Ignis fatuus, a luminous phenomenon witnessed over the centuries by observers around the world, is no longer seen in modern times, suggesting that it is extinct. An explanation for this disappearance can be found in the description of ignis fatuus as a cool flame of methane. Unlike a conventional flame, which generates large amounts of heat, ignis fatuus is a flame that glows without heat through a chemiluminescence process. Its characteristic bluish color is due to the emission of excited formaldehyde, which is formed in the slow combustion of methane. It is generally accepted that the phenomenon is a spontaneous combustion of swamp gas in contact with the oxygen in air, but an analysis of the energies involved in the cool flame process indicates that the phenomenon is not spontaneous in nature. Experiments carried out in the 19th century show torches being used to ignite ignis fatuus. The abandonment of fire in favor of night lighting may hold the secret to this mystery of ignis fatuus’s extinction. world times extinct methane formaldehyde air nature th fatuuss s extinction

The assessment of the carcinogenic potential of polycyclic aromatic hydrocarbons (PAH) is obtained by a principal component analysis (PCA) and quantitative structure-activity relationship (QSAR) using hydrophobic (LogP), stereo and electronic parameters (electron affinity, dipole moment and HOMO-LUMO gap) calculated from the AM1 method. The PAH-DNA interaction model is based on the unsynchronized resonating valence bond theory (RVB) developed by L. Pauling. The QSAR study reproduces the experimental values of LD50 in rats with 95% confidence. The PCA analysis classify all the selected compounds as potential carcinogens, an important result since many of these PAH are not classified as carcinogens, indicating the need for an urgent revision of its classification.

The carcinogenic potential of carbendazim and its metabolites was analyzed using statistical treatment of electronic parameters obtained from DFT/ 6-311++G(d,p) and AM1 calculations. The carcinogen-DNA interaction is described in the framework of the theory of unsynchronized resonance of covalent bond as a process of electron transfer involving the HOMO and LUMO frontier orbitals. Through a Principal Component Analysis (PCA) of the electron affinity, carcinogen-DNA interaction energy, electrostatic attraction and cell membrane permeability (dipole moment m and partition coefficient LogP) evidence was obtained showing carbendazim displays carcinogenic activity. For the metabolites of carbendazim, no evidence was found in the literature of their carcinogenic activities. However, the electronic parameters for these metabolites exhibited similarity to known carcinogens, thereby showing the importance of the results obtained in this study for a policy based on the precautionary principle.

Cálculos DFT em modelos de cluster de cupratos (LaBa2Cu3O6.7, La1.85Sr0.15CuO4, YBa2Cu3O7, TlBa2Ca2Cu3O8.78, HgBa2Ca2Cu3O8.27), de sistemas metálicos (Nb3Ge, MgB2) e do pnictido LaO0.92F0.08FeAs indicaram a ocorrência da ressonância não-sincronizada no estado supercondutor, como prevê a teoria RVB (resonating valence bond) de Pauling. Para os cupratos, a ressonância não-sincronizada envolve transferência de elétron entre átomos de Cu, acompanhada pela redução da carga dos átomos La, Sr, Y e Ca. Para o MgB2, a transferência de elétron ocorre na camada do Mg, enquanto a do B comporta-se como reservatório de cargas. Para o Nb3Ge, a ressonância ocorre entre átomos de Ge, que devem ser os responsáveis pela transferência de carga. Para o LaO0.92F0.08FeAs, ambas as camadas de La-O e Fe-As estão envolvidas no mecanismo da supercondutividade. A observação de ressonâncias não-sincronizadas nestes sistemas fornece uma evidência em favor da RVB como uma teoria apropriada para a supercondutividade em altas temperaturas (high-T C).

DFT calculations performed on different cluster models of cuprates (LaBa2Cu3O6.7, La1.85Sr0.15CuO4, YBa2Cu3O7, TlBa2Ca2Cu3O8.78, HgBa2Ca2Cu3O8.27), metallic systems (Nb3Ge, MgB2) and the pnictide LaO0.92F0.08FeAs made evident the occurrence of unsynchronized resonance of covalent bonds in the superconducting state, as predicted by Pauling´s resonating valence bond (RVB) theory. For cuprates, the unsynchronized resonance involves electron transfer between Cu atoms accompanied by a decrease in the charge of the La, Sr, Y and Ca atoms. For MgB2, electron transfer occurs in the Mg layer, while the B layer behaves as charge reservoir. For Nb3Ge, unsynchronized resonance occurs among the Ge atoms, which should be responsible for charge transfer. For LaO0.92F0.08FeAs, the results suggest that both La-O and Fe-As layers are involved in the mechanism of superconductivity. The identification of unsynchronized resonances in these systems provides evidence which supports RVB as a suitable theory for high-temperature superconductivity (high-T C).

Um século após a descoberta deste fascinante fenômeno, a supercondutividade continua sendo um campo de pesquisa atual e vem contribuindo de modo significativo para o desenvolvimento científico e tecnológico. Apesar de muitos desafios terem sido superados ao longo destes anos, dois permanecem notavelmente destacados: a) o desenvolvimento de uma teoria microscópica ab initio (de primeiros princípios) que seja capaz de explicar a supercondutividade em qualquer intervalo de temperatura e b) a obtenção de um material que seja supercondutor a temperatura ambiente ou em temperatura maior que a ambiente. Depois de 5 prêmios Nobel em Física terem sido concedidos a pesquisadores desta área, é possível conjeturar que mais serão entregues aos que superarem os desafios destacados acima. Apresentamos uma sucinta discussão concernente aos principais acontecimentos relacionados à supercondutividade: sua descoberta, os materiais, as teorias propostas, os protagonistas e os avanços tecnológicos. Em um universo ocupado quase que exclusivamente por físicos teóricos e experimentais, destacamos a pouco conhecida contribuição do físico-químico americano Linus Pauling, que propôs um modelo simples e eficiente para a descrição da supercondutividade baseado em sua teoria da ressonância não-sincronizada das ligações covalentes (RVB). Estes importantes aspectos são apresentados e discutidos.

One after century the discovery of this fascinating phenomenon, the superconductivity remains a current field of research and has significantly contributed to the scientific and technological development. Although many challenges have been overcome through the years, two remain remarkably highlighted: a) the development of a microscopic theory ab initio (first principles) that is able to explain superconductivity in any temperature range and b) the production of a material that is superconducting at room temperature or at higher temperatures than the room. After five Nobel Prizes in Physics have been awarded to researchers in this area, it is possible to conjecture that more will be delivered to those who overcome the challenges above outlined. We present a brief discussion regarding the main events related to superconductivity: its discovery, materials, proposed theories, protagonists and technological advances. In a universe occupied almost exclusively by theoretical and experimental physicists, we highlight the contribution little known of the american physical chemist Linus Pauling, who proposed a simple and effective model for the description of superconductivity based on his unsynchronizedresonating-covalent-bond theory (RVB). These important aspects are presented and discussed.

Diferentes propriedades da química de quarks são estudadas por cálculos ab initio Hartree-Fock em átomos com carga nuclear fracionária. Os estados fundamental e excitado de átomos de sódio com quarks ligados ao núcleo são obtidos usando cálculos de interação de configuração. Este estudo sugere que a transição eletrônica ²P -> ²S no sódio pode ser usada como guia para observação de quarks não confinados. A variação da energia de ligação eletrônica com a carga nuclear para a série isoeletrônica de átomos com carga nuclear fracionária A±2/3 e A±1/3 (A = H, Li, Na, P and Ca) foi analisada. Os cálculos apresentados sugerem, que os quarks não confinados preferem se ligar a núcleos pesados, e que o par quark-antiquark poderia ser estabilizado na presença da matéria atômica.

Different properties of quark chemistry are studied by performing accurate ab initio Hartree-Fock calculations on fractionally nuclear charged atoms. Ground and first excited states of sodium atoms with quarks attached to the nucleus are obtained using CI calculations. It is suggested that the sodium ²P -> ²S electronic transition can be used as a guide in searching for unconfined quarks. Also, the variation of the binding electronic energy with nuclear charge in the isoelectronic series of fractionally nuclear charged atoms A±2/3 and A±1/3 (A = H, Li, Na, P and Ca) is analyzed. The present calculations suggest that unconfined colored particles have large appetite for heavy nuclei and that quark-antiquark pairs could be stabilized in presence of the atomic matter.