Motion in a Central Field in the Presence of a Constant Perturbing Acceleration in a Coordinate System Comoving with the Velocity Vector     

N. Batmunkh  T. N. Sannikova  K. V. Kholshevnikov 《Astronomy Reports》2018,62(4):288-298

The motion of a zero-mass point under the action of gravitation toward a central body and a perturbing acceleration P is considered. The magnitude of P is taken to be small compared to the main acceleration due to the gravitation of the central body, and the components of the vector P are taken to be constant in a reference frame with its origin at the central body and its axes directed along the velocity vector, normal to the velocity vector in the plane of the osculating orbit, and along the binormal. The equations in the mean elements were obtained in an earlier study. The algorithm used to solve these equations is given in this study. This algorithm is analogous to one constructed earlier for the case when P is constant in a reference frame tied to the radius vector. The properties of the solutions are similar. The main difference is that, in the most important cases, the quadratures to which the solution reduces lead to non-elementary functions. However, they can be expressed as series in powers of the eccentricity e that converge for e < 1, and often also for e = 1.  相似文献   

Polarization of radiation in turbulent magnetized atmospheres     

N. A. Silant’ev 《Astronomy Reports》2007,51(1):67-80

Multiple scattering of radiation in a semi-infinite electron atmosphere in the absence of true absorption (the Milne problem) is considered. The electron plasma is assumed to be turbulent, i.e., the magnetic field B has a regular B ₀ and a stochastic B′ component (B = B ₀ + B′). Faraday rotation of the plane of polarization (s8 λ² B ₀ cos gJ) due to the field B ₀ depolarizes the outcoming radiation due to the superposition of rays with different polarization-angle rotations, corresponding to different paths traveled before they left the atmosphere. Stochastic Faraday rotation due to isotropic fluctuations, B′, efficiently decreases the amplitude of the polarization of each individual beam as it travels through the turbulent atmosphere. This effect is proportional to λ⁴ 〈(B′)²〉, and becomes the dominant factor at large λ. We use the Ambartsumian-Chandrasekhar invariance principle, which results in six nonlinear equations (for the field B ₀ perpendicular to the surface of the medium). We also compute the degree of polarization for the cases B ₀ = 0, B′ ≠ 0, and B′ = 0, B ₀ ≠ 0, and for a number of versions of the general case, B ₀ ≠ 0, B′ ≠ 0. The spectra of the degree of polarization (for the case B ₀ = 0) are presented for optical (λ = 0 ? 1 μm), infrared (λ = 1?5 μm), and X-ray (1–50 keV) wavelengths.  相似文献   

Analytical expressions for three-phase generalized relative permeabilities in water- and oil-wet capillary tubes     

Emanuela Bianchi Janetti  Monica Riva  Alberto Guadagnini 《Computational Geosciences》2016,20(3):555-565

We analyze three-phase flow of immiscible fluids taking place within an elementary capillary tube with circular cross-section under water- and oil-wet conditions. We account explicitly for momentum transfer between the moving phases, which leads to the phenomenon of viscous coupling, by imposing continuity of velocity and shear stress at fluid-fluid interfaces. The macroscopic flow model which describes the system at the Darcy scale includes three-phase effective relative permeabilities, K _{i j,r} , accounting for the flux of the ith phase due to the presence of the jth phase. These effective parameters strongly depend on phase saturations, fluid viscosities, and wettability of the solid matrix. In the considered flow setting, K _{i j,r} reduce to a set of nine scalar quantities, K _{i j,r} . Our results show that K _{i j,r} of the wetting phase is a function only of the fluid phase own saturation. Otherwise, K _{i j,r} of the non-wetting phase depends on the saturation of all fluids in the system and on oil and water viscosities. Viscous coupling effects (encapsulated in K _{i j,r} with i ≠ j) can be significantly relevant in both water- and oil-wet systems. Wettability conditions influence oil flow at a rate that increases linearly with viscosity ratio between oil and water phases.  相似文献   

Predictive crystal-chemical relations in Ti-silicates based on the TS block     

E. V. Sokolova 《Geology of Ore Deposits》2010,52(5):410-427

In a group of minerals of reasonable complexity in which the structure topology is related but not identical, the general relation between structure topology and chemical composition is not known. This problem is of major significance. The structural hierarchy and stereochemistry are described for 27 titanium disilicate minerals that contain the TS (titanium-silicate) block, a central trioctahedral (O) sheet and two adjacent (H) sheets of [5]- and [6]-coordinated polyhedra and (Si₂O₇) groups and related delindeite. The TS block is characterized by a planar cell based on translation vectors, t ₁ and t ₂ , with t ₁ ～ 5.5 and t ₂ ～ 7 Å and t ₁ ∧ t ₂ close to 90°. The general formula of the TS block is A ₂ ^P B ₂ ^P M ₂ ^H M ₄ ^O (Si ₂ O ₇ ) ₂ X _{4 + n}, where M ₂ ^H and M ₄ ^O = cations of the H and O sheets; M^H = Ti (= Ti + Nb), Zr, Mn²⁺, Ca; M^O = Ti, Zr, Mn²⁺, Ca, Na; A ^P and B ^P are cations at the peripheral (P) sites = Na, Ca, Ba; X = anions = O, OH, F; n = 0, 2, 4; the core part of the TS block is shown in bold and is invariant. Cations in each sheet of the TS block form a close-packed layer and the three layers are cubic close packed.There are three topologically distinct TS blocks, depending on the type of linkage of two H sheets and the central O sheet. The H sheets of one TS block attach to the O sheet in the same manner. All structures consist of a TS block and an I (intermediate) block that comprises atoms between two TS blocks. Usually, the I block consists of alkali and alkaline-earth cations, (H₂O) groups and oxyanions (PO₄)^3?, (SO₄)^2? and (CO₃)^2?. These structures naturally fall into four groups, based on differences in topology and stereochemistry of the TS block. In Group I, Ti = 1 apfu Ti occurs in the O sheet, and (Si₂O₇) groups link to a Na polyhedron of the O sheet (linkage 1). In Group II, Ti = 2 apfu, Ti occurs in the H sheet, and (Si₂O₇) groups link to two M ²⁺ octahedra of the O sheet adjacent along t ₂ (linkage 2). In Group III, Ti = 3 apfu, Ti occurs in the O and H sheets, and (Si₂O₇) groups link to the Ti octahedron of the O sheet (linkage 1). In Group IV, Ti = 4 apfu (the maximum possible content of Ti in the TS block), Ti occurs in the O and H sheets, and (Si₂O₇) groups link to two Ti octahedra of the O sheet adjacent along t ₁ (linkage 3). The stability of the TS block is due to the ability of Ti (Nb) to have an extremely wide range in Ti (Nb)-anion bond lengths, 1.68–2.30 Å, which allows the chemical composition of the TS block to vary widely. In crystal structures so far known, only one type of TS block occurs in a structure. The TS block propagates close-packing of cations onto the I block. The general structural principles and the relation between structure topology and chemical composition are described for the TS-block minerals. These principles allow prediction of structural arrangements and possible chemical compositions, and testing whether or not all aspects of the structure and chemical formula of a mineral are correct. Here, I show how these principles work, and review recent results that show the effectiveness of these principles as a predictive technique.  相似文献   

The pulsar PSR B1931+24 as an orthogonal rotator     

I. F. Malov 《Astronomy Reports》2007,51(6):477-480

The angles of the magnetic moment μ and the line of sight L to the rotation axis Ω are estimated for the pulsar PSR B1921+24, which displays “on” and “off” periods in its radio emission. It is shown that this object is an orthogonal rotator, i.e., the angle β between μ and Ω is equal to 88°.2 and the angle between L and Ω is ζ = 98.7°, and that its rotation period should be twice the usually adopted value (P = 1.626 s). One possible reason for the peculiarities of this pulsar could be the precession of a relic disk in the equatorial region of the object. Further observations (in particular, in the infrared) are required to confirm the existence of such a disk. Polarization data for other pulsars whose radiation switches on and off (transients) are also required, to determine if they are likewise orthogonal rotators. Calculations for PSR B0656+14 show that β ∼ 20°, and the sharp increase of its pulse intensities is due to intrinsic reasons, and is not associated with a relic disk. Original Russian Text ? I.F. Malov, 2007, published in Astronomicheskiĭ Zhurnal, 2007, Vol. 84, No. 6, pp. 531–535.  相似文献   

Snow avalanches striking water basins: behaviour of the avalanche’s centre of mass and front     

G. Zitti  C. Ancey  M. Postacchini  M. Brocchini 《Natural Hazards》2017,85(3):1297-1322

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Assessment of potential sediment contamination using screening methods (XRF,TGA/MS) taking into account principles of green chemistry,Eastern Slovakia     

Lenka Findoráková  Oľga Šestinová  Milota Kováčová 《Environmental Earth Sciences》2017,76(3):119

Mining and milling of metal ores coupled with industries have bequeathed many countries the legacy of wide distribution of metal contaminants in sediments. The aim of this study was to assess potential sediment contamination via useful screening methods (XRF, CHNS, TGA/MS). The sediments were collected from the water reservoir Krompachy Eastern Slovakia in April 2015. Within the frame of evaluation it was found that the concentrations of the study elements (Cu, Zn, As, Pb, Cr, Ni, Cd) exceeded some of the MPC, TV and IV values. Sample c was the most polluted by metals, which evident according to it’s the highest CHNS proportion as well as the highest clay and silt proportion. In the samples studied the best correlation was confirmed between weight losses in the temperature range (400–620 °C) and the following metal concentrations: Cu (r = 0.89), Zn (r = 0.88), As (r = 0.93), Hg (r = 0.83), Pb (r = 0.87). The greatest proportions of m/z 44, m/z 18 were detected at temperatures (400–620 °C) associated with decomposition of minerals such as siderite, barite, and exothermic loss of more refractory aromatic C took also place.  相似文献   

The mineralogy,geochemistry, and suitability for ceramic applications of Akharım (Afyonkarahisar,W Turkey) kaolinitic clay     

M. Kuşcu  Ahmet Yıldız 《Arabian Journal of Geosciences》2016,9(7):510

Kaolinitic clays associated with sedimentary rocks cover widespread in the Yeniköy formation from the Akhar?m district, (Afyonkarahisar, W Anatolia). Due to the proximity to the ceramic industry areas such as Kütahya and U?ak Province of Turkey, the clays in the Akhar?m district have been intensively exploited for the last few years. The Akhar?m kaolinitic clays were hosted by Middle-Upper Miocene-aged Yeniköy formation and divided into two parts as northeastern and southwestern via normal fault. The alteration degree increases from lower levels to surface in the NE part of deposit. Besides layered structure in their N70° W/30° SW direction and gray-beige, yellowish brown colored in SW part. This study focused on mineralogy, geochemistry, and ceramic properties of kaolinitic clays. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, chemical, physical, and mechanical tests were conducted on studied samples from the wall of clay quarry. Akhar?m clay deposits consist of mainly kaolinite and quartz. Additionally, they include smectite, biotite, feldspar, jarosite, calcite, and hematite minerals. Akhar?m clays are characterized with their moderate plasticity (PL = 17.07–24.09), low water absorption (3.64–9.53 wt.%), low linear shrinkage (8.08–15.55 wt.%), high bending strength (17.72–32.69 N/mm²), and ideal lightness values (L* = 46.50–82.74) and color values (a* = 4.71–29.87; b* = 14.67–28.72). These properties vary related with mineralogical and geochemical features of Akhar?m clays. In conclusion, Akhar?m clays have desired specifications for floor and wall t to their mineralogical, geochemical, and ceramic properties.  相似文献   

The orphan Sanriku tsunami of 1586: new evidence from coral dating on Kaua‘i     

Rhett Butler  David A. Burney  Kenneth H. Rubin  David Walsh 《Natural Hazards》2017,88(2):797-819

We have re-examined the historical evidence in the circum-Pacific for the origin of the 1586 orphan tsunami of Sanriku, Japan, previously attributed to a Lima, Peru, earthquake and tsunami in 1586. New evidence comes from corals found in a unique paleotsunami deposit on Kaua‘i. Dated by ²³⁰ Th- ²³⁸ U geochronology these corals determine an absolute age in high precision of a Pacific tsunami event that was previously dated to approximately the sixteenth century by ¹⁴ C methodology. Detrital corrected ages of three low thorium, well-preserved coral clasts range from 415 to 464 years old (relative to 2016), with a mean age of 444 years ±21 (\( 2\sigma_{{\bar{X}}} \)). Literature evidence for circum-Pacific paleotsunami in this time range is reviewed in light of the new high-precision dating results. Modeled and observed tsunami wave amplitudes in Japan from several Peruvian events are insufficient to match the 1586 Sanriku observation, and paleodated earthquakes from Cascadia, the Alaskan Kodiak region, and Kamchatka are incompatible with the Sanriku data in several ways. However, a mega-earthquake (M _w > 9.25) in the Aleutians is consistent with the Kaua‘i evidence, Pacific Northwest observations, and the Sanriku tsunami amplitude. The Kaua‘i coral paleotsunami evidence therefore supports the origin of the 1586 Sanriku tsunami in the Aleutian Islands.  相似文献   

Permeability of granular soil employing flexible wall permeameter     

Srikanth Kandalai  Purnendu Narayan Singh  Kunal Kumar Singh 《Arabian Journal of Geosciences》2018,11(2):28

Understanding the changes in permeability of soil, when soil is subjected to high confining pressure and flow pressure, which may alter the textural and geomechanical characteristics of soil, is of great importance to many geo-engineering activities such as, construction of high-rise buildings near the coast or the water bodies, earthen dams, pavement subgrades, reservoir, and shallow repositories. It is now possible to evaluate the changes in permeability of soil samples under varying conditions of confining pressure and flow pressure using flexible wall permeameter (FWP). In the present study, investigation was carried out on a cylindrical sample of granular soil employing FWP under varied conditions of confining pressure (σ₃)—50–300 kPa, which can simulate the stress conditions equivalent to depth of about 20 m under the earth’s crust, and a flow pressure (f_p)—20–120 kPa, which is mainly present near the small earthen embankment dams, landfill liners, and slurry walls near the soft granular soil with high groundwater table. The obtained results indicate a linear relationship between hydraulic conductivity (k) with effective confining pressure (σ_eff.), k, decreasing linearly with an incremental change in σ_eff.. Further, k increases significantly with an increase in f_p corresponding to each σ_eff., and q increases significantly with increase in the f_p corresponding to each (σ₃). It was also observed that corresponding to the low f_p of 20 kPa, the reduction in k is nonlinear with σ_3. The percentage reduction in k is observed to be 9, 13, and 27% corresponding to σ₃ of 50–100, 100–200, and 200-300 kPa, respectively.  相似文献   

Theoretical investigations of the local structures and the <Emphasis Type="Italic">g</Emphasis> factors for 3d<Superscript>9</Superscript> ions in CdS     

S. Y. Wu  H. M. Zhang  H. N. Dong  X. F. Wang  Y. X. Hu 《Physics and Chemistry of Minerals》2009,36(9):483-487

The local structures and the g factors g _// and g _⊥ for the isoelectronic 3d⁹ ions Cu²⁺ and Ni⁺ in CdS are theoretically investigated from the perturbation formulas of these parameters for a 3d⁹ ion under trigonally distorted tetrahedral environments. In consideration of significant covalency of the [MS₄] combinations (M = Cu and Ni), the ligand orbital and spin–orbit coupling contributions are taken into account using the cluster approach. Based on the studies, the substitutional impurity Cu²⁺ (or Ni⁺) on Cd²⁺ site is found to undergo a small inward displacement 0.026 Å (or a slight outward shift 0.017 Å) towards (or away from) the ligand triangle along C ₃ axis. The theoretical g factors for both ions based on the above impurity displacements are in good agreement with the experimental data.  相似文献   

Compressibility of Sands of Various Geologic Origins at Pre-crushing Stress Levels     

Junxing Zheng  Roman D. Hryciw  Andrea Ventola 《Geotechnical and Geological Engineering》2017,35(5):2037-2051

This study quantifies the influence of various intrinsic soil properties including particle roundness, R, sphericity, S, 50% size by weight, D ₅₀, coefficient of uniformity, C _u, and the state property of relative density, D _r, on the compression and recompression indices, C _c and C _r, of sands of various geologic origins at pre-crushing stress levels. Twenty-four sands exhibiting a wide range of particle shapes, gradations, and geologic origins were collected for the study. The particle shapes were determined using a computational geometry algorithm which allows characterization of a statistically large number of particles in specimens. One dimensional oedometer tests were performed on the soils. The new data was augmented with many previously published results. Through statistical analyses, simple functional relationships are developed for C _c and C _r. In both cases, the models utilized only R and D _r since other intrinsic properties proved to have lesser direct influence on the compression indices. However, previous studies showed that the contributions of S and C _u are felt through their effects on index packing void ratios and thus on D _r. The accuracy of the models was confirmed by comparison of predicted and observed C _c and C _r values.  相似文献   

Sequence signal processing of 2012 Ahar–Varzaghan earthquake (<Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> 6.4) of NW Iran     

Majid Nemati 《Environmental Earth Sciences》2017,76(14):495

Before starting seismic cycle of Ahar–Varzaghan 2012 event, a partial gap in the form of a pre-seismic calm sequence (seismicity rate, r = 0.46 event/year, b = 1.4) with duration of 303 days spatially has dominated over the entire seismogenic area. From April 17, 2012, to May 31, 2012, r significantly increased to 2.16, indicating strong foreshock sequence, and b value changed to 1.9, remarkably. In the last two months before the mainshock, foreshocks have partially migrated toward the earthquake fault (with a decrease in size, b = 2.0). Significantly, high rate of seismicity and low V _P /V _S (1.64) in the foreshocks sequence and also very high seismicity rate (17.3) and high V _P /V _S (1.76) in the aftershocks sequence make substantial differences between the seismic cycle and the background seismicity. Moreover, a significant E–W migration of the microseismicity was confirmed in the study area.  相似文献   

Simplified method for calculating inflow into a deep excavation with consideration of the effects of cutoff walls     

G. Y. Luo  J. S. Qiu  H. Cao  H. Pan 《Hydrogeology Journal》2018,26(8):2853-2865

Water inflow into deep excavations is a key parameter in the evaluation of environmental impact, and a simplified method is needed to calculate the inflow with adequate accuracy, especially for a deep excavation with a cutoff wall around it. This paper presents a model for calculating inflow based on the method of fragments, assuming two-dimensional sectional flow. The effects of cutoff wall thickness (w), wall penetration, and excavation width on the inflow are well considered in this model. Explicit formulas for the form factor are given. The accuracy and scope of this method are discussed. The method can be applied in both flooding and no flooding cases. Extensive verification shows that, for the flooding case and when one of four conditions is satisfied, the error of the proposed method will be within 10%. These conditions are b/d?≥?0.8 or w/d?≥?0.03 or s/d?≥?0.2 or s₁/d?≥?0.2, for which b is the half width of the excavation, d is the thickness of the soil layer underlying the wall, and s and s₁ are the wall penetration depths on the non-excavation side and excavation side, respectively. For the case of no flooding and when the ratio of the distance from the recharge boundary to the aquifer thickness (a/T) is?≥2, the error does not exceed 15%.  相似文献   

The morphological characteristics of gully systems and watersheds in Dry-Hot Valley,SW China     

Zhen Xu  Fachao Qin  Bin Zhang  Qingchun Deng  Hui Liu  Jie Jin  Liangtao Shi 《中国地球化学学报》2018,37(6):854-866

Gully systems and watersheds are geomorphic units with clear boundaries that are relatively independent of basin landscapes and play an important role in natural geography. In order to explore the morphological characteristics of gully systems and watersheds in the Dry-Hot Valley [South West (SW) China], gullies are interpreted from online Google images with high resolution and watersheds are extracted from digital elevation model at a scale of 1:50,000. The results show that: (1) There are 17,382 gullies (with a total area of 1141.66 km²) and 42 watersheds in the study area. (2) The average gully density of the study area (D) is 4.29 km/km², gully frequency (F) is 14.39 gullies/km², the branching ratio (B) is 5.13, the length ratio (L) is 3.12, and the coefficient of the main and tributary gullies (M) is 0.06. The degree of gully erosion is strong to extremely strong, the main development intensity of gully erosion ranges from intense to moderate, and the type of gully system is tributary. (3) The watershed areas (A) are between 0.39 and 96.43 km², the relief ratio (R) is from 0.10 to 0.19, the circularity ratio (C) is from 0.30 to 0.83, the texture ratio (T) is from 0.82 to 39.35, and the dominant geomorphological texture type is fine. (4) There is a quantitative relationship between F and D:F?=?0.624D² (R?=0.84) and T is closely related to D, F, M (R²?>?0.7). A, R and C are related to M (R²?>?0.5). The development of gully systems is the result of coupling effects between multiple factors. In this area, the degree of erosion and the condition of the main and tributary gullies can be controlled by the degree of topographic breakage in the watershed, which provides some theoretical basis for the evaluation of gully erosion by the latter. In addition, the scale, relief, and shape have a significant impact on the locations of the main and tributary gullies. For tributary gullies, attention should be paid to the interception and control of runoff and sediment in the small confluence branches in order to prevent gully expansion and head advance. These features can inform the development of targeted measures for the control of soil erosion.  相似文献   

The transfer of oxygen isotopic signals from precipitation to drip water and modern calcite on the seasonal time scale in Yongxing Cave,central China     

Quan Wang  Yongjin Wang  Kan Zhao  Shitao Chen  Dianbing Liu  Zhenqiu Zhang  Wei Huang  Shaohua Yang  Yijia Liang 《Environmental Earth Sciences》2018,77(12):474

Stable isotope data of precipitation (δ¹⁸O_p and deuterium excess), drip water (δ¹⁸O_d), and modern calcite precipitates (δ¹⁸O_c and δ¹³C_c) from Yongxing Cave, central China, are presented, with monthly sampling intervals from June 2013 to September 2016. Moderate correlations between the monthly variation of δ¹⁸O_p values (from ??11.5 to ??0.7‰) and precipitation amount (r = ??0.59, n?=?34, p?<?0.01) and deuterium excess (r?=?0.39, n?=?31, p?<?0.01) imply a combined effect of changes in precipitation amount and atmospheric circulation. At five drip sites, the δ¹⁸O_d values have a much smaller variability (from ??9.1 to ??7.5‰), without seasonal signals, probably a consequence of the mixing in the karst reservoir with a deep aquifer. The mean δ¹⁸O_d value (??8.4‰) for all drip waters is significantly more negative than the mean δ¹⁸O_p value (??6.9‰) weighted by precipitation amount, but close to the wet season (May to September) mean value (??8.3‰), suggesting that a threshold of precipitation amount must be exceeded to provide recharge. Calculation based on the equilibrium fractionation factor indicates that the δ¹⁸O_c values are not in isotopic equilibrium with their corresponding drip waters, with a range of disequilibrium effects from 0.4 to 1.4‰. The δ¹⁸O_c and δ¹³C_c values generally increase progressively away from the locus of precipitation on glass plates. The disequilibrium effects in the cave are likely caused by progressive calcite precipitation and CO₂ degassing related to a high gradient of CO₂ concentration between drip waters and cave air. Our study provides an important reference to interpret δ¹⁸O_c records from the monsoon region of China.  相似文献   

Characteristics of deuterium excess parameters for geothermal water in Beijing     

Kai Liu  Xiaojuan Qiao  Baoling Li  Ying Sun  Zhiping Li  Conglin Pu 《Environmental Earth Sciences》2016,75(23):1485

This study investigates the characteristics of geothermal water in 10 geothermal fields in Beijing. The relationships between the deuterium excess parameter (d) and temperature, depth, age of geothermal groundwater, groundwater flow field, and Eh were investigated using geothermal groundwater samples. Results showed that (1) the average d value of geothermal water is 5.4, whereas that of the groundwater in normal temperature is 6.04. The differences are induced by the oxygen isotope exchange during the water–rock interaction, which may be more easily completed in geothermal water than in cold groundwater. (2) The d value increases remarkably with the age of the geothermal groundwater. The d value increases from 11.2 to 14.6 when the age of the geothermal water is 12,760 ± 130 a and 38,960 ± 630 a, respectively. Moreover, the isotope heat exchange for composition of the hydrogen and oxygen isotopes in the geothermal groundwater proceeds sufficiently with time. (3) The d value decreases from 5.72 to 3.03 when the depth increases from 125.13 to 3221 m. Generally, in the same area, the d value decreases with depth because the temperature is increasing. (4) The d value of the groundwater gradually reduces from the northern recharge area to the southern discharge area. The average d value is 7.31 in the northern recharge area and 5.68 in the middle Beijing Depression, whereas the d value in the southern area of Fengheying is ?9.20. The larger difference in d values between the recharge and discharge areas is due to the slower velocity of underwater flow, which induces longer time for oxygen exchange. (5) The relationship between the d and Eh is complex. When Eh is <200 mV, the d value of the geothermal water decreases with the decrease in Eh. When Eh is higher than 200 mV, the d value increases slightly with the decrease in Eh. The study of the characteristics of deuterium excess parameters for geothermal water could provide a scientific isotopic evidence for assessment and exploitation measures in geothermal groundwater systems.  相似文献   

High-pressure displacive phase transition of a natural Mg-rich pigeonite     

Matteo Alvaro  Fabrizio Nestola  Fernando Cámara  M. Chiara Domeneghetti  Vittorio Tazzoli 《Physics and Chemistry of Minerals》2011,38(5):379-385

A high-pressure single-crystal X-ray diffraction study has been carried out on a P2₁/c natural Mg-rich pigeonite sample with composition ca. Wo₆En₇₆Fs₁₈ using a diamond anvil-cell. The unit-cell parameters were determined at 14 different pressures to 7.14 GPa. The sudden disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 2.8%) in the unit-cell volume indicated a first-order P2₁/c–C2/c phase transition between 4.66 and 4.88 GPa. The P(V) data of the P2₁/c phase were fitted to 4.66 GPa by a third-order Birch–Murnaghan equation of state (BM3 EoS), whereas the limited number of experimental data collected within the C2/c phase between 4.88 and 7.14 GPa were fitted using the same equation of state but with K′ constrained to the value obtained for the P2₁/c fitting. The equation of state coefficients are V ₀ = 424.66(6) ų, K _T0 = 104(2) GPa and K′ = 8(1) for the P2₁/c phase, and V ₀ = 423.6(1) ų, K _T0 = 112.4(8) GPa, and K′ fixed to 8(1) for the C2/c phase. The axial moduli for a, b, and c for the P2₁/c phase were obtained using also a BM3-EoS, while for the C2/c phase only a linear calculation could be performed, and therefore the same approach was applied for comparison also to the P2₁/c phase. In general the C2/c phase exhibits axial compressibilities (β _c > β _a >> β _b) lower than those of the P2₁/c phase (β _b > β _c ≈ β _a; similar to those found in previous studies in clinopyroxenes and orthopyroxenes). The lower compressibility of the C2/c phase compared with that of the P2₁/c could be ascribed to the greater stiffness along the b direction. A previously published relationship between P _c and M2 average cation radius (i.r.) has been updated using all the literature data on P2₁/c clinopyroxene containing large cations at M2 site and our new data. The following weighted regression was obtained: P _c (GPa) = 26(4) ? 28(5) ×  i.r (Å), R ² = 0.97. This improved equation can be used to predict the critical pressure of natural P2₁/c clinopyroxene samples just knowing the composition at M2 site.  相似文献   

Observations of late-type variable stars in the water vapor radio line. The long-period variable R cassiopeia     

M. I. Pashchenko  G. M. Rudnitskii 《Astronomy Reports》2004,48(5):380-392

Observations of circumstellar maser emission from the long-period variable R Cas in the 1.35-cm water-vapor line are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 1980–2003 (JD=2444409–2452724). Over the 23 years of observations, strong flares in the H₂O line profile were recorded in 1982 (with a peak flux density up to 400 Jy) and 1986–1989 (up to 750 Jy). Subsequently, from 1990 to March 2003, the H₂O line flux was usually below the detection threshold of the radio telescope (<5–10 Jy). Episodic small increases of the emission with peak flux densities of 20–60 Jy were observed. The variations of the H₂O line flux F are correlated with variations in the visual brightness of the star. The phase delay Δ_γ of the F variations relative to the optical light curve of R Cas ranged from 0.2–0.3P during the observations (P=430.46^d is the star's period). A model for the variability of the H₂O maser in R Cas is discussed. If the variations are due to periodic impacts by shock waves driven by the stellar pulsations, the time for the shock to travel from the photosphere to the inner boundary of the H₂O-masing shell may reach 2–4P. The flares could be due to transient episodes of enhanced mass loss by the star or to the propagation of an exceptionally strong shock from the stellar surface.  相似文献   

Comparison of the magnetic properties of leading and following spots and the overlying ultraviolet emission     

Yu. S. Zagainova  V. G. Fainshtein  V. N. Obridko  G. V. Rudenko 《Astronomy Reports》2017,61(6):533-549

SDO/HMI and SDO/AIA data for the 24th solar-activity cycle are analyzed using a quicker and more accurate method for resolving π ambiguities in the transverse component of the photospheric magnetic field, yielding new results and confirming some earlier results on the magnetic properties of leading and following magnetically connected spots and single spots. The minimum inclination of the field lines to the positive normal to the solar surface α _min within umbrae is smaller in leading than in following spots in 78% of the spot pairs considered; the same trend is found for the mean angle 〈α〉 in 83% of the spot pairs. Positive correlations between the α _min values and the 〈α〉 values in leading and following spots are also found. On average, in umbrae, the mean values of 〈B〉, the umbra area S, and the angles α _min and 〈α〉 decrease with growth in the maximum magnetic field B _max in both leading and following spots. The presence of a positive correlation between B _max and S is confirmed, and a positive correlation between 〈B〉 and S in leading and following spots has been found. Themagnetic properties of the umbrae of magnetically connected pairs of spots are compared with the contrast of the He II 304 emission above the umbrae, C ₃₀₄. Spots satisfying certain conditions display a positive correlation between C _304?L and 〈α _L 〉 for the leading (L) spots, and between C _304?L /C _304?F and l _L /l _F , where l _L (l _F ) are the lengths of the field lines connecting leading (L) or following (F) spots from the corresponding spot umbrae to the apex of the field line.  相似文献