Critical Delay Research Articles

Stability, Hopf Bifurcation and Optimal Control of Multilingual Rumor-Spreading Model with Isolation Mechanism

The propagation of rumors on online social networks (OSNs) brings an awful lot of trouble to people’s life and society. Aiming at combating rumors spreading on OSNs, two novel rumor-propagation models without and with time delays are proposed, which combine with the influence of the immune mechanism, isolation mechanism and network structure. Firstly, we analyze the existence of rumor equilibria and obtain some existence conditions of backward bifurcation. Secondly, the local stabilities of rumor-free and rumor equilibria are proved by using the Jacobian matrix method, and some critical conditions for the existence of Hopf bifurcation are acquired by selecting critical parameters and delays as bifurcation parameters. Furthermore, an optimal control method is proposed, which can prevent the spread of rumors within an expected time period and minimize the cost of control. Finally, some numerical simulations are provided to verify the effectiveness of the proposed theoretical results.

Correlation and causality between carbon and energy markets: a complexity perspective.

Global warming obliges humans to focus on the relationships between carbon and energy markets. This study considers the relationship between carbon and energy markets from a complexity perspective. Chinese carbon prices and four energy indexes are selected as empirical variables. First, the complexities of carbon and energy markets are measured by multi-scale fuzzy entropy. The critical time delay of the series is then obtained by maximizing the Pearson coefficients between these markets. Further, analysis of the detrended cross-correlation coefficient confirms the existence of time delay. Finally, transfer entropy is applied to investigate the causality pertaining to dynamic complexity. Results of fuzzy entropy analysis reveal that the carbon market has lower complexity than energy markets. Meanwhile, multi-scale results indicate greater complexity on the small time scales in all markets than on the large time scales. The critical time delay is found to be about 50, which maximizes the correlation coefficient. Finally, causality between carbon and energy markets varies. Expectations in the carbon market impact oil gas and coal markets; electricity and new energy affect the carbon market; and cross-causality exists in the relationship between coal and carbon markets. The participants should focus on the information transmission between carbon and energy markets.

Transistor-Level Radiation Hardening by Design Techniques in Complex Gates

Single Event Transients (SETs) have become a major reliability concern for integrated circuits used in critical applications. Research to improve the radiation robustness of digital circuits has been conducted, assessing all abstraction levels (from the device up to the system). This study evaluates transistor-level radiation-hardened techniques in combinational logic, such as transistor folding, sizing and reordering. In addition, the efficiency of using supergates, including series-parallel and non-series-parallel CMOS structures, to harden the combinational logic is discussed. The dependence of input signals probability on a logic cell susceptibility to SET is assessed. Moreover, a new concept of electrical masking is introduced. The robustness of the investigated logic cells was evaluated regarding their SET rate. The CREME96 tool was used to generate the SET rates, and an electrical model was used to perform particle hit simulations. Obtained results have indicated that modifying the structure of logic gates can substantially improve circuit robustness without necessarily worsening its performance. Besides, using supergates in combinational logic design has demonstrated to be a promising hardening strategy. The most robust supergate implementation of a five-input logic function provided up to [Formula: see text] SET rate reduction regarding an approach based on standard cells, along with lower critical delay ([Formula: see text]) and average power ([Formula: see text]).

Delay effects on the stability of large ecosystems

The common intuition among the ecologists of the midtwentieth century was that large ecosystems should be more stable than those with a smaller number of species. This view was challenged by Robert May, who found a stability bound for randomly assembled ecosystems; they become unstable for a sufficiently large number of species. In the present work, we show that May's bound greatly changes when the past population densities of a species affect its own current density. This is a common feature in real systems, where the effects of species' interactions may appear after a time lag rather than instantaneously. The local stability of these models with self-interaction is described by bounds, which we characterize in the parameter space. We find a critical delay curve that separates the region of stability from that of instability, and correspondingly, we identify a critical frequency curve that provides the characteristic frequencies of a system at the instability threshold. Finally, we calculate analytically the distributions of eigenvalues that generalize Wigner's as well as Girko's laws. Interestingly, we find that, for sufficiently large delays, the eigenvalues of a randomly coupled system are complex even when the interactions are symmetric.

Stability and Hopf bifurcation of a love model with two delays

We analyze the stability and Hopf bifurcation of a proposed nonlinear love model with two delays. The nonlinearity stems from a logistic term injected to meticulously depict a couple’s cautious love affairs. The analysis is based on the linearization theory and starts with a single-delay case assuming that one of the two characters is always impulsive. The critical delay values and existence conditions for the Hopf bifurcation are obtained. Subsequently, we extend to the more practical but also more involved dual-delay case where the delays affect the emotions of both individuals. Accordingly, a non-trivial resultant-based analysis framework is proposed, and the corresponding Hopf bifurcation is detected intuitively and exhaustively by an obtained stability map in the delay domain. The results explain an interesting and well-known feature in our daily life, i.e., proper time delays stabilize the love dynamics. Furthermore, the spectral analysis based on a numerical case reveals another common emotional experience, that proper delays not only lead to a smoother transition process but also yield a shorter settling time for the love convergence. The numerical bifurcation diagram and computational cost are also considered to demonstrate the effectiveness and efficiency of the presented analysis framework. Finally, some additional suggestions are provided for the studied couple to earn a sweet love relationship.

Studying the causes of delays in construction projects: the case of Qatar infrastructure projects

Background: This study aims to examine the causes of delay in construction projects, particularly in the case of infrastructure projects in Qatar. The most critical delay causes were analyzed in the perception of the project’s three participants: clients, contractors, and consultants. A literature review was conducted to highlight possible delay causes in other countries. There were gaps in detecting the causes of delay due to the lack of studies on Qatar infrastructure projects. Methods: The deductive approach has been used in this study for the quantitative method. It provides a new framework or theory for identifying the causes of delay. The quantitative method used a questionnaire that was created through Survey Monkey. The number of participants was one hundred thirty-three. The questionnaire included forty-one questions in four sections, one sheet for participant information, nine questions about personal data, thirty questions about delay causes, and two questions about delay effects. Results and Discussion: The data analysis was conducted on a questionnaire to rank the causes of delays by the Relative Importance Index (RII) method. Further analysis was undertaken to interpret the data by regression analysis. The results showed that client changing orders during construction was the most significant delay cause in Qatar infrastructure projects. Conclusions: The research aim was achieved by meeting its objectives. Several recommendations were suggested to reduce delays’ influence on Qatar's infrastructure projects. Research limitations were identified for this study.

Queues with Delayed Information: Analyzing the Impact of the Choice Model Function

In this paper, we study queueing systems with delayed information that use a generalization of the multinomial logit choice model as its arrival process. Previous literature assumes that the functional form of the multinomial logit model is exponential. However, in this work we generalize this to different functional forms. In particular, we compute the critical delay and analyze how it depends on the choice of the functional form. We highlight how the functional form of the model can be interpreted as an exponential model where the exponential rate parameter is uncertain. Furthermore, the rate parameter distribution is given by the inverse Laplace–Stieltjes transform of the functional form when it exists. We perform numerous numerical experiments to confirm our theoretical insights.

K-Nearest Neighbor Queues with Delayed Information

In this paper, we analyze a model called the k-nearest neighbor queue with the possibility of having delayed queue length feedback. We prove fluid limits for the stochastic queueing model and show that the fluid limit converges to a system of delay differential equations. Using the properties of circulant matrices, we derive a closed form expression for the value of the critical delay, which governs whether the delayed information will induce oscillations or a Hopf bifurcation in our queueing system.

Critical delay factors for construction projects in Central Aceh District, Indonesia

Background: Construction development in Indonesia is growing rapidly, especially in Central Aceh District. Construction projects often experience risks, so that risk events can have a serious impact on the viability of the project. Project delays can result in cost overruns and project losses. Therefore, it is necessary to identify the factors causing project delays.The purpose of this study was to (1) identify the risk factors that cause delays in construction projects and (2) determine those particular risk factors that have a greater influence on construction projects. The location of this research was Central Aceh District. Methods: The data in this study were primary data in the form of a questionnaire and secondary data obtained from the literature related to this particular type of research. Questionnaires were distributed to respondents, namely contractor companies located in the Central Aceh District. The questionnaires were distributed to determine respondents' opinions about the level of influence of risk factors causing project delays. We used a validity test, reliability test, and descriptive analysis for data processing. Results: Based on the results of the study from 47 respondents, the “very high influence” category (Mode=5) for the tool malfunction factor, cost estimation inaccuracy, increased work costs, implementation of new technologies, details, accuracy and conformity to specifications that are not appropriate, worker quarrels, poor project planning and management, poor condition at locations and accessibility difficulty. Conclusions: Of the 80 risk factors that caused project delays, eight risk factors were found to have a very high influence on the implementation of construction projects in Central Aceh District. Practical implications: The results of this study provide knowledge to contractor companies about the delay factors that have the most influence on project implementation so that they are expected to be able to manage risks to avoid losses.

Integrated Sensory Throughput and Traffic-Aware Arbiter for High Productive Multicore Architectures

The increasing demand for network and high-performance devices requires large data throughputs with minimal loss or repetition. Network on chips (NoC) provides excellent connectivity among multiple on-chip communicating devices with minimal loss compared with old bus systems. The motivation is to improve the throughput of the NoC that integrated on multicores for communication among cores by reducing the communication latency. The design of the arbiter in the crossbars switch of an NoC’s router has a vital role in judging the system’s speed and performance. Low latency and high-speed switching are possible with high performance and good switching equipment at the network level. One of the significant components in NoC under SoC design is the arbiter, which governs the system’s performance. Proper arbitrations can avoid network or traffic congestions like livelock and buffer waiting. The proposed work in this paper is to design an efficient and high productive arbiter for multicore chips, especially SoCs and CMPs. The proposed arbiter is showing good improvement in the throughput at higher data rates; an average of more than 10% throughput improvement is noticed at higher flit injection rates independent of the VCs implemented. Further, the critical delays are reduced to 15.84% with greater throughputs.

Toward a big picture of COVID-19.

The paper aims to illustrate and explain the problems and opportunities for improvement in Covid management that become evident when taking a systems perspective. Critical time delays occurred in the regulation of the pandemic that the management cycle of political cybernetics makes explicit. In general, the executive management of the pandemic in global, regional, and national organizations was unprepared in detecting and responding to the onset of the waves and making appropriate decisions towards differential instead of general lockdowns based on available data. This was further complicated by the mutants of SARS‐CoV2 that perpetuated the high dynamics of the pandemic. In addition, the diversity of medical specialisms, without appropriate big picture thinking, led to an imbalanced response that failed to appreciate the role of virology and epidemiology compared to clinical and public health‐related issues. In consequence, laboratory experts suggested everyday regulations for the citizens without taking into account wider considerations for empirical research. There was an insufficient effort made for proposed treatment studies using existing agents based on the established understanding of essential physiology and the role of local and systemic chronic inflammation. In contrast, driven by media popularization, drugs that later proved beneficial were put in doubt and other drugs that lacked benefit and potentially caused harm were driven to clinical trials and utilization. Person‐centered systems view backed by scientific knowledge and established data would have set better priorities. Finally, we need to take a step back and consider the Corona crisis pandemic in the context of the unidimensional utility‐driven handling of natural ecosystems by the culture of industrialized countries. This ever‐accelerating destruction of life spaces for species drives adaptations are the basis of zoonoses. There is strong evidence that future pandemics should be faced with a more systemic socio‐ecological conceptual framework that also reflects the fatal impact of human civilization on natural ecosystems, no matter if SARS CoV2 is a zoonosis or a laboratory accident. It is critical for the future of our species that we collectively learn from this experience, address limitations in our perspectives, enhance our system‐based science and bolster global, regional, and national crisis management. The impact of climate change and biodiversity loss has crossed the horizon and is now clearly in full sight.

Mutual Synchronization of Spatially Distributed 24 GHz Oscillators up to Distances of 500 m

This brief studies how mutual synchronization of oscillators can be achieved for cross-coupling time delays much larger than the period of the oscillations. Using the closed loop transfer function for a system of two mutually delay-coupled phase-locked loops (PLLs) and applying the Nyquist stability criterion, the critical time delay for which stable in- and anti-phase synchronized states become unstable is calculated. The analysis reveals the range of feed-forward loop gains for a given time delay value so that stable in- or anti-phase synchronized states can exist. These theoretical predictions are then verified by measurements with PLLs operating at 24GHz and for cross-coupling time delays ranging from the nano- to the microseconds domain. Such delays are equivalent to coupling at distances of up to 500m. The experimental results show a good agreement with the theoretical predictions. Hence, this brief shows how to setup a network of mutually delay-coupled PLLs and achieve stable synchronized states for a given time delay.

A New Quaternary Full Adder Cell based on CNFET for Use in Fast Arithmetic Circuits

Multi-valued logic potentially increases the efficiency of arithmetic circuits and digital signal processing. Quaternary logic can be suggested as a solution to the problem of power consumption and connection complexity in binary digital systems. The possibility of having several threshold voltage levels using the Carbon Nanotube Field Effect Transistor (CNFET) results in the widespread use of this technology in the design of multi-valued circuits. In this paper, a quaternary full adder cell has been proposed. The main goal of the proposed circuit is to reduce the critical delay path in the quaternary full adder circuit using a parallel design. The proposed circuit is compared with four quaternary full adders based on simulation results using HSPICE in 32 nm technology. The experimental results show the higher performance of the proposed quaternary full adder cell than the state-of-the-art designs.

Critical delay factors for construction projects in Central Aceh District, Indonesia

Background: Construction development in Indonesia is growing rapidly, especially in Central Aceh District. Construction projects have distinctive characteristics and are very complex, so that risk events can have a serious impact on the viability of the project. Project delays can result in cost overruns and project losses. Therefore, it is necessary to identify the factors causing project delays.The purpose of this study was to (1) identify the risk factors that cause delays in construction projects and (2) determine those particular risk factors that have a greater influence on construction projects. The location of this research was Central Aceh District. Methods: The data in this study were primary data in the form of a questionnaire and secondary data obtained from the literature related to this particular type of research. Questionnaires were distributed to respondents, namely contractor companies located in the Central Aceh District. The questionnaires were distributed to determine respondents' opinions about the level of influence of risk factors causing project delays. We used a validity test, reliability test, and descriptive analysis for data processing. Results: Based on the results of the study from 47 respondents, the "very high influence" category (Mode=5) for the tool malfunction factor, cost estimation inaccuracy, increased work costs, implementation of new technologies, details, accuracy and conformity to specifications that are not appropriate, worker quarrels, poor project planning and management, poor condition at locations and accessibility difficulty. Conclusions: Of the 80 risk factors that caused project delays, eight risk factors were found to have a very high influence on the implementation of construction projects in Central Aceh District. Practical implications: The results of this study provide knowledge to contractor companies about the delay factors that have the most influence on project implementation so that they are expected to be able to manage risks to avoid losses.

Influence of detonator delay scatter on rock fragmentation by bunch-holes blasting

Bunch-holes blasting (several blastholes arranged in a bunch with short spacing and detonated simultaneously to form a large common blasting crater) is typically used in underground mines to increase blasting efficiency under a single free surface. Considering the low accuracy of pyrotechnic detonators, which are commonly used in Chinese mines, bunch-holes blasting with the same nominal times is actually short-delay blasting, and the actual delay intervals induced by the delay scatter of detonators can lead to unsuccessful bunch-hole blasting, which seriously affects rock fragmentation. In this study, theoretical analysis is firstly conducted to explore the mechanism of short-delay bunch-holes blasting, and the formation time of a new free surface is defined as the critical delay interval of bunch holes. Then, the formula of the new free surface forming time is deduced to determine the critical delay interval of the short-delay bunch-holes blasting. Considering the delay scatter of the detonator, the probability method is used to quantitatively analyse the probability of successful bunch-holes blasting with different delay nominal time detonators. Field experiments are performed to verify the results. This research demonstrates that as the detonator delay scatter increases, the probability of successful bunch-holes blasting generally decreases. In addition, the charge length also has an impact on the probability, which is positively correlated but not as dramatic as the detonator delay scatter. Hence, it is recommended to use high-precision detonators or low-segment detonators for bunch-holes blasting to ensure the quality of the cutting blasting.

AHP-DEMATEL modelling of consultant related delay factors affecting sustainable housing construction in Saudi Arabia

Considering the significance of project consultants in the delivery of sustainable housing, it is imperative to recognize the performance of Saudi Arabian-based consultants as a critical factor in the delay of construction projects. However, most of the related literatures focus more on project owners and contractors. Thus, this study examined the relationship between consultant-related delay factors affecting sustainable housing development in Saudi Arabia. The Content Analysis was combined with an expert-driven survey to determine the critical consultant related delay factors while the results were analyzed using the AHP and DEMATEL techniques. Lack of communication between consultant and contractor was the most crucial consultant related delay factor affecting timely completion of mass housing development in Saudi Arabia. The outcomes of this paper are important to practitioners and policymakers to support the establishment of sustainable strategies for mitigating the impact of construction projects delay associated with the consultants and in turn enhance the efficiency of project team members in timely delivery of projects and promoting sustainable housing development in Saudi Arabia. While the outcomes of this study are predominantly based on issues peculiar to the local construction sector, the study findings may perhaps be applicable to construction sectors in other developing countries.

Energy transfer and coherence in coupled oscillators with delayed coupling: a classical picture of two-level systems

The Frimmer-Novotny model to simulate two-level systems by coupled oscillators is extended by incorporating a constant time delay in the coupling. The effects of the introduced delay on system dynamics and two-level modeling are then investigated and found substantial. Mathematically, introducing a delay converts the dynamical system from a finite one into an infinite-dimensional system. The resulted system of delay differential equations is solved using the Krylov method with Chebyshev interpolation and post-processing refinement. The calculations and analyses reveal the critical role that a delay can play. It has oscillatory effects as the main dynamical eigenmodes move around a circle with a radius proportional to the coupling strength and an angle linear with the delay. This alteration governs the energy transfer dynamics and coherence. Accordingly, both, the delay and the coupling strength dictate the stability of the system. The delay is the main related parameter as for certain intervals of it, the system remains stable regardless of the coupling. A significant effect occurs when one of the main modes crosses the imaginary axis, where it becomes pure imaginary and dampingless. Thus, the two states energies can live and be exchanged for an extremely long time. Furthermore, it is found that the delay alters both the splitting and the linewidth in a way further influencing the energy transfer and coherence. It is found also that the delay should not be large to have significant effect. For example, for an optical system with 500 nm wavelength, the critical delay can be in tens of attoseconds.

Analysis on risk factors related delay in PCPs

PurposeRisk factors related delay hinder the schedule performance of most construction projects in the world. It is a critical challenge to realize the advantages of prefabricated construction projects (PCPs) under the negative effect of schedule delay. This paper aims to propose an exhaustive list of risk factors impeding the progress of PCPs and evaluate the collected risk factors based on the cause–effect relations. The ultimate goal is to improve the understanding of the complex relations among various risk factors related delay in PCPs, and also offer managers a reference on aspect of schedule risk management.Design/methodology/approachThis paper proposes a hybrid method of GT–DEMATEL–ISM, that is combing grounded theory, DEMATEL (decision-making trial and evaluation laboratory) and ISM (Interpretative Structural Modeling), to collect, evaluate and structure risk factors related delay for PCPs. The research procedure of this methodology is divided into three stages systematically involving qualitative and quantitative analysis. In the first stage, GT is utilized to implement qualitative analysis to collect the risk factors leading to schedule delay in PCPs. While, the quantitative analysis is to analyze and evaluate the collected risk factors based on the cause–effect relations in the next two stages evaluation by the DEMATEL focuses on quantifying the priority and intensity of the relations between factors. Additionally, ISM is employed to construct the hierarchical structure and graphically represent the pairwise relations between factors.FindingsThe outcome of qualitative investigation by grounded theory proposes a theoretical framework of risk factors related delay for PCPs. The framework contains three levels of category, namely, core category, main category and initial category and provides a list of risk factors related delay. Following this finding, evaluation results by the DEMATEL classify factors into cause and effect groups and determine 11 critical delay risk factors. Meanwhile, the findings show that risks referring to organizational management issue foremost impact the progress of PCPs. Furthermore, a systemic multilevel hierarchical structure model is visually constructed by ISM to present the pairwise linkages of critical factors. The model provides the risk transmission chains to map the spread path of delay impact in the system.Originality/valueThe contribution of the study involves twofold issues. Methodologically, this research proposes a hybrid method GT–DEMATEL–ISM used to identify and analyze factors for a complex system. It is also applicable to other fields facing similar problems that require collecting, evaluating and structuring certain elements as a whole in a comprehensive perspective. The theoretical contribution is to fill the relevant research gap of the existing body of knowledge. To the best knowledge of the authors, this paper is the first attempt to integrate qualitative and quantitative research for risk analysis related delay and take the insight into the whole process of PCPs covering off-site manufacture and on-site construction. Furthermore, the analysis of findings provided both a micro view focusing on individual risk factor and a managerial view from a systematic level. The findings also contribute the effective information to improve the risk management related schedule delay in PCPs.

On the critical strain of thermal-mechanical processing to tailor grain boundary character distribution in INCOLOY 925 alloy

Through a series of thermal-mechanical processing (TMP) routes with various ratios of cold rolling and subsequent high-temperature annealing, the samples with different critical strain states were prepared to explore the evolution of grain boundary character distribution (GBCD) in INCOLOY 925 during grain boundary engineering (GBE). The GBE microstructure was characterized using the electron backscatter diffraction to study the influence of TMP parameters on the evolution of GBCD and the penetration of random high angle grain boundaries. The results show that the different states of pre-strain correspond to the variational formation mechanism of grain boundary network (GBN). The strain induced boundary migration is the predominant mechanism with the rolling reduction lower than critical strain. With the slight increase of strain, the recrystallization nucleation can be initiated to generate the strain-free grains at a certain annealing temperature. Moderate strain is needed to ensure adequate growth for twin related domains (TRDs). Besides, with the increase of strain and temperature, the dominant mechanism of GBCD gradually transfers from the new twinning mechanism to the Σ3 regeneration mechanism. Specifically, the TMP sample with 10% rolling reduction followed by annealing at 1075 °C for 10min shows relatively higher grain size difference ratio and average grains numbers in the TRDs, indicating that a larger initial grain size can increase critical strain and delay the nucleation of strain-free grains during TMP treatment. The moderately higher grain size shows an opposite effect on the formation of GBN. Finally, an estimation model of critical strain, as a function of initial grain size and annealing temperature, was constructed based on the artificial neural network, and the predicted results show a high consistency with the actual microstructure evolution.

Effect of delay on the emergent stability patterns in generalized Lotka-Volterra ecological dynamics.

Understanding the conditions of feasibility and stability in ecological systems is a major challenge in theoretical ecology. The seminal work of May in 1972 and recent developments based on the theory of random matrices have shown the existence of emergent universal patterns of both stability and feasibility in ecological dynamics. However, only a few studies have investigated the role of delay coupled with population dynamics in the emergence of feasible and stable states. In this work, we study the effects of delay on generalized Loka-Volterra population dynamics of several interacting species in closed ecological environments. First, we investigate the relation between feasibility and stability of the modelled ecological community in the absence of delay and find a simple analytical relation when intra-species interactions are dominant. We then show how, by increasing the time delay, there is a transition in the stability phases of the population dynamics: from an equilibrium state to a stable non-point attractor phase. We calculate analytically the critical delay of that transition and show that it is in excellent agreement with numerical simulations. Finally, following a similar approach to characterizing stability in empirical studies, we investigate the coefficient of variation, which quantifies the magnitude of population fluctuations. We show that in the oscillatory regime induced by the delay, the variability at community level decreases for increasing diversity. This article is part of the theme issue 'Emergent phenomena in complex physical and socio-technical systems: from cells to societies'.