Differences

This shows you the differences between two versions of the page.

en:nuno:home [2018/09/19 09:59]
nuno
en:nuno:home [2018/09/19 10:00] (current)
nuno old revision restored
Line 47: Line 47:
-  * [[doi>10.1016/j.physa.2018.09.023|Phase transitions and universality in the Sznajd model with anticonformity]], Matheus Calvelli, **Nuno Crokidakis**, Thadeu J. P. Penna, //Physica A// +  * [[doi>10.1016/j.physa.2018.09.023|Phase transitions and universality in the Sznajd model with anticonformity]], Matheus Calvelli, **Nuno Crokidakis**, Thadeu J. P. Penna, //Physica A//
  * [[doi>10.1142/S0129183118500948|Can honesty survive in a corrupt parliament?]], **Nuno Crokidakis**, Jorge S. Sá Martins, //International Journal of Modern Physics C// (2018).   * [[doi>10.1142/S0129183118500948|Can honesty survive in a corrupt parliament?]], **Nuno Crokidakis**, Jorge S. Sá Martins, //International Journal of Modern Physics C// (2018).
Line 107: Line 107:
  * [[doi>10.1016/j.physa.2011.11.038|Effects of mass media on opinion spreading in the Sznajd sociophysics model]] - **Nuno Crokidakis**, //Physica A// 391, 1729 (2012).   * [[doi>10.1016/j.physa.2011.11.038|Effects of mass media on opinion spreading in the Sznajd sociophysics model]] - **Nuno Crokidakis**, //Physica A// 391, 1729 (2012).
-  * [[http:///www.ij-css.org/volume-01_02/ijcss01_02-141.pdf|Branching process for network growth with geometric restrictions]] - F. L. Forgerini, **N. Crokidakis**, S. N. Do+  * [[http:///www.ij-css.org/volume-01_02/ijcss01_02-141.pdf|Branching process for network growth with geometric restrictions]] - F. L. Forgerini, **N. Crokidakis**, S. N. Dorogovtsev and J. F. F. Mendes, //International Journal of Complex Systems in Science// 1, 141 (2011). 
 + 
 + 
 +  * [[doi>10.1088/1742-5468/2011/11/P11004|The Sznajd model with limited persuasion: competition between high-reputation and hesitant agents]] - **Nuno Crokidakis** and Paulo Murilo Castro de Oliveira, //Journal of Statistical Mechanics// P11004 (2011). 
 + 
 + 
 +  * [[doi>10.1016/j.physleta.2010.06.036|Consequence of reputation in the Sznajd consensus model]] - **Nuno Crokidakis** and Fabricio L. Forgerini, //Physics Letters A// 374, 3380 (2010). 
 + 
 +  * [[doi>10.1103/PhysRevE.81.041138|Nonequilibrium phase transitions and tricriticality in a three-dimensional lattice system with random-field competing kinetics]] - **Nuno Crokidakis**, //Physical Review E// 81, 041138 (2010). 
 + 
 +  * [[doi>10.1103/PhysRevE.80.051101|Finite-size analysis of a two-dimensional Ising model within a nonextensive approach]] - **N. Crokidakis**, D. O. Soares-Pinto, M. S. Reis, A. M. Souza, R. S. Sarthour and I. S. Oliveira, //Physical Review E// 80, 051101 (2009). 
 + 
 +   * [[doi>10.1103/PhysRevE.80.011143|Effect of platykurtic and leptokurtic distributions in the random-field Ising model: Mean-field approach]] - Silvio M. Duarte Queiros, **Nuno Crokidakis** and Diogo O. Soares-Pinto, //Physical Review E// 80, 011143 (2009). 
 + 
 +  * [[doi>10.1088/1742-5468/2009/04/P04018|Emergence of clusters in growing networks with ageing]] - **Nuno Crokidakis** and Marcio Argollo de Menezes, //Journal of Statistical Mechanics// P04018 (2009). 
 +  
 + 
 + 
 +  * [[doi>10.1088/1742-5468/2009/02/P02058|First-order phase transition in a 2D random-field Ising model with conflicting dynamics]] - **Nuno Crokidakis**, //Journal of Statistical Mechanics// P02058 (2009). 
 + 
 + 
 +  * [[doi>10.1088/0953-8984/21/5/056005|Multicritical behavior in a random-field Ising model under a continuous-field probability distribution]] - Octavio R. Salmon, **Nuno Crokidakis** and Fernando D. Nobre, //Journal of Physics: Condensed Matter// 21, 056005 (2009). 
 + 
 +  * [[doi>10.1103/PhysRevE.77.041124|Ising spin glass under continuous-distribution random magnetic fields: Tricritical points and instability lines]] - **Nuno Crokidakis** and Fernando D. Nobre, //Physical Review E// 77, 041124 (2008). 
 + 
 +  * [[doi>10.1088/0953-8984/20/14/145211|Destruction of first-order phase transition in a random-field Ising model]] - **Nuno Crokidakis** and Fernando D. Nobre, //Journal of Physics: Condensed Matter// 20, 145211 (2008). 
 +   
 + 
 +====== Work in Progress ====== 
 + 
 + 
 +  * [[http://arxiv.org/abs/1011.3337|Fat-tailed and compact random-field Ising models on cubic lattices]] - ** Nuno Crokidakis** and Silvio M. Duarte Queiros, arXiv:1011.3337 (2010)   
 + 
 +  * [[http://arxiv.org/abs/1110.3315|Evolution of spatially embedded branching trees with interacting nodes]] - F. L. Forgerini, **N. Crokidakis**, S. N. Dorogovtsev and J. F. F. Mendes, arXiv:1110.3315 (2011) 
 + 
 +  * [[http://arxiv.org/abs/1212.2547|Information spreading with aging in heterogeneous populations]] -  Marlon Ramos, **Nuno Crokidakis** and Celia Anteneodo, arXiv:1212.2547 (2012) 
 + 
 +  
 +   
 +   
 + 
 +====== Book ====== 
 + 
 + 
 +[[http://www.amazon.com/transitions-disordered-systems-random-magnetic/dp/3838381297|{{:novidades:livronuno.jpg?220  }}]] My master thesis was published in 2010 in a book format by the [[http://www.lap-publishing.com/|Lambert Academic Publishing]], Germany. The title is [[http://www.amazon.com/transitions-disordered-systems-random-magnetic/dp/3838381297|Phase Transitions in Disordered Systems under Random Magnetic Fields]]. In this book, I discuss the effects of different kinds of disorder in the phase diagrams of Ising-type models, using the mean-field theory. Those kind of models are of great theoretical interest, because they exhibit a rich critical phenomenon. In addition, there are experimental realizations of spin models in the presence of random magnetic fields: antiferromagnets like Fe_{x}Mg_{1-x}Cl_{2} and Fe_{x}Zn_{1-x}F_{2} submitted to an uniform magnetic field. 
 + 
 + 
 +====== Numerical Codes (C language) ====== 
 + 
 +  * {{:en:nuno:op_ep_phtr_lambda.txt|HERE}} you can download the numerical code for simulate the model of reference [[http://arxiv.org/abs/1605.03914|Dynamics of epidemic spreading with vaccination: impact of social pressure and engagement]] - Marcelo A. Pires and Nuno Crokidakis, arXiv:1605.3914 (2016) 
 + 
 + 
 + 
 + 
 + 
 + 
 + 
 + 
 +====== Colaborations ====== 
 + 
 +  * [[http://emap.fgv.br/people/alexandre.evsukoff.html|Alexandre Evsukoff]] - Federal University of Rio de Janeiro - Rio de Janeiro, Brazil 
 + 
 +  * [[http://www.fis.puc-rio.br/celia.php|Celia Anteneodo]] - Pontifical Catholic University of Rio de Janeiro - Rio de Janeiro, Brazil 
 + 
 +  * [[http://arxiv.org/find/all/1/all:+brigatti/0/1/0/all/0/1|Edgardo Brigatti]] - Federal University of Rio de Janeiro - Rio de Janeiro, Brazil   
 + 
 +  * [[http://sites.google.com/site/fforgerini/home---english|Fabrício L. Forgerini]] - Federal University of Amazonas- Coari, Brazil 
 + 
 +  * [[http://portal.cbpf.br/index.php?page=DadosPessoa&pessoa=128|Fernando D. Nobre]] - Brazilian Center for Physics Research - Rio de Janeiro, Brazil   
 + 
 +  * [[http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4703748P9|Francisco Welington de Sousa Lima]] - Federal University of Piauí 
 + 
 +  * [[http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4785278E4|José Ricardo de Sousa]] - Federal University of Amazonas - Manaus, Brazil 
 + 
 +  * [[http://complex.if.uff.br/marcio|Marcio Argollo de Menezes]] - Fluminense Federal University - Rio de Janeiro, Brazil 
 + 
 +  * [[http://emap.fgv.br/people/moacyr.silva.html|Moacyr Alvim Barbosa]] - Getulio Vargas Foundation - Rio de Janeiro, Brazil 
 + 
 +  * [[http://arxiv.org/find/cond-mat/1/au:+Salmon_O/0/1/0/all/0/1|Octavio D. Rodriguez Salmon]] - Federal University of Amazonas - Manaus, Brazil 
 + 
 +  * [[http://www.if.uff.br/pt/contato/contatos-professores/48-professores-do-departamento/56-pmco|Paulo Murilo Castro de Oliveira]] - Fluminense Federal University - Rio de Janeiro, Brazil   
 + 
 +  * [[http://arxiv.org/find/all/1/all:+AND+duarte+queiros/0/1/0/all/0/1|Silvio M. Duarte Queirós]] - Brazilian Center for Physics Research - Rio de Janeiro, Brazil 
 + 
 +====== Teaching Experience ====== 
 + 
 +  * Experimental Physics - 2007 
 + 
 +  * Newtonian Mechanics - 2008  
 + 
 +  * Newtonian Mechanics - 2011  
 + 
 +  * Newtonian Mechanics - 2014 
 + 
 +  * Fluids, Thermodynamics and Optics - 2015 
 + 
 +  * Computational Physics - 2015 
 + 
 + 
 + 
 + 
 +====== Contributed Talks ====== 
 + 
 + 
 +  * //Epidemic diffusion in random adaptive networks: effects of quarantine and presence of distinct types of connections// - Conference Models in Population Dynamics and Ecology, Brazil (2015) 
 + 
 +  * //Modeling Social Phenomena: an approach from Statistical Physics// - Departament of Physics, Piauí Federal University (2015) 
 + 
 +  * //How effective are the self-isolation public policies of infected individuals?// - Oswaldo Cruz Foundation, Brazil (2015) 
 + 
 +  * //How can Statistical Physics contribute to Social Sciences?// - Institute of Physics, Fluminense Federal University, Brazil (2015) 
 + 
 +  * //Natural selection in a model of opinion dynamics// - Workshop on Mathematical Methods and Modeling of Biophysical Phenomena, Cabo Frio/RJ (2015) 
 + 
 +  * //Modeling brazilian proportional elections// - International School and Conference on Network Science, Netsci-X, Rio de Janeiro/RJ (2015) 
 + 
 +  * //Analysis of tax evasion dynamics via an agent-based model// - Econofis 2014, Brazil (2014) 
 + 
 +  * //Dynamics of electoral processes: modeling and data analysis// - School of Applied Mathematics, Getulio Vargas Foundation, Brazil (2014) 
 + 
 +  * //Critical phenomena and universality in models of opinion dynamics with heterogeneous agents// - Brazilian Center for Physics Research, Brazil (2014) 
 + 
 +  * //Influence of contrarian, inflexible and independent individuals in kinetic models of opinion formation// - Instituto de Ciencias Exatas, Fluminense Federal University, Brazil (2014) 
 + 
 +  * //Consequence of self isolation in epidemic spreading in social networks// - Institute of Physics, Fluminense Federal University, Brazil (2014) 
 + 
 +  * //SocioPhysics and EconoPhysics: aplications of statistical physics to socio-economic problems// - Department of Mathematics, Pontifical Catholic University of Rio de Janeiro, Brazil (2013) 
 + 
 +  * //The Peter Principle and the efficiency of an organization// - Brazilian School of Public and Business Administration, Getulio Vargas Foundation, Brazil (2013) 
 + 
 +  * //Modeling rumor spreading in social networks// - Department of Physics, Pontifical Catholic University of Rio de Janeiro, Brazil (2013) 
 + 
 +  * //Phase transitions in a three-state opinion model with heterogeneous agents// - XXXVI Brazilian Meeting on Condensed Matter Physics, Brazil (2013) 
 + 
 +  * //Agent-based models in Sociophyiscs: critical phenomena and universality// - Institute of Physics, Fluminense Federal University, Brazil (2013) 
 + 
 +  * //The Neuron and the Hodgkin-Huxley model// - Event of Neuroscience, Mathematics and Applied Social Sciences, Getulio Vargas Foundation, Brazil (2013) 
 + 
 +  * //Epidemic dynamics in Social networks: when diversity makes us more vulnerable// - School of Applied Mathematics, Getulio Vargas Foundation, Brazil (2013) 
 + 
 +  * //Statistical physics of social dynamics// - 3rd Summer School, Department of Physics, Pontifical Catholic University of Rio de Janeiro, Brazil (2013) 
 + 
 +  * //Critical behavior of an epidemic model with time-dependent infection rate// - XXX Encontro de Físicos do Norte e Nordeste, Brazil (2012) 
 + 
 + 
 +  * //Phase transition in opinion models// - I Workshop of Complex Systems, Fluminense Federal University, Brazil (2012) 
 + 
 +  * //Computer simulation and modeling of systems of social and biological interest// - School of Applied Mathematics, Getulio Vargas Foundation, Brazil (2012) 
 + 
 +  * //Are self-isolation policies actually effective in epidemic control?// - XXXV Brazilian Meeting on Condensed Matter Physics, Brazil (2012) 
 + 
 +  * //Nonequilibrium phase transitions in opinion models// - Department of Physics, Ceara Federal University, Brazil (2012) 
 + 
 + 
 +  * //The Sznajd model with limited persuasion: competition between high-reputation and hesitant agents// - Conference of Sociophysics: do humans behave like atoms? , Ecole Polytechnique, Paris, France (2011) 
 + 
 + 
 +  * //Statistical physics applied to nonphysical systems: sociology and epidemiology// - Department of Physics, Pontifical Catholic University of Rio de Janeiro, Brazil (2011) 
 +  
 + 
 +  * //Critical behavior of the majority-vote model with diffusion// - Institute of Physics, Fluminense Federal University, Brazil (2011) 
 + 
 +  * //Effects of mass media on opinion spreading in the Sznajd sociophysics model// - Institute of Physics, Fluminense Federal University, Brazil (2011) 
 + 
 +  * //Consequence of reputation in the Sznajd sociophysics model: spontaneous emergence of democratic states// - Brazilian Meeting, Foz do Iguaçu/PR, Brazil (2011) 
 + 
 +  * //Critical behavior of the SIS model with decaying infection rate// - Institute of Physics, Fluminense Federal University, Brazil (2010) 
 + 
 +  * //Efects of reputation in the opinion dynamics of the Sznajd model// - Institute of Physics, Fluminense Federal University, Brazil (2010) 
 + 
 +  * //Nonequilibrium phase transitions in Ising models with conflicting dynamics// - XXVIII Encontro de Fisicos do Norte e Nordeste, Brazil (2010) 
 + 
 +  * //Optimization in Transportation Networks: occupation transition and fluctuation patterns// - Department of Physics, Aveiro University, Portugal (2010)   
 + 
 +  * //First-order phase transition in a 2D random-field Ising model with conflicting dynamics// - XXXII Brazilian Meeting on Condensed Matter Physics, Brazil (2009) 
 + 
 +  * //Universality breaking in the three-dimensional random field Ising model// - Institute of Physics, Fluminense Federal University (2009) 
 + 
 +  * //Monte Carlo simulation of the 2D Ising model: nonextensive approach// - Institute of Physics, Fluminense Federal University, Brazil (2009)   
 + 
 +  * //Dynamical phase transition in growing networks with aging of sities// - Institute of Physics, Fluminense Federal University, Brazil (2008) 
 + 
 +  * //Topological phase transition and optimal fluxes in transportation networks// - Institute of Physics, Fluminense Federal University, Brazil (2008) 
 + 
 +  * //Tricritical behavior of disordered systems in the presence of random magnetic fields// - Institute of Physics, Fluminense Federal University, Brazil (2007) 
 + 
 +====== Contributed Posters ====== 
 + 
 +  * //The effect of influential groups on the stability of a democracy in the Sznajd sociophysics model// - VIIth Brazilian Meeting on Simulational Physics, João Pessoa/PB (2013) 
 + 
 +  * //Empirical investigation of power-law behavior in modularity based community structures// - NetSci: International School and Conference on Network Science, Copenhague/Dinamarca (2013) 
 + 
 +  * //Dynamics of information spreading in heterogeneous populations// - Workshop on Mathematical Methods and Modeling of Biophysical Phenomena, Cabo Frio/RJ (2013) 
 + 
 +  * //Dynamics of epidemic spreading in adaptive networks with household structure// - Workshop on Mathematical Methods and Modeling of Biophysical Phenomena, Cabo Frio/RJ (2013) 
 + 
 +  * //Qualitative aspects of the phase diagrams of J1-J2 model in the cubic lattice// - XXX Encontro de Físicos do Norte e Nordeste, Salvador/BA (2012) 
 + 
 +  * //Nonequilibrium phase transition in a discrete opinion model with quenched disorder// - Brazilian Meeting on Condensed Matter Physics, Águas de Lindóia/SP (2012) 
 + 
 +  * //Percolation transition in growing networks: competition between aging and preferential attachment// - Perspectives and Challenges in Statistical Physics and Complex Systems for the Next Decade, Natal/RN (2011) 
 + 
 +  * Effects of mass media on opinion spreading in the Sznajd sociophysics model - Brazilian Meeting 2011, Foz do Iguaçu/PR (2011) 
 + 
 +  * Critical behavior of the SIS epidemic model with time-dependent infection rate - Workshop on Mathematical Methods and Modeling of Biophysical Phenomena, Foz do Iguaçu/PR (2011) 
 + 
 +  * Efects of reputation in the opinion dynamics of the Sznajd model - II Escola e Conferência em Modelagem Computacional, Volta Redonda/RJ (2010) 
 + 
 +  * Geometrical phase transitions in growing networks: competition between aging and preferential attachment - XI Latin American Workshop on Nonlinear Phenomena, Búzios/RJ (2009) 
 + 
 +  * Finite size analysis of a 2D Ising model within a nonextensive approach - XXXII Brazilian Meeting on Condensed Matter Physics, Águas de Lindóia/SP (2009) 
 + 
 +  * Emergence of clusters in growing networks with aging of sites - XXXII Brazilian Meeting on Condensed Matter Physics, Águas de Lindóia/SP (2009)  
 + 
 +  * Topological Phase Transition and Optimal Fluxes in Transportation Networks - Conference on Computational Physics, Ouro Preto/MG (2008) 
 + 
 +  * Tricritical Points in Magnetic Models under Continuous-Distribution Random Magnetic Fields - XXV Regional Meeting on Physics, Natal/RN (2007) 
 +    
 + 
 +====== Served as Reviewer ====== 
 + 
 + 
 +  * Physics Letters A 
 + 
 +  * Physical Review E 
 + 
 +  * Physica A 
 + 
 +  * International Journal of Modern Physics C 
 + 
 +  * Physical Review Letters 
 + 
 +  * IEEE Journal of Selected Topics in Signal Processing 
 + 
 +  * Journal of Magnetism and Magnetic Materials 
 + 
 +  * International Journal of Modern Physics B 
 + 
 +  * Revista Boliviana de Física 
 + 
 +  * Journal of Physics A: Mathematical and Theoretical 
 + 
 +  * Journal of Physics D: Applied Physics 
 + 
 +  * Journal of Physics: Condensed Matter 
 + 
 +  * Journal of Dynamics and Games 
 + 
 +  * Journal of Statistical Mechanics 
 + 
 + 
 + 
 + 
 + 
 +====== Member of Editorial Board ====== 
 + 
 +  * Multi-disciplinary Journal [[http://www.heliyon.com/|Heliyon]], from Elsevier 
 + 
 + 
 + 
 +====== Brazilian Music ====== 
 + 
 +  * [[http://www.youtube.com/watch?v=9aXseIGq3I8|Velha Guarda da Portela]] 
 + 
 +  * [[http://www.youtube.com/watch?v=L8U1Y9PBfig|Cartola]] 
 + 
 +  * [[http://www.youtube.com/watch?v=EbVm1EXbAuA|Chico Buarque e Francis Hime]] 
 + 
 +  * [[http://www.youtube.com/watch?v=Dl5sJaJRewc|Zé Keti]] 
 + 
 +  * [[http://www.youtube.com/watch?v=pBdqU5uf_Vw|Paulinho da Viola e Elton Medeiros]] 
 + 
 +  * [[http://www.youtube.com/watch?v=BtEhO4hYKbg|Nelson Cavaquinho]] 
 + 
 +  * [[http://www.youtube.com/watch?v=MByVS9mhvzU|Lupicínio Rodrigues]] 
 + 
 +  * [[http://www.youtube.com/watch?v=72fYqSPSFEc|Martinho da Vila]] 
 + 
 + 
 + 
 + 
 +====== Images ====== 
 + 
 + 
 +  * [[http://www.google.com/search?q=rio+de+janeiro&hl=pt-BR&client=ubuntu&hs=pDy&channel=fs&prmd=ivnsum&tbm=isch&tbo=u&source=univ&sa=X&ei=OGSwTZP7Ecia0QHr4dGaCQ&ved=0CG0QsAQ&biw=1366&bih=541|Rio de Janeiro]] 
 + 
 +  * [[http://www.google.com/search?q=niteroi&hl=pt-BR&client=ubuntu&hs=Xap&channel=fs&prmd=ivnsum&tbm=isch&tbo=u&source=univ&sa=X&ei=JPK1TcXnNobW0QHl-bn0Bw&ved=0CGwQsAQ&biw=1366&bih=541|Niterói]] 
 + 
 +  * [[http://www.google.com/search?q=fortaleza&hl=pt-BR&client=ubuntu&hs=tvI&channel=fs&prmd=ivnsum&tbm=isch&tbo=u&source=univ&sa=X&ei=3mSwTaHTG6Lf0gG8s_j1CA&ved=0CGQQsAQ&biw=1366&bih=541|Fortaleza]] 
 + 
 +  * [[http://www.google.com/search?q=aveiro&hl=pt-BR&client=ubuntu&hs=nHy&channel=fs&prmd=ivnslm&tbm=isch&tbo=u&source=univ&sa=X&ei=LmWwTZzIDOj10gHJod3xAg&ved=0CFwQsAQ&biw=1366&bih=541|Aveiro]] 
 + 
 + 
 +{{:nuno:flamengo2.gif?200}}           {{:nuno:camisao.jpg?290}}                  {{:nuno:portela.jpg?220}} 
 +====== Contact ====== 
 + 
 +<box blue> 
 +Instituto de Física \\ 
 +Universidade Federal Fluminense\\ 
 +Av. Litorânea s/n, CEP 24210-340\\ 
 +Niterói - Rio de Janeiro\\ 
 +E-mail: [[nuno@if.uff.br]], [[nuno@mail.if.uff.br]]\\ 
 +Room: 419, new building of Institute of Physics\\ 
 +Phone: +55 (21) 2629-5845\\ 
 +</box> 
 + 
 + 
 +<html> 
 +<p> 
 +<a href="http://www2.clustrmaps.com/counter/maps.php?url=http://complex.if.uff.br/nuno" id="clustrMapsLink"><img src="http://www2.clustrmaps.com/counter/index2.php?url=http://complex.if.uff.br/nuno" style="border:0px;" alt="Locations of visitors to this page" title="Locations of visitors to this page" id="clustrMapsImg" onerror="this.onerror=null; this.src='http://clustrmaps.com/images/clustrmaps-back-soon.jpg'; document.getElementById('clustrMapsLink').href='http://clustrmaps.com';" /> 
 +</a> 
 +</p> 
 +</html> 
 + 
 + 
 + 
 + 
 + 
 +[[http://www.uff.br|{{:nuno:logouff.jpg?180}}]] 
 +[[http://complex.if.uff.br|{{:en:nuno:logo_en.jpg?320}}]] \\ 
 +[[http://www.cnpq.br|{{:nuno:cnpq_v9.jpg?200}}]] 
 +[[http://www.faperj.br|{{:nuno:logo_faperj.jpg?200|}}]] 
en/nuno/home.txt · Last modified: 2018/09/19 10:00 by nuno
CC Attribution-Share Alike 3.0 Unported
www.chimeric.de Valid CSS Driven by DokuWiki do yourself a favour and use a real browser - get firefox!! Recent changes RSS feed Valid XHTML 1.0