Adaptive optics for large telescopes

The performance of large telescopes is determined both by their angular resolution and by their collection area. It is, therefore, important to achieve as high an angular resolution as possible by site selection, by avoiding image deterioration by the telescope and its environment, and by real time image restoration by adaptive optics. We summarize the principles of adaptive optics, their predicted performance and the current programs underway to implement adaptive optics for astronomical purposes.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

Probability of capture for the second fundamental model of resonance

The extension of the adiabatic invariant theory for one-degree of freedom Hamiltonian systems with varying parameters proposes a way of evaluating the probability of capture from one domain of the phase space into another. We derive here analytic expressions for these probabilities for a typical model of resonance of orderN. We show that the probabilities depend only upon two parameters and not four as expected a priori.     

Photospheric brightness differences associated with the solar supergranulation

The large scale (> 5000 km) intensity structure of the photosphere has been examined. The power per frequency unit indicates a continuous increase towards smaller spatial frequency. No excess power exists at wavelengths near the size of the supergranulation (30000 km) or at any other wavelength between 5000 and 100000 km. However, direct measurement of the intensity distribution in 1652 supergranulation cells shows a very small increase of the intensity towards the cell boundary. The amount of this increase is larger near the solar limb. It is probably due to a weak continuum emission associated with the chromospheric network. Any temperature difference arising from the supergranulation convection is obscured by this emission and is probably less than 1 K.     

Expériences sur la précipitation directe de l'apatite dans l'eau de mer: Implication dans la genèse des phosphorites

The direct precipitation of apatite in seawater is inhibited by Mg ions. The action of various factors on this precipitation is studied: addition of Ca, addition of F, reduction of pH and simultaneous effect of reduction of pH and addition either of F or of Ca. It is established that the reduction of the pH of seawater to 7 allows the precipitation of the apatite with a Ca/Mg ratio in the water of 1.2. The favourable environment for the settlement of natural apatite must then be either neutral or acid. This result is corroborated by the re-study of Gulbrandsen's equation. Such an acid environment with a high phosphorus content may be the result of oxidation of large quantities of organic matter due to previous intense biological activity. The acidity is probably brought about by bubbling of CO₂.     

Sweeping through a second order resonance

The adiabatic invariant theory and its extension to the case of separatrix crossing have been instrumental in setting up simple models describing the effects of the passage through a first order resonance forced by small non conservative forces. These models have been helpful in understanding the processes of capture into resonance and of formation of gaps at resonances. Second order resonances (3/1 or 5/3 ...) have not been so thoroughly investigated and present some special features. We shall show how to disencumber first the problem from its secular term and how to modelize the mixed resonance term involving the sum of the resonant angles. A modelization of the two single satellite resonant terms has already been proposed by Lemaître and Borderies and Goldreich. We shall then assemble those three simple models to show the effect of a passage through the resonance under the assumption that the natural precession rates are large enough for the three individual resonances to be sufficiently separated.     

缓变型地球化学灾害:特征、模型和应用

“缓变型地球化学灾害”是通过长期积累而存在于土壤或沉积物中的包括重金属和有机污染物在内的环境污染物,因环境物理化学条件（例如温度、pH值、湿度、有机质含量等）的改变减小了环境容量,某种或某些形态的污染物大量地被重新活化和突然释放出来并造成严重生态和环境损害的灾害现象。这种灾害具有明显的特征,其定量数学模型可较完整地概括出环境系统从“干净”到“污染”再到“灾害”的整个过程,可以用于灾害的风险概率评估、预测、灾害爆发轨迹等方面的研究,为土壤污染防治和灾害预警提供了定量研究工具和可供实际采用的基本手段,对当前国土资源调查中的“生态环境地球化学评价”具有重要的借鉴意义。     

Constraints on the ore fluids in the Sando Alcalde AuAg epithermal deposit,southwestern Peru: fluid inclusions and stable isotope data

The Sando Alcalde ore deposit (southwestern Peru) has been studied in order to characterize the physicochemical parameters of the ore fluids and to determine the fluid process (mixing or boiling) which involves the precious metal mineralization. Mineralogy, ${\delta }^{18}{\mathrm{O}}_{\mathrm{quartz}}$ isotopic values and fluid inclusion data give arguments in favour of a boiling phenomenon. This conclusion corroborates fluid inclusion studies previously performed in this area on the low-sulphidation epithermal deposits of Arcata, Orcopampa and Apacheta, where boiling has been described as the main factor for ore deposition. To cite this article: A.-S. André-Mayer et al., C. R. Geoscience 337 (2005).     

Experimental study of the stability of aluminate-borate complexes in hydrothermal solutions

Formation of aqueous aluminate-borate complexes was characterized at 25°C using ²⁷Al NMR spectroscopy, and at 50-200°C via measurements of gibbsite and boehmite solubility in the presence of boric acid. ²⁷Al spectra performed at pH = 9 in Al-B solution with m(B) = 0.02 show the presence of two peaks at 80.5 and 74.5 ppm which correspond to Al(OH)₄⁻ and a single Al-substituted Q¹_Al dimer, Al(OH)₃OB(OH)₂⁻, respectively. In 0.08 m and 0.2 m borate solution, a third peak appears at 68.5 ppm which can be assigned to the Q²_Al trimer Al(OH)₂O₂(B(OH)₂)₂⁻. These chemical shifts are close to those measured for Al(OH)₃OSi(OH)₃⁻ and Al(OH)₂O₂(Si(OH)₃)₂⁻ (74 and 69.5 ppm, respectively; Pokrovski et al., Min. Mag.62a (1998), 1194) which demonstrates the similar structure of Al-B and Al-Si complexes formed in alkaline solutions. Gibbsite and boehmite solubility were measured in weakly basic solutions as a function of boric acid concentration at 50°C and 78 to 200°C, respectively. Equilibrium was reached within several days at m(B) = 0.01-0.1, but more slowly at higher boron concentrations, and at 50°C and m(B) = 0.2, Al concentration increased continuously during at least 3 months as a result of the sluggish formation of Al-polyborates. The equilibrium constant of the reaction Al(OH)₄⁻ + B(OH)₃⁰_(aq) = Al(OH)₃OB(OH)₂⁻ + H₂O decreases very slowly with increasing temperature to 200°C. The log K values are 1.58 ± 0.10, 1.46 ± 0.10, 1.52 ± 0.15, and 1.25 ± 0.15 at 50, 78, 150 and 200°C, respectively, which result in the following values of the standard thermodynamic properties for this reaction: Δ_rG⁰ = −9.22 ± 3.25 kJ/mol, Δ_rH⁰ = −4.6 ± 2.5 kJ/mol, Δ_rS⁰ = 15.5 ± 6.9 J/mol K. The thermodynamic data generated in this study indicate that Al-B complexes can dominate aqueous aluminum speciation in solutions containing ≥0.7 g/L of boron at temperature to at least 400°C.