Cooling characteristics of an impinging spray jet which forms an ellipsoidal liquid film

The cooling characteristics of an impinging spray jet which forms an ellipsoidal liquid film were experimentally investigated in order to estimate the cooling performance of a rotating roll in a hot mill system. The following four conclusions were reached in the study. (1) In the case of a single spray jet, the local heat transfer coefficient at the center position depends on the forced convective heat transfer by the impinging jet. However, the average heat transfer coefficient is proportional to the flow rate density of the cooling water, and it does not depend on the distance between the nozzle and heated surface. (2) In the case of a double spray jet, liquid film interference occurs. The local heat transfer coefficient at the center position is greater, and the cooling performance increases with the increasing flow rate density of the cooling water. (3) The cooling performance of a multispray jet is proportional to the flow rate density of the cooling water. It does not depend on the nozzle construction, distance, or specifications. Also, there is no relation to the liquid film interference. (4) When the optimum specifications of the spray nozzle are used, thermal analysis of a rotating roll shows that the temperature at a depth of 1.3 mm from the surface is below 130 °C. © 2000 Scripta Technica, Heat Trans Asian Res, 29(4): 280–299, 2000     

High-Voltage Pulse Generation in Nonlinear Transmission Line with Ceramic Capacitors

Usual axial cables and aerial lines are distributed constant linear transmission lines which can transmit a pulse without changing its initial shape. On the other hand, a nonlinear transmission line consisting of nonlinear capacitors can sharpen the front of a propagating pulse. In this study, a transmission line with commercially available ferroelectric BaTiO₃ ceramic capacitors is constructed to obtain high-voltage pulses with short rise-time. Strong dependence of their capacitance on the applied voltage has been found. The rise-time of the input pulse with 300 V in amplitude was shortened from 60 ns after propagating through the line.     

Thrombogenicity and blood coagulation of a microcatheter prepared from carbon nanotube-nylon-based composite

Here we describe the fabrication of nanocomposite-based microcatheter through-melt extrusion utilizing high-purity carbon nanotubes as filler and nylon as matrix. Homogeneous dispersion of carbon nanotubes in nylon can provide novel microcatheters with enhanced mechanical properties (easier to handle) and extremely reduced thrombogenicity or antithrombotic property. The present microcatheter with high performance is highly promising for medical applications.     

Modified determination method of total bromine in agricultural products by gas chromatography

In the official method for determination of total bromine in fruit and grain foods, bromine is derivatized with 3-pentanone for GC analysis. Co-existing substances sometimes interfere with measurement of the derivative, though the method is highly selective. In this study, the notification method was modified to reduce impurity peaks by applying 3-hexanone. Samples were alkalized and reduced to ash in an electric furnace. After ashing, samples were oxidized with potassium permanganate solution and derivatized with 3-hexanone. The calibration curve was linear from 0.1 microg/mL up to 5.0 microg/mL. The detection limit (S/N = 10) was 0.1 microg/mL, i.e., 5 microg/g for herb, 2.5 microg/g for grains and 1.0 microg/g for fruits. The recoveries of bromine from fruit, grain foods and herbs added at the levels of 5 to 25 microg/g ranged from 84.2 to 96.9%. The values of relative standard deviation (RSD) were from 1.4 to 6.3%. This method should be useful for routine examination of total bromine in foods.     

Role of systemic T-cells and histopathological aspects after subcutaneous implantation of various carbon nanotubes in mice

We have evaluated the biological responses to four different types of carbon nanotubes (CNTs), by measuring CD4⁺ and CD8⁺ T-cells in peripheral blood, and by the histopathological study on tissues surrounding subcutaneously implanted CNTs for up to 3 months. All mice survived, and no large changes in their weights were observed within our experimental period. After 1 week, only single-walled carbon nanotubes (SWNTs) activated major histocompatibility complex (MHC) class I pathway of antigen-antibody response system (higher CD4⁺/CD8⁺ value), resulting in the appearance of an edematous aspect. After 2 weeks, significantly high values in CD4⁺ and CD4⁺/CD8⁺ without change in CD8⁺ signified an activated MHC class II for all samples. It is worth noting that the toxicological response of CNTs was absolutely lower than that of asbestos. As a result, we envisaged that our result (relatively low toxicity of CNTs) will spur the mass-production, as well widespread application of CNTs in the near future.     

Doping saturation in dye-sensitized solar cells based on ZnO:Ga nanostructured photoanodes

The origins of the performance of dye-sensitized solar cells based on ZnO:Ga nanostructured photoelectrodes, compared to analogous ZnO solar cells, were studied by means of impedance spectroscopy under illumination as a function of forward bias voltage. The film capacitance is governed by Ga doping. It can be assumed that the higher donor density of states of ZnO materials and, principally, ZnO:Ga-doped materials pin the Fermi level at a certain shallow energy level so that there is no photovoltage variation as a function of doping level. On the other hand, short circuit current is determined by the increasing roughness factor obtained at the higher doping levels while the lower fill factor values of DSCs based on ZnO:Ga, compared to analogous ZnO, were attributed to the higher ohmic resistive losses associated with the increasing photocurrent densities. In any case, the microstructure and morphological aspects were also considered as a possible origin of the low fill factor values. The estimated donor density level exceeds 10²¹ cm⁻³, indicating a high doping level in the semiconductor. As a consequence of the synthesis process of ZnO:Ga nanoparticles its size diminishes with the higher Ga contents producing an increase in the overall roughness factor of the films, and then a larger dye upload and short circuit current.     

Acid Neutralization Capacity of a Tricalcium Silicate-Containing Calcium Phosphate Cement as an Endodontic Material

A calcium phosphate cement (CPC) was shown to have the necessary attributes for endodontic materials except adequate basicity needed for antimicrobial properties. To enhance its basicity, tricalcium silicate (Ca₃SiO₅), a highly alkaline compound, was added to CPC at a mass fraction of 0.25, 0.5 or 0.75. The basicity, acid neutralization and physical properties of the CPC-Ca₃SiO₅ composites were investigated. Mineral trioxide aggregate (MTA) was used as the control. The acid neutralizing capacity of the CPC-Ca₃SiO₅ composites and MTA were measured by titrating the suspensions of ground set samples with a 0.2 mol / L HCl at predetermined pH levels, i.e., 11, 9.0, and 7.4. The setting time of CPC-Ca₃SiO₅ composites determined by the Gilmore needle method was 40 ± 10 min. Acid neutralizing capacity of CPC depended (p < 0.05) on Ca₃SiO₅ content. CPC containing 75 % Ca₃SiO₅ could neutralize slightly less acid than MTA (p < 0.05), but it had a shorter setting time than that of MTA (> 4 h) and excellent handling properties.     

Giant magnetoresistance due to electron-hole pair mechanism in poly(N-vinylcarbazole)

An amorphous molecular semiconductor, poly(N-vinylcarbazole) (PVCz), exhibits negative giant magnetoresistance (MR) under ambient conditions. The application of a weak magnetic field of 10 mT to PVCz films doped with lumichrome, in which light excitation immediately creates triplet electron-hole (e-h) pairs that are precursors of photocarriers, causes a steep decrease in resistivity by more than 20% at ambient temperature. Further, the resistivity of the doped film gradually reduces by approximately one-half under a field of 1 T, equivalent to an MR ratio of ?55%. In addition, anomalous spikes are also detected at 0.07, 0.30, and 9.0 T, indicative of an exponential dependence with a decay distance of 0.1 nm in the exchange interaction of the e-h pair. A quantum mechanical calculation based on the density operator formalism clarifies that the observed MR effect can be comprehensively understood by the spin-selective charge dynamics and the coherent and incoherent spin dynamics of the e-h pair in a quasi-one-dimensional lattice for photocarrier generation. Model calculations also indicate the importance of the spin-lattice relaxation for the giant MR effect in organic molecular semiconductors.