Melt structure and its transformation by sequential crystallization of the two blocks within poly(L-lactide)-block-poly(epsilon-caprolactone) double crystalline diblock copolymers

Sequential crystallization of poly(L-lactide) (PLLA) followed by poly(epsilon-caprolactone) (PCL) in double crystalline PLLA-b-PCL diblock copolymers is studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). Three samples with different compositions are studied. The sample with the shortest PLLA block (32 wt.-% PLLA) crystallizes from a homogeneous melt, the other two (with 44 and 60% PLLA) from microphase separated structures. The microphase structure of the melt is changed as PLLA crystallizes at 122 degrees C (a temperature at which the PCL block is molten) forming spherulites regardless of composition, even with 32% PLLA. SAXS indicates that a lamellar structure with a different periodicity than that obtained in the melt forms (for melt segregated samples). Where PCL is the majority block, PCL crystallization at 42 degrees C following PLLA crystallization leads to rearrangement of the lamellar structure, as observed by SAXS, possibly due to local melting at the interphases between domains. POM results showed that PCL crystallizes within previously formed PLLA spherulites. WAXS data indicate that the PLLA unit cell is modified by crystallization of PCL, at least for the two majority PCL samples. The PCL minority sample did not crystallize at 42 degrees C (well below the PCL homopolymer crystallization temperature), pointing to the influence of pre-crystallization of PLLA on PCL crystallization, although it did crystallize at lower temperature. Crystallization kinetics were examined by DSC and WAXS, with good agreement in general. The crystallization rate of PLLA decreased with increase in PCL content in the copolymers. The crystallization rate of PCL decreased with increasing PLLA content. The Avrami exponents were in general depressed for both components in the block copolymers compared to the parent homopolymers. Polarized optical micrographs during isothermal crystalli zation of (a) homo-PLLA, (b) homo-PCL, (c) and (d) block copolymer after 30 min at 122 degrees C and after 15 min at 42 degrees C.

The effect of PEG crystallization on the morphology of PEG/peptide block copolymers containing amyloid beta-peptide fragments

Ordered nanostructures are observed in the melt and solid state for a series of three peptide/PEG conjugates containing fragments of amyloid beta-peptides. These are conjugated to PEG with (M) over bar (n) = 3 300 g.mol(-1) and a melting temperature T-m = 45-50 degrees C. The morphology at room temperature is examined by AFM and POM. This shows spherulite formation for the weakly fibrillizing KLVFF-PEG sample but fibril formation for FFKLVFF-PEG. The fibrillization tendency of the latter is enhanced by multiple phenylalanine residues. Simultaneous SAXS and WAXS was used to investigate the morphology as a function of temperature. The secondary structure is probed by FTIR.

One-pot synthesis and characterization of soluble poly(aryl ether-ketone)s having pendant carboxyl groups

Aromatic poly(ether-ketone)s having pendant carboxyl groups have been obtained by direct, one-pot, Friedel-Crafts copolycondensation of 4,4'-diphenoxybenzophenone with a mixture of terephthaloyl chloride (TC) and trimellitic anhydride acid chloride (TAAC), over a wide range of TAAC/TC molar ratios, in the presence of anhydrous aluminum chloride. The syntheses were performed as precipitation-polycondensations, and the polymers were obtained in particulate form. Besides globular particles of polymer, small quantities of elongated, needlelike particles were observed when the mole ratio TAAC/TC was less than 1. Use of X-ray microdiffraction with synchrotron radiation has revealed that the needlelike material consists of a cyclic compound containing 10 phenylene units, i.e., the crystals are of a [2 + 2] macrocyclic dimer. The polymers obtained are soluble in strong acids and in mixtures of methanesulfonic acid or trifluoroacetic acid with chlorinated hydrocarbons. The molecular structures of the polymers were confirmed by H-1 and C-13 NMR spectroscopy. Reaction of TAAC with 4,4'-diphenoxybenzophenone produced mainly meta-orientation of the resulting ketone linkages. The size of the polymer particles, their molecular weights, and the melting behavior of the products obtained depend on the TAAC/TC ratio used. Ortho-keto acid residues, formed during reaction of anhydride groups of TAAC with 4,4'-diphenoxybenzophenone, exhibit ring-chain tautomerism. A carboxyl-containing aromatic polyketone derived from p-terphenyl, and thus having with no ether linkages in the main chain, was prepared by analogous chemistry, and functional derivatives of carboxy-substituted polyketones were also obtained and characterized.

Performance of phase change material boards under natural convection

The high thermal storage capacity of phase change material (PCM) can reduce energy consumption in buildings through energy storage and release when combined with renewable energy sources, night cooling, etc. PCM boards can be used to absorb heat gains during daytime and release heat at night. In this paper, the thermal performance of an environmental chamber fitted with phase change material boards has been investigated. During a full-cycle experiment, i.e. charging–releasing cycle, the PCM boards on a wall can reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than that of the other walls during the heat releasing process. It is found that the heat flux density of the PCM wall in the melting zone is almost twice as large as that of ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy. The convective heat transfer coefficient of PCM wall surface calculated using equations for a normal wall material produces an underestimation of this coefficient. The high convective heat transfer coefficient for a PCM wall is due to the increased energy exchange between the wall and indoor air.

Effects of composition on fat rheology and crystallisation

The crystallisation behaviour of three fat blends, comprising a commercial shortening, a blend of fats with a very low trans fatty acid content ("low-trans") and a blend including hardened rapeseed oil with a relatively high trans fatty acid content ("high-trans") was studied. Molten fats were lowered to a temperature of 31 degrees C and stirred for 0, 15, 30, 45 and 60 min. Samples were removed and their rheological properties studied, using a controlled stress rheometer, employing a frequency sweep procedure. Effects of the progressive crystallisation at 31 degrees C on the melting profile of fat samples removed from the stirred vessel and solidified at -20 degrees C were also studied by differential scanning calorimetry (DSC). The rheological profiles obtained suggested that all of the fats studied had weak viscoelastic "liquid" structures when melted, but these changed to structures perceived by the rheometer as weak viscoelastic "gels" in the early stages of crystallisation (G' (storage modulus) > G" (loss modulus) over most of the measured frequency range). These subsequently developed into weak viscoelastic semi-solids, showing frequency dependent behaviour on further crystallisation. These changes in behaviour were interpreted as changes from a small number of larger crystals "cross-linking" in a liquid matrix to a larger number of smaller crystals packed with a "slip plane" of liquid oil between them. The rate of crystallisation of the three fats was in the order high trans > low-trans > commercial shortening. Changes in the DSC melting profile due to fractionation of triacylglycerols during the crystallisation at 31 degrees C were evident for all three fats. (c) 2006 Elsevier Ltd. All rights reserved.

Polymer-mediated disruption of drug crystallinity

Ibuprofen (IB), a BCS Class II compound, is a highly crystalline substance with poor solubility properties. Here we report on the disruption of this crystalline structure upon intimate contact with the polymeric carrier cross-linked polyvinylpyrrolidone (PVP-CL) facilitated by low energy simple mixing. Whilst strong molecular interactions between APIs and carriers within delivery systems would be expected on melting or through solvent depositions, this is not the case with less energetic mixing. Simple mixing of the two compounds resulted in a significant decrease in the differential scanning calorimetry (DSC) melting enthalpy for IB, indicating that approximately 30% of the crystalline content was disordered. This structural change was confirmed by broadening and intensity diminution of characteristic IB X-ray powder diffractometry (PXRD) peaks. Unexpectedly, the crystalline content of the drug continued to decrease upon storage under ambient conditions. The molecular environment of the mixture was further investigated using Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopy. These data suggest that the primary interaction between these components of the physical mix is hydrogen bonding, with a secondary mechanism involving electrostatic/hydrophobic interactions through the IB benzene ring. Such interactions and subsequent loss of crystallinity could confer a dissolution rate advantage for IB. (C) 2006 Elsevier B.V. All rights reserved.

The sea-level conundrum: case studies from palaeo-archives

Uncertainties in sea-level projections for the 21st century have focused ice sheet modelling efforts to include the processes that are thought to be contributing to the recently observed rapid changes at ice sheet margins. This effort is still in its infancy, however, leaving us unable to make reliable predictions of ice sheet responses to a warming climate if such glacier accelerations were to increase in size and frequency. The geological record, however, has long identified examples of nonlinear ice sheet response to climate forcing (Shackleton NJ, Opdyke ND. 1973. Oxygen isotope and paleomagnetic stratigraphy of equatorial Pacific core V28–239, late Pliocene to latest Pleistocene. Geological Society of America Memoirs145: 449–464; Fairbanks RG. 1989. A 17,000 year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep ocean circulation. Nature342: 637–642; Bard E, Hamelin B, Arnold M, Montaggioni L, Cabioch G, Faure G, Rougerie F. 1996. Sea level record from Tahiti corals and the timing of deglacial meltwater discharge. Nature382: 241–244), thus suggesting an alternative strategy for constraining the rate and magnitude of sea-level change that we might expect by the end of this century. Copyright © 2009 John Wiley & Sons, Ltd.

Oxidatively drying coating composition

coating composition comprising an oxidatively drying coating binder and a chelate comprising at least one group according to the following formula (I): forming a complex with a metal ion, A1 and A2 both being an aromatic residue, R1 and R3 being covalently bonded groups, and R2 being a divalent organic radical, wherein at least one solubilizing group is coivalently bonded to the chelating compound. The solubilizing group is a non-polar group, preferable an aliphatic group having at least four carbon atoms, covalently bonded to A1 and/or A2. The metal ion is a divalent ion of a metal selected from the group of manganese, cobalt, copper, lead, zirconium, iron, lanthanium, cerium, vanadium, and clacium or a trivalent ion of a metal selected from the group of manganese, cobalt, lead, zirconium, iron, lanthanium, cerium, and vanadium, combined with a monovalent counterion.

Unusually high differential attenuation at C band: Results from a two-year analysis of the French Trappes polarimetric radar data

The differential phase (ΦDP) measured by polarimetric radars is recognized to be a very good indicator of the path integrated by rain. Moreover, if a linear relationship is assumed between the specific differential phase (KDP) and the specific attenuation (AH) and specific differential attenuation (ADP), then attenuation can easily be corrected. The coefficients of proportionality, γH and γDP, are, however, known to be dependent in rain upon drop temperature, drop shapes, drop size distribution, and the presence of large drops causing Mie scattering. In this paper, the authors extensively apply a physically based method, often referred to as the “Smyth and Illingworth constraint,” which uses the constraint that the value of the differential reflectivity ZDR on the far side of the storm should be low to retrieve the γDP coefficient. More than 30 convective episodes observed by the French operational C-band polarimetric Trappes radar during two summers (2005 and 2006) are used to document the variability of γDP with respect to the intrinsic three-dimensional characteristics of the attenuating cells. The Smyth and Illingworth constraint could be applied to only 20% of all attenuated rays of the 2-yr dataset so it cannot be considered the unique solution for attenuation correction in an operational setting but is useful for characterizing the properties of the strongly attenuating cells. The range of variation of γDP is shown to be extremely large, with minimal, maximal, and mean values being, respectively, equal to 0.01, 0.11, and 0.025 dB °−1. Coefficient γDP appears to be almost linearly correlated with the horizontal reflectivity (ZH), differential reflectivity (ZDR), and specific differential phase (KDP) and correlation coefficient (ρHV) of the attenuating cells. The temperature effect is negligible with respect to that of the microphysical properties of the attenuating cells. Unusually large values of γDP, above 0.06 dB °−1, often referred to as “hot spots,” are reported for 15%—a nonnegligible figure—of the rays presenting a significant total differential phase shift (ΔϕDP > 30°). The corresponding strongly attenuating cells are shown to have extremely high ZDR (above 4 dB) and ZH (above 55 dBZ), very low ρHV (below 0.94), and high KDP (above 4° km−1). Analysis of 4 yr of observed raindrop spectra does not reproduce such low values of ρHV, suggesting that (wet) ice is likely to be present in the precipitation medium and responsible for the attenuation and high phase shifts. Furthermore, if melting ice is responsible for the high phase shifts, this suggests that KDP may not be uniquely related to rainfall rate but can result from the presence of wet ice. This hypothesis is supported by the analysis of the vertical profiles of horizontal reflectivity and the values of conventional probability of hail indexes.

Oxygen isotope composition of bivalve seasonal growth increments and ambient water in the rivers Rhine and Meuse

The application of oxygen isotope ratios ({delta}18O) from freshwater bivalves as a proxy for river discharge conditions in the Rhine and Meuse rivers is investigated. We compared a dataset of water temperature and water {delta}18O values with a selection of recent shell {delta}18O records for two species of the genus Unio in order to establish: (1) whether differences between the rivers in water {delta}18O values, reflecting river discharge conditions, are recorded in unionid shells; and (2) to what extent ecological parameters influence the accuracy of bivalve shell {delta}18O values as proxies of seasonal, water oxygen isotope conditions in these rivers. The results show that shells from the two rivers differ significantly in {delta}18O values, reflecting different source waters for these two rivers. The seasonal shell {delta}18O records show truncated sinusoidal patterns with narrow peaks and wide troughs, caused by temperature fractionation and winter growth cessation. Interannual growth rate reconstructions show an ontogenetic growth rate decrease. Growth lines in the shell often, but not always, coincide with winter growth cessations in the {delta}18O record, suggesting that growth cessations in the shell {delta}18O records are a better age estimator than counting internal growth lines. Seasonal predicted and measured {delta}18O values correspond well, supporting the hypothesis that these unionids precipitate their shells in oxygen isotopic equilibrium. This means that (sub-) fossil unionids can be used to reconstruct spring-summer river discharge conditions, such as Meuse low-discharge events caused by droughts and Rhine meltwater-influx events caused by melting of snow in the Alps.

Análise das regiões polimórficas do gene HASPB (K26) de Leishmania infantum em amostras clínicas positivas para leishmaniose visceral e coinfecção LV/HIV

A leishmaniose visceral (LV) é uma doença grave que afeta a população de vários países, onde o Brasil apresenta a maior prevalência da infecção nas Américas. Com o estudo do gene codificante da proteína B de superfície (HASPB ou K26) de Leishmania infantum é possível identificar as variações polimórficas intraespecíficas e, assim, será possível consolidar a descrição de um perfil polimórfico presente no Estado de Pernambuco. O objetivo do trabalho foi analisar as regiões polimórficas do gene HASPB (K26) de Leishmania infantum em amostras clínicas positivas para leishmaniose visceral e coinfecção LV/HIV. O sistema K26 PCR foi otimizado utilizando concentrações variadas de DNA genômico de L. infantum. Foi realizado o screening de amostras clínicas de DNA através de dois sistemas de PCR simples, kDNA e ITS1/RFLP, para ensaios posteriores com a K26 PCR nas amostras positivas. A curva de dissociação de alta definição (qPCR-HRM) foi empregada na localização de temperaturas de melting específicas para L. infantum. Os amplicons do gene K26 foram sequenciados e alinhados as sequencias selecionadas em base de dados. A K26 PCR apresentou limiar de detecção de 1 pg para amplicon de 700 pb. A especificidade dos primers foi avaliada experimentalmente e in silico, apresentando anelamento inespecífico com DNA humano. Em paralelo, foram selecionadas 78 amostras de DNA através dos dois sistemas screening, sendo 17 caracterizadas como L. infantum. Os ensaios com DNA das amostras clínicas para o sistema K26 PCR revelaram bandas espúrias. A análise através qPCR-HRM em DNA genômico do parasita resultou em amplificação com Tm de 88,2 °C, já o ensaio com amostra clínica revelou duas amplificações com distintas temperaturas de melting, 84,6 e 88,2 °C. Três amplicons do gene K26 foram sequenciados e alinhados a cinco sequencias da base de dados, indicando 38,2 % de similaridade. Pode-se concluir que o sistema K26 PCR é recomendável para análise dos polimorfismos genéticos, contanto que o DNA seja extraído diretamente de espécies isoladas em meio de cultura.

Crystallization and stereocomplexation behavior of poly(D- and L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) block copolymers

The thermal properties, crystallization, and morphology of amphiphilic poly(D-lactide)-b-poly(N,N-dimethylamino- 2-ethyl methacrylate) (PDLA-b-PDMAEMA) and poly (L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) (PLLA-b-PDMAEMA) copolymers were studied and compared to those of the corresponding poly(lactide) homopolymers. Additionally, stereocomplexation of these copolymers was studied. The crystallization kinetics of the PLA blocks was retarded by the presence of the PDMAEMA block. The studied copolymers were found to be miscible in the melt and the glassy state. The Avrami theory was able to predict the entire crystallization range of the PLA isothermal overall crystallization. The melting points of PLDA/PLLA and PLA/PLA-b-PDMAEMA stereocomplexes were higher than those formed by copolymer mixtures. This indicates that the PDMAEMA block is influencing the stability of the stereocomplex structures. For the low molecular weight samples, the stereocomplexes particles exhibited a conventional disk-shape structure and, for high molecular weight samples, the particles displayed unusual star-like shape morphology.

Identifying and investigating pesticide application types to promote a more sustainable pesticide use: the case of smallholders in Boyacá, Colombia

The present paper investigates pesticide application types adopted by smallholder potato producers in the Department of Boyacá , Colombia. In this region, environmental, health and adverse economic effects due to pesticide mis- or over-use respectively have been observed. Firstly, pesticide application types were identified based on input-effectiveness. Secondly, their determinants of adoption were investigated. Finally suggestions were given to develop intervention options for transition towards a more sustainable pesticide use. Three application types were identified for fungicide and insecticide. The types differed in terms of input (intensity of pesticide application), effect (damage control), frequency of application, average quantity applied per application, chemical class, and productivity. Then, the determinants of different pesticide application types were investigated with a multinomial logistic regression approach and applying the integrative agent centred (IAC) framework. The area of the plot, attendance at training sessions and educational and income levels were among the most relevant determinants. The analysis suggested that better pesticide use could be fostered to reduce pesticide-related risks in the region. Intervention options were outlined, which may help in targeting this issue. They aim not only at educating farmers, but to change their social and institutional context, by involving other agents of the agricultural system (i.e. pesticide producers), facilitating new institutional settings (i.e. cooperatives) and targeting social dynamics (i.e. conformity to social norms).

Towards an improved understanding of farmers' behaviour: the integrative agent-centred (IAC) framework

An effective approach to research on farmers' behaviour is based on: i) an explicit and well-motivated behavioural theory; ii) an integrative approach; and iii) understanding feedback processes and dynamics. While current approaches may effectively tackle some of them, they often fail to combine them together. The paper presents the integrative agent-centred (IAC) framework, which aims at filling this gap. It functions in accordance with these three pillars and provides a conceptual structure to understand farmers' behaviour in agricultural systems. The IAC framework is agent-centred and supports the understanding of farmers' behavior consistently with the perspective of agricultural systems as complex social-ecological systems. It combines different behavioural drivers, bridges between micro and macro levels, and depicts a potentially varied model of human agency. The use of the framework in practice is illustrated through two studies on pesticide use among smallholders in Colombia. The examples show how the framework can be implemented to derive policy implications to foster a transition towards more sustainable agricultural practices. The paper finally suggests that the framework can support different research designs for the study of agents' behaviour in agricultural and social-ecological systems.