دانلود و نمایش مقالات مرتبط با Math::صفحه 9
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نتیجه جستجو - Math

تعداد مقالات یافته شده: 386
ردیف عنوان نوع
81 A mathematical model for neuronal differentiation in terms of anevolved dynamical system
یک مدل ریاضی برای تمایز عصبی از نظر سیستم دینامیکی برهم خورده-2020
We attempted to create a mathematical model for neuronal differentiation. The present study wasperformed within the framework of self-organization with constraints by looking for an optimized infor-mational unit. We treated networks of individual dynamical system units with an external input, whichwas provided by coupled one-dimensional maps with possible forms of unidirectionally feed-forwardnetwork, random network, small-world network, and fully-connected network. We used a genetic algo-rithm to maximize the information transmission for each type of network. Optimized maps were obtaineddepending on the coupling strength and network structure. These maps can be classified into three types:passive, excitable, and oscillatory. In particular, the excitable and oscillatory types of dynamical systemspossess characteristics that are quite similar to those of neurons, whereas the passive and oscillatorytypes of dynamical system may represent glial cells.
Keywords:Self-organization with constraints | Coupled dynamical systems | Evolutionary dynamics | Neuronal differentiation | Oscillology
مقاله انگلیسی
82 Project schedule performance under general mode implementation disruptions
عملکرد برنامه پروژه تحت اختلال در اجرای کلی حالت-2020
This paper presents a simulation study for a resource-constrained project scheduling problem with mul- tiple alternatives. We decide on a set of baseline schedules at the project planning phase, resulting in options to switch between execution modes of activities during project execution. We assess the perfor- mance of the set of baseline schedules under general mode implementation disruptions. A simple, yet effective algorithm is presented to construct the set of baseline schedules. Moreover, a general disruption system is proposed to model different disruption types, disruption dependencies and disruption sizes.
Keywords: Project management | Execution alternatives | Matheuristic | Disruption system
مقاله انگلیسی
83 Qualitative and quantitative project risk assessment using a hybrid PMBOK model developed under uncertainty conditions
ارزیابی کیفی و کمی ریسک پروژه با استفاده از یک مدل ترکیبی PMBOK که در شرایط عدم اطمینان ایجاد شده است-2020
This study presented a qualitative and quantitative project risk assessment using a hybrid PMBOK model developed under uncertainty conditions. Accordingly, an exploratory and applied research design was employed in this study. The research sample included 15 experienced staff working in main and related positions in Neyr Perse Company. After reviewing the literature and the Project Management Body of Knowledge (PMBOK), 32 risk factors were identified and their number reduced to 17 risks using the expert opinions via the fuzzy Delphi technique run through three stages. The results of the confirmatory factor analysis showed that all risks were confirmed by the members of the research sample. Then the identified risks were structured and ranked using fuzzy DEMATEL and fuzzy ANP techniques. The final results of the study showed that the political and economic sanctions had the highest weight followed by foreign investors’ attraction and the lack of regional infrastructure.
Keywords: Project risks | Project management body of knowledge(PMBOK) | Uncertainty | Mixed qualitative and quantitative risk | assessment approach | Mathematics | Probability theory | Engineering | Industrial engineering | Business
مقاله انگلیسی
84 Running power meters and theoretical models based on laws of physics: Effects of environments and running conditions
معیارهای قدرت دویدن و مدلهای نظری مبتنی بر قوانین فیزیک: تأثیر محیط و شرایط دویدن-2020
Training prescription and load monitoring in running activities have benefited from power output (PW) data offered by new technologies. Nevertheless, to date, the sensitivity of PW data provided by these tools is still not completely clear. The aim of this study was to analyze the level of agreement between the PW estimated by five commercial technologies and the two main internationally theoretical models based on laws of physics, in different environments and running conditions. Ten endurance-trained male athletes performed three submaximal running protocols on a treadmill (indoor) and an athletic track (outdoor), with changes in speed, body weight, and slope. PW was simultaneously registered by the commercial technologies Stryd (StrydApp and StrydWatch), RunScribe, GarminRP and PolarV, whereas theoretical power output (TPW) was calculated by the two mathematical models (TPW1 and TPW2). Statistics included, among others, the Pearsons correlation coefficient (r) and standard error of measurement (SEM). The PolarV, and above all Stryd, showed the closest agreement with the TPW1 (Stryd: r≥0.947, SEM ≤ 11 W; PolarV: r≥0.931, SEM ≤ 64 W) and TPW2 (Stryd: r≥0.933, SEM ≤ 60 W; PolarV: r≥0.932, SEM ≤ 24 W), both indoors and outdoors. On the other hand, the devices GarminRP (r≤0.765, SEM ≥ 59 W) and RunScribe. (r≤0.508, SEM ≥ 125 W) showed the lowest agreement with the TPW1 and TPW2 models for all conditions and environments analyzed. The closest agreement of the Stryd and PolarV technologies with the TPW1 and TPW2 models suggest these tools as the most sensitive, among those analyzed, for PW measurement when changing environments and running conditions.
Keywords: Endurance | Accelerometer | Variability | Physiology | Biomechanics
مقاله انگلیسی
85 Optimal energy management for a grid connected PV-battery system
مدیریت بهینه انرژی برای سیستم باتری PV متصل به شبکه-2020
The increase demand for electricity and the non-renewable nature of fossil energy makes the move towards renewable energies required. However, the common problem of renewable sources, which is the intermittence, is overcome by the hybridization of complementary sources. Thus, whenever the load demand is not fully covered by the primary source, the second one will absolutely support it. Furthermore, the production, the interaction with the grid and the storage system must be managed by the grid-connected hybrid renewable energy system, which is the main objective of this paper. Indeed, we propose a new system of a grid-connected PV-battery, which can manage its energy flows via an optimal management algorithm. The DC bus source connection topology in our proposed hybrid architecture tackles the synchronization issues between sources when the load is powered. We consider in this work that choosing a battery discharge and charge limiting power provides an extension of the battery life. On the other hand, we simulated the dynamic behavior of the architecture’s various components according to their mathematical modeling. Following this, an energy management algorithm was proposed, and simulated using MATLAB/SIMULINK to serve the load. The results have shown that the load was served in all cases, taking into account the electrical behavior of the inhabitants as well as the weather changes on a typical day. Indeed, the load was served either by instant solar production between sunrise and sunset, or the recovery from sunset to 10pm, which could be a stored or injected energy without exceeding the 1000W per hour
Keywords: Renewable energy | PV-battery | Hybrid renewable system | Energy management | Hybrid architecture
مقاله انگلیسی
86 Research on BP network for retrieving extinction coefficient from Mie scattering signal of lidar
تحقیقات بر روی شبکه BP برای بازیابی ضریب خاموشی از سیگنال پراکندگی میای LIDAR-2020
Mie lidar is a powerful tool for detecting the optical properties of atmospheric aerosols. However, there are two unknown parameters in the Mie lidar equation: the extinction coefficient and the backscattering coefficient. In the common methods for solving the equation, it is necessary to make assumptions about the relationship between the two unknown parameters. These assumptions will reduce the detection precision of extinction coefficient. In view of this, the back propagation (BP) neural network is used to retrieve extinction coefficient from the Mie scattering signal of lidar. Firstly, the structure and main parameters of the BP network are designed according to the practical application. In order to improve the convergence speed and prevent falling into local minima, the initial weights and thresholds of BP network are optimized by genetic algorithm (GA). Then the GA-BP network is trained with Mie scattering signal and the extinction coefficient retrieved by Raman method. Thus the mathematical relationship between Mie scattering signal and the extinction coefficient is stored in the BP network. The trained GA-BP network is then used to retrieve the extinction coefficient from Mie scattering signal in different conditions and the applicability of the GA-BP network is researched. The research will promote the development of Mie lidar retrieving algorithm.
Keywords: Aerosol | Mie scattering | Lidar | Extinction coefficient | BP network | Genetic algorithm
مقاله انگلیسی
87 Diverse cognitive skills and team performance: A field experiment based on an entrepreneurship education program
Diverse cognitive skills and team performance: A field experiment based on an entrepreneurship education program-2020
Verbal and mathematical reasoning are key cognitive skills which individuals use throughout their lives to create economic value. We argue that individuals undertaking entrepreneurial tasks also draw on these skills, and we study how best these skills should be combined in entrepreneurial teams. To that purpose we conduct a randomized field experiment using data from the BizWorld entrepreneurship education program. Four different types of teams are created which differ in terms of their cognitive skill composition. Our results show that balanced skills are beneficial for a team’s venture performance only if it comes from within-person skill balance, and that combining team members with different skills in mixed teams does not compensate for a lack of members who individually possess balanced cognitive skills.
Keywords: Skill balance | Entrepreneurship | Team performance | Team diversity | Field experiment
مقاله انگلیسی
88 A new stochastic gain adaptive energy management system for smart microgrids considering frequency responsive loads
یک دستاورد تصادفی جدید سیستم مدیریت انرژی تطبیقی ​​برای میکروگریدهای هوشمند با توجه به بارهای پاسخگو فرکانس-2020
Islanded microgrids as flexible, adaptive and sustainable smart cells of distribution power systems should be operated in accordance to both techno-economic purposes. Motivated by this need, the microgrid operators are in charge to elevate the active accommodation of both demand-side and supply-side distributed energy resources. To that end, in this paper, a new flexible frequency dependent energy management system is proposed through which distributed generators have time varying droop controllers with a gain-adaptive strategy. Besides to cope economically with uncertainty arise frequency excursions, a new, comfort-aware and versatile frequency dependent demand response program is mathematically formulated and conducted to the energy management system. It is aimed to co-optimize the microgrid energy resources such a way the day-ahead operational costs are managed subject to a secure frequency control portfolio. The presented model is solved using a two-stage stochastic programming and by a tractable efficient mixed integer linear programming approach. The simulation results are derived in 24-h scheduling time horizon and implemented on a typical test microgrid. The effectiveness of the proposed hourly gain assignment and frequency responsive load management program has been verified thoroughly by analyzing the results.
Keywords: Hierarchical control structure | Islanded microgrids | Droop gain scheduling | Frequency responsive loads | Two-stage stochastic optimization
مقاله انگلیسی
89 Structural models based on 3D constitutive laws: Variational structure and numerical solution
مدل های ساختاری مبتنی بر قوانین سازنده سه بعدی: ساختار تغییرات و راه حل عددی-2020
In all structural models, the section or fiber response is a relation between the strain measures and the stress resultants. This relation can only be expressed in a simple analytical form when the material response is linear elastic. For other, more complex and interesting situations, kinematic and kinetic hypotheses need to be invoked, and a constrained three-dimensional constitutive relation has to be employed at every point of the section in order to implement non-linear and dissipative constitutive laws into dimensionally reduced structural models. In this article we explain in which sense reduced constitutive models can be expressed as minimization problems, helping to formulate the global equilibrium as a single optimization problem. Casting the problem this way has implications from the mathematical and numerical points of view, naturally defining error indicators. General purpose solution algorithms for constrained material response, with and without optimization character, are discussed and provided in an open-source library.
Keywords: Structural models | Constitutive models | Variational method | Error estimation
مقاله انگلیسی
90 Exploring the role of the sharing economy in disasters management
بررسی نقش اقتصاد مشترک در مدیریت بلایا-2020
Improvements in information and communications technologies (ICTs) have facilitated the inclusion of the sharing economy (SE) in societies more than ever. In the aftermath of recent disasters, the SE played significant roles to help the affected people and support official responders. However, the literature has not effectively explored these roles, and thus, no framework can support the systematic inclusion of the SE in disasters management. This paper aims to address the gap through a two-stage exploratory research approach. First, we conduct a systematic literature review to identify the extent to which the SE is taken into consideration in disasters. After that, we investigate the role of three Iranian SE-based companies that were involved in the 2019 Iran floods response. We collect empirical data by conducting semi-structured interviews and reviewing official reports. Our findings indicate that very few studies discuss the different roles of the SE in disasters, although SE companies have often provided effective solutions to address critical post-disaster logistics challenges. Four research propositions are presented to describe emerging roles for SE companies. The contribution of our study is twofold. First, our research identifies the different roles that the SE could play in disasters and therefore, brings a new perspective to the literature. Second, the study suggests opportunities for collaboration and partnership models from the point of origin to delivery that can support coordination and logistics in disasters.
Keywords: Sharing economy | Disaster management | Cross-sector collaboration | The 2019 Iran floods
مقاله انگلیسی
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