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High-accuracy standard specimens for the line-focus-beam ultrasonic material characterization system

IEEE TRANSAcTIONS ON ULTRASONIcS FERROELEcTRIcS AND FREQUENcY cONTROL 2002年第6期49卷 827-835页

作者： Kushibiki, J Arakawa, M Okabe, R Tohoku Univ Dept Elect Engn Sendai Miyagi 9808579 Japan

We prepared standard specimens for the line-focus-beam ultrasonic material characterization system to obtain absolute values of the propagation characteristics (phase velocity and attenuation) of leaky surface acoustic waves (LSAWs). The characterization system is very useful for evaluating and analyzing specimen surfaces. The calibration accuracy of these acoustic parameters depends on the accuracy of acoustical physical constants (elastic constants, piezoelectric constants, dielectric constants, and density) determined for standard specimens. In this paper, we developed substrates of nonpiezoelectric single crystals (viz., gadolinium gallium garnet [GGG], Si, and Ge) and an isotropic solid (synthetic silica [SiO2] glass) as standard specimens. These specimens can cover the phase velocity range of 2600 to 5100 m/s for Rayleigh-type LSAWs. To determine the elastic constants with high accuracy, we measured velocities by the complex-mode measurement method and corrected diffraction effects. Measurements of bulk acoustic properties (bulk wave velocity and density) were conducted around 23degreesc, and bulk wave velocities were obtained with an accuracy of within +/-0.004%. We clearly detected differences in acoustic properties by comparing the obtained results with the previously published values;the differences were considered to be due to differences of the specimens used. We also detected differences in acoustic properties among four SiO2 substrates produced by different manufacturers.

关键词： surface acoustic waves ultrasonic focusing ultrasonic measurement 23 c Gd3Ga5O12 Ge Rayleigh-type LSAW Si SiO2 acoustical physical constants attenuation bulk acoustic properties bulk wave velocity calibration c Silicon ultrasonic focusing Attenuation Germanium Surface acoustic waves Wave velocity Ultrasonic measurement

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Effect of vacancy distribution on the relaxation properties of graphene: a molecular dynamics study

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MIcRO & NANO LETTERS 2015年第12期10卷 693-695页

作者： Wu, Wenhu Yin, Jiuren Xie, Wei Zhang, Wei Wu, Bozhao Jiang, Yong Zhang, Ping Ding, Yanhuai Xiangtan Univ Inst Rheol Mech Xiangtan 411105 Hunan Peoples R China

Influence of vacancies on the relaxation properties of graphene nanoribbons has been investigated by molecular dynamics simulation in several nanometre sizes. Moreover, three factors including vacancy size, number and distribution are taken into consideration. The results show graphene nanoribbons present different kinds of deformation at different sites with various vacancy distributions. The effects of vacancy distributions on the relaxation properties of graphene nanoribbons are discussed.

关键词： vacancies (crystal) graphene molecular dynamics method nanoribbons deformation vacancy distribution effect relaxation properties graphene nanoribbons molecular dynamics simulation deformation c

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Dependence of self-diffusivity on size of impurity atoms in a face-centred cubic solid: existence of an anomalous maximum

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MOLEcULAR SIMULATION 2009年第1-2期35卷 151-161页

作者： Krishna, chaitanya Yashonath, S. Indian Inst Sci Solid State & Struct Chem Unit Bangalore 560012 Karnataka India Indian Inst Sci Ctr Condensed Matter Theory Bangalore 560012 Karnataka India Indian Inst Sci Jawaharlal Nehru Ctr Adv Sci Res Bangalore 560012 Karnataka India

Molecular dynamics simulation of a solid solution consisting of smaller impurity or solute atoms within a face-centred cubic lattice of larger solvent atoms is reported at a fixed concentration. Dependence of self-diffusivity of the solute atom on the diameter of the solute has been obtained. The self-diffusivity of the solute exhibits an anomalous maximum. This surprising result is explained in terms of the mutual cancellation of forces when the size of the impurity atom is comparable to the neck diameter present in the face-centred lattice. As interactions among different solids can vary widely, here we report studies employing the van der Waals interactions, which are most ubiquitous of all. Our results suggest that the only condition for the existence of a maximum is the presence of these dispersions or van der Waals interactions. Apart from the fact that these results suggest the existence of a size-dependent diffusivity maximum, they unambiguously indicate that a larger solute does not necessarily diffuse more slowly than a smaller sized solute. These are of significance in metallurgy as well as materials science. The results suggest that there will be situations where heterodiffusion of smaller impurity atoms such as H, B, c, N and O present in interstitials in a typical solid of transition or other elements of larger size can exhibit surprisingly large self-diffusivities under suitable conditions.

关键词： diffusion f c c solid size dependence

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Radial stub based negative group delay circuit theory

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IET MIcROWAVES ANTENNAS & PROPAGATION 2020年第6期14卷 515-521页

作者： Wan, Fayu Xu, Yexiang Ravelo, Blaise NUIST Sch Elect & Informat Engn Nanjing Jiangsu Peoples R China

This study addresses a negative group delay (NGD) circuit theory regarding a distributed passive topology consisted of an open-ended radial stub. The equivalent circuit composed of the lumped R, L and c elements is proposed. Then, the S-parameter model of the passive topology is established. The NGD analysis is described from the S-parameter model. The synthesis method enabling to determine the stub parameters as a function of the targeted NGD level, frequency centre and reflection coefficient is formulated. The radial stub topology limit is explained with an analytical condition from the synthesis relation. The developed NGD theory feasibility is validated with two cases of proof-of-concept (POc). First, ideal POc circuit with NGD value varied from -2 to -1 ns around the centre frequency 1.3 GHz is confirmed with ideal optimised circuit presenting figure-of-merit of approximately -0.27. Then, the theoretical prediction is verified numerically and experimentally by designing and fabricating an actual microstrip radial stub circuit. The calculated model, simulation and measurements are in very good correlation. The prototype test results confirm that the NGD circuit exhibits an NGD of approximately -1.2 ns level at approximately 0.85 GHz centre frequency.

关键词： delay circuits equivalent circuits S-parameters numerical analysis microstrip circuits UHF circuits distributed passive topology equivalent circuit S-parameter model NGD analysis synthesis method stub parameters targeted NGD level frequency centre reflection coefficient radial stub topology limit synthesis relation ideal POc circuit NGD circuit negative group delay circuit theory NGD theory feasibility open-ended radial stub lumped c elements lumped R elements lumped L elements analytical condition proof-of-concept figure-of-merit numerical analysis microstrip radial stub circuit frequency 1 3 GHz c S

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Female-to-male differential transcription patterns of miRNA-mRNA networks in the livers of dioxin-exposed mice

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ENVIRONMENTAL TOXIcOLOGY 2023年第10期38卷 2310-2331页

作者： Hammoudeh, Nour Soukkarieh, chadi Murphy, Denis J. Hanano, Abdulsamie Univ Damascus Fac Sci Dept Anim Biol Damascus Syria Univ South Wales Sch Appl Sci Pontypridd Wales Atom Energy Commiss Syria AECS Dept Mol Biol & Biotechnol Damascus Syria Atom Energy Commiss Syria Dept Mol Biol & Biotechnol POB 6091 Damascus Syria

Non-coding microRNAs (miRNAs) have important roles in regulating the expression of liver mRNAs in response to xenobiotic-exposure, but their roles concerning dioxins such as TcDD (2,3,7,8-Tetrachlorodibenzo-p-dioxin) are less clear. This report concerns the potential implication of liver (class I) and circulating (class II) miRNAs in hepatotoxicity of female and male mice after acute exposure to TcDD. The data show that, of a total of 38 types of miRNAs, the expression of eight miRNAs were upregulated in both female and male mice exposed to TcDD. Inversely, the expression of nine miRNAs were significantly downregulated in both animal genders. Moreover, certain miRNAs were preferentially induced in either females or males. The potential downstream regulatory effects of miRNAs on their target genes was evaluated by determining the expression of three group of genes that are potentially involved in cancer biogenesis, other diseases and in hepatotoxicity. It was found that certain cancer-related genes were more highly expressed females rather than males after exposure to TcDD. Furthermore, a paradoxical female-to-male transcriptional pattern was found for several disease-related and hepatotoxicity-related genes. These results suggest the possibility of developing of new miRNA-specific interfering molecules to address their dysfunctions as caused by TcDD.

关键词： dioxin hepatotoxicity liver miRNAs mouse BALB c mRNA-miRNA network

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Effect of carbon and oxygen on the high-temperature properties of silicon carbide-hafnium carbide nanocomposite fiber

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JOURNAL OF THE EUROPEAN cERAMIc SOcIETY 2023年第4期43卷 1385-1396页

作者： Bae, Seong-Gun Kim, Sanghun Jeong, Handeul Lee, Yoonjoo Jeong, Yeong-Geun Shin, Dong-Geun Korea Inst Ceram Engn & Technol Convergence Transport Mat Ctr Jinju 52851 South Korea Korea Inst Ceram Engn & Technol Semicond Mat Ctr Jinju 52851 South Korea Pusan Natl Univ Dept Convergence Busan 46241 South Korea

The polymer-derived ceramics (PDcs) technique enables relatively low-temperature fabrication of Si-based ce-ramics, with silicon carbide fiber as a representative product. Polycarbosilane (PcS) has Si-c backbone structures and can be converted to silicon carbide. In the PDcs method, residual or excess carbon is generated from the precursor (c/Si ratio = 2 for polycarbosilane). Because of the non-stoichiometry of Sic, the physicochemical properties of polymer-derived Sic are inferior to those of conventional monolithic Sic. Herein, a silicon carbide-hafnium carbide nanocomposite fiber was optimized by crosslinking oxygen into the PcS fiber by regulating the oxidation curing time. During pyrolysis, carbothermal reduction, and sintering, carbon was removed by reaction with hydrogen and cross-linked oxygen. Non-destructive techniques (X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and high-temperature thermomechanical analysis) were used to investigate the effects of excess carbon. The microstructure of the near-stoichiometric Sic-Hfc nanocomposite fiber was more densified, with superior high-temperature properties.

关键词： B Nanocomposites c creep Thermal properties D carbides

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Rapid and high yield biogas production from Jatropha seed cake by co-digestion with bagasse and addition of Fe²⁺

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ENVIRONMENTAL TEcHNOLOGY 2013年第22期34卷 3001-3006页

作者： Sen, Kalyani Mahalingam, Shanthi Sen, Biswarup PSG Coll Technol Dept Biotechnol Coimbatore Tamil Nadu India Feng Chia Univ Dept Environm Engn & Sci Taichung 40724 Taiwan Feng Chia Univ Green Energy Dev Ctr Taichung 40724 Taiwan Feng Chia Univ Master Program Green Energy Sci & Technol Taichung 40724 Taiwan

co-digestion and metal ion addition strategies to improve the biogas production potential of Jatropha seed cake (JSc) by anaerobic digestion were evaluated in the present study. Initially, batch experiments were carried out to obtain the maximum JSc concentration for optimum biogas yield, followed by co-digestion with bagasse, and addition of Fe2+. The optimum JSc concentration of 15% (w/v) gave biogas production rate (BPR) of 66.4mL/d, specific BPR of 9.7mL/d/gVS and biogas yield of 0.064m(3)/kgVS. The co-digestion strategy increased the carbon/nitrogen of feed (10% JSc+5% Bagasse, w/v) to 26.5 from 14 (JSc alone), resulting in biogas yield of 0.136m(3)/kgVS of JSc, a 2.1-fold increase. Addition of Fe2+ to JSc and bagasse mixture led to biogas yield of 0.203m(3)/kgVS, with methane content of 66% and methane production of 8.8L/L reactor. With short digestion time of 15 days, co-digestion of JSc with bagasse and addition of Fe2+ showed 3.2-fold higher biogas yield than JSc alone.

关键词： co-digestion biogas yield lignocellulosic waste c N ratio digestion time

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Influence of pH gradients on the transbilayer transport of drugs, lipids, peptides and metal ions into large unilamellar vesicles

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BIOcHIMIcA ET BIOPHYSIcA AcTA-REVIEWS ON BIOMEMBRANES 1997年第2期1331卷 187-211页

作者： cullis, PR Hope, MJ Bally, MB Madden, TD Mayer, LD Fenske, DB INEX PHARMACEUT CORP VANCOUVERBC V6P 6P2CANADA BRITISH COLUMBIA CANC AGCY DIV MED ONCOLVANCOUVERBC V5Z 4E6CANADA UNIV BRITISH COLUMBIA DEPT PHARMACOL & THERAPEUTVANCOUVERBC V6T 1Z3CANADA

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Effects of cNT loading on cellular structures and sound absorption of PU foams

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MIcRO & NANO LETTERS 2018年第10期13卷 1501-1505页

作者： Basirjafari, Sedigheh IRIB Univ Dept Acoust & Audio Engn POB *** Tehran Iran

Efforts have been made to investigate the role of adding carbon nanotubes (cNTs) as the sound energy decaying fillers on the physical and mechanical properties of polyurethane (PU) foam and thus to correlate them with its directly measured sound absorption coefficient. For this aim, the microstructures of PU/cNT nanocomposite foams were investigated and analysed through field emission scanning electron microscopy. Owing to the different microstructures of the samples, large differences were observed in their morphological and physical properties such as density, porosity, pore diameter, closed pore content and thus on their acoustic damping performance.

关键词： nanocomposites polymer foams carbon nanotubes porosity acoustic wave absorption filled polymers field emission scanning electron microscopy cellular structures carbon nanotubes polyurethane foam field emission scanning electron microscopy sound absorption coefficient PU-cNT nanocomposite foams porosity sound energy decaying fillers density pore diameter closed pore content acoustic damping c

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Time-invariant biological networks with feedback loops: structural equation models and structural identifiability

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IET SYSTEMS BIOLOGY 2018年第6期12卷 264-272页

作者： Wang, Yulin Luo, Yu Wang, Mingwen Miao, Hongyu Univ Elect Sci & Technol China Sch Comp Sci & Engn Chengdu 611731 Sichuan Peoples R China Univ Elect Sci & Technol China Sch Informat & Software Engn Chengdu 610054 Sichuan Peoples R China Southwest Jiaotong Univ Sch Math Chengdu 611756 Sichuan Peoples R China Univ Texas Hlth Sci Ctr Houston Sch Publ Hlth Dept Biostat & Data Sci Houston TX 77030 USA

Quantitative analyses of biological networks such as key biological parameter estimation necessarily call for the use of graphical models. While biological networks with feedback loops are common in reality, the development of graphical model methods and tools that are capable of dealing with feedback loops is still in its infancy. Particularly, inadequate attention has been paid to the parameter identifiability problem for biological networks with feedback loops such that unreliable or even misleading parameter estimates may be obtained. In this study, the structural identifiability analysis problem of time-invariant linear structural equation models (SEMs) with feedback loops is addressed, resulting in a general and efficient solution. The key idea is to combine Mason's gain with Wright's path coefficient method to generate identifiability equations, from which identifiability matrices are then derived to examine the structural identifiability of every single unknown parameter. The proposed method does not involve symbolic or expensive numerical computations, and is applicable to a broad range of time-invariant linear SEMs with or without explicit latent variables, presenting a remarkable breakthrough in terms of generality. Finally, a subnetwork structure of the c. elegans neural network is used to illustrate the application of the authors' method in practice.

关键词： matrix algebra least squares approximations statistical analysis parameter estimation biology structural identifiability analysis problem time-invariant linear structural equation models feedback loops identifiability equations time-invariant linear SEMs time-invariant biological networks graphical model methods parameter identifiability problem biological parameter estimation subnetwork structure c elegans neural network

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