bluuebunny/crossref_metadata_2025 huggingface dataset:
Downlink training scheme for massive MIMO systems
Authors: Qian Chen , Wang Zhaocheng , Dai Linglong , Chen Jinhui , Sun Chen
Published: October 2015

A novel downlink training scheme is proposed for time‐division duplex massive MIMO systems. Different from conventional solutions, including the cell‐specific reference signal in LTE, the UE‐specific reference signal in LTE‐A and the commonly used method without the downlink training sequence, the cell‐specific demodulation reference signal is proposed by utilising the inherent asymptotic orthogonality, which is shared by all users within one cell and used for the estimation of effective channel coefficients. The training overhead is reduced and the downlink spectral efficiency can be improved considerably.
Bidirectional optical transcutaneous telemetric link for brain machine interface
Authors: Liu T. , Anders J. , Ortmanns M.
Published: October 2015

A wavelength division multiplexing‐based bidirectional optical transcutaneous telemetric data link for brain machine interfaces is reported. By converting the digitised electronic signals to a stream of infrared and visible optical pulses, the optical telemetry wirelessly transmits data between the implanted neural recorder/stimulator and the external control devices. A red visible vertical cavity surface emitting laser (VCSEL) with a peak wavelength of 680 nm is used in the downlink to transmit data from the external base unit to the implant. A near infrared VCSEL with a peak wavelength of 850 nm is utilised in the uplink for data transmission from the implants to the external device. An optical filter is applied to minimise the interference between the two channels. In‐vitro experiments show that the uplink is capable of transmitting data at 100 Mbps through 2 mm of porcine skin while the downlink is simultaneously working at a rate of 1 Mbps. The power consumption of the implant part of the telemetry, including the transmitter for the uplink and the receiver for the downlink are 3.2 mW and 290 μW, corresponding to a transmission power efficiencies of 32 and 290 pJ/bit, respectively, which are among the best reported and unseen for bidirectional high‐speed transcutaneous communication.
EM‐based SNR estimator for faster‐than‐Nyquist signalling system
Authors: Liang Xiaohu , Liu Aijun , Pan Xiaofei , Wu Gang
Published: October 2015

Considering the intentionally introduced inter‐symbol interference and coloured noise, proposed is a new signal‐to‐noise ratio (SNR) estimator based on the expectation–maximisation algorithm for the faster‐than‐Nyquist signalling system. The proposed SNR estimator can maximise the likelihood function by iteratively using the soft information from the channel decoder. Moreover, the new SNR estimator can be applied into high‐order modulation. The performance of the proposed SNR estimator is verified and tested.
Joint structure–texture sparse coding for quality prediction of stereoscopic images
Authors: Li Kemeng , Shao Feng , Jiang Gangyi , Yu Mei
Published: October 2015

A quality prediction method for stereoscopic images is proposed based on joint structure–texture sparse coding. The goal is to predict the perceptual quality of a stereoscopic image by solving the joint structure–texture sparse coding problem. First, structure and texture dictionaries from a training database are learnt. Then, the quality score for a testing stereoscopic image is predicted by computing left and right sparse feature similarity indexes, respectively, and combining them together. Experimental results on two 3D image‐quality assessment databases demonstrate that the proposed method can achieve high consistent alignment with subjective assessment.
Impulse radio UWB receiver analysis of non‐coherently detected orthogonal signal
Authors: Niemelä V. , Kumpuniemi T. , Hämäläinen M. , Iinatti J.
Published: October 2015

In this Letter, performance analysis of an impulse radio (IR) ultra wideband (UWB) correlation based receiver utilising non‐coherent detection of orthogonal signalling is provided. The receiver's performance is presented through analysis and simulations in the additive white Gaussian noise (AWGN) channel. Results which show that in non‐coherent detection of binary orthogonal signalling there is a difference between the traditional narrowband and IR approaches are provided. In the narrowband communication, there is a well‐known, approximately 1 dB, difference between coherent and non‐coherent orthogonal signal detection in AWGN. It is demonstrated here that in the binary orthogonal signalling of IR receiver the difference between coherent and non‐coherent detection is insignificant, only tenths of decibels. This can be significant piece of information while considering different receiver structures for wireless sensor networks.
Partial spectral search‐based DOA estimation method for co‐prime linear arrays
Authors: Sun Fenggang , Lan Peng , Gao Bin
Published: October 2015

A computationally efficient method for direction‐of‐arrival (DOA) estimation is proposed for co‐prime linear arrays. For each DOA, multiple peaks are generated in the spatial spectrum for each subarray, which are proven to be uniformly distributed in the transformed domain. By searching over a limited sector to find an arbitrary peak, all the others can be recovered without a spectral search. Finally, the DOAs can be uniquely estimated by finding the common peaks of the two decomposed subarrays. The proposed method provides increased estimation accuracy with a substantially reduced computational burden. Simulation results validate the effectiveness of the proposed method.
Key‐layered normal distributions transform for point cloud registration
Authors: Hong Hyunki , Lee B.H.
Published: October 2015

A new scan matching algorithm is proposed using the concept of key layers. In the conventional multi‐layered normal distributions transform (MLNDT), the number of layers and iterations per layer are fixed and mismatches in point clouds occur due to the limited number of optimising iterations per layer. Moreover, the accuracy of registration is low and the number of layers is heuristically determined in MLNDT. The proposed key‐layered normal distributions transform (KLNDT) works well with both enhanced success rate and accuracy. It is also possible for KLNDT to register in higher layers than the traditional MLNDT.
High performance LPF Structure with sharp roll‐off and low VSWR
Authors: Mousavi S.M.H. , Makki S.V.A. , Hooshangi Sh. , Alirezaee Sh. , Siahkamari H. , Ahmadi M.
Published: October 2015

A symmetrical compact microstrip lowpass filter (LPF) with ultra‐wide rejection band and low voltage standing wave ratio (VSWR) using a novel structure of stepped impedance and butterfly‐shaped resonators is presented and fabricated. The LPF has a 3 dB cut‐off frequency at 1.513 GHz. The series structure of the butterfly‐shaped resonators result in a high roll‐off rate of 187.8 dB/GHz. By generating multiple transmission zeros, a wide stopband (with 35 dB rejection degree) is achieved. To reach a small circuit, the bended transmission line is properly utilised. Moreover, 171% relative stopband bandwidth and dimensions of 0.087λg × 0.157λg (λg is the guided wavelength at 1.513 GHz) are other specifications of this LPF. In addition, an acceptable match is obtained between the simulated and measured responses. In the end, the LPF achieves a high figure‐of‐merit of 82288.
Reduction of detuning effects using robust parameter design for implantable antennas
Authors: Chen Yen‐Sheng
Published: October 2015

A new design framework for implantable antennas to reduce detuning effects due to various dielectric properties is presented. Conventionally, in order to overcome the detuning effects, it is highly demanded to have a broadband impedance matching to compensate the frequency shift. However, achieving a wider impedance bandwidth leads to larger antenna dimensions, and lack a mathematical treatment to optimise implantable antennas against the variation of tissue properties to date. A new methodology based on robust parameter design is proposed to cope with the detuning effects. Instead of designing the antenna in one single tissue environment, the proposed technique analyses the variation of dielectric properties in distinct tissue environments. The optimised performances show that robust impedance matching in the medical implant communication services band is achieved, although the dielectric constant varies from 35 to 55. Simulated and measured results are presented to demonstrate the validity of the proposed design methodology.
5 GHz all‐digital delay‐locked loop for future memory systems beyond double data rate 4 synchronous dynamic random access memory
Authors: Lee Dongyeol , Kim Jongsun
Published: October 2015

A new low‐power, fast‐locking, all‐digital delay‐locked loop (DLL) that uses a disposable time‐to‐digital converter (TDC) is presented for future memory systems beyond double data rate 4. To achieve fast locking and high‐frequency operation, the proposed DLL utilises a new hybrid (TDC + binary + sequential) search algorithm that results in a fast locking time of 11 clock cycles without the false lock and harmonic lock problems. By minimising the intrinsic delay of the digital delay line, the proposed DLL achieves an operating frequency range of 1.5–5.0 GHz which is higher than that of the current state‐of‐the‐art all‐digital DLLs. The DLL is fabricated in a 65 nm CMOS process and it achieves a peak‐to‐peak (p–p) output clock jitter of 14 ps (with a p–p input clock jitter of 8 ps) at 5 GHz. The DLL consumes 6.9 mW at 1 V and occupies an active area of 0.025 mm2.
Extremely compact ultra‐wideband power divider using hybrid slotline/microstrip‐line transition
Authors: Song Kaijun , Zhu Yu , Duan Qi , Fan Maoyu , Fan Yong
Published: October 2015

A novel extremely compact ultra‐wideband (UWB) power divider using hybrid slotline/microstrip‐line transition is proposed, designed, and implemented. The even‐ and odd‐mode equivalent‐circuit method is applied to the proposed power divider. Measured results show that excellent impedance matching at the input/output ports, amplitude and phase balance, and the isolation between the two output ports are observed within the UWB band. The UWB power divider has a simple structure and good performance.
Simple sampling clock synchronisation scheme for reduced‐guard‐interval coherent optical OFDM systems
Authors: Omomukuyo O. , Chang D. , Dobre O.A. , Venkatesan R. , Ngatched T.M.N.
Published: October 2015

A simple data‐aided scheme for sampling clock synchronisation in reduced‐guard‐interval coherent optical OFDM (RGI‐CO‐OFDM) systems is proposed. In the proposed scheme, the sampling clock offset (SCO) is estimated by using the training symbols reserved for channel estimation, thus avoiding extra training overhead. The SCO is then compensated by resampling, using a time‐domain interpolation filter. The feasibility of the proposed scheme is demonstrated by means of numerical simulations in a 32 Gbaud 16‐QAM dual‐polarisation RGI‐CO‐OFDM system.
Block sparse memory improved proportionate affine projection sign algorithm
Authors: Liu J. , Grant S.L.
Published: October 2015

A block sparse memory improved proportionate affine projection sign algorithm (BS‐MIP‐APSA) is proposed for block sparse system identification under impulsive noise. The new BS‐MIP‐APSA not only inherits the performance improvement for block‐sparse system identification, but also achieves robustness to impulsive noise and the efficiency of the memory improved proportionate affine projection sign algorithm (MIP‐APSA). Simulations indicate that it can provide both faster convergence rate and better tracking ability under impulsive interference for block sparse system identification as compared with APSA and MIP‐APSA.
Effective approach for calculating critical speeds of high‐speed permanent magnet motor rotor‐shaft assemblies
Authors: Huang Ziyuan , Han Bangcheng
Published: October 2015

An effective approach is presented for large errors in calculating critical speed of rotor‐shaft assembly with the commercial finite element software, is intended to develop the discrete model of the rotor‐shaft assembly by using lumped mass method, which is supported by active magnetic bearings. The first two bending critical speeds are analysed by optimising the flexural rigidity coefficient based on transfer matrix method. Compared with experimental modal testing and finite element analysis, the results of the transfer matrix method are in good agreement with modal measurement, the percentage errors of the first two bending natural frequencies are 0.21 and 2.1%, respectively. Owing to the higher accuracy and numerical stability, the method used in this study is an effective way to calculate the critical speed of the rotor‐shaft assembly.
Parameter identification and prediction of Jiles–Atherton model for DC‐biased transformer using improved shuffled frog leaping algorithm and least square support vector machine
Authors: Wang Fenghua , Geng Chao , Su Lei
Published: October 2015

This study presents a novel approach for the modelling of transformer core magnetisation characteristics under DC bias condition by using the inverse Jiles–Atherton (J–A) model. An improved shuffled frog leaping algorithm (SFLA) is proposed to identify the five parameters of J–A model, where an adaptive chaotic mutation operation is added in the global searching process to increase the identification accuracy. With the proposed algorithm, the J–A model parameters under different DC components are identified based on the DC‐bias experiment on the real transformer. The conventional SFLA and particle swarm optimisation (PSO) method are also applied to identify the parameters of J–A model. All the identified results are compared with the measured B–H curves to verify their identification accuracy. Moreover, the least square support vector machine (LSSVM) algorithm is used to predict the J–A model parameters of transformer under larger DC component from the previously identified parameters in smaller DC. The calculated results have shown that the improved SFLA has higher identification accuracy than the conventional SFLA and PSO methods. Furthermore, LSSVM algorithm can effectively forecast the transformer magnetisation character under large DC bias condition, which is beneficial for the research of transformer DC bias problem.
Reliability modelling and assessment of electric motor driven systems in hydrocarbon industries
Authors: Al Badawi Fahad S. , AlMuhaini Mohammad
Published: October 2015

Reliability is a significant performance index for any electrical equipment in the industry, especially for electric motor driven (EMD) systems. Modelling the reliability of an EMD system is a difficult and challenging task. However, based on field data, the dominant failure modes of some motor system parts can be used to develop a simple and credible reliability model. This study proposes a failure rate prediction model for an EMD system that is currently in use in hydrocarbon industries. In addition, a fault tree model was designed to identify the root causes of the failures and the failure mechanism of the most dominates failure modes in EMD systems. To accomplish the study's objectives, an existing failure databank of over 100 failures of EMD systems was collected and surveyed from the field. The historical information and failure rate models that were collected for the electric motors are investigated and used to model the prediction model of the EMD system. Three competing failure modes were found to dominate motor life: bearing failures, winding failures and shaft failures. A mathematical model for each of these failure modes with dominant variables is developed, and a risk failure model is established.
Control strategy for hybrid‐excited switched‐flux permanent magnet machines
Authors: Pothi Nattapong , Zhu Z.Q. , Afinowi Ibrahim A. A. , Lee B. , Ren Y.
Published: October 2015

Hybrid‐excited permanent magnet (PM) machines utilise the coordinated operation between the PM and the field excitation current. To enhance the effectiveness of the field excitation current, iron flux bridges are applied to hybrid‐excited switched‐flux PM machines. This study proposes a new control strategy in which the d‐axis current is utilised, while the field excitation current is controlled towards zero rather than negative in the flux‐weakening mode. These reference currents are determined by the voltage error regulation method. The special magnetic circuit can effectively reduce the d‐axis flux‐linkage by either partially short‐circuiting the PM flux via the iron bridge or removing the field excitation current. The proposed method exhibits advantages, such as highly enhanced torque response in the constant torque region, extended speed range, robustness against machine parameters, and higher efficiency in flux‐weakening region. The feasibility of the proposed method is verified by detailed experimental results.
Performance investigation of hybrid excited switched flux permanent magnet machines using frozen permeability method
Authors: Li Guang‐Jin , Zhu Zi‐Qiang , Jewell Geraint
Published: October 2015

This study investigates the electromagnetic performance of a hybrid excited switched flux permanent magnet (SFPM) machine using the frozen permeability (FP) method. The flux components due to PMs, field excitation windings and armature windings have been separated using the FP method. It has been used to separate the torque components due to the PMs and excitations, providing a powerful insight into the torque generation mechanism of hybrid excited SFPM machines. It also allows the accurate calculation of d‐ and q‐axis inductances, which will then be used to calculate the torque, power and power factor against rotor speed to compare the relative merits of hybrid excited SFPM machines with different types of PMs (i.e. NdFeB, SmCo and Ferrite). This offers the possibility of choosing appropriate PMs for different applications (maximum torque or maximum speed). Although only one type of hybrid excited PM machine has been employed to carry out the investigations, the method used in this study can also be extended to other hybrid excited PM machines. The predicted results have been validated by tests.
Model predictive torque control of induction motor drives with reduced torque ripple
Authors: Zhang Yongchang , Yang Haitao , Xia Bo
Published: October 2015

Model predictive torque control (MPTC) is emerging as a high‐performance control strategy for induction motor (IM) drives, due to its intuitive nature, flexibility to incorporate constraints and quick dynamic response. However, the implementation of MPTC requires high computational ability and the use of single voltage vector during one control period fails to reduce the torque ripple to the minimal value. This study proposes an improved MPTC for IM drives with reduced torque ripple and low complexity. On the basis of the relationship between stator current and stator flux, the complicated current prediction for each voltage vector is eliminated, reducing the control complexity significantly. Torque ripple reduction is achieved by allocating only a fraction of control period to the active vector selected from conventional MPTC, whereas the rest of time is allocated for a null vector. Two kinds of methods for optimising the duty ratio of the active vector are proposed and evaluated in detail. Presented experimental results prove that, compared with conventional MPTC, the proposed MPTC achieves better steady‐state performance by reducing the torque ripple significantly. Meanwhile, the quick dynamic response of conventional MPTC is reserved.
Segmentation strategy for the efficient analysis and design of substrate integrated waveguide directly coupled cavity filters
Authors: Angel Martinez Juan , Belenguer Ángel , Esteban Héctor , Boria Vicente E.
Published: October 2015

In this study, a new segmentation strategy is presented for the full‐wave analysis of directly coupled cavity filters in substrate integrated waveguide (SIW) technology. The whole SIW filter is enclosed inside an external fictitious rectangular waveguide, which does not affect the propagation inside the SIW assuming that the SIW is well designed and there is no significant power leakage. The external rectangular waveguide allows to easily segment the structure into building blocks that are composed of circular metallic vias inside a rectangular waveguide. The generalised scattering matrix of these building blocks is obtained with highly efficient techniques specifically suited for the analysis of H‐plane rectangular waveguide devices. Some building blocks are repeated along the structure, and their scattering matrix has to be computed only once. The scattering matrices of all the building blocks are cascaded and the scattering matrix of the whole filter is obtained. A SIW filter of eight coupled cavities with a bandpass response centred at 11 GHz is analysed. Results from this analysis show that the computational time has been significantly reduced when compared with other specific SIW analysis methods or with commercial general purpose software, while maintaining a good accuracy.
Magnonic crystals—Prospective structures for shaping spin waves in nanoscale
Authors: Rychły J. , Gruszecki P. , Mruczkiewicz M. , Kłos J. W. , Mamica S. , Krawczyk M.
Published: October 2015

We have investigated theoretically band structure of spin waves in magnonic crystals with periodicity in one- (1D), two- (2D) and three-dimensions (3D). We have solved Landau–Lifshitz equation with the use of plane wave method, finite element method in frequency domain and micromagnetic simulations in time domain to find the dynamics of spin waves and spectrum of their eigenmodes. The spin wave spectra were calculated in linear approximation. In this paper we show usefulness of these methods in calculations of various types of spin waves. We demonstrate the surface character of the Damon–Eshbach spin wave in 1D magnonic crystals and change of its surface localization with the band number and wavenumber in the first Brillouin zone. The surface property of the spin wave excitation is further exploited by covering plate of the magnonic crystal with conductor. The band structure in 2D magnonic crystals is complex due to additional spatial inhomogeneity introduced by the demagnetizing field. This modifies spin wave dispersion, makes the band structure of magnonic crystals strongly dependent on shape of the inclusions and type of the lattice. The inhomogeneity of the internal magnetic field becomes unimportant for magnonic crystals with small lattice constant, where exchange interactions dominate. For 3D magnonic crystals, characterized by small lattice constant, wide magnonic band gap is found. We show that the spatial distribution of different materials in magnonic crystals can be explored for tailored effective damping of spin waves.
Graded-index magnonics
Authors: Davies C. S. , Kruglyak V. V.
Published: October 2015

The wave solutions of the Landau–Lifshitz equation (spin waves) are characterized by some of the most complex and peculiar dispersion relations among all waves. For example, the spin-wave (“magnonic”) dispersion can range from the parabolic law (typical for a quantum-mechanical electron) at short wavelengths to the nonanalytical linear type (typical for light and acoustic phonons) at long wavelengths. Moreover, the long-wavelength magnonic dispersion has a gap and is inherently anisotropic, being naturally negative for a range of relative orientations between the effective field and the spin-wave wave vector. Nonuniformities in the effective field and magnetization configurations enable the guiding and steering of spin waves in a deliberate manner and therefore represent landscapes of graded refractive index (graded magnonic index). By analogy to the fields of graded-index photonics and transformation optics, the studies of spin waves in graded magnonic landscapes can be united under the umbrella of the graded-index magnonics theme and are reviewed here with focus on the challenges and opportunities ahead of this exciting research direction.
Magnetic states in multiply-connected flat nanoelements
Authors: Bogatyrev Andrei B. , Metlov Konstantin L.
Published: October 2015

Flat magnetic nanoelements are an essential component of current and future spintronic devices. By shaping an element it is possible to select and stabilize chosen metastable magnetic states, control its magnetization dynamics. Here, using a recent significant development in mathematics of conformal mapping, complex variable based approach to the description of magnetic states in planar nanoelements is extended to the case when elements are multiply-connected (that is, contain holes or magnetic antidots). We show that presence of holes implies a certain restriction on the set of magnetic states of nanoelement.
Effective magnetization damping for a dynamical spin texture in metallic ferromagnet
Authors: Sukhostavets Oksana V. , Gonzalez Julian M. , Guslienko Konstantin Y.
Published: October 2015

An additional magnetization damping for an inhomogeneous spin texture in metallic ferromagnets is calculated on the basis of the s–d exchange model. The effect of conduction electrons on the magnetization dynamics is accounted for the case of slowly varying spin texture within adiabatic approximation by using a coordinate transformation to the local quantization axis. The moving magnetic vortex in a circular nanodot made of permalloy is considered as an example. The dependence of the damping on the dot geometrical sizes is obtained. It is found that the additional damping can reach up to 50% of magnitude of the phenomenological Gilbert damping in the Landau–Lifshitz equation of magnetization motion and should be taken into account for any inhomogeneous spin texture dynamics in ferromagnetic metals.
Vortex-antivortex dynamics driven by spin-torque in a nanocontact
Authors: Zaspel C. E. , Kireev V. E.
Published: October 2015

A spin-polarized current in a nanocontact has been shown to induce the formation of a magnetic vortex at the nanocontact by the Oersted field, and spin-torque drives the vortex core in an elliptical orbit about the nanocontact. For the case of an external in-plane magnetic field in an extended free layer, the magnetization will be uniform far from the nanocontact, implying that vortex formation must be accompanied by the formation of an antivortex. Using the Thiele approach to describe the vortex-antivortex dynamics it is shown that the frequency of gyrotropic motion of the vortex is a function of the nanocontact current which is linear for large vortex-antivortex separations and it becomes nonlinear as the separation is decreased. The equilibrium vortex -antivortex separation can be controlled by the nanocontact current as well as the external magnetic field.
Formation of Bose–Einstein magnon condensate via dipolar and exchange thermalization channels
Authors: Bozhko D. A. , Clausen P. , Chumak A. V. , Kobljanskyj Yu. V. , Hillebrands B. , Serga A. A.
Published: October 2015

Thermalization of a parametrically driven magnon gas leading to the formation of a Bose–Einstein condensate at the bottom of a spin-wave spectrum was studied by time- and wavevector-resolved Brillouin light scattering spectroscopy. Two distinct channels of the thermalization process related on dipolar and exchange parts of a magnon gas spectrum are clearly determined. It has been found that the magnon population in these thermalization channels strongly depends on applied microwave pumping power. The observed magnon redistribution between the channels is caused by the downward frequency shift of the magnon gas spectrum due to the decrease of the saturation magnetization in the course of injection of parametrically pumped magnons.
Thermoelectric spin transport through ferromagnetic heterostructures
Authors: Bender Scott A.
Published: October 2015

We study how spin is transferred by ferromagnetic dynamics in a charge insulator in response to a thermoelectric bias, which is established by supplying heat and/or spin accumulation via normal leads. At zero temperature, magnetic anisotropies pin the macroscopic order, which necessitates a finite threshold bias to induce a spin current in a steady state of unpinned dynamics. At finite temperatures, however, thermal spin waves provide a spin transport channel in response to a linear thermoelectric bias. The theoretical description is rooted in the Landau–Lifshitz–Gilbert phenomenology both for the macroscopic dynamics of the magnetic order and quantum kinetics of thermal magnons. In this paper we connect the classical and quantum aspects of the underlying magnetic dynamics and spin transport, as well as provide a unified view of the exchange mediated bias of spin See-beck physics of the magnetic interface and bulk.
Magnetic droplet solitons in orthogonal spin valves
Authors: Chung Sunjae , Majid Mohseni S. , Eklund Anders , Dürrenfeld Philipp , Ranjbar Mojtaba , Sani Sohrab R. , Anh Nguyen T. N. , Dumas Randy K. , Åkerman Johan
Published: October 2015

We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented.
Analysis of the beam halo in negative ion sources by using 3D3V PIC code
Authors: Miyamoto K. , Nishioka S. , Goto I. , Hatayama A. , Hanada M. , Kojima A. , Hiratsuka J.
Published: October 2015

The physical mechanism of the formation of the negative ion beam halo and the heat loads of the multi-stage acceleration grids are investigated with the 3D PIC (particle in cell) simulation. The following physical mechanism of the beam halo formation is verified: The beam core and the halo consist of the negative ions extracted from the center and the periphery of the meniscus, respectively. This difference of negative ion extraction location results in a geometrical aberration. Furthermore, it is shown that the heat loads on the first acceleration grid and the second acceleration grid are quantitatively improved compared with those for the 2D PIC simulation result.
Rapid trench initiated recrystallization and stagnation in narrow Cu interconnect lines
Authors: O'Brien Brendan B. , Rizzolo Michael , Prestowitz Luke C. , Dunn Kathleen A.
Published: October 2015

Understanding and ultimately controlling the self-annealing of Cu in narrow interconnect lines has remained a top priority in order to continue down-scaling of back-end of the line interconnects. Recently, it was hypothesized that a bottom-up microstructural transformation process in narrow interconnect features competes with the surface-initiated overburden transformation. Here, a set of transmission electron microscopy images which captures the grain coarsening process in 48 nm lines in a time resolved manner is presented, supporting such a process. Grain size measurements taken from these images have demonstrated that the Cu microstructural transformation in 48 nm interconnect lines stagnates after only 1.5 h at room temperature. This stubborn metastable structure remains stagnant, even after aggressive elevated temperature anneals, suggesting that a limited internal energy source such as dislocation content is driving the transformation. As indicated by the extremely low defect density found in 48 nm trenches, a rapid recrystallization process driven by annihilation of defects in the trenches appears to give way to a metastable microstructure in the trenches.
Nonperturbative renormalization of scalar quantum electrodynamics in d=3
Authors: Dimock J.
Published: October 2015

For scalar quantum electrodynamics on a three-dimensional toroidal lattice with a fine lattice spacing, we consider the renormalization problem of choosing counter terms depending on the lattice spacing, so that the theory stays finite as the spacing goes to zero. We employ a renormalization group method which analyzes the flow of the mass and the vacuum energy as a problem in discrete dynamical systems. The main result is that counter terms can be chosen so that at the end of the iteration these quantities take preassigned values. No use is made of perturbation theory. The renormalization group transformations are defined with bounded fields, an approximation which can be justified in Balaban’s approach to the renormalization group.
Tensorial analysis of Eshelby stresses in 3D supercooled liquids
Authors: Lemaître Anaël
Published: October 2015

It was recently proposed that the local rearrangements governing relaxation in supercooled liquids impress on the liquid medium long-ranged (Eshelby) stress fluctuations that accumulate over time. From this viewpoint, events must be characterized by elastic dipoles, which are second order tensors, and Eshelby fields are expected to show up in stress and stress increment correlations, which are fourth order tensor fields. We construct here an analytical framework that permits analyzing such tensorial correlations in isotropic media in view of accessing Eshelby fields. Two spherical bases are introduced, which correspond to Cartesian and spherical coordinates for tensors. We show how they can be used to decompose stress correlations and thus test such properties as isotropy and power-law scalings. Eshelby fields and the predicted stress correlations in an infinite medium are shown to belong to an algebra that can conveniently be described using the spherical tensor bases. Using this formalism, we demonstrate that the inherent stress field of 3D supercooled liquids is power law correlated and carries the signature of Eshelby fields, thus supporting the idea that relaxation events give rise to Eshelby stresses that accumulate over time.
Understanding the sensitivity of nucleation free energies: The role of supersaturation and temperature
Authors: Keasler Samuel J. , Siepmann J. Ilja
Published: October 2015

Simulations are used to investigate the vapor-to-liquid nucleation of water for several different force fields at various sets of physical conditions. The nucleation free energy barrier is found to be extremely sensitive to the force field at the same absolute conditions. However, when the results are compared at the same supersaturation and reduced temperature or the same metastability parameter and reduced temperature, then the differences in the nucleation free energies of the different models are dramatically reduced. This finding suggests that comparisons of experimental data and computational predictions are most meaningful at the same relative conditions and emphasizes the importance of knowing the phase diagram of a given computational model, but such information is usually not available for models where the interaction energy is determined directly from electronic structure calculations.
Tuning of magnetic ordering by Y substitution onto Tb site in the nanocrystalline TbMnO3
Authors: Chakraborty Keka R. , Shukla Rakesh , Kaushik S. D. , Mukadam M. D. , Siruguri V. , Tyagi A. K. , Yusuf S. M.
Published: October 2015

We report the magnetic properties, of nano-crystalline powders Tb1−xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4), as perceived by neutron diffraction, and elucidate the effect of Tb site substitution on the magnetic structure of TbMnO3. All samples crystallized in the orthorhombic structure conforming to space group Pnma, and exhibited an incommensurate collinear antiferromagnetic ordering of the Mn ions below ∼40 K. Furthermore, at T ≤ 20 K, all these samples showed a change in magnetic structure (of Mn moments) to a spiral ordering down to 2 K, the lowest measured temperature. For the samples with x = 0, 0.1, and 0.2, a short-ranged two dimensional (2D) ordering of Tb moments was also observed at 2 K. However, for the other samples (x = 0.3 and 0.4), no magnetic ordering of Tb moments was found down to 2 K. So with Y substitution, a crossover from 2D ordering to a disordering of Tb moments was observed. The moments at the Mn site were found to be lower than the full Mn3+ (4μB) moment for all the samples below 40 K. The magnetic properties of all the samples studied by us in nano form are more pronounced than those of the reported single crystals of same compositions [V. Yu. Ivanov et al., JETP Lett. 91, 392–397 (2010)].
Interaction of a pseudo-π C—C bond with cuprous and argentous chlorides: Cyclopropane⋯CuCl and cyclopropane⋯AgCl investigated by rotational spectroscopy and ab initio calculations
Authors: Zaleski Daniel P. , Mullaney John C. , Bittner Dror M. , Tew David P. , Walker Nicholas R. , Legon Anthony C.
Published: October 2015

Strongly bound complexes (CH2)3⋯MCl (M = Cu or Ag), formed by non-covalent interaction of cyclopropane and either cuprous chloride or argentous chloride, have been generated in the gas phase by means of the laser ablation of either copper or silver metal in the presence of supersonically expanded pulses of a gas mixture containing small amounts of cyclopropane and carbon tetrachloride in a large excess of argon. The rotational spectra of the complexes so formed were detected with a chirped-pulse, Fourier transform microwave spectrometer and analysed to give rotational constants and Cu and Cl nuclear quadrupole coupling constants for eight isotopologues of each of (CH2)3⋯CuCl and (CH2)3⋯AgCl. The geometry of each of these complexes was established unambiguously to have C2v symmetry, with the three C atoms coplanar, and with the MCl molecule lying along a median of the cyclopropane C3 triangle. This median coincides with the principal inertia axis a in each of the two complexes (CH2)3⋯MCl. The M atom interacts with the pseudo-π bond linking the pair of equivalent carbon atoms FC (F = front) nearest to it, so that M forms a non-covalent bond to one C—C edge of the cyclopropane molecule. The (CH2)3⋯MCl complexes have similar angular geometries to those of the hydrogen- and halogen-bonded analogues (CH2)3⋯HCl and (CH2)3⋯ClF, respectively. Quantitative details of the geometries were determined by interpretation of the observed rotational constants and gave results in good agreement with those from ab initio calculations carried out at the CCSD(T)(F12*)/aug-cc-pVTZ-F12 level of theory. Interesting geometrical features are the lengthening of the FC—FC bond and the shrinkage of the two equivalent BC—FC (B = back) bonds relative to the C—C bond in cyclopropane itself. The expansions of the FC—FC bond are 0.1024(9) Å and 0.0727(17) Å in (CH2)3⋯CuCl and (CH2)3⋯AgCl, respectively, according to the determined r0 geometries. The C—C bond lengthening is in each case about four times that observed by similar methods in the corresponding complexes of MCl with ethyne and ethene, even though the cyclopropane complexes are more weakly bound than their ethyne and ethene analogues. Reasons for the larger increase in r(CC) in the pseudo-π complexes are discussed.
Dissipative function of a ferromagnet and the theory of Onsager's kinetic equations
Authors: Baryakhtar V. G. , Danilevich A. G.
Published: October 2015

It is shown that using the general theory of Onsager's kinetic equations allows us to build a model for a dissipative function for a ferromagnet, as well as the corresponding relaxation component in the Landau-Lifshitz equation. We present a model for constructing the dissipative function for ferromagnets with varying symmetries. We show the fundamental role of the effective magnetic field, first introduced by Landau and Lifshitz.
Model of exchange bias in a trilayer FM/AFM/FM structure
Authors: Pankratova M. L. , Kovalev A. S.
Published: October 2015

A theoretical examination of the properties of the exchange bias phenomenon for sandwich FM/AFM/FM structures, which are actively studied in experiments. Magnetization dependences on the external magnetic field are obtained under the proposed discrete model of ferromagnetic layers of such multilayer structures. It is shown that the magnetization field dependences have a horizontal plateau, a splitting of the hysteresis loop, and asymmetry. We examine the influence of the interface defects on the exchange bias phenomenon and its features. The results are qualitatively consistent with experimental data.
Modeling and control of variable speed wind turbine using laboratory simulator
Authors: Bajpai R. S. , Goyal Megha , Gupta Rajesh
Published: October 2015

An important challenge associated with wind power is the unpredictable nature of the wind. As wind power forecasting is usually based on the relationship between wind speeds and wind power, wind farm data is a critical prerequisite for wind speed prediction, meanwhile it plays an important role on the reliability and safety of the grids. For development of new controls, converter topologies, modulation methods, and maximum power extraction algorithms for wind energy conversion systems, the provision of a controlled test environment showing dynamic and steady state characteristics of wind turbines is desired. In this paper, a small scale wind turbine experimental laboratory model based on separately excited dc-shunt motor and permanent magnet synchronous generator (PMSG) is proposed, which reproduces the static and dynamic characteristics of the wind turbine without any wind environment. A programmable wind speed model is established that can satisfactorily simulate the spatial effect of the wind behavior, including gust change, ramp variations, and noise effect. The dynamics of the simulator is studied using the drive train model of the armature controlled dc shunt motor. A microcontroller along with high frequency buck converter has been used for acceleration and deceleration of the dc motor. It is shown through the frequency response characteristics that the simulator model approximates the wind turbine model dynamics. Simulation and experimental results illustrate that the speed of the motor changes with variation in the applied terminal voltage, like in the real wind turbine where the turbine speed changes according to the wind speed. Simulation results are obtained through PSCAD/EMTDC simulation software and experimental results are obtained through the programmable microcontroller used with the DC-motor-PMSG set.
Charred shrimp shells treated with potassium fluoride used as a catalyst for the transesterification of soybean oil with methanol
Authors: Biondo Carlos E. G. , Biondo Polyana B. F. , Visentainer Jesuí V. , Muñiz Graciela I. B. , Neves Andressa C. , Ballester Eduardo L. C. , Wiest Angela M. , Alves Helton J.
Published: October 2015

A basic catalyst made of charred shrimp shells treated with potassium fluoride (KF) was employed in the transesterification reaction of soybean oil in the presence of methanol to produce methyl esters. The shells used here are wastes from freshwater shrimp farming in the western region of the state of Paraná, Brazil, which are normally discarded in dumps/landfills and are a rich source of the biopolymer chitin (poly-β-1,4-N-acetyl-D-glucosamine). Charring of the shells (at 450 °C for 2 h) is aimed at partially eliminating rests of proteins and fibers, as well as acetyl groups (-CH3CO), carbon dioxide (-CO2) and water, causing the rearrangement of the chitin structure. The subsequent treatment of the shells with KF (impregnation and activation at 250 °C for 2 h) potentiated the basic sites on the catalyst surface, rendering it active in the transesterification reaction. The catalysts and shrimp shells were characterized by thermal gravimetric analysis, differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, N2 physisorption (Braunauer, Emmet and Teller) (BET), and Hammett basicity. An experimental design was created to evaluate the effect of the following variables of the transesterification reaction:temperature, catalyst weight ratio, and molar ratio of oil:alcohol. The results indicate that the treatment with KF increased the basicity of the catalyst. The highest conversion into methyl esters obtained with the experimental design was 86.3%, using an oil:alcohol molar ratio of 1:9, 3.0% (w/w) of catalyst, 85 °C, and 3 h of reaction. Leaching tests indicated that, after 10 h of refluxing in methanol, a conversion rate of 52.4% was achieved using the catalyst leached in optimized conditions. Kinetic studies showed that chemical equilibrium was established after 8 h of reaction, reaching a conversion rate of 96.7%, which reveals the potential of the catalyst to produce methyl esters (biodiesel).
Recent progress in plasma modelling at INFN-LNS
Authors: Neri L. , Castro G. , Torrisi G. , Galatà A. , Mascali D. , Celona L. , Gammino S.
Published: October 2015

At Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud (INFN-LNS), the development of intense ion and proton sources has been supported by a great deal of work on the modelling of microwave generated plasmas for many years. First, a stationary version of the particle-in-cell code was developed for plasma modelling starting from an iterative strategy adopted for the space charge dominated beam transport simulations. Electromagnetic properties of the plasma and full-waves simulations are now affordable for non-homogenous and non-isotropic magnetized plasma via “cold” approximation. The effects of Coulomb collisions on plasma particles dynamics was implemented with the Langevin formalism, instead of simply applying the Spitzer 90° collisions through a Monte Carlo technique. A wide database of different cross sections related to reactions occurring in a hydrogen plasma was implemented. The next step consists of merging such a variety of approaches for retrieving an “as-a-whole” picture of plasma dynamics in ion sources. The preliminary results will be summarized in the paper for a microwave discharge ion source designed for intense and high quality proton beams production, proton source for European Spallation Source project. Even if the realization of a predictive software including the complete processes involved in plasma formation is still rather far, a better comprehension of the source behavior is possible and so the simulations may support the optimization phase.