Hop Length Research Articles

Y3+ composition and particle size influenced magnetic and dielectric properties of nanocrystalline Ni0.5Cu0.5YxFe2-xO4 ferrites

The rare earth Yttrium (Y3+) doped Ni–Cu nanoferrites (NCY ferrites) with chemical formulation, Ni0.5Cu0.5YxFe2-xO4 (x = 0–0.125) were prepared successfully by the sol gel route. The X-ray diffraction (XRD) of NCY ferrites revealed that a single phase of cubic spinel is created within the synthesized ferrites. The crystallite sizes obtained by XRD pattern are in the range of 51–84 nm, in good agreement with those obtained by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FSEM). The calculated lattice parameter of NCY ferrite unit cells initially decreases up to x = 0.1 and increase afterwards for x = 0.125. From FESEM and TEM micrographs, surface morphology and microstructure of NCY nanoferrites were studied. The energy dispersive X-ray spectroscopy (EDS) patterns have confirmed the stoichiometric presence of Ni, Cu, Y, O and Fe, those were used to prepare the samples. The variations in the magnetic properties with Y3+ compositions were investigated by obtaining the hysteresis loops of NCY ferrites. The magnetic hopping lengths LA and LB were calculated from XRD. The saturation magnetization, Bohr magneton number, coercivity and retentivity of the ferrites were influenced by the structural parameters like crystallite size and lattice strain. The frequency variation of dielectric constant and loss tangent exhibit space charge polarization as a phenomenon governing the dielectric behavior of the ferrites.

Artificial Noise Shielded Frequency-Hopping Systems: Transceiver Design and Performance Analysis

To further protect frequency-hopping (FH) systems against severe wiretapping, an architecture of artificial noise (AN) shielded FH systems (ANS-FH) is proposed, wherein an AN cancellation architecture is utilized at the authorized receiver, and the secrecy performance is analyzed in the presence of an eavesdropper. First, an inter-frequency interference (IFI) model is employed to depict the residual AN after AN cancellation. Then, the tolerable range of frequency deviation is given, and the signal to AN plus noise ratio (SANR) is provided to measure the AN cancellation performance. Finally, the secrecy performance is analyzed using secrecy capacity under the assumption that frequency deviation is uniformly distributed within frequency synchronization accuracy. Theoretical and simulation results confirm that frequency deviation in practical FH systems will degrade both AN cancellation and system secrecy performance, and shorter hop length or proper power allocation for secret data and AN can mitigate the negative impact of frequency deviation, which in turn guides the practical transceiver design.

The Effect of X‐Ray Irradiation on Conductivity of C and 2C Polytype TlInS2 Ferroelectrics

The influence of X‐ray irradiation on DC conductivity of TlInS2 C and 2C polytypes is studied in the temperature range of 100–300 K. The X‐ray irradiation (absorbed doses are 0.9 and 2.7 kGy) leads to an increasing conductivity of both C‐ and 2C‐samples in proportion to the absorbed dose; the conductivity decreases on cooling in the temperature region of 100–300 K. An anomalous increase in conductivity is observed in C‐polytype samples on cooling in the temperature range of the incommensurate phase (197–214 K). The X‐ray irradiation causes the “blur” of that anomaly. It is established that the mechanism of hopping conductivity with variable hopping length takes place for both polytypes in the temperature range of 125–175 K, and the densities of localized states near the Fermi level (NF) are determined. Under irradiation, the density NF increases from 3.7 × 1018 eV−1 cm−3 (C) to 6.9 × 1018 eV−1 cm−3 (2C) and exceeds the initial value more than three times at D = 2.7 kGy. Using the 1D Kroning–Penney model, the role of incommensurate periodic potential in modification of electron band structure at creation of the incommensurate phases in crystals is discussed.

Optimal Tree Topology for a Submarine Cable Network With Constrained Internodal Latency

This paper provides an optimized cable path planning solution for a tree-topology network in an irregular 2D manifold in a 3D Euclidean space, with an application to the planning of submarine cable networks. Our solution method is based on total cost minimization, where the individual cable costs are assumed to be linear to the length of the corresponding submarine cables subject to latency constraints between pairs of nodes. These latency constraints limit the cable length and number of hops between any pair of nodes. Our method combines the Fast Marching Method (FMM) and a new Integer Linear Programming (ILP) formulation for Minimum Spanning Tree (MST) where there are constraints between pairs of nodes. We note that this problem of MST with constraints is NP-complete. Nevertheless, we demonstrate that ILP running time is adequate for the great majority of existing cable systems. For cable systems for which ILP is not able to find the optimal solution within an acceptable time, we propose an alternative heuristic algorithm based on Prim's algorithm. In addition, we apply our FMM/ILP-based algorithm to a real-world cable path planning example and demonstrate that it can effectively find an MST with latency constraints between pairs of nodes.

Dual topological characterization of non-Hermitian Floquet phases

Non-Hermiticity is expected to add far more physical features to the already rich Floquet topological phases of matter. Nevertheless, a systematic approach to characterize non-Hermitian Floquet topological matter is still lacking. In this work we introduce a dual scheme to characterize the topology of non-Hermitian Floquet systems in momentum space and in real space, using a piecewise quenched nonreciprocal Su-Schrieffer-Heeger model for our case studies. Under the periodic boundary condition, topological phases are characterized by a pair of experimentally accessible winding numbers that make jumps between integers and half-integers. Under the open boundary condition, a Floquet version of the so-called open boundary winding number is found to be integers and can predict the number of pairs of zero and $\pi$ Floquet edge modes coexisting with the non-Hermitian skin effect. Our results indicate that a dual characterization of non-Hermitian Floquet topological matter is necessary and also feasible because the formidable task of constructing the celebrated generalized Brillouin zone for non-Hermitian Floquet systems with multiple hopping length scales can be avoided. This work hence paves a way for further studies of non-Hermitian physics in non-equilibrium systems.

Electrical transport in lead-free Na0.5Bi0.5TiO3 ceramics

Lead-free Na0.5Bi0.5TiO3 (NBT) ceramics were prepared via a conventional oxide-mixed sintering route and their electrical transport properties were investigated. Direct current (DC, σDC) and alternating current (AC, σAC) electrical conductivity values, polarization current (first measurements) and depolarization current, current–voltage (I–U) characteristics (first measurements), and the Seebeck coefficient (α) were determined under various conditions. The mechanism of depolarization and the electrical conductivity phenomena observed for the investigated samples were found to be typical. For low voltages, the I–U characteristics were in good agreement with Ohm’s law; for higher voltages, the observed dependences were I–U2, I–U4, and then I–U6. The low-frequency σAC followed the formula σAC–ωs (ω is the angular frequency and s is the frequency exponent). The exponent s was equal to 0.18–0.77 and 0.73–0.99 in the low- and high-frequency regions, respectively, and decreased with temperature increasing. It was shown that conduction mechanisms involved the hopping of charge carriers at low temperatures, small polarons at intermediate temperatures, and oxygen vacancies at high temperatures. Based on AC conductivity data, the density of states at the Fermi-level, and the minimum hopping length were estimated. Electrical conduction was found to undergo p–n–p transitions with increasing temperature. These transitions occurred at depolarization temperature Td, 280 ℃, and temperature of the maximum of electric permittivity Tm is as typical of NBT materials.

Synthesis of three-dimensional graphene architectures from chicken feather and its unusual dimensional crossover in electronic conductivity

Three-dimensional graphene architectures were synthesized from a new source, chicken feather, a bio-waste. Here ferric chloride (FeCl3) was used as a self-originator template, with a high C/O ratio (21:1). The introduction of Fe3＋ ion into the activated frame of carbon generated graphene nanostructure. X-ray photoelectron spectroscopy was used to analyse the defects in the prepared graphene. The obtained structures were found to be unique nanoplatelets and three-dimensional pyramid-like structure. Its DC conductivity has been tested within the temperature range of 20 to 300K and their temperature-dependent conduction mechanism was established. At ∼100 K and ∼50 K, a 3D–2D and Mott–ES type cross-over were observed respectively, with varied hopping length. The conductivity was found to be decreased with lowering temperature which was similarly observed in metals.

Facile co-precipitation route for magnesium ferrites nanostructure: Synthesis, influence of pH variation on structural properties

This report presents the synthesis of magnesium ferrite (MgFe2O4) by coprecipitation method and its subsequent characterization by using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. XRD results confirm the formation of single phase cubic spinel structure, having lattice constant from 8.3216 ? to 8.3252 ?. An infrared spectroscopy study confirms the presence of two main absorption bands indicating tetrahedral and octahedral group complexes, within the spinel lattice. We also report hopping length (LA and LB), strain (?) and dislocation density (?D) of ferrite sample.

Influence of bismuth doping on structural, electrical and dielectric properties of Ni–Zn nanoferrites

Bismuth doped Ni–Zn ferrites of the composition Ni0.5Zn0.5BixFe2-xO4 with (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.1) have been synthesized by a citrate precursor method. Bismuth was doped to tailor the properties of Ni–Zn spinel ferrite. X-Ray Diffraction (XRD) data was used to calculate lattice parameter, density, porosity and hopping length values which revealed that all annealed bismuth doped nickel zinc nanoferrites display a single phase cubic spinel structures. Average crystallite size was found to be in the range of 15–28 nm. Williamson-Hall method was used to deduce the average lattice strain experienced by the nanocrystalline. A tensile strain was observed with an increase in the bismuth concentration from x = 0.00 to x = 0.04 which leads to an expansion of lattice while a compressive lattice strain was observed for the concentration x = 0.06 due to contraction of the lattice. Fourier Transform Infra Red (FTIR) peaks confirmed the appearance of absorption bands at a wave number 405 cm−1 and at a wave number 580 cm−1 confirming tetrahedral and octahedral modes of vibrations respectively. I–V characteristics at 4 V voltage were studied at room temperature. A highly resistive behaviour of the samples of the order of 1010 Ω-cm was observed making these materials suitable for high frequency applications. The investigations on real part, imaginary part of dielectric constant and dielectric loss tangent were carried out in the frequency range 10 kHz to 10 MHz at room temperature. Dielectric behaviour showed that with an increase in concentration of bismuth, the value of real part of dielectric constant increases from 5.161 to 11.162 at 104 Hz frequency and the value of dielectric loss tangent decreases from 0.79 to 0.33. AC conductivity of all the samples was found to increase with an increase in frequency which is explained on the basis of Koop's Phenomenological theory.

A study of hopping transport during discharging in SiNx films for MEMS capacitive switches

A more realistic approach of the discharging process in MEMS capacitive switches is presented with the introduction of the effective temperature in order to determine the behavior of the microscopic parameters of hopping conduction, which dominates the process. The use of Kelvin Probe method in MIM capacitors that simulates the discharging process in MEMS switches during up-state revealed that both the increase of temperature and stressing field intensity results the decrease of mean hopping length. This result arises from the simultaneous contribution of the transport energy levels associated with the impact of the stressing field and temperature. Also, a correlation was found experimentally between the stretched exponential decay and the hopping process. The proposed method was also applied in MEMS switches where a similar behavior of the hopping parameters was found, providing evidence that the control of the hopping length to an optimum value can provide fast discharging and low leakage currents, increasing the device lifetime.

Three-dimensional wireless ad hoc networks with random nodes distribution

ABSTRACT This paper proposes a model for three-dimensional (3-D) wireless ad hoc networks with randomly distributed nodes and unknown node locations. In this model, the nodes are assumed to be randomly distributed in a cubic torus. The distances between neighbouring nodes (hop lengths) and the distance between thesource and destination nodes (route length) are assumed to be random. In the first part of this paper, exact analytical expressions are derived for the cumulative distribution function (CDF) and the probability density function (PDF) of the hop and route lengths.Then, these distributions are used to find the average hop length,route length and number of hops analytically and numerically. The performance of the system is studied in terms of the average route bit error rate (BER) and the optimal transmit power needed to achieve a given threshold BER to maintain network connectivity. Moreover, the performance of decode-and-forward (DF) relaying scheme over Rayleigh fading channels in the presence of cochannelinterference (CCI) is studied. It is assumed that CCI is modelled as the sum of independent-not-identically distributed Rayleigh variates.

Bipedal hopping as a new measure to detect subtle sensorimotor impairment in people with multiple sclerosis

Background Bipedal hopping has the potential to detect subtle multiple sclerosis (MS)-related impairments, especially among patients who “pass” typical movement tests. In this narrative review, we outline the biomechanics of bipedal hopping and propose its usefulness as a novel outcome measure for people with MS having mild disability. Methods We summarize articles that (1) examined the biomechanics of jumping or hopping and (2) tested the validity and/or reliability of hopping tests. We consolidated consistencies and gaps in research and opportunities for future development of the bipedal hop test. Results Bipedal hopping requires immense power, coordination, balance, and ability to reduce co-contraction; movement components typically affected by MS. These impairments can be measured and differentiated by examining specific variables, such as hop length (power), symmetry (coordination), center of pressure (balance), and coefficient of variability (co-contraction/spasticity). Bipedal hopping challenges these aspects of movement and exposes sensorimotor impairments that may not have been apparent during walking. Conclusions Testing of bipedal hopping on an instrumented walkway may detect and monitor sensorimotor control in people with MS who do not currently present with clinical deficits. Early measurement is imperative for precise rehabilitation prescription to slow disability progression prior to onset of measurable gait impairment. Implications for rehabilitation Jumping and hopping tests detect lower limb and balance impairments in children, athletes, and older adults. Bipedal hop test measures multiple domains: power, coordination, balance, and muscle timing. Bipedal hop test may expose subtle sensorimotor impairments in people with multiple sclerosis. Multiple variables measured can discern type of sensorimotor impairment to direct personalized rehabilitation programs.

LED Light Increases Leaf Area and Root Length of Humulus lupulus (var. Tettnanger) In Vitro

Propagation of hops has traditionally been accomplished through vegetative techniques. A more modern technique, micropropagation, can be used to propagate hops and offers several advantages to vegetative techniques. Research examining the use of LED lights in plant production has observed its ability to promote growth in plants through emission of higher light quality, such as enhanced red and blue wavelength discharge. This new 5-page EDIS publication provides information on the use and application of LED lights to enhance leaf area and root length of hops. Written by Chi D. Nguyen, Dominic Vu, Heqiang Huo, and Brian Pearson, and published by the UF/IFAS Environmental Horticulture Department.https://edis.ifas.ufl.edu/ep583

Capturing Subdiffusive Solute Dynamics and Predicting Selectivity in Nanoscale Pores with Time Series Modeling.

Fitting mathematical models with a direct connection to experimental observables to the outputs of molecular simulations can be a powerful tool for extracting important physical information from them. In this study, we present two new approaches that use stochastic time series modeling to predict long-time-scale behavior and macroscopic properties from molecular simulation, which can be generalized to other molecular systems where complex diffusion occurs. In our previous work, we studied long molecular dynamics (MD) simulation trajectories of a cross-linked HII phase lyotropic liquid crystal (LLC) membrane, where we observed subdiffusive solute transport behavior characterized by intermittent hops separated by periods of entrapment. In this work, we use our models to parameterize the behavior of the same systems, so we can generate characteristic trajectory realizations that can be used to predict solute mean-squared displacements (MSDs), solute flux, and solute selectivity in macroscopic length pores. First, using anomalous diffusion theory, we show how solute dynamics can be modeled as a fractional diffusion process subordinate to a continuous time random walk. From the MD simulations, we parameterize the distribution of dwell times, hop lengths between dwells, and correlation between hops. We explore two variations of the anomalous diffusion modeling approach. The first variation applies a single set of parameters to the solute displacements and the second applies two sets of parameters based on the solute's radial distance from the closest pore center. Next, we present an approach that generalizes Markov state models, treating the configurational states of the system as a Markov process where each state has distinct transport properties. For each state and transition between states, we parameterize the distribution and temporal correlation structure of positional fluctuations as a means of characterization and to allow us to predict solute MSDs. We show that both stochastic models reasonably reproduce the MSDs calculated from MD simulations. However, qualitative differences between MD and Markov state-dependent model-generated trajectories may in some cases limit their usefulness. With these parameterized stochastic models, we demonstrate how one can estimate the flux of a solute across a macroscopic length pore and, based on these quantities, the membrane's selectivity toward each solute. This work therefore helps to connect microscopic, chemically dependent solute motions that do not follow simple diffusive behavior with long-time-scale behavior, in an approach generalizable to many types of molecular systems with complex dynamics.

Solid-state synthesis of heterogeneous Ni0.5Cu0.5-xZnxFe2O4 spinel oxides with controlled morphology and tunable dielectric properties

Heterogeneous Ni0.5Cu0.5−xZnxFe2O4 (0.0 ≤ x ≤ 0.5) nanoparticles are prepared via a green, solventless and additive-free, soft mechanochemical process at room temperature. This solid-state synthetic procedure yields ternary and quaternary oxide nanoparticles with uniform morphology (average particle size: 104–136 nm). X-ray diffraction analyses of Ni0.5Cu0.5−xZnxFe2O4 nanoparticles reveal a cubic spinel structure with crystallite size in the range of 24–31 nm. The lattice parameter (a) and hopping length for tetrahedral (LA) and octahedral (LB) lattice sites are found to increase with the increase in Zn2+ content, while X-ray (ρxrd) and bulk (ρbulk) densities decrease slightly due to increasing lattice volume. Ni0.5Cu0.5−xZnxFe2O4 nanoparticles with (x = 0.2, 0.3, 0.4) exhibit excellent dielectric performance with high permittivity (e = 92–111) and suppressed dielectric loss (e = 1.8–2.8) at high frequency (~ 106 Hz). The polarization mechanism is discussed, involving major contributions from the electron hopping (Fe2+ ↔ Fe3+) at the octahedral sites. The influence of Cu2+ and Zn2+ concentration on the cationic distribution and dielectric performance is analyzed. The electrical conductivity is found to follow the power law (σac = Aωn) with n = 0.7, which confirms the ac conduction phenomenon driven by the electron hopping mechanism. The dielectric behavior of Ni0.5Cu0.5−xZnxFe2O4 nanoparticles reveals their potential for applications in high-frequency microwave devices.

Polaron transport mechanism in maricite NaFePO4: A combined experimental and simulation study

We report, for the first time, systematic investigations on electronic properties of maricite NaFePO4 with different crystallite sizes by a combined experimental and theoretical approach. Ac impedance spectroscopy has been used to study the polaron transport behaviour in maricite NaFePO4 structure with different crystallite sizes over a wide range of temperatures. With the decrease in crystallite size, we observe a polaronic conductivity enhancement of approximately an order of magnitude at the nanoscale level as compared with its bulk counterpart. The temperature dependent dc conductivity has been analysed within the framework of the Mott model of polaron hopping and various physical parameters relevant for the polaron hopping process were extracted. Additionally, by introducing an approximated Mott model with calculated hole polaron migration barrier from density functional theory, we evaluated the polaronic conductivity as function of crystallite size in fair agreement with experimental data. The enhanced polaronic conductivity with crystallite size reduction is found to be due to the combined effect of increased polaron concentration, reduced hopping length, and lowered migration barrier.

Polaronic Conductivity in Iron Phosphate Glasses Containing B2O3.

We report on the electrical properties of glasses with nominal composition xB2O3–(100 − x)[40Fe2O3–60P2O5],x = 2–20, mol.%. The conduction transport in these glasses is polaronic and shows a strong dependence on Fe2O3 content and polaron number density. The changes in DC conductivity are found not to be directly related to B2O3, however structural changes induced by its addition impact frequency-dependent conductivity. All glasses obey Summerfield and Sidebottom procedures of scaling conductivity spectra indicating that the polaronic mechanism does not change with temperature. An attempt to produce a super-master curve revealed that shape of the conductivity dispersion is the same for glasses with up to 15.0 mol.% B2O3 but differs for glass with the highest B2O3 content. This result could be related to the presence of borate units in the glass network. Moreover, the spatial extent of localized polaron motions increases with the decrease of polaron number density, however, this increase shows a larger slope than for previously reported iron phosphate glasses most probably due to the influence of B2O3 on glass structure and formation of polarons. While Summerfield scaling procedure fails, Sidebottom scaling yields a super-master curve, which indicates that polaronic hopping lengths also change with changing polaron number density in these glasses.

Ferroelectric polymer/ceramic nanocomposites with low energy losses

AbstractIn order to meet the continuously increasing demand of modern electronic industries, there is an urgent need to develop the advanced energy storage materials. In this regard, polymer‐based dielectric composites are promising materials for futuristic technological applications. Herein, we synthesized a (1 − x) PVDF + xBFO composite by means of sol‐gel auto‐combustion route to explore its energy storage capabilities using impedance spectroscopy. After synthesis, field emission scanning electron microscope was utilized to examine exterior texture and obtained images showed the uniform distribution of BiFeO3 particles in polyvinylidene fluoride matrix with considerable amount of porosity. The particle size was measured using the ImageJ software. In conjunction with scanning electron microscopy, the stoichiometric amounts of all constituents were confirmed using energy dispersive X‐rays spectroscopy, working on the measurement of relative abundance of X‐rays vs their energy. Dielectric traits of these polymer composite ceramics were explored using precision impedance analyzer with varying frequency from 20 Hz to 20 MHz which explored their energy storage potential. The analysis of Nyquist plot helped to define the range of impedance spectrum where the different electroactive regions participated significantly in impedance response of the material. The effect of reinforcement contents on the nature of hopping length and relaxation phenomenon was probed through the complex modulus analysis. The energy storage capacity in terms of energy density was analyzed by checking the polarization response of the composite material in varying electric field which is a key feature for grading a material for energy storage devices.

Impact of calcination temperature on structural, optical, and magnetic properties of spinel CuFe2O4 for enhancing photocatalytic activity

Variation in temperature during synthesis is a favorite aspect to get enhanced structural, optical, magnetic, and catalytic properties. Here, in this work, Spinel (CuFe2O4) ferrites were formulated with various calcination temperatures. The method used is a simple, economical, and eco-friendly microwave combustion method. Impact of annealing temperature on structural analysis is confirmed by XRD analysis. Under the following parameters, the structural changes are discussed: diametrical size, lattice parameter, strain, tetrahedral and octahedral hopping length, and bond length, respectively. HR-TEM results assure the spherical-shaped morphology. The average diametrical size calculated is in good agreement with the XRD results. The EDAX spectrum confirms the composition of sample and its purity. A FT-IR study exemplifies the ferrite characteristic peaks available as synthesized sample. The UV–Vis analysis and Tauc’s plot of the samples give us the optical bandgaps as 2.2, 2.1, and 2.08 eV, respectively. An increase in calcination temperature exhibits an enhancement in saturation magnetization (Ms), remnant magnetization (Mr), and coercivity (Hc) at room temperature. Degradation activity of methylene blue (MB) studied by catalyst CuF-MW, CuF-500, and CuF-600 expresses the degradation efficiency of the catalyst. CuF-MW exhibits an excellent result than other samples, due to large surface area and the small diametrical size.

A Hybrid Energy Efficient Cooperative Transmission Scheme in Multi‐Hop Wireless Sensor Networks

This letter proposes a hybrid cooperative transmission scheme for energy reduction in multi‐hop clustered wireless sensor networks (WSNs) where single‐input single‐output (SISO) and spatial modulation (SM)‐based cooperative MIMO (CMIMO‐SM) schemes are jointly used as the transmission candidates. In this work, we consider a linear all‐transmission scenario where the intermediate clusters act not only as forwarding clusters but also transmitting clusters. The numerical experiments demonstrate that the energy reduction of WSN is achieved by choosing the optimal hop length and appropriate transmission candidate. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.