Mosquito larvae borne viruses from the central travancore region of kerala: isolation and characterization

The present study was initiated when several massive outbreaks of Chikungunya, Dengue and Japanese Encephalitis were frequently reported across the State of Kerala. Multiple symptoms persisted among the affected individuals and the public health officials were in search of aetiological agents responsible for the out breaks and, other than clinical samples no resources were available. In this context, a study was undertaken to focus on mosquito larvae to investigate the viruses borne by them which remain silently prevalent in the environment. The study was not a group specific investigation limited to either arbovirus or enterovirus, but had a broad spectrum approach. The study encompassed the viral pathogens that could be isolated, their impact when passaged through cell lines, growth kinetics, titer of the working stocks in specific cell line, the structure by means of transmission electron microscopy(TEM), the one step growth and molecular characterization using molecular tools.

Differential induction, isolation, physicochemical and molecular characterization of temperate phages of environmental Vibrio cholerae as evidence of phage mediated Horizontal Gene Transfer

The resurgence of the enteric pathogen Vibrio cholerae, the causative organism of epidemic cholera, remains a major health problem in many developing countries like India. The southern Indian state of Kerala is endemic to cholera. The outbreaks of cholera follow a seasonal pattern in regions of endemicity. Marine aquaculture settings and mangrove environments of Kerala serve as reservoirs for V. cholerae. The non-O1/non-O139 environmental isolates of V. cholerae with incomplete ‘virulence casette’ are to be dealt with caution as they constitute a major reservoir of diverse virulence genes in the marine environment and play a crucial role in pathogenicity and horizontal gene transfer. The genes coding cholera toxin are borne on, and can be infectiously transmitted by CTXΦ, a filamentous lysogenic vibriophages. Temperate phages can provide crucial virulence and fitness factors affecting cell metabolism, bacterial adhesion, colonization, immunity, antibiotic resistance and serum resistance. The present study was an attempt to screen the marine environments like aquafarms and mangroves of coastal areas of Alappuzha and Cochin, Kerala for the presence of lysogenic V. cholerae, to study their pathogenicity and also gene transfer potential. Phenotypic and molecular methods were used for identification of isolates as V. cholerae. The thirty one isolates which were Gram negative, oxidase positive, fermentative, with or without gas production on MOF media and which showed yellow coloured colonies on TCBS (Thiosulfate Citrate Bile salt Sucrose) agar were segregated as vibrios. Twenty two environmental V. cholerae strains of both O1 and non- O1/non-O139 serogroups on induction with mitomycin C showed the presence of lysogenic phages. They produced characteristic turbid plaques in double agar overlay assay using the indicator strain V. cholerae El Tor MAK 757. PCR based molecular typing with primers targeting specific conserved sequences in the bacterial genome, demonstrated genetic diversity among these lysogen containing non-O1 V. cholerae . Polymerase chain reaction was also employed as a rapid screening method to verify the presence of 9 virulence genes namely, ctxA, ctxB, ace, hlyA, toxR, zot,tcpA, ninT and nanH, using gene specific primers. The presence of tcpA gene in ALPVC3 was alarming, as it indicates the possibility of an epidemic by accepting the cholera. Differential induction studies used ΦALPVC3, ΦALPVC11, ΦALPVC12 and ΦEKM14, underlining the possibility of prophage induction in natural ecosystems, due to abiotic factors like antibiotics, pollutants, temperature and UV. The efficiency of induction of prophages varied considerably in response to the different induction agents. The growth curve of lysogenic V. cholerae used in the study drastically varied in the presence of strong prophage inducers like antibiotics and UV. Bacterial cell lysis was directly proportional to increase in phage number due to induction. Morphological characterization of vibriophages by Transmission Electron Microscopy revealed hexagonal heads for all the four phages. Vibriophage ΦALPVC3 exhibited isometric and contractile tails characteristic of family Myoviridae, while phages ΦALPVC11 and ΦALPVC12 demonstrated the typical hexagonal head and non-contractile tail of family Siphoviridae. ΦEKM14, the podophage was distinguished by short non-contractile tail and icosahedral head. This work demonstrated that environmental parameters can influence the viability and cell adsorption rates of V. cholerae phages. Adsorption studies showed 100% adsorption of ΦALPVC3 ΦALPVC11, ΦALPVC12 and ΦEKM14 after 25, 30, 40 and 35 minutes respectively. Exposure to high temperatures ranging from 50ºC to 100ºC drastically reduced phage viability. The optimum concentration of NaCl required for survival of vibriophages except ΦEKM14 was 0.5 M and that for ΦEKM14 was 1M NaCl. Survival of phage particles was maximum at pH 7-8. V. cholerae is assumed to have existed long before their human host and so the pathogenic clones may have evolved from aquatic forms which later colonized the human intestine by progressive acquisition of genes. This is supported by the fact that the vast majority of V. cholerae strains are still part of the natural aquatic environment. CTXΦ has played a critical role in the evolution of the pathogenicity of V. cholerae as it can transmit the ctxAB gene. The unusual transformation of V. cholerae strains associated with epidemics and the emergence of V. cholera O139 demonstrates the evolutionary success of the organism in attaining greater fitness. Genetic changes in pathogenic V. cholerae constitute a natural process for developing immunity within an endemically infected population. The alternative hosts and lysogenic environmental V. cholerae strains may potentially act as cofactors in promoting cholera phage ‘‘blooms’’ within aquatic environments, thereby influencing transmission of phage sensitive, pathogenic V. cholerae strains by aquatic vehicles. Differential induction of the phages is a clear indication of the impact of environmental pollution and global changes on phage induction. The development of molecular biology techniques offered an accessible gateway for investigating the molecular events leading to genetic diversity in the marine environment. Using nucleic acids as targets, the methods of fingerprinting like ERIC PCR and BOX PCR, revealed that the marine environment harbours potentially pathogenic group of bacteria with genetic diversity. The distribution of virulence associated genes in the environmental isolates of V. cholerae provides tangible material for further investigation. Nucleotide and protein sequence analysis alongwith protein structure prediction aids in better understanding of the variation inalleles of same gene in different ecological niche and its impact on the protein structure for attaining greater fitness of pathogens. The evidences of the co-evolution of virulence genes in toxigenic V. cholerae O1 from different lineages of environmental non-O1 strains is alarming. Transduction studies would indicate that the phenomenon of acquisition of these virulence genes by lateral gene transfer, although rare, is not quite uncommon amongst non-O1/non-O139 V. cholerae and it has a key role in diversification. All these considerations justify the need for an integrated approach towards the development of an effective surveillance system to monitor evolution of V. cholerae strains with epidemic potential. Results presented in this study, if considered together with the mechanism proposed as above, would strongly suggest that the bacteriophage also intervenes as a variable in shaping the cholera bacterium, which cannot be ignored and hinting at imminent future epidemics.

Silbernanoteilchen auf Magnesiumoxid - Über den Vergleich von optischer Spektroskopie, Rasterkraftmikroskopie und Transmissionselektronenmikroskopie

In der vorliegenden Arbeit wurde das Wachstum von Silbernanoteilchen auf Magnesiumoxid und dabei insbesondere deren Größen- und Formrelation untersucht. Hierzu wurden Silbernanoteilchen auf ausgedehnten Magnesiumoxidsubstraten sowie auf Magnesiumoxid-Nanowürfeln präpariert. Zur Charakterisierung wurde die optische Spektroskopie, die Rasterkraftmikroskopie und die Transmissionselektronenmikroskopie eingesetzt. Während die Elektronenmikroskopie direkt sehr exakte Daten bezüglich der Größe und Form der Nanoteilchen liefert, kann mit den beiden anderen in dieser Arbeit verwendeten Charakterisierungsmethoden jeweils nur ein Parameter bestimmt werden. So kann man die Größe der Nanoteilchen indirekt mit Hilfe des AFM, durch Messung der Teilchananzahldichte, bestimmen. Bei der Bestimmung der Form mittels optischer Spektroskopie nutzt man aus, dass die spektralen Positionen der Plasmonresonanzen in dem hier verwendeten Größenbereich von etwa 2 - 10~nm nur von der Form aber nicht von der Größe der Teilchen abhängen. Ein wesentliches Ziel dieser Arbeit war es, die Ergebnisse bezüglich der Form und Größe der Nanoteilchen, die mit den unterschiedlichen Messmethoden erhalten worden sind zu vergleichen. Dabei hat sich gezeigt, dass die mit dem AFM und dem TEM bestimmten Größen signifikant voneinander Abweichen. Zur Aufklärung dieser Diskrepanz wurde ein geometrisches Modell aufgestellt und AFM-Bilder von Nanoteilchen simuliert. Bei dem Vergleich von optischer Spektroskopie und Transmissionselektronenmikroskopie wurde eine recht gute Übereinstimmung zwischen den ermittelten Teilchenformen gefunden. Hierfür wurden die gemessenen optischen Spektren mit Modellrechnungen verglichen, woraus man die Relation zwischen Teilchengröße und -form erhielt. Eine Übereinstimmung zwischen den erhaltenen Daten ergibt sich nur, wenn bei der Modellierung der Spektren die Form- und Größenverteilung der Nanoteilchen berücksichtigt wird. Insgesamt hat diese Arbeit gezeigt, dass die Kombination von Rasterkraftmikroskopie und optischer Spektroskopie ein vielseitiges Charakterisierungsverfahren für Nanoteilchen. Die daraus gewonnenen Ergebnisse sind innerhalb gewisser Fehlergrenzen gut mit der Transmissionselektronenmikroskopie vergleichbar.

The Surface Plasmon Resonance of Supported Noble Metal Nanoparticles: Characterization, Laser Tailoring, and SERS Application

This work deals with the optical properties of supported noble metal nanoparticles, which are dominated by the so-called Mie resonance and are strongly dependent on the particles’ morphology. For this reason, characterization and control of the dimension of these systems are desired in order to optimize their applications. Gold and silver nanoparticles have been produced on dielectric supports like quartz glass, sapphire and rutile, by the technique of vapor deposition under ultra-high vacuum conditions. During the preparation, coalescence is observed as an important mechanism of cluster growth. The particles have been studied in situ by optical transmission spectroscopy and ex situ by atomic force microscopy. It is shown that the morphology of the aggregates can be regarded as oblate spheroids. A theoretical treatment of their optical properties, based on the quasistatic approximation, and its combination with results obtained by atomic force microscopy give a detailed characterization of the nanoparticles. This method has been compared with transmission electron microscopy and the results are in excellent agreement. Tailoring of the clusters’ dimensions by irradiation with nanosecond-pulsed laser light has been investigated. Selected particles are heated within the ensemble by excitation of the Mie resonance under irradiation with a tunable laser source. Laser-induced coalescence prevents strongly tailoring of the particle size. Nevertheless, control of the particle shape is possible. Laser-tailored ensembles have been tested as substrates for surface-enhanced Raman spectroscopy (SERS), leading to an improvement of the results. Moreover, they constitute reproducible, robust and tunable SERS-substrates with a high potential for specific applications, in the present case focused on environmental protection. Thereby, these SERS-substrates are ideally suited for routine measurements.

Molecular Beam Epitaxial Growth of III-V Semiconductor Nanostructures on Silicon Substrates

The main focus and concerns of this PhD thesis is the growth of III-V semiconductor nanostructures (Quantum dots (QDs) and quantum dashes) on silicon substrates using molecular beam epitaxy (MBE) technique. The investigation of influence of the major growth parameters on their basic properties (density, geometry, composition, size etc.) and the systematic characterization of their structural and optical properties are the core of the research work. The monolithic integration of III-V optoelectronic devices with silicon electronic circuits could bring enormous prospect for the existing semiconductor technology. Our challenging approach is to combine the superior passive optical properties of silicon with the superior optical emission properties of III-V material by reducing the amount of III-V materials to the very limit of the active region. Different heteroepitaxial integration approaches have been investigated to overcome the materials issues between III-V and Si. However, this include the self-assembled growth of InAs and InGaAs QDs in silicon and GaAx matrices directly on flat silicon substrate, sitecontrolled growth of (GaAs/In0,15Ga0,85As/GaAs) QDs on pre-patterned Si substrate and the direct growth of GaP on Si using migration enhanced epitaxy (MEE) and MBE growth modes. An efficient ex-situ-buffered HF (BHF) and in-situ surface cleaning sequence based on atomic hydrogen (AH) cleaning at 500 °C combined with thermal oxide desorption within a temperature range of 700-900 °C has been established. The removal of oxide desorption was confirmed by semicircular streaky reflection high energy electron diffraction (RHEED) patterns indicating a 2D smooth surface construction prior to the MBE growth. The evolution of size, density and shape of the QDs are ex-situ characterized by atomic-force microscopy (AFM) and transmission electron microscopy (TEM). The InAs QDs density is strongly increased from 108 to 1011 cm-2 at V/III ratios in the range of 15-35 (beam equivalent pressure values). InAs QD formations are not observed at temperatures of 500 °C and above. Growth experiments on (111) substrates show orientation dependent QD formation behaviour. A significant shape and size transition with elongated InAs quantum dots and dashes has been observed on (111) orientation and at higher Indium-growth rate of 0.3 ML/s. The 2D strain mapping derived from high-resolution TEM of InAs QDs embedded in silicon matrix confirmed semi-coherent and fully relaxed QDs embedded in defectfree silicon matrix. The strain relaxation is released by dislocation loops exclusively localized along the InAs/Si interfaces and partial dislocations with stacking faults inside the InAs clusters. The site controlled growth of GaAs/In0,15Ga0,85As/GaAs nanostructures has been demonstrated for the first time with 1 μm spacing and very low nominal deposition thicknesses, directly on pre-patterned Si without the use of SiO2 mask. Thin planar GaP layer was successfully grown through migration enhanced epitaxy (MEE) to initiate a planar GaP wetting layer at the polar/non-polar interface, which work as a virtual GaP substrate, for the GaP-MBE subsequently growth on the GaP-MEE layer with total thickness of 50 nm. The best root mean square (RMS) roughness value was as good as 1.3 nm. However, these results are highly encouraging for the realization of III-V optical devices on silicon for potential applications.

The Effect of Periodic Silane Burst on the Properties of GaN on Si (111) Substrates

The periodic silane burst technique was employed during metalorganic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111). Periodic silicon delta doping during growth of both the AlN and GaN layers led to growth of GaN films with decreased tensile stresses and decreased threading dislocation densities, as well as films with improved quality as indicated by x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The possible mechanism of the reduction of tensile stress and the dislocation density is discussed in the paper.

High Density Single Crystalline GaN Nanodot Arrays Fabricated Using Template-Assisted Selective Growth

High density, uniform GaN nanodot arrays with controllable size have been synthesized by using template-assisted selective growth. The GaN nanodots with average diameter 40nm, 80nm and 120nm were selectively grown by metalorganic chemical vapor deposition (MOCVD) on a nano-patterned SiO2/GaN template. The nanoporous SiO2 on GaN surface was created by inductively coupled plasma etching (ICP) using anodic aluminum oxide (AAO) template as a mask. This selective regrowth results in highly crystalline GaN nanodots confirmed by high resolution transmission electron microscopy. The narrow size distribution and uniform spatial position of the nanoscale dots offer potential advantages over self-assembled dots grown by the Stranski–Krastanow mode.

Strained Silicon on Silicon by Wafer Bonding and Layer Transfer from Relaxed SiGe Buffer

We report the creation of strained silicon on silicon (SSOS) substrate technology. The method uses a relaxed SiGe buffer as a template for inducing tensile strain in a Si layer, which is then bonded to another Si handle wafer. The original Si wafer and the relaxed SiGe buffer are subsequently removed, thereby transferring a strained-Si layer directly to Si substrate without intermediate SiGe or oxide layers. Complete removal of Ge from the structure was confirmed by cross-sectional transmission electron microscopy as well as secondary ion mass spectrometry. A plan-view transmission electron microscopy study of the strained-Si/Si interface reveals that the lattice-mismatch between the layers is accommodated by an orthogonal array of edge dislocations. This misfit dislocation array, which forms upon bonding, is geometrically necessary and has an average spacing of approximately 40nm, in excellent agreement with established dislocation theory. To our knowledge, this is the first study of a chemically homogeneous, yet lattice-mismatched, interface.

Association Behavior of Biotinylated and Non-Biotinylated PolyEthylene Oxide-b-Poly(2-(Diethylamino)Ethyl Methacrylate)

Biotinylated and non-biotinylated copolymers of ethylene oxide (EO) and 2-(diethylamino)ethyl methacrylate (DEAEMA) were synthesized by the atom transfer radical polymerization technique (ATRP). The chemical compositions of the copolymers as determined by NMR are represented by PEO₁₁₃PDEAEMA₇₀ and biotin-PEO₁₀₄PDEAEMA₉₃ respectively. The aggregation behavior of these polymers in aqueous solutions at different pHs and ionic strengths was studied using a combination of potentiometric titration, dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM). Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers form micelles at high pH with hydrodynamic radii (Rh) of about 19 and 23 nm, respectively. At low pH, the copolymers are dispersed as unimers in solution with Rh of about 6-7 nm. However, at a physiological salt concentration (cs) of about 0.16M NaCl and a pH of 7-8, the copolymers form large loosely packed Guassian chains, which were not present at the low cs of 0.001M NaCl. The critical micelle concentrations (CMC) and the cytotoxicity of the copolymers were investigated to determine a suitable polymer concentration range for future biological applications. Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers possess identical CMC values of about 0.0023 mg/g, while the cytotoxicity test indicated that the copolymers are not toxic up to 0.05mg/g (> 83% cell survival at this concentration).

Self-Assembly of Stimuli-Responsive Water-Soluble [60]Fullerene End-Capped Ampholytic Block Copolymer

Well-defined, water-soluble, pH and temperature stimuli-responsive [60]fullerene (C₆₀) containing ampholytic block copolymer of poly((methacrylic acid)-block-(2-(dimethylamino)ethyl methacrylate))-block–C₆₀ (P(MAA-b-DMAEMA)-b-C₆₀) was synthesized by the atom transfer radical polymerization (ATRP) technique. The self-assembly behaviour of the C₆₀ containing polyampholyte in aqueous solution was characterized by dynamic light scattering (DLS), and transmission electron microscopy. This amphiphilic mono-C₆₀ end-capped block copolymer shows enhanced solubility in aqueous medium at room and elevated temperatures and at low and high pH but phase-separates at intermediate pH of between 5.4 and 8.8. The self assembly of the copolymer is different from that of P(MAA-b-DMAEMA). Examination of the association behavior using DLS revealed the co-existence of unimers and aggregates at low pH at all temperatures studied, with the association being driven by the balance of hydrophobic and electrostatic interactions. Unimers and aggregates of different microstructures are also observed at high pH and at temperatures below the lower critical solution temperature (LCST) of PDMAEMA. At high pH and at temperatures above the LCST of PDMAEMA, the formation of micelles and aggregates co-existing in solution is driven by the combination of hydrophobic, electrostatic, and charge-transfer interactions.

Coloraciones histológicas vs microscopia electrónica de transmision para detección de Biopeliculas en pacientes con Rinosinusitis Crónica en el Hospital Universitario de la Samaritana en el año 2011

Objetivo: Determinar la concordancia entre microscopia de luz vs microscopia electrónica de transmisión para la detección de Biopeliculas en pacientes con Rinosinusitis Crónica Diseño: Estudio de concordancia. Materiales y Métodos: Analizamos 34 muestras de pacientes llevados a Cirugía Endoscópica Funcional por Rinosinusitis Crónica. Fueron procesadas para valoración mediante microscopia de luz usando Hematoxilina-Eosina, Gram, Acido Peryódico de Schiff, Giemsa y Microscopia Electrónica de Transmisión (MET). Resultados: No se identificaron Biopelícula en ninguna de las muestras analizadas bajo Microscopía Electrónica de Transmisión (MET), estos resultados son concordantes con los resultados obtenidos con las coloraciones histológicas Hematoxilina-Eosina (H-E), Gram, Giemsa y Acido Peryódico de Schiff (PAS), mostrando una concordancia absoluta con test de Kappa para resultados negativos del 100%. Conclusión: Existe una alta concordancia entre los hallazgos observados entre la MET y la Microscopia de luz para los resultados negativos

Estudi estructural, ultraestructural i histoquímic de les glàndules sexuals accessòries del mascle reproductor porcí (Sus domesticus)

El present treball analitza al microscopi òptic i al microscopi electrònic de transmissió les glàndules sexuals accessòries de Sus domesticus (raça Landrace - varietat anglesa) a partir de mascles reproductors porcins adults i sans. Un millor coneixement dels patrons estructural i ultraestructural normals de las glàndules sexuals accessòries permetrà diagnosticar amb facilitat quina ha estat l'estructura o la funció glandular afectada en mascles en els que s'observa una disminució de la qualitat del semen. Per altra banda, els estudis anatomopatològics s'han de complementar amb tècniques histoquímiques que generalment permeten confirmar o excloure un diagnòstic histopatològic previ. Les glàndules sexuals accessòries del mascle reproductor porcí estan molt desenvolupades i inclouen les glàndules vesiculars, la pròstata i les glàndules bulbouretrals. L'epiteli secretor de les glàndules vesiculars està format per cèl·lules columnars, cèl·lules basals i mastòcits. Les cèl·lules columnars es caracteritzen per presentar tres morfologies diferents que es consideren diferents estadis d'un mateix tipus cel·lular: les cèl·lules principals, les cèl·lules clares i les cèl·lules denses. Les cèl·lules principals secreten activament glicoproteïnes N- i O- glicosilades amb residus d'α-L-fucosa, α(16)fucosa, α-D-mannosa, α-D-glucosa, α- i -D-N-acetilgalactosamina, -D-galactosa-(13)-D-N-acetilgalactosamina, α-D-galactosa, galactosa-(14)-N-acetilglucosamina, D-N-acetilglucosamina i àcid neuramínic. Aquestes glicoproteïnes afavoreixen les interaccions entre l'espermatozoide i l'occit i regulen la permeabilitat de la membrana espermàtica. La pròstata està formada per dues porcions glandulars, el cos de la pròstata (BP) y la pròstata disseminada (DP), entre las quals s'observen diferencies estructurals, ultraestructurals, histoquímiques i funcionals. En ambdues porcions, l'epiteli secretor està constituït per cèl·lules columnars principals, denses i cèl·lules basals, i també per cèl·lules cúbiques en el BP i per cèl·lules mucoses en la DP. En ambdues porcions glandulars, se sintetitzen i secreten N- i O- glicoproteïnes neutres i àcides. Aquestes glicoproteïnes s'alliberen mitjançant un mecanisme regulat en el BP y mitjançant un mecanisme regulat i un constitutiu en la DP. Les glucoproteïnes luminals del BP contenen residus de fucosa, mannosa, α- i -D-N-acetilgalactosamina, galactosa-(14)-N-acetilglucosamina, D-N-acetilglucosamina i àcid neuramínic. En la DP les glicoproteïnes presenten, a més, -D-galactosa-(13)-D-N-acetilgalactosamina i α-D-galactosa. Les glicoproteïnes secretades en el BP i en la DP per via regulada, participen en el control de l'estabilitat del plasmalemma dels espermatozoides, eviten la resposta immune uterina i l'aglutinació dels espermatozoides i afavoreixen la seva motilitat progressiva. Les glicoproteïnes secretades per via constitutiva en la DP protegeixen i lubrifiquen la uretra pelviana. L'epiteli secretor de les glàndules bulbouretrals està format per cèl·lules piramidals principals i denses. Les cèl·lules principals sintetitzen i secreten principalment O-glicoproteïnes àcides carboxilades i sulfatades amb residus glicosídics d'N-acetilgalactosamina, -D-galactosa-(13)-D-N-acetilgalactosamina, α-D-galactosa, D-N-acetilglucosamina i àcid neuramínic. Aquests residus proporcionen resistència a la proteolisi a les O-glicoproteïnes secretades, les quals participen en la lubrificació y protecció de l'epiteli, i intervenen en el control de la permeabilitat del plasmalemma dels espermatozoides i en el transport d'ions al seu través.

Influence of molecular composition on the development of microstructure from sheared polyethylene melts: Molecular and lamellar templating

A combination of in situ and ex situ X-ray scattering techniques and transmission electron microscopy has been used to study the crystallization behaviour of polyethylene, following the imposition of melt shear. In the case of a branched material, the imposition of shear flow up to a rate of 30 s(-1) was found to induce no anisotropy. Although shearing the linear material only ever induced a very small degree of anisotropy in the melt, for shear rates > 0.15 s(-1), subsequent crystallization resulted in increasing anisotropy. Blends of the above two polyethylenes were produced, in which the linear material constituted the minority fraction (similar to 10%). Isothermal crystallization at temperatures where extensive crystallization of the branched material does not occur demonstrated that the behaviour of the linear component of the sheared blend mirrored that of the linear polyethylene alone. However, in addition, it was found that when crystallized in the presence of an oriented morphology, the branched polymer also formed anisotropic structures. We have termed the process templating, in which the crystallization behaviour of the bulk of the system (similar to 90% branched material) is completely altered (spherulitic to oriented lamellar) by mapping it onto a pre-existing minority structure (similar to 10% linear polymer). (c) 2006 Elsevier Ltd. All rights reserved.

Weathering microenvironments on feldspar surfaces: implications for understanding fluid-mineral reactions in soils

The mechanisms by which coatings develop on weathered grain surfaces, and their potential impact on rates of fluid-mineral interaction, have been investigated by examining feldspars from a 1.1 ky old soil in the Glen Feshie chronosequence, Scottish highlands. Using the focused ion beam technique, electron-transparent, foils for characterization by transmission electron microscopy were cut from selected parts of grain surfaces. Some parts were bare whereas others had accumulations, a few micrometres thick, of Weathering products, often mixed with mineral and microbial debris. Feldspar exposed at bare grain surfaces is crystalline throughout and so there is no evidence for the presence of the amorphous 'leached layers' that typically form in acid-dissolution experiments and have been described from some natural Weathering contexts. The weathering products comprise sub-mu m thick crystallites of an Fe-K aluminosilicate, probably smectite, that have grown within an amorphous and probably organic-rich matrix. There is also evidence for crystallization of clays having been mediated by fungal hyphae. Coatings formed within Glen Feshie soils after similar to 1.1 ky are insufficiently continuous or impermeable to slow rates Of fluid-feldspar reactions, but provide valuable insights into the complex Weathering microenvironments oil debris and microbe-covered mineral surfaces.

Characterization of mineral surfaces using FIB and TEM: a case study of naturally weathered alkali feldspars

Using a focused ion beam (FIB) instrument, electron-transparent samples (termed foils) have been cut from the naturally weathered surfaces of perthitic alkali feldspars recovered from soils overlying the Shap granite, northwest England. Characterization of these foils by transmission electron microscopy (TEM) has enabled determination of the crystallinity and chemical composition of near-surface regions of the feldspar and an assessment of the influence of intragranular microtextures on the microtopography of grain surfaces and development of etch pits. Damage accompanying implantation of the 30 kV Ga+ ions used for imaging and deposition of protective platinum prior to ion milling creates amorphous layers beneath outer grain surfaces, but can be overcome by coating grains with > 85 nm of gold before FIB work. The sidewalls of the foil and feldspar surrounding original voids are also partially amorphized during later stages of ion milling. No evidence was found for the presence of amorphous or crystalline weathering products or amorphous "leached layers" immediately beneath outer grain surfaces. The absence of a leached layer indicates that chemical weathering of feldspar in the Shap soils is stoichiometric, or if non-stoichiometric, either the layer is too thin to resolve by the TEM techniques used (i.e., <=similar to 2.5 nm) or an insufficient proportion of ions have been leached from near-surface regions so that feldspar crystallinity is maintained. No evidence was found for any difference in the mechanisms of weathering where a microbial filament rests on the feldspar surface. Sub-micrometer-sized steps on the grain surface have formed where subgrains and exsolution lamellae have influenced the propagation of fractures during physical weathering, whereas finer scale corrugations form due to compositional or strain-related differences in dissolution rates of albite platelets and enclosing tweed orthoclase. With progressive weathering, etch pits that initiated at the grain surface extend into grain interiors as etch tubes by exploiting preexisting networks of nanopores that formed during the igneous history of the grain. The combination of FIB and TEM techniques is an especially powerful way of exploring mechanisms of weathering within the "internal zone" beneath outer grain surfaces, but results must be interpreted with caution owing to the ease with which artifacts can be created by the high-energy ion and electron beams used in the preparation and characterization of the foils.