826 research outputs found
Mechanism of thermally activated c-axis dissipation in layered High-T superconductors at high fields
We propose a simple model which explains experimental behavior of -axis
resistivity in layered High-T superconductors at high fields in a limited
temperature range. It is generally accepted that the in-plane dissipation at
low temperatures is caused by small concentration of mobile pancake vortices
whose diffusive motion is thermally activated. We demonstrate that in such
situation a finite conductivity appears also in -direction due to the phase
slips between the planes caused by the mobile pancakes. The model gives
universal relation between the components of conductivity which is in good
agreement with experimental data.Comment: RevTeX, 4 pages, 2 Postscript figure
The BARD1 C-Terminal Domain Structure and Interactions with Polyadenylation Factor CstF-50†
The BARD1 N-terminal RING domain binds BRCA1 while the BARD1 C-terminal ankyrin and tandem BRCT repeat domains bind CstF-50 to modulate mRNA processing and RNAP II stability in response to DNA damage. Here we characterize the BARD1 structural biochemistry responsible for CstF- 50 binding. The crystal structure of the BARD1 BRCT domain uncovers a degenerate phosphopeptide binding pocket lacking the key arginine required for phosphopeptide interactions in other BRCT proteins.Small angle X-ray scattering together with limited proteolysis results indicates that ankyrin and BRCT domains are linked by a flexible tether and do not adopt a fixed orientation relative to one another. Protein pull-down experiments utilizing a series of purified BARD1 deletion mutants indicate that interactions between the CstF-50 WD-40 domain and BARD1 involve the ankyrin-BRCT linker but do not require ankyrin or BRCT domains. The structural plasticity imparted by the ANK-BRCT linker helps to explain the regulated assembly of different protein BARD1 complexes with distinct functions in DNA damage signaling including BARD1-dependent induction of apoptosis plus p53 stabilization and interactions. BARD1 architecture and plasticity imparted by the ANK-BRCT linker are suitable to allow the BARD1 C-terminus to act as a hub with multiple binding sites to integrate diverse DNA damage signals directly to RNA polymerase
Erratum: Dynamics of Energy Transfer in a Conjugated Dendrimer Driven by Ultrafast Localization of Excitations (Journal of the American Chemical Society (2015) 137 (11637-11644) DOI: 10.1021/jacs.5b04075)
The 3′ processing factor CstF functions in the DNA repair response
Following DNA damage, mRNA levels decrease, reflecting a coordinated interaction of the DNA repair, transcription and RNA processing machineries. In this study, we provide evidence that transcription and polyadenylation of mRNA precursors are both affected in vivo by UV treatment. We next show that the polyadenylation factor CstF, plays a direct role in the DNA damage response. Cells with reduced levels of CstF display decreased viability following UV treatment, reduced ability to ubiquitinate RNA polymerase II (RNAP II), and defects in repair of DNA damage. Furthermore, we show that CstF, RNAP II and BARD1 are all found at sites of repaired DNA. Our results indicate that CstF plays an active role in the response to DNA damage, providing a link between transcription-coupled RNA processing and DNA repair
Gratitude and suicide risk among college students: Substantiating the protective benefits of being thankful
Objective: Gratitude, or thankfulness for positive aspects of life, is related to psychosocial well-being and decreased psychopathology, and may reduce suicide risk. We explored four potential hypotheses purported to explain the beneficial outcomes of gratitude (schematic, positive affect, broaden-and-build, and coping), hypothesizing that hopelessness (schematic), depression (positive affect), social support (broaden-and-build), and substance use (coping) would mediate the gratitude-suicide linkage. Participants: 913 undergraduate students from a mid-size, southeastern U.S. university. Methods: Respondents completed online self-report questionnaires including the Suicidal Behaviors Questionnaire-Revised, Gratitude Questionnaire, Beck Hopelessness Scale, Beck Depression Inventory, Duke Social Support Index, Alcohol Use Disorders Identification Test, and Drug Abuse Screening Test. Results: Supporting theory and hypotheses, gratitude was related to less suicide risk via beneficial associations with hopelessness, depression, social support, and substance misuse. Conclusions: The linkage between gratitude and suicide risk appears to be predicated on the beneficial association of gratitude to negative mood and interpersonal functioning
Odd Frequency Pairing in the Kondo Lattice
We discuss the possibility that heavy fermion superconductors involve
odd-frequency pairing of the kind first considered by Berezinskii. Using a toy
model for odd frequency triplet pairing in the Kondo lattice we are able to
examine key properties of this new type of paired state. To make progress
treating the strong constraint in the Kondo lattice model we use the
technical trick of a Majorana representation of the local moments, which
permits variational treatments of the model without a Gutzwiller approximation.
The simplest mean field theory involves the development of bound states between
the local moments and conduction electrons, characterized by a spinor order
parameter. We show that this state is a stable realization of odd frequency
triplet superconductivity with surfaces of gapless excitations whose spin and
charge coherence factors vanish linearly in the quasiparticle energy. A
NMR relaxation rate coexists with a linear specific heat. We discuss possible
extensions of our toy model to describe heavy fermion superconductivity.Comment: 67 page
Ground State Vortex Lattice Structures in d-wave Superconductors
We show in a realistic symmetry gap model for a cuprate
superconductor that the clean vortex lattice has discontinuous structural
transitions (at and near T=0), as a function of the magnetic field along
the c-axis. The transitions arise from the singular nonlocal and anisotropic
susceptibility of the superconductor to the perturbation
caused by supercurrents associated with vortices. The susceptibility, due to
virtual Dirac quasiparticle-hole excitation, is calculated carefully, and leads
to a ground state transition for the triangular lattice from an orientation
along one of the crystal axis to one at 45 to them, i.e, along the gap zero
direction. The field scale is seen to be 5 Tesla , where is the gap maximum, is the
nearest neighbour hopping, is the lattice constant, and is the
flux quantum. At much higher fields () there is a discontinuous
transition to a centred square structure. The source of the differences from
existing calculations, and experimental observability are discussed, the latter
especially in view of the very small (a few degrees per vortex) differences
in the ground state energy.Comment: To be published in Phys. Rev.
The underscreened Kondo effect: a two S=1 impurity model
The underscreened Kondo effect is studied within a model of two impurities
S=1 interacting with the conduction band and via an interimpurity coupling
. Using a mean-field treatment of the bosonized
Hamiltonian, we show that there is no phase transition, but a continuous
cross-over versus K from a non Kondo behaviour to an underscreened Kondo one.
For a small antiferromagnetic coupling (K>0), a completely asymmetric situation
is obtained with one s= component strongly screened by the Kondo effect
and the other one almost free to yield indirect magnetism, which shows finally
a possible coexistence between a RKKY interaction and a local Kondo effect, as
observed in Uranium compounds such as .Comment: 27 pages, RevTeX, to be published in PR
Meu modo de falar mudou bastante, as pessoas notaram a diferença em mim: quando o letramento é desenvolvido fora do contexto escolar
Building Babies - Chapter 16
In contrast to birds, male mammals rarely help to raise the offspring. Of all mammals, only among rodents, carnivores, and primates, males are sometimes intensively engaged in providing infant care (Kleiman and Malcolm 1981). Male caretaking of infants has long been recognized in nonhuman primates (Itani 1959). Given that infant care behavior can have a positive effect on the infant’s development, growth, well-being, or survival, why are male mammals not more frequently involved in “building babies”? We begin the chapter defining a few relevant terms and introducing the theory and hypotheses that have historically addressed the evolution of paternal care. We then review empirical findings on male care among primate taxa, before focusing, in the final section, on our own work on paternal care in South American owl monkeys (Aotus spp.). We conclude the chapter with some suggestions for future studies.Deutsche Forschungsgemeinschaft (HU 1746/2-1)
Wenner-Gren Foundation, the L.S.B. Leakey Foundation, the National Geographic Society, the National Science Foundation (BCS-0621020), the University of Pennsylvania Research Foundation, the Zoological Society of San Dieg
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