Number Of Kinks Research Articles

Counterion-Mediated Attraction and Kinks on Loops of Semiflexible Polyelectrolyte Bundles

The formation of kinks in a loop of bundled polyelectrolyte filaments is analyzed in terms of the thermal fluctuations of charge density due to polyvalent counterions adsorbed on the polyelectrolyte filaments. It is found that the counterion-mediated attraction energy of filaments depends on their bending. By consideration of curvature elasticity energy and counterion-mediated attraction between polyelectrolyte filaments, the characteristic width of the kink and the number of kinks per loop is found to be in reasonable agreement with existing experimental data for rings of bundled actin filaments.

A study on 170 MeV Au13+ irradiated nanostructured metal oxide (Fe2O3 and CuO) thin films for PEC applications

One hundred and seventy MeV Au13+ irradiation induced modification in photoelectrochemical (PEC) and structural properties of nanostructured 2%Cr–Fe2O3 and CuO thin films has been investigated. The X-ray diffractogram of both oxides indicated diffused nature of peaks with the appearance of crystalline peaks, indicative of partial amorphization taking place at higher fluence i.e. 1013ionscm−2. Upon irradiation, the band gap energy was found to decrease marginally. The irradiated 2%Cr–Fe2O3 samples (fluence 1012ionscm−2) used as working electrode in the PEC cell showed enhanced photocurrent generation. A decrease in photocurrent generation was recorded in case of irradiated 2%Cr–Fe2O3/CuO at higher fluence i.e. 1013ionscm−2 and irradiated CuO sample at fluence 1012ionscm−2, which may be attributed to the creation of greater number of kink sites/dislocations, that are probably acting as recombination centers for photogenerated electrons.

Degree of mapping for general relativistic kinks

The Finkelstein-Misner metrical kinks of general relativity are homotopically nontrivial light cone configurations that can occur on space-time hypersurfaces. The number of kinks corresponds to the winding number of a timelike vector field that that is determined from the metric. This paper uses the usual Euclidean integral formula for degree of mapping as a starting point and so produces a covariant formula that call be applied to counting general relativistic kinks in any dimension. The kink number is calculated for some simple-to-visualize examples in 2 + 1 dimensions. These include hypersurfaces of differing topologies and so have relevance to mechanisms of topology change in semi-classical theories of quantum gravity.

Shortest multiple disconnected path for the analysis of entanglements in two- and three-dimensional polymeric systems

We present an algorithm which returns a shortest path and related number of entanglements for a given configuration of a polymeric system in 2 or 3 dimensions. Rubinstein and Helfand, and later Everaers et al. introduced a concept to extract primitive paths for dense polymeric melts made of linear chains (a multiple disconnected multibead 'path'), where each primitive path is defined as a path connecting the (space-fixed) ends of a polymer under the constraint of non-interpenetration (excluded volume) between primitive paths of different chains, such that the multiple disconnected path fulfills a minimization criterion. The present algorithm uses geometrical operations and provides a-model independent-efficient approximate solution to this challenging problem. Primitive paths are treated as 'infinitely' thin (we further allow for finite thickness to model excluded volume), and tensionless lines rather than multibead chains, excluded volume is taken into account without a force law. The present implementation allows to construct a shortest multiple disconnected path (SP) for 2D systems (polymeric chain within spherical obstacles) and an optimal SP for 3D systems (collection of polymeric chains). The number of entanglements is then simply obtained from the SP as either the number of interior kinks, or from the average length of a line segment. Further, information about structure and potentially also the dynamics of entanglements is immediately available from the SP. We apply the method to study the 'concentration' dependence of the degree of entanglement in phantom chain systems.

Growth of InAs/InP(0 0 1) nanostructures: The transition from quantum wires to quantum dots

The evolution of InAs nanostructures grown by solid source molecular beam epitaxy on InP(0 0 1) substrates has been studied by atomic force microscopy (AFM), with specific emphasis on the effects of the incident V:III flux ratio. Wire structures oriented along 〈 1 ¯ 1 0 〉 are generally formed at moderate V:III flux ratios (∼10:1). AFM images show that the wires are generally kinked with small three-dimensional (3D) islands appearing at the kinks. Higher V:III ratios (>100:1) lead to an increase in the number of kinks and the formation of much larger 3D features. By contrast, low V:III ratios (∼2:1) favour the formation of small 3D islands (quantum dots) with densities of ∼5×10 10 cm −2. The results indicate that it is possible to produce arrays of InAs/InP quantum wires or quantum dots through careful control of the growth conditions.

Classification of unit-vector fields in convex polyhedra with tangent boundary conditions

A unit-vector field n on a convex three-dimensional polyhedron P is tangent if, on the faces of P, n is tangent to the faces. A homotopy classification of tangent unit-vector fields continuous away from the vertices of P is given. The classification is determined by certain invariants, namely edge orientations (values of n on the edges of P), kink numbers (relative winding numbers of n between edges on the faces of P), and wrapping numbers (relative degrees of n on surfaces separating the vertices of P), which are subject to certain sum rules. Another invariant, the trapped area, is expressed in terms of these. One motivation for this study comes from liquid crystal physics; tangent unit-vector fields describe the orientation of liquid crystals in certain polyhedral cells.

A study on 170 MeV Au 13+ irradiation induced modifications in structural and photoelectrochemical behavior of nanostructured CuO thin films

The effect of 170 MeV Au 13+ irradiation on photoelectrochemical (PEC) and structural properties of CuO thin films has been investigated. The X-ray diffractograms of post-irradiated CuO thin films showed diffused nature towards higher theta value with the appearance of crystalline peaks, indicative of some randomization taking place at higher fluence, i.e. 10 13 ions cm −2. While, upon irradiation, the size of particles/grains decreased, the band gap energy also marginally shifted. ERDA analysis indicated no change in stoichiometry of thin films even at higher fluence. The observed decrease in photoelectrochemical response, upon irradiation, has been attributed to the creation of greater number of kink sites/dislocations, which seemingly act as recombination centers for photogenerated charge carriers.

On Some Peculiar Aspects of Axial Motions of Closed Loops of String in the Presence of a Singular Supply of Momentum

We consider the dynamics of a closed loop of inextensible string which is undergoing an axial motion. At each instant, one material point of the string is in contact with a singular supply of linear momentum (also known as an external constraint). Several peculiar features of this problem which have not been previously discussed are presented. These include the possible presence of an arbitrary number of kinks, the vanishing nature of the singular supply of momentum, and the critical nature of the tension in the string. When the linear momentum is supplied by a mass-spring-dashpot system, we are also able to establish an exact expression for the frequency of the resulting vibrations, prove that dissipation cannot be present, show that these vibrations only occur for discrete speeds of axial motion, and establish that Coulomb friction is absent.

Effect of load type on failure mechanisms of spruce in compression parallel to grain

Failure mechanisms of small clear specimens (6×6×24 mm) of air-dried black spruce (Picea mariana) under parallel-to-grain compression were investigated by polarised-light microscopy. Fatigue load was used with a peak stress level of 90% static strength, a load frequency of 0.5 Hz, and a square waveform with a duty ratio of 0.50. Matched ‘pure’ creep and static load tests were carried out. Damage was quantified in terms of the permanent microstructural changes (kinks) in tracheid walls. In static load tests, kinks develop quickly with any increase in stress beyond the limit of proportionality. In creep tests, damage develops mainly from kinks formed during the initial load application. In fatigue tests, damage develops both from kinks formed during the initial load cycle, and kinks formed during subsequent cycles. The number of kinks exhibits a strong relationship with relative cyclic creep or relative creep.

Preparation of the atomically straight step-edge Si (111) substrates as templates for nanostructure formation

ABSTRACTWe report on the experimental discovery that the distribution of kinks along steps on vicinal Si(111) surfaces depends on the direction of the dc current passed along the steps for resistive annealing. The as-cleaned Si(111) surface miscut ∼1° towards [112] has a small (<3°) unavoidable azimuthal deviation, which produces a number of kinks along the step-edges. When the azimuthal misorientation is from [112] towards [110] [110], dc current flowing in the direction [110] [110] climbing up the kinks straightens the step-edges as opposed to the current flowing in the opposite [110] [110]direction. During annealing around 800°C, the dc current in the direction climbing up the kinks straightens the steps. The up-climbing current direction transports and concentrates the kinks in a region outside the template area, leaving a kink-free atomic step-edge region as an ideal template for a variety of nanostructure formations. The straight step edges produced in this manner have uniform atomic configuration known as U(2, 0).

Collective rotational tunneling of methyl groups and quantum solitons in 4-methylpyridine: Neutron scattering studies of single crystals

The structure of the 4-methylpyridine crystal has been determined at 10 and 260 K with the single-crystal neutron-diffraction technique. The space-group symmetries are ${I4}_{1}/a$ and ${I4}_{1}/amd,$ respectively. In both cases, there are eight molecular entities in the unit cell. The rotational axes of the methyl groups are aligned along the c axis. The shortest intermolecular distances occur between face-to-face methyl groups. The next shortest distances correspond to infinite chains of rotors parallel to the orthogonal axes a and b. The angular probability densities of the methyl groups are clear evidence of orientational disorder. The incoherent scattering function ${S(Q}_{a}{,Q}_{b},\ensuremath{\omega})$ has been measured with the inelastic neutron scattering technique at 1.7 K. The energy-transfer ranges, $\ensuremath{\Elzxh}\ensuremath{\omega}=\ifmmode\pm\else\textpm\fi{}(500\ifmmode\pm\else\textpm\fi{}60)\ensuremath{\mu}\mathrm{eV},$ encompass transitions due to rotational tunneling. The anisotropy in $\mathbf{Q}$ is distinctive of dynamics in one dimension. These are represented with the quantum sine-Gordon equation that is an approximation to the Hamiltonian for an infinite chain of coupled rotors. Spots of intensity observed for neutron-energy loss at $|{Q}_{a}|$ or $|{Q}_{b}|\ensuremath{\approx}1.55{\mathrm{\AA{}}}^{\ensuremath{-}1}$ are distinctive of stationary states for breathers. Weaker peaks at $|{Q}_{a}|$ or $|{Q}_{b}|\ensuremath{\approx}1.0{\mathrm{\AA{}}}^{\ensuremath{-}1}$ reveal collective tunneling. This is a thermally activated process arising from rather heavy pseudoparticles composed of large numbers (from 22 to 25) of kinks or antikinks. Quantization of the kinetic momentum arises from the chain discreteness and from conservation of the angular momentum. Traveling states are stationary when the kinetic energy is within the tunneling energy band. In the ground state, the chain dynamics are represented with a single collective angular coordinate. The incoherent scattering function for neutron-energy-gain reveals bound excited states with lifetimes of several days.

Semiclassical theory for transmission through open billiards: convergence towards quantum transport.

We present a semiclassical theory for transmission through open quantum billiards which converges towards quantum transport. The transmission amplitude can be expressed as a sum over all classical paths and pseudopaths which consist of classical path segments joined by "kinks," i.e., diffractive scattering at lead mouths. For a rectangular billiard we show numerically that the sum over all such paths with a given number of kinks K converges to the quantum transmission amplitude as K--> infinity. Unitarity of the semiclassical theory is restored as K approaches infinity. Moreover, we find excellent agreement with the quantum path-length power spectrum up to very long path length.

BPS kinks in the Gross-Neveu model

We find the exact spectrum and degeneracies for the Gross-Neveu model in two dimensions. This model describes N interacting Majorana fermions; it is asymptotically free, and has dynamical mass generation and spontaneous chiral symmetry breaking. We show here that the spectrum contains 2^{N/2} kinks for any $N$. The unusual \sqrt{2} in the number of kinks for odd $N$ comes from restrictions on the allowed multi-kink states. These kinks are the BPS states for a generalized supersymmetry where the conserved current is of dimension N/2; the N=3 case is the {\cal N}=1 supersymmetric sine-Gordon model, for which the spectrum consists of 2\sqrt{2} kinks. We find the exact S matrix for these kinks, and the exact free energy for the model.

Gödel Kink Spacetime

A 2+1 version of a rotating perfect fluid spacetime of Godel type is examined to see whether it has a Finkelstein-Misner kink. It is shown, by three different methods, that the kink number is one.

Modelling of HREM and nanodiffraction for dislocation kinks and corereconstruction

The ability to directly image individual dislocation kinks (Kolar H et al 1996Phys. Rev. Lett. 77 4031) opens up many possibilities for the study of kink dynamicsby in situ TEM. Unfortunately, this technique is limited by surfaceroughness. For ceramics, however, high temperature annealing has been found toproduce inert and atomically smooth surfaces that even survive ambientpressures (Susnitzky D 1992 J. Am. Ceram. Soc. 75 2463). We haveprepared such samples of 3C-SiC, in order to image kinks by the forbiddenreflections method. Using multislice simulations for 30 and 90° partialdislocations in Si we show that not only the number of kinks along thedislocation core can be determined, but also their structure assuming anaberration corrected TEM.We also show how the recently proposed double period reconstruction along the90° partial dislocation in Si can easily be verified experimentallyusing convergent beam electron diffraction.

Observation of crystal growth of lysozyme protein crystals by atomic force microscopy

Surface structure and the propagation of elementary growth layers over the (010) face of orthorhombic lysozyme crystal is examined at a molecular-scale resolution by the method of atomic force microscopy (AFM). The steps have a small number of kinks spaced by about 150 growth units. The step motion occurs via successive deposition of rows of growth units. The data obtained are discussed in terms of the model of one-dimensional nucleation.

Thin films of Co on Pt(111): Strain relaxation and growth

The growth, structure and morphology of thin Co layers with a thickness ranging from 1 to 15 monolayers deposited at room temperature on Pt(111) have been studied by the use of scanning tunneling microscopy. We demonstrate that the first Co layer grows preferably in the Pt fcc lattice sites, with a high density of defects due to the lattice mismatch. The second Co layer is found to exhibit a moir\'e structure, with the Co in-plane lattice distance close to that of bulk Co. The growth of thin Co films is observed to be mostly in terms of flat layers (two dimensional) up to a Co coverage of about 3.5 ML. At higher coverages, we find that the Co grows in (three dimensional) islands and we show that the growth is characterized by a mainly twinned fcc-like stacking. We argue that the reason for the two dimensional growth mode at lower Co coverages is due to the strained interface between the Co overlayers and the Pt(111) surface resulting in a large number of kinks and corners which facilitate interlayer diffusion. For higher coverage such sites become less common, due to the decreasing influence of the strained interface, resulting in no interlayer diffusion leading to a three dimensional growth mode. The implications by these observations on the magnetic properties of the Co/Pt(111) interface system are discussed.

The ultrasonic Bordoni peak in copper crystals and the kink picture

The ultrasonic logarithmic decrement and modulus defect in high purity copper crystals was measured at 10, 30 and 50 MHz in the temperature interval 5-373 K. The samples were deformed at room temperature in the 3-20% range along the 111 crystallographic direction. The experimental data were fitted over the whole interval of temperatures, assuming the contribution of two kink mechanisms: (i) relaxation by kink pair formation with diffusion in the dislocation line and (ii) overdamped resonance of the kink chain with a temperature dependent number of kinks in the dislocation lines. With this procedure both primary and secondary properties of the high frequency Bordoni peak could be satisfactorily explained. Numerical data are reported for peak parameters and for the kink diffusion coefficient.

Stress intensity factors for curved and kinked cracks in plane extension

A singular integral equation containing the crack opening displacement (COD) is developed for solving plane elasticity problems. The crack may contain any number of kinks at different intervals and orientations, such as a saw-tooth shape. Cracks in the form of a sine wave can also be treated. The crack tip stress intensity factors are evaluated for a variety of crack shapes and the results are displayed graphically. The distance between the crack tips is found to be a dominant factor on the crack tip stress intensity while the angle between the tangent to the crack tip and load direction determines the proportion of Mode I and II stress intensity factors.

C6‐oxidized cellulose: Ion interactions with mono‐ and divalent cations

The conformational behavior of different molecular weight fractions of a synthetic C6-oxidized derivative of cellulose were investigated by means of capillary viscometry, CD, and microcalorimetric measurements. Experiments were carried out in the presence of either monovalent or divalent counterions. The experimental data indicated that C6-oxidized cellulose can assume an ordered extended conformation at low ionic strength, induced by the intrachain repulsions of negative charges. This conformation was suggested to be very similar to the fully extended structure of cellulose. In addition to this, upon increasing the ionic strength, a conformational transition of the order-to-disorder type occurred. In fact, the screening of the electrostatic repulsions introduced a number of conformational kinks into the cellulosic backbone, which enabled the polymer to assume a more coiled conformation hence producing less viscous aqueous solutions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 157–163, 1998