Porous Segment Research Articles

Investigation on mussel periostracum, a viscoelastic-to-poro-gel graded material, as an interface between soft tissue and rigid materials

Mussel periostracum, a nonliving multifunctional gel that covers the rigid inorganic shells of mussels, provides protection against mechanical impacts, biofouling, and corrosion in harsh ocean environments. The inner part of the periostracum, which emerges from biological tissues, functions as a natural interface between tissue and inorganic materials. The periostracum shows significant potential for application in implantable devices that provide interfaces; however, this system remains unexplored. In this study, we revealed that the inner periostracum performs graded mechanical functions and efficiently dissipates energy to accommodate differences in stiffness and stress types on both sides. On the tissue end, the lightly pigmented periostracum exhibits extensibility and energy dissipation under repetitive tension. This process was facilitated by the slipping and reassembly of β-strands in the discovered major proteins, which we named periostracin proteins. On the shell end, the highly pigmented, mineralized, and porous segment of the periostracum provided stiffness and cushioned against compressive stresses exerted by the shell valves during closure. These findings offer a novel possibilities for the design of interfaces that bridge human tissue and devices.

Tissue distribution of ethanol after intraprostatic injection using a porous needle.

To develop a safe and precise method for intraprostatic injection, and to establish correlation between the volume of ethanol injectate and the volume of subsequent infiltrated prostate tissue. We performed intraprostatic injection of 96% ethanol using a needle which has a segment of its wall made of capillary membrane with hundreds of pores in an acute and chronic canine experiment, in heart-beating cadaveric organ donors, and in a xenograft model of human prostate cancer. Whole mount tissue sections were used for three-dimensional reconstruction of the necrotic lesions and calculation of their volumes. The ethanol injection resulted in oval shaped lesions of well-delineated coagulative necrosis. In both healthy human and canine prostates, the prostatic pseudocapsule and neurovascular bundle remained intact without evidence of disruption. There was a linear correlation between administered volume of ethanol and the volume of necrotic lesion. Regression analysis showed strong correlation in the acute canine experiments and in experiments performed on xenografts of human prostate cancer. A formula was calculated for each experiment to estimate the relationship between the injected volume and the volume of infiltrated prostate tissue area. Intraprostatic injection using a porous needle allows for effective and predictable tissue distribution of the injectate in the prostate. Through varying the volume of the agent injected and use of needles with a different length of the porous segment, the volume of infiltrated tissue could be adjusted allowing for targeted focal treatment.

Crack Initiation Criteria in EBC under Thermal Stress

For design of multi-layered environmental barrier coatings (EBCs), it is essential to assure mechanical reliability against interface crack initiation and propagation induced by thermal stress owing to a misfit of the coefficients of thermal expansion between the coating layers and SiC/SiC substrate. We conducted finite element method (FEM) analyses to evaluate energy release rate (ERR) for interface cracks and performed experiment to obtain interface fracture toughness to assess mechanical reliability of an EBC with a function of thermal barrier (T/EBC; SiC/SiAlON/mullite/Yb-silicate gradient composition layer/Yb2SiO5 with porous segment structure) on an SiC/SiC substrate under thermal stress due to cooling in fabrication process. Our FEM analysis revealed that a thinner SiAlON layer and a thicker mullite layer are most suitable to reduce ERRs for crack initiation at the SiC/SiAlON, SiAlON/mullite and mullite/Yb2Si2O7 interfaces. Interface fracture tests of the T/EBC with layer thicknesses within the proposed range exhibited fracture at the SiC/SiAlON and SiAlON/mullite interfaces. We also estimated the approximate fracture toughness for the SiC/SiAlON and SiAlON/mullite interfaces and lower limit of fracture toughness for the mullite/Yb2Si2O7 interface. Comparison between ERR and fracture toughness indicates that the fabricated T/EBC possesses sufficient mechanical reliability against interface crack initiation and propagation.

Near-Infrared Photoresponse in Photon-Triggered Nanowire Transistors

We investigated a photon-triggered nanowire transistor with near-infrared spectral photoresponse. To understand the mechanism of operation of the nanowire transistor consisting of crystalline Si and porous Si segments, we performed a qualitative analysis of trapped carriers in the porous Si and modeling of a transistor operated by photon gating. We then fabricated a photon-triggered transistor device with a nanowire diameter of 200 nm and a porous Si length of 400 nm. Systematic measurements and analyses demonstrate that the wavelength dependence of the photon-triggered current generation is caused by a broad range of energy levels for the localized trap states of the porous Si segment. We believe that these results pave the way for simplification of the fabrication and operation of ultracompact nanoprocessors and development of efficient nanoscale photodetectors for high-resolution imaging.

Photon-Triggered Current Generation in Chemically-Synthesized Silicon Nanowires.

A porous Si segment in a Si nanowire (NW), when exposed to light, generates a current with a high on/off ratio. This unique feature has been recently used to demonstrate photon-triggered NW devices including transistors, logic gates, and photodetection systems. Here, we develop a reliable and simple procedure to fabricate porous Si segments in chemically synthesized Si NWs for photon-triggered current generation. To achieve this, we employ 100 nm-diameter chemical-vapor-deposition grown Si NWs that possess an n-type high doping level and extremely smooth surface. The NW regions uncovered by electron-beam resist become selectively porous through metal-assisted chemical etching, using Ag nanoparticles as a catalyst. The contact electrodes are then fabricated on both ends of such NWs, and the generated current is measured when the laser is focused on the porous Si segment. The current level is changed by controlling the power of the incident laser and bias voltage. The on/off ratio is measured up to 1.5 × 104 at a forward bias of 5 V. In addition, we investigate the porous-length-dependent responsivity of the NW device with the porous Si segment. The responsivity is observed to decrease for porous segment lengths beyond 360 nm. Furthermore, we fabricate nine porous Si segments in a single Si NW and measure the identical photon-triggered current from each porous segment; this single NW device can function as a high-resolution photodetection system. Therefore, our fabrication method to precisely control the position and length of the porous Si segments opens up new possibilities for the practical implementation of programmable logic gates and ultrasensitive photodetectors.

Effect of Heat Transfer on Oscillatory Flow of Blood through a Permeable Capillary

Of concern in the paper is a study on heat transfer in the unsteady magnetohydrodynamic (MHD) flow of blood through a porous segment of a capillary subject to the action of an external magnetic field. Nonlinear thermal radiation and velocity slip condition are taken into account. The time-dependent permeability and suction velocity are considered. The governing non-linear patial differential equations are transformed into a system of coupled non-linear ordinary differential equations using similarity transformations and then solved numerically using Crank-Nicolson scheme. The computational results are presented in graphical/tabular form and thereby some theoretical predictions are made with respect to the hemodynamical flow of blood in a hyperthermal state under the action of a magnetic field. Effects of different parameters are adequately discussed. The results clearly indicate that the flow is appreciably influenced by slip velocity and also by the value of the Grashof number. It is also observed that the thermal boundary layer thickness enhances with increase of thermal radiation.

Ultrafast capillary electrophoresis/mass spectrometry with adjustable porous tip for a rapid analysis of protein digest in about a minute

This paper introduces a novel ultrafast capillary electrophoresis (UFCE) mass spectrometry (MS) method comprised of a short (< 20 cm) and narrow (≤ 5 µm) capillary, with an integrated porous segment at the terminus of the capillary, for sheathless interfacing of CE to MS. The sheathless nature of the interface minimizes dead volume which is particularly important for ultrafast CE because of the small diameters of the capillaries. The separation voltage across the capillary was set to produce an electric field of ≥1000 V/cm to provide an analysis time of approximately 1 min. For the analysis of peptides and protein digests, a background electrolyte containing 0.1% cationic polymer (polybrene or Poly-E) in 0.1% acetic acid in water was used to prevent analyte-wall interaction. Uniquely, the porous tip of the capillary is adjustable. This allows the porous tip to be pulled inside the sheath liquid for sample stacking during injection, or sample focusing in isoelectric focusing (IEF), or, alternatively, pushed outside of the sheath liquid for electrospray ionization (ESI). The adjustable interface preserves electrical conductivity during electrokinetic injection with reverse electro-osmotic flow. Therefore, pre-concentration of analytes at the capillary inlet is achieved without the need to disassemble the interface, improving the throughput. As a proof of concept, the application of UFCE-MS was demonstrated by the analysis of a peptide mixture and a protein digest in ~1 min.

MHD flow of blood through a dually stenosed artery: Effects of viscosity variation, variable hematocrit and velocity‐slip

AbstractOf concern in the paper is a study on blood flow through a porous segment of an artery subject to the action of an external magnetic field. Effects of viscosity variation and variable hematocrit as well as velocity‐slip at the arterial wall have been duly taken care of in the study. A model has been developed to perform the study by using the principles of magnetohydrodynamics (MHD). The model has been analysed theoretically by employing suitable mathematical methods. Analytical expressions have been derived for the velocity, minute expenditure of blood (volumetric flow rate), wall shear stress and pressure gradient. The said physical variables are computed by using a specific set of values of the various parameters involved in the analysis. This serves as an illustration of the validity of the mathematical model developed in the paper. The computational results are presented graphically. The study also provides important insight into the effects of slip velocity on blood velocity, wall shear stress and pressure gradient. The study further shows that the flow of blood in a porous artery is significantly influenced by the action of an external magnetic field.

NUMERICAL SIMULATION OF A THREE-LAYERED RADIANT POROUS HEAT EXCHANGER INCLUDING LATTICE BOLTZMANN SIMULATION OF FLUID FLOW

This paper deals with the hydrodynamic and thermal analysis of a new type of porous heat exchanger (PHE). This system operates based on energy conversion between gas enthalpy and thermal radiation. The proposed PHE has one high temperature (HT) and two heat recovery (HR1 and HR2) sections. In HT section, the enthalpy of flowing high temperature gas that is converted to thermal radiation to gas enthalpy takes place. In each section, a 2-D rectangular porous segment which is assumed to be absorbing, emitting and scattering is present. For theoretical analysis of the PHE, the gas and solid are considered in non-local thermal equilibrium and separate energy equations are used for the two phases. Besides, in the gas flow simulation, the lattice Boltzmann method (LBM) is applied to obtain the velocity distribution through the porous segments. For the purpose of thermal analysis of the proposed PHE, volume-averaged velocities through the porous matrix obtained by LBM are used in the gas energy equation, and then the coupled energy equations for gas and porous medium of each section are numerically solved using finite difference method. The radiative transfer equation is solved by discrete ordinates method to calculate the distribution of radiative heat flux in the porous medium. The numerical results consist of the gas and porous media temperature distributions. The variation of radiative heat flux are also presented. Furthermore, the effects of scattering albedo, optical thickness and inlet gas temperature on the efficiency of the proposed PHE are investigated. It is revealed that this type of heat exchanger has high efficiency in comparison to conventional one. Also, the present numerical results for a porous radiant burner are compared with theoretical finding by the other investigator and good agreement is found.

Thermal analysis of a 2-D heat recovery system using porous media including lattice Boltzmann simulation of fluid flow

The present work deals with the fluid flow simulation and thermal analysis of a two-dimensional heat recovery system using porous media. A basic high-temperature flow system is considered in which a high-temperature non-radiating gas flows through a random porous matrix. The porous medium, in addition to its convective heat exchange with the gas, may absorb, emit and scatter thermal radiation. It is desirable to have large amount of radiative heat flux from the porous segment in the upstream direction (towards the thermal system). The lattice Boltzmann method (LBM) is used to simulate fluid flow in the porous medium. The gas and solid phases are considered in non-local thermal equilibrium, and separate energy equations are applied to these phases. Convection, conduction and radiation heat transfers take place simultaneously in solid phase, but in the gas flow, heat transfer occurs by conduction and convection. In order to analyze the thermal characteristics of the heat recovery system, volume-averaged velocities through the porous matrix obtained by LBM are used in the gas energy equation and then the coupled energy equations for gas and porous medium are numerically solved using finite difference method. For computing of radiative heat flux in the porous medium, discrete ordinates method is used to solve the radiative transfer equation. Finally the effect of various parameters on the performance of porous heat recovery system is studied.

Special type of plasma dielectric barrier discharge reactor for direct ozonization of water and degradation of organic pollution

A system based on the dielectric barrier discharge (DBD) with improved discharge homogeneity, used for direct ozonization and purification of water, is presented here. A special design of the atmospheric DBD system is characterized by incorporation of a porous ceramic segment in the zone between electrodes. This porous segment was placed on the metallic electrode and served as a guide for flowing water. Due to the hydrophilic force it allowed the water to remain undisturbed by the electrical discharge. This feature enabled a reduction of the discharge gap and subsequently an increase in the intensity, stability and homogeneity of the discharge. It was observed that under such a configuration a transition from the filamentary mode to the semi-homogeneous mode of the plasma discharge could be realized. Discharge properties were investigated by the optical emission spectroscopy method and the results showed the domination of nitrogen lines in the UV-A region. Further it was observed that the system can be operated in a wide range of liquid conductivities and under negligible heat deposition to the liquid solution. Finally, the formation of dissolved ozone and hydrogen peroxide in the deionized water was measured and decomposition tests with organic dye were performed.

Forced Convection Over a Backward-Facing Step with a Porous Floor Segment

Forced convection after a backward-facing step, with a porous floor segment, is investigated numerically using the SIMPEC method. The Brinkman-Forcheimmer extended model is used to govern the flow in the porous-medium region. At the interface, the flow boundary condition imposed is a shear stress jump, which includes the inertial effect, together with a continuity of normal stress. The thermal interfacial condition is continuities of temperature and heat flux. Results are presented for Reynolds number up to 800 and Darcy number up to 10−1. Also varied are the length and depth of the porous segment. Compared with the case with no porous floor, the local heat transfer is augmented after the porous floor. Within the porous floor, the heat transfer is reduced, but this may be offset by using a porous medium of higher conductivity than the fluid. To obtain good heat enhancement after the porous segment, it should approximately match the length of the recirculation region. The porous segment should have large permeability (Darcy number around 10−1), but it is not necessary that it be of great depth. The interfacial stress jump coefficients β and β 1 are varied from − 5 to + 5, and some effects are observed on the local Nusselt numbers, velocity profile, and temperature distribution.

Using a Porous Segment to Increase Thermal Efficiency by Converting Gas Enthalpy to Thermal Radiation in High-Temperature Industrial Furnaces: Exact Solution;

In this paper, effect of a porous segment in the outlet of a high-temperature one-dimensional duct such as an industrial furnace is investigated numerically. The target was to increase the efficiency of these furnaces containing high-temperature gases by undertaking energy conversion and to recover the energy of the gas flows inside the duct. Enthalpy of high-temperature gas was converted to thermal radiation by means of this porous segment. The two-flux method was taken into account for this problem and to perform the numerical procedure the forth order Runge-Kutta scheme was utilized. The porous layer was supposed to have a high-porosity causing a high area/volume ratio and also it was considered highly emissive to radiate absorbed convective energy. Solving the energy equation numerically along and outside the porous segment simultaneously, it was shown that a huge part of convective energy could be converted to recovered energy in the form of thermal radiation. It was shown that due to massive difference between the inlet and outlet temperature of the porous segment, heat could be transferred to upstream. Also it was seen that, the more optic length is the higher efficiency is gained.

Using a Porous Segment to Increase Thermal Efficiency by Converting Gas Enthalpy to Thermal Radiation in High-Temperature Industrial Furnaces

In this paper, effect of a porous segment in the outlet of a hightemperature one-dimensional duct such as an industrial furnace is investigated numerically. The target was to increase the efficiency of these furnaces containing high-temperature gases by undertaking energy conversion and to recover the energy of the gas flows inside the duct. Enthalpy of high-temperature gas was converted to thermal radiation by means of this porous segment. The two-flux method was taken into account for this problem and to perform the numerical procedure the forth order Runge–Kutta scheme was utilized. The porous layer was supposed to have a high-porosity causing a high area/volume ratio and also it was considered highly emissive to radiate absorbed convective energy. Solving the energy equation numerically along and outside the porous segment simultaneously, it was shown that a huge part of convective energy could be converted to recovered energy in the form of thermal radiation. It was shown that due to massive difference between the inlet and outlet temperature of the porous segment, heat could be transferred to upstream. Also it was seen that, the more optic length is the higher efficiency is gained.

A model of trabecular bone and an application to osteoporosis

Large bones consists of an outer compact shaft and an inner porous segment, known as the trabecular architecture (TA). The TA is the principal load carrier in bones from older adults, and the aim of therapeutic interventions is to preserve their strength. It is argued that forms for broad-based diagnostic tools for osteoporosis can be identified through an analysis of simple model systems. A model based on elastic networks is introduced, and shows that weak networks can only utilize a small fraction of themselves for stress transmission. This observation is used to argue that the ratio of linear response of a network to DC and AC strain can be used as a surrogate for bone strength. We discuss the possibility of using this measure to identify osteoporotic bone and to monitor the efficacy of therapy.

Incompressible Turbulent Reattaching Shear Layer Flow Over a Backward Facing Step with Orthotropic Porous Floor Segments

The incompressible turbulent reattaching flow over a 2-D backward facing step with different length porous floor segments was investigated numerically. The flow field was solved using the finite element numerical method and the RNG turbulence model. The porous segment can be used to model solid fuel being entrained by the incoming flow in a combustor. The effect of the porous segment length, depth, and anisotropic and orthotropic pressure loss coefficient on the normalized reattachment length (Xr), normalized maximum recirculation velocity (Urec), and normalized maximum turbulent kinetic energy (TKE) are reported and discussed. Depending on the combination of segment length, depth, pressure loss coefficient, and orthotropicity, a floor with porous segments can be used to change the location and magnitude Xr, Urec, and TKE.

CONVECTION HEAT TRANSFER FROM A LAMINAR FLOW OVER A 2-D BACKWARD FACING STEP WITH ASYMMETRIC AND ORTHOTROPIC POROUS FLOOR SEGMENTS

The fluid and energy equations for the incompressible laminar reattaching flow over a 2-D backward facing step with a porous floor segment were solved numerically using the finite element method. The focus of this study was the change in die forced convection heat transfer characteristics of the flow field due to the addition of a porous floor segment. Several porous flow segment configurations with different lengths and depths were studied. The effect of orthotropicity of the porous segments was also studied. The porosity of the segments was varied over a wide range by changing the value of the pressure loss coefficients in either or both of the x and y directions. The changes in the local and overall Nusselt numbers were reported and discussed. Depending on the configuration, the overall Nusselt number increased or decreased relative to the case of a solid floor. For all configurations, the maximum local Nusselt number increased.

Thermal convective instability of a horizontal saturated porous layer with a segment of inhomogeneity

Convective stability is studied for an infinite horizontal porous layer containing a vertical porous segment of different properties. The critical Rayleigh number depends on the aspect ratio of the nonhomogeneous region and the ratios of permeability, thermal conductivity, and thermal diffusivity of the matrix. Incipient streamlines may be either symmetric or antisymmetric.

Thermal Insulation in Flow Systems: Combined Radiation and Convection Through a Porous Segment

The present work reports analytical findings on a new concept for thermal insulation in flow systems. The basic operating principles are illustrated by a duct flow system with a nonradiating gas passing through a porous segment, where convection and radiation take place. The radiative properties of the porous segment are computed from electromagnetic theory assuming that the porous medium is of homogeneous composition. The coupled energy and radiative transfer equations are solved numerically by iterative method in conjunction with over-relaxation. For the limiting case of no scattering, the present results based on the two-flux radiation model agree well with the exact calculations reported recently. It is found that in order to have higher recaptured radiation and temperature drop, a porous medium with large optical thickness and low scattering albedo is preferred. Two illustrative examples indicate that the pressure drop which resulted from installation of the porous segment is of little concern, especially in view of the resulting huge energy savings.

Supersonic flow past axisymmetric body with strong local two-phase surface injection

It is known [1–3] that in order to provide heat shield or to improve the aerodynamics of the body strong injection of cooling gas into the supersonic stream is utilized. Analysis of flow characteristics in the neighborhood of the solid body in the presence of strong single-phase injection and the effect of injection on the aerodynamic characteristics of some axisymmetric bodies are given, e.g., in [2–4]. Supersonic flow past a blunt-nosed axisymmetric body with blowing of a mixture of gas and solid particles through a porous segment in the leading edge region is considered in the present paper. Such a situation could occur in modeling the breakdown of the heat shield of a flight vehicle during its reentry into the thick layers of atmosphere and also in the case of forced introduction of particles in the flow of the injected gas in order to break up the leading edge shock and accordingly the variation in the drag of the body [5]. A description of the trajectory of the particles has been obtained as a result of numerical and analytical solution of the problem and their analysis is used to arrive at conclusions on their intersection and, consequently, also on the multiple-valued nature of the flow parameters in the neighborhood of the line dividing the external flow and the injected two-phase mixture. Sufficient conditions for multiple-valuedness have been analytically found which agree with numerical results. It has been established that with a change in composition of sufficiently small particles within the limits 0.1 to 0.6 by weight of the injected mixture the drag coefficient of the body does not change by more than 10%.