Neutron star models based on an improved equation of state

Using an equation of state for cold degenerate matter which takes nuclear forces and nuclear clustering into account, neutron star models are constructed. Stable models were obtained in the mass range above 0.065M and density range 10^14.08 to 10^15.4 gm/cm³. All of these models were found to be bound. The outer crystalline layer of the star was found to have a thickness of 200 m or more depending on the mass of the model.     

Positions and motions of solar bursts at decameter wavelengths

The positions and motions of solar bursts in the range 20 to 60 MHz have been measured by the means of a sweep-frequency grating interferometer with angular resolution of 5 arc at 60 MHz decreasing to 15 arc at 20 MHz. The positional characteristics of the decameter wavelength bursts are discussed in terms of the commonly accepted theories of the origin of radio bursts from plasma and synchrotron radiations.     

The melting of asteroidal-sized bodies by unipolar dynamo induction from a primordial T Tauri sun

This paper examines the heating of asteroidal parent bodies by electrical induction during early solar evolution and prior to positioning of the sun onto the main sequence. Under the conditions assumed, which include a high initial solar spin rate, interplanetary electric fields of order 1 V/m would have existed in frames of reference comoving with the planets, leading to electrical heating from joule losses in the asteroidal interiors. The mechanism additionally requires the high plasma efflux characteristic of T Tauri objects and the presence of a circumstellar obscuration of the type commonly associated with early stellar objects. The proper combination of circumstellar obscuration, solar spin, solar wind flow, and starting planetary temperatures is shown to lead to asteroidal heating competitive with that found for a class of fossil radioactive species. The time dependence of the solar spin and plasma flow are shaped so as to be consistent with current views on the evolution to T Tauri objects and of the spin down of stars. Calculations also include cases of joint heating by fossil radionuclides and electrical induction, and show a complicated relationship due to the intrinsic nonlinearity of the electrical heating mechanism. Implications regarding the pre-main sequence dynamics of the sun are contained in the hypothesis of electrical heating if the contribution from radionuclides and gravitational accretion can be shown to be insufficient to account for the heating episode. Finally, some consequences of the mechanism applied to planets in the presence of an intense solar wind are considered.     

Evidence for a coronal magnetic bottle at 10 solar radii

The Faraday rotation of a radio source (Pioneer 6) occulted by the solar corona has been measured by Levy et al. (1969). During the course of these measurements, three large-scale transient phenomena were observed. These events were preceded by subflares and class 1 flares. These transient events are interpreted as evidence for a coronal magnetic bottle at 10 R _⊙. The velocity of propagation for the disturbance is set at 200 km/sec; the dimension of the region, 10 R _⊙; field strength at 10 R _⊙, 0.02 G; particle density, 2.0 × 10⁴/cm³; Alfvén speed, 320 km/sec. From the nature of the observations and the lack of related effects from similar flares on the interplanetary sector pattern observed at 1 AU, it is suggested that such coronal magnetic bottles expand to perhaps 10–30 R _⊙ and then contract to a few solar radii. Such a phenomena is evidence for an expansion of the corona with a sub-Alfvénic velocity. It is further suggested that such magnetic bottles may be important in the storage and diffusion of solar generated cosmic ray particles. NAS-NRC Postdoctoral Resident Research Associate.     

Evidence for high-pressure core-mantle differentiation from the metal-silicate partitioning of lithophile and weakly-siderophile elements

Liquid Fe metal-liquid silicate partition coefficients for the lithophile and weakly-siderophile elements Ta, Nb, V, Cr, Si, Mn, Ga, In and Zn have been measured in multianvil experiments performed from 2 to 24 GPa, 2023-2873 K and at oxygen fugacities of −1.3 to −4.2 log units relative to the iron-wüstite buffer. Compositional effects of light elements dissolved in the metal liquid (S, C) have been examined and experiments were performed in both graphite and MgO capsules, specifically to address the effect of C solubility in Fe-metal on siderophile element partitioning. The results were used to examine whether there is categorical evidence that a significant portion of metal-silicate equilibration occurred under very high pressures during core-mantle fractionation on Earth. Although the depletion of V from the mantle due to core formation is significantly greater than that of Nb, our results indicate that both elements have similar siderophile tendencies under reducing conditions at low pressures. With increasing pressure, however, Nb becomes less siderophile than V, implying that average metal-silicate equilibration pressures of at least 10-40 GPa are required to explain the Nb/V ratio of the mantle. Similarly the moderately-siderophile, volatile element ratios Ga/Mn and In/Zn are chondritic in the mantle but both volatility and core-mantle equilibration at low pressure would render these ratios strongly sub-chondritic. Our results indicate that pressures of metal-silicate partitioning exceeding 30-60 GPa would be required to render these element ratios chondritic in the mantle. These observations strongly indicate that metal-silicate equilibration must have occurred at high pressures, and therefore support core-formation models that involve deep magma oceans. Moreover, our results allow us to exclude models that envisage primarily low-pressure (<1 GPa) equilibration in relatively small planetary bodies. We also argue that the core cannot contain significant U as this would require metal-silicate equilibration at oxygen fugacities low enough for significant amounts of Ta to have also been extracted from the mantle. Likewise, as In is more siderophile than Pb but similarly volatile and also quite chalcophile it would have been difficult for Pb to enter the core without reversing the relative depletions of these elements in the mantle unless metal-silicate equilibration occurred at high pressures >20 GPa.     

Crystal Accumulation and Magma Mixing in the Petrogenesis of Tholeiitic Andesites from Fukujin Seamount, Northern Mariana Island Arc

Fukujin Seamount is a large, active, submarine volcano on thevolcanic front in the northernseamount province (NSP) of theMariana island arc (MIA). Five dredge hauls from the summitand upper flanks of Fukujin recovered mainly highly porphyriticbasaltic andesites. A few nearly aphyric samples are medium-Ksiliceous andesites (SiO₂ = 62%, K₂O = 1•5%). Fukujin andmost other large arc-front volcanoes of the northern MIA havetholeiitic (iron-enrichment) fractionation trends. This contrastswith the calc-alkaline trends of many smaller seamounts. A negativecorrelation of modal plagioclase content with bulk-rock SiO₂,as well as bulk-rock major and trace element variation trends,and glass analyses, suggests that lavas with >30 vol.% phenocrystsand <55 wt.% SiO₂ are partial cumulates. The presence ofbimodal phenocryst populations along with reversed to normalzoning of phenocrysts is explained by magma mixing of andesiticand basaltic liquids. Hybrid basaltic andesites probably formedby the accumulation of plagioclase in a tholeiitic magma chamberundergoing replenishment and mixing at a shallow crustal level.A petrogenetic model is presented for the origin of basalticandesite by combined magma mixing and fractional crystallization.Aphyric siliceous andesites can be modelled by simple fractionationof basaltic andesite. The early fractionating assemblage consistedmainly of plagioclase and clinopyroxene, with lesser olivineand minor magnetite, but plagioclase remained suspended in themelt. The later fractionating assemblage was dominated by plagioclasewith orthopyroxene instead of olivine. ^*Present address: 2260 rue Panet, Montreal, Quebec, H2L 3A6, Canada.     

An Improved Perturbation Mechanism for Simulated Annealing Simulation

Simulated annealing (SA) is being increasingly used for the generation of stochastic models of spatial phenomena because of its flexibility to integrate data of diverse types and scales. The major shortcoming of SA is the extensive CPU requirements. We present a perturbation mechanism that significantly improves the CPU speed. Two conventional perturbation mechanisms are to (1) randomly select two locations and swap their attribute values, or (2) visit a randomly selected location and draw a new value from the global histogram. The proposed perturbation mechanism is a modification of option 2: each candidate value is drawn from a local conditional distribution built with a template of kriging weights rather than from the global distribution. This results in accepting more perturbations and in perturbations that improve the variogram reproduction for short scale lags. We document the new method, the increased convergence speed, and the improved variogram reproduction. Implementation details of the method such as the size of the local neighborhood are considered.     

Topographic Constraints on Deviatoric Stress Field in the Indo-Eurasian Collision Region: Seismo-Tectonic Implications

The deviatoric stress field are computed from the inversion of Gravitational Potential Energy (GPE) for the Indo-Eurasian plate collision region including the Himalaya and the Tibet Plateau. The resulting stress pattern in combination with stress and strain rates obtained by inverting, respectively, the focal mechanism solution of large earthquakes and GPS derived plate motions are used to study the nature of the present-day deformations. A narrow belt bordering the Himalayan collision zone from the south is characterized by strong compressive stresses. The variations in stress pattern along this belt coincide with arc-normal ridges extending into the Himalaya and are able to explain arc-parallel segmentation of seismicity. Gravitational collapse seems to play an important role in the southeastern Tibet Plateau. Depth sensitivity of the seismic derived stresses and GPS derived surface strain rates coupled with evidence of arcuate shaped high electrical conductivity favour strong ductile flow around the Eastern Himalaya Syntaxis (EHS) at mid-crustal depth. The deflection of crustal flow indicted by the viscous resistance offered by the rigid Sichuan basin adds to the traction stresses to cause clockwise rotation of the block around EHS.     

Energy spectra of cosmic ray nuclei: 4≤Z≤26 and 0.3≤E≤2 GeV amu−1

Energy spectra of cosmic ray nuclei in the charge range 5Z26 have been derived from the response of an acrylic plastic erenkov detector. Data were obtained using a balloon-borne detector and cover the energy range 320E2200 MeV amu^–1. Spectra are derived from a formal deconvolution using the method of Lezniak (1975). Relative spectra of different elements are compared by observing the charge ratios. Secondary-primary ratios are observed to decrease with increasing energy, consistent with the effect previously observed at higher energy. Primary-to-primary ratios are constant for 6Z10 and 14Z26 but vary for 10Z14. This data is found to be consistent with existing data, where comparable, and lends strong support to the idea of two separate source populations contributing to the cosmic ray composition.Work supported by University of Maryland Grant NGR 21-002-316.