The dominant forces determining the motion of interplanetary particulates are gravitation, solar radiation pressure and Lorentz force. The latter two becoming significant for micron- and submicron- sized particles. In situ measurements by spaceprobes, microcrater distributions and remote observations both in the IR and visible wavelength range have established the mass frequency and spatial distribution of dust particles in interplanetary space. Consequences of the Poynting-Robertson effect and mutual collisions on these distributions and the contributions of various sources (interstellar dust, asteroids and comets) are discussed. It is shown that the contribution from a distributed source of large particles in the inner solar system is most important. Collisions between these meteor sized particles (m > 10^-5 g) produce large amounts of zodiacal light particles (10^-5 g to 10^-10 g) and
β-meteoroids (m < 10^-10 g) which leave the solar system on hyperbolic orbits. At the present time the Poynting-Robertson effect transports into the inner solar system less than 10% of the zodiacal light particles which are produced by collisions from bigger particles.
In arid and semiarid ecosystems, plant interspaces are frequently covered by communities of cyanobacteria, algae, lichens and mosses, known as biocrusts. These crusts often act as runoff sources and are involved in soil stabilization and fertility, as they prevent erosion by water and wind, fix atmospheric C and N and contribute large amounts of C to soil. Their contribution to the C balance as photosynthetically active surfaces in arid and semiarid regions is receiving growing attention. However, very few studies have explicitly evaluated their contribution to organic carbon (OC) lost from runoff and erosion, which is necessary to ascertain the role of biocrusts in the ecosystem C balance. Furthermore, biocrusts are not resilient to physical disturbances, which generally cause the loss of the biocrust and thus, an increase in runoff and erosion, dust emissions, and sediment and nutrient losses. The aim of this study was to find out the influence of biocrusts and their removal on dissolved and sediment organic carbon losses. One-hour extreme rainfall simulations (50 mm h-1) were performed on small plots set up on physical soil crusts and three types of biocrusts, representing a development gradient, and also on plots where these crusts were removed from. Runoff and erosion rates, dissolved organic carbon (DOC) and organic carbon bonded to sediments (SdOC) were measured during the simulated rain. Our results showed different SdOC and DOC for the different biocrusts and also that the presence of biocrusts substantially decreased total organic carbon (TOC) (average 1.80±1.86 g m-2) compared to physical soil crusts (7.83±3.27 g m-2). Within biocrusts, TOC losses decreased as biocrusts developed, and erosion rates were lower. Thus, erosion drove TOC losses while no significant direct relationships were found between TOC losses and runoff. In both physical crusts and biocrusts, DOC and SdOC concentrations were higher during the first minutes after runoff began and decreased over time as nutrient-enriched fine particles were washed away by runoff water. Crust removal caused a strong increase in water erosion and TOC losses. The strongest impacts on TOC losses after crust removal occurred on the lichen plots, due to the increased erosion when they were removed. DOC concentration was higher in biocrust-removed soils than in intact biocrusts, probably because OC is more strongly retained by BSC structures, but easily blown away in soils devoid of them. However, SdOC concentration was higher in intact than removed biocrusts associated with greater OC content in the top crust than in the soil once the crust is scraped off. and Consequently, the loss of biocrusts leads to OC impoverishment of nutrient-limited interplant spaces in arid and semiarid areas and the reduction of soil OC heterogeneity, essential for vegetation productivity and functioning of this type of ecosystems.
Organic matter properties of soils were studied in a territory covered by Stagnosols after afforestation. We quantified the impact of afforestation on the amount and distribution of free organic matter, microaggregates (unstable and stable under low-intensity sonification) and their components in the upper horizons of former arable soils overgrown by different species of forest vegetation. The duration of 45 years after afforestation was revealed to be not sufficient for a complete renewal of soil humus state, which appears only after till 115 years of the duration of forest cenosis. The carbon storage in light fractions remains lower by 21–40 % relative to that of forest soil, including significant losses of free organic matter (42–58 %) and occluded organic matter (12–33 %), which present the most active part of soil organic matter. The positive impact of the deposit regime, expressed by a sharp improvement of the carbon cycle balance, is reflected by the Cunstable/Cstable ratio, which decreases from 6.2 in arable soil to 2.4 on average in forest stands.
We consider autonomous systems where two scalar differential equations are coupled with the input-output relationship of the Preisach hysteresis operator, which has an infinite-dimensional memory. A prototype system of this type is an LCR electric circuit where the inductive element has a ferromagnetic core with a hysteretic relationship between the magnetic field and the magnetization. Further examples of such systems include lumped hydrological models with two soil layers; they can also appear as a component of the recently proposed models of population dynamics. We study dynamics of such systems near an equilibrium point. In particular, we show and examine a similarity in the behaviour of trajectories between the system with the Preisach memory operator and a planar slow-fast ordinary differential equation. The nonsmooth Preisach operator introduces a singularity into the system. Furthermore, we classify the robust equilibrium points according to their stability properties. Conditions for stability, instability and partial stability are presented. A robust partially stable point simultaneously attracts many trajectories and repels many trajectories (a behaviour which is not generic for smooth ordinary differential equations). We discuss implications of such local dynamics for the excitability properties of the system.
High resolution {OV5) two-dimensional spectra performed with the Multichannel Soustractive Double Pass (MSDP) spectrograph of the Pie du Midi Observatory, were analysed. An adapted image processing provides two-dimensional intensity and velocity maps of the solar granulation at two intensity levels of the photospheric line NaD2, filtered for the 5 min oscillations. An inspection of such
maps confirms that the bright granules at the continuum level are well correlated witli rising material as well as the dark intergranular spaces with falling material, and that the velocity fluctuations
penetrate much high into the photosphere than the intensity fluctuations. The one-dimensional power spectrum has a slope close to - 5/3, characteristic of a turbulent medium, in the size range
of the granulation. It is suggested that the convectivc energy is supplied by the mesogranulation and the supergranulation; this energy is then cascading toward the smaller scales through the granulation, which thus appears to be turbulent.
Based on the biological significance of the ubiquitin-proteasome pathway (UPP) and its potential role during sepsis, burns and ischemia-reperfusion injury, we hypothesized that the systemic response to traumatic shock (TS) is accompanied by tissue-specific UPP alterations. Therefore, we studied tissue ubiquitin pools, chymotryptic- and tryptic-like proteasome peptidase activities and ubiquitin-protein ligation (UbPL) rates in skeletal muscle, heart, lung, liver, spleen and kidney using a clinically relevant porcine model (bilateral femur fracture/hemorrhage followed by fluid resuscitation). TS induced a systemic reduction of tissue- specific high molecular mass ubiquitin-protein conjugates (>50 kDa). Free ubiquitin was unaffected. The dynamic organ patterns of ubiquitin pools paralleled the typical physiological response to TS and resuscitation. Reduction of ubiquitin-protein conjugates was most pronounced in heart and lung (p<0.05 vs. control) and accompanied by significant increases in proteasome peptidase and UbPL activities in these organs. Unlike all other tissues, spleen proteasome peptidase and UbPL activities were significantly reduced 10 h after TS. These findings support the concept that the UPP could play an important role in regulation of cell functions during the early whole-body response to TS. The UPP might be a therapeutic target to improve the metabolic care after TS, particularly in the heart, lung, and spleen., M. B. Patel, S. A. Earle, M. Majetschak., and Obsahuje bibliografii a bibliografické odkazy
The article covers the topic of women's migration from poorer countries to the so called First World to provide domestic work and care giving. On the one hand, their movement is caused by the demand for domestic labour in rich countries where double career couples resolve the dilemma of reconciliation of public and private spheres by externalization of domestic work. On the other hand, the supply is significant. Migration and provision of domestic service is often the only survival strategy available to women from developing countries due to high unemployment and few working opportunities. The practice of hiring a migrant as domestic worker creates global care chains (Hochschild, 2001) that connect women engaged in care giving - those who are postponing it and those who are providing it. Migrant women hold an unequal position in these chains. They comprise a cheap labour in the informal private sector and so are vulnerable to abusive treatment. To tackle such discrimination, the patriarchal system stereotyping both women's and men's roles has to be challenged on the both sides of the care chain: in the developed as well developing countries.
Syria changed from a seemingly stable and slowly modernising country to the site of a regional conflict in a matter of months. The factors of escalation are to be sought in three interrelated aspects: in the power structures of the Asad regime, that choose to deal with the reverberations of the Arab Spring through intensified security alone; in the transformation of social protest into a sectarian conflict; in the unconditional support that all sides receive from abroad. As a result, Syria ceased to be what it was three years ago: a country, a state, and a society., Zora Hesová., and Obsahuje bibliografii
[Zprávy Československé společnosti pro dějiny věd a techniky při ČSAV 9-10, 29-66 (1968)] and I. Bernard Cohen ; úvod redakce společný i pro předchozí článek je uveden na straně 220.