Academy of Sciences of the Czech Republic

About: Academy of Sciences of the Czech Republic is a government organization based out in Prague, Czechia. It is known for research contribution in the topics: Population & Catalysis. The organization has 27866 authors who have published 71021 publications receiving 1821686 citations.

Spatio-temporal dynamics of plant invasions: Linking pattern to process

Abstract: Biological invasions are characterized by remarkable spatio-temporal dynamics, with many species having extended their distribution range from within a single region to much of the globe within the last century. The comparative analysis of the spatio-temporal dynamics of over 100 taxa from studies undertaken worldwide provides the basis of a critical assessment of current knowledge. At the scale of single habitats, simple reaction-diffusion models may be accurate enough to predict the spread of new invaders without recourse to complex life history parameterization. Average rates of local spread reported for invasive species in the literature range from 2 m·y-1 to a maximum of 370 m·y-1. Average rates of long-distance dispersal are at least two orders of magnitude greater than estimates of local dispersal, with a maximum of 167 km·y-1. While local-scale studies do pick up dispersal events of several kilometres, study sites are rarely sufficiently large or monitored for long enough to characterize these events accurately. Long-distance dispersal events may occur during periods of negligible population increase and appear to bear little relationship to population size. At regional scales, invasive species rarely move across the landscape as a continuous front and both local and long-distance dispersal determine spatial patterns. At these larger spatial scales, both local and long-distance dispersal require parameterization, and this has been achieved through spatially explicit individual-based simulation models using two or more dispersal functions. It is doubtful whether a single estimate of spread encapsulates the spatio-temporal dynamics of invasive species at this scale. Thus, estimates of spread drawn from successive distribution maps will tend to be biased towards long-distance dispersal events. The frequency and distribution of introduction events play a key role in invasion trajectories, and the stochastic nature of such events may explain why the longer a species has been introduced into a region the greater the likelihood that it becomes invasive. However, cumulative counts of localities or samples only provide one perspective on the invasion process and need to be associated with spatial information to depict spread more realistically. This review highlights that monitoring of invasive species must be approached from a hierarchical perspective with data gathered at more than one spatial scale. Such an approach will improve predictions and integrate landscape attributes into invasion dynamics.

Magnetic-field-induced structural phase transition in Gd 5 ( S i 1.8 Ge 2.2 )

Abstract: We present direct evidence that the giant magnetocaloric effect recently discovered in the ${\mathrm{Gd}}_{5}{(\mathrm{S}\mathrm{i}}_{1.8}{\mathrm{Ge}}_{2.2})$ alloy is associated with a field-induced first-order structural transition from a ${P112}_{1}/a$ monoclinic (paramagnetic) to a Pnma orthorhombic (ferromagnetic) structure. A large volume contraction of $\ensuremath{\Delta}V/V\ensuremath{\cong}0.4%$ takes place spontaneously at the transition temperature, ${T}_{C}\ensuremath{\cong}240\mathrm{K}.$ The reported structural transition can be induced reversibly by application of an external magnetic field, producing strong magnetoelastic effects.

The nature of improper, blue-shifting hydrogen bonding verified experimentally.

Abstract: In the infrared spectra of solutions in liquid argon of dimethyl ether ((CH3)2O) and fluoroform (HCF3), bands due to a 1:1 complex between these monomers have been observed. The C−H stretch of the HCF3 moiety in the complex appears 17.7 cm-1 above that in the monomer, and its intensity decreases by a factor of 11(2). These characteristics situate the interaction between the monomers in the realm of improper, blue-shifting hydrogen bonding. The complexation shifts the C−F stretches downward by some 9 cm-1, while the C−H stretches in (CH3)2O are shifted upward by 9−15 cm-1, and the C−O stretches are shifted downward by 5 cm-1. These shifts are in very good agreement with those calculated by means of correlated ab initio methods, and this validates a two-step mechanism for improper, blue-shifting hydrogen bonding. In the first step, the electron density is transferred from the oxygen lone electron pairs of the proton acceptor ((CH3)2O) to fluorine lone electron pairs of the proton donor (CHF3) which yields e...

Synchronization as adjustment of information rates: detection from bivariate time series.

Abstract: An information-theoretic approach for studying synchronization phenomena in experimental bivariate time series is presented. "Coarse-grained" information rates are introduced and their ability to indicate generalized synchronization as well as to establish a "direction of information flow" between coupled systems, i.e., to discern the driving from the driven (response) system, is demonstrated using numerically generated time series from unidirectionally coupled chaotic systems. The method introduced is then applied in a case study of electroencephalogram recordings of an epileptic patient. Synchronization events leading to seizures have been found on two levels of organization of brain tissues and "directions of information flow" among brain areas have been identified. This allows localization of the primary epileptogenic areas, also confirmed by magnetic resonance imaging and pasitron emission tomography scans.

Ligninolytic fungi in bioremediation: extracellular enzyme production and degradation rate

Abstract: Ligninolytic fungi can be used for remediation of pollutants in water and soil. Extracellular peroxidases and laccases have been shown to oxidize recalcitrant compounds in vitro but the likely significance of individual enzyme levels in vivo remains unclear. This study documents the amounts and activities of Mn-dependent peroxidase (MnP), lignin peroxidase and laccase (LAC) in various species of ligninolytic fungi grown in liquid medium and soil and their effect on degradation of polycyclic aromatic hydrocarbons (anthracene and pyrene), a polychlorinated biphenyl mixture (Delor 106) and a number of synthetic dyes. Stationary cultures of a highly degradative strain Irpex lacteus exhibited 380-fold and 2-fold increase in production of MnP and LAC, respectively, compared to submerged cultures. Addition of Tween 80 to the submerged culture increased MnP levels 260-fold. High levels of MnP correlated with efficient decolorization of Reactive Orange 16 azo dye but not of Remazol Brilliant Blue R anthraquinone dye. Degradation of anthracene and pyrene in spiked soil by straw-grown explorative mycelium of Phanerochaete chrysosporium, Trametes versicolor and Pleurotus ostreatus showed the importance of MnP and LAC levels secreted into the soil. The importance of high fungal enzyme levels for efficient degradation of recalcitrant compounds was better demonstrated in liquid media compared to the same strains growing in soil.