Pore Placement Research Articles

How venom pore placement may influence puncture performance in snake fangs.

When designing experimental studies, it is important to understand the biological context of the question being asked. For example, many biological puncture experiments embed the puncture tool to a standardized depth based on a percentage of the total tool length, to compare the performance between tools. However, this may not always be biologically relevant to the question being asked. To understand how definitions of penetration depth may influence comparative results, we performed puncture experiments on a series of venomous snake fangs using the venom pore location as a functionally relevant depth standard. After exploring variation in pore placement across snake phylogeny, we compared the work expended during puncture experiments across a set of snake fangs using various depth standards: puncture initiation, penetration to a series of depths defined by the venom pore and penetration to 15% of fang length. Contrary to our hypothesis, we found almost no pattern in pore placement between clades, dietary groups or venom toxicity. Rank correlation statistics of our experimental energetics results showed no difference in the broad comparison of fangs when different puncture depth standards were used. However, pairwise comparisons between fangs showed major shifts in significance patterns between the different depth standards used. These results imply that the interpretation of experimental puncture data will heavily depend upon which depth standard is used during the experiments. Our results illustrate the importance of understanding the biological context of the question being addressed when designing comparative experiments.

Towards Performant Design of Carbon-Based Nanomotors for Hydrogen Separation through Molecular Dynamics Simulations.

Clean energy technologies represent a hot topic for research communities worldwide. Hydrogen fuel, a prized alternative to fossil fuels, displays weaknesses such as the poisoning by impurities of the precious metal catalyst which controls the reaction involved in its production. Thus, separating H2 out of the other gases, meaning CH4, CO, CO2, N2, and H2O is essential. We present a rotating partially double-walled carbon nanotube membrane design for hydrogen separation and evaluate its performance using molecular dynamics simulations by imposing three discrete angular velocities. We provide a nano-perspective of the gas behaviors inside the membrane and extract key insights from the filtration process, pore placement, flux, and permeance of the membrane. We display a very high selectivity case (ω = 180° ps−1) and show that the outcome of Molecular Dynamics (MD) simulations can be both intuitive and counter-intuitive when increasing the ω parameter (ω = 270° ps−1; ω = 360° ps−1). Thus, in the highly selective, ω = 180° ps−1, only H2 molecules and 1–2 H2O molecules pass into the filtrate area. In the ω = 270° ps−1, H2, CO, CH4, N2, and H2O molecules were observed to pass, while, perhaps counter-intuitively, in the third case, with the highest imposed angular velocity of 360° ps−1 only CH4 and H2 molecules were able to pass through the pores leading to the filtrate area.

Thermal conductivity in disordered porous nanomembranes

In this work we study the effects of disorder on the thermal conductivity of porous 100 nm thick silicon membranes, in which the size, shape and position of the pores were varied randomly. Measurements using two-laser Raman thermometry on both non-patterned and porous membranes revealed more than a 10-fold reduction of the thermal conductivity compared to that of bulk silicon and a six-fold reduction compared to non-patterned membranes for the sample with random pore shapes. Using Monte Carlo methods we solved the Boltzmann transport equation for phonons and compared different possibilities of pore organization and its influence on the thermal conductivity of the samples. The simulations confirmed that the strongest reduction of thermal conductivity is achieved for a distribution of pores with arbitrary shapes that partially overlap. Up to a 15% reduction of the thermal conductivity with respect to the purely circular pores was predicted for a porous membrane with 37% filling fraction. The effect of the pore shape and distribution was further studied. Maps of temperature and heat flux distributions clearly showed that for particular pore placement heat transport can be efficiently blocked and hot spots can be found in narrow channels between pores. These findings have an impact on the fabrication of membrane-based thermoelectric devices, where low thermal conductivity is required. This work shows that for porous membranes with a given filling fraction the thermal conductivity can be further modified by introducing disorder in the shape and placement of the pores.

A detailed study on phonon transport in thin silicon membranes with phononic crystal nanostructures

A common method to improve thermoelectric performance is to reduce thermal conductivity by enhancing phonon scattering. In this paper, a frequency-dependent phonon radiative transport equation (PRTE) solver, based on the discrete ordinates method, is developed to simulate phonon transport in thin silicon membranes with phononic crystal nanostructures. The influence of geometric parameters on phonon transport is discussed in detail. Besides, a nonlinear regression model is attained for predicting the thermal conductivity of thin silicon membranes with phononic crystal nanostructures using the non-linear least-squares method. The results indicate that thermal conductivity is reduced by phononic crystal nanostructures mainly due to the back scattering of phonons with pore boundaries, and phonons with larger mean free path have stronger back scattering. When the pore placement is fixed, pore configuration affects phonon transport in thin silicon membranes with phononic crystal nanostructures. In addition, thermal conductivity is primarily controlled by three geometric parameters, including r⊥, r||, and Au. Moreover, the obtained regression model reveals the relationship between thermal conductivity and geometric parameters well, which can offer useful suggestions for fabricating thin silicon membranes with low thermal conductivity.

Development of dielectrophoresis separator with an insulating porous membrane using DC-Offset AC Electric Fields.

Our previous studies revealed that the dielectrophoresis method is effective for separating cells having different dielectric properties. The purpose of this study was to evaluate the separation characteristics of two kinds of cells by direct current (DC) voltage offset/alternating current (AC) voltage using an insulating porous membrane dielectrophoretic separator. The separation device gives dielectrophoretic (DEP) force and electrophoretic (EP) force to dispersed particles by applying the DC-offset AC voltage. This device separates cells of different DEP properties by adopting a structure in which only the parallel plate electrodes and the insulating porous membrane are disposed in the flow path through which the cell-suspension flows. The difference in the retention ratios of electrically homogeneous 4.5 μm or 20.0 μm diameter standard particles was a maximum of 82 points. Furthermore, the influences of the AC voltage or offset voltage on the retention ratios of mouse hybridoma 3-2H3 cells and horse red blood cells (HRBC) were investigated. The difference in the retention ratio of the two kinds of cells was a maximum of 56 points. The separation efficiency of this device is expected to be improved by changing the device shape, number of pores, and pore placement. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1292-1300, 2016.

Thermal conduction in nano-porous silicon thin film

Controlling the thermal conductivity of thermoelectric materials continues to be a goal for energy conversion applications. The Phonon Boltzmann Transport Equation is solved by using the Discrete Ordinates Method to numerically study the phonon thermal conductivity of nano-structured silicon thin film with pores in this study. The effects of the film thickness, film porosity, and porous structure are concerned. The numerical results show that the nano-pores are able to reduce the thermal conductivity of the silicon thin film sharply by the phonon boundary scattering, and the scattering boundary area has significant effect on the thermal conductivity. The method of local angle distribution between heat fluxes is introduced for the first time to optimize the pore placement for reducing the thermal conductivity.

Young’s modulus and volume porosity relationships for additive manufacturing applications

Recent advancements in additive manufacturing (or rapid prototyping) technologies allow the fabrication of end-use components with defined porous structures. For example, one area of particular interest is the potential to modify the flexibility (bending stiffness) of orthopedic implants through the use of engineered porosity (i.e., design and placement of pores) and subsequent fabrication of the implant using additive manufacturing processes. However, applications of engineered porosity require the ability to accurately predict mechanical properties from knowledge or characterization of the pore structure and the existence of robust equations characterizing the property–porosity relationships. As Young’s modulus can be altered by variations in pore shape as well as pore distribution, numerous semi-analytical and theoretical relationships have been proposed to describe the dependence of mechanical properties on porosity. However, the utility and physical meaning of many of these relationships is often unclear as most theoretical models are based on some idealized physical microstructure, and the resulting correlations often cannot be applied to real materials and practical applications. This review summarizes the evolution and development of relationships for the effective Young’s modulus of a porous material and concludes that verifiable equations yielding consistently reproducible results tied to specific pore structures do not yet exist. Further research is needed to develop and validate predictive equations for the effective Young’s modulus over a volume porosity range of 20–50 %, the range of interest over which existing equations, whether based on effective medium theories or empirical results, demonstrate the largest disparity and offers the greatest opportunity for beneficial modification of bending stiffness in orthopedic applications using currently available additive manufacturing techniques.

MOLECULAR DYNAMICS SIMULATION OF THERMAL CONDUCTION IN NANOPOROUS THIN FILMS

Molecular dynamics simulations of thermal conduction in nanoporous thin films are performed. Thermal conductivity displays an inverse temperature dependence for films with small pores and a much less pronounced dependence for larger pores. Increasing porosity reduces thermal conductivity, while pore shape has little effect except in the most anisotropic cases. The pores separate the film into local regions with distinctly different temperature profiles and thermal conductivities, and the effective film thermal conductivity is lowest when the pores are positioned in the center of the film. Such tunability by pore placement highlights new possibilities for engineering nanoscale thermal transport.

Identification of Clones within Four Tree Fruit Species by Pollen Exine Patterns1

Abstract Twenty sample clones of peach (Prunus persica [L.] Batsch) and ten clones each of nectarine (P. persica var. nectarina [Ait.] Maxim.), European plum (P. domestica L.), sweet cherry (P. avium [L.] L.) and apple (Malus domestica Borkh.) were compared by scanning electron microscope (SEM) for characteristics of their pollen exine. The 4 taxa were separated into 3 groups by pollen grain size. Exine differences distinguished apple and sweet cherry pollens, which had similar size, and separated clones within each of the species. Peach and nectarine clones varied within the same ranges of pollen size and exine characteristics. Within P. persica, two patterns of ridging and the relative frequency, depth of impression, and size of pores categorized the clones individually. Plum exine patterns were distinct from those of other tree fruits, but ridging and pore characteristics of the exine separated plum clones into distinct categories. Apple cultivars, which had the narrowest ridges, were separated by the abundance and placement of pores in the exine. Sweet cherry clones also were distinguished by exine characteristics.