Swelling tests on material from the Guabirotuba Formation, Parana, Brazil, with suction control

This paper presents the swelling behaviour of clayey materials under controlled suction imposed both by a Richards chamber and by controlling the relative humidity with concentrated saline solutions. Soil-water characteristic curves (matrix and total) were determined by the filter paper method. The materials under study belong to the Guabirotuba Formation, of Pleistocene age, in the Curitiba Basin in the state of Parana, southern Brazil. Materials under several stages of suction of 5000-40 000 kPa were subjected to swelling tests in an oedometer press. The results indicated that the greater the suction the higher the swelling pressure. However, when swelling tests were carried out with suction variation controlled by relative humidity, in which the increase in moisture was very slow, the samples showed no swelling.

Influence of the magnetization damping on dynamic hysteresis loops in single domain particles

This article reports on the influence of the magnetization damping on dynamic hysteresis loops in single-domain particles with uniaxial anisotropy. The approach is based on the Neel-Brown theory and the hierarchy of differential recurrence relations, which follow from averaging over the realizations of the stochastic Landau-Lifshitz equation. A new method of solution is proposed, where the resulting system of differential equations is solved directly using optimized algorithms to explore its sparsity. All parameters involved in uniaxial systems are treated in detail, with particular attention given to the frequency dependence. It is shown that in the ferromagnetic resonance region, novel phenomena are observed for even moderately low values of the damping. The hysteresis loops assume remarkably unusual shapes, which are also followed by a pronounced reduction of their heights. Also demonstrated is that these features remain for randomly oriented ensembles and, moreover, are approximately independent of temperature and particle size. (C) 2012 American Institute of Physics. [doi:10.1063/1.3684629]

The Effect of Contact on the Filter Paper Method for Measuring Soil Suction

The filter paper method is one of the most commonly used and critiqued techniques for measuring soil suction. However, many aspects related to its use still require some clarification. The results of a comprehensive study on the effect of the contact between the soil grains and soil water and the filter paper are presented herein. We investigated the influence of the equilibration time, the texture of the porous material and the degree of contact, or lack thereof, between the soil grains and the filter paper using Miamian #42 and three different types of porous material. To enhance the difference between the total suction and the matrix suction, osmotic suction was induced by saturating the specimens with a sodium chloride solution.

Subdivision of Hysteresis Loss in Mn-Zn Ferrite Toroidal Cores

The hysteresis loss subdivision method proved to be a strong tool to help in the analysis of different energy dissipation mechanisms along the quasi-static hysteresis loop measured on electrical steels. This paper used the samemethod to discuss the mechanisms involving the energy loss dissipation in Mn-Zn ferrite toroidal cores. The samples, sintered under controlled atmosphere in industrial conditions, were measured under triangular waveform excitation at very low frequency (5 mHz) and peak flux densities varying from 0.05 T to 0.45 T. The results show a different behavior between the low inductions hysteresis loss (WLI) and the high induction hysteresis loss (WHI) which proves the existence of different energy dissipation mechanisms affecting these loss components.

Magnetic hyperthermia investigation of cobalt ferrite nanoparticles: Comparison between experiment, linear response theory, and dynamic hysteresis simulations

Considerable effort has been made in recent years to optimize materials properties for magnetic hyperthermia applications. However, due to the complexity of the problem, several aspects pertaining to the combined influence of the different parameters involved still remain unclear. In this paper, we discuss in detail the role of the magnetic anisotropy on the specific absorption rate of cobalt-ferrite nanoparticles with diameters ranging from 3 to 14 nm. The structural characterization was carried out using x-ray diffraction and Rietveld analysis and all relevant magnetic parameters were extracted from vibrating sample magnetometry. Hyperthermia investigations were performed at 500 kHz with a sinusoidal magnetic field amplitude of up to 68 Oe. The specific absorption rate was investigated as a function of the coercive field, saturation magnetization, particle size, and magnetic anisotropy. The experimental results were also compared with theoretical predictions from the linear response theory and dynamic hysteresis simulations, where exceptional agreement was found in both cases. Our results show that the specific absorption rate has a narrow and pronounced maxima for intermediate anisotropy values. This not only highlights the importance of this parameter but also shows that in order to obtain optimum efficiency in hyperthermia applications, it is necessary to carefully tailor the materials properties during the synthesis process. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729271]

Dynamic symmetry loss of high-frequency hysteresis loops in single-domain particles with uniaxial anisotropy

Understanding how magnetic materials respond to rapidly varying magnetic fields, as in dynamic hysteresis loops, constitutes a complex and physically interesting problem. But in order to accomplish a thorough investigation, one must necessarily consider the effects of thermal fluctuations. Albeit being present in all real systems, these are seldom included in numerical studies. The notable exceptions are the Ising systems, which have been extensively studied in the past, but describe only one of the many mechanisms of magnetization reversal known to occur. In this paper we employ the Stochastic Landau-Lifshitz formalism to study high-frequency hysteresis loops of single-domain particles with uniaxial anisotropy at an arbitrary temperature. We show that in certain conditions the magnetic response may become predominantly out-of-phase and the loops may undergo a dynamic symmetry loss. This is found to be a direct consequence of the competing responses due to the thermal fluctuations and the gyroscopic motion of the magnetization. We have also found the magnetic behavior to be exceedingly sensitive to temperature variations, not only within the superparamagnetic-ferromagnetic transition range usually considered, but specially at even lower temperatures, where the bulk of interesting phenomena is seen to take place. (C) 2011 Elsevier B.V. All rights reserved.

Temperature Effects on Suction Measurement Using the Filter Paper Technique

This paper presents the results of an experimental study of thermal effects on filter paper calibration curves used to obtain the soil suction. When the temperature is significantly different from ambient values, it is essential to consider the influence of temperature on the filter paper calibration curves to obtain a reliable soil suction measurement. The calibration curve of Whatman No. 42 filter paper was determined at 10 degrees C, 25 degrees C, and 50 degrees C using the vapor equilibrium technique with sodium chloride solutions at different concentrations and the axis translation technique. The experimental results showed a major influence of temperature on the filter paper calibration curves. Using the obtained experimental data a calibration equation was proposed, taking into account the effect of temperature. The obtained calibration curves were then used to determine the soil water retention curve of kaolin clay, which showed lower retention capacity at higher temperatures.

Unconfined shear strength of compacted unsaturated plastic soils

A central goal in unsaturated soil mechanics research is to create a smooth transition between traditional soil mechanics approaches and an approach that is applicable to unsaturated soils. Undrained shear strength and the liquidity index of reconstituted or remoulded saturated soils are consistently correlated, which has been demonstrated by many studies. In the liquidity index range from 1 (at w(l)) to 0 (at w(p)), the shear strength ranges from approximately 2 kPa to 200 kPa. Similarly, for compacted soil, the shear strength at the plastic limit ranges from 150 kPa to 250 kPa. When compacted at their optimum water content, most soils have a suction that ranges from 20 kPa to 500 kPa; however, in the field, compacted materials are subjected to drying and wetting, which affect their initial suction and as a consequence their shear strength. Unconfined shear tests were performed on five compacted tropical soils and kaolin. Specimens were tested in the as-compacted condition, and also after undergoing drying or wetting. The test results and data from prior literature were examined, taking into account the roles of void ratio, suction, and relative water content. An interpretation of the phenomena that are involved in the development of the undrained shear strength of unsaturated soils in the contexts of soil water retention and Atterberg limits is presented, providing a practical view of the behaviour of compacted soil based on the concept of unsaturated soil. Finally, an empirical correlation is presented that relates the unsaturated state of compacted soils to the unconfined shear strength.

Effects of the Compaction Pressure on the Magnetic Properties of a Sintered Fe-Based Alloy

The structural and magnetic properties of a Fe-based alloy before and after sintering have been analyzed. X ray diffraction measurements confirm the deformation of the magnetic particles in the compacted samples. After sintering, hysteresis energy dissipation, remanence and intrinsic coercivity differ by less than 10% as porosity changes from 15 to 7%.

Effect of Plastic Deformation on the Excess Loss of Electrical Steel

The interpretation of the effect of plastic deformation on the calculated excess loss component (anomalous-loss) supports the concept of loss separation. Magnetic losses and Barkhausen noise of nonoriented electrical steel sheets were measured on Epstein strips taken from a single coil of 0.8% Si nonoriented electrical steel. Sheets were extracted in the annealed condition, without any skin pass and with a grain size of 18 mu m. This material was cold rolled in order to obtain sets of samples with true strain from 2% up to 29%. X-ray diffraction was used to estimate the dislocation density. The analysis of magnetic properties was performed by Barkhausen noise measurements and also by analyzing the hysteresis loops obtained from Epstein frame measurements for different inductions and different frequencies (including the quasi-static regime for hysteresis loss measurements). These data allowed us to observe that most of the well known total loss increase with plastic deformation is due to an increase in the hysteresis loss component, while excess loss decreases to become negligible. This behavior can be explained if it is assumed that the plastic deformation lead to an increase in the number of domain walls per unit volume, thereby decreasing the excess loss. Barkhausen peak area increases with plastic deformation, reproducing results taken from samples of different silicon content.

Field dependent transition to the non-linear regime in magnetic hyperthermia experiments: Comparison between maghemite, copper, zinc, nickel and cobalt ferrite nanoparticles of similar sizes

Further advances in magnetic hyperthermia might be limited by biological constraints, such as using sufficiently low frequencies and low field amplitudes to inhibit harmful eddy currents inside the patient's body. These incite the need to optimize the heating efficiency of the nanoparticles, referred to as the specific absorption rate (SAR). Among the several properties currently under research, one of particular importance is the transition from the linear to the non-linear regime that takes place as the field amplitude is increased, an aspect where the magnetic anisotropy is expected to play a fundamental role. In this paper we investigate the heating properties of cobalt ferrite and maghemite nanoparticles under the influence of a 500 kHz sinusoidal magnetic field with varying amplitude, up to 134 Oe. The particles were characterized by TEM, XRD, FMR and VSM, from which most relevant morphological, structural and magnetic properties were inferred. Both materials have similar size distributions and saturation magnetization, but strikingly different magnetic anisotropies. From magnetic hyperthermia experiments we found that, while at low fields maghemite is the best nanomaterial for hyperthermia applications, above a critical field, close to the transition from the linear to the non-linear regime, cobalt ferrite becomes more efficient. The results were also analyzed with respect to the energy conversion efficiency and compared with dynamic hysteresis simulations. Additional analysis with nickel, zinc and copper-ferrite nanoparticles of similar sizes confirmed the importance of the magnetic anisotropy and the damping factor. Further, the analysis of the characterization parameters suggested core-shell nanostructures, probably due to a surface passivation process during the nanoparticle synthesis. Finally, we discussed the effect of particle-particle interactions and its consequences, in particular regarding discrepancies between estimated parameters and expected theoretical predictions. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi. org/10.1063/1.4739533]

Magnetic Ionic Liquids Produced by the Dispersion of Magnetic Nanoparticles in 1-n-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf2)

This paper reports on the advancement of magnetic ionic liquids (MILs) as stable dispersions of surface-modified gamma-Fe2O3, Fe3O4, and CoFe2O4 magnetic nanoparticles (MNPs) in a hydrophobic ionic liquid, 1-n-butyl 3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf2). The MNPs were obtained via coprecipitation and were characterized using powder X-ray diffraction, transmission electron microscopy, Raman spectroscopy and Fourier transform near-infrared (FT-NIR) spectroscopy, and magnetic measurements. The surface-modified MNPs (SM-MNPs) were obtained via the silanization of the MNPs with the aid of 1-butyl-3[3-(trimethoxysilyl)propyl]imidazolium chloride (BMSPI.Cl). The SM-MNPs were characterized by Raman spectroscopy and Fourier trail: form infrared attenuated total reflectance (FTIR-ATR) spectroscopy and by magnetic measurements. The FTIR-ATR spectra of the SM-MNPs exhibited characteristic absorptions of the imidazolium and those of the Fe-O-Si-C moieties, confirming the presence of BMSPI.Cl on the MNP surface. Thermogravimetric analysis (TGA) showed that the SM-MNPs were modified by at least one BMSPI.Cl monolayer. The MILs were characterized using Raman spectroscopy, differential scanning calorimetry (DSC), and magnetic measurements. The Raman and DSC results indicated an interaction between the SM-MNPs and the IL. This interaction promotes the formation of a supramolecular structure close to the MNP surface that mimics the IL structure and is responsible for the stability of the MIL. Magnetic measurements of the MILs indicated no hysteresis. Superparamagnetic behavior and a saturation magnetization of similar to 22 emu/g could be inferred from the magnetic measurements of a sample containing 50% w/w gamma-Fe2O3 SM-MNP/BMI-NTf2.

Models of passive and active dendrite motoneuron pools and their differences in muscle force control

Motoneuron (MN) dendrites may be changed from a passive to an active state by increasing the levels of spinal cord neuromodulators, which activate persistent inward currents (PICs). These exert a powerful influence on MN behavior and modify the motor control both in normal and pathological conditions. Motoneuronal PICs are believed to induce nonlinear phenomena such as the genesis of extra torque and torque hysteresis in response to percutaneous electrical stimulation or tendon vibration in humans. An existing large-scale neuromuscular simulator was expanded to include MN models that have a capability to change their dynamic behaviors depending on the neuromodulation level. The simulation results indicated that the variability (standard deviation) of a maintained force depended on the level of neuromodulatory activity. A force with lower variability was obtained when the motoneuronal network was under a strong influence of PICs, suggesting a functional role in postural and precision tasks. In an additional set of simulations when PICs were active in the dendrites of the MN models, the results successfully reproduced experimental results reported from humans. Extra torque was evoked by the self-sustained discharge of spinal MNs, whereas differences in recruitment and de-recruitment levels of the MNs were the main reason behind torque and electromyogram (EMG) hysteresis. Finally, simulations were also used to study the influence of inhibitory inputs on a MN pool that was under the effect of PICs. The results showed that inhibition was of great importance in the production of a phasic force, requiring a reduced co-contraction of agonist and antagonist muscles. These results show the richness of functionally relevant behaviors that can arise from a MN pool under the action of PICs.

Tectonic implications of the 1419 Ma Nova Guarita mafic intrusives paleomagnetic pole (Amazonian Craton) on the longevity of Nuna

The Nuna supercontinent was probably assembled in the Paleoproterozoic, but its paleogeography and the timing for its demise are stills matter of debate. A paleomagnetic and geochronological study carried out on the Mesoproterozoic Nova Guarita dyke swarm (northern Mato Grosso State, SW Amazonian Craton) provides additional constraints on the duration of this supercontinent. Paleomagnetic AF and thermal treatment revealed south/southwest (northeast) magnetic directions with downward (upward) inclinations for 19 analyzed sites. These directions are carried by PSD magnetite with high unblocking temperatures as indicated by additional magnetic tests, including thermomagnetic curves, hysteresis loops and the progressive acquisition of isothermal remanence in selected samples. A positive contact test with the host granite in one of the studied dykes further attests to the primary origin of the characteristic magnetic component. A mean site direction was calculated at D-m = 220.5 degrees, I-m = 45.9 degrees (alpha(95) = 6.5 degrees, K = 27.7), which yielded a paleomagnetic pole located at 245.9 degrees E, 47.9 degrees S (A(95) = 7.0 degrees). Ar-40/Ar-39 dating carried out on biotites from four analyzed dykes yielded well-defined plateau ages with a mean of 1418.5 +/- 3.5 Ma. The Nova Guarita pole precludes a long-lived Nuna configuration in which Laurentia, Baltica, North China, and Amazonia formed a long and continuous block as previously proposed for the Paleoproterozoic. It is nevertheless fully compatible with a SAMBA (Amazonia-Baltica) link at Mesoproterozoic times. (C) 2011 Elsevier B.V. All rights reserved.

Experimental investigation of gravitational gas separation in an inclined annular channel

The oil industry uses gas separators in production wells as the free gas present in the suction of the pump reduces the pumping efficiency and pump lifetime. Therefore, free gas is one of the most important variables in the design of pumping systems. However, in the literature there is little information on these separators. It is the case of the inverted-shroud gravitational gas separator. It has an annular geometry due to the installation of a cylindrical container in between the well casing and pioduction pipe (tubing). The purpose of the present study is to understand the phenomenology and behavior of inverted-shroud separator. Experimental tests were performed in a 10.5-m-length inclinable glass tube with air and water as working fluids. The water flow rate was in the range of 8.265-26.117 l/min and the average inlet air mass flow rate was 1.1041 kg/h, with inclination angles of 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, 80 degrees and 85 degrees. One of the findings is that the length between the inner annular level and production pipe inlet is one of the most important design parameters and based on that a new criterion for total gas separation is proposed. We also found that the phenomenology of the studied separator is not directly dependent on the gas flow rate, but on the average velocity of the free surface flow generated inside the separator. Maps of efficiency of gas separation were plotted and showed that liquid flow rate, inclination angle and pressure difference between casing and production pipe outlet are the main variables related to the gas separation phenomenon. The new data can be used for the development of design tools aiming to the optimized project of the pumping system for oil production in directional wells. (C) 2012 Elsevier Inc. All rights reserved.