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Projected Nesterov’S Proximal-Gradient Signal Recovery From Compressive Poisson Measurements, Renliang Gu, Aleksandar Dogandžić
Projected Nesterov’S Proximal-Gradient Signal Recovery From Compressive Poisson Measurements, Renliang Gu, Aleksandar Dogandžić
Aleksandar Dogandžić
We develop a projected Nesterov’s proximal-gradient (PNPG) scheme for reconstructing sparse signals from compressive Poisson-distributed measurements with the mean signal intensity that follows an affine model with known intercept. The objective function to be minimized is a sum of convex data fidelity (negative log-likelihood (NLL)) and regularization terms. We apply sparse signal regularization where the signal belongs to a nonempty closed convex set within the domain of the NLL and signal sparsity is imposed using total-variation (TV) penalty. We present analytical upper bounds on the regularization tuning constant. The proposed PNPG method employs projected Nesterov’s acceleration step, function restart, and …
Outage Constrained Robust Secure Transmission For Miso Wiretap Channels, Shuai Ma, Mingyi Hong, Engin Song, Xiangfeng Wang, Dechun Sun
Outage Constrained Robust Secure Transmission For Miso Wiretap Channels, Shuai Ma, Mingyi Hong, Engin Song, Xiangfeng Wang, Dechun Sun
Mingyi Hong
In this paper, we consider the robust secure beam-former design for multiple-input-single-output wiretap channels. Assuming that the eavesdroppers' channels are only partially available at the transmitter, we seek to maximize the secrecy rate under the transmit power and the secrecy rate outage probability constraint. The outage probability constraint requires that the secrecy rate exceed certain thresholds with high probability. Therefore, including such constraint in the design naturally ensures the desired robustness. Unfortunately, the presence of the probabilistic constraints makes the problem nonconvex and, hence, difficult to solve. In this paper, we investigate the outage probability constrained secrecy rate maximization problem …
Base Station Activation And Linear Transceiver Design For Optimal Resource Management In Heterogeneous Networks, Wei-Cheng Liao, Mingyi Hong, Ya-Feng Liu, Zhi-Quan Luo
Base Station Activation And Linear Transceiver Design For Optimal Resource Management In Heterogeneous Networks, Wei-Cheng Liao, Mingyi Hong, Ya-Feng Liu, Zhi-Quan Luo
Mingyi Hong
In a densely deployed heterogeneous network (HetNet), the number of pico/micro base stations (BS) can be comparable with the number of the users. To reduce the operational overhead of the HetNet, proper identification of the set of serving BSs becomes an important design issue. In this work, we show that by jointly optimizing the transceivers and determining the active set of BSs, high system resource utilization can be achieved with only a small number of BSs. In particular, we provide formulations and efficient algorithms for such joint optimization problem, under the following two common design criteria: i) minimization of the …
Min Flow Rate Maximization For Software Defined Radio Access Networks, Wei-Cheng Liao, Mingyi Hong, Hamid Farmanbar, Xu Li, Zhi-Quan Luo, Hang Zhang
Min Flow Rate Maximization For Software Defined Radio Access Networks, Wei-Cheng Liao, Mingyi Hong, Hamid Farmanbar, Xu Li, Zhi-Quan Luo, Hang Zhang
Mingyi Hong
We consider a cloud-based heterogeneous network of base stations (BSs) connected via a backhaul network of routers and wired/wireless links with limited capacity. The optimal provision of such networks requires proper resource allocation across the radio access links in conjunction with appropriate traffic engineering within the backhaul network. In this paper, we propose an efficient algorithm for joint resource allocation across the wireless links and flow control over the entire network. The proposed algorithm, which maximizes the min-rate among all the transmitted commodities, is based on a decomposition approach that leverages both the alternating direction method of multipliers (ADMM) and …
Sparse Signal Reconstruction From Polychromatic X-Ray Ct Measurements Via Mass Attenuation Discretization, Renliang Gu, Aleksandar Dogandžić
Sparse Signal Reconstruction From Polychromatic X-Ray Ct Measurements Via Mass Attenuation Discretization, Renliang Gu, Aleksandar Dogandžić
Aleksandar Dogandžić
We propose a method for reconstructing sparse images from polychromatic x-ray computed tomography (ct) measurements via mass attenuation coefficient discretization. The material of the inspected object and the incident spectrum are assumed to be unknown. We rewrite the Lambert-Beer’s law in terms of integral expressions of mass attenuation and discretize the resulting integrals. We then present a penalized constrained least-squares optimization approach forreconstructing the underlying object from log-domain measurements, where an active set approach is employed to estimate incident energy density parameters and the nonnegativity and sparsity of the image density map are imposed using negative-energy and smooth ℓ1-norm penalty …
Joint User Grouping And Linear Virtual Beamforming: Complexity, Algorithms And Approximation Bounds, Mingyi Hong, Zi Xu, Meisam Razaviyayn, Zhi-Quan Luo
Joint User Grouping And Linear Virtual Beamforming: Complexity, Algorithms And Approximation Bounds, Mingyi Hong, Zi Xu, Meisam Razaviyayn, Zhi-Quan Luo
Mingyi Hong
In a wireless system with a large number of distributed nodes, the quality of communication can be greatly improved by pooling the nodes to perform joint transmission/reception. In this paper, we consider the problem of optimally selecting a subset of nodes from potentially a large number of candidates to form a virtual multi-antenna system, while at the same time designing their joint linear transmission strategies. We focus on two specific application scenarios: 1) multiple single antenna transmitters cooperatively transmit to a receiver; 2) a single transmitter transmits to a receiver with the help of a number of cooperative relays. We …
Joint Access Point Selection And Power Allocation For Uplink Wireless Networks, Mingyi Hong, Alfredo Garcia, Jorge Barrera, Stephen G. Wilson
Joint Access Point Selection And Power Allocation For Uplink Wireless Networks, Mingyi Hong, Alfredo Garcia, Jorge Barrera, Stephen G. Wilson
Mingyi Hong
We consider the distributed uplink resource allocation problem in a multi-carrier wireless network with multiple access points (APs). Each mobile user can optimize its own transmission rate by selecting a suitable AP and by controlling its transmit power. Our objective is to devise suitable algorithms by which mobile users can jointly perform these tasks in a distributed manner. Our approach relies on a game theoretic formulation of the joint power control and AP selection problem. In the proposed game, each user is a player with an associated strategy containing a discrete variable (the AP selection decision) and a continuous vector …
Distributed Linear Precoder Optimization And Base Station Selection For An Uplink Heterogeneous Network, Mingyi Hong, Zhi-Quan Luo
Distributed Linear Precoder Optimization And Base Station Selection For An Uplink Heterogeneous Network, Mingyi Hong, Zhi-Quan Luo
Mingyi Hong
In a heterogeneous wireless cellular network, each user may be covered by multiple access points such as macro/pico/relay/femto base stations (BS). An effective approach to maximize the sum utility (e.g., system throughput) in such a network is to jointly optimize users' linear procoders as well as their BS associations. In this paper, we first show that this joint optimization problem is NP-hard and thus is difficult to solve to global optimality. To find a locally optimal solution, we formulate the problem as a noncooperative game in which the users and the BSs both act as players. We introduce a set …
Joint Base Station Clustering And Beamformer Design For Partial Coordinated Transmission In Heterogeneous Networks, Mingyi Hong, Ruoyu Sun, Hadi Baligh, Zhi-Quan Luo
Joint Base Station Clustering And Beamformer Design For Partial Coordinated Transmission In Heterogeneous Networks, Mingyi Hong, Ruoyu Sun, Hadi Baligh, Zhi-Quan Luo
Mingyi Hong
We consider the interference management problem in a multicell MIMO heterogeneous network. Within each cell there is a large number of distributed micro/pico base stations (BSs) that can be potentially coordinated for joint transmission. To reduce coordination overhead, we consider user-centric BS clustering so that each user is served by only a small number of (potentially overlapping) BSs. Thus, given the channel state information, our objective is to jointly design the BS clustering and the linear beamformers for all BSs in the network. In this paper, we formulate this problem from a {sparse optimization} perspective, and propose an efficient algorithm …
Derivative Estimation With Local Polynomial Fitting, Kris De Brabanter, Jos De Brabanter, Bart De Moor, Irene Gijbels
Derivative Estimation With Local Polynomial Fitting, Kris De Brabanter, Jos De Brabanter, Bart De Moor, Irene Gijbels
Kris De Brabanter
We present a fully automated framework to estimate derivatives nonparametrically without estimating the regression function. Derivative estimation plays an important role in the exploration of structures in curves (jump detection and discontinuities), comparison of regression curves, analysis of human growth data, etc. Hence, the study of estimating derivatives is equally important as regression estimation itself. Via empirical derivatives we approximate the qth order derivative and create a new data set which can be smoothed by any nonparametric regression estimator. We derive L1 and L2 rates and establish consistency of the estimator. The new data sets created by this technique are …
Empirical Data And Regression Analysis For Estimation Of Infrastructure Resilience With Application To Electric Power Outages, Cameron A. Mackenzie, Kash Barker
Empirical Data And Regression Analysis For Estimation Of Infrastructure Resilience With Application To Electric Power Outages, Cameron A. Mackenzie, Kash Barker
Cameron A. MacKenzie
Recent natural disasters have highlighted the need for increased planning for disruptive events. Forecasting damage and time that a system will be inoperable is important for disruption planning. The resilience of critical infrastructure systems, or their ability to recover quickly from a disruption, can mitigate adverse consequences of the disruption. This paper quantifies the resilience of a critical infrastructure sector through the dynamic inoperability input-output model (DIIM). The DIIM, which describes how inoperability propagates through a set of interdependent industry and infrastructure sectors following a disruptive event, includes a resilience parameter that has not yet been adequately assessed. This paper …
Linear Transceiver Design For A Mimo Interfering Broadcast Channel Achieving Max–Min Fairness, Meisam Razaviyayn, Mingyi Hong, Zhi-Quan Luo
Linear Transceiver Design For A Mimo Interfering Broadcast Channel Achieving Max–Min Fairness, Meisam Razaviyayn, Mingyi Hong, Zhi-Quan Luo
Mingyi Hong
This problem can be formulated as maximizing the minimum rate among all the users in an interfering broadcast channel (IBC). In this paper we show that when the number of antennas is at least two at each of the transmitters and the receivers, the min rate maximization problem is NP-hard in the number of users. Moreover, we develop a low-complexity algorithm for this problem by iteratively solving a sequence of convex subproblems. We theoretically establish the global convergence of the proposed algorithm to the set of stationary points, which may be suboptimal due to the non-convexity of the original minimum …
Mechanism Design For Base Station Association And Resource Allocation In Downlink Ofdma Network, Mingyi Hong, Alfredo Garcia
Mechanism Design For Base Station Association And Resource Allocation In Downlink Ofdma Network, Mingyi Hong, Alfredo Garcia
Mingyi Hong
We consider a resource management problem in a multi-cell downlink OFDMA network whereby the goal is to find the optimal combination of (i) assignment of users to base stations and (ii) resource allocation strategies at each base station. Efficient resource management protocols must rely on users truthfully reporting privately held information such as downlink channel states. However, individual users can manipulate the resulting resource allocation (by misreporting their private information) if by doing so they can improve their payoff. Therefore, it is of interest to design efficient resource management protocols that are strategy-proof, i.e. it is in the users' best …
An Analytical Model Of A Ferrite-Cored Inductor Used As An Eddy Current Probe, John R. Bowler, Yi Lu, Theodoros P. Theodoulidis
An Analytical Model Of A Ferrite-Cored Inductor Used As An Eddy Current Probe, John R. Bowler, Yi Lu, Theodoros P. Theodoulidis
John R. Bowler
An analytical model of an axisymmetric eddy current ferrite-cored probe above a multi-layered conducting half-space has been developed using a procedure in which the domain of the problem is truncated radially. This means that solutions can be expressed in the form of generalized Fourier-Bessel series. The expansion coefficients are found by matching the field across the interfaces between the subregions of the problem. Initially, the magnetic vector potential of a simple circular current filament is expanded in a series form. The solution is then modified to accommodate an infinitely long coaxial ferrite core, and the principle of superposition is invoked …
Considering Etiquette In The Design Of An Adaptive System, Michael C. Dorneich, Patricia May Ververs, Santosh Mathan, Stephen Whitlow, Caroline C. Hayes
Considering Etiquette In The Design Of An Adaptive System, Michael C. Dorneich, Patricia May Ververs, Santosh Mathan, Stephen Whitlow, Caroline C. Hayes
Michael C. Dorneich
In this article, the authors empirically assess the costs and benefits of designing an adaptive system to follow social conventions regarding the appropriateness of interruptions. Interruption management is one area within the larger topic of automation etiquette. The authors tested these concepts in an outdoor environment using the Communications Scheduler, a wearable adaptive system that classifies users' cognitive state via brain and heart sensors and adapts its interactions. Designed to help dismounted soldiers, it manages communications in much the same way as a good administrative assistant. Depending on a combination of message priority, user workload, and system state, it decides …
Evaluation Of Eddy-Current Probe Signals Due To Cracks In Fastener Holes, John R. Bowler, Theodoros P. Theodoulidis, Hui Xie, Yuan Ji
Evaluation Of Eddy-Current Probe Signals Due To Cracks In Fastener Holes, John R. Bowler, Theodoros P. Theodoulidis, Hui Xie, Yuan Ji
John R. Bowler
Cracks in conductors are detected through changes in the impedance of a coil that induces current in the material. In order to gain insight into the physics of the inspection, we have developed a theoretical and computational model that predicts the signals due to cracks in circular cylindrical holes using a boundary element calculation. In formulating the problem, the electromagnetic field is decomposed into transverse electric and transverse magnetic scalar modes. The effect of a planar crack in an electromagnetic field is represented by an electric current dipole layer orientated normal to the crack surface. The dipole density is determined …
Analysis Of Arc-Electrode Capacitive Sensors For Characterization Of Dielectric Cylindrical Rods, Tianming Chen, Nicola Bowler, John R. Bowler
Analysis Of Arc-Electrode Capacitive Sensors For Characterization Of Dielectric Cylindrical Rods, Tianming Chen, Nicola Bowler, John R. Bowler
John R. Bowler
An arc-electrode capacitive sensor has been developed for quantitative characterization of permittivity of cylindrical dielectric rods. The material property of the cylindrical test piece can be inversely determined from the sensor output capacitance based on a theoretical model. For the modeling process, the electrostatic Green’s function due to a point source exterior to a dielectric rod is derived. The sensor output capacitance is numerically calculated using the method of moments (MoM), in which the integral equation is set up based on the electrostatic Green’s function. Numerical calculations on sensor configuration optimization are performed. Calculations also demonstrate the quantitative relationship between …
Kernel Regression In The Presence Of Correlated Errors, Kris De Brabanter, Jos De Brabanter, Johan A.K. Suykens, Bart De Moor
Kernel Regression In The Presence Of Correlated Errors, Kris De Brabanter, Jos De Brabanter, Johan A.K. Suykens, Bart De Moor
Kris De Brabanter
It is a well-known problem that obtaining a correct bandwidth and/or smoothing parameter in nonparametric regression is difficult in the presence of correlated errors. There exist a wide variety of methods coping with this problem, but they all critically depend on a tuning procedure which requires accurate information about the correlation structure. We propose a bandwidth selection procedure based on bimodal kernels which successfully removes the correlation without requiring any prior knowledge about its structure and its parameters. Further, we show that the form of the kernel is very important when errors are correlated which is in contrast to the …
Structures, Electronic Properties And Solid State Luminescence Of Cu(I) Iodide Complexes With 2,9-Dimethyl-1,10-Phenanthroline And Aliphatic Aminomethylphosphines Or Triphenylphosphine, Radoslaw Starosta, Malgorzata Puchalska, Joanna Cybinska, Maciej Barys, Anja V. Mudring
Structures, Electronic Properties And Solid State Luminescence Of Cu(I) Iodide Complexes With 2,9-Dimethyl-1,10-Phenanthroline And Aliphatic Aminomethylphosphines Or Triphenylphosphine, Radoslaw Starosta, Malgorzata Puchalska, Joanna Cybinska, Maciej Barys, Anja V. Mudring
Anja V. Mudring
The luminescent complexes of triphenylphosphine and two interesting aminomethylphosphines: P(CH2N(CH2CH2)2NCH3)3 and P(CH2N(CH2CH2)2O)3 with copper(I) iodide and 2,9-dimethyl-1,10-phenanthroline (dmp): [CuI(dmp)PPh3], [CuI(dmp)P(CH2N(CH2CH2)2NCH3)3] and [CuI(phen)P(CH2N(CH2CH2)2O)3] are presented in this work. These complexes were characterized in solution by means of NMR spectroscopy and their structures were crystallographically determined in the solid state. All complexes crystallize as the discrete dimers bound by π-stacking interactions between dmp rings. The coordination geometry about the Cu(I) centre is pseudo-tetrahedral showing small flattening and large rocking distortions. The investigated compounds exhibit intense orange photoluminescence in the solid state (emission peaks at r.t.: λmax = 588–592 nm; τ = 1.7–2.2 …
Long Term Resource Planning For Electric Power Systems Under Uncertainty, Sarah M. Ryan, James D. Mccalley, David L. Woodruff
Long Term Resource Planning For Electric Power Systems Under Uncertainty, Sarah M. Ryan, James D. Mccalley, David L. Woodruff
Sarah M. Ryan
Electric power systems are subject to uncertainties of many types and at many levels. In addition to the uncertain fuel prices, demand growth, and equipment outages included in traditional models, current trends portend increasing uncertainty due to such factors as the growth in generation from renewable sources which may be intermittent, the possibility of regulations to control carbon emissions, and the increasing price responsiveness of demand encouraged by smart grid technologies. This paper begins by discussing issues that confront electric system planners and explains the requirements for useful tools. We continue with a description of academic and commercial planning models …
Influence Of Reactive Atmosphere On Properties Of Cobalt Ferrite Thin Films Prepared Using Pulsed-Laser Deposition, A. Raghunathan, David C. Jiles, J. E. Snyder
Influence Of Reactive Atmosphere On Properties Of Cobalt Ferrite Thin Films Prepared Using Pulsed-Laser Deposition, A. Raghunathan, David C. Jiles, J. E. Snyder
David C. Jiles
A series of cobaltferrite (CFO) thin films were grown on SiO2/Si(100) substrates using pulsed-laser deposition (PLD) at substrate temperature (T DEP) of 250 °C and oxygen pressures (P O2) from 0.67 to 6.7 Pa. The influence of PO2 on crystal structure, phase mixture, deposition rate, and magnetic properties was investigated. It is shown in this study that there is a window of PO2 for optimized growth of nanograined CFO films at low T DEP and that either higher or lower values of PO2 produce undesirable multiphase mixtures. CFO filmsgrown at such low substrate temperature and optimized oxygen pressure on thermal …
Evaluation Of The Transient Potential Drop Of A Four-Point Probe, John R. Bowler
Evaluation Of The Transient Potential Drop Of A Four-Point Probe, John R. Bowler
John R. Bowler
The time-dependent voltage across the pick-up electrodes of a four point probe has been determined analytically for a transient current pulse injected into a thick conductive plate modeled as a half-space. This is a step towards analyzing more complex transient four point probe signals from measurements on inhomogeneous conductors. Potential applications include the evaluation of depth-dependent conductivity profiles in metals and semiconductors. The analysis of homogeneous conductors shows how the signals are characterized by a time constant of the drive current and additional time constants dependent on the electromagnetic material properties and electrode spacings
A Microflow Cytometer On A Chip, Joel P. Golden, Jason Kim, George P. Anderson, Nicole N. Hashemi, Peter J. Howell, Frances S. Ligler
A Microflow Cytometer On A Chip, Joel P. Golden, Jason Kim, George P. Anderson, Nicole N. Hashemi, Peter J. Howell, Frances S. Ligler
Nastaran Hashemi
A rapid, automated, multi-analyte Microflow Cytometer is being developed as a portable, field-deployable sensor for onsite diagnosis of biothreat agent exposure and environmental monitoring. The technology relies on a unique method for ensheathing a sample stream in continuous flow past an interrogation region where optical fibers provide excitation and collect emission. This approach efficiently focuses particles in the interrogation region of the fluidic channel, avoids clogging and provides for subsequent separation of the core and sheath fluids in order to capture the target for confirmatory assays and recycling of the sheath fluid. Fluorescently coded microspheres provide the capability for highly …
Effect Of Temperature Variation On The Magnetostrictive Properties Of Coalxfe2−Xo4, Ikenna C. Nlebedim, N. Ranvah, Y. Melikhov, P. I. Williams, J. E. Snyder, A. J. Moses, David C. Jiles
Effect Of Temperature Variation On The Magnetostrictive Properties Of Coalxfe2−Xo4, Ikenna C. Nlebedim, N. Ranvah, Y. Melikhov, P. I. Williams, J. E. Snyder, A. J. Moses, David C. Jiles
David C. Jiles
The effect of temperature variation on the magnetoelasticproperties of the CoAlxFe2−xO4 system (for x=0.0, 0.2, 05, and 0.7) has been studied. Substitution of Al3+ for Fe3+ was found to lower the Curie temperature of the samples and to change the lattice parameter. The magnitude of peak to peak magnetostriction, strain sensitivity, magnetomechanical hysteresis, and relative contributions of λ111 and λ100 to the resultant magnetostriction were found to vary with temperature. The results show the possibility of tailoring the magnetoelasticproperties of highly magnetostrictive cobalt ferrite at temperatures of interest by cation substitution.
Growth Of Crystalline Cobalt Ferrite Thin Films At Lower Temperatures Using Pulsed-Laser Deposition Technique, A. Raghunathan, David C. Jiles, Ikenna C. Nlebedim
Growth Of Crystalline Cobalt Ferrite Thin Films At Lower Temperatures Using Pulsed-Laser Deposition Technique, A. Raghunathan, David C. Jiles, Ikenna C. Nlebedim
David C. Jiles
Cobaltferritethin films were grown on SiO2/Si(100) substrates using pulsed-laser deposition technique at substrate temperatures ranging from 250 to 600 °C. Thermal expansion mismatch between the film and substrate appears to have a substantial effect on the magnetic properties of the cobaltferritefilms, due to the large magnetoelastic coupling of cobaltferrite. It was shown in this study, that polycrystalline films with (111)-preferred orientation could be prepared at substrate temperatures as low as 250 °C. The growth of crystalline cobaltferritefilms at such low temperatures indicates the potential to use cobaltferrite for microelectromechanical systemsdevices and sensor applications including integration with a wider range of …
Resistivity Recovery In Gd5si2.09ge1.91 By Annealing, Ravi L. Hadimani, David C. Jiles
Resistivity Recovery In Gd5si2.09ge1.91 By Annealing, Ravi L. Hadimani, David C. Jiles
David C. Jiles
Irreversible change in resistivity occurs in Gd5(SixGe1−x)4 (with 0.41
On The Interaction Of An Eddy Current Coil With A Right-Angled Conductive Wedge, John R. Bowler, Theodoros Theodoulidis
On The Interaction Of An Eddy Current Coil With A Right-Angled Conductive Wedge, John R. Bowler, Theodoros Theodoulidis
John R. Bowler
A fundamental problem in eddy-current nondestructive evaluation is one of finding the quasi-static electromagnetic field of a cylindrical coil in the vicinity of the edge of a metal block. Although the field can be calculated numerically, an effective analytical approach can potentially provide a better understanding of the edge fields and form the basis of a procedure for solving a whole class of related edge problems including edge structures that contain corner cracks. One can represent the metal block as a conductive quarter space in an unbounded region. However, it has been found that the analysis is more straightforward if …
Generalized Form Of Anhysteretic Magnetization Function For Jiles–Atherton Theory Of Hysteresis, A. Raghunathan, Y. Melikhov, J. E. Snyder, David C. Jiles
Generalized Form Of Anhysteretic Magnetization Function For Jiles–Atherton Theory Of Hysteresis, A. Raghunathan, Y. Melikhov, J. E. Snyder, David C. Jiles
David C. Jiles
A generalized form of anhysteretic magnetization function to extend Jiles–Atherton theory to different forms of anisotropy has been derived. The general equation for the function has been compared with those of calculations made on the basis of known equations for specific cases: axially anisotropic (one-dimensional), planar anisotropic (two-dimensional), and isotropic (three-dimensional). The Jiles–Atherton model using the proposed functional form of generalized anhysteretic magnetization function for anisotropy dependence has been validated and the necessary equations derived. It has been shown in this work that this functional form of anhysteretic magnetization with necessary boundary conditions can be reduced to the familiar specific …
Field Induced Structural Phase Transition At Temperatures Above The Curie Point In Gd5(Sixge1−X)4, Ravi L. Hadimani, Y. Melikhov, J. E. Snyder, David C. Jiles
Field Induced Structural Phase Transition At Temperatures Above The Curie Point In Gd5(Sixge1−X)4, Ravi L. Hadimani, Y. Melikhov, J. E. Snyder, David C. Jiles
David C. Jiles
Gd5(SixGe1−x)4 exhibits a field induced first order phase transition from a monoclinic paramagnetic to an orthorhombic ferromagnetic at temperatures above its Curie temperature for 0.41≤x≤0.51. The field required to induce the transition increases with temperature. This field induced first order phase transition was observed even above the projected second order phase transitiontemperature of the orthorhombic phase. This may be due to the fact that the applied magnetic field is so high that it causes the broadening to a wider range of higher temperatures of the second order phase transition of the orthorhombic phase, and at such high magnetic fields the …
Temperature Dependence Of Magnetic Anisotropy Of Germanium/Cobalt Cosubstituted Cobalt Ferrite, N. Ranvah, Y. Melikhov, Ikenna C. Nlebedim, David C. Jiles, J. E. Snyder, A. J. Moses, P. I. Williams
Temperature Dependence Of Magnetic Anisotropy Of Germanium/Cobalt Cosubstituted Cobalt Ferrite, N. Ranvah, Y. Melikhov, Ikenna C. Nlebedim, David C. Jiles, J. E. Snyder, A. J. Moses, P. I. Williams
David C. Jiles
The variations in magnetization and magnetic anisotropy of Ge4+/Co2+ cosubstituted cobaltferrite with temperature were investigated for a series of compositions Co1+xGexFe2−2xO4 (0≤x≤0.4). The magnetization at 5 T and low temperature were observed to increase for all Ge/Co cosubstituted samples compared to pure CoFe2O4. Hysteresis loops were measured for each sample over the magnetic field range of −5 T to +5 T for temperatures in the range of 10–400 K. The high field regions of these loops were modeled using Law of Approach to saturation, which represents the rotational and forced magnetization processes. The first order cubic magnetocrystalline anisotropy coefficient K1 …