Random Energy Research Articles

Scavenging energy from wind-induced power transmission line vibration using an omnidirectional harvester in smart grids

Wind-induced power transmission line vibration is harmful to smart grids, and electronic devices that monitor the status of power lines require uninterrupted energy. Scavenging energy from wind-induced transmission line vibration to power these electronic devices is a feasible solution to these issues. In this study, an omnidirectional energy harvester was proposed, analyzed, fabricated, and tested. The harvester comprises a flexible rope, a one-way bearing, a three-phase direct current motor, and a spiral spring. One end of the flexible rope is attached to a power line and follows the disordered movement of the vibration, making it possible for the harvester to scavenge energy from all directions. The one-way bearing and spiral spring enable the harvester to scavenge random vibration energy. A theoretical analysis was carried out to determine the factors that would influence the energy harvester’s performance. The harvester was then fabricated and experiments were conducted. The simulation and experimental results correlated well. The maximum output voltage and output power of the harvester were 10 V (peak voltage) and 41.6 mW, respectively. The harvested energy can power a monitoring device for more than 1440 s. It can also power a temperature/humidity sensor, which can detect the status of the power line effectively. The proposed energy harvester can be used in smart grids for damping power line vibrations and powering electronic devices simultaneously.

Microscale Schottky superlubric generator with high direct-current density and ultralong life

Miniaturized or microscale generators that can effectively convert weak and random mechanical energy into electricity have significant potential to provide solutions for the power supply problem of distributed devices. However, owing to the common occurrence of friction and wear, all such generators developed so far have failed to simultaneously achieve sufficiently high current density and sufficiently long lifetime, which are crucial for real-world applications. To address this issue, we invent a microscale Schottky superlubric generator (S-SLG), such that the sliding contact between microsized graphite flakes and n-type silicon is in a structural superlubric state (an ultra-low friction and wearless state). The S-SLG not only generates high current (~210 Am−2) and power (~7 Wm−2) densities, but also achieves a long lifetime of at least 5,000 cycles, while maintaining stable high electrical current density (~119 Am−2). No current decay and wear are observed during the experiment, indicating that the actual persistence of the S-SLG is enduring or virtually unlimited. By excluding the mechanism of friction-induced excitation in the S-SLG, we further demonstrate an electronic drift process during relative sliding using a quasi-static semiconductor finite element simulation. Our work may guide and accelerate the future use of S-SLGs in real-world applications.

Design of biodegradable wheat-straw based triboelectric nanogenerator as self-powered sensor for wind detection

With the development of Internet of things and sensor network, exploring distributed energy is important for their sustainable operation. Finding the best devices and suitable materials that can convert random mechanical energy into electric power has become a hot research topic. In this work, wheat straw, a biodegradable material, was utilized to fabricate single-electrode mode triboelectric nanogenerators (TENGs). Herein, the wheat straw TENG (WS-TENG) was applied to convert mechanical energy with low frequency and small amplitude into electrical energy. The maximum output power density of WS-TENG is 404 mW / m2, and more than 60 LEDs can be lit up. Moreover, the WS-TENG can not only charge capacitors but also power hygrometers, electronic watch and some other low-power portable electronic devices. Furthermore, the WS-TENG was designed as windmill and bionic lawn, which can be used as wind velocity sensor for detection of wind speed and wind direction. Because the WS-TENG is degradable, low-cost and portable, this work provides a novel solution for the advanced science technology to be applied in agricultural production and self-powered sensor for energy harvesting and energy application.

Density of states in locally ordered amorphous organic semiconductors: Emergence of the exponential tails.

We present a simple model of the local order in amorphous organic semiconductors, which naturally produces a spatially correlated exponential density of states (DOS). The dominant contribution to the random energy landscape is provided by electrostatic contributions from dipoles or quadrupoles. An assumption of the preferable parallel orientation of neighbor quadrupoles or antiparallel orientation of dipoles directly leads to the formation of the exponential tails of the DOS even for a moderate size of the ordered domains. The insensitivity of the exponential tail formation to the details of the microstructure of the material suggests that this mechanism is rather common in amorphous organic semiconductors.

Evolution of cooperation in networked heterogeneous fluctuating environments

Fluctuating environments are situations where the spatio-temporal stochasticity plays a significant role in the evolutionary dynamics. The study of the evolution of cooperation in these environments typically assumes a homogeneous, well mixed population, whose constituents are endowed with identical capabilities. In this paper, we generalize these results by developing a systematic study for the cooperation dynamics in fluctuating environments under the consideration of structured, heterogeneous populations with individual entities subjected to general behavioral rules. Considering complex network topologies, and a behavioral rule based on generalized reciprocity, we perform a detailed analysis of the effect of the underlying interaction structure on the evolutionary stability of cooperation. We find that, in the presence of environmental fluctuations, the cooperation dynamics can lead to the creation of multiple network components, each with distinct evolutionary properties. This is paralleled to the freezing state in the Random Energy Model. We utilize this result to examine the applicability of our generalized reciprocity behavioral rule in a variety of settings. We thereby show that the introduced rule leads to steady state cooperative behavior that is always greater than or equal to the one predicted by the evolutionary stability analysis of unconditional cooperation. As a consequence, the implementation of our results may go beyond explaining the evolution of cooperation. In particular, they can be directly applied in domains that deal with the development of artificial systems able to adequately mimic reality, such as reinforcement learning.

Investigation on secondary electron emission characteristics of double-layer structures

Secondary electron (SE) emission (SEE) from material surfaces is a frequent phenomenon in space and vacuum environments. SEE modulation is important since it governs the performance of some devices such as electronic multipliers or induces some detrimental effects such as multipactors. Surface coating has been reported to modulate SEE effectively, whereas SEE behaviors of coating structures are not clearly understood yet, and the appropriate theory to describe SEE characteristics quantitatively for coating structures is less developed so far. Here, we have prepared four alumina coatings possessing various thicknesses to research the SEE characteristics of coating structures and have shown how the coating thickness affects the SEE behaviors. Besides, by considering coating/substrate as an ideal double-layer structure, we have derived several equations to describe the producing, transmitting, and escaping processes of excited inner SEs and finally constructed a unidimensional SEE model for double-layer structures. The model is applicable to reveal the dependence of true SE yield (TSEY) on the top and bottom layers’ physical properties and estimate TSEY proportions contributed by the top and bottom layers at random energy points. By employing the concept, SEE characteristics of Al2O3/Si, MgO/Si, and TiO2/Si double-layer structures have been quantitatively interpreted. Moreover, the abnormal SEY curve with a double-hump shape, which is induced by the peak position distinction of SiO2/Si structures, can also be explained. This work is of great significance to comprehend TSEY modulating regularities of various double-layer structures applied in surface engineering.

Effect of random anisotropy in stabilization of skyrmions and antiskyrmions

Ever increasing demand of skyrmion manipulation in nanodevices has brought up interesting research to understand the stabilization of these topologically protected chiral structures. To understand the actual shape and size of skyrmions and antiskyrmions observed experimentally, we have performed micromagnetic simulations to investigate their stabilization in presence of random anisotropy in magnetic thin film system. Previous experimental reports of skyrmion imaging in thin films depicts that the skyrmion shape is not perfectly circular. Here we show via simulations that the shape of a skyrmion and an antiskyrmion can get distorted due to the presence of different local anisotropy energy. The values of uniaxial anisotropy constant (Ku) and random aniostropy constant (Kr) are varied to understand the change in shape and size of a skyrmion and an antiskyrmion stabilized in a square magnetic nanoelement. The skyrmion or antiskyrmion shape gets distorted with the presence of random anisotropy energy in the system.

Noise-tolerant quantum speedups in quantum annealing without fine tuning

Quantum annealing is a powerful alternative model of quantum computing, which can succeed in the presence of environmental noise even without error correction. However, despite great effort, no conclusive demonstration of a quantum speedup (relative to state of the art classical algorithms) has been shown for these systems, and rigorous theoretical proofs of a quantum advantage (such as the adiabatic formulation of Grover’s search problem) generally rely on exponential precision in at least some aspects of the system, an unphysical resource guaranteed to be scrambled by experimental uncertainties and random noise. In this work, we propose a new variant of quantum annealing, called RFQA, which can maintain a scalable quantum speedup in the face of noise and modest control precision. Specifically, we consider a modification of flux qubit-based quantum annealing which includes low-frequency oscillations in the directions of the transverse field terms as the system evolves. We show that this method produces a quantum speedup for finding ground states in the Grover problem and quantum random energy model, and thus should be widely applicable to other hard optimization problems which can be formulated as quantum spin glasses. Further, we explore three realistic noise channels and show that the speedup from RFQA is resilient to 1/f-like local potential fluctuations and local heating from interaction with a sufficiently low temperature bath. Another noise channel, bath-assisted quantum cooling transitions, actually accelerates the algorithm and may outweigh the negative effects of the others. We also detail how RFQA may be implemented experimentally with current technology.

Limited frequency domain of the ac conductivity of some As2O3.V2O5.CuO.Nd2O3 glasses

Quaternary semiconducting glass system of the composition 25%As2O3.70%V2O5.(5-x)% CuO.x%Nd2O3 is prepared by the ordinary melt quenching technique. Electrical conductivity is measured in the temperature and frequency ranges of 303–473K and 0-5MHz, respectively. Dc conductivity is found to increase with increasing the mol%Nd2O3 with activation energy decreases from 0.43 to 0.39 eV. Ac conductivity shows strong temperature and limited frequency range dependences. The ac frequency dependence region is controlled by the lowest and the highest effective jump frequencies, flj and fmj, respectively. Dc and Ac conductivities show an acceptable fitting to the random potential energy (RPE) model. A reproducible threshold switching properties with Vth values decreases with increasing the mol% Nd2O3 is verified for the studied glasses. The recorded switching properties show also temperature and thickness dependences. Measured and calculated temperatures during the switching cycles confirm that, the produced joule heating does not affect negatively the structure of the samples. Finally, the magnetic properties of the studied glasses show weak paramagnetic properties resulted from the composition variation.

Out-of-equilibrium phase diagram of the quantum random energy model

In this paper we study the out-of-equilibrium phase diagram of the quantum version of Derrida's Random Energy Model, which is the simplest model of mean-field spin glasses. We interpret its corresponding quantum dynamics in Fock space as a one-particle problem in very high dimension to which we apply different theoretical methods tailored for high-dimensional lattices: the Forward-Scattering Approximation, a mapping to the Rosenzweig-Porter model, and the cavity method. Our results indicate the existence of two transition lines and three distinct dynamical phases: a completely many-body localized phase at low energy, a fully ergodic phase at high energy, and a multifractal "bad metal" phase at intermediate energy. In the latter, eigenfunctions occupy a diverging volume, yet an exponentially vanishing fraction of the total Hilbert space. We discuss the limitations of our approximations and the relationship with previous studies.

One step replica symmetry breaking and overlaps between two temperatures

We obtain an exact analytic expression for the average distribution, in the thermodynamic limit, of overlaps between two copies of the same random energy model (REM) at different temperatures. We quantify the non-self averaging effects and provide an exact approach to the computation of the fluctuations in the distribution of overlaps in the thermodynamic limit. We show that the overlap probabilities satisfy recurrence relations that generalise Ghirlanda–Guerra identities to two temperatures. We also analyse the two temperature REM using the replica method. The replica expressions for the overlap probabilities satisfy the same recurrence relations as the exact form. We show how a generalisation of Parisi’s replica symmetry breaking ansatz is consistent with our replica expressions. A crucial aspect to this generalisation is that we must allow for fluctuations in the replica block sizes even in the thermodynamic limit. This contrasts with the single temperature case where the extremal condition leads to a fixed block size in the thermodynamic limit. Finally, we analyse the fluctuations of the block sizes in our generalised Parisi ansatz and show that in general they may have a negative variance.

Magnetism of dimer ensemble with random exchange energy

We present the study of magnetism of dimer ensemble deposited on a non-magnetic conducting substrate. The dimers consist of ions with spin 1/2 and have a random size. The magnetic ions are coupled by RKKY-interaction with random energy value. We consider two interaction models. The first assumes that dimer coupling energy has a Gaussian distribution, and the second model is based on a log-normal distribution of dimer size. The magnetization and susceptibility are evaluated from the exact solution for dimer energy and eigenstates. We show that the average exchange value and its dispersion have a strong effect on the system properties. The magnetic saturation exists under strong magnetic fields. High-temperature leads to the Curie’s law for susceptibility. The saturation magnetization of system with ferromagnetic coupling lowers, while the antiferromagnetic dimer ensemble can have non-zero magnetization under the strong magnetic field. It is determined by the dispersion of exchange energy.

Development of a Nuclear Energy Spectrum Signal Generator

A digital nuclear pulse and digital nuclear energy spectrum signal generator was designed using FPGA and digital frequency synthesizer (DDS). It also includes slip signal, triangle wave, square wave, sine wave output. By randomly sampling the amplitude information and time information of the reference spectrum line, the complex algorithm of nuclear signal reproduction is avoided, and the simulation of the nuclear signal random pulse and nuclear energy spectrum (137Cs gamma spectrum) is realized. The signal amplitude is adjustable from 0.1V to 10V, and the frequency is adjustable from 10Hz to 10kHz.

Method for increasing ground movement characteristics of an unmanned aerial vehicle of an aerodynamic scheme of a flying wing and its virtual testing

The first part of the research discusses the possibility to introduce an integrated control contour for landing gear systems for an unmanned aerial vehicle of the aerodynamic scheme 'flying wing' as a way of increasing ground movement characteristics. The analysis of peculiarities of movement on the ground is carried out, and disadvantages and limits of application of available control methods are specified. The second part of the paper is devoted to development of a dynamic aircraft model for virtual testing of integral contour. The development allows to obtain the maximum benefits on flying wing aircraft. Nevertheless, with certain modifications, the system can be used for aircraft of the classic aerodynamic design. It will improve the safety of flights in a strong crosswind and improve takeoff and landing characteristics. The technical solution can be used on passenger aircraft as an auxiliary system that helps the pilot to withstand take-off and flight direction under random energy disturbances, similar to the electronic stability program (ESP) auxiliary systems used on modern cars - an electronic dynamic stabilisation system.

Optimizing Energy Harvesting Decode-and-Forward Relays With Decoding Energy Costs and Energy Storage

Energy harvesting (EH) relay communication systems with decoding energy costs in multiple block cases have not been widely studied. This paper investigates the relay network with a decode-and-forward relay powered by EH. Unlike other works, we consider the relay with energy decoding costs which harvests random energy from both a dedicated transmitter and other ambient radio-frequency (RF) sources. The EH relay adopts a harvest-receive-forward time-switching architecture. We optimize the time fractions of the three phases and the reception rate at the relay to maximize the offline throughput for single and multiple block cases under two EH scenarios. The multi-block optimization problem constitutes a complex non-convex problem, which we decouple into a single block problem with two auxiliary variables determined by an outer optimization problem. The original problem is finally solved at the cost of linear optimization after series of tricks. Several conclusions are derived: (i) energy storage is necessary (unnecessary) when the relay harvests energy from the transmitter (ambient RF sources), (ii) the optimal reception rate remains unchanged, while the optimal time fractions vary with the energy harvested from ambient RF sources leading to different average throughput. We give numerical simulations to verify our theoretical analysis.

Gravity triboelectric nanogenerator for the steady harvesting of natural wind energy

Triboelectric nanogenerator (TENG), as a renewable energy harvesting technology, has been verified as an effective approach for converting mechanical energy into electric energy. In a natural environment, the unsteadiness of TENG energy harvesting restricts the application and development of TENG. From this perspective, a gravity triboelectric nanogenerator (G-TENG) is developed for the first time to convert natural wind energy into steady electric energy, achieving the steady harvesting of natural wind energy. The G-TENG mainly comprises an energy input module, energy storage module, and energy output module. Random wind energy is transmitted from the input module to the storage module and converted into gravitational potential energy. Steady electric energy is ultimately obtained from the output module. The standard deviation ( I SD ) of the short-circuit current peaks is under 0.31 μA. Additionally, the fluctuation degree ( I FD ) of the short-circuit current peaks is defined to describe the steady output capability of TENG. I FD of the G-TENG can reach 2.3%. A steady current is thus achieved by the G-TENG in a natural environment. This research provides essential guidance for the steady harvesting of natural energy by the TENG. • Gravity triboelectric nanogenerator (G-TENG) is proposed for the steady harvesting of natural wind energy. • The fluctuation degree ( I FD ) of short-circuit current peaks is defined to describe the steady output capability of TENG. • A commercial thermometer is powered by the G-TENG with the assistance of a bridge rectifier in a natural wind environment.

Relativistic gravitational collapse by thermal mass

Gravity and thermal energy are universal phenomena which compete over the stabilization of astrophysical systems. The former induces an inward pressure driving collapse and the latter a stabilizing outward pressure generated by random motion and energy dispersion. Since a contracting self-gravitating system is heated up one may wonder why is gravitational collapse not halted in all cases at a sufficient high temperature establishing either a gravo-thermal equilibrium or explosion. Here, based on the equivalence between mass and energy, we show that there always exists a temperature threshold beyond which the gravitation of thermal energy overcomes its stabilizing pressure and the system collapses under the weight of its own heat.

Energy Flow Analysis of One-Dimensional Structures with Random Properties

In this work, the energy density responses of one-dimensional structures with random properties are investigated analytically. Based on Green kernels, analytical representations of energy density for vibrating rods and beams are proposed using the superposition of energy waves. Considering random properties in rods and beams, formulations of energy density responses are obtained. Then, the mathematical expectations and variances are derived. And response intervals for random responses are developed. Finally, numerical simulations are performed to validate the proposed formulations, and characteristics of the random energy density responses of rods and beams are analysed. The main contribution of this work is that a new approach to energy density responses is proposed which facilitates the vibration analysis of structures with uncertainty parameters.

A pendulum hybrid generator for water wave energy harvesting and hydrophone-based wireless sensing

The environmental monitoring system is of great significance in marine scientific research and exploration. However, battery-operated sensors in such a system limit its working time and make maintenance difficult. Harvesting water wave energy to power these sensors becomes a promising way to overcome challenges. Herein, a pendulum type hybrid generator to scavenge wave energy and power the hydrophone is presented. The proposed pendulum structure can harvest random water wave energy from arbitrary directions sensitively. The combination of a freely rolling mode triboelectric nanogenerator (TENG) and a magnetic sphere based electromagnetic generator (EMG) provides complementary advantages and harvests wave energy in a wide frequency range. The hybrid generator is demonstrated to drive 177 LEDs and power an electronic device. At a wave driving frequency of 1.4 Hz, the output power of the EMG and TENG is 6.7 mW and 8.01 µW, respectively. A capacitor can be charged to 26 V by the hybridized generator within 200 seconds at the frequency of 1.8 Hz. The new type of hydrophone-based system realizes sustainable wireless sensing of acoustic signals and positioning information and has important application value for long-term synchronous ocean monitoring.

The Dickman–Goncharov distribution

In the 1930s and 40s, one and the same delay differential equation appeared in papers by two mathematicians, Karl Dickman and Vasily Leonidovich Goncharov, who dealt with completely different problems. Dickman investigated the limit value of the number of natural numbers free of large prime factors, while Goncharov examined the asymptotics of the maximum cycle length in decompositions of random permutations. The equation obtained in these papers defines, under a certain initial condition, the density of a probability distribution now called the Dickman–Goncharov distribution (this term was first proposed by Vershik in 1986). Recently, a number of completely new applications of the Dickman–Goncharov distribution have appeared in mathematics (random walks on solvable groups, random graph theory, and so on) and also in biology (models of growth and evolution of unicellular populations), finance (theory of extreme phenomena in finance and insurance), physics (the model of random energy levels), and other fields. Despite the extensive scope of applications of this distribution and of more general but related models, all the mathematical aspects of this topic (for example, infinite divisibility and absolute continuity) are little known even to specialists in limit theorems. The present survey is intended to fill this gap. Both known and new results are given. Bibliography: 62 titles.