Characteristics investigation on heat transfer growth of sonochemically synthesized ZnO-DW based nanofluids inside square heat exchanger

Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...     

The effect of rapid rotation on a vertical bridgman furnace at large Rayleigh number

In quasi-steady operation, convection currents in a Bridgmandevice, used for producing a semi-conductor crystal, createinhomogeneities that may make the crystal unusable. It has oftenbeen suggested that additional forces due to rotation or magnetismmight be efficacious in reducing the segregation of the elementsof the alloy. It has been found that, over a wide range of rotationrates, there is no improvement in performance due to rotationabout the vertical axis. However, numerical results that havebeen obtained previously (Lee & Pearlstein, J. Crys. Growth240, 2002) indicate that, when effects of centrifugal buoyancyare introduced, a substantial reduction in segregation is achieved.In the work reported here, by contrast, in which we extend previouslarge-Rayleigh-number asymptotic analysis to include centrifugalbuoyancy, we find no improvement in radial segregation, butrather increasing segregation with increasing rotation rate.     

Graphic tool to produce tailored symmetrical phase-shifting algorithms

We employ the Fourier-transform graphic representation of a set of antisymmetrical and symmetrical sampling reference harmonics to obtain new symmetrical phase-shifting algorithms tailored to specific characteristics. As an example, a new detuning-insensitive seven-point algorithm, with a third signal harmonic insensitivity and which is detuning insensitive at this frequency, is derived.     

Controlled hydrothermal growth of ZnO nanostructures by sequestering the Zn metal ions with the chelating agent EDTA

In the present work, a controlled growth of ZnO nanostructures by manipulating Zn metal ion concentration by the chelating action of ethylene diaminetetra acetic acid in hydrothermal method is studied. EDTA produces metal–chelate complex by the formation of bidentate ligand with Zn²⁺ in the solution and diminishes the reactivity of Zn metal cations. Concentration of EDTA in the mother solution was varied in different ranges like 3, 5 and 10 mM while retaining the zinc metal salt and the NaOH concentration the same. Three different morphologies of wurtzite structured ZnO nanostructures such as nanorods-bunch, separate/discrete uniformly sized hexagonal nanorods and tapered flower petals like shapes are achieved by 3, 5 and 10 mM strengths of EDTA, respectively. The medium concentration 5 mM of EDTA is found to have moderate control over producing ZnO nanostructures of uniform diameter and a high aspect (length to diameter) ratio. An array of vertically aligned free standing ZnO nanorods with uniform spacing is successfully achieved by the addition of 5 mM of EDTA in the mother solution and the same is studied for its fluorescence property at an excitation of 325 nm and it has exhibited a characteristic UV emission of ZnO around 383 nm.     

Magneto-transport properties of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction

Hole-doped rare-earth manganite La_0.7Ca_0.3MnO₃ and the electron-doped manganite La_0.7Ce_0.3MnO₃ both show a metal-insulator transition around 250 K associated with a ferromagnetic transition and colossal magnetoresistance. In an earlier publication we have reported the rectifying characteristic of La_0.7Ca_0.3MnO₃/SrTiO₃/La_0.7Ce_0.3MnO₃ tunnel junction at room temperature, showing that it is possible to fabricate a diode out of the polaronic insulator regime of doped manganites. Here we report the magneto-transport properties of such a tunnel junction above and below the metal-insulator transition. We show, from the large positive magnetoresistance of the tunnel junction at low temperature, that La_0.7Ce_0.3MnO₃ could be a minority spin carrier ferromagnet. The implication of this observation is discussed.     

Synthesis and Antitumor Activity of Heterocycles Related to Carbendazim

Three types of compounds were synthesized from carbendazim ( 1 ), a benzimidazole derivative (Scheme 1 ). They included a group of esters at N1 prepared by treating carbendazim with isocyanates bearing ester groups ( 2a , 2b , 2c ), carboxyalkyl‐1,2,3,4‐tetrahydro‐s‐triazino[1,2‐a]benzimidazole‐2,4‐dione esters ( 3a and 3b , 3d and 3c derived from 3a . The antitumor potencies of the N1 esters were in the range of 7 to 40 μM, which compares favorably with carbendazim, but their water solubilities were low. The s‐triazine derivatives showed activity against pancreatic tumor cells, and one of them ( 3b ) was active in mice, but they were not effective against other tumor types. Treatment of carbendazim with 3‐bromopropionyl chloride produced 1‐methoxycarbonyl‐4‐oxo‐1,2,3,4‐tetrahydropyrimido[1,2‐a]benzimidazole ( 4 ), which gave 1‐(3‐aminopropionyl)benzimidazole 2‐methylcarbamates, substituted on the amino nitrogen ( 5a , 5b , and 5d ), when treated with amines. These products showed some antitumor activity in cell cultures, and an ethoxy derivative ( 5c ), obtained by treating 1‐methoxycarbonyl‐4‐oxo‐1,2,3,4‐tetrahydropyrimido[1,2‐a]benzimidazole with sodium ethoxide, was active in the 67–150 μM range. Some of the new compounds had good water solubility. Carbendazim kills tumor cells by inhibiting tubulin; however, s‐triazine 3b , which differs from it in size and functional groups, does not act by this mechanism.     

A numerical algorithm for the solution of a phase-field model of polycrystalline materials

We describe an algorithm for the numerical solution of a phase-field model (PFM) of microstructure evolution in polycrystalline materials. The PFM system of equations includes a local order parameter, a quaternion representation of local orientation and a species composition parameter. The algorithm is based on the implicit integration of a semidiscretization of the PFM system using a backward difference formula (BDF) temporal discretization combined with a Newton–Krylov algorithm to solve the nonlinear system at each time step. The BDF algorithm is combined with a coordinate-projection method to maintain quaternion unit length, which is related to an important solution invariant. A key element of the Newton–Krylov algorithm is the selection of a preconditioner to accelerate the convergence of the Generalized Minimum Residual algorithm used to solve the Jacobian linear system in each Newton step. Results are presented for the application of the algorithm to 2D and 3D examples.     

Impaction of spray droplets on leaves: influence of formulation and leaf character on shatter,bounce and adhesion

This paper combines experimental data with simple mathematical models to investigate the influence of spray formulation type and leaf character (wettability) on shatter, bounce and adhesion of droplets impacting with cotton, rice and wheat leaves. Impaction criteria that allow for different angles of the leaf surface and the droplet impact trajectory are presented; their predictions are based on whether combinations of droplet size and velocity lie above or below bounce and shatter boundaries. In the experimental component, real leaves are used, with all their inherent natural variability. Further, commercial agricultural spray nozzles are employed, resulting in a range of droplet characteristics. Given this natural variability, there is broad agreement between the data and predictions. As predicted, the shatter of droplets was found to increase as droplet size and velocity increased, and the surface became harder to wet. Bouncing of droplets occurred most frequently on hard-to-wet surfaces with high-surface-tension mixtures. On the other hand, a number of small droplets with low impact velocity were observed to bounce when predicted to lie well within the adhering regime. We believe this discrepancy between the predictions and experimental data could be due to air layer effects that were not taken into account in the current bounce equations. Other discrepancies between experiment and theory are thought to be due to the current assumption of a dry impact surface, whereas, in practice, the leaf surfaces became increasingly covered with fluid throughout the spray test runs.