179,583 research outputs found
Perpendicular orders
AbstractWe construct pairs of orders which have only the trivial order-preservinig self-maps in common: the identity and the constants
Pure Even Harmonic Generation from Oriented CO in Linearly Polarized Laser Fields
The first high harmonic spectrum, containing only the odd orders, was
observed in experiments 30 years ago (1987). However, a spectrum containing
pure even harmonics has never been observed. We investigate the generation of
pure even harmonics from oriented CO molecules in linearly polarized laser
fields employing the time-dependent density-functional theory. We find that the
even harmonics, with no odd orders, are generated with the polarization
perpendicular to the laser polarization, when the molecular axis of CO is
perpendicular to the laser polarization. Generation of pure even harmonics
reveals a type of dipole acceleration originating from the permanent dipole
moment. This phenomenon exists in all system with permanent dipole moments,
including bulk crystal and polyatomic molecules
Cyclotron enhancement of tunneling
A state of an electron in a quantum wire or a thin film becomes metastable,
when a static electric field is applied perpendicular to the wire direction or
the film surface. The state decays via tunneling through the created potential
barrier. An additionally applied magnetic field, perpendicular to the electric
field, can increase the tunneling decay rate for many orders of magnitude. This
happens, when the state in the wire or the film has a velocity perpendicular to
the magnetic field. According to the cyclotron effect, the velocity rotates
under the barrier and becomes more aligned with the direction of tunneling.
This mechanism can be called cyclotron enhancement of tunneling
Hydrogen atom in crossed external fields reexemined by the moment method
Recurrence relations of perturbation theory for hydrogen ground state are
obtained. With their aid polarizabilities in constant perpendicular electric
and magnetic fields are computed up to 80th order. The high orders asymptotic
is compared with its quasiclassical estimate. For the case of arbitrary mutual
orientation of external fields a general sixth order formula is given.Comment: 11 pages, LaTeX, 2 figures (eps
Electron-transport properties of ethyne-bridged diphenyl zinc-porphyrin molecules
We investigate the electron-transport properties of ethyne-bridged diphenyl
zinc-porphyrin molecules suspended between gold (111) electrodes by
first-principles calculations within the framework of density functional
theory. It is found that the conductance of a molecular junction in which
phenyl and porphyrin rings are perpendicular is reduced by three orders of
magnitude compared with that of a junction in which the phenyl and porphyrin
rings are coplanar. In the coplanar configuration, electrons are transmitted
through states, which extend over the whole molecule. In the
perpendicular configuration, the conductance is suppressed because of the
reduction of electron hopping between states of the phenyl ring and
states of the porphyrin ring.Comment: 11 page
Electric fields in solar magnetic structures due to gradient driven instabilities: heating and acceleration of particles
The electrostatic instabilities driven by the gradients of the density,
temperature and magnetic field, are discussed in their application to solar
magnetic structures. Strongly growing modes are found for some typical plasma
parameters. These instabilities i) imply the presence of electric fields that
can accelerate the plasma particles in both perpendicular and parallel
directions with respect to the magnetic field vector, and ii) can
stochastically heat ions. The perpendicular acceleration is to the leading
order determined by the \bmath{E}\times \bmath{B}-drift acting equally on
both ions and electrons, while the parallel acceleration is most effective on
electrons. The experimentally confirmed stochastic heating is shown to act
mainly in the direction perpendicular to the magnetic field vector and acts
stronger on heavier ions. The energy release rate and heating may exceed for
several orders of magnitude the value accepted as necessary for a
self-sustained heating in the solar corona. The energy source for both the
acceleration and the heating is stored in the mentioned background gradients.Comment: To appear in MNRA
Velocity of domain-wall motion induced by electrical current in a ferromagnetic semiconductor (Ga,Mn)As
Current-induced domain-wall motion with velocity spanning over five orders of
magnitude up to 22 m/s has been observed by magneto-optical Kerr effect in
(Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to
verify theories of spin-transfer by the Slonczewski-like mechanism as well as
by the torque resulting from spin-flip transitions in the domain-wall region.
Evidence for domain-wall creep at low currents is found.Comment: 5 pages, 3 figure
Field induced anisotropic cooperativity in a magnetic colloidal glass
The translational dynamics in a repulsive colloidal glass-former is probed by
time-resolved X-ray Photon Correlation Spectroscopy. In this dense dispersion
of charge-stabilized and magnetic nanoparticles, the interaction potential can
be tuned, from quasi-isotropic to anisotropic by applying an external magnetic
field. Structural and dynamical anisotropies are reported on interparticle
lengthscales associated with highly anisotropic cooperativity, almost two
orders of magnitude larger in the field direction than in the perpendicular
direction and in zero field
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