Numerical evaluation of the free surface effect on the hydrodynamics and dynamics of underwater vehicles

The present thesis seeks to evaluate the free surface effect on the hydrodynamics and dynamics of a generic underwater vehicle (UV) in the horizontal plane. Accordingly, the captive tests, including the straight-ahead resistance, drift and rotating arm tests, are performed on the bare hull of a UV model by using numerical simulations based on URANS equations with a Reynolds stress turbulence model implemented in the commercial code STARCCM+. These tests are carried out for various submergence depths and proper ranges of UV velocity components. For the purpose of maneuverability assessment, the forces and moments arising from the velocity components obtained from the simulations of the captive tests are implemented in the equations of motion for various submergence depths. Additionally, analytical equations are used to calculate the forces and moments arising from the UV accelerations, thrust and rudder, which all are assumed to remain constant with respect to submergence depth. The obtained results show that, generally, a decrease in submergence depth causes an increase in all the forces arising from the velocity components. The results further show that approaching the free surface has a negligible effect on the lateral force and yaw moment generated by the bow and stern regions. Moreover, it is seen that with a decrease in submergence depth, the region between the UV midlength and the aft shoulder is mainly responsible for the increase or decrease in the lateral force and yaw moment acting on the UV hull. It is also observed that, with a decrease in submergence depth, due to an increase in the UV damping characteristics, the dynamic stability increases remarkably, which leads to a decrease in the UV maneuverability.A presente tese tem como objetivo avaliar o efeito da superfície livre na hidrodinâmica e dinâmica de um veículo submarino (UV) genérico no plano horizontal. Portanto, os testes cativos, incluindo os testes de reboque e de braço rotativo, são realizados num modelo UV usando as simulações numéricas baseadas nas equações de URANS com um modelo de turbulência de Reynolds implementados no código comercial STARCCM+. Estes testes são realizados nas várias profundidades de submersão e faixas apropriadas das velocidades. Para fins de avaliação de manobrabilidade, as forças e os momentos obtidos a partir das simulações dos testes cativos são implementados nas equações de movimento nas várias profundidades. Adicionalmente, as equações analíticas são usadas para calcular as forças e os momentos que surgem das acelerações, impulso e leme, os quais são assumidos constantes em relação à profundidade. Os resultados obtidos mostram que, geralmente, uma diminuição na profundidade provoca um aumento em todas as forças geradas pelas velocidades. Os resultados ainda mostram que aproximar a superfície livre tem um efeito insignificante na força lateral e no momento de yaw ambos gerados pelas regiões de proa e popa. Além disso, observa-se que, com a diminuição da profundidade, a região entre o meio do UV e o ombro de ré é o principal responsável pelo aumento ou diminuição da força lateral e do momento de yaw atuantes sobre o casco do UV. Observa-se também que, com um decréscimo na profundidade, devido a um aumento nas características de amortecimento do UV, a estabilidade dinâmica aumenta consideravelmente, o que leva a uma diminuição da manobrabilidade do UV

Lens-Based Millimeter Wave Reconfigurable Antenna NOMA

This paper proposes a new multiple access technique based on the millimeter wave lens-based reconfigurable antenna systems. In particular, to support a large number of groups of users with different angles of departures (AoDs), we integrate recently proposed reconfigurable antenna multiple access (RAMA) into non-orthogonal multiple access (NOMA). The proposed technique, named reconfigurable antenna NOMA (RA-NOMA), divides the users with respect to their AoDs and channel gains. Users with different AoDs and comparable channel gains are served via RAMA while users with the same AoDs but different channel gains are served via NOMA. This technique results in the independence of the number of radio frequency chains from the number of NOMA groups. Further, we derive the feasibility conditions and show that the power allocation for RA-NOMA is a convex problem. We then derive the maximum achievable sum-rate of RA-NOMA. Simulation results show that RA-NOMA outperforms conventional orthogonal multiple access (OMA) as well as the combination of RAMA with the OMA techniques

A Link Prediction Strategy for Personalized Tweet Recommendation through Doc2Vec Approach

Nowadays with growth of using Internet as a principle way of communication, likes different social medias channels (Twitter, Facebook, etc.) and also access to huge amount of information like News, there appear a main research subject to help users to find his/her interests among vast amount of relevant and irrelevant information. Recommender systems are helped to handle information overload problem and in this paper we introduce our Tweet Recommendation System that implement user’s Twitter information (Tweets, Retweet, Like,...) as a source of user’s information. In this work the semantic of tweets that regard as a User’s Explicit Interests (e.g., person, events, product mentioned in user’s tweets) are identified with the Doc2vec approach and recommend similar tweets through link-prediction strategy. The experiment results show that Doc2Vec approach is a better approach than the other previous approaches

Ideology and Ethics of Transitional Entrepreneurs: Legitimacy, Soft Law, and Overcoming a Distressed Economy

Purpose – Transitional entrepreneurship in distressed economies is a fairly new concept with respect to new ventures in such challenging economic environments. Formal institutional voids are sometimes held up as a reason for the difficulties present in distressed economies, along with exogenous shocks and other upheavals. In this research, the authors seek to contribute empirically and theoretically as to ways in which formal institutions voids can be filled by a culture developed by transitional entrepreneurs. Indeed, in transition economies, formal institutions need to be enhanced by informal institutions to control corruption and other misbehavior by authorities. Iranian economists emphasize these essential reforms to be able to manage current difficulties, yet top down policies cannot help transitional entrepreneurs benefit from the country’s value adding cultural heritage to informally address this. To study this, qualitative research methods were used to interpret transitional entrepreneurs’ ideology and ethical routines as the ingredients of a commercial culture that can establish soft law that substitutes for formal institutions. This helps to reduce the disfunctionality of formal institutions in distressed economies. Design/methodology/approach – A thematic analysis interviewing key Iranian entrepreneurs and economists is conducted. Also based on an interpretive paradigm, a hermeneutic cycle has been carried out on selected texts. Results have been verified throughout related literature as to come up with a solid synthesized interpreted outcome. Findings – This paper contributes to theory from a new perspective by discussing transitional entrepreneurship and navigating a distressed economy; in which, ideology and ethics as the ingredients of soft law (Newman and Posner, 2018) are discussed as the base to further develop a commercial culture that fills voids of formal institutions. The formal–informal institutional cycle in distressed economies as the major difficulty entrepreneurs face (Peng and Luo, 2000) is important, because they try to increasingly enhance their move toward a market orientation (Bruton et al., 2008). The authors contribute as to how transitional entrepreneurs can complete this process of adaptation and also the fact that those informal institutions do actually respond to those adaptations. The other contribution is to enrich theories about institutions from the point of view of culture. Knowing these facts helps transitional entrepreneurs, because in distressed communities, formal institutions’ function has an important effect on economic performance (Amoros, 2009). This research’s contributions shed light to help government leaders understand the pros and cons of their actions forced on the industry. As it has been characterized in this research, it can turn in to new formal set of legitimacies (Ahlstrom et al., 2008) to root out corruption and help set the economy on a path to innovation and new venture creation. Originality/value – Transitional entrepreneurs can depend on the less formal cultural-cognitive aspect of ethics and ideology. These entrepreneurs can be working on the burgeoning private sector, who want to connect with the outside effectively to overcome an economy in distress. Transitional entrepreneurs may face governmental institutional intermediaries as a barrier. Formal intermediaries tend to benefit from inefficiencies caused by hierarchal orders and will improve informality in order to overcome difficulties. In this research, institutional theory from the third pillar of the cultural-cognitive sheds light on transitional entrepreneurship in distressed economies, where inquiry is to fill voids of formal institutions as a process of possible linking between new generated soft law derived by beliefs, ideology and professional morality in order to influence (old) legitimacies. The research’s focus evolves on values transitional entrepreneurs utilize to build informal institutions and then impact further on formal institutions to handle distressed communities. This theoretical background expands on subsections to define conceptual building blocks for the study, essential aspects such as individuals as transitional entrepreneurs, the values they utilize to generate soft law, informal institutions and soft law, to manage voids in formal institutions and legitimacy building aspects in policy agenda setting for transitional entrepreneurship in distressed economies

Reference Database of CrossLaps and Osteocalcin for a Healthy Iranian Population

Markers of bone turnover are becoming an important tool for practitioners in the management of osteoporosis. Therefore, it is essential to establish a reference database of the markers before using them in various clinical settings. A total of 785 individuals (37% males, 63% females) without apparent or suggested abnormalities affecting bone mass were randomly selected from 13 clusters in Bushehr Port in southern Iran. The serum CrossLaps ELISA and the N-MID Osteocalcin ELISA were used for the quantitative measurement of CrossLaps and osteocalcin in sera. Bone mineral density was determined for the lumbar spines (L2-L4), proximal femur (neck), and forearm (the distal part) using dual-energy X-ray absorptiometry. Men had higher biochemical serum bone markers (P<0.0001). In women, there were progressive increases in serum CrossLaps after 30 years of age, peaking at >60 years. In men, serum CrossLaps levels were decreased progressively by increases in age, with the peak at 20 – 29 years. In women, there was a significant decrease in serum osteocalcin from 20 – 29 years to 30–49 years, followed by a progressive increases during 50 – 59 years, with the peak at >60 years. In men, the highest concentrations for serum osteocalcin occurred at 20 – 29 years. At all sites checked for bone mineral densitys, women in the high osteocalcin quartile had the lowest mean bone mineral densitys values, but women in the high CrossLaps quartile had the lowest mean bone mineral densitys at lumbar and radial sites. However, in men, bone mineral densitys values at neither site differed between the lowest and the highest quartiles of serum biochemical bone markers. We presented a five- year age-specific mean values of bone markers in a general healthy Iranian population. Only women in the high osteocalcin and CrossLaps quartiles had the lowest mean bone mineral densitys values at the lumbar and radial sites. Our results suggest that the significance of osteoclastic bone resorption or bone formation as a determinant of bone mineral densitys may depend on sex. Archives of Iranian Medicine, Volum

Reference Database of CrossLaps and Osteocalcin for a Healthy Iranian Population

Markers of bone turnover are becoming an important tool for practitioners in the management of osteoporosis. Therefore, it is essential to establish a reference database of the markers before using them in various clinical settings. A total of 785 individuals (37% males, 63% females) without apparent or suggested abnormalities affecting bone mass were randomly selected from 13 clusters in Bushehr Port in southern Iran. The serum CrossLaps ELISA and the N-MID Osteocalcin ELISA were used for the quantitative measurement of CrossLaps and osteocalcin in sera. Bone mineral density was determined for the lumbar spines (L2-L4), proximal femur (neck), and forearm (the distal part) using dual-energy X-ray absorptiometry. Men had higher biochemical serum bone markers (P60 years. In men, serum CrossLaps levels were decreased progressively by increases in age, with the peak at 20 – 29 years. In women, there was a significant decrease in serum osteocalcin from 20 – 29 years to 30–49 years, followed by a progressive increases during 50 – 59 years, with the peak at >60 years. In men, the highest concentrations for serum osteocalcin occurred at 20 – 29 years. At all sites checked for bone mineral densitys, women in the high osteocalcin quartile had the lowest mean bone mineral densitys values, but women in the high CrossLaps quartile had the lowest mean bone mineral densitys at lumbar and radial sites. However, in men, bone mineral densitys values at neither site differed between the lowest and the highest quartiles of serum biochemical bone markers. We presented a five- year age-specific mean values of bone markers in a general healthy Iranian population. Only women in the high osteocalcin and CrossLaps quartiles had the lowest mean bone mineral densitys values at the lumbar and radial sites. Our results suggest that the significance of osteoclastic bone resorption or bone formation as a determinant of bone mineral densitys may depend on sex

Canopy gaps characteristics of pure and mixed stands in the Hyrcanian forests of north Iran

Canopy gaps play an important role in forest ecology helping to preserve biodiversity, influence nutrient cycles, maintain the complex stand structure, and also they substantially contribute to regeneration of forests. To survey the characteristics of canopy gaps in the Hyrcanian forests of Iran, three main old-growth and intact stands were studied. For each canopy gap, two parameters were measured: the length (L) as the longest distance within the gap and the width (W) as the largest distance perpendicular to the length. The gap maker (DBH≥20 cm) was considered to be a tree from the upper tree layer whose death caused an opening in the canopy. A total of 89 canopy gaps were studied in three old-growth stands (48 gaps in hornbeam-ironwood, 21 in hornbeam, and 19 in beech-hornbeam stands). The given canopy gaps cover 5.4% of the land area with an average of eight gaps per hectare. The mean size of the canopy gaps were 291, 353 and 565m2 for hornbeam-ironwood, hornbeam, and beech-hornbeam stands, respectively. Frequency distribution of the gap sizes the mentioned three forest stands showed a lognormal distribution. The number of gap makers ranged from one to eight with a median of 4.5. Amongst the studied 261 gap makers in all canopy gaps, 61.2% belonged to hornbeam-ironwood stand. Also, there were canopy gaps formed by one to four gap makers within the three forest types, while gaps formed by five, six and eight gap makers were only observed within hornbeam stand. The results showed that the characteristics of the canopy gaps were different in terms of the composition, complexly of structure, environmental characteristics, size, number and species of gap makers in different forests. As a whole, hornbeam-ironwood stands present in lower altitudes, are more susceptible to wind-throw and create smaller gaps but more gap makers

Meta-Synthesis as a Method for Synthesizing Qualitative Researches

Among studies in Humanities and Social Sciences, there is an increasing number of studies using qualitative methods for studying and interpreting various phenomena. Several studies have used qualitative methods to investigate a single phenomena. The variety of qualitative studies about a single phenomenon has enabled the synthesis of these studies to provide new interpretations of a social phenomenon. The meta-synthesis method is one of the emerging methods in qualitative studies that is expanding its use in social science research. This method is used to systematically interpret the results of qualitative studies to provide a new explanation of the single phenomenon under investigation. Increasing use of this method leads more researchers to familiarize themselves with the importance of meta-synthesis, its applications, the steps involved, the validation process, and the common difficulties researchers have to deal with when using this approach. Using the diverse literature on the methodology of meta-synthesis, here we present similarities and differences of meta-syntehsis compared with other similar methods, identify the processes needed to conduct this type of research, to improve the reliability of it, and finally we address the common errors researchers face when using this metho

The Mediating Role of Coping Strategies in Relation with Psychological Needs and Internet Addiction among College Student

Introduction: Internet addiction has negative consequences, including physical, psychological, social and educational problems. The current research intended to assess the mediation role of coping strategies in relation with psychological needs and internet addiction.Methods: This cross-sectional study assessed 375 students (129 male, 244 female) from Karaj Islamic Azad University in 2018 selected by stratified sampling. Data collected by self-report method. Research instruments were internet addiction test, satisfaction of psychological needs questionnaire and coping response scale. Data were analyzed by SPSS v.19 and using descriptive statistics, Pearson correlation coefficients and Concurrent hierarchical Regression analysis.Results: Pearson correlation coefficients showed negative correlations between autonomy, relatedness, competence and internet addiction (P&lt;0.01). There is negative correlation between autonomy, relatedness, competence and maladaptive coping strategy (P&lt;0.01) and positive correlation between maladaptive coping and internet addiction (P&lt;0.01). Also, Hierarchical regression analysis by Baron and Kenny method showed that maladaptive coping is mediator between and satisfaction of psychological needs and internet addiction.Conclusion: in general, this results indicate that high level of satisfaction of psychological needs are associated with low level of internet addiction and unsatisfied of psychological needs has positive impact in maladaptive coping strategy, subsequently maladaptive coping increases internet addiction.Declaration interest: None.

Reinforcement Learning for Self Organization and Power Control of Two-Tier Heterogeneous Networks

Self-organizing networks (SONs) can help manage the severe interference in dense heterogeneous networks (HetNets). Given their need to automatically configure power and other settings, machine learning is a promising tool for data-driven decision making in SONs. In this paper, a HetNet is modeled as a dense two-tier network with conventional macrocells overlaid with denser small cells (e.g. femto or pico cells). First, a distributed framework based on multi-agent Markov decision process is proposed that models the power optimization problem in the network. Second, we present a systematic approach for designing a reward function based on the optimization problem. Third, we introduce Q-learning based distributed power allocation algorithm (Q-DPA) as a self-organizing mechanism that enables ongoing transmit power adaptation as new small cells are added to the network. Further, the sample complexity of the Q-DPA algorithm to achieve ϵ-optimality with high probability is provided. We demonstrate, at density of several thousands femtocells per km2, the required quality of service of a macrocell user can be maintained via the proper selection of independent or cooperative learning and appropriate Markov state models