Neutron star masses: dwarfs, giants and neighbors     

Sergei Popov  David Blaschke  Hovik Grigorian  Mikhail Prokhorov 《Astrophysics and Space Science》2007,308(1-4):381-385

We discuss three topics related to the neutron star (NS) mass spectrum. At first we discuss the possibility to form low-mass (M≲1M _⊙) objects. In our opinion this and suggest this is possible only due to fragmentation of rapidly rotating proto-NSs. Such low-mass NSs should have very high spatial velocities which could allow identification. A critical assessment of this scenario is given. However, the mechanism has its own problems, and so formation of such objects is not very probable. Secondly, we discuss mass growth due to accretion for NSs in close binary systems. With the help of numerical population synthesis calculations we derive the mass spectrum of massive (M>1.8M _⊙) NSs. Finally, we discuss the role of the mass spectrum in population studies of young cooling NSs. We formulate a kind of mass constraint which can be helpful, in our opinion, in discussing different competitive models of the thermal evolution of NSs. S.B.P. wants to thank the Organizers for support and hospitality. The work of S.B.P. was supported by the RFBR grant 06-02-16025 and by the “Dynasty” Foundation (Russia). The work of M.E.P.—by the RFBR grant 04-02-16720 and that of H.G. by DFG grant 436 ARM 17/4/05.  相似文献   

Martian gullies in the southern mid-latitudes of Mars: Evidence for climate-controlled formation of young fluvial features based upon local and global topography     

James L. Dickson  Mikhail Kreslavsky 《Icarus》2007,188(2):315-323

A new survey of Mars Orbiter Camera (MOC) narrow-angle images of gullies in the 30°-45° S latitude band includes their distribution, morphology, local topographic setting, orientation, elevation, and slopes. These new data show that gully formation is favored over a specific range of conditions: elevation (−5000 to +3000 m), slope (>10°), and orientation (83.8% on pole-facing slopes). These data, and the frequent occurrence of gullies on isolated topographic highs, lead us to support the conclusion that climatic-related processes of volatile accumulation and melting driven by orbital variations are the most likely candidate for processes responsible for the geologically recent formation of martian gullies.  相似文献   

KREEPy lunar meteorite Dhofar 287A: A new lunar mare basalt     

Mahesh Anand  Lawrence A. Taylor  Kula C. Misra  Svetlana I. Demidova  Mikhail A. Nazarov 《Meteoritics & planetary science》2003,38(4):485-499

Abstract— Dhofar 287 (Dho 287) is a new lunar meteorite, found in Oman on January 14, 2001. The main portion of this meteorite (Dho 287A) consists of a mare basalt, while a smaller portion of breccia (Dho 287B) is attached on the side. Dho 287A is only the fourth crystalline mare basalt meteorite found on Earth to date and is the subject of the present study. The basalt consists mainly of phenocrysts of olivine and pyroxene set in a finer‐grained matrix, which is composed of elongated pyroxene and plagioclase crystals radiating from a common nucleii. The majority of olivine and pyroxene grains are zoned, from core to rim, in terms of Fe and Mg. Accessory minerals include ilmenite, chromite, ulvöspinel, troilite, and FeNi metal. Chromite is invariably mantled by ulvöspinel. This rock is unusually rich in late‐stage mesostasis, composed largely of fayalite, Si‐K‐Ba‐rich glass, fluorapatite, and whitlockite. In texture and mineralogy, Dho 287A is a low‐Ti mare basalt, with similarities to Apollo 12 (A‐12) and Apollo 15 (A‐15) basalts. However, all plagioclase is now present as maskelynite, and its composition is atypical for known low‐Ti mare basalts. The Fe to Mn ratios of olivine and pyroxene, the presence of FeNi metal, and the bulk‐rock oxygen isotopic ratios, along with several other petrological features, are evidence for the lunar origin for this meteorite. Whole‐rock composition further confirms the similarity of Dho 287A with A‐12 and A‐15 samples but requires possible KREEP assimilation to account for its rare‐earth‐element (REE) contents. Cooling‐rate estimates, based on Fo zonation in olivine, yield values of 0.2–0.8°C/hr for the lava, typical for the center of a 10–20 m thick flow. The recalculated major‐element concentrations, after removing 10–15% modal olivine, are comparable to typical A‐15 mare basalts. Crystallization modeling of the recalculated Dho 287A bulk‐composition yields a reasonable fit between predicted and observed mineral abundances and compositions.  相似文献   

An experimental facility for the investigation of magma fragmentation by rapid decompression     

Mikhail Alidibirov  Donald B. Dingwell 《Bulletin of Volcanology》1996,58(5):411-416

 A special experimental facility has been developed to investigate the fragmentation of vesicular magma undergoing rapid decompression. The facility operates in a regime similar to that of shock tubes and at temperatures up to 950  °C and pressures up to 200 bar. Cylindrical samples (diameter ca. 17 mm, length ca. 50 mm) undergo rapid decompression in a high-temperature, high-pressure section of the facility following the disruption of a diaphragm separating that section from a low-pressure, low-temperature section. Actual vesicular magma samples have been experimentally fragmented at elevated temperatures and pressures corresponding to those observed during explosive volcanic eruptions and the resulting pyroclastics have been photographically resolved in flight and collected for physical characterization. The results of these experiments show that the rapid decompression of highly viscous vesicular magma can generate pyroclastic ejecta via rapid and complete fragmentation of magma at high temperature. This new fragmentation facility is presented as a tool for experimental volcanology under well-constrained conditions. Received: 19 March 1996 / Accepted: 25 August 1996  相似文献   

Parameters of Tsunami Source Versus Earthquake Magnitude     

Anna V. Bolshakova  Mikhail A. Nosov 《Pure and Applied Geophysics》2011,168(11):2023-2031

This study employs an empirical-analytical approach in combination with Monte-Carlo method to establish relationships between earthquake moment magnitude and upper limits of tsunami source parameters: double-amplitude of vertical bottom deformation, displaced water volume, and potential energy of initial elevation. The approach is based on the Okada solution for a finite rectangular fault and empirical scaling laws for earthquake sources. Results are compared to empirical and theoretical relationships published previously. Parameters of some recent tsunami sources, those for which USGS provides slip distribution data, are considered in light of the established relationships.  相似文献   

Geochemistry of volcanic and hydrothermal gases of Mutnovsky volcano,Kamchatka: evidence for mantle,slab and atmosphere contributions to fluids of a typical arc volcano     

Mikhail Zelenski  Yuri Taran 《Bulletin of Volcanology》2011,73(4):373-394

We report chemical compositions (major and trace components including light hydrocarbons), hydrogen, oxygen, helium and nitrogen isotope ratios of volcanic and geothermal fluids of Mutnovsky volcano, Kamchatka. Several aspects of the geochemistry of fluids are discussed: chemical equilibria, mixing of fluids from different sources, evaluation of the parent magmatic gas composition and contributions to magmatic vapors of fluids from different reservoirs of the Kamchatkan subduction zone. Among reactive species, hydrogen and carbon monoxide in volcanic vapors are chemically equilibrated at temperatures >300°C with the SO₂-H₂S redox-pair. A metastable equilibrium between saturated and unsaturated light hydrocarbons is attained at close to discharge temperatures. Methane is disequilibrated. Three different sources of fluids from three fumarolic fields in the Mutnovsky craters can be distinguished: (1) magmatic gas from a large convecting magma body discharging through Active Funnel, a young crater with the hottest fumaroles (up to 620°C) contributing ~80% to the total volcanic gas output; (2) volcanic fluid from a separate shallow magma body beneath the Bottom Field of the main crater (96–280°C fumaroles); and (3) hydrothermal fluid with a high relative and absolute concentrations of CH₄ from the Upper Field in the main crater (96–285°C fumaroles). The composition of the parent magmatic gas is estimated using water isotopes and correlations between He and other components in the Active Funnel gases. The He-Ar-N₂ systematics of volcanic and hydrothermal fluids of Mutnovsky are consistent with a large slab-derived sedimentary nitrogen input for the nitrogen inventory, and we calculate that only ~1% of the magmatic N₂ has a mantle origin and <<1% is derived from the arc crust.  相似文献   

Appearance of the nonlinearity from the nonlocality in diffusion through multiscale fractured porous media     

Mikhail Panfilov  Mojdeh Rasoulzadeh 《Computational Geosciences》2013,17(2):269-286

We shall consider diffusion or single-phase flow in a multiscale porous medium which represents an infinite set of self-similar double-porosity media. At each scale, the medium consists of a highly permeable network of connected channels and low-permeable blocks. The characteristic scale of heterogeneity is ε at the highest level of hierarchy, wherein ε is a small parameter. The ratio between the channel and block permeability at each scale is ε ². The process analyzed is described using a diffusion equation with an oscillating multiscale diffusion parameter. The macroscale behavior is of interest. The transition to the macroscale is performed by means of the two-scale homogenization procedure. One step of averaging at each level of hierarchy leads to the appearance of the memory terms in the averaged equation. The successive averaging steps lead to progressive memory accumulation, so at each step of averaging, the macroscale model changes its type, and even the result of the second step is unknown a priori. The objective was to determine the macroscopic limit model for the infinite number of scales. By the method of induction, we obtained the macroscale model for an arbitrary number of scales and its limit for the infinite hierarchy. The limit model represents the system of two equations with memory terms. The kernel of the memory operator is the solution of a nonlinear integro-differential equation. Its solution is obtained through Laplace transform.  相似文献   

The Suavjärvi impact structure,NW Russia     

Mikhail S. MASHCHAK  Mikhail V. NAUMOV 《Meteoritics & planetary science》2012,47(10):1644-1658

Abstract– We present the geology and interpreted shock features of the Suavjärvi circular structure. Suavjärvi is a circular feature (illustrated by satellite imagery, topography, and magnetic data) located in the central part of the Karelian Craton (lat. 63°07′N, long. 33°23′E). To date, little information on the geologic and impact features of the Suavjärvi structure is available in the literature. The structure is characterized by gravity and magnetic lows and disruption of the regional magnetic fabric. In the northeastern and southwestern parts of the structure, several erosional remnants of highly disturbed rocks occur referred to as monomict and polymict megabreccia. These comprise blocks of both basement granitoids and supracrustal greenstone rocks. The impact origin of polymict megabreccia and therefore of the Suavjärvi structure is confirmed by observations of closely spaced planar microstructures at angles consistent with planes that have Miller indices indicative of impact shock effects, mostly of ω{10¯13}. The Suavjärvi is considered to be a remnant of a deeply eroded and metamorphosed impact structure, which has a diameter of 16 km and was formed during the Paleoproterozoic (older than 2.2 Ga); this is inferred from the age of the overlying volcanic‐sedimentary Jatulian sequence. Suavjärvi underwent regional metamorphism that resulted in obliteration or transformation of shock metamorphic effects. Massive sulfides occur within megabreccia; originating probably from postimpact redeposition of pre‐existing mineralization.  相似文献   

Late Permian palaeomagnetic data east and west of the Urals     

Mikhail L. Bazhenov  Alexander N. Grishanov  Rob Van der Voo  Natalia M. Levashova 《Geophysical Journal International》2008,173(2):395-408

  相似文献   

Slope streaks on Mars: A new “wet” mechanism     

Mikhail A. Kreslavsky  James W. Head 《Icarus》2009,201(2):517-743

Slope steaks are one of the most intriguing modern phenomena observed on Mars. They have been mostly interpreted as some specific type of granular flow. We propose another mechanism for slope streak formation on Mars. It involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin, and runaway propagation of percolation fronts. Given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions, this mechanism is consistent with the observational constraints; it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride, and a small part of the observed hydrogen to be in form of water ice. This “wet” mechanism has a number of appealing advantages in comparison to the widely accepted “dry” granular flow mechanism. Potential tests for the “wet” mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation.  相似文献