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911.
Seonghyeon Seo 《Journal of Mechanical Science and Technology》2003,17(6):906-913
Lean premixed combustion has been considered as one of the promising solutions for the reduction of NOx emissions from gas
turbines. However, unstable combustion of lean premixed flow becomes a real challenge on the way to design a reliable, highly
efficient dry low NOx gas turbine combustor. Contrary to a conventional diffusion type combustion system, characteristics
of premixed combustion significantly depend on a premixing degree of combusting flow. Combustion behavior in terms of stability
has been studied in a model gas turbine combustor burning natural gas and air. Incompleteness of premixing is identified as
significant perturbation source for inducing unstable combustion. Application of a simple convection time lag theory can only
predict instability modes but cannot determine whether instability occurs or not. Low frequency perturbations are observed
at the onset of instability and believed to initiate the coupling between heat release rate and pressure fluctuations. 相似文献
912.
Ouk Sub Lee Seung Suk You Ju Ho Chong Hee Soo Kang 《Journal of Mechanical Science and Technology》1998,12(6):1143-1149
This paper presents a modified split-Hopkinson pressure bar (SHPB) technique. The dynamic stress-strain behaviors were estimated
at room temperature and subzero temperature to −75°C by using the conventional SHPB and compared with a modified SHPB technique.
A computer simulation using a finite element algorithm is also performed to study the dynamic material responses. Furthermore,
we attempt to find a proper material constitutive law by using the simulation process. It is suggested that the modified SHPB
test used in this study can be successfully utilized to offer an experimental condition of a higher strain rate than that
obtained from the conventional SHPB test. 相似文献
913.
Few‐Layered WS2 Nanoplates Confined in Co,N‐Doped Hollow Carbon Nanocages: Abundant WS2 Edges for Highly Sensitive Gas Sensors 下载免费PDF全文
Won‐Tae Koo Jun‐Hwe Cha Ji‐Won Jung Seon‐Jin Choi Ji‐Soo Jang Dong‐Ha Kim Il‐Doo Kim 《Advanced functional materials》2018,28(36)
Edges of 2D transition metal dichalcogenides (TMDs) are well known as highly reactive sites, thus researchers have attempted to maximize the edge site density of 2D TMDs. In this work, metal‐organic framework (MOF) templates are introduced to synthesize few‐layered WS2 nanoplates (a lateral dimension of ≈10 nm) confined in Co, N‐doped hollow carbon nanocages (WS2_Co‐N‐HCNCs), for highly sensitive NO2 gas sensors. WS2 precursors are assembled in the surface cavity of Co‐based zeolite imidazole framework (ZIF‐67) and subsequent pyrolysis produced WS2_Co‐N‐HCNCs. During the pyrolysis, the carbonized ZIF‐67 are doped by Co and N elements, and the growth of WS2 is effectively suppressed, creating few‐layered WS2 nanoplates functionalized Co‐N‐HCNCs. The WS2_Co‐N‐HCNCs exhibit outstanding NO2 sensing characteristics at room temperature, in terms of response (48.2% to 5 ppm), selectivity, response and recovery speed, and detection limit (100 ppb). These results are attributed to the enhanced adsorption and desorption kinetics of NO2 on abundant WS2 edges, confined in the gas permeable HCNCs. This work opens up an efficient way for the facile synthesis of edge abundant few‐layered TMDs combined with porous carbon matrix via MOF templating route, for applications relying on highly active sites. 相似文献
914.
Microstructure Evolution of Concentration Gradient Li[Ni0.75Co0.10Mn0.15]O2 Cathode for Lithium‐Ion Batteries 下载免费PDF全文
Chong S. Yoon Suk Jun Kim Un‐Hyuck Kim Kang‐Joon Park Hoon‐Hee Ryu Hee‐Soo Kim Yang‐Kook Sun 《Advanced functional materials》2018,28(28)
Detailed analysis of the microstructural changes during lithiation of a full‐concentration‐gradient (FCG) cathode with an average composition of Li[Ni0.75Co0.10Mn0.15]O2 is performed starting from its hydroxide precursor, FCG [Ni0.75Co0.10Mn0.15](OH)2 prior to lithiation. Transmission electron microscopy (TEM) reveals that a unique rod‐shaped primary particle morphology and radial crystallographic texture are present in the prelithiation stage. In addition, TEM detected a two‐phase structure consisting of MnOOH and Ni(OH)2, and crystallographic twins of MnOOH on the Mn‐rich precursor surface. The formation of numerous twins is driven by the lattice mismatch between MnOOH and Ni(OH)2. Furthermore, the twins persist in the lithiated cathode; however, their density decrease with increasing lithiation temperature. Cation disordering, which influences cathode performance, is observed to continuously decrease with increasing lithiation temperature with a minimum observed at 790 °C. Consequently, lithiation at 790 °C (for 10 h) produced optimal discharge capacity and cycling stability. Above 790 °C, an increase in cation disordering and excessive coarsening of the primary particles lead to the deterioration of electrochemical properties. The twins in the FCG cathode precursor may promote the optimal primary particle morphology by retarding the random coalescence of primary particles during lithiation, effectively preserving both the morphology and crystallographic texture of the precursor. 相似文献
915.
Hierarchical NiMoS and NiFeS Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors 下载免费PDF全文
Jayaraman Balamurugan Chao Li Vanchiappan Aravindan Nam Hoon Kim Joong Hee Lee 《Advanced functional materials》2018,28(35)
Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free‐standing Ni?Mo?S and Ni?Fe?S nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni2+ is optimized to attain hierarchical Ni?Mo?S and Ni?Fe?S NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of Ni?Mo?S and Ni?Fe?S NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g?1 at 1 mA cm?2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm?2, respectively), and superior cycling stabilities. Most importantly, a flexible Ni?Mo?S NS//Ni?Fe?S NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm?3, excellent energy density of ≈82.13 Wh kg?1 at 0.561 kW kg?1, exceptional power density (≈13.103 kW kg?1 at 61.51 Wh kg?1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes. 相似文献
916.
MicroRNAs (miRNAs) are short RNA molecules that negatively regulate gene expression primarily by degrading target mRNA or inhibit the translation of protein product. Recently, many reports have shown the altered miRNA expression in various diseases. However, there are no reports on miRNA expression related to periodontitis. Thus, this study aimed to compare the miRNAs differentially expressed in healthy and chronic periodontitis tissues and to determine the miRNAs closely associated with chronic periodontitis. To find out the miRNAs differentially induced in healthy and chronic periodontitis tissues, miRNA microarray was carried out and the expression of miRNAs was confirmed by real-time PCR. According to miRNA microarray analyses, six miRNA genes, let-7a, let-7c, miR-130a, miR301a, miR-520d, and miR-548a, were up-regulated more than 8 fold compared to the healthy gingiva. The expression of twenty-two miRNAs was increased more than 4 fold. Among these miRNAs, eight miRNAs which are known to be closely related to inflammation were selected. Six of these miRNA genes, miR-181b, miR-19b, miR-23a, miR-30a, miR-let7a, and miR-301a, were amplified successfully and increased much more in periodontitis gingivae than in healthy ones. In summary, this study indicate that six miRNAs up-regulated in periodontitis gingiva may play a key role in chronic periodontitis. 相似文献
917.
Kook?Nam?ParkEmail author Chuel?Muu?Sim Chang?Oong?Choi Chang?Hee?Lee Jong?Hark?Park 《Journal of Mechanical Science and Technology》2002,16(7):927-934
The HANARO (High-flux Advanced Neutron Application Reactor) has been operated since 1995. The Cold Neutron (CN) hole was implanted
in the reflector tank from the design stage. Before a vacuum chamber and a moderator cell for the cold neutron source are
installed into the CN hole, it is necessary to measure exactly the size of the inside diameter and thickness of the CN hole
to prevent the interference problem. Due to inaccessibility and high radiation field in the CN hole, a mechanical measurement
method is not permitted. The immersed ultrasonic technique is considered as the best way to measure the thickness and the
diameter of the CN hole. The 4-Axis manipulator was designed and fabricated for locating the ultrasonic sensors. The transducer
of an ultrasonic sensor having 10 MHz frequency leads to high resolution as much as 0.03mm. The inside diameter and thickness
of 550 points of the CN hole were measured using 2 channel ultrasonic sensors. The results show that the thickness and inside
diameter of the CN hole is in the range of 3.3 - 6.7mm and 0 156-165mm, respectively. This data will be a good reference for
the design of the cold neutron source facility. 相似文献
918.
Wireless Networks - The Wi-Fi fingerprint, which can be used on existing wireless networks, is one of the main indoor positioning techniques that utilizes the received signal strength (RSS). In... 相似文献
919.
Camouflage is an emerging application of metamaterials owing to their exotic electromagnetic radiative properties. Based on the use of a selective emitter and an absorber as the metamaterials, most reported articles have suggested the use of single‐band camouflage, however, multispectral camouflage is a challenging issue owing to a difference of several orders of magnitude in the unit cell structure. Herein, hierarchical metamaterials (HMMs) for multispectral signal control when dissipating the absorbed energy of microwaves through the selective emission of infrared (IR) waves from the unit cell structure of the HMM are demonstrated. Integrating an IR selective emitter (IRE) with a microwave selective absorber, multispectral signal control with the large‐sized unit cell structures of up to 10 cm are realized. With an IRE, the emissive power from the HMM toward 5–8 µm is 1570% higher than the Au surface, which is preventing the occurrence of thermal instability. Furthermore, we determine that the signature levels of targeted IR waves (8–12 µm) and microwaves (2.5–3.8 cm) are reduced by up to 95% and 99%, respectively, when applying the HMM. 相似文献
920.
Hyunmin Kim Minjeong Seo Jong‐Woo Kim Do‐Kyun Kwon Song‐Ee Choi Jin Woong Kim Jae‐Min Myoung 《Advanced functional materials》2019,29(24)
Due to the increasing interest in wearable devices, flexible and stretchable film heaters have been widely studied, as alternatives to heaters with conventional rigid shapes. Herein, a highly stretchable film heater (SFH) based on the silver nanowire (Ag NW)–single‐walled carbon nanotube composite with a thermochromic display on a polydimethylsiloxane (PDMS) substrate is successfully fabricated. The SFH shows excellent electrical conductivity, high mechanical stretchability, and outstanding reliability, with no significant degradation after 10 000 stretching cycles under tensile strain. The SFH can be heated to the target temperature (≈60 °C) within 30 s at a low applied voltage. In addition, a thermochromic display is fabricated to help prevent the risk of low‐temperature burns. Red (R), green (G), and blue (B) thermochromic microparticles (TMPs) are synthesized using drop‐based microfluidic technology. The TMPs show RGB colors at room temperature but change to a white color above a certain temperature. The TMPs are arrayed into a PDMS stencil on the basis of their particle sizes using the rubbing technique. The micropatterned thermochromic display, which functions as a visual alarm, combined with the SFH can pave the way for the development of thermotherapy pads for next‐generation wearable devices in the medical field. 相似文献