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1.
Sized fractions of x = 0.6, 0.4, 0.2 and 0.0 titanomagnetites were studied with a vibration magnetometer. In the course particles (d > 150 μm), no compositional dependence of hysteresis parameters was found. HC was less than 50 Oe, HR/HC > 4 and JR/JS < 10?2, reflecting multi-domain behaviour. In contrast, fine particles (d ? 0.1 μm) revealed systematic grain-size dependence of parameters with coercive force as high as 2,000 Oe in x = 0.6 titanomagnetite. Grain-size dependence studies revealed broad transition sizes for the onset of true multi-domain behaviour depending upon which factor is chosen. In magnetite it varies from 10 to 20 μm. The experimental critical size for single-domain behaviour for magnetite is about 0.1 μm and for x = 0.6 titanomagnetite 1–2 μm.  相似文献   

2.
Methods for determining the Curie temperature (Tc) of titanomaghemites from experimental saturation magnetization-temperature (Js-T) data are reviewed.Js-T curves for many submarine basalts and synthetic titanomaghemites are irreversible and determining Curie temperatures from these curves is not a straightforward procedure. Subsequently, differences of sometimes over 100°C in the values ofTc may result just from the method of calculation. Two methods for determiningTc will be discussed: (1) the graphical method, and (2) the extrapolation method. The graphical method is the most common method employed for determining Curie temperatures of submarine basalts and synthetic titanomaghemites. The extrapolation method based on the quantum mechanical and thermodynamic aspects of the temperature variation of saturation magnetization nearTc, although not new to solid state physics, has not been used for estimating Curie temperatures of submarine basalts. The extrapolation method is more objective than the graphical method and uses the actual magnetization data in estimatingTc.  相似文献   

3.
Fine suspended materials in the particle-size range1 < r < 6 μm (r, equivalent sphere radius) from the equatorial North Atlantic, between the ocean surface and greater depths (30–5100 m), can be consistently described by a size-distribution relationshipdN/dr = Ar?b, where the parametersA andb are independent ofr. The shape of the particle-size distribution is essentially constant and independent of depth, as reflected in the values of the logarithmic slope of the size distributionb = 4.0 ± 0.3. The particle-number and mass concentration, however, decrease strongly with depth, most of the decrease taking place in the surface layer 200 m deep. In the surface layer, mass concentration decreases exponentially with the half-concentration depthz1/2 ? 60m; in the deep layer (200–5000 m),z1/2 ? 1000m. The computed removal half-lives of the particulate material are0.8 ± 0.6yr in the surface layer, and60 ± 20yr in the deep layer, both half-lives being considerably shorter than Stokes settling residence times. The fast turnover or removal rate in the surface layer is compatible with the rates of zooplankton growth and carbon assimilation.  相似文献   

4.
Dredged rocks from an area of about 15 km2 within the inner floor and on the adjacent walls of the Rift Valley were collected. Based on petrographic and chemical data, four types of basaltic rocks were recognized: (1) picritic basalts with olivine xenocrysts, TiO2 < 0.6%, K2O < 0.1%, (2) olivine basalts with olivine megacrysts, TiO2 = 0.8–1.5%,K2O = 0.1–0.2%, (3) highly phyric and moderately phyric plagioclase basalts with megacrystic plagioclase, TiO2 < 1.3%, K2O < 0.3%, and (4) pyroxene basalts with pyroxene > plagioclase, TiO2 = 0.8–1%,K2O = 0.2–0.4%. The Cr and Ni having high partition coefficients show different variation trends for each type of rock and their values decrease continuously as crystallization proceeds within each type of basalt. It is speculated that two different magmas have given rise to the above-mentioned rocks. One has yielded the picritic basalts and subsequently the olivine basalts after a separation of the olivine cumulates; the other gave rise to the plagioclase basalts.  相似文献   

5.
Systematic magnetic and crystallographic studies were made on 57 titanomaghemite samples produced from sintered titanomagnetites with x values of 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0. Curie temperature and lattice parameter values are often significantly different from results of previous studies (Ozima and Sakamoto, 1971; Readman and O'Reilly, 1972; Nishitani, 1979), particularly for x values of 0.4 and 0.6. Other important results are: (1) Oxidation of titanomagnetite is mainly a function of temperature. Atmosphere and Ti content have little influence. (2) Progressive oxidation of homogeneous titanomaghemites can take place in the presence of a rhombohedral phase. The amount of rhombohedral phase produced during oxidation increases with increasing temperature and (less conclusively) with decreasing Ti content. (3) Saturation magnetization measurements at low temperatures show both P- and Q-type ferrimagnetic behavior in titanomaghemites, and also show the Verwey (?) transition in titanomaghemites with composition x=0.0. (4) The temperature of spinel inversion increases with degree of oxidation. Slightly oxidized samples invert near 300°C; for samples with z > 0.8 the inversion temperature is above 450°C. This last result, although neither expected nor understood, is supported by results of thermomagnetic studies on some oceanic basalts.  相似文献   

6.
A suite of synthetic titanomagnetites were prepared with compositions Fe2.6?δTi0.4AlδO4 and Fe2.4?δTi0.6AlδO4 (δ = 0, 0.1, 0.2 in both cases). Ball-milling of the synthesized samples produced material in the magnetic monodomain state as indicated by hysteresis loops and the Lowrie-Fuller test. The coercive force of the specimens depends on the Al concentration and lies in the range 1–2 kOe. The TRM induced in the samples is correspondingly “hard”. The low-field (0–1 Oe) TRM acquisition curve is linear. The higher field TRM-H curve is not in agreement with either monodomain or two-domain theoretical models.  相似文献   

7.
Motivated by the high degree of correlation between the variable parts of the magnetic and gravitational potentials of the Earth discovered by Hide and Malin (using a harmonic analysis approach and utilizing the geomagnetic data) when one field is suitably displaced relative to the other, Moffatt and Dillon (1976) studied a simple planar model in an attempt to find a quantitative explanation for the suggestion that this high degree of correlation may be due to the influences produced by bumps on the core-mantle interface. Moffatt and Dillon assumed that the core-mantle interface was z = η(x) where |?η/?χ| ? 1 and such that in the core [z < η(x)] a uniform flow (U0, 0, 0) prevails in the presence of a uniform ‘toroidal’ field (B0, 0, 0); (here z is the vertical coordinate and x is the eastward distance). The whole system rotates uniformly about the vertical with angular velocity Ω. The present work extends the model discussed by Moffatt and Dillon to include a horizontal component of angular velocity ΩH and a uniform small poloidal field Bp. In addition, the uniform toroidal field is here replaced by one which vanishes everywhere in the mantle and increases linearly, from zero on the interface, with z. It is shown that the presence of ΩH and Bp, together with the present choice of toroidal magnetic field, has a profound effect both on the correlation between the variable parts of the magnetic and gravitational fields of the Earth, and on how far the disturbances caused by the topography of the interface [which is necessarily three-dimensional i.e. z = η(x, y) here] can penetrate into the liquid core. In particular it is found that the highest value of the correlation function is +0.79 which corresponds to a situation in which the magnetic potential is displaced both latitudinally and longitudinally relative to the gravitational potential.  相似文献   

8.
K/Rb and (87Sr/86Sr)0 ratios were measured for 14 submarine basalts dredged from seamounts in the Pacific Ocean. The K/Rb ranges from 200 to 700, which is significantly lower than that of oceanic ridge tholeiites. Petrographic examination and the low value of K/Rb indicate that seamount basalts are alkaline.  相似文献   

9.
This work investigated an interrelationship between the monthly means of time derivatives of horizontal geomagnetic field, dH/dt, sunspot number, R z , and aa index for the period of substorms (from ?90 to ?1800 nT) during the years 1990–2009. A total of 232 substorms were identified during the period of study. The time derivative of horizontal geomagnetic field, dH/dt, used as a proxy for geomagnetically induced current (GIC) exhibited high positive correlation with sunspot number (0.86) and aa index (0.8998). The obtained geomagnetic activity is in 92.665% explicable by the combined effect of sunspot number and aa index. The distribution of substorms as a function of years gives a strong support for the existence of geomagnetic activity increases, which implies that as the sunspot number increases the base level of geomagnetic activity increases too.  相似文献   

10.
We present the distribution of226Ra in eight vertical profiles from the eastern Pacific. The profiles are located along a meridional trend near 125°W, from 43°S to 29°N. Surface226Ra concentrations are about 7 dpm/100 kg, except for the two stations south of 30°S where the higher values are due to the Antarctic influence. Deep waters show a distinctive south-to-north increase in the226Ra content, from about 26 to 41 dpm/100 kg near the bottom. Unlike in the Atlantic and Antarctic Oceans, the effect of226Ra injection from bottom sediments is clearly discernible in the area. The presence of this primary226Ra can be traced up to at least 1–1.5 km above the ocean floor, making this part of the sea bed among the strongest source regions for the oceanic226Ra. Numerical solutions of a two-dimensional vertical advection-diffusion model applied to the deep (1.2–4 km)226Ra data give the following set of best fits: upwelling velocity(Vz) = 3.5m/yr, vertical eddy diffusivity(Kz) = 0.6cm2/s, horizontal (north-south) eddy diffusivity(Ky) = 1 × 107cm2/s, and water-column regeneration flux of226Ra(J) = 3.3 × 10?5dpmkg?1yr?1 as an upper limit. These parametric values are in general agreement with one-dimensional (vertical) model fits for the Ra-Ba system. However, consideration of226Ra balance leads us to suspect the appropriateness of describing the vertical exchange processes in the eastern Pacific with constantVz and Kz. If future modeling is attempted, it may be preferable to treat the area as a diffusion-dominant mixing regime with depth-dependent diffusivities.  相似文献   

11.
The droplet size distribution of dispersed phase (oil and/or gas) in submerged buoyant jets was addressed in this work using a numerical model, VDROP-J. A brief literature review on jets and plumes allows the development of average equations for the change of jet velocity, dilution, and mixing energy as function of distance from the orifice. The model VDROP-J was then calibrated to jets emanating from orifices ranging in diameter, D, from 0.5 mm to 0.12 m, and in cross-section average jet velocity at the orifice ranging from 1.5 m/s to 27 m/s. The d50/D obtained from the model (where d50 is the volume median diameter of droplets) correlated very well with data, with an R2 = 0.99. Finally, the VDROP-J model was used to predict the droplet size distribution from Deepwater Horizon blowouts. The droplet size distribution from the blowout is of great importance to the fate and transport of the spilled oil in marine environment.  相似文献   

12.
Geomagnetic pulsation in the Pc3-4 bands have been studied at high Antarctic latitudes during the local summer. The statistical relation between the occurrence probability of Pc3 and Pc4 pulsations and the solar wind (SW) and IMF parameters has been revealed by verifying the hypothesis that an indication is identical in two distributions. Different dependences of the occurrence probability of high-latitude Pc3 and Pc4 pulsations on the IMF value and orientation and SW density and velocity have been found out. It has been indicated that these dependences remain unchanged in the range of geomagnetic latitudes from 66° to 87°. It has been established that the Pc3 observation probability at small (20°–50°) IMF cone angles (θ = cos?1(B x/|B|)) is a factor of 1.5 higher than the average statistical probability and depends on the IMF value, which confirms the hypothesis that the Pc3 source is the turbulent region upstream of the magnetospheric quasiparallel low shock. On the contrary, the probability of occurrence of Pc4 weakly depends on the IMF cone angle and is maximal at θ ～ 0° and ～90°. With increasing negative B z values, the generation probability increases in the Pc4 band and tends to decrease in the Pc3 band. It has been found out for the first time that the dependence of the Pc4 occurrence probability on the IMF clock angle (? = tan?2 (B/B z) is identical in the regions of projections of closed and open field lines, whereas this dependence is different for Pc3. In the region of projections of closed field lines, the Pc3 occurrence probability increases at B z < 0 and B y > 0 (the condition under which the cusp shifts on the dawn side) and at B y < 0 and B z > 0 (which is typical of the formation of the low-latitude boundary plasma sheet). In the region of projections of open field lines such a probability increases at B y < 0 and B z < 0 (which results in the formation of the high-latitude boundary plasma sheet). Based on the discovered regularities, the conclusion has been made that the sources of generation of high-latitude Pc3 and Pc4 pulsations are different.  相似文献   

13.
The STARE system (Scandinavian Twin Auroral Radar Experiment) provides estimates of electron drift velocities, and hence also of the electric field in the high-latitude E-region ionosphere between 65 and 70 degrees latitude. The occurrence of drift velocities larger than about 400 m/s (equivalent to an electric field of 20 mV/m) have been correlated with the magnitude of the Interplanetary Magnetic Field (IMF) components Bz and By at all local times. Observation days have been considered during which both southward (Bz<0) and northward (Bz>0) IMF occurred. The occurrence of electric fields larger than 20 mV/m increases with increases in Bz magnitudes when Bz<0. It is found that the effects of southward IMF continue for some time following the northward turnings of the IMF. In order to eliminate such residual effects for Bz<0, we have, in the second part of the study, considered those days which were characterized by a pure northward IMF. The occurrence is considerably lower during times when Bz>0, than during those when Bz is negative. These results are related to the expansion and contraction of the auroral oval. The different percentage occurrences of large electric field for By>0 and By<0 components of the IMF during times when Bz>0, clearly display a dawn-dusk asymmetry of plasma flow in the ionosphere. The effects of the time-varying solar-wind speed, density, IMF fluctuations, and magnetospheric substorms on the occurrence of auroral-backscatter observations are also discussed.  相似文献   

14.
Controlling factors for the occurrence of littoral macrophyte species were investigated in Lipno Reservoir (area: 46.5 km2; zmean: 6.6 m; zmax: 22 m; water residence time: 0.6 yr), a dam impoundment with moderately fluctuating water level (amplitude up to 4 m) which is used for hydropower and downstream flow augmentation. The options of supporting littoral macrophyte growth for improving the reservoir's ecological potential were evaluated according to the European Water Framework Directive's definitions. Macrophytes were examined at 115 sites, each 50 m long, along the whole reservoir perimeter at regular 1 km intervals. Sites were surveyed for their phytocoenology, shore morphometry, pedological characteristics of substrate, transparency of water, and anthropogenic impacts. Most of the sites were characterised by a wide eulittoral zone with a tenuous cover of terrestrial hydrophilic, amphibious, and/or emergent macrophytes and a low proportion of silt, clay, and organic fractions in the substrate. Infralittoral submerged and floating-leaved macrophytes were restricted to a few sites within the mouths of the main and side tributaries where transparency was maintained by clear inflow water independent of reservoir pool fluctuations. Water transparency was low (1-2 m) compared to annual changes of water level (2 to >3 m). Multivariate statistical analysis (DCA, CCA) confirmed relationships between the occurrence of macrophyte species and morphological and substrate characteristics of the shore. Improvement of macrophyte cover and establishment of vital infralittoral zones requires improvements in water transparency and changes in reservoir operation, i.e., limiting the range of water level fluctuation to less than ca. 1 m.  相似文献   

15.
Determining surface precipitation phase is required to properly correct precipitation gage data for wind effects, to determine the hydrologic response to a precipitation event, and for hydrologic modeling when rain will be treated differently from snow. In this paper we present a comparison of several methods for determining precipitation phase using 12 years of hourly precipitation, weather and snow data from a long-term measurement site at Reynolds Mountain East (RME), a headwater catchment within the Reynolds Creek Experimental Watershed (RCEW), in the Owyhee Mountains of Idaho, USA. Methods are based on thresholds of (1) air temperature (Ta) at 0 °C, (2) dual Ta threshold, −1 to 3 °C, (3) dewpoint temperature (Td) at 0 °C, and (4) wet bulb temperature (Tw) at 0 °C. The comparison shows that at the RME Grove site, the dual threshold approach predicts too much snow, while Ta, Td and Tw are generally similar predicting equivalent snow volumes over the 12 year-period indicating that during storms the cloud level is at or close to the surface at this location. To scale up the evaluation of these methods we evaluate them across a 380 m elevation range in RCEW during a large mixed-phase storm event. The event began as snow at all elevations and over the course of 4 h transitioned to rain at the lowest through highest elevations. Using 15-minute measurements of precipitation, changes in snow depth (zs), Ta, Td and Tw, at seven sites through this elevation range, we found precipitation phase linked to the during-storm surface humidity. By measuring humidity along an elevation gradient during the storm we are able to track changes in Td to reliably estimate precipitation phase and effectively track the elevation of the rain/snow transition during the event.  相似文献   

16.
A well-defined relationship has been identified between the belts, zones and areas of higher seismicity in the Russian Far East on the one hand and, on the other, maxima in the gradient of surface density of spherical sources that give rise to gravity anomalies (μ z ) equivalent to quasi-isometric density inhomogeneities in the lower crust and upper mantle. The highest epicenter density is observed in the marginal parts of maxima of the μ z parameter, these parts being interpreted as boundaries of rigid (sialic metamorphic and oceanic mafic) tectonic blocks and plates. The overwhelming majority of crustal seismicity is spatially related to uplifts of the asthenospheric layer reflected in the minima of the μ z parameter, and is concentrated in uplifted crustal blocks. In addition to the linear type of seismicity due to deep-seated faults, the crust shows a concentrically zonal type of epicenter location associated with plume-generated central-type features (the Olekma-Stanovoi seismic zone). It is shown that seismic fields can be ranked by the depths of earthquake source zones using 3D models, μ z (x,y,z).  相似文献   

17.
Stoichiometric titanomagnetites Fe3?xTixO4 with compositions between x = 0 (magnetite) and x = 0.72 (a titanomagnetite having a Curie temperature of 60°C) have been synthesised using the double-sintering technique in controlled atmospheres. The quality of these materials was tested by various mineralogical and magnetic measurements. Isolated small multidomain (MD) and pseudo-single-domain (PSD) particles within pores of the bulk material were investigated with respect to their domain structures, and threshold sizes for the transition from the PSD to the SD stage determined for titanomagnetites of various compositions by extrapolation from the domain state of small MD grains. The threshold size was found to be 0.7 and 0.5 μm, respectively, for TM72 (x = 0.72) and TM62 (x = 0.62). The threshold size decreases slightly for smaller x values; however, the experimental data obtained to date are not sufficiently reliable to yield precise results.Preliminary experiments concerning hysteresis loops and TRM generation are also reported.  相似文献   

18.
The correlation discovered by Hide and Malin between the variable parts of the Earth's gravitational field and magnetic field (suitably displaced in longitude) was tentatively and qualitatively explained by them in terms of the influence on both fields of irregularities (or “surface bumps”) at the core-mantle interface. In this paper, a quantitative analysis of this phenomenon is developed, through study of an idealised problem in which conducting fluid occupying the region z < η(x) flows over the surface z = η(x) in the presence of a magnetic field (B0,0,0), the whole system rotating with angular velocity (0,0,Ω). It is assumed that |η′(x)| « 1 so that perturbation methods are applicable. Determination of the magnetic potential in the “mantle” region z < η(x) requires solution of the full hydromagnetic problem in the fluid. It is shown that three wave modes are excited, two of which (for values of the parameters of the problem of geophysical interest) have a boundary layer character. Phase interactions between these modes lead to a shift and a distortion of the magnetic pattern relative to the gravitational pattern. The correlation between the gravitational potential and the magnetic potential (shifted by a distance x0) is determined on the plane z = d (d a? |η|) as a function of x0/d and the curves obtained are qualitatively similar to that based on the observed data; the maximum correlation obtained varies between 0.67 and 1, depending on values of the parameters of the problem, and is about 0.72 for reasonable estimates of these parameters in the geophysical context.  相似文献   

19.
The lake without any outlet (11 ha, 55000 m3, zmax 2,25 m) has a weak thermal stratification with maximum surface temperatures of 32.5 °C. The annual variation of temperature and depth of visibility is unimodal, with the maxima or minima in August. Phytoplankton consists mainly of Cyanophyceae. The primary production determined by the light-dark bottle technique (oxygen method) varies in the annual variation between 0.3… 0.5 g m?2 d?1 C (winter) and 3.4… 4.6 g m?2 d?1 C (summer); as the annual means of 1975 and 1976 there were found 1.9 and 2.4 g m?2 d?1 C, resp., gross production at a utilization of 0.42… 2.85% of the radiation energy. The chemism is a well-buffered hydrogen-carbonate water (pH 8.1… 9.0) with 74… 90 mg/1 Na and 20.5… 31.5 mg/1 K and with a good nutrient supply (20… 40 μg/1 PO4—P and 100… 240 μg/1 NO3—N) at the same time.  相似文献   

20.
We report normalized AF demagnetization curves of anhysteretic remanences (ARM's) produced by 1-, 10- and 40-Oe steady fields and of saturation isothermal remanence (IRMs) in a suite of dispersed, unannealed magnetite powders with median sizes of 2, 4, 6, 10 and 14 μm (pseudo-single-domain or PSD size range) and 100 μm (multidomain or MD size). Interpreted in the light of the domain structure test first proposed by Lowrie and Fuller [12], the relative stability trend of curves for the 2 μm sample is of single-domain (SD) type, the 1-Oe ARM being most resistant to demagnetization followed by the 10-Oe and 40-Oe ARM's and IRMs. For the 100-μm sample, the trend is exactly reversed and is of MD-type. In the 4–14 μm samples, hitherto undescribed transitional trends between SD-type and MD-type occur. At 6 μm, 1-Oe, 10-Oe and 40-Oe ARM's preserve an SD-type trend but for all AF's > 75 Oe, IRMs is more resistant than any of these remanences. At 10 μm, this trend is unmistakable, and only at 14 μm do the 1-Oe, 10-Oe and 40-Oe ARM curves merge. We conclude (1) that the Lowrie-Fuller test distinguishes between small MD grains enhanced by PSD remanence and large MD grains lacking PSD remanence, rather than between SD and MD structures per se, and (2) that in the PSD transition region from 6 to 14 μm in magnetite, IRMs changes over to MD-type relative stability around 6 μm, whereas 10-Oe and 40-Oe ARM's achieve an MD-type trend around 14 μm, in accord with the predicted field dependence of the PSD threshold size.Our theoretical interpretation assumes that the intrinsic (internal field) coercive force spectra of weak-field and strong-field remanences are identical but that the observed (external field) spectrum is shifted to lower fields as a result of the internal demagnetizing field — NJr of the remanence Jr. The effect is slight for weak-field Jr's but substantial for IRMs. Since all coercivities, high as well as low, are shifted, the result of the Lowrie-Fuller test is determined simply by the shape of the intrinsic coercivity spectrum or the corresponding AF demagnetization curve. Depending on the model of self-demagnetization used, either subexponential or sublinear AF decay curves of weak-field remanence will automatically lead to an MD-type trend, whereas by either model the decay curves that characterize SD and PSD remanences (decaying slowly initially and then more rapidly) will always produce and SD-type trend.  相似文献   

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