Elastic Properties of Carbon Nanotubes and Nanoropes

Elastic properties of carbon nanotubes and nanoropes are investigated using an empirical force-constant model. For single and multi-wall nanotubes the elastic moduli are shown to be insensitive to details of the structure such as the helicity, the tube radius and the number of layers. The tensile Young's modulus and the torsion shear modulus calculated are comparable to that of the diamond, while the the bulk modulus is smaller. Nanoropes composed of single-wall nanotubes possess the ideal elastic properties of high tensile elastic modulus, flexible, and light weight.Comment: 10 page

Phenomenological Analysis of pppp and pˉp\bar{p}p Elastic Scattering Data in the Impact Parameter Space

We use an almost model-independent analytical parameterization for $pp$ and $\bar{p}p$ elastic scattering data to analyze the eikonal, profile, and inelastic overlap functions in the impact parameter space. Error propagation in the fit parameters allows estimations of uncertainty regions, improving the geometrical description of the hadron-hadron interaction. Several predictions are shown and, in particular, the prediction for $pp$ inelastic overlap function at $\sqrt{s}=14$ TeV shows the saturation of the Froissart-Martin bound at LHC energies.Comment: 15 pages, 16 figure

Deviation of light curves of gamma-ray burst pulses from standard forms due to the curvature effect of spherical fireballs or uniform jets

As revealed previously, under the assumption that some pulses of gamma-ray bursts are produced by shocks in spherical fireballs or uniform jets of large opening angles, there exists a standard decay form of the profile of pulses arising from very narrow or suddenly dimming local (or intrinsic) pulses due to the relativistic curvature effect (the Doppler effect over the spherical shell surface). Profiles of pulses arising from other local pulses were previously found to possess a reverse S-feature deviation from the standard decay form. We show in this paper that, in addition to the standard decay form shown in Qin et al. (2004), there exists a marginal decay curve associated with a local $\delta$ function pulse with a mono-color radiation. We employ the sample of Kocevski et al. (2003) to check this prediction and find that the phenomenon of the reverse S-feature is common, when compared with both the standard decay form and the marginal decay curve. We accordingly propose to take the marginal decay curve (whose function is simple) as a criteria to check if an observed pulse could be taken as a candidate suffered from the curvature effect. We introduce two quantities $A_1$ and $A_2$ to describe the mentioned deviations within and beyond the $FWHM$ position of the decay phase, respectively. The values of $A_1$ and $A_2$ of pulses of the sample are calculated, and the result suggests that for most of these pulses their corresponding local pulses might contain a long decay time relative to the time scale of the curvature effect.Comment: 24 pages, 7 figures, 1 table accepted for publication in MNRA

Methods of calculation of a friction coefficient: Application to the nanotubes

In this work we develop theoretical and numerical methods of calculation of a dynamic friction coefficient. The theoretical method is based on an adiabatic approximation which allows us to express the dynamic friction coefficient in terms of the time integral of the autocorrelation function of the force between both sliding objects. The motion of the objects and the autocorrelation function can be numerically calculated by molecular-dynamics simulations. We have successfully applied these methods to the evaluation of the dynamic friction coefficient of the relative motion of two concentric carbon nanotubes. The dynamic friction coefficient is shown to increase with the temperature.Comment: 4 pages, 6 figure

PT-symmetric sine-Gordon breathers

In this work, we explore a prototypical example of a genuine continuum breather (i.e., not a standing wave) and the conditions under which it can persist in a $\mathcal{P T}$-symmetric medium. As our model of interest, we will explore the sine-Gordon equation in the presence of a $\mathcal{P T}$- symmetric perturbation. Our main finding is that the breather of the sine-Gordon model will only persist at the interface between gain and loss that $\mathcal{P T}$-symmetry imposes but will not be preserved if centered at the lossy or at the gain side. The latter dynamics is found to be interesting in its own right giving rise to kink-antikink pairs on the gain side and complete decay of the breather on the lossy side. Lastly, the stability of the breathers centered at the interface is studied. As may be anticipated on the basis of their "delicate" existence properties such breathers are found to be destabilized through a Hopf bifurcation in the corresponding Floquet analysis

Triaxiality and shape coexistence in Germanium isotopes

The ground-state deformations of the Ge isotopes are investigated in the framework of Gogny-Hartree-Fock-Bogoliubov (HFB) and Skyrme Hartree-Fock plus pairing in the BCS approximation. Five different Skyrme parametrizations are used to explore the influence of different effective masses and spin-orbit models. There is generally good agreement for binding energies and deformations (total quadrupole moment, triaxiality) with experimental data where available (i.e., in the valley of stability). All calculations agree in predicting a strong tendency for triaxial shapes in the Ge isotopes with only a few exceptions due to neutron (sub-)shell closures. The frequent occurrence of energetically very close shape isomers indicates that the underlying deformation energy landscape is very soft. The general triaxial softness of the Ge isotopes is demonstrated in the fully triaxial potential energy surface. The differences between the forces play an increasing role with increasing neutron number. This concerns particularly the influence of the spin-orbit model, which has a visible effect on the trend of binding energies towards the drip line. Different effective mass plays an important role in predicting the quadrupole and triaxial deformations. The pairing strength only weakly affects binding energies and total quadrupole deformations, but considerably influences triaxiality.Comment: 9 page

A simple entanglement measure for multipartite pure states

A simple entanglement measure for multipartite pure states is formulated based on the partial entropy of a series of reduced density matrices. Use of the proposed new measure to distinguish disentangled, partially entangled, and maximally entangled multipartite pure states is illustrated.Comment: 8 pages LaTe

The open string pair-production rate enhancement by a magnetic flux

We extend the amplitude calculations of \cite{Lu:2009yx} to exhaust the remaining cases for which one set of D$_p$ branes carrying a flux (electric or magnetic) is placed parallel at separation to the other set carrying also a flux but with the two fluxes sharing at most one common field-strength index. We then find that the basic structure of amplitudes remains the same when the two fluxes share at least one common index but it is more general when the two fluxes share no common index. We discuss various properties of the amplitudes such as the large separation limit, the onset of various instabilities and the open string pair production. In particular, when one flux is electric and weak and the other is magnetic and fixed, we find that the open string pair production rate is greatly enhanced by the presence of this magnetic flux when the two fluxes share no common field-strength index and this rate becomes significant when the separation is on the order of string scale.Comment: 33 pages, no figures, a few points refined to the published version JHEP09(2009)09