This paper discusses the significance and prospects of low altitude small satellite aerial vehicles to ensure smooth aerial-ground communications for next-generation broadband networks.To achieve the generic goals of ...This paper discusses the significance and prospects of low altitude small satellite aerial vehicles to ensure smooth aerial-ground communications for next-generation broadband networks.To achieve the generic goals of fifthgeneration and beyondwireless networks,the existing aerial network architecture needs to be revisited.The detailed architecture of low altitude aerial networks and the challenges in resource management have been illustrated in this paper.Moreover,we have studied the coordination between promising communication technologies and low altitude aerial networks to provide robust network coverage.We talk about the techniques that can ensure userfriendly control and monitoring of the low altitude aerial networks to bring forth wireless broadband connectivity to a new dimension.In the end,we highlight the future research directions of aerial-ground communications in terms of access technologies,machine learning,compressed sensing,and quantum communications.展开更多
The anionic redox has been widely studied in layered-oxide-cathodes in attempts to achieve highenergy-density for Na-ion batteries(NIBs).It is known that an oxidation state of Mn^(4+) or Ru^(5+) is essential for the a...The anionic redox has been widely studied in layered-oxide-cathodes in attempts to achieve highenergy-density for Na-ion batteries(NIBs).It is known that an oxidation state of Mn^(4+) or Ru^(5+) is essential for the anionic reaction of O^(2-)/O~-to occur during Na^(+) de/intercalation.However,here,we report that the anionic redox can occur in Ru-based layered-oxide-cathodes before full oxidation of Ru^(4+)/Ru^(5+).Combining studies using first-principles calculation and experimental techniques reveals that further Na^(+) deintercalation from P2-Na_(0.33)[Mg_(0.33)Ru_(0.67)]O_(2) is based on anionic oxidation after 0.33 mol Na^(+) deintercalation from P2-Na_(0.67)[Mg_(0.33)Ru_(0.67)]O_(2) with cationic oxidation of Ru^(4+)/Ru^(4.5+).Especially,it is revealed that the only oxygen neighboring 2Mg/1 Ru can participate in the anionic redox during Na^(+) de/intercalation,which implies that the Na-O-Mg arrangement in the P2-Na_(0.33)[M9_(0.33)Ru_(0.67)]O_(2) structure can dramatically lower the thermodynamic stability of the anionic redox than that of cationic redox.Through the O anionic and Ru cationic reaction,P2-Na_(0.67)[Mg_(0.33)Ru_(0.67)]O_(2) exhibits not only a large specific capacity of~172 mA h g^(-1) but also excellent power-capability via facile Na^(+) diffusion and reversible structural change during charge/discharge.These findings suggest a novel strategy that can increase the activity of anionic redox by modulating the local environment around oxygen to develop high-energy-density cathode materials for NIBs.展开更多
The intermediate phase formation and surface protection effects between SKD61 die mold alloys and aluminum alloys were investigated during a simulated die-casting process.The surface coatings of SKD61 alloy were carri...The intermediate phase formation and surface protection effects between SKD61 die mold alloys and aluminum alloys were investigated during a simulated die-casting process.The surface coatings of SKD61 alloy were carried out via Si pack cementation coatings at 900 ℃ for 10 h and the ε-FeSi phase formed.When the coated SKD61 alloy was dipped in the liquid aluminum alloy(ALDC12),the surface coated SKD61 alloys showed better surface properties compared with uncoated SKD61 alloys,i.e.,the intermediate phases(FeSiAl compound) were not produced for the coated SKD61 alloy.The coating layer of ε-FeSi served as a diffusion barrier for the formation of FeSiAl compounds.展开更多
A graphene-CdSe composite was synthesized by a facile hydrothermal method,and characterized by X-ray diffraction,scanning electron microscopy with energy dispersive X-ray analysis,transmission electron microscopy and ...A graphene-CdSe composite was synthesized by a facile hydrothermal method,and characterized by X-ray diffraction,scanning electron microscopy with energy dispersive X-ray analysis,transmission electron microscopy and UV-vis diffuse reflectance spectrophotometry.The graphene-CdSe composite efficiently catalyzed the photodegradation of methylene blue(MB),methyl orange(MO) and rhodamine B(Rh.B) in aqueous solution under UV or visible light irradiation.The graphene-CdSe composite exhibited a higher photocatalytic activity for the MB solution.展开更多
Melatonin plays a critical role in regulating photoperiodic signals and has recently been shown to decrease immunosenescence with age. In this study, we examined whether melatonin activates T lymphocytes as major adap...Melatonin plays a critical role in regulating photoperiodic signals and has recently been shown to decrease immunosenescence with age. In this study, we examined whether melatonin activates T lymphocytes as major adaptive immune cells in in vitro and in vivo models. Splenocytes, CD4+, and naive CD4 T lymphocytes were isolated from the spleen of BALB/c mice and the cell population patterns and mRNA profiles associated with T cell activation (CD28 and p21) and the melatonin receptor (MT1A and MT1B) were assessed. The T cell activation- related proteins Ki67 and Bcl2 were also evaluated to confirm the relationship between gene and protein levels. Our data clearly revealed that CD28, p21, MT 1 A, and MT 1B mRNA were highly expressed in the presence of melatonin. Co-culture of CD4+ T lymphocyte and peritoneal macrophage 7 days after melatonin administration to young and aged mice significantly increased APRIL mRNA, suggesting induction or maintenance of T lymphocyte responses. We also found that the intracellular amount of Ki67 and Bcl2 proteins were significantly upregulated in aged CD4+ T lymphocytes, suggesting enhancing T cell proliferation and ling-term maintenance of memory T cells. Taken together, we conclude that melatonin supplementation may enhance immunity in aged individuals by upregulating immunosenescence indices in association with T lymphocytes and may be an attractive pharmacological candidate for aged and immunocompromised individuals.展开更多
Recently, a semi-solid metal processing has been acknowledged as a cost-effective technique to be able to manufacture high quality product for the transportation industry. In this study a hypo-eutectic Al alloy was fa...Recently, a semi-solid metal processing has been acknowledged as a cost-effective technique to be able to manufacture high quality product for the transportation industry. In this study a hypo-eutectic Al alloy was fabricated by means of an electromagnetic stirrer in continuous casting process and the microstructural change during solidification due to a fluid flow by electromagnetic stirring was examined. Due to the forced fluid flow during solidification a dendritic phase of primary α phase of Al alloy was turned into a globular phase, which can make the Al alloy get a thixotropic behavior in the semi-solid region. In order to establish the quantitative relationship between microstructure and the process parameters, the morphology shape, a silicon distribution and a size of primary α phase were observed according to casting speed in continuous casting machine. The primary α phase was turned into the degenerate dendrites approaching a spherical configuration with increasing casting speed. The fine-grained and equiaxed microstructure appeared at higher casting speed. A segregation behavior of Si element was declined with increasing casting speed and a very uniform distribution of Si element was observed on the billet at a casting speed of 600 mm·min-1. A thickness of the solidifying shell of the billet was shortened with increasing the casting speed.展开更多
The aim of this work is to investigate microstructure,corrosion resistance characteristics and nanohardness of the oxide layer on AZ91 Mg alloy by applying different voltage with KMnO4 contained solution.There are lot...The aim of this work is to investigate microstructure,corrosion resistance characteristics and nanohardness of the oxide layer on AZ91 Mg alloy by applying different voltage with KMnO4 contained solution.There are lots of closed pores that are filled with another oxide compound compared with the typical surface morphology with pore coated until 350 V of coating voltage.The thickness of oxide layer increases with increasing coating voltage.The oxide layer formed on AZ91 Mg alloy in electrolyte with potassium permanganate consists of MgO and Mn2O3.Corrosion potential of the oxide layer on AZ91 Mg alloy obtained at different plasma electrolytic oxidation(PEO) reaction stages increases with increasing coating voltage.The corrosion resistance of AZ91 Mg alloy depends on the existence of the manganese oxide in the oxide layer.The inner barrier layer composed of the MgO and Mn2O3 may serve as diffusion barrier to enhance the corrosion resistance and may partially explain the excellent anti-corrosion performance in corrosion test.Nanohardness values increase with increasing coating voltage.The increase in the nanohardness may be due to the effect of manganese oxide in the oxide layer on AZ91 Mg alloy coated from electrolyte containing KMnO4.展开更多
Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy.The thermal performance was affected by many different design parameters,such as configuratio...Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy.The thermal performance was affected by many different design parameters,such as configuration type and borehole size of geothermal heat exchanger.These eventually determined the operation and cost efficiency of the geothermal heat exchanger system.The main purpose of this work was to assess the thermal performance of geothermal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole.For this,a thermal response test rig was established with line-source theory.The thermal response test was performed with in-line variable input heat source.Effective thermal conductivity and thermal resistance were obtained from the measured data.From the measurement,the effective thermal conductivity is found to have similar values for twopair type(4 U-tubes)and three-pair type(6 U-tubes)borehole heat exchanger systems indicating similar heat transfer ability.Meanwhile,the thermal resistance shows lower value for the three-pair type compared to the two-pair type.Measured data based resistance have lower value compared to computed result from design programs.Overall comparison finds better thermal performance for the three-pair type,however,fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.展开更多
This paper considers an optimal sequential inspection schedule for a second-hand product after that the free nonrenewable warranty is expired. The length of warranty is prespecified and during the warranty period, the...This paper considers an optimal sequential inspection schedule for a second-hand product after that the free nonrenewable warranty is expired. The length of warranty is prespecified and during the warranty period, the product is minimally repaired by the dealer when it fails. Following the expiration of the non-renewing warranty, the product is inspected and upgraded sequentially a fixed number of times at the expenses of the customer.At each inspection, the failure rate of the product is reduced proportionally so that the product is upgraded. The product is assumed to deteriorate as it ages and the replacement of the product occurs when a fixed number of inspections are rendered. In addition,the intervals between two successive inspections are assumed to decrease monotonically. The main objective of this paper is to determine the optimal improvement level to upgrade the product at each inspection so that the expected maintenance cost during the life cycle of the product is minimized from the perspective of the customer. Under the given cost structures, we derive an explicit formula to obtain the expected maintenance cost incurred during the life cycle of the product and discuss the method to find the optimal level of the improvement analytically in case the failure times follow the Weibull distribution. Numerical results are analyzed to observe the impact of relevant parameters on the optimal solution.展开更多
In the production(as co-fuel or alone)of solid refuse fuel(SRF),knowledge about the characteristics of the raw materials is required for an ecofriendly and effective combustion process.SRFs are commonly produced by dr...In the production(as co-fuel or alone)of solid refuse fuel(SRF),knowledge about the characteristics of the raw materials is required for an ecofriendly and effective combustion process.SRFs are commonly produced by drying combustible waste and removing incombustible matter,resulting in a higher combustibility as compared to the original waste.However,the characteristics of SRFs may highly vary depending on where and from which materials they were produced.Thus,we investigated the characteristics of various SRFs using thermogravimetric analysis(TGA).As a TGA sample is commonly small,on the scale of milligrams,and,unlike homogeneous fuels,SRFs are heterogeneous,individual SRF samples analysed with this method may not represent the bulk material,and sample properties may vary significantly between batches.Therefore,we further performed combustion experiments using a small-scale combustor and sample sizes from 1 to 10 g.To optimise SRF combustor design and determine the SRF characteristics,proximate,elemental,heating value,TG,and differential thermogravimetric analyses were conducted,and weight losses and gas concentrations at different temperatures were measured upon combustion.The lower heating values of the three analysed SRFs were 20,976,16,873,and 19,762 kJ/kg,and their Cl contents were 0.89,0.95,and 1.27 wt.%(legal criterion[Cl]<2.0 wt.%).TGA and small combustor experiments showed that complete weight loss was achieved below 500°C.However,CO was detected until 620°C.展开更多
Large-area polydimethylsiloxane(PDMS)films with variably sized moth-eye structures were fabricated to improve the efficiency of perovskite solar cells.An approach that incorporated photolithography,bilayer PDMS deposi...Large-area polydimethylsiloxane(PDMS)films with variably sized moth-eye structures were fabricated to improve the efficiency of perovskite solar cells.An approach that incorporated photolithography,bilayer PDMS deposition and replication was used in the fabrication process.By simply attaching the moth-eye PDMS films to the transparent substrates of perovskite solar cells,the optical properties of the devices could be tuned by changing the size of the moth-eye structures.The device with 300-nm moth-eye PDMS films greatly enhanced power conversion efficiency of ~21 % due to the antireflective effect of the moth-eye structure.Furthermore,beautiful coloration was observed on the 1000-nm moth-eye PDMS films through optical interference caused by the diffraction grating effect.Our results imply that moth-eye PDMS films can greatly enhance the efficiency of perovskite solar cells and building-integrated photovoltaics.展开更多
Existing pen and ink sketch technologies can be applied to general images, but they could not produce optimal output for images of traditional architecture, because most images consist of exquisite straight lined patt...Existing pen and ink sketch technologies can be applied to general images, but they could not produce optimal output for images of traditional architecture, because most images consist of exquisite straight lined patterns in traditional architecture, such as root tiles and window bars. The lines of roofs and eaves need to be described delicately to express pen and ink sketch most effectively. Therefore, by proposing a method to create white noise for light and shade of input images, to extract input vector directions from the white noise, and to determine the direction and length of stroke, a new expression technique is proposed for pen and ink sketch that could best reflect the characteristics of traditional architecture.展开更多
Mechanical properties of Mg-Al based alloys at different fabrication state,namely as-cast,hot rolled,and annealed,were investigated to develop the alloys that are suitable for the casting/hot working process.Exper- im...Mechanical properties of Mg-Al based alloys at different fabrication state,namely as-cast,hot rolled,and annealed,were investigated to develop the alloys that are suitable for the casting/hot working process.Exper- imental results indicated that the castability such as hot cracking resistance tends to improve with increasing the aluminum content.However,the elongation at elevated temperatures was observed to decrease as the AI content increases,implying difficulties in hot forming.A small amount of Zr additions could significantly enhance the room temperature mechanical properties of hot-rolled Mg-6%Al-1%Zn alloy.The tendency of remarkable grain coarsening at high temperatures was effectively reduced by the Zr additions.TEM analyses suggested that very fine Al-3Zr precipitates formed in the Zr-added alloy are responsible for the obtained results.展开更多
Conductive cementitious composites are innovated materials that have improved electrical conductivity compared to general types of cement,and are expected to be used in a variety of future infrastructures with unique ...Conductive cementitious composites are innovated materials that have improved electrical conductivity compared to general types of cement,and are expected to be used in a variety of future infrastructures with unique functionalities such as self-heating,electromagnetic shielding,and piezoelectricity.In the present study,machine learning methods that have been recently applied in various fields were proposed for the prediction of piezoelectric characteristics of carbon nanotubes(CNTs)-incorporated cement composites.Data on the resistivity change of CNTs/cement composites according to various water/binder ratios,loading types,and CNT content were considered as training values.These data were applied to numerous machine learning techniques including linear regression,decision tree,support vector machine,deep belief network,Gaussian process regression,genetic algorithm,bagging ensemble,random forest ensemble,boosting ensemble,long short-term memory,and gated recurrent units to estimate the time-independent and-dependent electrical properties of conductive cementitious composites.By comparing and analyzing the computed results of the proposed methods,an optimal algorithm suitable for application to CNTs-embedded cementitious composites was derived.展开更多
Thermal performance is the most important factor in the development of a borehole heat exchanger utilizing geothermal energy.The thermal performance is affected by many different design parameters and different operat...Thermal performance is the most important factor in the development of a borehole heat exchanger utilizing geothermal energy.The thermal performance is affected by many different design parameters and different operating conditions such as bleeding.This eventually determines the operation and cost efficiency of the borehole heat exchanger system.The thermal performance of an open standing column well (SCW) type geothermal heat exchanger was assessed under the influence of bleeding.For this,a thermal response test rig was established with line-source theory.The test rig also had a bleeding function by releasing fluid while taking additional underground water through the heat exchanger.The thermal response test was performed with an additional constant input heat source.Effective thermal conductivity and thermal resistance were obtained from the measured data.From the measurement,the effective thermal conductivity is found to have 1.47 times higher value when bleeding is applied.The thermal resistance also increases by 1.58 times compared to a non-bleeding case.This trend indicates enhanced heat transfer in the SCW type heat exchanger with a bleeding function.Bleeding,therefore,could be an effective method of achieving a high heat transfer rate in the SCW type heat exchanger with sufficient underground water supply.展开更多
文摘This paper discusses the significance and prospects of low altitude small satellite aerial vehicles to ensure smooth aerial-ground communications for next-generation broadband networks.To achieve the generic goals of fifthgeneration and beyondwireless networks,the existing aerial network architecture needs to be revisited.The detailed architecture of low altitude aerial networks and the challenges in resource management have been illustrated in this paper.Moreover,we have studied the coordination between promising communication technologies and low altitude aerial networks to provide robust network coverage.We talk about the techniques that can ensure userfriendly control and monitoring of the low altitude aerial networks to bring forth wireless broadband connectivity to a new dimension.In the end,we highlight the future research directions of aerial-ground communications in terms of access technologies,machine learning,compressed sensing,and quantum communications.
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (2021R1A2C1014280)supported by the “Regional Innovation Strategy (RIS)” through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2021RIS-004)+1 种基金the Fundamental Research Program of the Korea Institute of Material Science (KIMS) (PNK9370)the calculation resources were supported by the Supercomputing Center in Korea Institute of Science and Technology Information (KISTI) (KSC-2022-CRE-0030)。
文摘The anionic redox has been widely studied in layered-oxide-cathodes in attempts to achieve highenergy-density for Na-ion batteries(NIBs).It is known that an oxidation state of Mn^(4+) or Ru^(5+) is essential for the anionic reaction of O^(2-)/O~-to occur during Na^(+) de/intercalation.However,here,we report that the anionic redox can occur in Ru-based layered-oxide-cathodes before full oxidation of Ru^(4+)/Ru^(5+).Combining studies using first-principles calculation and experimental techniques reveals that further Na^(+) deintercalation from P2-Na_(0.33)[Mg_(0.33)Ru_(0.67)]O_(2) is based on anionic oxidation after 0.33 mol Na^(+) deintercalation from P2-Na_(0.67)[Mg_(0.33)Ru_(0.67)]O_(2) with cationic oxidation of Ru^(4+)/Ru^(4.5+).Especially,it is revealed that the only oxygen neighboring 2Mg/1 Ru can participate in the anionic redox during Na^(+) de/intercalation,which implies that the Na-O-Mg arrangement in the P2-Na_(0.33)[M9_(0.33)Ru_(0.67)]O_(2) structure can dramatically lower the thermodynamic stability of the anionic redox than that of cationic redox.Through the O anionic and Ru cationic reaction,P2-Na_(0.67)[Mg_(0.33)Ru_(0.67)]O_(2) exhibits not only a large specific capacity of~172 mA h g^(-1) but also excellent power-capability via facile Na^(+) diffusion and reversible structural change during charge/discharge.These findings suggest a novel strategy that can increase the activity of anionic redox by modulating the local environment around oxygen to develop high-energy-density cathode materials for NIBs.
基金supported by Korea Institute of Industrial Technology and Gwangju Metropolitan City through ‘The Advanced Elements and Materials Industry Development Program
文摘The intermediate phase formation and surface protection effects between SKD61 die mold alloys and aluminum alloys were investigated during a simulated die-casting process.The surface coatings of SKD61 alloy were carried out via Si pack cementation coatings at 900 ℃ for 10 h and the ε-FeSi phase formed.When the coated SKD61 alloy was dipped in the liquid aluminum alloy(ALDC12),the surface coated SKD61 alloys showed better surface properties compared with uncoated SKD61 alloys,i.e.,the intermediate phases(FeSiAl compound) were not produced for the coated SKD61 alloy.The coating layer of ε-FeSi served as a diffusion barrier for the formation of FeSiAl compounds.
基金supported by Research Foundation of Hanseo University in2011
文摘A graphene-CdSe composite was synthesized by a facile hydrothermal method,and characterized by X-ray diffraction,scanning electron microscopy with energy dispersive X-ray analysis,transmission electron microscopy and UV-vis diffuse reflectance spectrophotometry.The graphene-CdSe composite efficiently catalyzed the photodegradation of methylene blue(MB),methyl orange(MO) and rhodamine B(Rh.B) in aqueous solution under UV or visible light irradiation.The graphene-CdSe composite exhibited a higher photocatalytic activity for the MB solution.
基金supported by High Value-added Food Technology Development Program,Ministry of Agriculture,Food and Rural Affairs(MAFRAgrant number 113034-3)
文摘Melatonin plays a critical role in regulating photoperiodic signals and has recently been shown to decrease immunosenescence with age. In this study, we examined whether melatonin activates T lymphocytes as major adaptive immune cells in in vitro and in vivo models. Splenocytes, CD4+, and naive CD4 T lymphocytes were isolated from the spleen of BALB/c mice and the cell population patterns and mRNA profiles associated with T cell activation (CD28 and p21) and the melatonin receptor (MT1A and MT1B) were assessed. The T cell activation- related proteins Ki67 and Bcl2 were also evaluated to confirm the relationship between gene and protein levels. Our data clearly revealed that CD28, p21, MT 1 A, and MT 1B mRNA were highly expressed in the presence of melatonin. Co-culture of CD4+ T lymphocyte and peritoneal macrophage 7 days after melatonin administration to young and aged mice significantly increased APRIL mRNA, suggesting induction or maintenance of T lymphocyte responses. We also found that the intracellular amount of Ki67 and Bcl2 proteins were significantly upregulated in aged CD4+ T lymphocytes, suggesting enhancing T cell proliferation and ling-term maintenance of memory T cells. Taken together, we conclude that melatonin supplementation may enhance immunity in aged individuals by upregulating immunosenescence indices in association with T lymphocytes and may be an attractive pharmacological candidate for aged and immunocompromised individuals.
基金This work was financiallysupported bythe KISTProgram(No.2E19470)and by the Components&Materials Technology Development Program of Ministry of Commerce,Industry and Energy of Korea.
文摘Recently, a semi-solid metal processing has been acknowledged as a cost-effective technique to be able to manufacture high quality product for the transportation industry. In this study a hypo-eutectic Al alloy was fabricated by means of an electromagnetic stirrer in continuous casting process and the microstructural change during solidification due to a fluid flow by electromagnetic stirring was examined. Due to the forced fluid flow during solidification a dendritic phase of primary α phase of Al alloy was turned into a globular phase, which can make the Al alloy get a thixotropic behavior in the semi-solid region. In order to establish the quantitative relationship between microstructure and the process parameters, the morphology shape, a silicon distribution and a size of primary α phase were observed according to casting speed in continuous casting machine. The primary α phase was turned into the degenerate dendrites approaching a spherical configuration with increasing casting speed. The fine-grained and equiaxed microstructure appeared at higher casting speed. A segregation behavior of Si element was declined with increasing casting speed and a very uniform distribution of Si element was observed on the billet at a casting speed of 600 mm·min-1. A thickness of the solidifying shell of the billet was shortened with increasing the casting speed.
基金supported by a grant from the Center of Advanced Materials Processing(CAMP) of the 21st Centry Froniter R&D Program Funded by the Ministry of Knowledge Economy(MKE),Koreasupported by the Korea Science and Engineering Foundation (No.2009-0079807)
文摘The aim of this work is to investigate microstructure,corrosion resistance characteristics and nanohardness of the oxide layer on AZ91 Mg alloy by applying different voltage with KMnO4 contained solution.There are lots of closed pores that are filled with another oxide compound compared with the typical surface morphology with pore coated until 350 V of coating voltage.The thickness of oxide layer increases with increasing coating voltage.The oxide layer formed on AZ91 Mg alloy in electrolyte with potassium permanganate consists of MgO and Mn2O3.Corrosion potential of the oxide layer on AZ91 Mg alloy obtained at different plasma electrolytic oxidation(PEO) reaction stages increases with increasing coating voltage.The corrosion resistance of AZ91 Mg alloy depends on the existence of the manganese oxide in the oxide layer.The inner barrier layer composed of the MgO and Mn2O3 may serve as diffusion barrier to enhance the corrosion resistance and may partially explain the excellent anti-corrosion performance in corrosion test.Nanohardness values increase with increasing coating voltage.The increase in the nanohardness may be due to the effect of manganese oxide in the oxide layer on AZ91 Mg alloy coated from electrolyte containing KMnO4.
基金Project financially supported by the Second Stage of Brain Korea 21 Projects and Changwon National University,Korea
文摘Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy.The thermal performance was affected by many different design parameters,such as configuration type and borehole size of geothermal heat exchanger.These eventually determined the operation and cost efficiency of the geothermal heat exchanger system.The main purpose of this work was to assess the thermal performance of geothermal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole.For this,a thermal response test rig was established with line-source theory.The thermal response test was performed with in-line variable input heat source.Effective thermal conductivity and thermal resistance were obtained from the measured data.From the measurement,the effective thermal conductivity is found to have similar values for twopair type(4 U-tubes)and three-pair type(6 U-tubes)borehole heat exchanger systems indicating similar heat transfer ability.Meanwhile,the thermal resistance shows lower value for the three-pair type compared to the two-pair type.Measured data based resistance have lower value compared to computed result from design programs.Overall comparison finds better thermal performance for the three-pair type,however,fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2012026094)
基金supported by the Research Base Construction Fund Support Program funded by Chonbuk National University in 2013the Mid-career Research Program(2016R1A2B4010080)through NRF Grant funded by MEST
文摘This paper considers an optimal sequential inspection schedule for a second-hand product after that the free nonrenewable warranty is expired. The length of warranty is prespecified and during the warranty period, the product is minimally repaired by the dealer when it fails. Following the expiration of the non-renewing warranty, the product is inspected and upgraded sequentially a fixed number of times at the expenses of the customer.At each inspection, the failure rate of the product is reduced proportionally so that the product is upgraded. The product is assumed to deteriorate as it ages and the replacement of the product occurs when a fixed number of inspections are rendered. In addition,the intervals between two successive inspections are assumed to decrease monotonically. The main objective of this paper is to determine the optimal improvement level to upgrade the product at each inspection so that the expected maintenance cost during the life cycle of the product is minimized from the perspective of the customer. Under the given cost structures, we derive an explicit formula to obtain the expected maintenance cost incurred during the life cycle of the product and discuss the method to find the optimal level of the improvement analytically in case the failure times follow the Weibull distribution. Numerical results are analyzed to observe the impact of relevant parameters on the optimal solution.
基金supported by the Korea Environment Industry&Technology Institute(KEITI)through a Public Technology Program based on the Environmental Policy Program funded by the Korea Ministry of Environment(MOE)[Grant number:2016000710008].
文摘In the production(as co-fuel or alone)of solid refuse fuel(SRF),knowledge about the characteristics of the raw materials is required for an ecofriendly and effective combustion process.SRFs are commonly produced by drying combustible waste and removing incombustible matter,resulting in a higher combustibility as compared to the original waste.However,the characteristics of SRFs may highly vary depending on where and from which materials they were produced.Thus,we investigated the characteristics of various SRFs using thermogravimetric analysis(TGA).As a TGA sample is commonly small,on the scale of milligrams,and,unlike homogeneous fuels,SRFs are heterogeneous,individual SRF samples analysed with this method may not represent the bulk material,and sample properties may vary significantly between batches.Therefore,we further performed combustion experiments using a small-scale combustor and sample sizes from 1 to 10 g.To optimise SRF combustor design and determine the SRF characteristics,proximate,elemental,heating value,TG,and differential thermogravimetric analyses were conducted,and weight losses and gas concentrations at different temperatures were measured upon combustion.The lower heating values of the three analysed SRFs were 20,976,16,873,and 19,762 kJ/kg,and their Cl contents were 0.89,0.95,and 1.27 wt.%(legal criterion[Cl]<2.0 wt.%).TGA and small combustor experiments showed that complete weight loss was achieved below 500°C.However,CO was detected until 620°C.
基金supported in part by the Global Frontier R&D Program of the Center for Multiscale Energy Systems funded by the National Research Foundation under the Ministry of Education, Science and Technology, Korea (2012M3A6A7054855)supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2017RICIB1005834)newly appointed professor research fund of Hanbat National University in 2018
文摘Large-area polydimethylsiloxane(PDMS)films with variably sized moth-eye structures were fabricated to improve the efficiency of perovskite solar cells.An approach that incorporated photolithography,bilayer PDMS deposition and replication was used in the fabrication process.By simply attaching the moth-eye PDMS films to the transparent substrates of perovskite solar cells,the optical properties of the devices could be tuned by changing the size of the moth-eye structures.The device with 300-nm moth-eye PDMS films greatly enhanced power conversion efficiency of ~21 % due to the antireflective effect of the moth-eye structure.Furthermore,beautiful coloration was observed on the 1000-nm moth-eye PDMS films through optical interference caused by the diffraction grating effect.Our results imply that moth-eye PDMS films can greatly enhance the efficiency of perovskite solar cells and building-integrated photovoltaics.
基金Project(2010-0021154)supported by National Research Foundation of Korea(NRF)funded by the Ministry of Education,Science and Technology through the Basic Science Research ProgramProject(2012H1B8A2025982)supported by Human Resource Training Project for Regional Innovation,Korea
文摘Existing pen and ink sketch technologies can be applied to general images, but they could not produce optimal output for images of traditional architecture, because most images consist of exquisite straight lined patterns in traditional architecture, such as root tiles and window bars. The lines of roofs and eaves need to be described delicately to express pen and ink sketch most effectively. Therefore, by proposing a method to create white noise for light and shade of input images, to extract input vector directions from the white noise, and to determine the direction and length of stroke, a new expression technique is proposed for pen and ink sketch that could best reflect the characteristics of traditional architecture.
文摘Mechanical properties of Mg-Al based alloys at different fabrication state,namely as-cast,hot rolled,and annealed,were investigated to develop the alloys that are suitable for the casting/hot working process.Exper- imental results indicated that the castability such as hot cracking resistance tends to improve with increasing the aluminum content.However,the elongation at elevated temperatures was observed to decrease as the AI content increases,implying difficulties in hot forming.A small amount of Zr additions could significantly enhance the room temperature mechanical properties of hot-rolled Mg-6%Al-1%Zn alloy.The tendency of remarkable grain coarsening at high temperatures was effectively reduced by the Zr additions.TEM analyses suggested that very fine Al-3Zr precipitates formed in the Zr-added alloy are responsible for the obtained results.
文摘Conductive cementitious composites are innovated materials that have improved electrical conductivity compared to general types of cement,and are expected to be used in a variety of future infrastructures with unique functionalities such as self-heating,electromagnetic shielding,and piezoelectricity.In the present study,machine learning methods that have been recently applied in various fields were proposed for the prediction of piezoelectric characteristics of carbon nanotubes(CNTs)-incorporated cement composites.Data on the resistivity change of CNTs/cement composites according to various water/binder ratios,loading types,and CNT content were considered as training values.These data were applied to numerous machine learning techniques including linear regression,decision tree,support vector machine,deep belief network,Gaussian process regression,genetic algorithm,bagging ensemble,random forest ensemble,boosting ensemble,long short-term memory,and gated recurrent units to estimate the time-independent and-dependent electrical properties of conductive cementitious composites.By comparing and analyzing the computed results of the proposed methods,an optimal algorithm suitable for application to CNTs-embedded cementitious composites was derived.
基金Project supported by the Second Stage of Brain Korea 21 Projects and Changwon National University in2011-2012
文摘Thermal performance is the most important factor in the development of a borehole heat exchanger utilizing geothermal energy.The thermal performance is affected by many different design parameters and different operating conditions such as bleeding.This eventually determines the operation and cost efficiency of the borehole heat exchanger system.The thermal performance of an open standing column well (SCW) type geothermal heat exchanger was assessed under the influence of bleeding.For this,a thermal response test rig was established with line-source theory.The test rig also had a bleeding function by releasing fluid while taking additional underground water through the heat exchanger.The thermal response test was performed with an additional constant input heat source.Effective thermal conductivity and thermal resistance were obtained from the measured data.From the measurement,the effective thermal conductivity is found to have 1.47 times higher value when bleeding is applied.The thermal resistance also increases by 1.58 times compared to a non-bleeding case.This trend indicates enhanced heat transfer in the SCW type heat exchanger with a bleeding function.Bleeding,therefore,could be an effective method of achieving a high heat transfer rate in the SCW type heat exchanger with sufficient underground water supply.