Magnetic losses in lunar materials

Physical constants which define the complex magnetic susceptibility of lunar materials in the frequency domain can be easily determined at frequencies in the vicinity of 1 MHz using a very simple electromagnetic absorption technique. This particular application of absorption measurements derives from the interrelation of the real and imaginary components of the susceptibility of lunar material, and the direct proportionality of the latter component to the power absorbed by the sample when it is exposed to an alternating magnetic field.The results obtained confirm the validity of the theoretical model of viscous magnetization in lunar material put forward by Hanneken et al. (1976) and agree very well with data obtained by Stephenson (1971) using an entirely different measurement technique.     

Magnetic properties of natural Mn-oxides

Summary The paper is devoted to the study of the magnetic properties, of the volume magnetic susceptibility in a weak magnetic field, of the specific magnetic susceptibility in a strong magnetic field, of natural remanent magnetization and its stability in A.C. fields, and of the temperature dependence of magnetic susceptibility of natural Mn-oxides. Samples of pyrolusite, polianite, manganite, hausmannite, psilomelan and wad from different localities all over the world were studied; the measured values are statistically treated so that the given values are valid in general. Hausmannite displayed typical values of the magnetic susceptibility, different from the values of the other Mn-oxides. In general, many natural Mn-oxides contain heterogeneous admixtures of Fe-oxides, which are responsible for their ferromagnetic properties. A high degree of magnetic hardness, predetermining the minerals for palaeomagnetic research, was proved with many of the natural Mn-oxides.     

Magnetic mineralogy and grain-size dependence of hysteresis parameters of single spherules from industrial waste products

The use of magnetic susceptibility as a proxy for the relative degree of industrial pollution of soils and sediments is only qualitative and complications arise when unmixing the contributions from different sources. Detailed characterization of anthropogenic magnetic phases is needed in order to discriminate the input from different sources. The present study investigates magnetic fractions from fly ashes from different thermoelectric power plants and lagooned ash from metal works in Bulgaria, to further our knowledge of potential sources. Thermomagnetic analysis of saturation magnetization (M_s) and magnetic susceptibility (K) revealed a low-substituted magnetite-like phase in power-plant fly ashes and magnetite/maghemite phases in lagooned ash. Magnetic hysteresis measurements on single spherules from the wastes are combined with subsequent SEM/EDX examination of the same grains, allowing for the grain size dependence of the hysteresis parameters to be directly obtained for the studied anthropogenic phases. The results suggest that the structure-sensitive magnetic parameters for the lagooned ash show stronger size dependence compared to the published data for synthetic crushed magnetites, which is due to the complex internal structure and stress level in the anthropogenic phases formed under fast cooling conditions. Moreover, the Day plot for the studied single grains shows the presence of different correlation lines for fly ashes and the lagooned ash, i.e. it discriminates between the sources.     

Magnetic domain observations of nucleation processes in natural pyrrhotite and titanomagnetite

Magnetic domain patterns have been observed on particles of natural pyrrhotite and titanomagnetite undergoing hysteresis. These observations indicate that hysteresis properties are governed by two distinct mechanisms: (1) wall-pinning and (2) nucleation of reverse domains. Particles which are dominated by wall-pinning spontaneously nucleate reverse domains in saturation remanence (J_rs). The coercivity of such grains is determined by the presence of potential wells encountered by the wall in its traverse across the grain. However, many pseudosingle-domain particles (PSD) between 5 and 30 μm in diameter do not nucleate reverse domains in J_rs, but remain as saturated single-domains. These particles require a reverse field H_n to nucleate domain walls. When H_n is sufficiently large, the nucleating field controls magnetization reversal by driving the wall across the particle in a single Barkhausen jump, and the muscopic coercivity is nucleation-dominated.

The proportion P (w=0) of particles of a given size d which fail to nucleate walls in J_rs is found to be given by A exp(−Bd^1/2), where A and B are experimentally determined constants. The nucleation field H_n in pyrrhotite is observed to increase with decreasing grain size, exceeding 500 Oe in 5 μm particles.

The difficulty with which reverse domains are nucleated subsequent to saturation may thus provide a mechanism for achieving the high values of J_rs/J_s and coercive force observed in fine, pseudosingle-domain particles.     

Magnetic anisotropy of laboratory materials in which magma flow is simulated

Summary The magnetic anisotropy of lava flows has been simulated using plaster of Paris containing about 2% of nickel filings. The ellipsoid of magnetic anisotropy was oriented with its long axis close to but tilted with respect to the flow direction and its intermediate axis in the flow plane perpendicular to the flow direction; the same alignment was obtained with four different experimental conditions. This result is at variance with observations on basalt flows in which the long axis of the magnetic ellipsoid is perpendicular to the flow direction. It appears likely that the favoured alignment of elongated grains in a fluid or semi-fluid flow is sensitive to physical parameters which have not yet been examined adequately. Reliable magnetic determinations of flow directions in lavas must await clarification of this problem.     

A novel hysteresis model in unsaturated soil

This study presents a novel hysteresis model based on van Genuchten's soil‐moisture relationships. The proposed model yields a series of closed‐form relationships in which two shape factors α and η are determined from the main drying and wetting curves. Experimental and literature‐cited data were used to assess model accuracy. The proposed model was also compared with the Scott and KP models. Analytical results indicate that the present model is simple, accurate and effective in constructing the series of wetting and drying scanning curves. Notably, the proposed model outperforms the Scott and KP models in terms of model accuracy. Moreover, the novel model eliminates the pumping effect and has perfect closure at scanning curve reversal points. Copyright © 2004 John Wiley & Sons, Ltd.     

Characterizing stream temperature hysteresis in forested headwater streams

Stream temperature (T_s) is a key water quality parameter that controls several biological, ecological, and chemical processes in aquatic systems. In forested headwaters, exchanges of energy across air-water-streambed interfaces may influence T_s regimes, especially during storm events as the sources of runoff change over space and time. Analysis of the hysteretic behaviour of T_s during storm events may provide insights into rainfall-runoff responses, but such relationships have not been thoroughly investigated. As such, our objectives were to (a) quantify the variability of stream temperature hysteresis across seasons in different sub-regions and (b) investigate the relationship between the hysteretic response and catchment characteristics. T_s hysteresis during storm events was assessed based on the hysteresis index (HI), which describes the directionality of hysteresis loops, and the temperature response index (TRI), which indicates whether T_s increased or decreased during a storm event. We analysed T_s data from 10 forested headwater reaches in two sub-regions (McGarvey and West Fork Tectah) in Northern California. We also performed a clustering analysis to examine the relationship amongst HI, TRI, topographic metrics, and meteorological characteristics of the study areas. Overall, the hysteretic behaviour of T_s varied across seasons—the greatest HI occurred during spring and summer. Interestingly, in the McGarvey streams the variability in T_s hysteresis co-varied strongly with topographic metrics (i.e., upslope accumulative area, average channel slope, topographic wetness index). Comparatively, in West Fork Tectah the variability of T_s hysteresis co-varied most strongly with meteorological metrics (i.e., antecedent rainfall events, solar radiation, and air temperature). Variables such as the gradient between stream and air temperatures, slope, and wetted width were significant for both sub-regional hysteretic patterns. We posit that the drivers of T_s response during storms are likely dependent on catchment physiographic characteristics. Our study also illustrated the potential utility of stream temperature as a tracer for improving the understanding of hydrologic connectivity and shifts in the dominant runoff contributions to streamflow during storm events.     

Magnetic hysteresis as a function of low temperature for deep-sea basalts containing large titanomagnetite grains-inference of domain state and controls on coercivity

Hysteresis loops to 1200 oersteds (9.55×10⁴ A m^?1) are measured between 295 K and 105 K for two deep-sea basalts (DSDP, Leg 34 and 37) containing large (～200 μm) unexsolved titanomagnetite grains. The Curie points, electron microprobe analyses and saturation magnetizations of the magnetic grains are the same as for unoxidized synthetic titanomagnetite (xFe₂TiO₄·(l ? x)Fe₃O₄) with x=0.6.As temperature is lowered from 295 to 190 K, coercive force H_c slowly rises from ～40 Oe to ～95 Oe approximately in proportion to the rise in the magnetostriction constant λ. Presumably, H_c is controlled by λ through internal stresses impeding domain wall motion. As expected of multidomain grains, the ratio of saturation remanence to saturation magnetization (in 1200 oersted cycles) j_R/j_S rises approximately in proportion to H_c, with a constant of proportionality consistent with titanomagnetite (x=0.6).As temperature is lowered from 190 to 120 K, H_c rises rapidly to ～400 Oe as a roughly linear function of the magnetocrystalline anisotropy constant K₁. Perhaps H_c is now controlled by K₁ through non-magnetic inclusions impeding domain wall motion.As temperature is lowered from 120 to 105 K, H_c rises even more rapidly to ～600 Oe. The control over H_c seems to have changed again, though most of the titanomagnetite is in grains large enough to still contain a few domains. The ratio j_R/j_S reaches 0.7 by 105 K and appears to be saturating towards the theoretical limit of 0.83.     

Remanent hysteresis study of dolerite dykes

Saturation remanent hysteresis studies were carried out on numerous dolerite dyke samples from the peninsular India. These studies result in four types of remanent hysteresis curves which indicate that the magnetic material is magnetite or titanomagnetite with variable grain-size having remanent coercive forces (H _cr ) of 8 to 30 mT, requiring saturating fields (H _s ) up to 250 mT. Two extreme types of samples with (1) low coercive forces requiring high saturating fields and (2) high coercive forces requiring low saturating fields are noticed along with the generally observed ones. The Granulometric and Lowrie-Fuller Tests on these samples indicated that the magnetic material i.e., magnetite or titanomagnetite in these rocks is in the form of Multi-Domain (MD), Cation Deficient (CD) and a mixture of these two forms (MD+CD) within.     

A simple model for non-vanishing rotational hysteresis in haematite

The model, applicable to fine-grained haematite, assumes that the magnetization of a grain is constrained to lie in the basal plane, within which there is a single easy axis. Following Stoner and Wohlfarth (1948), torque curves and rotational hysteresis are calculated, for various field strengths, as a function of the orientations of the basal plane and easy axis. The results show that, for certain orientations, rotational hysteresis may be expected to persist to very high field strengths. Further, the dependence of rotational hysteresis on orientation implies that rotational hysteresis is anisotropic and thus, that, for a distribution of grains, the anisotropy of resultant rotational hysteresis will reflect the degree of preferred orientation. It may therefore serve as a rock fabric parameter. Calculated models of resultant rotational hysteresis for assumed preferred orientation distributions compare favourably with measurements on a sample of Cambrian purple slate from North Wales.     

An evaluation of an automated hollow-fibre ultrafiltration apparatus for the isolation of colloidal materials in natural waters

Colloidal materials and macromolecules that are less than 0.45 mircons in diameter can act to transport both hydrophobic and hydrophilic contaminations in subsurface waters. An automated hollow-fibre ultrafiltration apparatus is described and evaluated regarding its ability to physically size and isolate colloidal materials from natural waters. Sufficient size-fractionated colloidal samples can be obtained from 60 litre samples to perform inorganic, organic, and radionuclide characterizations, as well as allow the binding capacities of humic and fulvic materials to be evaluated. Samples processed in the field with the automated system were compared with laboratory analyses using single cartridge hollow-fibre ultrafilters and found to agree well with each other. Typical sample reproducibilities were with 15 per cent. The results indicate that field collection of colloidal materials is feasible with minimal sample perturbation using the automated sampler.     

钢骨混凝土框架滞回分析研究

根据非线性有限元原理，编制了基于恢复力模型的钢骨混凝土框架滞回全过程分析程序。程序设计中考虑了材料非线性、几何非线性、预应力作用、轴力二次矩等因素的影响，并考虑了钢骨的特点。通过与已有钢骨混凝土框架试验结果的对比，验证了该程序的合理性。在此基础上，应用该程序对八榀钢骨混凝土框架进行了滞回分析，分析表明钢骨混凝土框架具有良好的抗震性能。     

Bedload hysteresis in a glacier‐fed mountain river

Sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before (counterclockwise hysteresis) or after (clockwise hysteresis) the peak of bedload. Hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability. Counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions, respectively. Hysteresis has been mainly explored for the case of suspended sediment transport, but it was rarely reported for bedload transport in mountain streams. This work focuses on the temporal variability of bedload transport in an alpine catchment (Saldur basin, 18.6 km², Italian Alps) where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0.5m‐long steel pipe. Runoff dynamics are dominated by snowmelt in late spring/early summer, mostly by glacier melt in late summer/early autumn, and by a combination of the snow and glacier melt in mid‐summer. The results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period, likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin. On the contrary, counterclockwise hysteresis tend to be more frequent during late glacier melting period, possibly due to the time lag needed for sediment provided by the glacial and peri‐glacial area to be transported to the monitoring section. However, intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis, thus indicating the activation of different sediment sources. These results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams. Copyright © 2014 John Wiley & Sons, Ltd.     

Truly isotropic biaxial hysteresis with arbitrary knee sharpness

The inelastic responses of framed structures and seismic isolation systems undergoing biaxial (horizontal) shaking are coupled. In existing models for biaxial coupling of hysteretic behavior, the smoothness (or ‘knee') of the transition from elastic to yielding behavior cannot be modified without affecting the shape of the yield surface. This paper presents a model for coupled biaxial hysteretic behavior in which the knee from pre‐yield to post‐yield can be adjusted while maintaining an isotropic yield surface. Copyright © 2014 John Wiley & Sons, Ltd.     

Low-temperature magnetic hysteresis properties of multidomain single-crystal titanomagnetite

The low-temperature magnetic hysteresis characteristics of multidomain titanomagnetite were fitted by a mixed coercivity model in which magnetocrystalline-controlled and magnetostriction-controlled domain-wall pinning play an important part. The effective contribution of the former was found to decrease systematically with increasing titanium content for compositions in the range Fe_2.48Ti_0.52O₄Fe_2.35Ti_0.65O₄. In agreement with the model, the observed magnetic remanence transitions and the characteristic peaks on the susceptibility vs. temperature curve became less pronounced as the titanium content increased. The problems in using these features as a means of identifying the carriers of natural remanent magnetization are discussed.     

Magnetic hysteresis in the F.M.R. spectra of fine-grained spherical iron: Possible evidence for a new carrier of hard remanence in lunar soils and rocks

Magnetic hysteresis effects have been observed in ferromagnetic resonance (FMR) spectra obtained at 9 and 16 GHz for certain simulated lunar glasses which were reduced by H₂ in the melt and rapidly quenched. Transmission electron microscopy has revealed that these samples contained spherical particles in the size range ～0.01–0.5 μm. FMR spectra obtained at 35 GHz (applied field ～ 12.5 kOe) exhibited a line shape characteristic of spherical, single-domain (SD) iron particles with no hysteresis. Computer simulations of the latter spectra confirmed that the average deviation from sphericity must be ?3% and that (2K₁/M_s) ≈ + 600 Oe for the precipitated magnetic phases. The principal features of the spectra obtained at all three frequencies have been explained on the basis of a simple theoretical treatment for spherical iron particles which have 2 domains in applied fields ?7 kOe, but become saturated at higher fields. Isothermal remanent magnetization (IRM) of these samples has been studied by both FMR and standard static techniques; the mean coercive force measured by the former (～4 kOe) contrasts with the mean value determined by the latter (～550 Oe). Apparently, FMR singles out and even amplifies the contributions of two-domain particles (which are magnetically hard), while the static measurement is more sensitive to the average of all particles present. The intensity of the FMR hysteresis of typical lunar soils is found to be ～1% of the total FMR intensity. In spite of this seemingly small value, two-domain iron particles may be important carriers of natural remanent magnetization (NMR) in certain lunar rocks.     

Mechanical hysteresis in rocks at low strain amplitudes and seismic frequencies

A sensitive capacitance displacement transducer has been used to record hysteresis loops in the stress-strain diagrams of laboratory samples of granite, basalt, sandstone and concrete subjected to cyclic axial strains with amplitudes of order 10^?5 and periods of 10–300 sec. The ends of the loops are always cusped, whether the load cycle is sinusoidal or not, and at low strain amplitudes the loop shape becomes symmetrical and appears to be independent of amplitude. Thermal relaxation influences the observed loop shapes, so that the strain cycles represent a compromise between adiabatic and isothermal compressions. However, this does not affect the conclusion that stress-strain loops are always cusped. This observation does not appear to be consistent with linear theories of damping of acoustic and seismic waves, which indicate elliptical loops.     

Reinforced concrete hysteresis model based on the damage concept

Reinforced concrete members subjected to cyclic inelastic deformation may exhibit both stiffness and strength degradation, depending on the maximum amplitude and the number of cycles experienced by the member. Many of the currently available models do not simulate the cycle-dependent stiffness loss often observed during the experiments. An analytical model based on a damage parameter which is a function of the cumulative cyclic inelastic deformation is proposed. A small-scale reinforced concrete beam–column joint was constructed and subjected to cyclic loading to calibrate the damage parameter. The model is able to approximate the complete hysteretic response and is simple to implement. The sensitivity of the analytical model was examined by comparing the model with several experimental results.     

巨型钢柱空间滞回特性的试验研究

巨型钢柱是巨型钢框架结构的关键受力构件,组成杆件多,构造复杂,建立其空间恢复力模型是进行巨型框架简化弹塑性地震反应分析的必要条件。通过两端简支巨型钢柱在双向水平往复荷载下的伪静力试验,研究了其空间滞回特性和模拟方法,为将巨型钢柱折算为等效单一柱提供了试验依据。     

A generalized hysteresis model for biaxial response of pile foundations in sands

We present the development and calibration of a macroelement model that captures the response of piles in cohesionless soils subjected to biaxial lateral loading. The model is founded on actual physical mechanism of soil resistance and provides the framework for extending a uniaxial model to biaxial case by means of a single cross-stiffness parameter. Both upper and lower bounds for the cross-stiffness parameter are also presented. The model is calibrated and verified using three-dimensional finite element (FE) simulations of soil-pile interaction for uniformly prescribed displacement along the pile length. Comparison of predictions from uniaxial and biaxial models with the FE results for transient loading indicates that the response assuming no coupling between the two horizontal directions for biaxial loading can differ significantly from the ‘true’ response for some cases. Accounting for coupling in the lateral direction, the proposed model captures the transverse pile response with very good accuracy while retaining the simplicity and computational efficiency of macroelement formulations compared to 3D FE analyses.