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71.
72.
研究某水库蓄水对区域地下水动态的影响,以期为水库后期建设以及区域水资源管理提供相关科学依据。通过建立水库试验段气象-地下水监测系统,运用M-K趋势分析法分析研究区地下水位动态特征,选用变异系数法分析地下水位的时空间变异特征,采用灰色关联度法揭示其主导影响因子。结果表明:水库试验段地下水位整体表现为上升趋势且具有明显的丰枯特征,升幅约为0.5~2.0m/a;试验段渗漏量与地下水位变化呈负相关关系,渗漏对地下水位的影响存在一定空间差异,即对东部地下水位的影响大于西部;西部地下水位的主导影响因子为降雨量,东部地下水位的主导影响因子为渗漏量和降雨量。 相似文献
73.
J. Osenbach A. Amin M. Bachman F. Baiocchi D. Bitting D. Crouthamel J. DeLucca D. Gerlach J. Goodell C. Peridier M. Stahley R. Weachock 《Journal of Electronic Materials》2009,38(2):303-324
The thermal stability of flip-chip solder joints made with trilayer Al/Ni(V)/Cu underbump metalization (UBM) and eutectic
Pb-Sn solder connected to substrates with either electroless Ni(P)-immersion gold (ENIG) or Pb-Sn solder on Cu pad (Cu-SOP)
surface finish was determined. The ENIG devices degraded more than 50 times faster than the Cu-SOP devices. Microstructural
characterization of these joints using scanning and transmission electron microscopy and ion beam microscopy showed that electrical
degradation of the ENIG devices was a direct result of the conversion of the as-deposited Ni(V) barrier UBM layer into a porous
fine-grained V3Sn-intermetallic compound (IMC). This conversion was driven by the Au layer in the ENIG surface finish. No such conversion
was observed for the devices assembled on Cu-SOP surface finish substrates. A resistance degradation model is proposed. The
model captures changes from a combination of phenomena including increased (1) intrinsic resistivity, (2) porosity, and (3)
electron scattering at grain boundaries and surfaces. Finally, the results from this study were compared with results found
in a number of published electromigration studies. This comparison indicates that degradation during current stressing in
the Pb-Sn bump/ENIG system is in part due to current-crowding-induced Joule heating and the thermal gradients that result
from localized Joule heating. 相似文献
74.
Subspace analysis of spatial time-frequency distribution matrices 总被引:10,自引:0,他引:10
Spatial time-frequency distributions (STFDs) have been previously introduced as the natural means to deal with source signals that are localizable in the time-frequency domain. Previous work in the area has not provided the eigenanalysis of STFD matrices, which is key to understanding their role in solving direction finding and blind source separation problems in multisensor array receivers. The aim of this paper is to examine the eigenstructure of the STFD matrices. We develop the analysis and statistical properties of the subspace estimates based on STFDs for frequency modulated (FM) sources. It is shown that improved estimates are achieved by constructing the subspaces from the time-frequency signatures of the signal arrivals rather than from the data covariance matrices, which are commonly used in conventional subspace estimation methods. This improvement is evident in a low signal-to-noise ratio (SNR) environment and in the cases of closely spaced sources. The paper considers the MUSIC technique to demonstrate the advantages of STFDs and uses it as grounds for comparison between time-frequency and conventional subspace estimates 相似文献
75.
Soroosh Sharifi‐Asl Fernando A. Soto Tara Foroozan Mohammad Asadi Yifei Yuan Ramasubramonian Deivanayagam Ramin Rojaee Boao Song Xuanxuan Bi Khalil Amine Jun Lu Amin Salehi‐khojin Perla B. Balbuena Reza Shahbazian‐Yassar 《Advanced functional materials》2019,29(23)
LiCoO2 is a prime example of widely used cathodes that suffer from the structural/thermal instability issues that lead to the release of their lattice oxygen under nonequilibrium conditions and safety concerns in Li‐ion batteries. Here, it is shown that an atomically thin layer of reduced graphene oxide can suppress oxygen release from LixCoO2 particles and improve their structural stability. Electrochemical cycling, differential electrochemical mass spectroscopy, differential scanning calorimetry, and in situ heating transmission electron microscopy are performed to characterize the effectiveness of the graphene‐coating on the abusive tolerance of LixCoO2. Electrochemical cycling mass spectroscopy results suggest that oxygen release is hindered at high cutoff voltage cycling when the cathode is coated with reduced graphene oxide. Thermal analysis, in situ heating transmission electron microscopy, and electron energy loss spectroscopy results show that the reduction of Co species from the graphene‐coated samples is delayed when compared with bare cathodes. Finally, density functional theory and ab initio molecular dynamics calculations show that the rGO layers could suppress O2 formation more effectively due to the strong C? Ocathode bond formation at the interface of rGO/LCO where low coordination oxygens exist. This investigation uncovers a reliable approach for hindering the oxygen release reaction and improving the thermal stability of battery cathodes. 相似文献
76.
Asif Hussain Khoja Arslan Mazhar Faisal Saleem Muhammad Taqi Mehran Salman Raza Naqvi Mustafa Anwar Sehar Shakir Nor Aishah Saidina Amin Muhammad Bilal Sajid 《International Journal of Hydrogen Energy》2021,46(29):15367-15388
The catalyst has a significant role in gas processing applications such as reforming technologies for H2 and syngas production. The stable catalyst is requisite for any industrial catalysis application to make it commercially viable. Several methods are employed to synthesize the catalysts. However, there is still a challenge to achieve a controlled morphology and pure catalyst which majorly influences the catalytic activity in reforming applications. The conventional methods are expansive, and the removal of the impurities are major challenges. Nevertheless, it is not straightforward to achieve the desired structure and stability. Therefore, significant interest has been developed on the advanced techniques to take control of the physicochemical properties of the catalyst through non-thermal plasma (NTP) techniques. In this review, the systematic evolution of the catalyst synthesis using NTP technique is elucidated. The emerging DBD plasma to synthesized and effective surface treatment is reviewed. DBD plasma synthesized catalyst performance in reforming application for H2 and syngas production is summarised. Furthermore, the status of DBD plasma for catalyst synthesis and proposed future avenues to design environmentally suitable and cost-effective synthesis techniques are discussed. 相似文献
77.
Hadi Fekrmandi Muhammad Unal Amin Baghalian Shervin Tashakori Kathleen Oyola Abdullah Alsenawi Ibrahim Nur Tansel 《The International Journal of Advanced Manufacturing Technology》2016,83(1-4):13-20
Surface response to excitation (SuRE) method was originally developed for structural health monitoring (SHM) applications. SuRE was used to evaluate the performance of completed milling operations. The method generates surface waves on the plate and studies the spectrum changes at selected points to detect defects and change of compressive forces. In this study, the length, depth, and width of a slot were changed step by step. The surface of the aluminum plate was excited in the 20–400 kHz range with a piezoelectric element. A laser scanning vibrometer was used to monitor the vibrations at the predetermined grid points after the dimensions of the slot were changed methodically. The frequency spectrums of measured vibrations were calculated by using the Fast Fourier Transformation (FFT). The sums of the squares of the differences (SSD) of the spectrums were calculated to evaluate the change of the spectrums. The SuRE method was able to determine if the dimensions were changed in each case at all the selected points. The scanning laser vibrometer is not feasible to be used at the shop floor. However, the study demonstrated that a piezoelectric element attached to any of the grid points would be able to evaluate the completed machining process. 相似文献
78.
Recent advances in the production of γ‐valerolactone from biomass‐derived feedstocks via heterogeneous catalytic transfer hydrogenation
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Amin Osatiashtiani Adam F Lee Karen Wilson 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2017,92(6):1125-1135
γ‐valerolactone (GVL) is an important intermediate chemical with a wide range of applications as fuel, fuel additive and as a green solvent which has received a great deal of attentions from both academia and industry. This review aims to summarise the advances in conversion of renewable feedstocks into GVL through heterogeneous catalytic transfer hydrogenation (CTH) with a strong emphasis on discussing preparation, characterisation and performance of the catalysts in order to provide a better understanding of various catalytic systems and also to compare them in terms of catalytic performance. © 2017 Society of Chemical Industry 相似文献
79.
A planar antenna array that includes 12 corrugated tapered slot elements for use in ultrawideband (UWB) biomedical microwave imaging systems is presented. The used corrugate tapered slot antenna has a compact size, low profile, moderate gain, and distortionless performance in the time domain. The array is immersed in a carefully designed matching liquid of suitable dielectric constant to improve the matching between the array and the imaged object, and thus, to increase the dynamic range of the imaging system. A suitable platform is designed and fabricated to accommodate the array, breast phantom, and a coupling liquid for the case of UWB breast imaging. The design of the whole system is optimized using trust‐region framework method in the simulation tool CST Microwave Studio. The performance of the designed array is confirmed via measurements in a realistic imaging environment. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013. 相似文献
80.
Bahareh Sarmadi Farhana Aminuddin Muhajir Hamid Nazamid Saari Azizah Abdul-Hamid Amin Ismail 《Food chemistry》2012
Fat, alkaloid and polyphenol contents of two clones of cocoa (UIT1 and PBC 140) were removed and the remaining powder was autolyzed at pH 3.5 and 5.2. Based on the results, autolysates of UIT produced at pH 3.5 exhibited the highest ability to inhibit α-amylase activity. However, no α-glucosidase inhibition activity was observed under the conditions specified. Autolysates produced under pH 3.5 caused the highest amount of insulin secretion. In streptozotocin-diabetic rats, all cocoa autolysates significantly decreased blood glucose at 4 h. To assure that the results from the assays were not due to the polyphenols of cocoa autolysates qualitative and quantitative tests were applied. According to their results cocoa autolysates were found to be free from polyphenols. Analysis of amino acid composition revealed that cocoa autolysates were abundant in hydrophobic amino acids. It can be suggested that besides other compounds of cocoa, its peptides and amino acids could contribute to its health benefits. 相似文献