2,321 research outputs found
Effect of insulating-nanoparticles addition on ion current and voltage-holding ratio in nematic liquid crystal cells
No full textNumerical Analysis of Transient Pressure Behaviors with Shale Gas MFHWs Interference
No full textAfter the large-scale horizontal well pattern development in shale gas fields, the problem of fast pressure drop and gas well abandonment caused by well interference becomes more serious. It is urgent to understand the downhole transient pressure and flow characteristics of multi-stage fracturing horizontal well (MFHW) with interference. Therefore, the reservoir around the MFHW is divided into three regions: fracturing fracture, Stimulated reservoir volume (SRV), and unmodified matrix. Then, multi-region coupled flow model is established according to reservoir physical property and flow mechanism of each part. The model is numerically solved using the perpendicular bisection (PEBI) grids and the finite volume method. The accuracy of the model is verified by analyzing the measured pressure recovery data of one practical shale gas well and fitting the monitoring data of the later production pressure. Finally, this model is used to analyze the effects of factors, such as hydraulic fractures' connectivity, well distance, the number of neighboring wells and well pattern arrangement, on the transient pressure and seepage characteristics of the well. The study shows that the pressure recovery double logarithmic curves fall in later part when the well is disturbed by a neighboring production well. The earlier and more severe the interference, the sooner the curve falls off and the larger the amplitude shows. If the well distance is closer, and if there are more neighboring wells and interconnected corresponding fracturing segments, the more severe interference appears among the wells. Moreover, the well interference may still exist even without interlinked fractures or SRV. Especially, severe interference will affect production when the hydraulic fractures are connected directly, and the interference is weaker when only SRV induced fracture network combined between wells, which is beneficial to production sometimes. When severe well interference occurs, periodic well shut-in is needed to help restore the reservoir pressure and output capacity. In the meanwhile, the daily output should be controlled reasonably to prolong the stable production time. This research will help to understand the impact of well interference to gas production, and to optimize the well spacing and achieve satisfied performance.</p
C(t) dominance of the mixed I/II creep crack: Part II. Extensive creep
No full textIn the Part II of this paper, two typical specimens, i.e. compact tension shear (CTS) specimen and single edge notched (SEN) specimen, are selected as the numerical cases to analyse the dominance of C*-integral for mixed I/II creep crack under extensive creep. C*-integrals under different loading angles are presented with the same loading level for CTS specimens and SEN specimens. The equivalent creep zone enlarges with the decrease of the loading angle, which implies that the lower creep mixity occupies the larger equivalent creep zone under the same loading level. A normalized stress function method based on the FE calculation is given to obtain the distribution functions of mixed I/II creep crack tip fields. The comparisons of the FE solutions and HRR field are made for CTS and SEN specimens with various crack depths, and it can be found that the loss dominance of C(t) becomes remarkable under those cases close to mode I loading. The Q-parameter computed with the tangential stress is found to be invalid to be used as the constraint parameter for mixed mode creep crack under the extensive creep regime because of the influence of blunting effect. The stress triaxiality along maximum tangential stress (MTS) direction is suitable to be selected as the constraint parameter for the mixed I/II creep crack tip field. The stress triaxiality is independent on the radial distance even in a wide range away from creep crack tip along the MTS direction.</p
Synthesis and Properties of Water-Soluble Core–Shell–Shell Silica–CdSe/CdS–Silica Nanoparticles
No full text[[abstract]]This paper describes the synthesis of highly water-soluble and fluorescent core–shell–shell silica–CdSe/CdS–silica nanoparticles (CSS silica–QDs–silica NPs). We used cadmium nitrate and 1,1-dimethyl-2-selenourea precursors to synthesize CdSe quantum dots (QDs)in aqueous solution under simultaneous illumination with a diode-pumped solid state green laser and a Xe–Hg lamp. After passivation of the CdSe QDs with CdS, the CdSe/CdS QDs were then conjugated covalently to (3-mercaptopropyl)trimethoxysilane (MPS); we call these nanoparticles "MPS-QDs". We mixed the MPS-QDs with tetraethoxysilane (TEOS), ethanol, and NH3. By controlling the concentrations of the reagents, the stirring speed, and the reaction time, we synthesized CSS silica–QDs–silica NPs having sizes ranging from 75 to 190 nm. The incubation time for preparing the MPS-QDs and their concentrations are important parameters in determining the morphologies of the CSS silica–QDs–silica NPs. When we mixed 50 nM MPS-QDs, 1.1 mM TEOS, and 78 mM NH3 and reacted them at a stirring speed of 750 rpm, we obtained 85-nm-diameter CSS silica–QDs–silica NPs having a QD shell thickness of about 20 nm. The CSS silica–QDs–silica NPs provide a strong photoluminescence intensity (quantum yield 88%)and exhibit enhanced stability both photochemically and in high-conductivity media (e.g., 1.0 M NaCl)
Using Classifiers to Find Domain-Specific Online Databases Automatically
No full textWang H, Liu YW, Zuo WL. Using classifiers to find domain-specific online databases automatically. Journa
Dissection of the enhancer activity of beta-globin 5' DNase I-hypersensitive site 2 in transgenic mice
No full texthe beta-globin locus control region (LCR) consists of four erythroid-specific DNase I-hypersensitive sites, which are necessary for high-level expression of the beta-like globin genes in erythroid tissues. One of these sites, designated 5'HS-2, functions as an erythroid-specific enhancer element in transfection and transgenic mouse experiments. Recent transfection experiments and studies of DNA-protein interactions have localized the 5'HS-2 enhancer to 18 nucleotides that contain a binding site for both the erythroid-specific factor nuclear factor erythroid 2 (NFE-2) and for activator protein 1 (AP-1). To define the sequences necessary for in vivo enhancer activity, several deletion mutants of 5'HS-2 were linked to the human beta-globin gene and their activity was tested in transgenic mice. Three upstream fragments of 5'HS-2 [341, 374, and 412 base pairs (bp)], each of which contained the NFE-2/AP-1 sequences, resulted in beta-globin expression at levels equivalent to or higher than those observed with the entire 732-bp 5'HS-2 fragment. In contrast, a 358-bp downstream portion of 5'HS-2, which lacked the NFE-2/AP-1 sequences, resulted in beta-globin expression at the low levels seen with the beta-globin gene alone. Removal of the NFE-2/AP-1 sequences by a 67-bp internal deletion resulted in similar low levels of beta-globin expression. A 100-bp 5' fragment that contained the NFE-2/AP-1 sequences resulted in beta-globin expression that was higher than the beta-globin gene alone but lower than the entire 5'HS-2 fragment or the three larger upstream fragments. These studies demonstrate that the NFE-2/AP-1 sequences are essential for enhancer activity of 5'HS-2 but that other sequences are required for full activity in vivo
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Event-triggered robust control for multi-player nonzero-sum games with input constraints and mismatched uncertainties
Full text linkIn this article, an event-triggered robust control (ETRC) method is investigated for multi-player nonzero-sum games of continuous-time input constrained nonlinear systems with mismatched uncertainties. By constructing an auxiliary system and designing an appropriate value function, the robust control problem of input constrained nonlinear systems is transformed into an optimal regulation problem. Then, a critic neural network (NN) is adopted to approximate the value function of each player for solving the event-triggered coupled Hamilton-Jacobi equation and obtaining control laws. Based on a designed event-triggering condition, control laws are updated when events occur only. Thus, both computational burden and communication bandwidth are reduced. We prove that the weight approximation errors of critic NNs and the closed-loop uncertain multi-player system states are all uniformly ultimately bounded thanks to the Lyapunov's direct method. Finally, two examples are provided to demonstrate the effectiveness of the developed ETRC method
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