Narrow Results

In this paper, we give formulas for the Hodge numbers of a nodal complete intersection in a complex projective space. We apply these formulas to construct examples of Calabi–Yau threefolds with $h^{1,1}=2$.

We utilize the original Hodgkin–Huxley (HH) model to consider the effects of defective ion channels to the temporal response of neurons. Statistics of firing rate and inter-spike interval (ISI) reveal that production of action potentials (APs) in neurons is not sensitive to changes in membrane conductance for sodium and potassium ions, as well as to the reversal potential for sodium ions, as long as the relevant parameters do not exceed 13% from their normal levels. We also found that blockage of a critical fraction of either sodium or potassium channels (dependent on constant input current) respectively limits the firing activity or increases spontaneous spiking activity of neurons. Our model may be used to guide experiment designs related to ion channel control drug development.

The classical sine–Gordon model is a two-dimensional integrable field theory, with particle-like solutions — the so-called solitons. Using its integrability one can define the quantum theory without the process of canonical quantization. The bootstrap method employs the fundamental properties of the model to restrict the structure of the scattering matrix as far as possible. The classical model can be extended with integrable discontinuities, purely transmitting jump defects. Then the quantum version of the extended model can be determined via the bootstrap method again. The resulting quantum theory contains the so-called CDD uncertainty. The aim of this article is to carry out the semiclassical approximation on both the classical and the quantum side of the defect sine–Gordon theory. The CDD ambiguity can be restricted by comparing the two results. To complete the comparison we have to calculate the relation between the classical and quantum parameters. We determine the quantum parameters from the poles of the T matrix, and we find that there are resonances in the spectrum.

In this review paper, we address the important research topic of adsorption on the silicon surface. The deposition of single Si ad-species (adatom and ad-dimer) on the p(2×2) reconstructed Si(100) surface has been simulated by the empirical tight-binding method. Using the clean and defective Si surfaces as the deposition substrates, the deposition energies are mapped out around the clean surface, dimer vacancies, steps and kink structures. The binding sites, saddle points and several possible diffusion paths are obtained from the calculated energy. With further analysis of the deposition and diffusion behaviors, the influences of the surface defects can be found. Then, by adopting the first-principle calculations, the adsorptions of the II-VI group elements on the clean and As-passivated Si(211) substrates have been calculated as the example of adsorption on the high-miller-index Si surface.

We study the vortex configuration in a superconducting macroscopic flat disk with central defects in the presence of a uniform applied magnetic field. Owing to the defects nature on the thin disk, vortices are able to form geometry induced, quasi-symmetric configurations of disk, triangle and concentric shells in the rest of the disk. The theoretical study made on this mesoscopic systems allows us to trace not only how the vortex pattern evolves with magnetic field, but also how the defect can be used to show the pinning and anti-pinning effect. The magnetic induction, vortex number, magnetization and Cooper pairs density as a function of the external magnetic field are calculated, we show that in our sample novels vortex configurations are possible due to the size of the disk and if the hole or barrier defect is considered.

In the present work, we report the blue phase (BP) in a binary mixture of cholesteryl nonanoate (CN) and N-(4-ethoxybenzylidene)-4-butylaniline (EBBA). The mixture exhibits BP over a temperature range of 2.3 K at optimum composition (50:50) of liquid crystals (LCs). The effect of silica nanoparticles (SNPs) doping on thermal stability of BPs has also been demonstrated and nearly 6 K wide BP temperature range was achieved at 0.5 wt.% of SNPs. A porous type texture was also observed during the BP formation process in the doped samples.

The influence of Nb₂O₅-doped concentration on the positive temperature coefficient of resistance (PTCR) effect, electrical properties and microdefects of (Ba${}_{0.95}$Sr${}_{0.05}$)(TiNb${}_x$)O₃ (BSTN) ceramics were investigated. Firing was conducted at 1350${}^{\circ }$C for 2 h in air. The donor-doped content affected the electrical properties, PTCR effect and formation of the microdefect type of the BSTN samples. The room temperature resistivity of the BSTN specimens first decreased and then increased with increasing donor-doped content in the range of 0.2 mol.% Nb${}^{5+}$ to 0.5 mol.% Nb${}^{5+}$. Moreover, the information on microdefects in BSTN ceramics was demonstrated by coincidence Doppler broadening spectrum. The influence of the defects on the PTCR characteristics of the ceramics was also revealed.

Graphene has vast promising applications in nanoelectronics and spintronics because of its unique magnetic and electronic properties. Making use of an ab initio spin-polarized density functional theory, implemented by the method of the Heyd–Scuseria–Ernzerhof 06 (HSE06) hybrid functional, the properties of various defect dopants in a supercell of a semi-metal monolayer graphene were investigated. We found from our calculation that introducing one defect dopant in a supercell would break the spin sublattice symmetry, and will induce a magnetic state at some appropriate doping concentrations. This paper systematically analyzes the magnetic effects of three types of defects on graphene, that is, vacancy, substitutional dopant and adatoms. Different types of defects will induce various new properties in graphene. The energies and electronic properties of these three types of defects were also calculated.

In this paper, we theoretically investigate the transmittance characteristics of one-dimensional defective photonic crystal in microwave radiations based on the fundamentals of the characteristic matrix method. Here, the defect layer is magnetized plasma. The numerical results show the appearance of defect peaks inside the Photonic Band Gap. The external magnetic field has a significant effect on the permittivity of the defect layer. Therefore, the position and intensity of the defect peak are strongly affected by the external magnetic field. Moreover, we have investigated the different parameters on the defect peaks as the plasma density, the thickness of the plasma layer and the angle of incidence. Wherefore, the proposed structure could be the cornerstone for many applications in microwave regions such as narrowband filters.

Surface modification has been used as a method to create defects on ${\mathrm{\text{TiO}}}_2$ materials, which can improve their desirable properties. In this paper, defected ${\mathrm{\text{TiO}}}_2$ nano-powder was successfully synthesized by chemical reduction using ${\mathrm{\text{NaBH}}}_4$ as the reducing agent at 300–400${}^{\circ }\mathrm{\text{C}}$ under argon atmosphere. High defect concentration can be produced by increasing process temperature. The modified ${\mathrm{\text{TiO}}}_2$ shows good visible light absorption and photocatalytic activity on degradation of Rhodamine B (4–9 times higher than the pristine ${\mathrm{\text{TiO}}}_2$) with the visible light irradiation. Further XPS analysis and theoretical studies using full potential linearized augmented plane wave (FP-LAPW) method as implemented in wien2k code revealed the existence of oxygen vacancy and ${\mathrm{\text{Ti}}}^{3+}$ in the modified samples. These types of defects were responsible for the modifications of the electronic and optical properties of ${\mathrm{\text{TiO}}}_2$, resulting in the improved photocatalytic activity in visible light irradiation.

By introducing a stress potential function, we transform the plane elasticity equations of two-dimensional quasicrystals of point group 10, to a partial differential equation. And then we use the complex variable function method for classical elasticity theory to that of the quasicrystals. As an example, a decagonal quasicrystal in which there is an arc is subjected to a uniform pressure p in the elliptic notch of the decagonal quasicrystal is considered. With the help of conformal mapping, we obtain the exact solution for the elliptic notch problem of quasicrystals. The work indicates that the stress potential and complex variable function methods are very useful for solving the complicated boundary value problems of higher order partial differential equations which originate from quasicrystal elasticity.

We present a systematic study of the local distortions produced upon doping metal ions to lithium niobate (LiNbO₃, LN) single crystals. The impurity bond length can be predicted by a radial force constant model, when the dopant ions substitute for Li⁺ or Nb⁵⁺ ions in the LN crystallographic frame. From the viewpoint of constituent chemical bonds, the lattice energy can be described as the function of bond valence on the basis of Born–Haber cycle for the formation of an ionic oxide M_mO_n. The dopant occupancy in the LN matrix can be determined by comparing the deviation of its lattice energy in different locations at both Li⁺ and Nb⁵⁺ sites, on the basis of the bond length relaxation of impurity ions, which can agree well with the experiment results. The effect of impurity ions on the property modification of LN crystals is also discussed according to our calculated results.

Theoretical calculation based on density function theory (DFT) and generalized gradient approximation (GGA) has been carried out in studying the magnetic properties of nitrogen-doped ZnO. The results show that ferromagnetism (FM) coupling between N atoms is more stable for the majority of 11 geometrically distinct configurations, and N atoms in ZnO have a clear clustering tendency. In addition, the formation and ionization energy of native defects in ZnO is analyzed and discussed. The effect of native defects on FM properties of nitrogen-doped ZnO has also been investigated. It is found that FM state is more favored than the AFM state in the presence of zinc vacancy or oxygen interstitial. In the paper, we also analyze strain effect on FM of nitrogen-doped ZnO.

Proton-irradiation induced defects in Te-doped GaSb have been studied by photoluminescence (PL) and positron annihilation spectroscopy (PAS). A 2.6 MeV proton irradiation with fluences of 1×10¹⁴ cm^-2, and 3×10¹⁵ cm^-2 was used to produce defects in the Te-doped GaSb samples with free electron concentration of 1×10¹⁷ cm^-3 and 1×10¹⁸ cm^-3 respectively. The change of S parameters in Te-doped samples irradiated with different proton fluences, indicates that the defects induced by proton irradiation are most likely the V_Ga-related defects. The PL spectra of Te-doped GaSb with different proton irradiation doses were measured at 77 K. The results show that the V_Ga-related defects induced by proton irradiation are acceptors in Te-doped GaSb. We have also found that the dopant-induced vacancies which are related to Te have existed in unirradiated samples.

Using the first principle method based on density function theory (DFT), we study the electronic and ferromagnetic stability in Cu-doped ZnO. The calculated results based on the local density approximation (LDA) showed that the ferromagnetism (FM) coupling between Cu atoms is more energetically favorable for eight geometrically distinct configurations. In this paper, we also analyze the ferromagnetic properties of Cu-doped ZnO within LDA + U scheme. The dominant ferromagnetic interaction is due to the hybridization between O 2p and Cu 3d. We investigate the effects of oxygen vacancies and nitrogen impurities on FM properties of Cu-doped ZnO. It is obvious that oxygen vacancies and nitrogen impurities are unfavorable in stabilizing the FM of Cu-doped ZnO. In addition, the origin of the FM state of Cu-doped ZnO has also been discussed by analyzing the coupling of Cu 3d levels. Also in this paper, we analyze the strain effect on the FM properties of Cu-doped ZnO.

Using the first principle method based on density functional theory (DFT), we have studied the magnetic properties in Cu-doped GaN. The result shows that Cu in GaN exhibits spontaneous spin polarization. The energies of ferromagnetism (FM) and antiferromagnetism (AFM) coupling are calculated for eleven different configurations. It is found that Cu-doped GaN has a FM ground state. It is not found that Cu atoms have a clear clustering tendency. Origin of FM properties is also explained by energy level coupling model. In the paper, we also investigate the effect of nitrogen, gallium vacancies and carbon impurities on magnetic properties. The results show that nitrogen, gallium vacancies and carbon impurities cannot enhance FM coupling of Cu-doped GaN. In addition, exchange coupling coefficient and Curie temperature are also investigated. The Cu-doped GaN is proposed to be weak ferromagnetism according to Curie temperature and magnetic moment. The present study provides some theoretical understanding for the experiments on Cu-doped GaN.

We consider a discrete model that describes a linear chain of particles coupled to two defects. This model can be regarded as a linear generalization of the familiar Fano–Anderson model. The analytical result for the plane wave transmission coefficient is obtained. Comparing the transmission coefficient of Gaussian wave with that of plane wave, we can draw a conclusion that arising perfect reflection due to destructive interference depends on the input waveform of incident particle and a necessary switching condition of Fano resonance is the input plane wave. This interesting feature may play a guiding role in devising various particle switches in theory and experiment.

Theoretical calculation based on density functional theory (DFT) and generalized gradient approximation (GGA) has been carried out in studying defect formation energies, ionization energies and magnetic properties of copper doped ZnO nanowires (NW). It is found from formation energy calculation that n-type Cu-doped ZnO NW is non-FM and p-type Cu-doped ZnO NW could be FM. The results show that total energies of FM coupling are lower than those of AFM coupling for majority of 12 configurations, indicating that the FM coupling between Cu atoms is more stable than AFM coupling. The FM stability is interpreted by Cu 3d energy level coupling. In addition, zinc and oxygen vacancies affecting FM coupling is also discussed. It is found that FM coupling can be tuned by zinc and oxygen vacancies.

In this paper, we report on the influence of an internal defect on the vortex entrance in a mesoscopic superconducting sample. Effects associated to the pinning force of the defect on the configuration and on the vortex entry fields are studied for a very thin disk. We calculate the supercurrent, magnetization, vorticity, free energy and Cooper pairs density for a disk in presence of external magnetic field applied perpendicular to the disk plane. Due to vortex–defect attraction (repulsion), the vortices always (never) are found to be sitting on the defect position.

The electronic behavior of semiconducting carbon nanotubes based CNTFET under the influence of radial deformation defect present in the channel is theoretically investigated using nonequilibrium Green's function method self-consistently coupled with three-dimensional electrostatics. It was found that deformation in the CNTFET channel composed of a small diameter semiconducting carbon nanotube can increase its conductance by a factor of 4 or more depending upon the average reduction in the C–C bond length after compression. This increase in CNTFET conductance is directly related to the movement of the electronic states toward the Fermi level when the tubes are squeezed. Furthermore, the device ON–OFF current ratio also decreases with increase in applied compression which makes it hard to switch-OFF the device.