9,728 research outputs found
Laboratory photo-chemistry of pyrene clusters: an efficient way to form large PAHs
In this work, we study the photodissociation processes of small PAH clusters
(e.g., pyrene clusters). The experiments are carried out using a quadrupole ion
trap in combination with time-of-flight (QIT-TOF) mass spectrometry. The
results show that pyrene clusters are converted into larger PAHs under the
influence of a strong radiation field. Specifically, pyrene dimer cations
(e.g., [CHCH] or CH), will
photo-dehydrogenate and photo-isomerize to fully aromatic cations (PAHs) (e.g.,
CH) with laser irradiation. The structure of new formed PAHs
and the dissociation energy for these reaction pathways are investigated with
quantum chemical calculations. These studies provide a novel efficient
evolution routes for the formation of large PAHs in the interstellar medium
(ISM) in a bottom-up process that will counteract the top-down conversion of
large PAHs into rings and chains, and provide a reservoir of large PAHs that
can be converted into C and other fullerenes and large carbon cages
Zero sound in a two-dimensional dipolar Fermi gas
We study zero sound in a weakly interacting 2D gas of single-component
fermionic dipoles (polar molecules or atoms with a large magnetic moment)
tilted with respect to the plane of their translational motion. It is shown
that the propagation of zero sound is provided by both mean field and many-body
(beyond mean field) effects, and the anisotropy of the sound velocity is the
same as the one of the Fermi velocity. The damping of zero sound modes can be
much slower than that of quasiparticle excitations of the same energy. One thus
has wide possibilities for the observation of zero sound modes in experiments
with 2D fermionic dipoles, although the zero sound peak in the structure
function is very close to the particle-hole continuum.Comment: 15 pages, 2 figure
Strongly nonlinear waves in capillary electrophoresis
In capillary electrophoresis, sample ions migrate along a micro-capillary
filled with a background electrolyte under the influence of an applied electric
field. If the sample concentration is sufficiently high, the electrical
conductivity in the sample zone could differ significantly from the
background.Under such conditions, the local migration velocity of sample ions
becomes concentration dependent resulting in a nonlinear wave that exhibits
shock like features. If the nonlinearity is weak, the sample concentration
profile, under certain simplifying assumptions, can be shown to obey Burgers'
equation (S. Ghosal and Z. Chen Bull. Math. Biol. 2010, 72(8), pg. 2047) which
has an exact analytical solution for arbitrary initial condition.In this paper,
we use a numerical method to study the problem in the more general case where
the sample concentration is not small in comparison to the concentration of
background ions. In the case of low concentrations, the numerical results agree
with the weakly nonlinear theory presented earlier, but at high concentrations,
the wave evolves in a way that is qualitatively different.Comment: 7 pages, 5 figures, 1 Appendix, 2 videos (supplementary material
Stable dilute supersolid of two-dimensional dipolar bosons
We consider two-dimensional bosonic dipoles oriented perpendicularly to the
plane. On top of the usual two-body contact and long-range dipolar interactions
we add a contact three-body repulsion as expected, in particular, for dipoles
in the bilayer geometry with tunneling. The three-body repulsion is crucial for
stabilizing the system, and we show that our model allows for stable continuous
space supersolid states in the dilute regime and calculate the zero-temperature
phase diagram.Comment: revised version, 5 pages, 2 figures, with 3 pages supplementary
materia
Effective SU(2)_L x U(1) theory and the Higgs boson mass
We assume the stability of vacuum under radiative corrections in the context
of the standard electroweak theory. We find that this theory behaves as a good
effective model already at cut off energy scales as low as 0.7 TeV. This
stability criterion allows to predict m_H= 318 +- 13 GeV for the Higgs boson
mass.Comment: Latex, 5 pages, 1 Postscript figure include
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