Multiscale simulation of nutrient transport in hollow fibre membrane bioreactor for growing bone tissue: Sub-cellular scale and beyond

Recent experimental studies suggest that hollow fibre membrane bioreactors (HFMBs) may be used to grow 3-D bone tissues in the laboratory, which may then be implanted into patients to repair skeletal defects. The HFMBs mimic the capillary network that exists in bones and are very effective in supplying nutrients to cells (to maintain cell metabolism) and removing waste products (e.g., excreta from micro-organisms, etc.). In order to guide the design of HFMBs for bone tissue engineering, it is necessary to elucidate the quantitative relationships between the cell environment and tissue behaviour in HFMBs and their relationship with nutrient supply. However, the nutrient transport processes in these bioreactors depend on several scales: from the scale of the individual cell to the scale of the bioreactors (laboratory scale). Further, the significance of the mass transfer processes is different from one scale to another. At the sub-cellular scale (i.e., within individual cell), the transport processes are dominated by diffusive-reaction mechanisms. At the extracellular matrix, these processes are primarily diffusion dominated. The transport of nutrients in the capillary network is convection dominated. At the scale of the laboratory device, the transport behaviour is governed by non-linear coupled convection-diffusion and reaction processes. Therefore, to characterise the ‘overall’ nutrient transfer processes and function of the HFMB, one needs an understanding of the processes at the smaller scale (e.g., sub-cellular scale) and their manifestation at larger scale, such as the bioreactor.This paper presents an approach for modelling and simulating nutrient transport in HFMB for growing bone tissues where the separations of scales from individual cell to the scales of bioreactor are considered. We use direct numerical simulation (finite element method) instead of more tedious applied mathematics based upscaling theorems for modelling nutrient transport in HFMB. The advantage of this approach is that it does not rely on the determination of averaged transport properties (e.g., diffusion coefficient) that appear in averaged transport equations which are often difficult to measure experimentally or may not have significant physical meaning. In this paper, the developed computational framework is used to upscale the mass transfer processes at sub-cellular scale to the scale of HFMB (laboratory scale). The developed framework is then employed to carry out a systematic analysis of the influence of various process parameters of HFMB (e.g., fluid velocity, cell density, cellular size, etc.) on the nutrient transport behaviour. It is envisaged that the developed multiscale tool will provide better understanding of the functioning of HFMB for the purposes discussed above.     

Screening for counterfeit electronic parts

Counterfeit electronic parts have become a significant cause of worry in the electronic parts supply chain. Counterfeit parts detected in the electronics industry can be new or surplus parts that are modified in some manner, or they can be salvaged scrap parts that are refurbished to look like new. In the latter case, the packaging of these parts is altered to modify their identity or disguise the effects of salvaging. The modification can be as simple as the removal of old markings and the addition of new markings, or as complicated as the recovery of a die and repackaging in a new package. In this paper, we discuss the types of parts used to create counterfeit semiconductor parts and the defects/degradation inherent in these parts due to the nature of the sources they come from. We also discuss proposed inspection standards and their limitations. The processes used to modify the packaging of these parts to create counterfeits are then discussed along with the traces left behind from each of the processes. We then present a methodology for detecting signs of possible part modifications to determine the risk of a part or part lot being counterfeit.     

Copolymers of bulky fumarate: synthesis and their properties

The free radical copolymerization of di-n-docosyl fumarate with vinyl acetate and n-alkyl (meth)acrylates was carried out in toluene at 70°C using benzoyl peroxide as an initiator. ¹H NMR and carbon analysis was used to determine the copolymer compositions. Monomer reactivity ratios for high conversion polymerization were calculated by Fineman-Ross, Kelen-Tüdös and conversion extension Kelen-Tüdös methods. Gel permeation chromatography was used to determine the molecular weights and polydispersity indexes. In order to determine the stability of polymers against thermal degradation, the kinetics and mechanism of the thermal degradation of copolymers were investigated by differential scanning calorimetry and thermogravimetric analysis techniques. The energy of activation of the degradation process was determined by several thermogravimetric analysis models.     

Synthesis and characterization of a new hyperbranched organic–inorganic solid polymer electrolyte with cyanuric chloride as a core element

A new hyperbranched organic–inorganic hybrid electrolyte based on the use of 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride, CC) as the coupling core to couple with oligo(oxyalkylene)-amines, followed by condensation with (3-glycidoxypropyl)-trimethoxysilane (GLYMO) and complexed with LiClO₄, has been prepared and characterized. The Vogel–Tamman–Fulcher (VTF) like conductivity behavior is observed in the present organic–inorganic hybrid electrolytes with a maximum ionic conductivity value of 4.4 × 10⁻⁵ S cm⁻¹ at 30 °C. Multinuclear NMR techniques are used to provide a microscopic view for the specific interaction between the polymer chains and Li⁺ cations and their dynamic behaviors. The results of 2D ¹H–¹³C wide-line separation (WISE) and ⁷Li static line NMR width measurements divulge that the mobility of the ⁷Li cations is strongly related to a dynamic environment created by the polymer motion in the amorphous phase. The combined results of conductivity and ⁷Li pulse-gradient spin-echo (PGSE) NMR self-diffusion coefficient measurements reveal that the conductivity enhancement at low salt concentrations is mainly caused by the high mobility of the lithium cations.     

Toffoli Netlist and QCA implementations for existing four variable reversible gates: a comparative analysis

Microsystem Technologies - With CMOS reaching its fundamental physical heat threshold limits, reversible logic has emerged as a viable alternative due to its heat arresting attributes. CMOS started...     

Non-uniqueness in capillary pressure-saturation-relative permeability relationships for two-phase flow in porous media: Interplay between intensity and distribution of random micro-heterogeneities

The two-phase flow behaviour in porous media is determined on the basis of capillary pressure-saturation-relative permeability relationships (P^c-S-K_r). These relationships are highly non-linear and obtained by laboratory experiments on porous samples, typically around 10-12 cm in length. It is normally assumed that these samples are homogeneous; however it is well-known that this is in fact not the case and that even at this scale micro-scale heterogeneities exist. Two-phase flow experiments on soils with different properties (e.g., particle and pore size distribution, permeabilities, etc) result in different P^c-S-K_r relationships implying that they cause non-uniqueness in these curves. Recent work has shown that the presence of the micro-heterogeneities has a significant effect on the measured P^c-S-K_r relationships and they cause non-uniqueness in these relationships. In the previous work in this area, the micro-heterogeneity effects on the P^c-S-K_r relationships have been analysed in a number of contexts, e.g., uniformly distributed heterogeneities (simplified cases), various binary sand combinations, hydraulic parameters (e.g., entry pressure, permeability), boundary conditions, etc. There is also some evidence that the intensity and distribution of the micro-heterogeneities affect the P^c-S-K_r relationships. In the present work we use numerical simulations to investigate further the nature of these effects, in particular how the interplay between the intensity and random distribution of micro-heterogeneities affect the P^c-S-K_r relationships. Seven randomly heterogeneous patterns have been defined. These domains represent coarse sand media with fine sand blocks embedded in them. The domain size () has been chosen so that it represents a typical laboratory scale device. The results of the simulations show that it is particularly important to take into account both the intensity and distribution of heterogeneity when determining the effective P^c-S-K_r relationships of a sample. Further, there is a complex interplay between the intensity and distribution of micro-scale heterogeneities which determines the P^c-S-K_r curves. This observation is in contrast to the results of domains with uniformly distributed heterogeneities. We have found that in general if the intensity of heterogeneity is high; the irreducible wetting phase saturation (S_iw) of the sample is also high. The direction of flow and the orientation of the samples also have significant effects. For example, the injection of an immiscible phase from the top (vertically downward) of water saturated porous domain leads to a lower S_iw than injecting on horizontal plane. On the other hand, injection from the bottom (vertically upwards) leads to a higher S_iw. As expected, the distribution of heterogeneity has a significant effect on the saturation distribution and the shape of the P^c-S-K_r curves. However, we show that if the heterogeneities are distributed in such a way that they are closer to the boundary of injection, the irreducible wetting phase saturation is higher.     

Synthesis,characterization, and thermal properties of copolymers of behenyl acrylate and behenyl fumarate

Radical copolymerization of behenyl (systematic IUPAC nomenclature: n‐docosyl) acrylate and behenyl fumarate has been carried out in toluene at 70°C using benzoyl peroxide as initiator. Gel permeation chromatography was used to determine molecular weights (MW) and molecular weight distribution (MWD) of behenyl acrylate–behenyl fumarate (BA‐BF) copolymers. ¹H NMR and carbon analysis was used to determine the composition of BA‐BF copolymers. Monomer reactivity ratios for high conversion polymerization were calculated by conversion‐extended Kelen‐Tudos plot. Differential scanning calorimetric (DSC) measurements shows sharp melting peaks at about 64°C. Thermal stability studies were performed with thermogravimetric analyzer (TGA). By using these DSC and TGA data in several nonisothermal methods, the activation energies were calculated. X‐ray diffraction studies show the linearity of the copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2721–2726, 2003     

Simple,efficient location‐based routing for data center network using IP address hierarchy

Increasing demand and sophistication of applications deployed on data centers resulted in various designs for data center networks (DCNs). One of the major challenges in the design of DCNs is the design of routing protocol that scales to support millions of servers that a typical DCN hosts. Many alternative routing protocols are proposed to overcome the scalability problem of conventional routing protocols such as Open Shortest Path First and Routing Information Protocol. These alternative protocols that use topology characteristics of DCN are broadly classified as source routing and location‐based routing. In the process of fixing the scalability problem, these protocols introduced additional complexities such as large network control overhead and reprogramming of network elements. The extra control overhead in these protocols is the result of their effort to determine the relative location of the end hosts in a given topology. Further, existing location‐based routing is not entirely location based and covers only the latter half of a route. In our work, we present a new location‐based routing based on IP address hierarchy that (a) does not need any additional network control plane and management planes, (b) deployable on proven network technologies, and (c) covers entire path of the route. We establish the correlation between topology design and address assignments that helps determining the location of an end host directly from the address assigned to it. We demonstrate our proposed location‐based routing on an existing proven architecture for DCN, BCube‐IP and on our proposed architecture 4‐4, 1‐4. We give proper justification for proposing 4‐4, 1‐4, a better design for our proposed location‐based routing. Copyright © 2016 John Wiley & Sons, Ltd.     

Film cooling on a gas turbine blade pressure side or suction side with axial shaped holes

The film cooling effectiveness on the surface of a high pressure turbine blade is measured using the pressure sensitive paint (PSP) technique. Four rows of axial laid-back, fan-shaped cooling holes are distributed on the pressure side while two such rows are provided on the suction side. The coolant is only injected to either the pressure side or suction side of the blade at five average blowing ratios ranging from 0.4 to 1.5. The presence of wakes due to upstream vanes is simulated by placing a periodic set of rods upstream of the test blade. Effect of the upstream wakes is recorded at four different phase locations with equal intervals along the pitch-wise direction. The freestream Mach numbers at cascade inlet and exit are 0.27 and 0.44, respectively. Results reveal that the tip leakage vortices and endwall vortices sweep the coolant film on the suction side to the midspan region. The film cooling effectiveness on the suction side is usually higher than that on the pressure side except the regions affected by the secondary vortices. The presence of upstream wakes results in lower film cooling effectiveness on the blade surface. The moderate blowing ratios (M = 0.6 or M = 0.9) give higher film cooling effectiveness immediately downstream of the film cooling holes. Further downstream of the holes, higher blowing ratios cover wider surface area.