Newtonian flow inside carbon nanotube with permeable boundary taking into account van der Waals forces

Here, water flow inside large radii semi-infinite carbon nanotubes is investigated. Permeable wall taking into account the molecular interactions between water and a nanotube, and the slip boundary condition will be considered. Furthermore, interactions among molecules are approximated by the continuum approximation. Incompressible and Newtonian fluid is assumed, and the Navier-Stokes equations, after certain assumptions, transformations and derivations, can be reduced into two first integral equations. In conjunction with the asymptotic expansion technique, we are able to derive the radial and axial velocities analytically, capturing the effect of the water leakage, where both mild and exceptionally large leakages will be considered. The radial velocity obeys the prescribed boundary condition at the (im)permeable wall. Through the mean of the radial forces, the sufficiently large leakages will enhance the radial velocity at the center of the tube. On the other hand, unlike the classical laminar flow, the axial velocity attains its maximum at the wall due to the coupling effect with the radial forces as water is being pushed into the proximity of the inner wall. In addition, the axial velocity and the flux with the consideration of the suck-in forces, induced by the tubes’ entry turn out to be one order higher than that without the suck-in forces. All the aforementioned considerations might partially resolve the mysteriously high water penetration through nanotubes. Axial velocity also drops with the tube’s length when the water leakage is permitted and the suck-in forces will ease the decline rate of the axial velocity. The present mathematical framework can be directly employed into the water flow inside other porous nano-materials, where large water leakage is permitted and therefore are of huge practical impact on ultra-filtration and environmental protection

Trends in template/fragment-free protein structure prediction

Predicting the structure of a protein from its amino acid sequence is a long-standing unsolved problem in computational biology. Its solution would be of both fundamental and practical importance as the gap between the number of known sequences and the number of experimentally solved structures widens rapidly. Currently, the most successful approaches are based on fragment/template reassembly. Lacking progress in template-free structure prediction calls for novel ideas and approaches. This article reviews trends in the development of physical and specific knowledge-based energy functions as well as sampling techniques for fragment-free structure prediction. Recent physical- and knowledge-based studies demonstrated that it is possible to sample and predict highly accurate protein structures without borrowing native fragments from known protein structures. These emerging approaches with fully flexible sampling have the potential to move the field forward

Syndromics: A Bioinformatics Approach for Neurotrauma Research

Substantial scientific progress has been made in the past 50 years in delineating many of the biological mechanisms involved in the primary and secondary injuries following trauma to the spinal cord and brain. These advances have highlighted numerous potential therapeutic approaches that may help restore function after injury. Despite these advances, bench-to-bedside translation has remained elusive. Translational testing of novel therapies requires standardized measures of function for comparison across different laboratories, paradigms, and species. Although numerous functional assessments have been developed in animal models, it remains unclear how to best integrate this information to describe the complete translational “syndrome” produced by neurotrauma. The present paper describes a multivariate statistical framework for integrating diverse neurotrauma data and reviews the few papers to date that have taken an information-intensive approach for basic neurotrauma research. We argue that these papers can be described as the seminal works of a new field that we call “syndromics”, which aim to apply informatics tools to disease models to characterize the full set of mechanistic inter-relationships from multi-scale data. In the future, centralized databases of raw neurotrauma data will enable better syndromic approaches and aid future translational research, leading to more efficient testing regimens and more clinically relevant findings

The effect of intertube van der Waals interaction on the stability of pristine and functionalized carbon nanotubes under compression

This paper investigates the effect of intertube van der Waals interaction on the stability of pristine and covalently functionalized carbon nanotubes under axial compression, using molecular mechanics simulations. After regulating the number of inner layers of the armchair four-walled (5, 5)at(10, 10)at(15, 15)at(20, 20) and zigzag four-walled (6, 0)at(15, 0)at(24, 0)at(33, 0) carbon nanotubes, the critical buckling strains of the corresponding tubes are calculated. The results show that each of the three inner layers in the functionalized armchair nanotube noticeably contributes to the stability of the outermost tube, and together increase the critical strain amplitude by 155%. However, the three inner layers in the corresponding pristine nanotube, taken together, increase the critical strain of the outermost tube by only 23%. In addition, for both the pristine and functionalized zigzag nanotubes, only the (24, 0) layer, among the three inner layers, contributes to the critical strain of the corresponding outermost tube, by 11% and 29%, respectively. The underlying mechanism of the enhanced stability related to nanotube chirality and functionalization is analyzed in detail. © 2010 IOP Publishing Ltd.link_to_subscribed_fulltex

A Continuum Model of the Van der Waals Interface for Determining the Critical Diameter of Nanopumps and its Application to Analysis of the Vibration and Stability of Nanopump Systems

Carbon nanotubes make ideal nanopumps for the transport of fluid. To analyze the vibration and stability of nanopump systems with inner fluid effectively, it is necessary to incorporate nanoscale effects into continuum-based simulations. This paper first proposes a continuum model for the van der Waals (vdW) interface between a single-wall carbon nanotube (SWCNT) and incompressible inner fluid to determine the critical tube diameter above which continuum fluid mechanics may be reasonably applied to that inner fluid. Then, with overall consideration of the scale effects, including the nonlocal effects of the carbon nanotube, the surface tension of the inner fluid and the vdW interface, an improved Euler beam/plug fluid model is developed to investigate the vibration and stability of the nanopump system. The two models are both validated by comparing with molecular dynamic simulations. The results show that the critical diameter for water flow is about 1.8 nm. Nanopump stability is noticeably enhanced by the surface tension of the inner fluid for a high slenderness ratio. Both coaxial vibration frequency and stability decline as the system temperature is increased. Moreover, the proposed models predict that the transverse vibration of the inner fluid inside a nearly rigid SWCNT occurs due to the existence of the vdW interface gap and the negligible bending rigidity of the fluid. ©Freund Publishing House Ltd.link_to_subscribed_fulltex

Self-assembly of carbon nanotubes and boron nitride nanotubes into coaxial structures

Coaxial carbon nanotube/boron nitride nanotube (CNT/BNNT) multi-walled structures are ideal components in nanoelectronic systems. Our molecular dynamics simulations show that separate CNTs and BNNTs can self-assemble into stable coaxial structures in water under appropriate conditions. In case study three types of representative coaxial structures: (5, 5) CNT/(10, 10) BNNT, (5, 5) BNNT/(10, 10) CNT and (5, 5) BNNT/(10, 10) BNNT are obtained. Simulation results also reveal that the self-assembly time between two separate BNNTs is increased remarkably due to the polarization of BNNTs in water. The mechanism of self-assembly among these tubes is demonstrated in detail. Further, coaxial (10, 10) BNNT/(10, 10) CNT/(15, 15) BNNT nanoheterojunctions are achieved for potential application in nanoelectronic systems. The present work shows the feasibility to fabricate the coaxial nanodevices such as insulating high-strength cables, high frequency oscillators and nanojunctions using self-assembly approach. © 2010 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Theoretical and experimental studies on the electric impedance of active piezoelectric sensors bonded on cracked beams

The electric impedance of symmetrically surface-bonded piezoelectric sensors on a cracked beam is studied. To investigate the effect of the crack on the electric impedance in a convenient fashion, an analytical expression is derived that is correlated to the physical parameters of the crack and the host beam. The beam segment covered with piezoelectric patches and the cracked region are regarded as a bimorph segment and an equivalent spring, respectively, and the entire beam system is then represented by three elastic beam segments and a bimorph segment together with the spring. Electric impedance experiments are also conducted for uncracked beams and for cracked beams with single-edge or double-edge cracks. The experimental results agree with those generated by the analytical expression. The crack depth has little effect on the corresponding mode frequency for cracks located at the mode node of a beam. For cracks located away from the mode node, the corresponding mode frequency decreases as the crack depth increases. Moreover, the closer the crack to the anti-node of the mode, the greater the decrease in the corresponding mode frequency. The mechanism of these changes is discussed. The findings should prove helpful for structural health monitoring using active piezoelectric sensors. © IOP Publishing Ltd.link_to_subscribed_fulltex