Neutronic analysis of a high power density hybrid reactor using innovative coolants

In this study, neutronic investigation of a deuterium-tritium (DT) driven hybrid reactor using ceramic uranium fuels, namely UC, UO₂ or UN under a high neutron wall load (NWL) of 10MW/m² at the first wall is conducted over a period of 24 months for fissile fuel breeding for light water reactors (LWRs). New substances, namely, Flinabe or Li₂₀Sn₈₀ are used as coolants in the fuel zone to facilitate heat transfer out of the blanket. Natural lithium is also utilized for comparison to these two innovative coolants. Neutron transport calculations are performed on a simple experimental hybrid blanket with cylindrical geometry with the help of the SCALE 4.3 System by solving the Boltzmann transport equation with the XSDRNPM code in 238 neutron groups and an S₈-P₃ approximation. The investigated blanket using Flinabe or Li₂₀Sn₈₀ shows better fissile fuel breeding and fuel enrichment characteristics compared to that with natural lithium which shows that these two innovative coolants can be used in hybrid reactors for higher fissile fuel breeding performance. Furthermore, using a high NWL of 10MW/m² at the first wall of the investigated blanket can decrease the time for fuel rods to reach the level for charging in LWRs.     

High-power CMUTs: design and experimental verification

Capacitive micromachined ultrasonic transducers (CMUTs) have great potential to compete with piezoelectric transducers in high-power applications. As the output pressures increase, nonlinearity of CMUT must be reconsidered and optimization is required to reduce harmonic distortions. In this paper, we describe a design approach in which uncollapsed CMUT array elements are sized so as to operate at the maximum radiation impedance and have gap heights such that the generated electrostatic force can sustain a plate displacement with full swing at the given drive amplitude. The proposed design enables high output pressures and low harmonic distortions at the output. An equivalent circuit model of the array is used that accurately simulates the uncollapsed mode of operation. The model facilities the design of CMUT parameters for high-pressure output, without the intensive need for computationally involved FEM tools. The optimized design requires a relatively thick plate compared with a conventional CMUT plate. Thus, we used a silicon wafer as the CMUT plate. The fabrication process involves an anodic bonding process for bonding the silicon plate with the glass substrate. To eliminate the bias voltage, which may cause charging problems, the CMUT array is driven with large continuous wave signals at half of the resonant frequency. The fabricated arrays are tested in an oil tank by applying a 125-V peak 5-cycle burst sinusoidal signal at 1.44 MHz. The applied voltage is increased until the plate is about to touch the bottom electrode to get the maximum peak displacement. The observed pressure is about 1.8 MPa with -28 dBc second harmonic at the surface of the array.     

Synthesis and Thermal Conductivity of Ytterbium Silicate Doped with Sm and Gd for Environmental Barrier Coatings Application

Powder Metallurgy and Metal Ceramics - SiC/SiC ceramic matrix composite parts have begun to be used in the hot section of gas turbine engines. It is essential to prevent atmospheric corrosion in...     

Development of an Amperometric Hydrogen Peroxide Biosensor based on the Immobilization of Horseradish Peroxidase onto Nickel Ferrite Nanoparticle-Chitosan Composite

Nano-Micro Letters - Nickel ferrite (NiFe2O4) nanoparticles have been dispersed in chitosan solution in order to fabricate nanocomposite films. Horseradish peroxidase (HRP) has been immobilized...     

The cutting tool stresses in finish turning of hardened steel with mixed ceramic tool

Precision hard machining is an interesting topic in manufacturing die and mold, automobile parts, and scientific research. While the hard machining has benefit advantages such as short cutting cycle time, process flexibility, and low surface roughness, there are several disadvantages such as high tooling cost, need of rigid machine tool, high cutting stresses, and residual stresses. Especially, tool stresses should be understood and dealt with to achieve successful performance of finish hard turning with ceramic cutting tool. So, the influence of cutting parameters on cutting stresses during dry finish turning of hardened (52 HRC) AISI H13 hot work steel with ceramic tool is investigated in this paper. For this aim, a series finish turning tests were performed, and the cutting forces were measured in tests. After literature procedure about finite element model (FEM), FEM is established to predict cutting stresses in finish turning of hardened AISI H13 steel with Ceramic 650 grade insert. As shown, effect of the cutting parameters on cutting tool stresses in finish turning of AISI H13 steel is obtained. The suggested results are helpful for optimizing the cutting parameters and decreasing the tool failure in finish turning applications of hardened steel.     

Determination of some physical and mechanical properties of laminated veneer lumber impregnated with boron compounds

The viability of producing environment‐friendly blends of HDPE and LDPE with a commercial biodegradable masterbatch containing starch and polyethylene was studied. The service life of these blends was simulated by means of a thermo‐oxidative treatment, and their further disposal in landfill was modeled using an accelerated soil burial test. Characterization was carried out in terms of their calorimetric and thermogravimetric properties. Thermo‐oxidative treatment causes an increase in the crystalline content of both components of the blends, and promotes a segregation of the crystallite sizes of polyethylene. The soil burial test leads to changes in the crystalline content of the biodegradable material, which is influenced by the polyolefinic matrix used. The kinetics of the thermal decomposition of these blends was studied using the Hirata and the Broido models. Thermogravimetric results reveal that the thermo‐oxidative treatment causes a decrease in the activation energy of the thermal decomposition process of both components in the blends, regardless of the type of polyethylene used. The thermo‐oxidative treatment mainly modifies the thermal properties of starch during the degradation process in soil, especially in the LDPE blends. Synergetic degradation of these blends is a complex process that is dependent on the polyolefinic matrix used and mainly causes morphological changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of Genotype and Environment on Malt β-Glucanase Activity

Fifteen genotypes of barley grown in two different locations (Gönen and Besni) were used in this study. The malting characteristics and β-glucanase activities of their malts were determined. Although, malt β-glucanase activities of the samples grown in the Besni location were much higher than those of Gönen samples, the malting quality of the samples from both locations were comparable. The results indicate that both genotype and environment affected β-glucanase activity with a more pronounced effect of the latter.     

Low dose MK-801 protects against iron-induced oxidative changes in a rat model of focal epilepsy

We have used chemiluminescence measurements to examine the relationship between free radical formation and excitotoxicity in a post-traumatic epilepsy model. For this purpose, seven days after injecting iron in rat brain cortices, we measured luminol- and lucigenin-enhanced chemiluminescence in different brain regions (ipsilateral cortex, contralateral cortex, hypothalamus and hippocampus). In all brain regions (except contralateral cortices) both luminol- and lucigenin-enhanced chemiluminescence were increased in iron-injected group compared to saline-injected control group. These increases returned to control values in iron-injected rats pretreated with MK-801. Our results suggest that both free radicals and excitatory amino acids play important roles in the development of post-traumatic epilepsy and that MK-801 has protective effects against iron-induced chemiluminescence formation.     

Intraoperative bowel irrigation improves anastomotic collagen metabolism in the left-sided colonic obstruction but not covering colostomy

This study investigated the effects of intraoperative colonic irrigation and proximal diverting end colostomy after segmental bowel resection in experimental left-colonic obstruction on anastomotic healing. Simple obstruction of descending colon was performed in male Sprague-Dawley rats. After 24 h we performed segmental colonic resection and anastomosis in the control group (n = 15); resection, anastomosis, and covering colostomy in the colostomy group (n = 14); resection and anastomosis after antegrade colonic lavage through cecum by using isotonic saline solution in the irrigation group (n = 13). In rats that were killed 7 days later anastomotic dehiscence and bursting pressure and tissue hydroxyproline concentration at the anastomosis were measured. No significant differences were observed between groups in terms of anastomotic dehiscence, bursting site, or pressure. The hydroxyproline concentration was significantly higher in the irrigation group than the control group (P = 0.025) and the colostomy group (P = 0.029), but no difference was noted between the control group and the colostomy group. These findings suggest that intraoperative antegrade colonic irrigation in the acute left-sided colonic obstruction positively affects collagen metabolism at the anastomotic site; if the anastomosis is performed without bowel cleansing, covering colostomy does not improve collagen metabolism.