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Indentation is widely used to extract material elastoplastic properties from measured force-displacement curves. Many previous studies argued or implied that such a measurement is unique and the whole material stress-strain curve ...
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Indentation is widely used to extract material elastoplastic properties from measured force-displacement curves. Many previous studies argued or implied that such a measurement is unique and the whole material stress-strain curve can be measured. Here we show that first, for a given indenter geometry, the indentation test cannot effectively probe material plastic behavior beyond a critical strain, and thus the solution of the reverse analysis of the indentation force-displacement curve is nonunique beyond such a critical strain. Secondly, even within the critical strain, pairs of mystical materials can exist that have essentially identical indentation responses (with differences below the resolution of published indentation techniques) even when the indenter angle is varied over a large range. Thus, fundamental elastoplastic behaviors, such as the yield stress and work hardening properties (functions), cannot be uniquely determined from the force-displacement curves of indentation analyses (including both plural sharp indentation and deep spherical indentation) Explicit algorithms of deriving the mystical materials are established, and we qualitatively correlate the sharp and spherical indentation analyses through the use of critical strain. The theoretical study in this paper addresses important questions of the application range, limitations, and uniqueness of the indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material constitutive properties.
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Traditional video coding algorithms usually undergo several coding steps for each frame before transmission, which reduces the efficiency at the encoder. The compressed sensing (CS) as an innovative method in signal processing can...
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Traditional video coding algorithms usually undergo several coding steps for each frame before transmission, which reduces the efficiency at the encoder. The compressed sensing (CS) as an innovative method in signal processing can make the encoder much easier than ever before, with which each frame only needs to multiply a projection matrix at the encoder, if the frame is sparse in a transform domain. Frames in a video usually exhibit sparsity in different parts on different bases; however, existing compressed sensing reconstruction methods usually recover a frame in a fixed set of bases for the entirety of the frame. Therefore, the frames cannot be recovered faithfully by the conventional CS reconstruction methods from a small number of measurements. In this paper, in order to rectify the flaw, we construct an initial estimation frame by motion estimation from neighboring frames and through the observation of the current frame. Then, nonlocally adaptive sparse signal presentation facilitation by a 2D piecewise autoregressive (AR) model is integrated into the reconstruction. The piecewise AR model is generated from the pattern classification of subimages of the initial estimation frame and its neighboring frames. An iterative procedure is proposed to recover a new estimated frame and its AR model alternatively, until the termination threshold is satisfied. The experimental results demonstrating the capabilities of the proposed method are presented.
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By using effective properties derived from homogenization techniques, a heterogeneous medium is transformed into a homogenous one, and the number of the degrees of freedom (DOF) can therefore be significantly reduced. This dimensi...
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By using effective properties derived from homogenization techniques, a heterogeneous medium is transformed into a homogenous one, and the number of the degrees of freedom (DOF) can therefore be significantly reduced. This dimension reduction approach has been a most widely used computational approach for efficient simulation of heterogeneous materials. The success of such a deterministic Representative Volume Element (RVE) practice critically relies on satisfaction of the assumption on scale decoupling, i.e. the size of heterogeneity is significantly smaller than the size of finite elements or RVE. The condition however has been incautiously or unknowingly ignored in quite a number of engineering practices. One typical example is finite element modeling of concrete materials where the element size is often chosen to be comparable to or even smaller than the size of aggregates. In computational modeling of small scale systems such as NEMS and MEMS, the scale decoupling assumption is commonly invalid. For such circumstances, the use of deterministic homogenization to reduce DOF results in large errors and new methodology using stochastic homogenization and non-deterministic material constants in finite elements should be considered. This paper is aimed to quantify the size effect of RVE and therefore provide estimates for the threshold of scale separation. The generalized varia-tional principles developed in Xu [Xu, X.F., submitted for publication. Generalized varia-tional principles for uncertainty quantification of boundary value problems of random heterogeneous materials] are adapted to stochastic homogenization problems, which results in size-dependent energy bounds and Hashin-Shtrikman (HS) bounds. The difference between the size dependent stochastic bounds and the classical deterministic bounds demonstrates the size effect of RVE. Numerical characterization suggests that for three-dimensional problems the size threshold of scale-decoupling, or equivalently the minimum size of deterministic RVE, is approximately between 10 and 20 times of "correlation diameter" based on a range of accuracy criteria between 1% and 0.1%. The threshold for two-dimensional problems is approximately between 15 and 50 times of correlation diameter for the same criteria, which shows stronger size effect than the 3-D cases.
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The TRMM Multi-satellite Precipitation Analysis (TMPA) system underwent a crucial upgrade in early 2009 to include a climatological calibration algorithm (CCA) to its realtime product 3B42RT, and this algorithm will continue to be...
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The TRMM Multi-satellite Precipitation Analysis (TMPA) system underwent a crucial upgrade in early 2009 to include a climatological calibration algorithm (CCA) to its realtime product 3B42RT, and this algorithm will continue to be applied in the future Global Precipitation Measurement era constellation precipitation products. In this study, efforts are focused on the comparison and validation of the Version 6 3B42RT estimates before and after the climatological calibration is applied. The evaluation is accomplished using independent rain gauge networks located within the high-latitude Laohahe basin and the low-latitude Mishui basin, both in China. The analyses indicate the CCA can effectively reduce the systematic errors over the low-latitude Mishui basin but misrepresent the intensity distribution pattern of medium-high rain rates. This behavior could adversely affect TMPA's hydrological applications, especially for extreme events (e.g., floods and landslides). Results also show that the CCA tends to perform slightly worse, in particular, during summer and winter, over the high-latitude Laohahe basin. This is possibly due to the simplified calibration-processing scheme in the CCA that directly applies the climatological calibrators developed within 40° latitude to the latitude belts of 40°N-50°N. Caution should therefore be exercised when using the calibrated 3B42RT for heavy rainfall-related flood forecasting (or landslide warning) over high-latitude regions, as the employment of the smooth-fill scheme in the CCA bias correction could homogenize the varying rainstorm characteristics. Finally, this study highlights that accurate detection and estimation of snow at high latitudes is still a challenging task for the future development of satellite precipitation retrievals.
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Ecosystem in the karst region of southwest China is very fragile due to a very limited amount of water storage for plant
uptake in the thin and rocky soils underlain by rock fractures. Plants in these karst regions are thought to ...
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Ecosystem in the karst region of southwest China is very fragile due to a very limited amount of water storage for plant
uptake in the thin and rocky soils underlain by rock fractures. Plants in these karst regions are thought to take water from the
soils and shallow fractured rock zone (subcutaneous zone) as well. However, the role of subcutaneous water in maintaining
karst vegetation remains unclear, and proportions of the water sources for plant uptake in different environment conditions
are unknown. In this study, five typical species of plants at two sites were selected in a karst plateau of Qingzhen, central
Guizhou Province of China. Proportions of the possible water sources contributed for the plant uptake from two soil layers
and subcutaneous zone were determined on the basis of υD and υ18O values of plant stem water, soil water and subcutaneous
water. The analysis reveals that most plants take water from the soil layers and the subcutaneous zone as well, but proportions
of these water contributions for plant uptake vary seasonally and depend on site-specific conditions and plant species. Plant
uptake of the subcutaneous water for all species averages less than 30% of the total monthly amount in June and September,
compared with more than 60% in dry December. Plants tend to take a larger proportion of water from the upper soil layer
at the bush site than at the forest site in June and September (63 vs 28% in July; 66 vs 54% in September for all species in
average). In December, however, 98% of water is taken from the subcutaneous zone at the bush site which is much greater
than 68% at the forest site. Compared to deciduous arbor, evergreen shrub takes a greater proportion of subcutaneous water
in the December drought. Copyright 2011 John Wiley & Sons, Ltd.
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Indentation is widely used to probe the fracture toughness of brittle materials such as ceramics or glass. In use, a hardened surface layer is inevitable in ceramics due to grinding and polishing; the surface layer also exists dur...
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Indentation is widely used to probe the fracture toughness of brittle materials such as ceramics or glass. In use, a hardened surface layer is inevitable in ceramics due to grinding and polishing; the surface layer also exists during sample preparation for indentation test. We study the mechanics of indentation induced lateral cracking in TiB_2 (titanium di-boride) ceramics, and show that the surface hardened layer has a pronounced effect on the initiation position of lateral crack, thereby affecting the wear resistance rate. The occurrence of lateral crack underneath the surface is detected in situ by an integrated acoustic emission (AE) and corrosion potential fluctuation (CPF) technique. By computing the detailed stress distribution, we discuss the mechanics of lateral crack formation in ceramics under the influence of surface hardening. It is found that when the maximum contact force is low, the lateral crack is confined within the surface layer, whereas when the maximum indentation force is high, the crack prefers to nucleate at the interface. The findings in this paper may be useful to optimize the surface polishing process and improve wear properties of ceramics.
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Despite years of effort, exact pathogenesis of nonalcoholic fatty liver disease (NAFLD) remains obscure. To gain an insight into the regulatory roles of microRNAs (miRNAs) in aberrant energy metabolic status and pathogenesis of NA...
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Despite years of effort, exact pathogenesis of nonalcoholic fatty liver disease (NAFLD) remains obscure. To gain an insight into the regulatory roles of microRNAs (miRNAs) in aberrant energy metabolic status and pathogenesis of NAFLD, we analyzed the expression of miRNAs in livers of ob/ob mice, streptozotocin (STZ)-induced type 1 diabetic mice, and normal C57BL/6 mice by miRNA mi-croarray. Compared with normal C57BL/6 mice, ob/ob mice showed upregulation of eight miRNAs and down-regulation of four miRNAs in fatty livers. Upregulation of miR-34a and downregulation of miR-122 was found in livers of STZ-induced diabetic mice. These results demonstrate that distinct miRNAs are strongly dysregulated in NAFLD and hyperglycemia. Comparison between miRNA expressions in livers of ob/ob mice and STZ-administered mice further revealed upregulation of four miRNAs and downregulation of two miRNAs in livers of ob/ob mice, indicating that these miRNAs may represent a molecular signature of NAFLD. A distinctive miRNA expression pattern was identified in ob/ ob mouse liver, and hierarchical clustering of this pattern could clearly discriminate ob/ob mice from either normal C57BL/6 mice or STZ-administered mice.
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We study the detailed mechanism of formation and propagation of spiral cracks upon spherical indentation on a thick diamond-like carbon (DLC) film deposited on a ductile steel substrate. Unlike the conventional ring cracks appeare...
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We study the detailed mechanism of formation and propagation of spiral cracks upon spherical indentation on a thick diamond-like carbon (DLC) film deposited on a ductile steel substrate. Unlike the conventional ring cracks appeared just outside the impression, the non-axisymmetric spiral cracks are formed within the crater. Integrated acoustic emission (AE) and corrosion potential fluctuation (CPF) techniques are applied to monitor the crack process in situ. It is found that spiral cracking is possible only within a relatively narrow range of maximum indentation force, below which there is no fracture and above which the ring cracks are formed. Detailed stress analyses show that the spiral cracks are nucleated below the indenter when the equivalent stress is above a critical level, which then extends during unloading. The proposed theory agrees well with experimental observations and it is expected such mechanism can be extended to similar brittle film/ductile substrate systems.
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In the paper, we propose a robust and fast image denoising method. The approach integrates both Non-Local means algorithm and Laplacian Pyramid. Given an image to be denoised, we first decompose it into Laplacian pyramid. Exploiti...
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In the paper, we propose a robust and fast image denoising method. The approach integrates both Non-Local means algorithm and Laplacian Pyramid. Given an image to be denoised, we first decompose it into Laplacian pyramid. Exploiting the redundancy property of Laplacian pyramid, we then perform non-local means on every level image of Laplacian pyramid. Essentially, we use the similarity of image features in Laplacian pyramid to act as weight to denoise image. Since the features extracted in Laplacian pyramid are localized in spatial position and scale, they are much more able to describe image, and computing the similarity between them is more reasonable and more robust. Also, based on the efficient Summed Square Image (SSI) scheme and Fast Fourier Transform (FFT), we present an accelerating algorithm to break the bottleneck of non-local means algorithm - similarity computation of compare windows. After speedup, our algorithm is fifty times faster than original non-local means algorithm. Experiments demonstrated the effectiveness of our algorithm.
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Different techniques to speed up quantum adiabatic processes are currently being explored for applications
in atomic, molecular, and optical physics, such as transport, cooling and expansion, wave-packet splitting, or
internal sta...
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Different techniques to speed up quantum adiabatic processes are currently being explored for applications
in atomic, molecular, and optical physics, such as transport, cooling and expansion, wave-packet splitting, or
internal state control. Here we examine the limitations and capabilities of superadiabatic iterations to produce a
sequence of shortcuts to adiabaticity. The general formalism is worked out as well as examples for population
inversion in a two-level system.
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