Narrow Carbon Research Articles

Combining simulation and on-line measurements to determine moisture transport dynamics throughout the heatset offset printing process

The aim of the study was to explain the transportation of liquid (fountain solution) during transfer to coated paper in the heatset offset printing process, together with the subsequent drying of the printed paper, by using statistical and experimental methods.A coating dispersion, applied as a single coating onto a fine paper substrate, was formulated using a narrow fine particle size distribution natural ground calcium carbonate pigment and a styrene acrylic binder. The moisture variation in the paper during printing was monitored by using online multipoint sensors based on near-infrared diffuse reflectance spectroscopy. Based on the results, a simulation model was created to determine the transfer of liquid thin films in the printing units, the evaporation in the printing units, followed by liquid absorption and evaporation in the heatset offset drying process. An accurate simulation depends on precise determination of the different process parameters that influence these factors.The absolute liquid/moisture amount transferred to the paper showed an increased trend as the paper passed through the application nips, though the proportion varied due to limited capillary absorption capacity properties of the paper. The background evaporation in the printing nips was evaluated with the simulation model as well as the drying stages in the dryer including surface and bulk condensation followed by rapid evaporation and cooling.

Displacement of Methane by Coadsorbed Carbon Dioxide Is Facilitated In Narrow Carbon Nanopores

By using simulation methods, we studied the adsorption of binary CO2–CH4 mixtures on various CH4 preadsorbed carbonaceous materials (e.g., triply periodic carbon minimal surfaces, slit-shaped carbon micropores, and Harris’s virtual porous carbons) at 293 K. Regardless of the different micropore geometry, two-stage mechanism of CH4 displacement from carbon nanospaces by coadsorbed CO2 has been proposed. In the first stage, the coadsorbed CO2 molecules induced the enhancement of CH4 adsorbed amount. In the second stage, the stronger affinity of CO2 to flat/curved graphitic surfaces as well as CO2–CO2 interactions cause the displacement of CH4 molecules from carbonaceous materials. The operating conditions of CO2-induced cleaning of the adsorbed phase from CH4 mixture component strongly depend on the size of the carbon micropores, but, in general, the enhanced adsorption field in narrow carbon ultramicropores facilitates the nonreactive displacement of CH4 by coadsorbed CO2. This is because in narrow carbon ultramicropores the equilibrium CO2/CH4 selectivity (i.e., preferential adsorption toward CO2) increased significantly. The adsorption field in wider micropores (i.e., the overall surface energy) for both CO2 and CH4 is very similar, which decreases the preferential CO2 adsorption. This suppresses the displacement of CH4 by coadsorbed CO2 and assists further adsorption of CH4 from the bulk mixture (i.e., CO2/CH4 mixing in adsorbed phase).

Design and development of thick plate concept for rotatable plugs and technology development for future Indian FBR

► Thick plate concept and design for rotatable plugs of future Indian FBR described. ► Salient aspects of 800 mm thick plate welding technology development presented. ► Non-destructive examination (NDE) and destructive testing aspects discussed. ► Ultrasonic wave is attenuated less in narrow gap carbon steel weld than base metal. ► Recommendation made regarding RCC-MR code rules for NDE of carbon steel weld. Prototype fast breeder reactor (PFBR) is at an advanced stage of construction in Kalpakkam, India. Top shield (consisting of roof slab and rotatable plugs) of PFBR is of box type construction. It is a Class-1 component being a part of the primary leak-tight boundary of the reactor assembly. In the future commercial fast breeder reactor (CFBR), it is planned to adopt thick plate concept for rotatable plugs. The thickness of the plates required for the rotatable plugs of CFBR was arrived at based on finite element analysis considering mechanical and thermal loads. The main advantage of using thick plate for the rotatable plugs is that it eliminates the possibility of lamellar tearing which exists in the box type construction. The successful realisation of this concept necessitates the indigenous development of thick plate narrow gap welding technology. Hence a technology development programme for realising 800 mm thick narrow gap welds using submerged arc welding process was undertaken. Three numbers of welded joints were made to demonstrate the successful development of thick plate narrow gap welding technology. Repair procedure for the weld was also established. Non-destructive examination and destructive testing were carried out and the results were analysed critically. The attenuation of ultrasonic wave in narrow gap weld as compared to that in the base metal was examined. This paper discusses the need and conceptual design of thick plate concept for rotatable plugs in CFBR, the approach adopted for technology development of thick plate narrow gap welding and the salient experiences gained during the developmental project. Recommendations are made regarding the RCC-MR code rules for the non-destructive volumetric examination of welds of thick carbon steel plates.

Molecular wire of urea in carbon nanotube: a molecular dynamics study

We perform molecular dynamics simulations of narrow single-walled carbon nanotubes (SWNTs) in aqueous urea to investigate the structure and dynamical behavior of urea molecules inside the SWNT. Even at low urea concentrations (e.g., 0.5 M), we have observed spontaneous and continuous filling of SWNT with a one-dimensional urea wire (leaving very few water molecules inside the SWNT). The urea wire is structurally ordered, both translationally and orientationally, with a contiguous hydrogen-bonded network and concerted urea's dipole orientations. Interestingly, despite the symmetric nature of the whole system, the potential energy profile of urea along the SWNT is asymmetric, arising from the ordering of asymmetric urea partial charge distribution (or dipole moment) in confined environment. Furthermore, we study the kinetics of confined urea and find that the permeation of urea molecules through the SWNT decreases significantly (by a factor of ∼20) compared to that of water molecules, due to the stronger dispersion interaction of urea with SWNT than water, and a maximum in urea permeation happens around a concentration of 5 M. These findings might shed some light on the better understanding of unique properties of molecular wires (particularly the wires formed by polar organic small molecules) confined within both artificial and biological nanochannels, and are expected to have practical applications such as the electronic devices for signal transduction and multiplication at the nanoscale.

Confinement induced conformational changes in n-alkanes sequestered within a narrow carbon nanotube

While alkanes in solution exhibit predominantly extended conformations, nanoscale confinement of these chains within protein binding sites and synthetic receptors can significantly alter the conformer distribution. As a simple model for the effect of confinement on the conformation, we report molecular simulations of n-alkanes absorbed from a bulk solvent into narrow carbon nanotubes. We observe that confinement of butane, hexane, and tetracosane induces a trans to gauche conformational redistribution. Moreover, confined hexane and tetracosane exhibit cooperative interactions between neighboring dihedral angles, which promote a helical gauche conformation for the portions of the chain within the nanotube. Hexane absorbed into the nanotube from water or benzene exhibits essentially the same conformation regardless of the bulk solvent. The PMF between the nanotube and hexane along the central nanotube axis finds that nanotube absorption is favorable from aqueous solution but neutral from benzene. The interaction between hexane and the nanotube in water is dominated by the direct interaction between the alkane and the nanotube and weakly opposed by indirect water-mediated forces. In benzene, however, the direct alkane/nanotube interaction is effectively balanced by the indirect benzene-mediated interaction. Our simulations in water stand in difference to standard interpretations of the hydrophobic effect, which posit that the attraction between non-polar species in water is driven by their mutual insolubility.

Physical characterization of activated carbons with narrow microporosity by nitrogen (77.4 K), carbon dioxide (273 K) and argon (87.3 K) adsorption in combination with immersion calorimetry

In order to get more insight into the characterization of nanoporous carbons by gas adsorption, the use of different probe molecules has been compared. A series of activated carbons with ranging porosity (burn-off) have been prepared from olive stones using CO2 as activating agent and characterized using nitrogen and argon adsorption at low temperature (77.4K for N2 and 87.3K for Ar) together with CO2 adsorption at 273K and immersion calorimetry into liquids of different molecular dimensions. Experimental results show that argon adsorption in narrow carbon micropores takes place at a higher relative pressure compared to nitrogen due to a weaker effective adsorption potential (lower strength of dispersion forces), including the absence of specific interactions of argon with the adsorbent surface. We show further that application of advanced theoretical approaches based on the density functional theory (NLDFT and QSDFT) provides an accurate description of the pore-size distribution (PSD). The PSD obtained from the argon adsorption data at 87.3K is in good agreement with immersion calorimetry measurements. Our results demonstrate that argon adsorption at 87.3K in combination with the application of advanced DFT methods (e.g. QSDFT) allows for a reliable characterization of the narrow microporosity in highly heterogeneous activated carbons.

Origin of Giant Ionic Currents in Carbon Nanotube Channels

Fluid flow inside carbon nanotubes is remarkable: transport of water and gases is nearly frictionless, and the small channel size results in selective transport of ions. Very recently, devices have been fabricated in which one narrow single-walled carbon nanotube spans a barrier separating electrolyte reservoirs. Ion current through these devices is about 2 orders of magnitude larger than predicted from the bulk resistivity of the electrolyte. Electroosmosis can drive these large excess currents if the tube both is charged and transports anions or cations preferentially. By building a nanofluidic field-effect transistor with a gate electrode embedded in the fluid barrier, we show that the tube carries a negative charge and the excess current is carried by cations. The magnitude of the excess current and its control by a gate electrode are correctly predicted by the Poisson-Nernst-Planck-Stokes equations.

Sedimentación y paleogeografía del Cretacico y Cenozoico del Litoral Pacifico de Costa Rica

The systematic stratigraphy of the Pacific littoral of Costa Rica has been reorganized in three supergroups: 1. Papagayo: mafic and ultramafic oceanic basements and volcanicaIly or tectonically associated sediments. 2. Garza: oceanic sedimentary cover including pelagics (Sabana Grande Group) and slope deposits (Samara Group). 3. Mal Pais: neritic sedimentary cover, subdivided into 5 epochs. A major, upper Santonian tectonic event divides the geologic history into two phases: 1. The Nicoya Complex with its Bathonian/Callovian Santonian (BAUMGARTNER 1984) oceanic sedimentary cover and the Santa Elena Peridotite form together a nappe edifice with a southern vergence (BOURa15— et al. in press). 2. Since the Campanian, this structure is part of the stable isthmic crust, the substrate of the studied upper Senonian-Cenozoic sedimentary sequen ces, affected by open folding and normal faulting only. No accretionary struc-tures related to subduction along the Middle-American Trench, effective since ttat latest Senonian, have been observed. Ocean floor continued te form during the latest Senonian-early Paleocene in a primitive island arc environment (Que-pos, Osa). Campanian-middle Eocene pelagic (and background) sedimentation followed the paleooceanographic trends observed in the Pacific, amplified by local (equatorial, eastern ocean margin) high fertility. A shallow CCD is reflected by Santonian-lower Campanian and upper Paleocen-middle Eocene radiolarian-rich siliceous deposits. In the late Campanian-Maestrichtian a drastic drop of the CCD overruled subsidence and resulted in deposition of foraminifer-rich pelagic limestones. Thick Maestrichtian-Paleocene turbidite and mass flow sequences were deposited in YW-SE trending elongate basins and document the erosion of an emerged andesitic volcanic are, che product of active subduction, surrounded by narrow carbonate and silicic/astio shelves, set aboye steep, unstable slopes. A tectonic event at the middleilate ocene boundary caused mayor gravitative s/iding and slumping of the upper part of the oceanic sequence, subsequent uplift and a regional, unconformable onset of shallow carbonate deposition, while turbiditc sedimentation persisted in some arcas (Santa Elena, Quepos). An inferred thickened oceanic crust in isostatic equilibrium should form a sea floor at subphotie depths. However, tectonie uplift has repeatdly brought the substrate te shallow depth and allowed the deposition of unconformable, thin, shortlived, neritic sequences, forffied during five succesive epochs: Epoch 1. Campanian-Maestriehtian: The structurally highest parts of the upper Santonian orogen were uplifted te subaerial and shallow photic depths where rudis-tid limestones developed. Epoch 2. Paleocene-early Encone: Voleanic activity related tu subduction gave rise tu an island are surrounded by shallow platforms NE of the study area, only known from reworked carbonate elasts in slope deposits (Samara, Quepos). Epoch 3. Middle-late Eoeene: Tectonic uplift brought most of the area tu shallow photic depth which led tu the formation uf the widespread largor foramini-fer - red algal limestones. Epoch 4. Oligocene-early Miocene: Most of the central area was emerged and only near the trench (Nosara-Mal Pais) thin shallow clastic sequences developed, while turbidite basins persisted in the NW and SE (Dept. Rivas, Nicaragua, Fila Costena). Epoch 5. Late Miocene-Pleistocene: Littoral deposits are concentrated around the south of Nieoya, in areas of recent uplift (FISCHER 1980).

Nanoconfinement effects on the reversibility of hydrogen storage in ammonia borane: A first-principles study

We investigate atomistic mechanisms governing hydrogen release and uptake processes in ammonia borane (AB) within the framework of the density functional theory. In order to determine the most favorable pathways for the thermal inter-conversion between AB and polyaminoborane plus H(2), we calculate potential energy surfaces for the corresponding reactions. We explore the possibility of enclosing AB in narrow carbon nanotubes to limit the formation of undesirable side-products such as the cyclic compound borazine, which hinder subsequent rehydrogenation of the system. We also explore the effects of nanoconfinement on the possible rehydrogenation pathways of AB and suggest the use of photoexcitation as a means to achieve dehydrogenation of AB at low temperatures.

A comparative assessment of biofiltration and activated sludge diffusion for odour abatement

The deodorization performance of a biofilter and an activated sludge diffusion (AS) system was comparatively evaluated in terms of removal efficiency (RE) and process stability at empty bed residence times (EBRT) ranging from 94 to 32 s. Both bioreactors were fed with a synthetic odorous emission containing H 2S, butanone and toluene at 23.6–43.3, 4.3–6.3 and 0.4–0.6 mg m −3, respectively. While the outlet H 2S concentration was always lower than 1.4 mg m −3, the REs for butanone and toluene remained higher than 95% in both bioreactors regardless of the EBRT. The continuous supply of wastewater in the AS unit did not affect removal and appeared to be a requirement for efficient pollutant abatement. Despite the narrow carbon source spectrum treated, the AS system maintained a large bacterial diversity over time. Therefore, the results obtained confirmed the potential of AS systems as a robust and efficient biotechnology for odour treatment in WWTPs.

Multicomponent ballistic transport in narrow single wall carbon nanotubes: Analytic model and molecular dynamics simulations

The transport of gas mixtures through molecular-sieve membranes such as narrow nanotubes has many potential applications, but there remain open questions and a paucity of quantitative predictions. Our model, based on extensive molecular dynamics simulations, proposes that ballistic motion, hindered by counter diffusion, is the dominant mechanism. Our simulations of transport of mixtures of molecules between control volumes at both ends of nanotubes give quantitative support to the model's predictions. The combination of simulation and model enable extrapolation to longer tubes and pore networks.

Quantum fluctuations increase the self-diffusive motion of para-hydrogen in narrow carbon nanotubes

Quantum fluctuations significantly increase the self-diffusive motion of para-hydrogen adsorbed in narrow carbon nanotubes at 30 K comparing to its classical counterpart. Rigorous Feynman's path integral calculations reveal that self-diffusive motion of para-hydrogen in a narrow (6,6) carbon nanotube at 30 K and pore densities below ∼29 mmol cm(-3) is one order of magnitude faster than the classical counterpart. We find that the zero-point energy and tunneling significantly smoothed out the free energy landscape of para-hydrogen molecules adsorbed in a narrow (6,6) carbon nanotube. This promotes a delocalization of the confined para-hydrogen at 30 K (i.e., population of unclassical paths due to quantum effects). Contrary the self-diffusive motion of classical para-hydrogen molecules in a narrow (6,6) carbon nanotube at 30 K is very slow. This is because classical para-hydrogen molecules undergo highly correlated movement when their collision diameter approached the carbon nanotube size (i.e., anomalous diffusion in quasi-one dimensional pores). On the basis of current results we predict that narrow single-walled carbon nanotubes are promising nanoporous molecular sieves being able to separate para-hydrogen molecules from mixtures of classical particles at cryogenic temperatures.

Kinetics of water filling the hydrophobic channels of narrow carbon nanotubes studied by molecular dynamics simulations

The kinetics of water filling narrow single-walled carbon nanotubes was studied using molecular dynamics simulations. The time required to fully fill a nanotube was linear with respect to the tube length. We observed that water molecules could enter into nanotubes of different lengths, either from one end or from both ends. The probability of having a nanotube filled completely from both ends increased exponentially with the tube length. For short tubes, filling usually proceeded from only one end. For long tubes, filling generally proceeded from both tube ends over three stages, i.e., filling from one end, filling from both ends, and filling from both ends with the dipole reorientation of water molecules to give a concerted ordering within the fully filled tube. The water molecules in the partially filled nanotube were hydrogen bonded similarly to those in the fully filled nanotube. Simulations for the reference Lennard-Jones fluid without hydrogen bonds were also performed and showed that the filling behavior of water molecules can be attributed to strong intermolecular hydrogen bonding.

Different possible hydrogenation in narrow SWCNTs and their electronic characteristics

Density functional theory (DFT) calculations have been employed for a systematic study of electronic dispersion and morphologic characteristics (length and angle of chemical bonds) of bare and hydrogenated narrow zigzag single walled carbon nanotubes (SWCNTs), d < 7 Å. For these narrow tubes, the “band gap” and the bond character show a strong dependence on the diameter of the tubes. Our results show that exo-hydrogenation changes the band gap substantially. The gap shows essential dependence on the coverage of the exo-hydrogenation and increases with decreasing tube diameter. These properties can be useful in sensing and characterising applications. However, endo-hydrogenation in wider tubes occurs mainly by storing H 2 gas molecules inside them and their electronic structure changes slightly whereas for very narrow tubes, there is an interplay between the curvature and chirality effects. The nature of hydrogen adsorption in these cases can be a mixture of the internal C–H bonds and H 2 molecules and existence of free atomic hydrogen gas inside the tubes cannot be ruled out.

Single-particle and collective dynamics of methanol confined in carbon nanotubes: acomputer simulation study

We present the results of computer simulations of methanol confined in carbon nanotubes.Different levels of confinement were identified as a function of the nanotube radiusand characterized using a pair-distribution function adapted to the cylindricalgeometry of these systems. Dynamical properties of methanol were also analysed as afunction of the nanotube size, both at the level of single-particle and collectiveproperties. We found that confinement in narrow carbon nanotubes strongly affects thedynamical properties of methanol with respect to the bulk phase, due to thestrong interaction with the carbon nanotube. In the other cases, confined methanolshows properties quite similar to those of the bulk phase. These phenomena arerelated to the peculiar hydrogen bonded network of methanol and are compared tothe behaviour of water confined in similar conditions. The effect of nanotubeflexibility on the dynamical properties of confined methanol is also discussed.

PH-Tunable Ion Selectivity in Carbon Nanotube Pores

The selectivity of ion transport in nanochannels is of primary importance for a number of physical, chemical, and biological processes ranging from fluid separation to ion-channel-regulated cellular processes. Fundamental understanding of these phenomena requires model nanochannels with well-defined and controllable structural properties. Carbon nanotubes provide an ideal choice for nanofluidic studies because of their simple chemistry and structure, the atomic scale smoothness and chemical inertness of the graphitic walls, and the tunability of their diameter and length. Here, we investigate the selectivity of single and, for the first time, binary salt mixtures transport through narrow carbon nanotubes that act as the only pores in a silicon nitride membrane. We demonstrate that negatively charged carboxylic groups are responsible for the ion rejection performance of carbon nanotube pores and that ion permeation of small salts can be tuned by varying solution pH. Investigation of the effect of solution composition and ion valences for binary electrolytes with common cation in a pressure-driven flow reveals that the addition of slower diffusing multivalent anions to a solution of faster diffusing monovalent anions favors permeation of the monovalent anion. Larger fractions and valences of the added multivalent anions lower the rejection of the monovalent anion. In some cases, we observe negative rejection at low monovalent ion content.

Spin Controlling in Narrow Zigzag Silicon Carbon Nanoribbons by Carrier Doping

By means of first-principles calculations we predict that it is possible to manipulate the magnetization and magnetization direction in narrow zigzag silicon carbon nanoribbons (ZSiC NRs) by carrier (hole and electron) doping. Without doping, the ground state of the ZSiC NRs wider than 0.6 nm is ferrimagnetic with local magnetic moments at the edge atoms C and Si that are passivated by the hydrogen atoms, and their orientations are parallel at each zigzag edge and are antiparallel between the two edges. Consequently, the magnetic moment per cell of the ZSiC NR is almost zero. It is found that the hole doping enhances the local magnetic moment at the edge C atoms, but weakens the local magnetic moment at the edge Si atoms. As a result, the ZSiC NR is magnetized, and the magnetization direction conforms to the local magnetic moment at the edge C atoms. In contrast, the electron doping weakens the local magnetic moment at the edge C atoms, while it enhances the local magnetic moment at the edge Si atoms. As a result, the ZSiC NR is also magnetized, and the magnetization direction conforms to the local magnetic moment at the edge Si atoms. Thus, the magnetization direction of the ZSiC NRs depends on the type of carrier doping.

A Quasi-One-Dimensional Model for a Chain of Water Molecules on the Nanometer Scale

Water confined into the interior channels of narrow carbon nanotubes or transmembrane proteins can form collectively oriented molecular chains held together by tight hydrogen bonds. We develop a quasi-one-dimensional model for a chain of water molecules which interact with each other via the Coulomb and power-like repulsive interactions. We explore the equilibrium property of the water chain and derive an exact analytical expression for the total interaction energy of the water chain, denoted by W(0)int. It is found that W(0)int is minimal when the distance between the two neighboring water molecules in a hydrogen-bonded chain is equal to 0.265nm. The model is expected to be useful for studying analytically the properties of single-file water molecules inside water channels, such as the concerted motion of water molecules.

Single-File Diffusion of Water Inside Narrow Carbon Nanorings

We use atomistic molecular dynamics (MD) simulations to study the diffusion of water molecules confined inside narrow (6,6) carbon nanorings. The water molecules form two oppositely polarized chains. It is shown that the effective interaction between these two chains is repulsive in nature. The computed mean-squared displacement (MSD) clearly shows a scaling with time Deltatheta(2)(t) approximately t(1/2), which is consistent with single-file diffusion (SFD). The time up to which the water molecules undergo SFD is shown to be the lifetime of the water molecules inside these chains. Simulations of "uncharged" water molecules inside the nanoring show the formation of several water chains and yield SFD. These observations conclusively prove that the diffusion is Fickian when there is a single chain of water and SFD is observed only when two or more chains are present.

First-principles study of ultrathin (2×2) Gd nanowires encapsulated in carbon nanotubes

Using density-functional calculations, we investigate the structural and magnetic properties of ultrathin Gd and Gd-carbide nanowires (NWs) encapsulated in narrow carbon nanotubes (CNTs). The equilibrium geometry of an encapsulated (2×2) Gd-NW is markedly different from that of bulk Gd crystals. The charge-density analysis shows pronounced spin-dependent electron transfer in the encapsulated Gd-NW in comparison with that of Gd-carbide NWs. We conclude that Gd-CNT hybridization is primarily responsible for both the structural difference and electron transfer in the encapsulated Gd-NW.