Close Surroundings Research Articles

A model of metal–silicate separation on growing planets

The thermal evolution of planets during their accretionary growth is strongly influenced by impact heating. The temperature increase following a collision takes place mostly below the impact location in a volume a few times larger than that of the impactor. Impact heating depends essentially on the radius of the impacted planet. When this radius exceeds ~ 1000 km, the metal phase melts and forms a shallow and dense pool that penetrates the deep mantle as a diapir. To study the evolution of a metal diapir we propose a model of thermo-chemical readjustment that we compare to numerical simulations in axisymmetric spherical geometry and with variable viscosity. We show that the metallic phase sinks with a velocity of order of a Stokes velocity. The thermal energy released by the segregation of metal is smaller but comparable to the thermal energy buried during the impact. However as the latter is distributed in a large undifferentiated volume and the former potentially liberated into a much smaller volume (the diapir and its close surroundings) a significant heating of the metal can occur raising its temperature excess by at most a factor of 2 or 3. When the viscosity of the hot differentiated material decreases, the proportion of thermal energy transferred to the undifferentiated material increases and a protocore is formed at a temperature close to that of the impact zone.

Species composition and diversity of aero-terrestrial algae and cyanobacteria of the Boreč Hill ventaroles.

The algal flora of the Boreč Hill ventaroles was examined and compared with the flora of their close surroundings. In comparison to unaffected sites, the ventaroles differ in seasonal temperature fluctuation as well as in soil pH. Winter exhalations caused by continual air circulation in the cranny system of rock massive result in a significant increase in air temperature and soil pH. The ventaroles were inhabited by a markedly richer and more diversified algal flora. Over half of investigated species occurred only in the ventaroles, including all chrysophyte, eustigmatophyte and desmid taxa. In contrast to the unaffected sites, different algal populations were discovered in the ventaroles. The investigated species could be separated into two groups: ventarole-specific ones preferentially occurred in both the ventaroles, and those occurred only in a large ventarole. There, water condensation in moss plants during winter exhalations enables a short-term occurrence of several algal species preferring aquatic environments. The diatom flora of the ventaroles resembles well the species composition found in the caves. By contrast, the desmid flora is rather similar to algal communities found in ephemeral water bodieslike temporary peat bog pools or dripping rocks. Thus, the Boreč Hill ventaroles represent a unique type of biotope, with a specific algal flora adapted to periodical periods of warm, moist air exhalations of several months' duration.

Echelle Long‐Slit Optical Spectroscopy of Evolved Stars

We present echelle long-slit optical spectra of a sample of objects evolving off the AGB, most of them in the pre-planetary nebula (pPN) phase, obtained with the ESI and MIKE spectrographs at Keck-II and Magellan-I, respectively. The total wavelength range covered with ESI (MIKE) is ~3900 to 10900 A (~3600 to 7200A). In this paper, we focus our analysis mainly on the Halpha profiles. Prominent Halpha emission is detected in half of the objects, most of which show broad Halpha wings (up to ~4000 km/s). In the majority of the Halpha-emission sources, fast, post-AGB winds are revealed by P-Cygni profiles. In ~37% of the objects Halpha is observed in absorption. In almost all cases, the absorption profile is partially filled with emission, leading to complex, structured profiles that are interpreted as an indication of incipient post-AGB mass-loss. All sources in which Halpha is seen mainly in absorption have F-G type central stars, whereas sources with intense Halpha emission span a larger range of spectral types from O to G. Shocks may be an important excitation agent of the close stellar surroundings for objects with late type central stars. Sources with pure emission or P Cygni Halpha profiles have larger J-K color excess than objects with Halpha mainly in absorption, which suggests the presence of warm dust near the star in the former. The two classes of profile sources also segregate in the IRAS color-color diagram in a way that intense Halpha-emitters have dust grains with a larger range of temperatures. (abridged)

ADONIS high contrast infrared imaging of Sirius-B

Context. Sirius is the brightest star in the sky and a strong source of diffuse light for modern telescopes so that the immediate surroundings of the star are still poorly known. Aims. We study the close surroundings of the star (2 to 25 �� ) by means of adaptive optics and coronographic device in the near-infrared, using the ESO/ADONIS system. Methods. The resulting high contrast images in the JHKs bands have a resolution of ∼0.2 �� and limiting apparent magnitude ranging from mK = 9. 5a t 3 �� from Sirius-A to mK = 13. 1a t 10 �� . These are the first and deepest images of the Sirius system in this infrared range. Results. From these observations, accurate infrared photometry of the Sirius-B white dwarf companion is obtained. The JH magnitudes of Sirius-B are found to agree with expectations for a DA white dwarf of temperature (T = 25 000 K) and gravity (log g = 8.5), consistent with the characteristics determined from optical observations. However, a small, significant excess is measurable for the K band, similar to that detected for “dusty” isolated white dwarfs harbouring suspected planetary debris. The possible existence of such circumstellar material around Sirius-B has still to be confirmed by further observations. Conclusions. These deep images allow us to search for small but yet undetected companions to Sirius. Apart from Sirius-B, no other source is detected within the total 25 �� field. A comparison of the flux expected from the faintest known brown dwarfs at the distance of Sirius demonstrates that the above limiting magnitudes correspond to a star of spectral type later than T5 at 5 �� and T7 at 10 �� . Using theoretical spectra of brown dwarfs and planet-size objects, we also show that the end of the brown dwarf sequence is reached in the outer part of the image. The minimum detectable mass is around 10 MJup inside the planetary limit, indicating that an extrasolar planet at a projected distance of ∼25 AU from Sirius would have been detected.

Outliers from the Mainstream: How a Massive Star Can Produce a Gamma-Ray Burst

It is now recognized that long-duration gamma-ray Bursts (GRBs) are linked to the collapse of massive stars, based on the association between (low redshift) GRBs and (Type Ic) core-collapse supernovae (SNe). The census of massive stars and GRBs reveals, however, that not all massive stars produce a GRB. Only ~1% of core-collapse SNe are able to produce a highly relativistic collimated outflow, and hence a GRB. The extra crucial parameter has long been suspected to be metallicity and/or rotation. We find observational evidence strongly supporting that both ingredients are necessary in order to make a GRB out of a core-collapsing star. A detailed study of the absorption pattern in the X-ray spectrum of GRB 060218 reveals evidence of material highly enriched in low-atomic-number metals ejected before the SN/GRB explosion. We find that, within the current scenarios of stellar evolution, only a progenitor star characterized by a fast stellar rotation and subsolar initial metallicity could produce such a metal enrichment in its close surrounding.

Impact of Formica exsecta Nyl. on seed bank and vegetation patterns in a subalpine grassland ecosystem

AbstractThe mound building ant Formica exsecta Nyl. is widely distributed in grassland ecosystems of the Central European Alps. We studied the impact of these ants on seed bank and vegetation patterns in a 11 ha subalpine grassland, where we counted over 700 active ant mounds. The mounds showed a distinct spatial distribution with most of them being located in tall‐grass, which was rarely visited by ungulates (red deer; Cervus elaphus L.). Heavily grazed short‐grass, in contrast, seemed to be completely avoided by ants as only few mounds were found in this vegetation type. The species composition of the ant mound and grassland seed banks was quite similar, i.e. from 15 common plant species 12 were found in both seed bank types. We found the same proportions of myrmecochorous seeds in ant mound and grassland soil samples. In contrast, the number of seeds was 15 times higher in mound compared with the grassland soil samples. Also, the vegetation growing on ant mounds significantly differed from the vegetation outside the mounds: graminoids dominated on ant mounds, herbaceous and myrmecochorous species in the grassland vegetation. We found significant continuous changes in vegetation composition on gradients from the ant mound centre to 1 m away from the mound edge. Overall, F. exsecta was found to have a considerable impact on seed bank and vegetation patterns in the grassland ecosystem studied. These insects not only altered grassland characteristics in the close surrounding of their mounds, but also seem to affect the entire ecosystem including, for example, the spatial use of the grassland by red deer.

Pseudofluorose: psychische Aspekte der Umweltbelastung

A middle-aged woman who had been living in close surroundings of a fluorine-emitting factory for many years, was examined because she claimed to be suffering from skeletal fluorosis. Radiological, histological and laboratory findings did not give evidence of fluorosis. Fluoride concentrations were normal in samples of blood, bone, pooled urine, nails and hair. Even this proof to the contrary did not shake her conviction of many years that she was suffering from fluorosis. Thus, psychological aspects have to be considered in the assessment of health implications of pollutants.

The effects of resolving the Canadian Arctic Archipelago in a finite element sea ice model

Though narrow straits may have a strong influence on the large-scale sea ice mass balance, they are often crudely represented in coarse resolution sea ice models. Unstructured meshes, with their natural ability to fit boundaries and locally increase the mesh resolution, propose an alternative framework to capture the complex oceanic areas formed by coasts and islands. In this paper, we develop a finite element sea ice model to investigate the sensitivity of the Arctic sea ice cover features to the resolution of the narrow straits constituting the Canadian Arctic Archipelago. The model is a two-level dynamic-thermodynamic sea ice model, including a viscous-plastic rheology. It is run over 1979–2005, forced by daily NCEP/NCAR reanalysis data. Confronting qualitatively numerical experiments with observations shows a good agreement with satellite and buoys measurements. Due to its simple representation of the oceanic interactions, the model overestimates the sea ice extent during winter in the southernmost parts of the Arctic, while the Baffin Bay and Kara Sea remain ice-covered during summer. In order to isolate the benefits from resolving the Canadian Arctic Archipelago, a numerical experiment is performed where we artificially close the archipelago. Focusing on the large-scale sea ice thickness pattern, no significant change is found in our model, except in the close surroundings of the archipelago. However, the local and short-term influences of the ice exchanges are nonnegligible. In particular, we show that the ice volume associated to the Canadian Arctic Archipelago represents 10% of the Northern Hemisphere sea ice volume and that the annual mean ice export towards Baffin Bay amounts to 125 km 3 yr −1, which may play an important role on the convective overturning in the Labrador Sea.

Geographical variation in the determinants of seed dispersal success of a myrmecochorous herb

1 This paper draws together geographical variation and various correlates of individual seed dispersal success to evaluate spatial variation in major determinants of seed removal rates of the myrmecochore Helleborus foetidus, whose ant assemblages and diaspores vary geographically. 2 We censused seed removal by ants directly from individual plants in 12 populations and four regions across the Iberian Peninsula, and measured the elaiosomed seed, plant fecundity, and the biotic and abiotic environment in the close vicinity of each plant. The relative effect of these three groups of variables on seed removal was then modelled at each region using structural equation models and path analyses. 3 We found a pervasive effect of the close surroundings of each plant on dispersal. We also found a geographically variable influence of diaspore traits on dispersal. Such variable influence of the diaspore was closely related to the compositional and functional variation in ant guilds. 4 Synthesis: The appearance of an effect of diaspore and plant traits on dispersal depended on the surroundings of the plant, the identity of the ant visitors and ant abundance. This dependence itself might lead to different directions of selection among populations, a conclusion that has not emerged from seed offerings to ants, which is the usual protocol in myrmecochory research.

Why the near field radiation from a large distributed source is independent of position

Background radiation from terrestrial sources of uranium, thorium, and potassium complicate the counting of radiation from a weak source. Although radiation from a localized point source decreases as the inverse square of the distance from the source, moving a counter further from a concrete table or floor does not decrease the background. Measurements of the intensity of radiation versus height above a local surface were made and found not to vary with height. A simple model is proposed assuming a uniform volume distribution with self-absorption as a source. It is shown that most of the radiation comes from relatively close surroundings.

Indices de fréquentation humaine dans les grottes à ours au Paléolithique moyen final: L’exemple de la Caverna Generosa dans les Préalpes lombardes, Italie

Already known like a palaeontological site for the study of Ursus spelaeus, Caverna Generosa also records ephemeral traces of human visits during the late Middle Palaeolithic. The cave opens at an altitude of 1450 m on the steep southern slope of the Monte Generoso Massif between the Lugano and the Como lakes and forms a complex group of narrow galleries and inner chambers. Sedimentological and palaeontological data and radiocarbon dates place both the cave-bear and the human frequentations in the first part of the isotopic stage 3 with climatic conditions shifting from cool and dry to more temperate and wet. Environment progressively changed from scarcely arboreal to arboreal-brush with small open spaces. Few flakes and Levallois flakes have been recovered scattered in the sediment and affected in most cases by intense postdepositional alteration. These items testify incursions of mousterian groups equipped with end-products and radiolarite flakes struck from blocks provisioned at lower locations southwards. End-products, namely Levallois flakes, prove that lithic reduction sequences were spatiotemporally fractionated in the covered territory. Conversely, it cannot be excluded a priori that sublocal radiolarite has been chipped at the entrance of the cave or at the very close surroundings for extraction of rudimental tools for immediate use. It is worth to mention that the small chert slabs in the Moltrasio limestone which crop throughout the cave walls were totally ignored. Caverna Generosa can be viewed as a refugia-location used in function of more or less constrained factors strongly influenced by high-altitude and bioclimatic situations. This type of site might well be integrated within the seasonal movements of humans in the western Lombard Pre-Alps area.

Farmers as initiators and farms as attractors for non-agricultural economic activities in peri-urban areas in Denmark

Geografisk Tidsskrift, Danish Journal of Geography 107(2):13–27, 2007 Changes in rural economy have been conceptualized as a post-pro-ductivistic transition with growing importance of non-agricultural economic activities as an important component. It is here hypothesized that these activities are profound in peri-urban areas and the importance of non-agricultural activities—here defined as on-farm business structure diversification—has been investigated on farm properties in an agricultural area in the vicinity of Copenhagen, Denmark. It has been explored what types of farm household adopt on-farm business structure diversification, and whether these activities evolved while living on the farm (farmers as initiators) or if opportunities for diversification were an important rationale for buying the farm property (farms as attractors). The case study area has 169 registered farm properties, and statistical inquiry (of business register information), questionnaire survey and qualitative interviews have been performed. The results show that agriculture is absent as an economic activity on half of the 169 farm properties. On a third of the farm properties, the buildings or their close surroundings are used for on-farm business structure diversification. It is a heterogeneous group of farmers that adopt diversification strategies, but especially the situation “farm as attractors” concerns many newcomers: They are attracted by the opportunities that the farm offers for economic activities traditionally located in urban areas. However, the attractor perspective is usually combined with other reasons for farm purchase. The total number of jobs generated by on-farm business structure diversification exceeds the employment in traditional farming. It is concluded that the peri-urban area to a certain extent has been transformed into a functionally urbanized countryside though it is still dominated by agricultural land use.

Bartonella henselae in the human environment in Poland

The aim of the study was to determine the occurrence of Bartonella henselae reservoir and vectors of infection in the close surroundings of human beings in urban areas of central Poland. The study included mammals (54 dogs, 137 cats) and 102 adult Ixodes ricinus ticks removed from cats and dogs. Blood samples were drawn from each animal and cultured on chocolate agar plates and in mouse fibroblasts L-929 cell line culture. The levels of Bartonella henselae IgG antibodies were determined by indirect immunofluorescence assay. Bartonella spp. strains were isolated from blood of 14 cats (10.2%). Isolates were identified by PCR methods as: B. henselae (18), B. clarridgeiae (1). Blood samples from dogs were consistently negative for Bartonella spp. 59 (45.0%) of 131 tested cats had B. henselae antibodies. B. henselae antibodies were present in 50% of tested dogs, although mostly (96.2%) in low titres <or= 1:64. In 4.9% of Ixodes ricinus ticks examined, B. henselae DNA was detected. These data demonstrate that in the urban area of central Poland B. henselae occurs in environmental sources, both in cats and dogs (reservoir) and ticks (possible vector).

Evidence for a 3p25 Breakpoint Hot Spot Region in Thyroid Tumors of Follicular Origin

Epithelial tumors of the thyroid are cytogenetically well-investigated tumors. So far, the main cytogenetic subgroups, characterized by trisomy 7 and by rearrangements of either 19q13 or 2p21, respectively, have been described. Recently, we have been able to describe the involvement of a novel gene called THADA in benign thyroid lesions with 2p21 rearrangements. Other fusion genes found in thyroid lesions are RET/PTC and PAX8/PPAR(gamma). The latter occurs in follicular thyroid carcinomas with a t(2;3)(q13;p25). Here we present molecular-cytogenetic and cytogenetic investigations on a follicular thyroid adenoma with a t(2;20;3)(p21;q11.2; p25). In this case, an intronic sequence of PPAR(gamma) is fused to exon 28 of THADA. We used BAC clones containing the genomic sequence of PPARgamma for fluorescence in situ hybridization to confirm the localization of the breakpoint within intron 2 of PPAR(gamma) . Our findings suggest that the close surrounding of PPAR(gamma) is a breakpoint hot spot region, leading to recurrent alterations of this gene in thyroid tumors of follicular origin including carcinomas as well as adenomas with or without involvement of PAX8.

Domains of Safety

It is considered that providing safety in universal dimension is exclusively responsibility of a public authority and the authority is fully responsible for efficient implementation of systems concerned with it. In reality, there is no prospect of not having incidents and therefore, there is no absolute safety. If such ideas exist anywhere, they are only theoretical concepts. Safety is a condition of the surroundings and natural environment of a local community. The condition level is defined by the degree of existing risk in that community. The risk is ubiquitous and inevitable as it exists in nature and civilian space. So the local governing body must decide what level of risk it is able to accept.Safety includes a wide range of undertakings be realized in order to provide security in all areas of concern in the state. Therefore, safety is the result of activities of different institutions, services, organizations, and also individual human being, its closest surroundings, local and central authorities.

Thermomechanical analysis of quartz porcelain in temperature cycles

Samples made from a mixture of 50% kaolin and clay, 25% quartz and 25% feldspar were tested by non-destructive sonic resonant method, which is sensitive to the structure defects. Sound velocity and Young's modulus of the green samples were measured during a cooling stage of the firing from temperature 1250 °C. Fired samples were also measured in temperature cycles 20–800–20 °C to reveal a role of the quartz grains in porcelain structure. A microcracking was begun in the cooling stage at the glass phase transformation point (∼760 °C) and continued to room temperature as a consequence of different thermal expansions of phases. A sharp drop of the mechanical strength (∼25%) measured during cooling between 600 and 500 °C confirms an important function of the β → α transformation of quartz. Unsolved quartz grains decrease their volume and generate tensile stress in their close surroundings, which causes the microcracks. Sound velocity and Young's modulus of the fired samples evidenced hysteresis on heating and cooling, attributed to microcracking during cooling and healing the microcracks during heating in the region of the α–β transformation of quartz. Given those conditions, there follows a rapid change of the sound velocity (∼21%) and Young's modulus (∼46%).

Methanol masers and massive star formation

AbstractIt has been established that massive stars form in dense clusters, when large molecular clouds collapse. However, the high obscuration and small spatial scales make it difficult to investigate the earliest stage of high–mass protostellar objects (HMPOs). Therefore methanol masers are of special interests as they are closely associated with HMPOs and offer high spatial resolution; they probe the massive star formation environment at the unique scale of a few AU (1 mas corresponds to 5 AU at 5 kpc).We present VLBI observations of methanol masers discovered in an unbiased survey along the Galactic plane. We compare their positions with infrared surveys. In general, the masers do not coincide with infrared objects. That implies they are already present at a very early evolution stage of HMPOs when the dense surroundings still absorb other radiation. In addition we present maps of five methanol masers towards HMPOs with milliarcsecond resolution taken with the recently extended European VLBI Network. These sources show a wide variety of morphologies, indicating they arise in different events going on in close surroundings of HMPOs, i.e. outflows, discs or shocks. One source G23.657−00.127 displays a regularly shaped ring which appears as a great laboratory for further research of a single HMPO. Proper motion studies should reveal an expansion or rotation of the maser components in 2–3 years.

Skeletal elements in the vertebrate eye and adnexa: Morphological and developmental perspectives

Although poorly appreciated, the vertebrate eye and adnexa are relatively common sites for skeletogenesis. In many taxa, the skeleton contributes to internal reinforcement in addition to the external housing of the eye (e.g., the circumorbital bones and eyelids). Eyeball elements such as scleral cartilage and scleral ossicles are present within a broad diversity of vertebrates, albeit not therian mammals, and have been used as important models for the study of condensations and epithelial-mesenchymal interactions. In contrast, other elements invested within the eye or its close surroundings remain largely unexplored. The onset and mode of development of these skeletal elements are often variable (early versus late; involving chondrogenesis, osteogenesis, or both), and most (if not all) of these elements appear to share a common neural crest origin. This review discusses the development and distribution of the skeletal elements within and associated with the developing eye and comments on homology of the elements where these are questionable.

Theory of pulsar's electrosphere

Although discovered almost forty years ago, pulsars still rank amongst the most fascinating astrophysical objects in the universe. They are believed to be strongly magnetised rotating neutron stars, whose existence had already been predicted soon after the discovery of the neutron in the beginning of the 30 s. However, relatively little progress has been made in understanding the fundamental physical mechanisms at work. Due to the lack of a satisfactory equation of state at very high densities, the internal structure of the neutron star remains enigmatic. Moreover, a global self-consistent picture of the close surrounding of the star, responsible for the emission of electromagnetic waves as well as for the launch of the pulsar wind and the energy loss due to interaction with the ambient medium, has not yet been proposed. Here, we give a brief review on the theory of pulsar's electrosphere (and magnetosphere) as well as on some recent developments. After a historical introduction, we recall some basic properties of these compact objects and the main observational characteristics, describing our present knowledge about pulsars. We then present our understanding of the pulsar magnetosphere, explaining in some detail a few theoretical ideas such as the polar cap and outer gap models. Some promising recent developments will be discussed: the electrospheric structure and the striped wind model.

Exciton characteristics and exciton luminescence of silicon quantum dot structures

The exciton binding energy, the energies of the basic radiative exciton transition, and the zerophonon radiative lifetime of excitons in silicon quantum dots embedded in the SiOx matrix are calculated in effective mass approximation with quadratic dispersion relation. In addition, the spectra of steady-state photoluminescence and of time-resolved photoluminescence of excitons in the silicon quantum dots are calculated, and the kinetics of the photoluminescence relaxation is considered. The theory is compared with the experiment. It is shown that, for nanostructures involving silicon quantum dots with diameters smaller than 4 nm, the governing factor in the broadening of the spectral photoluminescence bands is the effect of mesoscopic quantum fluctuations. In this case, either an even one dangling bond at the interface, or one intrinsic point defect, or one foreign atom located inside the small-sized nanocrystallite or in its close surroundings produces a pronounced effect on the energy of the exciton transition.