Portfolio Selection Using Multivariate Semiparametric Estimators and a Copula PCA-Based Approach

Computational Economics - This paper investigates the implications for portfolio theory of using multivariate semiparametric estimators and a copula-based approach, especially when the number of...     

Macropore formation in p-type silicon: toward the modeling of morphology

The formation of macropores in silicon during electrochemical etching processes has attracted much interest. Experimental evidences indicate that charge transport in silicon and in the electrolyte should realistically be taken into account in order to be able to describe the macropore morphology. However, up to now, none of the existing models has the requested degree of sophistication to reach such a goal. Therefore, we have undertaken the development of a mathematical model (phase-field model) to describe the motion and shape of the silicon/electrolyte interface during anodic dissolution. It is formulated in terms of the fundamental expression for the electrochemical potential and contains terms which describe the process of silicon dissolution during electrochemical attack in a hydrofluoric acid (HF) solution. It should allow us to explore the influence of the physical parameters on the etching process and to obtain the spatial profiles across the interface of various quantities of interest, such as the hole concentration, the current density, or the electrostatic potential. As a first step, we find that this model correctly describes the space charge region formed at the silicon side of the interface.     

Catalytic Sulfation of Betulin with Sulfamic Acid: Experiment and DFT Calculation

Betulin is an important triterpenoid substance isolated from birch bark, which, together with its sulfates, exhibits important bioactive properties. We report on a newly developed method of betulin sulfation with sulfamic acid in pyridine in the presence of an Amberlyst^®15 solid acid catalyst. It has been shown that this catalyst remains stable when being repeatedly (up to four cycles) used and ensures obtaining of sulfated betulin with a sulfur content of ~10%. The introduction of the sulfate group into the betulin molecule has been proven by Fourier-transform infrared, ultraviolet-visible, and nuclear magnetic resonance spectroscopy. The Fourier-transform infrared (FTIR) spectra contain absorption bands at 1249 and 835–841 cm⁻¹; in the UV spectra, the peak intensity decreases; and, in the nuclear magnetic resonance (NMR) spectra, of betulin disulfate, carbons С3 and С28 are completely shifted to the weak-field region (to 88.21 and 67.32 ppm, respectively) with respect to betulin. Using the potentiometric titration method, the product of acidity constants K₁ and K₂ of a solution of the betulin disulfate H⁺ form has been found to be 3.86 × 10^–6 ± 0.004. It has been demonstrated by the thermal analysis that betulin and the betulin disulfate sodium salt are stable at temperatures of up to 240 and 220 °C, respectively. The density functional theory method has been used to obtain data on the most stable conformations, molecular electrostatic potential, frontier molecular orbitals, and mulliken atomic charges of betulin and betulin disulfate and to calculate the spectral characteristics of initial and sulfated betulin, which agree well with the experimental data.     

Formation of nanostructured silicon surfaces by stain etching

In this work, we report the fabrication of ordered silicon structures by chemical etching of silicon in vanadium oxide (V₂O₅)/hydrofluoric acid (HF) solution. The effects of the different etching parameters including the solution concentration, temperature, and the presence of metal catalyst film deposition (Pd) on the morphologies and reflective properties of the etched Si surfaces were studied. Scanning electron microscopy (SEM) was carried out to explore the morphologies of the etched surfaces with and without the presence of catalyst. In this case, the attack on the surfaces with a palladium deposit begins by creating uniform circular pores on silicon in which we distinguish the formation of pyramidal structures of silicon. Fourier transform infrared spectroscopy (FTIR) demonstrates that the surfaces are H-terminated. A UV-Vis-NIR spectrophotometer was used to study the reflectance of the structures obtained. A reflectance of 2.21% from the etched Si surfaces in the wavelength range of 400 to 1,000 nm was obtained after 120 min of etching while it is of 4.33% from the Pd/Si surfaces etched for 15 min.     

Performance enhancement of batch aerobic digesters via addition of digested sludge

The impact of the feed sludge (FS) concentration and addition of digested sludge (DS) to an aerobic digester was evaluated with respect to its capability for removal of the total suspended solids (TSS) and volatile suspended solids (VSS). The aerobic digesters, which operated in a batch mode at constant temperature and mixing rate, were initially filled with FS to 25%, 50%, 75%, and 100% of the reactor's volume. The remaining volume of the reactor was occupied by the DS, having DS/FS ratio of 3, 1, 1/3, and 0. Analysis of the experimental data showed that in the absence of DS, TSS, and VSS destruction rates are very small; however, increasing DS/FS ratio from 1/3 to 3 results in 74-77% increase in VSS and TSS destruction, respectively. The increase of the DS/FS ratio associated with increased ratio of the measured viable biomass (Cc) to VSS concentration (Xv) suggested that DS serves as the source of viable cell mass needed for degradation of organic solids. Assuming pseudo-first-order kinetics, it was shown that while organic solid destruction rate constants (k) are inversely related to initial concentrations of sludge, their values increase with increasing DS/FS ratios.     

电压表的微控制器

图1中的电路是以前一个设计实例的扩展(在无内置ADC的微控制器中如何使用模拟输入),并参考了另一篇设计实例(不用外接开关晶体管如何驱动一个七段LED显示屏)介绍的技巧(参考文献1和参考文献2).本电路增加了一个串行连接,只需要一个双绞线对就可以向一台兼容PC发送每个测量值.     

Combining finite learning automata with GSAT for the satisfiability problem

A large number of problems that occur in knowledge-representation, learning, very large scale integration technology (VLSI-design), and other areas of artificial intelligence, are essentially satisfiability problems. The satisfiability problem refers to the task of finding a satisfying assignment that makes a Boolean expression evaluate to True. The growing need for more efficient and scalable algorithms has led to the development of a large number of SAT solvers. This paper reports the first approach that combines finite learning automata with the greedy satisfiability algorithm (GSAT). In brief, we introduce a new algorithm that integrates finite learning automata and traditional GSAT used with random walk. Furthermore, we present a detailed comparative analysis of the new algorithm's performance, using a benchmark set containing randomized and structured problems from various domains.     

Computer and network security risk management: theory,challenges, and countermeasures

The need to secure information systems and networked infrastructures is now commonplace in most enterprises. The use of novel communication technologies has became a crucial factor that can considerably improve or affect productivity. This is essentially due to the importance of the information transmitted across communication networks and stored in servers. As a consequence, strong ties are being built between security and the enterprise business activity. Risk management, which is the discipline that deals with this aspect, integrates a litany of architectures, techniques, and models that are described in this paper. A global view is proposed to the reader through a presentation of the research activity that has been directed towards this field. Copyright © 2005 John Wiley & Sons, Ltd.