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.     

Super-High Resolution Time Interval Measurement Method Based on Time-Space Relationships

Based on the principle of quantized delay-time, a super-high resolution time interval measurement method is proposed based on time-space relationships. Using the delay-time stability that time and frequency signal travel in a specific medium, the measured time interval can be quantized. Combined with the phase coincidence detection technique, the measurement of time can be changed into the measurement of space length. The resolution and the stability of the measurement system are easily improved. Experimental results show that the measurement resolution of the measured time interval depends on the length difference of the double delay-time unit. When the length difference is set up on millimeter level or sub-millimeter level, super-high measurement resolution from hundreds of picosecond to tens of picosecond can be obtained.     

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.     

A VUV isochromat spectrometer for surface analysis

A vacuum ultraviolet isochromat spectrometer employing an energy selective Geiger-Müller photon counter is described. The mean energy of the spectrometer is 9.7 eV with a standard deviation of ±0.23 eV. Together with the thermal energy distribution of the electrons emitted from a directly heated tungsten cathode, an overall resolution of ±0.33 eV is obtained. Pulsed operation of the x-ray tube avoids additional broadening due to the voltage drop across the filament. Further, pulsed operation of the accelerating voltage is employed to avoid counting losses due to the relatively large dead time of the radiation detector. Operating frequencies of up to 2 kHz are possible. With sensitivities of typically 10⁷ pulses per Coulomb, the anode currents are in the range of 100–200 μA. These attractive properties suggest to employ the method to study surface electronic properties of solids.     

Influence of post-annealing on the properties of Sc-doped ZnO transparent conductive films deposited by radio-frequency sputtering

Sc-doped ZnO transparent conductive films are deposited on glass substrates by radio-frequency sputtering. The influence of post-annealing on the structural, morphologic, electrical, and optical properties of the films is investigated by energy dispersion X-ray spectroscopy, X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The experimental results show that these films are polycrystalline with a preferred [0 0 1] orientation. The lowest resistivity of 2.6 × 10⁻⁴ Ω cm is obtained from the film annealed at 500 °C. The average optical transmittance of the films is over 90%. These results suggest that Sc-doped ZnO is a good candidate for fabricating high performance transparent conductive films.     

Monte-Carlo simulation of optical trap stiffness measurement

The high precision calibration of optical trap stiffness is the foundation of the weak force measurement in an optical tweezers system. And the accuracy of the trap stiffness measurement is limited by the bandwidth of the acquisition system. In this article, such an influence is analyzed and discussed. The stiffness measuring process using an acquisition system with a finite acquisition time is numerically simulated by using Monte-Carlo method. Then the simulated results are analyzed by thermal motion analysis method to deduce the trap stiffness for different trapping system and for measuring systems with different acquisition time. As a comparison the power spectrum analysis method is used to study the thermal motion of the bead and to compute the trap stiffness for the same acquisition system, from which it is concluded that the bandwidth of the acquisition system is determined by its acquisition time, not the sampling frequency. The influence of the finite acquisition time or the limited bandwidth on the trap stiffness measurement is discussed. The numerical simulation shows that the measured position, which is here the average position within the acquisition time, shifts to the trap center due to the trapping force, which gives an alternative interpretation for the deviation of the measured stiffness from the true trap stiffness.     

Micro-Photoluminescence Confocal Mapping of Single V-Grooved GaAs Quantum Wire

We perform the micro-photoluminescence measurement at low temperatures and a scanning optical mapping with high spatial resolution of a single V-grooved GaAs quantum wire modified by the selective ion-implantation and rapid thermally annealing. While the mapping shows the luminescences respectively from the quantum wires and from quantum well areas between quantum wires in general, the micro-photoluminescence at liquid He temperatures reveals a plenty of spectral structures of the PL band for a single quantum wire. The spectral structures are attributed to the inhomogeneity and non-uniformity of both the space structure and compositions of real wires as well as the defects nearby the interface between quantum wire and surrounding quantum well structures. All these make the excitons farther localized in quasi-zero-dimensional quantum potential boxes related to these non-uniformity and/or defects. The results also demonstrate the ability of micro-photoluminescence measurement and mapping for the characterization of both opto-electronic and structural properties of real quantum wires.     

One-Step Implementation of Single Spin Measurement in Spin Star Network

We present an efficient one-step scheme for a single spin measurement based on nuclear magnetic resonance （NMR） techniques. This scheme considerably reduces the time of operation using a spin star network where a target spin and an ancillary spin are coupled to a ring of N spins. As opposed to the proposal in [Phys. Rev. Lett. 97 （2006） 100501] using a cubic lattice crystal to achieve a cubic speedup, the distinct advantage of this scheme is that under ideal conditions it requires the application of only one step to create a system of N correlated spins. In the process of single spin measurement, the total macroscopic magnetization, the individual magnetization and the transfer fidelity are calculated analytically as simple cosine functions of time and the amplitude of irradiation.     

Effect of Quantum Point Contact Measurement on Electron Spin State in Quantum Dots

We study the time evolution of two electron spin states in a double quantum-dot system, which includes a nearby quantum point contact （QPC） as a measurement device. We find that the QPC measurement induced decoherence is in the microsecond timescale. We also find that the enhanced QPC measurement will trap the system in its initial spin states, which is consistent with the quantum Zeno effect.     

Physical Explanation of Influence of Twin and Three Satellite Formation Mode on the Accuracy of Earth's Gravitational Field

The simulated results of the influence of twin and three satellite formation mode on the accuracy of GRACE Earth＇s gravitational field are interpreted from the viewpoint of physics. Because the effective satellite observation information of Earth＇s gravitational field recovery from three-satellite formation mode is only one time more than that of twin satellites, the improvement of the accuracy of Earth＇s gravitational field is far lower than one order of magnitude based on the simple two-times differences between three satellites. Three efficient ways of improving largely the accuracy of measurement of the Earth＇s gravitational field in the future international satellite gravity measurement programme, including proper decrease of satellite orbital altitude, the increase of accuracy from key payloads and an innovation of satellite observation mode are proposed.     

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.      

Analysis of a loss-compensated recirculating delayed self-heterodyne interferometer for laser linewidth measurement

A loss-compensated recirculating delayed self-heterodyne interferometer (LC-RDSHI) for laser linewidth measurement is theoretically analyzed. An analytical result for the output spectrum of the LC-RDSHI is obtained. It is found that the spectrum from a LC-RDSHI is equivalent to a spectrum from a conventional delayed self-heterodyne interferometer with equivalent time delay and frequency shift, but modified by a periodical function, which could significantly influence the laser linewidth measurement. The parameters of a LC-RDSHI must be optimized to permit an accurate and direct measurement of laser linewidth from the output spectrum.     

Numerical simulations of two-dimensional foam by the immersed boundary method

In this paper, we present an immersed boundary (IB) method to simulate a dry foam, i.e., a foam in which most of the volume is attributed to its gas phase. Dry foam dynamics involves the interaction between a gas and a collection of thin liquid-film internal boundaries that partition the gas into discrete cells or bubbles. The liquid-film boundaries are flexible, contract under the influence of surface tension, and are permeable to the gas, which moves across them by diffusion at a rate proportional to the local pressure difference across the boundary. Such problems are conventionally studied by assuming that the pressure is uniform within each bubble. Here, we introduce instead an IB method that takes into account the non-equilibrium fluid mechanics of the gas. To model gas diffusion across the internal liquid-film boundaries, we allow normal slip between the boundary and the gas at a velocity proportional to the (normal) force generated by the boundary surface tension. We implement this method in the two-dimensional case, and test it by verifying the von Neumann relation, which governs the coarsening of a two-dimensional dry foam. The method is further validated by a convergence study, which confirms its first-order accuracy.     

Stable Narrow Linewidth 689nm Diode Laser for the Second Stage Cooling and Trapping of Strontium Atoms

We report stable narrow linewidth laser systems based on self-developed Littman configuration external cavity diode lasers （ECDLs）. The frequency of the ECDL is stabilized to a high fineness ultralow-expansion glass reference cavity with the Pound-Drever-Hall technique. By heterodyne beating of two identical systems, we conclude that the linewidth 4.3× 10^-14 at an averaging measurement time. of each ECDL is reduced to lower than 150 Hz and its frequency stability reaches time of 1 s, the averaged long-term frequency drift is less than 0.2 Hz/s over 30 h     

Viscoelastic dewetting of a polymer film on a liquid substrate

The Dewetting of thin polymer films (60–300 nm) on a non-wettable liquid substrate has been studied in the vicinity of their glass transition temperature. In our experiment, we observe a global contraction of the film while its thickness remains uniform. We show that, in this case, the strain corresponds to simple extension, and we verify that it is linear with the stress applied by the surface tension. This allows direct measurement of the stress/strain response as a function of time, and thus permits the measurement of an effective compliance of the thin films. It is, however, difficult to obtain a complete viscoelastic characterization, as the short time response is highly dependant on the physical age of the sample. Experimental results underline the effects of residual stress and friction when dewetting is analyzed on rigid substrates.     

X光焦斑测量方法研究

采用组合型诊断技术获取Ｘ光辐射时间、空间、能谱相互关联的３维信息,得到了Ｘ光焦斑随时间和随入射激光能量的变化关系,并观测到膨胀等离子体、探测器阈值、测量能区以及测试方位对Ｘ光焦斑测量带来的影响。     

Convergence dynamics of 2-dimensional isotropic and anisotropic Bak-Sneppen models

The conventional Hamming distance measurement captures only short-time dynamics of the displacement between uncorrelated random configurations. The minimum difference technique introduced by Tirnakli and Lyra [U. Tirnakli, M.L. Lyra. Int. J. Mod. Phys. C 14 (2003) 805] is used to study short-time and long-time dynamics of the two distinct random configurations of isotropic and anisotropic Bak-Sneppen models on a square lattice. Similar to a 1-dimensional case, the time evolution of the displacement is intermittent. The scaling behavior of the jump activity rate and waiting time distribution reveal the absence of typical spatial-temporal scales in the mechanism of displacement jumps used to quantify convergence dynamics.     

Advanced analysis concepts for terahertz time domain imaging

Imaging based on ultrashort terahertz (THz) pulses (100-3000 μm) is investigated. The measured pulses are analyzed and the resulting amplitude and time delay information are compared. An algorithm for discrimination of multiple pulses is presented, which can distinguish several layers inside an object. A new measurement concept is presented, which accelerates the measurement of samples with small optical path differences about two orders of magnitudes. Exemplarily different applications from the field of quality management are shown.     

Manipulation of Nanoparticles Using Dark-Field-Illumination Optical Tweezers with Compensating Spherical Aberration

Based on our previous investigation of optical tweezers with dark field illumination [Chin. Phys. Left. 25（2008）329] nanoparticles at large trap depth are better viewed in wide field and real time for a long time, but with poor forces. Here we present the mismatched tube length to compensate for spherical aberration of an oil-immersion objective in a glass-water interface in an optical tweezers system for manipulating nanoparticles. In this way, the critical power of stable trapping particles is measured at different trap depths. It is found that trap depth is enlarged for trapping nanoparticles and trapping forces are enhanced at large trap depth. According to the measurement, 70-nm particles are manipulated in three dimensions and observed clearly at large appropriate depth. This will expand applications of optical tweezers in a nanometre-scale colloidal system.     

热线法测量材料热导率

讨论在SHT-20型热物性自动测量仪上,用热线法测量材料热导率的原理和方法,并给出了测量结果.