A Complete Foliation of Schwarzschild Spacetime by Free Falling Hypersurfaces

Free falling hypersurfaces in the Schwarzschild geometry have been studied to provide a complete foliation of spacetime. The hypersurfaces do not cross into the maximally extended spacetime and are well behaved everywhere except at the singularity r =0 the mean extrinsic curvature becomes infinity.     

How to Define the Equality of Durations in Measurement of Time

We develop the research on measurement of time worked by Poincarh, Einstein, Landau and other researchers. Based on the convention that the velocity of light is isotropic and is a constant in empty spacetime, we not only answer the question about the definition of the synchronization of rate of clocks located at different places, but also find the solution to the issue of how to define the equality of two durations in measurement of time.     

Quantum Radiation of a Non-stationary Kerr-Newman Black Hole in de Sitter Space-Time

Hawking radiation of Klein-Gordon and Dirac particles in a non-stationary Kerr-Newman-de-Sitter black hole is studied by introducing a new tortoise coordinate transformation. The result shows that the Fermi-Dirac radiant spectrum displays a new term that represents the interaction between the spin of spinor particles and the rotation of black holes, which is absent in the Bose-Einstein distribution of Klein-Gordon particles.     

Exact Timing of Returned Molecular Wavepacket

An ionizing wavepacket of electron will re-visit its parent molecular ion during photoionization by strong laser field. This scenario is associated with physical concepts such as molecular re-scattering/collision, interference, diffraction, molecular clock, and generation of XUV light via high-order harmonic generation. On the workbench of a reduced dimensionality model of molecular hydrogen ions irradiated by laser pulse of 0.01-10.0 a.u. intensities, one-cycle pulsewidth, and 800nm wavelength, by deploying a momentum operator on the time-dependent wavefunction of an ionizing wavepacket, we can determine, in a precise manner, the exact time instant for the re-visiting electron to come back to the cation position. The time value is 57.6% of an optical cycle of the exciting laser pulse. This result may be useful in attosecond pump-probe experiments or molecular clock applications.     

Electron Impact Ionization Cross Section of Nitrogen Atoms

The direct ionization cross sections for electron scattering by nitrogen are calculated by applying an equivalentlocal optical model from 15eV to 1100eV. The present results are compared with the experimental data and other theoretical calculation results.     

Inflationary solutions in general scalar tensor theory of gravitation

Extended inflation solution in Brans-Dicke theory given by Mathiazhagan and Johri (MJ) is shown as the unique solution only if the scale factor is assumed to be a power function of the scalar field. Only the consistent solution amongst the set of solutions given by Patra, Roy and Ray is found identical to the MJ solution. Both exponential inflation and power function inflation are studied in general scalar tensor theory where the parameter to is a function of the scalar, field. It is noted that exponential inflation is forbidden in Brans-Dicke theory wherew is a constant.     

Femtosecond laser-induced ZnSe nanowires on the surface of a ZnSe wafer in water

We present a simple route for ZnSe nanowire growth in the ablation crater on a ZnSe crystal surface. The crystal wafer, which was horizontally dipped in pure water, was irradiated by femtosecond laser pulses. No furnace, vacuum chamber or any metal catalyst were used in this experiment. The size of the nanowires is about 1-3 μm long and 50-150 nm in diameter. The growth rate is 1-3 μm/s, which is much higher than that achieved with molecular-beam epitaxy and chemical vapor deposition methods. Our discovery reveals a rapid and simple way to grow nanowires on designed micro-patterns, which may have potential applications in microscopic optoelectronics.     

Metrizability of spaces of homomorphisms between metric vector spaces

This note tries to give an answer to the following question: Is there a sufficiently rich class of metric vector spaces such that sufficiently large spaces of continuous linear maps between them are metrizable?     

La substitution in four-layers Aurivillius phase SrBi4Ti4O15

Ceramics with the nominal composition of SrBi_4−xLa_xTi₄O₁₅ have been prepared within the range of 0≤x≤1.8, and the dielectric properties are investigated. Single phase SrBi_4−xLa_xTi₄O₁₅ solid solution exists until the secondary phase of La_2/3TiO₃ appears at x=1.6. The Curie temperature is 520 °C for pure SrBi₄Ti₄O₁₅, and it shifts to low temperature with increasing x, which is due to the smaller structural distortion caused by La³⁺ substitution. In addition, the dielectric constant anomaly is suppressed with the substitution. No dielectric relaxation behavior is observed. When x≥1.2, the paraelectric state is attained in the present ceramics. La³⁺ substitution effects on the SrBi₄Ti₄O₁₅ ceramics are also compared with the previous work on Bi_4−xLa_xTi₃O₁₂.     

Optical Waveguide Formed in RbTiOPO4 Crystal by 6.0 MeV O^3＋ Implantation

A planar optical waveguide was formed in RbTiOP04 crystal by 6.0-MeV oxygen ion implantation with the dose of 2 × 10^15 ions/cm2 at room temperature. Annealing at 200℃ for 30min in air is performed to improve the thermal stability of the waveguide. The dark modes of the waveguide are measured at wavelengths 633 and 1539 nm, respectively. The refractive index profiles in the guiding layer are reconstructed by using the reflectivity calculation method. TRIM＇98 code was carried out to simulate the damage profiles caused by the implantation process to obtain a better understanding of the waveguide formation.     

Extension of CASCADE.04 to estimate neutron fluence and dose rates and its validation

Capability to compute neutron dose rate is introduced for the first time in the new version of the CASCADE.04 code. Two different methods, ‘track length estimator’ and ‘collision estimator’ are adapted for the estimation of neutron fluence rate needed to calculate the ambient dose rate. For the validation of the methods, neutron dose rates are experimentally measured at different locations of a 5Ci Am-Be source, shielded in Howitzer-type system and these results are compared with those estimated using (i) modified CASCADE.04.d and (ii) MCNP4A codes and it is found that the agreement is good. The paper presents details of modification and results of the comparative study.      

High growth rate deposition of oriented InN pillar crystals

High growth rate deposition of highly oriented indium nitride (InN) pillar crystals were successfully grown on Si(100) substrate prepared under atmospheric pressure using a halide CVD method (AP-HCVD). The growth rate of InN pillar crystal can be enhanced threefold by AP-HCVD system with metal halide dual sources zone, and the maximum growth rate of 8.33 nm/s was achieved. X-ray diffraction and X-ray pole-figure analyses showed that the each InN pillar crystal grows with a different rotation angle around the 〈001〉 axis. Selected area transmission electron diffraction showed that that they are of high crystal quality.     

C-V studies on metal-ferroelectric bismuth vanadate (Bi2VO5.5)-semiconductor structure

Ferroelectric bismuth vanadate Bi₂VO_5.5 (BVO) thin films have been successfully grown on p-type Si(100) substrate by using chemical solution decomposition (CSD) technique followed by rapid thermal annealing (RTA). The crystalline nature of the films has been studied by X-ray diffraction (XRD). Atomic force microscopy (AFM) was used to study the microstructure of the films. The dielectric properties of the films were studied. The capacitance-voltage characteristics have been studied in metal-ferroelectric-insulator-semiconductor (MFIS) configuration. The dielectric constant of BVO thin films formed on Si(100) is about 146 measured at a frequency of 100 kHz at room temperature. The capacitance-voltage plot of a Bi₂VO_5.5 MFIS capacitor subjected to a dc polarizing voltages shows a memory window of 1.42 V during a sweep of ±5 V gate bias. The flatband voltage (V_f) shifts towards the positive direction rather than negative direction. This leads to the asymmetric behavior of the C-V curve and decrease in memory window. The oxide trap density at a ramp rate of 0.2 V/s was estimated to be as high as 1.45×10¹² cm⁻².     

Adhesive interfaces of enamel and dentin prepared by air-abrasion at different distances

The purpose of this study was to analyse, by scanning electron microscopy (SEM), the morphology of enamel and dentin/adhesive interfaces in cavities prepared by air-abrasion at different working distances. Thirty sound third human molars were selected and, on both their buccal and lingual surfaces, class V cavities were prepared by air-abrasion, at 2-, 4-, 6-, 8- and 10-mm working distances, or high-speed bur (control group). After preparation, all cavities were etched with 35% phosphoric acid gel and restored with Single Bond/Filtek Z-250. Buccal and lingual surfaces were separated and restorations sectioned in a buccolingual direction, providing two sections of each cavity, which were analysed by scanning electron microscopy. It was observed that the distances of 6 and 8 mm promoted more homogeneous dentin/adhesive interfaces, with tags formation, and more uniform for enamel, which were similar to the control group. It may be concluded that the air-abrasion working distance can influence the morphology of enamel and dentin/adhesive interfaces, and the intermediate distances provided better adhesive interfaces.     

Si80笼状分子的结构研究

采用基于密度泛函的第一性原理计算方法,构建了Si80笼状分子的模型,并对其结构和电学特性进行了考察. 研究发现,经过结构优化计算,Si80分子从Ih高对称性下降为Th,但仍然保持较好的笼状结构. 对Si80笼状分子的稳定性、轨道分布和电荷分布等性质进行了分析和讨论.     

Nonrelativistic calculation of the Lamb shift without applying the dipole approximation

By applying a method which exploits the O(4) symmetry of the nonrelativistic hydrogen atom, the Lamb shift is calculated without making the dipole approximation. Similar calculations in the dipole approximation have been previously carried out by Lieber. The advantage of our calculations is that, without introducing a cutoff-frequency, analytical and numerical results for energy-level (Lamb) shifts, in which the self-energy of the free electron is completely separated, are obtained. Since the obtained results are finite, the significance of the retardation effects is clearly demonstrated. Furthermore, a comparison is also made with the results obtained by other authors.     

Resonance fluorescence of strongly driven two-level system coupled to multiple dissipative reservoirs

We present a theoretical formalism for resonance fluorescence radiating from a two-level system (TLS) driven by any periodic driving and coupled to multiple reservoirs. The formalism is derived analytically based on the combination of Floquet theory and Born–Markov master equation. The formalism allows us to calculate the spectrum when the Floquet states and quasienergies are analytically or numerically solved for simple or complicated driving fields. We can systematically explore the spectral features by implementing the present formalism. To exemplify this theory, we apply the unified formalism to comprehensively study a generic model that a harmonically driven TLS is simultaneously coupled to a radiative reservoir and a dephasing reservoir. We demonstrate that the significant features of the fluorescence spectra, the driving-induced asymmetry and the dephasing-induced asymmetry, can be attributed to the violation of detailed balance condition, and explained in terms of the driving-related transition quantities between Floquet-states and their steady populations. In addition, we find the distinguished features of the fluorescence spectra under the biharmonic and multiharmonic driving fields in contrast with that of the harmonic driving case. In the case of the biharmonic driving, we find that the spectra are significantly different from the result of the RWA under the multiple resonance conditions. By the three concrete applications, we illustrate that the present formalism provides a routine tool for comprehensively exploring the fluorescence spectrum of periodically strongly driven TLSs.     

Decay of the metastable state in a chemical system: Different predictions between discrete and continuous models

We show, using a specific example of a chemical reaction, that the rate constants predicted from the discrete master equation and its continuum Fokker-Planck approximations differ in exponential order with respect to the size of the system.     

Theoretical basis for a new subnatural spectroscopy via correlation interferometry

A new line-narrowing effect in coincidence interferometry yielding subnatural resolution of atomic transition frequencies is proposed and analyzed. The approach utilizes second-order photon correlation properties of the radiation field. This is in contrast to the first-order measurements associated with time delay spectroscopy, which is known to yield subnatural resolution. Connections between the two techniques are investigated.Dedicated to the memory of Professor Julian Schwinger, a role model for us all     

Can surface preparation with CVD diamond tip influence on bonding to dental tissues?

This study evaluated the influence of chemical vapor deposition (CVD) tips surface treatments of enamel and dentin on bonding resistance of two adhesive systems. Thirty embedded samples were divided in 12 groups (n = 10), according to factors: substrate (enamel and dentin), adhesive system [etch-and-rinse (SB) and self-etch]; and the surface treatments (paper discs, impact CVD tips and tangential CVD tip). When CVD tip was used in the impact mode the tip was applied perpendicular to dental surface, while at tangential mode, the tip worked parallel to dental surface. Specimens were tested in tension after 24 h at 0.5 mm/min of cross-head speed. ANOVA results, in MPa showed that in enamel, only adhesive system factor was statistically significant (p = 0.015) under tested conditions, with higher bond strength observed for SB groups. However, in dentin the best bonding performance was obtained in SE groups (p = 0.00). In both tested substrates, results did not show statistically significant difference for factors treatment and its interactions.

Conclusions

It may be concluded that CVD-tip surface treatment, in both tested modes, did not influence on adhesion to enamel and dentin. But, it is important to choose adhesive system according to the tissue available to bonding.