• Current Optics and Photonics
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• 제2권1호
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• pp.90-95
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• 2018

Stimulated polariton scattering from the $B_1$-symmetry modes of a $KNbO_3$ crystal to generate a terahertz wave (THz-wave) with a noncollinear phase-matching scheme is investigated. The frequency-tuning characteristics of the THz-wave by varying the phase-matching angle and pump wavelength are analyzed. The expression for the effective parametric gain length under the noncollinear phase-matching condition is deduced. Parametric gain and absorption characteristics of the THz-wave in $KNbO_3$ are theoretically simulated. The characteristics of $KNbO_3$ for a terahertz parametric oscillator (TPO) are compared to those of $MgO:LiNbO_3$. The analysis indicates that $KNbO_3$ is an excellent optical crystal for a TPO, to enhance the THz-wave output.

• 한국수산과학회지
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• 제48권6호
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• pp.977-981
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• 2015

The proximate, fatty acid and dimethyl acetal (DMA) compositions of domestic and imported melania snails Semisulcospira sp. being sold commercially were studied. The protein content ranged from 8.09% (China) to 11.3% (North Korea). The lipid content ranged from 0.84 (China) to 2.36% (North Korea). Domestic melania snail had protein (10.5%) and lipid (1.02%) contents intermediate between those of the two imported melania snails. The prominent fatty acids were 16:0 and 18:0 saturated fatty acids, 16:1n-7, 20:1n-11, 18:1n-9, 18:1n-7 and 16:1n-9 monounsaturated fatty acids, and 20:4n-6, 20:5n-3 (eicosapentaenoic acid, EPA), 22:2 non-methylene-interrupted diene (NMID), 18:3n-3, 18:2n-6 and 22:5n-3 (docosapentaenoic acid, DPA) polyunsaturated fatty acids (PUFA). The percentage of n-3 PUFA was higher in domestic (19.6%) and North Korean (imported, 19.5%) snails than in that from China (imported, 16.8%), while the n-6 PUFA level was higher in snails from China (21.2%) and domestic snails (14.7%) than in that from North Korea (9.87%). The total DMA, i.e., 18:0 DMA, 16:0 DMA and 18:1 DMA was 7.30, 7.27, and 4.86% domestic snail and those from China and North Korea, respectively. These results suggest that melania snail is a source of n-3 PUFA, and DMA derived from plasmalogen.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.648-658
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• 2018

Regarding the fact that wind power forecast accuracy is gradually improved as time is approaching, this paper proposes a two-stage rolling dispatch approach based on model predictive control (MPC), which contains an intra-day rolling optimal scheme and a real-time rolling base point tracing scheme. The scheduled output of the intra-day rolling scheme is set as the reference output, and the real-time rolling scheme is based on MPC which includes the leading rolling optimization and lagging feedback correction strategy. On the basis of the latest measured thermal unit output feedback, the closed-loop optimization is formed to correct the power deviation timely, making the unit output smoother, thus reducing the costs of power adjustment and promoting wind power accommodation. We adopt chance constraint to describe forecasts uncertainty. Then for reflecting the increasing prediction precision as well as the power dispatcher's rising expected satisfaction degree with reliable system operation, we set the confidence level of reserve constraints at different timescales as the incremental vector. The expectation of up/down reserve shortage is proposed to assess the adequacy of the upward/downward reserve. The studies executed on the modified IEEE RTS system demonstrate the effectiveness of the proposed approach.

• Current Optics and Photonics
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• 제2권3호
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• pp.261-268
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• 2018

Stimulated polariton scattering (SPS) from the $A_1$ transverse optical (TO) modes of $BaTiO_3$ bulk crystal generating a terahertz (THz) wave with the noncollinear phase-matching (NPM) condition is theoretically investigated. To our best knowledge, this is the first report on THz wave generation from $BaTiO_3$ bulk crystal via SPS. Phase-matching (PM) characteristics in the NPM configuration are analyzed. Effective parametric gain lengths for the Stokes and THz waves in the NPM configuration are calculated. The effective parametric gain coefficient and absorption coefficient of the THz wave in $BaTiO_3$ are theoretically simulated. The THz phonon flux densities generated via SPS in $BaTiO_3$ are theoretically calculated by solving the coupled wave equations under the NPM condition. The PM characteristics and THz-wave parametric gain characteristics in $BaTiO_3$ are compared to those in $MgO:LiNbO_3$. The results of the analysis indicate that $BaTiO_3$ is an attractive optical crystal for efficient THz wave generation via SPS.

• Journal of Power Electronics
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• 제17권3호
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• pp.766-776
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• 2017

In modern power systems, high penetration of distributed generators (DGs) results in high stress on system stability. Apart from the intermittent nature of DGs, most DGs do not contribute inertia or damping to systems. As a result, a new control method named virtual synchronous machine (VSM) was proposed, which brought new characteristics to inverters such as synchronous machines (SMs). In addition, different active power droop controls for VSMs are being proposed in literatures. However, they are quite different in terms of their dynamic characteristics despite of the similar control laws. In this paper, mathematical models of a VSM adopting different active power droop controls are built and analyzed. The dynamic performance of the VSM output active power and virtual rotor angular frequency are presented for different models. The influences of the damping factor and droop coefficient on the VSM dynamic behaviors are also investigated in detail. Finally, the theoretical analysis is verified by simulations and experimental results.

• Journal of Power Electronics
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• 제17권6호
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• pp.1625-1636
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• 2017

A power electronic transformer (PET) based on the cascaded H-bridge (CHB) and the isolated bidirectional DC/DC converter (IBDC) is capable of accommodating a large scale battery energy storage system (BESS) in the medium-voltage grid, and is referred to as a power electronic transformer based battery energy storage system (PET-BESS). This paper investigates the PET-BESS and proposes a coordinative control strategy for it. In the proposed method, the CHB controls the power flow and the battery state-of-charge (SOC) balancing, while the IBDC maintains the dc-link voltages with feedforward implementation of the power reference and the switch status of the CHB. State-feedback and linear quadratic Riccati (LQR) methods have been adopted in the CHB to control the grid current, active power and reactive power. A hybrid PWM modulating method is utilized to achieve SOC balancing, where battery SOC sorting is involved. The feedforward path of the power reference and the CHB switch status substantially reduces the dc-link voltage fluctuations under dynamic power variations. The effectiveness of the proposed control has been verified both by simulation and experimental results. The performance of the PET-BESS under bidirectional power flow has been improved, and the battery SOC values have been adjusted to converge.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권2호
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• pp.263-283
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• 2024

Users' comments after online shopping are critical to product reputation and business improvement. These comments, sometimes known as e-commerce reviews, influence other customers' purchasing decisions. To confront large amounts of e-commerce reviews, automatic analysis based on machine learning and deep learning draws more and more attention. A core task therein is sentiment analysis. However, the e-commerce reviews exhibit the following characteristics: (1) inconsistency between comment content and the star rating; (2) a large number of unlabeled data, i.e., comments without a star rating, and (3) the data imbalance caused by the sparse negative comments. This paper employs Bidirectional Encoder Representation from Transformers (BERT), one of the best natural language processing models, as the base model. According to the above data characteristics, we propose the F_MixBERT framework, to more effectively use inconsistently low-quality and unlabeled data and resolve the problem of data imbalance. In the framework, the proposed MixBERT incorporates the MixMatch approach into BERT's high-dimensional vectors to train the unlabeled and low-quality data with generated pseudo labels. Meanwhile, data imbalance is resolved by Focal loss, which penalizes the contribution of large-scale data and easily-identifiable data to total loss. Comparative experiments demonstrate that the proposed framework outperforms BERT and MixBERT for sentiment analysis of e-commerce comments.

• Steel and Composite Structures
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• 제50권6호
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• pp.675-688
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• 2024

Cold-formed steel (CFS) is prone to buckling failure under loading. Lightweight concrete (LC) made of lightweight aggregate has light weight and excellent thermal insulation performance. However, concrete is brittle in nature which is why different materials have been used to improve this inherent behavior of concrete. The distortional buckling (DB) performance of cold-formed steel-lightweight concrete (CFS-LC) composite columns was investigated in this paper. Firstly, the compressive strength test of foam concrete (FC) and ceramsite concrete (CC) was carried out. The performance of the CFS-LC members was investigated. The test results indicated that the concrete-filled can effectively control the DB of the members. Secondly, finite element (FE) models of each test specimen were developed and validated with the experimental tests followed by extensive parametric studies using numerical analysis based on the validated FE models. The results show that the thickness of the steel and the strength of the concrete-filled were the main factors on the DB and bearing capacity of the members. Finally, the bearing capacity of the test specimens was calculated by using current codes. The results showed that the design results of the AIJ-1997 specification were closer to the experimental and FE values, while other results of specifications were conservative.

• Parasites, Hosts and Diseases
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• 제44권3호
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• pp.265-268
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• 2006

The present authors investigated intestinal parasitic infections among North Korean residents and refugees in China in 2003. The Kato-Katz method was applied to 236 residents and soldiers in a town on the North Korea-China border and to 46 people at a refugee camp in China. Only eggs of Ascaris and Trichuris were detected, with egg positive rates of 41.1 % and 37.6%, respectively. The total egg positive rate was 55.0% and most of those who were egg positive were only lightly infected. Women of 61.2% and men of 53.1 % were egg positive. The refugees from rural areas showed higher egg positive rates than those from urban areas. The present investigation confirmed high prevalence of soil-transmitted intestinal helminths in rural borderline areas of North Korea.

• KDI Journal of Economic Policy
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• 제37권2호
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• pp.40-63
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• 2015

Anthracite exports have special value within the DPRK's economy. In this paper, we focus on what determines the DPRK's anthracite exports to China. We use panel data consisting of cross-section data from 30 provinces in China and quarterly time-series data from 1998 to 2013. Controlling for all other variables that affect anthracite imports, the variable for steel production in China is robust and statistically significant. This is consistent with on-site interviews which indicate that much of North Korean anthracite is consumed by China's steel industry. This implies that the North Korean authorities need to make adjustments to the foreign trade structure, as the import demand for anthracite in China may decline further.