Daily variation of the geomagnetic field near the focus of Sq-current system in Indian longitude

The paper presents the first results on the behaviour of solar quiet-day variations of the geomagnetic field components at Gulmarg. Combining the data from Russian stations in the same longitude belt, the annual average daily variations are calculated which show, in the horizontal component (H), a reversal of phase between Gulmarg and Tashkent. Studying the Sq-variations at Gulmarg separately for the three seasons, the daily variation of H duringd-months is predominantly diurnal in character with the maximum before noon. Duringe-months, and more so inj-months, daily variation of the H field is predominantly semidiurnal in character with minimum around 08–09 hr LT and maximum around 14 hr LT consistently during 1978, 1979 and 1980. These features of the Sq at Gulmarg are suggested to be due to the deformations of the current loops caused by the changing latitude of focus during the course of the day.     

Diffusion compensation in natural silicates

The temperature dependence of diffusion is usually found to follow the Arrhenius law: D = D₀e^?E/RT Winchell (1969) showed that there is commonly an inter-dependence between D₀ and E (for diffusion in silicate glasses), such that diffusion of different species show a positive correlation on a log D₀ vs E plot. A similar effect was noted by Hofmann (1980) for cation diffusion in basalt. This implies that diffusion rates of different species tend to converge at a particular temperature; this effect is known as the ‘compensation effect’. I will show that this effect is also present for diffusion in feldspars and olivines. The equations for the compensation lines (with E given in kcal/mol) are: basalt—E = 50 + 7.5 log D₀ feldspar—E = 50.7 + 3.4 log D₀ olivine—E = 78.0 + 7.5 log D₀ The convergence, or crossover, temperatures for diffusion in various materials are: obsidian—3400°C basalt—1370°C olivine—1360°C feldspar—460°C Compensation plots are useful for evaluating and comparing experimental diffusion data (though of limited usefulness in a predictive sense) and for understanding ‘closure temperatures’ for diffusion in petrogenetic processes (since closure temperature, the temperature at which natural diffusion processes are frozen in, is dependent on E, log d₀, and cooling rate). I show that most diffusing species in feldspar have a closure-temperature close to the crossover or convergence temperature, implying that all species in feldspars can be expected to ‘freeze-in’ simultaneously at temperatures in the range 400–600°C (for cooling rates in the range 10¹–10⁵°C/myr). Closure temperatures of various species in olivine, on the other hand, span a much larger range (800°C) for a similar range in cooling rates, implying that different elements in olivine will record different time-temperature stages in petrogenetic processes.     

Simplified DMT-based methods for evaluating liquefaction resistance of soils

This paper presents simplified dilatometer test (DMT)-based methods for evaluation of liquefaction resistance of soils, which is expressed in terms of cyclic resistance ratio (CRR). Two DMT parameters, horizontal stress index (K_D) and dilatometer modulus (E_D), are used as an index for assessing liquefaction resistance of soils. Specifically, CRR–K_D and CRR–E_D boundary curves are established based on the existing boundary curves that have already been developed based on standard penetration test (SPT) and cone penetration test (CPT). One key element in the development of CRR–K_D and CRR–E_D boundary curves is the correlations between K_D (or E_D) and the blow count (N) in the SPT or cone tip resistance (q_c) from the CPT. In this study, these correlations are established through regression analysis of the test results of SPT, CPT, and DMT conducted side-by-side at each of five sites selected. The validity of the developed CRR–K_D and CRR–E_D curves for evaluating liquefaction resistance is examined with published liquefaction case histories. The results of the study show that the developed DMT-based models are quite promising as a tool for evaluating liquefaction resistance of soils.     

Fluxes of heat and momentum over sea surface during the passage of a depression in the north Bay of Bengal

Time variation of surface fluxes of heat, moisture and momentum over a sea station (20°N 89°E) in the north Bay of Bengal has been computed by profile method for the period 18th–25th August 1990 using meteorological data of MONTBLEX-90 from ORVSagarkanya. The fluxes showed synoptic and diurnal variations which are marked during depression (20th–21st August) compared to their variation prior to and after this period. Variations of heat and water vapour fluxes were in phase. Night time fluxes are relatively high compared to day time. Average momentum transfer during depression was two to three times large. Variations in Bowen ratio were relatively large during day time. During depression, it varied between 0·2 in day time and about 0·3 at night and in the undisturbed period between ?0·1 and 0·2 during day time and 0·2 and 0·25 at night. The study shows that the assumptionC _D=C_H=C_E of the exchange coefficients normally used in estimating the fluxes by the bulk aerodynamic method is not appropriate becauseC _H/C_D≈2,C _E/C_D≈1·5 andC _H/C_E≈1·4.     

Thermodynamic study on the compositions of fluid phases in the C-O-H system under high temperature and pressure

Based on the fluid phase equilibrium of the C-O-H system, the compositions of various fluid phases under high temperatures and pressures have been calculated in terms of the available thermodynamic data and newP-V-T data and on the assumption ofP _T= ΣPi in this paper. The results indicate that in this system there are 5 major fluid phases in different proportions at variousT andP. CH₄ is the dominant phase (about 70%) under relatively lowerT andP. Its proportion obviously decreases with increasingT, P andfo₂. The results provide sufficient theoretical grounds for discussing the possibility of CH₄ formation and the physical-chemical conditions of its stable occurrence and proportion in the geological environment.     

Thermal emission of methanol and other molecules at millimeter wavelengths

The paper reports the results of a survey of Galactic star-forming regions in the methanol lines 8_?1–7₀ E at 229.8 GHz, 3_?2–4_?1 E at 230.0 GHz, 0₀–1_?1 E at 108.9 GHz, and a series of J ₁–J ₀ E lines near 165 GHz. In addition to the methanol lines, lines of methyl cyanide (CH₃CN), cyanoacetylene (HC₃N), methyl formate (HCOOCH₃), and sulphur dioxide (SO₂) were detected. Analysis of the data indicates that the methanol emission arises in warm (30–50 K) gas.     

Spectral characteristics of low latitude Pc3 geomagnetic pulsations in south-east Australia

Geomagnetic pulsations in the Pc3 period range (10–45 sec) were recorded simultaneously in south-east Australia using an array of four low latitude induction coil magnetometers over a longitudinal range of 17° atL=1·8 to 2·7. Geomagnetic data from March 25 to September 21, 1982 were digitized and spectral studies were carried out from Grey scale digital (GSD) dynamic spectra and contour sonagrams. Similar wave spectra were generally seen at the three stationsWM, BH andNC in the same latitude with Pc3 waves mostly being observed in the 40–45 mHz band. In addition the higher latitude station (LN) also showed lower frequency Pc4 bands (≈ 10mHz) on some days but higher frequency bands (60–80mHz) on others. Sometimes completely different wave frequencies were observed on theX andY components with the stations in the same latitude generally showing similar spectra on the corresponding components. Dynamic spectra also indicated that wave energy often turned off and on abruptly over short intervals of time implying solar wind control and Pc3 pulsation activity. A band harmonic structure was occasionally seen in wave spectra at the azimuthal stations mainly on theX component during the local afternoon with a harmonic spacing (Δf) of ≈ 10 mHz.     

OSL ages and possible bioturbation signals at the Upper Paleolithic site of Lagoa do Bordoal,Algarve, Portugal

Three sediment samples were collected from a soil profile at the Lagoa do Bordoal site, Algarve, Portugal. Quartz extracted from soil horizons within the profile, was optically dated using the single-aliquot regenerative-dose (SAR) protocol outlined by Murray and Wintle (Radiation Measurements 5 (2000) 523). The optically stimulated luminescence (OSL) emitted by quartz within the 90–150 μm size range was measured using three aliquot sizes. The equivalent doses (D_E) that were obtained show an asymmetric distribution. As the numbers of grains in each aliquot are reduced, the distribution of doses is clearly shifted to lower D_E values including zero doses on single grain aliquots. This shift is accompanied by an increase in the asymmetry of the distribution. These patterns indicate that as the aliquot size decreases, the distributions are increasingly characterized by aliquots with lower D_E's. With respect to the present day modern surface, this shift is most evident in the sample collected from a depth of 37 cm, within an ancient B-horizon. It is least evident in the sample located only 10 cm below it, within a sand unit. An asymmetric distribution of D_E's can be a result of a large number of grains that were well bleached at burial being mixed with a small number of grains that were partially bleached at that time (Radiation Measurements 30 (1999) 207). However, the shift in D_E's that is seen in the Lagoa East samples is most likely due to the postburial downward movement of fully and partially bleached grains from the surface, with possible contributions from the downward movement of grains that received low doses while buried in overlying horizons. The simplest explanation for our results is that grains carrying zero or small D_E's have been moved downward during bioturbation events. These results suggest that downward bioturbation in ancient soil profiles can be identified based on the OSL characteristics of quartz grains. We are also able to provide a minimum age of 24.4±3.2 ka for the Upper Palaeolithic lithic assemblage at the site.     

从西南天山超高压变质带多期构造变形看天山古生代构造演化

通过对西南天山阿克雅孜和木扎尔特地区高压-超高压变质带构造几何学和岩石变形相关运动学的详细剖析,厘定出高压-超高压变质岩石及其相关围岩的构造单元。详细研究表明,研究区可划分为三个构造单元:北部单元、中部单元和南部单元。确定了每个构造单元的构造几何学特征及各个构造单元之间的相互关系。通过分析岩石变形特征和叠加关系,确定了岩石所记录多期变形的运动学特征。根据研究区的多期构造变形特点,建立了阿克雅孜和木扎尔特河地区构造演化序列。共划分出四期构造可识别的事件(E1-E4),分别代表了E1:高压-超高压岩石折返过程;E2:高压-超高压岩石造山带的早期改造过程;E3:北部构造事件对高压-超高压造山带影响;E4:走滑构造对高压-超高压造山带的叠加。沿造山带系列构造分析表明,西南天山高压-超高压带中发育的四期构造事件沿中天山北缘具有很好的一致性,各期构造事件也有一定的横向可对比性。在此基础上通过对多期变形事件的构造背景的探讨,建立了整个天山在古生代的构造拼合过程,揭示我国西部洋壳相关的深俯冲造山带形成过程和参与深俯冲作用(超)高压变质岩的变形变质历史。     

Absorption of radio waves during a solar eclipse

In this paper, the results of our observations on Al-method ionospheric absorption of radio waves on 1.8 and 2.2 MHz during the solar eclipse of 16 February 1980 are presented. The absorption decreased by about 41% and 46% of the normal value respectively at the above two frequencies at Ahmedabad following the maximum phase of the eclipse (about 77% of full disc) with a delay of 18 minutes. The quantityA _T (f) which is a measure of εN vdh is now examined for better clarity of the influence of the changes in theE-layer. The results are discussed in relation to the observations of the ionizing radiations from the sun, changes in the electron density, recombination rate and absorption in the underlyingD andE regions.     

Single quartz grain electron spin resonance (ESR) dating of a contemporary desert surface deposit,Eastern Desert,Egypt

Signal resetting by sunlight prior to burial is a crucial assumption in electron spin resonance (ESR) dating of sediments. This resetting process is expected to be completed to a greater extent in arid than in fluvial environments. The present paper investigates the natural and artificially irradiated signal intensity of Ti related centres in single quartz grains collected from the desert surface (Eastern Desert, Egypt) in order to test this hypothesis. The results suggest that in most grains both the Ti–Li and Ti–H signal are completely reset to zero. Additive dose curves based on the sum of both Ti centres show an anomaly in the low dose region. Possible causes for this behaviour are briefly discussed. Three fitting procedures are conducted and each of them shows a different palaeodose distribution with a rather large spread in D_E values. It is concluded that similar fossil deposits would be datable by single grain ESR using Q-band measurements of the Ti–Li or Ti–H signals in quartz.     

Effect of stress history on CPT and DMT results in sand

In order to investigate the effect of stress history on in-situ test results in granular sediments, a series of CPTs and DMTs are performed on Busan sand prepared in the calibration chamber. K_D is found to be the most sensitive to the stress history among CPT and DMT measurements. E_D and q_c are observed to be similarly affected by the stress history and, therefore, the E_D–q_c relation appears to be almost independent of the stress history. The K_D–D_R relation established without considering the stress history is likely to overestimate the relative density of OC sand. It is shown that the existence of the pre-stress of the granular sediment can be indirectly recognized by an estimation of the relative density larger than 100% when using the K_D–σ_v′–D_R relation suggested for NC sand. Although q_c/σ_v′–K_D/K₀ and E_D/σ_v′–K_D/K₀ relations are heavily influenced by the stress history, q_c/σ_m′–K_D/K₀ and E_D/σ_m′–K_D/K₀ relations are observed to be independent of the stress history. Based on these relations, charts to evaluate the K₀ value from q_c and/or DMT indices are developed for both NC and OC sands. The design chart based on E_D/σ_m′–K_D/K₀ and E_D/σ_v′–K_D/K₀ relations is expected to be practically useful as the usage of this chart requires only DMT indices. The developed design charts are applicable to Busan sand but different sets of equations and charts may be developed for other sands.     

Daily variations ofE andF region drifts over Tiruchirapalli

Daily variations of the E-W and N-S components of ionospheric drifts, measured using closely spaced receiver method over Tiruchirapalli near magnetic equator, are described for the periods 1973–75 forE region and 1974–75 forF region. N-S component is not observed except for a few occasions during summer months for theE region. E-W component is generally eastward during night hours and westward during day hours. There is a large day-to-day variability in the magnitude as well as in the evening reversal time. Daily variations primarily consist of the diurnal component with average amplitude of about 90 m/sec forF region and of about 80 m/sec forE region. The drift speeds are found to decrease with magnetic activity. It is concluded that the abnormal electrojet region extends upto north of Tiruchirapalli in the Indian zone and drifts here can be used as a monitor of electric field.     

Source dynamic parameters of four Greek earthquakes and a possible correlation with the lead-times of their precursor seismic electric signals

Since 1982, eighteen telemetric stations in Greece have continuously been recording variations in the telluric field. Transient changes of the telluric field, called seismic electric signals, SES, have been observed simultaneously at some stations from several hours to several days before an earthquake. The lead-time, Δt, of the SES, which is the time difference between the occurrence of the earthquake and the SES, varies between 6 h and 4 days.Four large earthquakes (M = 5.3–6.4) which occurred in 1983 in the Cephalonia region in Greece, showed clear SES with lead-times falling into two groups (I and II) of several hours and a few days respectively.For the four events, we studied P-wave spectra of the UME Swedish seismological station, at a teleseismic distance of 26°. Both short- and long-period instruments were employed. Brune's model (1970) was used to calculate source dimensions and relative values of other source dynamic parameters.Two groups of high and low stress-drop were found. Events with lead-times of group I show high stress-drop, while events with lead-times of group II show low stress-drop. The relative values of stress-drop differ by a factor of 4 between the two groups (high and low) while within each group they exhibit only a small scatter.The largest relative seismic moment, M₀, is found for the largest event. The three other events with comparable magnitudes have similar seismic moments. The same relation was found for the radiated energy, E_s.     

Experimental determination of Ni diffusion coefficients in olivine and their dependence on temperature, composition, oxygen fugacity, and crystallographic orientation

Diffusion couple experiments were carried out with San Carlos olivine (Fo₉₀) and NiFe alloys (Ni₁₀₀, Ni₉₇Fe₃, Ni₉₀Fe₁₀) or other olivine compositions (Fo₁₀₀, Fo₂₅) in order to determine the dependence on temperature, oxygen fugacity, composition and crystallographic orientation of Ni diffusion coefficient (D_Ni) in olivine. Experiments at 1 atmosphere total pressure cover a temperature range of 900-1445°C with run durations from 48 to 2155 h at different oxygen fugacities. In an Arrhenius plot the best fit for all data for Fo₉₀ yields an activation energy (E_D) of 220 ± 14 kJ/mol and an fO₂ dependence of (1/4.25)·Δ log fO₂ = Δ log D_Ni. The relationship between diffusion coefficients along different crystallographic axes at 1200°C is given by D_[001] ≈ 6·D_[100] ≈ 6·D_[010]. D_Ni depends strongly on the major element (i.e. Fe/Mg) composition of olivine and decreases by about 1 order of magnitude as the olivine composition changes from Fo₃₅ to Fo₉₀. Thus, experimental investigations in Fe-free systems cannot be applied to natural samples. For calculation of residence times or cooling rates the present Ni data yield shorter timescales compared to those obtained using diffusion data published until now.In addition to Ni diffusion coefficients, Fe-Mg, Mn and Ca diffusion data were obtained from some of the same diffusion couples (Fo₉₀-Fo₁₀₀). It is found that the activation energies, E_D[Ni] ≅ E_D[Fe-Mg] ≅ E_D[Mn] ≤ E_D[Ca]. All diffusion coefficients are strongly dependent on the major element composition of olivine.     

Solar zenith angle and frequency dependence of ionosphericD-region absorption

In this paper, the results of a series of extensive measurements of multifrequency radio wave absorption in theD-region of the ionosphere during the epoch of the minium period of the solar cycle are presented. Experimental results for Udaipur, a low latitude station (24°35′N) are compared with the theoretically expected results. It is found that the experimental values of frequency indexm and cos χ indexn agree well with those obtained theoretically. The mean values ofm andn for the whole period of observation are found to be 1·76 and 1·4 respectively. The seasonal variation of the values ofm andn is also discussed.     

Argon retention properties of silicate glasses and implications for <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar age and noble gas diffusion studies

Sized aggregates of glasses (47–84 wt% SiO₂) were fused from igneous-derived cohesive fault rock and igneous rock, and step-heated from ~400 to >1,200 °C to obtain their ³⁹Ar diffusion properties (average E=33,400 cal mol^?1; D _o=4.63×10^?3 cm² s^?1). At T<~1,000 °C, glasses containing <~69 wt% SiO₂ and abundant network-forming cations (Ca, Fe, Mg) reveal moderate to strong non-linear increases in D and E, reflecting structural modifications as the solid transitions to melt. Extrapolation of these Arrhenius properties down to typical geologic T-t conditions could result in a 1.5 log₁₀ unit underestimation in the diffusion rate of Ar in similar materials. Numerical simulations based upon the diffusion results caution that some common geologic glasses will likely yield ⁴⁰Ar/³⁹Ar cooling ages rather than formation ages. However, if cooling rates are sufficiently high, ambient temperatures are sufficiently low (e.g., <65–175 °C), and coarse particles (e.g., radius (r) >~1 mm) are analyzed, glasses with compositions similar to ours may preserve their formation ages.     

Ground water colloid properties from the Bangombé system

The concentration and the role of colloids in the transport of elements in the vicinity of a fossil reactor at Bangombé, Gabon, were assessed. Colloid sampling was conducted in seven boreholes around and in the extinguished natural reactor. The ground waters are of Na–Mg–Ca–HCO₃ type, with variable salinities, pH 4.6–6.8 and anaerobic Eh values. Filtered ground water and colloid samples were taken from the reactor and the surroundings. Filtered fluids and colloid samples collected on membranes and resuspended in solution were analysed by ICP-MS and ICP-AES in order to examine the element association in the colloid phase within the size range 3000 to 400 to 50 nm. The colloid concentrations for the size 400 to 50 nm range from 80 to 300 ng ml⁻¹. They consist of silica particles associated with ferrihydrite coated with organics. Trace element results show that metals including Pb, Sc, Y, La, Ce, Pr, Nd, Bi, Th and U are associated to various degrees with the colloid phase. The distribution ratios of these trace elements between the water and the colloid phase (Kp) were experimentally determined. The high Pb distribution ratios of 10⁺⁷ ml g⁻¹ are specifically discussed. Values range from 10⁺⁶ to 10⁺⁵ ml g⁻¹for the trivalent elements (Sc, Y, La, Ce, … , Bi). For uranium, a Kp of the order of 10⁺⁵ ml g⁻¹ may be calculated and compared with data gained using the surface complexation model. These Kp values suggest that the uranium is partially sorbed or associated with ground water colloids. Measurements from the reactor zone show that about 2–4% of the uranium is associated with the colloid phase, which contributes partially to the uranium transport. The rather low colloid concentrations are due to the relatively high concentrations of Ca, Mg and Na in these quasi-neutral waters. These soluble elements contribute to the attachment of the colloids, restricting their transport. This indicates that the colloid phase may not be an important transport medium for the radionuclides in the Bangombé system if their association is reversible. The Bangombé colloid results are compared with those studied for other systems.     

The 1983, M 5.9 earthquake of Heze,Shandong Province,with its short-term and imminent precursory phenomena

An earthquake (M = 5.9) occurred on November 7, 1983 in the Heze area, Shandong Province (35°17′ N, 115°17∃, H = 12 km). This earthquake belongs to the isolated type of earthquakes. There were no foreshocks; the aftershocks were few in number with their energy decreasing quickly.Within the area surrounding the main shock and up to about 200 km from the epicenter, several types of short-term and imminent anomalies were observed. The major characteristics of the anomalies are as follows:The short-term and imminent anomalies are relatively few in number. The maximum radius of the area where the anomalies occur is about 150–200 km from the epicenter. The time durations of what have been called short-term and imminent anomalies here are small, being

• 1.(1) from 10–20 days to 3–4 months and
• 2.(2) from 1–2 hours to 2–3 days, respectively. The premonitory information was scanty.

Finally, the procedure to recognize the indications of a moderate earthquake is discussed.     

Analytical methods for measuring the parameters of interstellar gas using methanol observations

The excitation of methanol in the absence of external radiation is analyzed, and LTE methods for probing interstellar gas considered. It is shown that rotation diagrams correctly estimate the gas kinetic temperature only if they are constructed using lines whose upper levels are located in the same K-ladders, such as the J₀?J_?1E lines at 157 GHz, the J₁?J₀E lines at 165 GHz, and the J₂?J₁E lines at 25 GHz. The gas density must be no less than 10⁷ cm^?3. Rotation diagrams constructed from lines with different K values for their upper levels (e.g., 2_K?1_K at 96 GHz, 3_K?2_K at 145 GHz, 5_K?4_K at 241 GHz) significantly underestimate the temperature, but enable estimation of the density. In addition, diagrams based on the 2_K?1_K lines can be used to estimate the methanol column density within a factor of about two to five. It is suggested that rotation diagrams should be used in the following manner. First, two rotation diagrams should be constructed, one from the lines at 96, 145, or 241 GHz, and another from the lines at 157, 165, or 25 GHz. The former diagram is used to estimate the gas density. If the density is about 10⁷ cm^?3 or higher, the latter diagram reproduces the temperature fairly well. If the density is around 10⁶ cm^?3, the temperature obtained from the latter diagram should be multiplied by a factor of 1.5–2. If the density is about 10⁵ cm^?3 or lower, then the latter diagram yields a temperature that is lower than the kinetic temperature by a factor of three or more, and should be used only as a lower limit for the kinetic temperature. The errors in the methanol column density determined from the integrated intensity of a single line can be more than an order of magnitude, even when the gas temperature is well known. However, if the J₀?(J ? 1)₀E lines, as well as the J₁?(J ? 1)₁A⁺ or A^? lines are used, the relative error in the column density is no more than a factor of a few.