1,627 research outputs found
The PWWP domain and the evolution of unique DNA methylation toolkits in Hymenoptera.
DNMT3 in Hymenoptera has a unique duplication of the essential PWWP domain. Using GST-tagged PWWP fusion proteins and histone arrays we show that these domains have gained new properties and represent the first case of PWWP domains binding to H3K27 chromatin modifications, including H3K27me3, a key modification that is important during development. Phylogenetic analyses of 107 genomes indicate that the duplicated PWWP domains separated into two sister clades, and their distinct binding capacities are supported by 3D modeling. Other features of this unique DNA methylation system include variable copies, losses, and duplications of DNMT1 and DNMT3, and combinatorial generations of DNMT3 isoforms including variants missing the catalytic domain. Some of these losses and duplications of are found only in parasitic wasps. We discuss our findings in the context of the crosstalk between DNA methylation and histone methylation, and the expanded potential of epigenomic modifications in Hymenoptera to drive evolutionary novelties
Superconducting d-wave junctions: The disappearance of the odd ac components
We study voltage-biased superconducting planar d-wave junctions for arbitrary
transmission and arbitrary orientation of the order parameters of the
superconductors. For a certain orientation of the superconductors the odd ac
components disappear, resulting in a doubling of the Josephson frequency. We
study the sensitivity of this disappearance to orientation and compare with
experiments on grain boundary junctions. We also discuss the possibility of a
current flow parallel to the junction.Comment: 5 pages, 3 figure
Spectral and Fermi surface properties from Wannier interpolation
We present an efficient first-principles approach for calculating Fermi
surface averages and spectral properties of solids, and use it to compute the
low-field Hall coefficient of several cubic metals and the magnetic circular
dichroism of iron. The first step is to perform a conventional first-principles
calculation and store the low-lying Bloch functions evaluated on a uniform grid
of k-points in the Brillouin zone. We then map those states onto a set of
maximally-localized Wannier functions, and evaluate the matrix elements of the
Hamiltonian and the other needed operators between the Wannier orbitals, thus
setting up an ``exact tight-binding model.'' In this compact representation the
k-space quantities are evaluated inexpensively using a generalized
Slater-Koster interpolation. Because of the strong localization of the Wannier
orbitals in real space, the smoothness and accuracy of the k-space
interpolation increases rapidly with the number of grid points originally used
to construct the Wannier functions. This allows k-space integrals to be
performed with ab-initio accuracy at low cost. In the Wannier representation,
band gradients, effective masses, and other k-derivatives needed for transport
and optical coefficients can be evaluated analytically, producing numerically
stable results even at band crossings and near weak avoided crossings.Comment: 12 pages, 7 figure
Towards a better understanding of the dynamic role of the distance language learner: learner perceptions of personality, motivation, roles, and approaches
This study investigated the experience of learners enrolled on an Open University (UK) French course, and included personality factors, motivation, and tutor and student roles. The data gathered via multiple elicitation methods gave useful insights into issues of special relevance to distance language education, in particular the lack of fit between an inherently social discipline such as language learning and the distance context, whose main characterizing feature is remoteness from others. Motivation was seen to play a crucial role in success, along with tutor feedback, and personal responsibility for learning. Increased confidence and self?regulation were beneficial outcomes of the process of learning at a distance, and numerous suggestions for learning approaches based on personal experience were offered for language learners new to distance learning. The study concluded that the task for distance practitioners is to build on the insights shown by learners themselves, in order to target support where it is most needed
The chiral Anomalous Hall effect in re-entrant AuFe alloys
The Hall effect has been studied in a series of AuFe samples in the
re-entrant concentration range, as well as in part of the spin glass range. An
anomalous Hall contribution linked to the tilting of the local spins can be
identified, confirming theoretical predictions of a novel topological Hall term
induced when chirality is present. This effect can be understood in terms of
Aharonov-Bohm-like intrinsic current loops arising from successive scatterings
by canted local spins. The experimental measurements indicate that the chiral
signal persists, meaning scattering within the nanoscopic loops remains
coherent, up to temperatures of the order of 150 K.Comment: 7 pages, 11 eps figures Published version. Minor change
c-axis magnetotransport in CeCoIn
We present the results of out-of-plane electrical transport measurements on
the heavy fermion superconductor CeCoIn at temperatures from 40 mK to 400
K and in magnetic field up to 9 T. For 10 K transport measurements show
that the zero-field resistivity changes linearly with temperature
and extrapolates nearly to zero at 0 K, indicative of non-Fermi-liquid (nFL)
behavior associated with a quantum critical point (QCP). The longitudinal
magnetoresistance (LMR) of CeCoIn for fields applied parallel to the
c-axis is negative and scales as between 50 and 100 K, revealing
the presence of a single-impurity Kondo energy scale K.
Beginning at 16 K a small positive LMR feature is evident for fields less than
3 tesla that grows in magnitude with decreasing temperature. For higher fields
the LMR is negative and increases in magnitude with decreasing temperature.
This sizable negative magnetoresistance scales as from 2.6 K to
roughly 8 K, and it arises from an extrapolated residual resistivity that
becomes negative and grows quadratically with field in the nFL temperature
regime. Applying a magnetic field along the c-axis with B B restores
Fermi-liquid behavior in at less than 130 mK. Analysis of the
resistivity coefficient's field-dependence suggests that the QCP in
CeCoIn is located \emph{below} the upper critical field, inside the
superconducting phase. These data indicate that while high- c-axis transport
of CeCoIn exhibits features typical for a heavy fermion system, low-
transport is governed both by spin fluctuations associated with the QCP and
Kondo interactions that are influenced by the underlying complex electronic
structure intrinsic to the anisotropic CeCoIn crystal structure
A rigorous real time Feynman Path Integral and Propagator
We will derive a rigorous real time propagator for the Non-relativistic
Quantum Mechanic transition probability amplitude and for the
Non-relativistic wave function. The propagator will be explicitly given in
terms of the time evolution operator. The derivation will be for all
self-adjoint nonvector potential Hamiltonians. For systems with potential that
carries at most a finite number of singularity and discontinuities, we will
show that our propagator can be written in the form of a rigorous real time,
time sliced Feynman path integral via improper Riemann integrals. We will also
derive the Feynman path integral in Nonstandard Analysis Formulation. Finally,
we will compute the propagator for the harmonic oscillator using the
Nonstandard Analysis Feynman path integral formuluation; we will compute the
propagator without using any knowledge of classical properties of the harmonic
oscillator
Minimal Work Principle and its Limits for Classical Systems
The minimal work principle asserts that work done on a thermally isolated
equilibrium system, is minimal for the slowest (adiabatic) realization of a
given process. This principle, one of the formulations of the second law, is
operationally well-defined for any finite (few particle) Hamiltonian system.
Within classical Hamiltonian mechanics, we show that the principle is valid for
a system of which the observable of work is an ergodic function. For
non-ergodic systems the principle may or may not hold, depending on additional
conditions. Examples displaying the limits of the principle are presented and
their direct experimental realizations are discussed.Comment: 4 + epsilon pages, 1 figure, revte
Structural and electronic properties of Pb1-xCdxTe and Pb1-xMnxTe ternary alloys
A systematic theoretical study of two PbTe-based ternary alloys, Pb1-xCdxTe
and Pb1-xMnxTe, is reported. First, using ab initio methods we study the
stability of the crystal structure of CdTe - PbTe solid solutions, to predict
the composition for which rock-salt structure of PbTe changes into zinc-blende
structure of CdTe. The dependence of the lattice parameter on Cd (Mn) content x
in the mixed crystals is studied by the same methods. The obtained decrease of
the lattice constant with x agrees with what is observed in both alloys. The
band structures of PbTe-based ternary compounds are calculated within a
tight-binding approach. To describe correctly the constituent materials new
tight-binding parameterizations for PbTe and MnTe bulk crystals as well as a
tight-binding description of rock-salt CdTe are proposed. For both studied
ternary alloys, the calculated band gap in the L point increases with x, in
qualitative agreement with photoluminescence measurements in the infrared. The
results show also that in p-type Pb1-xCdxTe and Pb1-xMnxTe mixed crystals an
enhancement of thermoelectrical power can be expected.Comment: 10 pages, 13 figures, submitted to Physical Review
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