Stacking Number Research Articles

Study on the polarity, solubility, and stacking characteristics of asphaltenes

The structure and transformation of fused aromatic ring system in asphaltenes play an important role in the character of asphaltenes, and in step affect the properties of heavy oils. Polarity, solubility and structural characteristics of asphaltenes derived from Tahe atmospheric residue (THAR) and Tuo-826 heavy crude oil (Tuo-826) were analyzed for study of their internal relationship. A fractionation method was used to separate the asphaltenes into four sub-fractions, based on their solubility in the mixed solvent, for the study of different structural and physical–chemical properties, such as polarity, solubility, morphology, stacking characteristics, and mean structural parameters. Transmission electron microscope (TEM) observation can present the intuitive morphology of asphaltene molecules, and shows that the structure of asphaltenes is in local order as well as long range disorder. The analysis results showed that n-heptane asphaltenes of THAR and Tuo-826 had larger dipole moment values, larger fused aromatic ring systems, larger mean number of stacking layers, and less interlayer spacing between stacking layers than the corresponding n-pentane asphaltenes. The sub-fractions that were inclined to precipitate from the mixture of n-heptane and tetrahydrofuran had larger polarity and less solubility. From the first sub-fraction to the fourth sub-fraction, polarity, mean stacking numbers, and average layer size from the TEM images follow a gradual decrease. The structural parameters derived from TEM images could reflect the largest fused aromatic ring system in asphaltene molecule, yet the parameters derived from 1H NMR data reflected the mean message of poly-aromatic ring systems. The structural parameters derived from TEM images were more consistent with the polarity variation of sub-fractions than those derived from 1H NMR data, which indicates that the largest fused aromatic ring system will play a more important role in the stacking characteristics of asphaltene molecules than the mean parameters of poly-aromatic ring systems.

Synthesis, Characterization, and Hydrodesulfurization Activity of Diatomite-Dispersed NiMoW Composition

Diatomite-dispersed NiMoW composition was synthesized by deposition-precipitation method. Diatomite was employed to disperse active metals for full utilization of active components. BET analysis showed diatomite-dispersed NiMoW composition had a higher surface area (97.0 m2/g) and pore volume (0.24 mL/g) in comparison with pure NiMoW composition. Sulfided diatomite-dispersed NiMoW composition exhibited excellent catalytic activity in hydrogenation test transmission electron microscopy images indicate the main reason for this result should be the different stacking numbers and the curvature of MoS2 or WS2.

Optimization of hybrid laminated composites using the multi-objective gravitational search algorithm (MOGSA)

The multi-objective gravitational search algorithm (MOGSA) technique is applied to hybrid laminates to achieve minimum weight and cost. The investigated laminate is made of glass–epoxy and carbon–epoxy plies to combine the economical attributes of the first with the light weight and high-stiffness properties of the second in order to make the trade-off between the cost and weight as the objective functions. The first natural flexural frequency was considered as a constraint. The results obtained using the MOGSA, including the Pareto set, optimum stacking sequences and number of plies made of either glass or carbon fibres, were compared with those using the genetic algorithm (GA) and ant colony optimization (ACO) reported in the literature. The comparisons confirmed the advantages of hybridization and showed that the MOGSA outperformed the GA and ACO in terms of the functions’ value and constraint accuracy.

Improved temperature characteristics of highly stacked InGaAs/GaAs quantum dot lasers

AbstractUp to 24‐stacked‐layer In0.4Ga0.6As/GaAs quantum dot laser diodes were fabricated using ultrahigh‐rate molecular beam epitaxy. The operation of these devices was investigated between 298 and 353 K. The characteristic temperatures for the threshold currents improved from 72 K to 80 K with an increase in the stacking number from 12 to 19. The gain curves were also evaluated at 298 K for laser diodes with various cavity lengths. The obtained saturated modal gain increased with increasing stacking number. The laser diode with a stacking number of 24 exhibited the highest saturated modal gain at 155 cm‐1. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High Holding Voltage SCR-LDMOS Stacking Structure With Ring-Resistance-Triggered Technique

A novel ring-resistance-triggered stacked SCR-laterally diffused MOSs has been successfully verified in a 0.35 μm, 30-V/5-V bipolar CMOS DMOS process to solve the coupling of trigger voltage and holding voltage in stacking structures. The holding voltage of the proposed structure can be modulated by varying stacking numbers, and a high holding voltage of 22 V has been achieved using six stacks. On the other side, the trigger voltage almost keeps constant at ~ 53 V and a high failure current of 3.5 A has been achieved.

An Efficient Approach to Produce Clean Diesel Fuel: Development of Catalysts With Ultra-High Hydrogenation Performance

The sulfur specification for diesel fuel has been tightened exponentially over the years. To help resolve this question, the authors aimed to develop a novel unsupported Ni-Mo sulfide catalyst with ultra-high hydrogenation performance, for the production of clean diesel fuel. This catalyst was prepared directly with ammonium tetrathiomolybdate and basic nickel carbonate as the catalyst precursors through the low-temperature solid-state surface reaction. XRD and HRTEM characterization results indicate that the stacking number of MoS2 layers is very high in the unsupported Ni-Mo sulfide. The evaluation results of model compound (dibenzothiophene) and FCC diesel fuel demonstrate that the unsupported Ni-Mo sulfide catalyst has excellent hydrodesulfurization activity and ultra-high hydrogenation performance, which can be attributed to the high stacking number of MoS2 layers.

CMOS-Compatible Precise Placement of Ge Quantum Dots for Nanoelectronic, Nanophotonic, and Energy Conversion Devices

We have developed a self-assembled CMOS compatible scheme for the generation of Ge QDs through thermal oxidation of Si1-xGex patterned structures as well as demonstrated precise QD placement by guiding Ge nucleus migration along the oxidation path and thus arranging them onto targeted locations where the ultimate oxidation occurs. Thereby a single QD self-aligned with electrodes through nanoscale tunnel barriers of SiO2/Si3N4 is realized for an effective management of single electron tunneling. On the other hand, using the fidelity of lithographic patterning and selective oxidation of SiGe pillars well-organized 3D stacked Ge QDs are precisely placed vertically and laterally, and the stacking number is managed by conditions of etching and layer deposition. Stacked QDs luminescence tunable over the visible and possess low thermal conductivity, showing promise for nanophotonic and energy conversion devices.

적층각을 고려한 복합재료 라미네이트 자전거 휠의 설계

본 논문에서는 Tsai-Wu 파손이론을 적용하여 Carbon/Epoxy 복합재 적층판으로 이루어진 자전거 휠의 경량화를 위한 적층수와 적층각에 대한 강도설계에 대하여 연구하였다. 복합재료는 적층수와 적층각에 따라 강도와 강성이 변하기 때문에 적용되는 설계 하중 조건에 따른 구조물의 최취약부에서 파손이 일어나지 않도록 최적의 적층각과 최소의 적층수를 찾아야한다. 따라서 유한요소해석을 이용하여 복합재 자전거 휠에 부가되는 수직, 복합하중조건에 대하여 가장 안정적인 적층수 및 적층각을 구하였다. 휠에 적용되는 적층각은 <TEX>$[0]_{8n}$</TEX>, <TEX>$[90]_{8n}$</TEX>, <TEX>$[0/90]_{2ns}$</TEX>, <TEX>$[{\pm}45]_{2ns}$</TEX>, <TEX>$[0/{\pm}45/90]_{ns}$</TEX>으로 적층수를 변화시켜가며 유한요소해석을 수행하였다. 해석 결과로부터 <TEX>$[0/{\pm}45/90]_{3s}$</TEX>의 적층각이 파손에 안정적인 적층각 임을 제안하였다. 또한 이를 통하여 휠의 최취약부를 알 수 있었다. The strength design for the lightweight bicycle wheel made of the Carbon/Epoxy composite laminates has been discussed in this paper. For bicycle wheel design, lightness of the wheel is important. Also, it has to satisfy the required strength under specific loading cases. Two testing methods for the bicycle wheel, i.e. vertical and complex loadings, are adopted in this study. Because the strengths of composite wheel is different in relation to the stacking sequence and the number of plies, it is important to decide an appropriate stacking sequence and number of layers for the composite wheel. From the finite element analysis results, the most stable sequence orientation and number of layers are determined. The stacking sequence <TEX>$[0]_{8n}$</TEX>, <TEX>$[90]_{8n}$</TEX>, <TEX>$[0/90]_{2ns}$</TEX>, <TEX>$[{\pm}45]_{2ns}$</TEX>, <TEX>$[0/{\pm}45/90]_{ns}$</TEX> (n=1,2,3,4)are performed for finite element analysis. From results, <TEX>$[0/{\pm}45/90]_{3s}$</TEX> lay-up is a good selection for the composite bicycle wheel. Also, the weakest point and layer are found in this study.

Hydrodesulfurization of sulfur refractory compounds: Effect of gallium as an additive in NiWS/γ-Al2O3 catalysts

The effect of gallium over the NiW/γ-Al2O3 catalyst was investigated in the hydrodesulfurization (HDS) of 4,6-dimethyl-dibenzothiophene (4,6-DMDBT). The alumina carrier was modified with gallium by the addition of an aqueous solution of Ga(NO3)3·H2O in order to obtain supports with a nominal composition between 0.0 and 3.0wt.% of Ga. The Ni–W catalysts were prepared with respectively 2.8 W atoms and 1.9 Ni atoms per nm2 of initial surface area for the alumina support. The catalysts were characterized by different techniques such as temperature-programmed reduction, X-ray diffraction, UV–vis, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy and they were evaluated in the HDS of 4,6-DMDBT. The highest HDS activity for NiW catalysts was observed when the amount of gallium was 2.4wt.%, improving the value by ca. 90% as compared with that for the NiW gallium-free catalyst. This result was correlated to the effect of Ga over the dispersion of W and Ni entities. Indeed, the amount of WOx particles calculated by the Raman (OWO+WO)/WOW band intensities ratio was the highest for NiW/Ga(2.4)-γ-catalyst and HRTEM examination on the sulfided catalysts showed a decrease for the average stacking number and for the average length of WS2 particles with the gallium content. Moreover, change of the promoter (Ni2+) interaction with the support was induced by the affinity of gallium (at low loadings) to the tetrahedral sites of alumina, inducing an increase of the octahedral species of Ni in the oxidic state of the catalysts as evidenced from UV–vis and to a higher amount of the NiWS mixed phase in the sulfided samples as deduced from XPS analysis.

Fine Structure Evaluation of the Pair Distribution Function with Molecular Models of the Argonne Premium Coals

The pair distribution function (PDF) is one means of evaluating the atomic spatial arrangements of coals. Analysis of PDF based on X-ray diffraction data provides structural information on turbostratic crystalline parameters that can be utilized to further characterize coal structure. With coalification, expectations are of limited growth in aromatic stacking and a slight growth in the aromatic cluster size over the lignite to medium-volatile bituminous range. The PDF can be also used to construct and validate atomistic representations for carbonaceous materials including coal. Here, the PDF was evaluated with molecular slice models of several Argonne Premium coals (Beulah-Zap, Illinois No. 6, Upper Freeport, Pocahontas No. 3), also a non-Argonne Hon Gai anthracite, and compared to experimental observations. Atomistic representations were generated directly from high-resolution transmission electron microscope (HRTEM) lattice fringe images. The Fringe3D approach populates aromatic moieties matching the distributions of fringe: length, layers per stack, interlayer spacing, and orientations to produce an aromatic slice model of limited depth. Perl scripts incorporated appropriate aliphatic and heteroatom components. This approach creates atomistic representations with greater ease, improved accuracy, and reduced computational expense than other construction approaches. The constructed coal models were partially geometry-optimized to achieve realistic bond lengths but without displacement of coal molecules enabling the distribution of fringe length, stacking, and orientations to be duplicated in 3D modeling space. The resulting coal slice models, devoid of cross-links, captured a distribution of turbostratic crystalline dimensions with an average cluster size of about 1 nm, an average interlayer spacing ranging between 0.37 and 0.39 nm, and an average stacking number of ∼2–3 in accordance with HRTEM and XRD data for Argonne coals. These structural models were used to predict PDFs and to evaluate the fine detail of the frequency spectra via examination of intermolecular and intramolecular contributions. There was good agreement between predicted and experimental observations. Analysis of the simulated intermolecular PDF contribution showed strong intensities with increasing coal rank in agreement with the growth in the stacking number and stack height observed from low- to high-rank coals. The simulated intramolecular PDF contribution showed shorter peak amplitudes for low-rank coals in comparison to high-rank coals in agreement with the increase in stack width as coal rank increases. To further examine these contributions, lattice models composed of pyrene molecules were also constructed via Fringe 3D and manipulated to directly investigate the effect of aromatic orientation distributions and stacking on the simulated PDF. Peak intensities of simulated intermolecular PDFs at the average interlayer spacing increased with the degree of alignment (ϕ) according to g(r)interd002 = 0.0014ϕ2 + 0.0107ϕ + 4.2784. This result was consistent with the slight increase in the stacking number observed from low- to high-rank coals with a more dramatic transition for anthracite.

Infrared and Raman spectra of ABC-stacked few-layer graphene studied by first-principles calculations

The infrared (IR) absorption spectra and resonant Raman spectra of ABC-stacked tri- and tetra-layer graphene are studied using the density functional theory. It is found that they exhibit very different characteristic peaks in their IR spectra and G-band resonant Raman spectra, compared with those of AB-stacked ones, caused by the different stacking sequence and interlayer coupling. The anisotropy of the IR spectra with respect to the direction of the light electric field is significant. The IR spectra are more sensitive to the stacking number when the electric field is perpendicular to the graphene plane due to the interlayer polarization. On the other hand, the calculated first-order G-band resonant Raman spectra are also found to be sensitive to the different stacking sequence and stacking number, though the sensitivity will decay as the stacking number increases. The high sensitivities make both IR and Raman spectra possible to identify the stacking sequence and number of few-layer graphene by comparing theory and experiment.

Relation between the morphology of MoS 2 in NiMo catalyst and its selectivity for dibenzothiophene hydrodesulfurization

Two series of NiMo catalysts supported on alumina with different loadings of molybdenum and nickel were prepared and characterized by X-ray diffraction, N 2 sorption, and high-resolution transmission electron microscopy. The performance of NiMo catalysts for hydrodesulfurization was evaluated in a fixed-bed microreactor using dibenzothiophene as a model compound. The effect of morphology of MoS 2 phase in NiMo catalyst on its hydrogenation selectivity was investigated. The results indicated that the morphology of MoS 2 phases is affected by the loadings of molybdenum and nickel. Mo18Ni4 catalyst (containing 18% MoO 3 and 4% NiO), which is provided with the well-known MoS 2 slab structures with a multilayered morphology, exhibits high hydrodesulfurization activity and hydrogenation selectivity. The hydrogenation selectivity of NiMo catalyst is linearly correlated with the stacking number of MoS 2 slab; the higher the stacking number, the better is the hydrodesulfurization selectivity.

Statistical stacking and adaptive notch filter to remove high‐level electromagnetic noise from MRS measurements

ABSTRACTTraditionally, one of the major limitations for magnetic resonance sounding (MRS) measurement is that the weak signal generated by subsurface water molecules is prone to be disturbed by high‐level electromagnetic noise. In China, the power grid coverage is 94.6% and spiky noise and powerline harmonic noise are always present when utilizing MRS measurement in suburban areas or towns. In order to improve the performance of the MRS method, two new techniques, statistical stacking and adaptive notch filter, are introduced to remove spiky noise and power‐line harmonic noise. Firstly, four stacking procedures are analysed to suppress the natural noise and spiky noise. It could be found that statistical stacking can be utilized in the areas with serious spiky noise and can improve the signal‐to‐noise ratio by a factor of 4 to 7. Moreover, the stacking number is less than other stacking procedures and the measurement time may decrease by nearly 50% in some suburban areas or towns. Secondly, there are a variety of filtering procedures available to suppress power‐line harmonic noise, which are all based on analogue or digital notch filtering. But nearly all of them may cause distortion. An adaptive notch filter is applied here to remove power‐line harmonic noise because harmonic frequencies are away from and (or) close to the Larmor frequency, even when the frequency offset between them is zero. From simulation results, it could be noted that the signal can be recovered after adaptive notch filtering because it is not irretrievably distorted but proportionally attenuated. Thus, the amplitude attenuation can accurately be compensated. The effectiveness of the two techniques applied to MRS measurements is demonstrated by field testing with the prototype of the MRS system developed by Jilin University, China. The results show that the statistical stacking and adaptive notch filter are effective methods to remove high‐level electromagnetic noise from MRS measurements.

Convective assembly of linear gold nanoparticle arrays at the micron scale for surface enhanced Raman scattering

A convective assembly technique at the micron scale analogous to the writing action of a “pipette pen” has been developed for the linear assembly of gold nanoparticle strips with micron scale width and millimeter scale length for surface enhanced Raman scattering (SERS). The arrays with interparticle gaps smaller than 3 nm are hexagonally stacked in the vicinity of the pipette tip. Variable numbers of stacked layers and clean surfaces of the assembled nanoparticles are obtained by optimizing the velocity of the pipette tip. The SERS properties of the assembled nanoparticle arrays rely on their stacking number and surface cleanliness. Open image in new window

Essential role of citric acid in preparation of efficient NiW/Al 2O 3 HDS catalysts

The role of citric acid in preparation of NiW/Al 2O 3 HDS catalysts was investigated. Four catalysts with the same metal loading were prepared by pore filling method, with different supports (alumina or carbon modified alumina) and the impregnation solutions (adding citric acid or not), followed by drying. The UV–Vis spectra of the aqueous solution of nickel nitrate, ammonium metatungstate and citric acid shows no Ni-complex formation. The N 2 physisorption results indicated the addition of citric acid in the impregnation solution has slight effect on the pore structure of the corresponding sulfided catalysts. The TPR profiles of the oxidic catalysts showed metal species supported on carbon modified alumina are easier to be reduced than those on alumina. The results of TPO-MASS indicated there are two types of carbonaceous compounds of different combustive properties in the freshly sulfided samples. HRTEM images showed the addition of citric acid can decrease the average WS 2 slab length but increase stacking number. The addition of citric acid can facilitate the formation of Ni–W–S active phases, as determined by XPS. And the HDS tests showed the catalysts prepared by adding citric acid in the impregnation solution, exhibit higher HDS activity for 4, 6-DMDBT.

A Structure Design of HTS Current Leads With Respect to the Structure of Coated Conductor and the Current Terminal

High temperature superconductor (HTS) is a promising material as current leads for large current applications, because it has zero resistance. However, a single HTS tape has limitation on the capacity of current rating due to the critical current of the HTS tape. Therefore, stacking or parallel structure of the HTS tapes is inevitable in high temperature superconducting current leads (HTSCLs) for large current application. In this paper, several stacking methods with respect to the shape of the current terminal and the structure of the HTS tape are studied and the characteristics of the stacked samples are investigated by experimental analysis. The critical currents of the HTS modules were measured and the conductive heat leakage of a stabilizer layer was calculated. From this analysis, the characteristics of the current distribution and decrease in the critical current of HTS modules with respect to the shape of the current terminal were obtained. Based on the results, the required stacking number of the HTS tapes for certain operating current HTSCLs can be calculated.

Determination of Number of Layers and Stacking Sequence of Composite Bicycle Frame

Due to the high specific strength, high specific modulus and good fatigue characteristics, carbon/epoxy composite bicycle frame can have superior performance to aluminum bicycle. As the strength of composite frame varies according to the number of layers and stacking sequence, it is necessary to determine the appropriate number of layers and stacking sequence for designing light weight composite frame. The frame is divided into six parts, i.e. head tube, seat tube, top tube, bottom tube, seat stay, and chain stay parts. Since different stress levels are generated among the different parts, different numbers of layer with different stacking sequences are considered for each part. Three different loading conditions, i.e. horizontal loading, vertical loading, and pedal loading, are considered in the analysis. The superb stacking sequence and number of layers of the composite frame with the lowest failure index were determined which satisfy the three different loading conditions.

Using Modal Analysis and Optimization to Determine Elastic Constants of Thick Composite Plates

This paper presents an inverse method to derive the elastic constants of thick composite plates from the resonance frequencies of a free-edge test specimen based on modal vibration test. A mixed numerical experimental identification procedure is used for this purpose. The sum of the squared differences between the experimental frequencies and analytical frequencies from finite element method is chosen as the objective function. The optimization techniques, Hybrid Genetic /Simulated Annealing algorithm, have been applied to determine the elastic constants. As the objective function reaches its minimum, its corresponding design variables are the elastic constants of the material. The present method is applied to determine the elastic constants of AS4/PEKK material. The results indicate that different stacking sequences and numbers of frequencies have effects on the determination of elastic constants of the materials.

The relation between morphology of (Co)MoS 2 phases and selective hydrodesulfurization for CoMo catalysts

A series of CoMo catalysts were prepared by various methods with three different supports (Al 2O 3-1 of γ phase, Al 2O 3-2 containing γ and δ mixed phases, SiO 2). And the effect of morphology of (Co)MoS 2 phases on selective hydrodesulfurization was studied systematically. The TEM images showed, in general, the average slab length, the stacking number and the ratio of edge/corner of the sulfided catalysts increase remarkably in the order: SiO 2 > Al 2O 3-2 > Al 2O 3-1, with the extent of metal–support interaction decreasing in the order: SiO 2 < Al 2O 3-2 < Al 2O 3-1. And the hydrodesulfurization selectivity correlates linearly with the slab length (or the ratio of edge/corner) of (Co)MoS 2 phases, the longer average slab length, the higher ratio of edge/corner, and then the better hydrodesulfurization selectivity. Among all the catalysts, sulfided CoMo/SiO 2 of the longest average slab length and the highest edge/corner ratio exhibits the best hydrodesulfurization selectivity.

Characterization of Columnar InAs/GaAs Quantum-Dot Structures Using Grazing Incidence X-ray Diffraction

Grazing incidence X-ray diffraction (GIXD) measurement using equipment available for laboratories was realized for the evaluation of columnar InAs/GaAs quantum dots (QDs). The QDs were grown by direct stacking of small self-assembled islands in the growth direction on (001) GaAs substrates, and we prepared some samples by changing the number of units stacked. Using an imaging plate for a detector, we successfully observed that QD-related signals appeared around a GaAs(220) peak. The QD signals extended in the direction of the 2θ axis, and the extension increased with increasing number of stacks in the columnar QD growths. The results of the measurements were evaluated by a simulation based on the finite element method. Using a simple model that divides the QDs into an InAs columnar core and an InGaAs transition domain, we found that the core was expanded according to the increase in the stacking number. We also found that the lattice constant increased almost uniformly toward the upper part inside the QD. GIXD evaluation in laboratories will enhance the speed of the development of QD devices.