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Highly Efficient Continuous-Wave Mid-Infrared Intracavity Singly Resonant Optical Parametric Oscillator Based on MgO:PPLN
YAN Bo-Xia**, BI Yong, ZHOU Mi, WANG Dong-Dong, QI Yan, FANG Tao, WANG Bin, WANG Yan-Wei, ZHENG Guang, CHENG Hua
Chin. Phys. Lett. 2010, 27 (12):
124203
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DOI: 10.1088/0256-307X/27/12/124203
We present a compact all-solid-state cw mid-infrared intracavity singly resonant optical parametric oscillator (OPO) that is based on a self-fabricated 1-mm-thick 40-mm-long doped MgO periodically poled lithium niobate (MgO:PPLN). At a diode pump power of 15.6 W, the compact intracavity Nd:YVO4/MgO:PPLN OPO produced 1.9 W output power at 3.19 μm, corresponding to conversion efficiency of 12.2% from the laser diode pump to OPO idler output.
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Off-Resonant Third-Order Optical Nonlinearity of Au Nanoparticle Array by Femtosecond Z-scan Measurement
WANG Kai, LONG Hua, FU Ming, YANG Guang**, LU Pei-Xiang, **
Chin. Phys. Lett. 2010, 27 (12):
124204
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DOI: 10.1088/0256-307X/27/12/124204
A periodic triangular-shaped Au nanoparticle array is fabricated on a quartz substrate using nanosphere lithography and pulsed laser deposition, and the linear and nonlinear optical properties of metal particles are studied. The morphology of the polystyrene nanosphere mask (D=820 nm) and the Au nanoparticle array are investigated by scanning electron microscopy. The surface plasmon resonance absorption peak is observed at 606 nm, which is in good agreement with the calculated result using the discrete dipole approximation method. By performing the Z−scan method with femtosecond laser (800 nm, 50 fs), the optical nonlinearities of Au nanoparticle array are determined. The results show that the Au particles exhibit negative nonlinear absorption and positive nonlinear refractive index with the effective third-order optical nonlinear susceptibility χeff(3) can be up to (8.8±1.0)×10−10 esu under non-resonant femtosecond laser excitation.
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Stimulated Brillouin Scattering Damage of Large-Aperture Fused Silica Grating
HAN Wei, HUANG Wan-Qing, LI Ke-Yu, WANG Fang, FENG Bin, JIA Huai-Ting, LI Fu-Quan, XIANG Yong, JING Feng, ZHENG Wan-Guo
Chin. Phys. Lett. 2010, 27 (12):
124205
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DOI: 10.1088/0256-307X/27/12/124205
Laser induced damage experiment is carried out on a large aperture laser facility. Severe damage is observed on a large-aperture fused silica grating which presents dense craters on the front surface and six cracks alternatively located at the front and the rear surface. The bizarre fact about the damage on the grating is that, unlike other optics, the damage craters are almost on the front surface. According to observation, damage phenomenon is due to the stimulated Brillouin scattering (SBS) effect occurring in the grating, which includes the transverse SBS, the back SBS and the zigzag SBS.
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High-Quality Continuous-Wave Imaging with a 2.53THz Optical Pumped Terahertz Laser and a Pyroelectric Detector
BING Pi-Bin, **, YAO Jian-Quan, XU De-Gang, XU Xiao-Yan, LI Zhong-Yang,
Chin. Phys. Lett. 2010, 27 (12):
124209
.
DOI: 10.1088/0256-307X/27/12/124209
A cw terahertz (THz) transmission imaging system is demonstrated and a high-quality THz image can be obtained using a pyroelectric detector. The factors that affect the imaging quality, such as the THz wavelength, spot size on the sample surface, step length of the motor, and frequency of the chopper, are theoretically and experimentally investigated. The experimental results show that the maximum resolution of the THz image can reach 0.4 mm with the THz wavelength of 118.8 μm, the spot size of 1.8 mm and the step length of 0.25 mm.
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Cluster Model for Wave-Like Motions of a 2D Vertically Vibrated Granular System
CAI Hui, MIAO Guo-Qing
Chin. Phys. Lett. 2010, 27 (12):
124501
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DOI: 10.1088/0256-307X/27/12/124501
The fact that trapezoid clusters exist in 2D vertically vibrated granular systems leads us to construct a cluster model, in which wave-like motions are explained as the result of cluster-plate and cluster-cluster collisions. By analyzing the collision of one cluster with the plate in detail, we deduce a basic equation from velocity relationship, which could be separated into two correlative equations: one relates wave-like motion with exciting acceleration, and we call it the excitation condition; the other relates wavelength with exciting frequency, viz., the dispersion relation. The theoretical results are in agreement with the experimental ones, which supports the idea of the cluster model. Moreover, from the cluster model, we also predict a possibility of abnormal dispersion relation of a 2D granular system.
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Radiation Temperature Measurement of an Imploded X-Ray Source with a Filtered-Multi-Channel Pinhole Camera
WANG Shou-Jun, DONG Quan-Li**, ZHANG Yi, LI Yu-Tong, ZHANG Lei, Shinsuke Fujioka, Norimasa Yamamoto, Hiroaki Nishimura, ZHANG Jie, **
Chin. Phys. Lett. 2010, 27 (12):
125202
.
DOI: 10.1088/0256-307X/27/12/125202
The Plankian radiation temperature of an intense x-ray source driven by imploding spherical CH plastic shell is measured with a filtered-multi-channel pinhole camera. With all the twelve laser beams of the GEKKO-XII laser facility applied, the average radiation temperature is measured to be around 465 eV while the temperature at the core is as high as 818 eV. This value is confirmed by other instruments applied.
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Jet-Like Long Spike in Nonlinear Evolution of Ablative Rayleigh–Taylor Instability
YE Wen-Hua, **, WANG Li-Feng, , HE Xian-Tu,
Chin. Phys. Lett. 2010, 27 (12):
125203
.
DOI: 10.1088/0256-307X/27/12/125203
We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh–Taylor instability (ARTI) experiments by numerical simulations. A preheating model κ(T)=κSH[1+f(T)], where κSH is the Spitzer–Härm (SH) electron conductivity and f(T) interprets the preheating tongue effect in the cold plasma ahead of the ablative front [Phys. Rev. E 65 (2002) 57401], is introduced in simulations. The simulation results of the nonlinear evolution of the ARTI are in general agreement with the experiment results. It is found that two factors, i.e., the suppressing of ablative Kelvin–Helmholtz instability (AKHI) and the heat flow cone in the spike tips, contribute to the formation of jet-like long spike in the nonlinear evolution of the ARTI.
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Strain-Engineered Low-Density InAs Bilayer Quantum Dots for Single Photon Emission
LI Zhan-Guo, LIU Guo-Jun**, LI Lin, FENG Ming, LI Mei, LU Peng, ZOU Yong-Gang, LI Lian-He, GAO Xin
Chin. Phys. Lett. 2010, 27 (12):
126801
.
DOI: 10.1088/0256-307X/27/12/126801
We investigate the growth of strain-engineered low-density InAs bilayer quantum dots (BQDs) on GaAs by molecular beam epitaxy. Owing to increasing dot size and In composition of the upper QDs, low-density BQDs in a GaAs matrix with an emission wavelength up to 1.4 μm at room temperature are achieved. Such a wavelength is larger than that of conventional QDs in a GaAs matrix (generally of about 1.3 μm). The optical properties of the BQDs are sensitive to annealing temperature used after spacer layer growth. Significant decrease of integrated PL intensity is observed as the annealing temperature increases. At 10 K, single photon emission from the BQDs with wavelength around 1.3 μm is observed.
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Effect of High Temperature Annealing on Conduction-Type ZnO Films Prepared by Direct-Current Magnetron Sputtering
SUN Li-Jie, HE Dong-Kai, XU Xiao-Qiu, ZHONG Ze, WU Xiao-Peng, LIN Bi-Xia, FU Zhu-Xi
Chin. Phys. Lett. 2010, 27 (12):
126802
.
DOI: 10.1088/0256-307X/27/12/126802
We experimentally find that the ZnO thin films deposited by dc-magnetron sputtering have different conduction types after annealing at high temperature in different ambient. Hall measurements show that ZnO films annealed at 1100°C in N2 and in O2 ambient become n−type and p-type, respectively. This is due to the generation of different intrinsic defects by annealing in different ambient. X-ray photoelectron spectroscopy and photoluminescence measurements indicate that zinc interstitial becomes a main defects after annealing at 1100°C in N2 ambient, and these defects play an important role for n−type conductivity of ZnO. While the ZnO films annealed at 1100°C in O2 ambient, the oxygen antisite contributes ZnO films to p-type.
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Influence of O2 Flux on Compositions and Properties of ITO Films Deposited at Room Temperature by Direct-Current Pulse Magnetron Sputtering
WANG Hua-Lin, DING Wan-Yu, LIU Chao-Qian, CHAI Wei-Ping
Chin. Phys. Lett. 2010, 27 (12):
127302
.
DOI: 10.1088/0256-307X/27/12/127302
Indium tin oxide (ITO) films were deposited on glass substrates at room temperature by dc pulse magnetron sputtering. Varying O2 flux, ITO films with different properties are obtained. Both x−ray diffractometer and x-ray photoelectron spectrometer are used to study the change of crystalline structures and bonding structures of ITO films, respectively. Electrical properties are measured by four-point probe measurements. The results indicate that the chemical structures and compositions of ITO films strongly depend on the O2 flux. With increasing O2 flux, ITO films display better crystallization, which could decrease the resistivity of films. On the contrary, ITO films contain less O vacancies with increasing O2 flux, which could worsen the conductive properties of films. Without any heat treatment onto the samples, the resistivity of the ITO film could reach 6.0×10−4 Ω⋅cm, with the optimal deposition parameter of 0.2 sccm O2 flux.
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GaN-Based Thin Film Vertical Structure Light Emitting Diodes Fabricated by a Modified Laser Lift-off Process and Transferred to Cu
SUN Yong-Jian, YU Tong-Jun, JIA Chuan-Yu, CHEN Zhi-Zhong, TIAN Peng-Fei, KANG Xiang-Ning, LIAN Gui-Jun, HUANG Sen, ZHANG Guo-Yi
Chin. Phys. Lett. 2010, 27 (12):
127303
.
DOI: 10.1088/0256-307X/27/12/127303
GaN-based thin film vertical structure light-emitting diodes (VS-LEDs) were fabricated by a modified YAG laser lift-off (LLO) process and transferred to Cu substrates. With a comparison of the electrical and optical properties of conventional LEDs on sapphire substrates and of lateral structure thin film LEDs by a KrF LLO process, the vertical structure of LLO LEDs shows obvious superiority. LLO VSLEDs made by modified YAG LLO process show less increase of leakage current than the devices made by conventional KrF LLO process. Furthermore, owing to the well current spreading and less current path, the ideality factors and series resistance of vertical structure LEDs reduce greatly and the efficiency increases more obviously than the lateral structure LEDs, which is also reflected on the relative L–I curves. The output power of vertical structure LEDs is over 3 times greater than that of the lateral structure LLO LEDs within 300 mA.
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Effect of Indium Ambient on Electrical Properties of Mg-Doped AlxGa1-xN
XU Zheng-Yu, QIN Zhi-Xin**, SANG Li-Wen, ZHANG Yan-Zhao, SHEN Bo, ZHANG Guo-Yi, ZHAO Lan, ZHANG Xiang-Feng, CHENG Cai-Jing, SUN Wei-Guo
Chin. Phys. Lett. 2010, 27 (12):
127304
.
DOI: 10.1088/0256-307X/27/12/127304
Mg-doped AlxGa1−xN epilayers were grown on AlN/sapphire templates by metal organic chemical vapor deposition (MOCVD) using an indium-assisted growth method. At room temperature, the resistivity of Mg-doped Al0.43Ga0.57N epilayer grown under indium (In) ambient is of the order of 104 Ω⋅cm, while the resistivity of Mg−doped Al0.43Ga0.57N grown without In assistance is of the order of 106 Ω⋅cm. The ultraviolet light−emitting diodes (UV-LEDs) using the In-assisted Mg-doped Al0.43Ga0.57N as the p−type layers were fabricated to verify the function of indium ambient. It is found that there are a lower turn-on voltage and a lower diode series resistance in the UV-LEDs fabricated with p-type Al0.43Ga0.57N layers grown under In-ambient.
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Optical and Structural Properties of Cr-Doped GaN Grown by HVPE Method
YAN Huai-Yue, XIU Xiang-Qian, HUA Xue-Mei, LIU Zhan-Hui, ZHOU An, ZHANG Rong, XIE Zi-Li, HAN Ping, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2010, 27 (12):
127801
.
DOI: 10.1088/0256-307X/27/12/127801
Single crystalline Cr-doped GaN films are successfully grown by hydride vapor phase epitaxy. The structure analysis indicates that the film is uniform without detectable Cr precipitates or clusters and the Cr atoms are substituted for Ga sites. The impurity modes in the range 510–530 cm−1 are observed by the Raman spectra. The modes are assigned to the host lattice defects caused by substitutional Cr. The donor-acceptor emission is found to locate at Ec−0.20 eV by analyzing the photoluminescence spectrum obtained at different temperatures, and the emission is attributed to the structural defects caused by CrGa−VN complex. The superconductor quantum interference device results show that the Cr-doped GaN film without detectable Cr precipitates or clusters exhibits paramagnetic properties.
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Highly Efficient Simplified Organic Light-Emitting Diodes Utilizing F4-TCNQ as an Anode Buffer Layer
DONG Mu-Sen, , WU Xiao-Ming, , HUA Yu-Lin, **, QI Qing-Jin, , YIN Shou-Gen,
Chin. Phys. Lett. 2010, 27 (12):
127802
.
DOI: 10.1088/0256-307X/27/12/127802
We demonstrate that the electroluminescent performances of organic light-emitting diodes (OLEDs) are significantly improved by evaporating a thin F4-TCNQ film as an anode buffer layer on the ITO anode. The optimum Alq3−based OLEDs with F4-TCNQ buffer layer exhibit a lower turn-on voltage of 2.6 V, a higher brightness of 39820 cd/m2 at 13 V, and a higher current efficiency of 5.96 cd/A at 6 V, which are obviously superior to those of the conventional device (turn−on voltage of 4.1 V, brightness of 18230 cd/m2 at 13 V, and maximum current efficiency of 2.74 cd/A at 10 V). Furthermore, the buffered devices with F4−TCNQ as the buffer layer could not only increase the efficiency but also simplify the fabrication process compared with the p-doped devices in which F4-TCNQ is doped into β-NPB as p-HTL (3.11 cd/A at 7 V). The reason why the current efficiency of the p-doped devices is lower than that of the buffered devices is analyzed based on the concept of doping, the measurement of absorption and photoluminescence spectra of the organic materials, and the current density-voltage characteristics of the corresponding hole-only devices.
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Quantum-Confined Stark Effect in Ensemble of Colloidal Semiconductor Quantum Dots
WANG Zhi-Bing, ZHANG Hui-Chao, ZHANG Jia-Yu**, Huaipeng Su, Y. Andrew Wang
Chin. Phys. Lett. 2010, 27 (12):
127803
.
DOI: 10.1088/0256-307X/27/12/127803
The presence of a strong, changing, randomly-oriented, local electric field, which is induced by the photo-ionization that occurs universally in colloidal semiconductor quantum dots (QDs), makes it difficult to observe the quantum-confined Stark effect in ensemble of colloidal QDs. We propose a way to inhibit such a random electric field, and a clear quantum-confined Stark shift is observed directly in close-packed colloidal QDs. Besides the applications in optical switches and modulators, our experimental results indicate how the oscillator strengths of the optical transitions are changed under external electric fields.
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Preparation, Morphology Transformation and Magnetic Behavior of Co3O4 Nano-Leaves
MENG Ling-Rong, CHEN Wei-Meng, CHEN Chin-Ping, ZHOU He-Ping, PENG Qing**
Chin. Phys. Lett. 2010, 27 (12):
128101
.
DOI: 10.1088/0256-307X/27/12/128101
A series of cubic phase Co3O4 nano−leaves were prepared via a combined approach of solution reaction and calcination. According to x-ray diffraction and electron microscopy, we find that the Co3O4 grain size increases with calcination temperature. This can induce many gaps in the products. M–T and M–H magnetization measurements reveal the typical antiferromagnetic behavior of nano−leaves. The effective moments of the samples prepared at 300, 400 and 500°C are 5.6, 5.8 and 5.7 μB per formula unit (FU), respectively, larger than the bulk value of 4.14 μB/FU.
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Fabrication and Characteristics of AlInN/AlN/GaN MOS-HEMTs with Ultra-Thin Atomic Layer Deposited Al2O3 Gate Dielectric
MAO Wei, ZHANG Jin-Cheng, XUE Jun-Shuai, HAO Yao, MA Xiao-Hua, WANG Chong, LIU Hong-Xia, XU Sheng-Rui, YANG Lin-An, BI Zhi-Wei, LIANG Xiao-Zhen, ZHANG Jin-Feng, KUANG Xian-Wei
Chin. Phys. Lett. 2010, 27 (12):
128501
.
DOI: 10.1088/0256-307X/27/12/128501
Al0.85In0.15N/AlN/GaN metal−oxide-semiconductor high electron mobility transistors (MOS-HEMTs) employing a 3-nm ultra-thin atomic-layer deposited (ALD) Al2O3 gate dielectric layer are reported. Devices with 0.6 μm gate lengths exhibit an improved maximum drain current density of 1227 mA/mm at a gate bias of 3 V, a peak transconductance of 328 mS/mm, a cutoff frequency fT of 16 GHz, a maximum frequency of oscillation fmax of 45 GHz, as well as significant gate leakage suppression in both reverse and forward directions, compared with the conventional Al0.85In0.15N/AlN/GaN HEMT. Negligible C–V hysteresis, together with a smaller pinch−off voltage shift, is observed, demonstrating few bulk traps in the dielectric and high quality of the Al2O3/AlInN interface. It is most notable that not only the transconductance profile of the MOS-HEMT is almost the same as that of the conventional HEMT with a negative shift, but also the peak transconductance of the MOS-HEMT is increased slightly. It is an exciting improvement in the transconductance performance.
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Effect of Annealing on Microstructure and Electrical Characteristics of Doped Poly (3-Hexylthiophene) Films
MA Liang
Chin. Phys. Lett. 2010, 27 (12):
128502
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DOI: 10.1088/0256-307X/27/12/128502
The effect of annealing on the microstructure and electrical characteristics of poly (3-hexylthiophene) (P3HT) films doped with very small amounts of the electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4−TCNQ) is studied. X-ray diffraction and UV-vis spectrum studies show that unlike the pure P3HT film, the thermal treatment on the doped films under an Ar atmosphere can effectively enhance the crystalline order of P3HT films, as well as successfully facilitate the orientation of the polymer chains. This improvement is attributed to the electrostatic force between P3HT and F4−TCNQ molecules. This force induces the polymer chains to crystallize and orient during the annealing process. As a result, annealing significantly improves performance, especially for the Ion/Ioff ratio of the TFTs based on the doped P3HT films.
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ZnO-Based Transparent Thin-Film Transistors with MgO Gate Dielectric Grown by in-situ MOCVD
ZHAO Wang, DONG Xin, ZHAO Long, SHI Zhi-Feng, WANG Jin, WANG Hui, XIA Xiao-Chuan, CHANG Yu-Chun, ZHANG Bao-Lin, DU Guo-Tong
Chin. Phys. Lett. 2010, 27 (12):
128504
.
DOI: 10.1088/0256-307X/27/12/128504
ZnO transparent thin-film transistors with MgO gate dielectric were fabricated by in-situ metal organic chemical vapor deposition (MOCVD) technology. We used an uninterrupted growth method to simplify the fabrication steps and to avoid the unexpectable contaminating during epitaxy process. MgO layer is helpful to reduce the gate leakage current, as well as to achieve high transparency in visible light band, due to the wide band gap (7.7 eV) and high dielectric constant (9.8). The XRD measurement indicates that the ZnO layer has high crystal quality. The field effect mobility and the on/off current ratio of the device is 2.69 cm2V−1s−1 and ∼1×104, respectively.
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A Unifying Modularity in Networks
HAO Jun-Jun, CAI Shui-Ming, HE Qin-Bin, LIU Zeng-Rong, **
Chin. Phys. Lett. 2010, 27 (12):
128901
.
DOI: 10.1088/0256-307X/27/12/128901
We propose a new modularity criterion in complex networks, called the unifying modularity q which is independent of the number of partitions. It is shown that, for a given network, the relationship between the upper limit of Q and the number of the partitions, k, is sup(Qk)=(k−1)/k. Since the range of Q for each partition number is inconsistent, we try to extend the concept Q to unifying modularity q, which is independent of the number of partitions. Subsequently, we indicate that it is more accurately to determine the number of partitions by using unifying modularity q than Q.
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Chorus-Driven Outer Radiation Belt Electron Dynamics at Different L-Shells
ZHANG Sai, XIAO Fu-Liang**
Chin. Phys. Lett. 2010, 27 (12):
129401
.
DOI: 10.1088/0256-307X/27/12/129401
Energetic outer radiation belt electron phase space density (PSD) evolution due to interaction with whistler-mode chorus at different L−shells is investigated by solving the diffusion equation including cross diffusion terms. It is found that the difference of diffusion rates for different L−shells occurs primarily at pitch angles 0°–50° and around 90°. In particular, diffusion rates for L=6.5 are found to be 5–10 times larger than that for L=3.5 at these pitch angles. In the presence of cross terms, PSD for ∼ MeV electrons after 24 h decreases by about 25, 12, 10 and 8 times at L=3.5, 4.5, 5.5 and 6.5 near the loss cone, and increases by about 55, 45, 30 and 20 times at larger pitch angles, respectively. After 24 h, the ratios between ∼ MeV electron PSDs from simulations without and with cross diffusion at L=3.5, 4.5, 5.5 and 6.5 are about 350, 600, 800 and 800 near the loss cone, and become 5, 5.5, 6.5 and 8 at pitch angle 90°, respectively. These results demonstrate that neglect of cross diffusion generally results in the overestimate of PSD, and the cross diffusion plays a more significant role in the resonant interaction between chorus waves and outer radiation belt electrons at larger L.
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61 articles
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