O-11. Transformation of low-Energy High-Current Electron Beam in the Plasma Channel

Le Huy Dung, T.V. Koval

At the moment low-energy (10-30 keV) high-current (up to 20 kA) electron beams are very important and widely used in practice, such as for surface treatment of materials. Typically, the pulse duration of such beams are a few microseconds, the energy density of the beams is sufficient (up to 20J/cm2) for the pulsed surface melting of any materials, including refractory metals. As we know, the beam is easily created with circular shape, but the metal surface is diverse. Thus, the problem of the transformation of a circular high-current electron beam into other (particularly rectangular ) one arises. In this paper, we will investigate the electron beam transformation in the plasma channel under the influence of :bus-bars geometry current neutralization an external magnetic field and its gradient. Numerical simulation is carried out in MATLAB environment with the method of large particles. The results of theoretical investigations are compared with experiments.

Hoang Van Hung, Tran Trieu Phu, Le Van Hoang

By using the split operator FFT method we construct a exact numerical method for calculating wave-functions of a two dimensional molecular interacting with ultra-short laser pulses. From the calculated wave-functions we calculate high-order harmonic spectra. The concrete results obtained for 2D molecule H2+ are suitable with the previous calculations. Using the obtained HHG spectra of H2+ we analyze the interference effect of electron within the two-emitting-center model and apply them for extracting the information of inter-atomic distance with high precision down to 1%.

Hoang Do Ngoc Tram, Le Quy Giang, Nguyen Thi Man, Pham Dang Lan, Le Van Hoang

By using the Laplace transformation, we show that the FK operator method can be applied successfully to solving the Schrodinger equation of a negatively charged exciton in two-dimensional semiconductors to obtain exact numerical solutions. Especially, the algebraic form of the wave-functions built as a basis set in this work would be useful for further applications to other problems of two-dimensional atomic systems.

D. K. Phung(1,2), F. Rotermund(2), Kihong Kim(2) and H. Lim(3)

We study optical diode properties of one-dimensional photonic crystals made of alternating linear and nonlinear dielectric layers theoretically. More specifically, we consider a photonic crystal consisting of twelve periods of polydiacetylene and titanium dioxide bilayers, where polydiacetylene layers are assumed to have Kerr-type focusing nonlinearity. Using the invariant imbedding method developed by us recently, we calculated the rectify coefficient associated with the transmittances for visible electromagnetic wave incident from the left and right medium. We find that at the frequencies close the higher band edge and in the optical bistability region, the rectify coefficient is larger more than 10 when the intensity of the incident light is about 15MW/cm$^2$ even the total thickness of the medium is about 2$\mu$m. We also calculated the electric field distribution inside the medium and find that the electric field is strongly enhanced when the wave incident from the direction corresponding to a large transmission. We expect this phenomenon can be applied in designing optical diode devices

Vu Ngoc Tuoc(1), Le Thi Hong Lien(1), Luyen Thi San(1) and Tran Doan Huan(1,2)

We report a Density Functional Based Tight Binding (DFTB) study on the structural and electronics properties of multi-layered (ML) wall TiO2 Nanotube, created from some possible rolling-up nanotube's types of rutile and anatase (001) and (110) nanosheets. Strain energy is found to be negative in between the whole nanotube's diameter range of 30-150 Angstrom. We also examine the dependence of interface stress and formation energy on nanotube lateral size. The tensile test have been applied and the Young’s modulus of the tubes along the axial growth direction have been estimated showing the diameter's dependences of their mechanical properties. The electronic properties of tubes (e.g., bandstructure, gap, density of state ...) also exhibit diameter-dependent behavior.

Tran Van Nam, Nguyen Thuy Trang and Bach Thanh Cong

Recently, there has been a renewed interest in TiO2 anatase as charge transfer layer in dye-sensitized solar cells (DSSC). Some experiments suggested that metallic substitution can increase energy transformation efficiency of dye-sensitized solar cell. In this work, electronic structure of Mg-doped TiO2 anatase was calculated on the base of density functional theory (DFT). The results showed that the substitution of ions Mg2+ for ions Ti4+ induced a small lattice expansion ~ 0.8%. However noticeable negative shift of the Fermi energy ~ -0.812 eV and edge of conduction band ~ -1.16 eV as well as the enlargement of band gap ~ 0.04 eV were observed. The effects of such doping-induced changes on energy transformation efficiency were also discussed.

Dao Tien Khoa and Doan Thi Loan

The Hartree-Fock method with different choices of the effective nucleon-nucleon interaction has been recently used to study the equation of state of cold nuclear matter. In this work, the similar Hartree-Fock study is also done within the Thomas-Fermi model using CDM3Yn interaction to find out the equation of state of nuclear matter at finite temperature. The behaviors of energy per particle, free energy, entropy, and pressure are compared with cold nuclear matter. It is found that temperature effects are small but can be significant in studying hot β stable matter matter which is the main component of neutron star's core.

T. V. Nhan Hao(1, 2, 3), P. Quentin(2, 3), L. Bonneau(2, 3)

The restoration of the left-right symmetry has been performed in the framework of the Highly Truncated Diagonalization Approach (HTDA) suited to treat correlations in an explicitly particle-number conserving microscopic approach. To do so we have performed parity-projected calculations within a PAV (projection after variation) scheme making use of a generalized Wick's theorem due to L$\ddot{\mathrm{o}}$wdin. It has been implemented within a simple model approach using the Skyrme SkM$^*$ effective force for the particle-hole channel and a density-independent delta force for the residual interaction. It has been applied in the region of the second fission barrier of heavy nuclei considering first the example of the $^{240}$Pu compound nucleus. As a result [1,2], we have shown that the $K^{\pi} = 0^+$ fission isomeric state is statically unstable against intrinsic parity breaking modes while the projection does not affect the energy at the top of the intrinsic second fission barrier. Altogether, this leads to an increase of the height of the second fission barrier by about 350 keV affecting thus significantly eg the fission decay lifetime of the considered fission isomer.

Trinh Xuan Hoang(1), Antonio Trovato(2), Flavio Seno(2), Jayanth R. Banavar(3), Amos Maritan(2)

Repeat proteins are present in 14% of known protein amino acid sequences with specific functions generally associated to higher organisms. Frequently, repeat proteins do not have unique, stable 3D structures unlike a majority of globular proteins. Tandem repeats of amino acids are quite often found in proteins associated with neuro-degenerative diseases such as Alzheimer's, Parkinson's and Creutzfeldt-Jacob's. A recent insight shows that the level of sequence conservation in tandem repeats correlates with their propensities to be intrinsically disordered. In this study, we employ a coarse-grained model of protein with a two-letter amino acid alphabet, hydrophobic (H) and polar (P), to examine the sequence-structure relationship in the realm of repeated sequences. We found that unlike random sequences, a fraction of repeated sequences comprises a class of distinguishable bad folders. Our results indicate that Nature may have utilized this class of repeated sequences to design proteins that are intrinsically disordered at physiological temperature.

Ho Le Tuan Anh, Vu Thi Giang and Trinh Xuan Hoang

We investigate the ground state phase diagram of a thick polymer. Here, the polymer is modeled as a chain of spherical beads positioned along the axis of a tube of finite thickness. The tube self-avoidance is imposed by using a three-body potential. Addiotionally, the polymer is subject to a self-attraction given by a pairwise potential. We calculate the ground state phase diagram as function of the tube radius, $\Delta$, and the range of attractive interaction, $R_{int}$. Both Wang-Landau sampling and simulated annealing methods are utilized in this work. We found that in the vinicity of the line where $R_{int}=2\Delta$, there are separated regions in the phase diagram corresponding to a single helix, a double helix and a planar sheet. Interestingly, there regions are almost unchanged with inreasing chain length. The phase diagram could be used to elucidate the ubiquitous folding motifs of proteins and DNA.

Le Van Qui(1), Pham Cong Huy(2), and Nguyen Van Lien(1,3)

We study the energy band structure and the transport properties of magnetic graphene superlattices with delta-function magnetic barriers and zero average magnetic field (Magnetic Kronig-Penny-type graphene superlattice - MKPGS). Using the T-matrix approach we have exactly derived the dispersion relation for Dirac fermions in MKPGSs regardless of the magnetic field magnitude as well as the ratio between the well width and the barrier width in the periodic vector potential profile. The obtained relation shows an emergence of infinite number of Dirac-like points at finite energy while the original Dirac point is still located at the same place as that for pristine graphene. Importantly, near the original Dirac point the dispersion and therefore the group velocity renormalization seem to be isotropic that is in sharp contrast to the well-known case of electrostatic KPGSs. Contrarily, the dispersion and therefore the group velocity renormalization near all the finite energy Dirac-like points are strongly anisotropic. The degree of anisotropy is determined as a function of superlattice parameters. An asymmetry in width between the well and the barriers in the periodic vector potential induces a shift of the original Dirac point in the zero-energy plane, keeping the group velocity renormalization isotropic. To find the manifestation of the Dirac fermions behavior recognized we calculated the transmission probability and the conductivity and analyzed obtained results with respect to structure parameters.

T. Nguyet Nguyen(1), V. Thanh Ngo(2) and N. A. Viet(2)

As well know the daily rise and fall in sea level, so-called the tide, caused by gravity of the Moon and Sun. We study the forecasting of the daily sea level of tide at Hon Dau coast (Hai Phong city) with a prediction time of 24h. A classification of the historical sea level data is performed by Kohonena’s self-organizing map (SOM) technique. The actual forecast is obtained using a two layered feed forward neural network. For training stage, we use the historical tide data from 2000 to 2010 with including the dates of lunar calendar as an input parameter, trained with the back propagation with momentum learning algorithm. The results show the suitability of the adopted methodology for the short term tide forecasting.

Dao Vong Duc

In our previous work we have proposed a gauge mechanism for massive gauge bosons, where the main idea is to introduce some scalar function depending on space-time coordinates in the gauge transformations. Along this line we consider here the possibility of applying this idea to renormalization problem in field theory with gauge interaction. For illustration some simple examples are also given

Tran Dinh Tham(1), Dang Van Soa(2) and Dinh Phan Khoi(3)

We calculate the conversion cross-section of photon into axion in external electromagnetic fields, namely in static electric and magnetic fields and in a wave guide. Our result shows that conversion cross-sections in the strong magnetic field and in the wave guide are enough large to measure axion in the current experiments. We have found the resonant conversion in the wave guide, in which cross-sections are much enhanced.

Thoi Ngoc Tuan Quoc, Phan Ngoc Hung, Le Van Hoang

Dirac’s magnetic monopole and Yang’s SU(2) monopole are generalized to the non-abelian SO(8) gauge fields in a nine dimensional space. All potential components and strengths of the fields are obtained explicitly. The method used is based on the way that Yang generalized the Dirac’s magnetic monopole to the SU(2) gauge fields.

Nguyen Cong Kien(1), Nguyen Anh Ky(1), Le Ba Nam(2) and Nguyen Thi Hong Van(1)

The coherent state vector method has been used by some authors to construct representations of superalgebras, but it has just been extended to few simplest quantum superalgebras such as U_q[osp(2|1)] and U_q[gl(1|1)], whose creating/destroying operators are commutative with each other. In this talk, we show how to use this method to build boson-fermion realization of bigger quantum superalgebras U_q[gl(2|1)] and U_q[osp(2|2)]. These algebras have non-commutative creating/destroying operators, therefore, our works can be considered as a reference in utilizing the method for other quantum superalgebras. We choose these algebras because it has many applications in mathematical physics and quantum physics such as non-commutative geometry, conformal field theory, integrable system, quantum gravity, cosmology and condensed matter physics.

Bui Duc Tinh and Le Minh Thu

The time-dependent Ginzburg-Landau approach is used to investigate linear response of a strongly type-II superconductor. Thermal fluctuations, represented by the Langevin white noise, are assumed to be strong enough to melt the Abrikosov vortex lattice created by the magnetic field into a moving vortex liquid. The nonlinear interaction term in dynamics is treated within self-consistent Gaussian approximation and we go beyond the often used lowest Landau level approximation to treat arbitrary magnetic fields. The results are compared to experimental data on high-Tc superconductor Bi_{2}Sr_{2}CaCuO_{8}.

Bui Dinh Hoi, Le Thi Kim Dung, Nguyen Quang Bau

The Hall effect in a quantum well (QW) with a parabolic potential $V(z)=m\omega_{z}^{2}z^{2}/2$ (where $m$ and $\omega_{z}$ are the effective mass of electron and the confinement frequency of QW, respectively), subjected to a crossed dc electric field $\vec{E_{1}}=(0,0,E_{1})$ and magnetic field $\vec{B}=(0,B,0)$ ($\vec{B}$ is in-plane of the plane of free motion of electrons), in the presence of a strong electromagnetic wave (EMW) characterized by electric field $\vec{E}=(E_{0}\sin(\Omega t),0,0)$ (where $E_{0}$ and $\Omega$ are the amplitude and the frequency of EMW, respectively), is studied theoretically utilizing quantum kinetic equation for electrons. By considering the electron – acoustic phonon interaction, we obtain analytic expressions for the components $\sigma_{zz}$ and $\sigma_{xz}$ of the Hall conductivity as well as the Hall coefficient with a dependence on $B$, $E_{1}$, $E_{0}$, $\Omega$, temperature $T$ of the system and the characteristic parameters of QW. These expressions are fairly different in comparison to those obtained for bulk semiconductors. The results are numerically evaluated and graphed for a specific quantum well, GaAs/AlGaAs, to show clearly the dependence of the Hall conductivity and the Hall resistance on above parameters. The influence of the EMW is interpreted by using the dependences of the Hall conductivity and the Hall resistance on the amplitude $E_{0}$ and the frequency $\Omega$ of EMW and by using the dependences on the magnetic field B and the dc electric field $E_{1}$ as in the ordinary Hall effect.

Le Van Vinh, Nguyen Thi Trang and Pham Khac Hung

We present the simulation of amorphous silicon nitride (a-Si3N4) with density ranged from 2.4 to 3.4 g cm-3 using molecular dynamic method. The local structure has been analyzed through the pair radial distribution function, bond angle distribution. The simulation reveals that although the fractions of basic units SiNx strongly changes with the density, the partial bond angle distributions of basic units SiNx are identical for all constructed models. Here x=3, 4, 5. This result enables us to establish a relationship between the bond angle distributions and the fractions of basic units SiNx. The numerously ideal tetrahedrons SiN4 have been found in the a-Si3N4 upon compression. These tetrahedrons play an important role on the mechanical behavior of a-Si3N4 systems.

N. B. Yen, T. A. Chu, N. A. Viet

another application of autocatalic system has been shown in this presentation. this concept is quite familiar in chemical physics, but it's the very new one in econophysics. some comparisons has been made, thus we found that price index also follow the autocatalic systems rules, in a determined time. some important parameters has been introduced. the large application of this results on the prediction of financial crisis has also been presented