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In connection with the problem of the initial singularity in the framework of the Brans-Dicke scalar-tensor isotropic cosmology, the dynamics of the early stages of the expansion is studied on the basis of the general analytical solutions for flat models withP=n (0n1). The sourceless scalar field, which plays a role of effective source of the geometry, entirely changes the character of the initial expansion, whereas in the absense of it the dynamics of the models almost does not differ from GR-case. If the connecting parameter <–6 then the sourceless scalar field removes the initial singularity for any equations of state, and provides the regular transition form the compression to the expansion through the non-stationary state with
. If is positive, the singularity of vacuum nature necessarily exists; the sourceless scalar-field being prevalent over the material sources (at least for P1/3) near the singularity. For P>1/3 parallel with the vacuum singularity the singular initial state with dominant role of gravitating matter is possible. In the course of expansion, the influence of gravitating matter and curvature-which as nonessential at the early stage in comparison with sourceless -field — becomes dominant, and all models approach the Machian ones which differs slightly from corresponding GR-models. If is negative (<–6) the sourceless -field slows down the initial expansion and increases essentially the real age of the Universe; it can also influence the primordial nuclear synthesis by diminishing in particular the content of He4. It is shown that a knowledge of the sign gives us the information about the nature of the initial Universe state.
Zusammenfassung In diesem Artikel betrachtet man die Einwirkung des quellosen skalaren Feld auf die Dynamik der früheren Stadien der Ausdehnung der kosmologischen Modellen. Man zeigt auch die Möglichkeit der Existenz eines unsingulären ursprünglichen Zustand in der Brans-Dickeschen skalar-tensorischen Kosmologie.
Résumé On considère dans cet article l'influence du champ scalaire sans source sur la dynamique des étapes premières de l'expansion des modèles cosmologiques. On montre, en outre, la possibilité de l'existence de l'état initiale nonsingulier dans la cosmologie scalaire-tensorique de Brans-Dicke.相似文献
44.
K. S. Bhamra A. M. Finkelstein V. Ja. Kreinovich L. E. Gurevich 《Astrophysics and Space Science》1978,57(2):371-380
The complete analysis of possible types of non-relativistic and ultra-relativistic motions in the field of the naked singularity of the STGT is given. The problem of the infall of a monochromatic radiation emitter on the naked singularity is studied. In spite of the absence of a freezing effect in the STGT, the naked singularity is not observable, for the brightness of the falling emitter decreases much faster than in the GTR. Atrr
g
, the trajectory of particles and light are quite similar to that of the GTR, and due to this fact the naked singularity is observationally indistinguishable from a black hole. 相似文献
45.
Multiple proxies from a 319-cm peat core collected from the Hudson Bay Lowlands, northern Ontario, Canada were analyzed to determine how carbon accumulation has varied as a function of paleohydrology and paleoclimate. Testate amoeba assemblages, analysis of peat composition and humification, and a pollen record from a nearby lake suggest that isostatic rebound and climate may have influenced peatland growth and carbon dynamics over the past 6700 cal yr BP. Long-term apparent rates of carbon accumulation ranged between 8.1 and 36.7 g C m? 2 yr? 1 (average = 18.9 g C m? 2 yr? 1). The highest carbon accumulation estimates were recorded prior to 5400 cal yr BP when a fen existed at this site, however following the fen-to-bog transition carbon accumulation stabilized. Carbon accumulation remained relatively constant through the Neoglacial period after 2400 cal yr BP when pollen-based paleoclimate reconstructions from a nearby lake (McAndrews et al., 1982) and reconstructions of the depth to the water table derived from testate amoeba data suggest a wetter climate. More carbon accumulated per unit time between 1000 and 600 cal yr BP, coinciding in part with the Medieval Climate Anomaly. 相似文献
46.
Twenty high Arctic lakes and ponds were sampled for water chemistry and modern diatom assemblages in two distinct physiographic
sectors of Sirmilik National Park, Nunavut, Canada. Sites on southwestern Bylot Island were warmer, more alkaline, less dilute,
and had higher concentrations of nutrients, DOC and Chl-a (mesotrophic to oligo-mesotrophic), whereas sites on Qorbignaluk Headland on northern Baffin Island were deeper, very dilute,
mostly oligotrophic and had lower pH. Diatom assemblages differed markedly between these two regions as a consequence of limnological
differences between them. Paleolimnological records, spanning > 200 years and dated by 210Pb activity, were produced from each region to compare biological responses to recent warming inferred from glaciological
studies on Bylot Island and regional syntheses for the Arctic. Diatom assemblages began to change around AD 1900 at both sites.
At Qorbignaluk Headland, marked shifts in diatom community composition occurred during the twentieth century, with large increases
in the abundance of planktonic diatoms. At Bylot Island, diatom community changes began around the same time, and involved
modest decreases in planktonic diatoms and increases in inferred specific conductance, likely because of a decrease in the
areal extent of the small lake as a response to warming. The study confirms that responses of freshwater ecosystems to climate
warming vary depending on local physiographic factors. 相似文献
47.
V. P. Ivanov I. A. Rakhimov S. G. Smolentsev K. S. Stankevich A. M. Finkelstein 《Astronomy Letters》2004,30(4):240-246
We measured the flux densities of the radio source 3C 58, which was identified with the remnant of SN 1181, in April–May 2003 relative to the spectrum of the standard source 3C 295 at fourf requencies in the range 1550 to 8450 MHz using the RTF-32 radio telescope at the Svetloe Observatory of the Institute of Applied Astronomy (Russian Academy of Sciences). We found significant nonstationary frequency-dependent flux-density variations in 3C 58 and variations in its instantaneous spectrum. We established that these variations occurred between 1986 and 1998. Based on data for the instantaneous spectra, we show that the break in the spectrum of 3C 58 results from prolonged energy losses by relativistic electrons through synchrotron radiation that took place in a nebula with an age of 5400 yr, equal to the age of the pulsar PSR J0205+6449. SN 1181 is shown to have exploded without the birth of a pulsar, which is characteristic of type-I supernovae. The shock acceleration of relativistic electrons after the explosion may be responsible for the observed nonstantionarity of the flux densities. The long-term evolution of the radio spectrum for the nebula 3C 58 and the nonstationary flux-density variations due to the explosion of SN 1181 are reconciled in terms of a model of an evolved binary system. 相似文献
48.
Abstract Riparian vegetation has a fundamental influence on the biological, chemical and physical nature of rivers. The quantification of riparian landcover is now recognised as being essential to the holistic study of the ecosystem characteristics of rivers. Medium resolution satellite imagery is now commonly used as an efficient and cost effective method for mapping vegetation cover; however such data often lack the resolution to provide accurate information about vegetation cover within riparian corridors. To assess this, we measure the accuracy of SPOT multispectral satellite imagery for classification of riparian vegetation along the Taieri River in New Zealand. In this paper, we discuss different sampling strategies for the classification of riparian zones. We conclude that SPOT multispectral imagery requires considerable interpretative analysis before being adequate to produce sufficiently detailed maps of riparian vegetation required for use in stream ecological research. 相似文献
49.
A. M. Finkelstein A. V. Ipatov E. A. Skurikhina I. F. Surkis S. G. Smolentsev L. V. Fedotov 《Astronomy Letters》2012,38(6):394-398
The hardware and software upgrades to the Quasar VLBI network have allowed one to increase the measurement accuracy of the Earth orientation parameters (EOPs) and to improve the quality of geodynamic observations. At present, the observations are performed within two national programs: 24-h sessions on three radio telescopes of the network to determine all five EOPs (the Ru-E program) and 1-h sessions on the Zelenchukskaya-Badary and Svetloe-Badary baselines (the Ru-U program) for a prompt determination of the Universal Time. The results of processing the observations from January 2009 to November 2011 are presented. The rms deviations of the EOPs obtained in the Ru-E program from the IERS 08 C04 series are 1 mas for the coordinates of the Earth??s pole, 0.38 mas for the coordinates of the celestial pole, and 34 ??s for the Universal Time. The rms deviations of the Universal Time obtained in the Ru-U program are 53 ??s. 相似文献
50.
Karnit Bahartan Mohammad Zibdah Alvaro Israel Avigdor Abelson 《Marine pollution bulletin》2010,60(5):759-764
The current state of health of the coral reefs in the northern Gulf of Aqaba (Red Sea), notably the Eilat reefs, is under debate regarding both their exact condition and the causes of degradation. A dearth of earlier data and unequivocal reliable indices are the major problems hinder a clear understanding of the reef state. Our research objective was to examine coral-algal dynamics as a potential cause and an indication of reef degradation. The community structure of stony corals and algae along the northern Gulf of Aqaba reveal non-seasonal turf algae dominancy in the shallow Eilat reefs (up to 72%), while the proximate Aqaba reefs present negligible turf cover (<6%). We believe that turf dominancy can indicate degradation in these reefs, based on the reduction in essential reef components followed by proliferation of perennial turf algae. Our findings provide further evidence for the severe state of the Eilat coral reefs. 相似文献