77,683 research outputs found
Systematic {\it ab initio} study of the magnetic and electronic properties of all 3d transition metal linear and zigzag nanowires
It is found that all the zigzag chains except the nonmagnetic (NM) Ni and
antiferromagnetic (AF) Fe chains which form a twisted two-legger ladder, look
like a corner-sharing triangle ribbon, and have a lower total energy than the
corresponding linear chains. All the 3d transition metals in both linear and
zigzag structures have a stable or metastable ferromagnetic (FM) state. The
electronic spin-polarization at the Fermi level in the FM Sc, V, Mn, Fe, Co and
Ni linear chains is close to 90% or above. In the zigzag structure, the AF
state is more stable than the FM state only in the Cr chain. It is found that
the shape anisotropy energy may be comparable to the electronic one and always
prefers the axial magnetization in both the linear and zigzag structures. In
the zigzag chains, there is also a pronounced shape anisotropy in the plane
perpendicular to the chain axis. Remarkably, the axial magnetic anisotropy in
the FM Ni linear chain is gigantic, being ~12 meV/atom. Interestingly, there is
a spin-reorientation transition in the FM Fe and Co linear chains when the
chains are compressed or elongated. Large orbital magnetic moment is found in
the FM Fe, Co and Ni linear chains
A sharp stability criterion for the Vlasov-Maxwell system
We consider the linear stability problem for a 3D cylindrically symmetric
equilibrium of the relativistic Vlasov-Maxwell system that describes a
collisionless plasma. For an equilibrium whose distribution function decreases
monotonically with the particle energy, we obtained a linear stability
criterion in our previous paper. Here we prove that this criterion is sharp;
that is, there would otherwise be an exponentially growing solution to the
linearized system. Therefore for the class of symmetric Vlasov-Maxwell
equilibria, we establish an energy principle for linear stability. We also
treat the considerably simpler periodic 1.5D case. The new formulation
introduced here is applicable as well to the nonrelativistic case, to other
symmetries, and to general equilibria
From the Complete Yang Model to Snyder's Model, de Sitter Special Relativity and Their Duality
By means of Dirac procedure, we re-examine Yang's quantized space-time model,
its relation to Snyder's model, the de Sitter special relativity and their
UV-IR duality. Starting from a dimensionless dS_5-space in a 5+1-d Mink-space a
complete Yang model at both classical and quantum level can be presented and
there really exist Snyder's model, the dS special relativity and the duality.Comment: 7 papge
Measurement-induced nonlocality over two-sided projective measurements
Measurement-induced nonlocality (MiN), introduced by Luo and Fu [Phys. Rev.
Lett. 106(2011)120401], is a kind of quantum correlation that beyond
entanglement and even beyond quantum discord. Recently, we extended MiN to
infinite-dimensional bipartite system [arXiv:1107.0355]. MiN is defined over
one-sided projective measurements. In this letter we introduce a
measurement-induced nonlocality over two-sided projective measurements. The
nullity of this two-sided MiN is characterized, a formula for calculating
two-sided MiN for pure states is proposed, and a lower bound of (two-sided) MiN
for maximally entangled mixed states is given. In addition, we find that
(two-sided) MiN is not continuous. The two-sided geometric measure of quantum
discord (GMQD) is introduced in [Phys. Lett. A 376(2012)320--324]. We extend it
to infinite-dimensional system and then compare it with the two-sided MiN. Both
finite- and infinite-dimensional cases are considered.Comment: 12 page
A non-variational approach to nonlinear stability in stellar dynamics applied to the King model
In previous work by Y. Guo and G. Rein, nonlinear stability of equilibria in
stellar dynamics, i.e., of steady states of the Vlasov-Poisson system, was
accessed by variational techniques. Here we propose a different,
non-variational technique and use it to prove nonlinear stability of the King
model against a class of spherically symmetric, dynamically accessible
perturbations. This model is very important in astrophysics and was out of
reach of the previous techniques
Three Kinds of Special Relativity via Inverse Wick Rotation
Since the special relativity can be viewed as the physics in an inverse Wick
rotation of 4-d Euclid space, which is at almost equal footing with the 4-d
Riemann/Lobachevski space, there should be important physics in the inverse
Wick rotation of 4-d Riemann/Lobachevski space. Thus, there are three kinds of
special relativity in de Sitter/Minkowski/anti-de Sitter space at almost equal
footing, respectively. There is an instanton tunnelling scenario in the
Riemann-de Sitter case that may explain why \La be positive and link with the
multiverse.Comment: 3 pages, no figures, to appear in Chin. Phys. Let
Geometries for Possible Kinematics
The algebras for all possible Lorentzian and Euclidean kinematics with
isotropy except static ones are re-classified. The geometries
for algebras are presented by contraction approach. The relations among the
geometries are revealed. Almost all geometries fall into pairs. There exists correspondence in each pair. In the viewpoint of
differential geometry, there are only 9 geometries, which have right signature
and geometrical spatial isotropy. They are 3 relativistic geometries, 3
absolute-time geometries, and 3 absolute-space geometries.Comment: 40 pages, 7 figure
Entanglement detection beyond the CCNR criterion for infinite-dimensions
In this paper, in terms of the relation between the state and the reduced
states of it, we obtain two inequalities which are valid for all separable
states in infinite-dimensional bipartite quantum systems. One of them provides
an entanglement criterion which is strictly stronger than the computable
cross-norm or realignment (CCNR) criterion.Comment: 11 page
The Drosophila MicroRNA Mir-14 Suppresses Cell Death and Is Required for Normal Fat Metabolism
MicroRNAs (miRNAs) are small regulatory RNAs that are between 21 and 25 nucleotides in length and repress gene function through interactions with target mRNAs 1, 2. The genomes of metazoans encode on the order of several hundred miRNAs [3], but the processes they regulate have been defined for only two in C. elegans4, 5. We searched for new inhibitors of apoptotic cell death by testing existing collections of P element insertion lines for their ability to enhance a small-eye phenotype associated with eye-specific expression of the Drosophila cell death activator Reaper. Here we report the identification of the Drosophila miRNA mir-14 as a cell death suppressor. Loss of mir-14 enhances Reaper-dependent cell death, whereas ectopic expression suppresses cell death induced by multiple stimuli. Animals lacking mir-14 are viable. However, they are stress sensitive and have a reduced lifespan. Mir-14 mutants have elevated levels of the apoptotic effector caspase Drice, suggesting one potential site of action. Mir-14 also regulates fat metabolism. Deletion of mir-14 results in animals with increased levels of triacylglycerol and diacylglycerol, whereas increases in mir-14 copy number have the converse effect. We discuss possible relationships between these phenotypes
- …