Design and fabrication of 3D‐plotted polymeric scaffolds in functional tissue engineering

Regenerating the load‐bearing tissues requires 3D scaffolds that balance the temporary mechanical function with the biological requirements. In functional tissue engineering, designing scaffolds with biomimetic mechanical properties could promote tissue ingrowth since the cells are sensitive to their local mechanical environment. This work aims to design scaffolds that mimic the mechanical response of the biological tissues under physiological loading conditions. Poly(L ‐lactide) (PLLA) scaffolds with varying porosities and pore sizes were made by the 3D‐plotting technique. The scaffolds were tested under unconfined ramp compression to compare their stress profile under load with that of bovine cartilage. A comparison between the material parameters estimated for the scaffolds and for the bovine cartilage based on the biphasic theory enabled the definition of an optimum window for the porosity and pore size of these constructs. Moreover, the finite element prediction for the stress distribution inside the scaffolds, surrounded by the host cartilaginous tissue, demonstrated a negligible perturbation of the stress field at the site of implantation. The finite element modeling tools in combination with the developed methodology for optimal porosity/pore size determination can be used to improve the design of biomimetic scaffolds. POLYM. ENG. SCI., 47:608–618, 2007. © 2007 Society of Plastics Engineers.     

A segmentation approach for file broadcast scheduling

We study the broadcast scheduling problem in which clients send their requests to a server in order to receive some files available on the server. The server may be scheduled in a way that several requests are satisfied in one broadcast. When files are transmitted over computer networks, broadcasting the files by fragmenting them provides flexibility in broadcast scheduling that allows the optimization of per user response time. The broadcast scheduling algorithm, then, is in charge of determining the number of segments of each file and their order of transmission in each round of transmission. In this paper, we obtain a closed form approximation formula which approximates the optimal number of segments for each file, aiming at minimizing the total response time of requests. The obtained formula is a function of different parameters including those of underlying network as well as those of requests arrived at the server. Based on the obtained approximation formula we propose an algorithm for file broadcast scheduling which leads to total response time which closely conforms to the optimum one. We use extensive simulation and numerical study in order to evaluate the proposed algorithm which reveals high accuracy of obtained analytical approximation. We also investigate the impact of various headers that different network protocols add to each file segment. Our segmentation approach is examined for scenarios with different file sizes at the range of 100 KB to 1 GB. Our results show that for this range of file sizes the segmentation approach shows on average 13% tolerance from that of optimum in terms of total response time and the accuracy of the proposed approach is growing by increasing file size. Besides, using proposed segmentation in this work leads to a high Goodput of the scheduling algorithm.     

Effect of annealing process on the growth and surface properties of Au–ZnO nanowire films grown by chemical routes

Au–ZnO nanowire films have been synthesized by chemical routes, electrochemical deposition (ECD) and chemical bath deposition (CBD) techniques, on zinc foil followed by annealing in air at 400 °C. X-ray diffraction patterns reveal formation of the ZnO wurtzite structure along with binary phases Au₃Zn and AuZn₃. Scanning electron microscopy shows the presence of ZnO nanowires having several micrometers in length and less than 120 nm in diameter synthesized by ECD and in the range of 70–400 nm using the CBD technique. During the annealing process, different surface morphologies originating from different catalytic effects of Au atoms/layers were observed. In addition, the effect of synthesis routes on crystalline quality and optical properties were studied by Raman and photoluminescence spectrometers indicating varying concentration of defects on the films. The Raman results indicate that Au–ZnO nanowire film prepared by chemical bath deposition route had better crystalline quality.     

利用扩展Tao-Mason状态方程预测天然气混合物容积特性(p-V-T)

A statistical-mechanical-based equation of state(EOS)for pure substances,the Tao-Mason equation of state,is successfully extended to prediction of the(p-v-T)properties of fourteen natural gas mixtures at temperatures from 225 K to 483 K and pressures up to 60.5 MPa.This work shows that the Tao-Mason equation of state for multicomponent natural gas is predictable with minimal input information,namely critical temperature,critical pressure,and the Pitzer acentric factor.The calculated results agree well with the experimental data.From a total of 963 data of density and 330 data of compressibility factor for natural gases examined in this work,the average absolute deviations(AAD)are 1.704%and 1.344%,respectively.The present EOS is further assessed through the comparisons with Peng-Robinson(PR)equation of state.For the all of mixtures Tao-Mason(TM)EOS outperforms the PR EOS.     

Microparticle Transport and Deposition in the Human Oral Airway: Toward the Smart Spacer

A key issue in pulmonary drug delivery is improving the medical delivery device for effective and targeted treatment. Spacers are clear plastic containers attached to inhalers aimed at delivering more drug particles to the respiratory tract. The spacer's one-way valve plays an important role in controlling and initializing the particles into the oral cavity. This article studied particle inhalation and deposition in an idealized oral airway geometry to better optimize the spacer one-way valve shape and design. Three steady flow rates were used 15, 30, and 60 l/min and a Lagrangian, one-way coupling particle tracking model with near-wall turbulence fluctuation correction was used to determine the deposition rates. For all three breathing rates, the velocity field in the midsagittal plane showed similar gross fluid dynamics characteristics, such as the separation and recirculation regions that occur after the larynx. The particle deposition rates compared reasonably well with available experiments. Most particles deposited at the larynx, where the airway has a decreasing cross-sectional area. For different particles sizes, most particles introduced at the lower region of the mouth show higher possibility to pass through upper airway and enter the trachea and lung airways. The particle deposition patterns in the airway were traced back to their initial inlet position at the oral inlet; and this information provides the background for a conceptual and optimized design of the spacer one-way valve.

Copyright 2015 American Association for Aerosol Research     

Experimental and Numerical Investigation on Free Convection From a Horizontal Cylinder Located Above an Adiabatic Surface

Steady two-dimensional free convection heat transfer from an isothermal horizontal cylinder located above an adiabatic horizontal surface is studied experimentally and numerically. Experiments are carried out using a Mach–Zehnder interferometer for the ratios of cylinder spacing from the adiabatic surface to its diameter L/D = 0, 0.1, 0.2, 0.3, 0.5, 0.7, and 0.9 and the Rayleigh number range of 500 to 15,000. Also, a specifically developed computer code based on the finite-volume method, the SIMPLE algorithm, and nonorthogonal discretization grid system is used for the solution of the mass-, momentum-, and energy-governing equations for the Rayleigh numbers ranging from 100 to 100,000 and L/D ranging from 0.1 to 1.7. The effects of the Rayleigh number and spacing from the adiabatic surface on both local and average Nusselt numbers around the cylinder are investigated. A correlation based on the numerical data for the average Nusselt number of the cylinder as a function of Rayleigh number and L/D is presented in the aforementioned ranges.     

The Effect of Ethanol on Nanostructures of Mixed Cationic and Anionic Surfactants

Micellization of tetradecyl trimethyl ammonium bromide (TTAB) and sodium dodecyl sulfate (SDS) in water–ethanol (ET) micellar solutions, with the weight percent of ET changing within the range 0–30, was studied by means of surface tension and conductivity measurements. Surface tension measurements also provided information about the dependence of the surface excess concentration, the minimum area per surfactant molecule, and the standard Gibbs energy of adsorption on the added weight percent of the organic solvent. Information about the degree of counterion dissociation and phase transition was obtained through conductivity measurements. Cyclic voltammetry (CV) and dynamic light scattering (DLS) was also employed to investigate the mixed micellar behavior of the binary mixtures. It was shown that an excess of cationic surfactant and ET resulted in a phase transition of vesicles and large micelles to mixed micelles. The regular solution theory approximation was used to determine various micellar parameters of ideal systems. The regular solution interaction parameter (β) suggests that the formation of mixed micelles is due to the synergistic interactions in the case of TTAB/SDS systems and becomes affected by the water/ET ratio.     

Effects of structural variables on AUL and rheological behavior of SAP gels

The swelling properties of superabsorbent polymers (SAPs) under real conditions are extremely important for selecting the material suitable for a given application, e.g. feminine napkin or agriculture. This new practical research represents deeper synthetic and physicochemical studies on the structure–property relation in acrylic SAP hydrogels and composites. Thus, the values of saline‐absorbency under load (AUL; a measurable simulation of the real circumstances of SAP applications, at pressures 0.3–0.9 psi) were measured for the SAP or SAP composite samples prepared under different conditions, i.e. type and content of crosslinker, type and concentration of initiator, percentage of inorganic filler (kaolin), and type and percentage of porosity generators. The samples were subsequently used to determine the rheological and morphological characteristics. Dynamic storage modulus (G′) measurements were carried out at constant strain in a wide range of frequency. Linear correlations were frequently found to be active between AUL and G′ data over the rubber‐elastic plateau. Thus, for a given SAP: AUL = k_totalG′ + C. The coefficient k total is a function of (nature and content of crosslinker, initiator, inorganic component, particle morphology, etc.). Therefore, the easily measured AUL values could be simply correlated to the main synthesis variables and molecular structure of SAP gels through a rheological material function (G′). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dimensionless number for identification of flow patterns inside a T-micromixer

Results are presented from a numerical study examining the flow dynamics of the liquid phase inside T-type micromixers. The main aim of the study was to determine an identification number for the differentiation of the different flow regimes in the liquid phase in T-type micromixers. The critical value for the identification number at which the transition from vortex flow to engulfment flow occurs was obtained. The results were used to optimize the geometrical parameters and the operating conditions to achieve high mixing performance for the liquid phase in T-type micromixers. The model results were found to be consistent with experimental data for different T-mixers available in the literature.     

Effect of chlorine ion concentration on morphology and optical properties of Cl-doped ZnO nanostructures

Effect of Cl^?1 concentration on morphology and optical properties of Cl-doped ZnO nanostructures was studied. The Cl-doped ZnO nanostructures and undoped ZnO microstructures were grown on Si(1 1 1) substrates using a physical vapor deposition method. The ZnO nanostructures have been doped with different concentrations of chlorine. The Cl-doped ZnO nanostructures with 6% atom Cl, showed a nanodisk morphology with a hexagonal shape, while the Cl-doped ZnO nanostructures with 9% atom Cl, exhibited a stacked nanoplate morphology with smaller thickness in comparison to the Cl-doped ZnO nanodisks. In addition, with increasing Cl content to 13%, morphology of the products changed to more stacked nanoplates with nanoflakes morphology. X-ray diffraction results clearly showed a hexagonal structure for the all samples. Raman spectroscopy results showed a strong crystalline quality for the undoped ZnO microdisks and Cl-doped ZnO nanodisks; while these results indicated a weak crystalline quality for the Cl-doped ZnO nanoplates and nanoflakes. Photoluminescence (PL) studies also confirmed the Raman results and it exhibited a lower optical property for the Cl-doped ZnO nanoplates and nanoflakes in comparison to the undoped ZnO microdisks and Cl-doped ZnO nanodisks. Furthermore, the UV peak of the Cl-doped ZnO nanostructures was blue-shifted with respect to that of the undoped ZnO.