232 research outputs found
Purification and characterization of an extracellular amylase from Lactobacillus plantarum strain A6
Extracellular amylase from #Lactobacillus plantarum$ A6 was purified by fractionated precipitation with ammonium sulphate and by anion exchange chromatography. The homogeneity of the purified fraction was tested by polyacrylamide gel electrophoresis and showed multiple amylase forms. A major form had an estimated molecular weight of 50 kDa. It was identified as an alpha-amylase, with an optimum pH of 5.5, an optimum temperature of 65°C and Km value of 2.38 g l-1 with soluble starch substrate. The enzyme was inhibited by N-bromosuccinimide, iodine and acetic acid. The enzyme activation energy was 30.9 kJ mol-1. (Résumé d'auteur
Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions
We study the magnetic properties of spherical Co clusters with diameters
between 0.8 nm and 5.4 nm (25 to 7500$ atoms) prepared by sequential sputtering
of Co and Al2O3. The particle size distribution has been determined from the
equilibrium susceptibility and magnetization data and it is compared to
previous structural characterizations. The distribution of activation energies
was independently obtained from a scaling plot of the ac susceptibility.
Combining these two distributions we have accurately determined the effective
anisotropy constant Keff. We find that Keff is enhanced with respect to the
bulk value and that it is dominated by a strong anisotropy induced at the
surface of the clusters. Interactions between the magnetic moments of adjacent
layers are shown to increase the effective activation energy barrier for the
reversal of the magnetic moments. Finally, this reversal is shown to proceed
classically down to the lowest temperature investigated (1.8 K).Comment: 13 figures submitted to Phys. Rev.
Imprints of the Quantum World in Classical Mechanics
The imprints left by quantum mechanics in classical (Hamiltonian) mechanics
are much more numerous than is usually believed. We show Using no physical
hypotheses) that the Schroedinger equation for a nonrelativistic system of
spinless particles is a classical equation which is equivalent to Hamilton's
equations.Comment: Paper submitted to Foundations of Physic
Detection of Pionium with DIRAC
The aim of the DIRAC experiment at CERN is to provide an accurate determination of S-wave pion-pion scattering lengths from the measurement of the lifetime of the pi+ pi- atom. The measurement will be done with precision comparable to the level of accuracy of theoretical predictions, formulated in the context of Chiral Perturbation Theory. Therefore, the understanding of chiral symmetry breaking of QCD will be submitted to a stringent test
Locke on individuation and the corpuscular basis of kinds
In this paper, I examine the crucial relationship between Locke’s theory of individuation and his theory of kinds. Locke holds that two material objects -- e.g., a mass of matter and an oak tree -- can be in the same place at the same time, provided that they are ‘of different kinds’. According to Locke, kinds are nominal essences, that is, general abstract ideas based on objective similarities between particularindividuals. I argue that Locke’s view on coinciding material objects is incompatible with his view on kinds. In order for two material objects to be in the same place at the same time, they must differ with respect to at least one nominal essence. However, Locke thinks that it is impossible that x and y have the same real essence but differ with respect to any nominal essence; and coinciding material objects have the same real essence. Therefore, Locke cannot hold what he in fact holds, namely that distinct material objects can be in the same place at the same tim
Anthocorid predators learn to associate herbivore-induced plant volatiles with presence or absence of prey
Inflammatory biomarkers in Alzheimer's disease plasma
Introduction: Plasma biomarkers for Alzheimer's disease (AD) diagnosis/stratification are a \u201cHoly Grail\u201d of AD research and intensively sought; however, there are no well-established plasma markers. Methods: A hypothesis-led plasma biomarker search was conducted in the context of international multicenter studies. The discovery phase measured 53 inflammatory proteins in elderly control (CTL; 259), mild cognitive impairment (MCI; 199), and AD (262) subjects from AddNeuroMed. Results: Ten analytes showed significant intergroup differences. Logistic regression identified five (FB, FH, sCR1, MCP-1, eotaxin-1) that, age/APO\u3b54 adjusted, optimally differentiated AD and CTL (AUC: 0.79), and three (sCR1, MCP-1, eotaxin-1) that optimally differentiated AD and MCI (AUC: 0.74). These models replicated in an independent cohort (EMIF; AUC 0.81 and 0.67). Two analytes (FB, FH) plus age predicted MCI progression to AD (AUC: 0.71). Discussion: Plasma markers of inflammation and complement dysregulation support diagnosis and outcome prediction in AD and MCI. Further replication is needed before clinical translation
An ecological cost of plant defence: attractiveness of bitter cucumber plants to natural enemies of herbivores
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