368 research outputs found
Direct evidence for charge stripes in a layered cobalt oxide
Recent experiments indicate that static stripe-like charge order is generic to the hole-doped copper oxide superconductors and competes with superconductivity. Here we show that a similar type of charge order is present in La5/3 Sr1/3 CoO4 , an insulating analogue of the copper oxide superconductors containing cobalt in place of copper. The stripe phase we have detected is accompanied by short-range, quasi-one-dimensional, antiferromagnetic order, and provides a natural explanation for the distinctive hour- glass shape of the magnetic spectrum previously observed in neutron scattering mea- surements of La2−xSrx CoO4 and many hole-doped copper oxide superconductors. The results establish a solid empirical basis for theories of the hourglass spectrum built on short-range, quasi-static, stripe correlations
Hour-glass magnetic spectrum in an insulating, hole-doped antiferromagnet
Superconductivity in layered copper-oxide compounds emerges when charge
carriers are added to antiferromagnetically-ordered CuO2 layers. The carriers
destroy the antiferromagnetic order, but strong spin fluctuations persist
throughout the superconducting phase and are intimately linked to
super-conductivity. Neutron scattering measurements of spin fluctuations in
hole-doped copper oxides have revealed an unusual `hour-glass' feature in the
momentum-resolved magnetic spectrum, present in a wide range of superconducting
and non-superconducting materials. There is no widely-accepted explanation for
this feature. One possibility is that it derives from a pattern of alternating
spin and charge stripes, an idea supported by measurements on stripe-ordered
La1.875Ba0.125CuO4. However, many copper oxides without stripe order also
exhibit an hour-glass spectrum$. Here we report the observation of an
hour-glass magnetic spectrum in a hole-doped antiferromagnet from outside the
family of superconducting copper oxides. Our system has stripe correlations and
is an insulator, which means its magnetic dynamics can conclusively be ascribed
to stripes. The results provide compelling evidence that the hour-glass
spectrum in the copper-oxide superconductors arises from fluctuating stripes.Comment: 13 pages, 4 figures, to appear in Natur
Insertion of heterometals into the NifEN-associated iron–molybdenum cofactor precursor
The cofactors of Mo-, V-, Fe-dependent nitrogenases are believed to be highly homologous in structure despite the different types of heterometals (Mo, V, and Fe) they contain. Previously, a precursor form of the FeMo cofactor (FeMoco) was captured on NifEN, a scaffold protein for FeMoco biosynthesis. This all-Fe precursor closely resembles the Fe/S core structure of the FeMoco and, therefore, could reasonably serve as a precursor for all nitrogenase cofactors. Here, we report the heterologous incorporation of V and Fe into the NifEN-associated FeMoco precursor. EPR and activity analyses indicate that V and Fe can be inserted at much reduced efficiencies compared with Mo, and incorporation of both V and Fe is enhanced in the presence of homocitrate. Further, native polyacrylamide gel electrophoresis experiments suggest that NifEN undergoes a significant conformational rearrangement upon metal insertion, which allows the subsequent NifEN–MoFe protein interactions and the transfer of the cofactor between the two proteins. The combined outcome of these in vitro studies leads to the proposal of a selective mechanism that is utilized in vivo to maintain the specificity of heterometals in nitrogenase cofactors, which is likely accomplished through the redox regulation of metal mobilization by different Fe proteins (encoded by nifH, vnfH, and anfH, respectively), as well as the differential interactions between these Fe proteins and their respective scaffold proteins (NifEN and VnfEN) in the Mo-, V-, and Fe-dependent nitrogenase systems
Highly efficient catalysis of the Kemp elimination in the cavity of a cubic coordination cage.
The hollow cavities of coordination cages can provide an environment for enzyme-like catalytic reactions of small-molecule guests. Here, we report a new example (catalysis of the Kemp elimination reaction of benzisoxazole with hydroxide to form 2-cyanophenolate) in the cavity of a water-soluble M8L12 coordination cage, with two features of particular interest. First, the rate enhancement is among the largest observed to date: at pD 8.5, the value of kcat/kuncat is 2 × 10(5), due to the accumulation of a high concentration of partially desolvated hydroxide ions around the bound guest arising from ion-pairing with the 16+ cage. Second, the catalysis is based on two orthogonal interactions: (1) hydrophobic binding of benzisoxazole in the cavity and (2) polar binding of hydroxide ions to sites on the cage surface, both of which were established by competition experiments
Evolution of an adaptive behavior and its sensory receptors promotes eye regression in blind cavefish
Effect of a Fatty Acid Additive on the Kinetic Friction and Stiction of Confined Liquid Lubricants
Apresentamos neste texto parte das produções de pesquisa que acompanhou a construção de corpos inseridos num Centro de Atenção Psicossocial para Álcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenção é dada à tensão entre normalização de corpos e tentativas de (re)existências. A argumentação se desenvolve no campo da saúde pública, em particular o da saúde mental, e alicerçada nos estudos de gênero e sexualidade. A produção de dados se valeu de observações registradas em diário de campo, acompanhamento itinerante, composição de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diários de campo, rodas de conversa e oficinas com profissionais e usuári*s. A aposta metodológica foi a de forjar um modo de narrar coletivo que agenciasse experimentação e desaprendizagens corporais, junto a modos de produzir cuidado em saúde e de fazer pesquisa.Apresentamos neste texto parte das produções de pesquisa que acompanhou a construção de corpos inseridos num Centro de Atenção Psicossocial para Álcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenção é dada à tensão entre normalização de corpos e tentativas de (re)existências. A argumentação se desenvolve no campo da saúde pública, em particular o da saúde mental, e alicerçada nos estudos de gênero e sexualidade. A produção de dados se valeu de observações registradas em diário de campo, acompanhamento itinerante, composição de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diários de campo, rodas de conversa e oficinas com profissionais e usuári*s. A aposta metodológica foi a de forjar um modo de narrar coletivo que agenciasse experimentação e desaprendizagens corporais, junto a modos de produzir cuidado em saúde e de fazer pesquisa.Apresentamos neste texto parte das produções de pesquisa que acompanhou a construção de corpos inseridos num Centro de Atenção Psicossocial para Álcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenção é dada à tensão entre normalização de corpos e tentativas de (re)existências. A argumentação se desenvolve no campo da saúde pública, em particular o da saúde mental, e alicerçada nos estudos de gênero e sexualidade. A produção de dados se valeu de observações registradas em diário de campo, acompanhamento itinerante, composição de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diários de campo, rodas de conversa e oficinas com profissionais e usuári*s. A aposta metodológica foi a de forjar um modo de narrar coletivo que agenciasse experimentação e desaprendizagens corporais, junto a modos de produzir cuidado em saúde e de fazer pesquisa.Apresentamos neste texto parte das produções de pesquisa que acompanhou a construção de corpos inseridos num Centro de Atenção Psicossocial para Álcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenção é dada à tensão entre normalização de corpos e tentativas de (re)existências. A argumentação se desenvolve no campo da saúde pública, em particular o da saúde mental, e alicerçada nos estudos de gênero e sexualidade. A produção de dados se valeu de observações registradas em diário de campo, acompanhamento itinerante, composição de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diários de campo, rodas de conversa e oficinas com profissionais e usuári*s. A aposta metodológica foi a de forjar um modo de narrar coletivo que agenciasse experimentação e desaprendizagens corporais, junto a modos de produzir cuidado em saúde e de fazer pesquisa.Apresentamos neste texto parte das produções de pesquisa que acompanhou a construção de corpos inseridos num Centro de Atenção Psicossocial para Álcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenção é dada à tensão entre normalização de corpos e tentativas de (re)existências. A argumentação se desenvolve no campo da saúde pública, em particular o da saúde mental, e alicerçada nos estudos de gênero e sexualidade. A produção de dados se valeu de observações registradas em diário de campo, acompanhamento itinerante, composição de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diários de campo, rodas de conversa e oficinas com profissionais e usuári*s. A aposta metodológica foi a de forjar um modo de narrar coletivo que agenciasse experimentação e desaprendizagens corporais, junto a modos de produzir cuidado em saúde e de fazer pesquisa.Apresentamos neste texto parte das produções de pesquisa que acompanhou a construção de corpos inseridos num Centro de Atenção Psicossocial para Álcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenção é dada à tensão entre normalização de corpos e tentativas de (re)existências. A argumentação se desenvolve no campo da saúde pública, em particular o da saúde mental, e alicerçada nos estudos de gênero e sexualidade. A produção de dados se valeu de observações registradas em diário de campo, acompanhamento itinerante, composição de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diários de campo, rodas de conversa e oficinas com profissionais e usuári*s. A aposta metodológica foi a de forjar um modo de narrar coletivo que agenciasse experimentação e desaprendizagens corporais, junto a modos de produzir cuidado em saúde e de fazer pesquisa.The paper presents part of the research productions that accompanied the construction of bodies inserted in a Psychosocial Care Center for Alcohol and Other Drugs (CAPS-AD) of a city in the northern region of Brasil, focusing more sharply on masculinities arrangements. Special attention is given to the tension between normalized bodies and attempts at resistance and (re) exist. The argument is in the field of public health, particularly mental health, and rooted in gender and sexuality studies. The data production methodology made use of observations recorded in a diary, itinerant follow-up of a collective of research, interviews, focus groups where, among other things, was discussed diary topics, conversation circles and workshops. The attempt was to produce a way of collective narrating strategy, combining up experience and body (un)learn well as ways of producing health care and doing research
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
Recognition of aminoacyl-tRNA: a common molecular mechanism revealed by cryo-EM
The accuracy of ribosomal translation is achieved by an initial selection and a proofreading step, mediated by EF-Tu, which forms a ternary complex with aminoacyl(aa)-tRNA. To study the binding modes of different aa-tRNAs, we compared cryo-EM maps of the kirromycin-stalled ribosome bound with ternary complexes containing Phe-tRNAPhe, Trp-tRNATrp, or Leu-tRNALeuI. The three maps suggest a common binding manner of cognate aa-tRNAs in their specific binding with both the ribosome and EF-Tu. All three aa-tRNAs have the same ‘loaded spring' conformation with a kink and twist between the D-stem and anticodon stem. The three complexes are similarly integrated in an interaction network, extending from the anticodon loop through h44 and protein S12 to the EF-Tu-binding CCA end of aa-tRNA, proposed to signal cognate codon–anticodon interaction to the GTPase centre and tune the accuracy of aa-tRNA selection
Mechanism of Cancer Cell Death Induced by Depletion of an Essential Replication Regulator
Background: Depletion of replication factors often causes cell death in cancer cells. Depletion of Cdc7, a kinase essential for initiation of DNA replication, induces cancer cell death regardless of its p53 status, but the precise pathways of cell death induction have not been characterized. Methodology/Principal Findings: We have used the recently-developed cell cycle indicator, Fucci, to precisely characterize the cell death process induced by Cdc7 depletion. We have also generated and utilized similar fluorescent cell cycle indicators using fusion with other cell cycle regulators to analyze modes of cell death in live cells in both p53-positive and-negative backgrounds. We show that distinct cell-cycle responses are induced in p53-positive and-negative cells by Cdc7 depletion. p53-negative cells predominantly arrest temporally in G2-phase, accumulating CyclinB1 and other mitotic regulators. Prolonged arrest at G2-phase and abrupt entry into aberrant M-phase in the presence of accumulated CyclinB1 are followed by cell death at the post-mitotic state. Abrogation of cytoplasmic CyclinB1 accumulation partially decreases cell death. The ATR-MK2 pathway is responsible for sequestration of CyclinB1 with 14-3-3s protein. In contrast, p53-positive cancer cells do not accumulate CyclinB1, but appear to die mostly through entry into aberrant S-phase after Cdc7 depletion. The combination of Cdc7 inhibition with known anti-cancer agents significantly stimulates cell death effects in cancer cells in a genotype-dependent manner, providing a strategic basis for future combination therapies
Wave Vector Difference of Magnetic Bragg Reflections and Low Energy Magnetic Excitations in Charge-stripe Ordered La2NiO4.11
We report on the magnetism of charge-stripe ordered La2NiO4.11±0.01 by neutron scattering and μSR. On going towards zero energy transfer there is an observed wave vector offset in the centring of the magnetic excitations and magnetic Bragg reflections, meaning the excitations cannot be described as Goldstone modes of the magnetic order. Weak transverse field μSR measurements determine the magnetically order volume fraction is 87% from the two stripe twins, and the temperature evolution of the magnetic excitations is consistent with the low energy excitations coming from the magnetically ordered volume of the material. We will discuss how these results contrast with the proposed origin of a similar wave vector offset recently observed in a La-based cuprate, and possible origins of this effect in La2NiO4.11
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