Stable isotope study of antimony deposits in the Muratdagi region,western Turkey

The Muratdagi region is rich in antimony deposits having the following common characteristics: post Miocene age, location on the down-thrown blocks next to normal faults, in the vicinity of active or fossil thermal springs, and in contact with carbonate rocks. The isotopic composition of — 7. SMOW of the mineralizing fluid calculated from the measured ° ¹⁸O of quartz and the fluid inclusion microthermometry, is indicative of meteoric water origin. The ° ¹³C of the inclusion CO₂ of — 19.1 to — 25.4 PDB is indicative of interaction with organic material-graphite. The ° ³⁴S of stibnite — 3.6 to — 0.7 is, in view of the mineral assemblage, indicative of magmatic origin of the sulphur. A tightly confined set of structural, lithological, hydrological and geochemical features define a sequence of geochemical processes; formation of acid and reducing fluid, leaching and transport of antimony complexes and precipitation of stibnite within defined lithological units. The set of processes seems to have taken place within a space of 5000 m lateral and 1000 m vertical extension.     

Eta model forecasts of tropical cyclones from Australian Monsoon Experiment: Dynamical adjustment of initial conditions

Summary The University of Belgrade/National Meteorological Centre, Washington (UB/NMC) limited area Eta Model predicted the development, structure, associated precipitation and tracks of the Australian Monsoon Experiment (AMEX) (10 January through 15 February 1987) tropical cyclonesConnie, Irma, Damien andJason. The initial positions and intensities of the tropical cyclone vortices from the global European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, which are used as initial data, do not quite agree with the observations. These disagreements produce additional erros in predicting the tropical cyclone tracks.To improve the initial position of the vortex, the flow is split into the small and the large scale motions, and during the first two hours of the integration, the small-scale part is forced in small steps towards its observed position. The adjustment is performaed with the reduced model dynamics (adjustment processes only) and no physics.With the adjustment during the first two hours of the integration, the model successfully adjusts to the new position of the initial vortex. After the completion of the adjustment stage, the model runs normally, i.e., without any modification. The tracks of the 48-h forecasts with the adjusted initial vortices are parallel to the tracks obtained in the control forecasts without the adjustment. However, e.g., the mean absolute error of the positions during 48-h forecast of the tropical cycloneConnie was reduced from 174 km in the control case to 129 km in the case with adjustment of the position.The latent heat, the thermal energy, the kinetic energy and the total energy of the extracted small scale vortices are calculated every three hours of the integration time. These small-scale energies obtained in the 48-h control forecast are compared to those of the rund with the initial vortex adjustment to monitor the spin up of the model.With 7 Figures     

An analysis of close binaries (CB) based on photometric measurements (VII)

The paper is devoted to the actual problematics in the determination of orbital and physical parameters of active CB on the basis of the interpretation of photometric observations. One solves the problem in two stages: by obtaining a synthetic light curve in the case when the parameters of the corresponding CB model (Djuraevi, 1992a) are given a priori (direct problem) and by determining the parameters of the given model for which the best fit between the synthetic light curve and the observations is achieved (inverse problem) (Djuraevi, 1992b). In this paper, the above procedure is applied to a particular case of an interpretation of CB light curves AU Ser and RV Corvi.     

An analysis of close binaries (CB) based on photometric measurements (V)

The author considers the current problematics in the determination of the orbital and physical parameters for active close binaries (CB) of W Ser type based on the interpretation of photometric observations. In the particular case one analyses the light curves of CB RX Cas in the framework of the accretion-disc model explained in the second paper of this series (Djuraevi, 1992a). The change of the light curves with that of the system's physical-activity phase is analysed and the orbital and physical parameters of the system are determined for the maximum, minimum and the transition regime of the physical activity by applying the inverse-problem method described in the third paper of the series (Djuraevi, 1992b). In the paper a graphical illustration of the solutions obtained is also given.     

A note on the performance of the multiply-upstream semi-Lagrangian advection schemes for one-dimensional nonlinear momentum conservation equation

Summary Two-time-level multiply-upstream semi-Lagrangian schemes were examined in the case of the self-advecting, one-dimensional nonlinear momentum conservation equation. The shock formation process was analyzed. It is pointed out that the shocks cannot be created in the truncated systems satisfying the Pudykiewicz, Benoit and Staniforth criterion.The numerical integrations were restricted to 12 h. It was shown that, at least in the sub-CFL range, increased complexity of the scheme can compensate reduced horizontal resolution. A considerable sensitivity of the schemes with respect to the time step was detected. In the super-CFL mode, several windows on various time scales were found within which the Pudykiewicz, Benoit and Staniforth criterion was satisfied. The time step of 1.44 times the maximum time step allowed by the CFL criterion was used in the semi-Lagrangian runs.The super-CFL, semi-Lagrangian solutions were diverging progressively from the sub-CFL ones as the forecasts advanced. This was also reflected in the energy spectra.Unacceptably large energy losses were encountered in the super-CFL, semi-Lagrangian runs. Most of these losses could be explained by the reduced mean wind speed, i.e., the amplitude of the zero wavenumber wave. At the same time, the energy content in the shorter waves increased. In a more complex model, such a situation would resemble a loss of zonal, and an increase of transient eddy kinetic energy.A trajectory error measure was defined as the maximum absolute value of the distance between the actual arriving point of the particle originating at the estimated departure point, and the grid point assumed to be the arrival point in the semi-Lagrangian procedure. In contrast to the sub-CFL regime, this measure could reach a considerable fraction of the grid distance in the computations with the super-CFL time steps.In the physical system considered, the trajectories are determined only by the velocities at the departure points. With the semi-Lagrangian schemes the distances traveled by the particles are estimated on the basis of the velocities at the points downstream with respect to the departure points. Thus, unless the solution is smooth (in space and time) on the scales of the extrapolation distances/times, the upstream extrapolation does not promise the convergence of the solution.With 16 Figures     

Circumstellar dust and variability of carbon stars

A sample of 35 variable carbon stars has been considered. The stellar temperatures, radii, absolute luminosities, masses, and mass loss rates have been estimated. Then the spherical circumstellar dust shells around the analysed stars are discussed and the differences in the infrared properties between semi-regular, irregular, and long-period variables are indicated.     

Numerical case study of the Altai-Sayan lee cyclogenesis over East Asia

Summary Climatological studies show that the Altai-Sayan lee side is one of the major cyclogenesis areas in the Northern Hemisphere. In case of the Altai-Sayan lee cyclogenesis, the surface cyclone is generated when a primary cyclone is swept north of the mountains. In the mid-troposphere, a trough develops and finally turns into a cutoff low within 48 h. The main synoptic features are similar to those of Alpine cyclogenesis. Numerical simulations are performed to assess the effect of different representation of orography on the Altai-Sayan cyclogenesis. Two experiments are performed, a step-mountain (ETA) and an envelope orography (SGM) experiment. The ETA experiment produced the cyclogenesis in a way similar to that in the analysis both at the surface and at mid-troposphere. The SGM experiment failed in the simulation of the upper cutoff low. The difference in predicted pressure between the ETA and the SGM experiment shows a dipolar structure suggesting that the blocking effect of the mountains is essential in the development of the Altai-Sayan lee cyclogenesis.With 7 Figures     

Present day serpentinization in New Caledonia,Oman and Yugoslavia

Geochemical evidence for modern low-temperature serpentinization has been found in three new localities. Apparently the low-temperature reactions are a common mode of formation of the lizardite-chrysotile and brucite assemblage. Possibly the ¹⁸O content of serpentine formed at low temperatures is in part inherited from the pyroxene and olivine.