The arms of CdSe nano-tetrapods can be greatly elongated with the core diameters and arm width unchanged by multiple injections. Room-temperature absorption and photoluminescence (PL) spectra of tetrapods with different arm lengths show that these tetrapods have almost the same core size, which is consistent with the high resolution TEM results. Field emission characteristics show that the onset field required drawing a current density of ∼0.1 μAcm−2 from CdSe nano-tetrapods with different arm lengths are 22Vμm−1, 9Vμm−1, and 4Vμm−1, respectively, and the field enhancement factors are determined to be about 218, 554, and 946, respectively. Results show that the longer is the arm of the tetrapods, the lower the turn-on field and the higher the field enhancement factor.
We present estimates of threshold powers, growth rates and amplification factors for stimulated scattering of electromagnetic waves off electrostatic modes in a magnetized plasma, The magnetic field strength is assumed to influence only the electrostatic modes and not the propagation of incident and scattered electromagnetic waves.
A general analytical expression for the quasienergy state lifetime has been obtained without the assumption of the perturbation being small. As a special example, a two-level system placed in a slowly varying field is discussed in detail.
Quantum effects are considered in the dynamics of a system of N paramagnetic atoms in a resonant cavity interacting with a constant magnetic field and with a resonant external magnetic field. In the semi-classical limit (classical radiation field in the cavity) this resonantly driven system shows developed (global) chaos. Expectation-value dynamics shows however that quantum corrections cause a departure from the semi-classical chaotic dynamics on a time-scale τℏ∼lnN and that quantum correlation functions grow exponentially in time. The possibility of experimentally observing this effect is discussed.
The electronic structure and quantum transport properties of pristine armchair graphene nanoribbons (AGNRs) and AGNRs adsorbing super-halogen LiF2 and super-alkaline Li3 clusters (Li3/AGNRs/LiF2) were investigated using density functional theory and non-equilibrium Green's function calculations. It was found that LiF2 and Li3 clusters are stably adsorbed on the AGNRs, and the adsorption of Li3 and LiF2 endows AGNRs with the characteristics of n-type and p-type semiconductors, respectively. The Li3/AGNRs/LiF2 structure reduces the band gap and the turn-on voltage, and improves the transmission coefficient of the ANGRs device. This structure also exhibit the rectification characteristics of a pn junction with the forward bias current greater than the reverse bias current. This shows that adsorption of super-alkali and super-halogen clusters in different regions of AGNRs is a feasible approach for obtaining AGNRs with pn junction characteristics.
Based on the difference between negative refraction and negative refractive index, the phase compensating effect was proposed to distinguish negative refraction in left-handed materials (LHMs) and photonic crystals (PCs). With this effect, perfect lens (PL) of LHM in which both propagating and evanescent waves contribute to the image could be well understood, which is differed from superlens made of PCs. Furthermore, a 1D periodic structure consisted of ordinary materials and LHMs was predicted to realize higher and wider bandgaps than the 1D conventional photonic crystal due to phase compensating effect.
By using the equilibrium equations for a hollow cylindrical piezoelectric layer in absence of body forces and taking into the account a magnetized electron beam in hollow region of this system the effects of thermal pressure, electrostatic self field and the strength of external magnetic field of a non-relativistic magnetized electron beam column on radially polarized of an annular cylindrical piezoelectric crystal in the steady state are simulated. The electrostatic potential profile in piezoelectric layer due to the mechanical pressure and electrostatic self field of electron beam are studied. Furthermore the graphs of the difference of potential Δϕ between inner and outer surfaces of piezoelectric versus to electron temperature, density of beam and the strength of external magnetic field are presented.
DOI : 10.1016/j.physleta.2006.05.001 Anahtar Kelimeler :
Annular piezoelectric, Magnetized electron beam
ISSN: 0375-9601 Sayı: 2 Cilt: 358 Sayfa: 149-153
A method for constructing periodic solutions of the sine-Hilbert (sH) equation is developed. It is shown that the sH equation can be reducible to a linear differential equation. The explicit periodic solutions are then derived by solving the initial value problem for this linear equation.
We study disclination-induced electron scattering in materials with disclination vortices. Two kinds of scattering processes are shown to be of importance: the known deformation-potential scattering and an Aharonov-Bohm-like scattering generated by the topological nature of the disclinations. The relaxation time is calculated. The scattering process is found to depend essentially on the density of the conducting electrons as well as on the disclination core radius.
The magnitude and sign of the Na D1 signal in saturation spectroscopy are calculated, taking into consideration the velocity-selective optical pumping effects in a four-level atomic system, and are in good agreement with the experimental results.
The exact solution for a two-level atom interacting with a laser field in a gravitational field is given. The modifications due to a weak gravitational field are discussed and some applications are proposed.
The numerical study is presented of the zonal flow generation in shallow rotating fluids and in magnetized plasmas, in a strongly nonlinear regime described by the Charney–Hasegawa–Mima equation. It is demonstrated that coherent vortices, often regarded as the building blocks of the strong turbulence, are unstable in the presence of inhomogeneities. While the monopolar vortices, both cyclones and anticyclones, are rapidly dispersed by a finite Rossby velocity, the dipolar vortices (or modons) undergo a qualitative modification by the action of the scalar nonlinearity arising from the β effect. The westward propagating modons rapidly topple, disintegrating into two monopoles that propagate independently and rapidly disperse. Conversely, for the eastward propagating modons, the β-effect produces the change of the direction of the propagation, followed by the stretching in the east–west direction. On a long time scale, such modons expand to a length equal to the size of the computational box, and essentially an one-dimensional zonal flow is created, whose transverse (north–south) scale is determined by the initial size of the modon.
In previous literature, the realization of topological interface state in one-dimensional periodic system is strongly relied on the tedious parameter adjustment to search for the Dirac cone. In this paper, based on a strategy of zone folding, multiple topological interface modes for the shear horizontal guided waves in one dimensional phononic crystal plate are investigated by using finite element method and eigenmode matching theory, in which the Dirac points are formed by simply making the unit cell double. Significantly, by simply contracting or expanding the stubs can bring the topological phase transition. Furthermore, the topological phase transition is further achieved by varying the height of the stubs. The proposed designs will be more convenient to be applied in real engineering.
The hydrogen content on a stainless steel surface has been reduced by an argon glow discharge to 16 of its original value. The absolute number of the hydrogen atoms has been measured using the H(11B, α)2α reaction. The result is discussed in the context with the storage of ultra cold neutrons in material containers.
The electronic structures of perovskite oxides La1−xSrxMnO3 are studied with local spin-density approximation (LSDA). Results show that the lowest energy is obtained when the MnO bond length is 1.95 Å with ideal cubic crystal structure. This value of MnO bond length is consistent with the experimental data. Considering a proper tetragonal distortion of the crystal, the total energy of system becomes lower. A half-metal state can be got both for the undistorted structure (MnO bond lengths are 1.95–2.10 Å) and the distorted structure. It is suggested that the effect of Jahn–Teller distortion is not the main reason of formation of half-metal state. However, the electronic properties are very sensitive to the c/a ratio. Along with the increase of c/a ratio, system transforms from metal to half metal and further the insulator.
DOI : 10.1016/j.physleta.2005.10.095 Anahtar Kelimeler :
Electronic structures, LSDA, La1−xSrxMnO3, MnO bond length, c/a ratio, and half-metal state
ISSN: 0375-9601 Sayı: 4-5 Cilt: 351 Sayfa: 314-318
Numerical calculations of 4He-II hydrodynamics show that a dense tangle of superfluid vortices induces in an initially stationary normal fluid a highly dissipative, complex, vortical flow pattern (“turbulence”) with k−2.2 energy spectrum scaling and fluctuations Reynolds number of order unity. In this normal fluid flow the effects of mutual friction excitation from the superfluid vortices and those of viscous stresses are of the same order.
In this Letter, the problem of a spinless particle under the moving boundary condition is studied. It is found that the exact solution can be found if the boundary moves with the constant speed. It is proven that this restriction on the exact solvability is lifted if the electromagnetic field is introduced in the system. As an application, the exact solution for the particle confined in the sinusoidally vibrating cylindrical well is given.
A Hamiltonian describing a one-dimensional Coulomb field with an electric field in the same direction is useful for the discussion of electrons outside a free surface of liquid helium [1,2] and also for the study of far-infrared emission from Si inversion layers . We present both a semi-classical and a WKB solution to the problem, which exhibits many of the features found experimentally.
We present a theoretical investigation of a phase transition between ferromagnetic and paramagnetic phases of III-Mn-V diluted magnetic semiconductor quantum wires. The critical temperature Tc of the ferromagnetic phase in a diluted magnetic semiconductor quantum wire is inversely proportional to the one-dimensional carrier density and is enhanced by the hole–hole exchange energy Fxc.
The phase transition properties of temperature graded ferroelectric films are studied from the Transverse Ising model. The temperature dependence of the polarization and the pyroelectric coefficient of the film with various temperature gradients is given. The profiles of the polarization as well as the pyroelectric coefficient of the film are presented. A polarization gradient is predicted inside the film when there is a temperature gradient. At certain temperature gradients, the film contains both paraelectric and ferroelectric part. There exists a pyroelectric maximum inside the film which varies its position with the variation of the temperature gradient.
We calculate explicit corrections to the Weisskopf-Wigner laws governing the spontaneous radiative transition 2P → 1S in a non-relativistic two level hydrogenlike atom. Deviations from the usual exponential decay and lorentzian emission spectrum prove to be unobservably small, even at the sub-ppm detection levels characterizing experiments searching for atomic parity violations.
In actual experiments the frequency condition between the pump mode and the resonator mode can be broken. The stability of the orientation angle of the nonlinear crystal, which is necessary to achieve significant squeezing, is discussed.