Lateral dynamic analysis and classification of barotropic tidal inlets

The dynamical balances at shallow tidal inlets are highly nonlinear, and can vary substantially over sub-kilometer scales. In this study, barotropic dynamics are examined with numerical experiments on a series of idealized inlets with differing inlet widths and lengths. Circulation and elevation fields obtained from fully nonlinear depth-integrated circulation models are used to reconstruct the contribution of each term in the momentum equations. Momentum terms are rotated into a streamline coordinate system to simplify interpretation of the dynamics. Spatial patterns in momentum reveal that the lateral balances at inlets can vary from nearly geostrophic to strongly cyclostrophic. Marked dynamical differences are seen between inlets with different lengths and widths. Inlet regions of geostrophic or cyclostrophic balances can be predicted using two dimensionless parameters, the dynamic length L^* and dynamic width W^*. A classification scheme is proposed using L^* and W^* to compare the idealized inlets analyzed here with inlets from 20 previous studies. Four distinct inlet types are identified and discussed.     

Substitute conductors for electromagnetic response estimates

Various concepts exist to define substitute conductors for empirical response estimates at singular frequencies: Chapman's shell-core model, the Cagniard-Tikhonov apparent resistivity, the Niblett-Bostick and Molochnov transformation, thep ^* —z ^* transformation. They are all interrelated and assign comparable resistivities to the substitute conductor at a given frequency. Applications to synthetic response data of plane and spherical conductors show under which conditions these substitutions come closest to the model and which influence of source dimensions and Earth's sphericity can be expected.p ^* —z ^* transformed global response data forS andDst variations demonstrate how substitute conductors may serve as useful guides in inverse procedures.     

Melt segregation inside a partially molten zone: Theory,numerical models and implications

For the problem of matrix compaction and melt segregation a general mush continuity equation is derived, which explicitly expresses the coupling between the melt percolation and the inelastic matrix deformation and closes the governing equation set. Besides, a general equation is obtained, which describes the change in the volume of pore space due to all the possible reasons (inelastic matrix deformation, the phase transitions, and the advection of porosity by the matrix flow). The features of the isothermal melt segregation inside a partially molten zone are demonstrated using one-dimensional (1D) numerical solutions. It follows from the solutions that the pattern and the characteristic time of the melt segregation inside a partially molten zone of thickness L are controlled by the segregation parameter γ _c = (L/δ _c )², where the compaction length δ _c = k(φ₀)η/(φ₀μ) depends on the permeability, k, the value of characteristic porosity, φ₀, and the viscosities of the matrix, η, and melt, μ. The solutions demonstrate that at any value of γ _c , layers that are highly enriched in melt compared to the maximum initial porosity are formed in the upper part of the zone. At the same time, the evolution of the system and the segregation time differ considerably in the limits of γ _c ≪ γ* and γ _c ≫ γ*, where γ* depends on the boundary and initial conditions of the problem, and γ* is about 80 for the problem of melt segregation inside a partially molten zone with the maximum in the initial melt distribution located in the middle of the zone. At γ _c ≪ γ*, which corresponds to the segregation of low-viscosity ultrabasic melts (kimberlites, carbonatites), all the melt accumulates to the roof of the zone, and the segregation time does not depend on the matrix permeability and melt viscosity and decreases with an increase in the thickness of the zone as L ⁻¹. The latter can be the reason for the formation of clusters of the same age and same composition eruptions characteristic of the kimberlite provinces. In the opposite limiting case, γ _c ≫ γ*, the segregation time does not depend on the matrix viscosity and scales as L with a wave sequence forming in the upper part of the zone, which, probably, elucidates the origin of the rhythmical layering of the large tholeiitic basalt plutons.     

大型浅水湖泊水体对流混合速率分析

湖泊水体的对流混合是最基本的物理过程,其能显著影响湖泊生态系统温室气体等循环,但浅水湖泊水体对流混合的研究鲜有报道.本研究基于太湖(面积2400 km2,平均水深1.9 m)中尺度通量网的原位、高频、连续和多点的观测数据,分析该大型浅水湖泊水体对流混合速率w*的时空特征.结果表明太湖水体w*的均值为2.49 mm/s,因太湖的风速、水温和辐射等物理参数无空间变化,w*也无明显的空间变化.但是研究表明w*呈现显著的昼夜变化和季节变化,且昼夜变化幅度强于季节变化.总体上夜间w*是白天的4倍多,冬季w*(均值1.79 mm/s)明显低于春季(均值2.42 mm/s)、夏季(均值2.91 mm/s)和秋季(均值2.82 mm/s).太湖w*主要受风速和能量收支影响,白天风速是主要驱动因子,夜晚能量收支是主要驱动因子.     

The role of vibrationally excited oxygen and nitrogen in the D and E regions of the ionosphere

In this paper we present the results of a study of the effect of vibrationally excited oxygen, O^* ₂, and nitrogen, N^* ₂, on the electron density, N _e, and the electron temperature, T _e, in the D and E regions. The sources of O^* ₂ are O-atom recombination, the photodissociation of O₃, and the reaction of O₃ with O at D region altitudes. The first calculations of O^* ₂(j) number densities, N _j , are obtained by solving continuity equations for the models of harmonic and anharmonic oscillator energy levels, j=1-22. It is found that day time values of N _j are less than nighttime values. We also show that the photoionization of O^* ₂ (j\geq11) by L_<alpha>-radiation has no influence on the D region N _e . In the nighttime D region the photoionization O^* ₂ (j\geq11) by scattered L _<alpha>-radiation can be a new source of O⁺ ₂. We show that the N^* ₂ and O^* ₂ de-excitation effect on the electron temperature is small in the E region of the ionosphere and cannot explain experimentally observed higher electron temperatures.     

Storm time phase space density radial profiles of energetic electrons for small and large K values: SCATHA results

Measurements of the radial gradient of the phase space density (PSD) at constant first and second invariants provide a test of whether storm time electron acceleration processes are dominated by inward radial transport of electrons or whether other processes must be considered. We used the detailed energetic electron angular and spectral data from the SCATHA satellite to determine the evolution of electron PSD radial profiles through a moderate magnetic storm (2 May 1986; D_st=−95 nT). We compared the changes that occur in the profiles in the storm recovery period to the pre-storm profiles for first invariant values M=200–2500 MeV/G and for K values of 0.055–0.65 Re√G over the L* range of ∼5.2–7.3 Re. The PSD radial profiles showed a range of features from peaked in L* at small K and M during the pre-storm period to those in the late storm recovery phase, that were flat, had negative slopes for small K and had peaks in the L*=5.2–6.5 range for intermediate to large K. There were significant differences in the radial profiles for small and intermediate K values at constant M. For example, during the recovery period the PSD profiles were flat or decreasing for K=0.06 and M>1200 MeV/G, while they were peaked near L*=5.75 for K>0.2. These results imply that radial diffusion is a reasonable explanation of the near-equatorial post-storm PSD enhancements for L*>5.2 for this storm but that either significant electron pitch angle transport, losses, and/or acceleration of off-equatorial mirroring electrons by waves play an important role in the evolution off-equator PSD profiles during the storm recovery.     

Asymptotic regimes in unstable miscible displacements in random porous media

We study two asymptotic regimes of unstable miscible displacements in porous media, in the two limits, where a permeability-modified aspect ratio, R_L=L/H(k_v/k_h)^1/2, becomes large or small, respectively. The first limit is known as transverse (or vertical) equilibrium, the second leads to the problem of non-communicating layers (the Dykstra–Parsons problem). In either case, the problem reduces to the solution of a single integro-differential equation. Although at opposite limits of the parameter R_L, the two regimes coincide in the case of equal viscosities, M=1. By comparison with high-resolution simulation we investigate the validity of these two approximations. The evolution of transverse averages, particularly under viscous fingering conditions, depends on R_L. We investigate the development of a model to describe viscous fingering in weakly heterogeneous porous media under transverse equilibrium conditions, and compare with the various existing empirical models (such as the Koval, Todd–Longstaff and Fayers models).     

Graphical analysis of enthalpy-composition relationships in mixed magmas

Enthalpy-composition diagrams (H^*-X) calculated from existing temperature-composition (T-X) phase diagrams and thermodynamic data provide a simple and effective means for evaluating the enthalpy-temperature effects of magma mixing. If athermal mixing is assumed, adiabatic mixing lines on H^*-X diagrams are straight lines because enthalpy, unlike temperature, is an extensive property of a system. Comparison of binary T-X diagrams with their derivative H^*-X diagrams shows that incorrect predictions can be obtained when T-X diagrams are used to analyze mixing problems.An H^*-X diagram calculated using experimentally determined phase equilibria for anhydrous basalt-rhyolite mixtures predicts that adiabatic mixing of basalt and rhyolite at their respective liquidus temperatures will result in small amounts of crystallization ( < 2 wt.% ). Because the phase equilibria of hydrous basalt-rhyolite mixtures have not yet been determined, an H^*-X diagram for such mixtures cannot be constructed. However, existing hydrous phase equilibria can be used to predict whether adiabatic mixtures of anhydrous basalt and hydrous rhyolite will be super- or subliquidus. Calculations at P_total = 200 MPa show that on an H^*-X diagram a mixing chord drawn between anhydrous basalt and water-saturated rhyolite at their respective liquidus temperatures lies below the enthalpy values calculated for a Paricutin andesite and Mt. St. Helens dacite at their estimated liquidus temperatures. This indicates that the liquidus for mixtures of anhydrous basalt and water-saturated rhyolite is noticeably convex upward, suggesting that larger amounts of crystallization will occur than in the anhydrous case.     

The limits to growth: how large can subaqueous,flow-transverse bedforms ultimately become?

Based on field and experimental evidence, the average initial spacing (seed wavelength) of flow-transverse bedforms (ripples and dunes) appears to lie between 80 and 130 grain diameters (L = 80–130D_mm). Starting with an average initial spacing of L = 100D_mm, subsequent bedform growth proceeds by amalgamation of two successive bedforms, which results in a doubling of the spacing in each step. Geometric principles dictate that the combined volume of two smaller bedforms lacks about 40% of the volume required for a fully developed amalgamated bedform. The missing volume is gained by excavation of the troughs, i.e., by lowering the base level. Where base level lowering is prevented by the presence of a coarse-grained armor layer or hard ground pavement, the larger amalgamated bedform remains sediment starved. In its simplest form, bedform growth proceeds by continuous doubling of the spacing in response to increases in flow velocity, the process being reversible in response to flow decelerations. Bedform growth terminates when the shear velocity (u_*) at the crest reaches the mean settling velocity (w_s) of the sediment. At this point, 40% of the bed material is in suspension, at which point the missing volume can no longer be compensated by trough excavation. In shallow water, maximum bedform size is dictated by the water depth, whereas in deep water, bedforms can potentially grow to their ultimate size. Evaluation of bedform data from deep water settings suggests that the largest two-dimensional, flow-transverse bedforms in terms of grain size (phi) can be approximated by the equations: lnL_max = 13.72–4.03D_phi and lnH_max = 9.95–3.47D_phi for grain sizes <  ~ 0.2 mm (> ~ 2.32 phi), with L and H representing bedform spacing and height in meters and D the grain size in phi. For grain sizes >  ~ 0.2 mm (< ~ 3.23 phi), the corresponding relationships are lnL_max = 6.215–0.69 D_phi and lnH_max = 3.18–0.56D_phi, with notations as before, or in terms of grain diameters in mm: L_max = 5 × 10⁵D_mm.

     

Tracing of Peroxidase Activity in Humic Lake Water

An enzyme assay was developed for studies on peroxidase activities in humic lake water. 3,4-Dimethoxybenzyl alcohol (veratryl alcohol, VeraOH) was used as tracer substrate, and peroxidase (EC 1.11.1.7) activity was measured by high-performance liquid chromatography. The chemical stability of VeraOH and its application as peroxidase substrate was tested under light and dark conditions, different hydrogen peroxide (H₂O₂) concentrations and humic matter contents. VeraOH was stable under low UV radiation at in situ conditions in lake water (<0.010...0.25 kJ m^–2 d^–1), laboratory conditions (<0.05...0.30 kJ m^–2 d^–1), and low (1...100 μM) H₂O₂ concentrations. However, peroxides oxidized VeraOH above 1...10 mM H₂O₂ concentration in sterile Millipore-Q and humic lake water. Dark incubations showed little VeraOH oxidation products. The developed peroxidase assay was tested in the growth medium of Phanerochaete chrysosporium and a bacteria isolate (P.M.D. 20.4.3.1) from mesohumic lake Pääjärvi. Peroxidase activities were also measured in natural microbial communities under standard laboratory and under in situ conditions in humic lake water. Incubation times of about 5 to 12 days were usually needed to record significant (P < 0.05) peroxidase activities, in lake waters. In situ peroxidase activities varied in pelagial surface water (0...0.5 m) on a seasonal scale between 74 nmol L^–1 h^–1 and 273 nmol L^–1 (mean: 176 nmol L^–1 h^–1) and within the water column between 110 nmol L^–1 h^–1 and 800 nmol L^–1 h^–1 (mean: 500 nmol L^–1 h^–1) in polyhumic lake Mekkojärvi.     

A method to estimate the total magnetization direction from a distortion analysis of magnetic anomalies1

Knowledge of the declination and inclination of the total and induced magnetization vectors is normally required for the interpretation and analysis of magnetic anomalies. A new method of estimating the direction of the total magnetization vector of magnetized rocks from magnetic anomalies is proposed. The unknown declination and inclination (D*_T and I*_T) can be found by applying a reduction-to-the-pole operator to the measured anomalies for different couples of total magnetization direction parameters (D_T and I_T) and by observing the variation of the anomaly minimum as a function of both D_T and I*_T.and D*_T are estimated using the maximum of this function. Comparing our method to previous methods, one advantage is that our estimates are not zero-level dependent; furthermore, the method allows inclinations to be well estimated, with the same accuracy as declinations; finally declinations are not underestimated. Our method is applied to a real case and meaningful results are obtained; it is shown that the feasibility of the method is improved by removing the low-frequency components.     

A laboratory study of formative conditions for characteristic ripple patterns associated with a change in wave conditions

A wave‐?ume experiment was conducted to examine the formative condition for three types of distinctive bedforms that emerged through deformation of existing ripples due to waning wave power. They were ripple marks with: (1) a single secondary crest, (2) double secondary crests, and (3) a rounded crest. Data were analysed using two parameters, kh and d₀/λ_*, where k is the wave number, h is the water depth, d₀ is the near‐bottom orbital diameter, and λ_* is the spacing of existing ripples. The former quantity, kh, was employed as a surrogate for the degree of ?ow asymmetry. The result showed that ripples with secondary crests developed under a rather symmetrical ?ow ?eld with kh ? 0·7, if d₀/λ_* ? 1·2, whereas rounded‐crest ripples emerged under asymmetrical ?ow ?eld with kh ? 0·7, if d₀/λ_* ? ?2·9 kh + 3·2. The number of secondary crests, which initially occurred in each trough, was single if d₀/λ_* ? 0·8, or double if d₀/λ_* ? 0·8. Copyright © 2004 John Wiley & Sons, Ltd.     

Estimating ground motions using recorded accelerograms

A procedure for estimating ground motions using recorded accelerograms is described. The premise of the study is the assumption that future ground motions will be similar to those observed for similar site and tectonic situations in the past. Direct techniques for scaling existing accelerograms have been developed, based on relative estimates of local magnitude,M _L . Design events are described deterministically in terms of fault dimension, tectonic setting (stress drop), fault distance, and site conditions. A combination of empirical and theoretical arguments is used to develop relationships betweenM _L and other earthquake magnitude scales. In order to minimize scaling errors due to lack of understanding of the physics of strong ground motion, the procedure employs as few intermediate scaling laws as possible. The procedure conserves a meaningful measure of the uncertainty inherent when predicting ground motions from simple parameterizations of earthquake sources and site conditions.     

Inhibition Concentration of Phenolic Substances under Different Cultivation Conditions. Part I: Phenol Oxidation by Mixed Microbial Population in a Model System

The effects of oxygen supply rate and the presence or absence of nutrients on the kinetics of phenol degradation and oxygen consumption by a mixed microbial population were tested in a model system. The values for the maximum specific rate of phenol degradation (q_Smax), the saturation constant (K_S), and the inhibition concentration (S_CR) were determined for unlimited growth (K_La = 340 h^?1, growth medium) with 1.7 mmol g^?1 h^?1, 65 mg L^?1, and 190 mg L^?1. Under limitation conditions, alterations occur depending on the type of limitation. Nutrient limitations lead to values of 0.8 mmol g^?1 h^?1, 45 mg L^?1, and 160 mg L^?1, and oxygen limitations lead to 1.2 mmol g^?1 h^?1. 30 mg L^?1, and 120 mg L^?1, respectively. The results suggest that with excess oxygen, the rate of phenol degradation was higher and the inhibition effect of phenol was suppressed to some extent. Under the same high oxygen supply rate, the presence of nutrients in the model water significantly supported the phenol degradation rate.     

Particle dislodgement from a flat sand bed by wind

The rate, with respect to area and time, at which grains are dislodged from a sand bed for given wind conditions is an important factor in determining the grain transport rate and the intensity of grain activity in each of the transport modes. The literature of the subject contains little direct information about particle dislodgement. The paper describes a series of experiments in which dyed sand grains, spread on the surface of quartz dune sand in a wind-tunnel, were photographed at five second intervals while the sand was exposed to wind. The data on rate of loss of coloured grains was used, for two of three chosen size fractions, to deduce the dislodgement rate for each size fraction. The variation of this dislodgement rate with shear velocity is shown graphically for values of u_* between 24 cm s^?1 and 50 cm s^?1. Because of the artificial method of distribution of the coloured sand grains, the results should be applied with caution to natural conditions. The interpretation of the observations of dyed grain loss involved the numerical simulation of the process which comprises removal of coloured grains, slightly offset by replenishment as upwind coloured grains settle briefly in the observed zone. An estimation of grain excursion length has to be incorporated in the simulation. This estimation was made by trial, but general corroboration was found from earlier work. Comparisons are made between dislodgement rates obtained thus and rates estimated by Anderson (1986) and by Jensen and Sorensen (1986). Reasonable agreement with the latter is found in the u_* range 30 cm s^?1.     

LIMITING DEPTH OF DETECTION IN LINE ELECTRODE SYSTEMS*

An infinitely resistive/conductive horizontal bed is assumed in an otherwise homogeneous and isotropic half space. Schlumberger, three electrode, and unipole profiles are computed at right angles to the strike of the bed. The Schwarz-Christoffel method of conformal transformation and numerical methods of solving non-linear differential equations are used to solve the boundary value problem. It is observed that (i) the three electrode system is the most sensitive gradient electrode configurations for electrical profiling, (ii) the apparent resistivities for Schlumberger, three electrode, and unipole methods become maximum when the depth of the bed is 0.06 L, 0.1 L, and 0.055 L for a resistive bed and minimum when depths are 0.085 L, 0.04 L-0.02 L and indeterminate for conductive beds, respectively, (iii) the limiting depths of detection (defined in the text) by Schlumberger, three electrode, and unipole configurations are respectively 0.9 L, 6.6 L and 2.0 L for resistive beds and 0.58 L, 1.17 L and 1.5 L for conductive beds. The electrode separation L is the distance between the two farthest active electrodes.     

Occurrence of an Algal Mass Development in an Acidic (pH 2.5):, Iron and Aluminium‐rich Coal Mining Pond

A bloom of Chlamydomonas botryopara was observed in an extremely acid coal mining pond (pH 2.5) with high concentrations of iron and aluminium (1160...3760 mg L^–1 Fe, 133...387 mg L^–1 Al). Cell density of algae was counted as 6.45 · 10⁶ mL^–1 corresponding to 700 mg L^–1 fresh weight and 2660 μg L^–1 chlorophyll‐a. The nutrient concentrations were 3.5 mg L^–1 soluble reactive phosphorus and 0.15 mg L^–1 dissolved inorganic nitrogen. This observation supports the hypothesis that a low nutrient availability rather than extreme conditions (e.g. high acidity and low pH) limit the development of phytoplankton in many acidified lakes.     

FUNDAMENTAL FUNCTIONS FOR HORIZONTALLY STRATIFIED EARTH*

The potential distribution and the wave propagation in a horizontally stratified earth is considered and the analogy of the mathematical expression for seismic transfer function, electromagnetic and electric kernel functions, and magnetotelluric input impedance is discussed. Although these specific functions are conveniently treated by a separate expression in each method, it is indicated that the function for seismic and electromagnetic methods is mathematically the same with a change in the physical meaning of the variables from one method to the other. Similarly, the identity of the mathematical expressions of the resistivity kernel function and magnetotelluric input impedance is noticed. In each method a specific geophysical function depends on the thickness and the physical properties of the various layers. Every specific function involves two interdependent fundamental functions, that is P_n and Q_n, or P_n and P*_n, having different physical meaning for different methods. Specific functions are expressible as a ratio P_n/Q_n or P*_n/P_n. Fundamental functions may be reduced to polynomials. The fundamental polynomials Q*_n and P*_n describing the horizontally stratified media are a system of polynomials orthogonal on the unit circle, of first and second order, respectively. The interpretation of geophysical problems corresponds to the identification of the parameters of a system of fundamental orthogonal polynomials. The theorems of orthogonal polynomials are applied to the solution of identification problems. A formula for calculating theoretical curves and direct resistivity interpretation is proposed for the case of arbitrary resistivity of the substratum. The basic equation for synthetic seismograms is reformulated in appendix A. In appendix B a method is indicated for the conversion of the seismic transfer function from arbitrary to perfectly reflective substratum.     

Determining the dilation factor in 4D monitoring of compacting reservoirs by rock-physics models

Hydrocarbon depletion and fluid injection cause compaction and stretching of the reservoir and overburden layers. 4D prestack seismic data can be used to detect these changes because compaction/stretching causes changes in traveltimes and seismic velocities. We show that, by using two different petro‐elastic models at varying effective pressures, a good approximation is to assume that the fractional changes in layer thickness, ΔL/L, and seismic velocity, Δv/v, are related by a linear function of ΔL/L. The slope of this function (the dilation factor, α= (Δv/v)/(ΔL/L) ) is negative and its absolute value generally decreases (shale, low porosity) or increases (sandstone, high porosity) with increasing layer thickness and decreasing effective pressure. The analysis is mainly performed for isotropic deformations. The dilation factor for uniaxial deformations is smaller in absolute value. The dilation factor, which can be calculated from time‐lapse data, can be used to predict reservoir compaction/stretching as a function of depth and surface subsidence.