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Chebyshev multilevel absorber design concept 总被引:2,自引:0,他引:2
Gau J.-R.J. Burnside W.D. Gilreath M. 《Antennas and Propagation, IEEE Transactions on》1997,45(8):1286-1293
Pyramidal- and wedge-absorber materials are used extensively in anechoic measurement chambers to attenuate stray signals. Typical absorber layouts result in large absorber walls in which the absorber tips and bases are roughly aligned in the same plane. Such a quasi-periodic configuration produces a strong coherent specular reflection which dominates the absorber scattered field. Based on the multisection impedance transformer concept, one can divide absorber elements into different levels (layers) so that this coherence can be destroyed to reduce the specular absorber scattering level. The synthesis of this desired behavior can be implemented by the Chebyshev transformer technique, which provides the largest bandwidth given a passband ripple threshold. The resulting reflected field is then the product of the original absorber response times the Chebyshev reduction factor, which is independent of polarization and absorber properties. Various measured results are used to show that more than a 10-dB improvement can be achieved at the critical low end of the frequency band using this approach. This improvement cannot be achieved using conventional design concepts unless the absorber size is doubled 相似文献
3.
Location management of correlated mobile users in the UMTS 总被引:1,自引:0,他引:1
Rung-Hung Gau Chung-Wei Lin 《Mobile Computing, IEEE Transactions on》2005,4(6):641-651
In this paper, we propose concurrently searching for correlated mobile users in mobile communications networks. Previous work either focuses on locating a single mobile user or assumes that the locations of mobile users are statistically independent. We first propose a mobility model in which the movements of mobile users are statistically correlated. Next, we use the theory of Markov chain to derive the joint probability density function of the locations of mobile users. In addition, we propose a novel approach to discover the correlations among the locations of mobile users without explicitly calculating the joint probability density function. Our simulation results indicate that exploring the correlations among the locations of mobile users could significantly reduce the average paging delay and increase the maximum stable throughput. 相似文献
4.
The objective of this work was to study the relationship between daily sleep time and characteristics of students, e.g. grade level, gender, and academic program. A sleep habit questionnaire was designed to survey students at two junior high schools, one from northern Taipei and the other from southern Taipei. The impact of shortened duration of sleep on daily function was also evaluated. A total of 965 students and their parents were selected randomly in December 1993 for the questionnaire study. The response rate was 96.4% (930) for students and 88.6% (855) for parents. The self-reported daily sleep time of students declined, and daytime sleepiness and moodiness increased in the higher grades. The girls slept fewer hours than the boys and did not show an increase in daytime sleepiness. Those students not taking the senior high school joint entrance examination slept more hours at night and maintained more alertness in the daytime than those who were taking the examination. The more academic pressures that adolescents faced, the fewer hours they slept. Students not participating in the joint entrance examination seemed to show a healthier sleep pattern. Little sleep at night made the students feel sleepy in the daytime and tired, drowsy, moody and difficult at arising in the morning. The reason why girls slept less than boys needs further investigation. 相似文献
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Jyh‐Ping Dong Jyh‐Gau Huang Fuh‐Huah Lee Jiunn‐Wei Roan Yan‐Jyi Huang 《应用聚合物科学杂志》2004,91(5):3388-3397
The effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride) with different chemical structures and MWs on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during curing were investigated by an integrated approach of static phase characteristics of the ternary styrene (ST)/UP/LPA system, reaction kinetics, cured‐sample morphology, microvoid formation, and property measurements. The relative volume fraction of microvoids generated during the cure was controlled by the stiffness of the UP resin used, the compatibility of the uncured ST/UP/LPA systems, and the glass‐transition temperature of the LPAs used. On the basis of the Takayanagi mechanical model, the LPA mechanism on volume shrinkage control, which accounted for phase separation and microvoid formation, and factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3388–3397, 2004 相似文献
7.
Rung-Hung Gau Kuan-Mei Chen 《Mobile Computing, IEEE Transactions on》2006,5(6):725-737
In this paper, we propose the predictive multicast polling scheme for medium access control in wireless networks with multipacket reception capability. We concentrate on the case in which the packet arrival process is general and the maximum queue size is finite but larger than one. We derive both analytical results and simulation results. We use the theory of discrete-time Markov chain to analyze the evolution of the system state. In addition, we propose to use Markov reward processes to calculate the exact value of the network throughput. Furthermore, we obtain the average system size, the packet blocking probability, and the average packet delay. We show that our numerical results are consistent with simulation results. We also use simulation results to justify the usage of the proposed approach. Our study shows that the system performance can be significantly improved with a few additional buffers in the queues. 相似文献
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Riki Shiroma Yuan Li Jeung-yil Park Long Wu Satoshi Kaneko Tomoyuki Takai Mitsuru Gau Masakazu Ike Ken Tokuyasu 《Journal of Applied Glycoscience》2016,63(3):77
Abstract: Sorghum bagasse samples from two sets (n6 and bmr6; n18 and bmr18) of wild-type and corresponding “brown midrib” (bmr) mutant strains of sweet sorghum were evaluated as the feedstock for fermentable sugar recovery via the calcium capturing by carbonation (CaCCO) process, which involves Ca(OH)2 pretreatment of bagasse with subsequent neutralization with CO2 for enzymatic saccharification. Saccharification tests under various pretreatment conditions of the CaCCO process at different Ca(OH)2 concentrations, temperatures or residence periods indicated that bmr strains are more sensitive to the pretreatment than their counterparts are. It is expected that variant bmr6 is more suitable for glucose recovery than its wild-type counterpart because of the higher glucan content and better glucose recovery with less severe pretreatment. Meanwhile, bmr18showed higher scores of glucose recovery than its counterpart did, only at low pretreatment severity, and did not yield higher sugar recovery under the more severe conditions. The trend was similar to that of xylose recovery data from the two bmr strains. The advantages of bmr strains were also proven by means of simultaneous saccharification and fermentation of CaCCO-pretreated bagasse samples by pentose-fermenting yeast strain Candida shehatae Cs 4R. The amounts needed for production of 1 L of ethanol from n6, bmr6, n18, and bmr18samples were estimated as 4.11, 3.46, 4.03, and 3.95 kg, respectively. The bmr strains seem to have excellent compatibility with the CaCCO process for ethanol production, and it is expected that integrated research from the feedstock to bioprocess may result in breakthroughs for commercialization. 相似文献
10.
Yuh-Ching Gau Tsung-Jang Yeh Chin-Mu Hsu Samuel Yien Hsiao Hui-Hua Hsiao 《International journal of molecular sciences》2022,23(6)
Multiple myeloma is a hematologic malignancy of plasma cells that causes bone-destructive lesions and associated skeletal-related events (SREs). The pathogenesis of myeloma-related bone disease (MBD) is the imbalance of the bone-remodeling process, which results from osteoclast activation, osteoblast suppression, and the immunosuppressed bone marrow microenvironment. Many important signaling cascades, including the RANKL/RANK/OPG axis, Notch signaling, the Wnt/β-Catenin signaling pathways, and signaling molecules, such as DKK-1, sclerostin, osteopontin, activin A, chemokines, and interleukins are involved and play critical roles in MBD. Currently, bisphosphonate and denosumab are the gold standard for MBD prevention and treatment. As the molecular mechanisms of MBD become increasingly well understood, novel agents are being thoroughly explored in both preclinical and clinical settings. Herein, we will provide an updated overview of the pathogenesis of MBD, summarize the clinical management and guidelines, and discuss novel bone-modifying therapies for further management of MBD. 相似文献