Calculation of Grain-Boundary Bonding in Rare-Earth-Doped β-Si3N4

First-principles molecular orbital calculations are performed by the discrete variational Xalpha method using model clusters of rare-earth-doped β-Si₃N₄ and the interface between prismatic planes of β-Si₃N₄ and intergranular glassy films. On the basis of the total overlap population of each cluster, the rare-earth ions are implied to be stable in the grain-boundary model, while they are not stable in the bulk model. These results are consistent with experimental observations showing significant segregation of Ln³⁺ ions at the grain boundary and no solubility of Ln³⁺ into bulk β-Si₃N₄. Grain-boundary bonding is weakened with an increase of the ionic radius of the rare-earth ions, which provides a reasonable explanation for the ionic size dependence of the crack propagation behaviors as well as the growth rate of the prismatic plane in the rare-earth-doped β-Si₃N₄ during liquid-phase sintering.     

Trial of new intraocular lens power calculation following phototherapeutic keratectomy]

Thirty-one men (age range, 46-76 years; mean age, 64.8 years) with intrathoracic masses suggesting possible malignancy on the basis of chest radiography or CT underwent preoperative Tc-99m MIBI SPECT examinations. Diagnosis was confirmed on pathologic examinations of samples obtained either at thoracotomy, esophagectomy, or by biopsy. Twenty-five patients had primary lung cancer, including squamous cell carcinoma, large cell carcinoma, adenocarcinoma, and small cell carcinoma. Two patients had lymphomas with spread to the mediastinum, and three patients had extrathoracic primary cancers (one squamous cell carcinoma of esophagus, one squamous cell carcinoma originating from a head and neck tumor, and one metastatic mediastinal leiomyosarcoma). One patient with a tuberculoma had negative results of the Tc-99m MIBI examination. Tc-99m MIBI had a 86.7% sensitivity rate, a 0% false-positive rate, and a 100% positive predictive value to detect malignant intrathoracic masses. There was a 13% false-negative rate, however, suggesting that MIBI-SPECT may underdiagnose malignant lesions. SPECT findings of these 31 patients can be classified as 1) mass with increased uptake, n = 23; 2) ring-like appearance of increased uptake, n = 3; 3) mass with absent uptake, n = 4; and 4) photon-deficient mass, n = 1. Absent uptake in patients with mass lesions could be explained by necrosis of the lesion (caseation necrosis or massive tumor necrosis with or without bleeding). Most malignant intrathoracic masses are Tc-99m MIBI avid and may be detected with a high degree of sensitivity and with an excellent positive predictive value. A positive MIBI scan may help in the clinical diagnosis of malignancy. The use of Tc-99m MIBI could serve not only as a tumor imaging agent, but also may be used to determine the extent of spread and potentially the chemotherapeutic responsiveness of a tumor.     

Characterization of the PP2A alpha gene mutation in okadaic acid-resistant variants of CHO-K1 cells

Okadaic acid (OA)-resistant variants of Chinese hamster ovary cells, clones CHO/OAR6-6 and CHO/OAR2-3, were isolated from a CHO-K1 culture. These variant cells were 17- to 26-fold more resistant to OA than the parental cells. The phosphorylase phosphatase activity of the variant cell extracts was 2- to 4-fold more resistant to OA than that of the parental cells in the presence of inhibitor 2, a specific inhibitor of type 1 protein serine/threonine phosphatase (PP1). Nucleotide sequencing of PP2A alpha (an isotype of PP2A catalytic subunit) cDNA demonstrated that both variants have a T-->G transversion at the first base of codon 269 (805 nt), which results in substitution of glycine for cysteine. We expressed in COS-1 cells a mutant PP2A alpha tagged with the influenza hemagglutinin epitope. The recombinant mutant PP2A alpha protein immunoprecipitated with an anti-influenza hemagglutinin antibody was more resistant than the wild type to OA, their IC50 values being 0.65 nM and 0.15 nM, and their IC80 values being 4.0 nM and 0.45 nM, respectively. The cysteine at residue 269 present only in highly OA-sensitive protein serine/threonine phosphatase catalytic subunit isozymes, PP2A alpha, PP2A beta, and PPX, is suggested to be involved in the binding of OA. CHO/OAR6-6 and CHO/OAR2-3 cells also overexpressed the P-glycoprotein, and the efflux of OA was more rapid. It is suggested that the PP2A alpha mutation in cooperation with a high level of P-glycoprotein makes the CHO-K1 variants highly resistant to OA.     

An emergency aircraft evacuation simulation considering passenger emotions

The evacuation behavior of passengers was formulated as an autonomous agent and multi-agent model (AAMAS) evolving over a two-dimensional grid cell that represents aircraft cabins and passengers. In this model, the autonomous agents are initially placed in seat squares and move toward an emergency exit after an aircraft accident occurs. The autonomous agent mimics the behavior of passengers in the cabin, who must not only view their surroundings to collect the useful information but also select a route to an emergency exit. As the situation evolves, the agents feel the mental stress or strong fear or anxiety; thereby reacting unfavorably in the situation that they panic at. This abnormal evacuation behavior of panic agents generates time delays in the evacuation flow towards the exits. Therefore, such panic and its effect on evacuation behavior should be considered as an important factor in evacuation simulations. In this paper, it is supposed that the level of panic depends on three factors: remaining time, frequency of waiting and the difficulty of finding an exit. The dependencies of these factors on the time needed to complete an evacuation and the number of the panic agents in the aircraft were determined by the simulation. Considering the simulation results and situations of the actual aircraft accident “Garuda Indonesia Airways Accident”, it was possible to develop aircraft evacuation scenarios that considered passenger emotions.     

Reliability design of structural system with cost effectiveness during life cycle

This study deals with an economic analysis of structural systems using a reliability-based design method. In this paper, a new expected total cost concept, which includes initial cost, cost of reliability test, annual maintenance cost, penalty cost for designer's faults and losses by structural failure is proposed. In the proposed formulation, the minimum expected total cost during the life duration with the capital rate of interest and rate of price fluctuations could be evaluated by calculating the present currency and annual prediction procedure.     

Electronic Structures of Ln3+α-SiAIONs with Correlations to Solubility and Solution Effects

First-principles molecular-orbital calculations using the discrete-variational Xα method have been made on model clusters of α-Si₃N₄ and its solid solutions with lanthanide elements, which occupy interstitial sites in the structure. The formula is Ln_χSi_12–4.5χAl_4.5χO_1.5χN16–1.5χ (Ln = La, Nd, Gd, Dy, Ho, Er, Tm, Yb), i.e., a Ln-α-SiAION solid solution. Covalent bond strength between Si and N, evaluated by overlap population, increases because of the presence of trivalent charges at the interstitial sites. When a Ln³⁺ ion is present, antibondings occur between Ln orbitals and N/Si orbitals, and they depend significantly on the ionic radius of Ln³⁺. The total overlap population for the whole cluster is determined by the balance of Si-N bond reinforcement and Ln-N/Si antibonding. Although no lattice relaxation around the Ln³⁺ ion is included in the present calculation, good correlation between maximum solubility and the total overlap population for the whole cluster is demonstrated for the first time.