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  • Author: D. J. Chapman x
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Abstract

The maintenance of isomorphic life histories in algae has been difficult to explain when there is no difference between the ecological niche of the two adult phases. However, at the level of spores, physiological differences could exist in the reproduction and development between tetraspores and carpospores that could influence the composition of both phases in the field and interspecific competition. The release, attachment (winter vs. beginning of autumn) and survival (seasonal), of tetraspores and carpospores of Gracilaria pacifica Abbott from Estero de Punta Banda, Baja California, México, were studied in a gradient of temperature and irradiance. The release of tetraspores was directly affected by irradiance, while that of carpospores was affected by irradiance and temperature. The attachment of tetraspores was directly affected by temperature and season while the attachment of carpospores showed a response to changes in irradiance. Survival was influenced mainly by seasons. In spring, summer, and autumn (May, August–September, and November/December respectively) both types of spores responded similarly, with the lowest survival rate in summer and the highest in other seasons. However in winter (January/February), the rate of survival of tetraspores was an order of magnitude greater than in carpospores. The highest survival rate occurred at 21 °C and 24 °C, whereas the survival rate at 15 °C was close to zero for both types of spores. These different responses between tetraspores and carpospores, suggest a different ecophysiological response with regard to survival and interspecific competition in nature of the gametophyte vs sporophyte.

Abstract

Analysis of pressure-temperature dependent monochromatic X-ray powder diffraction data yield the bulk modulus [KT = 180.2(28) GPa] and thermal expansion coeficients [α0 = 2.841(34) × 10-5 K-1; α1 = 3.37(48) × 10-9 K-2] of CaIrO3, the structure model for post-perovskite MgSiO3. CaIrO3 is orthorhombic (Cmcm, space group 63, Z = 4) with best-fit unit-cell parameters, a = 3.14147(5) Å, b = 9.87515(19), c = 7.29711(11), and V = 226.3754(78) Å3 at 1 bar and 300 K. The c-axis of CaIrO3 has a small compressibility and a large thermal expansion when compared to the other principal axes. Rietveld structure refinement reveals changes in CaIrO3 as a function of temperature in terms of IrO6 octahedra distortion. Dissociation of CaIrO3 at high temperature has possible implications for the post-perovskite MgSiO3 structure, Earth.s lower mantle, and D’’ layer.

Abstract

Background: Cerebrospinal fluid (CSF) amyloid β1-42 (Aβ1-42), total tau (T-tau) and phosphorylated tau181 (P-tau) are finding increasing utility as biomarkers of Alzheimer’s disease (AD). The purpose of this study was to determine whether measured CSF biomarker concentrations were affected by aliquot storage volume and whether addition of detergent-containing buffer mitigates any observed effects.

Methods: AD and control CSF was distributed into polypropylene tubes in aliquots of different volumes (50–1500 μL). Aβ1-42, T-tau and P-tau were measured with and without addition of Tween 20 (0.05%).

Results: Measured concentrations of Aβ1-42 increased two-fold with aliquot storage volume. A volume increase of 10 µL caused an Aβ1-42 increase of 0.95 pg/mL [95% confidence interval (CI) 0.36–1.50, p=0.02] in controls, and 0.60 pg/mL (CI 0.23–0.98 pg/mL, p=0.003) in AD samples. Following addition of Tween 20, the positive relationship between Aβ1-42 and aliquot volume disappeared. T-tau and P-tau were not significantly affected.

Conclusions: CSF aliquot storage volume has a significant impact on the measured concentration of Aβ1-42. The introduction of a buffer detergent at the initial aliquoting stage may be an effective solution to this problem.