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.
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.
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.
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.
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.
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.
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.
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.
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}
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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
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.
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
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.
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
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
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
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.
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
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.
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.
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
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.
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
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.
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.
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.
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.
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.
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.
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.
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)].
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
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.
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.
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.
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.
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)
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.
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
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.
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
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.
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
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.
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.
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
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
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
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.
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
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
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
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
{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.
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.
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
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.
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.
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.
The Solution Structural Ensembles of RNA Kink-turn Motifs and Their Protein Complexes
Huang, Lin; Lilley, David M. J.
2015-01-01
With the growing number of crystal structures of RNA and RNA/protein complexes, a critical next step is understanding the dynamic behavior of these entities in solution in terms of conformational ensembles and energy landscapes. To this end, we have used X-ray scattering interferometry (XSI) to probe the widespread RNA kink-turn motif and its complexes with the canonical kink-turn binding protein L7Ae. XSI revealed that the folded kink-turn is best described as a restricted conformational ensemble. The ions present in solution alter the nature of this ensemble, and protein binding can perturb the kink-turn ensemble without collapsing it to a unique state. This study demonstrates how XSI can reveal structural and ensemble properties of RNAs and RNA/protein complexes in solution and uncovers the behavior of an important RNA/protein motif. This type of information will be necessary to understand, predict, and engineer the behavior and function of RNAs and their protein complexes. PMID:26727239
Sachdeva, Virender; Haque, Nazmul; Pathengay, Avinash; Kekunnaya, Ramesh
2015-01-01
Neurofibromatosis Type I if associated with aplasia of greater wing of sphenoid may be associated with a pulsatile exophthalmos. However, very rarely it may be associated with a pulsatile enophthalmos. This clinical image describes a rare presentation with pulsatile enophthalmos, esotropia and kinking of the optic nerve due to neurofibomatosis type I. PMID:26903735
Sachdeva, Virender; Haque, Nazmul; Pathengay, Avinash; Kekunnaya, Ramesh
2015-01-01
Neurofibromatosis Type I if associated with aplasia of greater wing of sphenoid may be associated with a pulsatile exophthalmos. However, very rarely it may be associated with a pulsatile enophthalmos. This clinical image describes a rare presentation with pulsatile enophthalmos, esotropia and kinking of the optic nerve due to neurofibomatosis type I. PMID:26903735
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.
Successive phase transitions and kink solutions in ϕ(8), ϕ(10), and ϕ(12) field theories.
Khare, Avinash; Christov, Ivan C; Saxena, Avadh
2014-08-01
We obtain exact solutions for kinks in ϕ(8), ϕ(10), and ϕ(12) field theories with degenerate minima, which can describe a second-order phase transition followed by a first-order one, a succession of two first-order phase transitions and a second-order phase transition followed by two first-order phase transitions, respectively. Such phase transitions are known to occur in ferroelastic and ferroelectric crystals and in meson physics. In particular, we find that the higher-order field theories have kink solutions with algebraically decaying tails and also asymmetric cases with mixed exponential-algebraic tail decay, unlike the lower-order ϕ(4) and ϕ(6) theories. Additionally, we construct distinct kinks with equal energies in all three field theories considered, and we show the coexistence of up to three distinct kinks (for a ϕ(12) potential with six degenerate minima). We also summarize phonon dispersion relations for these systems, showing that the higher-order field theories have specific cases in which only nonlinear phonons are allowed. For the ϕ(10) field theory, which is a quasiexactly solvable model akin to ϕ(6), we are also able to obtain three analytical solutions for the classical free energy as well as the probability distribution function in the thermodynamic limit. PMID:25215844
The solution structural ensembles of RNA kink-turn motifs and their protein complexes.
Shi, Xuesong; Huang, Lin; Lilley, David M J; Harbury, Pehr B; Herschlag, Daniel
2016-03-01
With the growing number of crystal structures of RNA and RNA-protein complexes, a critical next step is understanding the dynamic solution behavior of these entities in terms of conformational ensembles and energy landscapes. To this end, we have used X-ray scattering interferometry (XSI) to probe the ubiquitous RNA kink-turn motif and its complexes with the canonical kink-turn binding protein L7Ae. XSI revealed that the folded kink-turn is best described as a restricted conformational ensemble. The ions present in solution alter the nature of this ensemble, and protein binding can perturb the kink-turn ensemble without collapsing it to a unique state. This study demonstrates how XSI can reveal structural and ensemble properties of RNAs and RNA-protein complexes and uncovers the behavior of an important RNA-protein motif. This type of information will be necessary to understand, predict and engineer the behavior and function of RNAs and their protein complexes. PMID:26727239
RNA Tertiary Interactions in a Riboswitch Stabilize the Structure of a Kink Turn
Schroeder, Kersten T.; Daldrop, Peter; Lilley, David M.J.
2011-01-01
Summary The kink turn is a widespread RNA motif that introduces an acute kink into the axis of duplex RNA, typically comprising a bulge followed by a G⋅A and A⋅G pairs. The kinked conformation is stabilized by metal ions, or the binding of proteins including L7Ae. We now demonstrate a third mechanism for the stabilization of k-turn structure, involving tertiary interactions within a larger RNA structure. The SAM-I riboswitch contains an essential standard k-turn sequence that kinks a helix so that its terminal loop can make a long-range interaction. We find that some sequence variations in the k-turn within the riboswitch do not prevent SAM binding, despite preventing the folding of the k-turn in isolation. Furthermore, two crystal structures show that the sequence-variant k-turns are conventionally folded within the riboswitch. This study shows that the folded structure of the k-turn can be stabilized by tertiary interactions within a larger RNA structure. PMID:21893284
Linear calculations 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.
2014-10-01
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.
Molecular symmetry with quaternions.
Fritzer, H P
2001-09-01
A new and relatively simple version of the quaternion calculus is offered which is especially suitable for applications in molecular symmetry and structure. After introducing the real quaternion algebra and its classical matrix representation in the group SO(4) the relations with vectors in 3-space and the connection with the rotation group SO(3) through automorphism properties of the algebra are discussed. The correlation of the unit quaternions with both the Cayley-Klein and the Euler parameters through the group SU(2) is presented. Besides rotations the extension of quaternions to other important symmetry operations, reflections and the spatial inversion, is given. Finally, the power of the quaternion calculus for molecular symmetry problems is revealed by treating some examples applied to icosahedral symmetry. PMID:11666072
NASA Astrophysics Data System (ADS)
Golubitsky, Martin
2012-04-01
Many gaits of four-legged animals are described by symmetry. For example, when a horse paces it moves both left legs in unison and then both right legs and so on. The motion is described by two symmetries: Interchange front and back legs, and swap left and right legs with a half-period phase shift. Biologists postulate the existence of a central pattern generator (CPG) in the neuronal system that sends periodic signals to the legs. CPGs can be thought of as electrical circuits that produce periodic signals and can be modeled by systems with symmetry. In this lecture we discuss animal gaits; use gait symmetries to construct a simplest CPG architecture that naturally produces quadrupedal gait rhythms; and make several testable predictions about gaits.
NASA Astrophysics Data System (ADS)
Lovelady, Benjamin C.; Wheeler, James T.
2016-04-01
According to the Coleman-Mandula theorem, any gauge theory of gravity combined with an internal symmetry based on a Lie group must take the form of a direct product in order to be consistent with basic assumptions of quantum field theory. However, we show that an alternative gauging of a simple group can lead dynamically to a spacetime with compact internal symmetry. The biconformal gauging of the conformal symmetry of n-dimensional Euclidean space doubles the dimension to give a symplectic manifold. Examining one of the Lagrangian submanifolds in the flat case, we find that in addition to the expected S O (n ) connection and curvature, the solder form necessarily becomes Lorentzian. General coordinate invariance gives rise to an S O (n -1 ,1 ) connection on the spacetime. The principal fiber bundle character of the original S O (n ) guarantees that the two symmetries enter as a direct product, in agreement with the Coleman-Mandula theorem.
Dynamical symmetries for fermions
Guidry, M.
1989-01-01
An introduction is given to the Fermion Dynamical Symmetry Model (FDSM). The analytical symmetry limits of the model are then applied to the calculation of physical quantities such as ground-state masses and B(E{sub 2}) values in heavy nuclei. These comparisons with data provide strong support for a new principle of collective motion, the Dynamical Pauli Effect, and suggest that dynamical symmetries which properly account for the pauli principle are much more persistent in nuclear structure than the corresponding boson symmetries. Finally, we present an assessment of criticisms which have been voiced concerning the FDSM, and a discussion of new phenomena and exotic spectroscopy'' which may be suggested by the model. 14 refs., 8 figs., 4 tabs.
ERIC Educational Resources Information Center
Groetsch, C. W.
2005-01-01
Resistance destroys symmetry. In this note, a graphical exploration serves as a guide to a rigorous elementary proof of a specific asymmetry in the trajectory of a point projectile in a medium offering linear resistance.
NASA Astrophysics Data System (ADS)
Castaños, Octavio
2010-09-01
The purpose of this course is to study the evolution of the symmetry concept and establish its influence in the knowledge of the fundamental laws of nature. Physicist have been using the symmetry concept in two ways: to solve problems and to search for new understanding of the world around us. In quantum physics symmetry plays a key role in gaining an understanding of the physical laws governing the behavior of matter and field systems. It provides, generally, a shortcut based on geometry for discovering the secrets of the Universe. Because it is believed that the laws of physics are invariant under discrete and continuous transformation operations of the space and time, there are continuous symmetries, for example, energy and momentum together with discrete ones corresponding to charge, parity and time reversal operations.
Coronal loop seismology using damping of standing kink oscillations by mode coupling
NASA Astrophysics Data System (ADS)
Pascoe, D. J.; Goddard, C. R.; Nisticò, G.; Anfinogentov, S.; Nakariakov, V. M.
2016-05-01
Context. Kink oscillations of solar coronal loops are frequently observed to be strongly damped. The damping can be explained by mode coupling on the condition that loops have a finite inhomogeneous layer between the higher density core and lower density background. The damping rate depends on the loop density contrast ratio and inhomogeneous layer width. Aims: The theoretical description for mode coupling of kink waves has been extended to include the initial Gaussian damping regime in addition to the exponential asymptotic state. Observation of these damping regimes would provide information about the structuring of the coronal loop and so provide a seismological tool. Methods: We consider three examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) for which the general damping profile (Gaussian and exponential regimes) can be fitted. Determining the Gaussian and exponential damping times allows us to perform seismological inversions for the loop density contrast ratio and the inhomogeneous layer width normalised to the loop radius. The layer width and loop minor radius are found separately by comparing the observed loop intensity profile with forward modelling based on our seismological results. Results: The seismological method which allows the density contrast ratio and inhomogeneous layer width to be simultaneously determined from the kink mode damping profile has been applied to observational data for the first time. This allows the internal and external Alfvén speeds to be calculated, and estimates for the magnetic field strength can be dramatically improved using the given plasma density. Conclusions: The kink mode damping rate can be used as a powerful diagnostic tool to determine the coronal loop density profile. This information can be used for further calculations such as the magnetic field strength or phase mixing rate.
A CORONAL MASS EJECTION AND HARD X-RAY EMISSIONS ASSOCIATED WITH THE KINK INSTABILITY
Cho, Kyung-Suk; Bong, Su-Chan; Kim, Yeon-Han; Park, Young-Deuk; Lee, Jeongwoo; Joshi, Bhuwan
2009-09-20
We present a morphological study of the 2004 August 18 solar eruption that occurred in the active region NOAA 10656 near the west limb using extreme-ultraviolet (EUV) data from the Transition Region and Coronal Explorer (TRACE), Halpha filtergram of Big Bear Solar Observatory, white light images of Mauna Loa Solar Observatory (MLSO), hard X-ray (HXR) data of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and microwave data of the Owens Valley Solar Array. In this event, we have an excellent set of observations for tracing the early evolution of the coronal mass ejection (CME) from a flux rope emergence to its propagation into space as a well-connected series of events thanks to the coronameter's field of view (FOV) down to 1.1 solar radius in an overlap with that of the TRACE. This data set reveals continuously evolving EUV, Halpha, and WL features that suggest the rise of a small, low-lying loop, its writhing motion, break of the kinked loop at its crossing point, and transformation of the ejecta to the CME. The HXR and microwave sources are found in varying locations with a complicated temporal dependence, which, we interpret, is due to two successive flares in the event. The first flare appears to be associated with the rise of the small loop, which then triggers the second flare. During the second flare a HXR coronal source is detected at the crossing point of the kinked loop, and more intriguingly, the kinked loop apparently breaks at the crossing point of the two legs, which indicates a magnetic reconnection at the X-point configuration. After the break of the kinked UV loop, a CME structure shows up in the MLSO FOV, and propagates away from the Sun. It is concluded that this CME occurred due to the kink instability.
The transverse and rotational motions of magnetohydrodynamic kink waves in the solar atmosphere
Goossens, M.; Van Doorsselaere, T.; Soler, R.; Terradas, J.; Verth, G.
2014-06-10
Magnetohydrodynamic (MHD) kink waves have now been observed to be ubiquitous throughout the solar atmosphere. With modern instruments, they have now been detected in the chromosphere, interface region, and corona. The key purpose of this paper is to show that kink waves do not only involve purely transverse motions of solar magnetic flux tubes, but the velocity field is a spatially and temporally varying sum of both transverse and rotational motion. Taking this fact into account is particularly important for the accurate interpretation of varying Doppler velocity profiles across oscillating structures such as spicules. It has now been shown that, as well as bulk transverse motions, spicules have omnipresent rotational motions. Here we emphasize that caution should be used before interpreting the particular MHD wave mode/s responsible for these rotational motions. The rotational motions are not necessarily signatures of the classic axisymmetric torsional Alfvén wave alone, because kink motion itself can also contribute substantially to varying Doppler velocity profiles observed across these structures. In this paper, the displacement field of the kink wave is demonstrated to be a sum of its transverse and rotational components, both for a flux tube with a discontinuous density profile at its boundary, and one with a more realistic density continuum between the internal and external plasma. Furthermore, the Doppler velocity profile of the kink wave is forward modeled to demonstrate that, depending on the line of sight, it can either be quite distinct or very similar to that expected from a torsional Alfvén wave.
DFT Study of Optical Properties of Pt-based Complexes
NASA Astrophysics Data System (ADS)
Oprea, Corneliu I.; Dumbravǎ, Anca; Moscalu, Florin; Nicolaides, Atnanassios; Gîrţu, Mihai A.
2010-01-01
We report Density Functional Theory (DFT) calculations providing the geometrical and electronic structures, as well as the vibrational and optical properties of the homologous series of Pt-pyramidalized olefin complexes (CH2)n-(C8H10)Pt(PH3)2, where n = 0, 1, and 2, in their neutral and oxidized states. All complexes were geometry optimized for the singlet ground state in vacuum using DFT methods with B3LYP exchange-correlation functional and the Effective Core Potential LANL2DZ basis set, within the frame of Gaussian03 quantum chemistry package. We find the coordination geometry of Pt to be distorted square planar, with dihedral angles ranging from 0°, for n = 0 and 1, which have C2V symmetry to 3.4°, for n = 2 with C2 symmetry. The Mulliken charge analysis allows a discussion of the oxidation state of the Pt ion. Electronic transitions were calculated at the same level of theory by means of Time Dependant-DFT. For n = 2 the electronic absorption bands are located in the UV region of the spectrum, the transitions being assigned to metal to ligand charge transfers. The relevance of these Pt-based compounds as possible pigments for dye-sensitized solar cells is discussed.
On a family of (1+1)-dimensional scalar field theory models: Kinks, stability, one-loop mass shifts
Alonso-Izquierdo, A.; Mateos Guilarte, J.
2012-09-15
In this paper we construct a one-parametric family of (1+1)-dimensional one-component scalar field theory models supporting kinks. Inspired by the sine-Gordon and {phi}{sup 4} models, we look at all possible extensions such that the kink second-order fluctuation operators are Schroedinger differential operators with Poeschl-Teller potential wells. In this situation, the associated spectral problem is solvable and therefore we shall succeed in analyzing the kink stability completely and in computing the one-loop quantum correction to the kink mass exactly. When the parameter is a natural number, the family becomes the hierarchy for which the potential wells are reflectionless, the two first levels of the hierarchy being the sine-Gordon and {phi}{sup 4} models. - Highlights: Black-Right-Pointing-Pointer We construct a family of scalar field theory models supporting kinks. Black-Right-Pointing-Pointer The second-order kink fluctuation operators involve Poeschl-Teller potential wells. Black-Right-Pointing-Pointer We compute the one-loop quantum correction to the kink mass with different methods.
NASA Astrophysics Data System (ADS)
Vidal-Iglesias, F. J.; Solla-Gullón, J.; Montiel, V.; Feliu, J. M.; Aldaz, A.
Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle and to transport as liquid or as concentrated aqueous solution. However, on noble metal electrodes ammonia oxidation is a sluggish reaction and the electrocatalyst needs to be improved for developing efficient ammonia fuel cells. In this work, ammonia electrooxidation reaction on 3-4-nm bimetallic PtMe (Ir, Rh, Pd, Ru) and on preferentially oriented Pt(1 0 0) nanoparticles is reported. PtMe nanoparticles have been prepared by using water-in-oil microemulsions to obtain a narrow size distribution whereas preferentially oriented Pt nanoparticles have been prepared through colloidal routes. Among all the bimetallic samples tested, only Pt 75Ir 25 and Pt 75Rh 25 nanoparticles show, at the low potential range, an enhancement of the oxidation density current with respect to the behaviour found for pure platinum nanoparticles prepared by the same method. In addition, two Pt(1 0 0) preferentially oriented nanoparticles of different particle size (4 and 9 nm) have been also studied. These oriented nanoparticles show higher current densities than polycrystalline Pt nanoparticles due to the sensitivity of ammonia oxidation toward the presence of surface sites with square symmetry. The reactivity of the different 4-nm nanoparticles parallels well with that expected from bulk PtMe alloys and Pt single crystal electrodes.
Self-interconnecting Pt nanowire network electrode for electrochemical amperometric biosensor.
Wang, Shuqi; Xu, Li-Ping; Liang, Hai-Wei; Yu, Shu-Hong; Wen, Yongqiang; Wang, Shutao; Zhang, Xueji
2015-07-14
One-dimensional Pt nanostructures are of considerable interest for the development of highly stable and sensitive electrochemical sensors. This paper describes a self-interconnecting Pt nanowire network electrode (PtNNE) for the detection of hydrogen peroxide (H2O2) and glucose with ultrahigh sensitivity and stability. The as-prepared PtNNE consists of polycrystalline nanowires with high-index facets along the side surface which provides more active surface atoms on kinks and steps, those ultralong nanowires being interconnected with each other to form a free-standing network membrane. The excellent structural features of the PtNNE promoted its performance as a Pt-based electrochemical sensor both in terms of electrocatalytic activity and stability. Amperometric measurements towards hydrogen peroxide were performed; the PtNNE sensor showed an extremely high sensitivity of 1360 μA mM(-1) cm(-2). This excellent sensitivity is mainly attributed to the high-index facets of the nanowires resulting in their superior electrocatalytic activity towards H2O2, and the interconnected nanowire network forming an "electron freeway" transport model, which could provide multiple electron pathways and fast electron transport on the electrode, leading to rapid reaction and sensitive signal detection. The as-prepared PtNNE also holds promise as an oxidase-based biosensor. As a proof of concept, a PtNNE-based glucose biosensor also showed an outstanding sensitivity as high as 114 μA mM(-1) cm(-2), a low detection limit of 1.5 μM, and an impressive detection range from 5 μM to 30 mM. PMID:26083932
Peierls potential and kink-pair mechanism in high-pressure MgSiO3 perovskite: An atomic scale study
NASA Astrophysics Data System (ADS)
Kraych, A.; Carrez, Ph.; Hirel, P.; Clouet, E.; Cordier, P.
2016-01-01
The motion of [100](010) screw dislocations via a kink-pair mechanism is investigated in high-pressure MgSiO3 perovskite by means of atomistic calculations and an elastic interaction model for kink nucleation. Atomistic calculations based on the nudged elastic band method provide the Peierls potential, which is shown to be dynamically asymmetric and stress dependent. The elastic interaction model adjusted to match kink width computed atomistically, is used to evaluate the critical nucleation enthalpy. We demonstrate that the kink-pair mechanism in MgSiO3 perovskite is controlled by the nucleation of kinks along the [100] screw dislocation.
Is space-time symmetry a suitable generalization of parity-time symmetry?
Amore, Paolo; Fernández, Francisco M.; Garcia, Javier
2014-11-15
We discuss space-time symmetric Hamiltonian operators of the form H=H{sub 0}+igH{sup ′}, where H{sub 0} is Hermitian and g real. H{sub 0} is invariant under the unitary operations of a point group G while H{sup ′} is invariant under transformation by elements of a subgroup G{sup ′} of G. If G exhibits irreducible representations of dimension greater than unity, then it is possible that H has complex eigenvalues for sufficiently small nonzero values of g. In the particular case that H is parity-time symmetric then it appears to exhibit real eigenvalues for all 0
NASA Astrophysics Data System (ADS)
McClenaghan, J.; Lin, Z.; Holod, I.; Deng, W.; Wang, Z.
2014-12-01
The gyrokinetic toroidal code (GTC) capability has been extended for simulating internal kink instability with kinetic effects in toroidal geometry. The global simulation domain covers the magnetic axis, which is necessary for simulating current-driven instabilities. GTC simulation in the fluid limit of the kink modes in cylindrical geometry is verified by benchmarking with a magnetohydrodynamic eigenvalue code. Gyrokinetic simulations of the kink modes in the toroidal geometry find that ion kinetic effects significantly reduce the growth rate even when the banana orbit width is much smaller than the radial width of the perturbed current layer at the mode rational surface.
On the weak confinement of kinks in the one-dimensional quantum ferromagnet CoNb2O6
NASA Astrophysics Data System (ADS)
Rutkevich, S. B.
2010-07-01
In a recent paper Coldea et al (2010 Science 327 177) report observations of the weak confinement of kinks in the Ising spin chain ferromagnet CoNb2O6 at low temperatures. To interpret the entire spectra of magnetic excitations measured via neutron scattering, they introduce a phenomenological model, which takes into account only the two-kink configurations of the spin chain. We present the exact solution of this model. The explicit expressions for the two-kink bound-state energy spectra and for the relative intensities of neutron scattering on these magnetic modes are obtained in terms of the Bessel function.
McClenaghan, J.; Lin, Z.; Holod, I.; Deng, W.; Wang, Z.
2014-12-15
The gyrokinetic toroidal code (GTC) capability has been extended for simulating internal kink instability with kinetic effects in toroidal geometry. The global simulation domain covers the magnetic axis, which is necessary for simulating current-driven instabilities. GTC simulation in the fluid limit of the kink modes in cylindrical geometry is verified by benchmarking with a magnetohydrodynamic eigenvalue code. Gyrokinetic simulations of the kink modes in the toroidal geometry find that ion kinetic effects significantly reduce the growth rate even when the banana orbit width is much smaller than the radial width of the perturbed current layer at the mode rational surface.
NASA Astrophysics Data System (ADS)
Loebbert, Florian
2016-08-01
In these introductory lectures we discuss the topic of Yangian symmetry from various perspectives. Forming the classical counterpart of the Yangian and an extension of ordinary Noether symmetries, first the concept of nonlocal charges in classical, two-dimensional field theory is reviewed. We then define the Yangian algebra following Drinfel’d's original motivation to construct solutions to the quantum Yang–Baxter equation. Different realizations of the Yangian and its mathematical role as a Hopf algebra and quantum group are discussed. We demonstrate how the Yangian algebra is implemented in quantum, two-dimensional field theories and how its generators are renormalized. Implications of Yangian symmetry on the two-dimensional scattering matrix are investigated. We furthermore consider the important case of discrete Yangian symmetry realized on integrable spin chains. Finally we give a brief introduction to Yangian symmetry in planar, four-dimensional super Yang–Mills theory and indicate its impact on the dilatation operator and tree-level scattering amplitudes. These lectures are illustrated by several examples, in particular the two-dimensional chiral Gross–Neveu model, the Heisenberg spin chain and { N }=4 superconformal Yang–Mills theory in four dimensions.
High pressure Raman spectroscopic studies of Pt(II) complex trans-PtCl2(PEt3)2
NASA Astrophysics Data System (ADS)
Bajaj, Naini; Poswal, H. K.; Bhatt, Himal; Deo, M. N.; Sharma, Surinder M.
2016-05-01
We report here the high pressure Raman spectroscopy of the Pt(II) complex trans-PtCl2(P(C2H5)3)2 up to 5 GPa. We have analyzed the metal-ligand stretching modes as well as ligand internal vibrational modes of the complex under pressure. Many characteristic Raman modes show pressure induced splitting at pressures as low as 1 GPa. On careful analysis of the skeletal region, the new modes appeared could be corroborated with the position of corresponding modes in the infrared spectrum, thus indicating a loss of inversion symmetry in the trans- isomer.
Beyond the surface atlas: A roadmap and gazetteer for surface symmetry and structure
NASA Astrophysics Data System (ADS)
Jenkins, Stephen J.; Pratt, Stephanie J.
2007-10-01
Throughout the development of single-crystal surface science, interest has predominantly focussed on the high-symmetry planes of crystalline materials, which typically present simple stable structures with small primitive unit cells. This concentration of effort has rapidly and substantially advanced our understanding of fundamental surface phenomena, and provides a sound basis for detailed study of more complex planes. The intense current interest in these is partly motivated by their regular arrays of steps, kinks or other low-coordination structural features, whose properties are little understood and may mimic specific highly-reactive sites on dispersed nanoparticles. Furthermore, the lower symmetry of these planes may give rise to other equally interesting properties such as intrinsic chirality, with exciting potential applications in enantioselective heterogeneous catalysis, biosensors and surface magnetism. To aid exploration of this new territory for surface science requires a depth of understanding that goes beyond the character of individual surfaces to encompass the global relationships between all possible surfaces of a given material, both in their structure and in their symmetry. In this report we present a rigorous conceptual framework for ideal crystalline surfaces within which the symmetry and structure of all possible surface orientations are described. We illustrate the versatility of our generally-applicable approach by comparing fcc, bcc and hcp materials. The entire scheme naturally derives from the very simple basis that the fundamental distinction between symmetry and structure is paramount. Where symmetry is concerned, our approach recognises that the surface is not a two-dimensional (2D) object but actually a truncated three-dimensional (3D) one. We therefore derive a symmetry scheme specifically formulated for surfaces and naturally encompassing their chirality where necessary. Our treatment of surface structure, on the other hand
Possibility of charge density wave transition in a SrPt2Sb2 superconductor
NASA Astrophysics Data System (ADS)
Ibuka, Soshi; Imai, Motoharu
2016-04-01
The first-order transition at T 0 = 270 K for the platinum-based SrPt2Sb2 superconductor was investigated using x-ray diffraction and magnetic susceptibility measurements. When polycrystalline SrPt2Sb2 was cooled down through T 0, the structure was transformed from monoclinic to a modulated orthorhombic structure, and no magnetic order was formed, which illustrates the possibility of a charge density wave (CDW) transition at T 0. SrPt2Sb2 can thus be a new example to examine the interplay of CDW and superconductivity in addition to SrPt2As2, BaPt2As2, and LaPt2Si2. It is unique that the average structure of the low-temperature phase has higher symmetry than that of the high-temperature phase.
Solla-Gullón, J; Vidal-Iglesias, F J; López-Cudero, A; Garnier, E; Feliu, J M; Aldaz, A
2008-07-01
Reactivity towards methanol and formic acid electrooxidation on Pt nanoparticles with well characterised surfaces were studied and compared with the behaviour of single crystal electrodes with basal orientations. Polyoriented and preferential (100), (111) and (100)-(111) Pt nanoparticles were synthesised, cleaned preserving its surface structure, characterised and employed to evaluate the influence of the surface structure/shape of the Pt nanoparticles on these two relevant electrochemical reactions. The results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, the surface structure of the electrodes plays an important role on the reactivity of both oxidation processes, and thus the electrocatalytic properties strongly depend on the surface structure/shape of the nanoparticles, in particular on the presence of sites with (111) symmetry. These findings open the possibility of designing new and better electrocatalytic materials using decorated shape-controlled Pt nanoparticles as previously described with Pt single crystal electrodes. PMID:18563230
Possibility of charge density wave transition in a SrPt2Sb2 superconductor.
Ibuka, Soshi; Imai, Motoharu
2016-04-27
The first-order transition at T 0 = 270 K for the platinum-based SrPt2Sb2 superconductor was investigated using x-ray diffraction and magnetic susceptibility measurements. When polycrystalline SrPt2Sb2 was cooled down through T 0, the structure was transformed from monoclinic to a modulated orthorhombic structure, and no magnetic order was formed, which illustrates the possibility of a charge density wave (CDW) transition at T 0. SrPt2Sb2 can thus be a new example to examine the interplay of CDW and superconductivity in addition to SrPt2As2, BaPt2As2, and LaPt2Si2. It is unique that the average structure of the low-temperature phase has higher symmetry than that of the high-temperature phase. PMID:27023674
NASA Astrophysics Data System (ADS)
Fang, Yi-Nan; Dong, Guo-Hui; Zhou, Duan-Lu; Sun, Chang-Pu
2016-04-01
Symmetry is conventionally described in a polarized manner that the system is either completely symmetric or completely asymmetric. Using group theoretical approach to overcome this dichotomous problem, we introduce the degree of symmetry (DoS) as a non-negative continuous number ranging from zero to unity. DoS is defined through an average of the fidelity deviations of Hamiltonian or quantum state over its transformation group G, and thus is computable by making use of the completeness relations of the irreducible representations of G. The monotonicity of DoS can effectively probe the extended group for accidental degeneracy while its multi-valued natures characterize some (spontaneous) symmetry breaking. Supported by the National Natural Science Foundation of China under Grant Nos. 11421063, 11534002, 11475254 and the National 973 Program under Grant Nos. 2014CB921403, 2012CB922104, and 2014CB921202
Chanowitz, M.S.
1990-09-01
The Higgs mechanism is reviewed in its most general form, requiring the existence of a new symmetry-breaking force and associated particles, which need not however be Higgs bosons. The first lecture reviews the essential elements of the Higgs mechanism, which suffice to establish low energy theorems for the scattering of longitudinally polarized W and Z gauge bosons. An upper bound on the scale of the symmetry-breaking physics then follows from the low energy theorems and partial wave unitarity. The second lecture reviews particular models, with and without Higgs bosons, paying special attention to how the general features discussed in lecture 1 are realized in each model. The third lecture focuses on the experimental signals of strong WW scattering that can be observed at the SSC above 1 TeV in the WW subenergy, which will allow direct measurement of the strength of the symmetry-breaking force. 52 refs., 10 figs.
NASA Astrophysics Data System (ADS)
Ismael, Jenann Tareq
1997-04-01
Structures of many different sorts arise in physics, e.g., the concrete structures of material bodies, the structure exemplified by the spatiotemporal configuration of a set of bodies, the structures of more abstract objects like states, state-spaces, laws, and so on. To each structure of any of these types there corresponds a set of transformations which map it onto itself. These are its symmetries. Increasingly ubiquitous in theoretical discussions in physics, the notion of symmetry is also at the root of some time-worn philosophical debates. This dissertation consists of a set of essays on topics drawn from places where the two fields overlap. The first essay is an informal introduction to the mathematical study of symmetry. The second essay defends a famous principle of Pierre Curie which states that the symmetries of a cause are always symmetries of its effect. The third essay takes up the case of reflection in space in the context of a controversy stemming from one of Kant's early arguments for the substantivality of space. The fourth essay is a discussion of the general conditions under which an asymmetry in a phenomenon suggests an asymmetry in the laws which govern it. The case of reflection in time-specifically, the theoretical strategy used in statistical mechanics to subsume the time-asymmetric phenomena of Thermodynamics under the time-symmetric classical dynamical laws-is used to illustrate the general points. The philosophical heart of the thesis lies in its fifth essay. Here a somewhat novel way of conceiving scientific theorizing is articulated, one suggested by the abstract mathematical perspective of symmetry.
NASA Astrophysics Data System (ADS)
Wang, Juven C.; Santos, Luiz H.; Wen, Xiao-Gang
2015-05-01
The boundary of symmetry-protected topological states (SPTs) can harbor new quantum anomaly phenomena. In this work, we characterize the bosonic anomalies introduced by the 1+1D non-onsite-symmetric gapless edge modes of (2+1)D bulk bosonic SPTs with a generic finite Abelian group symmetry (isomorphic to G =∏iZNi=ZN1×ZN2×ZN3×⋯ ). We demonstrate that some classes of SPTs (termed "Type II") trap fractional quantum numbers (such as fractional ZN charges) at the 0D kink of the symmetry-breaking domain walls, while some classes of SPTs (termed "Type III") have degenerate zero energy modes (carrying the projective representation protected by the unbroken part of the symmetry), either near the 0D kink of a symmetry-breaking domain wall, or on a symmetry-preserving 1D system dimensionally reduced from a thin 2D tube with a monodromy defect 1D line embedded. More generally, the energy spectrum and conformal dimensions of gapless edge modes under an external gauge flux insertion (or twisted by a branch cut, i.e., a monodromy defect line) through the 1D ring can distinguish many SPT classes. We provide a manifest correspondence from the physical phenomena, the induced fractional quantum number, and the zero energy mode degeneracy to the mathematical concept of cocycles that appears in the group cohomology classification of SPTs, thus achieving a concrete physical materialization of the cocycles. The aforementioned edge properties are formulated in terms of a long wavelength continuum field theory involving scalar chiral bosons, as well as in terms of matrix product operators and discrete quantum lattice models. Our lattice approach yields a regularization with anomalous non-onsite symmetry for the field theory description. We also formulate some bosonic anomalies in terms of the Goldstone-Wilczek formula.
NASA Astrophysics Data System (ADS)
Arzano, Michele; Kowalski-Glikman, Jerzy
2016-09-01
We construct discrete symmetry transformations for deformed relativistic kinematics based on group valued momenta. We focus on the specific example of κ-deformations of the Poincaré algebra with associated momenta living on (a sub-manifold of) de Sitter space. Our approach relies on the description of quantum states constructed from deformed kinematics and the observable charges associated with them. The results we present provide the first step towards the analysis of experimental bounds on the deformation parameter κ to be derived via precision measurements of discrete symmetries and CPT.
Weakly broken galileon symmetry
Pirtskhalava, David; Santoni, Luca; Trincherini, Enrico; Vernizzi, Filippo
2015-09-01
Effective theories of a scalar ϕ invariant under the internal galileon symmetryϕ→ϕ+b{sub μ}x{sup μ} have been extensively studied due to their special theoretical and phenomenological properties. In this paper, we introduce the notion of weakly broken galileon invariance, which characterizes the unique class of couplings of such theories to gravity that maximally retain their defining symmetry. The curved-space remnant of the galileon’s quantum properties allows to construct (quasi) de Sitter backgrounds largely insensitive to loop corrections. We exploit this fact to build novel cosmological models with interesting phenomenology, relevant for both inflation and late-time acceleration of the universe.
NASA Astrophysics Data System (ADS)
Moore, Gregory
The vanishing of the one-loop string cosmological constant in nontrivial non supersymmetric backgrounds can be understood by viewing the path integral as an inner product of orthogonal wave functions. For special backgrounds the string theory has an extra symmetry, expressed as a transformation on moduli space. When left- and right-moving wave functions transform in different representations of this symmetry the cosmological constant must vanish. Specific examples of the mechanism are given at one loop for theories in two and four dimensions. Various suggestions are made for the higher loop extension of this idea.
BOOK REVIEW: Symmetry Breaking
NASA Astrophysics Data System (ADS)
Ryder, L. H.
2005-11-01
One of the most fruitful and enduring advances in theoretical physics during the last half century has been the development of the role played by symmetries. One needs only to consider SU(3) and the classification of elementary particles, the Yang Mills enlargement of Maxwell's electrodynamics to the symmetry group SU(2), and indeed the tremendous activity surrounding the discovery of parity violation in the weak interactions in the late 1950s. This last example is one of a broken symmetry, though the symmetry in question is a discrete one. It was clear to Gell-Mann, who first clarified the role of SU(3) in particle physics, that this symmetry was not exact. If it had been, it would have been much easier to discover; for example, the proton, neutron, Σ, Λ and Ξ particles would all have had the same mass. For many years the SU(3) symmetry breaking was assigned a mathematical form, but the importance of this formulation fell away when the quark model began to be taken seriously; the reason the SU(3) symmetry was not exact was simply that the (three, in those days) quarks had different masses. At the same time, and in a different context, symmetry breaking of a different type was being investigated. This went by the name of `spontaneous symmetry breaking' and its characteristic was that the ground state of a given system was not invariant under the symmetry transformation, though the interactions (the Hamiltonian, in effect) was. A classic example is ferromagnetism. In a ferromagnet the atomic spins are aligned in one direction only—this is the ground state of the system. It is clearly not invariant under a rotation, for that would change the ground state into a (similar but) different one, with the spins aligned in a different direction; this is the phenomenon of a degenerate vacuum. The contribution of the spin interaction, s1.s2, to the Hamiltonian, however, is actually invariant under rotations. As Coleman remarked, a little man living in a ferromagnet would
Bender, Carl M; DeKieviet, Maarten; Klevansky, S P
2013-04-28
PT-symmetric quantum mechanics (PTQM) has become a hot area of research and investigation. Since its beginnings in 1998, there have been over 1000 published papers and more than 15 international conferences entirely devoted to this research topic. Originally, PTQM was studied at a highly mathematical level and the techniques of complex variables, asymptotics, differential equations and perturbation theory were used to understand the subtleties associated with the analytic continuation of eigenvalue problems. However, as experiments on PT-symmetric physical systems have been performed, a simple and beautiful physical picture has emerged, and a PT-symmetric system can be understood as one that has a balanced loss and gain. Furthermore, the PT phase transition can now be understood intuitively without resorting to sophisticated mathematics. Research on PTQM is following two different paths: at a fundamental level, physicists are attempting to understand the underlying mathematical structure of these theories with the long-range objective of applying the techniques of PTQM to understanding some of the outstanding problems in physics today, such as the nature of the Higgs particle, the properties of dark matter, the matter-antimatter asymmetry in the universe, neutrino oscillations and the cosmological constant; at an applied level, new kinds of PT-synthetic materials are being developed, and the PT phase transition is being observed in many physical contexts, such as lasers, optical wave guides, microwave cavities, superconducting wires and electronic circuits. The purpose of this Theme Issue is to acquaint the reader with the latest developments in PTQM. The articles in this volume are written in the style of mini-reviews and address diverse areas of the emerging and exciting new area of PT-symmetric quantum mechanics. PMID:23509390
NASA Astrophysics Data System (ADS)
Takasao, Shinsuke; Fan, Yuhong; Cheung, Mark C. M.; Shibata, Kazunari
2015-11-01
We carried out an magnetohydrodynamic simulation where a subsurface twisted kink-unstable flux tube emerges from the solar interior to the corona. Unlike the previous expectations based on the bodily emergence of a knotted tube, we found that the kinked tube can spontaneously form a complex quadrupole structure at the photosphere. Due to the development of the kink instability before the emergence, the magnetic twist at the kinked apex of the tube is greatly reduced, although the other parts of the tube are still strongly twisted. This leads to the formation of a complex quadrupole structure: a pair of the coherent, strongly twisted spots and a narrow complex bipolar pair between it. The quadrupole is formed by the submergence of a portion of emerged magnetic fields. This result is relevant for understanding the origin of the complex multipolar δ-spot regions that have a strong magnetic shear and emerge with polarity orientations not following Hale-Nicholson and Joy Laws.
Hsu, S C; Bellan, P M
2003-05-30
The magnetohydrodynamic kink instability is observed and identified experimentally as a poloidal flux amplification mechanism for coaxial gun spheromak formation. Plasmas in this experiment fall into three distinct regimes which depend on the peak gun current to magnetic flux ratio, with (I) low values resulting in a straight plasma column with helical magnetic field, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma. Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit, and the kink acts as a dynamo which converts toroidal to poloidal flux. Regime II clearly leads to both poloidal flux amplification and the development of a spheromak configuration. PMID:12786562
Weakly-bound hydrogen on defected Pt(111)
NASA Astrophysics Data System (ADS)
Jo, Sam K.
2015-05-01
Step edges and kinks, abundant on multi-faceted nanoparticles, are catalytically active sites. Weakly-bound atomic H, at either topmost surface or subsurface sites, would be important for low-temperature hydrogenation in platinum-based catalysts. Here we report experimental results for such H atoms on Pt(111). Saturation-adsorbed atomic H from molecular H2 on the defect-free Pt(111) surface indeed gave only a single-peaked H2 desorption (β2) at 285 K. Instead, defected Pt(111) surfaces rendered triple peaks (β1 to β3) including a prominent feature (β1) at as low as 205 K in addition to another desorption (β3) at 360 K. This β1-H state was inhibited and created by pre- and post-adsorbed CO, respectively. We attribute the β1-H2 desorption to H atoms trapped at interstitial sites beneath surface defects on the basis of: (1) its desorption at a very low temperature in addition to two other peaks from terrace- and defect-adsorbed H; (2) its and total H uptakes by far larger than the surface defect density; (3) its desorption amount up to ~ 3.6 times that of the β3 desorption from defects; (4) its complete inhibition by a small pre-coverage of CO; and (5) the complete β3-to-β1 H conversion, while the β1-H state remaining intact, by postdosed CO. Our proposed mechanism is that the derelaxation (upward lifting) of the H- or CO-bound Pt lattice atoms at (step) defects, as a result of strong H-H and even stronger H-CO lateral repulsions under (near) saturation surface coverages, opens a low-barrier path for H diffusion into the subsurface.
TOPICAL REVIEW Stabilization of the external kink and the resistive wall mode
NASA Astrophysics Data System (ADS)
Chu, M. S.; Okabayashi, M.
2010-12-01
The pursuit of steady-state economic production of thermonuclear fusion energy has led to research on the stabilization of the external kink and the resistive wall mode. Advances in both experiment and theory, together with improvements in diagnostics, heating and feedback methods have led to substantial and steady progress in the understanding and stabilization of these instabilities. Many of the theory and experimental techniques and results that have been developed are useful not only for the stabilization of the resistive wall mode. They can also be used to improve the general performance of fusion confinement devices. The conceptual foundations and experimental results on the stabilization of the external kink and the resistive wall mode are reviewed.
Damping profile of standing kink oscillations observed by SDO/AIA
NASA Astrophysics Data System (ADS)
Pascoe, D. J.; Goddard, C. R.; Nisticò, G.; Anfinogentov, S.; Nakariakov, V. M.
2016-01-01
Aims: Strongly damped standing and propagating kink oscillations are observed in the solar corona. This can be understood in terms of mode coupling, which causes the wave energy to be converted from the bulk transverse oscillation to localised, unresolved azimuthal motions. The damping rate can provide information about the loop structure, and theory predicts two possible damping profiles. Methods: We used the recently compiled catalogue of decaying standing kink oscillations of coronal loops to search for examples with high spatial and temporal resolution and sufficient signal quality to allow the damping profile to be examined. The location of the loop axis was tracked, detrended, and fitted with sinusoidal oscillations with Gaussian and exponential damping profiles. Results: Using the highest quality data currently available, we find that for the majority of our cases a Gaussian profile describes the damping behaviour at least as well as an exponential profile, which is consistent with the recently developed theory for the damping profile due to mode coupling.
A New Series of Kinked Liquid Crystals: 2-(6-Alkoxynaphthalen-2-yl)-6-methoxyquinolines
Chia, Win-Long; Liu, Chih-Wei
2015-01-01
A new series of 2-(6-alkoxynaphthalen-2-yl)-6-methoxyquinolines (nO-NpQOMe, n = 3–8) liquid crystal compounds, a linear molecular structure with two kinks, were synthesized using a short two-step reaction with overall yields between 43% and 58%. Spectral analyses were in accord with the expected structures. Thermotropic behavior of these liquid crystal compounds were investigated using polarized optical microscopy and differential scanning calorimetry. All compounds exhibited purely enantiotropic nematic phase at the medium–high temperature range of 162.4–234.2 °C. However, short ranges of nematic phase, 20.5–16.6 °C at heating and 46.7–37.0 °C at cooling, were observed in these linear liquid-crystalline compounds with two kinks. PMID:25849658
Disorder-free localization around the conduction band edge of crossing and kinked silicon nanowires
Keleş, Ümit; Çakan, Aslı; Bulutay, Ceyhun
2015-02-14
We explore ballistic regime quantum transport characteristics of oxide-embedded crossing and kinked silicon nanowires (NWs) within a large-scale empirical pseudopotential electronic structure framework, coupled to the Kubo-Greenwood transport analysis. A real-space wave function study is undertaken and the outcomes are interpreted together with the findings of ballistic transport calculations. This reveals that ballistic transport edge lies tens to hundreds of millielectron volts above the lowest unoccupied molecular orbital, with a substantial number of localized states appearing in between, as well as above the former. We show that these localized states are not due to the oxide interface, but rather core silicon-derived. They manifest the wave nature of electrons brought to foreground by the reflections originating from NW junctions and bends. Hence, we show that the crossings and kinks of even ultraclean Si NWs possess a conduction band tail without a recourse to atomistic disorder.
NASA Astrophysics Data System (ADS)
Cooper, W. A.; Brunetti, D.; Duval, B. P.; Faustin, J. M.; Graves, J. P.; Kleiner, A.; Patten, H.; Pfefferlé, D.; Porte, L.; Raghunathan, M.; Reimerdes, H.; Sauter, O.; Tran, T. M.
2016-04-01
Free boundary magnetohydrodynamic equilibrium states with spontaneous three dimensional deformations of the plasma-vacuum interface are computed for the first time. The structures obtained have the appearance of saturated ideal external kink/peeling modes. High edge pressure gradients yield toroidal mode number n = 1 corrugations for a high edge bootstrap current and larger n distortions when this current is small. Deformations in the plasma boundary region induce a nonaxisymmetric Pfirsch-Schlüter current driving a field-aligned current ribbon consistent with reported experimental observations. A variation in the 3D equilibrium confirms that the n = 1 mode is a kink/peeling structure. We surmise that our calculated equilibrium structures constitute a viable model for the edge harmonic oscillations and outer modes associated with a quiescent H-mode operation in shaped tokamak plasmas.
Peeling-off of the external kink modes at tokamak plasma edge
Zheng, L. J.; Furukawa, M.
2014-08-15
It is pointed out that there is a current jump between the edge plasma inside the last closed flux surface and the scrape-off layer and that the current jump can lead the external kink modes to convert to the tearing modes, due to the current interchange effects [L. J. Zheng and M. Furukawa, Phys. Plasmas 17, 052508 (2010)]. The magnetic reconnection in the presence of tearing modes subsequently causes the tokamak edge plasma to be peeled off to link to the divertors. In particular, the peeling or peeling-ballooning modes can become the “peeling-off” modes in this sense. This phenomenon indicates that the tokamak edge confinement can be worse than the expectation based on the conventional kink mode picture.
Modeling of Kink-Shaped Carbon-Nanotube Schottky Diode with Gate Bias Modulation
NASA Technical Reports Server (NTRS)
Yamada, Toshishige; Biegel, Bryan (Technical Monitor)
2001-01-01
A model is proposed for the recent gate-voltage (V(sub G)) modulation experiment of a kink-shaped carbon nanotube (NT) Schottky diode. Since larger V(sub G) increases both the forward and the reverse turn-on voltages of the diode in the experiment, we show that: (1) the rectification must occur at the kink where the metallic and the semiconducting NTs meet, and not at the electrode contact, and (2) the semiconducting NT must be n-type. The turn-on voltages are derived analytically as a function of V(sub G) with the electrode contact contribution and a good agreement is obtained with the experimental data.
Landau resonant modification of multiple kink mode contributions to 3D tokamak equilibria
King, J. D.; Strait, E. J.; Ferraro, N. M.; Hanson, J. M.; Haskey, S. R.; Lanctot, M. J.; Liu, Y. Q.; Logan, N.; Paz-Soldan, C.; Shiraki, D.; Turnbull, A. D.
2015-12-17
Detailed measurements of the plasma's response to applied magnetic perturbations provide experimental evidence that the form of three-dimensional (3D) tokamak equilibria, with toroidal mode number n = 1, is determined by multiple stable kink modes at high-pressure. For pressures greater than the ideal magnetohydrodynamic (MHD) stability limit, as calculated without a stabilizing wall, the 3D structure transitions in a way that is qualitatively predicted by an extended MHD model that includes kinetic wave-particle interactions. These changes in poloidal mode structure are correlated with the proximity of rotation profiles to thermal ion bounce and the precession drift frequencies suggesting that these kinetic resonances are modifying the relative amplitudes of the stable modes. These results imply that each kink may eventually be independently controlled.
Landau resonant modification of multiple kink mode contributions to 3D tokamak equilibria
King, J. D.; Strait, E. J.; Ferraro, N. M.; Hanson, J. M.; Haskey, S. R.; Lanctot, M. J.; Liu, Y. Q.; Logan, N.; Paz-Soldan, C.; Shiraki, D.; et al
2015-12-17
Detailed measurements of the plasma's response to applied magnetic perturbations provide experimental evidence that the form of three-dimensional (3D) tokamak equilibria, with toroidal mode number n = 1, is determined by multiple stable kink modes at high-pressure. For pressures greater than the ideal magnetohydrodynamic (MHD) stability limit, as calculated without a stabilizing wall, the 3D structure transitions in a way that is qualitatively predicted by an extended MHD model that includes kinetic wave-particle interactions. These changes in poloidal mode structure are correlated with the proximity of rotation profiles to thermal ion bounce and the precession drift frequencies suggesting that thesemore » kinetic resonances are modifying the relative amplitudes of the stable modes. These results imply that each kink may eventually be independently controlled.« less
Ordinary versus PT-symmetric Φ³ quantum field theory
Bender, Carl M.; Branchina, Vincenzo; Messina, Emanuele
2012-04-02
A quantum-mechanical theory is PT-symmetric if it is described by a Hamiltonian that commutes with PT, where the operator P performs space reflection and the operator T performs time reversal. A PT-symmetric Hamiltonian often has a parametric region of unbroken PT symmetry in which the energy eigenvalues are all real. There may also be a region of broken PT symmetry in which some of the eigenvalues are complex. These regions are separated by a phase transition that has been repeatedly observed in laboratory experiments. This paper focuses on the properties of a PT-symmetric igΦ³ quantum field theory. This quantum fieldmore » theory is the analog of the PT-symmetric quantum-mechanical theory described by the Hamiltonian H=p²+ix³, whose eigenvalues have been rigorously shown to be all real. This paper compares the renormalization group properties of a conventional Hermitian gΦ³ quantum field theory with those of the PT-symmetric igΦ³ quantum field theory. It is shown that while the conventional gΦ³ theory in d=6 dimensions is asymptotically free, the igΦ³ theory is like a gΦ⁴ theory in d=4 dimensions; it is energetically stable, perturbatively renormalizable, and trivial.« less
Ordinary versus PT-symmetric Φ³ quantum field theory
Bender, Carl M.; Branchina, Vincenzo; Messina, Emanuele
2012-04-02
A quantum-mechanical theory is PT-symmetric if it is described by a Hamiltonian that commutes with PT, where the operator P performs space reflection and the operator T performs time reversal. A PT-symmetric Hamiltonian often has a parametric region of unbroken PT symmetry in which the energy eigenvalues are all real. There may also be a region of broken PT symmetry in which some of the eigenvalues are complex. These regions are separated by a phase transition that has been repeatedly observed in laboratory experiments. This paper focuses on the properties of a PT-symmetric igΦ³ quantum field theory. This quantum field theory is the analog of the PT-symmetric quantum-mechanical theory described by the Hamiltonian H=p²+ix³, whose eigenvalues have been rigorously shown to be all real. This paper compares the renormalization group properties of a conventional Hermitian gΦ³ quantum field theory with those of the PT-symmetric igΦ³ quantum field theory. It is shown that while the conventional gΦ³ theory in d=6 dimensions is asymptotically free, the igΦ³ theory is like a gΦ⁴ theory in d=4 dimensions; it is energetically stable, perturbatively renormalizable, and trivial.
Two-dimensional linear modes and solitons in parity-time symmetry bessel complex-valued potential
NASA Astrophysics Data System (ADS)
Chen, Haibo; Hu, Sumei
2015-11-01
We study the optical properties of two-dimensional linear modes and solitons in parity-time (PT) symmetry Bessel complex-valued potential. The PT-breaking points, the eigenvalues and eigenfunction for different modulated depths of two-dimensional PT symmetry Bessel complex potential are obtained numerically. The PT-breaking points increase linearly with increasing the real part of the modulated depths of PT potential. The existence of fundamental and dipole solitons are studied in self-focusing and self-defocusing media. The eigenvalue for linear case is equal to the critical propagation constant bc of the existing soliton. The fundamental solitons are stable in both the self-focusing and self-defocusing media, and the dipole solitons are stable in the self-defocusing media but unstable in the self-focusing media.
Kink-bands: Shock deformation of biotite resulting from a nuclear explosion
Cummings, D.
1965-01-01
Microscopic examination of granodiorite samples from the shock region around a nuclear explosion reveals sharply folded lens-shaped zones (kink-bands) in the mineral biotite. Fifty percent of these zones are oriented approximately 90?? to the direction of shock-wave propagation, but other zones are symmetrically concentrated at shear angles of 50?? and 70?? to the direction of shock-wave propagation.
M = 1 internal kink mode in the plateau and banana regimes in tokamaks
Mikhailovskii, A.B.; Tsypin, V.S.
1983-01-01
A theory is derived for the m = 1 internal kink mode of a tokamak in the plateau and banana regimes. The growth rate for this mode in the plateau regime is shown to be smaller by a factor of a/R than the MHD prediction (a and R are the minor and major radii of the torus). The growth rate in the banana regime is higher than in the plateau regime and approaches the standard MHD value.
Jalwal, Gopal Krishan; Rajagopalan, Vanitha; Bindra, Ashish; Rath, Girija Prasad; Goyal, Keshav; Kumar, Atin; Gamanagatti, Shivanand
2014-01-01
The placement of central venous catheter using Seldinger's technique, remains a commonly performed procedure with its own risks and benefits. Various complications have been reported with the use of guide wire as well as catheter. We report a unique problem during subclavian vein cannulation due to guidewire malposition which led to its kinking and difficult retrieval requiring removal in fluoroscopy suit. The probable mechanism of guide wire entrapment and possible bedside management of similar problems is described. PMID:24803771
Whisker Hair (Acquired Progressive Kinking of the Hair): An Indication for Finasteride 1 mg?
Bagazgoitia, Lorea; Aboín, Sonsoles
2016-01-01
Acquired progressive kinking of the hair (APKH) and whisker hair are relatively rare conditions. To our knowledge, fewer than 25 cases have been reported in the English literature. We present the case of a 23-year-old man whose hair on the parietal and occipital areas changed and turned curlier and shorter. Patients suffering from APKH have higher risk of developing androgenetic alopecia and therefore finasteride 1 mg daily is proposed as an adequate treatment for these patients. PMID:27127372
Zwart, P.H.; Grosse-Kunstleve, R.W.; Adams, P.D.
2006-07-31
Relatively minor perturbations to a crystal structure can in some cases result in apparently large changes in symmetry. Changes in space group or even lattice can be induced by heavy metal or halide soaking (Dauter et al, 2001), flash freezing (Skrzypczak-Jankun et al, 1996), and Se-Met substitution (Poulsen et al, 2001). Relations between various space groups and lattices can provide insight in the underlying structural causes for the symmetry or lattice transformations. Furthermore, these relations can be useful in understanding twinning and how to efficiently solve two different but related crystal structures. Although (pseudo) symmetric properties of a certain combination of unit cell parameters and a space group are immediately obvious (such as a pseudo four-fold axis if a is approximately equal to b in an orthorhombic space group), other relations (e.g. Lehtio, et al, 2005) that are less obvious might be crucial to the understanding and detection of certain idiosyncrasies of experimental data. We have developed a set of tools that allows straightforward exploration of possible metric symmetry relations given unit cell parameters and a space group. The new iotbx.explore{_}metric{_}symmetry command produces an overview of the various relations between several possible point groups for a given lattice. Methods for finding relations between a pair of unit cells are also available. The tools described in this newsletter are part of the CCTBX libraries, which are included in the latest (versions July 2006 and up) PHENIX and CCI Apps distributions.
ERIC Educational Resources Information Center
Crumpecker, Cheryl
2003-01-01
Describes an art lesson used with children in the third grade to help them learn about symmetry, as well as encouraging them to draw larger than usual. Explains that students learn about the belief called "Horror Vacui" of the Northwest American Indian tribes and create their interpretation of this belief. (CMK)
Introduction to chiral symmetry
Koch, V.
1996-01-08
These lectures are an attempt to a pedagogical introduction into the elementary concepts of chiral symmetry in nuclear physics. Effective chiral models such as the linear and nonlinear sigma model will be discussed as well as the essential ideas of chiral perturbation theory. Some applications to the physics of ultrarelativistic heavy ion collisions will be presented.
NASA Astrophysics Data System (ADS)
Maes, Christian; Salazar, Alberto
2014-01-01
In contrast with the understanding of fluctuation symmetries for entropy production, similar ideas applied to the time-symmetric fluctuation sector have been less explored. Here we give detailed derivations of time-symmetric fluctuation symmetries in boundary-driven particle systems such as the open Kawasaki lattice gas and the zero-range model. As a measure of time-symmetric dynamical activity over time T we count the difference (Nℓ - Nr)/T between the number of particle jumps in or out at the left edge and those at the right edge of the system. We show that this quantity satisfies a fluctuation symmetry from which we derive a new Green-Kubo-type relation. It will follow then that the system is more active at the edge connected to the particle reservoir with the largest chemical potential. We also apply these exact relations derived for stochastic particle models to a deterministic case, the spinning Lorentz gas, where the symmetry relation for the activity is checked numerically.
ERIC Educational Resources Information Center
McGehe, Carol
1991-01-01
Presents math activities, problems, and games for teaching elementary students to recognize the world's natural symmetry and understand the mathematical qualities it represents; suggests activities with construction paper, blocks, and calculators. Instructions for using the calculator to create palindromes are included. (SM)
OBSERVATIONAL EVIDENCE OF RESONANTLY DAMPED PROPAGATING KINK WAVES IN THE SOLAR CORONA
Verth, G.; Goossens, M.; Terradas, J. E-mail: marcel.goossens@wis.kuleuven.b
2010-08-01
In this Letter, we establish clear evidence for the resonant absorption damping mechanism by analyzing observational data from the novel Coronal Multi-Channel Polarimeter. This instrument has established that in the solar corona there are ubiquitous propagating low-amplitude ({approx}1 km s{sup -1}) Alfvenic waves with a wide range of frequencies. Realistically interpreting these waves as the kink mode from magnetohydrodynamic wave theory, they should exhibit a frequency-dependent damping length due to resonant absorption, governed by the Terradas-Goossens-Verth relation showing that transverse plasma inhomogeneity in coronal magnetic flux tubes causes them to act as natural low-pass filters. It is found that the observed frequency dependence on damping length (up to about 8 mHz) can be explained by the kink wave interpretation; and furthermore, the spatially averaged equilibrium parameter describing the length scale of transverse plasma density inhomogeneity over a system of coronal loops is consistent with the range of values estimated from Transition Region and Coronal Explorer observations of standing kink modes.
Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla)
NASA Astrophysics Data System (ADS)
Levesque, J. P.; Hughes, P. E.; Bialek, J.; Byrne, P. J.; Mauel, M. E.; Navratil, G. A.; Peng, Q.; Rhodes, D. J.; Stoafer, C. C.
2015-05-01
High-resolution active and passive kink mode studies are conducted in a tokamak with an adjustable ferromagnetic wall near the plasma surface. Ferritic tiles made from 5.6 mm thick Hiperco® 50 alloy have been mounted on the plasma-facing side of half of the in-vessel movable wall segments in the High Beta Tokamak-Extended Pulse device [D. A. Maurer et al., Plasma Phys. Controlled Fusion 53, 074016 (2011)] in order to explore ferritic resistive wall mode stability. Low-activation ferritic steels are a candidate for structural components of a fusion reactor, and these experiments examine MHD stability of plasmas with nearby ferromagnetic material. Plasma-wall separation for alternating ferritic and non-ferritic wall segments is adjusted between discharges without opening the vacuum vessel. Amplification of applied resonant magnetic perturbations and plasma disruptivity are observed to increase when the ferromagnetic wall is close to plasma surface instead of the standard stainless steel wall. Rapidly rotating m / n = 3 / 1 external kink modes have higher growth rates with the nearby ferritic wall. Feedback suppression of kinks is still as effective as before the installation of ferritic material in vessel, in spite of increased mode growth rates.
Active and passive kink mode studies in a tokamak with a movable ferromagnetic wall
Levesque, J. P.; Hughes, P. E.; Bialek, J.; Byrne, P. J.; Mauel, M. E.; Navratil, G. A.; Peng, Q.; Rhodes, D. J.; Stoafer, C. C.
2015-05-15
High-resolution active and passive kink mode studies are conducted in a tokamak with an adjustable ferromagnetic wall near the plasma surface. Ferritic tiles made from 5.6 mm thick Hiperco{sup ®} 50 alloy have been mounted on the plasma-facing side of half of the in-vessel movable wall segments in the High Beta Tokamak-Extended Pulse device [D. A. Maurer et al., Plasma Phys. Controlled Fusion 53, 074016 (2011)] in order to explore ferritic resistive wall mode stability. Low-activation ferritic steels are a candidate for structural components of a fusion reactor, and these experiments examine MHD stability of plasmas with nearby ferromagnetic material. Plasma-wall separation for alternating ferritic and non-ferritic wall segments is adjusted between discharges without opening the vacuum vessel. Amplification of applied resonant magnetic perturbations and plasma disruptivity are observed to increase when the ferromagnetic wall is close to plasma surface instead of the standard stainless steel wall. Rapidly rotating m/n=3/1 external kink modes have higher growth rates with the nearby ferritic wall. Feedback suppression of kinks is still as effective as before the installation of ferritic material in vessel, in spite of increased mode growth rates.
Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor
Ishida, Y.; Saitoh, T.; Mochiku, T.; Nakane, T.; Hirata, K.; Shin, S.
2016-01-01
In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. In high-Tc cuprates, it is still unknown how superconductivity vanishes at Tc. We provide evidence that the so-called ≲70-meV kink bosons that dress the quasi-particle excitations are playing a key role in the loss of superconductivity in a cuprate. We irradiated a 170-fs laser pulse on Bi2Sr2CaCu2O8+δ and monitored the responses of the superconducting gap and dressed quasi-particles by time- and angle-resolved photoemission spectroscopy. We observe an ultrafast loss of superconducting gap near the d-wave node, or light-induced Fermi arcs, which is accompanied by spectral broadenings and weight redistributions occurring within the kink binding energy. We discuss that the underlying mechanism of the spectral broadening that induce the Fermi arc is the undressing of quasi-particles from the kink bosons. The loss mechanism is beyond the conventional framework, and can accept the unconventional phenomena such as the signatures of Cooper pairs remaining at temperatures above Tc. PMID:26728626
Kink instability evidenced by analyzing the leg rotation of a filament
Yan, X. L.; Xue, Z. K.; Ma, L.; Kong, D. F.; Qu, Z. Q.; Liu, J. H.; Li, Z.
2014-02-20
Kink instability is a possible mechanism for solar filament eruption. However, it is very difficult to directly measure the twist of the solar filament from observation. In this paper, we measured the twist of a solar filament by analyzing its leg rotation. An inverse S-shaped filament in the active region NOAA 11485 was observed by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory on 2012 May 22. During its eruption, the leg of the filament exhibited a significant rotation motion. The 304 Å images were used to uncurl the circles, the centers of which are the axis of the filament's leg. The result shows that the leg of the filament rotated up to about 510° (about 2.83π) around the axis of the filament within 23 minutes. The maximal rotation speed reached 100 degrees/minute (about 379.9 km s{sup –1} at radius 18''), which is the fastest rotation speed reported. We also calculated the decay index along the polarity inversion line in this active region and found that the decline of the overlying field with height is not fast enough to trigger the torus instability. According to the kink instability condition, this indicates that the kink instability is the trigger mechanism for the solar filament eruption.
Observational evidence for buffeting-induced kink waves in solar magnetic elements
NASA Astrophysics Data System (ADS)
Stangalini, M.; Consolini, G.; Berrilli, F.; De Michelis, P.; Tozzi, R.
2014-09-01
The role of diffuse photospheric magnetic elements in the energy budget of the upper layers of the Sun's atmosphere has been the recent subject of many studies. This was made possible by the availability of high temporal and spatial resolution observations of the solar photosphere, allowing large numbers of magnetic elements to be tracked to study their dynamics. In this work we exploit a long temporal series of seeing-free magnetograms of the solar photosphere to study the effect of the turbulent convection on the excitation of kink oscillations in magnetic elements. We make use of the empirical mode decomposition technique in order to study the transverse oscillations of several magnetic flux tubes. This technique permits analysis of non-stationary time series like those associated to the horizontal velocities of these flux tubes, which are continuously advected and dispersed by granular flows. Our primary findings reveal the excitation of low frequency modes of kink oscillations, which are subharmonics of a fundamental mode with a 7.6 ± 0.2 min periodicity. These results constitute observational proof of the excitation of kink waves by the buffeting of the convection cells in the solar photosphere, and they are discussed in light of their possible role in the energy budget of the upper Sun's atmosphere.
The Current-driven Kink Instability of the Poynting Flux Dominated Jets
NASA Astrophysics Data System (ADS)
Nakamura, Masanori; Meier, David L.
2004-11-01
The spatial stability properties are one of the most important problem in astrophysical jets dynamics. The non-relativistic 3-D MHD simulations of Poynting flux dominated (PFD) jets are presented. Our study focuses on the propagation of strongly magnetized hypersonic, but sub-Alfvénic flow and on the subsequent development of a current-driven (CD) kink instability. This instability may be responsible for the ``wiggled'' structures seen in sub-parsec scale (VLBI) AGN jets and pulsar jets. Our numerical results show that the PFD jets can develop CD distortions in the trans-Alfvénic flow case. An internal non axisymmetric body mode grows on time scales of order of the Alfvén crossing time and distorts the structure and magnetic configuration of the jet. The kink (m=1) mode of the CD instability, driven by the asymmetrically distribution of hoop-stress, grows faster than other higher order modes (m>1). This could be caused by a sudden loss of kinetic angular momentum to the magnetic field via the reverse slow-mode MHD shock wave. In the jet frame the mode grows locally and expands radially at each axial position where the jet is unstable: the instability, therefore, does not propagate as a wave along the jet length. The wiggled structures saturate and advect with the bulk flow and then, the local plasma flow follows a helical path along the kinked magnetic field backbone. M.N. is supported by a NRC RRA award.
NASA Technical Reports Server (NTRS)
Lee, L. C.; Wang, S.; Wei, C. Q.; Tsurutani, B. T.
1988-01-01
This paper investigates the growth rates and eigenmode structures of the streaming sausage, kink, and tearing instabilities in a current sheet with a super-Alfvenic flow. The growth rates and eigenmode structures are first considered in the ideal incompressible limit by using a four-layer model, as well as a more realistic case in which all plasma parameters and the magnetic field vary continuously along the direction perpendicular to the magnetic field and plasma flow. An initial-value method is applied to obtain the growth rate and eigenmode profiles of the fastest growing mode, which is either the sausage mode or kink mode. It is shown that, in the earth's magnetotail, where super-Alfvenic plasma flows are observed in the plasma sheet and the ratio between the plasma and magnetic pressures far away from the current layer is about 0.1-0.3 in the lobes, the streaming sausage and streaming tearing instabilities, but not kink modes, are likely to occur.
Wall touching kink mode calculations with the M3D code
NASA Astrophysics Data System (ADS)
Breslau, J. A.
2014-10-01
In recent years there have been a number of results published concerning the transient vessel currents and forces occurring during a tokamak VDE, as predicted by simulations with the nonlinear MHD code M3D. The nature of the simulations is such that these currents and forces occur at the boundary of the computational domain, making the proper choice of boundary conditions critical to the reliability of the results. The M3D boundary condition includes the prescription that the normal component of the velocity vanish at the wall. It has been argued that this prescription invalidates the calculations because it would seem to rule out the possibility of advection of plasma surface currents into the wall. This claim has been tested by applying M3D to an idealized case - a kink-unstable plasma column - in order to abstract the essential physics from the complications involved in the attempt to model real devices. While comparison of the results is complicated by effects arising from the higher dimensionality and complexity of M3D, we have verified 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.
Phenomenological theory of the kink instability in a slender plasma column
NASA Astrophysics Data System (ADS)
Ryutov, D. D.; Furno, I.; Intrator, T. P.; Abbate, S.; Madziwa-Nussinov, T.
2006-03-01
In this paper we are concerned with the kink instability of a current-carrying plasma column whose radius a is much smaller than its length L. In the limit a ≪L, one can consider the column as a thin filament whose kinking can be adequately described simply by a two dimensional 2D displacement vector, ξx=ξx(z,t); ξy=ξy(z,t). Details of the internal structure of the column such as the radial distribution of the current, density, and axial flow can be lumped into some phenomenological parameters. This approach is particularly efficient in the problems with nonideal (sheath) boundary conditions (BC) at the end electrodes, with the finite plasma resistivity, and with a substantial axial flow. With the sheath BC imposed at one of the endplates, we find instability in the domain well below the classical Kruskal-Shafranov limit. The presence of an axial flow causes the onset of rotation of the kink and strong axial "skewness" of the eigenfunction, with the perturbation amplitude increasing in the flow direction. The limitations of the phenomenological approach are analyzed and are related to the steepness with which the plasma resistivity increases at the plasma boundary with vacuum.
Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor.
Ishida, Y; Saitoh, T; Mochiku, T; Nakane, T; Hirata, K; Shin, S
2016-01-01
In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. In high-Tc cuprates, it is still unknown how superconductivity vanishes at Tc. We provide evidence that the so-called ≲ 70-meV kink bosons that dress the quasi-particle excitations are playing a key role in the loss of superconductivity in a cuprate. We irradiated a 170-fs laser pulse on Bi2Sr2CaCu2O(8+δ) and monitored the responses of the superconducting gap and dressed quasi-particles by time- and angle-resolved photoemission spectroscopy. We observe an ultrafast loss of superconducting gap near the d-wave node, or light-induced Fermi arcs, which is accompanied by spectral broadenings and weight redistributions occurring within the kink binding energy. We discuss that the underlying mechanism of the spectral broadening that induce the Fermi arc is the undressing of quasi-particles from the kink bosons. The loss mechanism is beyond the conventional framework, and can accept the unconventional phenomena such as the signatures of Cooper pairs remaining at temperatures above Tc. PMID:26728626
Hanson, Jeremy M.; De Bono, Bryan; Levesque, Jeffrey P.; Mauel, Michael E.; Maurer, David A.; Navratil, Gerald A.; Pedersen, Thomas Sunn; Shiraki, Daisuke; James, Royce W.
2009-05-15
The simulation and experimental optimization of a Kalman filter feedback control algorithm for n=1 tokamak external kink modes are reported. In order to achieve the highest plasma pressure limits in ITER, resistive wall mode stabilization is required [T. C. Hender et al., Nucl. Fusion 47, S128 (2007)] and feedback algorithms will need to distinguish the mode from noise due to other magnetohydrodynamic activity. The Kalman filter contains an internal model that captures the dynamics of a rotating, growing n=1 mode. This model is actively compared with real-time measurements to produce an optimal estimate for the mode's amplitude and phase. On the High Beta Tokamak-Extended Pulse experiment [T. H. Ivers et al., Phys. Plasmas 3, 1926 (1996)], the Kalman filter algorithm is implemented using a set of digital, field-programmable gate array controllers with 10 {mu}s latencies. Signals from an array of 20 poloidal sensor coils are used to measure the n=1 mode, and the feedback control is applied using 40 poloidally and toroidally localized control coils. The feedback system with the Kalman filter is able to suppress the external kink mode over a broad range of phase angles between the sensed mode and applied control field. Scans of filter parameters show good agreement between simulation and experiment, and feedback suppression and excitation of the kink mode are enhanced in experiments when a filter made using optimal parameters from the scans is used.
Gauging without initial symmetry
NASA Astrophysics Data System (ADS)
Kotov, Alexei; Strobl, Thomas
2016-01-01
The gauge principle is at the heart of a good part of fundamental physics: Starting with a group G of so-called rigid symmetries of a functional defined over space-time Σ, the original functional is extended appropriately by additional Lie(G) -valued 1-form gauge fields so as to lift the symmetry to Maps(Σ , G) . Physically relevant quantities are then to be obtained as the quotient of the solutions to the Euler-Lagrange equations by these gauge symmetries. In this article we show that one can construct a gauge theory for a standard sigma model in arbitrary space-time dimensions where the target metric is not invariant with respect to any rigid symmetry group, but satisfies a much weaker condition: It is sufficient to find a collection of vector fields va on the target M satisfying the extended Killing equationv a(i ; j) = 0 for some connection acting on the index a. For regular foliations this is equivalent to requiring the conormal bundle to the leaves with its induced metric to be invariant under leaf-preserving diffeomorphisms of M, which in turn generalizes Riemannian submersions to which the notion reduces for smooth leaf spaces M / ∼. The resulting gauge theory has the usual quotient effect with respect to the original ungauged theory: in this way, much more general orbits can be factored out than usually considered. In some cases these are orbits that do not correspond to an initial symmetry, but still can be generated by a finite-dimensional Lie group G. Then the presented gauging procedure leads to an ordinary gauge theory with Lie algebra valued 1-form gauge fields, but showing an unconventional transformation law. In general, however, one finds that the notion of an ordinary structural Lie group is too restrictive and should be replaced by the much more general notion of a structural Lie groupoid.
Observation of spin rectification in Pt/yttrium iron garnet bilayer
Rao, Jinwei; Fan, Xiaolong Zhou, Hengan; Zhao, Xiaobing; Zhao, Jing; Zhang, Fengzhen; Xue, Desheng; Ma, Li; Zhou, Shiming
2015-05-07
We used the ferromagnetic resonance (FMR) to study the dc voltage generation in Pt 20 nm layer deposited on yttrium iron garnet. Although the main contribution to the FMR voltage comes from the inverse spin Hall effect associated with spin pumping, the spin rectification would also contribute the resonance signal via the “new” magnetoresistance effect in Pt layer. Based on a symmetry consideration, we can separate those two effects through angular dependent resonance amplitude.
NASA Astrophysics Data System (ADS)
Vekilov, Peter
2010-03-01
Crystals, likely rhombohedral, of Zn-insulin hexamers form in the islets of Langerhans in the pancreases of many mammals. The suggested function of crystal formation is to protect the insulin from proteases and increase the degree of conversion of soluble proinsulin. To accomplish this, crystal growth should be fast and adaptable to rate fluctuations in the conversion reaction. Zn-insulin crystals grow layer-by-layer. Each layer spreads by the attachment of molecules to kinks located at the layers' edges, also called steps. The kinks are thought to be generated either by thermal fluctuations, as postulated by Gibbs, or by one-dimensional nucleation of new crystalline rows. The kink density determines the rate at which steps advance, and these two kink-generation mechanisms lead to weak near-linear responses of the growth rate to concentration variations. We demonstrate for the crystallization of Zn-insulin a novel mechanism of kink generation, whereby 2D clusters of several insulin molecules pre-formed on the terraces between steps associate to the steps. This mechanism results in several-fold higher kink density, faster rate of crystallization, and a high sensitivity of the kinetics to small increases of the solute concentration. If the found mechanism operates during insulin crystallization in vivo, it could be a part of the biological regulation of insulin production and function. For other crystallizing materials in biological and non-biological systems, this mechanism provides an understanding of the often seen non-linear acceleration of the kinetics.
Kubota, Hisashi; Sanada, Yasuhiro; Tanikawa, Rokuya; Kato, Amami
2016-01-01
Background: The kinking of the internal carotid artery (ICA) after final closure in carotid endarterectomy (CEA) is thought to be uncommon. When it occurs, it is mandatory to reconstruct ICA to preserve normal blood flow. We herein present a case in which a fixation technique was applied to repair an ICA that became kinked during CEA. Case Description: A 68-year-old man presented with cerebral infarction due to an artery-to-artery embolism from the right cervical ICA stenosis. CEA was performed 12 days after admission. After final closure, a distal portion of ICA was found to have been kinked following plaque resection in CEA procedure. Fixation with fibrin glue and gelatin was used to reinforce the arterial wall and repair the kink. Postoperative magnetic resonance angiography demonstrated the release of the kink in ICA. Conclusion: Fixation with fibrin and gelatin is a salvage armamentarium that can be considered in CEA for the repair of kinked or tortuous ICA. PMID:27308092
Gravity from Lorentz Symmetry Violation
Potting, Robertus
2006-06-19
In general relativity, the masslessness of gravitons can be traced to symmetry under diffeomorphisms. In this talk, we consider another possibility, whereby the masslessness arises from spontaneous violation of Lorentz symmetry.
NASA Astrophysics Data System (ADS)
Arrington, C. A.; Unkefer, C. J.; Donohoe, R. J.; Huckett, S. C.; Kurita, S.; Swanson, B. I.
1992-12-01
The nitrogen isotope dependence of the EPR spectrum of the photoinduced paramagnetic defects in the halide-bridged platinum linear chain complex [Pt(en) 2][Pt(en) 2Cl 2](ClO 4) 4 (en = ethylenediamine) has been studied in order to clarify the origin of the 16G hyperfine structure which is superimposed on the 180G hyperfine pattern due to two equivalent Pt nuclei. An earlier study attributed the 16G pattern to the equatorial chelating nitrogens: however, we find that the EPR spectrum obtained for the 15N-substituted species is identical to that obtained for the normal isotopic species, demonstrating that these off-axis nitrogens are not the origin of this splitting. On the basis of this observation and simulations of the EPR spectrum, we attribute the 16G hyperfine pattern to coupling with three or more chlorine nuclei on the chain axis. The origin of the photoinduced paramagnetic defect in PtCl, whether polaronic or neutral kink soliton, is discussed in view of this new data. These results clearly demonstrate the importance of including halide orbitals in many-body models of the quasi-one-dimensional MX chain solids.
Chivukula, R. Sekhar; Simmons, Elizabeth H.; Di Chiara, Stefano; Foadi, Roshan
2009-11-01
We introduce a toy model implementing the proposal of using a custodial symmetry to protect the Zb{sub L}b{sub L} coupling from large corrections. This 'doublet-extended standard model' adds a weak doublet of fermions (including a heavy partner of the top quark) to the particle content of the standard model in order to implement an O(4)xU(1){sub X}{approx}SU(2){sub L}xSU(2){sub R}xP{sub LR}xU(1){sub X} symmetry in the top-quark mass generating sector. This symmetry is softly broken to the gauged SU(2){sub L}xU(1){sub Y} electroweak symmetry by a Dirac mass M for the new doublet; adjusting the value of M allows us to explore the range of possibilities between the O(4)-symmetric (M{yields}0) and standard-model-like (M{yields}{infinity}) limits. In this simple model, we find that the experimental limits on the Zb{sub L}b{sub L} coupling favor smaller M while the presence of a potentially sizable negative contribution to {alpha}T strongly favors large M. Comparison with precision electroweak data shows that the heavy partner of the top quark must be heavier than about 3.4 TeV, making it difficult to search for at LHC. This result demonstrates that electroweak data strongly limit the amount by which the custodial symmetry of the top-quark mass generating sector can be enhanced relative to the standard model. Using an effective field theory calculation, we illustrate how the leading contributions to {alpha}T, {alpha}S, and the Zb{sub L}b{sub L} coupling in this model arise from an effective operator coupling right-handed top quarks to the Z boson, and how the effects on these observables are correlated. We contrast this toy model with extradimensional models in which the extended custodial symmetry is invoked to control the size of additional contributions to {alpha}T and the Zb{sub L}b{sub L} coupling, while leaving the standard model contributions essentially unchanged.
Dynamical Symmetries in Classical Mechanics
ERIC Educational Resources Information Center
Boozer, A. D.
2012-01-01
We show how symmetries of a classical dynamical system can be described in terms of operators that act on the state space for the system. We illustrate our results by considering a number of possible symmetries that a classical dynamical system might have, and for each symmetry we give examples of dynamical systems that do and do not possess that…
Reflections on Symmetry and Proof
ERIC Educational Resources Information Center
Merrotsy, Peter
2008-01-01
The concept of symmetry is fundamental to mathematics. Arguments and proofs based on symmetry are often aesthetically pleasing because they are subtle and succinct and non-standard. This article uses notions of symmetry to approach the solutions to a broad range of mathematical problems. It responds to Krutetskii's criteria for mathematical…
PSEUDOSPIN SYMMETRY IN NUCLEI, SPIN SYMMETRY IN HADRONS
P. PAGE; T. GOLDMAN; J. GINOCCHIO
2000-08-01
Ginocchio argued that chiral symmetry breaking in QCD is responsible for the relativistic pseudospin symmetry in the Dirac equation, explaining the observed approximate pseudospin symmetry in sizable nuclei. On a much smaller scale, it is known that spin-orbit splittings in hadrons are small. Specifically, new experimental data from CLEO indicate small splittings in D-mesons. For heavy-light mesons we identify a cousin of pseudospin symmetry that suppresses these splittings in the Dirac equation, known as spin symmetry. We suggest an experimental test of the implications of spin symmetry for wave functions in electron-positron annihilation. We investigate how QCD can give rise to two different dynamical symmetries on nuclear and hadronic scales.
A broken symmetry ontology: Quantum mechanics as a broken symmetry
Buschmann, J.E.
1988-01-01
The author proposes a new broken symmetry ontology to be used to analyze the quantum domain. This ontology is motivated and grounded in a critical epistemological analysis, and an analysis of the basic role of symmetry in physics. Concurrently, he is led to consider nonheterogeneous systems, whose logical state space contains equivalence relations not associated with the causal relation. This allows him to find a generalized principle of symmetry and a generalized symmetry-conservation formalisms. In particular, he clarifies the role of Noether's theorem in field theory. He shows how a broken symmetry ontology already operates in a description of the weak interactions. Finally, by showing how a broken symmetry ontology operates in the quantum domain, he accounts for the interpretational problem and the essential incompleteness of quantum mechanics. He proposes that the broken symmetry underlying this ontological domain is broken dilation invariance.
Chiral symmetry and pentaquarks
Dmitri Diakonov
2004-07-01
Spontaneous chiral symmetry breaking, mesons and baryons are illustrated in the language of the Dirac theory. Various forces acting between quarks inside baryons are discussed. I explain why the naive quark models typically overestimate pentaquark masses by some 500 MeV and why in the fully relativistic approach to baryons pentaquarks turn out to be light. I discuss briefly why it can be easier to produce pentaquarks at low than at high energies.
NASA Technical Reports Server (NTRS)
Lopez, Hiram
1987-01-01
Transmission errors for zeros and ones tabulated separately. Binary-symmetry detector employs psuedo-random data pattern used as test message coming through channel. Message then modulo-2 added to locally generated and synchronized version of test data pattern in same manner found in manufactured test sets of today. Binary symmetrical channel shows nearly 50-percent ones to 50-percent zeroes correspondence. Degree of asymmetry represents imbalances due to either modulation, transmission, or demodulation processes of system when perturbed by noise.
Symmetries in laminated composite plates
NASA Technical Reports Server (NTRS)
Noor, A. K.
1976-01-01
The different types of symmetry exhibited by laminated anisotropic fibrous composite plates are identified and contrasted with the symmetries of isotropic and homogeneous orthotropic plates. The effects of variations in the fiber orientation and the stacking sequence of the layers on the symmetries exhibited by composite plates are discussed. Both the linear and geometrically nonlinear responses of the plates are considered. A simple procedure is presented for exploiting the symmetries in the finite element analysis. Examples are given of square, skew and polygonal plates where use of symmetry concepts can significantly reduce the scope and cost of analysis.
NASA Astrophysics Data System (ADS)
Ruderman, M. S.; Petrukhin, N. S.; Pelinovsky, E.
2016-04-01
We study kink oscillations of thin magnetic tubes. We assume that the density inside and outside the tube (and possibly also the cross-section radius) can vary along the tube. This variation is assumed to be of such a form that the kink speed is symmetric with respect to the tube centre and varies monotonically from the tube ends to the tube centre. Then we prove a theorem stating that the ratio of periods of the fundamental mode and first overtone is a monotonically increasing function of the ratio of the kink speed at the tube centre and the tube ends. In particular, it follows from this theorem that the period ratio is lower than two when the kink speed increases from the tube ends to its centre, while it is higher than two when the kink speed decreases from the tube ends to its centre. The first case is typical for non-expanding coronal magnetic loops, and the second for prominence threads. We apply the general results to particular problems. First we consider kink oscillations of coronal magnetic loops. We prove that, under reasonable assumptions, the ratio of the fundamental period to the first overtone is lower than two and decreases when the loop size increases. The second problem concerns kink oscillations of prominence threads. We consider three internal density profiles: generalised parabolic, Gaussian, and Lorentzian. Each of these profiles contain the parameter α that is responsible for its sharpness. We calculate the dependence of the period ratio on the ratio of the mean to the maximum density. For all considered values of α we find that a formula relating the period ratio and the ratio of the mean and maximum density suggested by Soler, Goossens, and Ballester ( Astron. Astrophys. 575, A123, 2015) gives a sufficiently good approximation to the exact dependence.
Pt, Co-Pt and Fe-Pt alloy nanoclusters encapsulated in virus capsids
NASA Astrophysics Data System (ADS)
Okuda, M.; Eloi, J.-C.; Jones, S. E. Ward; Verwegen, M.; Cornelissen, J. J. L. M.; Schwarzacher, W.
2016-03-01
Nanostructured Pt-based alloys show great promise, not only for catalysis but also in medical and magnetic applications. To extend the properties of this class of materials, we have developed a means of synthesizing Pt and Pt-based alloy nanoclusters in the capsid of a virus. Pure Pt and Pt-alloy nanoclusters are formed through the chemical reduction of [PtCl4]- by NaBH4 with/without additional metal ions (Co or Fe). The opening and closing of the ion channels in the virus capsid were controlled by changing the pH and ionic strength of the solution. The size of the nanoclusters is limited to 18 nm by the internal diameter of the capsid. Their magnetic properties suggest potential applications in hyperthermia for the Co-Pt and Fe-Pt magnetic alloy nanoclusters. This study introduces a new way to fabricate size-restricted nanoclusters using virus capsid.
Retroflection from slanted and kinked coastlines: models for Agulhas leakage variability
NASA Astrophysics Data System (ADS)
Zharkov, V.; Nof, D.; Weijer, W.
2010-12-01
Agulhas leakage, the transport of Agulhas Current water from the Indian Ocean to the Atlantic Ocean, has been shut off during past glacial periods, a phenomenon tentatively ascribed to northward migration of westerly wind bands. At present, the leakage is significant and its magnitude exhibits an anti-correlation with the current's incoming mass flux. Our work shows that both these phenomena can be explained by the orientation of the coastline along which the Agulhas Retroflection shifts. We developed two semi-analytical nonlinear 1 1/2 -layer models of current retroflection from slanted and ‘kinked’ coastlines on the β-plane. 'Slant,' γ, refers to the angle of the coastline relative to the zonal direction; a 'kink' is an abrupt change in that angle. Based on these models, we define lower and upper boundaries for the radius of a detached eddy, its propagation velocity, and its detachment period. For the case of a straightforward slanted coast, such limits are shown to intersect for a critical value of γ, thus imposing a strong restriction on ring detachment from the retroflection area when γ exceeds this critical value. In the case of a kinked coast with an eastern high-slant region and a western low-slant region, free westward propagation of eddies along the low-angle section is allowed. For a wide range of eastern slant, rings are shed from the retroflection area regardless of the degree of slant. However, when this eastern slant is nearly 90 degrees, the regime is nearly critical and few rings are shed. Glacial/interglacial migration of the Agulhas Retroflection was investigated using the slanted-coast (no-kink) model. Ring shedding in this case occurs only when the point of vanishing wind stress curl is located along a coastline of sufficiently low slant. During glacial periods, wind stress curl vanishes at a relatively low latitude, where the angle of the African coastline is greater than the critical angle, thus prohibiting the retroflection from
The permanent electric dipole moment of PtO, PtS, PtN, and PtC
Steimle, T.C.; Jung, K.Y.; Li, B.
1995-08-01
The permanent electric dipole moments of the ground, and the low-lying excited electronic states of platinum monocarbide, PtC, platinum monoxide, PtO, and platinum monosulfide, PtS, were measured using a molecular beam optical Stark spectroscopic scheme. The determined values were (in Debye): PtO({ital X} {sup 3}{Sigma}{sup {minus}}) 2.77(2); PtO({ital A} {sup 1}{Sigma}{sup +}) 1.15(4); PtS[{ital X}({Omega}=0)] 1.78(2); PtS[{ital B}({Omega}=0)] 0.54(6); PtC({ital X} {sup 1}{Sigma}{sup +}) 0.99(5); and PtC({ital A} {sup 1}{Pi}) 2.454(3). These results, along with the previous results for PtN({ital X} {sup 2}{Pi}{sub 1/2}) 1.977(9); PtN({ital d} {sup 4}{Pi}{sub 1/2}) 1.05(9) [J. Chem. Phys. {bold 102}, 643 (1995)], are used as a basis for a discussion of the nature of the electronic states. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Wang, Difei; Ulyanov, Nikolai B.; Zhurkin, Victor B.
2010-01-01
In addition to bending and twisting deformabilities, the lateral displacements of the DNA axis (Kink-and-Slide) play an important role in DNA wrapping around the histone core (M. Y. Tolstorukov, A. V. Colasanti, D. M. McCandlish, W. K. Olson, V. B. Zhurkin, J. Mol. Biol. 371, 725-738 (2007)). Here, we show that these Kink-and-Slide deformations are likely to be stabilized by the arginine residues of histones interacting with the minor groove of DNA. The arginines are positioned asymmetrically in the minor groove, being closer to one strand. The asymmetric arginine-DNA interactions facilitate lateral displacement of base pairs across the DNA grooves, thus leading to a stepwise accumulation of the superhelical pitch of nucleosomal DNA. To understand the sequence dependence of such Kink-and-Slide deformations, we performed all-atom calculations of DNA hexamers with the YR and RY steps in the center. We found that when the unrestrained DNA deformations are allowed, the YR steps tend to bend into the major groove, and RY steps bend into the minor groove. However, when the nucleosomal Kink-and-Slide deformation is considered, the YR steps prove to be more favorable for bending into the minor groove. Overall, the Kink-and-Slide deformation energy of DNA increases in the order TA < CA < CG < GC < AC < AT. We propose a simple stereochemical model accounting for this sequence dependence. Our results agree with experimental data indicating that the TA step most frequently occurs in the minor-groove kink positions in the most stable nucleosomes. Our computations demonstrate that the Kink-and-Slide distortion is accompanied by the BI to BII transition. This fact, together with irregularities in the two-dimensional (Roll, Slide) energy contour maps, suggest that the Kink-and-Slide deformations represent a nonharmonic behavior of the duplex. This explains the difference between the two estimates of the DNA deformation energy in nucleosome – the earlier one made using knowledge
Standing kink oscillations of thin twisted magnetic tubes with continuous equilibrium magnetic field
NASA Astrophysics Data System (ADS)
Ruderman, M. S.; Terradas, J.
2015-08-01
In this article we study standing kink waves in twisted magnetic tubes. We use the cold plasma and thin tube approximation. We assume that the plasma density is constant inside and outside the tube. We also assume that the magnetic twist is weak and take the ratio of the azimuthal and axial component of the magnetic field to be of the order of ratio of the tube radius and tube length. The azimuthal component of the magnetic field is proportional to the distance from the tube axis inside the tube, and inversely proportional to this distance outside the tube. Using the method of asymptotic expansions we derived the governing integral equation that determines the eigenfrequencies and eigenmodes of the tube kink oscillations. In the approximation of a very weak twist, we calculated analytically the corrections to the frequencies of the fundamental mode and first overtone of a straight magnetic tube related to the presence of twist. The analytical results are compared with the numerical results obtained using the full set of linear ideal magnetohydrodynamic equations. We also calculated the ratio of frequencies of the fist overtone and fundamental mode. We found that the magnetic twist enhances this ratio for moderate values of the density ratio, and reduces this ratio for large values of the density ratio. In general, the deviation of the frequency ratio from 2 caused by the magnetic twist is comparable to that found in simultaneous observations of the fundamental mode and first overtone of the coronal loop kink oscillations. Finally, we studied the eigenmode polarization. We found that, in a particular case of linear polarization, the polarization direction rotates along the tube.
Switch-on Shock and Nonlinear Kink Alfvén Waves in Solar Polar Jets
NASA Astrophysics Data System (ADS)
DeVore, C. Richard; Karpen, Judith T.; Antiochos, Spiro K.; Uritsky, Vadim
2016-05-01
It is widely accepted that solar polar jets are produced by fast magnetic reconnection in the low corona, whether driven directly by flux emergence from below or indirectly by instability onset above the photosphere. In either scenario, twisted flux on closed magnetic field lines reconnects with untwisted flux on nearby open field lines. Part of the twist is inherited by the newly reconnected open flux, which rapidly relaxes due to magnetic tension forces that transmit the twist impulsively into the outer corona and heliosphere. We propose that this transfer of twist launches switch-on MHD shock waves, which propagate parallel to the ambient coronal magnetic field ahead of the shock and convect a perpendicular component of magnetic field behind the shock. In the frame moving with the shock front, the post-shock flow is precisely Alfvénic in all three directions, whereas the pre-shock flow is super-Alfvénic along the ambient magnetic field, yielding a density enhancement at the shock front. Nonlinear kink Alfvén waves are exact solutions of the time-dependent MHD equations in the post-shock region when the ambient corona is uniform and the magnetic field is straight. We have performed and analyzed 3D Cartesian and spherical simulations of polar jets driven by instability onset in the corona. The results of both simulations are consistent with the generation of MHD switch-on shocks trailed predominantly by incompressible kink Alfvén waves. It is noteworthy that the kink waves are irrotational, in sharp contrast to the vorticity-bearing torsional waves reported from previous numerical studies. We will discuss the implications of the results for understanding solar polar jets and predicting their heliospheric signatures. Our research was supported by NASA’s LWS TR&T and H-SR programs.
Wahlberg, C.
2009-11-15
Analytical theory and two different magnetohydrodynamical stability codes are used in a study of the effects of toroidal plasma rotation on the stability of the ideal, internal kink mode in tokamaks. The focus of the paper is on the role that the centrifugal effects on the plasma equilibrium play for the stability of this mode, and results from one code where centrifugal effects are self-consistently included (CASTOR-FLOW) [E. Strumberger et al., Nucl. Fusion 45, 1156 (2005)] are compared with the results from another code where such effects are not taken into account (MISHKA-F) [I. T. Chapman et al., Phys. Plasmas 13, 062511 (2006)]. It is found that, even at rather modest flow speeds, the centrifugal effects are very important for the stability of the internal kink mode. While the results from the two codes can be quite similar for certain profiles in the plasma, completely opposite results are obtained for other profiles. A very good agreement between analytical theory and the numerical results are, both for inconsistent and consistent equilibria, found for plasmas with large aspect ratio. From the analytical theory, the distinctly different stability properties of equilibria with and without centrifugal effects included can be traced to the stabilizing effect of the geodesic acoustic mode (GAM) induced by the plasma rotation. This GAM exists solely as a consequence of the nonuniform plasma density and pressure created by the centrifugal force on the flux surfaces, and a stabilizing coupling of the internal kink instability to this mode cannot therefore take place if the centrifugal effects are not included in the equilibrium. In addition to the GAM stabilization, the effects of the radial profiles of the plasma density and rotation velocity are also found to be significant, and the importance of these effects increases with decreasing aspect ratio.
High-Speed Imaging of the First Kink Mode Instability in a Magnetoplasmadynamic Thruster
NASA Technical Reports Server (NTRS)
Walker, Jonathan A.; Langendof, Samuel; Walker, Mitchell L. R.; Polzin, Kurt; Kimberlin, Adam
2013-01-01
One of the biggest challenges to efficient magnetoplasmadynamic thruster (MPDT) operation is the onset of high-frequency voltage oscillations as the discharge current is increased above a threshold value. The onset regime is closely related to magnetohydrodynamic instabilities known as kink modes. This work documents direct observation of the formation and quasi-steady state behavior of an argon discharge plasma in a MPDT operating at discharge currents of 8 to 10 kA for a pulse length of approximately 4 ms. A high-speed camera images the quasi-steady-state operation of the thruster at 26,143 fps with a frame exposure time of 10 micro s. A 0.9 neutral density filter and 488-nm argon line filter with a 10-nm bandwidth are used on separate trials to capture the time evolution of the discharge plasma. Frame-by-frame analysis of the power flux incident on the CCD sensor shows both the initial discharge plasma formation process and the steady-state behavior of the discharge plasma. Light intensity levels on the order of 4-6 W/m2 indicate radial and azimuthal asymmetries in the concentration of argon plasma in the discharge channel. The plasma concentration exhibits characteristics that suggest the presence of a helical plasma column. This helical behavior has been observed in previous experiments that characterize plasma kink mode instabilities indirectly. Therefore, the direct imaging of these plasma kink modes further supports the link between MPDT onset behavior and the excitation of the magnetohydrodynamic instabilities.
NASA Astrophysics Data System (ADS)
Zhen, Tiejun
Dislocation-based deformation in crystalline solids is almost always plastic. Once dislocations are generated they entangle and render the process irreversible. In our recent work we show that this does not apply to a new class of materials, best characterized as kinking nonlinear elastic (KNE) solids. KNE solids include the MAX phases, mica, graphite, boron nitride, so called nonlinear mesoscopic elastic (NME) solids discussed in geological literature and most probably ice. The MAX phases are a new class of layered machinable ternary carbides and nitrides, with the chemical formula M n+1AXn, where M is an early transition metal, A is an A-group element (mostly IIIA and IVA) and X is C or N. The compressive loading-unloading stress-strain curves of KNE solids in the elastic regime outline nonlinear, fully reversible, reproducible, rate-independent, closed hysteresis loops whose shape and extent of energy dissipated are strongly influenced by grain size with the energy dissipated being significantly larger in the coarse-grained material. This unique property is attributed to the formation and annihilation of incipient kink bands (IKBs), defined to be thin plates of sheared material bounded by opposite walls of dislocations. As long as the dislocation walls remain attached, the response is fully reversible. Furthermore, because the dislocations are confined to the basal planes work hardening does not occur and the dislocations can move reversibly over relatively large distances. This kind of dislocation motion renders KNE solids potentially high damping material. The loss factor for Ti3SiC2, a prime member of KNE solids, is higher than most woods, and comparable to polypropylene and nylon. At higher temperatures or stress, since the IKB dissociate and coalesce to form regular irreversible kink bands. The close hystesis loops are open, the response is strain-rate dependent, and cyclic hardening is observed even at 1200°C.
Relativistic tearing and drift-kink instabilities in two-fluid simulations
NASA Astrophysics Data System (ADS)
Barkov, Maxim V.; Komissarov, Serguei S.
2016-05-01
The stability of current sheets in collisionless relativistic pair plasma was studied via two-dimensional two-fluid relativistic magnetohydrodynamic simulations with vanishing internal friction between fluids. In particular, we investigated the linear growth of the tearing and drift-kink modes in the current sheets both with and without the guide field and obtained the growth rates which are very similar to what has been found in the corresponding particle in cell (PIC) simulations. This suggests that the two-fluid simulations can be useful in studying the large-scale dynamics of astrophysical relativistic plasmas in problems involving magnetic reconnection.
Soft X-ray emission in kink-unstable coronal loops
NASA Astrophysics Data System (ADS)
Pinto, R. F.; Vilmer, N.; Brun, A. S.
2015-04-01
Context. Solar flares are associated with intense soft X-ray emission generated by the hot flaring plasma in coronal magnetic loops. Kink-unstable twisted flux-ropes provide a source of magnetic energy that can be released impulsively and may account for the heating of the plasma in flares. Aims: We investigate the temporal, spectral, and spatial evolution of the properties of the thermal continuum X-ray emission produced in such kink-unstable magnetic flux-ropes and discuss the results of the simulations with respect to solar flare observations. Methods: We computed the temporal evolution of the thermal X-ray emission in kink-unstable coronal loops based on a series of magnetohydrodynamical numerical simulations. The numerical setup consisted of a highly twisted loop embedded in a region of uniform and untwisted background coronal magnetic field. We let the kink instability develop, computed the evolution of the plasma properties in the loop (density, temperature) without accounting for mass exchange with the chromosphere. We then deduced the X-ray emission properties of the plasma during the whole flaring episode. Results: During the initial (linear) phase of the instability, plasma heating is mostly adiabatic (as a result of compression). Ohmic diffusion takes over as the instability saturates, leading to strong and impulsive heating (up to more than 20 MK), to a quick enhancement of X-ray emission, and to the hardening of the thermal X-ray spectrum. The temperature distribution of the plasma becomes broad, with the emission measure depending strongly on temperature. Significant emission measures arise for plasma at temperatures higher than 9 MK. The magnetic flux-rope then relaxes progressively towards a lower energy state as it reconnects with the background flux. The loop plasma suffers smaller sporadic heating events, but cools down globally by thermal conduction. The total thermal X-ray emission slowly fades away during this phase, and the high
Thermal symmetry in isoscaling
Escudero, C. R.; Lopez, J. A.; Dorso, C. O.
2007-02-12
It is determined that isoscaling data, if produced by two isotopic reactions under similar thermodynamic conditions, should satisfy a simple numerical relationship. This, which helps to explore the symmetry of thermodynamic conditions of isotopic reactions, is studied using molecular dynamics simulations of 40Ca+40Ca, 48Ca+48Ca, and 52Ca+52Ca, at beam energies from 35 MeV / A to 85 MeV / A, and as a function of time. Strong deviations from the rule are detected in the beginning of the collision, with an excellent convergence at long times for some energies. A comparison with experimental data and other calculations is also included.
Hillock formation of Pt thin films on single-crystal yttria-stabilized zirconia
NASA Astrophysics Data System (ADS)
Galinski, Henning; Ryll, Thomas; Schlagenhauf, Lukas; Gauckler, Ludwig J.; Stender, Patrick; Schmitz, Guido
2012-03-01
The stability of metal thin films on a dielectric substrate is conditioned by the magnitude of the interactive forces at the interface. In the case of a nonreactive interface and weak adhesion, the minimization of the free surface energy gives rise to an instability of the thin film. In order to study these effects, Pt thin films with a thickness of 50 nm were deposited via ion-beam sputtering on yttria-stabilized zirconia single crystals. All Pt films were subjected to heat treatments up to 973 K for 2 h. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy, atomic force microscopy, and standard image analysis techniques. Three main observations have been made: (i) The deposition method has a direct impact on the morphological evolution of the film during annealing. Instead of hole formation, which is typically observed as a response to a thermal treatment, anisotropic pyramidal-shaped hillocks are formed on top of the film. (ii) It is shown by comparing the hillocks’ aspect ratio with finite element method simulations that the hillock formation can be assigned to a stress relaxation process inside the thin film. (iii) By measuring the quasiequilibrium shapes and the shape fluctuations of the formed Pt hillocks the anisotropy of the step free energy and its stiffness have been derived in addition to the anisotropic kink energy of the hillocks’ edges.
Thermodynamic Modeling of the Pt-Te and Pt-Sb-Te Systems
NASA Astrophysics Data System (ADS)
Guo, Cuiping; Huang, Liang; Li, Changrong; Shang, Shunli; Du, Zhenmin
2015-08-01
The Pt-Te and the Pt-Sb-Te systems are modeled using the calculation of phase diagram (CALPHAD) technique. In the Pt-Te system, the liquid phase is modeled as (Pt, PtTe2, Te) using the associate model, and four intermediates, PtTe2, Pt2Te3, Pt3Te4 and PtTe, are treated as stoichiometric compounds and their enthalpies of formation are obtained by means of first-principles calculations. The solution phases, fcc(Pt) and hex(Te), are described as substitutional solutions. Combined with the thermodynamic models of the liquid phase in the Pt-Sb and Sb-Te systems in the literature, the liquid phase of the Pt-Sb-Te ternary system is modeled as (Pt, Sb, Te, Sb2Te3, PtTe2) also using the associate model. The compounds, PtTe2, Pt2Te3, Pt3Te4 and PtTe in the Pt-Te system and PtSb2, PtSb, Pt3Sb2 and Pt7Sb in the Pt-Sb system are treated as line compounds Pt m (Sb,Te) n in the Pt-Sb-Te system, and the compound Pt5Sb is treated as (Pt,Sb)5(Pt,Sb,Te). A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Pt-Te phase diagram, the experimental heat capacities of PtTe and PtTe2, the enthalpies of formation from first-principles calculations for PtTe2, Pt2Te3, Pt3Te4, and PtTe, and the ternary isothermal sections at 873 K, 923 K, 1073 K and 1273 K are well reproduced.
NASA Technical Reports Server (NTRS)
Rosensteel, George
1995-01-01
Riemann ellipsoids model rotating galaxies when the galactic velocity field is a linear function of the Cartesian coordinates of the galactic masses. In nuclear physics, the kinetic energy in the linear velocity field approximation is known as the collective kinetic energy. But, the linear approximation neglects intrinsic degrees of freedom associated with nonlinear velocity fields. To remove this limitation, the theory of symplectic dynamical symmetry is developed for classical systems. A classical phase space for a self-gravitating symplectic system is a co-adjoint orbit of the noncompact group SP(3,R). The degenerate co-adjoint orbit is the 12 dimensional homogeneous space Sp(3,R)/U(3), where the maximal compact subgroup U(3) is the symmetry group of the harmonic oscillator. The Hamiltonian equations of motion on each orbit form a Lax system X = (X,F), where X and F are elements of the symplectic Lie algebra. The elements of the matrix X are the generators of the symplectic Lie algebra, viz., the one-body collective quadratic functions of the positions and momenta of the galactic masses. The matrix F is composed from the self-gravitating potential energy, the angular velocity, and the hydostatic pressure. Solutions to the hamiltonian dynamical system on Sp(3,R)/U(3) are given by symplectic isospectral deformations. The Casimirs of Sp(3,R), equal to the traces of powers of X, are conserved quantities.
Applications of chiral symmetry
Pisarski, R.D.
1995-03-01
The author discusses several topics in the applications of chiral symmetry at nonzero temperature. First, where does the rho go? The answer: up. The restoration of chiral symmetry at a temperature T{sub {chi}} implies that the {rho} and a{sub 1} vector mesons are degenerate in mass. In a gauged linear sigma model the {rho} mass increases with temperature, m{sub {rho}}(T{sub {chi}}) > m{sub {rho}}(0). The author conjectures that at T{sub {chi}} the thermal {rho} - a{sub 1}, peak is relatively high, at about {approximately}1 GeV, with a width approximately that at zero temperature (up to standard kinematic factors). The {omega} meson also increases in mass, nearly degenerate with the {rho}, but its width grows dramatically with temperature, increasing to at least {approximately}100 MeV by T{sub {chi}}. The author also stresses how utterly remarkable the principle of vector meson dominance is, when viewed from the modern perspective of the renormalization group. Secondly, he discusses the possible appearance of disoriented chiral condensates from {open_quotes}quenched{close_quotes} heavy ion collisions. It appears difficult to obtain large domains of disoriented chiral condensates in the standard two flavor model. This leads to the last topic, which is the phase diagram for QCD with three flavors, and its proximity to the chiral critical point. QCD may be very near this chiral critical point, and one might thereby generated large domains of disoriented chiral condensates.
Pt and Pt/(Cu) Carbonyl clusters synthesized by radiolysis
NASA Astrophysics Data System (ADS)
Le Gratiet, B.; Remita, H.; Picq, G.; Delcourt, M. O.
1996-02-01
In the mixed solvent: 50/50% v/v water/2-propanol, [Pt 3(CO) 6] n2- clusters with n = 3-10 have been obtained by irradiating solutions containing K 2PtCl 4 under 1 atm CO. n is deduced from the very typical UV-visible and IR absorption spectra. The reduction occurs by a combined effect of CO and of the radicals produced by radiolysis (radiocatalysis). The synthesis is selective: the nuclearity n can be chosen by adjusting the dose (high doses yield low n values). Increasing the Pt salt concentration leads to CO-stabilized subcolloid particles. Intermetallic cluster compounds are expected from solutions containing two metal salts: bimetallic Pt/Cu carbonyl clusters have been obtained. Two distinct compounds have been characterized by their UV-visible spectra. Attempts with Pt/Ru and Pt/Sn systems were unsuccessful.
Leptogenesis and residual CP symmetry
NASA Astrophysics Data System (ADS)
Chen, Peng; Ding, Gui-Jun; King, Stephen F.
2016-03-01
We discuss flavour dependent leptogenesis in the framework of lepton flavour models based on discrete flavour and CP symmetries applied to the type-I seesaw model. Working in the flavour basis, we analyse the case of two general residual CP symmetries in the neutrino sector, which corresponds to all possible semi-direct models based on a preserved Z 2 in the neutrino sector, together with a CP symmetry, which constrains the PMNS matrix up to a single free parameter which may be fixed by the reactor angle. We systematically study and classify this case for all possible residual CP symmetries, and show that the R-matrix is tightly constrained up to a single free parameter, with only certain forms being consistent with successful leptogenesis, leading to possible connections between leptogenesis and PMNS parameters. The formalism is completely general in the sense that the two residual CP symmetries could result from any high energy discrete flavour theory which respects any CP symmetry. As a simple example, we apply the formalism to a high energy S 4 flavour symmetry with a generalized CP symmetry, broken to two residual CP symmetries in the neutrino sector, recovering familiar results for PMNS predictions, together with new results for flavour dependent leptogenesis.
Symmetry fractionalization and twist defects
NASA Astrophysics Data System (ADS)
Tarantino, Nicolas; Lindner, Netanel H.; Fidkowski, Lukasz
2016-03-01
Topological order in two-dimensions can be described in terms of deconfined quasiparticle excitations—anyons—and their braiding statistics. However, it has recently been realized that this data does not completely describe the situation in the presence of an unbroken global symmetry. In this case, there can be multiple distinct quantum phases with the same anyons and statistics, but with different patterns of symmetry fractionalization—termed symmetry enriched topological order. When the global symmetry group G, which we take to be discrete, does not change topological superselection sectors—i.e. does not change one type of anyon into a different type of anyon—one can imagine a local version of the action of G around each anyon. This leads to projective representations and a group cohomology description of symmetry fractionalization, with the second cohomology group {H}2(G,{{ A }}{{abelian}}) being the relevant group. In this paper, we treat the general case of a symmetry group G possibly permuting anyon types. We show that despite the lack of a local action of G, one can still make sense of a so-called twisted group cohomology description of symmetry fractionalization, and show how this data is encoded in the associativity of fusion rules of the extrinsic ‘twist’ defects of the symmetry. Furthermore, building on work of Hermele (2014 Phys. Rev. B 90 184418), we construct a wide class of exactly-solvable models which exhibit this twisted symmetry fractionalization, and connect them to our formal framework.
Symmetry of Magnetically Ordered Quasicrystals
NASA Astrophysics Data System (ADS)
Lifshitz, Ron
1998-03-01
The notion of magnetic symmetry is reexamined in light of the recent observation of long-range magnetic order in icosahedral quasicrystals [Charrier et al., Phys. Rev. Lett. 78, 4637 (1997)]. The relation between the symmetry of a magnetically ordered (periodic or quasiperiodic) crystal, given in terms of a ``spin space group,'' and its neutron diffraction diagram is established. In doing so, an outline of a symmetry classification scheme for magnetically ordered quasiperiodic crystals, is provided. Predictions are given for the expected diffraction patterns of magnetically ordered icosahedral crystals, provided their symmetry is well described by icosahedral spin space groups.
New picture of the 1/1 internal kink and sawtooth in compressible toroidal plasmas
NASA Astrophysics Data System (ADS)
Sugiyama, Linda
2013-10-01
The m = 1 , n = 1 internal kink mode and the sawtooth crash have been analyzed extensively in magnetically confined toroidal plasmas. Nevertheless, many questions remain. A new analysis, with the aid of numerical simulation, shows that small parameter expansions such as large aspect ratio break down in general for the MHD compressible toroidal 1/1 instability with realistically small growth rates. The perpendicular momentum rate of change ρ ∂v⊥ / ∂ t must be very small compared to the individual terms in - ρ (v . ∇) v |⊥ + J × B |⊥ -∇⊥ p . The lowest order mode still has the standard 1/1 internal kink form, but the v⊥ magnitude and growth rate are determined by the higher order terms. Terms containing B~ϕ , nominally associated with the compressional Alfvén wave are important. One corollary is that reduced MHD (RMHD) fails completely and Sweet-Parker-type reconnection never develops. At a critical nonlinear amplitude, associated with the growth of the higher toroidal harmonics, a fast, explosive crash begins with rapidly accelerating velocity growth that matches observations. Other transverse MHD instabilities experience analogous effects. Work supported by the U.S. Department of Energy.
Phenomenological Theory of the Kink Instability in a Slender Plasma Column
Ryutov, D D; Furno, I; Intrator, T P; Abbate, S; Madziwa-Nussinov, T
2005-11-18
When one deals with a plasma column whose radius a is much smaller than its length L, one can think of it as of a thin filament whose kink instability can be adequately described simply by a 2D displacement vector, {xi}{sub x} = {xi}{sub s}(z,t); {xi}{sub y} = {xi}{sub y}(z,t). Details of the internal structure of the column such as the current, density, and axial flow velocity distribution would be lumped into some phenomenological parameters. This approach is particularly efficient in the problems with non-ideal (sheath) boundary conditions (BC) at the end electrodes, with the finite plasma resistivity, and with a substantial axial flow. With the sheath BC imposed at one of the end-plates, we find instability in the domain well below the classical Kruskal-Shafranov limit. The presence of an axial flow causes the onset of rotation of the kink and strong axial ''skewness'' of the eigenfunction, with the perturbation amplitude increasing in the flow direction. We consider the limitations of the phenomenological approach and find that they are related to the steepness with which the plasma resistivity increases at the plasma boundary with vacuum.
Sausage Instabilities on top of Kinking Lengthening Current-Carrying Magnetic Flux Tubes
NASA Astrophysics Data System (ADS)
von der Linden, Jens; You, Setthivoine
2015-11-01
Observations indicate that the dynamics of magnetic flux tubes in our cosmos and terrestrial experiments involve fast topological change beyond MHD reconnection. Recent experiments suggest that hierarchies of instabilities coupling disparate plasma scales could be responsible for this fast topological change by accessing two-fluid and kinetic scales. This study will explore the possibility of sausage instabilities developing on top of a kink instability in lengthening current-carrying magnetic flux tubes. Current driven flux tubes evolve over a wide range of aspect ratios k and current to magnetic flux ratios λ . An analytical stability criterion and numerical investigations, based on applying Newcomb's variational approach to idealized magnetic flux tubes with core and skin currents, indicate a dependence of the stability boundaries on current profiles and overlapping kink and sausage unstable regions in the k - λ trajectory of the flux tubes. A triple electrode planar plasma gun (Mochi.LabJet) is designed to generate flux tubes with discrete core and skin currents. Measurements from a fast-framing camera and a high resolution magnetic probe are being assembled into stability maps of the k - λ space of flux tubes. This work was sponsored in part by the US DOE Grant DE-SC0010340.
Analytical model of wall forces produced by kink perturbations in tokamaks
Mironov, D. V.; Pustovitov, V. D.
2015-05-15
Analytical model of the electromagnetic forces produced by kink modes on the tokamak wall [H. R. Strauss et al., Phys. Plasmas 17, 082505 (2010)] is revisited. One of the main conclusions of the mentioned paper is that the largest force occurs at γτ{sub w}≈1, where γ is the kink growth rate and τ{sub w} is the wall penetration time. In the present study, a similar approach is developed under less restrictive assumptions on the plasma and dynamics of perturbation, and a different result is obtained: the force increases with γ and must be maximal at γτ{sub w}→∞. Additionally, the dependence of its amplitude on the plasma parameters is clarified. All distinctions and their reasons are explained in detail. The analysis is performed in the cylindrical model incorporating a resistive wall treated without traditional thin-wall constraints and covering therefore a full range in γτ{sub w}. It is applicable to either locked or rotating modes. Estimates of the sideways force are presented and compared with earlier forecasts.
How to distinguish between kink and sausage modes in flapping oscillations?
NASA Astrophysics Data System (ADS)
Kubyshkina, D. I.; Sormakov, D. A.; Sergeev, V. A.; Semenov, V. S.; Erkaev, N. V.; Kubyshkin, I. V.; Ganushkina, N. Yu.; Dubyagin, S. V.
2014-04-01
Flapping waves are most noticeable large-scale perturbations of the magnetotail current sheet, whose nature is still under discussion. They represent rather slow (an order of magnitude less than typical Alfven speed) waves propagating from the center of the sheet to its flanks with a typical speed of 20-60 km/s, amplitude of 1-2 Re and quasiperiod of 2-10 min. The double-gradient MHD model, which was elaborated in Erkaev et al. (2007) predicts two (kink and sausage) modes of the flapping waves with differences in their geometry and propagation velocity, but the mode structure is hard to resolve observationally. We investigate the possibility of mode identification by observing the rotation of magnetic field and plasma velocity vectors from a single spacecraft. We test theoretical results by analyzing the flapping oscillations observed by Time History of Events and Macroscale Interactions during Substorms spacecraft and confirm that character of observed rotation is consistent with kink mode determination made by using multispacecraft methods. Also, we checked how the existence of some obstructive conditions, such as noise, combined modes, and multiple sources of the flapping oscillations, can affect on the possibility of the modes separation with suggested method.
VERTICAL KINK OSCILLATION OF A MAGNETIC FLUX ROPE STRUCTURE IN THE SOLAR CORONA
Kim, S.; Cho, K.-S.; Nakariakov, V. M.
2014-12-20
Vertical transverse oscillations of a coronal magnetic rope, observed simultaneously in the 171 Å and 304 Å bandpasses of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO), are detected. The oscillation period is about 700 s and the displacement amplitude is about 1 Mm. The oscillation amplitude remains constant during the observation. Simultaneous observation of the rope in the bandpasses corresponding to the coronal and chromospheric temperatures suggests that it has a multi-thermal structure. Oscillatory patterns in 171 Å and 304 Å are coherent, which indicates that the observed kink oscillation is collective, in which the rope moves as a single entity. We interpret the oscillation as a fundamental standing vertically polarized kink mode of the rope, while the interpretation in terms of a perpendicular fast wave could not be entirely ruled out. In addition, the arcade situated above the rope and seen in the 171 Å bandpass shows an oscillatory motion with the period of about 1000 s.
Evidence for helical kink instability in the Venus magnetic flux ropes
NASA Technical Reports Server (NTRS)
Elphic, R. C.; Russell, C. T.
1983-01-01
Empirical models of the magnetic field structure of flux ropes found in the Venus ionosphere are seen as suggesting that the ropes are unstable to long-wavelength (more than 100 km) helical-kink perturbations. The onset of such an instability can explain the apparent volume distribution of flux ropes with altitude, as well as their orientation as a function of altitude. In the subsolar region, the fraction of volume occupied by flux ropes increases from approximately 20 percent at high altitudes to more than 50 percent at low altitudes; this is a greater increase than would be expected if ropes convect downward as simple straight horizontal cylinders. The helical kink instability raises the fractional volume occupied by ropes by turning the originally straight, horizontal flux tubes into corkscrew-shaped structures as they convect to lower altitudes. It is noted that this instability also explains why high altitude ropes tend to be horizontal and low altitude ropes appear to have almost any orientation.
Rotating kink modes in a non-line tied plasma column in the Reconnection Scaling experiment
NASA Astrophysics Data System (ADS)
Madziwa-Nussinov, Tsitsi; Ryutov, Dmitri; Abbate, Sara
2005-10-01
The screw pinch is one of the simplest MHD equilibria, and is relevant to fusion physics, astro-physics, and basic plasma physics. It has been studied for many years, but usually in the context of a periodic toroidal plasma column. Reconnection Scaling Experiment (RSX)[1] is a cylindrical device built to study the linear and non-linear evolution of the current carrying screw pinch. A plasma column is injected into one end of the chamber from a plasma gun, and terminates at an anode that can be biased to draw current. This anode acts as an adjustable non-line tied end boundary for the column. Line-tying appears to give rise to several unexpected characteristics including finite rotation frequency, and a kink instability threshold less than the Kruskal Shafranov predictions. Experimental data is compared to a phenomenological theory of the kink instability developed for a slender plasma[2] column, including effects such as boundary conditions at the electrodes, finite plasma resistivity and axial flow. [1] I. Furno et al., Rev. Sci. Instrum. 74, 2324 (2003).2] D. Ryutov et al., to be submitted to Phys. Plasmas.
Phenomenological theory of the kink instability in a slender plasma column
NASA Astrophysics Data System (ADS)
Ryutov, D. D.; Furno, I.
2005-10-01
When one deals with a plasma column whose radius a is much smaller than its length L, one can think of it as of a thin filament whose kink instability can be adequately described simply by a 2D displacement vector, x=x(z,t); y=y(z,t). Details of the internal structure of the column such as the current, density, and axial flow velocity distribution would be lumped into some phenomenological parameters. This approach is particularly efficient in the problems with non-ideal (sheath) boundary conditions at the end electrodes, the finite plasma resistivity, and the case of a substantial axial flow. For the non-ideal situation, we find instability in the domain well below the classical Kruskal-Shafranov limit. The presence of an axial flow causes the onset of a rotation of the kink and strong axial ``skewness'' of the eigenfunction. We consider the limitations of the phenomenological approach and find that they are related to the steepness with which the plasma resistivity increases at the plasma boundary with vacuum. Work performed for US DOE by UC LLNL under contract #W-7405-Eng-48.
Shock heating in numerical simulations of kink-unstable coronal loops
Bareford, M. R.; Hood, A. W.
2015-01-01
An analysis of the importance of shock heating within coronal magnetic fields has hitherto been a neglected area of study. We present new results obtained from nonlinear magnetohydrodynamic simulations of straight coronal loops. This work shows how the energy released from the magnetic field, following an ideal instability, can be converted into thermal energy, thereby heating the solar corona. Fast dissipation of magnetic energy is necessary for coronal heating and this requirement is compatible with the time scales associated with ideal instabilities. Therefore, we choose an initial loop configuration that is susceptible to the fast-growing kink, an instability that is likely to be created by convectively driven vortices, occurring where the loop field intersects the photosphere (i.e. the loop footpoints). The large-scale deformation of the field caused by the kinking creates the conditions for the formation of strong current sheets and magnetic reconnection, which have previously been considered as sites of heating, under the assumption of an enhanced resistivity. However, our simulations indicate that slow mode shocks are the primary heating mechanism, since, as well as creating current sheets, magnetic reconnection also generates plasma flows that are faster than the slow magnetoacoustic wave speed. PMID:25897092
Disconnections kinks and competing modes in shear-coupled grain boundary migration
NASA Astrophysics Data System (ADS)
Combe, N.; Mompiou, F.; Legros, M.
2016-01-01
The response of small-grained metals to mechanical stress is investigated by a theoretical study of the elementary mechanisms occurring during the shear-coupled migration of grain boundaries (GB). Investigating a model Σ 17 (410 ) GB in a copper bicrystal, both <110 > and <100 > GB migration modes are studied focusing on both the structural and energetic characteristics. The minimum energy paths of these shear-coupled GB migrations are computed using the nudge elastic band method. For both modes, the GB migration occurs through the nucleation and motion of disconnections. However, the atomic mechanisms of both modes qualitatively differ: While the <110 > mode presents no metastable state, the <100 > mode shows multiple metastable states, some of them evidencing some kinks along the disconnection lines. Disconnection kinks nucleation and motion activation energies are evaluated. Besides, the activation energies of the <100 > mode are smaller than those of the <110 > one except for very high stresses. These results significantly improve our knowledge of the GB migration mechanisms and the conditions under which they occur.
Phonon modes in cuprates possibly related to the 10 meV ARPES kink
NASA Astrophysics Data System (ADS)
Merritt, Adrian; Park, Seung-Ryong; Castellan, John-Paul; Gu, Genda; Reznik, Dmitry
One of the possible mechanisms of high Tc superconductivity is Cooper pairing with the help of bosons responsible for kinks in electronic dispersion observed by angle-resolved photoemission (ARPES). Up to now most effort has been devoted to the kinks near 70 meV. More recent ARPES experiments revealed an additional energy scale near 10 meV. Since no magnetic excitations peaked at these energies have been identified, the likeliest candidates appear to be phonons. We recently performed measurements of low-energy phonons in a large single crystal sample of optimally-doped 2212 BSCCO. We measured all phonons below 15 meV. There are many branches, in particular an optic branch disperses from 7 meV from the zone center with an anticrossing with an acoustic branch near h =0.2. In addition, there is evidence for a very low energy branch dispersing through 3-4 meV. I will present these results as well as similar data on LSCO and YBCO. A comparison with recent ultrafast optics experiment detecting lattice modes around 10 meV will also be made. This work was supported by the DOE Basic Energy Sciences Neutron Scattering Program.
The non-resonant kink modes triggering strong sawtooth-like crashes in the EAST tokamak
NASA Astrophysics Data System (ADS)
Li, Erzhong; Igochine, V.; Dumbrajs, O.; Xu, L.; Chen, K.; Shi, T.; Hu, L.
2014-12-01
Evolution of the safety factor (q) profile during L-H transitions in the Experimental Advanced Superconducting Tokamak (EAST) was accompanied by strong core crashes prior to regular sawtooth behavior. These crashes appeared in the absence of q = 1 (q is the safety factor) rational surface inside the plasma. Analysis indicates that the m/n = 2/1 tearing mode is destabilized and phase-locked with the m/n = 1/1 non-resonant kink mode (the q = 1 rational surface is absent) due to the self-consistent evolution of plasma profiles as the L-H transition occurs (m and n are the poloidal and toroidal mode numbers, respectively). The growing m/n = 1/1 mode destabilizes the m/n = 2/2 kink mode which eventually triggers the strong crash due to an anomalous heat conductivity, as predicted by the transport model of stochastic magnetic fields using experimental parameters. It is also shown that the magnetic topology changes with the amplitude of m/n = 2/2 mode and the value of center safety factor in a reasonable range.
Aschwanden, Markus J.; Schrijver, Carolus J.
2011-08-01
A detailed analysis of a coronal loop oscillation event is presented, using data from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO) for the first time. The loop oscillation event occurred on 2010 October 16, 19:05-19:35 UT and was triggered by an M2.9 GOES-class flare, located inside a highly inclined cone of a narrow-angle coronal mass ejection. This oscillation event had a number of unusual features: (1) excitation of kink-mode oscillations in vertical polarization (in the loop plane), (2) coupled cross-sectional and density oscillations with identical periods, (3) no detectable kink amplitude damping over the observed duration of four kink-mode periods (P=6.3 minutes), (4) multi-loop oscillations with slightly ({approx}10%) different periods, and (5) a relatively cool loop temperature of T {approx} 0.5 MK. We employ a novel method of deriving the electron density ratio external and internal to the oscillating loop from the ratio of Alfvenic speeds deduced from the flare trigger delay and the kink-mode period, i.e., n{sub e} /n{sub i} = (v{sub A} /v{sub Ae}){sup 2} = 0.08 {+-} 0.01. The coupling of the kink mode and cross-sectional oscillations can be explained as a consequence of the loop length variation in the vertical polarization mode. We determine the exact footpoint locations and loop length with stereoscopic triangulation using STEREO/EUVI/A data. We model the magnetic field in the oscillating loop using Helioseismic and Magnetic Imager/SDO magnetogram data and a potential-field model and find agreement with the seismological value of the magnetic field, B{sub kink} = 4.0 {+-} 0.7 G, within a factor of two.
Growth from Solutions: Kink dynamics, Stoichiometry, Face Kinetics and stability in turbulent flow
NASA Technical Reports Server (NTRS)
Chernov, A. A.; DeYoreo, J. J.; Rashkovich, L. N.; Vekilov, P. G.
2005-01-01
1. Kink dynamics. The first segment of a polygomized dislocation spiral step measured by AFM demonstrates up to 60% scattering in the critical length l*- the length when the segment starts to propagate. On orthorhombic lysozyme, this length is shorter than that the observed interkink distance. Step energy from the critical segment length based on the Gibbs-Thomson law (GTL), l* = 20(omega)alpha/(Delta)mu is several times larger than the energy from 2D nucleation rate. Here o is tine building block specific voiume, a is the step riser specific free energy, Delta(mu) is the crystallization driving force. These new data support our earlier assumption that the classical Frenkel, Burton -Cabrera-Frank concept of the abundant kink supply by fluctuations is not applicable for strongly polygonized steps. Step rate measurements on brushite confirms that statement. This is the1D nucleation of kinks that control step propagation. The GTL is valid only if l*
NASA Astrophysics Data System (ADS)
Hung, H. J.; Kuo, J. B.; Chen, D.; Tsai, C. T.; Yeh, C. S.
2010-05-01
This paper reports the shallow trench isolation (STI)-related narrow channel effect (NCE) on the kink behaviour of the 40 nm PD SOI NMOS device. As verified by the experimentally measured data, with a smaller channel width, the onset of the kink effect behaviour occurs at a higher drain voltage and the breakdown voltage is also larger due to the weaker parasitic bipolar device in the floating thin film as a result of a smaller electron recombination lifetime caused by the STI-related defect effect.
G.Y. Fu; W. Park; H.R. Strauss; J. Breslau; J. Chen; S. Jardin; L.E. Sugiyama
2005-08-09
Global hybrid simulations of energetic particle effects on the n=1 internal kink mode have been carried out for tokamaks. For the International Thermonuclear Experimental Reactor (ITER) [ITER Physics Basis Editors et al., Nucl. Fusion 39:2137 (1999)], it is shown that alpha particle effects are stabilizing for the internal kink mode. However, the elongation of ITER reduces the stabilization effects significantly. Nonlinear simulations of the precessional drift fishbone instability for circular tokamak plasmas show that the mode saturates due to flattening of the particle distribution function near the resonance region. The mode frequency chirps down rapidly as the flattening region expands radially outward. Fluid nonlinearity reduces the saturation level.
Characterization of azo dyes on Pt and Pt/polyaniline/dispersed Pt electrodes
NASA Astrophysics Data System (ADS)
Molina, J.; Fernández, J.; del Río, A. I.; Bonastre, J.; Cases, F.
2012-06-01
The electrochemical characterization of two organic dyes (amaranth and procion orange MX-2R) has been performed on Pt electrodes and Pt electrodes coated with polyaniline and dispersed Pt. Electrodes with different Pt loads have been synthesized and characterized obtaining that a load of 300 μg cm-2 was the optimum one. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) was employed to observe the distribution and morphology of the Pt nanoparticles. The electroactivity of the electrodes has also been characterized by means of scanning electrochemical microscopy (SECM). The chemical characterization of Pt dispersed Pani coated Pt electrodes (Pt-Pani-Pt) was performed by means of X-ray photoelectron spectroscopy (XPS). The electrochemical characterization of the dyes has been performed by means of cyclic voltammetry. Voltammograms have shown that the presence of the dyes diminishes characteristic Pt oxidation and reduction peaks. However, redox processes due to the dyes, appeared in the voltammograms. The different species responsible of these redox processes were generated in the vicinity of the electrode and were not adsorbed on the electrode surface since after stirring, the different redox processes disappeared. Characterization with different scan rates showed that redox processes of both dyes were controlled by diffusion.
NASA Astrophysics Data System (ADS)
Weber, S. V.; Casey, D. T.; Pino, J. E.; Rowley, D. P.; Smalyuk, V. A.; Spears, B. K.; Tipton, R. E.
2013-10-01
NIF CH ablator symmetry capsules are filled with hydrogen or helium gas. SymCaps have more moderate convergence ratios ~ 15 as opposed to ~ 35 for ignition capsules with DT ice layers, and better agreement has been achieved between simulations and experimental data. We will present modeling of capsules with CD layers and tritium fill, for which we are able to match the dependence of DT yield on recession distance of the CD layer from the gas. We can also match the performance of CH capsules with D3 He fill. The simulations include surface roughness, drive asymmetry, a mock-up of modulation introduced by the tent holding the capsule, and an empirical prescription for ablator-gas atomic mix. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
NASA Astrophysics Data System (ADS)
Dezerald, L.; Proville, L.; Ventelon, Lisa; Willaime, F.; Rodney, D.
2015-03-01
The atomistic study of kink pairs on screw dislocations in body-centered cubic (bcc) metals is challenging because interatomic potentials in bcc metals still lack accuracy and kink pairs require too many atoms to be modeled by first principles. Here, we circumvent this difficulty using a one-dimensional line tension model whose parameters, namely the line tension and Peierls barrier, are reachable to density functional theory calculations. The model parameterized in V, Nb, Ta, Mo, W, and Fe, is used to study the kink-pair activation enthalpy and spatial extension. Interestingly, we find that the atomistic line tension is more than twice the usual elastic estimates. The calculations also show interesting group tendencies with the line tension and kink-pair width larger in group V than in group VI elements. Finally, the present kink-pair activation energies are shown to compare qualitatively with experimental data and potential origins of quantitative discrepancies are discussed.
Surface-layered ordered alloy (Pt/Pt3Mn) on Pt(111)
NASA Astrophysics Data System (ADS)
Gallego, S.; Ocal, C.; Muñoz, M. C.; Soria, F.
1997-11-01
A Mn-Pt layered intermetallic compound formed by alternated planes of Pt(111) and Pt3Mn(111) composition has been stabilized in a controlled way by two different mechanisms, which confirm the great stability of the final system. The surface exhibits a 2×2 superstructure due to chemical order underneath a Pt topmost layer. The structural analysis by low-energy electron diffraction gives a Pendry reliability factor (R-factor) of RP=0.17. The hybridization of the Pt and Mn atomic levels leads to atomic magnetic moments of 3.17μB and ~0.10μB at the Mn and Pt sites of the topmost layers, respectively.
ERIC Educational Resources Information Center
Hancock, Karen
2007-01-01
In this article, the author presents a lesson on rotational symmetry which she developed for her students. The aim of the lesson was "to identify objects with rotational symmetry in the staff car park" and the success criteria were "pictures or sketches of at least six objects with different orders of rotation". After finding examples of…
Crystallographic and Spectroscopic Symmetry Notations.
ERIC Educational Resources Information Center
Sharma, B. D.
1982-01-01
Compares Schoenflies and Hermann-Mauguin notations of symmetry. Although the former (used by spectroscopists) and latter (used by crystallographers) both describe the same symmetry, there are distinct differences in the manner of description which may lead to confusion in correlating the two notations. (Author/JN)
Symmetry in Sign Language Poetry
ERIC Educational Resources Information Center
Sutton-Spence, Rachel; Kaneko, Michiko
2007-01-01
This paper considers the range of ways that sign languages use geometric symmetry temporally and spatially to create poetic effect. Poets use this symmetry in sign language art to highlight duality and thematic contrast, and to create symbolic representations of beauty, order and harmony. (Contains 8 tables, 14 figures and 6 notes.)
Generalized Atkin-Lehner symmetry
NASA Astrophysics Data System (ADS)
Dienes, Keith R.
1990-09-01
Atkin-Lehner symmetry was proposed several years ago as a mechanism for obtaining a vanishing one-loop cosmological constant in nonsupersymmetric superstring models, but for models formulated in four-dimensional spacetime this symmetry cannot be realized. We therefore investigate various means of retaining the general Atkin-Lehner idea without having strict Atkin-Lehner symmetry. We first explicitly construct non-Atkin-Lehner-symmetric partition functions which not only lead to vanishing cosmological constants but which also avoid a recent proof that Atkin-Lehner-symmetric partition functions cannot arise from physically viable string models in greater than two dimensions. We then develop a systematic generalization of Atkin-Lehner symmetry, basing our considerations on the use of non-Hermitian operators as well as on a general class of possible congruence subgroups of the full modular group. We find that whereas in many instances our resulting symmetries reduce to either strict Atkin-Lehner symmetry or symmetries closely related to it, in other cases we obtain symmetries of a fundamentally new character. Our results therefore suggest possible new avenues for retaining the general Atkin-Lehner ``selection rule'' approach for obtaining a vanishing one-loop cosmological constant.
Generalized Atkin-Lehner symmetry
Dienes, K.R. )
1990-09-15
Atkin-Lehner symmetry was proposed several years ago as a mechanism for obtaining a vanishing one-loop cosmological constant in nonsupersymmetric superstring models, but for models formulated in four-dimensional spacetime this symmetry cannot be realized. We therefore investigate various means of retaining the general Atkin-Lehner idea without having strict Atkin-Lehner symmetry. We first explicitly construct non-Atkin-Lehner-symmetric partition functions which not only lead to vanishing cosmological constants but which also avoid a recent proof that Atkin-Lehner-symmetric partition functions cannot arise from physically viable string models in greater than two dimensions. We then develop a systematic generalization of Atkin-Lehner symmetry, basing our considerations on the use of non-Hermitian operators as well as on a general class of possible congruence subgroups of the full modular group. We find that whereas in many instances our resulting symmetries reduce to either strict Atkin-Lehner symmetry or symmetries closely related to it, in other cases we obtain symmetries of a fundamentally new character. Our results therefore suggest possible new avenues for retaining the general Atkin-Lehner selection rule'' approach for obtaining a vanishing one-loop cosmological constant.
Ultraviolet completion without symmetry restoration
NASA Astrophysics Data System (ADS)
Endlich, Solomon; Nicolis, Alberto; Penco, Riccardo
2014-03-01
We show that it is not possible to UV complete certain low-energy effective theories with spontaneously broken spacetime symmetries by embedding them into linear sigma models, that is, by adding "radial" modes and restoring the broken symmetries. When such a UV completion is not possible, one can still raise the cutoff up to arbitrarily higher energies by adding fields that transform nonlinearly under the broken symmetries, that is, new Goldstone bosons. However, this (partial) UV completion does not necessarily restore any of the broken symmetries. We illustrate this point by considering a concrete example in which a combination of spacetime and internal symmetries is broken down to a diagonal subgroup. Along the way, we clarify a recently proposed interpretation of inverse Higgs constraints as gauge-fixing conditions.
Asymptotic symmetries from finite boxes
NASA Astrophysics Data System (ADS)
Andrade, Tomás; Marolf, Donald
2016-01-01
It is natural to regulate an infinite-sized system by imposing a boundary condition at finite distance, placing the system in a 'box.' This breaks symmetries, though the breaking is small when the box is large. One should thus be able to obtain the asymptotic symmetries of the infinite system by studying regulated systems. We provide concrete examples in the context of Einstein-Hilbert gravity (with negative or zero cosmological constant) by showing in 4 or more dimensions how the anti-de Sitter and Poincaré asymptotic symmetries can be extracted from gravity in a spherical box with Dirichlet boundary conditions. In 2 + 1 dimensions we obtain the full double-Virasoro algebra of asymptotic symmetries for AdS3 and, correspondingly, the full Bondi-Metzner-Sachs (BMS) algebra for asymptotically flat space. In higher dimensions, a related approach may continue to be useful for constructing a good asymptotically flat phase space with BMS asymptotic symmetries.
Symmetry inheritance of scalar fields
NASA Astrophysics Data System (ADS)
Smolić, Ivica
2015-07-01
Matter fields do not necessarily have to share the symmetries with the spacetime they live in. When this happens, we speak of the symmetry inheritance of fields. In this paper we classify the obstructions of symmetry inheritance by the scalar fields, both real and complex, and look more closely at the special cases of stationary and axially symmetric spacetimes. Since the symmetry noninheritance is present in the scalar fields of boson stars and may enable the existence of the black hole scalar hair, our results narrow the possible classes of such solutions. Finally, we define and analyse the symmetry noninheritance contributions to the Komar mass and angular momentum of the black hole scalar hair.
A nanoflare distribution generated by repeated relaxations triggered by kink instability
NASA Astrophysics Data System (ADS)
Bareford, M. R.; Browning, P. K.; van der Linden, R. A. M.
2010-10-01
Context. It is thought likely that vast numbers of nanoflares are responsible for the corona having a temperature of millions of degrees. Current observational technologies lack the resolving power to confirm the nanoflare hypothesis. An alternative approach is to construct a magnetohydrodynamic coronal loop model that has the ability to predict nanoflare energy distributions. Aims: This paper presents the initial results generated by a coronal loop model that flares whenever it becomes unstable to an ideal MHD kink mode. A feature of the model is that it predicts heating events with a range of sizes, depending on where the instability threshold for linear kink modes is encountered. The aims are to calculate the distribution of event energies and to investigate whether kink instability can be predicted from a single parameter. Methods: The loop is represented as a straight line-tied cylinder. The twisting caused by random photospheric motions is captured by two parameters, representing the ratio of current density to field strength for specific regions of the loop. Instability onset is mapped as a closed boundary in the 2D parameter space. Dissipation of the loop's magnetic energy begins during the nonlinear stage of the instability, which develops as a consequence of current sheet reconnection. After flaring, the loop evolves to the state of lowest energy where, in accordance with relaxation theory, the ratio of current to field is constant throughout the loop and helicity is conserved. Results: There exists substantial variation in the radial magnetic twist profiles for the loop states along the instability threshold. These results suggest that instability cannot be predicted by any simple twist-derived property reaching a critical value. The model is applied such that the loop undergoes repeated episodes of instability followed by energy-releasing relaxation. Hence, an energy distribution of the nanoflares produced is collated. This paper also presents the
Comparison of Properties of Pt/PZT/Pt and Ru/PZT/Pt Ferroelectric Capacitors
NASA Astrophysics Data System (ADS)
Jia, Ze; Ren, Tian-Ling; Liu, Tian-Zhi; Hu, Hong; Zhang, Zhi-Gang; Xie, Dan; Liu, Li-Tian
2006-04-01
Pb(Zr0.4Ti0.6)O3 film prepared by sol-gel spin coating on a Pt/Ti/SiO2/Si substrate is applied to ferroelectric capacitors with Pt or Ru as the top electrode. For the Pt/PZT/Pt and Ru/PZT/Pt ferroelectric capacitors, although with the same ferroelectric film, different top electrode materials incur different properties of PZT capacitors, such as fatigue, leakage, remanent and saturated polarization, except the similar crystal orientations of the PZT film. After 1010 switch cycles, the remanent polarizations of the Ru/PZT/Pt and Pt/PZT/Pt capacitors decrease to 70% and 84%, respectively. The leakage current density of the latter increases obviously at positive bias after 108 switch cycles, compared with the former. Different materials for the top electrode bring different conditions at the PZT/top electrode interface. The influence of oxygen-vacancy concentration at the PZT/electrode interface and the influence of oxides of the electrode material at the PZT/electrode interface to charge injection can explain the difference of properties of the PZT capacitors with Pt or Ru as the top electrodes.
Burger, Marga R; Kramer, J; Chermette, H; Koch, Klaus R
2010-12-01
A comparison between experimental and calculated gas-phase as well as the conductor-like screening model DFT (195)Pt chemical shifts of a series of octahedral [PtX(6-n)Y(n)](2-) complexes for X = Cl, Br, F, I was carried out to assess the accuracy of computed NMR shielding and to gain insight into the dominant σ(dia), σ(para) and σ(SO) shielding contributions. The discrepancies between the experimental and the DFT-calculated (195)Pt chemical shifts vary for these complexes as a function of the coordinated halide ions, the largest being obtained for the fluorido-chlorido and fluorido-bromido complexes, while negligible discrepancies are found for the [PtCl(6-n)Br(n)](2-) series; the discrepancies are somewhat larger where a significant deviation from the ideal octahedral symmetry such as for the geometric cis/trans or fac/mer isomers of [PtF(6-n)Cl(n)](2-) and [PtF(6-n)Br(n)](2-) may be expected. The discrepancies generally increase in the order [PtCl(6-n)Br(n)](2-) < [PtBr(6-n)I(n)](2-) < [PtCl(6-n)I(n)](2-) < [PtF(6-n)Br(n)](2-) ≈ [PtF(6-n)Cl(n)](2-), and show a striking correlation with the increase in electronegativity difference Δχ between the two halide ligands (X(-) and Y(-)) bound to Pt(IV) for these anions: 0.09 < 0.52 < 0.63 < 1.36 ≈ 1.27, respectively. The computed (195)Pt sensitivity to Pt-X bond displacement, ∂(δ(195)Pt)/∂(ΔPt-X), of these complexes is very large and depends on the halide ion, decreasing from 24 800, 18 300, 15 700 to 12 000 ppm/Å for [PtF(6)](2-), [PtCl(6)](2-), [PtBr(6)](2-) and [PtI(6)](2-), respectively. PMID:21104761
NASA Astrophysics Data System (ADS)
Vig, Sean; Kogar, Anshul; Mishra, Vivek; Norman, Mike; Gu, Genda; Abbamonte, Peter
2015-03-01
The kink features in the low energy quasiparticle dispersion in cuprate superconductors have been extensively studied using angle-resolved photoemission spectroscopy (ARPES). The existence of these kinks is a signature of a renormalization of the fermionic quasiparticles due to coupling to some bosonic collective mode at a scale related to the kink energy. In this talk, I will present angle-resolved inelastic electron scattering studies of the bosonic collective excitations in optimally doped Bi2Sr2CaCu2O8+δ. Performing a 2D momentum parameterization of these modes, we reconstruct the complete dynamical susceptibility, χ (q , ω) , which we use to perform a one-loop self energy correction to the quasiparticle dispersion. The result reproduces well the dispersion observed with ARPES, indicating that these excitations are the origin of the observed kinks. I will discuss the implications of our study for phonon vs. spin fluctuation interpretation of these effects. This work was supported as part of the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.
Chua, Gim Chuah; Snowden, Sue; Patel, Uday
2004-11-15
Significant transplant renal artery stenosis (TRAS) results in an intraarterial pressure gradient and increasing graft dysfunction correctable by endovascular therapy. Kinks of the transplant artery cause velocity gradients on Doppler ultrasound, but some will have no intraarterial pressure gradient across the kink. It is not known whether these nonflow limiting kinks progress further to threaten graft function and should undergo endovascular correction. This is a longitudinal study of conservatively managed arterial kinks to define their natural history. Fourteen patients who had undergone angiography over a 5-year period for suspected TRAS had kinks of the renal artery. True intraarterial pressures were measured in all cases by slow withdrawal of an end-hole catheter after intraarterial injection of a vasodilator. Those with a significant pressure change ({>=}10% change in peak systolic pressure across the area of suspicion) underwent endovascular treatment. The rest were managed conservatively, with maximal antihypertensive therapy. Outcome of all 14 cases was determined by follow-up of creatinine levels, blood pressure (BP) control and graft outcome over a 3-5-year period (median 4 years). Of the 14 patients with kinks, 10 were male and 4 female; age range 23-67 years (mean 47 years). Eleven had received cadaveric transplants and 3 were allografts; 12 had end-to-side and 2 end-to-end anastomosis, 11/14 cases had an intraarterial pressure ratio of <10% and at median 4 years follow-up on conservative treatment, the serum creatinine of these 11 patients did not differ significantly from those who underwent successful endovascular treatment (mean 118 {mu}mol/l versus 149 {mu}mol/l; p = 0.30, Mann Whitney test). Mean blood pressure was 137/82 mmHg, with a range of 124-155/56-95 mmHg. Only one patient has required an unexplainable increase in antihypertensive medication. Grafts (2/11) were lost and both had chronic rejection on histology. There were no unexplained
A dimer PT -symmetric model simulated in GaAs/AlGaAs quantum wells
NASA Astrophysics Data System (ADS)
Meng, Li-Chen; Zhang, Wen-Jing; Liu, Jibing; Xie, Xiao-Tao
2016-05-01
We perform the possibility to generate a dimer PT -symmetric model based on a double lambda four-level system in GaAs/AlGaAs quantum wells with biexcitonic transitions. By presenting the detuning management and modulating the Rabi frequencies of the two strong coupling laser fields, we show that the PT -symmetric model can be realized by the spatial evolution of the weak probe laser and four-wave mixing (FWM)-generated field along the propagation direction. The two weak fields in our model may be used to simulate two laser propagating in two PT -symmetric parallel waveguides. The diffraction effect also can be studied in some conditions. Our scheme offers two advantages: the complex refractive index is controlled by the strong coupling fields; the symmetry energy exchange between a dimer PT -symmetric structure is guaranteed by the four-wave mixing process. The present investigation may provide research opportunities in optical experiments.
Sign Learning Kink-based (SiLK) Quantum Monte Carlo for molecular systems.
Ma, Xiaoyao; Hall, Randall W; Löffler, Frank; Kowalski, Karol; Bhaskaran-Nair, Kiran; Jarrell, Mark; Moreno, Juana
2016-01-01
The Sign Learning Kink (SiLK) based Quantum Monte Carlo (QMC) method is used to calculate the ab initio ground state energies for multiple geometries of the H2O, N2, and F2 molecules. The method is based on Feynman's path integral formulation of quantum mechanics and has two stages. The first stage is called the learning stage and reduces the well-known QMC minus sign problem by optimizing the linear combinations of Slater determinants which are used in the second stage, a conventional QMC simulation. The method is tested using different vector spaces and compared to the results of other quantum chemical methods and to exact diagonalization. Our findings demonstrate that the SiLK method is accurate and reduces or eliminates the minus sign problem. PMID:26747795
Fractional valency and kink conduction mechanism in quasi-one-dimensional molecular systems
Ovchinnikov, A.A.; Ukrainskii, T.I.
1987-09-01
The authors consider the connection between fractional valence and electrical conductivity of donor-acceptor molecular crystals for which one-dimensional anisotropy is characteristic and seek to answer the observation that donor-acceptor crystals with fractional valence display higher conductivity than those with integral valence by proving, using a Hamiltonian and a Wigner lattice for the crystal, that donor-acceptor molecular crystals with fractional valence have some additional degeneracy in the ground state and that this circumstance is responsible for the existence in such systems of electronic excitations of the kink type which, in the general case, carry a fractional charge and may provide high electrical conductivity. Their qualitative analysis of Wigner lattices for the real molecular crystals TTF-TCNQ and NMP-TCNQ, compared against organic semiconductors, shows that energy-degenerate structures exist for ionic valences of one half, one third, and two thirds.
On the stability of the internal kink mode in the banana regime
Fogaccia, G.; Romanelli, F.
1995-01-01
The stability of the internal kink mode is investigated taking into account the kinetic response associated to the trapped thermal ions. Ion--ion collisions and diamagnetic effects in the layer are also considered. A significant stabilizing contribution is obtained, even at low-{beta} values, on the mode, which might be stable, on present experiments, even though predicted unstable according to the Bussac criterion [Bussac {ital et} {ital al}., Phys. Rev. Lett. {bold 35}, 1638 (1975)]. In addition, a trapped-ion instability is found, characterized by mode frequency of the order of the trapped-ion bounce-averaged magnetic drift frequency. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Weakly nonlinear kink-type solitary waves in a fully relativistic plasma
Tribeche, Mouloud; Boukhalfa, Soufiane; Zerguini, Taha Houssine
2010-08-15
A fully and coherent relativistic fluid model derived from the covariant formulation of relativistic fluid equations is used to study small but finite amplitude solitary waves. This approach has the characteristic to be consistent with the relativistic principle and consequently leads to a more general set of equations valid for fully relativistic plasmas with arbitrary Lorentz relativistic factor. A kink-solitary wave solution is outlined. Due to electron relativistic effect, the localized structure may experience either a spreading or a compression. This latter phenomenon (compression) becomes less effective and less noticeable as the relativistic character of the ions becomes important. Our results may be relevant to cosmic relativistic double-layers and relativistic plasma structures that involve energetic plasma flows.
Sign Learning Kink-based (SiLK) Quantum Monte Carlo for molecular systems
NASA Astrophysics Data System (ADS)
Ma, Xiaoyao; Hall, Randall W.; Löffler, Frank; Kowalski, Karol; Bhaskaran-Nair, Kiran; Jarrell, Mark; Moreno, Juana
2016-01-01
The Sign Learning Kink (SiLK) based Quantum Monte Carlo (QMC) method is used to calculate the ab initio ground state energies for multiple geometries of the H2O, N2, and F2 molecules. The method is based on Feynman's path integral formulation of quantum mechanics and has two stages. The first stage is called the learning stage and reduces the well-known QMC minus sign problem by optimizing the linear combinations of Slater determinants which are used in the second stage, a conventional QMC simulation. The method is tested using different vector spaces and compared to the results of other quantum chemical methods and to exact diagonalization. Our findings demonstrate that the SiLK method is accurate and reduces or eliminates the minus sign problem.
Fast Particle Effects on the Internal Kink, Fishbone and Alfven Modes
N.N. Gorelenkov; S. Bernabei; C.Z. Cheng; G.Y. Fu; K. Hill; S. Kaye; G.J. Kramer; Y. Kusama; K. Shinohara; R. Nazikian; T. Ozeki; W. Park
2000-11-15
The issues of linear stability of low frequency perturbative and nonperturbative modes in advanced tokamak regimes are addressed based on recent developments in theory, computational methods, and progress in experiments. Perturbative codes NOVA and ORBIT are used to calculate the effects of TAEs on fast particle population in spherical tokamak NSTX. Nonperturbative analysis of chirping frequency modes in experiments on TFTR and JT-60U is presented using the kinetic code HINST, which identified such modes as a separate branch of Alfven modes - resonance TAE (R-TAE). Internal kink mode stability in the presence of fast particles is studied using the NOVA code and hybrid kinetic-MHD nonlinear code M3D.
Exact kink solitons in the presence of diffusion, dispersion, and polynomial nonlinearity
NASA Astrophysics Data System (ADS)
Raposo, E. P.; Bazeia, D.
1999-03-01
We describe exact travelling-wave kink soliton solutions in some classes of nonlinear partial differential equations, such as generalized Korteweg-de Vries-Burgers, Korteweg-de Vries-Huxley, and Korteweg-de Vries-Burgers-Huxley equations, as well as equations in the generic form ut + P( u) ux + vuxx - δuxxx = A( u), with polynomial functions P( u) and A( u) of u = u( x, t), whose generality allows the identification with a number of relevant equations in physics. We focus on the analysis of the role of diffusion, dispersion, nonlinear effects, and parity of the polynomials to the properties of the solutions, particularly their velocity of propagation. In addition, we show that, for some appropriate choices, these equations can be mapped onto equations of motion of relativistic (1 + 1)-dimensional φ4 and φ6 field theories of real scalar fields. Systems of two coupled nonlinear equations are also considered.
Huang, Z. )
1992-12-01
We examine an interesting scenario to solve the domain-wall problem recently suggested by Preskill, Trivedi, Wilczek, and Wise. The effective potential is calculated in the presence of the QCD axial anomaly. It is shown that some discrete symmetries such as {ital CP} and {ital Z}{sub 2} can be anomalous due to a so-called {ital K} term induced by instantons. We point out that the {ital Z}{sub 2} domain-wall problem in the two-doublet standard model can be resolved by two types of solutions: the {ital CP}-conserving one and the {ital CP}-breaking one. In the first case, there exist two {ital Z}{sub 2}-related local minima whose energy splitting is provided by the instanton effect. In the second case, there is only one unique vacuum so that the domain walls do not form at all. The consequences of this new source of {ital CP} violation are discussed and shown to be well within the experimental limits in weak interactions.
Homogeneous Pt-bimetallic Electrocatalysts
Wang, Chao; Chi, Miaofang; More, Karren Leslie; Markovic, Nenad; Stamenkovic, Vojislav
2011-01-01
Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.
NASA Astrophysics Data System (ADS)
Qing, Quan; Jiang, Zhe; Xu, Lin; Gao, Ruixuan; Mai, Liqiang; Lieber, Charles M.
2014-02-01
Recording intracellular (IC) bioelectrical signals is central to understanding the fundamental behaviour of cells and cell networks in, for example, neural and cardiac systems. The standard tool for IC recording, the patch-clamp micropipette is applied widely, yet remains limited in terms of reducing the tip size, the ability to reuse the pipette and ion exchange with the cytoplasm. Recent efforts have been directed towards developing new chip-based tools, including micro-to-nanoscale metal pillars, transistor-based kinked nanowires and nanotube devices. These nanoscale tools are interesting with respect to chip-based multiplexing, but, so far, preclude targeted recording from specific cell regions and/or subcellular structures. Here we overcome this limitation in a general manner by fabricating free-standing probes in which a kinked silicon nanowire with an encoded field-effect transistor detector serves as the tip end. These probes can be manipulated in three dimensions within a standard microscope to target specific cells or cell regions, and record stable full-amplitude IC action potentials from different targeted cells without the need to clean or change the tip. Simultaneous measurements from the same cell made with free-standing nanowire and patch-clamp probes show that the same action potential amplitude and temporal properties are recorded without corrections to the raw nanowire signal. In addition, we demonstrate real-time monitoring of changes in the action potential as different ion-channel blockers are applied to cells, and multiplexed recording from cells by independent manipulation of two free-standing nanowire probes.
Effects of Field-Aligned Flows on Standing Kink and Sausage Modes Supported by Coronal Loops
NASA Astrophysics Data System (ADS)
Chen, S.-X.; Li, B.; Xia, L.-D.; Chen, Y.-J.; Yu, H.
2014-05-01
Fundamental standing modes and their overtones play an important role in coronal seismology. We examine the effects of a significant field-aligned flow on standing modes that are supported by coronal loops, which are modeled here as cold magnetic slabs. Of particular interest are the period ratios of the fundamental to its ( n-1)th overtone [ P 1/ nP n ] for kink and sausage modes, and the threshold half-width-to-length ratio for sausage modes. For standing kink modes, the flow significantly reduces P 1/ nP n in general, the effect being particularly strong for higher n and weaker density contrast [] between loops and their surroundings. That said, even when approaches infinity, this effect is still substantial, reducing the minimal P 1/ nP n by up to 13.7 % (24.5 %) for n=2 ( n=4) relative to the static case, when the Alfvén Mach number [ M A] reaches 0.8, where M A measures the loop flow speed in units of the internal Alfvén speed. Although it is not negligible for standing sausage modes, the flow effect in reducing P 1/ nP n is not as strong. However, the threshold half-width-to-length ratio is considerably higher in the flowing case than in its static counterpart. For in the range [9,1024] and M A in the range [0,0.5], an exhaustive parameter study yields that this threshold is well fitted by , which involves the two parameters in a simple way. This allows one to analytically constrain the combination for a loop with a known width-to-length ratio when a standing sausage oscillation is identified. It also allows one to examine the idea of partial sausage modes in more detail, and the flow is found to significantly reduce the spatial extent where partial modes are allowed.
Stabilization of the external kink and other MHD issues. Summary report
Freidberg, J.P.; Goldston, R.J.; Jardin, S.C.; Neilson, G.H.; Rosenbluth, M.N.; Taylor, T.S.; Thomassen, K.I.
1993-08-13
An MHD workshop entitled ``Stabilization of the External Kink and Other MHD Issues`` was held June 1993. This is a summary report of activities at that workshop, structured to respond to the three questions in the charge (letter from J. Willis). The experimental and theoretical status of these issues, and the R&D needs in each area, are addressed. We discuss the potential impact on the TPX and ITER programs of these issues. The workshop participants came from a broad and diverse range of institutions in the fusion program, including international participants. As a result, we believe the summary here reflects some consensus of the community on these very important program issues, and that the TPX and ITER programs will benefit from these discussions. The title of the workshop was chosen to indicate both our knowledge and our uncertainty of MHD phenomena limiting {beta} and causing disruptions in tokamaks. The purpose was to bring together theorists and experimentalist in order to assess our current understanding of the external kink instability at high {beta}, and to assess the potential for passive or active stabilization of the dominant modes. We also outlined the R&D needed for TPX and other future devices. Not only was the preworkshop theory clearly presented, but significant new theoretical results were described for the first time, emphasizing the roles of the resistivity of the cold edge plasma and of the plasma toroidicity in the stability criteria. Excellent reviews of the effects of the vessel walls on plasma stability were given as related to the DIII-D, TFTR, JET, PBX-M, and HBT-EP experiments. These results are generally consistent with the more complete theory.
Constructions for scale-invariant and kink-free vortex stretching
NASA Astrophysics Data System (ADS)
Dijkhuis, Geert C.
1996-10-01
Models for turbulent vortex stretching are presented as differentiable fractal curve constructions with circle arcs and screw segments replacing line elements in the usual definitions of non-analytic Koch- and Peano curves. Examples pf kink-free fractal curves are shown as self-intersecting, self-avoiding or (asymptotically) self-tangent loops, with flat versions partially or fully filling the plane, and spatial versions likewise for three dimensions. One set of kink-free fractal curves analytically models growing horseshoe vortices in Hinześ conceptual model for turbulence near a wall. From random walk analysis of transition layer vorticity on a defective lattice for intermittency, the inverse Von Karman constant emerges as fractal dimension threshold for escape of turbulence to infinity. A second curve sequence analytically models a vortex ring in superfluid helium stretching into a homogeneous vortex tangle moving between flat walls in a square channel. The deformation rule employs Hilbert's cube-filling loop construction with line segments bent into circle arcs with end points meeting at zero angle. Dynamically, the deformation geometry demands unequal skin friction on adjacent channel walls as boundary condition. The stretching process accelerates circulation velocities exponentially by conservation of angular momentum in vortex tubes with constant core volume. A third class of curves models deformation of a plasma vortex ring formed by (high-voltage or laser) discharge impact on a flat electrode surface, and carried sideways by turbulent shear flow. The construction rule now uses circle arcs twisted into Hopf-invariant screw segments for the streamlines, with mirror-symmetric halves preserving zero topoligical charge in the loop structure. Dynamically, skin friction from no-slip boundary conditions here exerts parallel torques on leading and trailing ring sections, twisting its right and left halves into mirror images with equal amounts of opposite helicity.
Guo, Y.; Hao, Q.; Cheng, X.; Chen, P. F.; Ding, M. D.; Erdélyi, R.; Srivastava, A. K.; Dwivedi, B. N.
2015-02-01
We report the observation of the first two harmonics of the horizontally polarized kink waves excited in a coronal loop system lying southeast of AR 11719 on 2013 April 11. The detected periods of the fundamental mode (P {sub 1}), its first overtone (P {sub 2}) in the northern half, and that in the southern one are 530.2 ± 13.3, 300.4 ± 27.7, and 334.7 ± 22.1 s, respectively. The periods of the first overtone in the two halves are the same considering uncertainties in the measurement. We estimate the average electron density, temperature, and length of the loop system as (5.1 ± 0.8) × 10{sup 8} cm{sup –3}, 0.65 ± 0.06 MK, and 203.8 ± 13.8 Mm, respectively. As a zeroth-order estimation, the magnetic field strength, B = 8.2 ± 1.0 G, derived by the coronal seismology using the fundamental kink mode matches with that derived by a potential field model. The extrapolation model also shows the asymmetric and nonuniform distribution of the magnetic field along the coronal loop. Using the amplitude profile distributions of both the fundamental mode and its first overtone, we observe that the antinode positions of both the fundamental mode and its first overtone shift toward the weak field region along the coronal loop. The results indicate that the density stratification and the temperature difference effects are larger than the magnetic field variation effect on the period ratio. On the other hand, the magnetic field variation has a greater effect on the eigenfunction of the first overtone than the density stratification does for this case.
NASA Astrophysics Data System (ADS)
Srivastava, A. K.; Singh, Talwinder; Ofman, Leon; Dwivedi, Bhola N.
2016-08-01
We analyze the observations from Solar TErrestrial RElations Observatory (STEREO) of an oscillating coronal streamer. STEREO-B Extreme Ultraviolet Imaging (EUVI) temporal data on 7 March 2012 shows an evolution of two consecutive EUV waves that interact with footpoint of a coronal streamer clearly evident in the co-spatial and co-temporal STEREO-B/COR-1 observations. The waves are observed in the STEREO-B/EUVI too, and its apparent energy exchange with coronal streamer generates kink oscillations. We apply the methodology of MHD seismology of the observed waves and determine the magnetic field profile of the coronal streamer. In particular, we estimate the phase velocities of the kink wave perturbations by tracking them at different heights. We also estimate electron densities inside and outside the streamer using spherically symmetric inversion of polarized brightness images in STEREO-B/COR-1. We detect two large scale kink wave oscillations that diagnose exponentially decaying radial profiles of magnetic field in streamer up to 3 solar radii. Within the limit of observational and systematic uncertainties, we find that magnetic field of streamer varies slowly at various heights, although its nature always remains exponentially decaying with height. It is seen that during evolution of second kink motion in streamer, it increases in brightness (thus mass density), and also in areal extent slightly, which may be associated with decreased photospheric magnetic flux at footpoint of streamer. As a result, magnetic field profile produced by second kink wave is reduced within streamer compared to the one diagnosed by the first one.
Geometrical spin symmetry and spin
Pestov, I. B.
2011-07-15
Unification of General Theory of Relativity and Quantum Mechanics leads to General Quantum Mechanics which includes into itself spindynamics as a theory of spin phenomena. The key concepts of spindynamics are geometrical spin symmetry and the spin field (space of defining representation of spin symmetry). The essence of spin is the bipolar structure of geometrical spin symmetry induced by the gravitational potential. The bipolar structure provides a natural derivation of the equations of spindynamics. Spindynamics involves all phenomena connected with spin and provides new understanding of the strong interaction.
Spectral theorem and partial symmetries
Gozdz, A.; Gozdz, M.
2012-10-15
A novel method of the decompositon of a quantum system's Hamiltonian is presented. In this approach the criterion of the decomposition is determined by the symmetries possessed by the sub-Hamiltonians. This procedure is rather generic and independent of the actual global symmetry, or the lack of it, of the full Hamilton operator. A detailed investigation of the time evolution of the various sub-Hamiltonians, therefore the change in time of the symmetry of the physical object, is presented for the case of a vibrator-plus-rotor model. Analytical results are illustrated by direct numerical calculations.
Hidden symmetries and black holes
NASA Astrophysics Data System (ADS)
Frolov, Valeri P.
2009-10-01
The paper contains a brief review of recent results on hidden symmetries in higher dimensional black hole spacetimes. We show how the existence of a principal CKY tensor (that is a closed conformal Killing-Yano 2-form) allows one to generate a `tower' of Killing-Yano and Killing tensors responsible for hidden symmetries. These symmetries imply complete integrability of geodesic equations and the complete separation of variables in the Hamilton-Jacobi, Klein-Gordon, Dirac and gravitational perturbation equations in the general Kerr-NUT-(A)dS metrics. Equations of the parallel transport of frames along geodesics in these spacetimes are also integrable.
Mechanisms of pattern formation in grazing-incidence ion bombardment of Pt(111)
Hansen, Henri; Redinger, Alex; Messlinger, Sebastian; Stoian, Georgiana; Michely, Thomas; Rosandi, Yudi; Urbassek, Herbert M.; Linke, Udo
2006-06-15
Ripple patterns forming on Pt(111) due to 5 keV Ar{sup +} grazing-incidence ion bombardment were investigated by scanning tunneling microscopy in a broad temperature range from 100 to 720 K and for ion fluences up to 3x10{sup 20} ions/m{sup 2}. A detailed morphological analysis together with molecular dynamics simulations of single ion impacts allow us to develop atomic scale models for the formation of these patterns. The large difference in step edge versus terrace damage is shown to be crucial for ripple formation under grazing incidence. The importance of distinct diffusion processes--step adatom generation at kinks and adatom lattice gas formation--for temperature dependent transitions in the surface morphology is highlighted. Surprisingly, ion bombardment effects like thermal spike induced adatom production and planar subsurface channeling are important for pattern ordering.
Quantum Criticality in an Ising Chain: Experimental Evidence for Emergent E8 Symmetry
NASA Astrophysics Data System (ADS)
Coldea, R.; Tennant, D. A.; Wheeler, E. M.; Wawrzynska, E.; Prabhakaran, D.; Telling, M.; Habicht, K.; Smeibidl, P.; Kiefer, K.
2010-01-01
Quantum phase transitions take place between distinct phases of matter at zero temperature. Near the transition point, exotic quantum symmetries can emerge that govern the excitation spectrum of the system. A symmetry described by the E8 Lie group with a spectrum of eight particles was long predicted to appear near the critical point of an Ising chain. We realize this system experimentally by using strong transverse magnetic fields to tune the quasi-one-dimensional Ising ferromagnet CoNb2O6 (cobalt niobate) through its critical point. Spin excitations are observed to change character from pairs of kinks in the ordered phase to spin-flips in the paramagnetic phase. Just below the critical field, the spin dynamics shows a fine structure with two sharp modes at low energies, in a ratio that approaches the golden mean predicted for the first two meson particles of the E8 spectrum. Our results demonstrate the power of symmetry to describe complex quantum behaviors.
Quantum criticality in an Ising chain: experimental evidence for emergent E8 symmetry.
Coldea, R; Tennant, D A; Wheeler, E M; Wawrzynska, E; Prabhakaran, D; Telling, M; Habicht, K; Smeibidl, P; Kiefer, K
2010-01-01
Quantum phase transitions take place between distinct phases of matter at zero temperature. Near the transition point, exotic quantum symmetries can emerge that govern the excitation spectrum of the system. A symmetry described by the E8 Lie group with a spectrum of eight particles was long predicted to appear near the critical point of an Ising chain. We realize this system experimentally by using strong transverse magnetic fields to tune the quasi-one-dimensional Ising ferromagnet CoNb2O6 (cobalt niobate) through its critical point. Spin excitations are observed to change character from pairs of kinks in the ordered phase to spin-flips in the paramagnetic phase. Just below the critical field, the spin dynamics shows a fine structure with two sharp modes at low energies, in a ratio that approaches the golden mean predicted for the first two meson particles of the E8 spectrum. Our results demonstrate the power of symmetry to describe complex quantum behaviors. PMID:20056884
Combining Flavour and CP Symmetries
NASA Astrophysics Data System (ADS)
Feruglio, Ferruccio
2013-07-01
I shortly review the impact of the most recent neutrino oscillation data on our attempts to construct a realistic model for neutrino masses and mixing angles. Models based on anarchy and its variants remain an open possibility, reinforced by the latest experimental findings. Many models based on discrete symmetries no longer work in their simplest realizations. I illustrate several proposals that can rescue discrete symmetries. In particular I discuss the possibility of combining discrete flavour symmetries and CP, and I describe a recently proposed symmetry breaking pattern that allows to predict all mixing parameters, angles and phases, in terms of a single real unknown. I analyze several explicit examples of this construction, providing new realistic mixing patterns.
Liu, Y.; Keller, J.
1996-09-01
It is proved that there exists an additional intrinsic symmetry in the left-handed and right-handed fermions (and other fields). The corresponding group of transformations is induced by the Poincar{acute e} translations in the space{endash}time manifold. This symmetry predicts an additional intrinsic energy-momentum for fermions. Considering this symmetry as local leads to introduction of a gauge field and of a nonintegrable phase angle, the corresponding Berry-type phase depends on the topology of the Riemannian space{endash}time manifold as determined by the vierbein. This additional symmetry provides us with the possibility of considering the fermions as gauge fields on the nonvector bundle. {copyright} {ital 1996 American Institute of Physics.}
Symmetries from the solution manifold
NASA Astrophysics Data System (ADS)
Aldaya, Víctor; Guerrero, Julio; Lopez-Ruiz, Francisco F.; Cossío, Francisco
2015-07-01
We face a revision of the role of symmetries of a physical system aiming at characterizing the corresponding Solution Manifold (SM) by means of Noether invariants as a preliminary step towards a proper, non-canonical, quantization. To this end, "point symmetries" of the Lagrangian are generally not enough, and we must resort to the more general concept of contact symmetries. They are defined in terms of the Poincaré-Cartan form, which allows us, in turn, to find the symplectic structure on the SM, through some sort of Hamilton-Jacobi (HJ) transformation. These basic symmetries are realized as Hamiltonian vector fields, associated with (coordinate) functions on the SM, lifted back to the Evolution Manifold through the inverse of this HJ mapping, that constitutes an inverse of the Noether Theorem. The specific examples of a particle moving on S3, at the mechanical level, and nonlinear SU(2)-sigma model in field theory are sketched.
Trace formula for broken symmetry
Creagh, S.C.
1996-05-01
We derive a trace formula for systems that exhibit an approximate continuous symmetry. It interpolates between the sum over continuous families of periodic orbits that holds in the case of exact continuous symmetry, and the discrete sum over isolated orbits that holds when the symmetry is completely broken. It is based on a simple perturbation expansion of the classical dynamics, centered around the case of exact symmetry, and gives an approximation to the usual Gutzwiller formula when the perturbation is large. We illustrate the computation with some 2-dimensional examples: the deformation of the circular billiard into an ellipse, and anisotropic and anharmonic perturbations of a harmonic oscillator. Copyright {copyright} 1996 Academic Press, Inc.
Momentum dependence of symmetry energy
NASA Astrophysics Data System (ADS)
Coupland, Daniel D.; Youngs, Michael; Chajecki, Zbigniew; Lynch, William; Tsang, Betty; Zhang, Yingxun; Famiano, Michael; Ghosh, Tilak; Giacherio, B.; Kilburn, Micha; Lee, Jenny; Lu, Fei; Russotto, Paulo; Sanetullaev, Alisher; Showalter, Rachel; Verde, Giuseppe; Winkelbauer, Jack
2014-09-01
One of the main uncertainties in the Equation of State of neutron-rich nuclear matter concerns the density and momentum dependence of the nuclear symmetry energy. Some constraints on the density dependence of the symmetry energy at sub-saturation densities have been recently obtained. However questions remain, especially concerning the momentum dependence of the symmetry mean-field potential that can make the neutron and proton effective masses different. We probe the momentum dependence of this isovector mean-field potential by comparing the energy spectra of neutrons and protons emitted in 112Sn+112Sn and 124Sn +124Sn collisions at incident energies of E/A = 50 and 120 MeV. We achieve an experimental precision that can discriminate between transport model predictions for the n/p double ratio for different momentum dependencies of the symmetry mean-field potential. One of the main uncertainties in the Equation of State of neutron-rich nuclear matter concerns the density and momentum dependence of the nuclear symmetry energy. Some constraints on the density dependence of the symmetry energy at sub-saturation densities have been recently obtained. However questions remain, especially concerning the momentum dependence of the symmetry mean-field potential that can make the neutron and proton effective masses different. We probe the momentum dependence of this isovector mean-field potential by comparing the energy spectra of neutrons and protons emitted in 112Sn+112Sn and 124Sn+124Sn collisions at incident energies of E/A = 50 and 120 MeV. We achieve an experimental precision that can discriminate between transport model predictions for the n/p double ratio for different momentum dependencies of the symmetry mean-field potential. PHY-1102511.
Symmetry and quaternionic integrable systems
NASA Astrophysics Data System (ADS)
Gaeta, G.; Rodríguez, M. A.
2015-01-01
Given a hyperkahler manifold M, the hyperkahler structure defines a triple of symplectic structures on M; with these, a triple of Hamiltonians defines a so-called hyperHamiltonian dynamical system on M. These systems are integrable when can be mapped to a system of quaternionic oscillators. We discuss the symmetry of integrable hyperHamiltonian systems, i.e. quaternionic oscillators, and conversely how these symmetries characterize, at least in the Euclidean case, integrable hyperHamiltonian systems.
Dynamical symmetries in nuclear structure
Casten, R.F.
1986-01-01
In recent years the concept of dynamical symmetries in nuclei has witnessed a renaissance of interest and activity. Much of this work has been developed in the context of the Interacting Boson Approximation (or IBA) model. The appearance and properties of dynamical symmetries in nuclei will be reviewed, with emphasis on their characteristic signatures and on the role of the proton-neutron interaction in their formation, systematics and evolution. 36 refs., 20 figs.
Broken Symmetries and Magnetic Dynamos
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2007-01-01
Phase space symmetries inherent in the statistical theory of ideal magnetohydrodynamic (MHD) turbulence are known to be broken dynamically to produce large-scale coherent magnetic structure. Here, results of a numerical study of decaying MHD turbulence are presented that show large-scale coherent structure also arises and persists in the presence of dissipation. Dynamically broken symmetries in MHD turbulence may thus play a fundamental role in the dynamo process.
Anomalies and Discrete Chiral Symmetries
Creutz, M.
2009-09-07
The quantum anomaly that breaks the U(1) axial symmetry of massless multi-flavored QCD leaves behind a discrete flavor-singlet chiral invariance. With massive quarks, this residual symmetry has a close connection with the strong CP-violating parameter theta. One result is that if the lightest quarks are degenerate, then a first order transition will occur when theta passes through pi. The resulting framework helps clarify when the rooting prescription for extrapolating in the number of flavors is valid.
Transport and thermodynamic properties of (Ca1-xLax)10(Pt3As8)(Fe2As2)5 superconductors
Ni, N.; Straszheim, Warren E.; Williams, D. J.; Tanatar, Makariy A.; Prozorov, Ruslan; Bauer, E. D.; Ronning, F.; Thompson, J. D.; Cava, R. J.
2013-02-22
Single crystals of (Ca1-xLax)(10)(Pt3As8)(Fe2As2)(5) (x = 0-0.182) superconductors have been grown and characterized by x-ray, microprobe, transport, and thermodynamic measurements. Features in the magnetic susceptibility, specific heat, and two kinks in the derivative of the electrical resistivity around 100 K in the x = 0 compound support the existence of decoupled structural and magnetic phase transitions. With La doping, the structural/magnetic phase transitions are suppressed and a half dome of superconductivity with a maximal T-c around 26 K is observed in the temperature-concentration phase diagram.
Emergence of Euclidean dynamical symmetry as a consequence of shape phase mixing
NASA Astrophysics Data System (ADS)
Budaca, R.; Budaca, A. I.
2016-08-01
A hybrid model which combines γ-stable and γ-rigid collective conditions through a rigidity parameter, is used to study the critical point of the phase transition between spherical and axially symmetric shapes. The model in the equally mixed case, called X (4), exhibits properties of the Euclidean symmetry in four dimensions. The spectral properties of the new model are investigated in connection to the exact symmetry. Experimental realisation of the X (4) model is found in two N = 90 nuclei and two Pt isotopes in vicinity of experimentally observed critical point.
Conserved correlation in PT-symmetric systems: Scattering and bound states
NASA Astrophysics Data System (ADS)
Abhinav, Kumar; Jayannavar, Arun; Panigrahi, Prasanta K.
2013-04-01
For one-dimensional PT-symmetric systems, it is observed that the non-local product ψ∗(-x,t)ψ(x,t), obtained from the continuity equation can be interpreted as a conserved correlation function. This leads to physical conclusions regarding both discrete and continuum states of such systems. Asymptotic states are shown to have necessarily broken PT-symmetry, leading to modified scattering and transfer matrices. This yields restricted boundary conditions, e.g., incidence from both sides, analogous to that of the proposed PT CPA laser (Longhi, 2010) [4]. The interpretation of 'left' and 'right' states leads to a HermitianS-matrix, resulting in the non-conservation of the 'flux'. This further satisfies a 'duality' condition, identical to the optical analogues (Paasschens et al., 1996) [17]. However, the non-local conserved scalar implements alternate boundary conditions in terms of 'in' and 'out' states, leading to the pseudo-Hermiticity condition in terms of the scattering matrix. Interestingly, when PT-symmetry is preserved, it leads to stationary states with real energy, naturally interpretable as bound states. The broken PT-symmetric phase is also captured by this correlation, with complex-conjugate pair of energies, interpreted as resonances.
Superconductivity, magnetism, and pairing symmetry in Fe-based superconductors
NASA Astrophysics Data System (ADS)
Eremin, Ilya
2009-03-01
We analyze antiferromagnetism and superconductivity within the renormalization group(RG) technique in novel Fe-based superconductors using the itinerant model of small electron and hole pockets near (0; 0) and (π,π), respectively, originating from the two strongly hybridized orbitals. We find that, for this model, the bare interactions in the Cooper channel are repulsive, and superconductivity does not occur at the mean-field level. However, under RG the effective interaction in the superconducting channel changes sign and becomes attractive. Furthermore, the effective interactions in antiferromagnetic and superconducting channels logarithmically flow towards the same absolute values at low energies, i.e., both must be treated on equal footings. The magnetic instability comes first for equal sizes of the two pockets, but looses to superconductivity upon doping. The superconducting gap has no nodes, but changes sign between the two Fermi surfaces (extended s-wave symmetry). We argue that the T dependencies of the spin susceptibility and NMR relaxation rate for such state are exponential only at very low T, and can be well fitted by power-laws over a wide T range below Tc. We further show that below Tc excitonic resonance appears in the spin excitations spectrum. [4pt] [1] M. Korshunov, and I. Eremin, Phys. Rev. B 78, 140509(R) (2008) [0pt] [2] A.V. Chubukov, D. Efremov, I. Eremin, Phys. Rev. B 78, 134512 (2008). [0pt] [3] M.M. Korshunov and I. Eremin, Europhys. Lett. 83, 67003 (2008).
Symmetry in polarimetric remote sensing
NASA Technical Reports Server (NTRS)
Nghiem, S. V.; Yueh, S. H.; Kwok, R.
1993-01-01
Relationships among polarimetric backscattering coefficients are derived from the viewpoint of symmetry groups. For both reciprocal and non-reciprocal media, symmetry encountered in remote sensing due to reflection, rotation, azimuthal, and centrical symmetry groups is considered. The derived properties are general and valid to all scattering mechanisms, including volume and surface scatterings and their interactions, in a given symmetrical configuration. The scattering coefficients calculated from theoretical models for layer random media and rough surfaces are shown to obey the symmetry relations. Use of symmetry properties in remote sensing of structural and environmental responses of scattering media is also discussed. Orientations of spheroidal scatterers described by spherical, uniform, planophile, plagiothile, erectophile, and extremophile distributions are considered to derive their polarimetric backscattering characteristics. These distributions can be identified from the observed scattering coefficients by comparison with theoretical symmetry calculations. A new parameter is then defined to study scattering structures in geophysical media. Observations from polarimetric data acquired by the Jet Propulsion Laboratory airborne synthetic aperture radar over forests, sea ice, and sea surface are presented. Experimental evidences of the symmetry relationships are shown and their use in polarimetric remote sensing is illustrated. For forests, the coniferous forest in Mt. Shasta area (California) and mixed forest near Presque Isle (Maine) exhibit characteristics of the centrical symmetry at C-band. For sea ice in the Beaufort Sea, multi-year sea ice has a cross-polarized ratio e close to e(sub 0), calculated from symmetry, due to the randomness in the scattering structure. First-year sea ice has e much smaller than e(sub 0) due to the preferential alignment of the columnar structure of the ice. From polarimetric data of a sea surface in the Bering Sea, it is
Quantum Noise and Self-Sustained Radiation of PT-Symmetric Systems
NASA Astrophysics Data System (ADS)
Schomerus, Henning
2010-06-01
The observation that PT-symmetric Hamiltonians can have real-valued energy levels even if they are non-Hermitian has triggered intense activities, with experiments, in particular, focusing on optical systems, where Hermiticity can be broken by absorption and amplification. For classical waves, absorption and amplification are related by time-reversal symmetry. This work shows that microreversibility-breaking quantum noise turns PT-symmetric systems into self-sustained sources of radiation, which distinguishes them from ordinary, Hermitian quantum systems.
Lifetime measurements in 180Pt
NASA Astrophysics Data System (ADS)
Chen, Q. M.; Wu, X. G.; Chen, Y. S.; Li, C. B.; Gao, Z. C.; Li, G. S.; Chen, F. Q.; He, C. Y.; Zheng, Y.; Hu, S. P.; Zhong, J.; Wu, Y. H.; Li, H. W.; Luo, P. W.
2016-04-01
Lifetimes of the yrast states in 180Pt have been measured from 4+ to 8+ using the recoil distance Doppler-shift technique in the coincidence mode. These states were populated by the reaction 156Gd(28Si,4 n )180Pt at a beam energy of 144 MeV. The differential decay curve method was applied to determine the lifetimes from experimental coincidence data. The B (E 2 ) values extracted from lifetimes increase with increasing spin, implying rotor behavior, but do not show the typical shape coexistence where the B (E 2 ) values present a rapid increase at very low spins. Calculations based on the triaxial projected shell model were performed for the yrast states in 180Pt and the results of both energies and E 2 transition probabilities reproduce the experimental data very well. The result also shows that a better description of the yrast band in 180Pt requires consideration of the γ degree of freedom.
Parity-time symmetry-breaking mechanism of dynamic Mott transitions in dissipative systems
NASA Astrophysics Data System (ADS)
Tripathi, Vikram; Galda, Alexey; Barman, Himadri; Vinokur, Valerii M.
2016-07-01
We describe the critical behavior of the electric field-driven (dynamic) Mott insulator-to-metal transitions in dissipative Fermi and Bose systems in terms of non-Hermitian Hamiltonians invariant under simultaneous parity (P ) and time-reversal (T ) operations. The dynamic Mott transition is identified as a PT symmetry-breaking phase transition, with the Mott insulating state corresponding to the regime of unbroken PT symmetry with a real energy spectrum. We establish that the imaginary part of the Hamiltonian arises from the combined effects of the driving field and inherent dissipation. We derive the renormalization and collapse of the Mott gap at the dielectric breakdown and describe the resulting critical behavior of transport characteristics. The obtained critical exponent is in an excellent agreement with experimental findings.
Kevrekidis, Panayotis G.; Cuevas–Maraver, Jesús; Saxena, Avadh; Cooper, Fred; Khare, Avinash
2015-10-01
In the present work, we combine the notion of parity-time (PT) symmetry with that of supersymmetry (SUSY) for a prototypical case example with a complex potential that is related by SUSY to the so-called Pöschl-Teller potential which is real. Not only are we able to identify and numerically confirm the eigenvalues of the relevant problem, but we also show that the corresponding nonlinear problem, in the presence of an arbitrary power-law nonlinearity, has an exact bright soliton solution that can be analytically identified and has intriguing stability properties, such as an oscillatory instability, which is absent for the corresponding solution of the regular nonlinear Schrödinger equation with arbitrary power-law nonlinearity. The spectral properties and dynamical implications of this instability are examined. Furthermore, we believe that these findings may pave the way toward initiating a fruitful interplay between the notions of PT symmetry, supersymmetric partner potentials, and nonlinear interactions.
Role of strong spin-orbit coupling in the superconductivity of the hexagonal pnictide SrPtAs
NASA Astrophysics Data System (ADS)
Youn, Suk Joo; Fischer, Mark H.; Rhim, S. H.; Sigrist, Manfred; Agterberg, Daniel F.
2012-06-01
In clean inversion symmetric materials, spin-orbit coupling is not thought to have a pronounced effect on spin-singlet superconductivity. Here we show that, for the recently discovered pnictide superconductor SrPtAs, this is not the case. In particular, for spin-singlet superconductivity in SrPtAs, strong spin-orbit coupling leads to a significant enhancement of both the spin susceptibility and the paramagnetic limiting field with respect to that usually expected for spin-singlet superconductors. The underlying reason for this is that, while SrPtAs has a center of inversion symmetry, it contains weakly coupled As-Pt layers that do not have inversion symmetry. This local inversion-symmetry breaking allows for a form of spin-orbit coupling that dramatically effects superconductivity. These results indicate that caution should be used when interpreting measurements of the spin susceptibility and the paramagnetic limiting field if superconductivity resides in regions of locally broken inversion symmetry.
Physical symmetry and lattice symmetry in the lattice Boltzmann method
Cao, N.; Chen, S.; Jin, S.; Martinez, D.
1997-01-01
The lattice Boltzmann method (LBM) is regarded as a specific finite difference discretization for the kinetic equation of the discrete velocity distribution function. We argue that for finite sets of discrete velocity models, such as LBM, the physical symmetry is necessary for obtaining the correct macroscopic Navier-Stokes equations. In contrast, the lattice symmetry and the Lagrangian nature of the scheme, which is often used in the lattice gas automaton method and the existing lattice Boltzmann methods and directly associated with the property of particle dynamics, is not necessary for recovering the correct macroscopic dynamics. By relaxing the lattice symmetry constraint and introducing other numerical discretization, one can also obtain correct hydrodynamics. In addition, numerical simulations for applications, such as nonuniform meshes and thermohydrodynamics can be easily carried out and numerical stability can be ensured by the Courant-Friedricks-Lewey condition and using the semi-implicit collision scheme. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Gusain, Abhay; Singh, Surendra; Chauhan, A. K.; Saxena, Vibha; Jha, P.; Veerender, P.; Singh, Ajay; Varde, P. V.; Basu, Saibal; Aswal, D. K.; Gupta, S. K.
2016-02-01
The efficiency of a bulk heterojunction (BHJ) solar cell critically depends upon quality of its interfaces. The imperfect interfaces can lead to S-kink in the current-voltage characteristics that reduce the efficiency of BHJ solar cells. In this letter, using PCDTBT:PCBM based BHJ solar cells, we demonstrate that non-destructive X-ray reflectivity is powerful technique to estimate the electron density profile across the BHJ solar cells. A direct correlation is observed between the enhanced electron density at PEDOT:PSS/PCDTBT:PCBM interface and appearance of S-kink in J-V characteristics, which is also supported by X-ray photoelectron spectroscopy and Kelvin probe measurements.
Hall, James P.; O’Sullivan, Kyra; Naseer, Abeer; Smith, Jayden A.; Kelly, John M.; Cardin, Christine J.
2011-01-01
We describe a crystal structure, at atomic resolution (1.1 Å, 100 K), of a ruthenium polypyridyl complex bound to duplex DNA, in which one ligand acts as a wedge in the minor groove, resulting in the 51° kinking of the double helix. The complex cation Λ-[Ru(1,4,5,8-tetraazaphenanthrene)2(dipyridophenazine)]2+ crystallizes in a 1∶1 ratio with the oligonucleotide d(TCGGCGCCGA) in the presence of barium ions. Each complex binds to one duplex by intercalation of the dipyridophenazine ligand and also by semiintercalation of one of the orthogonal tetraazaphenanthrene ligands into a second symmetrically equivalent duplex. The result is noncovalent cross-linking and marked kinking of DNA. PMID:21969542
Symmetry in finite phase plane
NASA Astrophysics Data System (ADS)
Zak, J.
2010-03-01
The known symmetries in one-dimensional systems are inversion and translations. These symmetries persist in finite phase plane, but a novel symmetry arises in view of the discrete nature of the coordinate xi and the momentum pi : xi and pi can undergo permutations. Thus, if xi assumes M discrete values, i = 0, 1,2,..., M - 1, a permutation will change the order of the set x0,x1,..., xM-1 into a new ordered set. Such a symmetry element does not exist for a continuous x-coordinate in an infinite phase plane. Thus, in a finite phase plane, translations can be replaced by permutations. This is also true for the inversion operator. The new permutation symmetry has been used for the construction of conjugate representations and for the splitting of the M-dimensional vector space into independent subspaces. This splitting is exhaustive in the sense that if M = iMi with Mi being prime numbers, the M-dimensional space splits into M1,M2,...Mn-dimensional independent subspaces. It is shown that following this splitting one can design new potentials with appropriate constants of motion. A related problem is the Weyl-Heisenberg group in the M-dimensional space which turns into a direct product of its subgroups in the Mi-dimensional subspaces. As an example we consider the case of M = 8.
On the symmetries of integrability
Bellon, M.; Maillard, J.M.; Viallet, C. )
1992-06-01
In this paper the authors show that the Yang-Baxter equations for two-dimensional models admit as a group of symmetry the infinite discrete group A{sub 2}{sup (1)}. The existence of this symmetry explains the presence of a spectral parameter in the solutions of the equations. The authors show that similarly, for three-dimensional vertex models and the associated tetrahedron equations, there also exists an infinite discrete group of symmetry. Although generalizing naturally the previous one, it is a much bigger hyperbolic Coxeter group. The authors indicate how this symmetry can help to resolve the Yang-Baxter equations and their higher-dimensional generalizations and initiate the study of three-dimensional vertex models. These symmetries are naturally represented as birational projective transformations. They may preserve non-trivial algebraic varieties, and lead to proper parametrizations of the models, be they integrable or not. The authors mention the relation existing between spin models and the Bose-Messner algebras of algebraic combinatorics. The authors' results also yield the generalization of the condition q{sup n} = 1 so often mentioned in the theory of quantum groups, when no q parameter is available.
Symmetry Guide to Ferroaxial Transitions
NASA Astrophysics Data System (ADS)
Hlinka, J.; Privratska, J.; Ondrejkovic, P.; Janovec, V.
2016-04-01
The 212 species of the structural phase transitions with a macroscopic symmetry breaking are inspected with respect to the occurrence of the ferroaxial order parameter, the electric toroidal moment. In total, 124 ferroaxial species are found, some of them being also fully ferroelectric (62) or fully ferroelastic ones (61). This ensures a possibility of electrical or mechanical switching of ferroaxial domains. Moreover, there are 12 ferroaxial species that are neither ferroelectric nor ferroelastic. For each species, we have also explicitly worked out a canonical form for a set of representative equilibrium property tensors of polar and axial nature in both high-symmetry and low-symmetry phases. This information was gathered into the set of 212 mutually different symbolic matrices, expressing graphically the presence of nonzero independent tensorial components and the symmetry-imposed links between them, for both phases simultaneously. Symmetry analysis reveals the ferroaxiality in several currently debated materials, such as VO2 , LuFe2 O4 , and URu2 Si2 .
An Over-and-out Halo Coronal Mass Ejection Driven by the Full Eruption of a Kinked Filament
NASA Astrophysics Data System (ADS)
Yang, Jiayan; Jiang, Yunchun; Bi, Yi; Li, Haidong; Hong, Junchao; Yang, Dan; Zheng, Ruisheng; Yang, Bo
2012-04-01
Over-and-out coronal mass ejections (CMEs) represent a broad class of CMEs that come from flare-producing magnetic explosions of various sizes but are laterally far offset from the flare, and their productions can be depicted by the magnetic-arch-blowout scenario. In this paper, we present observations of an over-and-out halo CME from the full eruption of a small kinking filament in an emerging active region (AR). In combination with the results of a derived coronal magnetic configuration, our observations showed that the CME was associated with a coronal helmet streamer, and the filament was located in the northern outskirts of the streamer base. Formed along a neutral line where flux cancellation was forced by the emerging AR with the surrounding opposite-polarity magnetic field, the filament underwent a full, non-radial eruption along the northern leg of the streamer arcade, accompanied by a clockwise deflection of the eruption direction. As a characteristic property of kink instability, the eruption displayed a clear inverse γ shape, indicative of a writhing motion of the filament apex. Coronal dimmings, including a remote one, formed in opposite-polarity footprint regions of the streamer arcade during the eruption, and the consequent CME was laterally offset from the AR. These observations suggest that the kink instability is likely to be the driver in the eruption. The event can be well explained by putting this driver into the magnetic-arch-blowout model, in which the eruption-direction deflection and the full-eruption nature of the kinking filament are caused by the guiding action of the streamer arcade and the external reconnection between them.
NASA Astrophysics Data System (ADS)
Hanson, David E.
2011-08-01
Based on recent molecular dynamics and ab initio simulations of small isoprene molecules, we propose a new ansatz for rubber elasticity. We envision a network chain as a series of independent molecular kinks, each comprised of a small number of backbone units, and the strain as being imposed along the contour of the chain. We treat chain extension in three distinct force regimes: (Ia) near zero strain, where we assume that the chain is extended within a well defined tube, with all of the kinks participating simultaneously as entropic elastic springs, (II) when the chain becomes sensibly straight, giving rise to a purely enthalpic stretching force (until bond rupture occurs) and, (Ib) a linear entropic regime, between regimes Ia and II, in which a force limit is imposed by tube deformation. In this intermediate regime, the molecular kinks are assumed to be gradually straightened until the chain becomes a series of straight segments between entanglements. We assume that there exists a tube deformation tension limit that is inversely proportional to the chain path tortuosity. Here we report the results of numerical simulations of explicit three-dimensional, periodic, polyisoprene networks, using these extension-only force models. At low strain, crosslink nodes are moved affinely, up to an arbitrary node force limit. Above this limit, non-affine motion of the nodes is allowed to relax unbalanced chain forces. Our simulation results are in good agreement with tensile stress vs. strain experiments.
NASA Astrophysics Data System (ADS)
Tchekhovskoy, Alexander; Bromberg, Omer
2016-09-01
Energy deposition by active galactic nuclei jets into the ambient medium can affect galaxy formation and evolution, the cooling of gas flows at the centres of galaxy clusters, and the growth of the supermassive black holes. However, the processes that couple jet power to the ambient medium and determine jet morphology are poorly understood. For instance, there is no agreement on the cause of the well-known Fanaroff-Riley (FR) morphological dichotomy of jets, with FRI jets being shorter and less stable than FRII jets. We carry out global 3D magnetohydrodynamic simulations of relativistic jets propagating through the ambient medium. We show that the flat density profiles of galactic cores slow down and collimate the jets, making them susceptible to the 3D magnetic kink instability. We obtain a critical power, which depends on the galaxy core mass and radius, below which jets become kink-unstable within the core, stall, and inflate cavities filled with relativistically hot plasma. Jets above the critical power stably escape the core and form powerful backflows. Thus, the kink instability controls the jet morphology and can lead to the FR dichotomy. The model-predicted dependence of the critical power on the galaxy optical luminosity agrees well with observations.
NASA Astrophysics Data System (ADS)
Tchekhovskoy, Alexander; Bromberg, Omer
2016-04-01
Energy deposition by active galactic nuclei jets into the ambient medium can affect galaxy formation and evolution, the cooling of gas flows at the centres of galaxy clusters, and the growth of the supermassive black holes. However, the processes that couple jet power to the ambient medium and determine jet morphology are poorly understood. For instance, there is no agreement on the cause of the well-known Fanaroff-Riley (FR) morphological dichotomy of jets, with FRI jets being shorter and less stable than FRII jets. We carry out global 3D magnetohydrodynamic simulations of relativistic jets propagating through the ambient medium. We show that the flat density profiles of galactic cores slow down and collimate the jets, making them susceptible to the 3D magnetic kink instability. We obtain a critical power, which depends on the galaxy core mass and radius, below which jets become kink-unstable within the core, stall, and inflate cavities filled with relativistically-hot plasma. Jets above the critical power stably escape the galaxy cores and form powerful backflows. Thus, the kink instability controls the jet morphology and can lead to the FR dichotomy. The model-predicted dependence of the critical power on the galaxy optical luminosity agrees well with observations.
NASA Astrophysics Data System (ADS)
Peng, Q.; Levesque, J. P.; Stoafer, C. C.; Bialek, J.; Byrne, P.; Hughes, P. E.; Mauel, M. E.; Navratil, G. A.; Rhodes, D. J.
2016-04-01
A new algorithm for feedback control of rotating, wall-stabilized kink modes in the High Beta Tokamak-Extended Pulse (HBT-EP) device maintains an accurate phase shift between the perturbation and the measured rotating mode through current control, with control power emphasizing fast rotation and phase jumps over fast amplitude changes. In HBT-EP, wall-stabilized kink modes become unstable above the ideal wall stability limit, and feedback suppression is aimed at delaying the onset of discharge disruption through reduction of the kink mode amplitude. Performance of the new feedback algorithm is tested under different experimental conditions, including variation of the plasma-wall coupling, insertion of a ferritic wall, changing mode rotation frequency over the range of 4-8 kHz using an internal biased electrode, and adjusting the feedback phase-angle to accelerate, amplify, or suppress the mode. We find the previously reported excitation of the slowly rotating mode at high feedback gain in HBT-EP is mitigated by the current control scheme. We also find good agreement between the observed and predicted changes to the mode rotation frequency and amplitude. When ferritic material is introduced, or the plasma-wall coupling becomes weaker as the walls are retracted from plasma, the feedback gain needs to be increased to achieve the same level of suppression. When mode rotation is slowed by a biased electrode, the feedback system still achieves mode suppression, and demonstrates wide bandwidth effectiveness.
Kolíbal, Miroslav; Pejchal, Tomáš; Vystavěl, Tomáš; Šikola, Tomáš
2016-08-10
Hydride precursors are commonly used for semiconductor nanowire growth from the vapor phase and hydrogen is quite often used as a carrier gas. Here, we used in situ scanning electron microscopy and spatially resolved Auger spectroscopy to reveal the essential role of atomic hydrogen in determining the growth direction of Ge nanowires with an Au catalyst. With hydrogen passivating nanowire sidewalls the formation of inclined facets is suppressed, which stabilizes the growth in the ⟨111⟩ direction. By contrast, without hydrogen gold diffuses out of the catalyst and decorates the nanowire sidewalls, which strongly affects the surface free energy of the system and results in the ⟨110⟩ oriented growth. The experiments with intentional nanowire kinking reveal the existence of an energetic barrier, which originates from the kinetic force needed to drive the droplet out of its optimum configuration on top of a nanowire. Our results stress the role of the catalyst material and surface chemistry in determining the nanowire growth direction and provide additional insights into a kinking mechanism, thus allowing to inhibit or to intentionally initiate spontaneous kinking. PMID:27458789
Symmetry breaking in molecular ferroelectrics.
Shi, Ping-Ping; Tang, Yuan-Yuan; Li, Peng-Fei; Liao, Wei-Qiang; Wang, Zhong-Xia; Ye, Qiong; Xiong, Ren-Gen
2016-07-11
Ferroelectrics are inseparable from symmetry breaking. Accompanying the paraelectric-to-ferroelectric phase transition, the paraelectric phase adopting one of the 32 crystallographic point groups is broken into subgroups belonging to one of the 10 ferroelectric point groups, i.e. C1, C2, C1h, C2v, C4, C4v, C3, C3v, C6 and C6v. The symmetry breaking is captured by the order parameter known as spontaneous polarization, whose switching under an external electric field results in a typical ferroelectric hysteresis loop. In addition, the responses of spontaneous polarization to other external excitations are related to a number of physical effects such as second-harmonic generation, piezoelectricity, pyroelectricity and dielectric properties. Based on these, this review summarizes recent developments in molecular ferroelectrics since 2011 and focuses on the relationship between symmetry breaking and ferroelectricity, offering ideas for exploring high-performance molecular ferroelectrics. PMID:27051889
CKM matrix and flavor symmetries
NASA Astrophysics Data System (ADS)
Araki, Takeshi; Ishida, Hiroyuki; Ishimori, Hajime; Kobayashi, Tatsuo; Ogasahara, Atsushi
2013-11-01
Following the way proposed recently by Hernandez and Smirnov, we seek possible residual symmetries in the quark sector with a focus on the von Dyck groups. We begin with two extreme cases in which both θ13 and θ23 or only θ13 are set to zero. Then, cases where all the Cabibbo-Kobayashi-Maskawa parameters are allowed to take nonzero values are explored. The Z7 symmetry is favorable to realize only the Cabibbo angle. On the other hand, larger groups are necessary in order to be consistent with all the mixing parameters. Possibilities of embedding the obtained residual symmetries into the Δ(6N2) series are also briefly discussed.
Symmetries in geometrical optics: theory
NASA Astrophysics Data System (ADS)
Szilagyi, M.; Mui, P. H.
1995-12-01
A study of light and charged-particle optical systems with inversion, reflection, rotation, translation, and/or glide symmetries is presented. The constraints imposed by the various symmetries on the first-order properties of a lens are investigated. In particular, the mathematical structures of the deflection vectors and the transfer matrices are described for various symmetrical systems. In the course of studying the translation and the glide symmetries, a simple technique for characterizing a general system of N identical components in series (or cascade) is also developed, based on the linear algebra theory of factoring matrices into Jordan canonical forms. Applications of these results are presented in a follow-up paper [J. Opt. Soc. Am. 12, XXXX (1995)]. Copyright (c) 1995 Optical Society of America
Heisenberg symmetry and hypermultiplet manifolds
NASA Astrophysics Data System (ADS)
Antoniadis, Ignatios; Derendinger, Jean-Pierre; Marios Petropoulos, P.; Siampos, Konstantinos
2016-04-01
We study the emergence of Heisenberg (Bianchi II) algebra in hyper-Kähler and quaternionic spaces. This is motivated by the rôle these spaces with this symmetry play in N = 2 hypermultiplet scalar manifolds. We show how to construct related pairs of hyper-Kähler and quaternionic spaces under general symmetry assumptions, the former being a zooming-in limit of the latter at vanishing scalar curvature. We further apply this method for the two hyper-Kähler spaces with Heisenberg algebra, which is reduced to U (1) × U (1) at the quaternionic level. We also show that no quaternionic spaces exist with a strict Heisenberg symmetry - as opposed to Heisenberg ⋉ U (1). We finally discuss the realization of the latter by gauging appropriate Sp (2 , 4) generators in N = 2 conformal supergravity.
Energy and frequency dependence of the alpha particle redistribution produced by internal kink modes
Farengo, R.; Ferrari, H. E.; Garcia-Martinez, P. L.; Firpo, M.-C.; Ettoumi, W.; Lifschitz, A. F.
2014-08-15
The redistribution of alpha particles due to internal kink modes is studied. The exact particle trajectories in the total fields, equilibrium plus perturbation, are calculated. The equilibrium has circular cross section and the plasma parameters are similar to those expected in ITER. The alpha particles are initially distributed according to a slowing down distribution function and have energies between 18 keV and 3.5 MeV. The (1, 1), (2, 2), and (2, 1) modes are included and the effect of changing their amplitude and frequency is studied. When only the (1, 1) mode is included, the spreading of high energy (E≳1 MeV) alpha particles increases slowly with the energy and mode frequency. At lower energies, the redistribution is more sensitive to the mode frequency and particle energy. When a (2, 1) mode is added, the spreading increases significantly and particles can reach the edge of the plasma. Trapped particles are the most affected and the redistribution parameter can have maxima above 1 MeV, depending on the mode frequency. These results can have important implications for ash removal.
Design of barrier coatings on kink-resistant peripheral nerve conduits.
Clements, Basak Acan; Bushman, Jared; Murthy, N Sanjeeva; Ezra, Mindy; Pastore, Christopher M; Kohn, Joachim
2016-01-01
Here, we report on the design of braided peripheral nerve conduits with barrier coatings. Braiding of extruded polymer fibers generates nerve conduits with excellent mechanical properties, high flexibility, and significant kink-resistance. However, braiding also results in variable levels of porosity in the conduit wall, which can lead to the infiltration of fibrous tissue into the interior of the conduit. This problem can be controlled by the application of secondary barrier coatings. Using a critical size defect in a rat sciatic nerve model, the importance of controlling the porosity of the nerve conduit walls was explored. Braided conduits without barrier coatings allowed cellular infiltration that limited nerve recovery. Several types of secondary barrier coatings were tested in animal studies, including (1) electrospinning a layer of polymer fibers onto the surface of the conduit and (2) coating the conduit with a cross-linked hyaluronic acid-based hydrogel. Sixteen weeks after implantation, hyaluronic acid-coated conduits had higher axonal density, displayed higher muscle weight, and better electrophysiological signal recovery than uncoated conduits or conduits having an electrospun layer of polymer fibers. This study indicates that braiding is a promising method of fabrication to improve the mechanical properties of peripheral nerve conduits and demonstrates the need to control the porosity of the conduit wall to optimize functional nerve recovery. PMID:26977288
Simulation of Non-resonant Internal Kink Mode with Toroidal Rotation in NSTX
Fu, Guoyong
2013-07-16
Plasmas in spherical and conventional tokamaks, with weakly reversed shear q pro le and minimum q above but close to unity, are susceptible to an non-resonant (m, n ) = (1, 1) internal kink mode. This mode can saturate and persist and can induce a (2; 1) seed island for Neoclassical Tearing Mode (NTMs)1 . The mode can also lead to large energetic particle transport and signi cant broadening of beam-driven current. Motivated by these important e ects, we have carried out extensive nonlinear simulations of the mode with nite toroidal rotation using parameters and pro les of an NTSX plasma with a weakly reversed shear pro le. The numerical results show that, at the experimental level, plasma rotation has little e ect on either equilibrium or linear stability. However, rotation can signi cantly inuence the nonlinear dynamics of the (1, 1) mode and the the induced (2, 1) magnetic island. The simulation results show that a rotating helical equilibrium is formed and maintained in the nonlinear phase at nite plasma rotation. In contrast, for non-rotating cases, the nonlinear evolution exhibits dynamic oscillations between a quasi-2D state and a helical state. Furthermore, the e ects of rotation are found to greatly suppress the (2, 1) magnetic island even at a low level.
Fawley, W.M.; Lee, E.P.
1980-02-08
A simulation code has been developed and exercised to study the time evolution and resultant liminosity of intersecting pulses of electrons and positrons. Under the extreme conditions of high current and small radius recently proposed for the SLAC facility, the pulses mutually pinch to a smaller mean radius than that achieved by free flight alone. The effective luminosity is enhanced by a factor of approx. 3 in the best case, corresponding to zero initial emittance and pulse length equal 1/4 the mean betatron wavelength. Gaussian profiles in the longitudinal and transverse coordinates are preferred over flat profiles in order to minimize disruptive oscillations in radius which reduce luminosity. A second potential source of disruption is the kink instability. This is always present to some degree during the interaction of opposed pulses. However, the maximum growth rate is only one half the angular betatron frequency and therefore mode growth is limited to a very low level if the pulses are short compared with a betatron wavelength.
Resistivity and sheared rotation effects on the toroidal external kink mode
NASA Astrophysics Data System (ADS)
Cole, A. J.; Brennan, D. P.; Finn, J. M.
2014-10-01
We present PEST-III analysis of the toroidal external kink with plasma resistivity and sheared rotation for a range of equilibria varying elongation, driven unstable by increasing β. The results show that the typical ordering for marginally stable β values is βrp,rw <βrp,iw <βip,rw <βip,iw , where rp,ip signify resistive or ideal plasma, and iw,rw indicate ideal wall or resistive wall (no-wall). The two resistive plasma β limits are significantly lower than the two ideal plasma values. We vary aspects of the tearing layer physics by means of a variational principle with Padé approximants, and compare with a general computational solution for the layers to gain insight. We also include pressure gradient and local velocity shear within the layers. Global rotation shear Ω' is included in the form of a relative rotation of the q = 2 , 3 , ... surfaces and we investigate the resultant effect on the poloidal mode number spectrum. We then present a model for active feedback control, which is the toroidal generalization building on recent results in cylindrical mode control theory [D. P. Brennan and J. M. Finn, submitted to Phys. Plasmas (2014)].
Free-Standing Kinked Silicon Nanowires for Probing Inter- and Intracellular Force Dynamics.
Zimmerman, John F; Murray, Graeme F; Wang, Yucai; Jumper, John M; Austin, Jotham R; Tian, Bozhi
2015-08-12
Silicon nanowires (SiNWs) have emerged as a new class of materials with important applications in biology and medicine with current efforts having focused primarily on using substrate bound SiNW devices. However, developing devices capable of free-standing inter- and intracellular operation is an important next step in designing new synthetic cellular materials and tools for biophysical characterization. To demonstrate this, here we show that label free SiNWs can be internalized in multiple cell lines, forming robust cytoskeletal interfaces, and when kinked can serve as free-standing inter- and intracellular force probes capable of continuous extended (>1 h) force monitoring. Our results show that intercellular interactions exhibit ratcheting like behavior with force peaks of ∼69.6 pN/SiNW, while intracellular force peaks of ∼116.9 pN/SiNW were recorded during smooth muscle contraction. To accomplish this, we have introduced a simple single-capture dark-field/phase contrast optical imaging modality, scatter enhanced phase contrast (SEPC), which enables the simultaneous visualization of both cellular components and inorganic nanostructures. This approach demonstrates that rationally designed devices capable of substrate-independent operation are achievable, providing a simple and scalable method for continuous inter- and intracellular force dynamics studies. PMID:26192816
Electromagnetic thin-wall model for simulations of plasma wall-touching kink and vertical modes
NASA Astrophysics Data System (ADS)
Zakharov, Leonid E.; Atanasiu, Calin V.; Lackner, Karl; Hoelzl, Matthias; Strumberger, Erika
2015-12-01
> The understanding of plasma disruptions in tokamaks and predictions of their effects require realistic simulations of electric current excitation in three-dimensional vessel structures by the plasma touching the walls. As discovered at JET in 1996 (Litunovski JET Internal Report contract no. JQ5/11961, 1995; Noll et al., Proceedings of the 19th Symposium on Fusion Technology, Lisbon (ed. C. Varandas & F. Serra), vol. 1, 1996, p. 751. Elsevier) the wall-touching kink modes are frequently excited during vertical displacement events and cause large sideways forces on the vacuum vessel which are difficult to withstand in large tokamaks. In disruptions, the sharing of electric current between the plasma and the wall plays an important role in plasma dynamics and determines the amplitude and localization of the sideways force (Riccardo et al., Nucl. Fusion, vol. 40, 2000, p. 1805; Riccardo & Walker, Plasma Phys. Control. Fusion, vol. 42, 2000, p. 29; Zakharov, Phys. Plasmas, vol. 15, 2008, 062507; Riccardo et al., Nucl. Fusion, vol. 49, 2009, 055012; Bachmann et al., Fusion Engng Des., vol. 86, 2011, pp. 1915-1919). This paper describes a flat triangle representation of the electric circuits of a thin conducting wall of arbitrary three-dimensional geometry. Implemented into the shell simulation code (SHL) and the source sink current code (SSC), this model is suitable for modelling the electric currents excited in the wall inductively and through current sharing with the plasma.
Design of barrier coatings on kink-resistant peripheral nerve conduits
Clements, Basak Acan; Bushman, Jared; Murthy, N Sanjeeva; Ezra, Mindy; Pastore, Christopher M; Kohn, Joachim
2016-01-01
Here, we report on the design of braided peripheral nerve conduits with barrier coatings. Braiding of extruded polymer fibers generates nerve conduits with excellent mechanical properties, high flexibility, and significant kink-resistance. However, braiding also results in variable levels of porosity in the conduit wall, which can lead to the infiltration of fibrous tissue into the interior of the conduit. This problem can be controlled by the application of secondary barrier coatings. Using a critical size defect in a rat sciatic nerve model, the importance of controlling the porosity of the nerve conduit walls was explored. Braided conduits without barrier coatings allowed cellular infiltration that limited nerve recovery. Several types of secondary barrier coatings were tested in animal studies, including (1) electrospinning a layer of polymer fibers onto the surface of the conduit and (2) coating the conduit with a cross-linked hyaluronic acid-based hydrogel. Sixteen weeks after implantation, hyaluronic acid-coated conduits had higher axonal density, displayed higher muscle weight, and better electrophysiological signal recovery than uncoated conduits or conduits having an electrospun layer of polymer fibers. This study indicates that braiding is a promising method of fabrication to improve the mechanical properties of peripheral nerve conduits and demonstrates the need to control the porosity of the conduit wall to optimize functional nerve recovery. PMID:26977288
NASA Astrophysics Data System (ADS)
He, H. D.; Dong, J. Q.; Fu, G. Y.; Zheng, G. Y.; Sheng, Z. M.; Long, Y. X.; He, Z. X.; Jiang, H. B.; Shen, Y.; Wang, L. F.
2010-08-01
The internal kink (fishbone) modes, driven by barely passing energetic ions (EIs), are numerically studied with the spatial distribution of the EIs taking into account. It is found that the modes with frequencies comparable to the toroidal precession frequencies are excited by resonant interaction with the EIs. Positive and negative density gradient dominating cases, corresponding to off- and near-axis depositions of neutral beam injection (NBI), respectively, are analyzed in detail. The most interesting and important feature of the modes is that there exists a second stable regime in higher βh (=pressure of EIs/toroidal magnetic pressure) range, and the modes may only be excited by the barely passing EIs in a region of βth1<βh<βth2 (βth is threshold or critical beta of EIs). Besides, the unstable modes require minimum density gradients and minimum radial positions of NBI deposition. The physics mechanism for the existence of the second stable regime is discussed. The results may provide a means of reducing or even preventing the loss of NBI energetic ions and increasing the heating efficiency by adjusting the pitch angle and driving the system into the second stable regime fast enough.
Forward Modeling of Standing Kink Modes in Coronal Loops. II. Applications
NASA Astrophysics Data System (ADS)
Yuan, Ding; Van Doorsselaere, Tom
2016-04-01
Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modeling) of the observables into the thermal and magnetic structures of the plasma. However, due to the limited availability of observables, this is an ill-posed issue. Forward modeling is designed to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses, and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation.
NASA Astrophysics Data System (ADS)
Li, Jiahua; Zhan, Xiaogui; Ding, Chunling; Zhang, Duo; Wu, Ying
2015-10-01
We present a perturbation technique to study the linear and nonlinear output characteristics of coherent photon transport in a parity-time (PT )-symmetric double-microcavity system where one passive cavity contains a single quantum emitter. It is found that (i) for the linear transmission of a low-power input probe field, the output spectra of the proposed PT -symmetric system exhibit a single transparent resonance dip and two symmetric, strongly amplifying sidebands, i.e., an inverted dipole-induced transparency; and (ii) for the nonlinear transmission of the input probe field, giant optical third-order nonlinearities with high linear transmission rate and vanishing nonlinear absorption can be achieved efficiently when the system parameters are tuned properly so that a PT -symmetry phase transition occurs. The obtained results can be useful for quantum information processing, quantum nondemolition measurements of photons, and optical signal processing.
New information on the occurrence of the O(6) symmetry in nuclei
Pietralla, N.; Möller, T.; Lister, C. J.; McCutchan, E. A.; Rainovski, G.; Bauer, C.; Carpenter, M. P.; Janssens, R. V.F.; Seweryniak, D.; Zhu, S.
2015-05-28
New γγ-coincidence relations and E2 decay transition rates in the isotopes 194,196Pt have been deduced from γ-ray spectroscopy experiments using the Gammasphere spectrometer in projectile-Coulomb excitation reactions of beams of 194,196Pt ions provided by the ATLAS accelerator facility. The results give access to observables that are crucial for a classification of excited quadrupole-collective states in terms of quantum numbers associated with the analytically solvable O(6) dynamical symmetry of the interacting boson model. The data on 196Pt corroborate the qualitative pattern of excitation energies and E2 transition rates expected from the O(6) solution but the excitation energies significantly deviate from itmore » on a quantitative level.« less
New information on the occurrence of the O(6) symmetry in nuclei
Pietralla, N.; Möller, T.; Lister, C. J.; McCutchan, E. A.; Rainovski, G.; Bauer, C.; Carpenter, M. P.; Janssens, R. V.F.; Seweryniak, D.; Zhu, S.
2015-05-28
New γγ-coincidence relations and E2 decay transition rates in the isotopes ^{194,196}Pt have been deduced from γ-ray spectroscopy experiments using the Gammasphere spectrometer in projectile-Coulomb excitation reactions of beams of ^{194,196}Pt ions provided by the ATLAS accelerator facility. The results give access to observables that are crucial for a classification of excited quadrupole-collective states in terms of quantum numbers associated with the analytically solvable O(6) dynamical symmetry of the interacting boson model. The data on ^{196}Pt corroborate the qualitative pattern of excitation energies and E2 transition rates expected from the O(6) solution but the excitation energies significantly deviate from it on a quantitative level.
PT quantum mechanics - Recent results
NASA Astrophysics Data System (ADS)
Bender, Carl M.
2012-09-01
Most quantum physicists believe that a quantum-mechanical Hamiltonian must be Dirac Hermitian (invariant under matrix transposition and complex conjugation) to be sure that the energy eigenvalues are real and that time evolution is unitary. However, the non-Dirac-hermitian Hamiltonian H = p2+ix3 has a real positive discrete spectrum and generates unitary time evolution and defines a fully consistent and physical quantum theory. Evidently, Dirac Hermiticity is too restrictive. While H = p2+ix3 is not Dirac Hermitian, it is PT symmetric (invariant under combined space reflection P and time reversal T). Another PT-symmetric Hamiltonian whose energy levels are real, positive and discrete is H = p2-x4, which contains an upside-down potential. The quantum mechanics defined by a PT-symmetric Hamiltonian is a complex generalization of ordinary quantum mechanics. When quantum mechanics and quantum field theory are extended into the complex domain, new kinds of theories having strange and remarkable properties emerge. In the past two years some of these properties have been verified in laboratory experiments. Here, we first discuss PT-symmetric Hamiltonians at a simple intuitive level and explain why the energy levels of such Hamiltonians may be real, positive, and discrete. Second, we describe a recent experiment in which the PT phase transition was observed. Third, we briefly mention that PT-symmetric theories can be useful at a fundamental level. While the double-scaling limit of an O(N)-symmetric gφ4 quantum field theory appears to be inconsistent because the critical value of g is negative, this limit is in fact not inconsistent because the critical theory is PT symmetric.
Non-local magnetoresistance in YIG/Pt nanostructures
Goennenwein, Sebastian T. B. Pernpeintner, Matthias; Gross, Rudolf; Huebl, Hans; Schlitz, Richard; Ganzhorn, Kathrin; Althammer, Matthias
2015-10-26
We study the local and non-local magnetoresistance of thin Pt strips deposited onto yttrium iron garnet. The local magnetoresistive response, inferred from the voltage drop measured along one given Pt strip upon current-biasing it, shows the characteristic magnetization orientation dependence of the spin Hall magnetoresistance. We simultaneously also record the non-local voltage appearing along a second, electrically isolated, Pt strip, separated from the current carrying one by a gap of a few 100 nm. The corresponding non-local magnetoresistance exhibits the symmetry expected for a magnon spin accumulation-driven process, confirming the results recently put forward by Cornelissen et al. [“Long-distance transport of magnon spin information in a magnetic insulator at room temperature,” Nat. Phys. (published online 14 September 2015)]. Our magnetotransport data, taken at a series of different temperatures as a function of magnetic field orientation, rotating the externally applied field in three mutually orthogonal planes, show that the mechanisms behind the spin Hall and the non-local magnetoresistance are qualitatively different. In particular, the non-local magnetoresistance vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance prevails.
NASA Astrophysics Data System (ADS)
Yang, H. F.; Liu, Z. T.; Fan, C. C.; Yao, Q.; Xiang, P.; Zhang, K. L.; Li, M. Y.; Li, H.; Liu, J. S.; Shen, D. W.; Jiang, M. H.
2016-03-01
Perovskite SrRuO3, a prototypical conductive ferromagnetic oxide, exhibits a kink in its band dispersion signaling the unusual electron dynamics therein. However, the origin of this kink remains elusive. By taking advantage of the combo of reactive molecular beam epitaxy and in situ angle-resolved photoemission spectroscopy, we systematically studied the evolution of the low-energy electronic structure of SrRuO3 films with thickness thinning down to a nearly two-dimensional limit in a well-controlled way. The kink structure persists even in the four-unit-cell-thick film. Moreover, through quantitative self-energy analysis, we observed the negligible thickness dependence of the binding energy of the kink, which is in sharp contrast to the downward trend of the Curie temperature with reducing the film thickness. Together with previously reported transport and Raman studies, this finding suggests that the kink of perovskite SrRuO3 should originate from the electron-phonon coupling rather than magnetic collective modes, and the in-plane phonons may play a dominant role. Considering such a kink structure of SrRuO3 is similar to those of many other correlated oxides, we suggest the possible ubiquity of the coupling of electrons to oxygen-related phonons in correlated oxides.
Quantum noise and mode nonorthogonality in non-Hermitian PT-symmetric optical resonators
Yoo, Gwangsu; Sim, H.-S.; Schomerus, Henning
2011-12-15
PT-symmetric optical resonators combine absorbing regions with active, amplifying regions. The latter are the source of radiation generated via spontaneous and stimulated emission, which embodies quantum noise and can result in lasing. We calculate the frequency-resolved output radiation intensity of such systems and relate it to a suitable measure of excess noise and mode nonorthogonality. The line shape differs depending on whether the emission lines are isolated (as for weakly amplifying, almost-Hermitian systems) or overlapping (as for the almost-degenerate resonances in the vicinity of exceptional points associated with spontaneous PT-symmetry breaking). The calculations are carried out in the scattering input-output formalism, and are illustrated for a quasi-one-dimensional resonator setup. In our derivations, we also consider the more general case of a resonator in which the amplifying and absorbing regions are not related by symmetry.
Segmented Pt/Ru, Pt/Ni, and Pt/RuNi nanorods as model bifunctional catalysts for methanol oxidation.
Liu, Fang; Lee, Jim Yang; Zhou, Wei Jiang
2006-01-01
Five-segment (Pt-Ru-Pt-Ru-Pt, Pt-Ni-Pt-Ni-Pt, and Pt-RuNi-Pt-RuNi-Pt) nanorods with the same overall rod length and the same total Pt segment length were prepared by sequential electrodeposition of the metals into the pores of commercially available anodic aluminum oxide (AAO) membranes. Field-emission scanning electron microscopy (FESEM) showed that the nanorods were about 210 nm in diameter and about 1.5 microm in length. The alternating Pt and oxophilic metal(s) segments could be easily differentiated in backscattered-electron images. X-ray diffraction (XRD) analysis of the nanorods indicated that Pt and Ni were polycrystalline with fcc structures, Ru was hcp, and the co-deposited RuNi adopted the nickel fcc structure with some negative shifts in the Bragg angles. The chemical states of Pt, Ru, and Ni on the nanorod surface were assayed by X-ray photoelectron spectroscopy (XPS), and the presence of Pt(0), Pt(II), Pt(IV), Ru(0), Ru(VI), Ni(0), and Ni(II) was observed. The nanorods were catalytically active for the room-temperature electrooxidation of methanol in acidic solutions. The relative rates of reaction showed the Pt-RuNi pair sites as having the lowest overpotential to dissociate water, the highest catalytic activity in methanol oxidation, and the strongest CO-tolerance in the potential window employed. The use of segmented nanorods with identifiable Pt-oxophilic metal(s) interfaces removes many of the ambiguities in the interpretation of experimental data from conventional alloy catalysts, thereby enabling a direct comparison of the activities of various types of pair sites in methanol oxidation. PMID:17193567
Unparticles and electroweak symmetry breaking
Lee, Jong-Phil
2008-11-23
We investigate a scalar potential inspired by the unparticle sector for the electroweak symmetry breaking. The scalar potential contains the interaction between the standard model fields and unparticle sector. It is described by the non-integral power of fields that originates from the nontrivial scaling dimension of the unparticle operator. It is found that the electroweak symmetry is broken at tree level when the interaction is turned on. The scale invariance of unparticle sector is also broken simultaneously, resulting in a physical Higgs and a new lighter scalar particle.
Kastner, Ruth E.
2011-11-29
This paper seeks to clarify features of time asymmetry in terms of symmetry breaking. It is observed that, in general, a contingent situation or event requires the breaking of an underlying symmetry. The distinction between the universal anisotropy of temporal processes and the irreversibility of certain physical processes is clarified. It is also proposed that the Transactional Interpretation of quantum mechanics offers an effective way to explain general thermodynamic asymmetry in terms of the time asymmetry of radiation, where prior such efforts have fallen short.
Symmetry analysis of cellular automata
NASA Astrophysics Data System (ADS)
García-Morales, V.
2013-01-01
By means of B-calculus [V. García-Morales, Phys. Lett. A 376 (2012) 2645] a universal map for deterministic cellular automata (CAs) has been derived. The latter is shown here to be invariant upon certain transformations (global complementation, reflection and shift). When constructing CA rules in terms of rules of lower range a new symmetry, “invariance under construction” is uncovered. Modular arithmetic is also reformulated within B-calculus and a new symmetry of certain totalistic CA rules, which calculate the Pascal simplices modulo an integer number p, is then also uncovered.
Iterates of maps with symmetry
NASA Technical Reports Server (NTRS)
Chossat, Pascal; Golubitsky, Martin
1988-01-01
Fixed-point bifurcation, period doubling, and Hopf bifurcation (HB) for iterates of equivariant mappings are investigated analytically, with a focus on HB in the presence of symmetry. An algebraic formulation for the hypotheses of the theorem of Ruelle (1973) is derived, and the case of standing waves in a system of ordinary differential equations with O(2) symmetry is considered in detail. In this case, it is shown that HB can lead directly to motion on an invariant 3-torus, with an unexpected third frequency due to drift of standing waves along the torus.
Symmetries of coupled harmonic oscillators
NASA Technical Reports Server (NTRS)
Han, D.; Kim, Y. S.
1993-01-01
It is shown that the system of two coupled harmonic oscillators possesses many interesting symmetries. It is noted that the symmetry of a single oscillator is that of the three-parameter group Sp(2). Thus two uncoupled oscillator exhibits a direct product of two Sp(2) groups, with six parameters. The coupling can be achieved through a rotation in the two-dimensional space of two oscillator coordinates. The closure of the commutation relations for the generators leads to the ten-parameter group Sp(4) which is locally isomorphic to the deSitter group O(3,2).
Atomic structure, alloying behavior, and magnetism in small Fe-Pt clusters
NASA Astrophysics Data System (ADS)
Chittari, Bheema Lingam; Kumar, Vijay
2015-09-01
We report results of the atomic structure, alloying behavior, and magnetism in F emP tn(m +n =2 -10 ) clusters using projector augmented wave (PAW) pseudopotential method and spin-polarized generalized gradient approximation (GGA) for the exchange-correlation energy. These results are compared with those obtained by using HCTH exchange-correlation functional and LANL2DZ basis set in the Gaussian program and the overall trends are found to be similar. As in bulk Fe-Pt alloys, clusters with equal composition of Fe and Pt have the largest binding energy and the largest heat of nanoalloy formation for a given number of atoms in the cluster. There are some deviations due to the different symmetries in clusters and in cases where the total number of atoms is odd. The lowest energy isomers tend to maximize bonds between unlike atoms with Fe (Pt) atoms occupying high (low) coordination sites in the core (surface) of the cluster. The binding energy, heat of formation, and the second order difference of the total energy show F e2P t2 , F e4P t4 , and F e4P t6 clusters to be the most stable ones among the different clusters we have studied. The magnetic moments on Fe atoms are high in Pt-rich clusters as well as in small Fe-rich clusters and decrease as the aggregation of Fe atoms and the cluster size increases. The maximum value of the magnetic moments on Fe atoms is ˜3.8 μB , whereas for Pt atoms it is 1 μB. These are quite high compared with the values for bulk Fe as well as bulk FePt and F e3Pt phases while bulk Pt is nonmagnetic. There is significant charge transfer from those Fe atoms that interact directly with Pt atoms. We discuss the hybridization between the electronic states of Pt and Fe atoms as well as the variation in the magnetic moments on Fe and Pt atoms. Our results provide insight into the understanding of the nanoalloy behavior of Fe-Pt and we hope that this would help to design Fe based nanoalloys and their assemblies with high magnetic moments for
Tuning Band Alignment Using Interface Dipoles at the Pt/Anatase TiO₂ Interface.
Tachikawa, Takashi; Minohara, Makoto; Hikita, Yasuyuki; Bell, Christopher; Hwang, Harold Y
2015-12-01
The Schottky barrier heights at the Pt/TiO2 (001) junctions are modulated over 0.8 eV by inserting <1 nm of LaAlO3. The large electric field in the LaAlO3 is stabilized by preserving the continuity of in-plane lattice symmetry at the oxide interface. These results greatly expand the application of dipole engineering to versatile polycrystalline metal/binary oxide functional interfaces. PMID:26502952
Tuning band alignment using interface dipoles at the Pt/anatase TiO2 interface
Tachikawa, Takashi; Minohara, Makoto; Hikita, Yasuyuki; Bell, Christopher; Hwang, Harold Y.
2015-10-27
The Schottky barrier heights at the Pt/TiO2 (001) junctions are modulated over 0.8 eV by inserting <1 nm of LaAlO3. The large electric field in the LaAlO3 is stabilized by preserving the continuity of in-plane lattice symmetry at the oxide interface. Lastly, these results greatly expand the application of dipole engineering to versatile polycrystalline metal/binary oxide functional interfaces.
Ring-whizzing in polyene-PtL2 complexes revisited
Oloba-Whenu, Oluwakemi A; Soubra-Ghaoui, Chirine
2016-01-01
Summary Ring-whizzing was investigated by hybrid DFT methods in a number of polyene–Pt(diphosphinylethane) complexes. The polyenes included cyclopropenium+, cyclobutadiene, cyclopentadienyl+, hexafluorobenzene, cycloheptatrienyl+, cyclooctatetraene, octafluorooctatetraene, 6-radialene, pentalene, phenalenium+, naphthalene and octafluoronaphthalene. The HOMO of a d10 ML2 group (with b2 symmetry) interacting with the LUMO of the polyene was used as a model to explain the occurrence of minima and maxima on the potential energy surface. PMID:27559391
Ring-whizzing in polyene-PtL2 complexes revisited.
Oloba-Whenu, Oluwakemi A; Albright, Thomas A; Soubra-Ghaoui, Chirine
2016-01-01
Ring-whizzing was investigated by hybrid DFT methods in a number of polyene-Pt(diphosphinylethane) complexes. The polyenes included cyclopropenium(+), cyclobutadiene, cyclopentadienyl(+), hexafluorobenzene, cycloheptatrienyl(+), cyclooctatetraene, octafluorooctatetraene, 6-radialene, pentalene, phenalenium(+), naphthalene and octafluoronaphthalene. The HOMO of a d(10) ML2 group (with b2 symmetry) interacting with the LUMO of the polyene was used as a model to explain the occurrence of minima and maxima on the potential energy surface. PMID:27559391
Franke, J.-H.; Kosov, D. S.
2015-01-28
We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.
Spin symmetry in the antinucleon spectrum.
Zhou, Shan-Gui; Meng, Jie; Ring, P
2003-12-31
We discuss spin and pseudospin symmetry in the spectrum of single nucleons and single antinucleons in a nucleus. As an example we use relativistic mean field theory to investigate single antinucleon spectra. We find a very well developed spin symmetry in single antineutron and single antiproton spectra. The dominant components of the wave functions of the spin doublet are almost identical. This spin symmetry in antiparticle spectra and the pseudospin symmetry in particle spectra have the same origin. However, it turns out that the spin symmetry in antinucleon spectra is much better developed than the pseudospin symmetry in normal nuclear single particle spectra. PMID:14754045
Charge symmetry at the partonic level
Londergan, J. T.; Peng, J. C.; Thomas, A. W.
2010-07-01
This review article discusses the experimental and theoretical status of partonic charge symmetry. It is shown how the partonic content of various structure functions gets redefined when the assumption of charge symmetry is relaxed. We review various theoretical and phenomenological models for charge symmetry violation in parton distribution functions. We summarize the current experimental upper limits on charge symmetry violation in parton distributions. A series of experiments are presented, which might reveal partonic charge symmetry violation, or alternatively might lower the current upper limits on parton charge symmetry violation.
Superdeformations and fermion dynamical symmetries
Wu, Cheng-Li . Dept. of Physics and Atmospheric Science Tennessee Univ., Knoxville, TN . Dept. of Physics and Astronomy Joint Inst. for Heavy Ion Research, Oak Ridge, TN )
1990-01-01
In this talk, I will present a link between nuclear collective motions and their underlying fermion dynamical symmetries. In particular, I will focus on the microscopic understanding of deformations. It is shown that the SU{sub 3} of the one major shell fermion dynamical symmetry model (FDSM) is responsible for the physics of low and high spins in normal deformation. For the recently observed phenomena of superdeformation, the physics of the problem dictates a generalization to a supershell structure (SFDSM), which also has an SU{sub 3} fermion dynamical symmetry. Many recently discovered feature of superdeformation are found to be inherent in such an SU{sub 3} symmetry. In both cases the dynamical Pauli effect plays a vital role. A particularly noteworthy discovery from this model is that the superdeformed ground band is not the usual unaligned band but the D-pair aligned (DPA) band, which sharply crosses the excited bands. The existence of such DPA band is a key point to understand many properties of superdeformation. Our studies also poses new experimental challenge. This is particularly interesting since there are now plans to build new and exciting {gamma}-ray detecting systems, like the GAMMASPHERE, which could provide answers to some of these challenges. 34 refs., 11 figs., 5 tabs.
ERIC Educational Resources Information Center
Brown, Laurie M.
This document is a monograph intended for advanced undergraduate students, or beginning graduate students, who have some knowledge of modern physics as well as classical physics, including the elementary quantum mechanical treatment of the hydrogen atom and angular momentum. The first chapter introduces symmetry and relates it to the mathematical…
Paper Models Illustrating Virus Symmetry.
ERIC Educational Resources Information Center
McCarthy, D. A.
1990-01-01
Instructions are given for constructing two models, one to illustrate the general principles of symmetry in T=1, T=3, and T=4 viruses, and the other to illustrate the disposition of protein subunits in the T=3 plant viruses and the picornaviruses. (Author/CW)
Entanglement renormalization and gauge symmetry
Tagliacozzo, L.; Vidal, G.
2011-03-15
A lattice gauge theory is described by a redundantly large vector space that is subject to local constraints and can be regarded as the low-energy limit of an extended lattice model with a local symmetry. We propose a numerical coarse-graining scheme to produce low-energy, effective descriptions of lattice models with a local symmetry such that the local symmetry is exactly preserved during coarse-graining. Our approach results in a variational ansatz for the ground state(s) and low-energy excitations of such models and, by extension, of lattice gauge theories. This ansatz incorporates the local symmetry in its structure and exploits it to obtain a significant reduction of computational costs. We test the approach in the context of a Z{sub 2} lattice gauge theory formulated as the low-energy theory of a specific regime of the toric code with a magnetic field, for lattices with up to 16x16 sites (16{sup 2}x2=512 spins) on a torus. We reproduce the well-known ground-state phase diagram of the model, consisting of a deconfined and spin-polarized phases separated by a continuous quantum phase transition, and obtain accurate estimates of energy gaps, ground-state fidelities, Wilson loops, and several other quantities.
Concomitant Ordering and Symmetry Lowering
ERIC Educational Resources Information Center
Boo, William O. J.; Mattern, Daniell L.
2008-01-01
Examples of concomitant ordering include magnetic ordering, Jahn-Teller cooperative ordering, electronic ordering, ionic ordering, and ordering of partially-filled sites. Concomitant ordering sets in when a crystal is cooled and always lowers the degree of symmetry of the crystal. Concomitant ordering concepts can also be productively applied to…
Turning Students into Symmetry Detectives
ERIC Educational Resources Information Center
Wilders, Richard; VanOyen, Lawrence
2011-01-01
Exploring mathematical symmetry is one way of increasing students' understanding of art. By asking students to search designs and become pattern detectives, teachers can potentially increase their appreciation of art while reinforcing their perception of the use of math in their day-to-day lives. This article shows teachers how they can interest…
From symmetries to number theory
Tempesta, P.
2009-05-15
It is shown that the finite-operator calculus provides a simple formalism useful for constructing symmetry-preserving discretizations of quantum-mechanical integrable models. A related algebraic approach can also be used to define a class of Appell polynomials and of L series.
Circular codes, symmetries and transformations.
Fimmel, Elena; Giannerini, Simone; Gonzalez, Diego Luis; Strüngmann, Lutz
2015-06-01
Circular codes, putative remnants of primeval comma-free codes, have gained considerable attention in the last years. In fact they represent a second kind of genetic code potentially involved in detecting and maintaining the normal reading frame in protein coding sequences. The discovering of an universal code across species suggested many theoretical and experimental questions. However, there is a key aspect that relates circular codes to symmetries and transformations that remains to a large extent unexplored. In this article we aim at addressing the issue by studying the symmetries and transformations that connect different circular codes. The main result is that the class of 216 C3 maximal self-complementary codes can be partitioned into 27 equivalence classes defined by a particular set of transformations. We show that such transformations can be put in a group theoretic framework with an intuitive geometric interpretation. More general mathematical results about symmetry transformations which are valid for any kind of circular codes are also presented. Our results pave the way to the study of the biological consequences of the mathematical structure behind circular codes and contribute to shed light on the evolutionary steps that led to the observed symmetries of present codes. PMID:25008961
Strong coupling electroweak symmetry breaking
Barklow, T.L.; Burdman, G.; Chivukula, R.S.
1997-04-01
The authors review models of electroweak symmetry breaking due to new strong interactions at the TeV energy scale and discuss the prospects for their experimental tests. They emphasize the direct observation of the new interactions through high-energy scattering of vector bosons. They also discuss indirect probes of the new interactions and exotic particles predicted by specific theoretical models.
Baryon and chiral symmetry breaking
Gorsky, A.; Krikun, A.
2014-07-23
We briefly review the generalized Skyrmion model for the baryon recently suggested by us. It takes into account the tower of vector and axial mesons as well as the chiral symmetry breaking. The generalized Skyrmion model provides the qualitative explanation of the Ioffe’s formula for the baryon mass.
Platonic Symmetry and Geometric Thinking
ERIC Educational Resources Information Center
Zsombor-Murray, Paul
2007-01-01
Cubic symmetry is used to build the other four Platonic solids and some formalism from classical geometry is introduced. Initially, the approach is via geometric construction, e.g., the "golden ratio" is necessary to construct an icosahedron with pentagonal faces. Then conventional elementary vector algebra is used to extract quantitative…
Quantitative Analysis of Face Symmetry.
Tamir, Abraham
2015-06-01
The major objective of this article was to report quantitatively the degree of human face symmetry for reported images taken from the Internet. From the original image of a certain person that appears in the center of each triplet, 2 symmetric combinations were constructed that are based on the left part of the image and its mirror image (left-left) and on the right part of the image and its mirror image (right-right). By applying a computer software that enables to determine length, surface area, and perimeter of any geometric shape, the following measurements were obtained for each triplet: face perimeter and area; distance between the pupils; mouth length; its perimeter and area; nose length and face length, usually below the ears; as well as the area and perimeter of the pupils. Then, for each of the above measurements, the value C, which characterizes the degree of symmetry of the real image with respect to the combinations right-right and left-left, was calculated. C appears on the right-hand side below each image. A high value of C indicates a low symmetry, and as the value is decreasing, the symmetry is increasing. The magnitude on the left relates to the pupils and compares the difference between the area and perimeter of the 2 pupils. The major conclusion arrived at here is that the human face is asymmetric to some degree; the degree of asymmetry is reported quantitatively under each portrait. PMID:26080172
Tunneling of obliquely incident waves through PT-symmetric epsilon-near-zero bilayers
NASA Astrophysics Data System (ADS)
Savoia, Silvio; Castaldi, Giuseppe; Galdi, Vincenzo; AlÃ¹, Andrea; Engheta, Nader
2014-02-01
We show that obliquely incident, transversely magnetic-polarized plane waves can be totally transmitted (with zero reflection) through epsilon-near-zero (ENZ) bilayers characterized by balanced loss and gain with parity-time (PT) symmetry. This tunneling phenomenon is mediated by the excitation of a surface wave localized at the interface separating the loss and gain regions. We determine the parameter configurations for which the phenomenon may occur and, in particular, the relationship between the incidence direction and the electrical thickness. We show that, below a critical threshold of gain and loss, there always exists a tunneling angle which, for moderately thick (wavelength-sized) structures, approaches a critical value dictated by the surface-wave phase-matching condition. We also investigate the unidirectional character of the tunneling phenomenon, as well as the possible onset of spontaneous symmetry breaking, typical of PT-symmetric systems. Our results constitute an interesting example of a PT-symmetry-induced tunneling phenomenon, and may open up intriguing venues in the applications of ENZ materials featuring loss and gain.
A Comprehensive Search for Stable Pt-Pd Nanoalloy Configurations and Their Use as Tunable Catalysts
Tan, Teck L.; Wang, Lin-Lin; Johnson, Duane D.; Bai, Kewu
2012-08-15
Using density-functional theory, we predict stable alloy configurations (ground states) for a 1 nm Pt–Pd cuboctahedral nanoparticle across the entire composition range and demonstrate their use as tunable alloy catalysts via hydrogen-adsorption studies. Unlike previous works, we use simulated annealing with a cluster expansion Hamiltonian to perform a rapid and comprehensive search that encompasses both high and low-symmetry configurations. The ground states show Pt(core)–Pd(shell) type configurations across all compositions but with specific Pd patterns. For catalysis studies at room temperatures, the ground states are more realistic structural models than the commonly assumed random alloy configurations. Using the ground states, we reveal that the hydrogen adsorption energy increases (decreases) monotonically with at. % Pt for the {111} hollow ({100} bridge) adsorption site. Such trends are useful for designing tunable Pd–Pt nanocatalysts for the hydrogen evolution reaction.
Transparency of the complex PT-symmetric potentials for coherent injection
NASA Astrophysics Data System (ADS)
Ahmed, Zafar; Nathan, Joseph Amal; Ghosh, Dona
2016-02-01
Two port s-matrix for a complex PT-symmetric potential may have uni-modular eigenvalues. If this happens for all energies, there occurs a perfect emission of waves at both ends. We call this phenomenon transparency which is distinctly different from coherent perfect absorption with or without lasing. Using the versatile PT-symmetric complex Scarf II (scattering) potential, we demonstrate analytically that the transparency can occur regardless of whether PT-symmetry is unbroken or broken or if there are only scattering states. In these three cases, for a given value of the strength of the real part, the strength of the imaginary part |V2 | of the potential lies in (0 ,Vα) , (Vα ,Vβ) and (0 ,Vβ) respectively. Several other numerically solved potentials also support our findings.
On PT-Symmetric Periodic Potential, Quark Confinement, and Other Impossible Pursuits
NASA Astrophysics Data System (ADS)
Christianto, V.; Smarandache, Florentin
2009-04-01
As we know, it has been quite common nowadays for particle physicists to think of six impossible things before breakfast, just like what their cosmology fellows used to do. In the present paper, we discuss a number of those impossible things, including PT-symmetric periodic potential, its link with condensed matter nuclear science, and possible neat link with Quark confinement theory. In recent years, the PT-symmetry and its related periodic potential have gained considerable interests among physicists. We begin with a review of some results from a preceding paper discussing derivation of PT-symmetric periodic potential from biquaternion Klein-Gordon equation and proceed further with the remaining issues. Further observation is of course recommended in order to refute or verify this proposition.
Characterization of NiPt, FePt, and NiFePt nanoparticles
NASA Astrophysics Data System (ADS)
Sutherland, Greg; Wood, Darren; Jackson, Amy; Warren, Andrew; Coffey, Kevin; Vanfleet, Richard
2012-10-01
Many metal alloys can form in chemically ordered structures, often resulting in significant changes in properties. The ordered structures are preferred at low temperatures and will go through an order-disorder phase transition at a critical temperature. The formation and stability of these ordered structures in alloy nanoparticles is not well understood but may give insight into the role size plays in phase transitions. To this end we are studying FePt, NiPt, and FeNiPt alloy nanoparticles. We will focus this presentation on the characterization of these nanoparticles in a Transmission Electron Microscope (TEM) for composition, size, and structure. These nanoparticles are made by co-sputtering the constituents and annealing at different temperatures in various gas mixtures. The nanoparticle samples are prepared for TEM viewing by wedge polishing. We find FePt to be ``well behaved'' meaning this alloy forms particles, retains the as deposited composition, and chemically orders as expected. However, the order-disorder temperature is too high for the desired further studies. NiPt, which has a lower order-disorder temperature, is not ``well behaved'' in that the nanoparticle compositions are not good matches to the as deposited conditions and no chemical ordering has been achieved even under conditions that should be sufficient based on bulk processing. We will discuss these results and possible implications.