MIXED CONVECTION IN CAVITIES WITH A LOCALLY HEATED LOWER WALL AND MOVING SIDEWALLS

An optimal control algorithm for cryopreservation of cells using ultrarapid freezing technique is applied successfully in the present study to determine the strength of optimal laser heating based on the desired limited temperature distribution of the cell. The validity of this optimal control analysis utilizing the conjugate gradient method of minimization is examined using numerical experiments. Three different heating times are given, and the corresponding optimal control heat fluxes are determined. Results show that the optimal boundary heat fluxes can be obtained with any arbitrary initial guesses within a very short CPU time on a Pentium III 600-MHz PC.     

Tensile Bond Strength of a Highly Cross-Linked Denture Tooth to the Compression-Molded and Injection-Molded Denture Base Polymers

This study compared tensile bond strengths between conventional compression-molded heat (HC)-, auto (AP)-, and microwave-polymerized (MC) poly(methyl methacrylate)-based denture resins and a relatively new injection-molded, microwave-polymerized polyurethane based resin (MI) bonded to a highly cross-linked denture tooth. In the first part of the experiments, denture teeth were used as received. In the second part, they were treated with dichloromethane to see its effect on bonding of conventional denture bases (HCS and APS). Bond strength was tested in tension according to ADA specification No.15. The results showed that the HC group failed cohesively because of higher interface bonding (49.95 MPa) compared with those of the others (AP: 25.41 MPa; MC: 22.06 MPa; MI: 20.02 MPa). The application of dichloromethane improved bond strengths of HCS and APS groups (60.61 and 32.03 MPa, respectively). It was suggested that dichloromethane could be applied on the denture teeth ridge lap area prior to denture base processing to enhance adhesion between the tooth/resin.     

A production insensitive compact power divider

Power dividers are inevitable components in most microwave systems. Well known topologies like Wilkinson power divider are widely studied in the literature. An “all 50 ohm power divider” is another topology presented in the some works. In this study, an all 50 ohm structure is taken as the basis and a compact-easy to implement modification the power divider is proposed. A sample structure is designed, implemented and measured to prove the topology. The decreased sensitivity to production tolerances is demonstrated by various design modifications. Comparisons with well-known topologies are given for reference.     

Hydrogen production via water splitting process in a molten-salt fusion breeder

This study presents the hydrogen production and fissile breeding potentials of Force-Free Helical Reactor (FFHR) fueled with the molten-salt mixtures. The sulfur–iodine (S–I) thermochemical water-splitting and high-temperature electrolysis cycles, which are the most promising water-splitting cycles, are selected to produce large-scale and pure hydrogen. The XSDRNPM/SCALE4.4a neutron transport code is used for the neutronic calculations. The analyses have been performed individually for four different molten-salt mixtures, (pure FLiBe, mixture of FLiBe and ThF₄, mixture of FLiBe and UF₄, and mixture of FLiBe, ThF₄ and ²³³UF₄). The numerical results bring out that the considered molten-salt fusion breeder reactor has a high neutronic performance and can produce a considerable amount of the hydrogen production (up to 40 kg/s), as well as the fissile fuel (up to 2.5 tons/yr).     

Chemical composition of white (Morus alba), red (Morus rubra) and black (Morus nigra) mulberry fruits

In this study, the chemical composition of white (Morus alba L.), red (Morus rubra L.) and black (Morus nigra L.) mulberry fruits grown in the East Anatolia Region of Turkey was investigated. The highest total phenolic and flavonoid contents were observed in black mulberry (1422 mg gallic acid equivalents/100 g fresh matter and 276 mg quercetin equivalents/100 g fresh matter). M. alba had the highest total fat content (1.10%), followed by M. nigra (0.95%) and M. rubra (0.85%), respectively. The major fatty acids in mulberry fruits were linoleic acid (54.2%), palmitic acid (19.8%) and oleic acid (8.41%), respectively. The total soluble solids content of mulberry species varied between 15.9% (M. rubra L.) and 20.4% (M. alba L.), acidity between 0.25% (M. alba L.) and 1.40% (M. nigra L.), pH between 3.52 (M. nigra L.) and 5.60 (M. alba L.), ascorbic acid 19.4 mg/100 g (M. rubra L.) and 22.4 mg/100 g (M. alba L.), respectively. Mineral compositions of the mulberry species were 0.83% N, 235 mg/100 g P, 1141 mg/100 g K, 139 mg/100 g Ca, 109 mg/100 g Mg, 60 mg/100 g Na, 4.3 mg/100 g Fe, 0.4 mg/100 g Cu, 4.0 mg/100 g Mn and 3.1 mg/100 g Zn, respectively.     

Visible PL Phenomenon at Room Temperature in Disordered Structure of SrWO4 Powder

The SrWO₄ (SWO) powders were synthesized by the polymeric precursor method and annealed at different temperatures. The SWO structure was obtained by X-ray diffraction and the corresponding photoluminescence (PL) spectra was measured. The PL results reveal that the structural order–disorder degree in the SWO lattice influences in the PL emission intensity. Only the structurally order–disordered samples present broad and intense PL band in the visible range. To understand the origin of this phenomenon, we performed quantum-mechanical calculations with crystalline and order–disordered SWO periodic models. Their electronic structures were analyzed in terms of band structure. The appearance of localized levels in the band gap of the order–disordered structure was evidenced and is a favorable condition for the intense PL to occur.     

Investigation of the indentation size effect through the measurement of the geometrically necessary dislocations beneath small indents of different depths using EBSD tomography

We study the link between the indentation size effect and the density of geometrically necessary dislocations (GNDs) through the following approach: four indents of different depth and hardness were placed in a Cu single crystal using a conical indenter with a spherical tip. The deformation-induced lattice rotations below the indents were monitored via a three-dimensional electron backscattering diffraction method with a step size of 50 nm. From these data we calculated the first-order gradients of strain and the GND densities below the indents. This approach allowed us to quantify both the mechanical parameters (depth, hardness) and the lattice defects (GNDs) that are believed to be responsible for the indentation size effect. We find that the GND density does not increase with decreasing indentation depth but rather drops instead. More precisely, while the hardness increases from 2.08 GPa for the largest indent (1230 nm depth) to 2.45 GPa for the smallest one (460 nm depth) the GND density decreases from ≈2.34 × 10¹⁵ m^?2 (largest indent) to ≈1.85 × 10¹⁵ m^?2 (smallest indent).     

Heat transfer enhancement in a tube using circular cross sectional rings separated from wall

A numerical study was undertaken for investigating the heat transfer enhancement in a tube with the circular cross sectional rings. The rings were inserted near the tube wall. Five different spacings between the rings were considered as p = d/2, p = d, p = 3d/2, p = 2d and p = 3d. Uniform heat flux was applied to the external surface of the tube and air was selected as working fluid. Numerical calculations were performed with FLUENT 6.1.22 code, in the range of Reynolds number 4475–43725. The results obtained from a smooth tube were compared with those from the studies in literature in order to validate the numerical method. Consequently, the variation of Nusselt number, friction factor and overall enhancement ratios for the tube with rings were presented and the best overall enhancement of 18% was achieved for Re = 15,600 for which the spacing between the rings is 3d.     

Determination of molecular, atomic, electronic cross-sections and effective atomic number of some boron compounds and TSW

The transmission of gamma-rays of some boron compounds (H₃BO₃, Na₂B₄O₇) and the trommel sieve waste (TSW) have been measured by using an extremely narrow-collimated-beam transmission method in the energy range 15.74-40.93 keV. Molecular, atomic and electronic cross-sections and effective atomic numbers have been determinated on the basis of mixture rule and compared with the results obtained from theory.     

Experimental and numerical investigation of heat and mass transfer during drying of Hayward kiwi fruits (Actinidia Deliciosa Planch)

In this paper we undertake an experimental and numerical study on heat and mass transfer analysis during drying of kiwi fruits. In the experimental part, the effects of various drying conditions in terms of air velocity, temperature and relative humidity on drying characteristics of kiwi fruits are investigated. In the numerical part, the external flow and temperature fields are studied using a commercial CFD package. From these fields, the local distributions of the surface convective heat transfer coefficients for the fruits are determined to predict the local convective mass transfer coefficients through the analogy between the thermal and concentration boundary layers (known as the Chilton–Colburn analogy). In addition, the time-dependent temperature and moisture distributions for different cases are obtained using the code developed to investigate heat and mass transfer aspects inside the fruits. Numerical results are then compared with experimental data and a considerably high agreement is obtained.