11,885 research outputs found
On the stability and growth of single myelin figures
Myelin figures are long thin cylindrical structures that typically grow as a
dense tangle when water is added to the concentrated lamellar phase of certain
surfactants. We show that, starting from a well-ordered initial state, single
myelin figures can be produced in isolation thus allowing a detailed study of
their growth and stability. These structures grow with their base at the
exposed edges of bilayer stacks from which material is transported into the
myelin. Myelins only form and grow in the presence of a driving stress; when
the stress is removed, the myelins retract.Comment: 4 pages, 8 figures. Revised version, 1 new figure, additional
reference
Role of gauge invariance in B -> V gamma radiative weak decays
The role of gauge invariance in calculating B -> V gamma radiative weak
decays is clarified. It is shown that the gauge invariance severely restricts
the contributions mediated by the usual weak non-leptonic Hamiltonian dominated
by u and c quaks with one photon attachment. Such contributions are found to be
almost negligible.Comment: 5 pages, Revtex, no figure
Spin-orbit coupling induced by a mass gradient
The existence of a spin-orbit coupling (SOC) induced by the gradient of the
effective mass in low-dimensional heterostructures is revealed. In structurally
asymmetric quasi-two-dimensional semiconductor heterostructures the presence of
a mass gradient across the interfaces results in a SOC which competes with the
SOC created by the electric field in the valence band. However, in graded
quantum wells subjected to an external electric field, the mass-gradient
induced SOC can be finite even when the electric field in the valence band
vanishes.Comment: 4 pages, 2 figures, 1 tabl
High-energy particles associated with solar flares
High-energy particles, the so-called solar cosmic rays, are often generated in association with solar flares, and then emitted into interplanetary space. These particles, consisting of electrons, protons, and other heavier nuclei, including the iron-group, are accelerated in the vicinity of the flare. By studying the temporal and spatial varation of these particles near the earth's orbit, their storage and release mechanisms in the solar corona and their propagation mechanism can be understood. The details of the nuclear composition and the rigidity spectrum for each nuclear component of the solar cosmic rays are important for investigating the acceleration mechanism in solar flares. The timing and efficiency of the acceleration process can also be investigated by using this information. These problems are described in some detail by using observational results on solar cosmic rays and associated phenomena
Identifying cross country skiing techniques using power meters in ski poles
Power meters are becoming a widely used tool for measuring training and
racing effort in cycling, and are now spreading also to other sports. This
means that increasing volumes of data can be collected from athletes, with the
aim of helping coaches and athletes analyse and understanding training load,
racing efforts, technique etc. In this project, we have collaborated with
Skisens AB, a company producing handles for cross country ski poles equipped
with power meters. We have conducted a pilot study in the use of machine
learning techniques on data from Skisens poles to identify which "gear" a skier
is using (double poling or gears 2-4 in skating), based only on the sensor data
from the ski poles. The dataset for this pilot study contained labelled
time-series data from three individual skiers using four different gears
recorded in varied locations and varied terrain. We systematically evaluated a
number of machine learning techniques based on neural networks with best
results obtained by a LSTM network (accuracy of 95% correctly classified
strokes), when a subset of data from all three skiers was used for training. As
expected, accuracy dropped to 78% when the model was trained on data from only
two skiers and tested on the third. To achieve better generalisation to
individuals not appearing in the training set more data is required, which is
ongoing work.Comment: Presented at the Norwegian Artificial Intelligence Symposium 201
The role of the lattice structure in determining the magnon-mediated interactions between charge carriers doped into a magnetically ordered background
We use two recently proposed methods to calculate exactly the spectrum of two
spin- charge carriers moving in a ferromagnetic background, at zero
temperature, for three types of models. By comparing the low-energy states in
both the one-carrier and the two-carrier sectors, we analyze whether complex
models with multiple sublattices can be accurately described by simpler
Hamiltonians, such as one-band models. We find that while this is possible in
the one-particle sector, the magnon-mediated interactions which are key to
properly describe the two-carrier states of the complex model are not
reproduced by the simpler models. We argue that this is true not just for
ferromagnetic, but also for antiferromagnetic backgrounds. Our results question
the ability of simple one-band models to accurately describe the low-energy
physics of cuprate layers.Comment: 15 pages, 10 figure
Sharpening cusps: the mass determination of semi-invisibly decaying particles from a resonance
We revisit mass determination techniques for the minimum symmetric event
topology, namely pair production followed by , where and
are unknown particles with the masses to be measured, and is an
invisible particle, concentrating on the case where is pair produced from a
resonance. We consider separate scenarios, with different initial constraints
on the invisible particle momenta, and present a systematic method to identify
the kinematically allowed mass regions in the plane. These allowed
regions exhibit a cusp structure at the true mass point, which is equivalent to
the one observed in the endpoints in certain cases. By considering the
boundary of the allowed mass region we systematically define kinematical
variables which can be used in measuring the unknown masses, and find a new
expression for the variable as well as its inverse. We explicitly
apply our method to the case that is pair produced from a resonance, and as
a case study, we consider the process , followed by ,
in the Minimal Supersymmetric Standard Model and show that our method provides
a precise measurement of the chargino and sneutrino masses, and , at
LHC with luminosity.Comment: 18 pages, 13 figures, version 2 updated to JHEP 06 (2014) 17
Kondo Temperature in Multilevel Quantum Dots
We develop a general method to evaluate the Kondo temperature in a multilevel
quantum dot that is weakly coupled to conducting leads. Our theory reveals that
the Kondo temperature is strongly enhanced when the intradot energy-level
spacing is comparable to or smaller than the charging energy. We propose an
experiment to test our result, which consists of measuring the size-dependence
of the Kondo temperature.Comment: 4 pages, 1 figure and supplementary material. Revised and improved
version, to appear in Phys. Rev. Let
meson in dense matter
We study the properties of mesons in nuclear matter using a
unitary approach in coupled channels within the framework of the local hidden
gauge formalism and incorporating the decay channel in matter. The
in-medium interaction accounts for Pauli blocking effects and
incorporates the self-energy in a self-consistent manner. We also
obtain the (off-shell) spectral function and analyze its behaviour
at finite density and momentum. At normal nuclear matter density, the meson feels a moderately attractive potential while the width
becomes five times larger than in free space. We estimate the transparency
ratio of the reaction, which we propose as
a feasible scenario at present facilities to detect the changes of the
properties of the meson in the nuclear medium.Comment: 26 pages, 9 figures, one new section added, version published in
Phys. ReV. C, http://link.aps.org/doi/10.1103/PhysRevC.82.04521
- …