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On the Energy-Momentum Problem in Static Einstein Universe
S. Aygün, I. Tarhan, H. Baysal,
Chin. Phys. Lett. 2007, 24 (2):
355-358
.
The energy-momentum distributions of Einstein's simplest static geometrical model for an isotropic and homogeneous universe are evaluated. For this purpose, Einstein, Bergmann--Thomson, Landau--Lifshitz (LL), Moller and Papapetrou energy-momentum complexes are used in general relativity. While Einstein and Bergmann--Thomson complexes give exactly the same results, LL and Papapetrou energy-momentum complexes do not provide the same energy densities. The Moller energy-momentum density is found to be zero everywhere in Einstein's universe. Also, several spacetimes are the limiting cases considered here.
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Determination of Tungsten Layer Profiles in Bilayer Structures Using X-Ray Reflectivity Method
XU Yao, WANG Zhan-Shan, WANG Bei, WANG Hong-Chang, WU Wen-Juan, ZHANG Shu-Min, ZHANG Zhong, WANG Feng-Li, QIN Shu-Ji, CHEN Ling-Yan
Chin. Phys. Lett. 2007, 24 (2):
366-369
.
An effectual method is presented to determine the profiles of a tungsten (W) layer, such as the density, the thickness and the roughness in the multilayer structures, using the x-ray reflectivity technique. To avoid oxidation effects of tungsten, a B4C capping layer is deposited onto to the W layer. To observe the profiles of the tungsten layer with different thicknesses, three groups of W/B4C bilayers with different thicknesses are prepared by using ultra high vacuum dc magnetron sputtering and measured by an x-ray diffractometer. A type of genetic algorithm called the differential evolution is used to simulate the measurement data so as to obtain the parameters of bilayers. According to the simulation, it is shown that the W layer density varies from 95.26% to 97.51% compared to the bulk. In our experiment, the deposition rate is .044nm/s, and the thickness is varied in the range of 9.8--19.4nm.
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Isoscaling in Statistical Sequential Decay Model
TIAN Wen-Dong, MA Yu-Gang, CAI Xiang-Zhou, FANG De-Qing, GUO Wei, MA Chun-Wang, LIU Gui-Hua, SHEN Wen-Qing, SHI Yu, SU Qian-Min, WANG Hong-Wei, WANG Kun, YAN Ting-ZHi
Chin. Phys. Lett. 2007, 24 (2):
385-388
.
A sequential decay model is used to study isoscaling, i.e. the factorization of the isotope ratios from sources of different isospins and sizes over a broad range of excitation energies, into fugacity terms of proton and neutron umber, R21(N,Z)=Y2(N,Z)/Y1(N,Z)=Cexp(αN+βZ). It is found that the isoscaling parameters α and β have a strong dependence on the isospin difference of equilibrated source and excitation energy, no significant influence of the ource size on α and β has been observed. It is found that α and β decrease with the excitation energy and are linear functions of 1/T and β(Z/A)2 or △(N/A)2 of the sources. Symmetry energy coefficient Csym is constrained from the relationship of α and source △(Z/A)2, β and source △(N/A)2.
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Origin of Unexpected Isotopic Trends in Synthesis of Superheavy Nuclei
LIU Zu-Hua, BAO Jing-Dong,
Chin. Phys. Lett. 2007, 24 (2):
393-396
.
We investigate the dependence of the yield of superheavy nuclei with Z=110, 112, 114 on the neutron excess of the projectile nucleus with a two-parameter Smoluchowski equation. It is confirmed that in some cases, the cold fusion reactions with less neutron excess are more favourable than those with more neutron excess. In order to probe the origin of these unexpected isotopic trends, we also investigate the probabilities of capture, fusion and survival in the cold fusion reactions in detail. It is found that the maximal ER cross sections of the superheavy nuclei exponentially increase as a function of Bf-Sn with Bf being the fission barrier and Sn being the neutron separation energy. Although the probabilities of capture and fusion have some influences, the unexpected isotopic trends mainly due to the ependence of the ER cross sections on the Bf-Sn value. Therefore, the reactions with larger Bf-Sn values should be more favourable for synthesis of superheavy nuclei.
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Calculation of Interaction Potentials between Spherical and Deformed Nuclei
ZHANG Gao-Long, ZHANG Huan-Qiao, LIU Zu-Hua, ZHANG Chun-Lei, LIN Cheng-Jian, YANG Feng, AN Guang-Peng, JIA Hui-Ming, WU Zhen-Dong, XU Xin-Xing, BAI Chun-Lin, YU Ning
Chin. Phys. Lett. 2007, 24 (2):
397-399
.
The interaction potential for spherical-deformed reaction partners is calculated. The shape, separation and orientation dependence of the interaction potential and fusion cross section of the system 32S+154Sm are investigated within the double-folding model of the deformed nuclei. The effective nucleon-nucleon interaction is taken to be the M3Y-Reid potential. The density is considered for three terms of the expansion using the truncated multipole expansion method, which is a deformed Fermi shape with quadrupole and hexadecapole for the density distribution of 154Sm. It is found for the interaction potential that the height and the position of barrier strongly depend on the deformations, the orientation angle of the deformed nucleus, and hence produce great effects on fusion cross section. The integrated fusion cross section is in good agreement with the experimental data.
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Low-Energy Rate Enhancement in Recombination Processes of Electrons into Bare Uranium Ions
WU Yong, ZENG Si-Liang, DUAN Bin, YAN Jun, WANG Jian-Guo, DONG Chen-Zhong, MA Xin-Wen
Chin. Phys. Lett. 2007, 24 (2):
404-407
.
Based on the Dirac--Fork--Slater method combined with the multichannel quantum defect theory, the recombination processes of electrons into bare uranium ions (U 92+ ) are investigated in the relative energy range close to zero, and the x-ray spectrum emitted in the direct radiative recombination and cascades processes are simulated. Compared with the recent measurement, it is found that the rate enhancement comes from the additional populations on high Rydberg states. These additional populations may be produced by other recombination mechanisms, such as the external electric-magnetic effects and the many-body correlation effects, which still remains an open problem.
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Giant Birefringence of Lithium Niobate Crystals in the Terahertz Region
SUN Yi-Min, MAO Zong-Liang, HOU Bi-Hui, LIU Guo-Qing, WANG Li
Chin. Phys. Lett. 2007, 24 (2):
414-417
.
Terahertz time-domain spectroscopy (THz-TDS) is used to study the spectral response of lithium niobate crystals (LiNbO3) in the far infrared region. The optical constants are derived from the measured complex refractive index. A giant birefringence is observed in this material, and the average refractive-index difference between the ordinary wave and the extraordinary wave, no-ne, can reach up to about 1.6. Such a large birefringence is attributed to the different phonon modes of A1(z) and E(x,y). This unusual property makes LiNbO3 a promising material to be used as a functional material in the terahertz region, e.g. employed as wave-plates and polarization separators.
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Interaction between Two-Dimensional White-Light Photovoltaic Dark Spatial Solitons
LIU Zhao-Hong, LIU Si-Min, GUO Ru, GAO Yuan-Mei, SONG Tao, ZHU Nan, QU Di
Chin. Phys. Lett. 2007, 24 (2):
446-449
.
Using fully incoherent white light emitted from an incandescent bulb (a line source) and amplitude mask, we study experimentally the interaction between two 2D white-light photovoltaic dark spatial solitons with three different separations (40μm, 50μm and 60μm) and arrangement directions (parallel to, perpendicular to and tilted at 45° with respect to the crystalline c axis) propagating in parallel in close proximity in self-defocusing LiNbO3:Fe crystal. Experimental results reveal that a 2D white-light dark soliton pair only experiences attractive forces when their mutual separation is sufficiently small (<60μm), and the degree of the attraction depends on their mutual separation and their arrangement direction. When the separation is larger than 60μm, the interaction is not evident.
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Magnetic Behaviour and Heating Effect of Fe3O4 Ferrofluids Composed of Monodisperse Nanoparticles
ZHANG Li-Ying, DOU Yong-Hua, ZHANG Ling, GU Hong-Chen
Chin. Phys. Lett. 2007, 24 (2):
483-486
.
Fe3O4 ferrofluids containing monodisperse Fe3O4 nanoparticles with different diameters of 8, 12, 16 and 18nm are prepared by using high-temperature solution phase reaction. The particles have single crystal structures with arrow size distributions. At room temperature, the 8-nm ferrofluid shows perparamagnetic behaviour, whereas the others display hysteresis properties and the coercivity increases with the increasing particle size. The spin glass-like behaviour and cusps near 190K are observed on all ferrofluids according to the temperature variation of field-cooled (FC) and zero-field-cooled (ZFC) magnetization measurements. The cusps are found to be associated with the freezing point of the solvent. As a comparison, the ferrofluids are dried and the FC and ZFC magnetization curves of powdery samples are also nvestigated. It is found that the blocking temperatures for the powdery samples are higher than those for their corresponding ferrofluids. Moreover, the size dependent heating effect of the ferrofluids is also investigated in ac magnetic field with a frequency of 55kHz and amplitude of 200Oe.
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Deuterium Clusters Fusion Induced by the Intense Femtosecond laser Pulse
LIU Hong-Jie, ZHENG Zhi-Jian, GU Yu-Qiu, ZHANG Bao-Han, RHEE Yong-Joo, NAM Sung-Mo, HAN Jae-Min, RHEE Yong-Woo, YEA Kwon-Hae, CHEN Jia-Bin, WANG Hong-Bin, JIAO Chun-Ye, HE Ying-Ling, WEN Tian-Shu, WEN Xian-Lun, CHEN Ming
Chin. Phys. Lett. 2007, 24 (2):
494-496
.
Neutrons (2.45MeV) from deuterium cluster fusion induced by the intense femtosecond (30fs) laser pulse are experimentally demonstrated. The average neutron yield 103 per shot is obtained. It is found that the yield slightly increases with the increasing laser spot size. No neutron can be observed when the laser intensity I<4.3×1015W/cm2.
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A Comparison between AlN Films Grown by MOCVD Using Dimethylethylamine Alane and Trimethylaluminium as the Aluminium Precursors
HU Wei-Guo, LIU Xiang-Lin, ZHANG Pan-Feng, ZHAO Feng-Ai, JIAO Chun-Mei, WEI Hong-Yuan, ZHANG Ri-Qing, WU Jie-Jun, CONG Guang-Wei, PAN Yi
Chin. Phys. Lett. 2007, 24 (2):
516-517
.
Aluminium nitride (AlN) films grown with dimethylethylamine alane (DMEAA) are compared with the ones grown with trimethylaluminium (TMA). In the high-resolution x-ray diffraction Ω scans, the full width at half maximum (FWHM) of (0002) AlN films grown with DMEAA is about 0.70 deg, while the FWHM of (0002) AlN films grown with TMA is only 0.11 deg. The surface morphologies of the films are different, and the rms roughnesses of the surface are approximately identical. The rms roughness of AlN films grown with DMEAA is 47.4nm, and grown with TMA is 69.4nm. Although using DMEAA as the aluminium precursor cannot improve the AlN crystal quality, AlN growth can be reached at low temperature of 673K. Thus, DMEAA is an alternative aluminium precursor to deposit AlN film at low growth temperatures.
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First-Principles Study of Electronic Structure of the Laves Phase ZrFe2
ZHANG Chang-Wen, ZHANG Zhong, WANG Shao-Qing, LI Hua, DONG Jian-Min, XING Nai-Sheng, GUO Yong-Quan, LI Wei
Chin. Phys. Lett. 2007, 24 (2):
524-526
.
We perform the ab initio calculation for obtaining the density of states and magnetic properties of ZrFe2 Laves phase compound based on the method of augmented plane waves plus local orbital. The results indicate that the ferromagnetic state is more stable than the paramagnetic one, but with a slightly larger volume. The 3d-4d exchange interactions between Fe and Zr electrons lead to the antiparallel coupling for Fe 3d and Zr 4d states, which is responsible for the ferrimagnetic ordering of the compound. The resulting magnetic moment of about 1.98μB for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin states causes a moment of about -0.44μB. Moreover, the resulting magnetic moments with the generalized gradient approximation are more consistent with experimental values than that of the local-spin density approximation.
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Broadband and High Efficient 1530nm Emission from Oxyfluoride Glass Ceramics Codoped with Er 3+ and Yb 3+ Ions
LIU Bao-Rong, ZHAO Li-Juan, SUN Jian, YU Hua, SONG Jie, XU Jing-Jun,
Chin. Phys. Lett. 2007, 24 (2):
527-529
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The emission at 1530nm and its applications in optical communications are discussed. The efficient width of the emission band Δeff, which is up to 91nm, is larger as compared with silica-based glass, bismuth glass and ZrF4--BaF2--LaF3--AlF3--NaF (ZBLAN) glass doped by Er 3+ ions. Under the excitation of 785\,nm laser, the emission integral intensity of 1530nm increases about five times in the glass ceramics higher than that in the glass. This is explained by the quantum cutting process by two-photon emission with phonon assistance. The results indicate that the glass ceramics are a promising candidate for developing broadband optical amplifiers in wavelength-division multiplexed systems.
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Magnetic Quantum Tunnelling in Faster Relaxation Process in Mn12Ac Molecular Magnets
LIU Hai-Qing, SU Shao-Kui, JING Xiu-Nian, LIU Ying, HE Lun-Hua, GE Pei-Wen, YAN Qi-Wei, WANG Yun-Ping
Chin. Phys. Lett. 2007, 24 (2):
532-535
.
The field-tuned ac susceptibility of Mn12Ac single crystal has been measured as functions of temperature and frequency. Two relaxation processes appear in our measurement. One is related to the magnetic quantum tunnelling of a collective spin S=12 by a 61K magnetic barrier and it has been well studied, while the other is faster than the former and its mechanism is unclear. We find that the relaxation time for the faster process shows the minima at H=0 and H=3.4kOe, indicating that the quantum tunnelling also takes place in this process while the resonant fields are different from what we have known before.
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Structural Stability of CaCuMn6O12 under High Pressure and Low Temperature
ZHANG Wang, YAO Li-De, YOU Shu-Jie, YANG Liu-Xiang, YANG Hua, LI Feng-Ying, CHEN Liang-Chen, BAO Zhong-Xing, LI Xiao-Dong, LIU Jing, JIN Chang-Qing, YU Ri-Cheng
Chin. Phys. Lett. 2007, 24 (2):
536-538
.
In situ high pressure energy-dispersive x-ray synchrotron radiation diffraction and resistance experiments are carried out on CaCuMn6O12. Its crystal structure is stable in the measured pressure range. The equation of state of CaCuMn6O12 is obtained from the V/V0-P relationship (V and V0 are the volumes at pressure P and at atmosphere). The bulk modulus B0 is calculated based on the Birch--Murnaghan equation. Low temperature x-ray diffraction shows no phase transition occurring down to 160K.
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Effects of Substrate Temperature and Nitrogen Pressure on Growth of AlN Films by Pulsed Laser Deposition
LV Lei, LI Qing-Shan, LI Li, ZHANG Li-Chun, WANG Cai-Feng, QI Hong-Xia
Chin. Phys. Lett. 2007, 24 (2):
552-554
.
Highly oriented aluminium nitride (AlN) films are grown on p-Si (100) substrates by pulsed laser deposition, and their characteristics of structure and composition are studied by x-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The results show that the deposited films exhibit good crystalline properties with a sharp x-ray diffraction peak at 2θ=33.15°corresponding to AlN h<100> crystalline orientation. The influences of substrate temperature and ambient nitrogen (N2) pressure on the crystallinity of AlN films are remarkable. At room temperature, when the ambient N2 pressure arises from 5×10-6 Pa to 5Pa, the crystallinity of the film becomes better. When the substrate temperature is 600°C, the film has the best crystallinity at 0.05Pa. Furthermore, the effects of substrate temperature and ambient N2 pressure on the combination of Al-N bonds and surface morphology of AlN films are also studied.
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Efficiency Enhancement of Dye-Sensitized Solar Cells: Using Salt CuI as an Additive in an Ionic Liquid
CHEN Lie-Hang, XUE Bo-Fei, LIU Xi-Zhe, LI Ke-Xin, LUO Yan-Hong, MENG Qing-Bo, WANG Rui-Lin, CHEN Li-Quan
Chin. Phys. Lett. 2007, 24 (2):
555-558
.
Energy conversion efficiency of the dye-sensitized solar cell is improved from 3.5% to 4.5% by adding a small amount of CuI into an ionic liquid electrolyte. It is found that other copper-I salts, for example, CuBr, have the same effect for the dye-sensitized solar cell. Experimental results show that no Cu 2+ ions exist in this electrolyte. It is suggested that this improvement is caused by the adsorption of Cu+ onto the TiO2 porous film.
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A New Dopant of NaN3 for High-Concentration-Nitrogen Diamond Synthesized by HPHT
LIANG Zhong-Zhu, JIA Xiao-Peng, Hisao Kanda, MA Hong-An, WANG Dong-Mei, LIU Wan-Qiang, YU Run-Ze
Chin. Phys. Lett. 2007, 24 (2):
559-562
.
Nitrogen is successfully doped in diamond by adding sodium azide (NaN3) as the source of nitrogen to the graphite and iron powders. The diamond crystals with high nitrogen concentration, 1000--2200ppm, which contain the same concentrations of nitrogen with natural diamond, have been synthesized by using the system of iron-carbon-additive NaN3. The nitrogen concentrations in diamond increase with the increasing content of NaN3. When the content of NaN3 is increased to 0.7--1.3wt.%, the nitrogen concentration in the diamond almost remains in a nitrogen concentration range from 1250ppm to 2200ppm, which is the highest value and several times higher than that in the diamond synthesized by a conventional method without additive NaN3 under high pressure and high temperature (HPHT) conditions.
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Optical Characterization of β-FeSi2 Thin Films Prepared by Femtosecond Laser Ablation
ZHOU You-Hua, YANG Guang, ZHANG Zhi-Hua, LONG Hua, DUAN Xiao-Feng, GAO Yi-Hua, ZHENG Qi-Guang, LU Pei-Xiang
Chin. Phys. Lett. 2007, 24 (2):
563-566
.
Iron disilicide thin films are prepared on fused quartz using femtosecond laser deposition (FsPLD) with a FeSi2 alloy target. X-ray diffraction results indicate the films are single-phase, orthorhombic, β-FeSi2. Field scanning electron microscopy, high resolution transmission electron microscopy, UV--VIS--NIR spectroscopy and Raman microscope are used to characterize the structure, composition, and optical properties of the β-FeSi2 films. Normal incidence spectral transmittance and reflectance data indicate a minimum, direct energy gap of 0.85eV. The two most intense lines of Raman scattering peaked at 181.3cm-1 and 235.6cm-1 for the film on fused quartz, and at 191.2cm-1 and 243.8cm-1 for the film on Si (100), are observed.
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Single-Photon Detection at Telecom Wavelengths
SUN Zhi-Bin, MA Hai-Qiang, LEI Ming, WANG Di, LIU Zhao-Jie, YANG Han-Dong, WU Ling-An, ZHAI Guang-Jie, FENG Ji
Chin. Phys. Lett. 2007, 24 (2):
574-576
.
A single-photon detector based on an InGaAs avalanche photodiode has been developed for use at telecom wavelengths. A suitable delay and sampling gate modulation circuit are used to prevent positive and negative transient pulses from influencing the detection of true photon induced avalanches. A monostable trigger circuit eliminates the influence of avalanche peak jitter, and a dead time modulation feedback control circuit decreases the afterpulsing. From performance tests we find that at the optimum operation point, the quantum efficiency is 12% and the dark count rate 1.5×10-6ns-1, with a detection rate of 500kHz.
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79 articles
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