Size modification of Au nanoparticles induced by slow highly charged ions Ar-40(q+) irradiation

Size modification of Au nanoparticles (NPs), deposited on the Au-thick film surface and irradiated by slow highly charged ions (SHCI) 40Arq+ (3 6 q 6 12) with fixed low dose of 4.3 1011 ions/cm2 and various energy ranging from 74.64 to 290.64 keV at room temperature (293.15 K), was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The effect of projectile kinetic energy on the modified size of NPs was explored by an appropriate choice of the fixed process parameters such as ion flux, irradiation temperature, incident angle, irradiation time, etc. The morphological changes of NPs were interpreted by models involving collisional mixing, Ostwald ripening (OR) and inverse Ostwald ripening (IOR) of spherical NPs on a substrate. A critical kinetic energy as well as a critical potential energy of the projectile in the Au NPs size modification process were observed.

Suppression of phase separation in PC/PMMA blend film by thermoset oligomer

Phase separation of bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) thin blend film is suppressed by addition of solid epoxy oligomer. Epoxy has strong intermolecular interactions with both PC and PMMA, while PC and PMMA are quite incompatible with each other. Consequently, phase separation in the PC/PMMA blend film pushes epoxy to the interface; at the same time, PC and epoxy react readily at the interface to form a cross-linking structure, binding PMMA chains together. Therefore, the interface between PC and PMMA is effectively reinforced, and the PC/PMMA thin blend film is stabilized against phase separation. On the other hand, only an optimal content of epoxy (i.e., 10 wt %) can serve as an efficient interfacial agent. In contrast to the traditional reactive compatibilization, here we observed that the cross-linking structure along the interface is much more stable than block or graft copolymers. Atomic force microscopy (AFM) is used to characterize the morphological changes of the blend films as a function of annealing time. Two-dimensional fast Fourier transform (2D-FFT) of AFM data allows quantitative investigation of the scaling behavior of phase separation kinetics.

The influence of hard-segments on two-phase structure and shape memory properties of PCL-based segmented polyurethanes

Poly(epsilon-caprolactone)-based segmented polyurethanes (PCLUs) were prepared from poly(epsilon-caprolactone) diol, diisocyanates (DI), and 1,4-butanediol. The DIs used were 4,4'-diphenylmethane diisocyanate (MDI), 2,4-toluenediisocyanate (TDI), iso-phorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small-angle X-ray scattering, and dynamic mechanical analysis were employed to characterize the two-phase structures of all PCLUs. It was found that HDI- and MDI-based PCLUs had higher degree of microphase separation than did IPDI- and TDI-based PCLUs, which was primarily due to the crystallization of HDI- and MDI-based hard-segments. As a result, the HDI-based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard-segment domains during the sample deformation was responsible for the incomplete shape-recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation.

Effect of annealing on the viscoelastic and viscoplastic responses of low-density polyethylene

Two series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low-density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 degreesC. Constitutive equations were derived for the time-dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress-strain relations involve five material constants that were found by fitting the observations.

Ring-opening polymerization and block copolymerization of L-lactide with divalent samarocene complex

Divalent samarocene complex [(C5H9C5H4)(2)Sm(tetrahydrofuran)(2)] was prepared and characterized and used to catalyze the ring-opening polymerization of L-lactide (L-LA) and copolymerization of L-LA with caprolactone (CL). Several factors affecting monomer conversion and molecular weight of polymer, such as polymerization time, temperature, monomer/catalyst ratio, and solvent, were examined. The results indicated that polymerization was rapid, with monomer conversions reaching 100% within 1 h, and the conformation of L-LA was retained. The structure of the block copolymer of CL/L-LA was characterized by NMR and differential scanning calorimetry. The morphological changes during crystallization of poly(caprolactone) (PCL)-b-P(L-LA) copolymer were monitored with real-time hot-stage atomic force microscopy (AFM). The effect of temperature on the morphological change and crystallization behavior of PCL-b-P(L-LA) copolymer was demonstrated through AFM observation.

Polydispersity of ethylene sequence length in metallocene ethylene/alpha-olefin copolymers. II. Influence on crystallization and melting behavior

In this work, crystallization and melting behavior of metallocene ethylene/alpha-olefin copolymers were investigated by differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The results indicated that the crystallization and melting temperatures for all the samples were directly related to the long ethylene sequences instead of the average sequence length (ASL), whereas the crystallization enthalpy and crystallinity were directly related to ASL, that is, both parameters decreased with a decreasing ASL. Multiple melting peaks were analyzed by thermal analysis. Three phenomena contributed to the multiple melting behaviors after isothermal crystallization, that is, the melting of crystals formed during quenching, the melting-recrystallization process, and the coexistence of different crystal morphologies. Two types of crystal morphologies could coexist in samples having a high comonomer content after isothermal crystallization. They were the chain-folded lamellae formed by long ethylene sequences and the bundlelike crystals formed by short ethylene sequences. The coexistence phenomenon was further proved by the AFM morphological observation.

New insight into melting and crystallization behavior in semicrystalline poly(ethylene terephthalate)

After isothermal crystallization, poly(ethylene terephthalate) (PET) showed double endothermic behavior in the differential scanning calorimetry (DSC) heating scan. During the heating scans of semicrystalline PET, a metastable melt which comes from melting thinner lamellar crystal populations formed between the low and the upper endothermic temperatures. The metastable melt can recrystallize immediately just above the low melting temperature and form thicker lamellae than the original ones. The thickness and perfection depends on the crystallization time and crystallization temperature. The crystallization kinetics of this metastable melt can be determined by means of DSC. The kinetics analysis showed that the isothermal crystallization of the metastable PET melt proceeds with an Avrami exponent of n = 1.0 similar to 1.2, probably reflecting one-dimensional or irregular line growth of the crystal occurring between the existing main lamellae with heterogeneous nucleation. This is in agreement with the hypothesis that the melting peaks are associated with two distinct crystal populations with different thicknesses. (C) 2000 John Wiley & Sons, Inc.

Atomic force microscopy imaging of molybdenum oxide film electrodeposited on a carbon electrode

Non-stoichiometric mixed-valent molybdenum(VI, V) oxide film was grown on carbon substrates by the electrodeposition method. Responses of the prepared molybdenum oxide thin films to potential and to different solution acidities were studied by cyclic voltammetry, and the corresponding morphological changes of the film were monitored by atomic force microscopy (AFM). AFM images of the molybdenum oxide film show that the characteristic domed structure on the film surface increased during the transition from the oxidized state to the reduced state without signification change in the KMS surface roughness value. Furthermore, AFM studies show that the solution acidity has great effect on the morphology of the films, and the films undergo a homogenizing process with increasing pH of the solutions. (C) 1999 Elsevier Science S.A. All rights reserved.

Extra- and intra-cellular ice formation of red seabream (Pagrus major) embryos at different cooling rates

The ice crystal formation is assumed as the most lethal factor for the failure of fish embryo cryopreservation and intracellular ice formation (IIF) plays a central role in cell injury during cooling. The objectives were to observe the morphological changes of red seabream (Pagrus major) embryo during the cooling-thawing process, and to examine the effect of cryoprotectant and cooling rate on the temperatures of oil globule ice formation (T-OIF), extra-cellular ice formation (T-EIF) and intracellular ice formation (T-IIF) using cryomicroscope. After thawing, the morphological changes of embryos were observed and recorded by the video attachment and monitor under the microscope. During the cooling process, three representative phenomena were observed: oil globule gradually turned bright firstly, then the whole field of view flashed and the embryo blackened. Cooling rate affect the temperature of both extra- and intra-cellular ice formations. T-EIF and T-IIF at high cooling rate were much lower than that at low cooling rate. And the value of T-EIF - T-IIF increased from 0.45 to 11.11 degrees C with the increase of cooling rate from 3 to 130 degrees C/min. Taken together, our results suggested that high cooling rate with proper cryoprotectant would be a good option for red seabream embryo cryopreservation. (C) 2009 Elsevier Inc. All rights reserved.

A novel anti-tumor protein extracted from Meretrix meretrix Linnaeus induces cell death by increasing cell permeability and inhibiting tubulin polymerization

Discovery and development of new pharmaceuticals from marine organisms are attracting increasing interest. Several agents derived from marine organisms are under preclinical and clinical evaluation as potential anticancer drugs. We extracted and purified a novel anti-tumor protein from the coelomic fluid of Meretrix meretrix Linnaeus by ammonium sulphate fractionation, ion exchange and hydrophobic interaction chromatography. The molecular weight of the highly purified protein, designated MML, was 40 kDa as determined by SDS-PAGE analysis. MML exhibited significant cytotoxicity to several cancer cell types, including human hepatoma BEL-7402, human breast cancer MCF-7 and human colon cancer HCT116 cells. However, no inhibitory effect was found when treating murine normal fibroblasts NIH3T3 and benign human breast MCF-10A cells with MML. The cell death induced by MML was characterized by cell morphological changes. The induction of apoptosis of BEL-7402 cells by MML was weak by DNA ladder assay. The possible mechanisms of its anti-tumor effect might be the changes in cell membrane permeability and inhibition of tubulin polymerization. MML may be developed as a novel, highly selective and effective anti-cancer drug.

Effect of heavy metals (Cd, Cu) on the gametophytes of Laminaria japonica Aresch

Effects of various concentrations of two heavy metals, namely Cd and Cu, on gametophytes of Laminaria japonica Aresch were determined by recording morphological changes of gametophytes, determining pH values and the heavy metal content of the culture solution, calculating the germination rate of sporophytes, and observing heavy metal (Cd) distribution using a fluorescence microscope. The results showed that heavy metals damaged the gametophytes, and were even lethal, and that the higher the concentration of heavy metal ions, the greater the injury to gametophytes. Gametophytes could not survive in culture solutions containing more than 100 mg/L Cd and 50 mg/L Cu and were only able to survive in culture solution containing a mixture of Cd and Cu tip to a concentration of 10 mg/L, which indicates that gametophytes have a higher tolerance to Cd than Cu and that multiple heavy metal ions in solution markedly aggravate the damage to gametophytes compared with individual heavy metal ions. With increases in the concentration of the heavy metal, the burgeoning rate of sporophytes decreased acutely, and solutions containing multiple heavy metal ions caused even more marked harm to sporophytes than solutions containing a single heavy metal ion, because most sporophytes died in mixed solutions. The pH value of the culture medium dropped immediately at the beginning (the first day) of treatment, increased over the following days, and then decreased again. The pH of culture media containing multiple heavy metal ions showed greater variation than media containing a single heavy metal ion, with the extent of the decrease in pH of culture media containing multiple ions being greatest during the last period of the experiment. With increases in the concentration of heavy metals, the capacity of gametophytes to accumulate these ions increased. The blue fluorescent light emitted by the Cd- and Cd-binding protein complex existing in gametophytes in media containing different concentrations of Cd showed clearly the distribution of the ion in gametophytes and the results obtained were consistent with distribution determined using other methods. All results of the present study showed that gametophytes of L. japonica play a remarkable role as heavy metal decontaminators, especially with regard to Cd.

River mouth bar formation, riverbed aggradation and channel migration in the modern Huanghe (Yellow) River delta, China

This paper addresses the recent (1970s-1990s) processes of river mouth bar formation, riverbed aggradation and distributary migration in the Huanghe River mouth area, in the light of station-based monitoring, field measurements and remote sensing interpretation. The results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load. Landforrn development such as bar progradation occurred in two phases, i.e. before and after 1989, which correspond to faster and lower bar growth rates, respectively. Fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation. During 1976-1996, about 2.8% of the total sediment loads were deposited in the river channel on the upper to middle delta. Therefore, the river water level rose by a few meters from 1984 to 1996. The frequent distributary channel migration, which switched the radial channel pattern into the SE-directed pattern in the mid-1980s, was linked with mouth bar formation. Marine conditions also constrain seaward bar progradation. Furthermore, the history of river mouth bar formation reflects human impacts, such as dredging and dyking in order to stabilize the coastal area. (c) 2005 Elsevier B.V. All rights reserved.

Recovery and fate of three species of marine dinoflagellates after yellow clay flocculation

The recovery and fate of three species of dinoflagellates, Alexandrium tamarense, Cochlodinium polykrikoides and Scrippsiella trochoidea, after having been sedimented by yellow clay, were investigated in the laboratory. The effect of burying period in yellow clay pellet and mixing on the recovery of settled algal cells were studied. The morphological changes of algal cells in yellow clay pellet were also tracked. Results showed that there was almost no recovery for A. tamarense and C. polykrikoides, and the cells decomposed after 2-3 days after visible changes in morphology and chloroplasts. There was some recovery for S. trochoidea. Moreover, S. trochoidea cysts were formed in clay pellet during the period of about 14 days, with the highest abundance of 87 000 cysts g(-1) clay and the incidence of cyst formation of 6.5%, which was considered as a potential threat for the further occurrence of algal blooms. S. trochoidea cysts were isolated from yellow clay and incubated to test their viability, and a germination ratio of more than 30% was obtained after incubation for 1 month. These results showed the species specificity of the mitigation effect of yellow clay. It is suggested that cautions be taken for some harmful species and thorough risk assessments be conducted before using this mitigation strategy in the field.

Preliminary studies on the vitrification of red sea bream (Pagrus major) embryos

The objective was to identify an appropriate cryoprotectant and protocol for vitrification of red sea bream (Pagrus major) embryos. The toxicity of five single-agent cryoprotectants, dimethyl sulfoxide (DMSO), propylene glycol (PG), ethylene glycol (EG), glycerol (GLY), and methyl alcohol (MeOH), as well as nine cryoprotectant mixtures, were investigated by comparing post-thaw hatching rates. Two vitrifying protocols, a straw method and a solid surface vitrification method (copper floating over liquid nitrogen), were evaluated on the basis of post-thaw embryo morphology. Exposure to single-agent cryoprotectants (10% concentration for 15 min) was not toxic to embryos, whereas for higher concentrations (20 and 30%) and a longer duration of exposure (30 min), DMSO and PG were better tolerated than the other cryoprotectants. Among nine cryoprotectant mixtures, the combination of 20% DMSO + 10% PG + 10% MeOH had the lowest toxicity after exposure for 10 min or 15 min. High percentages of morphologically intact embryos, 50.6 +/- 16.7% (mean +/- S.D.) and 77.8 +/- 15.5%, were achieved by the straw vitrifying method (20.5% DMSO + 15.5% acetamide + 10% PG, thawing at 43 degrees C and washing in 0.5 M sucrose solution for 5 min) and by the solid surface vitrification method (40% GLY, thawing at 22 degrees C and washing in 0.5 M sucrose solution for 5 min). After thawing, morphological changes in the degenerated embryos included shrunken yolks and ruptured chorions. Furthermore, thawed embryos that were morphologically intact did not consistently survive incubation. (C) 2007 Elsevier Inc. All rights reserved.

Mitochondrial DNA phylogeny of two morphologically enigmatic fishes in the subfamily Schizothoracinae (Teleostei : Cyprinidae) in the Qinghai-Tibetan Plateau

The complete mitochondrial DNA (mtDNA) cytochrome b gene (1140 bp) was sequenced in Herzenstein macrocephalus and Gymnocypris namensis and in 13 other species and sub-species (n = 22), representing four closely related genera in the subfamily Schizothoracinae. Conflicting taxonomies of H. macrocephalus and G. namensis have been proposed because of the character instability among individuals. Parsimony, maximum likelihood and Bayesian methods produced phylogenetic trees with the same topology and resolved several distinctive clades. Previous taxonomic treatments, which variously placed these two species of separate genera or as sub-species, are inconsistent with the mtDNA phylogeny. Both H. macrocephalus and G. namensis appear in a well-supported clade, which also includes nine species of Schizopygopsis, and hence should be transferred to the genus Schizopygopsis. Morphological changes are further illustrated, and their adaptive evolution in response to the local habitat shifts during the speciation process appears to be responsible for conflicting views on the systematics of these two species and hence the contrasting taxonomic treatments. These species are endemic to the Qinghai-Tibetan Plateau, a region with a history of geological activity and a rich diversity of habitats that may have result in the parallel and reversal evolution of some morphological characters used in their taxonomies. Our results further suggest that speciation and morphological evolution of fishes in this region may be more complex than those previously expected. (c) 2007 The Authors Journal compilation (c) 2007 The Fisheries Society of the British Isles.