Reactor design considerations for MOCVD growth of thin films

Metal-organic chemical vapor deposition (MOCVD) performance is optimized for growing titanium dioxide (TiO₂) thin films. Different gas flow directions and susceptor rotation, along with reactor geometry and shape variations are considered. Gravity proves to be an important parameter in changing the flow pattern in the reaction chamber. However, since film uniformity is not improved by changing the flow direction, modifying the reactor geometry is also proposed. Among the different geometrical parameters, the susceptor-inlet distance, inlet tube diameter, and susceptor size are considered. To minimize the occurrence of recirculation cells in the reaction chamber, modifications in the reactor shape are also suggested. Acceptable results are achieved by changing the cylindrical reactor to a diamond shape     

Allelopathic Effects of Volatile Monoterpenoids Produced by <Emphasis Type="Italic">Salvia leucophylla</Emphasis>: Inhibition of Cell Proliferation and DNA Synthesis in the Root Apical Meristem of <Emphasis Type="Italic">Brassica campestris</Emphasis> Seedlings

Salvia leucophylla, a shrub observed in coastal south California, produces several volatile monoterpenoids (camphor, 1,8-cineole, -pinene, -pinene, and camphene) that potentially act as allelochemicals. The effects of these were examined using Brassica campestris as the test plant. Camphor, 1,8-cineole, and -pinene inhibited germination of B. campestris seeds at high concentrations, whereas -pinene and camphene did not. Root growth was inhibited by all five monoterpenoids in a dose-dependent manner, but hypocotyl growth was largely unaffected. The monoterpenoids did not alter the sizes of matured cells in either hypocotyls or roots, indicating that cell expansion is relatively insensitive to these compounds. They did not decrease the mitotic index in the shoot apical region, but specifically lowered mitotic index in the root apical meristem. Moreover, morphological and biochemical analyses on the incorporation of 5-bromo-2-deoxyuridine into DNA demonstrated that the monoterpenoids inhibit both cell-nuclear and organelle DNA synthesis in the root apical meristem. These results suggest that the monoterpenoids produced by S. leucophylla could interfere with the growth of other plants in its vicinity through inhibition of cell proliferation in the root apical meristem.     

Wave propagation in functionally graded nanocomposites reinforced with carbon nanotubes based on second-order shear deformation theory

In the present article, as a first endeavor, the wave propagation in functionally graded nanocomposites reinforced with carbon nanotubes is investigated on the basis of second-order shear deformation theory. Four different types of functionally graded nanocomposites are presented. An analytical method is used to find the circular frequencies and phase velocities. To show the accuracy of the present methodology, our results for the free vibration are compared with the results of functionally graded plates available in the literature. The influences of different parameters are also investigated on the circular frequencies and phase velocities.     

A new MLPG method for elastostatic problems

This paper introduces a novel meshless local Petrov-Galerkin (MLPG) method by presenting a new test function as a schema to solve the elasto-static problems. It is seen that the four ordinary MLPG methods can also be approached using the present test function. Both the moving least square (MLS) and the direct method have been applied to the method to estimate the shape function and to impose the essential boundary conditions. The results of three studied elasto-static cases; “two dimensional cantilever beam”, “first mode fracture of a center-cracked strip” and “edge-cracked functionally graded strip” show that by using less number of nodes, the present work gives sufficiently more accurate results. Meanwhile the method can also unify various kinds of MPLGs and one may conclude that the model is a good replacement for other common approaches.     

Simple evaluation of aortic arch calcification by chest radiography in hemodialysis patients

Vascular calcification is associated with a poor prognosis in dialysis patients. It can be assessed with computed tomography but simple inoffice techniques may provide useful information. We compared the results obtained with a simple noninvasive technique with those obtained using multidetector computed tomography for aortic arch calcification volume (AoACV) in chronic hemodialysis (HD) patients. The enrolled study subjects were 63 (32 men and 31 women) maintenance HD patients. Calcification of the aortic arch was semiquantitatively estimated with a AoAC score (AoACS) on plain chest radiology. The AoACV was increased, with a mean value of 6.6 ranging from 0% to 36.5%. The coefficient of intraobserver variation was less than 2.5%. Aortic arch calcification score was highly correlated with AoACV (r=0.635, P<0.001). Multiple regression analysis showed age (F value=12.62, P<0.001) and pulse pressure (F value=4.54, P=0.037) to be significant independent determinants of AoACS. In conclusion, a simple measurement of AoACS may be useful for inoffice imaging to choose a therapeutic regimen in HD patients.     

CR-39 acceptance test and optimisation for fast neutron dosimetry applications

The ENEA fast neutron dosemeter is based on a planar PADC (poly allyl diglycol carbonate) placed in a polyethylene holder. The CR-39 (registered trademark of PPG Industries Inc.) material, produced by Intercast Europe S.p.A., has been used in the routine of the Individual Monitoring Service (IMS) since 1998. Since then, acceptance tests on average sheet background track density and sheet neutron sensitivity have been made on new batches as a quality control within a quality assurance programme of the IMS of ENEA-Institute for Radiation Protection (IRP). Dosemeters were irradiated with a 241Am-Be source at ENEA-IRP and processed through a chemical etching procedure (pre-etching with 40% KOH water solution 6.25 N and 60% ethyl alcohol at 70 degrees C followed by 12 h of etching in 6.25 N KOH water solution). In this paper we present the analysis of acceptance testing data for more than 30 sheets of CR-39 plastic produced in 1998, 1999 and 2000. Moreover, we compare the performance of sheets of CR-39 of standard composition with that of sheets of CR-39 with the addition of DOP (dioctylphthalate), in different concentrations, on the hasis of average background density, neutron sensitivity and background fluctuation that limit the lower detectable dose. This study demonstrates the need for acceptance tests to assure the quality of the dosimetric performance of these dosemeters, which is considerably dependent on the quality of the CR-39 plastic.     

Production of vitamin B12 in genetically engineered Propionibacterium freudenreichii

Since the chemical synthesis of vitamin B12 requires more than 70 steps, the production of vitamin B12 has been achieved by microorganism fermentation with additional brief chemical modifications. In an effort to increase the productivity of vitamin B12, we tried to express 10 genes belonging to the hem, cob and cbi gene families involved in the synthesis of vitamin B12 in Propionibacterium freudenreichii, which is a known producer of vitamin B12. In a recombinant P. freudenreichii clone that harbored the expression vector containing a cobA, cbiLF, or cbiEGH, we obtained an increase in vitamin B12 production of 1.7-, 1.9-, and 1.5-fold higher, respectively, than that in the microorganism without any cloned genes in the expression vector pPK705. The cobU and cobS genes caused a slight increase in the production of vitamin B12. Furthermore, we achieved multigene expression in P. freudenreichii. In a recombinant P. freudenreichii clone that harbored an exogenous gene, hemA, from Rhodobacter sphaeroides and endogenous hemB and cobA genes, we successfully achieved the production of about 1.7 mg/l vitamin B12, 2.2-fold higher than that produced by P. freudenreichii harboring pPK705.     

Structural studies of enzyme-based microfluidic biofuel cells

An enzyme-based glucose/O₂ biofuel cell was constructed within a microfluidic channel to study the influence of electrode configuration and fluidic channel height on cell performance. The cell was composed of a bilirubin oxidase (BOD)-adsorbed O₂ cathode and a glucose anode prepared by co-immobilization of glucose dehydrogenase (GDH), diaphorase (Dp) and VK₃-pendant poly-l-lysine. The consumption of O₂ at the upstream cathode protected the downstream anode from interfering O₂ molecules, and consequently improved the cell performance (maximum cell current) ca. 10% for the present cell. The cell performance was also affected by the channel height. The output current and power of a 0.1 mm-height cell was significantly less than those of a 1 mm-height cell because of the depletion of O₂, as determined by the shape of the E–I curve at the cathode. On the other hand, the volume density of current and power was several times higher for the narrower cell.