Solubilization of chitosan by bipolar membrane electroacidification

Chitosan, a partially deacetylated derivative of chitin, was solubilized by bipolar membrane electroacidification (BMEA). Bipolar/monopolar (anionic or cationic) configuration and chitosan addition mode (single step or stepwise) were examined. Chitosan solubility and electroacidification parameters were monitored during the process to determine the optimal conditions. Bipolar/anionic configuration and stepwise feeding mode led to chitosan solubilization yield of 91% in 60 min at 20 mA/cm(2). In this configuration, chitosan solution had a pH of 2.5, a conductivity of 8.5 mS/cm, and an ash content of 0.2%. Relative energy consumption was 0.05 kWh/L of 1% chitosan solution prepared. Although some chitosan particles were aggregated in the electrodialysis stack, limiting chitosan solubilization, BMEA allowed complete solubilization of chitosan circulating in the system.     

Electromigration behavior of a mixture of chitosan oligomers at different concentrations

In this study, the effect of the concentration of a chitosan oligomer mixture on its electrophoretic behavior was studied as a function of pH and ionic strength added. It was shown that the concentration has a significant effect on the average electrophoretic mobility of the chitosan oligomer mixture and on isoelectric point. At a concentration of 3%, the ionic strength added did not show any effect on the electromigration behavior of the chitosan oligomer mixture. By decreasing the concentration of the chitosan oligomer mixture, ionic strength showed a significant effect on the average electrophoretic mobility but not on the isoelectric point. The highest shift of the isoelectric point was recorded in water at 0.003% concentration of the oligomer mixture. Under these conditions, the isoelectric point was at pH 5 whereas it was at pH 8 at 3% concentration of chitosan oligomer mixture. Electrophoretic measurements were also taken in water/ethanol aqueous medium. By adding ethanol to the medium, the average electrophoretic mobility decreased. This would have been caused by the increase in viscosity of the medium. Increasing ethanol ratio in the running medium, the isoelectric point moved from pH 5 in water up to pH 6-8 dependently on chitosan oligomer mixture concentration and ethanol content of the medium.     

Subsoil improvement in a tropical coarse textured soil: Effect of deep-ripping and slotting

In many coarse textured soils, limited root development and biomass production are attributed to adverse physical conditions in the subsoil. The current study was undertaken on an Arenic Acrisol located in Northeast Thailand (i) to assess whether subsoil physical characteristics influence crop rooting depth, and (ii) to compare the benefits associated with conventional tillage with that of localised subsoil loosening on crop performance and selected soil attributes. Control plots consisted of disk ploughing; the implemented treatments were conventional deep-ripping and localised slotting below the planting line. A crop rotation consisting of a legume followed by maize was established annually to assess the impact of these treatments on crop performance. In the control treatment, root development was restricted to the topsoil (0–20 cm) due to high subsoil bulk density (>1.6 Mg m⁻³). After deep-ripping, no improvement was observed in bulk density, rooting depth and in crop performance. The implementation of a slotting treatment systematically improved root development in the slotted subsoil, root impact frequency increasing from <0.2 to 0.6–0.8 (P = 0.01) despite no change in the bulk densities of the subsoil. This systematic improvement in root development could be explained by (i) reduced slumping that enable root development prior to recompaction and/or (ii) preferential drainage in the slot and therefore decreased resistance to root penetration. In a dry year maize yield was improved by 78% (P = 0.01); the deep-rooting legume Stylosanthes was tested only a wet year and its biomass production increased by >40% (P = 0.03). This study highlights the detrimental impact of subsoil compaction on root development and the potential role of slotting in coarse textured soils as a long-term management tool in addressing adverse subsoil physical characteristics that limit deep-rooting.     

Abrupt climate events 500,000 to 340,000 years ago: evidence from subpolar north atlantic sediments

Subpolar North Atlantic proxy records document millennial-scale climate variations 500,000 to 340,000 years ago. The cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle. These findings suggest that such climate variations are inherent to the late Pleistocene, regardless of glacial state. Sea surface temperature during the warm peak of Marine Isotope Stage 11 (MIS 11) varied by 0.5 degrees to 1 degrees C, less than the 4 degrees to 4.5 degrees C estimated during times of ice growth and the 3 degrees C estimated for glacial maxima. Coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature.     

Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of approximately 100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date (<2 x 10(21) Gauss-cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported.     

The structure of the upper atmosphere of mars: In situ accelerometer measurements from mars global surveyor

The Mars Global Surveyor (MGS) z-axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near 90 degreesE and 90 degreesW, in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere.     

Risk factors associated with early respiratory disease complex in broiler chickens.

Early respiratory disease complex (ERDC) is a term coined to describe an acute disease characterized by depression, respiratory distress, and increased mortality in 2-to-3-wk-old broiler chickens. Postmortem lesions include airsacculitis, fibrinous pericarditis, and perihepatitis. Colisepticemia is the primary cause of death. In order to investigate the association between ERDC and farm management factors, a retrospective case-control study was conducted by collecting data covering a 6-mo period (January-June 1997) from four broiler integrators on the Delmarva peninsula. Univariate and multivariate statistical analyses revealed that flock size was positively associated (P = 0.02) and layout time was negatively associated (P = 0.05) with ERDC.     

Biotic and abiotic drivers of intraspecific trait variation within plant populations of three herbaceous plant species along a latitudinal gradient

Background

The importance of intraspecific trait variation (ITV) is increasingly acknowledged among plant ecologists. However, our understanding of what drives ITV between individual plants (ITV_BI) at the population level is still limited. Contrasting theoretical hypotheses state that ITV_BI can be either suppressed (stress-reduced plasticity hypothesis) or enhanced (stress-induced variability hypothesis) under high abiotic stress. Similarly, other hypotheses predict either suppressed (niche packing hypothesis) or enhanced ITV_BI (individual variation hypothesis) under high niche packing in species rich communities. In this study we assess the relative effects of both abiotic and biotic niche effects on ITV_BI of four functional traits (leaf area, specific leaf area, plant height and seed mass), for three herbaceous plant species across a 2300 km long gradient in Europe. The study species were the slow colonizing Anemone nemorosa, a species with intermediate colonization rates, Milium effusum, and the fast colonizing, non-native Impatiens glandulifera.

Results

Climatic stress consistently increased ITV_BI across species and traits. Soil nutrient stress, on the other hand, reduced ITV_BI for A. nemorosa and I. glandulifera, but had a reversed effect for M. effusum. We furthermore observed a reversed effect of high niche packing on ITV_BI for the fast colonizing non-native I. glandulifera (increased ITV_BI), as compared to the slow colonizing native A. nemorosa and M. effusum (reduced ITV_BI). Additionally, ITV_BI in the fast colonizing species tended to be highest for the vegetative traits plant height and leaf area, but lowest for the measured generative trait seed mass.

Conclusions

This study shows that stress can both reduce and increase ITV_BI, seemingly supporting both the stress-reduced plasticity and stress-induced variability hypotheses. Similarly, niche packing effects on ITV_BI supported both the niche packing hypothesis and the individual variation hypothesis. These results clearly illustrates the importance of simultaneously evaluating both abiotic and biotic factors on ITV_BI. This study adds to the growing realization that within-population trait variation should not be ignored and can provide valuable ecological insights.