Narrow Channel (narrow + channel)

Distribution by Scientific Domains


Selected Abstracts


High Definition Digital Fabrication of Active Organic Devices by Molecular Jet Printing,

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007
J. Chen
Abstract We introduce a high resolution molecular jet (MoJet) printing technique for vacuum deposition of evaporated thin films and apply it to fabrication of 30,,m pixelated (800,ppi) molecular organic light emitting devices (OLEDs) based on aluminum tris(8-hydroxyquinoline) (Alq3) and fabrication of narrow channel (15,,m) organic field effect transistors (OFETs) with pentacene channel and silver contacts. Patterned printing of both organic and metal films is demonstrated, with the operating properties of MoJet-printed OLEDs and OFETs shown to be comparable to the performance of devices fabricated by conventional evaporative deposition through a metal stencil. We show that the MoJet printing technique is reconfigurable for digital fabrication of arbitrary patterns with multiple material sets and high print accuracy (of better than 5,,m), and scalable to fabrication on large area substrates. Analogous to the concept of "drop-on-demand" in Inkjet printing technology, MoJet printing is a "flux-on-demand" process and we show it capable of fabricating multi-layer stacked film structures, as needed for engineered organic devices. [source]


A lattice Boltzmann method for solute transport

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2009
Jian Guo Zhou
Abstract A lattice Boltzmann method is developed for solute transport. Proper expressions for the local equilibrium distribution functions enable the method to be formulated on rectangular lattice with the same simple procedure as that on a square lattice. This provides an additional advantage over a lattice Boltzmann method on a square lattice for problems characterized by dominant phenomenon in one direction and relatively weak in another such as solute transport in shear flow over a narrow channel, where the problems can efficiently be approached with fine and coarse meshes, respectively, resulting in more efficient algorithm. The stability conditions are also described. The proposed method on a square lattice is naturally recovered when a square lattice is used. It is verified by solving four tests and compared with the analytical/exact solutions. They are in good agreement, demonstrating that the method is simple, accurate and robust for solute transport. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Critical evaluation of CFD codes for interfacial simulation of bubble-train flow in a narrow channel

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2007
Furkan Özkan
Abstract Computational fluid dynamics (CFD) codes that are able to describe in detail the dynamic evolution of the deformable interface in gas,liquid or liquid,liquid flows may be a valuable tool to explore the potential of multi-fluid flow in narrow channels for process intensification. In the present paper, a computational exercise for co-current bubble-train flow in a square vertical mini-channel is performed to investigate the performance of well-known CFD codes for this type of flows. The computations are based on the volume-of-fluid method (VOF) where the transport equation for the liquid volumetric fraction is solved either by the methods involving a geometrical reconstruction of the interface or by the methods that use higher-order difference schemes instead. The codes contributing to the present code-to-code comparison are an in-house code and the commercial CFD packages CFX, FLUENT and STAR-CD. Results are presented for two basic cases. In the first one, the flow is driven by buoyancy only, while in the second case the flow is additionally forced by an external pressure gradient. The results of the code-to-code comparison show that only the VOF method with interface reconstruction leads to physically sound and consistent results, whereas the use of difference schemes for the volume fraction equation shows some deficiencies. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Transient free-surface flow of a viscoelastic fluid in a narrow channel

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2004
Roger E. Khayat
Abstract The interplay between inertia and elasticity is examined for transient free-surface flow inside a narrow channel. The lubrication theory is extended for the flow of viscoelastic fluids of the Oldroyd-B type (consisting of a Newtonian solvent and a polymeric solute). While the general formulation accounts for non-linearities stemming from inertia effects in the momentum conservation equation, and the upper-convected terms in the constitutive equation, only the front movement contributes to non-linear coupling for a flow inside a straight channel. In this case, it is possible to implement a spectral representation in the depthwise direction for the velocity and stress. The evolution of the flow field is obtained locally, but the front movement is captured only in the mean sense. The influence of inertia, elasticity and viscosity ratio is examined for pressure-induced flow. The front appears to progress monotonically with time. However, the velocity and stress exhibit typically a strong overshoot upon inception, accompanied by a plug-flow behaviour in the channel core. The flow intensity eventually diminishes with time, tending asymptotically to Poiseuille conditions. For highly elastic liquids the front movement becomes oscillatory, experiencing strong deceleration periodically. A multiple-scale solution is obtained for fluids with no inertia and small elasticity. Comparison with the exact (numerical) solution indicates a wide range of validity for the analytical result. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Multiple functions of the paranodal junction of myelinated nerve fibers,

JOURNAL OF NEUROSCIENCE RESEARCH, Issue 15 2009
Jack Rosenbluth
Abstract Myelin sheaths include an extraordinary structure, the "paranodal axoglial junction" (PNJ), which attaches the sheath to the axon at each end of each myelin segment. Its size is enormous and its structure unique. Here we review past and current studies showing that this junction can serve multiple functions in maintaining reliable saltatory conduction. The present evidence points to three functions in particular. 1) It seals the myelin sheath to the axon to prevent major shunting of nodal action currents beneath the myelin sheath while still leaving a narrow channel interconnecting the internodal periaxonal space with the perinodal space. This pathway represents a potential route through which juxtaparanodal and internodal channels can influence nodal activity and through which nutrients, such as glucose, and other metabolites can diffuse to and from the internodal periaxonal space. 2) It serves as a mechanism for maintaining discrete, differentiated axolemmal domains at and around the node of Ranvier by acting as a barrier to the lateral movement of ion channel complexes within the axolemma, thus concentrating voltage-gated sodium channels at the node and segregating fast voltage-gated potassium channels to the juxtaparanode under the myelin sheath. 3) It attaches the myelin sheath to the axon on either side of the node and can thus maintain nodal dimensions in the face of mechanical stresses associated with stretch or other local factors that might cause disjunction. It is therefore the likely means for maintaining constancy of nodal surface area and electrical parameters essential for consistency in conduction. © 2009 Wiley-Liss, Inc. [source]


Photosynthetic Eukaryotes of Freshwater Wetland Biofilms: Adaptations and Structural Characteristics of the Extracellular Matrix in the Green Alga, Cosmarium reniforme (Zygnematophyceae, Streptophyta)

THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 4 2009
DAVID S. DOMOZYCH
ABSTRACT. Cosmarium reniforme (Zygnematophyceae, Streptophyta) is a green alga that is commonly found in biofilms of wetlands of the Adirondack region, NY (USA). Two distinctive characteristics that are critical to this alga's survival in a benthic biofilm are its elaborate cell morphology and extracellular matrix (ECM). In this study, ultrastructural, immunocytochemical, and experimental methodologies were employed in order to elucidate the cellular characteristics that are critical for survival in a biofilm. The ECM consists of a thick, outwardly lobed cell wall (CW), which contains a patterned network of structurally complex pores. Each pore consists of a narrow channel, terminating internally at a bulb that invaginates localized regions of the plasma membrane. The outer region of the pore contains arabinogalactan protein-like and extensin epitopes that are likely involved in adhesion mechanisms of the cell. External to the CW is the extracellular polymeric substance that is employed in ensheathment of the cell to the substrate and in gliding motility. The architectural design/biochemical make-up of the CW and a secretory system that encompasses the coordinated activities of the endomembrane and cytomotile/cytoskeletal systems provide the organism with effective mechanisms to support life within the biofilm complex. [source]


Roles of partly unfolded conformations in macromolecular self-assembly

GENES TO CELLS, Issue 1 2001
Keiichi Namba
From genes to cells there are many steps of hierarchical increments in building up complex frameworks that provide intricate networks of macromolecular interactions, through which cellular activities such as gene expression, signal processing, energy transduction and material conversion are dynamically organized and regulated. The self-assembly of macromolecules into large complexes is one such important step, but this process is by no means a simple aggregation of macromolecules with predefined, rigid complementary structures. In many cases the component molecules undergo either domain rearrangements or folding of disordered portions, which occurs only following binding to their correct partners. The partial disorder is used in some cases to prevent spontaneous assembly at inappropriate times or locations. It is also often used for finely tuning the equilibrium and activation energy of reversible binding. In other cases, such as protein translocation across membranes, an unfolded terminus appears to be the prerequisite for the process as an initiation signal, as well as the physical necessity to be taken into narrow channels. Self-assembly processes of viruses and bacterial flagella are typical examples where the induced folding of disordered chains plays a key role in regulating the addition of new components to a growing assembly. Various aspects of mechanistic roles of natively unfolded conformations of proteins are overviewed and discussed in this short review. [source]


Investigation on the characteristics of boiling heat transfer through narrow annular channels

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2005
Su Shun-yu
Abstract Factors concerning the characteristics of boiling heat transfer are analyzed theoretically. Based on the experimental data of boiling heat transfer through annular channels with the gaps of 1,2 mm, three correlations which will be used to calculate the heat transfer in the similar conditions are given. The results obtained from these correlations are compared with experimental data. The main factors having influence on boiling heat transfer through narrow channels, and the desirable correlation are determined. This correlation can be used to predict the flow boiling heat transfer within the range of this experiment. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 78,84, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20049 [source]


Critical evaluation of CFD codes for interfacial simulation of bubble-train flow in a narrow channel

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2007
Furkan Özkan
Abstract Computational fluid dynamics (CFD) codes that are able to describe in detail the dynamic evolution of the deformable interface in gas,liquid or liquid,liquid flows may be a valuable tool to explore the potential of multi-fluid flow in narrow channels for process intensification. In the present paper, a computational exercise for co-current bubble-train flow in a square vertical mini-channel is performed to investigate the performance of well-known CFD codes for this type of flows. The computations are based on the volume-of-fluid method (VOF) where the transport equation for the liquid volumetric fraction is solved either by the methods involving a geometrical reconstruction of the interface or by the methods that use higher-order difference schemes instead. The codes contributing to the present code-to-code comparison are an in-house code and the commercial CFD packages CFX, FLUENT and STAR-CD. Results are presented for two basic cases. In the first one, the flow is driven by buoyancy only, while in the second case the flow is additionally forced by an external pressure gradient. The results of the code-to-code comparison show that only the VOF method with interface reconstruction leads to physically sound and consistent results, whereas the use of difference schemes for the volume fraction equation shows some deficiencies. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Heat transfer from a plate impinging swirl jet

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2002
Kadir Bilen
Abstract Heat transfer and flow visualization experiments were conducted to investigate the performance of swirling and multi-channel impinging jets and compare the results with those of a multi-channel impinging jet (MCIJ) and conventional impinging jet (CIJ) for the present work at the same conditions. Swirling impinging jets (SIJs) employed the fixed blade lengths of 12.3 mm with four blades at the exit of the housing tube to divert the air flow through four narrow channels with a desired swirl angle (, of 22.5, 41 and 50°). The MCIJ jet had the same dimensions as the SIJs, except that the narrow channels in the solid insert were vertical (,=0°). The local and surface average Nusselt numbers of MCIJ were generally higher than those of the CIJ and SIJs. The SIJs, however, demonstrated significant improvement in radial uniformity of heat transfer compared to the MCIJ and CIJ. In the region of 2.7,X/D,0 for H/D=8 and Re=20 000, the average Nusselt number for the MCIJ was 11, 33, 72 and 98 per cent higher than that of the CIJ, ,=22.5, ,=41 and ,=50°, respectively. Copyright © 2002 John Wiley & Sons, Ltd. [source]


COMMUNITY, CONTEXT, AND THE PRESENTATION OF SELF IN DISTRIBUTED WORKPLACE INTERACTION

ANNALS OF ANTHROPOLOGICAL PRACTICE, Issue 1 2008
Michael Youngblood
Instantaneous communications technology has made it possible for distant coworkers to be interconnected to an unprecedented degree. Despite this, distributed workers often feel deeply disconnected from the production and performance of conventional workplace relationships and workplace culture. As the knowledge economy workforce trends toward ever-greater distribution and globalization, this raises important questions about the practice and experience of creative coengagement by colleagues who are not proximate to each other in time and space. How are shared understandings of workers' behavioral norms disseminated and practiced when workers are physically isolated from the collective workspace? How are relationships of collegiality and hierarchy constructed and performed through increasingly narrow channels of social interaction? How do workers signal their energy and commitment to a collective creative enterprise when their actual productive activity is largely invisible to others with whom and for whom they work? This article draws on my research with distributed knowledge workers, informal observations of colleagues, and personal experiences working as an independent consultant in distributed settings. It focuses on the challenges these workers face in defining their workplace community and effectively representing their professional selfhood when working at a distance. In this article I suggest that one key to alleviating these challenges is to extend the attributes of "placehood" to distant work spaces. [source]


BaY2Si3O10: a new flux-grown trisilicate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2006
Uwe Kolitsch
BaY2Si3O10, barium diyttrium trisilicate, is a new silicate grown from a molybdate-based flux. The structure is based on zigzag chains, parallel to [010], of edge-sharing distorted YO6 octa­hedra, linked by horseshoe-shaped trisilicate groups and Ba atoms in irregular eight-coordination. The layered character of the structure is caused by a succession of zigzag chains and trisilicate groups in planes parallel to (01). The Ba atoms occupy narrow channels extending parallel to [100]. The mean Y,O, Si,O and Ba,O bond lengths are 2.268, 1.626 and 1.633, and 2.872,Ĺ, respectively. The two symmetry-equivalent terminal SiO4 tetra­hedra in the Si3O10 unit adopt an eclipsed conformation with respect to the central SiO4 tetra­hedron; the Si,O,Si and Si,Si,Si angles are 136.35,(9) and 96.12,(4)°, respectively. One Ba, one Si and two O atoms are located on mirror planes; all remaining atoms are in general positions. The geometry of isolated trisilicate groups in inorganic compounds is briefly discussed. [source]


Ultra scale-down approaches for clarification of mammalian cell culture broths in disc-stack centrifuges

BIOTECHNOLOGY PROGRESS, Issue 6 2009
Ferhana Zaman
Abstract Ultra-scale down (USD) methodology developed by University College London for cell broth clarification with industrial centrifuges was applied to two common cell lines (NS0 and GS-CHO) expressing various therapeutic monoclonal antibodies. A number of centrifuges at various scales were used with shear devices operating either by high speed rotation or flow-through narrow channels. The USD methodology was found effective in accounting for both gravitational and shear effects on clarification performance with three continuous centrifuges at pilot and manufacturing scales. Different shear responses were observed with the two different cell lines and even with the same cell line expressing different products. Separate particle size analysis of the treated broths seems consistent with the shear results. Filterability of the centrifuged solutions was also evaluated to assess the utility of the USD approach for this part of the clarification operation. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]