| 441. |
- Ghaffari, Roujin, 1994, et al.
(författare)
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Mass Transport of Lignin in Confined Pores
- 2022
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 14:10
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Tidskriftsartikel (refereegranskat)abstract
- A crucial step in the chemical delignification of wood is the transport of lignin fragments into free liquor; this step is believed to be the rate-limiting step. This study has investigated the diffusion of kraft lignin molecules through model cellulose membranes of various pore sizes (1-200 nm) by diffusion cells, where the lignin molecules diffuse from donor to acceptor cells through a membrane, where diffusion rate increases by pore size. UV-vis spectra of the donor solutions showed greater absorbance at higher wavelengths (similar to 450 nm), which was probably induced by scattering due to presence of large molecules/clusters, while acceptor samples passed through small pore membranes did not. The UV-vis spectra of acceptor solutions show a characteristic peak at around 350 nm, which corresponds to ionized conjugated molecules: indicating that a chemical fractionation has occurred. Size exclusion chromatography (SEC) showed a difference in the molecular weight (M-w) distribution between lignin from the donor and acceptor chambers. The results show that small pore sizes enable the diffusion of small individual molecules and hinder the transport of large lignin molecules or possible lignin clusters. This study provides more detail in understanding the mass transfer events of pulping processes.
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| 442. |
- Ghandriz, Toheed, 1982, et al.
(författare)
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Structural topology optimization of multibody systems
- 2016
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Ingår i: Multibody System Dynamics. - : Springer Science and Business Media LLC. - 1384-5640 .- 1573-272X. ; 39:1, s. 135-148
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Tidskriftsartikel (refereegranskat)abstract
- Flexible multibody dynamics (FMD) has found many applications in control, analysis and design of mechanical systems. FMD together with the theory of structural optimization can be used for designing multibody systems with bodies which are lighter, but stronger. Topology optimization of static structures is an active research topic in structural mechanics. However, the extension to the dynamic case is less investigated as one has to face serious numerical difficulties. One way of extending static structural topology optimization to topology optimization of dynamic flexible multibody system with large rotational and transitional motion is investigated in this paper. The optimization can be performed simultaneously on all flexible bodies. The simulation part of optimization is based on an FEM approach together with modal reduction. The resulting nonlinear differential-algebraic systems are solved with the error controlled integrator IDA (Sundials) wrapped into Python environment by Assimulo (Andersson et al. in Math. Comput. Simul. 116(0):26–43, 2015). A modified formulation of solid isotropic material with penalization (SIMP) method is suggested to avoid numerical instabilities and convergence failures of the optimizer. Sensitivity analysis is central in structural optimization. The sensitivities are approximated to circumvent the expensive calculations. The provided examples show that the method is indeed suitable for optimizing a wide range of multibody systems. Standard SIMP method in structural topology optimization suggests stiffness penalization. To overcome the problem of instabilities and mesh distortion in the dynamic case we consider here additionally element mass penalization.
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| 443. |
- Ghandriz, Toheed, 1982, et al.
(författare)
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Structural Topology Optimization of Multibody Systems
- 2015
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Ingår i: Multibody Dynamics, ECCOMAS Thematic Conference, June 2015, Barcelona. - 9788494424403 ; , s. 828-838
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Flexible multibody dynamics (FMD) has found many applications in control, analysis and design of mechanical systems. FMD together with the theory of structural optimization can be used for designing multibody systems with bodies which are lighter, but stronger. Topology optimization of static structures is an active research topic in structural mechanics. However, the extension to the dynamic case is less investigated as one has to face serious numerical difficulties. One way of extending static structural topology optimization to topology optimization of dynamic flexible multibody system with large rotational and transitional motion is investigated in this paper. The optimization can be performed simultaneously on all flexible bodies. The simulation part of optimization is based on an FEM approach together with modal reduction. The resulting nonlinear differential-algebraic systems are solved with the error controlled integrator IDA (Sundials) wrapped into Python environment by Assimulo. A modified formulation of solid isometric material with penalization (SIMP) method is suggested to avoid numerical instabilities and convergence failures of the optimizer. Sensitivity analysis is central in structural optimization. The sensitivities are approximated to circumvent the expensive calculations. The provided examples show that the method is indeed suitable for optimizing a wide range of multibody systems. Standard SIMP method in structural topology optimization suggests stiffness penalization. To overcome the problem of instabilities and mesh distortion in the dynamic case we consider here additionally element mass penalization.
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| 444. |
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| 445. |
- Ghazzali, Mohamed I D M, 1974, et al.
(författare)
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Synthesis, EPR and DFT calculations of rare Ag(II)porphyrins and the crystal structure of [Zn(II)tetrakis(4-bromo-2-thiophene)porphyrin]
- 2008
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Ingår i: Inorganic Chemistry Communication. - : Elsevier BV. - 1387-7003 .- 1879-0259. ; 11:9, s. 1019-1022
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Tidskriftsartikel (refereegranskat)abstract
- Meso-tetrakis (4-bromo-2-thiophene) and (5-bromo-2-thiophene) porphyrins were synthesized in 18% yield from freshly distilled pyrrole and the corresponding aldehydes in refluxing propionic acid. Reaction of both porphyrins with either Zn(OAc) 2 · 2H 2 O or Ag(OAc) afforded the corresponding metal complexes in 20% yield. The free bases and metal complexes were characterized by IR, NMR, EPR, MS and XPS. The crystal structure of 5,10,15,20(4-bromo-2-thiophene)porphyrinato Zn(II) was determined by X-ray diffraction and shows a 'zigzag-like' packing pattern due to S···S intermolecular interaction. Structural features of these molecules are discussed by DFT quantum chemical calculations. © 2008 Elsevier B.V. All rights reserved.
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| 446. |
- Ghirmai, Semhar, 1993, et al.
(författare)
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In vivo evaluation of electron mediators for the reduction of methemoglobin encapsulated in liposomes using electron energies produced by red blood cell glycolysis
- 2017
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Ingår i: Artificial Cells, Nanomedicine and Biotechnology. - : Informa UK Limited. - 2169-1401 .- 2169-141X. ; 46:7, s. 1364-1372
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Tidskriftsartikel (refereegranskat)abstract
- Earlier studies have clarified that NADH and NADPH, re-energized repeatedly by red blood cell (RBC) glycolysis, can be used in extracellular chemical reactions, where electron energies are extracted by electron mediators, such as methylene blue (MB). The electron mediators, which are reduced by NAD(P)H, permeate both the membranes of RBC and phospholipid bilayer of liposomes encapsulating haemoglobin (Hb-vesicles, HbV) and reduce autoxidized ferric methemoglobin (metHb) in HbV to ferrous Hb. Moreover, in vitro screening study clarified some other potential electron mediators with comparable capacity to reduce metHb. Given this background, eight of these compounds: MB, 1,9-dimethyl MB, azure A, azure B (AB), azure, toluidine blue, brilliant cresyl blue and toluylene blue, were evaluated in both in vitro and in vivostudies in this work. Compared with MB as a reference, in vitro experiments demonstrated that most compounds caused effective metHb reduction of HbV in the presence of RBC. However, in vivo experiments of bolus injection of autoxidized HbV to rats (10 mL HbV/kg body weight) followed by injection of the dye (1.53 mL/kg body weight, 2.6 mM) led to some differences from in vitro results. Effective metHb reduction was found for the combination of AB. To evaluate AB effectiveness further, a haemorrhagic shock and resuscitation model was used, where the rats were resuscitated with HbV. When the level of metHb increased to 50%, a dye solution was injected. Again, AB caused sufficient reduction of metHb. Through these in vivo experiments, this study clarified that AB is a suitable electron mediator to prolong the functional lifetime of HbV.
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| 447. |
- Gilbert, Jennifer, et al.
(författare)
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Effect of encapsulated protein on the dynamics of lipid sponge phase: a neutron spin echo and molecular dynamics simulation study
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- Lipid membranes are highly mobile systems with hierarchical, time and length scale dependent, collective motions including thickness fluctuations, undulations, and topological membrane changes, which play an important role in membrane interactions. In this work we have characterised the effect of encapsulating two industrially important enzymes, β-galactosidase and aspartic protease, in lipid sponge phase nanoparticles on the dynamics of the lipid membrane using neutron spin echo (NSE) spectroscopy and molecular dynamics (MD) simulations. From NSE, reduced membrane dynamics were observed upon enzyme encapsulation, which were dependent on the enzyme concentration and type. By fitting the intermediate scattering functions (ISFs) with a modified Zilman and Granek model including nanoparticle diffusion, an increase in membrane bending rigidity was observed, with a larger effect for β-galactosidase than aspartic protease at the same concentration. MD simulations for the system with and without aspartic protease showed that the lipids relax more slowly in the system with protein due to the replacement of the lipid carbonyl-water hydrogen bonds with lipid-protein hydrogen bonds. This indicates that the most likely cause of the increase in membrane rigidity observed in the NSE measurements was dehydration of the lipid head groups. The dynamics of the protein itself were also studied, which showed a stable secondary structure of protein over the simulation, indicating no unfolding events occurred.
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| 448. |
- Gilbert, Jennifer, et al.
(författare)
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On the interactions between RNA and titrateable lipid layers: implications for RNA delivery with lipid nanoparticles
- 2023
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Ingår i: Nanoscale. - 2040-3372 .- 2040-3364. ; 16:2, s. 777-794
-
Tidskriftsartikel (refereegranskat)abstract
- Characterising the interaction between cationic ionisable lipids (CIL) and nucleic acids (NAs) is key to understanding the process of RNA lipid nanoparticle (LNP) formation and release of NAs from LNPs. Here, we have used different surface techniques to reveal the effect of pH and NA type on the interaction with a model system of DOPC and the CIL DLin-MC3-DMA (MC3). At only 5% MC3, differences in the structure and dynamics of the lipid layer were observed. Both pH and %MC3 were shown to affect the absorption behaviour of erythropoietin mRNA, polyadenylic acid (polyA) and polyuridylic acid (polyU). The adsorbed amount of all studied NAs was found to increase with decreasing pH and increasing %MC3 but with different effects on the lipid layer, which could be linked to the NA secondary structure. For polyA at pH 6, adsorption to the surface of the layer was observed, whereas for other conditions and NAs, penetration of the NA into the layer resulted in the formation of a multilayer structure. By comparison to simulations excluding the secondary structure, differences in adsorption behaviours between polyA and polyU could be observed, indicating that the NA's secondary structure also affected the MC3-NA interactions.
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| 449. |
- Gillgren, H., et al.
(författare)
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Morphology and Molecular Conformation in Thin Films of Poly-gamma-methyl-L-glutamate at the Air-Water Interface
- 2002
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 18:2, s. 462-469
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of poly-gamma-methyl-L-glutamate (pMeE) at the air-water interface has been studied with the surface film balance technique. In addition, Langmuir-Blodgett (LB) films of pMeE deposited on mica and quartz have been studied by atomic force microscopy (AFM) and circular and linear dichroism (CD and LD) spectroscopy. Depending on the spreading solvent, pMeE displays strikingly different compression isotherms. When spread from chloroform or trifluoroacetic acid (TFA) the surface pressure isotherms are consistent with that of a peptide in a-helix conformation. However, the latter solvent gives rise to isotherms with a considerably smaller apparent mean molecular area, A(0). When spread from pyridine, on the other hand, pMeE yields an isotherm that is expanded and inconsistent with the presence of a monolayer consisting entirely of a-helical peptides. Isotherms and AFM images strongly suggest that peptide aggregation and solvent retention are the main factors behind the isotherm differences. When the water-soluble spreading solvent TFA is used, pMeE forms discrete wormlike aggregates embedded in a monolayer matrix. In the pyridine case, aggregation in the spreading solvent and retention of pyridine in the film result in a rough aggregate network coexisting with discrete aggregates. No aggregation takes place when chloroform is used as spreading solvent. CD and LD spectra of the LB films reveal a pronounced lateral orientation of the alpha-helices in films spread from chloroform and TFA, while spectra of films spread from pyridine are consistent with unordered peptide strands in beta-sheet conformation. In conclusion, the results show that if water-soluble and/or low-volatile solvents are used as spreading media, hydrophobic peptides cannot, a priori, be assumed to form proper monolayers.
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| 450. |
- Gimperlein, H., et al.
(författare)
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On the magnitude function of domains in Euclidean space
- 2021
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Ingår i: American Journal of Mathematics. - : Project Muse. - 0002-9327 .- 1080-6377. ; 143:3, s. 939-967
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Tidskriftsartikel (refereegranskat)abstract
- We study Leinster's notion of magnitude for a compact metric space. For a smooth, compact domain X subset of R2m-1, we find geometric significance in the function M-X(R) = mag(R . X). The function M-X extends from the positive half-line to a meromorphic function in the complex plane. Its poles are generalized scattering resonances. In the semiclassical limit R -> infinity, M-X admits an asymptotic expansion. The three leading terms of M-X at R = +infinity are proportional to the volume, surface area and integral of the mean curvature. In particular, for convex X the leading terms are proportional to the intrinsic volumes, and we obtain an asymptotic variant of the convex magnitude conjecture by Leinster and Willerton, with corrected coefficients.
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