John Landers

Bio: John Landers is an academic researcher from Rutgers University. The author has contributed to research in topics: Membrane & Nanoporous. The author has an hindex of 9, co-authored 20 publications receiving 1019 citations. Previous affiliations of John Landers include National Research Council & United States Department of the Army.

Density Functional Theory Methods for Characterization of Porous Materials

Abstract: This review presents the state-of-the-art of adsorption characterization of mesoporous and microporous materials by using the density functional theory (DFT) methods. The DFT methods have found numerous applications for calculating pore size distributions in traditional and newly discovered nanoporous solids. We discuss the foundations of the non-local (NLDFT) and quench solid (QSDFT) density functional theories applied for modeling adsorption and capillary condensation in pores of different geometry and surface chemistry. Special attention is paid to the limitations of the theoretical models and critical analysis of the obtained data. The methods are demonstrated on a wide variety of systems, including microporous and mesoporous carbons and silicas, zeolites, mesoporous crystals of MCM and SBA families, metal–organic frameworks, and other designer nanoporous materials. Illustrated with many typical examples and detailed discussions of the advantages and limitations of the NLDFT and QSDFT methods, this review provides guidance for the practitioners interested in getting a better understanding of the current capabilities and limitations of the adsorption methods for characterization of porous solids

Biohybrid Carbon Nanotube/Agarose Fibers for Neural Tissue Engineering.

Abstract: A novel approach for producing carbon nanotube fi bers (CNF) composed with the polysaccharide agarose is reported. Current attempts to make CNFs require the use of a polymer or precipitating agent in the coagulating bath that may have negative effects in biomedical applications. It is shown that, by taking advantage of the gelation properties of agarose, one can substitute the bath with distilled water or ethanol and, hence, reduce the complexity associated with alternating the bath components or the use of organic solvents. It is also demonstrated that these CNF can be chemically functionalized to express biological moieties through available free hydroxyl groups in agarose. Agarose CNF are not only conductive and nontoxic; in addition, their functionalization is shown to facilitate cell attachment and response both in vitro and in vivo. Our fi ndings suggest that agarose/CNT hybrid materials are excellent candidates for applications involving neural tissue engineering and biointerfacing with the nervous system.

Insight into the Effect of Dealumination on Mordenite Using Experimentally Validated Simulations

Abstract: Mordenite (MOR-type zeolite) is a widely used catalyst, in particular for (hydro-) isomerization and alkylation reactions in the petrochemical industry. However, having a one-dimensional micropore system, this material is susceptible to diffusion limitations and deactivation. To circumvent this problem, typically additional (meso)porosity is created by applying dealumination and/or steaming processes. The detailed description of the dealumination process is of crucial importance to understand how mordenite can be modified into an efficient catalyst. In this work, we present for the first time a simulation model to describe the influence of the dealumination process on the structural properties of mordenite. Using kinetic Monte Carlo simulations, dealumination is described as a multiple-step process consisting of the removal of the framework Al as well as the self-healing of silanol nests by Si atoms. The simulation results are in very good agreement with experimental results from 29Si NMR, XRD, and N2 and...

Carbon Nanotube Composites as Multifunctional Substrates for In Situ Actuation of Differentiation of Human Neural Stem Cells

Abstract: Despite the promise of human neural stem cells (hNSCs) as an emerging cell source for neural tissue engineering, hNSC applications are hindered by the lack of advanced functional biomaterials that can promote cell adhesion, survival, and differentiation while also integrating neuronal stimulatory cues, specifically electrical stimulation. Electrospun fibrous substrates with controlled fiber architectures provide topographical cues to cells by presenting three dimensional (3-D) geometries that are representative of the extracellular matrix (ECM),1 defined by a high surface-to-volume ratio and porosity, and are thus better suited for differentiation studies of neural stem cells than standard two dimensional substrates. The architecture of ECM is of special importance because it supports 3 -D cellular networks together to form a tissue, allows for the proliferation and growth of cells, and regulates cellular processes capable of enhancing neurite outgrowth and neuronal differentiation of several cell types, including embryonic stem cells and hESC-derived NSCs2-6. Furthermore the inherently high surface to volume ratio of electrospun polymer substrates can facilitate mass transfer of nutrients and waste, promote cell attachment, and enable drug loading, properties that are inherent to bioactive matrix microniches. For stem cells, conductive substrates can promote neuronal maturation by providing electrical shortcuts between developing cells, while also permitting application of electrical stimuli that can mimic the electrophysiological environment experienced by cells in a variety of biological processes, including muscle contraction, wound healing, and synaptic transmission7-12. In addition to enhancing neurite outgrowth and neuronal maturation, applied electrical stimulation may also direct neural stem cell migration, opening the possibility to guide these cells towards injured sites8. Various methods of delivering electrical stimulation to cells in culture include 2 -dimensional (2-D) substrates such as etched ITO glass13 and conductive polymers1, 14-19 like polypyrrole17. However, the use of conductive polymers alone is impeded by their poor processability, electroactive stability, and mechanical properties after doping20, 21. Another alternative has emerged involving nanocarbon materials such as carbon nanotubes (CNT)22, 23 and graphene24. In particular, single-walled carbon nanotubes (SWNT) have been employed due to their inherently high conductivity and the ability to regulate neuronal behavior both structurally and functionally25. Along with their biocompatibility at low concentrations, SWNT are ideal candidates for biomedical composites26, 27. It has been shown that SWNT interfaced with neural cells can promote neuron growth28-30 and enhance differentiation of NSCs into neurons31, 32. This is likely a result of a combination of topographical cues, enhanced signal transmission from the tight contacts formed between the SWNTs and the neuron membranes, and differential production of ECM proteins that modulate synaptic stability7, 32-34. While multi-walled carbon nanotubes (MWNTs) have been incorporated into electrospun fibers35, the incorporation of SWNTs into fibrous composite substrates that mimic the ECM has proved challenging36. The use of SWNTs during the electrospinning process could be circumvented altogether if the SWNT incorporation or deposition can be designed post facto, thus avoiding any bulk modification of the substrate properties and thereby retaining the SWNT bio-interfacial features. Doing so yields the additional benefit of using insulating polymers, already extensively used for differentiation studies, and thereby providing grounds for the use of highly biocompatible substrates. Other methods to do so have included spraying SWNT onto substrates37, layer-by-layer deposition (LbL)31, 38 and the attachment of SWNT to self assembled monolayers (SAM)39. In the first method, the growth of SWNT on the substrates can leave behind unwanted catalyst particles detrimental to cell viability. Regarding the latter two methods, enhancement of the differentiation kinetics has been reported with mouse embryonic stem cells by the LbL31 approach and with immortalized human neural stem cells via SAM40 approach, neither of which makes use of electrical stimulation. This study is the first demonstration of electrically actuated SWNT-based composites for differentiation of human neural stem cells. We fabricated extracellular matrix-mimetic, composites by vacuum impregnation of electrospun poly(lactic-co-glycolic acid) (PLGA) membranes with single-walled carbon nanotubes (SWNTs) and investigated the ability of these substrates to enhance differentiation of induced pluripotent stem cell (iPSC)-derived NSCs. The SWNT-polymer substrates are electrically conductive, mechanically robust, and highly biocompatible with human NSC cultures in vitro and showed enhanced levels of electrically responsive cells. Notably, changes in the expression of two major neuronal markers, Neurofilament M (NFM) and microtubule -associated protein-2 (MAP2) of 14-day cultures showed that the composite enhanced neuronal differentiation of NSCs compared to PLGA controls without SWNT. To further utilize the multifunctional nature of SWNT-PLGA to affect neurogenesis, early NSC cultures on SWNT-PLGA were subjected to a 10 minute, 30μA direct current regimen of electrical stimulation. The electrical stimulation markedly increased neuronal differentiation after 14 days. These results highlight the multifunctionality of SWNT-PLGA, which afford a fibrous topography with high surface area to volume ratios to help to organize neuronal networks, along with the ability to exploit electro-conductivity to stimulate neuronal induction and neuronal maturation.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Quantum-mechanical condensed matter simulations with CRYSTAL

Abstract: The latest release of the Crystal program for solid-state quantum-mechanical ab initio simulations is presented. The program adopts atom-centered Gaussian-type functions as a basis set, which makes it possible to perform all-electron as well as pseudopotential calculations. Systems of any periodicity can be treated at the same level of accuracy (from 0D molecules, clusters and nanocrystals, to 1D polymers, helices, nanorods, and nanotubes, to 2D monolayers and slab models for surfaces, to actual 3D bulk crystals), without any artificial repetition along nonperiodic directions for 0–2D systems. Density functional theory calculations can be performed with a variety of functionals belonging to several classes: local-density (LDA), generalized-gradient (GGA), meta-GGA, global hybrid, range-separated hybrid, and self-consistent system-specific hybrid. In particular, hybrid functionals can be used at a modest computational cost, comparable to that of pure LDA and GGA formulations, because of the efficient implementation of exact nonlocal Fock exchange. Both translational and point-symmetry features are fully exploited at all steps of the calculation, thus drastically reducing the corresponding computational cost. The various properties computed encompass electronic structure (including magnetic spin-polarized open-shell systems, electron density analysis), geometry (including full or constrained optimization, transition-state search), vibrational properties (frequencies, infrared and Raman intensities, phonon density of states), thermal properties (quasi-harmonic approximation), linear and nonlinear optical properties (static and dynamic [hyper]polarizabilities), strain properties (elasticity, piezoelectricity, photoelasticity), electron transport properties (Boltzmann, transport across nanojunctions), as well as X-ray and inelastic neutron spectra. The program is distributed in serial, parallel, and massively parallel versions. In this paper, the original developments that have been devised and implemented in the last 4 years (since the distribution of the previous public version, Crystal14, occurred in December 2013) are described.