3,895 research outputs found
Evolution of antiferromagnetic domains in the all-in-all-out ordered pyrochlore NdZrO
We report the observation of magnetic domains in the exotic,
antiferromagnetically ordered all-in-all-out state of NdZrO,
induced by spin canting. The all-in-all-out state can be realized by Ising-like
spins on a pyrochlore lattice and is established in NdZrO below
0.31 K for external magnetic fields up to 0.14 T. Two different spin
arrangements can fulfill this configuration which leads to the possibility of
magnetic domains. The all-in-all-out domain structure can be controlled by an
external magnetic field applied parallel to the [111] direction. This is a
result of different spin canting mechanism for the two all-in-all-out
configurations for such a direction of the magnetic field. The change of the
domain structure is observed through a hysteresis in the magnetic
susceptibility. No hysteresis occurs, however, in case the external magnetic
field is applied along [100].Comment: Accepted for publication in Phys. Rev. B, 6 pages, 6 figure
Ászkarák (Crustacea, Isopoda) együttesek egyedszám változásai egy dániai urbanizációs grádiens mentén
Szárazföldi ászkarák együtteseket (Isopoda: Oniscidea) tanulmányoztunk egy urbanizációs
grádiens mentén 2004-ben a dániai Sorø mellett, a Globenet-protokoll szerint. Jelen tanulmányunkban
négy mintavételi periódust értékeltünk. Három hipotézist vizsgáltunk: (a) a fajdiverzitás a zavarás
növekvő mértékével csökken; (b) a fajdiverzitás a közepesen zavart területen a legnagyobb; (c) a zavartabb
területeken megjelennek kozmopolita és/vagy behurcolt fajok. A természetes – városszéli és városi élőhelyek
fajösszetétele megegyezett: Porcellio scaber, Oniscus asellus, Philoscia muscorum, Armadillidium
vulgare, Trachelipus rathkii, Ligidium hypnorum. Az urbanizáció hatása nem a fajok minőségi összetételében,
hanem azok egyedszám eltéréseiben tükröződött. Az egyes fajok élőhelytípusonkénti gyakorisága
– a P. muscorum kivételével – szignifikánsan különbözött egymástól
Stability of Boundary Conditions for the Sadowsky Functional
It has been proved by the authors that the (extended) Sadowsky functional can be deduced as the Γ -limit of the Kirchhoff energy on a rectangular strip, as the width of the strip tends to 0. In this paper, we show that this Γ -convergence result is stable when affine boundary conditions are prescribed on the short sides of the strip. These boundary conditions include those corresponding to a Möbius band. This provides a rigorous justification of the original formal argument by Sadowsky about determining the equilibrium shape of a free-standing Möbius strip. We further write the equilibrium equations for the limit problem and show that, under some regularity assumptions, the centerline of a developable Möbius band at equilibrium cannot be a planar curve
Evidence for a dynamical ground state in the frustrated pyrohafnate Tb2Hf2O7
We report the physical properties of Tb2Hf2O7 based on ac magnetic
susceptibility \chi_ac(T), dc magnetic susceptibility \chi(T), isothermal
magnetization M(H), and heat capacity C_p(T) measurements combined with muon
spin relaxation (\muSR) and neutron powder diffraction measurements. No
evidence for long-range magnetic order is found down to 0.1 K. However,
\chi_ac(T) data present a frequency-dependent broad peak (near 0.9 K at 16 Hz)
indicating slow spin dynamics. The slow spin dynamics is further evidenced from
the \muSR data (characterized by a stretched exponential behavior) which show
persistent spin fluctuations down to 0.3 K. The neutron powder diffraction data
collected at 0.1 K show a broad peak of magnetic origin (diffuse scattering)
but no magnetic Bragg peaks. The analysis of the diffuse scattering data
reveals a dominant antiferromagnetic interaction in agreement with the negative
Weiss temperature. The absence of long-range magnetic order and the presence of
slow spin dynamics and persistent spin fluctuations together reflect a
dynamical ground state in Tb2Hf2O7.Comment: 11 pages and 8 figure
CRISPaint allows modular base-specific gene tagging using a ligase-4-dependent mechanism
The site-specific insertion of heterologous genetic material into genomes provides a powerful means to study gene function. Here we describe a modular system entitled CRISPaint (CRISPR-assisted insertion tagging) that allows precise and efficient integration of large heterologous DNA cassettes into eukaryotic genomes. CRISPaint makes use of the CRISPR-Cas9 system to introduce a double-strand break (DSB) at a user-defined genomic location. A universal donor DNA, optionally provided as minicircle DNA, is cleaved simultaneously to be integrated at the genomic DSB, while processing the donor plasmid at three possible positions allows flexible reading-frame selection. Applying this system allows to create C-terminal tag fusions of endogenously encoded proteins in human cells with high efficiencies. Knocking out known DSB repair components reveals that site-specific insertion is completely dependent on canonical NHEJ (DNA-PKcs, XLF and ligase-4). A large repertoire of modular donor vectors renders CRISPaint compatible with a wide array of applications
The Optimal Control Landscape for the Generation of Unitary Transformations with Constrained Dynamics
The reliable and precise generation of quantum unitary transformations is
essential to the realization of a number of fundamental objectives, such as
quantum control and quantum information processing. Prior work has explored the
optimal control problem of generating such unitary transformations as a surface
optimization problem over the quantum control landscape, defined as a metric
for realizing a desired unitary transformation as a function of the control
variables. It was found that under the assumption of non-dissipative and
controllable dynamics, the landscape topology is trap-free, implying that any
reasonable optimization heuristic should be able to identify globally optimal
solutions. The present work is a control landscape analysis incorporating
specific constraints in the Hamiltonian corresponding to certain dynamical
symmetries in the underlying physical system. It is found that the presence of
such symmetries does not destroy the trap-free topology. These findings expand
the class of quantum dynamical systems on which control problems are
intrinsically amenable to solution by optimal control.Comment: Submitted to Journal of Mathematical Physic
On the unconstrained expansion of a spherical plasma cloud turning collisionless : case of a cloud generated by a nanometer dust grain impact on an uncharged target in space
Nano and micro meter sized dust particles travelling through the heliosphere
at several hundreds of km/s have been repeatedly detected by interplanetary
spacecraft. When such fast moving dust particles hit a solid target in space,
an expanding plasma cloud is formed through the vaporisation and ionisation of
the dust particles itself and part of the target material at and near the
impact point. Immediately after the impact the small and dense cloud is
dominated by collisions and the expansion can be described by fluid equations.
However, once the cloud has reached micro-m dimensions, the plasma may turn
collisionless and a kinetic description is required to describe the subsequent
expansion. In this paper we explore the late and possibly collisionless
spherically symmetric unconstrained expansion of a single ionized ion-electron
plasma using N-body simulations. Given the strong uncertainties concerning the
early hydrodynamic expansion, we assume that at the time of the transition to
the collisionless regime the cloud density and temperature are spatially
uniform. We do also neglect the role of the ambient plasma. This is a
reasonable assumption as long as the cloud density is substantially higher than
the ambient plasma density. In the case of clouds generated by fast
interplanetary dust grains hitting a solid target some 10^7 electrons and ions
are liberated and the in vacuum approximation is acceptable up to meter order
cloud dimensions. ..
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