Inverse method for identifying the underlying crack distribution in plates with random strengths

Summary In the current investigation we seek to identify the underlying crack number and crack length distributions in brittle plates with a known strength distribution. The inverse problem in probabilistic fracture mechanics is defined, and the numerical procedure to solve the inverse problem is constructed. The simulation process of generating simulated plates containing simulated random cracks is elaborated. The maximum strain energy release rate criterion (G _max) is applied to each simulated random crack to find the crack strength. The strength of the simulated plate is equated to the strength of the weakest simulated crack in the plate based on the weakest link notion. The underlying crack number and crack length distributions are obtained by minimizing the difference between the simulated plate strengths and the known plate strengths. The gamma, lognormal and two-parameter Weibull distributions are employed for the underlying crack length distribution, and are compared in order to identify the best choice. Numerical examples demonstrate that the three PDFs are all acceptable for reasons to be explained. In the appendix, the direct problem in probabilistic fracture mechanics is presented as part of the demonstration of a method for using the crack distribution identified in the inverse problem to predict the strength and the probability of fracture in a practical application.     

Investigation on the polymer particle growth in ethylene polymerization with PS beads supported rac-Ph2Si(Ind)2ZrCl2 catalyst

The mechanism of polyethylene particle growth was investigated using poly(styrene-co-divinylbenzene) (PS beads) supported rac-Ph₂Si(Ind)₂ZrCl₂ catalyst. From the analysis of the resulting polyethylene particles by SEM (scanning electron microscopy) and EPMA (electron probe microanalysis), it was found that the active species are located on the surface layer of catalyst particles and that the catalytic species are uniformly distributed throughout the polymer particles, whereas the cores of PS beads, which lack a potential active species, were not disintegrated during polymerization. These results suggest that the PS beads supported catalyst also follows the fragmentation and replication process as frequently observed with the MgCl₂ supported Ziegler–Natta catalysts.     

Synthesis of polycarbonate‐silica nanocomposites from copolymerization of CO2 with allyl glycidyl ether,cyclohexene oxide,and sol‐gel

The copolymerization of carbon dioxide, allyl glycidyl ether, and cyclohexene oxide catalyzed by the system consisting of Y(CF₃CO₂)₃, Zn(Et)₂, and pyrogallol in the solvent of 1, 3‐dioxolane was performed in this study. The IR, ¹H NMR, and ¹³C‐NMR spectra, as well as the elemental analysis, indicated that the resulting copolymer was an alternating polycarbonate possessing more than 90% of carbonate units. The molecular weight could be as high as 1.5 × 10⁵, and the polydispersity index was 4.5. The resultant polycarbonate was found to effectively react with 3‐(trimethoxysilyl)propyl methacrylate via a free radical reaction to result in a precursor used in the sol‐gel process to synthesize a polycarbonate‐silica nanocomposite. The nanocomposites were characterized by SEM, ²⁹Si NMR, TGA, DSC, and UV–Vis. Silica particles with size less than 100 nm were found to disperse uniformly in the nanocomposites. It was also found that the thermal properties were dependent on the content of cyclohexene carbonate units. Both the thermal and mechanical properties of the resultant nanocomposites could be adjusted with silica content, while the transparency was comparable to the base copolymer even at high silica contents. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 750–757, 2005     

A novel hybrid silica wide-band amplifier covering S+C+L bands with 105-nm bandwidth

We report a novel hybrid optical amplifier covering S+C+L bands with 105-nm total bandwidth using a silica fiber. The principle of amplification is based on the stimulated radiative transition of Er-ions for C-band and on the stimulated Raman scattering for S- and L-band, respectively. In this letter, we analyze the amplification characteristics for two types of active fiber mediums through numerical simulation. One is a silica fiber configured with Er-doped cladding and Ge-doped core and the other is a medium consisting of Er-doped fiber and dispersion-compensating fiber. By optimizing parameters such as fiber length and pump power, we newly achieve wide-band amplification with 105-nm bandwidth showing a flat gain characteristic over the entire S+C+L bands.     

Automatic construction of online catalog topologies

A good online catalog is crucial to the success of an e-commerce web site. Traditionally, an online catalog is mainly built by hand. To what extent this can be automated is a challenging problem. Recently, there have been investigations on how to reorganize an existing online catalog based on some criteria, but none of them has addressed the problem of organizing an online catalog automatically from scratch. This paper attempts to tackle this problem. We model an online catalog organization as a decision tree structure and propose a metric, based on the popularity of products and the relative importance of product attribute values, to evaluate the quality of a catalog organization. The problem is then formulated as a decision tree construction problem. Although traditional decision tree algorithms, such as C4.5, can be used to generate online catalog organization, the catalog constructed is generally not good based on our metric. An efficient greedy algorithm (GENCAT) is thus developed, and the experimental results show that GENCAT produces better catalog organizations based on our metric.     

Analysis of TFCI coding performance of WCDMA systems

In WCDMA system, transport format combination indicator (TFCI) is encoded by an encoder based on Reed-Muller code and transmitted in a time-multiplexed fashion. When the number of TFCI information bits is less than the number of input bits to encoder, subset of basis sequences should be used. In this paper, we analyze the upper bound of word error rate (WER) of TFCI coding and find the optimal subset of basis sequences that minimize the bound. Since the bound of the WER is dependent on the channel correlation, the basis sequences to mitigate the effect of channel correlation are selected. From the result, a basis sequence with uniformly distributed bit of '1' is firstly chosen in optimal subset of basis sequences. The choice of basis sequences is more significant for high mobile speed.     

Negative charge induced degradation of PMOSFETs with BF/sub 2/-implanted p/sup +/-poly gate

A new degradation phenomenon on thin gate oxide PMOSFETs with BF/sub 2/ implanted p/sup +/-poly gate has been demonstrated and investigated. The cause of this type of degradation is a combination of the boron penetration through the gate oxide and charge trap generation due to the presence of fluorine in the gate oxide and some other processing-induced effects. The negative charge-induced degradation other than enhanced boron diffusion is studied in detail here. The impact of this process-sensitive p/sup +/-poly gate structure on deep submicron CMOS process integration has been discussed.<>     

Nucleation and growth of aluminium oxide on silicon in the CVD process

Films of aluminium oxide have been formed on single crystal silicon substrates using AlCl₃-CO₂-H₂ gas mixtures in a cold-walled chemical vapour deposition (CVD) reactor. The nucleation and subsequent growth of the deposit have been observed under the varying process parameters. It is found that the nucleation and growth of the Al₂O₃ are dependent on the H₂O flux and H₂O supersaturation. An activation energy of 34.8 Kcal mol^–1 is obtained for the growth rate indicating that the CVD of Al₂O₃ on silicon is a thermally activated process and limited by surface reaction. Scanning electron micrographs (SEM) show that the deposited films are amorphous at low temperature, 850° C, but change to fine grained polycrystalline structure at high temperature, 1000° C.     

Mesoporous assembly of 2D manganate nanosheets intercalated with cobalt ions

Mesoporous compound of cobalt-layered manganese oxide was synthesized by self-assembly reaction between 2D manganate nanosheets and cobalt ions. It was found that 2D manganate nanosheets are interstratified with cobalt ions, leading to the formation of porous intercalation heterostructure with expanded surface area of ∼ 44-100 m²/g. The mesopores with the average diameters of ∼ 11-17 nm originate from the house-of-cards type stacking of the layered manganate crystallites. Co K- and Mn K-edge X-ray absorption spectroscopy revealed that both the cobalt and manganese ions are stabilized in octahedral symmetry with the mixed oxidation states of Mn³⁺/Mn⁴⁺ and Co²⁺/Co³⁺. Considering high oxidation states of component metal ions, this porous material is expected to be very useful as redox catalysts and/or lithium intercalation electrodes.     

Dual-Mode Dual-Band Filter With Band Notch Structures

A novel approach for designing dual-mode dual-band bandpass filters is proposed and experimentally studied. By embedding a pair of slits in the square patch, the dual-band response is realized and one transmission zero is introduced between the two passbands. Two degenerate modes are achieved by loading with a small square perturbation, which can be placed at the diagonal line. There are three transmission zeros. The slits control the first and third transmission zeros. On the other hand, the right crossed slots control the first and the second transmission zeros.