P and S arrival time anomalies at a dense array: Marker of the travale field

Arrival times of seismic waves propagated to a dense array (20 three-component seismometers on a 3 × 3 km area) from natural sources beneath the Travale field, have been analysed for lateral variations which can be related to the extent of the productive reservoir. Significant teleseismic delays between sites only a few hundred meters apart correlate with productive well R9. Spatial variation of both P and S travel arrival times from local earthquakes at the edge of the array and 4 km deep beneath the reservoir consistently delineate its lateral extent to the south and east as documented by drillholes.     

Mixed Convection Heat Transfer from an In-Line Row of Square Cylinders in Cross-Flow at Low Reynolds Number

This article presents a two-dimensional numerical study on the unsteady laminar mixed convection heat transfer from a row of five in-line isothermal square cylinders placed in an unconfined medium and subjected to cross-flow of a Newtonian fluid at low Reynolds number (Re = 125). The hydrodynamic and thermal transport phenomena are captured for the separation ratios (spacing to cylinder size ratio, s/d) of 0.5, 1, 1.5, 2, 3, and 4. The mixed convection heat transfer is studied for Richardson numbers (Ri) ranging from 0 to 3 with a fixed Prandtl number (Pr = 0.71). Numerical calculations are performed by using a PISO algorithm-based finite volume solver in a collocated grid system. The instantaneous vorticity fields along with the isotherm patterns are systematically presented and discussed for different separation ratios and Richardson numbers. Depending on the engineering application, the temperature difference between the surface and the free stream could vary to make buoyancy of primary importance, entailing major modification of the flow field. Additionally, the instantaneous and mean drag and lift coefficients, Strouhal numbers, and mean Nusselt numbers are determined and discussed.     

Resistivity monitoring at Cerro Prieto

In 1978 Lawrence Berkeley, Laboratory, in cooperation with Comisión Federal de Electricidad, began a program of dipole - dipole resistivity monitoring at the Cerro Prieto geothermal field. Dipole - Dipole measurements were first made in 1978, then repeated in 1979: (a) to determine whether the field boundaries could be defined by surface resistivity measurements; and (b) to determine if changes in reservoir conditions due to production may be monitored by surface measurements.In 1979 data accuracy was improved to where estimated measurement errors were less than 3 per cent. In addition, data coverage on a line over the field was expanded by 40 per cent for greater depth of investigation and more information on the newer, eastern part of the field. Resistivity modeling of the expanded 1979 profile indicates that the resistive body associated with the zone of production (Wilt et al., 1980) dips steeply eastward, and may underlie the eastern part of the field. The model also shows a thin steeply dipping conductor adjacent to the resistive body that may be associated with faulting and fluid movement. Model perturbation studies have shown that small changes associated with cold-water influx, fault zone migrations, and formation of a steam zone would all be detectable with precision dipole - dipole measurements. Telluric profile measurements taken along line E E′ were found to yield a significant amount of reconnaissance information but are unsuitable for monitoring purposes.     

A comparative study of SPCTRAL2 and SMARTS2 parameterised models based on spectral irradiance measurements at Valencia, Spain

Results obtained using the parametric models SPCTRAL2 and SMARTS2 for the urban area of Valencia, Spain, have been analysed and compared with experimental measurements at ground level obtained with two Li-cor 1800 spectroradiometers with a 6 nm resolution. The study used two different input parameters in both models for the aerosol characterisation: the aerosol optical thickness at 0.5 μm, τ_aλ(0.5), and the Angstrom turbidity coefficient β. The results obtained show that both algorithms reproduce quite correctly the spectral irradiance experimental values when an urban aerosol model parameterised by the τ_aλ(0.5) value is considered. In all the cases the deviations are lower when SMARTS2 code is used.     

A geothermal field model based on geophysical and thermal prospectings in Nea Kessani (NE Greece)

The present study completes a study by Thanassoulas et al. (1986) Geophys. Prosp.34, 83–97 and deals with geophysical exploration for geothermal resources in Nea Kessani area, NE Greece. The results of some deep electrical soundings (AB = 6000 m) with the interpretation of a gravity profile crossing the investigated area are considered together with thermal investigations. All subsequent information, along with the conclusions of an earlier paper dealing with a reconnaissance geophysical survey of the same area, are used to highlight a subsurface geothermal field model.     

Effect of an External Magnetic Field on the 3-D Oscillatory Natural Convection of Molten Gallium During Phase Change

In this article, a numerical study of the effect of an external magnetic field on three-dimensional (3-D) oscillatory natural convection during phase change is carried out. A parallelepiped enclosure filled with a molten gallium and subjected to an external magnetic field applied in X-, Y-, and Z-directions, separately, is considered. The finite-volume method with enthalpy formulation is used to solve the mathematical model in the solid and liquid phases. The Hartmann number is fixed to Ha = 20.The computer program developed in this study was validated with the experimental data founded in the literature. The critical Grashof numbers Gr _Cr and critical corresponding frequencies F r _Cr are determined with and without magnetic field. The results show that the oscillatory natural convection during phase change are characterized by low-frequency oscillations in the presence and absence of the magnetic field. The pattern flow shows a spiral development of the flow in Z- direction. A strong dependence between the direction of the magnetic field and the critical Grashof number and their corresponding frequency is determined. A strong stabilization of the flow field is shown when the magnetic field is oriented horizontally.     

Effect of selective surface degradation on the performance of solar water heating systems

Selective surface often degrade in the field. Their solar absorptivity α_s and thermal emittance change with time in service by some amount, say Δα_s and Δ, from their starting values. It is important to quantify the effect this degradation has on the annual fraction solar F_s. A given relative change in F_s can be caused by different combinations of Δα_s, and Δ. In this paper we use computer simulation of solar domestic hot water systems to graph these combinations, in a plot of Δα_s versus Δ, for relative changes in F_s, of 10% and 5%. The slope and intercepts of this plot, which is found to be linear, are studied for their dependence on a wide range of solar system parameters, such as geographical location, collector area, and set point temperature. We find that the slope, and - for starting values of F_s less than about 0.5 - the intercepts, are relatively insensitive to the system parameters. We show that this result is consistent with a simple model. For F_s 0.5, the intercepts rise sharply with F_s, in a way that is strongly (and to some extent, only) dependent on the geographical latitude of location. These results have direct application to projecting the useful service life of a selective surface.     

Isotopic composition of steam samples from Lanzarote, Canary Islands

The isotopic analysis of the steam samples collected in the geothermal area of Lanzarote show that the values of δD are practically constant, and those of δ¹⁸O range in a shift of 17‰ reaching a maximum of +14.7‰ versus SMOW, this last value being the highest found in steam samples.This composition can be explained as a consequence of the isotopic exchange at high temperature between limestones and a mixture of marine and local meteoric waters.This interpretation agrees with previous geological and geophysical studies which consider that a promising geothermal field could exist in Lanzarote.     

Natural Convection in an Enclosure with a Partially Active Magnetic Field

Chaotic natural convection flow of a molten gallium in a square enclosure with the upper and lower surfaces being insulated was studied by two-dimensional numerical simulation. Constant temperatures are imposed along the left and right walls of the enclosure with a volumetrically heated enclosure. In addition, a nonuniform partially active magnetic field is applied in a vertical direction. The flux lines spread out into a fringing field so the effective cross-sectional area of the gap is larger than that of the pole face. A chaotic regime is considered under steady state boundary condition. This study was done for an internal Rayleigh number of 10⁷, external Rayleigh number of 10⁵, and Prandtl number of 0.024. The study covers various magnet pole effect widths of 1/4, 1/2, and 3/4 from enclosure width and the magnetic field strength ranges 0.0 ≤ B _o  ≤ 10 Tesla. The transport equations for continuity, momentum, and energy are solved. The numerical results are reported for the effect of the partially active magnetic field on the velocity vectors, counters of temperature, streamline, and heat transfer coefficient. The numerical study shows that a magnetic field is damping chaotic oscillation behavior and decreases the amplitude of oscillation. Also, at a certain magnetic field strength the chaotic flow tend to becomes periodic flow at certain amplitude and frequency, and at high magnetic field strength the flow in the square enclosure flow tends to become steady laminar flow with stable average Nusselt number values; so, the random oscillation behavior disappeared. The effect of a nonuniform magnetic field tends to push the fluid to flow away from magnetic field region.     

Hydrogeochemistry and groundwater circulation in the Xi’an geothermal field, China

Geothermal waters from the Tertiary aquifers located at 1000–3000 m beneath Xi’an city, Shaanxi Province, China, show unique isotopic composition as compared to local groundwaters from shallower Quaternary aquifers. Positive oxygen shifts of as much as 8‰ VSMOW are observed, while the corresponding δ²H values remain essentially constant at about −80‰ VSMOW, which is significantly different from those of waters in the Quaternary aquifers with a mean δ²H value of −60‰ VSMOW. The strong ¹⁸O shift is a result of isotope exchange between geothermal water and carbonate minerals such as calcite over a residence time of several thousand years up to 30,000 years, based on ¹⁴C dating. A comparison of the isotopic composition of geothermal waters with neighbouring groundwater units on both sides of the Guanzhong Basin indicates that the geothermal reservoirs are recharged by rain that falls on the northern slope of the Qinling Mountains, south of the Xi’an geothermal field, but not from the North Mountains to the north of the field. Based on chemical geothermometers the highest temperature estimated for the Tertiary aquifers of the Xi’an area is around 130 °C.     

Effect of spatial variation of incident radiation on spectral response of a large area silicon solar cell and the cell parameters determined from it

Effect of spatial variation of incident monochromatic light on spectral response of an n⁺–p–p⁺ silicon solar cell and determination of diffusion length of minority carriers (L_b) in the base region and the thickness of the apparent dead layer (x_d) in the n⁺ emitter from the spectral response have been investigated. Spectral response of a few 10 cm diameter and 10×10 cm² pseudo-square silicon solar cells was measured with the help of a standard silicon solar cell of 2×2 cm² area in 400–1100 nm wavelength range. Different areas (4, 9, 16, 25 and total area 78.6 or 96 cm²) were exposed. The effect of the radial variation of incident radiation was determined quantitatively by defining a parameter f₁ as the ratio of the average intensity falling on the reference cell to that on the exposed area of the test cell. The value of f₁ varied between 1 and 1.15 (1.25) as the exposed area of the cell varied from 4 cm² to 78.6 (96) cm² indicating that the spatial inhomogeneity of intensity increased with the increase in the exposed cell area. Short-circuit current densities, J_sc, computed from spectral response data for AM1.5 spectrum were less compared to the directly measured values by a factor which was nearly equal to f₁. However, radial variation of intensity does not affect the determination of diffusion length of minority carriers in the base region (by the long wavelength spectral response, LWSR method using the measured spectral response data in 0.85<λ<1.05 μm range) and the thickness of the dead layer (by the method of Singh et al. using the data of 0.45<λ<0.65 μm range) significantly.     

Mass transfer effects on MHD flow and heat transfer past a vertical porous plate through a porous medium under oscillatory suction and heat source

This paper considers the effect of mass transfer on free convective flow and heat transfer of a viscous incompressible electrically conducting fluid past a vertical porous plate through a porous medium with time dependant permeability and oscillatory suction in presence of a transverse magnetic field and heat source. The solutions for velocity field, temperature field and concentration distribution are obtained using perturbation technique. The effects of the flow parameters such as magnetic parameter M, Grashof number for heat and mass transfer G_r,G_c, porosity parameter K_p, Prandtl number P_r, Schmidt number S_c, frequency parameter ω and heat source parameter S on the velocity, temperature and concentration distribution of the flow field and the skin friction, heat flux and the rate of mass transfer are studied analytically and presented with the aid of figures and tables. It is observed that the magnetic parameter and the Schmidt number retard the velocity of the flow field while the Grashof number for heat and mass transfer, the porosity parameter and the heat source parameter have accelerating effect on the velocity of the flow field at all points. Further, the Prandtl number reduces the temperature and the Schmidt number diminishes the concentration distribution of the flow field at all points. The skin friction coefficients τ₀ and τ increase due to increase in G_r,G_c and K_p while decrease due to increase in S_c, M, ω and P_r. Further, the rate of mass transfer S_h increases due to increase in S_c while an increase in ω results a decrease in S_h.     

Current sensitivity and efficiency of a CdO-<Emphasis Type="Italic">p</Emphasis>CdTe-Mo structure at low light levels

It is shown that the CdO-pCdTe-Mo structure established on the basis of large-block p-type films has a spectral range of photosensitivity of Δλ = 480–830 nm, which fully covers the visible area of solar radiation. It was found that the CdO-pCdTe-Mo structure has a high integral sensitivity of S _int = 430–520 mA/lm and a high efficiency of illumination by light of E = 10–100 lx. The anomalous behavior of S _int and the efficiency of this structure are explained by an increase in the photocurrent due to redistribution of the potential between the barrier and the series resistance of the structure as a result of illumination.     

Optical and electrochemical studies of transient free convection mass transfer at horizontal surfaces

The onset of free convection at upward facing horizontal surfaces adjacent to a free fluid environment has been studied using the electrochemical system involving the electrodeposition of Cu²⁺ ions. A transient potential step technique was employed and photography of the ensuing developing convective structure was synchronised with the recording of current-time transients. This enabled the interdependence of instantaneous mass-transfer rate and convective flow structure to be visualised. A number of distinctive flow structures in the transient and steady states were observed and these have been related to the correlation regimes for the overall mass-transfer rate. Interesting phenomena involving periodic instabilities have been discovered at transitional Rayleigh numbers leading to pulsations in the convective plume and corresponding regular oscillations in the steady state mass-transfer rate.The effect of surface roughening on mass transfer and hydrodynamic performance during extended experiments has been observed and a method of overcoming surface roughening difficulties in the application of the electrochemical technique is suggested.Diffusion transient undershoot times are correlated in terms of plate Rayleigh number by the equations in the range 10⁷ < Re_d < 10¹¹ and in the range 10⁴ < Ra_d < 10⁷.The periodic fluctuation frequencies are similarly correlated by the equation .     

Laser fired contacts applied to the rear surface of heterojunction silicon solar cells

In this work, we fabricate heterojunction silicon solar cells on p-type substrates whose rear surface configuration is based on dielectric passivation and laser fired contacts (LFC cells). This is an alternative to boron-doped amorphous silicon film, with which we also fabricate solar cells for direct comparison (HJ cells). As substrates, 3.5 and 0.8 Ω cm p-type double-side polished FZ c-Si wafers are used. Regarding surface passivation for highly doped substrates, LFC configuration has some advantage due to the higher difficulty in creating an efficient amorphous back surface field. Additionally, those substrates are also more advantageous in terms of carrier injection when the rear surface is locally contacted. Thus LFC cells made on 0.8 Ω cm substrates reach V_oc values up to 680 mV, in the same range as that of their HJ cell counterpart, with better FF demonstrating that LFC configuration is a feasible alternative for highly doped substrates. Focusing on the impact of the distance between rear contacts on cell performance, we found a trade-off between open circuit voltage V_oc and fill factor FF. Finally electroluminescence characterization and the dependence of V_oc on pitch, modeled by Fischer's equation, indicate that the depassivated area due to the laser processing of the contacts is bigger than the contacted area.     

Investigation of the electronic structure of the primary electron donor in bacterial photosynthesis - Measurements of the anisotropy of the electronic G-tensor using high-field/high-frequency EPR

Cation radicals of the primary electron donor (D⁺) in bacterial photosynthesis were investigated by high field, high frequency (95 GHz) EPR. Measurements on frozen solutions of D⁺, a dimeric π-cation radical, of various organisms (Rps. viridis, Rb. sphaeroides, Chloroflexus aurantiacus and a heterodimer mutant) are reported, revealing differences in the principal values of the G-tensor. Elements of a theory relating the magnitudes of G principal values to the electronic structure are discussed.     

Measurement of monochromatic emissivity of cement clinker with various Fe2O3 content at high temperature

An applicatiopn of the optical pyrometer is studied for measuring monochromatic emissivities of cement clinker with various Fe2O3 contnet.The idsa of using “brightness temperature” is introduced into the eimssivity measurement.In this method,there is no need for measuring an actual temperature of sample surfaces,only with determining both brightness temperatures of a sample and a blackbody can the required emissivity be evaluated according to Wien‘s radiation law.In practice,the cement clinker is regarded as a greybody,the monochromatic emissivity is approximately equal to the total emissivity,so a single-colour optical pyrometer is applied for this purpose,Test measurements are carried out on 10 kinds of cement clinkers,Experimental data are treated by the least square method.As a result ,the emissivity variation with temperature at a certain Fe2O3 content is quite well represented by εn=a+bT.Furthermore,this work first reported that the eimissivities of cement clinker change consierably with Fe2O3 contents.In multiple cement production this conclusion is very important.     

MHD heat transfer and entropy production of an Al2O3-water nanofluid in a horizontal cylinder

This paper deals with the effect of magnetic fields (B_r, B_θ, B_z) applied in r-, θ-, z-directions, respectively, on entropy production and heat transfer and in a horizontal cylinder filled with an Al₂O₃-water nanofluid. The results are verified using literature data. For different Richardson, Ri, and Hartmann numbers, Ha, the nanoparticles (NP) ϕ, and magnetic field orientation combined effect provide a better understanding of heat transfer and entropy optimization. The results indicate that entropy production and heat transfer and rates depend on magnetic field intensity and direction. Also, increasing Ri and NP increases entropy generation and heat transfer. Finally, applying a radial magnetic field promotes a better convective heat transfer and minimizes entropy production.     

Field solar photocatalytic purification of pesticides-containing rinse waters from tractor cisterns used for grapevine treatment

The objective was to assess in a vineyard the effect of purifying by solar photocatalysis the title rinse waters (presently rejected or, extremely rarely, cleaned in specific installations) in terms of efficacy and on-site ease-of-use for the wine grower. The on-site, self-functioning, solar purifying unit included a corrugated-steel inclined plate of area S=1 m² onto which a TiO₂-coated thin material had been stuck, a 100-l tank, and an aquarium-type pump powered by a photovoltaic panel. For a vineyard of area A=0.15 km², the rinse water (about 80 l) corresponding to each of four typical vine treatments was analysed (major pesticides for each treatment, TOC, Microtox test and, in one case, BOD₅) by independent laboratories, before and after purification for 8 days. These analyses showed that the S/A ratio tested was insufficient. From the relatively low final organic content reached in one case, it is calculated that a three-time higher S/A ratio might suffice, but new trials are necessary to determine whether it is valid for the other typical cases. Inferred contribution of inorganic ions to the post-photocatalytic treatment toxicity points out to the need for an additional detoxification. However, even with a too small S, the photocatalytic treatment markedly improved the quality of the rinse waters. These field experiments have also demonstrated that the purifying prototype is robust, and easy to install and use on site by the wine grower.