Edit Profile (opens in new tab) Sosík, Petr Co-Author Distance Author ID: sosik.petr Published as: Sosík, Petr; Sosik, Petr; Sosìk, Petr; Sosík, P. more...less Documents Indexed: 70 Publications since 1996 4 Contributions as Editor Co-Authors: 42 Co-Authors with 55 Joint Publications 943 Co-Co-Authors all top 5 Co-Authors 19 single-authored 16 Kari, Lila 11 Rodríguez-Patón, Alfonso 10 Konstantinidis, Stavros 8 Cienciala, Luděk 6 Drastík, Jan 6 Garzon, Max H. 5 Ciencialová, Lucie 5 Freund, Rudolf 5 Smolka, Vladimír 4 Păun, Andrei 3 Thierrin, Gabriel 2 Bradík, Jaroslav 2 Csuhaj-Varjú, Erzsébet 2 Losseva, Elena 2 Perez, David Machado 2 Salomaa, Arto Kustaa 1 Adleman, Leonard Max 1 Alhazov, Artiom 1 Daley, Mark 1 Domaratzki, Michael 1 García-Arnau, Marc 1 Gheorghe, Marian 1 Goel, Ashish 1 Ibarra, Oscar H. 1 Kari, Jarkko 1 Kelemen, Jozef 1 Langer, Miroslav 1 Manrique, Daniel 1 Matýsek, Jiří 1 Moore, Tyler 1 Oswald, Marion 1 Păun, Gheorghe 1 Pérez-Jiménez, Mario J. 1 Reishus, Dustin 1 Rozenberg, Grzegorz 1 Sainz de Murieta, Iñaki 1 Sebestyen, Peter 1 Seki, Shinnosuke 1 Simmel, Friedrich C. 1 Valík, Ondřej 1 Woodworth, Sara 1 Zandron, Claudio all top 5 Serials 13 Theoretical Computer Science 5 International Journal of Foundations of Computer Science 4 Fundamenta Informaticae 4 Natural Computing 3 Grammars 3 Lecture Notes in Computer Science 3 Journal of Membrane Computing 2 Information Sciences 2 Journal of Computer and System Sciences 2 Journal of Automata, Languages and Combinatorics 1 Acta Cybernetica 1 SIAM Journal on Computing 1 Computers and Artificial Intelligence 1 Computer Science Journal of Moldova 1 Bulletin of the European Association for Theoretical Computer Science EATCS 1 International Journal of Applied Mathematics all top 5 Fields 74 Computer science (68-XX) 12 Biology and other natural sciences (92-XX) 4 General and overarching topics; collections (00-XX) 2 Mathematical logic and foundations (03-XX) 2 Dynamical systems and ergodic theory (37-XX) 2 Information and communication theory, circuits (94-XX) 1 Combinatorics (05-XX) Publications by Year all cited Publications top 5 cited Publications Citations contained in zbMATH Open 55 Publications have been cited 381 times in 246 Documents Cited by ▼ Year ▼ Computationally universal P systems without priorities: Two catalysts are sufficient. Zbl 1078.68036 Freund, Rudolf; Kari, Lila; Oswald, Marion; Sosík, Petr 37 2005 Membrane computing and complexity theory: A characterization of PSPACE. Zbl 1178.68260 Sosík, Petr; Rodríguez-Patón, Alfonso 34 2007 Normal forms for spiking neural P systems. Zbl 1111.68040 Ibarra, Oscar H.; Păun, Andrei; Păun, Gheorghe; Rodríguez-Patón, Alfonso; Sosík, Petr; Woodworth, Sara 32 2007 The computational power of cell division in P systems: Beating down parallel computers? Zbl 1048.68044 Sosík, Petr 29 2003 P systems attacking hard problems beyond NP: a survey. Zbl 1431.68035 Sosík, Petr 19 2019 Aspects of shuffle and deletion on trajectories. Zbl 1070.68071 Kari, Lila; Sosík, Petr 16 2005 An optimal frontier of the efficiency of tissue P systems with cell separation. Zbl 1357.68067 Pérez-Jiménez, Mario J.; Sosík, Petr 14 2015 The undecidability of the infinite ribbon problem: implications for computing by self-assembly. Zbl 1191.68419 Adleman, Leonard; Kari, Jarkko; Kari, Lila; Reishus, Dustin; Sosik, Petr 13 2009 On hairpin-free words and languages. Zbl 1132.68451 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr; Thierrin, Gabriel 12 2005 Hairpin structures in DNA words. Zbl 1234.68216 Kari, Lila; Konstantinidis, Stavros; Losseva, Elena; Sosík, Petr; Thierrin, Gabriel 12 2006 On properties of bond-free DNA languages. Zbl 1080.68036 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 10 2005 P systems with proteins on membranes characterize PSPACE. Zbl 1293.68175 Sosík, Petr; Păun, Andrei; Rodríguez-Patón, Alfonso 10 2013 On the robust power of morphogenetic systems for time bounded computation. Zbl 1497.68203 Sosík, Petr; Smolka, Vladimír; Drastík, Jan; Bradík, Jaroslav; Garzon, Max 9 2018 On the weight of universal insertion grammars. Zbl 1145.68028 Kari, Lila; Sosík, Petr 8 2008 Bond-free languages: formalizations, maximality and construction methods. Zbl 1090.68046 Kari, Lila; Konstatinidis, Stavros; Sosík, Petr 8 2005 A formal language analysis of DNA hairpin structures. Zbl 1096.68084 Kari, L.; Losseva, E.; Konstantinidis, S.; Sosík, P.; Thierrin, G. 8 2006 On the power of catalytic P systems with one catalyst. Zbl 1473.68079 Freund, Rudolf; Sosík, Petr 8 2015 P colonies. Survey. Zbl 1431.68026 Ciencialová, Lucie; Csuhaj-Varjú, Erzsébet; Cienciala, Luděk; Sosík, Petr 8 2019 P systems without priorities are computationally universal. Zbl 1023.68053 Sosík, Petr; Freund, Rudolf 7 2003 On evolutionary lineages of membrane systems. Zbl 1135.68424 Sosík, Petr; Valík, Ondřej 6 2006 D0L system + Watson-Crick complementarity = universal computation. Zbl 0984.68088 Sosík, Petr 5 2001 Small (purely) catalytic P systems simulating register machines. Zbl 1336.68075 Sosík, Petr; Langer, Miroslav 5 2016 Morphogenetic and homeostatic self-assembled systems. Zbl 1486.68069 Sosík, Petr; Smolka, Vladimír; Drastík, Jan; Moore, Tyler; Garzon, Max 5 2017 Polynomial complexity classes in spiking neural P systems. Zbl 1259.68074 Sosík, Petr; Rodríguez-Patón, Alfonso; Ciencialová, Lucie 4 2010 Bond-free languages: Formalizations, maximality and construction methods. Zbl 1116.68457 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 4 2005 Small P systems with catalysts or anti-matter simulating generalized register machines and generalized counter automata. Zbl 1390.68299 Alhazov, Artiom; Freund, Rudolf; Sosik, Petr 4 2015 A limitation of cell division in tissue P systems by PSPACE. Zbl 1435.68099 Sosík, Petr; Cienciala, Luděk 3 2015 Computational power of cell separation in tissue P systems. Zbl 1354.68082 Sosík, Petr; Cienciala, Luděk 3 2014 The power of catalysts and priorities in membrane systems. Zbl 1062.68061 Sosík, Petr 3 2003 P colonies with evolving environment. Zbl 1483.68113 Ciencialová, Lucie; Cienciala, Luděk; Sosík, Petr 3 2017 Tissue P systems with cell separation: upper bound by PSPACE. Zbl 1374.68222 Sosík, Petr; Cienciala, Luděk 3 2012 Modeling plant development with M systems. Zbl 1522.68220 Sosík, Petr; Smolka, Vladimír; Bradík, Jaroslav; Garzon, Max 3 2019 From P systems to morphogenetic systems: an overview and open problems. Zbl 1469.68052 Sosík, Petr; Drastík, Jan; Smolka, Vladimír; Garzon, Max 3 2020 Autonomous resolution based on DNA strand displacement. Zbl 1347.68144 Rodríguez-Patón, Alfonso; de Murieta, Iñaki Sainz; Sosík, Petr 2 2011 On the power of computing with proteins on membranes. Zbl 1273.68136 Sosík, Petr; Păun, Andrei; Rodríguez-Patón, Alfonso; Pérez, David 2 2010 On the power of elementary features in spiking neural P systems. Zbl 1187.68235 García-Arnau, Marc; Pérez, David; Rodríguez-Patón, Alfonso; Sosík, Petr 2 2008 Membrane computing: When communication is enough. Zbl 1029.68065 Sosík, Petr; Matýsek, Jiří 2 2002 Preventing undesirable bonds between DNA codewords. Zbl 1116.68458 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 2 2005 Operations on trajectories with applications to coding and bioinformatics. Zbl 1097.68063 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 2 2005 On the scalability of biocomputing algorithms: the case of the maximum clique problem. Zbl 1242.68292 Manrique, Daniel; Rodríguez-Patón, Alfonso; Sosík, Petr 2 2011 Watson-Crick D0L systems: The power of one transition. Zbl 1022.68069 Salomaa, Arto; Sosík, Petr 2 2003 Morphogenetic systems for resource bounded computation and modeling. Zbl 1475.68125 Sosík, Petr; Garzon, Max; Smolka, Vladimír; Drastík, Jan 2 2021 Self-healing Turing-universal computation in morphogenetic systems. Zbl 07735515 Sosík, Petr; Garzon, Max; Drastík, Jan 2 2021 A logical representation of P colonies: an introduction. Zbl 1519.68086 Cienciala, Luděk; Ciencialová, Lucie; Csuhaj-Varjú, Erzsébet; Sosík, Petr 2 2018 On the power of families of recognizer spiking neural P systems. Zbl 1213.68277 Sosík, Petr; Rodríguez-Patón, Alfonso; Cienciala, Luděk 1 2011 On the hierarchy of extended conditional tabled eco-grammar systems. Zbl 0938.68053 Sosík, Petr 1 1999 Parallel accepting colonies and neural networks. Zbl 0945.68155 Sosík, Petr 1 1999 Selected topics in computational complexity of membrane systems. Zbl 1330.68081 Sosík, Petr 1 2011 On language equations with deletion. Zbl 1169.68480 Kari, Lila; Sosík, Petr 1 2004 Watson-Crick D0L systems: Generative power and undecidable problems. Zbl 1059.68070 Sosík, Petr 1 2003 Substitution on trajectories. Zbl 1055.68072 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 1 2004 Substitutions, trajectories and noisy channels. Zbl 1115.68442 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 1 2005 PSPACE limits the power of uniform families of P systems with active membranes. Zbl 1355.68099 Sosík, Petr 1 2014 Universal computation with Watson-Crick D0L systems. Zbl 1061.68087 Sosík, Petr 1 2002 Limits of the power of tissue P systems with cell division. Zbl 1388.68057 Sosík, Petr 1 2013 Morphogenetic systems for resource bounded computation and modeling. Zbl 1475.68125 Sosík, Petr; Garzon, Max; Smolka, Vladimír; Drastík, Jan 2 2021 Self-healing Turing-universal computation in morphogenetic systems. Zbl 07735515 Sosík, Petr; Garzon, Max; Drastík, Jan 2 2021 From P systems to morphogenetic systems: an overview and open problems. Zbl 1469.68052 Sosík, Petr; Drastík, Jan; Smolka, Vladimír; Garzon, Max 3 2020 P systems attacking hard problems beyond NP: a survey. Zbl 1431.68035 Sosík, Petr 19 2019 P colonies. Survey. Zbl 1431.68026 Ciencialová, Lucie; Csuhaj-Varjú, Erzsébet; Cienciala, Luděk; Sosík, Petr 8 2019 Modeling plant development with M systems. Zbl 1522.68220 Sosík, Petr; Smolka, Vladimír; Bradík, Jaroslav; Garzon, Max 3 2019 On the robust power of morphogenetic systems for time bounded computation. Zbl 1497.68203 Sosík, Petr; Smolka, Vladimír; Drastík, Jan; Bradík, Jaroslav; Garzon, Max 9 2018 A logical representation of P colonies: an introduction. Zbl 1519.68086 Cienciala, Luděk; Ciencialová, Lucie; Csuhaj-Varjú, Erzsébet; Sosík, Petr 2 2018 Morphogenetic and homeostatic self-assembled systems. Zbl 1486.68069 Sosík, Petr; Smolka, Vladimír; Drastík, Jan; Moore, Tyler; Garzon, Max 5 2017 P colonies with evolving environment. Zbl 1483.68113 Ciencialová, Lucie; Cienciala, Luděk; Sosík, Petr 3 2017 Small (purely) catalytic P systems simulating register machines. Zbl 1336.68075 Sosík, Petr; Langer, Miroslav 5 2016 An optimal frontier of the efficiency of tissue P systems with cell separation. Zbl 1357.68067 Pérez-Jiménez, Mario J.; Sosík, Petr 14 2015 On the power of catalytic P systems with one catalyst. Zbl 1473.68079 Freund, Rudolf; Sosík, Petr 8 2015 Small P systems with catalysts or anti-matter simulating generalized register machines and generalized counter automata. Zbl 1390.68299 Alhazov, Artiom; Freund, Rudolf; Sosik, Petr 4 2015 A limitation of cell division in tissue P systems by PSPACE. Zbl 1435.68099 Sosík, Petr; Cienciala, Luděk 3 2015 Computational power of cell separation in tissue P systems. Zbl 1354.68082 Sosík, Petr; Cienciala, Luděk 3 2014 PSPACE limits the power of uniform families of P systems with active membranes. Zbl 1355.68099 Sosík, Petr 1 2014 P systems with proteins on membranes characterize PSPACE. Zbl 1293.68175 Sosík, Petr; Păun, Andrei; Rodríguez-Patón, Alfonso 10 2013 Limits of the power of tissue P systems with cell division. Zbl 1388.68057 Sosík, Petr 1 2013 Tissue P systems with cell separation: upper bound by PSPACE. Zbl 1374.68222 Sosík, Petr; Cienciala, Luděk 3 2012 Autonomous resolution based on DNA strand displacement. Zbl 1347.68144 Rodríguez-Patón, Alfonso; de Murieta, Iñaki Sainz; Sosík, Petr 2 2011 On the scalability of biocomputing algorithms: the case of the maximum clique problem. Zbl 1242.68292 Manrique, Daniel; Rodríguez-Patón, Alfonso; Sosík, Petr 2 2011 On the power of families of recognizer spiking neural P systems. Zbl 1213.68277 Sosík, Petr; Rodríguez-Patón, Alfonso; Cienciala, Luděk 1 2011 Selected topics in computational complexity of membrane systems. Zbl 1330.68081 Sosík, Petr 1 2011 Polynomial complexity classes in spiking neural P systems. Zbl 1259.68074 Sosík, Petr; Rodríguez-Patón, Alfonso; Ciencialová, Lucie 4 2010 On the power of computing with proteins on membranes. Zbl 1273.68136 Sosík, Petr; Păun, Andrei; Rodríguez-Patón, Alfonso; Pérez, David 2 2010 The undecidability of the infinite ribbon problem: implications for computing by self-assembly. Zbl 1191.68419 Adleman, Leonard; Kari, Jarkko; Kari, Lila; Reishus, Dustin; Sosik, Petr 13 2009 On the weight of universal insertion grammars. Zbl 1145.68028 Kari, Lila; Sosík, Petr 8 2008 On the power of elementary features in spiking neural P systems. Zbl 1187.68235 García-Arnau, Marc; Pérez, David; Rodríguez-Patón, Alfonso; Sosík, Petr 2 2008 Membrane computing and complexity theory: A characterization of PSPACE. Zbl 1178.68260 Sosík, Petr; Rodríguez-Patón, Alfonso 34 2007 Normal forms for spiking neural P systems. Zbl 1111.68040 Ibarra, Oscar H.; Păun, Andrei; Păun, Gheorghe; Rodríguez-Patón, Alfonso; Sosík, Petr; Woodworth, Sara 32 2007 Hairpin structures in DNA words. Zbl 1234.68216 Kari, Lila; Konstantinidis, Stavros; Losseva, Elena; Sosík, Petr; Thierrin, Gabriel 12 2006 A formal language analysis of DNA hairpin structures. Zbl 1096.68084 Kari, L.; Losseva, E.; Konstantinidis, S.; Sosík, P.; Thierrin, G. 8 2006 On evolutionary lineages of membrane systems. Zbl 1135.68424 Sosík, Petr; Valík, Ondřej 6 2006 Computationally universal P systems without priorities: Two catalysts are sufficient. Zbl 1078.68036 Freund, Rudolf; Kari, Lila; Oswald, Marion; Sosík, Petr 37 2005 Aspects of shuffle and deletion on trajectories. Zbl 1070.68071 Kari, Lila; Sosík, Petr 16 2005 On hairpin-free words and languages. Zbl 1132.68451 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr; Thierrin, Gabriel 12 2005 On properties of bond-free DNA languages. Zbl 1080.68036 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 10 2005 Bond-free languages: formalizations, maximality and construction methods. Zbl 1090.68046 Kari, Lila; Konstatinidis, Stavros; Sosík, Petr 8 2005 Bond-free languages: Formalizations, maximality and construction methods. Zbl 1116.68457 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 4 2005 Preventing undesirable bonds between DNA codewords. Zbl 1116.68458 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 2 2005 Operations on trajectories with applications to coding and bioinformatics. Zbl 1097.68063 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 2 2005 Substitutions, trajectories and noisy channels. Zbl 1115.68442 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 1 2005 On language equations with deletion. Zbl 1169.68480 Kari, Lila; Sosík, Petr 1 2004 Substitution on trajectories. Zbl 1055.68072 Kari, Lila; Konstantinidis, Stavros; Sosík, Petr 1 2004 The computational power of cell division in P systems: Beating down parallel computers? Zbl 1048.68044 Sosík, Petr 29 2003 P systems without priorities are computationally universal. Zbl 1023.68053 Sosík, Petr; Freund, Rudolf 7 2003 The power of catalysts and priorities in membrane systems. Zbl 1062.68061 Sosík, Petr 3 2003 Watson-Crick D0L systems: The power of one transition. Zbl 1022.68069 Salomaa, Arto; Sosík, Petr 2 2003 Watson-Crick D0L systems: Generative power and undecidable problems. Zbl 1059.68070 Sosík, Petr 1 2003 Membrane computing: When communication is enough. Zbl 1029.68065 Sosík, Petr; Matýsek, Jiří 2 2002 Universal computation with Watson-Crick D0L systems. Zbl 1061.68087 Sosík, Petr 1 2002 D0L system + Watson-Crick complementarity = universal computation. Zbl 0984.68088 Sosík, Petr 5 2001 On the hierarchy of extended conditional tabled eco-grammar systems. Zbl 0938.68053 Sosík, Petr 1 1999 Parallel accepting colonies and neural networks. Zbl 0945.68155 Sosík, Petr 1 1999 all cited Publications top 5 cited Publications all top 5 Cited by 247 Authors 23 Zandron, Claudio 21 Leporati, Alberto 21 Mauri, Giancarlo 21 Sosík, Petr 20 Pérez-Jiménez, Mario J. 19 Freund, Rudolf 18 Alhazov, Artiom 18 Kari, Lila 18 Pan, Linqiang 17 Ibarra, Oscar H. 14 Porreca, Antonio E. 13 Păun, Gheorghe 12 Orellana-Martín, David 12 Song, Bosheng 12 Valencia-Cabrera, Luis 11 Ivanov, Sergiu 11 Manzoni, Luca E. 10 Rodríguez-Patón, Alfonso 9 Konstantinidis, Stavros 9 Salomaa, Kai T. 9 Verlan, Sergey 8 Cienciala, Luděk 8 Domaratzki, Michael 8 Mitrana, Victor 8 Zeng, Xiangxiang 7 Kopecki, Steffen 7 Mahalingam, Kalpana 7 Păun, Andrei 7 Zhang, Gexiang 6 Ciencialová, Lucie 6 Csuhaj-Varjú, Erzsébet 6 Manea, Florin 5 Cavaliere, Matteo 5 Ciobanu, Gabriel 5 Gazdag, Zsolt 5 Murphy, Niall 5 Oswald, Marion 5 Riscos-Núñez, Agustín 5 Summers, Scott M. 5 Yokomori, Takashi 4 Aman, Bogdan 4 Brun, Yuriy 4 Cabarle, Francis George C. 4 Drastík, Jan 4 Han, Yo-Sub 4 Ionescu, Mihai 4 Jiang, Suxia 4 Martínez-del-Amor, Miguel Ángel 4 Patitz, Matthew J. 4 Seki, Shinnosuke 4 Song, Tao 4 Woods, Damien 4 Woodworth, Sara 4 Zhang, Xingyi 3 Cho, Da-Jung 3 de la Cruz, Ren Tristan A. 3 Dong, Jianping 3 Egecioglu, Omer 3 Garzon, Max H. 3 Gutiérrez-Naranjo, Miguel A. 3 Hajagos, Károly 3 Ko, Sang-Ki 3 Langer, Miroslav 3 Luo, Biao 3 Okubo, Fumiya 3 Vaszil, Gyorgy 2 Bucci, Michelangelo 2 Cui, Bo 2 Czeizler, Eugen 2 Daley, Mark 2 Dang, Zhe 2 de Luca, Aldo 2 De Luca, Alessandro 2 Díaz-Pernil, Daniel 2 Diekert, Volker 2 Fernau, Henning 2 Ferretti, Claudio 2 Frisco, Pierluigi 2 García-Quismondo, Manuel 2 Hinze, Thomas 2 Honkala, Juha 2 Hoogeboom, Hendrik Jan 2 Ito, Masami 2 Kolonits, Gábor 2 Leupold, Peter 2 Liu, Xiangrong 2 Luo, Yueguo 2 Macababayao, Ivan Cedric H. 2 Macías-Ramos, Luis-Felipe 2 Martín-Vide, Carlos 2 McQuillan, Ian 2 Mercaş, Robert George 2 Păun, Mihaela 2 Pérez-Hurtado, Ignacio 2 Romero-Campero, Francisco José 2 Rong, Haina 2 Sainz de Murieta, Iñaki 2 Salomaa, Arto Kustaa 2 Santean, Nicolae 2 Schweller, Robert T. ...and 147 more Authors all top 5 Cited in 27 Serials 69 Theoretical Computer Science 36 Natural Computing 31 Journal of Membrane Computing 12 International Journal of Foundations of Computer Science 11 Information and Computation 10 Information Sciences 5 Acta Informatica 5 Journal of Computer and System Sciences 3 Mathematical Problems in Engineering 2 Journal of Automata, Languages and Combinatorics 2 Soft Computing 1 Discrete Applied Mathematics 1 Applied Mathematics and Computation 1 Kybernetika 1 European Journal of Combinatorics 1 European Journal of Applied Mathematics 1 Neural Computation 1 MSCS. Mathematical Structures in Computer Science 1 International Journal of Computer Mathematics 1 Complexity 1 Theory of Computing Systems 1 Journal of Discrete Mathematical Sciences & Cryptography 1 RAIRO. Theoretical Informatics and Applications 1 Journal of Evolution Equations 1 International Journal of Parallel, Emergent and Distributed Systems 1 Cryptography and Communications 1 RAIRO. Theoretical Informatics and Applications all top 5 Cited in 15 Fields 242 Computer science (68-XX) 27 Biology and other natural sciences (92-XX) 6 Mathematical logic and foundations (03-XX) 5 Combinatorics (05-XX) 5 Information and communication theory, circuits (94-XX) 2 Partial differential equations (35-XX) 2 Convex and discrete geometry (52-XX) 2 Operations research, mathematical programming (90-XX) 1 History and biography (01-XX) 1 Measure and integration (28-XX) 1 Dynamical systems and ergodic theory (37-XX) 1 Fluid mechanics (76-XX) 1 Optics, electromagnetic theory (78-XX) 1 Statistical mechanics, structure of matter (82-XX) 1 Systems theory; control (93-XX) Citations by Year