A Simulated Test of Algal Influence of Formation and Deposition of Phosphates

This paper deals with a simulated test of biogenic mineralization made with a blue-green alga species,Spirulina platensix. The data in the experiment were recorded by a computerized surveying system. The influ-ence of algae on the accumulation of phosphorus by changing their microenvironment to promote the forma-tion and deposition of phosphate was studied. The results show that the pH value of cultural liquor rose up to 10 and the redox potential (Eh) may dropby 100-200 mV during the algal logarithmic growth stage, and the cultrual liquor was changed into a mediumwith a weakly reducing condition. At the end of the logarithmic growth stage white deposits of Na_2Ca(CO_3)_2·5H_2O and Ca_2Mg (PO_4)_2·2H_2O were formed on the floor of cultural containers. The test presented a wduableevidence for the theory of biogenic mineralization.     

Additional evidence of existence of ancient rocks in the mid-Atlantic ridge and the age of the opening of the Atlantic

A metabasalt dredged at a junction of the median valley with the Atlantis fracture zone (30°01/tN, 42°04/tW) in the Mid-Atlantic Ridge shows complete recrystallization under a metasomatic condition, though the original igneous texture of a coarse-grained basalt is still recognizable. There is strong circumstantial evidence suggesting that this rock is not an ice-rafted erratic, but an authentic Mid-Atlantic Ridge rock. The ⁴⁰Ar-³⁹Ar age of this sample is 169 m.y. (Jurassic) which should represent the time of recrystallization. The initial value (^87Sr/86Sr)_O is 0.720, far above the values previously observed in oceanfloor basalts, including both tholeiitic and alkalic rocks (0.701–0.704). Sr with such a high isotopic ratio is considered to have been introduced by metasomatism during metamorphism by a solution coming from a continental mass or masses which were then located very close to the Mid-Atlantic Ridge. The ⁴⁰Ar−³⁹Ar age of sample AM50 may approximate the time of the commencement of the opening of the Atlantic. All these data support the possible existence of ancient rock masses in the Mid-Atlantic Ridge, as was formerly claimed by Bonatti, Melson and others.     

Retarding effect of concentration of cementation solution on biocementation of soil

Concentration of cementation solution (CCS) is one of the key factors influencing the cementation effect on soil improvement through the microbially induced carbonate precipitation (MICP) process. To precipitate more calcium carbonate per treatment, a higher CCS is needed. However, the MICP process may be retarded or even terminated with an increase in CCS. This retarding effect can be a major limitation for the MICP-based soil treatment and thus needs to be understood properly. This paper presents a systematic study on the conditions causing retarding and its effect on biocementation. The test results of this study have identified that there is retarding effect of CCS on the MICP process, showing that the calcium conversion efficiency, which represents the amount of calcium that has been converted into calcium carbonate in each treatment, reduces with the increase in CCS, and the concentration of calcium is the control factor. The retarding effect will dominate increasingly when CCS is higher than 1.0 M and the amount of calcium carbonate precipitation will reduce for the given amount and type of bacteria used in this study and become zero with CCS of 2.5 M. For the same calcium carbonate content, the unconfined compressive strength is greater for sand treated using a lower CCS as the contribution to the bonding strength by the calcium carbonate generated under a lower CCS is greater than that under a higher CCS.

     

Results of Back-Analysis of the Propagation of Rock Avalanches as a Function of the Assumed Rheology

Summary. Numerical simulation can provide a useful tool for investigating the dynamics of phenomena like rock avalanches, within realistic geological contexts and in the framework of a better risk assessment and decision making. Difficulties in numerical modelling of a heterogeneous moving mass are mainly linked to the simulation of the complex behaviour assumed by the mass during propagation. The numerical code RASH3D, based on a continuum mechanics approach and on the long wave approximation, is used to back-analyse two cases of rock avalanches: Frank (1903, Canada) and Val Pola (1987, Italy). The two events are characterised by approximately the same volume (about 30 × 10⁶ m³) while the run out area morphologies are widely different. Three alternative “rheologies” (Frictional, Voellmy and Pouliquen) are used. Comparison among obtained results underlines that the validation of a “rheology” requires not only a good agreement between the numerical simulation results and the run out area boundaries but also in term of depth distribution of the mass in the deposit. In case of a Frictional rheology, the obtained calibrated dynamic friction angle values are in a range of 15 ± 1° for both the cases; while assuming a Pouliquen or a Voellmy rheology it emerges a different behaviour of rheological parameters for each of the considered events. Besides the calibration of rheological parameters to better back-analyse each of the considered events, it is investigated how the behaviour due to the assumed rheology is influenced by the geometry of the run out area (e.g. narrow or broad valley). Authors’ addresses: Marina Pirulli, Department of Structural and Geotechnical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 Torino, Italy; Anne Mangeney, Equipe de Sismologie, Institut de Physique du Globe de Paris, Université Denis Diderot, 4 Place Jussieu, 75005 Paris, France     

An estimate of the probability of capture of a binary star by a supermassive black hole

A simple model for the dynamics of stars located in a sphere with a radius of one-tenth of the central parsec, designed to enable estimation of the probability of capture in the close vicinity (r < 10^?3 pc) of a supermassive black hole (SMBH) is presented. In the case of binary stars, such a capture with a high probability results in the formation of a hyper-velocity star. The population of stars in a sphere of radius <0.1 pc is calculated based on data for the Galactic rotation curve. To simulate the distortion of initially circular orbits of stars, these are subjected to a series of random shock encounters (“kicks”), whose net effect is to “push” these binary systems into the region of potential formation of hyper-velocity stars. The mean crossing time of the border of the close vicinity of the SMBH (r < 10^?3 pc) by the stellar orbit can be used to estimate the probability that a binary system is captured, followed by the possible ejection of a hyper-velocity star.     

Evaluation of the degree of saturation using Skempton coefficient B

ABSTRACT

Skempton coefficient B is commonly used to evaluate the saturation of a sample before the shearing stage in a triaxial test. For unsaturated soils, measuring the degree of saturation Sr at the end of the consolidation stage is very difficult whereas measuring Skempton coefficient B is very simple. Using this coefficient to obtain S_r of a sample in a triaxial apparatus without complex procedures might be an improvement, especially as regards testing procedures for unsaturated soils. Different authors have proposed a relationship between these two parameters based on the hypothesis that a variation of B coefficient with S_r is mostly due to the compressibility of air in the pores. However, the presence of air as a fluid phase gives rise to suction after the equilibrium is reached inside the sample leading to an increase in stiffness. Based on this observation, this article presents a new relationship that enables S_r to be evaluated with a given Skempton coefficient taking into account not only the initial void ratio and the isotropic elastic modulus but also the suction and the elastoplastic behaviour of the soil. The results of the proposed approach are then confronted with the original relationship and compared to experimental data.     

Analysis of the extinction of the Late Cretaceous foraminifer Afrobolivina afra

Afrobolivina afra, a Late Cretaceous bolivinid foraminifer, became extinct in the Early Paleocene. It was succeeded by the smaller, morphologically similar species Afrobolivina africana. Morphological variation in A. afra was in part correlated with environmental factors showing a pattern of random fluctuations about long-term ecological trends. A gradual, persistent and unbroken environmental trend, related to a eustatic fall in sea-level, is significantly correlated with the morphological evolution of the species. The micro-biogeography of A. afra at the time it was approaching extinction is consistent with its having given rise to A. afracana allopatrically in a manner which can be described by a fold-catastrophe adaptive model. This mode predicts that A. afra should undergo quantum evolution to A. africana in a restricted area in a near-shore environment.However, detailed study of borehole material reveals an apparent parabolic increase in the overall size of A. afra prior to extinction and it is argued that as a result, A. africana cannot be the direct descendant of A. afra without there having been some “discontinuity” in the environment or evolutionary process. This suggests that the sudden replacement of a species by a smaller, morphologically similar form may not be a straightforward succession. The apparent parabolic increase in size of A. afra can be modelled by the fold catastrophe of Thom theory if interpreted as representing the initial phase of a form of adaptive quantum evolution in which a gradual environmental change causes a fitness peak to be absorbed into the flank of a higher peak.In terms of such a model, the absence of a larger descendant species suggests that A. afra could have been replaced by A. africana before the quantum threshold had been reached. A possible cause for this could be that the changes in the environment might have lowered the height of the fitness function in the vicinity of the peak for A. afra to below that of the peak for A. africana, or vice versa.     

In situ atomic force microscopy measurements of biotite basal plane reactivity in the presence of oxalic acid

We have used a direct imaging technique, in situ atomic force microscopy (AFM), to observe the dissolution of the basal biotite surface by oxalic acid over a range of temperatures close to ambient conditions, using a specially designed AFM liquid cell and non-invasive intermittent contact mode of operation. From the 3-dimensional nanometre-resolution data sets, we observe a process characterised by the slow formation of shallow etch pits in the (0 0 1) surface and fast growth of etch pits from the resulting steps, which represent proxies for the {h k 0} surface. Measurements of dissolution rates as a function of temperature allow a determination of an apparent activation energy (E_a,app) for the process, via mass-loss calculations from image analysis. We obtain a value of E_a,app = 49 ± 2 kJ mol⁻¹, which is consistent with separate calculations based on planar area etch pit growth, and measurements of etch pit perimeters, indicating that this value of E_a,app is representative of {h k 0} surface dissolution. The measurement of etch pit perimeters also enables an estimation of apparent activation energy as a function of step density indicating substantially higher apparent activation energy, up to E_a,app = 140 kJ mol⁻¹, on extrapolation towards a pristine surface with no defects. We suggest that this higher value of E_a,app represents the slow formation of etch pits into the (0 0 1) surface.     

绿色翡翠颜色分布规律研究

采用国际照明委员会CIE LAB色度坐标,定量描述了翡翠的绿色,分析了颜色的分布情况,总结其分布规律,建立起翡翠绿色L^*、a^*、b^*、C^*、h_ab的分布关系。当明度较小时,色调角几乎不变,彩度和明度呈现近似的线性相关;当明度变大时,色调角的变化幅度稍大,彩度值在明度中等偏低时变为最大。这些信息将在很大程度上对翡翠绿色分级的细化起到积极作用,可以用来指导翡翠色卡的制备。     

EPR measurement of the effect of glass composition on the oxidation states of europium

The techniques of electron paramagnetic resonance (EPR) were used to measure the concentration ratio of Eu²⁺ to Eu³⁺ in quenched silicate liquids as a function of their compositions. The compositional end members were CaAl₂Si₂O₈ and either MSiO₃ or M₂Si0₄, M = Mg, (Ca_0.5, Mg_0.5), and Ca. All of the liquids were quenched from 1650 ± 25°C, 10^?6.9±0.6 atm of oxygen, and 10^?6.1±0.6 atm total pressure. For a particular choice of M, the ratio of Eu²⁺ to Eu³⁺ increased as much as a factor of 24 with increasing atomic ratio (Al + Si)/(O); for a constant value of (Al + Si)/(O), the ratio of Eu²⁺ to Eu³⁺ increased in the order Mg > (Ca_0.5,Mg_0.5) >Ca. In order to interpret the compositional dependence of the redox equilibrium of Eu in a systematic manner, the concept of a solvent coefficient was introduced.     

Pressure dependence of viscosity of rhyolitic melts

Viscosity of silicate melts is a critical property for understanding volcanic and igneous processes in the Earth. We investigate the pressure effect on the viscosity of rhyolitic melts using two methods: indirect viscosity inference from hydrous species reaction in melts using a piston cylinder at pressures up to 2.8 GPa and direct viscosity measurement by parallel-plate creep viscometer in an internally-heated pressure vessel at pressures up to 0.4 GPa. Comparison of viscosities of a rhyolitic melt with 0.8 wt% water at 0.4 GPa shows that both methods give consistent results. In the indirect method, viscosities of hydrous rhyolitic melts were inferred based on the kinetics of hydrous species reaction in the melt upon cooling (i.e., the equivalence of rheologically defined glass transition temperature and chemically defined apparent equilibrium temperature). The cooling experiments were carried out in a piston-cylinder apparatus using hydrous rhyolitic samples with 0.8-4 wt% water. Cooling rates of the kinetic experiments varied from 0.1 K/s to 100 K/s; hence the range of viscosity inferred from this method covers 3 orders of magnitude. The data from this method show that viscosity increases with increasing pressure from 1 GPa to 3 GPa for hydrous rhyolitic melts with water content ?0.8 wt% in the high viscosity range. We also measured viscosity of rhyolitic melt with 0.13 wt% water using the parallel-plate viscometer at pressures 0.2 and 0.4 GPa in an internally-heated pressure vessel. The data show that viscosity of rhyolitic melt with 0.13 wt% water decreases with increasing pressure. Combining our new data with literature data, we develop a viscosity model of rhyolitic melts as a function of temperature, pressure and water content.     

Optimization of sample preparation method of total sulphur measurement in mine tailings

A sample preparation method of total sulphur measurement of reactive mine tailings was optimized. The total sulphur was measured by inductively coupled plasma optical emission spectroscopy, and ultrasound technique was used for sample digestion. The optimization process was adopted by a combined approach of experimental design and response surface methodology. The digestion time, temperature and acid-oxidant combination (i.e. effect of H₂O₂ with a fixed amount of acid mixture) were investigated. A two-level and three-factor (2³) full factorial design of experiment was applied to identify the most significant factors, and a central composite design was used to optimize the digestion procedure. KZK-1, a sericite schist, was selected as the certified reference material. The optimum methodology at 95 % confidence level (P < 0.05) was identified to be 10 min of digestion at 77 °C, with a solution of 1 ml HNO₃:1 ml HCl:1.35 ml H₂O₂. This combination resulted in 100 % sulphur recovery. The investigated method was verified by X-ray diffraction analysis. The optimum digestion level was applied to a reactive mine tailings, which achieved satisfactory results with a percentage relative standard deviation < 3 %.     

A spectral analysis of microlensing variability of quasars

A procedure for calculating two-dimensional power spectra of microlensing magnification fields is presented. In the absence of a shift, the one-dimensional projections of the power spectra P(k) corresponding to the light curve of a point source moving in a linear trajectory can be approximated by the expression (a ² + k ²)^?1/2 (where a = const). The power spectrum of an extended source is treated like the product of the power spectrum of a point source and the power spectrum of the brightness distribution of the extended source. The effect of the extent of the source is that it acts like a filter, suppressing high-frequency components in the spectrum. Based on eight years of monitoring of the quad gravitational lens Q2237+0305 by the OGLE group, power spectra for all four images are constructed and the (temporal) size of the radiating region of the quasar in the V filter is estimated to be 24 ± 6 days; given the constraints on the transverse velocity of the lensing galaxy (<600 km/s), the linear size turns out to be <10¹⁵ cm.     

Mixing of metals during stripping of galactic gaseous halos

The mixing of metals in the intergalactic gas when a galaxy with a metal-rich envelope moves through the intergalactic medium is analyzed. Two simple models for the initial distribution of metals are considered. In the first case, the metals are concentrated in a fairly thin envelope with thickness ΔR _s =1 kpc, outer radius R _s =31 kpc, and metallicity Z=10^?3. In the second case, material with the same metallicity uniformly fills an entire spherical region of radius R _s . After 2.85 Gyr, the metals are distributed over a fairly extended volume with a typical size of ?200 kpc in the direction of the motion of the intergalactic gas, with a mean metallicity of ?4.6×10^?4 in metal-enriched regions. However, the distribution of metals remains extremely nonuniform, so that the main contribution to the overall metallicity is provided by metal-rich islands Z?6×10^?4 that occupy only ～10% of the total mixing volume. Moreover, metal-free regions remain in this volume.     

Comparison of Mathematical Methods of Potential Modeling

Various attempts are known to turn the “catalogue” of mineral deposit models compiled by Cox and Singer (1986) operational, and have initiated activities called “potential mapping”, “potential modeling”, or “targeting”. The common ultimate objective is to estimate the probability for a given location that a mineralization of a given type occurred. The mathematics range from “weights of evidence” and others featuring a Bayesian approach to logistic regression by maximum likelihood, and include other realizations by means of fuzzy methods, genetic programming, and artificial neural nets. Once developed and coded, applications are not restricted to mineral prospection and exploration but include any kind of occurrences and their estimated probabilities, e.g., risk assessment of land slides and many others.     

A New Approach to the Modeling of the Pressure Dependency of the Strength of Rocks

Based on the hypothesis that shearing stresses and normal tensile stresses both play a decisive role in fracturing and brittle failure of rock material, a novel strength criterion was developed in one of the earlier works of the author. In the criterion, a certain parameter ν′ occurs which depends on the structure of the material. Originally, the parameter was treated as a constant, which resulted in a linear form of the strength function ^F σ ₁ = f(σ ₃), where σ ₃ = σ ₂. Although the linear strength criterion is sometimes found to be applicable to various particular rock materials, it is not, in general, of a universal character. Analysis of the triaxial test results for 75 different sandstones revealed that parameter ν′ usually increases in an exponential or linear manner as confining pressure increases, and only in isolated cases does it seem to be independent of the confining pressure. For these three types of function ν′ = f(p) appropriate strength criteria ^F σ ₁ = f(σ ₃) are given in the present paper. These criteria were used to fit all of the collected empirical data sets. In general, a very good fit to the data was obtained.     

The role of external factors in the evolution of galaxies

We consider the evolution of galaxies in dense galactic clusters. Observations and theoretical estimates indicate that this evolution may be specified to a large extent by collisions between galaxies, as well as interactions between the gaseous components of disk galaxies and intergalactic gas. We analyze collisions between disk galaxies with gaseous components using a simple model based on a comparison of the duration of a collision and the characteristic cooling time for the gas heated by the collision, and also of the relative masses of stars and gas in the colliding disk galaxies. This model is used to analyze scenarios for collisions between disk galaxies with various masses as a function of their relative velocities. Our analysis indicates that galaxies can merge, lose one or both of their gaseous components, or totally disintegrate as a result of a collision; ultimately, a new galaxy may form from the gas lost by the colliding galaxies. Disk galaxies with mass M _G and velocities exceeding ～300 (M _G/10¹⁰ M _⊙)^1/2 km/s in intergalactic gas in clusters with densities ～10^?27 g/cm³ can lose their gas due to the pressure of inflowing intergalactic gas, thereby developing into E(SO) galaxies.     

The sampling distribution of theW statistic of disjunction for the arbitrary division of a random rectangular distribution

The sampling distribution of the Wstatistic of disjunction has been estimated by Monte Carlo simulation for the case where the underlying distribution is a random rectangular (Poisson) variable that is divided into two groups at an arbitrary position. A transformation to sinh ^?1 log _e Wgave a variable that was acceptably normal, and from this a simple approximation for the distribution is given, together with a diagram of confidence limits of Wfor this case.     

Compositional variations of volcanics along segments of recent spreading ridges

An investigation of glassy volcanics erupted within the last ten-million years along various segments of the mid-Atlantic Ridge and the East Pacific Rise has revealed major crustal compositional changes. The available data from the mid-Atlantic Ridge shows the existence of two petrological provinces: One, located between latitudes 33° and 53° N, is characterized by volcanics which have a tendency to be oversaturated ocean ridge basalts (OSORB) with respect to normative quartz; the second group of rocks, found between 25° S and 33° N, is generally composed of saturated ocean ridge basalts (SORB). In addition, the SORB volcanics have higher TiO₂ (1.7±0.3%), higher Na₂O (2.8±0.2%) and higher FeO^*/MgO (1.36±0.2) values than do the OSORB types (with 1.1±0.2%, 2.2±0.2% and 1.22±0.2 for the TiO₂, Na₂O, and FeO^*/MgO respectively), There is a correlation between the rate of crustal spreading and the compositional changes observed on the volcanics erupted along various segments of oceanic ridges. Slow-accreting plate boundaries having a total spreading rate of 2–3 cm/year are characterized by a low TiO₂ content (1.1±0.2%), low FeO^*/ MgO ratio (1.22±0.2) and a high an/an+ab ratio (0.62±0.05). Segments of fast-spreading ridges (total rate 11–13 cm/year) show a higher range of TiO₂ (2.1±0.4%) and FeO^*/MgO (1.6±0.4) and a lower range of the an/an + ab ratio (0.5±0.07). Ridge segments with a total spreading rate of 5–9 cm/year con sist of volcanics having intermediate values for the above parameters. Different degrees of partial melting of rising mantle material are suggested as a possible mechanism for explaining the compositional diversities encountered along oceanic ridge systems.Contribution n 677 du Département de Géophysique, Géologie, Géochimie Marines du C.O.B.