Influence of tensile damage on V–I curve and critical current of DyBCO coated conductor

The coated conductors are subjected to mechanical and electromagnetic stresses in preparation and service. When the stress is high, the coated layer is damaged, resulting in loss of superconducting property. The present work was carried out to reveal the influence of tensile damage on V–I curve, critical current and n-value of DyBa₂Cu₃O_7−δ coated conductor. The changes of the V–I curve, critical current and n-value with increasing applied tensile strain were measured experimentally. The features of the shift of the V–I curve to the lower current range and increase in its curvature, and accordingly the decrease in critical current and n-value, with increasing applied strain, were detected. For analysis of the experimental results, the model of Fang et al, which treats with the voltage generation due to the current shunting under existent crack, was applied. The experimentally observed features were described satisfactorily.     

Calculation of on-state I–V characteristics of LDMOSFETs based on an accurate LDD resistance modeling

In this paper, we present an I–V model for LDMOSFETs. It is based on modeling the Lightly-Doped Drain (LDD) region of the device as voltage-controlled resistors where velocity saturation effect is also taken into account. Using the LDD region model along with a model for the channel region of the device, the on-state I–V characteristic of the transistor is accurately calculated. The models for the LDD region resistors can be incorporated into a circuit simulator such as HSPICE which has an accurate model for the channel region of the transistor. The accuracy of the models is verified by comparing its results with those of a device simulator. The results show a maximum error of 1% for a wide range of voltages and overlapped LDD region lengths.     

I–V characterization of a quantum well infrared photodetector with stepped and graded barriers

I–V characterization of an n-type quantum well infrared photodetector which consists of stepped and graded barriers has been done under dark at temperatures between 20–300 K. Different current transport mechanisms and transition between them have been observed at temperature around 47 K. Activation energies of the electrons at various bias voltages have been obtained from the temperature dependent I–V measurements. Activation energy at zero bias has been calculated by extrapolating the bias dependence of the activation energies. Ground state energies and barrier heights of the four different quantum wells have been calculated by using an iterative technique, which depends on experimentally obtained activation energy. Ground state energies also have been calculated with transfer matrix technique and compared with iteration results. Incorporating the effect of high electron density induced electron exchange interaction on ground state energies; more consistent results with theoretical transfer matrix calculations have been obtained.     

Effect of series resistance and interface states on the I-V, C-V and G/ω-V characteristics in Au/Bi-doped polyvinyl alcohol (PVA)/n-Si Schottky barrier diodes at room temperature

The forward and reverse bias current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the Au/PVA (Bi-doped)/n-Si Schottky barrier diodes (SBDs) have been investigated at room temperature by taking the interface states (N_ss) and series resistance (R_s) effects into account. The voltage dependent profiles of resistance (R_i) were obtained from both the I-V and C/G-V measurements by using Ohm’s Law and Nicollian methods. The obtained values of R_i with agreement each other especially at sufficiently high bias voltages which correspond the value of R_s of the diode. Therefore, the energy density distribution profile of N_ss was obtained from the forward bias I-V data taking the bias dependence of the effective barrier height (BH) Φ_e and R_s into account. The high value of ideality factor (n) was attributed to high density of N_ss and interfacial polymer layer at metal/semiconductor (M/S) interface. In order to examine the frequency dependence of some of the electrical parameters such as doping donor concentration (N_D), Φ_e, R_s and N_ss values, C-V and G/ω-V measurements of the diode were performed at room temperature in the frequency range of 50 kHz-5 MHz. Experimental results confirmed that the N_ss, R_s and interfacial layer are important parameters that influence electrical characteristics of SBD.     

Damping and ferromagnetic resonance linewidth broadening in nanocrystalline soft ferromagnetic Fe–Co–Hf–N films

In order to describe high-frequency damping mechanisms of ferromagnetic films by means of the imaginary part of the frequency-dependant permeability, CMOS compatible ferromagnetic Fe₃₆Co₄₄Hf₉N₁₁ films were deposited by reactive r.f. magnetron sputtering on oxidised 5×5 mm²×380 μm (1 0 0)-silicon substrates with a 6-in. Fe₃₈Co₄₇Hf₁₅ target, as well as magnetic field annealing between 300 and 600 °C. An in-plane uniaxial anisotropy of around 4.5 mT as well as an excellent soft magnetic behaviour with a saturation polarisation of approximately 1.4 T could be observed after heat treatment at the above-mentioned temperatures, which drives these films to a high-frequency suitability. Ferromagnetic resonance frequencies of approximately up to 2.4 GHz could be obtained. The frequency-dependant permeability was measured with a broadband permeameter. Depending on the heat treatment, an increase of the full-width at half-maximum (FWHM) of the imaginary part of the frequency-dependant permeability is discussed in terms of two-magnon scattering, anisotropy-type competition and local resonance generation through predominant grain growth causing magnetisation and anisotropy inhomogeneities in the magnetic films. The grain size of the films was determined by (HRTEM) imaging and amounts from a few nanometres for films heat treated at 300 °C to more than 10 nm at 600 °C where the FWHM Δf_eff and the Landau–Lifschitz–Gilbert equation damping parameter α_eff increases with d_nm² and d_nm (e.g. d_nm is the grain diameter of the nonmagnetic Hf–N phase), respectively.     

Subharmonic aided pressure estimation for monitoring interstitial fluid pressure in tumours – In vitro and in vivo proof of concept

The feasibility of using subharmonic aided pressure estimation (SHAPE) to noninvasively estimate interstitial fluid pressure (IFP) was studied. In vitro, radiofrequency signals, from 0.2 ml/l of Definity (Lantheus Medical Imaging, N Billerica, MA) were acquired within a water-tank with a Sonix RP ultrasound scanner (Analogic Ultrasound, Richmond, BC, Canada; f_T/R = 6.7/3.35 MHz and f_T/R = 10/5 MHz) and the subharmonic amplitudes of the signals were compared over 0–50 mmHg. In vivo, five swine with naturally occurring melanomas were studied. Subharmonic signals were acquired from tumours and surrounding tissue during infusion of Definity and compared to needle-based pressure measurements. Both in vitro and in vivo, an inverse linear relationship between hydrostatic pressure and subharmonic amplitude was observed with r² = 0.63–0.95; p < 0.05, maximum amplitude drop 11.36 dB at 10 MHz and −8 dB, and r² as high as 0.97; p < 0.02 (10 MHz and −4/−8 dB most promising), respectively, indicating that SHAPE may be useful in monitoring IFP.     

Relaxation of the magnetic state of a ferromagnetic–superconducting layered structure

We have proposed a real-time method of neutron reflectometry. The magnetic state of the Ta/V/FM/Nb/Si ferromagnetic–superconducting system has been analyzed. Relaxation of the inhomogeneous magnetic state with a characteristic time of several hours, which depends on the magnetic field magnitude and temperature, has been observed. The relaxation of the domain structure has changed upon a transition of the V and Nb layers to the superconducting state. It has been concluded that real-time reflectometry data for polarized neutrons are important for determining the origin of magnetism in ferromagnetic–superconducting layered structures.     

Phase composition and magnetic structure in nanocrystalline ferromagnetic Fe–N–O films

The chemical and phase compositions and structure of the Fe–N–O films produced by reactive dc magnetron sputtering (in Ar or Ar + N₂ gas mixture atmospheres) under different conditions (energy parameters of magnetron, residual pressure in the magnetron chamber after preliminary pumping, operating pressure in gas mixture) have been investigated by energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and vibrating sample magnetometry. Impurity of nitrogen and oxygen, which are present in the sputtered films, participate in the formation of their phase composition and determine its features. Some phenomena inherent in the nanocrystalline films in the metastable state were found. These are the formation of supersaturated bcc interstitial αFe-based solid solution and precipitation of α’ nitrous martensite with bct crystal lattice. The magnetic structure of the Fe–N–O films, which is characterized by the existence of stochastic domains discovered by correlation magnetometry method, is discussed in terms of the random anisotropy model. It was found that two modes of the magnetic anisotropy field of stochastic domains are formed, which determine the existence of two modes of the coercive field found in the magnetic hysteresis loops.     

μ–τ symmetry in Zee–Babu model

We study the Zee–Babu two-loop neutrino mass generation model and look for a possible flavor symmetry behind the tri-bimaximal neutrino mixing. We find that there probably exists the μ–τ   symmetry in the case of the normal neutrino mass hierarchy, whereas there may not be in the inverted hierarchy case. We also propose a specific model based on a Froggatt–Nielsen-like Z₅$Z_5$ symmetry to naturally accomplish the μ–τ symmetry on the neutrino mass matrix for the normal hierarchy case.     

Type I and new seesaw in left–right symmetric theories

We extend the Type I seesaw and suggest a new   seesaw mechanism to generate neutrino masses within the left–right symmetric theories where parity is spontaneously broken. We construct a next to minimal left–right symmetric model where neutrino masses are determined irrespective of the B−L$B-L$ breaking scale and call it the new   seesaw mechanism. In this scenario B−L$B-L$ scale can be very low. This makes B−L$B-L$ gauge boson and the quasi-Dirac heavy leptons very light. These TeV scale particles could have large impact on lepton flavor and CP violating processes. We also shed light on the phenomenological aspects of the model within the reach of the LHC.     

Quasiparticle dynamics in ferromagnetic compounds of the Co–Fe and Ni–Fe systems

We report a theoretical study of the quasiparticle lifetime and the quasiparticle mean free path caused by inelastic electron-electron scattering in ferromagnetic compounds of the Co–Fe and Ni–Fe systems. The study is based on spin-polarized calculations, which are performed within the G ⁰ W ⁰ approximation for equiatomic and Co(Ni)-rich compounds, as well as for their constituents. We mainly focus on the spin asymmetry of the quasiparticle properties, which leads to the spin-filtering effect experimentally observed in spin-dependent transport of hot electrons and holes in the systems under study. By comparing with available experimental data on the attenuation length, we estimate the contribution of the inelastic mean free path to this length.     

Basic gravitational currents and Killing–Yano forms

It has been shown that for each Killing–Yano (KY)-form accepted by an n-dimensional (pseudo)Riemannian manifold of arbitrary signature, two different gravitational currents can be defined. Conservation of the currents are explicitly proved by showing co-exactness of the one and co-closedness of the other. Some general geometrical facts implied by these conservation laws are also elucidated. In particular, the conservation of the one-form currents implies that the scalar curvature of the manifold is a flow invariant for all of its Killing vector fields. It also directly follows that, while all KY-forms and their Hodge duals on a constant curvature manifold are the eigenforms of the Laplace–Beltrami operator, for an Einstein manifold this is certain only for KY 1-forms, (n − 1)-forms and their Hodge duals.     

Relaxation in Ni–Mn–Ga ferromagnetic shape memory alloys

Evidence of relaxation has been observed in ferromagnetic Ni–Mn–Ga single crystals. The relaxation may be explained by a change in symmetry-conforming short-range ordering according to Ren and Otsuka in this off-stoichimetric ordered alloy. Martensite stabilization has also been found after martensite ageing.     

Dynamics in mesoscopic superconducting rings: Multiple phase-slips and vortex–antivortex pairs

We investigate the situation where a mesoscopic 1D ring or 2D cylinder is subject to a magnetic field by simulating the time dependant Ginzburg–Landau equations with periodic boundary conditions. We investigate the different possible evolutions for the 1D phase slip phenomenon. The case of the multiple phase slips is analyzed in details and we study the competition between simultaneous and consecutive multiple phase slips analytically and numerically. In 2D we study the creation of vortex–antivortex pairs. Following the theory of the Kibble–Zurek mechanism, we quenched the sample by applying a strong current and observe vortex–antivortex pairs dynamics.     

Unusual metal–insulator transition in disordered ferromagnetic films

We present a theoretical interpretation of recent data on the conductance near and farther away from the metal–insulator transition in thin ferromagnetic Gd films of thickness b≈2$b\approx 2$–10 nm. For increasing sheet resistances a dimensional crossover takes place from d=2 to d  =3 dimensions, since the large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L_??b$L_{?}?b$ at strong disorder. The conductivity data in the various regimes obey fractional power-law or logarithmic temperature dependence. One observes weak localization and interaction induced corrections at weaker disorder. At strong disorder, near the metal–insulator transition, the data show scaling and collapse onto two scaling curves for the metallic and insulating regimes. We interpret this unusual behavior as proof of two distinctly different correlation length exponents on both sides of the transition.     

Magnetic and mechanical properties of Ni–Mn–Ga/Fe–Ga ferromagnetic shape memory composite

A ferromagnetic shape memory composite of Ni–Mn–Ga and Fe–Ga was fabricated by using spark plasma sintering method. The magnetic and mechanical properties of the composite were investigated. Compared to the Ni–Mn–Ga alloy,the threshold field for magnetic-field-induced strain in the composite is clearly reduced owing to the assistance of internal stress generated from Fe–Ga. Meanwhile, the ductility has been significantly improved in the composite. A fracture strain of 26% and a compressive strength of 1600 MPa were achieved.