Recovery of the star formation history of the LMC from the VISTA survey of the Magellanic system

The VISTA near infrared survey of the Magellanic System (VMC) will provide deep YJK(s) photometry reaching stars in the oldest turn-off point throughout the Magellanic Clouds (MCs). As part of the preparation for the survey, we aim to access the accuracy in the star formation history (SFH) that can be expected from VMC data, in particular for the Large Magellanic Cloud (LMC). To this aim, we first simulate VMC images containing not only the LMC stellar populations but also the foreground Milky Way (MW) stars and background galaxies. The simulations cover the whole range of density of LMC field stars. We then perform aperture photometry over these simulated images, access the expected levels of photometric errors and incompleteness, and apply the classical technique of SFH-recovery based on the reconstruction of colour-magnitude diagrams (CMD) via the minimisation of a chi-squared-like statistics. We verify that the foreground MW stars are accurately recovered by the minimisation algorithms, whereas the background galaxies can be largely eliminated from the CMD analysis due to their particular colours and morphologies. We then evaluate the expected errors in the recovered star formation rate as a function of stellar age, SFR(t), starting from models with a known age-metallicity relation (AMR). It turns out that, for a given sky area, the random errors for ages older than similar to 0.4 Gyr seem to be independent of the crowding. This can be explained by a counterbalancing effect between the loss of stars from a decrease in the completeness and the gain of stars from an increase in the stellar density. For a spatial resolution of similar to 0.1 deg(2), the random errors in SFR(t) will be below 20% for this wide range of ages. On the other hand, due to the lower stellar statistics for stars younger than similar to 0.4 Gyr, the outer LMC regions will require larger areas to achieve the same level of accuracy in the SFR( t). If we consider the AMR as unknown, the SFH-recovery algorithm is able to accurately recover the input AMR, at the price of an increase of random errors in the SFR(t) by a factor of about 2.5. Experiments of SFH-recovery performed for varying distance modulus and reddening indicate that these parameters can be determined with (relative) accuracies of Delta(m-M)(0) similar to 0.02 mag and Delta E(B-V) similar to 0.01 mag, for each individual field over the LMC. The propagation of these errors in the SFR(t) implies systematic errors below 30%. This level of accuracy in the SFR(t) can reveal significant imprints in the dynamical evolution of this unique and nearby stellar system, as well as possible signatures of the past interaction between the MCs and the MW.

A possible role of ground-based microorganisms on cloud formation in the atmosphere

The formation of clouds is an important process for the atmosphere, the hydrological cycle, and climate, but some aspects of it are not completely understood. In this work, we show that microorganisms might affect cloud formation without leaving the Earth's surface by releasing biological surfactants (or biosurfactants) in the environment, that make their way into atmospheric aerosols and could significantly enhance their activation into cloud droplets. In the first part of this work, the cloud-nucleating efficiency of standard biosurfactants was characterized and found to be better than that of any aerosol material studied so far, including inorganic salts. These results identify molecular structures that give organic compounds exceptional cloud-nucleating properties. In the second part, atmospheric aerosols were sampled at different locations: a temperate coastal site, a marine site, a temperate forest, and a tropical forest. Their surface tension was measured and found to be below 30 mN/m, the lowest reported for aerosols, to our knowledge. This very low surface tension was attributed to the presence of biosurfactants, the only natural substances able to reach to such low values. The presence of strong microbial surfactants in aerosols would be consistent with the organic fractions of exceptional cloud-nucleating efficiency recently found in aerosols, and with the correlations between algae bloom and cloud cover reported in the Southern Ocean. The results of this work also suggest that biosurfactants might be common in aerosols and thus of global relevance. If this is confirmed, a new role for microorganisms on the atmosphere and climate could be identified.

Investigating Giant (Gt) Repression in the Formation of Partially Overlapping Pair-Rule Stripes

Drosophila pair-rule genes are expressed in striped patterns with a precise order of overlap between stripes of different genes. We investigated the role of Giant (Gt) in the regulation of even-skipped, hairy, runt, and fushi tarazu stripes formed in the vicinity of Gt expression domains. In gt null embryos, specific stripes of eve, h, run, and ftz are disrupted. With an ectopic expression system, we verified that stripes affected in the mutant are also repressed. Simultaneously hybridizing gt misxpressing embryos with two pair-rule gene probes, we were able to distinguish differences in the repression of pairs of stripes that overlap extensively. Together, our results showed Gt repression roles in the regulation of two groups of partially overlapping stripes and that Gt morphogen activity is part of the mechanism responsible for the differential positioning of these stripes borders. We discuss the possibility that other factors regulate Gt stripe targets as well. Developmental Dynamics 239:2989-2999, 2010. (C) 2010 Wiley-Liss, Inc.

Glass formation of alloys selected by lambda and electronegativity criteria in the Ti-Zr-Fe-Co system

This work evaluates the glass formation of selected alloys based on the Ti-Zr-Fe-Co system, assuming the synergy of two distinct criteria: minimum topological instability and average electronegativity plots. Combining the minimum topological instability and the average electronegativity values result in a plot in which the most probable good glass former compositions are identified Ti-Zr rich alloys with Fe and Co additions were produced, compared against the final plot, and the best glass forming alloy composition was found to be very close the theoretically predicted ones on the Ti-Zr rich side, for both Ti-Zr-Fe and Ti-Zr-Co systems. (C) 2009 Elsevier B V All rights reserved

Cracking formation on the surface of extruded photodegraded polypropylene plates

The cracking formation during the photodegradation of polypropylene (PP) plates (1 mm thickness), with (PPOx) and without pro-oxidant [PP), has been investigated. The plates were produced by extrusion in an industrial production line and were exposed to ultraviolet radiation in the laboratory for periods of up to 480 hr. The samples were investigated by infrared spectroscopy- FTIR, optical light microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the extension of photodegradation process is more intense for PPOx than for PP samples. For both samples, cracks were formed at the surface perpendicularly to the flow-lines. However the cracks frequency was different for both samples and sides of sample. The crack frequency was correlated with chain orientation, A(110); it was shown that lower degrees of orientation resulted in lower crack frequency. POLYM. ENG. SCI., 48:365-372, 2008. (c) 2007 Society of Plastics Engineers.

Study on Iron Formation During the Carbothermic Reduction of Iron Ore in Carbon Composite Pellets in the Temperature Range 1423 K-1623 K

The aim of this work is to study the reaction rate and the morphology of the intermediary reaction products during reduction of iron ore, when iron ore and carbonaceous material are agglomerated together as a carbon composite iron ore pellet. The reaction was performed at high temperatures, and in order to avoid heat transfer constraints small size samples were used. The carbonaceous materials employed were coke breeze and pure graphite. Portland cement was employed as a binder, and the pellets diameter was 5.2 mm. The experimental technique involved the measurement of the pellets weight loss, as well as interruption of the reaction at different stages in order to submit the partially reduced pellet to scanning electron microscopy. It has been observed that above 1523 K there is the formation of liquid slag inside the pellets, which partially dissolves iron oxides. The apparent activation energies obtained were 255 kJ/mol for coke breeze containing pellets, and 230 kJ/mol for those pellets containing graphite. It was possible to avoid heat transfer control of the reaction rate up to 1523 K by employing small composite pellets.

Functional characterization of the oxaloacetase encoding gene and elimination of oxalate formation in the beta-lactam producer Penicillium chrysogenum

Penicillium chrysogenum is widely used as an industrial antibiotic producer, in particular in the synthesis of g-lactam antibiotics such as penicillins and cephalosporins. In industrial processes, oxalic acid formation leads to reduced product yields. Moreover, precipitation of calcium oxalate complicates product recovery. We observed oxalate production in glucose-limited chemostat cultures of P. chrysogenum grown with or without addition of adipic acid, side-chain of the cephalosporin precursor adipoyl-6-aminopenicillinic acid (ad-6-APA). Oxalate accounted for up to 5% of the consumed carbon source. In filamentous fungi, oxaloacetate hydrolase (OAH; EC3.7.1.1) is generally responsible for oxalate production. The P. chrysogenum genome harbours four orthologs of the A. niger oahA gene. Chemostat-based transcriptome analyses revealed a significant correlation between extracellular oxalate titers and expression level of the genes Pc18g05100 and Pc22g24830. To assess their possible involvement in oxalate production, both genes were cloned in Saccharomyces cerevisiae, yeast that does not produce oxalate. Only the expression of Pc22g24830 led to production of oxalic acid in S. cerevisiae. Subsequent deletion of Pc22g28430 in P. chrysogenum led to complete elimination of oxalate production, whilst improving yields of the cephalosporin precursor ad-6-APA. (C) 2011 Elsevier Inc. All rights reserved.

Brassinosteroids interact negatively with jasmonates in the formation of anti-herbivory traits in tomato

Given the susceptibility of tomato plants to pests, the aim of the present study was to understand how hormones are involved in the formation of tomato natural defences against insect herbivory. Tomato hormone mutants, previously introgressed into the same genetic background of reference, were screened for alterations in trichome densities and allelochemical content. Ethylene, gibberellin, and auxin mutants indirectly showed alteration in trichome density, through effects on epidermal cell area. However, brassinosteroids (BRs) and jasmonates (JAs) directly affected trichome density and allelochemical content, and in an opposite fashion. The BR-deficient mutant dpy showed enhanced pubescence, zingiberene biosynthesis, and proteinase inhibitor expression; the opposite was observed for the JA-insensitive jai1-1 mutant. The dpyxjai1-1 double mutant showed that jai1-1 is epistatic to dpy, indicating that BR acts upstream of the JA signalling pathway. Herbivory tests with the poliphagous insect Spodoptera frugiperda and the tomato pest Tuta absoluta clearly confirmed the importance of the JA-BR interaction in defence against herbivory. The study underscores the importance of hormonal interactions on relevant agricultural traits and raises a novel biological mechanism in tomato that may differ from the BR and JA interaction already suggested for Arabidopsis.

Influence of Phase Inversion on the Formation and Stability of One-Step Multiple Emulsions

A novel method of preparation of water-in-oil-in-micelle-containing water (W/O/W(m)) Multiple emulsions using the one-step emulsification method is reported. These multiple emulsions were normal (not temporary) and stable over a 60 day test period. Previously, reported multiple emulsion by the one-step method were abnormal systems that formed at the inversion point of simple emulsion (where there is an incompatibility in the Ostwald and Bancroft theories, and typically these are O/W/O systems). Pseudoternary phase diagrams and bidimensional process-composition (phase inversion) maps were constructed to assist in process and composition optimization. The surfactants used were PEG40 hydrogenated castor oil and sorbitan oleate, and mineral and vegetables oils were investigated. Physicochemical characterization studies showed experimentally, for the First time, the significance of the ultralow surface tension point oil multiple emulsion formation by one-step via phase inversion processes. Although the significance of ultralow surface tension has been speculated previously, to the best of our knowledge, this is the first experimental confirmation. The multiple emulsion system reported here was dependent not only upon the emulsification temperature, but also upon the component ratios, therefore both the emulsion phase inversion and the phase inversion temperature were considered to fully explain their formation. Accordingly, it is hypothesized that the formation of these normal multiple emulsions is not a result of a temporary incompatibility (at the inversion point) during simple emulsion preparation, as previously reported. Rather, these normal W/O/W(m) emulsions are a result of the simultaneous occurrence of catastrophic and transitional phase inversion processes. The formation of the primary emulsions (W/O) is in accordance with the Ostwald theory and the formation of the multiple emulsions (W/O/W(m)) is in agreement with the Bancroft theory.

The relationship between hetero-oligomer formation and function of the topological specificity domain of the Escherichia coli MinE protein

MinE is an oligomeric protein that, in conjunction with other Min proteins, is required for the proper placement of the cell division site of Escherichia coli. We have examined the self-association properties of MinE by analytical ultracentrifugation and by studies of hetero-oligomer formation in non-denaturing polyacrylamide gets. The self-association properties of purified MinE predict that cytoplasmic MinE is likely to exist as a mixture of monomers and dimers. Consistent with this prediction, the C-terminal MinE(22-88) fragment forms hetero-oligomers with MinE(+) when the proteins are co-expressed. In contrast, the MinE(36-88) fragment does not form MinE(+)/MinE(36-88) hetero-oligomers, although MinE36-88 affects the topological specificity of septum placement as shown by its ability to induce minicell formation when co-expressed with MinE(+) in wild-type cells. Therefore, hetero-oligomer formation is not necessary for the induction of mini-celling by expression of MinE(36-88) in wild-type cells. The interference with normal septal placement is ascribed to competition between MinE(36-88),nd the corresponding domain in the complete MinE protein for a component required for the topological specificity of septal placement.

Rheological behaviour of the mushy zone and its effect on the formation of casting defects during solidification

A new conceptual framework has been developed which explains the formation of shear-related casting defects such as porosity, segregation and tears. The theory relates defect formation to the mechanical behaviour of the partially solidified microstructure when shear stresses are developed during the filling of a casting and by the subsequent feeding processes during solidification. Two transition points, the dendrite coherency point and the maximum packing solid fraction, divide the mushy zone into three regions of different mechanical and feeding behaviours. The response of the mush to shear is related to the presence of these zones during solidification of a casting. The resulting defects are rationalized by considering the governing local shear stress and shear rate, local strength and time available for fluid flow. The design of the casting, the casting process used and the alloy composition all influence the relative importance of shearing on defect formation. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.

Acyclic permutants of naturally occurring cyclic proteins - Characterization of cystine knot and beta-sheet formation in the macrocyclic polypeptide kalata B1

Kalata B1 is a prototypic member of the unique cyclotide family of macrocyclic polypeptides in which the major structural features are a circular peptide backbone, a triple stranded beta-sheet, and a cystine knot arrangement of three disulfide bonds. The cyclotides are the only naturally occurring family of circular proteins and have prompted us to explore the concept of acyclic permutation, i.e. opening the backbone of a cross-linked circular protein in topologically permuted ways. We have synthesized the complete suite of acyclic permutants of kalata B1 and examined the effect of acyclic permutation on structure and activity. Only two of six topologically distinct backbone loops are critical for folding into the native conformation, and these involve disruption of the embedded ring in the cystine knot. Surprisingly, it is possible to disrupt regions of the p-sheet and still allow folding into native-like structure, provided the cystine knot is intact. Kalata B1 has mild hemolytic activity, but despite the overall structure of the native peptide being retained in all but two cases, none of the acyclic permutants displayed hemolytic activity. This loss of activity is not localized to one particular region and suggests that cyclization is critical for hemolytic activity.

Male Teachers in Feminised Teaching Areas: marching to the beat of the men's movement drums?

Calls for more male teachers are prevalent in current gender debates in education. A dominant argument in this debate is that boys are often alienated from school because of a lack of male role models in feminised areas of the school curriculum and in primary schools. Little research has investigated male teachers' accounts of their work within feminised environments. Drawing on data collected in two research studies in music education, this paper focuses on accounts given by male teachers about (a) practices adopted specifically to work with boys and (b) the role of the male music teacher. Analysis of these data suggests that some male teachers working in feminised areas of the school curriculum adopt practices which, rather than challenging dominant constructions of masculinity, sometimes reinforce gender stereotypical behaviours in boys. We argue that calls for increasing the number of male teachers in feminised areas of schooling need also to be informed by open discussion of the underlying assumptions about masculinity which teachers themselves bring to their work.

Galaxy threshing and the formation of ultracompact dwarf galaxies

Recent spectroscopic and morphological observational studies of galaxies around NGC 1399 in the Fornax Cluster have discovered several ultracompact dwarf galaxies with intrinsic sizes of similar to 100 pc and absolute B-band magnitudes ranging from -13 to -11 mag. In order to elucidate the origin of these enigmatic objects, we perform numerical simulations on the dynamical evolution of nucleated dwarf galaxies orbiting NGC 1399 and suffering from its strong tidal gravitational field. Adopting a plausible scaling relation for dwarf galaxies, we find that the outer stellar components of a nucleated dwarf are totally removed. This is due to them being tidally stripped over the course of several passages past the central region of NGC 1399. The nucleus, however, manages to survive. We also find that the size and luminosity of the remnant are similar to those observed for ultracompact dwarf galaxies, if the simulated precursor nucleated dwarf has a mass of similar to 10(8) M.. These results suggest that ultracompact dwarf galaxies could have previously been more luminous dwarf spheroidal or elliptical galaxies with rather compact nuclei.