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Morphology Transition (morphology + transition)
Selected AbstractsMorphology Transition of Block Copolymers under Curved ConfinementMACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2007Xingqing Xiao Abstract The morphology transitions in AB diblock and ABA triblock copolymers confined between flat and curved surfaces were investigated by MC simulations. Upon variation of the extent of frustration between thickness d and bulk lamellae period L0, parallel and vertical or distorted vertical lamellar structures appear in both flat and curved confinements. With increasing curvature, the compatibility of d and L0 becomes more perturbed so that perfectly parallel lamellae are formed with increasing difficulty. Owing to the smaller L0 of ABA as compared to AB, the transformation frequency of the incompatible region of d/L0(ABA) is more notable for ABA and the corresponding transformation period is larger than that of AB. [source] Mechanistic comparison of blood undergoing laser photocoagulation at 532 and 1,064 nmLASERS IN SURGERY AND MEDICINE, Issue 2 2005John F. Black PhD Abstract Background and Objectives We seek to compare and contrast the mechanisms of blood photocoagulation under 532 and 1,064 nm laser irradiation in vitro in order to better understand the in vivo observations. We also seek to validate a finite element model (FEM) developed to study the thermodynamics of coagulation. Study Design/Materials and Methods We study the photocoagulation of whole blood in vitro at 532 and 1,064 nm using time-domain spectroscopic and optical coherence tomography (OCT)-based imaging techniques. We model the coagulation using an FEM program that includes the latent heat of vaporization (LHV) of water, consideration of the pulse shape of the laser, and the bathochromic shift in the hemoglobin absorption spectrum. Results We find significant similarities in the spectroscopic, chemical, and structural changes occurring in hemoglobin and in the blood matrix during photocoagulation despite the very large difference in the absorption coefficients. The more uniform temperature profile developed by the deeper-penetrating 1,064 nm laser allows us to resolve the structural phase transition in the red blood cells (going from biconcave disc to spherocyte) and the chemical transition creating met-hemoglobin. We find that the RBC morphology transition happens first, and that the met-Hb transition happens at a much higher temperature (,>,90°C) than is found in slow bath heating. The FEM analysis with the LHV constraint and bathochromic shift predicts accurately the imaging results in both cases, and can be used to show that at 1,064 nm there is the potential for a runaway increase in absorption during the laser pulse. Conclusions Photothermally mediated processes dominate the in vitro coagulation dynamics in both regimes despite the difference in absorption coefficients. There is a significant risk under 1,064 nm irradiation of vascular lesions in vivo that the dynamic optical properties of blood will cause runaway absorption and heating. This may in turn explain some recent results at this wavelength where full-thickness burns resulted from laser treatment. Lasers Surg. Med. 36:155,165, 2005. © 2005 Wiley-Liss, Inc. [source] Pleomorphism of the marine bacterium Teredinobacter turniraeLETTERS IN APPLIED MICROBIOLOGY, Issue 1 2001G.M. Ferreira Aims:,A morphology transition for the marine bacterium, Teredinobacter turnirae is reported. Methods and Results:,When grown in the rod-shaped morphology, the cells require high concentrations of NaCl (0·3 mol l,1) and secrete extracellular protease and endoglucanase activity. When this bacterium is grown in a medium containing casein as a sole carbon and nitrogen source, a major change in morphology to a stable aggregated form is obtained. Conclusions:,In the aggregated morphology, much higher protease production rates (170 Units ml,1 d,1 for aggregates vs. 15 Units ml,1 d,1 for rods, for the same initial biomass) and negligible endoglucanase titres are obtained. In addition, the aggregated morphology does not require sodium chloride for growth. Significance and Impact of the Study:,The phenomenon reported here describes a novel relationship between the cell morphology and the biochemical characteristics of the bacterium. [source] Morphology and Properties of Polyethylene/Clay Nanocomposite Drawn FibersMACROMOLECULAR MATERIALS & ENGINEERING, Issue 1 2008Francesco Paolo La Mantia Abstract The influence of an elongational flow on the morphology of PE/clay nanocomposite drawn fibers was studied. An increase of the elastic modulus and the tensile strength as well as a decrease of the elongation at break are observed with increasing draw ratio. The applied elongational gradient orients the polymer chains and the clay particles along the spinning direction. When the applied flow results in the formation and the orientation of exfoliated nanoparticles, a pronounced increase of the mechanical properties is observed. The dispersed clay particles can be broken and oriented by the extensional flow, which might indicate a flow-induced intercalated/exfoliated morphology transition. [source] Mitochondrial morphology transition is an early indicator of subsequent cell death in ArabidopsisNEW PHYTOLOGIST, Issue 1 2008Iain Scott Summary ,,Mitochondrial morphology and dynamics were investigated during the onset of cell death in Arabidopsis thaliana. Cell death was induced by either chemical (reactive oxygen species (ROS)) or physical (heat) shock. ,,Changes in mitochondrial morphology in leaf tissue, or isolated protoplasts, each expressing mitochondrial-targeted green fluorescent protein (GFP), were observed by epifluorescence microscopy, and quantified. ,,Chemical induction of ROS production, or a mild heat shock, caused a rapid and consistent change in mitochondrial morphology (termed the mitochondrial morphology transition) that preceded cell death. Treatment of protoplasts with a cell-permeable superoxide dismutase analogue, TEMPOL, blocked this morphology change. Incubation of protoplasts in micromolar concentrations of the calcium channel-blocker lanthanum chloride, or the permeability transition pore inhibitor cyclosporin A, prevented both the mitochondrial morphology transition and subsequent cell death. ,,It is concluded that the observed mitochondrial morphology transition is an early and specific indicator of cell death and is a necessary component of the cell death process. [source] Enhanced control of porous silicon morphology from macropore to mesopore formationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005Huimin Ouyang Abstract Porous silicon (PSi) is a versatile material that possesses a wide range of morphologies. There are two main types of microstructures that are widely used and well studied: branchy mesoporous silicon with pore sizes from 10 nm to 50 nm and classical macroporous silicon with pore sizes from 500 nm to 20 µm. Much less work has been done on structures with intermediate pore sizes from 100 nm to 300 nm. Applications such as immunoassays biosensing can greatly benefit from the intermediate morphology due to the larger pore openings compared to mesopores, and increased internal surface compared to classical macropores. In this work we demonstrate well-defined macropore of 150 nm diameter in average and precise control of the porous silicon morphology transition from smooth macropores to branchy mesopores on one substrate with one electrolyte. A multilayer structure (microcavity) consisting of both mesopores and macropores is presented. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exploration of the morphological transition phenomenon of polyaniline from microspheres to nanotubes in acid-free aqueous 1-propanol solution in a single polymerization processPOLYMER INTERNATIONAL, Issue 9 2010Yu-Fong Huang Abstract Polyaniline micro- or nanostructures have been widely investigated due to their unique physical and chemical properties. Although several studies have reported the synthesis of polyaniline microspheres and nanotubes, their mechanisms of formation remain controversial. This study reports our observation of the morphological transition of polyaniline from microspheres to nanotubes in a single polymerization process and also tries to propose their mechanisms of formation. The polymerization of aniline monomer in acid-free aqueous 1-propanol solutions (1 and 2 mol L,1) produces polyaniline microspheres and nanotubes at different reaction stages through a morphology transition process with treatment using ultrasound. In the initial reaction stage, Fourier transform infrared spectra indicate that the aniline monomers form phenazine-like units, producing polyaniline microspheres with an outside diameter of 1,2 µm. The hydrogen bonds between 1-propanol and polyaniline serve as the driving force for the polyaniline chains to build microspheres. As the reaction continues, observation indicates the microspheres decompose and reform one-dimensional nanotubes. In this stage, a structure consisting of a head of phenazine-like units and a tail of acid-doping para -linked aniline units develops. The protonation of the para -linked aniline units provides the driving force for the formation of nanotubes through a self-curling process. We report here the unique morphology transition of polyaniline from microspheres to nanotubes in a single polymerization process. The results indicate that the structural change of polyaniline leads to this morphological change. The mechanisms of formation of the microspheres and nanotubes in a polymerization process are also well explained. Copyright © 2010 Society of Chemical Industry [source] | |||||||||||||