پیش بینی کوتاه مدت بار با استفاده از یک مدل هیبریدی با یک سری زمانی وزنی به صورت نمایی تصفیه شده و یک جستجوی هارمونی بهبودیافته
Short-term load forecasting using a hybrid model with a refined exponentially
weighted fuzzy time series and an improved harmony search
بهینه سازی رفتار فشاری بتن حاوی سنگ دانه های آجر نسوز بازیافتی ریزدانه در حضور سیمان کلسیم آلومینات و الیاف پلی وینیل الکل تحت اثر محیط اسیدی
Optimizing compressive behavior of concrete containing fine recycled refractory brick aggregate together with calcium aluminate cement and polyvinyl alcohol fibers exposed to acidic environment
abstract
In this study, a hybrid algorithm based on a refined high-order weighted fuzzy algorithm and an imperialist competitive algorithm (RHWFTS–ICA) is developed. This method is proposed to perform efficiently under short-term load forecasting (STLF). First, autocorrelation analysis was used to recognize the order of the fuzzy logical relationships. Next, the optimal coefficients and optimal intervals of adaption were obtained by means of an imperialist competitive algorithm in the training dataset. Lastly, the obtained information was employed to forecast the 48-step-ahead of the STLF problems. To validate the proposed method, eight case studies of real load data, collected from the UK and France during the years 2003 and 2004, were tested with the proposed algorithm and certain enhanced STLF forecasting models. The numerical results demonstrated the efficiency of the proposed algorithm in terms of the forecast accuracy.
Keywords:
Weighted fuzzy time series
Imperialist competitive algorithm
Short-term load forecasting
Forecast adjusting
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1. Introduction
Electricity distribution and transmission require the use of power transformers, so they are vital and strategic components of any electric power system [1–4]. It is known that the failure of power transformers can produce significant economic losses related to its reparation or replacement as well as financial losses compensations required by consumers [4,5]. The life span of transformers is basically determined by physicochemical, electrical and mechanical characteristics of their insula- tion system [6,7]. This insulation system generally consists of two types of materials, liquid and solid [8]. In power transformers, solid insulation is frequently based on cellulose which is used in different forms (paper, press-board...). The most common is Kraft paper, a mix of 78–80% cellulose, 10–20% hemicellulose and 2–6% lignin [9]. This paper is the main solid insulator for the winding conduc- tors. As insulator, the dielectric paper is a material that avoids the flow of electric current among conductors. Solid insulation is impregnated with dielectric oil which is also used as cooling medium [10]. In the case of a 150 MVA transformer it may contain as much as 80 tons of oil and up to 30 tons of paper. This insulation system under operational conditions suffers electrical, thermal, environmental and mechanical stress due to the presence of traces of air and water which worsen electrical properties of paper and oil [5,11]. Although, oil can be easily reclaimed or substituted this will not extend the cellulose’s life [2]. For this reason, the degradation of cellulose-based paper determines the useful life of a power transformer [12]. Cellulose degrades slowly but inevitably losing its mechanical properties [13] due to the breakage of glycosidic inter-monomer bonds in the polymer which reduces the chain- length [14]. Failure occurs when the mechanical strength of the paper decreases to the point where it is brittle and liable to damage by mechanical movement.
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Insulation Characteristics of Oil-immersed Power Transformer under Lightning Impulse and AC Superimposed Voltage
ABSTRACT
The insulation performance of an oil-immersed power transformer against lightning surges is verified by applying a lightning impulse (LI) voltage alone. However, the surge voltage generated at the transformer terminal in an actual system is superimposed over the ac operating voltage. Particularly for UHV- and 500 kV-class, where the ratio of ac operating voltage to the LI withstand voltage is high, the insulation characteristics for this LI and ac superimposed voltage are crucial factors to study the insulation design. Accordingly, this paper reviewed the research results of insulation characteristics of transformers for the superimposed voltage. Subsequently, these results were evaluated from perspectives of an insulation coordination and transformer insulation test. The insulation elements of transformers covered were the turn-to-turn and section-to section insulation, for which the LI test is key for insulation design. As a result, for the section-to-section insulation for a shell-type transformer and the turn-to-turn insulation, the breakdown (BD) voltage for the superimposed voltage remained unchanged from the result when the LI was applied alone. Conversely, for the section-to-section insulation of a continuous disk winding for a coretype transformer, the BD voltage attributable to the superimposed voltage declined by about 10% to 20% from that when the LI was applied alone if the oil-impregnated paper component ratio compared to the oil-gap length was low. This is because the oil gap was primarily responsible for the BD and flaws were generated there when the ac voltage was applied. On the other hand, when this ratio was increased, the oil-impregnated paper part was primarily responsible for BD and the decline in BD voltage could be suppressed. For the section-to-section insulation for the interleaved disk winding, the BD voltage attributable to the superimposed voltage remained constant from that when the LI was applied alone. This is because the BD was determined by the LI partial discharge inception at the turn-to-turn part of the section-to-section insulation, where the superimposed voltage made little impact on BD. Based on the above, the LI test is considered adequate to verify the insulation performance of the section-to-section insulation for a shell-type transformer and for an interleaved disk winding and the turn-to-turn insulation against surge overvoltage. Conversely, for the section-to-section structure of a continuous disk winding, the influence of the ac voltage must be taken into account. These results are key findings for rationalizing transformers while maintaining their insulation reliability.
Index Terms — Oil-immersed power transformer, lightning impulse and ac superimposed voltage, insulation characteristics, oil-impregnated paper, oil gap, turn-toturn insulation, section-to-section insulation.
THE insulation performance of a power transformer is verified by the lightning impulse (LI) voltage test and the ac voltage test [1, 2]. The LI test mainly verifies surge overvoltage whereas the ac test verifies the normal operating voltage and temporary overvoltage during operation [3, 4].
These tests are performed by applying the respective voltage waveforms alone. On the other hand, the surge voltage generated at the transformer terminal in an actual system is superimposed over the ac operating voltage to form a waveform that differs from the LI voltage waveform. Consequently, the insulation characteristics of a transformer for the voltage under combined conditions with the LI voltage superimposed over the ac voltage (hereinafter referred to as the “superimposed voltage”) are crucial factors to study the insulation design. For UHV- and 500 kV-class transformers in particular, with a high ratio of ac operating voltage to the lightning impulse withstand voltage (LIWV) [1, 2], it is important to clarify the insulation characteristics attributable to this difference in waveform. Where the insulation characteristics vary due to the presence of ac voltage, the influence of the ac voltage must be taken into consideration for the LI test.
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Abstract
Somatic symptoms tend to increase during early adolescence and although youth's social environments and emotional functioning play a role in somatic symptoms, few studies have examined mechanisms through which social interaction could influence youth's somatic wellbeing. Participants were 132 youth (61.6% girls, Mage ¼ 12.61 years, 84.7% Caucasian) and their mothers. Reciprocated best-friend dyads participated in a video-taped problem discussion task to assess peer emotion socialization responses. Two supportive friend responses (i.e., emotion-focused, problem-focused) and two unsupportive responses (i.e., punitive, neglect) were examined. Mothers reported on their child's somatic complaints. Friends who provided emotion-focused, problem-focused, punitive, and neglect responses to their close friend's emotional disclosures had significantly fewer somatic symptoms. However, youth who received punitive responses to their emotional disclosures from their close friends had more somatic complaints. These findings provide initial evidence of a link between emotion socialization responses within close friendships and somatic complaints in early adolescence.
Keywords:
Somatic symptoms
Friendship
Emotion socialization
Supportive responses
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Abstract
Working memory (WM) is a fundamental cognitive ability that supports complex thought but is limited in capacity. Thus, WM training interventions have become very popular as a means of potentially improving WM-related skills. Another promising intervention that has gained increasing traction in recent years is transcranial direct current stimulation (tDCS), a noninvasive form of brain stimulation that can modulate cortical excitability and temporarily increase brain plasticity. As such, it has the potential to boost learning and enhance performance on cognitive tasks. This study assessed the efficacy of tDCS to supplement WM training. Sixty-two participants were randomized to receive either right prefrontal, left prefrontal, or sham stimulation with concurrent visuospatial WM training over the course of seven training sessions. Results showed that tDCS enhanced training performance, which was strikingly preserved several months after training completion. Furthermore, we observed stronger effects when tDCS was spaced over a weekend break relative to consecutive daily training, and we also demonstrated selective transfer in the right prefrontal group to nontrained tasks of visual and spatial WM. These findings shed light on how tDCS may be leveraged as a tool to enhance performance on WM-intensive learning tasks.
INTRODUCTION
Working memory (WM) is a fundamental cognitive ability that is limited in capacity and supports complex thought. It is highly predictive of academic and professional success (Alloway & Alloway, 2010; Gathercole, Pickering, Knight, & Stegmann, 2004), and thus, interventions to improve WM are highly sought. Training of WM typically leads to substantial improvements on the trained task and has also been shown by many studies to enhance various aspects of cognitive functioning, from improving performance on nontrained WM and executive function tasks (Schwaighofer, Fischer, & Buhner, 2015; Melby-Lervåg & Hulme, 2013) to broader tests such as those indexing fluid intelligence (see Weicker, Villringer, & Thone-Otto, 2015; Au et al., 2014; Karbach & Verhaeghen, 2014, for recent meta-analyses). However, obtaining reliable results often requires extensive training on the order of weeks or even months, thereby rendering participant compliance difficult and research costs high. These practical constraints have often led to underpowered studies (Bogg & Lasecki, 2014) and inconsistent results in the literature. Therefore, the field would benefit from a catalyst to intensify or expedite the effects of WM training. Herein, we evaluated the efficacy of transcranial direct current stimulation (tDCS) to boost the effects of training on both trained and untrained measures of WM and executive function over a short period of 7 days. In contrast with previous investigations, the design of the current study included both a long-term follow-up as well as a training schedule that permitted us to explore the impact of spacing on training performance. Thus, the present research not only adds to the growing literature in support of the effects of tDCS on WM, but it also offers novel insights with regard to the cumulative efficacy of multisession stimulation, the effects of intersession spacing, and the long-term durability of stimulation- enhanced training.
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Abstract
Purpose – This study aims to explore the relationship between job standardization and employee innovative behavior, as well as the mediating and moderating effects of employee psychological empowerment. Little research has been focused on the conlicting concepts of job standardization and employee innovative behavior.
Design/methodology/approach – Respondents chosen from frontline services in tourist hotels in Taiwan were used to examine the mediating and moderating roles of psychological empowerment on the established relationships between job standardization and employee innovative behavior. The results were analyzed using hierarchical regression models.
Findings – The results show that job standardization had a negative effect on employee innovative behavior. In addition, employee psychological empowermentmediated the effect of job standardization on innovative behavior. Subsequently, employee psychological empowerment played a buffering role and moderated the job standardization–innovative behavior relationship.
Practical implications – Hotel management needs to use both training and work process review to help employees innovate while still understanding the meaning of their work, enhancing self-eficacy, self-determination and the impact of decision-making.
Originality/value – This study gives both theoretical and empirical evidence to clarify the effect of psychological empowerment on the importance of job standardization and innovative behavior in organizations. This is the only study that has investigated this topic in the hospitality ield and therefore makes signiicant strides in understanding the impact of psychological empowerment on hotel employees’ innovative behavior.
Keywords : Tourism, Hotels, Taiwan, Psychological empowerment, Frontline employee, Innovative behavior, Job standardization
Paper type : Research paper
Introduction
The nature of service heterogeneity and inseparability has caused numerous problems within service delivery (Zeithaml et al., 2006). Speciically, human factors lead to inconsistencies in service quality. Job standardization may reduce the deviation in employee service delivery (Jones et al., 1994), simplify the complexity of thework (Cohen et al., 1996) and enhance organizational citizenship behavior (Chen et al., 2009), aswell as improving customers’ perceptions of service quality (Hsieh and Hsieh, 2001; Hsieh et al., 2002; Karatepe et al., 2004).
To ensure consistent service delivery quality, hotel managers generally execute job standardization to regulate the behaviors of frontline service employees. However, heterogeneity also relects that no customer is exactly alike, with each having their own unique needs and demands (Parasuraman et al., 1985). Restaurant customers typically demand personalized, innovative and yet affordable service delivery (Zeng et al., 2012).
Maintaining and delivering products and services at the same standard makes long-term survival dificult for irms that also need innovation to maintain their competitive advantage. Therefore, various hotels (e.g. the Four Seasons) sought to gain insight into their services, enabling them to tailor both services and amenities to meet their guests’ high expectations, thereby constantly differentiating themselves from other hotels (Sengupta and Dev, 2011). Developing this insight is an integral part of innovation (Sengupta and Dev, 2011). Kanter (1988) pointed out that innovation is a highly complex and challenging task, including numerous cognitive abilities (i.e. generating, promoting, discussing, modifying and, ultimately, implementing creative ideas). Previous studies have indicated that frontline service employees play an important role in organization innovation (Coelho et al., 2011). Speciically, the diverse needs of customers require frontline service employees to respond in a lexible and innovative manner to deliver superior services (Chebat and Kollias, 2000; Wang and Netemeyer, 2004).
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ABSTRACT
Data warehouses have been successfully employed for assisting decision making by offering a global view of the enterprise data and providing mechanisms for On-Line Analytical processing. Traditionally, data warehouses are utilized within the limits of an enterprise or organization. The growth of Internet and WWW however, has created new opportunities for data sharing among ad-hoc, geographically spanned and possibly mobile users. Since it is impractical for each enterprise to set up a worldwide infrastructure, currently such applications are handled by the central warehouse. This often yields poor performance, due to overloading of the central server and low transfer rate of the network.
INTRODUCTION
A data warehouse is a collection of historical summarized information, which aims at improving decision-making. The process of accessing and manipulating these data is referred as On-Line Analytical Processing (OLAP) [CCS93]. OLAP operations typically deal with aggregations, which involve huge amounts of data, as opposed to accessing only a few tuples at a time in an On-Line Transaction Processing (OLTP) environment. Moreover, OLAP operations may require data, which are distributed in numerous geographically spanned databases. Therefore, although it is possible to execute such queries against operational databases, in practice a separate database is used to implement the data warehouse.
The implementation of a data warehouse, naturally involves many distributed database issues. The process of accessing the operational databases, extracting, cleaning and integrating the data in the warehouse, is a distributed database application. In [GLWZ99] the authors discuss the particular issues of the data warehouse environment for distributed and parallel computation. Some of the challenges include the maintenance of the warehouse data consistency given a set of autonomous sources, the process of resuming failed warehouse loads without undoing the incomplete load, and the parallelization of view maintenance tasks
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The relationship between dimensions of anger and aggression in contact and noncontact sports
رابطه ی بین ابعاد خشم (عصبانیت) و پرخاشگری در ورزش های تماسی و غیر تماسی
This study investigated the relationship between anger and aggression in contact and noncontact sports. A total of 210 volunteer athletes (94 contact, 116 noncontact) were included in this study. All participants were asked to complete the Tehran Multidimensional Anger Scale (TMAS) and the Competitive Aggression Questionnaire (CAQ). The results revealed that all anger subscales were positively associated with indices of competitive aggression in both contact and noncontact sports. However, only anger-in and anger-out could significantly predict changes related to competitive aggressive behaviors. The results also revealed that 'anger control-in' and 'anger control-out' were negatively associated with indices of competitive aggression in both contact and noncontact sports.
Previous studies concerning the antecedents of aggression have led to the formulation of several theories concerning this field. The most famous models for studying aggression in sport are frustration-aggression (Dollard, Doob, Miller, Mowrer, & Sears, 1939), the experienced frustration -aggression (Berkowitz, 1989), and social learning theory (Bandura, 1973). Dollard et al (1939) believed that frustration is the result of impediment in fulfilling certain goals and desires and inevitably ends in aggressive behavior. Berkowitz showed that all of the frustrated people do not react aggressively. But the situational symptoms and the learned responses affect the possibility of aggressive behavior. Based upon these evidences, Berkowitz (Berkowitz, 1989; Kimble, Russo, Bergman, & Gallindo, 2010) added cognitive factors to the frustration-aggression model, so that the role of emotional responses and personal motivation in tendency toward aggressive behaviors can be considered.
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