Switching Probability Research Articles

Resonant acoustic wave assisted spin-transfer-torque switching of nanomagnets

We report the possibility of achieving an order of magnitude reduction in the energy dissipation needed to write bits in perpendicular magnetic tunnel junctions by simulating the magnetization dynamics under a combination of resonant surface acoustic waves (r-SAWs) and spin-transfer-torque (STT). The magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert equation under macrospin assumption with the inclusion of thermal noise. The resonant magnetization dynamics in the magnetostrictive nanomagnet builds over few tens of cycles of SAW application that drives the magnetization to precess in a cone with a deflection of ∼45° from the perpendicular direction. This reduces the STT current density required to switch the magnetization direction without increasing the STT application time or degrading the switching probability in the presence of room temperature thermal noise. This could lead to a pathway to achieve energy efficient switching of spin-transfer-torque random access memory whose lateral dimensions can be scaled aggressively despite using materials with low magnetostriction by employing SAW excitation to drive ferromagnetic resonance.

A place too crowded to study: The impact of student cohort growth on the probability of university dropout

Introduction: This study examines the influence of major fluctuations in the number of students enrolling at university on the probability of dropout or a switch to a different course of study. Findings from the US show that a pronounced increase in student numbers leads to more dropouts. Materials and methods: This article provides an analysis of this relationship for the first time outside the US and for an entire university system. We use administrative data for all the students who started studying at Swiss universities between 1980 and 2001. Results: The results suggest a significant relationship between positive cohort growth and the probability of dropout. A reduction in student numbers, on the other hand, does not increase the probability of persistence. Discussion: Despite the negative influence of a big cohort on the probability of persistence, no statistically significant relationship exists, by contrast, between the change in student numbers and the probability of a student switching to a different course of study.

Northward range expansion in spring-staging barnacle geese is a response to climate change and population growth, mediated by individual experience.

All long-distance migrants must cope with changing environments, but species differ greatly in how they do so. In some species, individuals might be able to adjust by learning from individual experiences and by copying others. This could greatly speed up the process of adjustment, but evidence from the wild is scarce. Here, we investigated the processes by which a rapidly growing population of barnacle geese (Branta leucopsis) responded to strong environmental changes on spring-staging areas in Norway. One area, Helgeland, has been the traditional site. Since the mid-1990s, an increasing number of geese stage in another area 250km further north, Vesterålen. We collected data on goose numbers and weather conditions from 1975 to 2017 to explore the extent to which the increase in population size and a warmer climate contributed to this change in staging area use. During the study period, the estimated onset of grass growth advanced on average by 0.54days/year in each of the two areas. The total production of digestible biomass for barnacle geese during the staging period increased in Vesterålen but remained stable in Helgeland. The goose population has doubled in size during the past 25years, with most of the growth being accommodated in Vesterålen. The observations suggest that this dramatic increase would not have happened without higher temperatures in Vesterålen. Records of individually marked geese indicate that from the initial years of colonization onwards, especially young geese tended to switch to Vesterålen, thereby predominating in the flocks at Vesterålen. Older birds had a lower probability of switching to Vesterålen, but over the years, the probability increased for all ages. Our findings suggest that barnacle geese integrate socially learned behaviour with adjustments to individual experiences, allowing the population to respond rapidly and accurately to global change.

Importance Sampling for Thermally Induced Switching and Non-Switching Probabilities in Spin-Torque Magnetic Nanodevices

Spin-transfer torque magnetoresistive random access memory is a potentially transformative technology in the non-volatile memory market. Its viability depends, in part, on one's ability to predictably induce or prevent switching; however, thermal fluctuations cause small but important errors in both the writing and reading processes. Computing these very small probabilities for magnetic nanodevices using naive MC simulations is essentially impossible due to their slow statistical convergence, but variance reduction techniques can offer an effective way to improve their efficiency. Here, we provide an illustration of how importance sampling can be efficiently used to estimate low read and write soft error rates of macrospin and coupled-spin systems.

Optimum design of reinforced concrete retaining walls with the flower pollination algorithm

The flower pollination algorithm (FPA) is an efficient metaheuristic optimization algorithm mimicking the pollination process of flowering species. In this study, FPA is applied, for the first time, to the optimum design of reinforced concrete (RC) cantilever retaining walls. It is found that FPA offers important savings with respect to conventional design approaches and that it outperforms genetic algorithm (GA) and the particle swarm optimization (PSO) algorithm in this design problem. Furthermore, parameter tuning reveals that the best FPA performance is achieved for switch probability values ranging between 0.4 and 0.7, a population size of 20 individuals and a Levy flight step size scale factor of 0.5. Finally, parametric optimum designs show that the optimum cost of RC retaining walls increases rapidly with the wall height and smoothly with the magnitude of surcharge loading.

An Improved Flower Pollination Algorithm with Three Strategies and Its Applications

The flower pollination algorithm is a recently presented meta-heuristic algorithm, but limited in searching precision and convergence rate when solving some complex problems. In order to enhance its performance, this paper proposes an improved flower pollination algorithm, combined with three strategies, i.e., a new double-direction learning strategy to advance the local searching ability, a new greedy strategy to strengthen the diversity of population and a new dynamic switching probability strategy to balance global and local searching. These strategies can increase searching precision and make solution more accurate. Then 12 standard test functions and two structural design examples are selected to appraise the performance of the newly proposed algorithm. The results show that our new algorithm has outstanding performance, such as high accuracy, fast convergence speed and strong stability on solving some complex optimization problems.

ASSESSMENT OF RELIABILITY AND VITALITY OF SYSTEMS TAKING INTO ACCOUNT THE INTERRELATION OF ELEMENTS WITH SEISMIC EXPOSURE

ObjectivesThe aim of the study is to develop a model for assessing the reliability of frame systems, taking into account the redistribution of forces between vertical structures when plastic hinges are formed in them from horizontal seismic effects.MethodThe research method is based on the analysis of the schemes of mechanisms for the transition of frame systems to limit states, as well as probability theory, random processes and system reliability.ResultsBased on the analysis of the paths of transition of statically indefinable frame systems to failure states due to the formation of plastic hinges at the junction points of the posts with crossbars, a block diagram of the system elements connection has been developed, presented as a separate redundancy scheme. The expressions for estimating the probabilities of switching off the conditional elements in the computational model and transitions of the system, both to the backup and to the failure states are presented. Expressions are proposed for assessing the survivability of frame systems with a decrease in static indeterminacy due to the formation of plastic hinges in structures. The calculation example is given.ConclusionThe proposed model for assessing reliability allows, in contrast to the parametric model, to evaluate the reliability of structures with regard to the redistribution of effort in structures with damage accumulated in racks in the form of plastic hinges, and to identify reliability reserves embedded in statically indeterminable systems under strong seismic effects.

Iron ore price and the AUD exchange rate: A Markov approach

ABSTRACTThe present paper fitted the monthly data set into the Markov regime switching model to examine the relationship between the iron ore price and the Australian dollar (AUD) exchange rate. The study dichotomised the AUD into state 1 (depreciation) and state 2 (appreciation). The empirical results indicate evidence of an asymmetric relationship between an iron ore price change and the AUD exchange rate fluctuation based on states. The AUD appreciates with a fall in iron price and depreciates with a rise in iron ore price. The results contradict with the understanding of the commodity-currency theory. Additionally, iron ore price reduces the AUD state expected duration and the switching probability, but increases the AUD volatility. Based on the transition probability, the AUD has a higher chance of depreciating than appreciating. The statistical economic impact of the AUD currency is higher when appreciating than depreciating.

Banking goes digital: The adoption of FinTech services by German households

Germany is falling behind its peers in adopting new digital technologies and financial services offered by non-bank high-tech startups (e.g., FinTech). Using survey data, we analyze which FinTech services households are likely to adopt. Our results indicate that a household's level of trust and comfort with new technologies, financial literacy, and overall transparency impact its propensity to switch to a FinTech. Specifically, households with low levels of trust, good financial education, and preference for transparency are characterized by a higher probability of adopting FinTech. In contrast, household price perceptions do not appear to significantly impact switching probability.

Dependence of Switching Probability on Operation Conditions in GexSe1–xOvonic Threshold Switching Selectors

Ovonic threshold switching (OTS) selector is a promising candidate to suppress the sneak current paths in resistive switching random access memory (RRAM) arrays. Variations in the threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {th}}$ </tex-math></inline-formula> ), and the hold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {hd}}$ </tex-math></inline-formula> ) have been reported, but a quantitative analysis of the switching probability dependence on the OTS operation conditions is still missing. A novel characterization method is developed in this letter, and the time-to-switch- ON/OFF ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{t}_{ \mathrm{\scriptscriptstyle ON}}/\text{t}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ) at a constant <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {OTS}}$ </tex-math></inline-formula> is found following the Weibull distribution, based on which the dependence of switching probability on pulse bias and time can be extracted and extrapolated, and the switching probability can be ensured with appropriately chosen operation conditions. The difference between square and triangle switching pulses is also explained. This provides a practical guidance for predicting the switching probability under different operation conditions and for designing reliable one-selector-one-RRAM (1S1R) arrays.

Increasing trend of scientists to switch between topics

Despite persistent efforts in understanding the creativity of scientists over different career stages, little is known about the underlying dynamics of research topic switching that drives innovation. Here, we analyze the publication records of individual scientists, aiming to quantify their topic switching dynamics and its influence. We find that the co-citing network of papers of a scientist exhibits a clear community structure where each major community represents a research topic. Our analysis suggests that scientists have a narrow distribution of number of topics. However, researchers nowadays switch more frequently between topics than those in the early days. We also find that high switching probability in early career is associated with low overall productivity, yet with high overall productivity in latter career. Interestingly, the average citation per paper, however, is in all career stages negatively correlated with the switching probability. We propose a model that can explain the main observed features.

Interface moment dynamics and its contribution to spin-transfer torque switching process in magnetic tunnel junctions

A practical problem for memory applications involving perpendicularly magnetized magnetic tunnel junctions is the reliability of switching characteristics at high-bias voltage. Often it has been observed that at high-bias, additional error processes are present that cause a decrease in switching probability upon further increase of bias voltage. We identify the main cause of such error-rise process through examination of switching statistics as a function of bias voltage and applied field, and the junction switching dynamics in real time. These experiments show a coincidental onset of error-rise and the presence of a new low-frequency microwave emission well below that dictated by the anisotropy field. We show that in a few-macrospin coupled numerical model, this is consistent with an interface region with concentrated perpendicular anisotropy, and where the magnetic moment has limited exchange coupling to the rest of the layers. These results point to the important role high-frequency interface magnetic moment dynamics play in determining the switching characteristics of these tunnel junction devices.

Open-minded imitation can achieve near-optimal vaccination coverage.

Game-theoretic studies of voluntary vaccination predict that a socially unstructured population that is guided exclusively by individual rational self-interest always reaches a Nash equilibrium with vaccination coverage that is below the societal optimum. Human decision-making involves additional mechanisms, such as imitation of the successful strategies of others. However, previous research has found that imitation leads to vaccination coverage that is even below the Nash equilibrium. In this work, we note that these conclusions rely on the widely accepted use of Fermi functions for modeling the probabilities of switching to another strategy. We consider here a more general functional form of the switching probabilities. It involves one additional parameter[Formula: see text]. This parameter can be loosely interpreted as a degree of open-mindedness. The resulting dynamics are consistent with the ones that would be generated by functions that give best fits for empirical data in a widely cited psychological experiment. We show that sufficiently high levels of open-mindedness, as conceptualized by our parameter[Formula: see text], will drive equilibrium vaccination coverage levels above the Nash equilibrium, and in fact arbitrarily close to the societal optimum. These results were obtained both through mathematical analysis and numerical simulations.

Data-Driven Analysis of EEG Reveals Concomitant Superficial Sleep During Deep Sleep in Insomnia Disorder.

Study Objectives: The subjective suffering of people with Insomnia Disorder (ID) is insufficiently accounted for by traditional sleep classification, which presumes a strict sequential occurrence of global brain states. Recent studies challenged this presumption by showing concurrent sleep- and wake-type neuronal activity. We hypothesized enhanced co-occurrence of diverging EEG vigilance signatures during sleep in ID.Methods: Electroencephalography (EEG) in 55 cases with ID and 64 controls without sleep complaints was subjected to a Latent Dirichlet Allocation topic model describing each 30 s epoch as a mixture of six vigilance states called Topics (T), ranked from N3-related T1 and T2 to wakefulness-related T6. For each stable epoch we determined topic dominance (the probability of the most likely topic), topic co-occurrence (the probability of the remaining topics), and epoch-to-epoch transition probabilities.Results: In stable epochs where the N1-related T4 was dominant, T4 was more dominant in ID than in controls, and patients showed an almost doubled co-occurrence of T4 during epochs where the N3-related T1 was dominant. Furthermore, patients had a higher probability of switching from T1- to T4-dominated epochs, at the cost of switching to N3-related T2-dominated epochs, and a higher probability of switching from N2-related T3- to wakefulness-related T6-dominated epochs.Conclusion: Even during their deepest sleep, the EEG of people with ID express more N1-related vigilance signatures than good sleepers do. People with ID are moreover more likely to switch from deep to light sleep and from N2 sleep to wakefulness. The findings suggest that hyperarousal never rests in ID.

A Differential Evolution Flower Pollination Algorithm with Dynamic Switch Probability

For the shortcomings of the basic flower pollination algorithm, this paper proposes a differential evolution flower pollination algorithm with dynamic switch probability based on the Weibull distribution. This new algorithm improved the convergence rate and precision. The switch probability is improved by Weibull distribution function combined with the number of iterations. It can balance the relationship between the global pollination and the local pollination to improve the overall optimization performance of the algorithm. Random mutation operator is merged into the global pollination process to increase diversity of the population, enhance the ability of the algorithm's global search and avoid premature convergence. In the process of local pollination, directed mutation and crossover operation of the differential evolution are incorporated, it makes the individual flower position update with the memory function, which can choose the direction of variation reasonably. The use of cross-operation can avoid new solutions crossing the boundary. Convergence rate is improved and the algorithm can approach the global optimal solution continuously. Theoretical analysis proved the convergence and time complexity of the improved algorithm. The simulation results based on the function optimization problem show that the improved algorithm has better performance of optimization, faster convergence speed and higher convergence accuracy.

Collective decision making in dynamic environments

Collective decision making is the ability of individuals to jointly make a decision without any centralized leadership, but only relying on local interactions. A special case is represented by the best-of-n problem, whereby the swarm has to select the best option among a set of n discrete alternatives. In this paper, we perform a thorough study of the best-of-n problem in dynamic environments, in the presence of two options (n=2). Site qualities can be directly measured by agents, and we introduce abrupt changes to these qualities. We introduce two adaptation mechanisms to deal with dynamic site qualities: stubborn agents and spontaneous opinion switching. Using both computer simulations and ordinary differential equation models, we show that: (i) The mere presence of the stubborn agents is enough to achieve adaptability, but increasing its number has detrimental effects on the performance; (ii) the system adaptation increases with increasing swarm size, while it does not depend on agents’ density, unless this is below a critical threshold; (iii) the spontaneous switching mechanism can also be used to achieve adaptability to dynamic environments, and its key parameter, the probability of switching, can be used to regulate the trade-off between accuracy and speed of adaptation.

Thermally Activated Magnetic Switching Mode for Various Thicknesses of Perpendicularly Ferromagnetic Nano-dot

Background:Even applying thermal pulse has been succeeded to reduce the coercivity through randomization the magnetization in such a way stimulate the magnetic reversion, the efficiency of magnetic switching field consumption in writing process still turns out to be an exciting research field to implement the HAMR technology. One of the remarkable geometric properties of HAMR storage media that can be correlated to the writing field reduction issue is the nano-dot thickness. Furthermore, thermal fluctuation causes the magnetization switching process to be probabilistic. This magnetic switching probability determines the magnitude of the writing field. This paper aims to investigate the impact of changes in media thickness on the magnetization process in particular at high temperatures numerically.Methods:Nano-dot was modeled as a parallelepiped with uniaxial anisotropy which was regarded as a magnetically isolated system where no disturbance field of neighboring nano-dots. Simulation arrangements were implemented to evaluate the two viewpoints in the current heat-assisted magnetic recording, either coercivity, as well as writing field consume. Coercivity was gauged by inducing a magnetic field which linearly increased up to 2 Tesla for 2.5 ns at thermal equilibrium to the surrounding. In evaluating writing field consume, thermal field pulse which just below the Curie temperature was generated while the magnetic field inducing the nano-dot. These schemes investigations were based on the Landau-Lifshift- Gilbert equation which accommodates the fluctuation-dissipation theorem in calculating thermal fluctuation effect. Also, temperature dependent material parameters such as magnetic saturation, magnetic anisotropy, and exchange interaction, were taken into account.Results:At room temperature, the coercive and nucleation fields are highly sensitive to the nano-dot thickness. Under thermal assistance, the writing field for 10 nm and 100 nm of the chosen thicknesses are 0.110 T and 0.125 T respectively. These writing grades are significantly lower than the coercivity of the media. For both thicknesses, zero field magnetization reversal phenomena are observed as indicated by the existences of the switching probabilities at H = 0.Conclusion:This numerical study showed that using the heating assistance close to the Curie point, nanodots with the chosen thicknesses and magnetic parameters were probably to be magnetized even no driven magnetic field. Along with this result, magnetic field induction which required to utterly magnetizing was only in the sub-Tesla - about a tenth of the coercive field. During magnetization processes under thermal assistance, randomization of magnetic moments initiated the switching dynamic before the domain wall was nucleated and propagated to reach a single magnetized domain.

Robust write operation in Co slotted nanoring

In magnetic random access memory (MRAM), free layers are used to store data bits as “0” or “1” in binary system. The main bottleneck limiting the practical applications of current MRAM technology is its storage states’ transition probability. Although several generations of MRAM have been reported, the problem still puzzles us. Here, we utilize an external field to switch Co slotted nanoring, which is convenient to reveal the key factor in the control of magnetic moments’ flip. Based on such analysis, we present a robust write operation through setting the slot edge parallel to the external field. In comparison with the probabilistic storage states’ transition in previous MRAM, our new technology definitely increases the switching probability to 100%. The continuous and orderly data-input process results in an energy barrier to protect the storage state. In addition, the robust write operation can also significantly reduce the influence of the device’s dimension on the switching probability, which is vital in decreasing the complexity and difficulty of the manufacture process. Besides, the novel data-input method could afford linearly tunable write parameters to satisfy the different application scenarios of storage devices.

Design, implementation and analysis of cognitive radio enabled intelligent WBAN gateway for cost-efficient remote health monitoring

In this paper, we design and implement an intelligent gateway for Wireless Body Area Network (WBAN) that seeks opportunistic access of licensed Primary User (PU) channels using Cognitive Radio (CR) to facilitate spectral-efficient, cost-efficient and reliable Non-Real Time (NRT) backhaul transmission of WBAN data for ubiquitous healthcare monitoring. The controller is termed herein as BodyCog-BNC. We develop and implement a cross-layer based modified protocol stack at the BodyCog-BNC, comprising of BodyCog-BNC Management Entity (BME) and BodyCog-BNC CR Medium Access Control (BCR-MAC) units, to exploit cross layer message passing to support the novel idea of spectrum agility. A spectral agile BodyCog-BNC is capable of intelligently switching to conventional licensed Wide-Area Access Network (WAN) technology in case of lack of proper PU channels or occurrence of successive handoffs in multiple PU channels. Furthermore, the protocol stack facilitates session management and energy-efficient backhaul CR transmission over a PU channel employing a proposed Inter-Sensing Time Optimization (ISTO) algorithm. ISTO leverages on convex optimization to select the optimum inter-sensing time for a PU channel to maximize the energy-efficiency within a PU interference constraint under sensing uncertainties. Closed form analytical expressions are also derived to estimate the average consumed energy, switching probability, switching time and the cost-efficiency of BodyCog-BNC. Exhaustive performance analysis shows that the BodyCog-BNC (WBAN gateway), provides a cost-efficient solution for different healthcare applications under varied operating conditions and CR cost regimes. Finally, through a prototype implementation and proof of concept we validate the ability of BodyCog-BNC in enabling NRT remote healthcare monitoring.

Development of “spin dice” — A Scalable Random Number Generator Based on Spin-Torque Switching

We have developed a random-number-generator (RNG) named “spin dice,” which employs the stochastic nature of spin-torque switching (STS) in a magnetic tunnel junction. The principle of the idea is that the switching probability first tuned around 0.5 is varied linearly with the applied current. After that, the switching results are converted into binary random numbers. We fabricated several types of “spin dice” by combining magnetic tunnel junctions and single-board microcomputer, and achieved generation speed of random numbers up to several hundred kbit/sec. Because STS is scalable and magnetic tunnel junctions have compatibility to semiconductor fabrication process, “spin dice” can be considered as a promising candidate for truly random-number-generator (TRNG) for security applications.