Laser ablation of gadolinium targets in liquids for nanoparticle preparation

Tight focusing of a sub-picosecond laser pulse in a transparent dielectric provides a mean for localized deposition and plasma formation. A micro-explosion in a confined geometry results in a sub-micron cavity formation. Our numerical simulations show the cavity size is strongly dependent on the parameters of the equation of state such as the Grüneisen coefficient or the latent heat of sublimation. A comparison of numerical simulations with experimental data should allow a tuning of equations of state in the domain of extreme parameters     

Finite Space Complete Basis Method: Precision Computation of High-Resolution Spectrum near Ionization Threshold

A new method is proposed to describe quantum dynamical processes in finite space by using of a set of discretized complete bases. In this method, the finite space complete basis is obtained by solving the self-consistent field equation with reflecting boundary conditions. Hence, both negative and positive orbital energies can be obtained. Such method can be used in systems which involve dynamics only in the reaction zone, i.e., in a finite space. To illustrate the validity of the method, we present two examples: theoretical calculation of the high excited states spectra including the continuum of sodium and barium.     

Compressibility of Nickel Nanoparticle Chain

We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over the pressure range. The bulk modulus Ko, the first pressure derivative of bulk modulus K＇0 and the volume Vo are calculated from the pressure-volume data using the Birch-Murnaghan equation of state. A decrease of compressibility is observed, in agreement with the Hall-Perch effect.     

Multi-material two-temperature model for simulation of ultra-short laser ablation

We investigate the interaction of 100 fs laser pulses with metal targets at moderate intensities (10¹² to 5 × 10¹³ W/cm²). To take into account effects of laser energy absorption and relaxation we develop a multi-material two-temperature model based on a combination of different approaches. The backbone of the numerical model is a high-order multi-material Godunov method in a purely Eulerian form. This formulation includes an interface-tracking algorithm and treats spallation at high strain rates and negative pressures. The model consistently describes the hydrodynamic motion of a two-temperature plasma and accounts for laser energy absorption, electron-phonon/ions coupling and electron heat conductivity. In particular, phase transitions are accurately taken into account by means of a wide-range two-temperature multi-phase equation of state in a tabular form. The dynamics of the phase transitions and the evolution of the heat-affected zone are modeled and analyzed. We have found that a careful treatment of the transport coefficients, as well as consideration of phase transitions is of a great importance in obtaining reliable numerical results. Calculation results are furthermore compared for two metals with different electron-phonon coupling parameters (Au and Al). We have found that the main part of ablated material results from fragmentation of melted phase caused by tensile stresses. A homogeneous nucleation mechanism alone does not explain experimentally observed ablation depth.     

Cs^＋-K^＋ Exchange in Z-Cut KTiOPO4 Crystal Covered with Chromium Masking Layer

Cs^＋-K^＋ ion exchanges are performed on z-cut KTiOPO4 crystals with chromium coating covered. The temperature of ion exchange is 430℃, and the time range from 15min to 30min. The dark mode spectra of the samples are measured by the prism coupling method. The channel structures on the samples are observed by a microscope and the near field pattern of the channel waveguides are measured by the end-fire coupling method. The refractive index of the samples increases and the increments at surface are modulated due to the existence of Cr film. In the region covered by Cr film, the refractive index of the samples at the surface increases dramatically in a shallow layer. The results of energy dispersive x-ray spectra indicate that in the region covered with Cr film, Cr ions participate in the ion exchange process, and enhance the refractive index. The results may provide a possibility that achieves index enhancement and Cr doping synchronically.     

Coherence domains in matter interacting with radiation

The coupling of the electromagnetic field to matter polarization (dipole interaction) is examined in order to assess the possibility of setting up a coherent state as envisaged by Preparata and coworkers [G. Preparata, QED Coherence in Matter, World Scientific, 1995, and references therein]. It is found that coherence domains may set up in matter, their phases being arranged in a periodic lattice, as a consequence of, basically, a two-level interaction, which leads to a long-range ordered state, governed by a macroscopic occupation of both the photon state and the two levels. The non-linear equations of motion are solved for the new, non-perturbative ground-state, which is energetically favourable, provided the coupling strength exceeds a critical value. The elementary excitations with respect to this ground-state are derived, their energy being non-trivially affected by interaction. The “thermodynamics” of the coherent phase is computed and the super-radiant phase transition is re-derived in this context. Except for the general suggestion of coherence, the present results differ appreciably from Preparata's, loc cit.     

Sudden Death of Entanglement between Two Atoms with Initial Tripartite Entangled State in the Tavis--Cummings Model

We study the entanglement dynamics of two atoms with initial tripartite entangled W-like state in the Tavis-Cummings model. We find that the entanglement evolvement is sensitive not only to the entanglement degree of the initial state but also to the concrete form of the initial state. The so-called sudden death effect occurs only for some initial states.     

Quantum-Confined Stark Effects in a Single GaN Quantum Dot

Using analytical expressions for the polarization field in GaN quantum dot, and an approximation by separating the potential into a radial and an axial, we investigate theoretically the quantum-confined Stark effects. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. The results show that the electron and hole energy levels and the optical transition energies can cause redshifts for the lateral electric field and blueshifts for the vertical field. The rotational direction of electric field can also change the energy shift.     

Adsorption and Reaction of CO on （100） Surface of SrTiO3 by Density Function Theory Calculation

Adsorption and reaction of CO on two possible terminations of SrTiO3 （100） surface are investigated by the first-principles calculation of plane wave ultrasoft pseudopotentiai based on the density function theory. The adsorption energy, Mulliken population analysis, density of states （DOS） and electronic density difference of CO on SrTiO3 （100） surface, which have never been investigated before as far as we know are performed. The calculated results reveal that the Ti-CO orientation is the most stable configuration and the adsorption energy （0.449eV） is quite small. CO molecules adsorb weakly on the SrTiO3 （100） surface, there is predominantly electrostatic attraction between CO and the surface rather than a chemical bonding mechanism.     

First-Principles Study of Li Doping in a Double-Wall Carbon Nanotube

By performing first-principles calculations, we study Li doping in a double-wall carbon nanotube where a （5,0） tube is confined inside a （14,0） tube. There are three possible sites for Li doping and two of them are energetically favorable. The change of energy band structure is closely related to the doping sites and the charge transfer is investigated. Bader charge analysis indicates that Li prefers to donate its electron to the inner （5,0） tube. Moreover, the Li capacity of the system can reach LIC4.75 which makes it a promising candidate for Li-ion battery materials.     

Coherent Phase Control of Multiphoton Ionization in Three-Level Ladder-Type System

We present the theoretical investigation of photoelectron spectroscopy resulting from the strong field induced multiphoton ionization in a typical three-level ladder-style system. Our theoretical results show that the photo-electron spectral structure can be alternatively steered by spectral phase modulation. This physical mechanism for strong field quantum control is explicitly exploited by the time-dependent dressed state population. It is concluded that the phase-shaped laser pulses can be used to selectively manipulate the multiphoton ionization process in complicated quantum systems.     

Molecular interactions in fullerenes and equilibrium of higher fullerites C76 and C84 with their vapors

From simple topological considerations on the molecular shapes, a new method for calculating the coefficients of the Girifalco intermolecular potential for various fullerenes is proposed. This eliminates the necessity for fitting the coefficients to data of measurements for each specific fullerene. We calculate them for C₇₆ and C₈₄ and apply this potential to perform research on the equilibrium of these fullerites with their vapors. The temperature dependence of the lattice parameters, the saturated vapor pressures and the enthalpies of sublimation is studied. Results are in good agreement with available experimental data. Received 13 January 2000 and Received in final form 18 June 2000     

Continuous-Variable Quantum Teleportation of Entangled Coherent States

We propose a quantum teleportation scheme for tripartite entangled coherent state （ECS） with continuous variable. Our scheme is feasible and economical in the sense that we need only linear optical devices such as beam splitters, phase shifters and photon detectors and employ three bipartite maximally ECSs as quantum channels. We also generalize the tripartite scheme into multipartite ease and calculate the minimum average fidelity for the schemes in tripartite and multipartite cases.     

Theoretical Studies on Defects of Kaolinite in Clays

Using the first-principles methods, we study the formation energeties and charge doping properties of the extrinsic substitutional defects in kaolinite. Especially, we choose Be, Mg, Ca, Fe, Cr, Mn, Cu, Zn as extrinsic defects to substitute for Al atoms. By systematically calculating the impurity formation energies and transition energy levels, we find that all group-Ⅱ defects introduce the relative shallow transition energy levels in kaolinite. Among them, MgAl has the shallowest transition energy level at 0.08 eV above the valence band maximum. The transition- elemental defects FeAl, CrAl, and MnAl are found to have relative low formation energies, suggesting their easy formation in kaolinite under natural surrounding conditions. Our calculations show that the defects CuAl and ZnAl have the high formation energies and deep transition energy levels, which exclude the possibility of their formation in natural kaolinite.     

Bound State Solutions of Klein--Gordon Equation with the Kratzer Potential

The relativistic problem of spinless particle subject to a Kratzer potential is analysed. Bound state solutions for s-waves are found by separating the Klein-Gordon equation into two parts. Unlike the similar works in the literature, the separation make it possible to see explicitly the relativistic contributions, if any, to the solution in the non-relativistic limit.     

Microtubule as a Transmission Line for Ionic Currents

We establish a new model for ionic waves along microtubules based on polyelectrolyte features of cylindrical biopolymers. The nonlinear transmission line described by a nonlinear differential equation is obtained with stable kink solution pertinent to the shape of the front of accompanying potential. The localized ionic wave could be used to explain the behavior of microtubules as biomolecular transistors capable of amplifying electrical information in neurons.     

Phase Transition and Melting Curves of Calcium Fluoride via Molecular Dynamics Simulations

The phase transition and melting curves of CaF2 are investigated by using the general utility lattice programme （CULP） via the shell model with molecular dynamics method. By calculating the entropy H （at OK） and Cibbs free energy G^＊ （at 30OK）, we find that the phase transition pressure from the face-centred cubic （fee） structure to the orthorhombic structure is 11.40 CPa and 9.33 CPa at OK and 300K, respectively. The modified melting point of the fee CaF2 is in the range of 1650-1733K at OCPa. All these results are well consistent with the available experimental data and other theoretical results. We also obtain that the melting temperature of high pressure phase is 990-1073 K at 10 CPa. Moreover, the temperature dependences of the elastic constants Cij, bulk module B and shear module G are also predicted.     

Theoretical Study of Interesting Fine-Structure Splittings for 23P0, 1, 2 States along Helium Isoelectronic Sequence

Using the multi-configuration Dirac Fock method including the Breit interactions and QED corrections, we calculate the fine-structure energy levels of the 2^3 Po, 1,2 states along the helium isoelectronic sequence with atomic number up to Z = 36, where LS-coupling is appropriate. Our calculation results agree with the experimental results within about 1%. We elucidate the mechanism of the interesting fine-structure splittings for the 2^3Po,1,2 states along the helium isoelectronic sequence, i.e. the competitions between the spin-orbit interactions and the Breit interactions which represent the relativistic retardation effect of electromagnetic interactions.     

New Periodic Solution to Jacobi Elliptic Functions of a (2+1)-Dimensional BKP Equation and a Generalized Klein-Gordon Equation

With the help of the homogeneous balance method, the Jacobi elliptic expansion method and the auxiliary equation method, the first elliptic function equation is used to obtain the Jacobi doubly periodic wave solutions of the (2+1)-dimensional B-type Kadomtsev-Petviashvili (BKP) equation and the generalized Klein-Gordon equation. The method is also valid for other (1+1)-dimensional and higher dimensional systems.     

Pressure Effects on Solid State Phase Transformation of Aluminium Bronze in Cooling Process

Effects of high pressure （6 CPa） on the solid state phase transformation kinetic parameters of aluminum bronze during the cooling process axe investigated, based on the measurement and calculation of its solid state phase transformation temperature, duration and activation energy and the observation of its microstructures. The results show that high pressure treatment can reduce the solid phase transformation temperature and activation energy in the cooling process and can shorten the phase transformation duration, which is favorable when forming fine-grained aluminum bronze.