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C. Bhaskara Sarma - One of the best experts on this subject based on the ideXlab platform.

  • Effect of fluidizing solids on wall-liquid mass transfer in a cylindrical cell with rotating Central Rod
    Heat and Mass Transfer, 2021
    Co-Authors: G. M. Jagannadha Raju, K.v. Ramesh, G. V. S. Sarma, C. Bhaskara Sarma
    Abstract:

    Limiting current density data were obtained at point electRodes fixed flush with inner surface of the outer cylinder of an electrochemical cell in which a coaxially placed cylindrical Rod is rotated at different rotational velocities in the presence of fluidizing solids. The variables covered in the present study are rpm of inner annular Rod, diameter of Rod, solid fraction and flow rate of the electrolyte. Mass transfer coefficients, which were computed from limiting current density data, were found to increase with an increase in the velocity of the fluid electrolyte through the annular cell in the presence of fluidizing solids. No specific trend was observed with respect to the rpm of the Central annular Rod. The variation in mass transfer coefficient values due to change in the Rod diameter was just marginal. The bed expansion data represented Richardson-Zaki equation with an exponent of 2.15. Colburn j_ D -factor format has been used to correlate the data on mass transfer coefficients.

  • Mass transfer at the confining wall of an electrochemical cell in annular flow with a rotating Central Rod
    Indian Chemical Engineer, 2020
    Co-Authors: G. M. Jagannadha Raju, K.v. Ramesh, G. V. S. Sarma, C. Bhaskara Sarma
    Abstract:

    An electrochemical method (limiting current technique) was used to obtain mass transfer coefficient (k L) in a flow reactor in which the coaxial inner cylindrical Rod was rotated at different revol...

  • WALL-TO-BED MASS TRANSFER IN AN ELECTROCHEMICAL CELL WITH COAXIALLY ROTATING COMPOSITE PROMOTER IN THE PRESENCE OF FLUIDIZING SOLIDS
    Chemical Engineering Communications, 2011
    Co-Authors: G. M. Jagannadha Raju, K.v. Ramesh, G. V. S. Sarma, C. Bhaskara Sarma
    Abstract:

    Limiting current data have been obtained at point electRodes fixed flush with the inner surface of the outer cylinder of an annular electrochemical cell. A Central Rod with tape rigidly fixed at varying pitches served as composite promoter. It was coaxially placed in the test section and rotated by a transmission gear mechanism in a bed of fluidizing solids. The metered electrolyte through a rotameter was recirculated through the test section. The data were obtained at different flow rates and rotational speeds in the absence and presence of fluidizing solids. The effect of presence of solids and ϵ were analyzed using two different particle sizes. It was found that the rotation of the Central Rod enhanced the coefficients significantly, while the presence of solids had marginal improvements. The rotation in general was found to change the fixed bed status to expanded bed even for superficial velocities below 0.06 m/s. The data on mass transfer were correlated using an equation of jD-Re format, incorporati...

  • Studies on ionic mass transfer with coaxially placed helical tapes on a Rod in forced convection flow
    Chemical Engineering and Processing: Process Intensification, 1997
    Co-Authors: V. Sujatha, C. Bhaskara Sarma, G.j.v. Jagannadha Raju
    Abstract:

    Abstract This paper reports on studies on the augmentation of ionic mass transfer rates due to the presence of insert promoters—coaxially placed helical tapes on a Rod—in a forced convection flow of electrolyte. The experimental limiting current data were obtained at various flow rates using promoters of varying Central Rod diameter width and pitch of the helical tape. Altogether, 1200 experimental limiting current measurements were obtained covering a wide range of variables. The data are analysed and results are discussed in detail. The developed correlations based on experimental data are presented.

Elisabeth Le Rumeur - One of the best experts on this subject based on the ideXlab platform.

  • Computational study of the human dystrophin repeats: interaction properties and molecular dynamics.
    PLoS ONE, 2011
    Co-Authors: Baptiste Legrand, Emmanuel Giudice, Aurélie Nicolas, Olivier Delalande, Elisabeth Le Rumeur
    Abstract:

    Dystrophin is a large protein involved in the rare genetic disease Duchenne muscular dystrophy (DMD). It functions as a mechanical linker between the cytoskeleton and the sarcolemma, and is able to resist shear stresses during muscle activity. In all, 75% of the dystrophin molecule consists of a large Central Rod domain made up of 24 repeat units that share high structural homology with spectrin-like repeats. However, in the absence of any high-resolution structure of these repeats, the molecular basis of dystrophin Central domain's functions has not yet been deciphered. In this context, we have performed a computational study of the whole dystrophin Central Rod domain based on the rational homology modeling of successive and overlapping tandem repeats and the analysis of their surface properties. Each tandem repeat has very specific surface properties that make it unique. However, the repeats share enough electrostatic-surface similarities to be grouped into four separate clusters. Molecular dynamics simulations of four representative tandem repeats reveal specific flexibility or bending properties depending on the repeat sequence. We thus suggest that the dystrophin Central Rod domain is constituted of seven biologically relevant sub-domains. Our results provide evidence for the role of the dystrophin Central Rod domain as a scaffold platform with a wide range of surface features and biophysical properties allowing it to interact with its various known partners such as proteins and membrane lipids. This new integrative view is strongly supported by the previous experimental works that investigated the isolated domains and the observed heterogeneity of the severity of dystrophin related pathologies, especially Becker muscular dystrophy.

  • Mapping of the lipid-binding and stability properties of the Central Rod domain of human dystrophin.
    Journal of molecular biology, 2009
    Co-Authors: Sébastien Legardinier, Céline Raguénès-nicol, Christophe Tascon, Chantal Rocher, Serge Hardy, Jean-françois Hubert, Elisabeth Le Rumeur
    Abstract:

    Dystrophin is a cytoskeletal protein that confers resistance to the sarcolemma against the stress of contraction-relaxation cycles by interacting with cytoskeletal and membrane partners. Apart from several proteins, membrane phospholipids are a partner of the Central Rod domain made up of 24 spectrin-like repeats, separated into sub-domains by four hinges. We previously showed that repeats 1 to 3 bind to membrane anionic phospholipids, while repeats 20 to 24 are not able to do so. We focus here on the phospholipid-binding properties of the major part of the Central Rod domain, namely, the sub-domain delineated by hinges 2 and 3 comprising 16 repeats ranging from repeat 4 to 19 (R4-19). We designed and pRoduced multirepeat proteins comprising three to five repeats and report their lipid-binding properties as well as their thermal stabilities. When these proteins are mixed with liposomes including the anionic lipid phosphatidylserine, they form stable protein-vesicle complexes as determined by gel-filtration chromatography. The absence of an anionic lipid precludes the formation of such complexes. Spectroscopic analyses by circular dichroism and tryptophan fluorescence show that, while the alpha-helical secondary structures are not modified by the binding, protein trans conformation leads to the movement of tryptophan residues into more hydrophobic environments. In addition, the decrease in the molar ellipticity ratio at 222/208 nm as observed by circular dichroism indicates that lipid binding reduces the inter-helical interactions of multirepeat proteins, thus suggesting partly "opened" coiled-coil structures. Combining these results with data from our previous studies, we propose a new model of the dystrophin molecule lying along the membrane bilayer, in which the two sub-domains R1-3 and R4-19 interact with lipids and F-actin, while the distal sub-domain R20-24 does not exhibit any interaction. These lipid-binding domains should thus maintain a structural link between cytoskeletal actin and sarcolemma via the membrane phospholipids.

Thomas C S Keller - One of the best experts on this subject based on the ideXlab platform.

  • smooth muscle titin zq domain interaction with the smooth muscle α actinin Central Rod
    Journal of Biological Chemistry, 2008
    Co-Authors: Richard J Chi, Alanna R Simon, Ewa A Bienkiewicz, Augustine Felix, Thomas C S Keller
    Abstract:

    Actin-myosin II filament-based contractile structures in striated muscle, smooth muscle, and nonmuscle cells contain the actin filament-cross-linking protein α-actinin. In striated muscle Z-disks, α-actinin interacts with N-terminal domains of titin to provide a structural linkage crucial for the integrity of the sarcomere. We previously discovered a long titin isoform, originally smitin, hereafter sm-titin, in smooth muscle and demonstrated that native sm-titin interacts with C-terminal EF hand region and Central Rod R2-R3 spectrin-like repeat region sites in α-actinin. Reverse transcription-PCR analysis of RNA from human adult smooth muscles and cultured rat smooth muscle cells and Western blot analysis with a domain-specific antibody presented here revealed that sm-titin contains the titin gene-encoded Zq domain that may bind to the α-actinin R2-R3 Central Rod domain as well as Z-repeat domains that bind to the EF hand region. We investigated whether the sm-titin Zq domain binds to α-actinin R2 and R3 spectrin repeat-like domain loops that lie in proximity with two-fold symmetry on the surface of the Central Rod. Mutations in α-actinin R2 and R3 domain loop residues decreased interaction with expressed sm-titin Zq domain in glutathione S-transferase pull-down and solid phase binding assays. Alanine mutation of a region of the Zq domain with high propensity for α-helix formation decreased apparent Zq domain dimer formation and decreased Zq interaction with the α-actinin R2-R3 region in surface plasmon resonance assays. We present a model in which two sm-titin Zq domains interact with each other and with the two R2-R3 sites in the α-actinin Central Rod.

J. Haddad - One of the best experts on this subject based on the ideXlab platform.

  • Bubbles effect on sound dispersion in thin-walled tube with polymeric liquid and elastic Central Rod
    Journal of Sound and Vibration, 2011
    Co-Authors: S.p. Levitsky, R.m. Bergman, J. Haddad
    Abstract:

    Abstract The present study is devoted to the investigation of fine air bubbles effect on sound propagation in thin-walled elastic tube with compressible polymeric liquid and cylindrical elastic Rod in the Central part of the tube. The problem formulation and solution method follow the previous paper of the authors (S.P. Levitsky, R.M. Bergman, J. Haddad, Sound dispersion in deformable tube with polymeric liquid and elastic Central Rod, Journal of Sound and Vibration 275 (1–2) (2004) 267–281). In order to account for the bubbles' influence on sound dispersion and attenuation, dynamic equation of state of the mixture, formulated within homogeneous approximation, is used. It is assumed that the volume gas concentration is small. The resulting dispersion equation for the waveguide with viscoelastic liquid–gas mixture is studied in a long-wave range. Results of simulations illustrate the influence of free gas concentration, bubble radius and rheological properties of the liquid on sound dispersion and attenuation in the system.

  • Sound propagation in thin-walled elastic pipe with viscous liquid-bubble mixture and deformable Central Rod
    2009 IEEE International Ultrasonics Symposium, 2009
    Co-Authors: Rudolf Bergman, Semyon Levitsky, J. Haddad
    Abstract:

    Sound propagation in coaxial waveguide with bubbly liquid is investigated. It is assumed that the Central part of the pipe is occupied by circular elastic Rod, the tube wall can be treated as a thin elastic shell, and the liquid is pure viscous. Volume concentration of free gas is supposed to be small. The goal of the study is to estimate theoretically acoustic properties of such waveguide for different gas concentrations, bubble sizes, liquid viscosities and gap width. Results of analysis illustrate strong influence of liquid, gas, elastic shell and Rod parameters on sound dispersion and attenuation.

  • Sound dispersion in a deformable tube with polymeric liquid and elastic Central Rod
    Journal of Sound and Vibration, 2003
    Co-Authors: S.p. Levitsky, R.m. Bergman, J. Haddad
    Abstract:

    Sound waves in deformable tubes containing a compressible polymeric liquid are investigated. The Central part of the tube is occupied by a coaxial elastic Rod. A dispersion equation is derived for this system which accounts for viscoelastic effects in the fluid and elastic deformations of the tube and the Rod. The equation is valid in the low frequency range where the sound wavelength is greater than the tube radius. Its analysis has shown that rheological properties of the liquid essentially influence the speed and attenuation of sound in the waveguide. This influence depends on the gap width and elastic properties of both the tube wall and the internal Rod.

Klaus Weber - One of the best experts on this subject based on the ideXlab platform.

  • Assembly and architecture of invertebrate intermediate filaments reconcile features of vertebrate cytoplasmic and nuclear lamin-type intermediate filaments.
    Journal of molecular biology, 1998
    Co-Authors: Norbert Geisler, Klaus Weber, Jürgen Schünemann, Markus Häner, Ueli Aebi
    Abstract:

    The two major intermediate filament (IF) proteins from the esophagus epithelium of the snail Helix pomatia and the two major IF proteins from muscle tissue of the nematode Ascaris suum were investigated under a variety of assembly conditions. The lowest-order complexes from each of the four protostomic invertebrate (p-INV) IF proteins are parallel, unstaggered dimers involving two-stranded α-helical coiled coil formation of their ∼350 amino acid residue Central Rod domain (i.e. long-Rod). In the electron microscope these are readily recognized by their distinct ∼56 nm long Rod with two globular domains (i.e. representing the non-helical carboxy-terminal tail domain of the p-INV IF proteins) attached at one end, closely resembling vertebrate lamin dimers. The next-higher-order oligomers are tetramers, which are easily recognized by their two pairs of globular tail domains attached at either end of a ∼72 nm long Central Rod portion. According to their size and shape, these tetramers are built from two dimers associated laterally in an antiparallel, approximately half-staggered fashion via the amino-terminal halves of their Rod domains. This is similar to the NN-type tetramers found as the most abundant oligomer species in all types of vertebrate cytoplasmic IF proteins, which contain a ∼310 amino acid residue Central Rod domain (i.e. short-Rod). As a first step toward filament formation, the p-INV IF tetramers anneal longitudinally into protofilaments by antiparallel CC-type association of the carboxy-terminal halves of their dimer Rods. The next step involves radial growth, occurring initially through lateral association of two four-chain protofilaments into octameric subfibrils, which then further associate into mature, full-width filaments. Head-to-tail polymers of dimers and paracrystalline fibers commonly observed with vertebrate lamins were only rarely seen with p-INV IF proteins. The globular domains residing at the carboxy-terminal end of p-INV IF dimers were studding the surface of the filaments at regular, ∼24.5 nm intervals, thereby giving them a “beaded” appearance with an axial periodicity of about 24.5 nm, which is ∼3 nm longer than the corresponding ∼21.5 nm repeat pattern exhibited by short-Rod vertebrate IFs.

  • Epitope mapping and direct visualization of the parallel, in-register arrangement of the double-stranded coiled-coil in the NuMA protein.
    The EMBO journal, 1995
    Co-Authors: Jens Harborth, Klaus Weber, Mary Osborn
    Abstract:

    NuMA, a 238 kDa protein present in the nucleus during interphase, translocates to the spindle poles in mitosis. NuMA plays an essential role in mitosis, since microinjection of the NuMA SPN-3 monoclonal antibody causes mitotic arrest and micronuclei formation. We have mapped the approximate position of the epitopes of six monoclonal NuMA antibodies using recombinant NuMA fragments. The SPN-3 epitope has been located to residues 255-267 at the C-terminus of the first helical subdomain of the Central Rod domain and several residues crucial for antibody binding have been identified. To gain insight into the ultrastructure of NuMA, several defined fragments, as well as the full-length recombinant protein, were expressed in Escherichia coli and purified to homogeneity. They were then characterized by chemical cross-linking, circular dichroism spectra and electron microscopy. The results directly reveal the tripartate structure of NuMA. A long Central Rod domain is flanked by globular end domains. The Rod is 207 nm long and is at least 90% alpha-helical. It reflects a double-stranded coiled-coil with the alpha-helices arranged parallel and in register. The NuMA protein thus forms the longest coiled-coil currently known. Our analyses reveal no indication that recombinant NuMA assembles into filaments or other higher order structures.

  • The sequence of a cytoplasmic intermediate filament (IF) protein from theannelid Lumbricus terrestris emphasizes a distinctive feature of protostomic IF proteins
    FEBS letters, 1995
    Co-Authors: Marc Bovenschulte, Dieter Riemer, Klaus Weber
    Abstract:

    Abstract The complete cDNA clone for a cytoplasmic intermidiatefilament (IF) protein from the annelid Lumbricus terrestris reported here, shows an extra 42 residues in the coil 1b subdomain of the Central Rod, as do the IF proteins from nematodes and moluscs. These extra six heptads are also present in all nuclear lamins but not in any known vertebrate cytoplasmic IF protein. Thus, it seems that protostomic metazoa conserve a lamin-like structural element in their cytoplasmic IF proteins, which was lost in the deuterostomic metazoan branch leading to the vertebrates.