unstable in MHD limit. However, with kinetic effects of beam ions, a fishbone-like mode is excited with mode frequency about a few kHz depending on beam pressure profile. The mode frequency is higher at higher beam power and/or narrower radial profile consistent with the experimental observation. Nonlinear simulations have been performed to investigate mode saturation as well as energetic particle transport. The nonlinear MHD simulations show that the unstable kink mode becomes a saturated kink mode after a sawtooth crash. With beam ion effects, the fishbone-like mode can also transit to a saturated kink mode with a small but finite mode frequency. These results are consistent with the experimental observation of saturated kink mode between sawtooth crashes.
Li, Yanying; Wang, Yanming; Ryu, Seunghwa; Marshall, Ann F; Cai, Wei; McIntyre, Paul C
2016-03-01
Kinking, a common anomaly in nanowire (NW) vapor-liquid-solid (VLS) growth, represents a sudden change of the wire's axial growth orientation. This study focuses on defect-free kinking during germanium NW VLS growth, after nucleation on a Ge (111) single crystal substrate, using Au-Ge catalyst liquid droplets of defined size. Statistical analysis of the fraction of kinked NWs reveals the dependence of kinking probability on the wire diameter and the growth temperature. The morphologies of kinked Ge NWs studied by electron microscopy show two distinct, defect-free, kinking modes, whose underlying mechanisms are explained with the help of 3D multiphase field simulations. Type I kinking, in which the growth axis changes from vertical [111] to ⟨110⟩, was observed in Ge NWs with a nominal diameter of ∼20 nm. This size coincides with a critical diameter at which a spontaneous transition from ⟨111⟩ to ⟨110⟩ growth occurs in the phase field simulations. Larger diameter NWs only exhibit Type II kinking, in which the growth axis changes from vertical [111] directly to an inclined ⟨111⟩ axis during the initial stages of wire growth. This is caused by an error in sidewall facet development, which produces a shrinkage in the area of the (111) growth facet with increasing NW length, causing an instability of the Au-Ge liquid droplet at the tip of the NW. PMID:26837774
Proliferation of sharp kinks on cosmic (super)string loops with junctions
Binetruy, P.; Bohe, A.; Hertog, T.; Steer, D. A.
2010-10-15
Motivated by their effect on the gravitational wave signal emitted by cosmic strings, we study the dynamics of kinks on strings of different tensions meeting at junctions. The propagation of a kink through a Y junction leads to the formation of three 'daughter' kinks. Assuming a uniform distribution of the incoming wave vectors at the junction, we find there is a significant region of configuration space in which the sharpness of at least one of the daughter kinks is enhanced relative to the sharpness of the initial kink. For closed loops with junctions we show this leads to an exponential growth in time of very sharp kinks. Using numerical simulations of realistic, evolving cosmic string loops with junctions to calculate the distribution of kink amplitudes as a function of time, we show that loops of this kind typically develop several orders of magnitude of very sharp kinks before the two junctions collide. This collision, or other effects such as gravitational backreaction, may end the proliferation.
Xiao, Jing; Liu, Shuo; Tian, Na; Zhou, Zhi-You; Liu, Hai-Xia; Xu, Bin-Bin; Sun, Shi-Gang
2013-12-18
Systematic manipulation of nanocrystal shapes is prerequisite for revealing their shape-dependent physical and chemical properties. Here we successfully prepared a complex shape of Pt micro/nanocrystals: convex hexoctahedron (HOH) enclosed with 48 {15 5 3} high-index facets by electrochemical square-wave-potential (SWP) method. This shape is the last crystal single form that had not been achieved previously for face-centered-cubic (fcc) metals. We further realized the shape evolution of Pt nanocrystals with high-index facets from tetrahexahedron (THH) to the HOH, and finally to trapezohedron (TPH) by increasing either the upper (EU) or lower potential (EL). The shape evolution, accompanied by the decrease of low-coordinated kink atoms, can be correlated with the competitive interactions between preferentially oxidative dissolution of kink atoms at high EU and the redeposition of Pt atoms at the EL. PMID:24299234
Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys.
De Clercq, A; Giorgio, S; Mottet, C
2016-02-17
The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher. PMID:26795206
Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys
NASA Astrophysics Data System (ADS)
De Clercq, A.; Giorgio, S.; Mottet, C.
2016-02-01
The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher.
Soliton and kink jams in traffic flow with open boundaries.
Muramatsu, M; Nagatani, T
1999-07-01
Soliton density wave is investigated numerically and analytically in the optimal velocity model (a car-following model) of a one-dimensional traffic flow with open boundaries. Soliton density wave is distinguished from the kink density wave. It is shown that the soliton density wave appears only at the threshold of occurrence of traffic jams. The Korteweg-de Vries (KdV) equation is derived from the optimal velocity model by the use of the nonlinear analysis. It is found that the traffic soliton appears only near the neutral stability line. The soliton solution is analytically obtained from the perturbed KdV equation. It is shown that the soliton solution obtained from the nonlinear analysis is consistent with that of the numerical simulation. PMID:11969749
Nonlinear twist-kink instability of a coronal loop
NASA Technical Reports Server (NTRS)
Zaidman, E. G.; Tajima, T.
1989-01-01
Three-dimensional magnetoinductive particle simulations are used to demonstrate that the mechanical twisting motion applied to a magnetized plasma column induces a current aligned to the external magnetic field direction, pinches the plasma and magnetic fields, and stores the energy in poloidal magnetic fields. As the twist motion continues, the field lines locally begin to wrap around the plasma more than one revolution. A strong MHD instability sets in that is a mixture of kink and ballooning modes, releasing the magnetic energy and causing destruction of coherent column structure and flows of turbulent plasma. A similar episode ensues, exhibiting relaxation oscillations. The buildup of poloidal fields and structure and its sudden release driven by the twist motion may be a model for the solar coronal loop dynamics which exhibits a slow energy buildup with some photospheric motion and a sudden energy release by flares.
Polycyclic benzenoids: why kinked is more stable than straight.
Poater, Jordi; Visser, Ruud; Solà, Miquel; Bickelhaupt, F Matthias
2007-02-16
The enhanced stability of bent or kinked polycyclic benzenoids over linear ones is well established, phenanthrene and anthracene being archetypal representatives. The question why kinked is more stable than linear is, however, still a matter of discussion. Recently, it has been proposed that H-H bonding interactions between the two hydrogen atoms in the bay region of phenanthrene are responsible for the larger stability of this molecule as compared to anthracene. This conclusion conflicts with the vast body of evidence for nonbonded steric repulsion between these hydrogen atoms. In this work, we provide new, complementary evidence for the repulsive character of the H-H interactions in phenanthrene's bay region. We have traced the origin of phenanthrene's enhanced stability to the more efficient bonding in the pi-electron system using, among others, a quantitative energy decomposition analysis of the bonding between the two constituting 2-methtriyl-phenyl fragments in both phenanthrene and anthracene (i.e., C14H10 = C6H4*-CH** + C6H4*-CH**). The scope of our study is extended to polycyclic benzenoids by analyzing also hexacene and various bent isomers of the latter. Our results once more falsify one of the core concepts of the theory of atoms-in-molecules (AIM), namely, that the presence of bond paths and the presence of bond critical points (they exist indeed between the two bay H atoms in phenanthrene) are sufficient indicators for a stabilizing interaction. Instead, our results confirm that these AIM parameters merely diagnose the proximity or contact between charge distributions, be this contact stabilizing or destabilizing. PMID:17288368
DNA translocation through an array of kinked nanopores
NASA Astrophysics Data System (ADS)
Chen, Zhu; Jiang, Yingbing; Dunphy, Darren R.; Adams, David P.; Hodges, Carter; Liu, Nanguo; Zhang, Nan; Xomeritakis, George; Jin, Xiaozhong; Aluru, N. R.; Gaik, Steven J.; Hillhouse, Hugh W.; Jeffrey Brinker, C.
2010-08-01
Synthetic solid-state nanopores are being intensively investigated as single-molecule sensors for detection and characterization of DNA, RNA and proteins. This field has been inspired by the exquisite selectivity and flux demonstrated by natural biological channels and the dream of emulating these behaviours in more robust synthetic materials that are more readily integrated into practical devices. So far, the guided etching of polymer films, focused ion-beam sculpting, and electron-beam lithography and tuning of silicon nitride membranes have emerged as three promising approaches to define synthetic solid-state pores with sub-nanometre resolution. These procedures have in common the formation of nominally cylindrical or conical pores aligned normal to the membrane surface. Here we report the formation of `kinked' silica nanopores, using evaporation-induced self-assembly, and their further tuning and chemical derivatization using atomic-layer deposition. Compared with `straight through' proteinaceous nanopores of comparable dimensions, kinked nanopores exhibit up to fivefold reduction in translocation velocity, which has been identified as one of the critical issues in DNA sequencing. Additionally, we demonstrate an efficient two-step approach to create a nanopore array exhibiting nearly perfect selectivity for ssDNA over dsDNA. We show that a coarse-grained drift-diffusion theory with a sawtooth-like potential can reasonably describe the velocity and translocation time of DNA through the pore. By control of pore size, length and shape, we capture the main functional behaviours of protein pores in our solid-state nanopore system.
DNA translocation through an array of kinked nanopores
NASA Astrophysics Data System (ADS)
Chen, Zhu
Synthetic solid-state nanopores are being intensively investigated as single-molecule sensors for detection and characterization of DNA, RNA, and proteins. This field has been inspired by the exquisite selectivity and flux demonstrated by natural biological channels and the dream of emulating these behaviors in more robust synthetic materials that are more readily integrated into practical devices. To date, the guided etching of polymer films, focused ion beam sculpting, and electron-beam lithography and tuning of silicon nitride membranes have emerged as three promising approaches to define synthetic solid-state pores with sub-nanometer resolution. These procedures have in common the formation of nominally cylindrical or conical pores aligned normal to the membrane surface. Here we report the formation of 'kinked' silica nanopores, using evaporation induced self-assembly, and their further tuning and chemical derivatization using atomic layer deposition. Compared to 'straight-through' proteinaceous nanopores of comparable dimensions, kinked nanopores exhibit a factor of up to 5x reduction in translocation velocity, which has been identified as one of the critical issues in DNA sequencing. Additionally we demonstrate an efficient two-step approach to create a nanopore array exhibiting nearly perfect selectivity for ssDNA over dsDNA. We show that a coarse-grained drift-diffusion theory with a sawtooth like potential can reasonably describe the velocity and translocation time of DNA through the pore. By control of pore size, length, and shape, we capture the major functional behaviors of protein pores in our solid-state nanopore system.
Observations of pressure gradient driven m = 1 internal kink mode in EAST tokamak
Xu Liqing; Hu Liqun; Chen Kaiyun; Li Erzhong; Wang Fudi; Xu Ming; Duan Yanmin; Shi Tonghui; Zhang Jizong; Zhou Ruijie; Chen Yebin
2012-12-15
Pressure gradient driven m = 1 internal kink mode destabilization that follows an L-H transition is observed in the operational region of the EAST tokamak, which manifests in periodic oscillations in soft x-ray (SXR) and Mirnov coil signals. Using tomography with the high resolution soft x-ray detection array, we find that the rotation direction of the 1/1 kink mode is in the ion diamagnetic drift direction in poloidal cross-section. A large displacement of the hot core is attributable to the shift of the 1/1 internal kink mode. In contrast to stationary oscillations with fixed frequency, various frequency chirping behavior is observed with this 1/1 kink mode. Furthermore, we also occasionally observe that a 2/1 neoclassical tearing mode (NTM) is triggered by a 1/1 internal kink mode via mode coupling in a high-performance plasma. The spatial structure of a 2/2 mode, which is the harmonic mode of the 1/1 kink mode, is also presented in this paper. Large amounts of medium-Z impurities accumulate in the central plasma region where the 1/1 kink mode instability bursts. Finally, we also find that the frequency beating associated with a 1/1 kink mode is a consequence of plasma rotation. Based on all of these observations, we propose that the plasma pressure gradient, the driving force in kink modes, is plausibly the product of an intense concentration of impurities, which are related to plasma rotation.
Observations of pressure gradient driven m = 1 internal kink mode in EAST tokamak
NASA Astrophysics Data System (ADS)
Xu, Liqing; Hu, Liqun; Chen, Kaiyun; Li, Erzhong; Wang, Fudi; Xu, Ming; Duan, Yanmin; Shi, Tonghui; Zhang, Jizong; Zhou, Ruijie; Chen, Yebin
2012-12-01
Pressure gradient driven m = 1 internal kink mode destabilization that follows an L-H transition is observed in the operational region of the EAST tokamak, which manifests in periodic oscillations in soft x-ray (SXR) and Mirnov coil signals. Using tomography with the high resolution soft x-ray detection array, we find that the rotation direction of the 1/1 kink mode is in the ion diamagnetic drift direction in poloidal cross-section. A large displacement of the hot core is attributable to the shift of the 1/1 internal kink mode. In contrast to stationary oscillations with fixed frequency, various frequency chirping behavior is observed with this 1/1 kink mode. Furthermore, we also occasionally observe that a 2/1 neoclassical tearing mode (NTM) is triggered by a 1/1 internal kink mode via mode coupling in a high-performance plasma. The spatial structure of a 2/2 mode, which is the harmonic mode of the 1/1 kink mode, is also presented in this paper. Large amounts of medium-Z impurities accumulate in the central plasma region where the 1/1 kink mode instability bursts. Finally, we also find that the frequency beating associated with a 1/1 kink mode is a consequence of plasma rotation. Based on all of these observations, we propose that the plasma pressure gradient, the driving force in kink modes, is plausibly the product of an intense concentration of impurities, which are related to plasma rotation.
NASA Astrophysics Data System (ADS)
Pawel/ek, A.
1987-09-01
The paper deals with a modification of the classical expression derived by John P. Hirth and J. Lothe [Theory of Dislocations (McGraw-Hill, New York, 1972)] for the density of kinks on a dislocation segment in thermodynamic equilibrium imposed by external stresses. The dislocation kink-kink interaction is discussed in terms of soliton-antisoliton interaction, the analytical results obtained by J. Rubinstein [J. Math. Phys. 11, 258 (1970)] and the ones numerically obtained by M. Peyrard and David K. Campbell [Physica 9D, 33 (1983)] being applied for that purpose.
Gravitational-wave stochastic background from kinks and cusps on cosmic strings
Oelmez, S.; Mandic, V.; Siemens, X.
2010-05-15
We compute the contribution of kinks on cosmic string loops to stochastic background of gravitational waves (SBGW). We find that kinks contribute at the same order as cusps to the SBGW. We discuss the accessibility of the total background due to kinks as well as cusps to current and planned gravitational-wave detectors, as well as to the big bang nucleosynthesis (BBN), the cosmic microwave background (CMB), and pulsar timing constraints. As in the case of cusps, we find that current data from interferometric gravitational-wave detectors, such as LIGO, are sensitive to areas of parameter space of cosmic string models complementary to those accessible to pulsar, BBN, and CMB bounds.
Twofold transition in PT-symmetric coupled oscillators
NASA Astrophysics Data System (ADS)
Bender, Carl M.; Gianfreda, Mariagiovanna; Özdemir, Şahin K.; Peng, Bo; Yang, Lan
2013-12-01
The inspiration for this theoretical paper comes from recent experiments on a PT-symmetric system of two coupled optical whispering galleries (optical resonators). The optical system can be modeled as a pair of coupled linear oscillators, one with gain and the other with loss. If the coupled oscillators have a balanced loss and gain, the system is described by a Hamiltonian and the energy is conserved. This theoretical model exhibits two PT transitions depending on the size of the coupling parameter ɛ. For small ɛ, the PT symmetry is broken and the system is not in equilibrium, but when ɛ becomes sufficiently large, the system undergoes a transition to an equilibrium phase in which the PT symmetry is unbroken. For very large ɛ, the system undergoes a second transition and is no longer in equilibrium. The principal result presented here is that the classical and quantized versions of the system exhibit transitions at exactly the same values of ɛ.
Evidence for Triclinic Symmetry in Smectic Liquid Crystals of Bent-Shape Molecules
Jakli, A.; Kruerke, D.; Sawade, H.; Heppke, G.
2001-06-18
The first experimental evidence for triclinic symmetry of bulk smectic liquid-crystal samples of achiral banana-shaped molecules is presented. This phase corresponds to the so-called Sm-C{sub G} phase consisting of biaxial molecules and characterized by two tilt directions with respect to the layer normal: tilt of the molecular plane (clinic) and tilt of the molecular kink direction (leaning). Each smectic layer has a polarization component normal to the smectic layers (C{sub 1} symmetry). The observations suggest that the phase tentatively labeled as B{sub 7} is identical with the Sm-C{sub G} phase.
NASA Astrophysics Data System (ADS)
Brading, Katherine; Castellani, Elena
2003-12-01
Preface; Copyright acknowledgements; List of contributors; 1. Introduction; Part I. Continuous Symmetries: 2. Classic texts: extracts from Weyl and Wigner; 3. Review paper: On the significance of continuous symmetry to the foundations of physics C. Martin; 4. The philosophical roots of the gauge principle: Weyl and transcendental phenomenological idealism T. Ryckman; 5. Symmetries and Noether's theorems K. A. Brading and H. R. Brown; 6. General covariance, gauge theories, and the Kretschmann objection J. Norton; 7. The interpretation of gauge symmetry M. Redhead; 8. Tracking down gauge: an ode to the constrained Hamiltonian formalism J. Earman; 9. Time-dependent symmetries: the link between gauge symmetries and indeterminism D. Wallace; 10. A fourth way to the Aharanov-Bohm effect A. Nounou; Part II. Discrete Symmetries: 11. Classic texts: extracts from Lebniz, Kant and Black; 12. Review paper: Understanding permutation symmetry S. French and D. Rickles; 13. Quarticles and the identity of discernibles N. Hugget; 14. Review paper: Handedness, parity violation, and the reality of space O. Pooley; 15. Mirror symmetry: what is it for a relational space to be orientable? N. Huggett; 16. Physics and Leibniz's principles S. Saunders; Part III. Symmetry Breaking: 17: Classic texts: extracts from Curie and Weyl; 18. Extract from G. Jona-Lasinio: Cross-fertilization in theoretical physics: the case of condensed matter and particle physics G. Jona-Lasinio; 19. Review paper: On the meaning of symmetry breaking E. Castellani; 20. Rough guide to spontaneous symmetry breaking J. Earman; 21. Spontaneous symmetry breaking: theoretical arguments and philosophical problems M. Morrison; Part IV. General Interpretative Issues: 22. Classic texts: extracts from Wigner; 23. Symmetry as a guide to superfluous theoretical structure J. Ismael and B. van Fraassen; 24. Notes on symmetries G. Belot; 25. Symmetry, objectivity, and design P. Kosso; 26. Symmetry and equivalence E. Castellani.
NASA Astrophysics Data System (ADS)
Brading, Katherine; Castellani, Elena
2010-01-01
Preface; Copyright acknowledgements; List of contributors; 1. Introduction; Part I. Continuous Symmetries: 2. Classic texts: extracts from Weyl and Wigner; 3. Review paper: On the significance of continuous symmetry to the foundations of physics C. Martin; 4. The philosophical roots of the gauge principle: Weyl and transcendental phenomenological idealism T. Ryckman; 5. Symmetries and Noether's theorems K. A. Brading and H. R. Brown; 6. General covariance, gauge theories, and the Kretschmann objection J. Norton; 7. The interpretation of gauge symmetry M. Redhead; 8. Tracking down gauge: an ode to the constrained Hamiltonian formalism J. Earman; 9. Time-dependent symmetries: the link between gauge symmetries and indeterminism D. Wallace; 10. A fourth way to the Aharanov-Bohm effect A. Nounou; Part II. Discrete Symmetries: 11. Classic texts: extracts from Lebniz, Kant and Black; 12. Review paper: Understanding permutation symmetry S. French and D. Rickles; 13. Quarticles and the identity of discernibles N. Hugget; 14. Review paper: Handedness, parity violation, and the reality of space O. Pooley; 15. Mirror symmetry: what is it for a relational space to be orientable? N. Huggett; 16. Physics and Leibniz's principles S. Saunders; Part III. Symmetry Breaking: 17: Classic texts: extracts from Curie and Weyl; 18. Extract from G. Jona-Lasinio: Cross-fertilization in theoretical physics: the case of condensed matter and particle physics G. Jona-Lasinio; 19. Review paper: On the meaning of symmetry breaking E. Castellani; 20. Rough guide to spontaneous symmetry breaking J. Earman; 21. Spontaneous symmetry breaking: theoretical arguments and philosophical problems M. Morrison; Part IV. General Interpretative Issues: 22. Classic texts: extracts from Wigner; 23. Symmetry as a guide to superfluous theoretical structure J. Ismael and B. van Fraassen; 24. Notes on symmetries G. Belot; 25. Symmetry, objectivity, and design P. Kosso; 26. Symmetry and equivalence E. Castellani.
Unidirectional Invisibility Induced by PT-Symmetric Periodic Structures
Lin Zin; Ramezani, Hamidreza; Kottos, Tsampikos; Eichelkraut, Toni; Christodoulides, Demetrios N.; Cao Hui
2011-05-27
Parity-time (PT) symmetric periodic structures, near the spontaneous PT-symmetry breaking point, can act as unidirectional invisible media. In this regime, the reflection from one end is diminished while it is enhanced from the other. Furthermore, the transmission coefficient and phase are indistinguishable from those expected in the absence of a grating. The phenomenon is robust even in the presence of Kerr nonlinearities, and it can also effectively suppress optical bistabilities.
Super Bloch oscillation in a PT symmetric system
NASA Astrophysics Data System (ADS)
Turker, Z.; Yuce, C.
2016-07-01
Wannier-Stark ladder in a PT symmetric system is generally complex that leads to amplified/damped Bloch oscillation. We show that a non-amplified wave packet oscillation with very large amplitude can be realized in a non-Hermitian tight binding lattice if certain conditions are satisfied. We show that pseudo PT symmetry guarantees the reality of the quasi energy spectrum in our system.
Geometric intrinsic symmetries
Gozdz, A. Szulerecka, A.; Pedrak, A.
2013-08-15
The problem of geometric symmetries in the intrinsic frame of a many-body system (nucleus) is considered. An importance of symmetrization group notion is discussed. Ageneral structure of the intrinsic symmetry group structure is determined.
Rasin, A.
1994-04-01
We discuss the idea of approximate flavor symmetries. Relations between approximate flavor symmetries and natural flavor conservation and democracy models is explored. Implications for neutrino physics are also discussed.
Arnadottir, Liney; Stuve, Eric M.; Jonsson, Hannes
2010-10-01
Adsorption and rotation of water monomer, dimer, and trimer on the (111) terrace, (221) and (322) stepped, and (763) and (854) kinked surfaces of platinum were studied by density functional theory calculations using the PW91 approximation to the energy functional. On the (111) terrace, water monomer and the donor molecule of the dimer and trimer adsorb at atop sites. The permolecule adsorption energies of the monomer, dimer, and trimer are 0.30, 0.45, and 0.48 eV, respectively. Rotation of monomers, dimers, and trimers on the terrace is facile with energy barriers of 0.02 eV or less. Adsorption on steps and kinks is stronger than on the terrace, as evidenced by monomer adsorption energies of 0.46 to 0.55 eV. On the (221) stepped surface the zigzag extended configuration is most stable with a per-molecule adsorption energy of 0.57 eV. On the (322) stepped surface the dimer, two configurations of the trimer, and the zigzag configuration have similar adsorption energies of 0.55 ± 0.02 eV. Hydrogen bonding is strongest in the dimer and trimer adsorbed on the terrace, with respective energies of 0.30 and 0.27 eV, and accounts for their increased adsorption energies relative to the monomer. Hydrogen bonding is weak to moderate for adsorption at steps, with energies of 0.04 to 0.15 eV, as the much stronger water-metal interactions inhibit adsorption geometries favorable to hydrogen bonding. Correlations of hydrogen bond angles and energies with hydrogen bond lengths are presented. On the basis of these DFT/PW91 results, a model for water cluster formation on the Pt(111) surface can be formulated where kink sites nucleate chains along the top of step edges, consistent with the experimental findings of Morgenstern et al., Phys. Rev. Lett., 77 (1996) 703.
A phenomenological model on the kink mode threshold varying with the inclination of sheath boundary
Sun, X.; Intrator, T. P.; Sears, J.; Weber, T.; Liu, M.
2013-11-15
In nature and many laboratory plasmas, a magnetic flux tube threaded by current or a flux rope has a footpoint at a boundary. The current driven kink mode is one of the fundamental ideal magnetohydrodynamic instabilities in plasmas. It has an instability threshold that has been found to strongly depend on boundary conditions (BCs). We provide a theoretical model to explain the transition of this threshold dependence between nonline tied and line tied boundary conditions. We evaluate model parameters using experimentally measured plasma data, explicitly verify several kink eigenfunctions, and validate the model predictions for boundary conditions BCs that span the range between NLT and LT BCs. Based on this model, one could estimate the kink threshold given knowledge of the displacement of a flux rope end, or conversely estimate flux rope end motion based on knowledge of it kink stability threshold.
Sensual, erotic, and sexual behaviors of women from the "kink" community.
Rehor, Jennifer Eve
2015-05-01
Unconventional sensual, erotic, and sexual behaviors (herein referred to as kink behaviors) investigated by academia are based largely on clinical and criminal cases, and most published, peer-reviewed, quantitative research on these behaviors is based almost exclusively on male participants. For this study, information was collected and analyzed from 1580 female participants recruited from the kink community, using a non-clinical and non-criminal sample. We explored and described the preferences and diversity of more than 126 sensual, erotic, and sexual behaviors found among these participants, along with recommendations for continued research. Gaining a better understanding of the breadth and depth of activities engaged in by female kink practitioners could benefit educators, counselors, therapists, medical doctors, and other professionals when interacting with members of the kink community. PMID:25795531
Feedback suppression of rotating external kink instabilities in the presence of noise
Hanson, Jeremy M.; De Bono, Bryan; James, Royce W.; Levesque, Jeffrey P.; Mauel, Michael E.; Maurer, David A.; Navratil, Gerald A.; Pedersen, Thomas Sunn; Shiraki, Daisuke
2008-08-15
The authors report on the first experimental demonstration of active feedback suppression of rotating external kink modes near the ideal wall limit in a tokamak using Kalman filtering to discriminate the n=1 kink mode from background noise. The Kalman filter contains an internal model that captures the dynamics of a rotating, growing n=1 mode. Suppression of the external kink mode is demonstrated over a broad range of phase angles between the sensed mode and applied control field, and performance is robust at noise levels that render proportional gain feedback ineffective. Suppression of the kink mode is accomplished without excitation of higher frequencies as was observed in previous experiments using lead-lag loop compensation [A. J. Klein et al., Phys Plasmas 12, 040703 (2005)].
Neutrinos and flavor symmetries
Tanimoto, Morimitsu
2015-07-15
We discuss the recent progress of flavor models with the non-Abelian discrete symmetry in the lepton sector focusing on the θ{sub 13} and CP violating phase. In both direct approach and indirect approach of the flavor symmetry, the non-vanishing θ{sub 13} is predictable. The flavor symmetry with the generalised CP symmetry can also predicts the CP violating phase. We show the phenomenological analyses of neutrino mixing for the typical flavor models.
NASA Astrophysics Data System (ADS)
Chheda, T. D.; Nevitt, J. M.; Pollard, D. D.
2014-12-01
The formation of monoclinal right-lateral kink bands in Lake Edison granodiorite (central Sierra Nevada, CA) is investigated through field observations and mechanics based numerical modeling. Vertical faults act as weak surfaces within the granodiorite, and vertical granodiorite slabs bounded by closely-spaced faults curve into a kink. Leucocratic dikes are observed in association with kinking. Measurements were made on maps of Hilgard, Waterfall, Trail Fork, Kip Camp (Pollard and Segall, 1983b) and Bear Creek kink bands (Martel, 1998). Outcrop scale geometric parameters such as fault length andspacing, kink angle, and dike width are used to construct a representative geometry to be used in a finite element model. Three orders of fault were classified, length = 1.8, 7.2 and 28.8 m, and spacing = 0.3, 1.2 and 3.6 m, respectively. The model faults are oriented at 25° to the direction of shortening (horizontal most compressive stress), consistent with measurements of wing crack orientations in the field area. The model also includes a vertical leucocratic dike, oriented perpendicular to the faults and with material properties consistent with aplite. Curvature of the deformed faults across the kink band was used to compare the effects of material properties, strain, and fault and dike geometry. Model results indicate that the presence of the dike, which provides a mechanical heterogeneity, is critical to kinking in these rocks. Keeping properties of the model granodiorite constant, curvature increased with decrease in yield strength and Young's modulus of the dike. Curvature increased significantly as yield strength decreased from 95 to 90 MPa, and below this threshold value, limb rotation for the kink band was restricted to the dike. Changing Poisson's ratio had no significant effect. The addition of small faults between bounding faults, decreasing fault spacing or increasing dike width increases the curvature. Increasing friction along the faults decreases slip, so
FT-Raman spectroscopy of structural isomers of Pt(II) complex PtCl2(PEt3)2
NASA Astrophysics Data System (ADS)
Bhatt, Himal; Deo, M. N.; Vishwakarma, S. R.; Bajaj, Naini; Sharma, Surinder M.
2015-06-01
We report here the detailed spectroscopic aspects of the structural isomers of Pt(II) complex PtCl2(P(C2H5)3)2 using FT-Raman spectroscopy. A comparison of the structural contraction instigated by lowering the temperature up to liquid nitrogen temperature in the cis and trans isomers has been presented. The lattice region lying in the far infrared region upto 50cm-1 has been analyzed in detail to probe the structural modifications. It was found that the ambient temperature lower symmetry structure of the cis isomer is preserved at low temperatures. The trans isomer, stabilizing in a high symmetry structure at room temperature, transforms to a low symmetry structure on lowering the temperature, which can be attributed to a loss of inversion symmetry of the trans isomer.
External kink modes as a model for MHD activity associated with ELMs
Manickam, J.
1992-01-01
Tokamak plasmas in the high confinement mode of operation are known to exhibit edge localized activity referred to as ELMs. A model is proposed for the underlying cause in terms of the external kink mode. The build up of the current density near the plasma edge is shown to decrease the shear in the safety-factor, q, profile and lead to destabilization of the kink mode. The role of the plasma geometry and equilibrium profiles is discussed.
Kink instability in applied-field magneto-plasma-dynamic thrusters.
Zuin, M; Cavazzana, R; Martines, E; Serianni, G; Antoni, V; Bagatin, M; Andrenucci, M; Paganucci, F; Rossetti, P
2004-06-01
Measurements of magnetic and electrostatic fluctuations in an applied field magneto-plasma-dynamic thruster have shown that a m/n=1/1 kink mode becomes unstable whenever the Kruskal-Shafranov limit is violated. A positive correlation is established between the kink and performance degradation at high current, which has until now prevented the use of this kind of thruster in space missions. PMID:15245232
New multiple-soliton (kink) solutions for the high-order Boussinesq-Burgers equation
NASA Astrophysics Data System (ADS)
Guo, Peng; Wu, Xiang; Wang, Liangbi
2016-07-01
The homogeneous balance method is extended to find more new solutions of nonlinear evolution equations. As illustrative examples, many new multiple-soliton (kink) solutions of the high-order Boussinesq-Burgers equation are constructed. It is shown that the homogeneous balance method may provide us with a straightforward and effective mathematic tool for generating new multiple-soliton (kink) solutions of nonlinear evolution equations.
Polynomial Graphs and Symmetry
ERIC Educational Resources Information Center
Goehle, Geoff; Kobayashi, Mitsuo
2013-01-01
Most quadratic functions are not even, but every parabola has symmetry with respect to some vertical line. Similarly, every cubic has rotational symmetry with respect to some point, though most cubics are not odd. We show that every polynomial has at most one point of symmetry and give conditions under which the polynomial has rotational or…
Chiral symmetry and chiral-symmetry breaking
Peskin, M.E.
1982-12-01
These lectures concern the dynamics of fermions in strong interaction with gauge fields. Systems of fermions coupled by gauge forces have a very rich structure of global symmetries, which are called chiral symmetries. These lectures will focus on the realization of chiral symmetries and the causes and consequences of thier spontaneous breaking. A brief introduction to the basic formalism and concepts of chiral symmetry breaking is given, then some explicit calculations of chiral symmetry breaking in gauge theories are given, treating first parity-invariant and then chiral models. These calculations are meant to be illustrative rather than accurate; they make use of unjustified mathematical approximations which serve to make the physics more clear. Some formal constraints on chiral symmetry breaking are discussed which illuminate and extend the results of our more explicit analysis. Finally, a brief review of the phenomenological theory of chiral symmetry breaking is presented, and some applications of this theory to problems in weak-interaction physics are discussed. (WHK)
Modelling the kinked jet of the Crab nebula
NASA Astrophysics Data System (ADS)
Mignone, A.; Striani, E.; Tavani, M.; Ferrari, A.
2013-12-01
We investigate the dynamical propagation of the South-East jet from the Crab pulsar interacting with supernova ejecta by means of three-dimensional relativistic magnetohydrodynamic (MHD) numerical simulations with the PLUTO code. The initial jet structure is set up from the inner regions of the Crab nebula. We study the evolution of hot, relativistic hollow outflows initially carrying a purely azimuthal magnetic field. Our jet models are characterized by different choices of the outflow magnetization (σ parameter) and the bulk Lorentz factor (γj). We show that the jet is heavily affected by the growth of current-driven kink instabilities causing considerable deflection throughout its propagation length. This behaviour is partially stabilized by the combined action of larger flow velocities and/or reduced magnetic field strengths. We find that our best jet models are characterized by relatively large values of σ (≳1) and small values of γj ≃ 2. Our results are in good agreement with the recent X-ray (Chandra) data of the Crab nebula South-East jet indicating that the jet changes direction of propagation on a time-scale of the order of few years. The 3D models presented here may have important implications in the investigation of particle acceleration in relativistic outflows.
Diagnosis and Rescue of a Kinked Pulmonary Artery Catheter
Mouawad, Nicolas J.; Stein, Erica J.; Moran, Kenneth R.; Go, Michael R.; Papadimos, Thomas J.
2015-01-01
Invasive hemodynamic monitoring with a pulmonary catheter has been relatively routine in cardiovascular and complex surgical operations as well as in the management of critical illnesses. However, due to multiple potential complications and its invasive nature, its use has decreased over the years and less invasive methods such as transesophageal echocardiography and hemodynamic sensors have gained widespread favor. Unlike these less invasive forms of hemodynamic monitoring, pulmonary artery catheters require an advanced understanding of cardiopulmonary physiology, anatomy, and the potential for complications in order to properly place, manage, and interpret the device. We describe a case wherein significant resistance was encountered during multiple unsuccessful attempts at removing a patient's catheter secondary to kinking and twisting of the catheter tip. These attempts to remove the catheter serve to demonstrate potential rescue options for such a situation. Ultimately, successful removal of the catheter was accomplished by simultaneous catheter retraction and sheath advancement while gently pulling both objects from the cannulation site. In addition to being skilled in catheter placement, it is imperative that providers comprehend the risks and complications of this invasive monitoring tool. PMID:26075106
Excitation of external kink mode by trapped energetic particles
NASA Astrophysics Data System (ADS)
Guo, S. C.; Xu, X. Y.; Liu, Y. Q.; Wang, Z. R.
2016-05-01
An unstable fishbone-like non-resonant external kink mode (FLEM) is numerically found to be driven by the precessional drift motion of trapped energetic particles (EPs) in both reversed-field pinch (RFP) and tokamak plasmas, even under the ideal wall boundary condition. In the presence of a sufficiently large fraction of trapped energetic ions in high beta plasmas, the FLEM instability may occur. The excitation condition is discussed in detail. The frequency of the FLEM is linked to the precessional drift frequency of EPs, and varies with the plasma flow speed. Therefore, it is usually much higher than that of the typical resistive wall mode (RWM). In general, the growth rate of FLEM does not depend on the wall resistivity. However, the wall position can significantly affect the mode’s property. The drift kinetic effects from thermal particles (mainly due to the transit resonance of passing particles) play a stabilizing role on FLEMs. In the presence of EPs, the FLEM and the RWM can co-exist or even couple to each other, depending on the plasma parameters. The FLEM instabilities in RFP and tokamaks have rather similar physics nature, although certain sub-dominant characters appear differently in the two configurations.
Numerically Modeling Pulsed-Current, Kinked Wire Experiments
NASA Astrophysics Data System (ADS)
Filbey, Gordon; Kingman, Pat
1999-06-01
The U.S. Army Research Laboratory (ARL) has embarked on a program to provide far-term land fighting vehicles with electromagnetic armor protection. Part of this work seeks to establish robust simulations of magneto-solid-mechanics phenomena. Whether describing violent rupture of a fuse link resulting from a large current pulse or the complete disruption of a copper shaped-charge jet subjected to high current densities, the simulations must include effects of intense Lorentz body forces and rapid Ohmic heating. Material models are required that describe plasticity, flow and fracture, conductivity, and equation of state (EOS) parameters for media in solid, liquid, and vapor phases. An extended version of the Eulerian wave code CTH has been used to predict the apex motion of a V-shaped (``kinked'') copper wire 3mm in diameter during a 400 kilo-amp pulse. These predictions, utilizing available material, EOS, and conductivity data for copper and the known characteristics of an existing capacitor-bank pulsed power supply, were then used to configure an experiment. The experiments were in excellent agreement with the prior simulations. Both computational and experimental results (including electrical data and flash X-rays) will be presented.
High-m kink/tearing modes in cylindrical geometry
NASA Astrophysics Data System (ADS)
Connor, J. W.; Hastie, R. J.; Pusztai, I.; Catto, P. J.; Barnes, M.
2014-12-01
The global ideal kink equation, for cylindrical geometry and zero beta, is simplified in the high poloidal mode number limit and used to determine the tearing stability parameter, Δ‧. In the presence of a steep monotonic current gradient, Δ‧ becomes a function of a parameter, σ0, characterising the ratio of the maximum current gradient to magnetic shear and xs, characterising the separation of the resonant surface from the maximum of the current gradient. In equilibria containing a current ‘spike’, so that there is a non-monotonic current profile, Δ‧ also depends on two parameters: κ, related to the ratio of the curvature of the current density at its maximum to the magnetic shear and xs, which now represents the separation of the resonance from the point of maximum current density. The relation of our results to earlier studies of tearing modes and to recent gyrokinetic calculations of current driven instabilities, is discussed, together with potential implications for the stability of the tokamak pedestal.
Fishbone instability and kink mode stabilization in nonperturbative simulations
NASA Astrophysics Data System (ADS)
Gorelenkov, Nikolai
2011-10-01
Two phenomena relying on the nonperturbative treatment of the fast ion terms are the fishbone instability and ideal kink mode stabilization. We employ the global NOVA-KN hybrid kinetic-MHD code to study the stability properties of these low-n solutions, such as the resonant (fishbone) and non-resonant (ideal) branches. The nonperturbative approach treats fast ions with their realistic drift orbits numerically by computing the moments of their perturbed pressure tensors in order to include them into the eigenmode equation. We introduce this technique together with the new conforming velocity space grid to efficiently evaluate the wave-particle interaction matrix. The used method results in both resonant and modified non-resonant branches, which are further studied to understand their stability properties in the presence of energetic ions [C.Z. Cheng, Phys. Reports, v.211,p.1 (1992)]. We include the destabilizing effects from energetic beam ions and alpha particles, which seem to be important for the studied instabilities. A model used for beam ion distribution is also presented. We study the properties of those branches in details. The applications to the modified burning ITER plasma are discussed to understand how far the stability region is in the operating space from its nominal values. This work is supported by US DOE contract no. DE-AC02-09CH11466.
Kink modes and effective four dimensional fermion and Higgs brane models
George, Damien P.; Volkas, Raymond R.
2007-05-15
In the construction of a classical smoothed out brane world model in five dimensions, one uses a dynamically generated domain wall (a kink) to localize an effective four dimensional theory. At the level of the Euler-Lagrange equations the kink sets up a potential well, a mechanism which has been employed extensively to obtain localized, four dimensional, massless chiral fermions. We present the generalization of this kink trapping mechanism for both scalar and fermionic fields, and retain all degrees of freedom that were present in the higher dimensional theory. We show that a kink background induces a symmetric modified Poeschl-Teller potential well, and give explicit analytic forms for all the bound modes and a restricted set of the continuum modes. We demonstrate that it is possible to confine an effective four dimensional scalar field with a quartic potential of arbitrary shape. This can be used to place the standard model electroweak Higgs field on the brane, and also generate nested kink solutions. We also consider the limits of the parameters in the theory which give thin kinks and localized and delocalized scalar and fermionic fields.
Automated detection of kinks from blood vessels for optic cup segmentation in retinal images
NASA Astrophysics Data System (ADS)
Wong, D. W. K.; Liu, J.; Lim, J. H.; Li, H.; Wong, T. Y.
2009-02-01
The accurate localization of the optic cup in retinal images is important to assess the cup to disc ratio (CDR) for glaucoma screening and management. Glaucoma is physiologically assessed by the increased excavation of the optic cup within the optic nerve head, also known as the optic disc. The CDR is thus an important indicator of risk and severity of glaucoma. In this paper, we propose a method of determining the cup boundary using non-stereographic retinal images by the automatic detection of a morphological feature within the optic disc known as kinks. Kinks are defined as the bendings of small vessels as they traverse from the disc to the cup, providing physiological validation for the cup boundary. To detect kinks, localized patches are first generated from a preliminary cup boundary obtained via level set. Features obtained using edge detection and wavelet transform are combined using a statistical approach rule to identify likely vessel edges. The kinks are then obtained automatically by analyzing the detected vessel edges for angular changes, and these kinks are subsequently used to obtain the cup boundary. A set of retinal images from the Singapore Eye Research Institute was obtained to assess the performance of the method, with each image being clinically graded for the CDR. From experiments, when kinks were used, the error on the CDR was reduced to less than 0.1 CDR units relative to the clinical CDR, which is within the intra-observer variability of 0.2 CDR units.
Effects of Boundary Conditions and Flow on the Kink Instability in a Cylindrical Plasma Column
Furno, I; Intrator, T P; Lapenta, G; Dorf, L; Ryutov, D D
2007-02-06
An experimental investigation of the kink instability is presented in a linear plasma column where one end is line-tied to the plasma source, and the other end is not line-tied and therefore free to slide over the surface of the end-plate. This latter boundary condition is a result of plasma sheath resistance that insulates, at least partially, the plasma from the end-plate. The helical m = 1 kink mode is observed to grow when the plasma current exceeds a threshold and, close to the criticality, is characterized by an axial mode structure with maximum displacement at the free axial boundary. Azimuthal rotation of the mode is observed such that the helically kinked column always screws into the free axial boundary. The kink mode structure, rotation frequency and instability threshold are accurately reproduced by a recent kink theory [D. D. Ryutov, et al., Phys. Plasmas 13, 032105 (2006)], which includes axial plasma flow and one end of the plasma column that is free to move due to a perfect non-line-tying boundary condition which is experimentally verified. A brief review of the kink theory and its predictions for the boundary conditions relevant in the present experiments are presented.
The generation and damping of propagating MHD kink waves in the solar atmosphere
Morton, R. J.; Verth, G.; Erdélyi, R.; Hillier, A. E-mail: g.verth@sheffield.ac.uk
2014-03-20
The source of the non-thermal energy required for the heating of the upper solar atmosphere to temperatures in excess of a million degrees and the acceleration of the solar wind to hundreds of kilometers per second is still unclear. One such mechanism for providing the required energy flux is incompressible torsional Alfvén and kink magnetohydrodynamic (MHD) waves, which are magnetically dominated waves supported by the Sun's pervasive and complex magnetic field. In particular, propagating MHD kink waves have recently been observed to be ubiquitous throughout the solar atmosphere, but, until now, critical details of the transport of the kink wave energy throughout the Sun's atmosphere were lacking. Here, the ubiquity of the waves is exploited for statistical studies in the highly dynamic solar chromosphere. This large-scale investigation allows for the determination of the chromospheric kink wave velocity power spectra, a missing link necessary for determining the energy transport between the photosphere and corona. Crucially, the power spectra contain evidence for horizontal photospheric motions being an important mechanism for kink wave generation in the quiescent Sun. In addition, a comparison with measured coronal power spectra is provided for the first time, revealing frequency-dependent transmission profiles, suggesting that there is enhanced damping of kink waves in the lower corona.
Noncommutative Tachyon Kinks as D(p-1)-branes from Unstable Dp-brane
NASA Astrophysics Data System (ADS)
Banerjee, Rabin; Kim, Yoonbai; Kwon, O.-Kab
2005-01-01
We study noncommutative (NC) field theory of a real NC tachyon and NC U(1) gauge field, describing the dynamics of an unstable Dp-brane. For every given set of diagonal component of open string metric G 0 , NC parameter θ0 , and interpolating electric field hat E, we find all possible static NC kinks as exact solutions, in spite of complicated NC terms, which are classified by an array of NC kink-antikink and topological NC kinks. By computing their tensions and charges, those configurations are identified as an array of D0bar D0 and single stable D0 from the unstable D1, respectively. When the interpolating electric field has critical value as G 0 2 = hat E2 , the obtained topological kink becomes a BPS object with nonzero thickness and is identified as BPS D0 in the fluid of fundamental strings. Particularly in the scaling limit of infinite θ0 and vanishing G 0 and hat E, while keeping G 0θ0 = hat Eθ0 = 1, finiteness of the tension of NC kink corresponds to tensionless kink in ordinary effective field theory. An extension to stable D(p-1) from unstable Dp is straightforward for pure electric cases with parallel NC parameter and interpolating two-form field.
The Generation and Damping of Propagating MHD Kink Waves in the Solar Atmosphere
NASA Astrophysics Data System (ADS)
Morton, R. J.; Verth, G.; Hillier, A.; Erdélyi, R.
2014-03-01
The source of the non-thermal energy required for the heating of the upper solar atmosphere to temperatures in excess of a million degrees and the acceleration of the solar wind to hundreds of kilometers per second is still unclear. One such mechanism for providing the required energy flux is incompressible torsional Alfvén and kink magnetohydrodynamic (MHD) waves, which are magnetically dominated waves supported by the Sun's pervasive and complex magnetic field. In particular, propagating MHD kink waves have recently been observed to be ubiquitous throughout the solar atmosphere, but, until now, critical details of the transport of the kink wave energy throughout the Sun's atmosphere were lacking. Here, the ubiquity of the waves is exploited for statistical studies in the highly dynamic solar chromosphere. This large-scale investigation allows for the determination of the chromospheric kink wave velocity power spectra, a missing link necessary for determining the energy transport between the photosphere and corona. Crucially, the power spectra contain evidence for horizontal photospheric motions being an important mechanism for kink wave generation in the quiescent Sun. In addition, a comparison with measured coronal power spectra is provided for the first time, revealing frequency-dependent transmission profiles, suggesting that there is enhanced damping of kink waves in the lower corona.
PT; Pro-time; Anticoagulant-prothrombin time; Clotting time: protime; INR; International normalized ratio ... PT is measured in seconds. Most of the time, results are given as what is called INR ( ...
Spinor Structure and Internal Symmetries
NASA Astrophysics Data System (ADS)
Varlamov, V. V.
2015-10-01
Spinor structure and internal symmetries are considered within one theoretical framework based on the generalized spin and abstract Hilbert space. Complex momentum is understood as a generating kernel of the underlying spinor structure. It is shown that tensor products of biquaternion algebras are associated with the each irreducible representation of the Lorentz group. Space-time discrete symmetries P, T and their combination PT are generated by the fundamental automorphisms of this algebraic background (Clifford algebras). Charge conjugation C is presented by a pseudoautomorphism of the complex Clifford algebra. This description of the operation C allows one to distinguish charged and neutral particles including particle-antiparticle interchange and truly neutral particles. Spin and charge multiplets, based on the interlocking representations of the Lorentz group, are introduced. A central point of the work is a correspondence between Wigner definition of elementary particle as an irreducible representation of the Poincaré group and SU(3)-description (quark scheme) of the particle as a vector of the supermultiplet (irreducible representation of SU(3)). This correspondence is realized on the ground of a spin-charge Hilbert space. Basic hadron supermultiplets of SU(3)-theory (baryon octet and two meson octets) are studied in this framework. It is shown that quark phenomenologies are naturally incorporated into presented scheme. The relationship between mass and spin is established. The introduced spin-mass formula and its combination with Gell-Mann-Okubo mass formula allows one to take a new look at the problem of mass spectrum of elementary particles.
Kinks, loops, and protein folding, with protein A as an example
Krokhotin, Andrey; Liwo, Adam; Maisuradze, Gia G. Scheraga, Harold A.; Niemi, Antti J.
2014-01-14
The dynamics and energetics of formation of loops in the 46-residue N-terminal fragment of the B-domain of staphylococcal protein A has been studied. Numerical simulations have been performed using coarse-grained molecular dynamics with the united-residue (UNRES) force field. The results have been analyzed in terms of a kink (heteroclinic standing wave solution) of a generalized discrete nonlinear Schrödinger (DNLS) equation. In the case of proteins, the DNLS equation arises from a C{sup α}-trace-based energy function. Three individual kink profiles were identified in the experimental three-α-helix structure of protein A, in the range of the Glu16-Asn29, Leu20-Asn29, and Gln33-Asn44 residues, respectively; these correspond to two loops in the native structure. UNRES simulations were started from the full right-handed α-helix to obtain a clear picture of kink formation, which would otherwise be blurred by helix formation. All three kinks emerged during coarse-grained simulations. It was found that the formation of each is accompanied by a local free energy increase; this is expressed as the change of UNRES energy which has the physical sense of the potential of mean force of a polypeptide chain. The increase is about 7 kcal/mol. This value can thus be considered as the free energy barrier to kink formation in full α-helical segments of polypeptide chains. During the simulations, the kinks emerge, disappear, propagate, and annihilate each other many times. It was found that the formation of a kink is initiated by an abrupt change in the orientation of a pair of consecutive side chains in the loop region. This resembles the formation of a Bloch wall along a spin chain, where the C{sup α} backbone corresponds to the chain, and the amino acid side chains are interpreted as the spin variables. This observation suggests that nearest-neighbor side chain–side chain interactions are responsible for initiation of loop formation. It was also found that the individual
Kinks, loops, and protein folding, with protein A as an example
NASA Astrophysics Data System (ADS)
Krokhotin, Andrey; Liwo, Adam; Maisuradze, Gia G.; Niemi, Antti J.; Scheraga, Harold A.
2014-01-01
The dynamics and energetics of formation of loops in the 46-residue N-terminal fragment of the B-domain of staphylococcal protein A has been studied. Numerical simulations have been performed using coarse-grained molecular dynamics with the united-residue (UNRES) force field. The results have been analyzed in terms of a kink (heteroclinic standing wave solution) of a generalized discrete nonlinear Schrödinger (DNLS) equation. In the case of proteins, the DNLS equation arises from a Cα-trace-based energy function. Three individual kink profiles were identified in the experimental three-α-helix structure of protein A, in the range of the Glu16-Asn29, Leu20-Asn29, and Gln33-Asn44 residues, respectively; these correspond to two loops in the native structure. UNRES simulations were started from the full right-handed α-helix to obtain a clear picture of kink formation, which would otherwise be blurred by helix formation. All three kinks emerged during coarse-grained simulations. It was found that the formation of each is accompanied by a local free energy increase; this is expressed as the change of UNRES energy which has the physical sense of the potential of mean force of a polypeptide chain. The increase is about 7 kcal/mol. This value can thus be considered as the free energy barrier to kink formation in full α-helical segments of polypeptide chains. During the simulations, the kinks emerge, disappear, propagate, and annihilate each other many times. It was found that the formation of a kink is initiated by an abrupt change in the orientation of a pair of consecutive side chains in the loop region. This resembles the formation of a Bloch wall along a spin chain, where the Cα backbone corresponds to the chain, and the amino acid side chains are interpreted as the spin variables. This observation suggests that nearest-neighbor side chain-side chain interactions are responsible for initiation of loop formation. It was also found that the individual kinks are
Topological States in Partially-PT-Symmetric Azimuthal Potentials.
Kartashov, Yaroslav V; Konotop, Vladimir V; Torner, Lluis
2015-11-01
We introduce partially-parity-time (pPT)-symmetric azimuthal potentials composed from individual PT-symmetric cells located on a ring, where two azimuthal directions are nonequivalent in a sense that in such potential excitations carrying topological dislocations exhibit different dynamics for different directions of energy circulation in the initial field distribution. Such nonconservative ratchetlike structures support rich families of stable vortex solitons in cubic nonlinear media, whose properties depend on the sign of the topological charge due to the nonequivalence of azimuthal directions. In contrast, oppositely charged vortex solitons remain equivalent in similar fully-PT-symmetric potentials. The vortex solitons in the pPT- and PT-symmetric potentials are shown to feature qualitatively different internal current distributions, which are described by different discrete rotation symmetries of the intensity profiles. PMID:26588383
Studies of Kink-AntiKink Collisions in 1+1 D in φ^4 and Double Sine Gordon Nonlinear Wave Equations
NASA Astrophysics Data System (ADS)
Fasano, Christopher G.
1996-11-01
The manner in which kink and antikink solutions interact in nonlinear systems is strongly dependent upon the velocities in the collision. In certain velocity regions, the kink and antikink annihilate, while in other regions they bounce off of one another. We present studies of multiple bounce solutions for the collision of kinks and antikinks in a 1 + 1 dimensional φ^4 and Double Sine-Gordon systems. We confirm the existence of a repeated level structure for velocities at which 3, 4, 5, and 6 bounce solutions occur φ^4 as presented by previous authors ( Michael Peyrard and David K. Campbell, Physica 9D) (1983) 33, Peter Anninos, Samuel Oliveira, and Richard A. Matzner, Phys. Rev. D44 (1991) 1147 and we characterize the onset of each multiple bounce solution. The positions of these levels may be described by a simple extension of previous works, and imply that the system follows a specific ``route'' to ``chaotic'' annihilation. An analysis of kink-antinkink collisions in the Double-Sine Gordon equation will also be presented. This analysis reveals both interesting similarities and differences when compared to φ^4
SEISMOLOGY OF STANDING KINK OSCILLATIONS OF SOLAR PROMINENCE FINE STRUCTURES
Soler, R.; Arregui, I.; Oliver, R.; Ballester, J. L.
2010-10-20
We investigate standing kink magnetohydrodynamic (MHD) oscillations in a prominence fine structure modeled as a straight and cylindrical magnetic tube only partially filled with the prominence material and with its ends fixed at two rigid walls representing the solar photosphere. The prominence plasma is partially ionized and a transverse inhomogeneous transitional layer is included between the prominence thread and the coronal medium. Thus, ion-neutral collisions and resonant absorption are the damping mechanisms considered. Approximate analytical expressions of the period, the damping time, and their ratio are derived for the fundamental mode in the thin tube and thin boundary approximations. We find that the dominant damping mechanism is resonant absorption, which provides damping ratios in agreement with the observations, whereas ion-neutral collisions are irrelevant for damping. The values of the damping ratio are independent of both the prominence thread length and its position within the magnetic tube, and coincide with the values for a tube fully filled with the prominence plasma. The implications of our results in the context of the MHD seismology technique are discussed, pointing out that the reported short-period (2-10 minutes) and short-wavelength (700-8000 km) thread oscillations may not be consistent with a standing mode interpretation and could be related to propagating waves. Finally, we show that the inversion of some prominence physical parameters, e.g., Alfven speed, magnetic field strength, transverse inhomogeneity length scale, etc., is possible using observationally determined values of the period and damping time of the oscillations along with the analytical approximations of these quantities.
The current-driven kink instability in magnetically dominated relativistic jets
NASA Astrophysics Data System (ADS)
Mizuno, Yosuke; Lyubarsky, Yuri; Nishikawa, Ken-Ichi; Hardee, Philip E.
2012-04-01
We have investigated the development of current-driven (CD) kink instability in relativistic jets, via 3D relativistic magnetohydrodynamic simulations. For this purpose, a static force-free equilibrium helical magnetic configuration is considered in order to study its influence on the linear and nonlinear stages of the instability. We found that this configuration is strongly distorted but not disrupted by the CD kink instability. Both the linear growth and the nonlinear evolution of this in-stability depend moderately on the radial density profile but are strongly sensitive to the magnetic pitch profile. For decreasing magnetic pitch, kink amplitude growth leads, in the nonlinear regime, to a slender helically twisted column wrapped by magnetic field. Differently, for increasing magnetic pitch, the kink amplitude nearly saturates in the nonlinear regime. We have also investigated the influence of velocity shear on the linear and non-linear development of the instability. We found that helically distorted density structures propagate along the jet with a speed and a flow structure that are dependent on the location of the velocity shear relative to the characteristic radius of the helically twisted force-free magnetic field. At small radius, the plasma flows through the kink. The kink propagation speed increases with the velocity shear radius, and the kink becomes more em-bedded in the plasma flow. Larger velocity shear radius leads to slower linear growth, with a later transition to the nonlinear stage and a larger maximum amplitude than in the case of a static plasma column. However, when the velocity shear radius is much greater than the characteristic radius of the helical magnetic field, linear and non-linear developments become more similar to those of a static plasma column.
Parity-Time Symmetry Breaking in Coupled Nanobeam Cavities
NASA Astrophysics Data System (ADS)
Zhang, Senlin; Yong, Zhengdong; Zhang, Yuguang; He, Sailing
2016-04-01
The concept of parity-time symmetry (PT symmetry) originates from the canonical quantum mechanics and has become a hot topic recently. As a versatile platform to investigate the intriguing concept, both theoretical and experimental works in optics have been implemented. In this paper, the PT symmetry breaking phenomenon is investigated in a coupled nanobeam cavity system. An exceptional point is observed during the tuning of the gain/loss level and the coupling strength of the closely placed nanobeam pair. Unidirectional light propagation is investigated, as well as enhanced sensitivity of single particle detection in the vicinity of the exceptional point. The proposed system is easy to be integrated with photonic integrated circuits and can be strongly coupled to optical waveguides.
Parity-Time Symmetry Breaking in Coupled Nanobeam Cavities
Zhang, Senlin; Yong, Zhengdong; Zhang, Yuguang; He, Sailing
2016-01-01
The concept of parity-time symmetry (PT symmetry) originates from the canonical quantum mechanics and has become a hot topic recently. As a versatile platform to investigate the intriguing concept, both theoretical and experimental works in optics have been implemented. In this paper, the PT symmetry breaking phenomenon is investigated in a coupled nanobeam cavity system. An exceptional point is observed during the tuning of the gain/loss level and the coupling strength of the closely placed nanobeam pair. Unidirectional light propagation is investigated, as well as enhanced sensitivity of single particle detection in the vicinity of the exceptional point. The proposed system is easy to be integrated with photonic integrated circuits and can be strongly coupled to optical waveguides. PMID:27075817
Parity-Time Symmetry Breaking in Coupled Nanobeam Cavities.
Zhang, Senlin; Yong, Zhengdong; Zhang, Yuguang; He, Sailing
2016-01-01
The concept of parity-time symmetry (PT symmetry) originates from the canonical quantum mechanics and has become a hot topic recently. As a versatile platform to investigate the intriguing concept, both theoretical and experimental works in optics have been implemented. In this paper, the PT symmetry breaking phenomenon is investigated in a coupled nanobeam cavity system. An exceptional point is observed during the tuning of the gain/loss level and the coupling strength of the closely placed nanobeam pair. Unidirectional light propagation is investigated, as well as enhanced sensitivity of single particle detection in the vicinity of the exceptional point. The proposed system is easy to be integrated with photonic integrated circuits and can be strongly coupled to optical waveguides. PMID:27075817
Motoyama, Yasushi; Tanaka, Yoshitaka; Gurung, Pritam; Nakagawa, Ichiro; Park, Young-Soo; Nakase, Hiroyuki
2016-01-01
Background: During microscopic procedures for neurovascular disease, we sometimes encounter kinking of arterial branches resulting in ischemic sequelae. A simple and useful technique that involves inserting a small, ball-like prosthesis made of oxidized cellulose or shredded Teflon with fibrin glue that corrects the arterial branch kinking and avoids subsequent compromise is reported. Methods: Between January and December 2014, three patients developed arterial kinking during microscopic procedures, including two in the caudal loop of the posterior inferior cerebellar artery during microvascular decompression for glossopharyngeal neuralgia and one in a branch of the middle cerebral artery (MCA) during clipping for an unruptured MCA aneurysm. Blood flow insufficiency was confirmed by microvascular Doppler ultrasonography (MDU) and indocyanine green (ICG) videoangiography. The prosthesis, which was made of shredded Teflon in two cases and oxidized cellulose in one case, was inserted into the crotch of the kinked arteries to correct the kinking of the arteries and restore the proper vascular shape and normal blood flow. Results: The small, ball-shaped prosthesis corrected the kinked arteries and maintained the proper shape, which was confirmed by ICG videoangiography and MDU during the operation and three-dimensional computerized tomography angiography postoperatively. Postoperatively, the patients did not manifest any ischemic sequelae related to the kinked arteries. Conclusion: The insertion of prostheses with fibrin glue into the crotch of a kinked artery for repair is considered a simple and useful method for correcting a kinked artery that avoids ischemic sequelae. PMID:26862447
Sekhar Chivukula
2010-01-08
The symmetries of a quantum field theory can be realized in a variety of ways. Symmetries can be realized explicitly, approximately, through spontaneous symmetry breaking or, via an anomaly, quantum effects can dynamically eliminate a symmetry of the theory that was present at the classical level. Quantum Chromodynamics (QCD), the modern theory of the strong interactions, exemplify each of these possibilities. The interplay of these effects determine the spectrum of particles that we observe and, ultimately, account for 99% of the mass of ordinary matter.
Gray, J E; Vogt, A
1997-01-01
Is symmetry informative? The answer is both yes and no. We examine what information and symmetry are and how they are related. Our approach is primarily mathematical, not because mathematics provides the final word, but because it provides an insightful and relatively precise starting point. Information theory treats transformations that messages undergo from source to destination. Symmetries are information that leave some property of interest unchanged. In this respect the studies of information and symmetry can both be regarded as a Quest for the identity transformation. PMID:9224554
Kink and Sausage Modes in Nonuniform Magnetic Slabs with Continuous Transverse Density Distributions
NASA Astrophysics Data System (ADS)
Yu, Hui; Li, Bo; Chen, Shao-Xia; Guo, Ming-Zhe
2015-11-01
We examine the influence of a continuous density structuring transverse to coronal slabs on the dispersive properties of fundamental standing kink and sausage modes supported therein. We derive generic dispersion relations (DRs) governing linear fast waves in pressureless straight slabs with general transverse density distributions, and focus on cases where the density inhomogeneity takes place in a layer of arbitrary width and in arbitrary form. The physical relevance of the solutions to the DRs is demonstrated by the corresponding time-dependent computations. For all profiles examined, the lowest order kink modes are trapped regardless of longitudinal wavenumber k. A continuous density distribution introduces a difference to their periods of ≲13% when k is the observed range relative to the case where the density profile takes a step function form. Sausage modes and other branches of kink modes are leaky at small k, and their periods and damping times are heavily influenced by how the transverse density profile is prescribed, in particular the length scale. These modes have sufficiently high quality to be observable only for physical parameters representative of flare loops. We conclude that while the simpler DR pertinent to a step function profile can be used for the lowest order kink modes, the detailed information on the transverse density structuring needs to be incorporated into studies of sausage modes and higher order kink modes.
Forward Modeling of Standing Kink Modes in Coronal Loops. I. Synthetic Views
NASA Astrophysics Data System (ADS)
Yuan, Ding; Van Doorsselaere, Tom
2016-04-01
Kink magnetohydrodynamic (MHD) waves are frequently observed in various magnetic structures of the solar atmosphere. They may contribute significantly to coronal heating and could be used as a tool to diagnose the solar plasma. In this study, we synthesize the Fe ix λ171.073 Å emission of a coronal loop supporting a standing kink MHD mode. The kink MHD wave solution of a plasma cylinder is mapped into a semi-torus structure to simulate a curved coronal loop. We decompose the solution into a quasi-rigid kink motion and a quadrupole term, which dominate the plasma inside and outside of the flux tube, respectively. At the loop edges, the line of sight integrates relatively more ambient plasma, and the background emission becomes significant. The plasma motion associated with the quadrupole term causes spectral line broadening and emission suppression. The periodic intensity suppression will modulate the integrated intensity and the effective loop width, which both exhibit oscillatory variations at half of the kink period. The quadrupole term can be directly observed as a pendular motion at the front view.
Coupling of sausage, kink, and magneto-Rayleigh-Taylor instabilities in a cylindrical liner
Weis, M. R.; Zhang, P.; Lau, Y. Y. Gilgenbach, R. M.; Schmit, P. F.; Peterson, K. J.; Hess, M.
2015-03-15
This paper analyzes the coupling of magneto-Rayleigh-Taylor (MRT), sausage, and kink modes in an imploding cylindrical liner, using ideal MHD. A uniform axial magnetic field of arbitrary value is included in each region: liner, its interior, and its exterior. The dispersion relation is solved exactly, for arbitrary radial acceleration (-g), axial wavenumber (k), azimuthal mode number (m), liner aspect ratio, and equilibrium quantities in each region. For small k, a positive g (inward radial acceleration in the lab frame) tends to stabilize the sausage mode, but destabilize the kink mode. For large k, a positive g destabilizes both the kink and sausage mode. Using the 1D-HYDRA simulation results for an equilibrium model that includes a pre-existing axial magnetic field and a preheated fuel, we identify several stages of MRT-sausage-kink mode evolution. We find that the m = 1 kink-MRT mode has a higher growth rate at the initial stage and stagnation stage of the implosion, and that the m = 0 sausage-MRT mode dominates at the main part of implosion. This analysis also sheds light on a puzzling feature in Harris' classic paper of MRT [E. G. Harris, Phys. Fluids 5, 1057 (1962)]. An attempt is made to interpret the persistence of the observed helical structures [Awe et al., Phys. Rev. Lett. 111, 235005 (2013)] in terms of non-axisymmetric eigenmode.
Coupling of sausage, kink, and magneto-Rayleigh-Taylor instabilities in a cylindrical liner
NASA Astrophysics Data System (ADS)
Weis, M. R.; Zhang, P.; Lau, Y. Y.; Schmit, P. F.; Peterson, K. J.; Hess, M.; Gilgenbach, R. M.
2015-03-01
This paper analyzes the coupling of magneto-Rayleigh-Taylor (MRT), sausage, and kink modes in an imploding cylindrical liner, using ideal MHD. A uniform axial magnetic field of arbitrary value is included in each region: liner, its interior, and its exterior. The dispersion relation is solved exactly, for arbitrary radial acceleration (-g), axial wavenumber (k), azimuthal mode number (m), liner aspect ratio, and equilibrium quantities in each region. For small k, a positive g (inward radial acceleration in the lab frame) tends to stabilize the sausage mode, but destabilize the kink mode. For large k, a positive g destabilizes both the kink and sausage mode. Using the 1D-HYDRA simulation results for an equilibrium model that includes a pre-existing axial magnetic field and a preheated fuel, we identify several stages of MRT-sausage-kink mode evolution. We find that the m = 1 kink-MRT mode has a higher growth rate at the initial stage and stagnation stage of the implosion, and that the m = 0 sausage-MRT mode dominates at the main part of implosion. This analysis also sheds light on a puzzling feature in Harris' classic paper of MRT [E. G. Harris, Phys. Fluids 5, 1057 (1962)]. An attempt is made to interpret the persistence of the observed helical structures [Awe et al., Phys. Rev. Lett. 111, 235005 (2013)] in terms of non-axisymmetric eigenmode.
PT-symmetric dimer of coupled nonlinear oscillators
NASA Astrophysics Data System (ADS)
Cuevas, Jesús; Kevrekidis, Panayotis G.; Saxena, Avadh; Khare, Avinash
2013-09-01
We provide a systematic analysis of a prototypical nonlinear oscillator system respecting PT symmetry i.e., one of them has gain and the other an equal and opposite amount of loss. Starting from the linear limit of the system, we extend considerations to the nonlinear case for both soft and hard cubic nonlinearities identifying symmetric and antisymmetric breather solutions, as well as symmetry-breaking variants thereof. We propose a reduction of the system to a Schrödinger-type PT-symmetric dimer, whose detailed earlier understanding can explain many of the phenomena observed herein, including the PT phase transition. Nevertheless, there are also significant parametric as well as phenomenological potential differences between the two models and we discuss where these arise and where they are most pronounced. Finally, we also provide examples of the evolution dynamics of the different states in their regimes of instability.
Solitons and kinks in a general car-following model.
Kurtze, Douglas A
2013-09-01
We study a general car-following model of traffic flow on an infinitely long single-lane road, which assumes that a car's acceleration depends on time-delayed values of its own speed, the headway between it and the car ahead, and the rate of change of headway, but makes minimal assumptions about the functional form of that dependence. We present a detailed characterization of the onset of linear instability; in particular we find a specific limit on the delay time below which the marginal wave number at the onset of instability is zero, and another specific limit on the delay time above which steady flow is always unstable. Crucially, the threshold of absolute stability generally does not coincide with an inflection point of the steady-state velocity function. When the marginal perturbation at onset has wave number 0, we show that Burgers and Korteweg-de Vries (KdV) equations can be derived under the usual assumptions, and that corrections to the KdV equation "select" a single member of the one-parameter set of its one-soliton solutions by driving a slow evolution of the soliton parameter. While in previous models this selected soliton has always marked the threshold of a finite-amplitude instability of linearly stable steady flow, we find that it can alternatively be a stable, small-amplitude jam that occurs when steady flow is linearly unstable. The model reduces to the usual modified Korteweg-de Vries (mKdV) equation only in the special situation that the threshold of absolute stability coincides with an inflection point of the steady-state velocity function; in general, near the threshold of absolute stability the model reduces instead to a KdV equation in the regime of small solitons, while near an inflection point it reduces to a Hayakawa-Nakanishi equation. Like the mKdV equation, the Hayakawa-Nakanishi equation admits a continuous family of kink solutions, and the selection criterion arising from the corrections to this equation can be written down
Magneto-Rayleigh-Taylor, Sausage And Kink Mode In Cylindrical Liners
NASA Astrophysics Data System (ADS)
Lau, Y. Y.; Zhang, Peng; Weis, Matthew; Gilgenbach, Ronald; Hess, Mark; Peterson, Kyle
2014-10-01
This paper analyzes the coupling of magneto-Rayleigh-Taylor (MRT), sausage (azimuthal mode number m = 0) and kink mode (m = 1) in an imploding cylindrical liner, using ideal MHD. A uniform axial magnetic field of arbitrary value is included in each region: liner, its interior, and its exterior. The dispersion relation, the feedthrough factor, and the temporal evolution of perturbations were solved exactly, for arbitrary values of g (= gravity), k (= axial wavenumber), m, aspect ratio, and equilibrium quantities in each region. For small k, a positive g (inward radial acceleration in the lab frame) tends to stabilize the sausage mode, but destabilize the kink mode. For large k, a positive g destabilizes both the kink and sausage mode. This analysis might shed lights into some puzzling features in Harris' classic paper, and in the recent cylindrical liner experiments on MRT. M. R. Weis was supported by the Sandia National Laboratories.
Wall-touching kink mode calculations with the M3D code
Breslau, J. A. Bhattacharjee, A.
2015-06-15
This paper seeks to address a controversy regarding the applicability of the 3D nonlinear extended MHD code M3D [W. Park et al., Phys. Plasmas 6, 1796 (1999)] and similar codes to calculations of the electromagnetic interaction of a disrupting tokamak plasma with the surrounding vessel structures. M3D is applied to a simple test problem involving an external kink mode in an ideal cylindrical plasma, used also by the Disruption Simulation Code (DSC) as a model case for illustrating the nature of transient vessel currents during a major disruption. While comparison of the results with those of the DSC is complicated by effects arising from the higher dimensionality and complexity of M3D, we verify that M3D is capable of reproducing both the correct saturation behavior of the free boundary kink and the “Hiro” currents arising when the kink interacts with a conducting tile surface interior to the ideal wall.
Wall-touching kink mode calculations with the M3D code
NASA Astrophysics Data System (ADS)
Breslau, J. A.; Bhattacharjee, A.
2015-06-01
This paper seeks to address a controversy regarding the applicability of the 3D nonlinear extended MHD code M3D [W. Park et al., Phys. Plasmas 6, 1796 (1999)] and similar codes to calculations of the electromagnetic interaction of a disrupting tokamak plasma with the surrounding vessel structures. M3D is applied to a simple test problem involving an external kink mode in an ideal cylindrical plasma, used also by the Disruption Simulation Code (DSC) as a model case for illustrating the nature of transient vessel currents during a major disruption. While comparison of the results with those of the DSC is complicated by effects arising from the higher dimensionality and complexity of M3D, we verify that M3D is capable of reproducing both the correct saturation behavior of the free boundary kink and the "Hiro" currents arising when the kink interacts with a conducting tile surface interior to the ideal wall.
Resistive toroidal stability of internal kink modes in circular and shaped tokamaks
NASA Astrophysics Data System (ADS)
Bondeson, A.; Vlad, G.; Lütjens, H.
1992-07-01
The linear resistive magnetohydrodynamical stability of the n=1 internal kink mode in tokamaks is studied numerically. The stabilizing influence of small aspect ratio [Holmes et al., Phys. Fluids B 1, 788 (1989)] is confirmed, but it is found that shaping of the cross section influences the internal kink mode significantly. For finite pressure and small resistivity, curvature effects at the q=1 surface make the stability sensitively dependent on shape, and ellipticity is destabilizing. Only a very restricted set of finite pressure equilibria is completely stable for q0 < 1. A typical result is that the resistive kink mode is slowed down by toroidal effects to a weak resistive tearing/interchange mode. It is suggested that weak resistive instabilities are stabilized during the ramp phase of the sawteeth by effects not included in linear resistive magnetohydrodynamics. Possible mechanisms for triggering a sawtooth crash are discussed.
Stack, Andrew G
2009-09-01
Solvation and kink site formation on step edges are known to be controlling parameters in crystal growth and dissolution. However, links from classical crystal growth models to specific reactions at the mineral-water interface have remained elusive. Molecular dynamics is used here to examine the water structure on barium surface sites and kink site formation enthalpies for material adsorbed to and removed from the step parallel to the [120] direction on the {001} barite-water interface. The bariums at the interface are shown to be coordinatively unsaturated with respect to water, and it is suggested that this is due to a steric hindrance from the nature of the interface. Kink site detachment energies that include hydration energies are endothermic for barium and exothermic for sulfate. The implications and problems of using these parameters in a crystal growth model are discussed.
B-mode polarization induced by gravitational waves from kinks on infinite cosmic strings
Kawasaki, Masahiro; Miyamoto, Koichi; Nakayama, Kazunori
2010-11-15
We investigate the effect of the stochastic gravitational wave (GW) background produced by kinks on infinite cosmic strings, whose spectrum was derived in our previous work, on the B-mode power spectrum of the cosmic microwave background (CMB) anisotropy. We find that the B-mode polarization due to kinks is comparable to that induced by the motion of the string network and hence the contribution of GWs from kinks is important for estimating the B-mode power spectrum originating from cosmic strings. If the tension of cosmic strings {mu} is large enough, i.e., G{mu} > or approx. 10{sup -8}, B-mode polarization induced by cosmic strings can be detected by future CMB experiments.
PROPAGATING COUPLED ALFVEN AND KINK OSCILLATIONS IN AN ARBITRARY INHOMOGENEOUS CORONA
Pascoe, D. J.; Wright, A. N.; De Moortel, I.
2011-04-10
Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. We perform three-dimensional numerical simulations of footpoint-driven transverse waves propagating in a low {beta} plasma. We consider the cases of distorted cylindrical flux tubes and a randomly generated inhomogeneous medium. When density structuring is present, mode coupling in inhomogeneous regions leads to the coupling of the kink mode to the Alfven mode. The decay of the propagating kink wave is observed as energy is transferred to the local Alfven mode. In all cases considered, modest changes in density were capable of efficiently converting energy from the driving footpoint motion to localized Alfven modes. We have demonstrated that mode coupling efficiently couples propagating kink perturbations to Alfven modes in an arbitrary inhomogeneous medium. This has the consequence that transverse footpoint motions at the base of the corona will deposit energy to Alfven modes in the corona.
ERIC Educational Resources Information Center
Marchis, Iuliana
2009-01-01
Symmetry is one of the fundamental concepts in Geometry. It is a Mathematical concept, which can be very well connected with Art and Ethnography. The aim of the article is to show how to link the geometrical concept symmetry with interculturality. For this mosaics from different countries are used.
Symmetries in Lagrangian Dynamics
ERIC Educational Resources Information Center
Ferrario, Carlo; Passerini, Arianna
2007-01-01
In the framework of Noether's theorem, a distinction between Lagrangian and dynamical symmetries is made, in order to clarify some aspects neglected by textbooks. An intuitive setting of the concept of invariance of differential equations is presented. The analysis is completed by deriving the symmetry properties in the motion of a charged…
Symmetries of Spectral Problems
NASA Astrophysics Data System (ADS)
Shabat, A.
Deriving abelian KdV and NLS hierarchies, we describe non-abelian symmetries and "pre-Lax" elementary approach to Lax pairs. Discrete symmetries of spectral problems are considered in Sect. 4.2. Here we prove Darboux classical theorem and discuss a modern theory of dressing chains.
Adsorption of molecular hydrogen on Pd(Pt) decorated graphene
NASA Astrophysics Data System (ADS)
Adhikari, Narayan; Khaniya, Asim; Lamichhane, Saran; Pantha, Nurapati
2015-03-01
We have performed the first-principles based Density Functional Theory (DFT) calculations to study the stability, geometrical structures, and electronic properties of a Pd(Pt) atom adsorbed graphene to investigate the possibility of using Pd(Pt) decorated graphene as energy storage materials with reference to pristine graphene. The London dispersion forces have been incorporated by the DFT-D2 levels of calculations implemented in Quantum Espresso packages. Our findings show that Pd and Pt both adsorb on graphene at Bridge site. The electronic structures of Pd(Pt) adsorbed graphene possesses band gap opening due to breaking of the symmetry of graphene. Further we have studied the adsorption of moelcular hydrogen ((H 2) n , n = 1-7) on the Pd(Pt)-graphene system. The adatom Pd(Pt) enhances the binding energy per hydrogen molecule in Pd(Pt)-graphene system in comparison to that in the pristine graphene. The binding energy per hydrogen molecule of the adatom-graphene system decreases as the number of H 2 molecules increases and finally it saturates to 0.15 eV (0.16 eV) per hydrogen molecule for Pd-graphene (Pt-graphene) systems respectively. ICTP-NET 56/TWAS.
Symmetry Effects in Computation
NASA Astrophysics Data System (ADS)
Yao, Andrew Chi-Chih
2008-12-01
The concept of symmetry has played a key role in the development of modern physics. For example, using symmetry, C.N. Yang and other physicists have greatly advanced our understanding of the fundamental laws of physics. Meanwhile, computer scientists have been pondering why some computational problems seem intractable, while others are easy. Just as in physics, the laws of computation sometimes can only be inferred indirectly by considerations of general principles such as symmetry. The symmetry properties of a function can indeed have a profound effect on how fast the function can be computed. In this talk, we present several elegant and surprising discoveries along this line, made by computer scientists using symmetry as their primary tool. Note from Publisher: This article contains the abstract only.
Scattering of Klein–Gordon particles by a Kink-like potential
Hassanabadi, H.; Lu, Liangliang; Maghsoodi, E.; Liu, Guanghui; Zarrinkamar, S.
2014-03-15
The Klein–Gordon equation for the non-minimal vector and a scalar Kink-like potential is solved in terms of the hypergeometric functions. The scattering problem, i.e. the transmission and reflection coefficients, is studied as well. -- Highlights: •The Klein–Gordon equation for the non-minimal vector and a scalar Kink-like potential is solved. •We have calculated the corresponding transmission and reflection coefficients. •We discussed the behavior of the reflection and transmission coefficients vs. energy.
Kink-antikink, trapping bags and five-dimensional Gauss-Bonnet gravity
Giovannini, Massimo
2006-10-15
Five-dimensional Gauss-Bonnet gravity, with one warped extra-dimension, allows classes of solutions where two scalar fields combine either in a kink-antikink system or in a trapping-bag configuration. While the kink-antikink system can be interpreted as a pair of gravitating domain walls with opposite topological charges, the trapping-bag solution consists of a domain wall supplemented by a nontopological defect. In both classes of solutions, for large absolute values of the bulk coordinate (i.e. far from the core of the defects), the geometry is given by five-dimensional anti-de Sitter space.
Selective spatial damping of propagating kink waves due to resonant absorption
NASA Astrophysics Data System (ADS)
Terradas, J.; Goossens, M.; Verth, G.
2010-12-01
Context. There is observational evidence of propagating kink waves driven by photospheric motions. These disturbances, interpreted as kink magnetohydrodynamic (MHD) waves are attenuated as they propagate upwards in the solar corona. Aims: We show that resonant absorption provides a simple explanation to the spatial damping of these waves. Methods: Kink MHD waves are studied using a cylindrical model of solar magnetic flux tubes, which includes a non-uniform layer at the tube boundary. Assuming that the frequency is real and the longitudinal wavenumber complex, the damping length and damping per wavelength produced by resonant absorption are analytically calculated in the thin tube (TT) approximation, valid for coronal waves. This assumption is relaxed in the case of chromospheric tube waves and filament thread waves. Results: The damping length of propagating kink waves due to resonant absorption is a monotonically decreasing function of frequency. For kink waves with low frequencies, the damping length is exactly inversely proportional to frequency, and we denote this as the TGV relation. When moving to high frequencies, the TGV relation continues to be an exceptionally good approximation of the actual dependency of the damping length on frequency. This dependency means that resonant absorption is selective as it favours low-frequency waves and can efficiently remove high-frequency waves from a broad band spectrum of kink waves. The efficiency of the damping due to resonant absorption depends on the properties of the equilibrium model, in particular on the width of the non-uniform layer and the steepness of the variation in the local Alfvén speed. Conclusions: Resonant absorption is an effective mechanism for the spatial damping of propagating kink waves. It is selective because the damping length is inversely proportional to frequency so that the damping becomes more severe with increasing frequency. This means that radial inhomogeneity can cause solar
How to count kinks. From the continuum to the lattice and back
NASA Astrophysics Data System (ADS)
Gleiser, Marcelo; Müller, Hans-Reinhard
1998-03-01
We investigate the matching between (1+1)-dimensional nonlinear field theories coupled to an external stochastic environment and their lattice simulations. In particular, we focus on how to obtain numerical results which are lattice-spacing independent, and on how to extract the correct effective potential which emerges from the simulations. As an application, we study the thermal production of kink-antikink pairs, obtaining a number density of pairs which is lattice-spacing independent and the effective barrier for pair production, i.e., the effective kink mass.
{pi} kinks in the parametrically driven sine-Gordon equation and applications
Zharnitsky, V.; Mitkov, I.
1997-07-08
Parametrically driven sine-Gordon equation with a mean-zero forcing is considered. It is shown that the system is well approximated by the double sine-Gordon equation using the normal form technique. The reduced equation possesses {pi}-kink solutions, which are also observed numerically in the original system. This result is applied to domain walls dynamics in one-dimensional easy-plane ferromagnets. For such system the existence of {pi}-kinks implies the true domain structure in the presence of high-frequency magnetic field.
Tunable topological states in electron-doped HTT-Pt
NASA Astrophysics Data System (ADS)
Zhang, Xiaoming; Wang, Zhenhai; Zhao, Mingwen; Liu, Feng
2016-04-01
Modulating topologically nontrivial states in trivial materials is of both scientific and technological interest. Using first-principles calculations, we propose a demonstration of electron-doping- (or gate-voltage-) induced multiple quantum states; namely, quantum spin Hall (QSH) and quantum anomalous Hall (QAH) states, in a single material of the organometallic framework (HTT-Pt) synthesized from triphenylene hexathiol molecules (HTT) and PtC l2 . At a low doping level, the trivial HTT-Pt converts to a QSH insulator protected by time-reversal symmetry (TRS). When the electronic doping concentration is further increased, TRS will be broken, making the HTT-Pt a QAH insulator. The band gaps of these topologically nontrivial states can be as large as 42.5 meV, suggesting robustness at high temperatures. The possibility of switching between the QSH and QAH states offers an intriguing platform for a different device paradigm by interfacing between QSH and QAH states.
Observation of optical solitons in PT-symmetric lattices
Wimmer, Martin; Regensburger, Alois; Miri, Mohammad-Ali; Bersch, Christoph; Christodoulides, Demetrios N.; Peschel, Ulf
2015-01-01
Controlling light transport in nonlinear active environments is a topic of considerable interest in the field of optics. In such complex arrangements, of particular importance is to devise strategies to subdue chaotic behaviour even in the presence of gain/loss and nonlinearity, which often assume adversarial roles. Quite recently, notions of parity-time (PT) symmetry have been suggested in photonic settings as a means to enforce stable energy flow in platforms that simultaneously employ both amplification and attenuation. Here we report the experimental observation of optical solitons in PT-symmetric lattices. Unlike other non-conservative nonlinear arrangements where self-trapped states appear as fixed points in the parameter space of the governing equations, discrete PT solitons form a continuous parametric family of solutions. The possibility of synthesizing PT-symmetric saturable absorbers, where a nonlinear wave finds a lossless path through an otherwise absorptive system is also demonstrated. PMID:26215165
Aspects of emergent symmetries
NASA Astrophysics Data System (ADS)
Gomes, Pedro R. S.
2016-03-01
These are intended to be review notes on emergent symmetries, i.e. symmetries which manifest themselves in specific sectors of energy in many systems. The emphasis is on the physical aspects rather than computation methods. We include some background material and go through more recent problems in field theory, statistical mechanics and condensed matter. These problems illustrate how some important symmetries, such as Lorentz invariance and supersymmetry, usually believed to be fundamental, can arise naturally in low-energy regimes of systems involving a large number of degrees of freedom. The aim is to discuss how these examples could help us to face other complex and fundamental problems.
Sequential flavor symmetry breaking
Feldmann, Thorsten; Jung, Martin; Mannel, Thomas
2009-08-01
The gauge sector of the standard model exhibits a flavor symmetry that allows for independent unitary transformations of the fermion multiplets. In the standard model the flavor symmetry is broken by the Yukawa couplings to the Higgs boson, and the resulting fermion masses and mixing angles show a pronounced hierarchy. In this work we connect the observed hierarchy to a sequence of intermediate effective theories, where the flavor symmetries are broken in a stepwise fashion by vacuum expectation values of suitably constructed spurion fields. We identify the possible scenarios in the quark sector and discuss some implications of this approach.
An investigation of coupling of the internal kink mode to error field correction coils in tokamaks
NASA Astrophysics Data System (ADS)
Lazarus, E. A.
2013-12-01
The coupling of the internal kink to an external m/n = 1/1 perturbation is studied for profiles that are known to result in a saturated internal kink in the limit of a cylindrical tokamak. It is found from three-dimensional equilibrium calculations that, for A ≈ 30 circular plasmas and A ≈ 3 elliptical shapes, this coupling of the boundary perturbation to the internal kink is strong; i.e., the amplitude of the m/n = 1/1 structure at q = 1 is large compared with the amplitude applied at the plasma boundary. Evidence suggests that this saturated internal kink, resulting from small field errors, is an explanation for the TEXTOR and JET measurements of q0 remaining well below unity throughout the sawtooth cycle, as well as the distinction between sawtooth effects on the q-profile observed in TEXTOR and DIII-D. It is proposed that this excitation, which could readily be applied with error field correction coils, be explored as a mechanism for controlling sawtooth amplitudes in high-performance tokamak discharges. This result is then combined with other recent tokamak results to propose an L-mode approach to fusion in tokamaks.
Two high-mobility group box domains act together to underwind and kink DNA
Sánchez-Giraldo, R.; Acosta-Reyes, F. J.; Malarkey, C. S.; Saperas, N.; Churchill, M. E. A.; Campos, J. L.
2015-06-30
The crystal structure of HMGB1 box A bound to an unmodified AT-rich DNA fragment is reported at a resolution of 2 Å. A new mode of DNA recognition for HMG box proteins is found in which two box A domains bind in an unusual configuration generating a highly kinked DNA structure. High-mobility group protein 1 (HMGB1) is an essential and ubiquitous DNA architectural factor that influences a myriad of cellular processes. HMGB1 contains two DNA-binding domains, box A and box B, which have little sequence specificity but have remarkable abilities to underwind and bend DNA. Although HMGB1 box A is thought to be responsible for the majority of HMGB1–DNA interactions with pre-bent or kinked DNA, little is known about how it recognizes unmodified DNA. Here, the crystal structure of HMGB1 box A bound to an AT-rich DNA fragment is reported at a resolution of 2 Å. Two box A domains of HMGB1 collaborate in an unusual configuration in which the Phe37 residues of both domains stack together and intercalate the same CG base pair, generating highly kinked DNA. This represents a novel mode of DNA recognition for HMGB proteins and reveals a mechanism by which structure-specific HMG boxes kink linear DNA.
NASA Astrophysics Data System (ADS)
Soler, Roberto; Terradas, Jaume
2015-04-01
Magnetohydrodynamic (MHD) kink waves are ubiquitously observed in the solar atmosphere. The propagation and damping of these waves may play relevant roles in the transport and dissipation of energy in the solar atmospheric medium. However, in the atmospheric plasma dissipation of transverse MHD wave energy by viscosity or resistivity needs very small spatial scales to be efficient. Here, we theoretically investigate the generation of small scales in nonuniform solar magnetic flux tubes due to phase mixing of MHD kink waves. We go beyond the usual approach based on the existence of a global quasi-mode that is damped in time due to resonant absorption. Instead, we use a modal expansion to express the MHD kink wave as a superposition of Alfvén continuum modes that are phase mixed as time evolves. The comparison of the two techniques evidences that the modal analysis is more physically transparent and describes both the damping of global kink motions and the building up of small scales due to phase mixing. In addition, we discuss that the processes of resonant absorption and phase mixing are closely linked. They represent two aspects of the same underlying physical mechanism: the energy cascade from large scales to small scales due to naturally occurring plasma and/or magnetic field inhomogeneities. This process may provide the necessary scenario for efficient dissipation of transverse MHD wave energy in the solar atmospheric plasma.
Non-linear propagation of kink waves to the solar chromosphere
NASA Astrophysics Data System (ADS)
Stangalini, M.; Giannattasio, F.; Jafarzadeh, S.
2015-05-01
Small-scale magnetic field concentrations (magnetic elements) in the quiet Sun are believed to contribute to the energy budget of the upper layers of the Sun's atmosphere, as they are observed to support a large number of magneto-hydrodynamic modes. In recent years, kink waves in magnetic elements were observed at different heights in the solar atmosphere, from the photosphere to the corona. However, the propagation of these waves has not been fully evaluated. Our aim is to investigate the propagation of kink waves in small magnetic elements in the solar atmosphere. We analysed high-quality, long duration spectropolarimetric data of a photospheric quiet Sun region observed near the disk centre with the spectropolarimeter CRISP at the Swedish Solar Telescope (SST). We complemented these data with simultaneous and co-spatial broadband chromospheric observations of the same region. Our findings reveal a clear upward propagation of kink waves with frequency above 2.6 mHz. Moreover, the signature of a non-linear propagation process is also observed. By comparing photospheric to chromospheric power spectra, no signature of an energy dissipation is found at least at the atmospheric heights at which the data analysed originate. This implies that most of the energy carried by the kink waves (within the frequency range under study < 17 mHz) flows to upper layers in the Sun's atmosphere.
Linear calculations of edge current driven kink modes with BOUT++ code
Li, G. Q. Xia, T. Y.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Ma, C. H.; Xi, P. W.
2014-10-15
This work extends previous BOUT++ work to systematically study the impact of edge current density on edge localized modes, and to benchmark with the GATO and ELITE codes. Using the CORSICA code, a set of equilibria was generated with different edge current densities by keeping total current and pressure profile fixed. Based on these equilibria, the effects of the edge current density on the MHD instabilities were studied with the 3-field BOUT++ code. For the linear calculations, with increasing edge current density, the dominant modes are changed from intermediate-n and high-n ballooning modes to low-n kink modes, and the linear growth rate becomes smaller. The edge current provides stabilizing effects on ballooning modes due to the increase of local shear at the outer mid-plane with the edge current. For edge kink modes, however, the edge current does not always provide a destabilizing effect; with increasing edge current, the linear growth rate first increases, and then decreases. In benchmark calculations for BOUT++ against the linear results with the GATO and ELITE codes, the vacuum model has important effects on the edge kink mode calculations. By setting a realistic density profile and Spitzer resistivity profile in the vacuum region, the resistivity was found to have a destabilizing effect on both the kink mode and on the ballooning mode. With diamagnetic effects included, the intermediate-n and high-n ballooning modes can be totally stabilized for finite edge current density.
Localized stability criterion for kink modes in systems with small shear
Hastie, R.J.; Johnson, J.L.
1986-02-01
A localized magnetohydrodynamic stability criterion for ideal kink instabilities is determined for systems where the safety factor has a local minimum on a rational surface with no pressure gradient. These modes are stable in the cylindrical limit, but toroidal effects can make them unstable. They could provide a partial explanation for the rapid current penetration observed in tokamaks. 7 refs.