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Search Results: 1 - 10 of 297309 matches for " J. Mraz "
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Problems with reliability and safety of hot dip galvanized steel structures
Mraz, L.;Lesay, J.;
Soldagem & Inspe??o , 2009, DOI: 10.1590/S0104-92242009000200011
Abstract: hot dip galvanizing is very effective means of protection against corrosion. some recommendation concerning the steel quality are generally known and accepted. the process consists of cleaning (pickling or sand blasting) and dipping the structures or pieces into liquid zinc bath. the case study of hot dip galvanized steels is presented. some recent failures of hot dip galvanized welded structures and hot dip galvanized high strength steel screws are presented. structures were made of s355 grade steel and mig/mag process was applied for welding. large cracks were observed in the vicinity of welds after hot dip galvanizing process. the presence of both hydrogen and liquid metal embrittlement was identified and associated mainly with higher hardness of haz or the quenched and tempered steels. possible cracking mechanisms are discussed. the influence of chemical composition and production process (welding, heat treatment) was analyzed according to data published in literature. the solutions and recommendations for avoiding the failure in hot dip galvanized structures are proposed.
Hybrid M-FSK/DQPSK Modulations for CubeSat Picosatellites
I. Vertat,J. Mraz
Radioengineering , 2013,
Abstract: Conventional CubeSat radio systems typically use one of several basic modulations, such as AFSK, GMSK, BPSK, QPSK and OOK or switch between them on demand if possible. These modulations represent a bal anced trade-off between good energy efficiency of high order M-FSK modulation and good spectral efficiency of high order M-QAM modulation. Utilization of modulations with the best energy efficiency is not possible due to strict limits on occupied frequency bandwidth. In this paper the proposed group of hybrid modulations and proposed hybrid modulator and demodulator are presented. Novel solution offer interesting possibilities of increasing spectral efficiency as well as energy efficiency of basic M-FSK modulation by embedding DQPSK symbols between two M-FSK symbols. Such group of hybrid modulations offers suitable properties for picosatellite, e.g. simple realization onboard the picosatellite, better energy and spectral efficiency, low PAPR, wide range of adaptation by changing the order of M-FSK, suitable for easy non-coherent demodulation, good immunity to Doppler effect with DM-FSK coding.
Kohn-Luttinger instability of the t-t' Hubbard model in two dimensions: variational approach
J. Mraz,R. Hlubina
Physics , 2002, DOI: 10.1103/PhysRevB.67.174518
Abstract: An effective Hamiltonian for the Kohn-Luttinger superconductor is constructed and solved in the BCS approximation. The method is applied to the t-t' Hubbard model in two dimensions with the following results: (i) The superconducting phase diagram at half filling is shown to provide a weak-coupling analog of the recently proposed spin liquid state in the J_1-J_2 Heisenberg model. (ii) In the parameter region relevant for the cuprates we have found a nontrivial energy dependence of the gap function in the dominant d-wave pairing sector. The hot spot effect in the angular dependence of the superconducting gap is shown to be quite weak.
Chiral d+is superconducting state in the two dimensional t-t' Hubbard model
J. Mraz,R. Hlubina
Physics , 2003, DOI: 10.1103/PhysRevB.69.104501
Abstract: Applying the recently developed variational approach to Kohn-Luttinger superconductivity to the t-t' Hubbard model in two dimensions, we have found, for sizeable next-nearest neighbor hopping, an electron density controlled quantum phase transition between a d-wave superconducting state close to half filling and an s-wave superconductor at lower electron density. The transition occurs via an intermediate time reversal breaking d+is superconducting phase, which is characterized by nonvanishing chirality and density-current correlation. Our results suggest the possibility of a bulk time reversal symmetry breaking state in overdoped cuprates.
Josephson effect as a measure of quantum fluctuations in the cuprates
R. Hlubina,M. Grajcar,J. Mraz
Physics , 2003,
Abstract: Quantitative analysis of the Josephson effect is shown to provide direct information about phase fluctuations in the superconducting banks. Applying the analysis to the cuprates, substantial quantum fluctuations between d-wave and s-wave pairing are found at low temperatures. A phenomenological model of such fluctuations is introduced and solved in a self-consistent single-site approximation. The cuprate parameters are argued to lie close to an exotic superconductor phase with condensation of electron quadruplets.
War is hazardous for your health: photographs and testimonies about death, wounds, disease and medical care during the Mexican Revolution
Mraz, John;
História, Ciências, Saúde-Manguinhos , 2011, DOI: 10.1590/S0104-59702011000300017
Abstract: revolutionary wars have devastating and far-reaching effects on the health of the populations caught up in them. however, the deaths and injuries produced by weaponry are only part of the story, because diseases resulting from malnutrition and contaminated drinking water account for the majority of medical problems. this essay uses photographs and testimonies of participants to explore health issues during the mexican revolution (1910-1920), as well as incorporating secondary literature on this question. furthermore, photographic images are not presented as simple (indexical) windows onto the world. rather, the author attempts to identify the imagemakers and provide explanations that help in imagining the reasons behind the making of the photographs.
Más allá de la decoración: hacia una historia gráfica de las mujeres en México
John Mraz
Política y cultura , 1992,
Abstract:
Fotografiar el 68
John Mraz
Política y cultura , 1997,
Abstract:
What’s new in graphic historiography? Qué tiene de nuevo la historia grafica?
John Mraz
Diálogos , 2010, DOI: 10.4025/dialogos.v7i1.355
Abstract: This article attempts to redefine the discipline that utilizes technical images in history. It has been known as “historia gráfica,” but the author argues that a more useful term might be “fotofonohistoria,” above all in the particular applications: photohistory, cinehistory, and videohistory. Este artigo tenta redefinir a disciplina que utiliza as imagens técnicas na História. Ela é conhecida como “História Gráfica”, mas o autor argumenta que um termo mais adequado poderia ser o de “foto-fono-história”, sobretudo nas aplica es particulares: foto-história, cine-história, e video-história.
As duas Fridas: história e identidades transculturais
Bartra, Eli;Mraz, John;
Revista Estudos Feministas , 2005, DOI: 10.1590/S0104-026X2005000100005
Abstract: this article analyzes the film frida (2003), directed by julie taymor and starred by salma hayek, which features the love relationship between the mural artist diego rivera and the painter frida khalo. it is not a filmic biography, but focuses on a period of the painter's life. on the one hand, it presents some comparison with the mexican movie about the painter, frida, naturaleza viva (1983), by paul leduc, to contrast different views on the events of a life, as to, for example, what concerns sexual politics. on the other hand, the paper explores to what extent the polemical film by taymor/hayek is historical, based on reality, or whether it is a sight-and-sound fictional version of a written biography.
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