Reliability of AllnAs/lnGaAs/lnP HEMT with WSi ohmic contacts

We have investigated the degradation mechanism of Al_0.48In_0.52As/In_0.53Ga_0.47As/ InP high electron mobility transistors (HEMTs) using WSi ohmic electrodes. Cross-sectional transmission electron microscopy (TEM) observation and en-ergy dispersive x-ray (EDX) analysis reveal impurities diffusion of gate electrode (titanium: Ti) and fluorine (F) in the AlInAs layer after a high temperature (T_a = 170°C operating life test for 500 h. The decrease of drain current (I_ds) during life test shows linear dependence on square root of aging time. It suggests that the degradation is controlled by a diffusion mechanism. Hence, the estimated degradation mechanism of this device is related with decrease of carrier concentration in the epitaxial layer by these diffused impurities. On the other hand, TEM and EDX show no degradation of WSi/InGaAs interface after aging. Therefore, the WSi electrode for this type of HEMT demonstrates excellent high stability under the accelerated operating life test.     

“Deactivation of copper electrode” in electrochemical reduction of CO2

Metallic Cu electrode can electrochemically reduce CO₂ to CH₄, C₂H₄ and alcohols with high yields as revealed by the present authors. Many workers reported that formation of CH₄ and C₂H₄ rapidly diminishes during electrolysis of CO₂ reduction. This paper shows that such deactivation of Cu electrode is reproduced with electrolyte solutions prepared from reagents used by these workers. Deactivated Cu electrodes recovered the electrocatalytic activity for CO₂ reduction by anodic polarization at −0.05 V versus she in agreement with the previous reports. Features of the deactivation depend greatly on the individual chemical reagents. Purification of the electrolyte solution by preelectrolysis with a Pt black electrode effectively prevents the deactivation of Cu electrode. Anode stripping voltammetry of Cu electrodes, which were deactivated during electrolysis of CO₂ reduction, showed anodic oxidation peaks at ca. −0.1 or −0.56 V versus she. The severer the deactivation of the Cu electrode was, the higher electric charge of the anodic peak was observed. It is presumed that some impurity heavy metal, originally contained in the electrolyte, is deposited on the Cu electrode during the CO₂ reduction, poisoning the electrocatalytic activity. On the basis of the potential of the anodic peaks, Fe²⁺ and Zn²⁺ are assumed to be the major contaminants, which cause the deactivation of the Cu electrode. Deliberate addition of Fe²⁺ or Zn²⁺ to the electrolyte solutions purified by preelectrolysis exactly reproduced the deactivation of a Cu electrode in CO₂ reduction. The amount of the deposited Fe or Zn on the electrode was below the monolayer coverage. Electrothermal atomic absorption spectrometry (etaas) showed that Fe originally contained in the electrolyte solution is effectively removed by the preelectrolysis of the solution. Mechanistic difference is discussed between Fe and Zn in the deterioration of the electrocatalytic property of Cu electrode in the CO₂ reduction. The concentration of the impurity substances originally contained in the chemical reagents as Fe or Zn is estimated to be far below the standard of the impurity levels guaranteed by the manufacturers. Presence of trimethylamine in the electrolyte solution also severely poisons a Cu electrode in the CO₂ reduction. It was concluded that the deactivation of Cu electrode in CO₂ reduction is not caused by adsorption of the products or the intermediates produced in CO₂ reduction.     

Intelligential industrial management

In this paper, we propose the intelligential industrial management which is the new concept in the industrial management. In the intelligential industrial management, the know-how and experience in the production process are divided into the fact, relation, and action in whit many criteria are used. The rule is constructed from the relation and action. And the inference process shows the sequence of the action and rule by using the inference symbol proposed.     

Purification and characterization of recombinant human granulocyte colony-stimulating factor (rhG-CSF) derivatives: KW-2228 and other derivatives

Various derivatives of recombinant human granulocyte colony-stimulating factor (rhG-CSF) have been overproduced in Escherichia coli with the strong, inducible trp promoter. A derivative designated as KW-2228 in which the amino acids were replaced at five positions showed more potent granulopoietic activity and stability than those of wild-type both in vitro and in vivo. The purification involved a sequential renaturation process and three-step chromatography. Refolding succeeded in very high yield using a urea system. The purity of KW-2228 was greater than 99% as measured by SDS-PAGE and HPLC analysis. According to circular dichroism and nuclear magnetic resonance spectroscopy, rhG-CSF and KW-2228 have very similar conformations. This suggests that the substitution of five amino acids does not appreciably change the conformation of hG-CSF. KW-2228 ([Ala1, Thr3, Tyr4, Arg5, and Ser17]-hG-CSF) and derivative A ([Ala1, Thr3, Tyr4, Arg5]-hG-CSF) are easily crystallized and they show similar in vitro activity. On the other hand, neither rhG-CSF nor derivative B ([Ser17]-hG-CSF) are crystallized under the same conditions. Thus, the four amino acid substitution (Ala1, Thr3, Tyr4, Arg5) of the N-terminal sequence may facilitate crystallization. The change of Cys17 to Ser may not influence the stability and activity of hG-CSF.     

FDG uptake, GLUT-1 glucose transporter and cellularity in human pancreatic tumors

We previously reported that grading of GLUT-1 glucose transporter expression was related closely to FDG accumulation in FDG PET in human cancers. But in this strong GLUT-1 expression group, there was an enormous range of standardized uptake values (SUVs) within them. METHODS: To evaluate other factors determining the FDG PET uptake, FDG PET was performed in 36 preoperative patients (mean age 62.0 yr) suspected of having pancreatic tumors, including 33 malignant and 3 benign neoplastic tumors. FDG uptake at 50 min after injection of 185 MBq 18F-FDG with > 5 hr fasting condition was semiquantitatively analyzed as SUVs. The GLUT-1 expression was studied by immunohistochemistry of paraffin sections from these tumors after the operation using the antiGLUT-1 antibody. The number of tumor cells within a 5- x 5-mm square was counted manually using x200 magnification photographs and was graded immunohistochemically as strong, weak or negative. RESULTS: In all 36 cases there were 3 cases of GLUT-1 negative, 8 of GLUT-1 weak positive and 25 of GLUT-1 strong positive. In all cases, the total number of tumor cells had no significant value for SUVs. Among 33 GLUT-1 positive cases, the number of GLUT-1 positive tumor cells correlated significantly with SUVs (p < 0.01). Only in 25 strong grade cases, the number of GLUT-1 strong positive tumor cells had a more significant value for SUVs (p < 0.005). Computational multivariate analysis using multiple regression for SUVs was performed evaluating the five variables as follows: tumor size, GLUT-1 immunohistochemical grading, number of total tumor cells, number of total GLUT-1 positive tumor cells and number of GLUT-1 strong positive cells. This analysis revealed that only the variable, the number of GLUT-1 strong positive cells, had a significant regression coefficient for SUVs (standard regression coefficient = 0.855, p < 0.0001). CONCLUSION: These data indicate that GLUT-1 expression plays an essential role in higher FDG accumulation in pancreatic tumor FDG PET, and the cellularity has a significant influence on SUVs only in the condition of GLUT-1 strong positive expression.