Thermal rectifier from deformed carbon nanohorns

We study thermal rectification in single-walled carbon nanohorns (SWNHs) by using non-equilibrium molecular dynamics (MD) method. It is found that the horns with the bigger top angles show larger asymmetric heat transport due to the larger structural gradient distribution. This kind of gradient behavior can be further adjusted by applying external strain on the SWNHs. After being carefully elongated along the axial direction, the thermal rectification in the elongated SWNHs can become more obvious than that in undeformed ones. The maximum rectification efficiency of SWNHs is much bigger than that of carbon nanotube intramolecular junctions.Comment: 3 figure

Separation of suspended particles by arrays of obstacles in microfluidic devices

The stochastic transport of suspended particles through a periodic pattern of obstacles in microfluidic devices is investigated by means of the Fokker-Planck equation. Asymmetric arrays of obstacles have been shown to induce the continuous separation of DNA molecules of different length. The analysis presented here of the asymptotic distribution of particles in a unit cell of these systems shows that separation is only possible in the presence of a driving force with a non-vanishing normal component at the surface of the solid obstacles. In addition, vector separation, in which different species move, in average, in different directions within the device, is driven by differences on the force acting on the various particles and not by differences in the diffusion coefficient. Monte-Carlo simulations performed for different particles and force fields agree with the numerical solutions of the Fokker-Planck equation in the periodic system

Study of axial strain induced torsion of single wall carbon nanotubes by 2D continuum anharmonic anisotropic elastic model

Recent molecular dynamic simulations have found chiral single wall carbon nanotubes (SWNTs) twist during stretching, which is similar to the motion of a screw. Obviously this phenomenon, as a type of curvature-chirality effect, can not be explained by usual isotropic elastic theory of SWNT. More interestingly, with larger axial strains (before buckling), the axial strain induced torsion (a-SIT) shows asymmetric behaviors for axial tensile and compressing strains, which suggests anharmonic elasticity of SWNTs plays an important role in real a-SIT responses. In order to study the a-SIT of chiral SWNTs with actual sizes, and avoid possible deviations of computer simulation results due to the finite-size effect, we propose a 2D analytical continuum model which can be used to describe the the SWNTs of arbitrary chiralities, curvatures, and lengths, with the concerning of anisotropic and anharmonic elasticity of SWNTs. This elastic energy of present model comes from the continuum limit of lattice energy based on Second Generation Reactive Empirical Bond Order potential (REBO-II), a well-established empirical potential for solid carbons. Our model has no adjustable parameters, except for those presented in REBO-II, and all the coefficients in the model can be calculated analytically. Using our method, we obtain a-SIT responses of chiral SWNTs with arbitrary radius, chiralities and lengthes. Our results are in reasonable agreement with recent molecular dynamic simulations. [Liang {\it et. al}, Phys. Rev. Lett, ${\bf 96}$, 165501 (2006).] Our approach can also be used to calculate other curvature-chirality dependent anharmonic mechanic responses of SWNTs.Comment: 14 pages, 2 figure

A Mathematical Model for Estimating Biological Damage Caused by Radiation

We propose a mathematical model for estimating biological damage caused by low-dose irradiation. We understand that the Linear Non Threshold (LNT) hypothesis is realized only in the case of no recovery effects. In order to treat the realistic living objects, our model takes into account various types of recovery as well as proliferation mechanism, which may change the resultant damage, especially for the case of lower dose rate irradiation. It turns out that the lower the radiation dose rate, the safer the irradiated system of living object (which is called symbolically "tissue" hereafter) can have chances to survive, which can reproduce the so-called dose and dose-rate effectiveness factor (DDREF).Comment: 22 pages, 6 Figs, accepted in Journal of the Physical Society of Japa

Private-Public Sector Cooperation in Combating Cybercrime: in Search of a Model

Turnover taxes are generally considered to be risk-free from the tax competition point of view, forthey are levied exclusively at the place of consumption. The Value-Added Tax (VAT) imposed by all EuropeanUnion (EU) member states, though, has become a source of distortion in the trans-Atlantic trade: non-EUsuppliers of electronic services were not required to collect the VAT, while their EU competitors were. The levelplaying field in EU’s foreign trade in electronic services was restored in 2002 by the so-called e-VAT Directivethat obliged non-EU providers of electronic services to charge the VAT at the rate of the member state theirconsumer resides in. This paper argues that besides being largely unenforceable, the Directive has createdanother misbalance in the infra-EU electronic commerce. It is being demonstrated that since the Directive is notapplicable to EU vendors, non-EU businesses can and do circumvent it by establishing daughter companies inEU jurisdictions with the lowest VAT rates and thus spur the infra-EU tax competition