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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2014, 31 (9)   Published: 22 August 2014
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GENERAL

Higher-Order Localized Waves in Coupled Nonlinear Schrödinger Equations

WANG Xin, YANG Bo, CHEN Yong, YANG Yun-Qing
Chin. Phys. Lett. 2014, 31 (9): 090201 doi: 10.1088/0256-307X/31/9/090201
Full Text: [PDF 909 KB] (91)
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Higher-order localized waves in coupled nonlinear Schrödinger equations are investigated by the generalized Darboux transformation. We show that two dark-bright solitons together with a second-order rogue wave of fundamental or triangular pattern and two breathers together with a second-order rogue wave of fundamental or triangular pattern coexist in the second-order localized wave for the coupled system. Moreover, by increasing the value of one free parameter, the nonlinear waves in the second-order localized wave can merge with each other. The results further reveal the abundant dynamic behaviors of localized waves in coupled systems.

A Class of Two-Component Adler–Bobenko–Suris Lattice Equations

FU Wei, ZHANG Da-Jun, ZHOU Ru-Guang
Chin. Phys. Lett. 2014, 31 (9): 090202 doi: 10.1088/0256-307X/31/9/090202
Full Text: [PDF 466 KB] (42)
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We study a class of two-component forms of the famous list of the Adler–Bobenko–Suris lattice equations. The obtained two-component lattice equations are still consistent around the cube and they admit solutions with 'jumping properties' between two levels.

The Exact Harmonic Metric for a Moving Reissner–Nordström Black Hole

HE Guan-Sheng, LIN Wen-Bin
Chin. Phys. Lett. 2014, 31 (9): 090401 doi: 10.1088/0256-307X/31/9/090401
Full Text: [PDF 355 KB] (9)
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The exact harmonic metric for a moving Reissner–Nordström black hole with an arbitrarily constant speed is presented. As an application, the post-Newtonian dynamics of a non-relativistic particle in this field is calculated.

The Motion of Spinning Particles in the Spacetime of a Black Hole with a Cosmic String Topological Defect

LAI Chu-Yu, CHEN Ju-Hua, WANG Yong-Jiu
Chin. Phys. Lett. 2014, 31 (9): 090402 doi: 10.1088/0256-307X/31/9/090402
Full Text: [PDF 458 KB] (15)
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The geodesic motion of pseudo-classical spinning particles in the spacetime of a black hole with the topological defect of a cosmic string, is analyzed. The constants of motion are derived in terms of solving the generalized killing equations for spinning space. The bound state orbits in a plane are discussed. Our results are permitted to be regarded as a semiclassical approximation to the quantum Dirac theory which holds to first order in the spin. The existence of the cosmic string factor b distinguishes the case from the one in Schwarzschild spacetime. When one chooses b=1, our results reduce to the case of the Schwarzschild spacetime.

Diagonal Slices of 3D Young Diagrams in the Approach of Maya Diagrams

CAI Li-Qiang, WANG Li-Fang, WU Ke, YANG Jie
Chin. Phys. Lett. 2014, 31 (9): 090501 doi: 10.1088/0256-307X/31/9/090501
Full Text: [PDF 438 KB] (19)
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According to the correspondence between 2D Young diagrams and Maya diagrams and the relation between 2D and 3D Young diagrams, we construct 3D Young diagrams in the approach of Maya diagrams. Moreover, we formulate the generating function of 3D Young diagrams, which is the MacMahon function in terms of Maya diagrams.

The Interaction of Peregrine Solitons

WU Zhen-Kun, ZHANG Yun-Zhe, HU Yi, WEN Feng, ZHANG Yi-Qi, ZHANG Yan-Peng
Chin. Phys. Lett. 2014, 31 (9): 090502 doi: 10.1088/0256-307X/31/9/090502
Full Text: [PDF 764 KB] (47)
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We theoretically investigate the interaction of two in-phase and out-of-phase Peregrine solitons in a Kerr nonlinear medium, addressing both the cases of first- and second-order solitons. Upon adjusting the interval between the solitons, their interactions exhibit different properties. If the interval is sufficiently large, two Peregrine solitons will propagate individually and will not interact each other. However, if the interval is not very large, the Peregrine solitons will strongly interact and display varying behavior.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

The Production of Ξbb at the Photon Collider

YANG Zhong-Juan, ZHAO Xiao-Xia
Chin. Phys. Lett. 2014, 31 (9): 091301 doi: 10.1088/0256-307X/31/9/091301
Full Text: [PDF 541 KB] (12)
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The inclusive production of the doubly heavy baryon Ξbb is investigated with a polarized and unpolarized photon collider. The bb pair in both a color triplet and sextet has been considered to transform into Ξbb. The results indicate that the contribution from the color sextet is about 8% for Ξbb production. For the international linear collider collision energy ranging from 91 GeV to 1000 GeV, the total cross section of Ξbb shows a downtrend, i.e., the production of Ξbb has the maximal rate at √S=91 GeV. Our results indicate that the initial beam polarization may be an important asset for the production of Ξbb. At some collision point, the production rate of Ξbb can be increased by about 17% with an appropriate choice of the initial beam polarization.
NUCLEAR PHYSICS

Maxwellian Averaged Neutron Capture Cross Sections in 56Fe and 57Fe

WANG Tao-Feng, LEE Man-Woo, KIM Guin-Yun, RO Tae-Ik, KANG Yeong-Rok, IGASHIRA Masayuki, KATABUCHI Tatsuya
Chin. Phys. Lett. 2014, 31 (9): 092101 doi: 10.1088/0256-307X/31/9/092101
Full Text: [PDF 1538 KB] (15)
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Measurements of the keV-neutron capture cross sections and radiative γ-ray spectrum of 56Fe and 57Fe are performed based on a 7Li(p,n)7Be reaction neutron source. The incident neutron spectrum on a capture sample is measured by means of a time-of-flight (TOF) method with a 6Li-glass detector. The radiative capture γ-rays emitted from an iron (56Fe or 57Fe) or standard gold (197Au) sample are detected by a large anti-Compton NaI(Tl) spectrometer covered with a heavy shield. The capture yields of samples are obtained by applying a pulse-height weighting technique to the corresponding capture γ-ray pulse-height spectrum. The Maxwellian averaged neutron capture cross sections of 56Fe and 57Fe are derived according to the present capture cross section results.

The Photon Polarization Parameter of 2H(n,γ)3H reaction with Inclusion of the Electric Quadrupole Contribution

H. Sadeghi, M. Mosavi-Khansari
Chin. Phys. Lett. 2014, 31 (9): 092102 doi: 10.1088/0256-307X/31/9/092102
Full Text: [PDF 639 KB] (18)
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We use effective field theory (EFT) for the calculation of neutron–deuteron radiative capture at very low energies. We present here the use of EFT to calculate a low-energy photo-nuclear observable in three-body systems, the photon polarization parameter and fore–aft asymmetry at thermal neutron energies up to next-to-next to leading order (N2LO), with inclusion of the electric quadrupole contribution. The photon polarization parameter in total is found to be Rc=−0.421±0.003 and is in good agreement with the other modern theoretical calculations based on modern nucleon–nucleon potentials. In comparison with our previous work, a satisfactory agreement with the available experimental data is found by inclusion of the electric quadrupole contribution.

Proton Spectroscopic Factors Deduced from Helium-3 Global Phenomenological and Microscopic Optical Model Potentials

Jenny LEE, PANG Dan-Yang, HAN Yin-Lu, M. B. Tsang
Chin. Phys. Lett. 2014, 31 (9): 092103 doi: 10.1088/0256-307X/31/9/092103
Full Text: [PDF 507 KB] (20)
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Global phenomenological GDP08 and microscopic helium-3 optical model potentials have been recently derived. We evaluate these two potential sets by comparing the elastic scattering data of 25 MeV 3He on 16O, 18O, 19F, 23Na, 24Mg, 25Mg, 26Mg, 27Al, 28Si, 30Si, 31P, 32S, 34S, 35Cl, 37Cl, and 39K isotopes. Using the deuteron angular distributions calculated with the distorted wave Born approximation model, we extract the ground-state proton spectroscopic factors from (3He, d) reactions on the same set of nuclei. The extracted proton spectroscopic factors are compared with the large-basis shell-model calculations.

A Sensitivity Test of Extracting the Optical Potential Parameters for 6He+209Bi from the Transfer Reaction 208Pb(7Li,6He)209Bi

WU Zhen-Dong, YANG Lei, LIN Cheng-Jian, JIA Hui-Ming, YANG Feng, XU Xin-Xing, ZHANG Huan-Qiao, LIU Zu-Hua, BAO Peng-Fei, SUN Li-Jie, MA Nan-Ru, ZHENG Lei
Chin. Phys. Lett. 2014, 31 (9): 092401 doi: 10.1088/0256-307X/31/9/092401
Full Text: [PDF 712 KB] (17)
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Recently, an indirect method has been proposed to study the optical model potential of exotic nuclear systems by fitting the transfer reaction angular distribution. The sensitivity test of this transfer method is performed with 208Pb(7Li,6He)209Bi as an example, by varying the potential parameters individually. The results indicate that, except for the ambiguity in the real potential depth V, other optical potential parameters of 6He+209Bi as well as the structural information of the reactions can be extracted reliably. Moreover, the radius parameter of the bound state, rbound, is an extraordinarily sensitive parameter, which should be taken care of in the calculation procedure. The present work provides a theoretical reference for the application of the transfer method.
ATOMIC AND MOLECULAR PHYSICS

The Scaling Law in the Fine-Structure Splitting of 1s2np States for the Lithium Isoelectronic Sequence

CAI Juan, YU Wei-Wei, ZHANG Nan
Chin. Phys. Lett. 2014, 31 (9): 093101 doi: 10.1088/0256-307X/31/9/093101
Full Text: [PDF 633 KB] (8)
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The 'full-core plus correlation' (FCPC) and the 'minimizing the expectation value of the Hamiltonian' methods are extended to calculate the fine-structure splitting of 1s2np (n=2–9) states for the lithium-like systems from Z=21 to 30. The leading order relativistic effect is included by using first-order perturbation theory. The higher-order relativistic and the quantum-electrodynamics contributions to the fine-structure splitting are investigated under a hydrogenic approximation with effective nuclear charges. Our results are compared with other theoretical calculations and experimental results. It is shown that the FCPC method is also effective to obtain the ionic structure for high nuclear ions of lithium-like systems. By fitting our theoretical results, the scaling law of the fine-structure splitting of the lithium isoelectronic sequence behaves like a quartic function of the screened nuclear charge Z*.

An Active Ion Optical Clock

ZHUANG Wei, ZHANG Tong-Gang, CHEN Jing-Biao
Chin. Phys. Lett. 2014, 31 (9): 093201 doi: 10.1088/0256-307X/31/9/093201
Full Text: [PDF 531 KB] (11)
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We propose a scheme for an active ion optical clock with a detailed description of the pumping method, lasing states, output power, linewidth and light shift. Considering 171Yb+ ions in a Paul trap, we propose utilizing a Fabry–Perot resonator to realize the lasing of active optical frequency standards. The quantum-limited linewidth of an active 171Yb+ ion optical clock is narrower than 1 mHz. Based on the mechanism and the advantages of an active optical clock at the ion optical clock transition frequency, this new laser light source as a stable local oscillator will be beneficial to the single-ion optical clock, which currently is one of the most accurate clocks.

The Effect of Polarization Potentials on Proton-Lithium Inelastic Scattering

S. A. Elkilany, A. A. Al-Dawy
Chin. Phys. Lett. 2014, 31 (9): 093401 doi: 10.1088/0256-307X/31/9/093401
Full Text: [PDF 490 KB] (25)
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We deal with the effect of polarization potentials on the inelastic scattering of protons by lithium atoms as a two-channel problem in which the elastic and hydrogen (2s-state) formation channels are open at energies between 10 and 1000 keV. For this purpose, we improve the coupled-static approximation within the framework of the frozen-core picture of the target atom. We use the Lippmann–Schwinger equation and an iterative numerical method to obtain the computer code. This can be carried out by calculating the reactance matrix then to obtain the transition matrix that gives partial and total cross sections. Our results and those determined by previous researchers give reasonable agreement.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

A 52-mJ Ho:YAG Master Oscillator and Power Amplifier with Kilohertz Pulse Repetition Frequency

QIAN Chuan-Peng, YAO Bao-Quan, DUAN Xiao-Ming, JU You-Lun, YU Kuai-Kuai, WANG Yue-Zhu
Chin. Phys. Lett. 2014, 31 (9): 094201 doi: 10.1088/0256-307X/31/9/094201
Full Text: [PDF 618 KB] (17)
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We report on a high energy, high repetition rate Ho:YAG master oscillator and power amplifier (MOPA), resonantly dual-end-pumped by Tm:YLF lasers at room temperature. At the pulse repetition frequency of 1 kHz, we demonstrate a maximum energy of 30 mJ per pulse with a 28.2 ns pulse width in a Ho:YAG oscillator system resonantly double-end-pumped by Tm:YLF lasers. A maximum energy of 52 mJ per pulse with a 30.5 ns pulse width is achieved in the Ho:YAG amplifier, corresponding to a peak power of approximately 1.7 MW. The output wavelength is at 2090.6 nm and 2096.9 nm, and a beam quality factor of M2∼2.1 is achieved.

A Mode-Locked Soliton Erbium-Doped Fiber Laser with a Single-Walled Carbon Nanotube Poly-Ethylene Oxide Film Saturable Absorber

R. Z. R. R. Rosdin, F. Ahmad, N. M. Ali, R. M. Nor, N. R. Zulkepely, S. W. Harun, H. Arof
Chin. Phys. Lett. 2014, 31 (9): 094202 doi: 10.1088/0256-307X/31/9/094202
Full Text: [PDF 584 KB] (36)
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We present a simple, compact and low-cost mode-locked erbium-doped fiber laser (EDFL) using single-walled carbon nanotubes (SWCNTs) embedded in a poly-ethylene oxide (PEO) thin film as a passive saturable absorber. The film is fabricated by using a prepared homogeneous SWCNT solution, which is mixed with a diluted PEO solution and cast onto a glass Petri dish to form, by evaporation, a thin film. The 50 μm-thick film is sandwiched between two fiber connectors to construct a saturable absorber, which is then integrated in an EDFL cavity to generate self-started stable soliton pulses operating at 1560.8 nm. The soliton pulse starts to lase at a pump power threshold of 12.3 mW with a repetition rate of 11.21 MHz, a pulse width of 1.02 ps, an average output power of 0.65 mW and a pulse energy of 57.98 pJ.

Entire Transmission in Negative Directions through a Single Layer of Nanorods

WU Kang-Xin, YU Li, DUAN Gao-Yan, WANG Lu-Lu, XIAO Jing-Hua
Chin. Phys. Lett. 2014, 31 (9): 094203 doi: 10.1088/0256-307X/31/9/094203
Full Text: [PDF 2082 KB] (10)
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We numerically investigate the regulation of beam direction by a single layer of high electrical permittivity nanorods with two kinds of cross-arranged radii. It is found that an oblique incident optical beam transmits more than 95% with a wide range wavelength of 80 nm near 1550 nm in a negative direction. In particular the efficiency can be up to 100% around the wavelength of 1550 nm at a wide-range angle. The results are very promising for designing subwavelength optical elements to realize beam steering in optical integrated circuits.

A Femtosecond-Laser-Induced Fiber Bragg Grating with Supermode Resonances for Sensing Applications

LIU Ning-Liang, LIU Shu-Hui, LU Pei-Xiang
Chin. Phys. Lett. 2014, 31 (9): 094204 doi: 10.1088/0256-307X/31/9/094204
Full Text: [PDF 667 KB] (11)
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A Bragg grating is inscribed into the cladding of an all-solid photonic bandgap fiber by use of side femtosecond illumination. Multimode resonances are observed, with calculations resulting from guided supermodes in the cladding by the phase matching condition. All supermode resonances show nearly the same sensitivity to strain and temperature, about 0.98 pm/μϵ and 12.78 pm/°C, respectively, while their resonant wavelengths are insensitive to bend. An annealing test shows that this grating can endure temperatures higher than 1100°C where it can still keep high reflectivity and good repeatability. Such a Bragg grating could have potential applications in fiber sensors for strain and temperature measurements, with low cross-sensitivity to bend or an external refractive index, especially in harsh environments.

Coherent Beam Combination Using a General Model-Based Method

HUANG Lin-Hai
Chin. Phys. Lett. 2014, 31 (9): 094205 doi: 10.1088/0256-307X/31/9/094205
Full Text: [PDF 719 KB] (9)
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Coherent beam combination techniques can increase the output laser power from a single gain medium. We demonstrate coherent beam combination using the general model-based wavefront error correction method. The experiments for wavefront error correction are performed by using a 7-segment deformable mirror. Both the general model-based method and the stochastic parallel gradient descent algorithm are used to correct the wavefront error generated by a turbulent simulator. The experimental results show that the residual error is obviously reduced in comparison with that by using the SPGD method.

Nonlinear Polarization Rotation-Based Mode-Locked Erbium-Doped Fiber Laser with Three Switchable Operation States

Zian Cheak Tiu, Sin Jin Tan, Arman Zarei, Harith Ahmad, Sulaiman Wadi Harun
Chin. Phys. Lett. 2014, 31 (9): 094206 doi: 10.1088/0256-307X/31/9/094206
Full Text: [PDF 521 KB] (48)
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A simple mode-locked erbium-doped fiber laser (EDFL) with three switchable operation states is proposed and demonstrated based on nonlinear polarization rotation. The EDFL generates a stable square pulse at a third harmonic pulse repetition rate of 87 kHz as the 1480 nm pump power increases from the threshold of 17.5 mW to 34.3 mW. The square pulse duration increases from 105 ns to 245 ns as the pump power increases within this region. The pulse operation switches to the second operation state as the pump power is varied from 48.2 mW to 116.7 mW. The laser operates at a fundamental repetition rate of 29 kHz with a fixed pulse width of 8.5 μs within the pump power region. At a pump power of 116.7 mW, the average output power is 3.84 mW, which corresponds to the pulse energy of 131.5 nJ. When the pump power continues to increase, the pulse train experiences unstable oscillation before it reaches the third stable operation state within a pump power region of 138.9 mW to 145.0 mW. Within this region, the EDFL produces a fixed pulse width of 2.8 μs and a harmonic pulse repetition rate of 58 kHz.

Narrow-Band Thermal Radiation Based on Microcavity Resonant Effect

HUANG Jin-Guo, XUAN Yi-Min, LI Qiang
Chin. Phys. Lett. 2014, 31 (9): 094207 doi: 10.1088/0256-307X/31/9/094207
Full Text: [PDF 680 KB] (18)
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The microcavity resonant effect is used to realize narrow-band thermal radiation. Periodic circular aperture arrays with square lattice are patterned on Si substrates by using standard photolithographic techniques and reactive ion etching techniques. Ag films are deposited on the surface of Si substrates with aperture arrays to improve the infrared reflectance. On the basis of the micromachining process, an Ag/Si structured surface exhibiting narrow-band radiation and directivity insensitivity is presented. The emittance spectra exhibit several selective emittance bands attributed to the microcavity resonance effect. The dependence of emittance spectra on sizes and direction is also experimentally examined. The results indicate that the emittance peak of the Ag/Si structured surface can be modulated by tailoring the structural sizes. Moreover, the emittance peak is independent of the radiant angle, which is very important for designing high-performance thermal emitters.

A Reflective Nonlinear Acoustic Microscope to Contour the Quantitative Adhesion at a Bonded Solid-Solid Interface

CHEN Jian-Jun, ZHANG De, LIU Xiao-Zhou
Chin. Phys. Lett. 2014, 31 (9): 094301 doi: 10.1088/0256-307X/31/9/094301
Full Text: [PDF 1014 KB] (13)
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We set up a reflective nonlinear acoustic microscope to contour the quantitative adhesion at a bonded solid-solid interface by a contact acoustic nonlinearity (CAN) method. The principle of the reflective nonlinear acoustic microscope is described. After the vibration amplitude of the incident, focusing wave at the bonded interface is calculated, the standard adhesion with a complete bonding state is established by the tension test, the reflective CAN parameter is calibrated, and the quantitative contour of the adhesion at the interface can be obtained. The experimental contours of two samples are also presented. Compared with the transmitted microscope, the reflective one is more convenient and more suitable for practical applications.

Effect of Source's Height on Air-to-Water Sound Transmission with a Small-Scale Rough Sea Surface

ZHANG Ling-Shan, PENG Zhao-Hui
Chin. Phys. Lett. 2014, 31 (9): 094302 doi: 10.1088/0256-307X/31/9/094302
Full Text: [PDF 1090 KB] (8)
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A self-consistent perturbation approach is presented for analyzing the effect of the airborne source's height on the air-to-water sound transmission in shallow water with a randomly rough sea surface. It is shown in early researches that, in shallow water with a smooth sea surface, the airborne source's height mostly affects the phase of the sound field and barely influences the amplitude. However, in shallow water with a rough sea surface, few researches about such a problem have been published. In this work, the sound fields in shallow water with a randomly rough sea surface induced by an airborne source at different heights are calculated by a self-consistent perturbation approach. The numerical simulation results show that the fluctuation of the scattered field decreases as the source's height increases, in contrast, the averaged energy of the total field is hardly influenced by the source's height in the statistical sense.

Design of the Coordinate Transformation Function for Cylindrical Acoustic Cloaks with a Quantity of Discrete Layers

CAI Li, WEN Ji-Hong, YU Dian-Long, LU Zhi-Miao, WEN Xi-Sen
Chin. Phys. Lett. 2014, 31 (9): 094303 doi: 10.1088/0256-307X/31/9/094303
Full Text: [PDF 732 KB] (32)
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Acoustic cloak based on coordinate transformation is of great topical interest and has promise in potential applications such as sound transparency and insulation. The frequency response of acoustic cloaks with a quantity of discrete homogeneous layers is analyzed by the acoustic scattering theory. The effect of coordinate transformation function on the acoustic total scattering cross section is discussed to achieve low scattering with only a few layers of anisotropic metamaterials. Also, the physics of acoustic wave interaction with the interfaces between the discrete layers inside the cloak shell is discussed. These results provide a better way of designing a multilayered acoustic cloak with fewer layers.

Crack Arrest in Brittle Ceramics Subjected to Thermal Shock and Ablation

WANG Yan-Wei, YU He-Long, TANG Hong-Xiang, FENG Xue
Chin. Phys. Lett. 2014, 31 (9): 094601 doi: 10.1088/0256-307X/31/9/094601
Full Text: [PDF 1311 KB] (7)
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Ceramics are suitable for high temperature applications, especially for aerospace materials. When serving in high temperature environments, ceramics usually have to deal with the challenge of both thermal shock and ablation. We report the crack arrest in brittle ceramics during thermal shock and ablation. In our experiment, the specimens of Al2O3 are subjected to oxygen-propane flame heating until the temperature arises up to 1046°C and then are cooled down in air. The crack occurs, however, it does not propagate when arrested by the microstructures (e.g., micro-bridges) of the crack tip. Such micro-bridge enhances the toughness of the brittle ceramics and prevents the crack propagation, which provides a hint for design of materials against the thermal shock.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Placement Scheme of Numerous Laser Beams in the Context of Fiber-Based Laser Fusion

XU Teng, XU Li-Xin, WANG An-Ting, GU Chun, WANG Sheng-Bo, LIU Jing, WEI An-Kun
Chin. Phys. Lett. 2014, 31 (9): 095201 doi: 10.1088/0256-307X/31/9/095201
Full Text: [PDF 762 KB] (13)
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A simple scheme based on the uniform distribution for the placement of numerous laser beams in the context of fiber-based laser fusion is proposed. It is theoretically demonstrated that all modes of the geometrical factor can be eliminated if sufficient laser beams are uniformly distributed on the sphere. In the case of a finite number of laser beams, a quasi-uniform distribution of beams can be achieved based on the equal area subdivision algorithm. Numerical simulations indicate that with the increasing number of laser beams, the order of the dominant geometrical mode increases, and the irradiation nonuniformity decreases accordingly.

Millimeter Propagation and High Confinement in Rhombus-Based Hybrid Plasmonic Waveguides

HU Ru, LANG Pei-Lin, ZHAO Yu-Fang, DUAN Gao-Yan, WANG Lu-Lu, DAI Jin, CHEN Zhao, YU Li, XIAO Jing-Hua
Chin. Phys. Lett. 2014, 31 (9): 095202 doi: 10.1088/0256-307X/31/9/095202
Full Text: [PDF 789 KB] (40)
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A hybrid plasmonic waveguide, consisting of two dielectric nanowires symmetrically put at the opposite corner angles of a rhombic metal, is proposed and numerically analyzed by the finite-element method. Simulations show that the present waveguide can achieve the millimeter propagation distance (1244 μm) and deep subwavelength mode area (5.5×10−3 μm2), simultaneously. Compared with the previous hybrid waveguides based on cylinder nanowires or flat films, the rhombic corner angles enable our waveguide to achieve both longer propagation distance and smaller mode area. This is due to the enhanced coupling between the dielectric guided mode in nanowires and the surface plasmon polariton mode at rhombic surface. Furthermore, the extreme confinement near the rhombic corner angles can strengthen the light-matter interaction greatly and make the present waveguide useful in many applications, such as nonlinear photonics, high-quality nanolasers and nanophotonic waveguides.

Dynamic Characteristics of a Microhollow Cathode Sustained Discharge with Split Third Electrodes for Potential Flow Application to Flow Velocimetry

Sharmin Sultana, Jichul Shin
Chin. Phys. Lett. 2014, 31 (9): 095203 doi: 10.1088/0256-307X/31/9/095203
Full Text: [PDF 1235 KB] (36)
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The dynamic behavior of a microhollow cathode sustained discharge with split third electrodes is experimentally investigated. The sustained discharge swells isotropically in the presence of a small amount of argon gas flow that is not clearly detectable with a conventional single third electrode. At high flow rates, the sustained discharge transitions to a fast-moving constricted discharge with an arc shape. The modified discharge structure causes a shift in current distribution over the third electrodes, and the current peak location varies linearly with the flow rate over a certain flow range. Such linear behavior may be applied to in situ flow velocity measurement.

Analysis of Atomic Electronic Excitation in Nonequilibrium Air Plasmas

HE Xin, DANG Wei-Hua, JIA Hong-Hui, YIN Hong-Wei, ZHANG Hai-Liang, CHANG Sheng-Li, YANG Jun-Cai
Chin. Phys. Lett. 2014, 31 (9): 095204 doi: 10.1088/0256-307X/31/9/095204
Full Text: [PDF 830 KB] (9)
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Electronic excitation of atoms is studied in nonequilibrium air plasmas with the electronic temperature between 8000 K and 20000 K. By using the modified Saha–Boltzmann equation, our simplified method takes into account significant radiative processes and strong self-absorption of the vacuum ultraviolet lines. Calculations are carried out at three trajectory points of the Fire II flight experiment. Good agreement with the detailed collisional-radiative model is obtained, and the performance of this method in applications to highly nonequilibrium conditions is better than Park's quasi-steady-state model and Spradian-9.0. A short discussion on the influence of optical thickness of the vacuum ultraviolet radiation is also given. It costs about 2.9 ms on the average to solve one cell of the shock layer on a low cost computer, which shows that the present method is fast and efficient.

Temporal Evolution of Excited Level Populations in a High-Velocity Argon Plasma Flow

SUN Su-Rong, WANG Hai-Xing
Chin. Phys. Lett. 2014, 31 (9): 095205 doi: 10.1088/0256-307X/31/9/095205
Full Text: [PDF 551 KB] (10)
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A simplified collisional-radiative model is applied to a high velocity plasma flow through the arcjet nozzle to investigate the temporal evolution of excited level population densities in the selected spatial positions inside arcjet thruster. Computations are carried out for various sets of input parameters such as electron temperature, electron number density, atom temperature, and pressure. The numerical results illustrate that the extent of the ionization-recombination non-equilibrium is strongly dependent on the electron temperature and pressure, and is significantly affected by resonance radiation.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Cu Segregation at Σ5 Symmetrical Grain Boundary in α-Fe: Atomic-Level Simulations

WANG Dong, GAO Ning, GAO Fei, WANG Zhi-Guang
Chin. Phys. Lett. 2014, 31 (9): 096801 doi: 10.1088/0256-307X/31/9/096801
Full Text: [PDF 635 KB] (6)
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Cu-rich precipitation is regarded as one of the main issues causing embrittlement of ferritic steels. In the present work, the Cu segregation at Σ5 {012} symmetrical grain boundary (GB) in BCC iron is investigated by combining Metropolis Monte Carlo and molecular statics approaches. The segregation driven energies of Cu clusters decrease with increasing the distance from GB and also depend on the cluster size. The length scales associated with Cu segregation at GB are determined. All these results indicate that Cu atoms prefer to segregate at Σ5 GB, which may account for the embrittlement of ferritic steels. The present results provide important knowledge to understand the detailed mechanisms of Cu segregation at GB and also the possible effects on mechanical properties of α-Fe.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Multiscale Study of Hydrogen Adsorption on Six Designed Covalent Organic Frameworks Based on Porphyrazine, Cyclobutane and Scandium

LI Le-Le, GAO Teng-Fei, ZHANG Ruan-Yu, ZHANG Hong
Chin. Phys. Lett. 2014, 31 (9): 097101 doi: 10.1088/0256-307X/31/9/097101
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The first-principles method of hydrogen adsorption is used to investigate the interaction of H2 with the scandium-porphyrazine (Sc-Pz) and porphyrazine (Pz) clusters. The result shows that the interaction of H2 with Sc-Pz is stronger than with Pz. Then grand canonical Monte Carlo simulations are used to investigate hydrogen adsorption in six designed covalent organic frameworks (COFs), which are designed based on porphyrazine, cyclobutane and scandium. When the pressure is from 0.1 to 100 bar and the temperature is 298 K and 77 K, the hydrogen adsorption capacities of the six COFs are calculated. We further study the importance of Sc and fillers to improve the H2 uptake in the modified COFs by analyzing the isosteric heat of hydrogen adsorption.

States of Excitons and Linear Optical Spectra in Metallic Single-Walled Carbon Nanotubes

YU Gui-Li, LI Gui-Chen, JIA Yong-Lei, TANG Gang
Chin. Phys. Lett. 2014, 31 (9): 097102 doi: 10.1088/0256-307X/31/9/097102
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Considering the exciton effect, the excitation energy and its binding energy of the metallic single-walled carbon nanotubes (SWNTs) are theoretically studied by using the simple tight-binding model, based on which the linear absorption spectra are also calculated. It is found that due to the trigonal warping effect, the excitation energies of the linear optical spectra all are split into two corresponding ones. Additionally, the splitting depends on both the chirality and the transition energy: (1) the splitting is maximal for the zigzag tubes, the splitting decreases with the increasing chiral angle; (2) the higher the transition energy is, the larger the splitting is. It is very interesting to find that the obtained results are in good agreement with the experimental results.

Transport Behavior in Spinel Oxide MgTi2O4

ZHU Yuan-Yuan, WANG Rong-Juan, WANG Li, LIU Yong, XIONG Rui, SHI Jing, AN Li-Heng, SUN Duo-Hua
Chin. Phys. Lett. 2014, 31 (9): 097201 doi: 10.1088/0256-307X/31/9/097201
Full Text: [PDF 683 KB] (16)
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Spinel oxide MgTi2O4 is synthesized by the spark plasma sintering method. The temperature dependences of magnetic susceptibility and resistance are measured and investigated in detail. It is shown that the transition of MgTi2O4 occurs at the phase transition temperature Tt258 K. The fits of resistance versus temperature curve demonstrate that MgTi2O4 displays metal behavior above Tt, while a dual conducting mechanism, the Mott-insulator-like variable range hopping and normal activated conduction, is suggested to be responsible for the transport behavior of MgTi2O4 below Tt.

Effects of Pretreatment on the Electronic Properties of Plasma Enhanced Chemical Vapor Deposition Hetero-Epitaxial Graphene Devices

ZHANG Lian-Chang, SHI Zhi-Wen, YANG Rong, HUANG Jian
Chin. Phys. Lett. 2014, 31 (9): 097301 doi: 10.1088/0256-307X/31/9/097301
Full Text: [PDF 641 KB] (16)
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Quasi-monolayer graphene is successfully grown by the plasma enhanced chemical vapor deposition hetero-epitaxial method we reported previously. To measure its electrical properties, the prepared graphene is fabricated into Hall ball shaped devices by the routine micro-fabrication method. However, impurity molecules adsorbed onto the graphene surface will impose considerable doping effects on the one-atom-thick film material. Our experiment demonstrates that pretreatment of the device by heat radiation baking and electrical annealing can dramatically influence the doping state of the graphene and consequently modify the electrical properties. While graphene in the as-fabricated device is highly p-doped, as confirmed by the position of the Dirac point at far more than +60 V, baking treatment at temperatures around 180°C can significantly lower the doping level and reduce the conductivity. The following electrical annealing is much more efficient to desorb the extrinsic molecules, as confirmed by the in situ measurement, and as a result, further modify the doping state and electrical properties of the graphene, causing a considerable drop of the conductivity and a shifting of Dirac point from beyond +60 V to 0 V.

Extraction of Channel Length Independent Series Resistance for Deeply Scaled Metal-Oxide-Semiconductor Field-Effect Transistors

MA Li-Juan, JI Xiao-Li, CHEN Yuan-Cong, XIA Hao-Guang, ZHU Chen-Xin, GUO Qiang, YAN Feng
Chin. Phys. Lett. 2014, 31 (9): 097302 doi: 10.1088/0256-307X/31/9/097302
Full Text: [PDF 563 KB] (12)
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The recently developed four Rsd extraction methods from a single device, involving the constant-mobility method, the direct IdVgs method, the conductance method and the Y-function method, are evaluated on 32 nm n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs). It is found that Rsd achieved from the constant-mobility method exhibits the channel length independent characteristics. The L-dependent Rsd extracted from the other three methods is proven to be associated with the gate-voltage-induced mobility degradation in the extraction procedures. Based on L-dependent behaviors of Rsd, a new method is proposed for accurate series resistance extraction on deeply scaled MOSFETs.

Electrical Control of Edge Magnetism in Two-Dimensional Buckled Honeycomb Lattice

BAO Wei-Cheng, ZOU Liang-Jian
Chin. Phys. Lett. 2014, 31 (9): 097501 doi: 10.1088/0256-307X/31/9/097501
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We theoretically study indirect spin coupling strength between two magnetic impurities located on honeycomb Kane–Mele zigzag ribbon (KMZR) with periodic and open boundary (PB and OB). We show that spin interaction J in PB ribbons displays an AFM-FM oscillating behavior with increasing the staggered potential and electron density, and approaches to maximum at the edges. While the spin coupling in OB KMZR shows a trivial smooth AFM coupling with varying staggered potential. Such a novel J(Δ) behavior is the combining effect of finite size, topological edge states and inversion symmetry breaking induced by the staggered potential. We propose that one could control the edge magnetism electrically in two-dimensional buckled honeycomb materials, e.g., silicence, germanene and stanene.

Preparation of Ni-B Coating on Carbonyl Iron and Its Microwave Absorption Properties in the X Band

LI Rong, ZHOU Wan-Cheng, QING Yu-Chang
Chin. Phys. Lett. 2014, 31 (9): 097701 doi: 10.1088/0256-307X/31/9/097701
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Ni−B coated carbonyl iron particles (CI@Ni−B) are prepared by the electroless plating technique. The structure, morphology, and antioxidant properties of the CI@Ni-B particles are analyzed. The results demonstrate that the CI particles have been coated with intact spherical-shell Ni-B coating, indicating the core-shell structure of CI@Ni-B particles, and the Ni-B coating can prevent the further oxidation of the CI particles. Compared with the raw CI particles/paraffin coatings with the same coating thickness of 2.0 mm and particles content of 70%, the CI@Ni-B particles/paraffin coatings possess higher microwave absorption (the RL exceeding -10 dB is obtained in the whole X band (8.2–12.4 GHz) with minimal RL of -35.0 dB at 9.2 GHz).

Efficient Phosphorescent Organic Light Emitting Diodes Using F4TCNQ as the Indium-Tin-Oxide Modification Layer

JIAO Bo, ZHU Xiao-Bo, WU Zhao-Xin, YU Yue, HOU Xun
Chin. Phys. Lett. 2014, 31 (9): 097801 doi: 10.1088/0256-307X/31/9/097801
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A phosphorescent organic light emitting diode by using tetrafluorotetracyanoquinodimethane (FTCNQ) as the indium-tin-oxide modification layer and 4,4'-bis(carbazol-9-yl)biphenyl (CBP) as the hole transporting layer is reported. CBP doped with a green phosphorescent dopant, tris(2-(p-tolyl)pyridine) iridium(III) (Ir(mppy)3) is used as the emission layer in this device, and the maximum current efficiency of 31.3 cd/A is achieved. Furthermore, low efficiency roll-off of 10.4% is observed with device luminance increasing from 100 cd/m2 (29.7 cd/A) to 10000 cd/m2 (26.5 cd/A). It is demonstrated that a charge-generation area is formed at F4TCNQ/CBP interface, which will benefit hole injection into the hole transporting layer. Moreover, use of the CBP hole transporting layer will benefit the low efficiency roll-off by broadening triplet exciton formation, as well as by avoiding accumulation of unbalanced carrier at the hole transporting layer/emission layer interface.

Optical Properties of Plate-Shaped ZnO Nanocrystals Grown by a Facile and Environmentally Friendly Molten Salt Method

WANG Wen-Zhong, LIANG Yu-Jie, SHI Hong-Long, ZHANG Gu-Ling
Chin. Phys. Lett. 2014, 31 (9): 097802 doi: 10.1088/0256-307X/31/9/097802
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Plate-shaped ZnO nanocrystals are prepared by a facile and environmentally friendly molten salt method, in which Zn5(CO3)2(OH)6 nanorods are first synthesized via a facile one-step, solid-state reaction route at room temperature and then decomposed in NaCl flux. Photoluminescence property demonstrates that the as-prepared plate-shaped ZnO nanocrystals exhibit a strong blue emission centered at about 483 nm. Raman scattering spectrum reveals that the as-prepared plate-shaped ZnO nanocrystals have the oxygen deficiency, which can be confirmed by the appearance of oxygen-deficiency-related vibrational mode at 583 cm−1 in the Raman spectrum. The oxygen deficiency existing in the plate-shaped ZnO nanocrystals results in the formation of the oxygen vacancy, which is most likely responsible for the strong blue emission of the plate-shaped ZnO nanocrystals. These new plate-shaped ZnO nanocrystals with strong blue emission are expected to show considerable potential applications in luminescence, lasing and optoelectronic devices.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Morphology and Microstructure of InAs Nanowires on GaAs Substrates Grown by Molecular Beam Epitaxy

SHI Sui-Xing, LU Zhen-Yu, ZHANG Zhi, ZHOU Chen, CHEN Ping-Ping, ZOU Jin
Chin. Phys. Lett. 2014, 31 (9): 098101 doi: 10.1088/0256-307X/31/9/098101
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We successfully grow high-quality wurtzite InAs nanowires on GaAs substrates. The influences of growth temperature and orientations of GaAs substrates on the morphology and microstructure of InAs nanowires are also investigated. We find that a low growth temperature (330°C) is beneficial to the synthesis of uniform defect-free InAs nanowires. Meanwhile, InAs nanowires along 〈111〉B direction are always dominated despite the variation of GaAs substrate orientations.

Insights of Unconventionally Long Exposure Time in Atomic Layer Deposition Al2O3 to Modify SnO2 Photoanode of Dye-Sensitized Solar Cells

DONG Wan, WANG Zheng-Duo, YANG Li-Zhen, MENG Tao, CHEN Qiang
Chin. Phys. Lett. 2014, 31 (9): 098401 doi: 10.1088/0256-307X/31/9/098401
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Porous SnO2 photoanodes coated by alumina through atomic layer deposition technology are reported. It is found that when the dosing time of precursor is extended over 11 s, the 125% maximum increase of cell efficiency is achieved. It is believed that besides the interfacial charge recombination being efficiently suppressed by this ultra-thin coating, the increased absorption of dyes and elimination of the high density of monoenergetic surface states on SnO2 might play a positive role in improving the cell efficiency. The reason is that a long exposure time of precursor can guarantee the 100% coverage of alumina on porous SnO2, which is further explained by a built three-step model. Then we conclude that for a high cell efficiency in porous photoelectrode a long exposure time is indispensable.

An Ultra-Miniature Cell-Type Rb Atomic Clock Based on a Novel Waveguide Cavity

BAI Li-Na, CAO Yuan-Hong, LIU Lei-Ji, YANG Lin, ZHENG Xing-Shi, ZHOU Wei
Chin. Phys. Lett. 2014, 31 (9): 098402 doi: 10.1088/0256-307X/31/9/098402
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We introduce a novel waveguide cavity for ultra-miniature cell-type Rb atomic clock. In the cavity, a coupling ring shaped to be a semi-circle imports an rf signal from electronics, a screw regulator acts as a medium coupler to transmit the microwave signal into the absorption cell, and both the parts serve as a filter to suppress useless components except 6.8 GHz. Furthermore, the waveguide cavity can be used to design a miniature Rb atomic clock, and spread it to a chip-scale atomic clock. We have completed the design of the smallest cell-type Rb atomic clock in the world based on this waveguide cavity. It has not only a small size but also obviously better key performances than those of other miniature Rb atomic clocks. This ultra-miniature cell-type Rb atomic clock aging is 4×10−13/d, which is obviously slower than that of other miniature Rb atomic clocks.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Gravitational Waves in f(R) Gravity

ZHOU Xiao-Ying, HE Jian-Hua
Chin. Phys. Lett. 2014, 31 (9): 099801 doi: 10.1088/0256-307X/31/9/099801
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We investigate the imprint of the tensor perturbation on the angular power spectra of the cosmic microwave background in the f(R) gravity. Comparing with the scalar perturbation, we find that the tensor perturbation in the f(R) gravity has little impact on the temperature angular power spectra. There is also little impact of the tensor perturbation in the f(R) gravity on the E and B types of angular power spectra.
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