• Journal of Information Processing Systems
• /
• 제15권3호
• /
• pp.694-706
• /
• 2019

In this study, we applied the long short-term memory (LSTM) model to classify the cryptocurrency price time series. We collected historic cryptocurrency price time series data and preprocessed them in order to make them clean for use as train and target data. After such preprocessing, the price time series data were systematically encoded into the three-dimensional price tensor representing the past price changes of cryptocurrencies. We also presented our LSTM model structure as well as how to use such price tensor as input data of the LSTM model. In particular, a grid search-based k-fold cross-validation technique was applied to find the most suitable LSTM model parameters. Lastly, through the comparison of the f1-score values, our study showed that the LSTM model outperforms the gradient boosting model, a general machine learning model known to have relatively good prediction performance, for the time series classification of the cryptocurrency price trend. With the LSTM model, we got a performance improvement of about 7% compared to using the GB model.

• Advances in Energy Research
• /
• 제6권1호
• /
• pp.17-33
• /
• 2019

This study aimed to observe trends in the literature on research, development, and innovation management in the energy sector, using performance assessment systems. The paper presented a bibliometric analysis of 40 studies on the subject. These materials come from ScienceDirect, Scopus and the Institute of Electrical and Electronics Engineers (IEEE) databases from 2006 to 2016. The results showed an increasing trend in the number of publications on the theme, showing the scientific community's interest in the subject. In addition, it was verified that the predominant language used to write the publications was English, the country that most published articles in the area was Brazil and most of the articles were produced through collaboration between researchers. It was found that the journal with the greatest number of publications on the subject was the Procedia - Social and Behavioral Sciences, while the Expert Systems with Applications journal presented the article with the greatest number of citations. This analysis allowed us to identify important points of the research and its future directions, in addition to enabling a better understanding of the world trend of the subject approached.

• 대기
• /
• 제34권2호
• /
• pp.107-121
• /
• 2024

In this study, we empirically analyzed the impact of physical risks due to climate change on the soundness and operational performance of the financial industry by combining economics and climatology. Particularly, unlike previous studies, we employed the Seasonal-Trend decomposition using LOESS (STL) method to extract trends of climate-related risk variables and economic-financial variables, conducting a two-stage empirical analysis. In the first stage estimation, we found that the delinquency rate and the Bank for International Settlement (BIS) ratio of commercial banks have significant negative effects on the damage caused by natural disasters, frequency of heavy rainfall, average temperature, and number of typhoons. On the other hand, for insurance companies, the damage from natural disasters, frequency of heavy rainfall, frequency of heavy snowfall, and annual average temperature have significant negative effects on return on assets (ROA) and the risk-based capital ratio (RBC). In the second stage estimation, based on the first stage results, we predicted the soundness and operational performance indicators of commercial banks and insurance companies until 2035. According to the forecast results, the delinquency rate of commercial banks is expected to increase steadily until 2035 under assumption that recent years' trend continues until 2035. It indicates that banks' managerial risk can be seriously worsened from climate change. Also the BIS ratio is expected to decrease which also indicates weakening safety buffer against climate risks over time. Additionally, the ROA of insurance companies is expected to decrease, followed by an increase in the RBC, and then a subsequent decrease.

• Asian-Australasian Journal of Animal Sciences
• /
• 제11권5호
• /
• pp.538-544
• /
• 1998

One hundred and twenty-eight finishing pigs (51.3 kg average initial body weight) were used to determine the effects of adding cellulase enzymes and lactobacillus acidophilus to sorghum-based diets on growth performance, carcass merit, and nutrient digestibility in finishing pigs. Treatments were: 1) corn-soybean meal-based positive control; 2) sorghum-soybean meal-based negative control; 3) Diet 2 with celluloytic enzymes; and 4) Diet 2 with a bacterial feed additive (lactobacillus acidophilus). There was a trend for greater average daily gain (ADG) in pigs fed com versus the sorghum treatments for day 0 to 28 (p < .09), but there was no effect of treatment (p > .15) on overall ADG (i.e., day 0 to 63). Feed consumption was not affected by treatment during the experiment (p > .19). Pigs fed the corn-soybean meal-based diet had 3.5% greater overall gain/feed than pigs fed the other diets (p < .009). Dressing percentage was not affected by treatment (p > .22), but there was a trend for backfat thickness at the last rib to be greater for pigs fed com versus the sorghum treatments (p < .09). Pigs fed the sorghum treatments had 1 % greater fat free lean index (p < .10) compared to pigs fed the corn-soybean meal-based positive control. Pigs fed com had greater apparent digestibilities of DM, N, and GE than pigs fed the sorghum treatments (p < .03), and greater DE intake (p < .07) suggesting that the increased carcass fatness for pigs fed the corn-based control diet resulted from greater energy status of those pigs. In conclusion, pigs fed the corn-soybean meal-based control diet had no improved growth performance but tended to be fatter than pigs fed sorghum. Adding cellulolytic enzymes or a bacterial feed additive to diets for finishing pigs did not affect growth performance, carcass merit, or nutrient utilization.

• 전기전자학회논문지
• /
• 제12권4호
• /
• pp.185-195
• /
• 2008

본 논문에서는 PCS(Personal Communication System) 대역에서 동작하는 PIFA(Planar Inverted F Antenna)를 설계하여 특성을 살펴보았다. 설계된 PIFA를 폴더와 바, 슬라이드 타입의 단말기에 장착하여 성능을 확인하였다. 실제 사용자가 사용하는 상태와 가장 유사한 환경을 만들기 위해 헤드 팬텀과 핸드 팬텀을 추가하여 단말기 안테나의 성능에 미치는 영향을 분석하였다. 인체의 영향으로 인해 방사패턴이 크게 변형되는 모습을 보였으며, 안테나 효율 또한 현저히 저하되는 것을 전산 모의 실험을 통해 확인할 수 있었다. 단말기와 헤드 팬텀과의 위치 관계에 따른 변화를 확인하기 위해 단말기와 헤드 팬텀의 각도가 $0^{\circ}$일 경우를 기준으로 하여, $2^{\circ},\;4^{\circ}$로 변화시켜가며 단말기 안테나의 성능 변화를 살펴보았다. 그 결과 안테나가 헤드 팬텀에서 멀어질수록 지향성을 갖던 특성이 조금씩 줄어들면서 효율이 좋아지는 경향을 보였다. 다만 안테나의 위치가 상대적으로 헤드 팬텀에 가까운 바 타입의 경우, 이 같은 경향이 나타나지 않았다. 단말기의 형태도 성능에 큰 영향을 주는 것을 확인할 수 있었다.

• 한국항공우주학회지
• /
• 제46권8호
• /
• pp.662-670
• /
• 2018

고도보정 노즐은 모든 고도에서 최적의 성능을 발휘할 수 있도록 고안된 노즐이다. 발사체의 비추력을 향상시키기 위한 방법으로는 연소실만의 특성인 특성배기속도를 향상시키는 방법과 노즐만의 특성인 추력계수를 향상시키는 방법이 있다. 고도보정 노즐은 동일한 연소기에서 노즐의 성능 개선을 통해 발사체의 성능향상을 가능하게 한다. 고도보정 노즐에 대한 연구는 독일 DLR에서 활발하게 진행되고 있으며, 미국, 러시아, 영국, 호주, 일본 등 항공우주선진국에서도 진행되고 있다. 본 논문에서는 고도보정 노즐에 대한 기술 현황 및 특허 동향에 대해 조사하였다. 이를 바탕으로 고도보정 노즐의 기술흐름을 파악하고 발사체 성능향상 연구에 기초자료로 활용하고자 한다.

• Asian-Australasian Journal of Animal Sciences
• /
• 제11권3호
• /
• pp.249-254
• /
• 1998

Two experiments were conducted to evaluate the effects of processing of barley on the growth performance and ileal and fecal digestibility of growing pigs. In Exp. 1, a total of 20 cannulated pigs (10.80 kg BW) were allotted to four treatments. Treatments were coarse ground barley as a control (CON), finely ground barley (FINE), extruded barley (EXT) and enzyme supplemented coarse ground barley (ENZ). In Exp. 2, a total of 100 growing pigs (36.50 kg BW) were allocated to the same treatments in completely randomized block design based on sex and body weight. In the first trial, pigs fed extruded barley showed significantly higher crude protein digestibility over pigs fed finely ground barley (p < 0.05). Pigs fed finely ground barley generally showed lower nutrients digestibility. Extrusion and ${\beta}$-glucanase supplementation showed a trend to improve nutrients digestibility. However, fine grinding rather reduced nutrients digestibility. The similar trend was found in the digestibility of essential amino acids. Fine grinding of barley significantly reduced amino acids digestibility. Extrusion and enzyme supplementation were found to improve amino acids digestibility of barley in growing pigs. In the growth trial, pigs fed extruded barley grew significantly faster than any other processed barley fed pigs. And extrusion of barley significantly improved feed/gain of pigs (p < 0.05). Fine grinding of barley and enzyme supplementation did not improve growth performance of pigs. In conclusion, fine grinding and enzyme supplementation does not appear to be an economical feed processing for growing pigs when barley is employed in the diets, while extrusion can be recommended as an effective feed processing technique for barley.

• Asian-Australasian Journal of Animal Sciences
• /
• 제15권5호
• /
• pp.627-632
• /
• 2002

Genetic parameters for dairy performance traits were estimated, breeding values for the traits of all breeding sires and cows were predicted and the genetic trends were estimated using the breeding values in the Central Cattle Breeding Station (CCBS). A total of 3,801 records for Bangladeshi Local, 756 records for Red Sindhi and 959 records for Sahiwal covering the period from 1961 to 1997 were used in this analysis. Traits considered were total milk production per lactation (TLP), lactation length (LL) and daily milk yield (DMY). The genetic parameters were estimated by the REML using MTDFREML program. The breeding values were predicted by a best linear unbiased prediction (BLUP). In all sets of data, the genetic trends for the dairy performance traits were computed as averages of breeding values for cows born in the particular year. The estimates of heritability for TLP (0.26 and 0.27) and DMY (0.28 and 0.27) were moderate in Bangladeshi local and Red Sindhi breed, respectively. Furthermore, the heritability estimate for LL (0.24) was moderate in Red Sindhi. The estimates of heritabilities for all traits were low in Sahiwal. The repeatability estimate was high for TLP, moderate for LL and moderate to high for DMY. All variances estimated in Bangladeshi Local were low, comparing the respective values estimated in both Red Sindhi and Sahiwal. On the other hand, additive genetic variances for the three traits were estimated very low in Sahiwal. The genetic trends for the three dairy production traits have not been positive except for the recent trend in Bangladeshi Local.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
• /
• pp.151-158
• /
• 1998

The screw compressor is first invented by a Swedish engineer, Alf Lysholm in 1934. Since then, the development of the screw compressor idea for industrial applications has been continued by the Swedish research organization Svenska Rotor Maskiner, often identified by its initials SRM. The first industrial application of the machine was marketed as an air compressor in the 1950s. The screw compressor which is a positive displacement type compressor compresses gases by the rotation of a pair of mating rotors. The operation of this compressor is entirely rotary and dynamically in balance. Also there is no need for any valve mechanism and there exists less mechanical wear between the parts compared to the conventional reciprocating compressors. Due to these prominent features, the screw compressor has been rapidly spread into the air compressor market replacing the conventional reciprocating compressors and begun to be applied as a refrigerant compressor since the 1960s. In this work, the operation principle of the screw compressor is described in brief and the major design parameters affecting the compressor performance are classified. The international research trend in screw compressor development is introduced and the current situation in our country is described.

• 한국군사과학기술학회지
• /
• 제14권5호
• /
• pp.859-870
• /
• 2011

The purpose of this paper is to develop reliability analysis procedures for repairable systems with interval failure time data and apply the procedures for assessing the storage reliability of a subsystem of a certain type of guided missile. In the procedures, the interval failure time data are converted to pseudo failure times using the uniform random generation method, mid-point method or equispaced intervals method. Then, such analytic trend tests as Laplace, Lewis-Robinson, Pair-wise Comparison Nonparametric tests are used to determine whether the failure process follows a renewal or non-renewal process. Monte Carlo simulation experiments are conducted to compare the three conversion methods in terms of the statistical performance for each trend test when the underlying process is homogeneous Poisson, renewal, or non-homogeneous Poisson. The simulation results show that the uniform random generation method is best among the three. These results are applied to actual field data collected for a subsystem of a certain type of guided missile to identify its failure process and to estimate its mean time to failure and annual mean repair cost.