Experimental evaluation of a spherical aberration-corrected TEM and STEM

We have successfully developed a spherical aberration (Cs)-corrected electron microscope for probe- and image-forming systems using hexapole correctors. The performance of the microscope has been evaluated experimentally. The point resolution attained using the image-forming Cs-corrector is better than 0.12 nm. For scanning transmission electron microscopy, the Ronchigram flat area was >40 mrad in half-angle using the probe-forming Cs-corrector.     

Self-assembly of concentric quantum double rings

We demonstrate the self-assembled formation of concentric quantum double rings with high uniformity and excellent rotational symmetry using the droplet epitaxy technique. Varying the growth process conditions can control each ring's size. Photoluminescence spectra emitted from an individual quantum ring complex show peculiar quantized levels that are specified by the carriers' orbital trajectories.     

Removal of B from Si by solidification refining with Si-Al melts

To discuss the removal of B by solidification refining of Si with a Si-Al melt, the segregation of B between solid Si and the Si-Al melt was investigated by use of the temperature-gradient-zone melting (TGZM) method. The segregation ratio of B at its infinite dilution was determined to be 0.49 (1473 K), 0.32 (1373 K), and 0.22 (1273 K), respectively. With the obtained segregation ratio, the activity coefficient of B in solid Si at its infinite dilution relative to pure solid B was determined by the following equation:

Effect of sulfur sources on specific desulfurization activity of Rhodococcus erythropolis KA2-5-1 in exponential fed-batch culture

The effects of sulfur sources on the desulfurization activity of Rhodococcus erythropolis KA2-5-1 were investigated by using an exponential fed-batch culture technique. The feed rate of a sulfur source was controlled independently of the feed rate of ethanol, which was used as a carbon and energy source. Among the sulfur sources examined were dibenzothiophene (DBT), ammonium sulfate, L-cysteine, L-methionine, and 2-amino-ethanesulfonic acid. When the fed-medium contained DBT as the sole sulfur source, KA2-5-1 cells showed a maximum desulfurization activity of approximately 130 mmol 2-HBP kg-cell(-1) h(-1). Similar levels of enzyme activity were also achieved with inexpensive ammonium sulfate by using the exponential fed-batch culture technique. In addition, higher levels of desulfurization activity were achieved by increasing the dosage of the DBT desulfurization (dsz) operon and dszD gene in R. erythropolis KA2-5-1. The recombinant strain showed a maximum desulfurization activity of approximately 250 mmol 2-HBP kg-cell(-1) h(-1) in the exponential fed-batch cultures.     

Effect of water vapor on proton conduction of cesium dihydrogen phosphateand application to intermediate temperature fuel cells

The proton conduction and superionic phase transition of cesium dihydrogen phosphate, CsH₂PO₄ (CDP), were investigated under various humid conditions to evaluate the applicability of a CsH₂PO₄ solid electrolyte to an intermediate temperature fuel cell operating between 230 °C and 300 °C. The phase stability, superionic phase transition, and reversibility of dehydration of CsH₂PO₄ were evaluated under different ambient water vapor concentrations, from 0 to 90 mol%, through the measurements of conductivity. The dependence of conductivity on the water vapor concentration and the demonstrated reversibility of dehydration clearly showed the range in which CsH₂PO₄ is applicable to the intermediate temperature fuel cell. Additionally, we evaluated the protonic transport number of CsH₂PO₄, which was almost unity, and demonstrated fuel cell operation at 250 °C using a single cell fabricated with the CsH₂PO₄ electrolyte.     

Long-term monitoring of post-fire aboveground biomass recovery in a lowland dipterocarp forest in East Kalimantan,Indonesia

Between 1988 and 2000, changes in the above-ground biomass (AGB) of trees in an East Kalimantan lowland forest, damaged by fires in 1982–83 and 1998, were estimated using allometric functions and an annual inventory of stem diameter. The original vegetation of the study site was lowland dipterocarp forest which has since been affected by selective logging and wild fires. The 1982–83 fire killed large trees of primary species and the opened sites became dominated by a few pioneer species. Between 1988 and 1997, a few pioneer tree species, namely Macaranga spp., dominated a heavily disturbed stand (HDS). Primary tree species that survived the 1982–83 fire dominated a lightly disturbed stand (LDS). A moderately disturbed stand (MDS) contained vegetation intermediate between the HDS and the LDS. In 1997, there were 553, 499 and 356 trees ha-1 in the HDS, MDS and LDS, respectively. Macaranga trees accounted for 70, 40 and 11 of the total number of trees in the HDS, MDS, and LDS, respectively. In 1997, the AGB of trees in the HDS, MDS, and LDS was 117, 280, and 315 Mg ha-1, respectively. The proportion of biomass accounted for by Macaranga trees for the HDS, MDS, and LDS was 34, 8 and 1, respectively. The pioneer trees did not compensate for the loss of aboveground biomass resulting from the death of large primary trees. The fire in 1998 again decreased AGB of the stands. In 2000, the AGB of trees in the HDS, MDS, and LDS was 27, 106, and 219 Mg ha-1, respectively. The sites opened up by the 1998 fire were covered with the pioneer seedlings and seemingly dominated by the pioneer trees with a larger number of stems per ha, but lower biomass as compared to the original forest (> 400 Mg ha-1).     

Metabolic engineering study on the direct fermentation of 2-keto-L-gulonic acid, a key intermediate of L-ascorbic acid in Pseudomonas putida IFO3738

We have achieved production of 2-keto-L-gulonic acid (2-KLGA) in recombinant Pseudomonas putida IFO3738. Firstly, the genes for sorbose dehydrogenase (SDH)/sorbosone dehydrogenase (SNDH) were introduced into P. putida. The recombinant P. putida/pBBR-SDH produced 0.7 mg/ml of 2-KLGA in a culture broth containing 5% L-sorbose. Replacement of the native SNDH promoter by the Escherichia coli tufB promoter (pBBR-SDH-tufB) improved the productivity of 2-KLGA up to 11.4 mg/ml. Secondly, the sorbitol dehydrogenase (SLDH) gene was also introduced into P. putida. The recombinant P. putida/pUCP19-3DH carrying the genes for SDH, SNDH and SLDH had the ability to produce 2-KLGA (7.5 mg/ml) in a 5% d-sorbitol broth. The productivity of 2-KLGA was improved up to 9.8 mg/ml by changing to an expression system with two plasmids, pBBR-SDH-tufB (for SDH/SNDH) and pUCP19-SLDH (for SLDH), respectively. Moreover, the replacement of the native SLDH promoter by the E. coli tufB promoter (pUCP19-SLDH-tufB) improved the 2-KLGA productivity up to 11.6 mg/ml. Optimization of cultivation conditions increased the conversion yield of 2-KLGA to 32% and that of l-idonate, a metabolite of 2-KLGA, to 40%. These results indicate P. putida IFO3738 is one of the candidate strains for direct fermentation of 2-KLGA.     

Preparation of Inorganic Consolidated Body Using Aluminium Hydroxide Mechanically Activated by Dry Milling

Aluminium hydroxide (Al(OH)₃) was mechanically activated by dry milling. In order to develop an inorganic consolidated material, the structure and reactivity of milled Al(OH)₃ were investigated and consolidated bodies were prepared using the reaction between activated Al(OH)₃ and a potassium silicate solution. Milling up to 1 h apparently reduced the grain size and promoted amorphization, although milling longer than 2 h did not give a significant physical change. Milled Al(OH)₃ directly transformed to -Al₂O₃ around 270°C. The transformation temperature decreased with increasing milling time. The remarkable enhancement of the reactivity was attained. The reactivity of Al(OH)₃ milled for 2 h improved 1000 times more than that of as-received Al(OH)₃. The preforming paste, prepared with as-received Al(OH)₃, could not consolidate at room temperature without drying. On the other hand, for Al(OH)₃ milled for 2 h, the preforming paste consolidated in 10 min and the consolidated material showed much better resistance against water than that prepared with as-received Al(OH)₃. The possibility of a new inorganic consolidated material was suggested using the reaction between mechanically activated Al(OH)₃ and the potassium silicate solution.     

Formation and characterization of self-organized CdSe quantum dots

We have investigated the formation and characteristic of self-organized CdSe quantum dots (QDs) on ZnSe(001) surfaces with the use of photoluminescence (PL) and transmission electron microscopy (TEM). Coherent CdSe QDs are naturally formed on ZnSe surfaces, when the thickness of CdSe layers is around 2 ML. The plan-view TEM images exhibit that CdSe QDs have a relatively narrow distribution of QD size, and that the density of CdSe QDs is about 10¹⁰ cm⁻². The base structure of the CdSe dot is rhombic, which has the long axis of about 20 nm in length along direction. The temperature dependence of macro-PL spectra reveals that the behavior of self-organized CdSe QDs is quite different from that of ZnCdSe quantum well (QW), resulting from characteristic features of zero-dimensional structures of QDs. Moreover, the macro-PL results suggest the existence of QW-like continuous state lying over QD states. Micro-PL measurements show several numbers of high-resolved sharp lines from individual CdSe QDs. The linewidth broadening with temperature depends on peak energy position of the QDs. The linewidths of lower energy lines, corresponding to larger size QDs, are more temperature dependent.     

Positologica: A Positron ECT Device with a Continuously Rotating Detector Ring

A rotary positron emission computed tomography device is developed for human brain and animal studies. The device utilizes 64 rectangular BGO detectors arranged at unequal spacing on a circular ring. The detector ring is continuously rotated at a constant speed of 60 rpm or less. This single continuous motion of the ring with the detector array provides excellent sampling characteristics and high detector redundancy. The device has a field of view 24 cm in diameter with a slice thickness adjustable from 1 cm to 2 cm. Measured width of system response to a 2 mm diameter line source is 5.8 mm FWHM at the center and less than 9 mm FWHM within a circle 16 cm in diameter. Measured sensitivity including scattered coincidence events is about 17 kcps/pCi/ml for a 20 cm diameter water phantom and 2 cm thick slice.