冰塞渗流阻力特性的实验研究

冰塞引起的上下游水位变化与内部水流阻力有关,其堆积演变形成的固液多孔介质中存在渗流问题,且渗流阻力对上下游水头压力具有一定影响。本研究基于实验室冰水力学模型实验,通过设定不同的水力条件,获取不同冰塞剖面形状及沿冰塞剖面累积方向冰盖下流速分布,采用非达西渗流理论对冰塞内渗流阻力进行率定,获得了渗流阻力能量损失的变化特征。结果表明,渗流阻力能量损失占总能量损失的比例为11%～21%,冰厚较大位置可达到42%,沿冰塞累积方向,渗流能量损失占比与冰厚和水深之比呈典型的正相关。渗流流量为河道内重要的槽蓄水量,孔隙率在0.39～0.51之间,冰厚与水深之比在0.6～1.4之间时,渗流流量占总流量的9%～26%。渗流流量的变化受孔隙率、冰塞结构及水力特征等共同影响,冰颗粒均匀且随机堆积情况下,冰塞厚度越厚,冰体排列越紧密,孔隙率和渗流系数越小,流体通过多孔介质的比表面积越大,渗流能量损失也越多。本研究进一步明晰了冰塞阻力机理及渗流阻力在冰塞中的重要性,为受凌汛灾害困扰流域解决实际问题提供理论科学依据。     

Preparation and densification of superconducting YBa2Cu3Ox ceramics

The solid-state reaction method to form the superconducting oxide YBa₂Cu₃O _x was studied. It was found that the starting cupric and yttrium components accelerated the decomposition of the BaCO₃ component. At a constant heating rate of 10 ° Cmin^–1 in thermogravimetric analysis, the temperature of complete decomposition,T _f, was lowered from greater than 1000 ° C in pure BaCO₃ to between 915 and 985 ° C. The effectiveness in decreasingT _f can be ranked in the order of oxalate, carbonate and oxide. The highest sintered density achieved in this study was 6.03 g cm^–3 (/_th = 95%) at 990 ° C and 5.85 g cm^–3 (/_th = 92%) at 960 ° C. The source of cupric ion had the largest effect on densification. The use of cupric carbonate resulted in a consistently high Archimedes density of about 6.00gcm^–3 and large dimensional shrinkage of about 20% at 990 ° C for 12h. In contrast, the use of cupric oxide gave the lowest density and smallest shrinkage. Within the same powder lot, higher sintered density and smaller dimensional shrinkage were observed in samples with higher initial green density and compaction pressure. However, the data suggested that the enhanced densification and higher density achieved by the use of cupric carbonate and oxalate cannot be accounted for by the different physical characteristics of the powders and the mechanics of powder compaction, measured collectively by the green density.     

Roll‐to‐roll UV embossing process applied for light bar‐based sub‐wavelength gratings for backlight

This study proposes a roll‐to‐roll process‐based sub‐wavelength grating, which is attached on a light bar to turn the side‐lit red/green/blue (620, 520, and 450 nm) incident rays into a uniformly and normally output white light with high illuminance from the light bar's surface. On the basis of the rigorous coupling wave analysis, the relationship between the first‐order transmission/reflection efficiency and the pitch of the gratings with different shapes was analyzed. The optimal design can effectively reduce the coupling length and enhance the white color balance for display applications.     

Effects of Adenine Methylation on the Structure and Thermodynamic Stability of a DNA Minidumbbell

DNA methylation is a prevalent regulatory modification in prokaryotes and eukaryotes. N¹-methyladenine (m¹A) and N⁶-methyladenine (m⁶A) have been found to be capable of altering DNA structures via disturbing Watson–Crick base pairing. However, little has been known about their influences on non-B DNA structures, which are associated with genetic instabilities. In this work, we investigated the effects of m¹A and m⁶A on both the structure and thermodynamic stability of a newly reported DNA minidumbbell formed by two TTTA tetranucleotide repeats. As revealed by the results of nuclear magnetic resonance spectroscopic studies, both m¹A and m⁶A favored the formation of a T·m¹A and T·m⁶A Hoogsteen base pair, respectively. More intriguingly, the m¹A and m⁶A modifications brought about stabilization and destabilization effects on the DNA minidumbbell, respectively. This work provides new biophysical insights into the effects of adenine methylation on the structure and thermodynamic stability of DNA.     

Porous structures printed by fused deposition of granules processed from a novel polyamide/alumina-based system

Alumina ceramic porous structures were shaped by the fused deposition of alumina/polyamide 612 composite granules using an FDM 3D printer with a modified extruder to process granulated powder instead of a filament. The composite granules were prepared via thermally induced phase separation (TIPS). Firstly, in order to determine the proportion of polymer/solvent to be used in the TIPS process, different volume fractions of PA612 in dimethyl sulfoxide (DMSO) were studied (0.01 to 0.20), and the granules obtained were characterized by SEM, DSC, and Raman spectroscopy. Secondly, the addition of different ceramic loadings to the PA612/DMSO solution was studied with the aim of determining the amount to be used for preparing the composite granules by TIPS. In particular, the effect of the alumina content on the morphology and size of the obtained composite granules was studied. In addition, rheological properties (oscillatory and rotational tests) of the feed materials were studied. Finally, the printing conditions, including the nozzle temperature and nozzle diameter, and the extrusion process, were optimized in order to obtain porous structures with good quality. Alumina porous structures were successfully printed, debinded, and sintered. Adequate bonding between layers was achieved, and no defects at interfaces were detected.     

Aging Behavior of xPb(Fe2/3W1/3)O3· (1 –x)Pb(Fe1/2Nb1/2)O3 Ceramic

The aging behavior of a series of lead perovskite dielectrics with the compositions x Pb(Fe_2/3W_1/3)O₃·(1 – x )Pb(Fe_1/2-Nb_1/2)O₃, where 0 ≤ x ≤ 1, and the effect of dopants were studied. Below the Curie temperature ( T _c), the capacitance and the dissipation factor (tan δ) decrease approximately linearly with logarithmic time. The aging rate depends on the temperature difference, Δ T , between the aging temperature and T _c, and on the dopant concentration, but is independent of the measurement frequency between 1 and 1000 kHz. The maximum aging rate is about 3% per decade of time for capacitance and 5% per decade for tan δ at 1 mol% dopant concentration, and increases to 6.3% for capacitance and 8.5% for tan δ at 0.7 mol% dopant concentration. These results are consistent with an aging mechanism caused by changing ferroelectric domain structure with time, as proposed for BaTiO₃.     

Parallelizing Complex Streaming Applications on Distributed Scratchpad Memory Multicore Architecture

Multicore processors can provide sufficient computing power and flexibility for complex streaming applications, such as high-definition video processing. For less hardware complexity and power consumption, the distributed scratchpad memory architecture is considered, instead of the cache memory architecture. However, the distributed design poses new challenges to programming. It is difficult to exploit all available capabilities and achieve maximal throughput, due to the combined complexity of inter-processor communication, synchronization, and workload balancing. In this study, we developed an efficient design flow for parallelizing multimedia applications on a distributed scratchpad memory multicore architecture. An application is first partitioned into streaming components and then mapped onto multicore processors. Various hardware-dependent factors and application-specific characteristics are involved in generating efficient task partitions and allocating resources appropriately. To test and verify the proposed design flow, three popular multimedia applications were implemented: a full-HD motion JPEG decoder, an object detector, and a full-HD H.264/AVC decoder. For demonstration purposes, SONY PlayStation \(^{\circledR }\) 3 was selected as the target platform. Simulation results show that, on PS3, the full-HD motion JPEG decoder with the proposed design flow can decode about 108.9 frames per second (fps) in the 1080p format. The object detection application can perform real-time object detection at 2.84 fps at \(1280 \times 960\) resolution, 11.75 fps at \(640 \times 480\) resolution, and 62.52 fps at \(320 \times 240\) resolution. The full-HD H.264/AVC decoder applications can achieve nearly 50 fps.     

Preparation and properties of (BATB–ODPA) polyimide–clay nanocomposite materials

A series of polymer–clay nanocomposite (PCN) materials consisting of 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene–4,4′‐oxydiphthalic anhydride (BATB–ODPA) polyimide (PI) and layered montmorillonite (MMT) clay were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. The synthesized PCN materials were subsequently characterized by Fourier‐Transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of material composition on thermal stability, mechanical strength, molecular permeability and optical clarity of bulk PI and PCN materials in the form of membranes were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), molecular permeability analysis (GPA) and ultraviolet‐visible (UV/VIS) transmission spectra, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1072–1079, 2004     

A group decision classifier with particle swarm optimization and decision tree for analyzing achievements in mathematics and science

Group decision making is a multi-criteria decision-making method applied in many fields. However, the use of group decision-making techniques in multi-class classification problems and rule generation is not explored widely. This investigation developed a group decision classifier with particle swarm optimization (PSO) and decision tree (GDCPSODT) for analyzing students’ mathematic and scientific achievements, which is a multi-class classification problem involving rule generation. The PSO technique is employed to determine weights of condition attributes; the decision tree is used to generate rules. To demonstrate the performance of the developed GDCPSODT model, other classifiers such as the Bayesian classifier, the k-nearest neighbor (KNN) classifier, the back propagation neural networks classifier with particle swarm optimization (BPNNPSO) and the radial basis function neural networks classifier with PSO (RBFNNPSO) are used to cope with the same data. Experimental results indicated the testing accuracy of GDCPSODT is higher than the other four classifiers. Furthermore, rules and some improvement directions of academic achievements are provided by the GDCPSODT model. Therefore, the GDCPSODT model is a feasible and promising alternative for analyzing student-related mathematic and scientific achievement data.     

Solar Photocatalytic Degradation of Textile Dyes in TiO2 Suspended Solutions

The degradation and decolourization of direct dye (Everdirect supra turguoise blue, FBL), acidic dye (Isolan orange S-RL) and vat dye (Indanthren red FBB) have been investigated by solar/TiO2 process. The effects of solution pH, dye concentration, dosage of TiO2 and nano-size of TiO2 have been studied. The increase in initial pH (3, 5 and 11) and dye concentration decrease the removal rate. The treatment for FBB and FBL dye solutions is more efficient than that of S-RL.Under optimum conditions, the color removal is found to be almost complete for FBB and FBL while that of S-RL also reaches 95%. Langmuir adsorption isotherm and modified Langmuir-Hinshelwood kinetic model (L-H model) have been fitted to the experimental data and found to correlate the adsorption patterns as well as the kinetics of the dyes studied.