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Accuracy Evaluation of NIM5 Cesium Fountain Clock
LIU Nian-Feng, FANG Fang, CHEN Wei-Liang, LIN Ping-Wei, WANG Ping, LIU Kun, SUO Rui, LI Tian-Chu
Chin. Phys. Lett. 2013, 30 (1):
010601
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DOI: 10.1088/0256-307X/30/1/010601
The NIM5 fountain clock is the second fountain clock built at NIM (National Institute of Metrology, China), and has been operating stably and sub-continually since 2008. The fountain operates with a simple one-stage optical molasses to collect cold atoms, which reduces the collisional frequency shift dramatically. The fractional frequency uncertainty is estimated to be 2×10?15. The typical frequency instability of 2.5×10?14 is obtained at 10 s. Comparisons with other fountain frequency standards worldwide demonstrate agreement within the stated uncertainties.
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Research of Infrared Imaging at Atmospheric Pressure Using a Substrate-Free Focal Plane Array
WU Jian-Xiong, CHENG Teng, ZHANG Qing-Chuan, ZHANG Yong, MAO Liang, GAO Jie, CHEN Da-Peng, WU Xiao-Ping
Chin. Phys. Lett. 2013, 30 (1):
010701
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DOI: 10.1088/0256-307X/30/1/010701
An equivalent circuit model to the substrate-free focal plane array (FPA) is established. Using this fast and effective model, the performance of infrared (IR) imaging at atmospheric pressure is investigated and it is found that the substrate-free FPA has the ability of IR imaging at atmospheric pressure, whereas it has a slightly degraded noise equivalent temperature difference (NETD) as compared with IR imaging under a high vacuum. This feature is also identified experimentally by a substrate-free FPA with pixel size of 50×50 μm 2. The NETDs are measured to be 160 mK at 10?2 Pa pressure and 1.08 K at atmospheric pressure.
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Visible Light Emission in Highly Charged Kr17+ Ions Colliding with an Al Surface
YANG Zhi-Hu, XU Qiu-Mei, GUO Yi-Pan, WU Ye-Hong, SONG Zhang-Yong
Chin. Phys. Lett. 2013, 30 (1):
013201
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DOI: 10.1088/0256-307X/30/1/013201
We report light emission during the bombardment of Kr ions on an Al surface in the wavelength range 300–700 nm. The three spectral lines of the sputtered Al atoms belong to transitions of Al I – at 309.26, Al I –4s 2S1/2 at 394.72 and Al I 3p 2Po3/2–4s 2S1/2 at 396.50 nm. During the neutralization process, the seven spectral lines of Kr I and Kr II from the incident ion of Kr17+ attribute to transitions of Kr I 5p 2[3/2]2–7d 2[1/2]o1 at 616.33, Kr II 5s 2D5/2–5p 2Do3/2 at 410.86, Kr II 5p 4Po5/2–6s 4P5/2 at 430.58, Kr II 4d 2D3/2–4f 2[3]o5/2 at 434.42, Kr II 4d 4D1/2–5p 2So1/2 at 485.80, Kr II 4p 4S3/2–6s 4Po3/2 at 618.57 and Kr II 5p 4Po3/2–4d 2D5/2 at 656.41 nm. Light emissions of sputtered species depend on energy of the incident ions deposited on the target surface atoms. Light emissions of the neutralized projectiles are formed due to many electrons of the conduction band of the solid surface captured in excited states of the incident ion.
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Research on High-Intensity Picosecond Pump Laser in Short Pulse Optical Parametric Amplification
PAN Xue, PENG Yu-Jie, WANG Jiang-Feng, LU Xing-Hua, OUYANG Xiao-Ping, CHEN Jia-Lin, JIANG You-En, FAN Wei, LI Xue-Chun
Chin. Phys. Lett. 2013, 30 (1):
014202
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DOI: 10.1088/0256-307X/30/1/014202
A 527 nm pump laser generating 1.7 mJ energy with peak power of more than 0.12 GW is demonstrated. The theoretical simulation result shows that it has 106 gain in the picosecond-pump optical parametric chirped pulse amplification when the pump laser peak power is 0.1 GW and the intensity is more than 5 GW/cm2, and that it can limit the parametric fluorescence in the picosecond time scale of pump duration. The pump laser system adopts a master-oscillator power amplifier, which integrates a more than 30 pJ fiber-based oscillator with a 150 μJ regenerative amplifier and a relay-imaged four-pass diode-pump Nd glass amplifier to generate a 1 Hz top hat spatial beam and about 14 ps temporal Guassian pulse with <2% pulse-to-pulse energy stability. The output energy of the power amplifier is limited to 4 mJ for B-integral concern, and the frequency doubling efficiency can reach 65% with input intensity 10 GW/cm2.
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Effect of Laser Pulse Width on the Laser Lift-off Process of GaN Films
CHEN Ming, ZHANG Jiang-Yong, LV Xue-Qin, YING Lei-Ying, ZHANG Bao-Ping
Chin. Phys. Lett. 2013, 30 (1):
014203
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DOI: 10.1088/0256-307X/30/1/014203
Laser lift-off (LLO), by which GaN is separated from sapphire, is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices. Its physical insight, however, is still not fully understood. We study systematically the effect of laser pulse width on the LLO process and the property of GaN. To estimate accurately the temperature distribution and the decomposed thickness of GaN, fluctuation in the pulse laser energy is taken into account. It is found that the temperature at the interface is increased in a higher speed for a narrower pulse width. In addition, less damage to the GaN film is expected for a narrower pulse width owing to the smaller heated area, lower transient temperature and lower N2 vapor pressure encountered during LLO. Some experimental results reported in literature are explained well. Our results are useful in understanding the effect of laser pulse width and can be taken as references in LLO of GaN/sapphire structures.
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Spectral Characteristic Based on Fabry–Pérot Laser Diode with Two-Stage Optical Feedback
WU Jian-Wei, Bikash NAKARMI
Chin. Phys. Lett. 2013, 30 (1):
014204
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DOI: 10.1088/0256-307X/30/1/014204
An optical device, consisting of a multi-mode Fabry–Pérot laser diode (MMFP-LD) with two-stage optical feedback, is proposed and experimentally demonstrated. The results show that the single-mode output with side-mode suppression ratio (SMSR) of ~21.7 dB is attained by using the first-stage feedback. By using the second-stage feedback, the SMSR of single-mode operation could be increased to ~28.5 dB while injection feedback power of ?29 dBm is introduced into the laser diode. In the case of up to ?29 dBm feedback power, the outcome SMSR is rapidly decayed to a very low level so that an obvious multi-mode operation in the output spectrum could be achieved at the feedback power level of ?15.5 dBm. Thus, a transition between single- and multi-mode operations could be flexibly controlled by adjusting the injected power in the second-stage feedback system. Additionally, in the case of injection locking, the outcome SMSR and output power at the locked wavelength are as high as ~50 dB and ~5.8 dBm, respectively.
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Principal State Analysis for a Compact in-Line Fiber Polarization Controller
LI Zheng-Yong, WU Chong-Qing, WANG Zhi-Hao, QIN Tao, WANG Yi-Xu
Chin. Phys. Lett. 2013, 30 (1):
014205
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DOI: 10.1088/0256-307X/30/1/014205
A compact in-line fiber-based polarization controller (FPC) made of a rotatable fiber squeezer is investigated in detail with the Mueller matrix model established based on the generalized principal state of polarization (PSP). The PSP caused by the fiber squeezing is in the equator plane, which turns around S3 axis on the Poincaré sphere when rotating the squeezer. Subsequently, a programmable polarization control method is proposed to realize the polarization conversion between arbitrary polarization states, in which only two parameters of phase shift and rotation angle need to be controlled. This type of FPC, which has a highly compact structure, lower insertion loss, and can be directly embedded into any fiber devices without any extra delay, will be an ideal PC for high-speed optical communication and all-optical signal processing.
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Magnetic Field Induced Spectroscopy of 88Sr Atoms Probed with a 10 Hz Linewidth Laser
LIN Yi-Ge, WANG Qiang, LI Ye, LIN Bai-Ke, WANG Shao-Kai, MENG Fei, ZHAO Yang, CAO Jian-Ping, ZANG Er-Jun, LI Tian-Chu, FANG Zhan-Jun
Chin. Phys. Lett. 2013, 30 (1):
014206
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DOI: 10.1088/0256-307X/30/1/014206
We present our experiment on magnetic field induced spectroscopy of the 1S0–3P0 transition of 88Sr atoms with a 10 Hz linewidth laser. The 88Sr atoms are cooled by two stage laser cooling. After the second stage narrow line laser cooling, the temperature of the atoms is reduced to ~3 μK. The atoms are then loaded into an 813 nm one-dimensional optical lattice. A homemade 698 nm laser with 10 Hz linewidth and maximum intensity of more than 100 W/cm2 is used to probe the 88Sr atoms in the lattice. By means of a magnetic field of ~1 mT and a probe laser with 50 ms pulse and ~6 W/cm2 intensity, the Doppler free 88Sr 1S0–3P0 transition spectrum with a linewidth of 208 Hz is obtained.
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Super-X Divertor Simulation for HCSB-DEMO Conception Design
ZHENG Guo-Yao, PAN Yu-Dong, FENG Kai-Ming, HE Hong-Da, CUI Xue-Wu
Chin. Phys. Lett. 2013, 30 (1):
015201
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DOI: 10.1088/0256-307X/30/1/015201
HCSB-DEMO concept design is carried out at SWIP. In order to handle power from a core plasma region, a super-X divertor is preliminarily designed and investigated for HCSB-DEMO. It increases the target surface area by expanding the magnetic flux surface with another X-point generated near the targets and increases the parallel connection length by moving the outer divertor target to larger R and Z. The heat load at the targets is investigated by B2.5-Eirene. With heating power flowing into SOL/divertor regions being P=600 MW, when the density at the separatrix is ne=3.5×1019 m?3, the peak heat load at the inner and outer divertor is 9.2 MW/m2 and 3.7 MW/m2, respectively, which is much less than those of the standard divertor without impurity seeding, and also below the design targets (10 MW/m2). Thus the super-X divertor may work well for HCSB-DEMO to solve the high heat load problem at the divertor target without impurity seeding from this preliminary concept design and simulation.
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Dynamic Mechanical Behavior and Failure Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Whiskers
RONG Ji-Li, WANG Dan, WANG Xi, LI Jian, XU Tian-Fu, LU Ming-Ming, CAO Mao-Sheng
Chin. Phys. Lett. 2013, 30 (1):
016203
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DOI: 10.1088/0256-307X/30/1/016203
Quasi-static and dynamic mechanical properties of glass-fiber reinforced polymer composites embedded with and without tetraneedle-shaped ZnO whiskers (T-ZnOw) in two loading directions are investigated by a split Hopkinson pressure bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by a high-speed camera and a scanning electron microscope. Strain rate effects on the mechanical behavior are discussed and the corresponding models are derived by fitting the experimental data. The experimental results show that the composites with T-ZnOw under dynamic loading have multiple failure modes and better mechanical properties. Finally, the strengthening and toughening mechanisms of T-ZnOw are analyzed. It is shown that T-ZnOw can improve mechanical properties of the composites, and can make the composites have some new features. The present results provide a reliable basis for advanced composite design and manufacture, and have broad applications in the field of aerospace.
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Efficiency Enhancement of MEH-PPV:PCBM Solar Cells by Addition of Ditertutyl Peroxide as an Additive
LI Yan-Fang, YANG Li-Ying, QIN Wen-Jing, YIN Shou-Gen, ZHANG Feng-Ling
Chin. Phys. Lett. 2013, 30 (1):
017202
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DOI: 10.1088/0256-307X/30/1/017202
Improved power conversion efficiency (PCE) and stability of organic bulk heterojunction (BHJ) solar cells based on poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends are obtained by using ditert butyl peroxide (DTBP) as an additive. The effect of the DTBP contents on the performance of photovoltaic cells is investigated. The results reveal that efficiency enhancement of MEH-PPV:PCBM solar cells can be realized by carefully tuning the contents of DTBP. Compared to the control device, the optimized device with 0.5wt% DTBP additive exhibits enhanced performance with Jsc of (3.51±0.21) mA/cm2, FF of (44.45±0.71)%, and PCE of (1.31±0.08)%, increased by 9.3%, 8.0% and 22.4%, respectively. The stability of the device is found to be improved by adding 0.5wt% of DTBP.
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On the Voltage and Frequency Distribution of Dielectric Properties and ac Electrical Conductivity in Al/SiO2/p-Si (MOS) Capacitors
Ahmet Kaya, Şemsettin Altındal, Yasemin Şafak Asar, Zekayi Sönmez
Chin. Phys. Lett. 2013, 30 (1):
017301
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DOI: 10.1088/0256-307X/30/1/017301
An Al/SiO2/p-Si (MOS) capacitor with a thick (826 ?) interfacial oxide layer (SiO2) which is formed by using the thermal oxidation method is fabricated to investigate both frequency and applied bias voltage dependences of real and imaginary parts of dielectric constant (ϵ' and ϵ") and electric modulus (M' and M"), loss tangent (tanδ) and ac electrical conductivity (σac) in a wide frequency range from 1 kHz to 1 MHz at room temperature. The dielectric properties of the MOS capacitor are obtained using the forward and reverse bias capacitance-voltage (C–V) and conductance-voltage (G/ω–V) measurements in the applied bias voltage range 1.4–5.6 V. The values of ϵ', ϵ", tanδ, M', M" and σac are found to be strong functions of frequency and applied bias voltage in the depletion region due to excess capacitance Cex and conductance Gex/ω especially at low frequencies. The experimental results show that the interfacial polarization can occur at low frequencies more easily, consequently contributing to the dispersion in ϵ', ϵ", tanδ, M', M" and σac values of the MOS capacitor. The other reason for dispersion in the dielectric properties may be attributed to a particular density distribution of interface states (Nss) localized at the Si/SiO2 interface, as well as space charge carriers and inhomogeneity of interfacial oxide layer. The increase in conductivity with increasing frequency can be attributed to the hopping type conduction mechanism. It can be concluded that the ϵ', ϵ", tanδ, M', M" and σac values of the Al/SiO2/p-Si (MOS) capacitor are strongly dependent on both the frequency and applied bias voltage especially in the depletion region.
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High Deep-Ultraviolet Quantum Efficiency GaN P–I–N Photodetectors with Thin P-GaN Contact Layer
LIAN Hai-Feng, WANG Guo-Sheng, LU Hai, REN Fang-Fang, CHEN Dun-Jun, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2013, 30 (1):
017302
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DOI: 10.1088/0256-307X/30/1/017302
GaN ultraviolet (UV) p-i-n photodetectors (PDs) with a 40 nm thin p-GaN contact layer are fabricated on sapphire substrates, which exhibit enhanced quantum efficiency especially in a deep-UV wavelength range. The PDs show good rectification behavior and low dark current in pA level for reverse bias up to ?10 V. Under zero bias, the maximum quantum efficiency of the PD at 360 nm is close to 59.4% with a UV/visible rejection ratio more than 4 orders of magnitude. Even at a short wavelength of 280 nm, the quantum efficiency of the PD is still around 47.5%, which is considerably higher than that of a control device with a thicker p-GaN contact layer. The room temperature thermal noise limited detectivity of the PD is calculated to be ~4.96×1014 cm?Hz1/2W?1.
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Experimental Investigation of the Electronic Structure of Ca0.83La0.17Fe2As2
HUANG Yao-Bo, RICHARD Pierre, WANG Ji-Hui, WANG Xiao-Ping, SHI Xun, XU Nan, WU Zheng, LI Ang, YIN Jia-Xin, QIAN Tian, LV Bing, CHU Ching-Wu, PAN Shu-Heng, SHI Ming, DING Hong
Chin. Phys. Lett. 2013, 30 (1):
017402
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DOI: 10.1088/0256-307X/30/1/017402
We performed a combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy study of the electronic structure of electron-doped Ca0.83La0.17Fe2As2. A surface reconstruction associated with the dimerization of As atoms is observed directly in the real space, as well as the consequent band folding in the momentum space. Besides this band folding effect, the Fermi surface topology of this material is similar to that reported previously for BaFe1.85Co0.15As2, with Γ-centered hole pockets quasi-nested to M-centered electron pockets by the antiferromagnetic wave vector. Although no superconducting gap is observed by ARPES possibly due to low superconducting volume fraction, a gap-like density of states depression of 7.7±2.9 meV is determined by scanning tunneling microscopy.
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Dosimetric Characteristics of a LKB:Cu,Mg Solid Thermoluminescence Detector
Yasser Saleh Mustafa Alajerami, Suhairul Hashim, Ahmad Termizi Ramli, Muneer Aziz Saleh, Ahmad Bazlie Bin Abdul Kadir, Mohd. Iqbal Saripan
Chin. Phys. Lett. 2013, 30 (1):
017801
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DOI: 10.1088/0256-307X/30/1/017801
We present the main thermoluminescence characteristics of a newly borate glass dosimeter modified with lithium and potassium carbonate (LKB) and co-doped with CuO and MgO. An enhancement of about three times has been shown with the increment of 0.1mol% MgO as a co-dopant impurity. The effects of dose linearity, storage capacity, effective atomic number and energy dose response are studied. The proposed dosimeter shows a simple glow curve, good linearity up to 103 Gy, close effective atomic number and photon energy independence. The current results suggest using the proposed dosimeter in different dosimetric applications.
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Phase Shift of Polarized Light after Transmission through a Biaxial Anisotropic Thin Film
HOU Yong-Qiang, LI Xu, HE Kai, QI Hong-Ji, YI Kui, SHAO Jian-Da
Chin. Phys. Lett. 2013, 30 (1):
017802
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DOI: 10.1088/0256-307X/30/1/017802
Based on the theoretical analysis of biaxial birefringent thin films with characteristic matrix method, we investigate the phase shift on transmission of a tilted columnar biaxial film at normal and oblique incidence over 300–1200 nm for s- and p-polarized waves. Compared with the simplified calculation method, the interference effects of the birefringent thin film are considered to yield more accurate results. The quarter wavelength phase shift calculated with the characteristic matrix method is consistent with that monitored with in situ measurement by two-angle ellipsometry, which validates our complied program for the calculation of the phase shift of the biaxial anisotropic thin film. Furthermore, the characteristic matrix method can be easily used to obtain continuous adjustable phase retardation at oblique incidence, whereas the simplified calculation method is valid for the case of normal incidence. A greater generality and superiority of the characteristic matrix method is presented.
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Fabrication of Thin Graphene Layers on a Stacked 6H-SiC Surface in a Graphite Enclosure
DENG Peng-Fei, LEI Tian-Min, LU Jin-Jun, LIU Fu-Yan, ZHANG Yu-Ming, GUO Hui, ZHANG Yi-Men, WANG Yue-Hu, TANG Xiao-Yan
Chin. Phys. Lett. 2013, 30 (1):
018101
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DOI: 10.1088/0256-307X/30/1/018101
Thin and homogeneous epitaxial graphene (EG) layers on a 6H-SiC (0001) substrate are fabricated and they cover the whole substrate (10×10 mm2). The sample surface is capped by another 6H-SiC (0001) wafer in a graphite enclosure to form a relatively high Si partial pressure between them, which significantly reduces the extremely high growth rate of EG. The structure and morphology of the EG layers are investigated by Raman spectroscopy, atomic force microscopy and field-emission scanning electronic microscopy. The results are compared with an uncapped sample surface, and reveal the obvious existence of ridges on the surface of the EG, and show that capping is indeed beneficial to obtain homogeneous graphene.
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Characterization of Modified Tapioca Starch in Atmospheric Argon Plasma under Diverse Humidity by FTIR Spectroscopy
P. Deeyai, M. Suphantharika, R. Wongsagonsup, S. Dangtip
Chin. Phys. Lett. 2013, 30 (1):
018103
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DOI: 10.1088/0256-307X/30/1/018103
Tapioca is economical crop grown in Thailand and continues to be one of the major sources of starch. Nowadays, tapioca starch has been widely used in industrial applications, however the native form of starch has limited the applications. Thus scientists try to modify the properties of starch for increasing the stability of the granules, pastes to low pH, heat, and shear during the food process. We modify the tapioca starch by plasma treatment under an argon atmosphere. The degree of modification is determined by following water content in the starch granules. The tablet samples of native starch are also prepared and compared with the plasma treated starch. Before plasma treatment, the starch tablets are stored under three different relative humilities (RH) including 11%, 68%, and 78%RH, respectively. The samples are characterized using FTIR spectroscopy associated with the degree of cross-linking. The results show that the water molecules are engulfed into the starch structure in two ways, a tight bond and a weak absorption of water molecules which is represented at two wave number of 1630 cm?1 and 3272 cm?1, respectively. The degree of cross-linking can be identified from the relative intensity of these two peaks with the C–O–H peak at 993 cm?1. The results show that the degree of cross-linking increase in the plasma treated starch. The degree of cross-linking of the treated starch with high relative humidity is less than that of the treated starch with low relative humidity.
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60 articles
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