A Friedmann-Lemaître Universe Model with a Positive Cosmological Constant     

M.G. Larionov 《Astrophysics and Space Science》1997,252(1-2):139-149

The possibility of using a Friedmann-Lemaître model with a non-zero cosmological constant q3t7k63165qt56q1/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0"> is investigated on the basis of analyses of the RATAN-600 and 87GB radio surveys and optical constraints. A zero deceleration parameter and critical matter density are features of the model. The model is in agreement with current observational data, including estimates of the age of the Universe, Hubble constant measurements, and the q3t7k63165qt56q1/xxlarge920.gif" alt="THgr" align="BASELINE" BORDER="0"> - z relation. A value for the cosmological constant is determined and its physical nature discussed.  相似文献   

A new octuple Earth-crossing meteoroid stream     

Yu. V. Obrubov 《Earth, Moon, and Planets》1995,68(1-3):443-449

It was shown that the orbit ofq06l/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0"> Virginid meteors is an octuple Earth-crosser so that the stream can produce eight related meteor showers. Of these eight theoretical showers five are identified in the catalogues; one of these is theq06l/xxlarge954.gif" alt="kappa" align="BASELINE" BORDER="0"> Cygnids.  相似文献   

Effect of Radiation on the Nonlinear Stability Zones of the Lagrangian Equilibrium Points     

K. E. papadakis 《Celestial Mechanics and Dynamical Astronomy》1998,72(4):235-244

The nonlinear stability zones of the triangular Lagrangian points are determined numerically and the effect of radiation of primaries is considered, in addition to the known effect of mass distribution, using the photogravitational restricted threeq243u06317v15/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">body problem model. It is found that radiation also has a considerable effect reducing the stability zones. In cases of resonances, these zones are reduced to negligible size for some parameter values within the linear stability regions.  相似文献   

The Phase Space Structure Around L4 in the Restricted Three-Body Problem     

Zsolt Sándor  Bálint Érdi  Christos Efthymiopoulos 《Celestial Mechanics and Dynamical Astronomy》2000,78(1-4):113-123

The phase space structure around L ₄ in the restricted three-body problem is investigated. The connection between the long period family emanating from L ₄ and the very complex structure of the stability region is shown by using the method of Poincaréq0103/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s surface of section. The zero initial velocity stability region around L ₄ is determined by using a method based on the calculation of finite-time Lyapunov characteristic numbers. It is shown that the boundary of the stability region in the configuration space is formed by orbits suffering slow chaotic diffusion.  相似文献   

Hubbert’s petroleum production model: an evaluation and implications for World Oil Production Forecasts     

Alfred J. Cavallo 《Natural Resources Research》2004,13(4):211-221

Following Hubbertq363778431537157/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s successful prediction of the timing of US peak oil production, Hubbertq363778431537157/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s model has been used extensively to predict peak oil production elsewhere. However, forecasts of world and regional peak oil and natural gas production using Hubbertq363778431537157/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s methodology usually have failed, leading to the implicit belief that such predictions always will fail and that we need not worry about finite resources. A careful examination of Hubbertq363778431537157/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s approach indicates that the most important reasons for his success in the US were stable markets, the high growth rate of demand, ready availability of low cost imports, and a reasonable estimate of easily extractable reserves. This analysis also shows that his model cannot predict ultimate oil reserves and that it should be considered an econometric model. Building on Hubbertq363778431537157/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s vital insight, that cheap fossil fuel reserves are knowable and finite, one can state that for world peak oil production, political constraints should be much more important than resource constraints.  相似文献   

Gaseous and Particulate Oxidation Products Analysis of a Mixture of α-pinene + β-pinene/O3/Air in the Absence of Light and α-pinene + β-pinene/NOx/Air in the Presence of Natural Sunlight     

M. Jaoui  R. M. Kamens 《Journal of Atmospheric Chemistry》2003,44(3):259-297

The gas and particle phase reaction products of a mixture of the atmospherically important terpenes q77024008/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-pinene and q77024008/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-pinene with the atmospheric oxidants O₃ and OH/NO_x were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of a mixture of q77024008/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-pinene and q77024008/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-pinene in the presence of O₃/air, and the daytime oxidation of a mixture of q77024008/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-pinene + q77024008/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-pinene with NO_x air in the presence of natural sunlight were carried out in the University of North Carolina's large outdoor smog chamber (190 m³) located in Chatham County, North Carolina. Mass balances for gaseous and aerosol reaction products are reported over the course of the reaction. More than twenty-nine products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for q77024008/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">74 to q77024008/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">80% of the reacted q77024008/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-pinen/q77024008/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-pinene mixture carbon. Measurements show that a number of reaction products were found in both O₃ and NO_x system [pinonaldehyde, pinic acid, pinonic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxy-nopinone, 3-hydroxy-nopinone, and nopinone]. Pinonic acid, pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, and 10-hydroxypinonic acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols.  相似文献   

Low-temperature study of natural melilite (Ca1.89Sr0.01Na0.08K0.02) (Mg0.92Al0.08)(Si1.97Al0.03)O7: towards a commensurate value of the q vector     

Bindi  L.  Bonazzi  P. 《Physics and Chemistry of Minerals》2003,30(9):523-526

As is usual for peculiar chemical compositions, melilite-type compounds exhibit a two-dimensional incommensurately modulated structure which can be described with two wave vectors: q ₁ =(a* + b*) and q ₂ =(–a* + b*), where a* and b* are the tetragonal reciprocal axes of the basic cell. The low-temperature dependence of the modulation wave vector of a natural melilite crystal with chemical composition (Ca_1.89Sr_0.01 Na_0.08K_0.02)(Mg_0.92Al_0.08)(Si_1.97Al_0.03)O₇ has been studied by X-ray single-crystal diffraction methods in the temperature range 298–100 K. The value of the coefficient shows a continuous linear increase, ranging from 0.281(1) at 298 K to 0.299(1) at 100 K. No plateau-like temperature dependence was observed throughout the temperature studied, thus indicating that no independent phase with a specific q stabilizes in this natural crystal. A comparison with the low-temperature behaviour of synthetic Ca₂MgSi₂O₇ is given.  相似文献   

Lacustrine organic matter and the Holocene paleoenvironmental record of Lake Albano (central Italy)     

D. Ariztegui  C. Chondrogianni  A. Lami  P. Guilizzoni  E. Lafargue 《Journal of Paleolimnology》2001,26(3):283-292

A combined bulk and detailed geochemical study of the sedimentary organic matter in Lake Albano, central Italy, provides critical data to track the response of this aquatic system to the environmental changes of variable amplitude that occurred during the Holocene. Rockq4/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">Eval pyrolysis of this predominantly laminated, organic carbonq4/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">rich sedimentary sequence shows changes in hydrogen and oxygen indices that are related to variations in the dominance of the primary producers. These variations are further confirmed by the pigments and the carbon isotopic composition of bulk organic matter showing that cyanobacteria dominated the lake waters during the early and late Holocene whereas diatoms have been the main producers during the middle Holocene. Sharp decreases in productivity, 2–3 centuries long, are identified at ca. 8.2, 6.4 and 3.8 ka. B.P. Changes in temperature and/or effective moisture are suggested as the most probable causes, although human impact cannot be ruled out for the latest part of the Holocene.  相似文献   

金刚石优化钻进的新途径          下载免费PDF全文

罗超  李世忠  李砚藻 《探矿工程》1994,(2):48-51

选择了优化钻进的衡量参数（ｈ／ｐ）／ｑ，并以此多数对具体岩石优选了钻头，对具体岩石和钻头优选了合理的钻头每转进尺范围。  相似文献   

The production of circumstellar26Al by massive stars     

N. Langer  H. Braun  J. Fliegner 《Astrophysics and Space Science》1995,224(1-2):275-278

We investigate the production of²⁶Al during hydrogen burning and its ejection by massive single and binary stars. Effects of convection and rotation are studied. We discuss the importance of RSGs, LBVs and WR stars to the total Galactic²⁶Al production, and the detection probability of the²⁶Al decay in individual objects as P Cygni,q477833ntt/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0"> Velorum andq477833ntt/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0"> Carinae.  相似文献