Al Distribution Research Articles

Study on Dynamic Risk Measurement Based on ARMA-GJR-AL Model

This paper established the ARMA-GJR-AL model of dynamic risk VaR and CVaR measurement. Considering from aspects of the correlation and volatility and residual distribution characteristics, studying the dynamic risk measures of VaR and CVaR based on ARMA-GJR-AL model. Through empirical research, Risk prediction and accuracy of inspection are given of the Shanghai stock market and the New York stock market. And we study the effectiveness of the model. The results show that the dynamic risk measurement model based on AL distribution is more reasonable and applicability, so it can effectively measure risk.

Study on Financial Market Risk Measurement Based on Asymmetric Laplace Distribution

In this paper, According to the returns distributions (of the financial assets returns series) with peak fat-tailed and asymmetric and the theory of Asymmetric Laplace distribution.AL-VaR (AL-CVaR) parametric method and Monte Carlo simulation are proposed which are based on Asymmetric Laplace distribution. We analyze the VaR (CVaR) measuring model of AL distribution and discuss its backtesting. And then we evaluate the pros and cons of each method combining with the characteristics of the stock market risk of three countries. (America、 China and Japan).

Synthesis temperature effect on Na-Mica-4 crystallinity and heteroatom distribution

The discovery of swelling brittle mica, Na-Mica-4, has been one of the most significant advances in the pursuit for a material with high ion-exchange capacity. For technical applications, the control of the phase evolution during the synthesis is crucial. The main aim of this study was to investigate the effect of Na-Mica-4 synthesis temperature on the crystalline phase evolution, Si–Al distribution in the tetrahedral sheet, the Al occupancy between tetrahedral and octahedral sites and their effects on the interlayer space composition. The synthesis temperature range between 600°C and 900°C was explored. At low temperature (600°C), the precursors were transformed in a low-charged swelling 2:1 phyllosilicate, saponite type, which was progressively aluminum enriched with temperature. The high-charged swelling mica was completely formed at 700°C, although a minor anhydrous contribution remained up to 850°C. Up to 800°C, silicates and fluorides secondary phases were detected as a minor contribution.

An oniom study of the distribution of skeletalAlatoms and Brønsted acidity in ZSM-23 zeolite

This paper, based on the density functional theory (DFT), mainly studies the distribution of Al in seven nonequivalent T sites as well as the acidity of the corresponding Brønsted acids (B-acids). The distribution of the acid sites in the double- Al models is also investigated. Using ONIOM (B3LYP/6-31g(d,p):AM1) method, substitution energies, proton affinities and frequencies are calculated to characterize the Al distribution and Brønsted acidity. The result shows that T6 is the most destabilized site after substitution, while T7 buried in the framework is the most favorable for Al . Besides, Al 4– O 4– Si 5 and Al 2– O 1– Si 1 are the most readily sites to form B-acids, and the acid strength of Al 4– O 3– Si 3 is the strongest. In the case that there are two B-acid sites on the 10-membered ring, one of the B-acid sites will be most likely to form at the Al 4– O 4– Si 5 site, and the other one forms either at the other Al 4– O 4– Si 5 or at Al 2– O 1– Si 1 site on the opposite side.

Effect of Al Doping on the Reliability of ALD HfO2

This work has demonstrated a high quality HfO2 based gate stack by depositing atomic layer deposited (ALD) HfAlOx along with HfO2 in a layered structure. In order to get multifold enhancement of the gate stack quality both Al percentage and distribution were observed by varying the HfAlOx layer thickness and it was found that < 2% Al/(Al+Hf)% incorporation can result in up to 18% reduction in average EOT along with up to six fold reduction in gate leakage current as compared to the dielectric with no Al content. On the other hand, excess Al presence in the interfacial layer moderately increased the interface state density (Dit). When devices were stressed in the gate injection mode at a constant field stress dielectrics with Al/(Hf+Al)% ~ 2% showed resistance to stress induced flat-band voltage shift (DVFB), and stress induced leakage current (SILC). The time dependent dielectric breakdown (TDDB) characteristics of these devices showed a reduced charge to breakdown and an increase in the extracted Weibull slope (β) that further confirms an enhanced dielectric reliability.

On the effects of circulation, sediment resuspension and biological incorporation by diatoms in an ocean model of aluminium*

Abstract. The distribution of dissolved aluminium in the West Atlantic Ocean shows a mirror image with that of dissolved silicic acid, hinting at intricate interactions between the ocean cycling of Al and Si. The marine biogeochemistry of Al is of interest because of its potential impact on diatom opal remineralisation, hence Si availability. Furthermore, the dissolved Al concentration at the surface ocean has been used as a tracer for dust input, dust being the most important source of the bio-essential trace element iron to the ocean. Previously, the dissolved concentration of Al was simulated reasonably well with only a dust source, and scavenging by adsorption on settling biogenic debris as the only removal process. Here we explore the impacts of (i) a sediment source of Al in the Northern Hemisphere (especially north of ~ 40° N), (ii) the imposed velocity field, and (iii) biological incorporation of Al on the modelled Al distribution in the ocean. The sediment source clearly improves the model results, and using a different velocity field shows the importance of advection on the simulated Al distribution. Biological incorporation appears to be a potentially important removal process. However, conclusive independent data to constrain the Al / Si incorporation ratio by growing diatoms are missing. Therefore, this study does not provide a definitive answer to the question of the relative importance of Al removal by incorporation compared to removal by adsorptive scavenging.

Mercury distribution in a toposequence of sub-Antarctic forest soils of Tierra del Fuego (Argentina) as consequence of the prevailing soil processes

The total content, distribution and assessment of Hg sources in five soils of a toposequence of sub-Antarctic forest soils in Tierra del Fuego were explained as a combination of pedogenetic processes and the interactions between Hg and the soil compounds. The soils of the toposequence were mainly podzols and podzolic soils, strongly acidic (water pH<5.0), organic matter rich in O horizons (239–444gkg−1) and non-crystalline compounds dominate Al and Fe distribution. The total Hg (HgT) values ranged between 12 and 375ngg−1 and diminished with soil depth although the secondary peaks of the HgT were observed in illuvial (Bhs or Bs) or buried A horizons. The total Hg was significantly correlated to the total contents of C, N and S (r>0.71) and to the contents of the non-crystalline Al and Fe compounds (0.44–0.71), whereas the Hg/C ratio increases with soil depth up to values of 11.3μgHgg−1 C. Exogenic Hg, i.e. Hg deposited from the atmosphere (HgExo), constitutes over 87% of the HgT in the O and A horizons, whilst lithogenic Hg (HgLit) is 36% of the average HgT.Podzolization seems to control the distribution of the HgT in the mid-slope and upslope soils (P480, P590, P630), as suggested by the HgT peaks in the Bhs or Bs horizons, where illuviated organic matter and non-crystalline Al and Fe compounds favour Hg retention. In the downslope soils (P340 and P220), both podzolization and polycyclism (that result in soils formed by two or more different and contrasting processes derived from a substantial change in soil formations factors, that lead to the accumulation of features over their lifetime), seem to influence the HgT depth pattern in light of the high values observed in the A and Bhs horizons of the buried soils. The significant correlation between the Hg/C and Cp/C ratios strengthens the efficiency of humified organic matter to complex Hg, whereas the peaks of the Hg/C ratio in the Bhs and Bs horizons also indicate that Al and Fe compounds are also involved in Hg retention.Polycyclic events, i.e. those contrasting soil processes that lead to different chemical and morphological signatures within the soil profile, could justify high HgLit values in the deeper horizons of the downslope soils, whilst the peaks of HgExo in the Bhs or Bs horizons could be considered to be a consequence of Hg mobilization and the subsequent retention by Al and Fe compounds during podzolization which is supported by the significant correlations of these soil compounds with HgExo.Environmentally, illuvial horizons and buried A horizons could act as a safety mechanism delaying the arrival of Hg to stream waters.

Periodic quantum chemical studies on anhydrous and hydrated acid clinoptilolite.

Periodic quantum chemistry methods as implemented in the crystal09 code were considered to study acid clinoptilolite (HEU framework type), both anhydrous and hydrated. The most probable location of acid sites and water molecules together with other structural details has been the object of particular attention. Calculations were performed at hybrid and pristine DFT levels of theory with a VDZP quality basis set in order to compare performances. It arises that PBE0 provides the best agreement with experimental data as concerns structural features and the most stable Al distribution in the framework. The role of the water molecule distribution in the stability of the systems, the most probable structure that they induce in the material, and their eventual influence on further chemical modification processes, such as dealumination, are discussed in detail. Results show that, apart from the usually considered interactions of water molecules with the zeolite framework, that is, a H-bond with Brönsted acid sites and coordination with framework Al as Lewis ones, it is necessary to consider cooperation of other weaker effects so as to fully understand the hydration effect in this kind of materials.

Theoretical ONIOM2/DFT study of Pd/ZSM-5 catalyst: CO and NO adsorption

In this study, we carried out two-layer ONIOMDFT:MM calculations to determine the adsorption enthalpies and vibrational frequencies of NO and CO molecules, on palladium exchanged zeolite Pd/ZSM-5 catalyst. The results reveal that the local Al distribution near to Pd^{+2} influence the stretching frequencies as well as the adsorption enthalpies. The nine possible Al distributions studied can be gathered in two groups. One responsible for high CO and NO frequencies e_{CO}= 2146 cm^{-1} and e_{NO}= 1880 cm^{-1} and the other one responsible for the low frequencies e_{CO} = 2127 cm^{-1} and e_{NO}= 1840 cm^{-1}. In general, the adsorption enthalpy of the CO is similar to the NO therefore; there is not a preferential adsorption of CO over the NO molecule.

定向凝固Ti-52%Al合金热稳定处理及其对微观组织的影响 *

摘要以Ti-52％Al合金为研究对象，在Bridgman定向凝固炉中进行不同时间的热稳定处理实验及相关的定向凝固实验，研究了定向凝固前糊状区的形成及其微观组织演化、界面形态和溶质分布，并考察了热稳定处理对定向凝固组织的影响．结果表明，试样熔化后形成了由a相晶粒、晶粒间富Al液滴和液相通道组成的糊状区，糊状区前沿为完全液相区．随着热稳定处理时间的增加，糊状区内a晶粒逐渐融合且沿温度梯度方向定向排布，富Al液滴和液相通道逐渐消失，固／液界面变得光滑平整．热稳定处理时间足够长时，糊状区内为单一的a相，溶质Al的成分在生长方向近似沿着a固相线变化．根据溶质守恒计算得出完全液相区内溶质Al含量为52．21％，高于试样原始成分，与实验测量结果相一致．进一步研究热稳定处理对后续定向凝固组织的影响，发现合理的热稳定处理时间（≥30min）确保了定向凝固启动界面处存在稳定的温度场和浓度场，柱状晶沿生长方向能够平行并列生长，试样具有良好的定向效果．

A study on high temperature oxidation behavior of double glow plasma surface metallurgy Fe–Al–Cr alloyed layer on Q235 steel

Abstract The high-temperature oxidation behavior of Q235 steel coated with Fe–Al–Cr by using double glow plasma surface metallurgy method was studied in air at different temperatures of 500, 600 and 700 °C, respectively. The Q235 and the 304 stainless steels were produced as the control samples. Electron microscopy, energy dispersive spectroscopy and X-ray diffractometry were carried out to investigate the surface morphologies, microstructures and phases of alloyed layer before and after oxidation. It showed that the structure of the Fe–Al–Cr alloyed layer was compact without any microstructure defects. This alloyed layer connected with the substrate metal by metallurgical bonding. At the temperatures of 500 and 600 °C, the high temperature oxidation resistance of the Fe–Al–Cr alloyed layer was similar to that of the 304 steel, but 2–3 times higher than that of the Q235 steel. While at 700 °C, the Fe–Al–Cr alloyed layer exhibited much better oxidation resistance than that of the 304 steel (2.5 times) and the Q235 steel (5.5 times). And this was because the special Al distribution (approximate Gaussian distribution) in the Fe–Al–Cr alloyed layer, which displayed the self-healing ability for the oxidation film on the surface of the Fe–Al–Cr alloyed layer in the high temperature oxidation conditions.

Phytotoxicity of aluminum on root growth and indole-3-acetic acid accumulation and transport in alfalfa roots

Aluminum (Al) toxicity in acid soils is a major constraint on crop production. The objective of this study of alfalfa (Medicago sativa L.) was to determine whether Al-induced inhibition of root growth in alfalfa (M. sativa L.) is related to Al distribution in different root tissues, changes in endogenous level of indole-3-acetic acid (IAA) in root tips, and the expression of key genes in IAA metabolism and translocation. Roots of alfalfa were exposed to 100μM Al3+ in half-strength Hoagland's nutrient solution. The inhibitory effects of Al on root elongation was more pronounced than on root and shoot biomass accumulation. Lumogallion, an Al specific stain, was used to monitor tissue locations of Al in the root. Lumogallion-Al was mainly detected in the root cap, epidermis, and stele of Al-treated roots. In the meristematic region of the root tip, Al accumulated mainly in the cell wall, intracellular membrane system and center of the nucleus. The similar distribution of Al ions in the root with that of auxin revealed that Al in roots may affect IAA levels. High performance liquid chromatography analysis demonstrated that IAA levels increased in the base of the root and decreased in the root tips treated with 100μM Al3+ for 3d compared to that of the control (without Al). Reverse transcription and quantitative PCR showed that the expressions of three genes, auxin transporter-like protein, auxin efflux carrier component, and cationic peroxidase, were significantly higher in Al-stressed alfalfa roots than in the control while the expression of auxin conjugate hydrolase was significantly lower. These results suggested that Al-inhibition of root elongation could be associated with Al accumulation in apoplast and membrane system, and alteration of IAA transport in the root.

Solvothermal synthesis and characterization of a layered silicate including a large quantity of Al atom and its mesoporous derivatives

A layered silicate K-LDS (K4H4Si8O20) analog including a large quantity of Al atom was synthesized by the solvothermal reaction of layered silicate H-RUB-18, potassium ethoxide, and aluminum isopropoxide. The overall Si/Al ratio of the layered compound (ca. 6) was much lower than other Al-substituted layered silicates (typically Si/Al>50). The presence of four- and six-coordinate Al nuclei was identified by 27Al MAS NMR spectra, and the relative ratio of AlO4:AlO6 was nearly 4:5. In contrast, the framework Si atoms presented only the Q3 (Si–OH) local structure. It was suggested that a large quantity of Al atoms was distributed over the crystal K-LDS surface as amorphous alumina. Mesoporous aluminosilicate derivatives were prepared by the treatment of Al-K-LDS with cationic surfactants (C16TMACl and C22TMACl). The products had foam-like mesopores with 2.4–3.7nm pore diameters and high Al contents with Si/Al=2–3. The mesoporous derivatives could be presumed as aluminosilicates because of their uniform Al distribution, and they exhibited high hydrophilicities owing to the presence of Al atoms or silanols. In addition, their ability to adsorb lysozyme into the mesopores was demonstrated under low equilibrium concentration conditions. The amount of lysozyme adsorbed and the adsorption velocity of these derivatives were considerably superior to those of typical mesoporous silica such as SBA-15, SBA-16, and FSM-16.

Suppressing Al memory effect on CVD growth of 4H-SiC epilayers by adding hydrogen chloride gas

The Al memory effect during the growth of Al-doped 4H-SiC by the hot-wall chemical vapor phase epitaxy method was investigated. To suppress unintentional incorporation of Al impurities during succeeding growth, a technique was developed by employing HCl-assisted “site-competition” growth. Three methods of introducing HCl, namely, HCl flushing before growth, HCl addition during growth, and the combination of the two preceding methods, have been performed and the Al suppression effects corresponding to the input C/Si ratio were studied separately. It is found that lowering the C/Si ratio reduces Al incorporation for all methods of introducing HCl and using the combination of HCl flushing and HCl addition is highly effective. Optimizing growth rate, temperature, and pressure can further improve Al suppression efficiency; thus, a highly abrupt change in Al distribution between Al-doped and undoped epilayers with Al concentration differences of more than five orders of magnitude was obtained, e.g., a steep change from 1020 to 1014 cm−3.

Measurement of the25Mg(α,n)28Si reaction cross section at LNL

The detection of the 1809 keV emission line associated with the decay of 26 Al in the interstellar medium provides a direct evidence of recent nucleosynthesis events in our galaxy. 26 Al is thought to be mainly produced in massive stars, but in order to have a quantita- tive understanding of the 26 Al distribution, the cross section of all the nuclear reactions involved in its production should be accurately known. A recent sensitivity study demonstrated that the 25 Mg( ,n) 28 Si is the reaction with the strongest impact on the synthesis of 26 Al during explosive Neon and Carbon burning (4). In order to improve the experimental knowledge of the 25 Mg( ,n) 28 Si cross section, a new direct measurement has been performed at Legnaro National Laboratories. The experimental setup, the data analysis and preliminary results are discussed.

Differences in physiological features associated with aluminum tolerance in Tibetan wild and cultivated barleys

Aluminum (Al) toxicity is a major limiting factor for plant production in acid soils. Wild barley germplasm is a treasure trove of useful genes and offers rich sources of genetic variation for crop improvement. Al-stress-hydroponic-experiments were performed, and the physiochemical characteristic of two contrasting Tibetan wild barley genotypes (Al-resistant XZ16 and Al-sensitive XZ61) and Al-resistant cv. Dayton were compared. Ultrastructure of chloroplasts and root cells in XZ16 was less injured than that in Dayton and XZ61. Moreover, XZ16 secreted significantly more malate besides citrate and exhibited less Al uptake and distribution than both of XZ61 and Dayton in response to Al stress, simultaneously maintained higher H+-, Ca2+Mg2+- and total-ATPase activities over XZ61. The protein synthesis inhibitor cycloheximide reduced citrate secretion from XZ16, but not from Dayton. In Tibetan wild barley, our findings highlight the significant correlations between Al tolerance, ATPase activity and citrate secretion, providing some insights into the physiological basis for Al-detoxification.

Differences in Al distribution and acidic properties between RTH-type zeolites synthesized with OSDAs and without OSDAs

In addition to the original preparation route of the RTH-type zeolites using 1,2,2,6,6-pentamethylpiperidine (PMP) as an organic structure directing agent (OSDA), we have found that simpler organic amines such as N-methylpiperidine and pyridine can be used as alternative OSDAs in place of PMP. Furthermore, we have established a synthesis method for preparing the RTH-type zeolites without using any OSDAs. In this study, RTH-type aluminosilicates were synthesized with different types of OSDA or without using any OSDAs. The obtained zeolites synthesized with different preparation methods were characterized by using various techniques, especially high-resolution (27)Al MAS NMR and in situ FT-IR techniques using CO adsorption. The relationship between the preparation method and the catalytic performance in the methanol to olefins (MTO) reaction was discussed. Finally, the distribution of Al species in the RTH-framework was clarified.

Probing silicon and aluminium chemical environments in silicate and aluminosilicate glasses by solid state NMR spectroscopy and accurate first-principles calculations

Silicon and aluminium chemical environments in silicate and aluminosilicate glasses with compositions 60SiO2·20Na2O·20CaO (CSN), 60SiO2·20Al2O3·20CaO (CAS), 78SiO2·11Al2O3·11Na2O (NAS) and 60SiO2·10Al2O3·10Na2O·20CaO (CASN) have been investigated by 27Al and 29Si solid state magic angle spinning (MAS) and multiple quantum MAS (MQMAS) nuclear magnetic resonance (NMR) experiments. To interpret the NMR data, first-principles calculations using density functional theory were performed on structural models of these glasses. These models were generated by Shell-model molecular dynamics (MD) simulations. The theoretical NMR parameters and spectra were computed using the gauge including projected augmented wave (GIPAW) method and spin-effective Hamiltonians, respectively. This synergetic computational–experimental approach offers a clear structural characterization of these glasses, particularly in terms of network polymerization, chemical disorder (i.e. Si and Al distribution in second coordination sphere) and modifier cation distributions. The relationships between the local structural environments and the 29Si and 27Al NMR parameters are highlighted, and show that: (i) the isotropic chemical shift of both 29Si and 27Al increases of about +5ppm for each Al added in the second sphere and (ii) both the 27Al and 29Si isotropic chemical shifts linearly decrease with the reduction of the average Si/Al–O–T bond angle. Conversely, 27Al and 29Si NMR parameters are much less sensitive to the connectivity with triple bridging oxygen atoms, precluding their indirect detection from 27Al and 29Si NMR.

Amelioration of iron toxicity: A mechanism for aluminum-induced growth stimulation in tea plants

Tea plants (Camellia sinensis) are well adapted to acid soils with high Al availability. These plants not only accumulate high leaf Al concentrations, but also respond to Al with growth stimulation. Decreased oxidative stress has been associated with this effect. Why tea plants not exposed to Al suffer from oxidative stress has not been clarified. In this study, hydroponically grown tea plants treated with 0 to 300μM Al were analyzed for growth, Al and Fe accumulation, and Al distribution by means of morin and hematoxylin staining. Roots of control plants stained black with hematoxylin. This indicates the formation of a Fe–hematoxylin complex. Young leaves of controls accumulated more than 1000mgFekg−1 dry weight. This concentration is above the Fe-toxicity threshold in most species. Supply of Al stimulated growth and reduced Fe uptake and transport. These results indicate that Al-induced growth stimulation might be due to alleviation of a latent Fe toxicity occurring in tea plants without Al supply.

Effect of Al doping on NO2 gas sensing of TiO2 at elevated temperatures

Undoped and Al-doped TiO2 layers were deposited by reactive magnetron sputtering using metallic targets and by adding oxygen to alumina sensor substrates that had previously been deposited with platinum-interdigitated circuits. The sensor behavior was investigated with the aim of determining the NO2 detection ability at temperatures between 400°C and 800°C. Morphological changes at elevated temperatures were recorded by scanning electron microscopy (SEM). Thin sensor layers were calcined at various temperatures between 500°C and 1000°C and analyzed by X-ray diffraction (XRD) to explore the anatase to rutile phase transformation. The lattice parameters, phase, and bonding constituents of the films were studied by Rietveld refinement, and the Al distribution was studied by ATEM mapping. All investigated layers consist of anatase phase on deposition by sputtering and convert to rutile on annealing at temperatures exceeding 600°C. The sensor response of the undoped and Al-doped TiO2 sensors toward NO2 was investigated in the temperature range of 400–800°C for concentrations varying from 50 to 100 and 200ppm. NO2/NO thermodynamic equilibrium conditions at 600°C and 800°C were analyzed. The response of Al-doped TiO2 sensor layers toward NO was tested in synthetic air. The observed sensing behavior toward NO2 in the temperature range of 400–800°C was evaluated using these analyses and compared with that of undoped TiO2 to define the effect of Al on the NO2 sensing of TiO2.