bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wellbore Effects in the Analysis of Two-Phase Geothermal Well Tests
Authors: Miller Constance W. , Benson Sally M. , O'Sullivan Michael J. , Pruess Karsten 
Published: December 2007

Abstract
A method of designing and analyzing pressure transient well tests of two-phase (steam/water) reservoirs is given. Wellbore storage is taken into account, and the duration of it is estimated. It is shown that the wellbore flow can dominate the downhole pressure signal completely such that large changes in the downhole pressure that might be expected because of changes in kinematic mobility are not seen. Changes in the flowing enthalpy from the reservoir can interact with the wellbore flow so that a temporary plateau in the downhole transient curve is measured. Application of graphical and nongraphical methods to determine reservoir parameters from drawdown tests is demonstrated.
Flow Characteristics of Surfactant Solutions in Porous Media and Their Role in Permeability Modification
Authors: Kalpakci B. , Klaus E. E. , Duda J. L. , Nagarajan R. 
Published: December 2007

Abstract
This paper presents results of a study on flow properties of surfactant solutions in porous media, using the Penn State porous media viscometer. The effects of permeability, shear rate, and surface characteristics of porous media on the flow of oil- and water-external microemulsions, as well as surfactant solutions with lamellar structures, are examined. Untreated Bradford and Berea sandstones, oil- and water-wet treated sandstones, and filter papers are used as porous media.
The study shows that the effective viscosity of the surfactant solution (as measured in porous media), on the basis of initial permeabilities, is greater than the bulk viscosity (as measured by conventional viscometers). This increase is small for Newtonian surfactant solutions but is quite substantial for non-Newtonian surfactant solutions. The difference between bulk and effective viscosities of Newtonian surfactant solutions is eliminated when the effective viscosity is determined on the basis of the final permeability of the porous medium to calibration solution. This indicates that the permeability of the porous medium during flow of these Newtonian surfactant solutions is equal to that during flow of postcalibration solutions. In contrast, in the case of the non-Newtonian surfactant solution with lamellar structures, the effective viscosity based on the final permeability remains higher than the bulk viscosity of the solution. Plausible explanations for the lower permeability during surfactant flow compared with the final permeability, in this case, are discussed.
It is found that the flow of surfactant solutions causes a permanent decrease in the permeability of the porous medium. Initial permeability is not restored even by thorough flushing of the porous medium with surfactant-free brine solution. Residual permeability reductions of 2 to 51% are observed. The residual permeability reduction increases with decreasing initial permeability. The residual permeability reduction is relatively insensitive to the type of surfactant solution. However, it depends on surface characteristics of the porous medium and decreases in this order: untreated ≫ fired &gt; oil-wet treated.
Use of Perspective Plots To Aid in Determining Factors Affecting Interfacial Tensions Between Surfactant Solutions and Crude Oil
Authors: Kellerhals G. E. , Chiou C. S. 
Published: December 2007

Abstract
In surfactant flooding, low interfacial tensions (IFT's) are required for recovery of additional significant quantities of crude oil from a reservoir rock. This paper indicates the usefulness of perspective plots to facilitate comparison of sets of IFT data. Such perspective plots simplify the process of screening various surfactant systems for enhanced oil recovery.
Fracture Evaluation With Pressure Transient Testing in Low-Permeability Gas Reservoirs
Authors: Lee W.J. , Holditch S.A. 
Published: December 2007

Summary
This paper presents theoretical and practical aspects of methods used to determine formation permeability, fracture length, and fracture conductivity permeability, fracture length, and fracture conductivity in low-permeability, hydraulically fractured gas reservoirs. Methods examined include Horner analysis, linear flow analysis, type curves, and finite-difference reservoir simulators.

Introduction
The purpose of this paper is to summarize the theoretical background of methods that we have attempted to use to determine formation permeability, fracture length, and fracture conductivity permeability, fracture length, and fracture conductivity in low-permeability, hydraulically fractured gas reservoirs. This summary is intended to emphasize the major strengths and weaknesses of the methods studied. These characteristics have not always been emphasized in the original literature and, in some cases, have remained obscure to the practicing engineer. The paper also includes examples from 13 wells in which postfracture-treatment pressure buildup surveys have been analyzed in detail.
Test analysis methods discussed in the paper include (1) a method applicable only after a pseudoradial flow pattern is developed in the pseudoradial flow pattern is developed in the reservoir, (2) a method applicable when linear flow dominates in the reservoir, (3) published type curves, with emphasis on those that include finite- conductivity fractures, (4) a modification of linear- flow techniques useful for finite-conductivity fractures, and (5) use of finite-difference reservoir simulators in a history-matching mode.
Pseudoradial Flow Pseudoradial Flow Russell and Truitt pioneered application of methods based on the assumption of pseudoradial flow in a fractured reservoir for determination of formation permeability and fracture length. A working permeability and fracture length. A working definition of pseudoradial flow is that sufficient time has elapsed in a buildup or drawdown test so that bottomhole pressure (BHP) varies linearly with the logarithm of flow time (drawdown) or the Horner time group (tp + delta t)/ delta t (buildup), as expected for radial flow in an unfractured reservoir.
In an infinite-acting (unbounded) reservoir, the analysis technique is based on the use of skin factor, s, which can be calculated from
(1)
and the observation that, for infinitely conductive vertical fractures,
(2)
Eqs. 1 and 2 can be combined to avoid the intermediate step of calculating s:
(3)
In principle, we can plot buildup test data on a conventional Horner graph, determine the slope m, and thus estimate formation permeability (k = 162.6 qgBga mu a/mh) and determine fracture half-length, Lf from Eq. 3 (see Fig. 1).
JPT
P. 1776
Refractory shoulder dystocia in term macrosomic newborn with verified complete meningoencephalomyelocele
Authors: Habek Dubravko , Horvat Gordana , Kulaš Tomislav , Janiška Ivanka , Stanojević Milan , Bauman Renato , Hafner Tomislav 
Published: December 2007

Abstract
The authors presented the birth course, in a primiparous woman with complicated, refractory, high shoulder dystocia, of a macrosomic term-born malformed child (4400/54) with complete occipital meningoencephalomyelocele and microcephaly. After head delivery, high shoulder dystocia occurred that could not be resolved with neither the McRoberts or Resnik maneuver nor with the Woods and Barnum maneuvers, despite recurred tries. Only on third attempt with the Barnum maneuver was the posterior arm released with hand traction, followed by the whole body of the macrosomic baby. The child was transferred to the Neurosurgery department where operative correction was performed, and after the intervention the child died because of respiratory insufficiency. Due to the strict parental decision on pregnancy continuation and prohibition of any obstetric interventions during delivery, unborn child and parturient, as well as the obstetric team, were put into high professional, forensic and ethical risk.
Dynamical Mean‐Field Theory of Itinerant Electron Magnetism
Authors: Lichtenstein Alexander I. , Katsnelson Mikhail I. 
Published: December 2007

AbstractA novel spectral density functional approach to electronic correlations and magnetism of crystals based on realistic electronic structure calculations is reviewed. In its simplest form, it is a combination of the density functional theory in the ‘local density approximation’ with dynamical mean‐field theory approaches. Using the numerically exact solution of an effective multi‐orbital quantum‐impurity problem, a successful description of the electronic structure and finite‐temperature magnetism of transition metals has been obtained. We discuss correlation effects in iron and nickel, as well as in an artificially prepared layered structure of manganese. A general scheme for calculation of effective exchange interactions in the strongly interacting magnetic systems is presented. Correlation effects in half‐metallic ferromagnets resulting in the formation of nonquasiparticle states within the minority (or majority) spin gap are also discussed.
Orbital Physics in Transition Metal Oxides: Magnetism and Optics
Authors: Horsch Peter 
Published: December 2007

Abstract

Orbital degeneracy and strong correlations in transition‐metal oxides generate spins and orbitals as low‐energy degrees of freedom. Their interplay with both real‐charge motion and virtual‐charge excitations lead to a fascinating richness of spin–charge–orbital‐ordered phases in transition‐metal oxides, to striking phenomena like the colossal magnetoresistance in manganites, the switching of charge‐ordered phases into metallic phases by applied magnetic field, and many other fascinating effects. Central topics of this review are the spin‐orbital superexchange models which provide a concise description of spin and orbital order, effective spin interactions, spin waves, and orbiton excitations in doped and undoped Mott insulators. Particular emphasis is put on recent developments of spin‐orbital superexchange models, the relation of magnetism and optical spectral weights and their temperature dependence, t
2g
systems with strong composite spin‐orbital fluctuations, the concepts of orbital liquid, orbital polarons, and the colossal magnetoresistance.
Quantum Phase Transitions
Authors: Sachdev Subir 
Published: December 2007

Abstract
Thermal fluctuations induced by increasing temperature can change the state of matter, for example, when water boils to steam. It also is possible to change the state of matter at absolute zero temperature by quantum fluctuations demanded by Heisenberg's uncertainty principle. In this case, the quantumphase transition from one state to another is provided by adjusting a tuning parameter other than temperature. A few characteristic examples of quantumphase transitions are reviewed, and their consequences for finite temperature experiments are discussed.
Electron Theory of Finite Temperature Magnetism
Authors: Kübler Jürgen 
Published: December 2007

Abstract

The theory of finite‐temperature magnetism of metals is formulated within the local spin‐density‐functional approximation. Orientational fluctuations of the local magnetization are at the basis of the thermodynamic theory, for which the excitations are obtained from the total‐energy differences of noncollinear spin configurations, modeled either in real or reciprocal space. The limit of weakly ferromagnetic metals (e.g., ZrZn
2
, Ni
3
Al, and MnSi) is formulated by including dissipation effects in the spin‐fluctuation theory. Moriya's unified theory is used to derive formulas for the Curie temperature in the spherical approximation which are used together with the mean‐field approximation and reported Monte Carlo results to deal with a number of cases of interest. These include Fe, Co, and Ni, as well as a selection of half‐metallic ferromagnets and diluted magnetic semiconductors which are important for the novel field of spin‐electronics (spintronics). Here the detection of different exchange mechanisms is emphasized. A brief excursion into the long‐range order of low‐dimensional systems like thin magnetic films closes this chapter.
Exchange Coupling in Magnetic Multilayers
Authors: Edwards David M. , Umerski Andrey 
Published: December 2007

Abstract
After a brief historical introduction, the origin of interlayer exchange coupling (IEC) in magnetic multilayers is explained with an emphasis on the role of quantum well states in the nonmagnetic spacer layers. Analytic results for a simple model are given and techniques for quantitative calculation of IEC in real systems are described. A full discussion is given on mechanisms for biquadratic exchange coupling and the temperature dependence of IEC arising from single‐electron and spin‐wave excitations. Theory and experiment are compared for systems with noble metal, transition metal, antiferromagnetic metal, and insulating spacers. Open questions are identified, particularly an order‐of‐magnitude discrepancy between theory and experiment for the strength of IEC in the case of transition‐metal spacers.
Magnetic Superconductors
Authors: Buzdin A. , Flouquet J. 
Published: December 2007

Abstract
We review the main mechanisms of the interplay between magnetism and superconductivity, and discuss first the properties of the conventional s‐wave antiferromagnetic and ferromagnetic superconductors. In the case of ferromagnetism, its antagonism with superconductivity leads to spectacular effects such as a reentrant superconductivity and the domain magnetic structure formation.

It is now accepted that in heavy‐fermion compounds (HFCs) the superconductivity is unconventional. Here we analyze the (
P
,
T
) phase diagram with special focus on the stability of the different phases at
T
→ 0 K. In the recently discovered ferromagnetic heavy‐fermion superconductors, the Cooper pairing appears to be a triplet. The studies of the properties of these compounds will certainly open a new chapter in the physics of superconductivity.

We also discuss the particularities of the proximity effect in superconductor–ferromagnet heterostructures: the damped oscillatory behavior of the Cooper pair wave function and the conditions for the novel π‐Josephson junctions formation, which open an interesting perspective for the potential applications of these structures.
Magnetization Configurations and Reversal in Small Magnetic Elements
Authors: Kläui Mathias , Vaz Carlos António Fernandes 
Published: December 2007

AbstractThis chapter presents an overview of the magnetization configurations and reversal in magnetic structures ranging from a few nanometers to a few micrometers in size that can be described using the theory of micromagnetics. A range of techniques for the characterization of magnetic structures is introduced and the theoretical micromagnetism background, including the energy terms governing the magnetic properties, are discussed. The simplest case of a single domain system with uniform magnetization is treated within the framework of the Stoner–Wohlfarth theory, and experimental examples of such systems are presented. The magnetization configurations in larger systems that exhibit nonuniform magnetization are discussed in detail with a particular emphasis on experimental examples for the geometries that have been studied most often, such as discs, rings, rectangles, wires and pillars. Theoretically, the formation of these states is explained as a result of the interplay between the different magnetic energy terms; multidomain states that occur for larger elements are also introduced. The dynamic properties of the reversal of these elements are addressed, starting with the evaluation of the Landau–Lifshitz–Gilbert equation to obtain the trajectories for single domain particles. This is then extended to cover the nonhomogeneous reversal of nonuniform states. The elementary processes occurring during nonhomogeneous reversal are introduced and used to explain the magnetization reversal in a set of instructive examples.
Magnetization Dynamics: Thermal‐driven Noise in Magnetoresistive Sensors
Authors: Zhu Jian‐Gang 
Published: December 2007

Abstract
The development of spin‐valve and magnetic tunnel junction read sensors in hard disk drives has enabled tremendous reduction of data track width, leading to the tremendous increase of storage capacity, over the past decade. As the physical dimensions of the read sensors decrease into the deep submicron regime, thermally excited magnetization precession in the sensing magnetic layer becomes nonnegligible with amplitude comparable to that induced by magnetic flux from written data bits in disk media. This article provides a detailed analysis, based on the phenomenological Gilbert damping, of the nature of the thermally excited magnetization precession and the resulting noise temporal and spectral characteristics in the read sensors for hard disk drive applications. Comparison between the analysis and experimental measurements shows a remarkable agreement. Previous research on this subject is also reviewed.
Magnetic Modes in Circular Thin Film Elements, Experiment and Theory
Authors: Back Christian H. , Buess Matthias 
Published: December 2007

Abstract
In this chapter we review recent advances in the field of magnetization dynamics in small, confined structures. We limit ourselves to a particularly simple magnetic object which nevertheless exhibits various interesting magnetic modes on various timescales. We investigate a ferromagnetic disk in the flux‐closed state. In this configuration, the magnetic flux circulates around the element and leads to a polarized vortex core with its magnetization pointing out of the plane of the element. We show that time‐resolved Kerr microscopy is able to reveal the details of the magnetostatic modes of these elements. We also present some hints for the vortex core motion and the switching of the vortex core.
Theory of Spin‐transfer Torque
Authors: Stiles Mark D. 
Published: December 2007

AbstractIn magnetic multilayers, the spin‐polarized currents flowing between the magnetic layers can exert torques on the magnetizations of the layers when the magnetizations are not collinear. The theory of these spin‐transfer torques is developed in terms of semiclassical transport calculations coupled with quantum‐mechanical calculations of the behavior of spins at interfaces. The result is an expression for the torque in terms of the geometry of the devices and the magnetic configuration.
Microwave Generation in Magnetic Multilayers and Nanostructures
Authors: Rippard William H. , Pufall Matthew R. 
Published: December 2007

AbstractWe present an overview of the coherent magnetic precessional dynamics induced by the spin‐transfer effect in magnetic nanostructures. The precessional frequencies of the magnetic oscillators can be tuned over a range of several gigahertz by varying the dc current through the devices. The oscillation frequencies also depend on the applied magnetic field, resulting in a nanoscale oscillator that can be tuned from a few gigahertz to greater than 40 GHz. Even at room temperature, the linewidths of these excitations are often only a few megahertz wide. This gives quality factors for the excitations of more than 18 000 at the highest frequencies. As the direction of the applied field changes from parallel to perpendicular to the film plane, the power output from the structures increases by several orders of magnitude. For fields applied nearly perpendicular to the film plane, the high‐frequency voltage output from the device can be a significant fraction of the maximum voltage expected from the giant magnetoresistance effect. The nanoscale oscillators also display a number of attributes making them attractive for potential technological applications. These include the ability to frequency modulate the devices, phase lock them to external reference signals, and electronically control their phase relative to that of an input signal.
Electron Holography of Ferromagnetic Materials
Authors: McCartney Martha R. , Smith David J. 
Published: December 2007

AbstractElectron holography in the transmission electron microscope provides a powerful approach for characterizing nanoscale ferromagnetic materials. By measuring the phase shift of an electron beam that has passed through the magnetic field of the sample, quantitative measurement at the nanometer scale can be achieved. Thus, the technique allows both visualization as well as quantification of magnetic fields with high spatial resolution and sensitivity. Off‐axis electron holography is the operating mode that is most commonly used. The theoretical basis and experimental geometry for the technique are described. Representative examples of a range of ferromagnetic materials are then described in more detail. Finally, prospects and problems for future developments are briefly discussed.
Spin‐polarized Low Energy Electron Diffraction
Authors: Elmers Hans‐Joachim 
Published: December 2007

AbstractWe review recent progress in the understanding of the physics of ultrathin ferromagnetic films and surfaces that has been made using elastic spin‐polarized low‐energy electron diffraction (SPLEED). Further development of the experimental technique including high efficient electron sources, spin manipulation and imaging allows a wide range of applications. We report on a quantitative comparison of relativistic dynamical scattering calculations with SPLEED experiments on Fe(110) surfaces and Fe(100)/W(100) thin films leading to an understanding of the spatial distribution of spin densities. Exploiting the surface sensitivity in combination with the large asymmetry of SPLEED, it becomes feasible to investigate magnetic order in low‐dimensional systems and nanostructures in the vicinity of the Curie temperature. We analyze possibilities to improve electron polarization detectors using SPLEED at very low energies.
Spin‐polarized Low Energy Electron Microscopy
Authors: Bauer Ernst 
Published: December 2007

AbstractSpin‐polarized low‐energy electron microscopy (SPLEEM) is the imaging counterpart to spin‐polarized low‐energy electron diffraction (SPLEED). Therefore, it has the same possibilities and limitations as SPLEED but allows the study of the magnetization distribution in the top several atomic layers of crystals and highly oriented thin films. This chapter discusses the basics of the method, its experimental realization, the experimental procedures, and its applications to the study of the magnetization distribution in thin films as a function of film thickness, temperature, and magnetic field.
Investigation of Ultrathin Ferromagnetic Films by Magnetic Resonance
Authors: Baberschke Klaus 
Published: December 2007

AbstractThe microwave spectroscopy in magnetism exists in two versions: (i) The electron paramagnetic resonance (EPR) at which magnetic dipole transitions are excited between various Zeeman levels. (ii) The ferromagnetic resonance (FMR), here the applied magnetic fieldHproduces a uniform torque motion on the total magnetization. Thus the technique is suitable for studying magnetism above and below the Curie temperature. Moreover, the technique is sensitive down to 1010–1014spins, that is, fractions of a para‐ or ferromagnetic monolayer. For nanomagnetism the FMR/EPR techniques are combined with state‐of‐the‐art ultrahigh vacuum (UHV) technique, allowing an in situ study of uncapped magnetic monolayers in UHV. This article gives an overview of three aspects of current research: Firstly, the experimental details of UHV‐FMR. Secondly, the static parameters of the magnetism in monolayers: orbital and spin magnetic moments,g‐factor, the magnetic anisotropy energy (MAE), and the interlayer exchange coupling (IEC) of multilayers. Thirdly, from the linewidth of the magnetic resonance signal one deduces information on critical spin fluctuations, Gilbert damping, and magnon–magnon scattering. Of course, the FMR/EPR technique and its analysis of the spectra are well established. However, the combination with in situ UHV preparation opens a new field of research. Todays ab initio calculations of the magnetism of magnetic monolayers and nanostructures will be discussed and compared with the experimental FMR/EPR results.