SOME PROPERTIES OF THE MAXIMUM LIKELIHOOD ESTIMATOR IN THE SIMULTANEOUS SWITCHING AUTOREGRESSIVE MODEL

Abstract. The simultaneous switching autoregressive (SSAR) model proposed by Kunitomo and Sato (A non-linearity in economic time series and disequilibrium econometric models. In Theory and Application of Mathematical Statistics (ed. A. Takemura). Tokyo:University of Tokyo Press (in Japanese), 1994; Asymmetry in economic time series and simultaneous switching autoregressive model. Struct. Change Econ. Dyn. , forthcoming (1994).) is a Markovian non-linear time series model. We investigate the finite sample as well as the asymptotic properties of the least squares estimator and the maximum likelihood (ML) estimator. Due to a specific simultaneity involved in the SSAR model, the least squares estimator is badly biased. However, the ML estimator under the assumption of Gaussian disturbances gives reasonable estimates.     

Resistance to sulfur poisoning of hot gas cleaning catalysts for the removal of tar from the pyrolysis of cedar wood

In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H₂S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO₂/SiO₂ using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H₂S. Steam reforming Ni catalyst was effective for the tar removal without H₂S addition, however, the addition of H₂S deactivated drastically. In contrast, Rh/CeO₂/SiO₂ exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H₂S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO₂/SiO₂, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis.     

Cardiac hemangioma of the right ventricle--report of a case

OBJECTIVE: The prevalence of obesity and thinness is unknown among Iranian high-school age girls. We determined the prevalence of overweight and underweight among Iranian high-school girls from Kerman (south-east province of Iran). DESIGN: A cross-sectional study of indicative cluster sample. MEASUREMENTS: Weight, height, body mass index (BMI), chest, waist, abdomen, hip and thigh circumference of 1000 Iranian high-school girls aged 14-21 y (mean (standard deviation, s.d.) 16.2 (1.3)) were measured. The criteria for very underweight, underweight, desirable weight, grade 1, 2 and 3 overweight used in the present study were: BMI in kg/m2 < 15, 15-19.9, 20-24.9, 25-29.9, 30-39.9 and > or = 40, respectively. RESULTS: 4.6% (95% confidence interval (CI): 3.4%-6.1%) were grade 1 overweight (BMI = 25.0-29.9), 0.7% (95% CI: 0.3%-1.4%) were grade 2 overweight (BMI = 30-39.9), and none were grade 3 overweight (BMI > or = 40), while 54.6% (95% CI: 51.5%-57.7%) were underweight (BMI = 15-19.9) and 1.6% (95% CI: 0.9%-2.6%) were very underweight (BMI < 15). The mean (s.d.) BMI was 19.8 (2.9) (95% CI: 19.6-20.0). The mean (s.d.) waist-to-hip ratio (WHR), abdomen-to-hip ratio and chest-to-hip ratio values were 0.8 (0.06) (95% CI: 0.8-0.81), 0.8 (0.07) (95% CI: 0.8-0.81) and 0.9 (0.07) (95% CI: 0.9-0.91), respectively, in this sample. CONCLUSION: The results suggest a low prevalence of overweight among Iranian young women.     

Arterial-venous carbon dioxide tension difference after hypothermic cardiopulmonary bypass

Arterial-venous carbon dioxide tension difference (Pv-aCO2) is known to become high after severe hemorrhage shock and resuscitation. We hypothesized that Pv-aCO2 might be high after cardiac surgery because of the oxygen debt occurred during hypothermic cardiopulmonary bypass (CPB). Blood pressure, cardiac index, hemoglobin, the arterial and mixed venous blood gases were repeatedly measured every 6 hours for 24 hours following cardiac surgery in 60 adult patients who underwent hypothermic CPB. Immediately after the surgery, Pv-aCO2 was extremely high, then gradually decreased to within normal ranges 12 hours later (8.0 +/- 2.9 mmHg vs 5.9 +/- 3.1 mmHg. p < 0.01). Factors which significantly correlated to Pv-aCO2 were cardiac index, oxygen delivery, minimum rectal temperature and duration of CPB. Oxygen debt during hypothermic CPB might cause significantly high Pv-aDO2. At least 12 hours were necessary to recover from anaerobic status to physiological condition.     

Effect of 8-sulfophenyl theophylline on endogenous noradrenaline release from sympathetic nerves of the rabbit ear artery

1. The release of endogenous noradrenaline (NA) and adenyl purine (ATP, ADP, AMP and adenosine) from the rabbit ear artery, evoked by electrical stimulation (ES; 16 Hz), was examined. 2. ES evoked a significant release of NA and purine; the ratio of the amount of total purine released to NA released was approximately 180 on a molar base. 3. ES-evoked purine release was significantly reduced by the denudation of the endothelium and abolished by the alpha 1-adrenoceptor antagonist, prazosin (1 mumol/L). 4. ES-evoked NA release was significantly reduced by a P1-purinoceptor antagonist, 8-sulfophenyl theophylline (8SPT). Purine release was slightly reduced by 8SPT. 5. These results suggest that endogenous NA released by ES results in the release of a large amount of purine, which may, in turn, increase the release of NA by acting on prejunctional purinoceptors on sympathetic nerve terminals.     

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 4. Preparation parameters and impact index

The effects of the volume and pH of the impregnation solution and of the calcination conditions were examined on the physicochemical and catalytic properties of a 13 wt% MoO₃/Al₂O₃ extrudate catalyst. The Al₂O₃ support and drying procedures (static conditions without flowing air) were fixed in the preparations. In the present series of catalysts, the amount of crystalline MoO₃ was marginally small. It was found that the dispersion of Mo oxide species increased as the volume of the impregnation solution increased, gradually approaching a maximum value. The increase in pH (2–8) of the impregnation solution was found to reduce the dispersion of Mo oxide species. The Mo dispersion increased slightly for the impregnation catalysts as the calcination temperature increased (673–873 K), whereas it decreased for the equilibrium adsorption catalysts. The effects of the calcination atmosphere (with or without flowing air, or with flowing humid air) were very small on the dispersion of Mo oxide species under the present preparation conditions. On the other hand, the methanol oxidation activity of MoO₃/Al₂O₃ was sensitive to the preparation parameters examined here. It was demonstrated by means of EPMA and XPS that a considerable migration of Mo took place during the calcination.

In the present study on the preparation of a 13 wt% MoO₃/Al₂O₃ catalyst, an impact index is proposed to measure the magnitude of the effects of the respective parameter(s) on the physicochemical and catalytic properties. With the Mo dispersion, the effects of the preparation parameter decreased in the order, surface area of the support >> drying process > volume of the impregnation solution > pH, calcination temperature and atmosphere. The size of the impact index for the dispersion of Mo sulfide species is 70–75% of that for the Mo oxide species. The HDS activity of the catalyst was less affected by the preparation parameters than the Mo sulfide dispersion. The preparation parameters affected the segregation of Mo on the outer surface of extrudates in a decreasing order: drying process > volume of the impregnation solution > pH, calcination conditions. It was found that the oxidation of methanol was affected most intensely by the drying procedures. The volume of the impregnation solution, calcination conditions and pH of the impregnation solution also strongly affected the oxidation activity. The impact index suggests that the sensitivity to the preparation variables of the physicochemical and catalytic properties of MoO₃/Al₂O₃ decreases in the order, methanol oxidation activity > surface Mo segregation > Mo oxide dispersion > Mo sulfide dispersion > HDS activity.     

Analysis of c-Ki-ras oncogene and p53 immunocytochemistry in the gallbladder mucosa of an experimental dog model of anomalous arrangement of the pancreaticobiliary ducts

Anomalous arrangement of the pancreaticobiliary ducts is a congenital condition which predisposes the affected person to biliary tract carcinoma. We developed an experimental dog model of anomalous arrangement of the pancreaticobiliary ducts to investigate the mechanism of carcinogenesis in this condition. We used this model to analyze point mutations in the c-Ki-ras gene, and to assess the expression of mutant p53 protein in the gallbladder mucosa. The histopathological appearance of the gallbladder mucosa was also examined. Glandular structures were seen in four of seven (57%) gallbladders examined 14 months after the surgical creation of an anastomosis between the gallbladder and the pancreatic duct. Goblet cells were seen in two of seven gallbladders (29%). However, dot-blot hybridization and immunohistochemical study did not reveal any mutations in the c-Ki-ras gene, or any over-expression of the p53 protein in the specimens. These results show that the gallbladder mucosa is damaged by refluxing pancreatic juice in this dog model of anomalous arrangement of the pancreaticobiliary ducts, but that severe damage may be necessary to induce mutations in the c-Ki-ras proto-oncogene, or in the p53 gene.     

Adhesive monomers to dental ceramics. I. Evaluation of N-substituted 3-amino-2-hydroxypropyl methacrylates as adhesives for calcium metaphosphate crystalline glass-ceramic

N-Substituted 3-amino-2-hydroxypropyl methacrylates have been evaluated as adhesives for calcium metaphosphate crystalline glass-ceramic, a potential esthetic dental restoration material. Although the adhesion to the ceramic was found to be much more difficult and dependent on the kinds of substituents than that of tooth enamel, monomers having a carboxyl group showed specifically high adhesive tensile strength. The strength tended to decrease as the hydrophobicity and molecular bulkiness increased. Surface treatment of the ceramic, especially with sodium hydroxide, proved effective in terms of both strength and durability for the carboxyl-containing monomers. Scanning electron microscopy analysis confirmed the importance of surface irregularity due to the alkaline treatment.